bluuebunny/crossref_metadata_2025 huggingface dataset:
Sawgrass Seedling Responses to Transplanting and Nutrient Additions
Authors: Miao S. L. , Borer R. E. , Sklar F. H.
Published: July 2003

Understanding Cladium jamaicense (sawgrass) seedling establishment is an important component of an Everglades restoration program because the degree of sawgrass recovery and concurrent Typha domingensis (cattail) decline will be used to evaluate restoration success. To understand sawgrass recovery at locations with increased soil nutrients, we tested the effects of transplanting sawgrass seedlings to pots at different densities and investigated how nutrient additions affect seedling growth. Survivorship of seedlings transplanted into moist commercial potting soil at three densities ranged from 61% to 95%. After 6 months, maximum survivorship (90%) occurred at medium densities (2–4 seedlings per pot 16 cm in diameter). Nutrient additions, totaling 6.5 N g/m2, 9.8 P g/m2, 6.5 g/m2, were applied approximately 4 months after seedlings were transplanted. The biomass of the plants receiving nutrient additions (pulsed) was significantly higher (by over 30%) than plants with no nutrient addition (control). Photosynthetic rates for nutrient‐enriched plants (measured 6‐weeks after the nutrient additions) were significantly greater (by 32–45%) than for control plants. Instantaneous leaf water use efficiency increased significantly (by more than 20%) in pulsed plants. The results suggest that preventing root damage is crucial for the success of trans planted sawgrass seedlings and that nutrient additions enhanced seedling growth.
Soil Ripping and Herbicides Enhance Tree and Shrub Restoration on Stripmines
Authors: Ashby W. Clark
Published: July 2003

I evaluated responses by 16 native woody species to differential soil compaction and density of ground cover. The trees and shrubs studied represent sites in southern Illinois that commonly have restrictions to root growth from soil or drainage conditions. The study site was a restored surface coal mine in southern Illinois with a rooting medium compacted by grading and a dense ground cover of pasture species. Soil compaction was alleviated in half the study area before tree planting by mechanically ripping the soil to a depth of 1.2 m. Roots of half the trees and shrubs were dipped in a Terra® slurry before planting, and the ground cover around all planting spots was afterwards sprayed with herbicide. In year 2 after planting the ground cover in half of the unripped and half of the ripped area was further controlled by repeated application of herbicides. Ripping significantly increased height growth of all trees combined and all species individually in each year of the study. Second‐year control of ground cover increased height growth of all trees combined and of seven species individually. Some species were damaged by herbicides. Terra® had little evident effect on species performance. Animal damage reduced early survival and growth, especially of Acer (maple) and Cornus (dogwood) species, and later growth of Quercus rubra (red oak). Removal of ground cover with herbicides tended to increase deer browse. Soil ripping, herbicide application, and choosing tree species unattractive to deer can be recommended to increase success in planting trees for forest restoration.
Restoration of Woody Plants to Capped Landfills: Root Dynamics in an Engineered Soil
Authors: Handel Steven N. , Robinson George R. , Parsons William F. J. , Mattei Jennifer H.
Published: July 2003

Closed or abandoned landfills represent significant land areas, often in or near urban centers, that are potential sites for ecological restoration of native woodlands. But current guidelines in many jurisdictions do not allow for the installation of trees or shrubs above landfill clay caps, although these plants have many environmental, functional, and aesthetic advantages, including a rapid start to community succession. Typical closure procedures for capped landfills include only a grass cover to control moisture infiltration and impede soil erosion. The main concern that limits the application of a woody cover to a closed landfill is that roots may penetrate and weaken the clay cap. As part of a comprehensive experimental program on woodland restoration, we installed 22 tree and shrub species on Staten Island, New York (the Fresh Kills Sanitary Landfill). We found no evidence that roots of the transplanted woody plants penetrate caps used on these landfills. Root growth requirements and dynamics stop penetration of these materials. Anoxic and acidic conditions were found in the sandy subsoil above the cap, as indicated by corrosion patterns on steel test rods. Also, the intensity of mycorrhizal infection on the experimental plants was high in the surface soil and decreased progressively with increasing soil depth. The potential vertical rooting depth during this time period was greater than that occurring over the clay cap. This was shown from data collected on a nearby control site, where seven of the species were installed on an engineered soil lacking a clay barrier layer, and roots of all seven species penetrated deeper than on the landfill. The engineered landfill soils are poor growth media for roots, and below ground constraints that limit restoration on these sites must be addressed.
Smoke Enhanced Seed Germination for Mine Rehabilitation in the Southwest of Western Australia
Authors: Roche Shauna , Koch John M. , Dixon Kingsley W.
Published: July 2003

Cool smoke treatments were applied to unmined Eucalyptus marginata (jarrah) forest soils, rehabilitated bauxite mine soils, and broadcast seed to determine if enhancement in germination could be effected with a view toward maximizng the establishment of species in bauxite mines in Western Australia.

Forest sites showed a 48‐fold increase in total germinants from the soil seed bank when treated with aerosol smoke. Newly returned bauxite mine soils showed a greater than threefold increase in total germinants after the same treatment. There were also significant increases in the number of species germinating in response to the aerosol smoke treatment in both the forest and the mined soils. Similarly, application of smoked water to the soil seed bank in previously mined sites elicited a significant positive germination response, increasing total germinants and species numbers by 56 and 33%, respectively.

