bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of fertilization levels, age and canopy height of Lycopersicon hirsutum on the resistance to Myzus persicae
Authors: Leite G.L.D. , Picanço M. , Guedes R.N.C. , Skowronski L.
Published: October 2003

The effects of different levels of fertilization with nitrogen and potassium (NK), height within the canopy and plant age of Lycopersicon hirsutum f. glabratum (PI 134417) C. H. Mull and L. esculentum on the density of foliar cristalliferous idioblasts and trichomes, and on the levels of 2‐ tridecanone (2‐TD) and 2‐undecanone (2‐UD) and their influence on the resistance to Myzus persicae (Sulzer) were investigated. NK levels were inversely related to densities of trichomes and cristalliferous idioblasts in L. esculentum, but only to densities of cristalliferous idioblasts in L. hirsutum. Trichome density increased with increasing height within the canopy and with plant age in L. esculentum and L. hirsutum. Density of cristalliferous idioblasts in L. hirsutum increased with canopy height reaching a maximum at mid‐height within the canopy in opposition to L. esculentum in which a small decrease in density with height within the canopy was found. There was also a small decrease of idioblast density with increasing plant age for L. esculentum, while a greater and opposite variation took place in L. hirsutum. L. esculentum has mainly non‐ glandular leaf trichomes (90%), while L. hirsutum has mainly glandular trichomes (97%). The main glandular trichomes of L. hirsutum are producers of 2‐TD and 2‐UD, whose leaf content increases with increase of trichome density. A negative effect of 2‐TD concentration and cristalliferous idioblast density on the survival and longevity of M. persicae was observed. Since L. hirsutum presented much higher levels of 2‐TD and cristalliferous idioblast density than L. esculentum, L. hirsutum seems a promising source of resistance to M. persicae for tomato breeding programs.
Increased damage by western flower thrips Frankliniella occidentalis in chrysanthemum intercropped with subterranean clover
Authors: den Belder E. , Valcheva R.I. , Guldemond J.A.
Published: October 2003

Suppressive effects of intercropping on Frankliniella occidentalis (Pergande) infestations have been reported in several crops. However, this study demonstrates that in year‐round chrysanthemum, Dendranthema grandiflora Tzvelev, undersowing with subterranean clover, Trifolium subterraneum L., results in an increased thrips feeding damage. In a pot experiment, performed with chrysanthemum plants (cultivars Reagan and Tiger) grown with or without subterranean clover, significantly more leaves with silver and growth damage were found in the chrysanthemum plants with subterranean clover in comparison with the monocropped chrysanthemum plants. Similarly, the degree of deformation of leaf perimeter and leaf surface was higher in the top leaves of the intercropped chrysanthemum plant. In the soil experiment (only performed with Tiger and plants were grown in the soil in the greenhouse) intercropped chrysanthemum plants suffered a higher feeding damage as well. Analysis of the relation between silver or growth damage and the thrips pressure demonstrates that at similar thrips pressure in the intercropped chrysanthemum plants suffered significantly more damage. The higher thrips pressure in the intercropped chrysanthemum only explains the differences in damage partly. Changes in the reaction of chrysanthemum plants to thrips feeding or in the behaviour of the thrips, mediated by the presence of the non‐host crop, are discussed. Our explanation is that chrysanthemum plants grown with clover are more susceptible to thrips feeding than monocropped plants. We conclude that undersowing with clover does not contribute to reduce damage by F. occidentalis in year‐round chrysanthemum. Also, the influence of crop diversification on a pest cannot be foreseen until the specific characteristics of each individual crop – pest system are studied.
Prey‐mediated effects of Cry1Ab toxin and protoxin and Cry2A protoxin on the predator Chrysoperla carnea
Authors: Hilbeck Angelika , Moar William J. , Pusztai‐Carey Marianne , Filippini Agata , Bigler Franz
Published: October 2003

Laboratory feeding experiments were carried out to study prey‐mediated effects of artificial diet containing Bacillus thuringiensis proteins on immature Chrysoperla carnea. Activated Cry1Ab toxin and the protoxins of Cry1Ab and Cry2A were mixed into standard meridic diet for Spodoptera littoralis (Boisduval) larvae at the following concentrations; for Cry1Ab toxin, 25, 50, 100 μg g−1 diet were used; for Cry1Ab protoxin, the concentration was doubled (50 μg g−1 diet, 100 μg g−1 diet and 200 μg g−1 diet) to give relative comparable levels of toxin concentration. Cry2A protoxin was incorporated into the meridic diet at one concentration only (100 μg g−1 diet). For the untreated control, the equivalent amount of double distilled water was added to the meridic diet. Individual C. carnea larvae were raised on S. littoralis larvae fed with one of the respective treated meridic diets described above. The objectives were to quantify and compare the resulting effects on mortality and development time of C. carnea with those observed in two previous studies investigating prey‐mediated effects of transgenic Cry1Ab toxin‐producing corn plants and the other studying effects of Cry1Ab toxin fed directly to C. carnea larvae. Mean total immature mortality for chrysopid larvae reared on B. thuringiensis‐fed prey was always significantly higher than in the control (26%). Total immature mortality of C. carnea reared on Cry1Ab toxin 100 μg g−1 diet‐fed prey was highest (78%) and declined with decreasing toxin concentration. Cry1Ab protoxin‐exposed C. carnea larvae did not exhibit a dose response. Prey‐mediated total mortality of Cry1Ab protoxin‐exposed chrysopid larvae was intermediate (46–62%) to Cry1Ab toxin exposed (55–78%) and Cry2A protoxin (47%) exposed C. carnea. In agreement with the previous studies, total development time of C. carnea was not consistently, significantly affected by the Bt‐treatments except at the highest Cry1Ab toxin concentration. However, both highest mortality and delayed development of immature C. carnea raised on Cry1Ab toxin 100 μg g−1 diet – fed prey may have been confounded with an increased intoxication of S. littoralis larvae that was observed at that concentration. At all other B. thuringiensis protein concentrations S. littoralis was not lethally affected. Comparative analysis of the results of this study with those of the two previous studies revealed that in addition to prey/herbivore by B. thuringiensis interactions, also prey/herbivore by plant interactions exist that contribute to the observed toxicity of B. thuringiensis– fed S. littoralis larvae for C. carnea. These findings demonstrate that tritrophic level studies are necessary to assess the long‐term compatibility of insecticidal plants with important natural enemies.
Effect of crowding, food deprivation, and diet on flight initiation and lipid reserves of the lesser grain borer, Rhyzopertha dominica
Authors: Perez‐Mendoza J. , Dover B.A. , Hagstrum D.W. , Hopkins T.L.
Published: October 2003

