Origin of giant enhancement of phase contrast in electron holography of modulation-doped n-type GaN.

The electron optical phase contrast probed by electron holography at n-n+ GaN doping steps is found to exhibit a giant enhancement, in sharp contrast to the always smaller than expected phase contrast reported for p-n junctions. We unravel the physical origin of the giant enhancement by combining off-axis electron holography data with self-consistent electrostatic potential calculations. The predominant contribution to the phase contrast is shown to arise from the doping dependent screening length of the surface Fermi-level pinning, which is induced by FIB-implanted carbon point defects below the outer amorphous shell. The contribution of the built-in potential is negligible for modulation doping and only relevant for large built-in potentials at e.g. p-n junctions. This work provides a quantitative approach to so-called dead layers at TEM lamellas.

Ultrafast-nonlinear ultraviolet pulse modulation in an AlInGaN polariton waveguide operating up to room temperature.

Ultrafast nonlinear photonics enables a host of applications in advanced on-chip spectroscopy and information processing. These rely on a strong intensity dependent (nonlinear) refractive index capable of modulating optical pulses on sub-picosecond timescales and on length scales suitable for integrated photonics. Currently there is no platform that can provide this for the UV spectral range where broadband spectra generated by nonlinear modulation can pave the way to new on-chip ultrafast (bio-) chemical spectroscopy devices. We demonstrate the giant nonlinearity of UV hybrid light-matter states (exciton-polaritons) up to room temperature in an AlInGaN waveguide. We experimentally measure ultrafast nonlinear spectral broadening of UV pulses in a compact 100 µm long device and deduce a nonlinearity 1000 times that in common UV nonlinear materials and comparable to non-UV polariton devices. Our demonstration promises to underpin a new generation of integrated UV nonlinear light sources for advanced spectroscopy and measurement.

Cavity-enhanced optical Hall effect in two-dimensional free charge carrier gases detected at terahertz frequencies.

The effect of a tunable, externally coupled Fabry-Perot cavity to resonantly enhance the optical Hall effect signatures at terahertz frequencies produced by a traditional Drude-like two-dimensional electron gas is shown and discussed in this Letter. As a result, the detection of optical Hall effect signatures at conveniently obtainable magnetic fields, for example, by neodymium permanent magnets, is demonstrated. An AlInN/GaN-based high-electron mobility transistor structure grown on a sapphire substrate is used for the experiment. The optical Hall effect signatures and their dispersions, which are governed by the frequency and the reflectance minima and maxima of the externally coupled Fabry-Perot cavity, are presented and discussed. Tuning the externally coupled Fabry-Perot cavity strongly modifies the optical Hall effect signatures, which provides a new degree of freedom for optical Hall effect experiments in addition to frequency, angle of incidence, and magnetic field direction and strength.

[The Onco-hematology clinical research unit at the Geneva University Hospital: example of a fruitful public-private partners]. / L'Unité de recherche clinique en onco-hématologie aux HUG: un exemple réussi de partenariat public-privé.

A better understanding of the molecular deregulation leading to carcinogenesis allows the development of numerous novel targeted therapeutic candidates. Clinical research in oncology is a critical step to evaluate in a thorough manner the safety and efficacy of these innovative compounds. During the last four years the fruitful partnership between the Geneva University Hospitals and the Dr. Henri Dubois-Ferriere Dinu Lipatti Foundation lead to a dedicated clinical research unit for cancer patients with a staff of ten people. Since 2010, more than 300 patients were enrolled in more than 70 distinct clinical trials evaluating novel therapies for both solid tumors and hematologic malignancies. Interestingly, classical cytostatic drugs now represent only a small fraction of the new anti-cancer therapies in the pipeline.

Near-infrared characterization of gallium nitride photonic-crystal waveguides and cavities.

We report the design and optical characterization of fully suspended wire waveguides and photonic crystal (PhC) membranes fabricated on a gallium nitride layer grown on silicon substrate operating at 1.5 µm. W1-type PhC waveguides are coupled with suspended wires and are investigated using a standard end-fire setup. The experimental and theoretical dispersion properties of the propagating modes in the wires and photonic-crystal waveguides are shown. Modified L3 cavities with quality factors of up to 2200 and heterostructure cavities with quality factors of up to 5400 are experimentally demonstrated.

