bluuebunny/crossref_metadata_2025 huggingface dataset:
Universal shape ratios for polymers grafted at a flat surface
Authors: Causo Maria Serena
Published: October 2002

We consider dilute nonadsorbed polymers grafted at an impenetrable surface and compute by Monte Carlo simulations several quantities which characterize the polymer shape: the asphericity and the ratios of the eigenvalues of the radius-of-gyration tensor. The results are only slightly different from those obtained for a single polymer in free space, showing that the surface has little influence on the polymer shape.
Prediction of absolute rate coefficients and product branching ratios for the C(3P)+allene reaction system
Authors: Schranz Harold W. , Smith Sean C. , Mebel Alexander M. , Lin Sheng H.
Published: October 2002

Complex chemical reactions in the gas phase can be decomposed into a network of elementary (e.g., unimolecular and bimolecular) steps which may involve multiple reactant channels, multiple intermediates, and multiple products. The modeling of such reactions involves describing the molecular species and their transformation by reaction at a detailed level. Here we focus on a detailed modeling of the C(3P)+allene (C3H4) reaction, for which molecular beam experiments and theoretical calculations have previously been performed. In our previous calculations, product branching ratios for a nonrotating isomerizing unimolecular system were predicted. We extend the previous calculations to predict absolute unimolecular rate coefficients and branching ratios using microcanonical variational transition state theory (μ-VTST) with full energy and angular momentum resolution. Our calculation of the initial capture rate is facilitated by systematic ab initio potential energy surface calculations that describe the interaction potential between carbon and allene as a function of the angle of attack. Furthermore, the chemical kinetic scheme is enhanced to explicitly treat the entrance channels in terms of a predicted overall input flux and also to allow for the possibility of redissociation via the entrance channels. Thus, the computation of total bimolecular reaction rates and partial capture rates is now possible.
The origin of the open-circuit voltage in polyfluorene-based photovoltaic devices
Authors: Ramsdale C. M. , Barker J. A. , Arias A. C. , MacKenzie J. D. , Friend R. H. , Greenham N. C.
Published: October 2002

The influence of device structure on the open-circuit voltage of polyfluorene-based photovoltaic devices has been investigated. Bilayers of hole- and electron-accepting polyfluorenes have been fabricated using an aqueous “float-off” lamination technique and subsequently incorporated into organic photovoltaic devices with a range of cathodes and anodes. A scaling of the open-circuit voltage with electrode work function difference has been observed with an additional intensity- dependent contribution from the active layer within the device. This additional contribution is attributed to photoinduced generation of carriers, whereby accumulation of charge at the polymer–polymer heterojunction results in a dipole across the interface and gives rise to a diffusion current that must be counterbalanced by a drift current at open circuit.
Metalorganic precursor decomposition and oxidation mechanisms in plasma-enhanced ZrO2 deposition
Authors: Cho Byeong-Ok , Wang Jianjun , Chang Jane P.
Published: October 2002

We investigated the gas phase reaction mechanisms in the ZrO2-deposition plasma using zirconium tert-butoxide (ZTB) as a metalorganic precursor, Ar as a carrier of the ZTB vapor, and O2 as an oxidant using quadrupole mass spectrometry (QMS). Zirconium containing ions including Zr+, ZrO+, ZrO2H+, ZrO3H3+, and ZrO4H5+ were clearly observed in the plasma, and ions of higher zirconium oxidation states become progressively favored at higher O2-to-ZTB carrying Ar flow rate ratio (O2/Ar), increased chamber pressure, and decreased microwave power. The average oxidation state calculated from the partition of ZrOxHy+ varied from 0.5 to 2.1 in the process range covering O2/Ar of 0 to 4, pressure of 5 to 40 mTorr, and power of 150 to 700 W. Based on the QMS analyses, we proposed two main opposing reaction paths responsible for the complex gas phase reactions, i.e., serial dissociations and serial oxidations. The increase in the electron temperature and density resulted in the shift of ZrOxHy+ to lower oxidation states by enhancing the dissociation of Zr–O bond and by depleting oxygen through gas phase reactions. The repartitioning of the ZrOxHy+ species was also contributed by their different Zr–O dissociation energies. To ascertain the effect of various process variables, we monitored the time evolutions of O2+ and ZrOxHy+ intensities as we abruptly change a process variable: the chemical effect (O2/Ar) led to gradual changes in their intensities, whereas physical effects (pressure and power) caused an abrupt step change in accordance with an instant response of the plasma electrons.
The van der Waals potential energy surfaces and structures of He–ICl and Ne–ICl clusters
Authors: Prosmiti Rita , Cunha Carlos , Villarreal Pablo , Delgado-Barrio Gerardo
Published: October 2002

