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The increase in size of an image produced by a high intensity source is particularly troublesome in silicon diode array imaging devices. This increase is caused by inversion of Si under the SiO 2 between the diodes or by the lateral diffusion of the excess minority carriers in the field-free region of the sensor array. The formation of inversion layers can be eliminated by proper choice of the sheet resistance of the resistive sea when the target is operated above flat-band voltage. However, when the diodes in the image are fully discharged in a time interval shorter than the frametime, the excess carriers diffuse to the adjacent diodes and cause an increase in the size of the image. Such "blooming" is related to the effective minority carrier lifetime that is a function of surface recombination velocity at the imaging side of the target, surface recombination velocity at the diode side of the target, and bulk minority carrier lifetime. Two methods for controlling blooming will be discussed. In one case, the effective minority carrier lifetime is reduced by adjusting the n+doping profile at the imaging side of the array. The second technique requires diffusion of a separate p-type region, placed between the sensing diodes elements, which provides a high recombination region when the sensing diodes are discharged due to the image overload. Devices have been constructed with good imaging quality, where a 1 percent scan diagonal bright spot bloomed to 4 percent in the first technique, and to 2.5 percent in the second technique with a 105overload above saturation. The data are in good agreement with the theory.

SUMMARY The average density of bright spots in the (200) region of field-ion microscope images is found to be related to the nominal molybdenum composition in a series of iron-molybdenum alloys containing 1/2 to 5 weight percent molybdenum. The bright spot density is found to be proportional to the square of the tip radius and is thus linearly related to the surface area. This indicates that a correlation between the observed bright spot density and a bulk property is permissable. The bright spot density is also found to increase approximately linearly with molybdenum content, at least up to 3% molybdenum. Observation of specimens with similar amounts of molybdenum in solid solution but different nitrogen contents shows that the observed correlation is independent of the nitrogen content. Similarly, it is shown that the correlation is also independent of carbon content. Thus, it is concluded that the bright spot density is directly related to the amount of molybdenum in solid solution and can be used as a measure of the local molybdenum concentration. The nature of the bright spot contrast is discussed and is shown to be consistent with a current theory of image formation.

1. Sterneck and Gilinsky assumest that the farther half of visually bisected distance is objectively not shorter than the nearer. The present investigation was undertaken to test the validity of this assumption in a space comparatively near to the observer in a dark room.2. Experimental setting was a modification of the Bourdon's bright spot. A minute bright spot out of a dark box containing an electric bulb was used to mark the distance. On the side of the box toward the observer there was a circular hole covered with paper. Spots of different diameters were used for different distances, so that their phenomenal brightness was kept constant for all distances. Two bright spots placed at the level of observer's eyes were moved along tracks diverging at an angle of 3 degrees from the point of observation. Care was taken to remove all the reflected light from the bright spot and to remove any other secondary cues of distance.3. With monocular vision every observer's discrimination of distance was entirely at sea. With binocular vision each observer was able to discriminate rather easily. Four observers who have normal visual (vernier) acuity gave the average depth acuity of 1.4′ in a two-spot setting, and 1.0′ in a three-spot setting. In both cases the values of depth acuity were consistent regardless of observation distance. These findings would mean that the visual factor participating in the measurements was confined only to convergence.4. In an experiment which used the two-spot setting, bisections were performed by stopping a movable spot at a point that appeared to be just halfway between the observer and the stationary spot designating the total distance to be bisected (Table 4). In another experiment, the task of observer was to bisect the interval of 2 (Table 5) or 4 meters (Table 6) at various distances of observation. Each interval was presented by means of two spots ; one indicating the near-end and the other the far-end.5. These experiments revealed that the phenomenal midpoint was farther than the objective one at the observation distance between 2 and 5 meters, in other words, the farther half of the distance was overestimated as compared with the nearer half. The amount of overestimation had a tendency to decrease in accordance with the increase in observation distance, though there were individual differences (Fig. 2).6. It seemed that non-visual factor might participate in the process of the overestimation of farther distance, and that the overestimation might correspond with the overconstancy of size.

Photographic observations of Jupiter and its Red Spot between 13 November 1969 and 21 September 1970 are reported. The Red Spot continues its 90-day oscillation in longitude with considerable regularity. An outstanding event of the apparition was the appearance of a new disturbance in the South Tropical Zone. A bright spot at zenographic latitude 23°.8 N displayed the shortest rotation period ever recorded on Jupiter, 9 h 47 m 3 s .

