bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficacy of Azimilide and Dofetilide in the Dog Right Atrial Enlargement Model of Atrial Flutter
Authors: RESTIVO MARK , HEGAZY MAHA , EL‐HAMAMI MOUSTAFA , YIN HONG , CAREF EDWARD B. , ASSADI MAHSHID A. , BROOKS ROBERT R. , EL‐SHERIF NABIL
Published: August 2003

Azimilide and Dofetilide Atrial Flutter Efficacy.
Introduction: Azimilide dihydrochloride blocks both the rapid (IKr) and slow (IKs) components of the delayed rectified K+ current; dofetilide blocks only IKr. Their efficacies were assessed on atrial flutter reentrant circuits in dogs with surgically induced right atrial enlargement.

Methods and Results: Multiple biopsies of the tricuspid valve and banding of the pulmonary artery in male mongrel dogs made them susceptible, about 3 weeks postoperatively, to stimulation‐induced sustained (5 min or longer) atrial flutter. Azimilide 3 mg/kg administered intravenously (IV) terminated flutter in 8 of 8 dogs, but a slower, nonsustained arrhythmia could be reinduced in 5. In these 5 dogs, azimilide 10 mg/kg terminated flutter and prevented reinduction. This dose increased effective refractory period significantly more in the slow conduction zone (25%) than in the normal zone (17%) and increased flutter cycle length (37%). Termination followed progressive conduction delay in the slow zone of the reentrant circuit. Dofetilide 1 μg/kg IV terminated flutter in 6 of 6 dogs, but the arrhythmia could be reinduced. At 3 μg/kg, flutter terminated in all dogs and could not be reinduced. Dofetilide also increased the effective refractory period significantly more in the slow zone (17%) than in the normal zone (12%) and increased cycle length (33%), leading to interruption of the arrhythmia circuit.

Conclusion: In the canine right atrial enlargement model of circus movement atrial flutter, both azimilide 10 mg/kg IV and dofetilide 3 μg/kg IV were 100% effective in terminating flutter and preventing reinduction. Efficacy relied on a similar mechanism of differentially prolonged refractoriness in the slow conduction component of the reentrant circuit where drug‐induced termination occurred.
Effects of Azimilide, a New Class III Antiarrhythmic Drug, on Reentrant Circuits Causing Ventricular Tachycardia and Fibrillation in a Canine Model of Myocardial Infarction
Authors: SCHMITT HEIKO , CABO CANDIDO , COROMILAS JAMES C. , WIT ANDREW L.
Published: August 2003

Effects of Azimilide on Reentrant Circuits.
Introduction: Azimilide blocks the slow (IKs) and fast (IKr) components of the delayed rectifier potassium channel. It also has blocking effects on sodium (INa) and calcium currents (ICaL). Its effects on reentrant circuits in infarct border zones causing ventricular tachyarrhythmias are unknown.

Methods and Results: Activation in reentrant circuits causing sustained ventricular tachycardia (SVT) and the initial polymorphic tachycardia that leads to ventricular fibrillation (VF) was mapped in the epicardial border zone (EBZ) of 4‐day‐old canine infarcts. Azimilide prolonged the effective refractory period (ERP) in both normal myocardium and EBZ, but reverse use‐dependence in EBZ was prominent. Azimilide abolished SVT initiation by programmed electrical stimulation by prolonging the ERP at the site of stimulation either in normal or EBZ, preventing the occurrence of early premature impulses and the formation of lines of block in the EBZ necessary for formation of reentrant circuits. Azimilide prevented VF initiation by programmed electrical stimulation by causing conduction block of reentrant impulses in the EBZ during the initial beats of rapid polymorphic ventricular tachycardia, despite the reverse use‐dependent effects on ERP.

Conclusion: Azimilide has antiarrhythmic effects to prevent reentry causing SVT and VF in a canine infarct model.
Effects of Linear, Irrigated‐Tip Radiofrequency Ablation in Porcine Healed Anterior Infarction
Authors: CALLANS DAVID J. , REN JIAN‐FANG , NARULA NAVNEET , MICHELE JOHN , MARCHLINSKI FRANCIS E. , DILLON STEPHEN M.
Published: August 2003

Irrigated‐Tip Ablation in Infarcted Myocardium.
Introduction: Radiofrequency (RF) catheter ablation for ventricular tachycardia (VT) in healed infarction is modestly successful. More extensive, anatomically based procedures and irrigated RF delivery may improve outcome. However, limited data exist regarding the characteristics of irrigated RF lesions in infarcted myocardium. This study addresses this shortcoming.

Methods and Results: Linear lesions were created at the medial border of a healed anterior infarct in eight pigs using irrigated RF energy guided by sinus rhythm electroanatomic voltage mapping and intracardiac echocardiography (ICE). Lesion morphology and effects on ventricular function were assessed with ICE imaging and pathologic analysis (n = 5). The response to programmed stimulation also was determined before and after linear lesions (n = 6). A mean of 9.4 ± 1.3 RF applications created linear lesions 37.0 ± 10.6 mm long, 5 to 12 mm wide, and 4 to 8 mm deep. Thrombus formation was not observed. Lesion delivery resulted acutely in increased local wall thickness at the RF site (26.9% ± 27.5%; P < 0.0001) and transient systolic dysfunction in adjacent normal myocardium (fractional shortening − 38% ± 34%; P < 0.01). Uniform sustained VT (cycle length 232 ± 41 msec) was induced in 4 of 6 pigs before ablation, but sustained VT could not be induced afterward.

