3,199 research outputs found
Dynamical friction and the evolution of satellites in virialized halos: the theory of linear response
The evolution of a small satellite inside a more massive truncated isothermal
spherical halo is studied using both the Theory of Linear Response for
dynamical friction and N-Body simulations. The analytical approach includes the
effects of the gravitational wake, of the tidal deformation and the shift of
the barycenter of the primary, so unifying the local versus global
interpretation of dynamical friction. Sizes, masses, orbital energies and
eccentricities are chosen as expected in hierarchical clustering models. We
find that in general the drag force in self-gravitating backgrounds is weaker
than in uniform media and that the orbital decay is not accompanied by a
significant circularization. We also show that the dynamical friction time
scale is weakly dependent on the initial circularity. We provide a fitting
formula for the decay time that includes the effect of mass and angular
momentum loss. Live satellites with dense cores can survive disruption up to an
Hubble time within the primary, notwithstanding the initial choice of orbital
parameters. Dwarf spheroidal satellites of the Milky Way, like Sagittarius A
and Fornax, have already suffered mass stripping and, with their present
masses, the sinking times exceed 10 Gyr even if they are on very eccentric
orbits.Comment: 27 pages including 9 figures. Accepted for publication in the
Astrophysical Journal. Part 2, issue November 10 1999, Volume 52
Identifying the quark content of the isoscalar scalar mesons f_0(980), f_0(1370), and f_0(1500) from weak and electromagnetic processes
The assignments of the isoscalar scalar mesons f0(980), f0(1370), and
f0(1500) in terms of their qqbar substructure is still a matter of heated
dispute. Here we employ the weak and electromagnetic decays D(s)(+) to f0+pi(+)
and f0 two-photon decays, respectively, to identify the f0(980) and f0(1500) as
mostly ssbar, and the f0(1370) as dominantly nonstrange, in agreement with
previous work. The two-photon decays can be satisfactorily described with quark
as well as with meson loops, though the latter ones provide a less
model-dependent and more quantitative description.Comment: v1, 15 pages, plain LaTeX, 1 eps figure. v2, 18 pages, plain LaTeX
(figure included). More discussion, especially on the f0(1370) and its
empirical two-photon widt
Spin dynamics in the optical cycle of single nitrogen-vacancy centres in diamond
We investigate spin-dependent decay and intersystem crossing in the optical
cycle of single negatively-charged nitrogen-vacancy (NV) centres in diamond. We
use spin control and pulsed optical excitation to extract both the
spin-resolved lifetimes of the excited states and the degree of
optically-induced spin polarization. By optically exciting the centre with a
series of picosecond pulses, we determine the spin-flip probabilities per
optical cycle, as well as the spin-dependent probability for intersystem
crossing. This information, together with the indepedently measured decay rate
of singlet population provides a full description of spin dynamics in the
optical cycle of NV centres. The temperature dependence of the singlet
population decay rate provides information on the number of singlet states
involved in the optical cycle.Comment: 11 pages, 5 figure
Muon identification for LHCb Run 3
Muon identification is of paramount importance for the physics programme of
LHCb. In the upgrade phase, starting from Run 3 of the LHC, the trigger of the
experiment will be solely based on software. The luminosity increase to
cms will require an improvement of the muon
identification criteria, aiming at performances equal or better than those of
Run 2, but in a much more challenging environment. In this paper, two new muon
identification algorithms developed in view of the LHCb upgrade are presented,
and their performance in terms of signal efficiency versus background reduction
is shown
Overexpression of wild-type human APP in mice causes cognitive déficits and pathological features unrelated to Abeta levels
Transgenic mice expressing mutant human amyloid precursor protein (APP) develop an age-dependent
amyloid pathology and memory deficits, but no overt neuronal loss. Here, in mice overexpressing wild-type
