90 research outputs found
Quantitative Mapping of Strains and Young Modulus Based on Phase-Sensitive OCT
In this chapter we consider mapping of local strains and tissue elasticity in optical coherence tomography (OCT) based on analysis of phase-sensitive OCT scans. Conventional structural OCT scans correspond to spatially resolved mapping of the backscattering intensity of the probing optical beam. Deeper analysis of such sequentially acquired multiple OCT scans can be used to extract additional information about motion of scatterers in the examined region. Such detailed analysis of OCT scans has already resulted in creation of OCT-based visualization of blood microcirculation, which has been implemented in several commercially available devices, especially for ophthalmic applications. Another functional extension of OCT emerging in recent years is the OCT-based elastography, i.e., mapping of local strains and elastic properties in the imaged region. Here, we describe the main principles of local strain mapping in phase-sensitive OCT with a special focus on the recently proposed efficient vector method of estimation of interframe phase-variation gradients. The initially performed mapping of local strains is then used for realization of quantitative compressional elastography, i.e., mapping of the Young modulus and obtaining stress-strain dependences for the studied samples. The discussed principles are illustrated by simulated and experimental examples of elastographic OCT-based visualization. The presented elastographic principles are rather general and can be used in a wide area of biomedical and technical applications
Designing the setup for testing of a 30 kW steam turbine
In order to investigate a low power steam turbine with a non-standard design, an experimental stand was assembled. The main tasks in the tests are to determine the turbine efficiency and obtain the turbine power dependence on the steam consumption in steady-state conditions. The stand scheme and the equipment characteristics are given. The testing technique is described. Based on obtained results, will be conclusion made about the turbine's preparedness for mass production.С целью исследования паровой турбины малой мощности с нестандартной конструкцией собран экспериментальный стенд. Основными задачами при испытаниях является определение эффективности турбины и получение зависимости мощности турбины от расхода пара в установившихся режимах. Приведена схема стенда и характеристики оборудования. Описана методика проведения испытаний. Основываясь на полученных результатах, будет сделан вывод о готовности турбины к серийному производству
Suppression of the vacuum space-charge effect in fs-photoemission by a retarding electrostatic front lens
The performance of time-resolved photoemission experiments at fs-pulsed photon sources is ultimately limited by the e–e Coulomb interaction, downgrading energy and momentum resolution. Here, we present an approach to effectively suppress space-charge artifacts in momentum microscopes and photoemission microscopes. A retarding electrostatic field generated by a special objective lens repels slow electrons, retaining the k-image of the fast photoelectrons. The suppression of space-charge effects scales with the ratio of the photoelectron velocities of fast and slow electrons. Fields in the range from −20 to −1100 V/mm for Ekin = 100 eV to 4 keV direct secondaries and pump-induced slow electrons back to the sample surface. Ray tracing simulations reveal that this happens within the first 40 to 3 μm above the sample surface for Ekin = 100 eV to 4 keV. An optimized front-lens design allows switching between the conventional accelerating and the new retarding mode. Time-resolved experiments at Ekin = 107 eV using fs extreme ultraviolet probe pulses from the free-electron laser FLASH reveal that the width of the Fermi edge increases by just 30 meV at an incident pump fluence of 22 mJ/cm2 (retarding field −21 V/mm). For an accelerating field of +2 kV/mm and a pump fluence of only 5 mJ/cm2, it increases by 0.5 eV (pump wavelength 1030 nm). At the given conditions, the suppression mode permits increasing the slow-electron yield by three to four orders of magnitude. The feasibility of the method at high energies is demonstrated without a pump beam at Ekin = 3830 eV using hard x rays from the storage ring PETRA III. The approach opens up a previously inaccessible regime of pump fluences for photoemission experiments
РАДОН В ВОЗДУХЕ ЗДАНИЙ НАСЕЛЕННЫХ ПУНКТОВ ВИТЕБСКОЙ ОБЛАСТИ