Summary of some recent measurements of Saturn, particularly latitudes of the faint atmospheric belts. The measurements reveal no seasonal variations in belt latitudes. A small, bright spot at Saturnigraphic latitude 57 deg has been photographed on 46 nights from Oct. 25, 1969, to Feb. 27, 1971. This feature, which is by far the longest lived spot ever observed on Saturn, has had an average rotation period of 10 hr 36 min 27.9 sec plus or minus 0.2 sec.

An investigation has been made of the origin of bright spot images in field ion micrographs of heavy ion, or neutron, irradiated tungsten.

A simple relation is established between the efficiency of an optical doubler excited by a multimode laser with partial mode-locking and the parameters of a two-photon fluorescence (TPF) trace of laser radiation. In general, the efficiency of two quantum processes can be obtained from the measurements of the contrast and the bright spot size of the TPF trace. In several cases these parameters of the TPF trace may be used for approximate estimation of the third and fourth harmonic generation and the stimulated scattering efficiency. It is also shown that for quasi-periodic random radiation the efficiency of nonlinear processes of arbitrary order can be calculated by using a set of correlation functions which depend on one argument only.

The diffraction of light inside the shadow, thrown by a small source of light, of a sphere and a circular disc of the same diameter, was studied, with special reference to the relative intensities of the central bright spots. With the source at about 2 metres from the obstacles, with a quarter-inch polished steel ball, the bright spot could be detected visually up to 3 cm. behind the obstacle, while with a steel disc of the same diameter, with the edges perfectly sharp, smooth and circular, the spot could be traced up to 2 cm. The relative intensities of the two spots were studied at different distances behind the obstacles, qualitatively by photography and quantitatively by visual photometry. At small distances behind the obstacles, the spot inside the shadow of the sphere is much feebler than the disc-spot, however approximating to the latter as we reach farther back from the obstacles, but even at 100 cm. remaining appreciably feebler. A general explanation is suggested.

The Television Eye Marker utilizes the reflection of a light from the cornea to record the position of a man's gaze upon a picture of the scene at which he is looking. This corneal reflection is viewed under magnification by a television camera while the scene is viewed by a second television camera and the outputs of the two cameras are combined. The resultant picture on the monitor television screen shows the scene with a bright spot superimposed, indicating the position and movements of the subject's gaze. This can be photographed by a motion picture camera. The bright spot is called the Eye Marker. Photocells are mounted against the monitor television screen and are thus activated when the Eye Marker passes beneath them. The position of each phootocell is correlated with a position in the scene so that when the subject looks at a point in the scene, the corresponding photocell is activated. The photocell output is used to record the positions of visual fixation, and also to control the visual or other information presented to the subject. A method of converting the photocell output into signals in the teletype code is described.

This phase curve tracer is a system for showing on the screen of a cathode-ray tube the phase curve of any network, plotted on a linear frequency scale from 0.1 to 5 megacycles. The test frequency is changed to a fixed frequency of 50 kilocycles for phase comparison, and the phase shift is converted to a time shift. A rectangular field on the screen is scanned in vertical lines, one for each test frequency. A bright spot is produced on each line at a vertical distance proportional to the phase angle of the circuit under test. Frequency and phase coordinate lines are superimposed. The full scale of phase indication is adjustable in multiples of 360 degrees by switching.

The field-ion microscope has been used to investigate some of the processes occurring during ion-implantation, in particular, the fate of the implanted species. Attention is therefore paid to point defect contrast in field-ion images to establish the validity of counting such defects. The importance of bright spots is emphasized since they may represent the only type of contrast which could lead to unambiguous detection of isolated implanted atoms. Since self-interstitial atoms released from traps by the imaging process contribute to the bright spot concentration, consideration is given to the imaging mechanism and to means of distinguishing between bright spots caused by different defects. It is shown that, in the case of oxygen implants, such a distinction is possible, and further, that the implanted species is trapped, possibly as part of a ‘complex’. Control experiments to ensure that real effects are observed, and errors in defect counts are briefly mentioned and it is concluded that signifi...

