Confinement-Induced Phonon Softening and Hardening in Sb2Te3 Thin Films

Scaling effects in Sesqui-chalcogenides are of major interest to understand and optimize their performance in heavily scaled applications, including topological insulators and phase-change devices. A combined experimental and theoretical study is presented for molecular beam epitaxy-grown films of antimony-telluride  (Sb₂Te₃). Structural,vibrational, optical, and bonding properties upon varying confinement are studied for thicknesses ranging from 1.3 to 56 nm. In ultrathin films, the low-frequency coherent phonons of A_1g¹ symmetry are softened compared to the bulk (64.5 cm⁻¹ at 1.3 nm compared to 68 cm⁻¹ at 55.8 nm). A concomitant increase of the high-frequency A_1g² Raman mode is seen. X-ray diffraction analyses unravel an accompanying out of plane stretch by 5%, mainly stemming from an increase in the Te-Te gap. This conclusion is supported by density functional theory slab models, which reveal a significant dependency of chemical bonding on film thickness. Changes in atomic arrangement, vibrational frequencies, and bonding extend over a thickness range much larger than observed for other material classes. The finding of these unexpectedly pronounced thickness-dependent effects in quasi-2D material Sb₂Te₃ allows tuning of the film properties with thickness. The results are discussed in the context of a novel bond-type, characterized by a competition between electron localization and delocalization.     

CAMP: cluster aided multi-path routing protocol for wireless sensor networks

Wireless Networks - In this article, we propose a novel routing algorithm for wireless sensor network, which achieves uniform energy depletion across all the nodes and thus leading to prolonged...     

In situ micro/nano-hydrogel synthesis from acrylamide derivates with lecithin organogel system

Acrylamide based hydrogel particles with variable charge were synthesized in different sizes using a biocompatible surfactant. We use microemulsion polymerization to synthesize the hydrogel particles in lecithin organogel systems. The phospholipid, lecithin, is a soybean extract that exhibits a rich phase behavior depending on various factors such as amount of water, co-solvent, additives and their concentrations. By UV irradiation of water-in-oil microemulsions of lecithin, containing different monomers, phospholipid coated hydrogels were synthesized in situ. The hydrogel particle size varies from a few hundred nanometers to tens of micrometer. The response time of these micron sized hydrogel particles, as measured by swelling experiments, is very fast (∼10⁰ s) in comparison with their corresponding bulk hydrogels (∼10¹ h). The positively charged cationic hydrogel microparticles were embedded/dispersed into another hydrogel matrix to render responsive behavior to a non-responsive matrix. Besides TEM and SEM studies, fluorescein dye absorption studies were also performed in order to visualize the hydrogel microparticles. Additionally, anionic hydrogel micro/nano-particles were also synthesized in the lecithin system.     

A comparative study of hard turned and cylindrically ground white layers

Compared with grinding, hard turning is competitive in many cases, with substantial benefits. However, hard turning applications are not preferred, due to the existence of the process-induced white layer on the component surface, which is often assumed to be detrimental to component life. Nevertheless, white layer properties have not been well understood or clearly defined, especially the properties of the white layer induced in hard turning as against grinding. A clear understanding of white layer properties will provide a solid physics basis for product performance analysis and useful data for process selection. In this study, benchmark hard turning and cylindrical grinding experiments were conducted to generate thick white layers for reliable measurement. It was found that the properties of white and dark layers by hard turning and grinding are fundamentally different in four aspects: surface structure characteristics, microhardness, microstructures, and chemical composition. A white layer is not untempered martensite in terms of retained austenite. Additionally, a thick white layer can be produced in grinding under certain conditions.     

Hypercube computing: Connected components

Several approaches to finding the connected components of a graph on a hypercube multicomputer are proposed and analyzed. The results of experiments conducted on an NCUBE hypercube are also presented. The experimental results support the analysis.This research was supported in part by the National Science Foundation under grants DCR84-20935 and MIP 86-17374.     

