Two-dimensional packing with conflicts

We study the two-dimensional version of the bin packing problem with conflicts. We are given a set of (two-dimensional) squares V = {1, 2, . . . ,n} with sides and a conflict graph G = (V, E). We seek to find a partition of the items into independent sets of G, where each independent set can be packed into a unit square bin, such that no two squares packed together in one bin overlap. The goal is to minimize the number of independent sets in the partition. This problem generalizes the square packing problem (in which we have ) and the graph coloring problem (in which s _i = 0 for all i = 1,2, . . . , sn). It is well known that coloring problems on general graphs are hard to approximate. Following previous work on the one-dimensional problem, we study the problem on specific graph classes, namely, bipartite graphs and perfect graphs. We design a -approximation for bipartite graphs, which is almost best possible (unless P = NP). For perfect graphs, we design a 3.2744-approximation. An extended abstract version of this paper has appeared in Proceedings of the 16th International Symposium on Fundamentals of Computation Theory (FCT 2007), pp 288–299. Rob van Stee was supported by the Alexander von Humboldt Foundation.     

Slag Treatment Followed by Acid Leaching as a Route to Solar-Grade Silicon

Refining of metallurgical-grade silicon was studied using a process sequence of slag treatment, controlled cooling, and acid leaching. A slag of the Na₂O-CaO-SiO₂ system was used. The microstructure of grain boundaries in the treated silicon showed enhanced segregation of impurities, and the formation of CaSi₂ and other Ca-rich phases. Boron and phosphorus were found in the grain boundary phases of silicon after the slag treatment and were successfully removed together with most of the metallic impurities by acid leaching. The interaction between silicon and slag and the distribution of impurities are discussed. A novel mechanism of the refining approach is proposed, based on the microstructure of silicon and the analysis of impurities at each refining step. Parallel processes of slag refining, segregation, and solvent refining were observed, which explains the relatively high efficiency of the proposed refining technology. The investigated combination of refining processes followed by acid leaching has great potential as an efficient and cost-saving route for upgrading metallurgical-grade to solar-grade silicon.     

The detection and sizing of flaws in components from the hot-end of gas turbines using phase-contrast radiography with neutrons: a feasibility study

In this paper we present a feasibility study of the use of phase contrast radiography in the examination of components from the hot-section of gas turbine engines. These components are usually made from dense materials (nickel or cobalt based superalloys) and, consequently, radiographic examination requires either high energy X-rays (above 60 keV) or neutrons. The relative merits of employing X-rays and neutrons for phase contrast radiography are compared. It is shown that, for similar penetration, neutrons offer better sensitivity and that it should be possible to detect even micron-wide cracks orientated perpendicular to the incident rays. Simulation shows that, for cracks parallel to the incident rays, crack growth in increments of microns can be resolved by monitoring the development of the Fresnel diffraction pattern. Some preliminary experimental results are also presented that demonstrate an improvement over conventional neutron radiography.     

Metal contamination in urban, suburban, and country park soils of Hong Kong: a study based on GIS and multivariate statistics

The urban environment quality is of vital importance as the majority of people now live in cities. Due to the continuous urbanisation and industrialisation in many parts of the world, metals are continuously emitted into the terrestrial environment and pose a great threat on human health. An extensive survey was conducted in the highly urbanised and commercialised Hong Kong Island area (80.3 km2) of Hong Kong using a systematic sampling strategy of five soil samples per km2 in urban areas and two samples per km2 in the suburban and country park sites (0-15 cm). The analytical results indicated that the surface soils in urban and suburban areas are enriched with metals, such as Cu, Pb, and Zn. The Pb concentration in the urban soils was found to exceed the Dutch target value. The statistical analyses using principal component analysis (PCA) and cluster analysis (CA) showed distinctly different associations among trace metals and the major elements (Al, Ca, Fe, Mg, Mn) in the urban, suburban, and country park soils. Soil pollution maps of trace metals (Cd, Co, Cr, Cu, Ni, Pb, and Zn) in the surface soils were produced based on geographical information system (GIS) technology. The hot-spot areas of metal contamination were mainly concentrated in the northern and western parts of Hong Kong Island, and closely related to high traffic conditions. The Pb isotopic composition of the urban, suburban, and country park soils showed that vehicular emissions were the major anthropogenic sources for Pb. The 206Pb/207Pb and 208Pb/207Pb ratios in soils decreased as Pb concentrations increased in a polynomial line (degree=2).     

