Polar View Research Articles

Polarized views

Polarized views

Polarized views

Polarized views

A finite fractal cluster theory of 1/f noise in percolation systems near metal-insulator transition

The problem of 1/f noise in thin metal films and metal-insulator composites in the scaling fractal regime near percolation threshold is considered. The correspondence between a percolation transition and a second order phase transition is extended from the point of view of electronic polarization and electrical fluctuations. The charge fluctuations on finite fractal clusters are argued to be analogous to spontaneous order parameter fluctuations in phase transitions, being correlated upto percolation correlation length. The charge relaxation times are shown to be related to the cluster sizes having distribution function of the formg(τ)∝τ−b, whereb is connected to Euclidean and fractal dimensionalities and critical exponents. This produces the 1/f noise spectrum. Below percolation threshold, the nodes-links-blobs picture is invoked such that the blobs represent metallic conductances of the finite clusters and the links are tunnelling conductances between them through narrowest barrier regions. Above threshold, the finite cluster network is visualized as connected to the infinite cluster through narrowest tunnelling regions. The correlated spontaneous charge fluctuation on finite fractal clusters is held responsible for conductance fluctuation on either side of the metal-insulator transition via tunnelling processes. Finally, the scaling behaviour of noise magnitude near percolation threshold is explained.

Advanced anisogamy in Chlamydomonas monadina (Chlorophyceae) with special reference to vacuolar activity during sexuality

A homothallic strain of Chlamydomonas monadina Stein, UTEX 760, produced cells of three sizes. The largest were always vegetative while the middle size and smallest cells could act as gametes. As observed in polar view, the macrogamete orientated itself at a right angle to the surface of the liquid medium and held this position by its flagella outstretched at a 180° angle to each other in the surface microlayer. No agglutination of the flagella of the gametes occurred. The anterior end of the microgamete penetrated the side of the macrogamete, with both gametes retaining their cell walls and flagella during the initial contact. The microgamete then formed an anterior papilla. As the papillar wall fused with the wall of the macrogamete, flagellar activity was lost. Although the macrogamete remained stationary prior to and during gametic union, it did not lose its flagella until the moment of fusion of the protoplasts within the macrogametangium. Attempted cases of polyspermy were noted, but none was successful. The contractile vacuolar rates in the macro- and microgametes were similar prior to gametic union. However, after contact of the gametic walls, the vacuolar pulsations in the microgamete increased from once every 40–50 s per vacuole to once every 30 s; pulsations in the macrogamete remained at once every 40–50 s; pulsations in a newly formed zygote were once every 60 s. Behavior of the contractile vacuoles before, during and after plasmogamy, in successful and in abortive gametic fusions, along with occasional new wall formation posteriorly in moving microgametoplasts, suggests that an increase in the rate of inflow of water into the microgamete provides the driving force for its movement into the gametangium of the macrogamete.

Metaphase position of an interchange quadrivalent of Allium triquetrum III. the expected distribution based on randomness

ABSTRACT The position of an interchange quadrivalent at metaphase I of Allium triquetrum was modelled so as to simulate the original placement of the quadrivalent in the spindle and the preparation of linear spreads through squashing. In this way an expected distribution for the quadrivalent in linear spreads was generated. The procedure used polar views of metaphase I to which the quadrivalent was assigned pairs of positions normally occupied by bivalents. The positions of the bivalents and assigned quadrivalent were then projected into a linear array and analysed as ‘real’ data. Comparisons with observed distributions showed that a general bias in favour of marginal placement of the quadrivalent in the linear array is expected; and also showed that the quadrivalent is positioned non-randomly in the metaphase plate prior to slide preparation.

A Palynological Study of the Staphyleaceae

Abstract Pollen of 23 species representing all five genera was examined by light microscopy, scanning electron microscopy, and a selected number in transmission electron microscopy. For the most part the family is palynologically rather uniform with the occurring variation forming a morphological continuum. Staphyleaceae pollen is tricolporate, tectate, circular to triangular in outline in polar view and usually spheroidal. Ectoapertures are long to very long, recessed, and granular. Endoapertures range from poorly developed in Huertea and Tapiscia to well defined in Euscaphis, Slaphylea, and Turpinia, and are either bounded by the colpi margins or transversely extended. Periapertural exine thinnings are present. The exine is stratified into tectum, columellae, foot layer and endexine. The endexine is either smooth, or as in Slaphylea, solid near the foot layer and granular on the inner surface. Tapiscia is characterized by the absence of endexine and an interrupted fool layer. The exine surface is tectat...

Pollen Tetrads in Stenomesson elwesii (Amaryllidaceae)

Pollen tetrads within Amaryllidaceae are reported for the first time for Stenomesson elwesii. Tetrads were examined with light and scanning and transmission electron microscopy. The tetrads are tetragonal in shape. Tetrad-members are rounded-triangular in equatorial view and elliptic in polar view. Average polar diam is 50.1 μm; average longest equatorial diam is 62.5 μm. Morphology of the aperture is monosulcate. Exine sculpturing of the intectate pollen is gemmate. Systematic implications are briefly discussed.

