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arxiv_dataset-500802.2703 | Optimal Medium Access Protocols for Cognitive Radio Networks
cs.IT cs.NI math.IT
This paper focuses on the design of medium access control protocols for
cognitive radio networks. The scenario in which a single cognitive user wishes
to opportunistically exploit the availability of empty frequency bands within
parts of the radio spectrum having multiple bands is first considered. In this
scenario, the availability probability of each channel is unknown a priori to
the cognitive user. Hence efficient medium access strategies must strike a
balance between exploring (learning) the availability probability of the
channels and exploiting the knowledge of the availability probability
identified thus far. For this scenario, an optimal medium access strategy is
derived and its underlying recursive structure is illustrated via examples. To
avoid the prohibitive computational complexity of this optimal strategy, a low
complexity asymptotically optimal strategy is developed. Next, the
multi-cognitive user scenario is considered and low complexity medium access
protocols, which strike an optimal balance between exploration and exploitation
in such competitive environments, are developed.
| arxiv topic:cs.IT cs.NI math.IT |
arxiv_dataset-501802.2803 | Quiver representations of maximal rank type and an application to
representations of a quiver with three vertices
math.RT math.RA
We introduce the notion of ''maximal rank type'' for representations of
quivers, which requires certain collections of maps involved in the
representation to be of maximal rank. We show that real root representations of
quivers are of maximal rank type. By using the maximal rank type property and
universal extension functors we construct all real root representations of a
particular wild quiver with three vertices. From this construction it follows
that real root representations of this quiver are tree modules. Moreover,
formulae given by Ringel can be applied to compute the dimension of the
endomorphism ring of a given real root representation.
| arxiv topic:math.RT math.RA |
arxiv_dataset-502802.2903 | Stable Sheaves Over K3 Fibrations
math.AG hep-th math-ph math.MP
We construct stable sheaves over K3 fibrations using a relative Fourier-Mukai
transform which describes the sheaves in terms of spectral data similar to the
construction for elliptic fibrations. On K3 fibered Calabi-Yau threefolds we
show that the Fourier-Mukai transform induces an embedding ion of the relative
Jacobian of spectral line bundles on spectral covers into the moduli space of
sheaves of given invariants. This makes the moduli space of spectral sheaves to
a generic torus fibration over the moduli space of curves of given arithmetic
genus on the Calabi-Yau manifold.
| arxiv topic:math.AG hep-th math-ph math.MP |
arxiv_dataset-503802.3003 | Discrete Fracture Model with Anisotropic Load Sharing
cond-mat.stat-mech
A two-dimensional fracture model where the interaction among elements is
modeled by an anisotropic stress-transfer function is presented. The influence
of anisotropy on the macroscopic properties of the samples is clarified, by
interpolating between several limiting cases of load sharing. Furthermore, the
critical stress and the distribution of failure avalanches are obtained
numerically for different values of the anisotropy parameter $\alpha$ and as a
function of the interaction exponent $\gamma$. From numerical results, one can
certainly conclude that the anisotropy does not change the crossover point
$\gamma_c=2$ in 2D. Hence, in the limit of infinite system size, the crossover
value $\gamma_c=2$ between local and global load sharing is the same as the one
obtained in the isotropic case. In the case of finite systems, however, for
$\gamma\le2$, the global load sharing behavior is approached very slowly.
| arxiv topic:cond-mat.stat-mech |
arxiv_dataset-504802.3103 | Novel Bonding technologies for wafer-level transparent packaging of
MOEMS
cs.OH
Depending on the type of Micro-Electro-Mechanical System (MEMS), packaging
costs are contributing up to 80% of the total device cost. Each MEMS device
category, its function and operational environment will individually dictate
the packaging requirement. Due to the lack of standardized testing procedures,
the reliability of those MEMS packages sometimes can only be proven by taking
into consideration its functionality over lifetime. Innovation with regards to
cost reduction and standardization in the field of packaging is therefore of
utmost importance to the speed of commercialisation of MEMS devices. Nowadays
heavily driven by consumer applications the MEMS device market is forecasted to
enjoy a compound annual growth rate (CAGR) above 13%, which is when compared to
the IC device market, an outstanding growth rate. Nevertheless this forecasted
value can drift upwards or downwards depending on the rate of innovation in the
field of packaging. MEMS devices typically require a specific fabrication
process where the device wafer is bonded to a second wafer which effectively
encapsulates the MEMS structure. This method leaves the device free to move
within a vacuum or an inert gas atmosphere.
| arxiv topic:cs.OH |
arxiv_dataset-505802.3203 | Magneto-spectroscopy of Highly-Aligned Carbon Nanotubes: Identifying the
Role of Threading Magnetic Flux
cond-mat.mes-hall cond-mat.mtrl-sci
We have investigated excitons in highly-aligned single-walled carbon
nanotubes (SWCNTs) through optical spectroscopy at low temperature (1.5 K) and
high magnetic fields ($\textbf{\textit{B}}$) up to 55 T. SWCNT/polyacrylic acid
films were stretched, giving SWCNTs that are highly aligned along the direction
of stretch ($\hat{n}$). Utilizing two well-defined measurement geometries,
$\hat{n}\parallel\textbf{\textit{B}}$ and $\hat{n}\perp\textbf{\textit{B}}$, we
provide unambiguous evidence that the photoluminescence energy and intensity
are only sensitive to the $\textbf{\textit{B}}$-component parallel to the tube
axis. A theoretical model of one-dimensional magneto-excitons, based on
exchange-split `bright' and `dark' exciton bands with
Aharonov-Bohm-phase-dependent energies, masses, and oscillator strengths,
successfully reproduces our observations and allows determination of the
splitting between the two bands as $\sim4.8$ meV for (6,5) SWCNTs.
| arxiv topic:cond-mat.mes-hall cond-mat.mtrl-sci |
arxiv_dataset-506802.3303 | Metallicity effects on the modified wind momentum of CSPN
astro-ph
Recent investigations on the central stars of planetary nebulae (CSPN)
indicate that the masses based on model atmospheres can be much larger than the
masses derived from theoretical mass-luminosity relations. Also, the dispersion
in the relation between the modified wind momentum and the luminosity depends
on the mass spread of the CSPN, and is larger than observed in massive hot
stars. Since the wind characteristics probably depend on the metallicity, we
analyze the effects on the modified wind momentum by considering the dispersion
in this quantity caused by the stellar metallicity. Our CSPN masses are based
on a relation between the core mass and the nebular abundances. We conclude
that these masses agree with the known mass distribution both for CSPN and
white dwarfs, and that the spread in the modified wind momentum can be
explained by the observed metallicity variations.
| arxiv topic:astro-ph |
arxiv_dataset-507802.3403 | Goldman flows on the Jacobian
math.DG
We show that the Goldman flows preserve the holomorphic structure on the
moduli space of homomorphisms of the fundamental group of a Riemann surface
into U(1), in other words the Jacobian.
| arxiv topic:math.DG |
arxiv_dataset-508802.3503 | Controlling subluminal to superluminal behavior of group velocity in an
f-deformed Bose-Einstein condensate beyond the rotating wave approximation
quant-ph
In this paper, we investigate tunable control of the group velocity of a weak
probe field propagating through an f-deformed Bose-Einstein condensate of
three-level atoms beyond the rotating wave approximation. For this purpose, we
use an f- deformed generalization of an effective two-level quantum model of
the three-level configuration without the rotating wave approximation in which
the Gardiners phonon operators for Bose-Einstein condensate are deformed by an
operator- valued function,f(n), of the particle- number operator n .
Corrections produced by the counter- rotating terms appear in the first order
as an intensity- dependent detuning and in the second order as an intensity-
dependent atom-field coupling. We consider the collisions between the atoms as
a special kind of f- deformation where the collision rate k is regarded as the
deformation parameter. We demonstrate the enhanced effect of subluminal and
superluminal propagation based on electromagnetically induced transparency and
electromagnetically induced absorption, respectively. In particular, we find
that (i) the absorptive and dispersive properties of the deformed condensate
can be controlled effectively in the absence of the rotating wave approximation
by changing the deformation parameter k, the total number of atoms N and the
counter- rotating terms parameter, (ii) by increasing the values of k, 1/N and
the counter- rotating terms parameter, the group velocity of the probe pulse
changes, from subluminal to superluminal and (iii) beyond the rotating wave
approximation, the subluminal and superluminal behaviors of the probe field are
enhanced.
| arxiv topic:quant-ph |
arxiv_dataset-509802.3603 | String Creation, D-branes and Effective Field Theory
hep-th
This paper addresses several unsettled issues associated with string creation
in systems of orthogonal Dp-D(8-p) branes. The interaction between the branes
can be understood either from the closed string or open string picture. In the
closed string picture it has been noted that the DBI action fails to capture an
extra RR exchange between the branes. We demonstrate how this problem persists
upon lifting to M-theory. These D-brane systems are analysed in the closed
string picture by using gauge-fixed boundary states in a non-standard lightcone
gauge, in which RR exchange can be analysed precisely. The missing piece in the
DBI action also manifests itself in the open string picture as a mismatch
between the Coleman-Weinberg potential obtained from the effective field theory
and the corresponding open string calculation. We show that this difference can
be reconciled by taking into account the superghosts in the (0+1)effective
theory of the chiral fermion, that arises from gauge fixing the spontaneously
broken world-line local supersymmetries.
| arxiv topic:hep-th |
arxiv_dataset-510802.3703 | On incidence algebras description of cobweb posets
math.CO cs.DM
The explicite formulas for Mobius function and some other important elements
of the incidence algebra of an arbitrary cobweb poset are delivered. For that
to do one uses Kwasniewski's construction of his cobweb posets . The digraph
representation of these cobweb posets constitutes a newly discovered class of
orderable DAG's named here down KoDAGs with a kind of universality now being
investigated. Namely cobweb posets' and thus KoDAGs's defining di-bicliques are
links of any complete relations' chains.
| arxiv topic:math.CO cs.DM |
arxiv_dataset-511802.3803 | On the nature of late X-ray flares in Swift Gamma-ray Bursts
astro-ph
Previously detected in only a few gamma-ray bursts (GRBs), X-ray flares are
now observed in ~50% of Swift GRBs, though their origins remain unclear. Most
flares are seen early on in the afterglow decay, while some bursts exhibit
flares at late times of 10^4 to 10^5 seconds, which may have implications for
flare models.We investigate whether a sample of late time (> 10^4s) flares are
different from previous samples of early time flares, or whether they are
merely examples on the tail of the early flare distribution. We examine the
X-ray light curves of Swift bursts for late flares and compare the flare and
underlying temporal power-law properties with those of early flares, and the
values of these properties predicted by the blast wave model. The burst sample
shows late flare properties consistent with those of early flares, where the
majority of the flares can be explained by either internal or external shock,
though in a few cases one origin is favoured over the other. The underlying
power laws are mainly consistent with the normal decay phases of the afterglow.
