Mathematical Models in Management Sciences. (1) - Consumer Behaviour as a Markov Process

Mathematical models based on Markov processes for consumer purchasing behavio

Analysis of plasma instabilities and verification of the BOUT code for the Large Plasma Device

The properties of linear instabilities in the Large Plasma Device [W. Gekelman et al., Rev. Sci. Inst., 62, 2875 (1991)] are studied both through analytic calculations and solving numerically a system of linearized collisional plasma fluid equations using the 3D fluid code BOUT [M. Umansky et al., Contrib. Plasma Phys. 180, 887 (2009)], which has been successfully modified to treat cylindrical geometry. Instability drive from plasma pressure gradients and flows is considered, focusing on resistive drift waves, the Kelvin-Helmholtz and rotational interchange instabilities. A general linear dispersion relation for partially ionized collisional plasmas including these modes is derived and analyzed. For LAPD relevant profiles including strongly driven flows it is found that all three modes can have comparable growth rates and frequencies. Detailed comparison with solutions of the analytic dispersion relation demonstrates that BOUT accurately reproduces all characteristics of linear modes in this system.Comment: Published in Physics of Plasmas, 17, 102107 (2010

Written in stone: a clinical case of compulsive note taking

Federal University of Pernambuco Neuropsychiatric DepartmentFederal University of São Paulo Department of PsychiatryHospital do Servidor Público Estadual de São PauloUNIFESP, Department of PsychiatrySciEL

Kinematic measures provide useful information after intracranial aneurysm treatment

Introduction; Current methods of assessing the outcomes of intracranial aneurysm treatment for aneurysmal subarachnoid haemorrhage are relatively insensitive, and thus unlikely to detect subtle deficits. Failures to identify cognitive and motor outcomes of intracranial aneurysm treatment might prevent delivery of optimal post-operative care. There are also concerns over risks associated with using intracranial aneurysm treatment as a preventative measure. Methods; We explored whether our kinematic tool would yield useful information regarding motor/cognitive function in patients who underwent intracranial aneurysm treatment for aneurysmal subarachnoid haemorrhage or unruptured aneurysm. Computerised kinematic motor and learning tasks were administered alongside standardised clinical outcome measures of cognition and functional ability, in 10 patients, as a pilot trial. Tests at post-intracranial aneurysm treatment discharge and six-week follow-up were compared to see which measures detected changes. Results; Kinematic tests captured significant improvements from discharge to six-week follow-up, indexed by reduced motor errors and improved learning. Increased Addenbrooke’s Cognitive Examination-Revised scores reflected some recovery of memory function for most individuals, but other standardised cognitive measures, functional outcome scores and a psychological questionnaire showed no changes. Conclusions; Kinematic measures can identify variation in performance in individuals with only slightly improved abilities post-intracranial aneurysm treatment. These measures may provide a sensitive way to explore post-operative outcomes following intracranial aneurysm treatment, or other similar surgical procedures

Current approaches and advances in the imaging of stroke

A stroke occurs when the blood flow to the brain is suddenly interrupted, depriving brain cells of oxygen and glucose and leading to further cell death. Neuroimaging techniques, such as computed tomography and magnetic resonance imaging, have greatly improved our ability to visualise brain structures and are routinely used to diagnose the affected vascular region of a stroke patient's brain and to inform decisions about clinical care. Currently, these multimodal imaging techniques are the backbone of the clinical management of stroke patients and have immensely improved our ability to visualise brain structures. Here, we review recent developments in the field of neuroimaging and discuss how different imaging techniques are used in the diagnosis, prognosis and treatment of stroke

Average Cross-Sectional Area of DebriSat Fragments Using Volumetrically Constructed 3D Representations

