bluuebunny/crossref_metadata_2025 huggingface dataset:
Cross‐Linked Hyaluronan‐Coated Stents in the Prevention of Airway Stenosis
Authors: Sondrup Cole , Liu Yanchun , Shu Xiao Zheng , Prestwich Glenn D. , Smith Marshall E.
Published: July 2006

OBJECTIVE

This project studies the use of airway stents coated with a cross‐linked derivative of hyaluronan (HA) in a rabbit airway model of subglottic stenosis (SGS).

STUDY DESIGN AND SETTING

An acute subglottic mucosal injury and airway stent placement design were used in a rabbit model. Thirty‐six rabbits were randomized to 6 different study groups. Four groups had the subglottic mucosa denuded at the cricoid, and 2 groups received no injury. Airway stents coated with Carbylan‐SX, a cross‐linked derivative of HA, and controls were placed for 3 weeks. After sacrifice at 6 weeks, morphometric measurements of subglottic lumen were taken.

RESULTS

In posttraumatic models, no significant differences were seen in airway area measures between groups (P = 0.86). In non‐injury groups, a significant difference between Carbylan‐SX versus non—HA‐derivative‐coated stents was seen (P = 0.05).

CONCLUSION

In this model of acute subglottic mucosal injury, the HA‐derivative—coated stent did not improve healing. However, in the absence of mucosal injury, the Carbylan‐SX film—coated stent yielded significantly larger airway areas compared with a noncoated stent.

SIGNIFICANCE

Stents or endotracheal tubes coated with a cross‐linked derivative of HA may prevent stenosis in patients without airway injury but require long‐term intubation or laryngotracheal stenting.
Reanimation of Paralyzed Laryngeal Muscles by Electrical Stimulation Synchronized with Inspiration
Authors: Chi Fang‐Lu , Jing Jiang‐Hua , Dai Chun‐Fu
Published: July 2006

OBJECTIVE

To determine the effects of electrical stimulation on denervated cat posterior cricoarytenoid (PCA) muscle.

STUDY DESIGN AND SETTING

This study was conducted on six cats with PCA muscle denervation. All animals were sacrificed 12 weeks after surgery and the glottal area in the live animals and the fiber diameters of PCA muscle were obtained.

RESULTS

Signals synchronized with inspiration were recorded and transmitted to stimulate PCA muscle. The abduction of the paralyzed vocal cord during inspiration was observed; this allows enough flow of air through the larynx to maintain the respiration. The stimulated fiber diameters of PCA muscle were different from that of nonstimulated (P< 0.01). Although all denervated muscles were degenerated, electrical stimulation was used to prevent muscular atrophy.

CONCLUSIONS

This study indicates that electrical stimulation of the PCA muscle synchronized with inspiration could restore the abduction of a paralyzed vocal cord and prevent the denervated muscles from atrophying.

SIGNIFICANCE

Electrical stimulation synchronized with inspiration may lead to reanimation of paralyzed laryngeal muscles.
Treatment of Pediatric Suppurative Mastoiditis: Is Peripherally Inserted Central Catheter (PICC) Antibiotic Therapy Necessary?
Authors: Jeremy A. Moore , Julie L. Wei , Holly J. Smith , Matthew S. Mayo
Published: July 2006

OBJECTIVE

A review of the treatment of pediatric acute mastoiditis requiring surgical intervention managed with and without PICC therapy postoperatively.

STUDY DESIGN AND SETTING

Retrospective study of 42 cases from 1989 to 2004 treated at a regional children's hospital.

RESULTS

Sixteen patients received postoperative PICC therapy and 26 received a course of oral antibiotics. The PICC group received on average 12.12 days of intravenous antibiotics compared to only 3.53 days for the non‐PICC group (P < 0.001). No differences were observed between the two groups in treatment outcomes. One patient from each group required rehospitalization. One minor complication was experienced in a patient in the PICC group. There were no surgical complications. The total cost for outpatient PICC therapy increased treatment costs by approximately $1500 to $2500.

CONCLUSIONS

Oral antibiotic therapy is sufficient after surgical intervention for acute pediatric suppurative mastoiditis without intracranial complications and does not result in adverse treatment outcome.

SIGNIFICANCE

Use of PICC therapy after surgical intervention for mastoiditis should be limited.

EBM rating: B‐3b
Post—Tympanostomy Tube Otorrhea: A Meta‐Analysis
Authors: Hochman Jordan , Blakley Brian , Abdoh Ahmed , Aleid Hazim
Published: July 2006

INTRODUCTION

Post—tympanostomy tube otorrhea is the most common complication of tympanostomy tube placement. The incidence of this problem varies from 3.4% to 74%. Trials that study post—tympanostomy tube otorrhea may involve valid randomization “by patient” or “by ear.” In an attempt to define “best practice,” we conduct a meta‐analysis to quantify the benefit of using topical prophylactic antibiotic drops in the postoperative period. We then compare our findings with previous results found in the literature.

METHODS

We selected randomized studies for which antibiotic drops had been used for at least 48 hours after tympanostomy tube insertion. Nine studies, 3 “by ear” and 6 “by patient,” met our inclusion criteria. The odds ratio and 95% confidence intervals were calculated for each to conduct the meta‐analysis.

RESULTS

Overall, prophylaxis appears to be effective at reducing the incidence of post—tympanostomy tube otorrhea. The odds ratios for all studies were less than 1.0. However, none of the 3 “by ear” studies and only 3 of the 6 “by patient” studies were statistically significant. The mean odds ratio was 52%, suggesting that prophylaxis may reduce the incidence of post—tympanostomy tube otorrhea by half.

