Cyclic permutations and nearly symmetric integer vectors

AbstractGiven an integer vector xT=(x1,…,xn) with the property x1>x2>⋯ >xn>0, it is shown that the convex hull of the n cyclic permutations of x contains all the nearly symmetric integer vectors majorized by x. A generalization to noninteger vectors and an application to a class of integer symmetric optimization problems are also given

Excessive noise as a test for many-body localization

Recent experimental reports suggested the existence of a finite-temperature insulator in the vicinity of the superconductor-insulator transition. The rapid decay of conductivity over a narrow temperature range was theoretically linked to both a finite-temperature transition to a many-body-localized state, and to a charge-Berezinskii-Kosterlitz-Thouless transition. Here we report of low-frequency noise measurements of such insulators to test for many-body localization. We observed a huge enhancement of the low-temperatures noise when exceeding a threshold voltage for nonlinear conductivity and discuss our results in light of the theoretical models

Educational data mining for students’ academic performance analysis in selected Ethiopian universities

Universities are working in a very dynamic and powerfully viable environment today. Due to the advent of information technology, they gather large volumes of data related to their students in electronic form in various formats like records, files, documents, images, sound, videos, scientific data and many new data formats. This study focuses on predicting performance of student at an early stage of the degree program, in order to help the university not only to focus more on bright students but also to initially identify students with low academic achievement and find ways to support them. The knowledge is hidden among the educational data set and it is extractable through data mining techniques. The aim of this paper is to use data mining methodologies to design and develop a Data Mining model to predict academic performance of students at the end of first year degree program in selected Ethiopian higher educational institutions (universities).The data of different undergraduate students has been mined with decision tree classifiers. A model is built using C4.5 Decision tree learning algorithm – generates five classification rule set classifiers (predictors) in an experiment. The experiment using a test data set produces 81.4% accuracy.Keywords: Educational Data, Educational Data mining, Decision tree, Classification rule, C4.

Continuous atom laser with Bose-Einstein condensates involving three-body interactions

We demonstrate, through numerical simulations, the emission of a coherent continuous matter wave of constant amplitude from a Bose-Einstein Condensate in a shallow optical dipole trap. The process is achieved by spatial control of the variations of the scattering length along the trapping axis, including elastic three body interactions due to dipole interactions. In our approach, the outcoupling mechanism are atomic interactions and thus, the trap remains unaltered. We calculate analytically the parameters for the experimental implementation of this CW atom laser.Comment: 11 pages, 4 figure

Deviation from Snell's Law for Beams Transmitted Near the Critical Angle: Application to Microcavity Lasers

We show that when a narrow beam is incident upon a dielectric interface near the critical angle for total internal reflection it will be transmitted into the far-field with an angular deflection from the direction predicted by Snell's Law, due to a phenomenon we call "Fresnel Filtering". This effect can be quite large for the parameter range relevant to dielectric microcavity lasers.Comment: 4 pages, 3 figures (eps), RevTeX 3.1, to be published in Optics Letter

Sensitivity of the superconducting state in thin films

For more than two decades, there have been reports on an unexpected metallic state separating the established superconducting and insulating phases of thin-film superconductors. To date, no theoretical explanation has been able to fully capture the existence of such a state for the large variety of superconductors exhibiting it. Here, we show that for two very different thin-film superconductors, amorphous indium oxide and a single crystal of 2H-NbSe2, this metallic state can be eliminated by adequately filtering external radiation. Our results show that the appearance of temperature-independent, metallic-like transport at low temperatures is sufficiently described by the extreme sensitivity of these superconducting films to external perturbations. We relate this sensitivity to the theoretical observation that, in two dimensions, superconductivity is only marginally stable

The MRI finding of the nerve root sedimentation sign: Its clinical validity and operative relativity for patients with lumbar spinal stenosis

AbstractBackgroundLumbar spinal stenosis (LSS) is increasingly being recognised as a cause of disabling low back and lower extremities pain in adult population. Advanced spinal imaging thought as confirmation tool for the diagnosis and as preoperative tool to delineate the extent and precise location of the pathology. Nerve roots normally sediment, due to gravity, to the dorsal part of the dural sac, which was known as negative sedimentation sign. If there is MRI finding of nerve roots in the ventral part of the dural sac the sedimentation sign is positive.ObjectivesTo evaluate the presence of the MRI finding of positive sedimentation sign in patients clinically suspected to have lumbar spinal stenosis and to follow up operated cases to identify the absence of the radiological signs in the operated cases.Material and methods70 patients clinically suspected to have lumbar spinal stenosis evaluated by MRI lumbosacral spine in supine position. A panel of two radiologists reviewed radiological data. MRI features were agreed by both radiologists in 48 patients. Out of these 48 patients; 25 were operated upon for central decompressive laminectomy, partial medial facetectomy and foraminotomy with instrumented fusion and fixation if indicated. Visual analogue score (VAS) collectively preoperative and postoperative was compared and the walking distance postoperative was reported and follow up MRI studies were done one year after the operation.ResultsOperated patients’ mean age was 58.2years; nineteen patients were operated upon for simple decompressive laminectomy for the affected levels. Walking distance preoperative range 100–700metres, improved postoperative to be 1474.0±601.1. VAS for pain preoperative was 9.28±0.84, improved at 12month follow up to be 0.84±0.62. Postoperative MRI done to evaluate the cross sectional area (CSA) became more than 80mm2 in the absence of the sedimentation sign and was negative in 22 cases.ConclusionThe MRI finding of positive sedimentation sign is a good positive sign to rule in lumbar spinal stenosis with high specificity and sensitivity; negative sedimentation sign can be used in postoperative follow up of decompression patients