bluuebunny/crossref_metadata_2025 huggingface dataset:
Molar excess enthalpies for some systems containing the OH and (or) O groups in the same or in different molecules
Authors: Cobos Jose Carlos , de la Fuente Isaias Garcia , Gonzalez Juan Antonio
Published: July 2002

In this work, HmE data at 298.15 K for the systems 1-nonanol + n-C12; 1-nonanol + n-C14; 1-hexanol + 3,6,9-trioxaundecane; and 2-(2-butoxyethoxyethanol) + n-C7 are reported. Measurements were carried out with a standard Calvet-type microcalorimeter. Molar excess functions, including enthalpies and entropies, are carefully examined to report on the main features of the studied solutions. Dipoledipole interactions between ether molecules are, therefore, of great importance in both 1-alkanols + polyoxaalkanes mixtures and between hydroxyether molecules in alkoxy ethanols + n-alkanes systems. In the second case, it has been attributed to the existence of intramolecular H-bonds in alkoxy ethanols as well as to their higher effective-dipole moment in comparison to that of homologous 1-alkanols. DISQUAC is the only model that can be used to accurately represent thermodynamic functions (except molar excess volumes, VmE) of all of the solutions under study. UNIFAC underestimates dipoledipole interactions in 1-alkanols + polyoxaalkanes and alkoxyethanols + n-alkanes systems. In exchange, the self-association of the alcohol is overestimated in mixtures of 1-nonanol with n-alkanes. Currently, the ERAS model can only be used to examine these solutions. The variation of the VmE with the size of the n-alkanes is well described. Key words: excess functions, OH group, O group, interactions, models.
CONTINUOUS CROSSED PRODUCT OF HILBERT C*-BIMODULES
Authors: KAJIWARA TSUYOSHI
Published: July 2002

We define crossed products of Hilbert C*-bimodules by locally compact not necessarily discrete groups. We show that they are countably generated Hilbert C*-bimodule of finite dimension, when bimodules and C*-algebras are separable and groups are second countable. In special cases, we construct a base and compute indices of them. Moreover, we show the formula concerning tensor products and show the Takesaki-Takai duality theory for locally compact abelian groups, and present an example of categorical equivalence holds between a dual of compact group and bimodules generated by this.
METRIC PAIRS AND THE FUTAKI CHARACTER
Authors: MASCHLER GIDEON
Published: July 2002

The non-vanishing of the Futaki character gives an obstruction to the existence of Kähler metrics of constant scalar curvature, having a Kähler form belonging to a fixed Kähler class [4, 6]. It is shown that, in combination with the resolution of the Calabi conjecture [18], one has an analogous obstruction on pairs of metrics having Kähler forms belonging to a fixed pair of Kähler classes. If the difference of the Futaki characters on two classes of fixed total volume does not vanish identically, there cannot exist a pair of metrics, with Kähler forms in these classes, having the same Ricci form and the same harmonic Ricci form. When the obstruction vanishes, results in [8] are used to construct non-trivial examples of such pairs, which are also extremal in the sense of Calabi [3].
COMPUTERIZED SYMBOLIC COMPUTATION FOR THE MODIFIED DISPERSIVE WATER WAVE EQUATIONS
Authors: GAO YI-TIAN , TIAN BO
Published: July 2002

With computerized symbolic computation, we present an auto-Bäcklund transformation and three families of soliton-like solutions to the modified dispersive water wave equations.
NONSTATIC AdS2 BRANES AND THE ISOMETRY GROUP OF AdS3 SPACE–TIME
Authors: RYANG SHIJONG
Published: July 2002

For the D-branes on the SL (2,R) WZW model we present a particular choice of outer automorphism for the gluing condition of currents that leads to a special AdS2 brane configuration. This configuration is shown to be a static solution in the cylindrical coordinates, and a nonstatic solution in the Poincaré coordinates to the nonlinear equation of motion for the Dirac–Born–Infeld action of a D-string. The generalization of it gives a family of nonstatic AdS2 brane solutions. They are demonstrated to transform to each other under the isometry group of AdS3 space–time.
HAMILTONIAN LATTICE QCD WITH WILSON FERMIONS AT STRONG COUPLING
Authors: FANG YI-ZHONG , LUO XIANG-QIAN
Published: July 2002

Hamiltonian lattice QCD with Wilson fermions is investigated systematically by strong-coupling expansion up to the second order. The effective Hamiltonian is diagonalized by Bogoliubov transformation. The vacuum energy, chiral condensate, pseudoscalar and vector meson masses are calculated. The comparison with the unitary transformation method by Luo and Chen is also made. The method discussed in this paper has potential application to QCD at finite density.
ASTROPHYSICAL NEUTRINOS: 20TH CENTURY AND BEYOND
Authors: BAHCALL J. N.
Published: July 2002

I summarize the first four decades of solar neutrino research and suggest what may be possible to learn with extragalactic neutrinos and with solar neutrinos in the next decade.
REAL-TIME NONEQUILIBRIUM DYNAMICS IN HOT QED PLASMAS
Authors: WANG SHANG-YUNG
Published: July 2002

