bluuebunny/crossref_metadata_2025 huggingface dataset:
TAKENS–BOGDANOV BIFURCATIONS OF PERIODIC ORBITS AND ARNOLD'S TONGUES IN A THREE-DIMENSIONAL ELECTRONIC MODEL
Authors: ALGABA A. , MERINO M. , RODRÍGUEZ-LUIS A. J.
Published: July 2002

In this paper we study Arnold's tongues in a ℤ2-symmetric electronic circuit. They appear in a rich bifurcation scenario organized by a degenerate codimension-three Hopf–pitchfork bifurcation. On the one hand, we describe the transition open-to-closed of the resonance zones, finding two different types of Takens–Bogdanov bifurcations (quadratic and cubic homoclinic-type) of periodic orbits. The existence of cascades of the cubic Takens–Bogdanov bifurcations is also pointed out. On the other hand, we study the dynamics inside the tongues showing different Poincaré sections. Several bifurcation diagrams show the presence of cusps of periodic orbits and homoclinic bifurcations. We show the relation that exists between two codimension-two bifurcations of equilibria, Takens–Bogdanov and Hopf–pitchfork, via homoclinic connections, period-doubling and quasiperiodic motions.
OPTIMAL FLUCTUATIONS AND THE CONTROL OF CHAOS
Authors: LUCHINSKY D. G. , BERI S. , MANNELLA R. , McCLINTOCK P. V. E. , KHOVANOV I. A.
Published: July 2002

The energy-optimal migration of a chaotic oscillator from one attractor to another coexisting attractor is investigated via an analogy between the Hamiltonian theory of fluctuations and Hamiltonian formulation of the control problem. We demonstrate both on physical grounds and rigorously that the Wentzel–Freidlin Hamiltonian arising in the analysis of fluctuations is equivalent to Pontryagin's Hamiltonian in the control problem with an additive linear unrestricted control. The deterministic optimal control function is identified with the optimal fluctuational force. Numerical and analogue experiments undertaken to verify these ideas demonstrate that, in the limit of small noise intensity, fluctuational escape from the chaotic attractor occurs via a unique (optimal) path corresponding to a unique (optimal) fluctuational force. Initial conditions on the chaotic attractor are identified. The solution of the boundary value control problem for the Pontryagin Hamiltonian is found numerically. It is shown that this solution is approximated very accurately by the optimal fluctuational force found using statistical analysis of the escape trajectories. A second series of numerical experiments on the deterministic system (i.e. in the absence of noise) show that a control function of precisely the same shape and magnitude is indeed able to instigate escape. It is demonstrated that this control function minimizes the cost functional and the corresponding energy is found to be smaller than that obtained with some earlier adaptive control algorithms.
CIRCUIT IMPLEMENTATIONS OF SOLITON SYSTEMS
Authors: SINGER ANDREW C. , OPPENHEIM ALAN V.
Published: July 2002

Recently, a large class of nonlinear systems which possess soliton solutions has been discovered for which exact analytic solutions can be found. Solitons are eigenfunctions of these systems which satisfy a form of superposition and display rich signal dynamics as they interact. In this paper, we view solitons as signals and consider exploiting these systems as specialized signal processors which are naturally suited to a number of complex signal processing tasks. New circuit models are presented for two soliton systems, the Toda lattice and the discrete-KdV equations. These analog circuits can generate and process soliton signals and can be used as multiplexers and demultiplexers in a number of potential soliton-based wireless communication applications discussed in [Singer et al.]. A hardware implementation of the Toda lattice circuit is presented, along with a detailed analysis of the dynamics of the system in the presence of additive Gaussian noise. This circuit model appears to be the first such circuit sufficiently accurate to demonstrate true overtaking soliton collisions with a small number of nodes. The discrete-KdV equation, which was largely ignored for having no prior electrical or mechanical analog, provides a convenient means for processing discrete-time soliton signals.
AMPLIFICATION PHENOMENA UNDER CHAOTIC DRIVING IN A MODEL OF CHEMICAL CHAOS
Authors: GONZÁLEZ-MIRANDA J. M.
Published: July 2002

Certain chaotic systems can exhibit phenomena of signal amplification when they are subjected to unidirectional chaotic driving. By studying a particular model, it is shown how this behavior is tied to system invariance properties under a particular type of continuous transformation. Such amplification phenomena can be uniformly stable, or asymptotically stable depending on the coupling arrangement. In the first case the degree of amplification is determined by the initial conditions, while in the second it is tunable from the driving arrangement.
IN SITU HALL MEASUREMENTS OF MACROSCOPIC ELECTRICAL PROPERTIES OF CHROMIUM-COVERED Si(111) SURFACES
Authors: GALKIN N. G. , GOROSHKO D. L. , KONCHENKO A. V. , IVANOV V. A. , GOURALNIK A. S.
Published: July 2002

