bluuebunny/crossref_metadata_2025 huggingface dataset:
On parallel evaluation of game trees
Authors: Karp Richard M. , Zhang Yangun
Published: July 2002

A class of parallel algorithms for evaluating game trees is presented. These algorithms parallelize a standard sequential algorithm for evaluating AND/OR trees and the α-β pruning procedure for evaluating MIN/MAX trees. It is shown that, uniformly on all instances of uniform AND/OR trees, the parallel AND/OR tree algorithm achieves an asymptotic linear speedup using a polynomial number of processors in the height of the tree. The analysis of linear speedup using more than a linear number of processors is due to J. Harting. A numerical lower bound rigorously establishes a good speedup for the uniform AND/OR trees with parameters that are typical in practice. The performance of the parallel α-β algorithm on best-ordered MIN/MAX trees is analyzed.
Confidence analysis for defect-level estimation of VLSI random testing
Authors: Jone Wen-Ben , Tsai K. S.
Published: July 2002

The defect level in circuit testing is the percentage of circuits such as chips, that are defective and shipped for use after testing. Our previously published results showed that the defect level of circuit fabrication and testing should be a probability distribution, rather than a single value, and the concept of confidence degree was proposed [Gondalia et al. 1993; Jone et al. 1995]. In this work, defect level is represented by a confidence interval which is more conventional and easier to interpret. The point estimate of defect level analysis and conditions to avoid meaningless confidence intervals are also investigated. Methods for adaptive random test length determination driven by different confidence intervals or interval length are proposed to meet both test requirements and test costs tradeoff. Finally, a complete test plan that can direct the test flow from fabrication infancy to maturity is suggested.
Profiles in computing: Donald E. Knuth: scholar with a passion for the particular
Authors: Frenkel Karen A.
Published: July 2002

"Age 30 is kind of appropriate because I got the first copy of volume 1 from the publisher nine days after my 30th birthday. So, a large part of the work had been done when I was 30 years old. They already were working on typesetting the second volume."

Commenting on his books' influence, Knuth says, "It's been phenomenal from my point of view. In 1976 a study was done of how many people writing papers on computer science made a reference to my book somewhere in their articles, and it was found that about 30 percent of the papers in
Communications, Journal of the ACM,
and
SIAM Journal on Computing
cited the book. So it has an impact in that way." What about sales? Knuth notes that publishers may joke about professors whose books never sell, but they don't apply here. "I know that people buy the book. I don't know how many read it. But the sales have been incredible. I think something between 1000 and 2000 copies [have been sold] per month for 20 years."
Shadowed management of free disk pages with a linked list
Authors: Hecht Matthew S. , Gabbe John D.
Published: July 2002

We describe and prove correct a programming technique using a linked list of pages for managing the free disk pages of a file system where shadowing is the recovery technique. Our technique requires a window of only two pages of main memory for accessing and maintaining the free list, and avoids wholesale copying of free-list pages during a
checkpoint
or
recover
operation.
Data file management in shift-register memories
Authors: Kluge Werner E.
Published: July 2002

The paper proposes a shift-register memory, structured as a two-dimensional array of uniform shift-register loops which are linked by flow-steering switches, whose switch control scheme is tailored to perform with great efficiency data management operations on sequentially organized files. The memory operates in a linear input/output mode to perform record insertion, deletion, and relocation on an existing file, and in a sublinear mode for rapid internal file movement to expedite file positioning and record retrieval and update operations.

The memory, implemented as a large capacity charge-coupled device or magnetic domain memory, permits efficient data management on very large databases at the level of secondary storage and lends itself to applications as a universal disk replacement, particularly in database computers.
A facility for defining and manipulating generalized data structures
Authors: Claybrook Billy G.
Published: July 2002

A data structure definition facility (DSDF) is described that provides definitions for several primitive data types, homogeneous and heterogeneous arrays, cells, stacks, queues, trees, and general lists. Each nonprimitive data structure consists of two separate entities—a head and a body. The head contains the entry point(s) to the body of the structure; by treating the head like a cell, the DSDF operations are capable of creating and manipulating very general data structures. A template structure is described that permits data structures to share templates.

The primary objectives of the DSDF are: (1) to develop a definition facility that permits the programmer to explicitly define and manipulate generalized data structures in a consistent manner, (2) to detect mistakes and prevent the programmer from creating (either inadvertently or intentionally) undesirable (or illegal) data structures, (3) to provide a syntactic construction mechanism that separates the implementation of a data structure from its use in the program in which it is defined, and (4) to facilitate the development of reliable software.
The Share 709 System: Programmed Input-Output Buffering
Authors: Mock Owen , Swift Charles J.
Published: July 2002

This paper deals with the dispatching problem that arises when a computer is able to execute asynchronous routines in parallel. It will contain a brief description of the pertinent features of such a computer (the IBM 709) and then describe a program which handles the dispatching semi-automatically fairly efficiently for a wide class of problems on the 709. This paper deals with the dispatching problem only and does not deal with conversion or with input-output constraints (such as record sizes or character coding) that are introduced by external equipment which cause tapes generated externally to differ from tapes written by the 709 itself.
A Generalization of a Theorem of Carr on Error Bounds for Rung-Kutta Procedures
Authors: Galler B. A. , Rozenberg D. P.
Published: July 2002

