55,081 research outputs found
Simultaneous muscle force and displacement transducer
A myocardial transducer for simultaneously measuring force and displacement within a very small area of myocardium is disclosed. The transducer comprised of an elongated body forked at one end to form an inverted Y shaped beam with each branch of the beam constituting a low compliant tine for penetrating the myocardium to a predetermined depth. Bonded to one of the low compliance tines is a small piezoresistive element for converting a force acting on the beam into an electrical signal. A third high compliant tine of the transducer, which measures displacement of the myocardium in a direction in line with the two low compliant tines, is of a length that just pierces the surface membrane. A small piezoresistive element is bonded to the third tine at its upper end where its bending is greatest. Displacement of the myocardium causes a deformation in curvature of the third tine, and the second small piezoresistive element bonded to the surface of its curved end converts its deformation into an electrical signal
Myocardium wall thickness transducer and measuring method
A miniature transducer for measuring changes of thickness of the myocardium is described. The device is easily implantable without traumatizing the subject, without affecting the normal muscle behavior, and is removable and implantable at a different muscle location. Operating features of the device are described
Catheter tip force transducer for cardiovascular research
A force transducer for measuring dynamic force activity within the heart of a subject essentially consists of a U-shaped beam of low elastic compliance material. Two lines extend from the beams's legs and a long coil spring is attached to the beam. A strain gauge is coupled to one of the beam's legs to sense deflections thereof. The beam with the tines and most of the spring are surrounded by a flexible tube, defining a catheter, which is insertable into a subject's heart through an appropriate artery. The tines are extractable from the catheter for implantation into the myocardium by pushing on the end of the spring which extends beyond the external end of the catheter
On finite-size Lyapunov exponents in multiscale systems
We study the effect of regime switches on finite size Lyapunov exponents
(FSLEs) in determining the error growth rates and predictability of multiscale
systems. We consider a dynamical system involving slow and fast regimes and
switches between them. The surprising result is that due to the presence of
regimes the error growth rate can be a non-monotonic function of initial error
amplitude. In particular, troughs in the large scales of FSLE spectra is shown
to be a signature of slow regimes, whereas fast regimes are shown to cause
large peaks in the spectra where error growth rates far exceed those estimated
from the maximal Lyapunov exponent. We present analytical results explaining
these signatures and corroborate them with numerical simulations. We show
further that these peaks disappear in stochastic parametrizations of the fast
chaotic processes, and the associated FSLE spectra reveal that large scale
predictability properties of the full deterministic model are well approximated
whereas small scale features are not properly resolved.Comment: Accepted for publication in Chao
Universal Properties of Linear Magnetoresistance in Strongly Disordered Semiconductors
Linear magnetoresistance occurs in semiconductors as a consequence of strong
electrical disorder and is characterized by nonsaturating magnetoresistance
that is proportional to the applied magnetic field. By investigating a
disordered MnAs-GaAs composite material, it is found that the magnitude of the
linear magnetoresistance (LMR) is numerically equal to the carrier mobility
over a wide range and is independent of carrier density. This behavior is
complementary to the Hall effect that is independent of the mobility and
dependent on the carrier density. Moreover, the LMR appears to be insensitive
to the details of the disorder and points to a universal explanation of
classical LMR that can be applied to other material systems.Comment: Accepted by Phys. Rev. B (2010
Multifunctional transducer
Several parameters of a small region of a muscle tissue or other object, can be simultaneously measured using with minimal traumatizing or damage of the object, a trifunctional transducer which can determine the force applied by a muscle fiber, the displacement of the fiber, and the change in thickness of the fiber. The transducer has three legs with inner ends joined together and outer ends formed to piece the tissue and remain within it. Two of the legs are relatively stiff, to measure force applied by the tissue, and a third leg is relatively flexible to measure displacement of the tissue relative to one or both stiff legs, and with the three legs lying in a common plane so that the force and displacement measurements all relate to the same direction of muscle movements. A flexible loop is attached to one of the stiff legs to measure changes in muscle thickness, with the upper end of the loop fixed to the leg and the lower end of the loop bearing against the surface of the tissue and being free to slide on the leg
Fluctuations and correlations in population models with age structure
We study the population profile in a simple discrete time model of population
dynamics. Our model, which is closely related to certain ``bit-string'' models
of evolution, incorporates competition for resources via a population dependent
death probability, as well as a variable reproduction probability for each
individual as a function of age. We first solve for the steady-state of the
model in mean field theory, before developing analytic techniques to compute
Gaussian fluctuation corrections around the mean field fixed point. Our
computations are found to be in good agreement with Monte-Carlo simulations.
