N = 138) and fourth (N = 164) graders were tested in the middle (T1) and end (T2) of the school year. The study focused on the cross-sectional and longitudinal development of monitoring and control, and aimed to investigate the development of metacognition for two test formats. After reading expository texts, children completed a comprehension test consisting of open-ended and true-false questions. They monitored their test performance by making confidence judgments, and controlled performance by deciding whether to maintain or withdraw their given answers. Overall, monitoring and control accuracy was higher for open-ended questions than for true-false questions. For open-ended questions, results indicated higher metacognitive accuracy for fourth graders than second graders. No such age effects were found for monitoring and control for true-false questions. Longitudinally, children of both age groups improved their monitoring and control accuracy from T1 to T2, for open-ended and true-false questions. For both test types, improvement mainly occurred for the monitoring and controlling of incorrect, rather than correct answers. Additionally, the results indicated inter-individual stability of performance, but no stability of monitoring and control accuracy over time. The findings indicate that developmental as well as task-related factors affect children’s metacognitive accuracy.This study investigated elementary school children’s development of monitoring and control when learning from texts. Second (The online version of this article (10.1007/s11409-019-09208-5) contains supplementary material, which is available to authorized users. Schools were selected by contacting principals from public schools in the larger vicinity of a mid-sized university town. Family backgrounds were lower to upper middle class. For the analyses, age outliers were excluded (N = 19). Further, sample attrition (N = 6) was due to incomplete test completion, insufficient language skills, eye problems when reading on a tablet, and change in residence. The data of 302 children were used for analyses to test our hypotheses . Sixty-five children (21.5%) were non-native speakers. Outcomes related to our hypotheses did not differ for non-native speakers, indicating that they had sufficient language skills to follow the instructions. Parental informed consent was received prior to testing. Children gave oral consent prior to the test sessions and were informed that they could withdraw participation at any time without consequences. No child ever did.The sample consisted of 327 children at T1 and T2, but also for second and fourth graders. Therefore, we piloted 18 texts with subsets of two open-ended questions and three true-false questions per text. The sample of the pilot study consisted of one second (N = 20) and one fourth grade classroom (N = 15), with children in the same age as children at T2. The texts and questions we used in this pilot study were translated and adapted from studies by De Bruin et al.  of six texts with four questions each, that cover a comparable range of easy, medium and difficult questions. That range in difficulty had to be as similar as possible not only for Tn et al.  and Van n et al. . Texts fThe goal of the pilot study was to select two subsets of six texts with two open-ended and two true-false questions per text that met the following criteria: First, text-question subsets that elicited ceiling or bottom effects in one of the open-ended questions or in more than one of the true-false questions were removed. We expected greater ceiling effects for true-false questions. Therefore, piloting three true-false questions allowed us to exclude one from each text-question set without removing the whole text-questions subset from the sample. Additionally, each sample of true-false questions at both measurement points included 6 true-false questions that were correct and 6 questions that were incorrect. Second, to ensure a suitable range of variance in question difficulty, we chose text-question sets that provided together a similar amount of easy (~ 30%), medium (~ 40%) and difficult (~ 30%) open-ended and true-false questions, for both age groups at both measurement points. And third, to make a comparison between the two age groups most reliable, for both age groups the same subsets of 12 texts (in a difficult and in an easier form) were chosen.The mean length of the 12 selected texts was 87 words for second graders and 126 words for fourth graders. The complexity of the texts as measured by the LIX . Prior to completing the task, children were instructed about the whole task procedure  by one of the experimenters. This instruction took place during the small-groups session, after separating the class in two groups. There were no more additional instructions given during the task, however, children could read instructions for each step and instructions were repeated for individual children if needed. With practical and interactive examples, the experimenters ensured that children understood the task.Each class was visited by four experimenters. At both measurement points the classes were split into two groups of 6 to 11 children, and each group was then tested in an individual room with two experimenters present. Shortly after completing the first measurement point in all classes, teachers were contacted by email to schedule a date for the second measurement point (number of days between the two measurement points: The text comprehension task included the following phases: 1) study (text reading)For the study phase, students read six expository texts on a tablet. Presenting the texts on a tablet enabled a complete randomization of the texts. Further, it standardized the reading procedure for children by not allowing them to move back and forth between texts. The study phase was self-paced; however, the minimum reading duration before having the option to move on to the next text was 10s, ensuring that children could not click through. The computer displays were 11.6 “monitors with a resolution of 1366 × 768 pixels. The text font was Futura Std. Book and the size was 30 for second graders and 25 for fourth graders. Complete texts were presented on screens; no scrolling was needed. The screen for each text contained the title of the text, the text, and a content-related picture. Topics were animals , geographical/ geological/ meteorological subjects , or physiological processes . An example of a text is presented in Appendix 1 and .60 at T2 for second graders, and .68 on T1 and .63 at T2 for fourth graders. Internal consistency for the 12 true-false questions was Cronbach’s α = .37 at T1 and .16 at T2 for second graders, and .45 on T1 and .20 at T2 for fourth graders. Internal consistency of the true-false questions is rather low, however, low internal consistency is not uncommon for text comprehension tests .The text comprehension test consisted of twelve open-ended and twelve true-false questions  presented in a booklet (for examples of questions see Appendix very unsure) to black (very sure), with different shades of grey in the middle  and T2 .To assess performance, answers to true-false and open-ended questions were scored as correct (1) or incorrect (0). In accordance with Van Loon et al. , compreh1 vs. T2) as within-subject factors and age (second vs. fourth grade) as a between-subjects factor were conducted for mean CJs and mean percentages of correct and incorrect answers maintained.To assess monitoring accuracy, mean CJs for correct and incorrect answers were compared to see whether children could discriminate between their correct and incorrect responses  as a within-subject factor and age (second vs. fourth grade) as a between-subjects factor were conducted to investigate whether there were effects of measurement point and age on monitoring and control. Stability between T1 and T2 was assessed with Pearson correlations for performance (percentage of correct answers) and accuracy of monitoring and control (gamma and phi correlations). To investigate the effects of test format, all analyses were conducted separately for both test formats  and true-false questions (M = .19%).Only completed test items were included in the analyses. In line with Roebers et al. , questioIn this section, we report the analyses testing the hypothesized effects of age group, measurement point and test format. Before reporting findings on accuracy and stability of monitoring and control, we report preliminary results on test performance for the two test formats.To investigate differences in performance between age groups and measurement points, we conducted repeated measures ANOVAs for both test formats separately. Table 2 compared to T1, F  = 23.73, p < .001, ηp2 = .07, whereas no difference was found between second and fourth graders (p = .35). The significant interaction between measurement point and age, F  = 12.73, p < .001, ηp2 = .04, showed that second graders’ increased their performance from T1 to T2, F , p < .001, ηp2 = .17, whereas fourth graders’ performance did not change (p = .295). For the number of incorrect answers, no differences were found between T1 and T2, and between second and fourth graders (ps ≥ .32). Children had fewer omission errors at T2 compared to T1, F  = 28.01, p < .001, ηp2 = .09, whereas no difference was found between second and fourth graders (p = .63). The significant interaction between measurement point and age, F  = 13.19, p < .001, ηp2 = .04, revealed that second graders reduced the number of omission errors from T1 to T2,F  = 28.02, p < .001, ηp2 = .17, whereas fourth graders did not show changes in the number of omissions (p = .15).For open-ended questions, children had more correct answers at T2 compared to T1, F  = 73.18, p < .001, ηp2 = .20, whereas no difference was found between second and fourth graders . Performance for true-false questions was above chance for second graders at T1, t (137) = 5.54, p < .001, Cohen’s d = .47, and T2, t (137) = 13.42, p < .001, Cohen’s d = 1.14, and for fourth graders at T1, t (162) = 5.84, p < .001, Cohen’s d = .46, and T2, t (163) = 13.22, p < .001, Cohen’s d = 1.03.For true-false questions, children had more correct answers at Tz = 1.788, p = 0.04) as well as fourth graders .Table 2 compared to T1,F  = 7.91, p = .005, ηp2 = .03, and fourth graders gave lower CJs compared to second graders, F  = 8.03, p = .005, ηp2 = .03. For true-false questions, there were no significant effects of measurement point and age (ps ≥ .47).To investigate effects of age and measurement point on CJs, repeated measures ANOVAs were conducted for open-ended and true-false questions separately. Table 2 compared to T1, we included correctness (correct vs. incorrect) in the repeated measures ANOVAs.To investigate if monitoring was more accurate for fourth graders than second graders, and more accurate at TM = 4.08, SE = .07) than for correct answers , F  = 461.14, p < .001, ηp2 = .64. Consistent with the hypothesis that fourth graders more accurately monitor their incorrect answers than second graders, the interaction between age and correctness was significant, F  = 19.52, p < .001, ηp2 = .07. Fourth graders gave lower CJs for incorrect answers  than second graders , F  = 20.48, p < .001, ηp2 = .07, whereas CJs for correct answers did not differ between second  and fourth graders , p = .32. Further, in line with the hypothesis that children improve their monitoring of incorrect answers from T1 to T2, the interaction between measurement point and correctness was significant, F  = 39.72, p < .001, ηp2 = .13. Children gave lower CJs for incorrect answers at T2  than at T1 , t (285) = 6.62, p < .001, Cohen’s d = 0.78, whereas there was no change over time for CJs for correct answers from T1  to T2 , p = .18. The finding that monitoring of answers to open-ended