14,506 research outputs found
Visible and ultraviolet reflectance and luminescence from various Saudi Arabian and Indiana limestone rocks
Visible and ultraviolet reflectance and luminescence for natural limeston
A crossing probability for critical percolation in two dimensions
Langlands et al. considered two crossing probabilities, pi_h and pi_{hv}, in
their extensive numerical investigations of critical percolation in two
dimensions. Cardy was able to find the exact form of pi_h by treating it as a
correlation function of boundary operators in the Q goes to 1 limit of the Q
state Potts model. We extend his results to find an analogous formula for
pi_{hv} which compares very well with the numerical results.Comment: 8 pages, Latex2e, 1 figure, uuencoded compressed tar file, (1 typo
changed
Signature Characters for A_2 and B_2
The signatures of the inner product matrices on a Lie algebra's highest
weight representation are encoded in the representation's signature character.
We show that the signature characters of a finite-dimensional Lie algebra's
highest weight representations obey simple difference equations that have a
unique solution once appropriate boundary conditions are imposed. We use these
results to derive the signature characters of all and highest
weight representations. Our results extend, and explain, signature patterns
analogous to those observed by Friedan, Qiu and Shenker in the Virasoro
algebra's representation theory.Comment: 22 p
Null vectors, 3-point and 4-point functions in conformal field theory
We consider 3-point and 4-point correlation functions in a conformal field
theory with a W-algebra symmetry. Whereas in a theory with only Virasoro
symmetry the three point functions of descendants fields are uniquely
determined by the three point function of the corresponding primary fields this
is not the case for a theory with algebra symmetry. The generic 3-point
functions of W-descendant fields have a countable degree of arbitrariness. We
find, however, that if one of the fields belongs to a representation with null
states that this has implications for the 3-point functions. In particular if
one of the representations is doubly-degenerate then the 3-point function is
determined up to an overall constant. We extend our analysis to 4-point
functions and find that if two of the W-primary fields are doubly degenerate
then the intermediate channels are limited to a finite set and that the
corresponding chiral blocks are determined up to an overall constant. This
corresponds to the existence of a linear differential equation for the chiral
blocks with two completely degenerate fields as has been found in the work of
Bajnok~et~al.Comment: 10 pages, LaTeX 2.09, DAMTP-93-4
Large cone angle magnetization precession of an individual nanomagnet with dc electrical detection
We demonstrate on-chip resonant driving of large cone-angle magnetization
precession of an individual nanoscale permalloy element. Strong driving is
realized by locating the element in close proximity to the shorted end of a
coplanar strip waveguide, which generates a microwave magnetic field. We used a
microwave frequency modulation method to accurately measure resonant changes of
the dc anisotropic magnetoresistance. Precession cone angles up to are
determined with better than one degree of resolution. The resonance peak shape
is well-described by the Landau-Lifshitz-Gilbert equation
WiFi Epidemiology: Can Your Neighbors' Router Make Yours Sick?
In densely populated urban areas WiFi routers form a tightly interconnected
proximity network that can be exploited as a substrate for the spreading of
malware able to launch massive fraudulent attack and affect entire urban areas
WiFi networks. In this paper we consider several scenarios for the deployment
of malware that spreads solely over the wireless channel of major urban areas
in the US. We develop an epidemiological model that takes into consideration
prevalent security flaws on these routers. The spread of such a contagion is
simulated on real-world data for geo-referenced wireless routers. We uncover a
major weakness of WiFi networks in that most of the simulated scenarios show
tens of thousands of routers infected in as little time as two weeks, with the
majority of the infections occurring in the first 24 to 48 hours. We indicate
possible containment and prevention measure to limit the eventual harm of such
an attack.Comment: 22 pages, 1 table, 4 figure
A uniform search for thermonuclear burst oscillations in the RXTE legacy dataset
We describe a blind uniform search for thermonuclear burst oscillations
(TBOs) in the majority of Type-I bursts observed by RXTE (2118 bursts from 57
neutron stars). We examined 2-2002 Hz power spectra from the Fourier transform
in sliding 0.5-2 s windows, using fine-binned light curves in 2-60 keV energy
range. The significance of the oscillation candidates was assessed by
simulations which took into account light curve variations, dead time and
sliding time windows. Some of our sources exhibited multi-frequency variability
below approximately 15 Hz that cannot be readily removed with light-curve
modeling and may have an astrophysical (non-TBO) nature. Overall, we found that
the number and strength of potential candidates depends strongly on the
parameters of the search. We found candidates from all previously known RXTE
TBO sources, with pulsations that had been detected at similar frequencies in
multiple independent time windows, and discovered TBOs from SAX J1810.8-2658.
We could not confirm most previously-reported tentative TBO detections or
identify any obvious candidates just below the detection threshold at similar
frequencies in multiple bursts. We computed fractional amplitudes of all TBO
candidates and placed upper limits on non-detections. Finally, for a few
sources we noted small excess of candidates with powers comparable to fainter
TBOs, but appearing in single independent time bins at random frequencies. At
least some of these candidates may be noise spikes that appear interesting due
to selection effects. The potential presence of such candidates calls for extra
caution if claiming single-bin TBO detections.Comment: Replaced to match the accepted version. Accepted to ApJS after
numerous minor correction
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