bluuebunny/crossref_metadata_2025 huggingface dataset:
The knowledge in multiple human relevance judgments
Authors: Wilber W. John
Published: July 2002

We show first that the pooling of multiple human judgments of relevance provides predictor of relevance that is superior to that obtained from a single human's relevance judgemts. A learning algorithm applied to a set of relevance judgments obtained from a single human would be expected to perform on new material at a level somewhat below that human. However, we examine two learning methods which when trained on the superior source of pooled human relevance judgments are able to perform at the level of a single human on new material. All performance comparisons are based on an independent human judge. Both algorithms function by producing term weights—one by a log odds calculation and the other by producing a least-squares fit to human relevance ratings. Some characteristics of the algorithms are examined.
A multiresolution framework for variational subdivision
Authors: Kobbelt Leif , Schröder Peter
Published: July 2002

Subdivision is a powerful paradigm for the generaton of curves and surfaces. It is easy to implement, computationally efficient, and useful in a variety of applications because of its intimate connection with multiresolution analysis. An important task in computer graphics and geometric modeling is the construction of curves that interpolate a griven set of points and minimize a fairness functional (variational design). In the context of subdivision, fairing leads to special schemes requiring the solution of a banded linear system at every subdivision step. We present several examples of such schemes including one that reproduces nonuniform interpolating cubic splines. Expressing the construction in terms of certain elementary operations we are able to embed variational subdivision in the lifting framework, a powerful technique to construct wavelet filter banks given a subdivision scheme. This allows us to extend the traditional lifting scheme for FIR filters to a certain class of IIR filters. Consquently, we how how to build variationally optimal curves
and
associated, stable wavelets in a straightforward fashion. The algorithms to perform the corresponding decomposition and reconstruction transformations are easy to implement and efficient enough for interactive applications.
Eavesdropping games
Authors: Franklin Matthew , Galil Zvi , Yung Moti
Published: July 2002

We initiate a graph-theoretic study of privacy in distributed environments with mobile eavesdroppers ("bugs"). For two privacy tasks—distributed database maintenance and message transmission—a computationally unbounded adversary “plays an eavesdrpping game,” coordinating the moment of the bugs among the sites to learn the current memory contents. Many different adversaries are considered, motivated by differences in eavesdropping technologies. We characterize the feasibility of the two privacy tasks combinatorially, construct protocols for the feasible cases, and analyze their computational complexity.
Self-organizing search lists using probabilistic back-pointers
Authors: Hester J. H. , Hirschberg D. H.
Published: July 2002

A class of algorithms is presented for maintaining self-organizing sequential search lists, where the only permutation applied is to move the accessed record of each search some distance towards the front of the list. During searches, these algorithms retain a back-pointer to a previous probed record in order to determine the destination of the accessed record's eventual move. The back-pointer does not traverse the list, but rather it is advanced occasionally to point to the record just probed by the search algorithm. This avoids the cost of a second traversal through a significant portion of the list, which may be a significant savings when each record access may require a new page to be brought into primary memory. Probabilistic functions for deciding when to advance the pointer are presented and analyzed. These functions demonstrate average case complexities of measures such as asymptotic cost and convergence, similar to some of the more common list update algorithms in the literature. In cases where the accessed record is moved forward a distance proportional to the distance to the front of the list, the use of these functions may save up to 50 percent of the time required for permuting the list.
Designing surfaces in 3-D
Authors: Clark James H.
Published: July 2002

An experimental system for computer-aided design of free-form surfaces in three dimensions is described. The surfaces are represented in the system as parametric basis splines. The principal features of the system are: (1) the surfaces are rendered as isoparametric line drawings on a head-mounted display, and they are designed with the aid of a three-dimensional “wand,” which allows 3-D movements of the points controlling the shapes of the surfaces, (2) all of the interactions with the surfaces are in real-time, and (3) the mathematical formulations used assume no knowledge of them by the user of the system. Also examined are some of the features that should be part of a practical 3-D system for designing space-forms.
Preliminary report on a system for general space planning
Authors: Eastman Charles M.
Published: July 2002

A computer language and a set of programs within that language are described which allow the formulating and solving of a class of space planning problems. The language is an extension of Algol and includes means to represent spaces and objects, to manipulate them, and to test the resulting arrangements according to a variety of constraints. The algorithms used to solve problems expressed in this language rely on heuristic programming. Both the language and the search algorithms are detailed.
A starting method for solving nonlinear Volterra integral equations of the second kind
Authors: Iguchi Ken
Published: July 2002

A fourth-order starting method is given for Volterra integral equations of the second kind and numerical examples are presented.
Construction of rational and negative powers of a formal series
Authors: Broucke R. A.
Published: July 2002

