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2023-06-20 | New results on controllability and stability for degenerate Euler-Bernoulli type equations | In this paper we study the controllability and the stability for a degenerate
beam equation in divergence form via the energy method. The equation is clamped
at the left end and controlled by applying a shearing force or a damping at the
right end. | 2306.11851v3 |
2023-07-18 | Nonlinear feedback, double bracket dissipation and port control of Lie-Poisson systems | Methods from controlled Lagrangians, double bracket dissipation and
interconnection and damping assignment -- passivity based control (IDA-PBC) are
used to construct nonlinear feedback controls which (asymptotically) stabilize
previously unstable equilibria of Lie-Poisson Hamiltonian systems. The results
are applied to find an asymptotically stabilizing control for the rotor driven
satellite, and a stabilizing control for Hall magnetohydrodynamic flow. | 2307.09235v1 |
2023-08-01 | Aerodynamics of the square-back Ahmed body under rainfall conditions | We report an experimental investigation about the aerodynamics of a
simplified road vehicle, the so-called square-back Ahmed body, under rainfall
conditions. A particular emphasis is put on the evolution of the body base
pressure distribution with respect to the operating conditions. It is found
that rainfall significantly damps both mean base pressure drag and wake
dynamics in comparison to dry conditions. | 2308.00276v1 |
2023-09-11 | Study of damped oscillating structures from charged and neutral K-meson electromagnetic form factors data | The damped oscillating structures (OS) were recently revealed in the proton
"effective" form factor (FF) data. For the time being they can be neither
confirmed nor disproved by investigations of timelike data on the individual
proton electric and proton magnetic FFs because their precision and reliability
(especially of the proton electric FF data) has not achieved required level for
this aim. On the other hand, conjectures that the OS are direct manifestations
of the quark-gluon structure of the proton indicate that they must not be
specific only for the proton and neutron, but that they should be present also
for other hadrons. This opens a plausibility to find damped oscillatory
structures also from the EM FFs data of such hadrons, for which adequate EM FFs
data exist, by using the same procedure as for the proton. Consequently in this
paper damped oscillatory structures are investigated in the EM FFs data of the
charged and neutral $K$-mesons to be extracted from the corresponding
production cross sections, $\sigma^{bare}_{tot}(e^+e^-\to K^+ K^-)$ measured
from the threshold up to 64 GeV$^2$ and $\sigma^{bare}_{tot}(e^+e^-\to K_s
K_L)$ measured from the threshold up to 9.5 GeV$^2$ of the total c.m. energy
squared. The following results have been obtained. If the charged and neutral
K-meson EM FFs timelike data are described by the three parametric formula by
means of which OS have been revealed from the "effective" proton FF data then
OS appear. If physically well founded Unitary and Analytic model of the K-meson
EM structure is used for a description of the charged K-meson EM FFs data, no
OS are visible. However, in the case of the neutral K-meson EM FF data one
cannot make a definite decision. The overall results indicate that OS obtained
from the "effective" proton FF data are likely an artefact of the three
parametric formula which does not describe these data well. | 2309.05354v1 |
2023-10-31 | Variational principle for a damped, quadratically interacting particle chain with nonconservative forcing | A method for designing variational principles for the dynamics of a possibly
dissipative and non-conservatively forced chain of particles is demonstrated.
Some qualitative features of the formulation are discussed. | 2311.00106v2 |
2024-01-30 | Linear stability analysis of the Couette flow for the 2D Euler-Poisson system | This paper is concerned with the linear stability analysis for the Couette
flow of the Euler-Poisson system for both ionic fluid and electronic fluid in
the domain $\bb{T}\times\bb{R}$. We establish the upper and lower bounds of the
linearized solutions of the Euler-Poisson system near Couette flow. In
particular, the inviscid damping for the solenoidal component of the velocity
is obtained. | 2401.17102v1 |
2024-03-21 | Non-resonant invariant foliations of quasi-periodically forced systems | We show the existence and uniqueness of invariant foliations about invariant
tori in analytic discrete-time dynamical systems. The parametrisation method is
used prove the result. Our theory is a foundational block of data-driven model
order reduction, that can only be carried out using invariant foliations. The
theory is illustrated by two mechanical examples, where instantaneous
frequencies and damping ratios are calculated about the invariant tori. | 2403.14771v1 |
2007-03-01 | Stellar Kinematics in the Complicated Inner Spheroid of M31: Discovery of Substructure Along the Southeastern Minor Axis and its Relationship to the Giant Southern Stream | We present the discovery of a kinematically-cold stellar population along the
SE minor axis of the Andromeda galaxy (M31) that is likely the forward
continuation of M31's giant southern stream. This discovery was made in the
course of an on-going spectroscopic survey of red giant branch (RGB) stars in
M31 using the DEIMOS instrument on the Keck II 10-m telescope. Stellar
kinematics are investigated in eight fields located 9-30 kpc from M31's center
(in projection). A likelihood method based on photometric and spectroscopic
diagnostics is used to isolate confirmed M31 RGB stars from foreground Milky
Way dwarf stars: for the first time, this is done without using radial velocity
as a selection criterion, allowing an unbiased study of M31's stellar
kinematics. The radial velocity distribution of the 1013 M31 RGB stars shows
evidence for the presence of two components. The broad (hot) component has a
velocity dispersion of 129 km/s and presumably represents M31's virialized
spheroid. A significant fraction (19%) of the population is in a narrow (cold)
component centered near M31's systemic velocity with a velocity dispersion that
decreases with increasing radial distance, from 55.5 km/s at R_proj=12 kpc to
10.6 km/s at R_proj=18 kpc. The spatial and velocity distribution of the cold
component matches that of the "Southeast shelf" predicted by the Fardal et al.
(2007) orbital model of the progenitor of the giant southern stream. The
metallicity distribution of the cold component matches that of the giant
southern stream, but is about 0.2 dex more metal rich on average than that of
the hot spheroidal component. We discuss the implications of our discovery on
the interpretation of the intermediate-age spheroid population found in this
region in recent ultra-deep HST imaging studies. | 0703029v3 |
2017-02-26 | Limits on the ultra-bright Fast Radio Burst population from the CHIME Pathfinder | We present results from a new incoherent-beam Fast Radio Burst (FRB) search
on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder. Its
large instantaneous field of view (FoV) and relative thermal insensitivity
allow us to probe the ultra-bright tail of the FRB distribution, and to test a
recent claim that this distribution's slope, $\alpha\equiv-\frac{\partial \log
N}{\partial \log S}$, is quite small. A 256-input incoherent beamformer was
deployed on the CHIME Pathfinder for this purpose. If the FRB distribution were
described by a single power-law with $\alpha=0.7$, we would expect an FRB
detection every few days, making this the fastest survey on sky at present. We
collected 1268 hours of data, amounting to one of the largest exposures of any
FRB survey, with over 2.4\,$\times$\,10$^5$\,deg$^2$\,hrs. Having seen no
bursts, we have constrained the rate of extremely bright events to
$<\!13$\,sky$^{-1}$\,day$^{-1}$ above $\sim$\,220$\sqrt{(\tau/\rm ms)}$ Jy\,ms
for $\tau$ between 1.3 and 100\,ms, at 400--800\,MHz. The non-detection also
allows us to rule out $\alpha\lesssim0.9$ with 95$\%$ confidence, after
marginalizing over uncertainties in the GBT rate at 700--900\,MHz, though we
show that for a cosmological population and a large dynamic range in flux
density, $\alpha$ is brightness-dependent. Since FRBs now extend to large
enough distances that non-Euclidean effects are significant, there is still
expected to be a dearth of faint events and relative excess of bright events.
Nevertheless we have constrained the allowed number of ultra-intense FRBs.
While this does not have significant implications for deeper, large-FoV surveys
like full CHIME and APERTIF, it does have important consequences for other
wide-field, small dish experiments. | 1702.08040v2 |
2019-04-01 | Astro2020 Science White Paper: Construction of an L* Galaxy: the Transformative Power of Wide Fields for Revealing the Past, Present and Future of the Great Andromeda System | The Great Andromeda Galaxy (M31) is the nexus of the near-far galaxy
evolution connection and a principal data point for near-field cosmology. Due
to its proximity (780 kpc), M31 can be resolved into individual stars like the
Milky Way (MW). Unlike the MW, we have the advantage of a global view of M31,
enabling M31 to be observed with techniques that also apply to more distant
galaxies. Moreover, recent evidence suggests that M31 may have survived a major
merger within the last several Gyr, shaping the morphology of its stellar halo
and triggering a starburst, while leaving the stellar disk largely intact. The
MW and M31 thus provide complementary opportunities for in-depth studies of the
disks, halos, and satellites of L* galaxies.
Our understanding of the M31 system will be transformed in the 2020s if they
include wide field facilities for both photometry (HST-like sensitivity and
resolution) and spectroscopy (10-m class telescope, >1 sq. deg. field, highly
multiplexed, R~ 3000 to 6000). We focus here on the power of these facilities
to constrain the past, present, and future merger history of M31, via
chemo-dynamical analyses and star formation histories of phase-mixed stars
accreted at early times, as well as stars in surviving tidal debris features,
M31's extended disk, and intact satellite galaxies that will eventually be
tidally incorporated into the halo. This will yield an unprecedented view of
the hierarchical formation of the M31 system and the subhalos that built it
into the L* galaxy we observe today. | 1904.01074v1 |
2021-09-28 | Diving Beneath the Sea of Stellar Activity: Chromatic Radial Velocities of the Young AU Mic Planetary System | We present updated radial-velocity (RV) analyses of the AU Mic system. AU Mic
is a young (22 Myr) early M dwarf known to host two transiting planets -
$P_{b}\sim8.46$ days, $R_{b}=4.38_{-0.18}^{+0.18}\ R_{\oplus}$,
$P_{c}\sim18.86$ days, $R_{c}=3.51_{-0.16}^{+0.16}\ R_{\oplus}$. With visible
RVs from CARMENES-VIS, CHIRON, HARPS, HIRES, {\sc
{\textsc{Minerva}}}-Australis, and TRES, as well as near-infrared (NIR) RVs
from CARMENES-NIR, CSHELL, IRD, iSHELL, NIRSPEC, and SPIRou, we provide a
$5\sigma$ upper limit to the mass of AU Mic c of $M_{c}\leq20.13\ M_{\oplus}$
and present a refined mass of AU Mic b of $M_{b}=20.12_{-1.57}^{+1.72}\
M_{\oplus}$. Used in our analyses is a new RV modeling toolkit to exploit the
wavelength dependence of stellar activity present in our RVs via
wavelength-dependent Gaussian processes. By obtaining near-simultaneous visible
and near-infrared RVs, we also compute the temporal evolution of RV-``color''
and introduce a regressional method to aid in isolating Keplerian from stellar
activity signals when modeling RVs in future works. Using a multi-wavelength
Gaussian process model, we demonstrate the ability to recover injected planets
at $5\sigma$ significance with semi-amplitudes down to $\approx$
10\,m\,s$^{-1}$ with a known ephemeris, more than an order of magnitude below
the stellar activity amplitude. However, we find that the accuracy of the
recovered semi-amplitudes is $\sim$50\% for such signals with our model. | 2109.13996v1 |
2022-03-04 | Scaling K2. V. Statistical Validation of 60 New Exoplanets From K2 Campaigns 2-18 | The NASA K2 mission, salvaged from the hardware failures of the Kepler
telescope, has continued Kepler's planet-hunting success. It has revealed
nearly 500 transiting planets around the ecliptic plane, many of which are the
subject of further study, and over 1000 additional candidates. Here we present
the results of an ongoing project to follow-up and statistically validate new
K2 planets, in particular to identify promising new targets for further
characterization. By analyzing the reconnaissance spectra, high-resolution
imaging, centroid variations, and statistical likelihood of the signals of 91
candidates, we validate 60 new planets in 46 systems. These include: a number
of planets amenable to transmission spectroscopy (K2-384 f, K2-387 b, K2-390 b,
K2-403 b, and K2-398 c), emission spectroscopy (K2-371 b, K2-370 b, and K2-399
b), and both (K2-405 b and K2-406 b); several systems with planets in or close
to mean motion resonances (K2-381, K2-398) including a compact, TRAPPIST-1-like
system of five small planets orbiting a mid-M dwarf (K2-384); an ultra-short
period sub-Saturn in the hot Saturn desert (K2-399 b); and a super-Earth
orbiting a moderately bright (V=11.93), metal-poor ([Fe/H]=-0.579+/-0.080) host
star (K2-408 b). In total we validate planets around 4 F stars, 26 G stars, 13
K stars, and 3 M dwarfs. In addition, we provide a list of 37 vetted planet
candidates that should be prioritized for future follow-up observation in order
to be confirmed or validated. | 2203.02087v2 |
1999-08-09 | On the possibility of variation of the fundamental constants of physics in the static universe | A variation of fundamental constants of physics is proposed in a frame of
static universe. It is shown when the velocity of light increases (decreases)
the Planck's constant increases (decreases) and mass of bodies decreases
(increases). This variation of constants leads to the variation of dimensions
of bodies and the energy levels of atoms, but a fine structure constant remains
unaltered. | 9908082v1 |
2002-06-17 | Cosmological constant and curved 5D geometry | We study the value of cosmological constant in de Sitter brane embedded in
five dimensions with positive, vanishing and negative bulk cosmological
constant. In the case of negative bulk cosmological constant, we show that not
zero but tiny four-dimensional cosmological constant can be realized by tiny
deviation from bulk curvature of the Randall-Sundrum model. | 0206153v1 |
2003-06-30 | Convex Bodies of Constant Width and Constant Brightness | In 1926 S. Nakajima (= A. Matsumura) showed that any convex body in $\R^3$
with constant width, constant brightness, and boundary of class $C^2$ is a
ball. We show that the regularity assumption on the boundary is unnecessary, so
that balls are the only convex bodies of constant width and brightness. | 0306437v1 |
2010-07-27 | The GL-l.u.st.\ constant and asymmetry of the Kalton-Peck twisted sum in finite dimensions | We prove that the Kalton-Peck twisted sum $Z_2^n$ of $n$-dimensional Hilbert
spaces has GL-l.u.st.\ constant of order $\log n$ and bounded GL constant. This
is the first concrete example which shows different explicit orders of growth
in the GL and GL-l.u.st.\ constants. We discuss also the asymmetry constants of
$Z_2^n$. | 1007.4692v1 |
2019-04-02 | On geometric constants for (small) Morrey spaces | In this article, we compute Von Neumann-Jordan constant, James constant, and
Dunkl-Williams constant for small Morrey spaces. Our approach can also be seen
as an alternative way in computing the three constants for the (classical)
Morrey spaces. In addition, we prove constructively that Morrey spaces are not
uniformly non-octahedral. | 1904.01712v3 |
2021-08-11 | Gravity can be caused by the difference of Coulomb's constants | Coulomb's constant is defined as a value for attraction and repulsion.
