1,721,018 research outputs found
Effect of Nanostructure and Crosslinks on Impact Resistance of Carbon Nanotube Films Under Micro-Ballistic Impact
No full textCarbon nanotube (CNT) films show great promise as an advanced bulletproof materials due to their excellent energy dissipation ability under impact loadings. However, it is challenging to determine the optimized architecture structure of CNTs to enhance the impact resistance of CNT films. In this study, the impact behavior of CNT films with various architecture structures were studied by micro-ballistic impact experiments and coarse-grained molecular dynamics (CGMD) simulations. The micro-ballistic impact experimental results showed that the cross-ply laminated (CPL) structure enhances significantly the specific energy absorption (SEA) of CNT films compared to that with disordered structure due to the synergistic interactions between covalent bonds in CNT chains. On this basis, four CPL-CNT (CCNT) films with the same areal density (rho 2D) but different single-layer areal density (rho s2D) and one disordered CNT (DCNT) film with the same rho 2D as the CCNT films were constructed in CGMD models. The simulation results showed that the SEAs of all the four CCNT films are higher than DCNT film, which is consistent with experiments. In addition, the SEAs of CCNT films increase with decreasing rho s2D. However, too small rho s2D can lead to local plugging failure of the CNT film and therefore decrease SEA of the CNT film. Moreover, adding crosslinks could further increase the SEAs of both the DCNT and the CCNT films due to the strengthened interactions of adjacent CNTs. The crosslinked CCNT films with appropriate rho 2D is still much higher than the crosslinked DCNT films. Furthermore, it was further found that when the strength of the crosslinks aligns with that of the CNT beads, the CNT film achieves preeminent impact resistance. This study provides a pathway for enhancing the impact resistance of CNT films by optimizing the microstructure and introducing crosslinks between CNTs
Study on performance degradation and damage modes of thin-film photovoltaic cell subjected to particle impact
No full textIt has been a key issue for photovoltaic (PV) cells to survive under mechanical impacts by tiny dust. In this paper, the performance degradation and the damage behavior of PV cells subjected to massive dust impact are investigated using laser-shock driven particle impact experiments and mechanical modeling. The results show that the light-electricity conversion efficiency of the PV cells decreases with increasing the impact velocity and the particles' number density. It drops from 26.7 to 3.9% with increasing the impact velocity from 40 to 185 m/s and the particles' number densities from 35 to 150/mm(2), showing a reduction up to 85.7% when being compared with the intact ones with the light-electricity conversion efficiency of 27.2%. A damage-induced conversion efficiency degradation (DCED) model is developed and validated by experiments, providing an effective method in predicting the performance degradation of PV cells under various dust impact conditions. Moreover, three damage modes, including damaged conducting grid lines, fractured PV cell surfaces, and the bending effects after impact are observed, and the corresponding strength of each mode is quantified by different mechanical theories.</p
Extraordinary impact resistance of carbon nanotube film with crosslinks under micro-ballistic impact
No full textThe crosslinks of carbon nanotubes (CNT) film has been demonstrated to owing the ability to reinforce the quasi-static mechanical properties. But it is unclear whether crosslinks improve the ballistic impact resistance of CNT film. Here, we investigated the impact resistance of CNT film with crosslinks by combining micro-ballistic impact experiments with coarse-grained molecular dynamics (CGMD) simulations. The impact resistance is quantitatively characterized in terms of the specific penetration energy. Meanwhile, the effective enhancement of impact resistance contributed to the crosslinks is directly observed in the experiment. CGMD simulations are employed to unveil the corresponding mechanisms in terms of deformation behavior, energy dissipation mode, and failure behavior. Our results indicate that with the increase of crosslink density, the energy dissipation mode of the CNT film transforms from bending-dominated to stretching-bending-dominated due to enhanced interaction between the adjacent CNTs. This leads to a transformation of perforated morphology from cascaded interfaces sliding to crosslink-restricted deformation with crosslinks. Our simulations also indicate that the length, bending stiffness of CNTs, and film's thickness play essential roles in the impact resistance of CNT film at various crosslink densities. These results provide a feasible strategy to improve the protective performance of CNT film. (C) 2021 Elsevier Ltd. All rights reserved.</p