The paper describes and discusses the diffraction effects observed when a beam of light traverses a transparent sphere immersed in a liquid of slightly lower index and emerges therefrom. The two most interesting features are firstly, a concentration of intensity along the periphery of the emerging light beam which is evidently in the nature of a caustic and secondly, a concentration of intensity along the axial ray which is in the nature of a continuous focus. These two features are each accompanied by a set of interference-rings and these appear superposed on each other. Significant alterations appear in these features when the particle has a spheroidal shape. With a birefringent sphere, two sets of caustics are, in general, observed. 12 Photographs illustrate the paper. *** DIRECT SUPPORT *** A00OCO56 00002

A detailed pulse field evaporation study was made of the field evaporation characteristics of atoms from the first five ledges of (011) planes of high purity (⩽1.5 × 10−6 at. fr. impurity level) tungsten of well-annealed specimens and specimens irradiated with 35 or 40 keV W+ ions at room temperature (middle of Stage II) in vacua of ∼ 10−6 torr. The detailed examination of > 1.8 × 10−4 frames of cine film of the well-annealed control specimens and > 2.6 × 10−4 frames of film of the irradiated specimens showed that the ‘bright spots’ identified by Buswell as vacancies decorated by surface contamination, were in reality normal tungsten atoms associated with the ledges of (011) planes. The identification of these ‘bright spots’ as tungsten ledge atoms was achieved by employing a field evaporation increment of ∼2.5 × 10−3 of an (011) plane per evaporation pulse. The concentrations of ledge ‘bright, spots’ in the control and in the irradiated specimens were almost identical. The vacancy concentrations...

A general method was presented for calculating the contrast pattern to be expected from a single self-interstitial atom (SIA) in a field ion microscope (FIM) image. It was assumed that the SIA was embedded inside a FIM specimen well below the surface. The SIA was uncovered and eventually removed by the field evaporation of successive atomic planes. Atoms on the surface were displaced outwards from the surface as a result of the dilatational field of the SIA. This outward displacement of atoms resulted in 3 possible contrast effects. These 3 contrast effects were: 1. (a) a bright spot; 2. (b) an extra bright spot; 3. (c) a vacant lattice site. A single SIA atom can produce all these contrast effects and the totality of these effects was termed a contrast pattern. The atom displacements were obtained from the α-iron inter-atomic potential of Johnson, without allowing for surface relaxation effects. Detailed atomic displacement maps were presented for the {111} planes with a 〈110〉 split and a 〈111〉 split crowdion SIA configurations located many interplanar spacings underneath these surfaces. It was shown that the resulting atomic displacement maps contained sufficient information to allow the configuration of the SIA to be determined. An atom displaced normal to a surface plane by a SIA was represented by an electric dipole whose strength was a function of the magnitude of the displacement. A local field enhancement factor was then calculated (the possibility of charge redistribution was allowed for in the enhancement factor) and converted to an extra ion current via the Chen-Seidman data on the ion current vs. electric field characteristic curves of individual planes. An application of the above principles was presented for a SIA contrast pattern detected in a (111) plane of tungsten irradiated with 20 keV W + ions at 18°K (Scanlan et al. ). This contrast pattern contained the three contrast effects suggested by the model.

A new technique for the display of picosecond light pulses is presented. Ultrashort (6 ps) green light pulses passing through a light-scattering medium are photographed from the side by a camera positioned behind a shutter of 10-ps framing time. The shutter is an ultrafast Kerr cell driven by infrared pulses 8 ps in duration. Color photographs show a bright spot on a dark background, revealing the unambiguous presence of well-isolated picosecond light pulses. The shape of the spot is the result of a convolution involving the three-dimensional shape of the green pulse and the time transmission function of the shutter, this function being dictated by the shape of the infrared pulse. The experiment indicates that a new technique for visualizing light pulses consists in simply observing their flight through a scattering medium from behind an ultrafast shutter having a framing time equal to the time resolution desired. The new technique has many advantages over the two-photon fluorescence display technique, such as higher sensitivity, wider spectral range, and easier interpretation. The ultrafast camera also can be used for the photographic measurement of ultrashort relaxation times in dielectrics and in fluorescent dyes.

