210 research outputs found
Synthesis of silicon oxide/VYCOR composite membrane structures by an optimized LPCVD process
This study is focused on development of highly selective ceramic membrane structures consisting of silicon dioxide films synthesized by low pressure chemical vapor deposition (LPCVD) on mesoporous Vycor substrates. The ability of easily altering the composition of such films by varying the LPCVD processing parameters affords the opportunity of microengineering the pore structure by reducing the diameters of pre-existing pores in the support. The process parameters investigated include, deposition temperature, total pressure, and flow rate of oxygen. Both the kinetics and select properties of the deposits were examined. The growth rate as a function of temperature was seen to follow an Arrhenius behavior in the range 350-475 °C with an apparent activation energy of 9 kcal/mol. The growth rate was seen to increase with higher oxygen flow rate and to vary as a function of the square root of pressure. Within the framework of the process window investigated a temperature of 450 °C, total pressure of 500 mTorr, oxygen and DES flow rate of 15 sccm and 30 scorn, respectively, yielded the best quality oxide with density 2.11 g/cm3, RI 1.45, and compressive stress 210 MPa. Permeation studies on Silicon Oxide/ Vycor composite membrane synthesized by the same side reaction geometry indicated poor permselectivity performance followed by cracking of the membrane structure. Opposing reactant geometry technique resulted in membrane structures of significantly higher selectivity than that predicted by Knudsen mechanism
Fourier transform for functions of bicomplex variables
This paper examines the existence and region of convergence of Fourier
transform of the functions of bicomplex variables with the help of projection
on its idempotent components as auxiliary complex planes. Several basic
properties of this bicomplex version of Fourier transform are examined.Comment: 1 figur
Structure, reactivity and electronic properties of V-doped Co clusters
Structures, physical and chemical properties of V doped Co clusters
have been studied in detail using density functional theory based
first-principles method. We have found anomalous variation in stability of the
doped clusters with increasing V concentration, which has been nicely
demonstrated in terms of energetics and electronic properties of the clusters.
Our study explains the nonmonotonic variation in reactivity of CoV
clusters towards H molecules as reported experimentally [J. Phys. Chem.
{\bf 94}, 2744 (1990)]. Moreover, it provides useful insight into the cluster
geometry and chemically active sites on the cluster surface, which can help to
design better catalytic processes.Comment: 10 pages, 9 figures, 4 table
Engineering the magnetic properties of the Mn cluster by doping
With a goal to produce giant magnetic moment in Mn cluster which will
be useful for practical applications, we have considered the structure and
magnetic properties of pure Mn cluster and substitutionally doped it
with X = Ti, V, Cr, Fe, Co, Ni atom to produce MnX clusters. We find
that Ti and V substitutions in Mn cluster are the most promising in
terms of gaining substantial binding energy as well as achieving higher
magnetic moment through ferromagnetic alignment of atom-centered magnetic
moments. This has been demonstrated in terms of energetics and electronic
properties of the clusters. For comparison, we have also studied the effect of
N-capping of Mn cluster, predicted in the earlier work [Phys. Rev. Lett.
{\bf 89}, 185504 (2002)] as a means to produce stable giant magnetic moment in
Mn clusters upto cluster size of 5 Mn atoms.Comment: 8 pages, 9 figures, 2 table
Electroweak Precision Data, Light Sleptons and Stability of the SUSY Scalar Potential
The light slepton-sneutrino scenario with non-universal scalar masses at the
GUT scale is preferred by the electroweak precision data. Though a universal
soft breaking mass at or below the Plank scale can produce the required
non-universality at the GUT scale through running, such models are in conflict
with the stability of the electroweak symmetry breaking vacuum. If the
supergravity motivated idea of a common scalar mass at some high scale along
with light sleptons is supported by future experiments that may indicate that
we are living in a false vacuum. In contrast SO(10) D-terms, which may arise if
this GUT group breaks down directly to the Standard Model, can lead to this
spectrum with many striking phenomenological predictions, without jeopardizing
vacuum stability.Comment: Plain Latex, 17 pages, 5 postscript figur
Recursive approach to study transport properties of atomic wire
In this study, we propose a recursive approach to study the transport
properties of atomic wires.
It is based upon a real-space block-recursion technique with Landauer's
formula being used to express the conductance as a scattering problem. To
illustrate the method, we have applied it on a model system described by a
single band tight-binding Hamiltonian. Results of our calculation therefore may
be compared with the reported results on Na-atom wire. Upon tuning the
tight-binding parameters, we can distinctly identify the controlling parameters
responsible to decide the width as well as the phase of odd-even oscillations
in the conductance.Comment: 9 pages, 8 figures, table
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