bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous stylet punctures of phloem sieve elements by aphids
Authors: Tjallingii W. Fred , Gabryś Beata
Published: October 2003

A deviating type of potential drop (pd), i.e. the electrically recorded intracellular punctures during the pathway phase of plant penetration by aphids, is described and discussed. This so‐called repetitive pd (R‐pd) has been observed in 4 aphid species, two on herbs and two on sycamore. Apart from a regular repetition with short intervals, the most characteristic feature of the R‐pd is the middle intracellular part, i.e. sub‐phase 2, which is extended, making the individual R‐pd 2–3 times longer than the normal pd. Differences between the normal and R‐pd are described, as well as differences within each pd type between species. The R‐pd's seem to reflect repeated punctures of phloem sieve elements. Their biological significance is unknown.
Acceptability of different species of Brassicaceae as hosts for the cabbage aphid
Authors: Gabryś Beata , Pawluk Magdalena
Published: October 2003

The probing and feeding behaviour of the cabbage aphid, Brevicoryne brassicae (L.), (Homoptera, Aphididae) was studied on several plant species that represented various levels of acceptability: Sinapis alba L. (a permanent host plant), Capsella bursa‐pastoris (L.) Med., Thlaspi arvense L., Lunaria annua L., Erysimum cheiranthoides L. (accidental host plants), Vicia faba L. (a non‐host plant), using the electrical penetration graph technique (EPG). B. brassicae on V. faba did not show any patterns related to penetration of phloem vessels. Stylet penetration was deterred on L. annua and E. cheiranthoides where non‐penetration prevailed, the periods of sap ingestion were short or did not occur, the percentage of time spent in the phloem was consistently low (5–6%) and E1 salivation predominated. The pathway activities were not suppressed on C. bursa‐pastoris and T. arvense and the aphids spent an average of 3 h in the phloem during the 8‐h experiment. However, a considerable delay between finding and accepting the phloem and a substantial proportion of E1 salivation (20–30% of all phloem activities) indicated a deterrent factor in the sieve elements of these plants. Aphid probing and sap ingestion were rarely interrupted on S. alba. The results of this study suggest that the deterrent agents vary in activity and may hinder stylet penetration at different levels (epidermis, parenchymatous tissues and/or phloem elements), depending on the plant species.
Active defence of herbivorous hosts against parasitism: Adult parasitoid mortality risk involved in attacking a concealed stemboring host
Authors: Potting R.P.J. , Vermeulen N.E. , Conlong D.E.
Published: October 2003

Phytophagous insects have several defence strategies to defend themselves against attack by parasitic wasps. Larval lepidopteran hosts can defend themselves actively to prevent oviposition by the parasitoid. Among the aggressive kinds of behaviour exhibited by hosts against parasitoids are violent wriggling, biting and spitting. The behaviour of the braconid parasitoid Cotesia sesamiae attacking stemboring larvae inside their feeding tunnel in the plant stem was investigated in maize and sugarcane stem pieces and transparent artificial tunnels. Attacking a defending stemborer host inside the confined space of a tunnel was shown to be risky for the female parasitoid. A considerable proportion (25%) of female wasps were killed in their attempt to attack the spitting and biting host. No difference was found in the behaviour of C. sesamiae attacking the suitable host Sesamia calamistis or the unsuitable host Eldana saccharina. The consequences of this high mortality risk involved in each host attack is discussed in relation to the ecology of the parasitoid.
Flowers in tri‐trophic systems: mechanisms allowing selective exploitation by insect natural enemies for conservation biological control
Authors: Baggen L.R. , Gurr G.M. , Meats A.
Published: October 2003

Many insects have coevolved with certain angiosperm taxa to act as pollinators. However, the nectar and pollen from such flowers is also widely fed upon by other insects, including entomophagous species. Conservation biological control seeks to maximise the impact of these natural enemies on crop pests by enhancing availability of nectar and pollen‐rich plants in agroecosystems. A risk with this approach is that pests may also benefit from the food resource. We show that the flowers of some plants (viz., buckwheat, Fagopyron esculentum Moench and dill, Anethum graveolens L.), and the extrafloral nectaries of faba bean (Vicia faba L.) benefit both Copidosoma koehleri Blanchard (Hymenoptera: Encyrtidae) and its host, the potato pest, Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae). In contrast, phacelia (Phacelia tanacetifolia Benth) and nasturtium (Tropaeoleum majus L.) benefited only the parasitoid. When adult moths of P. operculella were caged with flowers of phacelia or nasturtium, longevity of males and females, egg laying life, fecundity, average oviposition rate, and number of eggs in ovaries at death were no greater than in the control treatment with access to shoots without flowers plus water. All the foregoing measures were increased compared to the control when the moths were allowed access to dill, buckwheat or faba bean extrafloral nectaries. Such ‘selectivity’ has the potential to make the use of floral resources in conservation biological control more strategic. We present morphometric and observational evidence to illustrate how such mechanisms may operate.
Vive la variance: a functional oviposition theory for insect herbivores
Authors: Roitberg Bernard D. , Robertson Ian C. , Tyerman Jabus G.A.
Published: October 2003

