Magnetoplasmon excitations in an array of periodically modulated quantum wires

Motivated by the recent experiment of Hochgraefe et al., we have investigated the magnetoplasmon excitations in a periodic array of quantum wires with a periodic modulation along the wire direction. The equilibrium and dynamic properties of the system are treated self-consistently within the Thomas-Fermi-Dirac-von Weizsaecker approximation. A calculation of the dynamical response of the system to a far-infrared radiation field reveals a resonant anticrossing between the Kohn mode and a finite-wavevector longitudinal excitation which is induced by the density modulation along the wires. Our theoretical calculations are found to be in excellent agreement with experiment.Comment: 9 pages, 8 figure

Comparing Male Nyala and Male Kudu Classification using Transfer Learning with ResNet-50 and VGG-16

Reliable and efficient monitoring of wild animals is crucial to inform management and conservation decisions. The process of manually identifying species of animals is time-consuming, monotonous, and expensive. Leveraging on advances in deep learning and computer vision, we investigate in this paper the efficiency of pre-trained models, specifically the VGG-16 and ResNet-50 model, in identifying a male Kudu and a male Nyala in their natural habitats. These pre-trained models have proven to be efficient in animal identification in general. Still, there is little research on animals like the Kudu and Nyala, who are usually well camouflaged and have similar features. The method of transfer learning used in this paper is the fine-tuning method. The models are evaluated before and after fine-tuning. The experimental results achieved an accuracy of 93.2\% and 97.7\% for the VGG-16 and ResNet-50 models, respectively, before fine-tuning and 97.7\% for both models after fine-tuning. Although these results are impressive, it should be noted that they were taken over a small sample size of 550 images split in half between the two classes; therefore, this might not cater to enough scenarios to get a full conclusion of the efficiency of the models. Therefore, there is room for more work in getting a more extensive dataset and testing and extending to the female counterparts of these species and the whole antelope species

s-wave scattering and the zero-range limit of the finite square well in arbitrary dimensions

We examine the zero-range limit of the finite square well in arbitrary dimensions through a systematic analysis of the reduced, s-wave two-body time-independent Schr\"odinger equation. A natural consequence of our investigation is the requirement of a delta-function multiplied by a regularization operator to model the zero-range limit of the finite-square well when the dimensionality is greater than one. The case of two dimensions turns out to be surprisingly subtle, and needs to be treated separately from all other dimensions

HST Spectra of GW Librae: A Hot Pulsating White Dwarf in a Cataclysmic Variable

We have obtained Hubble Space Telescope UV spectra of the white dwarf in GW Lib, the only known non-radially pulsating white dwarf in a cataclysmic variable, and the first known DAZQ variable. The UV light curve reveals large amplitude (10%) pulsationsin the UV with the same periods (646, 376 and 237 s) as those seen at optical wavelengths, but the mean spectrum fits with an average white dwarf temperature (14,700K for a 0.6M_{odot} white dwarf) that is too hot to be in the normal instability strip for ZZ Ceti stars. A better fit is achieved with a dual temperature model (with 63% of the white dwarf surface at a temperature of 13300K and 37% at 17100K), and a higher mass (0.8M_{odot}) white dwarf with 0.1 solar metal abundance. Since the blue edge of the instability strip moves to higher temperature with increasing mass, the lower temperature of this model is within the instability strip. However, the presence of accretion likely causes abundance and atmospheric temperature differences in GW Lib compared to all known single white dwarf pulsators, and the current models that have been capable of explaining ZZ Ceti stars may not apply.Comment: 13 pages, 4 figure

Volumetric changes of maxillary sinus post augmentation using CBCT

>Magister Scientiae - MScBy evaluating the air volume of the maxillary sinus pre-operatively (Reading 1 – V1) and postoperatively, 3-6 months later (Reading 2 – V2) the changes using different augmentation materials will be ascertained. Additionally, the difference between maxillary sinus air volumes using Cone Beam Computed Tomography CBCT between readings 1 (V1) and 2 (V2) will be determined (preoperatively and postoperatively) and lastly the relationship between CBCT reading at V1 and V2 according to age and gender will be determined

A new mass-ratio for the X-ray Binary X2127+119 in M15?

