30,235 research outputs found
An Evening Spent with Bill van Zwet
Willem Rutger van Zwet was born in Leiden, the Netherlands, on March 31,
1934. He received his high school education at the Gymnasium Haganum in The
Hague and obtained his Masters degree in Mathematics at the University of
Leiden in 1959. After serving in the army for almost two years, he obtained his
Ph.D. at the University of Amsterdam in 1964, with Jan Hemelrijk as advisor. In
1965, he was appointed Associate Professor of Statistics at the University of
Leiden and promoted to Full Professor in 1968. He remained in Leiden until his
retirement in 1999, while also serving as Associate Professor at the University
of Oregon (1965), William Newman Professor at the University of North Carolina
at Chapel Hill (1990--1996), frequent visitor and Miller Professor (1997) at
the University of California at Berkeley, director of the Thomas Stieltjes
Institute of Mathematics in the Netherlands (1992--1999), and founding director
of the European research institute EURANDOM (1997--2000). At Leiden, he was
Dean of the School of Mathematics and Natural Sciences (1982--1984). He served
as chair of the scientific council and member of the board of the Mathematics
Centre at Amsterdam (1983--1996) and the Leiden University Fund (1993--2005).Comment: Published in at http://dx.doi.org/10.1214/08-STS261 the Statistical
Science (http://www.imstat.org/sts/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Remembering Wassily Hoeffding
Wasssily Hoeffding's terminal illness and untimely death in 1991 put an end
to efforts that were made to interview him for Statistical Science. An account
of his scientific work is given in Fisher and Sen [The Collected Works of
Wassily Hoeffding (1994) Springer], but the present authors felt that the
statistical community should also be told about the life of this remarkable
man. He contributed much to statistical science, but will also live on in the
memory of those who knew him as a kind and modest teacher and friend, whose
courage and learning were matched by a wonderful sense of humor.Comment: Published in at http://dx.doi.org/10.1214/08-STS271 the Statistical
Science (http://www.imstat.org/sts/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Optical Constants of Silver and Barium in the Vacuum Ultraviolet Spectral Region
Optical constants of silver and barium in vacuum ultraviolet spectral regio
The tunneling conductance between a superconducting STM tip and an out-of-equilibrium carbon nanotube
We calculate the current and differential conductance for the junction
between a superconducting (SC) STM tip and a Luttinger liquid (LL). For an
infinite single-channel LL, the SC coherence peaks are preserved in the
tunneling conductance for interactions weaker than a critical value, while for
strong interactions (g <0.38), they disappear and are replaced by cusp-like
features. For a finite-size wire in contact with non-interacting leads, we find
however that the peaks are restored even for extremely strong interactions. In
the presence of a source-drain voltage the peaks/cusps split, and the split is
equal to the voltage. At zero temperature, even very strong interactions do not
smear the two peaks into a broader one; this implies that the recent
experiments of Y.-F. Chen et. al. (Phys. Rev. Lett. 102, 036804 (2009)) do not
rule out the existence of strong interactions in carbon nanotubes.Comment: 8 pages, 3 figure
Preparation and evaluation of fiber metal nickel battery plaques third quarterly progress report, feb. 1 - apr. 30, 1965
Effect of fiber size opon internal surface area and pore size of nickel fiber metal plaque
Algebraic vortex liquid in spin-1/2 triangular antiferromagnets: Scenario for Cs_2CuCl_4
Motivated by inelastic neutron scattering data on Cs_2CuCl_4, we explore
spin-1/2 triangular lattice antiferromagnets with both spatial and easy-plane
exchange anisotropies, the latter due to an observed Dzyaloshinskii-Moriya
interaction. Exploiting a duality mapping followed by a fermionization of the
dual vortex degrees of freedom, we find a novel "critical" spin-liquid phase
described in terms of Dirac fermions with an emergent global SU(4) symmetry
minimally coupled to a non-compact U(1) gauge field. This ``algebraic vortex
liquid" supports gapless spin excitations and universal power-law correlations
in the dynamical spin structure factor which are consistent with those observed
in Cs_2CuCl_4. We suggest future neutron scattering experiments that should
help distinguish between the algebraic vortex liquid and other spin liquids and
quantum critical points previously proposed in the context of Cs_2CuCl_4.Comment: 4 pages, 3 figures; minor revisions, momenta in Fig. 2 correcte
Rate of Adaptation in Large Sexual Populations
Adaptation often involves the acquisition of a large number of genomic
changes which arise as mutations in single individuals. In asexual populations,
combinations of mutations can fix only when they arise in the same lineage, but
for populations in which genetic information is exchanged, beneficial mutations
can arise in different individuals and be combined later. In large populations,
when the product of the population size N and the total beneficial mutation
rate U_b is large, many new beneficial alleles can be segregating in the
population simultaneously. We calculate the rate of adaptation, v, in several
models of such sexual populations and show that v is linear in NU_b only in
sufficiently small populations. In large populations, v increases much more
slowly as log NU_b. The prefactor of this logarithm, however, increases as the
square of the recombination rate. This acceleration of adaptation by
recombination implies a strong evolutionary advantage of sex
D-wave correlated Critical Bose Liquids in two dimensions
We develop a description of a new quantum liquid phase of interacting bosons
in 2d which possesses relative D-wave two-body correlations and which we call a
D-wave Bose Liquid (DBL). The DBL has no broken symmetries, supports gapless
boson excitations residing on "Bose surfaces" in momentum space, and exhibits
power law correlations with continuously variable exponents. While the DBL can
be constructed for bosons in the 2d continuum, the state only respects the
point group symmetries of the square lattice. On the lattice the DBL respects
all symmetries and does not require a particular filling. But lattice effects
allow a second distinct phase, a quasi-local variant which we call a D-wave
Local Bose Liquid (DLBL). Remarkably, the DLBL has short-range boson
correlations and hence no Bose surfaces, despite sharing gapless excitations
and other critical signatures with the DBL. Moreover, both phases are metals
with a resistance that vanishes as a power of the temperature. We establish
these results by constructing a class of many-particle wavefunctions for the
DBL, which are time reversal invariant analogs of Laughlin's quantum Hall
wavefunction for bosons at . A gauge theory formulation leads to a
simple mean field theory, and an N-flavor generalization enables incorporation
of gauge field fluctuations to deduce the properties of the DBL/DLBL; various
equal time correlation functions are in qualitative accord with the properties
inferred from the wavefunctions. We also identify a promising Hamiltonian which
might manifest the DBL or DLBL, and perform a variational study comparing to
other competing phases. We suggest how the DBL wavefunction can be generalized
to describe an itinerant non-Fermi liquid phase of electrons on the square
lattice with a no double occupancy constraint, a D-wave metal phase.Comment: 33 pages, 17 figure
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