A New Limit on the Antiproton Lifetime

Measurements of the cosmic ray pbar/p ratio are compared to predictions from an inhomogeneous disk-diffusion model of pbar production and propagation within the Galaxy, combined with a calculation of the modulation of the interstellar cosmic ray spectra as the particles propagate through the heliosphere to the Earth. The predictions agree with the observed pbar/p spectrum. Adding a finite pbar lifetime to the model, we obtain the limit tau_pbar > 0.8 Myr (90 % C.L.).Comment: 13 pages, 3 encapsulated Postscript figures, uses AASTeX; accepted by Astrophysical Journal; minor change

Properties of quasi-periodic pulsations in solar flares from a single active region

We investigate the properties of a set of solar flares originating from a single active region (AR) that exhibit QPPs, and look for signs of the QPP periods relating to AR properties. The AR studied, best known as NOAA 12192, was unusually long-lived and produced 181 flares. Data from the GOES, EVE, Fermi, Vernov and NoRH observatories were used to determine if QPPs were present in the flares. For the soft X-ray GOES and EVE data, the time derivative of the signal was used. Power spectra of the time series data (without any form of detrending) were inspected, and flares with a peak above the 95% confidence level in the spectrum were labelled as having candidate QPPs. The confidence levels were determined taking account of uncertainties and the possible presence of red noise. AR properties were determined using HMI line of sight magnetograms. A total of 37 flares (20% of the sample) show good evidence of having QPPs, and some of the pulsations can be seen in data from multiple instruments and in different wavebands. The QPP periods show a weak correlation with the flare amplitude and duration, but this may be due to an observational bias. A stronger correlation was found between the QPP period and duration of the QPP signal, which can be partially but not entirely explained by observational constraints. No correlations were found with the AR area, bipole separation, or average magnetic field strength. The fact that a substantial fraction of the flare sample showed evidence of QPPs using a strict detection method with minimal processing of the data demonstrates that these QPPs are a real phenomenon, which cannot be explained by the presence of red noise or the superposition of multiple unrelated flares. The lack of correlation between the QPP periods and AR properties implies that the small-scale structure of the AR is important, and/or that different QPP mechanisms act in different cases.Comment: 23 pages, 57 figures. Accepted for publication by Astronomy & Astrophysic

Diffusion and Transport Coefficients in Synthetic Opals

Opals are structures composed of the closed packing of spheres in the size range of nano-to-micro meter. They are sintered to create small necks at the points of contact. We have solved the diffusion problem in such structures. The relation between the diffusion coefficient and the termal and electrical conductivity makes possible to estimate the transport coefficients of opal structures. We estimate this changes as function of the neck size and the mean-free path of the carriers. The theory presented is also applicable to the diffusion problem in other periodic structures.Comment: Submitted to PR

Metallic Xenon, Molecular Condensates, and Superconductivity

A possibility of explaining the light absorption observed to occur under pressure-induced xenon metallization as due to the transition to the superconducting state is analyzed. The mechanism of the van der Waals bonding is discussed.Comment: LaTeX 2.09 (RevTeX), 4 pages, 4 PostScript figures included in tex

Antimatter research in Space

Two of the most compelling issues facing astrophysics and cosmology today are to understand the nature of the dark matter that pervades the universe and to understand the apparent absence of cosmological antimatter. For both issues, sensitive measurements of cosmic-ray antiprotons and positrons, in a wide energy range, are crucial. Many different mechanisms can contribute to antiprotons and positrons production, ranging from conventional reactions up to exotic processes like neutralino annihilation. The open problems are so fundamental (i.e.: is the universe symmetric in matter and antimatter ?) that experiments in this field will probably be of the greatest interest in the next years. Here we will summarize the present situation, showing the different hypothesis and models and the experimental measurements needed to lead to a more established scenario.Comment: 10 pages, 7 figures, Invited talk at the 18th European Cosmic Ray Symposium, Moscow, July 2002, submitted to Journal of Physics

Информация о книге Joseph Dubrovkin «Data Compression in Spectroscopy», Cambridge Scholars Publishing. 2022, 355 pp. ISBN (10): 1-5275-8620-0 ISBN (13): 978-1-5275-8620-8