questions improved for older children and at the second measurement point is also supported by analyses using Gamma correlations, as shown in Table F  = 20.31, p < .001, ηp2 = .08, and children more accurately monitored their performance at T2 compared to T1, F  = 17.50, p < .001, ηp2 = .07.Figure M = 4.96, SE = .07) compared to correct answers , F  = 96.16, p < .001, ηp2 = .25. No significant interaction was found between age and correctness, indicating that second and fourth graders did not differ in their ability to discriminate between correct and incorrect answers to true-false questions, F  = 1.55, p = .22, ηp2 = .01. However, in line with the hypothesis that children improve their monitoring of incorrect answers from T1 to T2, the interaction between measurement point and correctness was significant, F  = 39.57, p < .001, ηp2 = .12. Children gave lower CJs for incorrect answers at T2  than at T1 , t (295) = 3.77, p < .001, Cohen’s d = .44, whereas CJs for correct answers were higher at T2  than at T1 , t (298) = −2.89, p = .004, Cohen’s d = .33. As shown in Table 1 and T2 was also supported with the gamma correlations, F  = 21.94, p < .001, ηp2 = .08.Figure , F 1, 29 = 96.16,1 and T2 with test format as a within-subject factor, collapsed across both grades. The difference between the gamma correlations for monitoring accuracy for open-ended and true-false questions was significant at T1, F  = 44.89, p < .001, ηp2 = .15, and T2, F  = 35.31, p < .001, ηp2 = .11, indicating that monitoring was significantly more accurate for open-ended than for true-false questions at both measurement points.To investigate the differences in monitoring accuracy between open-ended and true-false questions, we conducted repeated measures ANOVAs for Tt (280) = 2.59, p = .01, Cohen’s d = .16. The comparison between CJs for incorrect responses for detail open-ended questions and true-false questions was more pronounced, as indicated by the large effect size, t (289) = −11.94, p < .001, Cohen’s d = .70. Further, a comparison between CJs for incorrect answers to causal open-ended questions and true-false questions also showed a large effect size, t (291) = −14.35, p < .001, Cohen’s d = .88. Thus, even though CJs for incorrect answers were slightly lower for detail than for causal open-ended questions, CJs for incorrect answers to both open-ended question types were considerably lower than CJs for incorrect answers to true-false questions.Note that open-ended questions either had a detail or a causal focus. To investigate whether there are differences in monitoring accuracy for these two types of open-ended questions , we compared monitoring accuracy for these two question types. Moreover, monitoring for both of these open-ended question types was compared with monitoring for true-false questions. As mentioned above, we found differences between question formats for participants` monitoring of incorrect answers. Because this ability to accurately recognize errors is particularly relevant for improving performance, the following analyses focus on differences in CJs for incorrect answers. Table ps ≥ .87). For true-false questions, stability was not significant for second graders (p = .99), whereas for fourth graders, stability over time was low but significant, (p < .05).Table 2 compared to T1,F  = 9.52, p = .002, ηp2 = .03, and overall, fourth graders maintained fewer answers than second graders, F  = 19.65, p < .001, ηp2 = .06. For true-false questions, the effects of measurement point and age were not significant (p ≥ .19).To investigate effects of age and measurement point on the percentage of maintained answers, repeated measures ANOVAs were conducted for both test formats separately. Table 2 than at T1, we included correctness (correct/incorrect answers) in the repeated measures ANOVAs.To investigate the hypothesis that control for incorrect answers would be more accurate for fourth graders than second graders, and the hypothesis that control for incorrect answers would be more accurate at TM = 46.32, SE = 1.5) than correct answers , F  = 331.6, p < .001, ηp2 = .56. Consistent with the hypothesis that fourth graders control their incorrect answers more effectively than second graders, the interaction between age and correctness was significant, F  = 14.24, p < .001, ηp2 = .05. Fourth graders  maintained fewer incorrect answers than second graders , F  = 29.24, p < .001, ηp2 = .10, whereas second graders  maintained more correct answers than fourth graders , F  = 4.46, p = .036, ηp2 = .02. In line with the hypothesis that control of incorrect answers would be more accurate at T2 than T1, the interaction between measurement point and correctness was significant, F  = 20.5, p < .001, ηp2 = .07. Children maintained fewer incorrect answers at T2  than T1 , t (277) = 6.62, p < .001, Cohen’s d = 0.79, whereas the percentage of correct answers maintained did not differ between T1 (M = 73.94 SD = 27.04) and T2 , p = .26. The finding that control for open-ended questions improved for older children and at the second measurement point is also supported by phi correlations. As shown in Table F  = 5.17, p = .02, ηp2 = .02, at both measurement points, and children controlled their performance more accurately at T2 compared to T1, F  = 13.10, p < .001, ηp2 = .06, independent of age.Figure M = 61.99, SE = 1.48) than correct answers , F  = 69.86, p < .001, ηp2 = .19. Again, no significant interaction was found between age and correctness, indicating that second and fourth graders did not differ in their ability to discriminate between control of correct and incorrect answers to true-false questions, F  = .14, p = .71, ηp2 > .001. However, again, and in line with the hypothesis that control of incorrect answers would be more accurate at T2 than T1, the interaction between measurement point and correctness was significant, F  = 17.35, p < .001, ηp2 = .06. Children maintained fewer incorrect answers at T2  than T1 , t (294) = 2.73, p < .001, Cohen’s d = .32, whereas they maintained more correct answers at T2  compared to T1 , t  = −1.97, p = .05, Cohen’s d = −.23. As visible in Table 1 and T2, F  = 5.59, p = .02, ηp2 = .03.For true-false questions, as shown in Fig. , F 1, 29 = 69.86,F  = 12.84, p < .001, ηp2 = .05. Confirming our hypothesis of stronger monitoring-based control in the second measurement point, the results for open-ended questions indicated that the relationship between CJs and control was stronger at T2 compared to T1, F  = 11.73, p = .001, ηp2 = .05. For true-false questions the relation between monitoring and control did not differ between second and fourth graders, and between T1 and T2 (ps > .07).To examine the extent to which children related their control decisions to their CJs (monitoring-based control) we calculated gamma correlations between the CJs and the maintenance of answers  = 22.43, p < .001, ηp2 = .10, and T2, F  = 35.75, p < .001, ηp2 = .13; as visible in Table We also investigated the difference in control accuracy between the two test formats. The difference between control accuracy (Gamma correlations between maintenance and performance) for open-ended and true-false questions was significant at Tps ≥ .90).Table With the current study, we addressed elementary school children’s metacognition when taking a text comprehension test. The first aim was to investigate how monitoring and control develop during the elementary school years by examining developmental effects cross-sectionally and longitudinally. For this purpose, we tested second and fourth grade students twice within half a year with a text comprehension task for which children were asked to read texts, answer questions about the texts, give CJs for their answers, and decide whether they liked to maintain or withdraw each of their answers. The second aim was to examine how test format affects students’ accuracy of monitoring and control. To address this question, the text comprehension test consisted of open-ended and true-false questions.Previous research on young elementary school children’s metacognition mainly used associative learning tasks with forced choice test formats, and individual testing of children. The present study extends this research by using an educationally relevant and more complex text comprehension task. In school, children often need to study texts and answer recall and recognition questions. Several studies investigated elementary school students’ metacognition during reading, and this research shows rather low accuracy of monitoring and control  question difficulty. Thiede  showed tInterestingly, children of both age groups improved their metacognitive accuracy for their answers to true-false questions at the second measurement point. That is, half a year after the first testing, they were less overconfident for, and maintained fewer of their incorrect answers. Thus, improvement over time for true-false questions paralleled the improvement for open-ended questions. The finding that children improved their metacognitive accuracy for true-false questions longitudinally but not cross-sectionally indicates that task familiarity is likely to have an impact on the accuracy of monitoring and control  affects metacognitive accuracy in this task  from familiarity with the specific task by including a control group that completes the task only at the second measurement point.Taken together, our study sheds light on elementary school children’s metacognitive skills when learning from texts. Findings show that the developmental progression of monitoring and control, mainly found in paired associate tasks, also applies to a more educationally valid text-learning task. However, this age-dependent progression was only found when monitoring and controlling open-ended questions. The present study highlights the discrepancy in metacognitive accuracy between open-ended and true-false questions; metacognitive accuracy was considerably higher for open-ended questions. Additionally, it also demonstrated that children’s monitoring and control accuracy varies over time, rather than being a stable characteristic.Investigating the conditions under which metacognition is inaccurate can reveal important insights that can be applied in practice. Findings from intervention studies showed that the promotion of self-regulated learning, which includes metacognition, has an impact on students’ academic performance and metacognitive strategy use