The quantum kinetics of photons in hot QED plasmas is studied directly in real time by implementing the dynamical renormalization group. In contrast to conventional approach, the dynamical renormalization group method consistently includes off-shell (energy non-conserving) effects and accounts for time-dependent collisional kernel. To lowest order we find that in the relaxation time approximation the semihard photon distribution function relaxes with a power law.
DETERMINANT LINE BUNDLES AND TOPOLOGICAL INVARIANTS OF HYPERBOLIC GEOMETRY
Authors: BYTSENKO ANDREI A.
Published: July 2002

Some remarks on determinant line bundles and topological invariants are given. The index of the twisted Dirac operator acting on real hyperbolic manifolds is computed. We briefly discuss physical applications of results.
COMPETING QUANTUM ORDERINGS IN CUPRATE SUPERCONDUCTORS: A MINIMAL MODEL
Authors: MARTIN I. , ORTIZ G. , BALATSKY A. V. , BISHOP A. R.
Published: July 2002

We present a minimal model for cuprate superconductors. At the unrestricted mean-field level, the model produces homogeneous superconductivity at large doping, striped superconductivity in the underdoped regime and various antiferromagnetic phases at low doping and for high temperatures. On the underdoped side, the superconductor is intrinsically inhomogeneous and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. The model is applied to calculate experimentally measurable ARPES spectra.
STRUCTURAL ASPECTS OF THE FALSE 2212 IN A (Bi,Pb):2223 SUPERCONDUCTOR
Authors: CIURCHEA D.
Published: July 2002

The full pattern decomposition method by Le Bail was applied to the X-ray diffraction pattern of a ( Bi 1.8 Pb 0.46) Sr 1.88 Ca 2.06( Cu 0.97 Fe 0.01 Ca 0.02)3 O y superconductor presenting the same characteristics as the false 2212 reported by Masqood et al. (ICDD file 42-514). By using the Cmmm space group, AB5 coordination in the BiO planes was evidenced, yielding an explanation for the apparent cell colapse. Orthorombic-pseudohexagonal settings for the a and b lattice constants may be derived from the group-supergroup relationships, i.e. instead of [Formula: see text] one may take a=2×3.8Å and [Formula: see text]. Indexing with these values avoids the assumption for the strange [Formula: see text] peak, and yields the refined values of a=7.664Å, b=3.356Å and c=16.172Å, space group Pmmm.
ELECTRONIC STRUCTURE OF VORTICES IN HIGH Tc SUPERCONDUCTORS
Authors: BARNES S. E.
Published: July 2002

The formation of a pseudo gap and supercondctivity are described in terms of a Kondo band formed at the chemical potential. Pre-existing spin triplet bosons condense at Tc. For T>Tc or at the center of a vortex the condensate is absent and these bosons lead to a pseudo gap. Numerical comparison is made with STM results.
POLAR SURFACE-OPTICAL PHONON MODES IN A QUANTUM BOX
Authors: ZHOU HAIYANG , GU SHIWEI , SHI YAOMING
Published: July 2002

The polar surface-optical (SO) phonon modes and their dispersion relations in a quantum box are derived within the dielectric continuum approximation. Then, having quantized the vibrational eigenmodes, we give the electron-SO phonon interaction Hamiltonian in a quantum box.
Nonclassical Properties of the Even and Odd Intermediate Number Squeezed States
Authors: Roy B.
Published: July 2002

The even and odd intermediate number squeezed states are introduced. These states reduce to even (odd) number states and even (odd) squeezed coherent states in different limits. It is shown that these states exhibit nonclassical effects such as sub (super) Poissonian statistics, quadrature squeezing, antibunching for certain ranges of the parameters involved.
Persistent Currents in a Normal Metallic Loop Connected with A Normal Metal and a Superconductor
Authors: Cao Zhiliang , Xie Yuannan , Han Rushan
Published: July 2002

We have studied the effect of the Andreev reflection on the persistent currents in a normal metallic loop connected with a normal metal and a superconductor. It consist of two parts, one contributed by electrons and one by holes. They are periodic with a period equal to a single flux quantum, ϕ0, versus the threading magnetic flux and π versus the length of the lead bridging between the loop and the superconductor. They have sharp peaks at the gap edge. Both the sum of persistent currents and the electronic part increase to a same constant, but the hole part decreases to zero with the barrier strength rising to infinity.
140 MeV Si-ION IRRADIATION INDUCED Tc ENHANCEMENT IN YBCO THIN FILMS
Authors: MISHRA N. C. , BEHERA D. , MOHANTY T. , PATNAIK K. , SENAPTI L. , SINGH O. G. , KANJILAL D. , MEHTA G. K. , PINTO R.
Published: July 2002

On-line resistance measurement in a temperature range of 78 K to 124 K was performed on epitaxial thin films of YBCO irradiated with 140 MeV Si ions. The superconducting transition temperature (T c ), resistivity at 100 K (ρ 100 k ) and transition width (ΔT c ) all show peak at a fluence of 1.5×1013 ions/cm2. A crystallochemical analysis based on metastability induced charge and spin fluctuation due to irradiation induced oxygen disorder in the CuO chains explains the T c enhancement in the low fluence regime.
SOLVENT EFFECT ON ABSOLUTE FLUORESCENCE QUANTUM YIELD OF RHODAMINE 6G DETERMINED USING TRANSIENT THERMAL LENS TECHNIQUE
Authors: BINDHU C. V. , HARILAL S. S. , NAMPOORI V. P. N. , VALLABHAN C. P. G.
Published: July 2002

