2,176 research outputs found
Cosmic microwave background constraints on a physical model of reionization
We study constraints on allowed reionization histories by comparing predictions of a physical seminumerical model with secondary temperature and polarization anisotropies of the cosmic microwave background (CMB). Our model has four free parameters characterizing the evolution of ionizing efficiency ζ and the minimum mass Mmin of haloes that can produce ionizing radiation. Comparing the model predictions with the presently available data of the optical depth Ï and kinematic Sunyaev-Zeldovich signal, we find that we can already rule out a significant region of the parameter space. We limit the duration of reionization Îz = 1.30+0.19-0.60 (Îz < 2.9 at 99 per cent C.L.), one of the tightest constraints on the parameter. The constraints mildly favour Mmin âł 109 Mâ (at 68 per cent C.L.) at z ⌠8, thus indicating the presence of reionization feedback. Our analysis provides an upper bound on the secondary B-mode amplitude Dl=200BB < 18 nK2 at 99 per cent C.L. We also study how the constraints can be further tightened with upcoming space- and ground-based CMB missions. Our study, which relies solely on CMB data, has implications not only for upcoming CMB surveys for detecting primordial gravitational waves but also redshifted 21 cm studies
Class Transitions and Two Component Accretion Flow in GRS 1915+105
The light curve of the galactic micro-quasar GRS 1915+105 changes in at least
thirteen different ways which are called classes. We present examples of the
transitions from one class to another as observed by the IXAE instrument aboard
the Indian Satellite IRS-P3. We find that the transitions are associated with
changes in photon counts over a time-scale of only a few hours and they take
place through unknown classes. Assuming that the transitions are caused by
variation of the accretion rates, this implies that a significant fraction of
the matter must be nearly freely falling in order to have such dramatic changes
in such a short time.Comment: 9 pages, 6 figures, Astronomy and Astrophys. (in press
Properties of a mixed-valent iron compound with the kagomélattice
An organically templated iron sulfate of the formula [HN(CH2)6NH][FeIIIFe2IIF6(SO4)2]·[H3O] possessing the kagomé lattice has been prepared and characterized by single-crystal crystallography and other techniques. This mixed-valent iron compound shows complex magnetic properties including spin-glass behavior and magnetic hysteresis. The low-temperature specific heat data show deviation from the T2 behavior found in two-dimensional frustrated systems. Simple calculations have been carried out to understand the properties of this kagomé compound
Finding information about mental health in microblogging platforms: a Case study of depression
Searching for online health information has been well studied in web search, but social media, such as public microblogging services, are well known for different types of tacit information: personal experience and shared information. Finding useful information in public microblogging platforms is an on-going hard problem and so to begin to develop a better model of what health information can be found, Twitter posts using the word âdepressionâ were examined as a case study of a search for a prevalent mental health issue. 13,279 public tweets were analysed using a mixed methods approach and compared to a general sample of tweets. First, a linguistic analysis suggested that tweets mentioning depression were typically anxious but not angry, and were less likely to be in the first person, indicating that most were not from individuals discussing their own depression. Second, to un-derstand what types of tweets can be found, an inductive thematic analysis revealed three major themes: 1) dissemi-nating information or link of information, 2) self-disclosing, and 3) the sharing of overall opinion; each had significantly different linguistic patterns. We conclude with a discussion of how different types of posts about mental health may be retrieved from public social media like Twitter
Searching for new physics in decays
For any new physics possibly emerging in the future B experiments, the
problem is how to extract the signals from the SM background. We consider the
decay which is very small in the SM. In the MSSM this decay is
possibly accessible in the future experiments. In the supersymmetric models
with R-parity violating couplings, this channel is not strictly constrained,
thus being useful in obtaining bounds on the lepton-number violating couplings.
