bluuebunny/crossref_metadata_2025 huggingface dataset:
BILINEAR ESTIMATES AND APPLICATIONS TO NONLINEAR WAVE EQUATIONS
Authors: KLAINERMAN SERGIU , SELBERG SIGMUND
Published: July 2002

We undertake a systematic review of results proved in [26, 27, 30-32] concerning local well-posedness of the Cauchy problem for certain systems of nonlinear wave equations, with minimal regularity assumptions on the initial data. Moreover we give a considerably simplified and unified treatment of these results and provide also complete proofs for large data. The paper is also intended as an introduction to and survey of current research in the very active area of nonlinear wave equations. The key ingredients throughout the survey are the use of the null structure of the equations we consider and, intimately tied to it, bilinear estimates.
HIGHER DIMENSIONAL HONEYCOMB NETWORKS
Authors: CARLE JEAN , MYOUPO JEAN-FRÉDŔIC , STOJMENOVIC IVAN
Published: July 2002

We define the higher dimensional honeycomb graphs as a generalization of hexagonal plane tessellation, and consider it as a multiprocessor interconnection network. A 3-D honeycomb mesh network with n nodes has degree 4 and diameter approximately 3.63n. The network cost, defined as the product of degree and diameter, is about 20 percents better for the 3-D honeycomb than for the 3-D mesh. We describe the addressing scheme, the routing and broadcasting algorithms for three-dimensional and higher dimensional honeycombs. Furthermore, a formula for the diameter of a higher dimensional honeycomb network of given size is determined.
RECOGNIZING SYMBOLS BY DRAWING THEM
Authors: PARKER J. R. , PIVOVAROV JURAJ
Published: July 2002

Template matching is rarely used for symbol recognition in practice because of the variation in scale, orientation, and line thickness and position found in actual images. An answer to this is to use an adaptable template, one that can be scaled and rotated easily. Here the use of such a template, based on vector representation of symbols, is explored. Results from handprinted digits and electronic symbols will be presented.
A VISUALIZATION FRAMEWORK FOR THE ANALYSIS OF HYPERDIMENSIONAL DATA
Authors: SOLKA JEFFREY L. , CLARK BARTON T. , PRIEBE CAREY E.
Published: July 2002

The purpose of this article is to describe a new visualization framework for the analysis of hyperdimensional data. This framework was developed in order to facilitate the study of a new class of classifiers designated class cover catch digraphs. The class cover catch digraph is an original random graph technique for the construction of classifiers on high dimensional data. This framework allows the user to study the geometric structure of hyperdimensional data sets via the reduction of the original hyperdimensional space to a cover with a small number of balls. The framework allows for the elicitation of geometric and other structures through the visualization of the relationships between the balls and each other and the observations they cover.
RAPID GROWTH PATHS IN CONVEX-VALUED RANDOM DYNAMICAL SYSTEMS
Authors: EVSTIGNEEV IGOR V. , TAKSAR MICHAEL I.
Published: July 2002

This paper examines set-valued random dynamical systems defined by convex homogeneous stochastic operators. The operators under consideration transform elements of a cone contained in a space of random vectors into subsets of the cone. We study rapid paths of such dynamical systems, i.e. those paths which maximize (appropriately defined) growth rates at every time period. Questions of existence, uniqueness and asymptotic behavior of infinite rapid trajectories are considered. The study is motivated by problems related to stochastic models of economic growth.
VISCOELASTICITY WITH PERMANENT DEFORMATION IN INVESTIGATION OF PULSE PROPAGATION IN BLOOD VESSELS
Authors: SELEZOV IGOR , PALLOTTI GIOVANNI , FRATAMICO GIUSEPPE , PETTAZZONI PAOLO
Published: July 2002

The models of viscoelasticity are considered from the point of view of their applicability to describe the behavior of blood vessel wall material. First, some convenient and popular models are considered briefly. These models are widely used, particularly in engineering applications, because of their simplicity and clear physical treatment. At the same time, these models are not representative of many real (and particularly anatomical) materials. As a result, new nonlinear models have been developed by Fung and other researchers for biomaterials. However before them, one of the generalized model of viscoelasticity has been developed by Knopoff and MacDonald. Here this model is considered and applied for evaluation of blood vessel wall characteristics. Unlike the convenient models, this model is based on fundamental thermodynamic concepts, and takes into account some more realistic features of viscoelastic solids. Application of this model to determine the characteristics of blood vessel material is presented.
Landscapes, Gene Networks and Pattern Formation: On the Cambrian Explosion
Authors: Solé Ricard V. , Salazar-Ciudad Isaac , Garcia-Fernández Jordi
Published: July 2002

The Cambrian explosion involved an extraordinary evolutionary event with sudden appearance of most metazoan (animal) body plans. Different aspects are involved in this event, from the molecular organization of gene networks to ecological factors. In this review, this event is explored from different points of view, including all approaches from paleontological evidence, the study of gene regulatory networks and some proposed theoretical models based on adaptation on rugged landscapes.
An optimal on-line algorithm for metrical task system
Authors: Borodin Allan , Linial Nathan , Saks Michael E.
Published: July 2002

In practice, almost all dynamic systems require decisions to be made on-line, without full knowledge of their future impact on the system. A general model for the processing of sequences of tasks is introduced, and a general on-line decision algorithm is developed. It is shown that, for an important class of special cases, this algorithm is optimal among all on-line algorithms.