Treatment of mixed seed lots with aerosol smoke before broadcast resulted in highly significant improvement in germination when compared to untreated seed. Both total number of germinants, and number of species emerging from mined sites were positively influenced (85% and 34% increases, respectively).

Ten target species were used to determine the relative effectiveness of different methods of smoke treatment on the germination of broadcast seed. Nine of the species involved displayed a promotive effect with at least two of the treatments. Generally, however, aerosol smoking of seed before broadcast proved to be the more effective approach. As a result of these findings, all broadcast seed for use in Alcoa's bauxite mined areas in the southwest of Western Australia is now routinely smoke treated before application.
Response of Endangered Desert Fish Populations to a Constructed Refuge
Authors: Winemiller Kirk O. , Anderson Allison A.
Published: July 2003

The U.S. Bureau of Reclamation created a shallow, 110‐m channel to provide habitat for two endangered fishes, Cyprinodon elegans (Comanche Springs pupfish) and Gambusia nobilis (Pecos gambusia), at the site of the fishes' former natural habitat. The ciénega (marsh) associated with Phantom Lake Spring in Jeff Davis County, Texas, was destroyed by the creation of an irrigation canal system. In 1993, the endangered fishes were stocked into the refuge with individuals from the irrigation canals, and in the case of C. elegans, hatchery stocks. The condition of habitat, status of fish populations, and fish ecology within the refuge were then monitored for two years. The abundance and density of both species increased in accordance with aquatic plant development. Cyprinodon elegans abundance peaked after one year and stabilized at an average density of 14.7/m2 by the end of our study. Juvenile C. elegans were always rare, which may indicate that the population reached the refuge's carrying capacity and that recruitment is low. Gambusia nobilis was the most abundant fish in the refuge (average density 96/m2), used the entire refuge, and outcom‐peted nonindigenous G. geiseri. The two Gambusia species used similar habitats but showed almost no dietary overlap. High densities of aquatic plants reduced the amount of open water areas necessary for C. elegans. The refuge will sustain the two endangered fishes at this historic site of endemism while maintaining flow to the irrigation system; however, the refuge is not equivalent to a restored ciénega.
Restoring Native Perennial Grasses to Rural Roadsides in the Sacramento Valley of California: Establishment and Evaluation
Authors: Buss Robert L. , Brown Cynthia S. , Anderson John H.
Published: July 2003

Along rural roadsides of the Sacramento Valley of California, we seeded native and non‐native perennial grasses to gauge their potential value in roadside vegetation management programs. In trial I (polycultures), three seeded complexes and a control (resident vegetation only) were tested. Each seeded plant complex included a different mix of perennial grasses seeded into each of several roadside topographic zones. The seeded levels of plant complex were: native perennial grasses 1 (8 species); native perennial grasses 2 (13 species); and non‐native perennial grasses (3 species). In trial II, plots were seeded to monocultural plots of 15 accessions of native Californian and three cultivars of non‐native perennial grasses. Plots in both trials were seeded during January 1992 and evaluated for three successive years.
Response of Understory Species to Gap Formation and Soil Disturbance m Lonicera maackii Thickets
Authors: Luken J. O. , Kuddes L. M. , Tholemeier T. C.
Published: July 2003

We studied the utility of gap formation and soil disturbance as methods to enhance establishment of plant species in the understory of a northern Kentucky forest where Lonicera maackii (Amur honeysuckle) produced dense thickets. In May 1994, gaps (5 m diameter) were cut in the shrub thicket. In adjacent areas, the shrub canopy remained intact. Subplots were established where soil was either turned with a spade to a depth of 15 cm or not disturbed. We monitored plant establishment for three growing seasons (1994, 1995, and 1996). Shrub removal increased light availability to about 10% of full sun. Gap formation had a significant (p < 0.05) and positive influence on total plant density (exclusive of L. maackii), and soil disturbance did not (p > 0.05). After three growing seasons, the most important species were L. maackii, Alliaria petiolata, Parthenocissus quinquefolia, Vitis vulpina, and Acer negundo. Of these species, only V. vulpina showed significantly (p < 0.05) higher densities in gaps. Other less important species such as Phytolacca americana, Campsis radicans, and Eupatorium rugosum occurred almost exclusively in gaps. Of the 44 taxa observed in this study, most were generalist species that also occur in early successional habitats. Long‐term dominance of the understory by L. maackii has likely modified system attributes with corresponding effects on community development. Shrub removal provides a window of establishment for various plant species, but successful restoration may require further management species availability and to control new invaders.
Genetic Variation and the Reproduction of Cordylanthus maritimus ssp. maritimus to Sweetwater Marsh, California
Authors: Helenurm Kaius , Parsons Lorraine S.
Published: July 2003

