Vertical Diamond Research Articles

Diamond vacuum field emission devices

This article reports the development of (a) vertical and (b) lateral diamond vacuum field emission devices with excellent field emission characteristics. These diamond field emission devices, diode and triode, were fabricated using a self-aligning gate formation technique from silicon-on-insulator wafers using conventional silicon micropatterning and etching techniques. High emission current >0.1 A was achieved from the vertical diamond field emission diode with an indented anode design. The gated diamond triode in vertical configuration displayed excellent transistor characteristics with high DC gain of ∼800 and large AC output voltage of ∼100 V p–p. Lateral diamond field emission diodes with cathode–anode spacing less than 2 μm were fabricated. The lateral diamond emitter exhibited a low turn-on voltage of ∼5 V and a high emission current of 6 μA. The low turn-on voltage (field ∼3 V/μm) and high emission characteristics are the best of reported lateral field emitter structures.

2.5-D gravity model of the NiCuPGM mineralized Mount Ayliff Intrusion (Insizwa Complex), South Africa

The Mount Ayliff Intrusion is the largest and thickest Karoo-aged sill in South Africa. It contains a small NiCu-platinum-group metal (PGM) sulphide deposit, Waterfall Gorge, at the base of its largest lobe called Insizwa. The deposit was once mined for its Cu. In September 1990, a 900-m-deep, vertical diamond drill exploration borehole was drilled through a thick, central portion of the intrusion. This new geological control confirms an earlier gravity survey-based hypothesis that the intrusion has a thick, hidden keel of ultramafic rock with finite depth extent below the centre of the Insizwa lobe. Along with other new geological evidence, the borehole log affords a unique opportunity to further constrain models for three regional gravity profiles and to arrive at a new, 3-dimensional model for the Insizwa lobe. The background residual terrain-corrected Bouguer gravity anomaly of the Mount Ayliff Intrusion reaches up to +9 mgal. This results from an igneous slab of 0–150 m of picrite overlain by about 600 m of gabbronorite. Superimposed on this anomaly over the central and northwestern Insizwa lobe is a 10-km-wide gravity anomaly with an amplitude of +8 to + 17 mgal and having steep edges. This is interpreted to represent thickening of picrite to 400–800 m in a major, hidden basin bordered by two NW-striking fault lineaments that are believed to mark a hidden graben structure with major geological transgressions at the base of the Insizwa lobe. At least three discrete, thinner picrite basins are interpreted to extend above and beyond both flanks of the graben. Picrite in these basins is modelled to be less than 200 m in thickness. The basins are separated either by the major NW-striking geological transgressions, or by domes in the footwall of the Insizwa lobe, above which no picrite has developed. Locations of several hidden, narrow, discontinuous feeder dykes below the Mount Ayliff Intrusion are postulated. The role of ponding of picrite at the mostly hidden base of the intrusion emerges as being particularly significant. In view of the existence of Ni-Cu-PGM mineralization at Waterfall Gorge where exposed picrite is only 30 m thick, the recognition of much thicker picrite elsewhere at the base of the intrusion presents exciting exploration targets.

CHEMICALLY STIMULATED VISUAL ORIENTATION AND SHAPE DISCRIMINATION BY THE HERMIT CRAB CLIBANARIUS VITTATUS (BOSC)

ABSTRACT Orientation of the hermit crab Clibanarius vittatus (Bosc) to black geometric shapes of equal surface area was measured in a circular arena. This study tested the hypotheses that crabs can visually discriminate between different shapes and that attraction is related to the potential habitability of gastropod shells represented by the shapes. Test crabs were untrained and exhibited chemically induced shell-seeking behavior. This behavior indicated that they inhabit suboptimal gastropod shells (small relative to their body size). When presented with single silhouettes, crabs were significantly attracted to a horizontal rectangle, horizontal diamond, square, semicircle, and triangle, but not to a vertical rectangle or a vertical diamond. When exposed to pairs, the most and least attractive shapes were the horizontal rectangle and vertical diamond, respectively. Since responses were a complex function of the dimensional characteristics of the shapes, it was concluded that attraction was based on shape recognition. The hypotheses were further supported because crabs oriented poorly to the shape of the suboptimal shell which they inhabited (triangle), but oriented very well to shapes (horizontal rectangle, horizontal diamond, square, and semicircle) that represented more optimal gastropod shells.

Arcuate Keratotomy for the Correction of Spherical Hyperopia in Human Cadaver Eyes

A new experimental surgical technique to correct spherical hyperopia by steepening of the central corneal curvature was performed on human cadaver eyes. Ten eyes were used in the study. All were pretreated with glycerin to ensure a uniform corneal thickness between .55 and .65 mm on ultrasonic pachometry. A constant intraocular pressure of approximately 30 to 40 mm Hg was maintained in each eye by the injection of saline into the vitreous cavity. This was verified by pneumotonometry. A vertical blade diamond knife was set at 100% of the thinnest of four paracentral readings. Each eye underwent preoperative computed topography. One set of five eyes had 12 incisions made following a 5.75-millimeter diameter Mendez hexagonal marker that included unconnected T incisions at each junction (ie, "Hex T" pattern). The other set of five eyes had four arcuate incisions made following a 6-millimeter diameter zone marker; each incision was 60 degrees in arc. Immediately after surgery, computed topography was repeated. The hexagonal keratotomy set of eyes had an average steepening of the cornea of 0.80 D with a range of -1.05 to + 4.38 D. The arcuate keratotomy set had an average steepening of +2.12 D with a range of +1.27 to +3.27 D. This study suggests arcuate keratotomy may be a more effective procedure in the correction of spherical hyperopia when compared with hexagonal keratotomy. The amount of corneal steepening achieved in a cadaver eye model may not be the same as when performed in vivo.

