A Message to the Student Forester

Many times during his four years of academic life the average student forester is confronted with the problem of choosing between the subjects of forest management, forest utilization, or any one o£ the other allied subjects offered in this course. Whether he desires to work for private industry, or some governmental agency, any decision he makes will place him in one o£ these three categories. A student preparing for one type o£ work may be required to study subjects that are foreign to the other branches. However, the fundamental duties, the accompanying responsibilities, and the essential requirements of each after graduation, are practically the same

The Kawishiwi Experimental Forest

An experimental forest is an outdoor laboratory where investigations of plant life may be studied under natural conditions. To be most useful it should be typical of the forested area that it represents so that the results obtained may have general application

Excitation transfer in C-phycocyanin

Calculations of excitation transfer rates among the chromophores of C-phycocyanin using the Förster inductive resonance transfer mechanism have been carried out using the new coordinates for the position and orientation of the chromophores (Schirmer, T., Bode, W. and Huber, R. (1987) J. Mol. Biol. 196, 677–695). Several of the rate constants are significantly altered from the results of our calculations using the previously published coordinates (Sauer, K., Scheer, H. and Sauer, P. (1987) Photochem. Photobiol. 46, 427–440). In particular, for the (αβ)3-trimers of Mastigocladus laminosus or for the (αβ)3-trimers or the (αβ)6-hexamers of Agmenellum quadruplicatum, the new calculations predict excited state relaxation components with exponential time constants shorter than 1 ps. In fact, some of the interchromophore interactions are so strong that exciton coupling is probably the relevant mechanism of interaction. The largest exciton energy is calculated to be about 56 cm−1, for the interaction between the adjacent α84 and β84 chromophores of neighboring monomer units within the (αβ)3-trimers or (αβ)6-hexamers. An energy transfer model invoking a combination of pairwise exciton formation followed by slower Förster transfer steps is described

BEAM-CAVITY INTERACTION IN ELECTRON STORAGE RINGS

A formal expression is obtained for the energy loss per turn, of a rigid bunch of electrons, to a closed cylindrical cavity with quality factor Q. The expression is valid provided the diameter of the entrance and exit ports for the beam are small compared to the bunch length. The effect of the ports is studied in an independent computational method. The energy loss is numerically evaluated for a range of parameters of interest to electron storage rings

A general theory of the spectroscopic properties of partially ordered ensembles. II. Two‐vector problems

We have expanded on the results of an earlier paper [J. Chem. Phys. 72, 221 (1980)] which deals with a method for determining the response of a static, partially ordered ensemble of molecules to various types of electromagnetic probes. In this paper we consider types of spectroscopy whose response depends on the location of two vectors in an axis system fixed with respect to the molecule. Examples of such spectroscopies discussed in detail include fluorescence polarization, photoselection linear dichroism, Raman spectroscopy, and two‐photon absorption. We outline the kinds of structural information available from polarization experiments on partially ordered ensembles.Keywords: ENSEMBLE, POLARIZATION, SPECTROSCOPY, ORIENTATION, RAMAN SPECTRA, MOLECULES, DICHROISM, FLUORESCENC

A general theory of the spectroscopic properties of partially ordered ensembles. I. One vector problems

We have developed a method for determining the response of a static, partially ordered ensemble of molecules to various types of electromagnetic probes. In our formalism a physical model is constructued for the orientational distribution function, which is represented as a volume integral over a set of weighting functions. Procedures are given for obtaining geometrical and statistical parameters from analysis of the oriented line shapes and intensities. Explicit treatments of linear dichroism, circular dichroism, and magnetic resonance are developed as well as detailed mathematical techniques for calculation of the distribution function.Keywords: Spectroscopy, Molecules, Orientation, Magnetic resonance, Line widths, Distribution functions, DichroismKeywords: Spectroscopy, Molecules, Orientation, Magnetic resonance, Line widths, Distribution functions, Dichrois

Single photon timing system for picosecond fluorescence lifetime measurements

A single‐photon timing system is described which is capable of extracting fluorescence lifetimes as short as 25 ps. The system is an improved version of an earlier apparatus. The new system uses a synchronously pumped, mode‐locked dye laser with 10‐ps pulses operating at 82‐MHz repetition rate. A fast photodetector and a leading‐edge discriminator were developed to use with this light source. Also, a special rate reduction circuit was built to eliminate large oscillations in fluorescence decay spectra due to the excessive stop rates that overload commercial time‐to‐amplitude converters.This is the publisher’s final pdf. The published article is copyrighted by the American Institute of Physics and can be found at: http://rsi.aip.org/.Keywords: pulses, photodetectors, fluorescence, mode locking, experimental data, optical pumping, lifetime, photons, mhz range, synchronization, dye lasers, time measurement, time−to−amplitude converter

A new approach to the theory of linear dichroism in partially ordered systems. Application to reaction centers and whole cells of photosynthetic bacteria

We have developed a new approach to the theory of linear dichroism in partially ordered systems. The description of the partially ordered ensemble uses a density of states function, D(θ, ϕ, Δ), which gives the probability that the direction of polarization for incident polarized light has spherical angles θ and ϕ in an axis system fixed with respect to the molecule; Δ = (Δₜ, Δ₂ ... Δₙ.) is a set of parameters that describes the partial ordering. We derive new formulas for linear dichroism using the density of states function and then apply these formulas to the analysis of linear dichroism in reaction centers and whole cells of photosynthetic bacteria. One advantage of our approach is that the order parameter, Δ, provides a more complete description of the distribution function than the traditional order parameters used by other authors. Knowledge of Δ gives a good physical description of the partial ordering and allows one to calculate accurate limits for the range of possible orientations of the transition moments.This is the publisher’s final pdf. The published article is copyrighted by The Biophysical Society and published by Cell Press/Elsevier

Electronic Structure and Oxidation State Changes in the Mn4Ca Cluster of Photosystem II

Oxygen-evolving complex (Mn4Ca cluster) of Photosystem II cycles through five intermediate states (Si-states, i =0-4) before a molecule of dioxygen is released. During the S-state transitions, electrons are extracted from the OEC, either from Mn or alternatively from a Mn ligand. The oxidation state of Mn is widely accepted as Mn4(III2,IV2) and Mn4(III,IV3) for S1 and S2 states, while it is still controversial for the S0 and S3 states. We used resonant inelastic X-ray scattering (RIXS) to study the electronic structure of Mn4Ca complex in the OEC. The RIXS data yield two-dimensional plots that provide a significant advantage by obtaining both K-edge pre-edge and L-edge-like spectra (metal spin state) simultaneously. We have collected data from PSII samples in the each of the S-states and compared them with data from various inorganic Mncomplexes. The spectral changes in the Mn 1s2p3/2 RIXS spectra between the S-states were compared to those of the oxides of Mn and coordination complexes. The results indicate strong covalency for the electronic configuration in the OEC, and we conclude that the electron is transferred from a strongly delocalized orbital, compared to those in Mn oxides or coordination complexes. The magnitude for the S0 to S1, and S1 to S2 transitions is twice as large as that during the S2 to S3 transition, indicating that the electron for this transition is extracted from a highly delocalized orbital with little change in charge density at the Mn atoms