298 research outputs found
Laserlight visual cueing device for freezing of gait in Parkinson's disease: a case study of the biomechanics involved
AbstractBackground: Freezing of gait (FOG) is a serious gait disorder affecting up to two-thirds of people with Parkinson's disease (PD). Cueing has been explored as a method of generating motor execution using visual transverse lines on the floor. However, the impact of a laser light visual cue remains unclear. Objective: To determine the biomechanical effect of a laser cane on FOG in a participant with PD compared to a healthy age- and gender-matched control. Methods: The participant with PD and healthy control were given a task of initiating gait from standing. Electromyography (EMG) data were collected from the tibialis anterior (TA) and the medial gastrocnemius (GS) muscles using an 8-channel system. A 10-camera system (Qualisys) recorded movement in 6 degrees of freedom and a calibrated anatomical system technique was used to construct a full body model. Center of mass (COM) and center of pressure (COP) were the main outcome measures. Results: The uncued condition showed that separation of COM and COP took longer and was of smaller magnitude than the cued condition. EMG activity revealed prolonged activation of GS, with little to no TA activity. The cued condition showed earlier COM and COP separation. There was reduced fluctuation in GS, with abnormal, early bursts of TA activity. Step length improved in the cued condition compared to the uncued condition. Conclusion: Laserlight visual cueing improved step length beyond a non-cued condition for this patient indicating improved posture and muscle control
Structure of the silicon vacancy in 6H-SiC after annealing identified as the carbon vacancy–carbon antisite pair
We investigated radiation-induced defects in neutron-irradiated and subsequently annealed 6H-silicon carbide (SiC) with electron paramagnetic resonance (EPR), the magnetic circular dichroism of the absorption (MCDA), and MCDA-detected EPR (MCDA-EPR). In samples annealed beyond the annealing temperature of the isolated silicon vacancy we observed photoinduced EPR spectra of spin S=1 centers that occur in orientations expected for nearest neighbor pair defects. EPR spectra of the defect on the three inequivalent lattice sites were resolved and attributed to optical transitions between photon energies of 999 and 1075 meV by MCDA-EPR. The resolved hyperfine structure indicates the presence of one single carbon nucleus and several silicon ligand nuclei. These experimental findings are interpreted with help of total energy and spin density data obtained from the standard local-spin density approximation of the density-functional theory, using relaxed defect geometries obtained from the self-consistent charge density-functional theory based tight binding scheme. We have checked several defect models of which only the photoexcited spin triplet state of the carbon antisite–carbon vacancy pair (CSi-VC) in the doubly positive charge state can explain all experimental findings. We propose that the (CSi-VC) defect is formed from the isolated silicon vacancy as an annealing product by the movement of a carbon neighbor into the vacancy
Managing the supercell approximation for charged defects in semiconductors: finite size scaling, charge correction factors, the bandgap problem and the ab initio dielectric constant
The errors arising in ab initio density functional theory studies of
semiconductor point defects using the supercell approximation are analyzed. It
is demonstrated that a) the leading finite size errors are inverse linear and
inverse cubic in the supercell size, and b) finite size scaling over a series
of supercells gives reliable isolated charged defect formation energies to
around +-0.05 eV. The scaled results are used to test three correction methods.
The Makov-Payne method is insufficient, but combined with the scaling
parameters yields an ab initio dielectric constant of 11.6+-4.1 for InP. Gamma
point corrections for defect level dispersion are completely incorrect, even
for shallow levels, but re-aligning the total potential in real-space between
defect and bulk cells actually corrects the electrostatic defect-defect
interaction errors as well. Isolated defect energies to +-0.1 eV are then
obtained using a 64 atom supercell, though this does not improve for larger
cells. Finally, finite size scaling of known dopant levels shows how to treat
the band gap problem: in less than about 200 atom supercells with no
corrections, continuing to consider levels into the theoretical conduction band
(extended gap) comes closest to experiment. However, for larger cells or when
supercell approximation errors are removed, a scissors scheme stretching the
theoretical band gap onto the experimental one is in fact correct.Comment: 11 pages, 3 figures (6 figure files). Accepted for Phys Rev
Phosphorus donors in highly strained silicon
The hyperfine interaction of phosphorus donors in fully strained Si thin
films grown on virtual SiGe substrates with is
determined via electrically detected magnetic resonance. For highly strained
epilayers, hyperfine interactions as low as 0.8 mT are observed, significantly
below the limit predicted by valley repopulation. Within a Green's function
approach, density functional theory (DFT) shows that the additional reduction
is caused by the volume increase of the unit cell and a local relaxation of the
Si ligands of the P donor.Comment: 12 pages, 3 figure
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Research and development of a high efficiency gas-fired water heater. Volume 2. Task reports
Design and development of a cost-effective high efficiency gas-fired water heater to attain a service efficiency of 70% (including the effect of exfiltration) and a service efficiency of 78% (excluding exfiltration) for a 75 GPD draw at a 90/sup 0/F temperature rise, with a stored water to conditioned air temperature difference of 80/sup 0/F, are described in detail. Based on concept evaluation, a non-powered natural draft water heater was chosen as the most cost-effective design to develop. The projected installed cost is 200 for a conventional unit. When the project water heater is compared to a conventional unit, it has a payback of 3.7 years and life cycle savings of $350 to the consumer. A prototype water heater was designed, constructed, and tested. When operated with sealed combustion, the unit has a service efficiency of 66.4% (including the effect of exfiltration) below a burner input of 32,000 Btu/h. In the open combustion configuration, the unit operated at a measured efficiency of 66.4% Btu/h (excluding exfiltration). This compares with a service efficiency of 51.3% for a conventional water heater and 61% for a conventional high efficiency unit capable of meeting ASHRAE 90-75. Operational tests showed the unit performed well with no evidence of stacking or hot spots. It met or exceeded all capacity or usage tests specified in the program test plan and met all emission goals. Future work will concentrate on designing, building, and testing pre-production units. It is anticipated that both sealed combustion and open draft models will be pursued