Orientative lithogeochemistry of the archean and aphebian basement in the key lake uranium deposit region (Saskatchewan, Canada)

More than half of the proven uranium reserves in the Athabasca Basin are contained within the Key Lake U-Ni deposit at the basin's southeastern edge. The area studied comprises several orientatively explored areas within an intrabasin zone approximately 7 km wide, which extends from Blanchard Lake in the west to Wilson Lake in the east (45 km WNW and 10 km NE from the Key Lake deposit, respectively). The uranium and nickel regional background of the Aphebian metasediments covered by the Athabasca Basin platform sediments has been studied on samples taken from vertical diamond drill holes (DDH) crosscutting elongated electro-conductive zones. Three clusters of DDHs, each located within specific lithostructural subunits of the ensialic Hudsonian mobile Cree Lake Zone, provided in total 502 samples of pelitic, mostly carbonaceous, metasediments and some of the commonly associated anatexites. Uranium concentrations follow a “close-to-lognormal’ distribution with a median value of 3.0 ppm; 18% of the samples contain above 10 ppm and only one percent above 100 ppm. Nickel yields again a “close-to-lognormal” distribution with a median value of 33 ppm, and only 6% of samples above 100 ppm. To compare the regional background obtained from the orientatively explored areas with the mineralized environment, the Aphebian metasediments and Hudsonian anatexites hosting the primary halo of the Key Lake deposit have been selected as the local background from the mineralized vicinity. Fifty-seven composite samples, each representing a 10-m vertical section of the 50° dipping peribasal Aphebian sequence, were collected from two deep DDH's drilled 200 m downdip of the Gaertner orebody. The U values within this 220 m thick sequence range from 1 to 10 ppm with a “close-to-lognormal” distribution and median of 3.2 ppm. Nickel yielded a median of 46 ppm, with 7% of samples above 100 ppm. This peri-basal sequence, grossly subdivided into three stratigraphic units displays a definite tendency to concentrate Th, K and U within the hanging wall; Ni, Co, As, Fe, S, Cr, V, Ti and Mg in the main graphite horizon; and Na, Ca and Mn within the footwall series. The graphite horizon of about 40 m thickness contains 2% organic carbon, 0.6% sulphur, a mean Ni value of 106 ppm, but a low average uranium content of 2.5 ppm. To compare local Aphebian background with the potential Archean source, 10 samples from the nearest (to the Key Lake deposit) margin of the Zimmer Lake Archean inlier were assayed. The set is characterized by foliated highly potassic and low Q-granitoids. Uranium ranges from 2.5 to 10 ppm with an average of 6.0 ppm. Ni shows a characteristically low average of 16 ppm. Several tentative conclusions can be drawn from the comparison of three main sets of data and from their internal variations: 1. (1) Archean rocks display a granitoid source whose original composition probably became masked by introduced K during the Hudsonian event. 2. (2) Local Aphebian rocks compared with local Archean indicate a tendency to be more mafic with enhanced concentrations of Mg, Fe, Ca, Ti, P, and S, and by lower Th. Such a bulk Aphebian composition is caused by the contribution of the graphitic lithology to the geochemical background. 3. (3) Most of metallic elements except U (eg. Ni, Co, As, V), which are also concentrated in the Key Lake deposit, reach higher concentrations within this graphitic lithology. There are no Archean rocks in the vicinity which might provide these Aphebian concentrations by simple sedimentation of the Archean detritus. 4. (4) Contrary to the widespread assumption that the unconformity-related type of uranium deposit displays “hot” Archean in the vicinity and/or Aphebian “U-protores”, the observations in the Key Lake area show that the orebodies and their primary haloes are overprinted with a sharp U-gradient over the low-U environment. Uranium and nickel-clarke values are common to both regional and orebody-hosting Aphebian environments of the Key Lake region. 5. (5) The high-grade Key Lake deposit (2.6% U 3O 8), future Western world leading uranium producer, is located within geochemically (U s.s.) non-anomalous lithologies.

The role of the pretectum in the acquisition and retention of visual discrimination habits in monkeys

Seven rhesus monkeys were trained to discriminate between each of three pairs of stimulus plaques, namely (1) black vs. white, (2) horizontal vs. vertical stripes, and (3) triangle vs. diamond. Six animals were then subjected to subcortical electrolytic lesions. The three subjects that received bilateral damage to the pretectal region exhibited a significant loss in the retention of the horizontal vs. vertical stripe discrimination as compared to normal or brain-operated controls. Subjects that sustained bilateral damage to the area immediately ventral to the pretectal region showed significantly poorer retention of the triangle vs. diamond task compared to the other subjects. In addition, monkeys with bilateral pretectal damage needed significantly more trials to learn a new visual discrimination task than the control group. The pretectal animals were not impaired relative to controls on the number of trials necessary to learn a 5-sec delayed alternation task. Possible functions of the pretectal region are discussed in light of the present results.