753 research outputs found
Magnetic domain formation in itinerant metamagnets
We examine the effects of long-range dipolar forces on metamagnetic
transitions and generalize the theory of Condon domains to the case of an
itinerant electron system undergoing a first-order metamagnetic transition. We
demonstrate that within a finite range of the applied field, dipolar
interactions induce a spatial modulation of the magnetization in the form of
stripes or bubbles. Our findings are consistent with recent observations in the
bilayer ruthenate SrRuO.Comment: 4 pages, 3 figures, minor changes, references adde
Exploring the functional domain and the target of the tetanus toxin light chain in neurohypophysial terminals
The tetanus toxin light chain blocks calcium induced vasopressin release from neurohypophysial nerve terminals. Here we show that histidine residue 233 within the putative zinc binding motif of the tetanus toxin light chain is essential for the inhibition of exocytosis, in the rat. The zinc chelating agent dipicolinic acid as well as captopril, an inhibitor of zinc-dependent peptidases, counteract the effect of the neurotoxin. Synthetic peptides, the sequences of which correspond to motifs present in the cytoplasmic domain of the synaptic vesicle membrane protein synaptobrevin 1 and 2, prevent the effect of the tetanus toxin light chain.
Our results indicate that zinc bound to the zinc binding motif constitutes the active site of the tetanus toxin light chain. Moreover they suggest that cleavage of synaptobrevin by the neurotoxin causes the inhibition of exocytotic release of vasopressin from secretory granules
spl(2,1) dynamical supersymmetry and suppression of ferromagnetism in flat band double-exchange models
The low energy spectrum of the ferromagnetic Kondo lattice model on a N-site
complete graph extended with on-site repulsion is obtained from the underlying
spl(2,1) algebra properties in the strong coupling limit. The ferromagnetic
ground state is realized for 1 and N+1 electrons only. We identify the large
density of states to be responsible for the suppression of the ferromagnetic
state and argue that a similar situation is encountered in the Kagome,
pyrochlore, and other lattices with flat bands in their one-particle density of
states.Comment: 7 pages, 1 figur
Shared idiotypic determinants on B and T lymphocytes reactive against the same antigenic determinants. I. Demonstration of similar or identical idiotypes on IgG molecules and T-cell receptors with specificity for the same alloantigens.
Rapid selection of specific MAP kinase-binders from designed ankyrin repeat protein libraries
We describe here the rapid selection of specific MAP-kinase binders from a combinatorial library of designed ankyrin repeat proteins (DARPins). A combined in vitro/in vivo selection approach, based on ribosome display and the protein fragment complementation assay (PCA), yielded a large number of different binders that are fully functional in the cellular cytoplasm. Ribosome-display selection pools of four successive selection rounds were examined to monitor the enrichment of JNK2-specific DARPins. Surprisingly, only one round of ribosome display with subsequent PCA selection of this pool was necessary to isolate a first specific binder with micromolar affinity. After only two rounds of ribosome-display selection followed by PCA, virtually all DARPins showed JNK2-specific binding, with affinities in the low nanomolar range. The enrichment factor of ribosome display thus approaches 105 per round. In a second set of experiments, similar results were obtained with the kinases JNK1 and p38 as targets. Again, almost all investigated DARPins obtained after two rounds of ribosome display showed specific binding to the targets used, JNK1 or p38. In all three selection experiments the identified DARPins possess very high specificity for the target kinase. Taken together, the combination of ribosome display and PCA selections allowed the identification of large pools of binders at unparalleled speed. Furthermore, DARPins are applicable in intracellular selections and immunoprecipitations from the extract of eukaryotic cell
The Reconstruction Problem and Weak Quantum Values
Quantum Mechanical weak values are an interference effect measured by the
cross-Wigner transform W({\phi},{\psi}) of the post-and preselected states,
leading to a complex quasi-distribution {\rho}_{{\phi},{\psi}}(x,p) on phase
space. We show that the knowledge of {\rho}_{{\phi},{\psi}}(z) and of one of
the two functions {\phi},{\psi} unambiguously determines the other, thus
generalizing a recent reconstruction result of Lundeen and his collaborators.Comment: To appear in J.Phys.: Math. Theo
Van Hove singularity and spontaneous Fermi surface symmetry breaking in Sr3Ru2O7
The most salient features observed around a metamagnetic transition in
Sr3Ru2O7 are well captured in a simple model for spontaneous Fermi surface
symmetry breaking under a magnetic field, without invoking a putative quantum
critical point. The Fermi surface symmetry breaking happens in both a majority
and a minority spin band but with a different magnitude of the order parameter,
when either band is tuned close to van Hove filling by the magnetic field. The
transition is second order for high temperature T and changes into first order
for low T. The first order transition is accompanied by a metamagnetic
transition. The uniform magnetic susceptibility and the specific heat
coefficient show strong T dependence, especially a log T divergence at van Hove
filling. The Fermi surface instability then cuts off such non-Fermi liquid
behavior and gives rise to a cusp in the susceptibility and a specific heat
jump at the transition temperature.Comment: 11 pages, 4 figure
Efficiency of the flagellar propulsion of Escherichia coli in confined microfluidic geometries
Bacterial movement in confined spaces is routinely encountered either in a natural environment or in artificial structures. Consequently, the ability to understand and predict the behavior of motile bacterial cells in confined geometries is essential to many applications, spanning from the more classical, such as the management complex microbial networks involved in diseases, biomanufacturing, mining, and environment, to the more recent, such as single cell DNA sequencing and computation with biological agents. Fortunately, the development of this understanding can be helped by the decades-long advances in semiconductor microfabrication, which allow the design and the construction of complex confining structures used as test beds for the study of bacterial motility. To this end, here we use microfabricated channels with varying sizes to study the interaction of Escherichia coli with solid confining spaces. It is shown that an optimal channel size exists for which the hydrostatic potential allows the most efficient movement of the cells. The improved understanding of how bacteria move will result in the ability to design better microfluidic structures based on their interaction with bacterial movement
Strong Longitudinal Magnetic Fluctuations near Critical End Point in UCoAl: A ^59Co-NMR Study
We report ^59Co-NMR measurements in UCoAl where a metamagnetism occurs due to
enhancement of ferromagnetism by magnetic field. The metamagnetic transition
from a paramagnetic (PM) state to a ferromagnetic state is a first order
transition at low temperatures, but it changes to a crossover at high
temperatures on crossing the critical end pint (CEP) at T_CEP ~ 12 K. The
contrasting behavior between the relaxation rates 1/T_1 and 1/T_2 suggests that
the longitudinal magnetic fluctuation of U moment is strongly enhanced
especially near the CEP. A wide diffusion of the fluctuation from the CEP can
be confirmed even in the PM state where the magnetic transition does not occur.Comment: 5pages, 6 figures, to be published in J. Phys. Soc. Jp
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