Lower Segment (lower + segment)

Distribution by Scientific Domains

Selected Abstracts

Channel sedimentation and erosion of the Jiangsu reach of the Yangtze River during the last 44 years

Wang Jian
Abstract River channel sedimentation in the lower reaches of the Yangtze River can be affected by both changes in sea level and changes in solid discharge from the upper river. To evaluate dynamic changes of sedimentation and erosion in the Jiangsu reach of the Yangtze River (about 330 km in length) from 1959 to 2003, databases were designed and constructed using a digital elevation model (DEM) of channel topography based on the Jiangsu River Relief Map for 1959, 1970, 1985, 1992, and 2003. The results indicated that the main course of the Yangtze River in Jiangsu Province had experienced an obvious switch from sedimentation to erosion status around 1985 because of the decreasing amount of solid load from the upper parts of the river channel after that year. The sedimentation process in the main course of the Jiangsu reach of the Yangtze River demonstrated the propulsive process of ,downstream-ward aggradations.' Between 1985 and 2003, the erosion rate of the lower segment was greater than those of the middle and upper segments; this is probably because both channel flow and tide current had influenced the lower segment. When channel flow combines with tide current in the same direction, channel erosion can be intensified, especially if there is a solid load shortage in the channel. Copyright 2009 John Wiley & Sons, Ltd. [source]

Analysis of soil,pile,structure interaction in a two-layer ground during earthquakes considering liquefaction

C. W. Lu
Abstract This study is conducted with a numerical method to investigate the seismic behaviour among certain soils, single piles, and a structure. A series of numerical simulations of the seismic behaviour of a single-pile foundation constructed in a two-layer ground is carried out. Various sandy soils, namely, dense sand, medium dense sand, reclaimed soil, and loose sand, are employed for the upper layer, while one type of clayey soil is used for the lower layer. The results reveal that when a structure is built in a non-liquefiable ground, an amplification of the seismic waves is seen on the ground surface and in the upper structure, and large bending moments are generated at the pile heads. When a structure is built in a liquefiable ground, a de-amplification of the seismic waves is seen on the ground surface and in the upper structure, and large bending moments are generated firstly at the pile heads and then in the lower segment at the boundary between the soil layers when liquefaction takes place. Copyright 2007 John Wiley & Sons, Ltd. [source]

Investigations on two-segment dielectric resonator antennas

Atabak Rashidian
Abstract Two segmented dielectric-resonator antennas have been investigated. A weighted average model is used to predict the resonant frequency. A simple method is then introduced to optimize the lower segment of the antenna. Finally, a fast and efficient design algorithm is presented. Three examples are used to implement the methods and the algorithm in three different frequency bands. Impedance bandwidths of up to 30% are achieved with the optimum design. 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 533,537, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20871 [source]

REVIEW ARTICLE: The Contribution of Macrophages to Normal and Pathological Pregnancies

Takeshi Nagamatsu
Citation Nagamatsu T, Schust DJ. The contribution of macrophages to normal and pathological pregnancies. Am J Reprod Immunol 2010 Macrophages represent one of the major leukocyte subsets in the uterine decidua. Owing to their remarkable phenotypic plasticity, decidual macrophages can participate in diverse activities during pregnancy. At baseline, decidual macrophages are characterized by an immunosuppressive phenotype and M2 polarization, supporting feto-maternal immune tolerance. In early pregnancy, macrophage-derived pro-angiogenic factors prompt vascular remodeling within the uterine wall to ensure appropriate utero-placental circulation. Upon invasion by pathogens, pattern recognition receptors on decidual macrophages help to alter the characteristics of these malleable cells toward an M1, inflammatory phenotype. Similar inflammatory characteristics are seen in those macrophages that accumulate in the lower segment of the uterus to drive cervical ripening. Disturbances in the tight control that balances macrophage function during pregnancy can trigger the development of pregnancy complications. Here, we discuss the physiologic role of uterine macrophages at different stages of pregnancy and describe their relevance in selected pregnancy disorders. [source]

Immmunohistochemical Study of the Blood and Lymphatic Vasculature and the Innervation of Mouse Gut and Gut-Associated Lymphoid Tissue

B. Ma
Summary The blood and lymphatic vascular system of the gut plays an important role in tissue fluid homeostasis, nutrient absorption and immune surveillance. To obtain a better understanding of the anatomic basis of these functions, the blood and lymphatic vasculature of the lower segment of mouse gut and several constituents of gut-associated lymphoid tissue (GALT) including Peyer's patch, specialized lymphoid nodules in the caecum, small lymphoid aggregates and lymphoid nodules in the colon were studied by using confocal microscopy. Additionally, the innervation and nerve/immune cell interactions in the gut and Peyer's patch were investigated by using cell surface marker PGP9.5 and Glial fibrillary acidic protein (GFAP). In the gut and Peyer's patch, the nerves have contact with B cell, T cell and B220CD3 double-positive cells. Dendritic cells, the most important antigen-presenting cells, were closely apposed to some nerves. Some dendritic cells formed membrane,membrane contact with nerve terminals and neuron cell body. Many fine nerve fibres, which are indirectly detected by GFAP, have contact with dendritic cells and other immune cells in the Peyer's patch. Furthermore, the expression of Muscarinic Acetylcholine receptor (subtype M2) was characterized on dendritic cells and other cell population. These findings are expected to provide a route to understand the anatomic basis of neuron-immune regulation/cross-talk and probably neuroinvasion of prion pathogens in the gut and GALT. [source]

Rupture of the uterine scar during term labour: contractility or biochemistry?

Catalin S. Buhimschi
Objective Vaginal birth after a prior low transverse caesarean section (VBAC) is advocated as a safe and effective method to reduce the total caesarean section rate. However, the risk of uterine rupture has dampened the enthusiasm of practising clinicians for VBAC. Uterine rupture occurs more frequently in women receiving prostaglandins in preparation for the induction of labour. We hypothesised that similar to the cervix, prostaglandins induces biochemical changes in the uterine scar favouring dissolution, predisposing the uterus to rupture at the scar of the lower segment as opposed to elsewhere. Design We tested aspects of this hypothesis by investigating the location of uterine rupture associated with prostaglandins and compared it with the sites of rupture in the absence of prostaglandins. Settings Two North American University Hospitals. Population Twenty-six women with a prior caesarean section, experiencing uterine rupture in active labour. Methods Retrospective review of all pregnancies complicated by uterine rupture at two North American teaching hospitals from 1991 to 2000. Main outcome measure Site of the uterine rupture. Results Thirty-four women experienced rupture after a previous caesarean section with low transverse uterine incision. Ten of the women who ruptured (29%) received prostaglandins for cervical ripening (dinoprostone: n= 8 or misoprostol: n= 2) followed by either spontaneous contractions (n= 3) or oxytocin augmentation during labour (n= 7). In 16 women (47%), oxytocin alone was sufficient for the induction/augmentation of labour. Eight (23%) women ruptured at term before reaching the active phase of labour in the absence of pro-contractile agents or attempted VBAC. There were no differences among the groups in terms of age, body mass index, parity, gestational age, fetal weight or umbilical cord pH measurements. Women treated with prostaglandins experienced rupture at the site of their old scar more frequently than women in the oxytocin-alone group whose rupture tended to occur remote from their old scar (prostaglandins 90%vs oxytocin 44%; OR: 11.6, 95% CI: 1.2,114.3). Conclusion Women in active labour treated with prostaglandins for cervical ripening appear more likely to rupture at the site of their old scar than women augmented without prostaglandins. We propose that prostaglandins induce local, biochemical modifications that weaken the scar, predisposing it to rupture. [source]