However, atomic level study of PbI2 monolayer has been limited due to challenges in obtaining thin crystals. Here, we use liquid exfoliation to produce monolayer PbI2 nanodisks (30-40 nm in diameter and > 99% monolayer purity) and deposit them onto suspended graphene supports to enable atomic structure study of PbI2. Strong epitaxial alignment of PbI2 monolayers with the underlying graphene lattice occurs, leading to a phase shift from the 1 T to 1 H structure to increase the level of commensuration in the two lattice spacings. The fundamental point vacancy and nanopore structures in PbI2 monolayers are directly imaged, showing rapid vacancy migration and self-healing. These results provide a detailed insight into the atomic structure of monolayer PbI2, and the impact of the strong van der Waals interaction with graphene, which has importance for future applications in optoelectronics.Lead Iodide (PbI Imaging liquid phase exfoliated nanosheets on suspended graphene via annular dark-field STEM can enable identification of various defects, vacancies and their migration. Here, the authors report matching of zigzag edges of monolayer PbI2 with graphene arm-chairs leading to a phase shift from 1 T to 1 H structure to maximize commensuration of the lattices. Although graphene exhibits an exceptionally high carrier mobility (>106 cm2 V−1s−1 at 2 K), its zero bandgap poses difficulties for many semiconductor applications4. Monolayer transition metal dichalcogenides (TMDs), such as MoS2, can have direct band gaps of ~1.8 eV, but do not exhibit very high charge carrier mobility7. For Mo- and W-based TMDs, such as MoSe2, WS2, WSe2, etc., the band gaps fall within the range of 1.0–2.0 eV, which is the red to near infrared regions9. For optoelectronics, blue, green, and ultraviolet light-emitting diodes are also needed for full color displays and cameras. Currently, there are not many experimental studies of 2D materials that can satisfy the demands for the green to UV spectral regions and more research is needed to expand this area.Two-dimensional (2D) materials attract interest because of their unique chemical and physical properties, facilitating the study of novel physics, e.g., trions, valley polarization, etc2 is a layered direct bandgap semiconductor with bandgap of 2.4 eV in its bulk form, whereas its 2D monolayer has an indirect bandgap of ~2.5 eV, with possibilities to tune the bandgap between 1–3 eV13. PbI2 is frequently used to fabricate organic–inorganic halide perovskite solar cells15, and as a high-energy photon detector material for gamma-rays and X-rays18. PbI2 has a wide variety of I-Pb-I stacking and this gives rise to more than a dozen polymorphs19. However, the thickness of each single layer (0.7 nm), and the distance between each lead and iodide atoms (0.32 nm) is independent of the polytypes19. The 2H structure is the most commonly found polytype of three-dimensional PbI2, where each plane of Pb and I atoms are shifted with respect to each other and form overlapping hexagons.PbI2 has been shown to be excellent candidate for use in optoelectronic applications, photodetectors, and photon detection23. Ultrathin PbI2 is an interesting system for studying quantum-confinement effects because the exciton–phonon couplings are dependent on the degree of localization of electronic charge25. Cabana et al.26 fabricated PbI2 interfaces with carbon nanotubes and studied the change in the density of states of the system. Zhou et al.10 studied the graphene/PbI2 van der Waals interface and predicted 1.5 eV increase in the visible light absorption capability of the heterostructure as compared to pure 2D PbI2. Recent work on few layer shows PbI2 as a promising candidate for application in the field of ultrafast saturable absorbers27. However, research into the atomic structure of monolayer PbI2 has been limited to date because of the challenges in obtaining high-quality monolayer crystals and preparing suitable samples for transmission electron microscopy studies. Further work is needed to reveal the structure and dynamics of edges, point defects, vacancy clusters, and nanopores in PbI2 monolayer and its interaction with other 2D crystals, such as graphene.Layered PbI2 monolayer flakes from a starting bulk PbI2 powder. Liquid-phase exfoliation is one of the simplest methodologies for producing 2D materials on a large scale30. In the past decades, various research has been carried out to find suitable solvents based on their interactions with the 2D material to produce suspended 2D monolayer crystals. Surface tension, the Hilderbrand solubility parameter, the Hansen solubility parameter, surface tension components, etc. have been the widely used parameters to screen appropriate solvents35. Using these parameters, we screened the commonly used solvents and found chloroform (CHCl3) to produce monolayer 2D PbI2 crystals. We used annular dark-field scanning transmission electron microscopy (ADF-STEM) to studying the PbI2 atomic structure, by depositing it from solution onto a suspended graphene support and allowing it to dry38. The high electron transparency of graphene, enables provides excellent contrast from the Pb and I atoms in ADF-STEM. We report on the fundamental atomic structure, point vacancies, vacancy clusters, vacancy dynamics, edge terminations and edge etching, and the epitaxial interactions with the underlying graphene support.Here, we used liquid phase exfoliation (LPE) to isolate PbI2 is a unique exception to all the metal halide compounds that show CdI2 structure, in that it has the largest metal halide bond length39. As a result, the bonds are not as ionic as that of the other compounds that also show CdI2 crystal structure, such as MgI2, FeBr2, etc. However, it is sufficiently ionic to dissolve into polar solvents, such as dimethylformamide (DMF), n-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), and to some extent, water41. Recent research on Lewis basicity of solvents, also quantified by Gutmann’s donor number—Dn, has shown that solvents that solubilize the precursor (PbI2) at a total concentration of 1 M, have higher Dn values of >25 (ref. 42). Previous results on the liquid-phase exfoliation for other 2D materials have shown that the most efficient solvents have H-bonding components so as to maximize the dispersability of the material in the solution, which is in agreement with the Hansen solubility parameter theory44. We explored several different solvents and found that chloroform serves as an excellent medium to exfoliate PbI2. CHCl3 has low dipole moment (μ = 1.04), low dielectric constant (ϵT = 20 °C = 4.8), low donor number (Dn = 4), as well as has the ability to form hydrogen bonds47. In addition, CHCl3 has a very low boiling point of 61 °C which facilitates in quick and easy removal after solution dropcasting on to substrates.PbI2. Less sonication leaves multilayer PbI2 dispersed in the solution, whereas longer sonication time renders very small flakes or completely destroys the sheets , where the metal (Pb) atomic plane is in the middle and the two iodide atomic layers at the top and the bottom. A monolayer from a 2 H PbI2 bulk crystal structure  showed the same relative crystal orientation relative to the graphene crystal  results matching the experimental data. To understand why PbI2 adopts 1 H structure with concomitant alignment in these particular directions of graphene, we employed density functional theory (DFT) calculations to study the structural and energetic stability of the different alignments. We used a short-range relaxed atomic model of PbI2 on graphene, as shown in Fig. 2 and leads to these energetically favorable structure that are also observed in the experimental results.Interestingly, we also found that the crystal orientation of PbI2, because edges of 2D materials can influence the electrical, chemical, and catalytic properties due to the different bonding  between atoms54. Fig. 2 flakes, just after being deposited on the graphene. The edges are rough and do not appear to be highly faceted to a specific crystal lattice direction. After electron beam irradiation  transferred by an incident electron (@80 keV) to a single iodide or lead atom is calculated to be 1.38 and 0.85 eV, respectively58. This energy transfer from the incident electron to the specimen atoms is much lower than the required sputtering energy calculated by DFT. Hence, we can deduce that the mechanism of damage in this system is more complicated than purely knock-on damage from atomic sputtering, and likely involves radiolysis. This is not surprising, since PbI2 is a large bandgap semiconductor and therefore prone to ionization effects from the electron beam. Several different types of multiple atom point vacancies are identified, ranging from two atoms  than the single Pb atom (Z = 82), it has lower contrast in ADF-STEM. The line profiles in Fig. 2 structures59.We also observed multiple occasions where the defect Fig.  had one 6f, g,During electron beam irradiation, the vacancies migrated through the lattice and reconstructed. We performed DFT calculations for vacancy migration and found that the energy barrier for migration of lead atom, the in-plane migration of the iodide atom and the out-of-plane migration of iodide atom that corresponded to 0.32, 0.22, and 0.07 eV, respectively , 25% hydrogen in argon (H2), and 100% argon (Ar) were used for graphene synthesis. Before the reaction started, the system was first purged with 1000 sccm Ar, 500 sccm H2, and 100 sccm CH4 for 30 min. The furnace was then heated to 1060 °C with a ramp rate of 50 °C/min accompanied by a flow of 500 sccm Ar and 100 sccm H2. When the temperature reached 1060 °C, the copper was then annealed with the same flow rate for 1 h. Following the annealing process, the synthesis was carried out at 1060 °C for 1 hr with a flow of 500 sccm Ar, 100 sccm H2, and 5 sccm CH4. The furnace was removed from the sample, which allowed the sample to be fast cooled to room temperature.Graphene was synthesized by CVD on a copper substrate. A piece of copper foil was first sonicated in a diluted hydrochloric acid solution (1 mol/L) to remove the oxides on the copper surface. The copper foil was then sonicated in deionized water, acetone, and isopropanol for 5 min each to remove organic residues. To ensure uniformity of temperature during the whole growth process, the copper foil was positioned in the center of a furnace. A total of 1% methane in argon (CH2 powder from Sigma–Aldrich (99% purity) was added to chloroform to form a solution of concentration 1 mg/ml (~0.2 mM). The solution was sonicated in an unheated ultrasonic water bath  for ~30 min to make sure that all the lead iodide had exfoliated and dispersed in the solution. The dispersion was then left to stand for 24 h to let the bulk particles to settle down at the bottom of the container. Then, the supernatant of the dispersion (from the top) was extracted with a pipette and used for preparing TEM samples.PbI2 and vacuum annealing. A few drops (10–20 μl each) were taken from the supernatant of the dispersed solution of 1 mg/ml concentration of PbI2 in CHCl3 and dropcasted on to the TEM grid containing suspended graphene. The TEM holder was then baked in high vacuum at 60 °C to remove all the solvents and other impurities from the surface.Graphene was transferred onto a lacey carbon copper 400 mesh TEM grid using a poly (methyl methacrylate (PMMA) support and then the PMMA removed by acetone. It was then subsequently cleaned by Ar/HRoom temperature ADF-STEM imaging was performed using a JEOL ARM200F located at the David Cockayne Centre for Electron Microscopy (DCCEM) within the Department of Materials at the University of Oxford. An acceleration voltage of 80 kV was used for taking all the images, unless stated otherwise. Imaging conditions used a 30 µm condenser lens (CL) aperture with a convergence semiangle of 22.5 mrad and a beam current of 35 pA. The acquisition angles for these images was 70–220 mrad.2 crystal structure was drawn using Crystal Maker Version 10.3.1.Images were processed using the ImageJ software. Atomic models were constructed using Accelrys Discovery Studio Visualizer. Multislice image simulations were performed using JEMS. PbI63. A 10 × 10 × 1 supercell is used for calculating the sputtering energy and defect migration barriers, and two more different systems are designed to probe the short-range angle dependence of stacking energy: a hexagonal PbI2 flake  on continuous graphene substrate. The systems are varied with different angles between PbI2 and graphene . The elements are represented by projector-augmented wave potentials with 500 eV energy cutoff and the four (6s26p2) valence electrons for Pb, seven (5s25p5) for I, and four (2s22p2) for C are treated explicitly65. Initial relaxation and energetics are calculated via the generalized gradient approximation, Perdew−Burke−Ernzerhof, augmented by DFT-D3 method with Becke–Jonson damping for the interlayer dispersive interaction67. The first Brillouin zone is sampled by the tetrahedron method on a 4 × 4 × 1 k-mesh for the 10 × 10 × 1 supercell, and only gamma point for the angle-dependence studies. All structures are relaxed until the force on each atom is <0.01 meV/Å. The sputtering energy is defined by the energy difference between the crystalline structure and the one with a vacancy, for instance, the I sputtering energy is 69. A total of 10 × 10 supercells and 4 × 4 k-point grids are employed, and a criterion of 0.03 eV/Å is set for the force convergence. For VI migration, two pathways are considered: in-plane and out-of-plane directions, and only in-plane VPb migration is considered. The starting and end points for NEB search are prepared by removing the corresponding atoms from the relaxed pristine structure, and then further relaxed. The six intermediate images are interpolated by the Vasp TST toolkit70. The converged energy paths are the fitted by cubic spline functions.The structural, energetic, and defect migration calculations in this work are based on DFT implemented in the Vienna Ab-initio Simulation Package (VASP)2 intensity contrast, graphene sample without PbI2, different sizes of monolayer PbI2, proof of monolayer flakes instead of bilayer AA′ 1 H structure, T-phase structure on lacey carbon TEM grid, ADF-STEM images of structural transformation immediately after dropcasting on graphene, Moire pattern of 1 T and 1 H atomic models on graphene, zigzag alignment of PbI2 with graphene after edge etching, relative alignment of time frame of PbI2 etching from Fig. Effect of sonication duration and dropcasting, monolayer and bilayer PbISupplementary InformationPeer Review File


