Solid substrates often induce non-uniform strain and doping in graphene monolayer, therefore altering the intrinsic properties of graphene, reducing its charge carrier mobilities and, consequently, the overall electrical performance. Here, we exploit confocal Raman spectroscopy to study graphene directly free-floating on the surface of water, and show that liquid supports relief the preexisting strain, have negligible doping effect and restore the uniformity of the properties throughout the graphene sheet. Such an effect originates from the structural adaptability and flexibility, lesser contamination and weaker intermolecular bonding of liquids compared to solid supports, independently of the chemical nature of the liquid. Moreover, we demonstrate that water provides a platform to study and distinguish chemical defects from substrate-induced defects, in the particular case of hydrogenated graphene. Liquid supports, thus, are advantageous over solid supports for a range of applications, particularly for monitoring changes in the graphene structure upon chemical modification. Here, the authors report water as a superior platform to suspend graphene compared to solid substrates that induce non-uniformity and do not provide structural flexibility. They utilize confocal Raman spectroscopy to study graphene floating freely on the surface of water to show that a liquid support relieves the pre-existing strain. Use of supporting substrates facilitated its exploitability and prompted the development of the vast variety of graphene-based devices, such as field effect transistors4, transparent conducting electrodes5, gas and pressure sensors7, DNA single-molecule detectors, to name a few9. Although being widely adapted for the fabrication of current graphene-based devices and technologies, solid substrates largely affect graphene due to doping and induced strain, and thus hinder graphene’s intrinsic properties18. The effect is even more prominent for CVD -grown graphene samples, in which numerous inhomogeneities, inevitably caused by the growth and transfer processes, result in a wide variability in the band structure (and thus Raman signature)23 not only from sample to sample, but also from spot to spot within a single graphene sample. Here we study graphene supported by liquids, namely graphene at liquid/air and liquid/liquid interfaces, which provide well-defined interfacial boundaries, unlike solid/air interfaces.Graphene is typically perceived as a two dimensional film with outstanding electrical and optical characteristics, but impracticable as a fully self-standing material and, therefore, necessitating a solid support24. However, the exact effect of liquids on the morphology and the properties of large sheets of CVD graphene has not been ascertained yet. Although Raman spectroscopy has been recently successfully applied to characterize natural graphene flakes exfoliated in water26 in that case Raman spectrum is acquired as an average spectrum over all dispersed flakes and does not provide information about strain level and deviations in a single graphene flake. Moreover, no characterisation of CVD graphene at liquid–liquid interfaces has been reported so far.Graphene caged between two immiscible liquids displays strikingly higher charge carrier mobilities as compared to the same (e.g. grown under the same conditions) graphene supported by solid substrates, presumably attributed to fewer contamination and the absence of scattering from the substrate18. Additionally, statistical analysis of graphene Raman peaks showed that also the variations of strain and doping values across a graphene sheet are significantly smaller when supported by liquids, owing to more homogeneous and molecularly defined graphene-liquid interface, as opposed to a graphene-solid interface. We find that such exceptional stability of the Raman signature of graphene in a liquid environment can be used to characterize changes in the properties of graphene upon hydrogenation, and upon modifying the composition of liquid environment.In this work we demonstrate that liquids can be a standalone support for graphene and allow for important insights into intrinsic properties of graphene that are difficult to access otherwise. By applying confocal Raman spectroscopy to CVD-grown graphene free-floating at water/air and water/liquid interfaces, we found that graphene supported by liquid(s) undergoes very small to zero strain and doping effect, posing stark contrast with “conventional” solid-supported graphene, known to always be subjected to strain and doping28. Similarly, the use of a biphasic mixture of water (or aqueous etchant solution) with a nonpolar liquid causes the graphene/catalyst stack to float in between the two immiscible phases, which after the catalyst etching yields graphene free-floating at the liquid/liquid interface24. Such biphasic designs have been mostly employed for transferring CVD graphene and are advantageous over the conventional techniques in terms of preserving graphene’s intrinsic properties, particularly because graphene supported and protected by liquids on both of its sides is less subjected to contamination and mechanical perturbations29. However, up to now the only experimental insight into the graphene properties in situ at liquid/liquid and liquid/air interfaces has been the increase in charge carrier mobilities as compared to solid-supported graphene samples24, which indeed could be indicative of reduced contamination and strain.Graphene floats when placed on the surface of water due to the density and water surface tension. This property is routinely used when transferring CVD graphene from a catalyst substrate – the graphene/catalyst stack is placed on the surface of an aqueous solution of an etchant until the catalyst is fully dissolved and the graphene sheet remains free-floating at the water/air interface to be transferred further24) and graphene transferred onto SiO2/Si wafers . All graphene samples were grown according to the same growth protocol. The measurements were conducted at two excitation wavelengths, 457 nm and 532 nm respectively , see Fig. Here, we performed an extensive Raman study of a single-layer graphene at water/air, water/1-octanol and water/cyclohexane interfaces; graphene on copper (as-grown), free-standing graphene  or at ~2730 cm−1 (for 457 nm excitation wavelength). The G band originates from a first-order one-phonon scattering process and the 2D band from a second-order two-phonon intervalley scattering process, and are both typical of all sp2 carbon materials30. The frequencies, intensities and linewidths of the G and 2D bands of graphene are affected by the laser excitation energy (of the G band negligibly), number of graphene layers, strain and doping31. Presence of defects in graphene lattice  breaks the symmetry and activates the D band at ~1350 cm−1. The relative intensity of the D band with respect to the G band is commonly used to characterize the amount of defects and disorder in graphene materials.The two most intensive Raman bands of pristine graphene are the 2D band of graphene and one of the bands of 1-octanol at ~2730 cm−1 measured at 457 nm laser wavelength. But, given that the 2D band of graphene is at least three times as intensive, the overlap does not hinder the determination of the 2D band position , while no information about the location of the interface can be obtained by profiling the peaks of the liquids , and, in fact, can be quantified based on the shifts of the Raman bands31. Moreover, a correlative analysis of the G and 2D peaks frequencies allows for the disentanglement of the effects of strain and doping30. For that, the measured frequencies of G and 2D bands are plotted on a scatter plot with a non-orthogonal strain-doping framework . The correlation maps at 457 and 532 nm wavelengths were recalculated based on a 2D mode dispersion of 100 cm−1 eV−1 (ref. 35).The detailed analysis of Raman peaks shifts provide information about strain and doping in the graphene lattice, and, therefore, about the effect of the substrate and environment on graphene intrinsic properties. Strain and doping induced by the substrate and by the environment are known to alter the frequencies of the Remarkably, the correlation analysis displayed two critical distinctions of graphene supported by liquids from graphene supported by solid substrates and from free-standing graphene: very small absolute values and very small deviations of strain and doping induced by the liquids.15. In fact, the broadly scattered data points and wide frequency histograms in Fig. 2 and free-standing graphene indicate wide variations of strain and doping in these samples. We observed that graphene on copper (the growth substrate) undergoes a wide range of strain values – from −0.8% (compressive strain) till 0.7% (tensile strain) with no evident dominating values , in which the zero strain area is only in the centre of the suspended areaues Fig. . The wid37. Strain is known to vary significantly from spot to spot in suspended graphene films depending on the position of the spot towards the centre and the supported part36. Importantly, the measured strain values for free-standing CVD graphene are higher than those reported for an exfoliated free-standing graphene flake36, demonstrating that the CVD growth and possibly the transfer process induce the strain field that remains in graphene even when it is suspended, i.e. is in a theoretically zero- or low-strain geometry.Similarly, free-standing graphene exhibits very wide strain variations of −0.1–1% Fig. , c, indi2 substrate is known to have a strain relaxation effect on graphene21 and, agreeably, graphene transferred onto a Si/SiO2 wafer exhibits much narrower data scattering and strain variation from −0.3% to 0.2%  can also be used for monitoring strain and doping in graphene  than those of graphene on solid substrates, leading to less accurate determination of peak widths. The positions of peaks maximums, on the other hand, are not affected by increased noise level and can be determined accurately. Interestingly, the mean values of FWHM of the G bands of graphene on liquids are very close to that of graphene on copper and greater than those of graphene on Si/SiO2 wafer and free-standing graphene, indicating that the intrinsic charge density of the graphene is not affected by copper and the liquid supports  of the ene Fig. . A narroImportantly, the observed effect is stable in time, and the Raman signature and statistical distributions of the strain and doping values in graphene-on-water remained unchanged even after floating on the surface of water for eight days  results in an articulate relaxation of strain and reduction of doping level in graphene sheet. Additionally, the spot-to-spot deviations of strain and doping within the graphene sheet are significantly smaller for liquid-supported graphene, indicating more uniform properties of the graphene surface.G and 2D bands positions  and relative intensity (ID/IG ratio) of the Raman D band arising from the formation of C–H bonds and rehybridization of the graphene lattice46. Two types of samples with different hydrogenation degrees were prepared using a hydrogen plasma on as-grown graphene on copper (see Methods for details) – with plasma treatment duration of respectively 10 s and 60 s47. Raman spectra were recorded for a pristine graphene on copper and on water (same graphene sample before and after etching the copper and replacing the etchant with pure water) and for hydrogenated graphene samples on copper and water (same samples of hydrogenated graphene before and after etching the copper and replacing the etchant with pure water), Fig. Finally, we tested our technique for studying changes in the properties of graphene on the example of hydrogenation of graphene. Hydrogenated graphene (h-G) is typically characterized by the position , while in the case of h-G/Cu the multimodal distribution of wD could be caused by either presence of different types of defects (sp3 carbon atoms and other defects not related to hydrogenation) or by doping effect49. The samples of h-G/Cu and h-G/water are essentially the same sheet of graphene tested before and after copper etching, and, therefore, have identical types and amounts of defects. The main differences between the samples (accounting for the difference in D peaks) are the different levels of strain and doping induced by copper and water. In fact, although strain per se does not generate a D peak in graphene, the strain fields in graphene induced by copper can activate defects such as interstitials and vacancies along the grain boundaries of graphene 50, resulting in the shift and broadening of the D peak. This does not take place in the samples of h-G/water, because of lower strain induced by water .First, for the samples that underwent 10 s of hydrogenation, h-G floating on water have much narrower distributions of the ter Fig.  suggestster Fig. . AdditioD mode frequency and alter the D mode intensity51. As shown in Fig. D peak frequencies and intensities.In addition to strain-activated defects, doping is also known to cause shift in the D peak. Furthermore, not only the wD, but also the ID/IG ratio displays a lower variability across the h-G sheet when supported by water as opposed to copper  hydrogenation of the graphene sheet  of doping levels than h-G/Cu (within 15 × 1012 cm−2), which confirms that doping can