14,109 research outputs found
Optical Generation and Quantitative Characterizations of Electron-hole Entanglement
Using a method of characterizing entanglement in the framework of quantum
field theory, we investigate the optical generation and quantitative
characterizations of quantum entanglement in an electron-hole system, in
presence of spin-orbit coupling, and especially make a theoretical analysis of
a recent experimental result. Basically, such entanglement should be considered
as between occupation numbers of single particle basis states, and is
essentially generated by coupling between different single particle basis
states in the second quantized Hamiltonian. Interaction with two resonant light
modes of different circular polarizations generically leads to a superposition
of ground state and two heavy-hole excitonic states. When and only when the
state is a superposition of only the two excitonic eigenstates, the
entanglement reduces to that between two distinguishable particles, each with
two degrees of freedom, namely, band index, as characterized by angular
momentum, and orbit, as characterized by position or momentum. The band-index
state, obtained by tracing over the orbital degree of freedom, is found to be a
pure state, hence the band-index and orbital degrees of freedom are separated
in this state. We propose some basic ideas on spatially separating the electron
and the hole, so that the entanglement of band-indices, or angular momenta, is
between spatially separated electron and hole.Comment: 8 pages. Journal versio
Understanding brønsted-acid catalyzed monomolecular reactions of Alkanes in Zeolite Pores by combining insights from experiment and theory
Acidic zeolites are effective catalysts for the cracking of large hydrocarbon molecules into lower molecular weight products required for transportation fuels. However, the ways in which the zeolite structure affects the catalytic activity at BrOnsted protons are not fully understood. One way to characterize the influence of the zeolite structure on the catalysis is to study alkane cracking and dehydrogenation at very low conversion, conditions for which the kinetics are well defined. To understand the effects of zeolite structure on the measured rate coefficient (k(app)), it is necessary to identify the equilibrium constant for adsorption into the reactant state (Kads-H+) and the intrinsic rate coefficient of the reaction (k(int)) at reaction temperatures, since k(app) is proportional to the product of Kads-H+ and k(int). We show that Kads-H+ cannot be calculated from experimental adsorption data collected near ambient temperature, but can, however, be estimated accurately from configurational-bias Monte Carlo (CBMC) simulations. Using monomolecular cracking and dehydrogenation of C-3-C-6 alkanes as an example, we review recent efforts aimed at elucidating the influence of the acid site location and the zeolite framework structure on the observed values of k(app) and its components, Kads-H+ and k(int)
Andromeda XXIX: A New Dwarf Spheroidal Galaxy 200 kpc from Andromeda
We report the discovery of a new dwarf galaxy, Andromeda XXIX (And XXIX), using data from the recently released Sloan Digital Sky Survey Data Release 8, and confirmed by Gemini North telescope Multi-Object Spectrograph imaging data. And XXIX appears to be a dwarf spheroidal galaxy, separated on the sky by a little more than 15° from M31, with a distance inferred from the tip of the red giant branch of 730 ± 75 kpc, corresponding to a three-dimensional separation from M31 of 207 +20 – 2 kpc (close to M31's virial radius). Its absolute magnitude, as determined by comparison to the red giant branch luminosity function of the Draco dwarf spheroidal, is M V = –8.3 ± 0.4. And XXIX's stellar populations appear very similar to Draco's; consequently, we estimate a metallicity for And XXIX of [Fe/H] ~–1.8. The half-light radius of And XXIX is 360 ± 60 pc and its ellipticity is 0.35 ± 0.06, typical of dwarf satellites of the Milky Way and M31 at this absolute magnitude range.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90744/1/2041-8205_742_1_L15.pd
Andromeda XXVIII: A Dwarf Galaxy More Than 350 kpc from Andromeda
We report the discovery of a new dwarf galaxy, Andromeda XXVIII, using data
from the recently-released SDSS DR8. The galaxy is a likely satellite of
Andromeda, and, at a separation of kpc, would be one of the
most distant of Andromeda's satellites. Its heliocentric distance is
kpc, and analysis of its structure and luminosity show that
it has an absolute magnitude of and half-light
radius of pc, similar to many other faint Local Group