In [1] Carr established propagation error bounds for a particular Runge-Kutta (RK) procedure, and suggested that similar bounds could be established for other RK procedures obtained by choosing the parameters differently.
Computation of the Frequency Function of a Quadratic Form in Random Normal Variables
Authors: Freiberger Walter F. , Jones Richard H.
Published: July 2002

One of the outstanding problems in the theory of time series analysis is the distribution problem in spectral analysis for small samples. When the number of observations is sufficiently large for the Central Limit Theorem to be applicable, the normal approximation can be used to advantage. In recent years, work has aimed at the discovery of more generally applicable approximate methods and of more rational criteria for the sample size at which the large sample theory becomes useful; the state of the art is summarized in two recent papers by Grenander, Pollak and Slepian [1] and Freiberger and Grenander [2].
A Note on a Method of Computing the Gamma Function
Authors: Gordon N. L. , Flasterstein A. H.
Published: July 2002

Numerous formulas are available for the computation of the Gamma function [1, 2]. The purpose of this note is to indicate the value of a well-known method that is easily extended for higher accuracy requirements.

Using the recursion formula for the Gamma function, Γ(
x
+ 1) =
x
Γ(
x
), (1) and Stirling's asymptotic expansion for ln Γ(
x
) [3], we have ln Γ(
x
) ∼ (
x
- 1/2) ln
x
-
x
+ 1/2 ln 2π + ∑

N

r
=1

C
r

/
x

2
r
-1

. (2) It follows that, if
k
and
N
are appropriately selected positive integers, Γ(
x
+ 1) can be represented by Γ(
x
+ 1) ∼ √2π exp (
x
+
k
- 1/2) ln (
x
+
k
) - (
x
+
k
) exp ∑

N

r
=1

C
r

/(
x
+
k
)

2
r
-1

/(
x
+ 1)(
x
+ 2) … (
x
+
k
- 1) (3) where

C
r

= (- 1)

r
-1

B
r

/(2
r
- 1)(2
r
),

B
r

being the Bernoulli numbers [4]. These coefficients have been published by Uhler [5].

Requiring the range 0 ≦
x
≦ 1 is no restriction since, if necessary, Γ(
x
+ 1) can be generated for other arguments using (1).

For a given
N
, the error in (2) can be estimated from |ε| < |
C

N
+1

|/
x

2
N
+1

. (4)

The curves of Figure 1 show contours of constant error bound as a function of
N
and
x
. These curves represent single and double-precision floating-arithmetic requirements of ε < 5·10
-9
and ε < 5·10
-17
. For a given
N
,
k
is defined as the minimum integral
x
greater than or equal to those on the curves. Then
N
and
k
can be chosen to minimize round-off and computing time.

For
N
and
k
equal to 4, formula (3) yields Γ(
x
+ 1) ∼ √2π exp (
x
+ 4 - 1/2) ln (
x
+ 4) - (
x
+ 4) exp ∑
4

r
=1

C
r

/(
x
+ 4)

2
r
-1

/(
x
+ 1)(
x
+ 2)(
x
+ 3). (5)

A similar expression suitable for double precision results for
N
= 8 and
k
= 9.

The exponents in (5) are split to reduce roundoff. Various algebraic manipulations might result in a further reduction of roundoff.
Generalized Cascade Decompositions of Automata
Authors: Yoeli Michael
Published: July 2002

Incompletely specified (Mealy type) sequential machines and their generalizations to infinite machines are discussed. Convenient algebraic techniques for the study of such machines are introduced. These techniques are based on binary relations and on an extension of the usual concept of homomorphism to multivalued mappings. The first part of the paper gives a short, unified introduction to the algebraic theory of partial automata. The second part unifies and extends the algebraic approach to generalized cascade decompositions which combine conventional decomposition techniques with state-splitting procedures. The relationship between such generalized decompositions and state reductions of automata is investigated.
The Solvability of the Derivability Problem for One-Normal Systems
Authors: Cook Stephen A.
Published: July 2002

A one-normal system is a Post production system on a finite alphabet {
s
1
,
s
2
, · · ·,
s
σ
} with productions

s
i
P

→

PE
ij

, where
i
ranges over a subset of {1, 2, · · ·, σ} and, for fixed
i
,
j
takes on the values 1, 2, · · ·,

n
i

. The following derivability problem is shown to be solvable for each such system: Given two words
P
and
Q
, decide whether
Q
can be derived from
P
by successive applications of the production rules. The result was proved by Hao Wang for the monogenic case (i.e., when each

n
i

= 1).
A Theory of Computer Instructions
Authors: Maurer Ward Douglas
Published: July 2002

