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Nucleation of quantum dots
Kulveit, Jan ; Demo, Pavel (advisor) ; Polák, Karel (referee)
Quantum dots are increasingly important in many fields of science. Aminy other methods, quantum dots can also be formed by nucleation processes. In present work we study early stage of nucleation in NaCl and KCl crystals doped with PbCl2. Defect energies of small Pb clusters were calculated using numerical lattice methods. In NaCl-Pb system most stable small clusters have planar structure in {1; 1; 1}Na host lattice plane and intermittent planar phase nucleates. In contrast in KCl-Pb system small clusters with Suzuki phase structure are most stable and Suzuki phase nucleates. Formation of Suzuki phase hinders further transition to stable structure. These results of computer simulation are in agreemend with experimentally observed differences in KCl-Pb and NaCl-Pb systems behavior.
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Nucleation in complex systems
Kulveit, Jan ; Demo, Pavel (advisor) ; Slanina, František (referee) ; Vlček, Jaroslav (referee)
Title: Nucleation in complex systems Author: Jan Kulveit Institute: Institute of Physics of the Czech Academy of Sciences Supervisor: prof. Pavel Demo, Institute of Physics of the Czech Academy ofSciences, Department of Optical Materials Abstract: We studied nucleation in progressively more abstract contexts and systems, starting from classical nucleation theory and ending with nucleation in complex networks. The cases studied include impurity nucleation in a solid matrix on several alkali halide crystals, where we determined formation energies for clusters, treated as defects, starting from single impurity-vacancy dipole and small aggregates to possible configurations of larger clusters. In the next part, we turn to the study of heterogeneous nucleation. While in the usual treatment of heterogeneous nucleation the surface energy is assumed to be homogenous, we ask the question what happens if we consider the surface energy to be heteroge- neous.Utilizing umbrella sampling computer simulations we find the nucleation barrier can be significantly lowered in the presence of surface heterogeneity, even if the average surface energy is kept constant. In the last part we study influence of clustering coefficient on phase transitions in scale-free networks, using forward flux sampling (FFS). Keywords: nucleation,...
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An overview of foreign testing practices from an economic and statistical perspective
Steiner, Jakub ; Kulveit, J. ; Matysková, L. ; Jann, Ole ; Kocourek, Pavel ; Novák, Vladimír
Our testing algorithm for Covid-19 infection and how we adapt it in response to the epidemic's progress, contact tracing technology, and knowledge of the virus, will be crucial in our fight against the epidemic. That algorithm must be developed with input from epidemiologists, biochemists and others. As economists, we believe we also play a relevant role, since testing for Covid-19 infections is a classic case of the problem of allocating rare goods – tests. We have compiled the following annotated overview of testing practices abroad as a starting point for an interdisciplinary discussion, fully aware of our lack of sufficient knowledge in epidemiology, biochemistry and medicine.
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The economics of testing for Covid-19: beware of greater damage than benefit
Kulveit, J. ; Steiner, Jakub
There are limited numbers of tests for Covid-19, especially of the more precise type known as PCR tests. That means they must be used as efficiently as possible, in terms of which people are tested. Efficiency in the use of these tests is not only a matter of revealing how many people are infected, but also has to do with the potential ability of those tested to spread the infection further, which a positive test result can help to prevent. The algorithms by which the short supply of Covid-19 tests is assigned must therefore be grounded in the social, rather than individual benefits of testing. People whose testing brings maximum social benefit should be given priority. The social benefit of testing a particular person is calculated primarily in terms of the a priori likelihood (rough estimation) of that person being infected, based on information about where they live and their lifestyle. The second important criterion is that individual’s epidemiological significance, which is an indication of how much the individual in questions comes into contact with, and is likely to come into further contact with other at-risk people. This can also be established by asking pertinent questions to the individual themselves, complemented if desired by a survey in the place where they live. Although our estimations of the social benefit of testing are based on imprecise and incomplete data, the algorithm for allocating the limited numbers of PCR tests we have that is based on them is more socially effective than blanket use of them for testing anyone suspected of having contracted Covid-19. The greatest social benefit of testing comes from identifying the infection in people whose level of social interaction is high, during the phase of the infection in which they do not yet have any symptoms, that is, in so-called superspreaders. When evaluating the results of any test it is necessary to bear in mind that no test is ever entirely precise (reliable). Although PCR tests are very precise in laboratory conditions, errors can occur when samples are collected in the field, for example through poor sample handling. Our interpretation of the test result is then sensitive to the a priori likelihood that the person in question is infected, which might be low even when the test is positive, because the tests are not entirely reliable. It is not appropriate to use tests in situations in which nothing about the healthcare official’s decision about the next steps to take will change, regardless of the test result. If the healthcare official knows beforehand that they will not change their approach even if the result of the test is surprising, they should not waste one of those rather rare tests on testing the patient in question. Among the general public, testing can create undesirable motives that facilitate the spread of the infection. For example, if only people with a high a priori likelihood of infection are tested, people will exaggerate their own likelihood of being infected in an effort to gain access to testing. That’s why, for example, at the beginning of the Covid-19 epidemic in the Czech Republic, some Czechs who wanted to get themselves tested told healthcare officials they had been in Italy, when in fact they had not. Having been approved for testing, they then unnecessarily exposed themselves to the virus at the testing facilities. Social stigma surrounding infection with Covid-19 also poses complications, since it motivates people to conceal any symptoms they are experiencing and avoid being tested. For that reason, it may be sensible not to publicise details of the algorithm according to which individuals might be selected for testing, and to work systematically and intensively to prevent any stigma associated with Covid-19 infection through media campaigns and raising public awareness.
