Online Coloring of Bipartite Graphs with and without Advice

In the online version of the well-known graph coloring problem, the vertices appear one after the other together with the edges to the already known vertices and have to be irrevocably colored immediately after their appearance. We consider this problem on bipartite, i.e., two-colorable graphs. We prove that at least ?1.13746?log₂(n)?0.49887? colors are necessary for any deterministic online algorithm to be able to color any given bipartite graph on n vertices, thus improving on the previously known lower bound of ?log₂ n?+1 for sufficiently large n. Recently, the advice complexity was introduced as a method for a fine-grained analysis of the hardness of online problems. We apply this method to the online coloring problem and prove (almost) tight linear upper and lower bounds on the advice complexity of coloring a bipartite graph online optimally or using 3 colors. Moreover, we prove that \(O(\sqrt{n})\) advice bits are sufficient for coloring any bipartite graph on n vertices with at most ?log₂ n? colors.     

Occurrence patterns of alien freshwater turtles in a large urban pond ‘Archipelago’ (Rome,Italy): Suggesting hypotheses on root causes

The patterns of the occurrence and distribution of alien freshwater turtle species in an urban pond archipelago (Rome, Italy) were analysed, with the aim of exploring the role of a set of factors (type of ponds, landscape context, size area, distance from the nearest road) with a generalized linear model approach. A total of 311 ponds subdivided in three types (fountains, small basins, lakes) embedded in different landscape contexts (public parks, private parks, urban areas) at differing distances from the nearest road were sampled. Six non‐native freshwater turtle species in 31 sites were recorded (9.97%). Lakes exhibited the highest occurrence rates of alien freshwater turtles, compared to small basins and fountains. Freshwater turtle species in urbanized areas were only observed in parks (both public and private). In both the public and private parks, the lakes exhibited the highest percentage of occupied sites, with fountains being the lowest. A direct and significant relationship was observed between pond size and species richness. The distance from the nearest road did not appear to affect species richness. A first interpretation of the data from this study facilitated the postulation of two a posteriori hypotheses that should be tested, as follows: (i) the causal process of turtle release is random, and the rate of extinction (and recapture) is higher in smaller ponds, thus producing the observed pattern; and (ii) the turtle release is not random, and people actively select the ponds they consider more suitable for their pet animals. In this study, it appears the lakes were perceived by those who abandon their pets as the most ecologically suitable habitats among other pond types to accommodate the different species of turtles. Knowledge of people's attitudes in regard to releasing pet animals also might assist managers of public green spaces to develop strategies aimed to preserve local biodiversity, and to educate the public about the conservation issue represented by the alien species.     

Synthesis and characterization of polyurea microcapsules containing essential oils with antigerminative activity

In this paper we report on the preparation and characterization of polyurea‐based microencapsulated systems, containing essential oils as core materials, for potential applications in controlled‐release formulations of agrochemicals. Microcapsules were synthesized by interfacial polymerization in o/w emulsion between polyfunctional isocyanates and diamines, to investigate the effect of the monomer kind on the morphology and properties of the produced samples. The synthetic conditions that gave the best results were used to microencapsulate four essential oils, able to interfere with the seed germination and radicle elongation of some test plants. The produced samples were characterized, with the aim to analyze their morphology and to verify the effectiveness of essential oil microencapsulation. Moreover, preliminary bioassay based on seed germination and subsequent radical growth were carried out to study the effects of the microencapsulated essential oils. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The kinetics of gasification of carbon deposited on nickel catalysts

The kinetics of gasification of carbon deposited on nickel foils and nickel-alumina catalysts by steam, carbon dioxide and hydrogen are reported for the temperature range 450–850°C. At atmospheric pressure steam is the most effective gasifying agent. In all cases, the kinetic data obtained at lower temperatures (below 600°C) is consistent with control of the process by the chemical reaction. As the temperature increases, the rates of gasification by steam and carbon dioxide are limited by mass transfer effects. The concentration of methane near reaction sites affects the rate of hydrogen gasification above 650°C.     

A Complete and Highly Effective Mothproofing Agent Comprising a Pyrethroid and a Hexahydropyrimidine

Pyrethroids, considered as a general class of compounds, have been shown to provide effective protection from the larvae of the keratin-digesting insects Tineola bisselliella H., Tinea pellionella Linn., Hofmannophila pseudo-spretella Station and Attagenus piceus Oliv. The position regarding the susceptibility of the furniture carpet beetle to pyrethroids is less clear, however. It has been reported that both deltamethrin and permethrin are effective against Anthrenus flavipes Le Conte, whilst permethrin is also reported elsewhere to be effective against the same species. Results obtained in our laboratory, however, have indicated that pyrethroids may offer inadequate protection against Anthrenus vorax Waterh. [1, 2]. This latter species is identical to Anthrenus flavipes var. seminiveus Casey, a colour variety of Anthrenus flavipes Le Conte. The 1,3-disubstituted5-phenylcarbamoyl-2,4,6-trioxo- and 4,6-dioxo-2-thione-hexahydropyrimidine derivatives described in this paper exhibit a surprisingly high and selective toxicity to the Anthrenus species. Thus, a combination of an appropriate hexahydropyrimidine with a suitable pyrethroid, e.g. permethrin, provides complete control of a wide range of commonly encountered textile insect pests. The influence of substituents on the mothproofing activity is discussed.     