The potential energy surfaces of the ground electronic state of rare gas interhalogen van der Waals molecules, Rg–ICl (Rg=He, Ne), are calculated at CCSD(T) (coupled cluster using single and double excitations with a noniterative perturbation treatment of triple excitations) level of theory. Calculations have been performed with specific augmented correlation consistent basis sets for the noble atom (Rg), supplemented with an additional set of bond functions. For iodine atom a correlation consistent triple zeta valence basis set in conjunction with large-core Stuttgart–Dresden–Bonn relativistic pseudopotential has been employed. The CCSD(T) results predict the existence of three minima on the Rg–ICl potential energy surfaces at collinear (Rg–ICl), antilinear (Rg–ClI), and near T-shaped configurations, with the collinear structure to be the lowest one. Bound states calculated from the intermolecular potential surfaces show that zero-order vibrational corrections do not alter the stability of the three structures. Equilibrium intermolecular distances, binding energies, and isomerization barriers are evaluated using the CCSD(T) potentials and compared with previous theoretical and/or experimental results.
Green emission from poly(fluorene)s: The role of oxidation
Authors: Zojer Egbert , Pogantsch Alexander , Hennebicq Emmanuelle , Beljonne David , Brédas Jean-Luc , Scandiucci de Freitas Patricia , Scherf Ullrich , List Emil J. W.
Published: October 2002

Poly(fluorene)-type materials are widely used in polymer-based light emitting devices. In their pristine state, they emit in the deep blue spectral region. During operation there appears, however, an additional emission peak at around 2.3 eV. This observation has usually been attributed to aggregate or excimer formation. Recently, it has been shown that photo- and/or electro-oxidation of poly(fluorene) chains resulting in ketonic defects (i.e., formation of fluorenone groups) can also be held responsible for emission in that spectral region. In this contribution, we apply quantum-chemical techniques to gain a detailed understanding of the optical properties of poly(fluorene)s containing ketonic defects. In particular, we compare model systems for poly(fluorene) with their ketone-containing counterparts, focusing on the influence of excited-state localization effects. The results of the theoretical calculations are confirmed by experimental investigations on statistical copolymers of fluorene and 9-fluorenone.
Spatiotemporal patterns on cylindrical surfaces due to convection, conduction, and reaction
Authors: Nekhamkina O. , Savin I. , Sheintuch M.
Published: October 2002

Spatiotemporal patterns emerging on a cylindrical surface, representing an annular reactor with convection in the axial direction, are simulated with a model that incorporates an activator and a slow changing and localized inhibitor. This condensed polynomial model captures the main features of high- or low-pressure catalytic oscillations. The results are organized in bifurcation diagrams showing the coexisting solutions with varying convection. Steady rotating band solutions, that emerge with proper initial conditions, exist for sufficiently low fluid velocity (V) and bifurcate to steady patterns for a bistable kinetics. For the oscillatory kinetics the rotating solutions coexist with the oscillatory solutions that are independent of the angular coordinate. For large V a single homogeneous solution exists, which is mainly defined by the inlet boundary condition. In the limit of a very long cylinder, helix-shape rotating band may exist, allowing one to gain some insight into analytical solutions.
Equilibrium phase behavior of polyethylene oxide and of its mixtures with tetrahydronaphthalene or/and poly(ethylene oxide-block-dimethylsiloxane)
Authors: Madbouly Samy A. , Wolf Bernhard A.
Published: October 2002

Liquid/solid and liquid/liquid (LL) transition temperatures were measured by means of an automated device that monitors the light passing through the systems as a function of T at different constant cooling or heating rates q̇. For pure polyethylene oxide (PEO) crystallization and melting temperatures depend on |q̇|0.3 and become identical at the equilibrium transition temperature Tm=61.0 °C in the limit of infinitely slow cooling/heating. The reduction of Tm for PEO dissolved in tetrahydronaphthalene (THN) yields information on the Flory–Huggins interaction parameter ξ between these two compounds; ξ results negative and decreases markedly with rising polymer concentration. A tentative explanation for this finding is offered. The binary blend between PEO and poly(ethylene oxide-block-dimethylsiloxane) (COP, Tm=0 °C) exhibits a much more complex phase diagram than the system THN/PEO. An additional and extended miscibility gap (LL) is observed at high temperatures and there is no experimental evidence of an eutectic. From the details of the phase diagram we conclude that the EO-rich block copolymer can incorporate small amounts of PEO and form mixed crystals. The existence of two three-phase lines is postulated. The melting behavior of PEO in the ternary system THN/COP/PEO (constant weight fraction of PEO) fits well into the other results.
Photodissociation of the vinoxy radical through conical, and avoided, intersections
Authors: Matsika Spiridoula , Yarkony David R.
Published: October 2002

The mechanism for predissociation of the vinoxy radical after the excitation X̃ 2A″→B̃ 2A″ is studied theoretically. Critical points on the Ã 2A′ and B̃ 2A″ potential energy surfaces are determined at the multireference configuration interaction level using expansions of five million configuration state functions. A mechanism consisting of a sequence of internal conversions to the ground state is proposed. B̃ 2A″–Ã 2A′ conical intersections are shown to be too high in energy to participate in this process. The B̃ 2A″–Ã 2A′ radiationless transition is enabled by an avoided crossing which is accessible after a barrier of ca. 2000 cm−1, in agreement with experimental observations. Subsequently the Ã 2A′→X̃ 2A″ radiationless transition can occur very efficiently through easily accessible conical intersections. A one-dimensional coupled adiabatic state model of the process is developed. The radiationless decay rates of the vibrational levels obtained from this model serve to validate the proposed mechanism.
Molecular dynamics study of phase transitions in Xe
Authors: Belonoshko A. B. , LeBacq O. , Ahuja R. , Johansson B.
Published: October 2002