CONCLUSION

This meta‐analysis suggests that routine post—tympanostomy tube prophylaxis is beneficial, but this finding is dependent on selection criteria used.

EBM rating: A‐1a
Hyperostosis May Affect Prognosis after Primary Endoscopic Sinus Surgery for Chronic Rhinosinusitis
Authors: Hyo Yeol Kim , Hun‐Jong Dhong , Hyun Jong Lee , Young‐Jun Chung , Yoo Jeong Yim , Jae‐Won Oh , Seung‐Kyu Chung , Hyung Jin Kim
Published: July 2006

OBJECTIVE

To investigate the independent effect of hyperostosis on outcome after endoscopic sinus surgery (ESS) in patients with chronic rhinosinusitis (CRS).

STUDY DESIGN AND SETTING

The medical records of 81 consecutive patients who had undergone primary ESS for CRS were reviewed retrospectively. Sinus CT scans were evaluated for the presence of hyperostosis to investigate the association with postoperative outcomes. The independent effect of hyperostosis on surgical outcome was analyzed, controlling for possible confounding factors with a multiple logistic regression model.

RESULTS

Sixty percent of the patients showed hyperostosis, and there was a statistically significant association between the hyperostosis and postoperative outcome (P = 0.035, χ2 test), which was confirmed after adjustment for the possible confounding factors (P = 0.048, odds ratio [OR] = 3.19, logistic regression analysis).

CONCLUSIONS

Our study suggests that patients with CRS who have hyperostosis may have a poorer surgical outcome than those without hyperostosis.

EBM rating: B‐2b
Outpatient Tonsillectomy in Children: A Systematic Review
Authors: Brigger Matthew T. , Brietzke Scott E.
Published: July 2006

OBJECTIVE

To evaluate the level of evidence regarding the safety of outpatient pediatric tonsillectomy.

STUDY DESIGN AND SETTING

The medical literature addressing outpatient pediatric tonsillectomy was systematically reviewed. The level of evidence was assessed, and data were pooled.

RESULTS

Seventeen articles met inclusion criteria. Each article suggested that outpatient tonsillectomy was safe. The overall level of evidence was fair (grade B —). Pooled data analysis in the perioperative period showed a complication rate estimate of 8.8% (95% confidence interval [CI], 5.5%–12.1%; P ≤ 0.001) and an unplanned admission rate estimate of 8.0% (95% CI, 5.3%‐10.7%; P ≤ 0.001). Subgroup analysis suggests that children under age 4 are at a higher risk of complications in the perioperative period with an odds ratio of 1.64 (95% CI, 1.16–2.31).

CONCLUSION

The level of evidence supporting the safety of outpatient pediatric tonsillectomy is fair. The analyzed data show a higher rate of early complications and unplanned admissions in children under age 4.

SIGNIFICANCE

The current evidence supports the practice of outpatient tonsillectomy in properly selected children.

EBM rating: A‐1a
Quality of Life and Complications Following Image‐Guided Endoscopic Sinus Surgery
Authors: Abtin Tabaee , Amy K. Hsu , Mark G. Shrime , Scott Rickert , Lanny Garth Close
Published: July 2006

OBJECTIVES

To compare the quality of life (QOL) outcome and incidence of complications following image‐guided versus non–image‐guided endoscopic sinus surgery (ESS).

STUDY DESIGN

The operative, office, and hospital charts of patients who underwent primary ESS for chronic sinusitis by a single surgeon with (2002–2005) or without (1997–2002) image guidance were reviewed for patient demographics, incidence of complications, and revision procedures. A telephone survey was used to administer the QOL survey to both cohorts.

RESULTS

In comparing patients who underwent image‐guided (60) versus non–image‐guided surgery (179), respectively, there was no statistically significant difference in the incidence of major intraoperative complications (6.6% vs 5.6%), major postoperative complications (5% vs 3.9%), revision procedures (6.6% vs 7.3%), and postoperative SNOT‐20 symptom scores (23.6 vs 23.4). A higher incidence of intraoperative cerebrospinal fluid leak was noted in the non–image‐guided group (0% vs 2.2%).

CONCLUSIONS

Our study does not demonstrate an improvement in the incidence of complications, need for revision procedures, or quality‐of‐life outcome for patients undergoing primary ESS for chronic sinusitis. The use of image guidance may result in a lower incidence of skull base trauma and cerebrospinal fluid leak.

EBM rating: B‐2b
Passive Smoke Exposure as a Risk Factor for Airway Complications during Outpatient Pediatric Procedures
Authors: Jones Dwight T. , Bhattacharyya Neil
Published: July 2006

OBJECTIVE

Determine if passive smoke exposure (PSE) increases airway complications during outpatient mask anesthesia procedures in children.

METHODS

A prospective cohort of children who underwent surgical procedures under mask anesthesia was studied with the American Thoracic Society children's questionnaire on environmental and respiratory factors. Double‐blinded outcomes with respect to adverse airway events were recorded both intraoperatively and in the recovery room for patients with and without passive smoke exposure. Multivariate comparisons assessing the likelihood of these airway complications were conducted between the PSE and nonexposed groups.

RESULTS

Of 405 children, 168 (41.5%) had PSE. The incidence of airway complications during anesthesia or postanesthetic recovery was higher for all outcome measures for PSE children (all P ≤ 0.005), except for recovery room breath holding (P = 0.086). Intraoperative laryngospasm and airway obstruction were 4.9 and 2.8 times more likely with PSE, respectively.

CONCLUSIONS

PSE significantly increases the risk of anesthesia‐related airway complications during outpatient pediatric procedures.

