Photoelectric Activity Research Articles

Photoelectric activity of the shell staro And: New observations and discussion

Photoelectric observations of the shell staro And, obtained in 1979, are presented. The star shows variations of some hundredth of magnitudes during a few hours. The trend to retake the values of the luminosity and colour indices prior to the reduction happened between JD 42,714-27, seems to continue. We also give a qualitative model which explains satisfactorily the main features observed after the 1975 shell episode.

Photocurrents generated by bacteriorhodopsin on planar bilayer membranes

When purple-membrane fragments from Halobacterium halobium are added to one aqueous phase of a positively-charged black lipid membrane, the membrane becomes photoelectrically active. Under normal conditions the steady-state photo-current is extremely low, but increases considerably when the lipid bilayer is doped with proton-permeable gramicidin channels or with a lipophilic acid-base system. These findings indicate that the purple-membrane sheets are bound to the surface of the bilayer, forming a sandwich-like structure. The time-behaviour of the photocurrent may be interpreted on the basis of a simple equivalent circuit which contains the conductance and capacitance of the purple membrane in series with the conductance and capacitance of the lipid bilayer. From the dependence of the photocurrent on the polarization of the exciting light the average angle between the transition moment of the retinal chromophore and the plane of the bilayer was calculated to be about 28 degrees. Furthermore, it was shown that chromophore-free apomembrane binds to the lipid bilayer and that its photoelectrical activity can be restored in situ by adding all-trans-retinal to the aqueous phase.

Kinetics of the blue light-induced inhibition of photoelectric activity of bacteriorhodopsin

1. Introduction In previous photoelectron studies of bimolecular lipid membranes containing bacteriorhodopsin mem- brane sheets (BR) it was found that if this system is illuminated by green and blue light simultaneously, the latter is capable of decreasing the photopotential generated by green light [l] . It was proposed that the blue light induces fast conversion of BR412+BR570 in a fashion which is not coupled with proton pumping. A kinetic model of this effect has been elaborated [2] . The study of photoelectric activity of BR incor- porated into lipid-impregnated collodion film has revealed three electrogenic phases differing in time constants [3] On the basis of flash-photolysis absorp- tion measurements on BR water suspension, these phases were correlated with different steps in the photochemical cycle of BR. According to the com- parison of the kinetic parameters, simultaneously with the formation of BRaI a rise in the photo- potential indicates proton translocation from the Schiff-base in the pigment-protein complex. A further, slower rise in the photopotential following the regeneration of BR570 is due to the proton uptake from the opposite side of the membrane. The present paper deals with fast kinetic aspects of the blue light-induced decrease of the photopotential in connection with the BR photochemical cycle. The quenching was induced by a blue flash, following a green one, after appropriate delay times. It has been

Investigation by focused laser beam scanning of the photoelectric activity of bacteriorhodopsin-containing lipid bilayers

The photoelectric activity of different parts of lipid bilayer containing bacteriorhodopsin was investigated by moving a small actinic light spot across the Plateau-Gibbs border and the bimolecular part of this reconstituted model membrane. The results give direct evidence that bacteriorhodopsin incorporated into the bimolecular region of the lipid membrane is responsible for the photoelectric activity of this system. A technique for scanning the photoelectric activity of a modified bimolecular lipid membrane is described in detail.

Photoelectric activity of dried, oriented layers of purple membrane from halobacterium halobium

Summary Dried layers of purple membranes containing bacteriorhodopsin oriented by an electric field during drying were investigated by photoelectric and spectroscopic methods. There is evidence to show that the photochemical cycle of bacteriorhodopsin in a l&w hydration state is intact not only spectroscopically but also electronically in these layers. It has been observed that due to the blue-light excitation of the bleached form an intermediate absorbing at 520 nm is enriched. Thus this form seems to occur in the inhibitory pathway of bacteriorhodopsin.

Activity monitor for small animals

A photoelectric activity monitor which is easily moveable between cages is described, including a circuit diagram and set-up procedure. In a preliminary study, the number of squares traversed by mice on the cage floor was counted both instrumentally and visually; the instrument count ranged from 105 to 111 per 100 observer counts. In a correlation study, a simulated mouse was moved from square to square both laterally and diagonally while being counted by the instrument and a human observer. They agreed 994 and 977 times respectively in 1000 trials. The instrument should prove particularly useful in studying hyperactive mice, whose activity level is too high for the human observer to count accurately. Behavior monitor patterns may also be studied by feeding the channel outputs to a minicomputer.

A genetic analysis of the response to morphine in mice: analgesia and running.