If confirmed by the ever growing sample of late time flares, this would imply
that, in some cases, prolonged activity out to a day or a restarting of the
central engine is required.
| arxiv topic:astro-ph |
arxiv_dataset-512802.3903 | Constraining Galaxy Evolution With Bulge-Disk-Bar Decomposition
astro-ph
Structural decomposition of galaxies into bulge, disk, and bar components is
important to address a number of scientific problems. Measuring bulge, disk,
and bar structural parameters will set constraints on the violent and secular
processes of galaxy assembly and recurrent bar formation and dissolution
models. It can also help to quantify the fraction and properties of bulgeless
galaxies (those systems having no bulge or only a relatively insignificant
disky-pseudobulges), which defy galaxy formation paradigms requiring almost
every disk galaxy to have a classical bulge at its core. We demonstrate a proof
of concept and show early results of our ongoing three-component bulge-disk-bar
decomposition of NIR images for a sample of three complementary samples
spanning different epochs and different environments (field and cluster). In
contrast to most early studies, which only attempt two-component bulge-disk
decomposition, we fit three components using GALFIT: a bulge, a disk, and a
bar. We show that it is important to include the bar component, as this can
significantly lower the bulge-to-total luminosity ratio (B/T), in many cases by
a factor of two or more, thus effectively changing the Hubble type of a galaxy
from early to late.
| arxiv topic:astro-ph |
arxiv_dataset-513802.4003 | Modeling of diffuse molecular gas applied to HD 102065 observations
astro-ph
Aims. We model a diffuse molecular cloud present along the line of sight to
the star HD 102065. We compare our modeling with observations to test our
understanding of physical conditions and chemistry in diffuse molecular clouds.
Methods. We analyze an extensive set of spectroscopic observations which
characterize the diffuse molecular cloud observed toward HD 102065. Absorption
observations provide the extinction curve, H2, C I, CO, CH, and CH+ column
densities and excitation. These data are complemented by observations of CII,
CO and dust emission. Physical conditions are determined using the Meudon PDR
model of UV illuminated gas. Results. We find that all observational results,
except column densities of CH, CH+ and H2 in its excited (J > 2) levels, are
consistent with a cloud model implying a Galactic radiation field (G~0.4 in
Draine's unit), a density of 80 cm-3 and a temperature (60-80 K) set by the
equilibrium between heating and cooling processes. To account for excited (J
>2) H2 levels column densities, an additional component of warm (~ 250K) and
dense (nH>10^4 cm-3) gas within 0.03 pc of the star would be required. This
solution reproduces the observations only if the ortho-to-para H2 ratio at
formation is 1. In view of the extreme physical conditions and the unsupported
requirement on the ortho-to-para ratio, we conclude that H2 excitation is most
likely to be accounted for by the presence of warm molecular gas within the
diffuse cloud heated by the local dissipation of turbulent kinetic energy. This
warm H2 is required to account for the CH+ column density. It could also
contribute to the CH abundance and explain the inhomogeneity of the CO
abundance indicated by the comparison of absorption and emission spectra.
| arxiv topic:astro-ph |
arxiv_dataset-514802.4103 | Top-gated graphene field-effect-transistors formed by decomposition of
SiC
cond-mat.mes-hall cond-mat.mtrl-sci
Top-gated, few-layer graphene field-effect transistors (FETs) fabricated on
thermally-decomposed semi-insulating 4H-SiC substrates are demonstrated.
Physical vapor deposited SiO2 is used as the gate dielectric. A two-dimensional
hexagonal arrangement of carbon atoms with the correct lattice vectors,
observed by high-resolution scanning tunneling microscopy, confirms the
formation of multiple graphene layers on top of the SiC substrates. The
observation of n-type and p-type transition further verifies Dirac Fermions
unique transport properties in graphene layers. The measured electron and hole
mobility on these fabricated graphene FETs are as high as 5400 cm2/Vs and 4400
cm2/Vs respectively, which are much larger than the corresponding values from
conventional SiC or silicon.
| arxiv topic:cond-mat.mes-hall cond-mat.mtrl-sci |
arxiv_dataset-515802.4203 | Possible observation of energy level quantization in an intrinsic
Josephson junction
cond-mat.supr-con
Energy level quantization (ELQ) is studied to clarify the macroscopic quantum
dynamics of the d-wave Josephson junction (JJ). The influences of the nodal
quasiparticles of d-wave superconductivity on the damping effect are
numerically evaluated on the basis of a phenomenological model. The
calculation, based on realistic parameters for a Bi2Sr2CaCu2O8+d (Bi2212)
intrinsic JJ, shows that the observation of ELQ is possible when the sweep rate
of the bias current exceeds 10 A/sec. High-sweep- rate measurements (121A/sec)
performed on a Bi2212 intrinsic JJ result in the appearance of multiple peaks
in the switching current distribution suggesting the realization of ELQ in the
d-wave JJ.
| arxiv topic:cond-mat.supr-con |
arxiv_dataset-516802.4303 | A new signature for color octet pseudoscalars at the LHC
hep-ph
Color octet (pseudo)scalars, if they exist, will be copiously produced at the
CERN Large Hadron Collider (LHC). However, their detection can become a very
challenging task. In particular, if their decay into a pair of top quarks is
kinematically forbidden, the main decay channel would be into two jets, with a
very large background. In this Brief Report we explore the possibility of using
anomaly-induced decays of the color octet pseudoscalars into gauge bosons to
find them at the LHC.
| arxiv topic:hep-ph |
arxiv_dataset-517802.4403 | The puzzling MILAGRO hot spots
astro-ph
We discuss the reported detection by the MILAGRO experiment of localised hot
spots in the cosmic ray arrival distribution and the difficulty of interpreting
these observations. A model based on secondary neutron production in the
heliotail is shown to fail. An alternative model based on loss-cone leakage
through a magnetic trap from a local source region is proposed.
| arxiv topic:astro-ph |
arxiv_dataset-518803.004 | Minimal distance transformations between links and polymers: Principles
and examples
cond-mat.soft cond-mat.other
The calculation of Euclidean distance between points is generalized to
one-dimensional objects such as strings or polymers. Necessary and sufficient
conditions for the minimal transformation between two polymer configurations
are derived. Transformations consist of piecewise rotations and translations
subject to Weierstrass-Erdmann corner conditions. Numerous examples are given
for the special cases of one and two links. The transition to a large number of
links is investigated, where the distance converges to the polymer length times
the mean root square distance (MRSD) between polymer configurations, assuming
curvature and non-crossing constraints can be neglected. Applications of this
metric to protein folding are investigated. Potential applications are also
discussed for structural alignment problems such as pharmacophore
identification, and inverse kinematic problems in motor learning and control.
| arxiv topic:cond-mat.soft cond-mat.other |
arxiv_dataset-519803.014 | Non-critical String Cosmologies
hep-ph
Non-critical String Cosmologies are offered as an alternative to Standard Big
Bang Cosmology. The new features encompassed within the dilaton dependent
non-critical terms affect the dynamics of the Universe\'s evolution in an
unconventional manner being in agreement with the cosmological data.
Non-criticality is responsible for a late transition to acceleration at
redshifts z=0.2. The role of the uncoupled rolling dilaton to relic abundance
calculations is discussed. The uncoupled rolling dilaton dilutes the neutralino
relic densities in supersymmetric theories by factors of ten, relaxing
considerably the severe WMAP Dark Matter constraints, while at the same time
leaves almost unaffected the baryon density in agreement with primordial
Nucleosynthesis.
| arxiv topic:hep-ph |
arxiv_dataset-520803.024 | On the nature of Seyfert galaxies with high [OIII]5007 blueshifts
astro-ph
We have studied the properties of Seyfert galaxies with high [OIII]5007
blueshifts (`blue outliers'), originally identified because of their strong
deviation from the M_BH - sigma relation of normal, narrow-line Seyfert 1
(NLS1) and broad-line Seyfert 1 (BLS1) galaxies. These blue outliers turn out
to be important test-beds for models of the narrow-line region (NLR), for
mechanisms of driving large-scale outflows, for links between NLS1 galaxies and
radio galaxies, and for orientation-dependent NLS1 models. We report the
detection of a strong correlation of line blueshift with ionization potential
in each galaxy, including the measurement of coronal lines with radial
velocities up to 500--1000 km/s. All [OIII] blue outliers have narrow widths of
their broad Balmer lines and high Eddington ratios. While the presence of
non-shifted low-ionization lines signifies the presence of a classical outer
quiescent NLR in blue outliers, we also report the absence of any second,
non-blueshifted [OIII] component from a classical inner NLR. These results
place tight constraints on NLR models. We favor a scenario in which the NLR
clouds are entrained in a decelerating wind which explains the strong
stratification and the absence of a zero-blueshift inner NLR of blue outliers.
The origin of the wind remains speculative at this time (collimated radio
plasma, thermal winds, radiatively accelerated clouds). It is perhaps linked to
the high Eddington ratios of blue outliers. Similar, less powerful winds could
be present in all Seyfert galaxies, but would generally only affect the coronal
line region (CLR), or level off even before reaching the CLR. Similarities
between blue outliers in NLS1 galaxies and (compact) radio sources are briefly
discussed.
| arxiv topic:astro-ph |
arxiv_dataset-521803.034 | Dynamical Creation of Fractionalized Vortices and Vortex Lattices
cond-mat.other cond-mat.dis-nn
We investigate dynamic creation of fractionalized half-quantum vortices in
Bose-Einstein condensates of sodium atoms. Our simulations show that both
individual half-quantum vortices and vortex lattices can be created in rotating
optical traps when additional pulsed magnetic trapping potentials are applied.
