Vertically Separated Research Articles

Stereo transparency and the disparity gradient limit

Several studies ( Vision Research 15 (1975) 583; Perception 9 (1980) 671) have shown that binocular fusion is limited by the disparity gradient (disparity/distance) separating image points, rather than by their absolute disparity values. Points separated by a gradient >1 appear diplopic. These results are sometimes interpreted as a constraint on human stereo matching, rather than a constraint on fusion. Here we have used psychophysical measurements on stereo transparency to show that human stereo matching is not constrained by a gradient of 1. We created transparent surfaces composed of many pairs of dots, in which each member of a pair was assigned a disparity equal and opposite to the disparity of the other member. For example, each pair could be composed of one dot with a crossed disparity of 6 ′ and the other with uncrossed disparity of 6 ′, vertically separated by a parametrically varied distance. When the vertical separation between the paired dots was small, the disparity gradient for each pair was very steep. Nevertheless, these opponent–disparity dot pairs produced a striking appearance of two transparent surfaces for disparity gradients ranging between 0.5 and 3. The apparent depth separating the two transparent planes was correctly matched to an equivalent disparity defined by two opaque surfaces. A test target presented between the two transparent planes was easily detected, indicating robust segregation of the disparities associated with the paired dots into two transparent surfaces with few mismatches in the target plane. Our simulations using the Tsai–Victor model show that the response profiles produced by scaled disparity-energy mechanisms can account for many of our results on the transparency generated by steep gradients.

Superconducting superferric dipole magnet with cold iron core for the VLHC

Magnetic system of the stage I Very Large Hadron Collider (VLHC) is based on 2 Tesla superconducting magnets with combined functions. These magnets have a room temperature iron yoke with two 20 mm air gaps. Magnetic field in both horizontally separated air gaps is generated by a single, 100 kA superconducting transmission line. An alternative design with a cold iron yoke, horizontally or vertically separated air gaps is under investigation. The cold iron option with horizontally separated air gaps reduces the amount of iron, which is one of the major cost drivers for the 233-km magnet system of future accelerator. The vertical beam separation decreases the superconductor volume, heat load from the synchrotron radiation and eliminates fringe field from the return bus. Nevertheless, the horizontal beam separation provides lowest volume of the iron yoke and, therefore, smaller heat load on the cryogenic system during cooling down. All these options are discussed and compared in the paper. Superconducting correction system combined with the magnet that allows increasing the maximum field is also discussed. Preliminary cost analysis is performed for all these options.

Reversible Stepwise Formation of Mono- and Bilayers of a Fluorocarbon/Hydrocarbon Diblock on Top of a Phospholipid Langmuir Monolayer. A Case of Vertical Phase Separation

Compression of mixed Langmuir monolayers made from combinations of dipalmitoyl phosphatidylethanolamine (DPPE) and the semi-fluorinated alkane C8F17C16H33 (F8H16) results in expulsion of the diblock molecule at high pressure. Depending on the DPPE/F8H16 molar ratio, either a monolayer or a bilayer of F8H16 is formed on top of a DPPE-only monolayer. The structure of the hydrocarbon and fluorocarbon layers that constitute the resulting vertically separated bi- or trilayer was determined using grazing incidence X-ray diffraction. The phenomenon is reversible and represents a novel case of vertical, pressure-induced phase separation.

Ability of laying hens to negotiate horizontal perches at different heights, separated by different angles

1. This paper describes how birds move between horizontal perches at different heights with different angles separating them, using the time to complete the task and the number of birds failing to indicate ability. 2. For the first experiment, 4 groups of 15 birds (ISA Brown) were subjected to each of the experimental treatments (using three perches with angles of 0° (horizontal control), 30°, 45° or 60° between them). The birds were required to move upward between the perches for each treatment and then to move downward between the perches, as a second part of the experiment. 3. Birds moving up between the perches took significantly longer at 60° than at any other angle. No birds failed to complete the task. 4. For birds moving downward between the perches, the median time to complete the task increased significandy with angle. Furthermore, the number of birds failing to complete the task increased with angle. 5. A second experiment was conducted to test whether the vertical or horizontal component of distance affected birds’ ability to negotiate perches separated by different angles. 6. For the second experiment 4 groups of 10 Lohmann Brown laying hens were subjected to each of the following treatments: two horizontal perches separated by 30° or 60° and either direcdy, horizontally or vertically separated by a set distance of 50 cm. Birds were required to move both up and down between perches. 7. Birds negotiated horizontally‐separated perches more successfully at 30° than at 60°. However, when the vertical distance between the perches was 50 cm there was no significant difference in the ability of birds to move downward at 30° or 60°. For birds moving upward, 60° was easier to negotiate dian 30°. 8. The vertical and horizontal separations, as well as the different angles affected the ability of birds to move between perches. There was a general decreasing trend in ability with increasing vertical separation between perches. 9. The findings are important in terms of arrangements of perches to improve bird welfare. To minimise die risk of injury, the angle between perches at different heights should be no more than 45 degrees, and die horizontal and vertical distances between these perches minimised, to allow the birds to be able to move downwards more easily.