This study evaluated the genetic consequences of a reintroduction of the endangered annual plant Cordylanthus maritimus ssp. maritimus to Sweetwater Marsh (San Diego County, California). A survey of 21 enzyme loci in natural populations revealed that genetic diversity is very low and is primarily found as rare alleles at a few loci, making this species especially susceptible to the loss of alleles and heterozygosity through genetic drift. The reintroduction was performed in 1991 and 1992 by sowing seeds (collected from Tijuana Estuary) in numerous small patches of suitable habitat. For this study, leaf tissue was collected from all plants in all patches during flowering in 1995 and surveyed for genotype at the three enzyme loci that are polymorphic at Tijuana Estuary. Rare alleles were absent in 27 out of 30 patches for Pgm‐1, in 17 out of 30 patches for Pgm‐2, and in 10 out of 11 patches for Mdh‐1. In all, half of the patches lacked any rare allele. Rare alleles tended to occur in patches with few individuals. Overall rare allele frequency was lower than in the colonies from which seeds were collected at two of the three loci, and heterozygosity was reduced. The Sweetwater Marsh population is at risk of losing most of its genetic variation at enzyme loci through the extinction of patches with few individuals. Future reintroduction attempts should attempt to create contiguous sets of patches or to periodically reseed existing patches to reduce the loss of genetic variation.
Exotic Grass Competition in Suppressing Native Shrubland Re‐establishment
Authors: Eliason Scott A. , Allen Edith B.
Published: July 2003

Disturbance of coastal sage scrub in southern California has led to extensive displacement of native shrubs by exotic annual grasses. The initial conversion from shrubland to exotic grassland is typically associated with disturbance caused by intense grazing, high fire frequency, or mechanical vegetation removal. While native shrubs have been shown to recolonize annual grasslands under some conditions, other annual grasslands are persistent and show no evidence of shrub recolonization. This study examined the mechanisms by which annual grasses may exclude native shrubs and persist after release from disturbance. Grass density was manipulated in experimental plots to achieve a series of prescribed densities.Artemisia californica, a dominant native shrub, was seeded or planted into the plots and responses to the grass density treatments were measured over two growing seasons.A. californicagermination, first season growth, and survival were all negatively related to the density of neighboring annual grasses. The most probable mechanism underlying the reduction of first season growth and survival was depletion of soil water by the grasses. The effects of the grasses onA. californicawere no longer significant in the second season. The results of this study indicate that Mediterranean annual grasses reduce recruitment and can persist by inhibiting post‐disturbance establishment ofA. californicafrom seed. Although succession alone may not return disturbed annual grasslands to their former shrubland composition, the results suggest that restoration can be achieved by using container plantings or grass removal followed by seeding.
Role of Soils in Determining Sites for Lowland Heathland Reconstruction in England
Authors: Clarke Christopher T.
Published: July 2003

No guidelines are currently available that advise which soil properties of arable land can be used to suggest suitable locations for heathland reconstruction. This paper reviews studies comparing soil properties of heathland or semi‐natural grassland with those of adjacent arable fields, investigations in the autecology of the dominant heathland plant, Calluna vulgaris (common heather), and long‐term experiments of fertilizer inputs on arable soils. Three properties must be assessed before the suitability of a field can be determined: extractable phosphorus, exchangeable calcium, and pH. A number of other nutrients may also be important, but evidence is currently insufficient to substantiate this. Natural changes in levels of extractable phosphorus, exchangeable calcium, and pH appear to be very slow, so nutrient stripping and acidification will be necessary where recommended levels are exceeded to successfully restore heathland vegetation.
Effectiveness of Road Ripping in Restoring Infiltration Capacity of Forest Roads
Authors: Luce Charles H.
Published: July 2003

Many forest roads are being closed as a step in watershed restoration. Ripping roads with subsoilers or rock rippers is a common practice to increase the infiltration capacity of roads before closure. When considering the effectiveness of ripping for reducing runoff and erosion and the potential reduction in slope stability by saturating road fills, it is important to know how ripping changes the infiltration capacity of forest roads. Hydrographs from simulated rainfall on 1 × 1 m plots were analyzed to find the saturated hydraulic conductivity, an indicator of infiltration capacity. I examined saturated hydraulic conductivity for three treatments on two different soils. One road was built in a soil derived from the metamorphic belt series geology of northern Idaho, a soil noted for its high rock fragment content. The second road was built in a sandy soil derived from decomposed granitics of the Idaho batholith. On each soil, five plots were installed on a road before ripping, and nine plots were installed on the same road segment following ripping, four covered with a heavy straw mulch and five without. Three half‐hour rainfall events with intensities near 90 mm/hr were simulated on each plot. Results show that ripping increases hydraulic conductivities enough to reduce risk of runoff but does not restore the natural hydraulic conductivity of a forested slope. The unripped road surfaces had hydraulic conductivities in the range of 0–4 mm/hr, whereas ripped roads were in the range of 20–40 mm/hr after the second event. Surface sealing and tilled soil subsidence processes are important in reducing the hydraulic conductivity of the soils with repeated wetting. Subsidence appears to be important on the granitic soil, whereas surface sealing was more important on the belt series soil.
The Complex Epilepsy Patient: Intricacies of Assessment and Treatment
Authors: Kanner Andres M.
Published: July 2003

