Process based model sheds light on climate sensitivity of Mediterranean tree-ring width

We use the process-based VS (Vaganov-Shashkin) model to investigate whether a regional <i>Pinus halepensis</i> tree-ring chronology from Tunisia can be simulated as a function of climate alone by employing a biological model linking day length and daily temperature and precipitation (AD 1959–2004) from a climate station to ring-width variations. We check performance of the model on independent data by a validation exercise in which the model's parameters are tuned using data for 1982–2004 and the model is applied to generate tree-ring indices for 1959–1981. The validation exercise yields a highly significant positive correlation between the residual chronology and estimated growth curve (<i>r</i>=0.76 <i>p</i><0.0001, <i>n</i>=23). The model shows that the average duration of the growing season is 191 days, with considerable variation from year to year. On average, soil moisture limits tree-ring growth for 128 days and temperature for 63 days. Model results depend on chosen values of parameters, in particular a parameter specifying a balance ratio between soil moisture and precipitation. Future work in the Mediterranean region should include multi-year natural experiments to verify patterns of cambial-growth variation suggested by the VS model

Effects of CMB temperature uncertainties on cosmological parameter estimation

We estimate the effect of the experimental uncertainty in the measurement of the temperature of the cosmic microwave background (CMB) on the extraction of cosmological parameters from future CMB surveys. We find that even for an ideal experiment limited only by cosmic variance up to l = 2500 for both the temperature and polarisation measurements, the projected cosmological parameter errors are remarkably robust against the uncertainty of 1 mK in the FIRAS instrument's CMB temperature monopole measurement. The maximum degradation in sensitivity is 20%, for the baryon density estimate, relative to the case in which the monopole is known infinitely well. While this degradation is acceptable, we note that reducing the uncertainty in the current temperature measurement by a factor of five will bring it down to the per cent level. We also estimate the effect of the uncertainty in the dipole temperature measurement. Assuming the overall calibration of the data to be dominated by the dipole error of 0.2% from FIRAS, the sensitivity degradation is insignificant and does not exceed 10% in any parameter direction.Comment: 12 pages, 2 figures, uses iopart.cls, v2: added discussion of CMB dipole uncertainty, version accepted by JCA

Elastic Spin Relaxation Processes in Semiconductor Quantum Dots

Electron spin decoherence caused by elastic spin-phonon processes is investigated comprehensively in a zero-dimensional environment. Specifically, a theoretical treatment is developed for the processes associated with the fluctuations in the phonon potential as well as in the electron procession frequency through the spin-orbit and hyperfine interactions in the semiconductor quantum dots. The analysis identifies the conditions (magnetic field, temperature, etc.) in which the elastic spin-phonon processes can dominate over the inelastic counterparts with the electron spin-flip transitions. Particularly, the calculation results illustrate the potential significance of an elastic decoherence mechanism originating from the intervalley transitions in semiconductor quantum dots with multiple equivalent energy minima (e.g., the X valleys in SiGe). The role of lattice anharmonicity and phonon decay in spin relaxation is also examined along with that of the local effective field fluctuations caused by the stochastic electronic transitions between the orbital states. Numerical estimations are provided for typical GaAs and Si-based quantum dots.Comment: 57 pages, 14 figure

Atmospheric Gravity Perturbations Measured by Ground-Based Interferometer with Suspended Mirrors

A possibility of geophysical measurements using the large scale laser interferometrical gravitational wave antenna is discussed. An interferometer with suspended mirrors can be used as a gradiometer measuring variations of an angle between gravity force vectors acting on the spatially separated suspensions. We analyze restrictions imposed by the atmospheric noises on feasibility of such measurements. Two models of the atmosphere are invoked: a quiet atmosphere with a hydrostatic coupling of pressure and density and a dynamic model of moving region of the density anomaly (cyclone). Both models lead to similar conclusions up to numerical factors. Besides the hydrostatic approximation, we use a model of turbulent atmosphere with the pressure fluctuation spectrum f^{-7/3} to explore the Newtonian noise in a higher frequency domain (up to 10 Hz) predicting the gravitational noise background for modern gravitational wave detectors. Our estimates show that this could pose a serious problem for realization of such projects. Finally, angular fluctuations of spatially separated pendula are investigated via computer simulation for some realistic atmospheric data giving the level estimate 10^{-11} rad/sqrt(Hz) at frequency 10^{-4} Hz. This looks promising for the possibility of the measurement of weak gravity effects such as Earth inner core oscillations.Comment: 13 pages, 4 pigures, LaTeX. To be published in Classical and Quantum Gravit

