1,936 research outputs found
Multipass automata and group word problems
We introduce the notion of multipass automata as a generalization of pushdown
automata and study the classes of languages accepted by such machines. The
class of languages accepted by deterministic multipass automata is exactly the
Boolean closure of the class of deterministic context-free languages while the
class of languages accepted by nondeterministic multipass automata is exactly
the class of poly-context-free languages, that is, languages which are the
intersection of finitely many context-free languages. We illustrate the use of
these automata by studying groups whose word problems are in the above classes
Exponential beams of electromagnetic radiation
We show that in addition to well known Bessel, Hermite-Gauss, and
Laguerre-Gauss beams of electromagnetic radiation, one may also construct
exponential beams. These beams are characterized by a fall-off in the
transverse direction described by an exponential function of rho. Exponential
beams, like Bessel beams, carry definite angular momentum and are periodic
along the direction of propagation, but unlike Bessel beams they have a finite
energy per unit beam length. The analysis of these beams is greatly simplified
by an extensive use of the Riemann-Silberstein vector and the Whittaker
representation of the solutions of the Maxwell equations in terms of just one
complex function. The connection between the Bessel beams and the exponential
beams is made explicit by constructing the exponential beams as wave packets of
Bessel beams.Comment: Dedicated to the memory of Edwin Powe
Maxwell equations in matrix form, squaring procedure, separating the variables, and structure of electromagnetic solutions
The Riemann -- Silberstein -- Majorana -- Oppenheimer approach to the Maxwell
electrodynamics in vacuum is investigated within the matrix formalism. The
matrix form of electrodynamics includes three real 4 \times 4 matrices. Within
the squaring procedure we construct four formal solutions of the Maxwell
equations on the base of scalar Klein -- Fock -- Gordon solutions. The problem
of separating physical electromagnetic waves in the linear space
\lambda_{0}\Psi^{0}+\lambda_{1}\Psi^{1}+\lambda_{2}\Psi^{2}+ lambda_{3}\Psi^{3}
is investigated, several particular cases, plane waves and cylindrical waves,
are considered in detail.Comment: 26 pages 16 International Seminar NCPC, May 19-22, 2009, Minsk,
Belaru
Fremanezumab for the Preventive Treatment of Chronic Migraine.
BACKGROUND: Fremanezumab, a humanized monoclonal antibody targeting calcitonin gene-related peptide (CGRP), is being investigated as a preventive treatment for migraine. We compared two fremanezumab dose regimens with placebo for the prevention of chronic migraine.
METHODS: In this phase 3 trial, we randomly assigned patients with chronic migraine (defined as headache of any duration or severity on ≥15 days per month and migraine on ≥8 days per month) in a 1:1:1 ratio to receive fremanezumab quarterly (a single dose of 675 mg at baseline and placebo at weeks 4 and 8), fremanezumab monthly (675 mg at baseline and 225 mg at weeks 4 and 8), or matching placebo. Both fremanezumab and placebo were administered by means of subcutaneous injection. The primary end point was the mean change from baseline in the average number of headache days (defined as days in which headache pain lasted ≥4 consecutive hours and had a peak severity of at least a moderate level or days in which acute migraine-specific medication [triptans or ergots] was used to treat a headache of any severity or duration) per month during the 12 weeks after the first dose.
RESULTS: Of 1130 patients enrolled, 376 were randomly assigned to fremanezumab quarterly, 379 to fremanezumab monthly, and 375 to placebo. The mean number of baseline headache days (as defined above) per month was 13.2, 12.8, and 13.3, respectively. The least-squares mean (±SE) reduction in the average number of headache days per month was 4.3±0.3 with fremanezumab quarterly, 4.6±0.3 with fremanezumab monthly, and 2.5±0.3 with placebo (P
CONCLUSIONS: Fremanezumab as a preventive treatment for chronic migraine resulted in a lower frequency of headache than placebo in this 12-week trial. Injection-site reactions to the drug were common. The long-term durability and safety of fremanezumab require further study. (Funded by Teva Pharmaceuticals; ClinicalTrials.gov number, NCT02621931 .)
Vortex lines of the electromagnetic field
Relativistic definition of the phase of the electromagnetic field, involving
two Lorentz invariants, based on the Riemann-Silberstein vector is adopted to
extend our previous study [I. Bialynicki-Birula, Z. Bialynicka-Birula and C.
