470 research outputs found
Recovering 3D structural properties of galaxies from SDSS-like photometry
Because of the 3D nature of galaxies, an algorithm for constructing spatial
density distribution models of galaxies on the basis of galaxy images has many
advantages over surface density distribution approximations. We present a
method for deriving spatial structure and overall parameters of galaxies from
images and estimate its accuracy and derived parameter degeneracies on a sample
of idealised model galaxies. The test galaxies consist of a disc-like component
and a spheroidal component with varying proportions and properties. Both
components are assumed to be axially symmetric and coplanar. We simulate these
test galaxies as if observed in the SDSS project through ugriz filters, thus
gaining a set of realistically imperfect images of galaxies with known
intrinsic properties. These artificial SDSS galaxies were thereafter remodelled
by approximating the surface brightness distribution with a 2D projection of a
bulge+disc spatial distribution model and the restored parameters were compared
to the initial ones. Down to the r-band limiting magnitude 18, errors of the
restored integral luminosities and colour indices remain within 0.05 mag and
errors of the luminosities of individual components within 0.2 mag. Accuracy of
the restored bulge-to-disc ratios (B/D) is within 40% in most cases, and
becomes worse for galaxies with low B/D, but the general balance between bulges
and discs is not shifted systematically. Assuming that the intrinsic disc axial
ratio is < 0.3, the inclination angles can be estimated with errors < 5deg for
most of the galaxies with B/D < 2 and with errors < 15deg up to B/D = 6. Errors
of the recovered sizes of the galactic components are below 10% in most cases.
In general, models of disc components are more accurate than models of
spheroidal components for geometrical reasons.Comment: 15 pages, 13 figures, accepted for publication in RA
Entanglement, elasticity and viscous relaxation of actin solutions
We have investigated the viscosity and the plateau modulus of actin solutions
with a magnetically driven rotating disc rheometer. For entangled solutions we
observed a scaling of the plateau modulus versus concentration with a power of
7/5. The measured terminal relaxation time increases with a power 3/2 as a
function of polymer length. We interpret the entanglement transition and the
scaling of the plateau modulus in terms of the tube model for semiflexible
polymers.Comment: 5 pages, 4 figures, published versio
Milky Way potentials in CDM and MOND. Is the Large Magellanic Cloud on a bound orbit?
We compute the Milky Way potential in different cold dark matter (CDM) based
models, and compare these with the modified Newtonian dynamics (MOND)
framework. We calculate the axis ratio of the potential in various models, and
find that isopotentials are less spherical in MOND than in CDM potentials. As
an application of these models, we predict the escape velocity as a function of
the position in the Galaxy. This could be useful in comparing with future data
from planned or already-underway kinematic surveys (RAVE, SDSS, SEGUE, SIM,
GAIA or the hypervelocity stars survey). In addition, the predicted escape
velocity is compared with the recently measured high proper motion velocity of
the Large Magellanic Cloud (LMC). To bind the LMC to the Galaxy in a MOND
model, while still being compatible with the RAVE-measured local escape speed
at the Sun's position, we show that an external field modulus of less than
is needed.Comment: Accepted for publication in MNRAS, 13 pages, 7 figures, 3 table
Pre- and Posttranslational Regulation of Β-Endorphin Biosynthesis in the CNS: Effects of Chronic Naltrexone Treatment
There appear to be two anatomically distinct Β-endorphin (ΒE) pathways in the brain, the major one originating in the arcuate nucleus of the hypothalamus and a smaller one in the area of the nucleus tractus solitarius (NTS) of the caudal medulla. Previous studies have shown that these two proopiomelanocortin (POMC) systems may be differentially regulated by chronic morphine treatment, with arcuate cells down-regulated and NTS cells unaffected. In the present experiments, we examined the effects of chronic opiate antagonist treatment on ΒE biosynthesis across different CNS regions to assess whether the arcuate POMC system would be regulated in the opposite direction to that seen after opiate agonist treatment and to determine whether different ΒE-containing areas might be differentially regulated. Male adult rats were administered naltrexone (NTX) by various routes for 8 days (subcutaneous pellets, osmotic minipumps, or repeated intraperitoneal injections). Brain and spinal cord regions were assayed for total ΒE-ir, different molecular weight immunoreactive Β-endorphin (ΒE-ir) peptides, and POMC mRNA. Chronic NTX treatment, regardless of the route of administration, reduced total ΒE-ir concentrations by 30–40% in diencephalic areas (the arcuate nucleus, the remaining hypothalamus, and the thalamus) and the midbrain, but had no effect on ΒE-ir in the NTS or any region of the spinal cord. At the same time, NTX pelleting increased POMC mRNA levels in the arcuate to ∼ 140% of control values. These data suggest that arcuate POMC neurons are up-regulated after chronic NTX treatment (whereas NTS and spinal cord systems remain unaffected) and that they appear to be under tonic inhibition by endogenous opioids. Chromatographic analyses demonstrated that, after chronic NTX pelleting, the ratio of full length ΒE 1–31 to more processed ΒE-ir peptides (i.e., ΒE 1–27 and ΒE 1–26 ) tended to increase in a dose-dependent manner in diencephalic areas. Because ΒE 1–31 is the only POMC product that possesses opioid agonist properties, and ΒE 1–27 has been posited to function as an endogenous anatgonist of ΒE 1–31 , the NTX-induced changes in the relative concentrations of ΒE 1–31 and ΒE 1–27 /ΒE 1–26 may represent a novel regulatory mechanism of POMC cells to alter the opioid signal in the synapse.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65603/1/j.1471-4159.1993.tb05820.x.pd
The ALHAMBRA survey : band luminosity function of quiescent and star-forming galaxies at by PDF analysis
Our goal is to study the evolution of the band luminosity function (LF)
since using ALHAMBRA data. We used the photometric redshift and the
band selection magnitude probability distribution functions (PDFs) of those
ALHAMBRA galaxies with mag to compute the posterior LF. We
statistically studied quiescent and star-forming galaxies using the template
information encoded in the PDFs. The LF covariance matrix in
redshift-magnitude-galaxy type space was computed, including the cosmic
variance. That was estimated from the intrinsic dispersion of the LF
measurements in the 48 ALHAMBRA sub-fields. The uncertainty due to the
photometric redshift prior is also included in our analysis. We modelled the LF
with a redshift-dependent Schechter function affected by the same selection
effects than the data. The measured ALHAMBRA LF at and the
evolving Schechter parameters both for quiescent and star-forming galaxies
agree with previous results in the literature. The estimated redshift evolution
of is and , and of is
and . The measured faint-end slopes are and . We find a significant
population of faint quiescent galaxies, modelled by a second Schechter function
with slope . We find a factor decrease in the
luminosity density of star-forming galaxies, and a factor
increase in the of quiescent ones since , confirming the continuous
build-up of the quiescent population with cosmic time. The contribution of the
faint quiescent population to increases from 3% at to 6% at .
