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Search Results: 1 - 10 of 200937 matches for " P. Kowalski "
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Efficiency of the coherent biexciton admixture mechanism for multiple exciton generation in InAs nanocrystals
P. Kowalski,P. Machnikowski
Physics , 2015,
Abstract: We study the coherent mixing between two-particle (single exciton) and four-particle (biexciton) states of a semiconductor nanocrystal resulting from the coulomb coupling between states with different numbers of electron-hole pairs. Using a simple model of the nanocrystal wave functions and an envelope function approach, we estimate the efficiency of the multiple exciton generation (MEG) process resulting from such coherent admixture mechanism, including all the relevant states in a very broad energy interval. We show that in a typical ensemble of nanocrystals with 3~nm average radius, the onset of the MEG process appears about 1~eV above the lower edge of the biexciton density of states and the efficiency of the process reaches 50\% for photon energies around 5~eV. The MEG onset shifts to lower energies and the efficiency increases as the radius grows. We point out that the energy dependence of the MEG efficiency differs considerably between ensembles with small and large inhomogeneity of nancrystal sizes.
Continuous time evolution from iterated maps and Carleman linearization
P. Gralewicz,K. Kowalski
Physics , 2000,
Abstract: Using the Carleman linearization technique the continuous iteration of a mapping is studied. Based on the detailed analysis of the Carleman embedding matrix the precise mathematical meaning is given to such notion. The ordinary differential equations referring to continuous iterations are identified and the discussion of the relationship between them and the corresponding iterated maps is performed. Keywords: iterated systems, functional eigenequation
Attempt to use the SWATREZ and UNDYS models for the simulation of ground water pollution in agrosystems irrigated by municipal sewage
Gli?…??ski P.,Kowalski D.,Olszta W.
International Agrophysics , 2003,
Abstract: For the simulation of water movement and pollutant transport in the hydromorphic soil profile two numerical models SWATREZ and UNDYS were used. These models are based on water movement in porous materials and hydrodynamic dispersion equations. The results obtained by numerical simulation were verified by field research data from the Hajd 3w experimental station situated near Lublin (Poland). The Hajd 3w experiment combines the municipal waste treatment process with industrial plant production. Empirical verification obeyed the groundwater table level, nitrogen ion concentration in the soil water at various depths and in water outlets from the drainage system. The simulation results presented show the important role of plant roots in the use of nitrogen at Hajd 3w type stations. It indicates that the best design and management of such objects must take into account not only ground filter, but also plant growth theory. The SWATREZ model gives a quite good approximation of empirical data. It can be used for the water management process in Hajd 3w type stations. Simulation based on the UNDYS model shows that the continuation of numerical research is very necessary.
Using 3D scanner as a tool for the verification of prototype casting shape
A. Gil,P. Kowalski,K. Wańczyk
Archives of Foundry Engineering , 2011,
Abstract: The aim of the present study is to review information on modern methods of measurement engineering. The article illustrates the threedimensional scanning of prototype casting and compares the results with a virtual solid model, developed from flat file in a 3D graphic editor. The results of scanning are presented together with specified dimensions and colour map on the model surface. For scanning(digitising), an ATOS III optical scanner, which allows measurement of objects in sizes ranging from a few millimetres to a few dozenmeters, was used. This technique can be used in the measurement of both casting and pattern tooling.
The Free-Free Opacity in Warm, Dense, and Weakly Ionized Helium
P. M. Kowalski,S. Mazevet,D. Saumon
Physics , 2005, DOI: 10.1063/1.2263280
Abstract: We investigate the ionization and the opacity of warm, dense helium under conditions found in the atmospheres of cool white dwarf stars. Our particular interest is in densities up to $\rm 3 g/cm^{3}$ and temperatures from 1000K to 10000K. For these physical conditions various approaches for modeling the ionization equilibrium predict ionization fractions that differ by orders of magnitudes. Furthermore, estimates of the density at which helium pressure-ionizes vary from $\rm 0.3$ to $\rm 14 g/cm^{3}$. In this context, the value of the electron-atom inverse bremsstrahlung absorption is highly uncertain. We present new results obtained from a non-ideal chemical model for the ionization equilibrium, from Quantum Molecular Dynamics (QMD) simulations, and from the analysis of experimental data to better understand the ionization fraction in fluid helium in the weak ionization limit.
