539 research outputs found
The Two-Spectra Inverse Problem for Semi-Infinite Jacobi Matrices in The Limit-Circle Case
We present a technique for reconstructing a semi-infinite Jacobi operator in
the limit circle case from the spectra of two different self-adjoint
extensions. Moreover, we give necessary and sufficient conditions for two real
sequences to be the spectra of two different self-adjoint extensions of a
Jacobi operator in the limit circle case.Comment: 26 pages. Changes in the presentation of some result
On the Two Spectra Inverse Problem for Semi-Infinite Jacobi Matrices
We present results on the unique reconstruction of a semi-infinite Jacobi
operator from the spectra of the operator with two different boundary
conditions. This is the discrete analogue of the Borg-Marchenko theorem for
Schr{\"o}dinger operators in the half-line. Furthermore, we give necessary and
sufficient conditions for two real sequences to be the spectra of a Jacobi
operator with different boundary conditions.Comment: In this slightly revised version we have reworded some of the
theorems, and we updated two reference
The signed loop approach to the Ising model: foundations and critical point
The signed loop method is a beautiful way to rigorously study the
two-dimensional Ising model with no external field. In this paper, we explore
the foundations of the method, including details that have so far been
neglected or overlooked in the literature. We demonstrate how the method can be
applied to the Ising model on the square lattice to derive explicit formal
expressions for the free energy density and two-point functions in terms of
sums over loops, valid all the way up to the self-dual point. As a corollary,
it follows that the self-dual point is critical both for the behaviour of the
free energy density, and for the decay of the two-point functions.Comment: 38 pages, 7 figures, with an improved Introduction. The final
publication is available at link.springer.co
Mechanistic in situ and ex situ studies of phase transformations in molecular co-crystals
Co‐crystallisation is widely explored as a route to improve the physical properties of pharmaceutical active ingredients, but little is known about the fundamental mechanisms of the process. Herein, we apply a hyphenated differential scanning calorimetry—X‐ray diffraction technique to mimic the commercial hot melt extrusion process, and explore the heat‐induced synthesis of a series of new co‐crystals containing isonicotinamide. These comprise a 1:1 co‐crystal with 4‐hydroxybenzoic acid, 2:1 and 1:2 systems with 4‐hydroxyphenylacetic acid and a 1:1 crystal with 3,4‐dihydroxyphenylactic acid. The formation of co‐crystals during heating is complex mechanistically. In addition to co‐crystallisation, conversions between polymorphs of the co‐former starting materials and co‐crystal products are also observed. A subsequent study exploring the use of inkjet printing and milling to generate co‐crystals revealed that the synthetic approach has a major effect on the co‐crystal species and polymorphs produced
A device for feasible fidelity, purity, Hilbert-Schmidt distance and entanglement witness measurements
A generic model of measurement device which is able to directly measure
commonly used quantum-state characteristics such as fidelity, overlap, purity
and Hilbert-Schmidt distance for two general uncorrelated mixed states is
proposed. In addition, for two correlated mixed states, the measurement
realizes an entanglement witness for Werner's separability criterion. To
determine these observables, the estimation only one parameter - the visibility
of interference, is needed. The implementations in cavity QED, trapped ion and
electromagnetically induced transparency experiments are discussed.Comment: 6 pages, 3 figure
Western oceanus procellarum as seen by c1xs on chandrayaan-1
We present the analysis of an X-ray fluorescence (XRF) observation of the western part of Oceanus Procellarum on the Moon’s nearside made by the Chandrayaan-1 X-ray Spectrometer on 10th February 2009. Through forward modelling of the X-ray spectra, we provide estimates of the MgO/SiO2 and Al2O3/SiO2 ratios for seven regions along the flare’s ground track. These results are combined with FeO and TiO2 contents derived from Clementine multispectral reflectance data in order to investigate the compositional diversity of this region of the Moon. The ground track observed consists mainly of low-Ti basaltic units, and the XRF data are largely consistent with this expectation. However, we obtain higher Al2O3/SiO2 ratios for these units than for most basalts in the Apollo sample collection. The widest compositional variation between the different lava flows is in wt% FeO content. A footprint that occurs in a predominantly highland region, immediately to the north of Oceanus Procellarum, has a composition that is consistent with mixing between low-Ti mare basaltic and more feldspathic regoliths. In contrast to some previous studies, we find no evidence for systematic differences in surface composition, as determined through X-ray and gamma-ray spectroscopy techniques
Detecting genuine multipartite continuous-variable entanglement
We derive necessary conditions in terms of the variances of position and
momentum linear combinations for all kinds of separability of a multi-party
multi-mode continuous-variable state. Their violations can be sufficient for
genuine multipartite entanglement, provided the combinations contain both
conjugate variables of all modes. Hence a complete state determination, for
example by detecting the entire correlation matrix of a Gaussian state, is not
needed.Comment: 13 pages, 3 figure
Constraining warm dark matter with cosmic shear power spectra
We investigate potential constraints from cosmic shear on the dark matter
particle mass, assuming all dark matter is made up of light thermal relic
particles. Given the theoretical uncertainties involved in making cosmological
predictions in such warm dark matter scenarios we use analytical fits to linear
warm dark matter power spectra and compare (i) the halo model using a mass
function evaluated from these linear power spectra and (ii) an analytical fit
to the non-linear evolution of the linear power spectra. We optimistically
ignore the competing effect of baryons for this work. We find approach (ii) to
be conservative compared to approach (i). We evaluate cosmological constraints
using these methods, marginalising over four other cosmological parameters.
Using the more conservative method we find that a Euclid-like weak lensing
survey together with constraints from the Planck cosmic microwave background
mission primary anisotropies could achieve a lower limit on the particle mass
of 2.5 keV.Comment: 26 pages, 9 figures, minor changes to match the version accepted for
publication in JCA
Non-minimally coupled dark matter: effective pressure and structure formation
We propose a phenomenological model in which a non-minimal coupling between
gravity and dark matter is present in order to address some of the apparent
small scales issues of \lcdm model. When described in a frame in which gravity
dynamics is given by the standard Einstein-Hilbert action, the non-minimal
coupling translates into an effective pressure for the dark matter component.
We consider some phenomenological examples and describe both background and
linear perturbations. We show that the presence of an effective pressure may
lead these scenarios to differ from \lcdm at the scales where the non-minimal
coupling (and therefore the pressure) is active. In particular two effects are
present: a pressure term for the dark matter component that is able to reduce
the growth of structures at galactic scales, possibly reconciling simulations
and observations; an effective interaction term between dark matter and baryons
that could explain observed correlations between the two components of the
cosmic fluid within Tully-Fisher analysis.Comment: 18 pages, 6 figures, references added. Published in JCA
Boundary States for D-branes with Traveling Waves
We construct boundary states for D-branes which carry traveling waves in the
covariant formalism. We compute their vacuum amplitudes to investigate their
interactions. In non-compact space, the vacuum amplitudes become trivial as is
common in plane wave geometries. However, we found that if they are
compactified in the traveling direction, then the amplitudes are affected by
non-trivial time dependent effects. The interaction between D-branes with waves
traveling in the opposite directions (`pulse-antipulse scattering') are also
computed. Furthermore, we apply these ideas to open string tachyon condensation
with traveling waves.Comment: 30 pages. 1 figure, Latex, minor corrections, references adde
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