Specifically, a task system (
S,d
) for processing sequences of tasks consists of a set
S
of states and a cost matrix
d
where
d
(
i, j
is the cost of changing from state
i
to state
j
(we assume that
d
satisfies the triangle inequality and all diagonal entries are 0). The cost of processing a given task depends on the state of the system. A schedule for a sequence

T
1

,

T
2

,…,

T
k

of tasks is a sequence
s
1
,
s
2
,…,

s
k

of states where

s
i

is the state in which

T
i

is processed; the cost of a schedule is the sum of all task processing costs and the state transition costs incurred.

An on-line scheduling algorithm is one that chooses

s
i

only knowing
T
1
T
2
…

T
i

. Such an algorithm is
w
-competitive if, on any input task sequence, its cost is within an additive constant of
w
times the optimal offline schedule cost. The competitive ratio
w
(
S
,
d
) is the infimum
w
for which there is a
w
-competitive on-line scheduling algorithm for (
S
,
d
). It is shown that
w
(
S
,
d
) = 2|S|–1
for every task system
in which
d
is symmetric, and
w
(
S, d
) =
O
(|
S
|
2
) for every task system. Finally, randomized on-line scheduling algorithms are introduced. It is shown that for the uniform task system (in which
d
(
i,j
) = 1 for all
i,j
), the expected competitive ratio
w¯
(
S,d
) =
O
(log|S|).
Parallel and distributed incremental attribute evaluation algorithms for multiuser software development environments
Authors: Kaiser Gail E. , Kaplan Simon M.
Published: July 2002

The problem ofchange propagationin multiuser software development environments distributed across a local-area network is addressed. The program is modeled as an attributed parse tree segmented among multiple user processes and changes are modeled as subtree replacements requested asynchronously by individual users. Change propagation is then implemented using decentralized incremental evaluation of an attribute grammar that defines the static semantic properties of the programming language. Building up to our primary result, we first present algorithms that support parallel evaluation on a centralized tree in response to single edits using a singe editing cursor and multiple edits with multiple editing cursors. Then we present our algorithm for parallel evaluation on a decentralized tree. We also present a protocol to guarantee reliability of the evaluation algorithm as components of the decentralized tree become unavailable due to failures and return to availability.
Equivalence, reversibility, symmetry and concavity properties in fork-join queuing networks with blocking
Authors: Dallery Yves , Liu Zhen , Towsley Don
Published: July 2002

In this paper, we study quantitative as well as qualitative properties of Fork-Join Queuing Networks with Blocking (FJQN/Bs). Specifically, we prove results regarding the equivalence of the behavior of a FJQN/B and that of its duals and a strongly connected marked graph. In addition, we obtain general conditions that must be satisfied by the service times to guarantee the existence of a long-term throughput and its independence on the initial configuration. We also establish conditions under which the reverse of a FJQN/B has the same throughput as the original network. By combining the equivalence result for duals and the reversibility result, we establish a symmetry property for the throughput of a FJQN/B. Last, we establish that the throughput is a concave function of the buffer sizes and the initial marking, provided that the service times are mutually independent random variables belonging to the class of PERT distributions that includes the Erlang distributions. This last result coupled with the symmetry property can be used to identify the initial configuration that maximizes the long-term throughput in closed series-parallel networks.
C in the first course considered harmful
Authors: Johnson L. F.
Published: July 2002

To advice or not to advise, that is the dilemma. To be or not to be, that is the question. To see or not to see, that is the difficulty.
The integration of virtual memory management and interprocess communication in Accent
Authors: Fitzgerald Robert , Rashid Richard F.
Published: July 2002

The integration of virtual memory management and interprocess communication in the Accent network operating system kernel is examined. The design and implementation of the Accent memory management system is discussed and its performance, both on a series of message-oriented benchmarks and in normal operation, is analyzed in detail.
Hypervisor-based fault tolerance
Authors: Bressoud Thomas C. , Schneider Fred B.
Published: July 2002

Protocols to implement a fault-tolerant computing system are described. These protocols augment the hypervisor of a virtual-machine manager and coordinate a primary virtual machine with its backup. No modifications to the hardware, operating system, or application programs are required. A prototype system was constructed for HP's PA-RISC instruction-set architecture. Even though the prototype was not carefully tuned, it ran programs about a factor of 2 slower than a bare machine would.
Net.Speech
Authors: Press Larry
Published: July 2002

In the 1940s, the first research computers worked on numeric data. A few years later, the UNIVAC, was designed for both numeric and alphanumeric data. Over time, technology advances have made other data types economically feasible—text, images, sound, and video.
A modified Schur-complement method for handling dense columns in interior-point methods for linear programming
Authors: Andersen Knud D.
Published: July 2002

