1,850 research outputs found
Time for pulse traversal through slabs of dispersive and negative (, ) materials
The traversal times for an electromagnetic pulse traversing a slab of
dispersive and dissipative material with negative dielectric permittivity
() and magnetic permeability () have been calculated by using
the average flow of electromagnetic energy in the medium. The effects of
bandwidth of the pulse and dissipation in the medium have been investigated.
While both large bandwidth and large dissipation have similar effects in
smoothening out the resonant features that appear due to Fabry-P\'{e}rot
resonances, large dissipation can result in very small or even negative
traversal times near the resonant frequencies. We have also investigated the
traversal times and Wigner delay times for obliquely incident pulses and
evanescent pulses. The coupling to slab plasmon polariton modes in frequency
ranges with negative or is shown to result in large traversal
times at the resonant conditions. We also find that the group velocity mainly
contributes to the delay times for pulse propagating across a slab with n=-1.
We have checked that the traversal times are positive and subluminal for pulses
with sufficiently large bandwidths.Comment: 9 pages, 9 figures, Submitted to Phys. Rev.
Complete controllability of quantum systems
Sufficient conditions for complete controllability of -level quantum
systems subject to a single control pulse that addresses multiple allowed
transitions concurrently are established. The results are applied in particular
to Morse and harmonic-oscillator systems, as well as some systems with
degenerate energy levels. Morse and harmonic oscillators serve as models for
molecular bonds, and the standard control approach of using a sequence of
frequency-selective pulses to address a single transition at a time is either
not applicable or only of limited utility for such systems.Comment: 8 pages, expanded and revised versio
Extreme nonlinear electrodynamics in metamaterials with very small linear dielectric permittivity
We consider a sub-wavelength periodic layered medium whose slabs are filled
by arbitrary linear metamaterials and standard nonlinear Kerr media and we show
that the homogenized medium behaves as a Kerr medium whose parameters can
assume values not available in standard materials. Exploiting such a parameter
availability, we focus on the situation where the linear relative dielectric
permittivity is very small thus allowing the observation of the extreme
nonlinear regime where the nonlinear polarization is comparable with or even
greater than the linear part of the overall dielectric response. The behavior
of the electromagnetic field in the extreme nonlinear regime is very peculiar
and characterized by novel features as, for example, the transverse power flow
reversing. In order to probe the novel regime, we consider a class of fields
(transverse magnetic nonlinear guided waves) admitting full analytical
description and we show that these waves are allowed to propagate even in media
with since the nonlinear polarization produces a
positive overall effective permittivity. The considered nonlinear waves
exhibit, in addition to the mentioned features, a number of interesting
properties like hyper-focusing induced by the phase difference between the
field components.Comment: 12 pages, 7 figure
Store choice behavior in food and grocery retailing in India an empirical analysis
Shopping for food and grocery products has witnessed a paradigm shift in Indian retail market
with the changes in consumer buying behaviour driven by strong income growth, changing
lifestyles and favourable demographic patterns. But the very fast changing trends in consumption
patterns, food and eating habits of consumers have contributed immensely to the growth and
development of 'Western' format typologies such as convenience stores, discount stores, super
markets, and hyper markets. The present study is exploratory in nature to identify and examine
the determinant attributes influencing consumer behaviour towards super market store format
choice decisions in the fast growing food and grocery retailing in India. The population of the
study is confined to the retail customers (7.5 crore) ofAndhra Pradesh state and sampling sources
are twin cities of Secunderabad and Hyderabad (58 Lakh population). The 'mall intercept' survey
method is adopted to study the attitudes and opinions of retail customers through questionnaires.
