Slender structures are elegant aesthetically. The insufficiency in knowledge of the real resistance to buckling of very slender reinforced concrete columns leads to an exaggeration of the sizes of the columns. _The examples of concrete compression members cited and constructed in Industry on a global basis suggest that very slender columns have inherent safety both from the point of view of the ultimate strength and stability. The strengths of columns given. by the British codes would seem to be exceeded by many of the long slender reinforced concrete columns and struts which have been used Internationally. Both the theoretical and the experimental short term investigations have been carried out to establish the behaviour of hinged, very slender reinforced concrete columns at various stages'of axial loading. Forty three very slender reinforced concrete columns of two different square cross sections with two sizes of longitudinal reinforcements with lateral ties were cast. Slenderness rates, L A, were varied from 30 to 79. Special factors were obtained to relate the actual modulus of elasticity of concrete in columns at buckling failure to a knowledge of the initial modulus of elasticity of concrete in control cylinder specimens. Both theoretical and experimental graphs of load against moment, made dimensionless for critical sections of columns have been obtained. Dimensionless load-moment interaction diagrams using material failure as the criterion have been superimposed on these graphs to show considerable inherent material strength of the tested columns near buckling collapse failures. A theory using the fundamental approach has, been developed to predict the deflected shape and moments along the, heights of the columns at various stages of loading. The proposed theory predicts with good correlations the experimental deflections and moments of any loading stages of the columns. The theory has been used to obtain the required variables, to arrive at the initial predicted design loads of the investigated columns. Good correlations of the moments derived from observed strains have also been obtained. The developed theory predicts satisfactorily the buckling collapse loads of the columns. Although the theory has been derived for axially I loaded very slender reinforced concrete-columns, it seems to accept satisfactorily eccentricities of up to about 10 mm. This was confirmed after extensive comparisons of the theoretical buckling collapse loads with the applicable tests of other authors. Creep In the columns investigated was discovered to be one of the major factors for serious consideration. This was conclusively revealed from the observations on the last two very long term creep tests on columns. The actual safe sustained loads for these very slender columns of slenderness ratios, L/H, between 40 and 79 seem to be between 33% and 19% of the short term buckling collapse loads. The reduced modulus approach to predict the safe long term sustained loads seems to give reasonable values for L/H ratios of 40 and 50. The recommendations given for the proposed design of very slender reinforced concrete columns seem to be adequate and simple to use in practice. They are further simplified by the derivation of two equations for the reduction factors, R, for the slenderness ratios between 36 and 40 and between 40 and 79 respectively. The investigation has proved that very slender reinforced concrete columns are very dangerous structural members, as they tend to have violent buckling failures. Nevertheless, It must be prudent not to design against disaster at any cost. This Investigation seemed to have enhanced considerably knowledge of the design of very slender reinforced concrete columns.

In this paper we examine the extent of international trade synchronization during periods of international trade collapses and US recessions. Using dynamic correlations based on monthly trade data for the G7 economies over the period 1961-2011, our results suggest rather idiosyncratic patterns of international trade synchronization during collapses of international trade and US recessions. During the great recession of 2007-2009, however, international trade experienced the most sudden, severe and globally synchronized collapse. (author's abstract)

A computational model has been developed to study the effects of left ventricular assist devices (LVADs) on the cardiovascular system during a ventricular collapse. The model consists of a toroidal pulsatile blood pump and a closed loop circulatory system. Together, they predict the pump's motor current traces that reflect ventricular suck-down and provide insights into torque magnitudes that the pump experiences. In addition, the model investigates likeliness of a suction event and predicts reasonable outcomes for a few test cases. Ventricular collapse was modeled with the help of a mock circulatory loop consisting of a artificial left ventricle and centrifugal continuous flow pump. This study also investigates different suction detection schemes and proposes the most suitable suction detection algorithm for the TORVAD pump, toroidal left ventricular assist device. Model predictions were further compared against the data sampled during in vivo animal trials with the TORVAD system. The two sets of results are in good accordance. / text

