SpeechGraphs to calculate connectedness. Results revealed significant positive correlations between connectedness in the picture description task and measures of speech production (number of correct responses per minute) in the phonemic and semantic fluency tasks. These correlations were only significant for the participants’ L2- Spanish and Chinese. Results indicate that producing low connectedness narratives in L2 may be a marker of the initial stages of L2 oral development. These findings are consistent with the pattern reported in the early stages of L1 literacy. Future studies should further explore the interactions between graph structure and second language production proficiency, including more advanced stages of L2 learning and considering the role of cognitive abilities in this process.Language experience shapes the gradual maturation of speech production in both native (L1) and second (L2) languages. Structural aspects like the connectedness of spontaneous narratives reveal this maturation progress in L1 acquisition and, as it does not rely on semantics, it could also reveal structural pattern changes during L2 acquisition. The current study tested whether L2 lexical retrieval associated with vocabulary knowledge could impact the global connectedness of narratives during the initial stages of L2 acquisition. Specifically, the study evaluated the relationship between graph structure (long-range recurrence or connectedness) and L2 learners’ oral production in the L2 and L1. Seventy-nine college-aged students who were native speakers of English and had received classroom instruction in either L2-Spanish or L2-Chinese participated in this study. Three tasks were used: semantic fluency, phonemic fluency and picture description. Measures were operationalized as the number of words per minute in the case of the semantic and phonemic fluency tasks. Graph analysis was carried out for the picture description task using the computational tool  Much of what is known about speech production comes from the study of single word and sentence production. The production of units of language above a single sentence  has received less attention in the literature, even though it represents one of the most complex forms of communication. Speakers engage in the production of spontaneous monologic speech for pragmatic purposes, such as describing a scene or event, giving instructions, telling a story, or arguing for a point of view. A critical part of everyday conversation, monologic speech is a complex task that presents distinct demands on speech planning and production, involving multiple stages of processing. The most pervasive model of speech production  “bluepriThe production of connected speech is highly automatized in the native language (L1), yet remains open to the influence of age and education . In the Emergent findings from research on second language acquisition have revealed a positive relationship between L2 lexical access and various measures of L2 speech quality, such as fluency, accuracy and complexity . Yet it To measure discourse connectedness, we have employed graph structure analysis, a method originally created to characterize formal thought disorders in clinical populations , 2014, bIn the current study, long-range recurrences, measured by the number of nodes (or different words) inside the largest connected component (LCC), were used as a marker of speech connectedness during a spontaneous speaking task. Although the term “connectedness” is more commonly used in the field of mathematics, where it has emerged, we believe that the closest equivalent in psycholinguistics would be “textual cohesion.” It is assumed that the adjacency between lexical items in a discursive fragment, represented and measured here using graph theory, may be an alternative way to obtain a quantitative measure of text unity; that is, of the relationship between the elements that make up its unity and determine its comprehension. As far as we know, in psycholinguistics, there have been few attempts to find linguistic markers of speech connectivity, one being the measure of syntactic complexity in terms of T-Units .Previous work employing these quantitative measures of speech connectedness has revealed that the production of long-range recurrences changes across lifespan and is associated with L2 proficiency. In the realm of bilingualism, The current study tested the hypothesis that connected speech production in the weaker L2 is highly dependent upon L2 lexical retrieval (vocabulary knowledge), regardless of the structural distance between learners’ two languages. Critically, we predicted that the same association would not be found in the L1 because lexical retrieval is highly automatic in the L1 in adulthood. Alternatively, if lexical retrieval is equally challenging in speakers’ L1 and L2, then we should see an association between measures of lexical retrieval and discourse connectedness in both languages.n = 54, mean age = 20.35, SD ± 2.47, 15 male, average age of initial L2-Spanish exposure = 11.06, SD ± 4.22) or L2-Chinese  courses were recruited from the University of Missouri and Beijing Normal University and completed the study for payment. Participants reported normal hearing, normal or corrected-to-normal vision and no history of neurological, language or learning deficits.A total of seventy-nine college-aged students who were native speakers of English and reported past or current enrollment in L2-Spanish , which are described in detail below see . All parThe Cookie Theft scene from the Boston Diagnostic Aphasia Examination  was usedanimals, clothing, fruit, furniture).A minute-long semantic category fluency task assessed retrieval of lexical items. Data samples were transcribed offline by independent raters (98% interrater reliability) and scored separately in participants’ L1 and L2 in terms of the average number of correct responses (excluding simple and inflected repetitions) produced across four named semantic categories  and scored separately in participants’ L1 and L2 in terms of the average number of correct responses (excluding repetitions and proper names) produced by participants across three named letters  to 10 . The questionnaire was administered at the end of the testing session, after participants completed all other tasks.Language experience was measured using the Language Experience and Proficiency Questionnaire . ParticiDuring one in-person testing session, participants completed the picture description, semantic fluency and phonemic fluency tasks in both the L1 and the L2, as well as a language history questionnaire administered in the L1. Participants were tested in the L1 first and L2 second to avoid L1-inhibition following performance in the weaker L2 . The expTo characterize the language proficiency and dominance of the participant sample, we compared L2 and L1 proficiency scores for both L2-Spanish and L2-Chinese groups using Wilcoxon Ranksum Tests. The Wilcoxon Ranksum Test is a non-parametric statistical analysis aiming to check the null hypothesis that two independent samples are equal.SpeechGraphs software.1 The software represents each word as a node and the sequence of words as directed edges , we analyzed graphs of 20 words, using a step of two words (corresponding to an overlap of 90% between consecutive graphs) to plot the next graph see . We usedThe analysis revealed that the data were not normally distributed (Shapiro-Wilk test). Therefore, Spearman non-parametric analyses were conducted to assess the association between the graph scores (LCC) originated in the Cookie Theft analysis and both semantic and phonemic verbal fluency measures. We corrected the significance level by using the Bonferroni test for 4 comparisons (α = 0.0125). All the analyses were performed in Python 3.9.7 .p = 7E-17 in the case of L2 Spanish–L1 English phonemic fluency; and of W = –8.93, p = 4E-19 in the case of L2 Spanish–L1 English semantic fluency. In the case of L2-Chinese learners, a mean difference of W = –5.85, p = 5E-09 in the case of L2 Chinese–L1 English phonemic fluency; and of W = –5.84, p = 5E-09 in the case of L2 Chinese–L1 English semantic fluency were found. Taken together, differences in self-reported proficiency ratings and fluency means between the two languages have led us to characterize the present sample as two groups of beginner L2 learners who maintained dominance of their native language, English.Participants varied on measures of L1 and L2 production  and self-reported proficiency ratings on a 10-point scale see . Self-reR2 = 0.222, p < 0.001 for Spanish and R2 = 0.293, p < 0.005 for Chinese), in the case of L1-English we see a different pattern, with phonemic fluency and semantic fluency not contributing to the prediction model . In other words, phonemic and semantic fluency explained 22% of connectedness variance in the spontaneous narratives in Spanish, and 29% of connectedness variance in the spontaneous narratives in Chinese. These results confirm our hypothesis that the speech production of beginner L2 learners is highly dependent on L2 lexical and phonemic retrieval and that connectedness is better explained by fluency in L2 than in L1, regardless of the structural distance between learners’ two languages.Multiple regression analysis results in p = 0.02 for Spanish and R = 0.49, p = 0.014 for Chinese). Once more, these correlations were only significant for the participants’ L2–Spanish and Chinese . That led us to run Spearman correlations to evaluate more closely the relationship between phonemic fluency and connectedness in L2 and L1. Again, results revealed positive correlations between long-range recurrences (LCC), measured in the picture description task, and phonemic fluency , so the results should be replicated with larger samples. Third, we did not have access to participants with higher levels of L2 proficiency, which could reveal differences in the association between narrative production mechanisms and lexical retrieval. More studies with larger and more diverse samples in terms of proficiency levels are needed to advance our current understanding of the association between vocabulary acquisition and naturalistic use of a second language in the production of narratives. Future studies should further explore the interactions between graph structure and second language production proficiency, including more advanced stages of L2 learning and considering the role of cognitive abilities in this process. Associations between cognitive abilities , academic achievement and speech connectedness have been documented in the past , revealiGiven that individual difference factors can reveal disparities in L2 speech production among learners, such factors have attracted researchers’ growing interest. Here, we addressed individual differences in L2 speech production by employing graph structure analysis to evaluate the relationship between L2 lexical retrieval and the global connectedness of narratives during the initial stages of L2 acquisition and whether results can be replicated in the dominant L1. The current study contributes to the literature on second language acquisition by demonstrating that in the initial stages of L2 oral development, the connectedness of L2 speech is explained by variability in L2 lexical access. The study also demonstrates that a non-semantic graph strategy may be used to measure dynamics of narrative production in naturalistic settings, promoting the use of computational approaches to track L2 development, allowing for individualized feedback and helping to adjust speech trajectory over time. In addition, speech graphs may offer an alternative to refine the evaluation of L2 speech performance, with teachers and examiners being able to provide a faster and visually informative representation and assessment of learners’ L2 speech production.The 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 the University of Missouri Institutional Review Board. The patients/participants provided their written informed consent to participate in this study.MB contributed to the data collection, data analysis, and manuscript writing. JW, MR, IF, and NM contributed to the data analysis and manuscript writing. TG contributed to the data collection. All authors contributed to the article and approved the submitted version.