Some methods are described for the generation of fractional and negative powers of any formal series, such as Poisson series or Chebyshev series. It is shown that, with the use of the three elementary operations of addition, subtraction, and multiplication, all rational (positive and negative) powers of a series can be constructed. There are basically two approaches: the binomial theorem and the iteration methods. Both methods are described here, and the relationship between them is pointed out. Some well-known classical formulas are obtained as particular cases, and it is shown how the convergence properties of these formulas can be improved with very little additional computations. Finally, at the end of the article, some numerical experiments are described with Chebyshev series and with Fourier series.
Computer Systems: Reliable full-duplex file transmission over half-duplex telephone line
Authors: Lynch W. C.
Published: July 2002

A field-proven scheme for achieving reliable duplex transmission over a half-duplex communication line is presented, and to demonstrate the difficulty of the problem, another similar scheme, which is only slightly unreliable, is also presented. A flowchart for the reliable scheme and some interesting examples are given.
Analysis and comparison of two general sparse solvers for distributed memory computers
Authors: Amestoy Patrick R. , Duff Iain S. , L'excellent Jean-Yves , Li Xiaoye S.
Published: July 2002

This paper provides a comprehensive study and comparison of two state-of-the-art direct solvers for large sparse sets of linear equations on large-scale distributed-memory computers. One is a multifrontal solver called MUMPS, the other is a supernodal solver called superLU. We describe the main algorithmic features of the two solvers and compare their performance characteristics with respect to uniprocessor speed, interprocessor communication, and memory requirements. For both solvers, preorderings for numerical stability and sparsity play an important role in achieving high parallel efficiency. We analyse the results with various ordering algorithms. Our performance analysis is based on data obtained from runs on a 512-processor Cray T3E using a set of matrices from real applications. We also use regular 3D grid problems to study the scalability of the two solvers.
RECAL—a new efficient algorithm for the exact analysis of multiple-chain closed queuing networks
Authors: Conway A. E. , Georganas N. D.
Published: July 2002

RECAL, a
Re
cursion by
C
hain
Al
gorithm for computing the mean performance measures of product-form multiple-chain closed queuing networks, is presented. It is based on a new recursive expression that relates the normalization constant of a network with
r
closed routing chains to those of a set of networks having (
r
- 1) chains. It relies on the artifice of breaking down each chain into constituent subchains that each have a population of one. The time and space requirements of the algorithm are shown to be polynomial in the number of chains. When the network contains many routing chains, the proposed algorithm is substantially more efficient than the convolution or mean value analysis algorithms. The algorithm, therefore, extends the range of queuing networks that can be analyzed efficiently by exact means.
Dynamic functional dependencies and database aging
Authors: Vianu Victor
Published: July 2002

A simple extension of the relational model is introduced to study the effects of dynamic constraints on database evolution. Both static and dynamic constraints are used in conjunction with the model. The static constraints considered here are functional dependencies (FDs). The dynamic constraints involve global updates and are restricted to certain analogs of FDs, called “dynamic” FDs. The results concern the effect of the dynamic constraints on the static constraints satisfied by the database in the course of time. The effect of the past history of the database on the static constraints is investigated using the notions of age and age closure. The connection between the static constraints and the potential future evolution of the database is briefly discussed using the notions of survivability and survivability closure.
Using semantic knowledge of transactions to increase concurrency
Authors: Farrag Abdel Aziz , Özsu M. Tamer
Published: July 2002

When the only information available about transactions is syntactic information, serializability is the main correctness criterion for concurrency control. Serializability requires that the execution of each transaction must appear to every other transaction as a single atomic step (i.e., the execution of the transaction cannot be interrupted by other transactions). Many researchers, however, have realized that this requirement is unnecessarily strong for many applications and can significantly increase transaction response time. To overcome this problem, a new approach for controlling concurrency that exploits the semantic information available about transactions to allow controlled nonserializable interleavings has recently been proposed. This approach is useful when the cost of producing only serializable interleavings is unacceptably high. The main drawback of the approach is the extra overhead incurred by utilizing the semantic information. We examine this new approach in this paper and discuss its strengths and weaknesses. We introduce a new formalization for the concurrency control problem when semantic information is available about the transactions. This semantic information takes the form of transaction types, transaction steps, and transaction break-points. We define a new class of “safe” schedules called relatively consistent (RC) schedules. This class contains serializable as well as nonserializable schedules. We prove that the execution of an RC schedule cannot violate consistency and propose a new concurrency control mechanism that produces only RC schedules. Our mechanism assumes fewer restrictions on the interleavings among transactions than previously introduced semantic-based mechanisms.
Apologizing versus asking permission: optimistic concurrency control for abstract data types
Authors: Herlihy M.
Published: July 2002

An optimistic concurrency control technique is one that allows transactions to execute without synchronization, relying on commit-time validation to ensure serializability. Several new optimistic concurrency control techniques for objects in decentralized distributed systems are described here, their correctness and optimality properties are proved, and the circumstances under which each is likely to be useful are characterized.

Unlike many methods that classify operations only as Reads or Writes, these techniques systematically exploit type-specific properties of objects to validate more interleavings. Necessary and sufficient validation conditions can be derived directly from an object's data type specification. These techniques are also modular: they can be applied selectively on a per-object (or even per-operation) basis in conjunction with standard pessimistic techniques such as two-phase locking, permitting optimistic methods to be introduced exactly where they will be most effective.

