198 research outputs found
Valley filter and valley valve in graphene
It is known that the lowest propagating mode in a narrow ballistic ribbon of
graphene may lack the twofold valley degeneracy of higher modes. Depending on
the crystallographic orientation of the ribbon axis, the lowest mode mixes both
valleys or lies predominantly in a single valley (chosen by the direction of
propagation). We show, using a tight-binding model calculation, that a
nonequilibrium valley polarization can be realized in a sheet of graphene, upon
injection of current through a ballistic point contact with zigzag edges. The
polarity can be inverted by local application of a gate voltage to the point
contact region. Two valley filters in series may function as an
electrostatically controlled ``valley valve'', representing a
zero-magnetic-field counterpart to the familiar spin valve.Comment: RevTeX, 4 pages, 5 figure
Gauge symmetry and W-algebra in higher derivative systems
The problem of gauge symmetry in higher derivative Lagrangian systems is
discussed from a Hamiltonian point of view. The number of independent gauge
parameters is shown to be in general {\it{less}} than the number of independent
primary first class constraints, thereby distinguishing it from conventional
first order systems. Different models have been considered as illustrative
examples. In particular we show a direct connection between the gauge symmetry
and the W-algebra for the rigid relativistic particle.Comment: 1+22 pages, 1 figure, LaTeX, v2; title changed, considerably expanded
version with new results, to appear in JHE
Tunable metal-insulator transition in double-layer graphene heterostructures
We report a double-layer electronic system made of two closely-spaced but
electrically isolated graphene monolayers sandwiched in boron nitride. For
large carrier densities in one of the layers, the adjacent layer no longer
exhibits a minimum metallic conductivity at the neutrality point, and its
resistivity diverges at low temperatures. This divergence can be suppressed by
magnetic field or by reducing the carrier density in the adjacent layer. We
believe that the observed localization is intrinsic for neutral graphene with
generic disorder if metallic electron-hole puddles are screened out
Azimuthal anisotropy in Au+Au collisions at sqrtsNN = 200 GeV
The results from the STAR Collaboration on directed flow (v_1), elliptic flow
(v_2), and the fourth harmonic (v_4) in the anisotropic azimuthal distribution
of particles from Au+Au collisions at sqrtsNN = 200 GeV are summarized and
compared with results from other experiments and theoretical models. Results
for identified particles are presented and fit with a Blast Wave model.
Different anisotropic flow analysis methods are compared and nonflow effects
are extracted from the data. For v_2, scaling with the number of constituent
quarks and parton coalescence is discussed. For v_4, scaling with v_2^2 and
quark coalescence is discussed.Comment: 26 pages. As accepted by Phys. Rev. C. Text rearranged, figures
modified, but data the same. However, in Fig. 35 the hydro calculations are
corrected in this version. The data tables are available at
http://www.star.bnl.gov/central/publications/ by searching for "flow" and
then this pape
Rapidity and Centrality Dependence of Proton and Anti-proton Production from Au+Au Collisions at sqrt(sNN) = 130GeV
We report on the rapidity and centrality dependence of proton and anti-proton
transverse mass distributions from Au+Au collisions at sqrt(sNN) = 130GeV as
measured by the STAR experiment at RHIC. Our results are from the rapidity and
transverse momentum range of |y|<0.5 and 0.35 <p_t<1.00GeV/c. For both protons
and anti-protons, transverse mass distributions become more convex from
peripheral to central collisions demonstrating characteristics of collective
expansion. The measured rapidity distributions and the mean transverse momenta
versus rapidity are flat within |y|<0.5. Comparisons of our data with results
from model calculations indicate that in order to obtain a consistent picture
of the proton(anti-proton) yields and transverse mass distributions the
possibility of pre-hadronic collective expansion may have to be taken into
account.Comment: 4 pages, 3 figures, 1 table, submitted to PR
Movement Protein Pns6 of Rice dwarf phytoreovirus Has Both ATPase and RNA Binding Activities
Cell-to-cell movement is essential for plant viruses to systemically infect host plants. Plant viruses encode movement proteins (MP) to facilitate such movement. Unlike the well-characterized MPs of DNA viruses and single-stranded RNA (ssRNA) viruses, knowledge of the functional mechanisms of MPs encoded by double-stranded RNA (dsRNA) viruses is very limited. In particular, many studied MPs of DNA and ssRNA viruses bind non-specifically ssRNAs, leading to models in which ribonucleoprotein complexes (RNPs) move from cell to cell. Thus, it will be of special interest to determine whether MPs of dsRNA viruses interact with genomic dsRNAs or their derivative sRNAs. To this end, we studied the biochemical functions of MP Pns6 of Rice dwarf phytoreovirus (RDV), a member of Phytoreovirus that contains a 12-segmented dsRNA genome. We report here that Pns6 binds both dsRNAs and ssRNAs. Intriguingly, Pns6 exhibits non-sequence specificity for dsRNA but shows preference for ssRNA sequences derived from the conserved genomic 5′- and 3′- terminal consensus sequences of RDV. Furthermore, Pns6 exhibits magnesium-dependent ATPase activities. Mutagenesis identified the RNA binding and ATPase activity sites of Pns6 at the N- and C-termini, respectively. Our results uncovered the novel property of a viral MP in differentially recognizing dsRNA and ssRNA and establish a biochemical basis to enable further studies on the mechanisms of dsRNA viral MP functions
Cross sections and transverse single-spin asymmetries in forward neutral-pion production from proton collisions at root s=200 GeV
Measurements of the production of forward high-energy pi(0) mesons from transversely polarized proton collisions at root200 GeV are reported. The cross section is generally consistent with next-to-leading order perturbative QCD calculations. The analyzing power is small at x(F) below about 0.3, and becomes positive and large at higher x(F), similar to the trend in data at roots less than or equal to20 GeV. The analyzing power is in qualitative agreement with perturbative QCD model expectations. This is the first significant spin result seen for particles produced with p(T)>1 GeV/c at a polarized proton collider
Disappearance of back-to-back high-p(T) hadron correlations in central Au+Au collisions at root s(NN)=200 GeV
Azimuthal correlations for large transverse momentum charged hadrons have been measured over a wide pseudorapidity range and full azimuth in Au+Au and p+p collisions at roots(NN)=200 GeV. The small-angle correlations observed in p+p collisions and at all centralities of Au+Au collisions are characteristic of hard-scattering processes previously observed in high-energy collisions. A strong back-to-back correlation exists for p+p and peripheral Au+Au. In contrast, the back-to-back correlations are reduced considerably in the most central Au+Au collisions, indicating substantial interaction as the hard-scattered partons or their fragmentation products traverse the medium
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