bluuebunny/crossref_metadata_2025 huggingface dataset:
A model for distributed systems based on graph rewriting
Authors: Degano Pierpaolo , Montanari Ugo
Published: July 2002

In our model, a graph describes a net of processes communicating through ports and, at the same time, its computation history consisting of a partial ordering of events. Stand-alone evolution of processes is specified by context-free productions. From productions and a basic synchronization mechanism, a set of context-sensitive rewriting rules that models the evolution of processes connected to the same ports can be derived. A computation is a sequence of graphs obtained by successive rewritings. The result of a finite computation is its last graph, whereas the result of an infinite computation is the limit, infinite graph defined through a completion technique based on metric spaces. A result characterizes a concurrent computation, since it abstracts from any particular interleaving of concurrent events, while in the meantime providing information about termination, partial or complete deadlocks, and fairness. Not every result is acceptable, however, but only the computations that produce a result no longer rewritable are successful. Infinite successful computations are shown to coincide with weakly fair computations, and a scheduler yielding all and only such computations is defined.
A safe, efficient regression test selection technique
Authors: Rothermel Gregg , Harrold Mary Jean
Published: July 2002

Regression testing is an expensive but necessary maintenance activity performed on modified software to provide confidence that changes are correct and do not adversely affect other portions of the softwore. A regression test selection technique choses, from an existing test set, thests that are deemed necessary to validate modified software. We present a new technique for regression test selection. Our algorithms construct control flow graphs for a precedure or program and its modified version and use these graphs to select tests that execute changed code from the original test suite. We prove that, under certain conditions, the set of tests our technique selects includes every test from the original test suite that con expose faults in the modified procedfdure or program. Under these conditions our algorithms are
safe
. Moreover, although our algorithms may select some tests that cannot expose faults, they are at lease as precise as other safe regression test selection algorithms. Unlike many other regression test selection algorithms, our algorithms handle all language constructs and all types of program modifications. We have implemented our algorithms; initial empirical studies indicate that our technique can significantly reduce the cost of regression testing modified software.
Time-work tradeoffs for parallel algorithms
Authors: Spencer Thomas H.
Published: July 2002

Some parallel algorithms have the property that, as they are allowed to take more time, the total work that they do is reduced. This paper describes several algorithms with this property. These algorithms solve important problems on directed graphs, including breadth-first search, topological sort, strong connectivity, and and the single source shorest path problem. All of the algorithms run on the EREW PRAM model of parallel computer, except the algorithm for strong connectivity, which runs on the probabilistic EREW PRAM.
Using permutations in regenerative simulations to reduce variance
Authors: Calvin James M. , Nakayama Marvin K.
Published: July 2002

We propose a new estimator for a large class of performance measures obtained from a regenerative simulation of a system having two distinct sequences of regeneration times. To construct our new estimator, we first generate a sample path of a fixed number of cycles based on one sequence of regeneration times, divide the path into segments based on the second sequence of regeneration times, permute the segments, and calculate the performance on the new path using the first sequence of regeneration times. We average over all possible permutations to construct the new estimator. This strictly reduces variance when the original estimator is not simply an additive functional of the sample path. To use the new estimator in practice, the extra computational effort is not large since all permutations do not actually have to be computed as we derive explicit formulas for our new estimators. We examine the small-sample behavior of our estimators. In particular, we prove that for any fixed number of cycles from the first regenerative sequence, our new estimator has smaller mean squared error than the standard estimator. We show explicitly that our method can be used to derive new estimators for the expected cumulative reward until a certain set of states is hit and the time-average variance parameter of a regenerative simulation.
Expokit
Authors: Sidje Roger B.
Published: July 2002

Expokit provides a set of routines aimed at computing matrix exponentials. More precisely, it computes either a small matrix exponential in full, the action of a large sparse matrix exponential on an operand vector, or the solution of a system of linear OBEs with constant inhomogeneity. The backbone of the sparse routines consists of matrix-free Krylov subspace projection methods (Arnoldi and Lanczos processes), and that is why the toolkit is capable of coping with sparse matrices of large dimension. The software handles real and complex matrices and provides specific routines for symmetric and Hermitian matrices. The computation of matrix exponentials is a numerical issue of critical importance in the area of Markov chains and furthermore, the computed solution is subject to probabilistic constraints. In addition to addressing general matrix exponentials, a distinct attention is assigned to the computation of transient states of Markov chains.
An analysis of geometric modeling in database systems
Authors: Kemper Alfons , Wallrath Mechtild
Published: July 2002

