89,440 research outputs found
A deep photometric survey of the eta Chamaeleontis cluster down to the brown dwarf - planet boundary
We report the outcome of the deep optical/infrared photometric survey of the
central region (33 X 33 arcmin or 0.9 pc^2) of the eta Chamaeleontis pre-main
sequence star cluster. The completeness limits of the photometry are I = 19.1,
J = 18.2 and H = 17.6; faint enough to reveal low mass members down to the
brown dwarf and planet boundary of ~ 13 M_Jup. We found no such low mass
members in this region. Our result combined with a previous shallower (I = 17)
but larger area survey indicates that low mass objects (0.013 < M/M(solar mass)
< 0.075) either were not created in the eta Cha cluster or were lost due to the
early dynamical history of the cluster and ejected to outside the surveyed
areas.Comment: 5 pages with 4 figures, accepted by MNRA
Liquid-liquid phase separation and morphology of internally mixed dicarboxylic acids/ammonium sulfate/water particles
Knowledge of the physical state and morphology of internally mixed organic/inorganic aerosol particles is still largely uncertain. To obtain more detailed information on liquid-liquid phase separation (LLPS) and morphology of the particles, we investigated complex mixtures of atmospherically relevant dicarboxylic acids containing 5, 6, and 7 carbon atoms (C5, C6 and C7) having oxygen-to-carbon atomic ratios (O:C) of 0.80, 0.67, and 0.57, respectively, mixed with ammonium sulfate (AS). With micrometer-sized particles of C5/AS/H_2O, C6/AS/H_2O and C7/AS/H_2O as model systems deposited on a hydrophobically coated substrate, laboratory experiments were conducted for various organic-to-inorganic dry mass ratios (OIR) using optical microscopy and Raman spectroscopy. When exposed to cycles of relative humidity (RH), each system showed significantly different phase transitions. While the C5/AS/H_2O particles showed no LLPS with OIR = 2:1, 1:1 and 1:4 down to 20% RH, the C6/AS/H_2O and C7/AS/H_2O particles exhibit LLPS upon drying at RH 50 to 85% and ~90%, respectively, via spinodal decomposition, growth of a second phase from the particle surface or nucleation-and-growth mechanisms depending on the OIR. This suggests that LLPS commonly occurs within the range of O:C < 0.7 in tropospheric organic/inorganic aerosols. To support the comparison and interpretation of the experimentally observed phase transitions, thermodynamic equilibrium calculations were performed with the AIOMFAC model. For the C7/AS/H_2O and C6/AS/H_2O systems, the calculated phase diagrams agree well with the observations while for the C5/AS/H_2O system LLPS is predicted by the model at RH below 60% and higher AS concentration, but was not observed in the experiments. Both core-shell structures and partially engulfed structures were observed for the investigated particles, suggesting that such morphologies might also exist in tropospheric aerosols
Quark Orbital Angular Momentum in the Baryon
Analytical and numerical results, for the orbital and spin content carried by
different quark flavors in the baryons, are given in the chiral quark model
with symmetry breaking. The reduction of the quark spin, due to the spin
dilution in the chiral splitting processes, is transferred into the orbital
motion of quarks and antiquarks. The orbital angular momentum for each quark
flavor in the proton as a function of the partition factor and the
chiral splitting probability is shown. The cancellation between the spin
and orbital contributions in the spin sum rule and in the baryon magnetic
moments is discussed.Comment: 26 pages, 3 figures, revised version with minor eq. no and ref. no.