These techniques can be used to reduce the algorithmic complexity of achieving high levels of concurrency, since certain scheduling decisions that are NP-complete for pessimistic schedulers can be validated after the fact in time, independent of the level of concurrency. These techniques can also enhance the availability of replicated data, circumventing certain tradeoffs between concurrency and availability imposed by comparable pessimistic techniques.
Parallel asynchronous algorithms for discrete data
Authors: Üresin Aydin , Dubois Michel
Published: July 2002

Many problems in the area of symbolic computing can be solved by iterative algorithms. Implementations of these algorithms on multiprocessors can be synchronous or asynchronous. Asynchronous implementations are potentially more efficient because synchronization is a major source of performance degradation in most multiprocessor systems.

In this paper, sufficient conditions for the convergence of asynchronous iterations to desired solutions are given. The main sufficient condition is shown to be also necessary for the case of finite data domains. The results are applied to prove the convergence of three asynchronous algorithms for the all-pairs shortest path problem, the consistent labeling problem, and a neural net model.
Class management for software communities
Authors: Gibbs Simon , Casais Eduardo , Nierstrasz Oscar , Pintado X. , Tsichritzis Dennis
Published: July 2002

Object-oriented programming may engender an approach to software development characterized by the large-scale reuse of object classes. Large-scale reuse is the use of a class not just by its original developers, but by other developers who may be from other organizations, and may use the classes over a long period of time. Our hypothesis is that the successful dissemination and reuse of classes requires a well-organized community of developers who are ready to share ideas, methods, tools and code. Furthermore, these communities should be supported by software information systems which manage and provide access to class collections. In the following sections we motivate the need for software communities and software information systems. The bulk of this article discusses various issues associated with managing the very large class collections produced and used by these communities.
CARBON STARS
Authors: Wallerstein George , Knapp Gillian R.
Published: July 2002

▪ Abstract  Absolute magnitudes are estimated for carbon stars of various subtypes in the Hipparcos catalogue and as found in the Magellanic Clouds. Stellar radii fall within the limits of 2.4–4.7 AU. The chemical composition of carbon stars indicates that the C-N stars show nearly solar C/H, N/H, and 12C/13C ratios. This indicates that much of the C and N in our Galaxy came from mass-losing carbon stars. Special carbon stars such as the C-R, C-H, and dC stars are described.

Mass loss from asymptotic giant branch carbon stars, at rates up to several × 10−5 M[Formula: see text] year−1, contributes about half of the total mass return to the interstellar medium. R stars do not lose mass and may be carbon-rich red giants. The mass loss rates for Miras are about 10 times higher than for SRb and Lb stars, whose properties are similar enough to show that they are likely to belong to the same population. The distribution of carbon star mass loss rates peaks at about 10−7 M[Formula: see text] year−1, close to the rate of growth of the core mass and demonstrative of the close relationship between mass loss and evolution. Infrared spectroscopy shows that dust mixtures can occur. Detached shells are seen around some stars; they appear to form on the time scales of the helium shell flashes and to be a normal occurrence in carbon star evolution.
The Anaphase-Promoting Complex: New Subunits and Regulators
Authors: Page A. M. , Hieter P.
Published: July 2002

▪ Abstract  Ubiquitin-mediated proteolysis of cell cycle regulators is a crucial process during the cell cycle. The anaphase-promoting complex (APC) is a large, multiprotein complex whose E3-ubiquitin ligase activity is required for the ubiquitination of mitotic cyclins and other regulatory proteins that are targeted for destruction during cell division. The recent identification of new APC subunits and regulatory proteins has begun to reveal some of the intricate mechanisms that govern APC regulation. One mechanism is the use of specificity factors to impose temporal control over substrate degradation. A second mechanism is the APC-mediated proteolysis of specific APC regulators. Finally, components of both the APC and the SCF E3 ubiquitin-ligase complex contain several conserved sequence motifs, including WD-40 repeats and cullin homology domains, which suggest that both complexes may use a similar mechanism for substrate ubiquitination.
PLANT CELL MORPHOGENESIS: Plasma Membrane Interactions with the Cytoskeleton and Cell Wall
Authors: Fowler John E. , Quatrano Ralph S.
Published: July 2002