However, it is strange that only one value can be applied for both attraction
and repulsion. A very little difference between coulomb's constant for
attraction and coulomb's constant for repulsion can be the source of gravity.
The author verified if that theory is correct by calculating with slightly
bigger coulomb's constant for attraction. | 2108.05114v1 |
1994-06-27 | Reverberation mapping of active galactic nuclei : The SOLA method for time-series inversion | In this paper a new method is presented to find the transfer function of the
broad-line region in active galactic nuclei. The subtractive optimally
localized averages (SOLA) method is a modified version of the Backus-Gilbert
method and is presented as an alternative to the more often used
maximum-entropy method. The SOLA method has been developed for use in
helioseismology. It has been applied to the solar oscillation frequency
splitting data currently available to deduce the internal rotation rate of the
sun. The original SOLA method is reformulated in the present paper to cope with
the slightly different problem of inverting time series. We use simulations to
test the viability of the method and apply the SOLA method to the real data of
the Seyfert-1 galaxy NGC 5548. We investigate the effects of measurement errors
and how the resolution of the TF critically depends upon both the sampling rate
and the photometric accuracy of the data. A uuencoded compressed postscript
file of the paper which includes the figures is available by anonymous ftp at
ftp://solaris.astro.uu.se/pub/articles/atmos/frank/PijWan.uue | 9406070v1 |
1997-06-20 | Rejection of the Binary Broad-Line Region Interpretation of Double-Peaked Emission Lines in Three Active Galactic Nuclei | It has been suggested that the peculiar double-peaked Balmer lines of certain
broad-line radio galaxies come from individual broad-line regions associated
with the black holes of a supermassive binary. We continue to search for
evidence of the radial velocity variations characteristic of a double-lined
spectroscopic binary that are required in such a model. After spectroscopic
monitoring of three suitable candidates (Arp 102B, 3C 390.3, and 3C 332)
spanning two decades, we find no such long-term systematic changes in radial
velocity. A trend noticed by Gaskell in one of the Balmer-line peaks of 3C
390.3 before 1988 did not continue after that year, invalidating his inferred
orbital period and mass. Instead, we find lower limits on the plausible orbital
periods that would require the assumed supermassive binaries in all three
objects to have total masses in excess of 10^10 solar masses. In the case of 3C
390.3 the total binary mass must exceed 10^11 solar masses to satisfy
additional observational constraints on the inclination angle. Such large
binary black hole masses are difficult to reconcile with other observations and
with theory. In addition, there are peculiar properties of the line profiles
and flux ratios in these objects that are not explained by ordinary broad-line
region cloud models. We therefore doubt that the double-peaked line profiles of
the three objects arise in a pair of broad-line regions. Rather, they are much
more likely to be intimately associated with a single black hole. | 9706222v2 |
1999-08-13 | Infrared Spectroscopy of the High Redshift Radio Galaxy MRC~2025-218 and a Neighboring Extremely Red Galaxy | This paper presents infrared spectra taken with the newly commissioned
NIRSPEC spectrograph on the Keck Telescope of the High Redshift Radio Galaxy
MRC 2025-218 (z=2.630) and an extremely red galaxy (R-K > 6 mag) 9'' away.
These observations represent the deepest infrared spectra of a radio galaxy to
date and have allowed for the detection of Hbeta, OIII (4959/5007), OI (6300),
Halpha, NII (6548/6583) and SII (6716/6713). The Halpha emission is very broad
(FWHM~6000 km/s) and strongly supports AGN unification models linking radio
galaxies and quasars. The line ratios are most consistent with a partially
obscured nuclear region and very high excitation. The OIII (5007) line is
extended several arcseconds and shows high velocity clouds in the extended
emission. The nucleus also appears spectrally double and we argue that the
radio galaxy is undergoing a violent merger process. The red galaxy, by
comparison, is very featureless even though we have a good continuum detection
in the H and K bands. We suggest that this object is a foreground galaxy,
probably at a redshift less than 1.5. | 9908153v1 |
2000-01-11 | 2 micron Spectroscopy within 0.3 arcseconds of SgrA* | We present moderate (R~$\approx$~2,700) and high resolution
(R~$\approx$~22,000) 2.0$-$2.4 \micron\ spectroscopy of the central 0.1 square
arcseconds of the Galaxy obtained with NIRSPEC, the facility near-infrared
spectrometer for the Keck II telescope. The composite spectra do not have any
features attributable to the brightest stars in the central cluster, i.e.\
after background subtraction, W$_{\rm ^{12}CO(2-0)}$~$<$~2~\AA. This stringent
limit leads us to conclude that the majority, if not all, of the stars are
hotter than typical red giants. Coupled with previously reported photometry, we
conclude that the sources are likely OB main sequence stars. In addition, the
continuum slope in the composite spectrum is bluer than that of a red giant and
is similar to that of the nearby hot star, IRS16NW. It is unlikely that they
are late-type giants stripped of their outer envelopes because such sources
would be much fainter than those observed. Given their inferred youth
($\tau_{\rm age}$~$<$~20~\Myr), we suggest the possibility that the stars have
formed within 0.1 pc of the supermassive black hole. We find a newly-identified
broad-line component (V$_{\rm FWHM}$ $\approx$ 1,000 \kms) to the 2.2178
\micron\ [\ion{Fe}{3}] line located within a few arcseconds of Sgr~A$^*$. A
similar component is not seen in the Br-$\gamma$ emission. | 0001171v1 |
2000-02-17 | Discovery of an Obscured Broad Line Region in the High Redshift Radio Galaxy MRC 2025-218 | This paper presents infrared spectra taken with the newly commissioned
NIRSPEC spectrograph on the Keck II Telescope of the High Redshift Radio Galaxy
MRC 2025-218 (z=2.63) These observations represent the deepest infrared spectra
of a radio galaxy to date and have allowed for the detection of Hbeta, [OIII]
(4959/5007), [OI] (6300), Halpha, [NII] (6548/6583) and [SII] (6716/6713). The
Halpha emission is very broad (FWHM = 9300 km/s) and luminous (2.6x10^44
ergs/s) and it is very comparable to the line widths and strengths of radio
loud quasars at the same redshift. This strongly supports AGN unification
models linking radio galaxies and quasars, although we discuss some of the
outstanding differences. The [OIII] (5007) line is extremely strong and has
extended emission with large relative velocities to the nucleus. We also derive
that if the extended emission is due to star formation, each knot has a star
formation rate comparable to a Lyman Break Galaxy at the same redshift. | 0002335v1 |
2000-02-26 | Hot Stars and Cool Clouds: The Photodissociation Region M16 | We present high-resolution spectroscopy and images of a photodissociation
region (PDR) in M16 obtained during commissioning of NIRSPEC on the Keck II
telescope. PDRs play a significant role in regulating star formation, and M16
offers the opportunity to examine the physical processes of a PDR in detail. We
simultaneously observe both the molecular and ionized phases of the PDR and
resolve the spatial and kinematic differences between them. The most prominent
regions of the PDR are viewed edge-on. Fluorescent emission from nearby stars
is the primary excitation source, although collisions also preferentially
populate the lowest vibrational levels of H2. Variations in density-sensitive
emission line ratios demonstrate that the molecular cloud is clumpy, with an
average density n = 3x10^5 cm^(-3). We measure the kinetic temperature of the
molecular region directly and find T_H2 = 930 K. The observed density,
temperature, and UV flux imply a photoelectric heating efficiency of 4%. In the
ionized region, n_i=5x10^3 cm^(-3) and T_HII = 9500 K. In the brightest regions
of the PDR, the recombination line widths include a non-thermal component,
which we attribute to viewing geometry. | 0002491v1 |
2000-02-28 | The Rest-Frame Optical Spectrum of MS 1512-cB58 | Moderate resolution, near-IR spectroscopy of MS1512-cB58 is presented,
obtained during commissioning of the the Near IR Spectrometer (NIRSPEC) on the
Keck II telescope. The strong lensing of this z=2.72 galaxy by the foreground
cluster MS1512+36 makes it the best candidate for detailed study of the
rest-frame optical properties of Lyman Break Galaxies.
A redshift of z=2.7290+/-0.0007 is inferred from the emission lines, in
contrast to the z=2.7233 calculated from UV observations of interstellar
absorption lines. Using the Balmer line ratios, we find an extinction of
E(B-V)=0.27. Using the line strengths, we infer an SFR=620+/-18 Msun/yr
(H_0=75, q_0=0.1, Lambda =0), a factor of 2 higher than that measured from
narrow-band imaging observations of the galaxy, but a factor of almost 4 lower
than the SFR inferred from the UV continuum luminosity. The width of the Balmer
lines yields a mass of M_vir=1.2x10^10 Msun. We find that the oxygen abundance
is 1/3 solar, in good agreement with other estimates of the metallicity.
However, we infer a high nitrogen abundance, which may argue for the presence
of an older stellar population. | 0002508v1 |
2000-03-06 | The Sunyaev-Zel'dovich Effect in Abell 370 | We present interferometric measurements of the Sunyaev-Zel'dovich (SZ) effect
towards the galaxy cluster Abell 370. These measurements, which directly probe
the pressure of the cluster's gas, show the gas distribution to be strongly
aspherical, as do the x-ray and gravitational lensing observations. We
calculate the cluster's gas mass fraction in two ways. We first compare the gas
mass derived from the SZ measurements to the lensing-derived gravitational mass
near the critical lensing radius. We also calculate the gas mass fraction from
the SZ data by deprojecting the three-dimensional gas density distribution and
deriving the total mass under the assumption that the gas is in hydrostatic
equilibrium (HSE). We test the assumptions in the HSE method by comparing the
total cluster mass implied by the two methods and find that they agree within
the errors of the measurement. We discuss the possible systematic errors in the
gas mass fraction measurement and the constraints it places on the matter
density parameter, OmegaM. | 0003085v1 |
2000-12-04 | Galaxy Cluster Gas Mass Fractions from Sunyaev-Zel'dovich Effect Measurements: Constraints on Omega_M | Using sensitive centimeter-wave receivers mounted on the Owens Valley Radio
Observatory and Berkeley-Illinois-Maryland-Association millimeter arrays, we
have obtained interferometric measurements of the Sunyaev-Zel'dovich (SZ)
effect toward massive galaxy clusters. We use the SZ data to determine the
pressure distribution of the cluster gas and, in combination with published
X-ray temperatures, to infer the gas mass and total gravitational mass of 18
clusters. The gas mass fraction, f_g, is calculated for each cluster, and is
extrapolated to the fiducial radius r_{500} using the results of numerical
simulations. The mean f_g within r_{500} is 0.081+0.009 -0.011/(h_{100}
(statistical uncertainty at 68% confidence level, assuming OmegaM=0.3,
OmegaL=0.7). We discuss possible sources of systematic errors in the mean f_g
measurement. We derive an upper limit for OmegaM from this sample under the
assumption that the mass composition of clusters within r_{500} reflects the
universal mass composition: Omega_M h < Omega_B/f_g. The gas mass fractions
depend on cosmology through the angular diameter distance and the r_{500}
correction factors.
For a flat universe (OmegaL = 1 - OmegaM) and h=0.7, we find the measured gas
mass fractions are consistent with Omegam less than 0.40, at 68% confidence.
Including estimates of the baryons contained in galaxies and the baryons which
failed to become bound during the cluster formation process, we find OmegaM
\~0.25. | 0012067v1 |
2001-01-02 | Science Prospects for SPI | After the recent beautiful results on gamma-ray lines obtained with CGRO, the
INTEGRAL mission with the imaging-spectrometer SPI will set the next milestone,
combining improved sensitivity and angular resolution with a considerable
increase in spectral resolution. SPI is expected to provide significant new
information on galactic nucleosynthesis processes and star formation activity,
as traced by the distributions of annihilation radiation and radioactive
isotopes such as 26Al and 60Fe. The unprecedented spectral resolution will
allow the study of dynamic processes in stellar mass ejections and will provide
access to kinematic distance estimates for gamma-ray line sources. The study of
supernovae and their remnants will be prime objectives for SPI observations.
Nearby type Ia SN, within 15 Mpc or so, are in reach of the instrument and a
few such events are expected during the lifetime of INTEGRAL. Young galactic
supernova remnants, possibly hidden by interstellar dust, may be unveiled by
their characteristic gamma-ray line signature from the radioactive decay of
44Ti, as has been demonstrated by COMPTEL for Cas A and possibly RX
J0852.0-4622. Classical novae are also among the SPI targets, which may observe
the gamma-ray lines from radioactive 7Be and 22Na. Such observations can
constrain the physics of the nova explosions and will allow to evaluate their
role as nucleosynthesis sites. The interaction of cosmic rays with the dense
matter in molecular clouds may be another source of gamma-ray lines that is
potentially accessible to SPI. Finally after the SIGMA results on Nova Muscae
and 1E1740.7-2942, and a possible 2.223 MeV line detection by COMPTEL, the
search for lines from X novae is another way to participate in the
understanding of the physical conditions in these close binary systems. | 0101018v1 |
2002-08-07 | Massive Stars in the Arches Cluster | We present and use new spectra and narrow-band images, along with previously
published broad-band images, of stars in the Arches cluster to extract
photometry, astrometry, equivalent width, and velocity information. The data
are interpreted with a wind/atmosphere code to determine stellar temperatures,
luminosities, mass-loss rates, and abundances. We have doubled the number of
known emission-line stars, and we have also made the first spectroscopic
identification of the main sequence for any population in the Galactic Center.
We conclude that the most massive stars are bona-fide Wolf-Rayet (WR) stars and
are some of the most massive stars known, having M_{initial} > 100 Msun, and
prodigious winds, Mdot > 10^{-5} Msun yr^{-1}, that are enriched with helium
and nitrogen; with these identifications, the Arches cluster contains about 5%
of all known WR stars in the Galaxy. We find an upper limit to the velocity
dispersion of 22 kms^{-1}, implying an upper limit to the cluster mass of
7(10^4) Msun within a radius of 0.23 pc; we also estimate the bulk heliocentric
velocity of the cluster to be v_{cluster,odot} approximately +95 kms^{-1}. | 0208145v1 |
2003-02-05 | Cluster Sunyaev-Zeldovich Effect Scaling Relations | X-ray observations of an "entropy floor" in nearby groups and clusters of
galaxies offer evidence that important non-gravitational processes, such as
radiative cooling and/or "preheating", have strongly influenced the evolution
of the intracluster medium (ICM). We examine how the presence of an entropy
floor modifies the thermal Sunyaev-Zeldovich (SZ) effect. A detailed analysis
of scaling relations between X-ray and SZ effect observables and also between
the two primary SZ effect observables is presented. We find that relationships
between the central Compton parameter and the temperature or mass of a cluster
are extremely sensitive to the presence of an entropy floor. The same is true
for correlations between the integrated Compton parameter and the X-ray
luminosity or the central Compton parameter. In fact, if the entropy floor is
as high as inferred in recent analyses of X-ray data, a comparison of these
correlations with both current and future SZ effect observations should show a
clear signature of this excess entropy. Moreover, because the SZ effect is
redshift-independent, the relations can potentially be used to track the
evolution of the cluster gas and possibly discriminate between the possible
sources of the excess entropy. To facilitate comparisons with observations, we
provide analytic fits to these scaling relations. | 0302087v1 |
2003-03-20 | The SZ Effect Signature of Excess Entropy in Distant, Massive Clusters | Studies of cluster X-ray scaling relations have led to suggestions that
non-gravitational processes, e.g., radiative cooling and/or "preheating", have
significantly modified the entropy of the intracluster medium (ICM). For the
first time, we test this hypothesis through a comparison of predicted thermal
Sunyaev-Zeldovich (SZ) effect scaling relations with available data from the
literature. One of the relations that we explore, in principle, depends solely
on SZ effect observations, thus offering an X-ray independent probe of the ICM.
