bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Tonsillectomy and Adenoidectomy on Inattention and Impulsivity as Measured by the Test of Variables of Attention (TOVA) in Children with Obstructive Sleep Apnea Syndrome
Authors: Avior Galit , Fishman Gadi , Leor Agnes , Sivan Yakov , Kaysar Nehemia , DeRowe Ari
Published: October 2004

OBJECTIVE

To evaluate children with obstructive sleep apnea syndrome (OSAS) for features of attention deficit disorder (ADD) using an objective test of inattention and impulsivity: Test of Variables of Attention (TOVA) and then to determine whether tonsillectomy and adenoidectomy (T+A) results in an improvement in TOVA scores.

STUDY DESIGN AND SETTING

This study was a prospective interventional comparative trial in a tertiary care children's hospital. Nineteen children ages 5 to 14 years with OSAS, and otherwise healthy, with a clinical indication for T+A. Preoperative and 2 months postoperative OSA‐18, CBCL questionnaires, and TOVA scores were evaluated.

RESULTS

The preoperative TOVA scores were in the abnormal range in 12/19 (63%) of the children. The mean preoperative TOVA score was −2.9 (± 3.1). The mean postoperative TOVA score was −0.4 (±2.8). The improvement in the TOVA scores was significant (P < 0.0001, t‐test).

CONCLUSION

This preliminary data suggests that treatment of OSAS with T+A results in significant improvement in objective parameters of inattention and impulsivity.

SIGNIFICANCE

These findings may be important in understanding the impact of OSAS and therapeutic interventions on behavioral problems in children.
Mutant Nbs1 Enhances Cisplatin‐Induced DNA Damage and Cytotoxicity in Head and Neck Cancer
Authors: Tran Hao Mimi , Shi Guoli , Li Gouyan , Carney James P. , O'Malley Bert , Li Daqing
Published: October 2004

OBJECTIVE

Enhanced DNA double‐strand break (DSB) repair could be a primary cause for development of resistance in tumor cells to cisplatin, which induces crosslinks and DNA DSBs. A protein complex consisting of hMre11, hRad50, and Nbs1 (MRN) has been identified as a critical component in repair of DNA DSBs. The present study investigates whether the expression of a truncated form of Nbs1 interrupts the function of the MRN complex and therefore enhances cisplatin‐induced DNA damage and cytotoxicity in human head and neck squamous cell carcinoma (HNSCC).

METHODS AND MEASURES

Two human HNSCC cell lines, JHU006 and JHU029, were used. A dominant negative recombinant adenovirus expressing domains of Nbs1 was constructed. Adenovirus‐mediated mutant Nbs1 (Ad‐Nbs1) gene transfer was performed with replication‐defective virus (DL312) and no treatment as controls. Transgene expression and cell viability were evaluated in transfected cells. Neutral comet assay was performed and the “tail moment,” the product of the amount of DNA in the tail and the distance of tail migration, was analyzed for evaluating DNA DSB damage at 24, 48, and 72 hours.

RESULTS

Transgene expression of mutant Nbs1 was confirmed by Western blotting. Ad‐Nbs1 gene transfer significantly increased cisplatin‐induced cytotoxicity as shown by stunting of 6‐day growth curves. Neutral comet analysis revealed that the mean tail moment, indicative of DNA damage, was significantly elevated in cells treated with combined cisplatin and Ad‐Nbs1 compared to cisplatin alone in both cell lines.

CONCLUSIONS

Expression of mutant Nbs1 significantly increases cisplatin‐induced DNA DSBs and cytotoxicity. The increase in double‐strand DNA damage corresponds to the level of cytotoxicity in the different treatment groups and suggests that tumor chemosensitization occurs through augmentation of DNA DSBs.

CLINICAL SIGNIFICANCE

Alteration of DNA repair may provide a novel approach to enhancing sensitivity of HNSCC to chemotherapy. Our study supports the potential application of Ad‐Nbs1 in combination with cisplatin for treatment of advanced and metastatic HNSCC.
How Outbreaks of Infectious Disease are Detected: A Review of Surveillance Systems and Outbreaks
Authors: Dato Virginia , Wagner Michael M. , Fapohunda Abi
Published: October 2004

To learn how outbreaks of infectious disease are detected and to describe the entities and information systems that together function to identify outbreaks in the U.S., the authors drew on multiple sources of information to create a description of existing surveillance systems and how they interact to detect outbreaks. The results of this analysis were summarized in a system diagram. The authors reviewed a sample of recent outbreaks to determine how they were detected, with reference to the system diagram. The de facto U.S. system for detection of outbreaks consists of five components: the clinical health care system, local/state health agencies, federal agencies, academic/professional organizations, and collaborating governmental organizations. Primary data collection occurs at the level of clinical health care systems and local health agencies. The review of a convenience sample of outbreaks showed that all five components of the system participated in aggregating, analyzing, and sharing data. The authors conclude that the current U.S. approach to detection of disease outbreaks is complex and involves many organizations interacting in a loosely coupled manner. State and local health departments and the health care system are major components in the detection of outbreaks.
Factors Associated with Underimmunization at 3 Months of Age in Four Medically Underserved Areas
Authors: Bardenheier Barbara H. , Yusuf Hussain R. , Rosenthal Jorge , Santoli Jeanne M. , Shefer Abigail M. , Rickert Donna L. , Chu Susan Y.
Published: October 2004

Objective.

Risk factors for underimmunization at 3 months of age are not well described. This study examines coverage rates and factors associated with underimmunization at 3 months of age in four medically underserved areas.

Methods.

