bluuebunny/crossref_metadata_2025 huggingface dataset:
Training wheels in a user interface
Authors: Carroll John M. , Carrithers Caroline
Published: July 2002

New users of high-function application systems can become frustrated and confused by the errors they make in the early stages of learning. A training interface for a commercial word processor was designed to make typical and troublesome error states “unreachable,” thus eliminating the sources of some new-user learning problems. Creating a training environment from the basic function of the system itself afforded substantially faster learning coupled with better learning achievement and better performance on a comprehension post-test. A control group spent almost a quarter of their time recovering from the error states that the training interface blocked off. We speculate on how this training strategy might be refined, and more generally, on how function should be organized in a user interface.
Memory occupancy patterns in garbage collection systems
Authors: Davies D. Julia. M.
Published: July 2002

Some programming languages and computer systems use dynamic memory allocation with garbage collection. It would be useful to understand how the utilization of memory depends on the stochastic parameters describing the size and life distributions of the cells. We consider a class of dynamic storage allocation systems which use a first-fit strategy to allocate cells and perform noncompacting garbage collections to recover free memory space when memory becomes fully occupied. A formula is derived for the expected number of holes (available cells) in memory immediately following a garbage collection which specializes to an analogue of Knuth's 'Fifty Percent' rule for nongarbage-collection systems. Simulations confirm the rule for exponentially distributed cell lifetimes. Other lifetime distributions are discussed. The memory-size requirements for noncompacting garbage collection are also analyzed.
Form management
Authors: Tsichritzis D.
Published: July 2002

This paper consists of three interrelated parts. In the first part
forms
are intoduced as an abstraction and generalization of business paper forms. A set of facilities for the manipulation of forms and their contents is outlined. Forms can be created, stored, found, viewed in different media, mailed, and located by office workers. Data on forms can also be processed in a completely integrated way. The facilities are discussed both abstractly and in relation to a prototype system. In the second part a facility is outlined for the specification and implementation of automatic form procedures. These procedures specify actions on forms which are triggered automatically when certain preconditions are met. The preconditions, actions, and specification method are based on forms. The discussion is centered on our implementation of such a specification framework. Finally, in the third part, techniques for the analysis of office flow are specified. An algorithm is outlined for the categorization of forms into classes depending on the local routing and actions on the forms. In this way, we can obtain the paths that forms take and analyze the system for correctness and loading characteristics.
A user-friendly algorithm
Authors: Dwyer Barry
Published: July 2002

The interface between a person and a computer can be looked at from either side. Programmers tend to view it from the inside; they consider it their job to defend the machine against errors made by its users. From the outside, the user sees his/her problems as paramount. He/she is often at odds with this complex, inflexible, albeit powerful tool. The needs of both people and machines can be reconciled; users will respond more efficiently and intelligently if they receive meaningful feedback. A “user-friendly” algorithm that covers a wide range of interactive environments and is typical of most operating systems and many application programs is presented.
The Cornell program synthesizer
Authors: Teitelbaum Tim , Reps Thomas
Published: July 2002

Programs are not text; they are hierarchical compositions of computational structures and should be edited, executed, and debugged in an environment that consistently acknowledges and reinforces this viewpoint. The Cornell Program Synthesizer demands a structural perspective at all stages of program development. Its separate features are unified by a common foundation: a grammar for the programming language. Its full-screen derivation-tree editor and syntax-directed diagnostic interpreter combine to make the Synthesizer a powerful and responsive interactive programming tool.
Counting large numbers of events in small registers
Authors: Morris Robert
Published: July 2002

It is possible to use a small counter to keep approximate counts of large numbers. The resulting expected error can be rather precisely controlled. An example is given in which 8-bit counters (bytes) are used to keep track of as many as 130,000 events with a relative error which is substantially independent of the number
n
of events. This relative error can be expected to be 24 percent or less 95 percent of the time (i.e.
σ
=
n
/8). The techniques could be used to advantage in multichannel counting hardware or software used for the monitoring of experiments or processes.
Recursive computation of certain derivatives&a study of error propagation
Authors: Gautschi Walter , Klein Bruce J.
Published: July 2002

A brief study is made of the propagation of errors in linear first-order difference equations. The recursive computation of successive derivatives of

e
x

/
x
and (cos
x
)/
x
is considered as an llustration.
Selfcipher
Authors: Pelta Harold N.
Published: July 2002

Selfcipher is a programming system designed to provide a quasi-actual language for preparing programs automatically for large scale digital computers.
Coding isomorphisms
Authors: Lynch William C.
Published: July 2002

The coding of external symbols into symbols internal to a computer can sometimes be carried out in such a way that relevant informational properties are preserved, but in a form much more easily dealt with. A case in point is presented.
The department of computer mathematics at Moscow State University
Authors: Berezin I. S.
Published: July 2002

