119 research outputs found
Density Profile Asymptotes at the Centre of Dark Matter Halos
For the spherical symmetric case, all quantities describing the relaxed dark
matter halo can be expressed as functions of the gravitational potential
. Decomposing the radial velocity dispersion with respect to
at very large and very small radial distances the possible asymptotic
behavior for the density and velocity profiles can be obtained. If reasonable
boundary conditions are posed such as a finite halo mass and force-free halo
centre the asymptotic density profiles at the centre should be much less steep
than the profiles obtained within numerical simulations. In particular cases
profiles like Plummer's model are obtained. The reasons of that seeming
discrepancy with respect to the results of N-body simulations are discussed.Comment: Accepted for publication in Astronomy & Astrophysics, LaTeX, 7 pages,
2 figure
High Energy Neutrino Astronomy: Towards Kilometer-Scale Detectors
Of all high-energy particles, only neutrinos can directly convey astronomical
information from the edge of the universe---and from deep inside the most
cataclysmic high-energy processes. Copiously produced in high-energy
collisions, travelling at the velocity of light, and not deflected by magnetic
fields, neutrinos meet the basic requirements for astronomy. Their unique
advantage arises from a fundamental property: they are affected only by the
weakest of nature's forces (but for gravity) and are therefore essentially
unabsorbed as they travel cosmological distances between their origin and us.
Many of the outstanding mysteries of astrophysics may be hidden from our sight
at all wavelengths of the electromagnetic spectrum because of absorption by
matter and radiation between us and the source. For example, the hot dense
regions that form the central engines of stars and galaxies are opaque to
photons. In other cases, such as supernova remnants, gamma ray bursters, and
active galaxies, all of which may involve compact objects or black holes at
their cores, the precise origin of the high-energy photons emerging from their
surface regions is uncertain. Therefore, data obtained through a variety of
observational windows---and especially through direct observations with
neutrinos---may be of cardinal importance. In this talk, the scientific goals
of high energy neutrino astronomy and the technical aspects of water and ice
Cherenkov detectors are examined, and future experimental possibilities,
including a kilometer-square deep ice neutrino telescope, are explored.Comment: 13 pages, Latex, 6 postscript figures, uses aipproc.sty and epsf.sty.
Talk presented at the International Symposium on High Energy Gamma Ray
Astronomy, Heidelberg, June 200
Cardiogenesis with a focus on vasculogenesis and angiogenesis
The initial intraembryonic vasculogenesis occurs in the cardiogenic mesoderm. Here, a cell population of proendocardial cells detaches from the mesoderm that subsequently generates the single endocardial tube by forming vascular plexuses. In the course of embryogenesis, the endocardium retains vasculogenic, angiogenic and haematopoietic potential. The coronary blood vessels that sustain the rapidly expanding myocardium develop in the course of the formation of the cardiac loop by vasculogenesis and angiogenesis from progenitor cells of the proepicardial serosa at the venous pole of the heart as well as from the endocardium and endothelial cells of the sinus venosus. Prospective coronary endothelial cells and progenitor cells of the coronary blood vessel walls (smooth muscle cells, perivascular cells) originate from different cell populations that are in close spatial as well as regulatory connection with each other. Vasculoâ and angiogenesis of the coronary blood vessels are for a large part regulated by the epicardium and epicardiumâderived cells. Vasculogenic and angiogenic signalling pathways include the vascular endothelial growth factors, the angiopoietins and the fibroblast growth factors and their receptors
Dark matter and structure formation a review
This paper provides a review of the variants of dark matter which are thought
to be fundamental components of the universe and their role in origin and
evolution of structures and some new original results concerning improvements
to the spherical collapse model. In particular, I show how the spherical
collapse model is modified when we take into account dynamical friction and
tidal torques
Modified Friedmann Equations in R-Modified Gravity
Recently, corrections to Einstein-Hilbert action that become important at
small curvature are proposed. We discuss the first order and second order
approximations to the field equations derived by the Palatini variational
principle. We work out the first and second order Modified Friedmann equations
and present the upper redshift bounds when these approximations are valid. We
