bluuebunny/crossref_metadata_2025 huggingface dataset:
On the development of low‐level auditory discrimination and deficits in dyslexia
Authors: Fischer Burkhart , Hartnegg Klaus
Published: April 2004

Absolute auditory thresholds, frequency resolution and temporal resolution develop with age. It is still discussed whether low‐level auditory performance is of clinical significance—specifically, for delayed maturation of central auditory processing. Recently, five new auditory tasks were used to study the development of low‐level auditory discrimination. It was found that the development lasts up to the age of 16–18 years (on an average). Very similar tasks were now used with 432 controls and 250 dyslexic subjects in the age range of 7–22 years. For both groups the performance in one of the tasks was not related to the performance in another task indicating that the five tasks challenge independent subfunctions of auditory processing. Surprisingly high numbers of subjects were classified as low performers (LP), because they could not perform one or the other task at its easiest level and no threshold value could be assigned. For the dyslexics the incidence of LP was considerably increased in all tasks and age groups as compared with the age matched controls. The development of dynamic visual and optomotor functions and the corresponding deficits in dyslexia are discussed in relation to the auditory data presented here. Copyright © 2004 John Wiley & Sons, Ltd.
3D two phase flows numerical simulations by SL‐VOF method
Authors: Biausser Benjamin , Guignard Stephan , Marcer Richard , Fraunié Philippe
Published: April 2004

This paper describes the development of a semi‐Lagrangian computational method for simulating complex 3D two phase flows. The Navier–Stokes equations are solved separately in both fluids using a robust pseudo‐compressibility method able to deal with high density ratio. The interface tracking is achieved by the segment Lagrangian volume of fluid (SL‐VOF) method. The 2D SL‐VOF method using the concepts of VOF, piecewise linear interface calculation (PLIC) and Lagrangian advection of the interface is herein extended to 3D flows. Three different test cases of SL‐VOF 3D are presented for validation and comparison either with 2D flows or with other numerical methods. A good agreement is observed in each case. Copyright © 2004 John Wiley & Sons, Ltd.
Linear and non‐linear stability analysis for finite difference discretizations of high‐order Boussinesq equations
Authors: Fuhrman David R. , Bingham Harry B. , Madsen Per A. , Thomsen Per G.
Published: April 2004

This paper considers a method of lines stability analysis for finite difference discretizations of a recently published Boussinesq method for the study of highly non‐linear and extremely dispersive water waves. The analysis demonstrates the near‐equivalence of classical linear Fourier (von Neumann) techniques with matrix‐based methods for formulations in both one and two horizontal dimensions. The matrix‐based method is also extended to show the local de‐stabilizing effects of the non‐linear terms, as well as the stabilizing effects of numerical dissipation. A comparison of the relative stability of rotational and irrotational formulations in two horizontal dimensions provides evidence that the irrotational formulation has significantly better stability properties when the deep‐water non‐linearity is high, particularly on refined grids. Computation of matrix pseudospectra shows that the system is only moderately non‐normal, suggesting that the eigenvalues are likely suitable for analysis purposes. Numerical experiments demonstrate excellent agreement with the linear analysis, and good qualitative agreement with the local non‐linear analysis. The various methods of analysis combine to provide significant insight into the numerical behaviour of this rather complicated system of non‐linear PDEs. Copyright © 2004 John Wiley & Sons, Ltd.
The use of sensory evaluation and consumer preference for the selection of sweetpotato cultivars in East Africa
Authors: Tomlins Keith , Rwiza Elizabeth , Nyango Abdallah , Amour Rahila , Ngendello Theresia , Kapinga Regina , Rees Deborah , Jolliffe Flavia
Published: April 2004

Sweetpotato is an important staple crop in East Africa with great potential for introducing improved cultivars, but little is known about which sensory characteristics are desirable. Over a 2 year period, 600 consumers were interviewed at three locations (urban and rural) in the Lake Zone of Tanzania and their preference of 14 locally available sweetpotato cultivars in cooked form was evaluated. A simple questionnaire based on consumers first‐choice preference was used followed by socio‐economic questions. A trained sensory panel profiled the cooked sweetpotato samples, enabling comparisons with preference, location and season. Cluster analysis based on the sensory attributes was used to classify the cultivars into three groups; one cluster comprised the most preferred cultivars and another contained the least. Some cultivars were consistently preferred over the 2 year period while others were not. The location where the cultivars were grown also influenced preference. Stepwise regression indicated that the most discriminating sensory attributes were starch and stickiness. Target levels based on the mean intensity scores of these attributes are suggested as a means of screening new cultivars. The implications of these findings are discussed. Copyright © 2004 Society of Chemical Industry
Oleoylation of sugarcane bagasse hemicelluloses using N‐bromosuccinimide as a catalyst
Authors: Sun Xaio‐Feng , Sun Run‐Cang , Sun Jing‐Xia
Published: April 2004