For the preparation of specialists in computer and machine mathematics and the development of scientific work in this area, the department of computer mathematics was created in 1949 in Moscow State University within the staff of the mechanical-mathematics faculty. This was headed by Academician S. L. Sobolev beginning in 1952.
The multilingual terminology project
Authors: Holmstrom J. E.
Published: July 2002

One of the most important and useful of the tasks which an international organization concerned with some specialized branch of pure or applied science is particularly well able to perform is the improvement of the technical terminology appertaining to that.
Implementation of logical query languages for databases
Authors: Ullman Jeffrey D.
Published: July 2002

We examine methods of implementing queries about relational databases in the case where these queries are expressed in first-order logic as a collection of Horn clauses. Because queries may be defined recursively, straightforward methods of query evaluation do not always work, and a variety of strategies have been proposed to handle subsets of recursive queries. We express such query evaluation techniques as “capture rules” on a graph representing clauses and predicates. One essential property of capture rules is that they can be applied independently, thus providing a clean interface for query-evaluation systems that use several different strategies in different situations. Another is that there be an efficient test for the applicability of a given rule. We define basic capture rules corresponding to application of operators from relational algebra, a top-down capture rule corresponding to “backward chaining,” that is, repeated resolution of goals, a bottom-up rule, corresponding to “forward chaining,” where we attempt to deduce all true facts in a given class, and a “sideways” rule that allows us to pass results from one goal to another.
Modeling concepts for VLSI CAD objects
Authors: Batory D. S. , Kim Won
Published: July 2002

VLSI CAD applications deal with design objects that have an interface description and an implementation description. Versions of design objects have a common interface but differ in their implementations. A molecular object is a modeling construct which enables a database entity to be represented by two sets of heterogeneous records, one set describes the object's interface and the other describes its implementation. Thus a reasonable starting point for modeling design objects is to begin with the concept of molecular objects.

In this paper, we identify modeling concepts that are fundamental to capturing the semantics of VLSI CAD design objects and versions in terms of molecular objects. A provisional set of user operations on design objects, consistent with these modeling concepts, is also defined. The modeling framework that we present has been found useful for investigating physical storage techniques and change notification problems in version control.
Dagwood
Authors: Freeman Timothy S. , Imirzian Gregory M. , Kaltofen Erich , Yagati Lakshman
Published: July 2002

We discuss the design, implementation, and benchmarking of a system that can manipulate symbolic expressions represented by their straight-line computations. Our system is capable of performing rational arithmetic on, evaluating, differentiating, taking greatest common divisors of, and factoring polynomials in straight-line format. The straight-line results can also be converted to standard, sparse format. We show by example that our system can handle problems for which conventional methods lead to excessive intermediate expression swell.
Data compression
Authors: Lelewer Debra A. , Hirschberg Daniel S.
Published: July 2002

This paper surveys a variety of data compression methods spanning almost 40 years of research, from the work of Shannon, Fano, and Huffman in the late 1940s to a technique developed in 1986. The aim of data compression is to reduce redundancy in stored or communicated data, thus increasing effective data density. Data compression has important application in the areas of file storage and distributed systems. Concepts from information theory as they relate to the goals and evaluation of data compression methods are discussed briefly. A framework for evaluation and comparison of methods is constructed and applied to the algorithms presented. Comparisons of both theoretical and empirical natures are reported, and possibilities for future research are suggested.
A rule-based message filtering system
Authors: Pollock Stephen
Published: July 2002

Much computerized support for knowledge workers has consisted of tools to handle low-level functions such as distribution, storage, and retrieval of information. However, the higher level processes of making decisions and taking actions with respect to this information have not been supported to the same degree. This paper describes the ISCREEN prototype system for screening text messages. ISCREEN includes a high-level interface for users to define rules, a component that screens text messages, and a conflict detection component that examines rules for inconsistencies. An explanation component uses text generation to answer user queries about past or potential system actions based on Grice's conversational maxims.
HAM: a general purpose hypertext abstract machine
Authors: Campbell Brad , Goodman Joseph,M.
Published: July 2002

The HAM is a transaction-based server for a hyper text storage system. The server is designed to handle multiple users in a networked environment. The storage system consists of a collection of contexts, nodes, links, and attributes that make up a hypertext graph. The versatility of the HAM can be illustrated by showing how Guide buttons, intermedia webs, and NoteCard FileBoxes can be implemented using its storage model.
“Sometimes” and “not never” revisited
Authors: Emerson E. Allen , Halpern Joseph Y.
Published: July 2002

The differences between and appropriateness of branching versus linear time temporal logic for reasoning about concurrent programs are studied. These issues have been previously considered by Lamport. To facilitate a careful examination of these issues, a language, CTL
*
, in which a universal or existential path quantifier can prefix an arbitrary linear time assertion, is defined. The expressive power of a number of sublanguages is then compared. CTL* is also related to the logics MPL of Abrahamson and PL of Harel, Kozen, and Parikh. The paper concludes with a comparison of the utility of branching and linear time temporal logics.
A fully sequential procedure for indifference-zone selection in simulation
Authors: Kim Seong-Hee , Nelson Barry L.
Published: July 2002