A full account is given of our recent theoretical discovery [A. B. Belonoshko, R. Ahuja, and B. Johansson, Phys. Rev. Lett. 87, 165505 (2001)] of the fcc–bcc transition in Xe at high pressure and temperature. The interaction model and method for calculating phase boundaries are exhaustively tested by independent methods. The model was carefully checked against experimental data and results of ab initio molecular dynamics and it was found to perform very well. The two-phase method employed for finding the melting transition was compared with the robust thermodynamic approach and was found to provide data in exact agreement with the latter. The deviation of the calculated melting curve from the experimental one is quite tolerable at low pressures. After a reinterpretation of the experimental data, our results are also in good agreement with recent diamond anvil cell experiments. At a pressure of around 25 GPa and a temperature of about 2700 K, we find a triple fcc–bcc-liquid point. The fcc–bcc boundary is calculated without reference to the experimental data, in contrast to our previous work, and found to be in nice agreement with previous calculations as well as with the experimental data points, which, however, were interpreted as melting. Our finding concerning the fcc–bcc transition is confirmed by the direct molecular dynamics simulation of the fcc, bcc, and liquid phases in the same computational cell. In this simulation, it was observed that while the fcc phase melts, the bcc structure solidifies. Since Xe is a typical rare-gas solid, the fcc–bcc transition can now be expected for a number of other van der Waals systems, first of all in Ar and Kr. Our finding suggests, that the transition from close packed to bcc structure might be more common at high pressure and high temperature than was previously anticipated. The performed thorough test of methods and models in this study leads us to suggest that the original interpretation of experimental results is erroneous.
Atomic structure and defect densities in low dielectric constant carbon doped hydrogenated silicon oxide films, deposited by plasma-enhanced chemical vapor deposition
Authors: Ligatchev V. , Wong T. K. S. , Liu B. , Rusli
Published: October 2002

Results of structural characterization by Fourier transform infrared spectroscopy, x-ray diffraction, and specular x-ray reflectivity measurements are employed for the interpretation of electrical measurement data and the deconvoluted distribution of electron states, N(E) of carbon doped hydrogenated silicon oxide (SiOCH) low-k dielectric films. Atomic structure of the films is identified as a mixture of a dominant and totally amorphous SiO2-like phase with a partially polycrystalline SiC phase. The n-type dc conductivity that dominates in this material points to the principal role of the SiC-like phase in the dc transport of the SiOCH material. The deep level transient spectroscopy technique is applied for the N(E) shape studies in the energy range up to 0.7 eV below the conduction band bottom. Typical N(E) values lie in the 1010–1014 eV−1 cm−3 range for films deposited at different ratios of tri-methyl-silane to oxygen flow rate. No correlation between the N(E) shape and the film deposition conditions have been found in this case. The Fermi level position usually lies at 0.18–0.4 eV below conduction band bottom. For the SiOCH films prepared at different levels of rf power densities, the N(E) in the whole studied range increases nearly monotonically with increasing rf power, which is attributed to the SiC-like phase fraction increment. An N(E) peak at 0.25–0.35 eV below conduction band bottom has been found in the films. The possible origin of the peak appearance is discussed.
Hyperfine coupling and pseudorotational motion interaction in Na3
Authors: Coudert L. H. , Ernst W. E. , Golonzka O.
Published: October 2002

Hyperfine patterns calculations are carried out for the Na3 cluster with a view towards understanding the microwave measurements which were performed for three rotational transitions belonging to the ground X̃ electronic state. The calculations take simultaneously into account the pseudorotational motion, the spin-rotation coupling, and the magnetic electron spin-nuclear spin hyperfine coupling. Matching calculated and observed patterns suggests that the cluster is characterized by small pseudorotational tunneling and spin-rotation splittings, some amount of Fermi contact interaction at the two terminal nuclei, and significant dipolar spin-nuclear spin coupling for the central atom.
Identification of different phases in barriers of interface-engineered ramp-edge Josephson junctions: Formation mechanisms and influences on electrical properties
Authors: Wu Y. , Ishimaru Y. , Wakana H. , Adachi S. , Tarutani Y. , Tanabe K.
Published: October 2002

Interface-engineered ramp-edge Josephson junctions with different critical current values and different electrode materials are investigated by transmission electron microscopy. High- resolution transmission electron microscopic observations show the coexistence of Y2O3, Y2Ba2O5, and a Ba-based pseudocubic phase in the barrier. The formation mechanism is related to the etching time and the composition of electrode materials. It is found that Y2O3 domains with typical sizes between 4 and 25 nm2 frequently exist in the thick regions of the barrier and the more the base electrode is fully covered by the domains of these phases, the lower the critical current value; the higher the fraction of Y2O3 and Y2Ba2O5 to the Ba-based pseudocubic phase in the barrier, the larger the Ic spread. Moreover, the atomic structure and the composition of the barrier in the junctions with La-doped electrodes are examined. La doping seems to suppress the formation of Y2O3 and reduce the lattice mismatch between the barrier and the electrodes. In the junction with the highest critical current value, there are many Y extra planes, i.e., stacking faults rather than cubic or pseudocubic phases along the barrier, therefore, it seems that the barrier is composed of many minute grain boundaries between the 123 and 223 phases.
Study of the electronic structure of amorphous and crystallized low pressure chemically vapor deposited silicon films near the absorption threshold
Authors: Davazoglou D. , Kouvatsos D. N.
Published: October 2002