We also find that a distinct periodically modulated spin-density-wave spatial
structure is always embedded in square half-quantum vortex lattices; this
structure can be conveniently probed by taking absorption images of
ballistically expanding cold atoms in a Stern-Gerlach field.
| arxiv topic:cond-mat.other cond-mat.dis-nn |
arxiv_dataset-522803.044 | Ab-initio description of hole localization and Zhang-Rice singlets in
one-dimensional doped cuprates
cond-mat.str-el cond-mat.mtrl-sci
We present the first ab-initio band-theory-based description of
spin-compensated polarons (known as Zhang-Rice singlets) in a hole-doped
cuprate, specifically one-dimensional Ca_{2+x} Y_{2-x} Cu_5 O_10. Zhang-Rice
singlets are many-particle configurations relevant to the exotic behavior of
hole-doped cuprates, stemming from spontaneous charge localization. They appear
in our case-study material above a threshold doping, successively turning the
insulating undoped antiferromagnet into a gap insulator, a singlet-rich
metallic paramagnet, and finally, a singlet-saturated insulating diamagnet.
| arxiv topic:cond-mat.str-el cond-mat.mtrl-sci |
arxiv_dataset-523803.054 | The thermonuclear rate for the 19F(a,p)22Ne reaction at stellar
temperatures
nucl-ex
The $^{19}$F($\alpha$,p)$^{22}$Ne reaction is considered to be one of the
main sources of fluorine depletion in AGB and Wolf-Rayet stars. The reaction
rate still retains large uncertainties due to the lack of experimental studies
available. In this work the yields for both exit channels to the ground state
and first excited state of $^{22}$Ne have been measured and several previously
unobserved resonances have been found in the energy range E$_{lab}$=792-1993
keV. The level parameters have been determined through a detailed R-matrix
analysis of the reaction data and a new reaction rate is provided on the basis
of the available experimental information.
| arxiv topic:nucl-ex |
arxiv_dataset-524803.064 | Metric properties of Outer Space
math.GR math.GT
We define metrics on Culler-Vogtmann space, which are an analogue of the
Teichmuller metric and are constructed using stretching factors. In fact the
metrics we study are related, one being a symmetrised version of the other. We
investigate the basic properties of these metrics, showing the advantages and
pathologies of both choices. We show how to compute stretching factors between
marked metric graphs in an easy way and we discuss the behaviour of stretching
factors under iterations of automorphisms. We study metric properties of
folding paths, showing that they are geodesic for the non-symmetric metric and,
if they do not enter the thin part of Outer space, quasi-geodesic for the
symmetric metric.
| arxiv topic:math.GR math.GT |
arxiv_dataset-525803.074 | A Deep HST Study of the Globular Cluster NGC 6397: Reduction Methods
astro-ph
We describe here the reduction methods that we developed to study the
faintest red dwarfs and white dwarfs in an outer field of NGC6397, which was
observed by \hst for 126 orbits in 2005. The particular challenge of this data
set is that the faintest stars are not readily visible in individual exposures,
so special care must be taken to combine the information in all the exposures
in order to identify and measure them. Unfortunately, it is hard to find the
faintest stars without also finding a large number of faint galaxies, so we
developed specialized tools to distinguish between the point-like stars and the
barely resolved galaxies. We found that artificial-star tests, while obviously
necessary for completeness determination, can also play an important role in
helping us optimize our finding and measuring algorithms. Although this paper
focuses on this data set specifically, many of the techniques are new and might
find application in other work, particularly when a large number of images is
available for a single field.
| arxiv topic:astro-ph |
arxiv_dataset-526803.084 | Moufang symmetry X. Generalized Lie and Maurer-Cartan equations of
continuous Moufang transformations
math.RT
The differential equations for a continuous birepresentation of a local
analytic Moufang loop are established. The commutation relations for the
infinitesimal operators of the representation are found. These commutation
relations can be seen as a (minimal) generalization of the Maurer-Cartan
equations and do not depend on the particular birepresentation.
| arxiv topic:math.RT |
arxiv_dataset-527803.094 | A Smooth, Inductively Coupled Ring Trap for Atoms
physics.atom-ph cond-mat.other
We propose and numerically investigate a scalable ring trap for cold atoms
that surmounts problems of roughness of the potential and end--effects of trap
wires. A stable trapping potential is formed about an electrically isolated,
conducting loop in an ac magnetic field by time averaging the superposition of
the external and induced magnetic fields. We investigate the use of additional
fields to eliminate Majorana spin flip losses and to create novel trapping
geometries. The possibility of micro--fabrication of these ring traps offers
the prospect of developing Sagnac atom interferometry in atom--chip devices.
| arxiv topic:physics.atom-ph cond-mat.other |
arxiv_dataset-528803.104 | Geometric Measure of Entanglement and Shared Quantum States
quant-ph
We give an explicit expression for the geometric measure of entanglement for
three qubit states that are linear combinations of four orthogonal product
states. It turns out that the geometric measure for these states has three
different expressions depending on the range of definition in parameter space.
Each expression of the measure has its own geometrically meaningful
interpretation. Such an interpretation allows oneself to take one step toward a
complete understanding for the general properties of the entanglement measure.
The states that lie on joint surfaces separating different ranges of
definition, designated as shared states, seem to have particularly interesting
features. The properties of the shared states are fully discussed.
| arxiv topic:quant-ph |
arxiv_dataset-529803.114 | Incompressible Liquid, Stripes and Bubbles in rapidly rotating Bose
atoms at $\nu=1$
cond-mat.mes-hall
We numerically study the system of rapidly rotating Bose atoms at the filling
factor (ratio of particle number to vortex number) $\nu=1$ with the dipolar
interaction. A moderate dipolar interaction stabilizes the incompressible
quantum liquid at $\nu=1$. Further addition induces a collapse of it. The state
after the collapse is a compressible state which has phases with stripes and
bubbles.
There are two types of bubbles with a different array. We also investigate
models constructed from truncated interactions and the models with the
three-body contact interaction. They also have phases with stripes and bubbles.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-530803.124 | Partial Observations, Einstein Locality and Bell Inequalities in
Quantized Detector Networks
quant-ph
Quantized detector networks (QDN) deals with quantum information exchange
between observers and their apparatus rather than with systems under
observation. Partial observations in QDN involve subsets of the elementary
signal detectors which constitute an apparatus. We use them to prove that QDN
is consistent with Einstein locality and violations of Bell-type inequalities.
| arxiv topic:quant-ph |
arxiv_dataset-531803.134 | Quantum Field Theory and Differential Geometry
physics.pop-ph hep-th math-ph math.DG math.MP
We introduce the historical development and physical idea behind topological
Yang-Mills theory and explain how a physical framework describing subatomic
physics can be used as a tool to study differential geometry. Further, we
emphasize that this phenomenon demonstrates that the interrelation between
physics and mathematics have come into a new stage.
| arxiv topic:physics.pop-ph hep-th math-ph math.DG math.MP |
arxiv_dataset-532803.144 | X-ray absorption in distant type II QSOs
astro-ph
We present the results of the X-ray spectral analysis of an
XMM-Newton-selected type II QSO sample with z>0.5 and 0.5-10 keV flux of 0.3-33
x 10^{-14} erg/s/cm^2. The distribution of absorbing column densities in type
II QSOs is investigated and the dependence of absorption on X-ray luminosity
and redshift is studied.
We inspected 51 spectroscopically classified type II QSO candidates from the
XMM-Newton Marano field survey, the XMM-Newton-2dF wide angle survey (XWAS),
and the AXIS survey to set-up a well-defined sample with secure optical type II
identifications. Fourteen type II QSOs were classified and an X-ray spectral
analysis performed. Since most of our sources have only ~40 X-ray counts
(PN-detector), we carefully studied the fit results of the simulated X-ray
spectra as a function of fit statistic and binning method. We determined that
fitting the spectra with the Cash-statistic and a binning of minimum one count
per bin recovers the input values of the simulated X-ray spectra best. Above
100 PN counts, the free fits of the spectrum's slope and absorbing hydrogen
column density are reliable.
We find only moderate absorption (N_H=(2-10) x 10^22 cm^-2) and no obvious
trends with redshift and intrinsic X-ray luminosity. In a few cases a
Compton-thick absorber cannot be excluded. Two type II objects with no X-ray
absorption were discovered. We find no evidence for an intrinsic separation
between type II AGN and high X-ray luminosity type II QSO in terms of
absorption. The stacked X-ray spectrum of our 14 type II QSOs shows no iron
K-alpha line. In contrast, the stack of the 8 type II AGN reveals a very
prominent iron K-alpha line at an energy of ~ 6.6 keV and an EW ~ 2 keV.
| arxiv topic:astro-ph |
arxiv_dataset-533803.154 | Nonholonomic constraints in $k$-symplectic Classical Field Theories
math-ph math.MP
A $k$-symplectic framework for classical field theories subject to
nonholonomic constraints is presented. If the constrained problem is regular
one can construct a projection operator such that the solutions of the
constrained problem are obtained by projecting the solutions of the free
problem. Symmetries for the nonholonomic system are introduced and we show that
for every such symmetry, there exist a nonholonomic momentum equation. The
proposed formalism permits to introduce in a simple way many tools of
nonholonomic mechanics to nonholonomic field theories.
| arxiv topic:math-ph math.MP |
arxiv_dataset-534803.164 | Gravitational Lensing Constraints on Dynamical and Coupled Dark Energy
astro-ph
Upcoming Weak Lensing (WL) surveys can be used to constrain Dark Energy (DE)
properties, namely if tomographic techniques are used to improve their
sensitivity. In this work, we use a Fisher matrix technique to compare the
power of CMB anisotropy and polarization data with tomographic WL data, in
constraining DE parameters. Adding WL data to available CMB data improves the
detection of all cosmological parameters, but the impact is really strong when
DE--DM coupling is considered, as WL tomography can then succeed to reduce the
errors on some parameters by factors >10.
| arxiv topic:astro-ph |
arxiv_dataset-535803.174 | Primes in the form $[\alpha p+\beta]$
math.NT
Let \beta be a real number. Then for almost all irrational \alpha>0 (in the
sense of Lebesgue measure)
\limsup_{x\to\infty}\pi_{\alpha,\beta}^*(x)(\log x)^2/x>=1, where
\pi_{\alpha,\beta}^*(x)={p<=x: both p and [\alpha p+\beta] are primes}.
| arxiv topic:math.NT |
arxiv_dataset-536803.184 | About Essence of the Wave Function on Atomic Level and in
Superconductors
physics.gen-ph
The wave function was proposed for description of quantum phenomena on the
atomic level. But now it is well known that quantum phenomena are observed not
only on atomic level and the wave function is used for description of
macroscopic quantum phenomena, such as superconductivity. The essence of the
wave function on level elementary particles was and is the subject of heated
argument among founders of quantum mechanics and other physicists. This essence
seems more clear in superconductor. But impossibility of probabilistic
interpretation of wave function in this case results to obvious contradiction
of quantum principles with some fundamental principles of physics.
| arxiv topic:physics.gen-ph |
arxiv_dataset-537803.194 | Next-to-leading order QCD corrections to spin-dependent hadron-pair
photoproduction
hep-ph
We compute the next-to-leading order QCD corrections to the ``direct'' part
of the spin-dependent cross section for hadron-pair photoproduction. The
calculation is performed using largely analytical methods. We present a brief
phenomenological study of our results focussing on the $K$-factors and scale
dependence of the next-to-leading order cross sections. This process is
relevant for the extraction of the gluon polarization in present and future
spin-dependent lepton-nucleon scattering experiments.
| arxiv topic:hep-ph |
arxiv_dataset-538803.204 | Standard Model couplings and collider signatures of a light scalar
hep-ph hep-ex
The electroweak symmetry breaking (EWSB) sector of the Standard Model can be
far richer and more interesting than the usual single scalar doublet model. We
explore scenarios where the EWSB sector is nearly scale invariant and
consequently gives rise to a light CP even scalar particle. The one-doublet SM
is in that category, as are many other models with either weakly or strongly
coupled sectors that trigger EWSB. We study the couplings of the light scalar
to the SM particles that can arise from the explicit breaking of scale
invariance focusing on the possible differences with the minimal SM. The
couplings of the light scalar to light fermions, as well as to the massless
gauge bosons, can be significantly enhanced. We find possible new discovery
channels due to the decays of the conformal scalar into e^+e^- and mu^+mu^-
pairs as well as new production channels via light quark annihilation.
| arxiv topic:hep-ph hep-ex |
arxiv_dataset-539803.214 | Noise invoked resonances near a homoclinic bifurcation in the glow
discharge plasma
physics.plasm-ph nlin.CD physics.data-an
Stochastic Resonance (SR) and Coherence Resonance (CR) have been studied
experimentally in the discharge plasma close to a homoclinic bifurcation. For
the SR phenomena, it is observed that a superimposed subthreshold periodic
signal can be recovered via stochastic modulations of the discharge voltage.