During 1997–1998, cross-sectional household surveys using a two-stage cluster sample design were conducted in four federally designated Health Professional Shortage Areas. Respondents were parents or caregivers of children ages 12–35 months: 847 from northern Manhattan, 843 from Detroit, 771 from San Diego, and 1,091 from rural Colorado. A child was considered up-to-date (UTD) with vaccinations at 3 months of age if documentation of receipt of diphtheria-tetanus-pertussis, polio, haemophilus influenzae type B, and hepatitis B vaccines was obtained from a provider or a hand-held vaccination card, or both.

Results.

Household response rates ranged from 79% to 88% across sites. Vaccination coverage levels at 3 months of age varied across sites: 82.4% in northern Manhattan, 70.5% in Detroit, 82.3% in San Diego, and 75.8% in rural Colorado. Among children who were not UTD, the majority (65.7% to 71.5% per site) had missed vaccines due to missed opportunities. Factors associated with not being UTD varied by site and included having public or no insurance, ⩾2 children living in the household, and the adult respondent being unmarried. At all sites, vaccination coverage among WIC enrollees was higher than coverage among children eligible for but not enrolled in WIC, but the association between UTD status and WIC enrollment was statistically significant for only one site and marginally significant for two other sites.

Conclusions.

Missed opportunities were a significant barrier to vaccinations, even at this early age. Practice-based strategies to reduce missed opportunities and prenatal WIC enrollment should be focused especially toward those at highest risk of underimmunization.
Entwicklungsveränderungen in Konformität und in kognitiven Folgen sozialer Beeinflussung
Authors: Schwarz Stefanie , Roebers Claudia M. , Schneider Wolfgang
Published: October 2004

Zusammenfassung. Die vorliegende Studie beschäftigt sich mit Entwicklungsveränderungen bei sozialer Beeinflussung sowie deren Auswirkungen auf die Erinnerungsleistung. 89 Kinder im Alter von 7 bis 8 und 9 bis 10 Jahren wurden nach einer Woche zum Inhalt eines Kinderfilms befragt. Im ersten Interview wurde die Erinnerungsleistung über offene Fragen ermittelt. Anschließend wurde die Stärke des sozialen Einflusses von irreführenden und richtig lenkenden Suggestionen zusätzlich durch die Anwesenheit und das Antwortverhalten einer Verbündeten der Interviewerin variiert. Am nächsten Tag wurde die suggestive Befragung ohne Verbündete wiederholt. Eine Kontrollgruppe durchlief beide suggestiven Befragungen ohne Verbündete. Es zeigten sich deutliche Alterseffekte in der Fähigkeit sozialer Beeinflussung zu widerstehen: Während 7- bis 8-Jährige noch durch Suggestionen sowie zusätzlich durch die Verbündete beeinflussbar waren, bestand bei 9- bis 10-Jährigen nur noch ein Einfluss der Verbündeten. Dies zeigte sich auch in altersspezifischen Unterschieden in den Nachwirkungen der Befragungssituation mit der Verbündeten auf die spätere Befragung ohne Verbündete.
Paradoxe Auswirkungen von Lob und Tadel:
Authors: Binser Martin J. , Försterling Friedrich
Published: October 2004

Zusammenfassung. Lob nach Erfolg und eine neutrale Reaktion nach Misserfolg können der Person, auf die dieses Verhalten gerichtet ist, nahe legen, dass die sanktionierende Person ihre Begabung als gering einschätzt. Dagegen können neutrale Reaktionen nach Erfolg und Tadel nach Misserfolg zur Annahme führen, dass man sich als begabt wahrgenommen fühlt (s. Meyer, 1992 ). In zwei Studien wurden Bedingungen solcher scheinbar paradoxen Auswirkungen von Lob und Tadel untersucht. Im ersten Experiment wurden Annahmen über die Ursachen und Gründe von Lob und Tadel erfasst. Lob und Tadel führt bei Individuen, die Sanktionsverhalten als Ausdruck von Sympathie betrachteten, seltener zu “paradoxen Auswirkungen“ als bei Personen, die Sanktionen als fähigkeitsthematisch einstuften. Studie 2 benutzte eine Priming-Prozedur. Versuchspersonen, die vor der Erfassung der Fähigkeitsperzeptionen mit einem Bild mit sozialer Thematik konfrontiert waren, zeigten seltener “paradoxe“ Fähigkeitseinschätzungen als Individuen, die sich vorausgehend mit einem leistungsthematischen Bild auseinandergesetzt hatten.
Arbeitsgedächtnis und Aufmerksamkeit bei Vorschulkindern mit gestörter und unauffälliger Sprachentwicklung
Authors: Janczyk Markus , Schöler Hermann , Grabowski Joachim
Published: October 2004

Zusammenfassung. Eine Beeinträchtigung der Funktionen der Phonologischen Schleife wurde bei der Untersuchung von Sprachentwicklungsstörungen und ihren Bedingungsfaktoren mehrfach nachgewiesen. Durch ein Doppelaufgaben-Experiment wird nun im Vergleich von sprachunauffälligen mit sprachentwicklungsgestörten Kindern untersucht, ob auch die Funktion der Zentralen Exekutive, Aufmerksamkeit zuzuteilen, beeinträchtigt ist. Die Ergebnisse weisen darauf hin, dass nur die Phonologische Schleife, nicht aber die Zentrale Exekutive eine Rolle bei Sprachentwicklungsstörungen spielt.
Der Zusammenhang von habitueller körperlicher Aktivität und Gesundheit:
Authors: Wagner Petra , Singer Roland , Woll Alexander , Tittlbach Susanne , Bös Klaus
Published: October 2004