EBM rating: A‐1b
The Role of Gastric Helicobacter Pylori Infection in Laryngopharyngeal Reflux Disease
Authors: Ercan İIbrahim , Çakir Burak Ömür , Uzel Tulin Çentürk , Sakiz Damlanur , Karaca Çetin , Turgut Suat
Published: July 2006

OBJECTIVES

To investigate the role of Helicobacter pylori (H pylori) infection in laryngopharyngeal reflux (LPR).

STUDY DESIGN

A prospective multidisciplinary clinical study.

METHODS

Forty‐four adult patients who applied to our ENT clinic with LPR symptoms were evaluated. Then these patients underwent upper gastrointestinal system endoscopy and double probe pH monitoring. In addition, during the endoscopy multiple biopsies from the stomach were obtained to detect H pylori.

RESULTS

Results from 32 LPR positive patients were assessed (10 male and 22 female). There were no statistically significant differences between the presence of H pylori and sex, age, degree of gastritis and esophagitis, and also the number of reflux, fractional acid exposure time regarding proximal probe readings. Similarly for both proximal and distal probe readings, the average score of esophageal acid clearance was not statistically significant (P > 0.05). In addition, no statistically significant difference was found between the presence of H pylori and GERD (P > 0.05).

CONCLUSIONS

The results of this study demonstrated that there is no relationship between gastric H pylori infection and LPR.

EBM rating: B‐3b
Testgüte einer deutschsprachigen Version der Mehrdimensionalen Perfektionismus Skala von Frost, Marten, Lahart und Rosenblate (MPS-F)
Authors: Altstötter-Gleich Christine , Bergemann Niels
Published: July 2006

Zusammenfassung. Es wird eine deutschsprachige Version der Multidimensional Perfectionism Scale (MPS-F) von Frost, Marten, Lahart und Rosenblate (1990) vorgestellt. An einer Stichprobe von 1170 Personen wurden die faktorielle Validität und die internen Konsistenzen der sechs Subskalen ermittelt, wobei verschiedene Strukturannahmen verglichen wurden. Es ergab sich ein akzeptabler Fit für ein Modell mit sechs korrelierenden Faktoren, deren Skalen befriedigende bis gute interne Konsistenzen aufweisen. Anhand zweier theoretisch begründeter und in der vorliegenden Forschung eingesetzter Kriteriumsvariablen - Depressivität und gute vs. schlechte Stimmung - wurden an einer Teilstichprobe (N = 270) die Kriteriums- und die inkrementelle Validitäten der Skalen ermittelt. Drei Subskalen waren zufrieden stellend kriteriumsvalide (Hohe Standards, Fehlersensibilität, Leistungsbezogene Zweifel), drei nicht (Organisiertheit, Erwartungen der Eltern, Kritik durch Eltern). An einer weiteren Stichprobe (N = 387) wurde ein ebenfalls theoretisch und empirisch begründetes Prozessmodell geprüft, das den mediierenden Effekt von aktivem Coping und dem Erleben sozialer Unterstützung auf den Zusammenhang zwischen den drei zentralen Subskalen und Indikatoren subjektiven Wohlbefindens - Lebenszufriedenheit und Erfolgserleben im Beruf - belegt.
Ist der I-S-T 2000 R Rasch-skalierbar?
Authors: Bühner Markus , Ziegler Matthias , Krumm Stefan , Schmidt-Atzert Lothar
Published: July 2006

Zusammenfassung. Die vorliegende Untersuchung beschäftigt sich mit den psychometrischen Eigenschaften des Intelligenz-Struktur-Tests 2000 R ( Amthauer, Brocke, Liepmann & Beauducel, 2001 ) in der Kurzform A. Es wurden Analysen zur Rasch-Skalierbarkeit, zur psychometrischen Qualität und zur faktoriellen Struktur durchgeführt. Dazu wurden N = 273 Studenten verschiedener Fachrichtungen der Philipps-Universität Marburg untersucht. Trotz einiger Probleme bei der Skalierbarkeit der Untertests zeigte sich, dass der I-S-T 2000 R insgesamt eine gute psychometrische Qualität besitzt sowie weitgehend geeignete Distraktoren enthält. Mit den aus der Analyse hervorgehenden Modifikationen genügt der I-S-T 2000 R sogar den strengen Kriterien des Rasch-Modells. Lediglich die Reliabilität für den verbalen Reasoning-Summenwert erwies sich als zu niedrig.
Die Diagnostik von Stressbewältigung mit dem “Fragebogen zur Erhebung von Stress und Stressbewältigung im Kindes- und Jugendalter“ (SSKJ 3-8)
Authors: Eschenbeck Heike , Kohlmann Carl-Walter , Lohaus Arnold , Klein-Heßling Johannes
Published: July 2006

Zusammenfassung. In diesem Beitrag wird über die faktorielle und psychometrische Prüfung eines revidierten Fragebogens (SSKJ 3-8) zur Erfassung von Stressbewältigung im Kindes- und Jugendalter berichtet. Aspekte der Stressbewältigung werden mit fünf Subskalen erfasst (Suche nach sozialer Unterstützung, problemorientierte Bewältigung, vermeidende Bewältigung, konstruktiv-palliative Emotionsregulation und destruktiv-ärgerbezogene Emotionsregulation). Die Studien beruhen auf einer Gesamtstichprobe von insgesamt 1991 Kindern und Jugendlichen der Klassenstufen 3 bis 8. Die Ergebnisse zeigen gute bis befriedigende Reliabilitäten (interne Konsistenzen, Retest). Die Skalenstruktur konnte mit Hilfe von exploratorischen und konfirmatorischen Faktorenanalysen bestätigt werden. Zahlreiche Hinweise auf die Validität konnten durch Korrelationen mit Außenkriterien (Stressbewältigungs-, Persönlichkeits-, gesundheitsbezogene Lebensqualitätsvariablen) ermittelt werden.
Psychometrische Überprüfung der Social Phobia Scale (SPS) und der Social Interaction Anxiety Scale (SIAS) im stationären Setting
Authors: Rabung Sven , Jaeger Ulrich , Streeck Ulrich , Leichsenring Falk
Published: July 2006

