With the rapid development of wearable and portable electronic devices, it is increasingly important to develop conductive paper-like films (CPFs) with the characteristics of light, thin and self-supporting. In this paper, nanofibrillated cellulose (NFC) was used as reinforcing phase of film-forming to combine with graphene oxide (GO). Then graphene-based CPFs were prepared by directly reducing the GO/NFC composite film without any additional adhesives, which effectively avoided the difficulties of dispersion and combination with other materials caused by direct using of high content graphene. Meanwhile, three representative reduction methods for direct reduction of GO/NFC composite films were also compared. The results show that 450 °C thermal reduction and hydroiodic acid reduction were more effective than ascorbic acid reduction. On this basis, hydroiodic acid reduction and thermal reduction were used to discuss the effect of NFC addition to the conductivity of the film. This occured when increasing the content of NFC from 10% to 50%, the electrical conductivity of the composite film by hydroiodic acid reduction decreased from 153.8 S/m to 22.2 S/m. While the conductivity of composite film increased first and then decreased after thermal reduction both at 450 °C and 550 °C. What’s more, when NFC content was about 16.6% the electrical conductivity reached a high level which was 86.21 S/m and 168.9 S/m, respectively. This study provides a groundwork for the further development of graphene-based CPFs with low square resistance and high conductivity in large-scale preparation. Accordingly, three-dimensional conductive papers (CPs) or conductive paper-like films (CPFs) with light, thin, self-supporting and excellent durability features exhibit attracting prospect for applications in wearable device2 hybridization, which has attracted ever-increasing attention by researchers for its excellent electrical, thermal and mechanical properties7. And it also has been widely researched in the preparation of conductive materials by virtue of its high electron mobility and high conductivity8. El-Kady9et al. used LightScribe DVD optical drive to do the direct laser reduction of graphite oxide (GO) films to graphene with high electrical conductivity (1738 S/m), but the method requires high equipment and the laser-scribed process is difficult to control in actual production. Zhang10et al. prepared highly conductive graphene nanomesh films (27800–35400 S/m) by an in-situ carbothermal reduction strategy and well performed in supercapacitors. However, the preparation process is relatively complicated and the efficiency needs to be improved in large-scale preparation. Among various approaches to prepare graphene composite CPs or CPFs, the development of simple, low-cost, large-scale, commercial methods is still a challenge. Kang11et al. used traditional papermaking methods to prepare CPFs with conductivity of 11.6 S/m and square resistance of 1063 Ω/sq by mixing pulp with graphene. It exhibited high electrochemical performances in flexible electrodes for supercapacitors and lithium batteries. While Luong12et al. utilized hydrazine to reduce the mixture of graphene oxide(GO) and nanocellulose to prepare conductive film by filtering, when the graphene content was 10%, the composite film conductivity was 71.8 S/m. Besides, simple solution process such as dipping14, coating15 and casting16 were also studied by researchers. However, in the above report, graphene was combined with other materials at a lower content, the conductivity of the materials was limited which may affect the property of the final device. To fully demonstrate the prominent electrical property of graphene and further improve the electrical conductivity of composites, increasing the proportion of graphene or using graphene as the main component to prepare CPFs is concerned. But in this process, two problems are easy to occur: First, graphene agglomerate easily and disperse in poor state, it may cause local graphitization and affect its performance. Second, the surface inertness of graphene makes it difficult to form a film itself, and it’s also hard to combine well with other materials. So the preparation of graphene-based CPFs and the improvement of its conductive properties need to be further studied.Graphene is a two-dimensional carbon nanomaterial with carbon atoms formed by sp17. While nanofibrillated cellulose (NFC) not only has large specific surface area, high strength, good biodegradability, but also larger in length-diameter ratio which can easily interweave a network structure18. Besides, NFC has high hydrophilicity due to its large amount of hydroxyl groups, and is easy to form films or gelations19. Therefore, in this paper, NFC was used as the enhancement phase of film formation. By adding an appropriate amount of NFC to combine with well dispersed GO into film, the graphene-based CPFs were obtained by direct reduction of the GO/NFC composite film, thus it effectively avoided the difficulties of dispersion and combination with other materials caused by direct using of high content graphene.GO as an oxide of graphene, has a large number of oxygen-containing groups on its surface and edge, showing good dispersion in water. More importantly, it can be reduced into graphene to restore its conductivity22, sodium borohydride23, hydroiodic acid (HI)25 and green reducing agents such as ascorbic acid (VC)26, chitosan27 and glucose28. As an efficient, non-toxic reducing agent, HI can directly reduce GO film into high conductive graphene film without destroying the integrity and flexibility of the film24. When VC is used as reducing agent, RGO obtained after reduction has a good dispersibility, which is beneficial to the further application of the product26. In addition to the chemical reduction method, thermal reduction31 is also an efficient reduction method. The mechanism is that the oxygen-containing functional groups on GO escape from the sheet layer in the form of H2O, CO2 or CO at a high temperature by using GO under the protection of inert gas, then RGO can be obtained.Furthermore, different reduction methods are of notable effect on the conductivity of the reduced graphene oxide(RGO), which accordingly influence the conductivity of GO/NFC composite film after reduction. Commonly used methods for reducing GO are mainly divided into chemical reduction method and thermal reduction method. The high-efficiency reducing agents used in chemical reduction ordinarily includes hydrazine and its derivativesHence, HI reduction, VC reduction and thermal reduction were investigated to prepare graphene-based CPFs by direct reduction of the GO/NFC composite film. The effects of different reduction methods on the surface properties, microstructure and electrical conductivity of the composite film before and after reduction were discussed. On this basis, we also discussed the effect of NFC addition to the conductivity of the graphene-based CPFs, and analysed reasons for the change in conductivity.Bleached eucalyptus pulp, Graphene oxide dispersion . HI , VC, TEMPO, NaBr, NaClO, NaOH . Deionized water was used in this study. Vacuum tube furnace TF1200–200 .32, and washed with HCl (1 mol/L) three times, then homogenized by high pressure to obtain a gel-like NFC.Eucalyptus pulp is first oxidized by TEMPO2). After drying at room temperature (30 °C) for 24 h, the composite film was retained in the following reduction experiments.The above-mentioned prepared NFC and a certain concentration of GO were mixed by ultrasound. The mixed solution with different mass ratio of GO and NFC was prepared respectively (absolute dry mass ratio). Then, filtration of mixed solution into film  HI solution and reduced it in a constant temperature water bath at 90 °C for 1 hour. After that, the residual solution on the film was washed out by ethanol and dried naturally at room temperatureThe GO/NFC composite film was immersed in a sealed container containing VC solution (the mass of VC is 10 times than that of GO), which was reduced in a constant temperature water bath at 90 °C for 1 hour. After that, the residual solution on the film was washed out by ethanol and dried naturally at room temperature.The GO/NFC composite film is placed in a vacuum tube furnace under the protection of nitrogen, the film was heated to 450 °C for 0.5 h, then dropped to room temperature.−1–400 cm−1 was used to identify and analyze the structure and composition of the samples. Microscopic Raman spectroscopy  was used to analyze the microstructure changes of the samples. X-ray photoelectron spectroscopy (XPS) was used to further study the evolution of functional groups. Four-probe  was used to test the square resistance and conductivity of the sample. Multiple measurements and the average values were obtained. Tensile strength (TS), Young’s modulus (YM) and the stress-strain curves of GO films and GO/NFC composite films after different reduction methods were conducted by using the Universal Testing Machine  at a speed of 10 mm min−1 with films 1.5 cm wide and 3 cm long.The surface morphology and microstructure of the samples were analyzed by Field Emission Scanning Electron Microscopy(FESEM) . X-ray diffraction(XRD) patterns were recorded on a Bruker D8 advance X-ray diffractometer using Cu Kα radiation (λ = 0.15406 nm). Fourier transform infrared spectroscopy(FTIR)  with wave range of 4000Figure 2 hybridization when oxygen-containing functional groups were removed.Figure Next, the square resistance and conductivity of graphene-based CPFs were measured, which was shown in Table The relationship between sheet resistance and resistivity is as follows:To gain further insight into the level of the reduction effects of VC reduction, HI reduction and thermal reduction, Raman spectroscopy, XRD, FTIR, XPS were employed to investigate the structural evolution during the reduction process.