6,362 research outputs found
Probing the Light Pseudoscalar Window
Very light pseudoscalars can arise from the symmetry-breaking sector in many
extensions of the Standard Model. If their mass is below 200 MeV, they can be
long-lived and have interesting phenomenology. We discuss the experimental
constraints on several models with light pseudoscalars, including one in which
the pseudoscalar is naturally fermiophobic. Taking into account the stringent
bounds from rare K and B decays, we find allowed parameter space in each model
that may be accessible in direct production experiments. In particular, we
study the photoproduction of light pseudoscalars at Jefferson Lab and conclude
that a beam dump experiment could explore some of the allowed parameter space
of these models.Comment: 22 pages, 4 figure
An Approximate Maximum Common Subgraph Algorithm for Large Digital Circuits
This paper presents an approximate Maximum Common Subgraph (MCS) algorithm, specifically for directed, cyclic graphs representing digital circuits. \ud
Because of the application domain, the graphs have nice properties: they are very sparse; have many different labels; and most vertices have only one predecessor. The algorithm iterates over all vertices once and uses heuristics to find the MCS. It is linear in computational complexity with respect to the size of the graph. Experiments show that very large common subgraphs were found in graphs of up to 200,000 vertices within a few minutes, when a quarter or less of the graphs differ. The variation in run-time and quality of the result is low
Comparison of Dissipative Particle Dynamics and Langevin thermostats for out-of-equilibrium simulations of polymeric systems
In this work we compare and characterize the behavior of Langevin and
Dissipative Particle Dynamics (DPD) thermostats in a broad range of
non-equilibrium simulations of polymeric systems. Polymer brushes in relative
sliding motion, polymeric liquids in Poiseuille and Couette flows, and
brush-melt interfaces are used as model systems to analyze the efficiency and
limitations of different Langevin and DPD thermostat implementations. Widely
used coarse-grained bead-spring models under good and poor solvent conditions
are employed to assess the effects of the thermostats. We considered
equilibrium, transient, and steady state examples for testing the ability of
the thermostats to maintain constant temperature and to reproduce the
underlying physical phenomena in non-equilibrium situations. The common
practice of switching-off the Langevin thermostat in the flow direction is also
critically revisited. The efficiency of different weight functions for the DPD
thermostat is quantitatively analyzed as a function of the solvent quality and
the non-equilibrium situation.Comment: 12 pages, introduction improved, references added, to appear in Phys.
Rev.
Anomalous Hall effect as a probe of the chiral order in spin glasses
Anomalous Hall effect arising from the noncoplanar spin configuration
(chirality) is discussed as a probe of the chiral order in spin glasses. It is
shown that the Hall coefficient yields direct information about the linear and
nonlinear chiral susceptibilities of the spin sector, which has been hard to
obtain experimentally from the standard magnetic measurements. Based on the
chirality scenario of spin-glass transition, predictions are given on the
behavior of the Hall resistivity of canonical spin glasses.Comment: Order estimate of the effect given, one reference added. To appear in
Phys. Rev. Letter
First Principles Calculation of Anomalous Hall Conductivity in Ferromagnetic bcc Fe
We perform a first principles calculation of the anomalous Hall effect in
ferromagnetic bcc Fe. Our theory identifies an intrinsic contribution to the
anomalous Hall conductivity and relates it to the k-space Berry phase of
occupied Bloch states. The theory is able to account for both dc and
magneto-optical Hall conductivities with no adjustable parameters.Comment: 4 pages, 6 figures, author list correcte
On the Formation of Copper Linear Atomic Suspended Chains
We report high resolution transmission electron microscopy and classical
molecular dynamics simulation results of mechanically stretching copper
nanowires conducting to linear atomic suspended chains (LACs) formation. In
contrast with some previous experimental and theoretical work in literature
that stated that the formation of LACs for copper should not exist our results
showed the existence of LAC for the [111], [110], and [100] crystallographic
directions, being thus the sequence of most probable occurence.Comment: 4 pages, 3 figure
Investigation of the Domain Wall Fermion Approach to Chiral Gauge Theories on the Lattice
We investigate a recent proposal to construct chiral gauge theories on the
lattice using domain wall fermions. We restrict ourselves to the finite volume
case, in which two domain walls are present, with modes of opposite chirality
on each of them. We couple the chiral fermions on only one of the domain walls
to a gauge field. In order to preserve gauge invariance, we have to add a
scalar field, which gives rise to additional light mirror fermion and scalar
modes. We argue that in an anomaly free model these extra modes would decouple
if our model possesses a so-called strong coupling symmetric phase. However,
our numerical results indicate that such a phase most probably does not exist.