Dual beam thermal lens technique is successfully employed for the determination of absolute fluorescence quantum yield of rhodamine 6G laser dye in different solvents. A 532 nm radiation from a Q-switched Nd:YAG laser was used for the excitation purpose. The fluorescence quantum yield values are found to be strongly influenced by environmental effects. It has been observed that fluorescence yield is greater for rhodamine 6G in ethylene glycol system than in water or in methanol. Our results also indicate that parameters like concentration of the dye solution, aggregate formation and excited state absorption affect the absolute values of fluorescence yield significantly.
DIRECT DETERMINATION OF RELAXATION PARAMETER FROM LEED INTENSITY PATTERNS WITH THE SINGLE OVERLAYER RELAXED STRUCTURE MODEL
Authors: MUKHOPADHYAY S. , BALLABH T. K.
Published: July 2002

Using the analytical formulae for Low Energy Electron Diffraction (LEED) intensity patterns in the layer doubling method, we have shown that the relaxation parameter for single overlayer relaxed structure can be solved. Although it is difficult to obtain analytically, numerical method based on linear approximation successfully retrieves the parameter value for simulated pseudo-experimental data. This method uses the intensity pattern along the geometry and the chemistry of the bulk to solve the parameters and it may be thought of as a precursor to a full-fledged method for direct determination of surface structure from LEED pattern. Application of this method on the experimental data of Rh(110), which is known to be a two-overlayer relaxed structure, did not yield a single cluster of relaxation parameters. However, qualitative feature of contraction of top layer relaxation parameter has been properly retrieved at different energies.
SCALING LAWS IN NUMERICAL INSTABILITIES INDUCED BY FIXED-STEP INTEGRATION OF DYNAMICAL SYSTEMS
Authors: DE MARKUS ALICIA SERFATY
Published: July 2002

In the conventional integration of a continuous dynamical system, the interaction between the model and fixed-step algorithms may produce important numerical effects over the resulting discrete representation. Our results indicate that there are remarkably simple scaling laws connecting the relevant parameters of the system to that value of integration step capable of overflowing the calculations. Moreover, we have identified a new type of chaotic numerical instability, which appears as the step size approaches some critical value. This effect is accurately described by means of nonanalytical power laws characteristic of phase transition phenomena. Finally, it is shown that simple nonlocal replacements in the discrete constructions significantly reduce or eliminate some of these numerical instabilities. These discretization effects were tested in several nonlinear dynamical systems of physical importance.
AN OPTIMIZATION APPROACH TO LOCATING AND STABILIZING UNSTABLE PERIODIC ORBITS OF CHAOTIC SYSTEMS
Authors: TIAN YU-PING
Published: July 2002

In this paper, a novel method for locating and stabilizing inherent unstable periodic orbits (UPOs) in chaotic systems is proposed. The main idea of the method is to formulate the UPO locating problem as an optimization issue by using some inherent properties of UPOs of chaotic systems. The global optimal solution of this problem yields the desired UPO. To avoid a local optimal solution, the state of the controlled chaotic system is absorbed into the initial condition of the optimization problem. The ergodicity of chaotic dynamics guarantees that the optimization process does not stay forever at any local optimal solution. When the chaotic orbit approaches the global optimal solution, which is the desired UPO, the controller will stabilize it at the UPO, and the optimization process will cease simultaneously. The method has been developed for both discrete-time and continuous-time systems, and validated for some typical chaotic systems such as the Hénon map and the Duffing oscillator, among others.
COMBINATORIAL GROUP THEORY, INVERSE MONOIDS, AUTOMATA, AND GLOBAL SEMIGROUP THEORY
Authors: DELGADO MANUEL , MARGOLIS STUART , STEINBERG BENJAMIN
Published: July 2002

This paper explores various connections between combinatorial group theory, semigroup theory, and formal language theory.

Let G =  be a group presentation and ℬA, R its standard 2-complex. Suppose X is a 2-complex with a morphism to ℬA, R which restricts to an immersion on the 1-skeleton. Then we associate an inverse monoid to X which algebraically encodes topological properties of the morphism. Applications are given to separability properties of groups.

We also associate an inverse monoid M(A, R) to the presentation  with the property that pointed subgraphs of covers of ℬA, R are classified by closed inverse submonoids of M(A, R). In particular, we obtain an inverse monoid theoretic condition for a subgroup to be quasiconvex allowing semigroup theoretic variants on the usual proofs that the intersection of such subgroups is quasiconvex and that such subgroups are finitely generated. Generalizations are given to non-geodesic combings. We also obtain a formal language theoretic equivalence to quasiconvexity which holds even for groups which are not hyperbolic.

