Carbon clusters near the crossover to fullerene stability

The thermodynamic stability of structural isomers of $\mathrm{C}_{24}$, $\mathrm{C}_{26}$, $\mathrm{C}_{28}$ and $\mathrm{C}_{32}$, including fullerenes, is studied using density functional and quantum Monte Carlo methods. The energetic ordering of the different isomers depends sensitively on the treatment of electron correlation. Fixed-node diffusion quantum Monte Carlo calculations predict that a $\mathrm{C}_{24}$ isomer is the smallest stable graphitic fragment and that the smallest stable fullerenes are the $\mathrm{C}_{26}$ and $\mathrm{C}_{28}$ clusters with $\mathrm{C}_{2v}$ and $\mathrm{T}_{d}$ symmetry, respectively. These results support proposals that a $\mathrm{C}_{28}$ solid could be synthesized by cluster deposition.Comment: 4 pages, includes 4 figures. For additional graphics, online paper and related information see http://www.tcm.phy.cam.ac.uk/~prck

Ab initio many-body calculations on infinite carbon and boron-nitrogen chains

In this paper we report first-principles calculations on the ground-state electronic structure of two infinite one-dimensional systems: (a) a chain of carbon atoms and (b) a chain of alternating boron and nitrogen atoms. Meanfield results were obtained using the restricted Hartree-Fock approach, while the many-body effects were taken into account by second-order M{\o}ller-Plesset perturbation theory and the coupled-cluster approach. The calculations were performed using 6-31$G^{**}$ basis sets, including the d-type polarization functions. Both at the Hartree-Fock (HF) and the correlated levels we find that the infinite carbon chain exhibits bond alternation with alternating single and triple bonds, while the boron-nitrogen chain exhibits equidistant bonds. In addition, we also performed density-functional-theory-based local density approximation (LDA) calculations on the infinite carbon chain using the same basis set. Our LDA results, in contradiction to our HF and correlated results, predict a very small bond alternation. Based upon our LDA results for the carbon chain, which are in agreement with an earlier LDA calculation calculation [ E.J. Bylaska, J.H. Weare, and R. Kawai, Phys. Rev. B 58, R7488 (1998).], we conclude that the LDA significantly underestimates Peierls distortion. This emphasizes that the inclusion of many-particle effects is very important for the correct description of Peierls distortion in one-dimensional systems.Comment: 3 figures (included). To appear in Phys. Rev.

Description of the male of Psyllaephagus euphyllurae (Masi) (Hymenoptera, Encyrtidae), a parasitoid of the olive psylla, Euphyllura olivina (Costa) (Hemiptera, Liviidae), with notes on its reproductive traits and hyperparasitoids

A colony of the encyrtid wasp <em>Psyllaephagus</em> <em>euphyllurae</em> (Masi) (Hymenoptera, Encyrtidae) has been established in the quarantine laboratory at the University of California, Riverside, California, USA as part of a classical biological control program against its invasive host, the olive psylla, <em>Euphyllura</em> <em>olivina</em> (Costa) (Hemiptera, Psylloidea, Liviidae), an important pest of olives in some parts of the world. The colony originators were reared from the same host found on abandoned, commercial olives in Catalonia, Spain; additional collections were made in Murcia. The parasitoid reproduces primarily by thelytoky; however, a few occasional males have been found in the field in Spain, but not in colonies reared under quarantine or laboratory conditions. Here, the female of <em>P</em>. <em>euphyllurae</em> is redescribed and its male is described and illustrated for the first time; the only previous mention of male <em>P</em>. <em>euphyllurae</em> was from Tunisia, reared from the same psyllid host but without any details on its morphology. A lectotype is designated for <em>Encyrtus</em> <em>euphyllurae</em> Masi. Information is given on the results of genetic matching between the two sexes of the parasitoid and also on the presence of the bacterial <em>Wolbachia</em> symbiont that apparently is affecting reproduction of this species, including its sex ratio in the field. Two species of hyperparasitoids have also emerged from the parasitized olive psylla nymphs from Catalonia: numerous specimens of <em>Apocharips</em> <em>trapezoidea</em> (Hartig) (Hymenoptera, Figitidae) and one specimen of a <em>Pachyneuron</em> sp. (Hymenoptera, Pteromalidae)

Ring-testing and field-validation of a terrestrial model ecosystem - An instrument for testing potentially harmful substances: effects of carbendazim on nutrient cycling.

The effect of the fungicide carbendazim (applied in the formulation Derosal®) on nutrient cycling in soil was determined in Terrestrial Model Ecosystem (TME) tests and corresponding field-validation studies, which were performed in four different countries (United Kingdom, Germany, Portugal, and The Netherlands). The tests used different soil types, and lasted for 16 weeks. On three of the four sites, grassland soils were used while the fourth site had an arable soil. TMEs consisted of intact soil columns (diameter 17.5 cm; length 40 cm) and were taken from the site where the field study was performed. In the first series of TME tests, carbendazim applied at dosages unto 77.8 kg a.i./ha did not affect sulfate and phosphate concentrations in the top 15 cm soil layers. These nutrients were therefore no longer included in the second series of TME tests and the field-validation studies. Ammonium concentrations in the top soil layers of TMEs and field plots, and in the leachates of the TME columns did not show any effect of carbendazim treatment. Nitrate concentrations in soils and leachates did show some reduction at the highest treatment levels (77.8 kg a.i./ha in the first TME tests, 87.5 kg a,i/ha in the second TME tests and the field-validation studies). Since nitrate concentrations in both soils and leachates were correlated with soil moisture content, these effects could however, mainly be attributed to variations in soil moisture contents, and in some cases also indirectly to effects on earthworm activity. It is concluded that carbendazim, even at dosages as high as 87.5 kg a.i./ha, does not have a significant impact on soil nutrient cycling processes. Nutrient levels in TME tests and the field-validation studies generally showed similar patterns, thus confirming the predictive value of the TME test system

Ring-testing and field-validation of a terrestrial model ecosystem (TME) - An instrument for testing potentially harmful substances: effects of carbendazim on enchytraeids.

