17,993 research outputs found
Nonlocal vertices and analyticity: Landau equations and general Cutkosky rule
We study the analyticity properties of amplitudes in theories with nonlocal
vertices of the type occurring in string field theory and a wide class of
nonlocal field theory models. Such vertices are given in momentum space by
entire functions of rapid decay in certain (including Euclidean) directions
ensuring UV finiteness but are necessarily of rapid increase in others. A
parametric representation is obtained by integrating out the loop (Euclidean)
momenta after the introduction of generalized Schwinger parameters. Either in
the original or parametric representation, the well-defined resulting
amplitudes are then continued in the complex space of the external momenta
invariants. We obtain the alternative forms of the Landau equations determining
the singularity surfaces showing that the nonlocal vertices serve as UV
regulators but do not affect the local singularity structure. As a result the
full set of singularities known to occur in local field theory also occurs
here: normal and anomalous thresholds as well as acnodes, crunodes, and cusps
that may under certain circumstances appear even on the physical sheet.
Singularities of the second type also appear as shown from the parametric
representation. We obtain the general Cutkosky discontinuity rule for
encircling a singularity by employing contour deformations only in the finite
plane. The unitarity condition (optical theorem) is then discussed as a special
application of the rule across normal thresholds and the hermitian analyticity
property of amplitudes.Comment: 31 pages, 5 figures. Typos corrected, some additional clarifying
comments, one added referenc
Tracking Data-Flow with Open Closure Types
Type systems hide data that is captured by function closures in function
types. In most cases this is a beneficial design that favors simplicity and
compositionality. However, some applications require explicit information about
the data that is captured in closures. This paper introduces open closure
types, that is, function types that are decorated with type contexts. They are
used to track data-flow from the environment into the function closure. A
simply-typed lambda calculus is used to study the properties of the type theory
of open closure types. A distinctive feature of this type theory is that an
open closure type of a function can vary in different type contexts. To present
an application of the type theory, it is shown that a type derivation
establishes a simple non-interference property in the sense of information-flow
theory. A publicly available prototype implementation of the system can be used
to experiment with type derivations for example programs.Comment: Logic for Programming Artificial Intelligence and Reasoning (2013
Noise removal in multichannel images
A adaptive filtering method, the Windrow-Hoff algorithm, for enhancing multichannel signals against aditive noise was investigated. It removes noise for multichannel images containing correlated signal compoments but uncorrelated noise components. Its potential application is the enhancement of multichannel microwave satellite images as a preprocessing step for the extraction of geophysical parameters
Carbon Emission Trading Scheme and the Aviation Sector: An experimental analysis on allocation of allowances
The European Union has proposed a Directive to include aviation activities in the Emission Trading Scheme (ETS) in 2012. The allowance allocation method which will be put in place is relatively easy to implement with low administration cost. However, careful scrutiny suggests that the allocation method does not favor airlines with high energy efficiency. This study proposes an alternative allowance allocation method which is fairer in that it rewards energy efficient airlines. Further, the new method is easy to implement with low administrative cost. The Cournot model serves as the theoretical foundation upon which the experiments are designed to simulate the aviation industry under the ETS. The equilibrium is calculated for each allowance allocation method. Results from experiments suggest consistency with theoretical outcomes.
Small scale wind tunnel model investigation of hybrid high lift systems combining upper surface blowing with the internally blown flap
A small-scale wind tunnel test of a two engine hybrid model with upper surface blowing on a simulated expandable duct internally blown flap was accomplished in a two phase program. The low wing Phase I model utilized 0.126c radius Jacobs/Hurkamp flaps and 0.337c radius Coanda flaps. The high wing Phase II model was utilized for continued studies on the Jacobs/Hurkamp flap. Principal study areas included: basic data both engines operative and with an engine out, control flap utilization, horizontal tail effectiveness, spoiler effectiveness, USB nacelle deflector study and USB/IBF pressure ratio effects
Context sensitive formulations of antenna pattern correction and side lobe compensation for NOSS/LAMMR real time processing
Large antenna multi-channel microwave radiometer (LAMMR) software specifications were written for LAMMR ground processing. There is a need to determine more computationally-efficient antenna temperature correction methods in compensating side lobe contributions especially near continents, islands and weather fronts. One of the major conclusions was that the antenna pattern corrections (APC) processes did not accomplish the implied goals of compensating for the antenna side lobe influences on brightness temperature. A-priori knowledge of land/water locations was shown to be needed and had to be incorporated in a context sensitive APC process if the artifacts caused by land presence is to be avoided. The high temperatures in land regions can severely bias the lower ocean response
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Schwannomatosis of the Spinal Accessory Nerve: A Case Report.
Schwannomatosis is a distinct syndrome characterized by multiple peripheral nerve schwannomas that can be sporadic or familial in nature. Cases affecting the lower cranial nerves are infrequent. Here, the authors present a rare case of schwannomatosis affecting the left spinal accessory nerve. Upon genetic screening, an in-frame insertion at codon p.R177 of the Sox 10 gene was observed. There were no identifiable alterations in NF1, NF2, LZTR1, and SMARCB1. This case demonstrates a rare clinical presentation of schwannomatosis in addition to a genetic aberration that has not been previously reported in this disease context
Limit on the CH4/CO ratio in Comet Levy (1990c) and comparisons with other comets
Near-infrared observations of comet Levy (1900c) were made on UT 4.3 and 5.3 Sep. 1990 from the United Kingdom Infrared Telescope on Mauna Kea. A scanning Fabry-Perot interferometer in combination with a cooled grating spectrometer was used to make a sensitive search for fluorescent emission from the v zub 3 band of CH4 near lambda approx. 3.3 microns. If CH4 is a parent molecule released directly from the nucleus, then the 3 sigma limit on its abundance is CH4/H2O approx. less than 0.0031, assuming that the kinetic temperature of the inner coma is approx. 50 K and that the CH4 spin species are equilibrated at a temperature approx. greater than 50 K. Since International Ultraviolet Explorer (IUE) observations of CO in Levy indicate that CO/H2O approx. 0.04 (Feldman et al.), researchers find that CH4/CO approx. less than 0.1. Infrared spectroscopic searches for CH4 in Comet Halley also yielded no positive detections; the more sensitive upper limit from the latter observations is CH4/H2O approx. less than 0.002. Since CO/H2O approx. 0.05 in Halley (not including the extended source of CO), the upper limits on the CH4/CO ratios are almost identical for comets Levy and Halley. A marginal infrared detection of the CH4 v sub 3 band in comet Wilson yielded CH4/H2O approx. 0.01 to 0.05 (Larson et al.), but there was no positive detection of CO. If the identification of the feature in the infrared spectrum of comet Wilson is correct, then that would indicate a very high CH4/CO ratio in this comet
GEODYN system description, volume 1
A computer program for the estimation of orbit and geodetic parameters is presented. The areas in which the program is operational are defined. The specific uses of the program are given as: (1) determination of definitive orbits, (2) tracking instrument calibration, (3) satellite operational predictions, and (4) geodetic parameter estimation. The relationship between the various elements in the solution of the orbit and geodetic parameter estimation problem is analyzed. The solution of the problems corresponds to the orbit generation mode in the first case and to the data reduction mode in the second case
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