The main computational work in interior-point methods for linear programming (LP) is to solve a least-squares problem. The normal equations are often used, but if the LP constraint matrix contains a nearly dense column the normal-equations matrix will be nearly dense. Assuming that the nondense part of the constraint matrix is of full rank, the Schur complement can be used to handle dense columns. In this article we propose a modified Schur-complement method that relaxes this assumption. Encouraging numerical results are presented.
Comparison of surface and derivative evaluation methods for the rendering of NURB surfaces
Authors: Luken William L. , Cheng Fuhua
Published: July 2002

Three methods for evaluating the surface coordinates, first derivatives, and normal vectors of a NURB surface are compared. These methods include forward differencing, knot insertion, and a tow-stage Cox-de Boor technique. The computational complexity of each of these techniques is analyzed and summarized. The use of Hermite functions is shown to yield a poor approximation for the shading functions of a NURB surface. An improved method for computing derivatives by knot insertion is presented. An efficient algorithm for computing the foward difference matrix and a method for using foward differencing to compute the first derivatives of a NURB surface are also presented.
A recursive technique for computing lower-bound performance of schedules
Authors: Langevin M. , Cerny E.
Published: July 2002

We present a fast recursive technique for estimating lower-bound performance of data path schedules. The method relies on the determination of an ASAPUC a(s Soon As Possible Under Constraint) time-step value for each node of the DFG (Data-Flow Graph) that is based on the ASAPUC values of its predecessor nodes. That is, the lower-bound estimation is applied to each subgraph permitting the derivation of a tight lower bound on the performance of the complete DFG. Applying the greedy lower-bound estimator of Rim and Jain [1994] to each subgraph improves the complete lower bound in more than 50% of the experiments reported in Rim and Jain [1994], and the CPU time is only about twice as long. The recursive methodology can be extended to exploit other lower-bound techniques, for example, considering other constraints such as the number of busses or registers.
Smooth invariant interpolation of rotations
Authors: Park F. C. , Ravani Bahram
Published: July 2002

We present an algorithm for generating a twice-differentiable curve on the rotation group SO(3) that interpolated a given ordered set of rotation matrices at their specified knot times. In our approach we regard SO(3) as a Lie group with a bi-invariant Riemannian metriac, and apply the coordinate-invariant methods of Riemannian geometry. The resulting rotation curve is easy to compute, invariant with respect to fixed and moving reference frames, and also approximately minimizes angular acceleration.
How much can hardware help routing?
Authors: Borodin Allan , Raghavan Prabhakar , Schieber Baruch , Upfal Eli
Published: July 2002

We study the extent to which complex hardware can speed up routing. Specifically, we consider the following questions. How much does adaptive routing improve over oblivious routing? How much does randomness help? How does it help if each node can have a large number of neighbors? What benefit is available if a node can send packets to several neighbors within a single time step? Some of these features require complex networking hardware, and it is thus important to investigate whether the performance justifies the investment. By varying these hardware parameters, we obtain a hierarchy of time bounds for worst-case permutation routing.
Boundary representation deformation in parametric solid modeling
Authors: Raghothama Srinivas , Shapiro Vadim
Published: July 2002

One of the major unsolved problems in parametric solid modeling is a robust update (regeneration) of the solid's boundary representation, given a specified change in the solid's parameter values. The fundamental difficulty lies in determining the mapping between boundary representations for solids in the same parametric family. Several heuristic approaches have been proposed for dealing with this problem, but the formal properties of such mappings are not well understood. We propose a formal definition for boundary representation. (BR-)deformation for solids in the same parametric family, based on the assumption of continuity: small changes in solid parameter values should result in small changes in the solid's boundary reprentation, which may include local collapses of cells in the boundary representation. The necessary conditions that must be satisfied by any BR-deforming mappings between boundary representations are powerful enough to identify invalid updates in many (but not all) practical situations, and the algorithms to check them are simple. Our formulation provides a formal criterion for the recently proposed heuristic approaches to “persistent naming,” and explains the difficulties in devising sufficient tests for BR-deformation encountered in practice. Finally our methods are also applicable to more general cellular models of pointsets and should be useful in developing universal standards in parametric modeling.
Computational implementation of the multivariate Halley method for solving nonlinear systems of equations
Authors: Cuyt Annie A. M. , Rall L. B.
Published: July 2002

Cubicaliy convergent iterative methods for the solution of nonlinear systems of the multivariate Halley method, require first and second partial derivatives of the of the functions comprising the system. Automatic differentiation is used to automate the Halley method, HESSIAN and routines for the required operators and functions. A Pascal-SC which implements this method in a single-step iteration mode. The program nonlinear systems, and the results are compared with Newton's method.
Functional multiple-output decomposition with application to technology mapping for lookup table-based FPGAs
Authors: Wurth Bernd , Schlichtmann Ulf , Eckl Klaus , Antreich Kurt J.
Published: July 2002

Functional decomposition is an important technique for technology mapping to look up table-based FPGA architectures. We present the theory of and a novel approach to functional disjoint decomposition of multiple-output functions, in which common subfunctions are extracted during technology mapping.