be one of the reasons for the inhomogeneity of the D band position and intensity in the case of h-G/Cu. Similarly to pristine graphene, hydrogenated graphene is also subjected to greater and less uniform strain on copper, varying from −0.6% to 0.1%, than it is on water, where the strain varies from -0.2% to 0%  and is, therefore, a better indication of hydrogenation than the D peak of h-G/Cu. Interestingly, comparison between the ID/IG distributions of h-G/water in Fig. 53. Even more pronouncedly than in the case of 10 s hydrogenation  and possibly the presence of strain-activated defects , which adapts to and takes the shape of the surface the liquid is in contact with, i.e. graphene in our case62. Homogeneity, molecular smoothness, structural adaptability of liquid surfaces are direct consequences of the weak, soft intermolecular interactions and are universal properties of all liquids, independently of their chemical nature61. Remarkably, various liquid interfaces relax and unify strain in graphene down to similar values, indicating that the structural, rather than chemical, properties of liquids are responsible for the strain relaxation effect.A balance between attractive forces and thermal, repulsive forces enables free diffusion of molecules in fluidsD, G and 2D band remain unaffected by liquid substrates. Using liquids to support graphene, thus, can be beneficial over solid substrates whenever the properties of graphene need to be accurately monitored. Another big advantage of using liquid supports for graphene is that it does not require any handling or transfer of graphene. This essentially means that (1) obtaining and characterising graphene on water are technically easy and inexpensive (2) the results of the characterisation are highly reliable, because graphene is not contaminated (3) sample-to-sample variability is minimal due to the natural perfect uniformity of liquid surfaces. In contrast, properties of the solid substrates strongly depend on the fabrication and transfer methods, and may vary from manufacturer to manufacturer, and from lab to lab.In summary, we demonstrated that the functionality of confocal Raman spectroscopy for characterising CVD graphene can be amplified by studying graphene floating directly on a liquid or even buried in between two liquids. All three major Raman bands of graphene – the Finally, the advantages of a water support were showcased here through the example of hydrogenation of graphene, but can, in principle be applied for studying other effects on graphene structure.63).All graphene samples were grown on a copper foil with the thickness of 25 µm by chemical vapour deposition (CVD) method, after annealling the copper at 1035°  was added on top to form a biphasic system with graphene floating at the interface. During etching of the copper the samples were covered with lids to prevent evaporation of the top organic phase; more cyclohexane (or 1-octanol) was added during experiments to prevent full evaporation of the top phase. After copper removal the bottom phase underneath graphene was replaced with ultrapure water. As for Raman measurements it is important to minimise graphene movability on the surface of liquids, the size of graphene sample was to fit the size of the Petri dish.2 plasma in a computer controlled Diener plasma generator  for 10 and 60 s (ref. 47).Graphene on copper was hydrogenated using a HThe samples of hydrogenated graphene on copper were placed in a 0.1-M solution of APS for copper etching. After copper was etched away, the solution underneath hydrogenated graphene was replaced with ultrapure water.2 and free-standing graphene; ×70 immersion objective was used for graphene on liquid supports. Graphene/Cu samples were typically cut into 5 mm × 10 mm or 10 mm × 10 mm pieces, which were then studied by Raman spectroscopy directly on copper. Then graphene was transferred from copper to SiO2/Si substrate or TEM grid (for free-standing configuration) using the interfacial caging method24, or to liquid interfaces using the method described above. A comparative analysis showed no statistical difference between the samples of 5 mm × 10 mm and 10 mm × 10 mm  implemented in LAMMPS. The neighbour list was updated every single simulation step. The simulation cut-off was 10 Å for Lennard–Jones and 12 Å for short-range electrostatic interactions. Shifted cut-offs (charmm style) were used for Lennard-Jones interactions. In accordance with the Opls forcefield, 1–4 interactions were scaled by a factor 0.5. A time step of 0.0005 ps was used in all simulations. The dimensions of the simulation box were 60 × 60 × 160 Å3 . In all cases the graphene flake consisted of 678 atoms (~40 × 40 Å). The number of 1-octanol or cyclohexane molecules present was 490 and 512 respectively. All systems contained 4693 water molecules. Equilibration was inferred from systematic trends within the potential energy. The equilibration time of the simulated system was 0.5 ns, after which another additional 1 ns production run was performed. For the simulation of graphene in vacuum rigid body translational and angular momentum were removed in all dimensions. For the simulations of graphene on copper an additional simulated annealing was performed to prepare/equilibrate the system (the system was cooled from 1400 K to 300 K in 1 ps). All system were setup by stacking individual molecules into stacked layers, which were combined to compose the desired multi-layer system.All simulations where performed with the LAMMPS simulation package65. For 1-octanol and cyclohexane two recently developed models were used that are based on the Opls forcefield68. These two models were specifically refined on reproducing thermodynamic properties such as the bulk density. Water was modelled by the TIP3P model because of its compatibility with the Opls based n-alkane models. The non-bonded interactions between graphene and the different solvents were described by Lennard-Jones interactions. Here, Lorentz–Berthelot combining rules were used to calculate the interactions between the different atomic species  based on a graphene-graphene Lennard-Jones interaction of ε = 0.003035 eV and σ = 3.55 Å (graphene in Opls). For the interaction between graphene and TIP3P water we used Lennard-Jones interactions that were optimised to reproduce wetting angles via an evolutionary algorithm69 . Graphene was modelled as uncharged  to simulate the interaction of bulk graphene with the fluid interfaces (these are purely based on Lennard–Jones interactions). Finally, the simulations of graphene on copper on were performed using the reactive comb3 potential70 for both Cu–Cu, C–C and C–Cu interactions.Intra-molecular interactions within graphene flakes were described by the AIREBO potentialFurther information on research design is available in the Supplementary InformationReporting Summary


We present a novel strategy for designing a dual-band absorber based on graphene metasurface for terahertz frequencies. The absorber consists of a two-dimensional array of patches deposited on a metal-backed dielectric layer. Using an analytical circuit model, we obtain closed-form relatinos for the geometrical parameters of the absorber and the properties of the applied materials to achieve the dual-band absorber. Two absorption bands with perfect absorption at the preset frequencies of 0.5 and 1.5 THz are achieved. The results obtained by the analytical circuit model are compared to the simulations carried out by full-wave electromagnetic field analysis. The agreement between results is very good. We demonstrate that the graphene absorber remains as the dual band for a wide range of the chemical potential. Furthermore, the recommended dual band absorber is insensitive in terms of polarization and remain within various incident angles. Metamaterials are artificially-made media with uniquely engineered electric permittivities and magnetic permeabilities ,2 and enTo realize metamaterial-based absorbers in the low THz region, one can use the graphene patterned arrays. Graphene, consisting of a two-dimensional layer of carbon atoms arranged in a honeycomb lattice, has recently been demonstrated as one of the best materials for many applications in electrical and photonic devices due to its exotic properties ,21,22,23In this paper, a simple structure, composed of a period array of graphene patches deposited on a dielectric spacer terminated by a metallic back reflector, is used to design a dual-band THz absorber. We propose a circuit model to extract the geometrical parameters of the absorber and the properties of the material in the closed-form. Furthermore, we present a simple and effective approach for achieving perfect absorption at two preset frequencies. The input admittance of the absorber at the two frequencies is designed to match the admittance of free-space. Moreover, the imaginary part of the input admittance at the central frequency is set by applying an additional condition to be zero. To validate the approach, dual-band perfect THz absorbers have been investigated and designed. Then, full-wave simulations are used to confirm the design method. Excellent agreements have been achieved. It should be noted that the recommended absorber is polarization insensitive for normal incident electromagnetic waves owing to its symmetric structure. Besides, both dual-band and the high absorption effectiveness are affected slightly even at high angles of incidence for both TE and TMpolarizations.The paper is organized as follows. The equivalent circuit model of the proposed device is introduced, and then a design scheme leading to an dual-band absorber is proposed in D and gap g between the patches and the bottom layer of a reflective golden plate with finite conductivity of d. It is worth mentioning that in the fabrication process, the Si is used to support the graphene patches. The Au film is deposited on the Si bottom by gilding. Next, a continuous and uniform atomic monolayer of graphene can be grown by the chemical vapor deposition method, then patterned into closely packed square patch arrays using e-beam lithography.The geometry of the proposed absorber is schematically shown in x direction) is demonstrated in Based on transmission line theory, the whole structure can be modeled as circuit elements . The equS is the surface of a patch, An accurate circuit model has been proposed by Barzegar-Parizi et al. for a graphene patch array illuminated by a normally incident plane wave . The adme is the electron charge, ℏ is the reduced Planck’s constant. T is the temperature (fixed to 300 K) and It is known that graphene’s conductivity is derived using the Kubo formula, which is described with interband and intraband contributions ,33. For ntraband . TherefoDesigning the proposed absorber near the first resonance frequency of graphene patches, we can only consider the first mode and neglect the effect of higher-order modes. To avoid numerical calculation of the eigenvalues in the previous capacitance expression, we propose to replace the expression with the analytical capacitance admittance of metal patches proposed in . Therefoc is the speed of light) is the wavenumber of free space and the free-space admittance In the equivalent circuit model of Suppose perfect absorption can be achieved at two frequencies We consider a central frequency defined as Then, the admittance of the graphene array is seen as the input admittance of the structure, and it can be tuned to be matched to the free-space admittance near its resonant frequency . After sn. The relaxation time can be tuned by the chemical potential through the relation Choosing the two frequencies Equation  for give process ,39,40,41At the end, the geometrical parameters of the structure are computed by Equations –10) as as10) aWith the aid of the analytical equations presented in Equation , we havequations , the patThe absorption spectra of the structure are plotted in It should be pointed out that there are slight disagreements between the circuit model and FDTD simulation. These slight disagreements result from neglecting the effect of higher-order modes of graphene patches in the circuit model shown in Now, the tunability of the proposed device is investigated by changing the chemical potential of graphene. The polarization insensitive performance for the proposed absorber is important in practical applications. We plot the absorption spectra as a function of polarization angle and frequency in We have also investigated the omnidirectional characteristic for the proposed absorber. In summary, a dual-band perfect absorber based on graphene patches has been designed in the low terahertz regime by using impedance matching concept. First, we assigned an equivalent circuit to the absorber. We then adjusted the real part of the input admittance of the absorber to be close to the free space admittance and the imaginary part of the input admittance to be zero at two frequencies. In addition, the dielectric slab is considered as a quarter wavelength transmission line at the center of the two frequencies. This method resulted in closed-form relations for the geometry of the structure and the characteristics of the applied material. According to the results of simulation and analytical circuit model, the recommended absorber can operate with perfect absorption at 0.5 THz and 0.15 THz. Further, the device are insensitive to polarization and omnidirectional.