---- Note: 9 Postscript figures are appended as uuencoded compressed tar file.Comment: 27p. Latex; UCSD/PTH 93-28, Wash. U. HEP/93-6
Supernova Simulations with Boltzmann Neutrino Transport: A Comparison of Methods
Accurate neutrino transport has been built into spherically symmetric
simulations of stellar core collapse and postbounce evolution. The results of
such simulations agree that spherically symmetric models with standard
microphysical input fail to explode by the delayed, neutrino-driven mechanism.
Independent groups implemented fundamentally different numerical methods to
tackle the Boltzmann neutrino transport equation. Here we present a direct and
detailed comparison of such neutrino radiation-hydrodynamical simulations for
two codes, Agile-Boltztran of the Oak Ridge-Basel group and Vertex of the
Garching group. The former solves the Boltzmann equation directly by an
implicit, general relativistic discrete angle method on the adaptive grid of a
conservative implicit hydrodynamics code with second-order TVD advection. In
contrast, the latter couples a variable Eddington factor technique with an
explicit, moving-grid, conservative high-order Riemann solver with important
relativistic effects treated by an effective gravitational potential. The
presented study is meant to test both neutrino radiation-hydrodynamics
implementations and to provide a data basis for comparisons and verifications
of supernova codes to be developed in the future. Results are discussed for
simulations of the core collapse and post-bounce evolution of a 13 solar mass
star with Newtonian gravity and a 15 solar mass star with relativistic gravity.Comment: 23 pages, 13 figures, revised version, to appear in Ap
Anomalous Hall effect in ferromagnetic semiconductors
We present a theory of the anomalous Hall effect in ferromagnetic (Mn,III)V
semiconductors. Our theory relates the anomalous Hall conductance of a
homogeneous ferromagnet to the Berry phase acquired by a quasiparticle
wavefunction upon traversing closed paths on the spin-split Fermi surface of a
ferromagnetic state. It can be applied equally well to any itinerant electron
ferromagnet. The quantitative agreement between our theory and experimental
data in both (In,Mn)As and (Ga,Mn)As systems suggests that this disorder
independent contribution to the anomalous Hall conductivity dominates in
diluted magnetic semiconductors.Comment: 4 pages, 2 figure
Reproducibility of lymphovascular space invasion (LVSI) assessment in endometrial cancer
Aims Lymphovascular space invasion (LVSI) in endometrial cancer (EC) is an important prognostic variable impacting on a patient's individual recurrence risk and adjuvant treatment recommendations. Recent work has shown that grading the extent of LVSI further improves its prognostic strength in patients with stage I endometrioid EC. Despite this, there is little information on the reproducibility of LVSI assessment in EC. Therefore, we designed a study to evaluate interobserver agreement in discriminating true LVSI from LVSI mimics (Phase I) and reproducibility of grading extent of LVSI (Phase II). Methods and results Scanned haematoxylin and eosin (H&E) slides of endometrioid EC (EEC) with a predefined possible LVSI focus were hosted on a website and assessed by a panel of six European gynaecological pathologists. In Phase I, 48 H&E slides were included for LVSI assessment and in Phase II, 42 H&E slides for LVSI grading. Each observer was instructed to apply the criteria for LVSI used in daily practice. The degree of agreement was measured using the two-way absolute agreement average-measures intraclass correlation coefficient (ICC). Reproducibility of LVSI assessment (ICC = 0.64, P < 0.001) and LVSI grading (ICC = 0.62, P < 0.001) in EEC was substantial among the observers. Conclusions Given the good reproducibility of LVSI, this study further supports the important role of LVSI in decision algorithms for adjuvant treatment
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