bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear electrical behavior of the TiO2⋅WO3 varistor
Authors: Su Wen-Bin , Wang Jin-Feng , Chen Hong-Cun , Wang Wen-Xin , Zhang Guo-Zhong , Li Chang-Peng
Published: October 2002

The nonlinear electrical behavior and dielectric properties of TiO2-based ceramics with various WO3 contents have been investigated. It was found that 0.25% WO3+99.75% TiO2 has an optimal nonlinear coefficient of α=9.6, a breakdown electrical field of 44.5 V/mm, and ultrahigh relative dielectric constant of 7.41×104 (measured at 1 kHz). The theory of defects in the crystal lattice was introduced to explain the nonlinear electrical behavior of the TiO2⋅WO3 system. Schottky potential barriers at the grain boundaries that are analogies to the grain boundary defect model for ZnO varistors are introduced in the article. From this point, the nonlinear electrical behavior of the TiO2 system is explained.
Ionized and excited states of ferrocene: Symmetry adapted cluster–configuration–interaction study
Authors: Ishimura Kazuya , Hada Masahiko , Nakatsuji Hiroshi
Published: October 2002

The ground state, singlet, and triplet excited states, and ionized states of ferrocene Fe(C5H5)2 were studied by the symmetry adapted cluster (SAC)/SAC–configuration–interaction method. The calculated ionization energies and intensities fairly well reproduced the observed photoelectron spectrum in the wide region of 6–14 eV. In particular, the first two peaks (2E2′ and A1′2) were assigned to the ionizations from the occupied 3d orbitals of Fe, mixed already with the two-electron shake-up processes. This is the first ab initio quantitative assignment that is consistent with the experimental data. For the singlet states, three d–d transitions were calculated at 2.12, 2.26, and 4.02 eV, which correspond to the experimental peaks observed at 2.69, 2.97, and 3.82 eV. We propose possible assignments for other absorption bands in the range of 2.12–6.57 eV. In another three triplet d–d transition states we calculated, we found that the energy order of these states (1 3E1″, 1 3E2″, 2 3E1″) differs from that of singlet states (1 1E2″, 1 1E1″, 2 1E1″).
A cryostat for low-temperature spectroscopy of condensable species
Authors: Carrasco E. , Castillo J. M. , Escribano R. , Herrero V. J. , Moreno M. A. , Rodrı́guez J.
Published: October 2002

A simple experimental setup for the production of cold samples for spectroscopy is described. The samples are deposited under vacuum on a cold metallic surface whose temperature is controlled between 80 and 323 K by varying the heat flow balance between a liquid nitrogen reservoir and a power transistor. Tests of temperature stability and thermal inertia, as well as a set of reflection–absorption infrared and thermal desorption spectra, are reported as a demonstration of the performance of the system.
Using the scanning probe microscope to measure the effect of relative humidity on sample stiffness
Authors: Maxwell J. M. , Huson M. G.
Published: October 2002

The ability to manipulate environmental conditions while obtaining nanoscale information about a sample is invaluable. The current article describes the construction and use of a chamber to control the relative humidity while using the scanning probe microscope (SPM) to monitor changes in sample stiffness. Although the experimental setup described is simple, this work shows that the complex relationship between temperature and relative humidity needs to be fully understood for successful operation of the apparatus. In TappingMode™, increases in relative humidity caused the free amplitude of the oscillating cantilever to decrease. Force–distance measurements taken on glass, however, showed no changes in detector sensitivity, suggesting that force–distance mode could be used to measure changes sample stiffness as a function of relative humidity. Using the SPM in force–distance mode, three moisture-sensitive materials (gelatine, wool fibers, and cotton fibers), were examined as the relative humidity was gradually increased from ambient conditions to just under 100%. The results showed that each of the materials softened as the humidity increased and that the experiments were reproducible. From the data, it was estimated that gelatine passed through a glass transition at about 86% relative humidity at room temperature. Wool passed through a glass transition at about 85% relative humidity, which is consistent with previous findings.
Measurements of C2 and CH concentrations and temperatures in a dc arc jet using cavity ring-down spectroscopy
Authors: Wills J. B. , Smith J. A. , Boxford W. E. , Elks J. M. F. , Ashfold M. N. R. , Orr-Ewing A. J.
Published: October 2002

