1,890 research outputs found
Electronic structure of the muonium center as a shallow donor in ZnO
The electronic structure and the location of muonium centers (Mu) in
single-crystalline ZnO were determined for the first time. Two species of Mu
centers with extremely small hyperfine parameters have been observed below 40
K. Both Mu centers have an axial-symmetric hyperfine structure along with a
[0001] axis, indicating that they are located at the AB_{O,//} and BC_{//}
sites. It is inferred from their small ionization energy (~6 meV and 50 meV)
and hyperfine parameters (~10^{-4} times the vacuum value) that these centers
behave as shallow donors, strongly suggesting that hydrogen is one of the
primary origins of n type conductivity in as-grown ZnO.Comment: 4 pages, 4 figures, submitted to PR
A novel high dynamic six phase 120 kW Power Hardware in the Loop Emulation Test Bench for emulating AC/DC Grids and Electrical Machines
This paper presents a highly customizable 120kVA Power-Hardware-in-the-Loop test bench. The output stage consist of two identical Parallel Hybrid Converters each with a 17-level output voltage and an effective switching frequency of 1MHz. The Parallel Hybrid Converters can provide 3-phase AC or bipolar DC as output voltage. Thus, one 6-AC, 3-AC or DC system or two systems with 2x3-AC, 1x3-AC and 1xDC or 2xDC can be emulated
A novel high dynamic six phase 120 kW Power Hardware in the Loop Emulation Test Bench for emulating AC/DC Grids and Electrical Machines
This paper presents a highly customizable 120kVA Power-Hardware-in-the-Loop test bench. The output stage consist of two identical Parallel Hybrid Converters each with a 17-level output voltage and an effective switching frequency of 1MHz. The Parallel Hybrid Converters can provide 3-phase AC or bipolar DC as output voltage. Thus, one 6-AC, 3-AC or DC system or two systems with 2x3-AC, 1x3-AC and 1xDC or 2xDC can be emulated
Generation of spin currents via Raman scattering
We show theoretically that stimulated spin flip Raman scattering can be used
to inject spin currents in doped semiconductors with spin split bands. A pure
spin current, where oppositely oriented spins move in opposite directions, can
be injected in zincblende crystals and structures. The calculated spin current
should be detectable by pump-probe optical spectroscopy and anomalous Hall
effect measurement
Spin relaxation of conduction electrons in bulk III-V semiconductors
Spin relaxation time of conduction electrons through the Elliot-Yafet,
D'yakonov-Perel and Bir-Aronov-Pikus mechanisms is calculated theoretically for
bulk GaAs, GaSb, InAs and InSb of both - and -type. Relative importance
of each spin relaxation mechanism is compared and the diagrams showing the
dominant mechanism are constructed as a function of temperature and impurity
concentrations. Our approach is based upon theoretical calculation of the
momentum relaxation rate and allows understanding of the interplay between
various factors affecting the spin relaxation over a broad range of temperature
and impurity concentration.Comment: an error in earlier version correcte
The motor function measure to study limitation of activity in children and adults with Charcot-Marie-Tooth disease
AbstractObjectiveTo study the applicability and responsiveness of the motor function measure (total score and sub-scores D1, D2 and D3) in patients with Charcot-Marie-Tooth disease.Patients and methodsTwo hundred and thirty-three patients aged 4–86 years were included in the descriptive study. Scores and sub-scores were analyzed by age and by disease subtypes. Sensitivity to change (responsiveness) was estimated in patients having had at least two evaluations with at least six months between the first and the second.ResultsMotor function measure scores decrease with age, especially sub-scores D1 and D3. There were no significant differences between the scores according to type of Charcot-Marie-Tooth disease. The scores were significantly higher for ambulatory than for non-ambulatory patients. Significant responsiveness was demonstrated only in type 2 Charcot-Marie-Tooth disease.Discussion/conclusionsOur results suggest that, especially for D1 and D3 sub-scores, the motor function measure is a reliable and valid outcome measure that can be usefully applied in longitudinal follow-up. Studies of longer duration could demonstrate its responsiveness in other Charcot-Marie-Tooth disease subtypes
Gallium transformation under femtosecond laser excitation: Phase coexistence and incomplete melting
The reversible phase transition induced by femtosecond laser excitation of
Gallium has been studied by measuring the dielectric function at 775 nm with ~
200 fs temporal resolution. The real and imaginary parts of the transient