Summary:  The aim of treatment of all patients with epilepsy is the same: a complete remission of seizures with minimal or no adverse events. However, the means to reach that common goal may differ among patients, not only because of differences in their epileptic syndrome or type of seizures within the same syndrome, but also because of a variety of comorbid pathologic entities that are commonly identified in patients with epilepsy. In this article, we discuss some of the complexities inherent in the planning of therapeutic regimens for epilepsy patients. Comorbid conditions, whether intrinsic or extrinsic to the epileptic disorder, must play a paramount role in the choice of the therapeutic regimen for seizure control. We review the impact of psychiatric comorbidities on the quality of life of patients with epilepsy, with special attention to the tight relationship between depression and epilepsy. Yet, despite this close relationship, comorbid depression is more often than not underrecognized and undertreated. Next, we review the impact of antiepileptic drugs (AEDs) on comorbid medical disorders and give clear examples of the potentially deleterious impact of several AEDs on the therapeutic effects of concomitant medications used for their treatment. Clearly, treating epilepsy is not only about controlling seizures.
Beyond Pharmacotherapy: Surgical Management
Authors: Ryvlin Philippe
Published: July 2003

Summary:  Purpose: To review the recent advances in the field of temporal lobe epilepsy (TLE) surgery.

Results: TLE surgery has recently demonstrated a highly significant superiority over optimal medical therapy in a randomized trial. Accordingly, a median rate of 70% of class I outcome (patients free of disabling seizures postoperatively) has emerged from the pooling of all data published since the early 1990s. In addition, successful TLE surgery appears likely to reduce the risk of seizure‐related death. However, it remains largely underused and overly delayed, partly because of the legitimate fears of possible surgical complications, such as verbal memory deficits or failure to control seizures. Reasons for surgical failures are not completely understood, and include bitemporal, pseudotemporal, and temporal‐plus epilepsies, as well as insufficient resection of the mesial temporal structures. Developing techniques such as intraoperative MRI, gamma‐knife radiosurgery, and various types of cranial nerves or intracerebral chronic stimulation have the potential to alleviate part of the limitations of TLE surgery.

Conclusions: The overall benefit of surgical treatment in patients with drug‐resistant TLE should encourage a more frequent and earlier referral of such patients to epilepsy surgery centers. Important progress toward higher rates of seizure‐free outcome and lower morbidity remains to be made and may be obtained by taking advantage of the new available technologies.
Noninvasive Assessment of Significant Right Coronary Artery Stenosis Based on Coronary Flow Velocity Reserve in the Right Coronary Artery by Transthoracic Doppler Echocardiography
Authors: Ueno Yoshiki , Nakamura Yasuyuki , Kinoshita Masahiko , Fujita Tamotsu , Sakamoto Taizou , Okamura Hiroshi
Published: July 2003

Background: Coronary flow velocity reserve (CFVR) measured by transthoracic Doppler echocardiography (TTDE) has been reported to be useful for the noninvasive assessment of coronary stenosis in the left anterior descending artery. However, the measurement of CFVR in the right coronary artery by TTDE has not yet been validated in a clinical study. Objective: The aim of this study was to evaluate whether CFVR by TTDE can detect significant stenosis in the right coronary artery. Methods: We studied 50 patients who underwent coronary angiography. Coronary flow velocity in the posterior descending branch of the right coronary artery (PD) was measured by TTDE both at baseline and during hyperemia induced by the intravenous infusion of adenosine triphosphate. CFVR was calculated as the hyperemia/baseline (average diastolic peak velocity). Results: Adequate spectral Doppler recordings in the PD were obtained in 36 patients including 26 patients who were given an echocardiographic contrast agent to improve Doppler spectral signals. The study population was divided into 2 groups with (Group A;

n = 11

) and without (Group B;

n = 25

) significant stenosis in the right coronary artery. CFVR in Group A was significantly smaller than that in Group B (

1.6±0.3
versus

2.5±0.4
;

P < 0.0001

). The sensitivity of a CFVR of <2.0 for predicting the presence of significant stenosis in the right coronary artery was 91%, and the specificity was 88%. Conclusions: The measurement of CFVR in the PD by TTDE is useful for the noninvasive assessment of significant stenosis in the right coronary artery. (ECHOCARDIOGRAPHY, Volume 20, August 2003)
Extensive Neoplastic Cardiac Infiltration in a Patient With Acute Myelogenous Leukemia: Role of Echocardiography
Authors: Makaryus Amgad N. , Tung Frank , Liu Wei , Mangion Judy , Kort Smadar
Published: July 2003

We present the case of a 34‐year‐old man with a history of relapsed acute myelogenous leukemia with extensive metastatic infiltration of the endomyocardium. Transesophageal echocardiography revealed masses within all the cardiac chambers and associated vascular structures. Biopsy of the superior vena cava mass had the histological features of a granulocytic sarcoma (GS, chloroma). Massive involvement of the heart with GS is very rare, and only a few reports have been published in the literature. (ECHOCARDIOGRAPHY, Volume 20, August 2003)
Karzinogenese: Gestörte Kontrollsysteme und Optionen für die molekulare Therapie
Authors: Pfützner Wolfgang
Published: July 2003

