Analytical and experimental investigation of flow fields of annular jets with and without swirling flow

Analytical and experimental studies were performed to define the flowfield of annular jets, with and, without swirling flow. The analytical model treated configurations with variations of flow angularities, radius ratio, and swirl distributions. Swirl distributions characteristic of stator vanes and rotor blade rows, where the total pressure and swirl distributions are related were incorporated in the mathematical model. The experimental studies included tests of eleven nozzle models, both with and, without swirling exhaust flow. Flowfield surveys were obtained and used for comparison with the analytical model. This comparison of experimental and analytical studies served as the basis for evaluation of several empirical constants as required for application of the analysis to the general flow configuration. The analytical model developed during these studies is applicable to the evaluation of the flowfield and overall performance of the exhaust of statorless lift fan systems that contain various levels of exhaust swirl

Divergence of sun-rays by atmospheric refraction at large solar zenith angles

International audienceFor the determination of photolysis rates at large zenith angles it has been demonstrated that refraction by the earth's atmosphere must be taken into account. In fact, due to the modified optical path the optical transmittance is thereby increased in most instances. Here we show that in addition the divergence of sun-rays, which is also caused by refraction but which reduces the direct solar irradiance, should not be neglected. Our calculations are based on a spherically symmetric atmosphere and include extinction by Rayleigh scattering, ozone, and background aerosol. For rays with 10km tangent altitude the divergence yields a reduction of about 10% to 40% at solar zenith angles of 91° to 96°. Moreover, we find that the divergence effect can completely cancel the relative enhancement caused by the increase of transmittance

The H Lyman-? actinic flux in the middle atmosphere

International audienceThe penetration of solar H Lyman-a radiation into the terrestrial middle atmosphere is studied in detail. The Lyman-a actinic flux is calculated with a Monte Carlo approach including multiple resonance scattering of Lyman-a photons within the terrestrial atmosphere and a temperature dependent absorption cross section of molecular oxygen. The dependence of the actinic flux on the temperature profile is significant for O2 column densities greater than about 1024 m-2. For column densities greater than about 5 · 1024 m-2 resonance scattering becomes important at solar zenith angles > 60°. The \OD\ quantum yield of the O2 dissociation by Lyman-aphotons is found to decrease from 0.58 in the lower thermosphere to 0.48 in the lower mesosphere. Parameterisations for Lyman-a actinic flux, mean O2 absorption cross section and \OD\quantum yield including temperature dependence and resonance scattering are given valid up to a O2 column density of about 1025 m-2

Watching G proteins at work.

It has been known for over a century that rod photoreceptors in the living retina contract and swell in response to light. Although it is still not known whether this structural light-response is of any functional significance, it has recently been possible to correlate the underlying molecular processes with the activation and deactivation of the photoreceptor G protein, transducin. The technique of light-scattering allows the monitoring of minute changes in cell dimensions, and using this non-invasive experimental approach it can be shown that certain properties of the coupling between transducin and rhodopsin are different in a structurally well-preserved system as compared with rod material used for conventional biochemical studies. Thus, not unlike a psychiatrist, who often learns more about a patient's 'interiors' by observing the body language than by direct interrogation, a biochemist, studying the 'body language' of a cell, may extract information about delicate 'cell interior processes' that would be perturbed by more direct experimental approaches

The H Lyman-<b>a</b> actinic flux in the middle atmosphere

International audienceThe penetration of solar H Lyman-a radiation into the terrestrial middle atmosphere is studied in detail. The Lyman-a actinic flux is calculated with a Monte Carlo approach including multiple resonance scattering of Lyman-a photons within the terrestrial atmosphere and a temperature dependent absorption cross section of molecular oxygen. The dependence of the actinic flux on the temperature profile is significant for O2 column densities greater than about 1024 m-2. For column densities greater than about 5 · 1024 m-2 resonance scattering becomes important at solar zenith angles > 60°. The O(1D) quantum yield of the O2 dissociation by Lyman-a photons is found to decrease from 0.58 in the lower thermosphere to 0.48 in the lower mesosphere. Parameterisations for Lyman-a actinic flux, mean O2 absorption cross section and O(1D) quantum yield including temperature dependence and resonance scattering are given valid up to a O2 column density of about 1025 m-2

Calcium regulates the rate of rhodopsin disactivation and the primary amplification step in visual transduction.

The kinetics of the light-induced activation of transducin as well as the subsequent disactivation process can be monitored by means of a specific light scattering transient PA. In this communication it is demonstrated that the rate of transducin disactivation is calcium dependent, increasing when the calcium concentration is decreased. As a consequence of the accelerated recovery in low calcium, the time to the peak of the transducin activation process is shortened and the gain of the primary amplification step, i.e. the number of transducin molecules activated per bleached rhodopsin, is reduced. Experiments using hydroxylamine as an artificial quencher of rhodopsin activity suggest that calcium acts upon rhodopsin kinase and not upon the rate of the GTPase. This would indicate that calcium may control visual adaptation not only by regulating guanine cyclase activity, but also by affecting the primary step in the transduction cascade, the rhodopsin-transducin couplin

In vitro dark adaptation and preservation of electrical light responses in the retina from bovine eyes.