The first in situ Hall measurements of the ordered chromium surface phases on Si(111) substrate and CrSi(111) epitaxial films after their formation are presented. Formation of Si (111)-(1× 1)- Cr (0.1 nm Cr) and Si(111)-[([Formula: see text])/30°]-Cr (0.3 nm Cr) surface phases results in an increase in the sheet resistivity of Si(111)-Cr surface phase samples. The conductivities along the surface phases at these chromium thicknesses are very low. The conductivity decrease is caused by a decrease in the electron mobility in the surface phase layers. Formation of an epitaxial CrSi(111) layer with averaged Hall parameters (hole mobility of 440 cm 2· V -1· s -1, sheet resistivity of 2.2·104 Ω-1 and sheet hole concentration of 0.65·1012 cm -2) has been observed at 1.5–1.8 nm of chromium thickness.
CONSERVATIVE TREATMENT OF REDISPLACED COLLES' FRACTURES IN ELDERLY PATIENTS OLDER THAN 60 YEARS OLD — ANATOMICAL AND FUNCTIONAL OUTCOME
Authors: Chang H. C. , Tay S. C. , Chan B. K. , Low C. O.
Published: July 2002

A retrospective study was carried out to compare the functional outcome in two groups of patients who were 60 years old or older. One group had Colles' fractures, which had been reduced and did not redisplace. The other group's fractures redisplaced and were treated conservatively. Of the 11 patients in the first group, 82% had excellent or good functional outcome, which was not significantly different when compared with the second group of 25 patients with 68% having excellent or good functional outcome.
TREATMENT OF CHRONIC ULNAR WRIST DISORDERS
Authors: Ono H. , Yajima H. , Tamai S.
Published: July 2002

Forty-four patients underwent surgery for chronic ulnar-sided wrist disorders. Their diagnoses were malunion of distal radial fracture in 25 patients, ulnocarpal abutment syndrome in 11, and primary distal radioulnar joint (DRUJ) osteoarthrropathies in eight. The procedures performed included Darrach's procedure in three patients, ulnar shortening in 17, hemiresection interposition arthroplasty in six, and Sauvé-Kapandji's procedure in 18. Each case was assessed preoperatively and postoperatively using a modified Cooney's score. The overall result included 17 excellent outcomes, 12 good, 13 fair, and two poor. In order to select the best procedure for patients with disorders of the ulnar wrist joint, preoperative assessment of DRUJ congruity and stability is essential. In ulnocarpal disorders without DRUJ incongruity, ulnar shortening should be selected. In cases with DRUJ incongruity but stable, hemiresection interposition arthroplasty is indicated. In cases with an unstable, incongruous DRUJ, Sauvé-Kapandji's procedure is recommended. Darrach's procedure is indicated only in elderly, inactive patients.
DOWEL FUSION OF THE SCAPHO-TRAPEZIO-TRAPEZOID JOINT: A DESCRIPTION OF A NEW TECHNIQUE
Authors: Thurston A. J. , Stanley J. K.
Published: July 2002

We describe a modification of the technique for arthrodesis of the joints between the scaphoid, the trapezoid and the trapezium (the S-T-T joint) described by Sandow, that involves the en bloc resection of a cylinder of bone incorporating a portion of each of the scaphoid, trapezoid and the trapezium, using a hollow mill, and replacing it with a cylindrical graft of exactly the same size taken from the distal radius. The procedure is relatively quick and easy with a high rate of fusion and must be regarded as a preferable alternative to other, more complex procedures.
WORST-CASE SCENARIOS FOR AMERICAN OPTIONS
Authors: BUFF ROBERT
Published: July 2002

One approach to cope with uncertain diffusion parameters when pricing options portfolios is to identify the parameters [Formula: see text] in a subset [Formula: see text] of the parameter space which form the worst-case for a particular portfolio. For the sell-side, this leads to a nonlinear algorithm that maximizes the expected liability under the risk-neutral measure. [Formula: see text] depends on the portfolio under consideration. Moreover, the algorithm must take into account that the exposure to [Formula: see text]-risk changes when non-vanilla components such as barrier or American options knock out or are exercised early. In this paper, we describe techniques to price portfolios with American options under worst-case scenarios based on uncertain volatility models. We also present heuristics which reduce the computational complexity that arises from the necessity to consider many early exercise combinations at a time. These heuristics reduce the compute time by almost one half.
RANDOM MATRIX THEORY AND FINANCIAL CORRELATIONS
Authors: LALOUX LAURENT , CIZEAU PIERRE , POTTERS MARC , BOUCHAUD JEAN-PHILIPPE
Published: July 2002

We show that results from the theory of random matrices are potentially of great interest when trying to understand the statistical structure of the empirical correlation matrices appearing in the study of multivariate financial time series. We find a remarkable agreement between the theoretical prediction (based on the assumption that the correlation matrix is random) and empirical data concerning the density of eigenvalues associated to the time series of the different stocks of the S&P500 (or other major markets). Finally, we give a specific example to show how this idea can be sucessfully implemented for improving risk management.
Post-East Asian Financial Crisis: Challenges and Opportunities for the Banking and Financial Services Sector in Singapore
Authors: Fock Siew Tong , Wong Ann Chai
Published: July 2002

