Initial Brightness Research Articles

Simultaneous brightness discrimination and reversal: The effects of amphetamine administration in the two stages

Rats were trained in a Y-maze on a two-choice simultaneous brightness discrimination with light as S+ and dark as S- (Stage 1), and were then switched to reversal, where the reinforcement contingencies of the original training were reversed (Stage 2). d-Ampthetamine, 1 mg/kg, was administered in a 2 × 2 design, i.e., drug-no drug in Stage 1 and drug-no drug in Stage 2. The administration of the drug in Stage 1 improved the acquisition of the initial brightness discrimination and facilitated reversal learning independently of the drug administered in Stage 2. In addition, the administration of the drug in Stage 2 only improved performance towards the end of reversal training. The results indicate that amphetamine enhances the attention to, or the associability of, the discriminative stimuli, leading to a rapid learining to these stimuli under changed contingencies of reinforcement.

Reversal and nonreversal shifts under amphetamine.

Rats were trained in a Y maze on a two-choice simultaneous brightness discrimination with light as S+ and dark as S- (position irrelevant). Half of the animals were then switched to reversal, where the reinforcement contingencies of the original training were reversed, and the other half were switched to nonreversal, in which they learned a simultaneous right-left discrimination. Nonreversal was acquired faster than reversal in saline injected animals. The administration of 1 mg/kg d-amphetamine did not affect the acquisition of the initial brightness discrimination and of nonreversal. In contrast, the drug facilitated dramatically reversal learning. The results indicate that amphetamine enhances the attention to, or the associability of, the discriminative stimuli, leading to rapid learning to these stimuli under changed contingencies of reinforcement.

Amphetamine and the overtraining reversal effect.

Rats were trained in a Y-maze on a two choice simultaneous brightness discrimination with light as S+ and dark as S- (position irrelevant). Animals in the Mastery group were trained until they reached criterion and were then switched to reversal, where the reinforcement contingencies of the original training were reversed. Animals in the Overtraining group received a further 110 trials before being switched to reversal. The administration of 1 mg/kg d-amphetamine facilitated dramatically reversal learning in Mastery group. Overtraining improved reversal in saline injected animals and slowed down reversal in amphetamine-treated animals. The drug also facilitated the acquisition of the initial brightness discrimination.

Emission characteristics of single-crystal LaB6 electron gun

Characteristics of electron beams emitted from an electron gun employing [100], [110], and [111] axial orientation LaB6 cathodes were investigated over a long period of time. Although the [100] cathode has high initial brightness, emission characteristics are unstable. This instability is caused by vaporization of the (100) plane, which has a low work function, on the cathode top. However, the [110] and [111] cathodes are stable, because the {100} surfaces are formed on the sloping surface of the cathode with time. Therefore, the [110] and [111] cathodes may be more suitable for many applications in spite of a lower initial brightness.

Surface effects on the low-energy cathodoluminescence of zinc oxide

A rapid initial brightness slump and occasional subsequent recovery observed for the zinc-doped zinc oxide phosphor undergoing cathodoluminescence is shown to depend on the surface work function. A quantitative model leads to an explanation of the dependence on surface potential in terms of field-aided or retarded surface recombination. Evidence is given that temporarily recovered surfaces result from dynamic surface adsorption of barium.

The Mechanism Responsible for 'Shadow' Type III Solar Radio Bursts. I. Absorption due to Langmuir Turbulence

The hypothesis is advanced that for 'shadow' type III solar radio events (absorption features with drift rates and bandwidths typical of type III bursts or U-bursts) the absorption mechanism involves Langmuir turbulence, such absorption being the inverse of either fundamental (I = J;,) or second harmonic (f = 2/p) plasma emission. The theory for both absorption processes is developed and applied to shadow type III events with the following results: (1) the predicted absorption is confined to a very narrow frequency range (fl.I/ I ~ 10- 3); (2) effective absorption requires an energy density in Langmuir turbulence (with phase speeds ~tc) in excess of 10-9 ergcm- 3 for the fundamental and in excess of 3 x 10-6 ergcm- 3 for the second harmonic; (3) the brightness of the background source must exceed 109 and 1016 K for absorption at the fundamental and second harmonic respectively. Comparison of the theory with the properties of an event discussed by Kai (1973) leads to the conclusions: (1) absorption at the second harmonic is unacceptable because of the high brightness temperature required; (2) to explain the observed bandwidth in terms of absorption at the fundamental, the absorbing region and the background source must overlap in height; (3) to explain the observed reduction in brightness temperature requires that the initial brightness temperature exceed 5�5 X 109 K (the observed value was 109 K).

Luminescent Properties of Thiogallate Phosphors: II . Ce3+‐Activated Phosphors for Flying Spot Scanner Applications

The cathodoluminescence emission and decay properties of phosphors were investigated to determine their suitability for use in flying spot cathode ray tubes. The thiogallate phosphors exhibit radiant efficiencies as high as 7.0% and their fluorescence decays to 1% of initial brightness in 1.3–1.55 µsec. Strontium thiogallate phosphors with decay times as short as 0.6 µsec were obtained by compositional modifications. Maintenance measurements indicate that is more stable in CRT applications than .

A Coronal Disturbance Observed Simultaneously with a White-Light Coronameter and the 80 MHz Culgoora Radioheliograph

Observations on 1970 August 11 and 12 at Mauna Loa (Hawaii) of the white-light corona revealed a rare solar event in the form of a short-lived coronal brightening off the eastern limb of the Sun. The intensity of this region, as measured at a distance ρ = 1.5 (where ρ = R/R⊙), more than doubled over a period of five hours and then fell very abruptly (~10 min) to below its initial brightness. A complex radio event in the same region was observed simultaneously with the 80 MHz radioheliograph at Culgoora (Australia). Associations between the optical and radio events will be described and the physical implications briefly discussed.

