60,189 research outputs found
Non-Empirically Tuned Range-Separated DFT Accurately Predicts Both Fundamental and Excitation Gaps in DNA and RNA Nucleobases
Using a non-empirically tuned range-separated DFT approach, we study both the
quasiparticle properties (HOMO-LUMO fundamental gaps) and excitation energies
of DNA and RNA nucleobases (adenine, thymine, cytosine, guanine, and uracil).
Our calculations demonstrate that a physically-motivated, first-principles
tuned DFT approach accurately reproduces results from both experimental
benchmarks and more computationally intensive techniques such as many-body GW
theory. Furthermore, in the same set of nucleobases, we show that the
non-empirical range-separated procedure also leads to significantly improved
results for excitation energies compared to conventional DFT methods. The
present results emphasize the importance of a non-empirically tuned
range-separation approach for accurately predicting both fundamental and
excitation gaps in DNA and RNA nucleobases.Comment: Accepted by the Journal of Chemical Theory and Computatio
Anomalous Soft Photons in Hadron Production
Anomalous soft photons in excess of what is expected from electromagnetic
bremsstrahlung have been observed in association with the production of
hadrons, mostly mesons, in high-energy (K+)p, (pi+)p, (pi-)p, pp, and (e+)(e-)
collisions. We propose a model for the simultaneous production of anomalous
soft photons and mesons in quantum field theory, in which the meson production
arises from the oscillation of color charge densities of the quarks of the
underlying vacuum in the flux tube. As a quark carries both a color charge and
an electric charge, the oscillation of the color charge densities will be
accompanied by the oscillation of electric charge densities, which will in turn
lead to the simultaneous production of soft photons during the meson production
process. How the production of these soft photons may explain the anomalous
soft photon data will be discussed. Further experimental measurements to test
the model will be proposed.Comment: 19 pages, 2 figures, to be published in Physical Review
The yield and post-yield behavior of high-density polyethylene
An experimental and analytical evaluation was made of the yield and post-yield behavior of high-density polyethylene, a semi-crystalline thermoplastic. Polyethylene was selected for study because it is very inexpensive and readily available in the form of thin-walled tubes. Thin-walled tubular specimens were subjected to axial loads and internal pressures, such that the specimens were subjected to a known biaxial loading. A constant octahederal shear stress rate was imposed during all tests. The measured yield and post-yield behavior was compared with predictions based on both isotropic and anisotropic models. Of particular interest was whether inelastic behavior was sensitive to the hydrostatic stress level. The major achievements and conclusions reached are discussed
β-arrestin regulates estradiol membrane-initiated signaling in hypothalamic neurons.
Estradiol (E2) action in the nervous system is the result of both direct nuclear and membrane-initiated signaling (EMS). E2 regulates membrane estrogen receptor-α (ERα) levels through opposing mechanisms of EMS-mediated trafficking and internalization. While ß-arrestin-mediated mERα internalization has been described in the cortex, a role of ß-arrestin in EMS, which underlies multiple physiological processes, remains undefined. In the arcuate nucleus of the hypothalamus (ARH), membrane-initiated E2 signaling modulates lordosis behavior, a measure of female sexually receptivity. To better understand EMS and regulation of ERα membrane levels, we examined the role of ß-arrestin, a molecule associated with internalization following agonist stimulation. In the present study, we used an immortalized neuronal cell line derived from embryonic hypothalamic neurons, the N-38 line, to examine whether ß-arrestins mediate internalization of mERα. β-arrestin-1 (Arrb1) was found in the ARH and in N-38 neurons. In vitro, E2 increased trafficking and internalization of full-length ERα and ERαΔ4, an alternatively spliced isoform of ERα, which predominates in the membrane. Treatment with E2 also increased phosphorylation of extracellular-signal regulated kinases 1/2 (ERK1/2) in N-38 neurons. Arrb1 siRNA knockdown prevented E2-induced ERαΔ4 internalization and ERK1/2 phosphorylation. In vivo, microinfusions of Arrb1 antisense oligodeoxynucleotides (ODN) into female rat ARH knocked down Arrb1 and prevented estradiol benzoate-induced lordosis behavior compared with nonsense scrambled ODN (lordosis quotient: 3 ± 2.1 vs. 85.0 ± 6.0; p < 0.0001). These results indicate a role for Arrb1 in both EMS and internalization of mERα, which are required for the E2-induction of female sexual receptivity
On trivial words in finitely presented groups
We propose a numerical method for studying the cogrowth of finitely presented
groups. To validate our numerical results we compare them against the
corresponding data from groups whose cogrowth series are known exactly.
Further, we add to the set of such groups by finding the cogrowth series for
Baumslag-Solitar groups and prove
that their cogrowth rates are algebraic numbers.Comment: This article has been rewritten as two separate papers, with improved
exposition. The new papers are arXiv:1309.4184 and arXiv:1312.572
Spin-transfer mechanism for magnon-drag thermopower
We point out a relation between the dissipative spin-transfer-torque
parameter and the contribution of magnon drag to the thermoelectric
power in conducting ferromagnets. Using this result we estimate in iron
at low temperatures, where magnon drag is believed to be the dominant
contribution to the thermopower. Our results may be used to determine
from magnon-drag-thermopower experiments, or, conversely, to infer the strength
of magnon drag via experiments on spin transfer
Half-Monopole and Multimonopole
We would like to present some exact SU(2) Yang-Mills-Higgs monopole solutions
of half-integer topological charge. These solutions can be just an isolated
half-monopole or a multimonopole with topological magnetic charge, ,
where is a natural number. These static monopole solutions satisfy the
first order Bogomol'nyi equations. The axially symmetric one-half monopole
gauge potentials possess a Dirac-like string singularity along the negative
z-axis. The multimonopole gauge potentials are also singular along the z-axis
and possess only mirror symmetries.Comment: 12 pages and 4 figures; typos corrected, reference adde
The mystery of the 'Kite' radio source in Abell 2626: insights from new Chandra observations
We present the results of a new Chandra study of the galaxy cluster A2626.
The radio emission of the cluster shows a complex system of four symmetric arcs
without known correlations with the X-ray emission. The mirror symmetry of the
radio arcs toward the center and the presence of two optical cores in the
central galaxy suggested that they may be created by pairs of precessing radio
jets powered by dual AGNs inside the cD galaxy. However, previous observations
failed to observe the second jetted AGN and the spectral trend due to radiative
age along the radio arcs, thus challenging this interpretation. The new Chandra
observation had several scientific objectives, including the search for the
second AGN that would support the jet precession model. We focus here on the
detailed study of the local properties of the thermal and non-thermal emission
in the proximity of the radio arcs, in order to get more insights into their
origin. We performed a standard data reduction of the Chandra dataset deriving
the radial profiles of temperature, density, pressure and cooling time of the
intra-cluster medium. We further analyzed the 2D distribution of the gas
temperature, discovering that the south-western junction of the radio arcs
surrounds the cool core of the cluster. We studied the X-ray SB and spectral
profiles across the junction, finding a cold front spatially coincident with
the radio arcs. This may suggest a connection between the sloshing of the
thermal gas and the nature of the radio filaments, raising new scenarios for
their origin. A possibility is that the radio arcs trace the projection of a
complex surface connecting the sites where electrons are most efficiently
reaccelerated by the turbulence that is generated by the gas sloshing. In this
case, diffuse emission embedded by the arcs and with extremely steep spectrum
should be most visible at very low radio frequencies.Comment: 7 pages, 7 figures. Accepted for publication on A&
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