Effects of crowding, food deprivation, and type of cereal diet upon flight initiation, development, body weight, lipid content, and fatty acid composition of the lesser grain borer, Rhyzopertha dominica (F.), were studied in two field strains and one laboratory strain. Beetles of all strains reared under crowded conditions had significantly higher flight initiation than beetles reared on isolated kernels (uncrowded). Regardless of degree of crowding, flight initiation increased with the period of food deprivation up to a maximum at 24 h, after which flight initiation declined. Body weight and lipid content decreased as the food deprivation period increased, whereas fatty acid composition was not significantly affected by food deprivation. Beetles from a field strain collected in 1995 had higher flight initiation and increased lipid content compared with beetles from the laboratory strain. However, beetles from the laboratory strain were larger, developed faster, and were more fecund than beetles from this field strain. The cereal diet on which beetles were reared also had a significant effect on flight initiation, lipid content, and fatty acid composition. Beetles reared on whole rice and wheat produced adults with higher flight initiation, higher lipid content, and higher oleic acid concentration than beetles reared on whole corn and sorghum.
Development of an artificial host egg for in vitro egg laying of Trichogramma galloi and T. pretiosum using plastic membranes
Authors: Cônsoli F.L. , Parra J.R.P.
Published: October 2003

An artificial host egg was developed as a first attempt to improve the techniques for in vitro rearing of Trichogramma galloi Zucchi and T. pretiosum Riley (Hymenoptera, Trichogrammatidae). Plastic membranes (polyethylene, polypropylene and polystyrene) of different thickness were tested for their usefulness in manufacturing artificial eggs, using a thermal system to produce semi‐spherical cupules on the plastic surface. These artificial eggs were filled with larval hemolymph of Helicoverpa zea (Boddie) (Lepidoptera, Noctuidae), and the optimal size of the artificial egg and density of females/artificial egg for the highest host acceptance (percentage of artificial eggs with at least one parasitoid egg) as well as the ideal level of parasitism (eggs/artificial egg) were determined. High‐density polyethylene 7–8 and 9–10 μm thick resulted in the best acceptance and level of parasitization for both parasitoid species. Six females per artificial egg resulted in the best rate of parasitization for these parasitoids, although these data were not different when using 4 or 5 females of T. galloi. The size, shape and surface texture of the artificial eggs were found to provide enough cues to elicit parasitization behavior in Trichogramma females, since no chemical stimulus was provided.
Sampling epigeal arthropods: an evaluation of fenced pitfall traps using mark‐release‐recapture and comparisons to unfenced pitfall traps in arable crops
Authors: Holland John M. , Smith Simon
Published: October 2003

The efficiency of fenced pitfall traps for estimating the density of commonly occurring epigeal predatory beetles was examined using mark‐release‐recapture. Most beetles of those recovered were recaptured within one week of their release. For seven of the ten species tested recapture rates were over 70%, with higher rates for the larger species. The predatory arthropod species composition captured using fenced pitfall traps was compared to unfenced pitfall traps in winter wheat, spring barley and winter oilseed rape. Compositional analysis revealed that the dominance structure of seven carabid beetle (Coleoptera: Carabidae) taxa differed between the trap types and month of sampling in winter wheat and spring barley, but differences were small with the exception of a few taxa. Linear relationships between the two techniques were found for some carabid and rove beetles (Coleoptera: Staphylinidae). The dominance structure of seven linyphiid spider (Araneae: Linyphiidae) taxa differed between the two trap types in wheat but not barley, although large differences were restricted to two taxa. No linear relationships between the two techniques were found for any of the Linyphiidae examined. Rove beetles were more effectively sampled using the fenced compared to unfenced pitfall traps.
The NH and ND stretching fundamentals of 14ND2H
Authors: Snels Marcel , Hollenstein Hans , Quack Martin
Published: October 2003