A novel piezoelectric fiber sensor based on polyvinylidene fluoride piezoelectric (PVDF) doped with graphene is presented. The near-field electrospinning technology was used for developing the sensor. The uniform experimental design method was introduced to determine the ranges of experimental parameters, including the applied voltage, the drum speed range, the graphene doping ratios from 0% to 11 wt% in PVDF solution, and the electrode gap. By experimental results, the conductivities of PVDF solutions with different doping ratios of graphene increased from 19.6 μS/cm to 115.8 μS/cm. Tapping tests were performed to measure the voltages and currents produced by the piezoelectric fibers. The maximum output voltage was 4.56 V at 5 wt% graphene doping ratio in PVDF fibers, which was 11.54 times that of the pure PVDF sensors. Moreover, mechanical properties of the proposed sensor were measured. Motion intention and swallowing test, such as saliva-swallowing and eating, were carried out. When the subject spoke normally, the output voltage of the sensor was between 0.2 and 0.4 V, approximately. Furthermore, when the subject drank water and ate food, the output voltage of the sensor was between 0.5 and 1 V, approximately. The proposed sensor could be used to detect signals of the human body and serve as a wearable device, allowing for more diagnosis and medical treatment. In the past years, sensor systems have become important parts of our daily life. Sensors can be wearable devices and used for many applications, such as motion intention detection, real-time signal measurement, and a medical aid system. With peripherals, sensor systems can measure, detect, record and even analyze further health conditions of humans, which can also help more accurate diagnoses. Several types of sensors have been developed, including capacitive sensors ,2,3,4, pAmong the piezoelectric materials, Polyvinylidene fluoride (PVDF), zinc oxide, lead zirconate titanate (PZT) and aluminum nitride have high mutual conversion efficiency between electrical energy and mechanical energy. These piezoelectric materials are very sensitive to any small amount of strain, giving them excellent applicability in sensors. Although zinc oxide and aluminum nitride are easy to make into micro-nano-scale thin-film, the poor ductility and low piezoelectric coefficient of the materials will cause deflection and long-term deformation, making their application in the energy-harvesting sector very limited. PZT material has the advantages of good piezoelectric properties, but the material is brittle and cannot be used for long-term deformation. Furthermore, PZT material contains heavy-metal toxicity (lead), which is harmful to the human body. PVDF is a potential piezoelectric material in polymers. PVDF has the following advantages: light weight, low price, flexibility, decent piezoelectric coefficient, high response frequency and no elements of pollution by heavy metals, making it be selected as one of the main materials in this study.Graphene, achieved by delamination of layered graphene, was developed at the University of Manchester in 2004. It was exfoliated from high-regularity, high-temperature pyrolysis graphite , and it pacitors ,12, elecpacitors , dye-senpacitors  and flexpacitors .Electrospinning technology is an unsophisticated way to transform polymer materials into nano-scale fibers . When thBaumgarten et al.  presentePrevious research presented the non-invasive measurement of the swallowing function with developed sensors or sensor-based monitoring during the swallowing events ,27,28,29Different amounts of graphene added and different proportions of solutions during the preparation process will affect the piezoelectric properties of the piezoelectric fibers after the near-field electrospinning process. Moreover, they affect conductivity, material stress and other properties of the sensor. The materials required for the preparation of PVDF solution and PVDF/graphene composite solution are shown in The preparation of PVDF/graphene mixed solution was mainly divided into two parts: solution A and solution B. The proportion of the preparation is shown in For the PVDF/graphene mixed solution, the procedure was similar to the preparation of the pure PVDF solution, but the required amount of graphene needed to be added into prepared solution B. Since the specific weight of solution A was heavier than that of solution B, solution A was poured into solution B. It was better to mix the solution fully and evenly. Like the pure PVDF preparation of solution, the PVDF/graphene mixed solution was left to stand for 30 min at room temperature to reduce the air bubbles. The experimental procedure for the fabrication of the proposed sensor is shown in The uniform experimental design can reduce experiment time while maintaining high quality and valid experiment results. The Kriging model depends on mathematical and statistical methods, satisfying an interpolation condition at every data point used to construct them. The Kriging model has more accurate function values throughout the trust region than the linear fit method.As shown in With a specification of .Owing to the disordered and irregularly arranged fiber structures, the further application of the fibers obtained by the traditional electrospinning is limited. Compared with the fibers from the traditional electrospinning, the advantages of the fibers obtained by the near-field electrospinning include the large surface-to-volume ratio, smaller diameter, and aligned dipoles. Furthermore, the near-field electrospinning fabricates fibers at room temperature. Experiments can be conducted conveniently and flexibly. The main experimental equipment of the near-field electrospinning, as shown in First, the mixed solution was poured into the syringe and put on the infusion pump. The industrial dispensing needle was connected on the other end of the syringe. The positive high-voltage power supply generated a high-voltage electric field as a nozzle for ejecting the electrospinning fibers. The negative pole of the electric field was connected to the adjustable speed drum collector, copper-foil glass tube , and a negative high-voltage power supply. When the positive high-voltage power supply was applied to the needle of an industrial dispensing needle and the negative high-voltage power supply was applied to the drum collector simultaneously, a strong electric field was formed between the needle and the copper foil glass tube, causing the solution at the top of the needle to be affected by the additional electric field. When the strength of the electric field reached a value at which the repulsive force between the charges of the polymer solutions overcame the surface tension, the polymer solution in the original hemispherical shape elongated to form a cone, called a Taylor cone . MeanwhiAs shown in When the piezoelectric material is subjected to a stress, the material deforms and its polarization density changes, as does its piezoelectric performance. The instrument used in this experiment is the AGS-50KNXD  tensile testing machine. The length of the sample to be measured is 50 mm. By measuring the load and displacement of the sample, the stress-strain diagram and the Young’s coefficient are obtained.Based on the uniform experimental design method, the experimental parameters were determined. The voltage ranges of the electric field were from 11 kV to 16.5 kV, and the rotational speed of the drum collector was from 400 rpm to 950 rpm. The weight percentage of graphene in the PVDF mixed solution was from 0% to 11%. The type of industrial dispensing needle used in the experiment was 25 G (aperture: 0.261 mm). The distance between the needle and the drum collector was 1 mm, and the movement speed of the dual-axis precision control stage was 2 mm/s. The infusion pump was used to control the propulsion flow rate of the solution at 20 mL/h so that the fibers could be produced smoothly. The fibers of 1 wt% graphene in the PVDF mixed solution were shown in In the electrospinning process, the solution of electrospinning will make the droplets of the solution break through the surface tension to form a Taylor cone. When the concentration of the solution is too high, the droplets will be discontinuous. However, the solution resulted in insufficient viscosity and it was easy to form excessively large droplets.By mixing the graphene powders in the solution, the conductivity of the solution rose. The conductivities of 0 wt%, 3 wt%, 5 wt%, 8 wt% and 11 wt% of PVDF/graphene mixed solution were measured. The results showed that the conductivity of 11 wt% PVDF/graphene mixed solution is 115.3 Μs/cm, which is the highest conductivity among sample solutions. The higher conductivity meant that it was easier to accumulate charges on the droplets, so the droplets broke through the surface tension and formed electrospinning fibers much more easily. Moreover, as shown in The piezoelectric properties between pure PVDF sensor and PVDF/graphene piezoelectric sensor were discussed. Sensors were tested by tapping tests with a rotary beater. As shown in To interpret the relationship of each control factor in the uniform experimental design method in this study, the response surface of the Kriging model was used to depict four factors influencing the fiber. One of the codes is shown in From the results of the Kriging model, the optimal parameters of the electrospinning, as shown in The experimental results of the tensile test (stress-strength curve), Young’s modulus, tensile strength, and toughness test between the pure PVDF fiber, 7 wt%, and 8% wt% PVDF/graphene fibers, are shown in The proposed sensor has potential for motion measurement of the human body and for developing a wearable sensing device. Therefore, preliminary tests of motion intention were performed. For the motion intention test, the sensor was attached to the chair and stand–sit movement cycles continued as shown in From the experimental results, the maximum output voltage was 1.6 V when measuring the stand–sit movement of the human body. When measuring the extension and flexion of the wrist joint, the maximum voltage was 0.84 V. The experimental results showed that the proposed sensor has advantages of fit, flexibility, and elasticity, making it useful for more complex applications.Normal speaking: the subject spoke at about 150 words per minute.Swallowing : the subject swallowed saliva deliberately.Drinking: 30 mL water was drunk by the subject in each sip.Eating food: the subject ate bread by an appropriate amount per bite.In the study, the proposed sensors were enhanced by the addition of graphene. Beside the motion measurement of the human body, the sensor was used to test and detect swallowing, allowing for a more accurate diagnosis and treatment. As shown in When the subject spoke normally (at about 150 words per minute), the output voltage of the sensor was between 0.2 and 0.4 V approximately. Furthermore, when the subject drank water (50 mL each sip) and ate food (bread), the output voltage of the sensor was between 0.5 and 1 V, approximately. It could be observed that different swallowing behavior resulted in variant muscle contractions of the throat. Swallowing disorder (dysphagia) and swallowing dysfunction associated with muscle weakness due to natural aging could be detected by the proposed tactile sensor. The relationship between the muscle tremor of the throat and the output voltage of the proposed sensor was observed. The experimental results are shown in 2 = 0.14675. In the range 2–5 N, S = 0.07919 (V/N) and R2 = 0.79938. Characteristics of the proposed sensor are listed in The relationship between the output voltage of the proposed sensor and force was obtained by a force gauge HF-100 . The range of the applied force was between 0.2–60 N. The range of corresponding output voltage was 0.03–5.62 V. The relationship between the applied force and the corresponding output voltage is shown in In this study, a novel PVDF/graphene piezoelectric fiber sensor was developed using the near-field electrospinning technology. The applied voltage in electrospinning, rotational speed of the drum collector, weight percentage of graphene, and sensor electrode gap were process parameters. When the weight percentage of the graphene doping ratio was 11 wt%, the conductivity reached 115.3 μS/cm, which was 5.9 times that of the pure PVDF solution. From tapping tests, the output voltage of the 7 wt% doping ratio PVDF/graphene sensor was 3.672 V, which was 9.37 times that of the pure PVDF sensor, indicating that adding graphene to PVDF could improve the piezoelectric effect. Optimized by the uniform experimental design method and Kriging model, the optimal parameters were determined. The maximum output voltage was 4.56 V at 5 wt% graphene doping ratio in PVDF fibers, which was 11.54 times that of the pure PVDF sensors, indicating that the PVDF/graphene sensors were expected to provide a better piezoelectric effect. Through the mechanical property tests, it was observed that the tensile strengths of PVDF/graphene fibers at 7 wt% and 8 wt% doping ratio were 5.1 MPa and 3.6 MPa, which were larger than those of the pure PVDF fibers. Preliminary applications of the proposed sensor, such as the detections of the wrist extension/flexion and stand–sit movement intentions, were carried out. Furthermore, swallowing, such as saliva-swallowing, drinking and eating, were detected by the proposed sensor. The experimental results showed that the proposed sensor had the potential to be used to detect dysphagia and swallowing dysfunction. The PVDF/graphene piezoelectric fiber sensor made by the near-field electrospinning had the characteristics of ductility of PVDF polymer and piezoelectricity of graphene, which increases the possibility of practical applications.


The graphene–pyrrole composite was tested to ultra-low levels of cortisol in artificial saliva, consistent to the levels excreted in human salivary samples. The composite was further investigated by Raman spectroscopy and we modeled the interaction between the sensitive layer and cortisol using MarvinBeans software. It shows a good sensitivity for salivary values of cortisol cyclic voltammetry being able to detect a level down to 0.5 ng/mL cortisol.In this work, we study the sensing properties of multi-layer graphene combined with pyrrole in order to elaborate low-cost, high-sensitive material for cortisol detection. Graphene nanoplatelets and pyrrole were dispersed in a solution containing 1M HNO Electrochemical sensors are attractive devices with potential applications in quality control of food, water and pharmaceutical compounds ,2,3. In Furthermore, electrochemical sensors play an important role in clinical diagnostics. Detection of neurotransmitters is of great importance in investigation of neuro-degenerative diseases because neurotransmitters act as messengers in synaptic transmission. For instance, Wang et al.  developeModification of serotonin levels can induce anxiety, eating disorders, sleep disorders and depression. It even can lead to infantile autism. Serotonin is a neurotransmitter that influences muscle contraction and endocrine system regulation ,21. SeroStress is linked to a number of diseases and health issues, such as heart diseases , headachCortisol, which is considered a stress hormone, influences the circadian cycle and immune system response . It alsoCarbon-based materials are excellent for cortisol detection. An electrochemical sensor based on screen-printed, multi-walled carbon nanotubes-modified electrodes has been implemented for the detection of cortisol in saliva . The autSensors that use biogenic amines as analytes have found applications in freshness control of meat, seafood and generally, in foods rich in proteins. Biogenic amines are produced by the microbial decarboxylation of amino acids of foods and beverages that have undergone the fermentation process . PlatinuDue to its exceptional physical and electrochemical properties, graphene is an excellent candidate for electrochemical sensors . Food spTo the best of our knowledge, there are few attempts to use a graphene–polypyrrole composite to detect cortisol in a synthetic saliva matrix. Manickam et al. in 2017 used a molecularly imprinted polymer technique for the development of a polypyrrole-based sensor for cortisol in saliva , while BCarboxymethylcellulose sodium salt , potassium chloride , calcium acetate hydrate , potassium phosphate monobasic , dipotassium phosphate , pyrrole  and all other chemical compounds were used as delivered, without purification. The graphene nanoplatelets were purchased from Sigma Aldrich. We could not procure human cortisol, so we purchased the drug hidrocortizon hemisuccinat (Zentiva) from a local pharmacy. C11L sensor support  have working and auxiliary electrodes made of carbon and the reference electrode made from Ag/AgCl. They were used as support for the electropolymerization of the graphene–pyrrole composite.®  was employed to model the reaction of cortisol on the composite. The modelling of the reaction was based on the assumptions that pyrrole is polymerized on the edges of the graphene sheet and that hydrocortisone will react with the nitrogen atoms of the polymer via carboxyl/hydroxyl groups.Electrochemical characterization was performed with OrigaFlex 0.5A modular electrochemical system from OrigaLys ElectroChem SAS  and a three-electrode cell. Raman spectroscopy was performed with a LABRAM HR 800 spectrometer with the excitation laser wavelength 633 nm and laser power at the sample surface of 2.11 mW for each measurement. MarvinBeans3 with a Hielscher ultrasound probe  and centrifuged at 4000 rpm for 30 min to separate the deposit from the supernatant. The supernatant was collected and used in the following electrochemical polymerization. The amounts of precursor were selected under the principle of “green chemistry”—atom economy, which requires only the minimal amount of reactants to produce the composite .A quantity of ≈ 1.0 mg graphene nanoplatelets and 600 µL pyrrole were dispersed in 50 mL 1M HNOThe C11L electrode surface was washed and dried with an IR lamp before polymerization. As a mask for the auxiliary and reference electrodes, we used parafilm which was wrapped around the sensor keeping only the working electrode free and in contact with the composite solution. The supernatant was placed in the electrochemical cell, together with the saturated reference calomel electrode and a Pt wire acting as the auxiliary electrode. The potential was swept between 2,212,800 MV and 800 mV, for 20 cycles, with a scan rate of 100 mV/s. After polymerization, the sensors were washed in deionized water, and dried again with an IR lamp before use.2HPO4 and 0.08 KH2PO4. This solution was, however, too thick. Therefore, we diluted it with 230 mL distilled water. After two hours on the heating plate and under magnetic stirring, the solution had the consistency of a running saliva. The pH of the artificial saliva was 7, at 24.2 °C.We prepared artificial saliva samples based on the protocol of Macknight-Hane and Whitford, in 1992 . SorbitoWe wanted our solution to match the biological reference interval in salivary samples for cortisol, which is 0.5–5 ng/mL. Thus, we prepared a stock solution of 100 ng/mL hydrocortisone in artificial saliva and by successive dilutions we prepared six samples with concentrations in the biological intervals: 0.5 ng/mL, 1 ng/mL, 2 ng/mL, 3 ng/mL, 4 ng/mL and 5 ng/mL. 50 µL of each solution was dropcasted onto the modified electrode and tested via cyclic voltammetry.3 electrolyte solution or on the surface of the modified electrode (an impurity). In the subsequent cycles, this reduction peak disappears and is replaced by another broad reduction plateau in the range −100 to −200 mV. The oxidation peak is also broad and begins to be well defined after cycle 4. The shape of the reduction and oxidation peaks can be explained by the poor conductivity of the pyrrole in the beginning of the polymerization, conductivity which enhances as the number of cycles increases. By plotting the total charge exchanged in the polymerization process vs. the number of cycles . For all the other concentrations, the current density ratio is ranging from 0.3–0.49  but it can be explained by the low concentrations of cortisol in saliva. Compared to blood concentrations, salivary cortisol is at the ng/mL level . Previous studies concluded that the connection between cortisol and mental load depends on the individual; cortisol secretion is dependent on what the individual think is stressful .−1) and G (1579 cm−1) [−1, the inter-ring stretching of the C–C bond at 1386 cm−1, the C–C and C–N stretching at 1476 cm−1 and antisymmetrical in-plane bending of the C–H bond at 1241 cm−1 [−1 but the peak is “broader” which signifies that the dimensions of the graphene particle have increased. The G-band increases also due to polymerization of the pyrrole and bonding of the pyrrole to the graphene sheet. The peaks for the graphene are better represented in the composite, while the peaks for the polymer appear as shoulders . The position of the G-band in the spectrum of the composite remains the same as in the graphene spectrum but the ratio ID/IG is modified: from 1.86 in graphene it drops to 1.06 in the composite material. This decrease of the ID/IG ratio indicates an increase of the disorder . We assume this happens because the pyrrole is attached to the margin of the graphene rather than on top of the sheet [79 cm−1) , while t241 cm−1 . In the  Ferrari , the D-bhe sheet ,57.In order to better explain the way the composite and hydrocortisone interact, we developed a model for the composite–cortisol reaction. Even if the model in Perspectives: The following steps in the development of the cortisol sensor are: (a) Interferents measurements—we need to analyze the way other molecules common in human saliva could interfere with cortisol detection. This is particularly important when considering the salivary microbiome on top of other common interferents . (b) Reproducibility—we need to synthesize a larger number of sensors and to test all of them in the same conditions in order to establish the reproducibility of the synthesis method. (c) Another important aspect is the stability of the sensor in different conditions . (d) Miniaturization and incorporation into a wearable device similar to a holter monitor—this involves processing materials and integration into microfluidic channels.3 via ultrasound, after that centrifugation was implemented and cyclic voltammetry was acquired for polymerization. The composite was tested for six different ultra-low concentrations of cortisol in artificial saliva: 0.5 ng/mL, 1 ng/mL, 2 ng/mL, 3 ng/mL, 4 ng/mL and 5 ng/mL. We studied the spectroscopic properties of the composite via Raman spectroscopy. Moreover, we used MarvinBeans® software to visualize the interaction between cortisol and the graphene–pyrrole composite; the developed model was in accordance with the results obtained by electrochemical experimentation and provided a “best-guess” snapshot of the reaction.In summary, a graphene and pyrrole-based sensor has been investigated in this paper for detection of cortisol hormone levels in artificial saliva. The selected materials, graphene and pyrrole, allow for green chemistry implementation and exhibit the most needed properties such as safety and low cost. Graphene and pyrrole nanostructures were diffused in solution with 1M HNO


