bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-Density Lipoprotein Particle Concentration and Size as Determined by Nuclear Magnetic Resonance Spectroscopy as Predictors of Cardiovascular Disease in Women
Authors: Blake Gavin J. , Otvos James D. , Rifai Nader , Ridker Paul M
Published: October 2002

Background—

Nuclear magnetic resonance (NMR) offers an alternative, spectroscopic means of quantifying LDL and of measuring LDL particle size.

Methods and Results—

We conducted a prospective nested case-control study among healthy middle-aged women to assess LDL particle size (NMR) and concentration (NMR) as risk factors for future myocardial infarction, stroke, or death of coronary heart disease. Median baseline levels of LDL particle concentration (NMR) were higher (1597 vs 1404 nmol/L;
P
= 0.0001) and LDL particle size (NMR) was lower (21.5 vs 21.8 nm;
P
=0.046) among women who subsequently had cardiovascular events (n=130) than among those who did not (n= 130). Of these 2 factors, LDL particle concentration (NMR) was the stronger predictor (relative risk for the highest compared with the lowest quartile=4.17, 95% CI 1.96–8.87). This compared with a relative risk of 3.11 (95% CI 1.55–6.26) for the ratio of total cholesterol to HDL cholesterol and a relative risk of 5.91 (95% CI 2.65–13.15) for C-reactive protein. The areas under the receiver operating characteristic curves for LDL particle concentration (NMR), total cholesterol to HDL cholesterol ratio, and C-reactive protein were 0.64, 0.64, and 0.66, respectively. LDL particle concentration (NMR) correlated with several traditionally assessed lipid and nonlipid risk factors, and thus adjustment for these tended to attenuate the magnitude of association between LDL particle concentration (NMR) and risk.

Conclusions—

In this cohort, LDL particle concentration measured by NMR spectroscopy was a predictor of future cardiovascular risk. However, the magnitude of predictive value of LDL particle concentration (NMR) was not substantively different from that of the total cholesterol to HDL cholesterol ratio and was less than that of C-reactive protein.
Time from Newton to Einstein to Friedman
Authors: Rindler Wolfgang
Published: October 2002

This article traces in as untechnical a way as possible the metamorphoses that Newton's absolute time has undergone at the hands of Einstein, only to come round almost full-circle in present-day Friedmannian cosmology. The recurring theme is that of moments being slices through the spacetime of history, and how these slices are affected by gravity.
Intentionality and the Experience of Time
Authors: Modell Arnold
Published: October 2002

This paper explores the experience of time from the perspective of a concept of intentionality derived from Thomas Aquinas. As action directed at some future goal is determined by memorial categories, intentionality contains within it reference to past and future time. Meaning is achieved through action into the world and in turn the self is altered by that action. As the world is essentially an unlabeled place, we organize experience by means of memorial categories. Memorial categories serve as relatively stable templates, modified by the recontextualization that follows from novel experiences. Thus, the sense of the permanence of the past, that gives time its direction, is a construction of our brain. The now moment of experience is not emotionally neutral; our relation between past and future time is mediated by means of feeling rhythmic synchrony, keeping in time with the other provides the earliest medium for emotional bonding.
A Holocene Paleoclimatic and Environmental Record from Stoneman Lake, Arizona
Authors: Hasbargen Jim
Published: October 2002

Stoneman Lake, Coconino County, Arizona, occupies a 600,000-yr-old caldera on the southern edge of the Colorado Plateau. Changes in fossil diatom floras, pollen profiles, macrofossil remains, and geological characteristics of a sediment core show changing aquatic and terrestrial environments over the past 9000 yr. Cool temperatures and greater effective precipitation than at present are indicated during the early Holocene, prior to 8500 yr B.P. A warmer and drier period followed (8000 and 2000 yr B.P.) during which time a marsh-like environment developed within the caldera, and xeric pleat communities were established along the southern Colorado Plateau. Modern plant communities have existed in this region for the past 6000 yr, although lake conditions have fluctuated.
Sea Surface Temperature of the Western Equatorial Pacific Ocean during the Younger Dryas
Authors: Thunell Robert C. , Miao Qingmin
Published: October 2002

High resolution (∼200 yr sample spacing) records of sea surface temperature for the past 15,000 yr have been inferred from planktonic foraminiferal assemblages in a sediment core from the South China Sea. Although the assemblages imply a large glacial-to-interglacial temperature change (∼7°C for winter temperatures), they give no indication of a cooling during Younger Dryas time. This suggests that the Younger Dryas increase in δ18O observed in cores from the western equatorial Pacific is not due to a climatic cooling but rather to a change in the isotopic composition of the oceans.
Prediction of structure and functional residues for O‐GlcNAcase, a divergent homologue of acetyltransferases
Authors: Schultz Jörg , Pils Birgit
Published: October 2002