Studies on the response of the TLD badge for high-energy photons

Absorbed tissue dose measurements are carried out for high-energy photon beams using CaSO4:Dy thermo-luminescence dosemeter (TLD) badge and the results are also verified using ionisation chamber used in radiation therapy. The photon beams generated using linear accelerator at 6 and 18 MV photon beam energies have been used and the absorbed doses are measured at the surface as well as at various depths. It has been found that the depth at which maximum dose is delivered increases with the increase in photon energy and the depth of maximum absorbed dose in tissue occurs beyond 10 mm. It has also been found that the evaluation of the absorbed dose (or Hp(10) as well) using thermoluminescence readout of disc D1 clearly shows that the current TLD badge provides a reasonable estimate of the effective dose for photon fields from 6 to 18 MV linacs for anterior-posterior incidence. The paper also provides information regarding the misinterpretation of radiation pattern in multi-element/filter TLD badge.     

Crystallization of mixed rare earth (didymium) molybdates in silica gel

Experiments on the growth of mixed rare earth (didymium—a combination of La, Nd, Pr and Sm) molybdates in silica gel medium are reported. The optimum conditions conducive for the growth of these crystals are described and discussed. Concentration programming is reported to enhance the size of crystals by two-fold; the maximum size obtained being about 1 mm³. EDAX results suggest the crystals to be heptamolybdates of type R₂Mo₇O₂₄, bearing composition La_1.23Nd_0.43Pr_0.29 Sm_0.05Mo₇0₂₄. The didymium molybdate crystals assume morphologies corresponding to those of spherulites, platelets, cuboids and coalesced crystals. Twinned structure in didymium molybdate crystals are also reported. It is explained that spherulitic morphologies result from aggregates of crystals joining in a spherical envelope. It is suggested that the crystals of didymium molybdates grow by two-dimensional spreading and piling up of layers.     

Studies for Wear Property Correlation for Carbon Fabric-Reinforced PES Composites

Polyethersulfone (PES) composites were developed with carbon fabric (CF). Cold remote nitrogen oxygen plasma (CRNOP) treatment was employed to the CF to incorporate functional groups and promote fiber–matrix adhesion. This study includes the effect of PES melt flow index (MFI) on the wettability of CF and its influence on fretting wear performance. Evaluations of fretting wear properties of composites led to the conclusion that the CRNOP treatment proved beneficial to enhance performance properties significantly. Polymer MFI and treatment to CF proved to be the decisive parameters for controlling performance of composites apart from operating parameters. Perforations on the treated carbon fiber, evidently observed by FESEM, improved the fiber–matrix adhesion, and hence the performance properties. Artificial neuron network (ANN) was used for prediction of the wear behavior of composites.     

Electrostatic ion trap and Fourier transform measurements for high-resolution mass spectrometry

We report on the development of an electrostatic ion trap for high-resolution mass spectrometry. The trap works on purely electrostatic fields and hence trapping and storing of ions is not mass restrictive, unlike other techniques based on Penning, Paul, or radio frequency quadrupole ion traps. It allows simultaneous trapping and studying of multiple mass species over a large mass range. Mass spectra were recorded in "dispersive" and "self-bunching" modes of ions. Storage lifetimes of about 100 ms and mass resolving power of about 20,000 could be achieved from the fifth harmonic Fourier transform spectrum of Xe ions recorded in the self-bunching mode.     

Hill slope instability of Nainital City,Kumaun Lesser Himalaya,Uttarakhand, India

Nainital City of Kumaun Lesser Himalaya is prone to mass wasting processes during monsoon season, which mischievously triggers the hill slope instability in this region. Slate, dolomitic limestone, silty sandstone and rhythmite of the Krol Formation are the main rock types. The present study focuses on the investigation of slope stability in the region in terms of potential seismicity and landslide. Geological and geotechnical mapping indicates that the major portion of the area is characterized by slope wash materials and buildings. The combination of 3–4 joint sets with one random joint is the main structure at outcrops. The major geological structures of this area are Nainital lake fault passing from the center of the lake, Main Boundary Thrust at SW, and Khuriya Fault passing from the SE direction of Nainital City. This work finds that different types of discontinuities (e.g. joints and faults), overburden due to unplanned civil structures, and neotectonic activity in the vicinity of this area affect the stability of the city. The slate forms the base of the city, dipping slightly towards the lake side along the NW direction, thus accelerating the instability of this area. Rock mass rating (RMR), slope mass rating, factor of safety (FOS) and graphical analysis of the discontinuity for slope kinematics indicate that the study area is a landslide-prone zone. This study can facilitate reducing the risk of human life, and contribute to the ongoing construction works in the area.