While a Boolean function usually has a very large number of subfunctions, we show that not all of them are useful for multiple-output decomposition. We use a partition of the set of bound set vertices as the basis to computepreferabledecomposition functions, which are sufficient for an optimal multiple-output decomposition.

We propose several new algorithms that deal with central issues of functional multiple-output decomposition. First, an efficient algorithm to solve the variable partitioning problem is described. Second, we show how to implicitly compute all preferable functions of a single-output function and how to identify all common preferable functions of a multiple-output function. Due to implicit computation in the crucial steps, the algorithm is very efficient. Experimental results show significant reductions in area.
Parallel Program Schemata and Maximal Parallelism I. Fundamental Results
Authors: Keller Robert M.
Published: July 2002

The phenomenon of maximal parallelism is investigated in the framework of a class of parallel program schemata. Part I presents the basic properties of this model. Two types of equivalence relation on computations are presented, to each of which there corresponds a concept of determinacy and equivalence for schemata. The correspondence between these relations is shown and related to other properties of schemata. Then the concept of maximal parallelism using one of the relations as a basis is investigated. A partial order on schemata is defined which relates their inherent parallelism. The results presented are especially concerned with schemata which are maximal with respect to this order, i.e. maximally parallel schemata. Several other properties are presented and shown to be equivalent to the property of maximal parallelism. It is then shown that for any schema of a certain class, there exists a unique equivalent schema which is maximally parallel. We call such a schema the “closure” of the original schema.
Unit Refutations and Horn Sets
Authors: Henschen L. , Wos L.
Published: July 2002

The key concepts for this automated theorem-proving paper are those of Horn set and strictly-unit refutation. A Horn set is a set of clauses such that none of its members contains more than one positive literal. A strictly-unit refutation is a proof by contradiction in which no step is justified by applying a rule of inference to a set of clauses all of which contain more than one literal. Horn sets occur in many fields of mathematics such as the theory of groups, rings, Moufang loops, and Henkin models. The usual translation into first-order predicate calculus of the axioms of these and many other fields yields a set of Horn clauses. The striking feature of the Horn property for finite sets of clauses is that its presence or absence can be determined by inspection. Thus, the determination of the applicability of the theorems and procedures of this paper is immediate.

In Theorem 1 it is proved that, if
S
is an unsatisfiable Horn set, there exists a strictly-unit refutation of
S
employing binary resolution alone, thus eliminating the need for factoring; moreover, one of the immediate ancestors of each step of the refutation is in fact a
positive
unit clause. A theorem similar to Theorem 1 for paramodulation-based inference systems is proven in Theorem 3 but with the inclusion of factoring as an inference rule. In Section 3 two reduction procedures are discussed. For the first, Chang's splitting, a rule is provided to guide both the choice of clauses and the way in which to split. The second reduction procedure enables one to refute a Horn set by refuting but one of a corresponding family of simpler subproblems.
From Algol to polymorphic linear lambda-calculus
Authors: O'Hearn Peter W. , Reynolds John C.
Published: July 2002

In a linearly-typed functional language, one can define functions that consume their arguments in the process of computing their results. This is reminiscent of state transformations in imperative languages, where execition of an assignment statement alters the contents of the store. We explore this connection by translating two variations on Algol 60 into a purely functional language with polymorphic linear types. On the one hand, the translations lead to a semantic analysis of Algol-like programs, in terms of a model of the linear language. On the other hand, they demonstrate that a linearly-typed functional language can be at least as expressive as Algol.
Sliver exudation
Authors: Cheng Siu-Wing , Dey Tamal K. , Edelsbrunner Herbert , Facello Michael A. , Teng Shang-Hua
Published: July 2002

A sliver is a tetrahedon whose four vertices lie close to a plane and whose orthogonal projection to that plane is a convex quadrilateral with no short edge. Slivers are notoriously common in 3-dimensional Delaunay triangulations even for well-spaced point sets. We show that, if the Delaunay triangulation has the ratio property introduced in Miller et al. [1995], then there is an assignment of weights so the weighted Delaunay traingulation contains no slivers. We also give an algorithm to compute such a weight assignment.
Discrete least squares polynomial fits
Authors: Shampine L. F.
Published: July 2002

The recurrence relation between orthogonal polynomials is widely used for discrete least squares data fitting. A variant of the classical algorithm which has better numerical properties is presented and the reason for its improved performance is explained.
Towards a general theory of special functions
Authors: Moses Joel
Published: July 2002

A list of a number of natural developments for the field of algebraic manipulation is given. Then the prospects for a general theory of functions defined by ordinary differential equations are discussed. The claim is made that recent developments in mathematics indicate that it should be possible to algorithmically generate many properties of solutions to differential equations. Such a theory is preferable to a less general effort to make algebraic manipulation systems knowledgeable about the usual special functions (e.g. exponential, hypergeometric).
Minimizing wasted space in partitioned segmentation
Authors: Gelenbe Erol , Boekhorst J. C. A. , Kessels J. L. W.
Published: July 2002