Die Entwicklung eines malignen Tumors beruht auf DNS‐Mutationen, die zu multiplen Störungen unterschiedlicher Kontrollsysteme führen, welche für die koordinierte Regulation von Zellwachstum, Zelltod und Zellausbreitung zuständig sind. Dabei kann der Verlust einzelner dieser Kontrollsysteme durch die anderen Systeme noch kompensiert werden, erst das Zusammenbrechen des gesamten Kontrollnetzwerkes auf molekularer Ebene führt zum malignen Tumorwachstum. Das Wissen über diese Regelkreise und ihre Defekte im Rahmen der Karzinogenese ermöglicht die Entwicklung neuer Therapiestrategien. Die Gentherapie als molekulare Therapie offeriert hierbei vielversprechende Behandlungsansätze.
Resonance energy transfer: The unified theory revisited
Authors: Daniels Gareth J. , Jenkins Robert D. , Bradshaw David S. , Andrews David L.
Published: July 2003

Resonance energy transfer (RET) is the principal mechanism for the intermolecular or intramolecular redistribution of electronic energy following molecular excitation. In terms of fundamental quantum interactions, the process is properly described in terms of a virtual photon transit between the pre-excited donor and a lower energy (usually ground-state) acceptor. The detailed quantum amplitude for RET is calculated by molecular quantum electrodynamical techniques with the observable, the transfer rate, derived via application of the Fermi golden rule. In the treatment reported here, recently devised state-sequence techniques and a novel calculational protocol is applied to RET and shown to circumvent problems associated with the usual method. The second-rank tensor describing virtual photon behavior evolves from a Green’s function solution to the Helmholtz equation, and special functions are employed to realize the coupling tensor. The method is used to derive a new result for energy transfer systems sensitive to both magnetic- and electric-dipole transitions. The ensuing result is compared to that of pure electric-dipole–electric-dipole coupling and is analyzed with regard to acceptable transfer separations. Systems are proposed where the electric-dipole–magnetic-dipole term is the leading contribution to the overall rate.
Molecular dynamics simulation study of N-methylacetamide in water. I. Amide I mode frequency fluctuation
Authors: Kwac Kijeong , Cho Minhaeng
Published: July 2003

Carrying out molecular dynamics simulations of an N-methylacetamide (NMA) in H2O and D2O solutions, we investigated the amide I mode frequency fluctuation and dynamics. The ensemble averaged amide I mode frequency shift was found to be −78 cm−1 in comparison to that of the gas-phase NMA molecule, which is in excellent agreement with the experimental value of −81 cm−1. Similar to the solvation correlation function of a polar solute in liquid water, the correlation function of the fluctuating amide I mode frequency exhibits a bimodal decaying pattern and both the hindered translational and the librational motions of the water molecules directly hydrogen-bonded to the NMA are found to play critical roles in the pure dephasing of the amide I mode. The pure dephasing constant is estimated to be 11 cm−1. The vibrational broadening mechanism is mainly determined by the motional narrowing process. The vibrational Stokes shift of the amide I mode was estimated to be as small as 1.2 cm−1. The amide I IR absorption spectrum thus calculated without any adjustable parameters except for the lifetime of the first excited state has a full width at half maximum of 26.9 cm−1 and is found to be in good agreement with the experiment.
Molecular dynamics simulation study of N-methylacetamide in water. II. Two-dimensional infrared pump–probe spectra
Authors: Kwac Kijeong , Cho Minhaeng
Published: July 2003

A theoretical description of two-dimensional (2D) IR pump–probe spectroscopy of a three-level system is presented by taking into account the system–bath interaction. By using the correlation function of the fluctuating amide I mode frequency of N-methylacetamide in D2O, which was obtained by carrying out both ab initio calculations and MD simulations, the time-resolved 2D pump–probe spectra as a function of pump–probe pulse delay time are calculated and compared with experiment. We found that the vibrational dephasing becomes homogeneous on the 2 ps time scale, which is a bit faster than the experimental result. It is theoretically shown that the degree of slant of 2D contours is linearly proportional to the correlation function of the fluctuating amide I mode frequency. Consequently, it is suggested that the 2D IR pump–probe spectroscopy can provide a direct information on the vibrational frequency fluctuation dynamics and on the magnitude of static inhomogeneity.
Theoretical evaluation of hydrogen storage capacity in pure carbon nanostructures
Authors: Li Ju , Furuta Terumi , Goto Hajime , Ohashi Toshiyuki , Fujiwara Yoshiya , Yip Sidney
Published: July 2003

Carbon nanotubes have been proposed as promising hydrogen storage materials for the automotive industry. By theoretical analyses and total-energy density functional theory calculations, we show that contribution from physisorption in nanotubes, though significant at liquid nitrogen temperature, should be negligible at room temperature; contribution from chemisorption has a theoretical upper limit of 7.7 wt %, but could be difficult to utilize in practice due to slow kinetics. The metallicity of carbon nanotube is lost at full hydrogen coverage, and we find strong covalent C–H bonding that would slow down the H2 recombination kinetics during desorption. When compared to other pure carbon nanostructures, we find no rational reason yet why carbon nanotubes should be superior in either binding energies or adsorption/desorption kinetics.
Determination of quantum confinement in CdSe nanocrystals by cyclic voltammetry
Authors: Kucur Erol , Riegler Jürgen , Urban Gerald A. , Nann Thomas
Published: July 2003

