3,957 research outputs found
Confinement effects from interacting chromo-magnetic and axion fields
We study a non-Abelian gauge theory with a pseudo scalar coupling \phi
\epsilon ^{\mu \nu \alpha \beta} F_{\mu \nu}^a F_{\alpha \beta}^a in the case
where a constant chromo-electric, or chromo-magnetic, strength expectation
value is present. We compute the interaction potential within the framework of
gauge-invariant, path-dependent, variables formalism. While in the case of a
constant chromo-electric field strength expectation value the static potential
remains Coulombic, in the case of a constant chromo-magnetic field strength the
potential energy is the sum of a Coulombic and a linear potentials, leading to
the confinement of static charges.Comment: 12 pages, no figures, published versio
Calcitonin gene-related peptide receptor antagonist BIBN 4096 BS for the acute treatment of migraine
Background: Calcitonin gene–related peptide (CGRP) may have a causative role in migraine. We therefore hypothesized that a CGRP-receptor antagonist might be effective in the treatment of migraine attacks.
Methods: In an international, multicenter, double-blind, randomized clinical trial of BIBN 4096 BS, a highly specific and potent nonpeptide CGRP-receptor antagonist, 126 patients with migraine received one of the following: placebo or 0.25, 0.5, 1, 2.5, 5, or 10 mg of BIBN 4096 BS intravenously over a period of 10 minutes. A group-sequential adaptive treatment-assignment design was used to minimize the number of patients exposed.
Results: The 2.5-mg dose was selected, with a response rate of 66 percent, as compared with 27 percent for placebo (P=0.001). The BIBN 4096 BS group as a whole had a response rate of 60 percent. Significant superiority over placebo was also observed with respect to most secondary end points: the pain-free rate at 2 hours; the rate of sustained response over a period of 24 hours; the rate of recurrence of headache; improvement in nausea, photophobia, phonophobia, and functional capacity; and the time to meaningful relief. An effect was apparent after 30 minutes and increased over the next few hours. The overall rate of adverse events was 25 percent after the 2.5-mg dose of the drug and 20 percent for the BIBN 4096 BS group as a whole, as compared with 12 percent for placebo. The most frequent side effect was paresthesia. There were no serious adverse events.
Conclusions: The CGRP antagonist BIBN 4096 BS was effective in treating acute attacks of migraine
Quantum corrections from a path integral over reparametrizations
We study the path integral over reparametrizations that has been proposed as
an ansatz for the Wilson loops in the large- QCD and reproduces the area law
in the classical limit of large loops. We show that a semiclassical expansion
for a rectangular loop captures the L\"uscher term associated with
dimensions and propose a modification of the ansatz which reproduces the
L\"uscher term in other dimensions, which is observed in lattice QCD. We repeat
the calculation for an outstretched ellipse advocating the emergence of an
analog of the L\"uscher term and verify this result by a direct computation of
the determinant of the Laplace operator and the conformal anomaly
Simulation of effect of climate, soils and management on N2O emission from grassland
Nitrous oxide (N2O) is a potent greenhouse gas with a high contribution from agricultural soils and emissions that depend on soil type, climate, crops and management practices. The N2O emissions therefore need to be included as an integral part of environmental assessment of agricultural production systems. A dynamical algorithm for N2O production and emission from agricultural soils was developed and included in the FASSET whole-farm model. The model simulated carbon and nitrogen (N) turnover on a daily basis. Both nitrification and denitrification was included in the model as sources for N2O production, and the N2O emissions were simulated to depend on soil microbial and physical conditions. The model was tested on experimental data of N2O emissions from grasslands in UK, Finland and Denmark, differing in climatic conditions, soil properties and management. The model simulated the general time course of N2O emissions and captured the observed effects of fertiliser and manure management on emissions. However, emissions from a soil with high clay content were overestimated with the model. Scenario analyses for grazed and cut grasslands were conducted to evaluate the effects of soil type, climatic conditions, grassland management and N fertilisation on N2O emissions. The soils varied from sandy to sandy loam and the climatic variation was taken to represent the climatic variation within Denmark. N fertiliser rates were varied from 0 to 500 kg N ha-1. The simulated N2O emissions showed a non-linear response to increasing N rates with increasing emission factors at higher N rates. The simulated emissions increased with increasing soil clay contents. There was no effect of climatic conditions. Emissions were slightly higher from grazed grasslands compared with cut grasslands at similar rates of total N input (fertiliser and animal excreta). The results indicate higher emission factors and thus higher potentials for reducing N2O emissions for intensively grazed grasslands on fine textured soils than for extensive cut based grasslands on sandy soils