Debris fragments from the hypervelocity impact testing of DebriSat are being collected and characterized for use in updating existing satellite breakup models. One of the key parameters utilized in these models is the ballistic coefficient of the fragment which is directly related to its areatomass ratio. However, since the attitude of fragments varies during their orbital lifetime, it is customary to use the average crosssectional area in the calculation of the areatomass ratio. The average crosssectional area is defined as the average of the projected surface areas perpendicular to the direction of motion and has been shown to be equal to onefourth of the total surface area of a convex object. Unfortunately, numerous fragments obtained from the DebriSat experiment show significant concavity (i.e., shadowing) and thus we have explored alternate methods for computing the average crosssectional area of the fragments. An imaging system based on the volumetric reconstruction of a 3D object from multiple 2D photographs of the object was developed for use in determining the size characteristic (i.e., characteristics length) of the DebriSat fragments. For each fragment, the imaging system generates N number of images from varied azimuth and elevation angles and processes them using a spacecarving algorithm to construct a 3D point cloud of the fragment. This paper describes two approaches for calculating the average crosssectional area of debris fragments based on the 3D imager. Approach A utilizes the constructed 3D object to generate equally distributed crosssectional area projections and then averages them to determine the average crosssectional area. Approach B utilizes a weighted average of the area of the 2D photographs to directly compute the average crosssectional area. A comparison of the accuracy and computational needs of each approach is described as well as preliminary results of an analysis to determine the "optimal" number of images needed for the 3D imager to accurately measure the average cross sectional area of objects with known dimensions

Faecal sludge treatment by vermifiltration: proof of concept

The objective of this study was to determine if composting worms and their cocoons are able to survive in and digest faecal sludge. Eighteen vermifilters with different worm and cocoon densities were set-up, fed with faecal sludge (from portable pour-flush toilets) and ran for 38 days. Samples of the sludge, effluent and vermicompost were analysed for pH, total solids, chemical oxygen demand, faecal coliforms and Ascaris spp. number and viability. Worm and vermicompost mass, and cocoon numbers were assessed at the end of this period. It was found that the composting worms survived in these conditions and cocoons hatched. The validity of the sludge analysis results are questioned in this paper and without these results only estimates of effluent treatment and solids conversion could be made. Although this study was not completely definitive it has shown that worms are capable of converting faecal sludge into vermicompost and cocoons hatch in its presence. This trial was undertaken in India

Convective heat transfer in airflow through a duct with wall thermal radiation

This paper presents a numerical investigation on airflow through a heated horizontal rectangular duct wherein the model considers the combined modes of natural and forced convection heat transfer and the thermal radiation from duct walls. The duct periphery is differentially heated with known temperature profiles imposed on the two opposite vertical sidewalls while the other two walls are treated as adiabatic. The air enters into the duct hydrodynamically fully developed and flows steadily under laminar conditions undergoing thermal development within the duct. Considering several temperature profiles on the two vertical sidewalls, the numerical simulation generates the heat transfer rates and associated fluid flow patterns in the duct for a range of airflow rates, duct aspect ratios and surface emissivity. The variation of local Nusselt number at duct walls and the fluid flow patterns are critically examined to identify thermal instabilities and the significance of wall thermal radiation effects on the overall heat transfer rates

Use of anti-snake venom and clinical outcomes in snake envenomation: a prospective observational study

Background: The only effective measure to prevent or reverse most of the manifestations of venomous snake-bite is timely administration of antisnake venom (ASV) with or without adjunctive treatment as necessary in each case. But recently several concerns have been raised with regard to use of polyvalent ASV. Hence the present study was conducted to assess use of ASV, early adverse reactions to ASV, adjunctive treatment and clinical outcomes in snake-bite patients, which would help to identify areas of problem and provide basis for planning strategies to increase rational use of drugs.Methods: It was a prospective observational study approved by Institutional Ethics Committee. All indoor patients with systemic manifestations of snake envenomation were included in the study. All participants gave written informed consent. Data was obtained prospectively using a structured case record form. Descriptive statistics was used to express the results.Results: Among 52 patients, snake-bite predominantly affected males (59.62%) than females (40.38%). The most common site of snake-bite was lower limb (65.38%). The main indication for ASV administration was vasculotoxic snake-bite (59.62%). Mean dose of ASV use was 18.21±15.51 vials. Mortality was seen in one patient. Majority of patients (28/52, 53.85%) received ASV in the range of 1-10 vials for the management of snake-bite.Conclusions: The use and dose of ASV was appropriate in vasculotoxic snake-bite while few neurotoxic snake-bite patients needed higher than recommended dose.