Silicon films were chemically vapor deposited on quartz substrates from SiH4 decomposition in a conventional reactor at 230 mTorr and at a temperature of 550 °C. Samples were subsequently doped with phosphorus at a concentration of 1018 cm−3 and oxidized, in order to increase the grain size and to enhance crystallization. The optical properties of these films were studied with optical transmission measurements below their absorption threshold taken after every processing step, which were analyzed with the aid of a two-band model proposed by R. Forouhi and I. Bloomer [Phys. Rev. B 34, 7018 (1986)]. It was found that the energetic distance, separation, and magnitude of the Forouhi–Bloomer (FB) bands change with the various post-deposition treatments. For the as-deposited (amorphous) films, the FB model provides a picture of the distribution of the density of states (DOS) in very good agreement with that of vacuum evaporated films measured in the past with photoelectron spectroscopy. X-ray diffraction measurements taken on crystallized samples have shown that grains were oriented with the (111) and (220) crystallographic axes normal to the substrate. It was shown that the orientation of grains affects significantly the DOS and hence the optical properties of films, which are in this case influenced by electronic transitions near the L and K points of the Brillouin zone of Si [corresponding to the (111) and (220) crystallographic directions].
Interferometric correlation spectroscopy in single quantum dots
Authors: Kammerer C. , Cassabois G. , Voisin C. , Perrin M. , Delalande C. , Roussignol Ph. , Gérard J. M.
Published: October 2002

We report high-resolution spectroscopy by interferometric correlation measurements on the photoluminescence signal of a single quantum dot. We demonstrate that the insertion of a Michelson interferometer in the detection path gives a compact and flexible setup for linewidth measurements. We have used this technique to study self-assembled InAs/GaAs quantum dots. We observe linewidth variations from one quantum dot to another, and we bring evidence of environment effects on the broadening processes.
Hot-electron-temperature relaxation time in a two-dimensional electron gas: AlGaN/GaN at 80 K
Authors: Matulionis A. , Katilius R. , Liberis J. , Ardaravičius L. , Eastman L. F. , Shealy J. R. , Smart J.
Published: October 2002

The electron temperature method is developed for a high-density two-dimensional electron gas (2DEG). The relation of electronic noise and transport properties is obtained in the case of weakly inelastic scattering without considering the scattering mechanisms in detail. The method is applied to consider the experimental data on AlGaN/GaN 2DEG channels. The electron-temperature relaxation time and its dependence on electric field are extracted from the current–voltage and noise–voltage characteristics measured for two-terminal samples at 80 K. The method works in the field range up to 3 kV/cm in the considered 2DEG channels. In this range of fields, the electron temperature reaches 350 K, and the electron–temperature relaxation time diminishes from 5 ps at low fields to 0.4 ps at 3 kV/cm.
High-efficiency blue-light-emitting diodes with narrow linewidth based on blends of poly[2-(2′-ethylhexyloxy)-1,4-phenylene] and poly(dialkylfluorene-co-dibenzothiophene)
Authors: Niu Yu-Hua , Yang Wei , Cao Yong
Published: October 2002

High-efficiency blue light-emitting diodes were realized based on the blends of poly(dialkylfluorene-co-dibenzothiophene) in poly[2-(2′-ethylhexyloxy)-1,4-phenylene] host. The external quantum efficiency was increased by about four times, relative to devices with the guest polymer alone. Much more balanced carrier injection was assigned as the origin of the performance enhancement. Dramatic narrowing on linewidth, with the full width at half maximum reduced from more than 40 to 14.3 nm, produced more pure blue emission.
High internal quantum efficiency, narrow linewidth InGaAs/GaAs/AlGaAs quantum wire light-emitting diodes
Authors: Weman H. , Sirigu L. , Karlsson K. F. , Leifer K. , Rudra A. , Kapon E.
Published: October 2002

High internal quantum efficiency (∼60%), narrow linewidth (as narrow as 14 meV) exciton emission at room temperature has been obtained using strained InGaAs V-groove quantum wire (QWR) light-emitting diodes (LEDs). The high efficiency is achieved with the aid of selective carrier injection through self-ordered AlGaAs vertical quantum wells (VQWs), where the VQWs are separated from the InGaAs QWRs by thin GaAs spacer layers in order to reduce nonradiative recombination and inhomogeneous alloy broadening. Evidence for excitonic recombination in these LEDs up to RT is provided by measurements of the emission energy shifts at high magnetic fields.
Manifestation of the Jahn–Teller effect in the EPR spectrum of the metalorganic complex [Cu(en)2H2O]SO4
Authors: Anders A. G. , Kaplienko A. I. , Kravchina O. V. , Bondarenko V. S. , Feher A. , Orendáč M. , Orendáčová A. , Kajňaková M. , Černák J.
Published: October 2002

