OALib Journal期刊

ISSN: 2333-9721



匹配条件: “Koycho Koev” ,找到相关结果约8条。
Eco-Biological Characteristics of Medicinal Plants in the Protected Area “Nahodishte Na Blatno Kokiche”, Gradina Village, Parvomay (Bulgaria)
Stoyan Georgiev,Alexander Tashev,Koycho Koev
Ecologia Balkanica , 2012,
Abstract: In the present work we investigated medicinal plants of the flora of the protected area “Nahodishte na blatno kokiche” the village of Gradina, Parvomay Municipality. Eco-biological characterization of the plants was done, and the species were grouped according to biological groups, life forms, floral elements and flowering time. Medicinal plants are also classified according to their attitude towards water, light and heat.
The Efficient Evaluation of the Hypergeometric Function of a Matrix Argument
Plamen Koev,Alan Edelman
Mathematics , 2005,
Abstract: We present new algorithms that efficiently approximate the hypergeometric function of a matrix argument through its expansion as a series of Jack functions. Our algorithms exploit the combinatorial properties of the Jack function, and have complexity that is only linear in the size of the matrix.
Iliyan Koev,E. Slavov,D. Staykov,K. Halacheva
Journal of IMAB : Annual Proceeding (Scientific Papers) , 2010,
Abstract: Objective: Malignant gliomas are primary brain tumors with excessive mortality and high resistance to chemotherapy and radiotherapy. The survival time for glioblastoma multi-forme is about 6-12 months. As key pathogenetic mechanisms are recognized the massive necrosis, angiogenesis and hypoxia within the tumor, as well as the resistance to apoptosis. It is also suspected that altered immune response might contribute to the fatal clinical outcome.The aim of the present study was to determine the immune status of patients with malignant gliomas.Material and methods: Peripheral blood lymphocytes were collected preoperatively from 9 patients (aged 57-76) diagnosed as anaplastic astrocytoma grade III (n=4) and glioblastoma multiforme (n=5). The following lymphocyte populations were analyzed by flow cytometry: CD19+, CD3+, CD3+CD4+, CD3+CD8+, CD3-CD56+, CD3+CD56+, CD3+CD25+, CD8-CD11b+, CD8+CD11b+, CD8+CD11b-. The results obtained were compared to reference values for each cell population.Results: No significant alterations were detected in CD19+, CD3+, CD3+CD4+, CD3+CD8+ cells, but the CD4/CD8 ratio was below the reference range in some cases. No obvious decrease in (CD3-CD56+) NK cells and (CD3-CD56+) NKT cells was observed in most patients. A reproducible phenomenon of increased CD8+CD11b+ and decreased CD8+CD11b- cells was noticed. These preliminary results suggest that the immune response in patients with malignant glioma is seriously disregulated. The rapid clinical deterioration, relapses and high mortality could be at least partially explained with the suppressed activity of NK-cells which are the major cytotoxic antitumoral cells. The increase in the population of activated suppressor-effector cells also contributes to the unfavourable outcome in malignant brain tumors.Conclusion: This pilot study reveals the presence of altered immune response in malignant gliomas and opens possibilities for prospective investigations concerning immune status and clinical outcome.
Accurate and Efficient Expression Evaluation and Linear Algebra
James Demmel,Ioana Dumitriu,Olga Holtz,Plamen Koev
Mathematics , 2007, DOI: 10.1017/S0962492906350015
Abstract: We survey and unify recent results on the existence of accurate algorithms for evaluating multivariate polynomials, and more generally for accurate numerical linear algebra with structured matrices. By "accurate" we mean that the computed answer has relative error less than 1, i.e., has some correct leading digits. We also address efficiency, by which we mean algorithms that run in polynomial time in the size of the input. Our results will depend strongly on the model of arithmetic: Most of our results will use the so-called Traditional Model (TM). We give a set of necessary and sufficient conditions to decide whether a high accuracy algorithm exists in the TM, and describe progress toward a decision procedure that will take any problem and provide either a high accuracy algorithm or a proof that none exists. When no accurate algorithm exists in the TM, it is natural to extend the set of available accurate operations by a library of additional operations, such as $x+y+z$, dot products, or indeed any enumerable set which could then be used to build further accurate algorithms. We show how our accurate algorithms and decision procedure for finding them extend to this case. Finally, we address other models of arithmetic, and the relationship between (im)possibility in the TM and (in)efficient algorithms operating on numbers represented as bit strings.