Quantifying which assembly processes structure microbiomes can assist prediction, manipulation, and engineering of community outcomes. However, the relative importance of these processes might depend on whether DNA or RNA are used, as they differ in stability. We hypothesized that RNA-inferred community responses to (a)biotic fluctuations are faster than those inferred by DNA; the relative influence of variable selection is stronger in RNA-inferred communities , whereas homogeneous selection largely influences DNA-inferred communities . To test these hypotheses, we characterized soil bacterial communities by sequencing both 16S rRNA amplicons from the extracted DNA and RNA transcripts across distinct stages of soil primary succession and quantified the relative influence of each assembly process using ecological null model analysis. Our results revealed that variations in α-diversity and temporal turnover were higher in RNA- than in DNA-inferred communities across successional stages, albeit there was a similar community composition; in line with our hypotheses, the assembly of RNA-inferred community was more closely associated with environmental variability (variable selection) than using the standard DNA-based approach, which was largely influenced by homogeneous selection. This study illustrates the need for benchmarking approaches to properly elucidate how community assembly processes structure microbial communities. Research on ecological succession is key to advance our understanding of how communities are assembled and affect ecosystem functioning and dynamics. In accordance with classical studies on plant community succession, the relatively recent advances in high-throughput sequencing technologies and microbiome profiling have revealed that microbial communities across a broad range of habitats also undergo sequential changes through different time scales ,2,3.Most studies have profiled bacterial community composition across succession gradients by sequencing 16S rRNA gene from environmental DNA ,4,5,6. HDisentangling the relative influences of community assembly processes structuring the microbiome distribution is important for understanding community turnover during succession . For insQuantifying the assembly processes is often dependent on either taxonomic or phylogenetic information of the investigated meta-community. Interestingly, it was shown that the phylogenetic structure of RNA-inferred bacterial communities is significantly more clustered than that of the DNA-inferred communities, thus resulting in a stronger environmental filtering signal . SelectiIn this study, we investigated the dynamics of bacterial communities across five successional stages in a primary succession soil chronosequence. Soil samples were collected across the successional stages and within successional stages at four time points. The analysis of DNA-derived 16S rRNA gene sequences encompassed the total fraction of bacterial communities including DNA from non-viable cells; and the RNA-derived 16S rRNA sequences encompassed the content of bacterial ribosomes indicating the potentially active fraction of total bacteria communities. We first examined to what extent these two approaches affect the results of bacterial community turnover during primary succession, and then compared the interplay of community assembly processes, and evaluated whether these two approaches affect the outcomes and conclusions of microbial community successional dynamics in soils.The study was conducted in a salt marsh ecosystem at the island of Schiermonnikoog, the Netherlands . This island displays a progressive growth expansion eastwards caused by the continuous sedimentation of particles carried by wind, currents and flooding cycles. This natural chronosequence spans over 100 years of succession, in which early successional stages are located in the east and late stages in the west. Soil physicochemical properties, aboveground biomass, and ecosystem disturbances gradually change from early to late successional stages ,21. For To characterize the spatiotemporal variation of bacterial communities in this system, triplicate soil samples were collected from five successional stages  in May, July, September and November 2017 . At each replicate, 20 soil cores  were randomly sampled. A total of 2 g of the collected soil that was homogenously mixed was preserved in LifeGuard Soil Preservation Solution  and stored at −80 °C for further nucleic acid extraction.The total RNA and DNA were co-extracted from 2 g of soil for each of the 60 samples using the RNeasy PowerSoil Total RNA kit  with the RNeasy PowerSoil DNA Elution kit , following the manufacturer’s instructions . After eWe profiled the DNA- and RNA-inferred bacterial communities by sequencing the V4 region of the bacterial 16S rRNA gene and 16S rRNA transcripts, respectively, using primer pair 515F (5′-GTGCCAGCMGCCGCGGTAA-3′) and 806R (5′-GGACTACHVGGGTWTCTAAT-3′) ,23. Eachde novo phylogenetic tree was generated from representative sequences by aligning sequence fragments via MAFFT, masking ambiguous alignments and inferring a tree using the FastTree algorithm [We used the QIIME2 pipeline (version 2019.10) to process 16S rRNA gene and rRNA sequences . The demlgorithm . A rooteAll subsequent analyses were carried out in R (v3.5.0) ,29. To cbray). We did this by comparing the ASV taxonomic turnover between a pair of communities and the null distribution [bray metric, the Bray–Curtis dissimilarity between observed communities was first calculated. Then, the null distribution of the Bray–Curtis dissimilarity between simulated communities were constructed by randomly sampling ASVs 999 times. The RCbray matrix was generated by comparing the Bray–Curtis dissimilarity between a pair of communities and the null distribution of Bray–Curtis dissimilarity. When |βNTI| < 2 and RCbray > 0.95, community turnover is dominated by dispersal limitation, as the dissimilarity between observed communities is higher than the expectation. |βNTI| < 2 and RCbray < -0.95 indicates homogenizing dispersal, as the community turnover between observed communities is lower than the null expectation. If |βNTI| < 2 and |RCbray| < 0.95, both phylogenetic and taxonomic community turnover of observed communities are not different from the null distributions. In other words, neither selection nor dispersal dominate the assembly processes, their influences on community turnover act together with drift, thus being termed as ‘undominated processes’. Together, we quantify the relative influence of each assembly process by the proportion of each assembly process within each dataset or treatment.We applied a framework that assesses the phylogenetic and taxonomic turnover of communities, and further used null modelling distributions to quantify the relative influences of distinct assembly processes mediating community turnover ,32. In tribution . To creaThe analysis of βNTI relies on the correlation between relatedness of species phylogeny and their ecological niches. We estimated the optimal niche of ASVs (occurrence > 5) with soil pH, soil sodium concentration, soil organic carbon and soil water content using the function ‘wascores’ in the package vegan. Phylogenetic distance across ASVs was generated using the ‘cophenetic’ function in the package picante. Last, we tested the phylogenetic signal  using the function ‘mantel.correlog’ in the package vegan. For all the four soil parameters, significant positive correlations were observed at short phylogenetic distances, confirming the assumption for suitable ecological inferences using short phylogenetic distance based on βNTI .https://github.com/Jia-Xiu/Jia_et_al_Microorganisms_2020.Figures were made using the ggplot2 package . All scrAfter denoising, filtering the low quality, short length and chimeric sequences, as well as removing singleton and non-target taxa, the total dataset consisted of 12,741,738 reads . After rarefying the feature table to 15,000 reads per sample, the rarefaction curves for most DNA-based samples reached a steady plateau, but some RNA-based samples did not, which indicates the sampling efforts were enough for most DNA-based samples, while more sequencing depth was potentially needed for some RNA-based samples . In the R2 = 0.48 and R2 = 0.41, respectively; p < 0.001), followed by sequencing approach  in both DNA and RNA datasets to be Proteobacteria, Bacteroidetes, Actinobacteria, Acidobacteria and Planctomycetes . As ecolbray metric. The results show that selection  dominated the assembly processes of both DNA- and RNA-inferred communities  bacterial cells contain more ribosomes than inactive cells . In thisThe quantification of community assembly processes using both DNA- and RNA-based approaches was dominated by selection. In relative terms, the influence of variable selection was higher in the RNA-inferred communities, suggesting that RNA-inferred communities more rapidly respond to environmental fluctuations compared to a more ‘stable’ scenario of DNA-based communities. This is consistent with a previous finding showing that the phylogenetic community structure of RNA-based communities changes quickly in response to variations in pH and carbon to nitrogen ratios . MoreoveThe broad use of amplicon sequencing has greatly advanced our understanding of the ecological processes structuring bacterial communities during succession. However, DNA- and RNA-based approaches can generate distinct profiles of community composition. This can be caused by differences in the stability of DNA and RNA, differences in the copy numbers of the 16S rRNA gene, in addition to changes in the number of transcripts of this gene, i.e., differences in cell active states and lifestyle. Here, we used these two approaches to profile bacterial communities across a primary successional gradient and quantified the relative influences of community assembly processes governing community turnover. Our results demonstrate that RNA-based communities have greater variation in community composition and are relatively more influenced by variable selection; while DNA-inferred communities have less variation and are relatively more influenced by homogeneous selection. Future studies advancing knowledge on the community assembly of bacterial communities and successional dynamics must be cautious when interpreting data obtained from either DNA- or RNA-based sequencing approaches.