corrections. Discussion on the spin and a new ref. are adde
Determining SUSY Parameters in Chargino Pair-Production in Collisions
In most supersymmetric theories, charginos , mixtures
of charged color-neutral gauginos and higgsinos, belong to the class of the
lightest supersymmetric particles. They are easy to observe at
colliders. By measuring the total cross sections and the left-right asymmetries
with polarized electron beams in , the chargino masses and the gaugino-higgsino mixing angles can be
determined. From these observables the fundamental SUSY parameters can be
derived: the SU(2) gaugino mass , the modulus and
of the higgsino mass parameter, and , the ratio of the
vacuum expectation values of the two neutral Higgs doublet fields. The
solutions are unique; the CP-violating phase can be determined
uniquely by analyzing effects due to the normal polarization of the charginos.Comment: 20 pages, 4 figures, uses axodraw.st
The effects of disorder and interactions on the Anderson transition in doped Graphene
We undertake an exact numerical study of the effects of disorder on the
Anderson localization of electronic states in graphene. Analyzing the scaling
behaviors of inverse participation ratio and geometrically averaged density of
states, we find that Anderson metal-insulator transition can be introduced by
the presence of quenched random disorder. In contrast with the conventional
picture of localization, four mobility edges can be observed for the honeycomb
lattice with specific disorder strength and impurity concentration. Considering
the screening effects of interactions on disorder potentials, the experimental
findings of the scale enlarges of puddles can be explained by reviewing the
effects of both interactions and disorder.Comment: 7 pages, 7 figure
Drastic Reduction of Shot Noise in Semiconductor Superlattices
We have found experimentally that the shot noise of the tunneling current
through an undoped semiconductor superlattice is reduced with respect to the
Poissonian noise value , and that the noise approaches 1/3 of that value
in superlattices whose quantum wells are strongly coupled. On the other hand,
when the coupling is weak or when a strong electric field is applied to the
superlattice the noise becomes Poissonian. Although our results are
qualitatively consistent with existing theories for one-dimensional mulitple
barriers, the theories cannot account for the dependence of the noise on
superlattice parameters that we have observed.Comment: 4 Pages, 3Figure
Effect of excited states and applied magnetic fields on the measured hole mobility in an organic semiconductor
Copyright 2010 by the American Physical Society. Article is available at
Quantum information storage and state transfer based on spin systems
The idea of quantum state storage is generalized to describe the coherent
transfer of quantum information through a coherent data bus. In this universal
framework, we comprehensively review our recent systematical investigations to
explore the possibility of implementing the physical processes of quantum
information storage and state transfer by using quantum spin systems, which may
be an isotropic antiferromagnetic spin ladder system or a ferromagnetic
Heisenberg spin chain. Our studies emphasize the physical mechanisms and the
fundamental problems behind the various protocols for the storage and transfer
of quantum information in solid state systems.Comment: 11 pages, 9 figures, Review article on the quantum spin based quantum
information processing, to appear the special issue of Low Temperature
Physics dedicated to the 70-th anniversary of creation of concept
"antiferromagnetism" in physics of magnetis
Fuzzy Recommendations in Marketing Campaigns
The population in Sweden is growing rapidly due to immigration. In this
light, the issue of infrastructure upgrades to provide telecommunication
services is of importance. New antennas can be installed at hot spots of user
demand, which will require an investment, and/or the clientele expansion can be
carried out in a planned manner to promote the exploitation of the
infrastructure in the less loaded geographical zones. In this paper, we explore
the second alternative. Informally speaking, the term Infrastructure-Stressing
describes a user who stays in the zones of high demand, which are prone to
produce service failures, if further loaded. We have studied the
Infrastructure-Stressing population in the light of their correlation with
geo-demographic segments. This is motivated by the fact that specific
geo-demographic segments can be targeted via marketing campaigns. Fuzzy logic
is applied to create an interface between big data, numeric methods for
processing big data and a manager.Comment: conferenc
Quantum Communication through Spin Chain Dynamics: an Introductory Overview
We present an introductory overview of the use of spin chains as quantum
wires, which has recently developed into a topic of lively interest. The
principal motivation is in connecting quantum registers without resorting to
optics. A spin chain is a permanently coupled 1D system of spins. When one
places a quantum state on one end of it, the state will be dynamically
transmitted to the other end with some efficiency if the spins are coupled by
an exchange interaction. No external modulations or measurements on the body of
the chain, except perhaps at the very ends, is required for this purpose. For
the simplest (uniformly coupled) chain and the simplest encoding (single qubit
encoding), however, dispersion reduces the quality of transfer. We present a
variety of alternatives proposed by various groups to achieve perfect quantum
state transfer through spin chains. We conclude with a brief discussion of the
various directions in which the topic is developing.Comment: Material covered till Dec 200
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