The present study investigated the effects of L1-L2 congruency, collocation type, and restriction on L2 collocational processing. Advanced Chinese learners of English and native English-speaking controls performed an online acceptability judgment task to investigate how advanced L2 learners processed congruent (sharing the same meaning and structure in L1 language) collocations and English-only  collocations with the same node (right) word and a different collocate (left). The experimental materials included verb-noun (VN), adjective-noun (AN) collocations, free (less fixed), and restricted (more fixed) collocations chosen from BNC. The results revealed that (i) The non-native speakers were sensitive to L1-L2 congruency, but the native speakers were not. (ii) The native speakers were sensitive to collocation restriction, whereas the non-native speakers were not. These results lend initial support to the mapping hypothesis and open choice principle of L2 collocational processing for Chinese English learners. The language generated by the native speakers (NSs) is proportionally formulaic (up to 50%) in both written and spoken forms, according to previous studies  in this sense can collocate with a great number of nouns/verbs, and there are no arbitrary constraints on its substitutability. The other one is the frequency-based account  and verb-noun (VN) combinations are processed in one's L1 ?lock the door, full pay), (b) items that were acceptable in English but not Chinese n = 40), (b) English-only (n = 40), and (c) baseline items (n = 40). All the items consisted of VN (n = 80) and AN (n = 80) items which were distributed equally for the above three conditions. In addition, the VN and AN items were, respectively, composed of equivalent free (n = 40) and restricted (n = 40) collocations in congruent and English-only collocations.Since we were specifically concerned with the influence of L1 collocational patterns on learners' acceptability judgment on collocations in an L2, we needed to isolate (a) items that were acceptable in both the L1 and the L2 . We wanted to confirm that congruent and English-only collocations did represent corpus-verifiable items, and therefore, we only included items that had an MI score of at least 3.0 in BNC. Since the L1-L2 congruency involves translation and the constituents of the collocations are polysemic, the constituents' meaning of collocations adopted the following criteria: the meanings of verbs conformed to the first two definitions, but that of nouns and adjectives conformed to the first definition in WordNett-tests were conducted on the word length, word frequency, collocation frequency, and familiarityt(78) = −0.344, p = 0.732; familiarity: t(78) = 2.266, p = 0.108]. There were no significant differences in word frequency among the three types of collocations , F = 1.187, p = 0.317. Word length, t(78) = 1.330, p = 0.188, the word frequency, t(78) = 0.534, p = 0.595, collocation frequency, t(78) = 1.956, p = 0.056, and collocation familiarity, t(78) = 0.138, p = 0.890, between free and restricted collocations had no significant difference. The word length, t(78) = 1.898, p = 0.060, word frequency, t(78) = 1.045, p = 0.298, collocation frequency, t(78) = 0.090, p = 0.928, and familiarity, t(78) = 0.080, p = 0.936, between VN and AN collocations had no significant difference. Finally, experiment stimuli consisted of 40 congruent items, 40 English-only items, and 40 noncollocational items for a total of 120 items. An equal number of AN and VN collocational items were developed for the congruent, the English-only, and noncollocational items. Besides, the free and restricted collocations were also equally distributed in VN and AN collocations, respectively, only in congruent and English-only collocations since noncollocational items have nothing to do with the restriction. ANOVA analysis and n = 21) and English NNSs (n = 39). The NSs group consisted of 13 undergraduate and 8 graduate students, all from a university in North America. None of these individuals claimed to have more than a basic understanding of Chinese. The NNSs were all NSs of Chinese. All NNSs participants majoring in English were studying at the same university in China. All participants completed a questionnaire that asked for their age, eyesight, and manual dexterity. They all claimed no problem with their natural/corrected eyesight. The NNSs were also requested to provide their English learning experience and English competence in a self-reported way . Except for three participants who had studied or lived overseas for no more than 4 months, the rest 36 had not studied or lived overseas. The average vocabulary size was estimated by 2,000, 3,000, 5,000, and AWL  was first displayed in the center of the screen. After then, for around 66 ms, there was a blank screen, which was replaced by a stimulus. The stimulus stayed on the screen until it was either responded to or timed out at 4,000 ms. Participants completed the task in an average of fewer than 12 min. After the online experiment, participants received a nice present or 3$ for their participation.The experiment was done in compliance with regional ethical rules, and each participant gave informed consent, which ensured that all data were kept anonymous.The data from NSs and NNSs were examined independently. In terms of RT, with responses <200 ms or more than 3 SDs off the mean being removed Jiang, . For theThe data have been examined on the R statistic platform adopting linear mixed-effects modeling utilizing the lme4  values. In the stepwise method, there was no difference between main effects, interaction effects, or quadratic terms. The approach simply included removing the independent factors that had the least influence on AIC one by one until variables considerably improved the fit. Then, we visually evaluated a quantile plot of the residual of the model confirming normal distribution. For NSs, it was revealed that there was no significant main effect of L1-L2 congruency on ACC or RT, indicating no difference in ACC and RT for congruent and English-only collocations. There was no significant main effect of collocation type on RT or ACC, indicating no response difference between AN and VN collocations. There was a significant main effect of collocation restriction on ACC and RT, indicating that NSs were more accurate and faster on restricted collocations compared to free collocations. The L1-L2 congruency by collocation type interaction was not significant on RT or ACC. The L1-L2 congruency by collocation restriction interaction was not significant on RT or ACC. The collocation type by collocation restriction interaction was not significant on ACC or RT. The L1-L2 congruency by collocation type by collocation restriction interaction was not significant on ACC or RT.For NNSs, a significant main effect of L1-L2 congruency on ACC but not RT was observed, indicating that NNSs were more accurate on congruent collocations compared to English-only collocations. There was no significant main effect of collocation type on ACC or RT, indicating no response difference between VN and AN collocations. There was no significant main effect of collocation restriction on ACC or RT, indicating no response difference between restricted and free collocations. The L1-L2 congruency by collocation type interaction was not significant for RT or ACC. The collocation type by collocation restriction interaction was not significant for ACC but not RT. The L1-L2 congruency by collocation type by collocation restriction interaction was not significant on ACC or RT.Congruent collocations were processed considerably more accurately than English-only collocations for the NNSs group as predicted, whereas the NSs processed them at almost the precision. This suggests that congruent collocations bear a processing advantage compared to incongruent collocations for L2 learners. Similar findings have been found in previous studies that used different tasks and L2 learners. Employing an LDT 2011) and an acceptability judgment task 2013), Wolter and Gyllstad reported a congruency advantage in L1 Swedish learners. Furthermore, Wolter and Gyllstad  simultaneously, the results of our present study indicate that L2 speakers appear to follow the open choice principle, whereas L1 speakers adopt the idiom principle (Sinclair, According to Nesselhauf , phraseoThe current study was set out to investigate whether L1 and L2 speakers are sensitive to the L1-L2 congruency, type, and restriction of collocations. Evidence obtained from this research supports that native English speakers are not tuned to L1-L2 congruency underlying collocations, whereas Chinese L2 speakers are tuned. Furthermore, native English speakers are sensitive to the collocational restriction but Chinese L2 speakers are not. Moreover, there is no interaction effect between L1-L2 congruency, collocation type, and collocation restriction either for L1 or L2 speakers. For native English speakers, they are likely to process collocations considering the restriction of collocations ignoring the L1-L2 congruency of collocations. The findings suggested that L1 and L2 speakers have different sensitivity to collocational flexibility as measured by MI scores, with native speakers judging restricted collocations more feasible than free combinations, and L2 speakers finding it difficult to recognize collocational restriction. Furthermore, L2 English speakers seem to process collocations more explicitly consulting the L1-L2 congruency not considering the restriction