▪ Abstract  Because plants are composed of immobile cells, plant morphogenesis requires mechanisms allowing precise control of cell expansion and cell division patterns. Cortical domains, localized in response to directional cues, are of central importance in establishing cell polarity, orienting cell division, and determining daughter cell fates in a wide variety of prokaryotic and eukaryotic organisms. Such domains consist of localized macromolecular complexes that, in plant cells, provide spatial control of cell expansion and cell division functions. The role of the cytoskeleton, plasma membrane, and targeted secretion to the cell wall in the spatial regulation of cell morphogenesis in plants is discussed in light of recent results from model organisms, including brown algal zygotes (e.g. Fucus). A general model, emphasizing the importance of cortical sites and targeted secretion, is proposed for morphogenesis in higher plant cells based on current knowledge and principles derived from analysis of the establishment of a stable cortical asymmetry in Fucus. The model illustrates mechanisms to direct the orientation of an asymmetric division resulting in daughter cells with different fates.
EARLY HISTORY AND PROGRESS OF WOMEN ECOLOGISTS: Emphasis Upon Research Contributions
Authors: Langenheim Jean H.
Published: July 2002

▪ Abstract  Although women are increasingly prominent as ecologists, a report on their progress through the history of ecology in overcoming personal and societal obstacles provides interesting insights regarding their research achievements. Selected, predominantly American, women ecologists are presented within five time frames according to the date of their PhD, an event marking the beginning of their careers. A general view is given for pre-1900 Protoecologists, followed by brief professional sketches for 10 Early Pioneers (1900–1934), 16 Late Pioneers (1935–1960), and 28 members of the irst Modern Wave (1961–1975). The relatively large number of women who earned doctorates after 1975 precludes discussion of individuals from this time in this review. The following issues are discussed in the context of their research contributions: 1) motivating factors, 2) graduate education and subfield entered, 3) mentors and role models, 4) employment, 5) marriage and family constraints, and 6) recognition. These issues are compared with data from recent surveys for post-1976 women doctorates. Each selected woman still alive was contacted for her assessment of her research; 156 research citations display the significance and range of subjects studied. A steady, albeit slow, progress since 1900 is evident, although some problems regarding gender equality in professional development of women ecologists persist. These issues, however, are now more clearly recognized and addressed.
ELECTRIC POWER QUALITY
Authors: Emanuel Alexander Eigeles , McNeill John A.
Published: July 2002

▪ Abstract  The quality of electric power depends on the power network topology, the amount of harmonic pollution injected in the network by nonlinear loads, and the severity of switching transients. Many of the loads encountered in modern power electronics, such as arc and induction furnaces, welders, motor drives, and many types of converters, cause a significant level of harmonic pollution and/or recurrent voltage transients. This paper describes the major sources of disturbances that affect electric service quality and explains the indices that help quantify the severity of disturbances. The loads that are most sensitive to power quality are discussed, and techniques intended to avoid or mitigate power quality problems are detailed. Finally, a brief survey of the cost of harmonic pollution and consumer outages is presented.
DIRECT NUMERICAL SIMULATION OF NON-PREMIXED TURBULENT FLAMES
Authors: Vervisch Luc , Poinsot Thierry
Published: July 2002

▪ Abstract  Non-premixed turbulent combustion processes control most practical applications of combustion. Studying these mechanisms has been the objective of numerous theoretical and experimental works in the last century. In the past 10 years, direct numerical simulation (DNS) has emerged as a new methodology. It has become an essential tool to understand and model turbulent combustion. DNS numerically solves the set of equations describing turbulent flames by resolving all chemical and flow scales. Because formulated assumptions can be tested accurately, the resulting data provide unique information to build turbulent combustion models. This review first discusses the fundamental properties of laminar diffusion flames. It then presents various DNS results to illustrate the different problems that can be studied using this tool. These problems include validity of the modeling hypothesis, topology of flame surfaces, and ignition and extinction mechanisms. The review also discusses the different analysis techniques employed to extract information from DNS and explores the limits of these methods.
Mechanisms of Stationary Phase Mutation: A Decade of Adaptive Mutation
Authors: Foster P. L.
Published: July 2002

▪ Abstract  A decade of research on adaptive mutation has revealed a plethora of mutagenic mechanisms that may be important in evolution. The DNA synthesis associated with recombination could be an important source of spontaneous mutation in cells that are not proliferating. The movement of insertion elements can be responsive to environmental conditions. Insertion elements not only activate and inactivate genes, they also provide sequence homology that allows large-scale genomic rearrangements. Some conjugative plasmids can recombine with their host's chromosome, and may acquire chromosomal genes that could then spread through the population and even to other species. Finally, a subpopulation of transient hypermutators could be a source of multiple variant alleles, providing a mechanism for rapid evolution under adverse conditions.
CHOLESTEROL EMBOLI: A Common Cause of Renal Failure
Authors: Vidt, M.D Donald G.
Published: July 2002

▪ Abstract  Cholesterol embolization (CE), usually occurring in males in their sixth or seventh decade of life, can affect multiple organ systems, including the kidney. Interventive diagnostic procedures and aortic surgery greatly increase the risk of CE. Rapid or insidious progression of renal failure in association with surgical or diagnostic radiologic procedures should suggest this diagnosis. Progressive renal insufficiency in older patients with generalized arterial disease should suggest ischemic nephropathy secondary to bilateral renal artery stenosis, renal CE, or both. Recent worsening of hypertension is characteristic of either diagnosis. A number of clinical conditions can simulate renal CE, and final differentiation may be possible only by renal biopsy. Aggressive, supportive management of renal CE is warranted because renal function may stabilize and, in a limited number of cases, may even improve.
PARTICLEPHYSICS FROMSTARS
Authors: Raffelt Georg G.
Published: July 2002