Increasing the thermostability of a neutral protease by replacing positively charged amino acids in the N-terminal turn of {alpha}-helices

The 247–260 and 289–299 -helices of Bacillus subtilisneutral protease have a lysine in their N-terminal turn. Theselysines were replaced by Ser or Asp in order to improve electrostaticinteractions with the -helix dipole. After replacing Lys bySer at positions 249 or 290, the thermostability of the enzymewas increased by 0.3 and 1.0°C, respectively. The Asp249and Asp290 mutants exhibited a stabilization of 0.6 and 1.2°C,respectively. The results show the feasibility of stabilizingenzymes by introducing favourable residues at the end of -helices.     

Electrocatalytic activity and durability of Pt/NbO2 and Pt/Ti4O7 nanofibers for PEM fuel cell oxygen reduction reaction

In this paper, we report the synthesis of both NbO₂ and Ti₄O₇ nanofibers using an electrospinning technique in an effort to use metal oxides as a possible replacement for carbon as PEM fuel cell catalyst supports. The synthesized nanofibers are physically characterized using several methods including XRD, SEM, TEM, BET, ICP-MS as well as XPS. The thermal, chemical, and electrochemical stabilities as well as the electronic conductivities of these two supports are also evaluated in order to check their feasibility as catalyst supports in the temperature range of 95–200 °C. Two catalysts, 20-wt% Pt/NbO₂ and 20-wt% Pt/Ti₄O₇, are prepared and tested for both ORR mass activity and stability in acidic solution. XPS measurements of samples analyzed before and after the durability tests suggest the formation of electronically insulating surface oxides, which can be partially responsible for both low ORR mass activity and catalyst durability.     

The effect of changes in condom usage and antiretroviral treatment coverage on human immunodeficiency virus incidence in South Africa: a model-based analysis

This study aims to assess trends in human immunodeficiency virus (HIV) incidence in South Africa, and to assess the extent to which prevention and treatment programmes have reduced HIV incidence. Two models of the South African HIV epidemic, the STI (sexually transmitted infection)–HIV Interaction model and the ASSA2003 AIDS and Demographic model, were adapted. Both models were fitted to age-specific HIV prevalence data from antenatal clinic surveys and household surveys, using a Bayesian approach. Both models suggest that HIV incidence in 15–49 year olds declined significantly between the start of 2000 and the start of 2008: by 27 per cent (95% CI: 21–32%) in the STI–HIV model and by 31 per cent (95% CI: 23–39%) in the ASSA2003 model, when expressed as a percentage of incidence rates in 2000. By 2008, the percentage reduction in incidence owing to increased condom use was 37 per cent (95% CI: 34–41%) in the STI–HIV model and 23 per cent (95% CI: 14–34%) in the ASSA2003 model. Both models also estimated a small reduction in incidence owing to antiretroviral treatment by 2008. Increased condom use therefore appears to be the most significant factor explaining the recent South African HIV incidence decline.     

Functional mimicry of a discontinuous antigenic site by a designed synthetic peptide

Functional reproduction of the discontinuous antigenic site D of foot-and-mouth disease virus (FMDV) has been achieved by means of synthetic peptide constructions that integrate each of the three protein loops that define the antigenic site into a single molecule. The site D mimics were designed on the basis of the X-ray structure of FMDV type C-S8c1 with the aid of molecular dynamics, so that the five residues assumed to be involved in antigenic recognition are located on the same face of the molecule, exposed to solvent and defining a set of native-like distances and angles. The designed site D mimics are disulfide-linked heterodimers that consist of a larger unit containing VP2(71-84), followed by a polyproline module and by VP3(52-62), and a smaller unit corresponding to VP1(188-194) (VP=viral protein). Guinea pig antisera to the peptides recognized the viral particle and competed with site D-specific monoclonal antibodies, while inoculation with a simple (not covalently joined to one another) admixture of the three VP1-VP3 sequences yielded no detectable virus-specific serum conversion. Similar results have been reproduced in two bovines. Antisera to the peptides also moderately neutralize FMDV in cell cultures and partially protect guinea pigs against challenge with the virus. These results demonstrate functional mimicry of the discontinuous site D by the peptides, which are therefore obvious candidates for a multicomponent, peptide-based vaccine against FMDV.     

Fueling Open‐Source Drug Discovery: 177 Small‐Molecule Leads against Tuberculosis

With the aim of fuelling open‐source, translational, early‐stage drug discovery activities, the results of the recently completed antimycobacterial phenotypic screening campaign against Mycobacterium bovis BCG with hit confirmation in M. tuberculosis H37Rv were made publicly accessible. A set of 177 potent non‐cytotoxic H37Rv hits was identified and will be made available to maximize the potential impact of the compounds toward a chemical genetics/proteomics exercise, while at the same time providing a plethora of potential starting points for new synthetic lead‐generation activities. Two additional drug‐discovery‐relevant datasets are included: a) a drug‐like property analysis reflecting the latest lead‐like guidelines and b) an early lead‐generation package of the most promising hits within the clusters identified.