5,274 research outputs found
The flux pinning force and vortex phase diagram of single crystal FeTe0.60Se0.40
The flux pinning force density (Fp) of the single crystalline FeTe0.60Se0.40
superconductor has been calculated from the magnetization measurements. The
normalized Fp versus h (=H/Hirr) curves are scaled using the Dew-Hughes formula
to underline the pinning mechanism in the compound. The obtained values of
pinning parameters p and q indicate the vortex pinning by the mixing of the
surface and the point core pinning of the normal centers. The vortex phase
diagram has also been drawn for the first time for the FeTe0.60Se0.40, which
has very high values of critical current density Jc ~ 1.10(5) Amp/cm2 and the
upper critical field Hc2(0) = 65T, with a reasonably high transition
temperature Tc =14.5K.Comment: 12 pages, 4 figure
Transportation dynamics on networks of mobile agents
Most existing works on transportation dynamics focus on networks of a fixed
structure, but networks whose nodes are mobile have become widespread, such as
cell-phone networks. We introduce a model to explore the basic physics of
transportation on mobile networks. Of particular interest are the dependence of
the throughput on the speed of agent movement and communication range. Our
computations reveal a hierarchical dependence for the former while, for the
latter, we find an algebraic power law between the throughput and the
communication range with an exponent determined by the speed. We develop a
physical theory based on the Fokker-Planck equation to explain these phenomena.
Our findings provide insights into complex transportation dynamics arising
commonly in natural and engineering systems
Accelerated induction of apoptosis in insect cells by baculovirus-expressed SARS-CoV membrane protein
AbstractIt has been shown that severe acute respiratory syndrome-associated coronavirus (SARS-CoV) 3a and 7a proteins, but not membrane (M) protein, induce apoptosis in mammalian cells. Upon expression of SARS-CoV M protein using the baculovirus/insect cell expression system, however, we found that the expressed M protein triggered accelerated apoptosis in insect cells, as characterized by rapid cell death, elevated cytotoxicity, cell shrinkage, nuclear condensation and DNA fragmentation. Conversely, the M protein expressed in mammalian cells did not induce apoptosis. This is the first report describing the induction of apoptosis by SARS-CoV M protein in animal cells and possible implications are discussed
The contribution of methionine to the stability of the Escherichia coli MetNIQ ABC transporter-substrate binding protein complex
Despite the ubiquitous role of ATP-binding cassette (ABC) importers in nutrient uptake, only the Escherichia coli maltose and vitamin B_(12) ABC transporters have been structurally characterized in multiple conformations relevant to the alternating access transport mechanism. To complement our previous structure determination of the E. coli MetNI methionine importer in the inward facing conformation (Kadaba et al. (2008) Science 321, 250-253), we have explored conditions stabilizing the outward facing conformation. Using two variants, the Walker B E166Q mutation with ATP+EDTA to stabilize MetNI in the ATPbound conformation and the N229A variant of the binding protein MetQ, shown in this work to disrupt methionine binding, a high affinity MetNIQ complex was formed with a dissociation constant measured to be 27 nm. Using wild type MetQ containing a co-purified methionine (for which the crystal structure is reported at 1.6 Ã… resolution), the dissociation constant for complex formation with MetNI is measured to be ~40-fold weaker, indicating that complex formation lowers the affinity of MetQ for methionine by this amount. Preparation of a stable MetNIQ complex is an essential step towards the crystallographic analysis of the outward facing conformation, a key intermediate in the uptake of methionine by this transport system
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