218 research outputs found
Focusing by blocking: repeatedly generating central density peaks in self-propelled particle systems by exploiting diffusive processes
Over the past few years the displacement statistics of self-propelled
particles has been intensely studied, revealing their long-time diffusive
behavior. Here, we demonstrate that a concerted combination of boundary
conditions and switching on and off the self-propelling drive can generate and
afterwards arbitrarily often restore a non-stationary centered peak in their
spatial distribution. This corresponds to a partial reversibility of their
statistical behavior, in opposition to the above-mentioned long-time diffusive
nature. Interestingly, it is a diffusive process that mediates and makes
possible this procedure. It should be straightforward to verify our predictions
in a real experimental system.Comment: 6 pages, 6 figure
Cooperation of Sperm in Two Dimensions: Synchronization, Attraction and Aggregation through Hydrodynamic Interactions
Sperm swimming at low Reynolds number have strong hydrodynamic interactions
when their concentration is high in vivo or near substrates in vitro. The
beating tails not only propel the sperm through a fluid, but also create flow
fields through which sperm interact with each other. We study the hydrodynamic
interaction and cooperation of sperm embedded in a two-dimensional fluid by
using a particle-based mesoscopic simulation method, multi-particle collision
dynamics (MPC). We analyze the sperm behavior by investigating the relationship
between the beating-phase difference and the relative sperm position, as well
as the energy consumption. Two effects of hydrodynamic interaction are found,
synchronization and attraction. With these hydrodynamic effects, a multi-sperm
system shows swarm behavior with a power-law dependence of the average cluster
size on the width of the distribution of beating frequencies
On the General Analytical Solution of the Kinematic Cosserat Equations
Based on a Lie symmetry analysis, we construct a closed form solution to the
kinematic part of the (partial differential) Cosserat equations describing the
mechanical behavior of elastic rods. The solution depends on two arbitrary
analytical vector functions and is analytical everywhere except a certain
domain of the independent variables in which one of the arbitrary vector
functions satisfies a simple explicitly given algebraic relation. As our main
theoretical result, in addition to the construction of the solution, we proof
its generality. Based on this observation, a hybrid semi-analytical solver for
highly viscous two-way coupled fluid-rod problems is developed which allows for
the interactive high-fidelity simulations of flagellated microswimmers as a
result of a substantial reduction of the numerical stiffness.Comment: 14 pages, 3 figure
Coherent Hydrodynamic Coupling for Stochastic Swimmers
A recently developed theory of stochastic swimming is used to study the
notion of coherence in active systems that couple via hydrodynamic
interactions. It is shown that correlations between various modes of
deformation in stochastic systems play the same role as the relative internal
phase in deterministic systems. An example is presented where a simple swimmer
can use these correlations to hunt a non-swimmer by forming a hydrodynamic
bound state of tunable velocity and equilibrium separation. These results
highlight the significance of coherence in the collective behavior of
nano-scale stochastic swimmers.Comment: 6 pages, 3 figure
Cardiac MR Elastography: Comparison with left ventricular pressure measurement
Purpose of the Study: To compare magnetic resonance elastography (MRE) with ventricular pressure changes in an animal model.
Methods: Three pigs of different cardiac physiology (weight, 25 to 53 kg; heart rate, 61 to 93 bpm; left ventricular [LV] end-diastolic volume, 35 to 70 ml) were subjected to invasive LV pressure measurement by catheter and noninvasive cardiac MRE. Cardiac MRE was performed in a short-axis view of the heart and applying a 48.3-Hz shear-wave stimulus. Relative changes in LV-shear wave amplitudes during the cardiac cycle were analyzed. Correlation coefficients between wave amplitudes and LV pressure as well as between wave amplitudes and LV diameter were determined.
Results: A relationship between MRE and LV pressure was observed in all three animals (R-square [greater than or equal to] 0.76). No correlation was observed between MRE and LV diameter (R-square [less than or equal to] 0.15). Instead, shear wave amplitudes decreased 102 +/- 58 ms earlier than LV diameters at systole and amplitudes increased 175 +/- 40 ms before LV dilatation at diastole. Amplitude ratios between diastole and systole ranged from 2.0 to 2.8, corresponding to LV pressure differences of 60 to 73 mmHg.
