Pyramidal Faces Research Articles

Crystals of CTA-DNA: A growth and morphological study

During recent years DNA crystals have been grown from water-salt solutions. DNA fragments from calf thymus, chicken blood, phage T2 have been grown as the cetyltrimethylammonium salt (CTA-DNA) by gradually decreasing the NaCl concentration. The linear size of the crystals was 1.0mm–0.1 and the thickness was about 1–4μm. DNA crystals shows various morphological forms, such as spherulites, dendrites, needle-shaped crystals, etc. It has been found that the differences in the form of the CTA- DNA crystals are not due to different composition or crystallographic modification of the CTA-DNA crystals but are connected only with the crystallization conditions. The crystals have hexagonal symmetry and are in the form of rounded plates, with the optical axis being either perpendicular or parallel to the plane of the plate. Sometimes the crystals show pinacoid, prism and two pyramid faces. The growth rate of the prism faces is much greater than that of the pinacoid faces. The CTA-DNA crystals have perfect cleavages on the prism faces. They also have a tendency for repeated twinning. The optical axes of the twins are inclined to that of the initial crystal by 17–23°C. The twinning structure disappears when the crystal dissolves. The twins have a mechanical nature. The refractive indices were determined to be n e = 1.462 and n 0 =1.512. Before the crystal growth begins, an amorphous film of CTA-DNA arises, which has a great importance for the crystallization process. The crystal solubility is a little higher than the solubility of the amorphous film.

Wachstums- und schmelzvorgänge an gerundeten zink-einkristallen

The growth of rounded zinc single crystals grown from vapour (supersaturated between 1.6 and 28%) was investigated at temperatures close below the melting point. Besides of the equilibrium faces {0001}, {10 1 0} and {10 1 1} a pyramid plane surface of second kind appeared intermediately with a normal angle of 55°. It was developed best at high supersaturation and temperatures just below the melting point. It coarsened strongly at lower temperatures and smaller supersaturations. This can be explained by the assumption that the part of the surface which completely can be wetted is covered by a layer of quasi-melt. It cannot be explained by the action of long range lattice neighbours. The pyramid faces grow as equilibrium planes from this layer if the phase transition liquid-solid takes place with an activation energy which is caused by the structure of the melt and of the crystal surface. The process of melting can be explained now according to Tammann and Volmer by a shift of the phase boundary between crystal and layer of the melt depending on the orientation of the crystal.

LEED study of steps and facets on a Re surface

A rhenium single crystal with an initial (0001) orientation, recrystallized by twinning to yield {101̄ n} planes parallel to the surface. The LEED pattern displayed a one-dimensional superstructure which could be attributed to a system of regularly spaced steps. The 00 beam is diffracted from the (0001) plateaus of the steps, and not the high index plane. Heating the crystal in oxygen apparently modified the step system. Residual gas analysis showed that even after a “clean” LEED pattern has been obtained, carbon contamination is removed from the surface as CO by heating the sample in oxygen. Electropolishing of Re (0001) may result in basal plane etching. The faces of the rhombohedral pyramids thus formed were determined by analysis of LEED patterns and photomicrographs to be {112̄ n}, n = 2, 3, 4. The facet reflections are shifted in energy with respect to the normal reflections, due to a difference in inner potential. Also a dynamic interaction between the two sets of beams is suggested by observations. An intensity versus voltage plot for the normal 00 beam exhibits “forbidden” Laue maxima out to the 21st order. The absence of all but two secondary Bragg peaks may be explained with an Ewald sphere construction.

Crystal Structure of a Nitrogen Isostere of Pentacyclo-Octacosadodecaene

A NITROGEN isostere of pentacyclo-octacosadodecaene, namely, 2,8,14,20 tetraazapentacyclo [19,3,1,13,7,19,13,115,19] octacosa-1[25],3,5,7[28],9,ll,13[27],15,17,19[26],21, 23-dodecaene, recently prepared in these laboratories, has a structural formula as shown in Fig. 1 and has been examined by optical and X-ray diffraction methods. Crystals were grown from the mother liquid in bunches of long, thin needles, up to 1 cm in length and with a cross-section of 0.1–0.3 mm. The prism faces showed well-developed forms of {100} and {110} with all interfacial angles, constant within experimental error, of 45°. Frequently the form {110} showed the greater development, but pinacoid and pyramidal faces were not observed.