Conclusion: Irrigated RF energy produced relatively large lesions in infarcted myocardium without thrombus formation. Changes in tissue thickness and echo density observed with ICE verify irrigated RF lesion delivery. Temporary left ventricular dysfunction is consistently observed in the normal myocardium adjacent to the linear lesion.
Reentry in a Morphologically Realistic Atrial Model
Authors: VIGMOND EDWARD J. , RUCKDESCHEL RACHEL , TRAYANOVA NATALIA
Published: August 2003

Reentry in Morphologically Realistic Atria.
Introduction: Atrial fibrillation is the most common cardiac arrhythmia. In ablation procedures, identification of the reentrant pathways is vital. This has proven difficult because of the complex morphology of the atria. The purpose of this study was to ascertain the role of specific anatomic structures on reentry induction and maintenance.

Method and Results: A computationally efficient, morphologically realistic, computer model of the atria was developed that incorporates its major structural features, including discrete electrical connections between the right and left atria, physiologic fiber orientation in three dimensions, muscle structures representing the crista terminalis (CT) and pectinate muscles, and openings for the veins and AV valves. Reentries were induced near the venous openings in the left and right atria, the mouth of the coronary sinus, and the free wall of the right atrium. The roles of certain muscular structures were ascertained by selectively removing the structures and observing how the propagation of activity was affected.

Conclusion: (1) The muscular sheath of the coronary sinus acts as a pathway for a reentrant circuit and stabilizes any circuits that utilize the isthmus near the inferior vena cava. (2) Poor trans‐CT coupling serves to stabilize flutter circuits. (3) Wall thickness is an important factor in the propagation of electrical activity, especially in the left atrium. (4) The openings of the inferior and superior venae cavae form natural anatomic anchors that make reentry easier to initiate by allowing for smaller ectopic beats to induce reentry.
Simulation of Protective Zones During Quatrefoil Reentry in Cardiac Tissue
Authors: HILDEBRANDT MARISA C. , ROTH BRADLEY J.
Published: August 2003

Protective Zones During Quatrefoil Reentry.
Introduction: An S3 stimulus can exert a protective effect by terminating reentry induced by an S2 stimulus. Our goal was to examine the mechanism by which an S3 pulse terminates reentry and the role that virtual electrodes and break excitation play in this process.

Methods and Results: In our simulation, the bidomain model represents the electrical properties of the tissue and the Beeler‐Reuter model represents the membrane kinetics. Quatrefoil reentry is initiated by S1‐S2 stimulation, and then a third stimulus S3 is applied at different intervals after S2. All stimuli are applied through the same unipolar electrode. For some S2‐S3 intervals, the S2 and S3 wavefronts interact destructively, terminating reentry (protective zones). For other S2‐S3 intervals, S2 and S3 wavefronts interact constructively, and reentry continues. Protective zones appear recurrently, with approximately the period of the S2 reentrant circuit. The protective zones are wider for anodal stimulation than for cathodal stimulation.

Conclusion: Virtual electrodes, break excitation, and S2‐S3 timing all play important roles in determining the electrical response of the tissue.
Modulation of QT Interval by Cardiac Sympathetic Nerve Sprouting and the Mechanisms of Ventricular Arrhythmia in a Canine Model of Sudden Cardiac Death
Authors: ZHOU SHENGMEI , CAO JI‐MIN , TEBB ZACH D. , OHARA TOSHIHIKO , HUANG HSUN‐LUN A. , OMICHI CHIKAYA , LEE MOON‐HYOUNG , KENKNIGHT BRUCE H. , CHEN LAN S. , FISHBEIN MICHAEL C. , KARAGUEUZIAN HRAYR S. , CHEN PENG‐SHENG
Published: August 2003

QT Interval and Sudden Cardiac Death.
Introduction: We previously reported that there is a high incidence of sudden cardiac death (SCD) in dogs with myocardial infarction (MI), complete AV block (CAVB), and nerve growth factor (NGF) infusion to the left stellate ganglion (LSG). Whether or not QT interval prolongation underlines the mechanism of SCD was unclear.

Methods and Results: We analyzed QT intervals in three groups of dogs. All dogs had CAVB and MI. The LSG group (n = 9) and right stellate ganglion (RSG) group (n = 6) received NGF infusion via the osmotic pumps over a 5‐week period to LSG and RSG, respectively. The control group (n = 6) received no NGF. The dogs either died suddenly or were sacrificed within 2 to 3 months after MI. Heart rhythm and QT and RR intervals were monitored using implantable cardioverter defibrillator ECG recordings. There was a time‐dependent increase of QTc intervals in the LSG group and a time‐dependent decrease of QTc intervals in the RSG group. At the end of NGF infusion, QTc intervals in the LSG group (408 ± 41 msec) were significantly longer than those in the control (350 ± 41 msec; P < 0.05) and RSG groups (294 ± 23 msec; P < 0.01). In the LSG group, 4 of 9 dogs died of SCD. There was no SCD in either the RSG or control group. Immunocytochemical staining showed NGF infusion to LSG and RSG resulted in left and right ventricular sympathetic nerve sprouting and hyperinnervation, respectively.

Conclusion: NGF infusion to the LSG in dogs with MI and CAVB resulted in increased QT interval and incidence of ventricular tachycardia, ventricular fibrillation, and SCD, whereas NGF infusion to the RSG shortened QT interval and reduced the incidence of ventricular tachycardia. These findings indicate that QT interval prolongation is causally related to the occurrence of ventricular arrhythmia in dogs with nerve sprouting, MI, and CAVB.
Excessive Charge Time Delaying Ventricular Tachycardia Therapy
Authors: PANCHAL VIPUL R. , GROH WILLIAM J.
Published: August 2003

ICD Hardware Malfunction. A 70‐year‐old man with a single‐chamber implantable cardioverter defibrillator (ICD) placed for ventricular tachycardia presented with syncope. He was found to have ventricular flutter/fibrillation with capacitor charge time in excess of 1 minute before defibrillation. The excessive charge time was secondary to ICD capacitor malfunction. The generator was explanted and replaced, and the patient recovered uneventfully.
Accessory Pathway Associated with an Anomalous Coronary Vein in a Patient with Wolff‐Parkinson‐White Syndrome
Authors: TAKATSUKI SEIJI , MITAMURA HIDEO , IEDA MASAKI , OGAWA SATOSHI
Published: August 2003