Cavity ring-down spectroscopy has been used to measure the absorbances, concentrations and temperatures of C2(a3Πu v=0) and CH(X2Π v=0) radicals in a ⩽10 kW dc arc jet used for chemical vapor deposition (CVD) of polycrystalline diamond films and operated with CH4/H2/Ar gas mixtures. Gas temperatures derived from the intensities and widths of rotationally resolved C2 d3Πg−a3Πu spectral lines are 3300±200 K in the free plume, rising to ∼4800 K close to the substrate on which the diamond film is grown. For an input power of ∼6 kW, a 3.3% CH4/H2 ratio with excess Ar and a pressure of 50 Torr, the conditions typically employed for diamond film CVD, concentrations of C2(a) are between 6.0±0.2×1012 and 1.5±0.2×1013 cm−3 in the free plume at distances >5 mm from the substrate. These values are derived assuming a 1 cm column length as implied by spatially resolved studies of C2(d−a) optical emission; the spread reflects the decline in performance of the arc jet torch heads over time. The concentration of CH(X) in the free plume is 7.0±1.3×1012 cm−3 under similar operating conditions. Within 5 mm of the substrate, the measured absorption by both radicals rises steeply. The concentrations of C2(a) and CH(X) increase with added CH4 at fixed powers of 5.5 and 5.8 kW, but for mixing ratios in excess of 5% CH4/H2, the concentrations of both radicals become invariant. Measured C2(a) absorbance also increases with power input to the arc jet, but the CH absorbance is independent of this operating parameter.
Influence of temperature on percolation in a simple model of flexible chains adsorption
Authors: Kondrat Grzegorz
Published: October 2002

We study random sequential adsorption of flexible chains onto a two-dimensional lattice by computer Monte Carlo simulations. The flexibility of chains is controlled by the temperature of the solution via the Boltzmann factor. We investigate the percolation threshold in the system as a function of chain length and temperature. Several temperature regimes are identified, and respective characteristic types of behavior of the system are discussed. Especially, nonmonotonicity of percolation threshold is observed—there appears a characteristic temperature unique for all chain lengths for which the percolation threshold attains its minimum.
Dielectric-spontaneous polarization versus electron emission in perovskite cathodes
Authors: Boscolo I. , Cialdi S.
Published: October 2002

Strong electron emission in ferroelectric cathodes requires fast polarization change. We present the correlation between the emission of energetic electrons and the polarization change obtained experimentally. The shape of the emitted current pulse and its level depend on the amplitude and the rate of the polarization variation. The polarization variation showed a fast and a slow component, related to fast and slow nanodomain relaxation time respectively: The slow rate polarization of the relaxor samples used in our tests showed a relaxation time of a few microseconds. The emission in presence of the sole fast polarization naturally depends on the exciting pulse characteristics. The emission in presence of also the slow polarization depends strongly on the relaxation dynamics: The relatively long decay time leads to a freezing of screening electrons and consequently to a low emission level.
Dynamics in supercooled polyalcohols: Primary and secondary relaxation
Authors: Döß A. , Paluch M. , Sillescu H. , Hinze G.
Published: October 2002

We have studied details of the molecular dynamics in a series of pure polyalcohols by means of dielectric spectroscopy and H2 nuclear magnetic resonance (NMR). From glycerol to threitol, xylitol and sorbitol a systematic change in the dynamics of the primary and secondary relaxation is found. With increasing molecular weight and fragility an increase in the width of the α-peak is observed. Details of the molecular reorientation process responsible for the α-relaxation were exploited by two-dimensional NMR experiments. It is found that in the same sequence of polyalcohols the appearance of the secondary relaxation changes gradually from a wing type scenario to a pronounced β-peak. From NMR experiments using selectively deuterated samples the molecular origin of the secondary relaxation could be elucidated in more detail.
Random telegraph signal noise in SiGe heterojunction bipolar transistors
Authors: von Haartman Martin , Sandén Martin , Östling Mikael , Bosman Gijs
Published: October 2002

In this work, random telegraph signal (RTS) noise in SiGe heterojunction bipolar transistors (HBTs) was characterized both as a function of bias voltage and temperature. The RTS amplitudes were found to scale with the total base current, and the characteristic times in the higher and lower RTS state were found to decrease rapidly with bias voltage, approximately as 1/exp(qVBE/kT) or stronger. The RTS amplitudes were explained by a model based on voltage barrier height fluctuations across the base–emitter junction induced by trapped carriers in the space charge region. It was shown that the relative RTS amplitudes ΔIB/IB decrease exponentially with temperature in this model, which also was verified by measurements. The trapping/detrapping mechanism was suggested to be electron and hole capture, where the hole capture process occurs by tunneling. The characteristic times in both the lower and higher RTS state were in some cases found to decrease exponentially with temperature, characteristic for a thermally activated process, and in some cases found to be only weakly temperature dependent. The former behavior was explained by a multiphonon process with thermally activated capture cross sections, and an activation energy of 0.39 eV was extracted. RTS amplitudes proportional to the nonideal base current component or weaker were also found, originating from traps at the Si/SiO2 interface at the emitter periphery. The trapped carriers affect the recombination rate in the base–emitter space charge region, probably by changing the number of carriers. In this case, ΔIB/IB only showed a weak temperature dependence, which correlates well with this model. Characteristic times that decreased exponentially with temperature were observed, originating from a multiphonon process in the SiO2 with an activation energy for the capture cross section of 0.29 eV.
High resolution spectroscopy of carboxylic acid in the gas phase: Observation of proton transfer in (DCOOH)2
Authors: Madeja F. , Havenith M.
Published: October 2002