Most students of visual velocity perception implicitly assume that constant velocity is seen as such. This notion was challenged and shown to be inadequate in four experiments. A CRT-generated bright spot moved in a linear path according to different velocity time functions. Observers compared these movements pairwise as to their perceived constancy of velocity, or drew graphs describing perceived velocity along the track. Objects moving with constant velocity appear to move fast in the beginning and suddenly slow down to a much lower velocity. There is also a qualitative difference between the start phase and the rest. To be seen as constant, a movement must start smoothly with a certain acceleration and later level off to a constant velocity (natural motion). Such movements also look slower than others with the same average velocity. The results are taken to imply the existence of a perceptual concept of velocity which includes or presupposes a natural start. Consequences for velocity scaling, acceleration thresholds, and other motion perception studies, as well as relations to eye movements and conceptual problems, are discussed.

A search of several thousand plates in the Lowell Observatory collection yielded 28 groups of plates on which the positions of well-defined transient bright spots (often assumed to be clouds) could be followed on a nearly daily basis. These groups of plates were from 15 different oppositions of Mars, starting from 1907 and ending with 1958. All but two of these spanned four nights or more, and the maximum interval covered was thirty nights. Whether they appeared to show motion or not, the successive positions and shapes of all apparently associated bright spots or clouds were plotted on Mercator projections with the use of a projection plate reader especially designed at the Planetary Research Center for planet image studies of this kind. Clouds near the limb were avoided.

I VENTURE to suggest the following simple explanation of the phenomenon described by Colonel Herschel in NATURE of January 18. At the distance at which his experiments were made the light from the lantern or other source enters the lens practically as a pencil of parallel rays, which is concentrated as a bright spot on the retina. The divergent light from this bright spot, which passes backwards through the lens, is again made into an almost parallel pencil. If the retina is exactly in the focal plane of the source of light, and the image an absolutely sharp one, the whole of the light is again concentrated on to the bull's-eye of the lantern, and without the use of a transparent, but partially reflecting, surface, it must be impossible to see it. But the least blurring of the image, from whatever cause, leads to a slightly divergent pencil, which, however, is still narrow enough to concentrate the returning light within a degree or so from the direction of the original source. To an observer within this cone of rays the bright spot on the retina will appear to fill a part or the whole of the pupil, just as a black dot may be made to fill the whole aperture of a lens to an observer at a distance by holding the lens at its focal distance from the point in question.

Design and breadboarding of a technique to detect and locate a bright spot in a scanned image, employing video digital methods. Application is to detection and location of flares on the sun's disc, important primarily because of the danger to space travel from such flares. The conceptual design of the system is presented, and procedures employed in obtaining performance data are described. Experimental measurements and results are included.

Response characteristics of the previously categorized four types of cat retinal ganglion cells (ON-I, OFF-I, ON-II and OFF-II) were investigated using light and dark spot stimuli by recordings of unit discharges from the optic tract, and phasic and tonic nature of these four types of cells were further clarified. ON-I and OFF-I are phasic in nature and respond to only a transient increase and decrease in luminance, respectively. ON-II and OFF-II are tonic and continue to respond to a stationary light and dark contrast, respectively. Besides, a difference is also found between ON-I and ON-II in the firing patterns of the transient response to a bright spot stimulus. ON-I responds to the onset of a bright spot with an initial burst followed by dispersed discharges. In ON-II's transient response, initial discharge rate is as high as that of ON-I's burst, but in contrast with the case of ON-I's response, the discharge rate gradually decreases toward a mean rate of sustained responses to the spot.

A REVOLVING electric fan with gilt blade is illuminated by the light from a window. When we look fixedly on the revolving face an irregular patch of greyish-purple colour appears on the yellowish ground. The patch shows an amceba-like motion, and its size seems to increase with the speed of the fan. The border of the patch is coloured pale. In its centre a bright spot is often discerned. If we look at the fan after having closed or turned aside our eyes for a while the patch has disappeared, and it takes a few seconds before it reappears.

The field-ion microscope (FIM) allows the study of the atomic structure of a grain boundary and the adjacent regions. Certain impurities, such as oxygen, can be detected because they are associated with characteristic additional very bright image spots. The FIM has been used to investigate the distribution of oxygen in and around grain boundaries in tungsten. The oxygen was incorporated by a heat-treatment of specimen blanks ∼ 100 μm thick, for ∼ 8 h in an atmosphere of 133 × 10−3N/m2 (10−5 torr) oxygen at 1400° C (1673 K). The oxygen-associated bright spots are thought not to be the oxygen itself but to be solvent atoms stabilized in protruding positions adjacent to the solute. The spatial distribution of bright spots in and perpendicular to the grain-boundary plane has been investigated for doped and undoped material. In each case fine-scale field-evaporation sequences were carried out so that each oxygen-associated bright spot was recorded; counting was confined to the {110} region and the deco...