The data-modeling and computational requirements for integrated computer aided manufacturing (CAM) databases are analyzed, and the most common representation schemes for modeling solid geometric objects in a computer are described. The
primitive instancing
model, the
boundary representation,
and the
constructive solid geometry
model are presented from the viewpoint of database representation. Depending on the representation scheme, one can apply geometric transformations to the stored geometric objects. The standard transformations, scaling, translation, and rotation, are outlined with respect to the data structure aspects. Some of the more recent developments in the area of engineering databases with regard to supporting these representation schemes are then explored, and a classification scheme for technical database management systems is presented that distinguishes the systems according to their level of object orientation:
structural
or
behavioral object orientation
. First, several systems that are extensions to the relational model are surveyed, then the functional data model DAPLEX, the nonnormalized relational model NF
2
, and the database system R
2
D
2
that provides abstract data types in the NF
2
model are described.
Coyote
Authors: Bhatti Nina T. , Hiltunen Matti A. , Schlichting Richard D. , Chiu Wanda
Published: July 2002

Communication-oriented abstractions such as atomic multicast, group RPC, and protocols for location-independent mobile computing can simplify the development of complex applications built on distributed systems. This article describes Coyote, a system that supports the construction of highly modular and configurable versions of such abstractions. Coyote extends the notion of protocol objects and hierarchical composition found in existing systems with support for finer-grain microprotocol objects and a nonhierarchical composition scheme for use within a single layer of a protocol stack. A customized service is constructed by selecting microprotocols based on their semantic guarantees and configuring them together with a standard runtime system to form a composite protocol implementing the service. This composite protocol is then composed hierarchically with other protocols to form a complete network subsystem. The overall approach is described and illustrated with examples of services that have been constructed using Coyote, including atomic multicast, group RPC, membership, and mobile computing protocols. A prototype implementation based on extending
x
-kernel version 3.2 running on Mach 3.0 with support for microprotocols is also presented, together with performance results from a suite of microprotocols from which over 60 variants of group RPC can be constructed.
Stiffness detection and estimation of dominant spectrum with explicit Runge-Kutta methods
Authors: Ekeland Kersti , Owren Brynjulf , Øines Eivor
Published: July 2002

A new stiffness detection scheme based on explicit Runge-Kutta methods is proposed. It uses a Krylov subspace approximation to estimate the eigenvalues of the Jacobian of the differential system. The numerical examples indicate that this technique is a worthwhile alternative to other known stiffness detection schemes, especially when the systems are large and when it is desirable to know more about the spectrum of the Jacobian than just the spectral radius.
Public protection of software
Authors: Herzberg Amir , Pinter Shlomit S.
Published: July 2002

One of the overwhelming problems that software producers must contend with is the unauthorized use and distribution of their products. Copyright laws concerning software are rarely enforced, thereby causing major losses to the software companies. Technical means of protecting software from illegal duplication are required, but the available means are imperfect. We present protocols that enable software protection, without causing substantial overhead in distribution and maintenance. The protocols may be implemented by a conventional cryptosystem, such as the DES, or by a public key cryptosystem, such as the RSA. Both implementations are proved to satisfy required security criteria.
Calculations with Pseudo-Random Numbers
Authors: Stockmal Frank
Published: July 2002

Two pseudo-random number generators are considered, the multiplicative congruential method and the mixed congruential method. Some properties of the generated sequences are derived, and several algorithms are developed for the evaluation of

x
i

= @@@@(
i
) and
i
=
f
-1
(

x
i

is the
i
th element of a pseudo-random number sequence.
Solution of Ordinary Differential Equations Using Two ``Off-Step'' Points
Authors: Brush D. G. , Kohfeld J. J. , Thompson G. T.
Published: July 2002

In a previous paper the authors suggested that the accurate correctors proposed by Gragg and Stetter for solving ordinary differential equations should be accompanied by similar predictors. In each method in that paper the corrector and one of the predictors use one “nonstop” point within the interval of integration. In the present paper a corrector is dealt with in which two “nonstep” points are used, and in which, to some degree, the authors have “balanced” the contributions of the errors in the predictors to the total local truncation error, a technique due to Butcher.
Linear Least Squares by Elimination and MGS
Authors: Plemmons Robert J.
Published: July 2002

An algorithm combining Gaussian elimination with the modified Gram-Schmidt (MGS) procedure is given for solving the linear least squares problem. The method is based on the operational efficiency of Gaussian elimination for
LU
decompositions and the numerical stability of MGS for unitary decompositions and is designed for slightly overdetermined linear systems.
Adaptive Allocation of Central Processing Unit Quanta
Authors: Potier D. , Gelenbe E. , Lenfant J.
Published: July 2002

