Nonlinear dynamics of a solid-state laser with injection

We analyze the dynamics of a solid-state laser driven by an injected sinusoidal field. For this type of laser, the cavity round-trip time is much shorter than its fluorescence time, yielding a dimensionless ratio of time scales $\sigma \ll 1$. Analytical criteria are derived for the existence, stability, and bifurcations of phase-locked states. We find three distinct unlocking mechanisms. First, if the dimensionless detuning $\Delta$ and injection strength $k$ are small in the sense that $k = O(\Delta) \ll \sigma^{1/2}$, unlocking occurs by a saddle-node infinite-period bifurcation. This is the classic unlocking mechanism governed by the Adler equation: after unlocking occurs, the phases of the drive and the laser drift apart monotonically. The second mechanism occurs if the detuning and the drive strength are large: $k =O(\Delta) \gg \sigma^{1/2}$. In this regime, unlocking is caused instead by a supercritical Hopf bifurcation, leading first to phase trapping and only then to phase drift as the drive is decreased. The third and most interesting mechanism occurs in the distinguished intermediate regime $k, \Delta = O(\sigma^{1/2})$. Here the system exhibits complicated, but nonchaotic, behavior. Furthermore, as the drive decreases below the unlocking threshold, numerical simulations predict a novel self-similar sequence of bifurcations whose details are not yet understood.Comment: 29 pages in revtex + 8 figs in eps. To appear in Phys. Rev. E (scheduled tentatively for the issue of 1 Oct 98

Lucerne Production and Economics on Stakeholder Ranches on Coastal Plain Acid Soils

Research using small plots determined factors restricting lucerne (Medicago sativa) production on Coastal Plain soils of the southern USA. These acid soils, primarily Ultisols and Alfisols, become deficient in B when limed to pH 6.8 or 7.0 for lucerne. Other production-limiting soil problems include poor drainage and aeration, subsoil acidity, and low natural fertility. The objective of this study was to evaluate stand longevity on hectare-size stakeholder fields when growth-limiting factors were eliminated by site selection and soil treatment

Calculation of the positron bound state with the copper atom

A new relativistic method for calculation of positron binding to atoms is presented. The method combines a configuration interaction treatment of the valence electron and the positron with a many-body perturbation theory description of their interaction with the atomic core. We apply this method to positron binding by the copper atom and obtain the binding energy of 170 meV (+ - 10%). To check the accuracy of the method we use a similar approach to calculate the negative copper ion. The calculated electron affinity is 1.218 eV, in good agreement with the experimental value of 1.236 eV. The problem of convergence of positron-atom bound state calculations is investigated, and means to improve it are discussed. The relativistic character of the method and its satisfactory convergence make it a suitable tool for heavier atoms.Comment: 15 pages, 5 figures, RevTe

THE EFFECT OF TONE ON THE SUCCESSIVE COMPARISON OF BRIGHTNESS

Last updated: 6/12/200

Land Stewardship for the 21\u3csup\u3est\u3c/sup\u3e Century: Pasture and Livestock Management Workshop for Novices

Land ownership patterns in Texas and the southern USA are changing. Since 1994 (Wilkins et al., 2000) consumers interested primarily in recreational purposes have become the predominant owners of rural land. This land ownership change has created potential land stewardship problems associated with natural resource management. Few, if any, new landowners have any training related to the soil-plant-animal interface. New land owners need linkage with subject matter experts from land grant universities in a relaxed instructional setting while providing the opportunity for question and answer sessions. Thus, a programme was developed by a multi-disciplinary, multi-agency team at the Texas A&M University (TAMU) Agricultural Research & Extension Centre at Overton targeting novice landowners. The main goals in developing the programme were to a) provide basic information regarding management of soil-plant-animal resources that leads to sound, economic decisions and good land stewardship; and b) introduce the programme participants to the educational resources available to them through the land grant university system

Positronic lithium, an electronically stable Li-e+^+ ground state

Calculations of the positron-Li system were performed using the Stochastic Variational Method and yielded a minimum energy of -7.53208 Hartree for the L=0 ground state. Unlike previous calculations of this system, the system was found to be stable against dissociation into the Ps + Li$^+$ channel with a binding energy of 0.00217 Hartree and is therefore electronically stable. This is the first instance of a rigorous calculation predicting that it is possible to combine a positron with a neutral atom and form an electronically stable bound state.Comment: 11 pages, 2 tables. To be published in Phys.Rev.Let

Volunteering in the care of people with severe mental illness: a systematic review

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

Positron and positronium affinities in the work-formalism Hartree-Fock approximation

Positron binding to anions is investigated within the work formalism proposed by Harbola and Sahni for the halide anions and the systems Li^- through O^- excluding Be^- and N^-. The toal ground-state energies of the anion-positron bound systems are empirically found to be an upper bound to the Hartree-Fock energies. The computed expectation values as well as positron and positronium affinities are in good agreement with their restricted Hartree-Fock counterparts. Binding of a positron to neutral species is also investigated using an iterative method.Comment: 12 pages, to appear in Physical Review