13,569 research outputs found
Supersymmetric analogue of BC_N type rational integrable models with polarized spin reversal operators
We derive the exact spectra as well as partition functions for a class of
type of spin Calogero models, whose Hamiltonians are constructed by
using supersymmetric analogues of polarized spin reversal operators (SAPSRO).
The strong coupling limit of these spin Calogero models yields type of
Polychronakos-Frahm (PF) spin chains with SAPSRO. By applying the freezing
trick, we obtain an exact expression for the partition functions of such PF
spin chains. We also derive a formula which expresses the partition function of
any type of PF spin chain with SAPSRO in terms of partition functions of
several type of supersymmetric PF spin chains, where .
Subsequently we show that an extended boson-fermion duality relation is obeyed
by the partition functions of the type of PF chains with SAPSRO. Some
spectral properties of these spin chains, like level density distribution and
nearest neighbour spacing distribution, are also studied.Comment: 36 pages, 2 figures. arXiv admin note: text overlap with
arXiv:1402.275
New Asymptotic Expanstion Method for the Wheeler-DeWitt Equation
A new asymptotic expansion method is developed to separate the Wheeler-DeWitt
equation into the time-dependent Schr\"{o}dinger equation for a matter field
and the Einstein-Hamilton-Jacobi equation for the gravitational field including
the quantum back-reaction of the matter field. In particular, the nonadiabatic
basis of the generalized invariant for the matter field Hamiltonian separates
the Wheeler-DeWitt equation completely in the asymptotic limit of
approaching infinity. The higher order quantum corrections of the gravity to
the matter field are found. The new asymptotic expansion method is valid
throughout all regions of superspace compared with other expansion methods with
a certain limited region of validity. We apply the new asymptotic expansion
method to the minimal FRW universe.Comment: 24 pages of Latex file, revte
Coolant side heat transfer with rotation. Task 3 report: Application of computational fluid dynamics
An experimental and analytical program was conducted to investigate heat transfer and pressure losses in rotating multipass passages with configurations and dimensions typical of modern turbine blades. The objective of this program is the development and verification of improved analysis methods that will form the basis for a design system that will produce turbine components with improved durability. As part of this overall program, a technique is developed for computational fluid dynamics. The specific objectives were to: select a baseline CFD computer code, assess the limitations of the baseline code, modify the baseline code for rotational effects, verify the modified code against benchmark experiments in the literature, and to identify shortcomings in the code as revealed by the verification. The Pratt and Whitney 3D-TEACH CFD code was selected as the vehicle for this program. The code was modified to account for rotating internal flows, and these modifications were evaluated for flow characteristics of those expected in the application. Results can make a useful contribution to blade internal cooling
Relevance of Induced Gauge Interactions in Decoherence
Decoherence in quantum cosmology is shown to occur naturally in the presence
of induced geometric gauge interactions associated with particle production.A
new 'gauge '-variant form of the semiclassical Einstein equations is also
presented which makes the non-gravitating character of the vacuum polarisation
energy explicit.Comment: 10 pages, LATEX, IC/94/16
On the Magnetic Nature of Quantum Point Contacts
We present results for a model that describes a quantum point contact. We
show how electron-electron correlations, within the unrestricted Hartree-Fock
approximation, generate a magnetic moment in the point contact. Having
characterized the magnetic structure of the contact, we map the problem onto a
simple one-channel model and calculate the temperature dependence of the
conductance for different gate voltages. Our results are in good agreement with
experimental results obtained in GaAs devices and support the idea of Kondo
effect in these systems.Comment: 7 pages, 4 figure
The Born-Oppenheimer Approach to the Matter-Gravity System and Unitarity
The Born-Oppenheimer approach to the matter-gravity system is illustrated and
the unitary evolution for matter, in the absence of phenomena such as
tunnelling or other instabilities, verified. The Born-Oppenheimer approach to
the matter-gravity system is illustrated in a simple minisuperspace model and
the corrections to quantum field theory on a semiclassical background
exhibited. Within such a context the unitary evolution for matter, in the
absence of phenomena such as tunnelling or other instabilities, is verified and
compared with the results of other approaches. Lastly the simplifications
associated with the use of adiabatic invariants to obtain the solution of the
