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


We investigate the copper-wear-protective effects of graphene and boron nitride in single asperity sliding contact with a stiff diamond-coated atomic force microscopy (AFM)-tip. We find that both graphene and boron nitride retard the onset of wear of copper. The retardment of wear is larger with boron nitride than with graphene, which we explain based on their respective out-of-plane stiffnesses. The wear protective effect of boron nitride comes, however, at a price. The out-of-plane stiffness of two-dimensional materials also determines their friction coefficient in a wear-less friction regime. In this regime, a higher out-of-plane stiffness results in larger friction forces. Thin-film materials have long been used to enhance the tribological performances of substrate materials. For example, thin layers of soft metals, such as indium, have been used to lower friction forces due to their easy plastic deformation . In contWith the development of miniaturized metal-based components and devices , new 2), by chemical vapor deposition (CVD) methods [In the last decades, extensive work has targeted the preparation of high-quality two-dimensional materials, such as graphene, hexagonal boron nitride (BN), or molybdenum disulfide . Similar experimental results have been reported in References [2DE = 290 N/m and 2Dσ = 23.6 N/m, respectively. From these results, defect-free graphene is thus stiffer and stronger than pristine BN. The effect of folding on the mechanical properties of free-standing graphene has been investigated by the pressurized blister test [γ-number [γ = 105–107. A corresponding quantification of γ has not yet been published for BN. However, a monolayer BN’s bending stiffness has recently been reported twice as high than that for monolayer graphene . The growth of graphene and BN on copper was confirmed by x-ray photoelectron spectroscopy (XPS). The friction and wear of copper and coated copper were measured by successively scanning a diamond-coated tip over the same area under the action of increasing normal forces. Therefore, both topographical changes and friction forces were recorded. For each of the three systems investigated here, two distinct regimes are observed in the load dependence of friction. The lower load regime corresponds to wear-less friction and is governed by the shearing of adhesive junctions for bare copper and puckering for graphene and BN. At larger normal force values, plasticity-mediated plowing of copper occurs. We find that graphene and BN retard the onset of plastic deformation of the copper substrate. This effect is larger for BN and is attributed to its larger out-of-plane stiffness.2 at 1300 K for 30 min.A cold-rolled copper foil was purchased by Graphene Square, Republic of Korea, and a single layer of graphene on copper was prepared by chemical vapor deposition . The XPS measurements were recorded with a monochromated AlKα source  and a spot size of 400 mm. The measurements shown in −9 mbar), the samples were exposed to ambient conditions. To reduce the effect of surface contamination, a gentle Ar+ sputtering with low energy and current values was performed before XPS measurements on annealed copper , and NOx (399.96 eV) [In the case of BN-coated copper, the same peaks corresponding to metallic copper, water, and adventitious carbon contamination as for annealed copper and graphene-coated copper are observed. The XPS results on BN-coated copper exhibit a contribution from copper oxide or copper carbonate to the peaks corresponding to the Cu2p and O1s orbitals. As expected, the XPS results on BN-coated copper exhibit clear peaks at 190.13 eV and 397.78 eV, corresponding to the contributions of BN bonds to the B1s and N1s orbitals. In the B1s and N1s orbital cases, weaker convoluted peaks at 191.6 eV and 399.96 eV can be observed. These peaks have previously been attributed to oxygen saturated defects in BN (see Reference ). Furthe9.96 eV) ,34.T = 293 K and RH = 40%) by friction force microscopy (FFM) using an AFM XE-100 manufactured by Park Instruments, Republic of Korea. Therefore, a stiff diamond-coated AFM cantilever  was used. The cantilever’s normal and lateral stiffnesses were calculated according to the geometrical beam theory by:E is the Young’s modulus and G is the shear modulus. Therefore, the cantilever length L and width w were optically measured, and the tip height was set to h = 12 mm, according to the manufacturer’s data. The thickness of the cantilever t was determined according to:0f is the first free-bending resonance frequency of the cantilever and ρ is the mass density. Before the wear tests, the photodiode’s sensitivity S was calibrated by recording a force–distance curve on a noncompliant nanocrystalline diamond thin film and by extracting its slope 1/S in the range of repulsive forces. The wear tests consisted of repeated reciprocal sliding of the AFM tip with respect to the sample over a scan area sA = 2.5 × 2.5 μm2 with a velocity sv = 20 μm/s and under normal forces nF = 15 nN–6930 nN. Therefore, the scan areas were selected within single copper