Two progenitor strains, BALB/cBy and C57BL/6By, their reciprocal F1 hybrids, and seven of their recombinant-inbred derived lines were used to examine the genetic basis of the response to thermal pain, and morphine analgesia at doses of 2.5, 5.0 and 10.0mg/kg. Both the latency of response to thermal pain and the analgesic response differed significantly among the various strains tested. Strong genetic determinants appear to control their responses. Analyses of the data did not permit clarification regarding the linkage of these determinants. Photoelectric activity cages were used to test the running response of the same strains to 12.5, 25 and 40 mg/kg morphine sulfate. The genetic determinants for running activity were different from those for analgesia. There is clear evidence for two or more loci controlling the behavior at 60 and 75 min after injection, but not enough information to define the loci involved.

Effects of Centrally Acting Drugs on Confinement Motor Activity

A test procedure is described for use in quantitating the effects of drugs which stimulate or depress central nervous system function. Motor activity of rats is measured by photoelectric cells while the rats are confined in a small plastic chamber. The chamber is designed to permit the rats to exhibit “up and down” exploratory movements but not movement from place to place, i.e., locomotor activity. Drugs tested include caffeine, d-amphetamine, phenmetrazine, methylphenidate, pipradrol, tranylcypromine, chlorpromazine, prochlorperazine, trifluoperazine, and chlordiazepoxide. Advantages of the test include a high degree of reproducibility, selectivity, and sensitivity. Two of the drugs mentioned, namely caffeine and tranylcypromine, were especially potent by this test, in spite of the fact that they are essentially inactive by the conventional photoelectric cell locomotor activity test.

‘Thermal Regeneration’ in the Nickel-Oxygen System

OBSERVATIONS of photo-electric ‘activation’ (lowering of the photo-electric threshold energy) through the interaction of small quantities of oxygen with various metals are recorded in the literature1. Such activation, for which no satisfactory theory has been advanced, is obtained without heat treatment and most of the metals concerned possess a low work function (below about 3 eV.). Large admissions of oxygen always cause the reverse effect: the threshold is shifted to shorter wave-lengths. The phenomenon of ‘thermal regeneration’, that is the removal of oxygen from the surface of certain metals and semiconductors by heating in vacuo, is also well established. The oxygen which disappears from the surface in these cases is not desorbed; it is either incorporated by regions below the surface2,3 or it is effectively aggregated into islands on the surface as the result of recrystallization processes to leave bare areas4. We have observed photoelectric activation in nickel films (work function about 5.1 eV.) after interaction with oxygen followed by thermal regeneration of the surface. There appears, therefore, to be a close parallel between thermal regeneration and photo-electric activation. Further, we have found that regeneration of a nickel surface to which oxygen has been admitted at 20° C. occurs spontaneously on standing in vacuo at that temperature.

Photo-electric Activity of Iron and its Oxides

THE following results, obtained from a photoelectric examination of the oxidised surfaces of metallic iron, render previous results1 for other metals more complete.

XLVIII.The photo-electric activity of the silver halides and silver sulphide

XLVIII.<i>The photo-electric activity of the silver halides and silver sulphide</i>

The application of the method of the magnetic spectrum to the study of secondary electronic emission

There are two ways of investigating the velocity distribution of an electronic emission—the retarding potential and the magnetic deflection methods. These have been applied to the case of the photo-electrons by Millikan and Ramsauer respectively. On one important point the results disagreed; Millikan found a definite maximum velocity, while Ramsauer obtained an asymptotic falling off of the number of electrons with increasing velocities. In a critical discussion of the two methods Klemperer has shown that they agree when photoelectric activity of the collecting electrode in the first, and when electronic reflection at the walls and slits in the second, are eliminated.

On the total photo-electric emission of electrons from metals as a function of temperature of the exciting radiation

In the year 1913 K. T. Compton and O. W. Richardson ('Phil. Mag.,' vol. 26, p. 549 (1913)) published a paper containing an important investigation on the action of homogeneous mono-chromatic radiation on a number of metals. The essential characteristics of the photo-electric activity of various metals are set out in their experimental curves obtained by plotting photo-electric yield of electrons against exciting frequency. These curves contain double maxima in the case of extremely electro-positive elements like Na, and one maxium for a less electro-positive metal Al, while the curves for Pt exhibit no maximum in the range of frequencies covered by their experiments. Later investigations by Souder ('Phys. Rev.,' vol. 8, p. 327 (1916) and O. W. Richardson and A. F. A. Young ('Roy. Soc. Proc.,' A, vol. 107, p. 377 (1925)) have confirmed these general characteristics of photo-electric activity-frequency curves. A photo-electric maximum for the "selective" effect was observed by Pohl and Pringsheim ('Verh. d. Deutsch. Physik. Ges,' vol. 11. p. 1039 (1910)) as early as 1910 in the case of some electro-positive elements. The general shape of the humps in their curves appears to be a function of the angle of incidence of the exciting radiation; nevertheless, the position of the maximum is quite independent and definite. Lately, R. Döpel ('Zeits. für Phys.,' Vol. 33, p. 237 (1925)) has shown that a less electo-positive metal like Sr also shows the photo-electric maximum. It is therefore probable that all metals would exhibit such maximum. It is therefore probable that all metals would exhibit such maximum photo-electric effect if it were possible to extend the range of exciting frequencies far into the ultra-violet. The presence of double maxima in the curves for Na and K probably points to the existence of two photo-electric thresholds in these elements, as suggested by O. W. Richardson ('Proc. Phys. Soc. London,' vol. 36, p. 388 (1924)), and may lead to interesting developments in future. In the following Table I are collected the observed values of the long wavelength limit λ 0 and the wave-length λ m of the maximum photo-electric effect. A comparison of the figures in columns 1 and 3 shows that the frequencies v 0 and v m can be correlated within the range of accuracy and consistency attainable in photo-electric measurements by a simple relation, v m = 3/2 v 0 .