Эндоваскулярные методы лечения ишемического инсульта

Highlights. Mechanical thrombectomy is the “gold standard” treatment of patients with large-vessel occlusions. Five randomized trials conducted in 2015 made a significant contribution to the development and introduction of mechanical thrombectomy into clinical practice. The DAWN and DEFUSE-3 trials have provided new insights into the pathophysiology of ischemic stroke and ensured the advancement in the therapeutic field.Abstract. Stroke is one of the leading causes of death and disability worldwide. The general strategy for the treatment of ischemic stroke is aimed at restoring blood flow to the ischemic regions of the brain. Intravenous thrombolysis has been the treatment for acute ischemic stroke since 1996. However, since 2015, as a result of 5 randomized trials, endovascular mechanical thrombectomy has become the gold standard for the treatment of patients with large cerebral artery occlusion. The DAWN and DEFUSE 3 trials have provided new insights into the pathophysiology of ischemic stroke, shifting the paradigm from “time = brain” to “collaterals = brain”. In this article, the authors will consider development of endovascular devices, modern mechanical thrombectomy techniques, and directions for further research of endovascular treatment for ischemic stroke.Основные положения. Механическая тромбэкстракция – «золотой стандарт» лечения пациентов с окклюзией крупных церебральных артерий. Значительный вклад в развитие и внедрение в клиническую практику механической тромбэкстракции внесли пять рандомизированных исследований, проведенных в 2015 г. Исследования DAWN и DEFUSE 3 открыли новое понимание патофизиологии ишемического инсульта и расширения терапевтического окна.Резюме. Инсульт – одна из главных причин смертности и инвалидизации населения во всем мире. Общая стратегия терапевтических мер при ишемическом инсульте направлена на восстановление кровотока в ишемизированные отделы головного мозга. С 1996 г. внутривенная тромболитическая терапия была первой линией лечения больных ишемическим инсультом. Однако с 2015 г. на основании результатов пяти рандомизированных исследований «золотым стандартом» лечения пациентов с окклюзией крупных церебральных артерий стала эндоваскулярная механическая тромбэкстракция. Исследования DAWN и DEFUSE 3 способствовали новому пониманию патофизиологии ишемического инсульта со сменой парадигмы «время – мозг» на «коллатерали – мозг». В данной статье проанализированы этапы развития эндоваскулярных устройств, современные техники механической тромбэкстракции, а также возможные направления дальнейшего исследования эндоваскулярных методов лечения ишемического инсульта

SiPM-based azimuthal position sensor in ANITA-IV Hi-Cal Antarctic balloon experiment

Hi-Cal (High-Altitude Calibration) is a balloon-borne experiment that will be launched in December, 2016 in Antarctica following ANITA-IV (Antarctic Impulsive Transient Antenna) and will generate a broad-band pulse over the frequency range expected from radiation induced by a cosmic ray shower. Here, we describe a device based on an array of silicon photomultipliers (SiPMs) for determination of the azimuthal position of Hi-Cal. The angular resolution of the device is about 3 degrees. Since at the float altitude of ~38 km the pressure will be ~0.5 mbar and temperature ~ − 20 °C, the equipment has been tested in a chamber over a range of corresponding pressures (0.5 ÷ 1000) mbar and temperatures (−40 ÷ +50) °C

Реакция предварительно нагруженной оболочки вращения с жесткой носовой частью аппарата на ударную волну в жидкости

