14,809 research outputs found
The noisiness of tones plus noise
Judgment tests conducted to determine noise levels or loudness of tones plus nois
Coupled Cluster Method Calculations Of Quantum Magnets With Spins Of General Spin Quantum Number
We present a new high-order coupled cluster method (CCM) formalism for the
ground states of lattice quantum spin systems for general spin quantum number,
. This new ``general-'' formalism is found to be highly suitable for a
computational implementation, and the technical details of this implementation
are given. To illustrate our new formalism we perform high-order CCM
calculations for the one-dimensional spin-half and spin-one antiferromagnetic
{\it XXZ} models and for the one-dimensional spin-half/spin-one ferrimagnetic
{\it XXZ} model. The results for the ground-state properties of the isotropic
points of these systems are seen to be in excellent quantitative agreement with
exact results for the special case of the spin-half antiferromagnet and results
of density matrix renormalisation group (DMRG) calculations for the other
systems. Extrapolated CCM results for the sublattice magnetisation of the
spin-half antiferromagnet closely follow the exact Bethe Ansatz solution, which
contains an infinite-order phase transition at . By contrast,
extrapolated CCM results for the sublattice magnetisation of the spin-one
antiferromagnet using this same scheme are seen to go to zero at , which is in excellent agreement with the value for the onset of
the Haldane phase for this model. Results for sublattice magnetisations of the
ferrimagnet for both the spin-half and spin-one spins are non-zero and finite
across a wide range of , up to and including the Heisenberg point at
.Comment: 5 Figures. J. Stat. Phys. 108, p. 401 (2002
Bogoliubov transformations and exact isolated solutions for simple non-adiabatic Hamiltonians
We present a new method for finding isolated exact solutions of a class of
non-adiabatic Hamiltonians of relevance to quantum optics and allied areas.
Central to our approach is the use of Bogoliubov transformations of the bosonic
fields in the models. We demonstrate the simplicity and efficiency of this
method by applying it to the Rabi Hamiltonian.Comment: LaTeX, 16 pages, 1 figure. Minor additions and journal re
Quasi-Normal Modes of a Schwarzschild White Hole
We investigate perturbations of the Schwarzschild geometry using a
linearization of the Einstein vacuum equations within a Bondi-Sachs, or null
cone, formalism. We develop a numerical method to calculate the quasi-normal
modes, and present results for the case . The values obtained are
different to those of a Schwarzschild black hole, and we interpret them as
quasi-normal modes of a Schwarzschild white hole.Comment: 5 pages, 4 Figure
Assessment and diagnosis of Developmental Language Disorder: The experiences of speech and language therapists
© The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 License (http://www.creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.sagepub.com/en-us/nam/open-access-at-sage).Background: For many years research and practice have noted the impact of the heterogeneous nature of Developmental Language Disorder (also known as language impairment or specific language impairment) on diagnosis and assessment. Recent research suggests the disorder is not restricted to the language domain and against this background, the challenge for the practitioner is to provide accurate assessment and effective therapy. The language practitioner aims to support the child and their carers to achieve the best outcomes. However, little is known about the experiences of the language practitioner in the assessment process, in contrast to other childhood disorders, yet their expertise is central in the assessment and diagnosis of children with language disorder. Aims: This study aimed to provide a detailed qualitative description of the experiences of speech and language therapists involved in the assessment and diagnosis of children with Developmental Language Disorder. Methods & Procedures: The qualitative study included three focus groups to provide a credible and rich description of the experiences of speech and language therapists involved in the assessment of Developmental Language Disorder. The speech and language therapists who participated in the study were recruited from three NHS Trusts across the UK and all were directly involved in the assessment and diagnosis procedures. The lengths of practitioner experience ranged from 2 years to 38 years. The data was analysed using a thematic analysis in accordance with the principles set out by Braun & Clarke (2006). Outcomes & Results: The data showed a number of key themes concerning the experiences of speech and language therapists in assessing children with Developmental Language Disorder (DLD). These themes ranged from the participants’ experiences of the barriers to early referral, challenges for assessment and the concerns over continued future support. Conclusions & Implications: This study provides first-hand evidence from speech and language therapists in the assessment of children with Developmental Language Disorder, drawing together experiences from language practitioners from different regions. The findings provide insight to the barriers to referral, the potential variations in the assessment process, the role of practitioner expertise and the challenges faced them. The importance of early intervention, useful assessment tools and future support were expressed. Taken together, the results relate to some issues to be addressed on a practical level and a continuing need for initiatives to raise awareness of DLD in the public domain.Peer reviewe
Identification of novel chondroitin proteoglycans in Caenorhabditis elegans: embryonic cell division depends on CPG-1 and CPG-2.