We developed state‐dependent life‐history theory to explain the variance in clutch size decisions made by insect herbivores under a variety of ecological scenarios. An important aspect of our theory is explicit representation of the distribution of host quality and frequency of occurrence. Examination of the theory suggests that clutch size decisions can be highly non‐linear with respect to host quality and variability. We then use our theory to explore the potential for bet‐hedging strategies to evolve as a function of unpredictable catastrophic events that decimate entire clutches. Our analysis suggests that the benefits to employing such a strategy will frequently be outweighed by costs brought on by delayed oviposition.
The assimilation and allocation of nutrients by symbiotic and aposymbiotic pea aphids, Acyrthosiphon pisum
Authors: Wilkinson T.L. , Ishikawa H.
Published: October 2003

The failure of a nutritionally balanced diet to ameliorate the impact of symbiont disruption in the pea aphid Acyrthosiphon pisum (Harris) was investigated using two approaches. The assimilation of dietary nutrients by aphids was investigated using chemically‐defined diets containing 3H‐labelled inulin and 14C‐labelled sucrose or amino acids. Symbiotic aphids (i.e., aphids containing their bacteria) had a high sucrose demand and assimilated 72% of sucrose ingested in the diet, whereas the assimilation of sucrose by aposymbiotic aphids (in which the bacteria had been disrupted), was significantly reduced to 47%. The assimilation of individual dietary amino acids by symbiotic aphids varied between 61 and 92%, and there was no impact on the feeding or assimilation rate when the aphids were fed a ‘phloem sap‐like’ diet containing a reduced amount of essential amino acids. Consequently, the absolute amount of each essential amino acid assimilated by symbiotic aphids feeding on a ‘phloem sap‐like’ diet was reduced by 36–59%. Aposymbiotic aphids consistently assimilated a lower proportion of ingested amino acids, and lysine in particular was poorly assimilated from the diet. In a second experiment, the allocation of free amino acids in the haemocoel to aphid embryos was investigated following microinjection of 14C‐labelled amino acids. After 2 h, radiolabel could be detected at varying levels from the embryo complement of both symbiotic and aposymbiotic aphids, indicating rapid but selective uptake by the embryos. The essential amino acids phenylalanine and lysine were incorporated into the protein fraction of embryo tissues, but the rate of incorporation per unit biomass was approximately 4‐fold higher in the embryos of aposymbiotic aphids, possibly reflecting increased demand due to the lack of amino acid provisioning from the symbiotic bacteria.
How nutritionally imbalanced is phloem sap for aphids?
Authors: Sandström Jonas , Moran Nancy
Published: October 2003

Aphids harbour intracellular symbionts (Buchnera) that provide their host with amino acids present in low amounts in their diet, phloem sap. To find out the extent to which aphids depend on their symbionts for synthesis of individual essential amino acids, we have evaluated how well phloem sap amino acid composition matches the aphids' needs. Amino acid compositions of the ingested phloem sap were compared to amino acids in aphid body proteins and also to available information about optimal diet composition for other plant feeding insects. Phloem sap data from severed stylets of two aphid species, Rhopalosiphum padi (L.) (Homoptera: Aphididae) feeding on wheat, and Uroleucon sonchi (L.) (Homoptera: Aphididae) feeding on Sonchus oleraceus (L.), together with published information on phloem sap compositions from other plant species were used.

Phloem sap has in general only around 20% essential amino acids, with a range from 15–48%. Aphid body proteins and optimal diets for two other plant feeding insects have around 50%. The phloem sap of early flowering S. oleraceus ingested by U. sonchi contained 48%, which seems to be exceptional. Aphids feeding on different plants appear to be very differently dependent on their symbionts for their overall essential amino acid synthesis, due to the large variation in proportion of essential amino acids in phloem sap from different plants.

The profile of the essential amino acids in phloem sap from different plant species corresponds rather well to profiles of both aphid body proteins and optimal diets determined for plant feeding insects. However, methionine and leucine in phloem sap are in general low in these comparisons, suggesting a higher dependence on the symbiont for synthesis of these amino acids. Concentrations of several essential amino acids in phloem from different plant species seem to vary together, suggesting that levels of symbiont provisioning of different amino acids are adjusted in parallel.
Using hybrid and backcross larvae of Papilio canadensis and Papilio glaucus to detect induced phytochemical resistance in hybrid poplar trees experimentally defoliated by gypsy moths
Authors: Scriber J. Mark , Weir Kirsten , Parry Dylan , Deering Jessica
Published: October 2003

Sub‐plots of hybrid poplars were experimentally defoliated using 10 million gypsy moth larvae. Half of the defoliated (and undefoliated control) plots were fertilized to see if this would ameliorate the predicted induction of carbon‐based phenolic defenses in the regrowth leaves. In order to bioassay the leaves of the four different treatments, we employed a continuum of genotypes (different hybrids and backcrosses of two different species of tiger swallowtail butterflies) with different abilities to detoxify these allelochemicals. Based on our previous studies with phytochemicals from the Salicaceae plant family, Papilio canadensis was likely to consume and process all Populus spp treatments, whereas P. glaucus predicted to either not consume or else quickly die on all Populus treatment leaves. Hybrid and backcross larvae of these two butterfly species are known to have intermediate levels of esterase detoxication enzymes and would therefore be likely to provide a continuum or at least varying degrees of sensitivity in bioassays for even the most subtle induction responses in the regrowth leaves. This presumption was supported in the feeding and growth studies conducted at different times post‐defoliation during the 1997 growing season in Michigan.
Genetic basis for established and novel host plant use in a herbivorous ladybird beetle, Epilachna vigintioctomaculata
Authors: Ueno Hideki , Fujiyama Naoyuki , Irie Kiyoshi , Sato Yuji , Katakura Haruo
Published: October 2003

