211 research outputs found
Establishing the relationship between galaxies and dark matter
We use two methods to establish the relationship between galaxies and dark matter halos. One is based the conditional luminosity function model, which links galaxies and dark matter halos by matching the number density and clustering properties of galaxies with those of dark matter halos in the current CDM model. The second is based on galaxy systems identified from large redshift surveys of galaxies. The galaxy - dark halo relationships established by these two methods match well, and can provide important constraints on how galaxies form and evolve in the univers
Reciprocity of Knowledge Flows in Internal Network Forms of Organizing
Fundamental changes in the competitive landscape triggered many firms to leverage and build competencies by focusing on transition processes towards internal network forms of organizing. These forms ameliorate exploration through knowledge creation and transfer.
Internal networks are characterized by horizontal knowledge flows that supplement and
supplant the vertical knowledge flows that characterize other organization forms like the
functional and multi-divisional forms. As these horizontal knowledge flows facilitate
knowledge integration, internal networks have an advantage over other organization forms in
leveraging and building competencies. One characteristic that makes these horizontal
knowledge flows work is the reciprocity ensuing them. Reciprocity relates to the
interdependence and coordination modes that characterize internal networks. As reciprocity is
influenced by managerial coordination, by the intention to deploy knowledge, and by goal
attainment, creating and maintaining reciprocity of knowledge flows can be considered as a managerial competence.
In this paper, the attributes of organization form that impact the reciprocity in a firm are explored from structural, managerial and knowledge perspectives. Hypotheses are developed which suggest that specialization and the use of formal meetings restrict
reciprocity, whereas job rotation, the number of employees with a coordination function, and
teams have a positive effect on the level of reciprocity. These hypotheses are tested by means
of a questionnaire administered in a business unit of a multinational financial services firm.
Reciprocity of knowledge flows was found to be dependent on the characteristics mentioned above in a predicted way. Since none of the hypotheses needed to be rejected, the evidence suggests that reciprocity is a fundamental feature of internal networks and the horizontal knowledge flows that characterize them. This suggests reciprocity to be an important managerial competence
Hypoactivation of CRF receptors, predominantly type 2, in the medial-posterior BNST is vital for adequate maternal behavior in lactating rats
Maternal behavior ensures the proper development of the offspring. In lactating mammals, maternal behavior is impaired by stress, the physiological consequence of central corticotropin-releasing factor receptor (CRF-R) activation. However, which CRF-R subtype in which specific brain area(s) mediates this effect is unknown. Here we confirmed that an intracerebroventricularly injected nonselective CRF-R antagonist enhances, whereas an agonist impairs, maternal care. The agonist also prolonged the stress-induced decrease in nursing, reduced maternal aggression and increased anxiety-related behavior. Focusing on the bed nucleus of the stria terminalis (BNST), CRF-R1 and CRF-R2 mRNA expression did not differ in virgin versus lactating rats. However, CRF-R2 mRNA was more abundant in the posterior than in the medial BNST. Pharmacological manipulations within the medial-posterior BNST showed that both CRF-R1 and CRF-R2 agonists reduced arched back nursing (ABN) rapidly and after a delay, respectively. After stress, both antagonists prevented the stress-induced decrease in nursing, with the CRF-R2 antagonist actually increasing ABN. During the maternal defense test, maternal aggression was abolished by the CRF-R2, but not the CRF-R1, agonist. Anxiety-related behavior was increased by the CRF-R1 agonist and reduced by both antagonists. Both antagonists were also effective in virgin females but not in males, revealing a sexual dimorphism in the regulation of anxiety within the medial-posterior BNST. In conclusion, the detrimental effects of increased CRF-R activation on maternal behavior are mediated via CRF-R2 and, to a lesser extent, via CRF-R1 in the medial-posterior BNST in lactating rats. Moreover, both CRF-R1 and CRF-R2 regulate anxiety in females independently of their reproductive status
Alignment of galaxy spins in the vicinity of voids
We provide limits on the alignment of galaxy orientations with the direction
to the void center for galaxies lying near the edges of voids. We locate
spherical voids in volume limited samples of galaxies from the Sloan Digital
Sky Survey using the HB inspired void finder and investigate the orientation of
(color selected) spiral galaxies that are nearly edge-on or face-on. In
