467 research outputs found
Plectoneme creation reduces the rotational friction of a polymer
The torsional dynamics of a semiflexible polymer with a contour length
larger than its persistence length L_p that is rotated at fixed frequency
omega_0 at one end is studied by scaling arguments and hydrodynamic
simulations. We find a non-equilibrium transition at a critical frequency
omega_*: In the linear regime, omega_0 < omega_*, axial spinning is the
dominant dissipation mode. In the non-linear regime, omega_0 > omega_*, the
twist-dissipation mode involves the continuous creation of plectonemes close to
the driven end and the rotational friction is substantially reduced
Twist-induced snapping in a bent elastic ribbon
Snapping of a slender structure is utilized in a wide range of natural and
man-made systems, mostly to achieve rapid movement without relying on
muscle-like elements. Although several mechanisms for elastic energy storage
and rapid release have been studied in detail, a general understanding of the
approach to design such a kinetic system is a key challenge in mechanics. Here
we study a twist-driven buckling and fast flip dynamics of a geometrically
constraint ribbon by combining experiments, numerical simulations, and
analytical theory. We identify two distinct types of shape transitions; a
narrow ribbon snaps, whereas a wide ribbon forms a pair of localized helices.
We construct a phase diagram and explain the origin of the boundary, which is
determined only by geometry. We quantify effects of gravity and clarify time
scale dictating the rapid flipping. Our study reveals the unique role of
geometric twist-bend coupling on the fast dynamics of a thin constrained
structure, which has implications for a wide range of biophysical and applied
physical problems.Comment: 5pages, 4 figures, under revie
Indentation of an elastic arch on a frictional substrate: Pinning, unfolding and snapping
We investigate the morphology and mechanics of a naturally curved elastic
arch loaded at its center and frictionally supported at both ends on a flat,
rigid substrate. Through systematic numerical simulations, we classify the
observed behaviors of the arch into three distinct types of configurations in
terms of the arch geometry and the coefficient of static friction with the
substrate. A linear theory is developed based on a planar elastica model
combined with Amontons-Coulomb's frictional law, which quantitatively explains
the numerically constructed phase diagram. The snapping transition of a loaded
arch in a sufficiently large indentation regime, which involves a discontinuous
force jump, is numerically observed. The proposed model problem allows a fully
analytical investigation and demonstrates a rich variety of mechanical
behaviors owing to the interplay between elasticity, geometry, and friction.
This study provides a basis for understanding more common but complex systems,
such as a cylindrical shell subjected to a concentrated load and simultaneously
supported by frictional contact with surrounding objects
A shunt active filter based on voltage detection for harmonic termination of a radial power distribution line
This paper focuses on a shunt active filter based on the detection of harmonic voltages at the point of installation. The objective of the active filter is to attenuate harmonic propagation resulting from series/parallel resonance between capacitors for power factor correction and line inductors in a power distribution line. The active filter acts as a low resistor to the external circuit for harmonic frequencies, and it is installed on the end bus of the power distribution line, just like a 50 Ω terminator installed on the end terminal of a signal transmission line. Therefore, the function of the active filter is referred to as “harmonic termination” in this paper. Experimental results obtained from a laboratory system rated at 200 V and 20 kW verify that the active filter for the purpose of harmonic termination has the capability of harmonic damping throughout the power distribution line</p
Cell Cycle Abnormality in Metabolic Syndrome and Nuclear Receptors as an Emerging Therapeutic Target
In recent years, many researchers have emphasized the importance of metabolic syndrome based on its increasing prevalence and its adverse prognosis due to associated chronic vascular complications. Upstream of a cluster of metabolic and vascular disorders is the accumulation of visceral adipose tissue, which plays a central role in the pathophysiology. In the accumulation of adipose tissues, cell cycle regulation is tightly linked to cellular processes such as proliferation, hypertrophy and apoptosis. In addition, various cell cycle abnormalities have also been observed in other tissues, such as kidneys and the cardiovascular system, and they are critically involved in the progression of disease. Here, we discuss cell cycle abnormalities in metabolic syndrome in various tissues. Furthermore, we describe the role of nuclear receptors in cell growth and survival, and glucose and lipid metabolism in the whole body. Therapeutic strategies for modulating various cell cycles in metabolic disorders by targeting nuclear receptors may overcome obesity and its chronic vascular complications in the future
Re-evaluation of waist circumference in metabolic syndrome: a comparison between Japanese men and women
We re-evaluated the criteria for waist circumference to predict the accumulation of the components of metabolic syndrome. We used data for 3,185 Japanese, aged 20-79 years. Metabolic syndrome has recently been redefined by a new criterion in Japan, in which waist circumference cutoff points, i.e. 85 cm for men and 90 cm for women, are employed. Among the 3,185 Japanese considered in the present study, 335 men (26.8%) and 69 women (3.6%) were diagnosed as having metabolic syndrome. A cutoff point as a predictor for 2 or more components of metabolic syndrome was evaluated by sensitivity/specificity and a receiver operating characteristic (ROC) curve. The optimal point was estimated as being approximately 85 cm of waist circumference in men and 75 cm in women. We therefore recommend a cutoff value, 75 cm of waist circumference, for the criterion of metabolic syndrome in women
Galectins, galactoside-binding mammalian lectins: clinical application of multi-functional proteins.
Galectins are beta-galactoside binding mammalian lectins and they share homologous carbohydrate recognition domains. To date, 11 members of galectin family have been cloned and identified. They have been shown to play roles in diverse biological events, such as embryogenesis, oncogenesis, adhesion and proliferation of the cells, receptor for advanced glycation end products, mRNA splicing, bacterial colonization, apoptosis, and in the modulation of the immune response. The mechanisms by which galectins exert these diverse effects remain largely unknown. However, the elucidation of multi-functional proteins belong to galectin family are going to open new fields in clinical science including diagnosis and therapy of autoimmune disorders, cancers, and vascular complications in diabetes and hypertension.</P></p
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