Finally, we illustrate some applications of separability properties of relatively free groups to finite semigroup theory. In particular, we can deduce the decidability of various semidirect and Mal/cev products of pseudovarieties of monoids with equational pseudovarieties of nilpotent groups and with the pseudovariety of metabelian groups.
TIME IN QUANTUM GRAVITY
Authors: BISWAS S. , SHAW A. , MODAK B.
Published: July 2002

The Wheeler–DeWitt equation in quantum gravity is timeless in character. In order to discuss quantum to classical transition of the universe, one uses a time prescription in quantum gravity to obtain a time contained description starting from Wheeler–DeWitt equation and WKB ansatz for the WD wavefunction. The approach has some drawbacks. In this work, we obtain the time-contained Schrödinger–Wheeler–DeWitt equation without using the WD equation and the WKB ansatz for the wavefunction. We further show that a Gaussian ansatz for SWD wavefunction is consistent with the Hartle–Hawking or wormhole dominance proposal boundary condition. We thus find an answer to the small scale boundary conditions.
An Unusual Complication of the Thumb Following Abductor Digiti Minimi Opponensplasty
Authors: Wood V. E. , Skie M.
Published: July 2002

An unusual complication of thumb abduction at the metacarpophalangeal joint following an abductor digiti minimi opponensplasty in a hypoplastic thumb is presented in two cases. It is difficult to create a strong ulnar collateral ligament in these children with unstable thumb joints. In some children, the abductor digiti minimi transfer may be too strong for the function it is intended to provide. Reconstruction of the ulnar collateral ligament may not be strong enough to prevent overpull and secondary deformity. Fusion of the thumb metacarpophalangeal joint or chondrodesis may ultimately be required.
AN ARCHITECTURE FOR DATA WAREHOUSING SUPPORTING DATA INDEPENDENCE AND INTEROPERABILITY
Authors: CABIBBO LUCA , TORLONE RICCARDO
Published: July 2002

We report on the design of a novel architecture for data warehousing based on the introduction of an explicit "logical" layer to the traditional data warehousing framework. This layer serves to guarantee a complete independence of OLAP applications from the physical storage structure of the data warehouse and thus allows users and applications to manipulate multidimensional data ignoring implementation details. For example, it makes possible the modification of the data warehouse organization (e.g. MOLAP or ROLAP implementation, star scheme or snowflake scheme structure) without influencing the high level description of multidimensional data and programs that use the data. Also, it supports the integration of multidimensional data stored in heterogeneous OLAP servers. We propose [Formula: see text], a simple data model for multidimensional databases, as the reference for the logical layer. [Formula: see text] provides an abstract formalism to describe the basic concepts that can be found in any OLAP system (fact, dimension, level of aggregation, and measure). We show that [Formula: see text] databases can be implemented in both relational and multidimensional storage systems. We also show that [Formula: see text] can be profitably used in OLAP applications as front-end. We finally describe the design of a practical system that supports the above logical architecture; this system is used to show in practice how the architecture we propose can hide implementation details and provides a support for interoperability between different and possibly heterogeneous data warehouse applications.
Evaluating stereo and motion cues for visualizing information nets in three dimensions
Authors: Ware Colin , Franck Glenn
Published: July 2002

This article concerns the benefits of presenting abstract data in 3D. Two experiments show that motion cues combined with stereo viewing can substantially increase the size of the graph that can be preceived. The first experiment was designed to provide quantitiative measurements of how much more (or less) can be understood in 3D than in 2D. The 3D display used was configured so that the image on the monitor was coupled to the user's actual eye positons (and it was updated in real-time as the user moved) as well as bring in stereo. Thus the effect was like a local “virtual reality” display located in the vicinity of the computer monitor. The results from this study show that head-coupled stereo viewing can increase the size of an abstract graph that can be understood by a factor of three; using stereo alone provided an increase by a factor of 1.6 and head coupling along produced an increase by a factor of 2.2. The second experiment examined a variety of motion cues provided by head-coupled perspective (as in virtual reality displays), head-guided motion and automatic rotation, respectively, both with and without stereo in each case. The results show that structured 3D motion and stereo viewing both help in understanding, but that the kind of motion is not particularly important; all improve performance, and all are more significant than stereo cues. These results provide strong reasons for using advanced 3D graphics for interacting with a large variety of information structures.
AND/OR graph heuristic search methods
Authors: Mahanti A. , Bagchi A.
Published: July 2002

Two new marking algorithms for AND/OR graphs called CF and CS are presented. For admissible heuristics CS is not needed, and CF is shown to be preferable to the marking algorithms of Martelli and Montanari. When the heuristic is not admissible, the analysis is carried out with the help of the notion of the first and second discriminants of an AND/OR graph. It is proved that in this case CF can be followed by CS to get optimal solutions, provided the sumcost criterion is used and the first discriminant equals the second. Estimates of time and storage requirements are given. Other cost measures, such as maxcost, are also considered, and a number of interesting open problems are enumerated.
An experimental study of people creating spreadsheets
Authors: Brown Polly S. , Gould John D.
Published: July 2002

