bluuebunny/crossref_metadata_2025 huggingface dataset:
Transitions in the route of cocaine administration‐characteristics, direction and associated variables
Authors: Dunn John , Laranjeira Ronaldo R.
Published: July 2002

Aims. To examine transitions in the route of administration of cocaine and the variables associated with them. Design. A cross‐sectional study undertaken between January 1996 and October 1997. Setting. Fifteen different services that offer treatment, counselling or assistance to drug users or HIV positive patients in the State of Sao Paulo, Brazil. Participants. Two hundred and ninety‐four current or ex‐cocaine and crack cocaine users. Measurements. A structured interview schedule was developed consisting of 246 questions covering socio‐demographic details, drug history, cocaine transitions and HIV‐risk behaviours. Findings. Eighty‐seven per cent of patients began using cocaine by snorting and 74% subsequently underwent a transition of route‐ 68% towards smoking and 20% to injecting. Half of all transitions occurred in the first 3 years following initiation into cocaine use. Factors associated with transitions were: younger age at cocaine initiation, more frequent use at peak usage, initial use of cocaine by snorting or injecting, a lower level of scholastic attainment and experience with a wider range of drug classes. A cohort effect was apparent with younger cocaine users and those who had begun using after 1990 being more likely to undergo a transition to smoking crack and less likely to start injecting. Conclusions. Cocaine transitions are very common and are usually towards routes associated with a higher dependency potential and increased HIV‐risk behaviour. Further research is needed to see if transitions can be prevented by early identification of potential cases.
Alcohol‐related mortality as a function of socio‐economic status
Authors: Makela Pia
Published: July 2002

Aims. To describe the differences in acute, chronic and total alcohol‐related mortality by several measures of socio‐economic status (SES) and to unravel the influences of different dimensions of SES. Design. A register‐based follow‐up study of alcohol‐related mortality. Setting. Finland. Participants. The dataset was formed by linking census records with death records for 1987‐95 and included 21 922 alcohol‐related deaths. Measurements. SES indicators include education, occupational class, personal income, net household income per consumption unit (spending power) and housing tenure. The judgement of whether death was alcohol‐related was based on death certificates. Findings. Acute and chronic alcohol‐related mortality were much higher in low SES groups for all SES indicators, including spending power, even when controlling for the remaining SES variables. Among men, personal income was a better predictor of alcohol‐related death than spending power, while among women the situation was reversed. The effect of one SES measure was often stronger in low levels of another SES measure. Social selection and drift are likely to contribute to the large differentials in respect to personal income, while their effect on other differentials is likely to be smaller. Conclusions. SES is an important predictor of acute and chronic alcohol‐related mortality. The total impact of SES cannot fully be captured using only one or two measures of SES .
Fibroblast growth factor‐2 alters the effect of eroding polylactide‐polyglycolide on angiogenesis in the bone chamber
Authors: Winet Howard , Bao Joseph Y.
Published: July 2002

The effects of recombinant human fibroblast growth factor‐2 in the presence of eroding 50:50 poly(dl‐lactide‐co‐glycolide) on angiogenesis during acute bone defect healing were studied in the optical bone chamber. Bone chambers were loaded with disks of poly(dl‐lactide‐co‐glycolide) surrounded by one of four doses of recombinant human fibroblast growth factor‐2. Fifty‐two female rabbit right tibias were implanted. Commencing with the third postimplantation week, healing into the bone chamber compartment was observed weekly, with use of intravital microscopy, until week 8. The treatment groups were as follows: unloaded, loaded with polymer only, and loaded with polymer plus‐0.5, ‐1.0, and ‐10 µg recombinant human fibroblast growth factor‐2. Videotaped and photographed bone images were measured and analyzed with a frame‐grabber digitizing system. Comparison with controls or polymer alone revealed that angiogenesis rates were significantly above normal in rabbits loaded with polymer plus either of the two highest recombinant human fibroblast growth factor‐2 doses. The effects of these doses were not, however, significantly different from each other, indicating a plateauing rather than monotonically increasing response. It was concluded that recombinant human fibroblast growth factor‐2 in the dose‐ range studied can effectively overcome the retarding effects of eroding polymer on angiogenesis in bone, which has been reported previously by this laboratory. In contrast to these results, no statistically significant differences in angiogenesis rate as a function of time could be detected. It is suggested that this apparent lack of variation is linked to observed alterations in vessel patterns from week‐to‐week. The clinical relevance of these results is that inhibitory carrier effects can be compensated for by increasing the dose of loaded agent where the effect being inhibited is the one being treated, or by adding an agent specific for the inhibited effect. In either case, geometry of the carrier must be considered when programming for delivery rate.
Mouse models to study wound closure and topical treatment of infected wounds in healing‐impaired and normal healing hosts
Authors: Holder Ian Alan , Brown Rebeccah L. , Greenhalgh David G.
Published: July 2002