A paged virtual memory system using a finite number of page sizes is considered. Two algorithms for assigning pages to segments are discussed. Both of these algorithms are simple to implement. The problem of choosing the page sizes to minimize the expected value of total wasted space in internal fragmentation and in a page table, per segment, is then solved for a probability density function of segment size which may be expressed as a convex combination of Erlang densities.
Algebraic simplification
Authors: Moses Joel
Published: July 2002

Algebraic simplification is examined first from the point of view of a user who needs to comprehend a large expression, and second from the point of view of a designer who wants to construct a useful and efficient system. First we describe various techniques akin to substitution. These techniques can be used to decrease the size of an expression and make it more intelligible to a user. Then we delineate the spectrum of approaches to the design of automatic simplification capabilities in an algebraic manipulation system. Systems are divided into five types. Each type provides different facilities for the manipulation and simplification of expressions. Finally we discuss some of the theoretical results related to algebraic simplification. We describe several positive results about the existence of powerful simplification algorithms and the number-theoretic conjectures on which they rely. Results about the nonexistence of algorithms for certain classes of expressions are included.
Contextual understanding by computers
Authors: Weizenbaum Joseph
Published: July 2002

A further development of a computer program (ELIZA) capable of conversing in natural language is discussed. The importance of context to both human and machine understanding is stressed. It is argued that the adequacy of the level of understanding achieved in a particular conversation depends on the purpose of that conversation, and that absolute understanding on the part of either humans or machines is impossible.
Stalking the wily hacker
Authors: Stoll Clifford
Published: July 2002

An astronomer-turned-sleuth traces a German trespasser on our military networks, who slipped through operating system security holes and browsed through sensitive databases. Was it espionage?
Solving systems of nonlinear equations using the nonzero value of the topological degree
Authors: Vrahatis Michael N.
Published: July 2002

Two algorithms are described here for the numerical solution of a system of nonlinear equations
F(X)
= Θ, Θ(0,0,…,0)∈ ℝ, and
F
is a given continuous mapping of a region 𝒟 in ℝ
n
into ℝ
n
. The first algorithm locates at least one root of the sy stem within
n
-dimensional polyhedron, using the non zero v alue of the topological degree of
F
at θ relative to the polyhedron; th e second algorithm applies a new generalized bisection method in order to compute an approximate solution to the system. Teh size of the original
n
-dimensional polyhedron is arbitrary, and the method is globally convergent in a residual sense.

These algorithms, in the various function evaluations, only make use of the algebraic sign of
F
and do not require computations of the topological degree. Moreover, they can be applied to nondifferentiable continuous functions
F
and do not involve derivatives of
F
or approximations of such derivatives.
Calendar queues: a fast 0(1) priority queue implementation for the simulation event set problem
Authors: Brown R.
Published: July 2002

A new priority queue implementation for the future event set problem is described in this article. The new implementation is shown experimentally to be O(1) in queue size for the priority increment distributions recently considered by Jones in his review article. It displays hold times three times shorter than splay trees for a queue size of 10,000 events. The new implementation, called a calendar queue, is a very simple structure of the multiple list variety using a novel solution to the overflow problem.
A comparison of adaptive refinement techniques for elliptic problems
Authors: Mitchell William F.
Published: July 2002

Adaptive refinement has proved to be a useful tool for reducing the size of the linear system of equations obtained by discretizing partial differential equations. We consider techniques for the adaptive refinement of triangulations used with the finite element method with piecewise linear functions. Several such techniques that differ mainly in the method for dividing triangles and the method for indicating which triangles have the largest error have been developed. We describe four methods for dividing triangles and eight methods for indicating errors. Angle bounds for the triangle division methods are compared. All combinations of triangle divisions and error indicators are compared in a numerical experiment using a population of eight test problems with a variety of difficulties (peaks, boundary layers, singularities, etc.). The comparison is based on the
L
-infinity norm of the error versus the number of vertices. It is found that all of the methods produce asymptotically optimal grids and that the number of vertices needed for a given error rarely differs by more than a factor of two.
Knowledge and natural language processing
Authors: Barnett Jim , Knight Kevin , Mani Inderjeet , Rich Elaine
Published: July 2002

KBNL is a knowledge-based natural language processing system that is novel in several ways, including the clean separation it enforces between linguistic knowledge and world knowledge, and its use of knowledge to aid in lexical acquisition. Applications of KBNL include intelligent interfaces, text retrieval, and machine translation.
IMPROVING THE NUTRIENT COMPOSITION OF PLANTS TO ENHANCE HUMAN NUTRITION AND HEALTH
Authors: Grusak Michael A. , DellaPenna Dean
Published: July 2002

