Calcite Plates Research Articles

Logic gate modules using opto-optical birefringence switching

A birefringence phenomenon is used to construct Boolean logic gates that output three logic functions. Logic gate modules are proposed that consist of Bi12SiO20 opto-optical birefringence switches, LiNbO3 electro-optical half-wave plates, and calcite plates. The gate can be driven by optical inputs and can also be electrically programmed for different logic operations. An array-packed solid-state module is described.

A simple system for an accurate calibration of grating spectrometers

Various calibrating systems for grating spectrometers are proposed. The most simple system leading to a stable and accurate calibration consists in the generation of a channeled spectrum by means of a calcite plate put between two crossed polarizers.

Selective solution of macroinvertebrate calcareous hard parts: a laboratory study

Ten suites of 16 common types of invertebrate hard parts were placed in acid baths for 24 hours to determine relative rates and common styles of dissolution. Skeletal mineralogies included aragonite and both high-magnesium and low-magnesium calcite. Hard parts included barnacle cxoskelctons, cchinoid tests, gastropod opercula and gastropod and bivalve shells. Calcitic barnacle plates dissolved most rapidly, aragonitic and high magnesium calcitic hard parts showed intermediate rates, and the calcitic shells of the oyster dissolved at the lowest rate. The surface area to weight ratio of the hard parts correlated (r=0.650) significantly with the hard part's rate of dissolution. Skeletal remains with a high surface area to weight ratio dissolved faster than those with a low surface area to weight ratio. Skeletal porosity and mineralogy appeared to be responsible for additional variation in the rate of dissolution. The effect of the surface area to weight ratio is sufficient to overcome the effect of mineralogy. Dense, compact aragonitic hard parts can persist longer than porous, thin calcitic remains. Typical features associated with skeletal degradation include development of chalky textures, thinning of distal margins, surface etching and formation of holes in bivalve muscle scars. Such features may aid in the recognition of partial dissolution of skeletal remains in the rock record. □Taphonomy, paleoecology, fossil-diagenesis.

Surface coatings on ancient coccoliths

Coccoliths are rings of calcite plates, often of intricate design, produced by unicellular algae1 (Fig. 1). Still widespread in modern oceans, these algae must have been extremely abundant in the Cretaceous period, and their skeletal remains form the main component of natural chalk. Both modern and ancient coccoliths are well preserved even in the corrosive environments of seawater and sediments, and the surface properties of natural chalk are said to be different from those of synthetic calcite. It has been suggested that this may be the result of a surface membrane; the present study establishes the existence of a coating on ancient coccoliths, and discusses its nature.

A new setup for determining the optic axis of a calcite plate

The auto-collimation procedure of Arnulf and Francon (see Mesures Optiques, Editions de l'E.S.O., p.26, 1962) has been adapted for determining the optic axis of calcite. This apparatus measures the angle between the normal to the crystal surface and the optic axis.

SBS wave front reversal for the depolarized light — Theory and experiment

Theoretical results concerning the wave front reversal (WFR) of spatially depolarized light in stimulated scattering are presented. The modes of scattering medium are found and the deterioration of reversal quality for the depolarized light is predicted. Experimental investigation of WFR in backward stimulated Brillouin scattering (SBS) in acetone was carried out when the light beam with λ = 1.06 μm was depolarized by the etched calcite plate. The share of scattered energy which has exactly reversed configuration, was measured. Experimental results quantitatively coincide with the theoretical conclusions.

Tunable-wavelength, single transverse and longitudinal mode, Nd3+ glass Q-switched laser

A new tunable-wavelength, single transverse and longitudinal mode, Nd3+ glass Q-switching laser is described. Single-longitudinal-mode operation is achieved by using saturable absorber Q switching and intracavity resonators. Tunability is achieved over a 50-Å range by means of a birefringent filter, consisting of a single calcite plate and a polarizer. The energy is about 25 mJ, obtained in a 17-ns pulse.

Spectrophotometry of M and C Stars

Abstract and SummarySurveys of M and C stars down to infrared magnitudes 12.m0 in two galactic regions in the direction Cygnus and anticentre are described. Infrared magnitudes are derived by a new method of calibration based on the use of a combination of crossed calcite plates and Polaroid HN32. Spectral classification is based on spectrophotometric criteria which measure the relative strengths of the molecular bands visible in the infrared in the low dispersion objective prism spectra. Infrared absolute magnitudes and interstellar extinction in the infrared are obtained from the present material and published data, and the space densities of M stars are determined.Full accounts have been published in Publ. Edinburgh Roy. Obs.7, 1 (1970) and 7, 73 (1971).

