3,928 research outputs found
Analytic treatment of geodesics in five-dimensional Myers-Perry space--times
We present the complete set of analytical solutions of the geodesic equation
in the five-dimensional Myers-Perry space-time with equal rotation parameter in
terms of the Weierstra{\ss}' elliptic and Weierstra{\ss}' zeta and sigma
functions. We study the underlying polynomials in the polar and radial
equations which depend on the parameters of the metric and conserved quantities
of a test particle and characterize the motion by their zeros. We exemplify the
efficiency of the analytical method on the orbits of test particles.Comment: 15 pages, 7 figures, to be published in PRD. Version with improved
reference
Andreev Reflections in Micrometer-Scale Normal-Insulator-Superconductor Tunnel Junctions
Understanding the subgap behavior of Normal-Insulator-Superconductor (NIS)
tunnel junctions is important in order to be able to accurately model the
thermal properties of the junctions. Hekking and Nazarov developed a theory in
which NIS subgap current in thin-film structures can be modeled by multiple
Andreev reflections. In their theory, the current due to Andreev reflections
depends on the junction area and the junction resistance area product. We have
measured the current due to Andreev reflections in NIS tunnel junctions for
various junction sizes and junction resistance area products and found that the
multiple reflection theory is in agreement with our data
Star Formation and Tidal Encounters with the Low Surface Brightness Galaxy UGC 12695 and Companions
We present VLA H I observations of the low surface brightness galaxy UGC
12695 and its two companions, UGC 12687 and a newly discovered dwarf galaxy
2333+1234. UGC 12695 shows solid body rotation but has a very lopsided
morphology of the H I disk, with the majority of the H I lying in the southern
arm of the galaxy. The H I column density distribution of this very blue, LSB
galaxy coincides in detail with its light distribution. Comparing the H I
column density of UGC 12695 with the empirical (but not well understood) value
of Sigma_c = 10E21 atoms/cm^2 found in, i.e., Skillman's 1986 paper shows the
star formation to be a local affair, occurring only in those regions where the
column density is above this star formation threshold. The low surface
brightness nature of this galaxy could thus be attributed to an insufficient
gas surface density, inhibiting star formation on a more global scale.
Significantly, though, the Toomre criterion places a much lower critical
density on the galaxy (+/-10E20 atoms/cm^2), which is shown by the galaxy's low
SFR to not be applicable.
Within a projected distance of 300kpc/30kms of UGC 12695 lie two companion
galaxies - UGC 12687, a high surface brightness barred spiral galaxy, and
2333+1234, a dwarf galaxy discovered during this investigation. The close
proximity of the three galaxies, combined with UGC 12695's extremely blue color
and regions of localized starburst and UGC 12687's UV excess bring to mind
mutually induced star formation through tidal activity.Comment: 14 pages, 8 figures (2 color), To be published in A.J., May 2000
XWeB: the XML Warehouse Benchmark
With the emergence of XML as a standard for representing business data, new
decision support applications are being developed. These XML data warehouses
aim at supporting On-Line Analytical Processing (OLAP) operations that
manipulate irregular XML data. To ensure feasibility of these new tools,
important performance issues must be addressed. Performance is customarily
assessed with the help of benchmarks. However, decision support benchmarks do
not currently support XML features. In this paper, we introduce the XML
Warehouse Benchmark (XWeB), which aims at filling this gap. XWeB derives from
the relational decision support benchmark TPC-H. It is mainly composed of a
test data warehouse that is based on a unified reference model for XML
warehouses and that features XML-specific structures, and its associate XQuery
decision support workload. XWeB's usage is illustrated by experiments on
several XML database management systems
Basis-independent methods for the two-Higgs-doublet model II. The significance of tan(beta)
In the most general two-Higgs-doublet model (2HDM), there is no distinction
between the two complex hypercharge-one SU(2) doublet scalar fields, Phi_a
(a=1,2). Thus, any two orthonormal linear combinations of these two fields can
serve as a basis for the Lagrangian. All physical observables of the model must
therefore be basis-independent. For example, tan(beta)=/ is
basis-dependent and thus cannot be a physical parameter of the model. In this
paper, we provide a basis-independent treatment of the Higgs sector with
particular attention to the neutral Higgs boson mass-eigenstates, which
generically are not eigenstates of CP. We then demonstrate that all physical