Displaced left-turn (DLT) intersections are designed to increase the mobility of vehicles by relocating the left-turn lane (lanes) to the far-left side of the road upstream of the main signalized intersection. Since DLT is a relatively new design and very limited crash data are available, previous studies have focused mainly on the analysis of its operational performance rather than its safety performance. To fill this gap, in this study, we investigated the safety performance of two DLT intersections located in San Marcos, Texas. Crash data from 2011 to April 2018 were extracted from the TxDOT Crash Record Information System (CRIS). These crash data were analyzed using two different approaches, i.e., statistical analysis and collision diagram-based analysis. The results of this study indicated that DLT did not increase the overall crash frequencies at the studied intersections. Traffic crashes related to left turns and right turns were reduced significantly by DLT. Meanwhile, it also caused safety issues related to traffic signage, traffic signal, geometric design, and access management at DLT intersections. Thus, in the implementation of DLT intersections, traffic engineers need to carefully consider different aspects of the DLT intersection design, including access management, traffic signal coordination, and driver acceptance. As a result of these analyses, recommendations were provided for the safe implementation of the DLT design in the future. Intersections with the displaced left-turn (DLT) design are also known as continuous flow intersections (CFIs). Such innovative intersections were designed to increase the mobility of traffic by relocating the left-turn lane (lanes) to the far-left side of the road upstream of the main signalized intersection. DLT is being used increasingly in several states in the U.S., and some studies have been conducted to investigate the performance of this innovative design. However, previous studies have focused mainly on the operational performance, and the safety impacts of DLT have not been investigated thoroughly. Pitaksringkarn conducted a traffic simulation-based study to assess the operational performance of DLT, and the results indicated that DLT intersections had a significant reduction in average delay compared with traditional intersections . A subseOther researchers also have reported that DLT has successfully reduced intersection travel delays, number of stops, and queue lengths and increased intersection capacity. For example, Kim et al. found that, compared with the conventional T-intersection, the DLT intersection can result in a significant reduction of delay for through and left-turn movements . Esawey Some studies also compared the operational performance of DLT intersections with other innovative intersections. For example, Dhatrak compared the operational performance of DLT and parallel flow intersection (PFI) based on the maximum through and left-turn movement throughputs for three different high-volume scenarios using traffic simulation. The simulation results showed that the maximum throughput values of through movement in both designs were very close, but left-turn movement throughputs in DLT were higher than those at PFI .Olarte compared the operational performance of left-turn bypass, diverging flow, and displaced left-turn intersections. The results indicated that the DLT consistently operated with less delay in almost all cases .Compared to a large number of studies on the operational performance of DLT intersections, very few studies have focused on the safety impacts of such intersections. Federal Highway Administration (FHWA)’s Displaced Left-Turn Intersection Informational Guide indicated several safety outcomes of implementing the displaced left-turn design: (1) DLT has successfully reduced the conflict points by 6–12% in four-leg intersections compared to conventional intersections, (2) the DLT design can reduce the delay time and the number of stops on a major road, which could reduce the frequency of rear-end crashes, and (3) the DLT crossover layout increases the risk of wrong-way movements .Louisiana Department of Transportation and Development (LaDOTD) evaluated the safety performance of a pilot DLT intersection at Airline Highway/US 61 and Siegen Lane/Sherwood Forest Boulevard in Baton Rouge, LA, by conducting a before-and-after analysis of crash data. This is a partial DLT design with two crossovers located on the 200-foot-wide Airline Highway . They mePark and Hesham assessed the safety impacts of DLT based on the analysis of traffic conflicts . They seZlatkovic accessed the safety performance of DLT intersections by developing crash modification factors (CMFs) using the empirical Bayes (EB) methodology . Eight DHowever, Abdelrahman et al. found that DLTs could have a negative impact on intersection safety. In their study, the authors evaluated the safety performance of DLTs using two methods, a before-and-after study with a comparison group and a cross-sectional analysis. Both results showed that DLTs can significantly increase the total number of crashes as well as injury crashes and some other crash types . However, they have the potential to decrease non-motorized crashes and head-on crashes. In addition, the authors also found that some other factors have significant effects on the crash frequency. For example, they found that crash frequency decreases when the minor street has a low-speed limit .From the literature mentioned above, it is evident that most of the previous studies focused on the operational performance of DLTs. Very few studies evaluated the safety impacts of the DLT design, and these impacts have been analyzed mainly through the statistical analysis of historical crash data. Since the statistical analysis depends on the general crash attributes contained in the crash database, some local specific risk factors related to the crash location and its surrounding environment cannot be identified. To fill this gap, in this study, two different approaches were used for an in-depth assessment of the safety performance of two DLT intersections in San Marcos, Texas. These two approaches are (1) statistical analysis of crash data and (2) collision diagram-based analysis. By comparing the safety performance before and after the implementation of DLT at the intersections, the safety impacts of the DLT were analyzed, and recommendations for future implementation of DLT were provided. The results of these studies will provide traffic engineers/designers with a better understanding of the safety impacts associated with the implementation of the DLT design, and the results also will assist them in designing, installing, and managing better DLT intersections in the future.Two DLT intersections were selected as study locations, i.e., Loop 82 at Interstate Highway (IH) 35 and State Highway (SH) 80 at IH 35 in San Marcos, Texas. The Loop 82 project was completed on 1 May 2014 and the SH 80 project ended on 12 October 2014. These two DLT intersections were selected due to the following criteria.(1)The DLT intersections are in Texas. For all the crashes that occurred in Texas, the research team had full access to not only the crash data, but also the detailed police crash reports for conducting collision diagram-based analysis.(2)The DLT intersections need to be implemented for more than 3 years. In this way, enough crash data before and after the implementation of the DLT design can be available for conducting a statistical analysis.(3)These two DLT intersections represent the two different types of DLT design: single-leg DLT (Loop 82 at IH 35) and two-leg DLT (SH 80 at IH 35).To analyze the safety impacts of the DLT design at these two intersections, crash data for the past eight years (January 2011–April 2018) were obtained from TxDOT’s Crash Records Information System (CRIS) for conducting the before and after studies. In addition, detailed police crash reports for these crashes were also extracted from the CRIS system.For Loop 82 at IH 35, we studied a total of 36 months of data (from January 2011 to December 2013) before DLT was installed, a total of 4 months of data (from January 2014 to April 2014) during the construction, and a total of 48 months of data (from May 2014 to April 2018) after DLT was installed. In total, 336 crashes occurred at this intersection during the study time period.For SH 80 at IH 35, we studied a total of 40 months of before data (from January 2011 to April 2014), a total of 5 months of data (from May 2014 to September 2014) during the construction, and 43 months of after data (from 12 October 2014 to April 2017). In total, 513 crashes occurred at this intersection during the study time period.For these two intersections, two different approaches were used to analyze the safety impacts of converting a conventional intersection to a DLT intersection, i.e., a statistical analysis and a collision diagram-based analysis.t-test was conducted to ensure that the difference in crash frequency was statistically significant.For the statistical analysis approach, the following two methods were used. First, a direct comparison between the monthly crash frequency before and after implementing the DLT was conducted. Note that, for both study locations, crashes that occurred during the construction period were excluded from the data to eliminate crashes caused by construction. A statistical Second, the empirical Bayes (EB) method was applied to account for the effects of the changes in traffic volume before and after the implementation of DLT. The basic idea is that the changes in accident frequency may be due to contributing factors other than the treatments (the implementation of DLT in this study). Therefore, in order to assess the true effects of the treatments, the expected number of accidents that occurred during the after-treatment period in the absence of treatment will be estimated and compared with the observed number of accidents that occurred during the after-treatment period. If the expected accident number is less than the actual observed number, the treatment is effective; otherwise, it is ineffective or even adversely affects the intersection safety.a, b, c, d, e, and f are constants or the coefficients of independent variables and their values are given by Wang et al. [The EB method combines the observed crash frequency with the predicted average crash frequency to produce a more statistically reliable measure, which is referred to as expected crash frequencies. The details about the use of the EB method for transportation safety performance analysis can be found in Highway Safety Manual . To use g et al.  was seleg et al. .According to Equation (1), since it is assumed that there is no treatment at this location, i.e., both the traffic control and geometric conditions stay the same at this location and the expected crash frequency during the after-study time period, g et al. , VE=AADTCollision diagrams are used to identify the patterns and locations where certain types of crashes occurred frequently. To develop a collision diagram, the first step was to draw the background map. After that, detailed police reports of crashes that occurred in this area were examined carefully. The locations of the crashes were marked on the map with different symbols representing different types of crashes.The developed collision diagrams at both study locations before and after the implementation of DLT design are presented and discussed in the following sections.Intersection 1 is the first phase of the DLT intersection project in San Marcos, Texas. It is a signalized diamond interchange with two at-grade intersections at ramp terminals, where IH 35 frontage roads meet with Loop 82 (Aquarena Springs Drive). This location was converted to one DLT lane for the northbound traffic, which opened on 1 May 2014. The