Library

Notes: Starting from the hydrodynamic description of the positive column in a neon glow discharge, a numerical approach is used in order to study the nonlinear properties of ionization waves. Within the instability region of the homogeneous equilibrium state, a secondary instability of the Eckhaus type is found. Compared to the classical results, the plasma system shows some peculiarities, e.g., an asymmetric stability band and strong selection of periodic patterns. The dependency of the shape and the width of this band on the discharge parameters is investigated. The spatiotemporal dynamics connected with the transitions from the stability band to the instability region have been studied showing different behavior on the upper and lower border of the stability region. Normally a subcritical Eckhaus instability has been revealed. Moreover, at selected sets of plasma parameters the phenomenon of spatiotemporal intermittency is found. © 2000 American Institute of Physics.

Notes: Conditions for the onset of irregular wave dynamics are derived from a theoretical description of ionization waves in a glow discharge by means of amplitude equations. It is shown that the Benjamin–Feir condition of the cubic Ginzburg–Landau equation is a necessary but not sufficient condition for loss of stability of plane waves in a higher order amplitude equation. The onset conditions are numerically evaluated in the case of a neon discharge. Experimental findings concerning the onset of chaotic wave dynamics near the critical point agree very well with the theoretical predictions. This example reveals physical relevance of higher order nonlinearities close to the critical point. © 2001 American Institute of Physics.

Notes: © American Institute of Physics.

Notes: Experimental observation of transitions between discrete longitudinal wave modes in a dc neon glow discharge is reported. Experimental findings concerning the pattern selecting instability agree with observations of the Eckhaus instability in fluid systems. This is supported by theoretical considerations of a model equation (Complex Ginzburg–Landau equation) based on a fluid model. © 1998 American Institute of Physics.

Notes: We investigate the bifurcation phenomena and the change in phase space structure connected with the transition from regular to chaotic scattering in classical systems with unbounded dynamics. The regular systems discussed in this paper are integrable ones in the sense of Liouville, possessing a degenerated unstable periodic orbit at infinity. By means of a McGehee transformation the degeneracy can be removed and the usual Melnikov method is applied to predict homoclinic crossings of stable and unstable manifolds for the perturbed system. The chosen examples are the perturbed radial Kepler problem and two kinetically coupled Morse oscillators with different potential parameters which model the stretching dynamics in ABC molecules. The calculated subharmonic and homoclinic Melnikov functions can be used to prove the existence of chaotic scattering and of elliptic and hyperbolic periodic orbits, to calculate the width of the main stochastic layer and of the resonances, and to predict the range of initial conditions where singularities in the scattering function are found. In the second example the value of the perturbation parameter at which channel transitions set in is calculated. The theoretical results are supplemented by numerical experiments.

Notes: The pituitary adenylate cyclase activating polypeptide (PACAP) type I receptor, a seven-domain transmembrane receptor, is positively coupled to both adenylate cyclase and phospholipase C. PACAP exerts neurotrophic effects which are mainly mediated through the cAMP/protein kinase A pathway. Here we show that the cell-permeable C2-ceramide selectively blocks PACAP-activated cAMP production, without affecting phosphoinositide breakdown. Thus by blocking the neuroprotective cAMP signalling pathway, C2-ceramide will reinforce its direct death-inducing signalling. We found that a reactive oxygen species scavenger reversed the C2-ceramide effect and that H2O2 mimicked it. Together these data indicate that reactive oxygen species (ROS) mediates C2-ceramide-induced cAMP pathway uncoupling. This uncoupling did not involve ATP supply or Gαs protein function but rather adenylate cyclase function per se. Further, the tyrosine phophatases inhibitors, but not the serine/threonine phosphatases inhibitors, prevent inhibition of cAMP production by ROS. This suggests that H2O2 requires a functional tyrosine phopsphatase(s) to block PACAP-dependent cAMP production.

Notes: The leaf apoplast is a site of preferential accumulation of heavy metals in the shoot when barley seedlings are grown in the presence of cadmium, nickel or zinc in hydroponic medium. It was shown recently that apoplastic protein content increased concomitantly in plants grown in the presence of high Zn (Brune et al. 1994, Journal Experimental Botany 45, 1189). Here it is demonstrated that apoplastic proteins increase to an even greater extent in Ni-treated plants, and that the response is intermediate for Cd-treated plants. The paper focuses on possible causes for the increase in apoplastic proteins. (1) Synthesis of cell wall proteins was studied by in vivo pulse labelling of leaf proteins with 35S methionine followed by extraction of extracellular polypeptides. Depending on growth conditions and leaf age, 1–6% of the protein synthesized de novo in the leaf was allocated to the extractable protein fraction of the leaf apoplast. Under control conditions, labelling reached its maximum after 2 h; labelling continued to rise in Ni-treated plants, where the maximum level of final labelling was reached only after several hours. Labelling decreased with leaf age and increased proportionally with Ni concentration in the nutrient solution. (2) Autolysis experiments on extracted apoplastic proteins and in situ digestion of infiltrated ovalbumin revealed a low proteolytic activity in the apoplast which was not altered in heavy metal-treated leaves. (3) Following a sudden application of Ni to the growth medium, protein content and peroxidase activity increased with a 48 h delay and approached the level obtained for continuously Ni-treated plants, even in previously fully expanded leaf tissue. It is concluded that altered cell wall structure is probably not involved in increasing the extraction yield of apoplastic proteins. (4) The increase in extractable apoplastic proteins was also not due to inhibited ionical or covalent immobilization of proteins in the cell wall matrix of heavy metal-challenged plants. (5) Northern blotting revealed heavy metalinduced upregulation of mRNA levels of selected apoplastic proteins. Taken together, the data provide evidence for a transcriptional or translational level of regulation as the main cause of the strong response of apoplastic proteins to heavy metal stress.

Notes: Forty children with childhood asthma were conducted through a double-blind cross-over study to compare the effect of 400 μg beclomethasone dipropionate administered as aerosol and powder (Rotacaps). Children with severe asthma derived more benefit from the steroid administered as aerosol judged from their peak (low performance in the morning, although neither evening peak flow nor symptom scores revealed any difference. It is concluded that the Rotacaps are an advantageous supplement to available medication for the treatment of asthmatic children, although it should be observed that, using equal amounts of BDP. powder administration seems less effective than aerosol.