High resolution (0.004 cm−1 instrumental bandwidth) interferometric Fourier transform infrared spectra of N14D2H were obtained on a BOMEM DA002 spectrometer under essentially Doppler limited conditions. We report the analysis of the ND and NH stretching fundamentals of N14D2H with term values for the symmetric (s) and antisymmetric (a) sublevels with respect to the inversion plane of the planar geometry Tv (s)=2430.7990(7) cm−1 and Tv (a)=2434.6222(8) cm−1 for the ν3a fundamental, Tv (s)=2559.8069(8) cm−1 and Tv (a)=2559.9630(9) cm−1 for the ν3b fundamental and Tv (s)=3404.238(5) cm−1 and Tv (a)=3404.316(5) cm−1 for the ν1 fundamental. The two modes ν3 which are degenerate in ND3 and whose degeneracy is lifted in ND2H, are distinguished by the subscripts 3a or 3b, being symmetric (3a) or antisymmetric (3b) with respect to the Cs plane of symmetry of the equilibrium geometry of ND2H. Up to 20 molecular parameters of the effective S-reduced Hamiltonian could be determined accurately for each fundamental. In particular, the inversion-rotation interaction parameter could be determined for the two ND-stretching modes. Assignments were established with certainty by means of ground state combination differences. The results are important for the mode selective inhibition or catalysis of inversion at the nitrogen atom by exciting ND and NH stretching vibrations, for treatments of isotope effects on inversion of ammonia by means of effective Hamiltonians as well as true molecular Hamiltonians on high dimensional potential hypersurfaces.
Predicting mixing microstructure in three-dimensional chaotic systems
Authors: Szalai E. S. , Muzzio F. J.
Published: October 2003

This paper explores the application of asymptotic directionality to three-dimensional (3D) chaotic periodic flows by examining flow in a tank agitated by four impellers. Numerical simulations and experimental methods are employed to reveal the spatial structure of the evolving mixing patterns and its statistical properties. It is demonstrated that there exists an invariant field of orientations in the system that creates self-similar mixing structures. As a result, the frequency distributions of stretching can be collapsed onto an invariant curve by a simple homogeneous scaling. This statistical scaling behavior is a direct consequence of the asymptotic directionality property. It is also shown that striation thickness distributions (STDs) can be predicted directly from the stretching distributions in fully 3D chaotic systems, thus providing a method for calculation of STDs in complex flows.
Locally preferred structure in simple atomic liquids
Authors: Mossa S. , Tarjus G.
Published: October 2003

We propose a method to determine the locally preferred structure of model liquids. The latter is obtained numerically as the global minimum of the effective energy surface of clusters formed by small numbers of particles embedded in a liquidlike environment. The effective energy is the sum of the intracluster interaction potential and of an external field that describes the influence of the embedding bulk liquid at a mean-field level. Doing so we minimize the surface effects present in isolated clusters without introducing the full blown geometrical frustration present in bulk condensed phases. We find that the locally preferred structure of the Lennard-Jones liquid is an icosahedron, and that the liquidlike environment only slightly reduces the relative stability of the icosahedral cluster. The influence of the boundary conditions on the nature of the ground-state configuration of Lennard-Jones clusters is also discussed.
Generalized corresponding states model for bulk and interfacial properties in pure fluids and fluid mixtures
Authors: Kiselev S. B. , Ely J. F.
Published: October 2003

We have formulated a general approach for transforming an analytical equation of state (EOS) into the crossover form and developed a generalized cubic (GC) EOS for pure fluids, which incorporates nonanalytic scaling laws in the critical region and in the limit ρ→0 is transformed into the ideal gas equation EOS. Using the GC EOS as a reference equation, we have developed a generalized version of the corresponding states (GCS) model, which contains the critical point parameters and accentric factor as input as well as the Ginzburg number Gi. For nonionic fluids we propose a simple correlation between the Ginzburg number Gi and Zc, ω, and molecular weight Mw. In the second step, we develop on the basis of the GCS model and the density functional theory a GCS-density functional theory (DFT) crossover model for the vapor–liquid interface and surface tension. We use the GCS-DFT model for the prediction of the PVT, vapor–liquid equilibrium (VLE) and surface properties of more than 30 pure fluids. In a wide range of thermodynamic states, including the nearest vicinity of the critical point, the GCS reproduces the PVT and VLE surface and the surface tension of one-component fluids (polar and nonpolar) with high accuracy. In the critical region, the GCS-DFT predictions for the surface tension are in excellent agreement with experimental data and theoretical renormalization-group model developed earlier. Using the principle of the critical-point universality we extended the GCS-DFT model to fluid mixtures and developed a field-variable based GCS-FV model. We provide extensive comparisons of the GCS-FV model with experimental data and with the GCS-XV model formulated in terms of the conventional density variable—composition. Far from the critical point both models, GCS-FV and GCS-XV, give practically similar results, but in the critical region, the GCS-FV model yields a better representation of the VLE surface of binary mixtures than the GCS-XV model. We also show that by considering the Ginzburg number Gi as an independent CS parameter the GCS model is capable of reproducing the phase behavior of finite neutral nuclear matter.
A continuum theory of solvation in quadrupolar solvents. I. Formulation
Authors: Jeon Jonggu , Kim Hyung J.
Published: October 2003

