Steady state behaviour in atomic three-level lambda and ladder systems with incoherent population pumping

The steady state in three-level lambda and ladder systems is studied. It is well-known that in a lambda system this steady state is the coherent population trapping state, independent of the presence of spontaneous emission. In contrast, the steady state in a ladder system is in general not stable against radiative decay and exhibits a minimum in the population of the ground state. It is shown that incoherent population pumping destroys the stability of the coherent population trapping state in the lambda system and suppresses a previously discovered sharp dip in the steady state response. In the ladder system the observed minimum disappears in the presence of an incoherent pump on the upper transition.Comment: 4 pages, RevTex, 5 figures, to appear in Phys. Rev.

Електоральна культура в Україні (на прикладі виборів до Верховної Ради України 2012 року)

Електоральна культура – це відносно стійка система знань, оцінок і норм електоральної поведінки та відносин, виборчого процесу в цілому [1,72]. Електоральна культура виявляється у ставленні до партій, кандидатів, виборчих комісій, виборчого законодавства, у самоідентифікації себе як прихильника тієї чи іншої партії, політичної сили, у реалізації свого права на голос. Електорат, його рішення є ключовими у виборчих кампаніях, тому насамперед важливо визначити, чому і як виборці голосують на виборах. Визначальними при характеристиці електоральної культури є розуміння виборцями значимості виборів, інтерес до них і вміння оцінити ситуацію, співвіднести свої інтереси з пропозиціями і перевагами кандидатів і партій. При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/3477

Mesoscopic scattering in the half-plane: squeezing conductance through a small hole

We model the 2-probe conductance of a quantum point contact (QPC), in linear response. If the QPC is highly non-adiabatic or near to scatterers in the open reservoir regions, then the usual distinction between leads and reservoirs breaks down and a technique based on scattering theory in the full two-dimensional half-plane is more appropriate. Therefore we relate conductance to the transmission cross section for incident plane waves. This is equivalent to the usual Landauer formula using a radial partial-wave basis. We derive the result that an arbitrarily small (tunneling) QPC can reach a p-wave channel conductance of 2e^2/h when coupled to a suitable reflector. If two or more resonances coincide the total conductance can even exceed this. This relates to recent mesoscopic experiments in open geometries. We also discuss reciprocity of conductance, and the possibility of its breakdown in a proposed QPC for atom waves.Comment: 8 pages, 3 figures, REVTeX. Revised version (shortened), accepted for publication in PR

Biokinetic modeling and in vitro-in vivo extrapolations.

The introduction of in vitro methodologies in the toxicological risk assessment process requires a number of prerequisites regarding both the toxicodynamics and the biokinetics of the compounds under study. In vitro systems will need to be relevant for measuring those structural and physiological changes that are good indicators for adverse effects. Furthermore, the dose metric found to have an effect in the in vitro system should be relevant. One element in defining the appropriate dose metric is related to the kinetic behavior of the compound in the in vitro system: binding to proteins, binding to plastic, evaporation, and the interaction between the culture medium and the cells. Ways to measure and model "in vitro biokinetics" are described. Second, the appropriate dose metric in vitro, e.g., the effective concentration, will need to be extrapolated to relevant in vivo exposure scenarios. The application of physiologically based biokinetic modelling is essential in such extrapolations. The parameters needed to build these models often can be estimated based on nonanimal data, namely chemical properties (QSARs) and in vitro experiments

Kunnen we in de toxicologie toe met minder dierproeven?

Beoordeling van risico’s voor blootstelling aan stoffen is vooral gebaseerd op gegevens uit dierexperimenten. De vooruitgang in biologische kennis en toepassing van computermodellen maakt het mogelijk om die risico’s in te schatten zonder toepassing van diermodellen. Introductie van deze nieuwe strategieën in het vaststellen van normen door de overheid is noodzakelijk

Food for thought ... on education in alternative methods in toxicology.

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Transport of chlorpromazine in the Caco-2 cell permeability assay: a kinetic study

The intestinal transport of compounds can be measured in vitro with Caco-2 cell monolayers. We took a closer look at the exposure and fate of a chemical in the Caco-2 cell assay, including the effect of protein binding. Transport of chlorpromazine (CPZ) was measured in the absorptive and secretory direction, with and without albumin basolaterally. Samples were taken from medium, cells, and well plastic. For the secretory transport experiments with albumin, the free CPZ concentration at the start of the experiment was measured by negligible depletion-solid phase microextraction (nd-SPME). Recovery of CPZ from the medium was low, especially in the absorptive transport direction. CPZ was found in the cells (≤20%) and bound to the well plastic (≤25%), and 94% of CPZ was bound to albumin. An initial lag phase was observed, which was likely caused by partitioning of CPZ between the donor concentration and the Caco-2 cells; after 20 min, transport of CPZ to the receiver compartment was linear. The low recovery and the test compound found both inside the Caco-2 cells and bound to the well plastic complicate the calculation of the fraction transported and render reliable estimates of permeability constants impossible. For a chemical like chlorpromazine, which is hydrophobic in its neutral form, but in general also for more lipophilic compounds, the Caco-2 cell assay might not be straightforward, and a more detailed study into the fate and exposure of the test compound might be needed to arrive at meaningful data for transport and permeability