Vertebrates produce multiple chondroitin sulfate proteoglycans that play important roles in development and tissue mechanics. In the nematode Caenorhabditis elegans, the chondroitin chains lack sulfate but nevertheless play essential roles in embryonic development and vulval morphogenesis. However, assignment of these functions to specific proteoglycans has been limited by the lack of identified core proteins. We used a combination of biochemical purification, Western blotting, and mass spectrometry to identify nine C. elegans chondroitin proteoglycan core proteins, none of which have homologues in vertebrates or other invertebrates such as Drosophila melanogaster or Hydra vulgaris. CPG-1/CEJ-1 and CPG-2 are expressed during embryonic development and bind chitin, suggesting a structural role in the egg. RNA interference (RNAi) depletion of individual CPGs had no effect on embryonic viability, but simultaneous depletion of CPG-1/CEJ-1 and CPG-2 resulted in multinucleated single-cell embryos. This embryonic lethality phenocopies RNAi depletion of the SQV-5 chondroitin synthase, suggesting that chondroitin chains on these two proteoglycans are required for cytokinesis
Phase Transitions in the Spin-Half J_1--J_2 Model
The coupled cluster method (CCM) is a well-known method of quantum many-body
theory, and here we present an application of the CCM to the spin-half J_1--J_2
quantum spin model with nearest- and next-nearest-neighbour interactions on the
linear chain and the square lattice. We present new results for ground-state
expectation values of such quantities as the energy and the sublattice
magnetisation. The presence of critical points in the solution of the CCM
equations, which are associated with phase transitions in the real system, is
investigated. Completely distinct from the investigation of the critical
points, we also make a link between the expansion coefficients of the
ground-state wave function in terms of an Ising basis and the CCM ket-state
correlation coefficients. We are thus able to present evidence of the
breakdown, at a given value of J_2/J_1, of the Marshall-Peierls sign rule which
is known to be satisfied at the pure Heisenberg point (J_2 = 0) on any
bipartite lattice. For the square lattice, our best estimates of the points at
which the sign rule breaks down and at which the phase transition from the
antiferromagnetic phase to the frustrated phase occurs are, respectively, given
(to two decimal places) by J_2/J_1 = 0.26 and J_2/J_1 = 0.61.Comment: 28 pages, Latex, 2 postscript figure
High-Order Coupled Cluster Calculations Via Parallel Processing: An Illustration For CaVO
The coupled cluster method (CCM) is a method of quantum many-body theory that
may provide accurate results for the ground-state properties of lattice quantum
spin systems even in the presence of strong frustration and for lattices of
arbitrary spatial dimensionality. Here we present a significant extension of
the method by introducing a new approach that allows an efficient
parallelization of computer codes that carry out ``high-order'' CCM
calculations. We find that we are able to extend such CCM calculations by an
order of magnitude higher than ever before utilized in a high-order CCM
calculation for an antiferromagnet. Furthermore, we use only a relatively
modest number of processors, namely, eight. Such very high-order CCM
calculations are possible {\it only} by using such a parallelized approach. An
illustration of the new approach is presented for the ground-state properties
of a highly frustrated two-dimensional magnetic material, CaVO. Our
best results for the ground-state energy and sublattice magnetization for the
pure nearest-neighbor model are given by and ,
respectively, and we predict that there is no N\'eel ordering in the region
. These results are shown to be in excellent agreement
with the best results of other approximate methods.Comment: 4 page
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