Spatiotemporal Spin Noise Spectroscopy.

We report on the potential of a new spin noise spectroscopy approach by demonstrating all-optical probing of spatiotemporal spin fluctuations. This is achieved by homodyne mixing of a spatially phase-modulated local oscillator with spin-flip scattered light, from which the frequency and wave vector dependence of the spin noise power is unveiled. As a first application of the method we measure the spatiotemporal spin noise in weakly n-doped CdTe layers, from which the electron spin diffusion constant and spin relaxation rates are determined. The absence of spatial spin correlations is also shown for this particular system.

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.

XBP1 mitigates aminoglycoside-induced endoplasmic reticulum stress and neuronal cell death.

Here we study links between aminoglycoside-induced mistranslation, protein misfolding and neuropathy. We demonstrate that aminoglycosides induce misreading in mammalian cells and assess endoplasmic reticulum (ER) stress and unfolded protein response (UPR) pathways. Genome-wide transcriptome and proteome analyses revealed upregulation of genes related to protein folding and degradation. Quantitative PCR confirmed induction of UPR markers including C/EBP homologous protein, glucose-regulated protein 94, binding immunoglobulin protein and X-box binding protein-1 (XBP1) mRNA splicing, which is crucial for UPR activation. We studied the effect of a compromised UPR on aminoglycoside ototoxicity in haploinsufficient XBP1 (XBP1(+/-)) mice. Intra-tympanic aminoglycoside treatment caused high-frequency hearing loss in XBP1(+/-) mice but not in wild-type littermates. Densities of spiral ganglion cells and synaptic ribbons were decreased in gentamicin-treated XBP1(+/-) mice, while sensory cells were preserved. Co-injection of the chemical chaperone tauroursodeoxycholic acid attenuated hearing loss. These results suggest that aminoglycoside-induced ER stress and cell death in spiral ganglion neurons is mitigated by XBP1, masking aminoglycoside neurotoxicity at the organismal level.

Optical stark effect and dressed exciton states in a Mn-doped CdTe quantum dot.

We report on the observation of spin-dependent optically dressed states and the optical Stark effect on an individual Mn spin in a semiconductor quantum dot. The vacuum-to-exciton or the exciton-to-biexciton transitions in a Mn-doped quantum dot are optically dressed by a strong laser field, and the resulting spectral signature is measured in photoluminescence. We demonstrate that the energy of any spin state of a Mn atom can be independently tuned by using the optical Stark effect induced by a control laser. High resolution spectroscopy reveals a power-, polarization-, and detuning-dependent Autler-Townes splitting of each optical transition of the Mn-doped quantum dot. This experiment demonstrates an optical resonant control of the exciton-Mn system.

Optical spin orientation of a single manganese atom in a semiconductor quantum dot using quasiresonant photoexcitation.

An optical spin orientation is achieved for a Mn atom localized in a semiconductor quantum dot using quasiresonant excitation at zero magnetic field. Optically created spin-polarized carriers generate an energy splitting of the Mn spin and enable magnetic moment orientation controlled by the photon helicity and energy. The dynamics and the magnetic field dependence of the optical pumping mechanism show that the spin lifetime of an isolated Mn atom at zero magnetic field is controlled by a magnetic anisotropy induced by the built-in strain in the quantum dots.

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.

Polydispersity during the Formation and Growth of the Stöber Silica Particles from Small-Angle X-Ray Scattering Measurements.

The early stages of formation of Stöber silica particles have been investigated in situ during the hydrolysis and condensation of tetraethylorthosilicate under base-ammonia conditions in different alcoholic solvents. Time-resolved ultra-small-angle X-ray scattering by the entities produced in the solutions is used for structural characterization and monitoring of the growth kinetics of the particles. Our primary focus is to assess the polydispersity of the formed colloidal particles and its evolution as a function of time. We first applied a maximum entropy analysis of the scattering data to determine the size distribution and the time evolution of the size distribution of the colloidal particles. Second, we extended the cumulant method to analyze our earlier small-angle X-ray scattering data (H. Boukari, J. S. Lin, and M. T. Harris, J. Colloid Interface Sci. 194, 311, 1997; Chem. Mater. 9, 2376, 1997) and search for the presence of a distribution of fractal particles. The maximum entropy analysis indicates that there is a continuous nucleation of particles during the synthesis, and that this takes place within a relatively narrow size distribution. The cumulant analysis shows that, except at later times, the data are not adequate to confirm conclusively the presence of a distribution of fractal dimension at any time during the experiment. We discuss the impact of these results on growth kinetic models proposed for this system. Copyright 2000 Academic Press.

Small-Angle X-Ray Scattering Study of the Formation of Colloidal Silica Particles from Alkoxides: Primary Particles or Not?

The formation of colloidal silica particles and the dynamics of the nanostructure of the particles are investigated by small-angle X-ray scattering (SAXS) technique. Solute concentrations of 0.5 M tetraethylorthosilicate (TEOS), 1.1 or 2.2 M water (H2O), and 0.04 or 0.1 M ammonia base (NH3) in ethanol were used to obtain reaction conditions as close to those of the Stober method as possible and to have reaction kinetics that were slow enough to probe the changes in the nanostructure of the growing particles and to obtain good statistics from the SAXS measurements. We measured the changes in the radius of gyration and the fractal dimension as a function of time during growth. Remarkably, we find that, after an induction period, the first particles to appear in the solution have a radius of gyration of approximately 10 nm and are mass fractals characterized by their polymeric, open structure. This stage is followed by an intraparticle densification process and smoothing of the interface, leading to the usual compact nonfractal, stable structures. The growth models proposed so far cannot account for the observed continuous changes of stages during the formation and growth of the particles. Copyright 1997 Academic Press. Copyright 1997Academic Press

Experimental study of the effect of surface defects on the finesse and contrast of a Fabry-Perot interferometer.