−1 and G peak at 1575 cm−1 in Raman spectrum is often used to evaluate the sp2 hybrid domain size of carbon materials. What the sp3/sp2 carbon atom ratio can indirectly reflect the degree of disorder in the structure33. Figure 2 would be formed, which decreased the ratio of ID/IG accordingly. By comparing the ratio of ID/IG, 450 °C thermal reduction (0.744) is intense than VC reduction (0.762) due to the formation of larger sp2 hybrid region at high temperature. While the ID/IG ratio of the composite film after HI reduction (1.118) is higher than that of the GO/NFC composite film (1.033), the reason for this is that the removal of oxygen atoms in the reduction process of GO was too intense and it inevitably led to disorder. Although the size of the new hybrid domain is smaller than that of GO, the number of new hybrid domains is larger, which brings about the increasing of ID/IG ratio35.Raman spectroscopy is an effective method to characterize the structural changes of defects and edge groups in carbon materials. The intensity ratio of D peak at 1350 cm37. While 2θ = 10.8° corresponds to the characteristic peak of GO (001) lattice plane38. Additionally, the GO/NFC composite film exhibited the (002) crystal plane of NFC at 2θ = 22.6°, while the characteristic peak of the GO (001) crystal plane and the overlapping diffraction of NFC nearly covered, which indicates the good combination of GO and NFC.In addition, the changes of crystal structure before and after reduction of GO/NFC composite films were also characterized by XRD. Figure 39. When the GO/NFC composite film respectively reduced by VC reduction, HI reduction and thermal reduction, the characteristic peak of 24.8° shifted to large angle in turn. From the formula 2dsinθ = nλ, with the increase of θ angle, the corresponding crystal-plane spacing d decreases. The removal of oxygen-containing functional groups in different reduction processes would affect the spacing between lattice planes, which indicated that the composite film was closer to the crystal structure of graphene after thermal reduction. Meanwhile, the conclusion that new hybrid regions of sp2 were formed and the ratio of ID/IG decreased in Raman spectra was also verified.Figure −1) in the NFC and GO, C-O-C stretching vibration peak (890 cm−1), C-OH stretching vibration peak (1032 cm−1) and COOH stretching vibration peak (1635 cm−1) in GO (identification similar to that reported42). Typically, intensity of peak at 1425 cm−1 belongs to the bending vibration absorption peak of CH2 in NFC43, which was removed only after thermal reduction. This suggests that the carbonation of NFC during thermal reduction. At the same time, the strong absorption peak at 1543 cm−1in thermal reduction and HI reduction can be clearly observed, which caused by the stretching vibration of sp2 chemical bond in the graphene structure42. The results show that the sp2 electron conjugate structure of graphene can be reconstructed effectively after reduction.The change of functional groups of GO/NFC composite films (GO: NFC = 1:1) before and after reduction were characterized by FTIR. As shown in Fig. 40. This indicates the removal of epoxyl, carboxyl, and carbonyl functional groups, and a simultaneous increase in graphitic carbon after reduction.The evolution of functional groups in GO/NFC composite films (GO: CNFs = 1:1) surface before and after reduction were further determined by XPS. After reduction, the C/O atom ratio was increased accordingly in Table Furthermore, stress-strain curves of GO film and GO/NFC composite film (GO: NFC = 1:1) before and after reduction were shown in Fig. Nevertheless, due to the disappearance of hydrogen bonds caused by the remove of oxygen-containing functional groups, the compact lamellar structure is also damaged in varying degrees, which is approved by the description of SEM results Fig. , so the Because the conductivity of the composite film after HI reduction and thermal reduction were much better than that of VC reduction. Thus, the effect that addition of NFC in the conductivity of the graphene-based CPFs was discussed below.Figure Meanwhile, different from HI reduction, the conductivity of the film after thermal reduction increased first and then decreased both at 450 °C and 550 °C. When NFC content was about 16.6%, the electrical conductivity reached a high level which were 86.21 S/m and 168.9 S/m, respectively. That could be the composite film was well intertwined and formed a good conductive network structure.Both of these are beneficial to the electron transport after reduction and make the composite film achieve the best conductivity. When the dosage was less than 16.6%, NFC was not enough to form a uniform net conductive structure. What is the reason for the decrease of conductivity after the reduction is that the graphene was easily deposited and covered which could bring the thermal reduction reaction was not thorough and the carbonization of the NFC was also suppressed. Then, we took the film after HI reduction as a sample (NFC accounts for 12.5%) to do diode path experiment. When the LED lamp touched with the conductive film prepared above, the LED lamp can emit light stably. This indicates that prepared graphene-based CPFs possess excellent conductivity.In this paper, the graphene-based CPFs were successfully prepared by directly reducing the GO/NFC composite film without any additional adhesives, which effectively avoided the difficulties of dispersion and combination with other materials caused by direct using of high content graphene. Moreover, the surface characteristics, microstructure and electrical conductivity of composite films after HI reduction, VC reduction and thermal reduction were compared and analyzed. The results show that thermal reduction and HI reduction were more efficient than VC reduction, and NFC would be carbonized at the same time during thermal reduction. On this basis, we also discussed the effect of NFC addition to the conductivity of graphene-based CPFs prepared by HI reduction and thermal reduction. With the increase of NFC content from 10% to 50%, the conductivity of the composite film decreased gradually after HI reduction. In comparison, the conductivity of the film increase first and then decrease after thermal reduction both at 450 °C and 550 °C. When NFC content was about 16.6%, the electrical conductivity reached a high level, which were 86.21 S/m and 168.9 S/m, respectively. This work provides a basis for the further development of flexible conductive film with low square resistance and high conductivity, and contributes to its potential applications in portable and wearable electronic devices.Supporting information Direct Reduction of Graphene Oxide/Nanofibrillated Cellulose Composite Film and its Electrical Conductivity Research.


IFT) during the last stage of the 30-15 Intermittent Fitness Test, hemoglobin levels, and training load measures during SSG intervals among professional soccer players. Sixteen professional soccer players  participated in this study. Hemoglobin and aerobic performance were first tested, and then a 3-week SSG program was applied using a 3 vs. 3 format. During those 3 weeks, internal and external load of entire sessions were also monitored for all training sessions. Trivial-to-small, standardized differences were observed between sessions for external and internal measures during SSGs. Total distance (TD) and mechanical work (MW) were the only variables that indicated small changes. Large-to-very-large relationships were found between VIFT and external loads: TD , high-intensity running , and MW . Moderate-to-large negative relationships were found between hemoglobin levels and internal loads: Edwards’ TRIMP , %HRmax , and red zone . VIFT had unclear relationships with overall internal loads, while hemoglobin levels presented unclear relationships with overall external loads. In conclusion, no meaningful changes were found between sessions considering the format of play used. Additionally, the detected relationships indicate that VIFT and hemoglobin levels are good indicators of the performance capacity and physiological profile of players during SSGs. Also, the use of SSGs protocols as a monitoring complement of the 30-15IFT is suggested.The purposes of this study were (1) to analyze between-session variations of external and internal load measures during small-sided games (SSGs) and (2) to test the relationships between the maximum speed reached (V The practical operationalization of soccer training in recent years has placed great emphasis on the inclusion of small-sided games (SSGs), which encompass the psychological, physical, technical, and tactical aspects of the game . For coamax (red zone), %HRmax, during SSGs and YYIR performance  than players not living at sea-level locations (14.4 ± 0.7 g·dl−1). The mean VO2max value of the players residing at a moderate altitude (54.1 ml·kg−1·min−1) was also significantly greater than that of the players residing at low altitudes  to analyze the degree of changes/differences in performance between athletes instead of using percentages of changes , employed with the same conditions . The data collection occurred in 2018/2019, in the first 4 weeks of the pre-season. However, training time (between 17:00 and 20:00) and environmental conditions  varied greatly over the data-collection phase. Data related to external load measures were obtained using global positioning systems during all SSG sessions, while internal load was monitored using heart rate monitors. All players involved in the study were professionals and were familiar with SSGs prior to the experimental period.IFT of 17.9 ± 1.2 km/h. All players were informed of the experimental procedures and related risks and gave informed consent before commencing the study. The study protocol was approved by the University Research Ethics Committee. The study followed the ethical standards of the Declaration of Helsinki.Sixteen professional soccer players , all members of a professional club competing in the 2018–2019 season of Qatar Star League (Qatar first division), participated in this study. The inclusion criteria were (i) participation in all the moments of assessment and games; (ii) absence of injuries, physical constraints, or illnesses exhibited during sessions occurred in the period and two weeks prior to the data collection; and (iii) absence of signals of fatigue on assessment days. Players were assigned to different teams (of three elements), and comparisons between teams revealed no meaningful changes in the main outcome (aerobic performance). The baseline fitness levels of players revealed an average Vm, with two sets of three minutes performed in each session. The conditions involved touch limitations (a maximum of three consecutive touches permitted to each player) in accordance with a previous study suggesting ball limitation as a way to increase the intensity .The 3v3+Gk SSG format was used in the present study. This format was repeated over three trials of three ntensity . Three wThe coaching staff, which included one of the authors (a strength and conditioning coach), were directed to ensure the consistency of their supervision during all SSG sessions. Balls were kept near the SSG pitch so that coaches could restart the game immediately if a ball left the playing area. For each format, the teams were balanced based on their members’ physical and technical abilities (as determined by the coach); this reduced the possibility of any strength or weakness bias.max, Edwards’TRIMP, and time spent in the red zone , were analyzed following each session. The HRmax of each individual was extracted from a maximal field-based test  conducted during the pre-season. To standardize Edwards’ TRIMP and red zone measures so that fair comparisons, the corresponding data were divided by minutes played (Edwards’TRIMP.min−1 and Red zone.min−1).Heart rate data were recorded during all SSG sessions using Bluetooth HR sensors  that were synchronized to a validated portable 10-Hz VX Sport 350 GPS units . Each unit was used for the same player across the study to reduce inter-unit variability. HR measures, including HR−1), and mechanical work (MW), for which the numbers of acceleration and deceleration efforts above and below 2.2 m.s2 thresholds were calculated the sum. The thresholds used for acceleration/deceleration efforts (2.2 m.s2) were selected based on practical experiences using the VX GPS system by the coaching staff. All external load measures were standardized by being divided by minutes played  prior to the analysis so that they could be compared across different SSG formats.External load measures were recorded during all sessions using portable 10-Hz VX Sport GPS units , which are valid and reliable according to A blood sample (15 ml) was collected from each participant between 8:00 and 10:00 a.m. The samples were collected with an overnight fast and after a minimum of 12 h of rest (without exercise). Blood samples were centrifuged at 2500 rpm for 10 min, and the serum of each sample was stored. Hemoglobin (g/dl) was determined using flow cytometry.