Zusammenfassung. Da soziale Ängste bei stationär behandlungsbedürftigen Psychotherapiepatienten allgemein weit verbreitet sind, bestand das Ziel der vorliegenden Untersuchung in der psychometrischen Überprüfung der Social Phobia Scale (SPS) und der Social Interaction Anxiety Scale (SIAS) im stationären Setting. Untersucht wurde eine Stichprobe von 823 stationären Psychotherapiepatienten (190 mit sozialer Phobie, 129 mit sonstigen Angststörungen, 504 mit anderen klinischen Störungen). Die beiden Skalen erweisen sich angesichts hoher interner Konsistenz und Stabilität als reliabel. Korrelationen mit anderen Beschwerde-Fragebögen belegen eine gute konvergente, aber mangelnde diskriminante Validität. SPS und SIAS unterscheiden zwar zwischen den untersuchten Störungsgruppen, ihre Klassifikationsleistung im Einzelfall ist jedoch unbefriedigend und sinkt zudem mit zunehmender Komorbidität. Der Nutzen der beiden Skalen zur Bearbeitung differenzieller diagnostischer Fragestellungen im stationären Kontext erscheint damit begrenzt.
Psychologische Gesundheitsförderung im Kindes- und Jugendalter
Authors: Kaluza Gert , Lohaus Arnold
Published: July 2006

Zusammenfassung. Das Kindes- und Jugendalter ist von besonderer Bedeutung für die Gesundheitsförderung und Krankheitsprävention, da hier entscheidende Grundlagen für das Gesundheitsverhalten im Erwachsenenalter gelegt werden. Angesichts der besorgniserregenden Verbreitung von körperlichen und psychischen Risikofaktoren bei Kindern und Jugendlichen stellen Kinder und Jugendliche sowie Eltern, Pädagogen und weitere Bezugspersonen prioritäre Zielgruppen für Maßnahmen der Prävention und Gesundheitsförderung dar. Welche gesundheitspsychologisch fundierten Programme existieren in diesem Bereich derzeit im deutschsprachigen Raum? Der Artikel stellt auf der Basis einer Umfrage, die unter den Mitgliedern der Fachgruppen Gesundheitspsychologie, Klinische Psychologie und Pädagogische Psychologie der DGPs sowie der Sektion Gesundheitspsychologie des BDP durchgeführt wurde, eine Sammlung von 10 empirisch evaluierten Interventionsprogrammen zur Prävention und Gesundheitsförderung im Kindes- und Jugendalter vor.
Further study of flickering auroral roar emission: 2. Theory and numerical calculations
Authors: Weatherwax A. T. , Yoon P. H. , Hughes J. M. , LaBelle J. , Ziebell L. F.
Published: July 2006

Two recent papers report ground‐based observations of ∼3–30 Hz pulsations in the amplitude of 2fce auroral roar radio emissions. These pulsations occur in groups which last for ∼1 s with adjacent pulsation groups spaced from one to several seconds. We put forth that these pulsations reflect periodic modulation of precipitating auroral electron fluxes, which could include periodic downward field‐aligned bursts (FABs) and periodically modulated inverted‐V electron precipitation, similar to those that could account for flickering aurora. We calculate time and frequency variations in the growth rate of Z‐mode waves in the ionosphere for two different models of time‐varying electron distribution functions, one corresponding to acceleration by electromagnetic ion cyclotron waves (EMIC) and the other corresponding to a simple time‐varying accelerating potential (TVP). On the basis of these numerical calculations, the reported characteristics of ∼10 Hz flickering roar appear consistent with modulations induced in the electron distribution function via interaction with EMIC waves, since the modulation associated with EMIC waves results in flickering of only the lower portion of the auroral roar frequency band, as in most of the observations. The few observed cases of higher‐frequency flickering roar, at ∼20–30 Hz, fall above the O+ cyclotron frequency for the altitude range on interest, and may represent a different source of electron flux modulation such as a varying electrostatic potential. The radio observations provide an additional means of probing flickering phenomenon and in particular may put constraints on the form of modulations of the electron distribution function at the auroral roar source height of a few hundred kilometers.
Evolution of mantle structure beneath the northwest Pacific: Evidence from seismic tomography and paleogeographic reconstructions
Authors: Miller Meghan S. , Kennett Brian L. N.
Published: July 2006

