Impact Strength Of Glass And Glass Ceramic

Strength of glass and glass ceramic was measured with a bar impact technique. High-speed movies show regions of tensile and compressive failure. The borosilicatc glass had a compressive strength of at least 2.2 GPa, and the glass ceramic at least 4 GPa. However, the BSG was much stronger in tension than GC. In ballistic tests, the BSG was the superior armor.Mechanical Engineerin

Improved Bar Impact Tests Using A Photonic Doppler Velocimeter

Bar impact tests, using the techniques described elsewhere in this symposium, were used to measure compressive and tensile strengths of borosilicate glass, soda lime glass, and a glass ceramic. The glass ceramic was 25% crystalline spinel, furnished by Corning Inc. There are two measures of compressive strength: the peak stress that can be transmitted in unconfined compression, and the >steady state> strength. For borosilicate glass and soda lime glass, these values were similar, being about 1.8 and 1.5 GPa, respectively. The glass ceramic (25% spinel) was almost 50% stronger. Tensile failure in the glass and glass ceramic takes places via surface flaws, and thus tensile strength is an extrinsic, as opposed to intrinsic property.Mechanical Engineerin

X-Ray Tomography To Measure Size Of Fragments From Penetration Of High-Velocity Tungsten Rods

Behind-armor debris that results from tungsten rods penetrating armor steel at 2 km/s was studied by analysis of recovered fragments. Fragment recovery was by means of particle board. Individual fragments were analyzed by x-ray tomography, which provides information for fragment identification, mass, shape, and penetration down to masses of a few milligrams. The experiments were complemented by AUTODYN and EPIC calculations. Fragments were steel or tungsten generated from the channel or from the breakout through the target rear surface. Channel fragment motions were well described by Tate theory. Breakout fragments had velocities from the projectile remnant to the channel velocity, apparently depending on where in the projectile a fragment originated. The fragment size distribution was extremely broad and did not correlate well with simple uniform-fragment-size models.Mechanical Engineerin

The intracellular behaviour of Burkholderia cenocepacia in murine macrophages

Burkholderia cenocepacia is an opportunistic pathogen causing life-threatening infections in cystic fibrosis and other immunocompromised patients. The bacterium survives within macrophages by interfering with typical endocytic trafficking, resulting in delayed maturation of a B. cenocepacia-containing phagosome. We hypothesize that B. cenocepacia alters gene expression after internalization by macrophages, inducing genes involved in intracellular survival and host adaptation. Furthermore, we hypothesize that specialized bacterial secretion systems are involved in the interactions between intracellular bacteria and macrophages. In this work, we characterize later-stage infection of macrophages by B. cenocepacia, showing replication within an acidified endosomal compartment suggestive of a phagolysosome. We examine differential gene expression by intracellular B. cenocepacia using selective capture of transcribed sequences (SCOTS) with both competitive enrichment and microarray analysis. We identified 766 genes differentially regulated in intracellular bacteria, of which 329 were induced and 437 repressed. Affected genes are involved in all aspects of cellular life, including information storage and processing, cellular processes and signalling, and metabolism; in general, intracellular gene expression demonstrates a pattern of environmental sensing, bacterial response, and metabolic adaptation to the phagosomal environment. Deletion of various SCOTS-identified genes affects B. cenocepacia entry into macrophages and intracellular replication, as well as host-directed cytotoxicity and spread to neighbouring cells. Expression of secretion system genes is differentially-regulated by intracellular B. cenocepacia. Although none of the five major secretion systems are essential for growth in culture, we show that bacterial secretion systems are involved in macrophage entry, intracellular replication, and host-directed cytotoxicity. Type IV secretion systems play a role in early interactions with macrophages, while type II and IV secretion systems contribute to post-internalization intracellular replication and host-directed cytotoxicity. As a whole, secretion systems appear to increase pathogenicity in macrophages while limiting the spread of B. cenocepacia infection. Together, these studies advance our understanding of the intracellular behaviour of B. cenocepacia in macrophages. Further investigation into the remaining SCOTS-identified genes, as well as putative secreted effectors, will provide a better understanding of the adaptive responses of intracellular B. cenocepacia, leading to life in a phagosomal niche and host cell cytotoxicity

Relativistic gyratons in asymptotically AdS spacetime

We study the gravitational field of a spinning radiation beam-pulse (a gyraton) in a D-dimensional asymptotically AdS spacetime. It is shown that the Einstein equations for such a system reduce to a set of two linear equations in a (D-2)-dimensional space. By solving these equations we obtain a metric which is an exact solution of gravitational equations with the (negative) cosmological constant. The explicit metrics for 4D and 5D gyratons in asymptotically AdS spacetime are given and their properties are discussed.Comment: 10 page

Macroscopic proof of the Jarzynski-Wojcik fluctuation theorem for heat exchange

In a recent work, Jarzynski and Wojcik (2004 Phys. Rev. Lett. 92, 230602) have shown by using the properties of Hamiltonian dynamics and a statistical mechanical consideration that, through contact, heat exchange between two systems initially prepared at different temperatures obeys a fluctuation theorem. Here, another proof is presented, in which only macroscopic thermodynamic quantities are employed. The detailed balance condition is found to play an essential role. As a result, the theorem is found to hold under very general conditions.Comment: 9 pages, 0 figure

The Tolman-Bondi--Vaidya Spacetime: matching timelike dust to null dust

The Tolman-Bondi and Vaidya solutions are two solutions to Einstein equations which describe dust particles and null fluid, respectively. We show that it is possible to match the two solutions in one single spacetime, the Tolman-Bondi--Vaidya spacetime. The new spacetime is divided by a null surface with Tolman-Bondi dust on one side and Vaidya fluid on the other side. The differentiability of the spacetime is discussed. By constructing a specific solution, we show that the metric across the null surface can be at least $C^1$ and the stress-energy tensor is continuous.Comment: 5 pages, no figur

On the stable configuration of ultra-relativistic material spheres. The solution for the extremely hot gas

During the last stage of collapse of a compact object into the horizon of events, the potential energy of its surface layer decreases to a negative value below all limits. The energy-conservation law requires an appearance of a positive-valued energy to balance the decrease. We derive the internal-state properties of the ideal gas situated in an extremely strong, ultra-relativistic gravitational field and suggest to apply our result to a compact object with the radius which is slightly larger than or equal to the Schwarzschild's gravitational radius. On the surface of the object, we find that the extreme attractivity of the gravity is accompanied with an extremely high internal, heat energy. This internal energy implies a correspondingly high pressure, the gradient of which has such a behavior that it can compete with the gravity. In a more detail, we find the equation of state in the case when the magnitude of the potential-type energy of constituting gas particles is much larger than their rest energy. This equation appears to be identical with the general-relativity condition of the equilibrium between the gravity and pressure gradient. The consequences of the identity are discussed.Comment: 12 pages (no figure, no table) Changes in 3-rd version: added an estimate of neutrino cooling and relative time-scale of the final stage of URMS collaps