Polarization insensitivity of AlGaAs/GaAs interdiffused quantum wells

Modeling is used to show that interdiffusion can generate a polarization independent parabolic-like quantum well. Criteria to achieve the parabolic-like quantum wells by interdiffusion are discussed. The results indicated that interdiffused quantum wells can produce equal eigen-state spacing, polarization insensitive Stark shift and modulation characteristics similar to an ideal parabolic quantum well. The design process to obtain polarization insensitive ON- and OFF- states in the parabolic-like interdiffused quantum wells is discussed. The predicted modulation depth is comparable to those measured using parabolic quantum wells. The diffused quantum wells have the advantage of using an as-grown rectangular quantum well with post-growth annealing to tailor its confinement profile. These features suggest that the interdiffused quantum well structure can be use to produce polarization insensitive electro-absorptive modulation.published_or_final_versio

Interdiffusion contributions in optimized surface-acoustic-wave quantum-well modulators

The electro-absorption of AlGaAs/GaAs diffused quantum well (DFQW) modulator using surface acoustic wave (SAW) QW interactions was studied theoretically. The modulator was also optimized through the use of both the steeper potential at the device surface for modulation and a long λSAW and a low power SAW. The non-uniform feature of the SAW induced potential was also taken into account in optimizing the device structure. Interdiffusion took place into the W stack to modify modulation performance so that λop and the optical properties of the optimized structure can be further modified. The modulation efficiency of an incident optical field depended on the guiding properties in the QW active region.published_or_final_versio

The ACS LCID project IV: detection of the RGB bump in isolated galaxies of the Local Group

We report the detection and analysis of the red giant branch luminosity function bump in a sample of isolated dwarf galaxies in the Local Group. We have designed a new analysis approach comparing the observed color-magnitude diagrams with theoretical best-fit color-magnitude diagrams derived from precise estimates of the star formation histories of each galaxy. This analysis is based on studying the difference between the V-magnitude of the RGB bump and the horizontal branch at the level of the RR Lyrae instability strip (Delta_vhbb) and we discuss here a technique for reliably measuring this quantity in complex stellar systems. By using this approach, we find that the difference between the observed and predicted values of Delta_vhbb is +0.13 +/- 0.14 mag. This is smaller, by about a factor of two, than the well-known discrepancy between theory and observation at low metallicity commonly derived for Galactic globular clusters. This result is confirmed by a comparison between the adopted theoretical framework and empirical estimates of the Delta_vhbb parameter for both a large database of Galactic globular clusters and for four other dSph galaxies for which this estimate is available in the literature. We also investigate the strength of the red giant branch bump feature (R_bump), and find very good agreement between the observed and theoretically predicted R_bump values. This agreement supports the reliability of the evolutionary lifetimes predicted by theoretical models of the evolution of low-mass stars.Comment: Accepted for publication on Ap

The effect of age and font size on reading text on handheld computers

Though there have been many studies of computer based text reading, only a few have considered the small screens of handheld computers. This paper presents an investigation into the effect of varying font size between 2 and 16 point on reading text on a handheld computer. By using both older and younger participants the possible effects of age were examined. Reading speed and accuracy were measured and subjective views of participants recorded. Objective results showed that there was little difference in reading performance above 6 point, but subjective comments from participants showed a preference for sizes in the middle range. We therefore suggest, for reading tasks, that designers of interfaces for mobile computers provide fonts in the range of 8-12 point to maximize readability for the widest range of users

Methylmercury Contamination of Laboratory Animal Diets

In the midst of research focusing on the neurodevelopmental effects of mercury vapor in rats, we detected significant levels of mercury (30–60 ng/g) in the blood of nonexposed control subjects. We determined that the dominant form of the mercury was organic and that the standard laboratory chow we used in our vivarium was the source of the contamination. The dietary levels were deemed of potential biologic significance, even though they might have fallen below the limits of measurement specified by the supplier. All investigators employing animals in research must assess such potential contamination because dietary agents may alter a) conclusions based on intentionally administered doses, b) outcomes by interacting with other agents that are the primary focus of the research, and c) outcomes of research unrelated to the toxic effects of experimentally administered agents

Using a model of group psychotherapy to support social research on sensitive topics

This article describes the exploratory use of professional therapeutic support by social researchers working on a sensitive topic. Talking to recently bereaved parents about the financial implications of their child's death was expected to be demanding work, and the research design included access to an independent psychotherapeutic service. Using this kind of professional support is rare within the general social research community, and it is useful to reflect on the process. There are likely to be implications for collection and interpretation of data, research output and the role and experience of the therapist. Here, the primary focus is the potential impact on researcher well-being