▪ Abstract  Low-mass particles, such as neutrinos, axions, other Nambu-Goldstone bosons, and gravitons, are produced in the hot and dense interior of stars. Therefore, astrophysical arguments constrain the properties of these particles in ways that are often complementary to cosmological arguments and to laboratory experiments. This review provides an update on the most important stellar-evolution limits and discusses them in the context of other information from cosmology and laboratory experiments.
THE SHUTTLE GLOW PHENOMENON
Authors: Murad Edmond
Published: July 2002

▪ Abstract  Spacecraft in low earth orbit exhibit an unusual phenomenon: Surfaces facing the atmospheric wind produce a bright orange glow. This phenomenon was first noticed on the space shuttle but has since been verified as occurring on all spacecraft. The intensity of the glow depends on atmospheric density, on the angle between the velocity vector and the spacecraft surface, and on the temperature of the surface. This review summarizes the observations as well as the current explanation for the glow, namely its being due to NO*2 formed in surface-aided recombination between O and NO. Laboratory measurements and surface studies related to the phenomenon are briefly discussed.
O2-Sensing Mechanisms in Excitable Cells: Role of Plasma Membrane K+ Channels
Authors: Haddad Gabriel G. , Jiang Chun
Published: July 2002

Although carotid chemosensitive glomus cells have been the most extensively studied from the vantage point of how cells sense the lack of O2, it is clear that all tissues sense O2 deprivation. In addition, all mammalian cells can trigger a cascade of events that, depending on the severity and duration of hypoxia-induced stress, can lead to permanent injury and death or to adaptation and survival. Crucial in this cascade, we believe, how the cascade is initiated, how O2 lack is detected by cells, and how these initial steps can activate further processes. In this chapter, we focus on the initial steps of O2 sensing in tissues most commonly studied, i.e. carotid glomus cells, central neurons, smooth muscle cells, and neuro-epithelial bodies of the airways.

Recently it has become clear that plasma membranes of various tissues can sense the lack of O2, not only indirectly via alterations in the intracellular milieu (such as pH, Ca, ATP, etc), but also directly through an unknown mechanism that involves plasma-membrane K channels and possibly other membrane proteins. This latter mechanism is suspected to be totally independent of cytosolic changes because excised patches from plasma membranes were used in these experiments from carotid cells and neurons.

There are a number of questions in this exciting area of research that pertain to the role of this plasma-membrane O2-sensing mechanism in the overall cell response, identification of all the important steps in O2 sensing, differences between O2-tolerant and O2-susceptible cells, and differences between acute and chronic cell responses to lack of O2.
Role of Mitochondrial DNA in the Senescence and Hypovirulence of Fungi and Potential for Plant Disease Control
Authors: Bertrand Helmut
Published: July 2002

The unique coenocytic anatomy of the mycelia of the filamentous fungi and the formation of anastomoses between hyphae from different mycelia enable the intracellular accumulation and infectious transmission of plasmids and mutant mitochondrial DNAs (mtDNAs) that cause senescence. For reasons that are not fully apparent, mitochondria that are rendered dysfunctional by so-called “suppressive” mtDNA mutations proliferate rapidly in growing cells and gradually displace organelles that contain wild-type mtDNA molecules and are functional. The consequence of this process is senescence and death if the suppressive mtDNA contains a lethal mutation. Suppressive mtDNA mutations and mitochondrial plasmids can elicit cytoplasmically transmissible “mitochondrial hypovirulence” syndromes in at least some of the phytopathogenic fungi. In the chestnut-blight fungus Cryphonectria parasitica, the pattern of asexual transmission of mutant mtDNAs and mitochondrial plasmids resembles the pattern of “infectious” transmission displayed by the attenuating virus that is most commonly used for the biological control of this fungus. At least some of the attenuating mitochondrial hypovirulence factors are inherited maternally in crosses, whereas the viruses are not transmitted sexually. The natural control of blight in an isolated stand of chestnut trees has resulted from the invasion of the local population of C. parasitica by a senescence-inducing mutant mtDNA. Moreover, a mitochondrial plasmid, pCRY1, attenuates at least some virulent strains of C. parasitica, suggesting that such factors could be applied to control plant diseases caused by fungi.
Estrogen Increases Endothelial Nitric Oxide Synthase via Estrogen Receptors in Rat Cerebral Blood Vessels
Authors: McNeill Anne Marie , Zhang Chunying , Stanczyk Frank Z. , Duckles Sue P. , Krause Diana N.
Published: July 2002

Background and Purpose

—

In vivo and in vitro rat models of hormone therapy were used to test the following hypotheses: (1) estrogen acts directly on cerebrovascular estrogen receptors to increase endothelial nitric oxide synthase (eNOS); (2) increased protein correlates with higher NOS activity; and (3) effects of estrogen on eNOS are altered by concurrent treatment with either medroxyprogesterone acetate (MPA) or progesterone.