Full‐thickness wounds were made on the backs of wound healing‐impaired diabetic mice and their normally healing litter mates. The wounds were then inoculated with 104 colony‐forming units of Pseudomonas aeruginosa. In both cases, the inoculum increased rapidly to between 109 and 1010 colony‐forming units/wound area. The infection caused a significant decrease in wound closure in the normally healing mice. In the wound healing‐impaired diabetic mice, infection increased the size of the wound area over 100% by day 21. The wound became filled with inflammatory cells and serous fluid, and the mice lost significant amounts of weight, an additional sign of severe, ongoing infection. Early antimicrobial treatment of infected wounds in diabetic mice (1 hour after wounding and microbial inoculation) reversed the increase in wound size area, improved wound closure, and reduced to a significant degree the weight loss observed in untreated control mice. Delay in treatment for as little as 8 hours significantly reduces the efficacy of antimicrobial treatment. These models can be used to study the effects of infection as well as to determine the efficacy of topical antimicrobial and/or wound healing‐enhancing substances on these wounds in both normally healing and healing‐impaired hosts.
Effect of interferon‐α2b on guinea pig wound closure and the expression of cytoskeletal proteins in vivo
Authors: Nedelec Bernadette , Dodd Carole M. , Scott Paul G. , Ghahary Aziz , Tredget Edward E.
Published: July 2002

Scar contraction following the healing of deep partial‐thickness or full‐thickness dermal injury is a leading cause of functional and cosmetic morbidity. The therapeutic use of interferon for the treatment of fibroproliferative disorders associated with scar contraction, including hypertrophic scar, has been suggested because of its antifibrotic properties. Treatment of fibroblasts with interferon has been shown to reduce the rate and extent of contraction using the in vitro fibroblast‐populated collagen lattice model. In order to establish the effect of interferon‐α2b on full‐thickness wound contraction in vivo, osmotic pumps loaded with interferon or sterile saline were implanted intraperitoneally in guinea pigs. Seven days following implantation, six full‐thickness punch biopsy wounds were created and were monitored by daily assessment of the wound. There was a significant reduction in the rate of wound contraction in the interferon‐treated animals after day 3 (p < 0.01). Western blot analysis was used to quantitate selected cytoskeletal proteins in the normal skin and tissue biopsied from the wound at days 7, 14, and 21 postinjury. The amount of vimentin in the contracted wound increased following injury as compared with the amount present in normal skin (p < 0.0001); however, the relative amounts of the myofibroblast‐associated cytoskeletal proteins α‐smooth muscle actin and smooth muscle myosin were less than those found in normal, uninjured skin. By using vimentin to adjust the levels of cytoskeletal proteins for the increase in cellularity in the wounds, both α‐smooth muscle actin and smooth muscle myosin significantly increased after closure of the wounds on day 14, as compared with the open‐wound stage (day 7), before further reductions occurred with remodeling on day 21. Measurement of apoptotic cells using the terminal deoxynucleotidyl transferase‐mediated dUTP‐biotin nick end labeling assay revealed an increase in apoptosis in the interferon‐α2b‐treated animals at 21 days following wounding (p < 0.001), which did not colocalize with α‐smooth muscle actin staining. Taken together, these findings suggest that interferon‐α2b inhibits wound contraction in vivo, not through an appreciable alteration in myofibroblast number or cytoskeletal protein expression, but possibly through a reduction in fibroblast cellularity by the induction of apoptosis.
Retinoids as endogenous components of the regenerating limb and tail
Authors: Maden Malcolm
Published: July 2002

The role of retinoids (vitamin A derivatives) in limb and tail regeneration is the focus of this review. The dramatic effects of excess retinoids on regeneration are considered, which consist of the respecification of each of the cardinal axes of the limb and the transformation of tail regenerates into limbs. The evidence that retinoids are endogenous components of the regeneration blastema and are required for normal regeneration is then addressed. This evidence consists of the fact that various techniques can detect endogenous retinoic acid in the blastema and that retinoic acid receptors are present, and an individual function in regeneration has been established for each of three receptors. Finally, experiments are described in which retinoic synthesis has been inhibited, and this results in the inhibition of both limb development and limb and tail regeneration.
Expression of sonic hedgehog gene in regenerating newt limbs
Authors: Imokawa Yutaka , Yoshizato Katsutoshi
Published: July 2002

Urodele amphibians such as the newt can regenerate their limbs even as adults. We have focused on the expression of sonic hedgehog, a gene that plays an important role in pattern formation during limb development, in regenerating limbs. Our in situ hybridization experiments showed that the sonic hedgehog gene was expressed in mesenchymal cells of the posterior region of regenerating limb blastemas, strongly suggesting the presence of a zone of polarizing activity (ZPA) in blastemas. Experiments with axially reversed grafts of blastemas further supported this suggestion. Axial reversal of blastemas leads to the regeneration of supernumerary limbs. The sonic hedgehog gene, which was used as a posterior marker, was expressed not only in the original region (new anterior side) of the graft, but also ectopically in the other region (new posterior side) of the same graft. The formation of supernumerary limbs was closely related to the duplication of sonic hedgehog expression on axially reversed grafts of blastemas. This duplication of sonic hedgehog expression could represent the presence of two ZPAs in axially reversed grafts. Thus, we suggest that the limb‐regeneration blastema employs a ZPA as the signaling center for anterior‐posterior patterning, as is the case in the developing limb bud.
Studies on the biological activity of the dermal regeneration template
Authors: Yannas Ioannis V.
Published: July 2002

