Magnetization dynamics in disordered Fex_xCo1−x_{1-x} alloys : A first-principles augmented space approach and atomistic spin dynamics simulations

In this paper, we present a general method to study magnetization dynamics in chemically disordered alloys. This computationally feasible technique, which seamlessly combines three approaches : the density functional based linear muffin-tin orbitals (LMTO) for self-consistently obtaining a sparse Hamiltonian; the generalized recursion method to obtain the one and two-particle Green functions and augmented space approach to deal with disorder averaging. The same formalism applied to both spectral and response properties should make the errors compatible in different studies. %The underlying computational routines are optimized and parallelized for ease of handling. We have demonstrated a successful application to the binary chemically disordered Fe$_x$Co$_{1-x}$ alloys to explain several experimental features in magnon spectra. Our study captures significant magnon softening due to magnon-electron scattering for chemically disordered Fe$_x$Co$_{1-x}$ alloys within linear spin wave regime. As a complementary study, we have done atomistic spin dynamics simulations by solving Landau-Lifshitz-Gilbert equation with parameters obtained from ab initio multiple scattering theory to compare with the results obtained from augmented space approach.Comment: arXiv admin note: text overlap with arXiv:1102.4551, arXiv:1304.7091 by other author

Technology and Terrorism: The Effects of Cell Phone Coverage on Terrorism

The spread of mobile technology and coverage has had transformative effects, and most current literature focuses on the positive effects of this technology; it holds leaders accountable, facilitates democracy, and encourages transparency. More recently, there has been research done on the relationship between mobile phone availability and violent conflicts. However, there has yet to be research done on the link between cell phone coverage and terrorism. Moreover, most research does not take other characteristics of weak and failing states that may contribute to terrorism into account such as regime type. I will investigate this link using data from the START terrorism database and Collins Coverage by Harper Collins Publisher, and I will focus on the states in the Middle East and North African region. I contend that cell phone coverage helps terror cells overcome collective actions issues and create diaspora networks, and this will lead to more terror activity. I also hypothesize that the effects of cell coverage will be more pronounced in states where the technology rapidly improved and in those that score highest in the “state legitimacy” category on the Fragile States Index. This research can help states identify problem areas, understand the technology terror groups use, and help governments maintain a monopoly on organized violence

Limits on fine texture discrimination in humans and the role of friction

Science, Technology, Engineering and Mathematics (STEM) disciplines are challenging to blind and visually impaired (BVI) individuals. One of the possible reasons is the complexity in representing and understanding scientific content. Introducing tactile elements such as textures into existing Braille characters can potentially increase the information content of Braille and could likely simplify the complex notations. However, such a task requires a thorough understanding of the discrimination of textures through touch. The current dissertation focuses on: 1) Investigating the psychophysical factors involved in texture discrimination and, 2) Developing a testing system to assess friction induced skin damage from repetitive motion over textured surfaces. The tactile discrimination sensitivity for six fine textured non-patterned surfaces (fine-grit abrasive papers) was evaluated using a two-alternative forced choice technique. The surface roughness parameters and the coefficient of friction of the abrasive papers interacting with human skin were measured. Scanning electron microscopy images were used to observe the surface microstructure. The results suggest that differences in the mean spacing and the friction coefficients could be indicative of differentiability of fine textured samples. Three clearly differentiable textures identified from this study were used to investigate the effect of texture area on tactile discrimination sensitivity. A perception measurement experiment in combination with a friction measurement experiment was performed to understand the possible role of friction in touch-based texture discrimination. There was decrease in the discrimination ability with the decrease in the texture area. An elastomeric skin simulant with layered structure similar to that of human skin was constructed to replicate skin friction blisters. The relationship between applied normal load and number of cycles of reciprocating motion required for blistering was studied. Additionally, a crack-growth model was developed treating the skin simulant as an adhesive-bonded laminar composite. This study made it evident that complete profile of the tribological system is required to develop a skin simulant that can accurately predict skin friction damage. Based on the current literature, the role of surface topography and elastic properties of the human skin on friction was uncertain. Coefficient of friction of four probing surfaces, human index finger pad, silicone replicas of the finger with and without fingerprints, and a smooth silicone sphere, when sliding against fine grit abrasive papers were compared to identify these roles

Investigation of friction mechanisms in finger pad sliding against surfaces of varying roughness

Human finger pad friction and the effects of surface features on the fingerprint ridges, shape of the finger and the material properties of the finger were investigated. The friction coefficients for three fine-grit abrasive papers were measured to assess these effects. Four probing surfaces were used: human index finger pad, silicone replicas of the finger with and without fingerprints, and a smooth silicone sphere. Friction tests were performed at a constant normal load of 0.5 N in two probe orientations: normal and perpendicular to the orientation of the fingerprint ridges. Scanning electron microscopy of the abrasive papers was performed to examine their surface topography. Based on the trends in coefficients of friction, topography of the abrasive papers, surface features of the finger pad, and the shape and elastic properties of the finger, possible friction mechanisms were discussed. It was inferred that the change in the shape of the probe (from a sphere to the finger shape) changes the adhesion and deformation components of friction, the presence of fingerprints adds an interlocking contribution to the friction and decrease the adhesion and deformation components of friction, and the elastic properties of the finger lead to an increase in all the three components of friction

Investigation of the effect of the normal load on the incidence of friction blisters in a skin-simulant model

A laminar skin simulant was constructed to study the incidence of friction blisters. The skin simulant consists of a thin polyurethane top layer and textured gum foam rubber bottom layer adhered to an acrylic-backing plate to emulate the layered structure of the human skin. Friction blisters were produced on the skin simulant by using a dual-axis tribometer. The effect of the applied normal load on the number of cycles required to produce a blister was investigated. The skin simulant was also analyzed as an adhesive-bonded laminar composite to determine the relationship between the applied normal load and the number of cycles for blistering. The normal load and the number of cycles were found to be inversely related and vary by a power law function, as observed in previous work on human subjects in Naylor’s pioneering study. The results obtained from the experimental data and the fracture mechanics modeling of the skin simulant indicate the potential of elastomeric skin simulant in providing useful insight into blister mechanics and other tribological properties of skin

Production of extracellular amylase from agricultural residues by a newly isolated Aspergillus species in solid state fermentation

The production of extracellular amylases by solid state fermentation (SSF) was investigated employing our laboratory isolate Aspergillus sp.MK07. Various agricultural residual substrates like wheat bran, rice bran and green gram husk were studied for enzyme production. Highest enzyme production was obtained with wheat bran as a substrate. Effects of process variables, namely: incubation period, temperature, initial moisture content, pH, supplementary carbon, nitrogen source and inoculum level on production of amylase have been studied and accordingly, optimum conditions have been determined. It was found that amylase production was highest at 120 h of incubation period at 30°C, 70% initial moisture content, 5.0 pH and 5% inoculum level. Supplementation of carbon (starch) and nitrogen source (peptone) showed an increase in amylase production and the highest amount of amylase production obtained under all optimized conditions was 164 U/g.Key words: Solid state fermentation, optimization, Aspergillus, fermentation, amylas