Pinning and depinning of the polarization of exciton-polariton condensates at room temperature.

A room temperature polariton condensate realized in a microcavity with embedded GaN quantum wells emits linearly polarized light at threshold with the plane of polarization pinned to one of the crystallographic axes. With increasing pumping power, a depinning of the polarization is observed resulting in a progressive decrease of the polarization degree of the emitted light. This depinning is understood in terms of polariton-polariton repulsion competing with the static disorder potential effect. The polarization behavior differs from that of conventional lasers where the polarization degree usually increases as a function of pumping power.

Optical and structural properties of an Eu implanted gallium nitride quantum dots/aluminium nitride superlattice.

GaN/AIN structures made of GaN quantum dots (QDs) separated by AIN spacer layers, were doped with Europium by ion implantation. Rutherford Backscattering/Channelling measurements showed that Eu is incorporated mainly on near-substitutional cation sites within the superlattice region. Only slight deterioration of the crystal quality and no intermixing of the different layers are observed after implantation and annealing. After thermal annealing, photoluminescence associated with Eu3+ ions was observed. From its behaviour under different photon energy excitation and sample temperature we concluded that the Eu-related emitting centres are located inside the GaN QDs or dispersed in the GaN and AIN buffer or spacer layers. The 624 nm PL line, associated with Eu-doped GaN QDs, shows very low thermal quenching, suggesting recombination of confined carriers through rare-earth ion excitation.

Spontaneous polarization buildup in a room-temperature polariton laser.

We observe the buildup of strong (approximately 50%) spontaneous vector polarization in emission from a GaN-based polariton laser excited by short optical pulses at room temperature. The Stokes vector of emitted light changes its orientation randomly from one excitation pulse to another, so that the time-integrated polarization remains zero. This behavior is completely different from any previous laser. We interpret this observation in terms of the spontaneous symmetry breaking in a Bose-Einstein condensate of exciton polaritons.

Room-temperature polariton lasing in semiconductor microcavities.

We observe a room-temperature low-threshold transition to a coherent polariton state in bulk GaN microcavities in the strong-coupling regime. Nonresonant pulsed optical pumping produces rapid thermalization and yields a clear emission threshold of 1 mW, corresponding to an absorbed energy density of 29 microJ cm-2, 1 order of magnitude smaller than the best optically pumped (In,Ga)N quantum-well surface-emitting lasers (VCSELs). Angular and spectrally resolved luminescence show that the polariton emission is beamed in the normal direction with an angular width of +/-5 degrees and spatial size around 5 microm.

Recent interview-based measures of competency to stand trial: a critical review augmented with research data.

Forensic experts are frequently asked to conduct competency-to-stand trial evaluations and address the substantive prongs propounded in Dusky v. United States (1960). In understanding its application to competency evaluations, alternative conceptualizations of Dusky are critically examined. With Dusky providing the conceptual framework, three interview-based competency measures are reviewed: the Georgia Court Competency Test (GCCT), the MacArthur Competence Assessment Tool-Criminal Adjudication (Mac-CAT-CA), and the Evaluation of Competency to Stand Trial-Revised (ECST-R). This review has a twin focus on reliability of each measure and its correspondence to Dusky prongs. The current review is augmented by new factor analytic data on the MacCAT-CA and ECST-R. The article concludes with specific recommendations for competency evaluations.

Photoluminescence properties of multiple stacked planes of GaN/AlN quantum dots studied by near-field optical microscopy.

We have studied the photoluminescence properties of GaN quantum dots with submicrometre lateral resolution by means of near-field scanning optical microscopy. The instrument operated at room temperature and was implemented for near-ultra-violet spectroscopy in the illumination-mode configuration. The analysed sample consisted of several stacked planes of GaN/AlN quantum dots grown by molecular beam epitaxy on Si(111) substrate. The photoluminescence maps showed islands in the micrometre range emitting at different wavelengths, confirming the atomic force microscopy studies on the morphology of similar uncapped samples.

Dimensions of AIDS knowledge and risky sexual practices: a study of northern Thai males.

