The results demonstrated that the MoS2/graphene-coated separator is contributing to inhibit the shuttling phenomenon of polysulfides and improve the integrity of sulfur electrode. The initial discharge capacity of the battery using MoS2/graphene-coated separator at 0.2 C was up to 1516 mAh g−1. After 100 cycles, a reversible capacity of 880 mAh g−1 and a coulombic efficiency of 98.7% were obtained. The improved electrochemical behavior can be due to the nanostructure and Mo-S bond of the MoS2/graphene composite, which can combine physical shielding and chemisorption to prohibit the shuttle effect of polysulfides. The results prove that the MoS2/graphene-coated separator has the potential for feasible application in Li-S batteries to enhance their electrochemical performance.Lithium-sulfur (Li-S) batteries are the most prospective energy storage devices. Nevertheless, the poor conductivity of sulfur and the shuttling phenomenon of polysulfides hinder its application. In this paper, flower-like MoS Then 1 2/graphene-modified separator, a slurry was prepared with MoS2/graphene composite, carbon black and poly(vinylidene fluoride) (PVDF) in N-methylpyrrolidone (NMP) with a mass ratio of 8:1:1. The homogenous slurry was then pasted on a microporous membrane (Celgard 2400) which was employed here to provide mechanical strength. After drying at 70 °C under vacuum for 12 h, the MoS2/graphene-modified separator was stamped into round pieces with the size of 19 mm in diameter. The mass loading of the MoS2/graphene was 0.80 mg cm−2.To fabricate MoSTo prepare the S/graphene cathode material, 50 mL GO suspension was sealed in a 100 mL Teflon-lined autoclave and maintained at 180 °C for 12 h. After cooling to room temperature, the as-prepared RGO suspension was freeze-dried in vacuum overnight to evaporate the water solvent. Afterwards, the black precipitate was ground into powder and then RGO was obtained. Then, RGO and sublimed sulfur were mixed in the weight ratio of 75:25 using ball milling method. Finally, the mixture was then transferred into a 10 mL Teflon-lined autoclave and further maintained at 155 °C for 12 h to obtain the S/graphene composite.2/graphene-modified separator before and after cycling. The morphology of the samples was explored by transmission electron microscopy  and scanning electronic microscope  equipped with an energy dispersive spectroscopy (EDS) system. The dynamic mechanical analysis  was used to measure the tensile strain of the separators.The phase components of the composites were observed with X-ray diffraction  measurement. The X-ray photoelectron spectroscopy  was employed to investigate the compositions of the MoS3 dissolved in the mixture of dioxolane (DOL) and 1,2-dimethoxyethane (DME) (1:1 ratio vol%) were employed. The MoS2/graphene-modified separator was inserted between the cathode and the lithium foil with the MoS2/graphene coated side of the separator facing the cathode. The pristine Celgard 2400 was also used for comparison. The galvanostatic cycling experiments were conducted on a battery cycler  with a cut-off potential of 1.7–2.8 V (vs. Li+/Li). Cyclic voltammetry (CV) was tested on a CHI611C potentiostat  within the voltage range of 1.7–2.8 V with a scan rate of 0.1 mV s−1. Electrochemical impedance spectroscopy (EIS) was performed on a CHI611C potentiostat in the frequency range of 100 kHz–0.01 Hz.The cathode was prepared as follows. The sulfur/graphene composite, carbon black and PVDF (8:1:1 wt ratio) were mixed with NMP as the solvent. After grinding for 60 min, the resultant slurry was tape-cased onto aluminum foil. After drying at 60 °C under vacuum for 10 h, the obtained composite covered electrode was stamped into disks with diameter of 14 mm. The evaluation of electrochemical performance was carried out in CR2032-type coin cells and the assembly of cells was finished in an Ar-filled glovebox . The lithium foils served as the counter electrodes. For the electrolyte, 1 M lithium bis(trifluorometha-nesulfone)imide (LiTFSI) and 0.1 M LiNO−1, which correspond with the D band and G band of graphene, respectively. Moreover, D band is corresponding to the disordered sp3 structure and G band is assigned to the sp2 hybridized graphitic structure. The ID/IG value of S/graphene is 1.17, indicating a highly defective graphite structure, which is beneficial to fast electron transfer [−1, indicating the inclusion of sulfur in the composite [Raman characterization of S/graphene composite was shown in transfer . Moreoveomposite .2 and MoS2/graphene composite were characterized using X-ray diffraction (XRD). There are five similar diffraction peaks observed in two samples. According to the standard Powder Diffraction File (PDF) files of #75-1539, conspicuous peaks at 14.0°, 33.4°, 36.2°, 43.6° and 58.1° are indexed to (002), (100), (102), (103) and (110) planes of crystalline MoS2 respectively, indicating that the crystal structure of MoS2 was efficiently retained in the spray drying process. The peak of graphene was not obtained. As presented in 2 has been coated by graphene, which was further demonstrated by SEM and TEM results.XPS measurements were performed to investigate the surface chemical composition of the composite. The full spectrum in 2 and MoS2/graphene composite is revealed by SEM images and energy dispersive X-ray spectroscopy (EDS) mapping. As presented in 2 exhibits a flower-like structure with the average size of around 1.1 μm in diameter. The flower-like structure consisted of nanosheets with the thickness of around 30 nm. 2 nanospheres were effectively wrapped by graphene, and the three-dimensional flower-like structure was remained in MoS2/graphene composite. However, the diameter of the MoS2/graphene sphere is about 3.2 μm, which is much larger than that of MoS2. EDS mapping of Mo, S and C elements in 2 and graphene are tightly bonded.The morphology of as-prepared MoS2. The flower-like structure is clearly observed from the wrinkles. The inset of 2. 2/graphene composite, revealing that some nanospheres of MoS2 are well wrapped by thin graphene sheets. As illustrated by the HRTEM image in the inset of 2 and (200) planar spacing of graphene, respectively. The results indicate a strong interfacial bonding between graphene and MoS2, which can shorten electron/ion transport passage and supply more adsorption surfaces.The insight into inner structure of the samples was provided by transmission electron microscopy (TEM) analysis. 2/graphene-coated separators are investigated by SEM. As presented in 2/graphene-coated separator. Uniform MoS2/graphene spheres with the average size of 3.6 μm in diameter were observed. The contact angle of the MoS2/graphene-coated separator is 0° as shown in the inset in 2/graphene-coated separator with tiled and folded state are exhibited in 2/graphene-coated separator . The lower resistance of the batteries with MoS2/graphene-coated separator results from decreased insulating materials deposited on the surface of the electrode, leading to an excellent cycling stability.To study the kinetics process, EIS measurements for the batteries with pristine separator and MoS2/graphene-coated separator and the pristine separator were characterized. The batteries were rested for 72 h after the 10th cycle at 0.2 C. 2/graphene-modified separator shows a small attenuation from 2.3 to 2.26 V during the rest time, indicating the effective suppression of the self-discharge by the composite separator. 2/graphene-coated separator exhibited a decline rate of 13.52%.Since the self-discharge is one of the major defects of Li-S batteries, the self-discharge behavior of the electrodes with the MoS2/graphene-coated separator after 100 cycles at 0.2 C is detected and the results are exhibited in 2/graphene composite still remain uniform distribution on the surface, indicating that the coating is flexible and tightly coated to avoid dropping out from the separator during cycles. No obvious cluster was observed and the diameter of the MoS2/graphene sphere is about 4 μm. The corresponding EDS elemental maps (The morphology of the MoStal maps c further2/graphene-coated separator after 100 cycles at 0.2 C was presented in 2/graphene-modified separator. Here the peaks between 169.8 and 168.7 eV are assigned to the sulfates, which can be attributed to brief air exposure of the sample in the XPS loading process. Furthermore, the peaks at 163.0 and 161.7 eV prove the existence of polysulfides in the MoS2/graphene-modified separator, consistent with the previous SEM results. Therefore, we believe that the migrating polysulfide species can diffuse through the MoS2/graphene-modified separator and be effectively captured during cycling.XPS S 2p spectrum of the MoS2/graphene composite is synthesized on the routine separator via slurry coating process to substantially enhance the electrochemical capability of Li-S battery. The MoS2/graphene-coated separator serves as a high efficiency ionic sieve that can block the transportation of the polysulfide anions and effectively decreases the shuttle effect. In addition, the introduction of MoS2/graphene-coated separator possessed higher sulfur utilization as a result of the recycling of entrapped active materials. These advantages can significantly improve the specific capacity and cycling stability of battery, with an initial discharge capacity of 1516 mAh g−1 and a higher reversible capacity of 880 mAh g−1 with coulombic efficiency of 98.7% after 100 cycles at 0.2 C. Therefore, the separator modification by MoS2/graphene composite will provide an effective method to suppress the shuttling phenomenon and enhance the electrochemical capability of Li-S batteries.In summary, a multi-functional separator modified by MoS


The hierarchical structure of the communities is studied by the Infomap method, and most of the irreducible communities are found to be at the second level. The composition of some of the major communities, including overexpressions regarding their industrial or regional nature, and the connections that exist between the communities are studied in detail. The findings obtained here cause us to question the validity and accuracy of using the conventional input-output analysis, which is expected to be useful when firms in the same sectors are highly connected to each other.This paper studies the structure of the Japanese production network, which includes one million firms and five million supplier-customer links. This study finds that this network forms a tightly-knit structure with a core giant strongly connected component (GSCC) surrounded by IN and OUT components constituting two half-shells of the GSCC, which we call a A macro economy is the aggregation of the the dynamic behaviour of agents who interact with each other under diverse external (non-economic) conditions. Economic agents are numerous and include consumers, workers, firms, financial institutions, government agencies, and countries. The interactions of these agents result in the creation of economic networks, where nodes are economic agents, and links (edges) connect agents that interact with each other. Therefore, there are various kinds of economic networks depending on the nature of the interactions, which form an overlapping multi-level network of networks. Thus, any evidence-based scientific investigation of the macro economy must be based on an understanding of the real nature of these interactions and the economic network of networks that they form. This concept also applies to the micro-level perspective of economic agents: without knowing who a firm trades with, how