grains.Wear tests were performed in well-climatized and dehumidified laboratory conditions . The friction force maps were calculated as:l,fwdF and l,bwdF are the lateral force images recorded in the forward and backward directions, respectively. The mean friction value f><F and its standard deviation σ<Ff> were calculated for each normal force value. After tribological tests, the topography of the scanned areas was recorded by amplitude-modulation noncontact AFM, and the average depth of the worn area was evaluated by plotting the height distribution of these images. All AFM results presented in this work were analyzed using a home-written MATLAB script [During the experiments, the topography and the lateral deflection signals were recorded in the forward and backward directions. The topographical images were used to calculate the evolution of the roughness parameter B script .qR is indicated for each presented topographical image. The wear measurements consist of the recordings of 14 topographical and lateral force images in both the forward and backward directions with successively increased normal force values from 15 nN to 6930 nN. For the sake of clarity, nF = 153 nN, 616 nN, 1232 nN, 2310 nN, 3850 nN, 5390 nN, and 6930 nN. We also indicate the roughness qR values for each topographical image in nF = 2310 nN  model , in whicectively . Above anF = 1539 nN using the MATLAB software package. The choice of this limit for the normal force values was motivated by the appearance of signs of abrasion in the topographical images for nF ≥ 2039 nN , sE = 130 GPa, sν = 0.34, tE = 700 GPa, and tν = 0.1, we obtain τ = 6.32 GPa and adF = 0.2 nN. The obtained value τ = 6.32 GPa corresponds to G = 48 GPa is the shear modulus of copper. The determined τ-value is thus close to the theoretical strength of copper. The plowing force pF was subsequently determined by extrapolating the fit function up to nF = 6930 nN and by subtracting the sF-values from f><F. pμ = 0.449. In this case, the confidence factor is 2R = 0.8347.The JKR model was used to fit the experimental results in the regime of low normal force values for annealed copper. In 9 nN see d. InterenF-values for fitting was selected for which no appreciable topographical change was observed  error bar-plot, i.e., the σ<Ff>-values, increases more rapidly than in the puckering regime, though the values are more scattered.In the case of graphene-coated copper, it is found that, in the regime of low normal force-values, the load-dependent friction is best fitted by a linear function see h. This ilues see k. In thi<Ff>-values. This choice was motivated by the fact that the surface roughness parameter qR remained constant up to nF = 4500 nN while a clear change of slope in the fF (nF) plot is recognizable at a lower load. In <Ff>-values significantly increase for nF > 3079 nN. In the interval of nF-values between 15 nN and 3079 nN, we find a coefficient friction μ = 0.1989 and f0F = 453 nN. The confidence factor associated with this fit is far lower than for previous samples, at 2R = 0.5059. As for the previous samples, the plowing force values were determined by extending the fit function for the low load regime to higher nF-values and by subtracting it from the experimental friction force values. Here also, pF is found to increase linearly with the nF. Fitting this dependence with a linear function, we find pμ  = 0.5612 and 2R = 0.9144.For BN-coated copper, two linear regimes of friction as a function of the normal force are also observed see i. In thi6 nN see l. For thwδ = 30 nm, while for graphene-coated and BN-coated copper, they are wδ = 16 nm and wδ = 9 nm, respectively.τ = 12 GPa. Similarly, we find for copper τ = 6.3 GPa in this work. Furthermore, we observe that plowing becomes active beyond the normal force value The tribological response observed for annealed copper in this work agrees with observations made on annealed copper in Reference  or metalyp-value with copper’s hardness. According to the model developed by Nix and Gao to account for the depth dependence of metals’ hardness,0H is the hardness value in the absence of geometrically necessary dislocations, and *d characterizes the depth dependence of the hardness and depends both on the indenter geometry and 0H [0H is ≈0.3 GPa and *δ is ≈ 0.5 mm for copper. In this work, the indenter’s penetration depth at the onset of plowing can be estimated according to:Since the underlying mechanism for plowing is plastic deformation, it is interesting to compare the y and H0 . In Refey and H0 , the autH = 4.7 GPa, which is relatively close to the calculated value of the contact pressure at the plowing onset.This yields the hardness value nF = 1500 nN, it is observed that graphene folds gradually smooth out, indicating that an AFM diamond tip stamps graphene into copper. For graphene-coated copper, the plowing friction coefficient value is almost identical to the value found for annealed copper. This evidences that, in this case too, the plowing forces arise from plastic deformation of the underlying copper substrate. Graphene does not suppress plastic deformation of the copper substrate