Density-Independent,Scalable Search in Ad Hoc Networks

We analyze the asymptotic cost of discovering a route within a flat ad hoc network and we show that one can discover a route with cost that is proportional only to the area of the network, which is independent of the number of network nodes. Furthermore, we show that this is optimal and that bordercasting (a query propagation protocol where a node retransmits a query to a set of nodes at some hop-distance away) possesses this density-independence property. We present the design of bordercast and the associated maintenance protocols, and we evaluate their performance. In particular, we highlight that the aggregation of local information by bordercasting at each network node is a fundamental building block for the construction of scalable protocols in flat ad hoc networks.

Biochemical and molecular biological characterization of a lipase produced by the fungus Rhizopus delemar

The results of a comprehensive biochemical and molecular biological investigation of the lipase produced by the mycelial fungus Rhizopus delemar are described. This enzyme cleaves and synthesizes primary esters and related bonds, exhibits 1,3-positional selectivity in its actions on glycerides, and is a member of a family of enzymes that have been widely used in applied biocatalysis. Use of glycerol as main carbon source rather than glucose or lipid supported mycelial growth and lipase production. The enzyme was purified to homogeneity and characterized. Pure lipase was crystallized and its three-dimensional structure determined. The enzyme was found to adopt a configuration similar to those of other members of its homologous family. The structural data also indicated that lipases possess greater configurational mobility than had been previously appreciated. A complementary DNA clone was isolated that contained the full length lipase gene. The nucleic acid sequence of this cDNA indicated that it was initially synthesized as a preproenzyme, and allowed determination of the complete predicted amino acid sequence of the lipase, and its comparison to the sequences of related enzymes. Truncated forms of the cloned cDNA were produced that encoded either mature or prepro-lipase. These DNAs were introduced into a tightly regulated E. coli expression system, overcoming the toxicity of the enzyme while also allowing overproduction of lipase. Molecular modelling was employed to guide the rational mutagenesis of the enzyme, identifying sites within the substrate binding region that regulated substrate selectivity. Mutant lipases were generated with altered substrate specificities, creating novel enzymes and beginning the definition of structure-function relationships in the lipolytic enzymes.     

Vaporization of Protective Oxide Films into Different Gas Atmospheres

Oxidation of Metals - Vaporization often accompanies high-temperature oxidation and corrosion. In this review, vaporization under a vacuum as well as static gas and flowing gas conditions is...     

X-ray Microtomography Analysis of the Aluminum Alloy Composite Reinforced by SiC After Friction Stir Processing

Despite many years of using friction stir processing (FSP), there are many unexplained aspects concerning the processes which appear during FSP: determining the direction of flow and mixing of the materials and the degree of mixing and microstructure fragmentation in specific areas. This paper presents the impact of FSP on the micro- and macrostructure of the composite with hypo-eutectic Si matrix reinforced by SiC particles. The analysis of the structure of the processed area in FSP in the relation to the microstructure of the base material has been made using x-ray microtomography. The results of these studies have been juxtaposed with studies using microscopic methods (light microscopy and SEM). The microtomography images revealed an additional separation on the advancing side and the weld nugget, where on the basis of a 3D reconstruction a layer microstructure on the direction of linear movement of the tool has been demonstrated. The analyses have revealed a limited flow of the material above the weld nugget. The main advantages of the research method applied were the possibility to show the invisible or barely visible elements of the microstructure using standard test methods and the ability to analyze the microstructure changes uninterruptedly in different directions in the volume of the material.     

Scale growth process at 1473 K on unmodified and yttrium‐ or chromium‐implanted β‐NiAl

Early oxidation of unmodified and yttrium‐implanted or chromium‐implanted β‐NiAl intermetallic compound at 1473 K was studied using a combination of two‐stage‐oxidation exposure with ¹⁸O₂ as a tracer, SIMS elemental distribution analysis (depth profiling and imaging modes) and photoluminescence spectroscopy analysis of the scale phase composition. It was found that phase transformation of transient aluminium oxides, represented by θ‐ Al₂O₃ into stable and protective α‐Al₂O₃ occurs locally and is affected by implanted additions: Yttrium retarded while chromium appeared to accelerate it. Typical patch‐ and/or web‐like scale morphology of the growing scales was observed.     