A continuum theory to describe equilibrium and nonequilibrium solvation in polarizable, nondipolar, quadrupolar solvents is developed. By employing the densities of the solvent quadrupole and induced dipole moments as primary field variables, a reaction field theory formulation for quadrupolar solvents is constructed with account of their electronic polarizability. Nonequilibrium solvation aspects are effected via the solvent coordinate description for the quadrupole moment density. It is found that the theory is consistent with the macroscopic Maxwell equations and satisfies the continuity of the electric potential across the cavity boundaries. Solvation stabilization arising from the solvent quadrupoles is captured via novel reaction field factors analogous to those for dipolar solvents. Comparison is made with the dielectric continuum description of the polarizable, dipolar solvents as well as with previous theories of the quadrupolar solvents. Extensions and applications of the current theoretical formulation to study free energetics and dynamics of reactive and spectroscopic processes in the quadrupolar solvents are reported in the following paper [J. Jeon and H. J. Kim, J. Chem. Phys. 119, 8626 (2003)].
A continuum theory of solvation in quadrupolar solvents. II. Solvation free energetics, dynamics, and solvatochromism
Authors: Jeon Jonggu , Kim Hyung J.
Published: October 2003

The continuum theory of solvation developed in the preceding paper [J. Chem. Phys. 119, 8606 (2003)] is applied to study free energetics and dynamics relevant to charge shift processes in polarizable quadrupolar solvents in the Born–Oppenheimer regime of solvent electronic degrees of freedom. The outer-sphere solvent reorganization free energy and free energy of reaction for electron transfer systems are investigated in both one and two-sphere cavity descriptions. The quadrupolar susceptibility needed in the theory is determined using recent Stokes shift measurements by Reynolds et al. [J. Phys. Chem. 100, 10337 (1996)]. A good accord with measurements and molecular theory estimates of the solvent reorganization free energy for bridged donor–acceptor systems is obtained. The solvatochromic shifts associated with chromophores are examined with a first-order perturbation method. The application of the theory to electronic absorption of betaine in the quadrupolar solvents yields a good agreement with the ET(30) solvent polarity scale. By incorporating the collective motions associated with solvent quadrupoles, the theory is extended to study inertial solvation dynamics. In contrast with dipolar liquids, the solvent frequency in the quadrupolar solvents increases as the multipole character of the solute charge distribution increases. This is in accord with a recent molecular dynamics simulation result for supercritical CO2.
Simple molecular model for the binding of antibiotic molecules to bacterial ion channels
Authors: Mafé Salvador , Ramı́rez Patricio , Alcaraz Antonio
Published: October 2003

A molecular model aimed at explaining recent experimental data by Nestorovich et al. [Proc. Natl. Acad. Sci. USA 99, 9789 (2002)] on the interaction of ampicillin molecules with the constriction zone in a channel of the general bacterial porin, OmpF (outer membrane protein F), is presented. The model extends T. L. Hill’s theory for intermolecular interactions in a pair of binding sites [J. Am. Chem. Soc. 78, 3330 (1956)] by incorporating two binding ions and two pairs of interacting sites. The results provide new physical insights on the role of the complementary pattern of the charge distributions in the ampicillin molecule and the narrowest part of the channel pore. Charge matching of interacting sites facilitates drug binding. The dependence of the number of ampicillin binding events per second with the solution pH and salt concentration is explained qualitatively using a reduced number of fundamental concepts.
Enhancement of the recording stability of a photorefractive polymer composite by the introduction of a trapping layer
Authors: Kim Won-Sun , Lee Jong-Woo , Park Jung-Ki
Published: October 2003

A photorefractive polymer composite containing a trapping layer which exhibits a significant enhancement in its photorefractivity is reported. The photorefractive polymer composite containing a trapping layer showed a grating life time as high as 600 s, while the grating life time was only 7 s in the photorefractive polymer composite without a trapping layer. The grating growth rate was found to be unaffected by the introduction of a trapping layer. The diffraction efficiency and gain coefficient also increased by the introduction of a trapping layer. The enhancement in the photorefractive properties is due to the increase in the space-charge field developed in the photorefractive polymer composite containing a trapping layer.
Rotational spectroscopy of a weak complex of thiirane and ethyne: The identification and properties of a highly nonlinear S⋯H–C hydrogen bond
Authors: Batten R. C. , Cole G. C. , Legon A. C.
Published: October 2003

Rotational and centrifugal distortion constants were determined for eight isotopomers of a weakly bound complex of thiirane and ethyne. The observed complex is of Cs symmetry, with ethyne lying in the symmetry (ab principal inertial) plane and with H of HCCH forming a hydrogen bond to the S atom of thiirane. The r0 geometry is: r(S⋯H)=2.76(5) Å, φ=84.0(5)°, and θ=42.9(2)°, where φ is the angle made by the S⋯H internuclear line with the local C2 axis of the thiirane ring and θ is the angular deviation of the S⋯H–C nuclei from a linear arrangement. The nonlinearity of the hydrogen bond is attributed to a weak primary interaction S⋯H–C coupled with a secondary interaction involving the π bond of ethyne with the two equivalent H atoms of thiirane that are closest to it. The angular geometry of (CH2)2S⋯HCCH is compared with those of other species (CH2)2S⋯HX, where X=F, Cl, Br, and CN.
Structures, energies, and spectra of aqua-silver (I) complexes
Authors: Lee Eun Cheol , Lee Han Myoung , Tarakeshwar P. , Kim Kwang S.
Published: October 2003