but retards it. As a result, the average wear depth is observed to decrease from 30 nm for annealed copper down to 16 nm for graphene-coated copper. These results agree with the observations reported in Reference [Comparing these results for annealed copper with graphene- and BN-coated copper, it is found that the shearing friction model does not hold in both cases. This observation confirms recent results on the wear-less friction of graphene and can be explained by the chemical inertness of both graphene and BN, which prevents the formation of adhesive junctions with the indenter ,18,30. Ieference . There, μ = 0.19 than on graphene, where μ = 0.11. In this case, too, the governing mechanism of wear-less friction is assumed to pucker. The larger corresponding friction coefficient can be explained by a larger out-of-plane stiffness of BN compared to graphene. In Reference [pμ = 0.56 and is slightly larger than that for annealed copper and graphene-coated copper. In the range of normal force values nF = 3079 nN–3850 nN, no noticeable topographical changes are observed. As for graphene, it is assumed that the BN layer is stamped into copper. At nF = 4619 nN, fine ripples on the topography of BN-coated copper become visible. These ripples seem to be precursors of the BN layer rupture since we observe significant topographical changes beyond this normal force value. Although BN appears to rupture above nF = 4619 nN, its wear-protective effect is larger than that for graphene-coated copper and is characterized by a lower average wear depth wδ = 9 nm. The larger load-bearing capacity of BN compared to graphene can be explained by the larger out-of-plane stiffness of BN that leads to its higher resistance to be stamped into copper.In BN-coated copper, the wear-less friction is characterized by a slightly larger friction coefficient eference , the outThus, both graphene and BN retard the onset of plastic deformation-mediated plowing of copper. Both graphene and BN layers act as load supports. The more pronounced effect of BN is attributed to its larger out-of-plane stiffness than graphene. While a larger out-of-plane stiffness enhances the wear-protective effect of two-dimensional materials, it is detrimental to their performance as a solid lubricant.We investigated copper’s wear-protective effects by graphene and boron nitride in single asperity sliding contact with a stiff diamond-coated AFM tip. In the wear-less regime, shearing dominates the friction of bare copper. In contrast, the wear-less friction of graphene- and BN-coated copper is governed by puckering. Both graphene and boron nitride were found to retard the onset of wear of copper. This effect is larger for BN than graphene. The retarding effect on wear is attributed to the load-bearing capacity of graphene and BN, although the coefficient of plowing friction is not affected by the coatings. This indicates that the wear mechanism consists of plastic deformation of copper in all three investigated systems. Owing to its larger out-of-plane stiffness, BN exhibits a more pronounced wear protective effect than graphene. For the same reason, though, BN is a less effective solid lubricant than graphene.


Our calculation results reveal that G–D–O2 possesses the highest binding energy, indicating that it owns the highest stability. Moreover, the stabilities of the four structures are enhanced enormously by the compressive strain larger than 2%. In addition, the band gaps of G–O2 and G–D–O2 exhibit direct and indirect transitions. Our work aims to control the graphene-based structure and electronic properties via strain engineering, which will provide implications for the application of new elastic semiconductor devices.We report first-principles calculations on the structural, mechanical, and electronic properties of O In order to make the most of the potential values of graphene sensors, it is significant to understand the coactions between adsorbed molecules and graphene. It has been identified that gas molecules can effectively change the electronic and magnetic properties of graphene and graphene nanoribbons [2 adsorption is a rather extensive, effective means for modifying these species [2 [2. It is known that the graphenes probably have defects resulted from multiple fabrication methods, and graphene doping is everywhere. Currently, research on defects and doping of graphene sensors has attracted much attention because of its numbing applications. On the other hand, strain exists objectively in constructed graphene structures, showing up in the ridges and buckling generation [2 molecule will affect the characters of different graphenes. Actually, the characters of the deformed GO are very significant for the applications of two-dimensional elastic oxide devices.Due to good mechanical and electrical characteristics, graphene-based materials have attracted significant attention ,3,4,5,6.oribbons ,8. Furthoribbons ,10 and coribbons , and O2  species ,11. In gneration ,13. The neration , showingneration ,16,17. I2 molecule and various graphenes /B(boron)-doped graphene and defective graphene). We calculated the pristine