−1 for the first run, and speed was increased by 0.5 km/h for each subsequent run. Players had to run back and forth between two lines positioned 40 m apart. Running pace was set by an automatic beeper to control the running speed when players entered a 3-m zone placed in the middle and at both extremities of the field. During the recovery period, players walked toward the closest line, either at the middle or one of the ends of the running area, depending on where they stopped in the last run. Players were told to complete as many stages as possible, and the test was ended when the players could not maintain the required running speed or could not reach the 3-m zone before the beep three consecutive times. The final velocity registered in the last stage determined the player’s VIFT score , the relationship was deemed unclear; otherwise, the obtained magnitude was deemed to be the observed magnitude (Data are presented as mean and standard deviation (SD) or 90% of confidence limits (CL) where specified. Differences between sessions in terms of training load measures were analyzed using standardized differences or effect size ES; . Qualitary large . A magni perfect . If the agnitude . The staIFT and hemoglobin were 18.0 ± 1.2 km.h−1 and 14.5 ±0.7 g.dl−1, respectively. The mean ± SD of external and internal load measures during different sessions/sets of SSGs are represented in The mean ± SD values of players’ VTrivial-to-small standardized differences were observed in TD  and MW  between sessions  changes were observed in HIR between sessions , time spent in the red zone , and average HR as % of HRmax  between sessions  and HIR  in different sessions  with MW in different sessions .sessions . VIFT alsessions . Howevermoderate-to-large associations were observed between hemoglobin levels and Edwards’ TRIMP , as well as time spent in the red zone  in different sessions . The only clear associations observed between hemoglobin levels and external load measures were the moderate correlations observed when considering HIR in the second sets of the first and second sessions .Inversed sessions . The relIFT and hemoglobin levels with training loads during SSGs intervals among professional soccer players. The main findings were that the external measures had trivial-to-small standardized differences, while all internal measures revealed trivial standardized differences between sessions. VIFT showed large-to-very-large positive relationships with TD, HIR, and MW, while hemoglobin levels showed moderate-to-large negative relationships with TRIMP, time spent in red zone, and %HRmax during different sessions. However, VIFT presented unclear relationships with all internal loads, while hemoglobin levels presented unclear relationships with overall external load.This study was designed to analyze between-session standardized differences of external and internal load measures and the relationships between VBetween-session standardized differences of SSGs were more pronounced only for TD and MW when comparing session 1 and 2 to 3, representing a small degree of change. Meanwhile, HIR presented trivial changes between all sessions. Using different approaches, other study have analyzed between-sets variations of SSGs and reported trivial-to-small standardized differences from the first set to the second set for TD when considering SSGs shorter and longer regimens . Also, tIFT and TD measures revealed in the present study are in line with other study that demonstrated a strong association between Yo-Yo IR scores and total distance covered and high-intensity running speeds during match play, suggesting a strong validity  revealed similar associations with TD  during SSG drills. Also, in the study of r = 0.59) during 6v6 SSGs when considering only the elite population that was analyzed in their study. Considering the HIR measure, moderate-to-large  relationships were previously reported between YYIR2, YYIR1, and the time spent in HIR during a match . In the same way, The large-to-very-large relationships between Vvalidity . In fact a match . The preIFT in the present study. These results contrast with a previous study that reported only a moderate relationship without statistical significance between acceleration measure and YYIR2 during 6v6 SSGs. However, there is a possible explanation for this difference. In fact, shorter formats of play are characterized by more changes of direction and accelerations/decelerations, thus being in line with something that 30-15IFT is also sensitive to . This could mean that MW measures contain a higher factor of unexplainable variability – in fact, previous studies have reported a higher coefficient of variation for those metrics within SSGs  and HR measures during SSGs, which reported large-to-very-large inversed correlations . These results are similar to our results with regard to the unclear associations between hemoglobin levels and the external loads during SSGs  more players can be evaluated at the same time, (ii) SSGs involve technical and tactical demands, and (iii) players are performing soccer training during the test. As practical implications, this study suggests that the internal load and external load of SSGs (considering the outcomes used) are stable across the sessions, while training load is associated with the fitness and physiological status of the players. Based on that, coaches should consider adjusting the stimulus or drills to specific groups of players.Regardless, as far as we know, the present study is the first to analyze the relationships between VIFT is a good indicator of performance capacity during SSGs, given the large-to-very-large relationships between and external measures. Also, hemoglobin levels seem to decrease at higher intensity drills, revealing associations with internal loads. Despite that, VIFT and hemoglobin levels revealed unclear relationships with internal and external measures, respectively. For those reasons, it is suggested that practitioners consider both internal and external loads. It is also suggested that they use SSGs to monitor soccer players’ physiological and performance capacity to complement periodic assessment protocols such as the 30-15IFT.The present study revealed low between-sessions standardized differences for the overall internal and external measures of SSGs, with only TD and MW showing small changes. Thus, it is suggested that tactical behaviors might interfere with those metrics during SSGs. VThe raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.The studies involving human participants were reviewed and approved by University of Coimbra. The patients/participants provided their written informed consent to participate in this study.SY, AR, FC, and AF lead the project, collected the data, treated the data, wrote the statistical report, and revised the original manuscript. RS and HS wrote and revised the original 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.


To confine the terahertz electromagnetic wave, four different fractals are integrated into a supercell, and the coupling and superposition of adjacent resonant cavities form a broadband high-absorption absorber. Using finite element-based full-wave electromagnetic simulation software to simulate the response frequency of 0.4–2.0 THz, we found that the absorber achieves a broadband 1.26 THz range (absorption > 80%) and a relative bandwidth of 106.8%. By adjusting the Fermi energy, it can realize free switching and expand to wider broadband terahertz absorption, by adjusting the polarization angle (Φ) from 0 to 90° to prove that the structure is not sensitive to polarization, the absorber provides a 60° large angle of incidence, polarization for TE and TM the absorption pattern remains basically the same. Compared with the previous work, our proposed structure uses fractal technology to expand the bandwidth and provide dynamic adjustable characteristics with great degrees of freedom. The appearance of the fractal structure reduces the difficulty of actual processing.In this paper, a metasurface Terahertz absorber based on the fractal technology of a graphene geometry resonator to realize ultra-wideband, ultrathin, adjustable double-layer cross-fractal formation is introduced. This paper proposes a dynamically tuned graphene absorbing material. The structure is composed of one- to four-level-fractal graphene pattern layers, MgF The terahertz (THz) or T-ray region of the electromagnetic spectra is defined as the region between infrared (IR) light and microwave radiation, ranging from 100 GHz to 10 THz. This region lacks natural materials with valuable electromagnetic properties and is extremely precious . The tecGraphene is the thinnest 2D material found so far. Graphene has the characteristics of small thickness, high elasticity and durability, and low loss. It exhibits metallic properties when certain conditions are met and becomes one of the most promising materials ,23,24. GFractal theory is closely related to many research fields with a wide range of applications, and the fractal phenomenon of self-similarity will exist. Traditionally, all cells of the fractal have the same geometric shape, the same size, and the same arrangement direction, which are derived from the space filling of the fractal structure and are on the same plane, which reduces the difficulty of processing ,29. Howe2 layer and metal reflective layer. Based on this structure, we mainly integrate two layers of four different fractal structures into a supercell, so a broadband high-absorption absorber is formed. Therefore, our device provides dynamic adjustable characteristics with a great degree of freedom, and our proposed absorber can realize an ultra-wideband, ultrathin, and adjustable planar metasurface terahertz absorber. Using simulation software to simulate the response frequency of 0.4–2.0 THz, we found that the absorber achieves a broadband 1.26 THz range (absorption > 80%), where the center frequency fc= 1.18 THz and the relative bandwidth is 106.8%, achieving broadband absorption by optimizing each fractal structure. In addition, each level of fractal structure we design presents a periodic symmetry pattern, the polarization angle (Φ) is tuned from 0 to 90°, which means that the structure isn’t sensitive to the polarization angles. The oblique angle can be incident at a large angle up to 60° for both TE and TM polarizations is achieved.Compared with the previously reported fractal terahertz metamaterial absorbing materials, the structure we designed has the advantages of easy realization, low cost, miniaturized manufacturing and adjustable degree of freedom, which is useful for future terahertz detectors, terahertz communications and other emerging the realization of terahertz technology is particularly important.In this work, the structure we designed is composed of a one- to four-level fractal graphene pattern layer, MgF2 layer and an ideal electrical conductor , as shown in 2, the relative dielectric constant d =ε 1.9 [mt = 45 μm. The structure we designed underwent resonant increased cross by four-level fractals. As shown in L1 = 45 μm, L2 = 15 μm, L3 = 7.5 μm, L4 = 3.75 μm, w = 3.6 μm. The length of the three-level fractal is slightly increased to 48.6 μm, which is L1 + w, and the length of the four-level fractal is 48.75 μm, which is L1 + L4. For our design, the