Vertically Aligned GaAs Nanowires on Graphite and Few-Layer Graphene: Generic Model and Epitaxial Growth

By utilizing the reduced contact area of nanowires, we show that epitaxial growth of a broad range of semiconductors on graphene can in principle be achieved. A generic atomic model is presented which describes the epitaxial growth configurations applicable to all conventional semiconductor materials. The model is experimentally verified by demonstrating the growth of vertically aligned GaAs nanowires on graphite and few-layer graphene by the self-catalyzed vapor-liquid-solid technique using molecular beam epitaxy. A two-temperature growth strategy was used to increase the nanowire density. Due to the self-catalyzed growth technique used, the nanowires were found to have a regular hexagonal cross-sectional shape, and are uniform in length and diameter. Electron microscopy studies reveal an epitaxial relationship of the grown nanowires with the underlying graphitic substrates. Two relative orientations of the nanowire side-facets were observed, which is well explained by the proposed atomic model. A prototype of a single GaAs nanowire photodetector demonstrates a high-quality material. With GaAs being a model system, as well as a very useful material for various optoelectronic applications, we anticipate this particular GaAs nanowire/graphene hybrid to be promising for flexible and low-cost solar cells.     

Morphological operations with iterative rotation of structuring elements for segmentation of retinal vessel structures

Multidimensional Systems and Signal Processing - The development of computer aided diagnosis system has a great impact on early and accurate disease diagnosis. The segmentation of retinal blood...     

Serodiagnosis of extrapulmonary tuberculosis by ELISA

This study aims at evaluating the specificity and sensitivity of ELISA test in detection of Mycobacterial Antibodies using A60 antigen. Sera from 100 clinically suspected cases of extrapulmonary tuberculosis were studied along with 10 sputum positive cases 25 age and sex matched healthy control. Overall positivity of the test was 80.00 per cent with 100 percent sensitivity and 92 per cent specificity. The present study recommends ELISA as an adjunct to other investigative procedures.     

Synthesis of 2,3-trans-3,4-cis- and 2,3-trans-3,4-trans-2,3,4-triphenyltetrahydrofurans

The synthesis of 2,3-trans-3,4-cis- and 2,3-trans-3,4-trans-2,3,4-triphenyltetrahydrofurans was undertaken because these compounds incorportae the essential structural features of certain 2,3-diphenyl-benzofurans and 1,2,3-triphenylalkanones reported earlier to have marked antifertility activity. The synthesis of the 2 tetrahydrofurans was achieved by the cyclization of corresponding 2,3,4-triphenylbutane-1,4-diols upon heating with dimethyl sulfoxide (DMSO). The butane 1,4-diols were in turn prepared either by direct litium aluminum hydride (LAH) reduction of methyl 3-benzoyl-2,3-diphenylpropionates or by conversion of these propionates to delta-3,4-butryrolactones followed by LAH reduction. The propionates were prepared from the Fiedel-Crafts reaction of 2,3-diphenylsuccinic anhydride with benzene. Tetrahydrofurans were tested for their antiimplantation activity in rats. 2,3-trans-3,4-cis-2,4-diphenyl-3-p -(beta-pyrrolidinoethoxy) phenyltetrahydrofuran oxalate was found to inhibit implantation completely at 50 mg/kg, but was inefective at a lower dose.     

ISO 9000 standards: perceptions and experiences in the UK construction industry

Recently the South African government introduced new legislation to regulate the construction industry and, in particular, redistribute the responsibility for construction worker safety and health to include all industry participants. Consequently, the need to maintain and promote construction workers' health and working capacity has been given an increased prominence. Considering that the highest rates of new infections are reportedly occurring on the African continent, the fight against HIV and AIDS in the workplace has become an African priority. A comparative assessment is carried out on the levels of knowledge, perceptions and beliefs, and behaviours of construction workers in South Africa relative to HIV infection and AIDS. The levels of knowledge and awareness of HIV and AIDS among construction workers younger than 40 years of age (‘younger workers’) are compared with those of workers older than 40 years (‘older workers’). A regional exploratory study commenced in August 2002. Both age cohorts of construction workers generally had acceptable levels of knowledge, perceptions and attitudes on most issues relative to the disease. However, several areas are highlighted where they had deficient knowledge and attitudes or demonstrated high levels of uncertainty. Overall, younger workers had lower levels of uncertainty and deficient knowledge. There were several areas where these were common irrespective of age. These are the areas that deserve urgent employer driven interventions.     

Characteristic Signature of Specimen Using an Approximate Formula for 3D Circular Cone-Beam Tomography

The approximate nature of the Feldkamp–Davis–Kress (FDK) algorithm for circular cone-beam tomography motivates the error estimation in the reconstruction of three-dimensional (3D) objects. This algorithm is based on 3D cone-beam backprojection and 1D band-limiting filtering. The use of different window functions along with band-limiting filter in the convolution step of this algorithm lead to different reconstructions for the same projection data set, and a theoretical error gets incorporated in the reconstruction process. The present study is an attempt to understand this error in the reconstructed images from FDK algorithm using 3D version of “First Kanpur theorem” (KT-1). This theorem was proposed initially for error estimates in 2D reconstructions, and here it is extended to cone-beam volume reconstructions. The 3D version of KT-1 for circular cone-beam reconstructions is validated using industrial and medical numerical phantoms. It is then implemented on variety of real-life specimens. A characteristic signature is evolved as an application of the Kanpur Theorem (KT-1), which is a unique representation for a volumetric object. The preliminary obtained results are consistent and quite encouraging.     

PERFORMANCE EVALUATION OF ITERATIVE TOMOGRAPHIC ALGORITHMS APPLIED TO RECONSTRUCTION OF A THREE-DIMENSIONAL TEMPERATURE FIELD

Iterative tomographic algorithms have been applied to the reconstruction of a three-dimensional temperature field (from its projections) for Rayleigh-Renard-type natural-convection problems. Nine distinct algorithms with varying numbers of projections and projection angles have been considered. The three-dimensional temperature field is sliced into a set of two-dimensional planes and reconstruction algorithms are applied to each individual plane. Projection of the temperature field is interpreted as a path integral along a line in the appropriate direction. The integrals are evaluated numerically and are assumed to represent exact data. Errors in reconstruction are defined with field data as reference and are used to compare one algorithm with respect to another. The algorithms used in this work can be broadly classified into three groups: additive algebraic reconstruction technique (ART), multiplicative algebraic reconstruction technique (MART), and maximization reconstruction technique (MRT). Additive ART shows a systematic convergence with respect to number of the projections and the value of the relaxation parameter. MART algorithms produce less error at convergence compared to additive ARTs but converge only at low values of relaxation parameter. In the present work the MRT algorithm shows intermediate performance when compared to ART and MART. Increasing noise level in projection data increases the error in the reconstructed fidd. The maximum and root-mean-square errors are highest in ART and lowest in MART for a given projection data. Increasing noise levels in projection data decrease the convergence rates. For all algorithms, a 20% noise level is seen as an upper limit beyond which the reconstructed field is barely recognisable.     

Effect of prolactin on carbohydrate metabolism in human semen

In a pediatric office setting, car safety counseling was provided to 16 primigravida women during a prenatal pediatric interview. A control group of 19 women received no counseling during a similar interview. Forty-two percent of noncounseled mothers and 69% of counseled mothers were using a safe infant restraint system at the six-week well-child visit. Preventive counseling in car safety is an important role for the pediatrician.