The effects of the fungicide carbendazim (applied in the formulation Derosal®) on enchytraeids were determined in Terrestrial Model Ecosystem (TME) tests and field-validation studies. TMEs consisted of intact soil columns (diameter 17.5 cm; length 40 cm) taken from a grassland or, in one case, from an arable site. The TMEs were taken from the same site where the respective field study was performed. The tests were performed in Amsterdam (The Netherlands), Bangor (Wales, England), Coimbra (Portugal) and Flörsheim (Germany). Concerning the enchytraeid overall abundance and the number of species, differences between sampling points and differences between the TME tests and the respective field-validation studies were not found in the controls. Generally, a high variability of data which reduced the probability of determining statistically significant differences was determined. Effects of the model chemical carbendazim were determined for the overall abundance of enchytraeids and the number of enchytraeid species. The clearest dose-response relationship was found for the abundance of the genus Fridericia. The abundance of the genera Achaeta and Enchytraeus was not affected. Effects were most pronounced 8 and 16 weeks after application of the test chemical. The observed effects appeared not to differ between the TME tests and the respective field-validation studies. Due to the high variability of data NOEC-values could often not be determined. The E

Ring-testing and field-validation of a terrestrial model ecosystem (TME) - An instrument for testing potentially harmful substances: effects of carbendazim on earthworms.

The effects of the fungicide carbendazim (applied in the formulation Derosal®) on earthworms (Lumbricidae) was determined in Terrestrial Model Ecosystem (TME) tests and field-validation studies. TMEs consisted of intact soil columns (diameter 17.5 cm; length 40 cm) taken from a grassland or, in one case, from an arable site. The TMEs were taken from the same site where the respective field-validation study was performed. The tests were performed in Amsterdam (The Netherlands), Bangor (Wales, UK), Coimbra (Portugal) and Flörsheim (Germany). The sites selected had an earthworm coenosis representative of the different land use types and regions. In addition, the differences between the coenosis found in the TMEs and the respective field sites were in general low. A high variability was found between the replicate samples, which reduces the probability of determining significant differences by the statistical evaluation of the data. Similar effects of the chemical treatment were observed on abundance as well as on biomass. Effects were most pronounced 16 weeks after application of the test chemical. The observed effects on earthworm abundance and biomass did not differ between the TME tests and the respective field-validation studies. Effects on earthworm diversity were difficult to assess since the number of individuals per species was low in general. However, the genus Lumbricus and in particular L. terrestris and L. rubellus seemed to be more affected by the chemical treatment than others. NOEC and E

Ring-testing and field-validation of a terrestrial model ecosystem (TME) - An instrument for testing potentially harmful substances: effects of carbendazim on nematodes.

The effects of the fungicide carbendazim (applied in the formulation Derosal®) on nematodes was determined in Terrestrial Model Ecosystem (TME) tests and field-validation studies. TMEs consisted of intact soil columns (diameter 17.5 cm; length 40 cm) taken from a grassland or, in one case, from an arable site. The TMEs were taken from the same site where the respective field study was performed. The tests were performed in Amsterdam (The Netherlands), Bangor (Wales, England), Coimbra (Portugal) and Flörsheim (Germany). Differences concerning nematode overall abundance, the number of nematode families, the trophical structure of the nematode cenosis and the maturity index (MI) were not found between the controls of TME tests and the respective field-validation studies. Effects caused by the chemical treatment, however, were observed on the number of nematode families, on the trophical structure of the nematode cenosis and on the maturity index (MI). Effects on the relative abundance of the omnivorous nematodes were most pronounced, whereas the overall nematode abundance was not affected. The observed effects appear not to differ between the TME tests and the respective field-validation studies. All measurement endpoints in both TMEs and field, showed rather large variations. Therefore, NOEC-values were often equal or higher than the highest treatment level and E

Ring-testing and field-validation of a terrestrial model ecosystem - An instrument for testing potentially harmful substances: fate of the model chemical carbendazim.

The fate of the fungicide carbendazim (applied in the formulation Derosal) in soil was determined in Terrestrial Model Ecosystem (TME) tests and corresponding field-validation studies, which were performed in four different countries (United Kingdom, Germany, Portugal, and The Netherlands). The tests used different soil types, and lasted for 16 weeks. On three of the four sites, grassland soils were used while the fourth site had an arable soil. TMEs consisted of intact soil columns (diameter 17.5 cm; length 40 cm) and were taken from the site where the field study was performed. In the first series of TME tests, carbendazim was applied at four dosages ranging between 0.36 and 77. 8 kg a.i./ha, while in the second series of TME tests and the field-validation studies six dosages between 0.36 and 87.5 kg a.i./ha were applied. D