Sliwa, Phys. Rev. A 61, 032110 (2000)] of the motion of vortex lines embedded
in the solutions of wave equations from Schroedinger wave mechanics to Maxwell
theory. It is shown that time evolution of vortex lines has universal features;
in Maxwell theory it is very similar to that in Schroedinger wave mechanics.
Connection with some early work on geometrodynamics is established. Simple
examples of solutions of Maxwell equations with embedded vortex lines are
given. Vortex lines in Laguerre-Gaussian beams are treated in some detail.Comment: 11 pages, 6 figures, to be published in Phys. Rev.
The measurement of household consumption expenditures
Household-level data on consumer expenditures underpin a wide range of empirical research in modern economics, spanning micro-and macroeconomics. This research includes work on consumption and saving, on poverty and inequality, and on risk sharing and insurance. We review different ways in which such data can be collected or captured: traditional detailed budget surveys, less onerous survey procedures that might be included in more general surveys, and administrative or process data. We discuss the advantages and difficulties of each approach and suggest directions for future investigation. © 2014 by Annual Reviews. All rights reserved
Shift-Symmetric Configurations in Two-Dimensional Cellular Automata: Irreversibility, Insolvability, and Enumeration
The search for symmetry as an unusual yet profoundly appealing phenomenon,
and the origin of regular, repeating configuration patterns have long been a
central focus of complexity science and physics. To better grasp and understand
symmetry of configurations in decentralized toroidal architectures, we employ
group-theoretic methods, which allow us to identify and enumerate these inputs,
and argue about irreversible system behaviors with undesired effects on many
computational problems. The concept of so-called configuration shift-symmetry
is applied to two-dimensional cellular automata as an ideal model of
computation. Regardless of the transition function, the results show the
universal insolvability of crucial distributed tasks, such as leader election,
pattern recognition, hashing, and encryption. By using compact enumeration
formulas and bounding the number of shift-symmetric configurations for a given
lattice size, we efficiently calculate the probability of a configuration being
shift-symmetric for a uniform or density-uniform distribution. Further, we
devise an algorithm detecting the presence of shift-symmetry in a
configuration.
Given the resource constraints, the enumeration and probability formulas can
directly help to lower the minimal expected error and provide recommendations
for system's size and initialization. Besides cellular automata, the
shift-symmetry analysis can be used to study the non-linear behavior in various
synchronous rule-based systems that include inference engines, Boolean
networks, neural networks, and systolic arrays.Comment: 22 pages, 9 figures, 2 appendice
Groups, Graphs, Languages, Automata, Games and Second-order Monadic Logic
In this paper we survey some surprising connections between group theory, the
theory of automata and formal languages, the theory of ends, infinite games of
perfect information, and monadic second-order logic
Sustained Activation of Cell Adhesion Is a Differentially Regulated Process in B Lymphopoiesis
It is largely unknown how hematopoietic progenitors are positioned within specialized niches of the bone marrow microenvironment during development. Chemokines such as CXCL12, previously called stromal cell–derived factor 1, are known to activate cell integrins of circulating leukocytes resulting in transient adhesion before extravasation into tissues. However, this short-term effect does not explain the mechanism by which progenitor cells are retained for prolonged periods in the bone marrow. Here we show that in human bone marrow CXCL12 triggers a sustained adhesion response specifically in progenitor (pro- and pre-) B cells. This sustained adhesion diminishes during B cell maturation in the bone marrow and, strikingly, is absent in circulating mature B cells, which exhibit only transient CXCL12-induced adhesion. The duration of adhesion is tightly correlated with CXCL12-induced activation of focal adhesion kinase (FAK), a known molecule involved in integrin-mediated signaling. Sustained adhesion of progenitor B cells is associated with prolonged FAK activation, whereas transient adhesion in circulating B cells is associated with short-lived FAK activation. Moreover, sustained and transient adhesion responses are differentially affected by pharmacological inhibitors of protein kinase C and phosphatidylinositol 3-kinase. These results provide a developmental cell stage–specific mechanism by which chemokines orchestrate hematopoiesis through sustained rather than transient activation of adhesion and cell survival pathways
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