Genetic trade‐offs in host plant use are thought to promote the evolution of host specificity. Experiments on a range of herbivorous insects, however, have found negative genetic correlation in host plant use in only a limited number of species. To account for the general lack of negative genetic correlation, recent hypotheses advocate that different stages in evolution of host use must be distinguished: initial performance on a novel host in comparison with the established host, and performance on both hosts after the insect population has interacted with both hosts for a long time. The hypotheses suggest that genetic correlation may not necessarily be negative at the initial stage. The present study examines growth performance on both the established and a novel host in a herbivorous ladybird beetle, Epilachna vigintioctomaculata Motschulsky (Coccinellidae, Epilachninae). The results show that traits of growth performance across hosts were positively or neutrally correlated, but there was no evidence of a negative genetic correlation. In addition, significant genetic variance of growth performance on each host was detected, suggesting that E. vigintioctomaculata can potentially respond to selection for increased performance on both plant species. These results and similar results from experiments on other herbivores suggest that host expansion may not be constrained genetically, at least at the initial stage of host range evolution.
Host‐plant choice and larval growth in the cinnabar moth: do pyrrolizidine alkaloids play a role?
Authors: Vrieling Klaas , de Boer Nico J.
Published: October 2003

Witte et al. (1992) described two distinct chemotypes of Senecio jacobaea L. Asteraceae, a chemotype with jacobine as one of the major pyrrolizidine alkaloids (PAs) and a chemotype with erucifoline as one of the major PAs. We hypothesized that the presence of erucifoline might be the factor responsible for the lack of success of the cinnabar moth on Senecio erucifolius L. Asteraceae and the S. jacobaea erucifoline chemotype. We performed a survey of the distribution of the two chemotypes in the Netherlands and compared this with the distribution map of Tyria jacobaeae L. Lepidoptera, Arctiidae. The distribution of the two chemotypes in the Netherlands is poorly correlated with the distribution of the cinnabar moth. The jacobine chemotype occurs along the coast and the erucifoline chemotype predominantly inward.

An oviposition experiment showed that the cinnabar moth did not discriminate between the two chemotypes of S. jacobaea and S. erucifolius. Larval performance did not differ between the two chemotypes and species. Although the distribution of S. jacobaea jacobine chemotype is loosely associated with the abundance of the cinnabar moth the oviposition and growth experiments indicate that other factors than the presence of erucifoline play a role in this association.

The absence of recordings of S. erucifolius as a foodplant for the cinnabar moth might be explained by the phenology of the foodplant. Ovipositing females of the univoltine cinnabar moth prefer flowering plants for oviposition. S. erucifolius starts flowering about 1–2 month later than S. jacobaea just after the peak density of moths.
It's all in the neurones
Authors: Chapman R.F.
Published: October 2003

This paper views some of the work presented in the symposium from a neural perspective. It is argued that any change in hostplant selection depends on a change in the peripheral or central nervous systems. Any changes in hostplant use and, ultimately, the evolution and phylogeny of phytophagous insects have a neural basis.
The effects of mating, age at mating, and plant stimuli, on the lifetime fecundity and fertility of the generalist herbivore Epiphyas postvittana
Authors: Foster S.P. , Howard A.J.
Published: October 2003

The effects of mating, age at mating, the presence or absence of a plant leaf, and the deprivation of a suitable ovipositional substrate during when the first ovipositional bout after mating would normally take place, on the lifetime fecundity and fertility (percentage of fertile eggs laid) of female Epiphyas postvittana were investigated. Mating had a significant effect on lifetime fecundity, with mated females laying 2.5 times more eggs than virgin females. Age at mating had a significant effect on both fecundity and fertility, both declining with increasing age when the female was mated. In the presence of a leaf of C. japonica, mated females had a greater lifetime fecundity than when no leaf was present; females in the presence of a C. japonica leaf consistently laid more eggs each day during the first 4–6 days after mating than females without a leaf. When females were deprived of a suitable ovipositional substrate, for the first 22 h after mating, they were significantly less fecund over their lifetime than were control females. Finally, in no‐choice tests with three plants of different acceptability to females, the fecundity of females differed in the order C. japonica > Urtica ferox > Tibouchina multiflora. This different fecundity appeared to be inversely related to the pubescence of the leaves, suggesting that leaf texture may be a suitable antixenotic resistance factor for crops to be protected from this insect. These results suggest that strategies whereby mating is delayed or oviposition reduced within a critical period after mating, may result in significant reductions in pest populations.
Effectiveness of Trichogramma ostriniae and T. nubilale for controlling the European corn borer Ostrinia nubilalis in sweet corn
Authors: Wang Baode , Ferro David N. , Hosmer David W.
Published: October 2003