▪ Abstract  Plant foods contain almost all of the mineral and organic nutrients established as essential for human nutrition, as well as a number of unique organic phytochemicals that have been linked to the promotion of good health. Because the concentrations of many of these dietary constituents are often low in edible plant sources, research is under way to understand the physiological, biochemical, and molecular mechanisms that contribute to their transport, synthesis and accumulation in plants. This knowledge can be used to develop strategies with which to manipulate crop plants, and thereby improve their nutritional quality. Improvement strategies will differ between various nutrients, but generalizations can be made for mineral or organic nutrients. This review focuses on the plant nutritional physiology and biochemistry of two essential human nutrients, iron and vitamin E, to provide examples of the type of information that is needed, and the strategies that can be used, to improve the mineral or organic nutrient composition of plants.
INTERSTELLAR ABUNDANCES FROM ABSORPTION-LINE OBSERVATIONS WITH THE HUBBLE SPACE TELESCOPE
Authors: Savage Blair D. , Sembach Kenneth R.
Published: July 2002

▪ Abstract  The Goddard High-Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope (HST) has yielded precision abundance results for a range of interstellar environments, including gas in the local medium, in the warm neutral medium, in cold diffuse clouds, and in distant halo clouds. Through GHRS studies, investigators have determined the abundances of elements such as C, N, O, Mg, Si, S, and Fe in individual interstellar clouds. These studies have provided new information about the composition of interstellar dust grains, the origin of the Galactic high-velocity cloud system, and the processes that transport gas between the disk and the halo. Precision measurements of the interstellar D to H ratio and of the abundances of r- and s-process elements have also provided fiducial reference values for cosmological and stellar evolutionary observations and theoretical models.
HERBIG Ae/BeSTARS
Authors: Waters L. B. F. M. , Waelkens C.
Published: July 2002

▪ Abstract  We review the wide range of observed properties of Herbig Ae/Be stars and try to combine this rich data set into a consistent picture of their circumstellar environment and evolutionary status. We discuss in some detail the geometry of the circumstellar environment. The presence of disks in Herbig Ae/Be stars is inferred from direct and indirect observational evidence. Envelopes can dominate the spectral energy distributions on large angular scales. In some stars, a fairly massive disk persists until the star has reached the main sequence. The evidence for an evolutionary link between isolated Herbig Ae/Be stars and β Pictoris is summarized.
Peroxisome Proliferator–Activated Receptor γ and Metabolic Disease
Authors: Willson Timothy M. , Lambert Millard H. , Kliewer Steven A.
Published: July 2002

▪ Abstract  The nuclear peroxisome proliferator–activated receptor γ (PPARγ) is a transcription factor that is activated by polyunsaturated fatty acids and their metabolites and is essential for fat cell formation. Although obesity is a strong risk factor for type 2 diabetes mellitus and other metabolic diseases, potent PPARγ activators such as the glitazone drugs lower glucose and lipid levels in patients with type 2 diabetes and also have antiatherosclerotic and antihypertensive effects. We review recent studies providing insight into the paradoxical relationship between PPARγ and metabolic disease. We also review recent advances in understanding the structural basis for PPARγ activation by ligands. The unusual ligand-binding properties of PPARγ suggest that it will be possible to discover new chemical classes of receptor “modulators” with distinct pharmacological activities for the treatment of type 2 diabetes and other metabolic diseases.
Approaches to the Study of Territory Size and Shape
Authors: Adams Eldridge S.
Published: July 2002

▪ Abstract  Intraspecific variation in territory size and shape can have strong effects on population structure and dynamics. The traditional theoretical approach to the study of territory size is based on optimality models that analyze decisions of focal residents as responses to the costs and benefits of defense. These models have stimulated numerous empirical studies showing that territory holders adjust their behavior according to rates of intrusion and availability of food. However, models of optimal territory size are applicable only in limited circumstances because they focus on unilateral decisions rather than on interactions. Furthermore, observational and experimental studies often find that territory sizes are insensitive to food supply. Recently, greater emphasis has been placed on two alternative approaches. The first concerns interactions among contiguous neighbors and how these affect use of space. In these models territory size and shape are determined by the balance of pressure exerted at boundaries or arise as the results of local rules of movement and interaction. The second alternative approach views territory size as the outcome of interactions between established residents and potential settlers attempting to acquire territories. By considering the simultaneous actions of multiple competitors, these models allow quantitative prediction of the effects of territory defense on population density and spatial patterns as well as responses to environmental change.
ECOLOGY AND EVOLUTION OF GALLING THRIPS AND THEIR ALLIES
Authors: Crespi Bernard J. , Carmean, and David A. , Chapman Thomas W.
Published: July 2002

▪ Abstract  About 300 species of thrips belonging to 57 genera are known to form galls. Galls are caused by feeding, usually by one or more adults, on actively growing plant tissue. Most thrips genera with galling capabilities exploit multiple plant families, but there are several possible cases of thrips tracking the speciations of their host-plants. Gall morphology in thrips reflects insect phylogenetic relationships rather than those of plants. Galling species and their nongalling allies on Acacia in Australia exhibit a range of complex social behavior, including soldier castes, pleometrosis (i.e. joint colony founding), group foraging, and group defense, that is directly related to the nature of their domiciles. Galling thrips, by virtue of their haplodiploid genetic system and their ecological relationships with plants and natural enemies, are useful for analyzing a wide range of ecological, evolutionary, and behavioral questions.
Ecology and Behavior of First Instar Larval Lepidoptera
Authors: Zalucki Myron P. , Clarke Anthony R. , Malcolm Stephen B.
Published: July 2002