Owing to the utility of redox phenomena of silver in many chemical systems, it is important to understand the coordination chemistry of Ag+ ion and hence the hydration structure. The lowest-energy conformations of Ag+(H2O)1–6 are sensitive to the calculation method employed. The coordination number (Nc) of Ag+(H2O)n is predicted to be 2 for n=2–6 at the density functional theory level, while the Nc for n=3–5 is 3, and that for n=6 is 4 at the second-order Møller–Plesset perturbation level. Further accurate analysis based on coupled-cluster singles and doubles theory with perturbative corrections for triple excitations agrees with the MP2 results except that Nc of 4 is also as competitive as Nc of 3 for n=5. To identify the correct Nc, it would be useful to facilitate the IR experimental characterization. We thus provide the OH spectra for various possible structures. It is interesting to note that the hydration chemistry of Ag+ ion is somewhat different from that of alkali metal ions.
Polarizability anisotropies of rare gas van der Waals dimers studied by laser-induced molecular alignment
Authors: Minemoto Shinichirou , Tanji Haruka , Sakai Hirofumi
Published: October 2003

The molecular alignment technique utilizing the interaction between the intense nonresonant laser field and the induced dipole moment is applied to the homonuclear rare gas dimers Rg2 (Rg=Ar, Kr, and Xe). The degree of alignment is investigated by Coulomb exploding Rg2 and by measuring the angular distributions of the fragment ions. At the same peak intensity of the laser field, the degree of alignment ≪cos2 θ ≫ becomes larger in order of Ar2, Kr2, and Xe2, reflecting the order of magnitudes of their polarizability anisotropy Δα. By taking I2 molecules as a reference, Δα of Ar2, Kr2, and Xe2 are estimated to be 0.5, 0.7, and 1.3 Å3, respectively.
Backfiring and nonannihilation collisions in the Belousov–Zhabotinsky medium
Authors: Wang Jichang , Mann Indervir
Published: October 2003

In this paper pattern formation and interactions in a spatially extended Belousov–Zhabotinsky reaction medium are investigated numerically. Backfiring, nonannihilation collisions and reflections at nonflux boundaries have been observed in the vicinity of three types of bifurcations including supercritical and subcritical Hopf-bifurcations and the Canard bifurcation. In the vicinity of a supercritical Hopf-bifurcation, backfiring and collision-stable behavior do not appear until the system exhibits small amplitude oscillations. In complement to earlier investigations, this study illustrates that the collision-stable behavior also exists under the dynamics where the system has only one stable attractor. The influence of relative molecular diffusivities on the backfiring and nonannihilation collisions has been characterized over a broad range of bifurcation conditions, which shows that increasing the relative diffusivity of the activator favors the appearance of the above complex behavior. The transition from a supercritical Hopf-bifurcation to a Canard bifurcation has also been investigated.
Dilute granular flow around an immersed cylinder
Authors: Wassgren C. R. , Cordova J. A. , Zenit R. , Karion A.
Published: October 2003

In this paper we investigate a two-dimensional dilute granular flow around an immersed cylinder using discrete element computer simulations. Simulation measurements of the drag force acting on the cylinder, Fd, are expressed in terms of a dimensionless drag coefficient, Cd=Fd/[12ρν∞U∞2(D+d)], where ρ is the upstream particle mass density, ν∞ is the upstream solid fraction, U∞ is the upstream velocity, and (D+d) is the sum of the cylinder diameter, D, and surrounding particle diameter, d. The drag coefficient increases rapidly with decreasing Mach number for subsonic Mach numbers, but remains insensitive to Mach number for supersonic values. The drag coefficient is also a strong function of the flow Knudsen number, with the drag coefficient increasing with increasing Knudsen number and approaching an asymptotic value for very large Knudsen numbers. The drag coefficient decreases with decreasing normal coefficient of restitution and is relatively insensitive to the friction coefficient. Bow shock structures and expansion fans are also observed in the simulations and are compared to similar structures observed in compressible gas flows.
Adsorption of oppositely charged polyelectrolytes onto a charged rod
Authors: Messina René
Published: October 2003

The adsorption of highly charged flexible polycations and polyanions on a charged cylindrical substrate is investigated by means of Monte Carlo simulations. A detailed structural study, including monomer and fluid charge distributions, is provided. The influence of a short-range attraction between the polycation and negatively charged substrate is also considered. We demonstrate that the building up of multilayer structures is highly prohibited mainly due to the high entropy penalty stemming from the low dimensionality of the substrate at strong curvature.
Many-spin quantum dynamics during cross polarization in 8CB
Authors: Chattah Ana K. , Álvarez Gonzalo A. , Levstein Patricia R. , Cucchietti Fernando M. , Pastawski Horacio M. , Raya Jésus , Hirschinger Jérôme
Published: October 2003