The secretion and structure of the skeleton of living and fossil Bryozoa

Eighty species of living and extinct bryozoans have been studied to ascertain the mode of secretion of the skeleton and its structural diversity throughout geological time. In the growing tip of the cheilostomes Membranipora and Electra and the ctenostome Bowerbankia , periostracum secreted by a cap of palisade cells expands forwards by intussusception. Older periostracum, left behind by the advancing cell cap in cheilostomes and cyclostomes, becomes the seeding sheet of a calcitic layer (primary layer) of vertically disposed crystallites with minor banding, nodules and lenses, deposited by epithelium generated immediately proximal of the cell cap. The periostracum is composed of mucopolysaccharide and some chitin but its outer surface varies, being a fibrillar triple-unit membrane in cheilostomes and the cyclostomes Berenicea and Lichenopora , and a homogenous granular layer in Bowerbankia and the cyclostome Crisidia . The mineral skeleton of most cheilostomes is secreted on periostracum by succeeding epithelium. But coelocystic structures, deposited within folds of epithelium, also occur and vary from frontal walls and cryptocysts to almost complete skeletons of Cupuladria and Iodictyum . In some living cheilostomes and in most fossil species examined, only a primary shell, more commonly calcitic than aragonitic, is found, but in the majority of living species there occurs an organic-carbonate secondary layer usually composed of discrete laminar or lenticular aggregates of vertically disposed crystallites enclosed in proteinous sheets. In Celleporella , however, the laminae are more strongly defined because they consist of spirally growing calcitic plates separated from one another by simultaneously secreted proteinous sheets. More rarely, a tertiary layer is found in some species. It is almost entirely calcitic or aragonitic and may be banded, granular or composed of acicular crystallites. Puncta and basal kenozooids, as in Schizoporella and Cupuladria, penetrate the shell of some species and accommodate papillae with storage cells. The mineral skeleton of most cyclostomes, including the earliest known genera like the Ordovician Corynotrypa, has always been subperiostracal, and may also be pierced by puncta accommodating storage papillae and distally closed by periostracal plugs (e.g. Crisidia, Berenicea ). The skeleton of Heteropora , Hornera, Lichenopora and related genera which first appeared in early Mesozoic times, is coelocystic. It may also be ornamented by inwardly pointing cones of secondary shell (pseudopuncta) with or without axial rods of granular calcite (e.g. Hornera ) , or include vesicular tissue between radiating rows of zooecia as in Lichenopora . All cyclostomes, however, have always had a double-layered calcitic skeleton consisting of a primary layer of vertically disposed acicular crystallites, granules or tablets altered to a granular texture in the fossil state, and a laminar secondary layer with spirally growing plates and/or overlapping fibres coated by protein sheets. The mineral skeleton of the remaining stenolaemates represented by extinct trepostomes, cystoporates and cyclostomes, is exclusively double-layered and coelocystic. The primary layer is granular, the secondary composed of lenticular fibres. Pseudopuncta were almost invariably developed and interzooecial cavities (mesopores) commonly occurred and were filled with vesicular tissue as in Lichenopora . Phylogenetic considerations suggest that the prototypic bryozoans possessed a pseudopunctate coelocystic skeleton, indented by mesopores and composed of a chitinous or proteinous periostracum, a primary layer of acicular crystallites and a secondary layer of lenticular fibres. This structure was inherited by trepostomes, cystoporates and cryptostomes. It reappeared in Mesozoic cyclostomes subsequent to their divergence from a cystoporate-like ancestor by the development of a variably punctate subperiostracal skeleton which, however, was composed of the same shell types. The subperipheral skeleton of early cheilostomes may have evolved by extension of the ctenostome secretory regime. In any event a new type of secondary shell, composed of acicular crystallites arranged in proteinbound laminae and lentides, became characteristic mainly of Tertiary and Recent species. Nevertheless, a coelocystic skeleton and even a stenolaemate-like secondary shell have already appeared within the Order.

