An Estimate of the Tree-Width of a Planar Graph Which Has Not a Given Planar Grid as a Minor

We give a more simple than i

Exciton correlations in coupled quantum wells and their luminescence blue shift

In this paper we present a study of an exciton system where electrons and holes are confined in double quantum well structures. The dominating interaction between excitons in such systems is a dipole - dipole repulsion. We show that the tail of this interaction leads to a strong correlation between excitons and substantially affects the behavior of the system. Making use of qualitative arguments and estimates we develop a picture of the exciton - exciton correlations in the whole region of temperature and concentration where excitons exist. It appears that at low concentration degeneracy of the excitons is accompanied with strong multi-particle correlation so that the system cannot be considered as a gas. At high concentration the repulsion suppresses the quantum degeneracy down to temperatures that could be much lower than in a Bose gas with contact interaction. We calculate the blue shift of the exciton luminescence line which is a sensitive tool to observe the exciton - exciton correlations.Comment: 27 pages in PDF and DVI format, 8 figure

Pinning down the kaon form factors in K^+ -> mu^+ nu_mu gamma decay

We find that the normal muon polarization in the decay K->mu nu_mu gamma is very sensitive to the values of the kaon vector F_V and axial-vector F_A form factors. It is shown that the ongoing KEK-E246 experiment can definitely determine the signs of the sum of the form factors if their difference is fixed from other considerations. This method can also verify the form factor values and signs obtained from the K^+ -> l^+ nu_l e^+ e^- decays. A new experiment with sensitivity to the normal and transverse muon polarizations of about 10^-4 will provide a unique possibility to determine the F_V and F_A values with a few percent accuracy.Comment: revtex, 5 pages, 2 figures. Minor corrections made for the journal version of the pape

Upper limit on the ultra-high-energy photon flux from AGASA and Yakutsk data

We present the interpretation of the muon and scintillation signals of ultra-high-energy air showers observed by AGASA and Yakutsk extensive air shower array experiments. We consider case-by-case ten highest energy events with known muon content and conclude that at the 95% confidence level (C.L.) none of them was induced by a primary photon. Taking into account statistical fluctuations and differences in the energy estimation of proton and photon primaries, we derive an upper limit of 36% at 95% C.L. on the fraction of primary photons in the cosmic-ray flux above 10^20 eV. This result disfavors the Z-burst and superheavy dark-matter solutions to the GZK-cutoff problem.Comment: revtex, 8 pages, 4 figure

THE FEASIBILITY OF USING THE SYSTEM OF SOLAR COLLECTORS IN THE EASTERN REGIONS OF UKRAINE

У статті проведена оцінка доцільності використання системи сонячних колекторів у Східному регіоні України. Проведено оціночні розрахунки площі таких пристроїв з метою визначення можливості використовувати їх як основне джерелотеплової енергії. У результаті проведених попередніх розрахунків встановлено, що систему сонячних колекторів для даного конкретного випадку доцільно встановлювати тільки як другорядне (додатковий) джерело підігріву води, тому велике значення має об’єм затрачуваної при цьому енергії. Для використання цього виду альтернативної енергетики як основного і єдиного джерела, необхідно або зменшувати корисну площу опалювального приміщення, або збільшувати корисну площу теплопередачі.  В статье проведена оценка целесообразности использования системы солнечных коллекторов в Восточном регионе Украины. Проведены оценочные расчеты площади таких устройств с целью определения возможности использовать их как основной источник тепловой энергии.В результате проведенных предварительных оценочных расчетов установлено, что систему солнечных коллекторов для данного конкретного случая целесообразно устанавливать только как второстепенный (дополнительный) источник подогрева воды, т.к. велико значение затрачиваемой при этом энергии. Для использования этого вида альтернативной энергетики в качестве основного и единственного источника необходимо либо уменьшать полезную площадь отапливаемого помещения, либо увеличивать полезную площадь теплопередачи.The article contains assessment of the appropriateness of the use of solar collectors in the Eastern region of Ukraine. Estimated calculations of the solar collectors surface area were carried out in order to determine the feasibility of using them as the main source of thermal energy. As a result of preliminary estimations revealed that a system of solar collectors for this particular case it is advisable to install only as a secondary (additional) source of hot water, as great value with the energy expended. To use this type of alternative energy as the main and only source, you must either reduce the effective area of the heated space, or increase the effective area of heat transfer. &nbsp

Influence of Gamma-Ray Emission on the Isotopic Composition of Clouds in the Interstellar Medium

We investigate one mechanism of the change in the isotopic composition of cosmologically distant clouds of interstellar gas whose matter was subjected only slightly to star formation processes. According to the standard cosmological model, the isotopic composition of the gas in such clouds was formed at the epoch of Big Bang nucleosynthesis and is determined only by the baryon density in the Universe. The dispersion in the available cloud composition observations exceeds the errors of individual measurements. This may indicate that there are mechanisms of the change in the composition of matter in the Universe after the completion of Big Bang nucleosynthesis. We have calculated the destruction and production rates of light isotopes (D, 3He, 4He) under the influence of photonuclear reactions triggered by the gamma-ray emission from active galactic nuclei (AGNs). We investigate the destruction and production of light elements depending on the spectral characteristics of the gamma-ray emission. We show that in comparison with previous works, taking into account the influence of spectral hardness on the photonuclear reaction rates can increase the characteristic radii of influence of the gamma-ray emission from AGNs by a factor of 2-8. The high gamma-ray luminosities of AGNs observed in recent years increase the previous estimates of the characteristic radii by two orders of magnitude. This may suggest that the influence of the emission from AGNs on the change in the composition of the medium in the immediate neighborhood (the host galaxy) has been underestimated.Comment: 13 pages, 13 figures, 3 table

Radiative decay of a massive particle and the non-thermal process in primordial nucleosynthesis

We consider the effects on big bang nucleosynthesis (BBN) of the radiative decay of a long-lived massive particle. If high-energy photons are emitted after the BBN epoch ($t \sim 1 - 10^3$ sec), they may change the abundances of the light elements through photodissociation processes, which may result in a significant discrepancy between standard BBN and observation. Taking into account recent observational and theoretical developments in this field, we revise our previous study constraining the abundance of the radiatively-decaying particles. In particular, on the theoretical side, it was recently claimed that the non-thermal production of $^6$Li, which is caused by the photodissociation of \hefour, most severely constrains the abundance of the radiatively-decaying particle. We will see, however, it is premature to emphasize the importance of the non-thermal production of $^6$Li because (i) the theoretical computation of the $^6$Li abundance has large uncertainty due to the lack of the precise understanding of the $^6$Li production cross section, and (ii) the observational data of $^6$Li abundance has large errors.Comment: 15 pages, using REVTeX and 3 postscript figure