Surface properties of fluorinated hybrid coatings

A commercial perfluoropolyether containing alkoxysilane functionalities was employed to prepare organic–inorganic hybrid coatings by using the sol‐gel process in the presence of tetraethoxysilane. Contact angle analysis revealed a strong hydrophobic and oleophobic character of the coatings almost independently from the molecular weight of the starting fluorinated oligomer. Surface tension values were in the range of 14–16 mN/m, suggesting a preferential segregation of fluorinated segments onto the surface of the coating. Atomic force microscopy showed the presence very smooth surfaces permitting to neglect the contribution of the surface roughness to wettability. Friction coefficient values were markedly lower with respect to the value of uncoated glass substrate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1483–1488, 2006     

A porosimetric study of calcium sulfoaluminate cement pastes cured at early ages

Calcium sulfoaluminate and Portland cement pastes, both prepared with a water/solid mass ratio equal to 0.5 and cured for time periods comprised between 2 h and 28 days, show completely different pore size distributions by mercury intrusion. Portland cement pastes aged at 12 h and 1 day exhibit a unimodal distribution of pore sizes related to a continuous network of capillary pores with a threshold pore radius decreasing from nearly 650 to 350 nm. After 7 and 28 days of curing, this parameter shifts to about 150 nm and a region having smaller pores appears (with a second threshold pore radius roughly comprised between 10 and 30 nm), made discontinuous by blockages of hydration products which occlude the interconnected pore system and isolate the interior space. For calcium sulfoaluminate cement pastes, a bimodal distribution is rapidly established, in which the regions with a lower porosity (threshold pore radii up to about 25 nm) are dominant, while the decrease of total porosity almost ceases at later ages. The porosimetric behaviour of calcium sulfoaluminate-based cement is related to its very fast hydration rate and to the lack of water needed to continue the hydration reactions.     

Kinetic modeling of pentachlorophenol adsorption from aqueous solution on activated carbon fibers

The adsorption equilibrium data of pentachlorophenol (PCP) onto activated carbon fiber (ACF) in felt form were obtained in a batch adsorber at T = 25 °C and pH 12 and the Langmuir isotherm fitted reasonably well with the experimental data. The rate of adsorption of PCP on ACF was investigated in this work and the experimental concentration decay data were obtained in a differential column batch adsorber. The overall rate of adsorption of PCP was interpreted by a diffusional model that takes into account the external mass transport and intrafiber diffusion. The experimental concentration decay can be described quite well with the diffusional model if the overall rate of adsorption is mainly controlled by intrafiber diffusion and the external mass transport is not important to the overall rate of adsorption. Moreover, intrafiber diffusion was significantly affected by restricted diffusion since the molecular diameter of the PCP was closed to 55% of the average pore diameter. The effect of restricted diffusion was estimated using correlations reported in the literature. The molecules of PCP adsorbed on the surface of the pore also hindered the diffusion of PCP molecules inside the pores.     

The metabolism of 1-acyl-PAF in rabbit platelets and its possible interaction with PAF

The metabolism of 1-acyl-2-acetyl-sn-glycero-3-phosphocholine (1-acyl-PAF), a naturally occurring analogue of platelet activating factor (PAF), was investigated in rabbit platelets. Our studies showed that 1-acyl-[³H]PAF (1-palmitoyl-2-acetyl-sn-glycero-3-phospho[N-methyl-³H]-choline) was converted by platelets into phosphatidyl-[³H]choline ([³H]PC) in a time-dependent fashion. The formation of [³H]PC occurred at a rate similar to that observed when lyso-[³H]PC (palmitoyl-sn-glycero-3-phospho[N-methyl-³H]choline) was used as substrate. In addition, a time-dependent increase in the level of water-soluble radioactivity was observed during the incubation of platelets with either 1-acyl-[³H]PAF or lyso-[³H]PC. This increase was parallel to the formation of [³H]PC and was not observed in the presence of [¹⁴C]PAF (1-octadecyl-2-acetyl-sn-glycerol-3-phospho[N methyl-¹⁴C]choline). Analysis by thin-layer chromatography showed that the soluble radioactivity was mainly associated with glycerophosphocholine (GPC). On the other hand, the preincubation of platelets with phenylmethylsulfonyl fluoride, an inhibitor of the acetylhydrolase, reduced the hydrolysis of 1-acyl-[³H]PAF to [³H]GPC with a concomitant accumulation of radioactivity in 1-acyl-PAF. These findings suggest that 1-acyl-PAF is converted into PC through deacetylation-reacylation with lysoPC as an obligatory intermediate. The findings also indicate that the lysoPC resulting from 1-acyl-PAF is either reacylated to phosphatidylcholine (PC) or hydrolyzed to GPC by lysophospholipase. Finally, we showed that the stimulation of platelets with PAF led to a time- and concentration-dependent increase in the conversion of 1-acyl-[³H]PAF to [³H]PC. The stimulatory effect of PAF was not observed when platelets were lysed before incubation, suggesting that PAF enhances the metabolism of 1-acyl-PAF, probably by accelerating its translocation through the plasma membrane.     

Ceramic Microtubes from Preceramic Polymers

A novel process for the production of ceramic microtubes involving the microextrusion of preceramic polymers was studied. Microtubes with a wide range of inner and outer diameters and several centimeters long were produced from two silicone resins. A coextrusion approach was also used to extend the forming capability of the technique. The addition of carbon black resulted in electrically conductive silicon oxycarbide (SiOC) ceramic microtubes. SiOC microtubes possessed a high bending strength, ranging from ∼30–1100 MPa.