Conditions for the preparation of esters of sugarcane bagasse hemicelluloses with oleoyl chloride using N‐bromosuccinimide (NBS) as a catalyst in the N,N‐dimethylformamide/lithium chloride system under mild conditions were studied comparatively. The oleoylation was followed in terms of yield and degree of substitution (DS). The parameters optimised included oleoyl chloride concentration as the molar ratio of oleoyl chloride/anhydroxylose units in native hemicelluloses (1:1–8:1), NBS concentration (0.5–3.0%), reaction time (20–100 min) and reaction temperature (30–100 °C). Results were also compared with those for other catalysts such as H2SO4 and four tertiary amine catalysts, pyridine, 4‐dimethylaminopyridine, N‐methyl pyrrolidine and N‐methyl pyrrolidinone. An oleoyl chloride/hemicellulose molar ratio of 3:1 was found to be necessary for the reaction to proceed smoothly and to yield a product with a low DS. The new materials were characterised by FT‐IR and 1H and 13C NMR spectroscopies as well as thermal analysis. The thermal stability of the oleoylated hemicelluloses decreased slightly upon chemical modification, but no significant further decrease in thermal stability was observed for DS ≥ 0.29. Copyright © 2004 Society of Chemical Industry
Cover Picture: Macromol. Chem. Phys. 6/2004
Authors: Monteil Vincent , Spitz Roger , Barbotin Fanny , Boisson Christophe
Published: April 2004

Cover: The picture on the cover shows the microstructure of original poly(ethylene‐co‐butadiene) containing 1,2‐cyclohexane rings and the mechanism of cyclization.

Further details can be found in the Full Paper by V. Monteil, R. Spitz, F. Barbotin, and C. Boisson* on page 737.
e‐democracy and knowledge. A multicriteria framework for the new democratic era
Authors: Moreno‐Jiménez José María , Polasek Wolfgang
Published: April 2004

This paper presents a new procedure, e‐cognocracy, to deal with the democratic system in the emerging knowledge society. This is not a procedure to assist technically in the establishment of the representation corresponding to the parties, as in the traditional interpretation by using Internet (e‐voting). It is rather a procedure to add a new quality to the democratic system by means of the network. This new quality, related with the process that characterized the evolutionism of systems alive, consists in the creation and diffusion of the societal knowledge of the problem under investigation through the network and, specially, of the process to deal with the scientific resolution of problems. This proposed e‐cognocracy will allow us to highlight the inclusion of those interested in the resolution of highly complex problems (participatory decision‐making), and also in the democratic governance of societal systems. For this purpose, we suggest the multicriteria framework as the way to deal with the modelling and resolution of such complex problems. Similarly, in the context of one of the most widely used multicriteria techniques, namely the analytic hierarchy process (AHP), we propose some decisional tools (analytic and informatic tools) orientated towards searching for the relevant knowledge associated with the decision‐making process and the procedures employed within it. This knowledge, corresponding to the patterns of behaviour, trends, opportunities, decisions and stylized facts will be the starting point of the consensus building process suggested as the appropriate way to effectively solve problems of high complexity usually presented in the governance of society. Copyright © 2004 John Wiley & Sons, Ltd.
Modelling individual and global comparisons for multi‐attribute preferences
Authors: Mateos Alfonso , Jiménez Antonio , Ríos‐Insua Sixto
Published: April 2004

This paper describes a decision support system based on an additive multi‐attribute utility model for identifying the optimal strategy in complex decision‐making problems. The system allows for incomplete information on the component utility function and weight assessment, which leads to classes of utility functions and weight intervals, respectively. This makes the system suitable for group decision support, because individual conflicting views or judgements in a group of decision‐makers can be captured through imprecise responses in the respective assessment methods. Moreover, the system admits uncertainty about the multi‐attribute strategy consequences, which can be defined in term of ranges for each attribute instead of single values. The system computes non‐dominance and potential optimality to identify the most preferred strategy. We also propose an approach based on Monte Carlo simulation techniques for group decision‐making problems, which could be specially useful for e‐democracy, where several decision‐makers or groups of decision‐makers elicit their own preferences separately, which are then compared to try to reach a consensus on their respective preferences. Copyright © 2004 John Wiley & Sons, Ltd.
Gradient plasticity modelling of strain localization in granular materials
Authors: Al Hattamleh O. , Muhunthan B. , Zbib H. M.
Published: April 2004

The flow stress in the yield surface of plastic constitutive equation is modified with a higher order gradient term of the effective plastic strain to model the effect of inhomogeneous deformation in granular materials. The gradient constitutive model has been incorporated into the finite element code ABAQUS and used to simulate biaxial shear tests on dry sand. It is shown that the shape of the post‐peak segment of the load displacement curve predicted by the numerical analysis is dependent on the mesh size when gradient term is not used. Use of an appropriate gradient coefficient is shown to correct this and predict a unique shape of the load displacement curve regardless of the mesh size. The gradient coefficient required turns out to be approximately inversely proportional to the mesh elemental area. Use of the strain gradient term is found to diffuse the concentration of plastic strains within shear band resulting in its consistent width. The coefficient of the higher gradient term appears as a function of the grain size, the mean confining stress, and the plastic softening modulus. Copyright © 2004 John Wiley & Sons, Ltd.
Screening study for potential lead compounds for natural product‐based fungicides: I. Synthesis and in vitro evaluation of coumarins against Botrytis cinerea
Authors: Daoubi Mourad , Durán‐Patrón Rosa , Hmamouchi Mohamed , Hernández‐Galán Rosario , Benharref Ahmed , Collado Isidro G
Published: April 2004

