Probing the light hole/heavy hole switching with correlated magneto-optical spectroscopy and chemical analysis on a single quantum dot.

A whole series of complementary studies have been performed on the same single nanowire containing a quantum dot: cathodoluminescence spectroscopy and imaging, micro-photoluminescence spectroscopy under magnetic field and as a function of temperature, and energy-dispersive x-ray spectrometry and imaging. The ZnTe nanowire was deposited on a Si3N4 membrane with Ti/Al patterns. The complete set of data shows that the CdTe quantum dot features the heavy-hole state as a ground state, although the compressive mismatch strain promotes a light-hole ground state as soon as the aspect ratio is larger than unity (elongated dot). A numerical calculation of the whole structure shows that the transition from the heavy-hole to the light-hole configuration is pushed toward values of the aspect ratio much larger than unity by the presence of a (Zn, Mg)Te shell, and that the effect is further enhanced by a small valence band offset between the semiconductors in the dot and around it.

A tomography diagnostic in the visible spectrum to investigate turbulence and coherent modes in the linear plasma column Mistral.

In this paper, we describe a newly installed tomography diagnostic on the linear magnetized plasma device Mistral. The diagnostic is composed of 128 lines of sight covering a 20 cm diameter section and an acquisition rate up to 1 MHz. The measurements are done in the visible spectrum using silicon photomultiplier arrays that require a lower amplification voltage than photomultiplier tubes for similar gains and have a fast response. Tomographic reconstruction of a rotating plasma mode is shown to illustrate the capabilities of the diagnostic.

Quantitative Reconstructions of 3D Chemical Nanostructures in Nanowires.

Energy dispersive X-ray spectrometry is used to extract a quantitative 3D composition profile of heterostructured nanowires. The analysis of hypermaps recorded along a limited number of projections, with a preliminary calibration of the signal associated with each element, is compared to the intensity profiles calculated for a model structure with successive shells of circular, elliptic, or faceted cross sections. This discrete tomographic technique is applied to II-VI nanowires grown by molecular beam epitaxy, incorporating ZnTe and CdTe and their alloys with Mn and Mg, with typical size down to a few nanometers and Mn or Mg content as low as 10%.

Atomic-like spin noise in solid-state demonstrated with manganese in cadmium telluride.

Spin noise spectroscopy is an optical technique which can probe spin resonances non-perturbatively. First applied to atomic vapours, it revealed detailed information about nuclear magnetism and the hyperfine interaction. In solids, this approach has been limited to carriers in semiconductor heterostructures. Here we show that atomic-like spin fluctuations of Mn ions diluted in CdTe (bulk and quantum wells) can be detected through the Kerr rotation associated to excitonic transitions. Zeeman transitions within and between hyperfine multiplets are clearly observed in zero and small magnetic fields and reveal the local symmetry because of crystal field and strain. The linewidths of these resonances are close to the dipolar limit. The sensitivity is high enough to open the way towards the detection of a few spins in systems where the decoherence due to nuclear spins can be suppressed by isotopic enrichment, and towards spin resonance microscopy with important applications in biology and materials science.

Structure and morphology in diffusion-driven growth of nanowires: the case of ZnTe.

Gold-catalyzed ZnTe nanowires were grown at low temperature by molecular beam epitaxy on a ZnTe(111) B buffer layer, under different II/VI flux ratios, including with CdTe insertions. High-resolution electron microscopy and energy-dispersive X-ray spectroscopy (EDX) gave information about the crystal structure, polarity, and growth mechanisms. We observe, under stoichiometric conditions, the simultaneous presence of zinc-blende and wurtzite nanowires spread homogeneously on the same sample. Wurtzite nanowires are cylinder-shaped with a pyramidal-structured base. Zinc-blende nanowires are cone-shaped with a crater at their base. Both nanowires and substrate show a Te-ended polarity. Te-rich conditions favor zinc-blende nanowires, while Zn-rich suppress nanowire growth. Using a diffusion-driven growth model, we present a criterion for the existence of a crater or a pyramid at the base of the nanowires. The difference in nanowire morphology indicates lateral growth only for zinc-blende nanowires. The role of the direct impinging flux on the nanowire's sidewall is discussed.

Magnetization dynamics down to a zero field in dilute (Cd,Mn)Te quantum wells.

The evolution of the magnetization in (Cd,Mn)Te quantum wells after a short pulse of magnetic field was determined from the giant Zeeman shift of spectroscopic lines. The dynamics in the absence of a static magnetic field was found to be up to 3 orders of magnitude faster than that at 1 T. Hyperfine interaction and strain are mainly responsible for the fast decay. The influence of a hole gas is clearly visible: at zero field anisotropic holes stabilize the system of Mn ions, while in a magnetic field of 1 T they are known to speed up the decay by opening an additional relaxation channel.

