Ka-band Ga-As FET noise receiver/device development

The development of technology for a 30 GHz low noise receiver utilizing GaAs FET devices exclusively is discussed. This program required single and dual-gate FET devices, low noise FET amplifiers, dual-gate FET mixers, and FET oscillators operating at Ka-band frequencies. A 0.25 micrometer gate FET device, developed with a minimum noise figure of 3.3 dB at 29 GHz and an associated gain of 7.4 dB, was used to fabricate a 3-stage amplifier with a minimum noise figure and associated gain of 4.4 dB and 17 dB, respectively. The 1-dB gain bandwidth of this amplifier extended from below 26.5 GHz to 30.5 GHz. A dual-gate mixer with a 2 dB conversion loss and a minimum noise figure of 10 dB at 29 GHz as well as a dielectric resonator stabilized FET oscillator at 25 GHz for the receiver L0. From these components, a hybrid microwave integrated circuit receiver was constructed which demonstrates a minimum single-side band noise figure of 4.6 dB at 29 GHz with a conversion gain of 17 dB. The output power at the 1-dB gain compression point was -5 dBm

Local magnetometry at high fields and low temperatures using InAs Hall sensors

We characterize the temperature (0.3⩽T⩽300 K), magnetic field(0⩽H⩽80 kOe), and thickness (0.1, 0.5, and 2.5 μm) dependence of the Hall response of high purity InAs epilayers grown using metalorganic chemical vapor deposition. The high sensitivity, linearity, and temperature independence of the response make them attractive for local Hall probe magnetometry, and uniquely qualified for high field applications below liquid helium temperatures. As a stringent test of performance, we use a six element micron-sized array to monitor the internal field gradient during vortex avalanches at milliKelvin temperatures in a single crystal of YBa_2Cu_3O_(7−δ)

Mental health service acceptability for the armed forces veteran community

This is the author accepted manuscript. The final version is available from OUP via the DOI in this record Background Despite developments in mental health services for armed forces veterans and family members, barriers to access associated with poor levels of acceptability regarding service provision remain. Adapting a Step 2 mental health service based on low-intensity cognitive behavioural therapy (CBT) interventions to represent a familiar context and meet the needs of the armed forces veteran community may serve to enhance acceptability and reduce help-seeking barriers. Aims To examine acceptability of a Step 2 low-intensity CBT mental health service adapted for armed forces veterans and family members provided by a UK Armed Forces charity. Methods Qualitative study using individual semi-structured interviews with armed forces veterans and family members of those injured or becoming unwell while serving in the British Armed Forces. Data analysis was undertaken using thematic alongside disconfirming case analysis. Results Adapting a Step 2 mental health service for armed forces veterans and family members enhanced acceptability and promoted help-seeking. Wider delivery characteristics associated with Step 2 mental health services within the Improving Access to Psychological Therapies (IAPT) programme also contributed to service acceptability. However, limitations of Step 2 mental health service provision were also identified. Conclusion A Step 2 mental health service adapted for armed forces veterans and family members enhances acceptability and may potentially overcome help-seeking barriers. However, concerns remain regarding ways to accommodate the treatment of post-traumatic stress disorder and provide support for family members.Help for Heroe

Ambipolar charge injection and transport in a single pentacene monolayer island

Electrons and holes are locally injected in a single pentacene monolayer island. The two-dimensional distribution and concentration of the injected carriers are measured by electrical force microscopy. In crystalline monolayer islands, both carriers are delocalized over the whole island. On disordered monolayer, carriers stay localized at their injection point. These results provide insight into the electronic properties, at the nanometer scale, of organic monolayers governing performances of organic transistors and molecular devices.Comment: To be published in Nano Letter

Efficient Bayesian inference for natural time series using ARFIMA processes

Many geophysical quantities, such as atmospheric temperature, water levels in rivers, and wind speeds, have shown evidence of long memory (LM). LM implies that these quantities experience non-trivial temporal memory, which potentially not only enhances their predictability, but also hampers the detection of externally forced trends. Thus, it is important to reliably identify whether or not a system exhibits LM. In this paper we present a modern and systematic approach to the inference of LM. We use the flexible autoregressive fractional integrated moving average (ARFIMA) model, which is widely used in time series analysis, and of increasing interest in climate science. Unlike most previous work on the inference of LM, which is frequentist in nature, we provide a systematic treatment of Bayesian inference. In particular, we provide a new approximate likelihood for efficient parameter inference, and show how nuisance parameters (e.g., short-memory effects) can be integrated over in order to focus on long-memory parameters and hypothesis testing more directly. We illustrate our new methodology on the Nile water level data and the central England temperature (CET) time series, with favorable comparison to the standard estimators. For CET we also extend our method to seasonal long memory

Structure and distribution of the slope fish community in the vicinity of the sub-Antarctic Prince Edward Archipelago