Plate motions and subducting slab morphology are intricately connected, and through the integration of seismicity, tomographic images, and relative plate motions, the evolution of mantle structure can be interpreted. Tomographic images of P wave, shear wave speed, and bulk sound speed perturbations of the northwest Pacific region have been interpreted to define the extent and geometry of the subducting Pacific plate. We have found that the subducted Pacific plate beneath the Japan and Kurile arcs is coherent but is very complex at the junction of the two arcs near the Hokkaido corner, as the slab subduction angle decreases from north to south while the slab thickens. The Pacific slab beneath the Japan arc is slightly thinner and subducting through the upper mantle at a less steep angle than the slab beneath the Kurile arc. As the slab reaches the 660‐km discontinuity it becomes stagnant and lies in a horizontal position on top of the transition zone both beneath the Izu and Japan arcs. In contrast, the slab beneath the Kurile arc is subducting at a steeper angle and penetrates through the transition zone into the lower mantle. The difference in slab morphology appears to be due to a combination of change in dip of the subducting plate and the convergence velocity of the Pacific plate along the margin. A new paleogeographic reconstruction of northeast Asia was assembled to evaluate the plate motions that could explain the foundation of the current slab morphology. The plate reconstruction was based on Euler pole motions of the Pacific, Philippine, Amurian, Okhotsk, and North American plates relative to stable Eurasia plate. The new tectonic model illustrates the collision of the Japan and Kurile arcs, the opening of the Kurile Basin, disparity in Pacific plate velocities along the arc, and different rates of trench retreat along the Izu, Japan, and Kurile segments of the western Pacific margin. The plate motion model was interpreted in conjunction with the physical properties of the mantle imaged with the P wave and joint tomography to assess the evolution of the Pacific plate morphology since the mid‐Miocene and to provide constraints on the plausible plate motions in the region.
Character formulas and partition functions in higher dimensional conformal field theory
Authors: Dolan F. A.
Published: July 2006

A discussion of character formulas for positive energy, unitary irreducible representations of the conformal group is given, employing Verma modules and Weyl group reflections. Product formulas for various conformal group representations are found. These include generalizations of those found by Flato and Fronsdal for SO(3,2). In even dimensions the products for free representations split into two types depending on whether the dimension is divisible by four or not.
Closed form of the generalized Green’s function for the Helmholtz operator on the two-dimensional unit sphere
Authors: Szmytkowski Radosław
Published: July 2006

The closed representation of the generalized (known also as reduced or modified) Green’s function for the Helmholtz partial differential operator on the surface of the two-dimensional unit sphere is derived. In its compact form, the derived formula contains a Legendre polynomial and a derivative of the Legendre function of the first kind with respect to its index. An explicit expression for that derivative is found and used to obtain an expanded (and potentially more suitable in applications) form of the generalized Green’s function for the operator in question. The related problem of constructing the closed form of the generalized Green’s function for the Legendre ordinary differential operator on the segment −1<x<1, with the boundary conditions of finiteness at x=±1, is also solved.
Steering population flow in coherently driven lossy quantum ladders
Authors: Yatsenko Leonid P. , Rangelov Andon A. , Vitanov Nikolay V. , Shore Bruce W.
Published: July 2006

We present a detailed theory of a technique for the adiabatic control of the population flow through a preselected decaying excited level in a three-level ladder quantum system, as was experimentally demonstrated recently by Garcia-Fernandez et al. [Phys. Rev. Lett. 95, 043001 (2005)]. Specifically, we consider a three-state excitation chain of bound states, 1-2-3, of successively increasing excitation energy, in which probability loss via fluorescence occurs from states 2 and 3. We describe a laser excitation scheme that can, by adjustment of laser parameters, alter at will the relative fraction of population that, starting from state 1, is ultimately lost through states 2 and 3. We present analytical results for the conditions under which quasiadiabatic passage can take place.
On the characterization of three state conical intersections using a group homomorphism approach: Mapping the full N−5 dimensional seam space
Authors: Schuurman Michael S. , Yarkony David R.
Published: July 2006

A method for characterizing the degeneracy preserving seam space in the vicinity of a three state conical intersection is introduced. Second order degenerate perturbation theory is used to construct an approximately diabatic Hamiltonian whose eigenenergies and eigenstates accurately describe the vicinity of the three state conical intersection in its full dimensionality. The perturbative analysis enables the large number, 6(Nint(Nint+1)∕2), of unique second order parameters needed to construct this accurate Hamiltonian to be determined from ab initio data at a limited number of nuclear configurations, with (Nint+10) being minimal. Using the minimum energy three state conical intersection of the pyrazolyl radical (Nint=18), the potential of this approach is illustrated. A Hamiltonian comprised of the ten characteristic (linear) parameters and over 1440second order parameters is constructed and used to determine the locus of the conical intersection seam as well as to describe the 18 dimensional space in the vicinity of that point of intersection. Our results demonstrate the ability of this methodology to quantitatively reproduce the ab initio potential energy surfaces near a three state conical intersection.
Gibbs ensemble Monte Carlo simulation of supercritical CO2 adsorption on NaA and NaX zeolites
Authors: Liu Shanshan , Yang Xiaoning
Published: July 2006

Adsorption of supercritical carbon dioxide on two kinds of zeolites with identical chemical composition but different pore structure (NaA and NaX) was studied using the Gibbs ensemble Monte Carlo simulation. The model frameworks for the two zeolites with Si∕Al ratio being unity have been chosen as the solid structures in the simulation. The adsorption behaviors of supercritical CO2 on the NaA and NaX zeolites, based on the adsorption isotherms and isosteric heats of adsorption, were discussed in detail and were compared with the available experimental results. A good agreement between the simulated and experimental results is obtained for both the adsorbed amount and the bulk phase density. The intermediate configurational snapshots and the radial distribution functions between zeolite and adsorbed CO2 molecules were collected in order to investigate the preferable adsorption locations and the confined structure behavior of CO2. The structure behaviors of the adsorbed CO2 molecules show various performances, as compared with the bulk phase, due to the confined effect in the zeolite pores.
Multiexponential reconstruction algorithm immune to false positive peak detection
Authors: Cover Keith S.
Published: July 2006