A detailed comparison of the theoretical relations with the largest compilation
of high redshift SZ effect data to date indicates that the presence of an
entropy floor is favored by the data. Furthermore, the inferred level of that
floor, 300 keV cm^2 or higher, is comparable to that found in studies of X-ray
scaling relations of nearby massive clusters. Thus, we find no evidence for
significant evolution of the entropy floor out to z = 0.7. We further
demonstrate that the high quality data to be obtained from the upcoming
Sunyaev-Zeldovich Array (SZA) and the (soon-to-be) upgraded Owens Valley Radio
Observatory (OVRO) array will open powerful new windows into the properties of
the ICM. Specifically, the new measurements will allow for accurate
measurements of the ICM entropy for even the most distant galaxy clusters. | 0303451v2 |
2005-08-01 | Transit Photometry of the Core-Dominated Planet HD 149026b | We report g, V, and r photometric time series of HD 149026 spanning predicted
times of transit of the Saturn-mass planetary companion, which was recently
discovered by Sato and collaborators. We present a joint analysis of our
observations and the previously reported photometry and radial velocities of
the central star. We refine the estimate of the transit ephemeris to Tc [HJD] =
2453527.87455^{+0.00085}_{-0.00091} + N * 2.87598^{+0.00012}_{-0.00017}.
Assuming that the star has a radius of 1.45 +/- 0.10 R_Sun and a mass of 1.30
+/- 0.10 M_Sun, we estimate the planet radius to be 0.726 +/- 0.064 R_Jup,
which implies a mean density of 1.07^{+0.42}_{-0.30} g/cm^3. This density is
significantly greater than that predicted for models which include the effects
of stellar insolation and for which the planet has only a small core of solid
material. Thus we confirm that this planet likely contains a large core, and
that the ratio of core mass to total planet mass is more akin to that of Uranus
and Neptune than that of either Jupiter or Saturn. | 0508051v1 |
2005-10-28 | Photoionized HBeta Emission in NGC 5548: It Breathes! | Emission-line regions in active galactic nuclei and other photoionized
nebulae should become larger in size when the ionizing luminosity increases.
This 'breathing' effect is observed for the Hbeta emission in NGC 5548 by using
Hbeta and optical continuum lightcurves from the 13-year 1989-2001 AGN Watch
monitoring campaign. To model the breathing, we use two methods to fit the
observed lightcurves in detail: (i) parameterized models and, (ii) the MEMECHO
reverberation mapping code. Our models assume that optical continuum variations
track the ionizing radiation, and that the Hbeta variations respond with time
delays due to light travel time. By fitting the data using a delay map that is
allowed to change with continuum flux, we find that the strength of the Hbeta
response decreases and the time delay increases with ionizing luminosity. The
parameterized breathing models allow the time delay and the Hbeta flux to
depend on the continuum flux so that, the time delay is proportional to the
continuum flux to the power beta, and the Hbeta flux is proportional to the
continuum flux to the power alpha. Our fits give 0.1 < beta < 0.46 and 0.57 <
alpha < 0.66. alpha is consistent with previous work by Gilbert and Peterson
(2003) and Goad, Korista and Knigge (2004). Although we find beta to be flatter
than previously determined by Peterson et al. (2002) using cross-correlation
methods, it is closer to the predicted values from recent theoretical work by
Korista and Goad (2004). | 0510800v1 |
2006-07-25 | The Transit Light Curve (TLC) Project. I. Four Consecutive Transits of the Exoplanet XO-1b | We present RIz photometry of four consecutive transits of the newly
discovered exoplanet XO-1b. We improve upon the estimates of the transit
parameters, finding the planetary radius to be R_P = 1.184 +0.028/-0.018
R_Jupiter and the stellar radius to be R_S = 0.928 +0.018/-0.013 R_Sun,
assuming a stellar mass of M_S = 1.00 +/- 0.03 M_Sun. The uncertainties in the
planetary and stellar radii are dominated by the uncertainty in the stellar
mass. These uncertainties increase by a factor of 2-3 if a more conservative
uncertainty of 0.10 M_Sun is assumed for the stellar mass. Our estimate of the
planetary radius is smaller than that reported by McCullough et al. (2006) and
yields a mean density that is comparable to that of TrES-1 and HD 189733b. The
timings of the transits have an accuracy ranging from 0.2 to 2.5 minutes, and
are marginally consistent with a uniform period. | 0607571v1 |
2006-09-12 | TrES-2: The First Transiting Planet in the Kepler Field | We announce the discovery of the second transiting hot Jupiter discovered by
the Trans-atlantic Exoplanet Survey. The planet, which we dub TrES-2, orbits
the nearby star GSC 03549-02811 every 2.47063 days. From high-resolution
spectra, we determine that the star has T_eff = 5960 +/- 100 K and log(g) = 4.4
+/- 0.2, implying a spectral type of G0V and a mass of 1.08 +0.11/-0.05 M_sun.
High-precision radial-velocity measurements confirm a sinusoidal variation with
the period and phase predicted by the photometry, and rule out the presence of
line-bisector variations that would indicate that the spectroscopic orbit is
spurious. We estimate a planetary mass of 1.28 +0.09/-0.04 M_Jup. We model B,
r, R, and I photometric timeseries of the 1.4%-deep transits and find a
planetary radius of 1.24 +0.09/-0.06 R_Jup. This planet lies within the field
of view of the NASA Kepler mission, ensuring that hundreds of upcoming transits
will be monitored with exquisite precision and permitting a host of
unprecedented investigations. | 0609335v1 |
2006-10-19 | Precise Radius Estimates for the Exoplanets WASP-1b and WASP-2b | We present precise z-band photometric time series spanning times of transit
of the two exoplanets recently discovered by the SuperWASP collaboration. We
find planetary radii of 1.44 +/- 0.08 R_J and 1.04 +/- 0.06 R_J for WASP-1b and
WASP-2b, respectively. These error estimates include both random errors in the
photometry and also the uncertainty in the stellar masses. Our results are 5
times more precise than the values derived from the discovery data alone. Our
measurement of the radius of WASP-2b agrees with previously published models of
hot Jupiters that include both a 20-M_Earth core of solid material and the
effects of stellar insolation. In contrast, we find that the models cannot
account for the large size of WASP-1b, even if the planet has no core. Thus, we
add WASP-1b to the growing list of hot Jupiters that are larger than expected.
This suggests that ``inflated'' hot Jupiters are more common than previously
thought, and that any purported explanations involving highly unusual
circumstances are disfavored. | 0610589v1 |
2007-02-16 | The Extended Star Formation History of the Andromeda Spheroid at Twenty One Kiloparsecs on the Minor Axis | Using the HST ACS, we have obtained deep optical images of a southeast
minor-axis field in the Andromeda Galaxy, 21 kpc from the nucleus. In both star
counts and metallicity, this field represents a transition zone between the
metal-rich, highly-disturbed inner spheroid that dominates within 15 kpc and
the metal-poor, diffuse population that dominates beyond 30 kpc. The
color-magnitude diagram reaches well below the oldest main-sequence turnoff in
the population, allowing a reconstruction of the star formation history in this
field. Compared to the spheroid population at 11 kpc, the population at 21 kpc
is ~1.3 Gyr older and ~0.2 dex more metal-poor, on average. However, like the
population at 11 kpc, the population at 21 kpc exhibits an extended star
formation history; one third of the stars are younger than 10 Gyr, although
only a few percent are younger than 8 Gyr. The relatively wide range of
metallicity and age is inconsistent with a single, rapid star-formation
episode, and instead suggests that the spheroid even at 21 kpc is dominated by
the debris of earlier merging events likely occurring more than 8 Gyr ago. | 0702448v1 |
2007-02-23 | Discovery of Andromeda XIV: A Dwarf Spheroidal Dynamical Rogue in the Local Group? | In the course of our survey of the outer halo of the Andromeda Galaxy we have
discovered a remote, possible satellite of that system at a projected 162 kpc
(11.7 degrees) radius. The fairly elongated (0.31 +/- 0.09 ellipticity) dwarf
can be fit with a King profile of 1.07 kpc (d/784 kpc) limiting radius, where
the satellite distance, d, is estimated at ~630-850 kpc from the tip of the red
giant branch. The newfound galaxy, ``Andromeda XIV'' (``AndXIV''),
distinguishes itself from other Local Group galaxies by its extreme dynamics:
Keck/DEIMOS spectroscopy reveals it to have a large heliocentric radial
velocity (-481 km/s), or -206 km/s velocity relative to M31. Even at its
projected radius AndXIV already is at the M31 escape velocity based on the
latest M31 mass models. If AndXIV is bound to M31, then recent models with
reduced M31 virial masses need revision upward. If not bound to M31, then
AndXIV is just now falling into the Local Group for the first time and
represents a dwarf galaxy that formed and spent almost its entire life in
isolation. | 0702635v2 |
1998-05-27 | Survival Analysis, Master Equation, Efficient Simulation of Path-Related Quantities, and Hidden State Concept of Transitions | This paper presents and derives the interrelations between survival analysis
and master equation. Survival analysis deals with modeling the transitions
between succeeding states of a system in terms of hazard rates. Questions
related with this are the timing and sequencing of the states of a time series.
The frequency and characteristics of time series can be investigated by
Monte-Carlo simulations. If one is interested in cross-sectional data connected
with the stochastic process under consideration, one needs to know the temporal
evolution of the distribution of states. This can be obtained by simulation of
the associated master equation. Some new formulas allow the determination of
path-related (i.e. longitudinal) quantities like the occurence probability, the
occurence time distribution, or the effective cumulative life-time distribution
of a certain sequencing of states (path). These can be efficiently evaluated
with a recently developed simulation tool (EPIS). The effective cumulative
life-time distribution facilitates the formulation of a hidden state concept of
behavioral changes which allows an interpretation of the respective
time-dependence of hazard rates. Hidden states represent states which are
either not phenomenological distinguishable from other states, not externally
measurable, or simply not detected. | 9805361v1 |
1999-09-09 | Micromagnetic simulations of thermally activated magnetization reversal of nanoscale magnets | Numerical integration of a stochastic Landau-Lifshitz-Gilbert equation is
used to study dynamic processes in single-domain nanoscale magnets at nonzero
temperatures. Special attention is given to including thermal fluctuations as a
Langevin term, and the Fast Multipole Method is used to calculate dipole-dipole
interactions. It is feasible to simulate these dynamics on the nanosecond time
scale for spatial discretizations that involve on the order of 10000 nodes
using a desktop workstation. The nanoscale magnets considered here are single
pillars with large aspect ratio. Hysteresis-loop simulations are employed to
study the stable and metastable configurations of the magnetization. Each
pillar has magnetic end caps. In a time-dependent field the magnetization of
the pillars is observed to reverse via nucleation, propagation, and coalescence
of the end caps. In particular, the end caps propagate into the magnet and meet
near the middle. A relatively long-lived defect is formed when end caps with
opposite vorticity meet. Fluctuations are more important in the reversal of the
magnetization for fields weaker than the zero-temperature coercive field, where
the reversal is thermally activated. In this case, the process must be
described by its statistical properties, such as the distribution of switching
times, averaged over a large number of independent thermal histories. | 9909136v2 |
2000-10-12 | Thermal Magnetization Reversal in Arrays of Nanoparticles | The results of large-scale simulations investigating the dynamics of
magnetization reversal in arrays of single-domain nanomagnets after a rapid
reversal of the applied field at nonzero temperature are presented. The
numerical micromagnetic approach uses the Landau-Lifshitz-Gilbert equation
including contributions from thermal fluctuations and long-range dipole-dipole
demagnetizing effects implemented using a fast-multipole expansion. The
individual model nanomagnets are 9 nm x 9 nm x 150 nm iron pillars similar to
those fabricated on a surface with STM-assisted chemical vapor deposition [S.
Wirth, et al., J. Appl. Phys {\bf 85}, 5249 (1999)]. Nanomagnets oriented
perpendicular to the surface and spaced 300 nm apart in linear arrays are
considered. The applied field is always oriented perpendicular to the surface.
When the magnitude of the applied field is less than the coercive value, about
2000 Oe for an individual nanomagnet, magnetization reversal in the nanomagnets
can only occur by thermally activated processes. Even though the interaction
from the dipole moment of neighboring magnets in this geometry is only about 1
Oe, less than 1% of the coercive field, it can have a large impact on the
switching dynamics. What determines the height of the free-energy barrier is
the difference between the coercive and applied fields, and 1 Oe can be a
significant fraction of that. The magnetic orientations of the neighbors are
seen to change the behavior of the nanomagnets in the array significantly. | 0010184v2 |
2001-12-12 | High Magnetic Field NMR Studies of LiVGe$_2$O$_6$, a quasi 1-D Spin $S = 1$ System | We report $^{7}$Li pulsed NMR measurements in polycrystalline and single
crystal samples of the quasi one-dimensional S=1 antiferromagnet
LiVGe$_2$O$_6$, whose AF transition temperature is $T_{\text{N}}\simeq 24.5$ K.
