Low-temperature kinetics of exciton-exciton annihilation of weakly localized one-dimensional Frenkel excitons

We present results of numerical simulations of the kinetics of exciton-exciton annihilation of weakly localized one-dimensional Frenkel excitons at low temperatures. We find that the kinetics is represented by two well-distinguished components: a fast short-time decay and a very slow long-time tail. The former arises from excitons that initially reside in states belonging to the same localization segment of the chain, while the slow component is caused by excitons created on different localization segments. We show that the usual bi-molecular theory fails in the description of the behavior found. We also present a qualitative analytical explanation of the non-exponential behavior observed in both the short- and the long-time decay components.Comment: Published in J. Chem. Phys. 114, 1 April (2001

Investigation of pulse shape neutron-gamma discrimination

The role of neutron beam investigation is significant not only for fundamental science but also for various fields of applied science. This work is dedicated to the formation of neutron beams using the external 18-MeV proton beam of IBA cyclotron C18/18 with a beam current of up to 100 µA. The facility is located at the A. Alikhanyan National Science Laboratory (Yerevan Physics Institute). The possibility to obtain thermal or epithermal neutron beams using the external proton beam of the cyclotron is studied using Geant4 simulations. In this case, a quasimonoenergetic neutron source 9Be (p, n)9B reaction is chosen. As a result of the simulations, the optimal thickness of the 9Be beryllium isotope target is determined. The induced neutron beam is accompanied by a gamma ray background. To decrease the number of accompanying gamma rays, the lead absorber is considered. As a method of separating neutrons from gamma rays, the pulse shape discrimination (PSD) technique is developed. This study shows the possibility of neutron-gamma PSD and its applicability using the EJ-299-33A plastic scintillator

Superradiance from an ultrathin film of three-level V-type atoms: Interplay between splitting, quantum coherence and local-field effects

We carry out a theoretical study of the collective spontaneous emission (superradiance) from an ultrathin film comprised of three-level atoms with $V$-configuration of the operating transitions. As the thickness of the system is small compared to the emission wavelength inside the film, the local-field correction to the averaged Maxwell field is relevant. We show that the interplay between the low-frequency quantum coherence within the subspace of the upper doublet states and the local-field correction may drastically affect the branching ratio of the operating transitions. This effect may be used for controlling the emission process by varying the doublet splitting and the amount of low-frequency coherence.Comment: 15 pages, 5 figure

Lymphocyte apoptosis and immune response in patients with drug-resistant fibro-cavernous tuberculosis with different prevalence of destructive changes in the lungs

Disturbances of programmed cell death are at the heart of many immunopathological processes in tuberculosis. The relationship between activity of apoptosis and severity of immune response is of particular interest in the patients with fibrous-cavernous drug-resistant pulmonary tuberculosis at different extent of the process. The paper concerns features of apoptosis, proliferative activity of lymphocytes, cytokine’s production and subpopulation composition of peripheral blood lymphocytes in the patients with uni- and bilateral fibrous-cavernous drug-resistant pulmonary tuberculosis. It was shown that apoptotic rates in the examined patients is closely related to extent of pathological process. Extent of early and late apoptosis and, accordingly, the number of living cells reflected the progression degree of destructive process in the lungs affected by fibrous-cavernous tuberculosis. The possibility of predicting the extent of destructive changes in affected lungs based on expression of apoptosis markers is presumed. Index of activity for early apoptosis of T lymphocytes, exceeding normal values by 25% and higher were clinically significant. A clear relationship between the immune response and apoptosis level was revealed. Ambiguous changes of immunological parameters were shown with increasing apoptosis associated with the severity of destructive changes. Increased apoptotic cell death in all patients with fibrous-cavernous tuberculosis, regardless of extent of the process, was associated with inhibition of antigen-specific proliferative response, decrease in CD25+ lymphocytes, increased numbers of B cells, along with decreased production of IFNγ, IL-8, and increased IL-2 response to PPD. In cases of unilateral destruction, increased apoptotic rates were accompanied by a decrease in the CD95+ cell numbers, and a decrease in TNFα production. On the contrary, in patients with bilateral destruction it was characterized by a high content of CD95+ lymphocytes, increased production of TNFα and IL-10. An index of extremely unfavorable course of the process is a combination of high apoptosis levels and low antigen-specific response with low expression of CD25+ cells, increased number of CD19+ and CD95+ lymphocytes, decreased production of IFNγ, IL-8 and increased production of IL-2, TNFα, IL-10. The relationships found in the work indicate that the combined assessment of apoptosis indexes, together with immunological parameters, has a higher informative value when assessing the state of immunocompetent cells, the origin of the process and trends for its development. Detecting the features of programmed lymphocyte death, in conjunction with immune parameters, allows to evaluate the role of apoptosis in each single case and to predict the course of the process, with subsequent justification of immunotherapy administration

Agritourism Development Issues In Rural Places: Evidence From Armenia

The following paper summarizes the arguments and counterarguments within the scientific discussion on the issues of agritourism development issues in rural places. Agritourism development is a good source for rural development, as it will contribute to the investments in villages, increase rural income, emlpoyment, etc. The main purpose of the article is to analyze agritourism development opportunities and issues in Armenian rural place

Perioperative assessment of cardiological risk in non-cardiac surgical interventions