N‐Acetyl‐β‐D‐glucosaminidase (O‐GlcNAcase) is a key enzyme in the posttranslational modification of intracellular proteins by O‐linked N‐acetylglucosamine (O‐GlcNAc). Here, we show that this protein contains two catalytic domains, one homologous to bacterial hyaluronidases and one belonging to the GCN5‐related family of acetyltransferases (GNATs). Using sequence and structural information, we predict that the GNAT homologous region contains the O‐GlcNAcase activity. Thus, O‐GlcNAcase is the first member of the GNAT family not involved in transfer of acetyl groups, adding a new mode of evolution to this large protein family. Comparison with solved structures of different GNATs led to a reliable structure prediction and mapping of residues involved in binding of the GlcNAc‐modified proteins and catalysis.
Coexpression of a Cav1.2 protein lacking an N‐terminus and the first domain specifically suppresses L‐type calcium channel activity
Authors: Ebihara Tatsuhiko , Komiya Yuriko , Izumi-Nakaseko Hiroko , Adachi-Akahane Satomi , Okabe Shigeo , Okamura Yasushi
Published: October 2002

L‐type Ca2 channels play a critical role in many types of cells, including nerve, muscle and endocrine cells. The most popular and effective tools for analyzing the roles of L‐type calcium channels (L‐channels) are specific antagonists such as dihydropyrigines. With these drugs however, it is difficult to target specific cells. One solution is to develop a genetically targetable inhibitor coded by DNA. As a candidate for such an inhibitor, a dominant negative mutant of Cav1.2 was designed by mimicking an ascidian 3‐domain‐type α1 subunit (that inhibits the full‐length subunit's current). The 3‐domain‐type Cav1.2 subunit significantly inhibited wild‐type Cav1.2 current, but not other ionic currents such as Cav2.1 and Nav channels in Xenopus oocyte expression systems. Western blot analysis showed that the expression of the wild‐type protein into the plasma membrane was significantly suppressed on coexpression with the truncated protein. These findings support that an N‐terminus‐truncated mutant could serve as a specific genetically encoded inhibitor for L‐channels.
How the lipid‐free structure of the N‐terminal truncated human apoA‐I converts to the lipid‐bound form: new insights from NMR and X‐ray structural comparison
Authors: Wang Guangshun
Published: October 2002

The X‐ray structure of the N‐terminal truncated human apoA‐I [Borhani et al., Proc. Natl. Acad. Sci. USA 94 (1997) 12291] and the NMR structure of intact human apoA‐I [Okon et al., FEBS Lett. 517 (2002) 139] found similar repeating helices. The crystal structure is a twisted circular four‐helix bundle, consisting of four molecules of apoA‐I(44–243), where four copies of the lecithin:cholesterol acyltransferase (LCAT)‐activating domains are located outside the ring structure, while the aromatic‐rich strong lipid‐binding domains are inside. This architecture suggests a lipid‐binding mechanism that lipids directly enter the hole of the crystal structure. Indeed, four copies of Trp50 and Trp72 are exposed and oriented toward the center of the ring, initiating lipid binding. This is followed by the inside–out rotations of the terminal helices to make a belt with all the hydrophobic faces of the helices facing inward. Such lipid‐binding induced rotations have an impact on the conformation of the lipid‐free form. Indeed, the structure of residues 78–81 changes from helical (free) to disordered (bound) while the structure of residues 221–227 changes from extended to helical.
Identification of the ice‐binding face of antifreeze protein from Tenebrio molitor
Authors: Marshall Christopher B , Daley Margaret E , Graham Laurie A , Sykes Brian D , Davies Peter L
Published: October 2002

The beetle Tenebrio molitor produces several isoforms of a highly disulfide‐bonded β‐helical antifreeze protein with one surface comprised of an array of Thr residues that putatively interacts with ice. In order to use mutagenesis to identify the ice‐binding face, we have selected an isoform that folds well and is tolerant of amino acid substitution, and have developed a heating test to monitor refolding. Three different types of steric mutations made to the putative ice‐binding face reduced thermal hysteresis activity substantially while a steric mutation on an orthogonal surface had little effect. NMR spectra indicated that all mutations affected protein folding to a similar degree and demonstrated that most of the protein folded well. The large reductions in activity associated with steric mutations in the Thr array strongly suggest that this face of the protein is responsible for ice binding.
Sorsby's fundus dystrophy mutant tissue inhibitors of metalloproteinase‐3 induce apoptosis of retinal pigment epithelial and MCF‐7 cells
Authors: Majid Mohammed A , Smith Valerie A , Easty David L , Baker Andrew H , Newby Andrew C
Published: October 2002

C‐terminal domain tissue inhibitor of metalloproteinases‐3 (TIMP‐3) mutations cause the rare hereditary blindness Sorsby's fundus dystrophy (SFD), which involves loss of retinal pigment epithelial (RPE) cells. Since wild‐type TIMP‐3 causes apoptosis, we investigated whether SFD TIMP‐3 might kill RPE and other cells. Plasmid‐mediated overexpresion of Ser‐156, Gly‐167, Tyr‐168 and Ser‐181 SFD mutant TIMP‐3 decreased RPE viability to 22±8, 20±6, 32±5, 30±12% (SFD mutants all P<0.01 versus wild‐type 50±8%) and similarly increased propidium iodide staining and in situ end labelling. Adenovirus‐mediated overexpression of the Gly‐167 mutant also caused RPE apoptosis dose‐dependently. Apoptosis of RPE cells might therefore contribute to the pathology of SFD.
Determinants of time‐series properties of earnings and cash flows
Authors: Ismail Badr , Choi Kwan
Published: October 2002