The temperature dependence of the resonance spectrum of [Cu(en)2H2O]SO4 single crystals is investigated in the temperature range 2.3–60 K at a frequency of ∼73 GHz. At a temperature T>15 K the angular dependence of the spectrum is described by a spin Hamiltonian of axial symmetry. At T<15 K a lowering of the symmetry to rhombic and a splitting the resonance line for a field orientation H∥b are observed. These effects are discussed in a model of two nonequivalent Jahn–Teller centers with intercoupled dynamic distortions in the cell. The low-temperature behavior of the resonance line is due to critical broadening in the region of short-range magnetic order.
Quasiwetting and morphological phase transitions in confined far-from-equilibrium magnetic thin films
Authors: Candia Julián , Albano Ezequiel V.
Published: October 2002

The growth of confined magnetic films with ferromagnetic interactions between nearest-neighbor spins is studied in a stripped (1+1)-dimensional rectangular geometry. Magnetic films are grown irreversibly by adding spins at the boundaries of the growing interface. A competing situation with two opposite short range surface magnetic fields of the same magnitude is analyzed. Due to the antisymmetric condition considered, an interface between domains with spins having opposite orientations develops along the growing direction. Such interface undergoes a localization–delocalization transition that is identified as a quasiwetting transition, in qualitative agreement with observations performed under equilibrium conditions. In addition, the film also exhibits a growing interface that undergoes morphological transitions in the growth mode. It is shown that as a consequence of the nonequilibrium nature of the investigated model, the subtle interplay between finite-size effects, wetting, and interface growth mechanisms leads to more rich and complex physical features than in the equilibrium counterpart. Indeed, a phase diagram that exhibits eight distinct regions is evaluated and discussed. In the thermodynamic limit, the whole ordered phase (which contains the quasiwetting transition) collapses, while within the disordered phase, standard extrapolation procedures show that only two regions are present in the phase diagram of the infinite system.
Sr
3
Al
10
SiO
20
:
Eu
2+
as a blue luminescent material for plasma displays
Authors: Kubota Shunichi , Shimada Masahiko
Published: October 2002

A new luminescent material, Sr3Al10SiO20:Eu2+, has been synthesized. The material exhibits an emission peak at 466 nm for the (Sr0.993Eu0.007)3Al10SiO20 and a CIE chromaticity of (x=0.145, y=0.124), with relative intensity of 60% of commercial phosphor BaMgAl10O17:Eu2+ under vaccum ultraviolet excitation.
Conductivity-induced polarization buildup in poly(vinylidene fluoride)
Authors: von Seggern H. , Fedosov S. N.
Published: October 2002

During initial high-field poling of biaxially stretched poly(vinylidene fluoride) (PVDF) films, ferroelectric polarization continues to develop through times of five to six orders of magnitude longer than theoretically expected poling times. Considering a delayed poling process induced by a finite conductivity in the two phases of PVDF explains the effect. The fast poling component originates from the alignment of dipoles in the ferroelectric phase and is solely controlled by the electric field dependent switching time, while the second slow component is controlled by conductivity related charge accumulation at the interfacial boundaries whose time constant is governed by the Maxwell relaxation time.
Recording performance of high-density patterned perpendicular magnetic media
Authors: Albrecht M. , Rettner C. T. , Moser A. , Best M. E. , Terris B. D.
Published: October 2002

Isolated tracks of magnetic single-domain islands have been fabricated by patterning perpendicular Co70Cr18Pt12 continuous films using focused-ion-beam lithography, reaching areal densities as high as ∼200 Gbit/in2. We demonstrate writing and reading of individual islands using a quasistatic write/read tester. We present results on transition position jitter and signal-to-noise ratio (SNR) for patterned media and compare them with those on equivalent unpatterned strips of the media. We observe that patterning dramatically reduces jitter and improves SNR, which is independent of track width. Moreover, the synchronization requirements needed for writing bits in patterned media was investigated on a single row of islands revealing a significant “write window,” where islands can be written correctly, of about half the island period.
Nickel antidot arrays on anodic alumina substrates
Authors: Xiao Z. L. , Han Catherine Y. , Welp U. , Wang H. H. , Vlasko-Vlasov V. K. , Kwok W. K. , Miller D. J. , Hiller J. M. , Cook R. E. , Willing G. A. , Crabtree G. W.
Published: October 2002

Large-area nickel antidot arrays with a density up to 1010/cm2 have been fabricated by depositing nickel onto anodic aluminum oxide membranes that contain lattices of nanopores. Electron microscopy images show a high degree of order of the antidot arrays. Various sizes and shapes of the antidots were observed with increasing thickness of the deposited nickel. New features appear in the antidot arrays in both magnetization and transport measurements when the external magnetic field is parallel to the current direction, including an enhancement and a nonmonotonous field dependence of the magnetoresistance, larger values of the coercive field and remanence moment, and smaller saturation field.
Detection of DNA single‐strand breaks and glutathione in mononuclear blood cells of radiotherapy technicians
Authors: Akköse Ayfer , Ömer Beyhan , Deniz Günnur , Darendeliler Emin
Published: October 2002