of collocations. These findings shed important light on the understanding of the L1-L2 congruency, collocation type, and restriction effects on the processing of collocations.However, we still consider that in future research there might be reasons for reexamining the interaction effects among the three variables. Specifically, we argue that amendments to trial design, which demand more explicit attention to the collocational knowledge under certain contexts, may generate distinct and illuminating outcomes. Briefly, the influence of three-way interactions can be rejected too early to be fully based on the results of the current investigation. In addition, more research needs to be carried out to investigate whether and how other factors, including frequency and familiarity, influence the processing and acquisition of L2 collocations.The 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 South China Normal University. The patients/participants provided their written informed consent to participate in this study.The author confirms being the sole contributor of this work and has approved it for publication.The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Advanced sensing and measurement technology is the key to realizing the transparent power grid and electric internet of things. Meanwhile, sensors, as an indispensable part of the smart grid, can monitor, collect, process, and transmit various types of data information of the power system in real-time. In this way, it is possible to further control the power system. Among them, partial discharge (PD) sensors are of great importance in the fields of online monitoring of insulation condition, intelligent equipment control, and power maintenance of power systems. Therefore, this paper intends to focus on advanced sensing materials and study new materials for the improvement for partial discharge sensors. As two-dimensional material, graphene is introduced. The electromagnetic properties of graphene partial discharge sensor electrode plate material are analyzed theoretically. By studying the influence of different chemical potential, relaxation time, temperature, and frequency, we obtain the changing curve of conductivity, dielectric constant, and refractive index. A linear regression model based on the least-squares method was developed for the three electromagnetic properties. Finally, the simulation and experiment verified that the graphene partial discharge sensor has better absorption of the partial discharge signal. This study can apply to the design of graphene partial discharge sensors. High-voltage switchgear is an important type of transmission and distribution equipment, and its operational safety directly affects the reliability of the power system . PartialJatropha mollissima (Pohl) Baill plant for PD detection. Ref. [At present, PD detection methods mainly include the pulse current method (PCM), ultrahigh-frequency (UHF) method, ultra-acoustic wave (UAW) method, optical detection method, and transient Earth voltage (TEV) method . Many faon. Ref.  proposes3 magnetoelectric composite as a magnetic sensor, which can be used in the field of gear speed measurement. As a typical representative of two-dimensional planar superconducting materials, the special energy band structure of graphene gives it a series of excellent properties such as high conductivity, low magnetic permeability, and high dielectric constant [With the continuous research and development of new materials, many advanced materials are researched and prepared by researchers and further applied in the field of engineering. In , the layconstant . By micrIn the field of engineering, many experts and scholars have conducted extensive research on the excellent properties of graphene sensor devices. Ref.  proposesGraphene differs from ideal conductors. Its electromagnetic properties change with frequency, which can enhance electromagnetic wave absorption. Ref.  proposesTraditional TEV sensors only use the principle of capacitive voltage division to measure transient earth waves. This approach does not take into account the absorption of electromagnetic waves by the sensor itself. To further improve traditional PD sensors, this paper proposes the study of the electromagnetic properties of the electrode plate material of the new graphene partial discharge sensor. The electromagnetic properties, including conductivity, dielectric constant, magnetic permeability, and refractive index, are derived theoretically. We also analyze the influence of electrochemical potential, temperature, frequency, and relaxation time on electromagnetic properties. Based on the least-squares method, the prediction model of electromagnetic properties is established. Finally, by simulation and experiment, the partial discharge signal absorption properties of graphene partial discharge sensor and traditional partial discharge sensor are compared. This will lay the foundation for further research on the design of graphene partial discharge sensors.When partial discharge occurs in the switchgear, the partial discharge can produce time-varying electromagnetic waves. It is are usually seen as a source of pulse line current at a certain point. When it radiates outward, the frequency of electromagnetic signals can reach GHz. The electromagnetic wave radiates in the form of spherical waves and propagates in various media . TherefoTherefore, to analyze the propagation law of electromagnetic waves in PD sensors accurately, Maxwell’s equations must be used. Meanwhile, the analysis of electromagnetic properties is particularly important. As for electromagnetic materials, the description of electromagnetic properties mainly needs to start from electrical conductivity, magnetic permeability, and dielectric constant. Considering the electromagnetic properties of graphene copper-clad electrode plates are particularly complex, the electromagnetic properties of the new graphene PD sensor electrode plates were studied.Electrical conductivity is an important parameter for analyzing electromagnetic properties. Japanese scientist Kubo has proposed the relationship between energy level spacing and metal particle diameter and gave the famous Kubo formula. The Kubo equation for the electrical conductivity of graphene is (1)σσg=σiNg is small, the total conductivity can be written asσintra represents the scattering process of electrons and photons, which can be expressed ase represents the charge and ħ = h/2π represents the angular Planck constant. kB is the Boltzmann constant, a is the energy, and F1 represents the simplification factor. The Fermi–Dirac distribution function represents the Fermi–Dirac distribution, which can be expressed as [When the graphene layers number essed as (7)fd(a)σinter represents the leap process of the electron.F2 represents the simplification factor. Considering the electricity of graphene σg is a complex number, it also can be expressed asσgr is the real part of the surface conductivity and σgi is the imaginary part of the surface conductivity.The inter-band conductivity The dielectric constant of graphene can be derived from Maxwell’s equation, which is known to beσ3D is the three-dimensional conductivity of graphene. We can obtain σ3D by dividing the two-dimensional conductivity of graphene by the thickness of graphene.t represents the thickness of graphene. The two-dimensional conductivity of graphene can be written as σ2D = σg.By rewriting it in time-harmonic form, the above equation can be converted intoWe can get the total dielectric constant.εg can be obtained asThe relative dielectric constant of graphene Ng-layer graphene isThe relative dielectric constant of εgr can be approximated asSince graphene is very thin, when the thickness tends to 0, the real part of the dielectric constant of graphene εgi can be expressed asThe imaginary part of the dielectric constant The real part of the dielectric constant is determined by the imaginary part of the conductivity, and the imaginary part of the dielectric constant is determined by the real part of the conductivity.By substituting the relationship between conductivity and dielectric constant, we can obtain the relationship between the dielectric constant of graphene and the frequencyc is the velocity of the electromagnetic wave in a vacuum. According to the relationship between c and v, the refractive index n can be calculated asThe propagation speed of electromagnetic waves in the medium can be expressed asμg can be taken as 1 [It is known that the magnetic permeability of graphene ken as 1 . The comSince the refractive index of graphene is a complex number, the relationship between the refractive index and the dielectric constant can be expressed asBy analyzing the relationship between graphene conductivity and complex refractive index, the complex refractive index can be expressed by electrical conductivity.The above equations mean that the square of the refractive index is the relative dielectric constant.cu is 1, the relative permeability μcu of copper is 1, and the conductivity of copper αcu is 5.998 × 107 S/m. The above parameters are generally specific to a particular standard. For example, when the conductivity of copper is measured, the temperature is the standard temperature (25 °C).Since copper is a conductor, the relative dielectric constant of copper εThis section analyzes the influencing factors of the electromagnetic properties of graphene and copper. This analysis is mainly focused on the electromagnetic properties of graphene. Considering influencing factors such as scattering rate, electrochemical potential, temperature, and frequency, a theoretical qualitative analysis was performed. The quantitative analysis of each influencing factor will be carried out in the next calculation chapter.