Guarding a Terrain by Two Watchtowers

Given a polyhedral terrain T with n vertices, the two-watchtower problem for T asks to find two vertical segments, called watchtowers, of smallest common height, whose bottom endpoints (bases) lie on T, and whose top endpoints guard T, in the sense that each point on T is visible from at least one of them. There are three versions of the problem, discrete, semi-continuous, and continuous, depending on whether two, one, or none of the two bases are restricted to be among the vertices of T, respectively.     

Spray evaporation of liquid foods

‘Spray evaporation’ based on the principle of adiabatic humidification was examined as an evaporation technique for the concentration of two types of representative liquid foods, namely, fruit juice and milk. The concentration of apple juice could be increased from 10.0 to 13.0 °Brix by this technique without application of heat utilizing the humidity potential to an extent of 89%. Employing heated process air during processing increased the amount of water evaporation owing to increased saturation humidity level, enabling higher concentrations to be achieved in apple juice (48 °Brix), reconstituted milk (29 °Brix) and single toned milk (22 °Brix). Feed flow rate had an inverse effect on the final concentration under otherwise similar conditions. Evaporative cooling associated with spray evaporation actually delivered the concentrate at a relatively lower temperature. By manipulating the operating conditions, humidity potential could be utilized to the extent of 55% with heated process air. The spray evaporation technique seemed to have a good potential for the concentration of liquid foods.     

Influence of reactive compatibilizers on the rheometrical and mechanical properties of PA6/LDPE and PA6/HDPE blends

In this work, the influence of reactive compatibilizers on the rheometrical and mechanical properties of polyamide 6/low density polyethylene (PA6/LDPE) and polyamide 6/high density polyethylene (PA6/HDPE) blends was investigated. Polyethylene grafted with maleic anhydride (PEgMA), polyethylene grafted with acrylic acid (PEgAA), and ethylene-methyl acrylate-glycidyl methacrylate (EMA-GMA) were used as compatibilizers. The blends were characterized by torque rheometry, mechanical properties, and morphology. Rheometrical properties results show that PEgMA and PEgAA compatibilizers are more reactive with PA6 than EMA-GMA. Mechanical properties and scanning electron microscopy analysis results show that EMA-GMA compatibilizer is as effective as PEgMA and PEgAA for PA6/LDPE blend. For PA6/HDPE blend, PEgAA and EMA-GMA compatibilizers proved to be as effective as PEgMA. For PA6/HDPE blend compatibilized with PEgAA, an intriguing “web” or “bridge” like structure was observed.     

Organo-functionalized mesoporous supports for Jacobsen-type catalyst: Laponite versus MCM-41

In order to exploit the different textural properties of Laponite and MCM-41, specifically in terms of their external versus internal surface areas, in the covalent anchoring of a chiral Mn(III) salen complex, these materials were functionalized with 3-aminopropyltriethoxysilane (APTES), subsequently activated with sodium ethoxide, and finally used to anchor the Jacobsen catalyst derivative C1. All the materials were characterized by nitrogen elemental analysis, XPS, PXRD, nitrogen adsorption at −196 °C, FTIR and for those with the immobilized complex, they were additionally characterized by Mn AAS. The APTES anchored at the edges of the Laponite single crystals and inside the MCM-41 pores. Moreover, under the same preparative conditions, higher amount of APTES was anchored onto MCM-41 than onto Laponite, which is due to the higher surface area of MCM-41 compared to Laponite, as well as to its more exposed SiO₄ tetrahedra. Activation of the two organo-functionalized materials with sodium ethoxide originated anionic nitrogen groups as deduced by the increase of surface sodium content of these materials and N1s binding energy changes, but led to a small decrease in N bulk content as a result of some APTES leaching. Moreover, for MCM-41 some disruption of the silica framework occurred as a consequence of the basic treatment, as suggested by XPS, PXRD, and nitrogen adsorption study. The APTES functionalized Laponite and MCM-41 materials, as well as the activated analogs, were able to anchor C1 through axial coordination of the metal centre to the grafted surface nitrogen atoms. APTES functionalized MCM-41 presented similar complex content to Laponite analog, what points out for the fact that, at least for the bulky complex used in this work, there was no clear benefit in using a material of high internal area; for the ethoxide activated analogs, Laponite showed the highest complex content of all materials, but MCM-41 was able to anchor the lowest complex quantity, probably as a consequence of damaging effect caused by the basic treatment within its porous structure. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The Effect of Silicon Content on Impact Toughness of T91 Grade Steels

The impact resistance of silicon (Si)-containing modified 9Cr-1Mo steels has been investigated within a temperature regime of −40 to 440 °C using the Charpy method. The results indicate that the energies absorbed in fracturing the tested specimens were substantially lower at temperatures of −40, 25, and 75 °C compared to those at elevated temperatures. Lower impact energies and higher ductile-to-brittle-transition-temperatures (DBTTs) were observed with the steels containing 1.5 and 1.9 wt.% Si. The steels containing higher Si levels exhibited both ductile and brittle failures at elevated temperatures. However, at lower temperatures, brittle failures characterized by cleavage and intergranular cracking were observed for all four tested materials.     