WPW Syndrome and Coronary Venous Anomaly. We report a case of Wolff‐Parkinson‐White syndrome coexistent with atresia of the coronary sinus (CS) ostium and persistence of the left superior vena cava. The accessory pathway was located at the blind end of the CS, which was bumped with mechanical loss of preexcitation during mapping by a catheter from within the CS. The accessory pathway was successfully ablated with radiofrequency energy applied to this site from the right atrium. This unique combination of anatomically matched anomalies may be important in suggesting a potential embryologic link between the accessory pathway and the coronary vein.
Cardiac Arrhythmias: From (Transgenic) Mice to Men
Authors: London Barry
Published: August 2003

Cardiac Arrhythmias. Transgenic and gene‐targeted mice now are frequently used to study cardiac arrhythmias due to the ease with which the mouse genome can be manipulated. Marked electrophysiologic differences are present between the mouse and human heart, however, and the utility of the mouse as a model for arrhythmias and sudden death remains controversial. Tachyarrhythmias, bradyarrhythmias, and ECG in the mouse need to be interpreted with extreme care and without preconceptions based on our experience with humans. Despite its limitations, the mouse can provide a powerful tool to further our understanding of basic mechanisms that underlie human cardiac electrophysiology.
Immunpathogenese der Psoriasis
Authors: Ghoreschi Kamran , Röcken Martin
Published: August 2003

Die Psoriasis ist eine chronisch entzündliche Erkrankung der Haut und Gelenke. Die Entstehung einer Psoriasis unterliegt zahlreichen Einflüssen. Zu den am besten charakterisierten Faktoren gehören bestimmte genetische Merkmale wie Histokompatibilitätsantigene und sogenannte Psoriasis Suszeptibilitätsgene, sowie Triggerfaktoren, die eine Psoriasis auslösen oder ihren Verlauf verschlechtern können. Aus pathophysiologischer Sicht wird die Psoriasis heute überwiegend als eine durch T‐Lymphozyten vermittelte Autoimmunerkrankung angesehen, deren Autoantigen bis heute nicht bekannt ist. Diskutiert werden bakterielle Proteine mit Strukturähnlichkeit zu Keratinozytenproteinen. Ähnlich wie bei der Manifestation von Erkrankungsschüben anderer Autoimmunerkrankungen stehen Entzündungsmediatoren des angeborenen Immunsystems am Anfang einer Kaskade, die sowohl lokal in der Haut als auch generalisiert im Immunsystem eine Entzündungsreaktion hervorrufen. Eine zentrale Rolle nehmen IFN‐γ produzierende CD4+ T‐Lymphozyten, die Th1‐Lymphozyten ein, die durch direkte und indirekte Interaktionen mit Antigenpräsentierenden Zellen, Mastzellen, Neutrophilen Granulozyten und Endothelzellen für die Entstehung der Psoriasis verantwortlich sind. Diese Entzündungskaskade provoziert in der Haut gleichzeitig eine ausgeprägte Gefäßneubildung und die Keratinozytenproliferation. Eine Vielzahl von Rezeptoren und Mediatoren sind in dieses Netzwerk involviert. Neue Therapieansätze mit Zytokinen oder Zytokinantikörpern zielen entweder darauf ab, diese überschießende Immunantwort zu hemmen, oder darauf spezifisch die schädliche, gegen die Haut gerichtete Immunantwort, in einen schützenden Phänotyp mit anti‐entzündlichen Eigenschaften zu überführen.
Therapie der Akne mit Antiandrogenen – Eine evidenzbasierte Übersicht
Authors: Zouboulis Christos C.
Published: August 2003

Hintergrund: Zu den wichtigsten Faktoren, die zur Pathogenese der Akne beitragen, gehört eine erhöhte Talgdrüsenaktivität mit Seborrhoe. Die antiandrogene Therapie zielt auf die androgenmetabolisierenden follikulären Keratinozyten und die Talgdrüse mit primärer sebostatischer Wirkung, wobei eine Minderung der Talgsyntheserate von 12,5 % bis zu 65 % erreicht werden kann. Nach ihrem Mechanismus teilt man die Antiandrogene ein in Androgenrezeptorblocker sowie Hemmer der zirkulierenden Androgene durch Wirkung auf das Ovar (orale Kontrazeptiva), Hemmer der zirkulierenden Androgene durch Wirkung auf die Hypophyse (Gonadotropin‐releasing‐Hormone‐Agonisten und Dopamin‐Agonisten bei Hyperprolaktinämie), Hemmer der Nebennierenrindenaktivität und Hemmer des peripheren Androgenmetabolismus (5α‐Reduktase‐Inhibitoren, Hemmer anderer Enzyme).

Methoden: In dieser Studie wurden alle in MedLine publizierten Original‐ und Übersichtsarbeiten über die Therapie der Akne mit Antiandrogenen sowohl als Monotherapie als auch in Kombination mit Hilfe der Suchbegriffe „acne”, „seborrhea”, „polycystic ovary syndrome”, „hyperandrog*” und „treatment” ausgesucht und nach ihrer Evidenzebene eingeteilt.

Ergebnisse: Von den zur Verfügung stehenden therapeutischen Möglichkeiten zeigen die Kombinationen Cyproteronacetat (2 mg)/Ethinylestradiol (35 µg), Drospirenon (3 mg)/Ethinylestradiol (30 µg) und das kombiphasische Präparat mit Desogestrel (25 µg)/Ethinylestradiol (40 µg) für 1 Woche gefolgt von Desogestrel (125 µg)/Ethinylestradiol (30 µg) für 2 Wochen die stärkste Antiakne‐Wirkung. Gestagene oder Östrogene jeweils als Monotherapie, Spironolacton, Flutamid, Gonadotropin‐Releasing‐Hormone‐Antagonisten und Hemmer des peripheren Androgenmetabolismus werden nach dem heutigen Kenntnisstand nicht empfohlen. Niedrig dosiertes Prednisolon wird nur bei late‐onset kongenitaler adrenaler Hyperplasie eingesetzt und Dopamin‐Agonisten nur bei Hyperprolaktinämie. Die Therapie mit Antiandrogenen setzt voraus, daß keine entsprechenden Kontraindikationen vorliegen.

