45,307 research outputs found
Finite pseudo orbit expansions for spectral quantities of quantum graphs
We investigate spectral quantities of quantum graphs by expanding them as
sums over pseudo orbits, sets of periodic orbits. Only a finite collection of
pseudo orbits which are irreducible and where the total number of bonds is less
than or equal to the number of bonds of the graph appear, analogous to a cut
off at half the Heisenberg time. The calculation simplifies previous approaches
to pseudo orbit expansions on graphs. We formulate coefficients of the
characteristic polynomial and derive a secular equation in terms of the
irreducible pseudo orbits. From the secular equation, whose roots provide the
graph spectrum, the zeta function is derived using the argument principle. The
spectral zeta function enables quantities, such as the spectral determinant and
vacuum energy, to be obtained directly as finite expansions over the set of
short irreducible pseudo orbits.Comment: 23 pages, 4 figures, typos corrected, references added, vacuum energy
calculation expande
A psycho-educational programme for abused and neglected children
M.A.Statistics show an increase in the number of cases of abused and neglected children handled by the Child Protection Unit. These particular statistics indicate only the number of reported cases, which according to Lewis (1999) and Starke (1995) should be tripled to estimate the true number of children being abused every day. Action research was selected for this study to assist the parents and the children in extending their understanding of their situation and thus resolve problems that confront them. A high percentage of parents are aware that abuse and neglect exists in their relationships; they are also aware that behavioural problems may be exhibited by their children as a result of exposure to abuse and neglect. There is a growing need for counselling, guidance and support amongst the youth to be assertive, and be safe in their contexts. The psycho-education programme was based on the model of psychoeducation. Psycho-education as an alternative does not focus on sick or abnormal behaviour but rather has as its core a preventative focus-training in skills to solve problems now and in the future. During group work the children were trained to collectively experience, explore and communicate their feelings, and to learn alternative ways of dealing with abuse and neglect in their different contexts. The programme's effectiveness was evaluated. All the children acquired prevention concepts after the exposure to the programme. Fifty six percent of the parents observed some improvement in their children's behaviour, and eighty percent of the children reported that they were still afraid to talk to their parents about issues of discipline, for example corporal punishment
Lie point symmetries and the geodesic approximation for the Schr\"odinger-Newton equations
We consider two problems arising in the study of the Schr\"odinger-Newton
equations. The first is to find their Lie point symmetries. The second, as an
application of the first, is to investigate an approximate solution
corresponding to widely separated lumps of probability. The lumps are found to
move like point particles under a mutual inverse-square law of attraction
Stable, inflatable life raft for high seas rescue operations
Raft is easily deployed and highly maneuverable in water. It has false bottom of water ballast containers attached to underside, making it exceptionally stable platform from which swimmers can operate. Raft is attachable to external moorings
Experimental observation of Frohlich superconductivity in high magnetic fields
Resistivity and irreversible magnetisation data taken within the
high-magnetic-field CDWx phase of the quasi-two-dimensional organic metal
alpha-(BEDT-TTF)2KHg(SCN)4 are shown to be consistent with a field-induced
inhomogeneous superconducting phase. In-plane skin-depth measurements show that
the resistive transition on entering the CDWx phase is both isotropic and
representative of the bulk.Comment: ten pages, four figure
Distortion of the perfect lattice structure in bilayer graphene
We consider the instability of bilayer graphene with respect to a distorted
configuration in the same spirit as the model introduced by Su, Schrieffer and
Heeger. By computing the total energy of a distorted bilayer, we conclude that
the ground state of the system favors a finite distortion. We explore how the
equilibrium configuration changes with carrier density and an applied potential
difference between the two layers
Effect of strong localization of doped holes in angle-resolved photoemission spectra of LaSrFeO
We have performed an angle-resolved photoemission spectroscopy study of
LaSrFeO using {\it in situ} prepared thin films and
determined its band structure. The experimental band dispersions could be well
explained by an empirical band structure assuming the G-type antiferromagnetic
state. However, the Fe 3d bands were found to be shifted downward relative to
the Fermi level () by eV compared with the calculation and to
form a (pseudo)gap of eV at . We attribute this observation to a
strong localization effect of doped holes due to polaron formation.Comment: 5 pages, 5 figure
Constraints on the average magnetic field strength of relic radio sources 0917+75 and 1401-33 from XMM-Newton observations
We observed two relic radio sources, 0917+75 and 1401-33, with the XMM-Newton
X-ray observatory. We did not detect any X-ray emission, thermal or
non-thermal, in excess of the local background level from either target. This
imposes new upper limits on the X-ray flux due to inverse Compton scattering of
photons from the cosmic microwave background by relativistic electrons in the
relic sources, and new lower limits on the magnetic field strength from the
relative strength of the radio and X-ray emission. The combination of radio and
X-ray observations provides a measure of the magnetic field independent of
equipartition or minimum energy assumptions. Due to increasing sensitivity of
radio observations, the known population of cluster relics has been growing;
however, studies of non-thermal X-ray emission from relics remain scarce. Our
study adds to the small sample of relics studied in X-rays. In both relics, our
field strength lower limits are slightly larger than estimates of the
equipartition magnetic field.Comment: 11 pages, 5 figures. Accepted by MNRA
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