Furthermore, it is realized that even in the absence of a subthreshold
deterministic signal, the system dynamics can be recovered and optimized using
noise. This effect is defined as CR in the literature. In the present
experiments, induction of SR and CR are quantified using the Absolute Mean
Difference (AMD) and Normalized Variance (NV) techniques respectively. AMD is a
new statistical tool to quantify regularity in the stochastic resonance and is
independent of lag.
| arxiv topic:physics.plasm-ph nlin.CD physics.data-an |
arxiv_dataset-540803.224 | The Exo-planetary System of 55 Cancri and the Titius-Bode Law
astro-ph
The recent discovery of a fifth planet bound to 55 Cancri (Fischer et. al
2007) motivated us to investigate if this exo-planetary system fits some form
of the Titius-Bode (TB) law. We found that a simple exponential TB relation
reproduces very well the five observed major semi-axis, provided we assign the
orbital n = 6 to the largest a. This way of counting leaves empty the position
n = 5, a situation curiously reminiscent of TB law in our planetary system,
before the discovery of Ceres. The application of an exponential TB relation to
55 Cancri allows us to predict the existence of a planet at a = 2.0 AU with a
period of P = 1130 days located within the large gap between a = 0.781 AU (P =
260 days) and a = 5.77 AU (P = 5218 days). With less certainty, we also predict
a seventh planet at a = 15 AU with P = 62 years.
| arxiv topic:astro-ph |
arxiv_dataset-541803.234 | Noncommutative Standard Model in Top Quark Sector
hep-ph
In this article we aim to estimate the bounds on the noncommutative scale
$\Lambda_{NC}$ and to extract the 95% exclusion contours for some
$\theta_{\mu\nu}$ components using the recent measurements of the top quark
width and the $W$ boson polarization in top pair events from CDF experiment at
Tevatron.
| arxiv topic:hep-ph |
arxiv_dataset-542803.244 | Spin transfer torques in nonlocal lateral spin valve
cond-mat.mes-hall
We report a theoretical study on the spin and electron transport in the
nonlocal lateral spin valve with non-collinear magnetic configuration. The
nonlocal magnetoresistance, defined as the voltage difference on the detection
lead over the injected current, is derived analytically. The spin transfer
torques on the detection lead are calculated. It is found that spin transfer
torques are symmetrical for parallel and antiparallel magnetic configurations,
which is different from that in conventional sandwiched spin valve.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-543803.254 | When is Group Cohomology Finitary?
math.GR math.KT
If $G$ is a group, then we say that the functor $H^n(G,-)$ is finitary if it
commutes with all filtered colimit systems of coefficient modules. We
investigate groups with cohomology almost everywhere finitary; that is, groups
with $n$th cohomology functors finitary for all sufficiently large $n$. We
establish sufficient conditions for a group $G$ possessing a finite dimensional
model for $e.g.$ to have cohomology almost everywhere finitary. We also prove a
stronger result for the subclass of groups of finite virtual cohomological
dimension, and use this to answer a question of Leary and Nucinkis. Finally, we
show that if $G$ is a locally (polycyclic-by-finite) group, then $G$ has
cohomology almost everywhere finitary if and only if $G$ has finite virtual
cohomological dimension and the normalizer of every non-trivial finite subgroup
of $G$ is finitely generated.
| arxiv topic:math.GR math.KT |
arxiv_dataset-544803.264 | Antideuteron fluxes from dark matter annihilation in diffusion models
hep-ph astro-ph hep-ex
Antideuterons are among the most promising galactic cosmic ray-related
targets for dark matter indirect detection. Currently only upper limits exist
on the flux, but the development of new experiments, such as GAPS and AMS-02,
provides exciting perspectives for a positive measurement in the near future.
In this Paper, we present a novel and updated calculation of both the secondary
and primary antideuteron fluxes. We employ a two-zone diffusion model which
successfully reproduces cosmic-ray nuclear data and the observed antiproton
flux. We review the nuclear and astrophysical uncertainties and provide an up
to date secondary (i.e. background) antideuteron flux. The primary (i.e.
signal) contribution is calculated for generic WIMPs annihilating in the
galactic halo: we explicitly consider and quantify the various sources of
uncertainty in the theoretical evaluations. Propagation uncertainties, as is
the case of antiprotons, are sizeable. Nevertheless, antideuterons offer an
exciting target for indirect dark matter detection for low and intermediate
mass WIMP dark matter. We then show the reaching capabilities of the future
experiments for neutralino dark matter in a variety of supersymmetric models.
| arxiv topic:hep-ph astro-ph hep-ex |
arxiv_dataset-545803.274 | Unconventional sign-reversing superconductivity in LaFeAsO_(1-x)F_x
cond-mat.supr-con cond-mat.mtrl-sci
We argue that the newly discovered superconductivity in a nearly magnetic,
Fe-based layered compound is unconventional and mediated by antiferromagnetic
spin fluctuations, though different from the usual superexchange and specific
to this compound. This resulting state is an example of extended s-wave pairing
with a sign reversal of the order parameter between different Fermi surface
sheets. The main role of doping in this scenario is to lower the density of
states and suppress the pair-breaking ferromagnetic fluctuations.
| arxiv topic:cond-mat.supr-con cond-mat.mtrl-sci |
arxiv_dataset-546803.284 | IPHAS discoveries of young stars towards Cyg OB2 and its southern
periphery
astro-ph
We report on the discovery of over 50 strong Halpha emitting objects towards
the large OB association Cyg OB2 and the HII region DR 15 on its southern
periphery. This was achieved using the INT Photometric Halpha Survey of the
Northern Galactic Plane (IPHAS), combined with follow-up spectroscopy using the
MMT multi-object spectrometer HectoSpec. We present optical spectra,
supplemented with optical r', i' and Halpha photometry from IPHAS, and
near-infrared J, H, and K photometry from 2MASS. The position of the objects in
the (J - H) versus (H - K) diagram strongly suggests most of them are young.
Many show CaII IR triplet emission indicating that they are in a pre-main
sequence phase of evolution of T Tauri and Herbig Ae nature. Among these, we
have uncovered pronounced clustering of T Tauri stars roughly a degree south of
the centre of Cyg OB2, in an arc close to the HII region DR 15, and the radio
ring nebula G79.29+0.46, for which we discuss its candidacy as a luminous blue
variable (LBV). The emission line objects toward Cyg OB2 itself could be the
brightest most prominent component of a population of lower mass pre-main
sequence stars that has yet to be uncovered. Finally, we discuss the nature of
the ongoing star formation in Cyg OB2 and the possibility that the central OB
stars have triggered star formation in the periphery.
| arxiv topic:astro-ph |
arxiv_dataset-547803.294 | Operator fidelity susceptibility: an indicator of quantum criticality
quant-ph
We introduce the operator fidelity and propose to use its susceptibility for
characterizing the sensitivity of quantum systems to perturbations. Two typical
models are addressed: one is the transverse Ising model exhibiting a quantum
phase transition, and the other is the one dimensional Heisenberg spin chain
with next-nearest-neighbor interactions, which has the degeneracy. It is
revealed that the operator fidelity susceptibility is a good indicator of
quantum criticality regardless of the system degeneracy.
| arxiv topic:quant-ph |
arxiv_dataset-548803.304 | Astronomy with ultra high-energy particles
astro-ph
Recent measurements of the properties of cosmic rays above 10^17 eV are
summarized and implications on our contemporary understanding of their origin
are discussed. Cosmic rays with energies exceeding 10^20 eV have been measured,
they are the highest-energy particles in the Universe. Particles at highest
energies are expected to be only marginally deflected by magnetic fields and
they should point towards their sources on the sky. Recent results of the
Pierre Auger Observatory have opened a new window to the Universe - astronomy
with ultra high-energy particles.
| arxiv topic:astro-ph |
arxiv_dataset-549803.314 | Sharpness of some properties of Wiener amalgam and modulation spaces
math.FA math.AP
We prove sharp estimates for the dilation operator $f(x)\longmapsto f(\lambda
x)$, when acting on Wiener amalgam spaces $W(L^p,L^q)$. Scaling arguments are
also used to prove the sharpness of the known convolution and pointwise
relations for modulation spaces $M^{p,q}$, as well as the optimality of an
estimate for the Schr\"odinger propagator on modulation spaces.
| arxiv topic:math.FA math.AP |
arxiv_dataset-550803.324 | Structure and stability of two-dimensional Bose-Einstein condensates
under both harmonic and lattice confinement
nlin.PS
In this work, we study pancake-shaped Bose-Einstein condensates confined by
both a cylindrically symmetric harmonic potential and an optical lattice with
equal periodicity in two orthogonal directions. We first identify the spectrum
of the underlying two-dimensional linear problem through multiple-scale
techniques. Then, we use the results obtained in the linear limit as a starting
point for a nonlinear existence and stability analysis of the lowest energy
states, emanating from the linear ones, in the nonlinear problem. Two-parameter
continuations of these states are performed for increasing nonlinearity and
optical lattice strengths, and their instabilities and temporal evolution are
investigated. It is found that the ground state as well as one of the excited
states are either stable or weakly unstable for both attractive and repulsive
interatomic interactions.