graphene as a contrast. The graphenes are doped by N and B atoms, representing the most widely-applied n-type and p-type dopants. For the defective graphene, there is only one missing atom in each supercell in consideration of reducing complexity. The research aims to study the influence of equibiaxial strain effects on the structural, mechanical, and electronic properties of O2 molecules adsorption on various graphenes.In this work, we performed first-principles simulations to investigate the equibiaxial strain effects on the interactions between the Oz-axis direction. The N/B-doped graphene was modeled by replacing one carbon atom with one N/B atom in the unit cell. The Monkhorst–Pack scheme [−4 eV per formula unit. The equibiaxial strain (ε) is defined as [The first-principles calculations were performed through applying the Vienna ab-initio simulation package (VASP) ,20,21,22k scheme  of the kfined as (1)ε= in 2 adsorption on N-doped graphene (G–N–O2) in 2 adsorption on B-doped graphene (G–B–O2) in 2 adsorption on defected graphene (G–D–O2) in 2 molecule is placed at the top center of the supercell. After relaxation, for the G–O2, the O2 is parallel to graphene plane with or without strain, and the O2 molecule prefers to be located in the middle of a C6 ring , they generally keep a metal character. Thus, it is a very efficient and reversible approach for regulating electronic properties of different adsorption systems by applying strain. Such interesting phenomena in the electronic structures could pave the way for elastic electronic devices working under strain and mechanical sensors on the basis of new 2D crystals. The gap opens mainly because the sublattice symmetry is broken. The honeycomb sublattices  through applying first-principles calculations. It was found that under the same strain, G–D–O2 possesses the highest stability in contrast to G–O2, G–N/B–O2, and G–D–O2. The stability of O2 adsorption on various graphenes can be enhanced enormously by the compressive strain larger than 2%. However, the stability of O2 adsorption is reduced under the compressive strain smaller than 2% and the tensile strain. Moreover, the types of graphenes have little influence on the stress and Young’s modulus. For G–O2 and G–D–O2, the band gap direct–indirect transition occurs under equibiaxial strain. Our findings provide new approaches for designing and synthesizing elastic electronic devices based on graphene oxide. Significantly, these results do not account for the isotopic exchange studies where the isotopes of oxygen were reacted with graphene, which showed that the formation of different oxygen structures on graphene was the result of a number of sequential reactions [In summary, we studied the equibiaxial strain effects on the interactions between the Oeactions .


The development of biosensors with high sensitivity and low-detection limits provides a new direction for medical and personal care. Graphene and graphene derivatives have been used to prepare various types of biosensors due to their excellent sensing performance . This perspective review focuses on graphene-based biosensors for quantitative detection of cancer-related biomarkers such as DNA, miRNA, small molecules and proteins by integrating with different signal outputting approaches including fluorescent, electrochemistry, surface plasmon resonance, surface enhanced Raman scattering, etc. The article also discussed their challenges and potential solutions along with future prospects. According to the World Health Organization, there will be 24 million new cancer cases and 14.5 million cancer-related deaths each year by 2035 ,7. Biose2 electron orbital, has a high specific surface area, excellent electron transport capabilities and strong mechanical strength, which is essential for constructing biosensors. This review gives a detail of classification and characteristics of graphene, and a detail of the application of various types of graphene and graphene derivatives-based methods with diverse signals outputting approaches to achieve quantitative detection of different kinds of biomarkers including DNA, microRNA, small molecules and proteins. We also comprehensively summarized and compared the detection principle, target molecules, detection limits and detection range of graphene-based different sensors in recent years. Such graphene-based biosensors are expected to show great potential in biological analysis and clinical medicine.Recently, graphene has been drawing tremendous attraction owing to the outstanding feature of electrochemical, adsorption performance, mechanical strength and flexibility to serve as an attractive candidate for biosensors ,15,16,17Graphene-based nanomaterials mainly include graphene, graphene oxide (GO) and reduced graphene oxide (rGO) as demonstrated in Graphene has been making a tremendous influences in several research areas due to its unique physical and chemical properties ,22. Ther(1)2/g for single-layer graphene theoretically, which gives rise to high densities of attached recognition component or analyte molecules. It contributes to high detection sensitivity and the miniaturization of the device.High specific surface area. 2630 m(2)Excellent electronic properties and electron transport capabilities. The carbon atoms of graphene hybridized in the form of sp2 constitute a huge π–π conjugate system in which the electrons are freely moving. These properties make graphene a candidate in the field of electrochemical sensing.