We report the first fully analyzed high resolution spectrum of a carboxylic acid dimer in the gas phase. High resolution spectra in the region of the C–O stretch 1241.7–1250.7 cm−1 have been recorded for (DCOOH)2. The data could be fit within experimental uncertainty to a rigid rotor Watson S reduced Hamiltonian. The vibrational frequency of the C–O stretch in (DCOOH)2 is determined to be 1244.8461 (2) cm−1. Our spectra are the first direct experimental evidence for proton transfer tunneling in formic acid dimer (FAD), with FAD serving as a prototype for double hydrogen bonded organic complexes. Previous theoretical studies predicted proton transfer times covering a range of several orders of magnitude. Our measurements on (DCOOH)2 established a proton transfer time of 5.8 ns [tunneling splitting of 0.00286(25) cm−1]. The proton transfer was found to accelerate upon vibrational excitation of the skeleton motion (the vibrational C–O mode), corresponding to a tunneling splitting of 0.00999(21) cm−1. For this state the proton transfer time decreased to 1.7 ns, which corresponds to a vibrationally enhanced proton transfer mechanism. The moments of inertia are in agreement with a C2h structure which indicates a high tunneling barrier. The observed spin statistical weights follow a description of formic acid dimer in the molecular symmetry group G8, which is isomorphic to the point group D2h. Our results suggest an out-of-plane contribution to the proton transfer mechanism for the otherwise planar dimer.
Watching carbon nanotubes grow
Authors: Bonard Jean-Marc , Croci Mirko , Conus Fabien , Stöckli Thomas , Chatelain André
Published: October 2002

The growth of carbon nanotubes by chemical vapor deposition (CVD) is followed and characterized by performing field-emission microscopy directly in a modified CVD reactor, where the hydrocarbon gas is introduced at a partial pressure below 10−2 mbar and a high voltage is applied between the heated substrate and a phosphor screen. This allows us not only to detect a field-emission current that increases with the length of the nanotubes, but also to observe the growth of the individual emitters by following the evolution of their field-emission patterns on the phosphor screen. Nanotubes grow after an activation time of a few s and reach a length of 5–10 μm in typically 10 s. We deduce a growth rate in the range 1–10 μm/s that increases with the gas pressure.
Low-temperature electric conductivity of Yba2Cu3O7−δ ceramic high-Tc superconductors with different oxygen concentrations
Authors: Finkel V. A.
Published: October 2002

The electric conductivity of YBa2Cu3O7−δ ceramic high-Tc superconductors with different oxygen contents (6.28⩽7−δ⩽6.95) is measured in the temperature range ∼20–273 K. It is shown that the temperature dependence of the resistivity can be described by the relation ρ=α0(1+βT+eγ/T) at all oxygen concentrations. It is found that in the framework of resonant tunneling theory one can obtain information about the anisotropy of the electric conductivity of HTSCs from the results of experiments performed on polycrystalline samples.
Metallic properties of lead dioxide. Band structure and NMR of Pb207 at low temperatures
Authors: Boyarskiı̆ L. A. , Gabuda S. P. , Kozlova S. G. , Pletnev R. N.
Published: October 2002

The local magnetic fields at the Pb207 nuclei in lead dioxide with the rutile structure (β-PbO2) are measured by the NMR method at temperatures down to 20 K. It is shown that the values of the local fields and the character of their temperature dependence correspond to the Knight mechanism for the shifts of the NMR spectra in metals. The band structure of this compound is calculated with allowance for relativistic corrections. A conjecture is made as to the nature of the metallic conductivity of this oxide on the basis of the results obtained.
Instability zones and short-lived defects in the physics of crystals
Authors: Koshkin V. M.
Published: October 2002

A review is given of the role played in the problems of solid-state physics by the various manifestations of instability zones for interacting defects and the presence of equilibrium and radiation-induced unstable vacancy–interstitial-atom pairs. The unstable pairs determine the features of the diffusion process and of a number of thermal properties of metals, semiconductors, and insulators, including superionic crystals, and also determine the radiation stability of solids.
Band bending mechanism for field emission in wide-band gap semiconductors
Authors: Wang R. Z. , Wang B. , Wang H. , Zhou H. , Huang A. P. , Zhu M. K. , Yan H. , Yan X. H.
Published: October 2002

A theoretical model based on the band bending theory was developed for explaining the field-emission mechanism of wide-band gap semiconductors (WBGSs). It was shown that the maximum value of the band bending, which is nearly linearly proportional to the band gap of WBGSs, may amount to a few eV. Furthermore, the calculated field-emission energy distribution combined with the band bending analyzed on cubic boron nitride (c-BN) as typical one of WBGSs, indicated that the electron emission originates from the conduction band minimum resulting from the band bending. These results present a perspective to explain the field-emission mechanism, in which it is considered that the band bending, as well as the negative electron affinity, is of equal importance to the excellent field emission performances of WBGSs.
Highly efficient continuous-wave 946-nm Nd:YAG laser emission under direct 885-nm pumping
Authors: Lupei V. , Pavel N. , Taira T.
Published: October 2002

The 885-nm Ti:Sapphire pumping into the emitting level F43/2 of Nd:YAG produces a highly efficient (0.68 slope efficiency in absorbed power) 946-nm laser emission; a strong reduction of heat generation could be also obtained.
Relaxation of photoinjected spins during drift transport in GaAs
Authors: Sanada H. , Arata I. , Ohno Y. , Chen Z. , Kayanuma K. , Oka Y. , Matsukura F. , Ohno H.
Published: October 2002