Fermi energy of the top layer graphene corresponds to 1 eV.The metamaterial absorber we propose is composed of a fractal graphene pattern layer, an MgFεd = 1.9  and the 2 dielectric layer are consistent with the first layer, as shown in 2 dielectric layer/air interface) at a distance of dt = 12 μm, that is, the distance from the ground is 33 μm in Q1 = 50 μm. The supercell period Q = 100 μm, and the graphene thickness is gt = 0.5 nm.In the bottom layer, the size and arrangement of the cross shape embedded in the MgFThe conductivity of graphene is provided by the Kubo equation, and the Kubo equation determines the intraband and interband transitions by both ,37:(1)σgkB is Boltzmann’s constant, h is the Planck’s constant, T is the Kelvin temperature, ω is frequency of the electromagnetic wave, e is the elementary charge,Here, In the terahertz band, the conductivity of graphene is mainly provided by the intra-band transport of carriers, while the inter-band transport is suppressed. At this time, the above calculation formula for graphene conductivity is simplified as:In addition, electrical conductivity will directly affect the characteristics of surface plasmon polariton (SPP) excitation.It can be seen from formula Equation (5) that the conductivity affects the dielectric constant of the graphene film. Graphene is an ultra-thin film with a certain equivalent dielectric constant:εo is the dielectric constant of the vacuum and g =t 0.5 nm is the thickness of the graphene. The wavelength of electromagnetic waves is much greater than the thickness of graphene, which is a boundary condition that can be used in transition simulation.Therefore, it can be flexibly manipulated using applied voltage, temperature, carrier concentration, etc., which can be obtained by creating subwavelength composite materials, where ns, by the equation:The Fermi energy of graphene mainly depends on the carrier concentration ns is the carrier concentration. Bias voltage and chemical doping can change the carrier concentration, but it is proportional to the bias voltage applied to the graphene layer and εd is the relative permittivity of the dielectric layer, H is the thickness of the dielectric layer. Equation (7) gives a specific conversion relationship:Here The above theory fully demonstrates that the absorbing material applies bias voltage or chemical doping to achieve dynamic adjustment, so as to achieve the purpose of tunable absorption. This process qualitatively changes the frequency of surface plasmon polariton (SPP) excitation characteristics, thereby affecting the absorption the operating frequency of the wave material.In order to evaluate the function of the double-layer graphene terahertz absorber we designed, we performed numerical simulations using the electromagnetic simulation software based on the finite element method. In the simulation, a cell in the periodic structure is taken as the calculation object, the boundary conditions of the periodic cell in the X and Y directions are selected, and the Z direction is set as the open boundary condition.w) formula can be written as:ω) and R(ω) are the transmission coefficient and reflection coefficient, respectively, and the absorptivity is obtained by using simulation software, selecting the frequency domain solver, and deriving the absorptivity and S parameters. It can be seen from Equation (8) that, by reducing the transmission and reflection coefficients, higher absorption spectra can be obtained. The ideal electrical conductor in the simulation software is used as a thin metal film reflective layer ground plane to minimize the transmission coefficient. The result shows that the transmission coefficient of the metal layer is zero, A (ω) = 1 − R(ω).The absorptance A MgF2 dielectric layers of the structure with different thicknesses was studied, and the results are shown in mt = 45 μm and dt = 12 μm. It can be seen from dt does not change significantly between 11–15 μm, but at 0.6–0.9 THz, dt = 12 μm has a good absorption effect, and the bandwidth is relatively large when dt = 12 μm, and we can see dt = 12 μm has the best absorption effect. mt layer, the absorption becomes better and better. Under certain other conditions, when mt = 45 μm, a better absorption bandwidth and high absorption rate can be obtained.In order to better test the performance of our designed absorber, the influence of the absorption spectra of the top and bottom  in the range of 0.55 THz to 1.81 THz, where the center frequency


Botrytis cinerea is a ubiquitous necrotrophic filamentous fungal phytopathogen that lacks host specificity and can affect more than 1000 different plant species. In this work, we explored L1 [(E)-2-{[(2-aminopyridin-2-yl)imino]-methyl}-4,6-di-tert-butylphenol], a pyridine Schiff base harboring an intramolecular bond (IHB), regarding their antifungal activity against Botrytis cinerea. Moreover, we present a full characterization of the L1 by NMR and powder diffraction, as well as UV–vis, in the presence of previously untested different organic solvents. Complementary time-dependent density functional theory (TD-DFT) calculations were performed, and the noncovalent interaction (NCI) index was determined. Moreover, we obtained a scan-rate study on cyclic voltammetry of L1. Finally, we tested the antifungal activity of L1 against two strains of Botrytis cinerea . We found that L1 acts as an efficient antifungal agent against Botrytis cinerea at 26 °C, even better than the commercial antifungal agent fenhexamid. Although the antifungal activity was also observed at 4 °C, the effect was less pronounced. These results show the high versatility of this kind of pyridine Schiff bases in biological applications. Schiff base compounds are organic compounds containing an azomethine C=N group ,2,3,4. PBotrytis cinerea is a ubiquitous necrotrophic filamentous fungal phytopathogen, virtually lacking host specificity, able to infect more than 1000 different plant species -methyl}-4,6-di-tert-butylphenol]  calculations to corroborate the experimental UV–vis data, as well as the noncovalent interaction (NCI) index of L1, in order to better understand the nature of the IHB. Moreover, we performed a scan-rate study on cyclic voltammetry of L1 to determine whether these processes are controlled by diffusion of species. Finally, we tested the antifungal activity of L1 against two strains of Botrytis cinerea   , a pyridassessed . In addiberries) , and othL1 synthesis and some characterizations have already been reported -methyl}-4,6-di-tert-butyl-phenol), L1, exerted a cytotoxic effect against yeasts (Cryptococcus spp. MIC: 4.468 ppm) -methyl}-4,6-di-tert-butyl-phenol (L1) compound was prepared by direct interaction between 1,2-diaminopyridine and 3,5-di-tert-butyl-2-ol-benzaldehyde (1:1) in methanol, at room temperature, according to a previously described non-template method [(E)-2-{[(2-aminopyridin-2-yl)imino]-methyl}-4,6-di-tert-butyl-phenol (L1) yellow powder, 0.68 g ; FTIR : 3487 and 3255 (νOH), 2947 (νOH), 2947 and 2905 (νNH2), 2863 (νCH), 1607 (νHC=N), 1589 (νC=C). UV–Vis:  λ (nm)(ε) = 239 (25.63 × 103 mol-1 dm3 cm-1), 277 (18.07 × 103 mol−1 dm3 cm-1), 375 (15.26 × 103 mol−1 dm3 cm−1);  λ (nm)(ε)= 274 (32.78 × 103 mol−1 dm3 cm−1), 372 (15.80 × 103 mol−1 dm3 cm−1);  λ (nm)(ε)= 236 (23.77 × 103 mol−1 dm3 cm−1), 274 (16.15 × 103 mol−1 dm3 cm−1), 368 (13.69 × 103 mol−1 dm3 cm−1);  λ (nm)(ε) = 378 (7.24 × 103 mol−1 dm3 cm−1). 1H-NMR at 25 °C : δ =1.35 , 1.48 , 5.51 , 6.71 , 7.52–7.43 , 7.53 , 7.95 , 8.88 , 13.29 ; : δ =1.25 , 1.40 , 4.93 , 6.65 , 7.31-712 , 7.41 , 7.87 , 8.57 , 12.94 ; : δ =1.11 , 1.24 ,6.60-6.40 , 7.18 , 7.28 , 7.24 , 7.28 , 7.63 , 8.57 ; 1H-NMR at 4 °C : δ = 1.25 , 1.40 , 4.89 , 6.70 , 7.27–7.25 , 7.43 , 7.94 , 8.59 , 12.93 ; 13C-NMR at 25 °C : δ = 28, 113, 119, 125, 127, 130, 136, 140, 146, 154, 158, 165; : δ = 29, 30, 31, 34, 114, 118, 125, 127, 128, 130, 136, 141, 145, 153, 157, 165; : δ = 28, 29, 30, 100, 113, 125, 127, 128, 144, 165. DEPT at 25 °C : δ = 31, 113, 125, 127, 128, 146, 165; : δ = 29, 30, 31, 114, 125, 127, 128, 145, 165; : δ = 28, 29, 30, 114, 125, 127, 128, 144, 165.The (e method . (E)-2-{L1. We assessed the purity and corroborated the compound structure by a combination of techniques, including , and complemented with DFT and TD-DFT using standard CAM-B3LYP/TZ2P level of theory. Our analysis showed the high stability and strength of the intramolecular hydrogen bond in different solvents by performing noncovalent interactions index (NCI) studies. Furthermore, we determined the electrochemical profile of L1 (and compared it with L2), providing a scan-rate study, demonstrating that the electrochemical calculated processes are controlled by mass transfer (diffusion) only for L1. These results show that small structural changes in these compounds could lead to changes in their properties. Finally, we showed that L1 exerts an antifungal effect against two strains of Botrytis cinerea (mold), including a strain isolated directly from the field, primarily at 26 °C, remarking the potential of these king of Schiff bases as modulators of biological activities.In this manuscript, we provided a further characterization of


Spelling is a fundamental literacy skill facilitating word recognition and thus higher-level reading abilities via its support for efficient text processing . However Literacy is widely recognized as a foundational educational skill e.g., . AlthougIn contrast, spelling ability has received relatively little attention in second language (L2) learners. Existing research shows evidence both for overlap with L1 spelling  and L1-bTo address these gaps, the current study analyzed English spelling data from adult ESL users in three L1 groups , as well as a native speaker comparison group. Data were additionally collected on phonological awareness ability to facilitate cross-linguistic comparisons of not only spelling ability, but also how spelling is related to other key literacy skills.Although spelling ability frequently gets only secondary attention in literacy research , it is iSpelling is also a key component of writing. The Simple View of Writing e.g.,  describeFurther evidence for the interconnectedness of spelling with word recognition, reading comprehension, and writing comes from research examining the impact of instructional interventions. Targeted spelling instruction improves not only spelling and phonological awareness e.g.,  but alsoOne perennial point of contention in literacy research is whether word recognition is best modeled via a single-route, connectionist approach e.g.,  or a duaCross-linguistic research on spelling development suggests that the degree to which individuals rely on these two major sources of knowledge – phonological and visual/orthographic – varies across languages, and in particular across writing systems. As has been widely discussed in the literature on cross-linguistic literacy, the varying phonological and morphological characteristics of different languages are typically associated with particular approaches to encoding the language in writing, such that “every language gets the writing system it deserves” , p. 266.optional in abjads, and in fact are frequently omitted in texts written for fluent adult readers   . Howeverhope, and rimes such as -ough)  .Research has also indicated that individual spellers may take somewhat different approaches to spelling – either lexical (whole-word) or sub-lexical (based on