A non-mode-locked Nd:YAG laser Q -switched by a rotating mirror produces a bright spot at the mirror in a two photon fluorescence display which is 1.5 times as intense as the minimum two photon fluorescence track intensity in agreement with theoretical predictions.

IN reference to Mr. Douglas Archibald's letter, I may say that in 1873 I made three drawings of the “Sheaf rays” at the Isle of Wight. In these they are marked as “converging in the east,” but the point is apparently below the visible horizon. Shortly after I had, however, the opportunity of seeing the true convergence, as we were crossing the Peasemarsh, a large common near here. It was after rain, and there appeared a very bright spot in the east opposite the true sun, which to the best of my recollection was setting and not set, for I momentarily took the appearance to be some form of reflection of the sun itself. The rays were quite strong in the east and west, and though fainter could be distinctly traced across the sky. I believe that there were no clouds and that the ray intervals were equidistant, though I will not be certain on this point. I notice that one of my drawings also shows this peculiarity, though I confesss my impression has been hitherto that these rays were due to the interference of clouds.

Results of high-angular-resolution photography of the complex airglow structures present in the infrared sky. The photographs obtained all show bright cloud-like structures which moved on the sky and varied in brightness. It is concluded that these structures are due to varying airglow emission and not to any type of modulation of a uniform background by atmospheric clouds, dust, or haze. It is also concluded that observations of a bright spot from two widely separated sites will yield parallax determinations of the height of the OH emitting layer, so that it is no longer necessary to rely on infrequent rocket measurements at a few places.

WHILE carrying on some experiments with the electric arc between iron electrodes, one of my students, Mr. H. D. Arnold, noticed that there was a certain critical P.D. at which an abrupt change took place in the conditions of the arc. Subsequent investigation has shown that the effect is closely analogous to the “hissing point” of the carbon arc. How close the analogy is may be seen from the following remarks. If the iron arc is started with a large external resistance and maintained at such a length that the current is well below one ampere, it burns with little or no sound, and its appearance in the neighbourhood of the anode is very diffuse and ill-defined. As the external resistance is gradually decreased, the PD. falls and the current rises until a certain critical value, depending on the length of arc and size of electrodes, is reached. At this point a very small decrease in external resistance suffices to cause a sudden increase in current and drop in P.D., precisely as with the carbon arc. At the same time the arc contracts, a bright spot appears on the anode, and a characteristic hissing sound begins. Further increase of current is accompanied by a continued decrease in P.D. The hissing stage, in fact, begins at quite a different point on the P.D.-current diagram from that in the case of the carbon arc. If the experiment is carried out in the reverse order, starting with a large current, the discontinuity is encountered again, but not until the current has been diminished beyond the value that it had at the beginning of the hissing stage. Indeed, with arcs of 6 mm. and more, the current on the hissing stage can with care be decreased until it is smaller than its previous largest value on the quiet stage. Thus there are two possible values of P.D. for the same current and length of arc, one corresponding to the quiet, the other to the hissing stage.

REFERRING to the note on solar activity in your issue of July 20, I shall be glad to know whether any correspondent Observed a luminous outburst in the tail end of the great spot on the evening of July 16. I had been observing in the afternoon with an 8½-inch reflector, but remarked nothing of the sort. At 5.30, however (the sun having got beyond range of my reflector), I was observing him with a small refractor, power 12, and sun-cap, when I at once noted the luminous appearance in question. It was roundish and about the size of the small spot near following limb, and it was brighter than the bright bridge in the large group. I watched this bright spot until 7.30; next morning it had practically disappeared. Father Cortie courteously informs me that the Stonyhurst magnets were perfectly quiet on July 16, but that next morning, at 8.15, there was a “very small but sudden and sharp movement on both the declination and horizontal force curves.” By that time the locality where the luminous appearance occurred would not be far from central meridian. I also noticed a rosy hue pass over the bright bridge of great spot, but this may have been a mistake. I am, however, certain of the luminosity.