We wanted to investigate the effects of γ radiation on DNA single‐strand breaks (SSB) and glutathione (GSH) levels in mononuclear blood cells (MNC) of radiotherapy technicians. DNA SSB in MNC of radiotherapy technicians who use 60 Co‐ γ source in their works were detected by alkaline filter elution and compared to control subjects. In addition, GSH levels were measured using the enzymatic method in MNC. Blood samples were collected from radiotherapy technicians on Monday and Friday. DNA SSB levels were found to be significantly higher in smoking controls compared to non‐smoking controls. Significant increases of 36% and 49% in DNA SSB were detected from Monday to Friday for non‐smoking and smoking radiotherapy technicians, respectively. GSH levels were found to be decreased significantly from Monday to Friday. γ ‐Radiation resulted in increased DNA SSB levels of MNC in radiotherapy technicians throughout the working week and these breaks have been observed to be repaired at the weekend. Smoking habit caused an additional increase in the SSBs observed in radiotherapy technicians.
A specific anti‐aggressive effect of repeatedly administered lobeline
Authors: Redolat Rosa , Oterino M. Carmen , Carrasco M. Carmen , Brain Paul F.
Published: October 2002

The effects of chronic treatments with nicotinic agonists on agonistic encounters have received little attention. The effects of repeated (for 10 days) SC administration of (‐)‐lobeline (9.3, 18.6 and 37.2 μmol/kg) and (‐)‐nicotine (0.93, 1.86 and 3.72 μmol/kg) were evaluated using the mouse isolation‐induced aggression model. Individually housed OF1 male mice served as experimental animals and were confronted by ‘standard opponents’. Each mouse was tested only once on the last day of the repeated drug treatment. Videotaped agonistic encounters were analysed estimating the times allocated to 11 behavioural categories. Repeated treatment with the highest dose of lobeline diminished attack behaviour without significantly increasing immobility or changing any other behavioural category involving motor activity. In contrast, nicotine did not significantly alter time allocated to any behavioural category.
Representativeness of Radiologically Guided Fine‐NeedleAspiration Biopsy of Bone Lesions
Authors: Söderlund Veli , Tani Edneia , Domanski Henryk , Kreicbergs Andris
Published: October 2002

The consistency of the cellular yield as obtained by radiologically guided fine‐needle aspiration biopsy (FNAB) was investigated
in 29 cases with bone lesions. Aspirates from three different sites of the same lesion were analysed randomly and
independently by two cytologists unaware of the clinical and radiological findings.The series was grouped cytologically into
four categories: (1) benign, (2) sarcoma, (3) other malignancy, (4) non‐conclusive. A lesion was considered cytologically
homogenous, when all three aspirates were identically categorised. Among 29 lesions, 13 and 12, respectively, were assessed
as homogeneous by the two cytologists. In the remaining lesions, heterogeneity almost exclusively pertained to the mixture
of conclusive and non‐conclusive aspirates. An alternative diagnosis was suggested in one case by each cytologist.
Comparison of the two cytologists′ assessments showed that 21 cases were compliant, i.e., no inter‐observer difference in
63 out of 87 aspirates. In the remaining eight cases (24 aspirates), non‐compliance was mainly due to differences between
the cytologists in the ratio of conclusive versus non‐conclusive aspirates. Only the analysis of one and the same aspirate
resulted in two different diagnoses. A correct diagnosis was given by the cytologists in 22 and 23 cases, incorrect in two and
non‐conclusive in five and four, respectively.

Our cytological study of bone lesions, albeit limited, suggests that true tumour heterogeneity is rare. The
non‐compliance between the two cytologists and the diagnostic difficulties should mainly be attributed to the blind, random
approach of the study.The main problem of FNAB pertains to the high rate of non‐conclusive aspirates.This, however, does
not entail an increased risk of incorrect diagnosis, but rather prompts repeat FNAB.
Myxoid Malignant Fibrous Histiocytoma with Multiple Primary Sites
Authors: Muler Jeffrey H. , Paulino Augusto F. , Roulston Diane , Baker Laurence H.
Published: October 2002

Malignant fibrous histiocytoma (MFH) is one of the most common types of soft tissue sarcomas in adults. The most common location of MFH are the extremities and the trunk, with the most common site for distant metastases being the lung. We describe a case with multiple synchronous sites of myxoid MFH but no lung metastases and presence of abnormalities of 19p13.
The FKBP12‐rapamycin‐associated protein (FRAP) is a CLIP‐170 kinase
Authors: Choi Jae H , Bertram Paula G , Drenan Ryan , Carvalho John , Zhou Heather H , Zheng X F Steven
Published: October 2002

CLIP‐170/Restin belongs to a family of conserved microtubule (MT)‐associated proteins, which are important for MT organization and functions. CLIP‐170 is a phosphoprotein and phosphorylation is thought to regulate the binding of CLIP‐170 to MTs. However, little is known about the kinase(s) involved. In this study, we show that FKBP12‐rapamycin‐associated protein (FRAP, also called mTOR/RAFT) interacts with CLIP‐170. CLIP‐170 is phosphorylated in vivo at multiple sites, including rapamycin‐sensitive and ‐insensitive sites, and is phosphorylated by FRAP in vitro at the rapamycin‐sensitive sites. In addition, rapamycin inhibited the ability of CLIP‐170 to bind to MTs. Our observations suggest that multiple CLIP‐170 kinases are involved in positive and negative control of CLIP‐170, and FRAP is a CLIP‐170 kinase positively regulating the MT‐binding behavior of CLIP‐170.
A Biomechanical Model of Sagittal Tongue Bending
Authors: Napadow Vitaly J. , Kamm Roger D. , Gilbert Richard J.
Published: October 2002