We present procedures for selecting the best or near-best of a finite number of simulated systems when best is defined by maximum or minimum expected performance. The procedures are appropriate when it is possible to repeatedly obtain small, incremental samples from each simulated system. The goal of such a sequential procedure is to eliminate, at an early stage of experimentation, those simulated systems that are apparently inferior, and thereby reduce the overall computational effort required to find the best. The procedures we present accommodate unequal variances across systems and the use of common random numbers. However, they are based on the assumption of normally distributed data, so we analyze the impact of batching (to achieve approximate normality or independence) on the performance of the procedures. Comparisons with some existing indifference-zone procedures are also provided.
Searching in metric spaces
Authors: Chávez Edgar , Navarro Gonzalo , Baeza-Yates Ricardo , Marroquín José Luis
Published: July 2002

The problem of searching the elements of a set that are close to a given query element under some similarity criterion has a vast number of applications in many branches of computer science, from pattern recognition to textual and multimedia information retrieval. We are interested in the rather general case where the similarity criterion defines a metric space, instead of the more restricted case of a vector space. Many solutions have been proposed in different areas, in many cases without cross-knowledge. Because of this, the same ideas have been reconceived several times, and very different presentations have been given for the same approaches. We present some basic results that explain the intrinsic difficulty of the search problem. This includes a quantitative definition of the elusive concept of "intrinsic dimensionality." We also present a unified view of all the known proposals to organize metric spaces, so as to be able to understand them under a common framework. Most approaches turn out to be variations on a few different concepts. We organize those works in a taxonomy that allows us to devise new algorithms from combinations of concepts not noticed before because of the lack of communication between different communities. We present experiments validating our results and comparing the existing approaches. We finish with recommendations for practitioners and open questions for future development.
Cluster-aware iterative improvement techniques for partitioning large VLSI circuits
Authors: Dutt Shantanu , Deng Wenyong
Published: July 2002

Move-based iterative improvement partitioning (IIP) methods, such as the Fiduccia-Mattheyses (FM) algorithm [Fidducia and Mattheyses 1982] and Krishnamurthy's Look-Ahead (LA) algorithm [Krishnamurthy 1984], are widely used in VLSI CAD applications, largely due to their time efficiency and ease of implementation. This class of algorithms is of the "local/greedy improvement" type, and they generate relatively high-quality results for small and medium-size circuits. However, as VLSI circuits become larger, these algorithms suffer a rapid deterioration in solution quality. We propose new IIP methods CLIP and CDIP that select cells to move with a view to moving clusters that straddle the two subsets of a partition, into one of the subsets. The new algorithms significantly improve partition quality while preserving the advantage of time efficiency. Experimental results on 25 medium to large-size ACM/SIGDA benchmark circuits show up to 70% improvement over FM in mincut, and average mincut improvements of about 35% over all circuits and 47% over large circuits. They also outperform state-of-the-art non-IIP techniques, the quadratic-programming-based method Paraboli [Reiss et al. 1994] and the spectral partitioner MELO [Alpert and Yao 1995], by about 17% and 23%, respectively, with less CPU time. This demonstrates the potential of sophisticated IIP algorithms in dealing with the increasing complexity of emerging VLSI circuits. We also compare CLIP and CDIP to hMetis [Karypis et al. 1997], one of the best of the recent state-of-the-art partitioners that are based on the multilevel paradigm (others include ML

c

[Alpert et al. 1997] and LSR/MFFS [Cong et al. 1997]). The results show that one scheme of hMetis is 8% worse than CLIP/CDIP and the other two schemes are only 2--4% better. However, CLIP/CDIP have advantages over hMetis and other multilevel partitioners that outweigh these minimal mincut improvements. The first is much faster times-to-solution (for example, one of our best schemes CLIP-LA2 is 6.4 and 11.75 times faster than the two best hMetis schemes) and much better scalability with circuit size (e.g., for the largest circuit with about 162K nodes, CLIP-LA2 is 10.4 and and 21.5 times faster and obtains better solution qualities than the two best hMetis schemes). Second, CLIP/CDIP are "flat" partitioners, while multilevel techniques perform a sequence of node clustering/coarsening before partitioning the circuit. In complex placement applications such as timing-driven placement in the presence of multiple constraints, such circuit coarsening can hide crucial information needed for good-quality solutions, thus making the partitioning process oblivious to them. This, however, is not a problem with flat partitioners like CLIP/CDIP that can take all important parameters into account while partitioning. All these advantages make CLIP/CDIP suitable for use in complex physical design problems for large, deep-submicron VLSI circuits.
A tree-based algorithm for distributed mutual exclusion
Authors: Raymond Kerry
Published: July 2002

We present an algorithm for distributed mutual exclusion in a computer network of
N
nodes that communicate by messages rather than shared memory. The algorithm uses a spanning tree of the computer network, and the number of messages exchanged per critical section depends on the topology of this tree. However, typically the number of messages exchanged is
O
(log
N
) under light demand, and reduces to approximately four messages under saturated demand.