We analyze theoretically and experimentally the quantum dynamics of a three-spin-1/2 system during cross polarization (CP). Our analysis takes into account a Hamiltonian behavior for a carbon C13 coupled to two protons H1 while the coupling to a spin bath is treated in the fast fluctuation approximation. This model is applied to the methylene and biphenyl groups of the smectic and nematic phases of the liquid crystal 4-n-octyl-4′-cyanobiphenyl (8CB). Experimental data from standard CP, combined with our theoretical results, allow us to separate the homonuclear H1-H1 and heteronuclear H1-C13 residual dipolar couplings. These values are in good agreement with those obtained by using a combination of CP under Lee–Goldburg conditions and standard CP data. A well differentiated relaxation behavior among the two phases seems to indicate that while the extreme narrowing approximation is appropriate for the nematic phase, the description of the smectic phase requires consideration of the slow-motion limit.
Electron attachment to CO2 clusters
Authors: Sommerfeld Thomas , Posset Tobias
Published: October 2003

Vertical and adiabatic electron attachment to carbon dioxide clusters (CO2)N (N=2–5) is studied at high ab initio levels of theory. As a first step the geometries of neutral and anionic CO2 clusters are reexamined. The potential energy surfaces of both neutral and anionic CO2 clusters show many minima, and several isomers have been reported so far. Here we present new lowest-energy isomers for the tetramer and pentamer anion clusters, as well as high-level results for relative and CO2 evaporation energies. Electron correlation is crucial for the computed properties, and since we had to make certain compromises about the theoretical level in order to include larger clusters, a thorough investigation of different ab initio methods is performed for the dimer. The vertical affinities of the investigated (CO2)N clusters are found to be clearly negative; i.e., vertical attachment into valence orbitals leads to temporary anion states. The energies of these resonances as well as the associated autodetachment lifetimes are computed using complex absorbing potentials at the frozen-orbital and correlated second-order Green’s function levels. Whereas the cluster environment has a surprisingly weak influence on the negative vertical affinities, solvation has a strong effect on the adiabatic electron affinities. The computed trends suggest that the tetramer is at the brink of stability and that the pentamer cluster is the smallest species possessing an appreciable positive electron affinity. Our findings have profound implications for the interpretation of the low-energy electron attachment experiments and provide a basis for the discussion and modeling the attachment process.
Studies of electron transfer in NaI with pump–probe femtosecond photoelectron spectroscopy
Authors: Arasaki Yasuki , Takatsuka Kazuo , Wang Kwanghsi , McKoy Vincent
Published: October 2003

We discuss an extension of our formulation of energy- and angle-resolved photoelectron spectra for femtosecond pump–probe ionization of wave packets to nonadiabatically coupled states and present results of its applications to wave packet motion on the ionic (Na+I−) and covalent (NaI) states of sodium iodide. The results of these studies suggest that the energy and angular distributions of these photoelectron spectra provide a useful mapping of the bifurcation of the wave packets through the crossing region and a valuable window on the intramolecular electron transfer occurring between the covalent and ionic states (NaI→Na+I−).
H-substituted anionic carbon clusters CnH− (n⩽10): Density functional studies and experimental observations
Authors: Pan L. , Rao B. K. , Gupta A. K. , Das G. P. , Ayyub P.
Published: October 2003

We have studied the interaction of hydrogen with small neutral and anionic carbon clusters using density functional calculations. The geometry, stability, and electronic structure of these clusters show an odd–even alternation originating in the bonding nature of the carbon atoms. Our mass spectrometric measurements of the abundance of CnH− (n⩽10) cluster anions produced by gas-feed Cs sputtering from different crystallographic forms of carbon display similar odd–even alternation with the even-n clusters being relatively more abundant. The calculated trend in the adiabatic electron affinities shows a behavior similar to the experimental abundance pattern. We discuss a possible partial suppression of the chain-to-ring transformation (which normally occurs at n=10 in Cn−) in CnH− and compare it with our density functional calculations as well as observations in CnN−. We also observe that the size dependence of the abundance of CnH− clusters sputter ejected from a fullerene target exhibits a distinctly different power-law decline compared to crystalline and amorphous carbon.
The dynamics of gas-surface energy exchange in collisions of Ar atoms with ω-functionalized self-assembled monolayers
Authors: Day B. Scott , Shuler Shelby F. , Ducre Adonis , Morris John R.
Published: October 2003

Atomic-beam scattering experiments using n-alkanethiol and ω-functionalized alkanethiol self-assembled monolayers (SAMs) on gold are employed to explore the dynamics of gas-surface energy exchange in collisions with model organic surfaces. The studies are performed by directing a nearly monoenergetic beam of 80 kJ/mol Ar atoms onto a particular SAM at an incident angle of 30° with respect to the surface normal and recording the time-of-flight distributions for the atoms as they scatter from the surface at a final angle of 30°. Among the monolayers studied, long-chain CH3-terminated SAMs are found to be the most effective at dissipating the translational energy of impinging atoms. For alkanethiols with greater than seven total carbon atoms (HS(CH2)n>6CH3), we find that, for specular scattering conditions, over 80% of the incident energy is transferred to the surface and that over 60% of the impinging atoms approach thermal equilibrium with the surface before scattering back into the gas phase. In contrast to CH3-terminated monolayers, SAMs constructed from hydrogen-bonding alkanethiols: HS(CH2)11OH, HS(CH2)10COOH, and HS(CH2)11NH2, exhibit characteristics of more rigid collision partners. The Ar atoms transfer about 77% of their energy to these surfaces with only 43% of the atoms reaching thermal or near thermal equilibrium before recoiling. Further comparisons of mixed OH- and CH3-terminated SAMs and alkene-terminated SAMs suggest that intramonolayer hydrogen bonding of terminal functional groups may play an important role in determining the extent of energy transfer and thermalization.
Shear-induced mesostructure in nanoplatelet-polymer networks
Authors: Lin-Gibson S. , Schmidt G. , Kim H. , Han C. C. , Hobbie E. K.
Published: October 2003