We studied the transport of photoinjected spins in GaAs by time-resolved photoluminescence measurements. At low temperatures, the spin polarization after drift transport of 4 μm is found to decrease as the applied electric field E increases to a few kV/cm, and it disappears when E exceeds 3 kV/cm. The origin of the field-dependent spin relaxation is discussed.
Coherent generation of 100 GHz acoustic phonons by dynamic screening of piezoelectric fields in AlGaN/GaN multilayers
Authors: Makarona E. , Daly B. , Im J.-S. , Maris H. , Nurmikko A. , Han Jung
Published: October 2002

Ultrashort pulse laser techniques have been used to observe and characterize the generation of coherent phonons by rapid screening of strain-induced piezoelectric polarization fields in AlGaN/GaN multilayers. The results are compared with those where coherent phonons are launched by optical techniques without the carrier injections process to show consistency with the anticipated longitudinal phonon dispersion in the nitride semiconductor samples.
Contact effects in polymer transistors
Authors: Street R. A. , Salleo A.
Published: October 2002

Polymer thin film transistors based on the polyfluorene F8T2 exhibit a nonohmic contact resistance, particularly when in the coplanar device geometry. We show how to obtain the current–voltage relation for the contact from the transistor output characteristics measured with different channel lengths. The diode-type relation is attributed to the contact injection properties of the metal Schottky barrier. No significant increase in mobility with gate or drain field is observed.
Analysis of piezoresistance in n-type β-SiC for high-temperature mechanical sensors
Authors: Toriyama Toshiyuki , Sugiyama Susumu
Published: October 2002

Piezoresistance in n-type β-SiC was analyzed on the basis of electron transfer and mobility shift mechanisms for cubic many-valley semiconductors. Gauge factors were calculated by using shear deformation potential constant Ⅺu. The calculation was compared with experimental results taken from the literature. It was shown that incorporation of the electron transfer and the mobility shift mechanisms gives reasonable interpretation for piezoresistance in n-type β-SiC within the temperature range from 300 to 673 K, and impurity concentration range from 1018 to 1020 cm−3. These conditions correspond to typical operation ranges of high-temperature piezoresistive sensors. The effect of the intervalley scattering on piezoresistance can be neglected from the evidence that gauge factor is inversely proportional to temperature within the abovementioned conditions.
Polynucleated Urban Landscapes
Authors: Batty Michael
Published: October 2002

City systems show a degree of resilience and persistence that has rarely been emphasised in urban theory. There is a fascination for recent and contemporary change which suggests that phenomena such as the rise of the 'edge city', for example, comprise the predominant forces determining how a polynucleated landscape of cities is emerging. We argue here that such explanations of polynucleation are largely false. Urban settlement structures from much earlier times are persistent to a degree that is extraordinary. We show this in two ways: first, from empirical evidence of stable rank-size relations in the urban settlement system for Great Britain over the past 100 years; and, secondly, from simulations based on weak laws of proportionate effect which produce aggregate patterns entirely consistent with these empirical relations. We then propose various spatially disaggregate models of urban development which generate an evolution of polynucleated settlement from initial, random distributions of urban activity. These models simulate the repeated action of agents locating and trading in space which illustrate how early settlement patterns are gradually reinforced by positive feedback. These produce lognormally distributed settlement structures that are characteristic of city systems in developed countries. In this way, we begin to explain how aggregate urban structures persist in spite of rapid and volatile micro change at more local levels of locational decision-making. Polynucleated urban landscapes are clear evidence of this phenomenon.
On Creating the 'City' as a Collective Resource
Authors: Healey Patsy
Published: October 2002

There has been much critical comment on the 'narrowness' of conceptions of the 'city' mobilised in urban policy in many parts of Europe, which focus on images of the 'competitive' city, the 'European city' or the 'compact' city. This paper explores the multiple meanings of the 'city' and the way a richer array of meanings may be mobilised into strategic resources for collective action in urban governance contexts. The starting-point is the recognition of the complexity and diversity of urban life and its multiple time-space horizons. The first section explores different approaches to imagining cities. The second part comments on the way concepts of 'the city' are currently mobilised in urban governance contexts. In the third part, the paper considers how a richer array of concepts may be mobilised, contested and attached to the strategic governance capacity to 'shape' evolving city futures, converting the 'city' from an often implicit and sometimes contested array of concepts to an active force. In the final section, the paper elaborates on the role of on-going debate about 'the city' as a potentially integrative resource in governance contexts characterised by diffused power and dynamic relations. In such contexts, active debate about the ways to 'read' and give meanings to 'the city' may develop the strategic power to mobilise collective effort, inspire individual initiatives and provide resources for identity formation processes.
The Quest for a Balanced Ethnic Mix: Singapore's Ethnic Quota Policy Examined
Authors: Sin Chih Hoong
Published: October 2002