Seven field releases of Trichogramma ostriniae and T. nubilale (Hymenoptera: Trichogrammatidae) were made separately and in combination in a sweet corn field to compare the level of parasitism in sentinel eggs of the European corn borer, Ostrinia nubilalis (Lepidoptera: Pyralidae). The results indicate that the levels of egg parasitism among different release dates differed mainly because of changes in weather and plant architecture within the season. The level of egg parasitism by releasing T. ostriniae alone was found to be 15% higher than that by releasing T. nubilale alone, and 20% higher than by releasing the combination of the two species. Further analyses using the logistic regression model for independent and correlated data indicated T. ostriniae to be more efficient at discovering host egg masses and to have higher levels of egg parasitism than T. nubilale. Mutual interference between T. ostriniae and T. nubilale was the main factor for the lower level of egg parasitism when T. ostriniae and T. nubilale were released together. The results suggest that T. ostriniae is the better candidate for augmentative releases for control of the European corn borer, and the two species should not be released into a corn field at the same time.
Oviposition bioassay responses of Culex tarsalis and Culex quinquefasciatus to neem products containing azadirachtin
Authors: Su Tianyun , Mulla Mir S.
Published: October 2003

Neem (Azadirachta indica A. Juss) products have been shown to exert pesticidal properties against a variety of insect species. In mosquito control programs, such products may have the potential to be used successfully as larvicides. In exploring other advantages of neem products, we studied the oviposition responses of Culex tarsalis Coquillett and Cx. quinquefasciatus Say to two experimental azadirachtin (AZ) formulations, wettable powder Azad™ WP10 (WP) and emulsifiable concentrate Azad™ EC4.5 (EC). Gravid Cx. tarsalis exhibited a distinct preference for the neem suspension of the WP, where significantly more egg rafts were collected from the treatment than from the control. The minimum effective AZ concentration for this activity was 0.5 ppm. The aged suspensions from 1–7 days at 0.5 and 1 ppm AZ were more active in eliciting oviposition responses in Cx. tarsalis than the fresh preparations. This activity of the aged suspensions lasted up to 14 and 21 days at 0.5 and 1 ppm AZ, respectively. Negative ovipositional responses were indicated in the tests of the EC vs. Cx. tarsalis, as well as both neem formulations vs. Cx. quinquefasciatus. In the tests of the EC formulation, significantly less gravid females were trapped by oviposition cups in the treatment than in the control, and in the tests of the WP significantly less egg rafts were collected from the treatment than from the control. The minimum effective concentrations for oviposition avoidance activity were 5 ppm AZ for Cx. tarsalis and 10 ppm AZ for Cx. quinquefasciatus, which lasted up to 1 and 4 days for these two species respectively. Neem products potentially used as mosquito larvicides may have many additional benefits in mosquito control programs, the oviposition modification noted in the current studies is one such example.
Specificity of a Y‐linked gene in the flea beetle Phyllotreta nemorum for defences in Barbarea vulgaris
Authors: Nielsen Jens Kvist
Published: October 2003

A Y‐linked gene (R‐gene) in the flea beetle Phyllotreta nemorum L. (Coleoptera: Chrysomelidae: Alticinae) confer the ability of larvae to survive on types of the plant Barbarea vulgaris R.Br. (Brassicaceae) which are immune to attack by susceptible conspecifics. Two near‐isogenic flea beetle lines were developed. The YE‐line contained the Y‐linked R‐gene, and male larvae from this line survived on B. vulgaris. The ST‐line did not contain the gene and did not survive on the plant. The YE‐line had been developed through 8–9 generations of backcrosses (YE‐males with ST‐females) and the two lines were considered to be isogenic except for genes located on the Y‐chromosome.

A single copy of the Y‐linked gene is sufficient to transfer a susceptible genotype (ST) into a resistant genotype (YE) which is able to utilize a plant that is immune to attack by specimens without R‐genes. The Y‐linked gene had no effects on survival on other plant species tested. The gene did not have any effect on developmental times and weights of adult beetles reared on other plants than B. vulgaris. Developmental times of larvae with the Y‐linked gene were longer on B. vulgaris than on normal host plants, R. sativus and S. arvensis, but the adults obtained the same size on these plant species. No trade‐offs of the Y‐linked gene were discovered. The results suggest that the occurrence of the Y‐linked gene is a derived trait which has enabled the flea beetle to expand its host plant range. The evolution of a host shift to B. vulgaris seems not to be favoured by the presence of this single gene.
Nonlocal dielectric functions on the nanoscale: Screened forces from unscreened potentials
Authors: Spirina Jenkins Olga , Hunt Katharine L. C.
Published: October 2003

