Flow pattern transition for downward inclined two phase flow; horizontal to vertical

Data on the flow pattern transition for gas liquid flow in pipes for downward 0–90° inclination was collected. Mathematical models were developed to predict the flow pattern in the whole range of downward inclination.     

Fast Garbling of Circuits Under Standard Assumptions

Protocols for secure computation enable mutually distrustful parties to jointly compute on their private inputs without revealing anything, but the result. Over recent years, secure computation has become practical and considerable effort has been made to make it more and more efficient. A highly important tool in the design of two-party protocols is Yao’s garbled circuit construction (Yao 1986), and multiple optimizations on this primitive have led to performance improvements in orders of magnitude over the last years. However, many of these improvements come at the price of making very strong assumptions on the underlying cryptographic primitives being used (e.g., that AES is secure for related keys, that it is circular-secure, and even that it behaves like a random permutation when keyed with a public fixed key). The justification behind making these strong assumptions has been that otherwise it is not possible to achieve fast garbling and thus fast secure computation. In this paper, we take a step back and examine whether it is really the case that such strong assumptions are needed. We provide new methods for garbling that are secure solely under the assumption that the primitive used (e.g., AES) is a pseudorandom function. Our results show that in many cases, the penalty incurred is not significant, and so a more conservative approach to the assumptions being used can be adopted.     

Sparse communication networks and efficient routing in the plane

Traditional approaches to network design separate the issues of designing the network itself and designing its management and control subsystems. This paper proposes an approach termed routing-oriented network design, which is based on designing the network topology and its routing scheme together, attempting to optimize some of the relevant parameters of both simultaneously. This approach is explored by considering the design of communication networks supporting efficient routing in the special case of points located in the Euclidean plane. The desirable network parameters considered include low degree and small number of communication links. The desirable routing parameters considered include small routing tables, small number of hops and low routing stretch. Two rather different schemes are presented, one based on direct navigation in the plane and the other based on efficient hierarchical tree covers. On a collection of n sites with diameter D, these methods yield networks with a total of communication links and some bounds on the degree, coupled with routing schemes with constant routing stretch, memory bits per vertex and routes with at most or hops. Received: October 2000 / Accepted: May 2001     

Wavelet-based analysis of transient electromagnetic wave propagation in photonic crystals

Photonic crystals and optical bandgap structures, which facilitate high-precision control of electromagnetic-field propagation, are gaining ever-increasing attention in both scientific and commercial applications. One common photonic device is the distributed Bragg reflector (DBR), which exhibits high reflectivity at certain frequencies. Analysis of the transient interaction of an electromagnetic pulse with such a device can be formulated in terms of the time-domain volume integral equation and, in turn, solved numerically with the method of moments. Owing to the frequency-dependent reflectivity of such devices, the extent of field penetration into deep layers of the device will be different depending on the frequency content of the impinging pulse. We show how this phenomenon can be exploited to reduce the number of basis functions needed for the solution. To this end, we use spatiotemporal wavelet basis functions, which possess the multiresolution property in both spatial and temporal domains. To select the dominant functions in the solution, we use an iterative impedance matrix compression (IMC) procedure, which gradually constructs and solves a compressed version of the matrix equation until the desired degree of accuracy has been achieved. Results show that when the electromagnetic pulse is reflected, the transient IMC omits basis functions defined over the last layers of the DBR, as anticipated.     

Contribution to flashover modelling: Development of a validated numerical model for ignition of non-contiguous wood samples

A computational model of flashover is presented that closely follows the experimental setup at CNRS-ENSMA-Poitiers. A propane burner with thermal power of 55 kW is used as a primary source of fire and square beech wood samples (30 mm×30 mm×5 mm) as fire spread targets. The computational model describes the wood pyrolysis with a progress variable. Using the conservation of heat fluxes at the solid–gas interface, the thermal diffusion in the wood samples is coupled with the convective and the radiative heat transfer in the ambient gas phase. The incoming heat flux at the upper surface of the wood samples reaches values between 20 and 30 kW/m². With the ignition and subsequent combustion of the pyrolysis volatiles, the heat flux increases by approx. 12 kW/m². The results show that the ignition of the wood samples is triggered at an approx. surface temperature of 650 K. Due to large local variations in incident heat flux, significant differences in the ignition times of the wood samples are observed. The comparison of the calculated and the experimentally measured temperature shows a good agreement for the first wood sample and the model predicts the ignition time very well. But for the second and the third wood samples the model overpredicts the temperature, which leads to a premature ignition of these wood samples.     