The Beta-Wishart Ensemble
Alexander Dubbs,Alan Edelman,Plamen Koev,Praveen Venkataramana
Mathematics , 2013, DOI: 10.1063/1.4818304
Abstract: This paper proves a matrix model for the Wishart Ensemble with general covariance and general dimension parameter beta. In so doing, we introduce a new and elegant definition of Jack polynomials.
An Efficient Large-Area Grating Coupler for Surface Plasmon Polaritons
Stephan T. Koev,Amit Agrawal,Henri J. Lezec,Vladimir A. Aksyuk
Physics , 2011, DOI: 10.1007/s11468-011-9303-7
Abstract: We report the design, fabrication and characterization of a periodic grating of shallow rectangular grooves in a metallic film with the goal of maximizing the coupling efficiency of an extended plane wave (PW) of visible or near-infrared light into a single surface plasmon polariton (SPP) mode on a flat metal surface. A PW-to-SPP power conversion factor > 45 % is demonstrated at a wavelength of 780 nm, which exceeds by an order of magnitude the experimental performance of SPP grating couplers reported to date at any wavelength. Conversion efficiency is maximized by matching the dissipative SPP losses along the grating surface to the local coupling strength. This critical coupling condition is experimentally achieved by tailoring the groove depth and width using a focused ion beam.
Computing with rational symmetric functions and applications to invariant theory and PI-algebras
Francesca Benanti,Silvia Boumova,Vesselin Drensky,Georgi K. Genov,Plamen Koev
Mathematics , 2012,
Abstract: Let the formal power series f in d variables with coefficients in an arbitrary field be a symmetric function decomposed as a series of Schur functions, and let f be a rational function whose denominator is a product of binomials of the form (1 - monomial). We use a classical combinatorial method of Elliott of 1903 further developed in the Partition Analysis of MacMahon in 1916 to compute the generating function of the multiplicities (i.e., the coefficients) of the Schur functions in the expression of f. It is a rational function with denominator of a similar form as f. We apply the method to several problems on symmetric algebras, as well as problems in classical invariant theory, algebras with polynomial identities, and noncommutative invariant theory.
Strong Casimir force reduction through metallic surface nanostructuring
Francesco Intravaia,Stephan Koev,Il Woong Jung,A. Alec Talin,Paul S. Davids,Ricardo S. Decca,Vladimir A. Aksyuk,Diego A. R. Dalvit,Daniel Lopez
Physics , 2012, DOI: 10.1038/ncomms3515
Abstract: The Casimir force between bodies in vacuum can be understood as arising from their interaction with an infinite number of fluctuating electromagnetic quantum vacuum modes, resulting in a complex dependence on the shape and material of the interacting objects. Becoming dominant at small separations, the force plays a significant role in nanomechanics and object manipulation at the nanoscale, leading to a considerable interest in identifying structures where the Casimir interaction behaves significantly different from the well-known attractive force between parallel plates. Here we experimentally demonstrate that by nanostructuring one of the interacting metal surfaces at scales below the plasma wavelength, an unexpected regime in the Casimir force can be observed. Replacing a flat surface with a deep metallic lamellar grating with sub-100 nm features strongly suppresses the Casimir force and for large inter-surfaces separations reduces it beyond what would be expected by any existing theoretical prediction.

Copyright © 2008-2017 Open Access Library. All rights reserved.