Higgs couplings are indeed independent of tan(beta). In specialized versions of
the 2HDM, tan(beta) can be promoted to a physical parameter of the
Higgs-fermion interactions. In the most general 2HDM, the Higgs-fermion
couplings can be expressed in terms of a number of physical "tan(beta)--like"
parameters that are manifestly basis-independent. The minimal supersymmetric
extension of the Standard Model provides a simple framework for exhibiting such
effects.Comment: 56 pages, 5 tables, with Eq. (65) corrected (erratum to appear in
Physical Review D
Electrochemical deprotonation of phosphate on stainless steel
Voltammetric experiments performed in phosphate buffer at constant pH 8.0 on platinum and stainless steel revealed clear reduction
currents, which were correlated to the concentrations of phosphate. On the basis of the reactions proposed previously, a model was elaborated,
assuming that both H2PO4 and HPO4
2 underwent cathodic deprotonation, and including the acid–base equilibriums. A kinetic model was
derived by analogy with the equations generally used for hydrogen evolution. Numerical fitting of the experimental data confirmed that the
phosphate species may act as an efficient catalyst of hydrogen evolution via electrochemical deprotonation. This reaction may introduce an
unexpected reversible pathway of hydrogen formation in the mechanisms of anaerobic corrosion. The possible new insights offered by the
electrochemical deprotonation of phosphate in microbially influenced corrosion was finally discussed
Electronic transport in DNA
We study the electronic properties of DNA by way of a tight-binding model applied to four particular DNA sequences. The charge transfer properties are presented in terms of localization lengths (crudely speaking, the length over
which electrons travel). Various types of disorder, including random potentials, are employed to account for different real environments. We have performed calculations on poly(dG)-poly(dC), telomeric-DNA, random-ATGC DNA, and l-DNA. We find that random and l-DNA have localization lengths allowing for electron motion among a few dozen basepairs only. A novel enhancement of localization lengths is observed at particular energies for an increasing binary backbone disorder. We comment on the possible biological relevance of sequence-dependent charge transfer in DNA
Asymptotic stability, concentration, and oscillation in harmonic map heat-flow, Landau-Lifshitz, and Schroedinger maps on R^2
We consider the Landau-Lifshitz equations of ferromagnetism (including the
harmonic map heat-flow and Schroedinger flow as special cases) for degree m
equivariant maps from R^2 to S^2. If m \geq 3, we prove that near-minimal
energy solutions converge to a harmonic map as t goes to infinity (asymptotic
stability), extending previous work down to degree m = 3. Due to slow spatial
decay of the harmonic map components, a new approach is needed for m=3,
involving (among other tools) a "normal form" for the parameter dynamics, and
the 2D radial double-endpoint Strichartz estimate for Schroedinger operators
with sufficiently repulsive potentials (which may be of some independent
interest). When m=2 this asymptotic stability may fail: in the case of
heat-flow with a further symmetry restriction, we show that more exotic
asymptotics are possible, including infinite-time concentration (blow-up), and
even "eternal oscillation".Comment: 34 page
Is Unaided Active Learning an Effective Teaching Method for Those with Learning Disabilities?
The work presented here aims to address a critical knowledge gap in the engineering education literature through a preliminary study meant to determine if active learning is more effective when students with learning disabilities are first front-loaded with information. These preliminary findings aimed at not only determining if the work should be continued in the future, but also at evaluating if frontloading resulted in: (1) increased student engagement and (2) increased learning effectiveness. Preliminary findings conclude that students with documented, and undocumented, learning disabilities did have an increased understanding of the course content as a result of combining frontloading and active learning
Central precocious puberty in spina bifida children: Guidelines for the care of people with spina bifida
Children with spina bifida are at greater risk of developing central precocious puberty (CPP) compared to others. Therefore, early recognition and timely referral for further evaluation by a pediatric endocrinologist allows appropriate management that reduces the impact of CPP. This article discusses the diagnosis and management of CPP in children with spina bifida. This guideline was developed for SB Transition Healthcare Guidelines from the 2018 Spina Bifida Association's Fourth Edition of the Guidelines for the Care of People with Spina Bifida
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