Schlußfolgerung: Die antiandrogene Therapie ist weiblichen Patienten vorbehalten, die weitere Zeichen eines peripheren Hyperandrogenismus oder einer Hyperandrogenämie aufweisen. Zudem können Frauen mit Acne tarda oder persistierender therapieresistenter Akne mit gleichzeitigem Kontrazeptionswunsch mit Antiandrogenen behandelt werden sowie im Rahmen der Durchführung einer systemischen Isotretinoin‐Therapie. Die antiandrogene Therapie ist keine primäre Monotherapie einer nicht entzündichen und milden entzündlichen Akne.
Die Anwendung des Excimerlasers 308 nm zur Psoriasis‐Behandlung
Authors: Fikrle Tomáš , Pizinger Karel
Published: August 2003

Hintergrund: Mit den gängigen Methoden der Phototherapie bei Psoriasis, UVB bei 311 nm und Photochemotherapie, wird auch die gesunde Haut einer potentiell schädigenden Strahlenbelastung ausgesetzt. Bei Verwendung eines 308 nm XeCl Excimerlasers können die psoriatischen Läsionen hingegen gezielt behandelt werden. In der vorliegenden Studie wird die Wirksamkeit einer solchen Laserbehandlung untersucht.

Patienten/Methodik: Die Studie wurde an 28 Patienten mit Plaquepsoriasis begonnen, 26 waren zu Studienende auswertbar. Bei jedem Patienten wurde eine einzige Plaque zur Behandlung ausgewählt und dreimal wöchentlich mit dichtgesetzten Laserpulsen behandelt. Die Initialdosis entsprach der doppelten MED (minimale Erythemdosis), Steigerungen um je eine MED erfolgten in der Regel bei jeder zweiten Behandlung. Die verabreichten Dosen lagen zwischen 2 – 5 MED, die kumulative UVB‐Gesamtdosis zwischen 3,6 – 15,2 J/cm2. 17 Patienten wurden insgesamt 6‐mal, weitere 11 Patienten 10‐mal behandelt. Die Bewertung der klinischen Wirksamkeit erfolgte durch die Berechnung des Psoriasis Severity Indexes (PSI) für das jeweils behandelte Hautareal. Die Patienten wurden regelmäßig bis drei Monate nach der letzten Laserbehandlung beobachtet, eine Nachuntersuchung erfolgte nach einem Jahr.

Ergebnisse: Bei den meisten Patienten trat eine deutliche Besserung des klinischen Befundes ein: bei 90 % war bei Behandlungsende der PSI auf wenigstens 50 %, in 72 % auf wenigstens 33 % des urprünglichen Wertes abgesunken. Das Ansprechen der Patientengruppen mit 6‐maliger bzw. 10‐maliger Behandlung war weitgehend gleich. Bei 6 Patienten der gesamten Gruppe war die Laser‐behandelte psoriatische Läsion auch nach einem Jahr noch abgeheilt, bei weiteren 7 war eine langfristige Besserung eingetreten. Die häufigsten Nebenwirkungen waren Rötung und Juckreiz (100 %), Blasenbildung (35 %) sowie Hyperpigmentationen im Behandlungsareal (80 %).

Schlußfolgerung: Die Anwendung des Excimerlasers mit 308 nm ist bei chronischer, lokalisierter Psoriasis wirksam und kann zu langanhaltender Remission führen.
Aggregate nitrogen in synthetic diamond
Authors: McNamara Karen M.
Published: August 2003

Nitrogen is a commonly observed impurity in natural and synthetic diamond, yet there are still many questions in regard to its incorporation in the material. In all three common forms of diamond: natural, high-pressure high-temperature synthetic, and chemical vapor deposition (CVD) diamond; nitrogen has been observed in substitutional lattice sites. This configuration results in an unpaired electron which gives rise to an easily observed paramagnetic resonance. In addition, aggregate forms of nitrogen, such as A-center (paired nitrogen), B-center, and platelet-related nitrogen are the predominant form of nitrogen observed in natural Type Ia diamonds. These aggregate forms have yet to be observed unambiguously in any form of synthetic diamond. Here, we show evidence, based on quantitative secondary ion mass spectrometry and electron paramagnetic resonance spectroscopy measurements, of nonparamagnetic nitrogen in some CVD diamond films. Further examination of the symmetry-disallowed one-phonon absorption in the infrared spectra of these films indicates the presence of aggregate nitrogen in these materials.
An approximation to the ensemble Kohn–Sham exchange potential for excited states of atoms
Authors: Tasnádi F. , Nagy Á.
Published: August 2003

An approximation to the Kohn–Sham exchange potential (vx) in the Gross–Oliveira–Kohn theory of ensemble of states is proposed for excited states of atoms, making use of a coupled self-consistent fitting procedure to the parameters of an approximate potential generated from a nonlocal potential (vxnonlocal) coming from the Becke exchange energy density, the Xα(vXα) and the so-called short-ranged response potential (vxresp). The parameter values are obtained when the sum of the Coulomb and the approximate exchange potentials shows the least deviation from the analogous potential in the recently derived generalized Krieger–Li–Iafrate (KLI) approximation of the optimized potential method of ensembles. To test the quality of the proposed exchange potential, calculations are performed for the first two or three (excited-state) ensembles of Li, Be, Na, Mg, K, and Ca atoms and the ensemble energies and densities are compared with the ensemble KLI results. As the exact exchange potential is free from the ghost-interaction (i.e., the self-interaction between the elements of the ensemble) the proposed fitted potential reduces the ghost-interaction error as well.
The virtual mass of a spherical-cap bubble
Authors: Kendoush Abdullah Abbas
Published: August 2003

