176 research outputs found
Reconstructing the nucleon-nucleon potential by a new coupled-channel inversion method
A second-order supersymmetric transformation is presented, for the
two-channel Schr\"odinger equation with equal thresholds. It adds a
Breit-Wigner term to the mixing parameter, without modifying the eigenphase
shifts, and modifies the potential matrix analytically. The iteration of a few
such transformations allows a precise fit of realistic mixing parameters in
terms of a Pade expansion of both the scattering matrix and the effective-range
function. The method is applied to build an exactly-solvable potential for the
neutron-proton - case.Comment: 4 pages, 4 figure
Supersymmetric transformations for coupled channels with threshold differences
The asymptotic behaviour of the superpotential of general SUSY
transformations for a coupled-channel Hamiltonian with different thresholds is
analyzed. It is shown that asymptotically the superpotential can tend to a
diagonal matrix with an arbitrary number of positive and negative entries
depending on the choice of the factorization solution. The transformation of
the Jost matrix is generalized to "non-conservative" SUSY transformations
introduced in Sparenberg et al (2006 J. Phys. A: Math. Gen. 39 L639). Applied
to the zero initial potential the method permits to construct superpartners
with a nontrivially coupled Jost-matrix. Illustrations are given for two- and
three-channel cases.Comment: 17 pages, 3 explicit examples and figures adde
Aging and memory phenomena in magnetic and transport properties of vortex matter: a brief review
There is mounting experimental evidence that strong off-equilibrium
phenomena, such as ``memory'' or ``aging'' effects, play a crucial role in the
physics of vortices in type II superconductors. We give a short review, based
on a recently introduced schematic vortex model, of current progresses in
understanding out of equilibrium vortex behaviours. We develop a unified
description of ``memory'' phenomena in magnetic and transport properties, such
as magnetisation loops and their ``anomalous'' 2nd peak, logarithmic creep,
``anomalous'' finite creep rate in the limit of vanishing temperature,
``memory'' and ``irreversibility'' in I-V characteristics, time dependent
critical currents, ``rejuvenation'' and ``aging'' of the system response.Comment: updated versio
Eigenphase preserving two-channel SUSY transformations
We propose a new kind of supersymmetric (SUSY) transformation in the case of
the two-channel scattering problem with equal thresholds, for partial waves of
the same parity. This two-fold transformation is based on two imaginary
factorization energies with opposite signs and with mutually conjugated
factorization solutions. We call it an eigenphase preserving SUSY
transformation as it relates two Hamiltonians, the scattering matrices of which
have identical eigenphase shifts. In contrast to known phase-equivalent
transformations, the mixing parameter is modified by the eigenphase preserving
transformation.Comment: 16 pages, 1 figur
Effects of crack tip geometry on dislocation emission and cleavage: A possible path to enhanced ductility
We present a systematic study of the effect of crack blunting on subsequent
crack propagation and dislocation emission. We show that the stress intensity
factor required to propagate the crack is increased as the crack is blunted by
up to thirteen atomic layers, but only by a relatively modest amount for a
crack with a sharp 60 corner. The effect of the blunting is far less
than would be expected from a smoothly blunted crack; the sharp corners
preserve the stress concentration, reducing the effect of the blunting.
However, for some material parameters blunting changes the preferred
deformation mode from brittle cleavage to dislocation emission. In such
materials, the absorption of preexisting dislocations by the crack tip can
cause the crack tip to be locally arrested, causing a significant increase in
the microscopic toughness of the crack tip. Continuum plasticity models have
shown that even a moderate increase in the microscopic toughness can lead to an
increase in the macroscopic fracture toughness of the material by several
orders of magnitude. We thus propose an atomic-scale mechanism at the crack
tip, that ultimately may lead to a high fracture toughness in some materials
where a sharp crack would seem to be able to propagate in a brittle manner.
Results for blunt cracks loaded in mode II are also presented.Comment: 12 pages, REVTeX using epsfig.sty. 13 PostScript figures. Final
version to appear in Phys. Rev. B. Main changes: Discussion slightly
shortened, one figure remove
Linear, Deterministic, and Order-Invariant Initialization Methods for the K-Means Clustering Algorithm
Over the past five decades, k-means has become the clustering algorithm of
choice in many application domains primarily due to its simplicity, time/space
efficiency, and invariance to the ordering of the data points. Unfortunately,
the algorithm's sensitivity to the initial selection of the cluster centers
remains to be its most serious drawback. Numerous initialization methods have
been proposed to address this drawback. Many of these methods, however, have
time complexity superlinear in the number of data points, which makes them
impractical for large data sets. On the other hand, linear methods are often
random and/or sensitive to the ordering of the data points. These methods are
generally unreliable in that the quality of their results is unpredictable.
