Thermal Activation of Dry Sliding Friction at The Nano-scale

Molecular dynamic (MD) simulations are applied to investigate the dependency of the kinetic friction coefficient on the temperature at the nano-scale. The system is comprised of an aluminum spherical particle consisting of 32000 atoms in an FCC lattice sliding on a stack of several layers of graphene, and the simulations have done using LAMMPS. The interaction potential is charge-optimized many-body (COMB3) potential and a Langevin thermostat keep the system at a nearly constant temperature. With an assumption of linear viscous friction, $F_{fr}= - \gamma v$, the kinetic friction coefficient $\gamma$ is derived and plotted at different temperatures in the interval of $T \in [1, 600] K$. As a result, by increasing temperature, the kinetic friction coefficient is decreased. Consequently, while the friction is assumed as a linear viscous model, the results are similar to the thermal activation in atomic-scale friction. That is, (1) by increasing sliding velocity friction force will be increased and (2) by increasing temperature, kinetic friction coefficient decreases.Comment: 7 pages, 5 figure

A study of the UV and VUV degradation of FEP

UV and VUV degradation of fluorinated ethylene propylene (FEP) copolymer was studied using electron spin resonance (ESR) spectroscopy, x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The ESR study revealed the formation of a terminal polymer radical. The stability of this radical was investigated under different environments. An XPS study of FEP film exposed to VUV and atomic oxygen showed that oxidation takes place on the polymer surface. The study revealed also that the percentage of CF2 in the polymer surface decreased with exposure time and the percentage of CF, CF3, and carbon attached to oxygen increased. SEM micrographs of FEP film exposed to VUV and atomic oxygen identified a rough surface with undulations similar to sand dunes

The Role of Local Steps in Local SGD

We consider the distributed stochastic optimization problem where $n$ agents want to minimize a global function given by the sum of agents' local functions, and focus on the heterogeneous setting when agents' local functions are defined over non-i.i.d. data sets. We study the Local SGD method, where agents perform a number of local stochastic gradient steps and occasionally communicate with a central node to improve their local optimization tasks. We analyze the effect of local steps on the convergence rate and the communication complexity of Local SGD. In particular, instead of assuming a fixed number of local steps across all communication rounds, we allow the number of local steps during the $i$-th communication round, $H_i$, to be different and arbitrary numbers. Our main contribution is to characterize the convergence rate of Local SGD as a function of $\{H_i\}_{i=1}^R$ under various settings of strongly convex, convex, and nonconvex local functions, where $R$ is the total number of communication rounds. Based on this characterization, we provide sufficient conditions on the sequence $\{H_i\}_{i=1}^R$ such that Local SGD can achieve linear speed-up with respect to the number of workers. Furthermore, we propose a new communication strategy with increasing local steps superior to existing communication strategies for strongly convex local functions. On the other hand, for convex and nonconvex local functions, we argue that fixed local steps are the best communication strategy for Local SGD and recover state-of-the-art convergence rate results. Finally, we justify our theoretical results through extensive numerical experiments

The Prevalence of Needle sticks injuries among health care workers at a hospital in Tehran

ABSTRACT Needle stick injuries (NSIs) are one of the most significant and preventable hazards in relation to Healthcare workers (HCWs). Such injuries have been shown to be of high prevalence within developing countries. To determine the prevalence and circumstances pertaining to the occurrence of NSIs among HCWs employed at a special hospital. The study conducted was a cross-sectional study on HCWs and was carried out in one of Tehran's special hospitals in the year 2012. In this study, in order to identify and determine hazardous potential due to needle stick, HFMEA method was chosen. This resulted in the collection of 240 valid and reliable questionnaires. The validity and reliable nature of the questionnaires was confirmed by experts and by means of the test re-test method. The gathered data was analyzed with SPSS software, version 16.From the analysis of the data it was shown that, a total of 97 (40.42%) HCWs had suffered NSIs in the last year. The patient ward showed the highest prevalence of NSIs (47.42%) in the hospital. Nurses had the highest risk of suffering NSIs (56.7%) in comparison with the other occupational groups. All in all 175 NSIs occurred for the 240 HCWs trialed during the selected period of clinical practice. Of those that received injuries, only roughly 1 in 3 (38.14%) reported it to their infection control officer. Just over a quarter (26.80%) of the injured HCWs used post exposure prophylaxis (PEP) against HIV. Almost all (88.75%) of the HCWs had received a safe injection course. In general, NSIs and their subsequent underreporting are commonplace among hospital healthcare professionals. Significantly, more than two-thirds of the injured HCWs did not use post-exposure prophylaxis (PEP) against HIV. Improved prevention and reporting strategies are needed if the occupational health and safety of healthcare workers is to improve