Methods

—

Blood vessels were isolated from brains of ovariectomized female rats; some were treated for 1 month with estrogen, estrogen and progesterone, or estrogen and MPA. Isolated cerebral vessels were also treated in vitro with estrogen in the absence and presence of progesterone, MPA, tamoxifen, and the estrogen receptor antagonist ICI 182 780. Levels of eNOS were measured by Western blot, and NOS activity was measured by [
14
C]arginine-[
14
C]citrulline conversion.

Results

—

Chronic hormone treatment in vivo resulted in plasma levels of 17β-estradiol, progesterone, and MPA in the range of values found in humans. Estrogen treatment resulted in higher levels of cerebrovascular NOS activity that paralleled increases in eNOS protein. In vitro estrogen treatment for 18 hours also resulted in a concentration-dependent increase in eNOS protein (EC
50
≈300 pmol/L) that was completely prevented by estrogen receptor antagonists tamoxifen or ICI 182 780. However, cotreatment with progesterone or MPA, either in vivo or in vitro, did not alter the effect of estrogen on eNOS protein.

Conclusions

—

Estrogen receptor activation in cerebrovascular tissue results in increased eNOS activity and protein levels. The latter effect persists in the presence of either progesterone or MPA. Thus, increased NO production by eNOS may contribute to the neuroprotective effects of estrogen.
Monks, Canons, and the City: A Barren Relationship?
Authors: Milis Ludo J. R.
Published: July 2002

A close reading of selected texts that reflect routine life in monasteries during the early and high Middle Ages suggests that monastic culture, centered around stability and obedience, long rejected or ignored the urban communities that emerged in northwestern Europe. This monastic attitude persisted until the late twelfth century, when urban institutions began to wield sufficient authority to maintain order in their areas and thus contribute to the preservation of the status quo. Even so, monks continued to perceive cities in an essentially feudal guise, as fortified spaces.
When in Doubt, Do it Both Ways: Brain Evidence of the Simultaneous Activation of Conflicting Motor Responses in a Spatial Stroop Task
Authors: DeSoto M. Catherine , Fabiani Monica , Geary David C. , Gratton Gabriele
Published: July 2002

Response competition is often considered an important contributor to the delayed reaction to stimuli for which physical and semantic information are in conflict (“Stroop” effect). Response competition implies that brain areas associated with correct and incorrect responses (e.g., left and right motor cortices) should be simultaneously activated in conflict conditions. However, there is at present little direct evidence of this phenomenon, in part because of the paucity of brain imaging techniques that can independently monitor the time course of activation of adjacent brain areas, such as the motor areas. In the present study, we show that the event-related optical signal (EROS) can provide these types of data. The results confirm the prediction that conflict trials elicit simultaneous activation of both motor cortices, whereas nonconflict trials elicit brain activity only in the contralateral motor cortex. These data support a parallel view of the human information processing system.
Neural Basis of Endogenous and Exogenous Spatial Orienting: A Functional MRI Study
Authors: Rosen Allyson C. , Rao Stephen M. , Caffarra Paolo , Scaglioni Augusto , Bobholz Julie A. , Woodley Scott J. , Hammeke Thomas A. , Cunningham Joseph M. , Prieto Thomas E. , Binder Jeffrey R.
Published: July 2002

Whole-brain functional magnetic resonance imaging (MRI) was used to examine the neural substrates of internally (endogenous) and externally (exogenous) induced covert shifts of attention. Thirteen normal subjects performed three orienting conditions: endogenous (location of peripheral target predicted by a central arrow 80% of the time), exogenous (peripheral target preceded by a noninformative peripheral cue), and control (peripheral target preceded by noninformative central cue). Behavioral results indicated faster reaction times (RTs) for valid than for invalid trials for the endogenous condition but slower RTs for valid than for invalid trials for the exogenous condition (inhibition of return). The spatial extent and intensity of activation was greatest for the endogenous condition, consistent with the hypothesis that endogenous orienting is more effortful (less automatic) than exogenous orienting. Overall, we did not observe distinctly separable neural systems associated with the endogenous and exogenous orienting conditions. Both exogenous and endogenous orienting, but not the control condition, activated bilateral parietal and dorsal premotor regions, including the frontal eye fields. These results suggest a specific role for these regions in preparatory responding to peripheral stimuli. The right dorsolateral prefrontal cortex (BA 46) was activated selectively by the endogenous condition. This finding suggests that voluntary, but not reflexive, shifts of attention engage working memory systems.
Role of the Cerebellum in Tuning Anticipatory and Reactive Grip Force Responses
Authors: Serrien Deborah J. , Wiesendanger Mario
Published: July 2002

