A Ploidy-Sensitive Mechanism Regulates Aperture Formation on the Arabidopsis Pollen Surface and Guides Localization of the Aperture Factor INP1.

Pollen presents a powerful model for studying mechanisms of precise formation and deposition of extracellular structures. Deposition of the pollen wall exine leads to the generation of species-specific patterns on pollen surface. In most species, exine does not develop uniformly across the pollen surface, resulting in the formation of apertures-openings in the exine that are species-specific in number, morphology and location. A long time ago, it was proposed that number and positions of apertures might be determined by the geometry of tetrads of microspores-the precursors of pollen grains arising via meiotic cytokinesis, and by the number of last-contact points between sister microspores. We have tested this model by characterizing Arabidopsis mutants with ectopic apertures and/or abnormal geometry of meiotic products. Here we demonstrate that contact points per se do not act as aperture number determinants and that a correct geometric conformation of a tetrad is neither necessary nor sufficient to generate a correct number of apertures. A mechanism sensitive to pollen ploidy, however, is very important for aperture number and positions and for guiding the aperture factor INP1 to future aperture sites. In the mutants with ectopic apertures, the number and positions of INP1 localization sites change depending on ploidy or ploidy-related cell size and not on INP1 levels, suggesting that sites for aperture formation are specified before INP1 is brought to them.

Efficacy and safety of 3 versus 5 days of meloxicam as an analgesic for feline onychectomy and sterilization.

Three- or 5-day courses of meloxicam [0.2 mg/kg body weight (BW) subcutaneously pre- or postoperatively on Day 1 followed by 0.05 mg/kg BW, PO per day thereafter] were assessed for analgesic efficacy and safety in 50 client-owned cats undergoing onychectomy and sterilization. Primary outcome parameters were analgesia score, gait/lameness score, and need for rescue analgesia assessed at times 0, 1, 4, 7, 24, 28, 35, 48, 52, 57 hours and on Day 5. Packed cell volume/total solids and serum biochemistry were assessed at time 0 and Days 3 and 5. There were no differences in efficacy and safety parameters regardless of the treatment protocol employed and no cat required rescue analgesia. The patients that received meloxicam preoperatively had statistically better gait/lameness scores than those that received meloxicam postoperatively, supporting the principle of preemptive analgesia.

Prescriptive authority and psychology: a status report.

The progress of psychology toward the acquisition of prescriptive authority is critically reviewed. Advances made by other nonphysician health care professions toward expanding their scopes of practice to include prescriptive authority are compared with gains made by professional psychology. Societal trends affecting attitudes toward the use of psychotropic medications are reviewed, and the potential influence of such trends on the prescriptive authority movement is examined. A history of the prescriptive authority movement is documented, and recent legislative and policy initiatives are discussed.

Corporate funding and conflicts of interest: a primer for psychologists.

A presidential task force on external funding was established by the American Psychological Association (APA) in 2003 to review APA policies, procedures, and practices regarding the acceptance of funding and support from private corporations for educational and training programs; continuing education offerings; research projects; publications; advertising; scientific and professional meetings and conferences; and consulting, practice, and advocacy relationships. This article, based on the Executive Summary of the APA Task Force on External Funding Final Report, presents the findings and unanimous recommendations of the task force in the areas of association income, annual convention, research and journals, continuing education, education, practice, and conflicts of interest and ethics. The task force concluded that it is important for both APA and individual psychologists to become familiar with the challenges that corporate funding can pose to their integrity. The nature and extent of those challenges led the task force to recommend that APA develop explicit policies, educational materials, and continuing education programs to preserve the independence of psychological science, practice, and education.

Kinesin's biased stepping mechanism: amplification of neck linker zippering.

A physically motivated model of kinesin's motor function is developed within the framework of rectified Brownian motion. The model explains how the amplification of neck linker zippering arises naturally through well-known formulae for overdamped dynamics, thereby providing a means to understand how weakly-favorable zippering leads to strongly favorable plus-directed binding of a free kinesin head to microtubule. Additional aspects of kinesin's motion, such as head coordination and rate-limiting steps, are directly related to the force-dependent inhibition of ATP binding to a microtubule bound head. The model of rectified Brownian motion is presented as an alternative to power stroke models and provides an alternative interpretation for the significance of ATP hydrolysis in the kinesin stepping cycle.

