Incomplete inversion and double-valued fundamental linewidth ofinfrared HeNe and HeXe lasers

We have measured the quantum-limited linewidths of small HeNe 3.39 μm and HeXe 3.51 μm lasers. In contrast to the expected Schawlow-Townes behaviour strong deviations from the inverse power dependence are observed, leading to a double-valued relation between the linewidth and the output power. This phenomenon is analyzed in terms of the increase of spontaneous emission, by a factor N_sp, due to incompleteness of the inversion. Our analysis shows that typically N_sp has a value ranging from 1-10. Combining existing models for the pump power dependence of the level populations with measurements of the small signal gain, we are able to explain the observed double-valued linewidth behaviour in a quantitative way     

Ultrastructural co-localization of calmodulin and B-50/growth-associated protein-43 at the plasma membrane of proximal unmyelinated axon shafts studied in the model of the regenerating rat sciatic nerve

Calmodulin and de-phosphorylated B-50/growth-associated protein-43 (GAP-43) have been shown to bind in vitro in a molecular complex, but evidence for an in situ association in the nervous system does not exist. Previously, we have reported that, in the model of the regenerating rat sciatic nerve, the B-50/GAP-43 immunoreactivity is increased and concentrated at the axolemma of unmyelinated axons located proximal to the site of injury and axon outgrowth. To explore a putative function of B-50/GAP-43, namely, the capacity of binding calmodulin to the plasma membrane, we examined the ultrastructural distribution of calmodulin in the proximal unmyelinated axon shafts of this model, using double immunolabelling and detection by fluorescent or gold probes conjugated to second antibodies. Immunofluorescence showed that seven days post-sciatic nerve crush the calmodulin immunoreactivity, similar to B-50/GAP-43 immunoreactivity, was intense in unmyelinated axon shafts located proximal to the site of injury of the regenerating nerve. Ultrastructurally, calmodulin was located at the axolemma of these regenerating unmyelinated axon shafts and inside the axoplasm, where it was associated with vesicles and microtubules. The plasma membrane labelling (approximately 69%) was significantly higher than the axoplasmic labelling. Over 60% of the plasma membrane-associated calmodulin co-localized with B-50/GAP-43 in a non-random distribution. Since normally calmodulin is largely present in the cytoplasm, these data suggest that calmodulin has been concentrated at the plasma membrane of unmyelinated axons, most probably by B-50/GAP-43. If the concentrating effect is due to B-50/GAP-43, then there is a possibility that these proteins may be present as a molecular complex in situ. The physiological significance could be that this association regulates the local availability of both B-50/GAP-43 and calmodulin for other interactions.     

Interactions of cyclosporin A and amlodipine: blood cyclosporin A levels, hypertension and kidney function

The introduction of cyclosporin A has led to improved survival of allografts in humans. However, the use of cyclosporin A is associated with an increased prevalence of hypertension in kidney transplant recipients. Renal vasoconstriction and enhancement of tubular reabsorption contribute to this hypertensive effect. Concomitant treatment with calcium channel blockers blocks or ameliorates most of these adverse effects. This paper reviews the short-term effects of the calcium channel blocker amlodipine on plasma levels of cyclosporin A and its interaction with blood pressure and kidney function.     

An indirect method for transfer function estimation from closed loop data

An indirect method is introduced that is able to estimate consistently the transfer function of a linear plant on the basis of data obtained from closed loop experiments, even in the situation where the model of the noise disturbance on the data is not accurate. Moreover, the method allows approximate identification of the open loop plant with an explicit and tunable expression for the bias distribution of the resulting model.     

Identification and control — Closed-loop issues

An overview is given of some current research activities on the design of high-performance controllers for plants with uncertain dynamics, based on approximate identification and model-based control design. In dealing with the interplay between system identification and robust control design, some recently developed iterative schemes are reviewed and special attention is given to aspects of approximate identification under closed-loop experimental conditions.     

Observation of the geometric amplitude factor in an optical system

Abstract

By manipulating the discrete optical levels inside an optical resonator, we obtain a classical realization of a twisted Landau-Zener model. We experimentally demonstrate the geometric amplitude factor in the transition amplitude that arises for this model. We consider in particular the region of parameter space addressed in the original study of the geometric amplitude factor by M. V. Berry [7].