13,288 research outputs found
On the Distribution of MIMO Mutual Information: An In-Depth Painlev\'{e} Based Characterization
This paper builds upon our recent work which computed the moment generating
function of the MIMO mutual information exactly in terms of a Painlev\'{e} V
differential equation. By exploiting this key analytical tool, we provide an
in-depth characterization of the mutual information distribution for
sufficiently large (but finite) antenna numbers. In particular, we derive
systematic closed-form expansions for the high order cumulants. These results
yield considerable new insight, such as providing a technical explanation as to
why the well known Gaussian approximation is quite robust to large SNR for the
case of unequal antenna arrays, whilst it deviates strongly for equal antenna
arrays. In addition, by drawing upon our high order cumulant expansions, we
employ the Edgeworth expansion technique to propose a refined Gaussian
approximation which is shown to give a very accurate closed-form
characterization of the mutual information distribution, both around the mean
and for moderate deviations into the tails (where the Gaussian approximation
fails remarkably). For stronger deviations where the Edgeworth expansion
becomes unwieldy, we employ the saddle point method and asymptotic integration
tools to establish new analytical characterizations which are shown to be very
simple and accurate. Based on these results we also recover key well
established properties of the tail distribution, including the
diversity-multiplexing-tradeoff.Comment: Submitted to IEEE Transaction on Information Theory (under revision
Atmospheric Chemistry for Astrophysicists: A Self-consistent Formalism and Analytical Solutions for Arbitrary C/O
We present a self-consistent formalism for computing and understanding the
atmospheric chemistry of exoplanets from the viewpoint of an astrophysicist.
Starting from the first law of thermodynamics, we demonstrate that the van't
Hoff equation (which describes the equilibrium constant), Arrhenius equation
(which describes the rate coefficients) and procedures associated with the
Gibbs free energy (minimisation, rescaling) have a common physical and
mathematical origin. We address an ambiguity associated with the equilibrium
constant, which is used to relate the forward and reverse rate coefficients,
and restate its two definitions. By necessity, one of the equilibrium constants
must be dimensionless and equate to an exponential function involving the Gibbs
free energy, while the other is a ratio of rate coefficients and must therefore
possess physical units. We demonstrate that the Arrhenius equation takes on a
functional form that is more general than previously stated without recourse to
tagging on ad hoc functional forms. Finally, we derive analytical models of
chemical systems, in equilibrium, with carbon, hydrogen and oxygen. We include
acetylene and are able to reproduce several key trends, versus temperature and
carbon-to-oxygen ratio, published in the literature. The rich variety of
behavior that mixing ratios exhibit as a function of the carbon-to-oxygen ratio
is merely the outcome of stoichiometric book-keeping and not the direct
consequence of temperature or pressure variations.Comment: Accepted by ApJ. 9 pages, 4 figure
Transparency and International Investor Behavior
Does country transparency affect international portfolio investment? We examine this and related questions using some new measures of transparency and a unique micro dataset on international portfolio holdings. We distinguish between government and corporate transparency. There is clear evidence that international funds invest systematically less in less transparent countries. On the other hand, herding among funds tends to be more prevalent in less transparent countries. There is also some evidence that during crises, funds flee non-transparent countries by a greater amount.
Stationary state entanglement and total correlation of two qubits or qutrits
We investigate the mutual information and entanglement of stationary state of
two locally driven qubits under the influence of collective dephasing. It is
shown that both the mutual information and the entanglement of two qubits in
the stationary state exhibit damped oscillation with the scaled action time
of the local external driving field. It means that we can control
both the entanglement and total correlation of the stationary state of two
qubits by adjusting the action time of the driving field. We also consider the
influence of collective dephasing on entanglement of two qutrits and obtain the
sufficient condition that the stationary state is entangled.Comment: 5 pages, 2 figures, RevTex
Phase-reference VLBI Observations of the Compact Steep-Spectrum Source 3C 138
We investigate a phase-reference VLBI observation that was conducted at 15.4
GHz by fast switching VLBA antennas between the compact steep-spectrum radio
source 3C 138 and the quasar PKS 0528+134 which are about 4 away on the
sky. By comparing the phase-reference mapping with the conventional hybrid
mapping, we demonstrate the feasibility of high precision astrometric
measurements for sources separated by 4. VLBI phase-reference mapping
preserves the relative phase information, and thus provides an accurate
relative position between 3C 138 and PKS 0528+134 of
and
(J2000.0) in right ascension and declination, respectively. This gives an
improved position of the nucleus (component A) of 3C 138 in J2000.0 to be
RA= and Dec= under the
assumption that the position of calibrator PKS 0528+134 is correct. We further
made a hybrid map by performing several iterations of CLEAN and
self-calibration on the phase-referenced data with the phase-reference map as
an input model for the first phase self-calibration. Compared with the hybrid
map from the limited visibility data directly obtained from fringe fitting 3C
138 data, this map has a similar dynamic range, but a higher angular
resolution. Therefore, phase-reference technique is not only a means of phase
connection, but also a means of increasing phase coherence time allowing
self-calibration technique to be applied to much weaker sources.Comment: 9 pages plus 2 figures, accepted by PASJ (Vol.58 No.6
Critical English foreign language teacher education in China
This is the final version. Available on open access from Isaac Scientific Publishing via the DOI in this recordAbstract. This paper is an attempt to address two distinct approaches to English language teacher education in China. The first represents an established mainstream approach to teacher development which reflects the central role of linguistic and communicative elements within teacher knowledge. This approach is often characterised by a focus on communicative pedagogy, social interaction, language proficiency, standardisation, and language curricula that aspire to strike a balance between language and communication. The second approach, still in its infancy, espouses principles of critical language education and critical pedagogy in developing teacher education programmes. This approach stresses the centrality of the humanistic element of education. It aims to raise teachers’ awareness about the importance of relating content and classroom pedagogy to macro social issues beyond the boundary of the classroom. The paper will also consider the feasibility and challenges of adopting such a critical approach to English language teacher education in China
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