In this work, we prove that an intramolecular dielectric model yields accurate results for the forces between nonoverlapping molecules, at first order in the intermolecular interaction. The analysis is valid within the Born–Oppenheimer approximation. Within any perturbed molecule, a nonlocal dielectric function εv−1(r,r′) describes the screening of external potentials due to the induced redistribution of electronic charge, i.e., this function acts as the integral kernel that determines the effective potential at point r (within linear response), when an external potential φex(r′) acts on the molecule, at other points r′. The dielectric function εv−1(r,r′) depends on the nonlocal charge-density susceptibility, which can be calculated ab initio or by density functional techniques. From quantum mechanical perturbation theory, at first order the interaction energy of two molecules is determined by the unscreened Coulomb interaction energy of the unperturbed molecular charge distributions. Yet the first-order forces on the nuclei include dielectric screening effects, due to the redistribution of the electronic charge density of each molecule in the presence of the other. This counterintuitive result follows from a relation between the charge-density susceptibility and the derivatives of the electronic charge density with respect to nuclear coordinates. The derivation provides a quantum mechanical validation for dielectric screening models on the nanoscale, when the dielectric function for electronic response is nonlocal.
Viscoelasticity and rheology of depletion flocculated gels and fluids
Authors: Shah S. A. , Chen Y.-L , Schweizer K. S. , Zukoski C. F.
Published: October 2003

The flow properties of high volume fraction hard sphere colloid–polymer suspensions are studied as a function of polymer concentration, depletion attraction range, and solvent quality up to, and well beyond, the gelation boundary. As the gel boundary is approached, the shear viscosity tends to diverge in a critical power law manner at a polymer concentration that is a function of the polymer radius of gyration and solvency condition. The shear viscosity for different polymer size suspensions can be collapsed onto a master curve motivated by mode coupling theory (MCT). The low frequency elastic modulus grows rapidly with increasing depletion attraction near the gel boundary, but becomes a dramatically weaker function of polymer concentration as the gel state is more deeply entered. A simplified version of MCT with accurate, no adjustable parameter polymer reference interaction site model (PRISM) theory structural input has been applied to predict the gelation boundaries and elastic shear moduli. The calculated gel lines are in semiquantitative agreement with experiment at high volume fractions, but increasingly deviate upon particle dilution. Calculations of the dependence of the gel elastic shear moduli on particle-polymer size asymmetry and scaled polymer concentration are in excellent agreement with experiment, and deep in the gel follow a power law dependence on polymer concentration. Quantitatively, MCT-PRISM elastic moduli are higher than experiment by a nearly constant large factor. This discrepancy is suggested to be due to the heterogeneous nature of the gel structure which small angle scattering experiments show consists of dense clusters and voids of characteristic length scales ∼4–7 particle diameters. A simple idea for correcting the particle level MCT modulus by employing cluster network concepts is proposed.
The role of triplet states in the long wavelength absorption region of bromine nitrate
Authors: Peterson Kirk A. , Li Yumin , Francisco Joseph S. , Zou Peng , Webster Charles Edwin , Pérez Lisa M. , Hall Michael B. , North Simon W.
Published: October 2003

A theoretical study of the low-lying singlet and triplet electronic states of BrONO2 is presented. Calculations of excitation energies and oscillator strengths are reported using excited-state coupled cluster response methods, as well as the complete active space self-consistent field method with the full Breit–Pauli spin-orbit operator. The calculations predict that there is only one singlet state for BrONO2, the Ã 1A″ state, that is accessible at wavelengths longer than 300 nm. At energies below the first singlet state, i.e., λ>330 nm, the calculations reveal two triplet states with significant oscillator strength. Therefore, we propose that the origin of absorption in the long wavelength region from 350 to 500 nm, responsible for the majority of atmospheric photolysis, is due to transitions to triplet states and not singlet states. A comparison of the reported benchmark coupled cluster calculations (CCSD) with the results of (1) configuration interaction with all single substitutions and a perturbative correction for the double substitutions [CIS(D)] and (2) time-dependent density-functional (TDDF) calculations is provided. For the lowest energy excitations, CIS(D) calculations provide quantitative agreement with the CCSD results, while TDDF calculations yield qualitative agreement.
Delayed ionization of the zirconium Met-Car, Zr8C12
Authors: Stairs J. R. , Davis K. M. , Peppernick S. J. , Castleman A. W.
Published: October 2003

Measurements of the delayed ionization of the zirconium Metallocarbohedrene (Met-Car, Zr8C12), obtained employing a recently developed reverse field technique (RFT), are presented. Two methods have been used in the past to study delayed ionization: the “passive” method, where the shape of the mass peak in a mass spectrum is studied, and the “active” method, where a blocking field technique is used to sample the delayed ions created during specific time intervals. The RFT is a newly modified version of the blocking field technique, which allows the relative amount of delayed ionization during 50 ns time slices to be measured starting at the time the excitation laser interacts with the species under study. The fitting of the thermionic emission model to the delayed ionization data of the clusters investigated in the present study is described in detail. Previous use of the thermionic emission model, as applied to the blocking field technique, did not mathematically account for the longevity of the extraction pulse. A modified thermionic emission model, which accurately describes the reverse field technique, is presented. Comparisons between the data and model fit of the Met-Car are made, showing excellent agreement.
Continuum level treatment of electronic polarization in the framework of molecular simulations of solvation effects
Authors: Leontyev I. V. , Vener M. V. , Rostov I. V. , Basilevsky M. V. , Newton M. D.
Published: October 2003