can anyone hope to determine the future of that firm? Therefore, it is highly important to use actual network information when studying economic dynamics with either agent-based modelling/simulations or other means of systematic studies such as determining the debt-rank of an economic agent –5. Witho“walnut” structure. This type of structure is quite different from what is expected because of the existence of the IN-giant strongly connected component (GSCC)-OUT components: In the trade network, the flow of materials and goods begins with imported/mined/harvested raw materials such as oil, iron, other metals and food. Firms who engage in this business form the IN components. These compnoents are then processed to become various products such as semiconductors or powdered food by firms, which are considered to be GSCC components, before they are made into consumer goods by firms, which are considered to be the OUT components. One might think that the existence of IN-GSCC-OUT components is similar to a web network that has a bow-tie structure [In this paper, we study the structure of one of the most important networks, the production network, which is formed by firms (as nodes) and trade relationships (as links) –9. In thtructure . Howevertructure , 12.In previous studies , 8, the In our paper, we conduct a level-by-level analysis and identify both communities and “irreducible” communities (communities that are not decomposed into subcommunities at the lower level). We also study the overexpression of some of the major communities to identify both the industrial sector and the regional decomposition. The complex nature of the links that exist between the communities are also studied. A discussion and the conclusion as well as suggestions for future research are provided at the end. Some of the supporting materials are included as Appendices.Our data for the production network are based on a survey conducted by Tokyo Shoko Research (TSR), one of the leading credit research agencies in Tokyo, and was supplied to us through the Research Institute of Economy, Trade and Industry (RIETI). The data were collected by TSR by means of inquiry from firms who represent the top five suppliers and the top five customers. Although the large firms that have many suppliers and customers submitted replies that are incomplete, these data are supplemented with data on the other side of trade: smaller firms submit replies that include data on large firms, who are important trade partners. By combining all the submissions from both side of trade into one database, large firms are connected to numerous smaller firms, which provides a good approximation of the real complete picture. One might worry because some of the trades last for only a short time and sometimes they only occur once, such as when a firm seeks a good deal for just one particular occasion, and thus cast doubt on the definition of the trade network. The form of data collection used for this study solves this problem: it is most implausible that replies containing data on a one-time trade are included, instead, data on firms that maintain a certain trade frequency are likely to be listed. In this study, we use two datasets: ‘TSR Kigyo Jouhou’ (firm information), which contains basic financial information on more than a million firms, and ‘TSR Kigyo Soukan Jouhou’ (firm correlation information), which includes several million supplier-customer and ownership links and a list of bankruptcies. Both of these datasets were compiled in July 2016. (Some of the earlier studies on the production network include ).i → j denotes a supplier-customer link, where firm i is a supplier for another firm j, or equivalently, j is a customer of i. We extracted only the supplier-customer links for pairs of “active” firms and excluded inactive and failed firms by using an indicator flag for them when we retrieved the basic information. We eliminated self-loops and parallel edges (duplicate links recorded in the data), to create a network of firms (as nodes) and supplier-customer links (as edges). The network has the largest connected component when it is viewed as an undirected graph, which is the giant weakly connected component (GWCC) that includes 1,066,037 nodes  and 4,974,802 edges.In this study, This study not only analyzes the network but considers several attributes of each node: the financial information in terms of firm size, which is measured as sales, profit, number of employees and the firm’s growth; the major and minor classifications of industrial sectors, details regarding the firm’s products, the firm’s main banks, the principal shareholders, and miscellaneous other information including geographical location. For the purpose of our study, we focus on two attributes of each firm, namely the industrial sector and the geographical location of the head office.The industrial sectors are hierarchically categorized into 20 divisions, 99 major groups, 529 minor groups and 1,455 industries . See Table A in In terms of the flow of goods and services (and money in the reverse direction), the firms are classified in three categories: the “IN” component, the “GSCC”, and the “OUT” component. This structure is called “bow-tie” in a well-known study on the Internet . The GWCGWCC the giant weakly connected component: the largest connected component when the network is viewed as an undirected graph. An undirected path exists for each arbitrary pair of firms in the component.GSCC the giant strongly connected component: the largest connected component when the network is viewed as a directed graph. A directed path exists for each arbitrary pair of firms in the component.IN The firms through which the GSCC is reached via a direct path.OUT The firms that are reachable from the GSCC via a direct path.TE “Tendrils”; the remainder of the GWCCIt follows from the definitions thatWe, however, find it far more appropriate to call this structure a “Walnut” structure, as “IN” and “OUT” components are not as separated as in the two wings of a “bow-tie” but are more like the two halves of a walnut shell, surrounding the central GSCC core. This can be explained as follows. The number of firms in each component of the GSCC, IN, OUT and TE is shown in In contrast with the well-known “bow-tie structure” in the study conducted by   measures the per step average description length of the dynamics of a random walker migrating through the links between the nodes of a network with a given node partition C = {C1, ⋯, Cℓ} that consists of two parts. The first term arises from the movements of the random walker across communities, where H(C) is the average description length of the community index codewords given by the Shannon entropy. The second term arises from the movements of the random walker within the communities, where Ci, and i.The map equation method  is anothL(C).If the network has densely connected parts in which a random walker stays a long time, one can compress the description length of the random walk dynamics in a network by using a two-level codebook for nodes adapted to such a community structure; this is similar to geographical maps in which different cities recycle the same street names such as “main street’ . TherefoIn regard to the resolution limit problem, any two-level community detection algorithms including the map equation are not able to eliminate the limitation. However, the map equation significantly mitigates the problem as has been shown by a recent theoretical analysis . In prachttp://www.mapequation.org.Recently, the original map equation method has been extended to networks with multi-scale inhomogeneity. A network is decomposed into modules that include their submodules and then their subsubmodules and so forth. The hierarchical map equation  recursivNote that this study exclusively considers the community identification for nodes in our network. That is, each node belongs to a unique community at every hierarchical level. However, such community assignment may be too restrictive for a small number of giant conglomerate firms such as Hitachi and Toshiba because of the diversity of their businesses. The map equation is so flexible that it can detect the overlapping community structure of a network in which any node can be a member of multiple communities . HoweverMost real-world networks have a community structure . Such coH is used to measure the probability that X randomly selected nodes in community C of size NC will have attribute Q. The hypergeometric distribution H can be written asNQ is the total number of elements in the system with attribute Q. Further, one can associate a p valuep with NC,Q nodes, having attribute Q in community C with H by the following relation:We follow the procedure used in  to deterQ is overexpressed within community C if p is found to be lower than some threshold value pc. As we use a multiple-hypothesis test, we need to choose pc appropriately to exclude false positives. We assume that pc = 0.01/NA, as specified in [NA represents the total number of different attributes  for all the nodes of the system.The attribute ified in , which iified in . Here, NBy using the Infomap method , 12, we We visualize the hierarchical decomposition of the whole network into communities and their subcommunities in 1”. At the lower levels, the rank of the size is added after ‘:’. For example, community “C1:5” is the fifth largest 2nd level community among all the 2nd-level communities that belong to the largest top-level community C1.For the purpose of making the following discussion of communities transparent, let us adopt the following indexing convention: At the top modular level of the hierarchical tree structure, the communities are indexed by their rank in size (the number of firms in the community). Thus, the largest community at the top level is denoted as “CD(s) indicates the fraction of communities at the top level having a size of at least s, as shown in The complementary cumulative function Aij is the total number of links spanning from communities i to j and Aji and that of the opposite links. If the linkage between communities i and j is completely polarized, then Pij becomes ±1 depending on its direction; if the linkage is evenly balanced, then Pij = 0. If we assume that the links have no preference with respect to their direction as a null hypothesis, then the null model predicts that the polarization ratio for the connections between communities i and j fluctuates around 0 with the standard deviation σ given byLij = Aij + Aji is the total number of links between the two communities. If we focus on intercommunity linkages with Lij ≥ 100, we see that the ones whose direction is polarized in a statistically meaningful way occupy 86.7% of their total. The corresponding share of intercommunity linkages is 70.1% for Lij ≥ 10. Most of the connections between communities with more than 100 links are significantly polarized in reference to the random orientation model for intercommunity links.The map equation is a method that can be used to divide a directed network into communities in which nodes are tightly connected in both directions. Due to the nature of the network, the flows across communities thus detected should be biased in an either direction. We find the overexpression of the attributes in 1st level communities to determine the factors that play a crucial role in the formation of such communities. Our study considers both the location and the sector attributes. The location attributes are divided into 9 regions, and the sector attributes are categorized in 20 divisions. The