The developed methodology will be applied to future multi-filter surveys such
as J-PAS.Comment: Accepted for publication in Astronomy and Astrophysics. 25 pages, 20
figures, 7 table
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The impact of national context effects on HRM practices in Russian subsidiaries of Western MNCs
This article contributes to the research on comparative human resource management by providing a model of the Russian business system and its effect on human resource management practices at Russian subsidiaries of Western multinational companies. Whitley’s approach was adopted to illustrate the links between institutional arenas, business systems, and human resource management practices. The empirical part is based on interviews with senior human resources managers of Western multinational companies operating in Russia. The findings provide insight into the interaction between the national business system and human resource management practices in Russia
The global field of multi-family offices: An institutionalist perspective
We apply the notion of the organisational field to internationally operating multi-family offices. These organisations specialise on the preservation of enterprising and geographically dispersed families’ fortunes. They provide their services across generations and countries. Based on secondary data of Bloomberg’s Top 50 Family Offices, we show that they constitute a global organisational field that comprises two clusters of homogeneity. Clients may decide between two different configurations of activities, depending on their preferences regarding asset management, resource management, family management, and service architecture. The findings also reveal that multi-family offices make relatively similar value propositions all over the world. The distinctiveness of the clusters within the field is not driven by the embeddedness of the multi-family offices in different national environments or their various degrees of international experience. Rather, it is weakly affected by two out of four possible value propositions, namely the exclusiveness and the transparency of services
The Schrdinger-Poisson equations as the large-N limit of the Newtonian N-body system: applications to the large scale dark matter dynamics
In this paper it is argued how the dynamics of the classical Newtonian N-body
system can be described in terms of the Schrdinger-Poisson equations
in the large limit. This result is based on the stochastic quantization
introduced by Nelson, and on the Calogero conjecture. According to the Calogero
conjecture, the emerging effective Planck constant is computed in terms of the
parameters of the N-body system as , where is the gravitational constant, and are the
number and the mass of the bodies, and is their average density. The
relevance of this result in the context of large scale structure formation is
discussed. In particular, this finding gives a further argument in support of
the validity of the Schrdinger method as numerical double of the
N-body simulations of dark matter dynamics at large cosmological scales.Comment: Accepted for publication in the Euro. Phys. J.
Interplay between Fermi gamma-ray lines and collider searches
We explore the interplay between lines in the gamma-ray spectrum and LHC searches involving missing energy and photons. As an example, we consider a singlet Dirac
fermion dark matter with the mediator for Fermi gamma-ray line at 130 GeV. A new chiral or local U(1) symmetry makes weak-scale dark matter natural and provides the axion or
Z 0 gauge boson as the mediator connecting between dark matter and electroweak gauge bosons. In these models, the mediator particle can be produced in association with a
monophoton at colliders and it produces large missing energy through the decays into a DM pair or ZZ; Z with at least one Z decaying into a neutrino pair. We adopt the monophoton searches with large missing energy at the LHC and impose the bounds on the coupling and mass of the mediator field in the models. We show that the parameter space of the Z 0 mediation model is already strongly constrained by the LHC 8TeV data, whereas a certain region of the parameter space away from the resonance in axion-like mediator models are bounded. We foresee the monophoton bounds on the Z 0 and axion mediation models at the LHC 14 TeV
p-type delta-doped layers in silicon: structural and electronic properties
We report on the properties of p-type delta-doped layers prepared in molecular beam epitaxy-Si by growth interruption and evaporation of elemental B. Secondary-ion mass spectrometry measurements at several primary ion energies have been used to show that the full width at half maximum is ~2 nm. Hall measurements confirm that the layers are completely activated at 300 K with a mobility of 30±5 cm2/V s for a carrier density of (9±2)×1012 cm−2. At temperatures below 70 K nonmetallic behavior is observed which we have attributed to conduction between impurity states. It is concluded that the critical acceptor separation for the Mott metal-insulator transition in this system is significantly less than the value found in uniformly doped Si:B
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