An efficient, one‐pot synthesis of angular and linear dihydropyranocoumarins, along with C‐6 and C‐8 prenylated coumarins is reported. These compounds, together with single‐ and furanocoumarins, were tested for their potential antifungal activity against the phytopathogen Botrytis cinerea Pers ex Fr. The results show that furanocoumarins may be able to control the fungus B cinerea. Copyright © 2004 Society of Chemical Industry
Extracts from St John's wort and their antimicrobial activity
Authors: Avato P. , Raffo F. , Guglielmi G. , Vitali C. , Rosato A.
Published: April 2004

In an effort to carry out a more in‐depth investigation on the antimicrobial properties of H. perforatum, we have assayed different extracts (MeOH; petroleum ether; CHCl3 and EtOAc) from the aerial parts of the plant against selected microorganisms. Growth inhibition was observed only for Gram‐positive bacteria, B. subtilis and B. cereus being the most susceptible to the tested drugs. The Hypericum extract obtained with EtOAc was the most active. The main constituents of this extract, as determined by HPLC analysis, were ﬂavonoids, hypericins and hyperforins. Incubation of the selected microorganisms with the pure chemicals resulted in a signiﬁcant inhibition of their growth by hypericin, hyperforin and its stable dicyclohexilammonium salt. Flavonoids appeared inactive at all. Copyright © 2004 John Wiley & Sons, Ltd.
“On Table” Positioning for Optimal Access for Cancer Excision in the Lower Rectum
Authors: Maeda Koutarou , Maruta Morito , Sato Harunobu , Masumori Koji , Aoyama Hiroyuki
Published: April 2004

Poor visualization and restricted access often make tumor lesions in the lower rectum difficult to excise, particularly in a narrow male pelvis. The aim of this study was therefore to study whether (and if so to what extent) different positions of the patient on the operating table might improve accessibility. Twenty consecutive patients (men and women) undergoing laparotomy with surgery of the lower rectum were studied. The geometric configuration of the pelvis was studied and compared on lateral radiographs obtained at the operating table in each of four positions. Compared with the conventional lithotomy position, the thighs‐flat” position caused significant extension movement of the lumbosacral joint. Augmentation of the lumbar lordosis widened the pelvic view and enabled a more vertical view of the lower rectum (27.5 degrees in lithotomy position, 13.0 degrees in the thighs‐flat position). Insertion of a “lumbar pad“ contributed further to the augmentation (7 degrees). When compared on radiographic studies, the thighs‐flat position is preferable to the conventional lithotomy position in terms of facilitating low rectal surgery by improving both visibility and accessibility to the pelvic cavity.
Inguinal Hernia in the New Millennium
Authors: Cervantes Jorge
Published: April 2004

Since 1884, when Edoardo Bassini started the modern era of surgical correction of inguinal hernia (today the most common procedure performed by the general surgeon), many techniques have been introduced, some short‐lived, others with proven long‐term results. At the start of the new millennium, the surgeon has three clear alternatives: tension repairs, tension‐free repairs, and laparoscopic procedures. This paper analyzes these three options and offers an update regarding the pros and cons of the most commonly performed operations in surgical centers around the world.
Late Pleistocene mammoth remains from Coastal Maine, USA
Authors: Hoyle B. Gary , Fisher Daniel C. , Borns Harold W. , Churchill-Dickson Lisa L. , Dorion Christopher C. , Weddle Thomas K.
Published: April 2004

Remains identified as those of a woolly mammoth (Mammuthus primigenius) dated at 12,200 ± 55 14C yr B.P. were recovered while excavating in a complex sequence of glaciomarine sediments in Scarborough, Maine, USA. The mammoth was found in the top meter of a fossiliferous unit of mud and sand laminites. These sediments were deposited during a marine regressive phase following the transgression that accompanied northward retreat of the margin of the Laurentide ice sheet. A Portlandia arctica valve from the underlying transgressive unit provides a minimum age of 14,820 ± 105 14C yr B.P. for local deglaciation. The mammoth, an adult female, died in midwinter with no evidence of human involvement. Tusk growth rates and oxygen-isotope variation over the last few years of life record low seasonality. The mammoth was transported to the site as a partial carcass by the late-glacial proto-Saco River. It sank in a near-shore setting, was subjected to additional disarticulation and scattering of elements, and was finally buried in sediments reworked by the shallowing sea.
The effect of vascular disease on late onset Parkinson's disease
Authors: Papapetropoulos S. , Ellul J. , Argyriou A. A. , Talelli P. , Chroni E. , Papapetropoulos T.
Published: April 2004