details about the sixth largest 1st level communities and the overexpressed attributes within it are tabulated in The largest community: Manufacturing sectorsThe second largest community: Food sectorsThe third largest community: Construction sectorsThe fourth largest community: Wholesale and retail tradeThe fifth largest community: IT sector and scientific research, primarily based in TokyoThe sixth largest community: Medical and health careThe positions of the communities on the horizontal line clearly reflect their characteristics in terms of the walnut structure, as shown in At the 2nd level, some of the top level communities are decomposed to several subcommunities as shown in Tables D and E in D(s) ∼ sγ+1− with γ = 2.50 ± 0.02. The results indicate that the size of the communities is highly heterogeneous and spans over several orders of magnitude.The cumulative distribution of the community size at this level is plotted in C2:1, transport and postal activities, accommodations, eating and drinking services, living related and personal services, and amusement services dominate the overexpressed sectors, which are mainly based in urban regions (Tokyo and Chubu). The manufacturing, wholesale and retail trades in Tokyo and the Kansai region are overexpressed in C2:2. Wholesale and retail trade dominate the overexpressed attribute in C2:3, C2:4 and C2:5. A detailed account of the results is provided in We also analyzed the overexpressions of selected subcommunities. In terms of subcommunities, we observe wholesale and retail trade is the dominate overexpress attribute of the five largest subcommunities of the largest community. The Kansai region is the only overexpressed region in the 2nd largest subcommunity of the largest community. In The network diagram in x1, x2, and x3, respectively. The walnut composition of the community is described by point  on the plane of x1 + x2 + x3 = 1 in three-dimensional space. One can thereby establish one-to-one correspondence between a point inside an equilateral triangle and a composition of the three walnut components. The averaged composition of all the firms in the selected communities  is given by Although the IN components tend to to merge with the GSCC, we can see the large circle at the vertex of As is mentioned in the Introduction Section, detecting communities in the supply-chain network is crucial for understanding the agglomerative behavior of firms. This type of research is important because the detected communities are densely connected, and it is plausible that these firms affect each other through the links.On the other hand, industrial sectors commonly label firms, and these labels are widely used in the economics literature. If there is no difference between the detected communities and the industrial sectors, then there is no reason to make an effort to detect these communities. Therefore, in this section, we show how the detected communities are different from industrial sectors in terms of the interconnections between the groups.Although different classifications are used for industrial sectors, we discuss the one used in the input-output table . We use As previously mentioned, there are 209 communities in the 1st level and 66,133 communities in the 2nd level. On the other hand, the input-output tables have 13, 37, 108, 190, and 397 sectoral classifications, which are nested. We choose to compare 209 communities and 190 industrial sectors because these numbers are comparable.First, we counted the number of links between the communities and the industrial sectors. If the intra-links within the groups are dominant, then the diagonal elements of these matrices should have high density. As is shown in We can conclude that the detected communities in this paper explicitly illustrate the agglomeration of firms based on supply-chain networks rather than industrial sectors, which is more commonly used to categorize firms. This result also tells us that communities with densely connected firms consist of various industrial sectors, and they have their own economies, i.e., small universes.In this paper, we do not weight the links of the network. However, obviously, each transaction has a value, and there is a diversity of transactions. We can estimate the weights by using the sales of the firms. If we have totally different results with the results we have obtained here, a further analysis might be necessary. However, the additional analyses based on weighting the links in the networks do not show any significant difference. The details of these results are shown in We analyze the overall structure and hierarchical communities embedded in the production network of one million firms and five million links that represent trade relationships in Japan in 2016, with the aim of simulating the macro/micro level dynamics of the economy.For the former, we find that the IN and OUT components (20% and 26% of the firms) form tight shells (semi-spheres) around the GSCC component, which we call a “walnut” structure rather than a “bow-tie” structure, which is well-known for representing web networks and other type of networks that have loose wings made of IN and OUT components.For the latter, we use the Infomap method to detect a hierarchy that includes 5 layers of communities, of which most of the irreducible (those that do not have any lower level subcommunities) belong to the 2nd level. Furthermore, the size distribution of the 2nd level communities show clear power-law behavior at the large end. In addition to the large number of irreducible communities made primarily of GSCC components and those that exist in IN shells or Out shells, there is a fair number of communities made of IN and GSCC components, GSCC and OUT components, and even IN and OUT components. These communities are expected due to the walnut shape of the overall structure: IN and OUT components are not far from each other as they are in the bow-tie structure, but they form tight shells, whose ends are closely woven with each other. Furthermore, we examine the overexpression of the major communities in terms of industrial sectors and prefectures and find that they are not formed within a sector but span several sectors and prefectures. These communities have various shapes: in some cases, they are formed around goods and services related to a particular item, such as food. Sometimes these communities are made of small firms connected with a major hub such as a large construction company in a particular prefecture or a medical insurance agency.These findings have major implications for the study of the macro economy: Consider an economic crisis. Once this crisis starts, whether it is due to a natural disaster in a particular region of a country or a major failure of a large company, it is expected that it initially affects the community in which this region or company is located. Then the effects of this crisis will spread to other neighboring communities. This analysis is very different from input-output analysis and is expected to be useful because an input-output analysis is based on the assumption that firms in the same sectors are well-connected with each other. In contrast, what we find is that the effects of a crisis will spread throughout communities rather than industries. The hierarchical community structure studied in this paper can be immediately applied to the analysis of large-scale modelling and simulation: the macro economy of a country or countries is an aggregation of products that economically affect the trade network as well as a multitude of networks of networks. Constructing models that span all the networks would be an interesting but exhaustive elaboration of this work. Instead, we may study one community at a time and then connect the results to obtain an overall picture. Research in this direction has already begun and will appear in the near future , 31, 32), 3231, 3S1 Appendix(PDF)Click here for additional data file.


At low temperatures, however, it was found that the carbon diffusion rate (CDR) on the metal catalyst surface has a greater impact on the number and uniformity of graphene layers compared with that of the carbon solid solubility. The CDR decreases rapidly with decreasing temperatures, resulting in inhomogeneous and multilayer graphene. In the present work, a Ni–Cu alloy sacrificial layer was used as the catalyst based on the following properties. Cu was selected to increase the CDR, while Ni was used to provide high catalytic activity. By plasma-enhanced CVD, graphene was grown on the surface of Ni–Cu alloy under low pressure using methane as the carbon source. The optimal composition of the Ni–Cu alloy, 1:2, was selected through experiments. In addition, the plasma power was optimized to improve the graphene quality. On the basis of the parameter optimization, together with our previously-reported, in-situ, sacrificial metal-layer etching technique, relatively homogeneous wafer-size patterned graphene was obtained directly on a 2-inch SiO Graphene, since its “discovery” in 2004, has attracted worldwide attention because of its excellent properties, such as high carrier mobility, high mechanical strength and high transmittance ,2. SeverIn this work, we studied the growth of graphene by plasma enhanced CVD at a low temperature (~600 °C). Thin films of Ni–Cu alloy were chosen as catalysts. Cu was used to increase the carbon diffusion rate (CDR), while Ni was used to provide high catalytic activity. The plasma power was optimized, since it was found to have a significant impact on the graphene quality. We found that at a low temperature, the CDR, instead of the carbon solubility, played the dominant role in determining the number of graphene layers and uniformity. The CDR sharply decreased at decreasing temperature, leading to inhomogeneous and multilayer graphene formation. Nevertheless, relatively homogeneous, wafer-sized patterned graphene was still achieved after process parameter optimization. Our findings will be useful for further growth optimization, especially at low temperatures, because the information available in literature that can serve as guidelines for low temperature graphene growth is very limited.2. The equipment used for the deposition of Ni and Cu films was a Denton Vacuum sputtering platform. Radio frequency source was used for the sputtering. Ni–Cu alloy was prepared by depositing Ni and Cu films successively, followed by annealing at 600 °C for 40 min in a high-vacuum annealing furnace to make them alloy and grow the grains. When sputtering, the substrate was kept at 30 °C. The sputtering power of Ni and Cu is 300 W, the corresponding direct-current biases are 142 V for Ni and 188 V for Cu; the sputtering rate of Ni is about 1.6 Å/s; and the rate of Cu is about 3 Å/s. The total metal thickness was 300 nm. The compositions of Ni–Cu alloy are controlled by adjusting the thickness of Ni and Cu films. For example, the ratio of Ni to Cu 1:10 can be obtained by setting the thickness of Ni film to be 30 nm and the thickness of Cu film to be 270 nm.The substrate we used was heavily doped Si with 300 nm SiO2 atmosphere. The pressure was controlled to be 15 mbar. Then, 960 sccm Ar, 20 sccm H2 and 5 sccm CH4 were introduced into the chamber and the plasma  was ignited at the same time. The plasma was maintained for 5 min to grow graphene. Finally, the furnace was cooled down at 200 °C/min. The whole growth process (including heating and cooling) took approximately 15 min. The schematic illustrations of the growth equipment and growth process are shown in The growth