A computer is a set
M
(the memory), a set
B
, a class of maps
S
:
M
→
B
, known as states, and a class @@@@ of maps
T
: @@@@ → @@@@, known as instructions. Each instruction
I
has an input region
IR
(
I
), an output region
OR
(
I
), and affected regions
AR
(
M′
,
I
), for
M′
⊆
IR
(
I
). For example, let
I
be the instruction (
CLA Y
) on the IBM 7094. If
L
is the location counter and
AC
is the accumulator, then
IR
(
I
) =
Y
∪
L
and
OR
(
I
) =
AC
∪
L
; if
M′
is the address portion of
Y
, then
AR
(
M′
,
I
) is the address portion of
AC
. The fundamental properties of all these notions are derived, and computers are related to other models, such as sequential machines. The existence problem (how arbitrarily the input, output and affected regions of an instruction can be specified) is fully settled for countable memory
M
.
Computable Error Bounds for Direct Solution of Linear Equations
Authors: Chartres Bruce A. , Geuder James C.
Published: July 2002

An error analysis of direct methods (i.e., Gaussian elimination or triangular factorization) of solving simultaneous linear algebraic equations is performed in the backward mode, in which the computational errors are expressed as perturbations on the data. Bounds are found for perturbations on the coefficients of the equations, leaving the right-hand sides unchanged. These bounds can be evaluated concurrently with the computation itself, with only a small increase in computing effort. Because they use information obtained during the solution process, these bounds avoid exaggerating the magnitude of the error, and so are also useful as error estimates.
A Test for Instability in the Numerical Solution of Ordinary Differential Equations
Authors: Krogh Fred T.
Published: July 2002

A procedure is described to test the individual components of the numerical solution to a system of differential equations for relative instability. Although the test is based on the theory for linear differential equations, it has also worked for nonlinear problems. Extra computation is negligible; the test involves checking the signs of previously computed numbers
On Computing the Fixed-Point Probability Vector of Ergodic Transition Matrices
Authors: Odell P. L. , Decell E. P.
Published: July 2002

A technique for computing the fixed-point probability vector of an orgodic (cyclic) transition matrix
P
is developed. The technique utilizes generalized matrix inversion in a scheme which only necessitates calculation of the probability fixed point of a transition matrix having smaller dimensions than
P
.
Representation of Events in the von Neumann Cellular Model
Authors: Mukhopadhyay Amar
Published: July 2002

In this paper it is proved that regular events are representable in the cellular model proposed by John von Neumann, and a construction of a finite-state cellular automaton is presented. The procedure was motivated primarily by McNaughton's construction of an automaton using slow but well-timed elements.
A Model of Replication
Authors: Waksman Abraham
Published: July 2002

A one-dimensional array of finite-state machines is being considered as a model for sequence replication. The authors consider the initial state of the first
k
machines in the array as representing the sequence of
k
symbols to be replicated along the array. A construction scheme is developed which allows for such replication to take place. It is also shown that the speed of replication approaches synchronous speed.
Translation Networks and Function Composition
Authors: Wegner Peter
Published: July 2002

A notation for specifying translation networks is analyzed and shown to be a special case of a notation for specifying functions. Cancellation of domains and ranges and associativity is derived more simply than in a previous paper by Sklansky, Finkelstein, and Russell.
Efficient Ordering of Set Expressions for Symbolic Expansion
Authors: Worrell R. B. , Hulme B. L.
Published: July 2002

This paper gives an algorithm for efficiently ordering the terms and factors of a set (or Boolean) expression so that the work required for the symbolic expansion of the expression according to the distributive law is minimized. Formulas are given for computing the measure of work associated with any ordering of an expression. It is shown from these formulas that reordering the factors of the intersections can possibly reduce the cost of expansion, but this cost is invariant with respect to the ordering of the terms of the unions. A simple ordering algorithm is given for quickly determining an optimal (not necessarily unique) ordering of an intersection and a union. When this algorithm is applied to all intersections and unions in an expression, the resulting order is shown to minimize the total work over all possible orderings. Thus it is easy to establish an optimal ordering for an expression and estimate the machine time for its symbolic expansion before doing the expansion.
On a Statistical Model of Strand and Westwater for the Numerical Solution of a Fredholm Integral Equation of the First Kind
Authors: Herr David G.
Published: July 2002

A statistical model is presented which is useful in the solution of a Fredholm integral equation of the first kind and equivalent to one proposed by Strand and Westwater. The model and the related problem presented here are familiar to statisticians from the study of regression analysis and are essentially, “(GLM): Find the best linear unbiased estimate of
β
given the observation
y
which satisfies
y
=
Hβ
+
e, e
distributed as
N
(0, Γ).” Here
y, β c
are vectors,
H
is an (
m
+
n
) ×
k
matrix, and Γ is a certain (
m
+
n
) × (
m
+
n
) positive definite, known matrix. The main content of the paper is that (GLM) provides an equivalent way of considering the problem of Strand and Westwater and is to be preferred by virtue of the rich store of results available for the study of (GLM) and its intrinsic geometric nature.
Some a Posteriori Error Bounds in Floating-Point Computations
Authors: Tsao Nai-kuan
Published: July 2002

Efficiently computable a posteriori error bounds are attained by using a posteriori models for bounding roundoff errors in the basic floating-point operations. Forward error bounds are found for inner product and polynomial evaluations. An analysis of the Crout algorithm in solving systems of linear algebraic equations leads to sharper backward a posteriori bounds. The results in the analysis of the iterative refinement give bounds useful in estimating the rate of convergence. Some numerical experiments are included.
Further Results on the Problem of Finding Minimal Length Programs for Decision Tables
Authors: Pager David
Published: July 2002

