9,133 research outputs found
Generation of maximally entangled states with sub-luminal Lorentz boost
Recent work has studied entanglement between the spin and momentum components
of a single spin-1/2 particle and showed that maximal entanglement is obtained
only when boosts approach the speed of light. Here we extend the boost scenario
to general geometries and show that, intriguingly, maximal entanglement can be
achieved with boosts less than the speed of light. Boosts approaching the speed
of light may even decrease entanglement. We also provide a geometric
explanation for this behavior
Double Charge Exchange And Configuration Mixing
The energy dependence of forward pion double charge exchange reactions on
light nuclei is studied for both the Ground State transition and the
Double-Isobaric-Analog-State transitions. A common characteristic of these
double reactions is a resonance-like peak around 50 MeV pion lab energy. This
peak arises naturally in a two-step process in the conventional pion-nucleon
system with proper handling of nuclear structure and pion distortion. A
comparison among the results of different nuclear structure models demonstrates
the effects of configuration mixing. The angular distribution is used to fix
the single particle wave function.Comment: Added 1 figure (now 8) corrected references and various other change
Activity Dependent Branching Ratios in Stocks, Solar X-ray Flux, and the Bak-Tang-Wiesenfeld Sandpile Model
We define an activity dependent branching ratio that allows comparison of
different time series . The branching ratio is defined as . The random variable is the value of the next signal given
that the previous one is equal to , so . If
, the process is on average supercritical when the signal is equal to
, while if , it is subcritical. For stock prices we find
within statistical uncertainty, for all , consistent with an ``efficient
market hypothesis''. For stock volumes, solar X-ray flux intensities, and the
Bak-Tang-Wiesenfeld (BTW) sandpile model, is supercritical for small
values of activity and subcritical for the largest ones, indicating a tendency
to return to a typical value. For stock volumes this tendency has an
approximate power law behavior. For solar X-ray flux and the BTW model, there
is a broad regime of activity where , which we interpret as an
indicator of critical behavior. This is true despite different underlying
probability distributions for , and for . For the BTW model the
distribution of is Gaussian, for sufficiently larger than one, and
its variance grows linearly with . Hence, the activity in the BTW model
obeys a central limit theorem when sampling over past histories. The broad
region of activity where is close to one disappears once bulk dissipation
is introduced in the BTW model -- supporting our hypothesis that it is an
indicator of criticality.Comment: 7 pages, 11 figure
Color in context: psychological context moderates the influence of red on approach- and avoidance-motivated behavior.
A basic premise of the recently proffered color-in-context model is that the influence of color on psychological functioning varies as a function of the psychological context in which color is perceived. Some research has examined the appetitive and aversive implications of viewing the color red in romance- and achievement-relevant contexts, respectively, but in all existing empirical work approach and avoidance behavior has been studied in separate tasks and separate experiments. Research is needed to directly test whether red influences the same behavior differently depending entirely on psychological context. The present experiment was designed to put this premise to direct test in romance- and achievement-relevant contexts within the same experimental paradigm involving walking behavior. Our results revealed that exposure to red (but not blue) indeed has differential implications for walking behavior as a function of the context in which the color is perceived. Red increased the speed with which participants walked to an ostensible interview about dating (a romance-relevant context), but decreased the speed with which they walked to an ostensible interview about intelligence (an achievement-relevant context). These results are the first direct evidence that the influence of red on psychological functioning in humans varies by psychological context. Our findings contribute to both the literature on color psychology and the broader, emerging literature on the influence of context on basic psychological processes
Quantum Phase Transitions in the Ising model in spatially modulated field
The phase transitions in the transverse field Ising model in a competing
spatially modulated (periodic and oscillatory) longitudinal field are studied
numerically. There is a multiphase point in absence of the transverse field
where the degeneracy for a longitudinal field of wavelength is
for a system with spins, an exact
result obtained from the known result for . The phase transitions
in the (transverse field) versus (amplitude of the longitudinal
field) phase diagram are obtained from the vanishing of the mass gap .
We find that for all the phase transition points obtained in this way, shows finite size scaling behaviour signifying a continuous phase transition
everywhere. The values of the critical exponents show that the model belongs to
the universality class of the two dimensional Ising model. The longitudinal
field is found to have the same scaling behaviour as that of the transverse
field, which seems to be a unique feature for the competing field. The phase
boundaries for two different wavelengths of the modulated field are obtained.
Close to the multiphase point at , the phase boundary behaves as , where is also dependent.Comment: To appear in Physical Review
An X-Ray Study of the Supernova Remnant G290.1-0.8
G290.1-0.8 (MSH 11-61A) is a supernova remnant (SNR) whose X-ray morphology
is centrally bright. However, unlike the class of X-ray composite SNRs whose
centers are dominated by nonthermal emission, presumably driven by a central
pulsar, we show that the X-ray emission from G290.1-0.8 is thermal in nature,
placing the remnant in an emerging class which includes such remnants as W44,
W28, 3C391, and others. The evolutionary sequence which leads to such X-ray
properties is not well understood. Here we investigate two scenarios for such
emission: evolution in a cloudy interstellar medium, and early-stage evolution
of a remnant into the radiative phase, including the effects of thermal
conduction. We construct models for these scenarios in an attempt to reproduce
the observed center-filled X-ray properties of G290.1-0.8, and we derive the
associated age, energy, and ambient density conditions implied by the models.
