Magnetoresistance of a two-dimensional electron gas in a parallel magnetic field

The conductivity of a two-dimensional electron gas in a parallel magnetic field is calculated. We take into account the magnetic field induced spin-splitting, which changes the density of states, the Fermi momentum and the screening behavior of the electron gas. For impurity scattering we predict a positive magnetoresistance for low electron density and a negative magnetoresistance for high electron density. The theory is in qualitative agreement with recent experimental results found for Si inversion layers and Si quantum wells.Comment: 4 pages, figures included, PDF onl

Nanoscopic Current Effects on Photovoltaics

Silicon heterojunction (SHJ) solar cells represent a promising technological approach toward higher photovoltaic efficiencies and lower fabrication cost. While the device physics of SHJ solar cells has been studied extensively in the past, the ways in which nanoscopic electronic processes such as charge-carrier generation, recombination, trapping, and percolation affect SHJ device properties macroscopically are yet to be fully understood. We report the study of atomic-scale current percolation at state-of-the-art a-Si:H/c-Si heterojunction solar cells at room temperature, revealing the profound complexity of electronic SHJ interface processes. Using conduction atomic force microscopy, it is shown that the macroscopic current–voltage characteristics of SHJ solar cells are governed by the average of local nanometer-sized percolation pathways associated with bandtail states of the doped a-Si:H selective contact leading to above bandgap local photovoltages (VOCloc) as high as 1.2 V (eVOCloc > EgapSi). This is not in violation of photovoltaic device physics but a consequence of the nature of nanometer-scale charge percolation pathways that originate from trap-assisted tunneling causing dark leakage current. We show that the broad distribution of nanoscopic local photovoltage is a direct consequence of randomly trapped charges at a-Si:H dangling bond defects, which lead to strong local potential fluctuations and induce random telegraph noise of the dark current

Determinants of knowledge management systems success in the banking industry

Purpose – This study aims to examine the impact from technical and social aspects on knowledge management system (KMS) success. Moreover, this study also attempts to examine the interrelationships between KMS success and user satisfaction. Design/methodology/approach – A questionnaire survey was used to collect data from the commercial bank officers to test the proposed KMS success model. All the measurement scales adopted in this study were adopted from the existing literature. The data collected in this study were analysed using both SPSS and structural equation modelling approach via AMOS. Findings – The research results indicate that both technical (knowledge quality, system quality and service quality) and social factors (user trust and management support) play a significant and positive role in system user satisfaction. The results also show that user satisfaction have a direct influence on the success of KMS and vice versa. Originality/value – This study is one of the few studies on KMS which include both the technical and social perspectives in examining KMS success. This research study raises the importance of social factors, which have been earlier neglected by many studies on KMS success models. Moreover, the interrelationships relationship between KMS success and user satisfaction also been examined in this study

Possible Metal/Insulator Transition at B=0 in Two Dimensions

We have studied the zero magnetic field resistivity of unique high- mobility two-dimensional electron system in silicon. At very low electron density (but higher than some sample-dependent critical value, $n_{cr}\sim 10^{11}$ cm$^{-2}$), CONVENTIONAL WEAK LOCALIZATION IS OVERPOWERED BY A SHARP DROP OF RESISTIVITY BY AN ORDER OF MAGNITUDE with decreasing temperature below 1--2 K. No further evidence for electron localization is seen down to at least 20 mK. For $n_s<N_{cr}$, the sample is insulating. The resistivity is empirically found to SCALE WITH TEMPERATURE BOTH BELOW AND ABOVE $n_{cr}$ WITH A SINGLE PARAMETER which approaches zero at $n_s=n_{cr}$ suggesting a metal/ insulator phase transition.Comment: 10 pages; REVTeX v3.0; 3 POSTSCRIPT figures available upon request; to be published in PRB, Rapid Commu

Maternal mortality in the rural Gambia, a qualitative study on access to emergency obstetric care

BACKGROUND: Maternal mortality is the vital indicator with the greatest disparity between developed and developing countries. The challenging nature of measuring maternal mortality has made it necessary to perform an action-oriented means of gathering information on where, how and why deaths are occurring; what kinds of action are needed and have been taken. A maternal death review is an in-depth investigation of the causes and circumstances surrounding maternal deaths. The objectives of the present study were to describe the socio-cultural and health service factors associated with maternal deaths in rural Gambia. METHODS: We reviewed the cases of 42 maternal deaths of women who actually tried to reach or have reached health care services. A verbal autopsy technique was applied for 32 of the cases. Key people who had witnessed any stage during the process leading to death were interviewed. Health care staff who participated in the provision of care to the deceased was also interviewed. All interviews were tape recorded and analyzed by using a grounded theory approach. The standard WHO definition of maternal deaths was used. RESULTS: The length of time in delay within each phase of the model was estimated from the moment the woman, her family or health care providers realized that there was a complication until the decision to seeking or implementing care was made. The following items evolved as important: underestimation of the severity of the complication, bad experience with the health care system, delay in reaching an appropriate medical facility, lack of transportation, prolonged transportation, seeking care at more than one medical facility and delay in receiving prompt and appropriate care after reaching the hospital. CONCLUSION: Women do seek access to care for obstetric emergencies, but because of a variety of problems encountered, appropriate care is often delayed. Disorganized health care with lack of prompt response to emergencies is a major factor contributing to a continued high mortality rate

Characterisation of Oil Palm Acyl-CoA-Binding Proteins and Correlation of their Gene Expression with Oil Synthesis

Acyl-CoA-binding proteins (ACBPs) are involved in binding and trafficking acyl-CoA esters in eukaryotic cells. ACBPs contain a well-conserved acyl-CoA-binding domain (ACBD). Their various functions have been characterized in the model plant Arabidopsis and, to a lesser extent, in rice. In this study, genome-wide detection and expression analysis of ACBPs were performed on Elaeis guineensis (oil palm), the most important oil crop in the world. Seven E. guineensis ACBPs were identified and classified into four groups according to their deduced amino acid domain organization. Phylogenetic analysis showed conservation of this family with other higher plants. All seven EgACBPs were expressed in most tissues while their differential expression suggests various functions in specific tissues. For example, EgACBP3 had high expression in inflorescences and stalks while ACBP1 showed strong expression in leaves. Because of the importance of E. guineensis as an oil crop, expression of EgACBPs was specifically examined during fruit development. EgACBP3 showed high expression throughout mesocarp development, while EgACBP1 had enhanced expression during rapid oil synthesis. In endosperm, both EgACBP1 and EgACBP3 exhibited increased expression during seed development. These results provide important information for further investigations on the biological functions of EgACBPs in various tissues and, in particular, their roles in oil synthesis