| arxiv topic:nlin.PS |
arxiv_dataset-551803.334 | Type ${\rm III_1}$ factors generated by regular representations of
infinite dimensional nilpotent group $B_0^{\mathbb N}$
math.OA math.RT
We study the von Neumann algebra, generated by the unitary representations of
infinite-dimensional groups nilpotent group $B_0^{\mathbb N}$. The conditions
of the irreducibility of the regular and quasiregular representations of
infinite-dimensional groups (associated with some quasi-invariant measures) are
given by the so-called Ismagilov conjecture (see [1,2,9-11]). In this case the
corresponding von Neumann algebra is type ${\rm I}_\infty$ factor. When the
regular representation is reducible we find the sufficient conditions on the
measure for the von Neumann algebra to be factor (see [13,14]). In the present
article we determine the type of corresponding factors. Namely we prove that
the von Neumann algebra generated by the regular representations of
infinite-dimensional nilpotent group $B_0^{\mathbb N}$ is type ${\rm III}_1$
hyperfinite factor. The case of the nilpotent group $B_0^{\mathbb Z}$ of
infinite in both directions matrices will be studied in [6].
| arxiv topic:math.OA math.RT |
arxiv_dataset-552803.344 | Manipulating a single adsorbed DNA for a critical endpoint
cond-mat.soft cond-mat.stat-mech
We show the existence of a critical endpoint in the phase diagram of
unzipping of an adsorbed double-stranded (ds) polymer like DNA. The competition
of base pairing, adsorption and stretching by an external force leads to the
critical end point. From exact results, the location of the critical end point
is determined and its classical nature established.
| arxiv topic:cond-mat.soft cond-mat.stat-mech |
arxiv_dataset-553803.354 | The effect of rotation on the abundances of the chemical elements of the
A-type stars in the Praesepe cluster
astro-ph
We study how chemical abundances of late B-, A- and early F-type stars evolve
with time, and we search for correlations between the abundance of chemical
elements and other stellar parameters, such as effective temperature and Vsini.
We have observed a large number of B-, A- and F-type stars belonging to open
clusters of different ages. In this paper we concentrate on the Praesepe
cluster (log t = 8.85), for which we have obtained high resolution, high
signal-to-noise ratio spectra of sixteen normal A- and F-type stars and one Am
star, using the SOPHIE spectrograph of the Observatoire de Haute-Provence. For
all the observed stars, we have derived fundamental parameters and chemical
abundances. In addition, we discuss another eight Am stars belonging to the
same cluster, for which the abundance analysis had been presented in a previous
paper. We find a strong correlation between peculiarity of Am stars and Vsini.
The abundance of the elements underabundant in Am stars increases with Vsini,
while it decreases for the overabundant elements. Chemical abundances of
various elements appear correlated with the iron abundance.
| arxiv topic:astro-ph |
arxiv_dataset-554803.364 | Electrical control of spin coherence in ZnO
cond-mat.mtrl-sci
Electric field enhanced electron spin coherence is characterized using
time-resolved Faraday rotation spectroscopy in n-type ZnO epilayers grown by
molecular beam epitaxy. An in-plane dc electric field E almost doubles the
transverse spin lifetime at 20 K, without affecting the effective g-factor.
This effect persists till high temperatures, but decreases with increasing
carrier concentration. Comparisons of the variations in the spin lifetime, the
carrier recombination lifetime and photoluminescence lifetimes indicate that
the applied E enhances the radiative recombination rate. All observed effects
are independent of crystal directionality and are performed at low magnetic
fields (B < 0.2 T).
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-555803.374 | False discovery rate analysis of brain diffusion direction maps
stat.AP
Diffusion tensor imaging (DTI) is a novel modality of magnetic resonance
imaging that allows noninvasive mapping of the brain's white matter. A
particular map derived from DTI measurements is a map of water principal
diffusion directions, which are proxies for neural fiber directions. We
consider a study in which diffusion direction maps were acquired for two groups
of subjects. The objective of the analysis is to find regions of the brain in
which the corresponding diffusion directions differ between the groups. This is
attained by first computing a test statistic for the difference in direction at
every brain location using a Watson model for directional data. Interesting
locations are subsequently selected with control of the false discovery rate.
More accurate modeling of the null distribution is obtained using an empirical
null density based on the empirical distribution of the test statistics across
the brain. Further, substantial improvements in power are achieved by local
spatial averaging of the test statistic map. Although the focus is on one
particular study and imaging technology, the proposed inference methods can be
applied to other large scale simultaneous hypothesis testing problems with a
continuous underlying spatial structure.
| arxiv topic:stat.AP |
arxiv_dataset-556803.384 | Set families with a forbidden subposet
math.CO
We asymptotically determine the size of the largest family F of subsets of
{1,...,n} not containing a given poset P if the Hasse diagram of P is a tree.
This is a qualitative generalization of several known results including
Sperner's theorem.
| arxiv topic:math.CO |
arxiv_dataset-557803.394 | Saturation of $E_T/N_{ch}$ and Freeze-Out Criteria in Heavy-Ion
Collisions
hep-ph nucl-ex
The pseudorapidity densities of transverse energy, the charged particle
multiplicity and their ratios, $E_T/N_{ch}$, are estimated at mid-rapidity, in
a statistical-thermal model based on chemical freeze-out criteria, for a wide
range of energies from GSI-AGS-SPS to RHIC. It has been observed that in
nucleus-nucleus collisions, $E_T/N_{ch}$ increases rapidly with beam energy and
remains approximately constant at about a value of 800 MeV for beam energies
from SPS to RHIC. $E_T/N_{ch}$ has been observed to be almost independent of
centrality at all measured energies. The statistical-thermal model describes
the energy dependence as well as the centrality independence, qualitatively
well. The values of $E_T/N_{ch}$ are related to the chemical freeze-out
criterium, $E/N \approx 1 GeV$ valid for primordial hadrons. We have studied
the variation of the average mass $(<MASS>), N_{decays}/N_{primordial},
N_{ch}/N_{decays}$ and $E_T/N_{ch}$ with $\sqrt{s_{NN}}$ for all freeze-out
criteria discussed in literature. These observables show saturation around SPS
and higher $\sqrt{s_{NN}}$, like the chemical freeze-out temperature
($T_{ch}$).
| arxiv topic:hep-ph nucl-ex |
arxiv_dataset-558803.404 | Probability distribution of the resistance of a random network
physics.class-ph
The probability density of the resistance of a two dimensional rectangular
network between two conducting plates is calculated. The nodes form an $M$ by
$N$ lattice, and each edge has a random resistance. The Monte Carlo method is
used.
| arxiv topic:physics.class-ph |
arxiv_dataset-559803.414 | Stretching helical nano-springs at finite temperature
cond-mat.soft cond-mat.stat-mech
Using dynamic simulations and analytic methods, we study the elastic response
of a helical filament subject to uniaxial tension over a wide range of bend and
twist persistence length. A low-pitch helix at low temperatures exhibits a
stretching instability and the force-extension curve consists of a sequence of
spikes. At elevated temperature (i.e. small persistence lengths) the helix
melts and a pronounced force plateau is obtained in the fixed-extension
ensemble. The torque boundary condition significantly affects the resulting
elastic properties.
| arxiv topic:cond-mat.soft cond-mat.stat-mech |
arxiv_dataset-560803.424 | Neutral Fitness Landscape in the Cellular Automata Majority Problem
cs.NE
We study in detail the fitness landscape of a difficult cellular automata
computational task: the majority problem. Our results show why this problem
landscape is so hard to search, and we quantify the large degree of neutrality
found in various ways. We show that a particular subspace of the solution
space, called the "Olympus", is where good solutions concentrate, and give
measures to quantitatively characterize this subspace.
| arxiv topic:cs.NE |
arxiv_dataset-561803.434 | Possible Indications of New Physics in Bd-mixing and in sin(2 beta)
Determinations
hep-ph hep-ex hep-lat
Using the hadronic matrix elements from the lattice, B_K and xi_s, involving
only the 4-quark operators for Delta flavor (F) = 2 Hamiltonian relevant for K,
B_d and B_s mixing, along with V_cb, we deduce a non-trivial constraint on the
SM, sin (2 beta) = 0.87+-0.09. This deviates from direct experimental
measurements via the tree process, b -> c c s as well as the one via the
penguin-loop b -> s decays by around 2.1 and 2.7 sigma respectively. If these
deviations are confirmed they would imply the presence of new physics rather
pervasively in both B_d mixing (i.e. very likely in b -> d) as well as in b ->
s transitions requiring a beyond the SM CP-odd phase. Consequently,
improvements in the relevant lattice calculations should be given a high
priority.
| arxiv topic:hep-ph hep-ex hep-lat |
arxiv_dataset-562803.444 | Solar forced Dansgaard-Oeschger events and their phase relation with
solar proxies
physics.geo-ph physics.ao-ph
North Atlantic climate during glacial times was characterized by
large-amplitude switchings, the Dansgaard-Oeschger (DO) events, with an
apparent tendency to recur preferably in multiples of about 1470 years. Recent
work interpreted these intervals as resulting from a subharmonic response of a
highly nonlinear system to quasi-periodic solar forcing plus noise. This
hypothesis was challenged as inconsistent with the observed variability in the
phase relation between proxies of solar activity and Greenland climate. Here we
reject the claim of inconsistency by showing that this phase variability is a
robust, generic feature of the nonlinear dynamics of DO events, as described by
a model. This variability is expected from the fact that the events are
threshold crossing events, resulting from a cooperative process between the
periodic forcing and the noise. This process produces a fluctuating phase
relation with the periodic forcing, consistent with proxies of solar activity
and Greenland climate.
| arxiv topic:physics.geo-ph physics.ao-ph |
arxiv_dataset-563804.0021 | A Search for Interstellar CH$_2$D$^+$
astro-ph
We report on a search for Interstellar CH2D+. Four transitions occur in
easily accessible portions of the spectrum; we report on emission at the
frequencies of these transitions toward high column density star-forming
regions. While the observations can be interpreted as being consistent with a
detection of the molecule, further observations will be needed to secure that
identification. The CH2D+ rotational spectrum has not been measured to high
accuracy. Lines are weak, as the dipole moment induced by the inclusion of
deuterium in the molecule is small. Astronomical detection is favored by
observations toward strongly deuterium-fractionated sources. However, enhanced
deuteration is expected to be most significant at low temperatures. The
sparseness of the available spectrum and the low excitation in regions of high
fractionation make secure identification of CH2D+ difficult. Nonetheless, owing
to the importance of CH3+ to interstellar chemistry, and the lack of rotational
transitions of that molecule owing to its planar symmetric structure, a measure
of its abundance would provide key data to astrochemical models.
| arxiv topic:astro-ph |
arxiv_dataset-564804.0121 | Basic properties of nonlinear stochastic Schr\"{o}dinger equations
driven by Brownian motions
math.PR
The paper is devoted to the study of nonlinear stochastic Schr\"{o}dinger
equations driven by standard cylindrical Brownian motions (NSSEs) arising from
the unraveling of quantum master equations. Under the Born--Markov
approximations, this class of stochastic evolutions equations on Hilbert spaces
provides characterizations of both continuous quantum measurement processes and
the evolution of quantum systems. First, we deal with the existence and
uniqueness of regular solutions to NSSEs. Second, we provide two general
criteria for the existence of regular invariant measures for NSSEs. We apply
our results to a forced and damped quantum oscillator.
| arxiv topic:math.PR |
arxiv_dataset-565804.0221 | Thermodynamics of a model for RNA folding
q-bio.BM
We analyze the thermodynamic properties of a simplified model for folded RNA
molecules recently studied by G. Vernizzi, H. Orland, A. Zee (in {\it Phys.
