18,846 research outputs found

### Charge-transfer induced large nonlinear optical properties of small Al Clusters: Al4M4

We investigate the linear and nonlinear electric polarizabilities of small
Al4M4 (M=Li, Na and K) clusters. Quantum chemical calculations reveal that
these compounds exhibit an exceptionally high magnitude of linear and nonlinear
optical (NLO) coefficients which are orders of magnitude higher than the
conventional pi-conjugated systems of similar sizes. We attribute such
phenomenal increase to non-centrosymmetricity incorporated in the systems by
the alkali atoms surrounding the ring leading to charge transfer with small
optical gap and low bond length alternation (BLA). Such a low magnitude of the
BLA from a different origin, suggests the possibility that these clusters are
aromatic in character and along with the large NLO coefficients they appear to
be better candidates for next generation NLO fabrication devices

### Electron transport through a quantum interferometer with side-coupled quantum dots: Green's function approach

We study electron transport through a quantum interferometer with
side-coupled quantum dots. The interferometer, threaded by a magnetic flux
$\phi$, is attached symmetrically to two semi-infinite one-dimensional metallic
electrodes. The calculations are based on the tight-binding model and the
Green's function method, which numerically compute the conductance-energy and
current-voltage characteristics. Our results predict that under certain
conditions this particular geometry exhibits anti-resonant states. These states
are specific to the interferometric nature of the scattering and do not occur
in conventional one-dimensional scattering problems of potential barriers. Most
importantly we show that, such a simple geometric model can also be used as a
classical XOR gate, where the two gate voltages, viz, $V_a$ and $V_b$, are
applied, respectively, in the two dots those are treated as the two inputs of
the XOR gate. For $\phi=\phi_0/2$ ($\phi_0=ch/e$, the elementary flux-quantum),
a high output current (1) (in the logical sense) appears if one, and only one,
of the inputs to the gate is high (1), while if both inputs are low (0) or both
are high (1), a low output current (0) appears. It clearly demonstrates the XOR
gate behavior and this aspect may be utilized in designing the electronic logic
gate.Comment: 8 pages, 5 figure

### Constitutive behaviour of the metastable stainless steel: Sandvik Nanoflex

This article presents a model to describe the constitutive behaviour of corrosion-resistant Sandvik steel NanoflexTM [1] during metal forming and hardening. This material is characterised by different phenomena. The material is metastable, which causes strain-induced transformation to take place during metal forming. Depending on the annealing conditions, the material also transforms isothermally [2, 3] (as opposed to a-thermal martensite). This transformation can also take place immediately after forming, as a result of the residual stresses present in the material. The martensite phase of this material can be aged [4]. Results of the various measurements on Sandvik NanoflexTM are shown. The measurements mainly involved tensile tests and upsetting tests, during which both isothermal transformation and strain-induced transformation were measured by inductive sensors[5] and they were afterwards examined. The hardening of the material and the increase in hardness during ageing was also examined.\ud
Finally, a constitutive model based on literature and the measurement are presented. This model describes the isothermal,\ud
stress-assisted transformation, strain-induced transformation, work hardening and ageing. The model has been set up in such\ud
a way that it can be simply implemented in a FEM cod

### On the Observability of "Invisible" / "Nearly Invisible" Charginos

It is shown that if the charginos decay into very soft leptons or hadrons +
$\not{E}$ due to degeneracy/ near- degeneracy with the LSP or the sneutrino,
the observability of the recently proposed signal via the single photon (+ soft
particles) + $\not{E}$ channel crucially depends on the magnitude of the \SNU
mass due to destructive interferences in the matrix element squared. If the
\SNU's and, consequently, left-sleptons are relatively light, the size of the
signal, previously computed in the limit \MSNU \to \infty only, is
drastically reduced. We present the formula for the signal cross section in a
model independent way and discuss the observability of the signal at LEP 192
and NLC energies.Comment: 27 pages, Late

### NAND gate response in a mesoscopic ring: An exact study

NAND gate response in a mesoscopic ring threaded with a magnetic flux $\phi$
is investigated by using Green's function formalism. The ring is attached
symmetrically to two semi-infinite one-dimensional metallic electrodes and two
gate voltages, namely, $V_a$ and $V_b$, are applied in one arm of the ring
those are treated as the two inputs of the NAND gate. We use a simple
tight-binding model to describe the system and numerically compute the
conductance-energy and current-voltage characteristics as functions of the gate
voltages, ring-to-electrode coupling strength and magnetic flux. Our
theoretical study shows that, for $\phi=\phi_0/2$ ($\phi_0=ch/e$, the
elementary flux-quantum) a high output current (1) (in the logical sense)
appears if one or both the inputs to the gate are low (0), while if both the
inputs to the gate are high (1), a low output current (0) appears. It clearly
exhibits the NAND gate behavior and this feature may be utilized in designing
an electronic logic gate.Comment: 8 pages, 5 figure

### Is there New Physics in B Decays ?

Rare decays of the $B$ meson are sensitive to new physics effects. Several
experimental results on these decays have been difficult to understand within
the standard model (SM) though more precise measurements and a better
understanding of SM theory predictions are needed before any firm conclusions
can be drawn. In this talk we try to understand the present data assuming the
presence of new physics. We find that the data points to new physics of an
extended Higgs sector and we present a two higgs doublet model with a 2-3
flavor symmetry in the down type quark sector that can explain the deviations
from standard model reported in several rare B decays.Comment: 8 pages, Talk presented at Theory Canada II, Perimeter Institute,
Waterloo, Canada. New references added and update

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