3,798 research outputs found
Improved design of a high response slotted plate overboard bypass valve for supersonic inlets
The electrohydraulically actuated slotted-plate bypass valve used to control the position of the normal shock during wind-tunnel investigations of supersonic inlets also has proven to be a valuable device for determining inlet dynamics and creating airflow disturbances. Operation of previous valves at high frequencies (to 100 Hz) for extended testing has resulted in numerous failures. An improved bypass-valve design is presented which increases the cyclic tolerance of the device considerably over past designs. The use of dynamic limit criteria to obtain an optimum actuator-piston size results in a frequency response which is flat within + or - 3 decibels to 120 Hz for a peak-to-peak variation of 20 percent of full area
Effects of a fundamental mass term in two-dimensional super Yang-Mills theory
We show that adding a vacuum expectation value to a gauge field left over
from a dimensional reduction of three-dimensional pure supersymmetric
Yang-Mills theory generates mass terms for the fundamental fields in the
two-dimensional theory while supersymmetry stays intact. This is similar to the
adjoint mass term that is generated by a Chern-Simons term in this theory. We
study the spectrum of the two-dimensional theory as a function of the vacuum
expectation value and of the Chern-Simons coupling. Apart from some symmetry
issues a straightforward picture arises. We show that at least one massless
state exists if the Chern-Simons coupling vanishes. The numerical spectrum
separates into (almost) massless and very heavy states as the Chern-Simons
coupling grows. We present evidence that the gap survives the continuum limit.
We display structure functions and other properties of some of the bound
states.Comment: 17 pp., 10 figs; substantially revised version to be published in
Phys. Rev.
Improved results for N=(2,2) super Yang-Mills theory using supersymmetric discrete light-cone quantization
We consider the (1+1)-dimensional super Yang--Mills theory
which is obtained by dimensionally reducing super Yang--Mills
theory in four dimension to two dimensions. We do our calculations in the
large- approximation using Supersymmetric Discrete Light Cone
Quantization. The objective is to calculate quantities that might be
investigated by researchers using other numerical methods. We present a
precision study of the low-mass spectrum and the stress-energy correlator
. We find that the mass gap of this theory closes as the
numerical resolution goes to infinity and that the correlator in the
intermediate region behaves like .Comment: 18 pages, 8 figure
Differences in genotype and virulence among four multidrug-resistant <i>Streptococcus pneumoniae</i> isolates belonging to the PMEN1 clone
We report on the comparative genomics and characterization of the virulence phenotypes of four <i>S. pneumoniae</i> strains that belong to the multidrug resistant clone PMEN1 (Spain<sup>23F</sup> ST81). Strains SV35-T23 and SV36-T3 were recovered in 1996 from the nasopharynx of patients at an AIDS hospice in New York. Strain SV36-T3 expressed capsule type 3 which is unusual for this clone and represents the product of an in vivo capsular switch event. A third PMEN1 isolate - PN4595-T23 - was recovered in 1996 from the nasopharynx of a child attending day care in Portugal, and a fourth strain - ATCC700669 - was originally isolated from a patient with pneumococcal disease in Spain in 1984. We compared the genomes among four PMEN1 strains and 47 previously sequenced pneumococcal isolates for gene possession differences and allelic variations within core genes. In contrast to the 47 strains - representing a variety of clonal types - the four PMEN1 strains grouped closely together, demonstrating high genomic conservation within this lineage relative to the rest of the species. In the four PMEN1 strains allelic and gene possession differences were clustered into 18 genomic regions including the capsule, the blp bacteriocins, erythromycin resistance, the MM1-2008 prophage and multiple cell wall anchored proteins. In spite of their genomic similarity, the high resolution chinchilla model was able to detect variations in virulence properties of the PMEN1 strains highlighting how small genic or allelic variation can lead to significant changes in pathogenicity and making this set of strains ideal for the identification of novel virulence determinant
The H1 Forward Proton Spectrometer at HERA
The forward proton spectrometer is part of the H1 detector at the HERA
collider. Protons with energies above 500 GeV and polar angles below 1 mrad can
be detected by this spectrometer. The main detector components are
scintillating fiber detectors read out by position-sensitive photo-multipliers.
These detectors are housed in so-called Roman Pots which allow them to be moved
close to the circulating proton beam. Four Roman Pot stations are located at
distances between 60 m and 90 m from the interaction point.Comment: 20 pages, 10 figures, submitted to Nucl.Instr.and Method
Experimental Evidence of a Haldane Gap in an S = 2 Quasi-linear Chain Antiferromagnet
The magnetic susceptibility of the quasi-linear chain Heisenberg
antiferromagnet (2,-bipyridine)trichloromanganese(III), MnCl_{3}(bipy), has
been measured from 1.8 to 300 K with the magnetic field, H, parallel and
perpendicular to the chains. The analyzed data yield and K. The magnetization, M, has been studied at 30 mK and 1.4 K in H up to 16
T. No evidence of long-range order is observed. Depending on crystal
orientation, at 30 mK until a critical field is achieved ( and $H_{c\bot} = 1.8\pm 0.2 T), where M increases continuously
as H is increased. These results are interpreted as evidence of a Haldane gap.Comment: 11 pages, 4 figure
A comparison of the cosmic-ray energy scales of Tunka-133 and KASCADE-Grande via their radio extensions Tunka-Rex and LOPES
The radio technique is a promising method for detection of cosmic-ray air
showers of energies around PeV and higher with an array of radio
antennas. Since the amplitude of the radio signal can be measured absolutely
and increases with the shower energy, radio measurements can be used to
determine the air-shower energy on an absolute scale. We show that calibrated
measurements of radio detectors operated in coincidence with host experiments
measuring air showers based on other techniques can be used for comparing the
energy scales of these host experiments. Using two approaches, first via direct
amplitude measurements, and second via comparison of measurements with air
shower simulations, we compare the energy scales of the air-shower experiments
Tunka-133 and KASCADE-Grande, using their radio extensions, Tunka-Rex and
LOPES, respectively. Due to the consistent amplitude calibration for Tunka-Rex
and LOPES achieved by using the same reference source, this comparison reaches
an accuracy of approximately - limited by some shortcomings of LOPES,
which was a prototype experiment for the digital radio technique for air
showers. In particular we show that the energy scales of cosmic-ray
measurements by the independently calibrated experiments KASCADE-Grande and
Tunka-133 are consistent with each other on this level
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