It is widely accepted that if a forward problem is ill posed, any reconstruction algorithm must invoke prior information. However, as is shown, if the forward problem is linear and the reconstruction algorithm is representable as multiplication by a left invertible matrix, all the information in the original data will be conserved in the reconstructed spectrum. As a consequence of data conservation, the reconstructed spectrum shares many properties of the original data. These properties include that any model spectrum that is consistent with the original data will also be consistent with the reconstructed spectrum and any model spectrum that is inconsistent with the original data will also be inconsistent with the reconstructed spectrum. If, in addition, the rows of the matrix are chosen such that the reconstructed spectrum has optimal linear resolution, including minimum noise, a useful reconstruction algorithm can be produced. As a consequence, the algorithm will use no prior information and is immune to false positive peak detection caused by unreliable prior information. This formalism was used to design a multiexponential reconstruction algorithm that is useful when reliable prior information is not available. As an example of the application of the data conserving multiexponential reconstruction algorithm, it was applied to both simulated and in vivo T2 decays from white matter in the human brain. There are multiple reports in the literature of a detection of a small but distinct “myelin water” peak, in addition to the main peak, in relaxation spectra reconstructed from the in vivo T2 decays. Applying the algorithm to both simulated and in vivo T2 decays for signal to noise ratio of about 1000 yielded spectra with a main peak but with only a low shoulder in place of the myelin peak. Because of the limited resolution available without the use of prior information, these results indicated that the T2 decays are both consistent with the existence and nonexistence of a myelin peak distinct from the main peak. This neutral conclusion was confirmed by finding spectra that were as consistent with the T2 decays as those containing a myelin peak but which had low shoulders of a main peak in place of myelin peaks. Also, as would be expected given their comparable consistency with the decays, the spectra without the myelin peaks had comparable probability densities to those with myelin peaks. Therefore, the data conserving multiexponential reconstruction algorithm confirmed the existence of the main peak in white matter relaxation spectra without the use of prior information but demonstrated that the existence of a myelin peak distinct from the main peak depends on the choice of prior information.
Feedback loops for Shil’nikov chaos: The peroxidase-oxidase reaction
Authors: Sensse Anke , Hauser Marcus J. B. , Eiswirth Markus
Published: July 2006

Special structures in a chemical reaction network can give rise to bistability, oscillations, and chaos. It has been shown recently [A. Sensse and M. Eiswirth, J. Chem. Phys. 122, 044516 (2005)] that the introduction of an additional species in a supplementary feedback loop to a minimal autocatalytic oscillator gives rise to chaotic dynamics in a certain range of parameters, independent of the particular realization of the additional loop. This provides a possibility to decide if chaos may occur just by analyzing the network structure of an existing model. Here, we apply this concept to analyze the complex dynamics in several essential subsystems of the peroxidase-oxidase reaction system. The aim of the present paper is to determine the nature of the occurring chaos and its location in the parameter space by numerical bifurcation analysis and simulations.
The dynamical correlation in spacer-mediated electron transfer couplings
Authors: Yang Chou-Hsun , Hsu Chao-Ping
Published: July 2006

The dynamical correlation effect in electron transfer (ET) coupling was studied in this work, for cases where electrons tunnel through a many-electron environment. The ET couplings for three different bridge-mediated model systems were calculated: (I) trans-alkyl chains [H2C–(CH2)n–CH2, n=2–10], (II) two isomers of trans-1,4-dimethylenecyclohexane, and (III) two ethylenes spaced by a saturated ethane molecule. The couplings were calculated as half energy gaps of the two lowest adiabatic states. The dynamical correlation was included with spin-flip (SF) and ionization potential or electron affinity coupled-cluster singles and doubles (SF-CCSD and IP/EA-CCSD) and a ΔCCSD scheme. The direct coupling (DC) scheme is also used as a way to obtain a solution with nondynamical correlation, since DC uses approximated eigenstates that are symmetry-restoring linear combinations of two symmetry-broken unrestricted Hartree-Fock configurations. For all cases tested except for one, results from the DC scheme closely follow the CCSD data, indicating that the dual-configuration solutions can be a good approximation of wave functions with nondynamical correlation included, but there exist exceptions. Comparing the DC results with SF-CCSD and IP or EA-CCSD data, we concluded that the dynamical correlation effect is small for most of the cases we tested.
Laser-driven shock experiments on precompressed water: Implications for “icy” giant planets
Authors: Lee Kanani K. M. , Benedetti L. Robin , Jeanloz Raymond , Celliers Peter M. , Eggert Jon H. , Hicks Damien G. , Moon Stephen J. , Mackinnon Andrew , Da Silva Luis B. , Bradley David K. , Unites Walter , Collins Gilbert W. , Henry Emeric , Koenig Michel , Benuzzi-Mounaix Alessandra , Pasley John , Neely David
Published: July 2006

Laser-driven shock compression of samples precompressed to 1GPa produces high-pressure-temperature conditions inducing two significant changes in the optical properties of water: the onset of opacity followed by enhanced reflectivity in the initially transparent water. The onset of reflectivity at infrared wavelengths can be interpreted as a semiconductor↔electronic conductor transition in water, and is found at pressures above ∼130GPa for single-shocked samples precompressed to 1GPa. Our results indicate that conductivity in the deep interior of “icy” giant planets is greater than realized previously because of an additional contribution from electrons.
Experimental and theoretical investigation of the Raman and hyper-Raman spectra of acetonitrile and its derivatives
Authors: Quinet Olivier , Champagne Benoît , Rodriguez Vincent
Published: July 2006