Gas hydrate technology holds great potential in energy and environmental fields, and achieving efficient gas hydrate formation is critical for its industrial application. Graphene is a novel carbon-based nanostructured material with excellent thermal conductivity and a large specific surface area. Therefore, the use of graphene-based materials for the promotion of gas hydrate formation might be feasible and has aroused a lot of interests. Accordingly, to evaluate the current research on graphene-based promotion of gas hydrate formation, this work presents a review of existing studies involving graphene-based promoters of gas hydrate formation. Here, the studies applying various types of graphene-based promoters for gas hydrate formation are listed and detailed, the peculiar properties of graphene-based promoters are discussed, and the promotion mechanisms are analyzed. Through this review, comprehensive insight into graphene-based promotion of gas hydrate formation can be obtained, which can guide the design and applications of novel graphene-based promoters and might contribute to achieving efficient gas hydrate formation. Gas hydrates have captured an increasing amount of attention during the past decades because of their great potential for energy storage and environmental conservation  reduced the hydrate formation period by 45–80% and improved the hydrate formation rate and the storage capacity by 190–660% and 45–70%, respectively, compared with pure water. The results implied that the graphene nanosheets not only increased heterogeneous nucleation in the system and provided abundant active sites for hydrate nucleation but also produced a high transfer efficiency that could remove the heat generated by hydrate formation from the system, consequently improving the efficiency of methane hydrate formation. Due to similar promotion mechanisms, graphite nanoparticles also have positive effects on gas hydrate formation. Zhou et al.  compared in a pure water system. Adding SDBS into GN nanofluid could inhibit GN aggregation and greatly reduce the surface tension of the solution, making gas molecules dissolve in water more easily, which favored CO2 hydrate formation.In addition to the direct promotion of gas hydrate formation, graphene can also be mixed with surfactants to generate surfactant-stabilized nanofluids. Graphene usually exhibits poor dispersity and stability during gas hydrate formation, causing weak performance and cyclability during promotion. Therefore, a mixture of graphene and surfactants has been employed, where the surfactants function as both stabilizer and co-promoter. Hosseini et al.  used SDS−1 of SGO, and the storage capacity reached 140–150 v/v  onto surfaces of graphene/GO, aiming to obtain novel graphene-based promoters with desirable properties to significantly promote gas hydrate formation. Moreover, because of its nanostructure and remarkable electrical conductivity, graphene might serve as a nano-sized electric rotor under an electric field that could effectively stir within nano-sized confinement spaces, which might possibly be applied for HFP promotion via improving mass transfer.The existing studies on graphene-based promotion of gas hydrate formation were implemented in lab-scale experiments, so the promotion effects, stability, and cyclability of graphene-based promoters in gas hydrate formation need to be investigated in pilot tests, which could be conducted in future work. Additionally, further research can focus on grafting graphene/GO with functional groups to produce exceptional CMG or introducing functional nanoparticles (e.g., Ag and FeM-TS wrote and revised the manuscript. FW and G-DZ supervised and revised the manuscript. All authors contributed to the article and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


The multiple micronutrient supplement (MMS) based on the United Nations International Multiple Micronutrient Antenatal Preparation (UNIMMAP) formula provides women and their offspring with a healthy start to life in an efficacious, safe, and cost‐effective way. To date, however, no precise and transparent specifications exist to support the manufacturing and distribution of UNIMMAP–MMS globally. To palliate for this need, the MMS Technical Advisory Group at the New York Academy of Sciences and the Micronutrient Forum convened a technical consultation to develop an open access UNIMMAP–MMS Product Specification for the manufacturing of this product. The specifications offered in this paper cover: ingredients, excipients, and processing aids used in the manufacturing of UNIMMAP–MMS; stability studies recommended under different testing conditions and climatic zones; packaging considerations; manufacturing standards, including pharmacopeia standards, manufacturing practices, certificates of analysis, change control, and quality agreement; finished product specifications, including tablet characterization and purity, potency assay; analytical test methods; and storage and transportation requirements. This paper results from deliberations of a panel of international experts assembled in Washington DC, November 11 and 12, 2019 and commissioned by the MMS Technical Advisory Group at the New York Academy of Sciences and the Micronutrient Forum to ensure consistency in the manufacturing of quality and affordable UNIMMAP–MMS across antenatal care programs, while allowing for variances in national regulatory and pharmacopoeia standards. Micronutrient deficiencies can have deleterious impacts on maternal health and pregnancy outcomes.1aThis specification states a preference for a film coated tablet, which provides certain benefits, including lower cost and better performance and stability under expected conditions of high temperature and humidity. However, capsules that demonstrate equal or better performance may also be considered.The product defined by the following specification conforms to the UNIMMAP) formula and is an MMS for pregnant women that is delivered in the form of a film coated tablet.22.1bReaders should consider the following: (1) UNIMMAP–MMS might be considered a medicinal product in some countries, and if so, the product must comply with the respective regulatory requirements of that country; (2) no reference is made in this document to “pharmaceutical” or “medicinal” ingredients or products, although the product might be considered a medicinal product in some countries; and (3) this specification outlines the minimum requirements for the manufacture of a UNIMMAP–MMS; as previously indicated, if a country has stricter requirements, they must be met. Where such standards do not exist, ingredients may be used in the UNIMMAP formulation if they have been shown to be of acceptable food grade quality using other suitable procedures.Table 2.2Excipients used in the UNIMMAP formulation generally are prepared from ingredients that meet USP, National Formulary (NF), Food Chemical Codex, or other globally recognized pharmacopeia compendial standards. Where such standards do not exist, ingredients may be used in the UNIMMAP formulation if they have been shown to be of acceptable food grade quality using other suitable procedures.Ingredients may be added to the UNIMMAP formulation provided that the ingredients comply with applicable regulatory requirements, and do not interfere with the assay and tests prescribed for determining compliance with the bulk or finished UNIMMAP–MMS product specification.2.3Processing aids or other materials used in the manufacture of the UNIMMAP formulation that do not end up in the finished product should be of acceptable food grade quality using suitable procedures.purified water.Potable water must meet, at minimum, all the requirements for drinking water promulgated in the U.S. Environmental Protection Agency's National Primary Drinking Water Regulations (40 CFR Part 141), and any applicable state and local drinking water requirements that are more stringent. For manufacturers outside the United States, potable water meeting equivalent requirements may be acceptable with justification, for example, the drinking water regulations of the European Union (European Commission Directive 98/93/EC) or Japan Drinking Water Quality Standards. Water not meeting such requirements should not be permitted for use in the water purification system for 3The UNIMMAP–MMS finished product labeling must state a shelf‐life (expiration) date that is indicative of the date before which the product is ensured to meet applicable specifications of identity, strength, quality, and purity when stored under labeled conditions. The shelf‐life (expiration) date must be supported by suitable stability data, following the guidelines in International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) Q1A.A documented ongoing testing program must be designed to monitor the stability characteristics of the UNIMMAP–MMS, and the results must be used to establish appropriate storage conditions and shelf‐life (expiration) dates for the UNIMMAP–MMS finished product. Test procedures used in stability testing must be validated and indicate stability. Stability samples should be stored in container‐closure systems that simulate the packaging proposed to distribute the finished UNIMMAP–MMS for consumer/patient use. Stability studies should include testing of those attributes of the dietary supplement that are susceptible to change during storage and that influence the quality of the dietary supplement.The first three production batch(es) should be placed on the stability monitoring program to establish the product shelf‐life (expiration) date. The lots should be those that are manufactured at the regular manufacturing scale; however, two of the three production batches can be at least 1/10th the size of the manufacturing scale. Thereafter, at least one batch per year of manufactured UNIMMAP–MMS should be added to the stability monitoring program. All batches must comply with the finished product specification throughout the product shelf‐life (expiration) date.As appropriate, the stability storage conditions for temperature and relative humidity for product intended for use globally should be for Climate Zone IVb, hot and very humid. However, actual climatic conditions in the country of destination of the UNIMMAP–MMS may require stability studies to be carried out under the conditions of a different climatic zone . Table Long term = 0, 3, 6, 9, 12, 18, 24, 30, and 36 months;Accelerated = 0, 3, and 6 months.The frequency of testing should be sufficient to establish the stability profile of the dietary supplement. The storage conditions and length of studies chosen should be sufficient to cover storage, shipment, and subsequent use. Data from the accelerated storage condition can be used to evaluate the effect of short‐term excursions outside the label storage conditions, such as might occur during shipping. The shelf‐life (expiration) period of the UNIMMAP–MMS should be 30 months, at minimum. The following testing frequencies are recommended:Where an expectation (based on development experience) exists that results from accelerated studies are likely to approach significant change criteria, increased testing should be conducted by adding samples at the 1‐ and 2‐month time points. In general, a significant change for a dietary supplement is defined as a 5% change in the assay from its initial value; or failure to meet any of its product specification acceptance criteria.44.1cNo evidence currently exists yet in the literature indicating that packaging type/tablet count increases uptake, adherence rates, or clinical attendance. However, the 180‐count bottled product makes it less expensive per tablet to dispense and has a lesser environmental impact than other packaging. For these reasons, the 180‐count‐HDPE‐bottled product was selected as the packaging option of choice in the preparation of this document. If future implementation research, or if program needs indicate otherwise, other packaging options may be considered with appropriate modifications to these technical specifications.This specification focuses on the use of UNIMMAP–MMS packaged in bottles containing 180 tablets per bottle. Bottles (or blister packaging) containing 30 tablets are acceptable, but packaging options/tablet counts should be considered in light of cost and environmental implications, and evidence that may come later as to the impact that a particular packaging option or tablet count may have on distribution, uptake, adherence rates, or clinic attendance.Bulk packaging for business‐to‐business transactions is acceptable with demonstrated stability. Bulk packaging for clinics  should be avoided due to health and safety concerns to avoid inadvertent child exposure to UNIMMAP–MMS; and to avoid repackaging by clinic staff of MMS into other temporary less desirable packaging , which may cause premature product deterioration.4.2White/opaqueScrew capHigh‐density polypropylene (HDPE) material Tamper evidentChild resistantBottles must be:The need for desiccant depends on tablet formulation and must be determined by the manufacturer based on experience and supporting stability data.4.3®, should be used to ensure the stability of the product throughout the shelf‐life of the product. Using a child‐resistant version of a blister pack is deemed impractical, as the “child‐resistant” requirement makes a blister pack unusually difficult to dispense package contents.If blister packaging is used, a thermoformable moisture barrier film, such as Aclar4.4Labeling must comply with applicable country of destination regulatory requirements for the food/dietary/nutritional supplement.Quantitative label claims for the product must be truthful and accurately reflect the contents of the declared food/dietary/nutritional ingredients; fortified or fabricated nutrients must meet 100% of the quantitative label claim throughout the shelf‐life of the product for products that can be distributed in the United States. For products distributed outside the United States, fortified or fabricated nutrients must meet USP compendial assay acceptance criteria . The label must include a domestic address or phone number through which an adverse event report for a dietary supplement may be received.55.1United States Pharmacopoeia (USP);European Pharmacopoeia (Ph.Eur.);International Pharmacopoeia (Ph.Int.);British Pharmacopoeia (BP);Japanese Pharmacopoeia (JP).Compliance to the following international pharmacopoeial standards is acceptable for food/dietary/nutritional supplement ingredients and finished product:5.2U.S. FDA 21 CFR Part 111 Current Good Manufacturing Practice in Manufacturing, Packing, Labeling, or Holding Operations for Dietary Supplements; andUSP–NF general chapter 〈2750〉 Manufacturing Practices for Dietary Supplements.The UNIMMAP–MMS must be manufactured under current good manufacturing practice (cGMP) regulations promulgated by an internationally recognized regulatory authority , or other GMP guidelines by a stringent authority ), by a PIC/S member, or by a globally