Zusammenfassung. Vor dem Hintergrund effektiver Gesundheitsförderungsmaßnahmen ist die Beziehung von habitueller körperlicher Aktivität in verschiedenen Kontexten und Gesundheit bis heute ungeklärt. Auf der Datenbasis zweier Feldstudien an gesunden Erwachsenen wurde diese Beziehung unter Berücksichtigung einer differenzierten Erfassung der Aktivität in den Bereichen Sport, Freizeit und Arbeit sowie einer differenzierten Erfassung der Gesundheit mittels objektiver und subjektiver Parameter überprüft. Den Ergebnissen zufolge kovariiert habituelle körperliche Aktivität durchaus mit Gesundheit. Gleichwohl ist die aufgeklärte Varianz der Gesundheit insgesamt sehr gering, insbesondere wenn Personmerkmale wie Alter, Geschlecht und Schulabschluss berücksichtigt werden. Demgegenüber trägt körperliche Aktivität (über die drei Bereiche) immer zur Varianzaufklärung der betrachteten Gesundheitsindices bei. Das größte Gewicht kommt der Sportaktivität zu, auch unter Kontrolle von Personmerkmalen. Dabei zeigt sich zwischen Sporttreiben und subjektiver Gesundheit insgesamt eine lineare Beziehung. Körperliche Aktivität in Freizeit- und Arbeitsalltag haben deutlich weniger Gewicht im Hinblick auf Gesundheit. Weiterführende Analysen haben zu klären, inwieweit besondere Qualitäten der Aktivität in verschiedenen Settings von Bedeutung für die Gesundheit sind.
Interferometric meteor radar phase calibration using meteor echoes
Authors: Holdsworth David A. , Tsutsumi Masaki , Reid Iain M. , Nakamura Takuji , Tsuda Toshitaka
Published: October 2004

A technique for the phase calibration of interferometric meteor radar systems is presented. This technique uses phase differences of meteor echoes measured between spaced receiving antennas. The technique can be applied to data collected during routine observations, effectively allowing self phase calibration without the need for additional hardware or scheduled down time for off‐line phase calibration measurements. The technique can also be used to correct data collected using erroneous phase calibration estimates. Simulations of typical range and angle of arrival distributions are used to illustrate the technique and verify its performance. The results reveal that the phase offsets can be estimated to within 2° using realistic simulation parameters. The technique is also applied to data collected using the Buckland Park meteor radar, with the standard deviation of the daily phase offsets estimated over a four month period found to be less than 3°.
Surface temperature and spectral measurements at Santiaguito lava dome, Guatemala
Authors: Sahetapy‐Engel Steve T. M. , Flynn Luke P. , Harris Andrew J. L. , Bluth Gregg J. , Rose William I. , Matias Otoniel
Published: October 2004

An infrared thermometer, spectroradiometer and digital video camera were used to observe and document short‐term evolution of surface brightness temperature and morphology at Santiaguito lava dome, Guatemala. The thermometer dataset shows 40–70 minute‐long cooling cycles, each defined by a cooling curve that is both initiated and terminated by rapid increases in temperature due to regular ash venting. The average cooling rate calculated for each cycle range from 0.9 to 1.6°C/min. We applied a two‐component thermal mixture model to the spectroradiometer (0.4–2.5 μm) dataset. The results suggest that the observed surface morphology changed from a cool (120–250°C) crust‐dominated surface with high temperature fractures (>900°C) in the first segment of the measurement period to an isothermal surface at moderately high temperature (350–500°C) during the second segment. We attribute the change in the thermal state of the surface to the physical rearrangement of the dome's surface during the most energetic of the ash eruptions.
Nonlinear elongation of two-dimensional structures in electron temperature gradient driven turbulence
Authors: Gürcan Ö. D. , Diamond P. H.
Published: October 2004

The nonlinear evolution of the electron temperature gradient (ETG) driven mode can be described with a simple, two-dimensional reduced fluid model, similar to that used for the thermal Rossby wave system. Consistent with ballooning mode structure, primary instability drive with a strong anisotropy in wave number (i.e., ky≫kx) is considered for the inviscid limit of the ETG model. The amplitude equation, describing the initial envelope modulations of this system, is derived using reductive perturbation methods. The dynamics of the intensity field variance in radial and poloidal directions, i.e., the two diagonal elements of the covariance tensor), which follow from the amplitude equation, are investigated in an attempt to determine the basins of attraction for forming zonal flow and streamer secondary structures. It is found that the focusing (or diffracting) effect of Reynolds stress is essentially stronger in the radial direction than it is in the poloidal direction. Further analysis of the structure in the radially elongated limit of the amplitude equation yields interesting results, such as a poloidally localized sheared soliton solution. The approach used here is broadly applicable.
Charge exchange spectroscopy by Fabry–Pérot spectrometer in W7-AS
Authors: Yoshinuma M. , Ida K. , Baldzuhn J.
Published: October 2004

Charge exchange spectroscopy using a Fabry–Pérot spectrometer has been developed to study the dynamic of ion temperature and radial electric field in plasmas. A charge coupled device detecter with 80×80 pixels was used to gain the spectral resolution of the charge exchange spectroscopy system. This Fabry–Pérot charge exchange spectroscopy system has been applied to measure the ion temperature using the charge exchange line of carbon impurity with a time resolution of 5 ms for high density quasisteady discharges in W7-AS. The cold component due to the charge exchange reaction between the carbon impurity and thermal neutrals is subtracted from the change emission with the beam modulation technique
NSTX tangential divertor camera
Authors: Roquemore A. L. , Biewer Ted , Johnson D. , Zweben S. J. , Nishino Nobuhiro , Soukhanovskii V. A.
Published: October 2004