The East Asian financial crisis revealed the structural weaknesses of the banking systems in Asia. Post crisis, there were signs of limited recovery of the region in sight, but the region-wide reforms would take some time to complete. This paper identifies the main challenges and opportunities that are posed to the financial sector in Singapore in a post East Asian financial crisis scenario. Preserving the stability of the banking sector whilst engendering a more efficient use of capital remains a central issue in this paper. The paper also evaluates the liberalization measures adopted by the Monetary Authority of Singapore to enhance the development of Singapore as a leading international financial center.
GLASSY STATES IN A SHAKEN SANDBOX
Authors: STADLER PETER F. , MEHTA ANITA , LUCK JEAN-MARC
Published: July 2002

Our model of shaken sand, presented in earlier work, has been extended to include a more realistic 'glassy' state, i.e. when the sandbox is shaken at very low intensities of vibration. We revisit some of our earlier results, and compare them with our new results on the revised model. Our analysis of the glassy dynamics in our model shows that a variety of ground states is obtained; these fall into two categories, which we argue are representative of regular and irregular packings.
GRANULAR MEDIA AS A PHYSICS PROBLEM
Authors: EDWARDS S. F. , GRINEV D. V.
Published: July 2002

Although there is a vast engineering literature for granular materials, as a subject for physicists it has seen great growth in recent years. This is because, when stripped down to the fundamental problem, it is quite novel, and demands a rethink of the kind of laws familiar elsewhere in physics. We consider the transmission of stress in granular materials and investigate the simplest statically determinate problem.
A general approach to connected-component labeling for arbitrary image representations
Authors: Dillencourt Michael B. , Samet Hanan , Tamminen Markku
Published: July 2002

An improved and general approach to connected-component labeling of images is presented. The algorithm presented in this paper processes images in
predetermined order
, which means that the processing order depends only on the image representation scheme and not on specific properties of the image. The algorithm handles a wide variety of image representation schemes (rasters, run lengths, quadrees, bintrees, etc.). How to adapt the standard UNION-FIND algorithm to permit reuse of temporary labels is shown. This is done using a technique called
age balancing
, in which, when two labels are merged, the older label becomes the father of the younger label. This technique can be made to coexist with the more conventional rule of
weight
balancing
, in which the label with more descendants becomes the father of the label with fewer descendants. Various image scanning orders are examined and classified. It is also shown that when the algorithm is specialized to a pixel array scanned in raster order, the total processing time is linear in the number of pixels. The linear-time processing time follows from a special property of the UNION-FIND algorithm, which may be of independent interest. This property states that under certain restrictions on the input, UNION-FIND runs in time linear in the number of FIND and UNION operations. Under these restrictions, linear-time performance can be achieved without resorting to the more complicated Gabow-Tarjan algorithm for disjoint set union.
Generating parallel code for SIMD machines
Authors: McKenney Bruce , Szymanski Boleslaw K.
Published: July 2002

Massively parallel SIMD machines rely on data parallelism usually achieved by a careful hand coding to support program efficiency. This paper describes parallelization of code generated for SIMD machines by the compiler for the Equational Programming Language, EPL. The language supports architecture-independent scientific programming by recurrent equations. The EPL compiler serves as a programming aid for users of parallel machines by automating data partitioning and computation parallelization based on inherent data dependencies. In support of a Connection Machine architecture, the EPL compiler performs horizontal partitioning of the program, a process that selects a dimension of each data structure to be projected along the processor array. Each processor then holds a single instance of that structure and operations along the projected dimension are done in parallel. The paper describes horizontal partitioning, code generation in MPL and efficiency of programs generated for Maspar SIMD machine.
An Arnoldi code for computing selected eigenvalues of sparse, real, unsymmetric matrices
Authors: Scott Jennifer A.
Published: July 2002

Arnoldi methods can be more effective than subspace iteration methods for computing the dominant eigenvalues of a large, sparse, real, unsymmetric matrix. A code,
EB12
, for the sparse, unsymmetric eigenvalue problem based on a subspace iteration algorithm, optionally combined with Chebychev acceleration, has recently been described by Duff and Scott and is included in the Harwell Subroutine Library. In this article we consider variants of the method of Arnoldi and discuss the design and development of a code to implement these methods. The new code, which is called
EB13
, offers the user the choice of a basic Arnoldi algorithm, an Arnoldi algorithm with Chebychev acceleration, and a Chebychev preconditioned Arnoldi algorithm. Each method is available in blocked and unblocked form. The code may be used to compute either the rightmost eigenvalues, the eigenvalues of largest absolute value, or the eigenvalues of largest imaginary part. The performance of each option in the
EB13
package is compared with that of subspace iteration on a range of test problems, and on the basis of the results, advice is offered to the user on the appropriate choice of method. —
Author's Abstract
Procedure cloning
Authors: Vahid Frank
Published: July 2002

Functional partitioning assigns the functions of a system's program-like specification among system components, such as standard-software and custom-hardware processors. We introduce a new transformation, called procedure cloning, that significantly improves functional partitioning results. The transformation creates a clone of a procedure for sole use by a particular procedure caller, so the clone can be assigned to the caller's processor, which in turn improves performance through reduced communication. Heuristics are used to prevent the exponential size increase that could occur if cloning were done indiscriminately. We introduce a variety of cloning heuristics, highlight experiments demonstrating the improvements obtained using cloning, and compare the various cloning heuristics.
A Procedure for Nonlinear Least Squares Refinement in Adverse Practical Conditions
Authors: Maddison R. N.
Published: July 2002

