Accumulating behavioral and neurophysiological evidence supports the idea of language being grounded in sensorimotor processes, with indications of a functional role of motor, sensory and emotional systems in processing both concrete and abstract linguistic concepts. However, most of the available studies focused on native language speakers (L1), with only a limited number of investigations testing embodied language processing in the case of a second language (L2). In this paper we review the available evidence on embodied effects in L2 and discuss their possible integration into existing models of linguistic processing in L1 and L2. Finally, we discuss possible avenues for future research towards an integrated model of L1 and L2 sensorimotor and emotional grounding. Amodal system theories of language suggest that cognition is built of abstract amodal representations via formal rules, related to their referents . These tDespite the accumulating evidence, however, the exact functional role of these activations remains debated. One possibility is that embodied mechanisms are indeed an inseparable and functionally crucial part of language processing . OppositFundamental to the hypothesis of language grounding in sensorimotor processes, is the assumption that linguistic and sensorimotor experience develops with similar timings in early developmental stages. While this is mostly the case for a first language (L1), typically it is not for second language (L2) late learners who do not grow up as bilinguals . PulvermSubsequently, word learning is often accompanied by a direct association to objects, actions and properties of their referents in the environment . These sThus, while L1 is acquired in a strong connection to bodily sensations and motor programs and is used daily, L2 is usually learned through symbol manipulation, often based on L1 through analogy or translation and is used in specific settings . However, new concepts might borrow sensorimotor groundings from previously grounded symbols  might overcome this limitation but the available evidence is still insufficient. Evidence on L2 grounding effects induced by abstract words is particularly scarce, possibly as a result of the available contradicting evidence of embodiment in L1 for abstract linguistic concepts . A largeThe semantic aspects of abstract words might depend much more on the context in which they were learned . Thus, sFrom the reviewed evidence, an explicit sensorimotor and emotional grounding approach to L2 has so far been taken only by a limited number of studies. However, it is worth noting that evidence on L1 and L2 outside this particular approach is much more extensive and has produced several competing models and hypotheses regarding the neural bases of L1 and L2. It is worth briefly reviewing them in order to discuss whether and how the embodied cognition evidence might support the existing models.According to the so-called differential hypothesis , differeAccording to these models, if language is indeed embodied and grounded in sensorimotor  processes, then a similar engagement of these systems should be expected regardless of the use of L1 or L2. However, the time course might differ, with later L2 effects . These eSimilar temporal dynamics, on the other hand, would support effects directly produced by L2 linguistic stimuli, not mediated by L1. This would for instance be in line with the Revised Hierarchical Model (RHM) , a languIt is evident that approaching L1 and L2 processing from an embodied point of view is a new and complex area of research. On the one hand, L2 poses a challenge to strong views of embodied cognition: if linguistic concepts are deeply rooted in sensorimotor processes, then this should be true regardless of the use of L1 or L2. On the other hand, the same assumption of a strong link between sensorimotor experience and linguistic concepts, would predict differences between L1 and L2 grounding based on their age of acquisition.Furthermore, when approaching L1 and L2 existing competing models should be taken into account and integrated models should be produced including evidence based on the embodied and grounding hypothesis. In this sense, these models should take into account several parameters, including localization, magnitude and timing of the embodied effects.The use of methodologies with high temporal resolution, such as M/EEG, or allowing focal brain stimulation (TMS), will be crucial for disentangling the time course of effects in L1 and L2. In addition, behavioral measures collected in various tasks, will allow a more complete view of how L1 and L2 linguistic concepts are shared or differentially activated. The possible task-dependency of these effects– an issue already recognized in the embodied language literature – has to be even more carefully addressed when testing L2 as it might either support or conflict with existing strategies used for language acquisition and/or memory retrieval. Such an improved methodological approach would help in clarifying the different functional role of language grounding in L1 and L2.In the same vein, researchers should focus on formalizing the way linguistic experience  can be factored into the experimental design. Finally, the advancement of research on embodiment in L2 will necessary profit from the extension of the stimuli from single nouns or verbs to more complex sentences, as well as towards the use of abstract and emotional stimuli.CG and KK wrote and approved the final version of this manuscript.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.


N-Methyl pyrrolidone and deionized water to form a homogeneous GO suspension, which was finally added into electroless plating solutions for the reduction process. Copper-coated graphene (Cu@graphene) and nickel-coated graphene (Ni@graphene) were synthesized using this one-step and co-reduction method by mixing salt solutions containing metal ions and GOs into the plating solution. The Cu ions or Ni ions were adsorbed and bonded onto the edges and surfaces of graphene, which was reduced from the GOs using a strong reducing agent of ascorbic acid or sodium borohydride. Crystalline Cu particles with an average size of about 200 nm were formed on the surface of graphene, whereas amorphous or nanocrystalline Ni particles with an average size of 55 nm were formed on the surface of graphene. Distribution of these metal particles on the graphene is homogeneous and highly dispersed, which can effectively improve the sinterability of composite powders. Cohesive energy distribution between graphene and metal interface was analyzed using first-principle calculation method. Formation mechanism of metal coated graphene was identified to be that both the GO and metal ions were simultaneously reduced in the reducing agents and thus a chemical bonding of graphene/metal was formed between the metal particles and graphene.Nanocomposite powders based on metal-coated graphene were synthesized using an in-situ co-reduction method in order to improve wettability and interfacial bonding between graphene and metal. Graphene oxide (GO) of 2~3 atomic layers was synthesized using the Hummer’s method with graphite as a raw material and then dispersed into a dispersing agent solution mixed with  Graphene has excellent physical and mechanical properties owing to its unique structure . In factGraphene is commonly used as a reinforcing material in composites, including metal, polymer and ceramic matrix composites ,12,13,14An efficient method was proposed to pre-coat the surface of graphene with a layer of metal in order to prevent its agglomeration in the matrix ,16. Due Therefore, in the present work, we synthesized Cu@graphene and Ni@graphene using a new and efficient in-situ co-reduction method. The formation mechanism of the metal@graphene composite was analyzed based on various characterization results. The cohesive energy between metal and graphene was calculated and analyzed using the first principle calculation method.2O2 (30%), N-methyl pyrrolidone, NaOH (PH = 11), ammonia (25–28%), KMnO4, were bought from Sinopharm Chemical Reagent Co. Ltd., Shanghai, China. All the chemicals were used directly without further purification.In this work, the raw materials used were flakes of graphite powders . Chemical reagents, such as copper sulfate, nickel sulfate, sodium hydroxide, concentrated sulfuric acid (98%), HCl (37%), H2SO4 and then stirred using an ice-bath (at 0 °C) for 30 min; (b) At room temperature of 25 °C, 20 g of KMnO4 was slowly added into the above mixture and agitated for 120 min; (c) The temperature of above mixture solution was increased to 35 °C during the process; and then 50 mL of deionized water (DI) was gradually added into the above solution; (d) 80 mL of DI water was gradually added into the system; After all the reactions were completed, hydrogen peroxide (30 wt %) was added into the solution until it turned into a yellow color and no bubbles were further produced; (e) The mixture was filtered and washed using HCl (5 wt %) and DI water for ~28 times and then dried at 70 °C for 12 h using a vacuum freeze-drying method. In this paper, we did not perform the recycling of the residual product as reported in Reference [The standard Hummer’s method was employed to synthesize GO ,26,27. AAs illustrated in (a)N-Methyl pyrrolidone and DI mixture solution;20 mg of GO was dispersed into 100 mL dispersing agent solution in an ultrasound bath for 3 h to obtain a homogeneous GO suspension solution (0.2 mg/mL) as shown in (b)The salts , reducing agents  and surfactant agents were mixed together to form an electroless plating solution b;(c)Then the GO suspension solution was added into the electroless plating solution c;(d)The mixed solution was intensively stirred using a magnetic stirrer to disperse the GO suspension solution. The copper plating process was done at 90 °C for 3 h and the nickel plating was done at 30 °C for 30 min. Simultaneously the NaOH solution or ammonia solution was dripped into the mixed solution to adjust the pH value to between 9 and 10 d. The pH(e)The precipitates were separated from the solution after the chemical reactions were completed e. DI watThe detailed electroless plating processes are listed as follows:α radiation at 40 kV and 15 mA was used to analyze the crystalline structures of GO and metal@graphene. The scanning rate was 8°/min and the scanning range of 2θ was 5~65° with a step size of 0.02°. Surface morphology of the GO and metal@graphene was observed using a scanning electron microscope  and chemical element analysis was performed using an energy dispersive X-ray spectrometer . Detailed morphological characteristics of the GO and metal@graphene composites were obtained using a transmission electron microscope . Characterization of samples using Raman spectroscopy  were performed using a laser beam with a wavelength of 532 nm and a SWIFT detector over a range of 500–3500 cm−1 and all the spectra were taken at room temperature (20 °C). Fourier transform infrared (FT-IR) spectra of the GO and metal@graphene were obtained using a TENSOR 27 spectrophotometer  with wavelengths ranging from 500 to 4000 cm−1 at room temperature. Microscale surface morphologies of metal@graphene powders were obtained using an atomic force microscope  in a tapping mode.An X-ray diffractometer  with Cu KFor the graphene system after atomic adsorption, there are defects, grain boundaries and intrinsic atoms formed. The adsorption energy of defects on the graphene is maximum and those of the grain boundary and intrinsic atoms on the graphene are approximately equal. The binding between graphene and metal is generally weaker than a typical covalent bond. In the present study, we focused on analysis of cohesive energies of Cu and Ni atoms with both their (111) surfaces bonded onto a graphene of a few atomic layers. The modeling work only considered the intrinsic atoms and defects adsorption. The first principle calculation was used to evaluate the cohesive energy between graphene and metal interface, as the binding force cannot be obtained using experimental methods easily.k points for the Monkhorst–Packs.The detailed model information is described as follows: firstly, the lattice is established. The lattice constant is set as a = b = 2.46, c = 3.4 and carbon (related to graphene) atoms are added . Then, in order to eliminate the influence of molecular bond between graphene layers, the vacuum layer is expanded to 2 nm on the Z axis direction. Finally, a and b in the supercell are increased to 3 times of original values and the initial configuration of the model is obtained in . The strIn order to check the thickness and microstructure of the GO, TEM and AFM images were obtained and the results are shown in AFM and TEM images of graphene, Cu@graphene and Ni@graphene obtained from the in-situ co-reduction processes are shown in n is 1, λ is the X-ray wavelength of 0.154 nm from the Cu X-ray source, θ is half of the diffraction angle and d is the interlayer spacing. The calculated layer spacing of peak (001) of graphite oxide is ~0.80 nm, which indicates that the GO obtained is nearly a monolayer [The obtained XRD patterns of GO sheets, graphene, Cu@graphene sheets and Ni@graphene sheets are shown in onolayer .For XRD result of Cu@graphene c, there For XRD result of the Ni@graphene sheets d, there In order to verify that the graphene was still maintained after the in-situ co-reduction process, XRD analysis of the prepared composites b shows a−1, which represent the D peak, G peak and 2D peak of the GO. The intensity ratio of D peak and G peak (ID/IG) is often used to characterize the degree of defects in carbon materials [D/IG of GO in this study was measured to be 0.91 and it is similar to those reported in references [Raman spectra of GO, graphene, Cu@graphene and Ni@graphene powders are presented in aterials . The ID/ferences ,37.D/IG data of composites and graphite, we can confirm that the defects are increased after the graphite was oxidized and some of the carbon atoms in the defect structures are combined with the oxygen-containing functional groups [sp2 hybridization into sp3 hybridization. The oxygen-containing functional groups not only cause changes in crystallinity of hexagonal network structures of the graphite but also increase the defects, which causes the G peak to be widened and the strength of D peak to be increased [D/IG is 1.02 as shown in D/IG for the composite indicates that majority of oxygen-containing functional groups were removed during the reduction process, the reason of which has been reported in our previous work [Comparing the Il groups . Formatincreased . Whereasous work ,41.−1 and ~1593.06 cm−1, which represent the D peak and G peak of carbon. The calculated ID/IG values of GO and Cu@graphene are 0.91 and 1.09, respectively. This indicates that the reduction effect will result in the increases of defects, topological disorders and the degree of graphitization; as well as decrease of crystallinity. The Raman spectrum of the Ni@graphene composite  is originated from two phonon and double resonances of laser induced vibration process for carbon. Generally, the 2D peak is an indication if the graphene is single layer or a few layers [−1, whereas that of double-layer graphene is located at 2692.3 cm−1 and that of graphene having more than 10 layers is close to the position of the 2D peak of natural graphite which is located at 2716.5 cm−1. The 2D peak of GO in this study  and (3) [For the FT-IR spectrum of the Ni@graphene d, all th and (3) ,46:(2)4NTEM images of GO and Cu@graphene are shown in TEM image of the Ni@graphene is shown in Based on DFT calculation results, the binding energy of Ni atoms adsorbed onto the graphene is 2.078 eV, whereas the binding energy of Ni atoms adsorbed on the graphene with the defect is 3.214 eV. Meanwhile, the binding energy of Cu atoms adsorbed onto the intrinsic graphene is 1.778 eV, whereas that of Cu atoms adsorbed on the graphene with the defect is 5.114 eV. For both cases, the binding of metal atom and graphene is a chemical process, which verifies the experimental results in the previous sections. Meanwhile, results show that the binding energy of atomic adsorption on defect of graphene is larger than that on the intrinsic graphene, which clearly show that the metal atoms are preferably adsorbed on the defects in the graphene. This result is also consistent with the literature ,54.Pz orbital of carbon atoms and the metal atoms is strong. Therefore, we find that, except for the observed charge transfer between graphene and metal orbitals, a strong coupling is obtained between the band structures of graphene and metal.In order to understand the differences of binding strengths between Cu or Ni and graphene, we further analyzed the electronic coupling across the interfaces. The obtained band structures of graphene-Cu(111) system and graphene-Ni(111) system are plotted in Based on the characterization results, the formation mechanism of metal@graphene is proposed as illustrated in In the second stage, a suitable chemical reagent and a strong reducing agent  are applied depending on the type of metal to be plated and the chemical reduction processes to be initiated.The third step is the most important one which is in-situ and co-reaction process. The copper ions or nickel ions adsorbed on the edge and surfaces of graphene oxide are strongly reduced in the alkaline conditions to obtain metal particles and the specific reactions for copper plating are written in Equations (4)–(7). Those of the nickel plating are written in Equation (8):2OH with the reduction actions of ascorbic acid or sodium borohydride. The reduction reactions can be verified from our FT-IR analysis. The reactions that occur in this process can be expressed as follows:Simultaneously, GO is reduced by the strong reducing agent of ascorbic acid or sodium borohydride to produce a graphene layer. The –COOH functional group on the surface of the GO is reduced to –CHSince the newly formed graphene has a large surface energy, the metal ions in the solution are easily adsorbed onto the surface of the graphene and then deposited onto its surface and the inherent “defects” of the graphene cause the metal ions to form a good chemical bonding . This haIn this work, GO of 2~3 atomic layers were obtained using the Hummer’s method. Using GO, copper sulfate and ascorbic acids (or nickel sulfate and sodium borohydride), the Cu@graphene powders (or Ni@graphene powders) with a homogeneous distribution of metal nanoparticles on the surface of graphene were obtained using an efficient in-situ co-reduction method. The formation mechanism of metal@graphene can be explained: for example, the metal ions and graphene firstly form a chemical bond and the GO and the metal ions are simultaneously reduced by the reducing agents to finally obtain the metal@graphene. The binding of metal atom and graphene is a chemical process which can be verified based on the results from the first-principle calculations.