Strong magnetic field shear around the divertor x-point is numerically predicted to lead to strong spatial asymmetries in turbulence driven particle fluxes. To visualize the turbulence and associated impurity line emission near the lower x-point region, a new tangential observation port has been recently installed on NSTX. A reentrant sapphire window with a moveable in-vessel mirror images the divertor region from the center stack out to R∼80 cm and views the x-point for most plasma configurations. A coherent fiber optic bundle transmits the image through a remotely selected filter to a fast camera, for example, a 40 500 frames/s photron complementary metal-oxide-semiconductor camera. A gas puffer located in the lower inboard divertor will localize the turbulence in the region near the x-point. Edge fluid and turbulent codes UEDGE and BOUT will be used to interpret impurity and deuterium emission fluctuation measurements in the divertor.
New constraints for plasma diagnostics development due to the harsh environment of MJ class lasers (invited)
Authors: Bourgade J. L. , Allouche V. , Baggio J. , Bayer C. , Bonneau F. , Chollet C. , Darbon S. , Disdier L. , Gontier D. , Houry M. , Jacquet H. P. , Jadaud J. P. , Leray J. L. , Masclet-Gobin I. , Negre J. P. , Raimbourg J. , Villette B. , Bertron I. , Chevalier J. M. , Favier J. M. , Gazave J. , Gomme J. C. , Malaise F. , Seaux J. P. , Glebov V. Yu , Jaanimagi P. , Stoeckl C. , Sangster T. C. , Pien G. , Lerche R. A. , Hodgson E. R.
Published: October 2004

The design of plasma diagnostics for the future MJ class lasers (LMJ–Laser MégaJoule—in France or NIF—National Ignition Faciliy— in the USA) must take into account the large increased radiation field generated at the target and the effect on the diagnostics components. These facilities will focus up to 1.8 MJ ultraviolet laser light energy into a volume of less than 1 cm3 in a few nanoseconds. This very high power focused onto a small target will generate a large amount of x rays, debris, shrapnel, and nuclear particles (neutrons and gamma rays) if the DT fuel capsules ignite. Ignition targets will produce a million more of 14 MeV neutrons (1019 neutrons) by comparison with the present worldwide most powerful laser neutron source facility at OMEGA. Under these harsh environmental conditions the survivability goal of present diagnostic is not clear and many new studies must be carried out to verify which diagnostic measurement techniques, can be maintained, adapted or must be completely changed. Synergies with similar environment studies conducted for magnetic fusion diagnostic design for ITER facility are considered and must be enhanced.
The nonmetallicity of molybdenum clusters
Authors: Zhang Wenqin , Ran Xiaorong , Zhao Haitao , Wang Lichang
Published: October 2004

Molybdenum clusters consisting of 2–55 atoms were investigated using density functional theory calculations with a plane-wave basis set. The results show that the linear and planar molybdenum clusters have a strong tendency to form dimers. This tendency results in the formation of alternate short and long bonds within a linear cluster, in which the strength of these short bonds is covalent. Therefore, the linear and planar Mo clusters exhibit significant nonmetallic characteristics. Furthermore, the linear and planar Mo clusters show a strong even-odd effect in binding energy with the even-numbered clusters being more stable than their neighboring odd-numbered clusters. On the other hand, the even-odd effect in the energy gap between the highest occupied and the lowest unoccupied molecular orbitals, i.e., the HOMO-LUMO energy gap, for the linear and the planar clusters is different. The odd-numbered linear clusters and even-numbered planar clusters have larger HOMO-LUMO energy gaps than their corresponding neighboring clusters.
Structural and electronic properties of Sin, Sin+, and AlSin−1 (n=2–13) clusters: Theoretical investigation based on ab initio molecular orbital theory
Authors: Nigam Sandeep , Majumder Chiranjib , Kulshreshtha S. K.
Published: October 2004

The geometric and electronic structures of Sin, Sin+, and AlSin−1 clusters (2⩽n⩽13) have been investigated using the ab initio molecular orbital theory under the density functional theory formalism. The hybrid exchange-correlation energy function (B3LYP) and a standard split-valence basis set with polarization functions [6-31G(d)] were employed for this purpose. Relative stabilities of these clusters have been analyzed based on their binding energies, second difference in energy (Δ 2E) and fragmentation behavior. The equilibrium geometry of the neutral and charged Sin clusters show similar structural growth. However, significant differences have been observed in the electronic structure leading to their different stability pattern. While for neutral clusters, the Si10 is magic, the extra stability of the Si11+ cluster over the Si10+ and Si12+ bears evidence for the magic behavior of the Si11+ cluster, which is in excellent agreement with the recent experimental observations. Similarly for AlSin−1 clusters, which is isoelectronic with Sin+ clusters show extra stability of the AlSi10 cluster suggesting the influence of the electronic structures for different stabilities between neutral and charged clusters. The ground state geometries of the AlSin−1 clusters show that the impurity Al atom prefers to substitute for the Si atom, that has the highest coordination number in the host Sin cluster. The fragmentation behavior of all these clusters show that while small clusters prefers to evaporate monomer, the larger ones dissociate into two stable clusters of smaller size.
Photoelectron spectroscopy and density functional theory of puckered ring structures of Group 13 metal-ethylenediamine
Authors: Li Shenggang , Fuller Jason F. , Wang Xu , Sohnlein Bradford R. , Bhowmik Paragranjita , Yang Dong-Sheng
Published: October 2004