The Raman and hyper-Raman spectra of acetonitrile and its deuterated analog have been investigated by combining experimental analysis and theoretical interpretation. It has been observed that the Raman spectra can easily be reproduced at both the Hartree-Fock and Møller-Plesset second-order levels of approximation and that for these fundamental transitions, inclusion of anharmonicity effects is not essential. On the other hand, the hyper-Raman spectra are more difficult to simulate and interpret. In particular, electron correlation has to be included in order to describe properly the intensity of the CN stretching mode. Then, a pseudo-C∞v symmetry was assumed to better fit the experimental observations. This accounts for the fact that the a1- and e-symmetry modes correspond to time-decoupled vibrations. The e-symmetry modes, associated with nuclear motions perpendicular to the molecular axis are indeed subject to relaxation processes and, except the CCN bending mode, not visible in the hyper-Raman spectra of acetonitrile or of its deuterated analog. This assumption is supported by the gradual decrease of the phenomenon when going from acetonitrile to trichloroacetonitrile, where the presence of the heavier chlorine atoms in the latter reduces the relaxation processes.
Quantum state tomography of molecular rotation
Authors: Mouritzen Anders S. , Mølmer Klaus
Published: July 2006

We show how the rotational quantum state of a linear or symmetric top rotor can be reconstructed from finite time observations of the polar angular distribution under certain conditions. The presented tomographic method can reconstruct the complete rotational quantum state in many nonadiabatic alignment experiments. Our analysis applies for measurement data available in principle with existing measurement techniques. In practice, a full reconstruction requires a large amount of data and is thus experimentally challenging. Nonetheless, showing that the necessary information is present, we substantiate the use of approximate reconstruction methods with such data.
Experimental structure determination of silver cluster ions (Agn+,19⩽n⩽79)
Authors: Blom Martine N. , Schooss Detlef , Stairs Jason , Kappes Manfred M.
Published: July 2006

The structures of mass selected silver cluster cations Ag19+, Ag38+, Ag55+, Ag59+, Ag75+, and Ag79+ have been probed at a temperature of 100K by trapped ion electron diffraction. The structure assignment is carried out by comparison of the experimental scattering intensity with theoretical scattering functions of calculated candidate structures obtained by density functional theory. For the cluster sizes studied the resulting experimental data are invariably best described by structures based on the icosahedral motif, while closed packed structures can be ruled out.
Isotopic and internal CX3 (X=D,H) rotational motion effects in the Ba⋯FCX3+hν→BaF+CX3 intracluster reactions
Authors: Rinaldi C. A. , Gasmi K. , Skowronek S. , González Ureña A.
Published: July 2006

Photodepletion and action spectra of the laser-induced Ba⋯FCD3 fragmentation have been measured over the 16075–16380cm−1 range. The observed band and peak structures allowed us to estimate the vibrational and rotational structures of the excited complex at the transition state configuration. The relative reaction probability PR(E) for the intracluster Ba⋯FCD3+hν→BaF+CD3 reaction has been determined over the cited energy range. PR(E) shows a peak structure with an energy spacing of 8.9cm−1 which was attributed to an internal rotation of the CD3 group in the intermediate state. A comparison with previous Ba⋯FCH3 photofragmentation spectra reveals the dynamical role of the internal CX3 (X=H,D) motion which is manifested by the presence of rotational resonances in the laser-induced intracluster reaction.
Structures and rearrangements of LiCl clusters
Authors: Croteau T. , Patey G. N.
Published: July 2006

Molecular dynamics simulations are used to investigate the low-temperature structures and temperature-driven rearrangements of (LiCl)n clusters, with n ranging from 3 to 500. It is found that for n⩽32 expanded, ring-based structures are energetically more stable than cubic (rocksalt) forms at low temperature. For n⩾108, the cubic structures are lower in energy, but as the clusters are heated rearrangements to expanded structures occur well below the melting temperature. Hexagonal (LiCl)3 rings are a distinguishing feature of the expanded, ring-based structures. Highly asymmetric ion sizes are essential for the formation of the expanded structures. Similar transitions from more-ordered to less-ordered solid states are not found for corresponding (KCl)n clusters, which remain in the cubic structure until they melt.
Inverse scattering transform for the vector nonlinear Schrödinger equation with nonvanishing boundary conditions
Authors: Prinari Barbara , Ablowitz Mark J. , Biondini Gino
Published: July 2006

The inverse scattering transform for the vector defocusing nonlinear Schrödinger (NLS) equation with nonvanishing boundary values at infinity is constructed. The direct scattering problem is formulated on a two-sheeted covering of the complex plane. Two out of the six Jost eigenfunctions, however, do not admit an analytic extension on either sheet of the Riemann surface. Therefore, a suitable modification of both the direct and the inverse problem formulations is necessary. On the direct side, this is accomplished by constructing two additional analytic eigenfunctions which are expressed in terms of the adjoint eigenfunctions. The discrete spectrum, bound states and symmetries of the direct problem are then discussed. In the most general situation, a discrete eigenvalue corresponds to a quartet of zeros (poles) of certain scattering data. The inverse scattering problem is formulated in terms of a generalized Riemann-Hilbert (RH) problem in the upper/lower half planes of a suitable uniformization variable. Special soliton solutions are constructed from the poles in the RH problem, and include dark-dark soliton solutions, which have dark solitonic behavior in both components, as well as dark-bright soliton solutions, which have one dark and one bright component. The linear limit is obtained from the RH problem and is shown to correspond to the Fourier transform solution obtained from the linearized vector NLS system.
Capillary waves at the liquid-vapor interface and the surface tension of water
Authors: Ismail Ahmed E. , Grest Gary S. , Stevens Mark J.
Published: July 2006