Tracing the history of nuclear releases: determination of 129I in tree rings

Concentrations of the long-lived radioisotope 1291 were measured in dated tree rings in order to determine whether the distribution of this isotope reflects the history of nuclear deposition. 129I concentrations and 129I/127I ratios were analyzed in tree rings and bark samples from four trees at West Valley, NY, and from one tree at Rochester, NY. West Valley was the site of short-lived nuclear fuel reprocessing activities (1966-1972), while Rochester, located 115 km to the northeast, provided a regional control site for the study. The selected trees reflect different modes of fluid and nutrient transport in trees, with three species of ring-porous trees (elm, oak, and locust), one semidiffuse (cherry), and one diffuse-porous tree (maple). The results show that 1291 levels in ring-porous trees, in which xylem or hydrologic tissue is localized in the outermost growth ring, are generally well correlated with the expected 1291 deposition pattern for the region. In contrast, tree rings of the more common semidiffuse to diffuse-porous wood, where xylem is disseminated throughout the trunk, show a less well developed 129I signal, probably due to the transport of iodine ions across annual rings. Iodine concentrations in the tree rings range from 0.04 to 2 mg/kg, 129I/127I ratios from 6 x 10(-10) to 3.8 x 10(-6). Tree bark and the outermost rings show significantly higher 129I concentrations than the wood of the trunk. The 129I/127I ratios for bark are very similar to values obtained for surface soil and water at the two localities, while inner rings have ratios similar to those in deeper layers of the soil, reflecting different pathways for 129I uptake and the differences in ambient 1291 levels between the atmosphere and deep soil. Although ring porous trees preserve the depositional pattern of nuclear releases, rings older than or close to the onset of the nuclear age have 129I/127I ratios significantly above the preanthropogenic level, suggesting that even in these trees some redistribution of 129I occurs throughout the trunk. Our results indicate that growth rings from ring-porous wood are useful in time-series analyses of regional 129I deposition, yielding reliable information on relative changes in 129I concentrations but requiring caution in the reconstruction of absolute ambient concentrations during any given time.     

Fault tolerant processes

A process is said to be fault tolerant if the system provides proper service despite the failure of the process. For supporting fault-tolerant processes, measures have to be provided to recover messages lost due to the failure. One approach for recovering messages is to use message-logging techniques. In this paper, we present a model for message-logging based schemes to support fault-tolerant processes and develop conditions for proper message recovery in asynchronous systems. We show that requiring messages to be recovered in the same order as they were received before failure is a stricter requirement than necessary. We then propose a distributed scheme to support fault-tolerant processes that can also handle multiple process failures.Pankaj Jalote received the Bachelor of Technology degree in electrical engineering from the Indian Institute of Technology, Kanpur, India, in 1980, the M.S. degree in computer science from Pennsylvania State University, University Park, in 1982, and the Ph.D. degree in computer science from the University of Illinois at Urbana-Champaign in 1985. From August 1985 to July 1989 he was an Assistant Professor in the Department of Computer Science at the University of Maryland, College Park. Currently he is an Assistant Professor in the Department of Computer Science and Engineering at IIT Kanpur, India. His research interests include fault-tolerant computing, distributed systems, and software engineering.This work was supported in parts by the NSF grant DCI-8610337     

SAHAYOG: A test bed for evaluating dynamic load-sharing policies

This paper describes the implementation of a test bed called SAHAYOG, for evaluating dynamic load-sharing policies in which job-transfer decisions are based on the state of the system. The test bed is implemented on a network of AT&T 3B2 minicomputers. It provides an interactive user interface for conducting load-sharing experiments. Based on user-specified parameters it creates independent job streams at different nodes in the network. Jobs are transferred among the nodes by the load-sharing algorithm being evaluated. Each node collects data about the jobs, which are used to generate statistics about the experiment. Five load-sharing algorithms are implemented and evaluated using the test bed under different load conditions and for various parameter values. These experiments confirm some earlier results about load sharing and also provide some new insights. SAHAYOG also contains an optional fault-tolerance feature to handle single-node failures, and evaluates the effect of fault tolerance on the performance of different policies.     

Preparation and Optimization of Dry PLGA Nanoparticles by Spray Drying Technique

The aim of this article was to evaluate the potential of poly lactide-coglycolide (PLGA) nanoparticles (NPs) as carriers for controlling release of doxorubicin (DOX) via a spray drying technique. The challenge was to entrap a hydrophilic molecule into a lipophilic core molecule of PLGA. To achieve this objective, we modified conventional approach of drug loading to spray drying technique. The eight formulations of nanoparticles were prepared by modified double emulsion and solvent evaporation technique followed by spray drying using 2³ factorial designs. PLGA (A) and PVA (B) and stirring speed (C) were used as independent variables where particle size (Y₁), entrapment efficiency (Y₂) and percentage of drug release at the 32 hour (Y₃) were taken as dependant variables. The results showed that the method is easy and efficient for the entrapment of the drug as well as the formation of spherical nanoparticles. This modification improved DOX entrapment efficiency relative to controls real loadings up to 40%. The in vitro release studies indicated the DOX loaded PLGA nanoparticles provide controlled drug release over a period of 32 h. Hence, this investigation demonstrated the potential of the experimental design in understanding the effect of the formulation variables on the quality of DOX-PLGA nanoparticles.