The allocation of the central processing unit (CPU) of a computer system in quanta of fixed length in round-robin fashion favors jobs with shorter total CPU processing time by reducing the time they spend waiting in queue below what it would be if all the lobs were served in first-come-first-served order This effect can be accentuated by the use of short quanta. The main disadvantage of this allocation policy is the resulting time the CPU spends in overhead activities when switching from one task to the other, this too will increase with smaller quanta. Thus, it appears useful to consider adaptive CPU allocation policies to reduce the overhead during high traffic conditions when saturation of this resource is more likely while keeping a small quantum during periods of low arrival traffic. In this paper we analyse such a policy, it is assumed that each time at least r (a threshold) arrivals occur during a quantum, the job currently using the CPU is allocated an additional quantum (if It is needed). Thus, the number of job arrivals during a quantum is used as a sensor of the intensity of arrival traffic. This policy, which can be easily implemented in hardware, is analysed using a mathematical model yielding the average response time for jobs as a function of mean total CPU time, the quantum size, r, and a fixed overhead for switching tasks, with a Poisson arrival process. Numerical results to illustrate the effect of this policy are presented.
A Queueing Model with Finite Waiting Room and Blocking
Authors: Konheim Alan G. , Reiser Martin
Published: July 2002

A two-stage queueing network with feedback and a finite intermediate waiting room is studied. The first-stage server is blocked whenever
M
requests are enqueued in the second stage. The analysis of this system under exponential assumptions is carried out. An algorithm to calculate the stationary state probabilities is given and some special cases are considered.
The multiple prime random number generator
Authors: Haas Alexander
Published: July 2002

A new pseudorandom number generator, the Multiple Prime Random Number Generator, has been developed; it is efficient, conceptually simple, flexible, and easy to program. The generator utilizes cycles around prime numbers to guarantee the length of the period, which can easily be programmed to surpass the maximum period of any other presently available random number generator. There are minimum limits placed on the seed values of the variables because the period of the generator is not a function of the initial values of the variables. The generator passes thirteen standard random number generator tests. It requires only about fifteen lines of FORTRAN code to program and utilizes programming language constructs found in most major languages. Finally, it compares very favorably to the fastest of the other available generators.
Formal verification of parallel programs
Authors: Keller Robert M.
Published: July 2002

Two formal models for parallel computation are presented: an abstract conceptual model and a parallel-program model. The former model does not distinguish between control and data states. The latter model includes the capability for the representation of an infinite set of control states by allowing there to be arbitrarily many instruction pointers (or processes) executing the program. An induction principle is presented which treats the control and data state sets on the same ground. Through the use of “place variables,” it is observed that certain correctness conditions can be expressed without enumeration of the set of all possible control states. Examples are presented in which the induction principle is used to demonstrate proofs of mutual exclusion. It is shown that assertions-oriented proof methods are special cases of the induction principle. A special case of the assertions method, which is called parallel place assertions, is shown to be incomplete. A formalization of “deadlock” is then presented. The concept of a “norm” is introduced, which yields an extension, to the deadlock problem, of Floyd's technique for proving termination. Also discussed is an extension of the program model which allows each process to have its own local variables and permits shared global variables. Correctness of certain forms of implementation is also discussed. An Appendix is included which relates this work to previous work on the satisfiability of certain logical formulas.
Multiprocessing compactifying garbage collection
Authors: Steele Guy L.
Published: July 2002

Algorithms for a multiprocessing compactifying garbage collector are presented and discussed. The simple case of two processors, one performing LISP-like list operations and the other performing garbage collection continuously, is thoroughly examined. The necessary capabilities of each processor are defined, as well as interprocessor communication and interlocks. Complete procedures for garbage collection and for standard list processing primitives are presented and thoroughly explained. Particular attention is given to the problems of marking and relocating list cells while another processor may be operating on them. The primary aim throughout is to allow the list processor to run unimpeded while the other processor reclaims list storage The more complex case involving several list processors and one or more garbage collection processors are also briefly discussed.
Spline function methods for nonlinear boundary-value problems
Authors: Blue James L.
Published: July 2002

The solution of the nonlinear differential equation
Y
″ =
F
(
x, Y, Y
′) with two-point boundary conditions is approximated by a quintic or cubic spline function
y
(
x
). The method is well suited to nonuniform mesh size and dynamic mesh size allocation. For uniform mesh size
h
, the error in the quintic spline
y
(
x
) is
O
(
h
4
), with typical error one-third that from Numerov's method. Requiring the differential equation to be satisfied at the mesh points results in a set of difference equations, which are block tridiagonal and so are easily solved by relaxation or other standard methods.
Picture generation with a standard line printer
Authors: Perry Benson , Mendelsohn Mortimer L.
Published: July 2002

A method is described for producing gray-toned pictures on a line printer by utilizing the different degrees of blackness of standard print characters. Gray scales with 17, 32 and 64 levels have been devised. Scanned images of blood cells are used to display the technique.
A multiuser computation facility for education and research
Authors: Dennis Jack B.
Published: July 2002

Present-day computing facilities are limited in their value for scientific research by inability to interact strongly with users. The full power of a research computing instrument should be available at many terminals that give each user the ability to generate, correct and operate any procedure he wishes, either simple or complex.