We find that for reasonable values of the explosion energy, the remnant age is
of order (1 - 2) x 10^{4} yr. This places a fairly strong constraint on any
association between G290.1-0.8 and PSR J1105-610, which would require an
anomalously large velocity for the pulsar.Comment: 7 pages, 7 figures, ApJ, accepte
Amplitude Modulation and Relaxation-Oscillation of Counterpropagating Rolls within a Broken-Symmetry Laser-Induced Electroconvection Strip
We report a liquid-crystal pattern-formation experiment in which we break the
lateral (translational) symmetry of a nematic medium with a laser-induced
thermal gradient. The work is motivated by an improved measurement (reported
here) of the temperature dependence of the electroconvection threshold voltage
in planar-nematic 4-methoxybenzylidene-4-butylaniline (MBBA). In contrast with
other broken-symmetry-pattern studies that report a uniform drift, we observe a
strip of counterpropagating rolls that collide at a sink point, and a strong
temporally periodic amplitude modulation within a width of 3-4 rolls about the
sink point. The time dependence of the amplitude at a fixed position is
periodic but displays a nonsinusoidal relaxation-oscillation profile. After
reporting experimental results based on spacetime contours and wavenumber
profiles, along with a measurement of the change in the drift frequency with
applied voltage at a fixed control parameter, we propose some potential
guidelines for a theoretical model based on saddle-point solutions for
Eckhaus-unstable states and coupled complex Ginzburg-Landau equations.
Published in PRE 73, 036317 (2006).Comment: Published in Physical Review E in March 200
Coulomb and quantum oscillator problems in conical spaces with arbitrary dimensions
The Schr\"odinger equations for the Coulomb and the Harmonic oscillator
potentials are solved in the cosmic-string conical space-time. The spherical
harmonics with angular deficit are introduced.
The algebraic construction of the harmonic oscillator eigenfunctions is
performed through the introduction of non-local ladder operators. By exploiting
the hidden symmetry of the two-dimensional harmonic oscillator the eigenvalues
for the angular momentum operators in three dimensions are reproduced.
A generalization for N-dimensions is performed for both Coulomb and harmonic
oscillator problems in angular deficit space-times.
It is thus established the connection among the states and energies of both
problems in these topologically non-trivial space-times.Comment: 15 page
A Perturbative/Variational Approach to Quantum Lattice Hamiltonians
We propose a method to construct the ground state of local
lattice hamiltonians with the generic form , where
is a coupling constant and is a hamiltonian with a non degenerate ground
state . The method is based on the choice of an exponential ansatz
, which is a sort of generalized
lattice version of a Jastrow wave function. We combine perturbative and
variational techniques to get succesive approximations of the operator
. Perturbation theory is used to set up a variational method which
in turn produces non perturbative results. The computation with this kind of
ansatzs leads to associate to the original quantum mechanical problem a
statistical mechanical system defined in the same spatial dimension. In some
cases these statistical mechanical systems turn out to be integrable, which
allow us to obtain exact upper bounds to the energy. The general ideas of our
method are illustrated in the example of the Ising model in a transverse field.Comment: 27 pages, three .ps figures appended, DFTUZ 94-2
College student's academic goals and learning strategies
Tomando en cuenta que no existe concordancia en la literatura entre los resultados de diferentes estudios respecto de la relevancia de la adopción de un tipo u otro de meta para el aprendizaje académico, en el presente artÃculo se estudia la relación entre los diferentes tipos de orientaciones motivacionales
(metas de aprendizaje, metas de rendimiento y metas de evitación del trabajo) y el uso de estrategias cognitivas y de autorregulación. En el trabajo
participan 632 estudiantes universitarios de diversas titulaciones de la universidad española. Aunque el estudio es de tipo correlacional, los análisis de los
datos obtenidos, corroborando estudios anteriores, aportan información de interés para la discusión del problema que se investigó, por ejemplo que sólo
los niveles más altos de metas de aprendizaje se encuentran asociados con una mayor utilización de estrategias de aprendizaje. Son discutidas
implicaciones educativas de estos datos.Tomando em consideração que não existe concordância na literatura entre os resultados dos diferentes estudos a respeito da relevância da adopção de
um ou de outro tipo de meta na aprendizagem académica; no presente artÃculo é estudada a relação entre os diferentes tipos de orientações
motivacionais (metas de aprendizagem, metas de rendimento e metas de evitação do trabalho) e a utilização de estratégias cognitivas e de autoregulação.
Neste trabalho participam 632 estudantes universitários de diversas licenciaturas da Universidade espanhola. Apesar de este estudo ser de
tipo correlacional, a análise dos dados obtidos, corroborando estudos anteriores, aporta informação de interesse para a discussão do problema
investigado; por exemplo que só os nÃveles mais altos de metas de aprendizagem se encontram associados con uma maior utilização de estratégias de aprendizagem. São discutidas implicações educativas destes dados.Assuming that there isn’t much agreement among the results from different studies relating to the relevance of adopting one or another kind of academic
learning goal, this paper intends to study the relationship between the several types of motivational orientations (learning goals, achievement goals and
avoidance goals) and the use of cognitive and self-regulatory strategies. 632 Spanish college students from various university courses participated in this
research. Although this is a correlacional study data analysis, in line with previous studies, brings to light interesting information and highlights the
investigated issue for example only higher levels of learning goals are positively related with the use of learning strategies. Future educational implications
are also discussed
- …