detailed before and after geometric conditions at this location are presented in p-value of the t-test statistic was 47% > 5%.As we mentioned before, to account for the effects of the changes in traffic volume before and after the implementation of DLT, the EB method was applied. According to Equation (2) and the traffic volume conditions at this location before and after the implementation of DLT, the expected crash frequency during the after-study time period under the assumption of no treatment, i.e., (1)Disregarding the left-turn signage,(2)Drivers making left turns failed to yield the right of way, and(3)Drivers making dual left turns failed to keep their vehicles in a single lane.Traffic flow entering IH 35: Many vehicles move eastbound on Aquarena Springs Drive, make left turns at location A (blue circle), and then merge onto the IH 35 east frontage road. Due to the heavy left-turn traffic at location A, many crashes related to left turns occurred at this location, e.g., there were 10 left-turn angle crashes from January 2011 to December 2013. By conducting further analysis based on police crash reports, the following three major factors were identified that contributed to the high left-turn crash frequency before implementing DLT:Traffic flow exiting IH 35: Many vehicles exit from the southbound lanes of IH 35, merge onto the west frontage road of IH 35, and then make right turns at location B (green circle) to merge into the traffic on Aquarena Springs Drive. Before the implementation of DLT, this right-turn merge point was controlled by a “yield” sign. Due to the high volume of vehicles making right turns and the high volume of traffic on Aquarena Springs Drive, it is difficult for the right turn drivers to find a sufficient gap to make a safe merge, so a long queue of vehicles forms in the right turn lane, which is the reason for the high frequency of rear-end crashes at this location (30 crashes in 36 months).Before the implementation of DLT at this location, there were two places where crashes occurred frequently (presented below) due to the following two heavy-traffic flows:Finding A: Northbound left-turn-related crashes decreased after the implementation of DLT at location A (blue circle).Since DLT eliminated left-turn movements at this intersection, only one left-turn crash had occurred here since DLT was implemented. This crash occurred in November 2014, a few months after the completion of the DLT project. The driver was unfamiliar with the new design and disregarded the “no left turn” sign late at night. Subsequently, no other left-turn crash had occurred at this location during the after-study period from May 2014 to April 2017.Finding B: Rear-end crashes were reduced after the implementation of DLT at location B (green circle).At this location, another safety benefit gained by implementing the DLT design was the reduction of rear-end crashes at the point where traffic from IH 35 westbound frontage road merges onto Aquarena Springs Drive . After installing DLT, a traffic light was added at this point, and it coordinated with the signal light that was installed to control the DLT traffic at the left-turn crossover location. As a result of this change, the merging traffic can merge safely during the time the DLT traffic has the green light to move across to the left side. As a result, the frequency of rear-end crashes at this location decreased significantly to only 2 crashes in 35 months.Finding C: Left-turn crashes increased after the implementation of DLT at location C (red circle).Despite these improvements, some crash frequencies increased unexpectedly for the southbound left-turn traffic after the implementation of DLT. At location C (red circle) in Based on the descriptions in the police reports, the major cause for this type of crashes was that the left-turn drivers failed to yield the through traffic at the permissive left-turn phase. This was very likely caused by the geometric change after the implementation of DLT. To move the displaced left-turn traffic, an additional lane was added at the left-most side and the number of eastbound traffic through lane was reduced from two lanes to one lane. As a result, eastbound through traffic volume per lane increased, and it was difficult for the WB left-turn vehicles to find a safe space between the opposing through vehicles to make turns during the permissive phase.The second DLT intersection project on Hopkins Street opened on 12 October 2014, a few months later than the completion of the Aquarena Springs DLT project. It is a signalized diamond interchange with two at-grade intersections at ramp terminals, where IH 35 frontage roads meet with SH 80 (Hopkins Street). This location includes two displaced left-turn lanes, one of which allows eastbound traffic to turn north onto the IH35 frontage road (EB DLT), and the other allows the westbound traffic to move south of the IH 35 frontage road (WB DLT). The detailed before and after geometric conditions at this location are presented in p-value of the t-test statistic was 18% > 5%).The results of EB method-based before-and-after comparison are presented in Note that, at this study site, the two statistical methods employed by this research produced different results. Although the result of the direct comparison method indicated that the crash frequency increased by 14% after the implementation of DLT, the result of the EB method indicated that the implementation of DLT actually reduced crash frequency by about 15% by taking account of the effects of the increased traffic volume at this location. This result indicated that, when evaluating the effectiveness of a safety treatment, both the EB method and direct comparison method need to be used and their results need to be compared for a comprehensive evaluation.Finding A: Rear-end crashes decreased after the implementation of DLT at location A (green circle).After installing DLT, the rear-end crash frequency at location A was reduced significantly. Similar to Intersection 1, at this right-turn merge point, a traffic light was added, and the right-turn traffic can merge safely during the time the displaced left-turn traffic has the green light for moving across to the left side. As a result, the rear-end crash frequency at this location was reduced to only 1 crash in 43 months.Finding B: Angle crashes increased at a downstream location of the WB DLT at location B (purple circle).As indicated by a purple circle in Finding C: Illegal left-turn crashes increased after the implementation of DLT at location Cs (blue circles).At this intersection, there were 11 illegal left-turn crashes after the implementation of DLT because the drivers were unfamiliar with the design of this new intersection. Among the 11 crashes, 6 were southbound-turn crashes and 5 were northbound-turn crashes. All of these crashes occurred during the first year after the installation of DLT. According to police crash reports, most of these crashes occurred at night when there was inadequate lighting. Even though traffic signs prohibiting left turns were installed at these locations, drivers may still overlook or disregard them and make illegal left-turns, especially at night. Therefore, for the implementation of DLT intersections, improving the lighting conditions of intersections and installing more visible traffic signs (such as signs with flash beacons) are strongly recommended. In addition, more law enforcement and driver education are needed, especially during the first year after the implementation of DLT.Finding D: T-bone angle crashes caused by running red lights increased after the implementation of DLT at location Ds (red circles).From the crash diagram, we identified another type of crash that occurred frequently after the implementation of the DLT design, i.e., T-bone angle crashes between the DLT vehicles and the cross-street vehicles. (1)The implementation of DLT did not increase the overall crash frequencies at the studied intersections. It brought safety benefits at some locations for certain movements; meanwhile, it also caused safety problems at other locations for some other movements.(2)In general, DLT has good performance in reducing left-turn-related collisions at the main intersections.(3)DLT will also help right-turn vehicles merge safely and efficiently onto the intersection legs with DLT lanes, thereby reducing the rear-end crashes at the right-turn merge points.(4)Many illegal left-turn crashes occurred at late night and during the first year after the implementation of DLT. Therefore, improving the lighting conditions of intersections and installing more visible traffic signs (such as signs with flash beacons) are strongly recommended. In addition, more law enforcement and driver education are needed, especially during the first year after the implementation of DLT.(5)Left-turn vehicles are moved to the far-left side lane and, after making left turns from the DLT lanes, more lane changes are needed for them to access destinations on the right side of the roadway because of the design of DLT. The factors undoubtedly will increase the likelihood of collisions between the DLT vehicles and the through vehicles. Therefore, for DLT intersections where attractions are located , more access management is needed. For example, it is recommended that the entrance to the attractions be moved away from the area where the DLT exits are closely located to provide longer distances for DLT vehicles to make lane changes to access the attractions.(6)At DLT intersections, it is important to coordinate the signal timing between the left-turn crossover intersections and the main intersection to reduce the likelihood that DLT vehicles will have to stop at the main intersection. In addition, advanced signal warning systems could be used to assist drivers in obeying the traffic signals.In this study, the safety impacts of the DLT design were assessed by conducting both statistical analysis and the analysis of collision diagrams based on the crash data and police crash reports collected over eight years at two intersections in San Marcos, Texas. These analyses were conducted before and after the implementation of DLT. It identified the following key findings:The results of this study provide useful implications for both practitioners and researchers. First, in the implementation of DLT intersections, traffic engineers need to carefully consider different aspects of the intersection design, including access management, traffic signal coordination, and driver acceptance. Otherwise, DLT may mitigate the safety problem at some locations, but will cause more safety problems at other locations. Second, this study used both statistical analysis and collision diagram-based analysis. It was found that most of the key findings were obtained through the collision diagram-based approach. This result indicated that a collision diagram is an effective tool for analyzing the safety performance of a particular location such as an intersection. Currently, this method has not been widely used and most researchers are using the statistical analysis approach for crash risk analysis. Since the statistical analysis depends on the general crash attributes contained in the crash database, some local specific risk factors related to the crash location and its surrounding environment cannot be identified by the statistical analysis approach. Therefore, the collision diagram-based approach is recommended for intersection safety analysis because it can help us to better understand the safety problems at a particular intersection and identify effective solutions for these problems. Finally, given that these findings are based only on two selected DLT intersections in Texas, more studies at more DLT intersections are needed in the future to further validate and improve the findings of this study.


