Search results for "STRESS"
showing 10 items of 6278 documents
Method to compute the stress-energy tensor for a quantized scalar field when a black hole forms from the collapse of a null shell
2020
A method is given to compute the stress-energy tensor for a massless minimally coupled scalar field in a spacetime where a black hole forms from the collapse of a spherically symmetric null shell in four dimensions. Part of the method involves matching the modes for the in vacuum state to a complete set of modes in Schwarzschild spacetime. The other part involves subtracting from the unrenormalized expression for the stress-energy tensor when the field is in the in vacuum state, the corresponding expression when the field is in the Unruh state and adding to this the renormalized stress-energy tensor for the field in the Unruh state. The method is shown to work in the two-dimensional case wh…
Water diffusion and swelling stresses in ionizing radiation cured epoxies as matrices for carbon fiber composites
2017
Cross-linking polymerization initiated by high energy radiation is a very attractive technique for the production of high performance composite materials. This method in fact offers many advantages compared to conventional thermal curing processes, due to the possibility to operate at mild temperature and in short time, limiting both energy and time consuming [1-2]. High performance composite materials mainly consist of epoxy resins as matrix and carbon fibers as reinforce, due to their excellent properties in terms of thermal and mechanical resistance. An important requirement of such systems for structural applications is their ability to maintain the properties within a fixed range durin…
Compressive behavior of short high-strength concrete columns
2010
Abstract The focus of the present paper is the compressive response of short high strength reinforced concrete members. Members have square transverse cross-sections and they are reinforced with longitudinal steel bars and transverse stirrups. A preliminary analysis to check the stability condition of longitudinal bars was made to verify that buckling occurs after yielding in compression. Prescriptions on required diameter and spacing of stirrups are given. In the following, a model is presented which allows us to evaluate the confinement pressures exercised by transverse steel and by longitudinal bars during the loading process taking into account the interaction of the stirrups with the i…
Influence of steel reinforcements on the behavior of compressed high strength R.C. circular columns
2012
Abstract In the present paper the focus is on the compressive response of short high strength reinforced concrete members having circular transverse cross-sections and reinforced with longitudinal steel bars and transverse spirals or hoops. An analytical model is proposed which allows one to estimate the confinement pressures exerted by transverse steel and by longitudinal bars during the loading process, taking into account the interaction of the hoops or spirals with the inner core both in the plane of the transverse steel and in the space between two successive hoops. Yielding of steel spirals or hoops and longitudinal bars including buckling phenomena and damage to the concrete core are…
Large eddy simulations on the effect of the irregular roughness shape on turbulent channel flows
2019
Abstract Large Eddy Simulations (LES) are carried out to investigate on the mean flow in turbulent channel flows over irregular rough surfaces. Here the attention is focused to selectively investigate on the effect induced by crests or cavities of the roughness. The irregular shape is generated through the super-imposition of sinusoidal functions having random amplitude and four different wave-lengths. The irregular roughness profile is reproduced along the spanwise direction in order to obtain a 2D rough shape. The analysis of the mean velocity profiles shows that roughness crests induce higher effect in the outer-region whereas roughness cavities cause the highest effects in the inner-reg…
Granular chains for the assessment of thermal stress in slender structures
2015
Slender beams subjected to compressive stress are common in civil and mechanical engineering. The rapid in-situ measurement of this stress may prevent structural anomalies. In this paper, we describe the coupling mechanism between highly nonlinear solitary waves (HNSWs) propagating along an L-shaped granular system and a beam in contact with the granular medium. We evaluate the use of HNSWs as a tool to measure stress in thermally loaded structures and to estimate the neutral temperature, i.e. the temperature at which this stress is null. We investigated numerically and experimentally one and two L-shaped chains of spherical particles in contact with a prismatic beam subjected to heat. We f…
Functional assays of oxidative stress using genetically engineered Escherichia coli strains.
2003
Oxidative stress may be induced in bacteria by exogenous biocidal agents and is involved in endogenous metabolism. The oxyR operon is a main sensor of oxidative stress and oxyR-deficient bacteria show enhanced sensitivity to oxidative stress and increased accumulation of intracellular reactive oxygen species (ROS). Flow cytometric functional assays in bacteria are limited by the impaired penetration of vital dyes trough the cell wall. Escherichia coli B WP2 strains possess an altered cell-wall lipopolysaccharide that leads to increased membrane permeability. Flow cytometric analysis of WP2 strains is a convenient alternative for cytometric assays of bacterial function. This unit presents pr…
Blood flow shapes intravascular pillar geometry in the chick chorioallantoic membrane.
2010
The relative contribution of blood flow to vessel structure remains a fundamental question in biology. To define the influence of intravascular flow fields, we studied tissue islands--here defined as intravascular pillars--in the chick chorioallantoic membrane. Pillars comprised 0.02 to 0.5% of the vascular system in 2-dimensional projection and were predominantly observed at vessel bifurcations. The bifurcation angle was generally inversely related to the length of the pillar (R = -0.47, P .05). 3-dimensional computational flow simulations indicated that the intravascular pillars were located in regions of low shear stress. Both wide-angle and acute-angle models mapped the pillars to regio…
In vivo detection of cytokeratin filament network breakdown in cells treated with the phosphatase inhibitor okadaic acid.
2001
We have previously described vulva carcinoma-derived A-431 subclone AK13-1, which stably expresses fluorescently labeled cytokeratin filaments (CKFs). Time-lapse fluorescence microscopy of these cells permits the continuous monitoring of the dynamics of the CKF cytoskeleton in vivo. To study mechanisms and principles of CKF disassembly as it occurs, e.g., during mitosis and liver disease, we have treated cells with the phosphatase inhibitor okadaic acid (OA), which induces complete CKF network breakdown within 3–5 h without significantly affecting the organization of the actin- and tubulin-based cytofilaments. In time-lapse movies, we find that the network breakdown starts at the cell perip…
Immunohistochemical expression of apoptotic factors, cytokeratins, and metalloproteinase-9 in periapical and epithelialized gingival lesions
2012
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