POLLEN TETRADS IN STENOMESSON ELWESII (AMARYLLIDACEAE)

Pollen tetrads within Amaryllidaceae are reported for the first time for Stenomesson elwesii. Tetrads were examined with light and scanning and transmission electron microscopy. The tetrads are tetragonal in shape. Tetrad-members are rounded-triangular in equatorial view and elliptic in polar view. Average polar diam is 50.1 Am; average longest equatorial diam is 62.5 Am. Morphology of the aperture is monosulcate. Exine sculpturing of the intectate pollen is gemmate. Systematic implications are briefly discussed.

Chemical bonding in the oxides of the elements: A new appraisal

The role of electronegativity in the bonding of binary compounds is discussed and it is concluded that the usual electronegativity criteria for ionic, covalent, and metallic bonding do not apply to the oxides of the elements. One of the reasons for this is the wide variation observed in the electronegativity value of oxygen; for example, it is 3.5 in SiO 2 but 2.5 in Na 2O. It is argued that the electronegativity of oxygen is a better indication of ionicity (falling with decreasing covalency) than the electronegativity difference. Metallic bonding in oxides is treated from the point of view of polarization, and it is shown how experimental parameters of polarization and of band theory are closely related. These parameters are used for charting the proximity of oxides to the onset of metallization, while, simultaneously, the oxygen electronegativity is used for charting ionic/covalent bonding.

Pollen morphology of Ligusticum (Apiaceae) in Canada

The pollen morphology of the four Canadian taxa of Ligusticum (L. calderi, L. canbyi, L. scothicum ssp. scothicum, and L. scothicum ssp. hultenii) was studied under the light microscope and compared with that of other Apiaceae common on the Pacific coast of British Columbia and adjacent Alaska. Ligusticum calderi and L. canbyi compose one pollen type with a subrhomboidal outline in equatorial view and a triangular outline in polar view with pores located at the apices of the amb. Endopores are X-, H-, or dumbbell-shaped. The L. scothicum type is rectangular in equatorial view and circular in polar view, with pores arranged on the circumference. Endopores are usually rectangular to oval. Ligusticum calderi pollen is larger and thus distinct from L. canbyi pollen. All other Apiaceae pollen types examined are distinct from the L. calderi type because their pores are positioned between the lobes of the amb and because of differences in other characters. Since L. calderi pollen is readily separated from other Apiaceae on the British Columbia coast, it can be used to study the history of this geographically restricted species and the possibly refugial species associated with it. The size differences between L. calderi and L. canbyi pollen suggest that they are distinct species.

Pollen Morphology of the Genus Erythrina (Leguminosae: Papilionoideae) in Relation to Floral Structure and Pollinators

Pollen Morphology of the Genus Erythrina (Leguminosae: Papilionoideae) in Relation to Floral Structure and Pollinators

POLLEN MORPHOLOGY AND THE RELATIONSHIPS OF SIMMONDSIA CHINENSIS TO THE ORDER EUPHORBIALES

Pollen from Simmondsia chinensis (Simmondsiaceae) was examined in LM, SEM, and TEM. The pollen is shed as monads, triangular in shape in polar view, with a 3‐porate aperture type in which the pores are large and poorly defined. The tectum is irregularly scabrate, sometimes forming minute “islands” topped with spinules. In thin section, the endexine is thickened and lamellate in the aperture regions, and narrow in the mesoporus; the foot layer is well‐defined but noticeably thicker in the mesoporus; and thin columellae support an essentially complete tectum. The pollen of four genera, Buxus, Pachysandra, Sarcococca, and Styloceras, from the Buxaceae to which Simmondsia has been assigned by some authors, was also examined and illustrated. The pollen morphology of two families frequently aligned with Simmondsiaceae, Euphorbiaceae and Pandaceae, is briefly discussed. For the most part pollen morphology supports the treatment of Simmondsia as a monotypic family, Simmondsiaceae.

Polar views of the Earth's aurora with Dynamics Explorer

Preliminary examination of the first global auroral images gained with the vacuum‐ultraviolet imaging photometer on board DE 1 reveals a remarkable spatial configuration of auroral luminosities. Frequently the northern auroral oval is bifurcated by a sun‐aligned arc extending from the midday auroral zone to the nighttime sector of the oval. Simultaneous plasma measurements with the low‐altitude DE‐2 spacecraft are used to show that the character of plasmas above the polar arc is similar to those found over the poleward zones of the auroral oval. The spatial distribution of auroral luminosities is suggestive of a two‐cell structure of current systems and convection electric fields over the earth's polar cap and a similar division of the corresponding lobe in the magnetotail.

