53,476 research outputs found
Prototype Graphs for radiative Corrections to Polarized Chargino or Neutralino Production in Electron-Positron Annihilation
We present the contributions from all types of one-loop corrections to the
scattering amplitude for the pair production of polarized charginos or
neutralinos from polarized electron-positron annihilation. The contributions
are classified in terms of ``prototypes'' distinguished by the number of
particles inside the loops and their spins. The results are quoted in terms of
the Veltman-Passarino functions in terms of general couplings and internal
masses. The results can therefore be applied to any supersymmetric extension of
the Standard Model or indeed to any polarized fermion pair production process
in electron-positron annihilation.Comment: LATEX 38 pages, 26 figure
Borel singularities at small x
D.I.S. at small Bjorken is considered within the dipole cascade
formalism. The running coupling in impact parameter space is introduced in
order to parametrize effects that arise from emission of large size dipoles.
This results in a new evolution equation for the dipole cascade. Strong
coupling effects are analyzed after transforming the evolution equation in
Borel () space. The Borel singularities of the solution are discussed first
for the universal part of the dipole cascade and then for the specific process
of D.I.S. at small . In the latter case the leading infrared renormalon is
at indicating the presence of power corrections for the
small- structure functions.Comment: 5 pages, Latex (Talk presented at DIS'97, Chicago, IL
Strong Unification
We investigate the possibility that unification occurs at strong coupling. We
show that, despite the fact the couplings pass through a strong coupling
regime, accurate predictions for their low energy values are possible because
the couplings of the theory flow to infrared fixed points. We determine the
low-energy QCD coupling in a favoured class of strong coupling models and find
it is reduced from the weak coupling predictions, lying close to the
experimentally measured value. We extend the analysis to the determination of
quark and lepton masses and show that (even without Grand Unification) the
infra-red fixed point structure may lead to good predictions for the top mass,
the bottom to tau mass ratio and . Finally we discuss the
implications for the unification scale finding it to be increased from the MSSM
value and closer to the heterotic string prediction.Comment: 12 pages, LateX, no figure
Surface settling in partially filled containers upon step reduction in gravity
A large literature exists concerning the equilibrium configurations of free liquid/gas surfaces in reduced gravity environments. Such conditions generally yield surfaces of constant curvature meeting the container wall at a particular (contact) angle. The time required to reach and stabilize about this configuration is less studied for the case of sudden changes in gravity level, e.g. from normal- to low-gravity, as can occur in many drop tower experiments. The particular interest here was to determine the total reorientation time for such surfaces in cylinders (mainly), as a function primarily of contact angle and kinematic viscosity, in order to aid in the development of drop tower experiment design. A large parametric range of tests were performed and, based on an accompanying scale analysis, the complete data set was correlated. The results of other investigations are included for comparison
Optimal payload rate limit algorithm for zero-G manipulators
An algorithm for continuously computing safe maximum relative velocities for two bodies joined by a manipulator is discussed. The maximum velocities are such that if the brakes are applied at that instant, the ensuing travel between the bodies will be less than or equal to a predetermined amount. An improvement in the way this limit is computed for space manipulators is shown. The new method is explained, test cases are posed, and the results of these tests are displayed and discussed
Qualitative System Identification from Imperfect Data
Experience in the physical sciences suggests that the only realistic means of
understanding complex systems is through the use of mathematical models.
Typically, this has come to mean the identification of quantitative models
expressed as differential equations. Quantitative modelling works best when the
structure of the model (i.e., the form of the equations) is known; and the
primary concern is one of estimating the values of the parameters in the model.