The experiment performed by Itano, Heinzen, Bollinger and Wineland on the quantum Zeno effect is analyzed in detail through a quantum map derived by conventional quantum mechanics based on the Schrodinger equation. The analysis shows that a slight modification of their experiment leads to a significantly different result from the one that is predicted through von Neumann's hypothesis of collapse of the wave function in the quantum measurement theory. This may offer a possibility of an experimental test of von Neumann's quantum measurement theory. / text

Το ζήτημα της σταδιακής κατάρρευσης ήρθε στο προσκήνιο με την κατάρρευση του κτηρίου Ronan Point Apartment Building στο Ηνωμένο Βασίλειο, το 1968. Με αφορμή το γεγονός αυτό, σχεδόν το σύνολο των κανονισμών οπλισμένου σκυροδέματος ανά τον κόσμο απέκτησε διατάξεις σχετικά με την προστασία κατασκευών από σταδιακή κατάρρευση. Στα πλαίσια αυτού, εξετάζονται δύο διατάξεις πλακολωρίδας δύο ανοιγμάτων υπό το σενάριο της κατάρρευσης της ακραίας στήριξης. Η πρώτη διάταξη είναι οπλισμένη κατά τα συνήθη πρότυπα, ενώ η δεύτερη περιλαμβάνει επιπλέον οπλισμό στο άνω πέλμα των ανοιγμάτων. Οι αναλύσεις διεξάγονται σε περιβάλλον πεπερασμένων στοιχείων ANSYS και συγκρίνονται με αντίστοιχα πειραματικά αποτελέσματα. Συμπεραίνεται ότι οι συνήθεις πλάκες δεν έχουν την δυνατότητα ανάπτυξης μεγάλων μετατοπίσεων και ότι η προσθήκη οπλισμού στο άνω πέλμα των ανοιγμάτων των πλακών προσδίδει σε αυτές την απαραίτητη πλαστιμότητα, ώστε να μπορούν να αναπτύξουν μεγάλεις μετακινήσεις και να αναπτύσσονται δυνάμεις ελκυστήρα. / The issue of progressive collapse came to the foreground with the collapse of the Ronan Point Building in the UK, in 1968. In response to this event, most reinforced concrete codes around the work integrated regulations in regard to protection of buildings against progressive collapse. Two two-span slab assemblies are analysed for the collapse of the outer support. The first assembly is reinforce according to the common practice, while the second has added reinforced to the top end of the spans. The analyses are performed with ANSYS and compared with experimental results. It is concluded that commonly reinforced slabs do not have the ability to withstand large deflections. Additional top end reinforcement gives slabs the necessary plasticity in order for large deflections to be developed and tension (tie) forces to build up in the section.

In this thesis we model spherically symmetric radiating stars dissipating energy in the form of a radial heat flux. We assume that the spacetime for the interior matter distribution is shear-free. The junction conditions necessary for the matching of the exterior Vaidya solution to an interior radiating line element are obtained. In particular we show that the pressure at the boundary of the star is nonvanishing when the star is radiating (Santos 1985). The junction conditions, with a nonvanishing cosmological constant, were obtained. This generalises the results of Santos (1985) and we believe that this is an original result. The Kramer (1992) model is reviewed in detail and extended. The evolution of this model depends on a function of time which has to satisfy a nonlinear second order differential equation. We solve this differential equation in general and thereby completely describe the temporal behaviour of the Kramer model. Graphical representations of the thermodynamical and gravitational variables are generated with the aid of the software package MATHEMATICA Version 2.0 (Wolfram 1991). We also analyse two other techniques to generate exact solutions to the Einstein field equations for modelling radiating stars. In the first case the particle trajectories are assumed to be geodesics. We indicate how the model of Kolassis et al (1988) may be extended by providing an ansatz to solve a second order differential equation. In the second case we review the models of de Oliveira et al (1985, 1986, 1988) where the gravitational potentials are separable functions of the spatial and temporal coordinates. / Thesis (M.Sc.)-University of Natal, 1994.