Ionization potentials Ip, electron affinities E.A., and the quantum confinement in CdSe nanocrystals were determined by means of cyclic voltammetry. The results were compared to values obtained from spectroscopic measurements, especially UV/vis absorption and photoluminescence emission spectra. Absolute band gap positions were obtained from the electrochemical measurements and discussed with regard to vacuum level values. The results are in good agreement with theoretical expectations and spectroscopic data.
Experimental and theoretical investigation of the production of cations containing C–N bonds in the reaction of benzene with atomic nitrogen ions
Authors: Di Stefano Marco , Rosi Marzio , Sgamellotti Antonio , Ascenzi Daniela , Bassi Davide , Franceschi Pietro , Tosi Paolo
Published: July 2003

In the last few years, astronomical spectra have revealed the presence of aromatic and polyaromatic molecules in extraterrestrial environments, near carbon stars, in molecular clouds and meteorites. Moreover, the recent observation of benzene in interstellar space has noticeably increased the interest in the entire class of molecules and in their chemical behavior. In this work, we have investigated the reaction between the benzene molecule and the atomic nitrogen cation and, in particular, the mechanisms by which the reactants are converted into cationic products containing at least one C–N bond, according to the general scheme C6H6+N+→HmCnN++CxHy. We have measured the energy dependence of the cross section in a guided ion beam tandem mass spectrometer. Relevant stationary points of the potential energy surface have been studied by using the density functional theory hybrid functional B3LYP with the 6-31G* basis set. Thermochemical calculations, and the comparison with experimental results, allow us to distinguish between exoergic and endoergic processes and to obtain a detailed description of the reaction mechanisms. We show that aromatic hydrocarbons may be converted into organic-nitrogen compounds via the insertion of N+ into the benzene ring and the formation of C–N bonds from C–C ring reactants.
State-of-the-art correlated ab initio potential energy curves for heavy rare gas dimers: Ar2, Kr2, and Xe2
Authors: Slavı́ček Petr , Kalus René , Paška Petr , Odvárková Iva , Hobza Pavel , Malijevský Anatol
Published: July 2003

Characteristics of the heavy rare gas dimers (Ar2,Kr2,Xe2) have been studied by correlated ab initio calculations. All-electron CCSD(T) calculations were performed for Ar and Kr dimers, and calculations with relativistic effective core potentials were performed for Kr and Xe dimers. Extended basis sets (aug-cc-pVXZ, X=D, T, Q, 5, 6) were combined with bond functions (spd, spdfg). The use of bond functions significantly improves the basis set convergence. For the argon dimer, we have included also a CCSDT correction yielding a higher quality potential energy curve. This correction has been calculated using aug-cc-pVTZ+spd basis set. All possible sources of errors have been analyzed for the argon dimer [basis set saturation, correlation contributions going beyond CCSD(T) method, effect of core corrections and relativistic corrections]. In the case of the Ar dimer, the highest level of theory reproduces the semiempirical stabilization energy within 1.3 cm−1. To obtain even closer agreement with experiment it would be necessary to fully include quadruple and higher excitations as well as to account properly for the core corrections with yet unpublished core oriented basis sets. Further improvement of one electron basis set will not lead to a better agreement with experiment. In the case of the other two dimers, the agreement between theory and experiment is also acceptable but not quantitative as in the case of the Ar dimer. Apparently, current calculations are close to the basis set limit and better agreement can only be obtained by proper covering of contributions mentioned for the argon dimer. The newly developed ECP oriented aug-cc-pVXZ basis set is very effective and can be recommended for high level calculations of molecular clusters containing heavier rare gas elements. The fast DZ/TZ extrapolation technique has been extended so that the use of empirical parameters can be avoided. Results obtained by extrapolations with medium size basis sets are surprisingly close to the most accurate ones. Further, the MP2–CCSD(T) difference was shown to be much less dependent on the size of the basis set than the energies themselves. These two conditions allow to construct the true stabilization energy of extended complexes as a sum of extrapolated complete basis set limit of MP2 stabilization energy and [MP2–CCSD(T)] term determined in a smaller basis set. The ab initio pair intermolecular potential results have been fitted to suitably chosen analytical formulas, and tested on experimental data for the second virial coefficients, spectral characteristics, and scattering data. For argon, an excellent agreement between the theoretical and the experimental values has been found. In the case of krypton and xenon the agreement is not as good but still acceptable.
Two-dimensional vibrational spectroscopy of a double minimum system in a dissipative environment
Authors: Kühn O. , Tanimura Y.
Published: July 2003

A dissipative bistable system presents the simplest model to describe condensed phase reaction dynamics. Using a quantum master equation approach to calculate multitime dipole correlation functions we demonstrate how the dissipative dynamics can be characterized by time-resolved third-order infrared spectroscopy. Thereby we incorporate bilinear and linear–quadratic system–bath interaction into the Redfield relaxation tensor. Investigating equilibrium and nonequilibrium initial conditions for a symmetric system it is shown that bath-induced coherence transfer can have a dramatic influence on the two-dimensional signals. This occurs when the inverse of the ground state tunneling splitting is of the order of the coherence transfer time.
Phase transitions of short chains at ultralow temperature
Authors: Huang Lei , He Xuehao , Wang Yuanyuan , Chen Hanning , Liang Haojun
Published: July 2003