A typical candidate for the suggested search is the mode.Comment: 9 pages, one figure, late
A Note on Inflation with Tachyon Rolling on the Gauss-Bonnet Brane
In this paper we study the tachyonic inflation in brane world cosmology with
Gauss-Bonnet term in the bulk. We obtain the exact solution of slow roll
equations in case of exponential potential. We attempt to implement the
proposal of Lidsey and Nunes, astro-ph/0303168, for the tachyon condensate
rolling on the Gauss-Bonnet brane and discuss the difficulties associated with
the proposal.Comment: RevTex4, 5 pages, no figures, Minor clarifications added and
references updated, To appear in PR
Tachyonic Inflation in a Warped String Background
We analyze observational constraints on the parameter space of tachyonic
inflation with a Gaussian potential and discuss some predictions of this
scenario. As was shown by Kofman and Linde, it is extremely problematic to
achieve the required range of parameters in conventional string
compactifications. We investigate if the situation can be improved in more
general compactifications with a warped metric and varying dilaton. The
simplest examples are the warped throat geometries that arise in the vicinity
of of a large number of space-filling D-branes. We find that the parameter
range for inflation can be accommodated in the background of D6-branes wrapping
a three-cycle in type IIA. We comment on the requirements that have to be met
in order to realize this scenario in an explicit string compactification.Comment: Latex, JHEP class, 20 pages, 4 figures. v2: references added, small
error in section 7 corrected, published versio
Non-minimally Coupled Tachyonic Inflation in Warped String Background
We show that the non-minimal coupling of tachyon field to the scalar
curvature, as proposed by Piao et al, with the chosen coupling parameter does
not produce the effective potential where the tachyon field can roll down from
T=0 to large along the slope of the potential. We find a correct choice of
the parameters which ensures this requirement and support slow-roll inflation.
However, we find that the cosmological parameter found from the analysis of the
theory are not in the range obtained from observations. We then invoke warped
compactification and varying dilaton field over the compact manifold, as
proposed by Raeymaekers, to show that in such a setup the observed parameter
space can be ensured.Comment: minor typos corrected and references adde
Repurposing FDA approved drugs as radiosensitizers for treating hypoxic prostate cancer
Abstract Background The presence of hypoxia is a poor prognostic factor in prostate cancer and the hypoxic tumor microenvironment promotes radioresistance. There is potential for drug radiotherapy combinations to improve the therapeutic ratio. We aimed to investigate whether hypoxia-associated genes could be used to identify FDA approved drugs for repurposing for the treatment of hypoxic prostate cancer. Methods Hypoxia associated genes were identified and used in the connectivity mapping software QUADrATIC to identify FDA approved drugs as candidates for repurposing. Drugs identified were tested in vitro in prostate cancer cell lines (DU145, PC3, LNCAP). Cytotoxicity was investigated using the sulforhodamine B assay and radiosensitization using a clonogenic assay in normoxia and hypoxia. Results Menadione and gemcitabine had similar cytotoxicity in normoxia and hypoxia in all three cell lines. In DU145 cells, the radiation sensitizer enhancement ratio (SER) of menadione was 1.02 in normoxia and 1.15 in hypoxia. The SER of gemcitabine was 1.27 in normoxia and 1.09 in hypoxia. No radiosensitization was seen in PC3 cells. Conclusion Connectivity mapping can identify FDA approved drugs for potential repurposing that are linked to a radiobiologically relevant phenotype. Gemcitabine and menadione could be further investigated as potential radiosensitizers in prostate cancer
Dynamics of Tachyon and Phantom Field beyond the Inverse Square Potentials
We investigate the cosmological evolution of the tachyon and phantom-tachyon
scalar field by considering the potential parameter () as a function of another potential parameter
(), which correspondingly extends the
analysis of the evolution of our universe from two-dimensional autonomous
dynamical system to the three-dimension. It allows us to investigate the more
general situation where the potential is not restricted to inverse square
potential and .One result is that, apart from the inverse square potential,
there are a large number of potentials which can give the scaling and dominant
solution when the function equals for one or some
values of as well as the parameter satisfies
condition Eq.(18) or Eq.(19). We also find that for a class of different
potentials the dynamics evolution of the universe are actually the same and
therefore undistinguishable.Comment: 8 pages, no figure, accepted by The European Physical Journal
C(2010), online first,
http://www.springerlink.com/content/323417h708gun5g8/?p=dd373adf23b84743b523a3fa249d51c7&pi=
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