1,028 research outputs found
Molecular Devices. Chiral, Bichromophoric Silicones
The interaction of chromophores is proposed as a basis for the construction of devices with high complexity. Silicones are promising elements of structure to control the function of such devices
Large scale oceanic circulation and fluxes of freshwater, heat, nutrients and oxygen
Submitted in partial fulfillment of the requirements for the degree of Doctor of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution December 1999A new, global inversion is used to estimate the large scale oceanic circulation based on
the World Ocean Circulation Experiment and Java Australia Dynamic Experiment hydrographic
data. A linear inverse "box" model is used to combine consistently the transoceanic
sections. The circulation is geostrophic with an Ekman layer at the surface and oceanic
layers defined by neutral surfaces. Near-conservation of mass, salt and top-to-bottom silica
is required and, in addition, heat and the phosphate-oxygen combination (170[P04]+[02])
are conserved in layers that are not in contact with the surface. A globally-consistent solution
is obtained for a depth-independent adjustment to the thermal wind field, freshwater
flux divergenees, the Ekman transport, and the advective and diffusive dianeutral fluxes
between layers. A detailed error budget permits calculation of statistical uncertainties,
taking into account both the non-resolved part of the solution and the systematic errors
due to the temporal oceanic variability. The estimated water mass transports during the
WOCE period (1985-1996) are generally similar to previous published estimates. However,
important differences are found. In particular, the inflow of bottom waters into the
Pacific Ocean is smaller than in most previous estimates. Utilization of property anomaly
conservation constraints allows the estimation of significant dianeutral diffusivities in deep
layers, with a global average of 3 ± lcm2s- 1 north of 30°S. Dianeutral transfers indicate
that about 20 Sv of bottom water is formed in the Southern Ocean. Significant ocean-atmosphere
heat fluxes are found, with a global heating of 2.3 ± 0.4PW in the tropical
band and a corresponding cooling at high latitudes. The signature of a large-scale average
export production is found for nutrients in several temperate regions. Despite the large
uncertainties, the production magnitudes are consistent with independent measurements
from sediment traps and isotopic data. Net nutrient sources or sinks are found in several
regions, suggesting either transport of dissolved organic matter or a seasonal alias.
Oxygen indicates large exchanges with the atmosphere, with intake at high latitudes and
outgassing/remineralization at low latitudes.This work was supported in part by the Jet Propulsion Laboratory/CALTECH (contract
#958125), and by gifts from Ford, General Motors, and Daimler-Chrysler to MIT's
Climate Modelling Initiative
Secondary Electron Emission from Solids. II. Theoretical Descriptions
A primary beam impinging on a solid target suffers elastic and inelastic collisions with the components of the solid. These collisions can be incorporated into a Monte-Carlo simulation model if all the cross sections associated with the various types of collisions are known.
Elastic diffusion effects are mainly related to the interactions of the particles with the real potential V(r) surrounding each ionic core. An essential simplification of the inelastic interactions is to consider that the solid reacts as a whole to an external probe, which is the incident electron beam. The linear response of the solid to an external perturbation is described by its dielectric function.
In the present paper, the methods used to evaluate the elastic and inelastic cross-sections and to simulate the secondary electron emission are reviewed and discussed
Secondary Electron Emission from Solids. I. Secondary Electron Spectroscopy
The secondary electron emission spectroscopy can provide useful information about the transitions in the electronic structure from solids and deals with the detection of fine structures superimposed on the true secondary peak, in the kinetic energy range of the true secondary electrons.
Several mechanisms have been proposed for the creation of these fine structures: diffraction phenomena, plasmon decay, interband transitions to unoccupied levels, Auger transitions and more recently, autoionization emission. Some features could not be explained as being due to any bulk effect and were considered as indicative of a need to include surface wave-matching arguments in the analysis of secondary electron emission spectra.
The authors give a review of the recent literature on the topic, including their own experience on the subject
TPOS2020 : Tropical Pacific Observing System for 2020
This paper presents the new international TPOS2020 project: why it has been established, what are its scientific objectives, its proposed organization, governance, and what the expected outcomes are. It is aiming at informing Coriolis, Mercator Océan, and the operational oceanography communities, all concerned, and involved in generating interest and contributions to the project. Building upon its scientific activities in the Pacific and the surrounding countries, the French community is willing to take an active role in this international project. The TPOS 2020 Project is a focused, finite term project, which began in 2014 and will be completed in 2020. It will evaluate, and where necessary provide guidance, to change all elements that contribute to the Tropical Pacific Observing System (TPOS) based on a modern understanding of tropical Pacific science. Learning lessons from the great success-and finally partial collapse- of the TAO/TRITON array, the project objective is to build a renewed, integrated, internationally-coordinated and sustainable observing system in the Tropical Pacific, meeting both the needs of climate research and operational forecasting systems. The scientific objectives are: - To redesign and refine the TPOS to observe El Niño Southern Oscillation (ENSO) and advance scientific understanding of its causes, - To determine the most efficient and effective observational solutions to support prediction systems for ocean, weather and climate services, - To advance understanding of tropical Pacific physical and biogeochemical variability and predictability. TPOS2020 is coordinated by a steering committee with task teams and working groups working on specific aspects of the observing system. Since much of the use and benefit of TPOS data will be achieved through model assimilation and syntheses, the operational modeling centers are considered key partners. The TPOS2020 project also opens partnerships with other global ocean observing communities: the meteorological community, and the coastal and regional ocean communities. TPOS 2020 embraces the integration of complementary sampling technologies; it will consider the different observing system components as an integrated whole, targeting robustness and sustainability, along with a developed governance and coordination
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