1,045 research outputs found
Temporal distortion of annual modulation at low recoil energies
We show that the main features of the annual modulation of the signal
expected in a WIMP direct detection experiment, i.e. its sinusoidal dependence
with time, the occurrence of its maxima and minima during the year and (under
some circumstances) even the one-year period, may be affected by relaxing the
isothermal sphere hypothesis in the description of the WIMP velocity phase
space. The most relevant effect is a distortion of the time-behaviour at low
recoil energies for anisotropic galactic halos. While some of these effects
turn out to be relevant at recoil energies below the current detector
thresholds, some others could already be measurable, although some degree of
tuning between the WIMP mass and the experimental parameters would be required.
Either the observation or non-observation of these effects could provide clues
on the phase space distribution of our galactic halo.Comment: 4 pages, 4 figures, typeset with ReVTeX4. The paper may also be found
at http://www.to.infn.it/~fornengo/papers/distortion.ps.g
Do current WIMP direct measurements constrain light relic neutralinos?
New upper bounds on direct detection rates have recently been presented by a
number of experimental collaborations working on searches for WIMPs. In this
paper we analyze how the constraints on relic neutralinos which can be derived
from these results is affected by the uncertainties in the distribution
function of WIMPs in the halo. Various different categories of velocity
distribution functions are considered, and the ensuing implications for
supersymmetric configurations derived. We conservatively conclude that current
experimental data do not constrain neutralinos of small mass (below 50 GeV).Comment: 9 pages, 7 figures, typeset with ReVTeX4. The paper may also be found
at http://www.to.infn.it/~fornengo/papers/constraints05.ps.gz or through
http://www.astroparticle.to.infn.it/index.htm
Effects of serum proteins on corrosion behavior of ISO 5832–9 alloy modified by titania coatings
Stainless steel ISO 5832–9 type is often used to
perform implants which operate in protein-containing physiological
environments. The interaction between proteins and
surface of the implant may affect its corrosive properties. The
aim of this work was to study the effect of selected serum
proteins (albumin and γ-globulins) on the corrosion of ISO
5832–9 alloy (trade name M30NW) which surface was modified
by titania coatings. These coatings were obtained by sol–
gel method and heated at temperatures of 400 and 800 °C. To
evaluate the effect of the proteins, the corrosion tests were
performed with and without the addition of proteins with
concentration of 1 g L−1 to the physiological saline solution
(0.9 % NaCl, pH 7.4) at 37 °C. The tests were carried out
within 7 days. The following electrochemical methods were
used: open circuit potential, linear polarization resistance, and
electrochemical impedance spectroscopy. In addition, surface
analysis by optical microscopy and X-ray photoelectron spectroscopy
(XPS) method was done at the end of weekly corrosion
tests. The results of corrosion tests showed that M30NW
alloy both uncoated and modified with titania coatings exhibits
a very good corrosion resistance during weekly exposition
to corrosion medium. The best corrosion resistance in
0.9 % NaCl solution is shown by alloy samples modified by
titania coating annealed at 400 °C. The serumproteins have no
significant effect onto corrosion of investigated biomedical
steel. The XPS results confirmed the presence of proteins on
the alloy surface after 7 days of immersion in proteincontaining
solutions.The investigations were supported by the National Science Centre project No. N N507 501339. The authors gratefully acknowledge Dr. Janusz
Sobczak and Dr. hab. Wojciech Lisowski from Institute of Physical
Chemistry of PAS for XPS surface analyses
DECam integration tests on telescope simulator
The Dark Energy Survey (DES) is a next generation optical survey aimed at
measuring the expansion history of the universe using four probes: weak
gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and
Type Ia supernovae. To perform the survey, the DES Collaboration is building
the Dark Energy Camera (DECam), a 3 square degree, 570 Megapixel CCD camera
which will be mounted at the Blanco 4-meter telescope at the Cerro Tololo
Inter- American Observatory. DES will survey 5000 square degrees of the
southern galactic cap in 5 filters (g, r, i, z, Y). DECam will be comprised of
74 250 micron thick fully depleted CCDs: 62 2k x 4k CCDs for imaging and 12 2k
x 2k CCDs for guiding and focus. Construction of DECam is nearing completion.