Network Performance Assessment with Uniform and Non-Uniform Nodes Distribution in C+L Upgrades vs. Fiber Doubling SDM Solutions

Both spatial-division multiplexing (SDM) and band-division multiplexing (BDM) have been proposed to increase the traffic allocation in transparent optical networks. If available, SDM may take advantage of the already deployed dark fibers, otherwise BDM is a viable and cost-efficient solution by exploiting multiple bands on the deployed fibers just upgrading the required equipment. We assess the network capacity upgrades enabled by C+L BDM and fiber doubling SDM solutions as realistic upgrade scenario from a C-band only case, using the statistical network assessment process (SNAP). SNAP has been applied to the German, the US-NET and the COST networks by generating any-to-any traffic according to both an uniform or population-based joint probability density function. We show that both SDM and BDM upgrades double the network capacity, making the performances of the two solutions comparable

DOES SUPPLIER’S WILLINGNESS TO CUSTOMIZE INFLUENCE THE BUYER’S RETENTION?

Since the last decade, customer retention has become the central topic in the management and marketing decisions in many companies.  A 5% increase in customer retention can lead to 25-95 % increase in profits. A retained customer is the loyal one to the companies due to the attachment and commitment. This loyal customer will, recommend other customers to purchase and repurchase the companies’ products and services. How we can enhance customer retention? This is one of the main challenges for most of professionals, which requires a lot of investigations. Therefore, the antecedents of customer retention required enough attention. This study explores literatures on antecedents of customer retention in Business-to-Business relationship. Based on the thorough literatures done, a theoretical framework is proposed and some possible recommendations are put forward for future researches. Keywords: Customer retention; Supplier’s willingness to customize; Supplier-buye

Rarity in Astragalus: a California Perspective

Astragalus (Fabaceae), the largest genus of plants in the world with an estimated 3270 species, is known for large numbers of rare endemic species. An inventory of patterns of climatic, topographic, and edaphic diversity of Astragalus taxa in California (98 native species and 144 named taxa) provides a means to understand the occurrence of rarity in relation to climatic equitability and regional species richness of congeneric taxa. Most taxa in the genus have relatively small ranges of distribution, with 50% restricted geographically to a single Jepson Bioregion. The California Native Plant Society lists 51 Astragalus taxa (35% of the native Astragalus taxa) as rare, threatened, or endangered (RTE). Climate characteristics of geographic regions such as rainfall and temperature extremes show no obvious relationship to species richness or the proportion of listed taxa. Species richness is highest in the arid Great Basin (35 species and 53 taxa) combining both its components, followed by 29 species and 39 taxa in the Sierra Nevada East region that includes the White and Inyo Mountains. The Mojave Desert is also high in diversity with 32 species and 39 taxa, but in contrast the Sonoran Desert region is low with only 12 species and 14 taxa. Despite ranking highest in the number of Astragalus taxa present, the Great Basin regions are low in their proportion of RTE taxa (17%) compared to the South Coast Region (39.5%) and Mojave Desert (32%). Strong edaphic specialization is associated with the majority but not all RTE taxa. While no single ecophysiological adaptation can explain this pattern, it is significant that Astragalus taxa have the potential ability to develop symbiotic nitrogen fixation, and this trait is key to success in soils not conducive to growth of many potential competitors. Land use changes, alien grass invasion and grazing, among other threats, are increasing fragmentation of habitats for many rare taxa with consequent impacts on gene flow. The continued survival of rare and locally endemic taxa will require improved knowledge of their individual demographic traits and long-term population dynamics

Capacity and Energy Usage of Translucent and Multi-Band Transparent Optical Networks

This work shows that exploiting more bands in a transparent network design is a more effective and power-efficient way to increase the network capacity instead of relying on signal regenerators to increase spectral efficiency