During the postoperative period, cardiological complications occupy the first position regarding morbidity and mortality rates. They depend on various factors such as compromised cardiovascular history and type of surgical intervention, features and type of anesthesia, water balance and postoperative care of the patient. To prevent complications, one should reply two questions: is there a risk of cardiovascular complications in the perioperative period and how to avoid them. The article presents a review of the literature on current views on the perioperative assessment of cardiac risks in patients undergoing noncardiac surgery

Human psychology during emergencie

The article examines the psychology and behavior of those affected during the Spitak earthquake, also known as the Leninakan earthquake, magnitude 8- 10, which occurred on December 7, 1988 at 10 hours 41 minutes Moscow time (11:41 local time in the north-west of the Armenian USSR). The 1988 Spitak earthquake is not considered an exceptional event from a seismological point of view. Every year 15-20 earthquakes of this magnitude occur on the planet, nevertheless, it is known for its severe consequences and is considered one of the most thoroughly studied earthquakes in the whole world. There are many books and articles on this topicВ статье рассмотрена психология и поведение пострадавших во время Спитакского землетрясения, также известного как Ленинаканское, магнитудой 8 – 10 баллов, произошедшее 7 декабря 1988 года в 10 часов 41 минуту по московскому времени (11:41 по местному времени на северо-западе Армянской СССР). Спитакское землетрясение 1988 года не считается исключительным явлением с сейсмологической точки зрения. Ежегодно на планете происходит 15-20 землетрясений такой силы, тем не менее оно известно своими тяжелыми последствиями и считается одним из самых подробно изученных землетрясений во всем мире. Имеются много книг и статей на данную тем

Ibuprofen slows migration and inhibits bowel colonization by enteric nervous system precursors in zebrafish, chick and mouse

AbstractHirschsprung Disease (HSCR) is a potentially deadly birth defect characterized by the absence of the enteric nervous system (ENS) in distal bowel. Although HSCR has clear genetic causes, no HSCR-associated mutation is 100% penetrant, suggesting gene–gene and gene-environment interactions determine HSCR occurrence. To test the hypothesis that certain medicines might alter HSCR risk we treated zebrafish with medications commonly used during early human pregnancy and discovered that ibuprofen caused HSCR-like absence of enteric neurons in distal bowel. Using fetal CF-1 mouse gut slice cultures, we found that ibuprofen treated enteric neural crest-derived cells (ENCDC) had reduced migration, fewer lamellipodia and lower levels of active RAC1/CDC42. Additionally, inhibiting ROCK, a RHOA effector and known RAC1 antagonist, reversed ibuprofen effects on migrating mouse ENCDC in culture. Ibuprofen also inhibited colonization of Ret+/− mouse bowel by ENCDC in vivo and dramatically reduced bowel colonization by chick ENCDC in culture. Interestingly, ibuprofen did not affect ENCDC migration until after at least three hours of exposure. Furthermore, mice deficient in Ptgs1 (COX 1) and Ptgs2 (COX 2) had normal bowel colonization by ENCDC and normal ENCDC migration in vitro suggesting COX-independent effects. Consistent with selective and strain specific effects on ENCDC, ibuprofen did not affect migration of gut mesenchymal cells, NIH3T3, or WT C57BL/6 ENCDC, and did not affect dorsal root ganglion cell precursor migration in zebrafish. Thus, ibuprofen inhibits ENCDC migration in vitro and bowel colonization by ENCDC in vivo in zebrafish, mouse and chick, but there are cell type and strain specific responses. These data raise concern that ibuprofen may increase Hirschsprung disease risk in some genetically susceptible children

Dynamical ionization ignition of clusters in intense and short laser pulses

The electron dynamics of rare gas clusters in laser fields is investigated quantum mechanically by means of time-dependent density functional theory. The mechanism of early inner and outer ionization is revealed. The formation of an electron wave packet inside the cluster shortly after the first removal of a small amount of electron density is observed. By collisions with the cluster boundary the wave packet oscillation is driven into resonance with the laser field, hence leading to higher absorption of laser energy. Inner ionization is increased because the electric field of the bouncing electron wave packet adds up constructively to the laser field. The fastest electrons in the wave packet escape from the cluster as a whole so that outer ionization is increased as well.Comment: 8 pages, revtex4, PDF-file with high resolution figures is available from http://mitarbeiter.mbi-berlin.de/bauer/publist.html, publication no. 24. Accepted for publication in Phys. Rev.

Bose-Einstein correlations in hadron-pairs from lepto-production on nuclei ranging from hydrogen to xenon

Bose-Einstein correlations of like-sign charged hadrons produced in deep-inelastic electron and positron scattering are studied in the HERMES experiment using nuclear targets of $^1$H, $^2$H, $^3$He, $^4$He, N, Ne, Kr, and Xe. A Gaussian approach is used to parametrize a two-particle correlation function determined from events with at least two charged hadrons of the same sign charge. This correlation function is compared to two different empirical distributions that do not include the Bose-Einstein correlations. One distribution is derived from unlike-sign hadron pairs, and the second is derived from mixing like-sign pairs from different events. The extraction procedure used simulations incorporating the experimental setup in order to correct the results for spectrometer acceptance effects, and was tested using the distribution of unlike-sign hadron pairs. Clear signals of Bose-Einstein correlations for all target nuclei without a significant variation with the nuclear target mass are found. Also, no evidence for a dependence on the invariant mass W of the photon-nucleon system is found when the results are compared to those of previous experiments