4,588 research outputs found
Solitary waves and their stability in colloidal media: semi-analytical solutions
Spatial solitary waves in colloidal suspensions of spherical dielectric
nanoparticles are considered. The interaction of the nanoparticles is modelled
as a hard-sphere gas, with the Carnahan-Starling formula used for the gas
compressibility. Semi-analytical solutions, for both one and two spatial
dimensions, are derived using an averaged Lagrangian and suitable trial
functions for the solitary waves. Power versus propagation constant curves and
neutral stability curves are obtained for both cases, which illustrate that
multiple solution branches occur for both the one and two dimensional
geometries. For the one-dimensional case it is found that three solution
branches (with a bistable regime) occur, while for the two-dimensional case two
solution branches (with a single stable branch) occur in the limit of low
background packing fractions. For high background packing fractions the power
versus propagation constant curves are monotonic and the solitary waves stable
for all parameter values. Comparisons are made between the semi-analytical and
numerical solutions, with excellent comparison obtained.Comment: Paper to appear in Dynamics of Continuous, Discrete and Impulsive
Systems, Series
Data management study, volume 5. Appendix E - Contractor data package quality assurance /QA/ Final report
Manufacturing verification tests for quality assurance and control data management on Voyager spacecraf
Data management study, volume 5. Appendix C - Contractor data package manufacturing /MG/ Final report
Manufacturing contractor data project for Voyager spacecraft system
Numerical and analytical study of undular bores governed by the full water wave equations and bi-directional Whitham-Boussinesq equations
Undular bores, also termed dispersive shock waves, generated by an initial discontinuity in height as governed by two forms of the Boussinesq system of weakly nonlinear shallow water wave theory, the standard formulation and a Hamiltonian formulation, two related Whitham-Boussinesq equations, and the full water wave equations for gravity surface waves are studied and compared. It is found that the Whitham-Boussinesq systems give solutions in excellent agreement with numerical solutions of the full water wave equations for the positions of the leading and trailing edges of the bore up until the onset on modulational instability. The Whitham-Boussinesq systems, which are far simpler than the full water wave equations, can then be used to accurately model surface water wave undular bores. Finally, comparisons with numerical solutions of the full water wave equations show that the Whitham-Boussinesq systems give a slightly lower threshold for the onset of modulational instability in terms of the height of the initial step generating the undular bore
Hair cortisol concentrations in relation to ill-being and well-being in healthy young and old females
Hair cortisol concentration (HCC) provides a retrospective measure of long-term (i.e. over a period of months)
cortisol secretion and has been shown to be elevated in relation to chronic stress conditions. However associations
in healthy participants with subjective ill-being are less clear and associations with well-being have not
been explored. The current study examined HCC in relation to independent comprehensive measures of illbeing
(stress, depression, anxiety) and well-being (subjective happiness, life satisfaction, psychological wellbeing)
in healthy young and old females (mean ± SD: 19.5 ± 2.2 years and 78.6 ± 6.7 years respectively, total
N = 115). The data supported evidence of increased total cortisol secretion with increased age. No association
between ill-being and HCC was found in either the young or older group of participants. A positive association
between HCC and well-being was found in the older participant group which was independent of ill-being and
potential confounds. These findings do not support associations between HCC and ill-being in healthy young
or old females. However the results suggest that HCC is able to distinguish levels of well-being in healthy older
females
A Quantitative Comparison of Opacities Calculated Using the Distorted- Wave and -Matrix Methods
The present debate on the reliability of astrophysical opacities has reached
a new climax with the recent measurements of Fe opacities on the Z-machine at
the Sandia National Laboratory \citep{Bailey2015}. To understand the
differences between theoretical results, on the one hand, and experiments on
the other, as well as the differences among the various theoretical results,
detailed comparisons are needed. Many ingredients are involved in the
calculation of opacities; deconstructing the whole process and comparing the
differences at each step are necessary to quantify their importance and impact
on the final results. We present here such a comparison using the two main
approaches to calculate the required atomic data, the -Matrix and
distorted-wave methods, as well as sets of configurations and coupling schemes