Measurement of the electron cloud properties by means of a multi-strip detector in the CERN SPS

Electron cloud effects presently limit the performances of the CERN SPS with LHC type beams [1] and are of concern for the LHC itself [2]. Electron multipacting in the SPS produces dramatic dynamic pressure increases and strong transverse instabilities [3]. In the LHC the electron cloud is expected to significantly increase the heat load in the cryogenics system. Estimates of these effects are based on computer simulations of the electron cloud build-up and of its spatial distribution in field free regions and in strong magnetic fields. The accuracy of such simulations is therefore a key issue for component design and for the definition of the operating strategies for the LHC. In 2001 a multi-strip detector has been installed in the SPS to study the electron cloud and to provide experimental data to validate the models and to better constrain their input parameters. After a description of the monitor characteristics and of its associated electronics an overview of its performance and of the results of the measurements conducted with different proton beam parameters are presented. The measurements are compared with simulation results. Possible monitor upgrades are also discussed

Prototyping of automotive components with variable width and depth

Roll forming enables the manufacturing of longitudinal components from materials that combine high strength with limited formability and is increasingly used in the automotive industry for the manufacture of structural and crash components. An extension of conventional roll forming is the Flexible Roll Forming (FRF) process where the rolls are no longer fixed in space but are free to move which enables the forming of components with variable cross section over the length of the part. Even though FRF components have high weight saving potential the technology has found only limited application in the automotive industry. A new flexible forming facility has recently been developed that enables proof of concept studies and the production of FRF prototypes before a full FRF line is built; this may lead to a wider uptake of the FRF technology in the automotive industry. In this process, the pre-cut blank is placed between two clamps and the whole set up moves back and forth; a forming roll that is mounted on a servo-controlled platform with six degrees of freedom forms the pre-cut blank to the desired shape. In this study an initial forming concept for the flexible roll forming of an automotive component with variable height is developed using COPRA® FEA RF. This is followed by performing experimental prototyping studies on the new concept forming facility. Using the optical strain measurement system Autogrid Compact, material deformation, part shape and wrinkling severity are analysed for some forming passes and compared with the numerical results. The results show that the numerical model gives a good representation of material behaviour and that with increasing forming severity wrinkling issues need to be overcome in the process

Networks of gravitational wave detectors and three figures of merit

This paper develops a general framework for studying the effectiveness of networks of interferometric gravitational wave detectors and then uses it to show that enlarging the existing LIGO-VIRGO network with one or more planned or proposed detectors in Japan (LCGT), Australia, and India brings major benefits, including much larger detection rate increases than previously thought... I show that there is a universal probability distribution function (pdf) for detected SNR values, which implies that the most likely SNR value of the first detected event will be 1.26 times the search threshold. For binary systems, I also derive the universal pdf for detected values of the orbital inclination, taking into account the Malmquist bias; this implies that the number of gamma-ray bursts associated with detected binary coalescences should be 3.4 times larger than expected from just the beaming fraction of the gamma burst. Using network antenna patterns, I propose three figures of merit that characterize the relative performance of different networks... Adding {\em any} new site to the planned LIGO-VIRGO network can dramatically increase, by factors of 2 to 4, the detected event rate by allowing coherent data analysis to reduce the spurious instrumental coincident background. Moving one of the LIGO detectors to Australia additionally improves direction-finding by a factor of 4 or more. Adding LCGT to the original LIGO-VIRGO network not only improves direction-finding but will further increase the detection rate over the extra-site gain by factors of almost 2, partly by improving the network duty cycle... Enlarged advanced networks could look forward to detecting three to four hundred neutron star binary coalescences per year.Comment: 38 pages, 7 figures, 2 tables. Accepted for publication in Classical and Quantum Gravit

Particles and fields in fluid turbulence

The understanding of fluid turbulence has considerably progressed in recent years. The application of the methods of statistical mechanics to the description of the motion of fluid particles, i.e. to the Lagrangian dynamics, has led to a new quantitative theory of intermittency in turbulent transport. The first analytical description of anomalous scaling laws in turbulence has been obtained. The underlying physical mechanism reveals the role of statistical integrals of motion in non-equilibrium systems. For turbulent transport, the statistical conservation laws are hidden in the evolution of groups of fluid particles and arise from the competition between the expansion of a group and the change of its geometry. By breaking the scale-invariance symmetry, the statistically conserved quantities lead to the observed anomalous scaling of transported fields. Lagrangian methods also shed new light on some practical issues, such as mixing and turbulent magnetic dynamo.Comment: 165 pages, review article for Rev. Mod. Phy