This paper examines the relative ability of some economic factors in explaining systematic differences in the time‐series properties of earnings vs. cash flows. The factors used are: firm size, inventory level, capital intensity, degree of competition, and product type (durable‐ nondurable). The results confirm that these factors explain firms' cash flow properties better than earnings properties. Specifically, tests of the differences in the coefficients of variation and autocorrelation coefficients of the earnings series suggest size and product‐type effect. Cash flows, in contrast, indicate an effect with respect to all variables. These findings contribute to our understanding of how the structural forms of the processes generating earnings and cash flows are fundamentally different. The strength of the relationship between economic factors and cash flow properties is potentially relevant to some research efforts directed at cash flow prediction.
Wealth effects of reserve requirement reductions in the 1990s on depository institutions
Authors: Bartunek Kenneth S. , Madura Jeff
Published: October 2002

Reserves banks hold against deposits do not earn interest and hence, represent an implicit tax on deposits. Thus, adjustments to reserve requirements might be expected to influence the value of depository institutions because they would affect the present value of future implicit taxes on the institutions. This paper measures the share price response of banks to two unique reserve requirement adjustments in the early 1990s. The results indicate that not all of the benefit from the reduction in the implicit tax resulting from the lowering of reserve requirements was passed on to depositors and borrowers. The larger banks tended to experience strong favorable valuation effects.
Participation rates of dividend reinvestment plans: Differences between utility and nonutility firms
Authors: Todd Janet M. , Domian Dale L.
Published: October 2002

This paper examines survey data to study features of dividend reinvestment plans and their relationship to participation rates. Differences between utility and nonutility firms are examined. Discount features and new issue shares are found to be used more often by the utility group, while both groups allow cash contributions along with the dividend reinvestment. Discount features and high returns are correlated with higher participation rates. There is also some preliminary evidence that participation rates by large blockholders may increase trading volume.
Default probability on corporate bonds: A contingent claims model
Authors: Trussel John
Published: October 2002

The purpose of this paper is to develop and test a model of the probability of default on corporate bonds that is based upon the tenets of the contingent claims literature. Equity is considered a call option on the firm's assets, with the exercise price being the face value of the firm's debt. Using this framework, a model is developed with the probability of default as a function of five variables‐firm value, face value of the debt, time to maturity of the debt, instantaneous return and standard deviation of firm value. The model is found to be statistically significant, explains approximately 54 percent of the variation in the bond ratings, and correctly classifies, 68 percent and 66 percent of the bonds in an initial and holdout sample, respectively, according to their agency ratings. The model is also found to provide a reasonable estimate of the probability of default.
China's Economic Think Tanks: Their Changing Role in the 1990s
Authors: Naughton Barry
Published: October 2002

During the 1980s, economic think tanks played a key role as centres of expertise, with distinctive philosophies and approaches to economic transition. Although they were all government-sponsored, they served as important alternatives to the policies and advice available within the formal government bureaucracy. In the 1990s, think tanks continued to play an important role but lost some of their distinctive personality. Expertise was absorbed into the bureaucracy, but at the same time independent think tanks emerged. Think tanks were knit into a web of policy debate and advice which Premier Zhu Rongji, in particular, uses as a source of ideas and analysis. The total network of advisers has become more important, while think tanks have become less distinctive nodes of that network.
Growth and carbon partitioning in perennial ryegrass (Lolium perenne) cultivars selected for high water-soluble carbohydrate concentrations
Authors: SMITH K. F. , CULVENOR R. A. , HUMPHREYS M. O. , SIMPSON R. J.
Published: October 2002

Perennial ryegrass (Lolium perenne L.) cultivars with increased water-soluble carbohydrate (WSC) concentrations were evaluated under controlled environment conditions. The growth and carbon partitioning of these cultivars was compared with standard cultivars during vegetative growth. The high WSC cultivars had shoot growth rates that were not significantly different from the standard cultivars, confirming that the extra WSC in these cultivars was not made available through reductions in yield potential. The extra WSC stored in these cultivars coincided with lower concentrations of neutral detergent fibre in the dry matter. When the cultivars were grown in hydroponic solution the high WSC cultivars Aurora and Ba10727 were found to also have less root mass and a lower root[ratio ]shoot ratio than the standard cultivars. However, this trait was not consistent across all high WSC cultivars with Cariad having the same root[ratio ]shoot ratio as the standard cultivars at the end of the experiment. The reduction in the root mass of the cultivars Aurora and Ba10727 was far greater than necessary to provide the extra carbon stored as WSC in these cultivars. The implications of these results for the breeding of cultivars of perennial ryegrass with increased WSC concentrations are discussed.
Brief Encounter: Grenadian Prime Minister Maurice Bishop's Visit to Washington
Authors: WILLIAMS GARY
Published: October 2002

This article examines the visit of Grenadian Prime Minister Maurice Bishop to Washington DC in June 1983. Scholars have speculated that the visit was motivated by a desire to normalise Grenada's troubled relations with the United States or, alternatively, that it was a public relations and lobbying exercise. This article concludes that Grenadian government officials variously viewed the visit as a public relations exercise, an opportunity for dialogue and an opportunity to gain economic support. For the United States the prospect of Bishop's visit prompted a reassessment of its Grenada policy and, after Bishop met senior US officials, resulted in a hardening of existing policy.
Reproductive ecology of an intertidal red seaweed, Gracilaria gracilis: influence of high and low tides on fertilization success
Authors: Engel Carolyn R. , Destombe Christophe
Published: October 2002