Vertical integration versus vertical separation: An equilibrium model

In this paper, the role of strategic forces in vertical relationships is examined. Using a simple model of differentiated products with symmetric demands and costs, the Perfect equilibrium to a vertical integration-vertical separation game between manufacturers is determined. Given the assumptions of the model, I show that the manufacturer's decision whether to vertically integrate or to remain separate from its retailer depends on the degree of product differentiation. I show that when the products are poor substitutes, the only Perfect equilibrium is vertical integration by both manufacturers. As the products become closer substitutes, an additional Perfect equilibrium appears, both firms vertically separated. For manufacturers, the vertically separated equilibrium always Pareto dominates the vertical integration equilibrium when both equilibria exist.

Cross-correlation between 900 MHz signals received on vertically separated antennas in small-cell mobile radio systems

In order to establish the antenna separation necessary to receive sufficiently decorrelated samples of the signal at both base and mobile stations, extensive field trials have been carried out in which a CW signal was transmitted over a distance of 1.3 km. The receiving station was equipped with two vertical halfwave dipoles which were spaced in a vertical configuration. The received signals were coherently demodulated by a two-branch phase-locked receiver which could measure both the complex and envelope cross-correlation. Results show that a cross-correlation less than 0.7 can be achieved using an antenna separation of 8 lambda to 13 lambda at the base station and approximately=1 lambda at the mobile, for a 1.3 km cell radius. At 900 MHz such an antenna separation is easily obtained and, in both cases, the space required is small. The cross-correlation using vertically spaced antennas at the base station is independent of the incoming arrival angle and hence low correlation can be achieved whilst maintaining omnidirectional coverage. At the mobile the small vertical antenna separation required suggests that an unobtrusive antenna arrangement is feasible. >

Geophone differencing to attenuate horizontally propagating noise

Geophone differencing is a matter of taking the difference of the output response of two geophone elements that are vertically separated by a small distance. The primary purpose of this technique is to attenuate all horizontally propagating energy, such as ground roll, regardless of whether propagation is in line with the shot or out of the plane. The objective is met because horizontally propagating energy is received by the two elements in‐phase and is subtracted out. Vertically propagating energy, however, is slightly phase shifted due to the element separation. Differencing, rather than cancellation, results. The response operator of differencing depends upon several factors: (1) the vertical separation distance of the geophone elements; (2) the propagational velocity in the ground adjacent to and between the elements; (3) the distance of the upper element from the free surface; (4) the reflectivity of the free surface; and (5) the amplitude response of the lower geophone element relative to the response of the upper element. Models show that the best response may be obtained when the upper element is on or very near the free surface, and the other element is at a depth equal to half the shortest expected signal wavelength (highest frequency). Experimental results confirm the expectation that ground roll tends to be in‐phase with depth. In (mild) contrast with the model results, actual data show that best results might be obtained when the geophone elements are as close as possible, because the decay of ground‐roll amplitude depends upon wavelength and depth. Very shallow burial minimizes the amount of decay. How shallow the burial depth can be before it interferes with the reflection signal is unclear, although .9 m is not too shallow. Upcoming compressional (P)-waves are out‐of‐phase and have a reduced amplitude even when the geophone is buried only .9 m. Geophone differencing attenuates ground roll and does not adversely affect upcoming P-waves; it has a gentle high‐pass filtering effect on P-waves.

The Number of Fades in Space-Diversity Reception

Experimental and theoretical results are presented which show that deep fades due to multipath propagation on line-of-sight microwave links are greatly reduced in number when two vertically separated receiving antennas are used and the stronger of the two received signals is selected as the diversity signal. The experimental results are based on 6 GHz propagation data obtained for a 72-day period on a 28.5 mile path in Ohio, with a 27.5 foot vertical separation of the receiving antennas. The theoretical results are obtained by treating the received signals as correlated Rayleigh distributed random variables. Theoretically predicted variations with fade depth agree with experimental observations. Combination of the theoretical results with experimentally determined parameters provides results which can be used, for example, to calculate the reduction in the number of fades as a function of the vertical separation of the receiving antennas, wavelength, path length, fade depth, and the gain difference (if any) of the receiving antennas.