bluuebunny/crossref_metadata_2025 huggingface dataset:
Electric force microscopy investigation of the microstructure of thick film resistors
Authors: Alessandrini A. , Valdrè G. , Morten B. , Prudenziati M.
Published: October 2002

Maps of the electric field distribution on the surface of thick film resistors (TFRs) have been acquired by using electric force microscopy (EFM). TFRs based on various types of conducting phases (Bi-ruthenate, Pb-ruthenate, or RuO2) and with different volume fractions in the glassy matrix have been examined. Scanning electron microscopy, x-ray energy dispersive spectroscopy and x-ray diffraction have been used to correlate the EFM results to the morphological, microchemical, and structural characteristics of the samples. The evolution of the TFRs microstructure and the segregation characteristic with the firing conditions have been investigated. The results showed that the concentration of the electric field around the conductive grains is a general feature of all the films, independently of the resistor composition, and a meander-like path of charge carriers on a microscopic scale has been assessed. The observations also indicated that at high firing temperatures the segregated structure did not disappear, but on the contrary was enhanced. All the results are critically discussed in relation to the electrical and piezoresistive properties of the TFRs and suggestions for new models to correlate the microstructure and the electric properties are presented.
Epitaxial growth of BaTiO3/SrTiO3 structures on SrTiO3 substrate with automatic feeding of oxygen from the substrate
Authors: Shimoyama Kazuo , Kiyohara Masahiro , Kubo Kousuke , Uedono Akira , Yamabe Kikuo
Published: October 2002

Thin films of BaTiO3 and SrTiO3 and their superlattice were grown on SrTiO3 substrates using oxygen from the substrates as an oxygen source. Epitaxial growths were carried out by coevaporations of the component metals under ultrahigh vacuum without introducing any oxidants. The growth mechanism in the extremely low oxidation ambient was studied. Oxygen was automatically fed from the substrate to the growing film surface. As a result, oxygen vacancies were incorporated deep into the inside of the SrTiO3 substrate, confirmed by means of positron annihilation. The local oxygen deficiency at the growing surface is buffered by the fast diffusion of incorporated oxygen vacancies into deep inside of the substrate, avoiding decomposition or nucleation of the metallic phases on the surface. The BaTiO3/SrTiO3 interfaces were formed without intermixing, despite considerable amounts of oxygen having moved through the interfaces.
Swelling and stress–relaxation of poly(N-isopropylacrylamide) gels in the collapsed state
Authors: Takigawa Toshikazu , Ikeda Takuji , Takakura Yoshihito , Masuda Toshiro
Published: October 2002

Swelling and stress–relaxation under tension for poly(N-isopropylacrylamide) (PNIPA) hydrogels have been investigated in water and in liquid paraffin at various temperatures. Initial Young’s modulus is much enhanced due to the change from the swollen to collapsed state, but no difference has been observed in the initial and osmotic Poisson ratios for the gels not only in the collapsed but also in the swollen states. The enhancement of modulus originates from the introduction of physical crosslinks in the collapsed state. In liquid paraffin, the gels in the collapsed phase show large degree of stress reduction in the course of stress–relaxation due to the breakdown of the physical crosslinks. The stress–relaxation induced by swelling is observed for both phases in water, but the degree of stress reduction is larger in the collapsed phase than in the swollen phase. A comparison between experimental results and theory applicable to swelling and swelling-induced stress–relaxation is made to show that the agreement is not so good. For the stress–relaxation of the collapsed gel in water, it is suggested that the swelling couples with the breakdown of physical crosslinks at short times, and the trance of the coupling is observed even at long times.
Photodissociation of ethylbenzene and n-propylbenzene in a molecular beam
Authors: Huang Cheng-Liang , Jiang Jyh-Chiang , Lee Yuan T. , Ni Chi-Kung
Published: October 2002

The photodissociation of jet-cooled ethylbenzene and n-propylbenzene at both 193 and 248 nm was studied using vacuum ultraviolet photoionization/multimass ion imaging techniques. The photofragment translational energy distributions from both the molecules obtained at 193 nm show that the probability of portioning energy to product translational energy decreases monotonically with increasing translational energy. They indicate that the dissociation occurs from the ground electronic state. However, the photofragment translational energy distributions from both molecules obtained at 248 nm contain a fast and a slow component. 75% of ethylbenzene and 80% of n-propylbenzene following the 248 nm photoexcitation dissociate from electronic excited state, resulting in the fast component. The remaining 25% of ethylbenzene and 20% of n-propylbenzene dissociate through the ground electronic state, giving rise to the slow component. A comparison with an ab initio calculation suggests that the dissociation from the first triplet state corresponds to the fast component in translational energy distribution.
Magnetic tunnel junction field sensors with hard-axis bias field
Authors: Liu Xiaoyong , Ren Cong , Xiao Gang
Published: October 2002