Patterns of in situ fertilization success with respect to high and low tide periods are reported for the intertidal red seaweed Gracilaria gracilis which inhabits rock pools. Cystocarp (zygote) production was experimentally compared at high tide and low tide in both high- and low-shore tide pools at two sites using ten virgin female plants. High- and low-shore pools showed different patterns with respect to tide period. High-shore pools showed significantly greater numbers of cystocarps at low tide than at high tide whereas cystocarp production did not differ between high and low tide periods in low shore pools. The possible mechanisms of gamete release are discussed in light of these results.
Otolith microchemistry of the conger eel, Conger myriaster
Authors: Arai Takaomi , Ikemoto Tokutaka , Kunito Takashi , Tanabe Shinsuke , Miyazaki Nobuyuki
Published: October 2002

Elemental composition and ontogenic change patterns of Sr and Ca were examined in conger eel, Conger myriaster, otoliths. Accumulations of the major elements of seawater, K, Mg, and Na, into otoliths were smaller than the accumulations of 19 other minor elements whose concentrations were determined. Strontium content and Sr:Ca ratios in the otolith fluctuated during the life history transect at 100 to 200 μm from the core of the otolith, indicating a period of metamorphosis. Changes in Sr content and Sr:Ca ratios may be associated with internal physiological factors such as metamorphosis in the early developmental stage in the conger eel.
Abundance, growth and first-winter survival of young bass in nurseries of south-west England
Authors: Kelley Donovan
Published: October 2002

0-group bass were sampled from the shallow creeks of the Tamar and Camel estuaries at regular intervals from May to September in 1981 to 2000 to measure relative year-class abundance. From 1989 onwards classes were generally strong, especially those of 1989, 1992 (Tamar only), 1995 and 1998. Sampling at age-4, before departure from the nursery at the onset of adolescent movements, gave broadly similar relativities. Numbers were greater, and growth faster, in the Tamar than in the smaller and cooler Camel. Temperature was an important factor in both abundance and growth. Occasional major differences in abundance between the two estuaries were reported. Factors which might bias the age-4 result are considered. Other estuaries on the south side of the south-west peninsula, sampled less frequently, reflected Tamar abundances; others on the north side reflected Camel abundances. Limited analysis of stomach contents of older juvenile bass often present in the same habitats revealed no evidence of cannibalism on 0-groups. The shallow creeks of the Tamar and Camel were deserted in winter but a deeper creek on the Taw, frequented throughout winter, was sampled monthly in the 1982–1996 winters to measure losses, if any, in cold periods. In the mainly mild winters, losses were infrequent and small except in the five-week cold spell of early 1986, when the 1985 class suffered an estimated 58% loss in the Taw and possible total loss in the Camel and the Tamar. Sudden heavy flooding of the estuaries caused no apparent losses when they occurred in late summer and autumn but might be damaging if they occur soon after post-larvae arrive.
The significance of contrasting feeding strategies on the reproductive cycle in two coexisting tellinacean bivalves
Authors: Stead R.A. , Clasing E. , Lardies M.A. , Arratia L.P. , Urrutia G. , Garrido O.
Published: October 2002

Semele solida and Tagelus (Tagelus) dombeii are two tellinacean bivalves which coexist in the lower intertidal zone of a sandflat in south-central Chile but follow different feeding strategies. Wheras T. (T.) dombeii is a suspension-feeder, S. solida is a facultative deposit-feeder. In this study, digestive gland indices and reproductive cycles were described in relation to annual food availability and related to their feeding modes. Results showed that gonadic index cycles were similar for both species, with highest values being observed during the spring when water temperature was still on the rise and microflagellate and centric diatom density was at its peak. However, histological analyses indicated that the spawning period of T. (T.) dombeii extended from November 1995 to March 1996 and from August 1996 to January 1997, whereas S. solida presented a continuous spawning period that extended from September 1995 to December 1996. Results suggest that extended spawning throughout the winter by S. solida is a consequence of its ability to feed on bottom deposits when food in suspension is low.
The Role of the Extensor Digitorum Communis Muscle in Lateral Epicondylitis
Authors: FAIRBANK S. M. , CORLETT R. J.
Published: October 2002

A common finding in tennis elbow is pain in the region of the lateral epicondyle during resisted extension of the middle finger (Maudsley’s test). We hypothesized that the pain is due to disease in the extensor digitorum communis muscle, rather than to compression of the radial nerve or disease within extensor carpi radialis brevis. Thirteen human forearm specimens were examined. It was found that the extensor digitorum communis was separable into four parts. The part to the middle finger originated from the lateral epicondyle, but the muscle slips to the other fingers originated more distally. Pain ratings were measured in ten patients diagnosed with lateral epicondylitis during isometric finger and wrist extension tests. The results confirmed the high prevalence of a positive Maudsley’s test in lateral epicondylitis, and also that the patients with tenderness at the site of origin of the extensor digitorum communis slip to the middle finger had the greatest pain during middle finger extension. These anatomical and clinical findings clarify the anatomy of extensor digitorum communis, and suggest that this muscle forms the basis for the Maudsley’s test. The muscle may play a greater role in tennis elbow than previously appreciated.
Flexor Sheath Dilatation with a Fogarty Catheter
Authors: JARVIS W. T. , CAMPBELL A. C. , SINHA S.
Published: October 2002