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Research and development of a high efficiency gas-fired water heater. Volume 1. Final report summary
A summary of the work performed to design and develop a cost-effective high efficiency gas-fired water heater is presented. Details on the project plan showing the allocation of financial and personnel resources, the technical approach, the timing of principal events, decision, and milestones are described (Task 1). Studies necessary to determine the marketability of the high efficiency heaters in the residential sector are performed for Task 2. The necessary work to develop, fabricate, and test a prototype unit as specified in Task 2 is identified in Task 3. Test and evaluation specifications are also identified in Task 3. Task 4 consists of preparing the project plan for the production and field demonstration of the gas-fired water heater. (MCW
Defects in SiO2 as the possible origin of near interface traps in the SiC∕SiO2 system: A systematic theoretical study
A systematic study of the level positions of intrinsic and carbon defects in SiO2 is presented, based on density functional calculations with a hybrid functional in an alpha-quartz supercell. The results are analyzed from the point of view of the near interface traps (NIT), observed in both SiC/SiO2 and Si/SiO2 systems, and assumed to have their origins in the oxide. It is shown that the vacancies and the oxygen interstitial can be excluded as the origin of such NIT, while the silicon interstitial and carbon dimers give rise to gap levels in the energy range inferred from experiments. The properties of these defects are discussed in light of the knowledge about the SiC/SiO2 interface
Quadrupole Susceptibility and Elastic Softening due to a Vacancy in Silicon Crystal
We investigate the electronic states around a single vacancy in silicon
crystal by using the Green's function approach. The triply degenerate vacancy
states within the band gap are found to be extended over a large distance
from the vacancy site and contribute to the reciprocal
temperature dependence of the quadrupole susceptibility resulting in the
elastic softening at low temperture. The Curie constant of the quadrupole
susceptibility for the trigonal mode () is largely
enhanced as compared to that for the tetragonal mode ().
The obtained results are consistent with the recent ultrasonic experiments in
silicon crystal down to 20 mK. We also calculate the dipole and octupole
susceptibilities and find that the octupole susceptibilities are extremely
enhannced for a specific mode.Comment: 6 pages, with 5 figure
Electron paramagnetic resonance study of ferroelectric phase transition and dynamic effects in a Mn²⁺ doped [NH₄][Zn(HCOO)₃] hybrid formate framework
We present an X- and Q-band continuous wave (CW) and pulse electron paramagnetic resonance (EPR) study of a manganese doped [NH4][Zn(HCOO)3] hybrid framework, which exhibits a ferroelectric structural phase transition at 190 K. The CW EPR spectra obtained at different temperatures exhibit clear changes at the phase transition temperature. This suggests a successful substitution of the Zn2+ ions by the paramagnetic Mn2+ centers, which is further confirmed by the pulse EPR and 1H ENDOR experiments. Spectral simulations of the CW EPR spectra are used to obtain the temperature dependence of the Mn2+ zero-field splitting, which indicates a gradual deformation of the MnO6 octahedra indicating a continuous character of the transition. The determined data allow us to extract the critical exponent of the order parameter (β = 0.12), which suggests a quasi two-dimensional ordering in [NH4][Zn(HCOO)3]. The experimental EPR results are supported by the density functional theory calculations of the zero-field splitting parameters. Relaxation time measurements of the Mn2+ centers indicate that the longitudinal relaxation is mainly driven by the optical phonons, which correspond to the vibrations of the metal–oxygen octahedra. The temperature behavior of the transverse relaxation indicates a dynamic process in the ordered ferroelectric phase
Predictions for ASKAP Neutral Hydrogen Surveys
The Australian Square Kilometer Array Pathfinder (ASKAP) will revolutionise
our knowledge of gas-rich galaxies in the Universe. Here we present predictions
for two proposed extragalactic ASKAP neutral hydrogen (HI) emission-line
surveys, based on semi-analytic models applied to cosmological N-body
simulations. The ASKAP HI All-Sky Survey, known as WALLABY, is a shallow 3 Pi
survey (z = 0 - 0.26) which will probe the mass and dynamics of over 600,000
galaxies. A much deeper small-area HI survey, called DINGO, aims to trace the
evolution of HI from z = 0 - 0.43, a cosmological volume of 40 million Mpc^3,
detecting potentially 100,000 galaxies. The high-sensitivity 30 antenna ASKAP
core (diameter ~2 km) will provide an angular resolution of 30 arcsec (at z=0).
Our simulations show that the majority of galaxies detected in WALLABY (87.5%)
will be resolved. About 5000 galaxies will be well resolved, i.e. more than
five beams (2.5 arcmin) across the major axis, enabling kinematic studies of
their gaseous disks. This number would rise to 160,000 galaxies if all 36 ASKAP
antennas could be used; the additional six antennas provide baselines up to 6
km, resulting in an angular resolution of 10 arcsec. For DINGO this increased
resolution is highly desirable to minimise source confusion; reducing confusion
rates from a maximum of 10% of sources at the survey edge to 3%. We estimate
that the sources detected by WALLABY and DINGO will span four orders of
magnitude in total halo mass (from 10^{11} to 10^{15} Msol) and nearly seven
orders of magnitude in stellar mass (from 10^{5} to 10^{12} Msol), allowing us
to investigate the process of galaxy formation across the last four billion
years.Comment: 21 pages, accepted for publication in MNRAS, minor updates to
published version and fixed links. Movies and images available at
http://ict.icrar.org/store/Movies/Duffy12c
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