691 research outputs found
Programmed buckling by controlled lateral swelling in a thin elastic sheet
Recent experiments have imposed controlled swelling patterns on thin polymer
films, which subsequently buckle into three-dimensional shapes. We develop a
solution to the design problem suggested by such systems, namely, if and how
one can generate particular three-dimensional shapes from thin elastic sheets
by mere imposition of a two-dimensional pattern of locally isotropic growth.
Not every shape is possible. Several types of obstruction can arise, some of
which depend on the sheet thickness. We provide some examples using the
axisymmetric form of the problem, which is analytically tractable.Comment: 11 pages, 9 figure
Role of carbon dioxide and ion transport in the formation of sub-embryonic fluid by the blastoderm of the Japanese quail
1. The explanted blastoderm of the Japanese quail was used to explore the role of ions and carbon dioxide in determining the rate of sub-embryonic fluid (SEF) production between 54 and 72 h of incubation.
2. Amiloride, an inhibitor of Na+/H+ exchange, at concentrations of 10-3 to 10-6 M substantially decreased the rate of SEF production when added to the albumen culture medium. N-ethylmaleimide, an inhibitor of V type H+ ATPase, also decreased this rate but only to a small extent at the highest dose applied, 10-3 M. Both inhibitors had no effect on SEF production when added to the SEF. 3. The inhibitors of cellular bicarbonate and chloride exchange, 4-acetamido-4-'isothiocyano-2, 2-'disulphonic acid (SITS) and 4,4'diisothiocyanostilbene-2,2-'disulphonic acid (DIDS), had no effect upon SEF production.
4. Ouabain, an inhibitor of Na+/K+ ATPase, decreased SEF production substantially at all concentrations added to the SEF (10-3 to 10-6 M). Three sulphonamide inhibitors of carbonic anhydrase, acetazolamide, ethoxzolamide and benzolamide, decreased SEF production when added to the SEF at concentrations of 10-3 to 10-6 M. Benzolamide was by far the most potent. Neither ouabain nor the sulphonamides altered SEF production when added to the albumen culture medium.
5. Using a cobalt precipitation method, carbonic anhydrase activity was localised to the endodermal cells of the area vasculosa. The carbonic anhydrase activity was primarily associated with the lateral plasma membranes, which together with the potent inhibitory effect of benzolamide, suggests the carbonic anhydrase of these cells is the membrane-associated form, CA IV.
6. The changes in SEF composition produced by inhibitors were consistent with the production of SEF by local osmotic gradients.
7. It is concluded that a Na+/K+ ATPase is located on the basolateral membranes of the endodermal cells of the area vasculosa , and that a sodium ion/hydrogen ion exchanger is located on their apical surfaces. Protons for this exchanger would be provided by the hydration of CO2 catalysed by the membrane-associated carbonic anhydrase. Furthermore, it is proposed that the prime function of the endodermal cells of the area vasculosa is the production of SEF
Tilted and crossing vortex chains in layered superconductors
In the presence of the Josephson vortex lattice in layered superconductors, a
small c-axis magnetic field penetrates in the form of vortex chains. In
general, the structure of a single chain is determined by the ratio of the
London [] and Josephson [] lengths, . The chain is composed of tilted vortices at large
's (tilted chain) and at small 's it consists of a crossing
array of Josephson vortices and pancake-vortex stacks (crossing chain). We
study chain structures at intermediate 's and found two types of phase
transitions. For the ground state is given by the crossing
chain in a wide range of pancake separations .
However, due to attractive coupling between deformed pancake stacks, the
equilibrium separation can not exceed some maximum value depending on the
in-plane field and . The first phase transition takes place with
decreasing pancake-stack separation at , and rather
wide range of the ratio , . With
decreasing , the crossing chain goes through intermediate strongly-deformed
configurations and smoothly transforms into a tilted chain via a second-order
phase transition. Another phase transition occurs at very small densities of
pancake vortices, , and only when exceeds a
certain critical value . In this case a small c-axis field penetrates
in the form of kinks. However, at very small concentration of kinks, the kinked
chains are replaced with strongly deformed crossing chains via a first-order
phase transition. This transition is accompanied by a very large jump in the
pancake density.Comment: Proceeding of the NATO ARW "Vortex dynamics in superconductors and
other complex systems", Yalta, Crimea, Ukraine, 13-17 September 2004, To be
published in the Journ. of Low Temp. Phys., 16 pages, 6 figure
Incommensuration Effects and Dynamics in Vortex Chains
We examine the motion of one-dimensional (1D) vortex matter embedded in a 2D
vortex system with weak pinning using numerical simulations. We confirm the
conjecture of Matsuda et al. [Science 294, 2136 (2001)] that the onset of the
temperature induced motion of the chain is due to an incommensuration effect of
the chain with the periodic potential created by the bulk vortices. In
addition, under an applied driving force we find a two stage depinning
transition, where the initial depinning of the vortex chain occurs through
soliton like pulses. When an ac drive is added to the dc drive, we observe
phase locking of the moving vortex chain.Comment: 4 pages, 4 postscript figure
Field Dependence of the Josephson Plasma Resonance in Layered Superconductors with Alternating Junctions
The Josephson plasma resonance in layered superconductors with alternating
critical current densities is investigated in a low perpendicular magnetic
field. In the vortex solid phase the current densities and the squared bare
plasma frequencies decrease linearly with the magnetic field. Taking into
account the coupling due to charge fluctuations on the layers, we extract from
recent optical data for SmLa_{1-x} Sr_x CuO_{4-delta} the Josephson penetration
length lambda_{ab} approximately 1100 A parallel to the layers at T=10 K.Comment: 5 pages, 6 eps-figures, final version with minor misprints correcte
Vortex Collisions: Crossing or Recombination?