Rev. Lett.} {\bf 94} (2005) 168103). The model consists of a chain of
one-flavor base molecules with a flexible backbone and all possible pairing
interactions equally allowed. The spatial pseudoknot structure of the model can
be efficiently studied by introducing a $N \times N$ hermitian random matrix
model at each chain site, and associating Feynman diagrams of these models to
spatial configurations of the molecules. We obtain an exact expression for the
topological expansion of the partition function of the system. We calculate
exact and asymptotic expressions for the free energy, specific heat,
entanglement and chemical potential and study their behavior as a function of
temperature. Our results are consistent with the interpretation of $1/N$ as
being a measure of the concentration of $\rm{Mg}^{++}$ in solution.
| arxiv topic:q-bio.BM |
arxiv_dataset-566804.0321 | Existence of an infinite particle limit of stochastic ranking process
math.PR
We study a stochastic particle system which models the time evolution of the
ranking of books by online bookstores (e.g., Amazon). In this system, particles
are lined in a queue. Each particle jumps at random jump times to the top of
the queue, and otherwise stays in the queue, being pushed toward the tail every
time another particle jumps to the top. In an infinite particle limit, the
random motion of each particle between its jumps converges to a deterministic
trajectory. (This trajectory is actually observed in the ranking data on web
sites.) We prove that the (random) empirical distribution of this particle
system converges to a deterministic space-time dependent distribution. A core
of the proof is the law of large numbers for {\it dependent} random variables.
| arxiv topic:math.PR |
arxiv_dataset-567804.0421 | Backward retrieval in optical quantum memory controlled by an external
field
quant-ph
A scheme for backward retrieval in optical quantum memories in which
information is stored in collective states of an extended resonant atomic
ensemble is developed such that phase conjugation can be implemented by
application of an external nonuniform electric (magnetic) field without use of
coherent exciting pulses. The possibilities of realizing such a scheme using
resonant solid-state materials are discussed.
| arxiv topic:quant-ph |
arxiv_dataset-568804.0521 | The incidence of mid-infrared excesses in G and K giants
astro-ph
Using photometric data from the 2MASS and GLIMPSE catalogues, I investigate
the incidence of mid-infrared excesses (~10 microns) of G and K stars of
luminosity class III. In order to obtain a large sample size, stars are
selected using a near-IR colour-magnitude diagram. Sources which are candidates
for showing mid-IR excess are carefully examined and modelled to determined
whether they are likely to be G/K giants. It is found that mid-IR excesses are
present at a level of (1.8 +/- 0.4) x 10^-3. While the origin of these excesses
remains uncertain, it is plausible that they arise from debris discs around
these stars. I note that the measured incidence is consistent with a scenario
in which dust lifetimes in debris discs are determined by Poynting-Robertson
drag rather than by collisions.
| arxiv topic:astro-ph |
arxiv_dataset-569804.0621 | Is there anything special about GRB 080319B?
astro-ph
We show that the properties of gamma ray burst 080319B and its afterglow are
well reproduced by the cannonball model of long gamma ray bursts (GRBs). It was
an ordinary GRB, produced by a jet of highly relativistic plasmoids (CBs),
ejected in a core-collapse supernova (SN) and viewed, as some others before,
particularly close to the CB-emission axis. It still remains to be seen whether
GRB 080319B was associated with an SN akin to SN1998bw, the SN type ordinarily
associated with GRBs, or with a much more luminous SN.
| arxiv topic:astro-ph |
arxiv_dataset-570804.0721 | Bell correlations and equal time measurements
quant-ph
According to the Bell theorem, local hidden variable theories cannot
reproduce all the predictions of quantum mechanics. An important consequence is
that under physically reasonable assumptions quantum mechanics predicts
correlations that seem impossible to obtain from a realistic system. In this
paper, two simple binary apparatuses are discussed that can accurately mimic
correlations predicted by quantum mechanics \textit{if} the correlations are
determined by a coincidence measurement as is commonly done. It is argued that
in order to exclude local hidden variables, coincidence monitors should be
avoided.
| arxiv topic:quant-ph |
arxiv_dataset-571804.0821 | Signature of Magnetic Phase Separation in the Ground State of
Pr1-xCaxMnO3
cond-mat.str-el cond-mat.mtrl-sci
Neutron scattering has been used to investigate the evolution of the long-
and short-range charge-ordered (CO), ferromagnetic (FM), and antiferromagnetic
(AF) correlations in single crystals of Pr1-xCaxMnO3. The existence and
population of spin clusters as refected by short-range correlations are found
to drastically depend on the doping (x) and temperature (T). Concentrated spin
clusters coexist with long-range canted AF order in a wide temperature range in
x = 0.3 while clusters do not appear in x = 0.4 crystal. In contrast, both CO
and AF order parameters in the x = 0.35 crystal show a precipitous decrease
below ~ 35 K where spin clusters form. These results provide direct evidence of
magnetic phase separation and indicate that there is a critical doping x_c
(close to x = 0.35) that divides the phase-separated site-centered from the
homogeneous bond-centered or charge-disproportionated CO ground state.
| arxiv topic:cond-mat.str-el cond-mat.mtrl-sci |
arxiv_dataset-572804.0921 | Simplified Langevin approach to the Peyrard-Bishop-Dauxois model of DNA
cond-mat.soft
A simple Langevin approach is used to study stationary properties of the
Peyrard-Bishop-Dauxois model for DNA, allowing known properties to be recovered
in an easy way. Results are shown for the denaturation transition in
homogeneous samples, for which some implications, so far overlooked, of an
analogy with equilibrium wetting transitions are highlighted. This analogy
implies that the order-parameter, asymptotically, exhibits a second order
transition even if it may be very abrupt for non-zero values of the stiffness
parameter. Not surprisingly, we also find that for heterogeneous DNA, within
this model the largest bubbles in the pre-melting stage appear in
adenine-thymine rich regions, while we suggest the possibility of some sort of
not strictly local effects owing to the merging of bubbles.
| arxiv topic:cond-mat.soft |
arxiv_dataset-573804.1021 | Differentiation of Kaltofen's division-free determinant algorithm
cs.SC cs.MS
Kaltofen has proposed a new approach in [Kaltofen 1992] for computing matrix
determinants. The algorithm is based on a baby steps/giant steps construction
of Krylov subspaces, and computes the determinant as the constant term of a
characteristic polynomial. For matrices over an abstract field and by the
results of Baur and Strassen 1983, the determinant algorithm, actually a
straight-line program, leads to an algorithm with the same complexity for
computing the adjoint of a matrix [Kaltofen 1992]. However, the latter is
obtained by the reverse mode of automatic differentiation and somehow is not
``explicit''. We study this adjoint algorithm, show how it can be implemented
(without resorting to an automatic transformation), and demonstrate its use on
polynomial matrices.
| arxiv topic:cs.SC cs.MS |
arxiv_dataset-574804.1121 | Neutrino Oscillation Phenomenology
hep-ph
We explain the physics of neutrino oscillation in vacuum and in matter. We
attempt to clarify several features of oscillation that can be puzzling when
neutrinos are their own antiparticles.
| arxiv topic:hep-ph |
arxiv_dataset-575804.1221 | Strong cleanness of matrix rings over commutative rings
math.RA
Let $R$ be a commutative local ring. It is proved that $R$ is Henselian if
and only if each $R$-algebra which is a direct limit of module finite
$R$-algebras is strongly clean. So, the matrix ring $\mathbb{M}_n(R)$ is
strongly clean for each integer $n>0$ if $R$ is Henselian and we show that the
converse holds if either the residue class field of $R$ is algebraically closed
or $R$ is an integrally closed domain or $R$ is a valuation ring. It is also
shown that each $R$-algebra which is locally a direct limit of module-finite
algebras, is strongly clean if $R$ is a $\pi$-regular commutative ring.
| arxiv topic:math.RA |
arxiv_dataset-576804.1321 | High resolution spectroscopy for Cepheids distance determination. I.
Line asymmetry
astro-ph
The ratio of pulsation to radial velocity (the projection factor) is
currently limiting the accuracy of the interferometric Baade-Wesselink method.
This work aims at establishing a link between the line asymmetry evolution over
the Cepheids' pulsation cycles and their projection factor, with the final
objective to improve the accuracy of the Baade-Wesselink method for distance
determinations. We present HARPS high spectral resolution observations of nine
galactic Cepheids having a good period sampling. We fit spectral line profiles
by an asymmetric bi-Gaussian to derive radial velocity, Full-Width at
Half-Maximum in the line (FWHM) and line asymmetry for all stars. We then
extract correlations curves between radial velocity and asymmetry. A geometric
model providing synthetic spectral lines, including limb-darkening, a constant
FWHM (hereafter sigma_c) and the rotation velocity is used to interpret these
correlations curves. For all stars, comparison between observations and
modelling is satisfactory, and we were able to determine the projected rotation
velocities and sigma_c for all stars. We also find a correlation between the
rotation velocity (Vrot sin i) and the period of the star: Vrot sin i = (11.5
+- 0.9) log(P) + (19.8 +- 1.0) [km/s]. Moreover, we observe a systematic shift
in observational asymmetry curves (noted gamma_O), related to the period of the
star, which is not explained by our static model: gamma_O = (10.7+-0.1) log(P)
+ (9.7+-0.2) [in %] . For long-period Cepheids, in which velocity gradients,
compression or shock waves seem to be large compared to short- or medium period
Cepheids we observe indeed a greater systematic shift in asymmetry curves.