An iterative method is described for computing optimum values of a set of parameters for the best agreement in a least squares between a given set of (experimental) values and corresponding calculated (theoretical) values where these may be dependent non-linearly on the parameters. The method is for use when (a) the amount of work in the calculation of the theoretical values is large as compared with the amount required to solve a set of linear equations in the same number of unknowns; and (b) the amount of work in calculating the first order partial derivatives of all the theoretical values with respect to one parameter would be even greater, so that using finite difference approximations to the partial derivatives is preferable. In addition to setting up and solving the normal equations at each step, the latent vectors of their matrix and estimates of the errors on the current parameter values are computed and used. Also the known physical limits of the range of each parameter are used. The procedure has second order convergence.
Theorem Proving with Lemmas
Authors: Peterson G. E.
Published: July 2002

The concern here is with proof procedures which are generalizations of input or unit deduction. The author's generalizations of input deduction involve lemmas, whereas those of unit deduction involve longer clauses and are akin to Robinson's P1 deduction. Chang's theorem, which establishes the equivalence of input and unit refutation, is extended to these generalizations. Completeness results of Henschen, Wos, and Kuehner for input or unit deduction applied to Horn sets are generalized to apply also to non-Horn sets. A key result is that any unsatisfiable set can be refuted by a lock linear resolution procedure in which the only lemmas are positive clauses composed entirely of instances of a small set of literals which can be specified in advance. In an implementation such lemmas would be generated only infrequently, thus allowing one to periodically gather the lemmas, discard other generated clauses, and restart the proof procedure.
Computer science as empirical inquiry
Authors: Newell Allen , Simon Herbert A.
Published: July 2002

Computer science is the study of the phenomena surrounding computers. The founders of this society understood this very well when they called themselves the Association for Computing Machinery. The machine—not just the hardware, but the programmed, living machine—is the organism we study.
A vector space model for automatic indexing
Authors: Salton G. , Wong A. , Yang C. S.
Published: July 2002

In a document retrieval, or other pattern matching environment where stored entities (documents) are compared with each other or with incoming patterns (search requests), it appears that the best indexing (property) space is one where each entity lies as far away from the others as possible; in these circumstances the value of an indexing system may be expressible as a function of the density of the object space; in particular, retrieval performance may correlate inversely with space density. An approach based on space density computations is used to choose an optimum indexing vocabulary for a collection of documents. Typical evaluation results are shown, demonstating the usefulness of the model.
Use of the Hough transformation to detect lines and curves in pictures
Authors: Duda Richard O. , Hart Peter E.
Published: July 2002

Hough has proposed an interesting and computationally efficient procedure for detecting lines in pictures. This paper points out that the use of angle-radius rather than slope-intercept parameters simplifies the computation further. It also shows how the method can be used for more general curve fitting, and gives alternative interpretations that explain the source of its efficiency.
Algorithm 338: algol procedures for the fast Fourier transform
Authors: Singleton Richard C.
Published: July 2002

The following procedures are based on the Cooley-Tukey algorithm [1] for computing the finite Fourier transform of a complex data vector; the dimension of the data vector is assumed here to be a power of two. Procedure
COMPLEXTRANSFORM
computes either the complex Fourier transform or its inverse. Procedure
REALTRANSFORM
computes either the Fourier coefficients of a sequence of real data points or evaluates a Fourier series with given cosine and sine coefficients. The number of arithmetic operations for either procedure is proportional to
n
log
2
n
, where
n
is the number of data points.
An algorithm for generating projective reduction formulas for matrix elements of many-electron wavefunctions
Authors: Reeves C. M.
Published: July 2002

An ALGOL procedure is given for automatically generating formulas for matrix elements arising in the variational solution of the Schrödinger equation for many-electron systems.
Automatic error bounds on real zeros of rational functions
Authors: Dargel Robert H. , Loscalzo Frank R. , Witt Thomas H.
Published: July 2002

A procedure for implementing an interval arithmetic version of the Newton-Raphson method is proposed. The procedure requires only a starting interval over which the zeros of a given rational function are to be located. The method automatically provides bounds for roundoff error.
Interprocedural control dependence
Authors: Sinha Saurabh , Harrold Mary Jean , Rothermel Gregg
Published: July 2002

Program-dependence information is useful for a variety of applications, such as software testing and maintenance tasks, and code optimization. Properly defined, control and data dependences can be used to identify semantic dependences. To function effectively on whole programs, tools that utilize dependence information require information about interprocedural dependences: dependences that are identified by analyzing the interactions among procedures. Many techniques for computing interprocedural data dependences exist; however, virtually no attention has been paid to interprocedural control dependence. Analysis techniques that fail to account for interprocedural control dependences can suffer unnecessary imprecision and loss of safety. This article presents a definition of interprocedural control dependence that supports the relationship of control and data dependence to semantic dependence. The article presents two approaches for computing interprocedural control dependences, and empirical results pertaining to teh use of those approaches.
Nonlinear regression and the solution of simultaneous equations
Authors: Baer Robert M.
Published: July 2002