dielectric function were calculated from absolute reflectivity of Gallium layer
measured at two different angles of incidence, using Fresnel formulas. The
time-dependent electron-phonon effective collision frequency, the heat
conduction coefficient and the volume fraction of a new phase were restored
directly from the experimental data, and the time and space dependent electron
and lattice temperatures in the layer undergoing phase transition were
reconstructed without ad hoc assumptions. We converted the temporal dependence
of the electron-phonon collision rate into the temperature dependence, and
demonstrated, for the first time, that the electron-phonon collision rate has a
non-linear character. This temperature dependence converges into the known
equilibrium function during the cooling stage. The maximum fraction of a new
phase in the laser-excited Gallium layer reached only 60% even when the
deposited energy was two times the equilibrium enthalpy of melting. We have
also demonstrated that the phase transition pace and a fraction of the
transformed material depended strongly on the thickness of the laser-excited
Gallium layer, which was of the order of several tens of nanometers for the
whole range of the pump laser fluencies up to the damage threshold. The
kinetics of the phase transformation after the laser excitation can be
understood on the basis of the classical theory of the first-order phase
transition while the duration of non-thermal stage appears to be comparable to
the sub-picosecond pulse length.Comment: 28 pages, including 9 figs. Submitted to Phys. Rev. B 14 March 200
First-principles study of the phonon-limited mobility in n-type single-layer MoS2
In the present work we calculate the phonon-limited mobility in intrinsic
n-type single-layer MoS2 as a function of carrier density and temperature for T
> 100 K. Using a first-principles approach for the calculation of the
electron-phonon interaction, the deformation potentials and Fr\"ohlich
interaction in the isolated MoS2 layer are determined. We find that the
calculated room-temperature mobility of ~410 cm^2 V^-1 s^-1 is dominated by
optical phonon scattering via deformation potential couplings and the
Fr\"ohlich interaction with the deformation potentials to the intravalley
homopolar and intervalley longitudinal optical phonons given by 4.1 x 10^8
eV/cm and 2.6 x 10^8 eV/cm, respectively. The mobility is weakly dependent on
the carrier density and follows a \mu ~ T^-1 temperature dependence with \gamma
= 1.69 at room temperature. It is shown that a quenching of the characteristic
homopolar mode which is likely to occur in top-gated samples, boosts the
mobility with 70 cm^2 V^-1 s^-1 and can be observed as a decrease in the
exponent to \gamma = 1.52. Our findings indicate that the intrinsic
phonon-limited mobility is approached in samples where a high-kappa dielectric
that effectively screens charge impurities is used as gate oxide.Comment: Submitted to Phys. Rev.
Burns disasters - a plan for South Africa
The need for a burns disaster plan integrated with national and provincial disaster plans was highlighted during the South African Burns Society Congress in Pretoria in 2009. In recent times, a fire at a large printing works in Paarl and a nightclub in Durban, and bush fires around Cape Town, have questioned both the prevention strategies and our preparedness to cope with the potential number of burn casualties. The likelihood of a burns disaster increases when large numbers of people are gathered in an environment where powerful sources of energy are harnessed in industry or where there has been a significant growth in transportation and technology.
Acts of terrorism have highlighted the need for national disaster plans in all countries. The Australian Burns Disaster Plan (Ausburnplan), for instance, was drawn up in the aftermath of the Bali catastrophe. Analysis of major terrorist attacks has revealed that up to 15% of the total live casualties sustained severe burn injuries; but the arrival of even 10 new major burns would overwhelm most burns units in South Africa.
The International Society for Burns Injuries (ISBI) guidelines for the management of large numbers of burns casualties recommend that ‘each country has or should have a disaster planning system that addresses its own particular needs.’ The essential elements of any disaster plan are descriptions of how medical facilities should provide appropriate treatment, and how to ensure access to such facilities. The South African Burns Society (SABS) should assist in evaluating these facilities, help to maintain standards, and formulate and implement provincial and national burns disaster plans
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