The clinical severity of late onset Parkinson's disease (PD) varies from patient to patient and it is further complicated by the increasing prevalence of accompanying disorders in the elderly. We set out to study the impact of ischemic heart disease, minor stroke, hypertension and diabetes mellitus in a group of late onset PD patients (age ≥70 years). Consecutive late onset PD patients seen in the Department of Neurology, Medical School of Patras, Greece were included in this study. We used very strict criteria to eliminate the possibility of including patients with vascular parkinsonism. Comparisons were made between groups of patients suffering with idiopathic Parkinson's disease (IPD) and the above‐mentioned diseases. One hundred and sixty‐seven consecutive late onset PD patients were included in this study. The most common accompanying disorders in our group were hypertension in 31 (18%) of the patients and minor stroke in 20 (12%). The Hoen and Yahr score in late onset IPD patients who suffered from minor stroke, ischemic heart disease or diabetes mellitus was significantly higher when compared with patients without the above disorders. The results clearly suggest that the presence of vascular disease on an IPD patient may aggravate PD severity. In clinical grounds, these findings can be proved significant since early and aggressive prevention of vascular disease and treatment of vascular risk may contribute in controlling symptom severity in PD.
Preserved cognitive function after 12 months of treatment with rivastigmine in mild Alzheimer's disease in comparison with untreated AD and MCI patients
Authors: Almkvist O. , Darreh‐Shori T. , Stefanova E. , Spiegel R. , Nordberg A.
Published: April 2004

Cholinesterase inhibitors (ChEIs) have shown positive symptomatic effects on cognition, activities of daily living, and behavior in patients with Alzheimer's disease (AD). Rivastigmine is a slowly reversible ChEI that inhibits acetylcholinesterase and butyrylcholinesterase. We evaluated the effects of long‐term rivastigmine treatment on cognitive function and plasma levels of ChE activity, and the relationship between ChE activity and cognition. Patients with mild AD (n = 11) treated with rivastigmine for 12 months were compared with matched groups of untreated patients with AD (n = 21) or mild cognitive impairment (MCI; n = 22) representing the natural course of the pre‐clinical and very early stage of disease. For untreated AD patients, neuropsychological assessment was made at baseline and 12 months. Determination of ChE activity in plasma and assessment of global cognition, episodic memory, visuospatial ability, and attention were performed at 0 (baseline), 3, 6, and 12 months for treated AD patients and untreated MCI patients. At 12 months, cognitive function was slightly improved or maintained in mild AD patients treated with rivastigmine. In contrast, cognition was markedly worsened in untreated AD patients and unchanged or slightly worsened in untreated MCI patients. In the group of treated AD patients, there was a significant correlation between plasma ChE inhibition and cognition, particularly in relation to attention. This effect was most apparent at 3 months of treatment. In conclusion, a clear beneficial effect of rivastigmine was shown on cognitive function for patients with mild AD and plasma values of ChE inhibition were associated with attention.
Spectrally resolved femtosecond two-color three-pulse photon echoes: Study of ground and excited state dynamics in molecules
Authors: Dao Lap Van , Lincoln Craig , Lowe Martin , Hannaford Peter
Published: April 2004

We report the use of spectrally resolved femtosecond two-color three-pulse photon echoes as a potentially powerful multidimensional technique for studying vibrational and electronic dynamics in complex molecules. The wavelengths of the pump and probe laser pulses are found to have a dramatic effect on the spectrum of the photon echo signal and can be chosen to select different sets of energy levels in the vibrational manifold, allowing a study of the dynamics and vibrational splitting in either the ground or the excited state. The technique is applied to studies of the dynamics of vibrational electronic states in the dye molecule Rhodamine 101 in methanol.
Quantum trajectories in atom–surface scattering with single adsorbates: The role of quantum vortices
Authors: Sanz A. S. , Borondo F. , Miret-Artés S.
Published: April 2004

In this work, a full quantum study of the scattering of He atoms off single CO molecules, adsorbed onto the Pt(111) surface, is presented within the formalism of quantum trajectories provided by Bohmian mechanics. By means of this theory, it is shown that the underlying dynamics is strongly dominated by the existence of a transient vortitial trapping with measurable effects on the whole diffraction pattern. This kind of trapping emphasizes the key role played by quantum vortices in this scattering. Moreover, an analysis of the surface rainbow effect caused by the local corrugation that the CO molecule induces on the surface, and its manifestation in the corresponding intensity pattern, is also presented and discussed.
Mechanism of linear and nonlinear optical effects of chalcopyrite AgGaX2 (X=S, Se, and Te) crystals
Authors: Bai Lei , Lin Zheshuai , Wang Zhizhong , Chen Chuangtian , Lee Ming-Hsien
Published: April 2004

The electronic band structures for AgGaX2 (X=S, Se, Te) chalcopyrites have been calculated using a pseudopotential total energy method. First-principles calculations of the linear and nonlinear optical properties are presented for these crystals, with the electronic band structures obtained from pseudopotential method as input. The theoretical refractive indices and nonlinear optical coefficients are in good agreement with available experimental values. The origin of the nonlinear optical effects is explained through real-space atom-cutting analysis. The contribution of the GaX2 group (X=S, Se, Te) for second harmonic generation (SHG) effect is dominant while that of the cation Ag is negligible. In addition, the percentage contribution to the SHG coefficients from the different bonds increase with increase of the bond order.
A long-range-corrected time-dependent density functional theory
Authors: Tawada Yoshihiro , Tsuneda Takao , Yanagisawa Susumu , Yanai Takeshi , Hirao Kimihiko
Published: April 2004