Multicolour Photometry of the Stars in NGC 2264*

The young cluster NGC 2264 contains early type and non-emission stars, as well as T Tauri-like variables which populate the elevated main sequence (Walker 1956). The astrometric study of Vasilevskis et al . (1965) indicates a high probability of these variable stars being cluster members. The generally accepted view is that the stars which lie above the zero-age main sequence are still undergoing contraction. They exhibit infra-red, blue and ultra-violet excesses (Mendoza 1968, Smak 1964), and they are characterized by H α emission, the intensity of which is correlated with ultra-violet excess (Kuhi 1966). In the (U–B, B–V) diagram these stars occupy the same region as would the heavily reddened OB stars. It is necessary to distinguish between them and this can be achieved by the application of multi-colour (UBVRI) photometry. In the present paper UBV photometry of the stars of NGC 2264 has been extended to R and I magnitudes in Johnson's (1966) system, and the infra-red and ultra-violet excesses of the T Tauri-like stars have been studied. The UBV data have been taken from Walker (1956). The plates were taken with the 40/60/150 cm Schmidt telescope of the Royal Observatory, Edinburgh's outstation at Monte Porzio during the period from October 1968 to January 1969. For R and I magnitudes the emulsion/filter combinations used are Kodak IaE + Ilford colour filter 204 and Kodak IN+ Ilford colour filter 207 respectively. The photographic calibration has been achieved by using a pair of doubly refracting calcite plates in conjunction with a polaroid (Bruck et al . 1969). The limiting magnitudes are R = 14 m .0 and I = 13 m .0. No attempt has been made to search for variables. Variability of the known or suspected variables has been studied over the period of observations, and mean magnitudes have been derived from plates taken in the same interval of time. The standard error of photographic magnitudes due to different sources of errors including the variability of stars is ± 0 m .14 The separation of T Tauri-like stars from background early type stars which are heavily reddened can be achieved in the following way: The (U–V) and (V–I) colours can be predicted for the early type stars from the parameter Q defined as Q = (U–B)–0.70 (B–V) (Nandy 1968), which determines the spectral type and colour excesses E B–V , E V–R , E V–I . In the case of reddened early type stars the predicted colours would agree with the observed (V–R) and (V–I) colours. On the other hand, if the difference between the predicted and observed colours is much larger than the errors of observation, the stars are likely to be of later types with anomalous colours characteristic of T Tauri stars. For these stars, an additional parameter (V–R) 0 , which is the observed (V–R) colour corrected for reddening has been found necessary to estimate their spectral types, and infrared and ultraviolet excesses can be directly computed. The variables, in particular the H α emission stars in NGC 2264, exhibit infra-red and ultra-violet excesses, and there appears to be a positive correlation between them. These stars may be more luminous than indicated by their colour magnitude diagrams, and following Mendoza (1968) the mean ratio L total /L cm has been assumed to be 3. Masses and ages of these variables as faint as V = 15 m .0 have been computed on this assumption. It is found that their average age is 10 6 years, in agreement with the estimated age of the B stars of the cluster, and their masses range from one to two solar masses.

The Optical Effects of a Double Calcite Plate on a Converging Beam of Light

The aberrations and variation in transmission of a beam of light converging to a focus and passing through plates of calcite have been investigated, in order to estimate possible photometric errors due to these effects when a crossed calcite plate is used to calibrate photographic plates. The aberrations are calculated in terms of ray deviations whose magnitudes are derived, and the transmission coefficient is determined by solution of electromagnetic boundary conditions. The resultant formulae are evaluated numerically, and set limits on the photometric accuracy of images formed by a Schmidt telescope used with a calcite plate calibrator.

Determination des indices d'absorption de la calcite dans la region d'absorption dichroïque (1910-1690Å)

Absorption indices of calcite in the 1910-1690 Å region have been determined from transmittance at non normal incidence of polished thin calcite plates cut obliquely to the optic axis.

Birefringence of Quartz and Calcite

The measured birefringences of quartz and calcite plates are given at several visible wavelengths for temperatures of 20° and 40°C.

Photographic polarization results for extragalactic nebulae in Coma, southern stars, and HD 14633.