Capillary waves occurring at the liquid-vapor interface of water are studied using molecular dynamics simulations. In addition, the surface tension, determined thermodynamically from the difference in the normal and tangential pressure at the liquid-vapor interface, is compared for a number of standard three- and four-point water models. We study four three-point models (SPC/E, TIP3P, TIP3P-CHARMM, and TIP3P-Ew) and two four-point models (TIP4P and TIP4P-Ew). All of the models examined underestimate the surface tension; the TIP4P-Ew model comes closest to reproducing the experimental data. The surface tension can also be determined from the amplitude of capillary waves at the liquid-vapor interface by varying the surface area of the interface. The surface tensions determined from the amplitude of the logarithmic divergence of the capillary interfacial width and from the traditional thermodynamic method agree only if the density profile is fitted to an error function instead of a hyperbolic tangent function.
Short wavelength analysis of the evolution of perturbations in a two-component cosmological fluid
Authors: Gailis R. M. , Frankel N. E.
Published: July 2006

The equations describing a two-component cosmological fluid with linearized density perturbations are investigated in the small wavelength or large k limit. The equations are formulated to include a baryonic component, as well as either a hot dark matter (HDM) or cold dark matter (CDM) component. Previous work done on such a system in static space–time is extended to reveal some interesting physical properties, such as the Jeans wave number of the mixture, and resonant mode amplitudes. A WKB technique is then developed to study the expanding universe equations in detail, and to see whether such physical properties are also of relevance in this more realistic scenario. The Jeans wave number of the mixture is reinterpreted for the case of an expanding background space–time. The various modes are obtained to leading order, and the amplitudes of the modes are examined in detail to compare to the resonances observed in the static space–time results. It is found that some conclusions made in the literature about static space–time results cannot be carried over to an expanding cosmology.
Geometrical and electronic structures of AumAgn (2⩽m+n⩽8)
Authors: Zhao G. F. , Zeng Z.
Published: July 2006

The structural and electronic properties of AumAgn binary clusters (2⩽m+n⩽8) have been investigated by density functional theory with relativistic effective core potentials. The results indicate that Au atoms tend to occupy the surface of AumAgn clusters (n⩾2 and m⩾2). As a result, segregation of small or big bimetallic clusters can be explained according to the atomic mass. The binding energies of the most stable AumAgn clusters increase with increasing m+n. The vertical ionization potentials of the most stable AumAgn clusters show odd-even oscillations with changing m+n. The possible dissociation channels of the clusters considered are also discussed.
The heat of formation of chlorine-isocyanate and the relative stability of isoelectronic molecules: An experimental and theoretical study
Authors: Ji Yuanyuan , Bobadova-Parvanova Petia , Larson Chris , Samartzis Peter C. , Morokuma Keiji , Lin Jim Jr-Min , Ching Tao-Tsung , Chaudhuri Chanchal , Lee Shih-Huang , Wodtke Alec M.
Published: July 2006

Accurate thermochemical data of small molecules are invaluable to the progress of every aspect of chemistry, especially in the atmosphere, combustion and industry. In this work, photofragmentation translational spectroscopy and 1st principles electronic structure theory reveal the literature value of the heat of formation of chlorine-isocyanate to be in error by more than 40kcal∕mol. We report a revised experimental value for D0(Cl–NCO)=51±3kcal∕mol which leads to a ΔHf(ClNCO)=8.5±3kcal∕mol. High level ab initio (CCSD(T)) electronic structure calculations extrapolated to the complete basis set limit give D0(Cl–NCO)=56.3kcal∕mol, in good agreement with experiment. In light of the present results, the destabilization of azides relative to isoelectronic isocyanates has been evaluated empirically for three pairs of related molecules. It is found to be 90–110kcal∕mol, and has been attributed mainly to the weakening of the N–NN bond relative to the N–CO bond. Electronic structure calculations employing decomposition analysis suggest that, compared to homopolar N2, the CO−δ+δ π polarity provides better orbital interaction (charge transfer) and electrostatic attraction and results in a closer encounter and larger stabilization between the fragments and that this is the origin of isoelectronic destabilization of azides relative to the isocyanates.
Quantum mechanical and quasiclassical investigations of the time domain nonadiabatic dynamics of NO2 close to the bottom of the XA12-AB22 conical intersection
Authors: Sanrey Michaël , Joyeux Marc
Published: July 2006

We use the effective Hamiltonian that we recently fitted against the first 306 experimentally observed vibronic transitions of NO2 [Joyeux et al., J. Chem. Phys. 119, 5923 (2003)] to investigate the time domain nonadiabatic dynamics of this molecule on the coupled XA12 and AB22 electronic states, using both quantum mechanical and quasiclassical techniques. From the quantum mechanical point of view, we show that the transfer of population to the electronic ground state originating from a wave packet launched on the excited state occurs in a stepwise fashion. The evolution of wave packets launched on the electronic ground state is instead more complex because the crossing seam is located close to the bottom of the electronic excited state. We next use the mapping formalism, which replaces the discrete electronic degrees of freedom by continuous ones, to obtain a classical description of the coupled electronic states. We propagate Gaussian swarms of trajectories to show that this approach can be used to calculate the populations in each electronic state. We finally propose a very simple trajectory surface hopping model, which assumes that trajectories have a constant probability to jump onto the other state in a particular region of the phase space and a null hopping probability outside from this region. Quasiclassical calculations show that this model enables a precise estimation of complex quantities, as for example the projection of the instantaneous probability density on given planes.