We apply the long-range correction (LC) scheme for exchange functionals of density functional theory to time-dependent density functional theory (TDDFT) and examine its efficiency in dealing with the serious problems of TDDFT, i.e., the underestimations of Rydberg excitation energies, oscillator strengths, and charge-transfer excitation energies. By calculating vertical excitation energies of typical molecules, it was found that LC-TDDFT gives accurate excitation energies, within an error of 0.5 eV, and reasonable oscillator strengths, while TDDFT employing a pure functional provides 1.5 eV lower excitation energies and two orders of magnitude lower oscillator strengths for the Rydberg excitations. It was also found that LC-TDDFT clearly reproduces the correct asymptotic behavior of the charge-transfer excitation energy of ethylene–tetrafluoroethylene dimer for the long intramolecular distance, unlike a conventional far-nucleus asymptotic correction scheme. It is, therefore, presumed that poor TDDFT results for pure functionals may be due to their lack of a long-range orbital–orbital interaction.
Quantum scattering calculation of the O(1D)+HBr reaction
Authors: Tang Bi-Yu , Tang Qian-Kun , Chen Mao-Du , Han Ke-Li , Zhang John Z. H.
Published: April 2004

Three-dimensional time-dependent quantum wave packet calculation for the O(1D)+HBr reaction has been carried out using an accurate ab initio global potential energy surface [K. A. Peterson, J. Chem. Phys. 113, 4598 (2000)]. The calculations show that the initial state-selected reaction probabilities are dominated by resonance structures, and the lifetime of the resonance is generally in the subpicosecond time scale. The energy dependence of the reaction cross section is computed, which manifests still resonance structures, and is a decreasing function of the translational energy. The thermal rate constants are also computed, which are nearly independent on the temperature. The calculation results are discussed and compared to similar reaction with deep well.
Electron solvation by polar molecules: The interaction of Na atoms with solid methanol films studied with MIES and density functional theory calculations
Authors: Borodin A. , Höfft O. , Kahnert U. , Kempter V. , Ferro Y. , Allouche A.
Published: April 2004

The interaction of Na atoms with CH3OH films was studied with metastable impact electron spectroscopy (MIES) under UHV conditions. The films were grown at 90(+/−10) K on tungsten substrates and exposed to Na. Na-induced formation of methoxy (CH3O) species takes place, and Na atoms become ionized. At small Na exposures the outermost solvent layer remains largely intact as concluded from the absence of MIES signals caused by the reaction products. However, emission from CH3O, located at the film surface, occurs at larger exposures. In the same exposure range also Na species can be detected at the surface. The spectral feature from 3s Na ionization occurs at an energetic position different from that found for metals or semiconductors. The results are compared with density functional theory calculations [see Y. Ferro, A. Allouche, and V. Kempter, J. Chem. Phys. 120, 8683 (2004), preceding paper]. Experiment and theory agree in the energetic positions of the main spectral features from the methanol and sodium ionization. The calculations suggest that the 3s Na emission observed experimentally originates from solvated 3s electrons which are located far from the Na core and become stabilized by solvent molecules. The simultaneous emergence of emission from CH3O and from solvated 3s electrons suggests that the delocalization and, consequently, the solvation play an important role in the Na-induced formation of CH3O from CH3OH.
Electron solvation by highly polar molecules: Density functional theory study of atomic sodium interaction with water, ammonia, and methanol
Authors: Ferro Y. , Allouche A. , Kempter V.
Published: April 2004

This study further extends the scope of a previous paper [Y. Ferro and A. Allouche, J. Chem. Phys. 118, 10461 (2003)] on the reactivity of atomic Na with water to some other highly polar molecules known for their solvation properties connected to efficient hydrogen bonding. The solvation mechanisms of ammonia and methanol are compared to the hydration mechanism. It is shown that in the case of ammonia, the stability of the solvated system is only ensured by electrostatic interactions, whereas the methanol action is more similar to that of water. More specific attention is given to the solvation process of the valence 3s Na electron. The consequences on the chemical reactivity are analyzed: Whereas ammonia is nonreactive when interacting with atomic sodium, two chemical reactions are proposed for methanol. The first process is dehydrogenation and yields methoxy species and hydrogen. The other one is dehydration and the final products are methoxy species, but also methyl radical and water. The respective roles of electron solvation and hydrogen bonds network are analyzed in detail in view of the density of states of the reactive systems.
A first-principles density-functional calculation of the electronic and vibrational structure of the key melanin monomers
Authors: Powell B. J. , Baruah T. , Bernstein N. , Brake K. , McKenzie Ross H. , Meredith P. , Pederson M. R.
Published: April 2004

We report first-principles density-functional calculations for hydroquinone (HQ), indolequinone (IQ), and semiquinone (SQ). These molecules are believed to be the basic building blocks of the eumelanins, a class of biomacromolecules with important biological functions (including photoprotection) and with the potential for certain bioengineering applications. We have used the difference of self-consistent fields method to study the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, ΔHL. We show that ΔHL is similar in IQ and SQ, but approximately twice as large in HQ. This may have important implications for our understanding of the observed broadband optical absorption of the eumelanins. The possibility of using this difference in ΔHL to molecularly engineer the electronic properties of eumelanins is discussed. We calculate the infrared and Raman spectra of the three redox forms from first principles. Each of the molecules have significantly different infrared and Raman signatures, and so these spectra could be used in situ to nondestructively identify the monomeric content of macromolecules. It is hoped that this may be a helpful analytical tool in determining the structure of eumelanin macromolecules and hence in helping to determine the structure-property-function relationships that control the behavior of the eumelanins.
Vacuum ultraviolet pulsed field ionization study of ND3: Accurate thermochemistry for the ND2–ND2+ and ND3–ND3+ system
Authors: Qian X.-M. , Lau K.-C. , He G. Z. , Ng C. Y. , Hochlaf M.
Published: April 2004