τ. The relaxation time is used to represent scattering rate in the subsequent research. The relaxation time τ of graphene is related to its carrier mobility nc, and the relationship is τ = ncμc/(evF2) [vF is the Fermi velocity. In this paper, the value of the Fermi rate is 106 m/s and the carrier mobility of graphene is 2 m2/V·s.The scattering rate of graphene Γ is related to the relaxation time τ, and the relationship can be expressed as Γ = 1/2c/(evF2) . vF is tµc of thin graphene layer can be determined by the carrier concentration ns [In the ideal case, the chemical potential ation ns :(24)ns=2The carrier concentration can be adjusted by chemical doping or gate bias.Temperature affects the motion of electrons, which will change the conductivity of graphene. However, we generally consider only room temperature T = 300 K.w = 2πf. For better analysis of electromagnetic properties, we consider a wide range of frequency bands of the electromagnetic wave. Therefore, we chose to analyze the full frequency band from Hz to THz. The selected frequency bands are shown in The same electromagnetic wave has different wavelengths in different mediums, which in turn affects the graphene conductivity. Frequency can be expressed as Since copper is a conductor, for its electromagnetic properties, we mainly analyzed the conductivity. The conductivity of copper can be generally affected by the temperature, the degree of doping, and the processing method. As for temperature, the conductivity of copper decreases as the temperature increases. As for the degree of doping, the impurities in copper have a great influence on the conductivity of copper. As for the processing method, it mainly includes cold processing and heat treatment.In this section, the conductivity, dielectric constant, and refractive index of graphene are calculated by MATLAB under different influencing factors. Additionally, we obtained the curves of the electromagnetic properties with frequency when the temperature was taken as 100 K, 200 K, 300 K, 400 K, and 500 K; the electrochemical potential taken as 0.1 eV, 0.2 eV, 0.3 eV, 0.4 eV, and 0.5 eV; and the relaxation time taken as 1 ps, 2 ps, 3 ps, 4 ps, and 5 ps, respectively. These analyses are based on the full frequency band, ranging from Hz to THz.Fixing temperature as 300 K, relaxation time as 3 ps, we analyze the variation of real and imaginary parts of graphene conductivity with frequency, when the electrochemical potential is taken as 0.1 eV, 0.2 eV, 0.3 eV, 0.4 eV, and 0.5 eV, respectively.Fixing electrochemical potential is 0.3 eV, and relaxation time as 3 ps; we calculated the variation of the real and imaginary parts of graphene conductivity with frequency, when the temperature was taken as 100 K, 200 K, 300 K, 400 K, and 500 K, respectively.Fixing electrochemical potential is 0.3 eV, and the temperature is 300 K; we analyzed the variation of real and imaginary parts of graphene conductivity with frequency, when the relaxation time was taken as 1 ps, 2 ps, 3 ps, 4 ps, and 5 ps, respectively.Fixing temperature is 300 K, and the relaxation time is 3 ps; we analyzed the variation of the real and imaginary parts of the dielectric constant of graphene with frequency when the electrochemical potential was taken as 0.1 eV, 0.2 eV, 0.3 eV, 0.4 eV, and 0.5 eV, respectively.17 F/m, and its value tends to be 0 in the high-frequency band. The effect of electrochemical potential is the same as the real part.Fixing electrochemical potential is 0.3 eV, and the relaxation time is 3 ps; we analyzed the variation of the real and imaginary parts of the dielectric constant of graphene with frequency when the temperature was taken as 100 K, 200 K, 300 K, 400 K, and 500 K, respectively.Fixing electrochemical potential is 0.3 eV, and the temperature is 300 K; we analyzed the variation of the real and imaginary parts of the dielectric constant of graphene with frequency, when the relaxation time was taken as 1 ps, 2 ps, 3 ps, 4 ps, and 5 ps.17 F/m at lower frequencies and tends to 0 at higher frequency bands. The effect of the relaxation time is the same as the real part.Fixing temperature is 300 K, and the relaxation time is 3 ps; we analyzed the variation of the real and imaginary parts of the refractive index of graphene with frequency when the electrochemical potential was taken as 0.1 eV, 0.2 eV, 0.3 eV, 0.4 eV, and 0.5 eV, respectively.8 F/m at low frequencies and tend to be 0 at high frequencies. Additionally, these two parts increase with the increasing electrochemical potential.Fixing electrochemical potential is 0.3 eV, and the relaxation time is 3 ps; we analyzed the variation of the real and imaginary parts of the refractive index of graphene with frequency when the temperature was taken as 100 K, 200 K, 300 K, 400 K, and 500 K, respectively.8 F/m at low frequencies, and both tend to be 0 at higher frequency bands. The effect of temperature is not reflected.Fixing electrochemical potential is 0.3 eV, and the temperature is 300 K; we analyzed the variation of the real and imaginary parts of the refractive index of graphene with frequency, when the relaxation time was taken as values of 1 ps, 2 ps, 3 ps, 4 ps, and 5 ps, respectively.8 F/m at low frequencies, and both tend to be 0 at high-frequency bands. These two parts increase with the effect of relaxation time.According to By analyzing the variation relationship of electromagnetic properties of the above electrode plate materials, we can see the existence of multiple iterations and relatively independent relationships between different influencing factors. When solving electromagnetic properties of graphene PD sensor, to further simplify electromagnetic properties calculations and facilitate engineering applications, this section establishes multiple linear regression models of three electromagnetic properties based on the least-square method.Based on the conductivity, a dataset with four different influencing factors as independent variables and conductivity as the dependent variable was constructed. Additionally, a scatter plot was created to view the linearity correlation between the independent variables and the predictor variables. The linearity is shown in Next, the four independent variables of temperature, electrochemical potential, relaxation time, and frequency were used to establish multiple linear regression equations with conductivity, and the regression coefficients corresponding to the four independent variables were calculated using the least-squares method. The real and imaginary regression equations of conductivity are as follows.Based on the dielectric constant, a dataset with four different influencing factors as independent variables and dielectric constant as the dependent variable was constructed. Additionally, a scatter plot was created to view the linearity correlation between the independent variables and the predictor variables. The linearity is shown in Next, the four independent variables of temperature, electrochemical potential, relaxation time, frequency, and dielectric constant are established as multiple linear regression equations. The regression coefficients corresponding to the four independent variables are calculated using the least-squares method. The regression equations for the real and imaginary parts of the dielectric constant are as follows:Based on the refractive index, a dataset with four different influencing factors as independent variables and a refractive index as the dependent variable was constructed. Additionally, a scatter plot was created to view the linearity correlation between the independent variables and the predictor variables. The linearity is shown in Next, the four independent variables of temperature, electrochemical potential, relaxation time, and frequency were used to establish the multiple linear regression equation with the refractive index. The regression coefficients corresponding to the four independent variables were calculated using the least-squares method. The regression equations of refractive index real part imaginary part are as follows.The simulation analysis uses the electromagnetic properties we derived, to construct finite element models of the traditional copper electrode plate and graphene copper-clad electrode plate, respectively. The simulation parameters are shown in In When partial discharge signals of 30 MHz, 60 MHz, and 90 MHz are incident, respectively, the response of different models to the signal is different. It can be seen that the electric field distribution on the surface of the graphene copper-clad electrode plate is significantly higher than that of the traditional copper electrode plate. This is because of the better absorption of the electromagnetic wave signal generated by partial discharge. This simulation can verify that the graphene partial discharge sensor can couple more electromagnetic than the traditional partial discharge sensor.A partial discharge detection system was established in the laboratory, which includes AC power supply, voltage regulator, switchgear with partial discharge defect model placed, traditional partial discharge sensor, improved partial discharge sensor, and data acquisition device. The electrode plate of the traditional partial discharge sensor is copper, and the electrode plate of the improved sensor is graphene copper-clad electrode plate instead, which is processed by the commissioned manufacturer. The experimental setup and schematic diagram are shown in (1)As for the conductivity, the higher the frequency, the smaller the real part of the conductivity, and the imaginary part firstly decreases and then increases. The higher the electrochemical potentials, the larger the real part of the conductivity, and the smaller the imaginary part. Temperature does not affect the real and imaginary part of the conductivity of graphene. When the relaxation time increases, the real part of the conductivity increases, and the imaginary part decreases;(2)As for the dielectric constant, the higher the frequency, the less the real part gradually decreases. The imaginary part has a huge value in the low-frequency band, and its value tends to 0 in the high-frequency band. The higher the electrochemical potentials, the larger the real part of the dielectric constant. Temperature does not affect the real and imaginary parts of the dielectric constant. When the relaxation time increases, the real part and imaginary part of the dielectric constant increase;(3)As for the refractive index, because of the large frequency span of the sampling frequency band, the real and imaginary parts of the refractive index are larger when the frequency is small, but the high-frequency band tends to be 0. Additionally, the real and imaginary parts increase with the electrochemical potentials and relaxation time, and these two parts cannot reflect the effects of temperature.(4)A multiple linear regression model based on the least-squares method is established for the three electromagnetic properties, which can further simplify the calculation of electromagnetic properties and provide a good fit to the data.(5)The simulation and experiment verify that the graphene partial discharge sensor can better absorb the partial discharge signal compared with the traditional partial discharge sensor.Aiming at the improvement of traditional PD sensor materials, this paper proposes a method to analyze the electromagnetic properties of the electrode plate material of the graphene PD sensor. This method can lay the foundation for further analysis of the electromagnetic wave propagation law and further design of PD sensor material structure. The following conclusions are obtained:This article mainly focuses on the electromagnetic properties of the electrode plate material of the graphene partial discharge sensor and verifies the feasibility of graphene partial discharge sensors. In future work, it will be important to know how to modulate the electromagnetic properties of graphene around the four factors and find the optimal parameters for the optimization and customization of the sensor. Additionally, we will further deepen the design of the graphene partial discharge sensor from the micromechanical aspects for the graphene-copper composite using the first principle and experiments.


