59 research outputs found

    Correlated Fast Ion Stopping in Magnetized Classical Plasma

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    The results of a theoretical investigation on the stopping power of ion pair in a magnetized electron plasma are presented, with particular emphasis on the two-ion correlation effects. The analysis is based on the assumptions that the magnetic field is classically strong (λBacλD\lambda_B\ll a_c\ll \lambda_D, where λB\lambda_B, aca_c and λD\lambda_D are respectively the electron de Broglie wavelength, Larmor radius and Debye length) and that the velocity of the two ions is identical and fixed. The stopping power and % vicinage function in a plasma are computed by retaining two-ion correlation effects and is compared with the results of the individual-projectile approximation.Comment: LaTeX, 7 pages, 4 figure

    ВОЗМОЖНОСТИ СОВРЕМЕННЫХ КЛЕТОЧНЫХ ТЕХНОЛОГИЙ ДЛЯ ВОССТАНОВЛЕНИЯ ПОВРЕЖДЕНОГО СУСТАВНОГО ХРЯЩА (АНАЛИТИЧЕСКИЙ ОБЗОР ЛИТЕРАТУРЫ)

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    Despite a wide variety of surgical procedures utilized in clinical practice for treatment of articular cartilage lesions, the search for other options of articular reconstruction remains a relevant and open issue at the current stage of medicine and biotechnologies development. The recent years demonstrated a strong belief in cellular methods of hyaline cartilage repair such as implantation of autologous chondrocytes (ACI) or cultures of mesenchymal stem cells (MSC) including techniques for genetic modification of cells.The purpose of presented review is to summarize the published scientific data on up to date results of perspective cellular technologies for articular cartilage repair that are being developed. Autologous chondrocyte transplantation originally performed by Swedish researchers in 1987 is considered the first clinically applied technique for restoration of hyaline cartilage using cellular technologies. However, the transplanted cell culture featured low proliferative capacity and inability to form a regenerate resistant to high physical activity. Another generation of methods originated at the turn of the century utilized mesenchymal stem cells instead of autologous chondrocytes. Preparation of MSCs is a less invasive procedure compared to chondrocytes harvesting and the culture is featured by a higher proliferative ability. Researchers use various biodegradable carriers (matrices) to secure cell fixation. Despite good clinical mid-term outcomes the transplanted tissue-engineering structures deteriorate with time due to cellular de-differentiation. Next generation of techniques being currently under pre-clinical studies is featured by the preliminary chondrogenic modification of transplanted cell culture. Usage of various growth factors, modified cell product and gene-activated matrices allow to gain a stable regulatory and key proteins synthesis and achieve a focused influence on regenerate's chondrogenic proliferation and in result to form a good hyaline cartilage resistant to high physical load in long term period.Thus, development of methods for articular cartilage repair has long ago went beyond the interests of clinical physicians, and only the close interdisciplinary cooperation of clinicians and specialists for cytology, molecular genetics and, probably, virology would enable replacement of a defect with a rigorous hyaline cartilage.Несмотря на внедрение в клиническую практику  широкого спектра хирургических методик лечения повреждений суставного  хряща,  на современном  этапе  развития медицины  и биотехнологий поиск  методов восстановления суставных  поверхностей  остается  очень актуальной и нерешённой  задачей. В последние  годы все больше надежд связывают  с разработкой клеточных  методов восстановления гиалинового хряща, таких как аутологичная имплантация хондроцитов,  имплантация клеточной культуры мезенхимальных стволовых клеток (МСК), в том числе с технологиями генной модификации клеток.  Целью настоящего  обзора было обобщение опубликованной в научной  литературе  информации о полученных  на современном  этапе результатах при разработке перспективных клеточных  технологий  восстановления суставного хряща.Первой клинически применяемой методикой  для восстановления гиалинового хряща с использованием клеточных  технологий   считается   аутологичная трансплантация  хондроцитов,   впервые  осуществлённая группой шведских  учёных  в 1987 г. Однако  пересаженная культура  клеток  характеризуется низким  пролиферативным потенциалам и  неспособностью  сформировать устойчивый к  повышенным  физическим нагрузкам  регенерат. Следующее  поколение  методик,  появившееся на рубеже  веков, использует  вместо  аутологичных хондроцитов мезенхимальные стволовые  клетки,  заготовка  которых  является менее  инвазивной процедурой  по сравнению с получением хондроцитов,  а сама культура  обладает повышенным  пролиферативным потенциалом.  Для надёжной фиксации клеток  исследователи используют различные биодеградируемые носители  (матрицы). Несмотря на хорошие клинические результаты,  полученные  в среднесрочной перспективе,  с течением времени в результате клеточной де-дифференцировки имплантированная тканеинженерная конструкция деградирует. Следующим поколением методов, находящимся в стадии доклинических исследований, является предварительная хондрогенная модификация имплантированной клеточной  культуры. Использование различных факторов  роста, модифицированного клеточного  продукта  и  гено-активирующих матриц, позволяет  достичь стабильного  синтеза регуляторных и ключевых белков, точечно повлиять на пролиферацию регенерата в хондрогенном направлении и, как следствие, сформировать полноценный гиалиновый хрящ, устойчивый во времени к большим физическим нагрузкам.Таким  образом, разработка  путей восстановления суставного  хряща давно вышла за рамки интересов  врачей клинических специальностей, и только тесное междисциплинарное взаимодействие клиницистов со специалистами в области клеточной  биологии, молекулярной генетики, и, возможно,  вирусологии позволит  восстановить на месте дефекта полноценный гиалиновый хрящ