The Algerian bureaucracy

Algeria has a form of ‘state capitalism’ and thus the role of the bureaucracy is crucial. The approach here to this question rejects as simplistic the two polar views: on the one hand, the belief that Algeria is undergoing some kind of transition to socialism and though there may be a ‘problem of bureaucracy’, this is treated outside the class structure; on the other, the notion that if there is state capitalism then the bureaucracy is a ruling class, which ignores the fact of social as opposed to private accumulation. Analysing it as a bureaucracy and in its context of the working of the Algerian state, reveals that the relationships between it and a bourgeois class with a seprate existence are mediated through and by other features that affect the ‘rationality’ of the Algerian bureaucracy. Religion plays an important role, but not one that dictates the pattern of politics as in some Islamic or Catholic countries, but as an ideological and legitimating link with the people. The pursuance of personal benefits and traditional obligations through the bureaucratic system limits its effectiveness in pursuing policy goals, however. Patronage in turn feeds into a pattern of factions that rend the bourgeoisie, thus limiting its emergence as a national class, and also the bureaucracy, thus further impairing its efficacy. This situation may now undergo change as the state tries to respond to demands from below for a second stage of industrialisation going beyond the initial accumulation in heavy industry. But consumer goods production could be met by the expansion of either privatecapital or statecapital. The first would require a shift to economic liberalisation. The second strategy implies greater effectiveness of the bureaucracy and its greater political direction. A political struggle over these two lines is discernible but has not lead to a complete polarisation of the party.

The upper Triassic fernphlebopteris smithii(daugherty) Arnold and its spores

Abstract Phlebopteris smithii (Daugherty) Arnold is a palmate fern leaf that appears to be monopodial, with an odd number (5 to 15) of spreading pinnatifid pinnae. The sori occur in a single row on either side of the pinnule midrib and presumably are not protected by indusia. Each sorus typically contains 14 to 20 sporangia which have oblique annulii. The spores are triangular in polar view with psilate walls and trilete laesurae with straight radii which extend almost to the equatorial margins. They most closely resemble the dispersed spores Diclyophyllidites harrisii which ranges from the Carnian Stage of the Late Triassic to the Bathonian Stage of the Middle Jurassic. Phlebopteris smithii is widely distributed in Upper Triassic to Lower Jurassic units of the United States and is particularly common in the Upper Triassic (middle Carnian) Chinle Formation in the Southwest. Dispersed spores similar to those produced by P. smithii occur also in the same units. P. smithii is one of the oldest representative...

Polarized views of Quaternary ice sheets

The Last Great Ice Sheets. Edited by George H. Denton and Terence J. Hughes. Pp.484 plus maps. ISBN 0-471-06006-2. (Wiley: 1981.) £70.20, $126.35.

ULTRASTRUCTURE OF STEWARTIOTHECA (MEDULLOSACEAE) PREPOLLEN

Ultrastructure of prepollen from the medullosan seed fern Stewartiotheca warrenae Eggert and Rothwell has been studied with the scanning electron microscope. Nitrocellulose (“liquid” type) peel preparations of pollen organ sections were placed on millipore filters and the grain fragments were extracted by rinsing the peels with acetone. Prepollen is of the Monoletes‐type and is elliptical in polar view, averaging 264 μm long and 183 μm wide. Individual grains possess two deep, crescent‐shaped grooves on the distal surface and a monolete suture with a median deflection proximally. The exine is constructed of a thick (1–2 μm), homogeneous nexine layer overlain by a sexine that is characterized by interconnecting spheroidal chambers. Chamber diameter decreases only slightly from the exterior of the sexine, inward, but the frequency and degree of interconnection among the chambers increases noticeably toward the interior of the wall layer. With regard to this latter feature the prepollen of Stewartiotheca appears intermediate between the organizations known for other Monoletes grains. The grains of Stewartiotheca compare most closely with those of Dolerotheca and Sullitheca.

On the polarity and tetrad arrangements in some mono- and diaperturate angiosperm pollen grains

Abstract The mono- and diaperturate pollen grains have been found to be widely different in the orientation of apertures with regard to their polarity. The nature, position and polarity of eleven apertural types from widely unrelated taxa of angiosperms, have been studied in tetrad as well as in monad states, e.g. monosulcate (both ana- and catasulcate), extended-sulcate, sulculate, meridiono-sulculate, monoulcerate, disulcate, diulcerate, disulculate, diporate and dicolpate conditions. Illustrations have been provided to demonstrate the respective positions in tetrad conditions and equatorial and polar views in the monad condition. Avolutionary sequence transpires from these apertural types, from simple to more complex, which have been shown in a phylogenetic tree

Kudoa tetraspora n.sp. (Myxosporidea: Protozoa) parasitic in the brain tissue ofMugil cephalus

A new species of histozois myxosporidean,Kudoa tetraspora, infecting the tissue around the optic lobes of a fish,Mugil cephalus is, described. This is the second report of a species ofKudoa from India and the second in the world which establishes around the brain. The cysts range varies from 0·3–1·5 mm in diameter and are attached superficially to the tissue around the optic lobes. The spores are quadrate in polar view each measuring 9·0×9·0 μm and contains 4 polar capsules. The polar filaments are thick and each measures 10·0–12·0 μm in length. The spores are characteristically arranged in groups of four for which the name ‘tetraspora’ is proposed.

Mortoniodendron (Tiliaceae) and Sphaeropteris/Trichipteris (Cyatheaceae) in Cenozoic Deposits of the Gulf-Caribbean Region

Mortoniodendron (Tiliaceae) and Sphaeropteris/Trichipteris (Cyatheaceae) in Cenozoic Deposits of the Gulf-Caribbean Region