Radon from natural and anthropogenic radiation sources contributes significantly to the public exposure. For that reason, systematic radon monitoring is carried out in Belarus. The main source of radon in the air of premises is its emanation from the geological space under the buildings. The results of radon monitoring in 665 premises in 21 settlements of Vitebsk region are presented. The parameters investigated were: radon volumetric activity in the air of home accommodations and industrial premises (ОАRn), radon equivalent equilibrium volumetric activity and annual effective dose of public exposure due to radon-222 and its progenies (ERn). The excess values of radon volumetric activity in relation to the statutory criteria (200 Bq/m3 ) have been detected for 18 premises (2.7 %). Among them 16 are living accommodation and 2 are industrial premises. The weighted average annual effective dose of public exposure due to radon and its progenies in Vitebsk region is 4.5 mSv per year. Its value for Polatsk district is 2 mSv per year and 7.6 mSv per year – for Glubokae district. Maximum of the weighted average annual effective dose is reported for Garadok dictrict and it makes 32.4 mSv per year. The population exposure to radon and its progenies is the main dose forming factor in comparison with other natural and anthropogenic radiation sources, including exposure from Chernobyl radionuclides.Проведение систематических радонометрических исследований на территории Беларуси обусловлено значительным вкладом радона в облучение населения от природных и техногенных источников ионизирующего излучения. При этом основным источником поступления радона в воздух зданий является геологическое пространство под зданиями. Представлены данные, полученные при проведении мониторинга на территории 21 административного района Витебской области: объемная активность радона в воздухе жилых и административных зданий (ОАRn), эквивалентная равновесная объемная активность радона и годовая эффективная доза облучения населения (ERn), обусловленная радоном и дочерними продуктами его распада (ДПР). Общее количество обследованных помещений составило 665. Превышение нормируемого законодательством Республики Беларусь значения ЭРОАRn (200 Бк/м3 ) наблюдалось в 18 помещениях (2,7%), среди которых 16 – жилые дома, 2 – административные здания. Средневзвешенная годовая эффективная доза облучения населения Витебской области, обусловленная радоном и его ДПР, составляет 4,5 мЗв/год, при вариации в отдельных районах от 2 (Полоцкий район) до 7,6 мЗв/год (Глубокский район). Наибольшее значение ЕRn, равное 32,4 мЗв/год, наблюдается в административном помещении Городокского района. Показано, что облучение населения Витебской области радоном и его ДПР является основным дозообразующим фактором по сравнению со всеми остальными компонентами природного и техногенного радиоактивных излучений, включая облучение от чернобыльских радионуклидов.
РАДОН В ВОЗДУХЕ ЗДАНИЙ НАСЕЛЕННЫХ ПУНКТОВ НА ТЕРРИТОРИИ БРЕСТСКОЙ ОБЛАСТИ И ЭФФЕКТИВНЫЕ ДОЗЫ ОБЛУЧЕНИЯ НАСЕЛЕНИЯ, ОБУСЛОВЛЕННЫЕ РАДОНОМ-222 И ДОЧЕРНИМИ ПРОДУКТАМИ ЕГО РАСПАДА
The analysis of specific features of the geological structure within the Brest region territory has been performed, on the basis of which settlements for radon monitoring have been selected. The technique has been described and results of the volume activity of radon in air of living, public and industrial buildings, equivalent to equilibrium volume activity of radon (EROARn) and annual effective doses (ERn) population’s irradiation caused by radon and its decay products, have been shown. Average values in various administrative districts of Brest region are within the range from 15 to 60 Bq/m3 . The value of 200 Bq/m3 has been determined in one building of Kamenets district of Brest region. The maximum average of annual effective doses of population’s irradiation is from 6,8 to 13,9 m3v/year.Проведен анализ особенностей геологического строения территории Брестской области, на основе которого выбраны населенные пункты для мониторинга радона. Описана методика и представлены результаты исследований объемной активности радона в воздухе жилых, общественных и производственных зданий, эквивалентной равновесной объемной активности радона (ЭРОАRn) и годовых эффективных доз (ERn) облучения населения, обусловленных радоном и его дочерними продуктами распада. Средние значения ЭРОАRn в различных административных районах Брестской области варьируются от 15 до 60 Бк/м3 . Значение ЭРОАRn более 200 Бк/м3 определено в одном помещении Каменецкого района Брестской области. Максимальные значения среднегодовых эффективных доз облучения населения составляют от 6,8 до 13,9 мЗв/год.
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