Each node holds information only about its immediate neighbors in the spanning tree rather than information about all nodes, and failed nodes can recover necessary information from their neighbors. The algorithm does not require sequence numbers as it operates correctly despite message overtaking.
gIBIS: a hypertext tool for exploratory policy discussion
Authors: Conklin Jeff , Begeman Michael L.
Published: July 2002

This paper describes an application-specific hypertext system designed to facilitate the capture of early design deliberations. It implements a specific method, called Issue Based Information Systems (IBIS), which has been developed for use on large, complex design problems. The hypertext system described here, gIBIS (for graphical IBIS), makes use of color and a high-speed relational database server to facilitate building and browsing typed IBIS networks. Further, gIBIS is designed to support the collaborative construction of these networks by any number of cooperating team members spread across a local area network. Early experiments suggest that the IBIS method is still incomplete, but there is a good match between the tool and method even in this experimental version.
Performance evaluation of programs for certain Bessel functions
Authors: Cody W. J. , Stoltz L.
Published: July 2002

This paper presents methods for performance evaluation of the
K
Bessel functions. Accuracy estimates are based on comparisons involving the multiplication theorem. Some ideas for checking robustness are also given. The techniques used here are easily extended to the
Y
Bessel functions and, with a little more effort, to the
I
and
J
functions. Details on a specific implementation for testing the
K
Bessel functions are included.
A framework for effective retrieval
Authors: Yu C. T. , Meng W. , Park S.
Published: July 2002

The aim of an effective retrieval system is to yield high recall and precision (retrieval effectiveness). The nonbinary independence model, which takes into consideration the number of occurrences of terms in documents, is introduced. It is shown to be optimal under the assumption that terms are independent. It is verified by experiments to yield significant improvement over the binary independence model. The nonbinary model is extended to normalized vectors and is applicable to more general queries.

Various ways to alleviate the consequences of the term independence assumption are discussed. Estimation of parameters required for the nonbinary independence model is provided, taking into consideration that a term may have different meanings.
Unification in primal algebras, their powers and their varieties
Authors: Nipkow Tobias
Published: July 2002

This paper examines the unification problem in the class of
primal algebras
and the varieties they generate. An algebra is called primal if every function on its carrier can be expressed just in terms of the basic operations of the algebra. The two-element Boolean algebra is the simplest nontrivial example: Every truth-function can be realized in terms of the basic connectives, for example, negation and conjunction.

It is shown that unification in primal algebras is unitary, that is, if an equation has a solution, it has a single most general one. Two unification algorithms, based on equation-solving techniques for Boolean algebras due to Boole and Lo¨wenheim, are studied in detail. Applications include certain finite Post algebras and matrix rings over finite fields. The former are algebraic models for many-valued logics, the latter cover in particular modular arithmetic.

Then unification is extended from primal algebras to their direct powers, which leads to unitary unification algorithms covering finite Post algebras, finite, semisimple Artinian rings, and finite, semisimple nonabelian groups.

Finally the fact that the variety generated by a primal algebra coincides with the class of its subdirect powers is used. This yields unitary unification algorithms for the equational theories of Post algebras and
p
-rings.
Practicing Social Anthropology in India
Authors: Srinivas M. N.
Published: July 2002

After completing a BA in social philosophy from Mysore, I went to Bombay to do graduate work in sociology with GS Ghurye, who had been a student of WHR Rivers at Cambridge in the 1920s. At the end of eight years, I became disillusioned with diffusionism and unfocused ethnography. I then went to Oxford, where I worked first with AR Radcliffe-Brown and then EE Evans-Pritchard. At Oxford, I became a structural- functionalist, albeit a somewhat skeptical one. After teaching at Oxford from 1948 to 1951, I returned to India to teach sociology at the University of Baroda. Eight years later, I went to the University of Delhi as Professor of Sociology, and finally moved to Bangalore in 1972 to start, with VKRV Rao, the Institute for Social and Economic Change. As an anthropologist, I am somewhat of a maverick in that I study my own culture and not any distant Other.
Europeanization
Authors: Borneman John , Fowler Nick
Published: July 2002

