Electronic structure of strained InP/GaInP quantum dots

We calculate the electronic structure of nm scale InP islands embedded in $Ga_{0.51}In_{0.49}P$. The calculations are done in the envelope approximation and include the effects of strain, piezoelectric polarization, and mixing among 6 valence bands. The electrons are confined within the entire island, while the holes are confined to strain induced pockets. One pocket forms a ring at the bottom of the island near the substrate interface, while the other is above the island in the GaInP. The two sets of hole states are decoupled. Polarization dependent dipole matrix elements are calculated for both types of hole states.Comment: Typographical error corrected in strain Hamiltonia

Geothermal Development in Malawi -a Country Update

ABSTRACT Malawi, one of the poorest countries in Africa, has major electricity generating difficulties, due to limited conventional fossil fuel resources and an over reliance on one form of electricity generation, viz. hydroelectricity, with very low generation capacity. Due to its location within the East African Rift System (EARS), one of the hottest geothermal zones in the world, it is endowed with significant potential geothermal energy resources. In recent decades, there has been major global growth in geothermal energy utilization, both in direct utilization applications and in electricity generation. However, despite its favourable location, Malawi has been slow in harnessing its potentially significant geothermal resources. Geological investigations of the Malawi sector of the EARS indicates that the Malawi Rift is controlled by N-S rift parallel normal faults, that also control upwards migration of the geothermal waters feeding hot springs, which occur along the length of the rift. The hot springs with the most potential for electricity generation occurs mainly in the northern half of the country and are thought to be sourced from porous sedimentary reservoirs at depth, either deeply buried young Neogene rift floor deposits or older Karoo sandstones, occurring in fault-bound basins within the Precambrian framework of the country. A recent investigation to catalogue all of the hot springs in Malawi has led to the identification of 15 previously undocumented springs including the third hottest spring recorded in the investigation. This exercise has resulted in the delineation of 6 or 7 groups of springs with appropriate temperatures and geological settings that suggest a potential for electricity generation. These merit further detailed surface geological, geophysical and geochemical exploration and monitoring, which should be undertaken, prior to any decisions on drilling. Other lower temperature hot springs in the country have the potential for utilisation for various direct applications, which could bring major benefits to local communities. Icelandic International Development Agency (ICEIDA) is positive to support Malawi in coming up with proper legal frameworks in geothermal development while the World Bank, under the Energy Sector Support Programme (ESSP), is supporting in the development of Terms of Reference for pre-feasibility studies in geothermal development. Some reputable international institutions, through their fact finding missions, have also made advances to assist in the exercise. Major challenges hindering geothermal development in Malawi have been the absence of both technical and financial capacity, and the lack of government leadership in spearheading an assessment of the geothermal resources of the country. This has resulted in a spirit of individualism, coupled with an absence of collaborative cooperation between government agencies, research organisations and institutes of higher learning, which has led to a failure to share information, consequent duplication of tasks and unnecessary waste of resources. The Government of Malawi claims to have instituted a geothermal working group, consisting of all the stakeholders from government, industry, research organisations and teaching institutions which seems to be non-existent due to its non-functionality. Malawi also needs to develop its technical capacity through specialized geothermal training programmes such as the United Nations University -Geothermal Training Program (UNU-GTP) in Iceland and the Postgraduate Certificate in Geothermal Energy Technology (PGCertGeothermTech) at the University of Auckland, New Zealand. With support from UNU -GTP and Government of Kenya, eleven Malawians have undergone a three week course in surface exploration of geothermal resources and one underwent a six month training fellowship to study geothermal and geological exploration while another one underwent a six month training fellowship to study geothermal utilization

A survey on worries of pregnant women - testing the German version of the Cambridge Worry Scale

Background: Pregnancy is a transition period in a woman's life characterized by increased worries and anxiety. The Cambridge Worry Scale (CWS) was developed to assess the content and extent of maternal worries in pregnancy. It has been increasingly used in studies over recent years. However, a German version has not yet been developed and validated. The aim of this study was (1) to assess the extent and content of worries in pregnancy on a sample of women in Germany using a translated and adapted version of the Cambridge Worry Scale, and (2) to evaluate the psychometric properties of the German version. Methods: We conducted a cross-sectional study and enrolled 344 pregnant women in the federal state of Baden-Wurttemberg, Germany. Women filled out structured questionnaires that contained the CWS, the Spielberger-State-Trait-Anxiety Inventory (STAI), as well as questions on their obstetric history. Antenatal records were also analyzed. Results: The CWS was well understood and easy to fill in. The major worries referred to the process of giving birth (CWS mean value 2.26) and the possibility that something might be wrong with the baby (1.99), followed by coping with the new baby (1.57), going to hospital (1.29) and the possibility of going into labour too early (1.28). The internal consistency of the scale (0.80) was satisfactory, and we found a four-factor structure, similar to previous studies. Tests of convergent validity showed that the German CWS represents a different construct compared with state and trait anxiety but has the desired overlap. Conclusions: The German CWS has satisfactory psychometric properties. It represents a valuable tool for use in scientific studies and is likely to be useful also to clinicians

