1,367 research outputs found
Adaptive NLMS Partial Crosstalk Cancellation in Digital Subscriber Lines
Crosstalk is a major limitation to achieving high data-rates in next generation VDSL systems. Whilst crosstalk cancellation can be applied to completely remove crosstalk, it is often too complex for application in typical VDSL binders, which can contain up to hundreds of lines. A practical alternative, known as partial cancellation limits the cancellation to crosstalkers that cause severe interference to the other lines within the binder. In real VDSL systems, the crosstalk environment changes rapidly as new lines come online; old lines go offline, and the crosstalk channels change with fluctuations in ambient temperature. Therefore, adaptive crosstalk cancellers are often required. In this paper, we propose a new detection guided adaptive NLMS method for Adaptive Partial Crosstalk Cancellation that detects significant crosstalkers and tracks variations in their crosstalk channels. This exploits the sparse and column-wise diagonal dominant properties of the crosstalk channel matrix and leads to fast convergence, accurate crosstalk channel tracking, with a lower update complexity. The end result is an adaptive Partial Crosstalk Cancellation algorithm that has lower run-time complexity than prior state-of-the-art whilst yielding comparatively high data-rates and reliable service
Nonlinear Evolution Equations Invariant Under Schroedinger Group in three-dimensional Space-time
A classification of all possible realizations of the Galilei,
Galilei-similitude and Schroedinger Lie algebras in three-dimensional
space-time in terms of vector fields under the action of the group of local
diffeomorphisms of the space \R^3\times\C is presented. Using this result a
variety of general second order evolution equations invariant under the
corresponding groups are constructed and their physical significance are
discussed
New variable separation approach: application to nonlinear diffusion equations
The concept of the derivative-dependent functional separable solution, as a
generalization to the functional separable solution, is proposed. As an
application, it is used to discuss the generalized nonlinear diffusion
equations based on the generalized conditional symmetry approach. As a
consequence, a complete list of canonical forms for such equations which admit
the derivative-dependent functional separable solutions is obtained and some
exact solutions to the resulting equations are described.Comment: 19 pages, 2 fig
Hidden Conformal Symmetry of Extremal Kerr-Bolt Spacetimes
We show that extremal Kerr-Bolt spacetimes have a hidden conformal symmetry.
In this regard, we consider the wave equation of a massless scalar field
propagating in extremal Kerr-Bolt spacetimes and find in the "near region", the
wave equation in extremal limit can be written in terms of the
quadratic Casimir. Moreover, we obtain the microscopic entropy of the extremal
Kerr-Bolt spacetimes also we calculate the correlation function of a
near-region scalar field and find perfect agreement with the dual 2D CFT.Comment: 13 page
Therapistsâ and non-therapistsâ constructions of heterosex: A qualitative story completion study
© 2018 The British Psychological Society Objectives: Little research has examined the discourses that shape therapistsâ sense-making around heterosex. This paper explores the discourses of sexuality and gender underpinning therapistsâ and non-therapistsâ responses to a sexual experimentation scenario in a heterosexual relationship. It also considers the value of the novel technique of story completion (SC), in which participants are asked to write a story in response to a hypothetical scenario, for qualitative psychology and psychotherapy research. Design: This research used a comparative SC design (Kitzinger & Powell,). Participants were sequentially presented with and invited to complete two story stems: one in which a male character suggested âtrying something newâ to his female partner and one in which the female character made the suggestion. The stems were otherwise identical. Methods: A total of 100 SCs were written by 49 (28 female; 21 male) therapists and 51 (29 female; 22 male) non-therapists. Participants were recruited mainly via UK-based email lists and Facebook groups, and therapeutic training organizations, and the data were analysed using a feminist post-structuralist thematic analysis (Braun & Clarke,). Results: Both groups of participants drew on heteronormative discourses of sexuality and gender to make sense of the stem. Engaging in sexual experimentation was often depicted as a demonstration of being normal. In some stories written by women, sex was framed as a site for negotiating âequalityâ and reciprocity in relationships. Therapists were more likely than non-therapists to frame âdifficultiesâ within relationships as opportunities for personal growth and increased emotional depth, and their stories included greater emotional complexity. Conclusion: These findings raise questions about practitioner training and whether it results in therapists drawing on narrow and restrictive discourses of heterosex in clinical practice. Practitioner points: Training on sexual issues is largely absent from non-specialist practitioner training courses, which potentially means therapists are ill-equipped to respond to clientsâ anxiety about sexual issues. Evidence from this and other research indicates that therapistsâ sense-making around heterosexual sexual relationships is underpinned by narrow and restrictive discourses that entrench traditional gender relations and limit sexual agency. Psychologists are increasingly taking up positions of clinical leadership and are looked to for models of best practice. Drawing on theorizations of sexual difficulties, and of anxieties about sexual practice, that challenge traditional gender and heteronorms, and the commodification and medicalization of sex, is important for effective psychological leadership relating to the treatment of sexual issues and the furthering of social justice agendas
