7,337 research outputs found
Early Archean tonalite gneiss in the upper peninsula of Michigan
Geochronological results on tonalite gneiss of northern Michigan that is 3.56 Ga or slightly older is presented. Tonalitic augen gneiss and structurally overlying biotite gneiss and schist are exposed in a dome near Watersmeet. They are part of an extensive gneiss terrane of southern Minnesota, Wisconsin and Michigan that includes rocks of early to late Archean ages and lies south of the Wawa volcanic subprovince. Two samples of the augen gneiss and one of the biotite gneiss show zircon grains of similar shape, zoning, color, and development of crystal faces. These zircons give Pb/U isotopic ratios that plot on a chord of 3,560 + or - 40 m.y. upper intersect and of 1,250 + or m.y. lower intersect. The 3,560 m.y. number is believed to be a minimum age because analysis of one of the least discordant zircon fractions by ion microprobe that gave a nearly concordant age of 3,650 m.y. The 1,250 m.y. lower intersect is without geological significance: it is interpreted to be a result of multiple lead loss at 2.7, 1.8, and 0.5 Ga by U/Pb in zircon. Archean rocks 10 to 25 km northwest of the Watersmeet dome give a 2.75 Ga age on zircons. Quartz monzonite here is dated at 2.65 Ga
A study of marine fouling ecosystems
The aim of the project was the provision of information regarding the effect of various toxins on members of the fouling ecosystems. This was undertaken in two parts: A background survey to provide information for the main study, the latter consisting of experimental work. Part 1 - the Introduction - deals with fouling, importance and implications to the Shipping Companies and provides information on the costs and historical aspects of fouling among other things. Part 2 - the Surveys - provide information on the fouling patterns of ships both laid up and in service, as well as details of the distribution of fouling algae along the British Coast and their fouling systems, the results obtained are discussed in relation to the changes in fouling ecosystems observed with the changes in toxins used in antifoullng paints. The implications of this being discussed in Part 4. A summary of the findings is also included. Part 3 - the experimental work - provides supporting evidence for the changes observed in Part 2 as well as providing other information on the effect of the toxins used on the algae. The results obtained are discussed in relation to the general effect of the toxin; applications of the methods used into future research in marine fouling and possible methods of bioasaay. Part 4 - discusses the implications of the change over in the components of the fouling ecosystem. Explores the possibility of new lines of research into fouling based on the experiments undertaken and discusses the possible occurrence of resistance of algae to toxins being used as antifoulants. Standard experimental methods are given in the appendix, the remainder being included in the main text
Effect of Local Electron-Electron Correlation in Hydrogen-like Impurities in Ge
We have studied the electronic and local magnetic structure of the hydrogen
interstitial impurity at the tetrahedral site in diamond-structure Ge, using an
empirical tight binding + dynamical mean field theory approach because within
the local density approximation (LDA) Ge has no gap. We first establish that
within LDA the 1s spectral density bifurcates due to entanglement with the four
neighboring sp3 antibonding orbitals, providing an unanticipated richness of
behavior in determining under what conditions a local moment hyperdeep donor or
Anderson impurity will result, or on the other hand a gap state might appear.
Using a supercell approach, we show that the spectrum, the occupation, and the
local moment of the impurity state displays a strong dependence on the strength
of the local on-site Coulomb interaction U, the H-Ge hopping amplitude, the
depth of the bare 1s energy level epsilon_H, and we address to some extent the
impurity concentration dependence. In the isolated impurity, strong interaction
regime a local moment emerges over most of the parameter ranges indicating
magnetic activity, and spectral density structure very near (or in) the gap
suggests possible electrical activity in this regime.Comment: 9 pages, 5 figure
Femtosecond probing of bimolecular reactions: The collision complex
Progress has been made in probing the femtosecond
dynamics of transition states of chemical reactions.(1) The
"half-collision" case of unimolecular reactions has been
experimentally investigated for a number of systems and
much theoretical work has already been developed.(2) For
bimolecular reactions, the case of full collision, the zero of
time is a problem which makes the femtosecond temporal
resolution of the dynamics a difficult task
Femtosecond real-time probing of reactions. VIII. The bimolecular reaction Br+I2
In this paper, we discuss the experimental technique for real-time measurement of the lifetimes of the collision complex of bimolecular reactions. An application to the atom–molecule Br+I_2 reaction at two collision energies is made. Building on our earlier Communication [J. Chem. Phys. 95, 7763 (1991)], we report on the observed transients and lifetimes for the collision complex, the nature of the transition state, and the dynamics near threshold. Classical trajectory calculations provide a framework for deriving the global nature of the reactive potential energy surface, and for discussing the real-time, scattering, and asymptotic (product-state distribution) aspects of the dynamics. These experimental and theoretical results are compared with the extensive array of kinetic, crossed beam, and theoretical studies found in the literature for halogen radical–halogen molecule exchange reactions
Bioremediation of Contaminated Surface Soils
Biological remediation of soils contaminated with organic chemicals is an alternative treatment technology that can often meet the goal of achieving a permanent clean-up remedy at hazardous waste sites, as encouraged by the U.S. Environmental Protection Agency (U.S. EPA) for implementation of The Superfund Amendments and Authorization Act (SARA) of 1986. Bioremediation is consistent with the philosophical thrust of SARA, for it involves the use of naturally occurring microorganisms to degrade and/or detoxify hazardous constituents in the soil at a contaminated slip to protect public health and the environment.Bioremediation of contaminated soils, including applications and limitations, has been addressed
In Situ Bioremediation of Contaminated Unsaturated Subsurface Soils
An emerging technology for the remediation of unsaturated subsurface soils involves the use of microorganisms to degrade contaminants which are present in such soils. Understanding the processes which drive in situ bioremediation, as well as the effectiveness and efficiency of the utilization of these systems, are issues which have been identified by the Regional Superfund Engineering Forum as concerns of Superfund decision makers
Absence of reflection as a function of the coupling constant
We consider solutions of the one-dimensional equation where is locally integrable, is integrable with supp, and
is a coupling constant. Given a family of solutions
which satisfy for all , we prove that the zeros of , the Wronskian of and , form a discrete set
unless . Setting , one sees that a particular
consequence of this result may be stated as: if the fixed energy scattering
experiment gives rise to a reflection coefficient
which vanishes on a set of couplings with an accumulation point, then .Comment: To appear in Journal of Mathematical Physic
Recommended from our members
Beagle to the Moon: nn experiment package to measure polar ice and volatiles in permanently shadowed areas or beneath the lunar surface
The Beagle Science Package is a flight qualified set of instruments which should be deployed to the lunar surface to answer the questions about water and volatiles present in permanently shadowed regions and/or beneath the surface
- …