In this paper it is shown that whatever the length function employed, the problem of finding the shortest program for a decision table with two (or more) entries is not recursively solvable (whereas for decision tables with a single entry the problem is solvable for some length functions and unsolvable for others). Moreover, it is shown that there is a pair of finite sets of programs and a single entry
E
such that the shortest program for the decision table formed by adding a single additional entry to
E
is in all cases in one of the two sets, but it is undecidable in which. Some consequences of these results are then presented, such as showing that for a wide range of restrictions the results remain true, even when the repertoire of possible programs for a decision table is narrowed by only considering programs which meet certain restrictions.
On Almost Everywhere Complex Recursive Functions
Authors: Gill John , Blum Manuel
Published: July 2002

Let
h
be a recursive function. A partial recursive function
ψ
is i.o. (infinitely often)
h
-complex if every program for
ψ
requires more than
h
(
χ
) steps to compute
ψ
(
χ
) for infinitely many inputs
χ
. A more stringent notion is that of
ψ
being a.e. (almost everywhere)
h
-complex:
ψ
is a.e.
h
-complex if every program for
ψ
requires more than
h
(
χ
) steps to compute
ψ
(
χ
) for all but finitely many inputs
χ
.

These two definitions of
h
-complex functions do not yield the same theorems. Although it is possible to prove of every i.o.
h
-complex recursive function that it is i.o.
h
-complex, it is not possible to prove of every a.e.
h
-complex recursive function that it is a.e.
h
-complex. Similarly, recursive functions not i.o.
h
-complex can be proven to be such, but recursive functions not a.e.
h
-complex cannot be so proven.

The construction of almost everywhere complex recursive functions appears much more difficult than the construction of infinitely often complex recursive functions. There have been found no “natural” examples of recursive functions requiring more than polynomial time for all but finitely many inputs. It is shown that from a single example of a moderately a.e. complex recursive function, one can obtain a.e. very complex recursive functions.
Context-Limited Grammars
Authors: Hibbard Thomas N.
Published: July 2002

A phrase structure grammar is called
context-limited
if there exists a partial ordering on its alphabet such that any letter on the left of any production is less than some letter on the right of the same production. It is proved that context-limited grammars are equivalent to context-free grammars, the equivalence including ambiguity. The notion of ambiguity in phrase structure grammars is discussed, and a new formal model for ambiguity, based on directed plane graphs with labeled edges, is outlined and compared with other models.
Resolution Strategies as Decision Procedures
Authors: Joyner William H.
Published: July 2002

The resolution principle, an automatic inference technique, is studied as a possible decision procedure for certain classes of first-order formulas. It is shown that most previous resolution strategies do not decide satisfiability even for “simple” solvable classes. Two new resolution procedures are described and are shown to be complete (i.e. semidecision procedures) in the general case and, in addition, to be decision procedures for successively wider classes of first-order formulas. These include many previously studied solvable classes. The proofs that a complete resolution procedure will always halt (without producing the empty clause) when applied to satisfiable formulas in certain classes provide new, and in some cases more enlightening, demonstrations of the solvability of these classes. A technique for constructing a model for a formula shown satisfiable in this way is also described.
An Analysis of Binary Search Trees Formed from Sequences of Nondistinct Keys
Authors: Burge William H.
Published: July 2002

The expected depth of each key in the set of binary search trees formed from all sequences composed from a multiset {
p
1
· 1,
p
2
· 2,
p
3
· 3, ···,
p
n
·
n
} is obtained, and hence the expected weight of such trees. The expected number of left-to-right local minima and the expected number of cycles in sequences composed from a multiset are then deduced from these results.
Solution of Integer Programs with a Quadratic Objective Function
Authors: Phuong Ta Huu
Published: July 2002

This paper presents a branch and bound method for solving problems in which the objective function is quadratic, the constraints are linear, and some or all variables are required to be integer. The algorithm is obtained by grafting an inverse-basis version of Beale's method onto the Land-Doig procedure. The code has been tested on a computer, and computational results with various strategies of branching are reported.
Proof, Completeness, Transcendentals, and Sampling
Authors: Davis Philip J.
Published: July 2002

This paper considers informally the relationship between computer aided mathematical proof, formal algebraic languages, computation with transcendental numbers, and proof by sampling.
Informedia Experience-on-Demand
Authors: Wactlar Howard D. , Christel Michael G. , Hauptmann Alexander G. , Gong Yihong
Published: July 2002

The Informedia Experience-on-Demand system uses speech, image, and natural language processing combined with GPS information to capture, integrate, and communicate personal multimedia experiences. This paper discusses in initial prototype of the EOD system.
A technique for software module specification with examples
Authors: Parnas D. L.
Published: July 2002

This paper presents an approach to writing specifications for parts of software systems. The main goal is to provide specifications sufficiently precise and complete that other pieces of software can be written to interact with the piece specified without additional information. The secondary goal is to include in the specification no more information than necessary to meet the first goal. The technique is illustrated by means of a variety of examples from a tutorial system.
An intelligent analyzer and understander of English
Authors: Wilks Yorick
Published: July 2002