recognized pharmacopeia , including but not limited to:The manufacturing site and operations should be audited by an accredited third‐party certification body.5.3Certificates of analysis (CoA) must be issued for each batch of UNIMMAP–MMS product. The CoA should list the name and item code of the UNIMMAP–MMS product, batch number, tested and released dates, and the expiration date. The CoA should list each test performed, the specific identity of the test procedure, the acceptance limits or criteria, and the results with numerical units, as appropriate. The CoA should be dated and signed by authorized quality unit personnel. For CoAs issued for external use, the CoA should list the name, address, and telephone number of the manufacturer.The testing protocol should include the performance of full specification testing. However, a reduced level of testing (or sampling) for particular specified parameters may be allowed based upon one or more of the following: statistical analysis of an adequate quantity of historical test data; statistical confidence in the capability of the manufacturing process as determined by suitable verification; or ongoing monitoring of the process using recognized statistical process control techniques. The manufacturer must notify the purchaser of the UNIMMAP–MMS product in writing of any change to the testing protocol.5.4The UNIMMAP–MMS product may be manufactured meeting Halal requirements. The exact requirements shall be obtained from local authorities or from an accredited source.5.5A manufacturer might make changes to the UNIMMAP–MMS product's specification, raw material source, manufacturing processing steps and/or equipment, testing protocols, or any other criteria deemed to be essential or significant to product quality. Manufacturers must notify the purchaser of the UNIMMAP–MMS product of any significant changes that might affect product quality, in writing upon implementation, along with the rationale for the change(s).A manufacturer must also notify the purchaser of the UNIMMAP–MMS product of any change to its manufacturing site, including any changes to the certification status held by the manufacturer from a GMP issuing authority.5.6There should be a written and approved contract or quality agreement between the contract giver and the contract acceptor that defines in detail the GMP responsibilities, including the quality measures, of each party. The contract should permit the purchaser to audit the manufacturer's (seller's) facilities for compliance with GMPs. Where subcontracting is allowed, the seller should not pass to a third party any of the work entrusted to it under the contract without the buyer's prior evaluation and approval of the arrangements.6The UNIMMAP is a formulation for use by pregnant women. UNIMMAP–MMS was developed during a workshop of experts organized by the WHO, UNICEF, and the United Nations University in 1999 specifically to identify an MMS formula for efficacy clinical trials. It contains 15 micronutrients at dosages that approximate the recommended dietary allowances for pregnancy.Tables 7Tests and examinations that are used to determine whether UNIMMAP–MMS specifications are met must be appropriate for their intended use, and scientifically validated methods. Test methods or procedures must meet proper standards of accuracy and reliability.If the test procedure is not in an official compendium, the procedure must be validated according to USP general chapter <1225> Validation of Compendial Procedures or ICH Q2(R1) Validation of Analytical Procedures: Text and Methodology. Method performance characteristics include specificity, linearity, range accuracy, precision, detection limit, and quantitation limit, and those of interest may vary depending on the type of test: identification, assay, impurities, or performance.If the test procedure is in an official compendium, such as USP‐NF, the procedure only needs to be verified for its suitability under actual conditions of use, according to USP general chapter <1226> Verification of Compendial Procedures. Verification requirements should be based on an assessment of the complexity of both the procedure and material to which the procedure is applied. Verification is not required for basic compendial procedures, such as loss on drying, residue on ignition, and simple instrumental determinations, such as pH measurements.An alternative method or procedure is defined as any method or procedure other than the compendial method or procedure for the article in question. The alternative method or procedure must be fully validated and must produce comparable results to the compendial method or procedure within allowable limits established on a case‐by‐case basis. Alternative methods or procedures can be developed for any number of reasons not limited to simplification of sample preparation, enhanced precision and accuracy, improved (shortened) run time, or being better suited to automation than the compendial method or procedure. Only those results obtained by the methods and procedures given in the compendia are conclusive.8The UNIMMAP–MMS product must be held under appropriate conditions of temperature, humidity, and light so that its identity, purity, strength, and composition are not affected .The UNIMMAP–MMS product must be distributed under conditions that will protect it against contamination and deterioration. The manufacturer and purchaser need to work together to ensure that this requirement is met.Segregation, isolation, or the use of packaging to protect the UNNIMAP‐MMS product from contamination from other articles in the same load;Use of vehicles and transportation equipment that are adequately designed and maintained in a sanitary condition to prevent the UNIMMAP–MMS product from becoming contaminated during transportation operations; andUse of vehicles and transportation equipment that are adequately designed, maintained, and equipped to transport UNNIMAP‐MMS product under adequate temperature and humidity control to prevent UNNIMAP‐MMS product from becoming adulterated during transportation.All transportation operation must be conducted under such conditions and controls necessary to prevent UNIMMAP–MMS product from becoming adulterated during transportation. Responsibility for ensuring that transportation operations are carried out adequately must be assigned to competent supervisory personnel. Shippers, receivers, loaders, and carriers engaged in transportation must conduct all transportation operations under such conditions and controls necessary to protect the UNNIMAP‐MMS product from becoming adulterated during transportation. Such operations include, but are not limited to, taking effective measures such as:The first manufactured batch of the UNIMMAP–MMS product should be distributed first. Distributing operations must be designed to facilitate its recall, if necessary.9The authors declare no competing interests.


We perform a numerical simulation of the effects of an orthogonal magnetic field on charge transport and shot noise in an armchair graphene ribbon with a lattice of antidots. This study relies on our envelope-function based code, in which the presence of antidots is simulated through a nonzero mass term and the magnetic field is introduced with a proper choice of gauge for the vector potential. We observe that by increasing the magnetic field, the energy gap present with no magnetic field progressively disappears, together with features related to commensurability and quantum effects. In particular, we focus on the behavior for high values of the magnetic field: we notice that when it is sufficiently large, the effect of the antidots vanishes and shot noise disappears, as a consequence of the formation of edge states crawling along the boundaries of the structure without experiencing any interaction with the antidots. Graphene, a planar hexagonal lattice of carbon atoms, represents one of the currently most studied and promising materials ,2,3,4,5.Since its envelope-function transport equation is formally equivalent to the relativistic Dirac equation ,12,13,14Due, in particular, to its very high mobility and its current carrying capability, graphene has been often considered as a candidate to replace commonly used semiconductors, such as silicon, in “Beyond Moore” nanoelectronics ,30,31,32It has been shown that a gap can be opened in graphene by means of lateral confinement, i.e., by defining a nanoribbon ,33,34; hOther methods have been proposed for opening up an energy gap in graphene ,37, and,B on the transport and noise behavior of armchair graphene ribbons both with a regular and an irregular distribution of antidots , its effect on transport was simulated by introducing a vector potential We have added to our code for the unction)  simulatielocity) ,19,54,65 A→=Bxy^ .x, the condition on the longitudinal invariance of the vector potential within each section translates into a limitation on the magnetic flux threading each section, which has to be much less than the flux quantum. Therefore, we have to divide the device into a large number of thin sections.We compute the transmission matrix of the device using a recursive scattering matrix technique . We subdx of all the physical and geometrical parameters, within each section the four envelope functions of monolayer graphene x and of a transverse component depending only on y: e is the elementary charge; h the Planck constant); E is the injection energy; Due to the invariance along uivalent ,67 to thdomain 0,W˜)(1)φ→domain 0,W˜)(1)φ→A and B of the four envelope functions at the interface between neighboring sections, we have computed the scattering matrix of the transverse region containing this interface [t. The conductance G and the Fano factor F  have been obtained using the Landauer–Büttiker approach:Then, by enforcing the continuity on the two graphene sublattices nterface . FinallyThe number of transport modes considered in the calculation was chosen in such a way that a further increase of this number would not alter the transport results within a given accuracy.At the entrance and at the exit of the considered nanostructure, we have included two regions with low potentials, which emulate the effects of the input and output contacts and guarantee the injection of a sufficient number of propagating modes into the ribbon.The correctness of the presented approach has been confirmed by performing some tests also with the alternative gauge Equation  with a nWe have also used our code to simulate the results of a conductance measurement on a nanopatterned graphene nanoribbon that is available in the literature. In reference  a 100 nmeference  yields gx and y directions) by a random quantity uniformly distributed between In order to obtain an aspect ratio among those commonly used in experiments and an overall size yielding a problem of manageable computational complexity, we have considered a 110 nm wide and 200 nm long armchair graphene ribbon (corresponding to a width of 894 dimer lines) containing a set of circular antidots, all with a radius of gion see . We haveE: 0.02, 0.1 and 0.3 eV) the conductance  ,46 and bis case) ,33,34. SE for several values of the magnetic field, for the cases of ordered and disordered antidots. We see that, starting from an energy gap of the order of 0.06 eV for In order to analyze the effect of the magnetic field on the energy gap, in ferences ,62 for uWe notice that this agrees with the behavior . In the absence of confinement, for high values of the magnetic field B the electrons can propagate only through the Landau state with E. Therefore, for high values of B the conductance is equal to B, the Landau levels decrease and therefore the number of propagating modes increases. When B reaches the value Now let us focus on the values of energy and magnetic field for which the sample has a nonzero conductance. In particular, let us consider the behavior of the conductance as a function of the magnetic field obtained for E , because a semi-classical approximation is accurate if the Fermi wavelength is sufficiently small with respect to the geometrical feature sizes of the device. As a rule of thumb for the validity of the semi-classical approximation, we can compare [A is the area of the antidot lattice unit cell) due to the Aharonov–Bohm interference between the components of the wave function scattered by an antidot [When the antidots are present, the behavior is less regular and several minima and oscillations appear. These features can be explained with the effects studied in GaAs/AlGaAs  heterostructures in reference  and in girection . This ap compare  the Fermdots see a, it givdots see a for B=8 antidot .B, we notice that for large enough B the effect of the antidots vanishes. Indeed, for the energies and magnetic fields for which an energy gap is not present, from a semiclassical point of view the motion of the charges can be described in terms of cyclotron orbits. By increasing the magnetic field B, the cyclotron radius Finally, let us look at the conductance and noise behavior for high magnetic fields (which represents the main focus of this work). By examining the behavior of the conductance as a function of the magnetic field E/(evFB)  decreasetructure b withoutWe have presented an extension of our envelope-function simulator with the inclusion of a mass term (in order to define regions in which particles cannot penetrate) and of the effect of magnetic field, in order to study the transport and noise behavior in an armchair graphene ribbon of a realistic size, with an antidot lattice and an orthogonal magnetic field. We have observed that, as for a graphene sheet, in the case of a confined perforated graphene structure, the energy gap decreases as the magnetic field is increased. Moreover, our results show that, as could be expected from the analogy with ordinary disordered semiconductors, for high values of the magnetic field, the effects of the antidot lattice on the conductance and noise behavior of the structure vanish, as a consequence of the formation of the edge states moving along the boundaries of the structure. In such conditions, transport becomes ballistic and shot noise vanishes. Therefore, such an effect is insensitive to the particular nature of the material. From the point of view of the application of graphene-based devices to digital electronics, nanopatterning with an array of antidots does indeed lead to a gap significantly larger that the one achievable by means of lateral confinement alone; however, the antidots act also as scatterers, thereby lowering the maximum achievable current and therefore the resulting effective mobility. Thus, the antidot density and layout must be chosen carefully, as a result of a trade-off between gap opening and conductance suppression. Our simulation approach and the presented results can be of assistance in establishing such a trade-off, and, in general, in the design and optimization of graphene-based devices and sensors operating in the presence of magnetic fields.