Etched Hillocks in BaTiO3

Two kinds of mounds or hillocks have been found on BaTiO3 single crystals after etching. Rounded, flat-topped hillocks were found after etching with 1% HF for 30 sec at room temperature. These hillocks were found where a 180° domain wall had been left for several days and had been removed shortly before etching. Their behavior can be explained by the ad hoc assumption that negative charges are attracted to the 180° domain wall at the crystal surface. Mounds shaped like Egyptian pyramids were found after etching BaTiO3 single crystals for 30 min in H3PO4 at 155°C. The edges between pyramidal faces always project onto the crystal surface (a 100 plane) in 110 directions.

Apparatus Drawings Project. Report Number 29. Accessory Apparatus for Large Electromagnet

The four devices described are designed to fit the large electromagnet, described earlier in this series, thus greatly enhancing its usefulness. (1) A magnetic force on a current-carrying conductor apparatus is intended for undergraduate laboratory investigations. A current of 50 amp in a magnetic field of 0.8 weber/m2 will produce a force on the conductor of nearly 3.2 newtons. The conductor current is normally obtained from lead storage cells. (2) An eddy current pendulum, 1 meter long, is used for lecture demonstrations. (3) Truncated square pyramidal pole faces provide the intense magnetic fields (about 1.3 weber/m2) required for a practical sophomore laboratory experiment on the Zeeman splitting of spectral lines. (4) The last device described is a single pole face specially tapered to produce a highly inhomogeneous magnetic field for experiments and demonstrations dealing with para- and dia-magnetism. Detailed information regarding construction of the apparatus is given.

On the Relation between the Vickers Hardness Numbers and the Face Angles of Pyramidal Indenters

Vickers hardness numbers of 45 test specimens have been measured by 4 pyramidal indenters with different magnitudes of face angles (angles between opposite faces of pyramids), in order to find the relation between the Vickers hardness numbers Hv and the magnitudes of the face angles θ. Then, this relation was formulated in a mathematical form, in which the mean pressure, i.e. Hv/sinθ/2 was represented by the experimental function of tan θ/2. This is the same as the result already obtained by one of the authors in the measurement with pyramidal indenters of tungsten carbide. In the present experiment, it has been found that the value of the exponent for each specimen depends on its material ranging 0.15∼0.40 and is in a simple relation with the hardness of the test specimen. From this result, it can be expected that the maximum error in the Vickers hardness number measured will not exceed 0.2∼0.5%, if pyramidal indenters of face angles of 136°±0.5°are used. The experimental formula for the mean pressure may also be expressed by the experimental function of cosθ/2 instead of tan θ/2, in which case the value of the exponent for each specimen depends on the work-hardening characteristics of its material.

A tangent arc of the halo of 24½ °

AbstractA remarkable halo complex observed in Germany in 1944 is described and theoretically discussed. There appear to be two possible crystal forms. Only one, however, with an inclination of the pyramidal faces of 25° 14′ fulfills the theoretical conditions. As far as we know there is only one other observation of a tangent are of an uncommon halo (in the Netherlands in 1933). It requires an inclination of the pyramidal face of 54° 44′, just the angle measured by Clarke (1822). In both phenomena we are concerned with similar refraction in similar plate‐shaped ice crystals.

Crystals of quartz with iridescent faces

The paper is a study of the iridescence exhibited by some of the pyramidal faces of two crystals of transparent quartz in the possession of the author. Spectroscopic examination shows the reflections and the corresponding extinctions to be monochromatic. The thickness of the iridescent layer may be directly observed, and the number of laminations inferred to be present is sufficient to explain the observed characters of the iridescence. The nature of the stratifications in the crystal giving rise to the iridescence is discussed. Photographs of one of the crystals and of the spectral character of the reflections and extinctions illustrate the paper. *** DIRECT SUPPORT *** A00OC061 00002

