511 research outputs found
Effects of point defects on thermal and thermoelectric properties of InN
No full textIn contrast to most semiconductors, electrical conductivity of InN is known to increase upon high-energy particle irradiation. The effects of irradiation on its thermal and thermoelectric properties have yet to be investigated. Here we report the thermal conductivity of high-quality InN to be 120 W/m K and examine the effects of point defects generated by irradiation on the thermal conductivity and Seebeck coefficient. We show that irradiation can be used to modulate the thermal and thermoelectric properties of InN by controlling point defect concentrations. The thermoelectric figure of merit of InN was found to be insensitive to irradiation
Measuring Human Capital in Education
No full textWe consider education as a number of multistage creative processes and analyse one of them - teaching knowledge (Process P1) in detail. We describe the idea of a virtual production line (VPL) in the sense introduced by Walukiewicz in 2006 as an extension of Henry Ford's classical production line (CPL). Teachers connected by the Internet provide education to students on a VPL - a kind of virtual belt - teaching a given set of subjects (tasks), offering knowledge by a prescribed methodology, etc. In contrast to a CPL, teachers on a VPL will use their brain power mostly and divide the teaching process into a number of tasks in what is called "self-organization of a VPL". Thus, a VPL shall be defined as a division of labor into tasks, while a CPL will just remain a partition of labor into a fixed number of jobs (tasks). Next, we introduce the value of human capital represented by a given student as a measure of P1 efficiency and compare it with the indicators used so far. In Poland, the problem is that different skills of students are not measured within one, integrated system. We propose a solution to this problem and furnish relevant field study results. (original abstract
Data from: Possible Origin of Preformed Hole Pairs and Superconductivity in Cuprates
No full textCalculations associated with
Wang, S.; Ager, J. W.; Walukiewicz, W. Possible Origin of Preformed Hole Pairs and Superconductivity in Cuprates. arXiv 2202.03686
Abstract:
This paper addresses the long standing and controversial issue of the origin in superconducting cuprates. It is shown that the superconductivity can be attributed to amphoteric defects associated with vacancy sites in copper oxide planes. A local defect lattice relaxation results in a negative U energy binding two holes on amphoteric defects in the donor configuration that act as preformed boson pair. Thermodynamic equilibrium between defects in the donor and acceptor configurations stabilizes Fermi energy at the amphoteric defect charge transition state assuring resonant coupling between free holes and the localized hole pairs. Model calculations provide explanation for most important superconducting properties of cuprates. They show that the critical temperature is primarily determined by the density of the amphoteric defects in the donor configuration. This explains ubiquity of dome-like dependence of the critical temperature on the doping as well as its universal dependence on the superfluid density. Intentional doping with chemical acceptors or donors is neither necessary nor sufficient condition for superconductivity that is fully determined by the amphoteric defects whose concentration can be controlled by crystal nonstoichiometry. The only role of chemical doping
is changing the balance between concentrations of amphoteric defects in the donor and acceptor configurations resulting in an increase of the superfluid density and thus also the critical temperature for acceptor and a decrease for donor doping. This accounts for the experimentally observed distinct asymmetry between the dome structures for the chemical doping with acceptors
and donors. The unusual sensitivity of the critical temperature to external perturbations is explained by the resonant nature of the coupling between free holes and preformed hole pairs. The work has broader implications as it could be applicable to other superconductors with dome-like dependence of the critical temperature on doping.Jupyter notebook
This work was partially funded by the National Science Centre (Poland) NCN Opus grant no. UMO-2019/33/B/ST3/03021. Initial work was supported by by the Singapore-Berkeley Research Initiative in Sustainable Energy (SinBeRISE) which is supported by the National Research Foundation (NRF) of Singapore. JWA and initial work by WW were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract no. DE-AC02-05CH11231 within the Electronic Materials Program (KC1201)
Charge Carrier Transport in Artificially Structured Two-Dimensional Semiconductor Systems
No full textGeneral aspects of the electronic transport in two-dimensional and quasi-three-dimensional semiconductor systems are discussed. Contributions of different scattering processes to the total electron and hole mobilities in various types of modulation doped heterostructures are calculated. It is shown that in a wide temperature range phonon scattering is the principal scattering mechanism limiting electron and hole mobilities in high quality AlGaAs/GaAs modulation doped heterostructures. Scattering from rough walls in wide parabolic wells is briefly reviewed
Virtual Production Line as a model to analyze the process of creating open source software
No full textCelem artykułu jest pokazanie, w jaki sposób wirtualna taśma produkcyjna (WTP) może być wykorzystywana jako model do analizy procesu tworzenia oprogramowania open source, czyli takiego, do którego kodów źródłowych mamy pełen, wolny i swobodny dostęp. Termin wirtualna taśma produkcyjna (WTP), zaproponowany został w 2006 roku przez S. Walukiewicza i jest efektem uogólnienia pojęcia klasycznej taśmy produkcyjnej, wprowadzonej przez H. Forda w przemyśle samochodowym. Obecnie otwarte aplikacje są budowane, modyfikowane, poprawiane i rozpowszechniane dzięki wspólnej pracy twórczej programistów z całego świata. To właśnie kapitał ludzki każdego z tych twórców/programistów, czyli ich pasja, umiejętność programowania oraz chęć współpracy na WTP (kapitał społeczny) decydują o dynamicznym rozwoju i sukcesie takich rozwiązań..The main objective of this paper is to emphasize the essential role of social capital in IT companies and to demonstrate how Virtual Production Line (VPL) can be used as a model to analyze the process of creating open source software. VPL was introduced in 2006 by Walukiewicz as a model to analyze creative process and it is a natural extension of well-known Classical Production Line. Currently, open applications are built, modified, corrected and distributed owing to joint creative work of programmers. The human capital of each of these creators/programmers, their passion, programming skills and willingness to cooperate in the Virtual Production Line (social capital) decide of dynamic growth and success of such solution
SOFT COMPUTING FOR MODELLING THE VALUE OF SOCIAL CAPITAL AT RED HAT
No full textThe main objective of this paper is to predict the value of social capital at Red Hat Corporation, using a developed neural network model.
Training data were collected and calculated based on balance sheets published for the years 2005 - 2012. Five variables were proposed as an input of the neural network. The output variable presented the value of social capital, calculated by fundamental equation [Walukiewicz 2006].
The artificial neural network had been trained in Statistica Automated Neural Network
The concept of territorial cohesion – how to apply it to monitoring development of northern Polish regions.
No full textTerritorial cohesion (TC) is a multi dimensional concept, but lacking precision and not easy to be operationalized. Analysed are different scopes (or segments) of the concept and the indicators of its implementation in policy planning and decisionmaking. Amongst the already used in practice or being proposed by other authors. In the focus more interest is devoted to those which concern the segments seldomly touched so far like place- based development potential of a given territory or its landscape identity. The author recognises all the indicators of TC in the context of regional sustainable development monitoring system. The availablity of information and relevancy for solving development issues are criteria proposed to use for assessment and selection of the relevant indicators for regions in northern Poland. Their feasibility are checked at the NUTS2 and NUTS3 levels.
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