The ethylenediamine (en) complexes of Al, Ga, and In atoms were prepared in laser-vaporization supersonic molecular beams and studied with pulsed field ionization zero electron kinetic energy photoelectron spectroscopy and density functional theory. Several conformers of each metal complex are obtained by B3LYP calculations, and a five-membered cyclic structure is identified by combining the experimental measurements and theoretical calculations. Adiabatic ionization potentials, vibrational frequencies, and bond dissociation energies are determined for the ring structure. The ionization potentials of the Al, Ga, and In species are measured to be 32 784 (5), 33 324 (5), and 33 637 (7) cm−1, respectively, and metal-ligand dissociation energies of the ionic and neutral complexes are calculated to be 60.2/16.2 (Al+/Al), 55.5/13.0 (Ga+/Ga), and 50.0/11.4 (In+/In) kcal mol−1. Metal-ligand stretch and bend as well as a number of ligand-based vibrations are measured. Harmonic frequencies and anharmonicities of the M+-N (M=Al,Ga,In) stretch are determined for all three M+-en ions and the C-C-N bend of Ga+-en and In+-en. In comparison to monodentate methylamine, the bidentate binding of ethylenediamine leads to a significantly lower ionization potential and higher metal-ligand bond strength of the metal complexes.
Full aperture backscatter station measurement system on the National Ignition Facility
Authors: Bower D. E. , McCarville T. J. , Alvarez S. S. , Ault L. E. , Brown M. D. , Chrisp M. P. , Damian C. M. , DeHope W. J. , Froula D. H. , Glenzer S. H. , Grace S. E. , Gu K. , Holdener F. R. , Huffer C. K. , Kamperschroer J. H. , Kelleher T. M. , Kimbrough J. R. , Kirkwood R. , Kurita D. W. , Lee A. P. , Lee F. D. , Lewis I. T. , Lopez F. J. , MacGowan B. J. , Poole M. W. , Rhodes M. A. , Schneider M. B. , Sewall N. R. , Shimamoto F. Y. , Shiromizu S. J. , Voloshin D. , Warrick A. L. , Wendland C. R. , Young B. K.
Published: October 2004

A full aperture backscatter station (FABS) target diagnostic has been activated on the first four beams of the National Ignition Facility. FABS measures both stimulated Brillouin scattering and stimulated Raman scattering with a suite of measurement instruments. Digital cameras and spectrometers record spectrally resolved energy for both P and S polarized light. Streaked spectrometers measure the spectral and temporal behavior of the backscattered light. Calorimeters and fast photodetectors measure the integrated energy and temporal behavior of the light, respectively. This article provides an overview of the FABS measurement system and detailed descriptions of the diagnostic instruments and the optical path.
Hybrid atomistic-coarse-grained treatment of thin-film lubrication. II
Authors: Wu Z.-B. , Diestler D. J. , Zeng X. C.
Published: October 2004

A new hybrid atomistic-coarse-grained (HACG) treatment of reversible processes in multiple-scale systems involving fluid-solid interfaces was tested through isothermal-isobaric Monte Carlo simulations of the quasistatic shearing of a model two-dimensional lubricated contact comprising two planar Lennard-Jones solid substrates that sandwich a softer Lennard-Jones film. Shear-stress profiles (plots of shear stress Tyx versus lateral displacement of the substrates) obtained by the HACG technique, which combines an atomistic description of the interfacial region with a continuum description of regions well removed from the interface, are compared with “exact” profiles (obtained by treating the whole system at the atomic scale) for a selection of thermodynamic states that correspond to systematic variations of temperature, load (normal stress), film-substrate coupling strength, and film thickness. The HACG profiles are in excellent agreement overall with the exact ones. The HACG scheme provides a reliable description of quasistatic shearing under a wide range of conditions. It is demonstrated that the elastic response of the remote regions of the substrates can have a significant impact on the static friction profile (plot of maximum magnitude of Tyx versus load).
The acidity of tert-butyl alcohol in near- and supercritical water: A polarizable continuum approach
Authors: Jitariu Luminita C. , Masters Andrew J. , Hillier Ian H.
Published: October 2004

We use a polarizable continuum approach to study the acidity of tert-butyl alcohol in water at ambient, near-critical, and supercritical conditions. In the most straightforward calculation, the bare ionic species (the tert-butoxy anion and the hydronium cation) are placed in cavities surrounded by a dielectric continuum, using a dielectric constant corresponding to the state point. A second method is first to solvate these ions with a small number of explicit water molecules and then surround this cluster with the dielectric. This is the cluster-continuum approach. We discuss the advantages and disadvantages of these two schemes and we also discuss various ways in which the second method can be implemented. No method showed quantitative agreement with all available experimental results but the first, straightforward method was the most successful in predicting the correct trends. From both a numerical and a theoretical point of view, we believe this is the method of choice.
Water motion in reverse micelles studied by quasielastic neutron scattering and molecular dynamics simulations
Authors: Harpham Michael R. , Ladanyi Branka M. , Levinger Nancy E. , Herwig Kenneth W.
Published: October 2004