An analytical solution was obtained for the virtual mass coefficient of a spherical-cap bubble. The flow field around the bubble was divided into two regions: the frontal and the wake region. The solution is valid by its asymptotic approach to the two geometric limits of the circular disk and the complete sphere.
Mixing of concentrated oil-in-water emulsions measured by nuclear magnetic resonance imaging
Authors: d’Avila Marcos A. , Shapley Nina C. , Walton Jeffrey H. , Phillips Ronald J. , Dungan Stephanie R. , Powell Robert L.
Published: August 2003

Mixing of concentrated oil-in-water emulsions in a horizontal, concentric-cylinder geometry was studied using nuclear magnetic resonance imaging. Time-of-flight and chemical shift imaging methods were used to measure velocity profiles and concentration maps in an emulsion that was mixed after being allowed to cream for several hours. The results revealed detailed information about mixing in concentrated emulsions. In the initial state, before mixing, the emulsion system formed three layers: an upper, oil-rich, “creamed” layer; a lower, water-rich layer; and a bulk concentration layer in between. It was found that the thickness of the creamed layer remained constant during mixing, while the oil concentration in that layer decayed exponentially as a function of time. It was also observed that most of the emulsion is quiescent while mixing occurs; the only motion detected occurs in a thin layer close to the rotating, outer cylinder. The velocity profile only begins to transition to its steady-state configuration after the emulsion becomes well mixed. A simple model is introduced that gives a plausible explanation of these experimental observations. These results indicate that the mixing mechanism in concentrated emulsions is significantly different from that in single-phase liquids.
Tracer diffusion of ionic and hydrophobic solutes in water–dimethyl sulfoxide mixtures: Effects of varying composition
Authors: Chowdhuri Snehasis , Chandra Amalendu
Published: August 2003

We have performed a series of molecular dynamics simulations of water–dimethyl sulfoxide (DMSO) mixtures containing either an ionic or a neutral atomic solute to investigate the effects of composition of the mixture on the diffusion of these solutes. Several different compositions of the mixtures ranging from pure DMSO to pure water are considered. Altogether, 23 different systems are simulated in the present work. The diffusion coefficients of both ionic and neutral solutes are found to show strong nonideal behavior with variation of composition of the solvent mixture. The extent of nonideality of the solute diffusion is found to be similar to the nonideality that is observed for the diffusion and orientational relaxation of water and DMSO molecules in these mixtures and is attributed to the presence of rather strong water–DMSO hydrogen bonds in these mixtures. The simulation results are compared with those of experiments wherever available.
Instability mechanisms in swirling flows
Authors: Gallaire F. , Chomaz J.-M.
Published: August 2003

We investigate the stability of the screened Rankine vortex with added plug flow where the azimuthal velocity decreases abruptly outside the core of the vortex. The jump in circulation is known to induce centrifugal and azimuthal Kelvin–Helmholtz instabilities. Their effect on the stability of the different azimuthal wave number m is discussed using physical considerations associated with asymptotic expansions and numerical computations of the dispersion relation. It is shown that the axial shear and centrifugal instability are active for all m, and that modes with |m|⩾2 are also destabilized by azimuthal shear. In contrast, the bending modes m=±1 are stabilized by a coupling with Kelvin waves in the core. Effects of rotation on the absolute/convective transition are also discussed. The absolute instability of positive helical modes is seen to be promoted by centrifugal instability and azimuthal shear.
Integral equation theory of penetrable sphere fluids: A modified Verlet bridge function approach
Authors: Choudhury Niharendu , Ghosh Swapan K.
Published: August 2003

Structure of penetrable sphere fluids, which are generally used to model micelles in a solvent or star polymer solutions, has been studied by integral equation theory with a very simple closure relation based on a modification of the Verlet-modified bridge function, which has been known to be very successful for hard body fluids. Conventional integral equation theories, which use Percus–Yevick and hypernetted chain closures, are unable to correctly model the behavior of the pair distribution functions of the penetrable sphere fluids, particularly in the core overlap region. The results for the pair-distribution or radial distribution functions obtained from the present theory are found to be in excellent agreement with the corresponding computer simulation results. The bridge functions at various temperatures and densities have also been compared with the corresponding results extracted from the computer simulation.
A new approach to density matrix functional theory
Authors: Kollmar Christian , Heß Bernd A.
Published: August 2003

Starting from a pair-excitation multiconfiguration self-consistent field approach considering pairwise excitations of two electrons of opposite spin from a single occupied molecular orbital to a single virtual molecular orbital, we present a natural orbital functional for the electronic energy containing the natural orbitals and the pair-excitation coefficients as variational parameters to be optimized. The occupation numbers of the natural orbitals can be determined from the pair-excitation coefficients in this implicit functional. Test calculations for the water molecule give occupation numbers of the natural orbitals in reasonable agreement with the results of full configuration interaction calculations.
The 4 3Σ+ state of NaK: Potential energy curve and hyperfine structure
Authors: Burns P. , Sibbach-Morgus L. , Wilkins A. D. , Halpern F. , Clarke L. , Miles R. D. , Li Li , Hickman A. P. , Huennekens J.
Published: August 2003