As a strategy of self-representation and a device of power, Europeanization is fundamentally reorganizing territoriality and peoplehood, the two principles of group identification that have shaped modern European order. It is the result of a new level and intensity of integration that has been a reaction to the destruction of this century's first and second world wars and the collapse of the cold-war division of Europe into an East and West. Driven above all by the organizational and administrative power of the European Union (EU), Europeanization is still distinct from the EU. Neither Europeanization nor the EU will replace the nation-state, which, for now, remains a superior form for organizing democratic participation and territoriality. Nonetheless, they will likely force states to yield some questions of sovereignty—above all, military, political, and economic—to the EU or other transnational bodies. Nations are now being brought into new relations with each other, creating new alliances and enmities, and are even recreating themselves. The authors explore five domains of practice where the process of Europeanization might be fruitfully studied: language, money, tourism, sex, and sport. They suggest dealing with the EU as a continental political unit of a novel order and with Europeanization pragmatically as both a vision and a process.
OPTICAL SPECTRA OF SUPERNOVAE
Authors: Filippenko Alexei V.
Published: July 2002

▪ Abstract  The temporal evolution of the optical spectra of various types of supernovae (SNe) is illustrated, in part to aid observers classifying supernova candidates. Type II SNe are defined by the presence of hydrogen, and they exhibit a very wide variety of photometric and spectroscopic properties. Among hydrogen-deficient SNe (Type I), three subclasses are now known: those whose early-time spectra show strong Si II (Ia), prominent He I (Ib), or neither Si II nor He I (Ic). The late-time spectra of SNe Ia consist of a multitude of blended emission lines of iron-group elements; in sharp contrast, those of SNe Ib and SNe Ic (which are similar to each other) are dominated by several relatively unblended lines of intermediate-mass elements. Although SNe Ia, which result from the thermonuclear runaway of white dwarfs, constitute a rather homogeneous subclass, important variations in their photometric and spectroscopic properties are undeniably present. SNe Ib/Ic probably result from core collapse in massive stars largely stripped of their hydrogen (Ib) and helium (Ic) envelopes, and hence they are physically related to SNe II. Indeed, the progenitors of some SNe II seem to have only a low-mass skin of hydrogen; their spectra gradually evolve to resemble those of SNe Ib. In addition to the two well-known photometric subclasses (linear and plateau) of SNe II, which may exhibit minor spectroscopic differences, there is a new subclass (SNe IIn) distinguished by relatively narrow emission lines with little or no P Cygni absorption component and slowly declining light curves. These objects probably have unusually dense circumstellar gas with which the ejecta interact.
Structure and Function of CytochromebcComplexes
Authors: Berry Edward A. , Guergova-Kuras Mariana , Huang Li-shar , Crofts Antony R.
Published: July 2002

▪ Abstract  The cytochrome bc complexes represent a phylogenetically diverse group of complexes of electron-transferring membrane proteins, most familiarly represented by the mitochondrial and bacterial bc1complexes and the chloroplast and cyanobacterial b6f complex. All these complexes couple electron transfer to proton translocation across a closed lipid bilayer membrane, conserving the free energy released by the oxidation-reduction process in the form of an electrochemical proton gradient across the membrane. Recent exciting developments include the application of site-directed mutagenesis to define the role of conserved residues, and the emergence over the past five years of X-ray structures for several mitochondrial complexes, and for two important domains of the b6f complex.
Function, Structure, and Mechanism of Intracellular Copper Trafficking Proteins
Authors: Huffman David L. , O'Halloran Thomas V.
Published: July 2002

▪ Abstract  Genetic, biochemical, and spectroscopic studies have established a new function for an intracellular protein, i.e., guiding and inserting a copper cofactor into the active site of a target enzyme. Studies of these new proteins have revealed a fundamental aspect of copper physiology, namely the vast overcapacity of the cytoplasm for copper sequestration. This finding framed the mechanistic, energetic, and structural aspects of intracellular copper trafficking proteins. One hallmark of the copper chaperones is the similarity of the protein fold between the chaperone and its target enzyme. The surface residues presented by each partner, however, are quite different, and some initial findings concerning the complementarity of these interfaces have led to mechanistic insights. The copper chaperones appear to lower the activation barrier for metal transfer into specific protein-binding sites. The manner in which they facilitate metal insertion appears to involve a docking of the metal donor and acceptor sites in close proximity to one another. Although the intimate mechanism is still open, it appears that a low activation barrier for metal transfer is achieved by a network of coordinate-covalent, electrostatic, and hydrogen bonding interactions in the vicinity of the metal-binding site itself.
In Vivo Near-Infrared Spectroscopy
Authors: Rolfe Peter
Published: July 2002

▪ Abstract  Interrogation of tissue with light offers the potential for noninvasive chemical measurement, and penetration with near-infrared wavelengths (750–1000 nm) is greater than with visible light. Specific absorption by clinically relevant compounds such as oxy- and deoxyhemoglobin and the intracellular respiratory enzyme cytochrome oxidase enable in vivo measurement of these to be performed safely and conveniently. This is the basis of in vivo near-infrared spectroscopy (ivNIRS). Multiple scattering of the interrogating beam by tissues leads to an optical path that is considerably longer than the simple physical pathlength and this complicates the analysis. Modeling of photon propagation through tissues with, for example, finite element and Monte Carlo methods, is assisting in improving the ivNIRS methodology. Instrumentation has advanced from simple continuous wave approaches, through time-resolved methods based on either time-domain or frequency-domain approaches, to spatially resolved measurement based on diffuse reflectance. Initial clinical applications were for monitoring the brain in the neonate and fetus and muscle in adults. Currently, use in adults and children for neurological assessments are of growing interest.
SCF and Cullin/RING H2-Based Ubiquitin Ligases
Authors: Deshaies R. J.
Published: July 2002

