10,051 research outputs found
Jamming in finite systems: stability, anisotropy, fluctuations and scaling
Athermal packings of soft repulsive spheres exhibit a sharp jamming
transition in the thermodynamic limit. Upon further compression, various
structural and mechanical properties display clean power-law behavior over many
decades in pressure. As with any phase transition, the rounding of such
behavior in finite systems close to the transition plays an important role in
understanding the nature of the transition itself. The situation for jamming is
surprisingly rich: the assumption that jammed packings are isotropic is only
strictly true in the large-size limit, and finite-size has a profound effect on
the very meaning of jamming. Here, we provide a comprehensive numerical study
of finite-size effects in sphere packings above the jamming transition,
focusing on stability as well as the scaling of the contact number and the
elastic response.Comment: 20 pages, 12 figure
Cell contraction induces long-ranged stress stiffening in the extracellular matrix
Animal cells in tissues are supported by biopolymer matrices, which typically
exhibit highly nonlinear mechanical properties. While the linear elasticity of
the matrix can significantly impact cell mechanics and functionality, it
remains largely unknown how cells, in turn, affect the nonlinear mechanics of
their surrounding matrix. Here we show that living contractile cells are able
to generate a massive stiffness gradient in three distinct 3D extracellular
matrix model systems: collagen, fibrin, and Matrigel. We decipher this
remarkable behavior by introducing Nonlinear Stress Inference Microscopy
(NSIM), a novel technique to infer stress fields in a 3D matrix from nonlinear
microrheology measurement with optical tweezers. Using NSIM and simulations, we
reveal a long-ranged propagation of cell-generated stresses resulting from
local filament buckling. This slow decay of stress gives rise to the large
spatial extent of the observed cell-induced matrix stiffness gradient, which
could form a mechanism for mechanical communication between cells
Observational constraints on the sensitivity of two calving glaciers to external forcings
Future mass loss projections of the Greenland ice sheet require understanding of the processes at a glacier terminus, especially of iceberg calving. We present detailed and high-rate terrestrial radar interferometer observations of Eqip Sermia and Bowdoin Glacier, two outlet glaciers in Greenland with comparable dimensions and investigate iceberg calving, surface elevation, velocity, strain rates and their links to air temperature, tides and topography. The results reveal that the two glaciers exhibit very different flow and calving behaviour on different timescales. Ice flow driven by a steep surface slope with several topographic steps leads to high velocities, areas of extension and intense crevassing, which triggers frequent but small calving events independent of local velocity gradients. In contrast, ice flow under smooth surface slopes leaves the ice relatively intact, such that sporadic large-scale calving events dominate, which initiate in areas with high shearing. Flow acceleration caused by enhanced meltwater input and tidal velocity variations were observed for terminus sections close to floatation. Firmly grounded terminus sections showed no tidal signal and a weak short-term reaction to air temperature. These results demonstrate reaction timescales to external forcings from hours to months, which are, however, strongly dependent on local terminus geometry
Instability of the O(5) multicritical behavior in the SO(5) theory of high-Tc superconductors
We study the nature of the multicritical point in the three-dimensional
O(3)+O(2) symmetric Landau-Ginzburg-Wilson theory, which describes the
competition of two order parameters that are O(3) and O(2) symmetric,
respectively. This study is relevant for the SO(5) theory of high-Tc
superconductors, which predicts the existence of a multicritical point in the
temperature-doping phase diagram, where the antiferromagnetic and
superconducting transition lines meet.
We investigate whether the O(3)+O(2) symmetry gets effectively enlarged to
O(5) approaching the multicritical point. For this purpose, we study the
stability of the O(5) fixed point. By means of a Monte Carlo simulation, we
show that the O(5) fixed point is unstable with respect to the spin-4 quartic
perturbation with the crossover exponent , in substantial
agreement with recent field-theoretical results. This estimate is much larger
than the one-loop -expansion estimate , which has
often been used in the literature to discuss the multicritical behavior within
the SO(5) theory. Therefore, no symmetry enlargement is generically expected at
the multicritical transition.