The field ($B_0$) and temperature ($T$) ranges covered were 9-44.5 T and
1.7-300 K respectively. The measurements included NMR spectra, the spin-lattice
relaxation rate ($T_1^{-1}$), and the spin-phase relaxation rate ($T_2^{-1}$),
often as a function of the orientation of the field relative to the crystal
axes. The spectra indicate an AF magnetic structure consistent with that
obtained from neutron diffraction measurements, but with the moments aligned
parallel to the c-axis. The spectra also provide the $T$-dependence of the AF
order parameter and show that the transition is either second order or weakly
first order. Both the spectra and the $T_1^{-1}$ data show that $B_0$ has at
most a small effect on the alignment of the AF moment. There is no spin-flop
transition up to 44.5 T. These features indicate a very large magnetic
anisotropy energy in LiVGe$_2$O$_6$ with orbital degrees of freedom playing an
important role. Below 8 K, $T_1^{-1}$ varies substantially with the orientation
of $B_0$ in the plane perpendicular to the c-axis, suggesting a small energy
gap for magnetic fluctuations that is very anisotropic. | 0112203v1 |
2003-10-07 | Endogenous Versus Exogenous Shocks in Complex Networks: an Empirical Test Using Book Sale Ranking | Are large biological extinctions such as the Cretaceous/Tertiary KT boundary
due to a meteorite, extreme volcanic activity or self-organized critical
extinction cascades? Are commercial successes due to a progressive reputation
cascade or the result of a well orchestrated advertisement? Determining the
chain of causality for extreme events in complex systems requires disentangling
interwoven exogenous and endogenous contributions with either no clear or too
many signatures. Here, we study the precursory and recovery signatures
accompanying shocks, that we test on a unique database of the Amazon sales
ranking of books. We find clear distinguishing signatures classifying two types
of sales peaks. Exogenous peaks occur abruptly and are followed by a power law
relaxation, while endogenous sale peaks occur after a progressively
accelerating power law growth followed by an approximately symmetrical power
law relaxation which is slower than for exogenous peaks. These results are
rationalized quantitatively by a simple model of epidemic propagation of
interactions with long memory within a network of acquaintances. The slow
relaxation of sales implies that the sales dynamics is dominated by cascades
rather than by the direct effects of news or advertisements, indicating that
the social network is close to critical. | 0310135v2 |
2004-08-18 | Irreversible spin-transfer and magnetization reversal under spin-injection | In the context of spin electronics, the two spin-channel model assumes that
the spin carriers are composed of two distinct populations: the conduction
electrons of spin up, and the conduction electrons of spin down. In order to
distinguish the paramagnetic and ferromagnetic contributions in spin injection,
we describe the current injection with four channels : the two spin populations
of the conduction bands ($s$ or paramagnetic) and the two spin populations of
the more correlated electrons ($d$ or ferromagnetic). The redistribution of the
conduction electrons at the interface is described by relaxation mechanisms
between the channels. Providing that the $d$ majority-spin band is frozen,
$s-d$ relaxation essentially concerns the minority-spin channels. Accordingly,
even in the abscence of spin-flip scattering (i.e. without standard
spin-accumulation or giant magnetoresistance), the $s-d$ relaxation leads to a
$d$ spin accumulation effect. The coupled diffusion equations for the two
relaxation processes ($s-d$ and spin-flip) are derived. The link with the
ferromagnetic order parameter $\vec{M}$ is performed by assuming that only the
$d$ channel contributes to the Landau-Lifshitz-Gilbert equation. The effect of
magnetization reversal induced by spin injection is explained by these
relaxations under the assumption that the spins of the conduction electrons act
as environmental degrees of freedom on the magnetization. | 0408410v1 |
2004-12-02 | Dielectric resonances in disordered media | Binary disordered systems are usually obtained by mixing two ingredients in
variable proportions: conductor and insulator, or conductor and
super-conductor. and are naturally modeled by regular bi-dimensional or
tri-dimensional lattices, on which sites or bonds are chosen randomly with
given probabilities. In this article, we calculate the impedance of the
composite by two independent methods: the so-called spectral method, which
diagonalises Kirchhoff's Laws via a Green function formalism, and the Exact
Numerical Renormalization method (ENR). These methods are applied to mixtures
of resistors and capacitors (R-C systems), simulating e.g. ionic
conductor-insulator systems, and to composites consituted of resistive
inductances and capacitors (LR-C systems), representing metal inclusions in a
dielectric bulk. The frequency dependent impedances of the latter composites
present very intricate structures in the vicinity of the percolation threshold.
We analyse the LR-C behavior of compounds formed by the inclusion of small
conducting clusters (``$n$-legged animals'') in a dielectric medium. We
investigate in particular their absorption spectra who present a pattern of
sharp lines at very specific frequencies of the incident electromagnetic field,
the goal being to identify the signature of each animal. This enables us to
make suggestions of how to build compounds with specific absorption or
transmission properties in a given frequency domain. | 0412061v1 |
2005-01-12 | Current induced magnetization switching in exchange biased spin-valves for CPP-GMR heads | In contrast to earlier studies performed on simple Co/Cu/Co sandwiches, we
have investigated spin transfer effects in complex spin-valve pillars with a
diameter of 130nm developed for current-perpendicular to the plane (CPP)
magneto-resistive heads. The structure of the samples included an exchange
biased synthetic pinned layer and a free layer both laminated by insertion of
several ultrathin Cu layers. Despite the small thickness of the polarizing
layer, our results show that the free layer can be switched between the
parallel (P) and the antiparallel (AP) states by applying current densities of
the order of 10^7 A/cm^2. A strong asymmetry is observed between the two
critical currents IcAP-P and IcP-AP, as predicted by the model of Slonczewski
model. Thanks to the use of exchange biased structures, the stability phase
diagrams could be obtained in the four quadrants of the (H, I) plan. The
critical lines derived from the magnetoresistance curves measured with
different sense currents, and from the resistance versus current curves
measured for different applied fields, match each other very well. The main
features of the phase diagrams can be reproduced by investigating the stability
of the solutions of the Landau Lifshitz Gilbert equation including spin torque
term within a macrospin model. A spin-transfer saturation effect was observed
in the positive currents range. We attribute it to a de-depolarization effect
which appears as a consequence of the asymmetric heating of the pillars, whose
top and the bottom leads are made of different materials. | 0501281v1 |
2005-12-20 | Theory of Spin Torque in a nanomagnet | We present a complete theory of the spin torque phenomena in a ultrasmall
nanomagnet coupled to non-collinear ferromagnetic electrodes through tunnelling
junctions. This model system can be described by a simple microscopic model
which captures many physical effects characteristic of spintronics: tunneling
magneto resistance, intrinsic and transport induced magnetic relaxation,
current induced magnetization reversal and spin accumulation. Treating on the
same footing the magnetic and transport degrees of freedom, we arrive at a
closed equation for the time evolution of the magnetization. This equation is
very close to the Landau-Lifshitz-Gilbert equation used in spin valves
structures. We discuss how the presence of the Coulomb blockade phenomena and
the discretization of the one-body spectrum gives some additional features to
the current induced spin torque. Depending on the regime, the dynamic induced
by the coupling to electrode can be viewed either as a spin torque or as a
relaxation process. In addition to the possibility of stabilizing uniform spin
precession states, we find that the system is highly hysteretic: up to three
different magnetic states can be simultaneously stable in one region of the
parameter space (magnetic field and bias voltage).We also discuss how the
magneto-resistance can be used to provide additional information on the
non-equilibrium peaks present in the nanomagnet spectroscopy experiments. | 0512508v1 |
2005-09-19 | Capacity-Achieving Codes with Bounded Graphical Complexity on Noisy Channels | We introduce a new family of concatenated codes with an outer low-density
parity-check (LDPC) code and an inner low-density generator matrix (LDGM) code,
and prove that these codes can achieve capacity under any memoryless
binary-input output-symmetric (MBIOS) channel using maximum-likelihood (ML)
decoding with bounded graphical complexity, i.e., the number of edges per
information bit in their graphical representation is bounded. In particular, we
also show that these codes can achieve capacity on the binary erasure channel
(BEC) under belief propagation (BP) decoding with bounded decoding complexity
per information bit per iteration for all erasure probabilities in (0, 1). By
deriving and analyzing the average weight distribution (AWD) and the
corresponding asymptotic growth rate of these codes with a rate-1 inner LDGM
code, we also show that these codes achieve the Gilbert-Varshamov bound with
asymptotically high probability. This result can be attributed to the presence
of the inner rate-1 LDGM code, which is demonstrated to help eliminate high
weight codewords in the LDPC code while maintaining a vanishingly small amount
of low weight codewords. | 0509062v3 |
2006-07-20 | List decoding of noisy Reed-Muller-like codes | First- and second-order Reed-Muller (RM(1) and RM(2), respectively) codes are
two fundamental error-correcting codes which arise in communication as well as
in probabilistically-checkable proofs and learning. In this paper, we take the
first steps toward extending the quick randomized decoding tools of RM(1) into
the realm of quadratic binary and, equivalently, Z_4 codes. Our main
algorithmic result is an extension of the RM(1) techniques from Goldreich-Levin
and Kushilevitz-Mansour algorithms to the Hankel code, a code between RM(1) and
RM(2). That is, given signal s of length N, we find a list that is a superset
of all Hankel codewords phi with dot product to s at least (1/sqrt(k)) times
the norm of s, in time polynomial in k and log(N). We also give a new and
simple formulation of a known Kerdock code as a subcode of the Hankel code. As
a corollary, we can list-decode Kerdock, too. Also, we get a quick algorithm
for finding a sparse Kerdock approximation. That is, for k small compared with
1/sqrt{N} and for epsilon > 0, we find, in time polynomial in (k
log(N)/epsilon), a k-Kerdock-term approximation s~ to s with Euclidean error at
most the factor (1+epsilon+O(k^2/sqrt{N})) times that of the best such
approximation. | 0607098v2 |
2002-11-21 | SuSpect: a Fortran Code for the Supersymmetric and Higgs Particle Spectrum in the MSSM | We present the Fortran code SuSpect version 2.3, which calculates the
Supersymmetric and Higgs particle spectrum in the Minimal Supersymmetric
Standard Model (MSSM). The calculation can be performed in constrained models
with universal boundary conditions at high scales such as the gravity (mSUGRA),
anomaly (AMSB) or gauge (GMSB) mediated breaking models, but also in the
non-universal MSSM case with R-parity and CP conservation. Care has been taken
to treat important features such as the renormalization group evolution of
parameters between low and high energy scales, the consistent implementation of
radiative electroweak symmetry breaking and the calculation of the physical
masses of the Higgs bosons and supersymmetric particles taking into account the
dominant radiative corrections. Some checks of important theoretical and
experimental features, such as the absence of non desired minima, large
fine-tuning in the electroweak symmetry breaking condition, as well as
agreement with precision measurements can be performed. The program is user
friendly, simple to use, self-contained and can easily be linked with other
codes; it is rather fast and flexible, thus allowing scans of the parameter
space with several possible options and choices for model assumptions and
approximations. | 0211331v2 |
2004-11-04 | Theoretical and Experimental Analysis of a Randomized Algorithm for Sparse Fourier Transform Analysis | We analyze a sublinear RAlSFA (Randomized Algorithm for Sparse Fourier
Analysis) that finds a near-optimal B-term Sparse Representation R for a given
discrete signal S of length N, in time and space poly(B,log(N)), following the
approach given in \cite{GGIMS}. Its time cost poly(log(N)) should be compared
with the superlinear O(N log N) time requirement of the Fast Fourier Transform
(FFT). A straightforward implementation of the RAlSFA, as presented in the
theoretical paper \cite{GGIMS}, turns out to be very slow in practice. Our main
result is a greatly improved and practical RAlSFA. We introduce several new
ideas and techniques that speed up the algorithm. Both rigorous and heuristic
arguments for parameter choices are presented. Our RAlSFA constructs, with
probability at least 1-delta, a near-optimal B-term representation R in time
poly(B)log(N)log(1/delta)/ epsilon^{2} log(M) such that
||S-R||^{2}<=(1+epsilon)||S-R_{opt}||^{2}. Furthermore, this RAlSFA
implementation already beats the FFTW for not unreasonably large N. We extend
the algorithm to higher dimensional cases both theoretically and numerically.
The crossover point lies at N=70000 in one dimension, and at N=900 for data on
a N*N grid in two dimensions for small B signals where there is noise. | 0411102v2 |
2006-12-04 | Krull dimension and deviation in certain parafree groups | Hanna Neumann asked whether it was possible for two non-isomorphic residually
nilpotent finitely generated (fg) groups, one of them free, to share the lower
central sequence. Gilbert Baumslag answered the question in the affirmative and
thus gave rise to parafree groups. A group G is termed parafree of rank n if it
is residually nilpotent and shares the lower central sequence with a free group
of rank n. The deviation of a finitely generated (fg) parafree group G is the
difference between the minimum possible number of generators of G and the rank
of G.
Let G be a fg group, then Hom(G,SL(2, C)) inherits the structure of an
algebraic variety, denoted by R(G), and known as its "representation variety".
