bluuebunny/crossref_metadata_2025 huggingface dataset:
INTERDIFFUSION, SEGREGATION, AND DISSOLUTION IN InAs/GaAs QUANTUM DOT SUPERLATTICES
Authors: LITA B. , GOLDMAN R. S. , PHILLIPS J. D. , BHATTACHARYA P. K.
Published: August 2002

We have investigated the effects of in situ and ex situ post-growth thermal annealing on the organization of InAs/GaAs quantum dot superlattices, which consist of regular arrays of InAs islands embedded in GaAs. Using large-scale and high resolution cross-sectional scanning tunneling microscopy, we have mapped out the spatial distributions of the island arrays and the positions of indium atoms located both vertically and laterally between the island arrays. Both in situ and ex situ annealing induce vertical and lateral dissolution of the islands, which in turn significantly affects the organization of the island arrays. Annealing-induced variations in the positions of the indium atoms between the island arrays have enabled us to directly measure indium–gallium interdiffusion and indium segregation lengths. We discuss the effects of residual strain on these processes, which are critical for the design of novel devices based upon semiconductor nanostructures.
ROLE OF SCANNING PROBES IN NANOELECTRONICS: A CRITICAL REVIEW
Authors: SHEN T.-C.
Published: August 2002

The continuous downsizing of electronic devices has promoted many ideas of lithography and fabrication techniques at the nanometer scale. Scanning probe lithography (SPL) has been intensively explored as a potential alternative. The conceptual development of the SPL endeavors and their basic mechanisms in the past decade are briefly reviewed. Scaling down the conventional field effect transistors below 30 nm may present enormous technical and economical challenges. Random polarization and fabrication of reproducible lateral tunneling junctions continue to be two major barriers for quantum devices. Instead of trying to compete with other projection type lithographic techniques at the nanometer scale, scanning probes are best suited to explore atom scale devices.
THEORETICAL INVESTIGATIONS OF QUANTUM TRANSPORT THROUGH CARBON NANOTUBE DEVICES
Authors: ROLAND C. , NARDELLI M. BUONGIORNO , GUO H. , MEHREZ H. , TAYLOR J. , WANG J. , WEI Y.
Published: August 2002

By combining a nonequilibrium Green's function analysis with a standard tight-binding model, we have investigated quantum transport through carbon nanotube devices. For finite-sized nanotubes, transport is dominated by resonant tunneling, with the conductance being strongly dependent on the length of the nanotubes. Turning to nanotube devices, we have investigated spin-coherent transport in ferromagnetic–nanotube–ferromagnetic devices and nanotube-superconducting devices. The former shows a significant spin valve effect, while the latter is dominated by resonant Andreev reflections. In addition, we discuss AC transport through carbon nanotubes and the role of photon-assisted tunneling.
IN-SITU HIGH-TEMPERATURE SCANNING-TUNNELING-MICROSCOPY STUDIES OF TWO-DIMENSIONAL ISLAND-DECAY KINETICS ON ATOMICALLY SMOOTH TiN(001)
Authors: KODAMBAKA S. , PETROVA V. , VAILIONIS A. , DESJARDINS P. , CAHILL D. G. , PETROV I. , GREENE J. E.
Published: August 2002

In-situ high-temperature scanning tunneling microscopy was used to follow the coarsening (Ostwald ripening) and decay kinetics of single and multiple two-dimensional TiN islands on atomically flat TiN (001) terraces and in single-atom deep vacancy pits at temperatures of 750–950°C. The rate-limiting mechanism for island decay was found to be surface diffusion rather than adatom attachment/detachment at island edges. We have modeled island-decay kinetics based upon the Gibbs–Thomson and steady state diffusion equations to obtain a step-edge energy per unit length of 0.23±0.05 eV/Å and an activation energy for adatom formation and diffusion of 3.4±0.3 eV.
USING METADATA TO QUERY PASSIVE DATA SOURCES
Authors: MARTIN PATRICK , POWLEY WENDY , WESTON ANDREW , ZION PETER
Published: August 2002

In the not too distant past, the amount of online data available to general users was relatively small. Most of the online data was maintained in organizations' database management systems and accessible only through the interfaces provided by those systems. The popularity of the Internet, in particular, has meant that there is now an abundance of online data available to users in the form of Web pages and files. This data, however, is maintained in passive data sources, that is sources that do not provide facilities to search or query their data. The data must be queried and examined using applications such as browsers and search engines. In this paper, we explore an approach to querying passive data sources based on the extraction, and subsequent exploitation, of metadata from the data sources. We describe two situations in which this approach has been used, evaluate the approach and draw some general conclusions.
DIFFERENTIAL GAME-THEORETIC THOUGHTS ON OPTION PRICING AND TRANSACTION COSTS
Authors: OLSDER GEERT JAN
Published: August 2002

