234 research outputs found
Demonstration of a New Transport Regime of Photon in Two-dimensional Photonic Crystal
A new transport regime of photon in two-dimensional photonic crystal near the
Dirac point has been demonstrated by exact numerical simulation. In this
regime, the conductance of photon is inversely proportional to the thickness of
sample, which can be described by Dirac equation very well. Both of bulk and
surface disorders always reduce the transmission, which is in contrast to the
previous theoretical prediction that they increase the conductance of electron
at the Dirac point of grephene. However, regular tuning of interface structures
can cause the improvement of photon conductance. Furthermore, large conductance
fluctuations of photon have also been observed, which is similar to the case of
electron in graphene.Comment: 5 figure
A lower bound on the local extragalactic magnetic field
Assuming that the hard gamma-ray emission of Cen A is a result of synchrotron
radiation of ultra-relativistic electrons, we derive a lower bound on the local
extragalactic magnetic field, G. This result is consistent with
(and close to) upper bounds on magnetic fields derived from consideration of
cosmic microwave background distortions and Faraday rotation measurements.Comment: Includes extensive discussion of particle acceleration above 10^20 eV
in the hot spot-like region of Cen
Performance of Optimum Combining in a Poisson Field of Interferers and Rayleigh Fading Channels
This paper studies the performance of antenna array processing in distributed
multiple access networks without power control. The interference is represented
as a Poisson point process. Desired and interfering signals are subject to both
path-loss fading (with an exponent greater than 2) and to independent Rayleigh
fading. Using these assumptions, we derive the exact closed form expression for
the cumulative distribution function of the output
signal-to-interference-plus-noise ratio when optimum combining is applied. This
results in a pertinent measure of the network performance in terms of the
outage probability, which in turn provides insights into the network capacity
gain that could be achieved with antenna array processing. We present and
discuss examples of applications, as well as some numerical results.Comment: Submitted to IEEE Trans. on Wireless Communication (Jan. 2009
With Gordon, Kitchener and Others in the Sudan: Mapping Fictional Engagement with the Imperial Frontier
The protracted military engagement in the Sudan (1884-1899) can be regarded as the most iconic among the \u201clittle wars\u201d late-Victorian Britain fought on its imperial frontiers. Numberless historical studies have addressed its events, its protagonists, its politics, and aspects of its immense discursive fallout. In recent years, its impact on popular literature has been discussed, most notably, in connection with the \u201cparanoid imaginary\u201d underlying \u201cImperial Gothic\u201d fictions, with fantasies of retaliatory invasions and reverse colonization. On the other hand, as a fictional corpus, the adventure narratives inspired more directly by the military events and the concomitant political debate have not attracted attention. Having identified ten novels \u2013 written between 1885 and 1907, all at least partly set in the Sudan \u2013 I set out to outline the development of this strain of historical/military adventure over roughly two decades, highlighting its narrative strategies in articulating the changing perception of the conflict. In order to do so, I focus on the novelists\u2019 selection, or evasion, of historical \u201cfacts,\u201d the intertwining of the factual strain of adventure fiction with the conventions of the quest romance, and the uses of their often multiple protagonists. I also foreground aspects of divergence as well as of consonance between the children\u2019 novels and those written for the general public, showing how they experimented with varying narrative takes on the same highly topical subject-matter
Non-Parametric Causality Detection: An Application to Social Media and Financial Data
According to behavioral finance, stock market returns are influenced by
emotional, social and psychological factors. Several recent works support this
theory by providing evidence of correlation between stock market prices and
collective sentiment indexes measured using social media data. However, a pure
correlation analysis is not sufficient to prove that stock market returns are
influenced by such emotional factors since both stock market prices and
collective sentiment may be driven by a third unmeasured factor. Controlling
for factors that could influence the study by applying multivariate regression
models is challenging given the complexity of stock market data. False
assumptions about the linearity or non-linearity of the model and inaccuracies
on model specification may result in misleading conclusions.
In this work, we propose a novel framework for causal inference that does not
require any assumption about the statistical relationships among the variables
of the study and can effectively control a large number of factors. We apply
our method in order to estimate the causal impact that information posted in
social media may have on stock market returns of four big companies. Our
results indicate that social media data not only correlate with stock market
returns but also influence them.Comment: Physica A: Statistical Mechanics and its Applications 201
Metallo-dielectric diamond and zinc-blende photonic crystals
It is shown that small inclusions of a low absorbing metal can have a
dramatic effect on the photonic band structure. In the case of diamond and
zinc-blende photonic crystals, several complete photonic band gaps (CPBG's) can
open in the spectrum, between the 2nd-3rd, 5th-6th, and 8th-9th bands. Unlike
in the purely dielectric case, in the presence of small inclusions of a low
absorbing metal the largest CPBG for a moderate dielectric constant
(epsilon<=10) turns out to be the 2nd-3rd CPBG. The 2nd-3rd CPBG is the most
important CPBG, because it is the most stable against disorder. For a diamond
and zinc-blende structure of nonoverlapping dielectric and metallo-dielectric
spheres, a CPBG begins to decrease with an increasing dielectric contrast
roughly at the point where another CPBG starts to open--a kind of gap
competition. A CPBG can even shrink to zero when the dielectric contrast
increases further. Metal inclusions have the biggest effect for the dielectric
constant 2<=epsilon<=12, which is a typical dielectric constant at near
infrared and in the visible for many materials, including semiconductors and
polymers. It is shown that one can create a sizeable and robust 2nd-3rd CPBG at
near infrared and visible wavelengths even for a photonic crystal which is
composed of more than 97% low refractive index materials (n<=1.45, i.e., that
of silica glass or a polymer). These findings open the door for any
semiconductor and polymer material to be used as genuine building blocks for
the creation of photonic crystals with a CPBG and significantly increase the
possibilities for experimentalists to realize a sizeable and robust CPBG in the
near infrared and in the visible. One possibility is a construction method
using optical tweezers, which is analyzed here.Comment: 25 pp, 23 figs, RevTex, to appear in Phys Rev B. For more information
look at
http://www.amolf.nl/research/photonic_materials_theory/moroz/moroz.htm
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