Demersal fish community structure, distribution and trophic relationships on the slope (depth range 200–1500 m) of the sub-Antarctic Prince Edward Islands and surrounding sea rises were investigated during a pilot survey conducted in April 2001 onboard fishing vessel MV Iris. A total of 56 fish taxa were collected during the survey, of which 44 were identified to the species level, seven to the genus level and five to the family level. Among the identified taxa, 36 constituted new records for the area investigated. Total catch per unit effort (cpue) during the survey ranged from 1•1 to 241•2 individuals h 1. Both average fish diversity and total cpue positively correlated with trawling depth. Overall, mean sampling depth and near-bottom temperature explained 56% of total fish cpue. Hierarchal cluster analysis identified three distinct fish assemblages with pronounced dominant species. Major shifts in fish community composition occurred at 500–600 m and 800–900 m depth strata and could probably be a result of physical and biological vertical zonation. Analysis of the diet of selected fish species showed that they were generalist feeders, consuming predominantly pelagic, including epipelagic, meso- and benthopelagic, prey. Diets of six species and nitrogen stable isotope signatures of 22 species revealed that with a few exceptions most fishes occupied the fourth trophic level and were tertiary consumers. Wide variability in carbon isotopic signatures is discussed with respect to alternative, e.g. possible importance of high Antarctic and chemoautotrophic v. photoautotrophic sub-Antarctic primary production, organic matter sources at the base of deep-sea food webs

100 years of chemistry at Rhodes University

The history of Grahamstown is well documented and two books deal with the history of Rhodes University.1,2 Although the Chemistry Department was one of the founding departments, coverage in the official histories is minimal and sometimes inaccurate or misleading. The Rhodes University Centenary is an appropriate time to look back on some of the achievements of the department and some of its graduates over the past 100 years

A Survey for Circumstellar Disks Around Young Substellar Objects

(Abridged) We have completed the first systematic survey for disks around spectroscopically identified young brown dwarfs and very low mass stars. We have obtained L'-band (3.8 um) imaging for 38 very cool objects in IC 348 and Taurus. Our targets span spectral types from M6 to M9.5 (~100 to ~15 Mjup). Using the objects' measured spectral types and extinctions, we find that most of our sample (77%+/-15%) possess intrinsic IR excesses, indicative of disks. Because the excesses are modest, conventional analyses using only IR colors would have missed most of the sources with excesses. The observed IR excesses are correlated with Halpha emission, consistent with a common accretion disk origin. The excesses can be explained by disk reprocessing of starlight alone; the implied accretion rates are at least an order of magnitude below typical values for classical T Tauri stars. The observed distribution of IR excesses suggests the presence of inner disk holes. The disk frequency appears to be independent of the mass and age. In the same star-forming regions, disks around brown dwarfs are at least as long-lived (~3 Myr) as disks around the T Tauri stars. Altogether, the frequency and properties of young circumstellar disks appear to be similar from the stellar regime down to the substellar and planetary-mass regime. This provides prima facie evidence of a common origin for most stars and brown dwarfs.Comment: ApJ, in press, 28 pages. Minor change to the online, abridged version of the abstract. No change to the actual pape

Role of autobiographical memory in patient response to cognitive behavioural therapies for depression: protocol of an individual patient data meta-analysis.

This is the final version. Available from the publisher via the DOI in this record.INTRODUCTION: Cognitive behavioural therapies (CBTs) are one of the most effective treatments for major depression. However, ~50% of individuals do not adequately respond to intervention and of those who do remit from a depressive episode, over 50% will experience later relapse. Identification of patient-level factors which moderate treatment response may ultimately help to identify cognitive barriers that could be targeted to improve treatment efficacy. This individual patient data meta-analysis explores one such potential moderator-the ability to retrieve specific, detailed memories of the autobiographical past-as cognitive-based therapeutic techniques draw heavily on the ability to use specific autobiographical information to challenge the dysfunctional beliefs which drive depression. METHODS AND ANALYSIS: We have formed a collaborative network which will contribute known datasets. This will be supplemented by datasets identified through literature searches in Medline, PsycInfo, Web of Science, the Cochrane Central Register of Controlled Trials and WHO trials database between December 2018 and February 2019. Inclusion criteria are delivery of a cognitive or cognitive behavioural therapy for major depression, and measurement of autobiographical memory retrieval at preintervention. Primary outcomes are depressive symptoms and clinician-rated diagnostic status at postintervention, along with autobiographical memory specificity at postintervention. Secondary outcomes will consider each of these variables at follow-up. All analyses will be completed using random-effects models employing restricted maximum likelihood estimation. Risk of bias in included studies will be measured using the Revised Cochrane Risk of Bias Tool. ETHICS AND DISSEMINATION: The findings will be published in a peer-reviewed journal. Study results will contribute to better understanding of the role of autobiographical memory in patient response to CBTs, and may help to inform personalised medicine approaches to treatment of depression. PROSPERO REGISTRATION NUMBER: CRD42018109673.Economic and Social Research Council (ESRC