This paper investigates some differential game applications to option pricing mechanisms and related problems. Two players, an investor and "Nature", play a zero-sum game. The usual uncertainty modelling (log-normality for instance) in systems describing the price evolution of stocks is replaced by "Nature", a player who counteracts the investor as much as possible. A relationship between a restricted version of the Black-Scholes and the Hamilton-Jacobi-Bellman partial differential equations is given. This paper, is a first step to possibly solve various option pricing problems (with constraints and/or transactions costs for instance) by means of the available numerical software for optimal control problems. In the second part of the paper, another model, now with three players, is considered. The third player is the bank interested in maximising its own profits by choosing the right formula for transaction costs. Thus a three-person nonzero-sum game, with a special kind of Stackelberg information structure, results. Some simple examples hint in the direction that the bank will be a clear winner.
The Effect of Contrast Randomisation on the Discrimination of Changes in the Slopes of the Amplitude Spectra of Natural Scenes
Authors: Párraga C Alejandro , Tolhurst David J
Published: August 2002

It has been suggested (Tadmor and Tolhurst, 1994 Vision Research34 541–554) that the psychophysical task of discriminating changes in the slope of the amplitude spectrum of a complex image may be similar to detecting differences in the degree of blur. It has also been suggested that human observers may perform this discrimination by detecting changes in the effective contrast within single narrow spatial-frequency bands, rather than by detecting changes in the slope per se which would involve the use of contrast information across many different frequency bands. To distinguish between these two possibilities, we have developed an experiment where observers were asked to discriminate changes in the spectral slope while different amounts of random contrast variation were introduced, with the purpose of disrupting their performance. This disruptive effect was designed to be particularly manifest if the observer really was performing a single-frequency-band contrast discrimination but to be unnoticeable if the observer was discriminating the change of slope per se. Our results imply that the observers do not usually detect changes in contrast in just one narrow spatial-frequency band when they discriminate changes in the slope of the amplitude spectrum. Rather, they must compare contrast between bands or, at least, they use contrast information from more than one band. However, for edge-enhanced (whitened) pictures, there is some evidence to suggest that observers rely on contrast changes in only a limited low-spatial-frequency band.
A Comparison of Natural-Image-Based Models of Simple-Cell Coding
Authors: Willmore Ben , Watters Paul A , Tolhurst David J
Published: August 2002

Models such as that of Olshausen and Field (O&F, 1997 Vision Research37 3311–3325) and principal components analysis (PCA) have been used to model simple-cell receptive fields, and to try to elucidate the statistical principles underlying visual coding in area V1. They connect the statistical structure of natural images with the statistical structure of the coding used in V1. The O&F model has created particular interest because the basis functions it produces resemble the receptive fields of simple cells.

We evaluate these models in terms of their sparseness and dispersal, both of which have been suggested as desirable for efficient visual coding. However, both attributes have been defined ambiguously in the literature, and we have been obliged to formulate specific definitions in order to allow any comparison between models at all. We find that both attributes are strongly affected by any preprocessing (eg spectral pseudo-whitening or a logarithmic transformation) which is often applied to images before they are analysed by PCA or the O&F model. We also find that measures of sparseness are affected by the size of the filters—PCA filters with small receptive fields appear sparser than PCA filters with larger spatial extent. Finally, normalisation of the means and variances of filters influences measures of dispersal. It is necessary to control for all of these factors before making any comparisons between different models.

Having taken these factors into account, we find that the code produced by the O&F model is somewhat sparser than the code produced by PCA. However, the difference is rather smaller than might have been expected, and a measure of dispersal is required to distinguish clearly between the two models.
Molecular phylogeny of the tribe Anthospermeae (Rubiaceae): Systematic and biogeographic implications
Authors: Anderson Cajsa L. , Rova Johan H. E. , Andersson Lennart
Published: August 2002

Phylogeny of the tribe Anthospermeae is estimated on the basis of nucleotide
sequence variation in the ITS region (nuclear ribosomal DNA) and the
rps16 intron (plastid DNA). It is concluded that it is
dubious whether the tribe is monophyletic including
Carpacoce. If Carpacoce does
belong to the tribe, then it is the sister group of all other genera. There is
no support for the traditional subdivision of the tribe into three subtribes.
Anthospermum, Galopina,
Nenax and Phyllis form one
strongly supported subclade. Coprosma,
Durringtonia, Leptostigma,
Nertera, Normandia,
Opercularia and Pomax form another
subclade in all most parsimonious trees, but this subclade lacks jackknife
support. Opercularia and Pomax,
referred to the subtribe Operculariinae, form a basal grade of this second
group. However, trees on which Operculariinae are monophyletic are only one
step longer than the most parsimonious ones. Normandia
is deeply nested within Coprosma. The subdivision of
Coprosma into two subgenera is shown to be artificial.
It is suggested that the ancestral area of Anthospermeae is Africa, and that
the group was spread by long-distance dispersal to north-eastern Antarctica.
It is further suggested that occurrences in Hawaii, Tristan da Cunha, and
America are due to long-distance dispersal at a time much later than primary
cladogenesis.
Annotated catalogue of the benthic marine algae of the Palolo Deep National Marine Reserve of Samoa
Authors: Skelton Posa A. , South G. Robin
Published: August 2002