We have fabricated and studied the magnetic properties of the Ni81Fe19/Al2O3/Ni81Fe19 based magnetic tunnel junction sensors. Magnetoresistance (MR) of 35% is achieved with a small applied field (<10 Oe). The introduction of a hard axis bias field linearizes the MR response. The hysteresis disappears in hard-axis fields greater than 3 Oe, which corresponds to the effective anisotropy field along the easy axis. A sensitivity of 3.5%/Oe has been demonstrated in this linear region. Low-frequency noise measurements indicate that sensor noise is dominated by field-dependent 1/f noise caused by magnetization fluctuations. Finally, a noise level as low as 1 nT/Hz1/2 has been obtained.
Hydrogen transfer in photoexcited phenol/ammonia clusters by UV–IR–UV ion dip spectroscopy and ab initio molecular orbital calculations. I. Electronic transitions
Authors: Ishiuchi Shun-ichi , Daigoku Kota , Saeki Morihisa , Sakai Makoto , Hashimoto Kenro , Fujii Masaaki
Published: October 2002

The electronic spectra of reaction products via photoexcited phenol/ammonia clusters (1:2–5) have been measured by UV-near-IR–UV ion dip spectroscopy. Compared with the electronic spectra of hydrogenated ammonia cluster radicals the reaction products have been proven to be (NH3)n−1NH4 (n=2–5), which are generated by excited-state hydrogen transfer in PhOH–(NH3)n. By comparing the experimental results with ab initio molecular orbital calculations at multireference single and double excitation configuration interaction level, it has been found that the reaction products (NH3)n−1NH4 (for n=3 and 4), contain some isomers.
Low-frequency noise in GaN/AlGaN heterostructure field-effect transistors at cryogenic temperatures
Authors: Rumyantsev S. L. , Deng Y. , Borovitskaya E. , Dmitriev A. , Knap W. , Pala N. , Shur M. S. , Levinshtein M. E. , Khan M. Asif , Simin G. , Yang J. , Hu X.
Published: October 2002

The low-frequency noise in GaN/AlGaN heterostructure field-effect transistors (HFETs) was studied in the temperature range from 8 to 300 K. A contribution of generation-recombination noise with extremely small activation energy Ea=(1−3) meV was observed at T<50 K. At 70⩽T⩽150 K, the temperature dependence of noise in HFETs with a doped channel exhibited a broad maximum. The position of the maximum was practically independent of the frequency of analysis. The model linking this maximum to the electron tunneling from the channel to the silicon donor level in GaN is discussed.
Magnetic-field and laser effects on the electronic and donor states in semiconducting quantum dots
Authors: Brandi H. S. , Latgé A. , Oliveira L. E.
Published: October 2002

Light shifts induced in the electronic and shallow on-center donor states in spherical semiconductor quantum dots, including magnetic field effects, are theoretically investigated. The interaction of light with the spherical GaAs–(Ga, Al)As quantum dot is treated within a dressed-band approach in which the Kane band structure scheme is used to model the GaAs bulk semiconductor whereas the dressing by the laser field is treated through the renormalization of the GaAs energy gap and conduction/valence effective masses. This nonperturbative approach is valid far from resonances and has been successfully adopted for other confined semiconductor heterostructures. The discrete nature of the electronic and impurity states, characteristic of quantum dot systems, and the possibility of adding extra confining effects by laser and applied magnetic fields opens up a promising route of applicability and/or manipulation of quantum-dot states in recent quantum-computer proposals.
Suppression of thermally activated flux entry through a flux dam in high Tc superconducting quantum interference device magnetometer
Authors: Enpuku K. , Kuroda D. , Tokimizu D. , Yang T. Q.
Published: October 2002

Thermally activated magnetic-flux entry into a pickup coil through a flux dam in high-Tc superconducting quantum interference device (SQUID) magnetometer is studied. Since the thermally activated flux entry strongly depends on the circulating current in the pickup coil, the behavior of the circulating current is studied with numerical simulation when an external field is applied. It is shown that the circulating current becomes near the critical current of the flux dam after the large external field is applied. In this case, thermally activated flux entry becomes large, and degrades the SQUID performance. In order to suppress the thermal activation, the circulating current must be much below the critical current. For this purpose, two methods are proposed. One is to use a compensation field in the case of the flux dam, and the other is to use a switch instead of the flux dam. Numerical simulation shows that we can rapidly decrease the circulating current much below the critical current, and hence, can suppress the thermally activated flux entry by using these methods. The usefulness of these methods is confirmed experimentally.
Role of paramagnetic ions in the formation of the low-temperature current through a molecular wire
Authors: Petrov É. G.
Published: October 2002

The mechanism of formation of the inelastic current through a molecular wire is considered under conditions of strong interaction between the electrons being transported and rapid vibrational and spin relaxation within each electron localization center in the wire. It is shown that paramagnetic ions with “frozen” orbital moments in the electron localization centers are capable not only of giving rise to a spin-polarized current but also of blocking the current itself.
Nonmonotonic temperature dependence of the spontaneous magnetization of the antiferromagnetic crystal LiCoPO4
Authors: Kharchenko N. F. , Desnenko V. A. , Kharchenko Yu. N. , Szymczak R. , Baran M.
Published: October 2002