This study shows that covert Mandarin wh-questions do not elicit anterior negativities associated with memory maintenance, even when such a dependency is unambiguously cued. N = 37 native speakers of Mandarin Chinese read Chinese questions and declarative sentences word-by-word during EEG recording. In contrast to prior studies, no sustained anterior negativity (SAN) was observed between the cue word, such as the question-embedding verb “wonder,” and the in-situ wh-filler. SANs have been linked with working memory maintenance, suggesting that grammatical features may not impose the same maintenance demands as the content words used in prior work.Event-related potential components are sensitive to the processes underlying how questions are understood. We use so-called “covert”  These are called long-distance, or non-local, dependencies. Previous studies have investigated the processing of different kinds of long-distance dependencies, including topicalization (1), relativization (2), and wh-filler is necessary until the gap site is found and thus working memory capacity is required when processing the filler-gap dependency. Studies have shown that dependencies are recognized actively: comprehenders anticipate a gap as soon as possible after encountering a filler ; when the wh-word who is encountered at the beginning of the sentence, a speaker makes a prediction about the presence of a gap and tries to find the gap as soon as possible.Long-distance dependency formation affects memory in several ways. First, the filler must be maintained in working memory. Indeed, long-distance dependencies show a distance effect: processing time increases as the distance between the filler and the gap increases Gibson, . The maiwh-dependencies involve the following four elements: (i) wh-filler reactivation, (ii) thematic role assignment, (iii) semantic integration between the verb and the wh-filler, and (iv) maintenance of a wh-filler and prediction of the incoming gap  components. The current study focuses on ERP components that have been connected with the maintenance of a filler element in working memory; we provide novel data from the processing of Mandarin wh-questions to shed light on the functional interpretation of these components.The above properties reflect processing that is elicited by the filler. Additionally, the filler is retrieved at the appropriate part of the sentence and its thematic role and grammatical function needs to be resolved. Drawing the processing evidence together, long-distance wh-filler. The SAN component is an increased negative voltage over the anterior of the scalp between the interval of interest  post-stimulus and is associated with maintenance of information in working memory  and the gap. They found that the amplitude of the SAN became larger as the distance from the wh-filler became greater, a finding that they explain by suggesting that it is more costly to maintain the incomplete dependency in working memory. The SAN is thus associated with the cost of holding information available in working memory since information stored in working memory declines with time  is an ERP component that appears to correlate with storage and retrieval of a wh-dependencies with a greater amplitude of SAN in the long dependencies. The SAN effect is seen between the wh-filler and the gap position, consistent with the idea that the SAN is associated with the cost of retaining the wh-filler in working memory. Interestingly, their SAN effect was already observed in the first clause of the long wh-dependencies. They point out that it is insufficient to conclude that the SAN can be evoked by the manipulation of the length of wh-dependencies as the SAN amplitude only increases in the first clause and is sustained, but not further increased subsequently. While not identical, this result is consistent with the results from Fiebach et al.  whether-questions, and (c) which N-questions; examples are given in (4). For wh-fillers such as “who” and “which,” the SAN effect was predicted to be evoked between the filler words and the corresponding gaps since the incomplete dependency must be maintained until the gap is encountered. To explain the absence of such a sustained effect in their data, Kaan and colleagues suggest that expectations of some optional phrases such as “or not” could minimize processing differences between the wh-filler conditions and the whether-condition.In contrast, some studies have failed to find a SAN effect between a filler and a gap  the maintenance of the syntactic prediction for filler itself. These two hypotheses differ in terms of the type of information that is driving this observation: for the former, the information is born by the wh-feature itself. In the latter, the relevant information is born by the linguistic content that is actively maintained to fill the gap site. Crucially, English wh-dependencies cannot tease apart these two possibilities. The existing data leave open whether a SAN effect could only be elicited by the maintenance of the wh-feature, of a contentful word. The present study examines the processing of Mandarin wh-questions, which has the wh-feature to trigger the prediction of the in-situ wh-word encountered later. In doing so, we can tease apart whether the SAN effect is elicited either by the wh-feature only or by the prediction formed by the tail of a dependency.The inconsistency between previous findings about the SAN for English indirect questions render unclear how different kinds of information may modulate working memory maintenance, and thus the elicitation of a SAN. Lau  identifiwh-dependencies: the P600. This component begins about 600 ms after the onset of a target word with a central-parietal scalp distribution  and (4-c), extra integration is required between the wh-element and the embedded verb imitated in terms of thematic role assignment to the wh-element. The embedded verb needs to assign the thematic role patient to the previous encountered wh-word who. The results are consistent with a functional role of the P600 that is linked with thematic analysis and/or syntactic integration. Kaan et al. further report a second experiment in which grammatical indirect questions (with who and whether) were paired with ungrammatical indirect questions that had agreement violations. In addition to the elicitation of the P600 at the embedded verb in the grammatical indirect questions, an P600 was also found at the embedded target verb in the ungrammatical sentences. Taken together, these findings strongly suggest that the P600 is not restricted to unpredicted structure alone, but can be elicited by grammatical and predictable structure that none-the-less imposes a greater burden on syntactic integration.In terms specific to wh-dependencies by manipulating the length between filler and gap. Their EEG results show that the P600 occurs around 300–500 ms in the short wh-dependencies but at 500–700 ms in the long wh-dependencies, suggesting that the differences in latency might indicate the timing for reactivating the wh-filler. However, there is no significant difference in the peak amplitude of the P600 when the dependency is finished in wh-dependencies, regardless of the short wh-dependencies or long wh-dependencies. They interpret this result to suggest that the amplitude of the P600 seems to be associated with the subprocesses of thematic role assignment and/or semantic integration between the verb and the wh-filler.Building on this, Phillips et al.  suggest wh-questions is “overt.” This contrasts with languages, like Mandarin, where the wh-element stays in-situ but is none-the-less found to have similar syntactic properties as overt-movement languages. If the P600 relates to the reactivation of the wh-filler, we should not expect to see the P600 in the Mandarin wh-questions. Unlike English wh-questions, the wh-element in Mandarin wh-questions stays in-situ, as detailed in section 1.3. However, if the P600 relates to the integration cost and thematic role assignment, the predictions are more complicated as they depend on the relative cost of integration between a verb and different kinds of arguments. If the integration cost of a question word is greater than a non-question word, perhaps due to interference effects during retrieval . (5-a) shows that the English wh-element what moves from the verb phrase (VP) to a clause-initial position. We review, below, evidence suggesting that the Mandarin wh-element sheme “what” behaves in a syntactically parallel way to English in that it moves to a clause-initial position despite the fact that such movement is not apparent in the overt word order of the sentence (5-b)  Huang, .wh-question involves covert movement comes from the scope-taking properties of wh-elements associated with different kinds of verbs. Huang (xiang-zhidao “wonder”), the sentence forms an embedded, or “indirect,” question interpretation , the sentence forms a direct question. Huang argues that this interpretive difference follows from a structural difference. Huang suggests that if the wh-element moves (covertly) to front of the embedded clause, the sentence is interpreted as an indirect question. However, if the wh-element moves covertly to the front of the main clause, it forms a direct question. This hypothesis has theoretical parsimony: the different interpretation between the direct question and the indirect question is achieved in the same way in English and Mandarin. Therefore, Huang concludes that the wh-element moves but as this movement is reflected only in interpretation and not in surface word order, hence “covert.”The key evidence that Mandarin s. Huang  points on Huang, . If the wh-questions show lower asymptotic accuracy than the short wh-questions. That is, relative to the short wh-questions, the latency of response time is delayed for the long wh-questions when the asymptotic accuracies are equal. The observation Mandarin wh-questions show such a distance effect is consistent with the hypothesis that the parser needs to construct a covert dependency.Indeed, previous findings have shown that memory resources required by questions are similar between the two languages  and the wh-word increased processing load in a way similar to what has been previously observed for English overt long-distance dependencies . They argue that the RAN effects they found should be comparable to SAN effects discussed in section 1.1. They speculate that this hemispheric bias may be due to the non-alphabetic Japanese kanji writing system. Interestingly, Ueno and Kluender do not find a P600 at the wh-word, in contrast to prior work with English (discussed in section 1.2). This absence suggests that the P600 might be elicited due to the overt movement of the wh-filler: since the wh-word stays in-situ in Japanese wh-questions, they claimed that there is nothing to be integrated at the clause-final question particle and thus no P600 is elicited in the Japanese wh-questions.The above findings indicate that formation of covert wh-questions by examining indirect questions, direct questions, declarative sentences, and whether-questions, with two different length of wh-dependencies. The background literature we have reviewed offers concrete predictions for the SAN ERP component in Mandarin wh-in-situ questions. If the parser takes a question-selecting verb as a cue for an upcoming covert dependency, a SAN effect should be elicited between