If G is an n generated parafree group, then the deviation of G is 0 iff
Dim(R(G))=3n. It is known that for n \ge 2 there exist infinitely many parafree
groups of rank n and deviation 1 with non-isomorphic representation varieties
of dimension 3n. In this paper it is shown that given integers n \ge 2, and k
\ge 1, there exist infinitely many parafree groups of rank n and deviation k
with non-isomorphic representation varieties of dimension different from 3n; in
particular, it is shown that there exist infinitely many parafree groups G of
rank n with Dim(R(G))> q, where q \ge 3n is an arbitrary integer. | 0612102v2 |
2004-07-27 | Domain wall dynamics driven by adiabatic spin transfer torques | In a first approximation, known as the adiabatic process, the direction of
the spin polarization of currents is parallel to the local magnetization vector
in a domain wall. Thus the spatial variation of the direction of the spin
current inside the domain wall results in an adiabatical spin transfer torque
on the magnetization. We show that domain wall motion driven by this spin
torque has many unique features that do not exist in the conventional wall
motion driven by a magnetic field. By analytically and numerically solving the
Landau-Lifshitz-Gilbert equation along with the adiabatic spin torque in
magnetic nanowires, we find the domain wall has its maximum velocity at the
initial application of the current but the velocity decreases to zero as the
domain wall begins to deform during its motion. We have computed domain wall
displacement and domain wall deformation of nanowires, and concluded that the
spin torque based on the adiabatic propagation of the spin current in the
domain wall is unable to maintain wall movement. We also introduce a novel
concept of domain wall inductance to characterize the capacity of the
spin-torque induced magnetic energy stored in a domain wall. In the presence of
domain wall pinning centers, we construct a phase diagram for the domain wall
depinning by the combined action of the magnetic field and the spin current. | 0407064v1 |
1997-02-07 | Two-pion correlations in Au+Au collisions at 10.8 GeV/c per nucleon | Two-particle correlation functions for positive and negative pions have been
measured in Au+Au collisions at 10.8~GeV/c per nucleon. The data were analyzed
using one- and three-dimensional correlation functions. From the results of the
three-dimensional fit the phase space density of pions was calculated. It is
consistent with local thermal equilibrium. | 9702008v1 |
2007-01-30 | Huddling behavior in emperor penguins : dynamics of huddling | Although huddling was shown to be the key by which emperor penguins
(Aptenodytes forsteri) save energy and sustain their breeding fast during the
Antarctic winter, the intricacies of this social behavior have been poorly
studied. We recorded abiotic variables with data loggers glued to the feathers
of eight individually marked emperor penguins to investigate their
thermoregulatory behavior and to estimate their "huddling time budget"
throughout the breeding season (pairing and incubation period). Contrary to the
classic view, huddling episodes were discontinuous and of short and variable
duration, lasting 1.6+/-1.7 (S.D.) h on average. Despite heterogeneous huddling
groups, birds had equal access to the warmth of the huddles. Throughout the
breeding season, males huddled for 38+/-18% (S.D.) of their time, which raised
the ambient temperature that birds were exposed to above 0 degrees C (at
average external temperatures of -17 degrees C). As a consequence of tight
huddles, ambient temperatures were above 20 degrees C during 13+/-12% (S.D.) of
their huddling time. Ambient temperatures increased up to 37.5 degrees C, close
to birds' body temperature. This complex social behavior therefore enables all
breeders to get a regular and equal access to an environment which allows them
to save energy and successfully incubate their eggs during the Antarctic
winter. | 0701051v1 |
2003-10-14 | The Minimum Distance Problem for Two-Way Entanglement Purification | Entanglement purification takes a number of noisy EPR pairs and processes
them to produce a smaller number of more reliable pairs. If this is done with
only a forward classical side channel, the procedure is equivalent to using a
quantum error-correcting code (QECC). We instead investigate entanglement
purification protocols with two-way classical side channels (2-EPPs) for finite
block sizes. In particular, we consider the analog of the minimum distance
problem for QECCs, and show that 2-EPPs can exceed the quantum Hamming bound
and the quantum Singleton bound. We also show that 2-EPPs can achieve the rate
k/n = 1 - (t/n) \log_2 3 - h(t/n) - O(1/n) (asymptotically reaching the quantum
Hamming bound), where the EPP produces at least k good pairs out of n total
pairs with up to t arbitrary errors, and h(x) = -x \log_2 x - (1-x) \log_2
(1-x) is the usual binary entropy. In contrast, the best known lower bound on
the rate of QECCs is the quantum Gilbert-Varshamov bound k/n \geq 1 - (2t/n)
\log_2 3 - h(2t/n). Indeed, in some regimes, the known upper bound on the
asymptotic rate of good QECCs is strictly below our lower bound on the
achievable rate of 2-EPPs. | 0310097v4 |
2007-10-24 | The Impact of Halo Properties, Energy Feedback and Projection Effects on the Mass-SZ Flux Relation | We present a detailed analysis of the intrinsic scatter in the integrated SZ
effect - cluster mass (Y-M) relation, using semi-analytic and simulated cluster
samples. Specifically, we investigate the impact on the Y-M relation of energy
feedback, variations in the host halo concentration and substructure
populations, and projection effects due to unresolved clusters along the line
of sight (the SZ background). Furthermore, we investigate at what radius (or
overdensity) one should measure the integrated SZE and define cluster mass so
as to achieve the tightest possible scaling. We find that the measure of Y with
the least scatter is always obtained within a smaller radius than that at which
the mass is defined; e.g. for M_{200} (M_{500}) the scatter is least for
Y_{500} (Y_{1100}). The inclusion of energy feedback in the gas model
significantly increases the intrinsic scatter in the Y-M relation due to larger
variations in the gas mass fraction compared to models without feedback. We
also find that variations in halo concentration for clusters of a given mass
may partly explain why the integrated SZE provides a better mass proxy than the
central decrement. Substructure is found to account for approximately 20% of
the observed scatter in the Y-M relation. Above M_{200} = 2x10^{14} h^{-1}
msun, the SZ background does not significantly effect cluster mass
measurements; below this mass, variations in the background signal reduce the
optimal angular radius within which one should measure Y to achieve the
tightest scaling with M_{200}. | 0710.4555v1 |
2007-10-31 | Spin-Torque Driven Magnetization Dynamics: Micromagnetic Modelling | In this paper we present an overview of recent progress made in the
understanding of the spin-torque induced magnetization dynamics in nanodevices
using mesoscopic micromagnetic simulations. We first specify how a spin-torque
term may be added to the usual Landau-Lifshitz-Gilbert equation of
magnetization motion and detail its physical meaning. After a brief description
of spin-torque driven dynamics in the macrospin approximation, we discuss the
validity of this approximation for various experimentally relevant geometries.
Next, we perform a detailed comparison between accurate experimental data
obtained from nanopillar devices and corresponding numerical modelling. We show
that, on the one hand, many qualitatively important features of the observed
magnetization dynamics (e.g., non-linear frequency shift and frequency jumps
with increasing current) can be satisfactory explained by sophisticated
micromagnetic models, but on the other hand, understanding of these experiments
is still far from being complete. We proceed with the numerical analysis of
point-contact experiments, where an even more complicated magnetization
dynamics is observed. Simulations reveal that such a rich behaviour is due to
the formation of several strongly non-linear oscillation modes. In the last
part of the paper we emphasize the importance of sample characterization and
conclude with some important remarks concerning the relation between
micromagnetic modelling and real experiments. | 0710.5924v1 |
2007-11-19 | The Kohn-Sham system in one-matrix functional theory | A system of electrons in a local or nonlocal external potential can be
studied with 1-matrix functional theory (1MFT), which is similar to density
functional theory (DFT) but takes the one-particle reduced density matrix
(1-matrix) instead of the density as its basic variable. Within 1MFT, Gilbert
derived [PRB 12, 2111 (1975)] effective single-particle equations analogous to
the Kohn-Sham (KS) equations in DFT. The self-consistent solution of these
1MFT-KS equations reproduces not only the density of the original electron
system but also its 1-matrix. While in DFT it is usually possible to reproduce
the density using KS orbitals with integer (0 or 1) occupancy, in 1MFT
reproducing the 1-matrix requires in general fractional occupancies. The
variational principle implies that the KS eigenvalues of all fractionally
occupied orbitals must collapse at self-consistency to a single level, equal to
the chemical potential. We show that as a consequence of the degeneracy the
iteration of the KS equations is intrinsically divergent. Fortunately, the
level shifting method, commonly introduced in Hartree-Fock calculations, is
always able to force convergence. We introduce an alternative derivation of the
1MFT-KS equations that allows control of the eigenvalue collapse by
constraining the occupancies. As an explicit example, we apply the 1MFT-KS
scheme to calculate the ground state 1-matrix of an exactly solvable two-site
Hubbard model. | 0711.2996v1 |
2007-12-01 | On Myopic Sensing for Multi-Channel Opportunistic Access: Structure, Optimality, and Performance | We consider a multi-channel opportunistic communication system where the
states of these channels evolve as independent and statistically identical
Markov chains (the Gilbert-Elliot channel model). A user chooses one channel to
sense and access in each slot and collects a reward determined by the state of
the chosen channel. The problem is to design a sensing policy for channel
selection to maximize the average reward, which can be formulated as a
multi-arm restless bandit process. In this paper, we study the structure,
optimality, and performance of the myopic sensing policy. We show that the
myopic sensing policy has a simple robust structure that reduces channel
selection to a round-robin procedure and obviates the need for knowing the
channel transition probabilities. The optimality of this simple policy is
established for the two-channel case and conjectured for the general case based
on numerical results. The performance of the myopic sensing policy is analyzed,
which, based on the optimality of myopic sensing, characterizes the maximum
throughput of a multi-channel opportunistic communication system and its
scaling behavior with respect to the number of channels. These results apply to
cognitive radio networks, opportunistic transmission in fading environments,
and resource-constrained jamming and anti-jamming. | 0712.0035v3 |
2007-12-12 | Two-connected graphs with prescribed three-connected components | We adapt the classical 3-decomposition of any 2-connected graph to the case
of simple graphs (no loops or multiple edges). By analogy with the
block-cutpoint tree of a connected graph, we deduce from this decomposition a
bicolored tree tc(g) associated with any 2-connected graph g, whose white
vertices are the 3-components of g (3-connected components or polygons) and
whose black vertices are bonds linking together these 3-components, arising
from separating pairs of vertices of g. Two fundamental relationships on graphs
and networks follow from this construction. The first one is a dissymmetry
theorem which leads to the expression of the class B=B(F) of 2-connected
graphs, all of whose 3-connected components belong to a given class F of
3-connected graphs, in terms of various rootings of B. The second one is a
functional equation which characterizes the corresponding class R=R(F) of
two-pole networks all of whose 3-connected components are in F. All the
rootings of B are then expressed in terms of F and R. There follow
corresponding identities for all the associated series, in particular the edge
index series. Numerous enumerative consequences are discussed. | 0712.1869v2 |
2008-03-13 | Optimal spatial transportation networks where link-costs are sublinear in link-capacity | Consider designing a transportation network on $n$ vertices in the plane,
with traffic demand uniform over all source-destination pairs. Suppose the cost
of a link of length $\ell$ and capacity $c$ scales as $\ell c^\beta$ for fixed
$0<\beta<1$. Under appropriate standardization, the cost of the minimum cost
Gilbert network grows essentially as $n^{\alpha(\beta)}$, where $\alpha(\beta)
= 1 - \frac{\beta}{2}$ on $0 < \beta \leq {1/2}$ and $\alpha(\beta) = {1/2} +
\frac{\beta}{2}$ on ${1/2} \leq \beta < 1$. This quantity is an upper bound in
the worst case (of vertex positions), and a lower bound under mild regularity
assumptions. Essentially the same bounds hold if we constrain the network to be
efficient in the sense that average route-length is only $1 + o(1)$ times
average straight line length. The transition at $\beta = {1/2}$ corresponds to
the dominant cost contribution changing from short links to long links. The
upper bounds arise in the following type of hierarchical networks, which are
therefore optimal in an order of magnitude sense. On the large scale, use a
sparse Poisson line process to provide long-range links. On the medium scale,
use hierachical routing on the square lattice. On the small scale, link
vertices directly to medium-grid points. We discuss one of many possible
variant models, in which links also have a designed maximum speed $s$ and the
cost becomes $\ell c^\beta s^\gamma$. | 0803.2037v1 |
2008-03-24 | Was the Andromeda Stream Produced by a Disk Galaxy? | The halo region of M31 exhibits a startling level of stellar inhomogeneities,
the most prominent of which is the "giant southern stream". Our previous
analysis indicates that this stream, as well as several other observed
features, are products of the tidal disruption of a single satellite galaxy
with stellar mass ~10^9 solar masses less than 1 Gyr ago. Here we show that the
specific observed morphology of the stream and halo debris favors a cold,
rotating, disk-like progenitor over a dynamically hot, non-rotating one. These
observed characteristics include the asymmetric distribution of stars along the
stream cross-section and its metal-rich core/metal-poor sheath structure. We
find that a disk-like progenitor can also give rise to arc-like features on the
minor axis at certain orbital phases that resemble the recently discovered
minor-axis "streams", even reproducing the lower observed metallicity of these
streams. Though interpreted by the discoverers as new, independent tidal
streams, our analysis suggests that these minor-axis streams may alternatively
arise from the progenitor of the giant southern stream. Overall, our study
points the way to a more complete reconstruction of the stream progenitor and
its merger with M31, based on the emerging picture that most of the major
inhomogeneities observed in the M31 halo share a common origin with the giant
stream. | 0803.3476v2 |
2008-04-23 | Geometric dynamics of Vlasov kinetic theory and its moments | The Vlasov equation of kinetic theory is introduced and the Hamiltonian
structure of its moments is presented. Then we focus on the geodesic evolution
of the Vlasov moments. As a first step, these moment equations generalize the
Camassa-Holm equation to its multi-component version. Subsequently, adding
electrostatic forces to the geodesic moment equations relates them to the
Benney equations and to the equations for beam dynamics in particle
accelerators. Next, we develop a kinetic theory for self assembly in
nano-particles. Darcy's law is introduced as a general principle for
aggregation dynamics in friction dominated systems (at different scales). Then,
a kinetic equation is introduced for the dissipative motion of isotropic
nano-particles. The zeroth-moment dynamics of this equation recovers the
classical Darcy's law at the macroscopic level. A kinetic-theory description
for oriented nano-particles is also presented. At the macroscopic level, the
zeroth moments of this kinetic equation recover the magnetization dynamics of
the Landau-Lifshitz-Gilbert equation. The moment equations exhibit the
spontaneous emergence of singular solutions (clumpons) that finally merge in
one singularity. This behaviour represents aggregation and alignment of
oriented nano-particles. Finally, the Smoluchowski description is derived from
the dissipative Vlasov equation for anisotropic interactions. Various levels of
approximate Smoluchowski descriptions are proposed as special cases of the
general treatment. As a result, the macroscopic momentum emerges as an
additional dynamical variable that in general cannot be neglected. | 0804.3676v1 |
2008-05-14 | Path Diversity over Packet Switched Networks: Performance Analysis and Rate Allocation | Path diversity works by setting up multiple parallel connections between the
end points using the topological path redundancy of the network. In this paper,
\textit{Forward Error Correction} (FEC) is applied across multiple independent
paths to enhance the end-to-end reliability. Network paths are modeled as
erasure Gilbert-Elliot channels. It is known that over any erasure channel,
\textit{Maximum Distance Separable} (MDS) codes achieve the minimum probability
of irrecoverable loss among all block codes of the same size. Based on the
adopted model for the error behavior, we prove that the probability of
irrecoverable loss for MDS codes decays exponentially for an asymptotically
large number of paths. Then, optimal rate allocation problem is solved for the
asymptotic case where the number of paths is large. Moreover, it is shown that
in such asymptotically optimal rate allocation, each path is assigned a
positive rate \textit{iff} its quality is above a certain threshold. The
quality of a path is defined as the percentage of the time it spends in the bad
state. Finally, using dynamic programming, a heuristic suboptimal algorithm
with polynomial runtime is proposed for rate allocation over a finite number of
paths. This algorithm converges to the asymptotically optimal rate allocation
when the number of paths is large. The simulation results show that the
proposed algorithm approximates the optimal rate allocation (found by
exhaustive search) very closely for practical number of paths, and provides
significant performance improvement compared to the alternative schemes of rate
allocation. | 0805.2185v1 |
2008-06-25 | HAT-P-9b: A Low Density Planet Transiting a Moderately Faint F star | We report the discovery of a planet transiting a moderately faint (V=12.3
mag) late F star, with an orbital period of 3.92289 +/- 0.00004 days. From the
transit light curve and radial velocity measurements we determine that the
radius of the planet is R_p = 1.40 +/- 0.06 R_Jup and that the mass is M_p =
0.78 +/- 0.09 M_Jup. The density of the new planet, rho = 0.35 +/- 0.06 g
cm^{-3}, fits to the low-density tail of the currently known transiting
planets. We find that the center of transit is at T_c = 2454417.9077 +/- 0.0003
(HJD), and the total transit duration is 0.143 +/- 0.004 days. The host star
has M_s = 1.28 +/- 0.13 M_Sun and R_s = 1.32 +/- 0.07 R_Sun. | 0806.4008v2 |
2008-07-07 | Micropropagation of three genotypes of Indian mustard [{Brassica juncea} (L.) Czern.] using seedling-derived transverse thin cell layer (tTCL) explants | Micropropagation of three genotypes of Indian mustard [\textit{Brassica
juncea} (L.) Czern.] using 7-days old seedling-derived transverse thin cell
layer (tTCL) explants was accomplished.
