Why do cracks branch? A peridynamic investigation of dynamic brittle fracture

In this paper we review the peridynamic model for brittle fracture and use it to investigate crack branching in brittle homogeneous and isotropic materials. The peridynamic simulations offer a possible explanation for the generation of dynamic instabilities in dynamic brittle crack growth and crack branching. We focus on two systems, glass and homalite, often used in crack branching experiments. After a brief review of theoretical and computational models on crack branching, we discuss the peridynamic model for dynamic fracture in linear elastic–brittle materials. Three loading types are used to investigate the role of stress waves interactions on crack propagation and branching. We analyze the influence of sample geometry on branching. Simulation results are compared with experimental ones in terms of crack patterns, propagation speed at branching and branching angles. The peridynamic results indicate that as stress intensity around the crack tip increases, stress waves pile-up against the material directly in front of the crack tip that moves against the advancing crack; this process “deflects” the strain energy away from the symmetry line and into the crack surfaces creating damage away from the crack line. This damage “migration”, seen as roughness on the crack surface in experiments, modifies, in turn, the strain energy landscape around the crack tip and leads to preferential crack growth directions that branch from the original crack line. We argue that nonlocality of damage growth is one key feature in modeling of the crack branching phenomenon in brittle fracture. The results show that, at least to first order, no ingredients beyond linear elasticity and a capable damage model are necessary to explain/predict crack branching in brittle homogeneous and isotropic materials.     

Investigation of the interactions between molecules of β-Carotene, Vitamin A and CNTs by MD simulations

Two typical phenomena (wrapping and filling), mainly about the interactions between biological molecules and carbon nanotubes (CNTs), were investigated by performing molecular dynamics (MD) simulations. We calculated the center of mass (COM) distance and the interaction energy between the biological molecules and single-walled nanotubes (SWNTs). The influence of nanotube wall number, chirality, radius and temperature was also investigated by a series of MD simulations. The results indicated that Vitamin A and β-Carotene were two promising biomaterials for decoration of CNTs. The interactions between biological molecules and CNTs could be influenced by those four factors. The general conclusions derived from this study may be of importance in medical and biological areas.     

Why is graphene an extraordinary material? A review based on a decade of research

During this decade, graphene which is a thin layer of carbon material along at ease with synthesis and functionalization has become a hot topic of research owing to excellent mechanical strength, very good current density, high thermal conductivity, superior electrical conductivity, large surface area, and good electron mobility. The research on graphene has exponentially accelerated specially when Geim and Novoselov developed and analyzed graphene. On this basis, for industrial application, researchers are exploring different techniques to produce high-quality graphene. Therefore, reviewed in this article is a brief introduction to graphene and its derivatives along with some of the methods developed to synthesize graphene and its prospective applications in both research and industry. In this work, recent advances on applications of graphene in various fields such as sensors, energy storage, energy harvesting, high-speed optoelectronics, supercapacitors, touch-based flexible screens, and organic light emitting diode displays have been summarized.     

Why Internet use? A quantitative examination of the role of everyday life and Internet policy and regulation

Regardless of the technological advances achieved so far and the often techno-deterministic approaches to the information society, inequalities in the access to, distribution and use of ICTs such as the Internet still highlight the importance of digital divides. The complex nature and continuing importance of the unequal rates of use of ICTs such as the Internet invite research to examine their drivers. Ordinary people’s everyday life and their awareness and evaluation of policy and regulation are influential factors in how Internet use takes shape today. This is the argument made by this article and supported by a survey of 1001 Internet users and non-users in Greece. Particular attention is paid to how aspects of everyday life and culture, such as resistance to ICTs, and people’s awareness and evaluation of Internet policy and regulation in areas such as online security and privacy can explain Internet use.     

Do types of collaboration change citation? A scientometric analysis of social science publications in South Africa

Scientometrics - Scientometric studies have, by and large, focused on the features of the hard sciences rather than the soft sciences. Prior research has been highly centered around natural science...     

Tools, methods, and strategies. Do innovative models of health care delivery improve quality of care for selected vulnerable populations? A systematic review.