that verb and the embedded wh-element in the indirect questions, relative to direct questions or declarative control sentences  working memory demands, a SAN effect is not expected to appear. In other words, if the SAN effect can be elicited in the indirect questions, this can suggest that the SAN effect can be elicited for maintaining the wh-dependency itself, not a particular contentful memory object. In terms of length effects, a greater SAN effect is expected to be observed in the comparison of indirect questions and direct questions in the long condition, compared to the comparison of indirect questions and direct question in the short condition  the reactivation of the wh-filler, (ii) thematic role assignment, and (iii) semantic integration between the verb and the wh-filler, regarding the processing of the overt wh-dependencies. Under the reactivation hypothesis, like Japanese wh-questions, the P600 should not be elicited since there is no overt displacement for the wh-filler in Mandarin. However, the semantic integration and thematic role assignment hypotheses, together with the results of Xiang et al.  participated in the study at the University of Michigan. They were all right-handed and had normal or corrected-to-normal vision. They self-reported that they did not have any neurological disorders. They gave informed consent and were reimbursed for their experiment time (15 USD/hour). Data from five participants was excluded from the analysis because of low accuracy on the comprehension questions (<80%). Data from one participant was excluded due to having many problematic noisy trials (>20%). Thus, data from 37 participants  were included in the final analysis. The experiment was conducted in accordance with the University of Michigan Health Sciences and Behavioral Sciences Institutional Review Board (# HUM00081060).Forty-three native speakers  of Mandarin Chinese between the age of 21 and 40 (wonder) or a non-question verb . If the main verb is a question-selecting verb, the whole sentence forms an indirect question. Otherwise, the sentence forms a direct question. The main verbs were matched on the number of strokes of a word and the log frequency of the first and the second character from SUBTLEX-CH  = 4.59, p < 0.001] was found in the log word frequency between question-selecting verbs  and non-question verb  since we wanted to make sure that the question-selecting verbs introduce a wh-feature afterwards and thus the question-type verbs we selected all included the character wen “ask.” This type of verb is not as common as the non-question verbs. For this type of verb, it is possible to can take several different types of complements. Based on Xiang et al. . But, the embedded clause does not have any question words, thus there is no long-distance dependency. This serves as a control for the target direct questions. The embedded yes/no questions (g-h) combine the same verbs from the indirect questions  with the question word you-mei-you “whether” to serve as a control for the wonder-type sentences. In both Indirect Question and Whether condition, the complement of the matrix verb is a CP; and they are differentiated by the presence of a wh-word, or a functional item like you-mei-you, respectively.An example of the experimental sentences is given in One hundred and twenty sentence sets were created initially and organized into eight lists. These were submitted to an acceptability judgment norming study. Twenty-four native Mandarin speakers recruited from social media  judged the sentences on-line through Qualtrics . Data were collected anonymously. Subjects were instructed to rate the sentences from 1 (least acceptable) to 5 (most acceptable). Forty ungrammatical filler sentences were also included in this norming test. The stimuli were presented randomly and fully counterbalanced such that each participant saw a list including 120 target sentences and 40 fillers. The norming test took 20–30 min to finish.F = 63.51, p < 0.001, such that the average acceptability rating was higher for the short version  compared to long version . The main effect of sentence type also shows significance, F = 3.6, p < 0.05. A post-hoc Tukey's test shows that the direct question sentences are significantly different from the other three sentence types (adjusted p < 0.05), such that the direct question  is less acceptable than the indirect question . The declarative  and the yes/no question  are not different from the indirect question. Note that the differences between indirect question and direct question work against the prediction that indirect question will be costly to process due to increased working memory maintenance cues by the question-selecting verb.Sixty-four acceptable sentence sets were selected based on the results . While these sentence sets were judged to be acceptable overall, some conditions were judged to be more acceptable than others. A two-way analysis of variance shows a main effect for length, Eight lists were created out of these 64 sentence sets. Sentences were distributed across these lists in the following way, which balances two constraints: ensuring participants see sufficient trials per condition, and minimizing the overall length of the experiment. First, each condition was divided into eight chunks of eight sentences each. Each list contains six chunks, or 48 sentences, from each condition (six sentences from each set), for a total of 384 experimental sentences. The chunks were distributed across the lists according to a Latin square. One hundred and twenty grammatical fillers were also included . Therefore, each participant saw 504 sentences in total.Participants sat comfortably in front of a computer screen in a quiet room. Prior to the main session, participants were fitted with an electrode cap. Electrodes were also affixed above and below the left eye. Electrolyte gel was applied to minimize impedance. The set-up process took about 30 min.Before the main experiment, participants chose if they would like to read a version using traditional or simplified Chinese characters. Participants were instructed to read the sentences appearing word by word on the computer screen. Sentences were presented with PsychoPy2  in a 0.1–200 Hz band with on-line reference to an electrode placed on the right mastoid. Impedance were kept below 25 kOhms. FieldTrip software  the interval between the main verb and the wh-word to examine the dependency between the main verb and the wh-filler. The epoch around the target wh-word included a 0.3 s pre-stimulus baseline and a 1 s post-stimulus period. The non-parametric permutation test was used to correct for multiple comparisons across timepoints from 0 to 1 s and across different electrodes by following these steps: (i) One-way repeated measures ANOVAs were conducted at each timepoint and electrode, (ii) tests with p < 0.05 were clustered based on spatial-temporal adjacency and their F-statistics were summed, (iii) Steps (i) and (ii) were repeated 1,000 times by randomly permuting the condition labels for each subject, and (iv) clusters with summed statistics that surpassed at least 95% from the permutation test were kept as “statistically significant.” Intervals between the verb and the wh-word start from 0.3 s prior to the main verb . This is shown in p = 0.87). The figure is shown in Indirect Questions, Direct Questions, and Declaratives were compared across the interval between the main verb and the p = 0.67). The Bayes factor in favor of the null model is 1.28 in favor of the null model . If the memory maintenance cost for question features does elicit a SAN, such an anterior negativity should be elicited between the question-selecting verb and the words with question-type feature. The interval overlapping in both Indirect questions and Whether-question  was compared. However, as our results show in wh-word was also analyzed separately: data epochs were re-baselined with 100 ms before the onset of each word. No reliable differences were found in this analysis . These analyses show no anterior negativity within the dependency interval, as seen in p = 0.39; Embedded subject: p = 0.78; Embedded verb: p = 0.82). The figures are shown in Following Phillips et al. , each wowh-element in Indirect questions, compared to Direct questions and Declarative sentences. Also, no anterior negativity was found at each word between the question-selecting verb and the wh-element in the Indirect Questions, relative to the Direct questions and the Declarative sentences.To summarize, no SAN was found in the interval between the question-selection verb and the wh-word naxie “which” appeared in both the direct question and the indirect question and the demonstrative zhexie “these” in the declarative sentences were compared. A significant difference (p = 0.03) was found at about 170–250 ms in anterior and left posterior regions. The wh-word naxie “which” in the indirect questions and the direct questions is more positive-going than the demonstrative zhexie “these” in the declarative sentences (see wh-word (p = 0.25), relative to the demonstrative zhexie “these” in the declarative sentences. The Bayes factor is 0.01 in favor of the difference between conditions and is 89.33 in favor of the null model in the time-window of the P600. The results of time-frequency analysis did not find statistically significance (p = 0.44). The figure is shown in To test for P600 effects, a one-way repeated-measures ANOVA was computed for the target word region, comparing Indirect questions, Direct questions, and Declaratives. That is, activity evoked by the nces see . Howeverwh-word in Indirect question vs. Direct question was also compared in the short (p = 0.67). The Bayes factor in favor of the null model is 9.74 . However, a significant difference was found in the long condition (p = 0.03) at approximately 300 ms after the onset of the first embedded subject . The effect was found in bilateral anterior and right posterior regions. p = 0.72) and long comparisons (p = 0.59). The figures are shown in The interval between the main verb and the he short  and longhe short  conditiot p = 0.6. The Baypost-hoc, explanation for this sustained positivity might be due to the inhibition of expectation for the wh-element. This is further addressed in section 4, below.To sum up, no SAN was found in the short indirect questions, compared to the short direct questions, and in long questions a bilateral and posterior sustained positivity was found in approximately 1,500–2,800 ms in the indirect relative to the direct questions. One possible, albeit wh-word. A t-test was computed for the wh-word in the short and long conditions separately for indirect and direct questions. No effects were observed in either the short or long conditions . The Bayes factor analysis favors, albeit not strongly, the null models . This comparison is shown in p = 0.18). The figure is shown Despite the absence of apparent anterior negativities or P600 effects relating to covert dependencies in Mandarin, we conducted a planned analysis separating out short from long dependencies at the target post-hoc simulation test. In addition to serving our present goals, this approach may provide a way to assess replicability in ERP studies, an issue which has drawn increased attention recently though few studies examine the effect sizes that can be reliably detected with standard ERP analyses  are repeated 100 