In mammals, the skin normally responds to injury by the processes of wound contraction and scar formation. However, if a unique acellular dermal regeneration template is placed into the wound, wound contraction is strongly inhibited, and the skin undergoes a regenerative‐type healing. It is proposed that these phenomena result from the disruption of a “mechanically coherent” organization of myofibroblasts within the wound. Evidence suggests that the dermal regeneration template prevents the formation of cell‐extracellular matrix interactions (fibronexi), which foster the assemblage of a mechanically coherent wound bed. Additional studies support a similar mechanism for the enhanced regenerative‐like response to peripheral nerves when extracellular matrix tubes are used to facilitate healing.
Use of enzyme treatment to enhance reactivity of HLA and platelet‐specific antibodies in solid‐phase RBC adherence assays
Authors: Leach Miriam Fogg , AuBuchon James P.
Published: July 2002

BACKGROUND: Solid‐phase RBC adherence (SPRCA) assays (Immucor) detect HLA and/or platelet‐specific antibodies. Pretreatment of reagent platelets with enzymes was investigated to determine whether the sensitivity of the assay could be increased.

STUDY DESIGN AND METHODS: SPRCA testing, following the manufacturer's directions, was performed on 51 sera from patients with either a positive SPRCA antibody screen, suboptimal clinical responses to platelet transfusions, and/or suspected immune thrombocytopenic purpura; testing was also performed following pretreatment of the reagent platelets with bromelin, papain, or ficin. Sera from 23 patients having negative routine SPRCA antibody screens and good clinical responses to transfusion were tested as controls. Lymphocytotoxic antibody testing was also performed on selected samples. The effectiveness of enzyme treatment was judged by the increase in the proportion of reagent platelets reacting with the sample and the observed reaction strengths.

RESULTS: Pretreatments of reagent platelets with all three enzymes increased the reactivity of known antibodies and detected some HLA and platelet‐specific antibodies that had not reacted in routine testing. The clinical significance of the antibody specificities detected only after enzyme pretreatment was verified by a correlation with results from transfusing antigen‐negative units. Only occasional false‐positive results after enzyme pretreatment were observed.

CONCLUSIONS: The use of enzyme pretreatment of SPRCA screening strips can provide information that is useful in selecting appropriate units for transfusion.
Syndromic Diagnosis at the Epilepsy Clinic: Role of MRI in Lobar Epilepsies
Authors: Lee Byung In , Heo Kyoung , Kim Jang Sung , Kim Ok Joon , Park Sun Ah , Lim Sung Ryong , Kim Dong Ik , Yoon Pyung Ho , Kim Dong Kee
Published: July 2002

Summary:  Purpose: Magnetic resonance imaging (MRI) is an essential diagnostic tool for the management of epilepsy at modern epilepsy clinics. This study was conducted to incorporate MRI features into the international classification of epilepsies and epilepsy syndromes (ICEES) proposed by the International League Against Epilepsy (ILAE).

Methods: Three hundred consecutive patients newly registered in the Yonsei Epilepsy Clinic underwent stepwise classifications based on clinical features, clinical EEG, and clinical EEG–MRI correlations. The patients were required to have epilepsy and have undergone both EEG and MRI for inclusion in the study. Interictal epileptiform discharges (IEDs) in the EEG were divided into lobar, multilobar, and generalized. MRI lesions were divided into lobar and multilobar lesions. Lobar epilepsies (LEs) were divided into temporal, frontal, parietal, occipital, rolandic, temporoparietooccipital junctional, multilobar, and nonlocalized LEs.

Results: Two hundred forty‐nine patients satisfied the inclusion criteria. In the first‐step diagnosis, 190 patients were classified as having localization‐related epilepsy; 24 patients, generalized epilepsy; 34 patients, undetermined epilepsy; and one patient, a special syndrome. EEG revealed IEDs in 124 (50%) patients, and the second‐step diagnosis changed the diagnostic categories of 79 (32%) patients. MRI detected lesions in 106 (43%) patients, and the third‐step diagnosis changed the diagnostic categories of 30 (12%) patients. The nonspecific diagnostic categories of ICEES decreased from 49% to 37% and then to 29%, as diagnosis progressed from steps one to three. In cases of LE, MRI was superior to EEG in its clinical correlation. Additionally, the diagnostic precision in temporal lobe epilepsy was far better than that for other LEs.

Conclusions: The impact of MRI on ICEES was only modest in terms of changing diagnostic categories, although MRI provided a structural substrate for epilepsy in 38% of patients with negative EEGs. In LE, MRI was as sensitive as EEG, and its clinical correlation was superior to that of EEG, which strongly supports the rationale of incorporating MRI into ICEES.
Selective Embryo Abortion Hypothesis Revisited ‐ A Molecular Approach
Authors: Korbecka G. , Klinkhamer P. G. L. , Vrieling K.
Published: July 2002