explicitly time dependent evolution equation for matter are evidenced.Comment: Latex, 12 pages. Revised version as accepted for publication by
Class. and Quant. Grav. Some points explained and misprints correcte
Electrical Conductance of Molecular Wires
Molecular wires (MW) are the fundamental building blocks for molecular
electronic devices. They consist of a molecular unit connected to two continuum
reservoirs of electrons (usually metallic leads). We rely on Landauer theory as
the basis for studying the conductance properties of MW systems. This relates
the lead to lead current to the transmission probability for an electron to
scatter through the molecule. Two different methods have been developed for the
study of this scattering. One is based on a solution of the Lippmann-Schwinger
equation and the other solves for the {\bf t} matrix using Schroedinger's
equation. We use our methodology to study two problems of current interest. The
first MW system consists of 1,4 benzene-dithiolate (BDT) bonded to two gold
nanocontacts. Our calculations show that the conductance is sensitive to the
chemical bonding between the molecule and the leads. The second system we study
highlights the interesting phenomenon of antiresonances in MW. We derive an
analytic formula predicting at what energies antiresonances should occur in the
transmission spectra of MW. A numerical calculation for a MW consisting of
filter molecules attached to an active molecule shows the existence of an
antiresonance at the energy predicted by our formula.Comment: 14 pages, 5 figure
A computationally efficient method for calculating the maximum conductance of disordered networks: Application to 1-dimensional conductors
Random networks of carbon nanotubes and metallic nanowires have shown to be
very useful in the production of transparent, conducting films. The electronic
transport on the film depends considerably on the network properties, and on
the inter-wire coupling. Here we present a simple, computationally efficient
method for the calculation of conductance on random nanostructured networks.
The method is implemented on metallic nanowire networks, which are described
within a single-orbital tight binding Hamiltonian, and the conductance is
calculated with the Kubo formula. We show how the network conductance depends
on the average number of connections per wire, and on the number of wires
connected to the electrodes. We also show the effect of the inter-/intra-wire
hopping ratio on the conductance through the network. Furthermore, we argue
that this type of calculation is easily extendable to account for the upper
conductivity of realistic films spanned by tunneling networks. When compared to
experimental measurements, this quantity provides a clear indication of how
much room is available for improving the film conductivity.Comment: 7 pages, 5 figure
The effect of magnetic field and disorders on the electronic transport in graphene nanoribbons
We developed a unified mesoscopic transport model for graphene nanoribbons,
which combines the non-equilibrium Green's function (NEGF) formalism with the
real-space {\pi}-orbital model. Based on this model, we probe the spatial
distributions of electrons under a magnetic field, in order to obtain insights
into the various signature Hall effects in disordered armchair graphene
nanoribbons (AGNR). In the presence of a uniform perpendicular magnetic field
(B\perp-field), a perfect AGNR shows three distinct spatial current profiles at
equilibrium, depending on its width. Under non-equilibrium conditions (i.e. in
the presence of an applied bias), the net electron flow is restricted to the
edges and occurs in opposite directions depending on whether the Fermi level
lies within the valence or conduction band. For electrons at energy level below
the conduction window, the B\perp-field gives rise to local electron flux
circulation, although the global flux is zero. Our study also reveals the
suppression of electron backscattering as a result of the edge transport which
is induced by the B\perp-field. This phenomenon can potentially mitigate the
undesired effects of disorders, such as the bulk and edge vacancies, on the
transport properties of AGNR. Lastly, we show that the effect of B\perp-field
on electronic transport is less significant in the multimode compared to the
single mode electron transport.Comment: 21 pages, 4 figure
Third edge for a graphene nanoribbon: A tight-binding model calculation
The electronic and transport properties of an extended linear defect embedded
in a zigzag nanoribbon of realistic width are studied, within a tight binding
model approach. Our results suggest that such defect profoundly modify the
properties of the nanoribbon, introducing new conductance quantization values
and modifying the conductance quantization thresholds. The linear defect along
the nanoribbon behaves as an effective third edge of the system, which shows a
metallic behavior, giving rise to new conduction pathways that could be used in
nanoscale circuitry as a quantum wire.Comment: 6 pages, 6 figures. Two new figures and a few references adde
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