times, yielding a distribution of statistical outcomes where the true effect E = 2.5 mV, our procedure detects significance 90% of the time with N = 30 or N = 37. For E = 3.0 mV, significant effects are detected nearly 99% of the time with N = 30 or N = 37. Note that when E = 1.0 mV, a smaller effect than those reported in the SAN literature, significant effects are detected 25% of the time or less. As for the P600, for E = 2 mV, the simulation detects significance 90% of the time with N = 37. For E = 1.5 mV, effects can be detected nearly 60% of the time with N = 30 or N = 37. For E = 1 mV, a smaller effect than those reported in the P600 literature, significant effects are detected <25% of the time. The simulation results suggest that null statistical findings in the current study indicate a true effect of the sizes generally reported in the literature may indeed be absent in our data.The results of the simulations are shown in wh-dependencies, we address the issue of whether the SAN reflects the maintenance of wh-features in working memory, or the maintenance of a contentful prediction. There are several key findings in this study. First, there was not strong evidence for a sustained negativity between the question-selecting verb and the wh-word in indirect questions. This result is inconsistent with the hypothesis that the SAN effect seen in prior studies reflects active maintenance of the wh-dependency itself. It is consistent with the hypothesis that memory resources used to store and retrieve the question-selecting feature cued by the main verb impose lower or no processing demands. Second, no P600 was found at the wh-word naxie “which,” relative to the demonstrative zhexie “these.” This result is most consistent with the hypothesis that the P600 is an indicator of the reactivation of the wh-filler: since the wh-word does not move overtly in Mandarin, such reactivation does not happen and thus there is no P600. Third, regarding the length effects, no P600 was elicited at the wh-word in the long condition, suggesting that the P600 reflects several sub-processes as a whole, not the length effect only. However, a sustained positivity was found in the long condition, and this unexpected result might, as we suggest below, indicate the inhibition of the expected incoming words.In this study, we recorded EEG data during a word-by-word reading in Mandarin task to examine the functional role of the SAN and other ERP components that have been linked with dependency processing during language comprehension. In particular, by examining Mandarin covert wh-questions.Importantly, the principle results from the present study are based on the absence of the predicted ERP components. We contend that these null results indeed reflect some important aspects about how to interpret the functional role of the anterior negativity and the P600 in terms of the processing of the Mandarin wh-word is parsed, an anterior negativity is expected to be elicited in the indirect question. The results show that there is no SAN in the interval between the question-selecting verb and the wh-word, suggesting that the maintenance of the question feature of question-selecting verb in Mandarin wh-questions requires lower demands in working memory than the maintenance of a contentful wh-filler in English wh-questions. For the English wh-questions, the wh-word is encountered before the gap. Same as the Japanese wh-questions, the wh-word is also encountered before the question particle. Both English and Japanese wh-questions elicit an anterior negativity in the wh-dependencies. However, the wh-word is encountered after the question-selecting verb in Mandarin wh-question, suggesting different “memory loads” as a function of the different representations. That is, the memory load for the question-feature of the question-selecting verb is lower than the memory load for the wh-word in the English wh-questions.As mentioned earlier, the anterior negativity correlates with the storage and the retention in working memory . Our experiment always included an embedded interrogative clause in Indirect questions and thus we reason that the parser is likely to form dependencies between the question-type verb and the wh-element.Another possibility for the absence of the SAN might be due to the fact that the question-type verb can be followed by a non- Nathan, . These awh-questions carries two implications for how the parser treats cues for dependencies. First, if the anterior negativity does correlate with working memory demands, it is possible that language users do not need to store the question-selecting verb as a cue and then retrieve it. Instead of storing the cue for the wonder-type verb, under the expectation-based account, the parser uses cues from the main verb to make prediction for the upcoming words and build the expected syntactic structure. Xiang et al. (wh-dependencies in Mandarin. We suggest that our null results indicate that the SAN effect might correlate with the maintenance of contentful words with question feature, like wh-filler in English wh-questions, but not the maintenance or prediction of question dependency alone.The above interpretation for the lack of anterior negativities in the Mandarin g et al.  also poiwh-word is expected to appear soon. However, the fulfillment of this prediction is delayed in the Long condition due to the embedded clause between the main verb and the wh-word. Such delay might cause inhibition of the expectation for the target question feature, thus eliciting the sustained positivity. More fine-grained studies are needed for testing the interpretation of this sustained positivity. As one final caveat, our results cannot tease apart whether a parser needs to store the verb as a cue or only uses the verb to make prediction without storing it.However, if we examine the Short and Long condition separately, a statistically reliable effect was found in the Long conditions. A sustained positivity was found in the Indirect question, compared to the Direct question. This result is in opposite direction of a SAN, and this unexpected finding may suggest that the question feature has an alternative effect on processing. Interestingly, previous studies have found the sustained anterior positivity correlates with the inhibition of highly expected words (DeLong et al., wh-questions, we see no P600 effect at the wh-word in the Mandarin indirect questions. The Mandarin wh-questions does not have overt displacement for the wh-word and there is no need to refer back to the wh-filler. This result is consistent with the hypothesis that the P600 is an index for the reactivation of the wh-filler since there is no need to reactivate the wh-filler in the Mandarin wh-questions.Consistent with Ueno and Kluender's findings for Japanese wh-filler under the assumption that wh-words impose stronger integration costs (Xiang et al., wh-element does not need to be integrated with the question particle in the processing of Japanese wh-questions. To reconcile these findings, we suggest, rather, that there is some integration between the question-selecting verb and the wh-element in the processing of the Mandarin wh-questions, but crucially thematic and/or syntactic integration that is indexed by the P600 is nearly equivalent when the parser encounters the wh- and non-wh- target words, leading to no P600 differences. On this particular formulation, the effects of retrieval interference for covert wh-questions identified by Xiang et al. (The absence of the P600 appears to be inconsistent with the hypothesis linking this component with thematic and syntactic integration between the main verb and the g et al.  may not wh-word in the long wh-dependency, compared to the short wh-dependency. This is consistent with the view from Phillips et al. (wh-filler in the English wh-questions, the length effect might also be less significant.As for the length effects, consistent with the results from Phillips et al. , no relis et al. , suggestwh-word, compared to the demonstrative zhexie “these.” A P2 is an earlier positive-going ERP component that distributed in the central-frontal regions at about 150–250 ms post-stimulus (Federmeier et al., wh-word and the demonstrative might be a consequence of visual detection of lexical differences. The P2 effects found at the wh-word also suggest that participants did pay attention to the stimuli.A significant early positivity was found at the wh-word, nor was SAN or P600 observed at the in-situ wh-word. The absence of sustained negativities in Mandarin wh-questions suggests two possibilities. The first is that there is no need to store the question-selecting verb as a cue and then retrieve it. The second is that there are lower working memory demands for the storage and retrieval of the question feature of the question-selecting verb, which is different from the storage of the contentful wh-word in the processing of English and Japanese wh-questions. We did observe a sustained positivity for the longer wh-dependencies, which could suggest that a prediction of some sort is being maintained and causing to lexical inhibition when that prediction is not rapidly satisfied. Taken together, these results narrow down the kind of memory mechanisms indexed by ERP components, like the SAN, during language comprehension.In contrast to prior work, no sustained anterior negativity was found between the main verb and the The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.The studies involving human participants were reviewed and approved by University of Michigan Health Sciences and Behavioral Sciences Institutional Review Board. The patients/participants provided their written informed consent to participate in this study.C-WL: conceptualization, material design, acquisition of data, data analysis, data curation, interpretation of data, manuscript preparation, and visualization. JB: conceptualization, interpretation of data, manuscript review and editing, funding acquisition, and project administration. All authors contributed to manuscript revision, read and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