Abstract: Many plant species abort a large fraction of their embryos. It has often been suggested that embryos of genotypes that would perform worse later in life are preferentially aborted. Such selective embryo abortion would lead to investment of resources only in the offspring with the highest potential fitness. Many studies have shown that otherwise viable embryos are aborted. However, only few manipulative studies have indeed shown a correlation between the level of abortion and offspring quality and these studies have been challenged for their experimental design. Molecular techniques open new opportunities to study selective embryo abortion. Non‐random abortion at the level of molecular markers can be observed as a deviation from Mendelian segregation: over‐ or under‐representation of markers in the offspring. Subsequently, the over‐ or under‐represented markers can be related to offspring quality later in life. We reviewed the literature on the genetic maps of intraspecific crosses of wild plant species and the selection of cultivated species. The level of non‐Mendelian segregation we found in these maps is high. On average, 11.5 % of the tested markers in the genetic maps of wild species and 14.6 % in the cultivated ones, show a departure from Mendelian segregation. From six studies, providing sufficient data, it was calculated that in 68 % of loci segregating in non‐Mendelian fashion post‐fertilization selection is involved. We propose that the deviation from Mendelian segregation can be partly explained by selective embryo abortion. We describe an experimental design that allows for attributing selective embryo abortion to the non‐Mendelian segregation that is found in a genetic map.
Electron Transport Activities of Isolated Thylakoids from Wheat Plants Grown in Salicylic Acid
Authors: Sahu G. K. , Kar M. , Sabat S. C.
Published: July 2002

Abstract: Wheat (Triticum aestivum cv. Sonalika) plants were grown with three different concentrations of salicylic acid (SA; 50/500/1000 μM) for 7 days and the effects on the level of thylakoid photochemical activities were examined. SA treatment stimulated photosystem II‐catalyzed electron flow in all concentrations tested. Photosystem I‐associated electron transport activity was stimulated at low concentrations of SA (50 μM) but at higher concentrations (500 and 1000 μM) the electron transport activity was drastically attenuated. Thylakoids isolated from the leaves of seedlings grown with high concentrations of SA (500 and 1000 μM) showed a substantial reduction in uncoupler (NH4Cl)‐mediated stimulation in electron flow. In addition, they failed to support ADP‐dependent stimulation of electron transport activity and induced a significant reduction in ATPase activity. Incubation of isolated thylakoids with SA, however, had no effect on thylakoid photofunction, indicating no direct effect of SA on photoelectron transport activity. Furthermore, high concentrations of SA specifically reduce the thylakoid cytochrome f554 level. The results suggest that SA, depending on its concentration, imparts differential effects on the photofunction of thylakoids. A low concentration of SA favours photosynthetic activity while the high concentration induces drastic attenuation of photosynthetic activity because of the decline in cytochrome f554.
Equilibrium of field reversed configurations with rotation. I. One space dimension and one type of ion
Authors: Rostoker Norman , Qerushi Artan
Published: July 2002

Self-consistent solutions of the Vlasov–Maxwell equations are obtained. They involve rigid rotor distributions. This selection is justified on physical grounds. For this selection the Vlasov equation can be replaced by moment equations which terminate without any additional assumptions. For one-dimensional equilibria with one type of ion these equations have exact solutions. A complete equilibrium solution appropriate to a field reversed configuration with rotation can be obtained by solving a generalized Grad–Shafranov equation for the flux function. From this solution all other physical quantities can be determined. A Green’s function method is developed to solve this equation, which provides a basis for an iterative solution. This method has the advantage that at every iteration the boundary conditions are satisfied. In this paper cylindrical geometry with one space dimension and one type of ion is considered, where analytic solutions are available. The convergence of the Green’s function method is established. For this nonlinear problem there is usually more than one solution for completely specified boundary conditions (bifurcation). The present method selects one solution. It is applicable to equilibria with many ion species and to two dimensions.
Equilibrium of field reversed configurations with rotation. II. One space dimension and many ion species
Authors: Qerushi Artan , Rostoker Norman
Published: July 2002

In a previous paper [N. Rostoker and A. Qerushi, Phys. Plasmas 9, 3057 (2002)] it was shown that a complete description of equilibria of field reversed configurations with rotation can be obtained by solving a generalized Grad–Shafranov equation for the flux function. In this paper we show how to solve this equation in the case of one space dimension and many ion species. The following fusion fuels are considered: D–T, D–He3, and p-B11. Using a Green’s function the generalized Grad–Shafranov equation is converted to an equivalent integral equation. The integral equation can be solved by iteration. Approximate analytic solutions for a plasma with many ion species are found. They are used as starting trial functions of the iterations. They turn out to be so close to the true solutions that only a few iterations are needed.
An overview of the effect of large-scale inhomogeneities on small-scale turbulence
Authors: Danaila L. , Anselmet F. , Antonia R. A.
Published: July 2002

The well-known isotropic relations [see Kolmogorov, Dokl. Akad. Nauk. SSSR 30, 301 (1941); 32, 16 (1941); A. M. Yaglom, ibid 69, 743 (1949)] between second-order and third-order structure functions are, in general, unlikely to be satisfied in turbulent flows encountered in the laboratory at moderate values of the Reynolds number. The main reason for this is the non-negligible correlation between the length scales at which the initial injection of turbulent energy occurs, those which dominate the transfer of this energy down the “cascade” and those which are responsible for dissipating this energy. In the majority of flows, there is a non-negligible inhomogeneity (sometimes nonstationarity) which may be caused by different physical phenomena. This paper presents an overview of how the equations of Kolmogorov and Yaglom can be “generalized” to provide a more realistic description of small-scale turbulence. The focus is mainly on locally isotropic regions of the flow, investigated using one-point measurements and Taylor’s hypothesis. We are concerned principally with decaying grid turbulence, for which several results have already been obtained, but other flows, e.g., fully developed channel and jet flows, are also discussed.
Contact metric 5-manifolds, CR twistor spaces and integrability
Authors: Itoh Mitsuhiro
Published: July 2002