While investigating the instrumental function of a Fabry-Perot interferometer [Appl. Opt. 34, 58 (1995), we noticed some variation in finesse and contrast in the measured spectra when a 1.5-mm-diameter aperture was used at various spots within the standard 8-mm aperture. By comparing experimentally determined finesse versus contrast plots for many such spectra with calculated plots, we found spots on the plates that gave non-Airy-function line shapes over the entire order of interference, unlike the Airy line shape we determined previously by using the entire 8-mm aperture. We have reviewed several models that describe the effects of various types of surface defects, such as Gaussian-height distribution of roughness, curvature and tilt of plates, sinusoidal roughness, and asymmetrical roughness on the finesse and contrast. Our experimental results can be accounted for if we assume that the reflectivity is nonuniform over the Fabry-Perot plates and that there is some reasonable contribution that is due to Gaussian roughness, curvature, or tilt.

Line-shape studies for single- and triple-pass Fabry-Perot interferometer systems.

To test the model developed in the preceding paper [Appl. Opt. 34, this issue (1994)] regarding the line shape produced by a Fabry-Perot interferometer system in a multipass mode, we have used three Lorentzian line shapes formed in scattering processes and subjected them to single and triple passes with some variation in the pinhole diameter. In most cases we find good agreement with the calculations with the only adjustable parameter being the single-pass contrast C(1). Where differences occur, plausible explanations are offered.

Closed-form expressions to fit data obtained with a multipass Fabry-Perot interferometer.

We have studied the effect of a multipass Fabry-Perot interferometer (FP) on a scattering line. Here we describe a method that we applied to derive a closed-form expression for a line shape obtained with an ideal, multipass FP. The method reduces the convolution problem between the multipass function and the scattering line to the corresponding single-pass problem. We illustrate the method with a Lorentzian and a damped-harmonic-oscillator line passed through a single-, triple-, and quintuple-pass FP. Furthermore we have applied the method to a study of the effect of the collecting pinhole on a sharp line obtained by multipassing. We show how we used these functions to fit the complete spectra obtained with a single- and triple-pass FP.

Ensayo de evaluación de los cambios producidos por la quimioterapia de corta duración en la atención de los tuberculosis en un dispensario de Argelia / Evaluation assay of the changes produced by short course chemotherapy during tuberculosis care in an ambulatory of Argélia

Intentanse evaluar los cambios producidos por la puesta en marcha y generalización, en 1980, de los regímenes de quimioterapia de corta duración (6 meses), en un sector urbano de la capital de Argelia. El estudio se desarrolló en los dos años (1978 y 1979), que precedieron a la implantación de los regímenos de corta duración y sobre los cuatro años siguientes (1980 a 1983). Las mejorías registradas que parece que deben colocarse en el activo de la disminución de la duración de la quimioterapia, se refieren esencialmente a: - la forma del tratamiento, que es más frecuentemente ambulatoria de entrada, durante el segundo período; - la tasa de curación, que es superior durante todo el segundo período; - las tasas de fallecimiento, de los perdidos de vista y de los enfermos transferidos, que disminuyen de una forma más o menos importante después de la institución de los regímenes de corta duración; - finalmente, las tasas de inasistencia al tratamiento, que disminuyen netamente durante el segundo período. Con la condición de que sean confirmados por un estudio más amplio, nuestros resultados parecen indicar que la disminución de la duración de la quimioterapia de la tuberculosis implica una mejoría substancial en la atención de los tuberculosos sobre el terreno (AU)

Ensayo de evaluación de los cambios producidos por la quimioterapia de corta duración en la atención de los tuberculosis en un dispensario de Argelia / Evaluation assay of the changes produced by short course chemotherapy during tuberculosis care in an ambulatory of Argélia

Intentanse evaluar los cambios producidos por la puesta en marcha y generalización, en 1980, de los regímenes de quimioterapia de corta duración (6 meses), en un sector urbano de la capital de Argelia. El estudio se desarrolló en los dos años (1978 y 1979), que precedieron a la implantación de los regímenos de corta duración y sobre los cuatro años siguientes (1980 a 1983). Las mejorías registradas que parece que deben colocarse en el activo de la disminución de la duración de la quimioterapia, se refieren esencialmente a: - la forma del tratamiento, que es más frecuentemente ambulatoria de entrada, durante el segundo período; - la tasa de curación, que es superior durante todo el segundo período; - las tasas de fallecimiento, de los perdidos de vista y de los enfermos transferidos, que disminuyen de una forma más o menos importante después de la institución de los regímenes de corta duración; - finalmente, las tasas de inasistencia al tratamiento, que disminuyen netamente durante el segundo período. Con la condición de que sean confirmados por un estudio más amplio, nuestros resultados parecen indicar que la disminución de la duración de la quimioterapia de la tuberculosis implica una mejoría substancial en la atención de los tuberculosos sobre el terreno