phoneme-grapheme correspondences) e.g., . These iGiven the importance of high-quality lexical representations to support word recognition and overall reading skill, surprisingly few studies have included a detailed consideration of L2 spelling skills. This is true even for English as a second/foreign language (ESL/EFL), despite the international prevalence of this second language e.g., . HoweverA number of studies on ESL spelling have found substantial overlap between L1 (English) spelling development and L2 (ESL/EFL) spelling development. For example, ESL spelling ability relies on largely the same component literacy skills  as does monolingual L1 English spelling ability . In addiThese general tendencies also influence the types of spelling errors or misidentifications that are made most frequently by learners from different L1 backgrounds. For example, Wang and colleagues  examinedAnother well-established domain of L1 influence on L2 spelling is L1 phonology: when examining the specific misspellings produced by L2 spellers, errors frequently appear for the spellings of sounds that do not exist or are not contrastive in learners’ L1. For example, very) and < s > and < z > , as well as the spellings of /i/ and /I/ . Similarly, in L1 Arabic speakers, spelling errors frequently involve confusion between graphemes representing sounds present in Arabic  and their voicing pairs, representing sounds absent from Modern Standard Arabic ; examples include < cabable > for capable and < habet > for habit. Similar evidence of L1 phonological influence on L2 spelling has been documented for L1 German  show less awareness of, lower sensitivity to, or less robust representations of vowels compared to consonants – “vowel blindness” . Early sIn sum, the limited research on ESL spelling abilities indicates that there is substantial overlap with L1 spelling development, including the reliance on phonological versus orthographic information. However, ESL spelling is also influenced by both L1 phonology (often leading to difficulties spelling non-native phonemes or distinguishing spellings for non-native phonemic contrasts) and the L1 writing system .As detailed above, despite the centrality of spelling ability to overall literacy skill, relatively little research has examined ESL spelling abilities. Most of the research that has been conducted – like L1 spelling studies  – has foThe current study was conducted in an effort to begin filling in these gaps. In contrast to much of the existing research, the target participants were adult learners of ESL at the university level (rather than children in elementary or middle school). Data were collected from learners with a range of L1 backgrounds; these were grouped into three main categories on the basis of L1 writing system: alphabet, abjad, or morphosyllabary. Collecting data from this range of L1 backgrounds facilitates cross-linguistic comparisons using uniform task items and procedures. In addition, data were collected from a comparison group of L1 English speakers, so that ESL performance (across L1 groups) could be understood in the context of native-level performance. Finally, participants also completed a phonological awareness task, so that spelling ability could be examined in relation to this key literacy skill. Phonological awareness was chosen because it is a critical component skill for literacy, particularly in the opaque orthography employed in English e.g., . It alsoData were collected from 70 participants: 47 ESL learners and 23 L1 English speakers (serving as a native speaker reference group). All participants were adult (18 years or older) students recruited from the intensive English program, undergraduate, and graduate student populations at a mid-sized regional university in the midwestern United States. The 47 ESL learners  were either preparing for or enrolled in undergraduate or graduate studies. They were classified into three groups based on the type of writing system employed in their L1: 27 alphabetic L1 participants ; 7 abjad L1 participants ; and 13 L1 morphosyllabary participants . Specific age data were not available for the 23 L1 English speakers , though all participants fell within the typical undergraduate student age range of 18–25 years old.For the ESL learners, L2 proficiency information was available in the form of a score from one or both of two different standardized English proficiency tests: the Test of English as a Foreign Language (TOEFL) or the Oxford Online Placement Test (OOPT). Because there is no established, validated method of converting scores from one of these two assessments to an equivalent score on the other, the scores on each assessment were instead converted to the corresponding level of proficiency as described in the Common European Framework of Reference : A1, A2,1. The 16 pseudoword items were taken from a variety of published studies examining pseudoword spelling in ESL/EFL learners  were resolved through discussion between a trained research assistant and the first author. A strict scoring procedure (implemented via an Excel formula) was used to determine accuracy: if the participant’s production was spelled exactly correct it was marked as correct, and any deviations from the correct spelling resulted in an incorrect marking.Responses to the Elision items were also transcribed into a digital spreadsheet for scoring and analysis. All responses to the Elision task were transcribed by a minimum of two trained research assistants; inter-rater reliability was initially 89% and items for which there was disagreement were resolved after consulting a third coder.r = 0.17, p = 0.30 with word accuracy, r = 0.24, p = 0.15 with pseudoword accuracy, r = 0.21, p = 0.23 with elision accuracy; gender: r = 0.09, p = 0.47 with word accuracy, r = 0.18, p = 0.15 with pseudoword accuracy, r < 0.01, p = 0.98 with elision accuracy) and were thus not included in any of the mixed effects models.Pearson correlations and generalized linear mixed effects models with random intercepts for participants and items , a number of item characteristics were significantly associated with real word spelling accuracy . Thus, length and number of orthographic and phonological neighbors were considered in model building. Log frequency  was also considered due to its substantial influence in general lexical processing; however, age of acquisition was not included in models because of its high correlation with length  and concerns regarding issues with multicollinearity.Correlations were also used to guide the selection of item characteristics to consider in modeling word and pseudoword spelling accuracy. Although no item characteristics were significantly associated with pseudoword spelling accuracy  were used to calculate semi-partial correlation coefficients between real word spelling accuracy, pseudoword spelling accuracy, and elision accuracy, controlling for L2 English proficiency.Pearson correlations  among real word spelling accuracy, pseudoword spelling accuracy, and elision accuracy are in 2(df = 3) = 35.86, p < 0.001, and the L1 English speakers were significantly more accurate than all three ESL groups: alphabetic L1 speakers , abjad L1 speakers , and morphosyllabic L1 speakers . Next, the ESL speaker groups were examined in more detail to explore the influence of both L1 writing system and L2 English proficiency on Elision accuracy. The overall effect of L1 writing system was significant, χ2(df = 2) = 8.11, p = 0.02. Specifically, the abjad L1 and morphosyllabic L1 speakers were both significantly more accurate than the alphabetic L1 speakers . However, the difference between the abjad L1 and morphosyllabic L1 speakers was not significant, β = 0.04, z = 0.07, p = 0.94. The effect of L2 English proficiency was also significant, β = 1.60, z = 3.97, p < 0.001, such that higher proficiency participants were significantly more accurate than lower proficiency participants. However, the interaction between L1 writing system and proficiency was not significant, χ2(df = 2) = 2.21, p = 0.33, suggesting that the effect of proficiency is the same regardless of L1 writing system.The means and standard deviations for Elision accuracy are given in z = 6.01, p < 0.001; the effect of length was marginally significant, β = −0.24, z = −1.80, p = 0.07; and the effect of orthographic neighborhood size was not significant, β = −0.004, z = −0.08, p = 0.93. The effect of elision accuracy was significant, β = 2.77, z = 5.71, p < 0.001, as was the overall effect of L1 writing system, χ2(df = 12) = 69.51, p < 0.001. Critically, L1 writing system also interacted significantly with lexicality, χ2(df = 3) = 13.50, p = 0.004. Therefore, further analyses were conducted for real words and pseudowords separately.The means and standard deviations for real word and pseudoword spelling accuracy are given in 2(df = 3) = 25.11, p < 0.001, as were the effects of elision accuracy  and word length . In addition, there were two significant interactions involving comparisons between the L1 English speakers and the alphabetic L1 speakers  as well as two marginally significant interactions involving comparisons between the L1 English speakers and the abjad L1 speakers . Thus, the final models of real word spelling accuracy examined L1 English speakers and the ESL speakers separately, and L2 English proficiency was also added as a factor for the ESL model.For real word spelling, model building initially considered all participant characteristics  and item characteristics  that correlations had suggested may be relevant, as well as log frequency. The overall effect of L1 writing system was significant, χ2(df = 2) = 0.20, p = 0.91 (though it was maintained in the model due to significant interactions with other variables). There were significant effects of proficiency and elision accuracy, such that participants with higher L2 English proficiency and with higher phonological awareness had significantly higher spelling accuracy than participants with lower L2 English proficiency and with lower phonological awareness. There were also significant effects of orthographic and phonological neighborhood size, with lower spelling accuracy for words with larger orthographic or phonological neighborhoods.These final models are given in 2(df = 2) = 7.82, p = 0.02; follow-up analyses within each L1 writing system group were used to examine this further. For the alphabetic and morphosyllabic L1 participants, the effect of phonological awareness was significant and positive: participants with higher elision accuracy had higher real word spelling accuracy . In contrast, for the abjad L1 participants, the effect of phonological awareness was marginally significant, but in the opposite direction: abjad speakers with higher elision accuracy had lower real word spelling accuracy, β = −4.60, z = −1.89, p = 0.06.There were also a number of significant interactions that qualified these overall effects. The interaction between L1 writing system and elision accuracy was significant, χThe interactions between elision accuracy and orthographic neighborhood size and phonological neighborhood size were also significant. In each case, participants who had higher phonological awareness experienced a larger effect of both orthographic neighborhood size and phonological neighborhood size. Finally, the interactions between word frequency and orthographic neighborhood size and phonological neighborhood size were significant. These