The CR twistor space is defined over a contact metric 5-manifold M. Like the 4-dim twistor theory, the integrability of the almost CR twistor structure is discussed in terms of the Weyl conformal curvature and also the scalar curvature of M.
Ion beam etching of lead–zirconate–titanate thin films: Correlation between etching parameters and electrical properties evolution
Authors: Soyer C. , Cattan E. , Rèmiens D. , Guilloux-Viry M.
Published: July 2002

Ion beam etching of sputtered Pb(Zrx,Ti1−x)O3 (PZT) with x equal to 0.54 thin films grown on Pt/Ti/SiO2/Si substrates has been performed using pure Ar gas. The etch rate dependence on the process parameters (current density, acceleration voltage, gas pressure) has been investigated. The PZT etch rate can reach 600 Å/min with acceleration voltage of 1000 V and current density of 1 mA/cm2. Selectivity ratios between PZT and masks of various natures (photoresist, Pt, Ti) have been evaluated to determine a pertinent material for etching mask. According to our etching conditions, titanium seems to be the best candidate. We evaluated the PZT surface damage by contact mode atomic force microscopy. It appears that the roughness increases after ion bombardment, and that the grain boundary zone is preferentially etched. For some etching parameters, we also observed electrical damage. Carrying out C(V) and hysteresis loops P(E) measurements before and after etching have provided evidence of degradation. We noted a large decrease in permittivity after the etching process irrespective of the current density and acceleration voltage. Ferroelectric damage was illustrated by a large increase in the average coercive field. For each of the electrical properties under study, the same behavior has been observed after etching: the increase of damage was obtained as a function of the current density and acceleration voltage. The evolution of electrical properties when the PZT layer is protected by a metallic mask has also been studied. We observed very slight variations in the electrical properties.
Particle-in-cell simulation of ion Bernstein wave excitation
Authors: Lönnroth J. S. , Heikkinen J. A. , Rantamäki K. M. , Karttunen S. J.
Published: July 2002

Ion Bernstein wave excitation is investigated with the self-consistent two-dimensional particle-in-cell method. The real ion to electron mass ratio is used in simulations in high harmonic frequency bands. The simulation results are compared with linear theory and ray tracing. Successful excitation of the ion Bernstein wave has been demonstrated with the particle-in-cell method. In some cases, the excited wave temporarily propagates in the opposite direction and slows down permanently due to complicated dispersive behavior, which makes it very difficult to use the particle-in-cell method. The excitation is studied as a function of temperature and frequency, i.e., it is determined how the dispersive behavior varies in the parameter space. The simulations indicate that there is a temperature-and-frequency-dependent critical level of coupled energy flux above which excitation fails. Possible effects causing the failure of excitation at high power intensity are identified.
Boundary values as Hamiltonian variables. II. Graded structures
Authors: Soloviev Vladimir O.
Published: July 2002

It is shown that the new formula for the field theory Poisson brackets arises naturally in the proposed extension of the formal variational calculus incorporating divergences. The linear spaces of local functionals, evolutionary vector fields, functional forms, multi-vectors and differential operators become graded with respect to divergences. The bilinear operations, such as the action of vector fields onto functionals, the commutator of vector fields, the interior product of forms and vectors and the Schouten–Nijenhuis bracket are compatible with the grading. A definition of the adjoint graded operator is proposed and antisymmetric operators are constructed with the help of boundary terms. The fulfilment of the Jacobi identity for the new Poisson brackets is shown to be equivalent to vanishing of the Schouten–Nijenhuis bracket of the Poisson bivector with itself.
Estimate of spontaneous emission coupling factor for GaAs quantum well embedded in planar microcavities with Bragg mirrors
Authors: Zhao Hong-Dong , Zhu Xiao-Guang , Zhang Yi-Mo
Published: July 2002

This article presents the spontaneous emission spectra for a single quantum well embedded in a planar microcavity with Bragg mirrors at 300 K. The confinements of vacuum fields and electrons are considered together in the microcavity. An estimate of the spontaneous emission coupling factor is given. We find that the maximum scaling of the spontaneous emission coupling factor is 0.0055.
Energy transfer in polymer electrophosphorescent light emitting devices with single and multiple doped luminescent layers
Authors: Kawamura Yuichiro , Yanagida Shozo , Forrest Stephen R.
Published: July 2002

We study energy transfer in efficient polymer electrophosphorescent organic light emitting diodes (PHOLEDs) using poly(9-vinylcarbazole) (PVK) host doped with one or more phosphorescent cyclometalated Ir(III) complexes. Single dopant double heterostructure PHOLEDs exhibited saturated color luminescence due to emissive triplet metal-to-ligand charge-transfer to ground state transitions of the Ir(III) dopants. Blue PHOLEDs, excited by an endothermic process from the host polymer, exhibited an emission maximum at a wavelength of λmax=474 nm, with an external quantum efficiency of ηext=1.3±0.1% and luminous power efficiency of ηp=0.8±0.1 lm/W. The green PHOLED exhibited ηext=5.1±0.1%, with ηext>2% for both red and yellow emission. Resonant energy transfer between green emitting fac-tris (2-phenylpyridyl)Ir(III) and red emitting bis[2-(2′-benzothienyl)-pyridinato-N,C3′](acetylacetonate)Ir(III) was observed to nearly double the efficiency of red emission when both dopants were simultaneously blended in a PVK host. PHOLEDs containing a blend of red, yellow, and blue Ir(III) complex dopants produced white light emission with ηext=2.1±0.1%. Our results suggest that deep lying energy states in the PVK conductive matrix may limit the energy transfer efficiency in phosphor doped polymer OLEDs.
Dissociation dynamics of gauche and anti conformations of 1-iodopropane ions prepared selectively by vacuum–ultraviolet mass-analyzed threshold ionization spectrometry: Photodissociation at 426 and 355 nm
Authors: Park Sang Tae , Kim Myung Soo
Published: July 2002