A total of 124 species of benthic marine algae is reported from the Palolo
Deep National Marine Reserve on the island of Upolu (Western) Samoa
(13°49′S, 171°45′W). Included in the catalogue are 88
Rhodophyceae, 12 Phaeophyceae and 24 Chlorophyceae. This represents the first
survey of benthic marine algae for any site in the Samoan Archipelago in the
last 76 years. A total of 90 species newly recorded for the region brings the
total reported species to 288 (includes Cyanophyceae not reported here). This
is about 68% of the current flora from, for example, nearby Fiji. Of
the 11 sites investigated, the eastern algal rim of the main Deep
(0–10-m depth) is the most diverse, with 68 species. The subtidal (up to
25 m deep) is also diverse with 57 species recorded. The least diverse of all
the sites is the Borrow Pit with only six species.
Comparative morphology of the Australian species of Geissois (Cunoniaceae)
Authors: Schimanski L. J. , Rozefelds Andrew C.
Published: August 2002

The comparative morphology of the two Australian species of
Geissois is described in detail. The two species can be
distinguished from each other by stipule morphology, leaf and venation
characters and fruit size. Stipule morphology is illustrated and compared with
other genera in the tribe Geissoieae. A model is presented to illustrate the
differences in stipule development and morphology in the tribe. Phylogenetic
relationships within the Geissoieae are briefly discussed.
Non-lichenised Australian ascomycetes
Authors: Hyde Kevin D.
Published: August 2002

The ascomycetes of Australia are generally poorly known. Some major
contributions to their study last century are those of G. Beaton and G. Weste,
C. G. Hansford, K. D. Hyde and co-workers, J. Kohlmeyer and H. J. Swart. A
preliminary list of more than 1657 Australian ascomycete species was located
in an extensive search of the literature. The Australian
Meliolaceae, Mycosphaerellaceae
and Xylariaceae are relatively well known. Most
ascomycete records are in the genera Meliola,
Hypoxylonand Xylaria.
Comprehensive treatments of Australian ascomycetes can be found in the
monographs of the genera Anthostomella,
Didymosphaeria, Hypoxylonand
Massarina and Orders Heliotales and Pezizales.
Freshwater and marine ascomycetes and ascomycetes associated with plant
diseases have been relatively well studied. There is also a relatively large
amount of literature on the ascomycetes occurring on palms. Ascomyceteous
pathogens may be host specific (e.g. Mycosphaerella,
Phyllachoraspp.) or probable generalists (e.g.
Diaporthe, Glomerellaspp.).
Saprobes are less likely to be host-specific, but examples from palms indicate
that several species may exhibit a host genus preference. Biogeographical
distributions of ascomycetes on
Archontophoenix alexandrae indicate that when a plant is
removed from its native surroundings (e.g. a rainforest) and planted elsewhere
(e.g. in botanical gardens) it looses its endemic fungal population and
ubiquituous fungi move in and fill the niche of these lost fungi. Most
ascomycetes are inconspicuous and poorly collected. Studies on most of the
larger families are already in progress. Therefore, a habitat approach is
recommended for future Australian ascomycete studies. This can provide data on
biodiversity, ecology and the roles of the fungi and specimens can be lodged
in herbaria for future taxonomic studies.
Pharmacokinetics of sertraline in relation to genetic polymorphism of CYP2C19
Authors: Wang Jiu‐Hui , Liu Zhao‐Qian , Wang Wei , Chen Xiao‐Ping , Shu Yan , He Nan , Zhou Hong‐Hao
Published: August 2002

Objective

Our objective was to evaluate the relationship between the disposition of sertraline and the presence of the CYP2C19 gene and to define the contribution of cytochrome P450 2C19 (CYP2C19) to sertraline N‐demethylation.

Methods

A single oral 100‐mg dose of sertraline was administered to 6 subjects who were extensive metabolizers and 6 subjects who were poor metabolizers recruited from 77 healthy Chinese volunteers whose genotypes were predetermined by polymerase chain reaction–based amplification, followed by restriction fragment length polymorphism analysis. Phenotypes were determined by use of the omeprazole metabolic rate. The plasma concentrations of sertraline and desmethylsertraline were determined by gas chromatography with electron‐capture detection.

Results

Six poor metabolizers with m1 mutation had area under the plasma concentration versus time curve (AUC0‐∞) values (983.6 ± 199.3 μg · h/L versus 697.6 ± 133.0 μg · h/L; P < .05) and terminal elimination half‐life values of sertraline (35.5 ± 5.6 hours versus 23.5 ± 4.4 hours; P < .01) that were significantly higher than the values in 6 extensive metabolizers who were either homozygous or heterozygous for CYP2C19*1. The oral clearance of sertraline in poor metabolizers (105.3 ± 19.4 L/h) was significantly lower than that of extensive metabolizers (148.4 ± 28.6 L/h). The area under the concentration‐time curve from 0 to 144 hours and the maximum plasma concentration of desmethylsertraline in poor metabolizers were significantly lower than the values of extensive metabolizers (627.6 ± 203.8 μg · h/L versus 972.1 ± 270.3 μg · h/L; P < .05; and 23.6 ± 6.5 nmol/L versus 32.4 ± 8.2 nmol/L; P < .01; respectively).