The human tongue is a structurally complex and extremely flexible organ. In order to better understand the mechanical basis for lingual deformations, we modeled a primitive movement of the tongue, sagittal tongue bending. We hypothesized that sagittal bending is a synergistic deformation derived from co-contraction of the longitudinalis and transversus muscles. Our model of tongue bending was based on classical bimetal strip theory, in which curvature is produced when one muscle layer contracts more so than another. Contraction was modulated via mismatched thermal expansion coefficients and temperature change (to simulate muscular contraction). Our results demonstrated that synergistic contraction produced curvature and strain results which were in better correspondence to empirical results derived from tagging MRI than were the results of contraction of the longitudinalis muscle alone. This fundamental reliance of tongue bending on the synergistic contraction of its intrinsic fibers supports the muscular hydrostat theory of tongue function.
Internal-wave time evolution effect on ocean acoustic rays
Authors: Flatté Stanley M. , Vera Michael D.
Published: October 2002

A range-dependent field of sound speed in the ocean, c(x,z), caused by internal waves, can give rise to instabilities in acoustic ray paths. Past work has shown the importance of the background, range-independent, sound-speed profile; the ray initial conditions; the source-receiver geometry (depths and range); and the strength of the internal waves. However, in the past the time evolution of the internal waves has been ignored on the grounds that the speed of internal waves is much slower than the speed of the acoustic wave. It is shown here by numerical simulation that two rays with identical initial conditions, traveling through an ocean with the same background profile and the same random realization of internal waves, but with the internal waves frozen in one case and evolving in the other, travel significantly different trajectories. The dependence of this “frozen–unfrozen” difference on the initial ray launch angle, the background profile, and the strength of the internal-wave spectrum, is investigated. The launch-angle difference that generates similar arrival-depth differences to those induced by internal-wave time evolution is on the order of 100 μrad. The pattern of differences is measured here by the arrival depth at the final range of 1000 km. The observed pattern as a function of launch angle, change in the background profile, and change in internal-wave strength is found to be nearly the same for “frozen–unfrozen” change as for a slight change in launch angle.
Perceptual learning following changes in the frequency-to-electrode assignment with the Nucleus-22 cochlear implant
Authors: Fu Qian-Jie , Shannon Robert V. , Galvin John J.
Published: October 2002

The goal of the present study was to investigate the time course of adaptation by experienced cochlear implant users to a shifted frequency-to-electrode assignment in their speech processors. Speech recognition performance of three Nucleus-22 cochlear implant users was measured over a 3-month period, during which the implant listeners continuously wore “experimental” speech processors that were purposely shifted by 2–4 mm in terms of the frequency-to-electrode assignment relative to their normal processor. Baseline speech performance was measured with each subject’s clinically assigned speech processor just prior to implementation of the experimental processor. Baseline speech performance was measured again after the 3-month test period, immediately following the reinstallation of the clinically assigned processor settings. Speech performance with the experimental processor was measured four times during the first week, and weekly thereafter over the 3-month period. Results showed that the experimental processor produced significantly lower performance on all measures of speech recognition immediately following implementation. Over the 3-month test period, consonant and HINT sentence recognition with the experimental processors gradually approached a performance level comparable to but still significantly below the baseline and postexperiment measures made with the clinically assigned processor. However, vowel and TIMIT sentence recognition with the experimental processors remained far below the level of the baseline measures even at the end of the 3-month experimental period. There was no significant change in performance with the clinically assigned processor before or after fitting with the experimental processor. The results suggest that a long-time exposure to a new pattern of stimulation may not be able to compensate for the deficit in performance caused by a 2–4-mm shift in the tonotopic location of stimulation, at least within a 3-month period.
Experimental verification of the quasi-steady approximation for aerodynamic sound generation by pulsating jets in tubes
Authors: Zhang Zhaoyan , Mongeau Luc , Frankel Steven H.
Published: October 2002

Voice production involves sound generation by a confined jet flow through an orifice (the glottis) with a time-varying area. Predictive models of speech production are usually based on the so-called quasi-steady approximation. The flow rate through the time-varying orifice is assumed to be the same as a sequence of steady flows through stationary orifices for wall geometries and flow boundary conditions that instantaneously match those of the dynamic, nonstationary problem. Either the flow rate or the pressure drop can then be used to calculate the radiated sound using conventional acoustic radiation models. The quasi-steady approximation allows complex unsteady flows to be modeled as steady flows, which is more cost effective. It has been verified for pulsating open jet flows. The quasi-steady approximation, however, has not yet been rigorously validated for the full range of flows encountered in voice production. To further investigate the range of validity of the quasi-steady approximation for voice production applications, a dynamic mechanical model of the larynx was designed and built. The model dimensions approximated those of human vocal folds. Airflow was supplied by a pressurized, quiet air storage facility and modulated by a driven rubber orifice. The acoustic pressure of waves radiated upstream and downstream of the orifice was measured, along with the orifice area and other time-averaged flow variables. Calculated and measured radiated acoustic pressures were compared. A good agreement was obtained over a range of operating frequencies, flow rates, and orifice shapes, confirming the validity of the quasi-steady approximation for a class of relevant pulsating jet flows.
Measurement and analysis of acoustic intensity fluctuations induced by South China Sea internal solitons
Authors: Chiu C.-S. , Ramp S. , Miller C. , Lynch J. , Duda T. , Newhall A. , von der Heydt K. , Kemp J.
Published: October 2002