    Nuclear de-excitation line spectrum of Cassiopeia A

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    The supernova remnant Cassiopeia A is a prime candidate for accelerating cosmic ray protons and ions. Gamma rays have been observed at GeV and TeV energies, which indicates hadronic interactions, but they could also be caused by inverse-Compton scattering of low-energy photons by accelerated electrons. We seek to predict the flux of nuclear de-excitation lines from Cas A through lower-energy cosmic rays and to compare it with COMPTEL measurements. Assuming a hadronic origin of the high-energy emission, we extrapolate the cosmic ray spectrum down to energies of 10 MeV, taking into account an equilibrium power-law momentum spectrum with a constant slope. We then calculate the nuclear line spectrum of Cassiopeia A, considering the most prominent chemical elements in the MeV band and their abundances as determined by X-ray spectroscopy. We show that the predicted line spectrum is close to the level of the COMPTEL sensitivity and agrees with conservative upper limits.Comment: 4 pages, 1 figure, accepted for publication by A&

    Cosmic-ray-induced ionization in molecular clouds adjacent to supernova remnants - Tracing the hadronic origin of GeV gamma radiation

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    Energetic gamma rays (GeV to TeV photon energy) have been detected toward several supernova remnants (SNR) associated with molecular clouds. If the gamma rays are produced mainly by hadronic processes rather than leptonic processes like bremsstrahlung, then the flux of energetic cosmic ray (CR) nuclei (>1 GeV) required to produce the gamma rays can be inferred at the site where the particles are accelerated in SNR shocks. It is of great interest to understand the acceleration of the CR of lower energy (<1 GeV) accompanying the energetic component. These particles of lower energy are most effective in ionizing interstellar gas, leaving an observable imprint on the interstellar ion chemistry. A correlation of energetic gamma radiation with enhanced interstellar ionization can thus support the hadronic origin of the gamma rays and constrain the acceleration of ionizing CR in SNR. We propose a method to test the hadronic origin of GeV gamma rays from SNR associated with a molecular cloud. We use observational gamma ray data for each of these SNR known, modeling the observations to obtain the underlying proton spectrum assuming that the gamma rays are produced by pion decay. Assuming that the acceleration mechanism does not only produce high energy protons, but also low energy protons, this proton spectrum at the source is then used to calculate the ionization rate of the molecular cloud. Ionized molecular hydrogen triggers a chemical network forming molecular ions. The relaxation of these ions results in characteristic line emission, which can be predicted. We show that the ionization rate for at least two objects is more than an order of magnitude above Galactic average for molecular clouds, hinting at an enhanced formation rate of molecular ions. There will be interesting opportunities to measure crucial molecular ions in the infrared and submillimeter-wave parts of the spectrum.Comment: published in Astronomy and Astrophysics, 13 pages, 19 figure

    Effect of recombinant Sox9 protein on the expression of cartilage-specific genes in human dermal fibroblasts cell culture

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    As a result of the experiments, it was shown that the recombinant Sox9 protein has practically no effect on chondrogenic differentiation and does not significantly change the expression of chondrogenesis gene

    Stopping of Charged Particles in a Magnetized Classical Plasma

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    The analytical and numerical investigations of the energy loss rate of the test particle in a magnetized electron plasma are developed on the basis of the Vlasov-Poisson equations, and the main results are presented. The Larmor rotation of a test particle in a magnetic field is taken into account. The analysis is based on the assumption that the energy variation of the test particle is much less than its kinetic energy. The obtained general expression for stopping power is analyzed for three cases: (i) the particle moves through a collisionless plasma in a strong homogeneous magnetic field; (ii) the fast particle moves through a magnetized collisionless plasma along the magnetic field; and (iii) the particle moves through a magnetized collisional plasma across a magnetic field. Calculations are carried out for the arbitrary test particle velocities in the first case, and for fast particles in the second and third cases. It is shown that the rate at which a fast test particle loses energy while moving across a magnetic field may be much higher than the loss in the case of motion through plasma without magnetic field.Comment: 14 pages, 3 figures, LaTe

    Luminescence from individual dislocations in II-VI and III-V semiconductors

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    Specificities of Scanning Electron Microscopy and Histological Methods in Assessing Cell-Engineered Construct Effectiveness for the Recovery of Hyaline Cartilage

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    Damage to the hyaline layer of the articular surface is an urgent problem for millions of people around the world. At present, a large number of experimental methods are being developed to address this problem, including the transplantation of a cell-engineered construct (CEC) composed of a biodegradable scaffold with a premixed cell culture into the damaged area of the articular surface. However, current methods for analyzing the effectiveness of such CECs have significant limitations. This study aimed to compare the SEM technique, classical histology, and cryosectioning for the analysis of CECs transplanted to hyaline cartilage

    Fluorescence dynamics of an ensemble of cold atoms

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    We have calculated the fluorescence dynamics of cold atoms excited by pulsed radiation. We have considered both Radon-Nikodym spectral method and multi-stage relaxation model describing collective effects in cold atomic gases. Relaxation times and amplitudes both at short times (superradiance) and long times (subradiance) have seen obtained
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