Lignin graphene oxide was oxidized after Kraft lignin was graphitized by thermal catalytic conversion. The reduced lignin graphene oxide was derived from lignin graphene oxide through thermal reduction treatment. These Kraft lignin, lignin graphite, lignin graphene oxide, and reduced lignin graphene oxide were characterized by scanning electron microscopy, raman microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy and thermogravimetric analysis. The results showed lignin graphite converted from Kraft lignin had fewer layers with smaller lateral size than natural graphite. Moreover, lignin graphene oxide was successfully produced from lignin graphite by an oxidation reaction with an hour-long reaction time, which has remarkably shorter reaction time than that of graphene oxide made from natural graphite. Meanwhile, this lignin-derived graphene oxide had the same XRD, FTIR and Raman peaks as graphene oxide oxidized from natural graphite. The SEM, TEM, and AFM images showed that this lignin graphene oxide with 1–3 average layers has a smaller lateral size than that of graphene oxide made from natural graphite. Moreover, the lignin graphene oxide can be reduced to reduced lignin graphene oxide to fabricate graphene-based aerogel, wire, and film for some potential applications. Lignin, as a component in the cell walls of plants, is used to strengthen their structure, and it is the most abundant aromatic biopolymer on Earth . There a2-bonded carbon atoms in a honeycomb crystal lattice structure displaying excellent electrical and mechanical properties [Graphene is an exciting material that has a one-atom-thick 1D planar sheet of spoperties . In receoperties ,10,11,12operties . Howeveroperties . The effoperties . Graphenoperties . This maIn this study, the Kraft lignin, as the carbon source, was used to make few-layered lignin graphite (LG), lignin graphene oxide (LGO) and reduced lignin graphene oxide (RLGO). The morphology, structure, characteristics and properties of LGO and its relative materials  were examined by a scanning electron microscope (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy and thermogravimetric analysis (TGA). The applications of LGO/cellulose nanofibrils (CNF) aerogel, LGO/CNF film, LGO/polyacrylonitrile (PAN) electrical wire, and LGO/PAN fiber sheet fabricated using this synthesized LGO were also developed in this study.3)3·9H2O), tetrahydrofuran (THF), potassium permanganate (KMnO4), and sodium nitrate (NaNO3) were purchased from Sigma-Aldrich ; hydrogen peroxide (H2O2) was obtained from Fisher scientific . Commercial Kraft lignin named Bio-Choice lignin was provided by Domtar Corporation , the specification provided by Domtar showed that the Kraft lignin contained 97.1% lignin and 1.7% sugar with a pH value of 6.2. The content of C, H, and O was 65.9%, 7.5%, and 26.3%, while proximate analysis showed the content of volatile, fixed carbon, and ash as 54.5%, 43,1%, and 2.4%, respectively [Iron(III) nitrate nonahydrate  nitrate was used in this study as metal catalyst source for the catalytic graphitization. Iron with 10% loading in the iron-lignin precursors was prepared at room temperature using a co-precipitation technique. Specifically, lignin solution was prepared by adding 50 g of Kraft lignin to 50 mL tetrahydrofuran (THF) in a 250-mL glass beaker and stirring the mixture for 2 h. Meanwhile, iron nitrate solution was prepared by adding 41 g of iron (III) nitrate nonahydrate to 20 mL DI water in a 100-mL glass beaker and stirring the mixture until the metal salt dissolved completely. Prepared iron nitrate solution drop-like (~10 mL/min) was added to the lignin solution, and the lignin-iron nitrate mixture was stirred for 2 h at 70 °C. The final iron-lignin mixture was kept at room temperature for 24 h, and then transferred to an oven and dried at 150 °C for one day. After drying process, a solid iron-promoted lignin mixture as a precursor was obtained. Then the iron-promoted lignin precursor was loaded in the middle of a 2-inch OD ceramic tubular reactor. The reactor was heated at a rate of 10°C /min to 1100 °C and kept at 1100 °C for 1 h with 50 mL/min argon and 50 mL/min methane. The furnace was naturally cooled down by 10 °C /min to room temperature. The few layers LG sample was collected from the 2-inch OD ceramic tubular reactor for further use.2SO4, and 5.5 g NaNO3 were added into 2000 mL flask with 15 g LG, and the mixture was cooled down to 0 °C in an ice bath and stirred 10 min. Subsequently, 33 g KMnO4 was slowly added and continuously stirred for 30 min. Following this, 1000 mL DI water was added into the flask and the temperature was increased to 75 °C for 20 min. The mixture was then treated with 500 mL 10% H2O2 to terminate the chemical reaction. The total reaction time from LG to LGO was an hour which is noticeably less than that of graphene oxide made from natural graphite [For LGO and purification, a modified Hummers’ method was employed to oxidize LG and remove catalyst from LG to produce LGO . Specifigraphite ,20. The For the RLGO, a simple thermal annealing process was used to produce it from LGO powder. The RLGO powder was obtained by heating LGO powder in an oven at 200 °C in air for 2 h.The morphology of the samples was investigated with a Scanning Electron Microscope (SEM). LG and LGO samples were mounted with conductive carbon tape, sputter coated with gold and imaged using field emission scanning electron microscope (LEO 1530 FESEM) at a 5 mm working distance and a 10 kV accelerating voltage.The morphologies of LG and LGO samples were examined using a JEOL JEM-100CX II Transmission Electron Microscope  operated at an accelerating voltage of 200 kV. All TEM samples were sonicated in ethanol solution for 1 min before transfer to copper grids.The thickness of LGO samples were measured using atomic force microscopy . Samples were diluted to solids consistency of 0.05% and deposited onto clean mica substrates and air dried overnight at room temperature. The samples were imaged by a silicon cantilever in vibrating tapping mode at 160–225 kHz with a radium of the tip curvature less than 10 nm. The thickness and length of samples in the image were measured by Gwyddion software.Thermal degradation and stability of Kraft lignin, LG, LGO, and RLGO was assessed by thermogravimetric analysis . Samples (1–3 mg) were heated from 50 °C to 800 °C with a ramp rate of 5 °C/min under a flowing nitrogen atmosphere (20 mL/min) by thermogravimetric analysis, respectively.X-ray diffraction (XRD) patterns for LG, LGO and RLGO were obtained with a Bruker Discovery 8 diffractometer  using a Cu Kα rotation tube at 50 kV and 1000 μA with scanning over the range of 2θ = 5–60°.Raman spectra of LG, LGO and RLGO were obtained by an Aramis Confocal Raman Microscope  equipped with an excitation laser source emitting at 514 nm and having an incident power around 1 mW on a thin surface.−1 for 64 scans in 500 to 4000 cm−1 range. All powdered samples were pressed against the diamond crystal of the ATR device. Background spectrum obtained by scanning the air was subtracted from the sample spectrum before being converted into transmittance units.The ATR-FTIR spectra of Kraft lignin, LG, LGO, and RLGO samples were recorded with the Thermo Scientific ATR-FTIR spectrometer  at a resolution of 4 cm−1), C=O stretching vibrations (1734 cm−1), C=C from sp2 bonds (1615 cm−1), O–C–O vibrations (1238 cm−1) and C–O vibrations (1068 cm−1) [−1) and C=C from sp2 bonds (1615 cm−1) were observed, and almost all functional groups had been removed through the thermal reduction process. It indicated that LGO can be successfully converted to RLGO through thermal reduction treatment.In 68 cm−1) . However68 cm−1) . For RLGIn −1 is the characteristic peak of sp2 hybrid structure, which represents the symmetry and crystallizability of graphene materials; and the D peak at 1350 cm−1 is the defect peak, which represents the surface defect and disorder of graphite layers [−1 of LG is a second order two phonon process [D/IG from 1.0 of LG to 1.2 of LGO confirms the grafting of oxygen containing functional groups to the graphitic planes. After reduction treatment, ID/IG of RLGO from 1.2 of LGO becomes 1.1, which indicates the removal of most of the oxygen containing functional group. The ID/IG of RLGO is higher than that of LG due to the sp2 domains which are newly formed during reduction and smaller than those of LG [Raman spectroscopy is a very important characterization tool to analyze carbon materials because Raman scattering has a close relationship with the electron structure of the substances. e layers ,29. In Fe layers . The 2D  process , which m process . It indise of LG .2 streaming from the most labile functional group. The result of LGO exhibits another mass loss (28%) in the range of 220 to 800 °C, which has been attributed to the loss of oxygen functional groups. In contrast, the TGA result of the RLGO sample shows higher thermal stability than the LGO sample. The total loss is 27% at temperatures below 800 °C. This lower mass-loss can be attributed to the absence of most oxygen functional groups [In l groups .The excellent dispersibility of LGO makes it a promising candidate to fabricate LGO based composite materials . A 3D bio-aerogel prepared by a synergistic assembly of 50% LGO and 50% cellulose nanofibrils (CNF) through a freeze drying process shows the same appearance and internal structure as an assembly of prepared pure CNF aerogel reported by our previous research . ResultsThe synthetic LGO and its relative materials produced from a new resource (Kraft lignin) have been established by catalytic graphitization, oxidation reaction and thermal reduction process. The experimental results obtained from XRD, FTIR, Raman, SEM, TEM and AFM showed this LGO has similar properties and characteristics to graphene oxide made from natural graphite, while the LGO has a one-hour oxidation reaction time that was remarkably less than that of graphene oxide made from natural graphite. Moreover, the nanoscaled lateral size of LGO that was observed by SEM, TEM and AFM was less than that of graphene oxide made from natural graphite, thus it could be used for some conductivity materials. In addition, the LGO has good dispersibility, and function groups of the LGO can be removed by thermal reduction processes to produce RLGO. Therefore, the LGO can be easily used to fabricate graphene based composites for various applications.


Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease for which diagnosis and management remain challenging. Defining the circulating proteome in IPF may identify targets for biomarker development. We sought to quantify the circulating proteome in IPF, determine differential protein expression between subjects with IPF and controls, and examine relationships between protein expression and markers of disease severity.This study involved 300 patients with IPF from the IPF-PRO Registry and 100 participants without known lung disease. Plasma collected at enrolment was analysed using aptamer-based proteomics (1305 proteins). Linear regression was used to determine differential protein expression between participants with IPF and controls and associations between protein expression and disease severity measures . Multivariable models were fit to select proteins that best distinguished IPF from controls.2(fold-change)| > 0.585 (i.e. > 1.5-fold difference). Among the proteins with the greatest difference in levels in patients with IPF versus controls were the glycoproteins thrombospondin 1 and von Willebrand factor and immune-related proteins C-C motif chemokine ligand 17 and bactericidal permeability-increasing protein. Multivariable classification modelling identified nine proteins that, when considered together, distinguished IPF versus control status with high accuracy (area under receiver operating curve = 0.99). Among participants with IPF, 14 proteins were significantly associated with FVC % predicted, 23 with DLco % predicted, 14 with CPI. Four proteins  demonstrated the expected relationship across all three disease severity measures. When considered in pathways analyses, proteins associated with the presence or severity of IPF were enriched in pathways involved in platelet and haemostatic responses, vascular or platelet derived growth factor signalling, immune activation, and extracellular matrix organisation.Five hundred fifty one proteins had significantly different levels between IPF and controls, of which 47 showed a |logPatients with IPF have a distinct circulating proteome and can be distinguished using a nine-protein profile. Several proteins strongly associate with disease severity. The proteins identified may represent biomarker candidates and implicate pathways for further investigation.ClinicalTrials.gov (NCT01915511). Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic interstitial lung disease of unknown cause . EstabliMost of the currently available clinical biomarkers are proteins. Proteomic profiling represents a highly translatable initiation point for biomarker discovery , 7. ProtPrior proteomics work has suggested that patients with IPF have a unique peripheral blood proteome , 9. A stIn the current study, we leveraged a multicentre cohort of well-characterised patients with IPF to quantify the peripheral blood proteome, determine differential protein expression in patients with IPF versus controls of similar age, sex and smoking history distribution, and identify combinations of proteins that best distinguished patients with IPF from controls. We also examined whether circulating proteins associated with measures of IPF severity.The IPF cohort consisted of 300 patients enrolled in the Idiopathic Pulmonary Fibrosis Prospective Outcomes (IPF-PRO) Registry NCT01915511)  between   betweenControls were drawn from the Measurement to Understand the Reclassification of Disease of Cabarrus/Kannapolis (MURDOCK) Study, a longitudinal cohort study of adults in North Carolina . ParticiEnrolment plasma samples were assayed using an aptamer-based platform encompassing 1305 proteins . Data were reported in relative fluorescent units (RFU). No values were reported as below the limit of detection/quantification.2 transformed protein measurements were modelled as a function of group status (IPF versus control) such that the slope coefficient for group status estimated the fold-change (FC) in protein concentration between participants with IPF and controls. The group comparison was characterised by this estimate, its 95% confidence interval and corresponding p Value. p Values were corrected for multiple comparisons using the Benjamini-Hochberg procedure to control the false discovery rate (FDR) at 5%. Differences in protein concentrations between patients with IPF and controls were considered significant if the corrected p Value was < 0.05.Descriptive statistics were used to analyse patient characteristics and the expression of each protein in participants with IPF and controls. Linear regression was used to assess whether protein concentrations differed by IPF or control status when considered in a univariable fashion. Specifically, logn = 143)  and secreted protein, acidic and rich in cysteine [SPARC]). Among the top proteins that were observed at lower levels in patients with IPF relative to controls were the matrix remodelling protein stromelysin-1 (MMP3), creatine kinase enzymes B and M, and the advanced glycosylation end products receptor (AGER).We sought to identify a set of proteins that optimally differentiated patients with IPF from controls by fitting models on a training set and a test set. Select performance measures by model in the training set are illustrated in Fig. To understand the proteins of importance in distinguishing patients with IPF from controls, we determined the variable importance measures of proteins selected by each multivariable model. Thirteen proteins were designated as among the 10 most influential proteins in at least two of the eight models , and extracellular matrix organisation.The majority of proteomic studies in IPF have focussed on the characterisation of protein expression in lung tissue or bronchoalveolar lavage fluid (BALF) –21, withOur observation related to expression of circulating PIGR, a transmembrane glycoprotein important in immunoglobulin A transport across mucosal epithelial cells, is particularly intriguing, as prior work has demonstrated that the lungs of patients with IPF have ectopic expression of PIGR within areas of type 2 alveolar cell hyperplasia . MoreoveIn prior work, an aptamer-based proteomic approach similar to that used in our analysis was used to quantify 1129 circulating proteins in 60 patients with IPF versus 21 healthy controls of older mean age who were lifetime non-smokers. Consistent with our observations, higher levels of complement C1r subcomponent, complement C4, fibronectin, ICAM 5, thrombospondin 1, and MMP1 were observed in the IPF cohort . HoweverWhile the peripheral blood proteome may not fully reflect intrapulmonary changes, several of our findings are consistent with those of proteomic studies of BALF or lung tissue. A study using mass spectrometry-based proteomics of BALF demonstrated a 3-fold increase in CCL18 and protein S100A9 in patients with IPF compared with controls . SeveralOur results support the importance of circulating proteins relevant to extracellular matrix remodelling in patients with IPF. Notably several extracellular matrix glycoproteins, MMPs 1 and 9, and the MMP inhibitor TIMP3 were present at higher levels in patients with IPF relative to controls. These data are of interest in view of prior work by Jenkins et al. demonstrating that circulating levels of protein fragments generated by MMP activity are increased in patients with IPF relative to healthy controls and may associate with disease progression . AlthougOur study has several strengths, including the multicentre nature of the IPF cohort and the inclusion of control participants of comparable age, sex and smoking distribution. However, we acknowledge some inherent limitations. First, we acknowledge that our cohort is a US-based population of predominantly white patients, thus broader generalisability to other populations of patients with IPF is uncertain. Additionally, although we characterised a broad array of proteins, our approach was targeted rather than discovery-based, so proteins of potential importance could have been missed if not included on our platform. Finally, we acknowledge that an aptamer-based approach to protein detection and quantification does not always yield results that are reproducible when using ELISA-based approaches. This may in fact explain the differences between previous studies and our results with regard to MMP3. Thus, the proteins we identified as of interest in our study need to be validated, both from a technical and a clinical viewpoint. In particular, the association of the circulating proteins identified herein with clinical measures of IPF severity warrants validation.The results of this study add to the evidence suggesting that circulating proteins are likely to hold value in the diagnostic approach to IPF. Additionally, these data indicate that profiling of circulating proteins may provide insights into biological pathways underlying the development of IPF or contributing to disease severity. Validation of candidate proteins will be necessary, as will extension of these analyses to examine the association of the circulating proteome with clinical outcomes. Rich longitudinal data collection through the IPF-PRO Registry, including serial pulmonary function measures, hospitalisation data, and information on vital status, will support these analyses and further the goal of improving the diagnosis and management of IPF.Additional file 1: Figure S1. Differential levels of circulating proteins in participants with IPF versus controls. Volcano plot of the Log2fold change in means by log10 of the corrected p Value for each protein. The horizontal line indicates the threshold for statistical significance. Figure S2. Histogram of the linear discriminant scores for each participant in the IPF and control cohort. Table S1. Summary statistics for all 1305 proteins assayed across the IPF and control cohorts. Protein data are reported in relative fluorescent units. Table S2. Operating characteristics of all models in the test set for the IPF versus control multivariable modelling. Table S3. Proteins designated as among the most influential in at least two of the eight multivariable models. Table S4. Proteins significantly associated with FVC % predicted (unadjusted and adjusted for anti-fibrotic treatment). Table S5. Proteins significantly associated with DLco % predicted (unadjusted and adjusted for anti-fibrotic treatment). Table S6. Proteins significantly associated with composite physiologic index (unadjusted and adjusted for anti-fibrotic treatment).