contrast with previous literature, we find no statistical evidence for
departure from random orientations. Expressed in terms of the parameter c,
introduced by Lee & Pen to describe the strength of such an alignment, we find
that c<0.11(0.13) at 95% (99.7%) confidence limit within a context of a toy
model that assumes a perfectly spherical voids with sharp boundaries.Comment: 8 pages, 4 figures; v2 discussion expanded, references fixed, matches
version accepted by JCA
Heparan sulfate facilitates Rift Valley fever virus entry into the cell
Rift Valley fever virus (RVFV), an emerging arthropod-borne pathogen, has a broad host and cell tropism. Here we report that the glycosaminoglycan heparan sulfate, abundantly present on the surface of most animal cells, is required for efficient entry of RVFV. Entry was significantly reduced by preincubating the virus inoculum with highly-sulfated heparin, by enzymatic removal of heparan sulfate from cells and in cells genetically deficient in heparan sulfate synthesis
Understanding Galaxy Formation and Evolution
The old dream of integrating into one the study of micro and macrocosmos is
now a reality. Cosmology, astrophysics, and particle physics intersect in a
scenario (but still not a theory) of cosmic structure formation and evolution
called Lambda Cold Dark Matter (LCDM) model. This scenario emerged mainly to
explain the origin of galaxies. In these lecture notes, I first present a
review of the main galaxy properties, highlighting the questions that any
theory of galaxy formation should explain. Then, the cosmological framework and
the main aspects of primordial perturbation generation and evolution are
pedagogically detached. Next, I focus on the ``dark side'' of galaxy formation,
presenting a review on LCDM halo assembling and properties, and on the main
candidates for non-baryonic dark matter. It is shown how the nature of
elemental particles can influence on the features of galaxies and their
systems. Finally, the complex processes of baryon dissipation inside the
non-linearly evolving CDM halos, formation of disks and spheroids, and
transformation of gas into stars are briefly described, remarking on the
possibility of a few driving factors and parameters able to explain the main
body of galaxy properties. A summary and a discussion of some of the issues and
open problems of the LCDM paradigm are given in the final part of these notes.Comment: 50 pages, 10 low-resolution figures (for normal-resolution, DOWNLOAD
THE PAPER (PDF, 1.9 Mb) FROM http://www.astroscu.unam.mx/~avila/avila.pdf).
Lectures given at the IV Mexican School of Astrophysics, July 18-25, 2005
(submitted to the Editors on March 15, 2006
Nelfinavir, efavirenz, or both after the failure of nucleoside treatment of HIV infection
Background. The optimal antiretroviral treatment for patients who have human immunodeficiency virus (HIV) viremia despite treatment with nucleoside reverse-transcriptase inhibitors (nucleoside analogues) remains uncertain. We studied treatment with regimens that combined two nucleoside analogues, at least one of which was new, with the protease inhibitor nelfinavir, the nonnucleoside reverse-transcriptase inhibitor efavirenz, or both. Methods. The study included 195 patients who had been treated with nucleoside analogues only, and had a plasma HIV type 1 (HIV-1) RNA level of at least 500 copies per milliliter. Patients were randomly assigned to receive, in addition to two nucleoside analogues, nelfinavir, efavirenz, or nelfinavir plus efavirenz. The primary end point was a plasma HIV-1 RNA level of less than 500 copies per milliliter at week 16. A secondary end point was the composite of the HIV-1 RNA levels measured at weeks 40 and 48. Results. At week 16 and at weeks 40 and 48, the proportions of patients in whom a plasma HIV-1 RNA level of less than 500 copies per milliliter was achieved were, respectively, 81 percent and 74 percent in the nelfinavir-plus-efavirenz group, 69 percent and 60 percent in the efavirenz group, and 64 percent and 35 percent in the nelfinavir group. Quadruple therapy resulted in a higher rate of viral suppression in both the short term (P=0.03) and the long term (P=0.001) than did triple therapy with nelfinavir. Triple therapy with efavirenz conferred a higher rate of long-term suppression than triple therapy with nelfinavir (P= 0.004). Quadruple therapy also achieved a higher rate of virologic suppression than triple therapy with efavirenz (P=0.008). Conclusions. In HIV-infected patients previously treated with nucleoside analogues, treatment with nelfinavir plus efavirenz and at least one new nucleoside analogue achieves a higher rate of viral suppression than do regimens with nucleoside analogues and nelfinavir or efavirenz alone
The evolution of galaxy groups and of galaxies therein
Properties of groups of galaxies depend sensitively on the algorithm for
group selection, and even the most recent catalogs of groups built from
redshift-space selection should suffer from projections and infalling galaxies.