Technology-Enabled Nurturing of Creativity and Innovation: A Specific Illustration from an Undergraduate Engineering Physics Course
F. V. Kowalski,S. E. Kowalski,P. B. Kohl,V. H. Kuo
Physics , 2013,
Abstract: There is general agreement that creativity and innovation are desirable traits in the toolbox of 21\textsuperscript{st} century engineers, as well as in the future workforce in general. However, there is a dearth of exemplars, pedagogical models, or best practices to be implemented in undergraduate engineering education to develop and nurture those talents. In this paper, we use a specific example of a classroom activity from a course designed to help bridge the transition from learning the fundamental principles of engineering physics in introductory courses to being able to creatively and innovatively apply them in more advanced settings, such as senior capstone projects and on-the-job challenges in the future workplace. Application of techniques for generating and evaluating ideas are described. To enhance the benefits of group creativity and facilitate real-time electronic brainstorming in the classroom, we use InkSurvey with pen-enabled mobile computing devices (iPads, tablet PCs, Android devices, etc.). Using this free, web-based software in this setting effectively mitigates many of the social issues that typically plague brainstorming in a group setting. The focus, instead, is on paying attention to the ideas of others while encouraging fluency, originality, and honing positive critical thinking skills. This emphasis is reflected as the group creates a metric to evaluate their potential solutions. A specific case from undergraduate and graduate level engineering physics courses is described to illustrate how the extensive work done in this arena in psychology, marketing, and business environments can be applied to STEM education. The classroom process is outlined and actual student results are presented to illustrate the method for other instructors who might be interested in employing similar activities in a non-threatening, low-stakes learning environment.
Investigación de la microestructura y propiedades físicas de la aleación intermetálica Ni3Al P/M consolidada por HIP bajo diferentes parámetros de compactación
Hünicke, U. D.,Adeva, P.,Kowalski, W.,Acosta, P.
Revista de Metalurgia , 2001,
Abstract: The aim of this work is to study the viability of using no-destructive techniques to study the effect of consolidation parameters in the microstructure and elastic constants of a PM Ni3Al with molybdenum additions synthesized by rapid solidification and hot isostatic pressing (HIP). Furthermore the homogeneity of the compacts and presence of pores and cracks were evaluated by X-ray. For this purpose, three capsules of the alloy consolidated by HIP at different temperatures, 900, 1100 and 1250 °C, have been studied using X-ray techniques, ultrasonic measurements and Eddy-current. Parameters such as ultrasonic velocity measurements of longitudinal and transverse waves, the ultrasonic signal attenuation for high frequency, electrical conductivity and density were determined to evaluate the physical constants Eo, Go y μo. The reflected and reverberation signals have been analysed using the Fast Fourier Transformation obtaining for both a frequency spectrum that have been interpreted as Acoustic Materials Signature functions. A lineal increase of Eo and Go with an increases of the consolidation temperature has been measured which has been related to the capsules densification condition. Similar results have been obtained by measuring the electrical conductivity of the capsules. Thus, the highest value was exhibited by the capsule hipped at 1250 °C indicating that no defects are present and therefore reaching the optimal consolidation temperature. El objetivo de este trabajo ha sido estudiar la viabilidad del empleo de ensayos no destructivos, para estudiar la influencia de los parámetros de compactación en la microestructura y en las constantes elásticas de la aleación pulvimetalúrgica Ni3Al con adiciones de molibdeno. Además, la homogeneidad del material y la presencia de defectos como poros, grietas se evaluaron con ayuda de la técnica de rayos-X. Las cápsulas enteras, consolidadas mediante HIP a tres diferentes temperaturas, 900, 1100 and 1250 °C han sido estudiadas mediante las técnicas de rayos-X, ultrasonidos y corrientes inducidas. Posteriormente se examinaron partes concretas de éstas, determinando en ellas parámetros como la velocidad de transmisión de ondas longitudinales y transversales en ultrasonidos, la atenuación de la se al en ultrasonidos para frecuencias elevadas, la conductividad eléctrica y la densidad, parámetros a partir de los cuales se evaluaron las constantes físicas Eo, Go y μo. Las se ales de reflexión y reverberación obtenidas por la técnica de ultrasonidos han sido analizadas con ayuda de la transformada rápida de Fourier, FFT (F
On the Quadratic Transportation Problem  [PDF]
Veena Adlakha, Krzysztof Kowalski
Open Journal of Optimization (OJOp) , 2013, DOI: 10.4236/ojop.2013.23012

We present a direct analytical algorithm for solving transportation problems with quadratic function cost coefficients. The algorithm uses the concept of absolute points developed by the authors in earlier works. The versatility of the proposed algorithm is evidenced by the fact that quadratic functions are often used as approximations for other functions, as in, for example, regression analysis. As compared with the earlier international methods for quadratic transportation problem (QTP) which are based on the Lagrangian relaxation approach, the proposed algorithm helps to understand the structure of the QTP better and can guide in managerial decisions. We present a numerical example to illustrate the application of the proposed method.

