3,621 research outputs found
Apparatus for disintegrating kidney stones
The useful life of the wire probe in an ultrasonic kidney stone disintegration instrument is enhanced and prolonged by attaching the wire of the wire probe to the tip of an ultrasonic transducer by means of a clamping arrangement. Additionally, damping material is applied to the wire probe in the form of a damper tube through which the wire probe passes in the region adjacent the transducer tip. The damper tube extends outwardly from the transducer tip a predetermined distance, terminating in a resilient soft rubber joint. Also, the damper tube is supported intermediate its length by a support member. The damper system thus acts to inhibit lateral vibrations of the wire in the region of the transducer tip while providing little or no damping to the linear vibrations imparted to the wire by the transducer
Device for removing foreign objects from anatomic organs
A device is disclosed for removing foreign objects from anatomic organs such as the ear canal or throat. It has a housing shaped like a flashlight, an electrical power source such as a battery or AC power from a wall socket, and a tip extending from the housing. The tip has at least one wire loop made from a shape-memory-effect alloy, such as Nitinol, switchably connected to the electrical power source such that when electric current flows through the wire loop the wire loop heats up and returns to a previously programmed shape such as a curet or tweezers so as to facilitate removal of the foreign object
Stochastic mean field formulation of the dynamics of diluted neural networks
We consider pulse-coupled Leaky Integrate-and-Fire neural networks with
randomly distributed synaptic couplings. This random dilution induces
fluctuations in the evolution of the macroscopic variables and deterministic
chaos at the microscopic level. Our main aim is to mimic the effect of the
dilution as a noise source acting on the dynamics of a globally coupled
non-chaotic system. Indeed, the evolution of a diluted neural network can be
well approximated as a fully pulse coupled network, where each neuron is driven
by a mean synaptic current plus additive noise. These terms represent the
average and the fluctuations of the synaptic currents acting on the single
neurons in the diluted system. The main microscopic and macroscopic dynamical
features can be retrieved with this stochastic approximation. Furthermore, the
microscopic stability of the diluted network can be also reproduced, as
demonstrated from the almost coincidence of the measured Lyapunov exponents in
the deterministic and stochastic cases for an ample range of system sizes. Our
results strongly suggest that the fluctuations in the synaptic currents are
responsible for the emergence of chaos in this class of pulse coupled networks.Comment: 12 Pages, 4 Figure
Cell assembly dynamics of sparsely-connected inhibitory networks: a simple model for the collective activity of striatal projection neurons
Striatal projection neurons form a sparsely-connected inhibitory network, and
this arrangement may be essential for the appropriate temporal organization of
behavior. Here we show that a simplified, sparse inhibitory network of
Leaky-Integrate-and-Fire neurons can reproduce some key features of striatal
population activity, as observed in brain slices [Carrillo-Reid et al., J.
Neurophysiology 99 (2008) 1435{1450]. In particular we develop a new metric to
determine the conditions under which sparse inhibitory networks form
anti-correlated cell assemblies with time-varying activity of individual cells.
We found that under these conditions the network displays an input-specific
sequence of cell assembly switching, that effectively discriminates similar
inputs. Our results support the proposal [Ponzi and Wickens, PLoS Comp Biol 9
(2013) e1002954] that GABAergic connections between striatal projection neurons
allow stimulus-selective, temporally-extended sequential activation of cell
assemblies. Furthermore, we help to show how altered intrastriatal GABAergic
signaling may produce aberrant network-level information processing in
disorders such as Parkinson's and Huntington's diseases.Comment: 22 pages, 9 figure
Statistical measure of complexity for quantum systems with continuous variables
The Fisher-Shannon statistical measure of complexity is analyzed for a
continuous manifold of quantum observables. It is probed then than calculating
it only in the configuration and momentum spaces will not give a complete
description for certain systems. Then a more general measure for the complexity
of a quantum system by the integration of the usual Fisher-Shannon measure over
all the parameter space is proposed. Finally, these measures are applied to the
concrete case of a free particle in a box.Comment: 6 pages, 5 figures. Published versio
The effects of halo alignment and shape on the clustering of galaxies
We investigate the effects of halo shape and its alignment with larger scale
structure on the galaxy correlation function. We base our analysis on the
galaxy formation models of Guo et al., run on the Millennium Simulations. We
quantify the importance of these effects by randomizing the angular positions
of satellite galaxies within haloes, either coherently or individually, while
keeping the distance to their respective central galaxies fixed. We find that
the effect of disrupting the alignment with larger scale structure is a ~2 per
cent decrease in the galaxy correlation function around r=1.8 Mpc/h. We find
that sphericalizing the ellipsoidal distributions of galaxies within haloes
decreases the correlation function by up to 20 per cent for r<1 Mpc/h and
increases it slightly at somewhat larger radii. Similar results apply to power
spectra and redshift-space correlation functions. Models based on the Halo
Occupation Distribution, which place galaxies spherically within haloes
according to a mean radial profile, will therefore significantly underestimate
the clustering on sub-Mpc scales. In addition, we find that halo assembly bias,
in particular the dependence of clustering on halo shape, propagates to the
clustering of galaxies. We predict that this aspect of assembly bias should be
observable through the use of extensive group catalogues.Comment: 8 pages, 6 figures. Accepted for publication in MNRAS. Minor changes
relative to v1. Note: this is an revised and considerably extended
resubmission of http://arxiv.org/abs/1110.4888; please refer to the current
version rather than the old on
Matched filter optimization of kSZ measurements with a reconstructed cosmological flow field
We develop and test a new statistical method to measure the kinematic
Sunyaev-Zel'dovich (kSZ) effect. A sample of independently detected clusters is
combined with the cosmic flow field predicted from a galaxy redshift survey in
order to derive a matched filter that optimally weights the kSZ signal for the
sample as a whole given the noise involved in the problem. We apply this
formalism to realistic mock microwave skies based on cosmological -body
simulations, and demonstrate its robustness and performance. In particular, we
carefully assess the various sources of uncertainty, cosmic microwave
background primary fluctuations, instrumental noise, uncertainties in the
determination of the velocity field, and effects introduced by miscentring of
clusters and by uncertainties of the mass-observable relation (normalization
and scatter). We show that available data (\plk\ maps and the MaxBCG catalogue)
should deliver a detection of the kSZ. A similar cluster catalogue
with broader sky coverage should increase the detection significance to . We point out that such measurements could be binned in order to
study the properties of the cosmic gas and velocity fields, or combined into a
single measurement to constrain cosmological parameters or deviations of the
law of gravity from General Relativity.Comment: 17 pages, 10 figures, 3 tables. Submitted to MNRAS. Comments are
welcome
- …