296 research outputs found
Similarity in targets with REST points to neural and glioblastoma related miRNAs
There are groups of genes that need coordinated repression in multiple contexts, for example if they code for proteins that work together in a pathway or in a protein complex. Redundancy of biological regulatory networks implies that such coordinated repression might occur at both the pre- and post-transcriptional level, though not necessarily simultaneously or under the same conditions. Here, we propose that such redundancy in the global regulatory network can be detected by the overlap between the putative targets of a transcriptional repressor, as identified by a ChIP-seq experiment, and predicted targets of a microRNA (miRNA). To test this hypothesis, we used publicly available ChIP-seq data of the neural transcriptional repressor RE1 silencing transcription factor (REST) from 15 different cell samples. We found 20 miRNAs, each of which shares a significant amount of predicted targets with REST. The set of predicted associations between these 20 miRNAs and the overlapping REST targets is enriched in known miRNA targets. Many of the detected miRNAs have functions related to neural identity and glioblastoma, which could be expected from their overlap in targets with REST. We propose that the integration of experimentally determined transcription factor binding sites with miRNA-target predictions provides functional information on miRNAs
Avoided energy cost of producing minerals: The case of iron ore
There is growing concern about the decline of the ore grade in mines and the increased energy usage for processing and refining metals. In the limit, where no concentrated deposits exist, minerals must be obtained from bare rock. A method for quantitatively assessing the “free bonus” granted by nature in providing concentrated minerals in mines and thus assessing the quality of the different resources is estimating how much energy is needed to concentrate the minerals, as they are already in mines, from bare rock. This bonus granted by nature reduces the costs of human mining and metallurgical processes, as well as the mining effort required of future generations. In this study, the concentration of high-iron-content minerals in common rocks was investigated via a computational model developed using the HSC software. As expected, the range of results for the specific energy for the concentration of iron from common rocks was considerably higher than the energy required by modern processes. This reveals the need to value current iron deposits and the challenge of developing sustainable methods of metal production to satisfy the needs of the present and future generations
Gravity and Geometric Phases
The behavior of a quantum test particle satisfying the Klein-Gordon equation
in a certain class of 4 dimensional stationary space-times is examined. In a
space-time of a spinning cosmic string, the wave function of a particle in a
box is shown to acquire a geometric phase when the box is transported around a
closed path surrounding the string. When interpreted as an Aharonov-Anandan
geometric phase, the effect is shown to be related to the Aharonov-Bohm effect.Comment: 11 pages, latex fil
Recent developments in the characterization of superconducting films by microwaves
We describe and analyze selected surface impedance data recently obtained by
different groups on cuprate, ruthenate and diboride superconducting films on
metallic and dielectric substrates for fundamental studies and microwave
applications. The discussion includes a first review of microwave data on MgB2,
the weak-link behaviour of RABiTS-type YBa2Cu3O7-d tapes, and the observation
of a strong anomalous power-dependence of the microwave losses in MgO at low
temperatures. We demonstrate how microwave measurements can be used to
investigate electronic, magnetic, and dielectric dissipation and relaxation in
the films and substrates. The impact of such studies reaches from the
extraction of microscopic information to the engineering of materials and
further on to applications in power systems and communication technology.Comment: Invited contribution to EUCAS2001, accepted for publication in
Physica C in its present for
The self-consistent bounce: an improved nucleation rate
We generalize the standard computation of homogeneous nucleation theory at
zero temperature to a scenario in which the bubble shape is determined
self-consistently with its quantum fluctuations. Studying two scalar models in
1+1 dimensions, we find the self-consistent bounce by employing a two-particle
irreducible (2PI) effective action in imaginary time at the level of the
Hartree approximation. We thus obtain an effective single bounce action which
determines the rate exponent. We use collective coordinates to account for the
translational invariance and the growth instability of the bubble and finally
present a new nucleation rate prefactor. We compare the results with those
obtained using the standard 1-loop approximation and show that the
self-consistent rate can differ by several orders of magnitude.Comment: 28 pages, revtex, 7 eps figure
Do Instantons Like a Colorful Background?