The paper describes a working analysis and generation program for natural language, which handles paragraph length input. Its core is a system of preferential choice between deep semantic patterns, based on what we call “semantic density.” The system is contrasted:

with syntax oriented linguistic approaches, and

with theorem proving approaches to the understanding problem.
Role-based authorization constraints specification
Authors: Ahn Gail-Joon , Sandhu Ravi
Published: July 2002

Constraints are an important aspect of role-based access control (RBAC) and are often regarded as one of the principal motivations behind RBAC. Although the importance of contraints in RBAC has been recogni zed for a long time, they have not recieved much attention. In this article, we introduce an intuitive formal language for specifying role-based authorization constraints named
RCL 2000
including its basic elements, syntax, and semantics. We give soundness and completeness proofs for
RCL 2000
relative to a restricted form of first-order predicate logic. Also, we show how previously identified role-based authorization constraints such as separtation of duty (SOD) can be expressed in our language. Moreover, we show there are other significant SOD properties that have not been previously identified in the literature. Our work shows that there are many alternate formulations of even the simplest SOD properties, with varying degree of flexibility and assurance. Our language provides us a rigorous foundation for systematic study of role-based authorization constraints.
Building A Global Learning Community
Authors: DeSanctis Gerardine , Wright Matthew , Jiang Lu
Published: July 2002

Communicating over differing continents and time zones is not an obstacle when the quality and tone of the communication are viewed as important as the project at hand.
SIGNALING TO THE ACTIN CYTOSKELETON IN PLANTS
Authors: Staiger Chris J.
Published: July 2002

▪ Abstract  Plants have developed finely tuned, cellular mechanisms to respond to a variety of intrinsic and extrinsic stimuli. In several examples, these responses necessitate rearrangements of the cytoplasm that are coordinated by a network of actin microfilaments and microtubules, dynamic polymers collectively known as the cytoskeleton. This review focuses on five different cellular responses in which the actin cytoskeleton redistributes following extracellular stimulation: pollen tube tip growth and the self-incompatibility response; root hair responses to bacterial nodulation factors; light-mediated plastid positioning; nonhost resistance to fungal attack; and guard cell shape and turgor changes. For each of these systems, there is reasonable knowledge about what signals induce the plant response and the function(s) of the actin rearrangement. This review aims to build beyond a description of cytoskeletal changes and look at specific actin-binding proteins that have been implicated as effectors of each response, as sites of action for second messengers, and as fundamental coordinators of actin dynamics.
Structural Motifs in RNA
Authors: Moore P. B.
Published: July 2002

▪ Abstract  An RNA motif is a discrete sequence or combination of base juxtapositions found in naturally occurring RNAs in unexpectedly high abundance. Because all the motifs examined so far have three-dimensional structures independent of the context in which they are embedded, they are important components of the “kit” of structural elements from which RNAs are constructed. This review discusses the structures of the motifs that have been identified so far and speculates on the importance of their role in determining RNA conformation and their evolutionary origin.
H2-M3, A FULL-SERVICE CLASS IbHISTOCOMPATIBILITY ANTIGEN
Authors: Fischer Lindahl Kirsten , Byers Derek E. , Dabhi Vikram M. , Hovik Rolf , Jones Elsy P. , Smith Geoffrey P. , Wang Chyung-Ru , Xiao Hong , Yoshino Masayasu
Published: July 2002

▪ Abstract  H2-M3 is an MHC class Ib molecule of the mouse with a unique preference for N-formylated peptides, which may come from the N-termini of endogenous, mitochondrial proteins or foreign, bacterial proteins. The crystal structure of M3 revealed a hydrophobic peptide-binding groove with an occluded A pocket and the peptide shifted one residue relative to class Ia structures. The formyl group is held by a novel hydrogen bonding network, involving His9 on the bottom of the groove, and the side chain of the P1 methionine is lodged in the B pocket. M3 is a full-service histocompatibility (H) antigen, i.e. self-M3 can present endogenous peptides as minor H antigens and foreign, bacterial antigens in a defensive immune response to infection; and foreign M3 complexed with endogenous self-peptides can be recognized as an alloantigen. The hydrophobic groove of M3 may also allow it to present nonpeptide ligands in the manner of human CD1.
POINT DEFECT CHEMISTRY OF METAL OXIDE HETEROSTRUCTURES
Authors: Aggarwal Sanjeev , Ramesh R.
Published: July 2002

▪ Abstract  This article reviews the defect chemistry of perovskite ferroelectric oxides such as barium titanate and lead zirconate titanate. Such metal oxides are being considered for a wide range of applications that include nonvolatile memories and dynamic random access memories. Time-dependent degradation of these devices is controlled at least in part by point defects, which are determined by the defect chemistry of the material. The role of point defects on Pb(Zr,Ti)O3 thin film device properties such as fatigue, switching, polarization relaxation and imprint is discussed.
Postural Hypotension: Causes, Clinical Features, Investigation, and Management
Authors: Mathias, DPhil, DSc, FRCP Christopher J. , Kimber, BSc, MB, BS, MRCP Jeffery R.
Published: July 2002

