The propagation of in-plane P-SV waves in a layered elastic plate with periodic interface cracks: exact versus spring boundary conditions

The propagation of in-plane (P-SV) waves in a symmetrically three-layered thick plate with a periodic array of interface cracks is investigated. The exact dispersion relation is derived based on an integral equation approach and Floquet's theorem. The interface cracks can be a model for interface damage, but a much simpler model is a recently developed spring boundary condition. This boundary condition is used for the thick plate and also in the derivation of plate equations with the help of power series expansions in the thickness coordinate. For low frequencies (cracks small compared to the wavelength) the three approaches give more or less coinciding dispersion curves, and this is a confirmation that the spring boundary condition is a reasonable approximation at low frequencies

Deformation Behavior under Static and Cyclic Tension of Polymer Grafts without and after Modification by RGD Peptides

The structure, mechanical properties, and deformation behavior under static and cyclic tension of biofunctionalized biodegradable vascular grafts based on polyhydroxybutyrate/valerate and polycaprolactone were studied. It is shown that the modification gives rise to an almost twofold decrease of the elongation at break as well as the ultimate strength. It is shown that under cyclic loading the modification of grafts results in decreasing cyclic durability by more than twice. In doing so, the level of deforming stress decreases to a much lesser extent and is practically inferior to that for unmodified material. The analysis of principal strain [epsilon]1 and [epsilon]2 component distribution patterns in grafts of both types is carried out while the reason for the observed changes is discussed

In Search of Possible Associations between Planetary Nebulae and Open Clusters

We consider the possibility of cluster membership for 13 planetary nebulae that are located in close proximity to open clusters lying in their lines of sight. The short lifetimes and low sample size of intermediate-mass planetary nebulae with respect to nearby open clusters conspire to reduce the probability of observing a true association. Not surprisingly, line of sight coincidences almost certainly exist for 7 of the 13 cases considered. Additional studies are advocated, however, for 6 planetary nebula/open cluster coincidences in which a physical association is not excluded by the available evidence, namely M 1-80/Berkeley 57, NGC 2438/NGC 2437, NGC 2452/NGC 2453, VBRC 2 & NGC 2899/IC 2488, and HeFa 1/NGC 6067. A number of additional potential associations between planetary nebulae and open clusters is tabulated for reference purposes. It is noteworthy that the strongest cases involve planetary nebulae lying in cluster coronae, a feature also found for short-period cluster Cepheids, which are themselves potential progenitors of planetary nebulae.Comment: Accepted for publication in PASP (December 2007

ALGORITHMS CHANNELS OF ONBOARD MEASUREMENT SYSTEM OF PARAMETERS OF WIND VECTOR IN THE PARKING AND TAKEOFF AND LANDING MODES OF HELICOPTER

The features of construction and algorithms of information processing at parking, taxiing and maneuvering on the earth's surface, during takeoff and landing are shown

Global survey of star clusters in the Milky Way: III. 139 new open clusters at high Galactic latitudes

Context. An earlier analysis of the Milky Way Star Cluster (MWSC) catalogue revealed an apparent lack of old (t � 1 Gyr) open clusters in the solar neighbourhood (d � 1 kpc). Aims. To fill this gap we undertook a search for hitherto unknown star clusters, assuming that the missing old clusters reside at high Galactic latitudes | b | > 20°. Methods. We were looking for stellar density enhancements using a star count algorithm on the 2MASS point source catalogue. To increase the contrast between potential clusters and the field, we applied filters in colour-magnitude space according to typical colour-magnitude diagrams of nearby old open clusters. The subsequent comparison with lists of known objects allowed us to select thus far unknown cluster candidates. For verification they were processed with the standard pipeline used within the MWSC survey for computing cluster membership probabilities and for determining structural, kinematic, and astrophysical parameters. Results. In total we discovered 782 density enhancements, 524 of which were classified as real objects. Among them 139 are new open clusters with ages 8.3 < log (t [yr]) < 9.7, distances d< 3 kpc, and distances from the Galactic plane 0.3 <Z< 1 kpc. This new sample has increased the total number of known high latitude open clusters by about 150%. Nevertheless, we still observe a lack of older nearby clusters up to 1 kpc from the Sun. This volume is expected to still contain about 60 unknown clusters that probably escaped our detection algorithm, which fails to detect sparse overdensities with large angular size