INTEGRAL deep observations of the Small Magellanic Cloud
Deep observations of the Small Magellanic Cloud (SMC) and region were carried
out in the hard X-ray band by the INTEGRAL observatory in 2008-2009. The field
of view of the instrument permitted simultaneous coverage of the entire SMC and
the eastern end of the Magellanic Bridge. In total, INTEGRAL detected seven
sources in the SMC and five in the Magellanic Bridge; the majority of the
sources were previously unknown systems. Several of the new sources were
detected undergoing bright X- ray outbursts and all the sources exhibited
transient behaviour except the supergiant system SMC X-1. They are all thought
to be High Mass X-ray Binary (HMXB) systems in which the compact object is a
neutron star.Comment: 7 pages, 10 figures Accepted for publication in MNRA
Nonclassical equivalence transformations associated with a parameter identification problem
A special class of symmetry reductions called nonclassical equivalence
transformations is discussed in connection to a class of parameter
identification problems represented by partial differential equations. These
symmetry reductions relate the forward and inverse problems, reduce the
dimension of the equation, yield special types of solutions, and may be
incorporated into the boundary conditions as well. As an example, we discuss
the nonlinear stationary heat conduction equation and show that this approach
permits the study of the model on new types of domains. Our MAPLE routine
GENDEFNC which uses the package DESOLV (authors Carminati and Vu) has been
updated for this propose and its output is the nonlinear partial differential
equation system of the determining equations of the nonclassical equivalence
transformations.Comment: 18 page
The Blue Straggler Population in Dwarf Galaxies
In this chapter I review the recent developments regarding the study of Blue
Stragglers (BSS) in dwarf galaxies. The loose density environment of dwarf
galaxies resembles that of the Galactic Halo, hence it is natural to compare
their common BSS properties. At the same time, it is unescapable to compare
with the BSS properties in Galactic Globular clusters, which constitute the
reference point for BSS studies. Admittedly, the literature on BSS in dwarf
galaxies is not plentiful. The limitation is mostly due to the large distance
to even the closest dwarf galaxies. Nevertheless, recent studies have allowed a
deeper insight on the BSS photometric properties that are worth examining.Comment: Chapter 6, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
Observational constraints on inhomogeneous cosmological models without dark energy
It has been proposed that the observed dark energy can be explained away by
the effect of large-scale nonlinear inhomogeneities. In the present paper we
discuss how observations constrain cosmological models featuring large voids.
We start by considering Copernican models, in which the observer is not
occupying a special position and homogeneity is preserved on a very large
scale. We show how these models, at least in their current realizations, are
constrained to give small, but perhaps not negligible in certain contexts,
corrections to the cosmological observables. We then examine non-Copernican
models, in which the observer is close to the center of a very large void.
These models can give large corrections to the observables which mimic an
accelerated FLRW model. We carefully discuss the main observables and tests
able to exclude them.Comment: 27 pages, 7 figures; invited contribution to CQG special issue
"Inhomogeneous Cosmological Models and Averaging in Cosmology". Replaced to
match the improved version accepted for publication. Appendix B and
references adde
B\"acklund transformations for the second Painlev\'e hierarchy: a modified truncation approach
The second Painlev\'e hierarchy is defined as the hierarchy of ordinary
differential equations obtained by similarity reduction from the modified
Korteweg-de Vries hierarchy. Its first member is the well-known second
Painlev\'e equation, P2.
In this paper we use this hierarchy in order to illustrate our application of
the truncation procedure in Painlev\'e analysis to ordinary differential
equations. We extend these techniques in order to derive auto-B\"acklund
transformations for the second Painlev\'e hierarchy. We also derive a number of
other B\"acklund transformations, including a B\"acklund transformation onto a
hierarchy of P34 equations, and a little known B\"acklund transformation for P2
itself.
We then use our results on B\"acklund transformations to obtain, for each
member of the P2 hierarchy, a sequence of special integrals.Comment: 12 pages in LaTeX 2.09 (uses ioplppt.sty), to appear in Inverse
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