The shear response of a model polymer–clay gel is measured using small-angle neutron and light scattering, optical microscopy, and rheometry. As the flow disrupts the transient network that forms between clay and polymer, coupling between composition and stress leads to the formation of a macroscopic domain pattern, while the clay platelets orient with their surface normal parallel to the direction of vorticity. We discuss similarities with shear-induced structural transitions observed in other complex fluids, and we offer a physical explanation for the orientation of the clay platelets.
The vibration–rotation emission spectrum of MgH2
Authors: Shayesteh A. , Appadoo D. R. T. , Gordon I. , Bernath P. F.
Published: October 2003

The gaseous MgH2 molecule has been discovered in an electrical discharge inside a high temperature furnace. The vibration–rotation emission spectrum of MgH242 was recorded with a Fourier transform spectrometer and the antisymmetric stretching mode (ν3) was detected near 1589 cm−1. In addition, three hot bands involving ν2 and ν3 were found and rotationally analyzed. The MgH2 molecule has a linear structure with an R0 Mg–H bond distance of 1.703 327(3) Å.
Dielectric relaxation of lower alcohols in the whole fluid phase
Authors: Hiejima Yusuke , Yao Makoto
Published: October 2003

Dielectric relaxation of ethanol and 1-propanol have been measured in a wide fluid phase including the supercritical condition for the first time. The results of the static permittivity ε(0) and the dielectric relaxation time τD are presented in the temperature and pressure range up to 670 K and 30 MPa. Kirkwood’s g-factor deduced from ε(0) suggests that the static orientational correlation of dipoles becomes prominent at densities above ∼2dc, dc being the critical density. We divide the fluid phase into four regions and discuss the dielectric relaxation mechanism by extending our model previously applied to water [K Okada et al., J. Chem. Phys. 110, 3026 (1999)]. In the vapor and low-density liquid, the dielectric relaxation is governed by binary collision of molecules. In the high-temperature liquid, the molecules that escape from the hydrogen bond (HB) network also contribute to the relaxation, and the HB breaking is promoted by thermal excitation of the intermolecular stretching modes. In the low-temperature liquid, the escape time is strongly enhanced relative to the HB lifetime. In the glass transition region, the HB breaking is induced in a more cooperative way than the intermolecular stretching vibrations. The present interpretation gives a reasonable explanation to three relaxation times that were obtained by precise measurements near room temperature, and also provide a microscopic basis for the glass transition scenario by Hansen et al. [J. Chem. Phys. 107, 1086 (1997)].
Modeling of DNA compaction by polycations
Authors: Dias R. S. , Pais A. A. C. C. , Miguel M. G. , Lindman B.
Published: October 2003

In this work we study polycations as efficient compacting agents of a medium size polyanion by means of Monte Carlo simulations. The systems are characterized in terms of a conformational analysis in which shape, overall dimensions, structure factors, radial distribution functions, and the degree of accumulation of the compaction agent near the polyanion are taken into consideration. Results show that the degree of compaction depends on the size of the positive chains and their number. The role of electrostatic interactions is paramount in the compaction process, and an increase in the number of molecules of the compacting agent or in the number of charges of each molecule leads to collapse, which may be followed by some unfolding in situations of overcharging. Compaction is associated with polycations promoting bridging between different sites in the polyanion. When the total charge of the polycations is significantly lower than that of the polyanion, interaction produces only a small degree of intrachain segregation in the latter, allowing for significant translational motion of the compacting agent along the longer chain. However, complete charge neutralization is not mandatory to achieve compact forms.
Crystallization control of sputtered Ta2O5 thin films by substrate bias
Authors: Huang A. P. , Xu S. L. , Zhu M. K. , Wang B. , Yan H. , Liu T.
Published: October 2003

This letter reports that, by applying a bias to Si substrates, crystalline tantalum pentoxide (Ta2O5) thin films were fabricated at low substrate temperatures. At 620 °C, it was found that the thin films as-prepared are amorphous without the bias and of high crystallinity with the bias over −100 V. Based on the present data, it is concluded that the crystallinity of the thin films is improved with increasing bias. Furthermore, when the bias was increased to −200 V, partially crystallized films could be attained at temperatures as low as 400 °C. The bias effect on the crystallization is attributed to the interaction of positive ions in the plasma with the growing surface.
Efficient real-space configuration-interaction method for the simulation of multielectron mixed quantum and classical nonadiabatic molecular dynamics in the condensed phase
Authors: Larsen Ross E. , Schwartz Benjamin J.
Published: October 2003