BACKGROUND: A criticism of conventional office or clinic-based models of care is that they focus on patients' urgent problems and do not provide the comprehensive assessments, education, and psychosocial support that vulnerable patients also need. Innovative models have emerged to address these needs. A systematic review of prospective studies involving searches of computerized databases, reviews of reference lists, and contacts with authors, was conducted to determine whether multidisciplinary teams, outreach or home care, and case management improve the quality of the care in two vulnerable populations-the terminally ill and the mentally ill. RESULTS: Literature searches identified 730 citations. 52 original articles met screening standards, and 24 studies fulfilled all criteria. Patient and caregiver satisfaction was consistently higher with innovative models. In no study was satisfaction lower. Functional, clinical, or psychological improvements were not consistently demonstrated. For mentally ill patients, multidisciplinary outreach strategies were effective in reducing inpatient hospitalizations. Costs were inadequately assessed in the studies to draw a summary conclusion. DISCUSSION: Like other interventions, health care delivery models can be assessed from an evidence-based perspective. More needs to be learned about the costs and health improvements of innovative models before we can determine whether the increased patient and caregiver satisfaction found justifies widespread use of these models. Development of a uniform set of quality outcome measures and encouragement to evaluate efforts and disseminate results will help accomplish this goal.     

Investigation of phase formation of RFe11V1 ? xTix (R = Pr, Ce) compounds

Phase formation of PrFe₁₁V_{1 – x}Ti_x and CeFe₁₁V_{1 – x}Ti_x compounds with the ThMn₁₂-type structure has been investigated by x-ray diffraction (XRD), differential thermal analysis (DTA) and ac initial susceptibility. The stable temperature range of the 1-12 phase for PrFe₁₁V_{1 – x}Ti_x alloys has been constructed as a function of Ti content. It is found that the PrFe₁₁V compound with the ThMn₁₂-type structure do not form. The PrFe₁₁Ti compound with the ThMn₁₂-type structure can only be obtained by annealing at a narrow temperature range between 1030 °C and 1113 °C. Furthermore, 1-12 phase can be obtained at lower temperature and wider temperature range with decreasing Ti content x(0.2 x 1). The CeFe₁₁V and CeFe₁₁Ti compound with ThMn₁₂-type structure can be synthesized, and it is more favorable to synthesis the 1-12 single phase for the pseudotenary CeFe₁₁V_{1 – x}Ti_x compounds. For PrFe₁₁V_{1 – x}Ti_x compounds with x = 0.2–1, the lattice parameters a and c do not vary very much: around 0.860 and 0.479 nm, and Curie temperature T_c is 268 °C–329 °C. For CeFe₁₁V_{1 – x}Ti_x compounds the lattice parameters a and c are around 0.857 and 0.478 nm, and Curie temperature T_c is 211 °C–252 °C.     

Thermally-Stimulated Current Investigation of Dopant-Related D ? and A + Trap Centers in Germanium for Cryogenic Detector Applications

Thermally-stimulated current measurements provide a sensitive tool to characterize carrier traps in germanium detectors for direct dark matter search. Using this technique at cryogenic temperatures, very shallow traps have been detected with binding energies of a fraction of a meV, associated with the dopant species in the D ^?(A ⁺) charge states. A positive identification of these traps is achieved through an analysis of the field dependence of the carrier emission rates, which demonstrates a potential well for the trapped carriers in the form of a polarization well in r ^?4, consistent with Lax’s model for carrier trapping by a neutral center. The density of these traps is assessed, and implications for the space-charge cancellation procedure in cryogenic Ge detectors are discussed.     

Membrane Fluidity Changes,A Basic Mechanism of Interaction of Gravity with Cells?

All life on earth has been established under conditions of stable gravity of 1g. Nevertheless, in numerous experiments the direct gravity dependence of biological processes has been shown on all levels of organization, from single molecules to humans. According to the underlying mechanisms a variety of questions, especially about gravity sensation of single cells without specialized organelles or structures for gravity sensing is being still open. Biological cell membranes are complex structures containing mainly lipids and proteins. Functional aspects of such membranes are usually attributed to membrane integral proteins. This is also correct for the gravity dependence of cells and organisms which is well accepted since long for a wide range of biological systems. However, it is as well established that parameters of the lipid matrix are directly modifying the function of proteins. Thus, the question must be asked, whether, and how far plain lipid membranes are affected by gravity directly. In principle it can be said that up to recently no real basic mechanism for gravity perception in single cells has been presented or verified. However, it now has been shown that as a basic membrane parameter, membrane fluidity, is significantly dependent on gravity. This finding might deliver a real basic mechanism for gravity perception of living organisms on all scales. In this review we summarize older and more recent results to demonstrate that the finding of membrane fluidity being gravity dependent is consistent with a variety of published laboratory experiments. We additionally point out to the consequences of these recent results for research in the field life science under space condition.     

Which h-index? — A comparison of WoS,Scopus and Google Scholar

This paper compares the h-indices of a list of highly-cited Israeli researchers based on citations counts retrieved from the Web of Science, Scopus and Google Scholar respectively. In several case the results obtained through Google Scholar are considerably different from the results based on the Web of Science and Scopus. Data cleansing is discussed extensively.