If one has a set of observables (
z
1
, ··· ,

z
m

) which are bound in a relation with certain parameters (
a
1
, ··· ,

a
n

) by an equation
ζ
(
z
1
, ··· ,
a
1
, ···) = 0, one frequently has the problem of determining a set of values of the

a
i

which minimizes the sum of squares of differences between observed and calculated values of a distinguished observable, say

z
m

. If the solution of the above equation for

z
m

,

z
m

=
η
(
z
1
, ··· ;
a
1
, ···) gives rise to a function
η
which is nonlinear in the

a
i

, then one may rely on a version of Gaussian regression [1, 2] for an iteration scheme that converges to a minimizing set of values. It is shown here that this same minimization technique may be used for the solution of simultaneous (not necessarily linear) equations.
A system for computer music performance
Authors: Anderson David P. , Kuivila Ron
Published: July 2002

A computer music performance system (CMPS) is a computer system connected to input devices (including musical keyboards or other instruments) and to graphic and audio output devices. A human performer generates input events using the input devices. The CMPS responds to these events by computing and performing sequences of output actions whose intended timing is determined algorithmically. Because of the need for accurate timing of output actions, the scheduling requirements of a CMPS differ from those of general-purpose or conventional real-time systems.

This paper describes the scheduling facilities of FORMULA, a CMPS used by many musicians. In addition to providing accurate timing of output action sequences, FORMULA provides other basic functions useful in musical applications: (1) per-process virtual time systems with independent relationships to real time; (2) process grouping mechanisms and language-level control structures with time-related semantics, and (3) integrated scheduling of tasks (such as compiling and editing) whose real-time constraints are less stringent than those of output action computations.
Six-digit coding method
Authors: Qiao Jinan , Qiao Yizheng , Qiao Sanzheng
Published: July 2002

The Six-Digit Coding Method (SDCM) is a new coding method for Chinese characters. It is based on the structural analysis of Chinese characters. We recently developed this method and have successfully used it to code 11,100 characters, including the simplified, traditional, and variant forms found in Xin Hua Dictionary [7]. This article illustrates the basic principes, features, and some viewpoints concerning the method.
THE PARADOX OF CHILD LABOR AND ANTHROPOLOGY
Authors: Nieuwenhuys Olga
Published: July 2002

▪ Abstract  In relating the child labor debate to the observed variety of children's work patterns, this review reveals the limits of current notions such as labor, gender, and exploitation in the analysis of this work. Particularly in the developing world, most work undertaken by children has for a long time been explained away as socialization, education, training, and play. Anthropology has helped disclose that age is used with gender as the justification for the value accorded to work. The low valuation of children's work translates not only in children's vulnerability in the labor market but, more importantly, in their exclusion from remunerated employment. I argue that current child labor policies, because they fail to address the exclusion of children from the production of value, reinforce paradoxically children's vulnerability to exploitation.
ANTHROPOLOGY AND THE CONSERVATION OF BIODIVERSITY
Authors: Orlove Benjamin S. , Brush Stephen B.
Published: July 2002

▪ Abstract  Conservation programs for protected areas and plant genetic resources have evolved in similar ways, beginning with a focus on single species and expanding to ecosystem strategies that involve the participation of local people. Anthropologists have described the increasing importance of the participation of local people in conservation programs, both of local populations in protected area management and of farmers in plant genetic resources. Both protected areas and plant genetic resources link local populations, national agencies, and international organizations. Anthropological research (a) documents local knowledge and practices that influence the selection and maintenance of crop varieties and the conservation of rare and endangered species in protected areas, and (b) clarifies the different concerns and definitions of biodiversity held by local populations and international conservationists. In addition, anthropologists operate in nongovernmental organizations (NGOs) and international agencies, participating in policy debates and acting as advocates and allies of local populations of farmers and indigenous peoples.
LIPID-TRANSFER PROTEINS IN PLANTS
Authors: Kader Jean-Claude
Published: July 2002

▪ Abstract  Lipid-transfer proteins (LTP) are basic, 9-kDa proteins present in high amounts (as much as 4% of the total soluble proteinss) in higher plants. LTPs can enhance the in vitro transfer of phospholipids between membranes and can bind acyl chains. On the basis of these properties, LTPs were thought to participate in membrane biogenesis and regulation of the intracellular fatty acid pools. However, the isolation of several cDNAs and genes revealed the presence of a signal peptide indicating that LTPs could enter the secretory pathway. They were found to be secreted and located in the cell wall. Thus, novel roles were suggested for plant LTPs: participation in cutin formation, embryogenesis, defense reactions against phytopathogens, symbiosis, and the adaptation of plants to various environmental conditions. The validity of these suggestions needs to be determined, in the hope that they will elucidate the role of this puzzling family of plant proteins.
ASCORBATE AND GLUTATHIONE: Keeping Active Oxygen Under Control
Authors: Noctor Graham , Foyer Christine H.
Published: July 2002

