337 research outputs found
Field effect two-dimensional electron gases in modulation-doped InSb surface quantum wells
We report on transport characteristics of field effect two-dimensional
electron gases in surface indium antimonide quantum wells. A 5 nm thin -InSb
capping layer is shown to promote the formation of reliable, low resistance
Ohmic contacts to surface InSb quantum wells. High quality single-subband
magnetotransport with clear quantized integer quantum Hall plateaus are
observed to filling factor =1 in magnetic fields of up to B=18 T. We show
that the electron density is gate-tunable, reproducible, and stable from
pinch-off to 410 cm, and peak mobilities exceed 24,000
cm/Vs. Rashba spin-orbit coupling strengths up to 130 meV\r{A} are
obtained through weak anti-localization measurements. An effective mass of
0.019 is determined from temperature-dependent magnetoresistance
measurements, and a g-factor of 41 at a density of 3.610
cm is obtained from coincidence measurements in tilted magnetic fields.
By comparing two heterostructures with and without a doping layer beneath the
quantum well, we find that the carrier density is stable with time when doping
in the ternary AlInSb barrier is not present. Finally, the effect of modulation
doping on structural asymmetry between the two heterostructures is
characterized
Nutritional status and HIV in rural South African children.
BACKGROUND: Achieving the Millennium Development Goals that aim to reduce malnutrition and child mortality depends in part on the ability of governments/policymakers to address nutritional status of children in general and those infected or affected by HIV/AIDS in particular. This study describes HIV prevalence in children, patterns of malnutrition by HIV status and determinants of nutritional status. METHODS: The study involved 671 children aged 12-59 months living in the Agincourt sub-district, rural South Africa in 2007. Anthropometric measurements were taken and HIV testing with disclosure was done using two rapid tests. Z-scores were generated using WHO 2006 standards as indicators of nutritional status. Linear and logistic regression analyses were conducted to establish the determinants of child nutritional status. RESULTS: Prevalence of malnutrition, particularly stunting (18%), was high in the overall sample of children. HIV prevalence in this age group was 4.4% (95% CI: 2.79 to 5.97). HIV positive children had significantly poorer nutritional outcomes than their HIV negative counterparts. Besides HIV status, other significant determinants of nutritional outcomes included age of the child, birth weight, maternal age, age of household head, and area of residence. CONCLUSIONS: This study documents poor nutritional status among children aged 12-59 months in rural South Africa. HIV is an independent modifiable risk factor for poor nutritional outcomes and makes a significant contribution to nutritional outcomes at the individual level. Early paediatric HIV testing of exposed or at risk children, followed by appropriate health care for infected children, may improve their nutritional status and survival.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are
HIV and risk of cardiovascular disease in sub-Saharan Africa: Rationale and design of the Ndlovu Cohort Study
First-principles envelope-function theory for lattice-matched semiconductor heterostructures
In this paper a multi-band envelope-function Hamiltonian for lattice-matched
semiconductor heterostructures is derived from first-principles norm-conserving
pseudopotentials. The theory is applicable to isovalent or heterovalent
heterostructures with macroscopically neutral interfaces and no spontaneous
bulk polarization. The key assumption -- proved in earlier numerical studies --
is that the heterostructure can be treated as a weak perturbation with respect
to some periodic reference crystal, with the nonlinear response small in
comparison to the linear response. Quadratic response theory is then used in
conjunction with k.p perturbation theory to develop a multi-band effective-mass
Hamiltonian (for slowly varying envelope functions) in which all interface
band-mixing effects are determined by the linear response. To within terms of
the same order as the position dependence of the effective mass, the quadratic
response contributes only a bulk band offset term and an interface dipole term,
both of which are diagonal in the effective-mass Hamiltonian. Long-range
multipole Coulomb fields arise in quantum wires or dots, but have no
qualitative effect in two-dimensional systems beyond a dipole contribution to
the band offsets.Comment: 25 pages, no figures, RevTeX4; v3: final published versio
Doublet structures in quantum well absorption spectra due to Fano-related interference
In this theoretical investigation we predict an unusual interaction between a
discrete state and a continuum of states, which is closely related to the case
of Fano-interference. It occurs in a GaAs/AlxGa1-xAs quantum well between the
lowest light-hole exciton and the continuum of the second heavy-hole exciton.