Mass-analyzed threshold ionization with coherent vacuum ultraviolet radiation was used to generate the gauche, or alternatively anti, ion beam of 1-iodopropane ion. Conformation-selective photodissociation of these ion beams was studied at 426 and 355 nm which correspond to excitation to the second and third electronic states appearing in the photoelectron spectrum, respectively, and compared with dissociation in the first excited state reported previously. Conformation-specificity was not observed at 426 and 355 nm unlike the dissociation in the first excited state. Plausible mechanisms for dissociations from the excited electronic states are discussed based on the presence/absence of conformation-specificity, dissociation anisotropy, and kinetic energy release.
Flexible transition state theory for a variable reaction coordinate: Derivation of canonical and microcanonical forms with angular momentum conservation
Authors: Robertson Struan H. , Wardlaw David M. , Wagner Albert F.
Published: July 2002

This paper extends work previously presented [J. Chem. Phys. 113, 2648 (2000)] to establish a rigorous expression for the angular momentum resolved microcanonical reactive flux. A kinetic energy expression in terms of the angular momentum, based on the coordinate system described in the above reference, is derived. Analytic integration over momenta conjugate to the coordinates that describe the relative orientation of the fragments is effected at the canonical level. The Laplace transform relation between canonical and microcanonical coefficients is then exploited to yield the angular momentum dependent microcanonical reactive flux. Evaluation of the resulting rate expression involves a numerical integral whose dimension, in most cases, is the same as the integrals in corresponding canonical and standard microcanonical forms.
Some characteristics of entrainment at a cylindrical turbulence boundary
Authors: Mathew Joseph , Basu Amit J.
Published: July 2002

Over the last 30 years, turbulent entrainment has come to be viewed as a large-scale process, directed by coherent structures, and described as engulfing. With turbulence simulations, we examined the process of entrainment directly, as growth of vorticity and concentration along fluid particle pathlines which were computed simultaneously. Our results indicate that the process is more often small scale. Growth occurs close to the turbulence boundary, within small radial displacements, and in times which are smaller than local large-scale times. These observations can be cast into a model to show that overall rates can be predicted by large-scale quantities even though the process occurs at small scales; the only requirement is a fixed relationship across scales as in fully developed turbulent flows. So it is not inconsistent that engulfment can be a successful, and accepted, model for fully developed flows even if it is not the more frequent process.
Unsteady mixed convection in a horizontal channel with protruding heated blocks and a rectangular vortex promoter
Authors: Wang Qinghua , Jaluria Yogesh
Published: July 2002

The objective of this research is to study the resonance oscillatory flow in a channel and the resulting effect on thermal transport, leading to cooling enhancement in electronic systems. The unsteady mixed convection through a horizontal channel with two isolated protruding blocks on the bottom wall has been studied numerically. For this geometry, at moderate Reynolds numbers, the flow is found to separate at the leading edge of the first block, and then reattach at the top surface of the second block. At a given Grashof number, when Re exceeds a critical value, vortex is shed only from the second block, and rolls over the bottom wall with its size decaying, while one or two recirculating cells are trapped in the groove. The base vortex shedding frequency is dependent on the buoyancy level Gr/Re2. The critical value of Re is much lower when perturbation is introduced by a rectangular or square promoter in the channel. The frequency and amplitude of perturbation are changed by adjusting the geometry of the promoter. An improved fluid exchange between the main flow and the recirculating cell occurs when the promoter is employed. The effects of frequency and perturbation amplitude on the flow and on the heat transfer are investigated. The study consists of three parts. The first studies the developing flow in the grooved channel; the second investigates the vortex shedding from a rectangular promoter confined in a smooth channel; and the last studies the effect of resonance by tuning the frequency of vortex shedding.
Stereodynamics and control effects in the ultraviolet photolysis of Ar–HBr
Authors: Prosmiti R. , Garcı́a-Vela A.
Published: July 2002

The ultraviolet photolysis of the Ar–HBr cluster is studied by means of quasiclassical trajectory simulations. The goal is to investigate the effect of the initial distribution of intracluster orientations on the photolysis process. Cluster photolysis is simulated starting from two different initial states of Ar–HBr(v=1), namely the ground and the first excited van der Waals states corresponding to the Ar–H–Br and Ar–Br–H isomers, respectively. These two states represent different initial situations for hydrogen dissociation, which in the first case is hindered to a large extent, and in the second case is not. The probability for the fragmentation pathway into H and Ar–Br radical fragments is found to be substantially higher (and therefore the efficiency of the total fragmentation pathway, into H+Ar+Br, is lower) for the cluster initial state where H dissociation is less hindered. The effect of the angular distributions shape of the initial state is also clearly manifested in the state distributions of the different photofragments. It is concluded that selecting the initial state of the cluster on the basis of the shape of its angular distribution provides an efficient means to control the yield of the different fragmentation pathways, and the final states of their corresponding photolysis products.
Absolute cross sections for electron impact ionization of NO2
Authors: Jiao C. Q. , DeJoseph C. A. , Garscadden A.
Published: July 2002