(abridged)
| arxiv topic:astro-ph |
arxiv_dataset-577804.1421 | A $O(\log m)$, deterministic, polynomial-time computable approximation
of Lewis Carroll's scoring rule
cs.GT cs.AI cs.MA
We provide deterministic, polynomial-time computable voting rules that
approximate Dodgson's and (the ``minimization version'' of) Young's scoring
rules to within a logarithmic factor. Our approximation of Dodgson's rule is
tight up to a constant factor, as Dodgson's rule is $\NP$-hard to approximate
to within some logarithmic factor. The ``maximization version'' of Young's rule
is known to be $\NP$-hard to approximate by any constant factor. Both
approximations are simple, and natural as rules in their own right: Given a
candidate we wish to score, we can regard either its Dodgson or Young score as
the edit distance between a given set of voter preferences and one in which the
candidate to be scored is the Condorcet winner. (The difference between the two
scoring rules is the type of edits allowed.) We regard the marginal cost of a
sequence of edits to be the number of edits divided by the number of reductions
(in the candidate's deficit against any of its opponents in the pairwise race
against that opponent) that the edits yield. Over a series of rounds, our
scoring rules greedily choose a sequence of edits that modify exactly one
voter's preferences and whose marginal cost is no greater than any other such
single-vote-modifying sequence.
| arxiv topic:cs.GT cs.AI cs.MA |
arxiv_dataset-578804.1521 | Tri-bimaximal neutrino mixing and neutrinoless double beta decay
hep-ph
We present a tri-bimaximal lepton mixing scheme where the neutrinoless double
beta decay rate (bb0v) has a lower bound which correlates with the ratio alpha
= Dmsol/Dmatm well determined by current data, as well as with the unknown
Majorana CP phase phi12 characterizing the solar neutrino sub-system. For the
special value phi12 = pi/2 (opposite CP-sign neutrinos) the bb0v rate vanishes
at tree level when Dmsol/Dmatm = 3/80, only allowed at 3 sigma. For all other
cases the rate is nonzero, and lies within current and projected experimental
sensitivities close to phi12=0. We suggest two model realizations of this
scheme in terms of an A4xZ2 and A4xZ4 flavour symmetries.
| arxiv topic:hep-ph |
arxiv_dataset-579804.1621 | Direct observation of Anderson localization of matter-waves in a
controlled disorder
cond-mat.dis-nn cond-mat.other
We report the observation of exponential localization of a Bose-Einstein
condensate (BEC) released into a one-dimensional waveguide in the presence of a
controlled disorder created by laser speckle . We operate in a regime allowing
AL: i) weak disorder such that localization results from many quantum
reflections of small amplitude; ii) atomic density small enough that
interactions are negligible. We image directly the atomic density profiles vs
time, and find that weak disorder can lead to the stopping of the expansion and
to the formation of a stationary exponentially localized wave function, a
direct signature of AL. Fitting the exponential wings, we extract the
localization length, and compare it to theoretical calculations. Moreover we
show that, in our one-dimensional speckle potentials whose noise spectrum has a
high spatial frequency cut-off, exponential localization occurs only when the
de Broglie wavelengths of the atoms in the expanding BEC are larger than an
effective mobility edge corresponding to that cut-off. In the opposite case, we
find that the density profiles decay algebraically, as predicted in [Phys. Rev.
Lett. 98, 210401 (2007)]. The method presented here can be extended to
localization of atomic quantum gases in higher dimensions, and with controlled
interactions.
| arxiv topic:cond-mat.dis-nn cond-mat.other |
arxiv_dataset-580804.1721 | Robust control of a bimorph mirror for adaptive optics system
math.AP
We apply robust control technics to an adaptive optics system including a
dynamic model of the deformable mirror. The dynamic model of the mirror is a
modification of the usual plate equation. We propose also a state-space
approach to model the turbulent phase. A continuous time control of our model
is suggested taking into account the frequential behavior of the turbulent
phase. An H_\infty controller is designed in an infinite dimensional setting.
Due to the multivariable nature of the control problem involved in adaptive
optics systems, a significant improvement is obtained with respect to
traditional single input single output methods.
| arxiv topic:math.AP |
arxiv_dataset-581804.1821 | Clustering Property of Wolf-Rayet Galaxies in the SDSS
astro-ph
We have analysed, for the first time, the clustering properties of Wolf-Rayet
(W-R) galaxies, using a large sample of 846 W-R galaxies selected from the Data
Release 4 (DR4) of the SDSS. We compute the cross-correlation function between
W-R galaxies and a reference sample of galaxies drawn from the DR4. We compare
the function to the results for control samples of non-W-R star-forming
galaxies that are matched closely in redshift, luminosity, concentration,
4000-\AA break strength and specific star formation rate (SSFR). On scales
larger than a few Mpc, W-R galaxies have almost the same clustering amplitude
as the control samples, indicating that W-R galaxies and non-W-R control
galaxies populate dark matter haloes of similar masses. On scales between
0.1--1$h^{-1}$ Mpc, W-R galaxies are less clustered than the control samples,
and the size of the difference depends on the SSFR. Based on both observational
and theoretical considerations, we speculate that this negative bias can be
interpreted by W-R galaxies residing preferentially at the centers of their
dark matter haloes. We examine the distribution of W-R galaxies more closely
using the SDSS galaxy group catalogue of Yang et al., and find that $\sim$82%
of our W-R galaxies are the central galaxies of groups, compared to $\sim$74%
for the corresponding control galaxies. We find that W-R galaxies are hosted,
on average, by dark matter haloes of masses of$10^{12.3}M_\odot$, compared to
$10^{12.1}M_\odot$ for centrally-located W-R galaxies and $10^{12.7}M_\odot$
for satellite ones. We would like to point out that this finding, which
provides a direct observational support to our conjecture, is really very crude
due to the small number of W-R galaxies and the incompleteness of the group
catalogue, and needs more work in future with larger samples.
| arxiv topic:astro-ph |
arxiv_dataset-582804.1921 | On the Extension of Pseudo-Boolean Functions for the Aggregation of
Interacting Criteria
cs.DM
The paper presents an analysis on the use of integrals defined for
non-additive measures (or capacities) as the Choquet and the \Sipos{} integral,
and the multilinear model, all seen as extensions of pseudo-Boolean functions,
and used as a means to model interaction between criteria in a multicriteria
decision making problem. The emphasis is put on the use, besides classical
comparative information, of information about difference of attractiveness
between acts, and on the existence, for each point of view, of a ``neutral
level'', allowing to introduce the absolute notion of attractive or repulsive
act. It is shown that in this case, the Sipos integral is a suitable solution,
although not unique. Properties of the Sipos integral as a new way of
aggregating criteria are shown, with emphasis on the interaction among
criteria.
| arxiv topic:cs.DM |
arxiv_dataset-583804.2021 | Parton fragmentation in the vacuum and in the medium
hep-ph
We present the mini-proceedings of the workshop on ``Parton fragmentation in
the vacuum and in the medium'' held at the European Centre for Theoretical
Studies in Nuclear Physics and Related Areas (ECT*, Trento) in February 2008.
The workshop gathered both theorists and experimentalists to discuss the
current status of investigations of quark and gluon fragmentation into hadrons
at different accelerator facilities (LEP, B-factories, JLab, HERA, RHIC, and
Tevatron) as well as preparations for extension of these studies at the LHC.
The main physics topics covered were: (i) light-quark and gluon fragmentation
in the vacuum including theoretical (global fits analyses and MLLA) and
experimental (data from e+e-, p-p, e-p collisions) aspects, (ii) strange and
heavy-quark fragmentation, (iii) parton fragmentation in cold QCD matter
(nuclear DIS), and (iv) medium-modified fragmentation in hot and dense QCD
matter (high-energy nucleus-nucleus collisions). These mini-proceedings consist
of an introduction and short summaries of the talks presented at the meeting.
| arxiv topic:hep-ph |
arxiv_dataset-584804.2121 | Self-properties of codimension-2 braneworlds
hep-th gr-qc
We consider four-dimensional de Sitter, flat and anti de Sitter branes
embedded in a six-dimensional bulk spacetime whose dynamics is dictated by
Lovelock theory. We find, applying a generalised version of Birkhoff's theorem,
that all possible maximally symmetric braneworld solutions are embedded in
Wick-rotated black hole spacetimes of Lovelock theory. These are warped
solitonic spaces, where the horizons of the black hole geometries correspond to
the possible positions of codimension-2 branes. The horizon temperature is
related via conical singularities to the tension or vacuum energy of the
branes. We classify the braneworld solutions for certain combinations of bulk
parameters, according to their induced curvature, their vacuum energy and their
effective compactness in the extra dimensions. The bulk Lovelock theory gives
an induced gravity term on the brane, which, we argue, generates
four-dimensional gravity up to some distance scale.
As a result, some simple solutions, such as the Lovelock corrected
Schwarzschild black hole in six dimensions, are shown to give rise to
self-accelerating braneworlds. We also find that several other solutions have
self-tuning properties. Finally, we present regular gravitational instantons of
Lovelock gravity and comment on their significance.
| arxiv topic:hep-th gr-qc |
arxiv_dataset-585804.2221 | Understanding Segmental Dynamics in Polymer Electrolytes: A Computer
Study
cond-mat.soft cond-mat.mtrl-sci
We study the segmental dynamics of poly(ethylene oxide) (PEO) from
microscopic simulations in the neat polymer and a polymer electrolyte
(PEO/LiBF$_4$) by analyzing the normal modes. We verify the applicability of
the Rouse theory, specifically for the polymer electrolyte where dynamic
heterogeneities, arising from cation-polymer interactions, alter the mobility
non-uniformly along the chains. We find that the Rouse modes for both the
systems are orthogonal despite the presence of non-exponential relaxation of
the modes and violation of the Gaussian self-similarity of the chains. The
slowdown of the segmental dynamics in the polymer electrolyte is rationalised
by an order of magnitude increase in the friction coefficient for those
monomers which are bound by cations. In general, for the electrolyte the Rouse
predictions for the dynamics of segments (both free and/or bound) agree well
except for very short times.
| arxiv topic:cond-mat.soft cond-mat.mtrl-sci |
arxiv_dataset-586804.2321 | Energy dissipation statistics in the random fuse model
cond-mat.stat-mech cond-mat.mtrl-sci
We study the statistics of the dissipated energy in the two-dimensional
random fuse model for fracture under different imposed strain conditions. By
means of extensive numerical simulations we compare different ways to compute
the dissipated energy. In the case of a infinitely slow driving rate
(quasi-static model) we find that the probability distribution of the released
energy shows two different scaling regions separated by a sharp energy
crossover. At low energies, the probability of having an event of energy $E$
decays as $\sim E^{-1/2}$, which is robust and independent of the energy
quantifier used (or lattice type). At high energies fluctuations dominate the
energy distribution leading to a crossover to a different scaling regime, $\sim
E^{-2.75}$, whenever the released energy is computed over the whole system. On
the contrary, strong finite-size effects are observed if we only consider the
energy dissipated at microfractures. In a different numerical experiment the
quasi-static dynamics condition is relaxed, so that the system is driven at
finite strain load rates, and we find that the energy distribution decays as
$\mathcal{P} (E) \sim E^{-1}$ for all the energy range.
| arxiv topic:cond-mat.stat-mech cond-mat.mtrl-sci |
arxiv_dataset-587804.2421 | A 610-MHz survey of the Lockman Hole with the Giant Metrewave Radio
Telescope - I. Observations, data reduction and source catalogue for the
central 5 square degrees
astro-ph
We present observations of the Lockman Hole with the Giant Metrewave Radio
Telescope (GMRT). Twelve pointings were observed, covering a total area of ~
five square degrees with a resolution of 6 x 5 arcsec, position angle +45deg.