Optical frequency combs, consisting of well‐controlled equidistant frequency lines, have been widely used in precision spectroscopy and metrology. Terahertz combs have been realized in quantum cascade lasers (QCLs) by employing either an active mode‐locking or phase seeding technique, or a dispersion compensator mirror. However, it remains a challenge to achieve the passive comb formation in terahertz semiconductor lasers due to the insufficient nonlinearities of conventional saturable absorbers. Here, a passive terahertz frequency comb is demonstrated by coupling a multilayer graphene sample into a QCL compound cavity. The terahertz modes are self‐stabilized with intermode beat note linewidths down to a record of 700 Hz and the comb operation of graphene‐coupled QCLs is validated by on‐chip dual‐comb measurements. Furthermore, the optical pulse emitted from the graphene‐coupled QCL is directly measured employing a terahertz pump–probe technique. The enhanced passive frequency comb operation is attributed to the saturable absorption behavior of the graphene‐integrated saturable absorber mirror, as well as the dispersion compensation introduced by the graphene sample. The results provide a conceptually different graphene‐based approach for passive comb formation in terahertz QCLs, opening up intriguing opportunities for fast and high‐precision terahertz spectroscopy and nonlinear photonics. Enhanced passive frequency comb operation and pulse generation in terahertz semiconductor lasers, i.e., quantum cascade lasers, are successfully demonstrated by coupling a multilayer graphene saturable absorber into a 6 mm long terahertz laser. Dual‐comb and pump–probe techniques are implemented to verify the frequency comb and pulsed operations  of graphene‐coupled terahertz lasers. Frequency combsThe general scheme employed for passive comb formation is to get a laser mode‐locked by incorporating saturable absorbers or other nonlinear reflectors in the laser cavity.FigureFigureIn this work, a relatively long laser cavity (6 mm) is intentionally used to obtain an intermode beat note frequency of ≈6 GHz . Since the terahertz photon energy is much smaller than the Fermi energy of 158 meV , the terahertz absorption in the graphene samples is an intraband transition process. Because the fabrication imperfection is accumulated during the layer‐by‐layer transferring process, the fitting curves show larger deviations from the experimental results for 30‐ and 40‐layer graphene samples. To make the graphene absorber function properly, we use a 15‐layer graphene sample in the following experiment to provide moderate linear absorption loss and sufficient nonlinearity.Both linear and nonlinear absorptions are critical for the functioning of graphene saturable absorbers. A moderate linear absorption loss can shorten the optical pulses for passive mode‐locking. However, if the linear absorption introduced by graphene absorbers is too high, the saturable absorption would hardly happen and optical pulses cannot be obtained. The linear transmission of the multilayer graphene samples in terahertz frequency range, as shown in Figure z‐scan experiment which has been used to characterize the saturable absorption of nonlinear materials.z‐scan technique is fully described in the Experimental Section and the Supporting Information. Figure z0) can be clearly observed. A theoretical fit is performed to extract the saturation parameters of the graphene sample. The average power of the QCL with a graphene‐integrated saturable absorber mirror (GiSAM) measured at z0 at 900 mA is 685 µW, which corresponds to a power density I0 = 2 W cm−2 by considering a beam waist diameter of 209 µm at z0 . The fit , an average power of 2 mW measured outside the cryostat is equivalent to 10 mW on the GiSAM in the cryostat. This can then be translated into a power density of 61 W cm−2 by considering the beam divergence and the air gap between the laser facet and the GiSAM. Finally, one can estimate a peak intensity of 610 W cm−2 or a pulse energy of 9.7 nJ cm−2. The estimated peak intensity of 610 W cm−2 is much larger than Is derived from the fit in Figure z‐scan experiment, normally the terahertz laser should be driven in pulsed mode or it is optically pulsing. However, the saturable absorption was also observed when terahertz QCLs operated in a quasi‐CW mode (with a duty cycle of 40%).z positions is shown. The nonlinear behavior of the graphene sample is related to the carrier absorption process. Once the absorption is fully saturated, the graphene will be transparent to the terahertz light. The nonlinear increase in transmission can be only observed before the graphene is fully saturated and afterward the power dependence of the transmission is linear. Since the saturation regime is easily realized in our experiment especially for z = 0, we are not able to observe the clear nonlinear increase in transmission with power. However, for z = −1 and 1 mm, as the threshold average power for saturable absorption is higher than the case of z = 0, the nonlinear behavior is observed as shown in Figure S12 in the Supporting Information.The nonlinear absorption behavior of the graphene sample is investigated using a z‐scan traces measured at 900 mA at different spots of the sample . As expected, all the z‐scan traces measured with the GiSAM‐QCL at 900 mA show almost identical behavior, which confirms that the graphene sample used in this work is uniform and the nonlinear saturable absorption is obtained when the sample is illuminated by the GiSAM‐QCL.Moreover, further experiments are implemented to investigate the saturable absorption of the graphene sample. In Figure S2 in the Supporting Information, the light–current curves for the QCL with Si mirror and GiSAM measured in the constant current mode are shown. We can see that the slope efficiency changes with increasing the current for the QCL with GiSAM, while it remains constant in the entire current dynamic range for the QCL with a Si mirror. This infers the nonlinearity introduced by the graphene sample. To verify that the saturable absorption observed in Figure The mode stability of GiSAM‐QCLs is first studied employing an electrical intermode beat note measurement  which has been widely used to characterize the mode coherence of terahertz lasers by recording the down‐converted beating signal of optical modes.FigureWe further monitor the long‐term frequency stability of the QCL modes by switching on the “max‐hold” function of the spectrum analyzer to record and store the spectral maxima during the time duration (3 min) of the measurement. Figure fb1 and fb2, are separated by 14 MHz. Here, we intentionally separate the two laser combs by 1.6 mm  of the Fourier transform infrared spectrometer. The down‐converted dual‐comb spectrum shown in Figure Figure igure −1  GHz of tigure −1  GHz of tigure −1  GHz of tWe next compare the dual‐comb spectrum of FP‐QCLs with that of GiSAM‐QCLs. Similarly with Figure FigureFinally, to further prove that the GiSAM‐QCL is pulsing, we perform a terahertz pump–probe experiment. The experimental data shown in Figures The other origin of the enhanced passive frequency comb operation in the GiSAM‐QCL is the dispersion compensation introduced by coupling the graphene sample that slightly changes the reflectivity of the GTI mirror. Theoretical studies show that the graphene is not able to significantly change the terahertz reflectivity at the air/Si interfaceCompared with existing methods such as active mode‐locking or using passive mirrors to compensate dispersions, the passive way of using a graphene absorber to achieve frequency comb operation shows two advantages/merits. First of all, the passive technique in this work can get rid of complex electronics and optics for intracavity loss modulation and active mode stabilization, and/or mirror designs and fabrications for compensating the group velocity dispersions in QCLs. Furthermore, the microwave impedance mismatching is not necessary to be taken into account in the passive scheme employed in this work. Thus, the passive comb system is more compact than the active terahertz QCL combs. Second, the passive scheme (in principle) allows the generation of much shorter pulses than the active one because a saturable absorber can modulate the losses much faster than electronic modulators. However, this doesn't mean that the absorber should be fast to achieve passive mode‐locking. We only require the absorber to respond fast to the leading wing of the pulse. Sometimes, a slow absorber is even better for achieving self‐starting mode‐locking in lasers.z‐scan measurements for a 15‐layer graphene sample yield a saturation peak intensity of 7.3 ± 0.12 W cm−2 and a saturable absorption coefficient of 0.21 ± 0.01 at 4.2 THz. The on‐chip dual‐comb has been successfully performed to prove the passive comb operation in the terahertz laser. Furthermore, a pulse width of 16 ps has been obtained from a terahertz pump–probe experiment, which directly proves the pulse generation in GiSAM‐QCLs. The possible origins of the enhanced passive frequency comb operation and pulse generation, i.e., saturable absorption and/or dispersion compensation introduced by the graphene sample, are discussed in detail. The highly stabilized passive frequency comb offers a powerful tool that can be used in terahertz metrology applications. For instance, the dual‐comb technique enables fast spectroscopy with Doppler‐limited resolution. The ultrashort terahertz pulses generated from GiSAM‐QCL combs could also find promising uses in studying the carrier dynamics of various materials, such as 2D materials and III‐V semiconductors.In summary, we have demonstrated a terahertz frequency comb that exhibits significant self‐mode stabilization owing to the incorporation of a multilayer graphene‐integrated saturable absorption mirror into a terahertz QCL. The intermode beat note linewidth is as narrow as 700 Hz. Nonlinear terahertz Terahertz QCL: The terahertz QCL used in this work was based on a hybrid active region structure that combines the bound‐to‐continuum optical transitions and the resonant phonon scattering for depopulation. The layer sequence of one period for the QCL active region with 76 cascade periods, from the injection barrier, is 4.1/3.8/1/23.6/1/13.8/2.1/11.8/3.1/9.6/3.1/8.7/3.1/7.7/3.1/17.2/3.4/14.8 nm, where Al 0.25Ga0.75 As layers are listed in bold, GaAs layers in normal font, and the 17.2 nm thick GaAs layer (in underlined font) is doped to 2 × 1011 cm−2. The entire QCL active region was grown using a molecular beam epitaxy system on a semi‐insulating GaAs substrate. The grown wafer was then processed into single plasmon waveguide laser ridges using traditional GaAs processing technology, such as optical lithography, electron beam evaporation, chemical and dry etching, lift‐off, etc. The ridges were cleaved into laser bars with cavity lengths ranging from 2 to 6 mm and then indium‐soldered onto copper bases (heat sink). Finally, the QCL device was mounted onto a cold finger of a cryostat for electrical and optical measurements.