The influence of surface stress on the equilibrium shape of strained quantum dots

The equilibrium shapes of InAs quantum dots (i.e., dislocation-free, strained islands with sizes >= 10,000 atoms) grown on a GaAs (001) substrate are studied using a hybrid approach which combines density functional theory (DFT) calculations of microscopic parameters, surface energies, and surface stresses with elasticity theory for the long-range strain fields and strain relaxations. In particular we report DFT calculations of the surface stresses and analyze the influence of the strain on the surface energies of the various facets of the quantum dot. The surface stresses have been neglected in previous studies. Furthermore, the influence of edge energies on the island shapes is briefly discussed. From the knowledge of the equilibrium shape of these islands, we address the question whether experimentally observed quantum dots correspond to thermal equilibrium structures or if they are a result of the growth kinetics.Comment: 7 pages, 8 figures, submitted to Phys. Rev. B (February 2, 1998). Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

The role of usability engineering in the development of an intelligent decision support system

This paper presents an overview of the usability engineering process for the development of a personalised clinical decision support system for the management of type 1 diabetes. The tool uses artificial intelligence (AI) techniques to provide insulin bolus dose advice and carbohydrate recommendations that adapt to the individual. We describe the role of human factors and user-centred design in the creation of medical systems that must adhere to international standards. We focus specifically on the formative evaluation stage of this process. The preliminary analysis of data shows promising results

Equilibrium shapes and energies of coherent strained InP islands

The equilibrium shapes and energies of coherent strained InP islands grown on GaP have been investigated with a hybrid approach that has been previously applied to InAs islands on GaAs. This combines calculations of the surface energies by density functional theory and the bulk deformation energies by continuum elasticity theory. The calculated equilibrium shapes for different chemical environments exhibit the {101}, {111}, {\=1\=1\=1} facets and a (001) top surface. They compare quite well with recent atomic-force microscopy data. Thus in the InP/GaInP-system a considerable equilibration of the individual islands with respect to their shapes can be achieved. We discuss the implications of our results for the Ostwald ripening of the coherent InP islands. In addition we compare strain fields in uncapped and capped islands.Comment: 10 pages including 6 figures. Submitted to Phys. Rev. B. Related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

GP-initiated preconception counselling in a randomised controlled trial does not induce anxiety

BACKGROUND: Preconception counselling (PCC) can reduce adverse pregnancy outcome by addressing risk factors prior to pregnancy. This study explores whether anxiety is induced in women either by the offer of PCC or by participation with GP-initiated PCC. METHODS: Randomised trial of usual care versus GP-initiated PCC for women aged 18–40, in 54 GP practices in the Netherlands. Women completed the six-item Spielberger State Trait Anxiety Inventory (STAI) before PCC (STAI-1) and after (STAI-2). After pregnancy women completed a STAI focusing on the first trimester of pregnancy (STAI-3). RESULTS: The mean STAI-1-score (n = 466) was 36.4 (95% CI 35.4 – 37.3). Following PCC there was an average decrease of 3.6 points in anxiety-levels (95% CI, 2.4 – 4.8). Mean scores of the STAI-3 were 38.5 (95% CI 37.7 – 39.3) in the control group (n = 1090) and 38.7 (95% CI 37.9 – 39.5) in the intervention group (n = 1186). CONCLUSION: PCC from one's own GP reduced anxiety after participation, without leading to an increase in anxiety among the intervention group during pregnancy. We therefore conclude that GPs can offer PCC to the general population without fear of causing anxiety. Trial Registration: ISRCTN5394291

Transmission electron microscopy study of InxGa1-xAs quantum dots on a GaAs(001) substrate

A transmission electron microscopy (TEM) investigation of the morphology of InxGa1-xAs quantum dots grown on a GaAs(001) substrate has been carried out. The size and the shape of the quantum dots have been determined using bright-field images of cross-section TEM specimens and [001] on-zone bright-field images with imaging simulation from plan-view TEM specimens. The results suggest that the coherent quantum dots are lens shaped with base diameters of 25-40 nm and aspect ratios of height to diameter of 1:6-1:4. [S0163-1829(99)00920-0]