The design and fabrication of a new effective manufacturing method of heteroatom-doped carbon materials is still ongoing. In this paper, we present alternative and facile methods to obtain N-rich graphene with the use of low energy gamma radiation. This method was used as a pure and facile method for altering the physical and chemical properties of graphene. The obtained materials have an exceptionally high N content—up to 4 wt %. (dry method) and up to 2 wt %. (wet method). High-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and X-ray photoelectron spectroscopy (XPS) studies allowed us to evaluate the quality of the obtained materials. The presented results will provide new insights in designing and optimizing N-doped carbon materials potentially for the development of anode or cathode materials for electrochemical device applications, especially supercapacitors, metal–air batteries and fuel cells. Nitrogen atoms are exclusively bonded as quaternary groups. The method is expandable to the chemical insertion of other heteroatoms to graphene, especially such as sulfur, boron or phosphorus. Graphene has recently attracted the attention of the research society as well as industry circles. It belongs to the materials category called nano-carbons and particularly to the 2D class of materials. Theoretically, pristine graphene comprises only carbon atoms with some hydrogen atoms at the edge of each graphene plane. The description applies to paternal graphene planes as defined in the materials science encyclopedia and IUPAC documents ,2. Howev3 [Thus, facile and high-yield methods are explored for N insertion to carbon matrixes  since graphene’s chemical reactivity is limited. On the contrary to graphene oxidation, which is relatively easy to perform and has been known for a long time by standard wet chemistry oxidants like KMnO3 , the nit3 ,25,26  like carbon black, pyrolytic chars and activated carbons, in which heteroatoms may appear due to their transfer from a source material upon carbonization. Another way of heteroatom insertion is based on the presence of some surface reactive centers on amorphous carbon surfaces . Graphene hardly undergoes such heteroatom modification scenarios. Therefore, any method enabling the insertion of heteroatoms has a practical meaning. This fact points out the importance of the research concept presented in this paper.The morphology details of representative materials and pristine graphene nanoplatelets are shown in the SEM and HRTEM images . Figure The elemental composition for the N-doped graphene samples are given in 2/g. The high surface area is achieved due to the diminishing size of graphene plates (single and π-π stacked). Size diminishing means an increase in reactive centers located at the edges of graphene sheets. For smaller sheet the ratio: number of edge atom-to-mass is higher and therefore better for processes exploiting the reactivity of outer carbon atoms. Due to the same reasoning, the intensity of N-doping for the 150 nanoplatelets series (150 m2/g) is less spectacular. Elemental composition regarding C content in pristine (raw) nanoplatelets is inconsistent with their surface area. Lower C-content of 150/750 series in comparison to 300 series is a sign of the natural reactivity of the material exposed to air/oxygen even at room temperature. The highest C-content for 300 raw nanoplatelets is expectedly accompanied by the lowest O-content bonded to graphene planes as a result of a spontaneous reaction between carbon (graphene) and oxygen atoms (air).Graphene nanoplatelets of the 750 kind are the most susceptible to N-doping by gamma radiation despite of the type of doping approach (“wet” or “dry”). The value 750 is the level of average surface area, which in this case is close to 750 mThus, the 300 platelets are the less reactive material among all graphene platelets under investigation. The assumed highest chemical stability for 300 nanoplatelets resulted in the lowest susceptibility to N-doping even in the experimental conditions conducive to chemical reaction (gamma irradiation).The “wet” and “dry” methods differ because of the triggering of co-reactivity to oxygen. In both methods, oxygen is present in the reaction space: atmospheric oxygen (“dry” method) and water included oxygen (“wet” method). The mentioned difference applies to the case of the most reactive material, i.e., 750 nanoplatelets treated with 3D dose, where the oxygen content increased to the range of 12.395–14.72% O (“wet” method) from 11.09% O for pristine material. A similar phenomenon did not occur for “dry” method, when a slight decrease in O-content might be observed upon doses 1D, 2D and 3D.All gamma radiation-treated samples are characteristic because of very high C-content, which is definitely better than that for graphene oxide (C/O 1.5–2.5). The C-to-O mass ratio is differentiated regarding the doping method and the nanoplatelets kind.Raw graphene: 12—150 platelets, 85—300 platelets, 8—750 platelets.“Dry” method: 16–85—150 platelets, 18–95—300 platelets, 8–9—300 platelets.“Wet” method: 12–14—150 platelets, 13–45—300 platelets, 6–7—750 platelets.C/O ratios for gamma irradiated 750 nanoplatelets (“dry” method) are on average similar to C/O ratios measured for pristine graphenes. C/O ratios for “wet” method modified platelets are the lower than for raw graphenes and lower than corresponding values for materials subjected to “dry” treatment. Thus, the “wet” method beside N-insertion doubtlessly leads to oxidation of graphene matrixes as a side (unwanted) effect.The XRD diffractograms of the obtained materials are shown in −1 and corresponds to the tangential vibrations of carbon atoms. Thus, G peak intensity may be a good measure of a sample’s graphitization. N-doped graphene exhibits two strong characteristic bands at 1340 cm−1 (D band) and 1580 cm−1 (G band). These bands are characteristic for graphene [The Raman spectra (532 nm laser) of the obtained materials are shown in graphene ,43. In tD/IG) depends on the level of the disorder. The ID/IG ratios for GF_150 series are between 0.23 and 0.50, for GF_300 series are between 0.45 and 0.70, and for GF_750 series are between 0.58 and 0.94, respectively, as shown in D/IG ratio clearly demonstrates the defects in the graphene structure. The differences in the ID/IG ratios for three obtained series confirm that the materials contain a different number of defects in the carbon structure.The ratio of the intensities between the D and G bands  investigations. Typical N-insertion methods reviewed in the introduction are characteristic because of diversification of N atoms bonding to graphene matrixes. Several structures are typically assumed: quaternary, pyridine, pyridone, amine, pyroll, imid, amid, lactam, among which quaternary groups are of primary importance for electrode-based applications . XPS studies were aimed at the detection of the chemical environment of inserted N atoms.2 hybridized atoms (band C 1s at binding energy 284.6 eV), which is characteristic for graphene materials. The C1s spectra of N-doped graphene are composed of seven peaks corresponding to: C=C bond (sp2) peak at 284.6 eV [3) peak at 285 eV [The XPS spectra of the two representative samples of investigated series were determined and are demonstrated in 284.6 eV , C–C bont 285 eV ,45, C–O–t 285 eV ,41, C=O t 285 eV ,45, O–C=t 285 eV , and peat 285 eV . The tott 285 eV ,45,47. It 285 eV ,45, respt 285 eV ,51,52,53Sliwak et al.  reportedGamma irradiation causes the formation of reactive sites in the carbon matrix of an ionic and/or radical nature. In the obtained systems, the carbon matrix is directly enriched. This means that the enrichment of graphene in heteroelements can be obtained after the production of a porous graphene matrix. The proposed methods are characterized by a negligible consumption of reagents and a negligible amount of waste.3 aq  to each container and the contents were well mixed, and the containers were closed. Then, we inserted the containers into a radiation device.N-doped graphene was synthesized in two ways. In the first method called the “dry method”, 1g of graphene nanoplatelets  purchased from Sigma Aldrich was opened in a container containing ice. This was caused by the fact that the boiling point of this substance is 17 °C. Next, 10 mL of ethylamine was placed in a separate and open test tube. All test tubes were sealed in a square transparent plastic box. Then, we inserted the box into a radiation device. In the second method called the “wet method”, 1 g of graphene nanoplatelets (three different series) purchased from Sigma Aldrich were added to 100 mL PVC containers . Next, we added 25 mL 6M NHIrradiation was carried out in a radiation device RChM-γ-20, where the source of gamma radiation is Co-60. The dosing rate during the experiments ranged from 19.3 to 21.0 Gy/h, average value ~20 Gy/h, determined using a Fricke dosimeter. Periodically, further samples were taken for analysis in a specified time schedule. After each irradiation step, the material was washed repeatedly with distilled water (2 L) using a Büchner funnel  to remove all impurities, in particular, the residues of ethylamine and ammonia. Then, it was dried in an electric furnace at 150 °C for 24 h.2/g; 300—graphene nanoplatelets with an surface area of 300 m2/g; 750—graphene nanoplatelets with an surface area of 750 m2/g), Y means the method used , and ZD means the dosing rate for dry method  and for wet method . GF_X_raw—means raw material before processing.The N-doped graphene samples obtained by the proposed methods were denoted as GF_X_Y_ZD, where: e.g., GF_X means the type of used raw material , were used. X-ray diffraction (XRD) patterns of the samples were obtained with an X-ray diffractometer  equipped with a Cu Kα source at 40 kV and 30 mA. X-ray photoelectron spectroscopy  measurements were performed using a monochromatic Al Kα x-ray source. Survey spectra were recorded for all samples in the energy range of 0 to 1300 eV with a 0.5 eV step, high-resolution spectra were recorded with a 0.1 eV step.The morphology of the N-doped graphene was analyzed by scanning electron microscopy . The obtained materials were also examined by high-resolution transmission electron microscopy . The carbon materials obtained prior to the HRTEM microscopic analysis were dispersed in ethanol and treated with an Inter Sonic IS-1K bath for 15 min and deposited on holey carbon-coated copper grids. The volumetric elemental composition  of the materials was analyzed by means of a combustion elemental analyzer . Raman spectra were obtained by a micro-Raman spectrometer . The laser was tightly focused on the sample surface through a 50× microscope objective. To prevent any damage of the sample, excitation power was fixed at 2 mW. The resolution was 4 cmIn summary, we have demonstrated new alternative methods and a low-cost strategy for obtaining N-rich graphene. The N-doped graphene was successfully prepared using gamma irradiation at a radiation dose lower than 30 kGy. The most efficient method is the “dry method” with the use of ethylamine, where the nitrogen content exceeds 4 wt.