show that the second order effects can be neglected on the cosmological
predictions involving only the Hubble parameter itself, e.g. the various
cosmological distances, but the second order effects can not be neglected in
the predictions involving the derivatives of the Hubble parameter. Furthermore,
the Modified Friedmann equations fit the SN Ia data at an acceptable level.Comment: 15 pages, 6 figures, v2: discussion added; v3: minor changes,
accepted by Class. and Quan. Gra
Driving vascular endothelial cell fate of human multipotent Isl1+ heart progenitors with VEGF modified mRNA
Distinct families of multipotent heart progenitors play a central role in the generation of diverse cardiac, smooth muscle and endothelial cell lineages during mammalian cardiogenesis. The identification of precise paracrine signals that drive the cell-fate decision of these multipotent progenitors, and the development of novel approaches to deliver these signals in vivo, are critical steps towards unlocking their regenerative therapeutic potential. Herein, we have identified a family of human cardiac endothelial intermediates located in outflow tract of the early human fetal hearts (OFT-ECs), characterized by coexpression of Isl1 and CD144/vWF. By comparing angiocrine factors expressed by the human OFT-ECs and non-cardiac ECs, vascular endothelial growth factor (VEGF)-A was identified as the most abundantly expressed factor, and clonal assays documented its ability to drive endothelial specification of human embryonic stem cell (ESC)-derived Isl1+ progenitors in a VEGF receptor-dependent manner. Human Isl1-ECs (endothelial cells differentiated from hESC-derived ISL1+ progenitors) resemble OFT-ECs in terms of expression of the cardiac endothelial progenitor- and endocardial cell-specific genes, confirming their organ specificity. To determine whether VEGF-A might serve as an in vivo cell-fate switch for human ESC-derived Isl1-ECs, we established a novel approach using chemically modified mRNA as a platform for transient, yet highly efficient expression of paracrine factors in cardiovascular progenitors. Overexpression of VEGF-A promotes not only the endothelial specification but also engraftment, proliferation and survival (reduced apoptosis) of the human Isl1+ progenitors in vivo. The large-scale derivation of cardiac-specific human Isl1-ECs from human pluripotent stem cells, coupled with the ability to drive endothelial specification, engraftment, and survival following transplantation, suggest a novel strategy for vascular regeneration in the heart
The differential impact of friendship on cooperative and competitive coordination
Friendship is commonly assumed to reduce strategic uncertainty and enhance tacit coordination. However, this assumption has never been tested across two opposite poles of coordination involving either strategic complementarity or substitutability. We had participants interact with friends or strangers in two classic coordination games: the stag hunt game, which exhibits strategic complementarity and may foster "cooperation", and the entry game, which exhibits strategic substitutability and may foster "competition". Both games capture a frequent trade-off between a potentially high paying but uncertain option and a low paying but safe alternative. We find that, relative to strangers, friends are more likely to choose options involving uncertainty in stag hunt games but the opposite is true in entry games. Furthermore, in stag hunt games, friends "tremble" less between options, coordinate better and earn more, but these advantages are largely decreased or lost in entry games. We further investigate how these effects are modulated by risk attitudes, friendship qualities and interpersonal similarities
Postpartum psychiatric disorders
Pregnancy is a complex and vulnerable period that presents a number of challenges to women, including the development of postpartum psychiatric disorders (PPDs). These disorders can include postpartum depression and anxiety, which are relatively common, and the rare but more severe postpartum psychosis. In addition, other PPDs can include obsessiveâcompulsive disorder, post-traumatic stress disorder and eating disorders. The aetiology of PPDs is a complex interaction of psychological, social and biological factors, in addition to genetic and environmental factors. The goals of treating postpartum mental illness are reducing maternal symptoms and supporting maternalâchild and family functioning. Women and their families should receive psychoeducation about the illness, including evidence-based discussions about the risks and benefits of each treatment option. Developing effective strategies in global settings that allow the delivery of targeted therapies to women with different clinical phenotypes and severities of PPDs is essential
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