Motion of water molecules in Aerosol OT [sodium bis(2-ethylhexyl) sulfosuccinate, AOT] reverse micelles with water content w0 ranging from 1 to 5 has been explored both experimentally through quasielastic neutron scattering (QENS) and with molecular dynamics (MD) simulations. The experiments were performed at the energy resolution of 85 μeV over the momentum transfer (Q) range of 0.36–2.53 Å−1 on samples in which the nonpolar phase (isooctane) and the AOT alkyl chains were deuterated, thereby suppressing their contribution to the QENS signal. QENS results were analyzed via a jump-diffusion/isotropic rotation model, which fits the results reasonably well despite the fact that confinement effects are not explicitly taken into account. This analysis indicates that in reverse micelles with low-water content (w0=1 and 2.5) translational diffusion rate is too slow to be detected, while for w0=5 the diffusion coefficient is much smaller than for bulk water. Rotational diffusion coefficients obtained from this analysis increase with w0 and are smaller than for bulk water, but rotational mobility is less drastically reduced than translational mobility. Using the Faeder/Ladanyi model [J. Phys. Chem. B 104, 1033 (2000)] of reverse micelle interior, MD simulations were performed to calculate the self-intermediate scattering function FS(Q,t) for water hydrogens. Comparison of the time Fourier transform of this FS(Q,t) with the QENS dynamic structure factor S(Q,ω), shows good agreement between the model and experiment. Separate intermediate scattering functions FSR(Q,t) and FSCM(Q,t) were determined for rotational and translational motion. Consistent with the decoupling approximation used in the analysis of QENS data, the product of FSR(Q,t) and FSCM(Q,t) is a good approximation to the total FS(Q,t). We find that the decay of FSCM(Q,t) is nonexponential and our analysis of the MD data indicates that this behavior is due to lower water mobility close to the interface and to confinement-induced restrictions on the range of translational displacements. Rotational relaxation also exhibits nonexponential decay. However, rotational mobility of O-H bond vectors in the interfacial region remains fairly high due to the lower density of water-water hydrogen bonds in the vicinity of the interface.
Multiscale quantum propagation using compact-support wavelets in space and time
Authors: Wang Haixiang , Acevedo Ramiro , Mollé Heather , Mackey Jeffrey L. , Kinsey James L. , Johnson Bruce R.
Published: October 2004

Orthogonal compact-support Daubechies wavelets are employed as bases for both space and time variables in the solution of the time-dependent Schrödinger equation. Initial value conditions are enforced using special early-time wavelets analogous to edge wavelets used in boundary-value problems. It is shown that the quantum equations may be solved directly and accurately in the discrete wavelet representation, an important finding for the eventual goal of highly adaptive multiresolution Schrödinger equation solvers. While the temporal part of the basis is not sharp in either time or frequency, the Chebyshev method used for pure time-domain propagations is adapted to use in the mixed domain and is able to take advantage of Hamiltonian matrix sparseness. The orthogonal separation into different time scales is determined theoretically to persist throughout the evolution and is demonstrated numerically in a partially adaptive treatment of scattering from an asymmetric Eckart barrier.
A mass spectrometric and density functional study of the intermetallic molecules AuBe, AuMg, and AuCa
Authors: Balducci G. , Ciccioli A. , Gigli G.
Published: October 2004

The intermetallic molecules AuBe and AuCa were identified by means of the Knudsen-Effusion Mass Spectrometry technique in the high-temperature vapors produced by vaporizing Au-Be-Ca alloys of proper composition. The gaseous equilibria AuBe(g)+Au(g)=Au2(g)+Be(g) and AuCa(g)+Au(g)=Au2(g)+Ca(g) were studied in the temperature ranges 1720–1841 K and 1669–1841 K, respectively, by monitoring the partial pressures of all the species involved. The equilibrium data were analyzed by the third-law method, obtaining for the first time the dissociation energy D0∘ of the two intermetallic species: D0∘(AuBe)=234.0±4.0 kJ/mol; D0∘(AuCa)=246.7±4.0 kJ/mol. These values are significantly higher than the recently published D0∘ of the species AuMg (175.4±2.7 kJ/mol). Furthermore, the ionization energies (IE) of AuBe, AuMg, and AuCa were obtained by measuring the electron impact ionization efficiency curves, IE(AuBe)=7.5±0.3 eV, IE(AuMg)=6.7±0.3 eV, and IE(AuCa)=5.5±0.3 eV. Theoretical calculations were also carried out for these species by density functional theory methods (PW91 and BP86) used in conjunction with Stuttgart relativistic effective core potentials. Both functionals were found to perform very well in reproducing experimental D0∘, IE, and molecular parameters.
Finite concentration effects on diffusion-controlled reactions
Authors: Senapati Sanjib , Wong Chung F. , McCammon J. Andrew
Published: October 2004

The algorithm by Northrup, Allison, and McCammon [J. Chem. Phys. 80, 1517 (1984)] has been used for two decades for calculating the diffusion-influenced rate-constants of enzymatic reactions. Although many interesting results have been obtained, the algorithm is based on the assumption that substrate–substrate interactions can be neglected. This approximation may not be valid when the concentration of the ligand is high. In this work, we constructed a simulation model that can take substrate–substrate interactions into account. We first validated the model by carrying out simulations in ways that could be compared to analytical theories. We then carried out simulations to examine the possible effects of substrate–substrate interactions on diffusion-controlled reaction rates. For a substrate concentration of 0.1 mM, we found that the diffusion-controlled reaction rates were not sensitive to whether substrate–substrate interactions were included. On the other hand, we observed significant influence of substrate–substrate interactions on calculated reaction rates at a substrate concentation of 0.1M. Therefore, a simulation model that takes substrate–substrate interactions into account is essential for reliably predicting diffusion-controlled reaction rates at high substrate concentrations, and one such simulation model is presented here.
Triplet instability in doublet systems
Authors: Szalay Péter G. , Vázquez Juana , Simmons Chris , Stanton John F.
Published: October 2004