%. The irradiation method is very selective regarding the chemical form of inserted N atoms, which are exclusively bonded as quaternary groups, i.e., functional groups exceptionally useful for the improvement of such doped graphene electrodes in batteries and supercapacitors. On the contrary, traditional N-doping methods yield very diversified forms of N bonding, among which only few are expected to be used in the mentioned electrochemical applications. The proposed methods are a simple and universal option to the already known methods of introducing nitrogen and other heteroatoms, such as sulfur, boron or phosphorus.This aspect of the performed study will be continued in further research. The future work should concentrate on two basic directions.Firstly, the influence of raw graphene structure on the qualitative and quantitative effectiveness of N-enrichment should be investigated. In this study, mostly MLG was investigated which meant that any of the applied N-bearing reagents had limited access to the reactive centers induced by gamma radiation in the intrinsic spaces inside the MLG granules. The authors assume that there might be a substantial difference whether SLG, FLG or MLG is subjected to the nitrogen enrichment according to the radiation procedures presented in this study. The less agglomerated graphene precursors like SLG or FLG should react intensively, yielding graphene-based materials of a higher N content than in the case of MLG. For this purpose, several graphene splitting methods seem to applicable like electroexfoliation combined with the wet-chemistry exfoliation by means of polar aprotic liquids . Intensively electroexfoliated graphene will be investigated as a continuation of the current study, which can serve as a reference point.Secondly, the discovered unified chemical bonding of nitrogen to graphene matrix should result in the advancement of the electrochemical properties of them. Therefore, such gamma radiation-modified graphene-based materials should be evaluated electrochemically as an electrode material in some batteries such as metal–air ones. Oxygen reduction reaction (ORR) will be investigated aiming at the determination of cathodic properties of the materials.Thirdly, there are neither theoretical nor experimental obstacles against nitrogen enrichment of other carbon-based materials like carbon nanotubes and even ordinary activated carbons. Nitrogen-rich activated carbons are still an emerging field in the search for effective electrode materials for plenty of electrochemical devices like metal–air batteries, supercapacitors, and fuel cells.


In this research, by utilizing the Very-High-Bond (VHB) 4905 elastomer, we carry out an experimental examination on the humidity effect on dynamic electromechanical performances of dielectric elastomers, including the dynamic response and viscoelastic creeping. Firstly, we experimentally analyze effects of the pre-stretch, peak voltage, waveform and frequency of the dynamic response of VHB 4905 elastomer under several ambient humidities. In general, the amplitude of dynamic deformation gradually adds up with the increasing humidity. Besides, it is found that the amplitude affected by different parameters shows diverse sensitivity to humidity. Subsequently, effect of humidity on the viscoelastic creeping of VHB 4905 is explored. The results demonstrate that, subject to different ambient humidities, the viscoelastic creeping under Alternating Current (AC) voltage is similar to that under Direct Current (DC) voltage. Furthermore, the equilibrium position of dynamic viscoelastic creep enlarges gradually with the humidity, regardless of voltage waveforms. For the dielectric elastomer with a pre-stretch ratio of 3, when the humidity increases from 20% to 80%, the increase of average equilibrium position of dynamic viscoelastic creep is larger than 1599%. Dielectric elastomers (DEs), a category of soft electro-active polymers, have gained much attention recently because of their excellent properties, such as high energy density, large deformability fast response and so on ,3,4,5,6.Nevertheless, the DEs are more widely used as dynamic actuators, and some researchers have analyzed the dynamic performances of DEs under constant environmental conditions. For example, Sheng et al.  proposedAlthough the above experiments have legitimately explored the humidity effects on static electromechanical properties of DEs and the dynamic electromechanical properties of DEs under constant environment conditions. However, too little work has been devoted to determination of the humidity effect on dynamic electromechanical properties of DEs. When the dynamic DE actuators in the moisture environment , the 3COOK), potassium carbonate (K2CO3), sodium bromide (NaBr) and potassium bromide (KBr), which are placed in the airtight container [In this article, under room temperature (20 °C), we investigate the humidity effect on the dynamic electromechanical properties of DEs, by applying an AC voltage. The electromechanical testing procedures are illustrated in ontainer . A high We vary the peak voltage , waveform, and frequency of applied voltage and pre-stretch ratio of VHB 4905 film under four humidity levels  in our experiments. Under different ambient humidities, we tested three pre-stretch ratios, three waveforms and four frequencies under the same nominal electric field. Furthermore, for each pre-stretch ratio , we also tested four different peak voltages. λp = 3, The voltage-induced dynamic deformation of VHB 4905 film under different ambient humidities is presented in λp = 2, λp = 3 and λp = 4), −1. It is noted that the amplitude increases gradually with the increasing humidity, especially when the humidity enlarges from 40% to 80%. Based on our previous research [λp = 2 to λp = 4. This can be explained as follows: a large pre-stretch stiffens the VHB film and limits a large deformation.For the VHB 4905 with three different equal-biaxial pre-stretch ratios  is investigated by using different peak voltages, which is displayed in λp = 2 and 1 kV~2.5 kV as the range of peak voltage for pre-stretch ratios λp = 3 and λp = 4. It is found that for a given pre-stretch ratio, the amplitude of VHB 4905 increases with the increasing humidity for all different peak voltages, and the high peak voltage greatly augments the amplitude of VHB 4905 with the increase of humidity, indicating that high peak voltage causes the dynamic deformation to be more sensitive to the humidity. This phenomenon may be due to the nonlinear characteristics of DE membranes, which is surely affected by the varying humidity.Next, using a sinusoidal voltage, the humidity effect on the amplitude of VHB 4905 under three equal-biaxial pre-stretch ratios , the humidity effect on the amplitude of VHB 4905 is investigated by using three voltage waveforms, which is displayed in Similarly, under three different pre-stretch ratios , the humidity effect on the amplitude of VHB 4905 is investigated by using a sinusoidal voltage with four different frequencies, which is illustrated in Finally, under three different pre-stretch ratios (λp = 3) when a sinusoidal voltage with a frequency of 1 Hz and a peak voltage of 2.5 kV is applied. Meanwhile, the effective DC voltage of the applied sinusoidal voltage is calculated, and the static deformation of the effective DC voltage is simultaneously measured. Under different ambient humidities, the increase of viscoelastic creep deformation for the VHB 4905 membrane under sinusoidal voltage is similar to that under the effective DC voltage. It is noted that the slopes of displacement-time curves are continuously declining, implying a gradually-weakened viscoelastic creep deformation of VHB 4905 elastomer. Based on these characteristics, it can be predicted that such creeping can be eliminated if the testing time is long enough. Similar results can be found when the triangle and sawtooth voltages are applied, which are shown in As is known, viscoelasticity is an inherent property of DE materials. In this section, we detect the humidity effect on the viscoelastic creep of VHB 4905 elastomer. We use the equilibrium position to evaluate the degree of viscoelastic creeping within the timescale of 198–200 s. The equilibrium position is defined as half of the sum of the peak value and valley value of the dynamic deformation. It can be seen, for each given voltage waveform, that the equilibrium position gradually increases with the increasing humidity, and the trend of increase is almost the same. From In this paper, we investigate the humidity effect on the dynamic electromechanical properties of VHB 4905 elastomer. Firstly, the effect of humidity on the dynamic response of VHB 4905 is explored. In general, the amplitude of dynamic deformation gradually increases with the increasing humidity. Among them, there are a variety of parameters that play distinct effects on the dynamic electromechanical performance of DE, such as pre-stretch, peak voltage, waveform and frequency. The amplitude is highly sensitive to the change of humidity at low pre-stretch ratio, high voltage peak value and low frequency. However, the amplitude under the random voltage waveform is less sensitive to humidity. In the following, the effect of humidity on the viscoelastic creeping of VHB 4905 is investigated. For different ambient humidities, the viscoelastic creeping is consistent when the DEs are under sinusoidal voltage, triangular voltage, sawtooth voltage and corresponding effective DC voltage. The experiment also analyzes the equilibrium position of viscoelastic creeping. For each given voltage waveform, the equilibrium position gradually rises with the increasing humidity. For the DE with a pre-stretch ratio of 3, when the humidity increases from 20% to 80%, the average equilibrium position of dynamic viscoelastic creep increases by 15.99 times. These investigations offer a strategy to comprehend the polyacrylic DEs for performance improvements and device explorations in some extremely moist environmental conditions. For future research, we hope to establish a dynamic model of the DE actuators incorporating the humidity effect.