To achieve a 'balanced' ethnic mix, Singapore has implemented an ethnic quota policy on public housing since 1 March 1989. With 86 per cent of the population living in public housing, this policy has immense repercussions on the configuration of the ethnic residential landscape. This article examines the impact of the quota policy on the buying and renting, as well as the selling or letting, of public housing. The differential response by the various ethnic groups is revealed. The policy per se may not achieve its intended impact and may, ironically, have the least impact on the group it was most intended for. Integration policies must be more holistic in approach and more sympathetic in execution.
Green tea as a potent antioxidant in alcohol intoxication
Authors: Skrzydlewska E. , Ostrowska J. , Stankiewicz A. , Farbiszewski R.
Published: October 2002

Ethanol oxidation to acetaldehyde and next to acetate is accompanied by free radical generation. Free radicals can affect cell integrity when antioxidant mechanisms are no longer able to cope with the free radical generation observed in ethanol intoxication. Natural antioxidants are particularly useful in such a situation. The present study was designed to investigate the efficacy of green tea as a source of water‐soluble antioxidants (catechins) on the liver and blood serum antioxidative potential of rats chronically (28 days) intoxicated with ethanol. Alcohol caused a decrease in liver superoxide dismutase, glutathione peroxidase and catalase activities and an increase in activity of glutathione reductase. Moreover, a decrease in the level of reduced glutathione, ascorbic acid, vitamins A and E and β‐carotene were observed. The activity of serum glutathione peroxidase decreased while glutathione reductase activity increased. The level of serum non‐enzymatic antioxidants was also decreased in the liver. Alcohol administration caused an increase in the liver and serum lipid peroxidation products, measured as thiobarbituric acid‐reactive substances. However, green tea prevents the changes observed after ethanol intoxication. Green tea also protects membrane phospholipids from enhanced peroxidation. These results indicate a beneficial effect of green tea in alcohol intoxication.
Structural organization of the endoplasmic reticulum
Authors: Voeltz Gia K , Rolls Melissa M , Rapoport Tom A
Published: October 2002

The endoplasmic reticulum (ER) is a continuous membrane system but consists of various domains that perform different functions. Structurally distinct domains of this organelle include the nuclear envelope (NE), the rough and smooth ER, and the regions that contact other organelles. The establishment of these domains and the targeting of proteins to them are understood to varying degrees. Despite its complexity, the ER is a dynamic structure. In mitosis it must be divided between daughter cells and domains must be re‐established, and even in interphase it is constantly rearranged as tubules extend along the cytoskeleton. Throughout these rearrangements the ER maintains its basic structure. How this is accomplished remains mysterious, but some insight has been gained from in vitro systems.
Rose Scent
Authors: Guterman Inna , Shalit Moshe , Menda Naama , Piestun Dan , Dafny-Yelin Mery , Shalev Gil , Bar Einat , Davydov Olga , Ovadis Mariana , Emanuel Michal , Wang Jihong , Adam Zach , Pichersky Eran , Lewinsohn Efraim , Zamir Dani , Vainstein Alexander , Weiss David
Published: October 2002

For centuries, rose has been the most important crop in the floriculture industry; its economic importance also lies in the use of its petals as a source of natural fragrances. Here, we used genomics approaches to identify novel scent-related genes, using rose flowers from tetraploid scented and nonscented cultivars. An annotated petal EST database of ∼2100 unique genes from both cultivars was created, and DNA chips were prepared and used for expression analyses of selected clones. Detailed chemical analysis of volatile composition in the two cultivars, together with the identification of secondary metabolism–related genes whose expression coincides with scent production, led to the discovery of several novel flower scent–related candidate genes. The function of some of these genes, including a germacrene D synthase, was biochemically determined using an Escherichia coli expression system. This work demonstrates the advantages of using the high-throughput approaches of genomics to detail traits of interest expressed in a cultivar-specific manner in nonmodel plants.
Importance of Nonlinear and Multivariable Flexibility Coefficients in the Prediction of Human Cervical Spine Motion
Authors: Winkelstein Beth A. , Myers Barry S.
Published: October 2002

The flexibility matrix currently forms the basis for multibody dynamics models of cervical spine motion. While studies have aimed to determine cervical motion segment behavior, their accuracy and utility have been limited by both experimental and analytical assumptions. Flexibility terms have been primarily represented as constants despite the spine’s nonlinear stiffening response. Also, nondiagonal terms, describing coupled motions, of the matrices are often omitted. Currently, no study validates the flexibility approach for predicting vertebral motions; nor have the effects of matrix approximations and simplifications been quantified. Therefore, the purpose of this study is to quantify flexibility relationships for cervical motion segments, examine the importance of nonlinear components of the flexibility matrix, and determine the extent to which multivariable relationships may alter motion prediction. To that end, using unembalmed human cervical spine motion segments, a full battery of flexibility tests were performed for a neutral orientation and also following an axial pretorque. Primary and coupled matrix components were described using linear and piecewise nonlinear incremental constants. A third matrix approach utilized multivariable incremental relationships. Measured motions were predicted using structural flexibility methods and evaluated using RMS error between predicted and measured responses. A full set of flexibility relationships describe primary and coupled motions for C3-C4 and C5-C6. A flexibility matrix using piecewise incremental responses offers improved predictions over one using linear methods (p<0.01). However, no significant improvement is obtained using nonlinear terms represented by a multivariable functional approach (p<0.2). Based on these findings, it is suggested that a multivariable approach for flexibility is more demanding experimentally and analytically while not offering improved motion prediction.
Influence of ultrasonic frequency on multibubble sonoluminescence
Authors: Yasui Kyuichi
Published: October 2002