The temperature dependence of the magnitude of the weak ferromagnetic moment is measured in the many-sublattice antiferromagnetic magnetoelectric crystal LiCoPO4. The dependence is found to be nonmonotonic—as the temperature is decreased below the Néel temperature TN, the ferromagnetic moment initially increases and then decreases markedly. It reaches its highest value, close to 0.12 G, at a temperature of around 10.5 K, which is roughly TN/2. The possible mechanisms for the appearance of weak ferromagnetism in LiCoPO4 and the causes of the nonmonotonic temperature dependence of the spontaneous magnetic moment are discussed. Among the possible mechanisms, there is a preference for one in which the weak ferromagnetism is due to a nonuniform antiferromagnetic structure which is proposed for this crystal.
Optical spectroscopy of antiferromagnetic correlations and the stripe state in the superconductor YBa2Cu3O6+x
Authors: Samovarov V. N. , Vakula V. L. , Libin M. Yu. , Uyutnov S. A. , Sergeeva G. G.
Published: October 2002

Results of measurements of the temperature dependence of the absorption spectra of YBa2Cu3O6+x films in the antiferromagnetic and metallic (superconducting, Tc=88 K) phases are presented. The temperature evolution of the absorption bands, which are diagnostic for the electron and spin correlations and the degree of metallization (oxygen–copper hybridization), is investigated in the energy region 1.3–2.6 eV. It is shown that in the metallic phase in the pseudogap state below T*=120±10 K there is a sharp rise of these absorption bands characteristic of the antiferromagnetic (AF) phase, including the electron–two-magnon (A+J) band, which reflects the development of strong AF correlations. In contrast to the insulator, here the (A+J) band has a fine structure due to the creation of both interacting and noninteracting magnons, and it coexists with the bands due to the strong metallization. The results demonstrate phase separation at Tc<T<T*, with the formation of a stripe superstructure consisting of metallic and insulating (with short-range antiferromagnetic ordering) regions. This superstructure is preserved in the superconducting state, and an additional enhancement of the AF correlations occurs at the superconducting transition. Taken together, the results provide independent optical evidence of the undoubted participation of AF correlations in the superconductivity.
Energy relaxation during hot-exciton transport in quantum wells: Direct observation by spatially resolved phonon-sideband spectroscopy
Authors: Zhao Hui , Moehl Sebastian , Kalt Heinz
Published: October 2002

We investigate the energy relaxation of excitons during the real-space transport in ZnSe quantum wells by using microphotoluminescence with spatial resolution enhanced by a solid immersion lens. The spatial evolution of the LO-phonon sideband, originating from the LO-phonon assisted recombination of hot excitons, is measured directly. By calculating the LO-phonon assisted recombination probability, we obtain the nonthermal energy distribution of excitons and observe directly the energy relaxation of hot excitons during their transport. We find the excitons remain hot during their transport on a length scale of several micrometers. Thus, the excitonic transport on this scale cannot be described by classical diffusion.
Imaging, structural, and chemical analysis of silicon nanowires
Authors: J. Barsotti R. , Fischer J. E. , Lee C. H. , Mahmood J. , Adu C. K. W. , Eklund P. C.
Published: October 2002

Laser ablation has been used to grow silicon nanowires with an average silicon crystal core diameter of 6.7 nm±2.9 nm surrounded by an amorphous SiOx sheath of 1–2 nm, the smallest silicon wires reported in the literature. Imaging, chemical, and structural analysis of these wires are reported. Due to the growth temperature and the presence of calcium impurities and trace oxygen, two distinct types of wires are found. They appear to grow by two different processes. One requires a metal catalyst, the other is catalyzed by oxygen. Suggestions for controlled synthesis based on these growth mechanisms are made.
ATP induced MUC5AC release from human airways in vitro
Authors: Roger Patricia , Gascard Jean-Pierre , Bara Jacques , de Montpreville Vincent Thomas , Yeadon Micheal , Brink Charles
Published: October 2002

Background: Chronic airway diseases are often associated with marked mucus production, however, little is known about the regulation of secretory activity by locally released endogenous mediators.

Aim: This investigation was performed to determine the release of MUC5AC mucin from human bronchial preparations using the purinergic agonists adenosine 5′‐triphosphate (ATP) and uridine 5′‐triphosphate (UTP).

Methods: Immunohistochemical and immunoradiometric assays (IRMA) were used to detect the MUC5AC mucin. Immunohistochemical analysis were performed using individual 1–13 M1 and 21 M1 MAbs recognizing a recombinant M1 mucin partially encoded by the MUC5AC gene. IRMA measurments were performed using a mixture of eight anti‐M1 mucin MAbs (PM8), which included both 1–13 M1 and 21 M1 MAbs. Lysozyme and protein were also measured in the biological fluids derived from human bronchial preparations obtained from patients who had undergone surgery for lung carcinoma.