to quantify the effects on the opacities for the and ions.Comment: 10 pages, 2 figure
Computing Role Assignments of Proper Interval Graphs in Polynomial Time
A homomorphism from a graph G to a graph R is locally surjective if its restriction to the neighborhood of each vertex of G is surjective. Such a homomorphism is also called an R-role assignment of G. Role assignments have applications in distributed computing, social network theory, and topological graph theory. The Role Assignment problem has as input a pair of graphs (G,R) and asks whether G has an R-role assignment. This problem is NP-complete already on input pairs (G,R) where R is a path on three vertices. So far, the only known non-trivial tractable case consists of input pairs (G,R) where G is a tree. We present a polynomial time algorithm that solves Role Assignment on all input pairs (G,R) where G is a proper interval graph. Thus we identify the first graph class other than trees on which the problem is tractable. As a complementary result, we show that the problem is Graph Isomorphism-hard on chordal graphs, a superclass of proper interval graphs and trees
The Effect of low Momentum Quantum Fluctuations on a Coherent Field Structure
In the present work the evolution of a coherent field structure of the
Sine-Gordon equation under quantum fluctuations is studied. The basic equations
are derived from the coherent state approximation to the functional
Schr\"odinger equation for the field. These equations are solved asymptotically
and numerically for three physical situations. The first is the study of the
nonlinear mechanism responsible for the quantum stability of the soliton in the
presence of low momentum fluctuations. The second considers the scattering of a
wave by the Soliton. Finally the third problem considered is the collision of
Solitons and the stability of a breather.
It is shown that the complete integrability of the Sine-Gordon equation
precludes fusion and splitting processes in this simplified model.
The approximate results obtained are non-perturbative in nature, and are
valid for the full nonlinear interaction in the limit of low momentum
fluctuations. It is also found that these approximate results are in good
agreement with full numerical solutions of the governing equations. This
suggests that a similar approach could be used for the baby Skyrme model, which
is not completely integrable. In this case the higher space dimensionality and
the internal degrees of freedom which prevent the integrability will be
responsable for fusion and splitting processes. This work provides a starting
point in the numerical solution of the full quantum problem of the interaction
of the field with a fluctuation.Comment: 15 pages, 9 (ps) figures, Revtex file. Some discussion expanded but
conclusions unchanged. Final version to appear in PR
Teachers as leaders in a knowledge society: encouraging signs of a new professionalism
[Abstract]: Challenges confronting schools worldwide are greater than ever,and, likewise, many teachers possess capabilities, talents, and formal credentials more sophisticated than ever. However, the responsibility and authority accorded
to teachers have not grown significantly, nor has the image of teaching as a profession advanced significantly. The question becomes, what are the implications for the image and status of the teaching profession as the concept of knowledge society takes a firm hold in the industrialized world? This article addresses the philosophical underpinnings of teacher leadership manifested in case studies where schools sought to achieve the generation of new knowledge as part of a process of whole-school revitalization. Specifically, this article reports on Australian research that has illuminated the work of teacher leaders engaged in the IDEAS project, a joint school revitalization initiative of the University
of Southern Queensland and the Queensland Department of Education and the Arts
The hypophysis and secretion of insulin
The action of the hypophysis on the pancreas has been demonstrated by a number of direct and indirect proofs. The latter, first reported from this Institute, are as follows: (a) Complete kypophysectomy or anterior (distal) lobe removal produces: (1) Marked sensitivity to the hypoglycemic and toxic action of insulin and other hypoglycemie agents such as phloridzin, fasting, etc. (2) Reduction of intensity of pancreatic and phloridzin diabetes. (3) A rapid fall in blood sugar and tissue glycogen during fasting; of non-pancreatic origin since it occurs after pancreatectomy. The hypoglycemic symptoms can be relieved by prompt administration of glucose, or prevented by a carbohydrate or protein, but not fat diet.Fil: Houssay, Bernardo Alberto. Universidad de Buenos Aires; ArgentinaFil: Foglia, Virgilio G.. Universidad de Buenos Aires; ArgentinaFil: Smyth, F. S.. Universidad de Buenos Aires; ArgentinaFil: Rietti, Ciro T.. Universidad de Buenos Aires; ArgentinaFil: Houssay, Alberto B.. Universidad de Buenos Aires; Argentinafond
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