Nine experienced users of electronic spreadsheets each created three spreadsheets. Although participants were quite confident that their spreadsheets were accurate, 44 percent of the spreadsheets contained user-generated programming errors. With regard to the spreadsheet creation process, we found that experienced spreadsheet users spend a large percentage of their time using the cursor keys, primarily for the purpose of moving the cursor around the spreadsheet. Users did not spend a lot of time planning before launching into spreadsheet creation, nor did they spend much time in a separate, systematic debugging stage. Participants spent 21 percent of their time pausing, presumably reading and/or thinking, prior to the initial keystrokes of spreadsheet creation episodes.
An Algorithm for Subgraph Isomorphism
Authors: Ullmann J. R.
Published: July 2002

Subgraph isomorphism can be determined by means of a brute-force tree-search enumeration procedure. In this paper a new algorithm is introduced that attains efficiency by inferentially eliminating successor nodes in the tree search. To assess the time actually taken by the new algorithm, subgraph isomorphism, clique detection, graph isomorphism, and directed graph isomorphism experiments have been carried out with random and with various nonrandom graphs.

A parallel asynchronous logic-in-memory implementation of a vital part of the algorithm is also described, although this hardware has not actually been built. The hardware implementation would allow very rapid determination of isomorphism.
Specification and implementation of exceptions in workflow management systems
Authors: Casati Fabio , Ceri Stefano , Paraboschi Stefano , Pozzi Guiseppe
Published: July 2002

Although workflow management systems are most applicable when an organization follows standard business processes and routines, any of these processes faces the need for handling exceptions, i.e., asynchronous and anomalous situations that fall outside the normal control flow.

In this paper we concentrate upon anomalous situtations that, although unusual, are part of the semantics of workflow applications, and should be specified and monitored coherently; in most real-life applications, such exceptions affect a significant fraction of workflow cases. However, very few workflow management systems are integrated with a highly expressive language for specifying this kind of exception and with a system component capable of handling it.

We present Chimera-Exc, a language for the specification of exceptions for workflows based on detached active rules, and then describe the architecture of a system, called FAR, that implements Chimera-Exc and integrates it with a commercial workflow management system and database server. We discuss the main issues that were solved by our implementation, and report on the performance of FAR. We also discuss design criteria for exceptions in light of the formal properties of their execution. Finally, we focus on the portability of FAR on its unbundling to a generic architecture with detached active rules.
Distributed cognition
Authors: Hollan James , Hutchins Edwin , Kirsh David
Published: July 2002

We are quickly passing through the historical moment when people work in front of a single computer, dominated by a small CRT and focused on tasks involving only local information. Networked computers are becoming ubiquitous and are playing increasingly significant roles in our lives and in the basic infrastructures of science, business, and social interaction. For human-computer interaction to advance in the new millennium we need to better understand the emerging dynamic of interaction in which the focus task is no longer confined to the desktop but reaches into a complex networked world of information and computer-mediated interactions. We think the theory of distributed cognition has a special role to play in understanding interactions between people and technologies, for its focus has always been on whole environments: what we really do in them and how we coordinate our activity in them. Distributed cognition provides a radical reorientation of how to think about designing and supporting human-computer interaction. As a theory it is specifically tailored to understanding interactions among people and technologies. In this article we propose distributed cognition as a new foundation for human-computer interaction, sketch an integrated research framework, and use selections from our earlier work to suggest how this framework can provide new opportunities in the design of digital work materials.
Computer rendering of stochastic models
Authors: Fournier Alain , Fussell Don , Carpenter Loren
Published: July 2002

A recurrent problem in generating realistic pictures by computers is to represent natural irregular objects and phenomena without undue time or space overhead. We develop a new and powerful solution to this computer graphics problem by modeling objects as sample paths of stochastic processes. Of particular interest are those stochastic processes which previously have been found to be useful models of the natural phenomena to be represented. One such model applicable to the representation of terrains, known as “fractional Brownian motion,” has been developed by Mandelbrot.

The value of a new approach to object modeling in computer graphics depends largely on the efficiency of the techniques used to implement the model. We introduce a new algorithm that computes a realistic, visually satisfactory approximation to fractional Brownian motion in faster time than with exact calculations. A major advantage of this technique is that it allows us to compute the surface to arbitrary levels of details without increasing the database. Thus objects with complex appearances can be displayed from a very small database. The character of the surface can be controlled by merely modifying a few parameters. A similar change allows complex motion to be created inexpensively.
On the criteria to be used in decomposing systems into modules
Authors: Parnas D. L.
Published: July 2002

This paper discusses modularization as a mechanism for improving the flexibility and comprehensibility of a system while allowing the shortening of its development time. The effectiveness of a “modularization” is dependent upon the criteria used in dividing the system into modules. A system design problem is presented and both a conventional and unconventional decomposition are described. It is shown that the unconventional decompositions have distinct advantages for the goals outlined. The criteria used in arriving at the decompositions are discussed. The unconventional decomposition, if implemented with the conventional assumption that a module consists of one or more subroutines, will be less efficient in most cases. An alternative approach to implementation which does not have this effect is sketched.
A technique for computer detection and correction of spelling errors
Authors: Damerau Fred J.
Published: July 2002