Postural hypotension may result from various neurogenic and non-neurogenic causes. It may be a key feature of certain disorders, such as the primary chronic autonomic failure syndromes; it can complicate a variety of diseases, such as diabetes mellitus; and its prevalence increases with advancing age. When symptomatic, it may result in loss of consciousness and thus cause injury. Postural hypotension can be suspected from the patient's history and is readily documented in the clinic by measuring lying and standing blood pressure. The diagnosis ideally should be confirmed in the laboratory with additional tests to determine the cause and evaluate the functional deficit, so as to aid treatment. Treatment of the causative disorder is often curative when there are non-neurogenic causes. A combination of nonpharmacological and pharmacological measures is needed in the management of neurogenic postural hypotension.
Constructing Polyketides: From Collie to Combinatorial Biosynthesis
Authors: Bentley Ronald , Bennett J. W.
Published: July 2002

▪ Abstract  In a new golden age, polyketides are investigated and manipulated with the tools of molecular biology and genetics; hybrid polyketides can be produced. Pharmaceutical companies hope to find new and useful polyketide products, including antibiotics, anthelminthics, and immunosuppressants. This review describes the past developments (largely chemical) on which the present investigations are based, attempts to make sense of the expanding scope of polyketides, looks at the shifting research focus around polyketides, presents a working definition in biosynthetic terms, and takes note of recent work in combinatorial biosynthesis. Also discussed is the failure of the classical enzymological approach to polyketide biosynthesis.
Legionella PneumophilaPathogenesis: A Fateful Journey from Amoebae to Macrophages
Authors: Swanson M. S. , Hammer B. K.
Published: July 2002

▪ Abstract  Legionella pneumophila first commanded attention in 1976, when investigators from the Centers for Disease Control and Prevention identified it as the culprit in a massive outbreak of pneumonia that struck individuals attending an American Legion convention ( 84 ). It is now clear that this gram-negative bacterium flourishes naturally in fresh water as a parasite of amoebae, but it can also replicate within alveolar macrophages. L. pneumophila pathogenesis is discussed using the following model as a framework. When ingested by phagocytes, stationary-phase L. pneumophila bacteria establish phagosomes which are completely isolated from the endosomal pathway but are surrounded by endoplasmic reticulum. Within this protected vacuole, L. pneumophila converts to a replicative form that is acid tolerant but no longer expresses several virulence traits, including factors that block membrane fusion. As a consequence, the pathogen vacuoles merge with lysosomes, which provide a nutrient-rich replication niche. Once the amino acid supply is depleted, progeny accumulate the second messenger guanosine 3′,5′-bispyrophosphate (ppGpp), which coordinates entry into the stationary phase with expression of traits that promote transmission to a new phagocyte. A number of factors contribute to L. pneumophila virulence, including type II and type IV secretion systems, a pore-forming toxin, type IV pili, flagella, and numerous other factors currently under investigation. Because of its resemblance to certain aspects of Mycobacterium, Toxoplasma, Leishmania, and Coxiella pathogenesis, a detailed description of the mechanism used by L. pneumophila to manipulate and exploit phagocyte membrane traffic may suggest novel strategies for treating a variety of infectious diseases. Knowledge of L. pneumophila ecology may also inform efforts to combat the emergence of new opportunistic macrophage pathogens.
Proteins Shared by the Transcription and Translation Machines
Authors: Squires Catherine L. , Zaporojets Dmitry
Published: July 2002

▪ Abstract  It is becoming increasingly clear that the complex machines involved in transcription and translation, the two major activities leading to gene expression, communicate directly with one another by sharing proteins. For some proteins, such as ribosomal proteins S10 and L4, there is strong evidence of their participation in both processes, and much is known about their role in both activities. The exact roles and interactions of other proteins, such as Nus factors B and G, in both transcription and translation remain a mystery. Although there are not, at present, many examples of such shared proteins, the importance of understanding their behavior and intimate involvement with two major cellular machines is beginning to be appreciated. Studies related to the dual activities of these proteins and searches for more examples of proteins shared between the transcription and translation machines should lead to a better understanding of the communication between these two activities and the purposes it serves.
Challenges for Biomedical Informatics and Pharmacogenomics
Authors: Altman Russ B. , Klein Teri E.
Published: July 2002

Pharmacogenomics requires the integration and analysis of genomic, molecular, cellular, and clinical data, and it thus offers a remarkable set of challenges to biomedical informatics. These include infrastructural challenges such as the creation of data models and databases for storing these data, the integration of these data with external databases, the extraction of information from natural language text, and the protection of databases with sensitive information. There are also scientific challenges in creating tools to support gene expression analysis, three-dimensional structural analysis, and comparative genomic analysis. In this review, we summarize the current uses of informatics within pharmacogenomics and show how the technical challenges that remain for biomedical informatics are typical of those that will be confronted in the postgenomic era.
BACTERIAL AVIRULENCE GENES
Authors: Leach Jan E. , White Frank F.
Published: July 2002

