233 research outputs found
Markowitz's portfolio selection model and related problems
No full textMarkowitz's portfolio selection theory is one of the pillars of theoretical finance. This formulation has an inherent instability once the mean and variance are replaced by their sample counterparts. The problem is amplified when the number of assets is large and the sample covariance is singular or nearly singular. This poses a fundamental problem, because solutions that are not stable under sample fluctuations may look optimal for a given sample, but are, in effect, very far from optimal with respect to the average risk. The paper starts with a general introduction to Markowitz’s portfolio theory and then discusses further developments and a few notable works in the area and later moves on to discuss the need for regularization and points out a few existing methods for regularization. After which a formulation of the optimal portfolio selection is presented and ends with a few numerical examples.M.S.Includes bibliographical referencesby Abhijit Ravipat
Signal analysis of the electromyogram
No full textThe author has postulated that the relevant information of the human neuromuscular system during voluntary muscle contractions is contained in the surface electromyogram, or EMG. This information is important in diagnosis, modelling and rehabilitation, and consists of two parts. The first is the action potential waveform of motor units, and the second the random firing pattern of several such units. This hypothesis is borne out by the existing state of art in electrophysiological analysis and modelling. Rigorous statistical analysis of the EMG of three muscles of volunteers showed gross similarities in variance, statistical bandwidth and spectral moments, which suggested that a common physical phenomenon was involved. A biphasic waveform model of the action potential was formulated, and its estimated parameters obtained from spectral-moment functions showed strong similarities for different subjects, as well as for all three muscle groups. On the basis of these preliminary analyses, and using digital filtering techniques, the EMG spectra were decomposed, with the expectation of obtaining the action-potential waveform and the firing-patterns. This was indeed found to be so, the spectrum off the model closely agreeing with that obtained from spectral decomposition of the real signal. Moreover, a realistic average waveform of the action-potential was obtained, in addition to estimates of the number of such waves in each data segment. A set of analytical results and statistics of similarity-parameters are presented, considered to be the first of their kind anywhere to be basedon the decoded surface electromyogram alone.</p
Exploiting Yahoo: Pipes to Teach Computing Concepts
No full textEducators always encounter challenges to teach computing concepts to students with different educational backgrounds and computing experience. In this paper the author attempts to explore methods to improve the teaching of computing concepts using Yahoo! Pipes to students with no prior programming experience. The author uses Yahoo! Pipes to teach various computing concepts and makes use of familiar applications that are easy to develop, fun to use and strengthen the student's motivation to learn
Nobel Laureate Abhijit Vinayak Banerjee: A Scientometric Portrait, 1987-2019
No full textNobel Memorial Prize in economics is selected by the Royal Swedish Academy of Sciences and first awarded in the domain in 1969; the latest in 2019 was awarded to the Indian-born American economist Prof. Abhijit Vinayak Banerjee along with Esther Duflo and Michael Kremer. The present study attempted to measure and analyse the research publications of Prof. Banerjee during 1987 to 2019 based on the data available in Google Scholar database. A total of 333 documents published during this period in which 35.74 percent were published as journal articles. Till 2004 the mean relative growth rate of his publications was 0.237 and doubling time was 3.29 whereas from 2005 to 2019 the relative growth rate decreased to 0.077 and the time for doubling increased to 10.20. Esther Duflo was the most prolific co-author of the publications of Prof. Banerjee with 120 documents shared out of 333 by them. The collaboration rate of all publications was 0.89 identifies most of his publications written in collaboration. The journal he used for most of his research to publish was mainly USA based. He has produced numbers of publications which received huge citations, and during May, 2020 the h-index counted 87 according to Goggle Scholar citation counts
An update on <i>Staphylococcus aureus</i> infective endocarditis from the International Society of Antimicrobial Chemotherapy (ISAC)
No full textNo fundingPeer reviewe
European confederation of medical mycology quality of clinical candidaemia management score: A review of the points based best practice recommendations
No full textCandidaemia is associated with high mortality. In the last few years, several guidelines have been published on the management of Candida bloodstream infection. However, adherence to the practice guidelines has been suboptimal. In order to facilitate and objectively measure the adherence to good practice recommendations, a scoring criterion was published by the European Confederation of Medical Mycology (ECMM). The ECMM Quality (EQUAL) of Clinical Candidaemia Management is an audit tool that comprises of 10 quality indicators. Each quality indicator is allotted between 1 and 3 points. The maximum achievable score is 22 or 19 in patients with or without a central venous catheter, respectively. This paper reviews each of the 10 quality indicators and provides the context for improving quality within the individual domains. The review also suggests areas that are in need of further clarity or areas which merit attention in the future updates of the EQUAL scoring system so that clinicians are able to derive maximum benefit from the audit tool. The EQUAL scoring tool is an important milestone in the quality improvement aspect of the management of candidaemia and contributes to the various components of clinical governance in the management of Candida infection of the bloodstream
Absence of xenotropic murine leukaemia virus-related virus in UK patients with chronic fatigue syndrome
No full textBackground: Detection of a retrovirus, xenotropic murine leukaemia virus-related virus (XMRV), has recently been reported in 67% of patients with chronic fatigue syndrome. We have studied a total of 170 samples from chronic fatigue syndrome patients from two UK cohorts and 395 controls for evidence of XMRV infection by looking either for the presence of viral nucleic acids using quantitative PCR (limit of detection <16 viral copies) or for the presence of serological responses using a virus neutralisation assay.
