17,270 research outputs found
Modeling Deformable Human Arm for Constrained Research Analysis
We are working on modeling a deformable human arm to improve the accuracy of constrained reach analysis. This work is a part of the project Crew Task Simulation for Maintenance, Training, and Safety . Crewmembers are performing constrained reaches with arm and body for both intra- and extra-vehicular activity (IVA and EVA). They tolerate a certain level of tissue deformation when compressed against a solid object such as an obstacle or the joint in an extravehicular mobility unit (EMU). We have created a deformable arm segment by measuring skin indentation as a function of applied load. In order to populate the model with reasonable tissue properties we have built a simple but effective measuring device to acquire the non-linear force-depth relation from numerous sample points on an arm surface. Given an obstacle, our goal is to determine the reachable space under a certain level of tolerable contact force. We use a finite element method based on living tissue properties and the measured force-depth relations. This work will be applied to estimate the increase in reachable volume of a crewmember an EMU for EVA operation as well as for shirt-sleeved IVA operations
Monolithic arrays of surface emitting laser NOR logic devices
Monolithic, cascadable, laser-logic-device arrays have been realized and characterized. The monolithic surface-emitting laser logic (SELL) device consists of an AlGaAs superlattice lasing around 780 nm connected to a heterojunction phototransistor (HPT) in parallel and a resistor in series. Arrays up to 8×8 have been fabricated, and 2×2 arrays show uniform characteristics. The optical logic output is switched off with 40 μW incident optical input
Monolithic arrays of surface emitting laser NOR logic devices
Monolithic, cascadable, laser-logic-device arrays have been realized and characterized. The monolithic surface-emitting laser logic (SELL) device consists of an AlGaAs superlattice lasing around 780 nm connected to a heterojunction phototransistor (HPT) in parallel and a resistor in series. Arrays up to 8×8 have been fabricated, and 2×2 arrays show uniform characteristics. The optical logic output is switched off with 40 μW incident optical input
Exact dimer ground state of the two dimensional Heisenberg spin system SrCu_2(BO_3)_2
The two dimensional Heisenberg model for SrCu_2(BO_3)_2 has the exact dimer
ground state which was proven by Shastry and Sutherland almost twenty years
ago. The critical value of the quantum phase transition from the dimer state to
the N\'{e}el ordered state is determined. Analysis of the experimental data
shows that SrCu_2(BO_3)_2 has the dimer ground state but is close to the
transition point, which leads to the unusual temperature dependence of the
susceptibility. Almost localized nature of the triplet excitations explains the
plateaus observed in the magnetization curve.Comment: 4 pages, 5 figures, to appear in PR
Time-domain Brillouin Scattering as a Local Temperature Probe in Liquids
We present results of time-domain Brillouin scattering (TDBS) to determine
the local temperature of liquids in contact to an optical transducer. TDBS is
based on an ultrafast pump-probe technique to determine the light scattering
frequency shift caused by the propagation of coherent acoustic waves in a
sample. Since the temperature influences the Brillouin scattering frequency
shift, the TDBS signal probes the local temperature of the liquid. Results for
the extracted Brillouin scattering frequencies recorded at different liquid
temperatures and at different laser powers - i.e. different steady state
background temperatures- are shown to demonstrate the usefulness of TDBS as a
temperature probe. This TDBS experimental scheme is a first step towards the
investigation of ultrathin liquids measured by GHz ultrasonic probing.Comment: arXiv admin note: substantial text overlap with arXiv:1702.0107
Resonant pairing between Fermions with unequal masses
We study the pairing between Fermions of different masses, especially at the
unitary limit. At equal populations, the thermodynamic properties are identical
with the equal mass case provided an appropriate rescaling is made. At unequal
populations, for sufficiently light majority species, the system does not phase
separate. For sufficiently heavy majority species, the phase separated normal
phase have a density larger than that of the superfluid. For atoms in harmonic
traps, the density profiles for unequal mass Fermions can be drastically
different from their equal-mass counterparts.Comment: 10 pages, 4 figure
Observation of Phase Separation in a Strongly-Interacting Imbalanced Fermi Gas
We have observed phase separation between the superfluid and the normal
component in a strongly interacting Fermi gas with imbalanced spin populations.
The in situ distribution of the density difference between two trapped spin
components is obtained using phase-contrast imaging and 3D image
reconstruction. A shell structure is clearly identified where the superfluid
region of equal densities is surrounded by a normal gas of unequal densities.
The phase transition induces a dramatic change in the density profiles as
excess fermions are expelled from the superfluid.Comment: 5 pages, 7 figure
A COMPARISON OF ACCURACY AND STROKE CHARACTERISTICS BETWEEN TWO PUTTING GRIP TECHNIQUES
Nowadays PGA golfers are experimenting with various golf putting grips. The purpose of this study was to investigate the traits of using two putting grips; reverse overlapping grip and finger bone grip at three different putting distances. 20 subjects with no previous golf experience participated in this study. The kinematic data of the subject and the putter’s shaft and head was recorded by 8 Qualisys cameras at 100Hz. There was no significant difference between the success rate of getting the ball in the hole at all distances. The finger bone grip produced statistically smaller radial error values than the reverse overlapping grip at the distances for 7 and 11 metres. The finger bone grip provided straighter putter head trajectories and less change in the movement of the COG, which implies more stability of the player and that the ball will travel in the desired path. In conclusion, the finger bone putting technique gave radial errors less than the reverse overlapping grip technique which seems to be due to the added stability and straighter putter head trajectories
Superfluid stability in BEC-BCS crossover
We consider a dilute atomic gas of two species of fermions with unequal
concentrations under a Feshbach resonance. We find that the system can have
distinct properties due to the unbound fermions. The uniform state is stable
only when either (a) beyond a critical coupling strength, where it is a gapless
superfluid, or (b) when the coupling strength is sufficiently weak, where it is
a normal Fermi gas mixture. Phase transition(s) must therefore occur when the
resonance is crossed.Comment: 4 pages, 4 figure
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