Implementation is described for a small-scale multiuser computer system that permits several users to work independently with the machine, and to obtain satisfactory response using typewriter communication.
Macro instruction extensions of compiler languages
Authors: McIlroy M. Douglas
Published: July 2002

Macroinstruction compilers constructed from a small set of functions can be made extremely powerful. In particular, conditional assembly, nested definitions, and parenthetical notation serve to make a compiler capable of accepting very general extensions to its ground language.
The state of the art in distributed query processing
Authors: Kossmann Donald
Published: July 2002

Distributed data processing is becoming a reality. Businesses want to do it for many reasons, and they often must do it in order to stay competitive. While much of the infrastructure for distributed data processing is already there (e.g., modern network technology), a number of issues make distributed data processing still a complex undertaking: (1) distributed systems can become very large, involving thousands of heterogeneous sites including PCs and mainframe server machines; (2) the state of a distributed system changes rapidly because the load of sites varies over time and new sites are added to the system; (3) legacy systems need to be integrated—such legacy systems usually have not been designed for distributed data processing and now need to interact with other (modern) systems in a distributed environment. This paper presents the state of the art of query processing for distributed database and information systems. The paper presents the “textbook” architecture for distributed query processing and a series of techniques that are particularly useful for distributed database systems. These techniques include special join techniques, techniques to exploit intraquery paralleli sm, techniques to reduce communication costs, and techniques to exploit caching and replication of data. Furthermore, the paper discusses different kinds of distributed systems such as client-server, middleware (multitier), and heterogeneous database systems, and shows how query processing works in these systems.
Concurrent threads and optimal parallel minimum spanning trees algorithm
Authors: Chong Ka Wong , Han Yijie , Lam Tak Wah
Published: July 2002

This paper resolves a long-standing open problem on whether the concurrent write capability of parallel random access machine (PRAM) is essential for solving fundamental graph problems like connected components and minimum spanning trees in
O
(log
n
) time. Specifically, we present a new algorithm to solve these problems in
O
(log
n
) time using a linear number of processors on the exclusive-read exclusive-write PRAM. The logarithmic time bound is actually optimal since it is well known that even computing the “OR” of
n
bit requires Ω(log
n
time on the exclusive-write PRAM. The efficiency achieved by the new algorithm is based on a new schedule which can exploit a high degree of parallelism.
Compiler-based I/O prefetching for out-of-core applications
Authors: Brown Angela Demke , Mowry Todd C. , Krieger Orran
Published: July 2002

Current operating systems offer poor performance when a numeric application's working set does not fit in main memory. As a result, programmers who wish to solve “out-of-core” problems efficiently are typically faced with the onerous task of rewriting an application to use explicit I/O operations (e.g., read/write). In this paper, we propose and evaluate a fully automatic technique which liberates the programmer from this task, provides high performance, and requires only minimal changes to current operating systems. In our scheme the compiler provides the crucial information on future access patterns without burdening the programmer; the operating system supports nonbindingprefetchandreleasehints for managing I/O; and the operating systems cooperates with a run-time layer to accelerate performance by adapting to dynamic behavior and minimizing prefetch overhead. This approach maintains the abstraction of unlimited virtual memory for the programmer, gives the compiler the flexibility to aggressively insert prefetches ahead of references, and gives the operating system the flexibility to arbitrate between the competing resource demands of multiple applications. We implemented our compiler analysis within the SUIF compiler, and used it to target implementations of our run-time and OS support on both research and commercial systems (Hurricane and IRIX 6.5, respectively). Our experimental results show large performance gains for out-of-core scientific applications on both systems: more than 50% of the I/O stall time has been eliminated in most cases, thus translating into overall speedups of roughly twofold in many cases.
Closures of database hypergraphs
Authors: Saccà Domenico
Published: July 2002

A hypergraph formalism is introduced to represent database schemata. In particular, a database schema
B
, described by one full join dependency and a set of functional dependencies, is represented by a (database) hypergraph
H
, containing both undirected and directed hyperedges. Undirected hyperedges correspond to the relations in the join dependency, and directed hyperedges correspond to the functional dependencies. In addition, two classes of database hypergraphs are defined:
e
-acyclic hypergraphs and
e
-independent hypergraphs. A hypergraph is
e
-acyclic if it is equivalent to some acyclic hypergraph; it is
e
-independent if it is equivalent to some independent (i.e., cover-embedding) hypergraph. Furthermore, the closure of a database hypergraph is defined as the extension of the transitive closure of a graph. By using a lower bound and an upper bound of the hypergraph closure (called L-closure and U-closure, respectively), it is proved that two
e
-acyclic (
e
-independent) hypergraphs are equivalent if and only if they have the same closure. Moreover, a hypergraph is
e
-acyclic (
e
-independent) if and only if its closure is acyclic (independent) and, in most cases, such a recognition can be done in polynomial time. Finally, it is shown how to use the database hypergraph closure to solve some database design problems.
Diplans: a new language for the study and implementation of coordination
Authors: Holt Anatol W.
Published: July 2002

