The capability of a proportional-type lateral control system in providing aerodynamic heading-angle trajectory control during reentry

Capability of lateral control system to provide aerodynamic heading-angle control of vehicle having maximum lift-drag ratio during reentr

An analytical investigation of a simplified thrust-vector orientation technique for establishing lunar orbits

Simplified thrust vector orientation technique for establishing lunar orbit

Comparison of X-ray and gamma-ray dose-response curves for pink somatic mutations in Tradescantia clone 02

Microdosimetric data indicate that the mean specific energy,zeta, produced by individual charged particles from X rays and gamma rays is different for the two radiation qualities by nearly a factor of two. In order to test whether this influences the initial, linear component in the dose-effect relations, a comparison was made between dose-response curves for pink somatic mutations inTradescantia clone 02 stamen hairs following X and gamma irradiations. Absorbed doses ranged from 2.66 to 300 rad. The results are in agreement with predictions made on the basis of microdosimetric data. At low doses gamma rays are substantially less effective than X rays. The RBE of gamma rays vs. X rays at low doses was approximately 0.6, a value lower than those usually reported in other experimental systems

The UK Voluntary Monitoring Schemes for Pig Health and Welfare: working towards improved health status

A pork industry with high health status will have less disease, use fewer antibiotics and present less risk to public health. The United Kingdom has three voluntary pig health schemes (PHS); Wholesome Pigs Scotland (WPS) in Scotland, the BPEX Pig Health Scheme (BPHS) in England and Wales and the Pig Regen health and welfare checks (NIH&W). They capture information on different macroscopic conditions detected in slaughter pigs. In this study, the prevalence, seasonal variations and year trends of eight conditions as assessed by these PHS were compared and evaluated. Data collected between July 2005 and December 2012 were used. In total 2,061,779 pigs, from 4,420 pig units in 46,321 batches of pigs supplied to 25 abattoirs were examined. The respiratory conditions assessed were: enzootic pneumonia-like lesions, pleurisy, pleuropneumonia, abscesses in the lung; while the non-respiratory conditions were: pericarditis (PC), milk spots (MS), papular dermatitis (PD) and tail biting. The shape of year and seasonal effects among schemes were visualised and the effects were quantified across schemes. The shapes of year trend differed between the PHS for respiratory conditions but were similar for non-respiratory conditions. WPS and NIH&W had a lower prevalence of respiratory conditions than BPHS. This was also observed for PC and PD; however, BPHS had a lower prevalence for MS compared to the other schemes. Non-respiratory lesions showed marked seasonal effects. Continuous standardised monitoring of lesions at slaughter is an effective tool for monitoring disease incidence. Early detection of changes, when combined with comparison of similar schemes in countries with a similar profile of pig production and management, could enable prompt investigation and ultimately lead to ‘safer’ pork

Symbolic Dynamics Analysis of the Lorenz Equations

Recent progress of symbolic dynamics of one- and especially two-dimensional maps has enabled us to construct symbolic dynamics for systems of ordinary differential equations (ODEs). Numerical study under the guidance of symbolic dynamics is capable to yield global results on chaotic and periodic regimes in systems of dissipative ODEs which cannot be obtained neither by purely analytical means nor by numerical work alone. By constructing symbolic dynamics of 1D and 2D maps from the Poincare sections all unstable periodic orbits up to a given length at a fixed parameter set may be located and all stable periodic orbits up to a given length may be found in a wide parameter range. This knowledge, in turn, tells much about the nature of the chaotic limits. Applied to the Lorenz equations, this approach has led to a nomenclature, i.e., absolute periods and symbolic names, of stable and unstable periodic orbits for an autonomous system. Symmetry breakings and restorations as well as coexistence of different regimes are also analyzed by using symbolic dynamics.Comment: 35 pages, LaTeX, 13 Postscript figures, uses psfig.tex. The revision concerns a bug at the end of hlzfig12.ps which prevented the printing of the whole .ps file from page 2

On the recurrence and robust properties of Lorenz'63 model

Lie-Poisson structure of the Lorenz'63 system gives a physical insight on its dynamical and statistical behavior considering the evolution of the associated Casimir functions. We study the invariant density and other recurrence features of a Markov expanding Lorenz-like map of the interval arising in the analysis of the predictability of the extreme values reached by particular physical observables evolving in time under the Lorenz'63 dynamics with the classical set of parameters. Moreover, we prove the statistical stability of such an invariant measure. This will allow us to further characterize the SRB measure of the system.Comment: 44 pages, 7 figures, revised version accepted for pubblicatio

Lorenz-like systems and classical dynamical equations with memory forcing: a new point of view for singling out the origin of chaos

A novel view for the emergence of chaos in Lorenz-like systems is presented. For such purpose, the Lorenz problem is reformulated in a classical mechanical form and it turns out to be equivalent to the problem of a damped and forced one dimensional motion of a particle in a two-well potential, with a forcing term depending on the ``memory'' of the particle past motion. The dynamics of the original Lorenz system in the new particle phase space can then be rewritten in terms of an one-dimensional first-exit-time problem. The emergence of chaos turns out to be due to the discontinuous solutions of the transcendental equation ruling the time for the particle to cross the intermediate potential wall. The whole problem is tackled analytically deriving a piecewise linearized Lorenz-like system which preserves all the essential properties of the original model.Comment: 48 pages, 25 figure

Analysis of the shearing instability in nonlinear convection and magnetoconvection

Numerical experiments on two-dimensional convection with or without a vertical magnetic field reveal a bewildering variety of periodic and aperiodic oscillations. Steady rolls can develop a shearing instability, in which rolls turning over in one direction grow at the expense of rolls turning over in the other, resulting in a net shear across the layer. As the temperature difference across the fluid is increased, two-dimensional pulsating waves occur, in which the direction of shear alternates. We analyse the nonlinear dynamics of this behaviour by first constructing appropriate low-order sets of ordinary differential equations, which show the same behaviour, and then analysing the global bifurcations that lead to these oscillations by constructing one-dimensional return maps. We compare the behaviour of the partial differential equations, the models and the maps in systematic two-parameter studies of both the magnetic and the non-magnetic cases, emphasising how the symmetries of periodic solutions change as a result of global bifurcations. Much of the interesting behaviour is associated with a discontinuous change in the leading direction of a fixed point at a global bifurcation; this change occurs when the magnetic field is introduced