Investigation into the performance of proximity coupled stacked patches

We investigate the parameters that control the impedance and radiation performance of proximity coupled stacked microstrip patch radiators. In particular we explore the relationship required between the dielectric layers to achieve broadband behavior and also how the dimensions of the stacked radiators and the relative location of the feed can influence the impedance response. Bandwidths in excess of 20% can be achieved with careful layer design. We also investigate the dielectric layer configurations required to achieve broadband impedance responses when higher dielectric constant feed material is used. This latter study is of particular importance when designing MMIC compatible printed antennas

Edge-fed patch antennas with reduced spurious radiation

In this paper, a technique to reduce the spurious feed radiation from edge-fed patch antennas by using a dual thickness substrate is presented. A thin microwave substrate is employed for the feed network, and then a transition is made to a thick substrate for the patch antenna element. The new feeding procedure allows the feed network and antenna elements to be optimized independently. Measured results on a single element prototype exhibit a reduction in the level of cross-polarized fields and decreased pattern distortion whilst preserving a reasonable impedance bandwidth. The technique is also proven to be beneficial in an array environment, as an extensive transmission line feed network is required. We present the theoretical and experimental results of a 1 x 8 edge-fed patch array that utilizes the dual thickness substrate configuration. Significant improvement in the radiation patterns and gain are observed for the new array compared to a standard edge-fed patch array

Comparison of outcome measures for patients with chronic obstructive pulmonary disease (COPD) in an outpatient setting

BACKGROUND: To assist clinicians and researchers in choosing outcome measures for patients with chronic obstructive pulmonary disease attending routine outpatient clinics, a comparative assessment was undertaken of four questionnaires designed to reflect the patients' perception of their physical and emotional health in terms of their feasibility, validity, reliability, and responsiveness to health change. METHODS: Two condition specific questionnaires, the St George's Respiratory Questionnaire (SGRQ) and Guyatt's Chronic Respiratory Questionnaire (CRQ), and two generic questionnaires, the Short Form-36 Health Survey (SF-36) and Euroqol (EQ), were compared for their discriminative and evaluative properties. Spirometric tests and a walking test were also performed. One hundred and fifty six adults who were clinically judged to have COPD and who attended an outpatient chest clinic were assessed at recruitment and six and 12 months later. Patients were also asked whether their health had changed since their last assessment. RESULTS: Completion rates and consistency between items for dimensions of the SGRQ were lower than for dimensions of the other questionnaires. The distributions of responses were skewed for certain dimensions in all questionnaires except the CRQ. Validity was supported for all instruments insofar as patients' scores were associated with differences in disease severity. The generic questionnaires better reflected other health problems. All instruments were reliable over time. The condition specific questionnaires were more responsive between baseline and first follow up visit but this difference did not persist. While certain dimensions of the SF-36 were responsive to patient perceived changes, this did not apply to the derived single index of the EQ. The rating scale of the EQ, however, provided a quick and easy indicator of change. CONCLUSIONS: Evidence from this study supports the CRQ and the SF-36 as comprehensive outcome measures for patients with longstanding COPD

Constraining the properties of neutron star crusts with the transient low-mass X-ray binary Aql X-1

Aql X-1 is a prolific transient neutron star low-mass X-ray binary that exhibits an accretion outburst approximately once every year. Whether the thermal X-rays detected in intervening quiescent episodes are the result of cooling of the neutron star or due to continued low-level accretion remains unclear. In this work we use Swift data obtained after the long and bright 2011 and 2013 outbursts, as well as the short and faint 2015 outburst, to investigate the hypothesis that cooling of the accretion-heated neutron star crust dominates the quiescent thermal emission in Aql X-1. We demonstrate that the X-ray light curves and measured neutron star surface temperatures are consistent with the expectations of the crust cooling paradigm. By using a thermal evolution code, we find that ~1.2-3.2 MeV/nucleon of shallow heat release describes the observational data well, depending on the assumed mass-accretion rate and temperature of the stellar core. We find no evidence for varying strengths of this shallow heating after different outbursts, but this could be due to limitations of the data. We argue that monitoring Aql X-1 for up to ~1 year after future outbursts can be a powerful tool to break model degeneracies and solve open questions about the magnitude, depth and origin of shallow heating in neutron star crusts.Comment: 14 pages, 5 figures, 3 tables, accepted to MNRA

A novel wide-band tunable RF phase shifter using a variable optical directional coupler

We present a novel RF phase-shifter design with a usable bandwidth of 80:1. The design is verified through demonstration of a proof of concept device, consisting of a readily available voltage variable optical coupler fabricated from LiNbO3, combined with an fiber-optic delay line. The design is analyzed theoretically and measurement of the device confirms the predicted range of operation. Methods of extension of this range of operation are discusse

Some genus 3 curves with many points

Using an explicit family of plane quartic curves, we prove the existence of a genus 3 curve over any finite field of characteristic 3 whose number of rational points stays within a fixed distance from the Hasse-Weil-Serre upper bound. We also provide an intrinsic characterization of so-called Legendre elliptic curves

Unsymmetrical shear loading and its influence on the frictional shakedown of incomplete contacts

Published versio

The Azur Decade: A Brief History of Mediterraneans

Millions of words are published every year by and about the peoples of the Mediterranean. Its place at the crux of Europe, the Middle East and North Africa and its historical importance overlaid with presentday relevance means that Mediterraneans are never far from the news. Many cultures, speaking many tongues, have shared interests and concerns, even if the act of sharing often seems more like smash and grab. Yet among all the words and images there are a precious few voices saying just what it is to be a Mediterranean today

Computing Hilbert Class Polynomials

We present and analyze two algorithms for computing the Hilbert class polynomial $H_D$ . The first is a p-adic lifting algorithm for inert primes p in the order of discriminant D < 0. The second is an improved Chinese remainder algorithm which uses the class group action on CM-curves over finite fields. Our run time analysis gives tighter bounds for the complexity of all known algorithms for computing $H_D$, and we show that all methods have comparable run times