Search Results - (Author, Cooperation:C. Lane)

2018-02-01

Institute of Physics Publishing (IOP)

1748-0221

Physics

2012-02-22

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Biological Evolution ; Cyanobacteria/genetics ; Cyanophora/*genetics ; *Evolution, Molecular ; Gene Transfer, Horizontal ; Genes, Bacterial ; *Genome, Plant ; Molecular Sequence Data ; Photosynthesis/*genetics ; Phylogeny ; Symbiosis

1551-2916

Blackwell Publishing Journal Backfiles 1879-2005

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

This paper quantifies the nucleation energy barrier that must be overcome if a faceted, defect-free particle with a nonequilibrium morphology is to change shape by intraparticle transport. Two types of crystals are considered: those whose equilibrium form is a truncated sphere and those whose equilibrium form is a cube. Numerical estimates show that, for a particle near equilibrium, the barrier becomes insurmountable for a facet larger than a few tens of nanometers. For nonequilibrium shapes where material must be transferred from faceted surfaces to uniformly curved surfaces to reach the equilibrium shape, the facets enlarge without a nucleation barrier (at a rate limited by diffusion or surface attachment kinetics) until they reach a fraction of their equilibrium size that is typically between 0.5 and 0.75. At this point, a significant barrier is encountered that, in the absence of step producing defects, prevents the particle from continuing toward equilibrium. For nonequilibrium shapes where material must be transferred to faceted surfaces from other parts of the crystal for it to reach the equilibrium shape, significant energy barriers for the nucleation of new layers persist even when the shape is far from equilibrium. Predictions from our model are compared to experimental observations reported by other researchers.

Electronic Resource

1551-2916

Blackwell Publishing Journal Backfiles 1879-2005

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

The influence of the nucleation energy barrier on the capillary-driven coarsening of faceted crystals that exchange material by diffusion is quantified. Our calculations are based on the assumption that the transport of material between particles must happen in series with the nucleation of partial layers on flat facets. Using a numerical model based on this idea, we simulate the time evolution of distributions of crystals that are made up of perfect faceted crystals (without step-producing defects), crystals containing step-producing defects, and mixtures of the two types. We find that the coarsening of a distribution containing only perfect faceted crystals is arrested at a size where the nucleation energy barrier becomes prohibitive. This critical size ranges from a few nanometers to several hundred nanometers, depending on material parameters and experimental conditions. When a small fraction of the crystals have step-producing defects (for these crystals the nucleation energy barrier vanishes), they can grow to large sizes at the expense of the perfect crystals and a bimodal grain size distribution is created. Based on these results, we hypothesize that when abnormal coarsening is observed in nature, it results from the presence of a small number of crystals with step-producing defects.

Electronic Resource

article

2024

Frau ; Lehre ; Arbeitskraft ; Berufstätigkeit ; Studium ; Hochschule ; Student ; Ausland ; Australien

Higher education quarterly, Bd. 78 (2024) H. 3, S. 934-956, 0263-9769

0951-5224

1468-2273

English

2018-05-10

Institute of Physics Publishing (IOP)

1748-0221

Physics

2018-11-15

American Physical Society (APS)

