Quasilinear Drift Of Cosmic Rays In Weak Turbulent Electromagnetic Fields

A general quasilinear transport parameter for particle drift in arbitrary turbulence geometry is presented. The new drift coefficient is solely characterized by a nonresonant term and is evaluated for slab and two-dimensional turbulence geometry. The calculations presented here demonstrate that fluctuating electric fields are a key quantity for understanding quasilinear particle drift in slab geometry. It is shown that particle drift does not exist in unpolarized and purely magnetic slab fluctuations. This is in stark contrast to previous models, which are restricted to slab geometry and the field line random walk limit. The evaluation of the general transport parameter for two-dimensional turbulence geometry, presented here for the first time for dynamical magnetic turbulence, results in a drift coefficient valid for a magnetic power spectrum and turbulence decay rate varying arbitrarily in wavenumber. For a two-component, slab/two-dimensional turbulence model, numerical calculations are presented. The new quasilinear drift, induced by the magnetic perturbations, is compared with a standard drift expression related to the curvature and gradient of an unperturbed heliospheric background magnetic field. The considerations presented here offer a solid ground and natural explanation for the hitherto puzzling observation that drift models often describe observations much better when drift effects are reduced.Comment: 23 pages, 6 figures, accepted for publication in Ap

Survival of children in Cape Town known to be vertically infected with HIV-1

Objective. To determine the survival patterns of children in Cape Town known to be vertically infected with HIV.Design. Retrospective record review of children diagnosed with symptomatic HIV infection during the period 1 December 1990 - 31 May 1995.Setting. Hospitals in the Cape Town metropolitan area.Patients. 193 children were known to be vertically HIV infected. HIV diagnosis was based on the following criteria: two positive HIV enzyme-linked immunosorbent assays (ELlSAs) in children older than 15 months and a positive ELlSA together with a positive polymerase chain reaction (PCR) in younger children. The mothers of the children were known to be HIV-positive. On the basis of the presenting clinical findings children were assigned to a disease severity category (A, B or C) according to the Centers for Disease Control and Prevention (CDC)'s 1994 revised classification system for HIV infection in children.Outcome measures. Survival was analysed according to the Kaplan-Meier method. Survival time was defined as the length of time between clinical diagnosis of HIV and death or last contact with the health services. Mortality risk in relation to specific variables at diagnosis such as age and clinical manifestations was determined by calculation of odds ratios (ORs) with 95% confidence intervals (Cls).Results. The median age at diagnosis was 5 months; 72% of children were aged less than 1 year at diagnosis. According to the CDC clinical classification, 47 (24%) fell into category A, 111 (58%) into category Band 35 (18%) into category C. Of the 193 patients 85 (44%) were alive at the time of review, 65 (34%) had died and 43 (22%) were lost to folloW-Up. Risk of death was significantly associated with age less than 6 months (OR 4.7, Cl 2.1 - 10.3) and severe disease, Le. CDC category C (OR 2.7; Cl 1.1 - 6.9) at time of diagnosis. The median survival for all the children from time of diagnosis was 32 months. Infants diagnosed before 6 months of age had significantly shorter median survival (10 months) compared with 36 months for those diagnosed at 7 - 12 months of age. For the children over the age of 12 months the cumulative proportion surviving at 48 months was 78%. Children with severe disease (category C) had a median survival of 21 months, significantly lower than that in category B (32 months). For the children in category A the cumulative proportion surviving at 48 months was 66%.Conclusion. The median survival of children with HIV was 32 months from time of diagnosis, and survival was influenced by age and disease severity

Hybrid deposition additive manufacturing: novel volume distribution, thermo-mechanical characterization, and image analysis

