21,185 research outputs found
Non-parametric reconstruction of an inflaton potential from Einstein-Cartan-Sciama-Kibble gravity with particle production
The coupling between spin and torsion in the Einstein-Cartan-Sciama-Kibble
theory of gravity generates gravitational repulsion at very high densities,
which prevents a singularity in a black hole and may create there a new
universe. We show that quantum particle production in such a universe near the
last bounce, which represents the Big Bang gives the dynamics that solves the
horizon, flatness, and homogeneity problems in cosmology. For a particular
range of the particle production coefficient, we obtain a nearly constant
Hubble parameter that gives an exponential expansion of the universe with more
than 60 -folds, which lasts about s. This scenario can thus
explain cosmic inflation without requiring a fundamental scalar field and
reheating. From the obtained time dependence of the scale factor, we follow the
prescription of Ellis and Madsen to reconstruct in a non-parametric way a
scalar field potential which gives the same dynamics of the early universe.
This potential gives the slow-roll parameters of cosmic inflation, from which
we calculate the tensor-to-scalar ratio, the scalar spectral index of density
perturbations, and its running as functions of the production coefficient. We
find that these quantities do not significantly depend on the scale factor at
the Big Bounce. Our predictions for these quantities are consistent with the
Planck 2015 observations.Comment: 9 pages, 11 figure
Evidence for inhomogeneous thermal sources of two similar solar spike event of 1978, May 5 and December 4
Two short duration single spike events of 1978 May 5 and December 4 exhibit similar time profiles in the microwave and hard X-ray ranges, indicating emission from compact sources. Microwave spectral observations exhibit inhomogeneities present in the source parameters. The existence of fine time structures in the microwave time profiles at 10.4 GHz from Berne are interpreted as a signature of the dynamics of a disturbance travelling through the souce at the ion-sound speed. Stereoscopic observations with the hard X-ray detector on the solar orbiter, Helios-2, and the Berne microwave antennae do not indicate any time lag or differences in the time profiles during the impulsive phase. This is taken as evidence for the absence of directionality of emission making beam models unlikely for short duration single spike events
Tellipsoid: Exploiting inter-gene correlation for improved detection of differential gene expression
Motivation: Algorithms for differential analysis of microarray data are vital
to modern biomedical research. Their accuracy strongly depends on effective
treatment of inter-gene correlation. Correlation is ordinarily accounted for in
terms of its effect on significance cut-offs. In this paper it is shown that
correlation can, in fact, be exploited {to share information across tests},
which, in turn, can increase statistical power.
Results: Vastly and demonstrably improved differential analysis approaches
are the result of combining identifiability (the fact that in most microarray
data sets, a large proportion of genes can be identified a priori as
non-differential) with optimization criteria that incorporate correlation. As a
special case, we develop a method which builds upon the widely used two-sample
t-statistic based approach and uses the Mahalanobis distance as an optimality
criterion. Results on the prostate cancer data of Singh et al. (2002) suggest
that the proposed method outperforms all published approaches in terms of
statistical power.
Availability: The proposed algorithm is implemented in MATLAB and in R. The
software, called Tellipsoid, and relevant data sets are available at
http://www.egr.msu.edu/~desaikeyComment: 19 pages, Submitted to Bioinformatic
Cosmic Neutrino Bound on the Dark Matter Annihilation Rate in the Late Universe
How large can the dark matter self-annihilation rate in the late universe be?
This rate depends on (rho_DM/m_chi)^2 , where rho_DM/m_chi is the
number density of dark matter, and the annihilation cross section is averaged
over the velocity distribution. Since the clustering of dark matter is known,
this amounts to asking how large the annihilation cross section can be.
Kaplinghat, Knox, and Turner proposed that a very large annihilation cross
section could turn a halo cusp into a core, improving agreement between
simulations and observations; Hui showed that unitarity prohibits this for
large dark matter masses. We show that if the annihilation products are
Standard Model particles, even just neutrinos, the consequent fluxes are ruled
out by orders of magnitude, even at small masses. Equivalently, to invoke such
large annihilation cross sections, one must now require that essentially no
Standard Model particles are produced.Comment: 4 pages, 2 figures; to appear in the proceedings of the TeV Particle
Astrophysics II Workshop, Madison, Wisconsin, 28-31 Aug 200
Constraining Managers without Owners: Governance of the Not-for-Profit Enterprise
In the absence of owners, how effective are the constraints imposed by the state in promoting effective firm governance? This paper develops state-level indices of the legal and reporting rules facing not-for-profits and examines the effects of these rules on not-for-profit behavior. Stronger non-distribution constraints are associated with greater charitable expenditures and foundation payouts while more stringent reporting requirements are associated with lower insider compensation. The paper also examines how governance influences an alternative metric of not-for-profit performance -- the provision of social insurance. Stronger governance measures are associated with intertemporal smoothing of resources and greater activity in response to negative economic shocks.
Competition and cooperation among receptor tyrosine phosphatases control motoneuron growth cone guidance in Drosophila
The neural receptor tyrosine phosphatases DPTP69D,
DPTP99A and DLAR are involved in motor axon guidance
in the Drosophila embryo. Here we analyze the requirements
for these three phosphatases in growth cone guidance decisions along the ISN and SNb motor pathways.
Any one of the three suffices for the progression of ISN
pioneer growth cones beyond their first intermediate target
in the dorsal muscle field. DLAR or DPTP69D can facilitate
outgrowth beyond a second intermediate target, and
DLAR is uniquely required for formation of a normal
terminal arbor. A different pattern of partial redundancy
among the three phosphatases is observed for the SNb
pathway. Any one of the three suffices to allow SNb axons
to leave the common ISN pathway at the exit junction.