equipment was a vertical, cold wall CVD furnace . First, the temperature rose to 600 °C at a rate of 200 °C/min in HWe measured the roughness of the Cu–Ni films by a stylus profiler . Before annealing, the average roughness and the root-mean-square roughness of the films were Ra = 3.03 nm and Rq = 3.76 nm, respectively. After annealing and graphene growth, the average roughness and the root-mean-square roughness of the films were Ra = 4.41 nm and Rq = 5.62 nm, respectively. On the whole, the surface roughness of the Ni–Cu alloy film did not change much, due to the relatively low annealing and growth temperature.4:HCl:H2O = 10 g:50 mL:50 mL) for about 35 min. The thickness of PMMA was about 100 nm. After the etching of the metal, the sample was immersed in deionized water for 15 min and blown dry. Then, the sample was baked at 150 °C in air for 10 min to improve the graphene-substrate adhesion. In the end, the PMMA was removed by acetone.First, the PMMA (poly(methyl methacrylate)) supporting layer was spun on the substrate ; that was followed by baking the substrate at 150 °C for 5 min. Then, the sample was immersed in a Ni–Cu alloy etchant  alloy should be much less than that of bilayer graphene. However, atomic force microscopy (AFM) measurements show that the maximum thickness of the graphene grown on the alloy was about 88 nm  and Ni2Cu1 (high Ni composition) alloys. As shown in ®, <www.thermocalc.se>, version 2019a, using the MOBCU2 atomic mobility database. As shown in −12 m2/s and 3 × 10−14 m2/s respectively, which are about two orders of magnitude different. In −13 m2/s is needed to ensure the uniformity of graphene layers. We also calculated the bulk CDR at 800 °C , in which D0 (the frequency factor) is approximately temperature-independent. Q is the diffusion activation energy, kB is the Boltzmann constant and T is the absolute temperature in Kelvin. We see that D0 depends on the crystal lattice. In the present case, Cu has a larger D0 value, mainly due to a larger lattice constant than Ni. The activation energy Q sitting in the exponent function should have a stronger impact on D, in comparison with D0 which is proportional to D. The high diffusivity in Cu can, therefore, be attributed to two factors: (1) a larger lattice constant, and (2) a lower diffusion barrier which can be further interpreted based on the filling status of the d electron shell. Hu et al. [The high CDR in/on Cu relative to that of Ni is attributed to the following factors. The diffusion coefficient is given as D = Du et al.  studied Thus, the performances of Ni–Cu alloys at low-temperature growth are dramatically different from the previous reports at high temperatures ,24,25,26This work also gave us inspiration for our follow-up work. We can further explore alloys with higher catalytic activity and higher CDR on its surface simultaneously, in order to obtain even more uniform and higher quality graphene at low temperatures. The selection of new alloys must meet the following requirements: (1) high catalytic activity, (2) fast CDR in the metal and (3) forming a homogenous single-phase solid solution alloy. We screened CDR in various metals  and the We also studied the influence of plasma on the quality of graphene. The purpose of applying plasma during the growth is mainly to accelerate the low temperature cracking of methane. Interestingly, we found that plasma is also very important to improving the quality of graphene. In fact, graphene can also be grown on the surface of Cu–Ni alloys at 600 °C even without plasma. It was found that the lowest growth temperature catalyzed by pure Ni without plasma is around 450 °C . HoweverThe growth equipment we used included a vertical, cold wall graphene growth system . As shown in 2/Si substrate.One of the applications of low temperature growth is the combination with direct growth technology, which makes it possible to directly grow graphene on a variety of substrates that cannot withstand very high temperatures. We combined this 600 °C graphene growth method with our previously-reported in situ growth technique ,29 and o2/Si and sapphire. The graphene is grown on the metal surface. After that, a PMMA supporting layer is spun on the sample. Therefore, the metal sacrificial layer is completely covered by the PMMA/graphene films. Interestingly, we find that when the sample is immersed in the metal etchant, the etchant can efficiently penetrate the PMMA and graphene to accomplish the metal etching (First, we need to give a brief introduction of our in situ growth technology. This method uses a sacrificial metal layer to assist growth. The essence of the growth method is the etching mechanism of the metal sacrificial layer. As shown in  etching b. As sho2/Si substrate. The plasma power was selected to be 50 W; the ratio of methane to hydrogen was 5 sccm/20 sccm; and the growth time was 5 min. D/IG lies in the range of 0.12–0.69. G/I2D of typically 0.97–3.6.Using this method, a patterned graphene film was grown directly on a 2-inch SiO2/Si substrate at 600 °C with relatively good quality and uniformity. Low temperature growth can expand the range of substrate choices and reduce the effect of temperature on substrates, which is a future direction for the development of direct graphene growth. We expect the work presented here will promote the application of directly grown graphene at low temperatures.In this work, the effect of CDR on the thickness and uniformity of graphene in low temperature growth has been revealed for the first time. The uniformity and quality of graphene can be improved by proper selection of the alloy compositions. Ni–Cu alloy was used in our work, where Cu acted to increase the CDR, while Ni provided high catalytic activity. Meanwhile, we found that the plasma power can have great influence on the quality of graphene. Finally, based on optimizing the growth parameters and combining them with the in-situ growth method, we obtained a wafer-scale graphene film directly on SiO


Graphene is an ideal material in the reinforcement of metal-matrix composites owing to its outstanding mechanical and physical properties. Herein, we have investigated the surface enhancement of iron via a computational nanoindentation process using molecular dynamics simulations. The findings of our study show that graphene can enhance the critical yield strength, hardness and elastic modulus of the composite to different degrees with the change of the number of graphene layers. In the six tested models, the composite with trilayer graphene on the surface produces the strongest reinforcement, with an increased magnitude of 432.1% and 169.5% in the hardness and elastic modulus, respectively, compared with pure iron. Furthermore, it is revealed that high temperature could weaken the elastic bearing capacity of the graphene, resulting in a decrease on the elastic mechanical properties of the graphene/Fe composite. Since its discovery , graphenExtensive studies have been conducted on metal matrix composites, including Fe, Al, Cu, Mg and Ni ,11,12,13Nanoindentation is an approach widely used to measure elastic modulus and hardness of nanocomposites ,16. In tThe MD method was used to examine the influence of graphene in the graphene/Fe composite at the atomic level. The large-scale atomic/molecular massively parallel simulator (LAMMPS) software was employed to calculate the MD simulations. The simulation cells are shown in The graphene/Fe composite models are shown in ijREBOE term describes the short-ranged interactions (r < 2 Å) between carbon atoms, the EijLJ term adds longer-ranged interactions (2 Å < r < cutoff) using a form similar to the standard Lennard Jones potential, and the EkijlTORSION term describes various dihedral angle preferences in hydrocarbon configurations, which is an explicit 4-body potential.The accuracy of the MD simulation results is determined by the selection of potential function. We used the Brenner-generation reactive empirical bond-order potential to model the C-C bonded interaction . The C-CiE of an atom i is specified asαF is the embedding energy which is a function of the atomic electron density βρ. αβΦ is the pair potential interaction between atoms I and J, as a function of the distance ijr between atom I and atom J. α and β are atomic element types. The C-Fe interaction between iron and carbon atoms of both diamond indenter and graphene layers was described by the classical Lennard Jones (LJ) potential, as shown in Equation (3)cr is the cutoff distance. The σ and ε for the C-Fe interaction are 2.221 Å and 0.043 eV [The embedded-atom method (EAM) potential was used to compute pairwise interactions between iron atoms . The totWe set a downward velocity of 30 m/s on the balls and kept the temperature at 300 K by the Nose-Hoover algorithm . After tf is the final displacement of the plastic unloading process. R is defined by R = (1/R1 + 1/R2)−1, where R1 is the radius of diamond indenter, R2 is the radius of the spherical hole in the surface of the substrate [r is given by [E and ν are Elastic modulus (Young’s modulus) and Poisson’s ratio of the composite matrix, iE and iν are the same parameters of the diamond indenter. The hardness is defined bymaxP is the max force at the initial unloading point, and cA is the contact area of spherically curved surface [The Hertzian contact analysis theory guided our model. To understand the influence of graphene sheets on the hardness and elastic modulus of the iron matrix, the load-displacement data was recorded for analysis. The load-displacement relation is described by (4)P=43Rubstrate . The indgiven by (5)1Er=( surface .The results of the simulated nanoindentation process are revealed by the load-displacement curves. The mechanical properties of multiple graphene have received growing interest in recent years ,28. To iTo investigate the influence of loading speed and temperature on the nanoindentation process of the graphene/Fe composite, we explored the nanoindentation simulation of the composite with monolayer graphene on surface at varied loading speeds and at different temperatures, as shown in The simulation results reveal the change of hardness and elastic modulus of iron matrix composites with the graphene of the different number of layers, which is well consistent with previous studies on metal-matrix composites reinforced by graphene ,31. BothTo conclude, we have investigated the mechanical properties change of graphene/Fe composites with different number of graphene layers on the surface and in the superficial zone by using the MD simulation method to model the nanoindentation process. The results from the loading-displacement curves show that the graphene layers have a significant effect on the critical yield strength, hardness and elastic modulus of iron matrix in different degrees due to its remarkable loading bearing capacity. The degree of reinforcement on iron matrix increases with the number of graphene layers, both in surface and superficial zone cases. It was demonstrated that the enhancement in hardness and elastic modulus of composite in the surface cases is slightly stronger than that in superficial zone cases with graphene of the same number of layers on account of the production of the local stress fields in the superficial situations. Finally, the loading speeds have a small effect on the simulation of the composite nanoindentation process, and the simulation results of different temperatures reveal that high temperature can effectively reduce the mechanical properties of the graphene/Fe composite by softening lattice rigidity.


