3,285 research outputs found
Low energy proton-proton scattering in effective field theory
Low energy proton-proton scattering is studied in pionless effective field
theory. Employing the dimensional regularization and MS-bar and power
divergence subtraction schemes for loop calculation, we calculate the
scattering amplitude in 1S0 channel up to next-to-next-to leading order and fix
low-energy constants that appear in the amplitude by effective range
parameters. We study regularization scheme and scale dependence in separation
of Coulomb interaction from the scattering length and effective range for the
S-wave proton-proton scattering.Comment: 23 pages, 6 eps figures, revised considerably, accepted for
publication in Phys. Rev.
Mth1 regulates the interaction between the Rgt1 repressor and the Ssn6-Tup1 corepressor complex by modulating PKA-dependent phosphorylation of Rgt1
Glucose uptake, the first, rate-limiting step of its utilization, is facilitated by glucose transporters. Expression of several glucose transporter (HXT) genes in yeast is repressed by the Rgt1 repressor, which recruits the glucose-responsive transcription factor Mth1 and the general corepressor complex Ssn6-Tup1 in the absence of glucose; however, it is derepressed when Mth1 is inactivated by glucose. Here we show that Ssn6-Tup1 interferes with the DNA-binding ability of Rgt1 in the absence of Mth1 and that the Rgt1 function abrogated by Ssn6 overexpression is restored by co-overexpression of Mth1. Thus Mth1 likely regulates Rgt1 function not by modulating its DNA-binding activity directly but by functionally antagonizing Ssn6-Tup1. Mth1 does so by acting as a scaffold-like protein to recruit Ssn6-Tup1 to Rgt1. Supporting evidence shows that Mth1 blocks the protein kinase A–dependent phosphorylation of Rgt1 that impairs the ability of Rgt1 to interact with Ssn6-Tup1. Of note, Rgt1 can bind DNA in the absence of Ssn6-Tup1 but does not inhibit transcription, suggesting that dissociation of Rgt1 from Ssn6-Tup1, but not from DNA, is necessary and sufficient for the expression of its target genes. Taken together, these findings show that Mth1 is a transcriptional corepressor that facilitates the recruitment of Ssn6-Tup1 by Rgt1
Optical properties of iron-based superconductor LiFeAs single crystal
We have measured the reflectivity spectra of the iron based superconductor
LiFeAs (Tc = 17.6 K) in the temperature range from 4 to 300 K. In the
superconducting state (T < Tc), the clear opening of the optical absorption gap
was observed below 25 cm-1, indicating an isotropic full gap formation. In the
normal state (T > Tc), the optical conductivity spectra display a typical
metallic behavior with the Drude type spectra at low frequencies, but we found
that the introduction of the two Drude components best fits the data,
indicating the multiband nature of this superconductor. A theoretical analysis
of the low temperature data (T=4K < Tc) also suggests that two superconducting
gaps best fit the data and their values were estimated as {\Delta}1 = 1.59 meV
and {\Delta}2 = 3.15 meV, respectively. Using the Ferrell-Glover-Tinkham (FGT)
sum rule and dielectric function {\epsilon}1({\omega}), the superconducting
plasma frequency ({\omega}ps) is consistently estimated to be 6,665 cm-1,
implying that about 59 % of the free carriers in the normal state condenses
into the SC condensate. To investigate the various interband transition
processes (for {\omega} > 200 cm-1), we have also performed the local-density
approximation (LDA) band calculation and calculated the optical spectra of the
interband transitions. The theoretical results provided a qualitative agreement
with the experimental data below 4000 cm-1Comment: 19 pages, 5 figures. This paper has been accepted for publication in
New Journal of Physic
Development of the MICROMEGAS Detector for Measuring the Energy Spectrum of Alpha Particles by using a 241-Am Source
We have developed MICROMEGAS (MICRO MEsh GASeous) detectors for detecting
{\alpha} particles emitted from an 241-Am standard source. The voltage applied
to the ionization region of the detector is optimized for stable operation at
room temperature and atmospheric pressure. The energy of {\alpha} particles
from the 241-Am source can be varied by changing the flight path of the
{\alpha} particle from the 241 Am source. The channel numbers of the
experimentally-measured pulse peak positions for different energies of the
{\alpha} particles are associated with the energies deposited by the alpha
particles in the ionization region of the detector as calculated by using
GEANT4 simulations; thus, the energy calibration of the MICROMEGAS detector for
{\alpha} particles is done. For the energy calibration, the thickness of the
ionization region is adjusted so that {\alpha} particles may completely stop in
the ionization region and their kinetic energies are fully deposited in the
region. The efficiency of our MICROMEGAS detector for {\alpha} particles under
the present conditions is found to be ~ 97.3 %
Rheological method for alpha test evaluation of developing superplasticizers' performance: Channel flow test
Advance in high-range water-reducing admixture revolutionizes the workability and constructability of conventional vibrated concrete as well as self-consolidating concrete. Its need from construction fields has increased, and consequently a variety of new-type polycarboxylates, base polymers for the admixture, are being formulated in these days. Synthesizing new polymers needs a quick, but reliable, test to evaluate its performance on concrete. The test is also asked for selecting the best applicable brand of them before a test concrete will be mixed. This paper proposes a channel flow test and its usage for the purpose. The proposed procedure for the test includes the mix proportion of a test mortar, the test method, and rheological interpretation of the test results.ope
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