When DLAR is not expressed, however, SNb axons
sometimes bypass their ventrolateral muscle targets after
leaving the common pathway, instead growing out as a
separate bundle adjacent to the ISN. This abnormal
guidance decision can be completely suppressed by also
removing DPTP99A, suggesting that DLAR turns off or
counteracts a DPTP99A signal that favors the bypass axon
trajectory. Our results show that the relationships among
the tyrosine phosphatases are complex and dependent on
cellular context. At growth cone choice points along one
nerve, two phosphatases cooperate, while along another
nerve these same phosphatases can act in opposition to one
another
Checking the validity of truncating the cumulant hierarchy description of a small system
We analyze the behavior of the first few cumulant in an array with a small
number of coupled identical particles. Desai and Zwanzig (J. Stat. Phys., {\bf
19}, 1 (1978), p. 1) studied noisy arrays of nonlinear units with global
coupling and derived an infinite hierarchy of differential equations for the
cumulant moments. They focused on the behavior of infinite size systems using a
strategy based on truncating the hierarchy. In this work we explore the
reliability of such an approach to describe systems with a small number of
elements. We carry out an extensive numerical analysis of the truncated
hierarchy as well as numerical simulations of the full set of Langevin
equations governing the dynamics. We find that the results provided by the
truncated hierarchy for finite systems are at variance with those of the
Langevin simulations for large regions of parameter space. The truncation of
the hierarchy leads to a dependence on initial conditions and to the
coexistence of states which are not consistent with the theoretical
expectations based on the multidimensional linear Fokker-Planck equation for
finite arrays
CosmoDM and its application to Pan-STARRS data
The Cosmology Data Management system (CosmoDM) is an automated and flexible
data management system for the processing and calibration of data from optical
photometric surveys. It is designed to run on supercomputers and to minimize
disk I/O to enable scaling to very high throughput during periods of
reprocessing. It serves as an early prototype for one element of the
ground-based processing required by the Euclid mission and will also be
employed in the preparation of ground based data needed in the eROSITA X-ray
all sky survey mission. CosmoDM consists of two main pipelines. The first is
the single-epoch or detrending pipeline, which is used to carry out the
photometric and astrometric calibration of raw exposures. The second is the co-
addition pipeline, which combines the data from individual exposures into
deeper coadd images and science ready catalogs. A novel feature of CosmoDM is
that it uses a modified stack of As- tromatic software which can read and write
tile compressed images. Since 2011, CosmoDM has been used to process data from
the DECam, the CFHT MegaCam and the Pan-STARRS cameras. In this paper we shall
describe how processed Pan-STARRS data from CosmoDM has been used to optically
confirm and measure photometric redshifts of Planck-based Sunyaev-Zeldovich
effect selected cluster candidates.Comment: 11 pages, 4 figures. Proceedings of Precision Astronomy with Fully
Depleted CCDs Workshop (2014). Accepted for publication in JINS
What does"entrepreneurship"data really show ? a comparison of the global entrepreneurship monitor and World Bank group datasets
This paper compares two datasets designed to measure entrepreneurship. The Global Entrepreneurship Monitor dataset captures early-stage entrepreneurial activity; the World Bank Group Entrepreneurship Survey dataset captures formal business registration. There are a number of important differences when the data are compared. First, GEM data tend to report significantly greater levels of early-stage entrepreneurship in developing economies than do the World Bank data. The World Bank data tend to be greater than GEM data for developed countries. Second, the magnitude of the difference between the datasets across countries is related to the local institutional and environmental conditions for entrepreneurs, after controlling for levels of economic development. A possible explanation for this is that the World Bank data measure rates of entry in the formal economy, whereas GEM data are reflective of entrepreneurial intent and capture informality of entrepreneurship. This is particularly true for developing countries. Therefore, this discrepancy can be interpreted as the spread between individuals who could potentially operate businesses in the formal sector - and those that actually do so: In other words, GEM data may represent the potential supply of entrepreneurs, whereas the World Bank data may represent the actual rate of entrepreneurship. The findings suggest that entrepreneurs in developed countries have greater ease and incentives to incorporate, both for the benefits of greater access to formal financing and labor contracts, as well as for tax and other purposes not directly related to business activities.Banks&Banking Reform,E-Business,Access to Finance,Microfinance,Information Security&Privacy
The Pulse Scale Conjecture and the Case of BATSE Trigger 2193
The pulses that compose gamma-ray bursts (GRBs) are hypothesized to have the
same shape at all energies, differing only by scale factors in time and
amplitude. This "Pulse Scale Conjecture" is confirmed here between energy
channels of the dominant pulse in GRB 930214c (BATSE trigger 2193), the single
most fluent single-pulsed GRB that occurred before May 1998. Furthermore,
pulses are hypothesized to start at the same time independent of energy. This
"Pulse Start Conjecture" is also confirmed in GRB 930214c. Analysis of GRB
930214c also shows that, in general, higher energy channels show shorter
temporal scale factors. Over the energy range 100 KeV - 1 MeV, it is found that
the temporal scale factors between a pulse measured at different energies are
related to that energy by a power law, possibly indicating a simple
relativistic mechanism is at work. To test robustness, the Pulse Start and
Pulse Scale Conjectures were also tested on the four next most fluent
single-pulse GRBs. Three of the four clearly passed, with a second smaller
pulse possibly confounding the discrepant test. Models where the pulse rise and
decay are created by different phenomena do not typically predict pulses that
satisfy both the Pulse Start Conjecture and the Pulse Scale Conjecture, unless
both processes are seen to undergo common time dilation.Comment: 19 pages, 9 figures, analysis revised and extended, accepted to Ap
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