10,141 research outputs found
Branes are Waves and Monopoles
In a recent paper it was shown that fundamental strings are null waves in
Double Field Theory. Similarly, membranes are waves in exceptional extended
geometry. Here the story is continued by showing how various branes are
Kaluza-Klein monopoles of these higher dimensional theories. Examining the
specific case of the E7 exceptional extended geometry, we see that all branes
are both waves and monopoles. Along the way we discuss the O(d; d)
transformation of localized brane solutions not associated to an isometry and
how true T-duality emerges in Double Field Theory when the background possesses
isometries.Comment: 32 pages, Latex, v2, typos correcte
Graded Lie algebras with finite polydepth
If A is a graded connected algebra then we define a new invariant, polydepth
A, which is finite if for some A-module M of at most
polynomial growth. Theorem 1: If f : X \to Y is a continuous map of finite
category, and if the orbits of H_*(\Omega Y) acting in the homology of the
homotopy fibre grow at most polynomially, then H_*(\Omega Y) has finite
polydepth. Theorem 2: If L is a graded Lie algebra and polydepth UL is finite
then either L is solvable and UL grows at most polynomially or else for some
integer d and all r, , some
Analysis of dependence among size, rate and duration in internet flows
In this paper we examine rigorously the evidence for dependence among data
size, transfer rate and duration in Internet flows. We emphasize two
statistical approaches for studying dependence, including Pearson's correlation
coefficient and the extremal dependence analysis method. We apply these methods
to large data sets of packet traces from three networks. Our major results show
that Pearson's correlation coefficients between size and duration are much
smaller than one might expect. We also find that correlation coefficients
between size and rate are generally small and can be strongly affected by
applying thresholds to size or duration. Based on Transmission Control Protocol
connection startup mechanisms, we argue that thresholds on size should be more
useful than thresholds on duration in the analysis of correlations. Using
extremal dependence analysis, we draw a similar conclusion, finding remarkable
independence for extremal values of size and rate.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS268 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
A future very-high-energy view of our Galaxy
The survey of the inner Galaxy with H.E.S.S. was remarkably successful in
detecting a wide range of new very-high-energy gamma-ray sources. New TeV
gamma-ray emitting source classes were established, although several of the
sources remain unidentified, and progress has been made in understanding
particle acceleration in astrophysical sources. In this work, we constructed a
model of a population of such very-high-energy gamma-ray emitters and
normalised the flux and size distribution of this population model to the
H.E.S.S.-discovered sources. Extrapolating that population of objects to lower
flux levels we investigate what a future array of imaging atmospheric
telescopes (IACTs) such as AGIS or CTA might detect in a survey of the Inner
Galaxy with an order of magnitude improvement in sensitivity. The sheer number
of sources detected together with the improved resolving power will likely
result in a huge improvement in our understanding of the populations of
galactic gamma-ray sources. A deep survey of the inner Milky Way would also
support studies of the interstellar diffuse gamma-ray emission in regions of
high cosmic-ray density. In the final section of this paper we investigate the
science potential for the Galactic Centre region for studying energy-dependent
diffusion with such a future array.Comment: Proceeding of "Heidelberg International Symposium on High Energy
Gamma-Ray Astronomy", held in Heidelberg, 7-11 July 2008, submitted to AIP
Conference Proceedings. 4 pages, 4 figure
Suzaku observation of TeV blazar the 1ES 1218+304: clues on particle acceleration in an extreme TeV blazar
We observed the TeV blazar 1ES 1218+304 with the X-ray astronomy satellite
Suzaku in May 2006. At the beginning of the two-day continuous observation, we
detected a large flare in which the 5-10 keV flux changed by a factor of ~2 on
a timescale of 5x10^4 s. During the flare, the increase in the hard X-ray flux
clearly lagged behind that observed in the soft X-rays, with the maximum lag of
2.3x10^4 s observed between the 0.3-1 keV and 5-10 keV bands. Furthermore we
discovered that the temporal profile of the flare clearly changes with energy,
being more symmetric at higher energies. From the spectral fitting of
multi-wavelength data assuming a one-zone, homogeneous synchrotron self-Compton
model, we obtain B~0.047 G, emission region size R = 3.0x10^16 cm for an
appropriate beaming with a Doppler factor of delta = 20. This value of B is in
good agreement with an independent estimate through the model fit to the
observed time lag ascribing the energy-dependent variability to differential
acceleration timescale of relativistic electrons provided that the gyro-factor
\xi is 10^5.Comment: 11 pages, 3 figures, Accepted for publication in ApJ
Low-field microwave absorption and magnetoresistance in iron nanostructures grown by electrodeposition on n-type lightly-doped silicon substrates
In this study we investigate magnetic properties, surface morphology and
crystal structure in iron nanoclusters electrodeposited on lightly-doped (100)
n-type silicon substrates. Our goal is to investigate the spin injection and
detection in the Fe/Si lateral structures. The samples obtained under electric
percolation were characterized by magnetoresistive and magnetic resonance
measurements with cycling the sweeping applied field in order to understand the
spin dynamics in the as-produced samples. The observed hysteresis in the
magnetic resonance spectra, plus the presence of a broad peak in the
non-saturated regime confirming the low field microwave absorption (LFMA), were
correlated to the peaks and slopes found in the magnetoresistance curves. The
results suggest long range spin injection and detection in low resistive
silicon and the magnetic resonance technique is herein introduced as a
promising tool for analysis of electric contactless magnetoresistive samples.Comment: 12 pages, 5 figure
High- and low energy nonthermal X-ray emission from the cluster of galaxies A 2199
We report the detection of both soft and hard excess X-ray emission in the
cluster of galaxies A 2199, based upon spatially resolved spectroscopy with
data from the BeppoSAX, EUVE and ROSAT missions. The excess emission is visible
at radii larger than 300 kpc and increases in strength relative to the
isothermal component. The total 0.1-100 keV luminosity of this component is 15
% of the cluster luminosity, but it dominates the cluster luminosity at high
and low energies. We argue that the most plausible interpretation of the excess
emission is an inverse Compton interaction between the cosmic microwave
background and relativistic electrons in the cluster. The observed spatial
distribution of the non-thermal component implies that there is a large halo of
cosmic ray electrons between 0.5-1.5 Mpc surrounding the cluster core. The
prominent existence of this component has cosmological implications, as it is
significantly changing our picture of a clusters's particle acceleration
history, dynamics between the thermal and relativistic media, and total mass
budgets.Comment: Accepted for publication in Astrophysical Journal, Letter
- …