Ubiquilin-2 (UBQLN2) is a member of the ubiquilin family, actively implicated in the degradation of misfolded and redundant proteins through the ubiquitin-proteasome system and macroautophagy. UBQLN2 received much attention after the discovery of gene mutations in amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD). The abnormal presence of positive UBQLN2 inclusion in the cytosol of degenerating motor neurons of familial and sporadic forms of ALS patients has been newly related to neurodegeneration. Only recently, data have emerged on its role in liquid-liquid phase separation, in stress granule development and in the formation of secondary amyloid structures. Furthermore, several animal models are available to investigate its involvement in TDP-43 pathology and neuroinflammation in ALS. This review addresses the molecular pathogenetic pathways involving UBQLN2 abnormalities which are converging toward defects in clearance mechanisms. UBQLN2. C9ORF72 (Chromosome 9 open reading frame 72), SOD1 (Superoxide dismutase 1), TDP-43 (TAR DNA-binding protein 43) and FUS (Fused in Sarcoma) [Amyotrophic lateral sclerosis (ALS) is a progressive and fatal disorder associated with degeneration of upper and lower motor neurons . The disSarcoma) , 53, 61.UBQLN2 gene were found to be associated with dysfunction of autophagy [UBQLN2 is a shuttle protein implicated in the ubiquitin-proteasome system (UPS). One of the most actively studied mechanism in UBQLN2-related pathology is the mutant-related dysfunction of the UPS. However, its implication in the cytoplasmic mislocalization of TDP-43 into insoluble aggregates is also well described in ALS. More recently, ALS-linked mutations in utophagy , neuroinutophagy , 50 and utophagy . These rIn this review we will describe the structure and the function of UBQLN2, and we will propose an integrative mechanism for the pathogenesis of UBQLN2 in ALS and FTD.UBQLN2 gene, also called Chap1/Dsk2 or PLIC, is located on the Xp11.21 chromosome. UBQLN2 is a single-exon coded, 66 kDa protein member of the ubiquilin family [UBQLN2 gene are located in the PXX domain. Yet, it is unclear how the mutations impact the secondary structure and functions of the PXX domain. The 3-dimensional structure of UBQLN2 is formed by five β-strands, an α-helix of 3.5 turns and an additional 310-helix [The n family , 29. UBQn family . UBQLN2 n family  Fig. 1)UBQLN2 ge10-helix .Fig. 1ScUBQLN2 is located in the cytosol and has been reported to be mainly expressed in the brain, spleen, heart, liver, pancreas and other tissues . The oth2+ homeostasis and maintaining mitochondrial function  proteins. UBQLN2 can interact with the ubiquitin regulatory X domain-containing protein 8 protein (Ubxd8), which is localized in the ER membrane and it facilitates the transport of endoplasmic-reticulum-associated protein degradation (ERAD) substrates to the cytosol . UBQLN2 P497H measured the autophagic flux with an LC3 turnover assay [P497H compromised autophagy-lysosomal pathways in an age-related manner.The implication of UBQLN2 in autophagy is now well established. Autophagy, specifically macroautophagy, is crucial for the bulk turnover of redundant cellular components, including protein aggregates and damaged organelles. A specific region of the cytosol is isolated in an intracellular double membrane stretch called autophagosome, secondarily fusing with lysosomes for degradation , 43, 68.UBQLN2 mutations were first identified in five unrelated families, suffering of ALS/FTD [n = 23), fALS without mutations in SOD1, TDP-43 and FUS (n = 5), ALS with dementia (n = 5) and fALS with G298S mutation in TDP-43 (n = 21) [P506T mutation were analysed. All fALS cases exhibited co-localization of UBQLN2 and TDP-43 cytoplasmic inclusions in the brain and the spinal cord neurons [ ALS/FTD . From th ALS/FTD , 60, 64  ALS/FTD . The aut(n = 21) . Also, b neurons . Interes neurons , 17.TablG76V_GFP was detected in Neuro2a cells expressing mutant UBQLN2P497H [G76V_GFP degradation were significantly slower in UBQLN2 mutations (P497H and P506T) when compared to the WT, suggesting the impairment of the protein degradation pathway by UBQLN2 mutations. Another group took advantage of the endogenous Myc as a proteasome efficiency reporter, as it is quickly degraded by the proteasome when its synthesis is blocked by cycloheximide [P497H in Neuro2A cells sequestered lys48_ bound ubiquitin and resulted in a reduction in the efficiency of the proteasome [The degradation of misfolded or redundant proteins is critical for the maintenance of cellular health, specifically in neurons which are not proliferating cells. There is evidence that UBQLN2 mutations can provoke proteasome as well as autophagy impairments. First, an accumulation of the proteasome efficacy reporter UbiquitinLN2P497H . They fuheximide . Indeed,heximide . Those rheximide . RecentlP506T mouse, that UBQLN2 works with the HSP70 system for proteasomal degradation of insoluble ubiquitylated protein aggregates [Another study reported, with a knocked-in hUBQLN2gregates . Under ngregates . Defect gregates . They algregates . Thus, aLastly, optineurin (OPTN) is a ubiquitin-binding multifunctional adaptor protein and is mainly implicated in the autophagy processes. It has also been proposed to be an important factor implicated in regulation of inflammation . UBQLN2 WT or mutated hUBQLN2P497H in Neuro2A cells can promote the formation of TDP-43 cytoplasmic inclusions [It has been reported that cytoplasmic inclusions of mutant C-terminal TDP-43 colocalized with either WT or mutant UBQLN2 in co-transfected Neuro2a cells . UBQLN2 clusions , 27, 34.clusions , 49.P497H and hTDP-43G348C vectors led to the accumulation of cytoplasmic TDP-43. However, ubiquitin overexpression reduced the cytoplasmic aggregation of TDP-43 [P497H and hTDP-43G348C transfected cells. This assay revealed a significant reduction in proteasome efficacy in all transfected cells as compared to control cells. The presence of up-regulated ubiquitin levels corrected the proteasome dysfunction in cells transfected with hUBQLN2P497H and in cells co-transfected with both hUBQLN2P497H and hTDP-43G348C. These results suggested that the proteasome impairment caused by hUBQLN2P497H up-regulation may participate to cytoplasmic TDP-43 accumulation. In summary, UBQLN2 overexpression or mutation exacerbated TDP-43 pathology in vitro , a potent inflammatory mediator [P497H;TDP-43G348C mutations also exhibited increased levels of NF-κB in spinal cord as compared to TDP-43G348C mice [P497H transgene was only expressed in neurons. The increased inflammation markers could suggest that microglia were hyperactivated in reaction to UBQLN2/TDP-43 neuronal pathology. These results also suggested that UBQLN2 pathology may favorize neuroinflammation and the reduction of UBQLN2 cytoplasmic accumulation may be a potential treatment approach to reduce glial cells activation observed in ALS.The implication of UBQLN2 in inflammation has emerged in the last two to 3 years. The overexpression of hUBQLN2mediator . Neverthmediator . TDP-43 mediator , 48, 58.48C mice . The douStress granules (SGs) are cytoplasmic inclusions of proteins and maintenance mRNAs with the aim of promoting stress response proteins translation in stressful situations, such as oxidative stress, osmotic stress, infection, ER stress and inhibition of the proteasome . Under sStress granules contain various proteins, including fALS related proteins, TDP-43, FUS, hnRNPA1 and 2. A disturbance in stress granules homeostasis can lead to disruption of RNA processing  L619A in neurons could prevent UBQLN2 self-assembly and could inhibit LLPS of UBQLN2 [L619A induced a 50% increase in neuronal death compared to WT. Collectively, those results suggest that the UBA domain promotes self-assembly of the protein leading to an increase in UBQLN2 aggregation with toxic consequences for neurons.Ubiquitin is also a common component of SGs , 33. Thef UBQLN2 . Also, eThe LLPS capacity of a protein is based on its multivalent interactions in “sticker” regions which are separated by “spacers” . RecentlP497H under the control of the hUBQLN2 promoter [P497H was comparable to the levels of endogenous UBQLN2WT. Another group used a transgenic hUBQLN2P497H rat model with TRE-doxycycline system [P506T mice were generated and showed cognitive impairment but no motor deficits [Animal models are essential to study in vivo pathological mechanisms as well as to test experimental therapeutic avenues, and numerous animal models were generated for ALS research (recently reviewed in ). Severapromoter . The anie system . Their mdeficits . The knoP497S or hUBQLN2P506T mutations exhibited motor neurons loss and cognitive impairments [P497S mice and 40% of hUBQLN2P506T mice developed hindlimb paralysis. Interestingly, TDP-43 mislocalization could be noted in neurons. Transgenic mice overexpressing hUBQLN2WT also showed loss of upper motor neurons as well as hippocampal neurons. Nevertheless, the effects were less important than those observed in the mutant transgenic mice. Knockout models were also generated, but phenotypes were highly divergent between species (Table Drosophila melanogaster (DM) created a severe motor phenotype with TDP-43/Ubiquitin/UBQLN2 aggregation [Transgenic mice bearing Thy1.2-driven hUBQLN2airments . The levregation . The cauregation . ConsequP497H and hTDP-43G348C mutations using a NFH promoter with low levels of expression [P497animal models are summarized in Table Lastly, our team generated the first double transgenic mouse model harboring both hUBQLN2pression . The simCollectively, these multiple reports suggest that UBQLN2 is acting on various ALS pathological mechanisms and is not only causing an UPS dysfunction as previously recognized. It is now documented that UBQLN2 is acting on stress granules formation, on TDP-43 mislocalization into cytoplasmic inclusions, on cellular clearance pathways and neuroinflammation. Thus far, the pathological role of mutated UBQLN2 is more defined, but many questions remain on the exact role of the WT UBQLN2 in sporadic cases of ALS. Nevertheless, the tight control in the levels of UBQLN2 appears to be a primary factor for its role in the clearance pathway and stress granules formation. A small disturbance in its levels could promote oligomerization and trigger dysfunction in LLPS formation, inducing aggregates formation and causing toxicity in neurons. To our knowledge, the levels of UBQLN2 in tissues from sporadic ALS cases without UBQLN2 mutation have never been evaluated nor neuropathological studied and this question should be addressed. Indeed, the WT UBQLN2 form also appears to have a toxic role when overexpressed , 49. It


By cooperatively tuning the input power on the IDTs, we can manipulate the propagation direction of Iae such that the measured Iae can be deliberately controlled to be positive, negative, or even zero. We define the zero-crossing Iae as Iae can be switched with a ratio We implement a logic switch by using a graphene acoustoelectric transducer at room temperature. We operate two pairs of inter-digital transducers (IDTs) to launch surface acoustic waves (SAWs) on a LiNbO Recent developments in graphene field-effect transistors (GFETs) suggest that graphene holds great promise in radio frequency (RF) applications5. For digital electronics, adopting new materials as a successor to Si must perform excellent switching capabilities with a low off-state dissipation power and a high on/off current ratio7. Nevertheless, graphene shows a serious hurdle for its applications in logic circuits2, because the pristine graphene does not possess an energy bandgap1. As a result, GFET cannot be turned off efficiently, leading to a low on/off current ratio typically less than 102. Subsequently, the research efforts are geared toward two different directions: engineering graphene material to open a bandgap9, or exploiting layered 2D semiconductors with a naturally occurring bandgap, e.g. transition metal dichalcogenides (TMDs) and black phosphorus (BP)7.Graphene –a two-dimensional (2D) sheet of carbon atoms arranged in a honeycomb lattice– exhibits various unique properties beneficial for post-silicon electronicsIae. We will show that Iae induced by dual SAWs can be modulated by discretizing RF signals. In this regard, a graphene acoustoelectric transducer(GAET) can function as a logic switch. The switching performance is demonstrated by the successful generation and detection of the digital text carried by Iae with a switching rate up to few tens kHz.In this work, we report a different approach to implementing graphene for logic devices by utilizing acoustoelectric effects. Here