interactions indicate that higher-frequency words were associated with smaller effects of both orthographic neighborhood size and phonological neighborhood size.2(df = 3) = 50.97, p < 0.001, as was the main effect of elision accuracy, β = 2.22, z = 4.36, p < 0.001. In addition, there were two significant interactions involving comparisons between the L1 English speakers and the abjad L1 speakers  as well as two significant interactions involving comparisons between the L1 English speakers and the morphosyllabic L1 speakers . Thus, the final models of pseudoword spelling accuracy again considered L1 English speakers and the ESL speakers separately, and L2 English proficiency was added as a factor for the ESL model.For pseudoword spelling, model building considered the same participant characteristics  and applicable item characteristics  that were considered with real word accuracy so that the results could be directly compared. The overall effect of L1 writing system was significant, χ2(df = 2) = 2.91, p = 0.23 (though it was again maintained in the model due to significant interactions with other variables). There was also a significant effect of proficiency, such that participants with higher L2 English proficiency had significantly higher pseudoword spelling accuracy than participants with lower L2 English proficiency.These final models are given in 2(df = 2) = 12.09, p = 0.002; and between L1 writing system and orthographic neighborhood size, χ2(df = 2) = 9.58, p = 0.01. Follow-up analyses within each L1 writing system group were used to examine these interactions further. For the alphabetic L1 participants, neither the effect of length  nor the effect of orthographic neighborhood size  were significant. However, within this alphabetic L1 model, the effect of proficiency was significant, β = 1.50, z = 1.98, p = 0.048, with higher pseudoword spelling accuracy among higher proficiency participants. For the abjad L1 participants, the effect of length was significant , with longer pseudowords being spelled more accurately than shorter pseudowords. The effect of orthographic neighborhood size was marginally significant , with larger orthographic neighborhoods associated with somewhat lower pseudoword spelling accuracy, but the effect of proficiency was not significant and was dropped from the final abjad L1 model. Finally, for the morphosyllabic L1 participants, the effect of length was significant , again with longer pseudowords being spelled more accurately than shorter pseudowords. The effect of orthographic neighborhood size was also significant , again with larger orthographic neighborhoods associated with lower pseudoword spelling accuracy, though the effect of proficiency was not significant and also dropped from the final morphosyllabic L1 model.There were two significant interactions that qualified these overall effects: between L1 writing system and length, χtypes and quantities of spelling errors committed by participants was conducted. First, the spelling of each grapheme in each item was examined to determine whether it was correct or incorrect. Generally following dress was divided into the following graphemes corresponding to phonemes: d| r| e| ss; separate was divided into s| e| p| a| r| aCe| t (with aCe representing the non-linear sequence of vowel + consonant + < e > indicating long vowel); and knowledge was divided into kn| ow| l| e| dge.Following the quantitative analysis of overall (strict) accuracy described above, a more in-depth investigation into the napkin); incorrect vowel grapheme (the wrong letter(s) representing a vowel phoneme in the word, e.g., < seperate > for separate); missing consonant grapheme (no letter(s) present to represent a consonant phoneme in the word, e.g., < resonsible > for responsible); missing vowel grapheme (no letter(s) present to represent a vowel phoneme in the word, e.g., < decsion > for decision); extra consonant grapheme  representing a consonant phoneme not present in the word, e.g., < grownd > for grown); or extra vowel grapheme  representing a vowel phoneme not present in the word, e.g., < recoganize > for recognize). Inter-rater reliability was initially 91% for real words and 63% for pseudowords; items for which there was disagreement were resolved through discussion among coders.Incorrect spellings of graphemes were further categorized in terms of whether the particular sound was misspelled or missing or whether additional sounds were represented in the spelling that were not present in the dictated word. More specifically, the categories were as follows (with examples drawn directly from the data): incorrect consonant grapheme (the wrong letter(s) representing a consonant phoneme in the word, e.g., < napcen > for rate of errors per item (rather than strict accuracy) as a function of L1 background, L2 English proficiency, and phonological awareness. The average number of errors per item of different types are given in Similar to the main analyses examining overall accuracy, linear mixed effects analyses were used, this time to examine the t = 4.40, p < 0.001, with significantly fewer errors made to real words than pseudowords. The overall effect of L1 writing system was also significant, χ2(df = 3) = 34.50, p < 0.001, as was the effect of phonological awareness, β = −0.44, t = −3.17, p = 0.002, with higher phonological awareness associated with fewer errors. The interaction between L1 writing system and item type was also significant, χ2(df = 3) = 9.66, p = 0.02. Thus, L1 English speakers and ESL speakers were further examined separately, with L2 English proficiency also added as a factor for the ESL model.The first error analysis examined the errors made to real words versus pseudowords . The effect of lexicality was significant β = −0.36, t = −0.19, p < 0.001, with higher phonological awareness associated with fewer errors. The effect of lexicality was also significant, with fewer errors made to real words than pseudowords, β = −0.61, t = 4.07, p < 0.001. The interaction between phonological awareness and lexicality was only marginally significant, β = 0.31, t = 1.70, p = 0.096; the trend was such that the effect of phonological awareness was slightly stronger for real words than it was for pseudowords.For the L1 English speakers, the effect of phonological awareness was significant, β = −54, 2(df = 2) = 3.28, p = 0.19. In addition, the effect of proficiency was not significant, β = −0.03, t = −0.30, p = 0.77. However, the effect of lexicality was significant, β = −0.74, t = −6.59, p < 0.001, with fewer errors made to real words than to pseudowords. The interaction between lexicality and proficiency was also significant, β = 0.49, t = 3.55, p < 0.001, with more errors made to real words than pseudowords among lower proficiency speakers, but more errors made to pseudowords than to real words among higher proficiency speakers.For the ESL speakers, the overall effect of L1 writing system was not significant, χFor the second error analysis, the incorrect, missing, and additional consonant errors and vowel errors were summed together by phoneme type to calculate the total number of consonant-related errors and vowel-related errors for each participant. These were then examined across L1 groups and L2 English proficiency to determine whether there were any differential accuracies by segment type (consonant versus vowel sounds), as has been demonstrated in previous research with abjad L1 speakers e.g., .2(df = 3) = 27.58, p < 0.001. The main effect of lexicality was not significant, β = 0.10, t = 1.42, p = 0.16, though the main effect of segment type was marginally significant, β = 0.05, t = 1.66, p = 0.099, with a slight trend toward more vowel errors than consonant errors. However, these main effects were qualified by a number of significant interactions, including between L1 writing system and lexicality, χ2(df = 3) = 18.38, p < 0.001 and between L1 writing system and segment type, χ2(df = 3) = 15.44, p = 0.001. Due to these significant interactions with L1 writing system, as with previous analyses, the L1 English speakers and ESL speakers were examined in more detail separately.There was a significant overall effect of L1 writing system, χt = −3.08, p = 0.01; lexicality, β = −0.15, t = −9.30, p < 0.001. Specifically, higher phonological awareness and real words were associated with fewer errors than were lower phonological awareness and pseudowords. Notably, the effect of segment type was not significant.For the L1 English speakers, only phonological awareness and lexicality were significant predictors: phonological awareness, β = −0.12, 2(df = 2) = 7.26, p = 0.03. However, a number of main effects were not significant: proficiency, β = −0.02, t = −0.33, p = 0.75; phonological awareness, β = 0.07, t = 0.52, p = 0.60; lexicality, β = 0.01, t = 0.10, p = 0.92; and segment type, β = 0.04, t = 1.11, p = 0.27. Importantly, these main effects were qualified by a significant interaction between L1 writing system and segment type, χ2(df = 2) = 14.44, p < 0.001. Thus, each L1 writing system group was examined separately.For the ESL speakers, the overall effect of L1 writing system was again significant, χt = −0.53, p = 0.60; phonological awareness, β = 0.04, t = 0.23, p = 0.82; and lexicality, β = −0.04, t = −0.40, p = 0.69. The main effect of segment type was marginally significant, β = 0.11, t = 1.97, p = 0.05, with somewhat more errors made involving vowels than consonants. However, there were a number of significant interactions among these variables. Proficiency interacted with lexicality, β = 0.20, t = 2.63, p = 0.01, such that there was no lexicality effect in higher proficiency participants, but there were more errors per item to real words than to pseudowords in lower proficiency participants. Proficiency also interacted with segment type, β = −0.15, t = −2.39, p = 0.02, such that higher proficiency participants made somewhat more errors involving vowels than consonants, but there was essentially no difference in lower proficiency participants. Lastly, phonological awareness interacted with lexicality, β = −0.35, t = −2.55, p = 0.01, such that phonological awareness was not related to the error rate among pseudowords, but higher phonological awareness was associated with a lower error rate among real words.For alphabetic L1 speakers, most main effects were not significant: proficiency, β = −0.05, t = −1.88, p = 0.08, with a lower error rate among real words than pseudowords. The effects of proficiency and phonological awareness were not significant and thus removed from the final model. However, the effect of segment type was significant, β = 0.16, t = 2.45, p = 0.02: abjad L1 speakers made significantly more errors involving vowels than consonants.For abjad L1 speakers, the effect of lexicality was marginally significant, β = −0.13, t = −2.66, p = 0.01, with a lower error rate among real words than pseudowords. The main effect of segment type was also significant, β = 0.24, t = 3.72, p < 0.001, with more errors involving vowels than consonants. As with the abjad L1 speakers, the effects of proficiency and phonological awareness were not significant and thus removed from the final model. However, the interaction between lexicality and segment type was also significant, β = −0.18, t = −2.05, p = 0.047; there were substantially more errors involving vowels than consonants among pseudoword items, but this difference was minimal among real