In this paper the reader is introduced to coordination in the workplace as an object of scientific study and computer automation.
Diplans
are the expressions of a new graphical language used to describe plans of operation in human organizations. With diplans, systems of constraint, which may or may not take the form of procedure definitions, can be specified. Among the special strengths of diplans is their ability to render explicit the interactive aspects of complex work distributed over many people and places—in other words, coordination. Diplans are central to coordination technology, a new approach to developing support for cooperative work on heterogeneous computer networks.
Paradoxes and Prerogatives in Global Virtual Collaboration
Authors: Qureshi Sajda , Zigurs Ilze
Published: July 2002

Case study findings from several corporate environments suggest that successful virtualization does not depend on the degree of technological sophistication. It's how the tools are used that matters.
Dynamic initial allocation and local reallocation procedures for multiple stacks
Authors: Yeh D. Yun , Munakata Toshinori
Published: July 2002

Two new procedures for manipulating multiple stacks which share sequential memory locations are discussed. The first is the dynamic initial allocation procedure in which each stack is allocated as its first element arrives rather than having every stack preallocated at the very beginning of the entire process. The second is the local reallocation procedure; in this scheme, when a stack overflows, only its neighboring stacks, rather than the entire memory area, are reorganized provided that a certain condition is satisfied. The results of simulation appear to suggest that these new approaches improve the operational performance in many applications. With appropriate modifications, these concepts may also be applied to any other type of multiple linear lists (e.g., multiple queues) sharing sequential memory locations.
Why students reject engineering teaching careers
Authors: Geils John W.
Published: July 2002

Many of the country's brightest engineering students have been passing up graduate school for the challenge and high salaries of industry. This is drying up the supply of new Ph.D.s interested in teaching at a time when U.S. engineering schools are struggling to cope with swelling enrollments and a severe faculty shortage.
Is Ada too big? A designer answers the critics
Authors: Wichmann Brian A.
Published: July 2002

Many have criticized the Department of Defense's new computer language, Ada, saying it is too large, too complicated, or too difficult to use. Are they right? And are there some simplifications that could be made to Ada without destroying its usefulness?
THE FOSSIL EVIDENCE FOR HUMAN EVOLUTION IN ASIA
Authors: Etler Dennis A.
Published: July 2002

▪ Abstract  The past decade has seen a dramatic increase in the number of fossil human specimens discovered in China. A better understanding of the tempo and mode of human evolution in Asia during the Pleistocene can be gained as a result. This new evidence has important implications for understanding the course of human evolution not only in Asia but throughout the world. Major issues in human evolutionary studies such as the timing of the initial hominid dispersal event and the factors behind major transitions in the fossil record are addressed in light of these recent finds.
PHOTOSYSTEMI: Function and Physiology
Authors: Chitnis Parag R
Published: July 2002

▪ Abstract  Photosystem I is the light-driven plastocyanin-ferredoxin oxidoreductase in the thylakoid membranes of cyanobacteria and chloroplasts. In recent years, sophisticated spectroscopy, molecular genetics, and biochemistry have been used to understand the light conversion and electron transport functions of photosystem I. The light-harvesting complexes and internal antenna of photosystem I absorb photons and transfer the excitation energy to P700, the primary electron donor. The subsequent charge separation and electron transport leads to the reduction of ferredoxin. The photosystem I proteins are responsible for the precise arrangement of cofactors and determine redox properties of the electron transfer centers. With the availability of genomic information and the structure of photosystem I, one can now probe the functions of photosystem I proteins and cofactors. The strong reductant produced by photosystem I has a central role in chloroplast metabolism, and thus photosystem I has a critical role in the metabolic networks and physiological responses in plants.
Radical Mechanisms of Enzymatic Catalysis
Authors: Frey Perry A.
Published: July 2002

▪ Abstract  Two classes of enzymatic mechanisms that proceed by free radical chemistry initiated by the 5′-deoxyadenosyl radical are discussed. In the first class, the mechanism of the interconversion of L-lysine and L-β-lysine catalyzed by lysine 2,3-aminomutase (LAM) involves four radicals, three of which have been spectroscopically characterized. The reversible formation of the 5′-deoxyadenosyl radical takes place by the chemical cleavage of S-adenosylmethionine (SAM) reacting with the [4 Fe–4S]+ center in LAM. In other reactions of SAM with iron-sulfur proteins, SAM is irreversibly consumed to generate the 5′-deoxyadenosyl radical, which activates an enzyme by abstracting a hydrogen atom from an enzymatic glycyl residue to form a glycyl radical. The glycyl radical enzymes include pyruvate formate-lyase, anaerobic ribonucleotide reductase from Escherichia coli, and benzylsuccinate synthase. Biotin synthase and lipoate synthase are SAM-dependent [4 Fe–4S] proteins that catalyze the insertion of sulfur into unactivated C–H bonds, which are cleaved by the 5′-deoxyadenosyl radical from SAM. In the second class of enzymatic mechanisms using free radicals, adenosylcobalamin-dependent reactions, the 5′-deoxyadenosyl radical arises from homolytic cleavage of the cobalt-carbon bond, and it initiates radical reactions by abstracting hydrogen atoms from substrates. Three examples are described of suicide inactivation through the formation of exceptionally stable free radicals at enzymatic active sites.
Cryosurgery
Authors: Rubinsky Boris
Published: July 2002