The aim of our study was to determine if load perturbations that could destabilize grasp control are adequately controlled by cerebellar patients. We examined patients with unilateral cerebellar lesions who had largely recovered from their initial symptoms and compared grip force regulation for the affected and unaffected hand during a drawer-opening task. Two experimental paradigms were included: (1) a brief load perturbation during a self-stopped drawer pull and (2) a loading impact when the drawer was pulled out to the mechanical stop. The results showed that when a self-stopped movement was perturbed during its trajectory, anticipatory grip force increase was smaller for the affected than for the unaffected hand, illustrating a disturbed gain control due to cerebellar dysfunction. When the mechanical stop arrested the movement, the amount of grip force did not differ significantly between the affected and unaffected side; however, both hands used different control strategies. Whereas the unaffected hand anticipated the load perturbation by a ramp-like increase of grip force toward the impending impact, the affected hand increased grip force at movement onset to a default level and maintained this value until the task was ended. In addition, the latency between impact and reactive peak in grip force was prolonged for the affected hand, suggesting a delayed cerebellar transmission of reactive responses. In conclusion, these findings demonstrate that the cerebellum is involved in anticipatory and reactive mechanisms dealing with load perturbations during goal-directed behavior.
Latent Attractors: A Model for Context-Dependent Place Representations in the Hippocampus
Authors: Doboli Simona , Minai Ali A. , Best Phillip J.
Published: July 2002

Cells throughout the rodent hippocampal system show place-specific patterns of firing called place fields, creating a coarse-coded representation of location. The dependencies of this place code—or cognitive map—on sensory cues have been investigated extensively, and several computational models have been developed to explain them. However, place representations also exhibit strong dependence on spatial and behavioral context, and identical sensory environments can produce very different place codes in different situations. Several recent studies have proposed models for the computational basis of this phenomenon, but it is still not completely understood. In this article, we present a very simple connectionist model for producing context-dependent place representations in the hippocampus. We propose that context dependence arises in the den-tate gyrus-hilus (DGH) system, which functions as a dynamic selector, disposing a small group of granule and pyramidal cells to fire in response to afferent stimulus while depressing the rest. It is hypothesized that the DGH system dynamics has “latent attractors,” which are unmasked by the afferent input and channel system activity into subpopulations of cells in the DG, CA3, and other hippocampal regions as observed experimentally. The proposed model shows that a minimally structured hippocampus-like system can robustly produce context-dependent place codes with realistic attributes.
Minimal Model for Intracellular Calcium Oscillations and Electrical Bursting in Melanotrope Cells of Xenopus Laevis
Authors: Cornelisse L. Niels , Scheenen Wim J. J. M. , Koopman Werner J. H. , Roubos Eric W. , Gielen Stan C. A. M.
Published: July 2002

A minimal model is presented to explain changes in frequency, shape, and amplitude of Ca2+ oscillations in the neuroendocrine melanotrope cell of Xenopus Laevis. It describes the cell as a plasma membrane oscillator with influx of extracellular Ca2+ via voltage-gated Ca2+ channels in the plasma membrane. The Ca2+ oscillations in the Xenopus melanotrope show specific features that cannot be explained by previous models for electrically bursting cells using one set of parameters. The model assumes a KCa-channel with slow Ca2+ -dependent gating kinetics that initiates and terminates the bursts. The slow kinetics of this channel cause an activation of the KCa-channel with a phase shift relative to the intracellular Ca2+ concentration. The phase shift, together with the presence of a Na+ channel that has a lower threshold than the Ca2+ channel, generate the characteristic features of the Ca2+ oscillations in the Xenopus melanotrope cell.
Mutualism Promotes Diversity and Stability in a Simple Artificial Ecosystem
Authors: Pachepsky Elizaveta , Taylor Tim , Jones Stephen
Published: July 2002

This work investigates the effect of ecological interactions between organisms on the evolutionary dynamics of a community. A spatially explicit, individual-based model is presented, in which organisms compete for space and resources. We investigated how introducing the potential for mutualistic relationships (where the presence of one type of organism stimulates the growth of another type, and vice versa) affected the evolutionary dynamics of the system. Without this potential, one or a small number of individual types of organisms dominated the simulated community from the onset. When mutualistic relationships were allowed, many persisting types arose, with new types appearing continually. Furthermore, we investigated how the stability of the community differed when mutualistic relationships were allowed and disallowed. Our results suggest that the existence of mutualistic relationships improved community stability.
Divergence in mitochondrial DNA of Near Eastern water frogs with special reference to the systematic status of Cypriote and Anatolian populations (Anura, Ranidae)
Authors: Ohst Torsten , Böhme Wolfgang , Schreiber Robert , Plötner Jörg
Published: July 2002

