反射三次谐波产生与晶体对称性

在单晶硅和经离子注入的硅样品上测得了反射三次谐波。像我们的理论计算中所证明的那样,当样品绕表面法线转动时,线偏振的三次谐波强度显示了晶体的旋转对称性,对于轻注入的样品,存在一个注入剂量的临界值,高于此值,三次谐波信号与转动无关。作为剂量的函数,三次谐波强度对晶格损伤极为敏感。这使三次谐波技术可以在半导体工艺中用作监测离子注入的均匀程度。 关键词：     

Report On ‘Examples in Modular Chemistry’

This issue of The Chemical Educator is devoted to the Proceedings from a workshop symposium that I organized for the weekend of May 10–11, 1997. The two-day event was held in the Willard H. Dow Chemical Sciences laboratory building on the central campus of The University of Michigan in Ann Arbor, Michigan.     

DYNAMICS OF SPATIAL EXPLOITATION: A METAPOPULATION APPROACH

ABSTRACT. In this paper we present a bioeconomic model of a harvesting industry operating over a heterogeneous environment comprised of discrete biological populations interconnected by dispersal processes. The model generalizes the Gordon [1954]/Smith [1968] model of open-access rent dissipation by accounting for intertemporal and spatial “Ricardian” patterns of exploitation. This model yields a simple, but insightful, framework from which one can investigate factors that contribute to the evolution of resource exploitation patterns over space and time. For example, we find that exploitation patterns are driven by biological and fleet dispersal and biological and economic heterogeneity. We conclude that one cannot really understand the biological processes operating in an exploited system without knowing as much about the harvesting system as about the biological system.     

THE FLUORESCENCE EXCITATION SPECTRUM OF QUININE BISULFATE

Abstract— A new measurement of the fluorescence excitation spectrum of chromatographically homogeneous quinine bisulfate has been made using a spectrometer offering high resolution and high sensitivity. Comparison of this spectrum with the absorption spectrum of the compound indicates that its quantum yield is independent of the wave number of the exciting light within ± 5 per cent for 2.57 μ^-l v 5.0μ^-1.     

REGIONAL ECONOMIC IMPACTS OF CLIMATE CHANGE: A COMPUTABLE GENERAL EQUILIBRIUM ANALYSIS FOR AN ALASKA FISHERY

We compute the effects on the Alaska economy of reduced pollock harvests from rising sea surface temperature using a regional dynamic computable general equilibrium model coupled with a stochastic stock‐yield projection model for eastern Bering Sea walleye pollock. We show that the effects of decreased pollock harvest are offset to some extent by increased pollock price, and that fuel costs and the world demand for the fish, as well as the reduced supply of the fish from rising sea surface temperature, are also important factors that determine the economic and welfare effects.     

A PREDICTIVE MODEL TO INFORM ADAPTIVE MANAGEMENT OF DOUBLE‐CRESTED CORMORANTS AND FISHERIES IN MICHIGAN

The proliferation of double‐crested cormorants (DCCOs; Phalacrocorax auritus) in North America has raised concerns over their potential negative impacts on game, cultured and forage fishes, island and terrestrial resources, and other colonial water birds, leading to increased public demands to reduce their abundance. By combining fish surplus production and bird functional feeding response models, we developed a deterministic predictive model representing bird–fish interactions to inform an adaptive management process for the control of DCCOs in multiple colonies in Michigan. Comparisons of model predictions with observations of changes in DCCO numbers under management measures implemented from 2004 to 2012 suggested that our relatively simple model was able to accurately reconstruct past DCCO population dynamics. These comparisons helped discriminate among alternative parameterizations of demographic processes that were poorly known, especially site fidelity. Using sensitivity analysis, we also identified remaining critical uncertainties (mainly in the spatial distributions of fish vs. DCCO feeding areas) that can be used to prioritize future research and monitoring needs. Model forecasts suggested that continuation of existing control efforts would be sufficient to achieve long‐term DCCO control targets in Michigan and that DCCO control may be necessary to achieve management goals for some DCCO‐impacted fisheries in the state. Finally, our model can be extended by accounting for parametric or ecological uncertainty and including more complex assumptions on DCCO–fish interactions as part of the adaptive management process.     

Particle tunnelling in the 7-azaindole dimer

A model has been developed that attempts to calculate the particle (proton and deuteron) tunnelling probability in the molecular dimer of 7-azaindole.     

HABITAT PATCH OCCUPANCY DYNAMICS OF GLAUCOUS‐WINGED GULLS (LARUS GLAUCESCENS) I: A DISCRETE‐TIME MODEL

ABSTRACT. Diurnal habitat occupancy dynamics of Glaucous‐winged Gulls were evaluated in a system of six habitats on and around Protection Island, Washington. Data were collected on the rates of gull movement between habitat patches, and from these data the probabilities of transitions between habitats were estimated as functions of tide height and time of day. A discrete‐time matrix model based on the transition probabilities was used to generate habitat occupancy predictions, which were then compared to hourly census data. All model parameters were estimated directly from data rather than through model fitting. The model made reasonable predictions for two of the six habitats and explained 45% of the variability in the data from 2003. The construction and testing of mathematical models that predict occupancies in multiple habitats may play increasingly important roles in the understanding and management of animal populations within complex environments.     

AN IDENTIFICATION OF THE RADICAL GIVING RISE TO THE LIGHT-INDUCED ELECTRON SPIN RESONANCE SIGNAL IN PHOTOSYNTHETIC BACTERIA

Abstract— A reaction-center fraction isolated from Rhodopseudomonas spheroides chromatophores exhibits light-induced changes in its optical and electron spin-resonance (ESR) spectra. In particular, a bleaching at 870nm (P870) has been found to be closely correlated with the appearance of an ESR signal with a g factor of 2.0025 and a peak-to-peak line width of 10 G. The ESR signal is indistinguishable from light-induced signals found in chromatophores or whole cells.
A careful measurement of the spin concentration showed that the ratio of the light-induced spins to bleached P870 molecules is 1.1 ± 0.1. In addition the formation and decay kinetics are identical within experimental error under a variety of experimental conditions.
Previous work has shown that P870 is a bacteriochlorophyll molecule in a specialized environment and that the bleaching signifies oxidation. The present work provides strong evidence that the photo-bleaching of P870 produces the radical cation of bacteriochlorophyll, P870⁺, and that this radical is the source of the ESR signal in whole cells.
The quantum yield for the bleaching of P870 in reaction centers has been measured, using actinic light of wavelengths 880, 800, 760 and 680 nm. For light absorbed at 880 or 800 nm the efficiency is close to 100 per cent. In a coupled reaction, the oxidation of mammalian cytochrome c by P870⁺ proceeds with nearly the same efficiency.
The above results place definite limits on the possibilities for the identity of the primary acceptor. These possibilities are discussed.