▪ Abstract  Cryosurgery is a surgical technique that employs freezing to destroy undesirable tissue. Developed first in the middle of the nineteenth century it has recently incorporated new imaging technologies and is a fast growing minimally invasive surgical technique. A historical review of the field of cryosurgery is presented, showing how technological advances have affected the development of the field. This is followed by a more in-depth survey of two important topics in cryosurgery: (a) the biochemical and biophysical mechanisms of tissue destruction during cryosurgery and (b) monitoring and imaging techniques for cryosurgery.
STRUCTURE, DYNAMICS, AND FUNCTION OF CHROMATIN IN VITRO
Authors: Widom J.
Published: July 2002

▪ Abstract  The substrates for the essential biological processes of transcription, replication, recombination, DNA repair, and cell division are not naked DNA; rather, they are protein-DNA complexes known as chromatin, in one or another stage of a hierarchical series of compactions. These are exciting times for students of chromatin. New studies provide incontrovertible evidence linking chromatin structure to function. Exceptional progress has been made in studies of the structure of chromatin subunits. Surprising new dynamic properties have been discovered. And, much progress has been made in dissecting the functional roles of specific chromatin proteins and domains. This review focuses on in vitro studies of chromatin structure, dynamics, and function.
Probing the Relation Between Force—Lifetime—and Chemistry in Single Molecular Bonds
Authors: Evans Evan
Published: July 2002

▪ Abstract  On laboratory time scales, the energy landscape of a weak bond along a dissociation pathway is fully explored through Brownian-thermal excitations, and energy barriers become encoded in a dissociation time that varies with applied force. Probed with ramps of force over an enormous range of rates (force/time), this kinetic profile is transformed into a dynamic spectrum of bond rupture force as a function of loading rate. On a logarithmic scale in loading rate, the force spectrum provides an easy-to-read map of the prominent energy barriers traversed along the force-driven pathway and exposes the differences in energy between barriers. In this way, the method of dynamic force spectroscopy (DFS) is being used to probe the complex relation between force—lifetime—and chemistry in single molecular bonds. Most important, DFS probes the inner world of molecular interactions to reveal barriers that are difficult or impossible to detect in assays of near equilibrium dissociation but that determine bond lifetime and strength under rapid detachment. To use an ultrasensitive force probe as a spectroscopic tool, we need to understand the physics of bond dissociation under force, the impact of experimental technique on the measurement of detachment force (bond strength), the consequences of complex interactions in macromolecular bonds, and effects of multiply-bonded attachments.
KUIPER BELT OBJECTS
Authors: Jewitt David
Published: July 2002

▪ Abstract  The region of the solar system immediately beyond Neptune's orbit is densely populated with small bodies. This region, known as the Kuiper Belt, consists of objects that may predate Neptune, the orbits of which provide a fossil record of processes operative in the young solar system. The Kuiper Belt contains some of the Solar System's most primitive, least thermally processed matter. It is probably the source of the short-period comets and Centaurs, and may also supply collisionally generated interplanetary dust. I discuss the properties of the Kuiper Belt and provide an overview of the outstanding scientific issues.
Modeling Complex, Nonlinear Geological Processes
Authors: Valentine Greg A. , Zhang Dongxiao , Robinson Bruce A.
Published: July 2002

▪ Abstract  We review selected geological processes to which numerical modeling has been applied, with the aim of describing some of the general approaches and applications of the modeling. All of these examples involve multiphase fluid flow, in some cases coupled with heat transport and phase changes. First, we describe modeling approaches to a human-made geological system—a potential underground radioactive waste repository. Next, we describe recent advances in modeling two-phase flow through random heterogeneous porous media. We review recent modeling studies of fluid processes in magmatic systems, especially focusing on melting and crystallization induced by magma chambers. Finally, several research directions are suggested, including improving our understanding of the linkage between small-scale and field-scale processes, coupling across regimes (e.g., surface water and ground water), and further developments in the modeling of stochastic geological processes.
BIONOMICS OF THE FACE FLY, MUSCA AUTUMNALIS
Authors: Krafsur Elliot S. , Moon Roger D.
Published: July 2002