The use of a Fogarty catheter to dilate a constricted flexor sheath is described. This relatively atraumatic method of dilating a constricted flexor sheath, may some times allow a one-stage rather than a two-stage tendon graft procedure.
Functional Absence of Flexor Digitorum Superficialis to the Little Finger and Absence of Palmaris Longus – Is There A Link?
Authors: THOMPSON N. W. , MOCKFORD B. J. , RASHEED T. , HERBERT K. J.
Published: October 2002

We examined 150 men and 150 women aged 18–40 years to assess flexor digitorum superficialis function to the little finger and the incidence of palmaris longus absence. All patients had flexor digitorum superficialis function to the little finger assessed by standard and modified tests. The presence or absence of palmaris longus was assessed by clinical inspection. Following modified testing, ten subjects (14 hands) displayed absolute superficialis deficiency to the little finger. Forty-nine subjects had unilateral absence of palmaris longus (16%). This tendon was absent bilaterally in 26 subjects (9%). On combining the clinical findings, one subject had unilateral absence of flexor digitorum superficialis function to the little finger with contralateral absence of palmaris longus, and one subject had bilateral absence of flexor digitorium superficialis function with unilateral absence of palmaris longus. We conclude that there is no link between an absent little finger flexor digitorium superficialis and an absent palmaris longus.
Silicone Arthroplasty for Trapeziometacarpal Arthritis
Authors: O’LEARY S. T. , GROBBELAAR A. O. , GOLDSMITH N. , SMITH P. J. , HARRISON D. H.
Published: October 2002

Twenty-three patients who had undergone trapeziectomy and Helal silicone rubber ball interposition for trapeziometacarpal arthritis were reviewed. The average age at operation was 63 (range 48–84) years and the mean follow-up was 59 (range 12–138) months. Of the 23 patients reviewed, two had pain at rest and four had some discomfort on exertion. Mean post-operative thumb extension was 37° whilst mean palmar abduction was 40°. Mean post-operative grip strength was 19 kg and thumb-pinch strength was 4.0 kg, 77% and 78% of the age- and sex-matched normal values. There were no cases of prosthetic dislocation, prosthetic fracture or silicone synovitis.
Calculated scattering length for spin-polarized metastable helium
Authors: Gadéa F. X. , Leininger T. , Dickinson A. S.
Published: October 2002

A theoretical study is performed to re-evaluate the scattering length for spin-polarized metastable helium. The Σ5g+ potential is calculated with three huge basis sets, as well as one previously proposed, using two ab initio approaches: a large configuration interaction method and a coupled-cluster method. The influence of a dummy basis set is analyzed and shown to yield spurious behavior in the energy decrease, roughly Gaussian with changing separation of the dummy basis from the molecule. The scattering length is found to be extremely sensitive here even to tiny details of the potential because the potential is very close to supporting a fifteenth rotationless vibrational level. This behavior can be rationalized using semiclassical methods. From this study we conclude that there are certainly 15 vibrational levels and that the dissociation energy is most probably 1045.2±1 cm−1, while our final result for the scattering length, a=291 a0, is best considered as an upper limit.
A high accuracy ultrasonic distance measurement system using binary frequency shift-keyed signal and phase detection
Authors: Huang S. S. , Huang C. F. , Huang K. N. , Young M. S.
Published: October 2002

A highly accurate binary frequency shift-keyed (BFSK) ultrasonic distance measurement system (UDMS) for use in isothermal air is described. This article presents an efficient algorithm which combines both the time-of-flight (TOF) method and the phase-shift method. The proposed method can obtain larger range measurement than the phase-shift method and also get higher accuracy compared with the TOF method. A single-chip microcomputer-based BFSK signal generator and phase detector was designed to record and compute the TOF, two phase shifts, and the resulting distance, which were then sent to either an LCD to display or a PC to calibrate. Experiments were done in air using BFSK with the frequencies of 40 and 41 kHz. Distance resolution of 0.05% of the wavelength corresponding to the frequency of 40 kHz was obtained. The range accuracy was found to be within ±0.05 mm at a range of over 6000 mm. The main advantages of this UDMS system are high resolution, low cost, narrow bandwidth requirement, and ease of implementation.
Molecular exchange and its influence on the condensation coefficient
Authors: Meland Roar
Published: October 2002

When a molecule condenses, it gains kinetic energy which is dissipated by collisions. There is then the possibility that a condensing molecule may kick out a molecule in the interphase or in the liquid. There has been reported a strong correlation between condensation and evaporation fluxes. This “molecular exchange” effect is modeled by assuming that certain molecules that condense, kick out one molecule each. In this paper the influence of the molecular exchange mechanism on the condensation coefficient is discussed and it is shown that under certain assumptions, molecular exchange has no effect on gas-kinetic calculations of phase change. However, an expression suitable for molecular dynamics simulations of the fraction of condensing molecules that induces molecular exchange is also derived.
Semiclassical initial value representation description of molecular structure problems: An elongated dihydrogen ruthenium complex
Authors: Torres Laia , Gelabert Ricard , Giménez Xavier , Moreno Miquel , Lluch José M.
Published: October 2002

