241 research outputs found
Diffusive Transport in Quasi-2D and Quasi-1D Electron Systems
Quantum-confined semiconductor structures are the cornerstone of modern-day
electronics. Spatial confinement in these structures leads to formation of
discrete low-dimensional subbands. At room temperature, carriers transfer among
different states due to efficient scattering with phonons, charged impurities,
surface roughness and other electrons, so transport is scattering-limited
(diffusive) and well described by the Boltzmann transport equation. In this
review, we present the theoretical framework used for the description and
simulation of diffusive electron transport in quasi-two-dimensional and
quasi-one-dimensional semiconductor structures. Transport in silicon MOSFETs
and nanowires is presented in detail.Comment: Review article, to appear in Journal of Computational and Theoretical
Nanoscienc
Electron mobility in silicon nanowires
The low-field electron mobility in rectangular silicon nanowire (SiNW)
transistors was computed using a self-consistent Poisson-Schr\"{o}dinger-Monte
Carlo solver. The behavior of the phonon-limited and surface-roughness-limited
components of the mobility was investigated by decreasing the wire width from
30 nm to 8 nm, the width range capturing a crossover between two-dimensional
(2D) and one-dimensional (1D) electron transport. The phonon-limited mobility,
which characterizes transport at low and moderate transverse fields, is found
to decrease with decreasing wire width due to an increase in the
electron-phonon wavefunction overlap. In contrast, the mobility at very high
transverse fields, which is limited by surface roughness scattering, increases
with decreasing wire width due to volume inversion. The importance of acoustic
phonon confinement is also discussed briefly
Shift of the 2 state of Be in the ternary cold fission of Cf
Recent experimental data indicate that in the ternary cold fission of
Cf the energy of the first excited state of the accompanying light
cluster Be is decreased by an amount ranging between 6 and 26
keV. A model is proposed to calculate the shift of the vibrational 2
state in Be when its heavy companions are the even-even nuclei
Ba and Sr. The stiffness parameters of the -vibrations
are calculated within the self-consistent Hartree-Fock method with BCS pairing
correlations taken into account, and its change is determined by the
interaction of the light cluster with the heavy fragments. The results are
pointing to a dependence of the shift magnitude and signature on the relative
distance between the three clusters and their mutual orientation. Eventually it
is the anharmonic perturbation of the spherical vibrator which is responsible
for obtaining a negative energy shift of the 2 state.Comment: 4 pages, 3 figure
Job Mix Formulation for Bituminous Concrete Grade II Using C# Programming
Bituminous Concrete mix design is a complex process and different methods are proposed by a number of researchers. Marshall’s method of mix design is one such process, which became very popular among the practitioners in India and elsewhere. SUPERPAVE method of mix design which takes into account climatic and traffic factors for aggregate and binder selection. It has gained its prominence and is observed to be superior to any other well-known mix design processes. Aggregate gradation adopted for the mix design plays a crucial role in the performance of the mix. Many researchers have developed mechanisms to work out Job Mix Formulations (JMF) so as to reach the appropriate aggregate mix in the field.The analytical phase of JMF deals with the method of blending of aggregates from the identified stockpiles in order to fulfill the requirements of gradation as specified by agencies for a given layer of flexible pavements. Methods proposed for aggregate blending includes the graphical methods, trial and error method and optimization techniques. The aim of these techniques is two-fold; the first is to optimize the cost involved in blending from the known unit cost of individual stockpiles; and the other is to fulfill the gradation recommendations of the local agencies and parameters suggested in other methods. In this research, an attempt has been made to develop C# (C-Sharp) application in .NET framework using the sequential search technique to work out the best blend of aggregate particles by ensuring the requirements mentioned in MoRTH’s (Ministry of Road Transport & Highways, India) recommended practice. Bailey’s method and the maximum density line have been recommended in 0.45 power chart and incorporating optimization criteria. Grade II bituminous concrete has been chosen for the research. It was clearly observed that the fine aggregate fraction in the stockpiles influences the final Job Mix Formulation. The devleloped tool can accommodate up to 5 stockpiles. It was also observed that the Bailey’s requirements are more stringent when compared with MoRTH requirements as far as JMF is considered. The developed tool is capable of generating the blends with Recycled Asphalt Pavement (RAP) aggregate blends
Ternary configuration in the framework of inverse mean-field method
A static scission configuration in cold ternary fission has been considered
in the framework of mean field approach. The inverse scattering method is
applied to solve single-particle Schroedinger equation, instead of constrained
selfconsistent Hartree-Fock equations. It is shown, that it is possible to
simulate one-dimensional three-center system via inverse scattering method in
the approximation of reflectless single-particle potentials.Comment: 8 pages, 1 figure, iopart.cls, to be published in Int.J.Mod.Phys.
On Landauer vs. Boltzmann and Full Band vs. Effective Mass Evaluation of Thermoelectric Transport Coefficients
The Landauer approach to diffusive transport is mathematically related to the
solution of the Boltzmann transport equation, and expressions for the
thermoelectric parameters in both formalisms are presented. Quantum mechanical
and semiclassical techniques to obtain from a full description of the
bandstructure, E(k), the number of conducting channels in the Landauer approach
or the transport distribution in the Boltzmann solution are developed and
compared. Thermoelectric transport coefficients are evaluated from an atomistic
level, full band description of a crystal. Several example calculations for
representative bulk materials are presented, and the full band results are
related to the more common effective mass formalism. Finally, given a full E(k)
for a crystal, a procedure to extract an accurate, effective mass level
description is presented.Comment: 33 pages, 8 figure
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