Results: The anti‐M1 monoclonal antibodies labelled epithelial goblet cells. After challenge of human bronchial preparations with ATP, the goblet cells exhibited less staining. In contrast, UTP did not alter the immunolabelling of goblet cells. MUC5AC mucin in the bronchial fluids derived from ATP‐ch allenged preparations was increased while UTP had no effect on release. ATP did not alter either the quantities of lysozyme or protein detected in the biological fluids.

Conclusion: These results suggest that ATP may regulate epithelial goblet cell secretion of MUC5AC mucin from human airways in vitro.
Three-dimensional, Unsteady Simulation of Alveolar Respiration
Authors: Kulish Vladimir V. , Lage Jose´ L. , Hsia Connie C. W. , Johnson, Robert L.
Published: October 2002

A novel macroscopic gas transport model, derived from fundamental engineering principles, is used to simulate the three-dimensional, unsteady respiration process within the alveolar region of the lungs. The simulations, mimicking the single-breath technique for measuring the lung diffusing capacity for carbon-monoxide (CO), allow the prediction of the red blood cell (RBC) distribution effects on the lung diffusing capacity. Results, obtained through numerical simulations, unveil a strong relationship between the type of distribution and the lung diffusing capacity. Several RBC distributions are considered, namely: normal (random), uniform, center-cluster, and corner-cluster red cell distributions. A nondimensional correlation is obtained in terms of a geometric parameter characterizing the RBC distribution, and presented as a useful tool for predicting the RBC distribution effect on the lung diffusing capacity. The effect of red cell movement is not considered in the present study because CO does not equilibrate with capillary blood within the time spent by blood in the capillary. Hence, blood flow effect on CO diffusion is expected to be only marginal.
A Dual-Pressure Boundary Condition for use in Simulations of Bifurcating Conduits
Authors: Gin Ron , Straatman Anthony G. , Steinman David A.
Published: October 2002

A dual-pressure boundary condition has been developed for computational modelling of bifurcating conduits. The condition involves the imposition of a constant pressure on one branch while adjusting iteratively the pressure on the other branch until the desired flow division is obtained. The dual-pressure condition eliminates the need for specifying fully-developed flow conditions, which thereby enables significant reduction of the outlet branch lengths. The dual-pressure condition is suitable for both steady and time-periodic simulations of laminar or turbulent flows.
Range-dependent seabed characterization by inversion of acoustic data from a towed receiver array
Authors: Siderius Martin , Nielsen Peter L. , Gerstoft Peter
Published: October 2002

The MAPEX2000 experiments were conducted in the Mediterranean Sea in March, 2000 to determine seabed properties using a towed acoustic source and receiver array. Towed systems are advantageous because they are easy to deploy from a ship and the moving platform offers the possibility for estimating spatially variable (range-dependent) seabed properties. In this paper, seabed parameters are determined using a matched-field geoacoustic inversion approach with measured, towed array data. Previous research has successfully applied matched-field geoacoustic inversion techniques to measured acoustic data. However, in nearly all cases the inverted data were collected on moored, vertical receiver arrays. Results here show that seabed parameters can also be extracted by inverting acoustic measurements from a towed array of receivers, and these agree with those inverted using data received simultaneously on a vertical array. These findings imply that a practical technique could be developed to map range-dependent seabed parameters over large areas using a towed acoustic system. An example of such a range-dependent inversion is given using measurements from the MAPEX2000 experiments.
An effective quiescent medium for sound propagating through an inhomogeneous, moving fluid
Authors: Godin Oleg A.
Published: October 2002

The idea of similarity between acoustic fields in a moving fluid and in a certain “effective” quiescent medium, first put forward by Lord Rayleigh, proved very helpful in understanding and modeling sound propagation in an atmosphere with winds and in an ocean with currents, as well as in other applications involving flows with small velocity compared to sound speed. Known as effective sound speed approximation, the idea is routinely utilized in the contexts of the ray theory, normal mode representation of the sound field, and the parabolic approximation. Despite the wide use of the concept of effective sound speed in acoustics of moving media, no theoretical justification of Rayleigh’s idea was published that would be independent of the chosen representation of the sound field and uniformly apply to distinct propagation regimes. In this paper, we present such a justification by reducing boundary conditions and a wave equation governing sound fields in the inhomogeneous moving fluid with a slow flow to boundary conditions and a wave equation in a quiescent fluid with effective sound speed and density. The derivation provides insight into validity conditions of the concept of effective quiescent fluid. Introduction of effective density in conjunction with effective sound speed is essential to ensure accurate reproduction of acoustic pressure amplitude in the effective medium. Effective parameters depend on sound speed, flow velocity, and density of the moving fluid as well as on sound propagation direction. Conditions are discussed under which the dependence on the propagation direction can be avoided or relaxed.
Acoustic modal analysis in an anisotropic internal wave field
Authors: Oba Roger , Finette Steven
Published: October 2002