The hybrid molecular–continuum model for polar solvation considered in this paper combines the dielectric continuum approximation for treating fast electronic (inertialess) polarization effects and a molecular dynamics (MD) simulation for the slow (inertial) polarization component, including orientational and translational solvent modes. The inertial polarization is generated by average charge distributions of solvent particles, composed of permanent and induced (electronic) components. MD simulations are performed in a manner consistent with the choice of solvent and solute charges such that all electrostatic interactions are scaled by the factor 1/ε∞, where ε∞ is the optical dielectric permittivity. This approach yields an ensemble of equilibrium solvent configurations adjusted to the electric field created by a charged or strongly polar solute. The electrostatic solvent response field is found as the solution of the Poisson equation including both solute and explicit solvent charges, with accurate account of electrostatic boundary conditions at the surfaces separating spatial regions with different dielectric permittivities. Both equilibrium and nonequilibrium solvation effects can be studied by means of this model, and their inertial and inertialess contributions are naturally separated. The methodology for computation of charge transfer reorganization energies is developed and applied to a model two-site dipolar system in the SPC water solvent. Three types of charge transfer reactions are considered. The standard linear-response approach yields high accuracy for each particular reaction, but proves to be significantly in error when reorganization energies of different reactions were compared. This result has a purely molecular origin and is absent within a conventional continuum solvent model.
Computations of solvation free energies for polyatomic ions in water in terms of a combined molecular–continuum approach
Authors: Vener M. V. , Leontyev I. V. , Basilevsky M. V.
Published: October 2003

The combined molecular–continuum approach developed in the preceding paper was applied for calculations of equilibrium solvation energies for a large number of polyatomic ions. The structure and charge distribution of the given ion were computed using the restricted Hartree–Fock level with the 6-31G** basis set. The standard Lennard-Jones (LJ) parameters, which were not specially calibrated to fit the solvation energies, were used in molecular dynamics simulations. Water (the SPC model) was considered as a solvent. The computations show that the new scheme works satisfactorily for nitrogen cations in the frame of a standard parametrization and can be further improved for oxygen ions by tuning solute–solvent LJ parameters. The calculated relative change of the energies in families of similar cations—i.e., ammonium-type or oxonium-type cations—fits the experimental trends. The present approach is specially addressed to separate the inertial contribution to solvation free energies, which is important in view of further applications to electron transfer reactions. Computed values of the inertial contribution to solvation energies of the ions and reorganization energies for the model two-site dumbbell system are found to be systematically lower than those obtained in terms of the standard treatments (using the Pekar factor or the polarizable continuum model (PCM)).
Dynamical nature of least stable fluctuation modes of lamellar structure observed in a nonionic surfactant/water system
Authors: Imai Masayuki , Nakaya Kaori , Kawakatsu Toshihiro , Seto Hideki
Published: October 2003

The nature of fluctuation modes of lamellar structure in a nonionic surfactant/water system has been investigated using a small angle x-ray scattering and a neutron spin echo technique. Approaching temperature from lamellar phase to double-gyroid phase, a diffuse scattering peak appears in the small angle scattering profile prior to the transition. This diffuse scattering is originated from the least stable fluctuation modes of lamellar structure predicted by Qi and Wang [Macromolecules 30, 4491 (1997)]. The intermediate scattering profiles of the lamellar phase just before the transition can be described by a undulation fluctuation mode and a least stable fluctuation mode of the lamellar structure. The relaxation rate of the least stable fluctuation mode decreases with approaching temperature to the double-gyroid phase. However, in the vicinity of the lamellar to double-gyroid transition temperature, the decrease of relaxation rate is suppressed and the lamellar structure transforms to the intermediate rhombohedral network structure. The behaviors of fluctuation modes are examined by a time dependent Ginzburg–Landau model using a Leibler free energy functional.
Dissociative electron attachment to nitroethane: C2H5NO2
Authors: Pelc A. , Sailer W. , Matejcik S. , Scheier P. , Märk T. D.
Published: October 2003

Dissociative electron attachment (DEA) to nitroethane (C2H5NO2) in the gas phase is studied using a crossed electron–molecule beams technique. The ion yields for particular fragment ions were measured in the electron energy range from 0 to 9.5 eV with an electron energy resolution of about 120 meV. In contrast to previous studies additional negative ions, i.e., HCN− and NO−, were observed. Measures for the absolute partial cross sections were obtained for the ions using a calibration technique involving a comparison with the known cross section of the 0.8 eV peak in DEA to CCl4. The dominant negative ion product is NO2− with a cross section of approximately 11×10−22 m2 at 0.75 eV. The values of the cross section estimates for the other ions are about σ(C2H3NO2−)=4×10−24 m2 at ∼0 eV, σ(O−)=5×10−24 m2 at 5.7 eV, σ(OH−)=2×10−24 m2 at 5.7 eV, σ(CN−)=5×10−25 m2 at 1.7 eV, σ(CNO−)=3×10−25 m2 at ∼4.5 eV, σ(HCN−)=2×10−25 m2 at ∼4.5 eV and σ(NO−)=3×10−25 m2 at ∼8 eV.
A detailed study of the dynamics of the O(1D)+HCl→OH+Cl, ClO+H reactions
Authors: Martı́nez Teresa , Hernández Marı́a Luz , Alvariño José Marı́a , Aoiz F. J. , Sáez Rábanos V.
Published: October 2003