Results: We have not identified XMRV DNA in any samples by PCR (0/299). Some serum samples showed XMRV neutralising activity (26/565) but only one of these positive sera came from a CFS patient. Most of the positive sera were also able to neutralise MLV particles pseudotyped with envelope proteins from other viruses, including vesicular stomatitis virus, indicating significant cross-reactivity in serological responses. Four positive samples were specific for XMRV.
Conclusions: No association between XMRV infection and CFS was observed in the samples tested, either by PCR or serological methodologies. The non-specific neutralisation observed in multiple serum samples suggests that it is unlikely that these responses were elicited by XMRV and highlights the danger of over-estimating XMRV frequency based on serological assays. In spite of this, we believe that the detection of neutralising activity that did not inhibit VSV-G pseudotyped MLV in at least four human serum samples indicates that XMRV infection may occur in the general population, although with currently uncertain outcomes
Transported PDF Modeling of Jet-in-Hot-Coflow Flames
No full textA probability density function (PDF)-based combustion modeling approach for RANS simulation of a jet issuing into a hot and diluted coflow is performed. A tabulated chemistry-based model, i.e., flamelet-generated manifold (FGM), is adopted in the PDF method. The manifolds are constructed using igniting counterflow diffusion flamelets with different coflow compositions. To handle the inhomogeneity of the coflow and the entrainment of the ambient air, a second mixture fraction is defined to quantify the mixing of a representative coflow composition with the ambient air. The chemistry is then parameterized as a function of two mixture fractions and a reaction progress variable. To assess the modeling approach, Adelaide JHC flames, namely HM1, HM2, and HM3, having different oxygen concentrations in the hot coflow, 3%, 6%, and 9% O2, respectively, have been simulated for Reynolds number (Re) = 10,000. Profiles of mean mixture fraction and major species are accurately captured by the model along with the mean temperature. The mean temperature profiles are also captured nicely, while the sensitivity of progress variable (PV) on the predictions is highlighted.Accepted Author ManuscriptFluid Mechanic
Telecom customer churn prediction
No full textCustomer churn is often referred to as customer attrition, or customer defection which is the rate at which the customers are lost. Telecom companies often use customer churn as a key business metrics to predict the number of customers that will leave a telecom service provider. Churn is significant in the telecommunication industry because it directly affects the competitiveness of the service provider. In this work, Logistic Regression and Random Forest performed better than Decision Tree for customer churn analysi
Candidaemia in the elderly: Epidemiology, management and adherence to the European Confederation of Medical Mycology quality indicators
No full textBackground:
Candidaemia in the elderly has not been extensively investigated.
Objectives:
We compared the management of candidaemia in the elderly patients (age ≥65 years) and the very elderly subgroup of patients (age ≥75 years) with those belonging to the younger group (age <65 years) using the European Confederation of Medical Mycology (ECMM) Quality (EQUAL) standard.
Patients & Methods:
Over a 10-year period (April 2011-March 2020), patients with candida bloodstream infection were identified. Data pertaining to demographics, clinical risk factors, antifungal treatment, central venous catheter and investigations such as echocardiogram and fundoscopy were obtained from electronic sources and medical case notes.
Results:
A total of 174 episodes of candidaemia were recorded, comprising of 74 episodes in younger patients and 100 in the elderly, of whom 56 were in the very elderly patients. Of the 177 Candida species recovered, 79 were Candida albicans. EQUAL scores were analysed for 148 patients. The mean score was significantly lower in the elderly (10.4) and the very elderly (9.7) patients compared to the patients in the younger age group (12.19) (P < .01). In particular, this was due to lower blood culture volume drawn (P < .01) and, in the very elderly group, significantly lower scores for the quality indicators pertaining to echocardiogram and fundoscopy (P = .03). The overall mean EQUAL score was 11.16 (median 11; interquartile range 8-14). The 30-day survival was 68% and was similar between all groups.
Conclusions:
Areas of improvement were identified in the management of candidaemia in the elderly patients
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