The luminous low-mass X-ray binary X2127+119 in the core of the globular cluster M15 (NGC 7078), which has an orbital period of 17 hours, has long been assumed to contain a donor star evolving off the main sequence, with a mass of 0.8 solar masses (the main-sequence turn-off mass for M15). We present orbital-phase-resolved spectroscopy of X2127+119 in the H-alpha and He I 6678 spectral region, obtained with the Hubble Space Telescope. We show that these data are incompatible with the assumed masses of X2127+119's component stars. The continuum eclipse is too shallow, indicating that much of the accretion disc remains visible during eclipse, and therefore that the size of the donor star relative to the disc is much smaller in this high-inclination system than the assumed mass-ratio allows. Furthermore, the flux of X2127+119's He I 6678 emission, which has a velocity that implies an association with the stream-disc impact region, remains unchanged through eclipse, implying that material from the impact region is always visible. This should not be possible if the previously-assumed mass ratio is correct. In addition, we do not detect any spectral features from the donor star, which is unexpected for a 0.8 solar-mass sub-giant in a system with a 17-hour period.Comment: 6 pages, 4 figures, accepted by A&

Calibration artefacts in radio interferometry. I. Ghost sources in WSRT data

This work investigates a particular class of artefacts, or ghost sources, in radio interferometric images. Earlier observations with (and simulations of) the Westerbork Synthesis Radio Telescope (WSRT) suggested that these were due to calibration with incomplete sky models. A theoretical framework is derived that validates this suggestion, and provides predictions of ghost formation in a two-source scenario. The predictions are found to accurately match the result of simulations, and qualitatively reproduce the ghosts previously seen in observational data. The theory also provides explanations for many previously puzzling features of these artefacts (regular geometry, PSF-like sidelobes, seeming independence on model flux), and shows that the observed phenomenon of flux suppression affecting unmodelled sources is due to the same mechanism. We demonstrate that this ghost formation mechanism is a fundamental feature of calibration, and exhibits a particularly strong and localized signature due to array redundancy. To some extent this mechanism will affect all observations (including those with non-redundant arrays), though in most cases the ghosts remain hidden below the noise or masked by other instrumental artefacts. The implications of such errors on future deep observations are discussed.Comment: 19 pages, 15 figures, submitted to MNRA

Contemporary Discourses in Qualitative Research: Lessons for Health Research in Nigeria

Quantitative research has permeated and dominated health research in Nigeria. One of the oldest and the most commonly used quantitative research designs are KAP (knowledge, attitude and practice) surveys. Although KAP surveys are important approaches to assessing distribution of community knowledge in large-scale projects, such surveys are often inundated by challenges, especially with regard to accurate measurement and understanding of social construction of health and illness. This paper examines contemporary ontological, epistemological, axiological and methodological discourses in the qualitative research approach and argues for adequate utilisation of the qualitative approach in health research in Nigeria. The qualitative approach deepens understanding of cultural milieu regarding health beliefs and socio-cultural issues surrounding medical therapy, as well as health seeking behaviour. Therefore, this paperargues for a more participatory research methodology in the understanding of health, illness and disease in Nigeria. Some case studies of qualitative research from Nigeria and abroad were reviewed from which health researchers (clinical managers and health social scientists and public health experts) could learn. The paper is thus a contribution to the ongoing discourses in global qualitative health research.Keywords: Qualitative research; quantitative research; ontology; epistemology; developing countries; Nigeria

Review Article: Medical management of opioid dependence in South Africa

Medical practitioners in South Africa are increasingly confronted with requests to treat patients with opioid use disorders. Many do not possess the required knowledge and skills to deal with these patients effectively. This overview of the medical treatment of opioid dependence was compiled by an elected working group of doctors working in the field of substance dependence. Recommendations are based on current best practice derived from scientific evidence and consensus of the working group, but should never replace individual clinical judgement.South African Medical Journal Vol. 98 (4) 2008: pp. 280-28