High-resolution spectra, including hyperfine structure, have been observed for numerous vibrational-rotational levels (v,N) of the 4 3Σ+ Rydberg state of the NaK molecule. The data have been used to construct a Rydberg–Klein–Rees potential curve, and this molecular potential has been further refined using the inverse perturbation approximation method. Bound-free emission from the 4 3Σ+ electronic state to the repulsive a(1) 3Σ+ state has also been measured and used to determine both the absolute vibrational numbering and the transition dipole moment function M(R). The experimentally derived potential curve and M(R) are compared with recent theoretical calculations of Magnier et al.; the agreement is very good. Each of the levels (v,N) is typically split into three sets of sublevels by the Fermi contact interaction bI⋅S. Further splitting (of order 0.004 cm−1) has been attributed to the spin-rotation interaction γN⋅S. The patterns observed exhibit a clear transition from Hund’s case bβS for small N toward Hund’s case bβJ for large N. The data can be fitted very well using a theoretical model based on setting up and diagonalizing a 12×12 Hamiltonian matrix with two adjustable parameters (b and γ). The values of b that fit the data best are ∼(0.99±0.04)×10−2 cm−1, with a weak dependence on v. The best fit values of γ are in the range 1–6×10−4 cm−1 and depend strongly on v. The values of γ appear to exhibit anomalous structure for (v,N) levels perturbed by nearby levels of the 3 3Π state.
Size-dependent dynamics of a quantum solvent: Laser spectroscopy of HCN–(HD)n grown in helium nanodroplets
Authors: Moore D. T. , Miller R. E.
Published: August 2003

The progressive solvation of HCN by molecular hydrogen (HD) is studied by high-resolution laser spectroscopy. The [HCN–(HD)n] clusters are grown in helium nanodroplets, an ideal spectroscopic medium which at sufficiently low temperatures permits the study of systems containing n=2–14 HD molecules. A single isomer is observed for each cluster size, independent of the order in which the molecules are added to the helium droplets, indicating that these systems are rather “fluid.” Clusters with an incomplete first solvent shell (n=1–11) rotate as a unit, having rotational constants that steadily decrease with increasing size. At n=12, the HCN undergoes nearly free internal rotation within the solvent cage of the hydrogens. The fine structure observed in the corresponding “R(0)” transition suggests that the solvent cage is somewhat anisotropic. The further addition of solvent molecules results in a quenching of the HCN internal rotation at n=14, suggestive of a significant increase in the anisotropy of the solvent environment.
Time-dependent free-surface thin film flows over topography
Authors: Bielarz Catherine , Kalliadasis Serafim
Published: August 2003

The lubrication equation governing free-surface thin film flows over topography is solved numerically including the effects of inertia and intermolecular forces. We study the initial value problem for a variety of initial conditions and perturbations and demonstrate that the free surface is strongly stable and can only be destabilized with large values of the dimensionless Hamaker’s constant and large amplitude free-surface perturbations, both of which are difficult to achieve in practice. The strong stability of thin film flows over topography is in agreement with the recent analysis by Kalliadasis and Homsy [J. Fluid Mech. 448, 387 (2001)].
Solvent-polarizability dependence of the relative 2 1Ag(S1)- and 1 1Bu(S2)-fluorescence intensities of 1,14-diphenyl-1,3,5,7,9,11,13-tetradecaheptaene
Authors: Itoh Takao
Published: August 2003

Emission, excitation, and absorption spectra of diphenyltetradecaheptaene (DP7) have been measured in solvents with different polarizabilities, together with the Raman spectrum at room temperature. DP7 exhibits dual fluorescence from the 2 1Ag(S1) and 1 1Bu(S2) states in room temperature solution. It is shown that the 2 1Ag/1 1Bu fluorescence intensity-ratio varies significantly depending on the solvent polarizability. This observation was interpreted on the basis of the coupling strength between the 2 1Ag/1 1Bu states which is determined mainly by the 2 1Ag–1 1Bu energy separation. Fitting of the spectra with sum of Gaussians reveals a significant difference in Franck–Condon envelop between the 2 1Ag and 1 1Bu fluorescence spectra, which is originating from the large difference in the C–C and C=C stretching mode displacements between the 2 1Ag and 1 1Bu states.
Effect of pulse propagation on the two-dimensional photon echo spectrum of multilevel systems
Authors: Keusters Dorine , Warren Warren S.
Published: August 2003

The effect of pulse propagation on the two-dimensional photon echo (2DPE) spectrum of multilevel systems is investigated using a perturbative method. At high optical densities (OD) peak profiles are broadened asymmetrically, in most cases more strongly along the ω2 direction than along the ω1 direction. The amount of broadening is determined both by the OD and by the dynamics of the system. In addition, especially if the different transitions in the system are of unequal strength, the relative intensity of the peaks changes with OD. But even if the transition strengths are the same, the behavior of the cross peaks is different from the diagonal peaks. Since peak shape and relative intensity are important parameters in the interpretation of 2DPE spectra, such OD effects should be taken into account.
Control of bimolecular reactions: Bond-selected reaction of vibrationally excited CH3D with Cl (2P3/2)
Authors: Yoon Sangwoon , Holiday Robert J. , Crim F. Fleming
Published: August 2003

Selective vibrational excitation permits control of the outcome of a reaction with two competing channels. The thermal reaction of CH3D with Cl (2P3/2) yields two reaction products: CH3 from the D-atom abstraction and CH2D from the H-atom abstraction. We prepare the first overtone of the C–D stretching vibration (2ν2) at ∼4300 cm−1 and react the vibrationally excited molecule with photolytic Cl atoms. The 2+1 resonance enhanced multiphoton ionization spectra for the products show that the 2ν2 vibrational excitation of CH3D exclusively increases the probability of breaking the C–D bond, yielding CH3 but no CH2D. By contrast, vibrational excitation of the combination of the antisymmetric C–H stretch and CH3 umbrella (ν4+ν3) vibrations, which has total energy similar to that of 2ν2, preferentially promotes the H-atom abstraction reaction to produce CH2D over CH3. The vibrational action spectra for the two products permit the separation of the two sets of interleaved transitions to give band origins and rotational constants of the 2ν2 state and the ν4+ν3 state of CH3D.
Viscoelastic properties of Na–Al–PO3 glasses and melts
Authors: Bogdanov V. , Kisliuk A. , Mamedov S. , Nemilov S. , Quitmann D. , Soltwisch M.
Published: August 2003