We introduce an efficient configuration interaction (CI) method for the calculation of mixed quantum and classical nonadiabatic molecular dynamics for multiple electrons. For any given realization of the classical degrees of freedom (e.g., a solvent), the method uses a novel real-space quadrature to efficiently compute the Coulomb and exchange interactions between electrons. We also introduce an approximation whereby the classical molecular dynamics is propagated for several time steps on electronic potential energy surfaces generated using only a particularly important subset of the CI basis states. By only updating the important-states subset periodically, we achieve significant reductions in the computational cost of solving the multielectron quantum problem. We test the real-space quadrature for the cases of two electrons confined in a cubic box with infinitely repulsive walls and two electrons dissolved in liquid water that occupy a single cavity, so-called hydrated dielectrons. We then demonstrate how to perform mixed quantum and classical nonadiabatic dynamics by combining these computational techniques with the mean-field with surface hopping algorithm of Prezhdo and Rossky [J. Chem. Phys. 107, 825 (1997)]. Finally, we illustrate the practicality of the approach to multielectron nonadiabatic dynamics by examining the nonadiabatic relaxation dynamics of both spin singlet and spin triplet hydrated dielectrons following excitation from the ground to the first excited state.
The structure of CaCl2 aqueous solutions over a wide range of concentration. Interpretation of diffraction experiments via molecular simulation
Authors: Chialvo Ariel A. , Simonson J. Michael
Published: October 2003

A detailed analysis of the water structure around the ionic species in aqueous CaCl2 solutions is performed by molecular dynamics over a wide range of concentration (0<m⩽9.26) at ambient conditions. The goals behind the study are to address a long-standing controversy regarding the actual coordination number of aqueous Ca+2, to characterize the hydration structure of Ca+2, and consequently to interpret the origin of the disparity in the reported experimental data, to describe the additional information available from simulation to augment the first-order difference method in the determination of the species coordination numbers from neutron diffraction with isotopic substitution (NDIS) experiments, and to attain additional insights into the distribution of the “tilting” and “wagging” ion–water angles and their relation with the conventional configurational definitions.
Chain entanglements and fracture energy in interfaces between immiscible polymers
Authors: Silvestri Leonardo , Brown Hugh R. , Carrà Stefano , Carrà Sergio
Published: October 2003

It is a very well-known experimental fact that the toughness of interfaces obtained by joining pairs of immiscible glassy polymers is strongly correlated to the interfacial width. Several models have been proposed in the literature to estimate the fracture energy of these interfaces, but the agreement displayed with the experimental data cannot be considered satisfactory. In this paper a new model is proposed for polymers with molecular weight higher than the critical value for the onset of entanglements. The model is based on a precise and realistic calculation of the areal density of entangled strands across the interface, that is the crucial parameter determining the toughness of the glassy joints. In this paper a new fracture regime is also introduced, called “partial crazing,” corresponding to a situation where, due to the fact that some of the load-bearing strands are broken during plastic deformation, the craze can start, but not fully develop. Model predictions are then compared with a series of literature fracture energy experimental data, showing excellent agreement.
Theory for the force-stretched double-stranded chain molecule
Authors: Liu Fei , Dai Luru , Ou-Yang Zhong-can
Published: October 2003

We modify and extend the recently developed statistical mechanical theory of chain molecules having noncovalent double-stranded conformations, as in RNA or single-stranded DNA, and β sheets in protein, to the force-stretched case as in a typical single-molecule experiment. The conformations of double-stranded regions of the molecules are calculated based on polymer graph-theoretic approach [S.-J. Chen and K. A. Dill, J. Chem. Phys. 109, 4602 (1998)], while the unpaired single-stranded regions are treated as self-avoiding walks. Two classes of conformations—the hairpin conformations and RNA secondary structures—are explored. For the hairpin conformations, all possible end-to-end distances corresponding to the different types of double-stranded regions are enumerated exactly. For the RNA secondary structures, a recursive formula incorporating the secondary structure and end-to-end distribution has been derived. The sequence dependence and excluded volume interaction are taken into account explicitly. Using the extended theory, we investigate the extension-force and force-extension curves, distribution of the extensions at fixed forces, and reentering phenomenon, respectively. We find that the mechanical behaviors of homogeneous chains of hairpin conformations and secondary structures are quite different: the unfolding of the hairpin case is two state, while the unfolding of the latter is one state. In addition, a reentering transition is observed in hairpin conformations.
Scaling function of the critical binary mixture methanol–cyclohexane
Authors: Behrends Ralph , Kaatze Udo , Schach Maximilian
Published: October 2003

Acoustical attenuation spectra of the methanol–cyclohexane mixture of critical composition have been measured at different temperatures near the critical temperature. The noncritical background contribution of the spectra has been determined and subtracted from the total attenuation to yield the critical contribution. The latter enabled an accurate experimental determination of the scaling function. Regression analysis of the experimental scaling function data in terms of theoretical models yielded the relaxation rate of order parameter fluctuations as a function of temperature. Close agreement with relaxation rate data from other experimental methods has been found. The amplitude of the acoustical attenuation at the critical temperature has been discussed in terms of the adiabatic coupling constant. Its amount is likewise as small (|g|=0.14) as that of the alcohol–alkane system ethanol–dodecane (|g|=0.1).
Time-dependent currents through small molecules using wide-band and narrow-band approximations
Authors: Burrows B. L. , Amos A. T.
Published: October 2003

The theory of time-dependent currents through small molecules, with attached leads, is examined. The wide-band and narrow-band approximations are used to describe the leads and the time-dependent Schrödinger is applied directly. A variety of possible boundary conditions are considered and, within the approximations of the model, exact solutions are obtained and their form discussed. Examples using two-atom chain molecules are analyzed in detail and series solutions are obtained for longer chains.