In order to verify that the camera meets technical specifications for DES and
to reduce the time required to commission the instrument, we have constructed a
full sized telescope simulator and performed full system testing and
integration prior to shipping. To complete this comprehensive test phase we
have simulated a DES observing run in which we have collected 4 nights worth of
data. We report on the results of these unique tests performed for the DECam
and its impact on the experiments progress.Comment: Proceedings of the 2nd International Conference on Technology and
Instrumentation in Particle Physics (TIPP 2011). To appear in Physics
Procedia. 8 pages, 3 figure
Chaotic Motion Around Prolate Deformed Bodies
The motion of particles in the field of forces associated to an axially
symmetric attraction center modeled by a monopolar term plus a prolate
quadrupole deformation is studied using Poincare surface of sections and
Lyapunov characteristic numbers. We find chaotic motion for certain values of
the parameters, and that the instability of the orbits increases when the
quadrupole parameter increases. A general relativistic analogue is briefly
discussed.Comment: RevTEX, 7 eps figures, To appear in Phys Rev E (March 2001
Crystal Structure of the C-type Lectin-like Domain from the Human Hematopoietic Cell Receptor CD69
CD69, one of the earliest specific antigens acquired during lymphoid activation, acts as a signal-transducing receptor involved in cellular activation events, including proliferation and induction of specific genes. CD69 belongs to a family of receptors that modulate the immune response and whose genes are clustered in the natural killer (NK) gene complex. The extracellular portion of these receptors represent a subfamily of C-type lectin-like domains (CTLDs), which are divergent from true C-type lectins and are referred to as NK-cell domains (NKDs). We have determined the three-dimensional structure of human CD69 NKD in two different crystal forms. CD69 NKD adopts the canonical CTLD fold but lacks the features involved in Ca(2+) and carbohydrate binding by C-type lectins. CD69 NKD dimerizes noncovalently, both in solution and in crystalline state. The dimer interface consists of a hydrophobic, loosely packed core, surrounded by polar interactions, including an interdomain beta sheet. The intersubunit core shows certain structural plasticity that may facilitate conformational rearrangements for binding to ligands. The surface equivalent to the binding site of other members of the CTLD superfamily reveals a hydrophobic patch surrounded by conserved charged residues that probably constitutes the CD69 ligand-binding site.Fil: Llera, Andrea Sabina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Viedma, Fernando. Universidad Autónoma de Madrid; EspañaFil: Sánchez Madrid, Francisco. Universidad Autónoma de Madrid; EspañaFil: Tormo, José. Universidad Autónoma de Madrid; Españ
Theoretical Directional and Modulated Rates for Direct SUSY Dark Matter Detection
Exotic dark matter together with the vacuum energy (cosmological constant)
seem to dominate in the flat Universe. Thus direct dark matter detection is
central to particle physics and cosmology. Supersymmetry provides a natural
dark matter candidate, the lightest supersymmetric particle (LSP). Furthermore
from the knowledge of the density and velocity distribution of the LSP, the
quark substructure of the nucleon and the nuclear structure (form factor and/or
spin response function), one is able to evaluate the event rate for LSP-nucleus
elastic scattering. The thus obtained event rates are, however, very low. So it
is imperative to exploit the two signatures of the reaction, namely the
modulation effect, i.e. the dependence of the event rate on the Earth's motion,
and the directional asymmetry, i.e. the dependence of the rate on the the
relative angle between the direction of the recoiling nucleus and the sun's
velocity. These two signatures are studied in this paper employing various
velocity distributions and a supersymmetric model with universal boundary
conditions at large tan(beta).Comment: 11 LATEX pages, 1 table and 4 ps figures included. Paper presented in
DARK2002, Fourth Heidelberg International Conference on Dark Matter in Astro-
and Particle Physics, Cape Town, South Africa, 4-9 February, 2002, to appear
in the proceedings (to be published by Springer Verlag
Mechanisms of the Vertical Secular Heating of a Stellar Disk
We investigate the nonlinear growth stages of bending instability in stellar
disks with exponential radial density profiles.We found that the unstable modes
are global (the wavelengths are larger than the disk scale lengths) and that
the instability saturation level is much higher than that following from a
linear criterion. The instability saturation time scales are of the order of
one billion years or more. For this reason, the bending instability can play an
important role in the secular heating of a stellar disk in the direction.
In an extensive series of numerical -body simulations with a high spatial
resolution, we were able to scan in detail the space of key parameters (the
initial disk thickness , the Toomre parameter , and the ratio of dark
halo mass to disk mass ). We revealed three distinct
mechanisms of disk heating in the direction: bending instability of the
entire disk, bending instability of the bar, and heating on vertical
inhomogeneities in the distribution of stellar matter.Comment: 22 pages including 8 figures. To be published in Astronomy Letters
(v.29, 2003
Dark matter and Colliders searches in the MSSM
We study the complementarity between dark matter experiments (direct
detection and indirect detections) and accelerator facilities (the CERN LHC and
a TeV Linear Collider) in the framework of the
constrained Minimal Supersymmetric Standard Model (MSSM). We show how
non--universality in the scalar and gaugino sectors can affect the experimental
prospects to discover the supersymmetric particles. The future experiments will
cover a large part of the parameter space of the MSSM favored by WMAP
constraint on the relic density, but there still exist some regions beyond
reach for some extreme (fine tuned) values of the supersymmetric parameters.
Whereas the Focus Point region characterized by heavy scalars will be easily
probed by experiments searching for dark matter, the regions with heavy
gauginos and light sfermions will be accessible more easily by collider
experiments. More informations on both supersymmetry and astrophysics
parameters can be thus obtained by correlating the different signals.Comment: 25 pages, 10 figures, corrected typos and reference adde
8th Annual Seminar on Legal Issues for Financial Institutions
Outline of speakers\u27 presentations from the 8th Annual Seminar on Legal Issues for Financial Institutions held by UK/CLE on March 11-12, 1988
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