▪ Abstract  To cope with environmental fluctuations and to prevent invasion by pathogens, plant metabolism must be flexible and dynamic. Active oxygen species, whose formation is accelerated under stress conditions, must be rapidly processed if oxidative damage is to be averted. The lifetime of active oxygen species within the cellular environment is determined by the antioxidative system, which provides crucial protection against oxidative damage. The antioxidative system comprises numerous enzymes and compounds of low molecular weight. While research into the former has benefited greatly from advances in molecular technology, the pathways by which the latter are synthesized have received comparatively little attention. The present review emphasizes the roles of ascorbate and glutathione in plant metabolism and stress tolerance. We provide a detailed account of current knowledge of the biosynthesis, compartmentation, and transport of these two important antioxidants, with emphasis on the unique insights and advances gained by molecular exploration.
THE UBIQUITIN SYSTEM
Authors: Hershko Avram , Ciechanover Aaron
Published: July 2002

The selective degradation of many short-lived proteins in eukaryotic cells is carried out by the ubiquitin system. In this pathway, proteins are targeted for degradation by covalent ligation to ubiquitin, a highly conserved small protein. Ubiquitin-mediated degradation of regulatory proteins plays important roles in the control of numerous processes, including cell-cycle progression, signal transduction, transcriptional regulation, receptor down-regulation, and endocytosis. The ubiquitin system has been implicated in the immune response, development, and programmed cell death. Abnormalities in ubiquitin-mediated processes have been shown to cause pathological conditions, including malignant transformation. In this review we discuss recent information on functions and mechanisms of the ubiquitin system. Since the selectivity of protein degradation is determined mainly at the stage of ligation to ubiquitin, special attention is focused on what we know, and would like to know, about the mode of action of ubiquitin-protein ligation systems and about signals in proteins recognized by these systems.
RIBONUCLEOTIDE REDUCTASES
Authors: Jordan A. , Reichard P.
Published: July 2002

Ribonucleotide reductases provide the building blocks for DNA replication in all living cells. Three different classes of enzymes use protein free radicals to activate the substrate. Aerobic class I enzymes generate a tyrosyl radical with an iron-oxygen center and dioxygen, class II enzymes employ adenosylcobalamin, and the anaerobic class III enzymes generate a glycyl radical from S-adenosylmethionine and an iron-sulfur cluster. The X-ray structure of the class I Escherichia coli enzyme, including forms that bind substrate and allosteric effectors, confirms previous models of catalytic and allosteric mechanisms. This structure suggests considerable mobility of the protein during catalysis and, together with experiments involving site-directed mutants, suggests a mechanism for radical transfer from one subunit to the other. Despite large differences between the classes, common catalytic and allosteric mechanisms, as well as retention of critical residues in the protein sequence, suggest a similar tertiary structure and a common origin during evolution. One puzzling aspect is that some organisms contain the genes for several different reductases.
THE TWO-COMPONENT SIGNALING PATHWAY OF BACTERIAL CHEMOTAXIS: A Molecular View of Signal Transduction by Receptors, Kinases, and Adaptation Enzymes
Authors: Falke Joseph J. , Bass Randal B. , Butler Scott L. , Chervitz Stephen A. , Danielson Mark A.
Published: July 2002

▪ Abstract  The chemosensory pathway of bacterial chemotaxis has become a paradigm for the two-component superfamily of receptor-regulated phosphorylation pathways. This simple pathway illustrates many of the fundamental principles and unanswered questions in the field of signaling biology. A molecular description of pathway function has progressed rapidly because it is accessible to diverse structural, biochemical, and genetic approaches. As a result, structures are emerging for most of the pathway elements, biochemical studies are elucidating the mechanisms of key signaling events, and genetic methods are revealing the intermolecular interactions that transmit information between components. Recent advances include (a) the first molecular picture of a conformational transmembrane signal in a cell surface receptor, (b) four new structures of kinase domains and adaptation enzymes, and (c) significant new insights into the mechanisms of receptor-mediated kinase regulation, receptor adaptation, and the phospho-activation of signaling proteins. Overall, the chemosensory pathway and the propulsion system it regulates provide an ideal system in which to probe molecular principles underlying complex cellular signaling and behavior.
MICROTUBULE POLYMERIZATION DYNAMICS
Authors: Desai Arshad , Mitchison Timothy J.
Published: July 2002

▪ Abstract  The polymerization dynamics of microtubules are central to their biological functions. Polymerization dynamics allow microtubules to adopt spatial arrangements that can change rapidly in response to cellular needs and, in some cases, to perform mechanical work. Microtubules utilize the energy of GTP hydrolysis to fuel a unique polymerization mechanism termed dynamic instability. In this review, we first describe progress toward understanding the mechanism of dynamic instability of pure tubulin and then discuss the function and regulation of microtubule dynamic instability in living cells.
Synthetic Aperture Radar Interferometry to Measure Earth’s Surface Topography and Its Deformation
Authors: Bürgmann Roland , Rosen Paul A. , Fielding Eric J.
Published: July 2002