▪ Abstract  The face fly was introduced from the Palearctic region and spread across North America in 20 years after World War II. Adults feed on cattle and horses, and larvae develop in fresh cattle dung. Little genetic differentiation appears between European and North American populations and among regions within North America. After an autumnally initiated diapause, overwintered flies emerge in spring and reproduce through late spring and summer. Generations after the first overlap, and age structure develops toward a stable age distribution. After three to ten generations, depending on weather, facultative diapause interrupts host feeding and oogenesis, and flies with hypertrophied fat body enter overwintering hibernaculae. Life table statistics and factors affecting population growth and diapause are reviewed. Early views on the fly's effects on animal productivity may have been exaggerated. On-farm control by conventional means has not been effective because of the fly's population dynamics and mobility. We suggest that the alternatives of classical biological control and area-wide control with the sterile insect technique should be considered.
Entomology in the Twentieth Century
Authors: Chapman R. F.
Published: July 2002

▪ Abstract  A number of landmark events in applied entomology are listed together with some insect-related studies that have had a major impact on biology in general. In large part, however, advances in our understanding of insects have depended on technological advances, especially in the second half of the century. The exponential increase in the ease and extent of communication has been critical. Sometimes, as in the field of insect/plant relations, the ideas of a few individuals have been critical with technological advances having a facilitating role. Elsewhere, as in the study of olfaction, major changes in understanding have been directly dependent on new technology. Very brief accounts of the impacts on insect-related science of developments in the fields of radio, radioactivity, immunology, imaging techniques, and chemical analysis are given. Despite the importance of technology, the lovers of their insects continue to have a key role.
Flows Induced by Temperature Fields in a Rarefied Gas and their Ghost Effect on the Behavior of a Gas in the Continuum Limit
Authors: Sone Yoshio
Published: July 2002

▪ Abstract  In the framework of the classical gas dynamics, no steady flow is induced in a gas without an external force, such as gravity, by the effect of a temperature field. In a rarefied gas, on the other hand, the temperature field of a gas (often in combination with a solid boundary) plays an important role in inducing a steady flow. In the present article, we introduce various kinds of flows induced by the temperature effect and discuss their physical mechanisms. These flows vanish in the continuum limit (the limit where the mean free path of the gas molecules tends to zero), but it has been found recently that they, strangely, affect the behavior of a gas in this limit. This interesting effect, called a ghost effect, is also discussed.
PERIPHERAL BLOOD STEM CELLS FOR AUTOGRAFTING
Authors: Shpall, MD Elizabeth J. , Cagnoni, MD Pablo J. , Bearman, MD Scott I. , Ross, MD, PhD Maureen , Jones, PhD, MD Roy B.
Published: July 2002

▪ Abstract  High-dose therapy with autologous hematopoietic progenitor cell support is effective treatment for patients with a variety of high-risk malignancies. Accelerating of marrow recovery from near-lethal or lethal toxicity with hematopoietic cell support improves the safety and cost effectiveness of the high-dose regimens. Peripheral blood progenitor cells will soon replace marrow as the major source of hematopoietic support. This chapter reviews the techniques of peripheral blood progenitor cell collection, mobilization, purification (for tumor removal), and ex vivo expansion.
Anorexia and Bulimia Nervosa
Authors: Kaye W. H. , Klump K. L. , Frank G. K. W. , Strober M.
Published: July 2002

▪ Abstract  Anorexia nervosa (AN) and bulimia nervosa (BN) are disorders characterized by abnormal patterns of weight regulation and eating behavior and by disturbances in attitudes and perceptions toward weight and body shape. Etiologic research has indicated substantial genetic influence on these disorders, suggesting significant biological contributions to their development. Obsessional, perfectionistic, and anxious personality styles may be premorbid traits that contribute to this pathogenesis. Studies of neuroendocrine, neuropeptide, and neurotransmitter functioning in patients with AN and BN indicate that disturbances of these systems may contribute to the maintenance as well as the etiology of these sometimes fatal disorders. The efficacy of psychological treatments and pharmacotherapy has been more clearly established for BN than for AN.
New Oral Therapies for Type 2 Diabetes Mellitus: The Glitazones or Insulin Sensitizers
Authors: Mudaliar Sunder , Henry Robert R.
Published: July 2002

▪ Abstract  Type 2 diabetes mellitus is a growing problem not only in the United States but also across the world. There is now strong evidence that intensive control of blood glucose can significantly reduce and retard the microvascular complications of retinopathy, nephropathy, and neuropathy. Ultimately however, up to 80% of type 2 diabetics die from macrovascular cardiovascular disease. This increased incidence of atherosclerotic disease is intricately associated with insulin resistance, which is a major pathophysiologic abnormality in type 2 diabetes. There is strong evidence that insulin resistance is involved in the development of not only hyperglycemia, but also dyslipidemia, hypertension, hypercoagulation, vasculopathy, and ultimately atherosclerotic cardiovascular disease. This cluster of metabolic abnormalities has been termed the insulin resistance or cardiovascular dysmetabolic syndrome. The thiazolidinediones (rosiglitazone and pioglitazone), a new class of oral antidiabetic agents, are “insulin sensitizers” and exert direct effects on the mechanisms of insulin resistance. These effects not only improve insulin sensitivity and glycemic control with reduced insulin requirements, but also have potentially favorable effects on other components of the cardiovascular dysmetabolic syndrome. Long-term studies are needed to determine whether the insulin-sensitizing effects of the glitazones can prevent or delay premature atherosclerotic cardiovascular disease, morbidity, and death.
Viral Persistence: HIV's Strategies of Immune System Evasion
Authors: Johnson Welkin E. , Desrosiers Ronald C.
Published: July 2002