human APP (hAPPwt) we found an early memory impairment, particularly in the water maze and to a lesser
extent in the object recognition task, but β-amyloid peptide (Aβ42) was barely detectable in the
hippocampus. In these mice, hAPP processing was basically non-amyloidogenic, with high levels of APP
carboxy-terminal fragments, C83 and APP intracellular domain. A tau pathology with an early increase in the
levels of phosphorylated tau in the hippocampus, a likely consequence of enhanced ERK1/2 activation, was
also observed. Furthermore, these mice presented a loss of synapse-associated proteins: PSD95, AMPA and
NMDA receptor subunits and phosphorylated CaMKII. Importantly, signs of neurodegeneration were found in
the hippocampal CA1 subfield and in the entorhinal cortex that were associated to a marked loss of MAP2
immunoreactivity. Conversely, in mice expressing mutant hAPP, high levels of Aβ42 were found in the
hippocampus, but no signs of neurodegeneration were apparent. The results support the notion of Aβ-
independent pathogenic pathways in Alzheimer's disease
Recommendations of Neuroendocrinology Department from Brazilian Society of Endocrinology and Metabolism for diagnosis and treatment of acromegaly in Brazil
A acromegalia é uma doença associada à elevada morbidade e à redução da expectativa de vida. Em virtude do seu caráter insidioso e do seu não reconhecimento, o diagnóstico é frequentemente realizado com atraso, o que, associado às complicações relacionadas ao excesso do GH/IGF-I, determina elevada morbimortalidade. No entanto, um diagnóstico precoce e um tratamento efetivo minimizam a morbidade e normalizam a taxa de mortalidade. Nesta publicação, o objetivo do Departamento de Neuroendocrinologia da Sociedade Brasileira de Endocrinologia e Metabologia é divulgar quando suspeitar clinicamente da acromegalia e como diagnosticá-la. Além disso, discute-se a maneira mais eficaz e segura de realizar o tratamento da acromegalia, enfatizando que este deve ser realizado em centros de referência. Assim, com base em dados publicados em periódicos de nível científico reconhecido e na experiência dos autores, são apresentadas as recomendações para o diagnóstico e tratamento da doença.Acromegaly is a disease associated with increased morbidity and reduced life expectancy. Because of its insidious character and its non-recognition, the diagnosis is often made with delay, which, along with the complications related to GH/IGF-I excess, determines high morbidity and mortality. However, an early diagnosis and an effective treatment reduce the morbidity and normalize the mortality rate. In this publication, the goal of Neuroendocrinology Department from Brazilian Society of Endocrinology and Metabolism is to disclose which clinical set should arouse the suspicious of acromegaly and how to diagnose it. Furthermore, we discuss the most effective and safe approach to perform the treatment of acromegaly, emphasizing that it must be carried out in reference centers. Therefore, based on data published in journals with recognized scientific level and authors' experience, recommendations are presented for diagnosis and treatment of the disease
The Metamorphosis of Tidally Stirred Dwarf Galaxies
We present results from high-resolution N-Body/SPH simulations of
rotationally supported dwarf irregular galaxies moving on bound orbits in the
massive dark matter halo of the Milky Way.The dwarf models span a range in disk
surface density and the masses and sizes of their dark halos are consistent
with the predictions of cold dark matter cosmogonies. We show that the strong
tidal field of the Milky Way determines severe mass loss in their halos and
disks and induces bar and bending instabilities that transform low surface
brightness dwarfs (LSBs) into dwarf spheroidals (dSphs) and high surface
brightness dwarfs (HSBs) into dwarf ellipticals (dEs) in less than 10 Gyr. The
final central velocity dispersions of the remnants are in the range 8-30 km/s
and their final falls to values , matching well the
kinematics of early-type dwarfs. The transformation requires the orbital time
of the dwarf to be \simlt 3-4 Gyr, which implies a halo as massive and
extended as predicted by hierarchical models of galaxy formation to explain the
origin of even the farthest dSph satellites of the Milky Way, Leo I and Leo II.
