15,545 research outputs found
Optimization of an Electromagnetic Energy Harvesting Device
This paper presents the modeling and optimization of an electromagnetic-based generator for generating power from ambient vibrations. Basic equations describing such generators are presented and the conditions for maximum power generation are described. Two-centimeter scale prototype generators, which consist of magnets suspended on a beam vibrating relative to a coil, have been built and tested. The measured power and modeled results are compared. It is shown that the experimental results confirm the optimization theory
Role of p-f Hybridization in the Metal-Non-Metal Transition of PrRu4P12
Electronic state evolution in the metal-non-metal transition of PrRu4P12 has
been studied by X-ray and polarized neutron diffraction experiments. It has
been revealed that, in the low-temperature non-metallic phase, two inequivalent
crystal-field (CF) schemes of Pr3+ 4f^2 electrons with Gamma_1 and Gamma_4^(2)
ground states are located at Pr1 and Pr2 sites forming the bcc unit cell
surrounded by the smaller and larger cubic Ru-ion sublattices, respectively.
This modulated electronic state can be explained by the p-f hybridization
mechanism taking two intermediate states of 4f^1 and 4f^3. The p-f
hybridization effect plays an important role for the electronic energy gain in
the metal-non-metal transition originated from the Fermi surface nesting.Comment: 5 pages, 5 figures. Accepted by J. Phys. Soc. Jp
On the Natural Convection Boundary Layer Adjacent to an Inclined Flat Plate Subject to Ramp Heating
An investigation of the natural convection boundary layer adjacent to an inclined semi-infinite plate subject to a temperature boundary condition which follows a ramp function up until some specified time and then remains constant is reported. The development of the flow from start-up to a steadystate has been described based on scaling analyses and verified by numerical simulations. Attention in this study has been given to fluids having a Prandtl number Pr less than unity. The boundary layer flow depends on the comparison of the time at which the ramp heating is completed and the time at which the boundary layer completes its growth. If the ramp time is long compared with the steady state time, the layer reaches a quasi steady mode in which the growth of the layer is governed solely by the thermal balance between convection and conduction. On the other hand, if the ramp is completed before the layer becomes steady; the subsequent growth is governed by the balance between buoyancy and inertia, as for the case of instantaneous heating
Probability for Primordial Black Holes in Multidimensional Universe with Nonlinear Scalar Curvature Terms
We investigate multi-dimensional universe with nonlinear scalar curvature
terms to evaluate the probability of creation of primordial black holes. For
this we obtain Euclidean instanton solution in two different topologies: (a)
- topology which does not accommodate primordial black holes and (b)
-topology which accommodates a pair of black holes. The
probability for quantum creation of an inflationary universe with a pair of
black holes has been evaluated assuming a gravitational action which is
described by a polynomial function of scalar curvature with or without a
cosmological constant () using the framework of semiclassical
approximation of Hartle-Hawking boundary conditions. We discuss here a class of
new gravitational instantons solution in the -theory which are relevant
for cosmological model building.Comment: 18 pages, no figure. accepted in Phys. Rev.
Determining physical properties of the cell cortex
Actin and myosin assemble into a thin layer of a highly dynamic network
underneath the membrane of eukaryotic cells. This network generates the forces
that drive cell and tissue-scale morphogenetic processes. The effective
material properties of this active network determine large-scale deformations
and other morphogenetic events. For example,the characteristic time of stress
relaxation (the Maxwell time)in the actomyosin sets the time scale of
large-scale deformation of the cortex. Similarly, the characteristic length of
stress propagation (the hydrodynamic length) sets the length scale of slow
deformations, and a large hydrodynamic length is a prerequisite for long-ranged
cortical flows. Here we introduce a method to determine physical parameters of
the actomyosin cortical layer (in vivo). For this we investigate the relaxation
dynamics of the cortex in response to laser ablation in the one-cell-stage {\it
C. elegans} embryo and in the gastrulating zebrafish embryo. These responses
can be interpreted using a coarse grained physical description of the cortex in
terms of a two dimensional thin film of an active viscoelastic gel. To
determine the Maxwell time, the hydrodynamic length and the ratio of active
stress and per-area friction, we evaluated the response to laser ablation in
two different ways: by quantifying flow and density fields as a function of
space and time, and by determining the time evolution of the shape of the
ablated region. Importantly, both methods provide best fit physical parameters
that are in close agreement with each other and that are similar to previous
estimates in the two systems. We provide an accurate and robust means for
measuring physical parameters of the actomyosin cortical layer.It can be useful
for investigations of actomyosin mechanics at the cellular-scale, but also for
providing insights in the active mechanics processes that govern tissue-scale
morphogenesis.Comment: 17 pages, 4 figure
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