Elastic and relaxational properties of (NaPO3)(1−x)(Al(PO3)3)x melts and glasses have been studied for x=0, 0.03, 0.06, 0.15, 0.60, and T=293–1433 K. Brillouin light scattering as well as ultrasound were used. The data were carefully analyzed using viscoelastic theory, with emphasis on the effect of added Al(PO3)3, and on searching for a fast relaxation channel (besides the α-relaxation common to glass formers). The fast process is present for x⩾0.03, and the T-dependence of the relative weight of both processes in the melts is derived. The replacement of Na+ by Al3+ increases the high-frequency LA sound velocity drastically, due to a twofold increase of shear modulus. Comparison with the shear viscosity is made. Viscosity and thermodynamic data are used for deriving an estimate of the size of the regions active in the slow relaxation process. Possible origins of the relaxation processes are discussed.
Photodissociation of ICN in polar solvents: Evidence for long lived rotational excitation in room temperature liquids
Authors: Moskun Amy C. , Bradforth Stephen E.
Published: August 2003

Ultrafast polarized pump–probe spectroscopy has been used to study the ICN Ã band photodissociation dynamics in several molecular liquids (water, ethanol, methanol, and chloroform). By exciting at 224 and 255 nm and probing at 385 nm near the gas phase CN B←X transition, the population and vector correlations in the resulting products have been followed with ∼150 fs time resolution. The exhaustive gas-phase reaction dynamics charted for this system indicate that a substantial torque is imparted to the CN fragment in the ground state I dissociation channel while the CN is rotationally cold in the I* channel. The fate of the highly rotationally excited fragment in a liquid environment is explored in the present study. The transient pump–probe anisotropy in ethanol and methanol shows two time scales for decay, ∼400 fs and 3–7 ps depending on excitation energy; the two time scales are assigned to the two product channels. The subpicosecond time scale is characteristic of rotational diffusion of thermalized CN while the longer several picosecond time scale suggests the rotationally hot CN rotate nearly freely for several picoseconds in the plane defined by the initial dissociative event. The rotational behavior of a diatomic fragment is considered between the free rotor and small-angle rotational diffusion limits. The CN photoproduct population dynamics are quite varied in the different solvents. In alcohols and chloroform, CN undergoes abstraction reactions with the solvent while in water there is no abstraction. Caging and diffusive geminate recombination dynamics apparently vary markedly in the different solvents; these effects are compared to molecular dynamics results for this photodissociation system. A large isotope effect is observed between H2O and D2O solvents in the product recombination dynamics.
On Löwdin’s projection technique and the energy-corrected approaches
Authors: Meißner Holger
Published: August 2003

Recently, a new energy correction to standard approaches of the coupled-cluster (CC) method has been proposed, namely the so-called (complete) renormalized CC method [K. Kowalski and P. Piecuch, J. Chem. Phys. 113, 5644 (2000) and references therein], as well as the energy-corrected CCSD approach [X. Li and J. Paldus, J. Chem. Phys. 117, 1941 (2002) and references therein], which are based on the method of moments of the CC method of Kowalski and Piecuch [Computational Chemistry: Reviews of Current Trends (World Scientific, Singapore, 2000), Vol. 5, p. 1]. These methods provide an efficient and noniterative, and thus less demanding, approach than do the iterative approaches and avoid, e.g., the fallacies of the standard CCSD(T) method. We show how this type of energy corrections may be related to Löwdin’s projection and bracketing techniques and also to a standard extrapolation scheme which is applied here to the results of the new energy corrections.
Instability of interfaces in phase-separating binary fluids at a finite Reynolds number
Authors: Kiwata Hirohito
Published: August 2003

We investigate a stability of a lamellar domain in phase-separating binary fluids under an external flow. Using the Navier–Stokes and the Cahn–Hilliard equations, we take into account effects of diffusion and surface tension at an interface. Stability eigenvalues are evaluated for various values of the Péclet number, the spacing between the interfaces, and the Reynolds number. It is found that the lamellar domain becomes unstable at a finite wavenumber before the flow when the Reynolds number increases. The instability of the interface occurs on conditions that the interface is situated near a wall or the Péclet number is large. The instability stems from the interaction between disturbances of the flow and the diffusive interface.
Wave function instabilities in the cis–trans isomerization and singlet–triplet energy gaps in a push–pull compound
Authors: Matus Myrna H. , Contreras Renato , Cedillo Andrés , Galván Marcelo
Published: August 2003

The energy barriers for the cis–trans isomerization are obtained for a sample of push–pull compounds. The appropriate trend in the values for the barriers is obtained after an instability treatment of the restricted Kohn–Sham solution. At the instability zone, some compounds exhibit a singlet open-shell configuration. The width of the instability region around the transition state is characterized in an asymmetric push–pull compound. These results show that the instabilities in the twisted configuration of double bonds are mainly related to spin symmetry effects rather than to the molecular symmetry. For the open-shell singlet, an ensemble model is used to compute the electronic properties. The singlet–triplet energy gap along the rotation coordinate is qualitatively described by the use of spin potential and hardness.
Aurophilic attraction and excited-state properties of binuclear Au(I) complexes with bridging phosphine and/or thiolate ligands: An ab initio study
Authors: Pan Qing-Jiang , Zhang Hong-Xing
Published: August 2003