The majority of the pointings have an rms noise of 60 microJy/beam before
correction for the attenuation of the GMRT primary beam. Techniques used for
data reduction and production of a mosaicked image of the region are described,
and the final mosaic is presented, along with a catalogue of 2845 sources
detected above 6 sigma. Radio source counts are calculated at 610 MHz and
combined with existing 1.4-GHz source counts, in order to show that pure
luminosity evolution of the local radio luminosity functions for active
galactic nuclei and starburst galaxies is sufficient to account for the two
source counts simultaneously.
| arxiv topic:astro-ph |
arxiv_dataset-588804.2521 | Scalar order: possible candidate for order parameters in skutterudites
cond-mat.str-el
Phenomenological Landau analysis shows that the properties of ordered phases
in some skutterudites are consistently accounted for by a scalar order
parameter which preserves the cubic symmetry, even in the ordered phase. A
universal value is found for the anisotropy ratio of the transition temperature
in a magnetic field, homogeneous magnetization, and induced staggered
magnetization. The difference in magnetic behavior between PrFe$_4$P$_{12}$ and
PrRu$_4$P$_{12}$ near their phase transitions is explained within a single
framework. For the low-field phase of PrFe$_4$P$_{12}$, the scalar order with
the $\Gamma_{1g}$ symmetry can explain (i) the absence of field induced dipoles
perpendicular to the magnetic field, (ii) isotropic magnetic susceptibility in
the ordered phase, (iii) the field angle dependence of the transition
temperature, and (iv) the splitting pattern of the $^{31}$P nuclear magnetic
resonance (NMR) spectra. It is proposed how the order parameter in
SmRu$_4$P$_{12}$ is identified by NMR analysis of a single crystal.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-589804.2621 | Design and Implementation of a Master of Science in Information and
Computer Sciences - An Inventory and retrospect for the last four years
cs.GL
This Master of Science in Computer and Information Sciences (MICS) is an
international accredited master program that has been initiated in 2004 and
started in September 2005. MICS is a research-oriented academic study of 4
semesters and a continuation of the Bachelor towards the PhD. It is completely
taught in English, supported by lecturers coming from more than ten different
countries. This report compass a description of its underlying architecture,
describes some implementation details and gives a presentation of diverse
experiences and results. As the program has been designed and implemented right
after the creation of the University, the significance of the program is
moreover a self-discovery of the computer science department, which has finally
led to the creation of the today's research institutes and research axes.
| arxiv topic:cs.GL |
arxiv_dataset-590804.2721 | Hilbert Transform: A New Integral Formula
math-ph math.MP
We give a number new examples analytically and numerically to confirm the
Kohler conjecture. It turned out that for a rather large class of nonnegative
functions the equality (A) hold.
| arxiv topic:math-ph math.MP |
arxiv_dataset-591804.2821 | Theoretical interpretation of luminosity and spectral properties of GRB
031203
astro-ph
We show how an emission endowed with an instantaneous thermal spectrum in the
co-moving frame of the expanding fireshell can reproduce the time-integrated
GRB observed non-thermal spectrum. An explicit example in the case of GRB
031203 is presented.
| arxiv topic:astro-ph |
arxiv_dataset-592804.2921 | The nature of Ho magnetism in multiferroic HoMnO3
cond-mat.other cond-mat.mtrl-sci
Using x-ray resonant magnetic scattering and x-ray magnetic circular
dichroism, techniques that are element specific, we have elucidated the role of
Ho3+ in multiferroic HoMnO3. In zero field, Ho3+ orders antiferromagnetically
with moments aligned along the hexagonal c direction below 40 K, and undergoes
a transition to another magnetic structure below 4.5 K. In applied electric
fields of up to 1x10^7 V/m, the magnetic structure of Ho3+ remains unchanged.
| arxiv topic:cond-mat.other cond-mat.mtrl-sci |
arxiv_dataset-593804.3021 | A narrow-linewidth external cavity quantum dot laser for high-resolution
spectroscopy in the near-infrared and yellow spectral ranges
physics.atom-ph
We demonstrate a diode laser system which is suitable for high-resolution
spectroscopy in the 1200 nm and yellow spectral ranges. It is based on a
two-facet quantum dot chip in a Littrow-type external cavity configuration. The
laser is tunable in the range 1125 -1280 nm, with an output power of more than
200 mW and exhibits a free-running linewidth of 200 kHz. Amplitude and
frequency noise were characterized, including the dependence of frequency noise
on the cavity length. Frequency stabilization to a high-finesse reference
cavity is demonstrated reducing the linewidth to about 20 - 30 kHz. Yellow
light (> 3 mW) at 578 nm was generated by frequency doubling in an enhancement
cavity containing a PPLN crystal. The source has potential application for
precision spectroscopy of ultra-cold Yb atoms and molecular hydrogen ions.
| arxiv topic:physics.atom-ph |
arxiv_dataset-594804.3121 | Particle-like solutions to classical noncommutative gauge theory
hep-th
We construct perturbative static solutions to the classical field equations
of noncommutative U(1) gauge theory for the three cases: a) space-time
noncommutativity, b) space-space noncommutativity and c) both a) and b). The
solutions tend to the Coulumb solution at spatial infinity and are valid for
intermediate values of the radial coordinate $r$. They yield a self-charge in a
sphere of radius $r$ centered about the origin which increases with decreasing
$r$ for case a), and decreases with decreasing $r$ for case b). For case a)
this may mean that the exact solution screens an infinite charge at the origin,
while for case b) it is plausible that the charge density is well behaved at
the origin, as happens in Born-Infeld electrodynamics. For both cases a) and b)
the self-energy in the intermediate region grows faster as $r$ tends to the
origin than that of the Coulumb solution. It then appears that the divergence
of the classical self-energy is more severe in the noncommutative theory than
it is in the corresponding commutative theory. We compute the lowest order
effects of these solutions on the hydrogen atom spectrum and use them to put
experimental bounds on the space-time and space-space noncommutative scales. We
find that cases a) and b) have different experimental signatures.
| arxiv topic:hep-th |
arxiv_dataset-595804.3221 | Photon orbital angular momentum in a plasma vortex
physics.plasm-ph physics.space-ph
We study theoretically the exchange of angular momentum between a photon beam
and a plasma vortex, and demonstrate the possible excitation of photon angular
momentum states in a plasma. This can be relevant to laboratory and space
plasma diagnostics; radio astronomy self-calibration; and generating photon
angular momentum beams. A static plasma perturbation with helical structure,
and a rotating plasma vortex are studied in detail and a comparison between
these two cases, and their relevance to the physical nature of photon OAM, is
established.
| arxiv topic:physics.plasm-ph physics.space-ph |
arxiv_dataset-596804.3321 | Exploring an S-matrix for gravitational collapse
hep-th
We analyze further a recently proposed S-matrix description of transplanckian
scattering in the specific case of axisymmetric collisions of extended sources,
where some of the original approximations are not necessary. We confirm the
claim that such an approximate description appears to capture the essential
features of (the quantum counterpart of) classical gravitational collapse. More
specifically, the S-matrix develops singularities whose location in the
sources' parameter space are consistent with (and numerically close to) the
bounds coming from closed-trapped-surface collapse criteria. In the vicinity of
the critical "lines" the phase of the elastic S-matrix exhibits a universal
fractional-power behaviour reminiscent of Choptuik's scaling near critical
collapse.
| arxiv topic:hep-th |
arxiv_dataset-597804.3421 | Coalitions in Cooperative Wireless Networks
cs.GT cs.IT math.IT
Cooperation between rational users in wireless networks is studied using
coalitional game theory. Using the rate achieved by a user as its utility, it
is shown that the stable coalition structure, i.e., set of coalitions from
which users have no incentives to defect, depends on the manner in which the
rate gains are apportioned among the cooperating users. Specifically, the
stability of the grand coalition (GC), i.e., the coalition of all users, is
studied. Transmitter and receiver cooperation in an interference channel (IC)
are studied as illustrative cooperative models to determine the stable
coalitions for both flexible (transferable) and fixed (non-transferable)
apportioning schemes. It is shown that the stable sum-rate optimal coalition
when only receivers cooperate by jointly decoding (transferable) is the GC. The
stability of the GC depends on the detector when receivers cooperate using
linear multiuser detectors (non-transferable). Transmitter cooperation is
studied assuming that all receivers cooperate perfectly and that users outside
a coalition act as jammers. The stability of the GC is studied for both the
case of perfectly cooperating transmitters (transferrable) and under a partial
decode-and-forward strategy (non-transferable). In both cases, the stability is
shown to depend on the channel gains and the transmitter jamming strengths.
| arxiv topic:cs.GT cs.IT math.IT |
arxiv_dataset-598804.3521 | The HI content of the advanced merger NGC 4441
astro-ph
NGC 4441 is a candidate for a merger between a spiral and an elliptical
galaxy (S+E merger), because it shows typical tidal structures such as an
optical tail and two shells. With a far-infrared luminosity of $\sim 5\cdot
10^9 L_{\odot}$ this galaxy belongs to the class of moderate luminosity
mergers, in which the merging process induces (if at all) only a moderate
starburst. The study of the atomic gas content allows us to investigate the
merger history and the impact on the star formation. In particular, it is not
clear from simulations whether an S+E merger leads to a gas concentration in
the nucleus, resulting in a starburst, or whether the gas is spread out and
therefore too diffuse for new star forming regions. We used the Westerbork
Radio Synthesis Telescope to observe the properties of the HI. By using this
interferometer, we are able to study the large-scale HI distribution and
kinematics with high spatial and velocity resolution. We found two HI tails
extending out to more than 40 kpc. In a central disc, the gas shows a fairly
regular rotation pattern indicating that the gas started to settle after the
merger. The total HI mass adds up to $1.5 \cdot 10^9 M_{\odot}$. By comparing
the high resolution HI maps with deep optical images, differences between the
stellar and gaseous tidal features are apparent, which indicates an S+E merger
origin.
| arxiv topic:astro-ph |
arxiv_dataset-599804.3621 | Representation Theory of the Algebra Generated By a Pair of Complex
Structures
math.RT hep-th math.DG
The objective of this paper is to determine the finite dimensional,
indecomposable representations of the algebra that is generated by two complex
structures over the real numbers. Since the generators satisfy relations that
are similar to those of the infinite dihedral group, we give the algebra the
name iD-infinity.
| arxiv topic:math.RT hep-th math.DG |
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