Computer simulations of bubble oscillations are performed under conditions of multibubble sonoluminescence (MBSL) in water for various ultrasonic frequencies. The range of the ambient bubble radius for sonoluminescing bubbles narrows as the ultrasonic frequency increases; at 20 kHz it is 0.1–100 μm while at 1 MHz it is 0.1–3 μm. At 1 MHz, any sonoluminescing bubble disintegrates into a mass of smaller bubbles in a few or a few tens of acoustic cycles, while at 20 kHz and 140 kHz some sonoluminescing bubbles are shape stable. The mechanism of the light emission also depends on the ultrasonic frequency. As the ultrasonic frequency increases, the amount of water vapor trapped inside bubbles at the collapse decreases. As a result, MBSL originates mainly in plasma emissions at 1 MHz while it originates in chemiluminescence of OH radicals and plasma emissions at 20 kHz.
Intraglottal pressure distributions for a symmetric and oblique glottis with a uniform duct (L)
Authors: Scherer Ronald C. , Shinwari Daoud , De Witt Kenneth J. , Zhang Chao , Kucinschi Bogdan R. , Afjeh Abdollah A.
Published: October 2002

A Plexiglas model of the larynx, having a uniform duct shape and minimal diameter of 0.04 cm, was used to obtain wall pressure distributions resulting from internal airflow. Both a symmetric glottis (obliquity of 0 degrees) and a slanted glottis (obliquity of 20 degrees) were used. The oblique glottis (i.e., a glottis that slants relative to the axial tracheal flow) is present in both normal and abnormal phonation. Obliquity has been shown to create unequal cross-channel pressures on the vocal fold surfaces [Scherer et al., J. Acoust. Soc. Am. 109, 1616 (2001)], and the study here continues this line of research. For the oblique glottis, one side was divergent and the other convergent. Transglottal pressures from 3 to 15 cm H2O using constant airflows were used. Results indicated that the pressure distributions on the two sides of the glottis were essentially equal for the symmetric uniform case (pressures differed slightly near the exit due to asymmetric flow downstream of the glottis). For the oblique glottis, the pressures on the vocal fold surfaces at glottal entry differed by 21.4% of the transglottal pressure, suggesting that this oblique glottis creates upstream glottal pressures that may influence out-of-phase motion of the two vocal folds.
Theory of inert gas-condensing vapor thermoacoustics: Transport equations
Authors: Slaton William V. , Raspet Richard , Hickey Craig J. , Hiller Robert A.
Published: October 2002

The preceding paper [J. Acoust. Soc. Am. 112, 1414–1422 (2002)] derives the propagation equation for sound in an inert gas-condensing vapor mixture in a wet-walled pore with an imposed temperature gradient. In this paper the mass, enthalpy, heat, and work transport equations necessary to describe the steady-state operation of a wet-walled thermoacoustic refrigerator are derived and presented in a form suitable for numerical evaluation. The requirement that the refrigerator operate in the steady state imposes zero mass flux for each species through a cross section. This in turn leads to the evaluation of the mass flux of vapor in the system. The vapor transport and heat transport are shown to work in parallel to produce additional cooling power in the wet refrigerator. An idealized calculation of the coefficient of performance (COP) of a wet-walled thermoacoustic refrigerator is derived and evaluated for a refrigeration system. The results of this calculation indicate that the wet-walled system can improve the performance of thermoacoustic refrigerators. Several experimental and practical questions and problems that must be addressed before a practical device can be designed and tested are described.
The concurrent language, Shared Prolog
Authors: Brogi Antonio , Ciancarini Paolo
Published: October 2002

Shared Prolog is a new concurrent logic language. A Shared Prolog system is composed of a set of parallel agents that are Prolog programs extended by a guard mechanism. The programmer controls the granularity of parallelism, coordinating communication and synchronization of the agents via a centralized data structure. The communication mechanism is inherited from the blackboard model of problem solving. Intuitively, the granularity of the logic processes to be elaborated in parallel is large, while the resources shared on the blackboard can be very fined grained.

An operational semantics for Shared Prolog is given in terms of a distributed model. Through an abstract notion of computation, the kinds of parallelism supported by the language, as well as properties of infinite computations, such as local deadlocks, are studied.

The expressiveness of the language is shown with respect to the specification of two classes of applications: metaprogramming and blackboard systems.
A self-applicable partial evaluator for the lambda calculus
Authors: Gomard Carsten K.
Published: October 2002

We describe theoretical and a few practical aspects of an implemented self-applicable partial evaluator for the untyped lambda calculus with constants, conditionals, and a fixed point operator.