Synthetic aperture radar interferometry (InSAR) from Earth-orbiting spacecraft provides a new tool to map global topography and deformation of the Earth’s surface. Radar images taken from slightly different viewing directions allow the construction of digital elevation models of meter-scale accuracy. These data sets aid in the analysis and interpretation of tectonic and volcanic landscapes. If the Earth’s surface deformed between two radar image acquisitions, a map of the surface displacement with tens-of-meters resolution and subcentimeter accuracy can be constructed. This review gives a basic overview of InSAR for Earth scientists and presents a selection of geologic applications that demonstrate the unique capabilities of InSAR for mapping the topography and deformation of the Earth.
INDUSTRIAL SYMBIOSIS: Literature and Taxonomy
Authors: Chertow Marian R.
Published: July 2002

▪ Abstract  Industrial symbiosis, as part of the emerging field of industrial ecology, demands resolute attention to the flow of materials and energy through local and regional economies. Industrial symbiosis engages traditionally separate industries in a collective approach to competitive advantage involving physical exchange of materials, energy, water, and/or by-products. The keys to industrial symbiosis are collaboration and the synergistic possibilities offered by geographic proximity.

This paper reviews the small industrial symbiosis literature and some antecedents, as well as early efforts to develop eco-industrial parks as concrete realizations of the industrial symbiosis concept. Review of the projects is organized around a taxonomy of five different material exchange types. Input-output matching, stakeholder processes, and materials budgeting appear to be useful tools in advancing eco-industrial park development. Evolutionary approaches to industrial symbosis are found to be important in creating the level of cooperation needed for multi-party exchanges.
Water Vapor Feedback and Global Warming
Authors: Held Isaac M. , Soden Brian J.
Published: July 2002

▪ Abstract  Water vapor is the dominant greenhouse gas, the most important gaseous source of infrared opacity in the atmosphere. As the concentrations of other greenhouse gases, particularly carbon dioxide, increase because of human activity, it is centrally important to predict how the water vapor distribution will be affected. To the extent that water vapor concentrations increase in a warmer world, the climatic effects of the other greenhouse gases will be amplified. Models of the Earth's climate indicate that this is an important positive feedback that increases the sensitivity of surface temperatures to carbon dioxide by nearly a factor of two when considered in isolation from other feedbacks, and possibly by as much as a factor of three or more when interactions with other feedbacks are considered. Critics of this consensus have attempted to provide reasons why modeling results are overestimating the strength of this feedback.

Our uncertainty concerning climate sensitivity is disturbing. The range most often quoted for the equilibrium global mean surface temperature response to a doubling of CO2 concentrations in the atmosphere is 1.5°C to 4.5°C. If the Earth lies near the upper bound of this sensitivity range, climate changes in the twenty-first century will be profound. The range in sensitivity is primarily due to differing assumptions about how the Earth's cloud distribution is maintained; all the models on which these estimates are based possess strong water vapor feedback. If this feedback is, in fact, substantially weaker than predicted in current models, sensitivities in the upper half of this range would be much less likely, a conclusion that would clearly have important policy implications. In this review, we describe the background behind the prevailing view on water vapor feedback and some of the arguments raised by its critics, and attempt to explain why these arguments have not modified the consensus within the climate research community.
LIFE-STYLES OF PHYTOSEIID MITES AND THEIR ROLES IN BIOLOGICAL CONTROL
Authors: McMurtry J. A. , Croft B. A.
Published: July 2002

▪ Abstract  This review categorizes the diversity of life-styles in the Phytoseiidae, based primarily on food habits and related biological and morphological traits. The life-styles proposed are as follows: Type I, specialized predators of Tetranychus species represented by the Phytoseiulus species; Type II, selective predators of tetranychid mites (most frequently associated with species that produce dense webbing) represented by Galendromus, some Neoseiulus, and a few Typhlodromus species; Type III, generalist predators represented by some Neoseiulus species and most Typhlodromus and Amblyseius species, as well as species in all other genera about which information is available; Type IV, specialized pollen feeders/generalist predators represented by Euseius species. Consideration is given to the relative importance of each of these types in biological control and pest management programs.
INSECT P450 ENZYMES
Authors: Feyereisen René
Published: July 2002

▪ Abstract  The P450 enzymes (mixed function oxidases, cytochrome P450 monooxygenases), a diverse class of enzymes found in virtually all insect tissues, fulfill many important tasks, from the synthesis and degradation of ecdysteroids and juvenile hormones to the metabolism of foreign chemicals of natural or synthetic origin. This diversity in function is achieved by a diversity in structure, as insect genomes probably carry about 100 P450 genes, sometimes arranged in clusters, and each coding for a different P450 enzyme. Both microsomal and mitochondrial P450s are present in insects and are best studied by heterologous expression of their cDNA and reconstitution of purified enzymes. P450 genes are under complex regulation, with induction playing a central role in the adaptation to plant chemicals and regulatory mutations playing a central role in insecticide resistance. Polymorphisms in induction or constitutive expression allow insects to scan their P450 gene repertoire for the appropriate response to chemical insults, and these evolutionary pressures in turn maintain P450 diversity.
Habitat Management to Conserve Natural Enemies of Arthropod Pests in Agriculture
Authors: Landis Douglas A. , Wratten Stephen D. , Gurr Geoff M.
Published: July 2002