The dissociation of energy-selected ND3+ to form ND2++D near its threshold has been investigated using the pulsed field ionization-photoelectron (PFI-PE)-photoion coincidence method. The breakdown curves for ND3+ and ND2+ give a value of 15.891±0.001 eV for the 0 K dissociation threshold or appearance energy (AE) for ND2+ from ND3. We have also measured the PFI-PE vibrational bands for ND3+(X̃;v2+=0, 1, 2, and 3), revealing partially resolved rotational structures. The simulation of these bands yields precise ionization energies (IEs) for ND3+ X̃(0,v2+=0–3,0,0)←ND3 X̃(0,0,0,0). Using the 0 K AE (ND2+) and IE(ND3)=10.200±0.001 eV determined in the present study, together with the known 0 K bond dissociation energy for ND3 [D0(D–ND2)=4.7126±0.0025 eV], we have determined the D0(ND2+–D), IE(ND2), and 0 K heat of formation for ND2+ to be 5.691±0.001 eV, 11.1784±0.0025 eV, and 1261.82±0.4 kJ/mol, respectively. The PFI-PE spectrum is found to exhibit a steplike feature near the AE(ND2+), indicating that the dissociation of excited ND3+ at energies slightly above the dissociation threshold is prompt, occurring in the time scale ⩽10−7 s, as observed for the NH3 system. The available energetic data for the NH2–NH2+ and NH3–NH3+ system are found to be in excellent accord with those for the ND2–ND2+ and ND3–ND3+ system after taking into account the zero-point vibrational energy corrections. This finding indicates that the thermochemical data for these two systems are reliable with well-founded error limits.
Angle-energy distributions of Penning ions in crossed molecular beams. IV. He*(2 1S,2 3S)+H2→He+H2++e−
Authors: Gulati Keerti , Longley Elizabeth J. , Dorko Michael J. , Bittinger Kyle L. , Siska P. E.
Published: April 2004

Relative doubly differential cross sections for the Penning ionization of H2 by spin-state-selected metastable He (1s2s) are reported at center-of-mass collision energies E of 3.1 and 4.2 kcal/mol in a crossed supersonic beam experiment employing a rotatable mass spectrometer detector. The measurements are sufficiently dense in velocity space as to avoid having to functionalize the differential cross sections in order to transform the intensities into the c.m. The H2+ product is scattered sharply forward, c.m. Δθ<10° half-width at half-maximum, with respect to the incident direction of H2 at both energies for both spin states. On the average the products have lost energy upon recoil, mean recoil energy 〈E′〉<E, and E′−θ coupling is significant and increasing with E. Extensive comparison is made with infinite-order-sudden quantum scattering calculations based on previous experimental He*+H2 optical potential surfaces and a recent ab initio He+H2+ exit channel surface. Aside from predicted even sharper forward scattering, agreement is fair to good for both spin states. The calculations allow an assessment of the possibility of observing quantum effects in the differential reactive scattering in these systems.
Effect of the erbium dopant architecture on the femtosecond relaxation dynamics of silicon nanocrystals
Authors: Samia A. C. S. , Lou Y. , Burda C. , Senter R. A. , Coffer J. L.
Published: April 2004

Femtosecond pump–probe absorption spectroscopy is used to investigate the role of Er3+ dopants in the early relaxation pathways of photoexcited Si nanocrystals. The fate of photoexcited electrons in three different Si nanostructures was studied and correlated with the effect of Er-doping and the nature of the dopant architecture. In Si nanocrystals without Er3+ dopant, a trapping component was identified to be a major electron relaxation mechanism. Addition of Er3+ ions into the core or surface shell of the nanocrystals was found to open up additional nonradiative relaxation pathways, which is attributed to Er-induced trap states in the Si host. Analysis of the photodynamics of the Si nanocrystal samples reveals an electron trapping mechanism involving trap-to-trap hopping in the doped nanocrystals, whereby the density of deep traps seem to increase with the presence of erbium. To gain additional insights on the relative depths of the trapping sites on the investigated nanostructures, benzoquinone was used as a surface adsorbed electron acceptor to facilitate photoinduced electron transfer across the nanocrystal surface and subsequently assist in back electron transfer. The established reduction potential (−0.45 V versus SCE) of the electron acceptor helped reveal that the erbium-doped nanocrystal samples have deeper trapping sites than the undoped Si. Furthermore, the measurements indicate that internally Er-doped Si have relatively deeper trapping sites than the erbium surface-enriched nanocrystals. The electron-shuttling experiment also reveals that the back electron transfer seems not to recover completely to the ground state in the doped Si nanocrystals, which is explained by a mechanism whereby the electrons are captured by deep trapping sites induced by erbium addition in the Si lattice.
Aging in short-ranged attractive colloids: A numerical study
Authors: Foffi G. , Zaccarelli E. , Buldyrev S. , Sciortino F. , Tartaglia P.
Published: April 2004