We also perform a five-loop field-theoretical analysis of the
renormalization-group flow. It shows that bicritical systems are not in the
attraction domain of the stable decoupled fixed point. Thus, in these
systems--high-Tc cuprates should belong to this class--the multicritical point
corresponds to a first-order transition.Comment: 18 page
Use of morphological, biochemical and SRAP molecular markers to differentiate varieties of Cynara cardunculus L. (Asteraceae)
Dentro del complejo primario de Cynara
cardunculus L. se encuentran diversas
variedades botánicas: var. scolymus (alcaucil),
var. altilis (cardo cultivado) y var. sylvestris
(cardo silvestre). A lo largo de la historia
del mejoramiento, la caracterización de
los materiales ha evolucionado desde el
uso de caracteres morfológicos hasta los
modernos análisis moleculares, pasando por
los marcadores bioquÃmicos. El objetivo del
presente trabajo fue comparar la utilidad de
los marcadores morfológicos, bioquÃmicos
y moleculares para la caracterización de
materiales pertenecientes a tres variedades
botánicas de Cynara cardunculus. Tres
cultivares de la var. scolymus, dos de la
var. altilis y dos de la var. sylvestris fueron
caracterizadas por variables morfovegetativas,
proteÃnas de reserva y por marcadores
moleculares a través de la técnica SRAP.
Estas metodologÃas permitieron discriminar
dos grupos: uno incluyendo las variedades
de cardo cultivado y silvestre, y el otro, las
variedades del alcaucil. Los datos moleculares
y morfológicos permitieron además diferenciar
los cultivares evaluados de la var. scolymus.
Se concluye que los marcadores analizados
son útiles para la caracterización intravarietal
e intervarietal en programas de mejoramiento.In the Cynara cardunculus L. primary
complex we can find a globe artichoke:
Cynara cardunculus var. scolymus and other
botanical varieties such as C. cardunculus var.
altilis (cultivated cardoon) and C. cardunculus
var. sylvestris (wild artichoke). Traditionally,
they varieties were grouped according to
morphological and biochemical traits and more
recently, based on molecular markers. The aim
of the present paper was to compare the use
of morphological, biochemical and molecular
markers to distinguish botanical varieties of
Cynara cardunculus. Three accessions of
var. scolymus, two accessions of var. altilis
and two accessions of var. sylvestris were
used. Different morphological variables,
electrophoresis seed protein patterns
by SDS-PAGE and SRAP markers were
evaluated. The three kinds of markers
grouped all materials in two clusters: one
of them included the globe artichoke and
the other the cardoons. SDS-PAGE is
a valid technique for botanical varieties
identification but the morphological and
molecular data were more effective at
discriminating botanical varieties and
accessions within the scolymus group.Fil: Espósito, Andrea.
Consejo Nacional de Investigaciones CientÃficas y TécnicasFil: Martin, Eugenia.
Consejo Nacional de Investigaciones CientÃficas y TécnicasFil: Cravero, Vanina P..
Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Genética y Mejoramiento Vegetal.Fil: Cointry, Enrique L..
Consejo Nacional de Investigaciones CientÃficas y Técnica
Cost effectiveness analysis of larval therapy for leg ulcers
Objective: To assess the cost effectiveness of larval therapy compared with hydrogel in the management of leg ulcers. Design: Cost effectiveness and cost utility analyses carried out alongside a pragmatic multicentre, randomised, open trial with equal randomisation. Population: Intention to treat population comprising 267 patients with a venous or mixed venous and arterial ulcers with at least 25% coverage of slough or necrotic tissue. Interventions: Patients were randomly allocated to debridement with bagged larvae, loose larvae, or hydrogel. Main outcome measure: The time horizon was 12 months and costs were estimated from the UK National Health Service perspective. Cost effectiveness outcomes are expressed in terms of incremental costs per ulcer-free day (cost effectiveness analysis) and incremental costs per quality adjusted life years (cost utility analysis). Results: The larvae arms were pooled for the main analysis. Treatment with larval therapy cost, on average, 96.70 pound ((sic)109.61; $140.57) more per participant per year (95% confidence interval -491.9 pound to 685.8) pound than treatment with hydrogel. Participants treated with larval therapy healed, on average, 2.42 days before those in the hydrogel arm (95% confidence interval -0.95 to 31. 91 days) and had a slightly better health related quality of life, as the annual difference in QALYs was 0.011 (95% confidence interval -0.067 to 0.071). However, none of these differences was statistically significant. The incremental cost effectiveness ratio for the base case analysis was estimated at 8826 pound per QALY gained and 40 pound per ulcer-free day. Considerable uncertainty surrounds the outcome estimates. Conclusions: Debridement of sloughy or necrotic leg ulcers with larval therapy is likely to produce similar health benefits and have similar costs to treatment with hydrogel. Trial registration: Current Controlled Trials ISRCTN55114812 and National Research Register N0484123692
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