2,617 research outputs found
Stabilized lowest order finite element approximation for linear three-field poroelasticity
A stabilized conforming mixed finite element method for the three-field
(displacement, fluid flux and pressure) poroelasticity problem is developed and
analyzed. We use the lowest possible approximation order, namely piecewise
constant approximation for the pressure and piecewise linear continuous
elements for the displacements and fluid flux. By applying a local pressure
jump stabilization term to the mass conservation equation we ensure stability
and avoid pressure oscillations. Importantly, the discretization leads to a
symmetric linear system. For the fully discretized problem we prove existence
and uniqueness, an energy estimate and an optimal a-priori error estimate,
including an error estimate for the divergence of the fluid flux. Numerical
experiments in 2D and 3D illustrate the convergence of the method, show the
effectiveness of the method to overcome spurious pressure oscillations, and
evaluate the added mass effect of the stabilization term.Comment: 25 page
AlScN: A III-V semiconductor based ferroelectric
Ferroelectric switching is unambigiously demonstrated for the first time in a
III-V semiconductor based material: AlScN -- A discovery which could help to
satisfy the urgent demand for thin film ferroelectrics with high performance
and good technological compatibility with generic semiconductor technology
which arises from a multitude of memory, micro/nano-actuator and emerging
applications based on controlling electrical polarization. The appearance of
ferroelectricity in AlScN can be related to the continuous distortion of the
original wurtzite-type crystal structure towards a layered-hexagonal structure
with increasing Sc content and tensile strain, which is expected to be
extendable to other III-nitride based solid solutions. Coercive fields which
are systematically adjustable by more than 3 MV/cm, high remnant polarizations
in excess of 100 \mu C/cm which constitute the first experimental estimate
of the previously inaccessible spontaneous polarization in a III-nitride based
material, an almost ideally square-like hysteresis resulting in excellent
piezoelectric linearity over a wide strain interval from -0.3% to +0.4% as well
as a paraelectric transition temperature in excess of 600{\deg}C are confirmed.
This intriguing combination of properties is to our knowledge as of now
unprecedented in the field of polycrystalline ferroelectric thin films and
promises to significantly advance the commencing integration of ferroelectric
functionality to micro- and nanotechnology, while at the same time providing
substantial insight to one of the central open questions of the III-nitride
semiconductors - that of their actual spontaneous polarization
Model Order Reduction for (Stochastic-) Delay Equations With Error Bounds
We analyze a structure-preserving model order reduction technique for delay
and stochastic delay equations based on the balanced truncation method and
provide a system theoretic interpretation. Transferring error bounds based on
Hankel operators to delay systems, we find error estimates for the difference
between the dynamics of the full and reduced model. This analysis also yields
new error bounds for bilinear systems and stochastic systems with
multiplicative noise and non-zero initial states
Reference Points and Effort Provision
A key open question for theories of reference-dependent preferences is what determines the reference point. One candidate is expectations: what people expect could affect how they feel about what actually occurs. In a real-effort experiment, we manipulate the rational expectations of subjects and check whether this manipulation influences their effort provision. We find that effort provision is significantly different between treatments in the way predicted by models of expectation-based reference-dependent preferences: if expectations are high, subjects work longer and earn more money than if expectations are low
A poroelastic model coupled to a fluid network with applications in lung modelling
Here we develop a lung ventilation model, based a continuum poroelastic
representation of lung parenchyma and a 0D airway tree flow model. For the
poroelastic approximation we design and implement a lowest order stabilised
finite element method. This component is strongly coupled to the 0D airway tree
model. The framework is applied to a realistic lung anatomical model derived
from computed tomography data and an artificially generated airway tree to
model the conducting airway region. Numerical simulations produce
physiologically realistic solutions, and demonstrate the effect of airway
constriction and reduced tissue elasticity on ventilation, tissue stress and
alveolar pressure distribution. The key advantage of the model is the ability
to provide insight into the mutual dependence between ventilation and
deformation. This is essential when studying lung diseases, such as chronic
obstructive pulmonary disease and pulmonary fibrosis. Thus the model can be
used to form a better understanding of integrated lung mechanics in both the
healthy and diseased states
Optimization of street lane usage
This paper contributes to discussion on introduction of exclusive lane for public transport. Analyses of results have been presented on effectiveness of usage of a 4 - lane and a 6 - lane street with and without an exclusive lane for buses. Two basic sub-models have been applied: - the binary logit model for modal split estimation; it takes into consideration the relation of travel time performed by private cars to public transport, - the polynomial model for predicting link impedance; the real travel time is affected by relation of traffic volume to the design capacity The parameters of both sub-models have been calibrated for the Polish conditions. The relationships are determined between number of person trips and traffic volume of buses/private cars, market share of public transport in motorised trips, average travel time lost in trips, average operation cost. An iterative technique addresses a feedback between the modal split and traffic volumes. Numerical calculations by use of EXCEL and MATLAB were carried out. Typical values of corridor length, occupancy rate of passenger car, design capacity of the bus, access and egress time to and from the parking/bus-stop in urban areas were applied. On the basis of the estimated results, the marginal parameter values: number of people carried at which separated lane for buses is most effective , traffic volume for private cars, traffic volume for buses and share of public transport in trips have been got by consideration of the average travel time lost and operational cost as criteria: Then introduction of street lanes with and without exclusive lane for buses in relation to number of person trips can be optimized
Intragenic meiotic recombination in Schizosaccharomyces pombe is sensitive to environmental temperature changes
Open Access via the Springer Compact Agreement Acknowledgments We are grateful to Miguel G. Ferreira, JĂŒrg Kohli, Josef Loidl, Fekret Osman, Gerald R. Smith, Walter W. Steiner, and Matthew Whitby for providing strains. We thank Josef Loidl for critically reading an earlier version of this manuscript. This work was supported by the Biotechnology and Biological Sciences Research Council UK (BBSRC) [grant number BB/F016964/1], and the University of Aberdeen (College of Life Sciences and Medicine Start-up grant to AL).Peer reviewedPublisher PD
A mollified Ensemble Kalman filter
It is well recognized that discontinuous analysis increments of sequential
data assimilation systems, such as ensemble Kalman filters, might lead to
spurious high frequency adjustment processes in the model dynamics. Various
methods have been devised to continuously spread out the analysis increments
over a fixed time interval centered about analysis time. Among these techniques
are nudging and incremental analysis updates (IAU). Here we propose another
alternative, which may be viewed as a hybrid of nudging and IAU and which
arises naturally from a recently proposed continuous formulation of the
ensemble Kalman analysis step. A new slow-fast extension of the popular
Lorenz-96 model is introduced to demonstrate the properties of the proposed
mollified ensemble Kalman filter.Comment: 16 pages, 6 figures. Minor revisions, added algorithmic summary and
extended appendi
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