16,813 research outputs found
Contractile stresses in cohesive cell layers on finite-thickness substrates
Using a minimal model of cells or cohesive cell layers as continuum active
elastic media, we examine the effect of substrate thickness and stiffness on
traction forces exerted by strongly adhering cells. We obtain a simple
expression for the length scale controlling the spatial variation of stresses
in terms of cell and substrate parameters that describes the crossover between
the thin and thick substrate limits. Our model is an important step towards a
unified theoretical description of the dependence of traction forces on cell or
colony size, acto-myosin contractility, substrate depth and stiffness, and
strength of focal adhesions, and makes experimentally testable predictions.Comment: 5 pages, 3 figure
The effects of non-abelian statistics on two-terminal shot noise in a quantum Hall liquid in the Pfaffian state
We study non-equilibrium noise in the tunnelling current between the edges of
a quantum Hall liquid in the Pfaffian state, which is a strong candidate for
the plateau at . To first non-vanishing order in perturbation theory
(in the tunneling amplitude) we find that one can extract the value of the
fractional charge of the tunnelling quasiparticles. We note however that no
direct information about non-abelian statistics can be retrieved at this level.
If we go to higher-order in the perturbative calculation of the non-equilibrium
shot noise, we find effects due to non-Abelian statistics. They are subtle, but
eventually may have an experimental signature on the frequency dependent shot
noise. We suggest how multi-terminal noise measurements might yield a more
dramatic signature of non-Abelian statistics and develop some of the relevant
formalism.Comment: 13 pages, 8 figures, a few change
Emission and absorption noise in the fractional quantum Hall effect
We compute the high-frequency emission and absorption noise in a fractional
quantum Hall effect (FQHE) sample at arbitrary temperature. We model the edges
of the FQHE as chiral Luttinger liquids (LL) and we use the non-equilibrium
perturbative Keldysh formalism. We find that the non-symmetrized high frequency
noise contains important signatures of the electron-electron interactions that
can be used to test the Luttinger liquid physics, not only in FQHE edge states,
but possibly also in other one-dimensional systems such as carbon nanotubes. In
particular we find that the emission and absorption components of the excess
noise (defined as the difference between the noise at finite voltage and at
zero voltage) are different in an interacting system, as opposed to the
non-interacting case when they are identical. We study the resonance features
which appear in the noise at the Josephson frequency (proportional to the
applied voltage), and we also analyze the effect of the distance between the
measurement point and the backscattering site. Most of our analysis is
performed in the weak backscattering limit, but we also compute and discuss
briefly the high-frequency noise in the tunneling regime.Comment: 26 pages, 11 figure
Extensive green roofs: different time approaches to runoff coefficient determination
Stormwater runoff in green roofs (GRs) is represented by the runoff coefficient, which is fundamental to assess their hydraulic performance and to design the drainage systems downstream. Runoff coefficient values in newly installed GR systems should be estimated by models that must be feasible and reproduce the retention behavior as realistically as possible, being thus adjusted to each season and climate region. In this study, the suitability of a previously developed model for runoff coefficient determination is assessed using experimental data, and registered over a 1 year period. Results showed that the previously developed model does not quite fit the experimental data obtained in the present study, which was developed in a distinct year with different climate conditions, revealing the need to develop a new model with a better adjustment, and taking into consideration other variables besides temperature and precipitation (e.g., early-stage moisture conditions of the GR matrix and climate of the study area). Runoff coefficient values were also determined with different time periods (monthly, weekly, and per rain event) to assess the most adequate approach, considering the practical uses of this coefficient. The monthly determination approach resulted in lower runoff coefficient values (0–0.46) than the weekly or per rain event (0.017–0.764) determination. When applied to a long-term performance analysis, this study showed no significant differences when using the monthly, weekly, or per rain event runoff, resulting on a variation of only 0.9 m3 of annual runoff. This indicates that the use of monthly values for runoff coefficient, although not suitable for sizing drainage systems, might be used to estimate their long-term performance. Overall, this pilot extensive GR of 0.4 m2 presented an annual retention volume of 469.3 L, corresponding to a retention rate of 89.6%, in a year with a total precipitation of 1089 mm. The assessment of different time scales for runoff coefficient determination is a major contribution for future GR performance assessments, and a fundamental decision support tool.info:eu-repo/semantics/publishedVersio
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