Progressive Strain of Sand Due to Cyclic Loading

Progressive axial strain produced by cyclic, triaxial loading conditions was measured on Ottawa sand samples of various relative densities. The theoretical cyclic shearing strain amplitude in each sample was determined using a modified, hyperbolic shearing stress-shearing strain relationship. The data shows a linear log-log correlation between the measured progressive axial strain and the calculated cyclic shearing strain amplitude. The correlation is proposed as a general procedure for predicting progressive strains resulting from general cyclic, triaxial loading conditions

Dynamics and microscopic origin of fast 1.5 μm emission in Er-doped SiO<inf>2</inf> sensitized with Si nanocrystals

We investigate the origin of fast 1.5 μm photoluminescence from Er-doped SiO2 sensitized with silicon nanocrystals, which appears and decays within the first microsecond after a short laser excitation pulse. Time-resolved and temperature-dependent measurements on the 1.5 μm emission from Er-doped and Er-free samples reveal that the major part of this emission is Er related. A possible contribution from other photoluminescence bands, specifically of the defect-related band centered around 1.3 μm, has also been considered. All the results obtained indicate the dominant contribution of Er3+ ions to the fast 1.5 μm emission in the investigated materials. We propose two possible mechanisms behind the fast excitation and quenching of Er3+ 1.5 μm emission, which are both facilitated by Er-related trap centers with ionization energy of EA ∼60 meV. © 2011 American Physical Society

Energy transfer processes in Er-doped SiO2 sensitized with Si nanocrystals

We present a high-resolution photoluminescence study of Er-doped SiO2 sensitized with Si nanocrystals (Si NCs). Emission bands originating from recombination of excitons confined in Si NCs and of internal transitions within the 4f-electron core of Er3+ ions, and a band centered at lambda = 1200nm have been identified. Their kinetics have been investigated in detail. Based on these measurements, we present a comprehensive model for energy transfer mechanisms responsible for light generation in this system. A unique picture of energy flow between subsystems of Er3+ and Si NCs is developed, yielding truly microscopic information on the sensitization effect and its limitations. In particular, we show that most of the Er3+ ions available in the system are participating in the energy exchange. The long standing problem of apparent loss of optical activity of majority of Er dopants upon sensitization with Si NCs is clarified and assigned to appearance of a very efficient energy exchange mechanism between Si NCs and Er3+ ions. Application potential of SiO2:Er sensitized by Si NCs is discussed in view of the newly acquired microscopic insight.Comment: 30 pages 13 figure

Лечение артериальной гипертензии в преклонном возрасте: от отрицания до признания необходимости

Представлен анализ результатов клинических исследований антигипертензивной терапии у пожилых пациентов, позволяющий сделать заключение о целесообразности ее проведения даже после достижения 80−летнего возраста.The analysis of the findings of clinical research of antihypertensive therapy in elderly patients, which allowed to conclude about the necessity about the expediency of its administration even in patients over 80, is presented