597 research outputs found
Towards Closing the Window on Strongly Interacting Dark Matter: Far-Reaching Constraints from Earth's Heat Flow
We point out a new and largely model-independent constraint on the dark
matter scattering cross section with nucleons, applying when this quantity is
larger than for typical weakly interacting dark matter candidates. When the
dark matter capture rate in Earth is efficient, the rate of energy deposition
by dark matter self-annihilation products would grossly exceed the measured
heat flow of Earth. This improves the spin-independent cross section
constraints by many orders of magnitude, and closes the window between
astrophysical constraints (at very large cross sections) and underground
detector constraints (at small cross sections). In the applicable mass range,
from about 1 to about 10^{10} GeV, the scattering cross section of dark matter
with nucleons is then bounded from above by the latter constraints, and hence
must be truly weak, as usually assumed.Comment: 12 pages, 2 figures; minor updates to match published versio
Statistics of Magnification Perturbations by Substructure in the Cold Dark Matter Cosmological Model
We study the statistical properties of magnification perturbations by
substructures in strong lensed systems using linear perturbation theory and an
analytical substructure model including tidal truncation and a continuous
substructure mass spectrum. We demonstrate that magnification perturbations are
dominated by perturbers found within a tidal radius of an image, and that
sizable magnification perturbations may arise from small, coherent
contributions from several substructures within the lens halo. We find that the
root-mean-square (rms) fluctuation of the magnification perturbation is 10% to
20% and both the average and rms perturbations are sensitive to the mass
spectrum and density profile of the perturbers. Interestingly, we find that
relative to a smooth model of the same mass, the average magnification in
clumpy models is lower (higher) than that in smooth models for positive
(negative) parity images. This is opposite from what is observed if one assumes
that the image magnification predicted by the best-fit smooth model of a lens
is a good proxy for what the observed magnification would have been if
substructures were absent. While it is possible for this discrepancy to be
resolved via nonlinear perturbers, we argue that a more likely explanation is
that the assumption that the best-fit lens model is a good proxy for the
magnification in the absence of substructure is not correct. We conclude that a
better theoretical understanding of the predicted statistical properties of
magnification perturbations by CDM substructure is needed in order to affirm
that CDM substructures have been unambiguously detected.Comment: ApJ accepted, minor change
Critical Dynamics of Burst Instabilities in the Portevin-Le Chatelier Effect
We investigate the Portevin-Le Chatelier effect (PLC), by compressing Al-Mg
alloys in a very large deformation range, and interpret the results from the
viewpoint of phase transitions and critical phenomena. The system undergoes two
dynamical phase transitions between intermittent (or "jerky") and "laminar"
plastic dynamic phases. Near these two dynamic critical points, the order
parameter 1/\tau of the PLC effect exhibits large fluctuations, and "critical
slowing down" (i.e., the number of bursts, or plastic instabilities, per
unit time slows down considerably).Comment: the published 4-page version is in the PRL web sit
DNA polymerase alpha inhibition by aphidicolin and fragile site expression in prometaphase chromosomes of the Italian Mediterranean River Buffalo (Bubalus bubalis, 2n=50)
The present study reports on the expression and localization of "fragile sites" (FS) on prometaphase chromosomes of two groups of river buffaloes (Bubalus bubalis, 2n=50; Mediterranean Italian breed), reared in two different farms, with the aim to characterize chromosome fragility in this species. Totally, 400 aphidicolin induced breakages were identified and localized on the standardized ideogram of the river buffalo karyotype. Preliminary results can be synthesized as follows: (a) aphidicolin showed a remarkable decondensing effect on chromosome structure, enabling further studies at high resolution level; (b) the chromosomal expression of the breakages was not different in the two groups of animals; (c) the most fragile chromosomes were the inactive-X, chromosomes 9, 8 and active-X, showing 42, 32, 31 and 30 breakages, respectively; (d) the breaks were localized in the RBG-negative bands (corresponding to eterochromatic regions) or at the band-interband regions; (e) the chromosomal distribution of the break sites was not random and only partially related to chromosome length. The study is in progress to determine the relative incidence of the fragile sites at chromosomal band level, in order to construct a 'fragile-site map' of river buffalo, which could be utilized for genetic improvement programs of the species
Prokineticin 2 upregulation in the peripheral nervous system has a major role in triggering and maintaining neuropathic pain in the chronic constriction injury model
The new chemokine Prokineticin 2 (PROK2) and its receptors (PKR1 and PKR2) have a role in inflammatory pain and
immunomodulation. Here we identified PROK2 as a critical mediator of neuropathic pain in the chronic constriction injury (CCI)
