Optimism Experiment and Development of Space-qualified Seismometers in France

The OPTIMISM experiment will put two magnetometers and two seismometers on the Martian floor in 1995, within the framework of the Mars '94 mission. The seismometers are put within the two small surface stations. The seismometer sensitivity will be better than 10 exp -9 g at 1 Hz, 2 orders of magnitude higher than the Viking seismometer sensitivity. A priori waveform modeling for seismic signals on Mars shows that it will be sufficient to detect quakes with a seismic moment greater than 10 exp 15 Nm everywhere on Mars. Such events, according to the hypothesis of a thermoelastic cooling of the Martian lithosphere, are expected to occur at a rate close to one per week and may therefore be observed within the l-year lifetime of the experiment. Other aspects of the experiment are discussed

Dynamics of Charge Leakage From Self-assembled CdTe Quantum Dots

We study the leakage dynamics of charge stored in an ensemble of CdTe quantum dots embedded in a field-effect structure. Optically excited electrons are stored and read out by a proper time sequence of bias pulses. We monitor the dynamics of electron loss and find that the rate of the leakage is strongly dependent on time, which we attribute to an optically generated electric field related to the stored charge. A rate equation model quantitatively reproduces the results.Comment: 4 pages, submitted to Applied Physics Letter

Optical manipulation of a single Mn spin in a CdTe-based quantum dot

A system of two coupled CdTe quantum dots, one of them containing a single Mn ion, was studied in continuous wave and modulated photoluminescence, photoluminescence excitation, and photon correlation experiments. Optical writing of information in the spin state of the Mn ion has been demonstrated, using orientation of the Mn spin by spin-polarized carriers transferred from the neighbor quantum dot. Mn spin orientation time values from 20 ns to 100 ns were measured, depending on the excitation power. Storage time of the information in the Mn spin was found to be enhanced by application of a static magnetic field of 1 T, reaching hundreds of microseconds in the dark. Simple rate equation models were found to describe correctly static and dynamical properties of the system.Comment: 4 pages, 3 figure

Child Maltreatment, Exposure to Violence, and Adolescent Weapon Carrying

This study examined associations between child maltreatment, violence exposure, and gender in predicting subsequent adolescent weapon carrying. Data from the National Survey of Child and Adolescent Well- Being, a nationally representative longitudinal study of families in contact with the child welfare system, were used. Participants included 821 youth who were followed over five years. Results from a logistic regression suggested that male youth who reported physical abuse at baseline were less likely to report carrying a weapon any time across the follow up period, while physical abuse did not predict weapon carrying in females. These counterintuitive findings demonstrated a complex relationship between violence exposure and subsequent risk behaviors among a vulnerable population of youth

Microstructure and Dielectric Properties of Barium-vanadate Glasses

AbstractThe ac and dc conductivity in barium-vanadate glasses was investigated as a function of temperature and frequency with the use of impedance spectroscopy. The topography and microstructure of glasses were investigated by the means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. The XRD results show that all samples are amorphous but microscopy investigation reveals that glasses with greater amount of V2O5 contain nanostructures. The influence of V2O5 quantity on dielectric properties was checked. The activation energy of dc conduction process was evaluated. On the basis of Jonscher universal dielectric response the temperature dependence of conductivity parameters were determined and compared to theoretical models collected by Elliott

Influence of exciton spin relaxation on the photoluminescence spectra of semimagnetic quantum dots

We present a comprehensive experimental and theoretical studies of photoluminescence of single CdMnTe quantum dots with Mn content x ranging from 0.01 to 0.2. We distinguish three stages of the equilibration of the exciton-Mn ion spin system and show that the intermediate stage, in which the exciton spin is relaxed, while the total equilibrium is not attained, gives rise to a specific asymmetric shape of the photoluminescence spectrum. From an excellent agreement between the measured and calculated spectra we are able to evaluate the exciton localization volume, number of paramagnetic Mn ions, and their temperature for each particular dot. We discuss the values of these parameters and compare them with results of other experiments. Furthermore, we analyze the dependence of average Zeeman shifts and transition linewidths on the Mn content and point out specific processes, which control these values at particular Mn concentrations.Comment: submitted to Phys. Rev.

Mapping of quantum well eigenstates with semimagnetic probes

We present results of transmission measurements on CdTe quantum wells with thin semimagnetic CdMnTe probe layers embedded in various positions along the growth axis. The presence of the probes allow us to map the probability density functions by two independent methods: analyzing the exciton energy position and the exciton Zeeman splitting. We apply both approaches to map the first three quantum well eigenstates and we find that both of them yield equally accurate results.Comment: Accepted for publication in Physical Review