Conclusion: Externally induced shear waves provide information reflecting intraventricular pressure changes which, if substantiated in further experiments, has potential to make cardiac MRE a unique noninvasive imaging modality for measuring pressure-volume function of the heart
How does mental health care perform in respect to service users' expectations? Evaluating inpatient and outpatient care in Germany with the WHO responsiveness concept
<p>Abstract</p> <p>Background</p> <p>Health systems increasingly try to make their services more responsive to users' expectations. In the context of the World Health Report 2000, WHO developed the concept of health system <it>responsiveness </it>as a performance parameter. <it>Responsiveness </it>relates to the system's ability to respond to service users' legitimate expectations of non-medical aspects. We used this concept in an effort to evaluate the performance of mental health care in a catchment area in Germany.</p> <p>Methods</p> <p>In accordance with the method WHO used for its <it>responsiveness </it>survey, <it>responsiveness </it>for inpatient and outpatient mental health care was evaluated by a standardised questionnaire. <it>Responsiveness </it>was assessed in the following domains: <it>attention, dignity</it>, <it>clear communication</it>, <it>autonomy, confidentiality, basic amenities, choice </it>of health care provider, <it>continuity</it>, and <it>access to social support</it>. Users with complex mental health care needs (i.e., requiring social and medical services or inpatient care) were recruited consecutively within the mental health services provided in the catchment area of the Hanover Medical School.</p> <p>Results</p> <p>221 persons were recruited in outpatient care and 91 in inpatient care. Inpatient service users reported poor <it>responsiveness </it>(22%) more often than outpatients did (15%); however this was significant only for the domains <it>dignity </it>and <it>communication</it>. The best performing domains were <it>confidentiality </it>and <it>dignity</it>; the worst performing were <it>choice</it>, <it>autonomy </it>and <it>basic amenities </it>(only inpatient care). <it>Autonomy </it>was rated as the most important domain, followed by <it>attention </it>and <it>communication</it>. <it>Responsiveness </it>within outpatient care was rated worse by people who had less money and were less well educated. Inpatient <it>responsiveness </it>was rated better by those with a higher level of education and also by those who were not so well educated. 23% of participants reported having been discriminated against in mental health care during the past 6 months.</p> <p>The results are similar to prior <it>responsiveness </it>surveys with regard to the overall better performance of outpatient care. Where results differ, this can best be explained by certain characteristics that are applicable to mental health care and also by the users with complex needs. The expectations of <it>attention </it>and <it>autonomy</it>, including participation in the treatment process, are not met satisfactorily in inpatient and outpatient care.</p> <p>Conclusion</p> <p><it>Responsiveness </it>as a health system performance parameter provides a refined picture of inpatient and outpatient mental health care. Reforms to the services provided should be orientated around domains that are high in importance, but low in performance. Measuring <it>responsiveness </it>could provide well-grounded guidance for further development of mental health care systems towards becoming better patient-orientated and providing patients with more respect.</p
Multi-Particle Collision Dynamics -- a Particle-Based Mesoscale Simulation Approach to the Hydrodynamics of Complex Fluids
In this review, we describe and analyze a mesoscale simulation method for
fluid flow, which was introduced by Malevanets and Kapral in 1999, and is now
called multi-particle collision dynamics (MPC) or stochastic rotation dynamics
(SRD). The method consists of alternating streaming and collision steps in an
ensemble of point particles. The multi-particle collisions are performed by
grouping particles in collision cells, and mass, momentum, and energy are
locally conserved. This simulation technique captures both full hydrodynamic
interactions and thermal fluctuations. The first part of the review begins with
a description of several widely used MPC algorithms and then discusses
important features of the original SRD algorithm and frequently used
variations. Two complementary approaches for deriving the hydrodynamic
equations and evaluating the transport coefficients are reviewed. It is then
shown how MPC algorithms can be generalized to model non-ideal fluids, and
binary mixtures with a consolute point. The importance of angular-momentum
conservation for systems like phase-separated liquids with different
viscosities is discussed. The second part of the review describes a number of
recent applications of MPC algorithms to study colloid and polymer dynamics,
the behavior of vesicles and cells in hydrodynamic flows, and the dynamics of
viscoelastic fluids
Physicochemical and textural quality attributes of gluten-free bread formulated with guar gum
The objective of this study was to assess the combined effect of guar gum (GG) and water content (WC) on the rheological properties of batter, and the physicochemical and textural properties of bread. Batches of gluten-free bread used a base formulation of rice (50%), maize (30%) and quinoa flour (20%), with different levels of GG (2.5, 3.0 or 3.5%) and water (90, 100 or 110%) in a full factorial design. Higher GG doses (p<0.001) tended to produce batters of lower stickiness, work of adhesion and cohesive strength; yet, of higher firmness, consistency, cohesiveness and viscosity index. These batters yielded loaves of lower (p<0.001) specific volume and baking loss; and crumbs of lower (p<0.001) aw, pH, mean cell area, void fraction, mean cell aspect ratio; and higher (p<0.001) hardness, adhesiveness, springiness, cohesiveness, chewiness, resilience, mean cell density, cell size uniformity and mean cell compactness. The sticker and less consistent batters produced with higher WC rendered larger bread loaves of softer and more cohesive and springy/resilient crumbs with greater mean cell size and void fraction. Gluten-free loaves of good appearance in terms of higher specific volume, lower crumb hardness, higher crumb springiness, and open grain visual texture were obtained in formulations with 110% WC and GG doses between 2.5 and 3.0%.Eng. Encina-Zelada acknowledges the financial aid provided by the Peruvian National Programme of Scholarships and Student Loans (PRONABEC) in the mode of PhD grants (Presidente de la República-183308). The authors are grateful to Eng. Andrea Oliveira from Prodipani, Portugal, for her kind advice and providing breadmaking ingredients.info:eu-repo/semantics/publishedVersio
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