Only dwarfs with central dark matter densities as high as those of Draco and
Ursa Minor can survive for 10 Gyr in the proximity of the Milky Way: this is
naturally achieved within hierarchical models, where the densest objects should
have small orbital times due to their early formation epochs. Part of the gas
is stripped and part is funneled to the center due to the bar, generating one
strong burst of star formation in HSBs and smaller, multiple bursts in LSBs.
Extended low-surface brightness stellar and gaseous streams originate from LSBs
and, when projected along the line of sight, can lead to overestimate the
mass-to-light ratio of the bound remnant by a factor \simlt 2,Comment: 29 pages, 34 figures, submitted to ApJ. Figures 5,11 and 32 are given
as separate GIF files. Other figures and the movies of the simulations can be
found at http://pcblu.mib.infn.it/~lucio/LG/LG.htm
Early Changes in Hippocampal Eph Receptors Precede the Onset of Memory Decline in Mouse Models of Alzheimer’s Disease
Abstract. Synapse loss occurs early in Alzheimer’s disease (AD) and is considered the best pathological correlate of cognitive
decline. Ephrins and Eph receptors are involved in regulation of excitatory neurotransmission and play a role in cytoskeleton
remodeling. We asked whether alterations in Eph receptors could underlie cognitive impairment in an AD mouse model
overexpressing human amyloid-β protein precursor (hAβPP) with familial mutations (hAβPPswe-ind mice). We found that
EphA4 and EphB2 receptors were reduced in the hippocampus before the development of impaired object recognition and spatial
memory. Similar results were obtained in another line of transgenic AβPP mice, Tg2576. A reduction in Eph receptor levels
was also found in postmortem hippocampal tissue from patients with incipient AD. At the time of onset of memory decline
in hAβPPswe-ind mice, no change in surface expression of AMPA or NMDA receptor subunits was apparent, but we found
changes in Eph-receptor downstream signaling, in particular a decrease in membrane-associated phospho-cofilin levels that may
cause cytoskeletal changes and disrupted synaptic activity. Consistent with this finding, Eph receptor activation in cell culture
increased phospho-cofilin levels. The results suggest that alterations in Eph receptors may play a role in synaptic dysfunction in
the hippocampus leading to cognitive impairment in a model of AD
Analyzing multitarget activity landscapes using protein-ligand interaction fingerprints: interaction cliffs.
This is the original submitted version, before peer review. The final peer-reviewed version is available from ACS at http://pubs.acs.org/doi/abs/10.1021/ci500721x.Activity landscape modeling is mostly a descriptive technique that allows rationalizing continuous and discontinuous SARs. Nevertheless, the interpretation of some landscape features, especially of activity cliffs, is not straightforward. As the nature of activity cliffs depends on the ligand and the target, information regarding both should be included in the analysis. A specific way to include this information is using protein-ligand interaction fingerprints (IFPs). In this paper we report the activity landscape modeling of 507 ligand-kinase complexes (from the KLIFS database) including IFP, which facilitates the analysis and interpretation of activity cliffs. Here we introduce the structure-activity-interaction similarity (SAIS) maps that incorporate information on ligand-target contact similarity. We also introduce the concept of interaction cliffs defined as ligand-target complexes with high structural and interaction similarity but have a large potency difference of the ligands. Moreover, the information retrieved regarding the specific interaction allowed the identification of activity cliff hot spots, which help to rationalize activity cliffs from the target point of view. In general, the information provided by IFPs provides a structure-based understanding of some activity landscape features. This paper shows examples of analyses that can be carried out when IFPs are added to the activity landscape model.M-L is very
grateful to CONACyT (No. 217442/312933) and the Cambridge Overseas Trust for funding. AB
thanks Unilever for funding and the European Research Council for a Starting Grant (ERC-2013-
StG-336159 MIXTURE). J.L.M-F. is grateful to the School of Chemistry, Department of
Pharmacy of the National Autonomous University of Mexico (UNAM) for support. This work
was supported by a scholarship from the Secretariat of Public Education and the Mexican
government
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