Societies and Academies

Societies and Academies

II.—The Variation in Photo-Electric Activity with Wave-Length for certain Metals in Air

Although a study of the photo-electric activity of metals in air can contribute little to the scientific interpretation of the phenomenon, yet it acquires a greater interest and some practical importance in connection with the physiological effect of ultra-violet light. In employing such light for therapeutic purposes, it is necessary to know which are the effective rays for the treatment under consideration, and how different sources vary as regards intensity of radiation. As the primary cause of the physiological change produced by light is probably photo-electric action, it is not surprising that several investigators have suggested the use of the photo-electric activity of a metal plate in air as a means of estimating the quality and intensity of the radiation.

XCVII. Photoelectric and photochemical activity

XCVII. <i>Photoelectric and photochemical activity</i>

XCI. The variation of the photo-electric activity of a potassium ferro-cyanide solution with the concentration of the solution

XCI. <i>The variation of the photo-electric activity of a potassium ferro-cyanide solution with the concentration of the solution</i>

A Photoelectric Theory of Colour Vision

IN view of the recent letters from Prof. Joly and Sir Oliver Lodge under the above heading, I may be allowed to point out that such a theory of colour vision was advanced by me in a lecture delivered before the Rontgen Society on January 7 last, and published in the Journal of the society for April. After referring to Prof. Joly's views as to the nature of the change taking place in the formation of the latent image and in radio-therapy, I said: “In my opinion, it is unnecessary to assume that a photochemical change is the cause of the visual sensation. It appears to me sufficient to suppose that photoelectric action takes place in the rods or cones, so that we have a separation of electrons resulting in electrification of the nerve-cells which set up the nervous impulse to the sensorium.” A number of familiar facts were adduced in support of this view, and it was mentioned that the peaked curve which shows the relation between the sensitiveness of the eye for light of different wave-lengths bears a very close resemblance to the curve which shows the variation of photoelectric activity with wave-length.

The photo-electric action of X-rays

The fundamental law of photo-electric activity states that ½ mv 2 = hv - w , (1) where the left-hand side represents the maximum kinetic energy of the liberated electrons, h is Planck’s constant, v is the frequency of the exciting light, and w is a constant which measures the work necessary for an electron to escape from the substance, and whose value is characteristic of the material under consideration. The equation (1) was first given by Einstein as a deduction from the view that the energy of radiation was distributed in discrete quanta. However, I succeeded in showing that it followed from Planck’s radiation formula; so that it evidently has a wider basis than the restricted and doubtful hypothesis used by Einstein. On the experimental side the evidence for several years was somewhat conflicting, but in 1912 I showed, as a result of experiments made in collaboration with Dr. K. T. Compton, that the equation represented the photo-electric behaviour in the visible and in the ultra-violet as far as λ= 2 x 10 -5 cm., for the metals sodium, aluminium, magnesium, zinc, tin, and platinum as accurately as it could be determined. The experiments also showed that the differences in the values of the constants w for different metals were connected with the corresponding contact potentials V by the relation w n - w m = e (V n -V m ). (2)

The photo-electric behaviour of iron in the active and passive state

The discoveries of Hertz and of Hallwachs showed that a polished metal plate exposed to ultra-violet light readily loses a negative electric charge, but retains a positive charge. If an electric Held is applied by making the metal form one plate of an air condenser, whose second plate is charged positively by a battery, the saturation current obtained may be regarded as a measure of the photo-electric activity of the metal. It has been known for more than a century that ordinary iron, which is acted on energetically by dilute nitric acid, can be made to assume a passive condition by immersion in strong nitric acid. The same condition can be produced by other powerful oxidising agents, or by using iron as the positive electrode in an electrolyte containing oxygen. The nature of the change that takes place when iron passes from the active to the passive state has given rise to much discussion, but none of the explanations suggested has yet met with general acceptance.