words.For morphosyllabic L1 speakers, the effect of lexicality was significant, β = −0.17, The correlations among real word spelling accuracy, pseudoword spelling accuracy, and phonological awareness accuracy showed different patterns in each L1 group. For the L1 English speakers, all three tasks were significantly positively correlated with one another, whereas for the morphosyllabic L1 speakers, there were no significant correlations among these three tasks. The alphabetic and abjad L1 speakers fell somewhere in the middle: phonological awareness accuracy was significantly correlated with real word spelling accuracy for the alphabetic L1 speakers and was significantly correlated with pseudoword spelling accuracy for the abjad L1 speakers, though these were the only significant correlations in these groups.Regarding spelling accuracy, the native speaker comparison group (L1 English speakers) had substantially higher real word and pseudoword spelling accuracy than the three ESL groups. Interestingly, the L1 English speakers had relatively few predictors of spelling accuracy: only phonological awareness  and length . No other lexical characteristics influenced L1 English speaker spelling accuracy.longer pseudowords and for those with smaller orthographic neighborhoods.The picture was much more complex among the ESL participants. L2 English proficiency was consistently related to both real word and pseudoword spelling accuracy, such that spelling accuracy increased along with increasing L2 proficiency. Similarly, higher phonological awareness scores were associated with higher real word spelling accuracy in the alphabetic and morphosyllabic L1 speakers, but the opposite pattern was found for the abjad L1 speakers: higher phonological awareness was associated with lower real word spelling accuracy. In contrast, higher phonological awareness scores were associated with higher pseudoword spelling accuracy across L1 groups. Lexical characteristics also influenced ESL spelling accuracy: higher phonological awareness scores were associated with larger effects of orthographic and phonological neighborhood size in real words, whereas higher word frequency was associated with smaller effects of orthographic and phonological neighborhood size in real words. Among pseudowords, the abjad and morphosyllabic L1 speakers had more accurate pseudoword spelling for Considering the phonological awareness scores themselves, the L1 English speakers had higher accuracy than all ESL groups on the elision task. Among the ESL participants phonological awareness accuracy increased along with higher L2 English proficiency across L1s. However, the alphabetic L1 speakers were significantly less accurate in their elision performance than the abjad and morphosyllabic L1 speakers, who did not differ from one another.Finally, the L1 English speakers and ESL speakers also showed different patterns regarding the rates at which they made specific types of spelling errors. Among L1 English speakers, the only two patterns that emerged were that higher phonological awareness was related to a significantly lower error rate, and that the error rate was lower to real words than pseudowords. Once again, the pattern of results was more complex when considering the ESL speakers. Considering error rates to real words versus pseudowords, there was no overall effect of L1 writing system or L2 English proficiency level, but there was an unexpected interaction between lexicality and proficiency, such that lower proficiency ESL speakers had a higher error rate to real words than pseudowords, whereas higher proficiency ESL speakers had a higher error rate to pseudowords than real words. Considering error rates involving vowels versus consonants, there was a general tendency for a higher error rate to vowels than consonants. This was found among higher proficiency alphabetic L1 speakers, with pseudowords in morphosyllabic L1 speakers, and in abjad L1 speakers regardless of proficiency level or item type.The current study examined real word and pseudoword spelling accuracy in adult learners of ESL from a variety of L1 backgrounds. To facilitate cross-linguistic comparisons, these ESL speakers were grouped by L1 writing system: alphabetic L1s, abjad L1s, and morphosyllabic L1s. Participants also completed the Elision subtest from the CTOPP to measure their phonological awareness. Analyses focused on the relationships among real word and pseudoword spelling and phonological awareness skills, detailed analyses of the types of errors made by participants, and the variations in these patterns across L1 groups.As a whole, the results were largely consistent with the findings from previous research on ESL spelling abilities. The comparison group of L1 English speakers consistently had higher spelling accuracy , fewer errors per item, and higher phonological awareness accuracy than all three ESL groups. Considering the three ESL groups, previous research has generally found that ESL speakers from a morphosyllabic L1 typically have relatively strong real word spelling skills, particularly for irregular/exception words, but have substantial difficulties reading and spelling pseudowords, whereas ESL speakers from an alphabetic L1 typically have stronger phonological skills and rely on them for word reading and spelling, resulting in a substantial number of overregularization errors e.g., . The resGiven the relatively strong phonological skills that are typically found in learners with an alphabetic L1, it may initially seem surprising that the alphabetic L1 speakers in this study had such low pseudoword spelling and phonological awareness performance. However, there are a number of factors that can help explain this result. First, as discussed further below, the distribution of participants with different L1 writing systems was not even across proficiency levels, and there were more alphabetic L1 speakers at the lowest levels of proficiency  than in the other ESL groups. Given that spelling accuracy was also significantly related to L2 English proficiency, it is likely that the overall lower proficiency level of the alphabetic L1 speakers contributed to their lower raw scores. This interpretation is supported by the fact that, when L2 English proficiency was considered, the differences among the ESL groups were much smaller and real word spelling accuracy did not differ between the alphabetic and morphosyllabic L1 speakers.Another contributing factor is likely the nature of phonological skill development in L1 Spanish . Due in part to the highly consistent nature of the Spanish orthography, fine-grained phonological awareness skills  are not needed for Spanish literacy and thus may not develop readily e.g., , 2011. IIt must also be noted that, although the alphabetic L1 speakers had low strict spelling accuracy, a different picture emerges if error rates per item are considered. In word spelling, the alphabetic L1 speakers frequently had low overall rates of errors per word, particularly on pseudowords. Thus, although their spellings may not have been accurate in terms of strict coding, the spellings produced by the alphabetic L1 speakers were relatively more target-like than those produced by the other ESL groups. This finding also highlights another important point: the conclusion that is reached from research results may be heavily dependent on the format of the task e.g., , 2011, tless consistent than pseudowords. If these items are not well-known words for participants (as may be the case for those with lower levels of proficiency), they are likely to be more difficult to spell and to result in an increased error rate. However, with increased proficiency (and increased vocabulary knowledge), this effect should diminish or disappear – as is attested in the current data.Examination of the results for error rates also highlights another initially unexpected pattern in the findings: a higher error rate to real words than to pseudowords, particularly in lower proficiency learners. Given that real words may be known, but pseudowords by definition are unknown, it might be expected that spellings, regardless of scoring approach, would be more accurate for real words than pseudowords. However, a closer examination of the characteristics of English words and pseudowords themselves helps illustrate why this may not always be the case. English spelling is notoriously opaque , meaningThe differential relationships between spelling and phonological skills found in the current study are also consistent with previous research. In the L1 English speakers, both real word and pseudoword spelling accuracy were significantly related to phonological awareness skills. This is consistent with the continuing importance of phonological skills for literacy in the opaque English orthography, compared to other languages in which the importance of phonological awareness decreases rapidly with increasing reading proficiency e.g., . Consistnegative beta weight for elision accuracy as a predictor of real word spelling accuracy among the abjad L1 speakers, in contrast to the positive beta weights for the alphabetic and morphosyllabic L1 speakers. Based on a reviewer recommendation, we examined whether proficiency was a significant predictor of elision accuracy, and whether this relationship was different among the ESL groups. This is in fact what we found: there was a significant positive relationship between proficiency and elision accuracy for the alphabetic L1  and morphosyllabic L1 speakers  but not for the abjad L1 speakers . Thus, larger and more detailed datasets would be beneficial in future research to more directly explore these interactions and what they can tell us about L1 differences in literacy skills.Examining the varying relationships between spelling and phonological skills is also an area where additional research with a larger number of participants at both lower and higher proficiency levels would be beneficial. In the current results there was an unexpected finding of a The results from the current study do provide new data to contribute to an unresolved issue in L2 spelling research: whether (L1-specific) errors decrease with increasing L2 proficiency, or whether they persist over continued L2 development. Some previous studies have found that such errors do decrease with increasing L2 proficiency e.g., , whereasAnother question addressed by the current study was whether there would be significant L1 differences in accuracy spelling consonant versus vowel phonemes, as has been found for both L1 Arabic and L1 Hebrew speakers in prior research e.g., . BroadlyAlthough this study makes important contributions toward our understanding of adult ESL spelling abilities, there are still a number of limitations that must be acknowledged. First, although data were collected from a wide range of L2 English proficiency levels and three representative L1 writing systems, there were relatively small sample sizes in some combinations of L2 English proficiency and L1 writing system. In addition, the number of participants from each L1 writing system was not consistent across all levels of proficiency, with somewhat more alphabetic L1 speakers at lower levels of proficiency compared to the abjad L1 and morphosyllabic L1 groups. Future research would benefit from a larger sample size, including targeted recruitment of a balanced sample of participants across L1 writing systems and proficiency levels; this