▪ Abstract  Many agroecosystems are unfavorable environments for natural enemies due to high levels of disturbance. Habitat management, a form of conservation biological control, is an ecologically based approach aimed at favoring natural enemies and enhancing biological control in agricultural systems. The goal of habitat management is to create a suitable ecological infrastructure within the agricultural landscape to provide resources such as food for adult natural enemies, alternative prey or hosts, and shelter from adverse conditions. These resources must be integrated into the landscape in a way that is spatially and temporally favorable to natural enemies and practical for producers to implement. The rapidly expanding literature on habitat management is reviewed with attention to practices for favoring predators and parasitoids, implementation of habitat management, and the contributions of modeling and ecological theory to this developing area of conservation biological control. The potential to integrate the goals of habitat management for natural enemies and nature conservation is discussed.
EVOLUTION ANDBEHAVIORALECOLOGY OFHETERONOMOUSAPHELINIDPARASITOIDS
Authors: Hunter Martha S. , Woolley James B.
Published: July 2002

▪ Abstract  In almost all species of parasitic wasps in the Coccophaginae, a subfamily of Aphelinidae, males have host relationships different from females. In these “heteronomous” species, females are generally endoparasitoids of sternorrhynchous Hemiptera, such as scale insects, mealybugs, and whiteflies. In contrast, males may be hyperparasitoids, developing in or on conspecific females or other primary parasitoids. In other species, females are endoparasitoids of whiteflies, and males are primary endoparasitoids of eggs of Lepidoptera. Males and females may both be primary parasitoids on the same species of scale insect hosts, but females develop as endoparasitoids, whereas males are ectoparasitoids. Here we review these life histories, focusing on examples of sexually dimorphic host relationships, development, and morphology. Coccophagine species may be sexual or parthenogenetic; we discuss reproductive modes and the interaction of sex ratio distorters with sex-specific host relationships. Sex allocation in the species in which males are hyperparasitoids involves choices of not what sex egg to lay, but whether to accept or reject a host of a given type; study in this area is reviewed as well as research in kin discrimination and ovicide. Last, we present the current understanding of phylogenetic relationships within this lineage and discuss hypotheses for the evolutionary origin of heteronomy in the Aphelinidae.
Omnivory in Terrestrial Arthropods: Mixing Plant and Prey Diets
Authors: Coll Moshe , Guershon Moshe
Published: July 2002

▪ Abstract  Many terrestrial communities include omnivorous arthropods that feed on both prey and plant resources. In this review we first discuss some unique morphological, physiological, and behavioral traits that enable omnivores to exploit such dissimilar foods, and we explore possible evolutionary pathways to omnivory. We then examine possible benefits and costs of omnivory, describe the relationships between omnivory and other high-order complex trophic interactions, and consider the stability level of communities with closed-loop omnivory. Finally, we explore some of the implications of omnivory for crop damage and for biological, chemical, and cultural control practices. We conclude that the growing realization of the ubiquity of omnivory in nature may require a change in our view of the structure and function of ecological systems.
PLANETARY-ENTRY GAS DYNAMICS
Authors: Gnoffo Peter A.
Published: July 2002

▪ Abstract  A review of planetary-entry gas dynamics is presented. Evolution of a blunt-body flowfield from a free molecular flow environment to a continuum environment is described. Simulations of near-wake flow phenomena, important for defining aerobrake payload environments, are also discussed. Some topics to be highlighted include aerodynamic coefficient predictions with emphasis on high-temperature gas effects; surface heating and temperature predictions for thermal protection system (TPS) design in a high-temperature, thermochemical nonequilibrium environment; and thermochemical models required for numerical flow simulation. Recent applications involving atmospheric entry into Jupiter (Galileo), Mars (Pathfinder and Global Surveyor), and a planned mission in which dust from the tail of a comet will be returned to Earth (Stardust) will provide context for this discussion.
SOUND PROPAGATION CLOSE TO THE GROUND
Authors: Attenborough Keith
Published: July 2002

▪ Abstract  Some applications of the study of outdoor acoustics and sets of data for sound-level spectra obtained close to the ground are described. Measurements and models of ground effects arising from the interaction between sound traveling directly from source to receiver and sound reflected from the ground are emphasized. Details are given concerning the influences of porosity, layering, small-scale surface roughness, and tall vegetation. Areas of related current and future research are outlined.
MICROSTRUCTURAL EVOLUTION IN POLYMER BLENDS
Authors: Tucker III Charles L. , Moldenaers Paula
Published: July 2002

▪ Abstract  Microstructure in an immiscible polymer blend consists of the size, shape, and orientation of the phases. Blends exhibit many interesting behaviors, including enhanced elasticity at small strains, drop-size hysteresis, enhanced shear thinning, and stress relaxation curves whose shapes are sensitive to deformation history. These behaviors are directly related to changes in the microstructure, which result from phase deformation, coalescence, retraction, and different types of breakup. These phenomena are reviewed, together with models that describe them. Rheological measurements can probe the microstructure because microstructure contributes directly to stress through interfacial tension. Rheo-optical experiments also provide important insights. Droplet theories explain most of the phenomena for Newtonian phases at low concentrations. Behaviors at high volume fractions or with strongly non-Newtonian phases are less well understood.