(c) The Author/sCAUL read and publish agreement 2022The structural integrity of additive manufacturing structures is a pronounced challenge considering the voids and weak layer-to-layer adhesion. One of the potential ways is hybrid deposition manufacturing (HDM) that includes fused filament fabrication (FFF) with the conventional filling process, also known as “HDM composites". HDM is a potential technique for improving structural stability by replacing the thermoplastic void structure with a voidless epoxy. However, the literature lacks investigation of FFF/epoxy HDM-based composites regarding optimal volume distribution, effects of brittle and ductile FFF materials, and fractographic analysis. This research presents the effects of range of volume distributions (10–90%) between FFF and epoxy system for tensile, flexure, and compressive characterization. Volume distribution in tensile and flexure samples is achieved using printable wall thickness, slot width, and maximum width. For compression, the printable wall thickness, slot diameter, and external diameter are considered. Polylactic acid and acrylonitrile butadiene styrene are used to analyze the brittle and ductile FFF structures. The research reports novel application of image analysis during mechanical characterization using high-quality camera and fractographic analysis using scanning electron microscopy (SEM). The results present surprising high tensile strain (0.038 mm/mm) and compressive strength (64.5 MPa) for lower FDM-percentages (10%, 20%) that are explained using in situ image analysis, SEM, stress–strain simulations, and dynamic mechanical analysis (DMA). In this regard, the proposed work holds novelty to apply DMA for HDM. The optimal volume distributions of 70% and 80% alongside fractographic mechanisms for lower percentages (10%, 20%) can potentially contribute to structural applications and future material-based innovations for HDM.fals

Evaluation of a new type of direct digital radiography machine

Objective. To evaluate a recently developed low-dose, largefield, direct digital X-ray scanning system for medical use.Method. Radiation dose, image quality, diagnostic capability and clinical utility of the unit were compared with those of conventional radiography.Results. Radiation doses ranged from 3% to 5% of conventional radiographic values, and a mean of 1 line-pair per millimetre could be detected. Ease of use, anatomical coverage and tolerance to patient motion were advantages. However, image quality was inferior to that of conventional radiographs, with limited fine detail visibility and penetration. Only 67 of 156 (42.9%) pathological features seen on conventional radiographs were detected, including 13 of 41 fractures (31.7%) and 11 of 18 pneumothoraces (61.1%).Conclusion. Although image quality and diagnostic performance were not ideal, potential roles in triage, foreign body detection and possibly screening were promising. Radiographic factors may have affected sensitivity. This machine demonstrated useful attributes that may, with improvement, be beneficial in the imaging of trauma and other patients

Selection of a suitable ligand for the supercritical extraction of gold from a low-grade refractory tailing

Reprocessing tailings for gold recovery is generating new low-grade refractory secondary tailings. Unlocking gold trapped within these secondary tailings potentially holds additional economic value. In this study, the use of supercritical carbon dioxide (scCO2) at 100 bar and 40 °C for gold extraction from such a secondary gold tailings sample (0.27 g Au/t) was investigated. The research identified and screened the following ligands as suitable extractants for gold in scCO2: 3-(trifluoromethyl)-phenyl-thiourea (TPT), 1,1,1-trifluoro-2,4-pentanedione (TFA), betaine bis(trifluoromethylsulfonyl)imide ([Hbet][TF2N]), 4-methyl-4H-1,2,4-triazole-3-thiol (MHTT) and hexafluoroacetylacetone (HFA). Results from screening experiments showed that extraction of gold for all ligands in the presence of a tri-n-butyl phosphate-nitric acid adduct (TBP-HNO3) as oxidant exceeded 50% after 18 h, with the highest extraction offered by [Hbet][TF2N] (82% after 24 h). A comparative study, where no scCO2 was present, showed that the presence of scCO2 offered a distinct advantage in extraction

Socio-cultural, geographical and financial factors that influence a tourist’s overall experience of Township Tours in the Western Cape, South Africa.

