1,899 research outputs found
Elasticity, fluctuations and vortex pinning in ferromagnetic superconductors: A "columnar elastic glass"
We study the elasticity, fluctuations and pinning of a putative spontaneous
vortex solid in ferromagnetic superconductors. Using a rigorous thermodynamic
argument, we show that in the idealized case of vanishing crystalline pinning
anisotropy the long-wavelength tilt modulus of such a vortex solid vanishes
identically, as guaranteed by the underlying rotational invariance. The
vanishing of the tilt modulus means that, to lowest order, the associated
tension elasticity is replaced by the softer, curvature elasticity. The effect
of this is to make the spontaneous vortex solid qualitatively more susceptible
to the disordering effects of thermal fluctuations and random pinning. We study
these effects, taking into account the nonlinear elasticity, that, in three
dimensions, is important at sufficiently long length scales, and showing that a
``columnar elastic glass'' phase of vortices results. This phase is controlled
by a previously unstudied zero-temperature fixed point and it is characterized
by elastic moduli that have universal strong wave-vector dependence out to
arbitrarily long length scales, leading to non-Hookean elasticity. We argue
that, although translationally disordered for weak disorder, the columnar
elastic glass is stable against the proliferation of dislocations and is
therefore a topologically ordered {\em elastic} glass. As a result, the
phenomenology of the spontaneous vortex state of isotropic magnetic
superconductors differs qualitatively from a conventional,
external-field-induced mixed state. For example, for weak external fields ,
the magnetic induction scales {\em universally} like , with .Comment: Minor editorial changes, version to be published in PRB, 39 pages, 7
figure
Floating phase in a dissipative Josephson junction array
We consider dissipative quantum phase transitions in Josephson junction
arrays and show that the disordered phase in this extended system can be viewed
as an unusual floating phase in which the states of local -dimensional
elements (single Josephson junctions) can slide past each other despite
arbitrary range spatial couplings among them. The unusual character of the
metal-superconductor quantum critical point can be tested by measurements of
the current voltage characteristic. This may be the simplest and most natural
example of a floating phase.Comment: 4 pages, RevTex4. The revised version contains higher order
renormalization group equations and the corresponding phase diagra
"Soft" Anharmonic Vortex Glass in Ferromagnetic Superconductors
Ferromagnetic order in superconductors can induce a {\em spontaneous} vortex
(SV) state. For external field , rotational symmetry guarantees a
vanishing tilt modulus of the SV solid, leading to drastically different
behavior than that of a conventional, external-field-induced vortex solid. We
show that quenched disorder and anharmonic effects lead to elastic moduli that
are wavevector-dependent out to arbitrarily long length scales, and non-Hookean
elasticity. The latter implies that for weak external fields , the magnetic
induction scales {\em universally} like , with
. For weak disorder, we predict the SV solid is a
topologically ordered vortex glass, in the ``columnar elastic glass''
universality class.Comment: minor corrections; version published in PR
The Fast Wandering of Slow Birds
I study a single "slow" bird moving with a flock of birds of a different, and
faster (or slower) species. I find that every "species" of flocker has a
characteristic speed , where is the mean speed of the
flock, such that, if the speed of the "slow" bird equals , it
will randomly wander transverse to the mean direction of flock motion far
faster than the other birds will: its mean-squared transverse displacement will
grow in with time like , in contrast to for the
other birds. In , the slow bird's mean squared transverse displacement
grows like , in contrast to for the other birds. If , the mean-squared displacement of the "slow" bird crosses over from
to scaling in , and from to scaling in
, at a time that scales according to .Comment: 10 pages; 5 pages of which did not appear in earlier versions, but
were added in response to referee's suggestion
The illusion of community ownership: community-based water management in Uchira, Kilimanjaro region
Water resource managementSocial participationWater users’ associationsWater policyWater shortagePricingWater costsWater supplyLabor
Social Workers in the New York Times: A National Portrayal
Social work is a profession that is diverse and difficult to define, and the way in which social workers are portrayed in the news provides information on the profession to the general public. There is little previous research on the subject of social workers portrayed in the news. To fill this gap in information, this study seeks to answer the question of how are social workers portrayed in national news stories published by the New York Times from 2010 to 2015. A textual analysis of 50 New York Times articles was collected using ProQuest Newsstand. Articles were then analyzed using grounded theory. Major themes that emerged included: how social workers are defined, what roles they play, stereotypes of social workers and their clients, the politics of emotion, and newsworthiness of social workers. Social workers in these articles are often vaguely defined and seldom the subject of the story. Future studies should help to further the understanding of how these portrayals influence public opinion and policy that govern the practice of social work
The illusion of community ownership: community-based water management in Uchira, Kilimanjaro region
Water resource managementWater governanceSocial participationWater users’ associationsWater policyWater shortagePricingWater costsWater supplyLabor
Social workers treating the whole person: the need for holistic therapy coursework
Holistic therapies have become an integral part of everyday life in the US. We use holistic therapies for many reasons, for exercising, relaxing, and healing alternatives to the traditional. This research survey explored the use of holistic therapies by social workers who are providing clinical social work to their clients primarily in the Twin Cities region of Minnesota. Using a quantitative design, the research measured the number of clinical social workers who are now or have previously provided mental health counseling services and are using holistic therapies in addition to standard interventions. This exploratory research additionally hoped to identify the holistic therapies being used by social workers and explore the amount and type of additional education the social workers have in order to utilize each of the reported holistic therapies. A purposive sampling of licensed LICSWs since 2004, from the Twin Cities metro area of Minnesota was used. Two-hundred and seventy-four LICSW licensed social workers responded to our Qualtrics survey stating that they are all using holistic therapies in addition to the clinical social work therapeutic modalities in the care of their clients. By the response, it is obvious that all those who completed the survey have an interest in and have taken the time to learn various holistic therapies to use in the care their clients. It is critical that clinical social worker education keep up with popular methods of self-care and client care so that the social worker can best practice and have the ability to serve their clients
A New Phase of Tethered Membranes: Tubules
We show that fluctuating tethered membranes with {\it any} intrinsic
anisotropy unavoidably exhibit a new phase between the previously predicted
``flat'' and ``crumpled'' phases, in high spatial dimensions where the
crumpled phase exists. In this new "tubule" phase, the membrane is crumpled in
one direction but extended nearly straight in the other. Its average thickness
is with the intrinsic size of the membrane. This phase
is more likely to persist down to than the crumpled phase. In Flory
theory, the universal exponent , which we conjecture is an exact
result. We study the elasticity and fluctuations of the tubule state, and the
transitions into it.Comment: 4 pages, self-unpacking uuencoded compressed postscript file with
figures already inside text; unpacking instructions are at the top of file.
To appear in Phys. Rev. Lett. November (1995
An evaluation of potentially useful separator materials for nickel-cadmium (Ni-Cd] satellite batteries
An evaluation intended to determine the potential suitability and probable efficacy of a group of separator materials for use in nickel-cadmium (Ni-Cd) satellite batteries was carried out. These results were obtained using test procedures established in an earlier evaluation of other separator materials, some of which were used in experimental battery cells subjected to simulated use conditions. The properties that appear to be most important are: high electrolyte absorptivity, good electrolyte retention, low specific resistivity, rapid wettability and low resistance to air permeation. Wicking characteristics and wet-out time seem to be more important with respect to the initial filling of the battery with the electrolyte
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