The Herman–Kluk initial value representation semiclassical approach has been applied, and proven effective, as well as accurate, to account for the intriguing elongated dihydrogen structure in a ruthenium coordination complex. Results are satisfactory even though the reduced dimensionality two-dimensional potential, involving the relevant distances, casts an extremely anharmonic, weakly bound species, with two exit channels. Comparatively short propagation times, to avoid complications due to chaotic trajectories, as well as discarding trajectories exiting the effective potential energy surface, has proven effective to converge results, as indicated by comparison with quantum mechanical discrete variable representation data.
A simplified joint density of states analysis of hydrogenated amorphous silicon
Authors: O’Leary Stephen K. , Malik Saad M.
Published: October 2002

We propose a simplified empirical model for the density of state functions of hydrogenated amorphous silicon that neglects the conduction band tail electronic states. The corresponding joint density of states function is then computed. We find, while this analysis is considerably simplified, that the resultant joint density of states function compares favorably with that determined from an empirical model for the density of states functions with the conduction band tail taken into account. Analytical and asymptotic results, relating the parameters characterizing the underlying density of states functions with the joint density of states function, are developed. The density of states parameters corresponding to hydrogenated amorphous silicon are then determined through an analysis of some hydrogenated amorphous silicon joint density of states experimental data. It is suggested that this simplified empirical model for the density of states functions will prove of greater utility to the experimentalist.
A Monte Carlo study of spectroscopy in nanoconfined solvents
Authors: Thompson Ward H.
Published: October 2002

The absorption and fluorescence spectra of a model diatomic molecule with a charge-transfer electronic transition are simulated. The effect of confining the solvent in which the diatomic molecule is dissolved is examined by comparing results for solutions contained within hydrophobic spherical cavities of varying size (radii of 10–20 Å). The effect of solvent polarity is also considered by comparing results of simulations with CH3I and CH3CN solvents. The spectra, solute radial and angular distribution functions, and free energy surfaces in the solvent and radial solute position coordinates are presented and discussed. It is found that the solute position in the cavity critically affects the absorption and fluorescence spectra and their dependence on cavity size. The implications of these results for time-dependent fluorescence measurements are discussed.
Brownian dynamics studies on DNA gel electrophoresis. I. Numerical method and “periodic” behavior of elongation-contraction motions
Authors: Azuma Ryuzo , Takayama Hajime
Published: October 2002

The dynamics of a DNA molecule which is undergoing constant field gel electrophoresis (CFGE) is studied by a Brownian dynamics simulation method we have developed. In the method a DNA molecule is modeled as a chain of spherical electrolyte beads and the gel as a three-dimensional array of immobile beads. With the constraint for the separation of each pair of bonded beads to be less than a certain fixed value, as well as with the excluded volume effect, the simultaneous Langevin equations of motion for the beads are solved by means of the Lagrangian multiplier method. The resultant mobilities μ as a function of electric field coincide satisfactorily with the corresponding experimental results, once the time, the length, and the field of the simulation are properly scaled. In relatively strong fields “periodic” behavior is found in the chain dynamics and is examined through the time evolution of the radius of the longer principal axis, Rl(t). It is found that the mean width of a peak in Rl(t), or a period of one elongation-contraction process of the chain, is proportional to the number of beads in the chain, M, while the mean period between two such adjacent peaks is independent of M for large M. These results, combined with the observation that the chain moves to the field direction by the distance proportional to M in each elongation-contraction motion, yield the saturation of mobility for large M. This explains the reason that CFGE cannot separate DNA according to their size L(∝M) for large L.
Brownian dynamics studies on DNA gel electrophoresis. II. “Defect” dynamics in the elongation-contraction motion
Authors: Azuma Ryuzo
Published: October 2002

By means of the Brownian dynamics (BD) method of simulations we have developed, we study the dynamics of individual DNA molecules which are undergoing constant field gel electrophoresis (CFGE), focusing on the relevance of the “defect” concept due to de Gennes in CFGE. The corresponding objects, which we call slack beads (s-beads), are explicitly introduced in our BD model. In equilibrium under a vanishing field, the distance between s-beads and their hopping range is found to be randomly distributed following a Poisson distribution. In strong fields, where a chain undergoes elongation-contraction motion, s-beads are observed to be alternately annihilated in elongation and created in the contraction of the chain. On the other hand, the distribution of hopping ranges of s-beads does not differ much from that in equilibrium. The results indicate that in the elongation-contraction motion of the chain, a large number of random movements of s-beads are involved. We have also confirmed that these features of s-beads agree qualitatively with those of s-monomers in the extended bond fluctuation model (EBFM) which we recently proposed. This agreement strongly supports the stochastic semilocal movement of s-monomers which we a priori introduced into the EBFM.
Monte Carlo simulation of low-noise avalanche photodiodes with heterojunctions
Authors: Ma F. , Wang S. , Li X. , Anselm K. A. , Zheng X. G. , Holmes A. L. , Campbell J. C.
Published: October 2002