▪ Abstract  Neonate Lepidoptera are confronted with the daunting task of establishing themselves on a food plant. The factors relevant to this process need to be considered at spatial and temporal scales relevant to the larva and not the investigator. Neonates have to cope with an array of plant surface characters as well as internal characters once the integument is ruptured. These characters, as well as microclimatic conditions, vary within and between plant modules and interact with larval feeding requirements, strongly affecting movement behavior, which may be extensive even for such small organisms. In addition to these factors, there is an array of predators, pathogens, and parasitoids with which first instars must contend. Not surprisingly, mortality in neonates is high but can vary widely. Experimental and manipulative studies, as well as detailed observations of the animal, are vital if the subtle interaction of factors responsible for this high and variable mortality are to be understood. These studies are essential for an understanding of theories linking female oviposition behavior with larval survival, plant defense theory, and population dynamics, as well as modern crop resistance breeding programs.
EXTRUSION INSTABILITIES AND WALL SLIP
Authors: Denn Morton M
Published: July 2002

▪ Abstract  Polymer melts exhibit extrusion instabilities at sufficiently high levels of stress, and they appear to exhibit wall slip. I explore the evidence for slip, the possible mechanisms of slip, and the relation between slip and extrusion instabilities.
DYNAMICALPHENOMENA INLIQUID-CRYSTALLINEMATERIALS
Authors: Rey Alejandro D. , Denn Morton M.
Published: July 2002

▪ Abstract  Recent progress in modeling and simulation of the flow of nematic liquid crystals is presented. The Leslie-Ericksen (LE) theory has been successful in elucidating the flow of low molar-mass nematics. The theoretical framework for the flow of polymeric nematic liquid crystals is still evolving; extensions of the Doi theory capture qualitative features of the flow of polymeric nematics in simple geometries, but these theories have not been shown to predict texture development in flow. Mesoscopic theories for textured materials based on spatial averaging capture only some qualitative features of nonrectilinear liquid-crystalline polymer flow. Interfacial effects in liquid-crystalline systems have begun to receive attention in the context of interfacial viscoelasticity and the dynamics of dispersed liquid-crystalline polymers in immiscible blends.
MOLECULAR GENETIC ANALYSIS OF SYNAPTIC PLASTICITY, ACTIVITY-DEPENDENT NEURAL DEVELOPMENT, LEARNING, AND MEMORY IN THE MAMMALIAN BRAIN
Authors: Chen Chong , Tonegawa Susumu
Published: July 2002

▪ Abstract  Recently, dozens of mutant mice generated with gene targeting or transgenic technologies have been shown to exhibit a distinct set of impairments in the brain and behavior. In this review, we discuss how studies of mutant mice have helped elucidate the mechanisms that underlie synaptic plasticity and the relationship of these synaptic mechanisms to the activity-dependent phase of neural development and learning and memory. We focus on the recent progress in the analysis of whisker-related pattern formation, elimination of climbing fibers, long-term potentiation, long-term depression, and various learning and memory tasks in mutant mice.
Nerve Growth Factor Signaling, Neuroprotection, and Neural Repair
Authors: Sofroniew Michael V , Howe Charles L , Mobley William C
Published: July 2002

▪ Abstract  Nerve growth factor (NGF) was discovered 50 years ago as a molecule that promoted the survival and differentiation of sensory and sympathetic neurons. Its roles in neural development have been characterized extensively, but recent findings point to an unexpected diversity of NGF actions and indicate that developmental effects are only one aspect of the biology of NGF. This article considers expanded roles for NGF that are associated with the dynamically regulated production of NGF and its receptors that begins in development, extends throughout adult life and aging, and involves a surprising variety of neurons, glia, and nonneural cells. Particular attention is given to a growing body of evidence that suggests that among other roles, endogenous NGF signaling subserves neuroprotective and repair functions. The analysis points to many interesting unanswered questions and to the potential for continuing research on NGF to substantially enhance our understanding of the mechanisms and treatment of neurological disorders.
ENERGETICS OF FREE-RANGING MAMMALS, REPTILES, AND BIRDS
Authors: Nagy K. A. , Girard I. A. , Brown T. K.
Published: July 2002