The purpose of this paper is first to announce the existence of (and to describe) a partial evaluator that is both higher-order and self-applicable; second to describe a surprisingly simple solution to the central problem of binding time analysis, and third to prove that the partial evaluator yields correct answers.

While λ-mix (the name of our system) seems to have been the first higher-order self-applicable partial evaluator to run on a computer, it was developed mainly for research purposes. Two recently developed systems are much more powerful for practical use, but also much more complex: Similix[3,5] and Schism[7].

Our partial evaluator is surprisingly simple, completely automatic, and has been implemented in a side effect-free subset of Scheme. It has been used to compile, generate compilers and generate a compiler generator.
A stepwise refinement heuristic for protocol construction
Authors: Shankar A. Udaya , Lam Simon S.
Published: October 2002

A stepwise refinement heuristic to construct distributed systems is presented. The heuristic is based on a conditional refinement relation between system specifications, and a “Marking”. It is applied to construct four sliding window protocols that provide reliable data transfer over unreliable communication channels. The protocols use modulo-
N
sequence numbers. The first protocol is for channels that can only lose messages in transit. By refining this protocol, we obtain three protocols for channels that can lose, reorder, and duplicate messages in transit. The protocols herein are less restrictive and easier to implement than sliding window protocols previously studied in the protocol verification literature.
Type matching, type-graphs, and the Schanuel conjecture
Authors: Katzenelson Jacob , Pinter Shlomit S. , Schenfeld Eugen
Published: October 2002

This work considers type systems that are defined by type-graphs (tgraphs), which are rooted directed graphs with order among the edges leaving each node. Tgraphs are uniquely mapped into polynomials which, in turn, are each evaluated at a special point to yield an irrational number named the tgraph's
magic number
. This special point is chosen using the Schanuel conjecture. It is shown that each tgraph can be uniquely represented by this magic number; namely, types are equal if and only if the corresponding magic numbers are equal. Since irrational numbers require infinite precision, the algorithm for generating magic numbers is carried out using a double-precision floating-point approximation. This approximation is viewed as a hashing scheme, mapping the infinite domain of the irrational numbers into finite computer words. The proposed hashing scheme was investigated experimentally, with the conclusion that it is a good and practical hashing method. In tests involving over a million randomly chosen tgraphs, we have not encountered a single collision. We conclude that this method for representation and management of types is practical, and offers novel possibilities for enforcing strict type matching at link time among separately compiled modules.
Time-constrained buffer specifications in CSP + T and timed CSP
Authors: Žic John J.
Published: October 2002

A finite buffer with time constraints on the rate of accepting inputs, producing outputs, and message latency is specified using both Timed CSP and a new real-time specification language, CSP + T, which adds expressive power to some of the sequential aspects of CSP and allows the description of complex event timings from within a single sequential process. On the other hand, Timed CSP encourages event-timing descriptions to be built up in a constraint-oriented manner with the parallel composition of several processes. Although these represent two complementary specification styles, both provide valuable insights into the specification of complex event timings.
Efficient implementation of adaptive software
Authors: Palsberg Jens , Xiao Cun , Lieberherr Karl
Published: October 2002

Adaptive programs compute with objects, just like object-oriented programs. Each task to be accomplished is specified by a so-called propagation pattern which traverses the receiver object. The object traversal is a recursive descent via the instance variables where information is collected or propagated along the way. A propagation pattern consists of (1) a name for the task, (2) a succinct specification of the parts of the receiver object that should be traversed, and (3) code fragments to be executed when specific object types are encountered. The propagation patterns need to be complemented by a class graph which defines the detailed object structure. The separation of structure and behavior yields a degree of flexibility and understandability not present in traditional object-oriented languages. For example, the class graph can be changed without changing the adaptive program at all. We present an efficient implementation of adaptive programs. Given an adaptive program and a class graph, we generate an efficient object-oriented program, for example, in C++. Moreover, we prove the correctness of the core of this translation. A key assumption in the theorem is that the traversal specifications are consistent with the class graph. We prove the soundness of a proof system for conservatively checking consistency, and we show how to implement it efficiently.
Optimization of functional programs by grammar thinning
Authors: Webber Adam
Published: October 2002

We describe a new technique for optimizing first-order functional programs. Programs are represented as graph grammars, and optimization proceeds by counterexample: when a graph generated by the grammar is found to contain an unnecessary computation, the optimizer attempts to reformulates the grammar so that it never again generates any graph that contains that counterexample. This kind of program reformulation corresponds to an interesting problem on context-free grammars. Our reformulation technique is derived from an (approximate) solution to this CFG problem. An optimizer called Thinner is the proof of concept for this technique. Thinner is a fully automatic, source-to-source optimizer for a Lisp-like language of purely functional, first-order programs. Thinner rediscovers a wide variety of common compiler optimizations. It also finds other more exotic transformations, including the well-known Fibonacci reformulation and the Knuth-Morris-Pratt optimization.
Influence of cross-interferences on blocked loops
Authors: Fricker Christine , Temam Olivier , Jalby William
Published: October 2002