The ground- and excited-state structures were fully optimized for a series of neutral binuclear Au(I) thiolates, [Au2(dpm)(SCH2S)] (1) (dpm=bis(diphosphino)methane), trans-[Au2(PH2CH2S)2] (2), and trans-[Au2(SHCH2S)2] (3), by using the MP2 and CIS methods, respectively. The calculated AuI–AuI distances of about 3.0 Å in the ground state of the complexes are indicative of aurophilic attraction between the two Au(I) atoms, while in their excited states the separations are greatly shortened (about 2.7–2.9 Å). The promotion of Au d electron or S p electron into the bonding sσ and/or pσ lowest unoccupied molecular orbital of AuI–AuI results in such reinforcement of aurophilicity in the excited state. In the CIS calculations of the three Au(I) thiolates, we obtained the lowest-energy phosphorescent emission in the solid state for each of the complexes. The 462 nm emission of 1 was assigned as Au→S charge transfer (MLCT) transition. But for 3, the charge transfer localized on the Au centers, Au3(sσ)→1Au(dσ*) (metal-centered charge transfer, MCCT), plays a main role in the 413 nm emission. Both the MCCT and MLCT transitions are important in the 323 nm emission of 2. The results indicated that AuI–AuI aurophilicity clearly influences luminescent properties of these complexes.
Orbital interactions and charge redistribution in weak hydrogen bonds: The Watson–Crick AT mimic adenine-2,4-difluorotoluene
Authors: Fonseca Guerra Célia , Bickelhaupt F. Matthias
Published: August 2003

The discovery by Kool and co-workers that 2,4-difluorotoluene (F) mimics thymine (T) in DNA replication has led to a controversy about the question if this mimic has the capability of forming hydrogen bonds with adenine (A). In the present study, we address not only the question about the strengths of the hydrogen bonds in AF as compared to those in AT but we focus in particular on the nature of these interactions. Thus, we have analyzed AF and AT at the BP86/TZ2P level of density functional theory (DFT). In line with previous experience, this approach is shown to achieve close agreement with the available data from ab initio computations and experiment: the complexation energy of AF (−3.2 kcal/mol) is confirmed to be much weaker indeed than that of AT (−13.0 kcal/mol). Interestingly, the weak hydrogen bonds in AF still possess a significant orbital interaction component that resembles the situation for the more strongly bound AT, as follows from (1) an analysis of the orbital electronic structure of AF and AT, (2) a quantitative decomposition of the A–F and A–T bond energies, as well as (3) a quantitative decomposition of the charge redistribution associated with the A–F and A–T interactions based on the Voronoi deformation density (VDD) method. The VDD method has been further developed such that the charge redistribution ΔQ per atom can be decomposed into a component associated with the Pauli repulsive orbital interactions and a component associated with the bonding orbital interactions: ΔQ=ΔQPauli+ΔQoi. Implications of our findings for the mechanism of DNA replication are discussed.
CCSD(T) intermolecular potential between He atom and ClF molecule: Comparison with experiment
Authors: Prosmiti Rita , Cunha Carlos , Villarreal Pablo , Delgado-Barrio Gerardo
Published: August 2003

The potential energy surface of the He–ClF complex is calculated using for He atom an efficient basis set of aug-cc-pV5Z augmented with a set of 3s3p2d2 f1g set of midbond functions and aug-cc-pVTZ, aug-cc-pVQZ for Cl and F atoms, respectively, at coupled-cluster with single and double excitations and a noniterative perturbation treatment of triple excitations [CCSD(T)] level. Three local minima are found for the He–ClF that correspond to linear He–Cl–F (collinear) and He–F–Cl (antilinear) configurations and a asymmetric T-shaped structure. The well depths and the equilibrium distances are 63.53 cm−1 and 3.54 Å (collinear), 41.09 cm−1 and 3.23 Å (T-shaped) and 33.80 cm−1 and 3.93 Å (antilinear). Bound states calculations are carried out for the CCSD(T) surface and the sensitivity of the rovibrational levels to the errors of the computed potential energy surface at different configuration regions is discussed. The computed energy levels up to a total angular momentum J=3 are in general accord with experimental data.
Guided ion beam studies of the reactions of Nin+ (n=2–18) with O2: Nickel cluster oxide and dioxide bond energies
Authors: Vardhan Dinesh , Liyanage Rohana , Armentrout P. B.
Published: August 2003

The kinetic energy dependences of the reactions of Nin+ (n=2–18) with O2 are studied in a guided ion beam tandem mass spectrometer. A variety of NimO2+, NimO+, and Nim+ product ions, where m⩽n, are observed, with the dioxide cluster ions dominating the products for all larger reactant cluster ions. Reaction efficiencies are near unity for all but the smallest clusters. The energy dependences of the product cross sections are analyzed in several different ways to determine thermochemistry for both the first and second oxygen atom binding to nickel cluster ions. These values show little dependence on cluster size for clusters larger than three atoms. The trends in this thermochemistry are discussed and compared to bulk phase oxidation values.
Regularity in highly excited vibrational dynamics of NOCl (X 1A′): Quantum mechanical calculations on a new potential energy surface
Authors: Yamashita Takefumi , Kato Shigeki
Published: August 2003

A new potential energy surface (PES) of NOCl in the ground electronic state (X 1A′) is constructed based on multireference configuration interaction calculations. Almost all the vibrational eigenstates up to the dissociation threshold are obtained using filter diagonalization method with the present PES. The vibrational excitation energies are in good agreement with the experimental values. The nearest neighbor level spacing distribution shows that the vibrational structure is regarded as regular up to the dissociation threshold. The distribution of radiative coupling elements also supports the regularity. It is further found out that the NO stretching mode is strongly decoupled from the other modes. Taking advantage of this result, the two-dimensional (2D) analyses are carried out with the NO distance fixed. The 2D wave functions have clear nodal patterns even near the dissociation threshold, indicating that the 2D quantum dynamics is regular as in the three-dimensional case. Comparing the 2D classical dynamics with the 2D wave functions, quasiperiodic trajectories closely related to the corresponding quantum dynamics are extracted. Although it is generally believed that the phase space becomes fully chaotic with approaching to the dissociation threshold, two stable islands of regular motion still remain even at this energy region.