−1 (3 GHz).To measure the CW power of the terahertz QCL, two off‐axis parabolic mirrors were used for collecting and focusing the terahertz light onto a terahertz sensor Ophir, 3A‐P THz), which was connected to a power meter for reading the CW power value. The power value shown in Figure S1b in the Supporting Information is the measured power without any calibration of light collection efficiency, window transmission, water absorption, or mirror reflection. The emission spectra shown in Figure A‐P THz, Multilayer Graphene Fabrication and GiSAM Integration: The multilayer graphene samples were fabricated through a layer‐by‐layer transfer technique of monolayer graphene film grown via chemical vapor deposition. Graphene layer growth was carried out in a quartz tube at reduced pressure with a copper foil  as the catalyst substrate. During the process, the copper foil was heated up to 1000 °C and kept for 1 h under a 10 sccm flow of hydrogen (≈400 mTorr) to reduce the oxide presence, increase the grain size, and ensure a smooth surface for graphene growth. Next, methane gas with a beam flux of 10 sccm was introduced into the chamber for the graphene synthesis, and the gas pressure was maintained at ≈750 mTorr for 30 min. Following that, the grown sheet was cooled to room temperature in an atmosphere of hydrogen. The transfer of the graphene films onto the double‐side‐polished Si mirror (with a diameter of 10 mm) was realized by utilizing the conventional float‐transfer method. A polymethyl methacrylate resist was used as the protective layer, and the iron chloride etchant was used to etch away the copper substrate. The number of graphene layers on the desired substrate was controlled by the number of times the transfer was repeated. It is worth noting that additional loss was introduced because of the interfacial dangling bonds, and graphene film quality degrades as the number of monolayer graphene transferred increases.c/2ln, where c is the speed of light in vacuum, l = 410 µm is the length of the air gap , and n is the refractive index of air. Since the modulation period was much larger than the emission spectral range shown in Figure The multilayer graphene and Si mirror constructed a nonlinear reflector, GiSAM, which was then coupled to the 6 mm long terahertz QCL using a sample fixture as shown in Figure S1e in the Supporting Information. It has to be clarified that by coupling the GiSAM into the QCL compound cavity, an etalon consisting of the air gap and the air/Si interface was introduced, which might result in loss modulation and mode selection in the QCL. The modulation period was calculated to be ≈360 GHz by following the formula Δν = Open‐Aperture z‐Scan: As shown in Figure S9a in the Supporting Information, the terahertz light emitted from the GiSAM‐QCL was collimated and then focused onto the graphene sample by a pair of off‐axis parabolic mirrors with a reflected focal length of 101.6 mm. The sample was placed on a motorized micrometric stage  moving along the optical axis (z). After being transmitted through the graphene sample, the light was collected and focused onto a terahertz power detector using another pair of parabolic mirrors, and the power value was read using a power meter . The beam focal spot size (w0) was measured to be 209 µm, with a Rayleigh length (zR) of 600 µm. The open‐aperture z‐scan was performed at different QCL drive currents  by recording transmittance versus sample position along the z‐axis. The step size of the stage was set to 0.4 mm. For each QCL drive current, the measurement of the transmitted terahertz intensity was repeated 10 times and the mean value for fitting was taken. The transmittance of the 0.3 mm thick Si‐substrate was also recorded and fitted with a third‐order polynomial function, which was used as a baseline for data normalization. Details of the fitting procedure can be found in the Supporting Information.Intermode Beat Note Measurement: The intermode beat note spectra were measured electrically using a spectrum analyzer with the assistance of a broadband Bias‐T . To extract the high‐frequency signal from the laser cavity, a microwave transmission line as shown in Figure Marki, BT‐0026. ToOn‐Chip Dual‐Comb: The on‐chip dual‐comb device that was investigated here consisted of two terahertz QCL combs, one of which acted as a local oscillator (LO) comb (Comb1) and the other one was a sample comb (Comb 2)  of both combs should be slightly different. Otherwise, no dual‐comb spectrum can be observed. Once two single narrow intermode beat notes as shown in Figure Terahertz Pump–Probe: The terahertz pump–probe experiment was carried out by exploiting the nonlinearity (saturable absorption) of the graphene sample. As the graphene film can be saturated by the terahertz light (see Figure The authors declare no conflict of interest.SupplementaryClick here for additional data file.SupplementaryClick here for additional data file.SupplementaryClick here for additional data file.


Classroom questioning can be considered a key factor in the promotion of student engagement. This case study explored classroom questioning practices and perceptions of a group of 47 first-year law students and their teacher. Eight lessons of 90 min were observed and audio-recorded and afterward the students and the teacher answered a questionnaire. The teacher was also interviewed. Researchers examined the number and type of questions asked by the teacher and by the students in the classroom and analyzed the students’ and the teacher’s perceptions about the importance of classroom questioning. Results indicated that the teacher and most students consider questioning important or very important for student learning. The number of questions posed by students as opposed to by their teacher was not balanced, as the teacher was responsible for 93% of the questions. The analysis of the type of questions posed by the teacher and by the students showed a predominance of low-order questions. Therefore, classroom questioning in this case study did not seem to promote students’ autonomous thinking. The current study suggests the importance of examining the teacher and students’ patterns of questioning together, analyzing its similarities and discrepancies. Colleges and universities are challenged to adopt teaching and learning methods that promote students’ agency and autonomy, as well as high levels of thinking skills and student engagement . ClassroResearch shows the relevance of questioning as a teaching technique that contributes to engaged learning and the promotion of deeper-level thinking by students . QuestioIn different levels of schooling, several studies emphasize the lack of high-order questions and the predominance of factual or recall-type questions, as well as procedural questions . The stiLiterature has highlighted the importance of teacher and student questioning for both teaching and learning , yet theM = 19.50, SD = 2.15) and their respective teacher  in a Portuguese private urban university that offers different study areas and degree levels. Among these students, 63.8% were attending college for the first time.Participants were 47 first-year law students  and student questioning (one item) in the classroom. The scale for the two items contained five possible answers ranging from 1, meaning After the observational and questionnaire data collection, a semi-structured interview was conducted with the teacher to give him feedback about the findings and explore possible explanations to the results. Interview questions referred to the importance of teacher’s and students’ questioning in the classroom and its main functions. The teacher presented his explanations for the observed data and reflected on the kind of questions he used to pose to his students.All the elements of this case study contributed to the purpose of the study. Besides the analysis of the typology of the questions posed by the teachers and by the students, the questionnaire allowed researchers to analyze participants’ perceptions about the value they attributed to teacher’s and students’ questioning, and the interview enabled them to collect relevant data about teacher perceptions of classroom questioning, reflecting from data from his own classes.We carried out this study following the recommendations from the ethics committee of the University of Minho. Participants gave written informed consent to participate in the research in accordance with the Declaration of Helsinki. Participants were informed about the objectives of the investigation and confidentiality and anonymity were assured. In addition, participation in our study was voluntary and researchers informed students about data usage.The number and the type of questions asked both by the teacher and by the students were analyzed. All issues recorded, after analysis, were categorized. These categories were created according to a semi-inductive process, keeping in mind the typologies consulted in the literature review e.g., . The selThe perceptions of the teacher and the students about the importance given to classroom questioning were analyzed (descriptive statistics) alongside the qualitative data collected through the teacher interview .pseudo questions when there was no expectation of a response and no waiting time was given after the question. Procedural questions referred to course functioning. Academic questions referred to the learning material and intended to support students’ learning and to build or assess students’ knowledge.The teacher’s and the students’ questions were classified in three categories see . Questiopseudo questions (50.0%), 356 academic questions (39.0%), and 101 procedural questions (11.1%). The average number of teacher questions per class was 57.1 (excluding pseudo questions).Considering the eight lessons observed see , the teapseudo questions category was the most prevalent (63.4%), followed by the emphasizing questions (16.1%), questions designed to check clarity of the exposition (15.2%), questions identifying students’ doubts (6.3%), and questions relating contents (0.2%). Content related questions, either open or closed, with the objective of constructing knowledge and helping students to think autonomously, were not observed. The teacher’s lectures could be characterized as utilizing an expository method, in which questions were mainly used to emphasize the discourse, as the