Therefore, it is common practice to perform multiple runs of such methods and
take the output of the run that produces the best results. Such a practice,
however, greatly increases the computational requirements of the otherwise
highly efficient k-means algorithm. In this chapter, we investigate the
empirical performance of six linear, deterministic (non-random), and
order-invariant k-means initialization methods on a large and diverse
collection of data sets from the UCI Machine Learning Repository. The results
demonstrate that two relatively unknown hierarchical initialization methods due
to Su and Dy outperform the remaining four methods with respect to two
objective effectiveness criteria. In addition, a recent method due to Erisoglu
et al. performs surprisingly poorly.Comment: 21 pages, 2 figures, 5 tables, Partitional Clustering Algorithms
(Springer, 2014). arXiv admin note: substantial text overlap with
arXiv:1304.7465, arXiv:1209.196
Watch me grow integrated (WMG-I): protocol for a cluster randomised controlled trial of a web-based surveillance approach for developmental screening in primary care settings
Introduction The increasing prevalence of developmental disorders in early childhood poses a significant global health burden. Early detection of developmental problems is vital to ensure timely access to early intervention, and universal developmental surveillance is recommended best practice for identifying issues. Despite this, there is currently considerable variation in developmental surveillance and screening between Australian states and territories and low rates of developmental screening uptake by parents. This study aims to evaluate an innovative web-based developmental surveillance programme and a sustainable approach to referral and care pathways, linking primary care general practice (GP) services that fall under federal policy responsibility and state government-funded child health services. Methods and analysis The proposed study describes a longitudinal cluster randomised controlled trial (c-RCT) comparing a â € Watch Me Grow Integrated' (WMG-I) approach for developmental screening, to Surveillance as Usual (SaU) in GPs. Forty practices will be recruited across New South Wales and Queensland, and randomly allocated into either the (1) WMG-I or (2) SaU group. A cohort of 2000 children will be recruited during their 18-month vaccination visit or opportunistic visit to GP. At the end of the c-RCT, a qualitative study using focus groups/interviews will evaluate parent and practitioner views of the WMG-I programme and inform national and state policy recommendations. Ethics and dissemination The South Western Sydney Local Health District (2020/ETH01625), UNSW Sydney (2020/ETH01625) and University of Queensland (2021/HE000667) Human Research Ethics Committees independently reviewed and approved this study. Findings will be reported to the funding bodies, study institutes and partners; families and peer-reviewed conferences/publications
"Watch Me Grow- Electronic (WMG-E)" surveillance approach to identify and address child development, parental mental health, and psychosocial needs : study protocol
Background: The COVID-19 pandemic and the associated economic recession has increased parental psychosocial stress and mental health challenges. This has adversely impacted child development and wellbeing, particularly for children from priority populations (culturally and linguistically diverse (CALD) and rural/regional communities) who are at an already increased risk of health inequality. The increased mental health and psychosocial needs were compounded by the closure of in-person preventive and health promotion programs resulting in health organisations embracing technology and online services. Watch Me Grow- Electronic (WMG-E) – developmental surveillance platform- exemplifies one such service. WMG-E was developed to monitor child development and guide parents towards more detailed assessments when risk is identified. This Randomised Controlled Trial (RCT) aims to expand WMG-E as a digital navigation tool by also
incorporating parents’ mental health and psychosocial needs. Children and families needing additional assessments and supports will be electronically directed to relevant resources in the ‘care-as-usual’ group. In contrast, the
intervention group will receive continuity of care, with additional in-person assessment and ‘warm hand over’ by a ‘service navigator’ to ensure their needs are met. Methods: Using an RCT we will determine: (1) parental engagement with developmental surveillance; (2) access to services for those with mental health and social care needs; and (3) uptake of service recommendations. Three hundred parents/carers of children aged 6 months to 3 years (recruited from a culturally diverse, or rural/regional site) will be randomly allocated to the ‘care-as-usual’ or ‘intervention’ group. A mixed methods implementation evaluation will be completed, with semi-structured interviews to ascertain the acceptability, feasibility and impact of the WMG-E platform and service navigator. Conclusions: Using WMG-E is expected to: normalise and de-stigmatise mental health and psychosocial screening; increase parental engagement and service use; and result in the early identification and management of child developmental needs, parental mental health, and family psychosocial needs. If effective, digital solutions such as WMG-E to engage and empower parents alongside a service navigator for vulnerable families needing additional support, will have significant practice and policy implications in the pandemic/post pandemic period. Trial registration: The trial (Protocol No. 1.0, Version 3.1) was registered with ANZCTR (registration number: ACTRN12621000766819) on July 21st, 2021 and reporting of the trial results will be according to recommendations in the CONSORT Statement
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