The genotype, explant source and addition of silver nitrate to the medium
significantly influenced shoot bud induction. MS medium with 26.6 $\mu$M of
6-Benzylaminopurin (BAP) and 3.22 $\mu$M of 1-naphtaleneacetic acid (NAA) was
identical (in the case of cotyledon tTCLs whatever the organ) and superior for
the induction of buds (in the cases of petiole tTCL explants of genotypes 1 and
2 and hypocotyl tTCL explants of genotypes 1 and 3) than 53.3 $\mu$M of BAP and
3.22 $\mu$M of NAA. However, 53.3 $\mu$M of BAP was superior for the induction
of buds than 26.6 $\mu$M in the presence of the same concentration of NAA for
petiole tTCL explants of genotype 3 and hypocotyl tTCL explants of genotype 2.
The addition of silver nitrate significantly enhanced the rate of shoot
induction in all genotypes. Cotyledon-derived tTCL explants exhibited the
highest shoot bud induction potential and was followed by petiole- and
hypocotyl-derived ones. Addition of 10 $\mu$M of silver nitrate to BAP and NAA
supplemented medium induced higher frequency shoot bud induction (up to 100 %)
with the highest means of 4.45 shoots per cotyledon-derived tTCL explants
obtained with the genotype 2. Shoot regenerated were rooted on MS basal medium
without PGRs which induced 99 % of roots per shoot. The plantlets established
in greenhouse conditions with 99 % survival, flowered normally and set seeds. | 0807.1061v1 |
2008-07-18 | On Probability Distributions for Trees: Representations, Inference and Learning | We study probability distributions over free algebras of trees. Probability
distributions can be seen as particular (formal power) tree series [Berstel et
al 82, Esik et al 03], i.e. mappings from trees to a semiring K . A widely
studied class of tree series is the class of rational (or recognizable) tree
series which can be defined either in an algebraic way or by means of
multiplicity tree automata. We argue that the algebraic representation is very
convenient to model probability distributions over a free algebra of trees.
First, as in the string case, the algebraic representation allows to design
learning algorithms for the whole class of probability distributions defined by
rational tree series. Note that learning algorithms for rational tree series
correspond to learning algorithms for weighted tree automata where both the
structure and the weights are learned. Second, the algebraic representation can
be easily extended to deal with unranked trees (like XML trees where a symbol
may have an unbounded number of children). Both properties are particularly
relevant for applications: nondeterministic automata are required for the
inference problem to be relevant (recall that Hidden Markov Models are
equivalent to nondeterministic string automata); nowadays applications for Web
Information Extraction, Web Services and document processing consider unranked
trees. | 0807.2983v1 |
2008-11-02 | Stretch-Twist torus dynamo in compact Riemannian manifolds | Earlier Arnold, Zeldovich, Ruzmaikin and Sokoloff [\textbf{JETP (1982)}] have
computed the eigenvalue of a uniform stretching torus transformation which
result on the first Riemann metric solution of the dynamo action problem.
Recently some other attempts to obtain Riemann metrics representing dynamo
action through conformal maps have been undertaken [{\textbf{Phys. Plasmas 14
(2007)}]. Earlier, Gilbert [\textbf{Proc. Roy. Soc. London A(2003)}] has
investigated a more realistic dynamo map solution than the one presented by
Arnold et al by producing a shearing of the Arnold's cat map, by eigenvalue
problem of a dynamo operator. In this paper, the eigenvalue of the Riemann
twisted torus dynamo flow metric is obtained as the ratio between the poloidal
and toroidal components of the flow. This result is obtained from the Euler
equation. In the twisted torus, the eigenvalue of the Riemann metric is
${m}_{\pm}=\frac{1\pm{\sqrt{5}}}{2}$, which is quite close to the value
obtained by Arnold. In the case the viscosity Reynolds number $Re\to{\infty}$,
the torus flow is unstable as one approaches the torus axis. In Arnold's dynamo
metric the eigenvalues are ${\chi}_{\pm}=\frac{3\pm{\sqrt{5}}}{2}$ which are
very close to the above value. Eigenvalues determine the growth rates of the
velocity ratio between poloidal and toroidal components of the flow. The curved
flow in torus follow previous work by Chen et al [\textbf{Phys Fluids (2006)}].
The ${\alpha}$-effect dynamo is shown to be a second-order effect in the torus
curvature and velocity flow. Loop dynamo flows and maps are also discussed. | 0811.0142v1 |
2008-12-03 | Gravitino Dark Matter and the Cosmic Lithium Abundances | Supersymmetric extensions of the standard model of particle physics assuming
the gravitino to be the lightest supersymmetric particle (LSP), and with the
next-to-LSP decaying to the gravitino during Big Bang nucleosynthesis, are
analyzed. Particular emphasis is laid on their potential to solve the "Li7
problem", an apparent factor 2-4 overproduction of Li7 in standard Big Bang
nucleosynthesis (BBN), their production of cosmologically important amounts of
Li6, as well as the resulting gravitino dark matter densities in these models.
The study includes several improvements compared to prior studies. Heavy
gravitinos in the constrained minimal supersymmetric standard model (CMMSM) are
reanalyzed, whereas light gravitinos in gauge-mediated supersymmetry breaking
scenarios (GMSB) are studied for the first time. It is confirmed that decays of
NLSP staus to heavy gravitinos, while producing all the dark matter, may at the
same time resolve the Li7 problem. For NLSP decay times ~ 1000 sec, such
scenarios also lead to cosmologically important Li6 (and possibly Be9)
abundances. However, as such scenarios require heavy > 1 TeV staus they are
likely not testable at the LHC. It is found that decays of NLSP staus to light
gravitinos may lead to significant Li6 (and Be9) abundances, whereas NLSP
neutralinos decaying into light gravitinos may solve the Li7 problem. Though
both scenarios are testable at the LHC they may not lead to the production of
the bulk of the dark matter. A section of the paper outlines particle
properties required to significantly reduce the Li7 abundance, and/or enhance
the Li6 (and possibly Be9) abundances, by the decay of an arbitrary relic
particle. | 0812.0788v2 |
2009-01-26 | A Bayesian framework for estimating vaccine efficacy per infectious contact | In vaccine studies for infectious diseases such as human immunodeficiency
virus (HIV), the frequency and type of contacts between study participants and
infectious sources are among the most informative risk factors, but are often
not adequately adjusted for in standard analyses. Such adjustment can improve
the assessment of vaccine efficacy as well as the assessment of risk factors.
It can be attained by modeling transmission per contact with infectious
sources. However, information about contacts that rely on self-reporting by
study participants are subject to nontrivial measurement error in many studies.
We develop a Bayesian hierarchical model fitted using Markov chain Monte Carlo
(MCMC) sampling to estimate the vaccine efficacy controlled for exposure to
infection, while adjusting for measurement error in contact-related factors.
Our method is used to re-analyze two recent HIV vaccine studies, and the
results are compared with the published primary analyses that used standard
methods. The proposed method could also be used for other vaccines where
contact information is collected, such as human papilloma virus vaccines. | 0901.4025v1 |
2009-01-28 | Theoretical characterization of a model of aragonite crystal orientation in red abalone nacre | Nacre, commonly known as mother-of-pearl, is a remarkable biomineral that in
red abalone consists of layers of 400-nm thick aragonite crystalline tablets
confined by organic matrix sheets, with the $(001)$ crystal axes of the
aragonite tablets oriented to within $\pm$ 12 degrees from the normal to the
layer planes. Recent experiments demonstrate that this orientational order
develops over a distance of tens of layers from the prismatic boundary at which
nacre formation begins.
Our previous simulations of a model in which the order develops because of
differential tablet growth rates (oriented tablets growing faster than
misoriented ones) yield patterns of tablets that agree qualitatively and
quantitatively with the experimental measurements. This paper presents an
analytical treatment of this model, focusing on how the dynamical development
and eventual degree of order depend on model parameters. Dynamical equations
for the probability distributions governing tablet orientations are introduced
whose form can be determined from symmetry considerations and for which
substantial analytic progress can be made. Numerical simulations are performed
to relate the parameters used in the analytic theory to those in the
microscopic growth model. The analytic theory demonstrates that the dynamical
mechanism is able to achieve a much higher degree of order than naive estimates
would indicate. | 0901.4482v1 |
2009-02-07 | Partially-erupting prominences: a comparison between observations and model-predicted observables | AIM: To investigate several partially-erupting prominences to study their
relationship with other CME-associated phenomena and to compare these
observations with observables predicted by a model of partially-expelled flux
ropes (Gibson & Fan, 2006a, b).
METHODS: We have studied 6 selected events with partially-erupting
prominences using multi wavelength observations recorded by the
Extreme-ultraviolet Imaging Telescope (EIT), Transition Region and Coronal
Explorer (TRACE), Mauna Loa Solar Observatory (MLSO), Big Bear Solar
Observatory (BBSO) and soft X-ray telescope (SXT). The observational features
associated with partially-erupting prominences were then compared with the
predicted observables from the model.
RESULTS: The partially-expelled-flux-rope (PEFR) model of Gibson & Fan
(2006a, b) can explain the partial eruption of these prominences, and in
addition predicts a variety of other CME-related observables that provide
evidence for internal reconnection during eruption. We find that all of the
partially-erupting prominences studied in this paper exhibit indirect evidence
for internal reconnection. Moreover, all cases showed evidence of at least one
observable unique to the PEFR model, e.g., dimmings external to the source
region, and/or a soft X-ray cusp overlying a reformed sigmoid.
CONCLUSIONS: The PEFR model provides a plausible mechanism to explain the
observed evolution of partially-erupting-prominence-associated CMEs in our
study. | 0902.1228v1 |
2009-03-03 | Proportional hazards models with continuous marks | For time-to-event data with finitely many competing risks, the proportional
hazards model has been a popular tool for relating the cause-specific outcomes
to covariates [Prentice et al. Biometrics 34 (1978) 541--554]. This article
studies an extension of this approach to allow a continuum of competing risks,
in which the cause of failure is replaced by a continuous mark only observed at
the failure time. We develop inference for the proportional hazards model in
which the regression parameters depend nonparametrically on the mark and the
baseline hazard depends nonparametrically on both time and mark. This work is
motivated by the need to assess HIV vaccine efficacy, while taking into account
the genetic divergence of infecting HIV viruses in trial participants from the
HIV strain that is contained in the vaccine, and adjusting for covariate
effects. Mark-specific vaccine efficacy is expressed in terms of one of the
regression functions in the mark-specific proportional hazards model. The new
approach is evaluated in simulations and applied to the first HIV vaccine
efficacy trial. | 0903.0487v1 |
2009-03-06 | Five More Massive Binaries in the Cygnus OB2 Association | We present the orbital solutions for four OB spectroscopic binaries, MT145,
GSC 03161-00815, 2MASS J20294666+4105083, and Schulte 73, and the partial
orbital solution to the B spectroscopic binary, MT372, as part of an ongoing
study to determine the distribution of orbital parameters for massive binaries
in the Cygnus OB2 Association. MT145 is a new, single-lined, moderately
eccentric (e=0.291+/-0.009) spectroscopic binary with period of 25.140+/-0.008
days. GSC 03161-00815 is a slightly eccentric (e=0.10+/-0.01), eclipsing,
interacting and double-lined spectroscopic binary with a period of
4.674+/-0.004 days. 2MASS J20294666+4105083 is a moderately eccentric
(e=0.273+/-0.002) double-lined spectroscopic binary with a period of
2.884+/-0.001 days. Schulte 73 is a slightly eccentric (e=0.169+/-0.009),
double-lined spectroscopic binary with a period of 17.28+/-0.03 days and the
first "twin" in our survey with a mass ratio of q=0.99+/-0.02. MT372 is a
single-lined, eclipsing system with a period of 2.228 days and low eccentricity
(e~0). Of the now 18 known OB binaries in Cyg OB2, 14 have periods and mass
ratios. Emerging evidence also shows that the distribution of log(P) is flat
and consistent with Oepik's Law. | 0903.1265v1 |
2009-03-19 | Approximation of Bounds on Mixed Level Orthogonal Arrays | Mixed level orthogonal arrays are basic structures in experimental design. We
develop three algorithms that compute Rao and Gilbert-Varshamov type bounds for
mixed level orthogonal arrays. The computational complexity of the terms
involved in these bounds can grow fast as the parameters of the arrays increase
and this justifies the construction of these algorithms. The first is a
recursive algorithm that computes the bounds exactly, the second is based on an
asymptotic analysis and the third is a simulation algorithm. They are all based
on the representation of the combinatorial expressions that appear in the
bounds as expectations involving a symmetric random walk. The Markov property
of the underlying random walk gives the recursive formula to compute the
expectations. A large deviation (LD) analysis of the expectations provide the
asymptotic algorithm. The asymptotically optimal importance sampling (IS) of
the same expectation provides the simulation algorithm. Both the LD analysis
and the construction of the IS algorithm uses a representation of these
problems as a sequence of stochastic optimal control problems converging to a
limit calculus of variations problem. The construction of the IS algorithm uses
a recently discovered method of using subsolutions to the Hamilton Jacobi
Bellman equation associated with the limit problem. | 0903.3438v2 |
2009-04-16 | Good Concatenated Code Ensembles for the Binary Erasure Channel | In this work, we give good concatenated code ensembles for the binary erasure
channel (BEC). In particular, we consider repeat multiple-accumulate (RMA) code
ensembles formed by the serial concatenation of a repetition code with multiple
accumulators, and the hybrid concatenated code (HCC) ensembles recently
introduced by Koller et al. (5th Int. Symp. on Turbo Codes & Rel. Topics,
Lausanne, Switzerland) consisting of an outer multiple parallel concatenated
code serially concatenated with an inner accumulator. We introduce stopping
sets for iterative constituent code oriented decoding using maximum a
posteriori erasure correction in the constituent codes. We then analyze the
asymptotic stopping set distribution for RMA and HCC ensembles and show that
their stopping distance hmin, defined as the size of the smallest nonempty
stopping set, asymptotically grows linearly with the block length. Thus, these
code ensembles are good for the BEC. It is shown that for RMA code ensembles,
contrary to the asymptotic minimum distance dmin, whose growth rate coefficient
increases with the number of accumulate codes, the hmin growth rate coefficient
diminishes with the number of accumulators. We also consider random puncturing
of RMA code ensembles and show that for sufficiently high code rates, the
asymptotic hmin does not grow linearly with the block length, contrary to the
asymptotic dmin, whose growth rate coefficient approaches the Gilbert-Varshamov
bound as the rate increases. Finally, we give iterative decoding thresholds for
the different code ensembles to compare the convergence properties. | 0904.2482v1 |
2009-10-10 | Multi-channel Opportunistic Access: A Case of Restless Bandits with Multiple Plays | This paper considers the following stochastic control problem that arises in
opportunistic spectrum access: a system consists of n channels (Gilbert-Elliot
channels)where the state (good or bad) of each channel evolves as independent
and identically distributed Markov processes. A user can select exactly k
channels to sense and access (based on the sensing result) in each time slot. A
reward is obtained whenever the user senses and accesses a good channel. The
objective is to design a channel selection policy that maximizes the expected
discounted total reward accrued over a finite or infinite horizon. In our
previous work we established the optimality of a greedy policy for the special
case of k = 1 (i.e., single channel access) under the condition that the
channel state transitions are positively correlated over time. In this paper we
show under the same condition the greedy policy is optimal for the general case