▪ Abstract  Protein degradation is deployed to modulate the steady-state abundance of proteins and to switch cellular regulatory circuits from one state to another by abrupt elimination of control proteins. In eukaryotes, the bulk of the protein degradation that occurs in the cytoplasm and nucleus is carried out by the 26S proteasome. In turn, most proteins are thought to be targeted to the 26S proteasome by covalent attachment of a multiubiquitin chain. Ubiquitination of proteins requires a multienzyme system. A key component of ubiquitination pathways, the ubiquitin ligase, controls both the specificity and timing of substrate ubiquitination. This review is focused on a conserved ubiquitin ligase complex known as SCF that plays a key role in marking a variety of regulatory proteins for destruction by the 26S proteasome.
Dating Modern Deltas: Progress, Problems, and Prognostics
Authors: Stanley Jean-Daniel
Published: July 2002

▪ Abstract  Radiocarbon dating is the method most frequently used to date Holocene deltaic sequences, but less than one quarter of 14C dates are within ±500 years of predicted age. Such dates tend to be unreliable, in other words, often too old and commonly inverted upsection, and core sample dates obtained near deltaic plain surfaces may be as old as mid- to late Holocene. Stratigraphic irregularities result primarily from downslope reworking of upland alluvial sediment, with displacement of “old carbon” in the sediment that accumulates in lower valleys and deltaic plains. Use of dates that are too old results in inaccurately calculated rates (most often too low) of relative sea-level rise and/or land subsidence. More reliable timing of deltaic sediment requires a multiple-method dating approach, including, where possible, identification of associated archaeological material. Developing an accurate dating strategy is a critical step for implementing reliable coastal protection measures needed for the rapidly increasing human populations in these low-lying, vulnerable nearshore settings.
THE ECOLOGICAL EVOLUTION OF REEFS
Authors: Wood Rachel
Published: July 2002

▪ Abstract  Many groups of extinct and extant organisms have aggregated to form reefs for over 3.5 billion yr (Ga). Most of these communities, however, grew under ecological and environmental controls profoundly different from those that govern modern coral reefs. Not only has the global distribution of reefs varied considerably through geological time—determined largely by sea level, and latitudinal temperature/saturation gradients—but more importantly the trophic demands of reef-building organisms have changed, as has the degree of biological disturbance faced by sessile biota in shallow marine environments.

Reefs differentiated into open surface and cryptic communities as soon as open frameworks developed in the Proterozoic, some 1.9 million yr ago (mya) and diverse and complex ecosystems were established by the early Cambrian (∼520 mya). Calcified heterotrophs were conspicuous in reefs during the Paleozoic and early Mesozoic, but considerable rigidity was imparted to these often otherwise fragile communities both by indirect microbial processes that induced the formation of carbonate and by rapid early cementation. While photosymbiosis was probably acquired by scleractinian corals early in their history (∼210 mya), this does not appear to have immediately conferred a superior reef-building ability. Large, modular corals and coralline algae showed notable powers of regeneration after partial mortality but poor ability to compete with macroalgae for limited substrate in the absence of intense herbivory; they did not rise to prominence in reef communities until the early to mid-Cenozoic. This may be related to the appearance at this time of major predator groups such as echinoids, limpets, and particularly fish that are capable of rapid algal denudation and excavation. The existence of this reciprocal relationship is corroborated by the observation that branching corals, which appear to flourish because and not in spite of breakage, show a particularly dramatic increase in diversity coincident with the increase in predation pressure from the late Mesozoic onwards.
HARMFUL ALGAL BLOOMS: An Emerging Public Health Problem with Possible Links to Human Stress on the Environment
Authors: Morris J. Glenn
Published: July 2002