A Monte Carlo model is developed to simulate avalanche photodiodes with AlGaAs/GaAs heterojunctions. The experimentally observed ultralow-noise behavior of a center-well avalanche photodiode is successfully reproduced in the model. It is found that the arrangement of different materials in the intrinsic region can modulate the positional dependence of impact ionization events, and hence the gain distribution. Consequently, the noise is sensitive to the structural parameters such as well thickness. Hot and energetic electrons are distinguished by their distribution in k space. This distinction is used to explain why the noise behavior is sensitive to the initial carrier excess energy from photogeneration but relatively insensitive to carrier energy gained from the electric field.
Vacuum ultraviolet surface photochemistry of water adsorbed on graphite
Authors: Baggott Simeon R. , Kolasinski Kurt W. , Perdigão Luı́s M. A. , Riedel Damien , Guo Quanmin , Palmer Richard E.
Published: October 2002

We report a study of the vacuum ultraviolet (VUV) surface photochemistry of H2O (D2O) films on a graphite substrate at 80 K. Experiments utilized a He discharge lamp to generate VUV photons. For 21 eV excitation, H+ (D+) is the only ionic fragment observed in desorption. When 41-eV photons are used, H+ (D+) is again observed: however, photochemically produced H3O+ (D3O+) is also detected. The ratio of D+ to D3O+ depends upon the water coverage. Furthermore, the D3O+ signal is larger than D+, whereas the H3O+ signal is smaller than H+ for irradiation of adsorbed D2O and H2O, respectively. At low coverages where the average coordination of water is also lower, D3O+ production is enhanced compared with higher coverages. The formation of D3O+ is attributed to the reaction of the photodissociation product D+ with adsorbed D2O. We suggest that the opening of the D3O+ product channel at 41 eV and its preponderance over D+ is related to the higher kinetic energy of, and consequently greater momentum transfer by, the D+ ions created through D2O photodissociation at this photon energy. We also suggest that there is a propensity for a hydrogen bonded O-D to break preferentially over a free O-D bond after photoexcitation.
Denucleation rates during Ostwald ripening: Distribution kinetics of unstable clusters
Authors: Madras Giridhar , McCoy Benjamin J.
Published: October 2002

During Ostwald ripening in vapor–liquid or liquid–solid systems, unstable clusters, which are smaller than the critical nucleus size, rapidly disappear. This denucleation process is distinct from the reversible dissolution of stable clusters that are larger than the critical size but are more soluble than larger clusters because of the Gibbs–Thomson effect. Thus, ripening involves larger clusters growing, smaller clusters shrinking, and unstable clusters rapidly disintegrating. We show how the denucleation rate can be estimated based on the appropriate cluster distribution dynamics (population balance) equations. Monomer addition and dissociation from an unstable cluster occur at rates determined by the energy profile, which is formulated with classical nucleation concepts. Effectively, the cluster loses free energy as monomers dissociate, and falls down the energy stair steps. Numerical results for the distribution dynamics equations reveal the influence of the minimum number of dimensionless parameters, and demonstrate that denucleation is very fast compared to the ripening rate.
Isomers of S2O: Infrared absorption spectra of cyclic S2O in solid Ar
Authors: Lo Wen-Jui , Wu Yu-Jong , Lee Yuan-Pern
Published: October 2002

Disulfur oxide (denoted as SSO) isolated in solid Ar at 13 K was irradiated with light at 308 nm from a XeCl excimer laser. New lines at 799.1 (797.0), 574.9, and 544.1 (545.6) cm−1, observed after photolysis, are assigned to cyclic S2O (denoted Cyc-S2O) with ∠S–O–S≅72.5±3.0° based on results of S34- and O18-isotopic experiments; lines in parentheses are associated with a minor matrix site and the broad line at 574.9 cm−1 may be deconvoluted to two lines at 575.4 and 574.6 cm−1. Secondary photolysis at 248 nm diminishes lines of cyc-S2O and produces SSO. Theoretical calculations using second-order Møller–Plesset theory with frozen core gradients and density-functional theories (Becke’s exchange functional with a correlation functional of Lee, Yang, and Parr) predict three stable isomers of S2O: cyc-S2O, SSO, and SOS, with the latter two having angular geometry. Relative energies, structures, vibrational wave numbers, and IR intensities were predicted for each isomer. According to calculations with Becke’s three-parameter exchange functional and the valence triplet-ζ basis set, cyc-S2O is bent with ∠S–O–S≅73.3° and has the S–S bond (2.058 Å) and both S–O bonds (1.724 Å) elongated relative to those of SSO (1.909 and 1.474 Å, respectively); it lies 41.3 kcal mol−1 above SSO. Isomer SOS, 62.0 kcal mol−1 greater in energy than SSO, has a S–O bond length 1.625 Å and ∠S–O–S≅128.5°. Calculated vibrational wave numbers, IR intensities, and isotopic shifts for cyc-S2O fit satisfactorily with experimental results. Two asymmetric transition states connecting SSO with SOS and cyc-S2O are characterized, yielding barriers for isomerization ∼104 and 122 kcal mol−1 (zero-point energy corrected), respectively. Photoconversion between angular SSO and cyc-S2O in a matrix cage is discussed. cyc-S2O might be responsible for some distinct features in thermal emission from the surface of Io, Jupiter’s moon.
Relationship between spatial resolution and noise in scanning superconducting quantum interference device microscopy
Authors: Chatraphorn S. , Fleet E. F. , Wellstood F. C.
Published: October 2002