We study the aging dynamics in a model for dense simple liquids, in which particles interact through a hard-core repulsion complemented by a short-ranged attractive potential, of the kind found in colloidal suspensions. In this system, at large packing fractions, kinetically arrested disordered states can be created both on cooling (attractive glass) and on heating (repulsive glass). The possibility of having two distinct glasses, at the same packing fraction, with two different dynamics offers the unique possibility of comparing—within the same model—the differences in aging dynamics. We find that, while the aging dynamics of the repulsive glass is similar to the one observed in atomic and molecular systems, the aging dynamics of the attractive glass shows novel unexpected features.
Double tunneling in dipole bound anions: A model study
Authors: Dufey Florian
Published: April 2004

The applicability of the Born–Oppenheimer approximation for the description of the coupled nuclear and electronic tunneling dynamics in anionic dimers of hydrogen fluoride and water is studied. These complex molecules are modeled by a simpler system, with only one nuclear coordinate, which can be solved easily with arbitrary accuracy. Although the Born–Oppenheimer approximation is not applicable in a strict sense in the tunneling region where the electron becomes unbound, quite accurate values for the binding energy can be obtained when working with a discrete electronic basis. Employing a basis which is diabatic with respect to the angular coordinates, but adiabatic with respect to the radial coordinate, the convergence of a nonadiabatic perturbation expansion is also studied. Inclusion of the lowest-order nonadiabatic corrections reduces the error in the binding energy already by a factor of 10–20, while for the correct prediction of the tunneling splitting, it proves necessary to take into account higher-order corrections. With increasing number of diffuse functions included in the electronic basis, the nonadiabatic effects increase and the perturbation series converges more slowly.
Excitation energies for a benchmark set of molecules obtained within time-dependent current-density functional theory using the Vignale–Kohn functional
Authors: van Faassen M. , de Boeij P. L.
Published: April 2004

In this article we explain how the existing linear response theory of time-dependent density-functional theory can be extended to obtain excitation energies in the framework of time-dependent current-density-functional theory. We use the Vignale–Kohn current-functional [G. Vignale and W. Kohn, Phys. Rev. Lett. 77, 2037 (1996)] which has proven to be successful for describing ultranonlocal exchange-correlation effects in the case of the axial polarizability of molecular chains [M. van Faassen, P. L. de Boeij, R. van Leeuwen, J. A. Berger, and J. G. Snijders, Phys. Rev. Lett. 88, 186401 (2002); J. Chem. Phys. 118, 1044 (2003)]. We study a variety of singlet excitations for a benchmark set of molecules. The π*←π transitions obtained with the Vignale–Kohn functional are in good agreement with experiment and other theoretical results and they are in general an improvement upon the adiabatic local density approximation. In case of the π*←n transitions the Vignale–Kohn functional fails, giving results that strongly overestimate the experimental and other theoretical results. The benchmark set also contains some other types of excitations for which no clear failures or improvements are observed.
Is the HCCS radical linear in the excited state?
Authors: He Sheng-Gui , Clouthier Dennis J.
Published: April 2004

The Ã 2Π–X̃ 2Π 415 nm band system of the linear HCCS radical has been known since 1978, but the vibronic structure in this complex spectrum, which has both spin–orbit and Renner-Teller complications, has never been satisfactorily assigned, despite serious experimental and theoretical efforts. In a further attempt to understand the spectrum, we have studied the laser-induced fluorescence spectra of jet-cooled HCCS and DCCS, produced from thiophene precursors using the discharge jet technique. The 000 bands of HCCS and DCCS have been rotationally analyzed, providing precise ground and excited state spin–orbit splittings. The energy levels of the v′=0 2Π3/2 component of DCCS are found to be perturbed by a very low-lying Σ2 vibronic level, indicating that the HCC bending mode Renner-Teller effect is much larger than predicted by ab initio calculations with a linear excited state geometry. With this observation, the vibronic bands in the spectra of both isotopomers have been consistently assigned for the first time. Model calculations show that the large Renner-Teller effect and substantially different HCCS and DCCS excited state zero-point spin–orbit splittings can be explained with the assumption of a quasilinear excited state geometry.
Intracluster stereochemistry in van der Waals complexes: Steric effects in ultraviolet photodissociation of state-selected Ar–HOD/H2O
Authors: Votava Ondrej , Mackenzie Stuart R. , Nesbitt David J.
Published: April 2004