▪ Abstract  In contrast to most animal viruses, infection with the human and simian immunodeficiency viruses results in prolonged, continuous viral replication in the infected host. Remarkably, viral persistence is not thwarted by the presence of apparently vigorous, virus-specific immune responses. Several factors are thought to contribute to persistent viral replication, most notably the destruction of virus-specific T helper cells, the emergence of antigenic escape variants, and the expression of an envelope complex that structurally minimizes antibody access to conserved epitopes. Not as well understood, though potentially important, is the ability of at least one viral encoded protein (Nef) to prevent presentation of viral antigens in the context of major histocompatibility complex. The future success of antiviral therapies and vaccination strategies may depend largely on understanding how and to what degree each of these factors (and presumably others) contributes to immune evasion.
Integrating DNA: Transposases and Retroviral Integrases
Authors: Haren L. , Ton-Hoang B. , Chandler M.
Published: July 2002

▪ Abstract  Transposable elements appear quite disparate in their organization and in the types of genetic rearrangements they promote. In spite of this diversity, retroviruses and many transposons of both prokaryotes and eukaryotes show clear similarities in the chemical reactions involved in their transposition. This is reflected in the enzymes, integrases and transposases, that catalyze these reactions and that are essential for the mobility of the elements. In this chapter, we examine the structure-function relationships between these enzymes and the different ways in which the individual steps are assembled to produce a complete transposition cycle.
GENETICS OF MANIC DEPRESSIVE ILLNESS
Authors: MacKinnon Dean F. , Jamison Kay Redfield , DePaulo J. Raymond
Published: July 2002

▪ Abstract  Manic depressive illness is a common and frequently debilitating familial psychiatric disorder. Efforts to understand the mechanisms of inheritance have been hindered by the complexity of the phenotype, which may range from benign mood swings to chronic psychosis, and by apparently nonmendelian modes of transmission. Early reports of linkage to chromosomal loci have fallen into doubt; however they have helped encourage the development of more sophisticated methods for analyzing complex phenotypes. Using such methods, linkage of manic depressive illness to loci on chromosome 18 has been reported and apparently replicated, and work is proceeding to identify genes associated with what is probably a genetically heterogeneous set of disorders. As molecular mechanisms of inheritance are elucidated, it will be important to consider the ethical implications of genetic testing in a clinically and genetically complex disorder such as manic depressive illness.
A REVIEW OF GRAVITATIONAL WAVE DETECTORS
Authors: Ricci Fulvio , Brillet Alain
Published: July 2002

▪ Abstract  This review is devoted to presenting the status of the experimental search of gravitational radiation. After a short history of the development of detectors, we present the state of the art for both resonant antennas and interferometers. The final section is devoted to possible future developments of both techniques.
SPIN STRUCTURE FUNCTIONS
Authors: HUGHES E. W. , VOSS R.
Published: July 2002

▪ Abstract  We review the study of the internal spin structure of the proton and neutron. High-energy scattering of polarized leptons by polarized protons, neutrons, and deuterons provides a measurement of the nucleon spin structure functions. These structure functions give information on the polarized quark contributions to the spin of the proton and the neutron and allow tests of the quark-parton model and quantum chromodynamics. We discuss the formalism of deep inelastic scattering of polarized leptons on polarized nucleons, the past decade of experimental progress, and future programs to measure the polarized gluon contribution to the proton spin.
Precision Nuclear Measurements with Ion Traps
Authors: Savard G. , Werth G.
Published: July 2002

▪ Abstract  Properties of charged particles confined in ion traps can be determined to high accuracy. The ability to capture stable and unstable isotopes in such traps with high efficiency has led to a series of measurements of gross properties of nuclei. These recent high-accuracy measurements, along with the enabling technological developments and propects for the field, are presented.
GENETIC ENGINEERING OF PLANT LIPIDS
Authors: Broun Pierre , Gettner Sharmeen , Somerville Chris
Published: July 2002

▪ Abstract  Vegetable oils are a major component of human diets, comprising as much as 25% of average caloric intake. Until recently, it was not possible to exert significant control over the chemical composition of vegetable oils derived from different plants. However, the advent of genetic engineering has provided novel opportunities to tailor the composition of plant-derived lipids so that they are optimized with respect to food functionality and human dietary needs. In order to exploit this new capability, it is essential for food scientists and nutritionists to define the lipid compositions that would be most desirable for various purposes.