Observation of strong-coupling effects in a diluted magnetic semiconductor Ga1-xFexN.

The giant Zeeman splitting of free excitons is measured in Ga(1-x)Fe(x)N. Magneto-optical and magnetization data imply the ferromagnetic sign and a reduced magnitude of the effective p-d exchange energy governing the interaction between Fe(3+) ions and holes in GaN, N_{0}beta(app)=+0.5+/-0.2 eV. This finding corroborates the recent suggestion that the strong p-d hybridization specific to nitrides and oxides leads to significant renormalization of the valence band exchange splitting.

Geometrical effects on the optical properties of quantum dots doped with a single magnetic atom.

The emission spectra of individual self-assembled quantum dots containing a single magnetic Mn atom differ strongly from dot to dot. The differences are explained by the influence of the system geometry, specifically the in-plane asymmetry of the quantum dot and the position of the Mn atom. Depending on both these parameters, one has different characteristic emission features which either reveal or hide the spin state of the magnetic atom. The observed behavior in both zero field and under magnetic field can be explained quantitatively by the interplay between the exciton-manganese exchange interaction (dependent on the Mn position) and the anisotropic part of the electron-hole exchange interaction (related to the asymmetry of the quantum dot).

Probing the spin state of a single magnetic ion in an individual quantum dot.

The magnetic state of a single magnetic ion (Mn2+) embedded in an individual quantum dot is optically probed using microspectroscopy. The fine structure of a confined exciton in the exchange field of a single Mn2+ ion (S=5/2) is analyzed in detail. The exciton-Mn2+ exchange interaction shifts the energy of the exciton depending on the Mn2+ spin component and six emission lines are observed at zero magnetic field. Magneto-optic measurements reveal that the emission intensities in both circular polarizations are controlled by the Mn2+ spin distribution imposed by the exchange interaction with the exciton, the magnetic field, and an effective manganese temperature which depends on both the lattice temperature and the density of photocreated carriers. Under magnetic field, the electron-Mn interaction induces a mixing of the bright and dark exciton states.

Light and electric field control of ferromagnetism in magnetic quantum structures.

A strong influence of illumination and electric bias on the Curie temperature and saturation value of the magnetization is demonstrated for semiconductor structures containing a modulation-doped p-type Cd(0.96)Mn(0.04)Te quantum well placed in various built-in electric fields. It is shown that both light beam and bias voltage generate an isothermal and reversible crossover between the paramagnetic and ferromagnetic phases, in the way that is predetermined by the structure design. The observed behavior is in quantitative agreement with the expectations for systems, in which ferromagnetic interactions are mediated by the weakly disordered two-dimensional hole liquid.

Large magnetoresistance effect due to spin injection into a nonmagnetic semiconductor.

A novel magnetoresistance effect, due to the injection of a spin-polarized electron current from a dilute magnetic into a nonmagnetic semiconductor, is presented. The effect results from the suppression of a spin channel in the nonmagnetic semiconductor and can theoretically yield a positive magnetoresistance of 100%, when the spin flip length in the nonmagnetic semiconductor is sufficiently large. Experimentally, our devices exhibit up to 25% magnetoresistance.

[Non-complicated Horton's disease: initial treatment with methylprednisolone 500 mg/day bolus for three days followed by 20 mg/day prednisone-equivalent. Evaluation of 15 patients]. / Maladie de Horton non compliquée: traitement initial par trois bolus de 500 mg de méthylprednisolone suivis de 20 mg/j d'équivalent-prednisone. Evaluation chez 15 patients.

PURPOSE: To assess the efficacy and tolerance of three methylprednisolone boluses (500 mg/d) followed by a standard dose of prednisolone, 20 mg/d, as the initial treatment of non-complicated giant-cell arteritis. METHOD: A retrospective study of 15 cases. RESULTS: Six men and nine women with a mean age of 70.9 years were treated and followed for 41.5 months. Initial mean ESR was 83 mm; mean C-reactive protein level was 94.6 mg/L. The boluses were well tolerated, excepted in one patient who developed acute psychosis. After initiating the oral treatment, two patients presented signs of clinical relapse during the first month, and were given higher doses of corticosteroids. At 1 month, 12 patients were asymptomatic, nine of whom had normalized ESR and CRP. Mean ESR was 23; mean CRP was 13 mg/L. At 3 months, the mean prednisone dose delivered was 18.2 mg/d. Mean ESR was 12 mm. The cumulative prednisone dose given during the first year was 5,349 (+/- 2,512) mg. In the 13 patients who necessitated no more than 20 mg/d prednisone, no sequelae of giant-cell arteritis, no fractures nor major treatment intolerance occurred-during the first 2 years of treatment. Treatment was stopped in eight patients after a mean duration of 48.6 months. CONCLUSION: Treatment with pulse methylprednisolone 500 mg/d for 3 days followed by 20 mg/d oral prednisone could be a valuable corticosteroid-sparing strategy in many patients with uncomplicated temporal arteritis.