Conclusions

The polymorphic CYP2C19 appears to be a major enzyme involved in the N‐demethylation of sertraline, and both extensive and poor metabolizers had marked differences in the disposition of sertraline.

Clinical Pharmacology & Therapeutics (2001) 70, 42–47; doi: 10.1067/mcp.2001.116513
Extensions to the Concept of Excess Commuting
Authors: Horner Mark W
Published: August 2002

When people commute to work longer or farther than the actual spatial arrangement of homes and workplaces suggest they could be commuting, people are engaging in excess commuting. In the aggregate, excess commuting is the nonoptimal or surplus work travel occurring in cities because people do not minimize their journeys to work. In this paper an alternative view of excess commuting based on a theoretical maximum commute is presented. The calculation of a theoretical maximum commute allows for an analysis of the range between the theoretical minimum and maximum commutes, which marks an improvement over current approaches to the measure of excess commuting. Conceptually, this range is taken to be the commuting capacity of a city. To what extent commuting capacity is consumed in terms of current levels of commuting forms a primary question of the analysis. A model is formulated and applied to 1990 Census data for a sample of US cities. Numerical and visual results suggest variation in the amount of excess commuting and consumed commuting potential for the sample of cities. The results also suggest a relationship between the jobs – housing balance of a city (as captured by its theoretical minimum commute) and its observed commute. Additionally, the maximization calculation is shown to provide insight into the degree of decentralized urban form. A conclusion is provided which relates the findings of this research to larger issues of urban sustainability.
The Elusive Concept of Localization Economies: Towards a Knowledge-Based Theory of Spatial Clustering
Authors: Malmberg Anders , Maskell Peter
Published: August 2002

A number of possible advantages of industry agglomeration—or spatial clustering—have been identified in the research literature, notably those related to shared costs for infrastructure, the build-up of a skilled labour force, transaction efficiency, and knowledge spillovers leading to firm learning and innovation. We identify two shortcomings of existing research on the clustering phenomenon. First, the abundance of theoretical concepts and explanations stands in sharp contrast with the general lack of work aimed at validating these mechanisms empirically and the contradictory evidence found in recent empirical work in the field. Second, there is still a lack of a unified theoretical framework for analyzing spatial clustering. In an attempt to remedy the latter shortcoming, this paper investigates the nature of the cluster from a knowledge-creation or learning perspective. We argue for the need to establish a specific theory of the cluster where learning occupies centre stage. The basic requirements for such a theory of the cluster are discussed. Two main components of such a theory are identified: it must explain the existence of the cluster on the one hand and its internal organization on the other.
Fractals and Picturesque Composition
Authors: Crompton Andrew
Published: August 2002

In this paper fractals are identified in classical mouldings by means of an algorithm for drawing Levy staircases. It is argued that traditional rules of composition favour fractal forms such as these, and advice on composition, taken from Ruskin, is examined to support this view. Because fractals are ubiquitous in nature their use in design offers a way to appear natural. The lack of fractals in modern architecture may therefore be connected to a lack of interest in picturesque composition.
Measuring the Public Costs and Benefits of Brownfield versus Greenfield Development in the Greater Toronto Area
Authors: De Sousa Christopher A
Published: August 2002

This paper summarizes the findings of a study comparing the environmental, social, and economic costs and benefits accruing to the public from redeveloping brownfields versus developing greenfields for both industrial and residential uses. With data taken from relevant projects in Toronto, Canada, four prototypical development scenarios were constructed for the purpose of a cost — benefit comparison. A quantitative model was then used to calculate the various public costs and benefits associated with the different scenarios. The findings shed light on the true costs and benefits involved in development and redevelopment projects, helping policymakers better assess the feasibility of brownfield redevelopment vis-à-vis greenfield development.
A Constrained CA Model for the Simulation and Planning of Sustainable Urban Forms by Using GIS
Authors: Yeh Anthony Gar-On , Li Xia
Published: August 2002

A constrained cellular automata (CA) model based on ‘grey cells’ for the simulation of different types of urban forms and developments is developed within a raster GIS. Remote sensing and GIS are used to supply information on environmental constraints and locations of growth centers for the simulation. The model is able to consider different criteria, such as urban forms, environmental suitability, and land consumption for the planning of sustainable cities. Seven different types of urban forms and developments that range from compact–monocentric, compact–polycentric, compact–monocentric–environmental, compact–polycentric–environmental, dispersed, highly dispersed, to very highly dispersed developments were simulated by using the model. The model can generate urban forms and developments with fractal structures that are close to real cities. The simulated patterns were evaluated by using different cost indicators related to sustainable development principles.
Property Rights and the Public Realm: Gates, Green Belts, and Gemeinschaft
Authors: Webster Chris
Published: August 2002

