38,174 research outputs found
Large exchange bias after zero-field cooling from an unmagnetized state
Exchange bias (EB) is usually observed in systems with interface between
different magnetic phases after field cooling. Here we report an unusual
phenomenon in which a large EB can be observed in Ni-Mn-In bulk alloys after
zero-field cooling from an unmagnetized state. We propose this is related to
the newly formed interface between different magnetic phases during the initial
magnetization process. The magnetic unidirectional anisotropy, which is the
origin of EB effect, can be created isothermally below the blocking
temperature.Comment: including supplementary information, Accepted by Physical Review
Letter
Enhanced visibility of graphene: effect of one-dimensional photonic crystal
We investigate theoretically the light reflectance of a graphene layer
prepared on the top of one-dimensional Si/SiO2 photonic crystal (1DPC). It is
shown that the visibility of the graphene layers is enhanced greatly when 1DPC
is added, and the visibility can be tuned by changing the incident angle and
light wavelengths. This phenomenon is caused by the absorption of the graphene
layer and the enhanced reflectance of the 1DPC.Comment: 4 pages, 4 figures. published, ApplPhysLett_91_18190
Coarse-grained microscopic model of glass formers
We introduce a coarse-grained model for atomic glass formers. Its elements
are physically motivated local microscopic dynamical rules parameterized by
observables. Results of the model are established and used to interpret the
measured behaviors of supercooled fluids approaching glass transitions. The
model predicts the presence of a crossover from hierarchical super-Arrhenius
dynamics at short length scales to diffusive Arrhenius dynamics at large length
scales. This prediction distinguishes our model from other theories of glass
formers and can be tested by experiment.Comment: 5 pages, 5 figure
Tests of a Novel Design of Resistive Plate Chambers
A novel design of Resistive Plate Chambers (RPCs), using only a single
resistive plate, is being proposed. Based on this design, two large size
prototype chambers were constructed and were tested with cosmic rays and in
particle beams. The tests confirmed the viability of this new approach. In
addition to showing an improved single-particle response compared to the
traditional 2-plate design, the novel chambers also prove to be suitable for
calorimetric applications
Extra Dimensions: A View from the Top
In models with compact extra dimensions, where the Standard Model fields are
confined to a 3+1 dimensional hyperplane, the production
cross-section at a hadron collider can receive significant contributions from
multiple exchange of KK modes of the graviton. These are carefully computed in
the well-known ADD and RS scenarios, taking the energy dependence of the sum
over graviton propagators into account. Using data from Run-I of the Tevatron,
95% C.L. bounds on the parameter space of both models are derived. For Run-II
of the Tevatron and LHC, discovery limits are estimated.Comment: Typos corrected, references added. 12 pages, LaTeX, 2 ps figure
Negative Cell Cycle Regulation and DNA Damage-inducible Phosphorylation of the BRCT Protein 53BP1
In a screen designed to discover suppressors of mitotic catastrophe, we identified the Xenopus ortholog of 53BP1 (X53BP1), a BRCT protein previously identified in humans through its ability to bind the p53 tumor suppressor. X53BP1 transcripts are highly expressed in ovaries, and the protein interacts with Xp53 throughout the cell cycle in embryonic extracts. However, no interaction between X53BP1 and Xp53 can be detected in somatic cells, suggesting that the association between the two proteins may be developmentally regulated. X53BP1 is modified via phosphorylation in a DNA damage-dependent manner that correlates with the dispersal of X53BP1 into multiple foci throughout the nucleus in somatic cells. Thus, X53BP1 can be classified as a novel participant in the DNA damage response pathway. We demonstrate that X53BP1 and its human ortholog can serve as good substrates in vitro as well as in vivo for the ATM kinase. Collectively, our results reveal that 53BP1 plays an important role in the checkpoint response to DNA damage, possibly in collaboration with ATM
Representations of the fundamental group of a surface in PU(p,q) and holomorphic triples
We count the connected components in the moduli space of
PU(p,q)-representations of the fundamental group for a closed oriented surface.
The components are labelled by pairs of integers which arise as topological
invariants of the flat bundles associated to the representations. Our results
show that for each allowed value of these invariants, which are bounded by a
Milnor-Wood type inequality, there is a unique non-empty connected component.
Interpreting the moduli space of representations as a moduli space of Higgs
bundles, we take a Morse theoretic approach using a certain smooth proper
function on the Higgs moduli space. A key step is the identification of the
function's local minima as moduli spaces of holomorphic triples. We prove that
these moduli spaces of triples are non-empty and irreducible.Comment: 6 pages, to appear in C. R. Acad. Sci. Paris Ser. I Mat
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