An inverse transformation based on the fast Fourier transform can convert a two-dimensional image of the normal component of magnetic field into a corresponding image of the two-dimensional source currents that generated the field. Applying such a transformation to a magnetic image from a scanning Superconducting Quantum Interference Device (SQUID) microscope reveals that the spatial resolution s in the current image can be over 20 times better than that found in the raw magnetic field image, and up to about 5 times smaller than the SQUID sample separation z. We describe a quantitative theory for the noise and spatial resolution found in such current density images. We find that s is proportional to z and logarithmically related to the magnetic field noise in the image, the current applied to the sample, and the pixel size. We discuss the unusual functional dependence of these parameters and compare our theory to experimental data obtained from a scanning SQUID microscope. Finally, we describe how selective filtering in Fourier space can reduce noise and other artifacts in the current density images.
Simulation of pump–probe spectroscopy of a highly-charged diatomic molecule: Role of intermediate charged states and electronic and vibrational excitation in the multiple ionization of Cl2 and strong-field spectroscopy of Cl23+
Authors: Verver R. J. , Wright J. S. , Ivanov M. Yu.
Published: October 2002

This paper is a theoretical study of the effect of a pulsed ir laser on a neutral Cl2 molecule, leading to the creation of highly-charged molecular ions. We also develop a new quantum-mechanical model for the ionization of diatomic molecules in the tunneling regime. We consider the effects of the pump pulse duration and also the wavelength of the probe laser on the trication Cl23+ which is metastable, and consider how an experiment could be performed which would lead to the observation of its vibrational spectrum. The treatment considers nuclear wave packet dynamics which begin with vertical ionization from neutral Cl2 to Cl22+, includes dynamics arising from the intermediate charged state Cl22+, and electronic excitation and dissociation from the trication Cl23+. The dynamical simulations of a pump–probe experiment show modulated signals which can be Fourier-transformed to yield vibrational spectra. The quality of the modulated signal changes dramatically at an intermediate (relative to the vibrational period) pump pulse duration (at ca. 50 fs). Analysis of this effect shows how to maximize the probability of observing a simple vibrational spectrum for a highly charged diatomic created in a laser field.
Discovery of a new class of stable gas-phase dianions: Mixed oxygen–carbon cluster OCn2− (n=5–19)
Authors: Gnaser Hubert , Dreuw Andreas , Cederbaum Lorenz S.
Published: October 2002

Small doubly charged negative cluster ions OCn2− were studied both by experimental and by theoretical means. In the experiments these dianions (with n=5–19) were produced by sputtering of a graphite specimen with a 14.5 keV Cs+ ion beam at an elevated oxygen partial pressure in the vicinity of the sample’s surface. The dianions and the corresponding singly charged OCn− (n⩽21) ions as well as homonuclear carbon dianions Cn2− were detected in a double-focusing mass spectrometer. The yields of the doubly and singly charged mixed oxygen-carbon ions increase with the ratio of the O2 arrival rate to the Cs+ flux density. The abundance distribution of OCn2− exhibits distinct even–odd alternations with the number of C atoms in the molecule. The flight time through the mass spectrometer of ∼15–25 μs establishes a lower limit with respect to the intrinsic lifetimes of the doubly charged ions. The theoretical studies investigated OCn2− dianions with n=5–8; the geometries of these species were optimized and the electronic stability was examined by the calculation of the electron detachment energies. In agreement with the low yield observed experimentally, OC52− is found to be weakly stable, whereas OC62−, OC72−, and OC82− are electronically stable gas-phase ions. In particular the latter is characterized by a large number of stable isomers.
What to do about unpaired electrons? A hydrocarbon hexaradical with three Closs diradicals linked by 1,3,5-trimethylbenzene as ferromagnetic coupler
Authors: Schuurman Michael S. , Pak Chaeho , Schaefer Henry F.
Published: October 2002

The relative energies of a series of high-spin polyradical organic compounds were investigated using density functional methods. The system under study involved the linking of Closs’s triplet diradical units (1,3-cyclopentanediyl) 1,3,5 to benzene. By successively closing the diradical units to form bi-cylo[2.1.0]pentane substituents, one obtains in addition to the septet hexaradical, a quintet tetraradical, a triplet diradical, and the completely ring-closed singlet. The DZP/BP86 method predicts that the lowest-energy structure is the ring-closed singlet, with the diradical 21.5 kcal/mol, the tetraradical 41.9 kcal/mol, and hexaradical 61.8 kcal/mol higher in energy. Of particular note is the failure of the UHF method to predict even the qualitative ordering of these four species, placing the septet as the lowest-energy state and ring-closed singlet as the highest. For this reason, the BP86 results are taken as somewhat more reliable, given the absence of Hartree-Fock exchange in the hybrid B3LYP functional. Furthermore, a structural analysis of the optimized geometries, in addition to nuclear-independent chemical shift values, suggests that the unusual stability of these high-spin compounds as explained in terms of the delocalization of the adjacent radical(s) into the benzene π system.