39,949 research outputs found
Lasercooled RaF as a promising candidate to measure molecular parity violation
The parameter , which characterizes nuclear spin-dependent
parity violation effects within the effective molecular spin-rotational
Hamiltonian, was computed for the electronic ground state of radium fluoride
(RaF) and found to be one of the largest absolute values predicted so far.
These calculations were performed with the complex generalised Hartree-Fock
method within a two-component (quasi-relativistic) zeroth-order regular
approximation framework. Peculiarities of the molecular electronic structure of
RaF lead to highly diagonal Franck-Condon matrices between vibrational states
of the electronic ground and first excited states, which renders the molecule
in principle suitable for direct laser cooling. As a trapped gas of cold
molecules offers a superior coherence time, RaF can be considered a promising
candidate for high-precision spectroscopic experiments aimed at the search of
molecular parity-violation effects.Comment: 4.5 pages, 1 figure, 2 tables. Supplementary material can be
requested from the authors. Minor changes to version
Collective Charge Excitations below the Metal-to-Insulator Transition in BaVS3
The charge response in the barium vanadium sulfide (BaVS3) single crystals is
characterized by dc resistivity and low frequency dielectric spectroscopy. A
broad relaxation mode in MHz range with huge dielectric constant ~= 10^6
emerges at the metal-to-insulator phase transition TMI ~= 67 K, weakens with
lowering temperature and eventually levels off below the magnetic transition
Tchi ~= 30 K. The mean relaxation time is thermally activated in a manner
similar to the dc resistivity. These features are interpreted as signatures of
the collective charge excitations characteristic for the orbital ordering that
gradually develops below TMI and stabilizes at long-range scale below Tchi.Comment: 6 pages, 3 figures, submitted to PR
Asymptotics for the Wiener sausage among Poissonian obstacles
We consider the Wiener sausage among Poissonian obstacles. The obstacle is
called hard if Brownian motion entering the obstacle is immediately killed, and
is called soft if it is killed at certain rate. It is known that Brownian
motion conditioned to survive among obstacles is confined in a ball near its
starting point. We show the weak law of large numbers, large deviation
principle in special cases and the moment asymptotics for the volume of the
corresponding Wiener sausage. One of the consequence of our results is that the
trajectory of Brownian motion almost fills the confinement ball.Comment: 19 pages, Major revision made for publication in J. Stat. Phy
Incorporation of Nitrogen into Organics Produced by Fischer-Tropsch Type Chemistry
Laboratory simulations have demonstrated that hydrothermal systems have the potential to produce a range of organic compounds through Fischer-Tropsch type (FTT) chemistry. The distribution of products depends on several factors, including the abundance and composition of feed-stock molecules, reaction temperature, and the physical and chemical characteristics of catalytic materials included in the reactions. The majority of studies per-formed to date have focused solely on inclusion of CO2 or CO and H2 as the carbon, oxygen and hydrogen sources, which limits the possible products to hydro-carbons, alcohols and carboxylic acids. A few studies have included nitrogen in the form of ammonia, which led to the production of amino acids and nitrogenous bases; and a separate suite of studies included sulfur as sulfide minerals or H2S, which yielded products such as thiols and amino acids. Although these demonstrations provide compelling evidence that FTT reactions can produce compounds of interest for the origins of life, such reactions have been conducted under a very limited range of conditions and the synthetic reaction mechanisms have generally not been well-characterized. As a consequence, it is difficult to extrapolate these results to geologic systems or to evaluate how variations in reactant compositions would affect the distribution of products over time. We have begun a series of laboratory experiments that will incorporate a range of precursor molecules in varying compositions to determine how these variables affect the relative amounts and speciation of life-essential elements in organic molecules produced under FTT conditions. In the present work, we focus on systems containing C, H, O and N
Cities in fiction: Perambulations with John Berger
This paper explores selected novels by John Berger in which cities play a central role. These cities are places, partially real and partially imagined, where memory, hope, and despair intersect. My reading of the novels enables me to trace important themes in recent discourses on the nature of contemporary capitalism, including notions of resistance and universality. I also show how Berger?s work points to a writing that can break free from the curious capacity of capitalism to absorb and feed of its critique
Covering problems in edge- and node-weighted graphs
This paper discusses the graph covering problem in which a set of edges in an
edge- and node-weighted graph is chosen to satisfy some covering constraints
while minimizing the sum of the weights. In this problem, because of the large
integrality gap of a natural linear programming (LP) relaxation, LP rounding
algorithms based on the relaxation yield poor performance. Here we propose a
stronger LP relaxation for the graph covering problem. The proposed relaxation
is applied to designing primal-dual algorithms for two fundamental graph
covering problems: the prize-collecting edge dominating set problem and the
multicut problem in trees. Our algorithms are an exact polynomial-time
algorithm for the former problem, and a 2-approximation algorithm for the
latter problem, respectively. These results match the currently known best
results for purely edge-weighted graphs.Comment: To appear in SWAT 201
Parity Effect in a Small Superconducting Particle
Matveev and Larkin calculated the parity effect on the ground state energy of
a small superconducting particle in the regimes where the mean level spacing is
either large or small compared to the bulk gap. We perform a numerical
calculation which extends their results into the intermediate regime, where the
level spacing is of the same order as the bulk gap.Comment: 6 LaTeX pages, including 2 EPS figures; corrected reference and
spellin
Harmonic coordinate method for simulating generic singularities
This paper presents both a numerical method for general relativity and an
application of that method. The method involves the use of harmonic coordinates
in a 3+1 code to evolve the Einstein equations with scalar field matter. In
such coordinates, the terms in Einstein's equations with the highest number of
derivatives take a form similar to that of the wave equation. The application
is an exploration of the generic approach to the singularity for this type of
matter. The preliminary results indicate that the dynamics as one approaches
the singularity is locally the dynamics of the Kasner spacetimes.Comment: 5 pages, 4 figures, Revtex, discussion expanded, references adde
Imaging and manipulation of skyrmion lattice domains in Cu2OSeO3
Nanoscale chiral skyrmions in noncentrosymmetric helimagnets are promising
binary state variables in high-density, low-energy nonvolatile memory.
Skyrmions are ubiquitous as an ordered, single-domain lattice phase, which
makes it difficult to write information unless they are spatially broken up
into smaller units, each representing a bit. Thus, the formation and
manipulation of skyrmion lattice domains is a prerequisite for memory
applications. Here, using an imaging technique based on resonant magnetic x-ray
diffraction, we demonstrate the mapping and manipulation of skyrmion lattice
domains in Cu2OSeO3. The material is particularly interesting for applications
owing to its insulating nature, allowing for electric field-driven domain
manipulation.Comment: 4 pages, 3 figure
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