The method described assumes that a word which cannot be found in a dictionary has at most one error, which might be a wrong, missing or extra letter or a single transposition. The unidentified input word is compared to the dictionary again, testing each time to see if the words match—assuming one of these errors occurred. During a test run on garbled text, correct identifications were made for over 95 percent of these error types.
The input/output complexity of sorting and related problems
Authors: Aggarwal Alok , Vitter Jeffrey,S.
Published: July 2002

We provide tight upper and lower bounds, up to a constant factor, for the number of inputs and outputs (I/OS) between internal memory and secondary storage required for five sorting-related problems: sorting, the fast Fourier transform (FFT), permutation networks, permuting, and matrix transposition. The bounds hold both in the worst case and in the average case, and in several situations the constant factors match. Secondary storage is modeled as a magnetic disk capable of transferring P blocks each containing B records in a single time unit; the records in each block must be input from or output to B contiguous locations on the disk. We give two optimal algorithms for the problems, which are variants of merge sorting and distribution sorting. In particular we show for P = 1 that the standard merge sorting algorithm is an optimal external sorting method, up to a constant factor in the number of I/Os. Our sorting algorithms use the same number of I/Os as does the permutation phase of key sorting, except when the internal memory size is extremely small, thus affirming the popular adage that key sorting is not faster. We also give a simpler and more direct derivation of Hong and Kung's lower bound for the FFT for the special case B = P = O(1).
Modeling software architectures in the Unified Modeling Language
Authors: Medvidovic Nenad , Rosenblum David S. , Redmiles David F. , Robbins Jason E.
Published: July 2002

The Unified Modeling Language (UML) is a family of design notations that is rapidly becoming a de facto standard software design language. UML provides a variety of useful capabilities to the software designer, including multiple, interrelated design views, a semiformal semantics expressed as a UML meta model, and an associated language for expressing formal logic constraints on design elements. The primary goal of this work is an assessment of UML's expressive power for modeling software architectures in the manner in which a number of existing software architecture description languages (ADLs) model architectures. This paper presents two strategies for supporting architectural concerns within UML. One strategy involves using UML "as is," while the other incorporates useful features of existing ADLs as UML extensions. We discuss the applicability, strengths, and weaknesses of the two strategies. The strategies are applied on three ADLs that, as a whole, represent a broad cross-section of present-day ADL capabilities. One conclusion of our work is that UML currently lacks support for capturing and exploiting certain architectural concerns whose importance has been demonstrated through the research and practice of software architectures. In particular, UML lacks direct support for modeling and exploiting architectural styles, explicit software connectors, and local and global architectural constraints.
Probabilistic robotics
Authors: Thrun Sebastian
Published: July 2002

Planning and navigation algorithms exploit statistics gleaned from uncertain, imperfect real-world environments to guide robots toward their goals and around obstacles.
Spreadsheet analysis and design
Authors: Ronen Boaz , Palley Michael A , Lucas Henry C.
Published: July 2002

Although spreadsheet programs and microcomputers have revolutionized information processing in organizations, a significant number of serious errors have been reported through the misuse of this technology. This article discusses several different contexts for the development of spreadsheet models and presents structured design techniques for these models.
Post implementation evaluation of computer-based information systems: current practices
Authors: Kumar Kuldeep
Published: July 2002

Contrary to the widely-held view that post implementation evaluations are performed to assess and improve the information system and the system development practices, this study suggests that in practice, the primary reason for such evaluations seems to be project closure and not project improvement.
More efficient computation of the complex error function
Authors: Poppe G. P. M. , Wijers C. M. J.
Published: July 2002

Gautschi has developed an algorithm that calculates the value of the Faddeeva function
w
(
z
) for a given complex number
z
in the first quadrant, up to 10 significant digits. We show that by modifying the tuning of the algorithm and testing the relative rather than the absolute error we can improve the accuracy of this algorithm to 14 significant digits throughout almost the whole of the complex plane, as well as increase its speed significantly in most of the complex plane. The efficiency of the calculation is further enhanced by using a different approximation in the neighborhood of the origin, where the Gautschi algorithm becomes ineffective. Finally, we develop a criterion to test the reliability of the algorithm's results near the zeros of the function, which occur in the third and fourth quadrants.
Still Looking for the Ivory Tower
Authors: Schachman Howard K.
Published: July 2002

Following graduate training, which was disrupted by my changing schools and serving in the Navy in World War II, I arrived in Berkeley in 1948 as an instructor in the Biochemistry Department. Despite numerous academic reorganizations and a host of struggles over the University-imposed Loyalty Oath, dismissal of a faculty member because of political affiliations, free speech for students, and my resistance to mandatory retirement, I survived with the help of great graduate students, postdoctoral fellows, undergraduates, superb research assistants, and a supportive wife. Studies on structure of tobacco mosaic virus led to our investigating an ultracentrifuge anomaly and the construction of a synthetic boundary cell. In turn, this resulted in about 15 years of research on the ultracentrifuge and its application to the study of biological macromolecules. Among the latter, the discovery of large ribonucleoprotein complexes, now known as ribosomes, and chromatophores in photosynthetic microorganisms attracted the most attention. But it was the development of the photoelectric absorption optical system and the incorporation of the Rayleigh interferometer onto the ultracentrifuge that had the greatest impact on our further research. These tools, when applied to our initial research on E. coli aspartate transcarbamoylase (ATCase), led to the discovery of distinct subunits for catalysis and regulation and the global conformational change in the enzyme associated with its role in regulation. For almost 35 years we have been using the techniques of protein chemistry and molecular biology in studies of structural and conformational changes in the enzyme, the genes encoding the different polypeptides, subunit interactions, and assembly of the enzyme from six catalytic and six regulatory chains. Hybrids constructed from inactive mutants were used to demonstrate shared active sites requiring the joint participation of amino acid residues from adjoining polypeptide chains. ATCase is still being studied as a model for understanding allostery as a regulatory mechanism. Circularly permuted polypeptide chains are being used to study the folding and assembly pathways, and the recently determined crystal structure of the active nonallosteric catalytic subunit has led to new questions regarding the activated form of ATCase.
Mechanisms Underlying Ubiquitination
Authors: Pickart Cecile M.
Published: July 2002

