Исследования ледников на основе акустических измерений

The possibility of glacier ice flow studies using the method of acoustic emission (AE) in frequency range from 15 Hz to 20 kHz has been considered. A portable acoustic line system has been developed and a number of methodological issues (mounting of acoustic sensors into glacial ice, their location, reliability of acoustic coupling, etc.) have been solved. Acoustic studies of glacial ice have been performed; rock fall effect, ice cracking and ice movement on bedrock have been simulated. Correspondences of AE parameters to specific sources have been identified. The results of acoustic studies on Aldegondabreen (Spitsbergen), Central Tuyuksu and Molodezhny glaciers (northern Tien Shan) have been summarized. The dependence of the adhesive strength of ice with smooth substrate (serpentenite) on the shear rate has been considered; the effect of tor-shaped obstacle on shear force has been estimated. It is shown that the acoustic effects at cohesive ice failure on obstacles are similar to the observed natural acoustic vibrations generated in glaciers from distant sources. The results might be applied in development of the mobile ice lab and system for remote acoustic monitoring the processes in the bottom layers of glaciers.Рассмотрены возможности исследования движения льда в леднике и его анализа с помощью метода акустической эмиссии в диапазоне частот 15–20 кГц. Создана портативная измерительная акустическая линия и решён ряд методических вопросов. Выполнены акустические исследования ледникового льда, имитированы камнепад, трещинообразование в леднике и его движение по ложу. Установлены соответствия параметров акустической эмиссии определённому источнику. Обобщены результаты акустических исследований на ледниках Альдегонда (Шпицберген), Центральный Туюксу и Молодёжный (Северный Тянь-Шань). Рассмотрена зависимость адгезионной прочности соединения льда с гладкой подложкой (серпентинит) от скорости сдвига, оценено влияние препятствия в виде тора на силу сдвига. В собственных акустических спектрах исследованных ледников обнаружены акустические эффекты, характерные для разрушения льда на препятствиях. Полученные результаты можно использовать для создания мобильной ледниковой лаборатории и системы дистанционного акустического мониторинга процессов в придонных слоях ледника

Measurement of the e+e−→K+K−π+π−e^+e^- \to K^+K^-\pi^+\pi^- cross section with the CMD-3 detector at the VEPP-2000 collider

The process $e^+e^- \to K^+K^-\pi^+\pi^-$ has been studied in the center-of-mass energy range from 1500 to 2000\,MeV using a data sample of 23 pb$^{-1}$ collected with the CMD-3 detector at the VEPP-2000 $e^+e^-$ collider. Using about 24000 selected events, the $e^+e^- \to K^+K^-\pi^+\pi^-$ cross section has been measured with a systematic uncertainty decreasing from 11.7\% at 1500-1600\,MeV to 6.1\% above 1800\,MeV. A preliminary study of $K^+K^-\pi^+\pi^-$ production dynamics has been performed

Study of the process e+e−→ppˉe^+e^-\to p\bar{p} in the c.m. energy range from threshold to 2 GeV with the CMD-3 detector

Using a data sample of 6.8 pb$^{-1}$ collected with the CMD-3 detector at the VEPP-2000 $e^+e^-$ collider we select about 2700 events of the $e^+e^- \to p\bar{p}$ process and measure its cross section at 12 energy ponts with about 6\% systematic uncertainty. From the angular distribution of produced nucleons we obtain the ratio $|G_{E}/G_{M}| = 1.49 \pm 0.23 \pm 0.30$

Физическое моделирование контакта ледника с ложем (эксперименты)