A detailed and comprehensive study of the dynamics has been performed using quasiclassical trajectory calculations on a recent version of the ground 1 1A′ potential energy surface (PES) [M. T. Martı́nez et al., Phys. Chem. Chem. Phys. 2, 589 (2000)] for this system. This PES was shown to account very well for the various experimental results available for the HOCl system. It has been found that this reaction occurs following different mechanisms depending on whether the HClO, HOCl, or both wells are visited in the course of the reaction. The different scalar and vector properties are strongly dependent on the type of mechanism through which a reaction takes place. Calculations have also been carried out to determine the distribution of collision times for each of the different mechanisms, and the time evolution of the differential cross section. For both reaction chemical channels the backward scattering is delayed with respect to the appearance of forward scattering. Although this reaction has been considered traditionally as an insertion reaction, it has been found that the first stages of the close interaction between the three atoms correspond to an attachment type of mechanism.
Coarse-graining description of solid systems at nonzero temperature
Authors: Wu Z.-B. , Diestler D. J. , Feng R. , Zeng X. C.
Published: October 2003

The quasicontinuum (QC) technique, in which the atomic lattice of a solid is coarse-grained by overlaying it with a finite-element mesh, has been employed previously to treat the quasistatic evolution of defects in materials at zero temperature. It is extended here to nonzero temperature. A coarse-grained Hamiltonian is derived for the nodes of the mesh, which behave as quasiparticles whose interactions are mediated by the underlying (non-nodal) atoms constrained to move in unison with the nodes. Coarse-grained thermophysical properties are computed by means of the Monte Carlo (MC) method. This dynamically constrained QC MC procedure is applied to a simple model: A pure single crystal of two-dimensional Lennard-Jonesium. The coarse-grained isotropic stress (τc) is compared with the “exact” τ computed by the usual atomistic MC procedure for several thermodynamic states. The observed linear dependence of the error in τc on the degree of coarse-graining is rationalized by an analytical treatment of the model within the local harmonic approximation.
Calorimetric search for a tricritical point in mixtures of water, 3-methylpyridine and sodium bromide
Authors: Van Roie B. , Pitsi G. , Thoen J.
Published: October 2003

We investigated the specific heat capacity near the demixing transition of ternary mixtures of water, 3-methylpyridine and sodium bromide as a function of salt concentration. In this system, a crossover from Ising to tricritical behavior caused by the appearance of a new “microheterogeneous” phase was reported from light-scattering measurements [Jacob et al., Phys. Rev. E 58, 2811 (1998)]. We used adiabatic scanning calorimetry, a very sensitive technique for detecting and characterizing phase transitions, to investigate this system and found no specific heat anomaly to be associated with the formation of a new phase. In the one phase region, the critical exponent α is consistent with the Ising value and is incompatible with the tricritical value for all the investigated samples. In the phase-separated region, the values of the exponent are substantially lower and even negative. This is probably caused by the change in salt concentration of the two phases close to the critical point.
Conformational evolution of initially straight flexible and stiff polymers over extended time periods via the scaling law methodology
Authors: Dimitrakopoulos P.
Published: October 2003

Knowledge of the conformational evolution of a polymer chain provides invaluable information for all polymer properties. However, the chain evolution is usually determined by monitoring single beads for short times only. In this paper, we numerically determine the configuration evolution over extended time periods by monitoring the eigenvalues of the gyration tensor and applying the scaling law methodology. Results of Brownian dynamics simulations of initially straight chains reveal that after the early free transverse diffusion, flexible polymers exhibit a transverse intermediate-time behavior of t3/4, while stiff polymers reveal two intermediate-time behaviors: an early t5/6 power law accompanied by a late t3/4 evolution. These results are associated with the inherent nonlinearity of the problem. The scaling law methodology we develop in this paper for monitoring the chain configuration should have wide applications in the study of polymer rheology.
Solvent rearrangement for an excited electron of I−(H2O)6: Analog to structural rearrangement of e−(H2O)6
Authors: Lee Han Myoung , Suh Seung Bum , Kim Kwang S.
Published: October 2003

The study of electron solvation dynamics is vital for understanding the phenomena related to the electron transfer process in solvents. On the basis of a recent femtosecond dynamics study of charge-transfer-to-solvent states in photoexcited iodide–water clusters [Lehr et al., Science 284, 635 (1999)], we have investigated the solvent rearrangement process for the excited electron in the iodide–water hexamer using ab initio calculations. Upon excitation of iodide–water hexamer, an electron transfers from the iodide anion to the water cluster. This results in release of the iodine atom and thereby formation of anionic water hexamer which undergoes rearrangement process toward the most stable conformation. The transformation pathway from the low-lying energy structures of the iodide–water hexamer to those of the electron–water hexamer is thus elucidated from the potential energy surface including the global and local minima and transition states of the electron–water hexamer.
Density matrix search using direct inversion in the iterative subspace as a linear scaling alternative to diagonalization in electronic structure calculations
Authors: Li Xiaosong , Millam John M. , Scuseria Gustavo E. , Frisch Michael J. , Schlegel H. Bernhard
Published: October 2003