graphene is used as a channel material to convert surface acoustic wave (SAW) into acoustoelectric current 10. SAW can be induced by distributed comb-like metallic structures, such as interdigital transducers (IDTs), deposited on the surface of the piezoelectric substrate. Triggered by the piezoelectric effect, the RF input signal at the transmitting IDT stimulates the SAW. For a typical SAW device, a second IDT is employed, served as a signal processing unit and a transducer, to convert the acoustic waves back into a RF signal. Nowadays, the SAW devices have been widely used in various RF signal processing techniques for telecommunications and sensors12.A surface acoustic wave is an acoustic wave traveling along the surface of the piezoelectric materials, with its displacement amplitude exponentially decaying into the material so that it is roughly confined within one wavelength beneath the surfacevs and the SAW attenuation factor Γ. For example, SAWs can interact with two-dimensional electron gas (2DEG) placed nearby and the corresponding changes in both vs and Γ have been used to probe the distinct electronic states of 2DEG16. In addition, the interaction between the SAW and the charge carriers of 2DEG can also induce a macroscopic direct current, acoustic current Iae, which is known as the acoustoelectric effect.The propagation of SAW is sensitively influenced by the local changes of the host medium, which causes the variations of the SAW velocity 25. Owning to the linear energy dispersion and gapless nature of graphene, electrons in graphene can absorb sound waves over a wide frequency range26 and in theory Γ is strikingly diminished as the Fermi level EF is tuned across the charge neutral point (CNP)20. However, graphene does not possess piezoelectricity because of its central symmetric lattice structure, unlike to GaAs-2DEG. The major obstacles in studying and utilizing the acoustoelectric effects of graphene lie on how to generate SAW and maintain its propagation under the control of EF. Early experiments reveal that SAW of graphene can be excited by placing graphene either on or in close contact to a substrate with high piezoelectricity, e.g. LiNbO3 substrate18. By incorporating ion liquid gate and IDTs, EF of graphene can be tuned across CNP, and Iae exhibits an ambipolar effect- the sign of Iae is reversed associated with the change of charge carriers from n- to p-type23. Furthermore, Γ of grapehene is extremely weak, approximately ~0.4 to 6.8 m−1 depending on the carrier density ns, which is three orders of magnitude smaller than that of GaAs 2DEG systems23. These fascinating properties make graphene an ideal material for various acoustoelectric devices, ranging from acoustic tweezers, branch switch, flip-chip devices etc.29.The acoustoelectric properties of graphene have been extensively studied30. The acoustic current in a closed-circuit measurement (or voltage in an open-circuit measurement) is induced by a loss of wave energy associated with a proportional loss of SAW momentum, which is analogous to a force applying on the absorber (the charge carriers of graphene in this study). For a 2D system, we can assume that the acoustic current density jae is proportional to Γ with the coefficient Λ and flows along the direction of SAW propagation31:i(=x or y) is the spatial index, x(y)-direction. It has been known that Λ can be described by16σ is the DC conductivity of graphene. We assume that both Γ and Λ are spatially uniform because graphene is an isotropic material. Note that one may need to treat Γ and Λ in a tensor form when the SAW propagates on an anisotropic substrate or the carriers are in the presence of an external magnetic field31.A theoretical model to describe acoustodynamic effects in semiconductors was developed by G. Weinreich23. Consequently, one can define a true zero-current state or an “off”-state at CNP although the channel is not completely closed. On the other hand, a fair on/off ratio ~20 has been reported by defining an on/off state away from CNP in our earlier study23. In principle, if the off-state is set exactly at CNP, one can get a much higher ratio (>107). There are competitive advantages to utilize GAET for logic devices. For commercial SAW filters used in the RF front-end, the device requires sufficient high-power durability. In general the SAW device can withstand power levels ≥30 dBm, which is high enough to generate Iae with a decent S/N ratio. Moreover, no quiescence power source is needed because GAET is activated by the energy of the RF input signals received by the IDT transceiver. Nevertheless, if one operated GAET like GFET that the RF signal is sent through the gate electrode4, the modulation speed of GAET would be too slow for practical applications23. It is mainly because the ionic liquid is adopted for the gate electrode in the present GAET design23. Note that the gate electrode made of conducting materials will severely damp the propagation of SAWs. This is the key bottleneck for GAET to be used for the logic devices.Because of the ambipolar effect of graphene, 3 piezoelectric substrate in a nearly orthogonal arrangement. Each IDT comprises two sets of interleaved fingers and the acoustic current density induced by IDT1 and IDT2 is indicated as jIDT1 and jIDT2, respectively. Two current sensing leads are placed along the positive x-direction , IDT1 functions as the source contact to inject the channel current and IDT2 serves as a gate electrode to turn “on/off” the device. We will demonstrate below that by digitizing RF signal applied on IDT2 or IDT1, the GAET can perform as a logic switch.Our design concept is illustrated in Fig. 3 substrate, graphene, four electrodes on graphene labeled as leads 1 to 4, and a micro-bead of an ion-gel coated on graphene33, a gate electrode of the polymer electrolyte for applying gate voltage Vg. The two sets of opposite ITDs, IDT1-IDT3 and IDT2-IDT4, are separated with a distance LT = 1.4 mm and backed by metallic strips to damp reflected waves. In this study, we only operate IDT1 and IDT2, and conduct their counterpart IDT3 and IDT4 as a passive receiver for checking the SAW properties. Each IDT comprises two sets of interleaved fingers with NIDT = 25 finger pairs made by 5 μm wide electrodes with 8/70 nm of Cr/Au. The acoustic aperture WT ~ 600 μm, the overlap between electrodes, is aligned between two opposite IDTs along the [011] direction of the z-cut single-crystal LiNbO3 substrate. The optical micrograph of device can be found in the Fig. λSAW determined by the pitch of the IDT electrode is 20 μm and the SAW velocity vs is approximately 3795 m/s34. The central resonance frequency f = vs/λSAW is estimated to be 190 MHz. Figure S21 as a function of frequency measured by a network analyzer (RS ZVA24). It exhibits a peak at approximately central frequency fc = 191 and 187 MHz for IDT1 → IDT3 and IDT2 → IDT4 respectively, which fairly agrees with the designed value.Figure 37. Graphene is gently placed between two IDTs, and tailored to a rectangular shape of length LG = 600 μm and of width WG = 400 μm. Caution must be taken to ensure that graphene residues will not short the Au electrodes of IDTs. Four electrodes deposited along the side border of graphene are used for resistance and acoustoelectric current measurements. They are made of an Au/Cr bilayer with 8/70 nm in thickness and 20 μm in width, among which 450 μm in length for leads 1 and 4, and 250 μm in length for leads 2 and 3  of graphene as a function of Vg, where V24 is the voltage measured across the lead 2 and 4, and I13 is the current passing through the lead 1 to 3. The R versus Vg trace of graphene reaches a maximum with resistance ~2.5 kΩ at CNP, where Vg ≡ VCNP = −0.549 V. We have measured five devices with the same structures and got consistent results. Data presented below are mainly obtained from one of the devices.Graphene is prepared by the chemical vapor deposition. We refer the readers to our previous publications for the details of graphene growth, characterization, and transfer proceduressee Fig. . FinallyIae measurement. Here we use IDT1 and IDT2 to generate the SAWs and take leads 4 and 1 to sense Iae, while keep the rest IDTs and electrodes inactive and open. We modulate RF signal at a frequency of 10 kHz and employ standard lock-in technique to measure Iae. Note that the propagation direction of the Iae measured by leads 4 and 1 aligns with that of the SAWs induced by IDT1. Figure Iae as a function of bias voltage Vg with various RF powers PIDT1 applied on IDT1 at the central frequency of 191 MHz, while keeping IDT2 inactive. With the present arrangement of the current leads displayed in Fig. Iae is positive, negative, or zero as graphene is biased in the hole-rich regime, electron-rich regime, or at Vg ~ VCNP. The gate bias dependence of Iae manifests the unique Dirac dispersion relation of graphene23. We note that an on/off ratio of Iae up to 107 can be achieved, for example, if one defines the on-state at Vg − VCNP = 0.5 V and the off-state at Vg = VCNP for PIDT1 = 10 dBm. Extracted from Fig. 18, as indicated in Eq.  and a duty cycle D(=0.2). Oscilloscope traces of the applied RF-signal on IDT2 is shown in Fig. Iae taken from the oscilloscope at various PIDT2. As PIDT2 is within active time of the pulse, Iae exhibits a dip feature due to the cancellation by negative Iae. As PIDT2 increases up to 6 dBm, Iae is nearly vanished. Here the GAET functions as an active-High logic switch that processes information as either a “1” or a “0”, depending on whether the switch is off − getting finite acoustoelectric current Iae− or on − Iae measured zero. We estimate the on/off ratio of Iae is approximately 104 based on the noise level of the on and off states.Next we will show that by dynamically controlling the on/off state of Iae, we note that the maximum switching rate - the key parameter to limit sampling rate in digital communications - is determined by the transition time of Iae in response to the modulated RF pulse. We can switch Iae simply by modulating RF signal applied on a single IDT. Unlike the dual-SAW scheme discussed above, one can view such operation as an active-Low logic switch. In terms of GFET, graphene provides a nature 2D conducting channel such that a digital on/off state can be simply achieved by modulating the source-drain bias without applying a gate voltage, if the signal gain is not a concern. On the other hand, a RF signal can be directly converted to an electric signal in GAET. In this regard, GAET has an advantage over GFET as a logic switch. Figure Iae by operating IDT1 alone. Figure Iae pulse waveform generated by a square wave-modulated PIDT1(=17 dBm). The on-time ton is set about 20 μs. Based on the 90% and 10% threshold levels of the pulse amplitude, we determine the Rise tR and Fall tF time to be about ~6 μs. Figure Iae with different modulation frequencies. For comparison, we normalize Iae to its quiescence value I0(=1.6 μA), and time to the modulated period Tm. As displayed in Fig. Tm up to 20 μs, corresponding to dynamic switch rate of 50 kHz. That is to say, the peak value of the Iae waveform with a pulse width ~4 μs is within 90% of the full amplitude. The propagation delay time tp - a parameter to evaluate the jitter effects- is about 0.6 μs. We find To characterize the response time of switching CIDT ~ 6.25 pF and the circuit input impedance around 448 Ω, giving rise to the RC time constant around 2.8 ns, which is much shorter than the tR and tF measured. Therefore, we argue that the intrinsic RC delay is likely due to the impedance mismatch. We conceive the switching rate can be immediately raised up by shrinking the channel width of graphene. To optimize impedance-matching one may employ tapered IDTs, functioning as an impedance-transformer40, which impedance match to 50 Ohm transmission line at one end and to the characteristic impedance of the tailored graphene and the leads at other end. To this end, one also needs to characterize the output impedance of GAET and match it with that of the transmission line extended to the measurement ports.Data shown in Figs 41 and would be interesting subjects for future studies.The dynamics of acoustoelectric effects of emerging post-graphene 2D materials – e.g. transition metal dichalcogenides (TMDs) and black phosphorus (BP) are much less exploredvs and the channel width. There are several approaches to increasing the switching rate. One may try to fabricate the device on substrates with a relatively large electromechanical coupling coefficient, e.g. 42° Y-X LiTaO3 or 64° Y-X LiTaO3 substrate, which have been widely applied to the SAW devices for mobile communications. However, the tradeoff