0556-2813

1089-490X

Physics

Nuclear Structure

1471-0528

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1477-9730

Blackwell Publishing Journal Backfiles 1879-2005

Architecture, Civil Engineering, Surveying

Antarctica, with its vast areas of snow, presents unusual problems to the photogrammetrist and the cartographer. The paper describes two methods used by the Directorate of Overseas Surveys to overcome these problems and to produce 1: 250 000 scale mapping. The first part of the paper gives an account of the use which was made of tricamera photography, with particular emphasis on the adaptation of Williamson multiplex equipment to operate with the oblique elements of tricamera photography. The second part of the paper, after outlining some of the fundamental principles of ERTS 1 (Landsat) imagery, goes on to describe the application of these principles when utilising imagery in the production of much needed image and line maps of Antarctic areas. Accuracies achieved by the two methods and their relative economies are discussed.〈section xml:id="abs1-2"〉〈title type="main"〉Résumé L'Antarctique, avec ses vastes étendues de neige, pose des problèmes particuliers au photogrammètre et au cartographe. On décrit ici deux méthodes utilisées par le Directorate of Overseas Surveys pour produire la carte au 1: 250 000. La première consiste à employer pour la prise de vues une chambre triple, associée pour la restitution à un multiplex Williamson modifié pour I'exploitation des vues obliques. La deuxième consiste en une tentative d'utilisation des images satellitaires ERTS 1 (Landsat). On analyse Vexactitude et le prix de revient des deux méthodes.〈section xml:id="abs1-3"〉〈title type="main"〉Zusammenfassung Die Antarktis bietet dem Photogrammeter und Kartographen mit ihren riesigen Schneeflächen ungewöhnliche Probleme. Im Artikel werden 2 vom Directorate of Overseas Surveys angewandte Verfahren beschrieben, um diese Schwierigkeiten zu überwinden und Karten im Massstab 1: 250 000 herzustellen. Im 1. Teil der Arbeit wird über die Anwendung von Dreikammer-Aufnahmen berichtet, wobei insbesondere auf die Adaption des Williamson-Multiplexgerätes zur Auswertung der dabei mit aufgenommenen Schrägbilder eingegangen wird. Im 2. Teil des Artikels werden die grundlegenden Prinzipien der ERTS (Landsat)-Aufnahmen skizziert und deren Anwendung zur Herstellung der dringend benötigten Bild- und Linienkarten antarktischer Gebiete beschrieben. Die mit den beiden Verfahren erzielten Genauigkeiten und ihre relative Wirtschaftlichkeit werden diskutiert.

Electronic Resource

1365-2427

Blackwell Publishing Journal Backfiles 1879-2005

Biology

1. The spatial and temporal abundance patterns, production and feeding habits of invertebrate predators were determined in a sand-bottomed, headwater stream in Virginia, U.S.A.2. Annual mean density and biomass of predators in debris dams were 3897 individuals m−2 and 2.5 g dry mass m−2, respectively, but only 711 individuals m−2 and 0.2 gm−2 on the sediment. Predator production was 8.36 gm−2yr−1 in debris dams compared to 1.52 gm−2yr−1 on the sediment. Annual predator production, weighted by habitat availability, was 1.73gm−2yr−1.3. The predominant taxa in terms of production were the chironomids Thienemannimyia spp, complex, Ablabesmyia parajanta, Zavrelimyia sp., and the odonate Cordulegaster maculata. Chironomidae and Odonata together comprised 77% of the production of the predator guild.4. Based on gut content analysis and calculations of the trophic basis of production, estimated predator production was supported mostly by Chironomidae (38%), detritus (20%), unidentifiable insects (14%), and Ephemeroptera (11%). Total food ingestion by predators was 9.8 gm−2yr−1, 63% of which was detritus and 37% of which was animal material on an areal basis. The predator guild consumed an estimated 94% of primary invertebrate consumer production on the channel surface of the stream.

Electronic Resource

1365-2427

Blackwell Publishing Journal Backfiles 1879-2005

Biology

1. An extensive series of PONAR grabs was used to determine the distribution and abundance of unionid clams in the freshwater tidal Hudson River.2. The five species of unionids collected were distributed very unevenly within the river. Mean river-wide density and biomass of unionids were 8.0m−2 and 6.2 g DM m−2 (shell-free)., respectively.3. The environmental variables that we measured (water depth, distance from shore, sediment granulometry and organic content, presence or absence of macrophytes, and the chlorophyll a and particulate organic matter content of the water) explained little of the variation in abundance of unionids.4. The distributions of the various species of clams did not differ significantly with respect to the environmental variables measured.5. We estimate that unionids filter a significant amount of water (0.14m3 m−2 day−1, on average) in the Hudson River estuary, roughly equivalent in magnitude to downstream flushing.6. We project that unionids will serve as a major substratum for the settlement of the zebra mussel (Dreissena polymorpha), which is now invading the estuary. We emphasize that unionids may play important non-trophic roles in large river ecosystems.

Electronic Resource

1365-3059

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Electronic Resource

1365-3059

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Electronic Resource

1365-3059

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Electronic Resource

1365-3059

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Electronic Resource

1365-3059

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Electronic Resource

1365-3059

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Electronic Resource

1365-3059

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Electronic Resource

1365-3059

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Electronic Resource

1365-3059

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Electronic Resource