A direct comparison of efficacy between desloratadine and rupatadine in seasonal allergic rhinoconjunctivitis: a randomized, double-blind, placebo-controlled study
Lukat KF,Rivas P,Roger A,Kowalski ML
Journal of Asthma and Allergy , 2013,
Abstract: KF Lukat,1 P Rivas,2 A Roger,3 ML Kowalski,4 U Botzen,5 F Wessel,6 F Sanquer,7 I Agache,8 I Izquierdo9Investigators working group clinical trial 1Institute Respiratory Science, Dusseldorf, Germany; 2Hospital Viladecans, ENT Department, Barcelona, Spain; 3Hospital Universitario “German Trias i Pujol,” Badalona, Spain; 4Medical University of Lodz, Immunology, Rheumatology, and Allergy, Lodz, Poland; 5ENT, private consult, Solingen, Germany; 6Allergologist, Private Practice, Nantes, France; 7Allergologist, Private Practice, Bordeaux, France; 8Medical Clinical SC Radoi Mariana SRL, Brasov, Romania; 9Clinical Research and Development, J Uriach y Compa ia, SA Barcelona, SpainBackground: H1-antihistamines are recommended as the first-line symptomatic treatment of allergic rhinitis. The objective of this study was to evaluate the effects of rupatadine (RUP) versus desloratadine (DES) in subjects with seasonal allergic rhinitis (SAR).Method: To assess the efficacy and safety of RUP in SAR in comparison with placebo (PL) and DES. A randomized, double-blind, multicenter, international, and PL-controlled study was carried out. The main selection criteria included SAR patients over 12 years old with a positive prick test to a relevant seasonal allergen for the geographic area. Symptomatic patients at screening with a nasal symptom sum score of ≥6 points (nasal discharge, nasal obstruction, sneezing, and nasal pruritus), a non-nasal score of ≥3 points (ocular pruritus, ocular redness, and tearing eyes), and a rhinorrhea score of ≥2 points with laboratory test results and electrocardiography within acceptable limits were included in the study. Change from baseline in the total symptom-score (T7SS) over the 4-week treatment period (reflective evaluation) was considered the primary efficacy variable. Secondary efficacy measures included total nasal symptom score (T4NSS) and conjunctival symptom score (T3NNSS), both of which are reflective and instantaneous evaluations. Furthermore questions related to quality of life (eg, sleep disturbances or impairment of daily activities) have also been evaluated. Safety was assessed according to adverse events reported, as well as laboratory and electrocardiography controls.Results: A total of 379 patients were randomized, of which 356 were included and allocated to PL (n = 122), RUP (n = 117), or DES (n = 117). Mean change of T7SS over the 4-week treatment period was significantly reduced in the RUP ( 46.1%, P = 0.03) and DES ( 48.9%, P = 0.01) groups, compared with PL. Similarly, RUP and DES were comparable and significantly super
11-12 Gyr old White Dwarfs 30 parsecs Away
Mukremin Kilic,John R. Thorstensen,P. M. Kowalski,J. Andrews
Physics , 2012, DOI: 10.1111/j.1745-3933.2012.01271.x
Abstract: We present a detailed model atmosphere analysis of two of the oldest stars known in the solar neighborhood, the high proper motion white dwarfs SDSS J110217.48+411315.4 (hereafter J1102) and WD 0346+246 (hereafter WD0346). We present trigonometric parallax observations of J1102, which places it at a distance of only 33.7 +- 2.0 pc. Based on the state of the art model atmospheres, optical, near-, mid-infrared photometry, and distances, we constrain the temperatures, atmospheric compositions, masses, and ages for both stars. J1102 is an 11 Gyr old (white dwarf plus main-sequence age), 0.62 Msol white dwarf with a pure H atmosphere and Teff = 3830 K. WD0346 is an 11.5 Gyr old, 0.77 Msol white dwarf with a mixed H/He atmosphere and Teff = 3650 K. Both stars display halo kinematics and their ages agree remarkably well with the ages of the nearest globular clusters, M4 and NGC 6397. J1102 and WD0346 are the closest examples of the oldest halo stars that we know of.
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