State-of-the art data locality optimizing algorithms are targeted for local memories rather than for cache memories. Recent work on cache interferences seems to indicate that these phenomena can severely affect blocked algorithms cache performance. Because of cache conflicts, it is not possible to know the precise gain brought by blocking. It is even difficult to determine for which problem sizes blocking is useful. Computing the actual optimal block size is difficult because cache conflicts are highly irregular. In this article, we illustrate the issue of precisely evaluating cross-interferences in blocked loops with blocked matrix-vector multiply. Most significant interference phenomena are captured because unusual parameters such as array base addresses are being considered. The techniques used allow us to compute the precise improvement due to blocking and the threshold value of problem parameters for which the blocked loop should be preferred. It is also possible to derive an expression of the optimal block size as a function of problem parameters. Finally, it is shown that a precise rather than an approximate evaluation of cache conflicts is sometimes necessary to obtain near-optimal performance.
Lattice frameworks for multisource and bidirectional data flow problems
Authors: Masticola Stephen P. , Marlowe Thomas J. , Ryder Barbara G.
Published: October 2002

Multisource
data flow problems involve information which may enter nodes independently through different classes of edges. In some cases, dissimilar meet operations appear to be used for different types of nodes. These problems include
bidirectional
and
flow-sensitive
problems as well as many static analyses of concurrent programs with synchronization.
K-tuple frameworks
, a type of standard data flow framework, provide a natural encoding for multisource problems using a single meet operator. Previously, the solution of these problems has been described as the fixed point of a set of data flow equations. Using our
k
-tuple representation, we can access the general results of standard data flow frameworks concerning convergence time and solution precision for these problems. We demonstrate this for the bidirectional component of partial redundancy suppression and two problems on the program summary graph. An interesting subclass of
k
-tuple frameworks, the
join-of-meets
frameworks, is useful for reachability problems, especially those stemming from analyses of explicitly parallel programs. We give results on function space properties for join-of-meets frameworks that indicate precise solutions for most of them will be difficult to obtain.
A practical method for LR and LL syntactic error diagnosis and recovery
Authors: Burke Michael G. , Fisher Gerald A.
Published: October 2002

This paper presents a powerful, practical, and essentially language-independent syntactic error diagnosis and recovery method that is applicable within the frameworks of LR and LL parsing. The method generally issues accurate diagnoses even where multiple errors occur within close proximity, yet seldom issues spurious error messages. It employs a new technique, parse action deferral, that allows the most appropriate recovery in cases where this would ordinarily be precluded by late detection of the error. The method is practical in that it does not impose substantial space or time overhead on the parsing of correct programs, and in that its time efficiency in processing an error allows for its incorporation in a production compiler. The method is language independent, but it does allow for tuning with respect to particular languages and implementations through the setting of language-specific parameters.
Handling floating-point exceptions in numeric programs
Authors: Hauser John R.
Published: October 2002

There are a number of schemes for handling arithmetic exceptions that can be used to improve the speed (or alternatively the reliability) of numeric code. Overflow and underflow are the most troublesome exceptions, and depending on the context in which the exception can occur, they may be addressed either: (1) through a “brute force” reevaluation with extended range, (2) by reevaluating using a technique known as
scaling
, (3) by substituting an infinity or zero, or (4) in the case of underflow, with gradual underflow. In the first two of these cases, the offending computation is simply reevaluated using a safer but slower method. The latter two cases are cheaper, more automated schemes that ideally are built in as options within the computer system. Other arithmetic exceptions can be handled with similar methods. These and some other techniques are examined with an eye toward determining the support programming languages and computer systems ought to provide for floating-point exception handling. It is argued that the cheapest short-term solution would be to give full support to most of the
required
(as opposed to recommended) special features of the IEC/IEEE Standard for Binary Floating-Point Arithmetic. An essential part of this support would include standardized access from high-level languages to the exception flags defined by the standard. Some possibilities outside the IEEE Standard are also considered, and a few thought on possible better-structured support within programming languages are discussed.
Principles and practice of unification factoring
Authors: Dawson Steven , Ramakrishnan C. R. , Skiena Steven , Swift Terrance
Published: October 2002

The efficiency of resolution-based logic programming languages, such as Prolog, depends critically on selecting and executing sets of applicable clause heads to resolve against subgoals. Traditional approaches to this problem have focused on using indexing to determine the smallest possible applicable set. Despite their usefulness, these approaches ignore the nondeterminism inherent in many programming languages to the extent that they do not attempt to optimize execution
after
the applicable set has been determined. Unification factoring seeks to rectify this omission by regarding the indexing and unification phases of clause resolution as a single process. This article formalizes that process through the construction of
factoring automata
. A polynomial-time algorithm is given for constructing optimal factoring automata that preserve the clause selection strategy of Prolog. More generally, when the clause selection strategy is not fixed, constructing such an optimal automaton is shown to be NP-complete, solving an open trie minimization problem. Unification factoring is implemented through a source code transformation that preserves the full semantics of Prolog. This transformation is specified in the article, and using it, several well-known programs show significant performance improvements across several different systems. A prototype of unification factoring is available by anonymous ftp.