451 research outputs found
Inverse eigenvalue problem for discrete three-diagonal Sturm-Liouville operator and the continuum limit
In present article the self-contained derivation of eigenvalue inverse
problem results is given by using a discrete approximation of the Schroedinger
operator on a bounded interval as a finite three-diagonal symmetric Jacobi
matrix. This derivation is more correct in comparison with previous works which
used only single-diagonal matrix. It is demonstrated that inverse problem
procedure is nothing else than well known Gram-Schmidt orthonormalization in
Euclidean space for special vectors numbered by the space coordinate index. All
the results of usual inverse problem with continuous coordinate are reobtained
by employing a limiting procedure, including the Goursat problem -- equation in
partial derivatives for the solutions of the inversion integral equation.Comment: 19 pages There were made some additions (and reformulations) to the
text making the derivation of the results more precise and understandabl
Small-Energy Analysis for the Selfadjoint Matrix Schroedinger Operator on the Half Line
The matrix Schroedinger equation with a selfadjoint matrix potential is
considered on the half line with the most general selfadjoint boundary
condition at the origin. When the matrix potential is integrable and has a
first moment, it is shown that the corresponding scattering matrix is
continuous at zero energy. An explicit formula is provided for the scattering
matrix at zero energy. The small-energy asymptotics are established also for
the corresponding Jost matrix, its inverse, and various other quantities
relevant to the corresponding direct and inverse scattering problems.Comment: This published version has been edited to improve the presentation of
the result
Survey Manual for Comprehensive Urban Planning: The Use of Opinion Surveys and Sampling Techniques in the Planning Process
This study examines the applications of scientific public opinion
and survey sampling techniques to comprehensive planning and other urban
planning programs.
The survey manual deals with two major elements: a case study in
Providence, Rhode Island, which illustrates the process of conducting
a survey and the kinds of findings and results which may be obtained; and
a methodology section which focuses on the techniques and methods used
in survey research. Research design, survey methodology, organization
of data collection, the plan for data processing and preparation of the
final report are discussed.
Scientific survey sampling is shown to be a useful instrument for
obtaining information on a variety of urban problems, including opinions
on quality of public facilities, reasons for moving, support for Urban
Renewal and Model Cities programs, and evaluation of social welfare programs.The State of Alask
The fastest unbound star in our Galaxy ejected by a thermonuclear supernova
Hypervelocity stars (HVS) travel with velocities so high, that they exceed
the escape velocity of the Galaxy. Several acceleration mechanisms have been
discussed. Only one HVS (US 708, HVS 2) is a compact helium star. Here we
present a spectroscopic and kinematic analysis of US\,708. Travelling with a
velocity of , it is the fastest unbound star in our
Galaxy. In reconstructing its trajectory, the Galactic center becomes very
unlikely as an origin, which is hardly consistent with the most favored
ejection mechanism for the other HVS. Furthermore, we discovered US\,708 to be
a fast rotator. According to our binary evolution model it was spun-up by tidal
interaction in a close binary and is likely to be the ejected donor remnant of
a thermonuclear supernova.Comment: 16 pages report, 20 pages supplementary material
Reconstruction of the optical potential from scattering data
We propose a method for reconstruction of the optical potential from
scattering data. The algorithm is a two-step procedure. In the first step the
real part of the potential is determined analytically via solution of the
Marchenko equation. At this point we use a diagonal Pad\'{e} approximant of the
corresponding unitary -matrix. In the second step the imaginary part of the
potential is determined via the phase equation of the variable phase approach.