For electronic structure calculations on large systems, solving the self-consistent-field (SCF) equations is one of the key bottlenecks. Density matrix search methods provide an efficient linear scaling approach for circumventing the traditional O(N3) diagonalization procedure for solving the SCF equations. The conjugate gradient density matrix search (CG-DMS) method is a successful implementation of this approach. An alternative density matrix search method, QN–DMS, employs direct inversion in the iterative subspace using a quasi-Newton (QN) step to estimate the error vector. For linear polyglycine chains of 10–100 residues, the present approach scales linearly and is 30% faster than CG-DMS. For clusters of up to 300 water molecules, this method shows smoother and efficient convergence, and displays nearly linear scaling.
Curvature of interatomic surfaces. I. Fundamentals
Authors: Pendás A. Martı́n , Luaña V.
Published: October 2003

Some basic aspects regarding the geometry of the interatomic surfaces of the theory of atoms in molecules are considered. After showing that the global Gauss–Bonnet theorem poses severe difficulties on the calculation of the total Gaussian curvatures of unbounded interatomic surfaces, we propose the use of the local value of the Gaussian curvature at the bond critical point as a better suited indicator of the geometry of the surfaces. To that end, we report analytical expressions for the curvatures of gradient lines and interatomic surfaces at critical points.
Curvature of interatomic surfaces. II. Origin and systematics
Authors: Pendás A. Martı́n , Luaña V.
Published: October 2003

We investigate the origin of the local curvatures of the interatomic surfaces of the theory of atoms in molecules. The analytic expressions obtained in a previous work are used as a basic guide to this end, and several simplified models of the electron density between a pair of interacting atoms demonstrate that the stiffness difference in the atomic densities near the bond critical points controls their signs and magnitudes. Some steps toward a systematic evaluation of the curvatures of simple molecules have also been taken, and a number of correlations between these curvatures and chemically relevant atomic properties are presented.
Reconstruction subgrid models for nonpremixed combustion
Authors: Mellado J. P. , Sarkar S. , Pantano C.
Published: October 2003

Large-eddy simulation of combustion problems involves highly nonlinear terms that, when filtered, result in a contribution from subgrid fluctuations of scalars, Z, to the dynamics of the filtered value. This subgrid contribution requires modeling. Reconstruction models try to recover as much information as possible from the resolved field Z̄, based on a deconvolution procedure to obtain an intermediate field ZM. The approximate reconstruction using moments (ARM) method combines approximate reconstruction, a purely mathematical procedure, with additional physics-based information required to match specific scalar moments, in the simplest case, the Reynolds-averaged value of the subgrid variance. Here, results from the analysis of the ARM model in the case of a spatially evolving turbulent plane jet are presented. A priori and a posteriori evaluations using data from direct numerical simulation are carried out. The nonlinearities considered are representative of reacting flows: power functions, the dependence of the density on the mixture fraction (relevant for conserved scalar approaches) and the Arrhenius nonlinearity (very localized in Z space). Comparisons are made against the more popular beta probability density function (PDF) approach in the a priori analysis, trying to define ranges of validity for each approach. The results show that the ARM model is able to capture the subgrid part of the variance accurately over a wide range of filter sizes and performs well for the different nonlinearities, giving uniformly better predictions than the beta PDF for the polynomial case. In the case of the density and Arrhenius nonlinearities, the relative performance of the ARM and traditional PDF approaches depends on the size of the subgrid variance with respect to a characteristic scale of each function. Furthermore, the sources of error associated with the ARM method are considered and analytical bounds on that error are obtained.
Influence of fluid thermal sensitivity on the thermo-mechanical stability of the Taylor–Couette flow
Authors: Thomas D. G. , Sureshkumar R. , Khomami B.
Published: October 2003

Recent theoretical [Al-Mubaiyedh et al., Phys. Fluids 11, 3217 (1999); J. Fluid Mech. 462, 111 (2002)] and experimental [White and Muller, Phys. Rev. Lett. 84, 5130 (2000); J. Fluid Mech. 462, 133 (2002)] studies have revealed that viscous heating causes significant destabilization of the Taylor–Couette flow of highly viscous and thermally sensitive fluids. In this work, the roles of thermal sensitivity of fluid properties and co-rotation on the thermo-mechanical stability of Taylor–Couette flow are investigated theoretically. In turn, our theoretical findings are compared with the recent experimental ones by White and Muller [Phys. Fluids 14, 3880 (2002)]. It is shown that a finite gap temperature is necessary to predict the time-dependent transitions observed in the experiments. A universal scaling between the critical Reynolds number and the Nahme number is obtained for intermediate values of Nahme number ranging from 0.01 to 1.0. Studies are also performed to determine the influence of co-rotation of the outer cylinder relative to the inner one on the thermo-mechanical stability. Overall, a very favorable comparison between theoretical and experimental results is obtained.