was unfortunately not possible given the current context of data collection. Such research will be useful for confirming the specific findings from this study.Another improvement that could be made by future research would be to include a wider variety of target items, both real words and pseudowords, and to specifically consider lexical characteristics during item selection. The items chosen for the current study were based on items previously used successfully in published research on ESL spelling abilities, but were not chosen with regard to their frequency, orthographic neighborhood size, or phonological neighborhood size. However, modeling the results for spelling accuracy suggested that these three lexical characteristics in particular may influence ESL spelling abilities, and are thus deserving of dedicated attention in future research.A strength of the current study was the use of a dictation task to assess spelling ability. Although this type of assessment is common in L1- and child-focused literacy research, it is much lesson common in adult L2 research, and using it in this study eliminated the influence of learner avoidance found in studies of spelling errors from naturalistic writing samples . HoweverAlthough spelling is a critical literacy skill it has received relatively little attention, especially in the domain of cross-linguistic L2 literacy research. The current study sought to address a number of gaps left by existing research, by focusing on adult ESL users (rather than children), considering not only real word spelling ability but also pseudoword spelling ability and phonological awareness, and using the same materials and procedure with participants from a variety of L1 backgrounds (thus facilitating cross-linguistic comparisons). In many ways the results were consistent with previous research, demonstrating relatively high  spelling accuracy yet somewhat weak phonological skills in morphosyllabic L1 speakers; more reliance on phonological skills in alphabetic L1 speakers; and significantly more errors involving vowels than consonants in abjad L1 speakers. However, there were also some unexpected patterns in the results, particularly the relatively low spelling accuracy and phonological awareness performance by the alphabetic L1 speakers. To some degree, these unexpected findings can be accounted for when considering another way to analyze the data: in terms of error rates, rather than strict accuracy. This highlights perhaps the most important individual finding from the study: the substantially different patterns of results, and conclusions, that may be reached when the data are scored differently. The field of L2 literacy research has much important work to do to document such variations and establish best practices for task choice, item selection, and particularly scoring procedures to improve reliability and validity.The datasets generated for this study are available on request to the corresponding author.The studies involving human participants were reviewed and approved by Human Subjects Committee at Southern Illinois University Carbondale. The patients/participants provided their written informed consent to participate in this study.KM contributed to study design, item selection, data collection, data analysis, and writing. EL contributed to data analysis and writing. KC contributed to study design, item selection, data collection, and writing. EH contributed to study design, item selection, data collection, and writing.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 development of polymer-based devices has attracted much attention due to their miniaturization, flexibility, lightweight and sustainable power sources with high efficiency in the field of wearable/portable electronics, and energy system. In this work, we proposed a polyvinylidene fluoride (PVDF)-based composite matrix for both energy harvesting and energy storage applications. The physicochemical characterizations, such as X-ray diffraction, laser Raman, and field-emission scanning electron microscopy (FE-SEM) analyses, were performed for the electrospun PVDF/sodium niobate and PVDF/reduced graphene oxide composite film. The electrospun PVDF/sodium niobate nanofibrous mat has been utilized for the energy harvester which shows an open circuit voltage of 40 V (peak to peak) at an applied compressive force of 40 N. The PVDF/reduced graphene oxide composite film acts as the electrode for the symmetric supercapacitor (SSC) device fabrication and investigated for their supercapacitive properties. Finally, the self-charging system has been assembled using PVDF/sodium niobate (energy harvester), and PVDF/reduced graphene oxide SSC (energy storage) and the self-charging capability is investigated. The proposed self-charging system can create a pathway for the all-polymer based composite high-performance self-charging system.  The extensive use of renewable energy/power sources paves the way for the growing energy crisis and the environmental pollution issues, which creates the demand towards the need for energy sources ,2. To ov2O5), potassium permanganate (KMnO4), sulfuric acid (H2SO4), hydrogen peroxide (H2O2), hydrochloric acid (HCl), sodium hydroxide (NaOH), hydrazine hydrate (assay 50%), polyvinyl alcohol (PVA), phosphoric acid (H3PO4), N,N-dimethylacetamide and acetone were obtained from Dae Jung Chemicals and Metal Co., Ltd. . All the chemicals used in this research were research-grade, and double distilled water was used throughout the experiments.Graphite powder and polyvinylidene fluoride (PVDF) were procured from Sigma Aldrich Ltd. Niobium oxide  and galvanostatic charge-discharge (CD) measurements using an Autolab PGSTAT302N electrochemical workstation.The supercapacitor device was fabricated using the prepared PVDF/reduced graphene oxide composite film as the electrode for the device with PVA/H+ ion laser. The data were collected using a 10 s data point acquisition time. The PVDF/sodium niobate nanofibers were prepared to utilize the electrospinning/spray system . The surface morphology of the PVDF/reduced graphene oxide composite film and electrospun PVDF/sodium niobate mat were analyzed using a field-emission scanning electron microscope . The external force applied to the nanogenerator device using a linear motor  and the open-circuit voltage and the short-circuit current were recorded using nano voltmeter  and a picoammeter (Keithley 6485), respectively.The phase formation and the crystallinity of the graphene nanosheets and sodium niobate nanostructures were determined using the Rigaku X-ray diffractometer operated at 40 keV and 40 mA Cu Kα radiation. The ultrasound irradiation used for the dissolution of PVDF polymer solution was carried out on a SONIC  VCX 500 system  with the aid of direct immersion titanium (Ti-6Al-4V) horn. The Raman spectra of the PVDF/reduced graphene oxide composite film and sodium niobate were obtained using Lab Ram HR Evolution Raman spectrometer , operated at 10 mW laser power with an excitation wavelength of 514 nm with an ArP21ma. −1 [−1 all correspond to the ferroelectric phase of sodium niobite [−1 (ν1) accompanied by a shoulder at around 571 cm−1 (ν2) confirms the orthorhombic perovskite structure of the sodium niobate in the PVDF matrix [The physicochemical characterization of the sodium niobate and PVDF/sodium niobate nanofibers are provided in 21ma. −1  whereas  niobite . The preF matrix . FurtherF matrix . The surThe piezoelectric characterization of the bare PVDF and electrospun PVDF/sodium niobate nanofibrous mat was investigated by fabricating the nanogenerator device . Figure From the obtained results, it is evident that the output of the PVDF/sodium niobate nanogenerator is highly dependent on the applied compressive force and directly proportional to its piezo-voltage. The electrospun PVDF/sodium niobate mat as the active piezoelectric layer shows enhanced output compared with the other reported piezoelectric nanogenerators and the improved performance is due to the following reasons: (i) high ferroelectric property of the PVDF and sodium niobate results in the enhancement of the piezoelectric property of the composite, (ii) high voltage applied in the fabrication methodology, which enhances the arrangement of dipoles in the prepared composite mat ,39. Thes−1 corresponds to the D and G band of the graphene in the PVDF matrix [−1 corresponds to the characteristic band of PVDF [In the view of energy storage application, PVDF/reduced graphene oxide has been chosen as the electrode material. F matrix , and the of PVDF . The sur of PVDF . The FES of PVDF . Besides3PO4 as the electrolyte. Initially, the cyclic voltammetric analysis for the fabricated PVDF/reduced graphene oxide SSC was recorded over the voltage window of 0–0.8 V measured at various scan rates ranging from 1 to 10 V s−1 as shown in −1) symbolizing the excellent capacitive nature of the PVDF/reduced graphene oxide SSC device. The current of the CV profiles is increasing with the increase in the scan rate, suggesting the better capacitive nature of the device [C) of the PVDF/reduced graphene oxide SSC device was calculated using the relation [The electrochemical properties of the prepared PVDF/reduced graphene oxide film were investigated by fabricating a symmetric solid-state supercapacitor device using PVDF/reduced graphene oxide as the electrode and PVA/He device . The gale device . The CD e device . From Fie device . The sperelation : C = I ×I” is the discharge current (A), “Δt” is the discharge time (s), “ΔV” is the voltage window (V), and “A” is the area of the PVDF/reduced graphene oxide SSC device the electrode (cm−2). The PVDF/reduced graphene oxide SSC device delivered a specific capacitance of 683 nF was calculated from the CD profile measured at a constant discharge current of 10 nA. The change in the specific capacitance of the PVDF/reduced graphene oxide SSC device with respect to the current is provided in −2 was obtained at a higher current density of 50 nA cm−2, which almost retained 69.69 % of its initial capacitance with an increase of 5-fold in the current suggesting the better rate capability of the PVDF/reduced graphene oxide SSC device [Here “C device . Figure C device . Figure To investigate the capability of the self-charging system as a practical power source for electronic devices, the PVDF/sodium niobate nanogenerator was integrated with the PVDF/reduced graphene oxide SSC device to form the self-charging power system as shown in the scheme provided in The charging behavior of the PVDF/reduced graphene oxide SSC connected with the PVDF/sodium niobate nanogenerator under various applied compressive force is provided in In this work, we successfully fabricated the PVDF/reduced graphene oxide electrode and electrospun PVDF/sodium niobate nanofibrous mat as the active materials for the supercapacitor and nanogenerator device. The individual performance has been examined by fabricating the PVDF/reduced graphene oxide supercapacitor device and PVDF/sodium niobate nanogenerator device, which shows an excellent performance as the energy storage and harvester, respectively. The integrated self-charging power system can charge the supercapacitor device to 0.8 V in 190 s. Collectively, from the obtained results, the novel self-charging power system will paves the way towards the development of polymer-based self-charging system for wearable/portable electronics applications.