637 research outputs found
Percutaneous reduction and fixation of intraarticular calcaneal fractures
Objective: Percutaneous reduction by distraction and subsequent percutaneous screw fixation to restore calcaneal and posterior talocalcaneal facet anatomy. The aim of this technique is to improve functional outcome and to diminish the rate of secondary posttraumatic arthrosis compared to conservative treatment and, secondly, to reduce infectious complications compared to open reduction and internal fixation (ORIF). Indications: Sanders type II-IV displaced intraarticular calcaneal fractures. Contraindications: Isolated centrally depressed fragment. Contraindications: Patients who are expected to be noncompliant. Surgical Technique: Four distractors (Synthes™) are positioned, two on each side of the foot, between the tuberosity of the calcaneus and talus and between the tuberosity and cuboid. A distracting force is given over all four distractors. A blunt drifter is then introduced from the plantar side to unlock and push up any remaining depressed parts of the subtalar joint surface of the calcaneus. The reduction is fixated with two or three screws inserted percutaneously. Postoperative Management: Directly postoperatively, full active range of motion exercises of the ankle joint can start, with the foot elevated in the 1st postoperative week. Stitches are removed after 14 days. Implant removal is necessary in 50-60% of patients. Results: Between 1999 and 2004, 59 patients with 71 fractures were treated by percutaneous skeletal triangular distraction and percutaneous fixation. A total of 50 patients with 61 fractures and a minimum follow-up of 1 year were available for follow-up. According to the American Orthopaedic Foot and Ankle Society Hindfoot Score, 72% had a good to excellent result. A secondary subtalar arthrodesis was performed in five patients and planned in four (total 15%). Böhler's angle increased by about 20° postoperatively. Sagittal motion was 90% andsubtalar motion 70% compared to the healthy foot
Training deep neural density estimators to identify mechanistic models of neural dynamics
Mechanistic modeling in neuroscience aims to explain observed phenomena in terms of underlying causes. However, determining which model parameters agree with complex and stochastic neural data presents a significant challenge. We address this challenge with a machine learning tool which uses deep neural density estimators-- trained using model simulations-- to carry out Bayesian inference and retrieve the full space of parameters compatible with raw data or selected data features. Our method is scalable in parameters and data features, and can rapidly analyze new data after initial training. We demonstrate the power and flexibility of our approach on receptive fields, ion channels, and Hodgkin-Huxley models. We also characterize the space of circuit configurations giving rise to rhythmic activity in the crustacean stomatogastric ganglion, and use these results to derive hypotheses for underlying compensation mechanisms. Our approach will help close the gap between data-driven and theory-driven models of neural dynamics
Stable Propagation of a Burst Through a One-Dimensional Homogeneous Excitatory Chain Model of Songbird Nucleus HVC
We demonstrate numerically that a brief burst consisting of two to six spikes
can propagate in a stable manner through a one-dimensional homogeneous
feedforward chain of non-bursting neurons with excitatory synaptic connections.
Our results are obtained for two kinds of neuronal models, leaky
integrate-and-fire (LIF) neurons and Hodgkin-Huxley (HH) neurons with five
conductances. Over a range of parameters such as the maximum synaptic
conductance, both kinds of chains are found to have multiple attractors of
propagating bursts, with each attractor being distinguished by the number of
spikes and total duration of the propagating burst. These results make
plausible the hypothesis that sparse precisely-timed sequential bursts observed
in projection neurons of nucleus HVC of a singing zebra finch are intrinsic and
causally related.Comment: 13 pages, 6 figure
Dispersion strengthening in vanadium microalloyed steels processed by simulated thin slab casting and direct charging. Part 2 - chemical characterisation of dispersion strengthening precipitates
The composition of the sub-15 nm particles in six related vanadium high strength low alloy steels, made by simulated thin slab direct charged casting, has been determined using electron energy loss spectroscopy (EELS). Such particles are considered to be responsible for dispersion hardening. For the first time, particles down to 4 nm in size have had their composition fully determined. In all the steels, the particles were nitrogen and vanadium rich and possibly slightly sub-stoichiometric carbonitrides. Equilibrium thermodynamics predicted much higher carbon to metal atomic ratios than observed in all cases so that kinetics and mechanical deformation clearly control the precipitation process. Thus it is important to formulate the steel with this in mind
Observation of Superfluid Flow in a Bose-Einstein Condensed Gas
We have studied the hydrodynamic flow in a Bose-Einstein condensate stirred
by a macroscopic object, a blue detuned laser beam, using nondestructive {\em
in situ} phase contrast imaging. A critical velocity for the onset of a
pressure gradient has been observed, and shown to be density dependent. The
technique has been compared to a calorimetric method used previously to measure
the heating induced by the motion of the laser beam.Comment: 4 pages, 5 figure
Four-Wave mixing in degenerate Fermi gases: Beyond the undepleted pump approximation
We analyze the full nonlinear dynamics of the four-wave mixing between an
incident beam of fermions and a fermionic density grating. We find that when
the number of atoms in the beam is comparable to the number of atoms forming
the grating, the dephasing of that grating, which normally leads to a decay of
its amplitude, is suppressed. Instead, the density grating and the beam density
exhibit large nonlinear coupled amplitude oscillations. In this case four-wave
mixing can persist for much longer times compared to the case of negligible
back-action. We also evaluate the efficiency of the four-wave mixing and show
that it can be enhanced by producing an initial density grating with an
amplitude that is less than the maximum value. These results indicate that
efficient four-wave mixing in fermionic alkali gases should be experimentally
observable.Comment: 9 pages, 8 figure
Electrophysiological correlates of high-level perception during spatial navigation
We studied the electrophysiological basis of object recognition by recording scalp\ud
electroencephalograms while participants played a virtual-reality taxi driver game.\ud
Participants searched for passengers and stores during virtual navigation in simulated\ud
towns. We compared oscillatory brain activity in response to store views that were targets or\ud
nontargets (during store search) or neutral (during passenger search). Even though store\ud
category was solely defined by task context (rather than by sensory cues), frontal ...\ud
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Direct observation of the phonon energy in a Bose-Einstein condensate by tomographic imaging
The momentum and energy of phonons in a Bose-Einstein condensate are measured
directly from a time-of-flight image by computerized tomography. We find that
the same atoms that carry the momentum of the excitation also carry the
excitation energy. The measured energy is in agreement with the Bogoliubov
spectrum. Hydrodynamic simulations are performed which confirm our observation.Comment: Letter, 5 figure
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