In May 2001, a suite of acoustic and oceanographic sensors was deployed by a team of US, Taiwan, and Singapore scientists in the NE South China Sea to study the effects of ocean variability on low-frequency sound propagation in a shelfbreak environment. The primary acoustic receiver was an L-shaped hydrophone array moored on the continental shelf that monitored a variety of signals transmitted parallel to and across the shelfbreak by fixed and towed sources. This talk discusses and contrasts the amplitude fluctuations in the signals measured by the vertical segment of the listening array in two different days, one with the passage of several huge solitons that depressed the shallow isotherms to the sea bottom, and one with a much less energetic soliton field. In addition to exhibiting large temporal changes, the acoustic data also show a much more vertically diffused sound intensity field as the huge solitons occupied and passed through the transmission path. Using a space-time continuous empirical sound speed model based on the moored temperature records and geoacoustic parameters estimated using the close-range towed source signals, the observed acoustic intensity fluctuations are explained using coupled-mode physics. [Work supported by ONR under the ASIAEX program.]
Incremental global reoptimization of programs
Authors: Pollock Lori L. , Soffa Mary Lou
Published: October 2002

Although optimizing compilers have been quite successful in producing excellent code, two factors that limit their usefulness are the accompanying long compilation times and the lack of good symbolic debuggers for optimized code. One approach to attaining faster recompilations is to reduce the redundant analysis that is performed for optimization in response to edits, and in particulars, small maintenance changes, without affecting the quality of the generated code. Although modular programming with separate compilation aids in eliminating unnecessary recompilation and reoptimization, recent studies have discovered that more efficient code can be generated by collapsing a modular program through procedure inlining. To avoid having to reoptimize the resultant large procedures, this paper presents techniques for incrementally incorporating changes into globally optimized code. An algorithm is given for determining which optimizations are no longer safe after a program change, and for discovering which new optimizations can be performed in order to maintain a high level of optimization. An intermediate representation is incrementally updated to reflect the current optimizations in the program. Analysis is performed in response to changes rather than in preparation for possible changes, so analysis is not wasted if an edit has no far-reaching effects. The techniques developed in this paper have also been exploited to improve on the current techniques for symbolic debugging of optimized code.
Subtyping recursive types
Authors: Amadio Roberto M. , Cardelli Luca
Published: October 2002

We investigate the interactions of subtyping and recursive types, in a simply typed λ-calculus. The two fundamental questions here are whether two (recursive)types are in the subtype relation and whether a term has a type. To address the first question, we relate various definitions of type equivalence and subtyping that are induced by a model, an ordering on infinite trees, an algorithm, and a set of type rules. We show soundness and completeness among the rules, the algorithm, and the tree semantics. We also prove soundness and a restricted form of completeness for the model. To address the second question, we show that to every pair of types in the subtype relation we can associate a term whose denotation is the uniquely determined coercion map between the two types. Moreover, we derive an algorithm that, when given a term with implicit coercions, can infer its least type whenever possible.
On the occur-check-free PROLOG programs
Authors: Apt Krzysztof R. , Pellegrini Alessandro
Published: October 2002

In most PROLOG implementations, for efficiency occur-check is omitted from the unification algorithm. This paper provides natural syntactic conditions that allow the occur-check to be safely omitted. The established results apply to most well-known PROLOG programs, including those that use difference lists, and seem to explain why this omission does not lead in practice to any complications. When applying these results to general programs, we show their usefulness for proving absence of floundering. Finally, we propose a program transformation that transforms every program into a program for which only the calls to the built-in unification predicate need to be resolved by a unification algorithm with the occur-check.
The definition of dependence distance
Authors: Wolfe Michael
Published: October 2002

Several definitions of dependence distance can be found in the literature. A single coherent definition is the vector distance between the iteration vectors of two iterations involved in a dependence relation. Different ways to associate iteration vectors with iterations can give different dependence distances to the same program, and have different advantages.
Efficiently counting program events with support for on-line queries
Authors: Ball Thomas
Published: October 2002

The ability to count events in a program's execution is required by many program analysis applications. We represent an instrumentation method for efficiently counting events in a program's execution, with support for on-line queries of the event count. Event counting differs from basic block profiling in that an aggregate count of events is kept rather than a set of counters. Due to this difference, solutions to basic block profiling are not well suited to event counting. Our algorithm finds a subset of points in a program to instrument, while guaranteeing that accurate event counts can be obtained efficiently at every point in the execution.
An old-fashioned recipe for real time
Authors: Abadi Martín , Lamport Leslie
Published: October 2002

Traditional methods for specifying and reasoning about concurrent systems work for real-time systems. Using TLA (the temporal logic of actions), we illustrate how they work with the examples of a queue and of a mutual-exclusion protocol. In general, two problems must be addressed: avoiding the real-time programming version of Zeno's paradox, and coping with circularities when composing real-time assumption/guarantee specifications. Their solutions rest on properties of machine closure and realizability.