The Thermal Etching of Single Crystals of Cadmium

The heating of single crystal wires of cadmium in circumstances that permit free evaporation produces a development of crystalline planes. When the basal plane makes a small angle with the axis of the wire there is a characteristic formation of hexagonal pits, the bottoms of which are mirror-like basal planes: when the basal planes make larger angles, characteristic elliptical traces appear, reminiscent of those formed by mechanical extension. The thermal etching reveals, by the formation of steps, thin laminae existing in the unstrained wire: the thickness of these, of the order of 1 μ, is the same as the spacing of the glide planes revealed by mechanical extension. The etched figures, in general, indicate that the substructure revealed by straining is already present in the unstrained crystal. The secondary pyramidal faces revealed agree with the calculations of Stranski, Kaischew and Krastanov. The mirror-like basal planes are sufficiently large to permit the application of an optical method to reveal a scatter in their inclination to the axis. This method shows that there is a variation, round about 20 minutes, of orientation among the basal planes about the direction of growth of the crystals, which were grown by the method of Andrade and Roscoe and showed good single crystal properties by the usual criteria.

Occurrence of Troilite

MINERALS described from the Daggafontein Gold Mine1 were later made available to me for detailed study. They included typical brownish magnetic tabular pyrrhotite crystals 2·5 mm. wide by 0·5 mm. thick, snowing steep pyramid, prism and basal pin-acoid faces. Some were intimately associated with black nodules of a hydrocarbon and grey chlorite streaks in lumps of white, finely crystalline dickite.

The Electromotive Behaviour of Single Zinc Crystals

To NATURE of Jan. 12, 1929, p. 49, Paul A. Anderson communicated some measurements of his on the potentials of single crystals of zinc. The investigation of a possible change of the electrochemical potential with the changing density of zinc atoms on different planes of the crystal was also the aim of an experimental research commenced in October 1928 in the Physicochemical Laboratory of the University of Latvia, in Riga, and is now in progress. The results obtained here do not agree with those of Anderson in so far as no difference could be found in the potentials of different, artificially prepared planes of single crystals of zinc against a neutral zinc sulphate solution. It must be admitted, however, that pyramidal faces were not investigated.

On some new forms prominently developed on crystals of Proustite

Whilst determining some crystals of proustite in the Mineralogical Museum at Cambridge, and which came from Bolivia or some other part of South America, my attention was attracted by faces of trigonal pyramids, which, as shown in figs. 1 and 2, are the most conspicuous on the crystals. On measurement, these faces were found to correspond very nearly to those of the rhombohedra {73̄3̄} = 10 R (fig. 1) and {94̄4̄} = 13R (fig. 2). The figures represent with fair accuracy the relatively large development of the faces of these new forms. Another form, {11.7̄.7̄} = –6 R, represented by a single face on the lower end of one crystal, is also new for proustite.

On a Group of Minerals from Lilleshall, Salop

The Carboniferous Limestone at Lilleshall has for very many years been worked, partly as a flux for iron-smelting, partly as a source of lime for agricultural purposes. Various workings in the neighbourhood have, from influx of water, been abandoned; and there remains now but one mine, known as Stump Leasow. It is situated by the canal, near a spot marked “Old Farm” on the one-inch Survey map. There are two distinct beds of limestone, known as White and Grey, lying one above the other, separated by a distance of 40 yards. The upper bands of the lower bed, or grey, are fall of vertical joints, which in many cases, speaking from memory, run from six inches to a foot in width. It is in these joints that the minerals occur. Quartz is extremcly rare. I have, in fact, met with but one minute crystal. It showed under the microscope both prismatic and pyramidal faces. Erubescite . Only a few minute patches in the massive form have been met with. Copper pyrites is met with occasionally. It occurs in more or less defined spheroids. One specimen has a peculiar radiated structure. Iron pyrites is not by any means common. It occurs in radiating masses of from 2/3 to 1 1/2 inch diameter, showing faces of the cube, octahedron, and other forms. I have one specimen of the decomposed iron pyrites, which in old mineralogical books is called “hepatic pyrites.” This hepatic pyrites is in cubes and octahedra. Hæ . Occurs in minute