Simulations show that an anisotropic, internal wave field in shallow water can cause significant horizontal redirection of acoustic propagation, requiring true three-dimensional sound modeling. Calculations are presented for a sound speed profile that is perturbed by both a nonlinear internal wave packet, and a linear background internal wave field that is homogeneous and isotropic. A 3D parabolic equation code is used to propagate a 400 Hz signal through the spatially and temporally varying sound speed distribution. A single mode starter field at the source is propagated to a receiver location, and there the field is decomposed into modes to determine the degree of modal coupling. If the compressional wave number vector is perpendicular to that of the nonlinear internal wave packet wave number vector, the modeled acoustic field is nearly adiabatic and can be approximated using horizontal mode decomposition. In this case the pressure wave shows horizontal refraction, and ducting. For propagation paths not perpendicular to the internal wave number vector, the acoustic field can b enonadiabatic, and mode coupling can be significant. Modal analysis shows similar refraction and coupling results for lower frequencies. [Work supported by ONR.]
Baseline tests or screening: what tests do family physicians order routinely on their healthy patients?
Authors: Nakar S. , Vinker S. , Neuman S. , Kitai E. , Yaphe J.
Published: October 2002

OBJECTIVE: The purpose of this study was to survey the attitudes of family doctors to the performance of baseline tests and to determine which doctors perform these tests. SETTING: Family physicians in a continuing medical education programme in Tel Aviv, Israel METHOD: An anonymous questionnaire was distributed focusing on performance of tests by doctors in healthy patients and not as part of a screening programme. RESULTS: Questionnaires were returned by 147 of 165 physicians surveyed (89% response rate). Baseline tests were performed by 98% of respondents: not routinely by 54%, 7% at the patient’s request, and 2% did not perform tests. The decision to perform baseline tests was influenced by the presence of other risk factors of disease (86%), patient age (61%), family history (59%), patient request for tests (24%), and patient sex (20%). The tests performed were blood counts, glucose, renal function tests, urinalysis, liver function tests, and electrocardiograms. Baseline tests were useful in case finding of new illnesses for 49% of physicians and 40% said the tests had proved useful during a subsequent illness. The remainder of the physicians found no use for baseline tests. Physicians from the former Soviet Union were more likely to favour baseline tests. CONCLUSION: Almost all of the physicians in this study reported that they perform baseline tests on most of their patients. Evidence based guidelines for these tests and education of physicians are needed.
Congenital toxoplasmosis in the United Kingdom: to screen or not to screen?
Authors: Gilbert R.E. , Peckham C.S.
Published: October 2002

The United Kingdom National Screening Committee recently reviewed the evidence for prenatal and neonatal screening for toxoplasma infection1 and concluded that there was insufficient evidence to recommend screening in the United Kingdom. This issue will need to be revisited as new information or treatments become available. In this paper, the extent to which the research evidence on toxoplasma infection meets the criteria that need to be fulfilled for the introduction of screening in the United Kingdom is reviewed.
Basic variables at different positivity thresholds of a quantitative immunochemical test for faecal occult blood
Authors: Castiglione G. , Grazzini G. , Miccinesi G. , Rubeca T. , Sani C. , Turco P. , Zappa M.
Published: October 2002

OBJECTIVES: Screening by faecal occult blood testing (FOBT) is effective in decreasing mortality and incidence of colorectal cancer (CRC). Immunochemical tests have proved to be more cost effective than guaiac FOBTs. The latex agglutination test (LAT) has the advantage of being a fully automated, quantitative test. The aim of this study is to interpret the overall experience with LAT according to different positivity thresholds. SETTING: A population based screening programme is currently running involving subjects aged 50–70, invited every 2 years to have an FOBT. LAT is the standard screening test and has a positivity threshold for further diagnostic tests of 100 ng haemoglobin/ml of sample solution. METHODS: Positivity rates, detection rates for CRC high risk adenomas, and positive predictive values for CRC, high risk adenomas, and low risk adenomas were calculated for several positivity thresholds. RESULTS: 19 132 attendances at screening were recorded (11 774 at first screening, 7358 at subsequent screenings). Progressively increasing the positivity threshold from 100 to 200 ng/ml showed (a) a decrease in positivity rate; (b) a decrease in detection rates for CRC or high risk adenomas; (c) an increase in positive predictive values for cancer; (d) an increase in positive predictive value for high risk adenomas. CONCLUSIONS: Increasing the positivity threshold of the LAT reduces recall rate and improves positive predictive value for cancer or high risk adenomas but substantially decreases the detection rate of CRC and high risk adenomas. For this reason increasing the positivity cut off for LATs is not advisable. On the other hand decreasing the positivity threshold would increase recall rate and sensitivity of screening. Careful evaluation of sensitivity of the quantitative results of the LAT for interval cancers is needed to definitively assess the optimal positivity threshold for LATs in population based screening programmes.
Adding fair choice to Dijkstra's calculus
Authors: Broy Manfred , Nelson Greg
Published: October 2002

The paper studies the incorporation of a fair nondeterministic choice operator into a generalization of Dijkstra's calculus of guarded commands. The generalization drops the law of the excluded miracle to allow commands that correspond to partial relations. Because of fairness, the new operator is not monotonic for the orderings that are generally used for proving the existence of least fixed points for recursive definitions. To prove the existence of fixed points it is necessary to consider several orderings at once, and to restrict the class of recursive definitions.
Optimal code motion
Authors: Knoop Jens , Rüthing Oliver , Steffen Bernhard
Published: October 2002