Discussions about gated communities, shopping malls, and industrial parks—proprietary developments produced by entrepreneurs—frequently espouse overly simplistic notions of private and public realms, viewing the encroachment of the latter by the former as a threat. In this essay I develop the thesis that, in reality, cities naturally fragment into many small publics, each of which may be thought of as a collective consumption club. The club realm may, therefore, be a more useful—and theoretically more powerful—idea than the public realm. I argue that proprietary communities are a particular case of urban consumption club—one in which legal property rights over neighbourhood public goods are assigned by property-market institutions. In other respects, the club realms that they create are not dissimilar from club realms created by other urban governance institutions. Government, the markets, and voluntary community action can all effectively assign property rights over shared neighbourhood goods, and in so doing create a set of included ‘members’ and a set of excluded ‘nonmembers’. In contextualising the discussions of gated communities in this way, I draw connections between three interrelated concepts: public goods, the public domain, and the public realm.
Categorical Perception of Race
Authors: Levin Daniel T , Angelone Bonnie L
Published: August 2002

Traditionally, research demonstrating categorical perception (CP) has assumed that CP occurs only in cases where natural continua are divided categorically by long-term learning or innate perceptual programming. More recent research suggests that this may not be true, and that even novel continua between novel stimuli such as unfamiliar faces can show CP effects as well. Given this, we ask whether CP is dependent solely on the representation of individual stimuli, or whether stimulus categories themselves can also cause CP. Here, we test the hypothesis that continua between individual faces that cross the categorical boundary between races show an enhanced CP effect. We find that continua running from a black face to a white face do, indeed, show stronger CP effects than continua between two black faces or two white faces. This suggests that CP effects are enhanced when continua run between two distinctly represented individual stimuli, and are further enhanced when those individuals are, in turn, members of different stimulus categories.
Morphological variation and speciation in Stylidium graminifolium (Stylidiaceae), description of S. montanum and reinstatement of S. armeria
Authors: Raulings E. J. , Ladiges P. Y.
Published: August 2002

Phenetic analyses of morphological variation within
Stylidium graminifolium Sw. ex Willd.
sens. lat. are presented. Plants collected from 65
localities throughout Victoria and southern New South Wales were scored for
eight leaf and 11 floral characters. Flowers collected from a subset of these
populations and preserved in ethanol were scored for 15 floral characters.
Five forms were identified in the analyses with three species warranting
taxonomic recognition.
Stylidium graminifolium Sw. ex Willd.
sens. str. has erect, glaucous, narrowly linear leaves
up to 2.5 mm wide with regular, fine serrations along the leaf margin. This
species has comparatively small, pale pink to white flowers with six prominent
and two reduced throat appendages surrounding the entrance to the nectary
tube. The scape is usually glandular–pubescent below the lowest flower
and bears 10–50 flowers. This species is widespread in eastern Australia
in well-drained sandy soils of lowlands and foothills.
Stylidium montanum Raulings & Ladiges sp. nov. has
suberect to spreading leaves with a fine, reddish scape bearing fewer than 30
deep pink flowers usually with six prominent and two reduced throat
appendages. It differs from S. graminifolium in its
habit, broader, oblanceolate leaves 3–5(–7) mm wide, pale to
mid-green leaves, deep pink flowers and a glabrescent scape below the lowest
flower. It occurs on peaty water-retentive soils in alpine and subalpine
situations above c. 1000 m.
Stylidium armeria (Labill.) Labill. is reinstated. This
species is characterised by narrowly oblanceolate leaves (3)5–15 mm wide
and 15–40 cm long, a glandular–hairy scape above the lowest flower
and 30–110 flowers per scape. Flowers are light pink to deep magenta
with eight prominent throat appendages. This species is widespread throughout
south-eastern Australia and is morphologically variable throughout its
distribution.
ON THE ENERGY OF TYPE-II SUPERCONDUCTORS IN THE MIXED PHASE
Authors: SANDIER ETIENNE , SERFATY SYLVIA
Published: August 2002

We study the Ginzburg–Landau energy of superconductors with high κ, put in a prescribed external field h ex , for h ex varying between the two critical fields Hc1 and Hc3. As κ → +∞, we give the leading term in the asymptotic expansion of the minimal energy and show that energy minimizers have vortices whose density tends to be uniform and equal to h ex .
Cholinergic toxic syndrome by the anticancer drug irinotecan: Acetylcholinesterase does not play a major role
Authors: Blandizzi Corrado , Danesi Romano , De Paolis Barbara , Di Paolo Antonello , Colucci Rocchina , Falcone Alfredo , Del Tacca Mario
Published: August 2002

Background

The anticancer drug irinotecan induces cholinergic side effects that are currently ascribed to the blockade of acetylcholinesterase. This study investigated (1) the pattern of acetylcholinesterase activity in patients receiving treatment with irinotecan and (2) the relationship between acetylcholinesterase activity and plasma concentrations of irinotecan, 7‐ethyl‐10‐hydroxycamptothecin (SN‐38), and SN‐38 glucuronide (SN‐38G).

Methods

Twenty‐five patients with advanced colorectal cancer were treated with 250 mg/m2 irinotecan administered by intravenous infusion for 60 minutes. Blood samples were collected before drug infusion and at 15 minutes and 45 minutes after the start of drug infusion. Blood acetylcholinesterase activity was determined by a colorimetric enzymatic assay, and irinotecan, SN‐38, and SN‐38G concentrations were determined in plasma by HPLC. The in vitro effects of irinotecan and other drugs on human acetylcholinesterase were also assessed.