▪ Abstract  The conjugation of ubiquitin to other cellular proteins regulates a broad range of eukaryotic cell functions. The high efficiency and exquisite selectivity of ubiquitination reactions reflect the properties of enzymes known as ubiquitin-protein ligases or E3s. An E3 recognizes its substrates based on the presence of a specific ubiquitination signal, and catalyzes the formation of an isopeptide bond between a substrate (or ubiquitin) lysine residue and the C terminus of ubiquitin. Although a great deal is known about the molecular basis of E3 specificity, much less is known about molecular mechanisms of catalysis by E3s. Recent findings reveal that all known E3s utilize one of just two catalytic domains—a HECT domain or a RING finger—and crystal structures have provided the first detailed views of an active site of each type. The new findings shed light on many aspects of E3 structure, function, and mechanism, but also emphasize that key features of E3 catalysis remain to be elucidated.
My Career in Molecular Biology
Authors: Davidson Norman
Published: July 2002

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▪ Abstract  Norman Davidson’s training as a physical chemist led him to make key early contributions to the chemistry of DNA. He described the details of DNA denaturation and renaturation, concepts that still form the basis for understanding hybridization. He also applied the single-molecule resolution of the electron microscope to describing the chemistry of circular DNA, mapping specific genes, and characterizing heteroduplexes. The latter became a dominant tool for the study of nucleic acids and contributed to our knowledge of transcription, polyadenylation, and retroviral structure. The advent of cDNA cloning and restriction enzymes enabled Davidson to describe the diversity of Drosophila actin genes and to isolate the gene encoding cAMP phosphodiesterase. Davidson then turned his attention to neuroscience and participated in cDNA cloning, oocyte expression, and structure-function studies of nicotinic acetylcholine receptors, voltage-gated sodium channels, a GABA transporter, a G protein-gated potassium channel, and calcium channels. His interests also extended to synaptic plasticity, and he helped to define the role of neuronal nitric oxide synthase and of trkB receptors. His final experiments concerned the role of protein kinase A in long-term potentiation. (The abstract was written posthumously by a colleague.)
Fast Kinetics and Mechanisms in Protein Folding
Authors: Eaton William A. , Muñoz Victor , Hagen Stephen J. , Jas Gouri S. , Lapidus Lisa J. , Henry Eric R. , Hofrichter James
Published: July 2002

▪ Abstract  This review describes how kinetic experiments using techniques with dramatically improved time resolution have contributed to understanding mechanisms in protein folding. Optical triggering with nanosecond laser pulses has made it possible to study the fastest-folding proteins as well as fundamental processes in folding for the first time. These include formation of α-helices, β-sheets, and contacts between residues distant in sequence, as well as overall collapse of the polypeptide chain. Improvements in the time resolution of mixing experiments and the use of dynamic nuclear magnetic resonance methods have also allowed kinetic studies of proteins that fold too fast (≳ 103 s−1) to be observed by conventional methods. Simple statistical mechanical models have been extremely useful in interpreting the experimental results. One of the surprises is that models originally developed for explaining the fast kinetics of secondary structure formation in isolated peptides are also successful in calculating folding rates of single domain proteins from their native three-dimensional structure.
Regulation of Mammalian O2Homeostasis by Hypoxia-Inducible Factor 1
Authors: Semenza Gregg L.
Published: July 2002

▪ Abstract  Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric basic-helix-loop-helix-PAS transcription factor consisting of HIF-1α and HIF-1β subunits. HIF-1α expression and HIF-1 transcriptional activity increase exponentially as cellular O2concentration is decreased. Several dozen target genes that are transactivated by HIF-1 have been identified, including those encoding erythropoietin, glucose transporters, glycolytic enzymes, and vascular endothelial growth factor. The products of these genes either increase O2delivery or allow metabolic adaptation to reduced O2availability. HIF-1 is required for cardiac and vascular development and embryonic survival. In fetal and postnatal life, HIF-1 is required for a variety of physiological responses to chronic hypoxia. HIF-1 expression is increased in tumor cells by multiple mechanisms and may mediate adaptation to hypoxia that is critical for tumor progression. HIF-1 thus appears to function as a master regulator of O2homeostasis that plays essential roles in cellular and systemic physiology, development, and pathophysiology.
Bone Development
Authors: Olsen Bjorn R. , Reginato Anthony M. , Wang Wenfang
Published: July 2002