▪ Abstract  Although more than 30 bacterial avirulence genes have been cloned and characterized, the function of the gene products in the elictitation of resistance is unknown in all cases but one. The product of avrD from Pseudomonas syringae pv. glycinea likely functions indirectly to elicit resistance in soybean, that is, evidence suggests the gene product is an enzyme involved in elicitor production. In most if not all cases, bacterial avirulence gene function is dependent on interactions with the hypersensitive response and pathogenicity (hrp) genes. Many hrp genes are similar to genes involved in delivery of pathogenicity factors in mammalian bacterial pathogens. Thus, analogies between mammalian and plant pathogens may provide needed clues to elucidate how virulence gene products control induction of resistance.
AMERICAN EXCEPTIONALISM
Authors: Shafer Byron E.
Published: July 2002

▪ Abstract  American exceptionalism is the oldest and most contentious of the alleged national exceptionalisms—arguments that a given nation must be understood in essentially idiosyncratic fashion. John Winthrop, Alexis de Tocqueville, and Karl Marx helped develop and sustain an American variant for the first 350 years of a separate American political life. Modern political scientists have addressed the notion in a more systematic and methodologically self-conscious manner during the past half century. Nevertheless, much of the argument revolves around conceptual issues, operational difficulties, and empirical traps, so that these must provide the contours of the subject here. Two major recent books with sharply divergent conclusions, both marshaling extensive empirical evidence, serve not only as a means of updating the classical argument and of presenting its modern opposition. Both also suggest—indeed, contribute—further reasons for the continuing lure of a difficult and divisive notion.
PUBLIC HEALTH IN CENTRAL AND EASTERN EUROPE AND THE ROLE OF ENVIRONMENTAL POLLUTION
Authors: Little R. E.
Published: July 2002

▪ Abstract  The central and eastern European countries that composed the former Eastern Bloc have experienced an alarming decline in public health since the dissolution of the Soviet Union. Death rates have increased in most age groups. Life expectancy, especially among males, has decreased in many countries; in Russia, male life expectancy dropped by six years between 1989 and 1994. By 2020, these countries are projected to have smaller increases in life expectancy than any other geographic region. The conditions responsible for the excess mortality are cardiovascular disease, cancer, and injuries among adults. The major factors in the sharp increase are poverty, social disintegration, and crime, overlaid on historically high rates of smoking, alcohol use, and psychosocial stress. Environmental pollution, although common and sometimes severe in the former Eastern Bloc, is another, albeit not the chief, cause of the sharp decline in public health since 1989.
Parallel Morning and Evening Surge in Stroke Onset, Blood Pressure, and Physical Activity
Authors: Stergiou George S. , Vemmos Kostas N. , Pliarchopoulou Kyriaki M. , Synetos Andreas G. , Roussias Leonidas G. , Mountokalakis Theodore D.
Published: July 2002

Background and Purpose

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A circadian variation with a morning peak on waking and arising is known to occur in both blood pressure (BP) and cardiovascular event onset. A second peak in BP has been described to occur after an afternoon sleep (siesta). This study was designed to investigate the hypothesis that the 2-peak diurnal variation of BP is dependent on physical activity and occurs in parallel with the diurnal variation of stroke onset.

Methods

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The diurnal variation of stroke onset was compared with the diurnal variation of BP, pulse rate (PR), and physical activity in 3 independent groups of Greek hypertensives 51 to 80 years of age (633 stroke patients, 379 subjects with 24-hour ambulatory BP monitoring, and 50 subjects with 24-hour physical activity monitoring through wrist devices).

Results

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The diurnal variation of stroke onset, BP, and PR all showed 1 morning and 1 evening peak with a decline in the afternoon and at night that occurred in parallel with the diurnal variation in physical activity (
P
<0.001 for differences among morning, afternoon, evening, and nighttime intervals in BP, PR, activity, and stroke). The afternoon decline in BP, PR, and activity was significant only in subjects with a siesta.

Conclusions

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The 2-peak diurnal variation in stroke onset occurred in parallel with the variation in BP, PR, and physical activity. These data support the hypothesis that an abrupt change in physical activity is not only a major determinant of the 2-peak diurnal variation of BP but also an important triggering factor for a cerebrovascular event.
Design and Enhanced Evaluation of a Robust Anaphor Resolution Algorithm
Authors: Stuckardt Roland
Published: July 2002

Syntactic coindexing restrictions are by now known to be of central importance to practical anaphor resolution approaches. Since, in particular due to structural ambiguity, the assumption of the availability of a unique syntactic reading proves to be unrealistic, robust anaphor resolution relies on techniques to overcome this deficiency.

This paper describes the ROSANA approach, which generalizes the verification of coindexing restrictions in order to make it applicable to the deficient syntactic descriptions that are provided by a robust state-of-the-art parser. By a formal evaluation on two corpora that differ with respect to text genre and domain, it is shown that ROSANA achieves high-quality robust coreference resolution. Moreover, by an in-depth analysis, it is proven that the robust implementation of syntactic disjoint reference is nearly optimal. The study reveals that, compared with approaches that rely on shallow preprocessing, the largely nonheuristic disjoint reference algorithmization opens up the possibility for a slight improvement. Furthermore, it is shown that more significant gains are to be expected elsewhere, particularly from a text-genre-specific choice of preference strategies.