Consumers are becoming more focused on the experience attached to a service or product, which can be created through the use of the experience economy. An experience is created through various indicators and becomes a main driver of overall satisfaction. This study focusses on the tourism industry in South Africa, specifically, township tourism in the Western Cape. The purpose of this article is to investigate the relation between authenticity, memorabilia, entertaining experience, safety, tour conditions, monetary value, flow of income, and the tourists’ overall satisfaction of township tours in the Western Cape. These variables or indicators of experience in the tourism industry are grouped into three categories; socio-cultural; geographical, and; financial factors. Furthermore, the disconfirmation theory as well as the expectancy value theory are utilised to explain the relation between the variables of the study. This study makes use of a quantitative research paradigm and the data was collected by means of a questionnaire. The findings of this article state tourist’ overall experience of township tours relate strongly on the interaction with the locals, availability of memorabilia, and arts and crafts. Tour guides provide tourists with adequate information and knowledge to provide a feeling of safety. From the findings, recommendations to the stakeholders of township tours are made, The managerial implication is that the tour operators of township tours need to be aware of the impact that the township tours has on the local economy and that tourists are willing to pay more for an authentic experience.The study is significant as it is one of very few studies conducted on township tours in South Africa, and the first in the Western Cape

Proteogenomic analysis of mycobacterium smegmatis using high resolution mass spectrometry

Biochemical evidence is vital for accurate genome annotation. The integration of experimental data collected at the proteome level using high resolution mass spectrometry allows for improvements in genome annotation by providing evidence for novel gene models, while validating or modifying others. Here, we report the results of a proteogenomic analysis of a reference strain of Mycobacterium smegmatis (mc2155), a fast growing model organism for the pathogenic Mycobacterium tuberculosis—the causative agent for Tuberculosis. By integrating high throughput LC/MS/MS proteomic data with genomic six frame translation and ab initio gene prediction databases, a total of 2887 ORFs were identified, including 2810 ORFs annotated to a Reference protein, and 63 ORFs not previously annotated to a Reference protein. Further, the translational start site (TSS) was validated for 558 Reference proteome gene models, while upstream translational evidence was identified for 81. In addition, N-terminus derived peptide identifications allowed for downstream TSS modification of a further 24 gene models. We validated the existence of six previously described interrupted coding sequences at the peptide level, and provide evidence for four novel frameshift positions. Analysis of peptide posterior error probability (PEP) scores indicates high-confidence novel peptide identifications and shows that the genome of M. smegmatis mc2155 is not yet fully annotated. Data are available via ProteomeXchange with identifier PXD003500

Time dependence of the electron and positron components of the cosmic radiation measured by the PAMELA experiment between July 2006 and December 2015

Cosmic-ray electrons and positrons are a unique probe of the propagation of cosmic rays as well as of the nature and distribution of particle sources in our Galaxy. Recent measurements of these particles are challenging our basic understanding of the mechanisms of production, acceleration and propagation of cosmic rays. Particularly striking are the differences between the low energy results collected by the space-borne PAMELA and AMS-02 experiments and older measurements pointing to sign-charge dependence of the solar modulation of cosmic-ray spectra. The PAMELA experiment has been measuring the time variation of the positron and electron intensity at Earth from July 2006 to December 2015 covering the period for the minimum of solar cycle 23 (2006-2009) till the middle of the maximum of solar cycle 24, through the polarity reversal of the heliospheric magnetic field which took place between 2013 and 2014. The positron to electron ratio measured in this time period clearly shows a sign-charge dependence of the solar modulation introduced by particle drifts. These results provide the first clear and continuous observation of how drift effects on solar modulation have unfolded with time from solar minimum to solar maximum and their dependence on the particle rigidity and the cyclic polarity of the solar magnetic field.Comment: 11 pages, 2 figure

Time dependence of the e^- flux measured by PAMELA during the July 2006 - December 2009 solar minimum

Precision measurements of the electron component in the cosmic radiation provide important information about the origin and propagation of cosmic rays in the Galaxy not accessible from the study of the cosmic-ray nuclear components due to their differing diffusion and energy-loss processes. However, when measured near Earth, the effects of propagation and modulation of galactic cosmic rays in the heliosphere, particularly significant for energies up to at least 30 GeV, must be properly taken into account. In this paper the electron (e^-) spectra measured by PAMELA down to 70 MeV from July 2006 to December 2009 over six-months time intervals are presented. Fluxes are compared with a state-of-the-art three-dimensional model of solar modulation that reproduces the observations remarkably well.Comment: 40 pages, 18 figures, 1 tabl