We assume that the real and the imaginary parts of the optical potential are
proportional. We use the phase equation to calculate the proportionality
coefficient. A numerical algorithm is developed for a single and for coupled
partial waves. The developed procedure is applied to analysis of
, , and data.Comment: 26 pages, 8 figures, results of nucl-th/0410092 are refined, some new
results are presente
Nitrogen and phosphorus limitation of oceanic microbial growth during spring in the Gulf of Aqaba
Bioassay experiments were performed to identify how growth of key groups within the microbial community was simultaneously limited by nutrient (nitrogen and phosphorus) availability during spring in the Gulf of Aqaba's oceanic waters. Measurements of chlorophyll a (chl a) concentration and fast repetition rate (FRR) fluorescence generally demonstrated that growth of obligate phototrophic phytoplankton was co-limited by N and P and growth of facultative aerobic anoxygenic photoheterotropic (AAP) bacteria was limited by N. Phytoplankton exhibited an increase in chl a biomass over 24 to 48 h upon relief of nutrient limitation. This response coincided with an increase in photosystem II (PSII) photochemical efficiency (F v /F m), but was preceded (within 24 h) by a decrease in effective absorption crosssection (σPSII) and electron turnover time (τ). A similar response for τ and bacterio-chl a was observed for the AAPs. Consistent with the up-regulation of PSII activity with FRR fluorescence were observations of newly synthesized PSII reaction centers via low temperature (77K) fluorescence spectroscopy for addition of N (and N + P). Flow cytometry revealed that the chl a and thus FRR fluorescence responses were partly driven by the picophytoplankton (æ10 μm) community, and in particular Synechococcus. Productivity of obligate heterotrophic bacteria exhibited the greatest increase in response to a natural (deep water) treatment, but only a small increase in response to N and P addition, demonstrating the importance of additional substrates (most likely dissolved organic carbon) in moderating the heterotrophs. These data support previous observations that the microbial community response (autotrophy relative to heterotrophy) is critically dependent upon the nature of transient nutrient enrichment. © Inter-Research 2009
A Cosmological Model with Dark Spinor Source
In this paper, we discuss the system of Friedman-Robertson-Walker metric
coupling with massive nonlinear dark spinors in detail, where the thermodynamic
movement of spinors is also taken into account. The results show that, the
nonlinear potential of the spinor field can provide a tiny negative pressure,
which resists the Universe to become singular. The solution is oscillating in
time and closed in space, which approximately takes the following form
g_{\mu\nu}=\bar R^2(1-\delta\cos t)^2\diag(1,-1,-\sin^2r ,-\sin^2r
\sin^2\theta), with light year, and
. The present time is about .Comment: 13 pages, no figure, to appear in IJMP
Inverse spectral problems for Sturm--Liouville operators with matrix-valued potentials
We give a complete description of the set of spectral data (eigenvalues and
specially introduced norming constants) for Sturm--Liouville operators on the
interval with matrix-valued potentials in the Sobolev space
and suggest an algorithm reconstructing the potential from the spectral data
that is based on Krein's accelerant method.Comment: 39 pages, uses iopart.cls, iopams.sty and setstack.sty by IO
Electrostatic and electrokinetic contributions to the elastic moduli of a driven membrane
We discuss the electrostatic contribution to the elastic moduli of a cell or
artificial membrane placed in an electrolyte and driven by a DC electric field.
The field drives ion currents across the membrane, through specific channels,
pumps or natural pores. In steady state, charges accumulate in the Debye layers
close to the membrane, modifying the membrane elastic moduli. We first study a
model of a membrane of zero thickness, later generalizing this treatment to
allow for a finite thickness and finite dielectric constant. Our results
clarify and extend the results presented in [D. Lacoste, M. Cosentino
Lagomarsino, and J. F. Joanny, Europhys. Lett., {\bf 77}, 18006 (2007)], by
providing a physical explanation for a destabilizing term proportional to
\kps^3 in the fluctuation spectrum, which we relate to a nonlinear ()
electro-kinetic effect called induced-charge electro-osmosis (ICEO). Recent
studies of ICEO have focused on electrodes and polarizable particles, where an
applied bulk field is perturbed by capacitive charging of the double layer and
drives flow along the field axis toward surface protrusions; in contrast, we
predict "reverse" ICEO flows around driven membranes, due to curvature-induced
tangential fields within a non-equilibrium double layer, which hydrodynamically
enhance protrusions. We also consider the effect of incorporating the dynamics
of a spatially dependent concentration field for the ion channels.Comment: 22 pages, 10 figures. Under review for EPJ
\pi\pi, K\pi and \pi N potential scattering and a prediction of a narrow \sigma meson resonance
Low energy scattering and bound state properties of the \pi N, \pi\pi and
K\pi systems are studied as coupled channel problems using inversion potentials
of phase shift data. In a first step we apply the potential model to explain
recent measurements of pionic hydrogen shift and width. Secondly, predictions
of the model for pionium lifetime and shift confirm a well known and widely
used effective range expression. Thirdly, as extension of this confirmation, we
predict an unexpected medium effect of the pionium lifetime which shortens by
several orders of magnitude. The \sigma meson shows a narrow resonance
structure as a function of the medium modified mass with the implication of
being essentially energy independent. Similarly, we see this medium resonance
effect realized for the K\pi system. To support our findings we present also
results for the \rho meson and the \Delta(1232) resonance.Comment: 42 pages, 17 PS figures, REFTeX, epsfig.sty needed, submitted to
Phys. Re
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