Some problems associated with unrestricted wave functions for open-shell molecules are discussed in the contest of coupled-cluster calculation of molecular properties. Particular attention is given to a phenomenon akin to the “triplet instability” of closed-shell molecules, where the approximate spin pairing of a nominal pair of electrons in the unrestricted Hartree-Fock wave function begins to give way to significant spin polarization. This problem—which gives rise to pronounced spin contamination—is discussed from the point of view of orbital instability and occupation numbers of the charge density matrix. The onset, rather than the magnitude of the spin contamination is analyzed in detail for diatomics, especially heteronuclear cases where the transition to significant spin contamination does not occur discontinuously. It is shown that the qualitative description of this phenomenon satisfactorily explains anomalous results for NO and PO, although the magnitude of spin contamination in these molecules is significantly less than in other cases where anomalous results are not observed. It appears that calculations of equilibrium molecular properties using coupled-cluster methods based on unrestricted Hartree-Fock reference should be monitored carefully for any molecule containing a multiple bond, especially when the bonded pair of atoms appear in different rows of the periodic table.
Evolution spectrum of C60 isomers in buffer gas
Authors: Li Peng , Ning Xi-Jing
Published: October 2004

The energy spectrum of C60 nonclassic fullerenes with single heptagon defects calculated by Brenner empirical potential is found to submerge into the spectrum of classic fullerenes. Geometry analysis indicates that these nonclassic fullerene isomers can be more attainable than classic fullerenes at higher Stone-Wales (SW) stacks. Molecular dynamic simulations of the C60 isomer evolution in He buffer gas at 2500 K demonstrate that nonclassic fullerenes, especially those with heptagon defects, play an important role in the dynamics of C60 annealing, and that the Stone-Wales stack-by-stack transition mainly occurs at lower SW stacks. A non-SW multistep rearrangement is first observed in the simulation with its transition sequence and intermediate state presented in detail.
Competitive interaction between two different spherical sinks
Authors: McDonald Nyrée , Strieder William
Published: October 2004

Competitive interactions within diverse mixed populations of chemically active sites are prevalent throughout nature, science, and engineering. Their effects are readily seen in the distribution of dead and surviving aerobic cells within a thick biofilm and particle shape changes during the growth and coarsening of crystals. Even in the most dilute case, competition for a reactant requires at least two spheres/cells, and the solution of the two-spherical sink problem is of interest for several reasons. The solution accurately describes lower cell concentration behavior (108 cells/l), and like the Smoluchowski diffusion-reaction treatment for a single sphere, the analysis is extremely helpful in understanding the fundamental phenomena of the effect on the first spherical sink of the presence of a second different spherical sink. In addition these exact solutions are required for the systematic extension to higher density behavior by rigorous expansions in the spherical sink densities. The method of the twin spherical expansion is used with a formal matrix elimination scheme to generate an exact solution for two distinct spherical sinks of differing sizes and kinetics. The two sinks exist in a medium, which supplies a reactant to the sinks via Fickian diffusion. The two sinks compete for the same reactant with different first-order reactions occurring at the surface of each sink. Earlier work focused on two spherical sinks of the same size with identical surface reaction kinetics. This work has been advanced to allow for diversity in the theory of cellular or reactive sink competition. A number of interesting higher order interactive phenomena are observed in this paper when the different reactive sinks are in close proximity.
Quantum-classical limit of quantum correlation functions
Authors: Sergi Alessandro , Kapral Raymond
Published: October 2004

A quantum-classical limit of the canonical equilibrium time correlation function for a quantum system is derived. The quantum-classical limit for the dynamics is obtained for quantum systems comprising a subsystem of light particles in a bath of heavy quantum particles. In this limit the time evolution of operators is determined by a quantum-classical Liouville operator, but the full equilibrium canonical statistical description of the initial condition is retained. The quantum-classical correlation function expressions derived here provide a way to simulate the transport properties of quantum systems using quantum-classical surface-hopping dynamics combined with sampling schemes for the quantum equilibrium structure of both the subsystem of interest and its environment.
Decay of correlation functions in hard-sphere mixtures: Structural crossover
Authors: Grodon C. , Dijkstra M. , Evans R. , Roth R.
Published: October 2004

We investigate the decay of pair correlation functions in a homogeneous (bulk) binary mixture of hard spheres. At a given state point the asymptotic decay r→∞ of all three correlation functions is governed by a common exponential decay length and a common wavelength of oscillations. Provided the mixture is sufficiently asymmetric, size ratios q≲0.7, we find that the common wavelength reflects either the size of the small or that of the big spheres. By analyzing the (complex) poles of the partial structure factors we find a sharp structural crossover line in the phase diagram. On one side of this line the common wavelength is approximately the diameter of the smaller sized spheres whereas on the other side it is approximately the diameter of the bigger ones; the wavelength of the longest ranged oscillations changes discontinuously at the structural crossover line. Using density functional theory and Monte Carlo simulations we show that structural crossover also manifests itself in the intermediate range behavior of the pair correlation functions and we comment on the relevance of this observation for real (colloidal) mixtures. In highly asymmetric mixtures, q⩽0.1, where there is metastable fluid-fluid transition, we find a Fisher-Widom line with two branches. This line separates a region of the phase diagram where the decay of pair correlations is oscillatory from one in which it is monotonic.
Phonons in suspensions of hard sphere colloids: Volume fraction dependence
Authors: Kriegs H. , Petekidis G. , Fytas G. , Penciu R. S. , Economou E. N. , Schofield A. B.
Published: October 2004