Zener model description of ferromagnetism in zinc-blende magnetic semiconductors

Ferromagnetism in manganese compound semiconductors not only opens prospects for tailoring magnetic and spin-related phenomena in semiconductors with a precision specific to III-V compounds but also addresses a question about the origin of the magnetic interactions that lead to a Curie temperature (T(C)) as high as 110 K for a manganese concentration of just 5%. Zener's model of ferromagnetism, originally proposed for transition metals in 1950, can explain T(C) of Ga(1-)(x)Mn(x)As and that of its II-VI counterpart Zn(1-)(x)Mn(x)Te and is used to predict materials with T(C) exceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.

DNA fragmentation induced in lymphocytes by gamma irradiation or dexamethasone: inhibition by diethyldithiocarbamate (DTC), potentiated by zinc.

Apoptosis is a process of physiological cell death characterized by DNA fragmentation, chromatin condensation, loss of membrane asymmetry and cell lethality. In the present study, apoptosis induced in thymocytes by dexamethasone or gamma irradiation is evaluated by flow cytometry, gel electrophoresis and other techniques. Treatment of thymocytes with DTC or zinc shows that these products can inhibit radiation- or dexamethasone-induced apoptosis. Moreover, a synergistic effect is observed by using associations of both products (5 microM DTC + 50 microM ZnSO4): ZnSO4 potentiates the effect of DTC at concentrations for which the molecules used separately show a low efficacy. These results indicate that DNA fragmentation induced by dexamethasone or irradiation in thymocytes share some identical mechanisms.

A stakeholder's communication approach for balancing hospital information systems investment priorities.

The Stakeholders Communication Approach is aimed at supporting the decision process in the choice of information systems (IS) applications at the start of a hospital IS planning cycle. It promotes discussion among senior management, key stakeholders, IS Department management, end users and the Accounting Department using specific tools and a negotiation process. The IS applications portfolio profile allows visualizing the hospital's strategic position and directions for development of IS. End users' responses to a questionnaire give a measure of "user functional value added" (UFVA) to inform management about the effectiveness and usefulness of the systems implemented. Stakeholders' evaluation of recently completed IS applications uses UFVA and cost, both separately and combined, along with assessment of strategic changes, to edify the priority-balancing process for deciding on investments in further IS applications.

Diagnosing strategic performance of the hospital information systems planning cycle.

Hospital information systems planning (HISP) involves large expenditures. Often the evaluation of its performance is unstructured, giving no direction for future strategic choices for information systems (IS) development. This article formulates the challenge facing senior management when it must define priorities for the next IS planning cycle. New IS applications are selected to enhance the IS portfolio profile and the users' functionality, taking account of the past and anticipated response to resources invested. A methodology, new tools, and analyses for conducting the diagnosis of the last planning cycle are described.

Pathologic elements in the planning of information systems: the case of hospitals in Quebec.

The existing usage of information technology for information systems in hospitals draws attention to the fact that: (a) health care units which operate sophisticated numerical instrumentation to support medical activities rarely employ computers for the management of their operations and (b) despite the availability of affordable information technologies (microcomputers, networks, etc.), few hospitals include such elements as health care unit management in the development of their information systems portfolio. Is this paradoxical situation a result of the planning methodologies or of factors affecting their use? Or can it be attributed to the failure of present planning methodologies to incorporate the diversity of computerization approaches of the various stakeholders involved? If this is the case, untapped potential computerization possibilities exist that could lead to the development of hospital services and increased organizational efficiency.

[Inter-radicular osteotomies. Apropos of 1 observation]. / Les ostéotomies inter-radiculaires. A propos d'une observation.

Although more common in recent years, inter-radicular osteotomies remain operations which pose the problem of the prognosis of the displaced teeth. In the light of one special case, the authors sought to assess these risks, in relation to the functional and aesthetic benefits of the surgical procedure.

[2 new methods of retention in sagittal osteotomy of the ascending ramus]. / Deux procédés nouveaux de contention dans les ostéotomies sagittales de branches montantes

The authors present two techniques designed to ensure contact between the two bone cortical plates in sagittal osteotomy of the superior ramus of the mandible used in the correction of prognathia and retrognathia. The first technique requires the use of a special suture guide, designed to aid in steel wire osteosynthesis. The second involves a bolt fixed by a screw, the role of which is to keep the external cortex applied against the medial fragment.