The effect of counter anions on corrosion resistance of steel covered by bi-layered polypyrrole film

The bi-layered polypyrrole (PPy) coatings were investigated for corrosion prevention of a carbon steel. The inner layer was doped with the Keggin structure anions of (PMo₁₂) and anions for stabilization of the passive oxide film at the metal-polymer interface, and the outer layer was doped with four organic anions of dihydroxynaphthalenedisulfonate (DHNDS), naphthalenedisulfonate (NDS), anthraquinonedisulfonate (AnqDS) or dodecylsulfate (DoS) for inhibition of the decomposition and release of PMo₁₂. The corrosion tests were performed in 3.5 wt.% NaCl aqueous solution. The corrosion resistance of the steels covered by the bi-layered PPy films was found in the following order: PPy-PMo₁₂/PPy-DHNDS < PPy-PMo₁₂/PPy-NDS < PPy-PMo₁₂/AnqDS < PPy-PMo₁₂/PPy-DoS. The performance of corrosion protection related to the oxidized state of the polymer was discussed.     

Kinetics and mechanism of ?-caprolactone and l,l-lactide polymerization coinitiated with zinc octoate or aluminum acetylacetonate: The next proofs for the general alkoxide mechanism and synthetic applications

Following our previous papers on mechanism of cyclic esters' polymerization coinitiated by tin(II) octoate [tin(II) bis-(2-ethylhexanoate), (Sn(Oct)₂)] in the presence of either the low molar mass coinitiator (an alcohol, hydroxy acid, or H₂O) or a macromolecule fitted with a hydroxy end group (ROH), the present work deals with ?-caprolactone (CL) and l,l-lactide (LA) polymerizations coinitiated with zinc octoate (Zn(Oct)₂) or aluminum acetylacetonate (Al(Acac)₃). A series of kinetic measurements revealed that similarly as in the Sn(Oct)₂ coinitiated process, these polymerizations proceed by simple monomer insertion into the …Mt-OR bond, reversibly formed in the reaction -Mt-L + ROH ? …-Mt-OR + LH (where Mt = Sn, Zn or Al; L = Oct or Acac), taking place throughout the whole polymerization process. MtL_n itself does not play an active role in the polymerization. Applicability of the commercially available Zn(Oct)₂ or Al(Acac)₃ for the aliphatic polyester (10³ ≤ M_n ≤ 4 × 10⁵) synthesis is also discussed.     

Wear of lubricated plastics-based precision pivot bearings and the effect of the surface free energy of polymers

The effect of oil spreading on plastic bushes on the wear of steel-polymer precision pivot bearings was investigated. Analysis of oil spreading allowed a comparative evaluation of the surface free energy of the various polymers used as bush materials to be made. Correlation was found between the influence of lubrication on the wear of the bearings and the spreading velocity of the oil.     

Survival of Mycobacterium paratuberculosis and preservation of immunoglobulin G in bovine colostrum under experimental conditions simulating pasteurization

OBJECTIVE: To determine whether Mycobacterium paratuberculosis could survive in colostrum after pasteurization. Additionally, this study investigated the effect pasteurization had on IgG concentration in colostrum. ANIMALS: Colostrum samples were collected from cattle (beef and dairy) owned by the state of Ohio. PROCEDURE: Colostrum was divided into aliquots and inoculated with variable concentrations of M paratuberculosis (ATCC No. 19698: 10(4), 10(3), and 10(2) colony-forming units/ml). Half the samples at each concentration were subjected to pasteurization temperatures (63 C) for 30 minutes and the remainder were kept at approximately 20 to 23 C. All samples were incubated (Herrold's egg yolk medium with and without mycobactin J) and observed for growth during the next 16 weeks. Additionally, the IgG concentration of colostrum was determined by radioimmunoassay before and after pasteurization. Samples that coagulated at pasteurization temperatures were mechanically resuspended before measurement of IgG concentration. RESULTS: Growth of M paratuberculosis was retarded but not eliminated by pasteurization. Growth was observed in all unpasteurized samples incubated on Herrold's egg yolk medium with mycobactin J but in only 2 of 18 pasteurized samples similarly cultured. Growth from pasteurized samples appeared 5 to 9 weeks after growth was observed from nonpasteurized samples. Mean colostral IgG concentration was 44.4 g/L in nonpasteurized samples and 37.2 g/L in pasteurized samples, a decrease of 12.3%. High-quality colostrum (> 48 g of IgG/L) had a significantly greater loss of IgG concentration than did colostrum of lesser quality (P = 0.002). CONCLUSIONS: Pasteurization lessened, but did not eliminate, growth of M paratuberculosis from experimentally inoculated colostrum samples. Pasteurization resulted in a significant decrease in colostral IgG concentration but not to an unmanageable level that would preclude the colostrum's use for passive transfer of immunity. CLINICAL RELEVANCE: Colostrum is macrophage rich and may serve as a source of M paratuberculosis infection to calves. Pasteurization of colostrum may lessen the risk of infection, but will not totally eliminate M paratuberculosis.