A method is described which allows the in vitro dark adaptation of rod photoreceptors from cattle eyes, enucleated under ambient light in the slaughterhouse. Without in vitro dark adaptation these eyes are light adapted and cannot be used for certain delicate biochemical studies and for an electrophysiological characterisation of rod responses. The method is very simple and yields large amounts of dark adapted retinal material, allowing experiments that require bulk amounts of photoreceptor cells. The only source of dark adapted photoreceptors so far have been retinae from dark adapted laboratory animals, which had to be killed and processed under infrared light. Eye cups were opened under red light as soon as possible after their enucleation. Their vitreous humor was removed and their retina thoroughly rinsed with ringer's. Then the eye cup was placed in a moist, light-tight box, where dark adaptation took place. Photoreceptors could thus be kept alive for more than 24 h without showing signs of deterioration. Humidity and free access of oxygen to the retina were the only prerequisites for their survival. The physiological intactness of the photoreceptors and their degree of dark adaptation was demonstrated by measuring mass receptor potentials (ERGs). A simple device is described which can be used for the electrophysiological characterisation of these eyes

Optical probes of intradiskal processes in rod photoreceptors. II: Light-scattering study of ATP-dependent light reactions.

Rod outer segment (ROS) disks, either stacked or freely floating, respond to flash illumination to yield a specific, ATP-dependent, light-scattering signal AL. In broken ROS AL signals occur only when AD signals (see Part I) have preceded them, The degree to which the preceding AD signal has been completed determines the amplitude of the following AL signal. However, in freshly detached ROS from dark-adapted frogs AL signals with maximal size can be obtained without pre-incubation with exogenous ATP. The energized state, which is restored in broken ROS with the help of ATP, appears to prevail in the living retina and must therefore be considered to be “physiological”. AL signals require structurally intact disks. Neither peripheral ROS proteins nor connecting filaments between adjacent disks are necessary. Their structural origin is the same as that of the preceding AD signal, i.e. osmotic disk swelling. AL signals consist of a single slow kinetic component (half-life 10 s at room temperature) and multiphase fast kinetic component (70 ms). The slow phase corresponds to a light-stimulated resumption of ATPase activity (this has been dealt with in a previous paper) whereas the fast component reflects an immediate response of the energized disk to the metarhodopsin I to metarhodopsin II transition. The latter effect is the subject of this paper. A variety of experiments, using different ATPase inhibitors, ionophores and membrane-permeable salts, have been carried out; they are all consistent with the notion that AL originates in the disk interior and probes the existence of a proton electrochemical potential difference Δμ(H+) across the disk membrane. A model is presented which can explain all given properties of AL satisfactorily. According to this model the photolysis of rhodopsin causes a proton release in the disk lumen. This, in turn, results in osmotic swelling of the disks, provided that the internal buffer sites have been (at least partially) titrated with protons prior to the flash. Such conditions, i.e. a low internal pH, are provided by the proton transport across the disk membrane, which presumably takes place during the course of the preceding AD signal

Design, fabrication and acoustic tests of a 36 inch (0.914 meter) statorless turbotip fan

The LF336/E is a 36 inch (0.914 meter) diameter fan designed to operate in a rotor-alone configuration. Design features required for modification of the existing LF336/A rotor-stator fan into the LF336/E statorless fan configuration are discussed. Tests of the statorless fan identified an aerodynamic performance deficiency due to inaccurate accounting of the fan exit swirl during the aerodynamic design. This performance deficiency, related to fan exit static pressure levels, produced about a 20 percent thrust loss. A study was then conducted for further evaluation of the fan exit flow fields typical of statorless fan systems. This study showed that through proper selection of fan design variables such as pressure ratio, radius ratio, and swirl distributions, performance of a statorless fan configuration could be improved with levels of thrust approaching the conventional rotor-stator fan system. Acoustic measurements were taken for the statorless fan system at both GE and NASA, and when compared to other lift fan systems, showed noise levels comparable to the quietest lift fan configuration which included rotor-stator spacing and acoustic treatment. The statorless fan system was also used to determine effects of rotor leading edge serrations on noise generations. A cascade test program identified the serration geometry based on minimum pressure losses, wake turbulence levels and noise generations

Detection of fixed points in spatiotemporal signals by clustering method

We present a method to determine fixed points in spatiotemporal signals. A 144-dimensioanl simulated signal, similar to a Kueppers-Lortz instability, is analyzed and its fixed points are reconstructed.Comment: 3 pages, 3 figure