▪ Abstract  Early development of the vertebrate skeleton depends on genes that pattern the distribution and proliferation of cells from cranial neural crest, sclerotomes, and lateral plate mesoderm into mesenchymal condensations at sites of future skeletal elements. Within these condensations, cells differentiate to chondrocytes or osteoblasts and form cartilages and bones under the control of various transcription factors. In most of the skeleton, organogenesis results in cartilage models of future bones; in these models cartilage is replaced by bone by the process of endochondral ossification. Lastly, through a controlled process of bone growth and remodeling the final skeleton is shaped and molded. Significant and exciting insights into all aspects of vertebrate skeletal development have been obtained through molecular and genetic studies of animal models and humans with inherited disorders of skeletal morphogenesis, organogenesis, and growth.
Dinosaur Reproduction and Parenting
Authors: Horner John R.
Published: July 2002

Non-avian dinosaur reproductive and parenting behaviors were mostly similar to those of extant archosaurs. Non-avian dinosaurs were probably sexually dimorphic and some may have engaged in hierarchical rituals. Non-avian coelurosaurs (e.g. Troodontidae, Oviraptorosauria) had two active oviducts, each of which produced single eggs on a daily or greater time scale. The eggs of non-coelurosaurian dinosaurs (e.g. Ornithischia, Sauropoda) were incubated in soils, whereas the eggs of non-avian coelurosaurs (e.g. Troodon, Oviraptor) were incubated with a combination of soil and direct parental contact. Parental attention to the young was variable, ranging from protection from predators to possible parental feeding of nest-bound hatchlings. Semi-altricial hadrosaur hatchlings exited their respective nests near the time of their first linear doubling. Some reproductive behaviors, once thought exclusive to Aves, arose first in non-avian dinosaurs. The success of the Dinosauria may be related to reproductive strategies.
THE GEOGRAPHIC RANGE: Size, Shape, Boundaries, and Internal Structure
Authors: Brown James H. , Stevens George C. , Kaufman Dawn M.
Published: July 2002

▪ Abstract  Comparative, quantitative biogeographic studies are revealing empirical patterns of interspecific variation in the sizes, shapes, boundaries, and internal structures of geographic ranges; these patterns promise to contribute to understanding the historical and ecological processes that influence the distributions of species. This review focuses on characteristics of ranges that appear to reflect the influences of environmental limiting factors and dispersal. Among organisms as a whole, range size varies by more than 12 orders of magnitude. Within genera, families, orders, and classes of plants and animals, range size often varies by several orders of magnitude, and this variation is associated with variation in body size, population density, dispersal mode, latitude, elevation, and depth (in marine systems). The shapes of ranges and the dynamic changes in range boundaries reflect the interacting influences of limiting environmental conditions (niche variables) and dispersal/extinction dynamics. These processes also presumably account for most of the internal structure of ranges: the spatial patterns and orders-of-magnitude of variation in the abundance of species among sites within their ranges. The results of this kind of “ecological biogeography”need to be integrated with the results of phylogenetic and paleoenvironmental approaches to “historical biogeography”so we can better understand the processes that have determined the geographic distributions of organisms.
Mechanisms of Maintenance of Species Diversity
Authors: Chesson Peter
Published: July 2002

▪ Abstract  The focus of most ideas on diversity maintenance is species coexistence, which may be stable or unstable. Stable coexistence can be quantified by the long-term rates at which community members recover from low density. Quantification shows that coexistence mechanisms function in two major ways: They may be (a) equalizing because they tend to minimize average fitness differences between species, or (b) stabilizing because they tend to increase negative intraspecific interactions relative to negative interspecific interactions. Stabilizing mechanisms are essential for species coexistence and include traditional mechanisms such as resource partitioning and frequency-dependent predation, as well as mechanisms that depend on fluctuations in population densities and environmental factors in space and time. Equalizing mechanisms contribute to stable coexistence because they reduce large average fitness inequalities which might negate the effects of stabilizing mechanisms. Models of unstable coexitence, in which species diversity slowly decays over time, have focused almost exclusively on equalizing mechanisms. These models would be more robust if they also included stabilizing mechanisms, which arise in many and varied ways but need not be adequate for full stability of a system. Models of unstable coexistence invite a broader view of diversity maintenance incorporating species turnover.
THE DEVELOPMENT OF THE SCIENCE OF AQUATIC ECOSYSTEMS
Authors: Patrick Ruth
Published: July 2002

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▪ Abstract  Ruth Patrick's scientific career has been devoted to the study of freshwater organisms in water. It started with studies of diatoms. She found one could interpret the condition of water by studying diatoms. This study of the ecology of diatoms expanded into ecological studies of communities of organisms that live in streams. By shifts in the structure of communities she was able to show the effects of various types of pollution on the aquatic ecosystem. This was the first time an organized team of biologists had been used to study the effects of pollution in streams. Through this research she showed that freshwater ecosystems were characterized by large numbers of species with very different environmental requirements operating in each stage of nutrient and energy transfer in the food web. These species belonged to many different phylogenetic groups. This redundancy gives stability to the system.