An implementation-oriented algorithm for
lazy code motion
is presented that minimizes the number of computations in programs while suppressing any unnecessary code motion in order to avoid superfluous register pressure. In particular, this variant of the original algorithm for lazy code motion works on flowgraphs whose nodes are basic blocks rather than single statements, since this format is standard in optimizing compilers. The theoretical foundations of the modified algorithm are given in the first part, where
t
-refined flowgraphs are introduced for simplifying the treatment of flow graphs whose nodes are basic blocks. The second part presents the “basic block” algorithm in standard notation and gives directions for its implementation in standard compiler environments.
Decompilation: the enumeration of types and grammars
Authors: Breuer Peter T. , Bowen Jonathan P.
Published: October 2002

While a compiler produces low-level object code from high-level source code, a decompiler produces high-level code from low-level code and has applications in the testing and validation of safety-critical software. The decompilation of an object code provides an independent demonstration of correctness that is hard to better for industrial purposes (an alternative is to prove the compiler correct). But, although compiler compilers are in common use in the software industry, a decompiler compiler is much more unusual.

It turns out that a data type specification for a programming-language grammar can be remolded into a functional program that enumerates all of the abstract syntax trees of the grammar. This observation is the springboard for a general method for compiling decompilers from the specifications of (nonoptimizing) compilers.

This paper deals with methods and theory, together with an application of the technique. The correctness of a decompiler generated from a simple occam-like compiler specification is demonstrated. The basic problem of enumerating the syntax trees of grammars, and then stopping, is shown to have no recursive solution, but methods of abstract interpretation can be used to guarantee the adequacy and completeness of our technique in practical instances, including the decompiler for the language presented here.
Improving abstract interpretations by combining domains
Authors: Codish Michael , Mulkers Anne , Bruynooghe Maurice , de la Banda Maria García , Hermenegildo Manuel
Published: October 2002

This article considers static analysis based on abstract interpretation of logic programs over combined domains. It is known that analyses over combined domains provide more information potentially than obtained by the independent analyses. However, the construction of a combined analysis often requires redefining the basic operations for the combined domain. A practical approach to maintain precision in combined analyses of logic programs which reuses the individual analyses and does not redefine the basic operations is illustrated. The advantages of the approach are that (1) proofs of correctness for the new domains are not required and (2) implementations can be reused. The approach is demonstrated by showing that a combined sharing analysis—constructed from “old” proposals—compares well with other “new” proposals suggested in recent literature both from the point of view of efficiency and accuracy.
Higher-order distributed objects
Authors: Cejtin Henry , Jagannathan Suresh , Kelsey Richard
Published: October 2002

We describe a distributed implementation of Scheme that permits efficient transmission of higher-order objects such as closures and continuations. The integration of distributed communication facilities within a higher-order programming language engenders a number of new abstractions and paradigms for distributed computing. Among these are user-specified load-balancing and migration policies for threads, incrementally linked distributed computations, and parameterized client-server applications. To our knowledge, this is the first distributed dialect of Scheme (or a related language) that addresses lightweight communication abstractions for higher-order objects.
Iteration abstraction in Sather
Authors: Murer Stephan , Omohundro Stephen , Stoutamire David , Szyperski Clemens
Published: October 2002

Sather extends the notion of an iterator in a powerful new way. We argue that iteration abstractions belong in class interfaces on an equal footing with routines. Sather iterators were derived from CLU iterators but are much more flexible and better suited for object-oriented programming. We retain the property that iterators are
structured
, i.e., strictly bound to a controlling structured statement. We motivate and describe the construct along with several simple examples. We compare it with iteration based on CLU iterators, cursors, riders, streams, series, generators, coroutines, blocks, closures, and lambda expressions. Finally, we describe experiences with iterators in the Sather compiler and libraries.
Retargetable microcode synthesis
Authors: Mueller Robert A. , Varghese Joseph
Published: October 2002

Most work on automating the translation of high-level microprogramming languages into microcode has dealt with lexical and syntactic analysis and the use of manually produced macro tables for code generation. We describe an approach to and some results on the formalization and automation of the more difficult problem of retargeting local code generation in a machine-independent, optimizing microcode synthesis system. Whereas this problem is similar in many ways to that of retargeting local code generation in high-level language compilers, there are some major differences that call for new approaches.