For complex biological systems, the model-structure is rarely known and the
modeler has to deal with both model-identification and parameter-estimation. In
this paper we are concerned with providing automated assistance to the first of
these problems. Specifically, we examine the identification by machine of the
structural relationships between experimentally observed variables. These
relationship will be expressed in the form of qualitative abstractions of a
quantitative model. Such qualitative models may not only provide clues to the
precise quantitative model, but also assist in understanding the essence of
that model. Our position in this paper is that background knowledge
incorporating system modelling principles can be used to constrain effectively
the set of good qualitative models. Utilising the model-identification
framework provided by Inductive Logic Programming (ILP) we present empirical
support for this position using a series of increasingly complex artificial
datasets. The results are obtained with qualitative and quantitative data
subject to varying amounts of noise and different degrees of sparsity. The
results also point to the presence of a set of qualitative states, which we
term kernel subsets, that may be necessary for a qualitative model-learner to
learn correct models. We demonstrate scalability of the method to biological
system modelling by identification of the glycolysis metabolic pathway from
data
OpenCL + OpenSHMEM Hybrid Programming Model for the Adapteva Epiphany Architecture
There is interest in exploring hybrid OpenSHMEM + X programming models to
extend the applicability of the OpenSHMEM interface to more hardware
architectures. We present a hybrid OpenCL + OpenSHMEM programming model for
device-level programming for architectures like the Adapteva Epiphany many-core
RISC array processor. The Epiphany architecture comprises a 2D array of
low-power RISC cores with minimal uncore functionality connected by a 2D mesh
Network-on-Chip (NoC). The Epiphany architecture offers high computational
energy efficiency for integer and floating point calculations as well as
parallel scalability. The Epiphany-III is available as a coprocessor in
platforms that also utilize an ARM CPU host. OpenCL provides good functionality
for supporting a co-design programming model in which the host CPU offloads
parallel work to a coprocessor. However, the OpenCL memory model is
inconsistent with the Epiphany memory architecture and lacks support for
inter-core communication. We propose a hybrid programming model in which
OpenSHMEM provides a better solution by replacing the non-standard OpenCL
extensions introduced to achieve high performance with the Epiphany
architecture. We demonstrate the proposed programming model for matrix-matrix
multiplication based on Cannon's algorithm showing that the hybrid model
addresses the deficiencies of using OpenCL alone to achieve good benchmark
performance.Comment: 12 pages, 5 figures, OpenSHMEM 2016: Third workshop on OpenSHMEM and
Related Technologie
Chiral effective field theory beyond the power-counting regime
Novel techniques are presented, which identify the chiral power-counting
regime (PCR), and realize the existence of an intrinsic energy scale embedded
in lattice QCD results that extend outside the PCR. The nucleon mass is
considered as a benchmark for illustrating this new approach. Using
finite-range regularization, an optimal regularization scale can be extracted
from lattice simulation results by analyzing the renormalization of the low
energy coefficients. The optimal scale allows a description of lattice
simulation results that extend beyond the PCR by quantifying and thus handling
any scheme-dependence. Preliminary results for the nucleon magnetic moment are
also examined, and a consistent optimal regularization scale is obtained. This
indicates the existence of an intrinsic scale corresponding to the finite size
of the source of the pion cloud.Comment: 6 pages, 4 figures, conferenc
Neonatal weight loss in breast and formula-fed infants
We have observed an increase in the number of breast fed babies presenting with dehydration and/or failure to thrive because of lactation failure and non-recognition of feeding problems. Recent reports1,2 support this experience and recommend monitoring of the weight of infants through the neonatal period. However, these reports acknowledge uncertainty as to what actually constitutes normal neonatal weight loss. Maisels and colleagues published two studies which have been quoted as giving guidance on normal loss. Both studies were designed primarily to study factors that influence breast milk jaundice. The first3 reported a mean weight loss of about 6% in 100 unselected well babies during the first 3 days. The subsequent study4 reported a mean weight loss of 6.86% in 186 infants. The timescale over which babies were weighed was not clearly indicated, although it may have only been 2-3 days. The sample was neither population based nor randomly selected, being largely preselected because of the presence of more pronounced jaundice. The distribution of data points for early neonatal weight loss are likely to be skewed, yet both studies reported the results as mean (SD). Owing to the design and method of data presentation, these studies cannot reliably inform the debate as to what constitutes the norm. Marchini and colleagues published reports also designed primarily to study other issues. One5 indicated a mean early weight loss of 5.7%. Measurements were recorded over a three day period, and no indication is given of the skewness of the data. Another study6 reported a median weight loss of about 6% recorded over a four day period. At least one baby lost > 15% of his/her birth weight during this time, but there is no clear information as to the frequency with which more extreme degrees of weight loss are observed
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