The cosmo-dynamical evolution of groups from initial Hubble expansion to
collapse and virialization leads to a fundamental track (FT) in
virial-theorem-M/L vs crossing time. The increased rates of mergers, both
direct and after dynamical friction, in groups relative to clusters, explain
the higher fraction of elliptical galaxies at given local number density in
X-ray selected groups, relative to clusters, even when the hierarchical
evolution of groups is considered. Galaxies falling into groups and clusters
should later travel outwards to typically 2 virial radii, which is somewhat
less than the outermost radius where observed galaxy star formation
efficiencies are enhanced relative to field galaxies of same morphological
type. An ongoing analysis of the internal kinematics of X-ray selected groups
suggests that the radial profiles of line of sight velocity dispersion are
consistent with isotropic NFW distributions for the total mass density, with
higher (lower) concentrations than LambdaCDM predictions in groups of high
(low) mass. The critical mass, at M200 ~ 10^13 M_sun is consistent with
possible breaks in the X-ray luminosity-temperature and Fundamental Plane
relations. The internal kinematics of groups indicate that the M-T relation of
groups should agree with that extrapolated from clusters with no break at the
group scale. The analyses of observed velocity dispersion profiles and of the
FT both suggest that low velocity dispersion groups (compact and loose, X-ray
emitting or undetected) are quite contaminated by chance projections.Comment: Invited review, ESO workshop "Groups of Galaxies in the Nearby
Universe", held in Santiago, Chile, 5-9 December 2005, ed. I. Saviane, V.
Ivanov & J. Borissova, 16 page
Indirect search for dark matter: prospects for GLAST
Possible indirect detection of neutralino, through its gamma-ray annihilation
product, by the forthcoming GLAST satellite from our galactic halo, M31, M87
and the dwarf galaxies Draco and Sagittarius is studied. Gamma-ray fluxes are
evaluated for the two representative energy thresholds, 0.1 GeV and 1.0 GeV, at
which the spatial resolution of GLAST varies considerably. Apart from dwarfs
which are described either by a modified Plummer profile or by a
tidally-truncated King profiles, fluxes are compared for halos with central
cusps and cores. It is demonstrated that substructures, irrespective of their
profiles, enhance the gamma-ray emission only marginally. The expected
gamma-ray intensity above 1 GeV at high galactic latitudes is consistent with
the residual emission derived from EGRET data if the density profile has a
central core and the neutralino mass is less than 50 GeV, whereas for a central
cusp only a substantial enhancement would explain the observations. From M31,
the flux can be detected above 0.1 GeV and 1.0 GeV by GLAST only if the
neutralino mass is below 300 GeV and if the density profile has a central cusp,
case in which a significant boost in the gamma-ray emission is produced by the
central black hole. For Sagittarius, the flux above 0.1 GeV is detectable by
GLAST provided the neutralino mass is below 50 GeV. From M87 and Draco the
fluxes are always below the sensitivity limit of GLAST.Comment: 14 Pages, 7 Figures, 3 Tables, version to appear on Physical Review
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