Quasiadiabatic analysis for ionization of a particle in a periodically perturbed delta(x) potential.

We study an ionization process for a particle bound by an attractive delta(x) potential of a certain depth defined on a finite lattice under an external periodic force. Ionization coincides with the time when first two time dependent energy eigenvalues get close to each other. We use a slow driving force away from the resonance frequency. We also observe intermittent high frequency oscillation which can be analyzed with two level approximation.

Evolution of escape processes with a time-varying load.

We study an escape process of a noisy particle with a time varying load. We present an effective nonperturbative method which works even when the time varying load amplitude is comparable to other parameters. It is based on the idea that for every instant of time, we know the quasiadiabatic eigenspectrum and the quasiadiabatic eigenfunctions of the instantaneous system. We show that when two time-varying quasiadiabatic eigenvalues in the spectrum get close to each other, the amplitudes of the quasiadiabatic eigenfuntions show an abrupt change; therefore, the escape rate is highly affected.

Entropy evolution for the Baker map.

Gibbs entropy is invariant for the Baker map. A Jordan basis spectral decomposition of the Baker Frobenius-Perron operator suggests that any initial density evolves to the stationary density that has maximal entropy. This entropy conundrum is resolved by considering the difference between weak and strong convergence. A binary representation is used to make these points transparent. (c) 1998 American Institute of Physics.

Construction of the Jordan basis for the Baker map.

The Jordan canonical form basis states for an invertible chaotic map, the Baker map, are constructed. A straightforwardly obtained recursion formula is presented for construction of the Jordan states and of the spectral decomposition of the Frobenius-Perron evolution operator. Comparison of this method with earlier, subdynamics techniques demonstrates that it is much more direct and simpler. The physical significance of the Jordan states is approached from the point of view of an entropy evolution equation. The method is also applied to the Bernoulli map, yielding its eigenstates more straightforwardly than done previously. (c) 1997 American Institute of Physics.

Unstable evolution of pointwise trajectory solutions to chaotic maps.

Simple chaotic maps are used to illustrate the inherent instability of trajectory solutions to the Frobenius-Perron equation. This is demonstrated by the difference in the behavior of delta-function solutions and of extended densities. Extended densities evolve asymptotically and irreversibly into invariant measures on stationary attractors. Pointwise trajectories chaotically roam over these attractors forever. Periodic Gaussian distributions on the unit interval are used to provide insight. Viewing evolving densities as ensembles of unstable pointwise trajectories gives densities a stochastic interpretation. (c) 1995 American Institute of Physics.

Enhanced quantum fluctuations in a chaotic single mode ammonia laser.

A detailed study of the effects of quantum fluctuations in a chaotic single mode laser is presented. It has been well established that the linear noise approximation eventually becomes invalid for the case of chaotic dynamics. A more accurate description of the laser is achieved through use of nonlinear Langevin equations. Simple expressions for the time evolution of the phases of the electric field and polarization are derived. These expressions predict that chaotic dynamics will greatly enhance phase diffusion. This prediction is verified through numerical simulations. A quantitative method, for determining the amount of amplification of quantum noise by chaos is discussed. This method makes use of a metric introduced in symbolic dynamics. The fluctuations are shown to have been amplified by over two orders of magnitude, making them macroscopically visible.

Amplification of intrinsic fluctuations by the Lorenz equations.

Macroscopic systems (e.g., hydrodynamics, chemical reactions, electrical circuits, etc.) manifest intrinsic fluctuations of molecular and thermal origin. When the macroscopic dynamics is deterministically chaotic, the intrinsic fluctuations may become amplified by several orders of magnitude. Numerical studies of this phenomenon are presented in detail for the Lorenz model. Amplification to macroscopic scales is exhibited, and quantitative methods (binning and a difference-norm) are presented for measuring macroscopically subliminal amplification effects. In order to test the quality of the numerical results, noise induced chaos is studied around a deterministically nonchaotic state, where the scaling law relating the Lyapunov exponent to noise strength obtained for maps is confirmed for the Lorenz model, a system of ordinary differential equations.