The relation between AIDS-related knowledge and sexual risk-taking for a sample of young men living in northern Thailand was examined. Data were collected during the fall of 1991. The sample of 1472 men includes university students, soldiers, store clerks, and laborers. Recent commercial sex patronage was variable among the subgroups, and consistent condom use among these recent patrons was far from universal. Several important misunderstandings among our respondents regarding the AIDS virus were identified. These misconceptions were most common among men of relatively low socioeconomic status (laborers and soldiers). Factor analysis identified four distinct domains of AIDS knowledge among the student and soldier groups: knowledge about the mechanics of contagion, knowledge about the consequences of infection, knowledge about appropriate strategies for avoiding the virus, and knowledge regarding inappropriate strategies for avoiding the virus. In multivariate logistic regression, knowledge about inappropriate strategies and knowledge about contagion were the only two domains predictive of recent commercial sex patronage: Men with a relatively good understanding regarding the inefficacy of inappropriate strategies and the mechanics of contagion had lower odds of recent commercial sex patronage compared with men who had a relatively poor understanding of these domains of AIDS knowledge. In the condom use analysis, knowledge about both appropriate and inappropriate strategies was predictive of consistent condom use among recent commercial sex patrons. Thus programs should attempt to improve knowledge about strategies for avoiding the virus and the mechanics of contagion. Special efforts should be made to debunk existing myths about the perceived effectiveness of inappropriate strategies.

Socio-demographic correlates, HIV/AIDS-related cofactors, and measures of same-sex sexual behaviour among northern Thai male soldiers.

We use data from an anonymous self-administered 1991 survey of military personnel in northern Thailand to estimate overall levels of and socio-demographic differentials in same-sex sexual behaviour in this population. Additionally, we examine the relationship between sexual experience with another male and a variety of outcomes relevant to HIV prevention and policy. Overall, 16.3 per cent of the sexually active soldiers report ever having had anal or oral sex with other males. Same-sex sexual behaviour in this sample is positively associated with several indicators of higher socio-economic status. All of the men who report having had sex with other men report having had vaginal intercourse with females as well. Comparison of our estimate of same-sex sexual behaviour with those obtained from two similar samples drawn in 1991 suggests that the lower estimates observed in the other two studies are largely due to differences in data collection methods. Regarding the HIV/AIDS-related outcomes we examined, men who have had sex with other men are significantly more likely than those who have not to have ever injected drugs, to personally know someone with HIV/AIDS, to have had sex with a female prostitute in the last six months, and to have had a sexually transmitted disease in the last six months. In this sample, men who have had sex with other men are also less knowledgeable about HIV/AIDS than are men who have not. These results are discussed in terms of their implications for HIV-prevention policy in Thailand.

Two views of risky sexual practices among northern Thai males: the Health Belief Model and the Theory of Reasoned Action.

We apply the Health Belief Model (HBM) and the Theory of Reasoned Action (TRA) to an analysis of unsafe sexual practices (inconsistent condom use with commercial sex workers) among men living in a high HIV-prevalence area. The empirical analysis is based primarily on a survey of sexual practices that was conducted by the authors during the fall of 1991. The survey sample includes university undergraduates, soldiers, clerks, and laborers living in Chiang Mai, Thailand. There is much overlap between the two theories, and both provide useful frameworks for examining condom use in this population. However, the Bayes Information Criterion (BIC) approach provides very strong evidence that TRA is the more plausible model, given the data. The success of TRA appears to be due to its more adequate incorporation of peer group effects. Other covariates positively associated with consistent condom use in the multivariate models include knowledge about the consequences of HIV infection, knowledge about the benefits of condom use for preventing infection, and positive attitudes about condoms.

Sexual activity among never-married men in northern Thailand.

We use data collected in 1991 to investigate sexual activity among never-married men in Thailand, with a focus on age at first intercourse, characteristics of sexual partners, and conditions under which men visit prostitutes. We sampled men from a broad spectrum of northern Thai society, including university undergraduates, soldiers, and semi-skilled/unskilled workers. We found that except for the students, the majority of each subsample is sexually experienced; prostitutes are the most common type of sexual partner for all groups. Alcohol consumption is associated with several measures of sexual activity. Condom use with prostitutes varies among the subsamples. Among men who have both prostitute and nonprostitute partners, the majority of those who do not use condoms with prostitutes also do not use condoms with their nonprostitute partners. We consider the implications of these results for the AIDS epidemic in Thailand.