The performance study of the ROSANA system crucially rests on an enhanced evaluation methodology for coreference resolution systems, the development of which constitutes the second major contribution of the paper. As a supplement to the model-theoretic scoring scheme that was developed for the Message Understanding Conference (MUC) evaluations, additional evaluation measures are defined that, on one hand, support the developer of anaphor resolution systems, and, on the other hand, shed light on application aspects of pronoun interpretation.
VI. Genome Structure and Cognitive Map of Williams Syndrome
Authors: Korenberg Julie R. , Chen Xiao-Ning , Hirota Hamao , Lai Zona , Bellugi Ursula , Burian Dennis , Roe Bruce , Matsuoka Rumiko
Published: July 2002

Williams syndrome (WMS) is a most compelling model of human cognition, of human genome organization, and of evolution. Due to a deletion in chromosome band 7q11.23, subjects have cardiovascular, connective tissue, and neurode-velopmental deficits. Given the striking peaks and valleys in neurocognition including deficits in visual-spatial and global processing, preserved language and face processing, hypersociability, and heightened affect, the goal of this work has been to identify the genes that are responsible, the cause of the deletion, and its origin in primate evolution. To do this, we have generated an integrated physical, genetic, and transcriptional map of the WMS and flanking regions using multicolor metaphase and interphase fluorescence in situ hybridization (FISH) of bacterial artificial chromosomes (BACs) and P1 artificial chromosomes (PACs), BAC end sequencing, PCR gene marker and microsatellite, large-scale sequencing, cDNA library, and database analyses. The results indicate the genomic organization of the WMS region as two nested duplicated regions flanking a largely single-copy region. There are at least two common deletion breakpoints, one in the centromeric and at least two in the telomeric repeated regions. Clones anchoring the unique to the repeated regions are defined along with three new pseudogene families. Primate studies indicate an evolutionary hot spot for chromosomal inversion in the WMS region. A cognitive phenotypic map of WMS is presented, which combines previous data with five further WMS subjects and three atypical WMS subjects with deletions; two larger (deleted for D7S489L) and one smaller, deleted for genes telomeric to FZD9, through LIMK1, but not WSCR1 or telomeric. The results establish regions and consequent gene candidates for WMS features including mental retardation, hypersociability, and facial features. The approach provides the basis for defining pathways linking genetic underpinnings with the neuroanatomical, functional, and behavioral consequences that result in human cognition.
Self-Organizing Dynamics of Lexical Access in Normals and Aphasics
Authors: McNellis Mark G. , Blumstein Sheila E.
Published: July 2002

The goal of this article is to illustrate the application of self-organizing dynamics in the design of a model of lexical access. We focus particularly on the mapping of sound structure on to the lexicon and the influence of that structure on lexical access. The approach is tested in a series of two sets of simulations that explicate how lexical access might occur in normal subjects and aphasic patients. Both sets of simulations address the behavioral effects of both phonological and phonetic variability of prime stimuli on the magnitude of semantic priming. Results show that the model can successfully account for the behavioral effects associated with several kinds of acoustic manipulation, competitor presence, and the unfolding of those effects over time—primarily because it balances three important control parameters: resting lexical activation, positive feedback, and negative feedback. These simulations are offered as support (in the form of an existence proof) that deficits in the degree of lexical activation can account for the lexical processing impairments shown by Broca's aphasics who have reduced lexical activation, and Wernicke's aphasics who have increased lexical activation. Overall, results suggest that the present approach promises to offer a coherent theoretical framework within which to link empirical evidence in language processing and cognitive neuroscience in terms of possible underlying mechanisms.
Auditory Priming within and across Modalities: Evidence from Positron Emission Tomography
Authors: Badgaiyan Rajendra D. , Schacter Daniel L. , Alpert Nathaniel M.
Published: July 2002

Previous neuroimaging studies of perceptual priming have reported priming-related decreases in the extrastriate cortex. However, because these experiments have used visual stimuli, it is unclear whether the observed decreases are associated specifically with some aspect of visual perceptual processing or with more general aspects of priming. We studied within-and cross-modality priming using an auditory word stem completion paradigm. Positron emission tomography (PET) images were obtained during stem completion and a fixation task. Within-modality auditory priming was associated with blood flow decreases in the extrastriate cortex (bilateral), medial/ right anterior prefrontal cortex, right angular gyrus, and precuneus. In cross-modality priming, the study list was presented visually, and subjects completed auditory word stems. Cross-modality priming was associated with trends for blood flow decreases in the left angular gyrus and increases in the medial/right anterior prefrontal cortex. Results thus indicate that reduced activity in the extrastriate cortex accompanies within-modality priming in both visual and auditory modalities.
Global Village, Local Universe: A Statement of Identity
Authors: Fischman Rajmil
Published: July 2002

In this article, the author presents a personal view of his compositional identity as an instance of one of the innumerable possible outcomes within a civilization that has become global and individualistic at the same time. The author situates identity within the context of historical, political and social backgrounds and examines it from the point of view of the mechanics of its realization, social function and reach, and cultural baggage—including musical influences from various traditions, technology and science.