Shaping Current Waveforms for direct Modulation of Semiconductor Lasers

We demonstrate a technique for shaping current inputs for the direct modulation of a semiconductor laser for digital communication. The introduction of shaped current inputs allows for the suppression of relaxation oscillations and the avoidance of dynamical memory in the physical laser device, i.e., the output will not be influenced by previously communicated information. On the example of time-optimized bits, the possible performance enhancement for high data rate communications is shown numerically.Comment: 8 pages, 6 figures, to be published in IEEE Journal of Quantum Electronic

User perceptions of multi-source feedback tools for junior doctors

Context:  The effectiveness of multi-source feedback (MSF) tools, which are increasingly important in medical careers, will be influenced by their users’ attitudes. This study compared perceptions of two tools for giving MSF to UK junior doctors, of which one provides mainly textual feedback and one provides mainly numerical feedback. We then compared the perceptions of three groups, including: trainees; raters giving feedback, and supervisors delivering feedback. Methods:  Postal questionnaires about the usability, usefulness and validity of a feedback system were distributed to trainees, raters and supervisors across the north of England. Results:  Questionnaire responses were analysed to compare opinions of the two tools and among the different user groups. Overall there were few differences. Attitudes towards MSF in principle were positive and the tools were felt to be usable, but there was little agreement that they could effectively identify doctors in difficulty or provide developmental feedback. The text-oriented tool was rated as more useful for giving feedback on communication and attitude, and as more useful for identifying a doctor in difficulty. Raters were more positive than other users about the usefulness of numerical feedback, but, overall, text was felt to be more useful. Some trainees expressed concern that feedback was based on insufficient knowledge of their work. This was not supported by raters’ responses, although many did use indirect information. Trainees selected raters mainly for the perceived value of their feedback, but also based on personal relationships and the simple pragmatics of getting a tool completed. Discussion:  Despite positive attitudes to MSF, the perceived effectiveness of the tools was low. There are small but significant preferences for textual feedback, although raters may prefer numerical scales. Concerns about validity imply that greater awareness of contextual and psychological influences on feedback generation is necessary to allow the formative benefits of MSF to be optimised and to negate the risk of misuse in high-stakes contexts

The Relationship of Coronal Mass Ejections to Streamers

We have examined images from the Large Angle Spectroscopic Coronagraph (LASCO) to study the relationship of Coronal Mass Ejections (CMEs) to coronal streamers. We wish to test the suggestion (Low 1996) that CMEs arise from flux ropes embedded in a streamer erupting, thus disrupting the streamer. The data span a period of two years near sunspot minimum through a period of increased activity as sunspot numbers increased. We have used LASCO data from the C2 coronagraph which records Thomson scattered white light from coronal electrons at heights between 1.5 and 6R_sun. Maps of the coronal streamers have been constructed from LASCO C2 observations at a height of 2.5R_sun at the east and west limbs. We have superposed the corresponding positions of CMEs observed with the C2 coronagraph onto the synoptic maps. We identified the different kinds of signatures CMEs leave on the streamer structure at this height (2.5R_sun). We find four types of CMEs with respect to their effect on streamers: 1. CMEs that disrupt the streamer 2. CMEs that have no effect on the streamer, even though they are related to it. 3. CMEs that create streamer-like structures 4. CMEs that are latitudinally displaced from the streamer. This is the most extensive observational study of the relation between CMEs and streamers to date. Previous studies using SMM data have made the general statement that CMEs are mostly associated with streamers, and that they frequently disrupt it. However, we find that approximately 35% of the observed CMEs bear no relation to the pre-existing streamer, while 46% have no effect on the observed streamer, even though they appear to be related to it. Our conclusions thus differ considerably from those of previous studies.Comment: Accepted, Journal of Geophysical Research. 8 figs, better versions at http://www.science.gmu.edu/~prasads/streamer.htm

Fluxtube model atmospheres and Stokes V zero-crossing wavelengths

First results of the inversion of Stokes I and V profiles from plage regions near disk center are presented. Both low and high spatial resolution spectra of FeI 6301.5 and FeI 6302.5 A obtained with the Advanced Stokes Polarimeter (ASP) have been considered for analysis. The thin flux tube approximation, implemented in an LTE inversion code based on response functions, is used to describe unresolved magnetic elements. The code allows the simultaneous and consistent inference of all atmospheric quantities determining the radiative transfer with the sole assumption of hydrostatic equilibrium. By considering velocity gradients within the tubes we are able to match the full ASP Stokes profiles. The magnetic atmospheres derived from the inversion are characterized by the absence of significant motions in high layers and strong velocity gradients in deeper layers. These are essential to reproduce the asymmetries of the observed profiles. Our scenario predicts a shift of the Stokes V zero-crossing wavelengths which is indeed present in observations made with the Fourier Transform Spectrometer.Comment: To appear in ApJ Letters (1997) (in press

