60 research outputs found
Shaping liquid drops by vibration
We present and analyze a minimal hydrodynamic model of a vertically vibrated
liquid drop that undergoes dynamic shape transformations. In agreement with
experiments, a circular lens-shaped drop is unstable above a critical vibration
amplitude, spontaneously elongating in horizontal direction. Smaller drops
elongate into localized states that oscillate with half of the vibration
frequency. Larger drops evolve by transforming into a snake-like structure with
gradually increasing length. The worm state is long-lasting with a potential to
fragmentat into smaller drops
Morphology changes in the evolution of liquid two-layer films
We consider two thin layers of immiscible liquids on a heated solid
horizontal substrate. The free liquid-liquid and liquid-gas interfaces of such
a two-layer (or bilayer) liquid film may be unstable due to effective molecular
interactions or the Marangoni effect. Using a long wave approximation we derive
coupled evolution equations for the interafce profiles for a general
non-isothermal situation allowing for slip at the substrate. Linear and
nonlinear analyses are performed for isothermal ultrathin layers below 100 nm
thickness under the influence of destabilizing long-range and stabilizing
short-range interactions. Flat films may be unstable to varicose, zigzag or
mixed modes. During the long-time evolution the nonlinear mode type can change
via switching between two different branches of stable stationary solutions or
via coarsening along a single such branch.Comment: 14 eps figures and 1 tex fil
Pattern formation in intracortical neuronal fields
The present article introduces a neuronal field model for both excitatory and inhibitory connections. A single integro-differential equation with delay is derived and studied at a critical point by stability analysis, which yields conditions for static periodic patterns and wave instabilities. It turns out that waves only occur below a certain threshold of the activity propagation velocity. An additional brief study exhibits increasing phase velocities of waves with decreasing slope subject to increasing activity propagation velocities, which are in accordance to experimental results. Numerical studies near and far from instability onset supplement the work
Patterns and predictors of statin prescription in patients with type 2 diabetes
<p>Abstract</p> <p>Background</p> <p>The benefit of statins for prevention of cardiovascular events in type 2 diabetes is established, but a gap exists between guideline recommendations and clinical practice. The aim of the study was to identify patient-related factors predicting statin prescription.</p> <p>Methods</p> <p>We assessed the quality of care in 51,640 patients with type 2 diabetes in a German diabetes registry. Patients were stratified according to primary and secondary prevention. Five-year risk for cardiovascular events was calculated in primary prevention patients. A multivariate adjusted logistic regression model was constructed to determine which parameters influenced statin prescription.</p> <p>Results</p> <p>34% had established atherosclerotic disease and 25.5% received a statin. Prescription was significantly higher in the secondary compared to the primary prevention group (38.1% [95% CI 37.4–38.9%] vs. 18.5% [95% CI 18.0–19.0%], respectively). In primary prevention the odds for statin prescription increased with estimated cardiovascular risk (OR 1.17 per 5% increase in 5-year risk, 95% CI 1.11–1.22). Positive predictors for statin prescription were secondary prevention, hypertension, former smoking, baseline LDL-cholesterol, and microalbuminuria. The odds of receiving a statin had an inverted U-shaped relation with age (nadir, 66 years), age at first diagnosis of diabetes (nadir, 56 years), and body mass index (nadir, 32 kg/m<sup>2</sup>). The model predicted prescription in 70% of the patients correctly.</p> <p>Conclusion</p> <p>The majority of patients with type 2 diabetes are not receiving statins. The predominant factors determining statin prescription are the patient's prevention status and, in primary prevention, estimated cardiovascular risk. The results suggest that although physicians are aware of the general concept of cardiovascular risk, they fail to consistently implement guidelines.</p
A four compartment epidemic model with retarded transition rates
We study an epidemic model for a constant population by taking into account
four compartments of the individuals characterizing their states of health.
Each individual is in one of the compartments susceptible (S); incubated -
infected yet not infectious (C), infected and infectious (I), and recovered -
immune (R). An infection is 'visible' only when an individual is in state I.
Upon infection, an individual performs the transition pathway S to C to I to R
to S remaining in each compartments C, I, and R for certain random waiting
times, respectively. The waiting times for each compartment are independent and
drawn from specific probability density functions (PDFs) introducing memory
into the model. We derive memory evolution equations involving convolutions
(time derivatives of general fractional type). We obtain formulae for the
endemic equilibrium and a condition of its existence for cases when the waiting
time PDFs have existing means. We analyze the stability of healthy and endemic
equilibria and derive conditions for which the endemic state becomes
oscillatory (Hopf) unstable. We implement a simple multiple random walker's
approach (microscopic model of Brownian motion of Z independent walkers) with
random SCIRS waiting times into computer simulations. Infections occur with a
certain probability by collisions of walkers in compartments I and S. We
compare the endemic states predicted in the macroscopic model with the
numerical results of the simulations and find accordance of high accuracy. We
conclude that a simple random walker's approach offers an appropriate
microscopic description for the macroscopic model.Comment: 26 pages, 11 figure
Alternative pathways of dewetting for a thin two-layer film of soft matter
We consider two stacked ultra-thin layers of different liquids on a solid
substrate. Using long-wave theory, we derive coupled evolution equations for
the free liquid-liquid and liquid-gas interfaces. Linear and non-linear
analyses show that depending on the long-range van-der-Waals forces and the
ratio of the layer thicknesses, the system follows different pathways of
dewetting. The instability may be driven by varicose or zigzag modes and leads
to film rupture either at the liquid-gas interface or at the substrate
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