Absolute partial cross sections for electron impact ionization of nitrogen dioxide (NO2) are determined using Fourier-transform mass spectrometry in the energy range from threshold to 200 eV. Data are presented for the production of the major ionic species, NO2+, NO+, O+, and N+. Ion intensity dependence on the trapping potential is studied for the purpose of probing the kinetic energy of the product ions from the electron impact ionization. O+ and N+ are found to have significant kinetically excited ion populations. The cross-section data are corrected for loss of energetic species from the trap and the results are compared with previous data.
Crystal orbital calculation of coupled-perturbed Hartree–Fock dynamic (hyper)polarizabilities for polydiacetylene and polybutatriene
Authors: Gu Feng Long , Aoki Yuriko , Bishop David M.
Published: July 2002

Crystal orbital coupled-perturbed Hartree–Fock static and dynamic (hyper)polarizabilities for polydiacetylene (PDA) and polybutatriene (PBT) are computed. Geometry effects have been investigated. The static CPHF/6-31G second-order hyperpolarizability of PBT is 67 times larger than that of PDA using the optimized geometries at the HF/6-31G level. However, this factor is reduced to 17 with the optimized geometries at the MP2/6-311G* level. One of the bond length alternations (BLA), the difference between the single and double bond lengths (S/D), of PDA is the most sensitive factor for the (hyper)polarizabilities. It has been shown from the calculations that a smaller S/D produces a larger polarizability and second-order hyperpolarizability of PDA. Unlike PDA, two different BLAs of PBT are competing to change the values of polarizability and second-order hyperpolarizability. The dynamic second-order hyperpolarizabilities have been checked with the general dispersion expression by fitting the results to a polynomial. Our theoretical results can also be compared with experiment and possible reasons for the discrepancies are addressed.
Semicollisional heat flux in laser heated plasmas
Authors: Tahraoui A. , Bendib A.
Published: July 2002

The semicollisional transport theory in laser heated plasmas is presented. The Fokker–Planck equation that includes the electron–electron interaction up to the first anisotropy is solved numerically for arbitrary collisionality range. The inverse bremsstrahlung absorption of the laser energy by the electrons is taken into account. Nonlocal heat flux formulas due to the thermal gradients and to the laser heating, which are in good agreement with the numerical results, are proposed. These transport coefficients are compared with the results of the literature.
A pulsed field gradient nuclear magnetic resonance study of a ternary homopolymer/diblock copolymer blend in the bicontinuous microemulsion phase
Authors: Gröger Stefan , Rittig Frank , Stallmach Frank , Almdal Kristoffer , Štěpánek Petr , Papadakis Christine M.
Published: July 2002

Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) was applied to study self-diffusion in a ternary blend containing equal molar volumes of the homopolymers poly(dimethylsiloxane) (PDMS) and poly(ethylethylene) (PEE), and the nearly symmetric PDMS-PEE diblock copolymer. The blend forms a bicontinuous microemulsion (BμE) below ∼83 °C, while it is in the disordered state at higher temperatures. PFG NMR has also been applied to the individual components of the blend. In the blend, we find one diffusional process in the disordered state and two diffusional processes in the BμE state. The fast process in the BμE is due to the diffusion of the PDMS homopolymers through the BμE. This diffusion is ten times slower than that of bulk PDMS at the same temperature, indicating restricted diffusion of PDMS in the BμE. The diffusion coefficient of the slower process in the ternary blend is slightly increased compared with bulk PEE. It is tentatively assigned to PEE self-diffusion. The changes in homopolymer diffusivities are semiquantitatively explained in terms of a model taking into account the tortuosity of the BμE as well as the fast exchange of homopolymers between the domains and the difference in viscosities of the PEE and the PDMS domains. Our results are compared with data obtained previously on the identical sample with dynamic light scattering experiments [T. L. Morkved et al., Faraday Discuss. 112, 335 (1998)].
Broad Raman scattering and luminescence in β-carotene solution
Authors: Nakamura R. , Yamamoto S. , Nakahara J.
Published: July 2002

Resonant secondary radiation spectra of dilute β-carotene solution (10−4–10−5 M) are measured under stationary excitation. The excitation energy is varied within 0–0 and 0–1 transition energies in the S2–S0 transition of β-carotene. When the excitation energy is varied from the peak of the 0–0 absorption band to the low-energy side at 60 K and 175 K, (a) the line shape of 0–0 emission band changes from symmetric to asymmetric, and (b) the intensity of luminescence rapidly decreases as compared with the intensity of Raman scattering by ν1, ν2, and ν3 intramolecular vibronic modes of β-carotene. When the 0–1 absorption band is excited, we successfully separate luminescence and broad Raman component (BR), which is resonant Raman scattering of low-frequency phonon modes in solution. The line shape of the density of vibronic states weighed by the coupling strength between electronic states in a dye molecule and vibrations of the surrounding atoms (WDOS) is determined by BR. Taking into account inhomogeneous broadening and assuming linear electron–phonon coupling, the resonant secondary radiation spectra are calculated using obtained WDOS. The above characters of the experimental results (a) and (b) are well reproduced by the calculations.
Grown-in defects in nitrogen-doped Czochralski silicon
Authors: Yu Xuegong , Yang Deren , Ma Xiangyang , Yang Jiansong , Li Liben , Que Duanlin
Published: July 2002