▪ Abstract  Of the thousands of species of microalgae that form the base of the marine food chain, only a small number are toxic or harmful. However, when these toxic species proliferate, they can cause massive kills of fish and shellfish, mortality among marine mammals and seabirds, substantive alterations of marine habitats, and human illness and death. Currently, six distinct human clinical syndromes associated with harmful algal blooms are recognized: ciguatera fish poisoning, paralytic shellfish poisoning, neurotoxic shellfish poisoning, diarrhetic shellfish poisoning, amnesic shellfish poisoning, and Pfiesteria-associated syndrome. Human illnesses are caused by toxins produced by these microorganisms, acquired either by passage through the food chain or direct skin or respiratory contact. Syndromes frequently include debilitating neurologic manifestations and, in some instances, may progress to death. There is a perception among investigators that the number of harmful algal blooms is increasing, as is the range of toxic species. It has been postulated that this increase is caused by human-related phenomena such as disruption of ecosystems, nutrient enrichment of waterways, and climatic change. In environmental studies, attention has traditionally focused on direct human health effects of pollutants. Harmful algal blooms are an example of an alternative paradigm, in which human-induced stress on complex ecologic systems leads to the emergence of new, potentially harmful microorganisms (or the reemergence of “old” pathogens from previously restricted environmental niches), which, in turn, cause human disease. Although data are lacking to fully substantiate this latter model, it provides a useful conceptual framework to assess data needs and consider public health interventions.
DIRECT SIMULATION MONTE CARLO: Recent Advances and Applications
Authors: Oran E.S. , Oh C.K. , Cybyk B.Z.
Published: July 2002

▪ Abstract  The principles of and procedures for implementing direct simulation Monte Carlo (DSMC) are described. Guidelines to inherent and external errors common in DSMC applications are provided. Three applications of DSMC to transitional and nonequilibrium flows are considered: rarefied atmospheric flows, growth of thin films, and microsystems. Selected new, potentially important advances in DSMC capabilities are described: Lagrangian DSMC, optimization on parallel computers, and hybrid algorithms for computations in mixed flow regimes. Finally, the limitations of current computer technology for using DSMC to compute low-speed, high–Knudsen-number flows are outlined as future challenges.
ATAXIA-TELANGIECTASIA AND THE NIJMEGEN BREAKAGE SYNDROME: Related Disorders But Genes Apart
Authors: Shiloh Y.
Published: July 2002

▪ Abstract  Gene mutations provide valuable clues to cellular metabolism. In humans such insights come mainly from genetic disorders. Ataxia-telangiectasia (A-T) and Nijmegen breakage syndrome (NBS) are two distinct, but closely related, single gene disorders that highlight a complex junction of several signal transduction pathways. These pathways appear to control defense mechanisms against specific types of damage to cellular macromolecules, and probably regulate the processing of certain types of DNA damage or normal intermediates of DNA metabolism. A-T is characterized primarily by cerebellar degeneration, immunodeficiency, genome instability, clinical radiosensitivity, and cancer predisposition. NBS shares all these features except cerebellar deterioration. The cellular phenotypes of A-T and NBS are almost indistinguishable, however, and include chromosomal instability, radiosensitivity, and defects in cell cycle checkpoints normally induced by ionizing radiation. The recent identification of the gene responsible for A-T, ATM, has revealed its product to be a large, constitutively expressed phosphoprotein with a carboxy-terminal region similar to the catalytic domain of phosphatidylinositol 3-kinases (PI 3-kinases). ATM is a member of a family of proteins identified in various organisms, which share the PI 3-kinase domain and are involved in regulation of cell cycle progression and response to genotoxic agents. Some of these proteins, most notably the DNA-dependent protein kinase, have an associated protein kinase activity, and preliminary data indicate this activity in ATM as well. Mutations in A-T patients are null alleles that truncate or destabilize the ATM protein. Atm-deficient mice recapitulate the human phenotype with slower nervous-system degeneration. Two ATM interactors, c-Abl and p53, underscore its role in cellular responses to genotoxic stress. The complexity of ATM's structure and mode of action make it a paradigm of multifaceted signal transduction proteins involved in many physiological pathways via multiple protein-protein interactions. The as yet unknown NBS protein may be a component in an ATM-based complex, with a key role in sensing and processing specific DNA damage or intermediates and signaling their presence to the cell cycle machinery.
Human Genetics: Lessons from Quebec Populations
Authors: Scriver Charles R.
Published: July 2002

The population of Quebec, Canada (7.3 million) contains ∼6 million French Canadians; they are the descendants of ∼8500 permanent French settlers who colonized Nouvelle France between 1608 and 1759. Their well-documented settlements, internal migrations, and natural increase over four centuries in relative isolation (geographic, linguistic, etc.) contain important evidence of social transmission of demographic behavior that contributed to effective family size and population structure. This history is reflected in at least 22 Mendelian diseases, occurring at unusually high prevalence in its subpopulations. Immigration of non-French persons during the past 250 years has given the Quebec population further inhomogeneity, which is apparent in allelic diversity at various loci. The histories of Quebec's subpopulations are, to a great extent, the histories of their alleles. Rare pathogenic alleles with high penetrance and associated haplotypes at 10 loci (CFTR, FAH, HBB, HEXA, LDLR, LPL, PAH, PABP2, PDDR, and SACS) are expressed in probands with cystic fibrosis, tyrosinemia, β-thalassemia, Tay-Sachs, familial hypercholesterolemia, hyperchylomicronemia, PKU, oculopharyngeal muscular dystrophy, pseudo vitamin D deficiency rickets, and spastic ataxia of Charlevoix-Saguenay, respectively) reveal the interpopulation and intrapopulation genetic diversity of Quebec. Inbreeding does not explain the clustering and prevalence of these genetic diseases; genealogical reconstructions buttressed by molecular evidence point to founder effects and genetic drift in multiple instances. Genealogical estimates of historical meioses and analysis of linkage disequilibrium show that sectors of this young population are suitable for linkage disequilibrium mapping of rare alleles. How the population benefits from what is being learned about its structure and how its uniqueness could facilitate construction of a genomic map of linkage disequilibrium are discussed.
Altered Peptide Ligand–Induced Partial T Cell Activation: Molecular Mechanisms and Role in T Cell Biology
Authors: Sloan-Lancaster Joanne , Allen Paul M.
Published: July 2002