(3)Strong mechanical strength and pliability. Single-layer graphene possesses a thickness of ~0.335 nm, the hardness of which is higher than diamond due to strong C=C bonding in the atom plane; while opposite to diamond, the interlayer bonding via Van der Waals forces makes it a soft material. This will greatly benefit the development of wearable sensor devices.Graphene and graphene derivatives with properties of a large specific surface area, high electron transport rate and high temperature resistance can be used as a signaling device or carrier of biometric components to achieve a quantitative detection of biomolecules, which is described in detail in the following sections. However, there are more than 10,000 publications about five types of graphene-based sensors , Electrochemistry, SPR (surface plasmon resonance), SERS (surface enhanced Raman scattering)). In this manuscript, we only focused on the recent graphene-based biosensors. Fluorescence is the emission of light by a fluorescent tag with labeled targets that have absorbed external incident light, which is a commonly used detection technique in biological monitoring owing to the high sensitivity, low detection limit, good accuracy, etc. . GraphenGO-based fluorescent sensors were firstly introduced for the sensitive and selective detection of DNA and proteins by Lu et al. The presence of target ssDNA or protein lead to the binding of dye-labeled ssDNA and target DNA or aptamer and target protein, releasing the ssDNA and aptamer from GO, thereby restoring the dye fluorescence, which enable the detection of target ssDNA and thrombin . The samEnzyme amplification technology can be applied to graphene-based fluorescent sensors. As demonstrated in Fluorescence anisotropy (FA) assay is an analytical method based on the rotation speed of fluorophore-induced signal differences upon the binding of targets . GO can Enzyme amplification technology was applied in a graphene-based FA biosensor. Huang et al. established two different FA sensors based on nicking enzyme amplification and GO enhancement for sensitive detection of biomolecules including adenosine and thrombin in homogeneous solution . As demoGraphene-based fluorescent biosensors have ultrahigh sensitivity and can achieve the quantitative detection of biomolecules in complex samples. However, the labeling of fluorophores and the reading of signal data by spectrometers are relatively complicated and cumbersome. Graphene-based FA sensors are a potential candidate for rapid and efficient detection methods without interference of background. Whereas, this method requires a module in fluorescence spectrometer for measuring the anisotropic signal, which is more complicated and expensive.Electrochemical sensors depend on the change of current, potential or impedance upon the occurrence of reaction on the surface of an electrode. Electrochemical methods have received much attention due to the relative low-cost, simplicity, low detection limits and ease of miniaturization . The larThe sensitive detection of DNA and miRNA, which play vital roles in storing and transmitting genetic information, are valuable in bioanalysis. Guo et al. reported a graphene-based electrochemical biosensor for detection of DNA with ultrahigh sensitivity with a detection limit of 9.4 zM . Huan et3O4 and polyaniline-modified GO electrochemical biosensor for non-enzymatic sensing of glucose was reported. The large surface of GO and Fe3O4 along with the enhanced charge transfer capability of polyaniline provided a pronounced electrochemical response, which enabled the detection of glucose with a detection limit of 10 nM . Th. Th45]. Recently, smart multifunction sensors that output multiple detection signals on one system were reported . Ouyang In conclusion, the recent progresses of graphene and its derivatives-based biosensors are reviewed including the design strategies and detection results. These biosensors always functioned with a DNA probe, antibody, aptamer, protein or small organic molecules for target recognition. Sensitive detection of DNA, miRNA, small molecules, and proteins have been achieved through the integrating of multiple outputting signals .Even though a large number of graphene-based sensors reported in the literature exhibited good stability and repeatability, performance of some sensors in actual biological samples (such as blood and urine) often failed to achieve the desired detection results, which was mainly due to some non-specificity of biological and chemical molecules during the interfacial reaction of graphene and targets. Although some sample preparations  are necessary before the final tests for biological samples, however, they always face the limits of complex procedures and are a time-consuming operation . One eff