dwarfs. With presently-available imaging we are unable to determine if there is
ongoing or recent star formation, which prevents us from classifying it as a
dwarf spheroidal or dwarf irregular.Comment: Accepted to ApJ Letter
Maximally Causal Quantum Mechanics
We present a new causal quantum mechanics in one and two dimensions developed
recently at TIFR by this author and V. Singh. In this theory both position and
momentum for a system point have Hamiltonian evolution in such a way that the
ensemble of system points leads to position and momentum probability densities
agreeing exactly with ordinary quantum mechanics.Comment: 7 pages,latex,no figures,to appear in Praman
Local and nonlocal entanglement for quasiparticle pairs induced by Andreev reflection
We investigate local and nonlocal entanglement of particle pairs induced by
direct and crossed Andreev reflections at the interfaces between a
superconductor and two normal conductors. It is shown theoretically that both
local and nonlocal entanglement can be quantified by concurrence and detected
from the violation of a Bell inequality of spin current correlators, which are
determined only by normal reflection and Andreev reflection eigenvalues. There
exists a one-to-one correspondence between the concurrence and the maximal
Bell-CHSH parameter in the tunneling limit
The migration of nearby spirals from the blue to red sequence: AGN feedback or environmental effects?
We combine ultraviolet to near-infrared photometry with HI 21cm line
observations for a complete volume-limited sample of nearby galaxies in
different environments (from isolated galaxies to Virgo cluster members), to
study the migration of spirals from the blue to the red sequence. Although our
analysis confirms that, in the transition region between the two sequences, a
high fraction of spirals host active galactic nuclei (AGN), it clearly shows
that late-types with quenched star formation are mainly HI deficient galaxies
preferentially found in the Virgo cluster. This not only suggests that
environmental effects could play a significant role in driving the migration of
local galaxies from the blue sequence, but it also implies that a physical link
between AGN feedback and quenching may not be assumed from a correlation
between nuclear activity and colour.Comment: Accepted for publication in MNRAS. 6 pages, 1 figur
Using gamma+jets Production to Calibrate the Standard Model Z(nunu)+jets Background to New Physics Processes at the LHC
The irreducible background from Z(nunu)+jets, to beyond the Standard Model
searches at the LHC, can be calibrated using gamma+jets data. The method
utilises the fact that at high vector boson pT, the event kinematics are the
same for the two processes and the cross sections differ mainly due to the
boson-quark couplings. The method relies on a precise prediction from theory of
the Z/gamma cross section ratio at high pT, which should be insensitive to
effects from full event simulation. We study the Z/gamma ratio for final states
involving 1, 2 and 3 hadronic jets, using both the leading-order parton shower
Monte Carlo program Pythia8 and a leading-order matrix element program Gambos.
This enables us both to understand the underlying parton dynamics in both
processes, and to quantify the theoretical systematic uncertainties in the
ratio predictions. Using a typical set of experimental cuts, we estimate the
net theoretical uncertainty in the ratio to be of order 7%, when obtained from
a Monte Carlo program using multiparton matrix-elements for the hard process.
Uncertainties associated with full event simulation are found to be small. The
results indicate that an overall accuracy of the method, excluding statistical
errors, of order 10% should be possible.Comment: 22 pages, 14 figures; Accepted for publication by JHE
Anomalous diffusion as a signature of collapsing phase in two dimensional self-gravitating systems
A two dimensional self-gravitating Hamiltonian model made by
fully-coupled classical particles exhibits a transition from a collapsing phase
(CP) at low energy to a homogeneous phase (HP) at high energy. From a dynamical
point of view, the two phases are characterized by two distinct single-particle
motions : namely, superdiffusive in the CP and ballistic in the HP. Anomalous
diffusion is observed up to a time that increases linearly with .
Therefore, the finite particle number acts like a white noise source for the
system, inhibiting anomalous transport at longer times.Comment: 10 pages, Revtex - 3 Figs - Submitted to Physical Review
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