is that larger leaky wave may yield a lower Iae. In principle, a high-slew rate of Iae can be obtained from a wide-band SAW device, which can be implemented by an apodized IDT design or simply reducing the number of fingers in the IDT. A narrower channel width may give a shorter response time, but it in turn reduces Iae or requires a larger PIDT. This drawback makes GAET unsuitable for latch operation. Regarding the operation scheme, a single IDT is sufficient for the active-Low switch. Using collinear dual IDTs such as IDT1 and IDT3 (or IDT2 and IDT4), one can apply lower and balanced PIDT for the active-High switch. Nevertheless, evident interference due to reflected waves should be taken into account. For the dual-SAW operation, two SAWs can be excited at different frequencies. However, it makes SAW attenuation become more pronounced at a higher frequency. In addition, by properly utilizing four leads and IDTs, we can directly measure Iae to make GAET act as an acoustoelectric branch switch28. We note that recent studies reveal several intriguing interface elastic properties of van der Waals materials44 and may offer a mean to speed up the switch rate of GAET by engineering the interfacial acoustoelectric properties. Maybe the switch rate is slow (audio frequencies) and the design is a little complex, we think that the GAET opens a route for developing graphene-based logic switch. In this work, we only demonstrate the feasibility of GAET as a logic switch and leave aforementioned issues for future studies.Finally, we wish to make few comments on future development of GAET logic devices. The ultimate response time of the GAET switch is limited by the SAW velocity 4 at room temperature. By manipulating the propagation direction of Iae, the measured values of Iae can be fine tuned to zero - an ideal off state for a logic switch. We demonstrate the dynamic switch rate of Iae can be up to 50 kHz by modulating the amplitude of the input RF-signal applied on IDTs. By deliberately controlling the digitized RF-power applied on a pair of crossed-IDT or a single IDT, the output Iae can be either active-High or active-Low, respectively. The digital modulation rate can achieve ~10 KB/s. The performance of the GAET is suitable for processing digital audio signals. Even the switch rate is slow, our work provides a means to integrate the SAW device and the acoustoelectric effects for future development of graphene-based logic devices.In conclusion, we present an accessible operation scheme of GAET for a logic switch with a moderate on/off rate of ~10


When calibrated, the weather station results were well within ±3% RH. During the winter 2015/2016 weather stations were placed in the living room in eight wooden buildings. A period of significantly increased fire risk was identified in January 2016. The results from the outdoor sensors compared favorably with the readings from a local meteorological station, and showed some interesting details, such as higher ambient relative humidity for a home close to a large and comparably warmer sea surface. It was also revealed that a forecast predicting low humidity content gave results close to the observed outdoor weather station data, at least for the first 48 h forecast.During January 2014, Norway experienced unusually cold and dry weather conditions leading to very low indoor relative humidity (RH) in inhabited (heated) wooden homes. The resulting dry wood played an important role in the two most severe accidental fires in Norway recorded since 1923. The present work describes testing of low cost consumer grade weather stations for recording temperature and relative humidity as a proxy for dry wood structural fire risk assessment. Calibration of the weather stations relative humidity (RH) sensors was done in an atmosphere stabilized by water saturated LiCl, MgCl Fire is a major cause of accidental injury and results in over 300,000 deaths annually ,2,3. TheIn these areas, as well as in the majority of the country, wooden homes dominate the building style due to the abundance of wood as a construction material. One of the precursors for the severe fires was ambient subzero temperature air of low relative humidity for a few weeks before these fires. This resulted in dry outdoor combustible materials and extremely dry indoor wood in inhabited (heated) wooden structures ,6. A cor2 capacitive high speed sensor with 35 s response time [However, such an application reveals the need for low cost sensors for recording ambient and indoor temperature and RH. Recently, a fast TiOnse time  and an ense time  have beeThe objective of the present work is to report on the experience of testing consumer grade weather stations for relative humidity measurements as a proxy for the winter fire risk in wooden constructions . Section−1) is the molecular mass of water and −1 mol−1) is the molar gas constant.The relative humidity in air is dependent on the absolute water vapor content as well as the air temperature. The saturation vapor pressure of water is a near exponential function of temperature and may be described by :(1)Psat=Cooling this air so that it theoretically contains more than 100% relative humidity, the surplus water condenses at small dust particles, etc. to make fog. It is a quite normal phenomenon to observe fog in a cold night and morning dew on the grass after a cold night. It should be noted that cooling the air results in a volume reduction, which also increases the water vapor concentration. The focus of the present paper is, however, the indoor heating of the air in cold climates. Heating the cold ambient air (at constant pressure) to the higher indoor temperature, www.eklima.no. In the Haugesund area, the meteorological station at the Haugesund airport is well equipped and professionally maintained for recording data relevant for the present study. Based on retrieved temperature and relative humidity data, the historic values for the ambient water vapor concentration may be calculated by using Equations (1) and (2).In Norway, historic weather data at 1 h frequency may be retrieved for free from a number of meteorological stations by the application provided at 3, was indeed very low compared to the rest of the year. If such dips are short, i.e., less than a day, a wooden home does not have time to adjust to the new dry conditions. This is partly due to the finite air exchange rate as well as slow diffusion processes of water in wood and humidity being released from the drying wood to the indoor air. However, if the dry conditions persist for some days or weeks, the wood dries out and the fire risk related to the drier wood increases [The calculated outdoor water concentration based on data from the meteorological station at the Haugesund airport for the period July 2015 through June 2016 is shown in Indoors, there are usually also sources of moisture supply present, e.g., humans, pets and pot plants. Hygroscopic materials, e.g., wood and other cellulose based materials such as upholstery, clothes, carpets, etc. may also release humidity when the indoor climate gets drier. If the indoor air gets more humid, these materials absorb humidity from the air. These materials may also show hysteresis when changing from the mode of adsorption to desorption and vice versa . Since sThe best way to measure the water content of indoor combustible hygroscopic materials would probably be to record the mass change of selected objects. This is not easy to do with a good precision. Measuring the indoor relative humidity does, however, provide a good alternative for obtaining information about the indoor climate contribution to structural wood fire risk. Recording the humidity levels, and keeping track of especially low indoor humidity levels, gives a good indication about the structural wood fire risk development. Warnings may be considered based on weather forecasts so that focus can be shifted to monitoring indoor relative humidity development and fire risk evaluations when needed.The first idea was to record the mass of representative indoor wooden objects in order to consider their combustibility. This could be e.g., wooden plates of different thicknesses placed on separate balances, and then record the mass at a convenient frequency. The recorded data could then be transferred via the internet to researchers analyzing the data. It was, however, realized that it would be quite challenging to e.g., have sufficiently stable balances. A number of precision balances would also have been very costly. During discussions with an automation engineer , it was A very low cost, and not web based, weather station was therefore purchased and evaluated against a precision psychrometer . The psychrometer calibration data are presented in The weather station and the precision psychrometer were placed in a 17 L transparent plastic box with a lid. Operation of the precision psychrometer without disturbing the internal atmosphere was provided for by a 2.5 mm plastic rod through a sealed hole. The internal relative humidity was adjusted to get varying relative humidity (RH) in the plastic box. To get a low RH, the box was taken outdoor and filled with low temperature air which became dry when adjusted to indoor conditions at 22 °C. To get high RH, droplets of water were allowed to evaporate in the plastic box, inspired by a previous study . Compari2-concentration. The outdoor unit sends the recorded data to the indoor unit, which automatically forwards the recorded indoor and outdoor data to the Netatmo servers for instant or later user access and data retrieval. The complete weather station, including indoor and outdoor units, is shown in Eight Netatmo weather stations , as sho® SP10302D Pt100 Temperature Reference Instrument, Ahlborn Mess- und Regelungstechnik GmbH, Holzkirchen, Germany) for the temperature interval relevant for the indoor and outdoor sensors. Only minor adjustments were needed to achieve temperature recordings well within ±0.3 °C for the temperature region of interest in the present work.The producer of the Netatmo units states that the equipment can read temperatures within ±0.5 °C and relative humidity (RH) within ±3% RH. The PC interface allows for a temperature calibration by the user. In the present work it was decided to calibrate the temperature output of the units against a precision temperature instrument , the sensors to be calibrated were placed, four at a time, in a transparent plastic box of dimensions 50 cm by 40 cm by 30 cm height. A lid was applied to the box and the USB power cables for the indoor units were let out through the back wall. The hole was sealed to prevent air exchange with the surroundings.2 and NaCl, all salts pro analysis quality, were used to respectively achieve RH values of 11.3 ± 0.31% RH, 33.07 ± 0.18% RH and 75.47 ± 0.14% RH [Water saturated inorganic salt solutions, i.e., LiCl, MgClSaturated water salt solutions were placed at four 8 cm diameter plastic plates. Two of these plates were placed on the plastic box floor level and two plates were placed at about 10 cm elevation. This was done in order to quickly obtain equilibrium RH conditions after any handling of salts or weather station units in the plastic box. Air circulation within the box was achieved using a USB fan, which also speeded up the process of establishing a constant RH level. When changing to NaCl solutions, water droplets were added to an aluminum plate (for good heat transfer to the droplets ) placed The previously mentioned battery powered precision psychrometer was also placed inside the plastic container for instant recordings of temperature and relative humidity. As with the preliminary testing, a plastic rod was arranged for operating the psychrometer. The psychrometer readings were observed through the transparent plastic box lid. The box was loosely covered by sheets of aluminum foil to reflect light radiation to prevent any plastic box “greenhouse effects”. The system was then left to achieve equilibrium conditions governed by the applied saturated salt solution. The psychrometer readings were used to confirm that a constant RH level was achieved inside the plastic box. Another two hours were allowed for ensuring constant weather station readings. The temperature and RH for each weather station unit were then obtained by the web interface together with the psychrometer readings. The procedure was repeated for all the relative humidity sensors (four at a time) and for all the saturated inorganic salt solutions. Separate testing was done to establish the sensor response times when exposed to a sudden change in relative humidity.The sensors generally gave very erroneous results compared to the equilibrium