Grown-in defects including oxygen precipitates and voids in nitrogen-doped Czochralski (NCZ) silicon have been investigated. It was found that the formation of grown-in oxygen precipitates in NCZ silicon can be divided into two stages. The large precipitates supposed to be enhanced by N2–V2–Ox complexes are generated around 1150 °C, while the small precipitates supposed to be enhanced by NmOn complexes are formed at 750 °C and below. Moreover, it was revealed that the oxygen precipitation behavior in the mixed-type NCZ silicon, which contains vacancy-type and interstitial-type defects distinguished by an OSF-ring in the oxidized wafer, is in sharp contrast to that in the mixed-type Czochralski (CZ) silicon, when subjected to one-step high temperature annealing (1050 °C/32 h) and two-step annealing (800 °C/4 h+1050 °C/16 h). On the other hand, it was found that, compared with CZ silicon, NCZ silicon has much denser crystal originated particles in smaller sizes, which were verified to have been annihilated at relatively lower temperatures. Based on the experimentally found phenomena, a tentative model that takes into account the formation of nitrogen-related complexes involving oxygen atoms and vacancies, void formation, and oxygen precipitation is presented.
Quantum mechanical scattering investigation of the thermionic and field induced emission components of the dark current in quantum well infrared photodetectors
Authors: Etteh N. E. I. , Harrison P.
Published: July 2002

The thermionic emission and field induced emission components of the dark current in quantum well infrared photodetectors are investigated using a quantum mechanical scattering theory approach. Calculations are performed for an experimentally reported device. Using this as a standard, the device dimensions were altered in order to increase its detection wavelength to cover the mid- (MIR) and far-infrared (FIR) regions of the spectrum. The behavior of the scattering mechanisms that contribute to the thermionic emission and field induced emission components were studied. The results highlight the change in the dominating scattering mediator across the MIR and FIR bands.
Reactivity of Ti(IV) sites in Ti-zeolites: An embedded cluster approach
Authors: Damin Alessandro , Bordiga Silvia , Zecchina Adriano , Lamberti Carlo
Published: July 2002

We report a complete cluster/embedded cluster study by means of ab initio methods in the ONIOM scheme, as implemented in GAUSSIAN 98 code, of the reactivity towards water and ammonia of Ti(IV) centers in zeolitic frameworks. For water adsorption, we observe a remarkable increment of the binding energies by moving from 2.1 kJ mol−1 for the unconstrained Ti(OSiH3)4 cluster to 16.9 kJ mol−1 for the TiSi17O26H20 cluster, obtained by cutting a portion of the MFI framework. The same holds for ammonia, where the binding energy increases from 17.4 to 35.4 kJ mol−1, all reported values being BSSE corrected. These results underline the fundamental role played by zeolitic framework constraints, in enhancing the reactivity of Ti(IV) centers towards both H2O and NH3 probes. On the geometrical ground the Ti–O distance of bare clusters and its modification in complexes are in good agreement with the first shell EXAFS data analysis.
Locating the Al atom in Ni14Al–Ni19Al clusters
Authors: Parks E. K. , Rexer E. F. , Riley S. J.
Published: July 2002

Reactions of N2 with NinAl clusters, n=14–19, are used to determine the location of the Al atom within the cluster framework. N2 saturation levels are consistent with cluster structures in which one surface atom of the corresponding Nin+1 cluster is replaced with an Al atom. For n=14 and 17–19 it is possible to precisely locate the Al atom within the surface. In general, its placement maximizes the number of Ni–Al bonds for a surface Al atom.
Jacobson generators, Fock representations and statistics of sl(n+1)
Authors: Palev T. D. , Van der Jeugt J.
Published: July 2002

The properties of A-statistics, related to the class A of simple Lie algebras [T. D. Palev, preprint JINR E17-10550 (1977); hep-th/9705032], are further investigated. The description of each sl(n+1) is carried out via generators a1±,…,an±, which we call Jacobson generators. With respect to these generators, the definition of a Fock space of sl(n+1) is given. It is proved that the Fock spaces Wp, p∈N are the simple symmetric (finite-dimensional) modules of sl(n+1). The Pauli principle of the underlying statistics is formulated. Within each Wp operators B(p)i±=ai±/p (i=1,…,n), called quasi-Bose creation and annihilation operators (CAOs), are defined. Then limp→∞B(p)i±=Bi±, where Bi± are ordinary Bose CAOs. Therefore A-statistics appears as an approximation of Bose statistics with CAOs acting in finite-dimensional state spaces. We indicate that the p=1 quasi-Bose operators B(1)1±,…,B(1)n± are natural operators for the description of hard-core Bose models and of the related Heisenberg spin models. We argue that (up to a certain natural assumption) A-statistics can be interpreted as an exclusion statistics.