1,594 research outputs found
Coherence of a room-temperature CW GaAs/GaAlAs injection laser
The temporal coherence of a stripe-geometry double-heterojunction GaAs/GaAlAs laser operating CW at room temperature was determined. A heterodyne detection scheme was used involving the mixing of the laser field with a frequency-shifted and time-delayed image of itself in an interferometer. Because the laser device oscillated in several longitudinal modes, the autocorrelation function of its output exhibited resonances for specific time delays. The rate at which the amplitude of these resonances decreased with increasing time delays provided a measure of an apparent coherence length associated with individual longitudinal modes. The coherence length, so defined, was found to increase linearly with drive current in excess of threshold. This observation is interpreted as evidence that the intrinsic linewidth of a longitudinal mode is inversely proportional to the coherent optical power in that mode. Apparent coherence lengths were a few centimeters for a few milliwatts of total optical power emitted per facet. For a perfectly balanced interferometer, a sharp heterodyne beat signal was also observed when the laser device was operated considerably below threshold, i.e., in the LED mode
Survivor Assistance through Technology Transfer in Tanzania
This article describes how cutting-edge technology is being developed and disseminated in landmine-affected countries. Focusing particularly on the Tanzania Training Center for Orthopedic Technologists, the authors examine how a process of appropriate, resource-effective casting is being advanced and then shared through training workshops. Improved technology and its successful transfer are vital to better assisting landmine survivors, a goal the Center for International Rehabilitation is working to achieve
Sub-unit cell layer-by-layer growth of Fe3O4, MgO, and Sr2RuO4 thin films
The use of oxide materials in oxide electronics requires their controlled
epitaxial growth. Recently, it was shown that Reflection High Energy Electron
Diffraction (RHEED) allows to monitor the growth of oxide thin films even at
high oxygen pressure. Here, we report the sub-unit cell molecular or block
layer growth of the oxide materials Sr2RuO4, MgO, and magnetite using Pulsed
Laser Deposition (PLD) from stoichiometric targets. Whereas for perovskites
such as SrTiO3 or doped LaMnO3 a single RHEED intensity oscillation is found to
correspond to the growth of a single unit cell, in materials where the unit
cell is composed of several molecular layers or blocks with identical
stoichiometry, a sub-unit cell molecular or block layer growth is established
resulting in several RHEED intensity oscillations during the growth of a single
unit-cell
Epitaxy of Fe3O4 on Si(001) by pulsed laser deposition using a TiN/MgO buffer layer
Epitaxy of oxide materials on silicon (Si) substrates is of great interest
for future functional devices using the large variety of physical properties of
the oxides as ferroelectricity, ferromagnetism, or superconductivity. Recently,
materials with high spin polarization of the charge carriers have become
interesting for semiconductor-oxide hybrid devices in spin electronics. Here,
we report on pulsed laser deposition of magnetite (Fe3O4) on Si(001) substrates
cleaned by an in situ laser beam high temperature treatment. After depositing a
double buffer layer of titanium nitride (TiN) and magnesium oxide (MgO), a high
quality epitaxial magnetite layer can be grown as verified by RHEED intensity
oscillations and high resolution x-ray diffraction.Comment: submitte
Randomness and early termination: what makes a game exciting?
In this paper we revisit an open problem posed by Aldous on the max-entropy
win-probability martingale: given two players of equal strength, such that the
win-probability is a martingale diffusion, which of these processes has maximum
entropy and hence gives the most excitement for the spectators? We study a
terminal-boundary value problem for the nonlinear parabolic PDE
derived by Aldous and prove its
wellposedness and regularity of its solution by combining PDE analysis and
probabilistic tools, in particular the reformulation as a stochastic control
problem with restricted control set, which allows us to deduce strict
ellipticity. We establish key qualitative properties of the solution including
concavity, monotonicity, convergence to a steady state for long remaining time
and the asymptotic behaviour shortly before the terminal time. Moreover, we
construct convergent numerical approximations. The analytical and numerical
results allow us to highlight the behaviour of the win-probability process in
the present case where the match may end early, in contrast to recent work by
Backhoff-Veraguas and Beiglb\"ock where the match always runs the full length
Present status and future direction of clinical trials in advanced endometrial carcinoma
Endometrial adenocarcinoma is staged surgically, and advanced endometrial carcinoma is considered to be FIGO stage III and IV. The Gynecologic Oncology Group (GOG) has come a long way in developing new strategies in the management of advanced endometrial carcinoma. Combining surgery, radiation, and chemotherapy, the 5-year survival has improved to between 40-60% in newly diagnosed advanced endometrial carcinoma. Recent findings in GOG184 indicate that multiple risk factors noted at the time of surgical staging could lead to concurrent clinical trials that could be completed expeditiously rather than a subsequent ten year long phase III trial including all the various risk subgroups of patients. This review is a focus on the accomplishments of the GOG in advanced endometrial carcinoma with an emphasis on future challenges. Originally published Journal of Gynecologic Oncology, Vol. 19, No. 3, Sep 200
Gauging the threat: the first population estimate for white sharks in South Africa using photo identification and automated software
South Africa is reputed to host the world’s largest remaining population of white sharks, yet no studies have accurately determined a population estimate based on mark-recapture of live individuals. We used dorsal fin photographs (fin IDs) to identify white sharks in Gansbaai, South Africa, from January 2007 - December 2011. We used the computer programme DARWIN to catalogue and match fin IDs of individuals; this is the first study to successfully use the software for white shark identification. The programme performed well despite a number of individual fins showing drastic changes in dorsal fin shape over time. Of 1682 fin IDs used, 532 unique individuals were identified. We estimated population size using the open-population POPAN parameterisation in Program MARK, which estimated the superpopulation size at 908 (95% confidence interval 808-1008). This estimated population size is considerably larger than those described at other aggregation areas of the species and is comparable to a previous South African population estimate conducted 16 years prior. Our assessment suggests the species has not made a marked recovery since being nationally protected in 1991. As such, additional international protection may prove vital for the long-term conservation of this threatened species
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