Results

Compared with basal values, the activity of acetylcholinesterase in blood specimens collected during irinotecan infusion at 15 minutes (−0.76%) and at 45 minutes (−1.50%) showed no changes. No relationships were established between the activity of blood acetylcholinesterase at 15 or 45 minutes and plasma concentrations of irinotecan, SN‐38, or SN‐38G measured at the same time points. In vitro, the activity of acetylcholinesterase was inhibited by 100‐μmol/L irinotecan (−24.8%) and markedly reduced by 1‐μmol/L physostigmine (−86.7%), whereas neither SN‐38 nor camptothecin had an effect.

Conclusions

Although the use of erythrocyte acetylcholinesterase as a surrogate marker of acetylcholinesterase activity in the nervous system has not been firmly established, our findings do not support the hypothesis that the toxic cholinergic syndrome associated with irinotecan treatment depends on acetylcholinesterase blockade.

Clinical Pharmacology & Therapeutics (2002) 71, 263–271; doi: 10.1067/mcp.2002.121909
Fixed Categories in a Portable Landscape: The Causes and Consequences of Land-Cover Categorization
Authors: Robbins Paul
Published: August 2002

In this paper I explore both the causes and the effects of defining land-cover categories for the mapping of landscapes. Utilizing a participatory remote sensing technique in a case example from Rajasthan, India, I demonstrate that local and expert characterizations of the environment are qualitatively and quantitatively divergent. Satellite imagery, I therefore conclude, is not an impartial tool for the settlement of debates about land cover but is instead the result of prior debates about the character of nature. Moreover, such imagery acts as a force in the transformation of the environment; by fixing certain interpretations of the environment and forcing certain forms of management, technology changes on the land through a process of reverse adaptation. I conclude, therefore, that bureaucratic efforts at mechanical objectivity serve to institutionalize and therefore create measurable, quantifiable, and aggressive land covers through the practice of ecological modernization.
‘Not in My City’: Local Governments and Homelessness Policies in the Los Angeles Metropolitan Region
Authors: Law Robin
Published: August 2002

To understand local government social welfare policies in large metropolitan areas, we need to pay attention to the processes by which amorphous social problems are translated into well-defined services amenable to local government structures of provision, and we need to place these processes within an interjurisdictional context that is more complex than a simple ‘city-suburb’ binary opposition. In this paper I explore the interjurisdictional allocation of responsibility for social welfare in a fragmented metropolitan region, through a case study of city responses to the suburbanisation of homelessness in Los Angeles County in the 1990s. The results of a 1991 survey of all eighty-five local governments in the county revealed wide variations in the extent to which cities acknowledged responsibility for dealing with homelessness, and in the forms of actions adopted by cities. Some city characteristics (population size, median household income, and charter city status) were significant factors affecting the level of action on homelessness. However, the variation in city action must also be understood as a product of the metropolitan context, where city officials develop welfare policies with close attention to the actions of neighbouring cities, and with a keen awareness of the opportunities for burden shifting and ‘beggar thy neighbour’ responses. Although the relative mobility of homeless people (both forced and voluntary) heightens the impact of policy disparities among cities, a similar scenario can be imagined for other social needs in a politically fragmented region.
The ‘Women of New York’: A Fashionable Moral Geography
Authors: Domosh Mona
Published: August 2002

The landscape of mid-19–century New York City was marked by pockets of consumer and leisure spaces. I argue that many of the fears and anxieties generated by this visual efflorescence of consumption focused on what became a socially constructed ‘type’: the New York Woman. The association of moral outrage at the dangers of consumption with spaces inhabited by the New York Woman created what I have called a fashionable moral geography. I suggest that this moral coding of the 19th-century city reverberates in contemporary discussion of late 20th-century cities.
1a. Qualified Quantitative Geography
Authors: Doel Marcus A
Published: August 2002

The rapprochement of humanism and structuralism on the one hand, and quantitative and qualitative approaches on the other hand, has not addressed an implacable difficulty which continues to haunt both spatial science and ‘critical’ human geographies. That difficulty concerns the ontological and ethical status of numbers, and their relationship to concepts, events, and sensations. The paper engages with this difficulty through a combination of theoretical and literary writings, most notably Woody Allen's film Deconstructing Harry, Samuel Beckett's play Not I, and Derrida's work of Dissemination. Insofar as ‘one’ lacks consistency—by disavowing difference, alterity, and innumerable numbers—its deployment is invariably unbecoming, repressive, and ill-mannered. The ethical response is to divine ‘another way of working with numbers’, as Derrida once intimated; to prevent some ones from taking hold. The outcome is a form of poststructuralist geography that takes flight from all kinds of pointillism. After an opening scene that lays out the general setup of quantification and its qualification, the first section of the paper employs the notion of a soft ontology in order to prepare the way for ‘another way of working with numbers’ that is occasioned by a sensitivity towards the ontological buzzing and solicitation that accompanies processes of subjectification, objectification, identification, and enumeration. The paper concludes with an affirmation of a ‘disturbing geography’ that leaves everything in perpetual suspense.
Porterfield and Wells on the Motions of Our Eyes
Authors: Wade Nicholas J
Published: August 2002