The items showing a significant difference between groups were used as independent variables, after the consideration of multicollinearity, for a logistic analysis where %6MWD < 80% was used as the dependent variable. Results: The 6MWD results show that there was no significant difference between IPF and IPPFE in the absolute value of 6MWD and in the number of people with 6MWD ≥ 250 m, but when 6MWD was compared with %6MWD, the IPPFE group showed a significantly lower value than the IPF group (p = 0.013). Logistic regression analysis showed that only BMI (p = 0.032), GAP index (p = 0.043), and mMRC (p = 0.026) were factors that caused a decrease in %6MWD in 100 patients. Conclusion: The results suggest that leanness, shortness of breath and severity of illness are the most important factors that determine exercise tolerance, regardless of disease entity in IPF and IPPFE.Background: In idiopathic pulmonary fibrosis (IPF), 6-minute walking distance (6MWD) is an independent factor for mortality. Idiopathic pleuroparenchymal fibroelastosis (IPPFE) is a rare disease with physical features such as emaciation, but the relationship between IPPFE and 6MWD is unclear. In this study, we investigated the factors that cause a decrease in the percent of the predicted value of a 6-minute walk distance (%6MWD), including the disease entities, IPF and IPPFE. Methods: This study included 100 patients  who visited the rehabilitation department. Patients with a %6MWD ≥ 80% were assigned to the normal group ( Idiopathic interstitial pneumonias (IIPs) are pneumonias of unknown cause, in which the pulmonary interstitium is the primary site of inflammatory and fibrotic lesions. The main symptoms of IIPs are dry cough and dyspnea on exertion . IIPs arThe 6-minute walk test (6MWT), a simple test of exercise tolerance, is used as an index for estimating motor function and disease severity and predicting prognosis in various chronic diseases . AlthougBased on idiopathic upper lobe localized pulmonary fibrosis, which was proposed by Amitani et al. in 1992 , idiopatFrom the progressive decline in lung function and poor prognosis, it could be predicted that IPPFE reduces 6MWD more than other IIPs. However, previous reports comparing IPPFE and other IIPs in lung transplant candidates have shown no significant difference in 6MWD ,15. WhenIn this study, we compared, for the first time, 6MWD as %6MWD between IPPFE and IPF, and the factors that cause a decrease in %6MWD in both IPF and IPPFE were examined to clarify the role of the disease entity as IPPFE.We recruited 273 consecutive patients who participated in the Toho University Interstitial Pneumonia Rehabilitation (TRIP) study from July 2014 to January 2020. The TRIP study was designed to clarify the long-term effect (2-year follow-up) of pulmonary rehabilitation in patients with interstitial lung disease (ILD), and it is an on-going project at the Toho University Omori Medical Center, Tokyo, Japan . All of The exclusion criteria for the TRIP study were active cancer, unstable cardiac disease, severe orthopedic or neurological disorder that limited exercise performance, previous participation in pulmonary rehabilitation (PR), and recent changes in medications, including antifibrotic drugs.In this study, 75 IPF patients and 25 IPPFE patients were included in the analysis, excluding those with missing data or other diseases entities . IPPFE was diagnosed both radiologically and physiologically. Probable IPPFE was diagnosed based on the criteria for diagnosis of IPPFE without surgical lung biopsy, as proposed by the Study Group on Diffuse Pulmonary Disorders, Scientific Research/Research on Intractable Diseases in Japan . IPF wasAll study participants provided written informed consent. This study was approved by the Ethics Committee of Toho University Omori Medical Center .1), FEV1/FVC ratio, TLC, RV, and DLco were measured using CHESTAC-8900 (DN) . Each measured value was divided by the predicted value of each item, and the percentage of the predicted value (%pred) was calculated.We performed pulmonary function tests, including spirometry, total lung capacity (TLC), residual volume (RV), diffusing capacity of the lung for carbon monoxide (DLco), and blood gas analysis. Forced vital capacity (FVC), forced expiratory volume in 1.0 s  index , and evaPhysical function was evaluated by grip strength, lower limb muscle strength, and 6MWT. The 6MWT was performed according to the published international guidelines . All patCSA) and the pectoralis major muscle (PMCSA) using CT images as indicators of skeletal muscle [https://imagej.net, accessed on 27 April 2020).We quantitatively evaluated the cross-sectional area of the erector spinae muscle . The significance level was set at 5%.The Mann–Whitney U test was used to compare ordinal and interval scales, and the χ2 test was used to compare nominal scales between disease types and groups for each endpoint. To examine whether %6MWD was relevant, binomial logistic regression analysis was performed using the items with 1, %FEV1, TLC, partial pressure of arterial carbon dioxide (PaCO2), muscle cross-sectional area, and muscle strength were significantly smaller in IPPFE than in IPF. FEV1/FVC and RV/TLC were significantly greater in patients with IPPFE than in those with IPF. There were no significant differences in age, gender, severity (GAP index), %TLC, %DLco, pH, partial pressure of oxygen in arterial blood (PaO2), and serum interstitial pneumonia markers  between the groups.Comparison of IPF and IPPFE is presented in p = 0.013).The 6MWD results show that there was no significant difference between IPF and IPPFE in the absolute value of 6MWD and in the number of people with 6MWD ≥ 250 m, but when 6MWD was compared with %6MWD, the IPPFE group showed a significantly lower value than the IPF group , GAP index , and mMRC . The difference in disease entity between IPF and IPPFE was not extracted as an independent factor for %6MWD decline.Finally, we conducted a binomial logistic analysis using the forced entry method with the following independent variables: disease entity, gender, GAP index, BMI, mMRC, %FEVa result , three fIn this study, although there was no significant difference in the absolute distance of the 6MWT, %6MWT was significantly smaller in IPPFE than in IPF. However, the results of logistic multivariate analysis of IPF and IPPFE together suggested that the difference was not related to the disease entity, i.e., IPF or IPPFE, but to BMI, dyspnea status, and severity of the disease evaluated by the GAP Index.2). It is widely used as a general indicator of whether a person has a healthy body weight for height. However, the prediction equation of 6MWD was generated as a gender-specific linear regression of age, weight, and height, not directly reflecting leanness or corpulence [One may wonder why BMI was a factor limiting the performance of 6MWT after the correction for weight and height. BMI is a measure of a person’s leanness or corpulence, calculated as weight in kilograms (kg) divided by height in meters squared  showed a more rapid progress in the clinical course than those without lower lobe UIP in previous studies ,37. TherIn addition, we did not investigate the effects of the Flat Chest Index and 6MWD associated with IPPFE respiratory function .Another possible limitation of the study is the limited sample size, which may compromise our ability to detect significant differences.Our results suggest that, in a mixed population of IPF and IPPFE patients, leanness, shortness of breath, and severity of illness are the most important factors that determine exercise tolerance regardless of disease entity, i.e., IPF or IPPFE.