▪ Abstract  We summarize the recent information on field metabolic rates (FMR) of wild terrestrial vertebrates as determined by the doubly labeled water technique. Allometric (scaling) relationships are calculated for mammals (79 species), reptiles (55 species), and birds (95 species) and for various taxonomic, dietary, and habitat groups within these categories. Exponential equations based on body mass are offered for predicting rates of daily energy expenditure and daily food requirements of free-ranging mammals, reptiles, and birds. Significant scaling differences between various taxa, dietary, and habitat groups (detected by analysis of covariance with P ≤ 0.05) include the following: (a) The allometric slope for reptiles (0.889) is greater than that for mammals (0.734), which is greater than that for birds (0.681); (b) the slope for eutherian mammals (0.772) is greater than that for marsupial mammals (0.590); (c) among families of birds, slopes do not differ but elevations (intercepts) do, with passerine and procellariid birds having relatively high FMRs and gallinaceous birds having low FMRs; (d) Scleroglossan lizards have a higher slope (0.949) than do Iguanian lizards (0.793); (e) desert mammals have a higher slope (0.785) than do nondesert mammals; (f) marine birds have relatively high FMRs and desert birds have low FMRs; and (g) carnivorous mammals have a relatively high slope and carnivorous, insectivorous, and nectarivorous birds have relatively higher FMRs than do omnivores and granivores. The difference detected between passerine and nonpasserine birds reported in earlier reviews is not evident in the larger data set analyzed here. When the results are adjusted for phylogenetic effects using independent contrasts analysis, the difference between allometric slopes for marsupials and eutherians is no longer significant and the slope difference between Scleroglossan and Iguanian lizards disappears as well, but other taxonomic differences remain significant. Possible causes of the unexplained variations in FMR that could improve our currently inaccurate FMR prediction capabilities should be evaluated, including many important groups of terrestrial vertebrates that remain under- or unstudied and such factors as reproductive, thermoregulatory, social, and predator-avoidance behavior.
Central Role of Peroxisome Proliferator–Activated Receptors in the Actions of Peroxisome Proliferators
Authors: Corton J. Christopher , Anderson Steven P. , Stauber Anja
Published: July 2002

Peroxisome proliferators (PPs) are a large class of structurally dissimilar chemicals that have diverse effects in rodents and humans. Most, if not all, of the diverse effects of PPs are mediated by three members of the nuclear receptor superfamily called peroxisome proliferator-activated receptors (PPARs). In this review, we define the molecular mechanisms of PPs, including PPAR binding specificity, alteration of gene expression through binding to DNA response elements, and cross talk with other signaling pathways. We discuss the roles of PPARs in growth promotion in rodent hepatocarcinogenesis and potential therapeutic effects, including suppression of cancer growth and inflammation.
THE USE OF ANIMAL MODELS TO STUDY THE EFFECTS OF AGING ON COGNITION
Authors: Gallagher Michela , Rapp Peter R.
Published: July 2002

▪ Abstract  This review addresses the importance of animal models for understanding the effects of normal aging on the brain and cognitive functions. First, studies of laboratory animals can help to distinguish between healthy aging and pathological conditions that may contribute to cognitive decline late in life. Second, research on individual differences in aging, a theme of interest in studies of elderly human beings, can be advanced by the experimental control afforded in the use of animal models. The review offers a neuropsychological framework to compare the effects of aging in human beings, monkeys, and rodents. We consider aging in relation to the role of the medial temporal lobe in memory, the information processing functions of the prefrontal cortex in the strategic use of memory, and the regulation of attention by distributed neural circuitry. We also provide an overview of the neurobiological effects of aging that may account for alterations in psychological functions.
Towards a Philosophy of Virtual Reality: Issues Implicit in “Consciousness Reframed”
Authors: Jones Stephen
Published: July 2002

This paper reviews the first “Consciousness Reframed” conference. A number of artists' works in media such as virtual reality and interactive installations are discussed, and various issues relating to “technoetic” artworks are raised. These issues include questions such as the potentially dehumanizing nature of technology, the transcendent states claimed for cyberspace, the nature of immersion, and aspects of the problem of consciousness. The author offers some suggestions regarding how technoetic art might tackle such issues.
Antecedent-Contained Deletion and the Copy Theory of Movement
Authors: Fox Danny
Published: July 2002

Antecedent-contained deletion poses a problem for theories of ellipsis, a problem that, according to much literature, is solved by Quantifier Raising. The solution, however, conflicts with the copy theory of movement. This article resolves this new conflict with the aid of a theory of extraposition and covert movement proposed by Fox and Nissenbaum (1999), together with certain assumptions about the structure of relative clauses and the way chains are interpreted. The resolution makes various new predictions and accounts for a range of otherwise puzzling facts.
Vehicle Change and Reconstruction in Ā-Chains
Authors: Safir Ken
Published: July 2002

Fiengo and May (1994) argue that what they call “vehicle change,” which permits copies of names to be evaluated as pronouns with respect to interpretive principles, plays a key role in accounting for reconstruction effects in ellipsis environments. It is argued here that the alleviation of Principle C violations (“antire construction effects”), where it occurs in Ā-chains, is due not to deletion of the lower copy, as in Chomsky 1995, but to vehicle change. The introduction of vehicle change into the theory of Ā-chains is independently motivated as essential to capturing a robust adjunct/nonadjunct distinction in the reconstruction of pronoun-as-bound-variable readings that has not been discussed up to now; at the same time it predicts the class of “weakest crossover” environments.