Thermal Spin-Transfer Torques in Magnetoelectronic Devices

We predict that the magnetization direction of a ferromagnet can be reversed by the spin-transfer torque accompanying spin-polarized thermoelectric heat currents. We illustrate the concept by applying a finite-element theory of thermoelectric transport in disordered magnetoelectronic circuits and devices to metallic spin valves. When thermalization is not complete, a spin heat accumulation vector is found in the normal metal spacer, i.e., a directional imbalance in the temperature of majority and minority spins.Comment: Accepted for publication by Physical Review Letter

Spin heat accumulation and its relaxation in spin valves

We study the concept of spin heat accumulation in excited spin valves, more precisely the effective electron temperature that may become spin dependent, both in linear response and far from equilibrium. A temperature or voltage gradient create non-equilibrium energy distributions of the two spin ensembles in the normal metal spacer, which approach Fermi-Dirac functions through energy relaxation mediated by electron-electron and electron-phonon coupling. Both mechanisms also exchange energy between the spin subsystems. This inter-spin energy exchange may strongly affect thermoelectric properties spin valves, leading, e.g., to violations of the Wiedemann-Franz law.Comment: 4 pages, 4 figures, close to published versio

The outcome of Mental Health Care Users admitted under Section 40 of the South African Mental Health Care Act (No 17 of 2002)

Objective: To determine the outcomes of mental health care users (MHCU’s) admitted in terms of Section 40 of the South African Mental Health Care Act (No 17 of 2002) (MHCA) and the factors, if any, that are associated with these outcomes. Method: The study was a retrospective record review of MHCU’s, 18 years and older, referred by the South African Police Service (SAPS) to Chris Hani Baragwanath Hospital (CHBH). All mental health care users handed over to CHBH by SAPS with completed MHCA form 22’s during the period July 2007 to December 2007 were included in the study. The outcomes, demographics and clinical characteristics of these referrals were obtained from hospital records. Results: During the six-month study period, 718 MHCU’s were referred by members of SAPS to the CHBH Emergency Department. Associations were found between discharged MHCU’s and i) being male, ii) being less than 35 years of age, iii) being unemployed, iv) having a lower level of education, v) having a past history of substance abuse and/or vi) a past psychiatric illness. Females were twice as likely to be unemployed and admitted to hospital (either to a psychiatric or general medical ward). MHCU’s diagnosed with delirium were more likely to be admitted intoa medical ward as compared to a psychiatric ward. Conclusion: As has been the case in most countries where police services have been incorporated into mental health acts, South Africa’s new Mental Health Care Act (No 17 of 2002) has resulted in a large number of referrals by the police to mental health services. However, many of these referrals may not be necessary as most MHCU’s end up not being admitted. The characteristics of police referrals suggest that the receiving facility should have thecapacity to identify factors that favour outpatient care (especially substance abuse problems) and divert MHCU’s presenting with such factors to appropriate treatment facilities without admitting them to the hospital.Keywords: Mental Health Care Act; Outcome; Police services; Mental illness, South Afric

Nutritional status of renal transplant patients

Objective. To assess the effect of renal transplantation on the nutritional status of patients.Design. Prospective descriptive study.Setting. Renal Transplant Clinic at Tygerberg Hospital, Western Cape.Subjects. Fifty-eight renal transplant patients from Tygerberg Hospital were enrolled in the study. The sample was divided into two groups of 29 patients each: group 1, less than 28 months post-transplant; and group 2, more than 28 months post-transplant.Outcome measures. Nutritional status assessment comprised biochemical evaluation, a dietary history, anthropometric measurements and a clinical examination.Results. Serum vitamin B6 levels were below normal in 56% of patients from group 1 and 59% from group 2. Vitamin B6 intake, however, was insufficient in only 14% of patients from group 1and10% from group 2. Serum vitamin C levels were below normal in 7% of patients from group 1 and 24% from group 2, while vitamin C intake was insufficient in 21%and14% of patients from groups 1 and 2 respectively. Serum magnesium levels were below normal in 55% of patients from group 1, and in 28% from group 2. Serum albumin and cholesterol levels increased significantly during the post-transplant period in the total sample (P = 0.0001). There was also a significant increase in body mass index (P = 0.0001) during the post-transplant period.Conclusions. Several nutritional abnormalities were observed, which primarily reflect the side-effects of immunosuppressive therapy. The causes, consequences and treatment of the vitamin B6 and vitamin C deficiencies in renal transplant recipients need further investigation

A wideband signal conditioning system for high voltage measurements using a transconductance topology