We investigate chiral symmetry breaking and color symmetry breaking in QCD.
The effective potential of the corresponding scalar condensates is discussed in
the presence of non-perturbative contributions from the semiclassical
one-instanton sector. We concentrate on a color singlet scalar background which
can describe chiral condensation, as well as a color octet scalar background
which can generate mass for the gluons. Whereas a non-vanishing singlet chiral
field is favored by the instantons, we have found no indication for a
preference of color octet backgrounds.Comment: 25 pages, 7 figure
Off-Diagonal Elements of the DeWitt Expansion from the Quantum Mechanical Path Integral
The DeWitt expansion of the matrix element M_{xy} = \left\langle x \right|
\exp -[\case{1}{2} (p-A)^2 + V]t \left| y \right\rangle, in
powers of can be made in a number of ways. For (the case of interest
when doing one-loop calculations) numerous approaches have been employed to
determine this expansion to very high order; when (relevant for
doing calculations beyond one-loop) there appear to be but two examples of
performing the DeWitt expansion. In this paper we compute the off-diagonal
elements of the DeWitt expansion coefficients using the Fock-Schwinger gauge.
Our technique is based on representing by a quantum mechanical path
integral. We also generalize our method to the case of curved space, allowing
us to determine the DeWitt expansion of \tilde M_{xy} = \langle x| \exp
\case{1}{2} [\case{1}{\sqrt {g}} (\partial_\mu - i
A_\mu)g^{\mu\nu}{\sqrt{g}}(\partial_\nu - i A_\nu) ] t| y \rangle by use of
normal coordinates. By comparison with results for the DeWitt expansion of this
matrix element obtained by the iterative solution of the diffusion equation,
the relative merit of different approaches to the representation of as a quantum mechanical path integral can be assessed. Furthermore, the
exact dependence of on some geometric scalars can be
determined. In two appendices, we discuss boundary effects in the
one-dimensional quantum mechanical path integral, and the curved space
generalization of the Fock-Schwinger gauge.Comment: 16pp, REVTeX. One additional appendix concerning end-point effects
for finite proper-time intervals; inclusion of these effects seem to make our
results consistent with those from explicit heat-kernel method
Categorizing Different Approaches to the Cosmological Constant Problem
We have found that proposals addressing the old cosmological constant problem
come in various categories. The aim of this paper is to identify as many
different, credible mechanisms as possible and to provide them with a code for
future reference. We find that they all can be classified into five different
schemes of which we indicate the advantages and drawbacks.
Besides, we add a new approach based on a symmetry principle mapping real to
imaginary spacetime.Comment: updated version, accepted for publicatio
Heavy Quarks and Heavy Quarkonia as Tests of Thermalization
We present here a brief summary of new results on heavy quarks and heavy
quarkonia from the PHENIX experiment as presented at the "Quark Gluon Plasma
Thermalization" Workshop in Vienna, Austria in August 2005, directly following
the International Quark Matter Conference in Hungary.Comment: 8 pages, 5 figures, Quark Gluon Plasma Thermalization Workshop
(Vienna August 2005) Proceeding
Single Electrons from Heavy Flavor Decays in p+p Collisions at sqrt(s) = 200 GeV
The invariant differential cross section for inclusive electron production in
p+p collisions at sqrt(s) = 200 GeV has been measured by the PHENIX experiment
at the Relativistic Heavy Ion Collider over the transverse momentum range $0.4
<= p_T <= 5.0 GeV/c at midrapidity (eta <= 0.35). The contribution to the
inclusive electron spectrum from semileptonic decays of hadrons carrying heavy
flavor, i.e. charm quarks or, at high p_T, bottom quarks, is determined via
three independent methods. The resulting electron spectrum from heavy flavor
decays is compared to recent leading and next-to-leading order perturbative QCD
calculations. The total cross section of charm quark-antiquark pair production
is determined as sigma_(c c^bar) = 0.92 +/- 0.15 (stat.) +- 0.54 (sys.) mb.Comment: 329 authors, 6 pages text, 3 figures. Submitted to Phys. Rev. Lett.
Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
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