SST/CRISP Observations of Convective Flows in a Sunspot Penumbra

Context. Recent discoveries of intensity correlated downflows in the interior of a sunspot penumbra provide direct evidence for overturning convection, adding to earlier strong indications of convection from filament dynamics observed far from solar disk center, and supporting recent simulations of sunspots. Aims. Using spectropolarimetric observations obtained at a spatial resolution approaching 0'.'1 with the Swedish 1-m Solar Telescope (SST) and its spectropolarimeter CRISP, we investigate whether the convective downflows recently discovered in the C i line at 538.03 nm can also be detected in the wings of the Fe i line at 630.15 nm Methods. We make azimuthal fits of the measured LOS velocities in the core and wings of the 538 nm and 630 nm lines to disentangle the vertical and horizontal flows. To investigate how these depend on the continuum intensity, the azimuthal fits are made separately for each intensity bin. By using spatially high-pass filtered measurements of the LOS component of the magnetic field, the flow properties are determined separately for magnetic spines (relatively strong and vertical field) and inter-spines (weaker and more horizontal field). Results. The dark convective downflows discovered recently in the 538.03 nm line are evident also in the 630.15 nm line, and have similar strength. This convective signature is the same in spines and inter-spines. However, the strong radial (Evershed) outflows are found only in the inter-spines. Conclusions. At the spatial resolution of the present SST/CRISP data, the small-scale intensity pattern seen in continuum images is strongly related to a convective up/down flow pattern that exists everywhere in the penumbra. Earlier failures to detect the dark convective downflows in the interior penumbra can be explained by inadequate spatial resolution in the observed data.Comment: Revised and expanded by 2.5 pages. Fig. 14 adde

Safe prescribing training provision for junior doctors: is this optimal?

Background The aim of this study was to determine the training provisions in practical safe prescribing for foundation doctors in NHS hospitals located in the South Thames region. Methods A web-based questionnaire was distributed by e-mail to all 1762 foundation doctors in the South Thames Foundation School (STFS) region. In addition, a separate questionnaire was distributed to prescribing training Leads at 15 NHS Hospital Trusts. Quantitative data were analysed using descriptive statistics and thematic analysis was performed on qualitative data. Results Trainers: 10 Prescribing Leads (67 %) responded. Of the 9 NHS Trusts that offered safe prescribing training in their induction programme, 5 included a practical prescribing session. By the end of the foundation year, 6 NHS Trusts had provided at least one dedicated practical prescribing session for F1s compared with 2 NHS Trusts for F2s. Trainees: A total of 124 foundation trainees (7.2 %) responded (69 F1s and 55 F2s). 87 % of F1s received dedicated training in safe prescribing at their Trust induction (n = 60) in comparison to 49 % of F2s (n = 27). 80 % of F1s (n = 55) had a practical prescribing session during induction versus 27 % of F2s (n = 15). The difference was significant, X2 (1, N = 124) = 34.23, p <0.0001. Emerging themes from qualitative data included, recognition of medical education as a continuum, importance of working relationships with pharmacists and neglect of F2s. Conclusions There appears to be a lack of emphasis on the training of F2 doctors in practical safe prescribing compared with F1 doctors. There should be standardisation of safe prescribing training provisions, particularly in the induction period and for F2 doctors

Endomicroscopic and transcriptomic analysis of impaired barrier function and malabsorption in environmental enteropathy

Introduction: Environmental enteropathy (EE) is associated with growth failure, micronutrient malabsorption and impaired responses to oral vaccines. We set out to define cellular mechanisms of impaired barrier function in EE and explore protective mechanisms. Methods: We studied 49 adults with environmental enteropathy in Lusaka, Zambia using confocal laser endomicroscopy (CLE); histology, immunohistochemistry and mRNA sequencing of small intestinal biopsies; and correlated these with plasma lipopolysaccharide (LPS) and a zinc uptake test. Results: CLE images (median 134 for each study) showed virtually ubiquitous small intestinal damage. Epithelial defects, imaged by histology and claudin 4 immunostaining, were predominantly seen at the tips of villi and corresponded with leakage imaged in vivo by CLE. In multivariate analysis, circulating log-transformed LPS was correlated with cell shedding events (β = 0.83; P = 0.035) and with serum glucagon-like peptide-2 (β = -0.13; P = 0.007). Zinc uptake from a test dose of 25mg was attenuated in 30/47 (64%) individuals and in multivariate analysis was reduced by HIV, but positively correlated with GLP-2 (β = 2.72; P = 0.03). There was a U-shaped relationship between circulating LPS and villus surface area. Transcriptomic analysis identified 23 differentially expressed genes in severe enteropathy, including protective peptides and proteins. Conclusions: Confocal endomicroscopy, claudin 4 immunostaining and histology identify epithelial defects which are probably sites of bacterial translocation, in the presence of which increased epithelial surface area increases the burden of translocation. GLP 2 and other protective peptides may play an important role in mucosal protection in EE