Функциональная и рентгенологическая оценка респираторной системы у пациентов с нарушениями диффузионной способности легких в постковидном периоде

The objective: to evaluate functional and radiological data of the respiratory system assessment in patients with impaired lung diffusion capacity in the post-COVID period.Subjects and Methods. Clinical, functional and radiological data were analyzed and compared in the patients divided into two groups according to the degree of lung diffusion capacity (LDC) impairment measured by carbon monoxide (Dlco) after 180 (135–196) days from the onset of acute symptoms of COVID-19: Group 1 included patients with Dlco of 80–60%, and Group 2 included patients with Dlco less than 60%. The lung functions were assessed by spirometry, body plethysmography and the Dlco level measurement. The data of CT scans of patients performed in the acute period of COVID-19, after 93 (89–103) days and 180 (135–196) days from the onset of acute symptoms were analyzed.Results. The patients of Group 2 developed a severe form of COVID-19 statistically significantly more often, they required high-flow oxygen therapy (HFO) and stayed in the intensive care unit (ICU): 13/20 (65%), 11/20 (55%), 10/20 (50%) versus 8/24(33,3%), 2/24 (8,3%) and 3/24 (13,5%) in the patients of Group 2, respectively. The level of Dlco (%) after 93 (89–103) days and 180 (135–196) days in Groups 1 and 2 made 66 (64–71) and 71 (67–73) versus 45 (41–53) and 51(47–58), respectively (p&lt;0,05). Honeycombing changes in the lungs were detected by chest CT only in the patients of Group 2 – 16.7% on 93 (89–103) and 180 (135–196) days of observation, respectively.Conclusion. A severe form of COVID-19, stay in the ICU and additional oxygen support are the factors indicating an unfavorable functional state of the respiratory system and presence of irreversible changes in the lung tissue in the post-COVID period.Цель исследования: оценить функциональные и рентгенологические данные респираторной системы у пациентов с нарушениями ДСЛ в постковидном периоде.Материалы и методы. Проведен сравнительный анализ клинических, функциональных и рентгенологических данных у пациентов, разделенных на две группы по уровню снижения диффузионной способности легких (ДСЛ), измеренной по моно-оксиду углерода (Dlco) через 180 (135–196) дней от появления острых симптомов COVID-19: 1-я группа – пациенты с уровнем Dlco 80–60%, 2-я группа – Dlco менее 60%. Исследование функции легких выполняли методами спирометрии, бодиплетизмографии и исследованием уровня Dlco. Проанализированы данные КТ пациентов, выполненные в остром периоде COVID-19 через 93 (89–103) дня и 180 (135–196) дней от появления острых симптомов.Результаты. Пациенты 2-й группы статистически значимо чаще переносили тяжелую форму COVID-19, нуждались в проведении высокопоточной кислородотерапии (ВПО) и пребывали в отделении реанимации и интенсивной терапии (ОРИТ): 13/20 (65%), 11/20 (55%), 10/20 (50%), против 8/24 (33,3%), 2/24 (8,3%) и 3/24 (13,5%) у пациентов 1-й группы соответственно. Уровень Dlco (%) через 93 (89–103) дня и 180 (135–196) дней в 1-й и 2-й группе составил 66 (64–71) и 71 (67–73) против 45 (41–53) и 51 (47–58) соответственно (p&lt;0,05). Сотовая перестройка легких при КТ ОГК выявлена только у пациентов 2-й группы – по 16,7% на 93 (89–103) и 180 (135–196) дни наблюдения соответственно.Заключение. Тяжелая форма перенесенной COVID-19, пребывание в ОРИТ и дополнительная кислородная поддержка – факторы, указывающие на неблагоприятное функциональное состояние респираторной системы и наличие необратимых изменений в легочной ткани в постковидном периоде