Viruses and bacteriophages

Many of the enteric viruses which are transmitted from person to person by thefecal-oral route are found in raw and treated wastewater, and because of their persistence under adverse conditions may also be found in slightly polluted waters.There is no routine examination procedure of water and wastewater for entero-viruses,mainly because of the cumbersome isolation techniques, high cost and the need for highly skilled laboratory personnel.Phages are specific to single species of bacteria, are known for many entericbacteria, and are very often used for final identification of enteric pathogenic bacteria.Coliphages are provalent in raw and treated sewage as well as in polluted water, where enteric viruses may also be found.Coliphages were often mentioned as possible viral indicators in polluted water.To be a perfect indicator, they should comply with minimum criteria as follows: (a) they should be present wherever human enteric viruses are present: (b) the coliphage numbers recovered should be equal to or larger than those of enteric viruses recovered: (c) the coliphages should be at least as resistant as enteric viruses to adverse environmental conditions: (d) isolation and quantification of the coliphage should be faster and less expensive than isolation of the enteroviruses.Comparative studies show that the coliphage to enterovirus ratio in wastewater is about 10³:1. Levels of poliovirus 1 (attenuated) to coliphage f2 remained stable for a few months in oxidation pond effluents.f2 coliphage exhibited higher resistance to chlorination than poliovirus 1 (attenuated). When the two strains were kept in water of different quality, f2 survived longer. In addition, all coliphage counts were completed within 24 h. while those of enteroviruses required about a week. Results indicate very strongly that coliphages can be used as viral indicators and this is already the practice in a few European and other countries.     

Porous track cores along wakes of swift Pb ions in LiF

Continuous density decreases of 50% within 98 μm long and 3.2 nm wide cylindrical ion damage trails, latent ion tracks, created in a {1 0 0} LiF platelet by 2.31 GeV Pb ions, have been measured by small-angle X-ray scattering. Structural alteration is attributed mainly to radiolytic decomposition of the crystal into Li atoms and fluorine molecules, and subsequent transport and release of the fluorine gas through the low-density tracks. Free volume and Li residues undoubtedly account for the observed enhanced etchability of the track-core region.     

The Photochemistry of Solutions of Eu(III) and Eu(II)

Irradiation in the CT band of Eu³⁺ in aqueous solution, in the presence of scavengers for H atoms, gives rise to formation of Eu²⁺ and evolution of molecular hydrogen. The kinetics of these processes were studied as functions of the concentrations of Eu³⁺ and scavenger, of pH, and of light intensity. The results are interpreted by means of a complex scheme in which an excited Eu²⁺ donates an electron to a proton, the resulting H* initiating a series of dark reactions which lead to evolution of H₂ and oxidation of the scavenger.     

The combined effect of radiation and carbonation on the immobilization of Sr and Cs ions in cementitious pastes

In the present study the effect of gamma irradiation on the transport of immobilized Sr and Cs ions in cementitious paste samples is described. During the irradiation process, the samples were exposed to atmospheric conditions. Hence, atmospheric carbonation of samples could takes place. Cementitious pastes, differing in their w/c ratio (0.3, 0.45), were exposed to an integral dose of 10⁷ grays (Gy) of γ irradiation during a period of approximately 6 months. The effect of irradiation on the transport properties of the immobilized Sr and Cs ions was studied by leaching experiments. The carbonation depth of the different samples was measured and found to markedly increase in the case of irradiated samples compared to samples not exposed to irradiation. The enhanced carbonation is associated with the dehydration due to radiolysis of pore water in the paste. It was found that the irradiation resulted in a marked decrease in the leached fraction of Sr ions. This is related to the increased carbonation found for the irradiated samples. On the other hand, a small increase in Cs diffusivity was found for irradiated samples. This increase in leachability might be associated with the formation of microcracks in the irradiated sample.