The descriptive statistical tools (like mean, standard deviation and median) and inferential
statistical tools like Factor Analysis, Chi-Square, ANOVA, Correlation, and Multiple regressions are
used to test the formulated hypotheses and validate the model. The study has found significant
association between shopper attributes and store format choice decisions. The findings revealed
that merchandise, customer service, location and atmospheric related store attributes are
affecting the store format choice behaviour. The study has discussed various academic and
managerial implications for retail industry in general and food & grocery in particular
Experimental Study of Thermal oxidation Damage in Ceramic Composites Using Ultrasonic Waves
One major concern about ceramic matrix composites (CMC) is their high temperature stability, especially in an oxidizing environment. In general CMC materials are composed of matrix, fiber, and interphase layers (mainly fiber coatings and/or reaction product layers). It is known [1,2] that the properties of CMC materials are dominated by the interphase. However, this interphase often suffers from oxidation reactions caused by diffusion of oxygen through the matrix [1,3]. As a result desirable properties are not retained
Morphological structures and drug release effect of multiple electrospun nanofibre membrane systems based on PLA, PCL, and PCL/Magnetic nanoparticle composites
Biopolymers are good carrier materials in relation to efficient release sustainability for encapsulated drugs. In particular, electrospun polymer/composite fibre membranes can offer greater benefits owing to their competitive release features as well as large specific surface areas. In this study, multiple electrospun nanofibre membrane systems were utilised including different material systems such as poly(lactic acid) (PLA), poly(ε-caprolactone) (PCL), and PCL/magnetic nanoparticle (MP) composites loaded with tetracycline hydrochloride (TCH) as a therapeutic compound for their potential use in drug delivery applications. Such electrospun nanofibres were investigated to understand how composite constituents could tailor surface morphology for drug release control and biodegradation effect of PCL electrospun nanofibers on a long term for different drug release systems. Fibre diameter appeared to be decreased considerably with the addition of TCH drug. It was also evident that average fibre diameter was reduced when embedding MPs owing to the enhancement of solution conductivity. The encapsulation of TCH drug was found to be effective, as evidenced by Fourier transform infrared (FTIR) spectra. Thermogravimetric analysis (TGA) data revealed no significant change in the thermal stability of PCL with the inclusion of TCH and MPs. However, the use of TCH to PLA delayed the thermal degradation. Glass transition temperature (TQ) and melting temperature (TM) of PCL were decreased with the inclusion of MPs and TCH. The degree of crystallinity (XC) for PCL diminished when incorporated with MPs. Additional TCH to PLA, PCL, and PCL/MP nanocomposites resulted in a moderate decrease in (XC). TCH might be dispersed in an amorphous state within nanofibre membranes. Over the short-term periods, it was clearly seen that TCH release from PCL nanofibre membranes was higher as opposed to PLC/MP and PLA counterparts. On the contrary, such a drug release from PLC membranes became relatively slow owing to its high (XC). Further, the mass loss results were consistent with those obtained from in vitro drug release. Overall, TCH release kinetics of PCL/TCH nanofibre membranes were better estimated by Zeng model as opposed to PLA/TCH counterparts
Silicon Nitride Plates for Turbine Blade Application: FEA and NDE Assessment
Engine manufacturers are continually attempting to improve the performance and the overall efficiency of internal combustion engines. The thermal efficiency is typically improved by raising the operating temperature of essential engine components in the combustion area. This reduces the heat loss to a cooling system and allows a greater portion of the heat to be used for propulsion. Further improvements can be achieved by diverting part of the air from the compressor, which would have been used in the combustor for combustion purposes, into the turbine components. Such a process is called active cooling. Increasing the operating temperature, decreasing the cooling air, or both can improve the efficiency of the engine. Furthermore, lightweight, strong, tough hightemperature materials are required to complement efficiency improvement for nextgeneration gas turbine engines that can operate with minimum cooling. Because of their low-density, high-temperature strength, and thermal conductivity, ceramics are being investigated as potential materials for replacing ordinary metals that are currently used for engine hot section components. Ceramic structures can withstand higher operating temperatures and other harsh environmental factors. In addition, their low densities relative to metals helps condense component mass (ref. 1). The objectives of this program at the NASA Glenn Research Center are to develop manufacturing technology, a thermal barrier coating/environmental barrier coating (TBC/EBC), and an analytical modeling capability to predict thermomechanical stresses, and to do minimal burner rig tests of silicon nitride (Si3N4) and SiC/SiC turbine nozzle vanes under simulated engine conditions. Furthermore, and in support of the latter objectives, an optimization exercise using finite element analysis and nondestructive evaluation (NDE) was carried out to characterize and evaluate silicon nitride plates with cooling channels
Nano-Engineered Environment for Nerve Regeneration: Scaffolds, Functional Molecules and Stem Cells
One of the most complex systems in the human body is the nervous system, which is divided into the central and peripheral nervous systems. The regeneration of the CNS is a complex and challenging biological phenomenon hindered by the low regenerative capacity of neurons and the prohibition factors in response to nerve injuries. To date, no effective approach can achieve complete recovery and fully restore the functions of the nervous system once it has been damaged. Developments in neuroscience have identified properties of the local environment with a critical role in nerve regeneration. Advances in biomaterials and biomedical engineering have explored new approaches of constructing permissive environments for nerve regeneration, thereby enabling optimism with regard to nerve-injury treatment. This article reviews recent progress in nanoengineered environments for aiding nerve-injury repair and regeneration, including nanofibrous scaffolds, functional molecules, and stem cells.postprin
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