A Measure of Space for Computing over the Reals

We propose a new complexity measure of space for the BSS model of computation. We define LOGSPACE\_W and PSPACE\_W complexity classes over the reals. We prove that LOGSPACE\_W is included in NC^2\_R and in P\_W, i.e. is small enough for being relevant. We prove that the Real Circuit Decision Problem is P\_R-complete under LOGSPACE\_W reductions, i.e. that LOGSPACE\_W is large enough for containing natural algorithms. We also prove that PSPACE\_W is included in PAR\_R

Calculation of the neutron electric dipole moment with two dynamical flavors of domain wall fermions

We present a study of the neutron electric dipole moment ($\vec d_N$) within the framework of lattice QCD with two flavors of dynamical lig ht quarks. The dipole moment is sensitive to the topological structure of the gaug e fields, and accuracy can only be achieved by using dynamical, or sea quark, calc ulations. However, the topological charge evolves slowly in these calculations, le ading to a relatively large uncertainty in $\vec d_N$. It is shown, using quenched configurations, that a better sampling of the charge d istribution reduces this problem, but because the CP even part of the fermion determinant is absent, both the topological charge dis tribution and $\vec d_N$ are pathological in the chiral limit. We discuss the statistical and systematic uncertainties arising from the topological charge distr ibution and unphysical size of the quark mass in our calculations and prospects fo r eliminating them. Our calculations employ the RBC collaboration two flavor domain wall fermion and DBW2 gauge action lattices with inverse lattice spacing $a^{-1}\approx$ 1.7 GeV, physical volume $V\approx (2$ fm)$^3$, and light quark mass roughly equal to the strange quark mass ($m_{sea}=0.03$ and 0.04). We determine a value of the electric dipole moment that is zero withi n (statistical) errors, $|\vec d_N| = -0.04(20)$ e-$\theta$-fm at the smaller sea quark mass. Satisfactory results for the magnetic and electric form factors of the proton and neutron are also obtained and presented.Comment: 46 pages. Changed one author addres

Microwave Scattering and Noise Emission from Afterglow Plasmas in a Magnetic Field

The microwave reflection and noise emission (extraordinary mode) from cylindrical rare‐gas (He, Ne, Ar) afterglow plasmas in an axial magnetic field is described. Reflection and noise emission are measured as a function of magnetic field near electron cyclotron resonance (ω ≈ ω_c) with electron density as a parameter (ω_p < ω). A broad peak, which shifts to lower values of ω_c/ω) as electron density increases, is observed for (ω_c/ω) ≤ 1. For all values of electron density a second sharp peak is found very close to cyclotron resonance in reflection measurements. This peak does not occur in the emission data. Calculations of reflection and emission using a theoretical model consisting of a one‐dimensional, cold plasma slab with nonuniform electron density yield results in qualitative agreement with the observations. Both the experimental and theoretical results suggest that the broad, density‐dependent peak involves resonance effects at the upper hybrid frequency ((ω_h)^2 = (ω_c)^2 + (ω_p)^2) of the plasma

Staggered Fermion Actions with Improved Rotational Invariance

We introduce a class of improved actions for staggered fermions which to O(p^4) and O(p^6), respectively, lead to rotationally invariant propagators. We discuss the resulting reduction of flavour symmetry breaking in the meson spectrum and comment on the improvement in the calculation of thermodynamic observables.Comment: 3 pages and 4 figures, Contribution to Lattice 97 (Poster Session), late

The three flavour chiral phase transition with an improved quark and gluon action in lattice QCD

The finite-temperature chiral phase transition is investigated for three flavours of staggered quarks on a lattice of temporal extent N_t=4. In the simulation we use an improved fermion action which reduces rotational symmetry breaking of the quark propagator (p4-action), include fat-links to improve the flavour symmetry and use the tree level improved (1,2) gluon action. We study the nature of the phase transition for quark masses of ma=0.025, ma=0.05 and ma=0.1 on lattices with spatial sizes of 8^3 and 16^3.Comment: LATTICE98(hightemp), 3 pages, 7 figures, LaTeX2e-File, espcrc2.st

The Pressure in 2, 2+1 and 3 Flavour QCD

We calculate the pressure in QCD with two and three light quarks on a lattice of size 16^3x4 using tree level improved gauge and fermion actions. We argue that for temperatures T > 2T_c systematic effects due to the finite lattice cut-off and non-vanishing quark masses are below 15% in this calculation and give an estimate for the continuum extrapolated pressure in QCD with massless quarks. We find that the flavour dependence of the pressure is dominated by that of the Stefan-Boltzmann constant. Furthermore we perform a calculation of the pressure using 2 light (m_u,d/T=0.4) and one heavier quark (m_s/T = 1). In this case the pressure is reduced relative to that of three flavour QCD. This effect is stronger than expected from the mass dependence of an ideal Fermi gas.Comment: 13 pages, LaTeX2

Ion observations from geosynchronous orbit as a proxy for ion cyclotron wave growth during storm times

[1] There is still much to be understood about the processes contributing to relativistic electron enhancements and losses in the radiation belts. Wave particle interactions with both whistler and electromagnetic ion cyclotron (EMIC) waves may precipitate or accelerate these electrons. This study examines the relation between EMIC waves and resulting relativistic electron flux levels after geomagnetic storms. A proxy for enhanced EMIC waves is developed using Los Alamos National Laboratory Magnetospheric Plasma Analyzer plasma data from geosynchronous orbit in conjunction with linear theory. In a statistical study using superposed epoch analysis, it is found that for storms resulting in net relativistic electron losses, there is a greater occurrence of enhanced EMIC waves. This is consistent with the hypothesis that EMIC waves are a primary mechanism for the scattering of relativistic electrons and thus cause losses of such particles from the magnetosphere

Active Semi-Supervised Learning Using Sampling Theory for Graph Signals

We consider the problem of offline, pool-based active semi-supervised learning on graphs. This problem is important when the labeled data is scarce and expensive whereas unlabeled data is easily available. The data points are represented by the vertices of an undirected graph with the similarity between them captured by the edge weights. Given a target number of nodes to label, the goal is to choose those nodes that are most informative and then predict the unknown labels. We propose a novel framework for this problem based on our recent results on sampling theory for graph signals. A graph signal is a real-valued function defined on each node of the graph. A notion of frequency for such signals can be defined using the spectrum of the graph Laplacian matrix. The sampling theory for graph signals aims to extend the traditional Nyquist-Shannon sampling theory by allowing us to identify the class of graph signals that can be reconstructed from their values on a subset of vertices. This approach allows us to define a criterion for active learning based on sampling set selection which aims at maximizing the frequency of the signals that can be reconstructed from their samples on the set. Experiments show the effectiveness of our method.Comment: 10 pages, 6 figures, To appear in KDD'1

The Functional Derivation of Master Equations

Master equations describe the quantum dynamics of open systems interacting with an environment. They play an increasingly important role in understanding the emergence of semiclassical behavior and the generation of entropy, both being related to quantum decoherence. Presently we derive the exact master equation for a homogeneous scalar Higgs or inflaton like field coupled to an environment field represented by an infinite set of harmonic oscillators. Our aim is to demonstrate a derivation directly from the path integral representation of the density matrix propagator. Applications and generalizations of this result are discussed.Comment: 10 pages; LaTex. - Contribution to the workshop Hadron Physics VI, March 1998, Florianopolis (Brazil); proceedings, E. Ferreira et al., eds. (World Scientific). Replaced by slightly modified published versio