6,963 research outputs found
Performance Analysis of the Spaceborne Laser Ranging System
The 'spaceborne laser ranging system' is a proposed short pulse laser on board an orbiting spacecraft. It measures the distances between the spacecraft and many laser retroreflectors (targets) deployed on the earth's surface. The precision of these range measurements was assumed to be about plus or minus 2 cm. These measurements were then used together with the orbital dynamics of the spacecraft to derive the intersite vector between the laser ground targets. The errors associated with this vector were on the order of 1 to 2 cm. The baseline distances determined range from 25 km to 1200 km. By repeating the measurements of the intersite vector, strain and strain rate errors were estimated. The realizable precision for intersite distance determination was estimated to be on the order of 0.5 cm at 300 km and about 1.5 cm at 1200 km. The corresponding inaccuracies for the intersite distances were larger, than is 1 cm and 3.5 cm respectively. The corresponding precision in the vertical direction was 1 cm and 3 cm
A Search for Instantons at HERA
A search for QCD instanton (I) induced events in deep-inelastic scattering
(DIS) at HERA is presented in the kinematic range of low x and low Q^2. After
cutting into three characteristic variables for I-induced events yielding a
maximum suppression of standard DIS background to the 0.1% level while still
preserving 10% of the I-induced events, 549 data events are found while
363^{+22}_{-26} (CDM) and 435^{+36}_{-22} (MEPS) standard DIS events are
expected. More events than expected by the standard DIS Monte Carlo models are
found in the data. However, the systematic uncertainty between the two
different models is of the order of the expected signal, so that a discovery of
instantons can not be claimed. An outlook is given on the prospect to search
for QCD instanton events using a discriminant based on range searching in the
kinematical region Q^2\gtrsim100\GeV^2 where the I-theory makes safer
predictions and the QCD Monte Carlos are expected to better describe the
inclusive data.Comment: Invited talk given at the Ringberg Workshop on HERA Physics on June
19th, 2001 on behalf of the H1 collaboratio
Two-Pion Exchange in Proton-Proton Scattering
The contribution of the box and crossed two-pion-exchange diagrams to
proton-proton scattering at 90 is calculated in the laboratory
momentum range up to 12 GeV/c. Relativistic form factors related to the nucleon
and pion size and representing the pion source distribution based on the quark
structure of the hadronic core are included at each vertex of the pion-nucleon
interaction. These form factors depend on the four-momenta of the exchanged
pions and scattering nucleons. Feynman-diagram amplitudes calculated without
form factors are checked against those derived from dispersion relations. In
this comparison, one notices that a very short-range part of the crossed
diagram, neglected in dispersion-relation calculations of the two-pion-exchange
nucleon-nucleon potential, gives a sizable contribution. In the Feynman-diagram
calculation with form factors the agreement with measured spin-separated cross
sections, as well as amplitudes in the lower part of the energy range
considered, is much better for pion-nucleon pseudo-vector vis \`a vis
pseudo-scalar coupling. While strengths of the box and crossed diagrams are
comparable for laboratory momenta below 2 GeV/c, the crossed diagram dominates
for larger momenta, largely due to the kinematics of the crossed diagram
allowing a smaller momentum transfer in the nucleon center of mass. An
important contribution arises from the principal-value part of the integrals
which is non-zero when form factors are included. It seems that the importance
of the exchange of color singlets may extend higher in energy than expected
Geometrothermodynamics
We present the fundamentals of geometrothermodynamics, an approach to study
the properties of thermodynamic systems in terms of differential geometric
concepts. It is based, on the one hand, upon the well-known contact structure
of the thermodynamic phase space and, on the other hand, on the metric
structure of the space of thermodynamic equilibrium states. In order to make
these two structures compatible we introduce a Legendre invariant set of
metrics in the phase space, and demand that their pullback generates metrics on
the space of equilibrium states. We show that Weinhold's metric, which was
introduced {\it ad hoc}, is not contained within this invariant set. We propose
alternative metrics which allow us to redefine the concept of thermodynamic
length in an invariant manner and to study phase transitions in terms of
curvature singularities.Comment: Revised version, to be published in Jour. Math. Phy
Discipline-Specific Compared to Generic Training of Teachers in Higher Education