The propagation of sound waves in suspensions of hard sphere colloids is studied as a function of their volume fraction up to random close packing using Brillouin light scattering. The rich experimental phonon spectra of up to five phonon modes are successfully described by theoretical calculations based on the multiple scattering method. Two main types of phonon modes are revealed: Type A modes are acoustic excitations which set up deformations in both the solid (particles) and the liquid (solvent) phases; for type B modes the stress and strain are predominantly localized near the interface between the solid particles and the surrounding liquid (interface waves). While the former become harder (increase their effective sound velocity) as the particle volume fraction increases the latter become softer (the corresponding sound velocity decreases).
Density functional theory for hyperfine coupling constants with the restricted-unrestricted approach
Authors: Rinkevicius Zilvinas , Telyatnyk Lyudmyla , Vahtras Olav , Ågren Hans
Published: October 2004

This work presents derivation, implementation, and the first applications of the restricted-unrestricted approach based on restricted Kohn-Sham formalism for evaluation of hyperfine coupling constants. By using the spin-restricted Kohn-Sham method the well-known spin contamination problem existing in the unrestricted Kohn-Sham formalism is avoided and a proper description of spin polarization is achieved via the restricted-unrestricted approach without introducing spin contamination into the evaluation of the hyperfine coupling constants. The performance of the proposed formalism is evaluated for a set of organic radicals and transition metal compounds. The results of this investigation indicate promising accuracy of the restricted-unrestricted approach for calculation of the isotropic hyperfine coupling constants in organic radicals as well as transition metal compounds.
Green’s function formalism coupled with Gaussian broadening of discrete states for quantum transport: Application to atomic and molecular wires
Authors: Tada Tomofumi , Kondo Masakazu , Yoshizawa Kazunari
Published: October 2004

A Green’s function formalism incorporating broadened density of states (DOS) is proposed for the calculation of electrical conductance. In cluster-molecule-cluster systems, broadened DOS of the clusters are defined as continuous DOS of electrodes and used to calculate Green’s function of electrodes. This approach combined with density functional theory is applied to the electrical transmission of gold atomic wires and molecular wires consisting of benzene-1,4-dithiolate, benzene-1,4-dimethanethiolate, 4,4′-bipyridine, hexane dithiolate, and octane dithiolate. The B3LYP, B3PW91, MPW1PW91, SVWN, and BPW91 functionals with the LANL2DZ, CEP, and SDD basis sets are employed in the calculation of conductance. The width parameter was successfully determined to reproduce the quantum unit of conductance 2e2/h in gold atomic wires. The combination of the B3LYP hybrid functional and the CEP-31G basis set is excellent in reproducing measured conductances of molecular wires by Tao et al. [Science 301, 1221 (2003); J. Am. Chem. Soc. 125, 16164 (2003); Nano Lett. 4, 267 (2004)].
Kinetics of polymer translocation through a pore
Authors: Matsuyama Akihiko
Published: October 2004

We theoretically study kinetics of a polymer threading through a pore embedded in a flat membrane. We numerically solve three coupled kinetic equations for the number n1 of polymer segments in one side of the membrane and expansion factors of the polymer chain in each side of the membrane. We find the time evolution n1∝t1/(1+ν) at late stages and the translocation time τt is scaled as τt∝n1+ν for large number n of the polymer segments, where ν is the effective size exponent of the radius of gyration of the polymer. When the polymer is translocated into a region with a good solvent condition (ν=3/5), we obtain n1∝t5/8 and τt∝n8/5.
Theoretical study of the local structure and Raman spectra of CaO-SiO2 binary melts
Authors: Wu Yong Quan , Jiang Guo Chang , You Jing Lin , Hou Huai Yu , Chen Hui , Xu Kuang Di
Published: October 2004

A procedure for the Raman spectra calculation of vitreous and molten silicates was presented in this paper. It includes molecular dynamics MD simulation for the generation of equilibrium configurations, Wilson’s GF matrix method for the calculations of eigenfrequencies and corresponding vectors, electro-optical parameters method (EOPM) for the Raman intensity calculations, and the bond polarizability model (BPM) for the determination of polarizability and polarizability derivative. One of the most important characteristics of this procedure is the achievement of the partial Raman spectra of five tetrahedral units, as well as the total spectral envelope. In this paper, the calculation was carried out for the vitreous and molten calcium silicates with different compositions and at various temperatures. It is worthwhile to note that the calculation is based on statistical configurations distribution in the space and so it is not needed to artificially adjust the full width at half maximum (FWHM) of spectra. It was also tested through the good agreement of the calculated spectra with the experimental, including some regularity of spectral properties. According to the calculation, the symmetrical stretching of whole tetrahedral units, to which the stretching of Si-Onb bond gives the main contribution to intensity, is proven to be the dominance in the high-frequency range (800–1200 cm−1) and the symmetrical bending of Si-Ob-Si, to which the stretching of Si-Ob bond exhibits the main contribution, is the dominance in the medium-frequency range (400–700 cm−1). As the first theoretical results, the Raman scattering coefficient of each Qi was found little change along with the variation of composition and temperature.
Comment on “Postnucleation droplet growth in supersaturated gas with arbitrary vapor concentration” [J. Chem. Phys. 120, 10455 (2004)]
Authors: Vesala Timo , Kulmala Markku , Wagner Paul E.
Published: October 2004

We provide the overview of the papers dealing with the growth of the liquid droplet. The purpose is to put the paper “Postnucleation droplet growth in supersaturated gas with arbitrary vapor concentration” [V. Pines, M. Zlatkowski, and A. Chait, J. Chem. Phys. 120, 10455 (2004)] in the right historical context. The original paper and this comment point the correct condensation formula to the atmospheric science community.