of the sciatic nerve in mice and demonstrated that blocking the prokineticin receptors with two PKR1-preferring antagonists (PC1
and PC7) reduces pain and nerve damage. PROK2 mRNA expression was upregulated in the injured nerve since day 3 post injury
(dpi) and in the ipsilateral DRG since 6 dpi. PROK2 protein overexpression was evident in Schwann Cells, infiltrating macrophages
and axons in the peripheral nerve and in the neuronal bodies and some satellite cells in the DRG. Therapeutic treatment of
neuropathic mice with the PKR-antagonist, PC1, impaired the PROK2 upregulation and signalling. This fact, besides alleviating
pain, brought down the burden of proinflammatory cytokines in the damaged nerve and prompted an anti-inflammatory repair
program. Such a treatment also reduced intraneural oedema and axon degeneration as demonstrated by the physiological skin
innervation and thickness conserved in CCI-PC1 mice. These findings suggest that PROK2 plays a crucial role in neuropathic pain
and might represent a novel target of treatment for this disease
Formation of molecular hydrogen on analogues of interstellar dust grains: experiments and modelling
Molecular hydrogen has an important role in the early stages of star
formation as well as in the production of many other molecules that have been
detected in the interstellar medium. In this review we show that it is now
possible to study the formation of molecular hydrogen in simulated
astrophysical environments. Since the formation of molecular hydrogen is
believed to take place on dust grains, we show that surface science techniques
such as thermal desorption and time-of-flight can be used to measure the
recombination efficiency, the kinetics of reaction and the dynamics of
desorption. The analysis of the experimental results using rate equations gives
useful insight on the mechanisms of reaction and yields values of parameters
that are used in theoretical models of interstellar cloud chemistry.Comment: 23 pages, 7 figs. Published in the J. Phys.: Conf. Se
Evidence for dark matter in the inner Milky Way
The ubiquitous presence of dark matter in the universe is today a central
tenet in modern cosmology and astrophysics. Ranging from the smallest galaxies
to the observable universe, the evidence for dark matter is compelling in
dwarfs, spiral galaxies, galaxy clusters as well as at cosmological scales.
However, it has been historically difficult to pin down the dark matter
contribution to the total mass density in the Milky Way, particularly in the
innermost regions of the Galaxy and in the solar neighbourhood. Here we present
an up-to-date compilation of Milky Way rotation curve measurements, and compare
it with state-of-the-art baryonic mass distribution models. We show that
current data strongly disfavour baryons as the sole contribution to the
galactic mass budget, even inside the solar circle. Our findings demonstrate
the existence of dark matter in the inner Galaxy while making no assumptions on
its distribution. We anticipate that this result will compel new
model-independent constraints on the dark matter local density and profile,
thus reducing uncertainties on direct and indirect dark matter searches, and
will shed new light on the structure and evolution of the Galaxy.Comment: First submitted version of letter published in Nature Physics on
Febuary 9, 2015:
http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3237.htm
Scaling of Island Growth in Pb Overlayers on Cu(001)
The growth and ordering of a Pb layer deposited on Cu(001) at 150 K has been
studied using atom beam scattering. At low coverage, ordered Pb islands with a
large square unit cell and nearly hexagonal internal structure are formed. This
is a high order commensurate phase with 30 atoms in the unit cell. From the
measurement of the island diffraction peak profiles we find a power law for the
mean island - size versus coverage with an exponent . A
scaling behavior of growth is confirmed and a simple model describing island
growth is presented. Due to the high degeneracy of the monolayer phase,
different islands do not diffract coherently. Therefore, when islands merge
they still diffract as separate islands and coalescence effects are thus
negligible. From the result for we conclude that the island density is
approximately a constant in the coverage range where the
ordered islands are observed. We thus conclude that most islands nucleate at
and then grow in an approximately self similar fashion as
increases.Comment: 23 pages, 10 Figures (available upon request). SU-PHYS-93-443-375
Dark Matter Candidates: A Ten-Point Test
An extraordinarily rich zoo of non-baryonic Dark Matter candidates has been
proposed over the last three decades. Here we present a 10-point test that a
new particle has to pass, in order to be considered a viable DM candidate: I.)
Does it match the appropriate relic density? II.) Is it {\it cold}? III.) Is it
neutral? IV.) Is it consistent with BBN? V.) Does it leave stellar evolution
unchanged? VI.) Is it compatible with constraints on self-interactions? VII.)
Is it consistent with {\it direct} DM searches? VIII.) Is it compatible with
gamma-ray constraints? IX.) Is it compatible with other astrophysical bounds?
X.) Can it be probed experimentally?Comment: 29 pages, 12 figure
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