Unlike the typical case for Fano-resonance, the discrete state here is outside
the continuum; we use uniaxial stress to tune its position with respect to the
onset of the continuum. State-of-the art calculations of absorption spectra
show that as the discrete state approaches the continuum, a doublet structure
forms which reveals anticrossing behaviour. The minimum separation energy of
the anticrossing depends characteristically on the well width and is unusually
large for narrow wells. This offers striking evidence for the strong underlying
valence-band mixing. Moreover, it proves that previous explanations of similar
doublets in experimental data, employing simple two-state models, are
incomplete.Comment: 21 pages, 5 figures and 5 equations. Accepted for publication in
Physical Review
Occurrence of campylobacter jejuni in diarrhoeic and non-diarrhoeic children in Sao Paulo, Brazil
Eating Fish and Risk of Type 2 Diabetes: A population-based, prospective follow-up study
Objective: To investigate the relation between total fish, type of fish (lean and fatty), and EPA&DHA intake and risk of type 2 diabetes in a population-based cohort. Research design and methods: The analysis included 4,472 Dutch participants aged =55 years without diabetes at baseline. Dietary intake was assessed with a semi-quantitative food frequency questionnaire. Hazard ratios (RR) with 95% confidence intervals (95% CI) were used to examine risk associations adjusted for age, sex, lifestyle, and nutritional factors. Results: After 15 years of follow-up, 463 participants developed type 2 diabetes. Median fish intake, mainly lean fish (81% ), was 10 g/d. Total fish intake was associated positively with risk of type 2 diabetes; the RR was 1.32 (95% CI 1.02, 1.70) in the highest total fish group (=28 g/d) compared with non-fish eaters (p for trend= 0.04). Correspondingly, lean fish intake tended to be associated positively with type 2 diabetes (RR highest group (=23 g/d): 1.30 (95% CI 1.01, 1.68), p for trend= 0.06), but fatty fish was not. No association was observed between EPA&DHA intake and type 2 diabetes (RR highest group (=149.4 mg/d): 1.22 (95% CI 0.97, 1.53)). When additionally adjusted for intake of selenium, cholesterol, and vitamin D this RR decreased to 1.05 (95% CI 0.80, 1.38) (p for trend= 0.77). Conclusion: The findings do not support a beneficial effect of total fish, type of fish, or EPA&DHA intake on the risk of type 2 diabetes. Alternatively, other dietary components, like selenium, and unmeasured contaminants present in fish might explain our result
Is social support associated with hypertension control among Ghanaian migrants in Europe and non-migrants in Ghana? The RODAM study
Hypertension (HTN) control is crucial in preventing HTN-related complications such as stroke and coronary heart disease. Yet, HTN control remains suboptimal particularly among sub-Saharan African (SSA) populations partly due to poor self-management. Self-management of HTN is influenced by social support, but the evidence on the role of social support on HTN control particularly among SSA populations is limited. This study assessed the association between multiple proxies for social support and HTN control among Ghanaians resident in Ghana and Europe. The Research on Obesity and Diabetes among African Migrants (RODAM) study participants with HTN and who self-reported HTN (n = 1327) were included in this analysis. Logistic regression was used to assess the association between proxies of social support and HTN control (SBP < 140 mmHg and DBP < 90 mmHg) with adjustments for age and socioeconomic status (SES). Among Ghanaian males in both Europe and Ghana, cohabiting with more than two persons was associated with increased odds of having HTN controlled. Male hypertensive patients cohabiting with ≥ 5 persons had the highest odds of having HTN controlled after adjustment for age and SES (OR 0.30; 95% CI 0.16–0.57; 0.60; 0.34–1.04, respectively). This association was not observed among females. Relationship status, frequency of religious activity attendance and satisfaction with social support did not show any significant association with HTN control. Our study shows that cohabitation is significantly associated with HTN control but in males only. The other proxies for social support appeared not to be associated with HTN control. Involving persons living with Ghanaian men with HTN in the treatment process may help to improve adherence to HTN treatment. Further research is needed to explore in-depth, how these social support proxies could contribute to improved HTN control among SSA populations
Val103Ile polymorphism of the melanocortin-4 receptor gene (MC4R) in cancer cachexia
<p>Abstract</p> <p>Background</p> <p>At present pathogenic mechanisms of cancer cachexia are poorly understood. Previous evidence in animal models implicates the melanocortin-4 receptor gene (<it>MC4R</it>) in the development of cancer cachexia. In humans, <it>MC4R </it>mutations that lead to an impaired receptor function are associated with obesity; in contrast, the most frequent polymorphism (Val103Ile, rs2229616; heterozygote frequency approximately 2%) was shown to be negatively associated with obesity. We tested if cancer patients that are homo-/heterozygous for the Val103Ile polymorphism are more likely to develop cachexia and/or a loss of appetite than non-carriers of the 103Ile-allele.</p> <p>Methods</p> <p>BMI (body mass index in kg/m<sup>2</sup>) of 509 patients (295 males) with malignant neoplasms was determined; additionally patients were asked about premorbid/pretherapeutical changes of appetite and weight loss. Cachexia was defined as a weight loss of at least 5% prior to initiation of therapy; to fulfil this criterion this weight loss had to occur independently of other plausible reasons; in single cases weight loss was the initial reason for seeing a physician. The average age in years (± SD) was 59.0 ± 14.5 (males: 58.8 ± 14.0, females 59.2 ± 14.0). Blood samples were taken for genotyping of the Val103Ile by PCR- RFLP.</p> <p>Results</p> <p>Most of the patients suffered from lymphoma, leukaemia and gastrointestinal tumours. 107 of the patients (21%) fulfilled our criteria for cancer cachexia. We did not detect association between the Val103Ile polymorphism and cancer cachexia. However, if we exploratively excluded the patients with early leucaemic stages, we detected a trend towards the opposite effect (p < 0.05); heterozygotes for the 103Ile-allele developed cancer cachexia less frequently in comparison to the rest of the study group. Changes of appetite were not associated with the 103Ile-allele carrier status (p > 0.39).</p> <p>Conclusion</p> <p>Heterozygotes for the 103Ile-allele are not more prone to develop cancer cachexia than patients without this allele; possibly, Ile103 carriers might be more resistant to cancer cachexia in patients with solid tumors. Further studies of the melanocortinergic system in cachexia of patients with solid tumors are warranted.</p
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