Herein, a graphene/Si-based device was introduced for bovine serum albumin (BSA) sensing. In this study, it is shown that the Schottky junction at the interface of graphene/Si is highly sensitive to BSA under UV light exposure. The reverse bias current of the junction, which is sensitive to UV light, changes under exposure to BSA at different concentrations. By UV light absorption, we showed that the addition of the BSA solution to the junction affected the output characteristic of the fabricated device. Moreover, the output characteristic of the device shows that the device can be considered as a self-powered detector that would reduce the need for batteries. The results obtained in this study would open up a way towards the fabrication of an on-chip biosensor for the sensing of biological agents such as BSA. Herein, a graphene/Si-based device was introduced for bovine serum albumin (BSA) sensing. Because of its structural homology with human serum albumin, bovine serum albumin (BSA) is an appropriate protein to be used as a model protein for investigations and studies. The determination of serum albumin concentration is a critical part of protein studies. Therefore, some studies focusing on the quantification of the amount of protein present in a sample using efficient and low-cost methods have been reported.13,14 The common method for the determination of BSA concentration is based on the detection of UV absorbance of the samples. Most proteins exhibit a distinct ultraviolet light absorption maximum at 280 nm due to the presence of tyrosine and tryptophan. Since the tyrosine and tryptophan contents of various enzymes vary within narrow limits, the absorption peak at 280 nm has been used as a rapid and sensitive measure of protein concentration.15 In this method, the ratio of the absorbance at 280 nm for the target samples versus the absorbance of the sample at known concentration is measured. This method has moderate sensitivity with high material requirement. To reduce the material requirement and increase the sensitivity, it is necessary to focus on the on-chip measurements. In this study, we report the on-chip detection of BSA using a graphene/Si-based device.Graphene, a two-dimensional material, has been widely used for the fabrication of chemical sensors, photodetectors and biosensors.−1.16–19 Due to its wide range of absorption, graphene/Si is a promising candidate for photo-detection from the UV to the IR range.20,21 Recently, we have reported the fabrication of highly sensitive broadband photodetectors based on the vertical Schottky junction of graphene/Si.22 On the other hand, graphene/Si-based diodes have been reported to be utilized for chemical and glucose sensing. Sakr et al. have utilized graphene-Schottky junction for non-enzymatic glucose sensing. Their sensor shows a linear response to glucose concentration in the range from 0 to 15 mmol L−1 with the detection limit of 0.5 mmol L−1.23 It has been shown that chemical adsorption on graphene sheets changes the electronic properties of graphene. Consequently, it is possible to modify the electrical characteristics of the graphene/Si junction via chemical adsorption. Based on this idea, Kim et al. have reported a graphene/Si-based diode sensor in which the chemical agent has been directly applied onto the graphene sheet using a pipette.24In recent years, the graphene/Si junction has been utilized for the fabrication of highly sensitive photodetectors with sensitivities as high as 1–10 A Wversus the serum albumin concentrations. Using this procedure, BSA sensing could be easily and quickly carried out on a chip without the need of bulky equipment.In this study, we report the fabrication of a graphene-based biosensor for the sensing of BSA to take advantage of both the optical and the electrical properties of the graphene/Si Schottky junction. This proposed sensor worked under exposure to UV light, and the junction photocurrent was plotted 2.2 layer using a thermal oxidation technique at 1200 °C. A 3 × 3 mm2 window in the SiO2 layer was then patterned using standard photolithography and then removed by the buffered hydrofluoric acid solution to obtain the desired pattern for the formation of the diode structure, as schematically shown in 2 structure and then patterned by photolithography to form contact electrodes  n-type silicon wafer using the RCA#1 solution. The cleaned wafer was then coated with a SiOodes see . To tranI–V) measurements were performed at room temperature under a DC field using a source unit IVM2.10.15 .The fabricated device was inspected and characterized by a field-emission scanning electron microscope (FEI Nova NanoSEM 450) and Raman spectroscopy . The wavelength of the Raman excitation laser was 532 nm. Current–voltage  of this figure.The scanning electron microscopy (SEM) and optical images of the graphene/Si-based protein sensor are shown in 2 substrate was analyzed by Raman spectroscopy, and the result is shown in −1) and 2D-band (2673 cm−1) Raman peaks of graphene can be seen in this figure. The high peak intensity ratio of 2D to G obtained via this analysis indicates high crystallinity and monolayer nature of the graphene sheet.25The transferred graphene on the Si/SiOvia monitoring of the electrical behavior of the graphene/Si Schottky junction under UV light irradiation. The electrical behavior of the device in the dark and under UV light irradiation is illustrated in I–V characteristic of the fabricated device shows a rectifying behavior, confirming the formation of the Schottky junction at the interface of graphene/Si. As abovementioned, the graphene/Si junction behaves as a Schottky diode. Our fabricated device was then utilized for the sensing of BSA To apply BSA in a buffer solution onto the device, a small open-base cuvette was directly placed on the device such that the solution covered the entire Si/graphene area. 26 Therefore, BSA behaves as an electron donor on the graphene surface. Moreover, pristine graphene is a p-type semiconductor because of the absorption of moisture or oxygen and PMMA residues. When the graphene surface is exposed to BSA, the Fermi level of graphene is shifted to the Dirac point; this causes an increase in the sheet resistance of graphene. As a result, upon increasing the BSA concentration, the forward current of the junction decreases.An increase in the BSA concentration leads to a decrement in the forward bias current of the device. This decrement can be explained by considering the electron-donating behavior of BSA that leads to charge concentration difference between the pristine and doped graphene. When graphene was exposed to electron donors, extra electrons were provided, causing an increase in the sheet resistance of graphene. As abovementioned, we have used pH 7.4 for the preparation of different concentrations of BSA. The isoelectric point of BSA is 5.4.27 Thus, UV light exposure leads to an increase in the reverse bias current of the device. When the graphene/Si junction is exposed to UV light, the incident photons generate electron–hole pairs in the structures. By applying a reverse bias, the generated electron–hole pairs are separated, and the injected holes in the graphene lead to a significant photocurrent.19,28 On the other hand, when the graphene/Si area is covered with the BSA solution, a decrement in the UV light absorption of the junction occurs because of the absorption of light by albumin. As shown in 29 Accordingly, log(I0/I) versus the BSA concentration has a linear response, as shown in the inset of 30,31 Note that we did not use any conjugated nanoparticles or markers for sensing; moreover, the sample was not manipulated and could be reused after testing.Interestingly, it can be seen that the reverse bias current significantly changes under exposure to BSA at different concentrations. It has been reported that the graphene/Si Schottky junction is highly sensitive in the UVB region.24η is the ideality factor, q is the electronic charge, kB is the Boltzmann constant, T is the absolute temperature, and VD is the voltage applied across the junction. VD can be expressed in the form VD = V − IRs, where Rs is the series resistance. Js is defined as the reverse saturation current and can be expressed byA is the area of the junction, and A* is known as the Richardson constant (112 A cm−2 K−2 for n-type silicon and 32 A cm−2 K−2 for p-type silicon). Moreover, ϕB is the Schottky barrier height (SBH). From the result of the J–V measurement  and rectification ratio were found to be 0.66 eV, 2.11, 28 kΩ, and 82, respectively.The rectifying current–voltage characteristics of the Schottky diode can be expressed by the thermionic emission model in which the diode current can be written as follows:surement  and its To monitor the light absorption spectra of BSA, BSA at different concentrations in the buffer solution was examined by a spectrometer (Avantes 2048 spectrometer), and the results are provided in −1 obtained by this graphene-based device makes it a promising candidate for accurate measurements in bio-sensing applications. The real-time response of the device to UV light exposure for BSA at different concentrations is also provided in The real time measurement of the reverse bias current of the device for different concentration of BSA is plotted in Output characteristics of the device near the zero voltage are shown in 32Moreover, we calculated the responsivity and detectivity of the device for BSA at different concentrations. The responsivity is defined as the ratio of photocurrent to incident optical power irradiated on the device.h, and υ are the external quantum efficiency, Planck's constant and frequency of incident light, respectively. The specific detectivity D* is calculated by the following equation:33Id represents the dark current density, and A is the junction area. For the incident light power of 3.25 mW cm−2, dark current of 800 nA and voltage bias of −2 V, the responsivity and detectivity of the device for BSA at different concentrations were calculated, and the results are provided in R and D* decrease with the increasing the BSA concentration.In the Currently, the use of mobile devices for biosensing and the point-of-care testing are the main approaches in the biosensing platform. The use of mobile and small devices, which just need a small sample volume to perform the measurement, for biological analysis offers numerous benefits such as rapid detection, reliable test results and simplicity. The graphene/Si-based device as a low cost, low power, sensitive, mobile and small device is actually the best candidate for protein sensing applications.4.−1 and the detection limit of 0.25 nM obtained by monitoring the reverse bias current of the fabricated device indicate good performance of the introduced graphene-based diode for bio-sensing applications. In addition, the hybrid graphene-Si exhibits a wide detection range (from 100 nM to 100 μM). The output characteristic of the sensor at the zero bias showed self-powered properties of the device that would reduce the need for batteries. This capability in addition to the simplicity of device fabrication as well as its operating mechanism and high sensitivity is very important in the field of on-chip bio-sensing applications.Herein, a graphene/Si-based Schottky diode was successfully fabricated and utilized for sensing BSA in a buffer solution. The device is very sensitive in the UVB region, and BSA effectively absorbs light in the UVB region. Using these features, we proposed a UVB-driven BSA sensor based on the graphene-Si junction. The output characteristic of the device during exposure to BSA showed that an increase in the BSA concentration leads to a decrease in the reverse bias current of the diode significantly. BSA has a significant light absorption around 280 nm. Consequently, when the Si/graphene area is covered by the BSA solution, a decrement in the UV light absorption of the junction occurs, leading to a decrease in the reverse bias current of the device. The sensitivity as high as 0.5 A MThere are no conflicts to declare.