Dynamic compressive behavior of ice at cryogenic temperatures
No full text
In the present study dynamic behavior of distilled water ice (polycrystalline ice Ih) is investigated under uniaxial compression at strain rates in the range of 100 s(-1) to 1350 s(-1) and at temperatures in the range of-15 degrees C to -173 degrees C using a modified split Hopkinson pressure bar (SHPB). The peak compressive strength is found to increase from 32 MPa to 112 MPa as the test temperatures are decreased from -15 degrees C to -125 degrees C. With a further decrease in test temperature from -125 degrees C to -173 degrees C the peak strength is observed to remain nearly constant and lie in the range of 110-120 MPa. In addition, the,ice samples show positive strain rate sensitivity over the range of strain rates employed in the present tests at test temperatures in the range of -15 degrees C to -125 degrees C. However, the sensitivity of the logarithmic of peak stress (strength) to logarithmic of strain rate decreases with decreasing test temperatures, and the ice samples are observed to be nearly insensitive to strain rate at test temperatures lower than -125 degrees C. An interesting feature of the dynamic compressive behavior of ice is the presence of a shoulder/double-peak in the dynamic stress versus strain curves at test temperatures in the range of -50 degrees C to -150 degrees C. Another feature of the post-peak stress regime of distilled water ice is the presence of a long tail in the dynamic stress versus strain curves at a test temperature of -15 degrees C. At lower test temperatures (from -150 degrees C to -173 degrees C) the residual strength of ice is observed to become negligible. These artifacts in the dynamic behavior of ice can be attributed to details associated with dynamic failure of the ice samples and geometric effects emanating from the finite size of the samples and the diameter of the loading bars. The residual dynamic strength of ice can be best understood by considering the damaged/fragmented ice as an assemblage of wet highly-fragmented granular material created by adiabatic heating during grain-to-grain frictional sliding and held together by ice melt and/or recrystallization in the post peak-stress regime. </p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The incidence of liver injury in Uyghur patients treated for TB in Xinjiang Uyghur autonomous region, China, and its association with hepatic enzyme polymorphisms nat2, cyp2e1, gstm1 and gstt1.
Get PDFBACKGROUND AND OBJECTIVE: Of three first-line anti-tuberculosis (anti-TB) drugs, isoniazid is most commonly associated with hepatotoxicity. Differences in INH-induced toxicity have been attributed to genetic variability at several loci, NAT2, CYP2E1, GSTM1and GSTT1, that code for drug-metabolizing enzymes. This study evaluated whether the polymorphisms in these enzymes were associated with an increased risk of anti-TB drug-induced hepatitis in patients and could potentially be used to identify patients at risk of liver injury. METHODS AND DESIGN: In a cross-sectional study, 2244 tuberculosis patients were assessed two months after the start of treatment. Anti-TB drug-induced liver injury (ATLI) was defined as an ALT, AST or bilirubin value more than twice the upper limit of normal. NAT2, CYP2E1, GSTM1 and GSTT1 genotypes were determined using the PCR/ligase detection reaction assays. RESULTS: 2244 patients were evaluated, there were 89 cases of ATLI, a prevalence of 4% 9 patients (0.4%) had ALT levels more than 5 times the upper limit of normal. The prevalence of ATLI was greater among men than women, and there was a weak association with NAT2*5 genotypes, with ATLI more common among patients with the NAT2*5*CT genotype. The sensitivity of the CT genotype for identifying patients with ATLI was 42% and the positive predictive value 5.9%. CT ATLI was more common among slow acetylators (prevalence ratio 2.0 (95% CI 0.95,4.20) )compared to rapid acetylators. There was no evidence that ATLI was associated with CYP2E1 RsaIc1/c1genotype, CYP2E1 RsaIc1/c2 or c2/c2 genotypes, or GSTM1/GSTT1 null genotypes. CONCLUSIONS: In Xinjiang Uyghur TB patients, liver injury was associated with the genetic variant NAT2*5, however the genetic markers studied are unlikely to be useful for screening patients due to the low sensitivity and low positive predictive values for identifying persons at risk of liver injury
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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