992 research outputs found
High-throughput assessment of context-dependent effects of chromatin proteins
Background: Chromatin proteins control gene activity in a concerted manner. We developed a high-throughput assay to study the effects of the local chromatin environment on the regulatory activity of a protein of interest. The assay combines a previously reported multiplexing strategy based on barcoded randomly integrated reporters with Gal4-mediated tethering. We applied the assay to Drosophila heterochromatin protein 1a (HP1a), which is mo
Equivalence of Nonstatic Two-Pion-Exchange Nucleon-Nucleon Potentials
Off-shell aspects of the one-pion-exchange potential and their relationship
to different forms of the nonstatic (subleading-order) chiral two-pion-exchange
nucleon-nucleon potential are discussed. Various types of off-shell behavior
are categorized and numerous examples are given. Recently derived potentials
based on chiral approaches are supplemented by a rather general form of the
two-pion-exchange potential derived using old-fashioned methods. The latter is
closely related to a general form of one-pion-exchange relativistic corrections
and nonstatic two-pion-exchange three-nucleon forces developed long ago.Comment: 16 pages, latex -- Phys. Rev. C (to appear) -- Published versio
Width of Radio-Loud and Radio-Quiet CMEs
In the present paper we report on the difference in angular sizes between
radio-loud and radio-quiet CMEs. For this purpose we compiled these two samples
of events using Wind/WAVES and SOHO/LASCO observations obtained during
1996-2005. It is shown that the radio-loud CMEs are almost two times wider than
the radio-quiet CMEs (considering expanding parts of CMEs). Furthermore we show
that the radio-quiet CMEs have a narrow expanding bright part with a large
extended diffusive structure. These results were obtained by measuring the CME
widths in three different ways.Comment: Solar Physic, in pres
Using the local density approximation and the LYP, BLYP, and B3LYP functionals within Reference--State One--Particle Density--Matrix Theory
For closed-shell systems, the local density approximation (LDA) and the LYP,
BLYP, and B3LYP functionals are shown to be compatible with reference-state
one-particle density-matrix theory, where this recently introduced formalism is
based on Brueckner-orbital theory and an energy functional that includes exact
exchange and a non-universal correlation-energy functional. The method is
demonstrated to reduce to a density functional theory when the
exchange-correlation energy-functional has a simplified form, i.e., its
integrand contains only the coordinates of two electron, say r1 and r2, and it
has a Dirac delta function -- delta(r1 - r2) -- as a factor. Since Brueckner
and Hartree--Fock orbitals are often very similar, any local exchange
functional that works well with Hartree--Fock theory is a reasonable
approximation with reference-state one-particle density-matrix theory. The LDA
approximation is also a reasonable approximation. However, the Colle--Salvetti
correlation-energy functional, and the LYP variant, are not ideal for the
method, since these are universal functionals. Nevertheless, they appear to
provide reasonable approximations. The B3LYP functional is derived using a
linear combination of two functionals: One is the BLYP functional; the other
uses exact exchange and a correlation-energy functional from the LDA.Comment: 26 Pages, 0 figures, RevTeX 4, Submitted to Mol. Phy
Non-LTE Model Atmospheres for Late-Type Stars II. Restricted NLTE Calculations for a Solar-Like Atmosphere
We test our knowledge of the atomic opacity in the solar UV spectrum. Using
the atomic data compiled in Paper I from modern, publicly available, databases,
we perform calculations that are confronted with space-based observations of
the Sun. At wavelengths longer than about 260 nm, LTE modeling can reproduce
quite closely the observed fluxes; uncertainties in the atomic line data
account fully for the differences between calculated and observed fluxes. At
shorter wavelengths, departures from LTE appear to be important, as our LTE and
restricted NLTE calculations differ. Analysis of visible-near infrared Na I and
O I lines, two species that produce a negligible absorption in the UV, shows
that observed departures from LTE for theses species can be reproduced very
accurately with restricted (fixed atmospheric structure) NLTE calculations.Comment: 13 pages, 11 figures, to appear in Ap
Radio-loud CMEs from the disk center lacking shocks at 1 AU
A coronal mass ejection (CME) associated with a type II burst and originating
close to the center of the solar disk typically results in a shock at Earth in
2-3 days and hence can be used to predict shock arrival at Earth. However, a
significant fraction (about 28%) of such CMEs producing type II bursts were not
associated with shocks at Earth. We examined a set of 21 type II bursts
observed by the Wind/WAVES experiment at decameter-hectometric (DH) wavelengths
that had CME sources very close to the disk center (within a central meridian
distance of 30 degrees), but did not have a shock at Earth. We find that the
near-Sun speeds of these CMEs average to ~644 km/s, only slightly higher than
the average speed of CMEs associated with radio-quiet shocks. However, the
fraction of halo CMEs is only ~30%, compared to 54% for the radio-quiet shocks
and 91% for all radio-loud shocks. We conclude that the disk-center radio-loud
CMEs with no shocks at 1 AU are generally of lower energy and they drive shocks
only close to the Sun and dissipate before arriving at Earth. There is also
evidence for other possible processes that lead to the lack of shock at 1 AU:
(i) overtaking CME shocks merge and one observes a single shock at Earth, and
(ii) deflection by nearby coronal holes can push the shocks away from the
Sun-Earth line, such that Earth misses these shocks. The probability of
observing a shock at 1 AU increases rapidly above 60% when the CME speed
exceeds 1000 km/s and when the type II bursts propagate to frequencies below 1
MHz.Comment: 33 pages, 11 figures, 2 table
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