of k >= 1; the methodology introduced here is thus more general. This problem
may be viewed as a special case of the restless bandit problem, with multiple
plays. We discuss connections between the current problem and existing
literature on this class of problems. | 0910.1954v1 |
2010-04-05 | A Prograde, Low-Inclination Orbit for the Very Hot Jupiter WASP-3b | We present new spectroscopic and photometric observations of the transiting
exoplanetary system WASP-3. Spectra obtained during two separate transits
exhibit the Rossiter-McLaughlin (RM) effect and allow us to estimate the
sky-projected angle between the planetary orbital axis and the stellar rotation
axis, lambda = 3.3^{+2.5}_{-4.4} degrees. This alignment between the axes
suggests that WASP-3b has a low orbital inclination relative to the equatorial
plane of its parent star. During our first night of spectroscopic measurements,
we observed an unexpected redshift briefly exceeding the expected sum of the
orbital and RM velocities by 140 m/s. This anomaly could represent the
occultation of material erupting from the stellar photosphere, although it is
more likely to be an artifact caused by moonlight scattered into the
spectrograph. | 1004.0692v2 |
2010-06-09 | NLTT 41135: a field M-dwarf + brown dwarf eclipsing binary in a triple system, discovered by the MEarth observatory | We report the discovery of an eclipsing companion to NLTT 41135, a nearby M5
dwarf that was already known to have a wider, slightly more massive common
proper motion companion, NLTT 41136, at 2.4 arcsec separation. Analysis of
combined-light and radial velocity curves of the system indicates that NLTT
41135B is a 31-34 +/- 3 MJup brown dwarf (where the range depends on the
unknown metallicity of the host star) on a circular orbit. The visual M-dwarf
pair appears to be physically bound, so the system forms a hierarchical triple,
with masses approximately in the ratio 8:6:1. The eclipses are grazing,
preventing an unambiguous measurement of the secondary radius, but follow-up
observations of the secondary eclipse (e.g. with the James Webb Space
Telescope) could permit measurements of the surface brightness ratio between
the two objects, and thus place constraints on models of brown dwarfs. | 1006.1793v1 |
2010-09-28 | Connectivity in Sub-Poisson Networks | We consider a class of point processes (pp), which we call {\em sub-Poisson};
these are pp that can be directionally-convexly ($dcx$) dominated by some
Poisson pp. The $dcx$ order has already been shown useful in comparing various
point process characteristics, including Ripley's and correlation functions as
well as shot-noise fields generated by pp, indicating in particular that
smaller in the $dcx$ order processes exhibit more regularity (less clustering,
less voids) in the repartition of their points. Using these results, in this
paper we study the impact of the $dcx$ ordering of pp on the properties of two
continuum percolation models, which have been proposed in the literature to
address macroscopic connectivity properties of large wireless networks. As the
first main result of this paper, we extend the classical result on the
existence of phase transition in the percolation of the Gilbert's graph (called
also the Boolean model), generated by a homogeneous Poisson pp, to the class of
homogeneous sub-Poisson pp. We also extend a recent result of the same nature
for the SINR graph, to sub-Poisson pp. Finally, as examples we show that the
so-called perturbed lattices are sub-Poisson. More generally, perturbed
lattices provide some spectrum of models that ranges from periodic grids,
usually considered in cellular network context, to Poisson ad-hoc networks, and
to various more clustered pp including some doubly stochastic Poisson ones. | 1009.5696v1 |
2010-10-26 | Dualities and Identities for Entanglement-Assisted Quantum Codes | The dual of an entanglement-assisted quantum error-correcting (EAQEC) code is
the code resulting from exchanging the original code's information qubits with
its ebits. To introduce this notion, we show how entanglement-assisted (EA)
repetition codes and accumulator codes are dual to each other, much like their
classical counterparts, and we give an explicit, general quantum shift-register
circuit that encodes both classes of codes.We later show that our constructions
are optimal, and this result completes our understanding of these dual classes
of codes. We also establish the Gilbert-Varshamov bound and the Plotkin bound
for EAQEC codes, and we use these to examine the existence of some EAQEC codes.
Finally, we provide upper bounds on the block error probability when
transmitting maximal-entanglement EAQEC codes over the depolarizing channel,
and we derive variations of the hashing bound for EAQEC codes, which is a lower
bound on the maximum rate at which reliable communication over Pauli channels
is possible with the use of pre-shared entanglement. | 1010.5506v4 |
2010-11-12 | Magnetization Dynamics, Bennett Clocking and Associated Energy Dissipation in Multiferroic Logic | It has been recently shown that multiferroic logic - where logic bits are
encoded in the magnetization orientation of a nanoscale magnetostrictive layer
elastically coupled to a piezoelectric layer - can be Bennett clocked with
small electrostatic potentials of few tens of mV applied to the piezoelectric
layer. The potential generates stress in the magnetostrictive layer and rotates
its magnetization by a large angle to carry out Bennett clocking. This method
of clocking is far more energy-efficient than using spin transfer torque. In
order to assess if such a clocking scheme can be also reasonably fast, we have
studied the magnetization dynamics of a multiferroic logic array with nearest
neighbor dipole coupling using the Landau-Lifshitz-Gilbert (LLG) equation. We
find that switching delays of ~ 3 ns (clock rates of 0.33 GHz) can be achieved
with proper design provided we clock non-adiabatically and dissipate ~48,000 kT
(at room temperature) of energy per clock cycle per bit flip in the clocking
circuit. This dissipation far exceeds the energy barrier separating the two
logic states, which we assumed to be 32 kT to yield a bit error probability of
. Had we used spin transfer torque to switch with the same ~ 3 ns delay, the
energy dissipation would have been much larger (~ $6 \times 106$ kT). This
shows that spin transfer torque, widely used in magnetic random access memory,
is an inefficient way to switch a magnet, and multiferroic logic clocked with
voltage-induced stress is a superior nanomagnetic logic scheme. | 1011.2914v2 |
2010-12-30 | One-dimensional Gromov minimal filling | The present paper opens a new branch in the theory of variational problems
with branching extremals, the investigation of one-dimensional minimal fillings
of finite pseudo-metric spaces. On the one hand, this problem is a
one-dimensional version of a generalization of Gromov's minimal fillings
problem to the case of stratified manifolds (the filling in our case is a
weighted graph). On the other hand, this problem is interesting in itself and
also can be considered as a generalization of another classical problem,
namely, the Steiner problem on the construction of a shortest network joining a
given set of terminals. Besides the statement of the problem, we discuss
several properties of the minimal fillings, describe minimal fillings of
additive spaces, and state several conjectures. We also include some
announcements concerning the very recent results obtained in our group,
including a formula calculating the weight of the minimal filling for an
arbitrary finite pseudo-metric space and the concept of pseudo-additive space
which generalizes the classical concept of additive space. We hope that the
theory of one-dimensional minimal fillings refreshes the interest in the
Steiner problem and gives an opportunity to solve several long standing
problems, such as the calculation of the Steiner ratio, in particular the
verification of the Gilbert--Pollack conjecture on the Steiner ratio of the
Euclidean plane. | 1101.0106v2 |
2011-02-02 | Kepler Input Catalog: Photometric Calibration and Stellar Classification | We describe the photometric calibration and stellar classification methods
used to produce the Kepler Input Catalog (KIC). The KIC is a catalog containing
photometric and physical data for sources in the Kepler Mission field of view;
it is used by the mission to select optimal targets. We derived atmospheric
extinction corrections from hourly observations of secondary standard fields
within the Kepler field of view. Repeatability of absolute photometry for stars
brighter than magnitude 15 is typically 2%. We estimated stellar parameters
Teff, log(g), log (Z), E_{B-V} using Bayesian posterior probability
maximization to match observed colors to Castelli stellar atmosphere models. We
applied Bayesian priors describing the distribution of solar-neighborhood stars
in the color-magnitude diagram (CMD), in log (Z)$, and in height above the
galactic plane. Comparisons with samples of stars classified by other means
indicate that in most regions of the CMD, our classifications are reliable
within about +/- 200 K and +/- 0.4 dex in log (g). It is difficult to assess
the reliability of our log(Z) estimates, but there is reason to suspect that it
is poor, particularly at extreme Teff. Of great importance for the Kepler
Mission, for Teff <= 5400 K, the distinction between main-sequence stars and
giants has proved to be reliable with better than 98% confidence. The KIC is
available through the MAST data archive. | 1102.0342v2 |
2011-05-10 | Interstellar Solid Hydrogen | We consider the possibility that solid molecular hydrogen is present in
interstellar space. If so cosmic-rays and energetic photons cause ionisation in
the solid leading to the formation of H6+. This ion is not produced by
gas-phase reactions and its radiative transitions therefore provide a signature
of solid H2 in the astrophysical context. The vibrational transitions of H6+
are yet to be observed in the laboratory, but we have characterised them in a
quantum-theoretical treatment of the molecule; our calculations include
anharmonic corrections, which are large. Here we report on those calculations
and compare our results with astronomical data. In addition to the H6+
isotopomer, we focus on the deuterated species (HD)3+ which is expected to
dominate at low ionisation rates as a result of isotopic condensation
reactions. We can reliably predict the frequencies of the fundamental bands for
five modes of vibration. For (HD)3+ all of these are found to lie close to some
of the strongest of the pervasive mid-infrared astronomical emission bands,
making it difficult to exclude hydrogen precipitates on observational grounds.
By the same token these results suggest that (HD)3+ could be the carrier of the
observed bands. We consider this possibility within the broader picture of ISM
photo-processes and we conclude that solid hydrogen may indeed be abundant in
astrophysical environments. | 1105.1861v1 |
2011-05-12 | The History of Star Formation in Galaxy Disks in the Local Volume as Measured by the ACS Nearby Galaxy Survey Treasury | We present a measurement of the age distribution of stars residing in spiral
disks and dwarf galaxies. We derive a complete star formation history of the
~140 Mpc^3 covered by the volume-limited sample of galaxies in the Advanced
Camera for Surveys (ACS) Nearby Galaxy Survey Treasury (ANGST). The total star
formation rate density history is dominated by the large spirals in the volume,
although the sample consists mainly of dwarf galaxies. Our measurement shows a
factor of ~3 drop at z~2, in approximate agreement with results from other
measurement techniques. While our results show that the overall star formation
rate density has decreased since z~1, the measured rates during this epoch are
higher than those obtained from other measurement techniques. This enhanced
recent star formation rate appears to be largely due to an increase in the
fraction of star formation contained in low-mass disks at recent times.
Finally, our results indicate that despite the differences at recent times, the
epoch of formation of ~50% of the stellar mass in dwarf galaxies was similar to
that of ~50% of the stellar mass in large spiral galaxies (z>~2), despite the
observed galaxy-to-galaxy diversity among the dwarfs. | 1105.2571v1 |
2011-06-30 | Revisiting No-Scale Supergravity Inspired Scenarios: Updated Theoretical and Phenomenological Constraints | We consider no-scale inspired supergravity scenarios, where the gravitino
mass and related soft supersymmetry-breaking parameters are determined
dynamically by radiative corrections to an essentially flat tree-level
potential in the supersymmetry breaking hidden sector. We examine the
theoretical and phenomenological viability of such a mechanism, when including
up-to-date calculations of the low energy sparticle spectrum and taking into
account the latest LHC results and other experimental constraints. We
(re)emphasize the role of the scale-dependent vacuum energy contribution to the
effective potential, in obtaining realistic no-scale electroweak minima,
examining carefully the impact of boundary conditions and of variants of the
minimization procedure. We also discuss and implement the B_0 (soft breaking
Higgs mixing parameter) input boundary condition at high scale, therefore
fixing tan beta(B_0) at low scales. For general high scale boundary conditions
with non-vanishing B_0, m_0..., our analysis provides theoretical correlations
among the supersymmetric, soft and vacuum energy parameters and related
phenomenological consequences at the LHC. For instance, a zero vacuum energy at
the GUT scale would lead to a decoupled supersymmetric spectrum, together with
a light standard model-like Higgs boson at the electroweak scale. Given the
experimental exclusion limits, a substantial class of the boundary conditions,
and in particular the strict no-scale with m_0=A_0=B_0=0, are only compatible
with a stau being the lightest MSSM particle. Then an enlarged allowed
parameter space emerges when assuming a gravitino LSP to account for the
observed dark matter relic density. | 1106.6325v2 |
2012-03-28 | Bispectrum of the Sunyaev-Zel'dovich Effect | We perform a detailed study of the bispectrum of the Sunyaev-Zel'dovich
effect. Using an analytical model for the pressure profiles of the intracluster
medium, we demonstrate the SZ bispectrum to be a sensitive probe of the
amplitude of the matter power spectrum parameter sigma_8. We find that the
bispectrum amplitude scales as B_SZ ~ sigma_8^{11-12}, compared to that of the
power spectrum, which scales as A_tSZ ~ sigma_8^{7-9}. We show that the SZ
bispectrum is principally sourced by massive clusters at redshifts around
z~0.4, which have been well-studied observationally. This is in contrast to the
SZ power spectrum, which receives a significant contribution from less-well
understood low-mass and high-redshift groups and clusters. Therefore, the
amplitude of the bispectrum at l~3000 is less sensitive to astrophysical
uncertainties than the SZ power spectrum. We show that current high resolution
CMB experiments should be able to detect the SZ bispectrum amplitude with high
significance, in part due to the low contamination from extra-galactic
foregrounds. A combination of the SZ bispectrum and the power spectrum can
sharpen the measurements of thermal and kinetic SZ components and help
distinguish cosmological and astrophysical information from high-resolution CMB
maps. | 1203.6368v3 |
2012-05-01 | A quasi-analytical model for energy-delay-reliability tradeoff studies during write operations in perpendicular STT-RAM cell | One of the biggest challenges the current STT-RAM industry faces is
maintaining a high thermal stability while trying to switch within a given
voltage pulse and energy cost. In this paper, we present a physics based
analytical model that uses a modified Simmons' tunneling expression to capture
the spin dependent tunneling in a magnetic tunnel junction(MTJ). Coupled with
an analytical derivation of the critical switching current based on the
Landau-Lifshitz-Gilbert equation, and the write error rate derived from a
solution to the Fokker-Planck equation, this model provides us a quick estimate
of the energydelay- reliability tradeoffs in perpendicular STTRAMs due to
thermal fluctuations. In other words, the model provides a simple way to
calculate the energy consumed during a write operation that ensures a certain
error rate and delay time, while being numerically far less intensive than a
full-fledged stochastic calculation. We calculate the worst case energy
consumption during anti-parallel (AP) to parallel (P) and P to AP switchings
and quantify how increasing the anisotropy field HK and lowering the saturation
magnetization MS, can significantly reduce the energy consumption. A case study
on how manufacturing variations of the MTJ cell can affect the energy
consumption and delay is also reported. | 1205.0183v1 |
2012-05-16 | Transients in porous media: asymptotic time-domain Green functions and limits of current frequency-domain models | Time domain responses of porous media have been studied by some authors, but
generally the possible descriptions have been given in the frequency domain.