The aperture of a perfect lens is divided into several concentric circular zones. The effects of the different zones having different phase retardations are studied. The following conditions are found by a straightforward consideration: When the aperture is divided into two zones, with the inner zone having a phase retardation of π rad with respect to the outer zone, the diffraction pattern in the focal plane of the lens has the smallest central bright spot; this assumes that the same irradiance is always produced at the focus. Conversely, for a given radius of the central bright spot in the diffraction pattern, the greatest irradiance at the focus of the lens is produced when the lens aperture is divided into two concentric circular zones, with the inner zone having a phase retardation of π rad. Such a lens also possesses the same advantages over a perfect lens with a circular stop in its center. It may also possess an effective focal depth greater than that of the latter. It may have one or two foci depending on the value of the radius of the circle that divides its aperture.

An extended study of diffraction of acoustic waves in the audible range is currently under progress in the anechoic chamber at Temple University. A probe microphone has been constructed by coupling to a 12‐in. Bruel and Kjaer (B&K) capacitor microphone a rigid steel tube with a precision‐drilled 1‐mm‐diam hole. The output is fed into a B&K audio‐frequency spectrum analyzer and recorder. Since the measuring apparatus is so important in experimental studies in diffraction, extensive tests have been run to check the free‐field characteristics of the chamber and the frequency and directional response of the probe microphone. As a test of the precision of the apparatus, the diffraction patterns for rigid cylinders and spheres have been analyzed for various values of ka (ratio of circumference to wavelength) from 0.2 to 10. To obtain continuous readings, the microphone has been mounted to rotate at 2 rpm. The results have followed theory predictions in every respect, and the details of the “bright spot” and the...

THE following observations may be useful to some of your readers:—On June 25 the comet was compared five times with the star O.A. 3268, with a ring micrometer (power 35); on June 28 it was compared eight times with the star Dm + 71°, 184 by means of a bar reticule with power 70. The comet has a bright spot near the centre which, on June 25, seemed to me to be nearly equal to a ninth magnitude star; but on June 28 it was much fainter, although easy to observe with precision after 11h. 30m. The diameter appears to be 2′ or 3′ in my telescope (of 4½ inches aperture) but I cannot see any trace of the tail mentioned by Mr. Swift. The comet is, however, immersed in the twilight now existing at midnight.

Cathode ray oscilloscopes are often used to portray Lissajous figures which show the phase relation between two sinusoidal stimuli or the correlation between two noise signals. When the signals are turned off, a small bright spot remains in the center of the screen which often burns a hole in the phosphor. The black pit seen on the face of many a laboratory scope is mute testimony to the frequency of this occurrence. Most oscilloscopes have an external connection to the brightening circuit. In some (Dumont, for example) this connection, labeled 'Z-axis,' appears on the front panel; in others (Hewlett-Packard) it is one of the terminals at the rear. In either case, a rather large alternating potential is needed to produce any useful change of brightness, and the signals being portrayed as a Lissajous figure are ordinarily not large enough to do this. The device to be described furnishes a voltage which is large enough and it does this only when there is an input signal. When there is no signal there is no brightening voltage and, consequently, no spot. By adjusting a threshold control on the device, one can display signals ranging from a few millivolts to several volts and still have the spot vanish before it becomes dangerously small. Fig. 1 is a diagram of the circuit. Tube V-2 is a monostable multivibrator which remains in its stable state until the potential on its input grid (pin 7) exceeds a certain value, at which time the multivibrator oscillates. The frequency of this oscillation is determined by the values of R1l and C7 and by the potential on the input grid. For the values given, this frequency is above 20 kc. If the frequency of oscillation is commensurate with the frequency to be displayed, gaps suill appear in the pattern. These can be eliminated by a slight adjustment of the threshold-control and hence of the frequency of oscillation. Tube V-1 provides two stages of voltage amplification, with a diode in the plate circuit of the second stage to furnish the additional bias needed to trigger the multivibrator. The potentiometer R8 provides the initial bias and serves, therefore, as a threshold control for the multivibrator. The device draws only about 1 ma. of current from the power supply. Any convenient source (250-300 v) can, therefore, be used instead of the power supply shown. If it is desired to attach the device permanently