conditions ensured by the water saturated salt solutions. Several of the detectors were up to, and even more than, 10% RH wrong either at low (11.3% RH) or high relative humidity (75.5% RH). The sensor outputs were, however, very linear with respect to the real relative humidity. This indicated that a linear equation could be used for converting the recorded result to correct relative humidity values. A linear correction curve, similar to the one shown in Equation (4), was therefore fit to the RH data recorded for the indoor units (at 22 °C) and outdoor units (at 2–5 °C). The results are presented in It should be noted that when extrapolating the linear curves based on the correction coefficients presented in A number of tests were also done in the range 40% to 60% RH, where the precision psychrometer, corrected by its calibration curve, was used as the reference. No deviation from linearity was detected for any of the weather station units. To the surprise of the author, when testing an outdoor unit at indoor temperatures, the results were still within 2% RH. The calibration of the outdoor sensors at 2 °C to 5 °C was therefore taken as valid also for temperatures below 0 °C.The sensor response time was also tested. This was done by setting the weather station number 1 indoor and outdoor units in an atmosphere stabilized by water saturated NaCl solution for 6 h. Then, the sensors were suddenly taken out and placed in the measurement container where the atmosphere was in equilibrium with water saturated LiCl solution. It should, however be mentioned that this does not represent a clean cut step function from humid (75% RH) atmosphere to dry atmosphere (11% RH) since during the sensor handling, the air in the plastic box chamber was partly diluted by indoor air of about 35% RH. Nevertheless, compared by the recording time of several hours, given the experimental setup this was as close to a step function as practicably possible. The results are shown in The most interesting period during the winter 2015/2016 was in January 2016. Early in January, the wind direction changed and the wind came from the mountain plains east of Haugesund, Norway. This led to adiabatically heated ambient air and lower than normal outdoor relative humidity. The recorded temperature and relative humidity from the local meteorological station at Haugesund airport for January 2016 is presented in The adiabatically heated dry subzero temperature air is easily identified in the first days of January. However, as both the temperature and the relative humidity vary, it is easier to interpret the data when studying the actual ambient air water concentration.The water vapor concentration calculated by Equations (1) and (2), based on the Netatmo weather stations outdoor temperature and relative humidity at two homes, as well as the Haugesund airport, is shown in The indoor relative humidity recorded at the homes presented in Especially during winter time, with large outdoor to indoor temperature differences, there will be, and should be, sufficient air changes in a building to prevent rot formation in colder parts of the thermal insulation, etc. Due to the chimney effect, the indoor air will gradually be exchanged with ambient air. The ambient air entrained into the home is then heated to the indoor temperature. Wind pressure also increases the air change rate. Indoors, there will usually be some moisture gain in inhabited buildings as a result of persons and pets breathing or perspiring, dishwashing, pot plants and wood sorption processes. The wood sorption processes may go both ways, i.e., represent a positive or negative humidity gain. This also holds for other hygroscopic materials, such as furniture upholstery, pot plant soil, etc. However, assuming that there is no moisture gain, and that the ambient air is heated to the indoor conditions, a theoretical indoor relative humidity may be calculated based on the ambient conditions. The indoor weather station unit supplies the indoor temperature needed for the calculations while the ambient temperature and RH may be taken from the outdoor unit or from the local meteorological station. The best way is, however, to record the indoor RH directly, as seen in It has recently been demonstrated in ¼ scale wooden compartments that the time for reaching flashover, i.e., the sudden transition from a gradually increasing fire to a fully engulfing compartment fire, was very dependent on the wood fuel moisture content (FMC). At equilibrium conditions at 20% RH, the wood equilibrium moisture content (EMC) is about 4.5% . This dr31 December 2015, at 23:00, a weather forecast API from the Norwegian Meteorological Institute was run to retrieve the forecasts for the following 10 days period. For the first 48 h, the data are detailed to each hour. Then, the data is gradually presented with less frequency. Five days later, the API was run again supplying data for the following 10 days period. The calculated ambient air water concentration based on the forecasted data is presented in The only outdoor weather station sensor results that differed significantly from those obtained by the other sensors were from the home in Skudeneshavn, see While the other homes studied were close to the town of Haugesund, the one standing out was in Skudeneshavn, i.e., on the southern tip of the Karmøy island. As can be seen in middle left part of The major fjord Boknafjorden, between Haugesund and Stavanger, has open water the whole year while the inner parts of the attached smaller fjords are covered by ice in January. In wind from east, the air passing over the open sea has a long fetch and therefore a long contact time for picking up humidity from the open water surface before arriving at Skudeneshavn. This is especially the case during winter time when the sea has a temperature well above the ambient air temperature, and when the ambient air from the east is dry due to adiabatically heating. The reason for the unit in Skudeneshavn showing the highest RH values is therefore most likely due to the dry wind from the east picking up humidity on this 25+ km long fetch during the first 12 days of January 2016.The smaller fjord arms and most upwind lakes east of Haugesund were covered by ice during January 2016. The other weather stations close to the town of Haugesund, as seen in the upper left part of The purpose of this study was to test whether consumer grade weather stations for recording temperature and relative humidity could be used for indicating structural wooden home fire risk during winter time. The present work demonstrated that calibration was needed for the relative humidity sensor results to be within ±3% RH. The correction curves were simple linear equations. Without calibration, the readings were quite erroneous, i.e., the errors in relative humidity were up to more than 10% RH.2 and NaCl pa salt saturated water solutions. Internal air circulation was ensured by an USB powered fan. This represented a low cost setup for the relative humidity calibration. An available high precision temperature unit was used to calibrate the weather station by the built-in user based temperature calibration app. The recorded temperatures were well within 0.3 °C when tested after this user calibration. Using the high precision temperature unit may, however, be seen as an overkill since a normal type K thermocouples would probably have been sufficiently accurate for the temperatures of interest in present work.The calibration was done in a transparent plastic box where the air was conditioned by LiCl, MgClThe precision psychrometer was used to check that the inorganic salts did indeed produce the correct relative humidity. This was also in principle not necessary, as the saturated salt solutions would ensure equilibrium conditions at a known relative humidity level . The psyThe selected weather stations had a built-in web application which allowed for remote retrieval of the data recorded at 5 min intervals. The recorded data was downloaded in the form of spread sheets. It was therefore easy to apply the proper relative humidity correction equation for each indoor and outdoor detector unit.The tested weather stations had a resolution of 1% RH. This made it difficult to detect any weather station hysteresis regarding the relative humidity recordings. The weather station response was slow, i.e., a time period of about 2 h was therefore allowed to ensure correct results. The sensors can therefore not be used in situations where a fast response time is required. When the ambient water vapor concentration decreased considerably in January 2016, it was seen that a typical home needed a few days to equilibrate to the new and drier condition, as seen in −1 allows for detecting quite rapid changes in the indoor relative humidity, e.g., as a result of airing. However, given the slow response of the units, i.e., close to two hours, any such potential sudden changes in indoor relative humidity could not be discovered. Peaks due to cooking activities were, however, discovered. Due to the slow response, the peak values were probably not reliable as the sensor recordings were probably lagging behind such rather rapid changes in indoor relative humidity.In principle, the measurement frequency of 12 hThe weather station response time must be compared to the building response time, i.e., a few days. The conservative two hours weather station response time was an order of magnitude faster than the building indoor response time. This was taken as a proof of the sensor response time being sufficiently fast for the purpose of the present work, i.e., demonstrating that consumer grade weather stations can be used to monitor the dry indoor climate fire risk levels of wooden buildings.It was clearly seen that the indoor sensor had a longer response time compared to the outdoor sensor when tested under the same conditions, i.e., 2 h versus 1 h to 95% of a step change in relative humidity. This may simply be due to the larger internal air volume of the indoor sensors. For future measurement campaigns it is recommended to try to optimize the response time by e.g., allowing for better air convection and thereby faster response.During the calibration, the outdoor relative humidity sensors were, as always, powered by internal batteries. The indoor relative humidity sensors were, however, supplied USB power from transformers outside the box, i.e., the current wires had to be led through the wall. This was also the case for the USB fan power cable. Instead of relying on external power, using USB power banks for supplying these units would take away the clutter of wires through the wall. Utilizing USB power banks as the power supply source are therefore recommended for future calibration and characterization studies.The accuracy of the recordings, after the calibration curves were established and applied to the retrieved data, was found to be within ±3% RH. This was also the case for three weather stations that were tested after four months of operation during December 2015 through March 2016. This accuracy was still well within the goal for the present study. Advanced relative humidity sensors may display results far better than this, and with response times of 35 s  or even 2 may be available at hardware stores as an ice melting powder, at least in cold climate areas. MgCl2, which in contrast to LiCl, is not poisonous, may therefore represent a safe second calibration point.An interesting research possibility regarding web based weather stations may be related to the geography teaching for primary and secondary schools. The influence of the sea and the mountains on the local relative humidity, as clearly observed in the present work, may be demonstrated in the class room. The changes in relative humidity when the temperature is changing may also be worthwhile presenting to school children. The calibration procedure for teaching purposes may be done without using pro analysis quality salts. Commercial grade NaCl is available in any grocery store, though maybe producing equilibrium conditions 1% RH off due to a minor content of other salts. Consumer grade MgClAnother research possibility may be to use private weather stations for suppling data for increased wildfire risk awareness, especially during summer time , but alsThe main conclusion of the present study is that consumer grade weather stations, at least the type tested in the present study, have been shown to quite accurately measure the indoor and outdoor relative humidity when properly calibrated. This indicates that such weather stations could become central in a future attempt to develop a cold climate structural fire risk warning system.