The simulations on equilibrium thermodynamic properties of short homopolymer chains, 3-, 4-, and 5-mer, by multicanonical Monte Carlo in a three-dimensional off-lattice model are quantitatively coincident with the exact analytical results of recently reported by Taylor [J. Chem. Phys. 114, 6472 (2001)], indicating that multicanonical algorithm is a permitted method in overcoming nonergodicity in observation of freezing transitions of single macromolecular chains. The investigation of freezing transition behaviors of 5-mer chains at ultralow temperatures reveals that four isomers coexist in the liquid state, then freeze into one of four isomers in the solid state depending on the bond length and bond fluctuation of the chain model after the occurrence of a liquid-to-solid-like first-order transition.
Monte Carlo simulations and dynamic field theory for suspended particles in liquid crystalline systems
Authors: Grollau S. , Kim E. B. , Guzmán O. , Abbott N. L. , de Pablo J. J.
Published: July 2003

Monte Carlo simulations and dynamic field theory are used to study spherical particles suspended in a nematic liquid crystal. Within these two approaches, we investigate the binding of the defects to the particles, the adsorption of a particle at a solid surface, and two particles interacting with each other. Quantitative comparisons indicate good agreement between the two approaches. A Monte Carlo method based on the combination of canonical expanded ensemble simulations with a density-of-state formalism is used to determine the potential of mean force between one particle and a hard wall. On the other hand, the potential of mean force is evaluated using a dynamic field theory, where the time-dependent evolution of the second rank tensor includes two major aspects of liquid crystalline materials, namely the excluded volume and the long-range order elasticity. The results indicate an effective repulsive force that acts between the particle and the wall. Layer formation at the surface of the hard wall gives rise to local minima in the potential of mean force. The director profile for a particle at contact with a solid surface is characterized by a disclination line distorted and attracted towards the wall. The structure of the nematic for two particles at short distances is also investigated. Our results indicate a structure where the two particles are separated by a circular disclination line. The potential of mean force associated with this configuration indicates an effective attractive interaction between the two particles.
Dynamics of the hydrogen and phosphate ions in proton conducting gel/D3PO4 electrolytes: A H2 and P31 nuclear magnetic resonance study
Authors: Jeffrey K. R. , Zukowska G. Z. , Stevens J. R.
Published: July 2003

The synthesis and characterization of protonic conducting polymeric gels is motivated by their possible application in various electrochemical devices. Nonaqueous proton-conducting gel electrolytes are being developed for use in various sensors and electrochromic devices operating at ambient temperatures. The electrolyte must have a relatively high conductivity and chemical and physical stability. One method of producing nonaqueous conducting polymeric gel electrolytes is to entrap organic solutions of a strong acid such as H3PO4 in a polymer matrix. Results are reported on the system consisting of phosphoric acid dissolved in N,N-dimethyl formamide (DMF) within a gel network formed with poly(glycidyl methacrylate) (PGMA). Using selective deuteration, the diffusion coefficients for both the deuteron and phosphorus from the phosphoric acid and the DMF are measured by field gradient nuclear magnetic resonance (NMR) techniques. Combining the diffusion with conductivity measurements in the Nernst–Einstein equation leads to a better understanding of the number of charge carriers in the mixture and the temperature dependence of this number. Nuclear spin-lattice relaxation is used as a tool to probe the ion dynamics in these materials. In addition to NMR measurements, the samples have been characterized by electrical conductivity, differential scanning calorimetry, and viscosity measurements. The results show that the Grotthus mechanism involving the hopping of the proton from one molecular site to another, as well as the vehicular mechanism due to the motion of the D2PO4− and D4PO4+ ions are most responsible for the motion of the proton in these electrolytes. The variety of protonation sites in the PGMA/DMF/H3PO4 system is much more diverse that in the previously studied PMMA/PC/D3PO4 system. In the PGMA/DMF/H3PO4 system there are sites on the polymer, DMF and H3PO4.
Microscopic two-fluid theory of rotational constants of the OCS–H2 complex in He4 droplets
Authors: Kwon Yongkyung , Whaley K. Birgitta
Published: July 2003

We present a microscopic quantum analysis for rotational constants of the OCS–H2 complex in helium droplets using the local two-fluid theory in conjunction with path integral Monte Carlo simulations. Rotational constants are derived from effective moments of inertia calculated assuming that motion of the H2 molecule and the local nonsuperfluid helium density is rigidly coupled to the molecular rotation of OCS and employing path integral methods to sample the corresponding H2 and helium densities. The rigid coupling assumption for H2–OCS is calibrated by comparison with exact calculations of the free OCS–H2 complex. The presence of the H2 molecule is found to induce a small local nonsuperfluid helium density in the second solvation shell which makes a non-negligible contribution to the moment of inertia of the complex in helium. The resulting moments of inertia for the OCS–H2 complex embedded in a cluster of 63 helium atoms are found to be in good agreement with experimentally measured values in large helium droplets. Implications for analysis of rotational constants of larger complexes of OCS with multiple H2 molecules in helium are discussed.
A scaling rule for molecular electronic transition dipole moments: Application to asymptotically allowed and forbidden transitions
Authors: Johnston C. W. , van der Mullen J. J. A. M.
Published: July 2003