Widespread use of instrumental methods of analysis, in particular analytical spectroscopy, in recent years has led to increasing volume of information about the objects being studied. Experimental results are stored on a computer in the form of multidimensional digital data arrays that need to be processed in a special way, for example, to remove noise, visualize, analyze, and compress for efficient storage. For these purposes, there are theoretical methods and algorithms of data compression. At the same time compression (decompression) algorithms must ensure minimum distortion of the original signals for processing hyperspectral data. Large volume of data implies a comprehensive analysis of information. When working with multidimensional arrays, it is important to use special methods and technologies for processing, analyzing and interpreting hyperspectral data. This article provides information about the monograph “Data Compression in Spectroscopy” by Joseph Dubrovkin. The book was published by Cambridge Scholars Publishing. The book was written by an expert with extensive experience in the field of multivariate data analysis and chemometrics. The book consists of a preface, information about the structure of the book, a list of abbreviations and symbols, an introduction for each of 4 chapters, 8 appendices, a list of references and a subject index. A large number of examples and exercises are illustrated with MATLAB programs, and bibliographic tables clearly demonstrate the use of compression methods in industrial and research laboratories. The material in the book is discussed chapter by chapter. This modern monograph on data compression in spectroscopy will be useful as a teaching aid for students and teaching staff, as well as for specialists in analytical laboratories.Keywords: analytical spectroscopy, data compression algorithms, multivariated data analysis, book review.Широкое применение инструментальных методов анализа, в частности, аналитической спектроскопии, в последние годы привело к увеличению объема информации об изучаемых объектах. Полученные результаты эксперимента сохраняются на компьютере в виде многомерных массивов цифровых данных, которые нужно специальным образом обрабатывать, например, убирать лишний шум, визуализировать, анализировать, сжимать для эффективного хранения. Для этих целей существуют теоретические методы и алгоритмы сжатия данных. При этом, алгоритмы сжатия (распаковки) должны обеспечивать минимальное искажение исходных сигналов обработки гиперспектральных данных. Большой объем данных подразумевает комплексный анализ информации. При работе с многомерными массивами важно использование специальных методов и технологий для обработки, анализа и интерпретации гиперспектральных данных. В настоящей статье представлена информация о монографии Joseph Dubrovkin «Data Compression in Spectroscopy». Книга опубликована издательством Cambridge Scholars Publishing. Представленная монография написана специалистом с огромным опытом работы в области анализа многомерных данных, хемометрики. Книга состоит из предисловия, информации о структуре книги, списка сокращений и символов, введения для каждой из 4 глав, 8 приложений, списка литературы и предметного указателя. Большое количество примеров и упражнений иллюстрируются программами на MATLAB, а библиографические таблицы наглядно демонстрируют применение методов сжатия в промышленных и исследовательских лабораториях. Материал книги в рецензии обсуждается по главам. Современная монография по сжатию данных в спектроскопии будет полезна в качестве учебного пособия для студентов и преподавателей, а также, специалистам аналитических лабораторий.Ключевые слова: аналитическая спектроскопия, алгоритмы сжатия данных, анализ многомерных данных, информация о книге

Gain limits of a Thick GEM in high-purity Ne, Ar and Xe

The dependence of the avalanche charge gain in Thick Gas Electron Multipliers (THGEM) on the purity of Ne, Ar and Xe filling gases was investigated. The gain, measured with alpha-particles in standard conditions (atmospheric pressure, room temperature), was found to considerably drop in gases purified by non-evaporable getters. On the other hand, small N2 admixtures to noble gases resulted in high reachable gains. The results are of general relevance in the operation of gas-avalanche detectors in noble gases, particularly that of two-phase cryogenic detectors for rare events.Comment: 15 pages, 6 figures, submitted to JINS

Polaron Transport in the Paramagnetic Phase of Electron-Doped Manganites

The electrical resistivity, Hall coefficient, and thermopower as functions of temperature are reported for lightly electron-doped Ca(1-x)La(x)MnO(3)(0 <= x <= 0.10). Unlike the case of hole-doped ferromagnetic manganites, the magnitude and temperature dependence of the Hall mobility for these compounds is found to be inconsistent with small-polaron theory. The transport data are better described by the Feynman polaron theory and imply intermediate coupling (alpha \~ 5.4) with a band effective mass, m*~4.3 m_0, and a polaron mass, m_p ~ 10 m_0.Comment: 7 pp., 7 Fig.s, to be published, PR