teacher frequently answered his own questions . The next most common categories were monitoring students’ attendance questions (20.8%), questions assessing individual students’ knowledge (19.2%), emphasizing questions (8.8%), questions checking exposition clarity (4.5%), questions identifying students’ doubts (2.6%), and finally content related questions: closed questions (1.5%) and open questions (1.3%).Throughout the practical classes, In practical lessons, the teacher opted for assessing students’ knowledge orally, asking questions about the learning material. Researchers observed an intense interaction between teacher and students, as students were individually questioned, in the context of a continuous assessment modality . In spitIn comparison to lectures, in practical lessons, content related questions, while they only represented a small percentage of the amount of total questions observed, were a novel addition. Moreover, all the content related questions corresponded to low-order questions, namely remembering and understanding, the first two categories of Bloom’s revised taxonomy . Thus, iIn the eight lessons observed, students asked 69 questions, namely academic questions (94.2%), and procedural questions (5.8%). The average number of students’ questions per class was 8.6.In both lectures and practical lessons, the content related open questions were predominant , followed by content related closed questions (39 and 32%), and by questions clarifying students’ assessment conditions (7 and 4%). The content related questions were mostly requests for clarification, concept definitions or repetition of certain concepts. Also in this case, questions posed by the students were low-order questions, namely Bloom’s taxonomy remembering and understanding categories .The findings also revealed that the number of questions asked by students in lectures and in practical lessons was higher before the exam and decreased after the exam, showing that students’ participation grows when they study more intensively. These data reinforce the importance of continuous assessment practices that promote regular academic engagement.Data from the questionnaire showed that the teacher and the students agreed that classroom questioning is important or very important for student learning and that both attribute more importance to their own questions.pseudo questions). These findings are congruent with prior studies conducted in this area (e.g., Through examination of the total number of questions asked in the eight classes, it was concluded that the number of questions asked by the teacher and the students was unbalanced: the teacher was responsible for 86.9% of the questions (excluding ea e.g.,  pointingThe analysis of the type of questions posed by the teacher and by the students revealed important similarities: the predominance of low-order questions, eliciting remembering and understanding processes; and the focus on basic comprehension of the concepts. In both cases, classroom questioning did not seem to be used in order to promote students’ autonomous thinking. These findings are consistent with literature e.g., .In the interview, teacher showed that his central concern was to transmit the contents in a very well organized and clear manner to the students, mainly because his students were first-years and were learning new concepts for the first time. This concern is consistent with the type of questions posed by the students. As referred by Overall the current study suggests the importance of examining the teacher’s and the students’ patterns of questioning and discussing their similarities and discrepancies. The findings of this case study suggest a mirror effect between the patterns of these two actors in the classroom. It could be important to explore the role of the modeling exerted by the teachers on their students.The findings of the current study, while limited, suggest interesting educational implications. There is a need for learning experiences aiming at promoting metacognition processes in college classes, allowing teachers and students to explore their perceptions about teaching and learning conceptions and approaches, student classroom participation and questioning beliefs, functions, and practices . Higher The datasets for this study will not be made publicly available because the researchers reported in the informed consent that the data would only be used by the research team who conducted the study.This study was reviewed and approved by the Ethics Committee of the University of Minho. All research participants provided written informed consent in accordance with the Declaration of Helsinki.LR and PR contributed to the conception and the design of the work. LR, PR, and IM were responsible for data collection, analysis, and interpretation of data. LR wrote the manuscript with valuable inputs from the remaining authors. RSC and IM made important intellectual contributions for the manuscript. All authors agreed for all aspects of the work and approved the version to be published.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.


N,N-dimethyl acrylamide) and poly(ethylene oxide) blocks and are used as humidity sensitive media. Instead of using glass or opaque wafer for substrates, polymer thin films are deposited on Bragg stacks and thin (30 nm) sputtered Au–Pd films thus bringing color for the colorless polymer/glass system and enabling transmittance measurements for humidity sensing. All samples are characterized by transmittance measurements at different humidity levels in the range from 5% to 90% relative humidity. Additionally, the humidity induced color change is studied by calculating the color coordinates at different relative humidity using measured spectra of transmittance or reflectance. A special attention is paid to the selection of wavelength(s) of measurements and discriminating between different humidity levels when sensing is performed by measuring transmittance at fixed wavelengths. The influence of initial film thickness, sensor architecture, and measuring configuration on sensitivity is studied. The potential and advantages of using top covered Bragg stacks and polymer/metal thin film structures as humidity sensors with simple optical read-outs are demonstrated and discussed.Thin films with nanometer thicknesses in the range 100–400 nm are prepared from double hydrophilic copolymers of complex branched structures containing poly( Humidity is present everywhere and is one of the mostly important physical parameters in our lives. The accurate monitoring of humidity is significant in semiconductors, electronics, food processing, and pharmaceutical industries where the quality of products is influenced sufficiently by the humidity. Humidity control is also essential in museums or archives in order to ensure the correct storage of artworks. Further, monitoring of relative humidity in office environments is in favor of human comfort and health and helps achieve hygienic conditions.The perfect humidity sensor should have high sensitivity, fast response, long-term durability, low cost, easy detection, and wide dynamic range, i.e., it should operate over a wide range of humidity. The established technology nowadays is an electrical measurement of humidity  where thIn recent years, optical sensing of humidity has gained increasing interest and great research efforts have been put in this field ,5. OpticCost effective and relatively simpler approaches are color sensing of humidity or monitoring of appropriately chosen optical parameters that change with humidity. In the first approach the detection is performed by visual inspection of color, or color monitoring by an inexpensive camera ,10,11. DPolymers attract considerable interest as optical sensing materials due to the advantageous features such as flexibility, light weight, ease of processability, useful mechanical properties, and compatibility with oxides and ceramics ,3. In geIt is already demonstrated that thin films with submicron thicknesses exhibit faster swelling than bulk hydrogels . We haveIn this paper, for detection of humidity we use transmittance measurements because they are simpler, more accurate, and less expensive compared to reflectance measurements. Moreover, observing sample color in transmittance mode, i.e., using the light transmitted through the sample, could overcome to a great extent the ambiguity related to the angle dependence of the color when reflectance mode is used. We study two sensor configurations. In the first one we deposit the sensitive film on top of the Bragg stack, instead of incorporating it in the stack’s backbone, thus overcoming possible issues of incompatibility that may arise when organic and inorganic materials are used for the stack. The second sensor configuration is comprised of a thin metal sublayer deposited on glass substrate and top-covered with the sensitive polymer film. The metal sublayer has dual purposes: to provide color for colorless polymer film and to increase the optical contrast between the polymer and glass substrate that have almost the same refractive indices (around 1.5).N,N-dimethyl acrylamide) (PDMA) and poly(ethylene oxide) (PEO) segments [In this study we prove the concept of utilization of top covered Bragg stacks and polymer/metal thin films as optical sensors for humidity. As humidity sensitive media we use thin films of previously developed multiblock copolymer with branched macromolecular architecture comprised of poly was purchased from Sigma–Aldrich  and purified from inhibitor by passing through a column of basic alumina before use. Poly(ethylene oxide) of molar mass 2000 g·mol–1 (PEO2000) was supplied from Fluka . Initiator diammonium cerium (IV) nitrate (NH4)2Ce(NO3)6 and crosslinker poly(ethylene glycol) diacrylate of reported average Mn 575 (PEGDA) were purchased from Sigma–Aldrich as well. Other solvents and reagents were of standard laboratory reagent grade and used as received.The monomer N,N-dimethylacrylamide (DMA) in deionized water was carried out using ammonium cerium (IV) nitrate as the initiator. Poly(ethylene oxide) and poly(ethylene glycol) diacrylate were implemented as a hydroxyl functionalized initiating moiety and as a cross-linker, respectively. The polymerization was carried out for 3 hours at 35 °C in nitrogen atmosphere under vigorous stirring and terminated by diluting the reaction mixture with methanol (1:1 volume ratio). The copolymer solution thus obtained was used for thin polymer film deposition without further isolation or purification. In order to control the thickness of the films, the copolymer solution was diluted to the appropriate concentration by using a water/methanol mixture (1:1 volume ratio). Chemical structure of the