The aim of this paper, limited to materials with rigid skeleton considered as
equivalent fluids, is to compare the descriptions by Johnson-Allard ($JA$%) as
well as by Pride-Lafarge ($PL$) with i) some analytical, approximate formulas,
based upon asymptotic high frequency expansion ; ii) the exact formula by
Zwikker and Kosten for the case of cylindrical pores. The paper starts with a
short summary of the statement of the different general full frequency models
($JA$ and $PL).$ The Green function in the time domain is shown to exhibit
interesting properties of materials. In particular the maximum response depends
on one dimensionless parameter only, which is denoted $\xi $ and is the ratio
of the travelled distance to the product of the \textquotedblleft
frozen\textquotedblright\ sound speed and a characteristic viscous relaxation
time. The distance $\xi $ is related to a time domain Stokes number. The
numerical computation of the Green function is done by FFT, with some
precautions, because of the importance of the higher frequencies on the
response shape. The $PL$ description is shown to be the best full frequency
general model, but some discrepancies with the exact model appear at short
times or short distances. When the distance $\xi $ increases from zero, the
asymptotic expansion shows that the maximum of the Green function decreases
first as $1/\xi ^{2}$, then exponentially. | 1205.3775v2 |
2012-05-20 | Externally-driven transformations of vortex textures in flat submicrometer magnets | Two effects of oscillatory transformations of vortex textures in flat
nanomagnets due to the application of an external field or a spin-polarized
electric current are analytically described with relevance to soft-magnetic
structures of submicrometer sizes (whose thickness is significantly bigger than
the magnetostatic exchange length). These are changes of a domain wall (DW)
structure in a long magnetic stripe (oscillations between a transverse DW, a
vortex DW, and an antivortex DW) and periodic vortex-core reversals in a
circular magnetic dot which are accompanied by oscillatory displacements of the
vortex from the dot center. In nanostructures of smaller thicknesses
(comparable to the exchange length), where nonlocal magnetostatic effects are
very strong because of fast spatial variation of the magnetization, similar
phenomena have been widely studied previously. Here, the dynamics is
investigated within a local approach including magnetostatic field via boundary
conditions on solutions to the Landau-Lifshitz-Gilbert equation only. Both the
DWs in stripes and vortex states of the dot are treated as fragments of a
cross-tie DW. Despite similarity of the cyclic transformations of the ordering
to the dynamics of more strongly confined nanomagnets, details of motion
(trajectories) of the vortices and antivortices (Bloch lines) of the textures
under study are different, which is related to prohibition of rapid jumps of
the polarization of Bloch lines. In addition to the magnetization rotation
about the direction of magnetic field or current polarization, the evolution of
textures is shown to relate to oscillatory changes of the direction of a
cross-tie DW with respect to any arbitrary axis in the magnet plane accompanied
by oscillations of the DW width. | 1205.5008v1 |
2012-06-11 | Multi-Gigabit Wireless data transfer at 60 GHz | In this paper we describe the status of the first prototype of the 60 GHz
wireless Multi-gigabit data transfer topology currently under development at
University of Heidelberg using IBM 130 nm SiGe HBT BiCMOS technology. The 60
GHz band is very suitable for high data rate and short distance applications as
for example needed in the HEP experments. The wireless transceiver consist of a
transmitter and a receiver. The transmitter includes an On-Off Keying (OOK)
modulator, an Local Oscillator (LO), a Power Amplifier (PA) and a BandPass
Filter (BPF). The receiver part is composed of a BandPass- Filter (BPF), a Low
Noise Amplifier (LNA), a double balanced down-convert Gilbert mixer, a Local
Oscillator (LO), then a BPF to remove the mixer introduced noise, an
Intermediate Amplifier (IF), an On-Off Keying demodulator and a limiting
amplifier. The first prototype would be able to handle a data-rate of about 3.5
Gbps over a link distance of 1 m. The first simulations of the LNA show that a
Noise Figure (NF) of 5 dB, a power gain of 21 dB at 60 GHz with a 3 dB
bandwidth of more than 20 GHz with a power consumption 11 mW are achieved.
Simulations of the PA show an output referred compression point P1dB of 19.7 dB
at 60 GHz. | 1206.2287v1 |
2012-06-14 | On the Interpretation of the Foundations of Quantum Mechanics | This study discusses the quantum behavior of a particle, which is controlled
by fluctuations in the physical space-time (ST) variables, rather than provides
a novel interpretation of quantum theory. The fluctuations, i.e.,
inhomogeneities in a homogeneous phase ST, are prescribed by their probability.
They determine the reciprocal space and correlate with the correlation entropy
different from zero. Alongside with the minimum entropy, action, and the
presence of the Winn-Ehrenfest adiabatic invariant (AI), the fluctuations
require the Gilbert information (probabilistic) space linking the physical and
the reciprocal ST. Physical quantities in the information space are represented
by linear Hermitian operators, which is due to the entropy production in the
presence of an AI. Evolution of a quantum system is described by the wave
functions having the meaning of information concerning all virtually possible
states of a quantum particle. The wave functions are the solutions to the
Schrodinger equation and represent a navigation 'roadmap' for the particle to
follow. A quantum system is in fact a classical Hamiltonian system in the space
of coefficients of the wave function decomposition with respect to the operator
eigenfunctions. It is the linearity and the Hermitian nature of the operators
which determine the trajectory and the superposition principle in case of the
wave behavior of fluctuations. The uncertainty principle, reflects correlation
of the fluctuations and, hence, their nonlocality. This study discusses the
wave function phase, the Berry phase and its relationship to quantization,
discriminability of states and macroscopic quantum effects caused by
localization of the particle, followed by a possible entropy change during its
transition into a new thermodynamic state. | 1206.2998v1 |
2012-08-08 | RMR-Efficient Randomized Abortable Mutual Exclusion | Recent research on mutual exclusion for shared-memory systems has focused on
"local spin" algorithms. Performance is measured using the "remote memory
references" (RMRs) metric. As common in recent literature, we consider a
standard asynchronous shared memory model with N processes, which allows atomic
read, write and compare-and-swap (short: CAS) operations.
In such a model, the asymptotically tight upper and lower bound on the number
of RMRs per passage through the Critical Section is Theta(log N) for the
optimal deterministic algorithms (see Yang and Anderson,1995, and Attiya,
Hendler and Woelfel, 2008). Recently, several randomized algorithms have been
devised that break the Omega(log N) barrier and need only o(log N) RMRs per
passage in expectation (see Hendler and Woelfel, 2010, Hendler and Woelfel,
2011, and Bender and Gilbert, 2011). In this paper we present the first
randomized "abortable" mutual exclusion algorithm that achieves a
sub-logarithmic expected RMR complexity. More precisely, against a weak
adversary (which can make scheduling decisions based on the entire past
history, but not the latest coin-flips of each process) every process needs an
expected number of O(log N/ log log N) RMRs to enter end exit the critical
section. If a process receives an abort-signal, it can abort an attempt to
enter the critical section within a finite number of its own steps and by
incurring O(log N/ log log N) RMRs. | 1208.1723v1 |
2012-08-16 | QIRAL: A High Level Language for Lattice QCD Code Generation | Quantum chromodynamics (QCD) is the theory of subnuclear physics, aiming at
mod- eling the strong nuclear force, which is responsible for the interactions
of nuclear particles. Lattice QCD (LQCD) is the corresponding discrete
formulation, widely used for simula- tions. The computational demand for the
LQCD is tremendous. It has played a role in the history of supercomputers, and
has also helped defining their future. Designing efficient LQCD codes that
scale well on large (probably hybrid) supercomputers requires to express many
levels of parallelism, and then to explore different algorithmic solutions.
While al- gorithmic exploration is the key for efficient parallel codes, the
process is hampered by the necessary coding effort. We present in this paper a
domain-specific language, QIRAL, for a high level expression of parallel
algorithms in LQCD. Parallelism is expressed through the mathematical struc-
ture of the sparse matrices defining the problem. We show that from these
expressions and from algorithmic and preconditioning formulations, a parallel
code can be automatically generated. This separates algorithms and mathematical
formulations for LQCD (that be- long to the field of physics) from the
effective orchestration of parallelism, mainly related to compilation and
optimization for parallel architectures. | 1208.4035v1 |
2012-08-22 | Entanglement Spectrum Classification of $C_n$-invariant Noninteracting Topological Insulators in Two Dimensions | We study the single particle entanglement spectrum in 2D topological
insulators which possess $n$-fold rotation symmetry. By defining a series of
special choices of subsystems on which the entanglement is calculated, or real
space cuts, we find that the number of protected in-gap states for each type of
these real space cuts is a quantum number indexing (if any) non-trivial
topology in these insulators. We explicitly show the number of protected in-gap
states is determined by a $Z^n$-index, $(z_1,...,z_n)$, where $z_m$ is the
number of occupied states that transform according to $m$-th one-dimensional
representation of the $C_n$ point group. We find that the entanglement spectrum
contains in-gap states pinned in an interval of entanglement eigenvalues
$[1/n,1-1/n]$. We determine the number of such in-gap states for an exhaustive
variety of cuts, in terms of the $Z_m$ quantum numbers. Furthermore, we show
that in a homogeneous system, the $Z^n$ index can be determined through an
evaluation of the eigenvalues of point group symmetry operators at all
high-symmetry points in the Brillouin zone. When disordered $n$-fold
rotationally symmetric systems are considered, we find that the number of
protected in-gap states is identical to that in the clean limit as long as the
disorder preserves the underlying point group symmetry and does not close the
bulk insulating gap. | 1208.4603v1 |
2012-09-25 | Multiscale modeling in micromagnetics: existence of solutions and numerical integration | Various applications ranging from spintronic devices, giant magnetoresistance
sensors, and magnetic storage devices, include magnetic parts on very different
length scales. Since the consideration of the Landau-Lifshitz-Gilbert equation
(LLG) constrains the maximum element size to the exchange length within the
media, it is numerically not attractive to simulate macroscopic parts with this
approach. On the other hand, the magnetostatic Maxwell equations do not
constrain the element size, but cannot describe the short-range exchange
interaction accurately. A combination of both methods allows to describe
magnetic domains within the micromagnetic regime by use of LLG and also
considers the macroscopic parts by a non-linear material law using the Maxwell
equations. In our work, we prove that under certain assumptions on the
non-linear material law, this multiscale version of LLG admits weak solutions.
Our proof is constructive in the sense that we provide a linear-implicit
numerical integrator for the multiscale model such that the numerically
computable finite element solutions admit weak $H^1$-convergence (at least for
a subsequence) towards a weak solution. | 1209.5548v2 |
2012-10-05 | Rapid Size-Controlled Synthesis of Dextran-Coated, 64Cu-Doped Iron Oxide Nanoparticles | Research into developing dual modality probes enabled for magnetic resonance
imaging (MRI) and positron emission tomography (PET) has been on the rise
recently due to the potential to combine the high resolution of MRI and the
high sensitivity of PET. Current synthesis techniques for developing multimodal
probes is largely hindered in part by prolonged reaction times during
radioisotope incorporation - leading to a weakening of the radioactivity. Along
with a time-efficient synthesis, the resulting products must fit within a
critical size range (between 20-100nm) to increase blood retention time. In
this work, we describe a novel, rapid, microwave-based synthesis technique to
grow dextran-coated iron oxide nanoparticles doped with copper (DIO/Cu).
Traditional methods for coprecipitation of dextran-coated iron oxide
nanoparticles require refluxing for 2 hours and result in approximately 50 nm
diameter particles. We demonstrate that microwave synthesis can produce 50 nm
nanoparticles with 5 minutes of heating. We discuss the various parameters used
in the microwave synthesis protocol to vary the size distribution of DIO/Cu,
and demonstrate the successful incorporation of 64Cu into these particles with
the aim of future use for dual-mode MR/PET imaging. | 1210.1823v1 |
2012-10-05 | Rapid Microwave-Assisted Synthesis of Dextran-Coated Iron Oxide Nanoparticles for Magnetic Resonance Imaging | Currently, magnetic iron oxide nanoparticles are the only nano-sized magnetic
resonance imaging (MRI) contrast agents approved for clinical use, yet
commercial manufacturing of these agents has been limited or discontinued.
Though there is still widespread demand for these particles both for clinical
use and research, they are difficult to obtain commercially, and complicated
syntheses make in-house preparation infeasible for most biological research
labs or clinics. To make commercial production viable and increase
accessibility of these products, it is crucial to develop simple, rapid, and
reproducible preparations of biocompatible iron oxide nanoparticles. Here, we
report a rapid, straightforward microwave-assisted synthesis of
superparamagnetic dextran-coated iron oxide nanoparticles. The nanoparticles
were produced in two hydrodynamic sizes with differing core morphologies by
varying the synthetic method as either a two-step or single step process. A
striking benefit of these methods is the ability to obtain swift and consistent
results without the necessity for air, pH, or temperature sensitive techniques;
therefore, reaction times and complex manufacturing processes are greatly
reduced as compared to conventional synthetic methods. This is a great benefit
for cost-effective translation to commercial production. The nanoparticles are
found to be superparamagnetic and exhibit properties consistent for use in MRI.
In addition, the dextran coating imparts the water-solubility and
biocompatibility necessary for in vivo utilization. | 1210.1827v1 |
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