We investigate the collision of two vortex lines moving with viscous dynamics
and driven towards each other by an applied current. Using London theory in the
approach phase we observe a non-trivial vortex conformation producing
anti-parallel segments; their attractive interaction triggers a violent
collision. The collision region is analyzed using the time-dependent
Ginzburg-Landau equation. While we find vortices will always recombine through
exchange of segments, a crossing channel appears naturally through a double
collision process.Comment: 4 pages, 3 figure
Effects of a novel, brief psychological therapy (Managing Unusual Sensory Experiences) for hallucinations in first episode psychosis (MUSE FEP): Findings from an exploratory randomised controlled trial
\ua9 2024Hallucinations are a common feature of psychosis, yet access to effective psychological treatment is limited. The Managing Unusual Sensory Experiences for First-Episode-Psychosis (MUSE-FEP) trial aimed to establish the feasibility and acceptability of a brief, hallucination-specific, digitally provided treatment, delivered by a non-specialist workforce for people with psychosis. MUSE uses psychoeducation about the causal mechanisms of hallucinations and tailored interventions to help a person understand and manage their experiences. We undertook a two-site, single-blind (rater) Randomised Controlled Trial and recruited 82 participants who were allocated 1:1 to MUSE and treatment as usual (TAU) (n = 40) or TAU alone (n = 42). Participants completed assessments before and after treatment (2 months), and at follow up (3–4 months). Information on recruitment rates, adherence, and completion of outcome assessments was collected. Analyses focussed on feasibility outcomes and initial estimates of intervention effects to inform a future trial. The trial is registered with the ISRCTN registry 16793301. Criteria for the feasibility of trial methodology and intervention delivery were met. The trial exceeded the recruitment target, had high retention rates (87.8%) at end of treatment, and at follow up (86.6%), with good acceptability of treatment. There were 3 serious adverse events in the therapy group, and 5 in the TAU group. Improvements were evident in both groups at the end of treatment and follow up, with a particular benefit in perceived recovery in the MUSE group. We showed it was feasible to increase access to psychological intervention but a definitive trial requires further changes to the trial design or treatment
Topological Defects in the Abrikosov Lattice of Vortices in Type-II Superconductors
The free energy costs for various defects within an Abrikosov lattice of
vortices are calculated using the lowest Landau level approximation (LLL).
Defect solutions with boundary conditions for lines to meet at a point
(crossing defect) and for lines to twist around each other (braid defect) are
sought for 2, 3, 6, and 12 lines. Many results have been unexpected, including
the nonexistence of a stable two- or three-line braid. This, and the high
energy cost found for a six-line braid lead us to propose that the equilibrium
vortex state is not entangled below the irreversibility line of the high-
superconductors or in a large part of the vortex-liquid phase above this line.
Also, the solution for an infinite straight screw dislocation is found, and
used to give a limiting form for the free energy cost of very large braids.
This depends on the area enclosed by the braid as well as its perimeter length.Comment: 30 pages, 17 Encapsulated PostScript figures, uses Revtex (with epsf
Defect-unbinding and the Bose-glass transition in layered superconductors
The low-field Bose-glass transition temperature in heavy-ion irradiated
Bi_2Sr_2CaCu_2O_8+d increases progressively with increasing density of
irradiation-induced columnar defects, but saturates for densities in excess of
1.5 x10^9 cm^-2. The maximum Bose-glass temperature corresponds to that above
which diffusion of two-dimensional pancake vortices between different vortex
lines becomes possible, and above which the ``line-like'' character of vortices
is lost. We develop a description of the Bose-glass line that is in excellent
quantitative agreement with the experimental line obtained for widely different
values of track density and material parameters.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
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Motivations for innovation in the built environment: new directions for research
Innovation in the built environment involves multiple actors with diverse motivations. Policy-makers find it difficult to promote changes that require cooperation from these numerous and dispersed actors and to align their sometimes divergent interests. Established research traditions on the economics and management of innovation pay only limited attention to stakeholder choices, engagement and motivation. This paper reviews the insights that emerge as research in these traditions comes into contact with work on innovation from sociological and political perspectives. It contributes by highlighting growing areas of research on user involvement in complex innovation, collective action, distributed innovation and transition management. To differing extents, these provide approaches to incorporate the motivations of different actors into theoretical understanding. These indicate new directions for research that promise to enrich understanding of innovation
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