56 research outputs found
Shear banding in nematogenic fluids with oscillating orientational dynamics
We investigate the occurrence of shear banding in nematogenic fluids under
planar Couette flow, based on mesoscopic dynamical equations for the
orientational order parameter and the shear stress. We focus on parameter
values where the sheared homogeneous system exhibits regular oscillatory
orientational dynamics, whereas the equilibrium system is either isotropic
(albeit close to the isotropic--nematic transition) or deep in its nematic
phase. The numerical calculations are restricted to spatial variations in shear
gradient direction. We find several new types of shear banded states
characterized by regions with regular oscillatory orientational dynamics. In
all cases shear banding is accompanied by a non--monotonicity of the flow curve
of the homogeneous system; however, only in the case of the initially isotropic
system this curve has the typical --like shape. We also analyze the
influence of different orientational boundary conditions and of the spatial
correlation length.Comment: 12 pages, 10 figure
Ising-like critical behavior of vortex lattices in an active fluid
Turbulent vortex structures emerging in bacterial active fluids can be
organized into regular vortex lattices by weak geometrical constraints such as
obstacles. Here we show, using a continuum-theoretical approach, that the
formation and destruction of these patterns exhibit features of a continuous
second-order equilibrium phase transition, including long-range correlations,
divergent susceptibility, and critical slowing down. The emerging vorticity
field can be mapped onto a two-dimensional (2D) Ising model with
antiferromagnetic nearest-neighbor interactions by coarse-graining. The
resulting effective temperature is found to be proportional to the strength of
the nonlinear advection in the continuum model
Anisotropic mesoscale turbulence and pattern formation in microswimmer suspensions induced by orienting external fields
This paper studies the influence of orienting external fields on pattern formation, particularly mesoscale turbulence, in microswimmer suspensions. To this end, we apply a hydrodynamic theory that can be derived from a microscopic microswimmer model (Reinken et al 2018 Phys. Rev. E 97, 022613). The theory combines a dynamic equation for the polar order parameter with a modified Stokes equation for the solvent flow. Here, we extend the model by including an external field that exerts an aligning torque on the swimmers (mimicking the situation in chemo-, photo-, magneto- or gravitaxis). Compared to the field-free case, the external field breaks the rotational symmetry of the vortex dynamics and leads instead to strongly asymmetric, traveling stripe patterns, as demonstrated by numerical solution and linear stability analysis. We further analyze the emerging structures using a reduced model which involves only an (effective) microswimmer velocity field. This model is significantly easier to handle analytically, but still preserves the main features of the anisotropic pattern formation. We observe an underlying transition between a square vortex lattice and a traveling stripe pattern. These structures can be well described in the framework of weakly nonlinear analysis, provided the strength of nonlinear advection is sufficiently weak.DFG, 163436311, SFB 910: Kontrolle selbstorganisierender nichtlinearer Systeme: Theoretische Methoden und AnwendungskonzepteDFG, 87159868, GRK 1558: Kollektive Dynamik im Nichtgleichgewicht: in kondensierter Materie und biologischen Systeme
Development of educational video at the technical university
This article discusses the development and production of the main types of video resources on the example of disciplines on technical areas
Erythrocyte Transketolase Activity, Markers of Cardiac Dysfunction and the Diagnosis of Infantile Beriberi
Infantile beriberi, or clinical thiamin (vitamin B1) deficiency in infants, is a forgotten disease in Asia, where ∼100 years ago it was a major public health problem. Children aged ∼2–3 months present in cardiac failure but usually rapidly improve if given thiamin injections. It remains relatively common in Vientiane, Lao PDR (Laos) probably because of prolonged intra- and post-partum maternal food avoidance behaviours. There has been very little recent research on the best diagnostic techniques. We conducted a case control study of 47 infants with beriberi and age-matched afebrile and febrile controls in Vientiane. The conventional measures of thiamin deficiency, basal and activated erythrocyte transketolase activities (ETK) and activation (α) coefficients, were assayed along with three markers of cardiac dysfunction - plasma brain natriuretic peptide, N-terminal pro-brain natriuretic peptide, and troponin T. Basal ETK was a better biochemical marker of infantile beriberi than the activation coefficient. Raised plasma troponin T may be a useful indicator of infantile beriberi in babies at risk and in the absence of other evident causes
\u3ci\u3eThe Lord of the Rings\u3c/i\u3e: A Christian Refounding of the Political Order
Examines the “severely classical moral doctrine” of The Lord of the Rings; discusses stewardship as “the proper subordination of Power to Care”; and approves of Tolkien’s “veiling of the Divine” by keeping overt religious references out of the work as a means of leading readers to understanding and affirmation. Reprinted from Christian Perspectives, Winter 1966
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