Nucleation of quark matter bubbles in neutron stars
The thermal nucleation of quark matter bubbles inside neutron stars is
examined for various temperatures which the star may realistically encounter
during its lifetime. It is found that for a bag constant less than a critical
value, a very large part of the star will be converted into the quark phase
within a fraction of a second. Depending on the equation of state for neutron
star matter and strange quark matter, all or some of the outer parts of the
star may subsequently be converted by a slower burning or a detonation.Comment: 13 pages, REVTeX, Phys.Rev.D (in press), IFA 93-32. 5 figures (not
included) available upon request from [email protected]
Naupliar and Metanaupliar development of Thysanoessa raschii (Malacostraca, Euphausiacea) from GodthĂĄbsfjord, Greenland, with a reinstatement of the ancestral status of the free-living Nauplius in Malacostracan evolution
The presence of a characteristic crustacean larval type, the nauplius, in many crustacean taxa has often been considered one of the few uniting characters of the Crustacea. Within Malacostraca, the largest crustacean group, nauplii are only present in two taxa, Euphauciacea (krill) and Decapoda Dendrobranchiata. The presence of nauplii in these two taxa has traditionally been considered a retained primitive characteristic, but free-living nauplii have also been suggested to have reappeared a couple of times from direct developing ancestors during malacostracan evolution. Based on a re-study of Thysanoessa raschii (Euphausiacea) using preserved material collected in Greenland, we readdress this important controversy in crustacean evolution, and, in the process, redescribe the naupliar and metanaupliar development of T. raschii. In contrast to most previous studies of euphausiid development, we recognize three (not two) naupliar (= ortho-naupliar) stages (N1-N3) followed by a metanauplius (MN). While there are many morphological changes between nauplius 1 and 2 (e.g., appearance of long caudal setae), the changes between nauplius 2 and 3 are few but distinct. They involve the size of some caudal spines (largest in N3) and the setation of the antennal endopod (an extra seta in N3). A wider comparison between free-living nauplii of both Malacostraca and non-Malacostraca revealed similarities between nauplii in many taxa both at the general level (e.g., the gradual development and number of appendages) and at the more detailed level (e.g., unclear segmentation of naupliar appendages, caudal setation, presence of frontal filaments). We recognize these similarities as homologies and therefore suggest that free-living nauplii were part of the ancestral malacostracan type of development. The derived morphology (e.g., lack of feeding structures, no fully formed gut, high content of yolk) of both euphausiid and dendrobranchiate nauplii is evidently related to their non-feeding (lecithotrophic) status
Scale Free Cluster Distributions from Conserving Merging-Fragmentation Processes
We propose a dynamical scheme for the combined processes of fragmentation and
merging as a model system for cluster dynamics in nature and society displaying
scale invariant properties. The clusters merge and fragment with rates
proportional to their sizes, conserving the total mass. The total number of
clusters grows continuously but the full time-dependent distribution can be
rescaled over at least 15 decades onto a universal curve which we derive
analytically. This curve includes a scale free solution with a scaling exponent
of -3/2 for the cluster sizes.Comment: 4 pages, 3 figure
Correlator of Fundamental and Anti-symmetric Wilson Loops in AdS/CFT Correspondence
We study the two circular Wilson loop correlator in which one is of
anti-symmetric representation, while the other is of fundamental representation
in 4-dimensional super Yang-Mills theory. This correlator has a
good AdS dual, which is a system of a D5-brane and a fundamental string. We
calculated the on-shell action of the string, and clarified the Gross-Ooguri
transition in this correlator. Some limiting cases are also examined.Comment: 22 pages, 5 figures, v2: typos corrected, v3: final version in JHE
Competition between Diffusion and Fragmentation: An Important Evolutionary Process of Nature
We investigate systems of nature where the common physical processes
diffusion and fragmentation compete. We derive a rate equation for the size
distribution of fragments. The equation leads to a third order differential
equation which we solve exactly in terms of Bessel functions. The stationary
state is a universal Bessel distribution described by one parameter, which fits
perfectly experimental data from two very different system of nature, namely,
the distribution of ice crystal sizes from the Greenland ice sheet and the
length distribution of alpha-helices in proteins.Comment: 4 pages, 3 figures, (minor changes
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