The article investigates the problem of hydro-elastic interaction of a weak shock wave with a rigid nosed rotation shell preloaded with axial forces. The shell is enclosed in a rigid parabolic screen, i.e. the impact of the end face and the shock wave diffraction are not considered. Liquid is regarded to be perfectly compressible. Its applied summing hydrodynamic pressure during complex interaction with the shell surface can be classified into the incident, reflected and radiated waves. The problem of hydro-elastic interaction of these shock fronts with a preloaded parabolic rigid nosed shell in a related setting is reduced to the solution of the wave equations of nonlinear system of equations for shell motion under particular initial and boundary conditions, in which the dimensionless displacement of this nose section under the impact of hydrodynamic forces is determined by integrating its motion equation. The equations, describing the dependences of nose section displacements on shock wave interaction time, take into account generalized hydrodynamic forces, including the second category directly related to the mass of the attached fluid. Determination of stress-strain state in case of interaction with the shock wave in the liquid of elastic rotation paraboloid in the form of the shell containing a rigid insertion in the nose section is reduced to the solution of a nonlinear equations system of shell motion considering the boundary conditions along fastenings at the end face of the shell and interface conditions of the shell and insertion. Dimensionless displacements of the nose section caused by hydrodynamic forces are defined by integrating the equations of motion under the initial conditions along insertion offsets in the axial directions.В статье исследуется задача гидроупругого взаимодействия слабой ударной волны с предварительно нагруженной осевыми усилиями оболочкой вращения с жесткой носовой частью. Оболочка заключена в жесткий параболический экран, то есть влияние торца и дифракция ударной волны не учитываются. Идеально сжимаемой считается жидкость, передаваемое полное гидродинамическое давление которой при комплексном взаимодействии с поверхностью оболочки может быть разложено на падающую, отраженную и излученную волны. Задача гидроупругого взаимодействия указанных ударных фронтов с нагруженной параболической оболочкой, имеющей жесткую носовую часть, в связанной постановке сводится к решению волновых уравнений нелинейной системы уравнений движения оболочки при соответствующих начальных и граничных условиях, в которых безразмерное смещение этой носовой части под действием гидродинамических сил определяется интегрированием ее уравнения движения. Уравнения, описывающие зависимости перемещений носовой части от времени взаимодействия с ударной волной, учитывают обобщенные гидродинамические силы, в том числе второй категории, непосредственно связанные с массой присоединенной жидкости. Определение напряженно-деформированного состояния при взаимодействии с ударной волной в жидкости упругого параболоида вращения в виде оболочки, содержащей в носовой части жесткую вставку, сводится к решению системы нелинейных уравнений движения оболочки с учетом граничных условий по закреплениям в торце оболочки и условий сопряжения оболочки и вставки. Безразмерные перемещения носовой части под действием гидродинамических сил определяются интегрированием уравнений движения при начальных условиях по смещениям вставки в осевых направлениях

Thermal properties and structure of cast carbon-containing invar and superinvar alloys after two-stage annealing

The effect of carbon content on thermal properties of cast superinvar alloys subjected to two-stage annealing is studied. It is shown that carbon improves the casting properties of the alloys but raises the temperature coefficient of linear expansion (CTLE). Two-stage high-temperature annealing makes it possible to remove carbon from the solid solution and to transfer it into graphite, which is accompanied by decrease in the CTLE. © 2013 Springer Science+Business Media New York

HeII->HeI Recombination of Primordial Helium Plasma Including the Effect of Neutral Hydrogen

The HeII->HeI recombination of primordial helium plasma (z = 1500 - 3000) is considered in terms of the standard cosmological model. This process affects the formation of cosmic microwave background anisotropy and spectral distortions. We investigate the effect of neutral hydrogen on the HeII->HeI recombination kinetics with partial and complete redistributions of radiation in frequency in the HeI resonance lines. It is shown that to properly compute the HeII->HeI recombination kinetics, one should take into account not only the wings in the absorption and emission profiles of the HeI resonance lines, but also the mechanism of the redistribution of resonance photons in frequency. Thus, for example, the relative difference in the numbers of free electrons for the model using Doppler absorption and emission profiles and the model using a partial redistribution in frequency is 1 - 1.3% for the epoch z = 1770 - 1920. The relative difference in the numbers of free electrons for the model using a partial redistribution in frequency and the model using a complete redistribution in frequency is 1 - 3.8% for the epoch z = 1750 - 2350.Comment: 28 pages, 9 figures, 2 tabel

Performance of the E715 Transition Radiation Detector

The transition radiation detector (TRD) consisted of 12 identical modules, each containing a radiator and a multiwire proportional counter (MWPC). A TRD is found to be an effective device for the identification of electrons in a large hadron background at Tevatron energies. The TRD proved to be a stable and reliable device with performance parameters in close agreement with theoretical predictions. The combination of a TRD with a lead glass calorimeter proved to be a very powerful method of electron identification. (LEW