Finally we discuss how similar methods may be applied to fluctuations in
continuous time population models.Comment: 4 page
Asteroid Cooling Rates Indicated by K-Feldspar Exsolution Textures in H4 Ordinary Chondrites
Undisturbed thermal metamorphism in ordinary chondrite (OC) asteroids, produced through the radioactive decay of 26Al, is expected to result in an onion-shell-like structure. In such a structure, the inner layers of the asteroid experience more extensive thermal metamorphism, as represented by higher petrologic type, than the exterior layers. Furthermore, cooling rates are expected to be slower for OCs of high petrologic type than those of low petrologic type. However, cooling rates determined using metallographic methods and pyroxene diffusion are inconsistent with onion-shell-style cooling and have resulted in new models. These models argue for the disruption of the asteroid after peak metamorphism followed by reaccretion into a rubble pile. Improved constraints on cooling rates would provide a better understanding of the timing and scale of disruptive events. Feldspar microtextures are another tool that can be used to determine asteroid cooling rates. In OC chondrules, plagioclase is present as either a primary phase, or a secondary phase forming from the crystallization of mesostasis glass through petrologic type 4, followed by chemical and textural equilibration. Potas-sium feldspar is observed in petrologic types 3.6-6, as either patches or lamellae exsolved from albite in a perthite texture, often near pores or fractures. Exsolution occurs most commonly, and most extensively, in petrologic type 4. Because the feldspar exsolution wavelength is related to the rate at which grains cooled from the solvus temperature, determined from the minerals bulk composition, the chondrite cooling rate can be measured from regions of exsolution. We have previously reported the perthite exsolution cooling rate of Avanhandava, an H4 chondrite, to be 1 C per 1-4 months over a temperature interval of 765-670 C. A peristerite exsolution texture was also present in the Na-rich lamellae for which we estimated a cooling rate of 1 C in 103-104 years from 570-540 C. Overall, the cooling rates determined from Avanhandava are consistent with pyroxene diffusion (fast cooling at high temperatures) and metallographic rates (slow cooling at low temperatures), hence with the rubble pile model of disruption and reaccretion. Here, we characterize feldspar microtextures in four additional H4 chondrites to test the consistency of feldspar cooling rates across a range of samples. We show that all H4s are similar and support rubble pile models
The perimeter of large planar Voronoi cells: a double-stranded random walk
Let be the probability for a planar Poisson-Voronoi cell to have
exactly sides. We construct the asymptotic expansion of up to
terms that vanish as . We show that {\it two independent biased
random walks} executed by the polar angle determine the trajectory of the cell
perimeter. We find the limit distribution of (i) the angle between two
successive vertex vectors, and (ii) the one between two successive perimeter
segments. We obtain the probability law for the perimeter's long wavelength
deviations from circularity. We prove Lewis' law and show that it has
coefficient 1/4.Comment: Slightly extended version; journal reference adde
Microlensing of Broad Absorption Line Quasars: Polarization Variability
Roughly 10% of all quasars exhibit Broad Absorption Line (BAL) features which
appear to arise in material outflowing at high velocity from the active
galactic nucleus (AGN). The details of this outflow are, however, very poorly
constrained and the particular nature of the BAL material is essentially
unknown. Recently, new clues have become available through polarimetric studies
which have found that BAL troughs are more polarized than the quasar continuum
radiation. To explain these observations, models where the BAL material
outflows equatorially across the surface of the dusty torus have been
developed. In these models, however, several sources of the BAL polarization
are possible. Here, we demonstrate how polarimetric monitoring of
gravitationally lensed quasars, such as H 1413+117, during microlensing events
can not only distinguish between two currently popular models, but can also
provide further insight into the structure at the cores of BAL quasars.Comment: 17 pages, 3 figures, accepted to PAS
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