In order to meet the requirements of mechanical seal, SiC ceramic sintered with 1 wt.% of graphene, for which the volume resistivity is of 397 Ω·cm, the bulk density is of 3.076 g/cm3, and the flexural strength is of 364 MPa, was optimized when all properties were taken into consideration. It is possible to fabricate low-resistivity SiC ceramic as a useful friction pair material for mechanical seal in a special condition, without excessive loss of their excellent mechanical properties by the introduction of partially connected graphene as conductive pathway into semiconducting ceramic.Silicon carbide (SiC) ceramic is an ideal material for mechanical seal because of its super hardness, high strength, low friction coefficient, good thermal conductivity, and resistance to friction and wear. However, due to relatively high resistivity of SiC ceramic, the triboelectric charge caused by rubbing of mechanical seal end-faces could not be released. It is terrible that the accumulation of triboelectric charge could cause electrochemical corrosion, which would accelerate wear. To decrease the resistivity of SiC ceramic is a desire for improving the performance of mechanical seal. In this research, decreasing resistivity of pressureless sintered SiC ceramic was investigated by conductive pathways through semiconductive grains in a body by incorporation of graphene, which has an extremely low resistivity. With the increasing of graphene from 0 to 2 wt.%, the volume resistivity of SiC ceramics sintered with graphene decreased logarithmically from >10 Silicon carbide ceramic (SiC ceramic) is one of the most widely used high-temperature structural ceramics, because of its high mechanical strength, high hardness, high-temperature strength, excellent thermal conductivity, resistance to friction and wear, resistance to oxidation, resistance to corrosion, and low specific gravity. Meanwhile, electrically conductive SiC ceramic is highly desired for some industrial applications, such as semiconductor manufacturing. 3 Ω·cm to conduct the triboelectric charge, which is generated from the rubbing of end-faces in operation and which could cause electrochemical corrosion. Meanwhile, SiC ceramic as a friction pair material is also required to have a flexural strength of more than 350 MPa and a bulk density more than 3.05 g/cm3, in order to provide sufficient mechanical performance. However, the resistivity of conventional SiC ceramics is 1 × 103 to 1 × 105 Ω·cm; thus, decreasing the resistivity of SiC ceramics while retaining the material’s excellent mechanical properties is of great interests these applications.For mechanical seals in a special condition, SiC ceramic, which is a very suitable material for friction pair, is required to have a resistivity less than 1 × 10To improve the electrical conductivity to SiC ceramic, dispersions of conducting second phase particles have been reported. In such composites, conducting particle contents above 12–30 vol% is necessary to produce conducting ceramics. However, the addition of large amounts of a second phase can potentially compromise the excellent mechanical properties of the matrix ceramics. Therefore, people are seeking ways to decrease the electrical resistivity of SiC ceramics by less addition of the second phase ,5,6,7. A2O3 [2 [2 [3N4 [Graphene is considered one of the strongest materials with exceptional charge transport, thermal, optical, and mechanical properties , because2O3 , SiO2 [12O3 [2 , ZrB2 [2O3 [2 [2 , and Si3 [2 [3N4  composit [2 [3N4  investigIn this study, the pressureless sintering was used to guarantee production efficiency and production cost. To decrease the resistivity of SiC ceramics without losing its excellent mechanical properties for mechanical seals, the amount of graphene was limited and optimized. The effect of graphene as dopants on the flexural strength, bulk density, and volume resistivity, which were crucial properties of SiC ceramic for mechanical seals, was investigated, and their mechanisms were preliminarily explored. Uniform graphene suspension was obtained by emulsification and ultrasound dispersing graphene powder  and carboxymethyl cellulose sodium , with the weight ratio of 10:1, into deionized water. 4C powder (size of 0.5–5 μm) as sintering additive with the weight ratio of 100:1, and various amounts of graphene suspension and ethanol were mixed by conventional wet-ball-milling with SiC balls, for 24 h, to obtain a homogeneous mixture. Commercially available SiC powder (size of 0.5–5 μm) as starting powder, BThe solvent was evaporated from the mixture at 90 °C. The prepared mixture was dried at 120 °C, and then it was dry-ball-milled for 6 h to eliminate hard agglomerations before sieving through a 74 μm mesh. The obtained powder compositions were dry-pressed at 50 MPa and then cold-isostatic-pressed at 200 MPa, to obtain a denser ceramic billet. The ceramic billet was dewaxed at 800 °C for 2 h, under around 10 Pa of vacuum atmosphere in the pre-firing furnace, and then pressureless sintered at 2050 °C for 2 h, under the protection of argon gas, in the final firing furnace. The content of graphene in the SiC ceramics was adjusted to 0.1, 0.5, 1, and 2 wt.%. The sample was labeled as 0.1 M, 0.5 M, 1 M, and 2 M respectively. SiC ceramic without graphene was also prepared as the control group and labeled as 0 M. The bulk density of graphene-doped SiC ceramics was measured by the Archimedes method via immersion in deionized water. The theoretical density was calculated by using the specific gravity of 3.21 for SiC. The flexural strength of the samples was determined by Three-Point Bending Test on an Instron Materials Testing Machine . At least 5 specimens were tested for each sample, to determine an average of flexural strength. The specimen thickness, width, span length, and crosshead speed were 3 mm, 4 mm, 30 mm, and 0.5 mm/min, respectively. The volume resistivity of the samples was measured by 2-probe method, using a Keithley electrometer  at room temperature. The upper and lower side of samples with size of Φ28 mm × h1.5 mm were polished and painted with silver paste, to improve the electrical contacts between the copper wires and the sample.The microstructure of the samples was observed by scanning electron microscopy  on polished fracture surfaces, to reveal the morphologies and locations of SiC grains and grain boundary phases. The chemical composition and elements distribution on cross-sections of the samples were determined by Electron Probe Microanalyzer . A user-defined image area of 30 μm × 30 μm was employed for the element mappings.−1. Raman spectra of the samples were recorded by confocal microscope Raman spectrometer , using the 532 nm laser wavelength excitation, and an acquisition up to 1800 cmThe flexural strength of SiC ceramics with the influence of the graphene doping amount is shown in 3. The bulk density of 0.1 M decreased to 99.23% of the original density. When the amount of doped graphene reached 2 wt.%, the bulk density of 2 M was only 3.039 g/cm3, which cannot meet the requirement of friction pair materials for mechanical seals. The bulk density of 1 M was 3.076 g/cm3, which just slightly exceeded the required density, 3.05 g/cm3. Therefore, the graphene should not be more than 1 wt.%.The influence of the graphene doping amount on the bulk density of SiC ceramics is shown in 6 Ω·cm, which was much larger than the target resistivity, 1 × 103 Ω·cm. When a small amount of graphene was doped into SiC ceramics, the resistivity of 0.1 M was two orders of magnitude lower than that of 0 M. When the graphene reached 1 wt.%, the resistivity of 1 M was 397 Ω·cm, which meets the requirements of the resistivity for mechanical seal. When more graphene was doped, the resistivity decrease was less sensitive to the graphene amount, and the resistivity of 2 M was 192 Ω·cm, half of that of 1 M. The influence of graphene on the volume resistivity of SiC ceramics is shown in It can be observed that the doping amount of graphene greatly influenced the porosity, grain boundary, and density of SiC ceramics from the microstructure morphology and the number of pores (randomly selected scanning areas with the same size on different samples) presented by SEM. In the 0 M samples without graphene a, grainsWith the doping amount of graphene in the 0.5 M sample c furtherElectron probe microanalysis (EPMA) was used to analyze the distribution of carbon elements in the micro regions of 0.1 M and 2 M samples. The area in the image was randomly selected, with a size of 45 μm × 45 μm. The signal color changed from blue to red, indicating the intensity of the carbon content, as shown in the scale bars in In the 2 M b with a −1 were detected on the fracture surface of 0 M , namely the “high-speed channel” of local electron transmission. When the doping of graphene reached a certain amount, the electron transmission of the “high-speed channels” could be connected to each other by graphene in grain boundary, forming a three-dimensional conductive network inside the whole block of SiC ceramics, meaning that the electron exceeded the minimum of percolation ,32,33 an3, and the flexural strength was 364 MPa. It is possible to fabricate low-resistivity SiC ceramic as a useful friction pair material for mechanical seal in a special condition, without excessively losing its excellent mechanical properties by the introduction of partially connected graphene as conductive pathways into semiconducting ceramic.In this study, a low resistivity pressureless sintering of SiC was fabricated by doping graphene into SiC as conducting grain boundary phases. The volume resistivity of the composite decreased logarithmically, while the bulk density decreased gradually, with the increasing of graphene from 0 to 2 wt.%. When the amount of graphene was smaller than 1 wt.%, graphene filled into the pores in the pressureless sintered SiC. This phenomenon enhanced the mechanical strength and decreased the resistivity of the composite significantly. When the amount of graphene was larger than 1 wt.%, graphene formed a spatially connected network in the SiC ceramics. Although the resistivity was further reduced, the volume density bulk density and flexural strength of the composite were greatly reduced, which may not meet the requirements of friction pair materials for mechanical seals. To decrease the resistivity of SiC ceramics without losing its excellent mechanical properties for mechanical seals, the additive amount of graphene was optimized to 1 wt.%. The resulting volume resistivity of the composite was of 397 Ω·cm, the bulk density was 3.076 g/cm


This editorial aims to summarize the eleven scientific papers published in the Special Issue “Graphene-Based Materials: Biological and Biomedical Applications”.The very important role of graphene and graphene derivatives in the biomedical field is rapidly growing. In this Special Issue, we aim to illustrate the areas of promise while identifying future challenges. In order to do this, we have invited papers from authors working in different graphene-based biomedical applications. For this reason, the Special Issue is rich in both innovative applications and hot reviews that cover a wide variety of topics of graphene in biomedicine.There is quite a lot of global discussion on whether graphene is a versatile nano-platform for regenerative medicine and tissue engineering applications. Regarding this topic, Memarian et al.  combinedStaphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus epidermidis (MRSE). Neither GO nor the CNFs exhibited cytotoxicity but had high antibacterial activity in direct contact with MRSE and MRSA cells. Furthermore, when the GO or CNFs were illuminated with LED light, the MRSE and MRSA cells lost viability. This combined antimicrobial approach opens up many biomedical research opportunities and provides an enhanced strategy for the prevention and treatment of Gram-positive multidrug-resistant infections.Due to the current antibiotic resistance worldwide, there is an urgent need to find new alternative antibacterial approaches capable of dealing with multidrug-resistant pathogens. Elias et al.  investigThe creation of graphene-based strategies able to deliver antitumor drugs to tumor cells is of immense importance, but the medical translation of these exciting developments is also crucial. Shan et al.  describeIn the general context of bio–nano interactions, Domi et al  studied Biosensors and optical devices are key assets when attempting the early diagnosis and monitoring of disease. The recent advances in functional magnetic graphene composites for making very sensitive and selective biosensor devices are vividly described in the Li et al. review . Due to