Studies of the adhesive strength of glacial ice connection with bedrock has been studied using the analysis of the amplitude-frequency characteristics of acoustic emission (AE) in the frequency range from 15 Hz to 20,000 Hz. Identification of signal source on bed is based on physical modeling of adhesive ice fracture at the complex shear and patterns of elastic waves propagation in the ice using data on ice thickness of the ice and its acoustic properties. The experimental dependence of the ice and serpentinite substrate adhesive strength with temperature (from 0 °C to −30 °C) has been obtained at constraint axial shear. It is shown that the destruction of adhesive ice contact with substrate begins long before the maximum shear stress achieved, and AE signals in the coordinates amplitude-frequency-time have been obtained for the for static friction and sliding parts of deformation curves. Influence of shear to normal stresses ratio on the adhesive ice/substrate strength has been shown. Influence of the ratio of longitudinal and transverse shear stresses on the adhesive bond strength of ice to the substrate has been shown. The natural glacier spectra revealed periodic reduction of AE signals frequency in the middle range of frequencies. The similar effect of AE signals shifting along the frequency axis to the low frequency domain was obtained by testing of freshwater ice samples and related with expansion of the destruction scale. Practical application of the strain AE results for remote determination of the local glacial stability and for studies of glacier ice mechanics is discussed.Проведены комплексные исследования адгезионной прочности соединения льда с подложкой, предусматривающие анализ амплитудно-частотных характеристик сигналов акустической эмиссии (АЭ) в диапазоне частот от 15 до 20 тыс. Гц. Данные физического моделирования процессов адгезионного разрушения льда подтверждены результатами полевых исследований ледников Центральный Туюксу и Молодежный в Заилийском Алатау. Получена экспериментальная зависимость адгезионной прочности соединения льда с серпентинитом (подложкой) от температуры (от 0 до −25 °С) при осевом сдвиге в условиях стеснения. Показано, что адгезионный контакт лёд–подложка начинает разрушаться намного раньше достижения максимальных напряжений сдвига, причём для участков деформационных кривых (трение покоя и скольжения) получены диаграммы сигналов АЭ в координатах амплитуда–частота–время. Показано влияние соотношения продольных и поперечных сдвиговых напряжений на адгезионную прочность соединения льда с подложкой. В среднем диапазоне частот собственных акустических спектров ледников установлено периодическое уменьшение частоты заполнения сигналов АЭ. Аналогичный эффект смещения сигналов АЭ по оси частот в сторону низкочастотного диапазона получен при испытании образцов пресноводного льда и обусловлен расширением масштаба разрушения. Результаты исследований можно использовать для дистанционного изучения кинетики накопления трещин в придонных слоях ледникового льда

Measurement of the Pion Form Factor in the Energy Range 1.04-1.38 GeV with the CMD-2 Detector

The cross section for the process $e^+e^-\to\pi^+\pi^-$ is measured in the c.m. energy range 1.04-1.38 GeV from 995 000 selected collinear events including 860000 $e^+e^-$ events, 82000 $\mu^+\mu^-$ events, and 33000 $\pi^+\pi^-$ events. The systematic and statistical errors of measuring the pion form factor are equal to 1.2-4.2 and 5-13%, respectively.Comment: 5 pages, 2 figure

The Determination of alpha_s from Tau Decays Revisited

We revisit the determination of alpha_s(m_tau) using a fit to inclusive tau hadronic spectral moments in light of (1) the recent calculation of the fourth-order perturbative coefficient K_4 in the expansion of the Adler function, (2) new precision measurements from BABAR of e+e- annihilation cross sections, which decrease the uncertainty in the separation of vector and axial-vector spectral functions, and (3) improved results from BABAR and Belle on tau branching fractions involving kaons. We estimate that the fourth-order perturbative prediction reduces the theoretical uncertainty, introduced by the truncation of the series, by 20% with respect to earlier determinations. We discuss to some detail the perturbative prediction and show that the effect of the incomplete knowledge of the series is reduced by using the so-called contour-improved calculation, as opposed to fixed-order perturbation theory which manifests convergence problems. The corresponding theoretical uncertainties are studied at the tau and Z mass scales. Nonperturbative contributions extracted from the most inclusive fit are small, in agreement with earlier determinations. Systematic effects from quark-hadron duality violation are estimated with simple models and found to be within the quoted systematic errors. The fit gives alpha_s(m_tau) = 0.344 +- 0.005 +- 0.007, where the first error is experimental and the second theoretical. After evolution to M_Z we obtain alpha_s(M_Z) = 0.1212 +- 0.0005 +- 0.0008 +- 0.0005, where the errors are respectively experimental, theoretical and due to the evolution. The result is in agreement with the corresponding NNNLO value derived from essentially the Z width in the global electroweak fit. The alpha_s(M_Z) determination from tau decays is the most precise one to date.Comment: 22 pages, 7 figure