Thesis (MScEng)--Stellenbosch University, 2000.ENGLISH ABSTRACT: Recent research has shown that standard substation capacitive voltage transformers (CVTs) and current transformers (CTs) can be used for the measurement of wideband high voltage phenomena by employing these apparatus in a transconductance topology. With this topology the voltage waveform can be obtained by integration of the ground return current in the earth straps of the CVT and the CT. This technique does, however, impose unique requirements on the amplification and integration instrumentation due to large dynamic range requirements and the strict offset specifications required for accurate integration. This thesis describes a programmable, wideband signal conditioning system for high voltage (HV) measurements using the transconductance topology. A suitable system topology, optimised to reduce the problems usually associated with grounding and electromagnetic interference (EMI) in HV environments, is proposed. This system consists of an analog signal conditioning subsystem, a digital signal conditioning subsystem and a high speed serial fibre-optic link. The analog signal conditioning subsystem conditions the signals from a sensor to levels suitable for the digitiser of the digital signal conditioning subsystem. The high bandwidth specification of the application made it necessary to consider both discrete and integrated implementation of the analog signal conditioning subsystem. Based on the simulated and laboratory test results of both implementations, the optimum design was chosen for the developed system. The digital signal conditioning subsystem, which performs the integration, as well as the serial optic-fibre link control logic was implemented using programmable logic array (PLA) technology. The digital data is transmitted across the fibre-optic link. This data is then converted back to an analog signal. Keywords: High voltage measurements, Transconductance topology.AFRIKAANSE OPSOMMING: Onlangse navorsing het aangetoon dat standaard substasie kapasitiewe spanningstransformators en stroomtransformators gebruik kan word om wyeband hoogspanningsverskynsels te meet deur hierdie apparatuur in 'n transkonduktansie topologie aan te wend. Met hierdie topologie kan die spanningsgolfvorm verkry word deur die integrasie van die aardstrome in die aardverbindings van die kapasitiewe spanningstransformators en stroomtransformators. Hierdie tegniek stel egter unieke vereistes vir die versterkings- en integrasieinstrumentasie te wyte aan groot dinamiese bereik vereistes en die streng afset spesifikasies wat benodig word vir akkurate integrasie. Hierdie tesis beskryf 'n programmeerbare, wyeband seinkondisioneringstelsel vir hoogspanningsmetings deur van die transkonduktansie topologie gebruik te maak. 'n Geskikte stelseltopologie, wat geoptimiseer is om probleme, wat gewoonlik met aarding en elektromagnetiese interferensie in hoogspanningsomgewings geassosieer word, te verminder, is voorgestel. Die stelsel bestaan uit 'n analoog seinkondisioneringsubstelsel, 'n digitale seinkondisioneringsubstelsel en 'n hoëspoed seriële optiese vesel koppelvlak. Die analoog seinkondisioneringsubstelsel kondisioneer die seine vanaf 'n sensor na geskikte vlakke vir die versyferaar van die digitale seinkondisioneringsubstelsel. Die hoë bandwydte spesifikasie van die toepassing vereis die inagneming van beide diskrete en geïntegreerde implementerings van die analoog seinkondisioneringsubstelsel. Gebaseer op gesimuleerde en laboratorium toetsresultate van beide implementerings is die optimale ontwerp vir die ontwikkelde stelsel gekies. Die digitale seinkondisioneringsubstelsel wat die integrasie uitvoer, asook die seriële optiese vesel koppelvlak beheerlogika is geïmplementeer met behulp van programmeerbare logika skikking tegnologie. Die digitale data word gestuur oor die optiese vesel koppelvlak. Hierdie data word dan terug geskakel na 'n analoog sein. Sleutelwoorde: Hoogspanningsmetings, Transkonduktansie topologie

ALICE: An Automatic Design Flow for eFPGA Redaction

Fabricating an integrated circuit is becoming unaffordable for many semiconductor design houses. Outsourcing the fabrication to a third-party foundry requires methods to protect the intellectual property of the hardware designs. Designers can rely on embedded reconfigurable devices to completely hide the real functionality of selected design portions unless the configuration string (bitstream) is provided. However, selecting such portions and creating the corresponding reconfigurable fabrics are still open problems. We propose ALICE, a design flow that addresses the EDA challenges of this problem. ALICE partitions the RTL modules between one or more reconfigurable fabrics and the rest of the circuit, automating the generation of the corresponding redacted design

Thyroid dysfunction in a cohort of South African children with Down syndrome

Background. While international studies show thyroid dysfunction occurs more commonly in individuals with Down syndrome (DS) than in the general population, there is a paucity of available data from sub-Saharan Africa.Objectives. To document the range of thyroid function in a cohort of South African children with DS, and to assess referral and treatment practices when thyroid dysfunction was present. Methods. A retrospective file-based study of 391 children with DS seen at the genetic clinics at three Johannesburg hospitals from 2003 to 2008. Thyroid function test (TFT) results (thyroid-stimulating hormone and free thyroxine) and demographic details were collected for each child. Endocrine clinic files from two of the hospitals were reviewed for additional referral and treatment information.Results. The majority (83.6%) of children had at least one TFT, in most cases performed between the ages of 2 and 12 months. The most common form of thyroid dysfunction was subclinical hypothyroidism (SCH) (28.7%). Up to one-third of the patients, including several neonates with abnormal results, were not referred for further evaluation and were therefore not receiving the necessary treatment. Inter- laboratory biochemical discrepancies and lack of population-specific reference ranges complicated the interpretation of results. The controversy surrounding whether, and how, to treat SCH influenced treatment practices. Conclusions. Thyroid dysfunction is prevalent in South African children with DS. There is an urgent need to address the laboratory biochemical discrepancies, and to establish guidelines for surveillance and treatment to prevent further irreversible neurological and physical impairment.

Thermoelectric Effects in Magnetic Nanostructures

We model and evaluate the Peltier and Seebeck effects in magnetic multilayer nanostructures by a finite-element theory of thermoelectric properties. We present analytical expressions for the thermopower and the current-induced temperature changes due to Peltier cooling/heating. The thermopower of a magnetic element is in general spin-polarized, leading to spin-heat coupling effects. Thermoelectric effects in spin valves depend on the relative alignment of the magnetization directions and are sensitive to spin-flip scattering as well as inelastic collisions in the normal metal spacer.Comment: 14 pages, 7 figures, 1 table. Publishe