Two‐Stage Excitation of the Phosphorescence of Ruby

AbstractA long‐time phosphorescence of ruby is found under intense optical excitation in the spectral region of the R‐lines. From the initial brightness decay, as a function of the intensity and wavelength of the exciting light, it is suggested that the phosphorescence has a recombination character. The long‐wavelength limit of excitation corresponds to about 2 eV. These results indicate a complex character for the phosphorescence excitation (two‐photon or two‐step). To differentiate between these two possibilities experiments are performed using two excitation pulses with various time delays between them. These experiments show that two‐step excitation of electrons into the conduction band of ruby takes place over 2E levels of the Cr ions. From the results, and absorption data of ruby and corundum, a band scheme is proposed which explains the long‐wavelength limit of phosphorescence excitation in terms of indirect transitions.

Aging Characteristics of Electroluminescent Phosphors

The brightness, B, of electroluminescent light sources is observed to decay gradually as a function of operating time, t, according to the empirical formula, B=B0/(1+t/tc), where B0 is the initial brightness and tc is the time to half-brightness. At 60 cps the values of tc range in the hundreds to thousands of hours, while at 5000 cps tc is observed to be less than 100 hr for the particular phosphor used. The value of tc depends slightly, if at all, on voltage; but a very significant change in the voltage dependence of brightness occurs during the aging process. The results are interpreted on the basis of the Piper-Williams theory and are thought to be consistent with a field-induced migration of the deep donor impurity.

The effect of field size and pattern on the change of visual sensitivity with time

Results are recorded showing the effect of size of a circular conditioning field on brightness threshold measurements made at the centre of the field : first, with the field steadily exposed and viewed ; when the conditioning field has been cut off and the eye is returning to a state of dark adaptation. Conditioning and test fields are both illuminated by white light. No field size effect is detectable over the range 60° diameter down to 3° diameter. Below 3°, for a steady state of adaptation, various rather complex effects of interference between the conditioning fields are shown ; these are explained in terms of the effect of distant parts of the conditioning field in raising the threshold and a perceptual interference between the conditioning fields are shown ; these are explained in terms of the effect of distant parts of the conditioning field in raising the threshold and a perceptual interference between the patterns of conditioning and test fields. For changing states of adaptation the effect of field size cancels out─except in an isolated case─if the initial conditioning field brightness are adjusted to give the same steady value of threshold : then, after cutting off these various conditioning fields, the decrease of brightness threshold follows the same course. However the test patch of retina be brought to a given steady state of adaptation, as measured by the brightness threshold, it will recover its dark adaptation in the same way. These considerations apply both to foveal vision and to vision in the parafovea at 8° from the fovea.

Luminescence of Pure Radium and Barium Compounds

Luminescence, excited in some carefully purified crystalline barium and radium compounds by alpha-, beta-, and gamma-rays has been examined. It is found that these compounds show a faint luminescence at ordinary room temperatures. When the compounds are heated to various temperatures and then cooled, they show a continuous increase in luminescence with increase of temperature of heat treatment until a maximum is reached. Heat treating at higher temperatures diminishes the brightness. The temperature of maximum brightness is not directly related to the melting point of the individual compounds. The maximum brightness in some cases was several hundred times the initial brightness of unheated crystals. No abrupt changes in intensity of luminescence, such as might be due to changes in crystalline form, were detected. The bearing of these experiments on the modern theories of luminescence in crystalline solids is discussed.

Luminescence due to Radioactivity

Results of several investigations on luminescence due to radioactivity carried on under the direction of the author are reviewed. It is shown that these results cannot be explained on the well-known active center theory advanced by Rutherford, or any modification of the same such as that proposed by Walsh. In certain substances, including zinc sulphide, there is an initial rise in brightness of the irradiated samples followed by a decay which cannot be represented by a simple exponential curve. It is also found that the rate of decay of brightness is not strictly proportional to the rate of emission of luminous energy as required by the theory. The observed facts can be explained qualitatively by assuming that the alpha, beta and gamma-rays produce excited molecules in the luminescent material. Return of these molecules to their initial state of more stable equilibrium results in emission of luminous energy. The rays also affect the transmission coefficient of the materials, and the apparent decay of brightness is explained as due to the increased absorption of light by the material itself, rather than to the destruction of the hypothetical active centers. This is evidenced also by the fact that in the materials studied, heating the samples usually restores the initial brightness. Quantitative application of these suggestions to the experimental curves was not possible, since the nature of the change in light absorption coefficients resulting from irradiation is not definitely determined.

The scattering of light by particles of metallic oxides dispersed in dry air

A cursory examination has been made of the time changes in the brightness of the tyndall-light from ZnO, CuO, CdO and As2O2 clouds. The changes found can be accounted for by supposing that the cloud particles disappear by aggregation and sedimentation. The curves obtained fluctuate in a similar way to the ionisation currents from the same cloud, as if aggregation produced unstable complex particles which periodically break up in large numbers. Evidence has been obtained that amicroscopic particles of cadmium oxide act as nuclei and collect cadmium oxide vapour during a condensation process. A series of clouds vaporised from various masses (m) of arsenic trioxide has been obtained in which the initial brightness of the tyndall-beam was approximately proportional to m2/3. In certain clouds, the rapid fluctuations in brightness appear to form groups which succeed one another at intervals given by the formula t = Arn, where A and r are constants and n is an integer.