High-resolution IR-UV multiple resonance methods are employed to elucidate the photodissociation dynamics of quantum state-selected Ar–HOD and Ar–H2O van der Waals clusters. A single mode pulsed OPO operating in the region of the OH second overtone is used to prepare individual rovibrational states that are selectively photodissociated at specific excimer wavelengths. Subsequent fluorescence excitation of the resulting OH (OD) fragments yields dynamical information on the photofragmentation event and any resulting intracluster collisions. This technique is used to characterize spectroscopically the Π(101), vOH=3←Σ(000), vOH=0 overtone band of the Ar–HOD complex with an origin at 10648.27 cm−1. The effects of Ar complexation on the dissociation dynamics are inferred by comparison of the OD photofragment quantum state distributions resulting from dissociation of single rovibrational states of the complex with those from isolated HOD photodissociation. The important role played by the initial internal state of the complex is demonstrated by comparison of the current Ar–HOD data with previously published results for the Ar–H2O Σ(000)|03−〉 state. We interpret the dramatic differences in the dynamics of the two systems as manifestations of the nodal structure of the vibrational state in the parent complex and the way in which it governs the collision probability between the Ar atom and the escaping photofragments.
H and D release in ∼243.1 nm photolysis of vibrationally excited 3ν1, 4ν1, and 4νCD overtones of propyne-d3
Authors: Ganot Yuval , Rosenwaks Salman , Bar Ilana
Published: April 2004

The photofragmentation of propyne-d3, D3C–C≡C–H, following ∼243.1 nm photodissociation of rovibrationally excited molecules promoted to the second (3ν1) and third (4ν1) acetylenic C-H overtone and to the third (4νCD) methyl overtone has been investigated. The resulting H and D photoproducts were detected via (2+1) resonantly enhanced multiphoton ionization. The measured room-temperature photoacoustic and jet-cooled action spectra allowed derivation of the molecular parameters of the C-H overtones and the Doppler profiles revealed the translational energies associated with the H(D) photofragments and the H to D branching ratios. Propensities toward the latter were encountered, while the translational energy disposal in both photofragments was essentially identical for a given preexcitation. This behavior agrees with that found for the almost isoenergetic 193.3 nm photolysis of propyne [Qadiri et al., J. Chem. Phys. 119, 12842 (2003)], but contradicts previous findings. The bond fission of C-H and C-D is preceded by internal conversion to, and isomerization on, the ground-state potential energy surface (PES), followed by extensive intramolecular vibrational redistribution. For molecules preexcited to 3ν1 and 4ν1 an additional minor channel opens, where elimination of H occurs directly on the accessed excited PES, while that of D on the ground state.
Pure intermolecular vibrational relaxation of the OH bending mode of water molecules
Authors: Seifert Gerhard , Patzlaff Toralf , Graener Heinrich
Published: April 2004

The vibrational energy relaxation of the OH bending vibration of H2O dissolved in liquid chloroform and d-chloroform is studied by picosecond IR pump–probe spectroscopy. This pure intermolecular energy transfer process is found to happen with a decay time constant of 8.5 ps in CHCl3 and 28 ps in CDCl3, respectively—i.e., depends strongly on the resonance structure of the solvent molecules.
Ion rotational distributions following vibrational autoionization of the Rydberg states of water
Authors: Glab W. L. , Pratt S. T.
Published: April 2004

Double-resonance laser excitation and high-resolution energy dispersive photoelectron spectroscopy were used to determine the ionic rotational-state distributions following vibrational autoionization of Rydberg states of water having principal quantum number n=8–10 and converging to the X̃ 2B1 (1,0,0) state of H2O+. Where possible, these states were identified by comparison with results of a calculation based on multichannel quantum defect theory. Symmetry and angular momentum constraints link the observed ionic rotational states to particular values of the orbital angular momentum of the Rydberg electron, ℓ, and to the partial-wave composition of the ejected electron. In particular, this connection allows an unambiguous determination of the even or odd character of the partial waves and provides a test of the predicted character of the autoionizing resonances. The effects of ℓ mixing induced by the nonspherical nature of the ionic field are plainly evident in the ion distributions. The present results also allow a tentative assignment of some resonances to the previously unidentified np Rydberg states.
First-principles study of the electronic structures of icosahedral TiN (N=13,19,43,55) clusters
Authors: Wang Shan-Ying , Yu Jing-Zhi , Mizuseki Hiroshi , Yan Jia-An , Kawazoe Yoshiyuki , Wang Chong-Yu
Published: April 2004

We have studied the electronic structures of icosahedral TiN clusters (N=13, 19, 43, and 55) by using a real-space first-principles cluster method with generalized gradient approximation for exchange-correlation potential. The hexagonal close-packed and fcc close-packed clusters have been studied additionally for comparisons. It is found that the icosahedral structures are the most stable ones except for Ti43, where fcc close-packed structure is favorable in energy. We present and discuss the variation of bond length, the features of the highest occupied molecular orbitals and the lowest unoccupied molecular orbital, the evolution of density of states, and the magnetic moment in detail. The results are in good agreement with the predictions from the collision-induced dissociation and size-selected anion photoelectron spectroscopy experiments.
Calculation of near-edge x-ray-absorption fine structure at finite temperatures: Spectral signatures of hydrogen bond breaking in liquid water
Authors: Hetényi Balázs , De Angelis Filippo , Giannozzi Paolo , Car Roberto
Published: April 2004

We calculate the near-edge x-ray-absorption fine structure of H2O in the gas, hexagonal ice, and liquid phases using heuristic density-functional based methods. We present a detailed comparison of our results with experiment. The differences between the ice and water spectra can be rationalized in terms of the breaking of hydrogen bonds around the absorbing molecule. In particular the increase in the pre-edge absorption feature from ice to water is shown to be due to the breaking of a donor hydrogen bond. We also find that in water approximately 19% of hydrogen bonds are broken.