The elucidation of the phenomena of T cell antagonism and partial activation by altered peptide ligands has necessitated a revision in the traditional concepts of TCR recognition of antigen and subsequent signal transduction. Whereas previous models supported a single ligand specificity for any particular T cell, many studies using analogs of immunogenic peptides have now demonstrated a flexibility in this recognition. Moreover, interaction with such altered peptide ligands can result in dramatically different phenotypes of the T cells, ranging from inducing selective stimulatory functions to completely turning off their functional capacity. Investigations of the biochemical basis leading to these phenotypes have shown that altered peptide ligands can induce a qualitatively different pattern of signal transduction events than does any concentration of the native ligand. Such observations imply that several signaling modules are directly linked to the TCR/CD3 complex and that they can be dissociated from each other as a direct result of the nature of the ligand bound. Interestingly, many in vivo models of T cell activation are compatible with a selective signaling model, and several studies have shown that peptide analogs can play a role in various T cell biologic phenomena. These data strongly suggest that naturally occurring altered peptide ligands for any TCR exist in the repertoire of self-peptides or, in nature, derived from pathogens, and recent reports provide compelling evidence that this is indeed the case. The concept of altered peptide ligands, their effects on T cell signaling, the hypothesized mechanisms by which they exert their effects, and their possible roles in shaping the T cell immune response are the scope of this review.
MOUSE CD1-SPECIFIC NK1 T CELLS: Development, Specificity, and Function
Authors: Bendelac Albert , Rivera Miguel N. , Park Se-Ho , Roark Jessica H.
Published: July 2002

▪ Abstract  NK1 T cells are a specialized population of α/β T cells that coexpress receptors of the NK lineage and have the unique potential to very rapidly secrete large amounts of cytokines, providing early help for effector cells and regulating the Th1 or Th2 differentiation of some immune responses. NK1 T cells express a restricted TCR repertoire made of an invariant TCR α chain, Vα14-Jα281, associated with polyclonal Vβ8, Vβ7, and Vβ2 TCR β chains. NK1 T cells recognize the products of the conserved family of MHC class I–like CD1 genes, apparently in the absence of foreign antigens. Thus, this novel regulatory pathway, which straddles the innate and the adaptive immune systems, is unique in that its activation may not require associative recognition of antigen. Here, we review the specificity and function of mouse NK1 T cells, and we discuss the relationship of this lineage to mainstream T cells and NK cells.
The Specific Regulation Of Immune Responses By CD8+T Cells Restricted By The MHC Class Ib Molecule, Qa-1
Authors: Jiang Hong , Chess Leonard
Published: July 2002

Over the last three decades considerable evidence has accumulated that CD8+T cells regulate peripheral immune responses, in part, by specifically controlling the outgrowth of antigen-triggered CD4+T cells. This regulatory function of CD8+T cells has been shown, in vivo, to control the emergence of autoreactive CD4+T cells as well as CD4+T cells reactive to conventional antigens, including alloantigens. In this review, we summarize the evidence that this immune suppression mediated by CD8+T cells is dependent, in part, on specific cognate interactions between MHC class I–restricted regulatory CD8+cells and antigen-activated CD4+T cells. Moreover, we review the evidence that regulatory CD8+T cells recognize antigen-activated CD4+T cells in a TCR specific manner restricted by the MHC class Ib molecule, Qa-1. The Qa-1 molecule may be uniquely qualified to serve this MHC restrictive function because, unlike conventional MHC molecules, it is preferentially and transiently expressed on activated and not resting CD4+T cells. This may assure that only recently antigen-activated CD4+T cells expressing Qa-1/TCR peptide complexes will induce regulatory CD8+T cells and subsequently become susceptible to regulation. Because Qa-1 also binds to self Qdm peptides that trigger NK (CD94/ NKG2) receptors on CD8+T cells, the machinery for homeostatic regulation of regulatory CD8+T cells can be envisioned. Finally, we propose a model by which these TCR specific, Qa-1-restricted regulatory CD8+T cells selectively downregulate antigen-activated T cells expressing TCRs of certain affinities. Ultimately these regulatory CD8+T cells control the peripheral TCR repertoire during the course of immune responses to both self and foreign antigens.