copolymer is schematically presented in The synthesis of the copolymer is described in detail in our previous papers ,27. Brie−1 and duration of 60 s using polymer solutions with concentrations of 4, 6.25, 7.3, and 8.3 g L−1, respectively. A post deposition annealing at 180 °C for 30 min in air was applied to all films. Silicon wafers, Bragg reflectors, and Au–Pd coated glasses were used as substrates. Five- and seven-layer Bragg reflectors were prepared on glass substrates by alternating deposition of sol-gel Nb2O5 [2 [2O5 films [−2 mbar using a Mini Sputter Coater SC7620 system. The thickness and diameter of the target were 0.2 and 57 mm, respectively. The purities of gold and palladium were 99.99% and 100%, respectively, and Au:Pd ratio was 80:20. The Au–Pd layers’ thickness was determined using mechanical profilometer Talystep  and confirmed by 3D optical profiler .Thin polymer films with thickness of 100, 200, 300, and 400 nm were deposited by the spin-coating method at a rotation speed of 4000 sel Nb2O5  and SiO2Nb2O5 [2  films orRefractive index, extinction coefficient, and thickness of polymer films were calculated using previously developed two-stage nonlinear curve fitting of reflectance spectra measured with UV-VIS-NIR spectrophotometer  at normal light incidence . The accIndeed, the reflectance and transmittance spectra of the obtained thin polymer films were registered in at least three consecutive experiments for each film sample. As the reflectance and transmittance data points derived from the subsequent experiments were practically equal, standard deviations were not added to the figures in the manuscript. The reported accuracy of the spectrophotometer measurement is 0.1% for transmittance and 0.26% for reflectance.S, measured in % per % RH, was calculated according to the following equation:R  is the change of sensor’s reflectance (or transmittance) in % which is provoked by the alteration of relative humidity from RH1 to RH2.The sensitivity of the sensors RH), measured in % RH, was calculated by Equation (2):errR  is the experimental error (measurement accuracy) of R or T and S is the sensitivity, calculated by Equation (1).The accuracy/resolution of detection , i.e., the swelling, is calculated according to Equation (3):d70% and d5% are the calculated film thicknesses at relative humidity of 70% RH and 5% RH, respectively.Thin polymer films with different thicknesses (from 100 to 400 nm) were deposited on Si-substrate and exposed sequentially to relative humidity of 5% RH and 70% RH. Reflectance spectra of the films were measured at both humidity levels and optical constants and film thicknesses were determined using non-linear curve fitting . Reflectd increases with thickness: 26%, 73%, and 97% for polymer films with initial thicknesses of 100, 200, and 300 nm, respectively. For the film with initial thickness of 400 nm a small decrease in Δd is observed (84%) compared to those of an initial thickness of 300 nm. The possible reason for the thickness dependence of the swelling is the adhesion to the substrate. It could be expected that the influence of substrate adhesion is the strongest for the thinnest film and decreases gradually with thickness. This explains the fourfold increase in swelling of polymer film with a thickness of 300 nm, as compared to this with a thickness of 100 nm.max) when the humidity in the measuring cell goes continuously from 5% RH to 80% RH. max is selected as the wavelength at which the humidity response is the strongest. Considering that the transmittance and reflectance of thin films are non-linear functions of film thickness  and thick (300 nm) polymer films we deposited them on glass substrate and monitored the temporal change of transmittance at fixed wavelength . This is beneficial for using the film as a sensing medium for a wide range of humidity. Similar linear dependence is obtained for 200 nm thick film in 40–90% RH. The expansion of the thickest film is exponential with the increase of the relative humidity and changes from 314 nm at 5% RH to 965 nm at 90% RH. The overall change of film thicknesses is 31%, 127%, and 207% for 100, 200, and 300 nm thick films, respectively.The swelling dynamic, i.e., the growth of film thickness with relative humidity, is shown in Considering the substantial change in thickness with humidity, we could expect also considerable change of color. If it turns out this is the case, the films could be used as color indicators for humidity. However, first the evolution of color with humidity should be investigated. Using the measured reflectance spectra of films at different humidity we calculated the CIE color coordinates  and plotThe color of the thinnest film is almost the same for RH values in the range from 5% to 40% RH and starts to change gradually from dark blue to light blue for RH higher than 40%. The color coordinates are well separated in the color space thus enabling color sensing of humidity in the range 40–90% RH. Although the thickness values at 5% RH and 90% RH are quite different for thicker films, 202 and 456 nm, respectively, the colors of the films at these humidity levels are very similar . RemainiThe main drawback when color sensing is used is the dependence of the color on the viewing angle. The observer cannot be sure whether the color change is due to the humidity change or it is because of his position during the color inspection. It is well known that reflectance and transmittance are functions of the incident angle of the light. Because the color perception of the observer is associated with reflectance or transmittance spectra, their change with incident angle of light results in different colors observed at different viewing angles. For example T or reflectance, R) at a fixed wavelength, λmax. As mentioned above, because T and R are nonlinear functions of n, k, d, and λ, the selection of λmax is not a trivial task and has an important role in detection. For example, if we pick a wavelength of 550 nm for λmax for polymer with a thickness of 100 nm  and the ambiguities associated with angle dependence of color are overcome to the great extent. However, to make transmittance measurements possible, a transparent substrate is required. The cheapest option is to use glass or plastic substrates but in our case they are not suitable because their refractive indexes match the refractive index of polymer thin film and the accuracy drops substantially. Besides, no color will be observed.Recently we have shown ,32 that Another advantage of using a Bragg stack as a transparent substrate is illustrated in T) of 5-layer Bragg stacks covered with polymer films with different thicknesses in the range 100–400 nm is shown in T increases with the thickness of the polymer film reaching a steady state for thicknesses higher than 250 nm. Therefore, in the next step of our investigation we use polymer films with a thickness of 300 nm and deposit them on four different Bragg stacks comprised of five and seven alternating layers of Nb2O5/SiO2 and dense/mesoporous Nb2O5. Our previous results have indicated that the characteristics of stacks, such as operating wavelength, number of layers, optical contrast, etc., do not substantially influence the sensitivity [2O5 and SiO2 layers. In order to achieve the highest sensitivity, we optimized the polymer film thickness through theoretical modeling. The calculated humidity induced change in transmittance  for measuring T are 650 and 730 nm , considering 0.1% experimental error in T.The detailed study of the spectra reveals that the most appropriate wavelengths  and the observer will need additional measurements to discriminate between them. We have shown that this could be overcome if color sensing is used simultaneously. Although the sensitivity and resolution are high, an ambiguity exists due to the same T decreases with the thickness of the Au–Pd film from 74% to 33% . For further experiments we selected Au–Pd film with a thickness of 30 nm because it has an average transmittance of 50%. The change of T spectra with humidity is shown in R of single film on opaque substrate . The respective resolutions are 0.7% RH and 0.3% RH. As in the case above, when using samples comprised of polymer and metal film, ambiguity in the sensing also exists due to the same T-values at different RH. In this case, the discrimination between different RH values is also possible if the color of the sample is monitored simultaneously. The dependence of T. As an example, the values of T measured at wavelength of 430 nm are presented as blue numbers in T values at 700 nm.Instead of observation of color, the discrimination between RH with the same transmittance values is possible if a second wavelength is used for monitoring of The obtained results are summarized in As mentioned in the Introduction section, the most widely spread and sensitive technology for humidity sensing is fiber optic sensing. Unfortunately they have disadvantages of relatively high cost of optical equipment, particularly spectrometers and optical spectrum analyzers, and complicated preparation of sensitive elements, especially in the case of side-polished optical fibers. The sensitivity of fiber optic sensors is calculated as nm per % RH because usually for detection the wavelength shift of the signal dip is monitored. The sensitivity values reported in the literature vary in a broad range from 0.023 nm/% RH to 1.01 nm/% RH . In ordeN,N-dimethylacrylamide)-based copolymer with optimized thickness. The sensitivity and resolution of detection as well the dynamic range were compared to the case of single film on silicon substrate. The widest dynamic range of sensing (5–90% RH) was obtained for polymer with a thickness of 100 nm deposited on silicon substrate. The sensitivity was 0.13%, while the resolution was 2% RH. The disadvantage to this method is that, in this case, monitoring of reflectance should be applied. The optimal sensing configuration was a 300 nm thick polymer film deposited on a Au–Pd thin film with a thickness of 30 nm and measuring transmittance signal at two appropriately chosen wavelengths. A sensitivity of 0.14 % was achieved for the 25–70% RH range, which increased to 0.39% for higher humidity (70–90% RH). Relative humidity of 0.7% and 0.3% could be resolved, respectively. There was a narrowing of the dynamic range (25–90% RH), which is acceptable. When a top-covered Bragg stack was used as a humidity sensor a sensitivity of 0.37% and resolution of 0.3% RH could be achieved for a relative humidity range of 40–80% RH.The concept of using polymer top-covered Bragg stacks and polymer/metal thin film structures for optical sensing of humidity was verified and confirmed. The sensing medium was a thin film of branched poly(