The primary issues addressed in this paper are the representation of target microprogrammable machines, the intermediate representation of local microprogram function, and general algorithmic methods for deriving local microcode from target machine and microcode function specifications. Of particular interest are the use of formal semantics and data flow principles in achieving both a general and reasonably efficient solution. Examples of the modeling of a representative horizontal machine (the PUMA) and the generation of microcode for the PUMA machine model from our working implementation are presented.
IDL: sharing intermediate representations
Authors: Lamb David Alex
Published: October 2002

IDL (Interface Description Language) is a practical and useful tool for controlling the exchange of structured data between different components of a large system. IDL is a notation for describing collections of programs and the data structures through which they communicate. Using IDL, a designer gives abstract descriptions of data structures, together with representation specifications that specialize the abstract structures for particular programs. A tool, the IDL translator, generates readers and writers that map between concrete internal representations and abstract exchange representations.
Optimal control dependence computation and the Roman chariots problem
Authors: Pingali Keshav , Bilardi Gianfranco
Published: October 2002

The control dependence relation plays a fundamental role in program restructuring and optimization. The usual representation of this relation is the control dependence graph (CDG), but the size of the CDG can grow quadratically with the input programs, even for structured programs. In this article, we introduce the augmented postdominator tree
(APT)
, a data structure which can be constructed in space and time proportional to the size of the program and which supports enumeration of a number of useful control dependence sets in time proportional to their size. Therefore,
APT
provides an optimal representation of control dependence. Specifically, the
APT
data structure supports enumeration of the set cd(e), which is the set of statements control dependent on control-flow edge e, of the set
conds
(w), which is the set of edges on which statement
w
is dependent, and of the set
cdequiv
(
w
), which is the set of statements having the same control dependences as
w
. Technically,
APT
can be viewed as a factored representation of the CDG where queries are processed using an approach known as filtering search.
Specifying representations of machine instructions
Authors: Ramsey Norman , Fernández Mary F.
Published: October 2002

We present SLED, a specification language for Encoding and Decoding, which describes, abstract, binary, and assembly-language representations of machine instructions. Guided by a SLED specification, the New Jersey Machine-Code Toolkit generates bit-manipulating code for use in applications that process machine code. Programmers can write such applications at an assembly language level of abstraction, and the toolkit enables the applications to recognize and emit the binary representations used by the hardware. SLED is suitable for describing both CISC and RISC machines; we have specified representations of MIPS R3000, SPARC, Alpha, and Intel Pentium instructions, and toolkit users have written specifications for the Power PC and Motorola 68000. The article includes representative excerpts from our SPARC and Pentium specifications. SLED uses four elements;
fields
and
tokens
describe parts of instructions;
patterns
describe binary representations of instructions or group of instructions; and
constructors
map between the abstract and binary levels. By combining the elements in different ways, SLED supports machine-independent implementations of machine-level concepts like conditional assembly, span-dependent instructions, relocatable addresses, object code, sections, and relocation. SLED specifications can be checked automatically for consistency with existing assemblers. The implementation of the toolkit is largely determined by our representations of patterns and constructors. We use a normal form that facilitates construction of encoders and decoders. The article describes the normal form and its use. The toolkit has been used to help build several applications. We have built a retargetable debugger and a retargetable, optimizing linker. Colleagues have built a dynamic code generator, a decompiler, and an execution-time analyzer. The toolkit generates efficient code; for example, the linker emits binary up to 15% faster than it emits assembly language, making it 1.7-2 times faster to produce an a.out directly than by using the assembler.
Utilizing symmetry when model-checking under fairness assumptions
Authors: Emerson E. A. , Sistla A. P.
Published: October 2002

One useful technique for combating the state explosion problem is to exploit symmetry when performing temporal logic model checking. In previous work it is shown how, using some basic notions of group theory, symmetry may be exploited for the full range of correctness properties expressible in the very expressive temporal logic CTL*. Surprisingly, while fairness properties are readily expressible in CTL*, these methods are not powerful enough to admit any amelioration of state explosion, when fairness assumptions are involved. We show that it is nonetheless possible to handle fairness efficiently by trading some group theory for automata theory. Our automata-theoretic approach depends on detecting fair paths subtly encoded in a quotient structure whose arcs are annotated with permutations, by using a threaded structure that reflects coordinate shifts caused by the permutations.
An approach for exploring code improving transformations
Authors: Whitfield Deborah L. , Soffa Mary Lou
Published: October 2002

Although code transformations are routinely applied to improve the performance of programs for both scalar and parallel machines, the properties of code-improving transformations are not well understood. In this article we present a framework that enables the exploration, both analytically and experimentally, of properties of code-improving transformations. The major component of the framework is a specification language, Gospel, for expressing the conditions needed to safely apply a transformation and the actions required to change the code to implement the transformation. The framework includes a technique that facilitates an analytical investigation of code-improving transformations using the Gospel specifications. It also contains a tool, Genesis, that automatically produces a transformer that implements the transformations specified in Gospel. We demonstrate the usefulness of the framework by exploring the enabling and disabling properties of transformations. We first present analytical results on the enabling and disabling properties of a set of code transformations, including both traditional and parallelizing transformations, and then describe experimental results showing the types of transformations and the enabling and disabling interactions actually found in a set of programs.
Fast algorithms for compressed multimethod dispatch table generation
Authors: Dujardin Eric , Amiel Eric , Simon Eric
Published: October 2002