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photographic polarization results for extragalactic nebulae in Coma, southern stars, and HD 14633. Markowitz, Wm. Abstract The observations were made with a calcite plate placed at the focal plane of the ~6-inch refractor. For a polarized star the intensity difference between the 0 and E images describes a double sine-wave as the crystal is rotated through 3600. Mean polarization was determined for 60 nebulae in the Coma cluster within 25' of the center. Included were the nebulae for which an unexplained color excess was found by Stebbins and Whitford. The faintest nebula measured is magnitude 17.4 photographic, 16.4 visual. Also measured were 100 faint stars in the region. Total image pairs measured, 1500. Polarization was not detected for nebulae or stars, the probable error of the mean result being ~0.I5 per cent. Hence, it appears that (I) the light from distant galaxies is not polarized by its passage through space, and (2) there is little polarization towards the galactic pole. HD 14633 is the bluest star in the catalog of Stebbins, Huffer and Whitford. Measurement of 500 image pairs shows a definite double wave, indicating a polarization of 0.5 per cent in position angle 330 This agrees closely with the result found previously with the 40-inch reflector. It appears that polarization can occur in the absence of perceptible reddening. Polarization was not found for the very blue southern stars, ~ Puppis and ~` Velorum, the probable errors being +0.15 per cent. A survey of polarization of southern stars was carried out in order to obtain data for as much of the galactic circle as possible. The polarization in Vela, Puppis, and Centaurus is small and the direction planes are nearly at random. The region near ~ Scorpii is the most highly reddened part, for the brighter stars, in the southern Milky Way.' Here again the polarization is moderate. A few degrees up, however, in Saggitarius, more heavily polarized stars are found. The star of highest polarization found in the southern sky is MWC 266 = HD 160529. The polarization is close to 8 per cent; further observations, photographic and photoelectric, are being made. This star is unique in that its polarization was first detected visually. Other stars of special interest are: Star P (I) HD 148379 2% (2) ~ Sco. 3% (3) HD 156134-154-201 2% (4) MWC 272 3% The three stars of line 3 are polarized parallel to the galactic plane; they probably are connected. The present results added to those obtained with the ~o-inch' give the polarization pattern for all but a sixth of the galactic circle. The data were analyzed in 100 intervals of longitude. The mean value of P2, the "vector" mean, is I per cent. The direction of the maximum magnetic vector is predominately at right angles to the galactic plane. It is inferred that the axes of the polarizing particles are (a) lined up perpendicular to the galactic plane, or (b) lying in the plane, but at random orientation. In either case little polarization would be observed in the Z-direction. The stars observed were selected for high space reddening. It is probable that our galaxy seen edge on would show only a few tenths of a per cent polarization, and much less if seen at right angles. I. Francis J. Hayden, S. J., Ap. J. 99, 8, 1944. 2.Hall and Mikesell, Pub. U. S. Naval Obs. `7, Pt. I, 1950. U.S. Naval Observatory, Washington, D. C. Publication: The Astronomical Journal Pub Date: October 1951 DOI: 10.1086/106554 Bibcode: 1951AJ.....56..134M full text sources ADS | data products SIMBAD (8)

A Short Wave X-Ray Spectrograph and Some K Series Emission Wave-Lengths

Transmission type spectrograph for short x-rays.---The spectrograph described is similar to that used by Rutherford and Andrade for $\ensuremath{\gamma}$ rays. A calcite plate 1.6 mm thick ground with the faces perpendicular to the (100) planes was placed midway between two slits, through one of which (3 mm wide) it was illuminated with x-rays from the source, and through the other (.15 mm wide) the rays reflected from (100) planes on both sides of the axis passed to the photographic plate. A strip of lead at the middle of the crystal intercepted the direct beam. The advantages of this spectrograph are (1) that all uncertainty as to the depth of penetration into the crystal is eliminated; (2) lines are obtained whose sharpness is independent of the distance of the photographic plate; (3) all the lines of the K series are obtained simultaneously without crystal rotation; and (4) the time of exposure may be greatly reduced by placing the crystal close to the source of the rays.Wave-lengths of K series emission lines for Ba,La,Ce,Pr,Nd,Sm,Gd,Ds,Er and W.---The substance under investigation was placed on the copper target of a special water cooled tube with both electrodes removable at ground joints. The lines for each element were photographed together with tungsten lines, on both sides of the zero position. The probable error is about.1 X units for $K{\ensuremath{\alpha}}^{\ensuremath{'}}$,$K\ensuremath{\alpha}$ and $K\ensuremath{\beta}$ and.3 for $K\ensuremath{\gamma}$.