Water frogs from Anatolia, Syria, Jordan, and central Asia (Turkmenistan, Uzbekistan, Kazakhstan) were compared on the basis of the complete mitochondrial (mt) ND3 gene (340 bp), two flanking mt t-RNA gene fragments (26 bp), and a 374 bp fragment of the mt 12S rRNA gene. A total of 27 haplotypes were found among the investigated individuals. Anatolian water frogs differed from Syrian and Jordanian Rana bedriagae by 2.2-3.4% of the analysed sites. The observed divergence (2.8-4.1%) between the Cypriote water frogs and frogs from the surrounding mainland (southern Turkey, west Syria) was in the same range as between R. bedriagae and European R. ridibunda (3.1-3.9%). These results suggest that neither the Cypriote nor the Anatolian water frogs represent R. bedriagae. Furthermore, maximum parsimony and neighbour-joining trees showed a clear subdivision of Asian water frogs into three Anatolian lineages, two central Asian lineages, a Cypriote lineage and the bedriagae lineage. In all trees the Cypriote lineage branches off first and a clade formed by two Anatolian lineages is placed as the sister group of water frogs from Turkmenistan and Uzbekistan, whereas the phylogenetic positions of R. bedriagae, the Ceyhan lineage, the Kazakhstan lineage and R. ridibunda remain unclear.
PARENTAL CARE AND PARENTAGE IN MONOGAMOUS GREAT SPOTTED WOODPECKERS (PICOIDES MAJOR) AND MIDDLE SPOTTED WOODPECKERS (PICOIDES MEDIUS)
Authors: Michalek Klaus , Winkler Hans
Published: July 2002

Paternal effort is high in some monogamous mating systems. Trivers' (1972) model predicts that high male investment in brood care should evolve only when males have a high certainty of paternity. For this study, we chose two woodpecker species: the great spotted woodpecker (Picoides major) and the middle spotted woodpecker (Picoides medius). Both species were socially monogamous despite a very high breeding density in the study area. We used DNA fingerprinting to determine whether these two species were also genetically monogamous. We found that in great spotted and middle spotted woodpeckers paternal effort was high. Multi-locus DNA-fingerprinting showed that its actual paternity was also very high. In P. major all 161 young from 36 broods and in P. medius all 61 young from 13 broods were sired by the male feeding at the nest hole. There were also no cases of intraspecific brood parasitism or quasi parasitism (P. major: 114 chicks from 24 broods; P.medius: 33 chicks from 8 broods). We further found no case of mate switching during the fertile period of the female. Great spotted and middle spotted woodpeckers are typical of a group of monogamous nonpasserine birds with high male investment in brood care having low frequencies of EPP. We did not find efficient paternity guards. High certainty of paternity may be explained by paternal care being essential for female reproductive success, as in many seabirds and birds of prey. Females rarely engage in extra-pair copulations probably because they are constrained by male care. Males in both species spend little effort in acquiring mates as well as in extrapair copulations. They expend their reproductive effort in defending territories and in parental care. Females compete intensely with members of their own sex for pair formation before the time of frequent copulation. Choosing and securing a high quality partner is the only possibility to achieve high reproductive success for both sexes.
VOCALIZATIONS AROUND THE TIME OF MILK EJECTION IN DOMESTIC PIGLETS: A RELIABLE INDICATOR OF THEIR CONDITION?
Authors: Illmann Gudrun , Špinka Marek , De Jonge Francien
Published: July 2002

In some nursings, piglets initiate nose contacts with their mother and emit typical 'croaking' vocalizations. We examined whether the croaking vocalizations reflect the condition of the piglets and whether the sows increase their maternal investments in response to those vocalizations. The following predictions were tested: (i) Piglets with lower weight gain should vocalize more than piglets with higher weight gain; (ii) piglets' milk intake is lower in those nursings in which they vocalize after milk ejection; (iii) piglets make more croaking vocalization in nursings which were preceded by longer intervals since the last nursing with milk ejection; (iv) sows permit longer post-ejection massage in nursings in which piglets vocalized immediately after milk ejection; (v) sows decrease the interval until the succeeding nursing after those nursings in which the piglets have vocalized. Hypotheses (i) and (ii) were investigated by controlling the inter-nursing intervals in 14 sows and recording the milk intake of individual piglets' over 24 hours during days 7 or 8 post partum (Experiment 1). Hypotheses (iii) to (v) were examined through analysing video recordings of undisturbed six h nursing sequences in 29 sows (Experiments 2 and 3). The majority of our predictions were not confirmed: piglets did not vocalize more (either before or after milk ejection) after longer intervals since last milk ejection; they did not vocalize more in nursing in which they received less milk; and it was not the piglets or the litter with a lower milk intake or lower weightgain that emitted more vocalization. Neither of our predictions regarding the influence of croaking vocalizations on maternal investment was confirmed. The vocalizations were in no way associated with the length of the following inter-nursing interval or with the permission of longer udder massage. To conclude, piglet croaking vocalizations during nursings are not reliable indicators of piglet condition and are not used by sows to adjust their maternal investment.
I Spy
Authors: Paul Trisha K.
Published: October 2024

In this narrative medicine essay, a pediatric oncology fellow who weaves storytelling into her practice to help patients process their illness describes how a young boy’s mother captures his story through photography.