1,721,051 research outputs found
Centrifuge modelling of tunnelling close to a diaphragm wall
No full textThe experimental set-up and some results of a series of centrifuge tests which were performed at City University are shown and discussed. Tests were carried out on a circular model tunnel in a clay ground and in undrained conditions. The basic idea being tested was whether or not a diaphragm wall embedded at different locations close to a shallow tunnel could reduce movements in the ground extending beyond the wall and further away from the tunnel. The length of the embedded diaphragm wall was varied, as well as its thickness. The influence of the soil-walI interface was also studied. An image processing system was used to measure displacement fields in the models.
The influence of the tunnel support pressure on the displacement field is discussed. Also, the influence of the walls edge and of the embedding technique is shown. In particular two different ways of achieving a rough interface are compared.
A significant influence of the wall self-weight and of the interface roughness on the model stability was observed during the tests. Two kinematically admissible collapse mechanisms are analysed in order to understand these experimental findings
Modellazione geotecnica in centrifuga
No full textIn quasi tutti i settori dell'Ingegneria la modellazione fisica costituisce una fase significativa del processo di progettazione. Ad esempio, il progetto di un aeroplano non sarebbe considerato completo se non venisse effettuata un'estesa campagna di prove su un modello in galleria del vento. Nei moderni laboratori di Meccanica dei Terreni attrezzati con una centrifuga si modellano i problemi geotecnici in scala ridotta con raffinate strumentazioni e tecniche sofisticate, ma ormai usuali. Forse proprio per la complessità della tecnica sperimentale, nell'opinione corrente la modellazione in centrifuga resta un fatto per iniziati e raramente viene considerata un mezzo a disposizione dei tecnici per la soluzione di problemi pratici. Al contrario, le prove in centrifuga sono uno strumento di grande efficacia nell'Ingegneria Geotecnica e possono svolgere un ruolo cruciale, anche in fase di progetto, a patto che vengano rispettate regole e condizioni per cui il comportamento del modello può essere messo in relazione con quello del prototipo (leggi di scala). In questo volumetto si segue il percorso della modellazione dai principi teorici agli aspetti pratici e si presentano alcuni esempi di applicazione a problemi di Ingegneria Geotecnica
Bearing capacity of screwed conical piles in sand: centrifuge modelling
No full textPhillips R. Guo P.J, Popescu R. Editors, BALKEM
Centrifuge Modelling of Embankment Construction on Soft Clay Foundation
No full textABSTRACT : A series af centrifuge model tests inveatigatlng embankment construction on soft clay is deacribed.
The tests were designed te correspond te a full scale embankment construction for which field monitoring data were
available. Reconstituted alluvial clay was used for the small scale model foundation and the embankrnent was
constructed by pouring layers of sand onto the model durinq the centrifuge test. The centrifuge model results
showed similarity with the prototype although movemente were overpredicted by about 30%
The Effect of Overlying Strata on the Distribution of Ground Movements Induced by Tunneling in Clay
No full textFrom biology to biochemical and biophysical diagnostic tools of ovarian tumors
No full textOvarian tumors represent a diffuse clinical problem in gynecology. In industrialized countries, an ovarian tumor will develop in about 1 women in 70. Most of the tumors are benign and do not require further treatment. Therefore, a frequent problem is how to distinguish the benign from the malignant forms. The pathologist recognizes 3 groups of tumors originating from the epithelial, germ, and stromal cells. It is surprising that 90% of ovarian benign and malignant tumors throughout the world originate from epithelial cells. In fact, the epithelial cells of coelomic origin that are on the ovarian surface represent the smallest percentage of ovarian cells and are devoid of any normal function. Even though the germ and stromal cells are characterized by biologic and endocrine activities, only in a minority of cases do these give rise to ovarian benign or malignant tumors. This observation may help to explain the limited value of circulating hormonal markers in the diagnosis of ovarian tumors as well as the scarce incidence of endocrine symptoms. The effort of this article is to describe how ovarian endocrine, autocrine, and paracrine regulation may have an impact on tumorogenesis. The interaction between sex steroid hormones, gonadotropins, growth factors, and cytokines is fundamental in ovarian growth, development, differentiation, and senescence. These balanced mechanisms get lost in ovarian tumors and, in particular, in malignant transformations
Endometriosis: hormone regulation and clinical consequences of chemotaxis and apoptosis
No full textBackground: The recruitment of immune cells by chemokines and the regulation of endometrial cell apoptosis are critical aspects of endometriosis biology. Here, we review the local (paracrine) and systemic hormone (endocrine) modulation of these two specific, but highly related phenomena. Methods: We searched Pubmed for items published in English between September 1991 and September 2011 and selected the studies evaluating the effects of hormones on chemokines or apoptosis in normal human endometrium and endometriosis. Results: Estradiol has proinflammatory and antiapoptotic effects in endometrial cells, and these effects appear to be exacerbated in women with endometriosis. In these women, physiological estradiol concentrations are able to induce an enhanced inflammatory response mediated by local chemokine production and to reinforce mechanisms of cell survival mediated by extracellular signal-regulated kinases and Bcl-2. The main effect of progestogens is to inhibit interleukin-8 and other chemokines in stromal cells from both eutopic and ectopic endometrium. Progesterone is also effective in inducing apoptosis in endometrial and endometriotic cells through the inhibition of Bcl-2 and nuclear factor-kB. Conclusions: Estrogens and progestogens modulate chemotaxis and apoptosis in human endometrium and endometriotic cells and tissues. These endocrine and paracrine pathways are perturbed in women with endometriosis, contributing to inflammatory responses, abnormal tissue remodeling, therapeutic refractoriness and disease persistence. Ultimately, they promote adhesion formation and the clinical symptoms of pelvic pain and infertility. A more detailed understanding of the molecular mechanisms involved will offer new opportunities for novel pharmacological strategies to diagnose and treat endometriosi
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