413 research outputs found
Effect of Na doping on flux pinning of YBa1.9Na0.1Cu3O7-d
We have prepared Na-doped YBa2Cu3Oy (YBa1.9Na0.1Cu3Oy +40mol%Y211) (YBNCO)
and Na-free YBa2Cu3Oy (YBCO) samples by the Melt-Textured Growth (MTG) method
to study the effect of doped Na ion on flux pinning. The ac susceptibility
curves (acs) as well as the hysteresis loops were measured for the samples.
Then the effective pinning energy (U(T,Hdc,J)), irreversibility line (Hirr(T))
and critical current density (jc(Hdc)) were determined, where T, Hdc and J are
temperature, dc magnetic field and current density, respectively. We found
that, with Na doping, the Hirr(T) line shifted to lower temperature while the
Jc(Hdc) and U(T,Hdc,J) became smaller. It indicates that the Na ions play a
negative role in the flux pinning of YBCO. The appearance of the second peak in
the Jc(Hdc) curves and the enhancement of anisotropy in YBNCO further support
this finding.Comment: 7 pages, 7figures. Submited to Physica.
Natural mutagenesis-enabled global proteomic study of metabolic and carbon source implications in mutant thermoacidophillic Archaeon Sulfolobus solfataricus PBL2025
The thermoacidophilic crenarchaeon Sulfolobus solfataricus has been widely used as a model organism for archaeal systems biology research. Investigation using its spontaneous mutant PBL2025 provides an effective metabolic baseline to study subsequent mutagenesis-induced functional process shifts as well as changes in feedback inhibitions. Here, an untargeted metabolic investigation using quantitative proteomics and metabolomics was performed to correlate changes in S. solfataricus strains P2 against PBL2025 and under both glucose and tryptone. The study is combined with pathway enrichment analysis to identify prominent proteins with differential stoichiometry. Proteome level quantification reveals that over 20% of the observed overlapping proteome is differentially expressed under these conditions. Metabolic-induced differential expressions are observed along the central carbon metabolism, along with 12 other significantly regulated pathways. Current findings suggest that PBL2025 is able to compensate through the induction of carbon metabolism, as well as other anabolic pathways such as Val, Leu and iso-Leu biosynthesis. Studying protein abundance changes after changes in carbon sources also reveals distinct differences in metabolic strategies employed by both strains, whereby a clear down-regulation of carbohydrate and nucleotide metabolism is observed for P2, while a mixed response through down-regulation of energy formation and up-regulation of glycolysis is observed for PBL2025. This study contributes, to date, the most comprehensive network of changes in carbohydrate and amino acid pathways using the complementary systems biology observations at the protein and metabolite levels. Current findings provide a unique insight into molecular processing changes through natural (spontaneous) metabolic rewiring, as well as a systems biology understanding of the metabolic elasticity of thermoacidophiles to environmental carbon source change, potentially guiding more efficient directed mutagenesis in archaea
Electronic States in Two-Dimensional Triangular Cobalt Oxides: Role of Electronic Correlation
We obtain the electronic states and structures of two-dimensional cobalt
oxides, NaCoO (x=0, 0.35, 0.5 and 0.75) by utilizing the
full-potential linear muffin-tin orbitals (FP-LMTO) methods, from which some
essential electronic interaction parameters are estimated: the bare on-site
Coulomb interaction of cobalt U=7.5 eV renormalizes to 5 eV for x=0.35,
the hybridizations t and t are -1.40 and 0.70 eV,
respectively. The density of states at E decreases from 6-7 states/eV in
the local density approximation (LDA) to about 1.0 states/eV in the LDA+U
scheme. The role of the intercalation of water molecules and the microscopic
mechanism of the superconductivity in NaCoOmHO is
discussed.Comment: minor errors correcte
Exciton swapping in a twisted graphene bilayer as a solid-state realization of a two-brane model
It is shown that exciton swapping between two graphene sheets may occur under
specific conditions. A magnetically tunable optical filter is described to
demonstrate this new effect. Mathematically, it is shown that two turbostratic
graphene layers can be described as a "noncommutative" two-sheeted
(2+1)-spacetime thanks to a formalism previously introduced for the study of
braneworlds in high energy physics. The Hamiltonian of the model contains a
coupling term connecting the two layers which is similar to the coupling
existing between two braneworlds at a quantum level. In the present case, this
term is related to a K-K' intervalley coupling. In addition, the experimental
observation of this effect could be a way to assess the relevance of some
theoretical concepts of the braneworld hypothesis.Comment: 15 pages, 3 figures, final version published in European Physical
Journal
Localization by disorder in the infrared conductivity of (Y,Pr)Ba2Cu3O7 films
The ab-plane reflectivity of (Y{1-x}Prx)Ba2Cu3O7 thin films was measured in
the 30-30000 cm-1 range for samples with x = 0 (Tc = 90 K), x = 0.4 (Tc = 35 K)
and x = 0.5 (Tc = 19 K) as a function of temperature in the normal state. The
effective charge density obtained from the integrated spectral weight decreases
with increasing x. The variation is consistent with the higher dc resistivity
for x = 0.4, but is one order of magnitude smaller than what would be expected
for x = 0.5. In the latter sample, the conductivity is dominated at all
temperatures by a large localization peak. Its magnitude increases as the
temperature decreases. We relate this peak to the dc resistivity enhancement. A
simple localization-by-disorder model accounts for the optical conductivity of
the x = 0.5 sample.Comment: 7 pages with (4) figures include
Performance Improvement of Microbial Fuel Cells by Lactic Acid Bacteria and Anode Modification
Au+Au Reactions at the AGS: Experiments E866 and E917
Particle production and correlation functions from Au+Au reactions have been
measured as a function of both beam energy (2-10.7AGeV) and impact parameter.
These results are used to probe the dynamics of heavy-ion reactions, confront
hadronic models over a wide range of conditions and to search for the onset of
new phenomena.Comment: 12 pages, 14 figures, Talk presented at Quark Matter '9
The PHENIX Experiment at RHIC
The physics emphases of the PHENIX collaboration and the design and current
status of the PHENIX detector are discussed. The plan of the collaboration for
making the most effective use of the available luminosity in the first years of
RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program
available at http://www.rhic.bnl.gov/phenix
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
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