Broadband Tuning (170nm) of InGaAs Quantum Well Lasers

The wavelength tuning properties of strained InGaAs quantum well lasers using an external grating for feedback is reported. Tunable laser oscillation has been observed over a range of 170 nm, between 840 and 1010 nm, under pulsed current excitation. The optimal conditions for broadband tunability for the InGaAs lasers are different from GaAs lasers, which is attributed to a difference in spectral gain curves. Together with an optimised GaAs quantum well laser the entire region between 740 and 1010 nm is spanned

Circular polarised microstrip antenna design using segmental methods

Research into the modelling and analysis of microstrip patch antenna have been reported in many studies. These include Transmission Line Modelling, Cavity Modelling, Coplanar Multiport Modelling and Full wave Modelling. Since the electromagnetic field elements are time harmonic, the phasor-form of the Maxwell field equations is used. In this thesis results are presented of the research that has been carried out into the segmental approach for the analysis of the microwave patch antennas. The segmental approach includes the "Segmentation" and the "Desegmentation" methods. In the segmentation method two distinct structural forms have been identified, cascade and shunt types. In the cascade type all consecutive segment elements share a common boundary, while for the shunt type, all appended segment elements have no common boundary. In the case of the shunt type structure a generalised input impedance matrix formula, for any number of appended segment elements, has been obtained. For the desegmentation method a generalised input impedance for any number of deleted segment elements, has been obtained. The above research studies have been applied in the design of a circular polarised two corner deleted square patch microstrip antenna with a single feed. For this structure the design involves both square and triangular patch geometries. The overall patch geometry for circular polarised is determined using perturbation analysis to determine the size of the deleted triangular segment elements. New computationally efficient impedance coupling expressions for the interconnecting port impedances on a rectangle, and, on a right angled isosceles triangle shaped antenna patch have been derived. In the determination of the input impedance of the overall antenna structure the coupling impedances constitute the elements of the individual segment coupling matrices. The matrices are used in a general multiport matrix circuit analysis to obtain the input impedance formula. It is established that, where applicable, the desegmentation method is computationally more efficient than the segmentation method. The new results obtained have been applied to the design of a corner deleted square patch antenna, and, the design procedure is fully described. The computer program implementation evaluates the perturbation quantity, and, the antenna input impedance. The structural properties of the coupling matrices, which are used for efficient computation, are described in detail. All the results from the above work show close agreement with full-wave software simulation and practical results. SIGNIFICANT RESEARCH ACHIEVEMENTS: Both segmentation and desegmentation methods have been studied and it has been shown that the desegmentation approach, when applicable, is in general significantly more computationally efficient. In the segmentation method two structural forms, cascade and shunt have been identified. In the latter case a new generalised input impedance matrix formula has been obtained for any number of appended segment elements. A new generalised input impedance matrix formula has been obtained for any number of deleted segment elements in the desegmentation method. New computationally efficient expressions for the coupling impedances have been derived and used in test applications. New computationally efficient expressions for the offset input impedance of a linear polarised rectangular patch, and, an isosceles right-angled triangular patch have been derived and experimentally verified. A program implementing the design procedure for the corner-deleted truncated square patch circular polarised microstrip antenna has been constructed using MATHCAD programming

Ancestry-Dependent Enrichment of Deleterious Homozygotes in Runs of Homozygosity.

Runs of homozygosity (ROH) are important genomic features that manifest when an individual inherits two haplotypes that are identical by descent. Their length distributions are informative about population history, and their genomic locations are useful for mapping recessive loci contributing to both Mendelian and complex disease risk. We have previously shown that ROH, and especially long ROH that are likely the result of recent parental relatedness, are enriched for homozygous deleterious coding variation in a worldwide sample of outbred individuals. However, the distribution of ROH in admixed populations and their relationship to deleterious homozygous genotypes is understudied. Here we analyze whole-genome sequencing data from 1,441 unrelated individuals from self-identified African American, Puerto Rican, and Mexican American populations. These populations are three-way admixed between European, African, and Native American ancestries and provide an opportunity to study the distribution of deleterious alleles partitioned by local ancestry and ROH. We re-capitulate previous findings that long ROH are enriched for deleterious variation genome-wide. We then partition by local ancestry and show that deleterious homozygotes arise at a higher rate when ROH overlap African ancestry segments than when they overlap European or Native American ancestry segments of the genome. These results suggest that, while ROH on any haplotype background are associated with an inflation of deleterious homozygous variation, African haplotype backgrounds may play a particularly important role in the genetic architecture of complex diseases for admixed individuals, highlighting the need for further study of these populations