A recurrent theme arising in the higher education sector is the suitability and effectiveness of generic versus discipline-specific training of university teachers, who are often recruited based on their disciplinary specialties to become teachers in higher education. We compared two groups of participants who had undergone training using a generic post-graduate certificate in higher education (PGCertGeneric) versus a discipline-specific course in veterinary education (PGCertVetEd). The study was conducted using a survey that allowed comparison of participants who completed PGCertGeneric (n=21) with PGCertVetEd (n=22). Results indicated that participants from both PGCertGeneric and PGCertVetEd considered teaching to be satisfying and important to their careers, valued the teaching observation component of the course, and identified similar training needs. However, the participants of the PGCertVetEd felt that the course made them better teachers, valued the relevance of the components taught, understood course design better, were encouraged to do further courses/reading in teaching and learning, changed their teaching as a result of the course, and were less stressed about teaching as compared to the PGCertGeneric participants (p<.05). It is likely that the PGCertVetEd, which was designed and developed by veterinarians with a wider understanding of the veterinary sector, helped the participants perceive the training course as suited to their needs
Evaluation of configurational entropy of a model liquid from computer simulations
Computer simulations have been employed in recent years to evaluate the
configurational entropy changes in model glass-forming liquids. We consider two
methods, both of which involve the calculation of the `intra-basin' entropy as
a means for obtaining the configurational entropy. The first method involves
the evaluation of the intra-basin entropy from the vibrational frequencies of
inherent structures, by making a harmonic approximation of the local potential
energy topography. The second method employs simulations that confine the
liquid within a localized region of configuration space by the imposition of
constraints; apart from the choice of the constraints, no further assumptions
are made. We compare the configurational entropies estimated for a model liquid
(binary mixture of particles interacting {\it via} the Lennard-Jones potential)
for a range of temperatures, at fixed density.Comment: 10 pages, 5 figures, Proceedings of "Unifying Concepts in Glass
Physics" Trieste 1999 (to appear in J. Phys. Cond. Mat.
On the Emergence of the Microcanonical Description from a Pure State
We study, in general terms, the process by which a pure state can
``self-thermalize'' and {\em appear} to be described by a microcanonical
density matrix. This requires a quantum mechanical version of the Gibbsian
coarse graining that conceptually underlies classical statistical mechanics. We
introduce some extra degrees of freedom that are necessary for this.
Interaction between these degrees and the system can be understood as a process
of resonant absorption and emission of ``soft quanta''. This intuitive picture
allows one to state a criterion for when self thermalization occurs. This
paradigm also provides a method for calculating the thermalization rate using
the usual formalism of atomic physics for calculating decay rates. We contrast
our prescription for coarse graining, which is somewhat dynamical, with the
earlier approaches that are intrinsically kinematical. An important motivation
for this study is the black hole information paradox.Comment: 58 pages, 2 figures. A reference adde
Energy Cost of Land and Shallow Water Walking in Females who are Overweight and Obese
Nineteen overweight or obese females completed three 10-minute experimental trials including a self-selected pace shallow water walking trial, a matched heart rate response land walking trial, and a self-selected pace land walking trial. Energy expenditure (kcal·min-1)was computed from expired gases assessed via indirect calorimetry. Results showed energy expenditure was lower (p= 0.046) during shallow water walking (6.46 ± 1.38 kcal·min-1) compared to matched heart rate response land walking trial (7.26 ± 1.29 kcal·min-1), with no significant difference in between shallow water and self-selected pace land walking (6.92 ± 1.61 kcal·min-1). The present study did not demonstrate superior energy cost of shallow water walking. However, results demonstrate that shallow water walking elicits an increase in energy expenditure, which may indicate that this form of activity is a reasonable alternative to land-based walking. Moreover, this form of activity may be particularly effective for individuals with mobility limitations during land-based exercise
Energy Cost of Land and Shallow Water Walking in Females who are Overweight and Obese
Nineteen overweight or obese females completed three 10-minute experimental trials including a self-selected pace shallow water walking trial, a matched heart rate response land walking trial, and a self-selected pace land walking trial. Energy expenditure (kcal·min-1) was computed from expired gases assessed via indirect calorimetry. Results showed energy expenditure was lower (p= 0.046) during shallow water walking (6.46 ± 1.38 kcal·min-1) compared to matched heart rate response land walking trial (7.26 ± 1.29 kcal·min-1), with no significant difference in between shallow water and self-selected pace land walking (6.92 ± 1.61 kcal·min-1 ). The present study did not demonstrate superior energy cost of shallow water walking. However, results demonstrate that shallow water walking elicits an increase in energy expenditure, which may indicate that this form of activity is a reasonable alternative to land-based walking. Moreover, this form of activity may be particularly effective for individuals with mobility limitations during land-based exercise
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