William Porterfield (ca 1696 – 1771) and William Charles Wells (1757 – 1817) conducted experimental investigations on eye movements related to accommodation, binocular vision, and vertigo. Porterfield gave a correct interpretation of Scheiner's experiment and invented an optometer to measure the near and far points of distinct vision. He also demonstrated the involvement of the crystalline lens in accommodation by examining vision in an aphakic person. Wells devised an alternative means of measuring the limits of vision and noted his own deterioration of sight with age; he studied the effects of belladonna on pupil size and accommodation. Their analyses of binocular visual direction contrasted Porterfield's view that perceived location was innately determined with Wells's argument that visual direction was innate whereas visual distance was learned. Both Porterfield and Wells investigated the involvement of eye movements in binocular vision and in postrotary visual motion. Porterfield maintained that the eyes did not move following body rotation, whereas Wells, using an afterimage as stabilised retinal image, described the characteristics of postrotary nystagmus and their dependence on head orientation. Despite the neglect of Wells's work, he should be considered as laying the foundations for the study of vestibular – visual interaction, even though the function of the vestibular system was not known at that time.
Spatial Factors of Brightness Illusion in the Ehrenstein Figure
Authors: Salvano-Pardieu Véronique
Published: August 2002

The strength of brightness illusion in an Ehrenstein figure has been examined as a function of two variables—inducing line length and gap size—by a two-alternative forced-choice procedure. The results show an interaction between the two variables; the length of the inducers and gap size are both involved in the formation of the brightness illusion, with gap size as the stronger factor. A spatial limit (corresponding to a gap size of 2.4 deg) was found, below which the illusion is always present regardless of the length of the inducers. An area ratio, defined as the ratio of the area of the ring formed by the four inducing lines of an Ehrenstein figure to the area of the illusory surface, takes into account the different spatial factors studied in the experiment and the global size of the Ehrenstein figure. The strength of the illusion was found to increase linearly with increasing values of the area ratio.
Form and Movement in Stereokinetic Cycloids: Motion Lost and Found
Authors: Wilson John A , Robinson James O
Published: August 2002

In exploring stereokinesis, we devised flat cycloidal display figures which, when rotated on a disc in the frontal plane, are perceived as illusory three-dimensional forms with movement in depth; the dominant percepts were of twisted loops with an internal writhing motion. These dominant forms could be convincingly represented by stereo pairs derived from the flat display; related forms, not seen in the illusion, could also be constructed, seeming to show a selectivity for preferred stereokinetic forms by the perceptual system. Models were made of the stereo forms; when rotated, they showed similar illusions and selectivity. We suggest that the illusions arise because some components of the real motion do not appear in the sensory field. The perceptual system accommodates for this by constructing percepts which are not necessarily veridical but do reconcile form and motion into a coherent unity. The results are discussed in relation to concepts of invariance and rigidity, and with regard to the creative response to sensory data by the perceptual system.
Developmental Changes in the Effect of Inversion: Using a Picture Book to Investigate Face Recognition
Authors: Brace Nicola A , Hole Graham J , Kemp Richard I , Pike Graham E , Van Duuren Michael , Norgate Lorraine
Published: August 2002

A novel child-oriented procedure was used to examine the face-recognition abilities of children as young as 2 years. A recognition task was embedded in a picture book containing a story about two boys and a witch. The story and the task were designed to be entertaining for children of a wide age range. In eight trials, the children were asked to pick out one of the boys from amongst eight distractors as quickly as possible. Response-time data to both upright and inverted conditions were analysed. The results revealed that children aged 6 years onwards showed the classic inversion effect. By contrast, the youngest children, aged 2 to 4 years, were faster at recognising the target face in the inverted condition than in the upright condition. Several possible explanations for this ‘inverted inversion effect’ are discussed.
Optic Flow Helps Humans Learn to Navigate through Synthetic Environments
Authors: Kirschen Matthew P , Kahana Michael J , Sekuler Robert , Burack Benjamin
Published: August 2002

Self-movement through an environment generates optic flow, a potential source of heading information. But it is not certain that optic flow is sufficient to support navigation, particularly navigation along complex, multi-legged paths. To address this question, we studied human participants who navigated synthetic environments with and without salient optic flow. Participants used a keyboard to control realistic simulation of self-movement through computer-rendered, synthetic environments. Because these environments comprised series of identically textured virtual corridors and intersections, participants had to build up some mental representation of the environment in order to perform. The impact of optic flow on learning was examined in two experiments. In experiment 1, participants learned to navigate multiple T-junction mazes with and without accompanying optic flow. Optic flow promoted faster learning, mainly by preventing disorientation and backtracking in the maze. In experiment 2, participants found their way around a virtual city-block environment, experiencing two different kinds of optic flow as they went. By varying the rate at which the display was updated, we created optic flow that was either fluid or choppy. Here, fluid optic flow (as compared with choppy optic flow) enabled participants to locate a remembered target position more accurately. When other cues are unavailable, optic flow can be a significant aid in wayfinding. Among other things, optic flow can facilitate path integration, which involves updating a mental representation of place by combining the trajectories of previously travelled paths.
Velocity Constancy in a Virtual Reality Environment
Authors: Distler Hartwig K , Gegenfurtner Karl R , van Veen Hendrik A H C , Hawken Michael J
Published: August 2002