Therapy-based exercise from the perspective of adult patients: a qualitative systematic review conducted using an ethnographic approach

© The Author(s) 2019.Objectives: Many patients do not meet recommended levels of therapy-based exercise. This review aims to explore how adult patients view being prescribed therapy-based exercise, the information/education they are given and receive and if/how they independently practise and adhere. Design: A qualitative systematic review conducted using an ethnographic approach and in accordance with the PRISMA statement. Sources: PubMed, CINAHL, SCOPUS and EMBASE databases (01 January 2000–31 December 2018). Methods: Qualitative studies with a focus on engagement/adherence with therapy-based exercise were included. Data extraction and quality appraisal were undertaken by two reviewers. Results were discussed and data synthesized. Results: A total of 20,294 titles were screened, with data extracted from 39 full texts and data from 18 papers used to construct three themes. ‘The Guidance received’ suggests that the type of delivery desired to support and sustain engagement was context-dependent and individually situated. ‘The Therapist as teacher’ advocates that patients see independent therapy-based exercise as a shared activity and value caring, kind and professional qualities in their therapist. ‘The Person as learner’ proposes that when having to engage with and practise therapy-based exercise because of ill-health, patients often see themselves as new learners who experience fear and uncertainty about what to do. Patients may have unacknowledged ambivalences about learning that impact on engagement and persistence. Conclusion: The quality of the interaction between therapists and patients appears integral to patients engaging with, and sustaining practice of, rehabilitation programmes. Programmes need to be individualized, and health care professionals need to take patients’ previous experiences and ambivalences in motivation and empowerment into account.Peer reviewe

On-board demux/demod

To make satellite channels cost competitive with optical cables, the use of small, inexpensive earth stations with reduced antenna size and high powered amplifier (HPA) power will be needed. This will necessitate the use of high e.i.r.p. and gain-to-noise temperature ratio (G/T) multibeam satellites. For a multibeam satellite, onboard switching is required in order to maintain the needed connectivity between beams. This switching function can be realized by either an receive frequency (RF) or a baseband unit. The baseband switching approach has the additional advantage of decoupling the up-link and down-link, thus enabling rate and format conversion as well as improving the link performance. A baseband switching satellite requires the demultiplexing and demodulation of the up-link carriers before they can be switched to their assigned down-link beams. Principles of operation, design and implementation issues of such an onboard demultiplexer/demodulator (bulk demodulator) that was recently built at COMSAT Labs. are discussed

Synthesis and Characterization of Some Triphenyltin(IV) Complexes from Sterically Crowded [((E)-1-{2-Hydroxy-5-[(E)-2-(aryl)-1-diazenyl]phenyl}methylidene)amino]acetate Ligands and Crystal Structure Analysis of a Tetrameric Triphenyltin(IV) Compound

Four new triphenyltin(IV) complexes containing [((E)-1-{2-hydroxy-5-[(E)-2-(aryl)-1-diazenyl]phenyl}methylidene) amino]acetate ligands (L) have been synthesized with formulations of Ph3SnLH. They have been studied by multinuclear (1H, 13C, 119Sn) NMR, 119Sn Mössbauer and IR spectroscopy. A full characterization of one complex, Ph3SnL1H (1), was accomplished by single crystal X-ray crystallography, which revealed the compound to be a macrocyclic tetramer. In the tetramer, the five coordinate tin atoms have distorted trigonal bipyramidal geometries with the three phenyl groups occupying equatorial positions, while an oxygen atom of the carboxylate group of one L ligand and the oxide O-atom (formerly the hydroxy group) of a second L ligand in an apical positions. The carboxylate ligands bridge adjacent tin atoms and coordinate in the zwitterionic form with the phenolic proton moved to the nearby nitrogen atom. 119Sn NMR results indicate that the tetrameric structures of the complexes in the solid state, in which the tin atoms are five-coordinated, dissociate in solution to yield four coordinate monomeric species