Guided by the work of Woerdman and Monyakin, we propose rules that allow the electronic transition dipole moment for a transition in one molecule to be determined from that of a similar one in an isovalent species. The rule can be applied to asymptotically allowed and forbidden transitions. We have tested it by applying it in two specific cases: the moments for the A 1Σ→X 1Σ and X 1Σ→B 1Π transitions in Na2 are found from those in Li2, which are asymptotically allowed and the moments for the B→X transition in O2, Se2, and Te2 which are asymptotically forbidden, are found from moment data for S2. Transition moments calculated with this rule are within 15% of the available literature values and behavior as a function of internuclear separation is well described.
Automated calculation of fundamental frequencies: Application to AlH3 using the coupled-cluster singles-and-doubles with perturbative triples method
Authors: Ruden T. A. , Taylor P. R. , Helgaker T.
Published: July 2003

An automated scheme for calculating numerical derivatives of functions is presented and applied to the Taylor expansion of potential energy surfaces. The computational cost is reduced by invoking the symmetry properties of noncubic groups. The scheme is applied to the quartic force field of isotopomers of AlH3 by numerical differentiation of the CCSD(T) energy, using the cc-pCVQZ basis for the harmonic part of the potential and the cc-pCVTZ basis for the anharmonic part. From this force field, zero-order vibrational corrections to the geometry and the fundamental frequencies are calculated by second-order perturbation theory. The results are compared with experiment and previous calculations.
Structure and phase transitions in confined binary colloid mixtures
Authors: Cui Bianxiao , Lin Binhua , Rice Stuart A.
Published: July 2003

We report the results of a study of crystallization in quasi-two-dimensional binary mixtures of large and small colloids. The experiments sample the parameter spaces of colloid particle diameter ratio, large particle density, and small particle packing fraction. The depletion potential between the large particles, induced by the presence of the small particles in the system, affects the density at which the large particles undergo a liquid-to-solid freezing transition. For systems with a large to small particle diameter ratio of 4.6, the addition of small particles increases the large particle liquidus transition density, a seemingly counterintuitive result given that the depletion potential is purely attractive when the small particle packing fraction is low. When the large to small particle diameter ratio is 8.8, the same trend in the large particle liquidus transition density is seen, but to a lesser extent. The other system properties for the system with diameter ratio 8.8 show the same trends as for the system with diameter ratio 4.6. Liquid–liquid phase separation is observed for binary mixtures with diameter ratios of 20 and 40. Although the particles used in our experiment can be well modeled as hard spheres, our results cannot be readily explained by extant descriptions of the depletion interaction developed for three-dimensional binary hard sphere mixtures. Inversion of the pair correlation functions obtained from our measurements yields a depletion interaction that is much stronger than predicted for the same densities and diameter ratio in a three-dimensional hard sphere mixture. Our results imply that the depletion interaction is strongly dependent on the degree of confinement of the system.
A self-consistent integral equation: Bridge function and thermodynamic properties for the Lennard-Jones fluid
Authors: Bomont J. M. , Bretonnet J. L.
Published: July 2003

A new approximate bridge function is proposed as an expansion in powers of the thermal potential, which ensures the thermodynamic consistency with the classical pressure-compressibility condition. The bridge function compares very well the simulation data at large separation as well as in the most important region of the core. The thermodynamic properties of the supercritical Lennard-Jones fluid calculated by means of standard formulas of statistical mechanics involving correlation functions and bridge function are in excellent agreement with those obtained from computer simulation.
The structures of fluorene–(H2O)1,2 determined by rotational coherence spectroscopy
Authors: Laman David M. , Joly Alan G. , Ray Douglas
Published: July 2003

Rotational coherence spectroscopy (RCS), via time-correlated single photon counting, and two-color resonant two-photon ionization (R2PI) time-of-flight mass spectrometry, have been used to characterize fluorene–(water)1,2 [FL–(H2O)1,2] van der Waals clusters generated in supersonic jets. Rotational coherence traces have been obtained at excitation energies corresponding to several resonant features in the S1←S0 R2PI spectra of FL–(H2O)1,2. RCS simulations and diagonalization of the moment of inertia tensor have been used to obtain S1 excited state rotational constants and structures of FL–(H2O)1,2 that are consistent with the experimental rotational coherence traces. The RCS results indicate that: (i) the water molecule in FL–H2O resides above the central five member ring and interacts with both aromatic sites; (ii) the water molecules in FL–(H2O)2 form a water dimer that is most likely oriented along the long axis of fluorene and is hydrogen-bonded to both aromatic sites. The S1←S0 R2PI spectra of FL–(D2O)1,2 and FL–HDO have also been obtained. The 000 transition is a doublet in the R2PI spectra of FL–H2O, FL–D2O, and a singlet in the R2PI spectrum of FL–HDO. The presence of this doublet in the FL–H2O/D2O spectra, and the absence of such a splitting in the FL–HDO spectrum, is an indication of internal rotation of the water molecule on a potential energy surface that changes upon electronic excitation. Lastly, the use of RCS and time-resolved fluorescence as a tool for assigning features in R2PI spectra that are of ambiguous origin due to fragmentation of higher mass clusters into lower mass channels is demonstrated.