This thesis relies on a Langrangian framework used for conservative tracer transport simulations through 2-D heterogeneous porous media. Conducted numerical simulations enable large sets of concentration values in both spatial and temporal domains. In addition to the advection, which acts on all scales, an additional mechanism considered is local scale dispersion (LSD), accounting for both mechanical dispersion and molecular diffusion. The ratio between these two mechanisms is quantified by the Peclet (Pe) number. In its base, the thesis gives answers to contaminant concentration features when influenced by: i) different log-conductivity variance; ii) log-conductivity structures defined by the same global variogram but with different log conductivity patterns cor-related; and iii) for a wide range of Peclet values. Results conducted by Monte Carlo (MC) analysis show a complex interplay between the aforementioned pa-rameters, indicating the influence of aquifer properties to temporal LSD evolu-tion. A stochastic characterization of the concentration scalar is done through moment analysis: mean, coefficient of variation (CVC), skewness and kurtosis as well as through the concentration probability density function (PDF). A re-markable collapse of higher order to second-order concentration moments leads to the conclusion that only two concentration moments are required for an accurate description of concentration fluctuations. This explicitly holds for the pure advection case, while in the case of LSD presence the Moment Deriv-ing Function (MDF) is involved to ensure the moment collapse validity. Fur-thermore, the expected mass fraction (EMF) concept is applied in groundwater transport. In its origin, EMF is function of the concentration but with lower number of realizations needed for its determination, compared to the one point PDF. From practical point of view, EMF excludes meandering effect and incorporates information about exposure time for each non-zero concentration value present. Also, it is shown that EMF is able to clearly reflect the effects of aquifer heterogeneity and structure as well as the Pe value. To demonstrate the uniqueness of the moment collapse feature and ability of the Beta distribution to account for the concentration frequencies even in real cases, Macrodisper-sion Experiment (MADE1) data sets are used. / <p>QC 20131104</p>

The current rate of species extinction is higher than at any other time in Earth’s history. Despite our understanding of the causes and consequences of extinction and the development of numerous species conservation plans, it is surprising how little we know about the dynamics of extinction and recovery. Here, I explore the dynamics of population extinction and recovery across a range of meio-invertebrate species embedded in aquatic multi-trophic communities under external pressure. My results indicate that external mortality frequency has a negative impact on the dynamics of population extinction and recovery and suggest that it may be possible to predict patterns of population extinction from patterns of population growth as well as patterns of recovery from patterns of population collapse. My findings provide a valuable empirical basis from which we may increase our understanding of the factors influencing extinction risk and recovery potential to develop sustainable management strategies.

No description available.

In thesis thesis, studies associated with the rehabilitation of the Malatya-Narli No: 7 Railroad Tunnel are presented. The rehabilitation work includes cleaning of two collapses and stopping of deformations occurring in the tunnel as well as characterizing the rock-mass by evaluating the cores obtained from 67 drill holes. Due to two collapses ocurred in the tunnel a large sinkhole (15x10x20 meters) was developed at the surface and the tunnel closed to train traffic for 10 months (September, 2002-July, 2003) covering the initiation of Iraq War. Originally, the tunnel had been opened into the paleo-landslide material in 1930. The rock-mass surrounding the tunnel consists of limestones, metavolcanics, and schists. Although the main problem in the tunnel is the reduced tunnel span caused by displacements triggerred by underground water, poor rock mass and time dependent deformations, from engineering point of view the other problems can be sited as collapses occurred in the tunnel, sinkhole devoloped at the surface and unstable sections existing in the tunnel. During the field studies, 15 deformation monitoring stations were installed aimed at determining the deviation from tunnel alignment. In order to provide stability of the tunnel Self Drilling Anchors (Mai bolts) were installed systematically around the tunnel. The details of the rock reinforcement design was presented in this thesis.