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Nucleation in complex systems
Kulveit, Jan ; Demo, Pavel (advisor) ; Slanina, František (referee) ; Vlček, Jaroslav (referee)
Title: Nucleation in complex systems Author: Jan Kulveit Institute: Institute of Physics of the Czech Academy of Sciences Supervisor: prof. Pavel Demo, Institute of Physics of the Czech Academy ofSciences, Department of Optical Materials Abstract: We studied nucleation in progressively more abstract contexts and systems, starting from classical nucleation theory and ending with nucleation in complex networks. The cases studied include impurity nucleation in a solid matrix on several alkali halide crystals, where we determined formation energies for clusters, treated as defects, starting from single impurity-vacancy dipole and small aggregates to possible configurations of larger clusters. In the next part, we turn to the study of heterogeneous nucleation. While in the usual treatment of heterogeneous nucleation the surface energy is assumed to be homogenous, we ask the question what happens if we consider the surface energy to be heteroge- neous.Utilizing umbrella sampling computer simulations we find the nucleation barrier can be significantly lowered in the presence of surface heterogeneity, even if the average surface energy is kept constant. In the last part we study influence of clustering coefficient on phase transitions in scale-free networks, using forward flux sampling (FFS). Keywords: nucleation,...
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Nucleation of quantum dots
Kulveit, Jan ; Polák, Karel (referee) ; Demo, Pavel (advisor)
Quantum dots are increasingly important in many fields of science. Aminy other methods, quantum dots can also be formed by nucleation processes. In present work we study early stage of nucleation in NaCl and KCl crystals doped with PbCl2. Defect energies of small Pb clusters were calculated using numerical lattice methods. In NaCl-Pb system most stable small clusters have planar structure in {1; 1; 1}Na host lattice plane and intermittent planar phase nucleates. In contrast in KCl-Pb system small clusters with Suzuki phase structure are most stable and Suzuki phase nucleates. Formation of Suzuki phase hinders further transition to stable structure. These results of computer simulation are in agreemend with experimentally observed differences in KCl-Pb and NaCl-Pb systems behavior.
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Zhodnocení ekosystémových a zdravotních rizik persistentních environmentálních polutantů HM‚ POPs ve vztahu k závazkům ČR v rámci koncepce CLRTAP a navazujících protokolů včetně cílů definovaných pracovní skupinou pro efekty (WG-UN ECE)
Český hydrometeorologický ústav, Praha ; Výzkumný ústav vodohospodářský T.G. Masaryka, Praha ; EGÚ Praha Engineering, a.s., Praha ; Český ekologický ústav, Praha ; TOCOEN, s.r.o., Brno ; Ekotoxa Opava, s.r.o., Opava ; Fottová, Daniela ; Kulveit, Jaroslav ; Ansorgová, Alena ; Kosubová, Petra ; Dušek, Ladislav ; Skořepová, Irena ; Pačes, Tomáš ; Fara, Milan ; Sáňka, Milan ; Rieder, Marek ; Kohoutek, Jiří ; Komprda, Jiří ; Holoubková, Irena ; Čupr, Pavel ; Holoubek, Ivan ; Zapletal, Miloš
Závěrečná zpráva za rok 2001 je členěna do 13 hlavních kapitol. Literární rešerše přístupů k hodnocení ekosystémových rizik plynoucích z přítomnosti HMs a POPs v prostředí. Literární rešerše a příprava podkladů pro odhady zdravotních rizik. Literární rešerše modelů distribuce POPs v prostředí. Inventarizace a sumarizace datových zdrojů o koncentracích POPs pro jednotlivé složky ekosystému. Stanovení cílových kritických limitů pro vybrané složky ekosystému a lidskou populaci. Emisní datové zdroje a jejich využití pro hodnocení ekologických a zdravotních rizik. Specifikace datových zdrojů jako vstupů do matematických modelů výpočtu kritických zátěží. Výpočet kritických zátěží těžkých kovů - statický přístup - příklad modelového povodí. Kritické zátěže těžkých kovů - semidynamický model. Využití údajů Národního onkologického registru a údajů UOC MU pro posouzení vztahů mezi výskytem zhoubných nádorů a kontaminací prostředí HMs a POPs. Odběry vzorků na modelových lokalitách pro zajištění základních dat pro modelování, jejich analýzy, vyhodnocování základních dat z experimentálních stanovišť na modelových lokalitách. Doplňkové sledování dosud málo sledovaných polutantů v hlavních složkách ekosystému: stanovení toxafenu, event. chlordanu. Atmosférická depozice těžkých kovů.
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