The efficiency of dynamic dispatch is a major impediment to the
adoption of multimethods in object-oriented languages. In this
article, we propose a simple multimethod dispatch scheme based on
compressed dispatch tables. This scheme is applicable to any
object-oriented language using a method precedence order that
satisfies a specific monotonous property (e.g., as Cecil and Dylan)
and guarantees that dynamic dispatch is performed in constant time,
the latter being a major requirement for some languages and
applications. We provide efficient algorithms to build the dispatch
tables, provide their worst-case complexity, and demonstrate the
effectiveness of our scheme by real measurements performed on two
large object-oriented applications. Finally, we provide a detailed
comparison of our technique with other existing techniques.
“Maximal-munch” tokenization in linear time
Authors: Reps Thomas
Published: October 2002

The lexical-analysis (or scanning) phase of a compiler attempts to partition an input string into a sequence of tokens. The convention in most languages is that the input is scanned left to right, and each token identified is a “maximal munch” of the remaining input—the
longest
prefix of the remaining input that is a token of the language. Although most of the standard compiler textbooks present a way to perform maximal-munch tokenization, the algorithm they describe is one that, for certain sets of token definitions, can cause the scanner to exhibit quadratic behavior in the worst case. In the article, we show that maximal-munch tokenization can always be performed in time linear in the size of the input.
Isomorph-free model enumeration
Authors: Jackson Daniel , Jha Somesh , Damon Craig A.
Published: October 2002

Software specifications often involve data structures with huge numbers of value, and consequently they cannot be checked using standard state exploration or model-checking techniques. Data structures can be expressed with binary relations, and operations over such structures can be expressed as formulae involving relational variables. Checking properties such as preservation of an invariant thus reduces to determining the validity of a formula or, equivalently, finding a model (of the formula's negation). A new method for finding relational models is presented. It exploits the permutation invariance of models—if two interpretations are isomorphic, then neither is a model, or both are—by partitioning the space into equivalence classes of symmetrical interpretations. Representatives of these classes are constructed incrementally by using the symmetry of the partial interpretation to limit the enumeration of new relation values. The notion of symmetry depends on the type structure of the formula; by picking the weakest typing, larger equivalence classes (and thus fewer representatives) are obtained. A more refined notion of symmetry that exploits the meaning of the relational operators is also described. The method typically leads to exponential reductions; in combination with other, simpler, reductions it makes automatic analysis of relational specifications possible for the first time.
A logical model for relational abstract domains
Authors: Giacobazzi Roberto , Scozzari Francesca
Published: October 2002

In this article we introduce the notion of Heyting completion in abstract interpretation. We prove that Heyting completion provides a model for Cousot's reduced cardinal power of abstract domains and that it supplies a logical basis to specify relational domains for program analysis and abstract interpretation. We study the algebraic properties of Heyting completion in relation with other well-known domain transformers, like reduced product and disjunctive completion. This provides a uniform algebraic setting where complex abstract domains can be specified by simple logic formulas, or as solutions of recursive abstract domain equations, involving few basic operations for domain construction, all characterized by a clean logical interpretation. We apply our framework to characterize directionality and condensing and in downward closed analysis of (constraint) logic programs.
A modular verifiable exception handling mechanism
Authors: Yemini Shaula , Berry Daniel M.
Published: October 2002

This paper presents a new model for exception handling, called the replacement model. The replacement model, in contrast to other exception-handling proposals, supports all the handler responses of resumption, termination, retry, and exception propagation, within both statements and expressions, in a modular, simple, and uniform fashion. The model can be embedded in any expression-oriented language and can also be adapted to languages which are not expression oriented with almost all the above advantages. This paper presents the syntactic extensions for embedding the replacement model into Algol 68 and its operational semantics. An axiomatic semantic definition for the model can be found in [27].
Java bytecode compression for low-end embedded systems
Authors: Clausen Lars Ræder , Schultz Ulrik Pagh , Consel Charles , Muller Gilles
Published: October 2002

A program executing on a low-end embedded system, such as a smart-card, faces scarce memory resources and fixed execution time constraints. We demonstrate that factorization of common instruction sequences in Java bytecode allows the memory footprint to be reduced, on average, to 85% of its original size, with a minimal execution time penalty. While preserving Java compatibility, our solution requires only a few modifications which are straightforward to implement in any JVM used in a low-end embedded system.
Programming by Refinement, as Exemplified by the SETL Representation Sublanguage
Authors: Dewar Robert B. K. , Grand Arthur , Liu Ssu-Cheng , Schwartz Jacob T. , Schonberg Edmond
Published: October 2002

“Pure” SETL is a language of very high level allowing algorithms to be programmed rapidly and succintly. SETL's representation sublanguage adds a system of declarations which allow the user of the language to control the data structures that will be used to implement an algorithm which has already been written in pure SETL, so as to improve its efficiency. Ideally no rewriting of the algorithm should be necessary. The facilities provided by the representation sublanguage and the run-time data structures that it can generate are described; based on this a heuristic which uses some of the methods of global program analysis and which should be capable of selecting an acceptably efficient representation automatically is given.