During everyday life the brain is continuously integrating multiple perceptual cues in order to allow us to make decisions and to guide our actions. In this study we have used a simulated (virtual reality—VR) visual environment to investigate how cues to speed judgments are integrated. There are two sources that could be used to provide signals for velocity constancy: temporal-frequency or distance cues. However, evidence from most psychophysical studies favours temporal-frequency cues. Here we report that two depth cues that provide a relative object–object distance—disparity and motion parallax—can provide a significant input to velocity–constancy judgments, particularly when combined. This result indicates that the second mechanism can also play a significant role in generating velocity constancy. Furthermore, we show that cognitive factors, such as familiar size, can influence the perception of object speed. The results suggest that both low-level cues to spatiotemporal structure and depth, and high-level cues, such as object familiarity, are integrated by the brain during velocity estimation in real-world viewing.
Recognition of Point-Light Biological Motion Displays by Young Children
Authors: Pavlova Marina , Krägeloh-Mann Ingeborg , Sokolov Alexander , Birbaumer Niels
Published: August 2002

We tested the ability of children 3–5 years of age to recognise biological motion displays. Children and adults were presented with moving point-light configurations depicting a walking person, four-legged animals (dogs), and a bird. Participants were able to reliably recognise displays with biological motion, but failed in the identification of a static (four consecutive frames taken from each sequence) version. The results indicate that, irrespective of the highly reduced and unusual structural information available in point-light displays, biological motion is sufficient for reliable recognition of human and non-human forms at an age as early as 3 years. Moreover, 5-year-olds exhibit the ceiling level of recognition. The findings are discussed in the context of the neuropsychological and brain mechanisms involved in biological motion perception.
Motion Capture Depends on Signal Strength
Authors: Festa-Martino Elena , Welch Leslie
Published: August 2002

When flickering dots are superimposed onto a drifting grating, the dots appear to move coherently with the grating. In this study we examine: (i) how the perceived direction of a compound stimulus composed of superimposed grating and dots, moving in opposite directions with equal speeds, is influenced by the relative strength of the motion signals; (ii) how the perceived speed of a compound stimulus composed of superimposed grating and dots, moving in the same direction but at different speeds, is influenced by the relative strength of the motion signals; and (iii) whether this stimulus is discriminable from its metameric speed match. Dot signal strength was manipulated by using different proportions of signal dots in noise and different dot lifetimes. Both the perceived direction and speed of these compound stimuli depended upon the relative motion-signal strengths of the grating and the dots. Those compound stimuli that appeared coherent were not discriminable from the speed-matched metameric compound stimuli. When the signals were completely integrated into a coherent compound stimulus, the local motion signals were no longer perceptually available, though both contributed to the global percept. These data strongly support a weighted-combination model where the relative weights depend on signal strength, instead of a winner-takes-all model.
Connectivity Perception of Partly Occluded Gratings in 4-Month-Old Infants
Authors: Kawabata Hideaki , Gyoba Jiro , Inoue Hajime , Ohtsubo Haruhiko
Published: August 2002

Four groups of eight 4-month-old infants were each habituated to one of four displays consisting of a grating of either low (0.4 cycle deg−1) or high (1.2 cycles deg−1) spatial frequency, whose central portion was covered up with a horizontal occluder which was either narrow (1.33 deg) or broad (4.17 deg). Posthabituation displays consisted of a complete grating of the same frequency as the habituated grating, along with a separate grating whose central portion was replaced with a black gap of the same height as the occluder in the habituation displays. All the infants, except those who were habituated to the high frequency with the broad occluder, looked longer at the separate grating than the complete grating display during posthabituation trials. Previously, we found that infants under 1 month of age perceive the grating continuation only when the occluder height is less than about 0.5 cycle of the grating; our present results show that this figure increases to about 1.6 cycles of the grating frequency in the case of 4-month-old infants. These findings indicate that those developmental changes depend on both the sufficiency of visual information available and the efficiency of the perceptual ability of infants for grasping spatial relationships.
Exploring the Link between Time to Collision and Representational Momentum
Authors: Gray Rob , Thornton Ian M
Published: August 2002

Previous research has shown that when a moving object is occluded prior to collision with another stationary object, observers tend to consistently underestimate the physical/actual time to collision (TTC). We examined whether mislocalization of the initial point of disappearance plays any role in this underestimation. To assess the contribution of mislocalization, we coupled a standard TTC paradigm with a representational-momentum paradigm. Representational momentum refers to the tendency to mislocalize the remembered stopping point of a moving object as being too far forward along an actual or implied path of motion. Using identical displays we found large representational-momentum shifts and consistent underestimation of TTC. When the displays were modified to disambiguate the point of disappearance, representational momentum was absent or significantly reduced and underestimates of TTC were effectively eliminated. These results strongly suggest that the represented point of disappearance is an important factor in TTC estimation and that systematic forward displacement of this point may partially explain frequently observed underestimation.