Pair Of Stripes Research Articles

Growth mechanisms and modeling for metalorganic chemical vapor deposition selective-area epitaxy on InP substrates

Selective area epitaxy of InP on masked (100) InP substrates is studied. InP layers are deposited between pairs of SiO2 stripes using low-pressure metalorganic chemical vapor deposition. Layer thickness is investigated by surface profiling and scanning electron microscopy. For growth between oxide stripes, the growth velocity is enhanced by lateral diffusion of growth species from the masked region to the exposed region. Two transport mechanisms are known to exist: vapor phase diffusion and surface migration. However, most existing quantitative models focus only on the former. A new computational model, based on the diffusion equation with time dependent boundary conditions, is presented which describes the growth enhancement component due to surface migration. The role played by surface migration is shown to depend on nominal film thickness. The model correctly predicts a super growth enhanced region adjacent to the oxide. Previous quantitative models have not successfully described this aspect of growth near the oxide film.

The SCL gene specifies haemangioblast development from early mesoderm.

The SCL gene encodes a basic helix-loop-helix (bHLH) transcription factor that is essential for the development of all haematopoietic lineages. SCL is also expressed in endothelial cells, but its function is not essential for specification of endothelial progenitors and the role of SCL in endothelial development is obscure. We isolated the zebrafish SCL homologue and show that it was co-expressed in early mesoderm with markers of haematopoietic, endothelial and pronephric progenitors. Ectopic expression of SCL mRNA in zebrafish embryos resulted in overproduction of common haematopoietic and endothelial precursors, perturbation of vasculogenesis and concomitant loss of pronephric duct and somitic tissue. Notochord and neural tube formation were unaffected. These results provide the first evidence that SCL specifies formation of haemangioblasts, the proposed common precursor of blood and endothelial lineages. Our data also underline the striking similarities between the role of SCL in haematopoiesis/vasculogenesis and the function of other bHLH proteins in muscle and neural development.

Pattern formation in granular avalanches

Three new experiments are described which exhibit strong pattern formation in the deposits left by successive granular avalanches. At low flow rates continuous deposition, erosion or rotation gives rise to intermittent avalanche release. Once in motion kinetic sieving of a bi-disperse granular mixture creates a two-layer shear band in which the larger particles overlie the smaller particles. When this is brought abruptly to rest by the upslope propagation of a shock wave a pair of str ipes is “frozen” into the deposited material. Successive releases create a large scale pattern, which strongly reflects the history of the granular flow. At faster deposition, erosion and rotation rates a new flow regime is entered in which intermittency and shock formation ceases, and the associated patterns change.

Head segmentation in the embryo of the Colorado beetleLeptinotarsa decemlineata as seen with anti-en immunostaining.

Segmentation in the head of the embryo of the Colorado beetleLeptinotarsa decemlineata is described on the basis of anti-engrailed (en) immunostaining of germ band stages. Six segmental units can be identified with this technique. Three segmentalen stripes can be distinguished in the gnathal region, a weak stripe interrupted medially shows the intercalary segment rudiment, a pair of oblique stripes indicate the antennal segment, and one pair of preantennalen spots are taken to indicate a sixth segment. In the broad head lobes of the beetle the spacing of the six segmental units as demarcated byen regions is similar to that in other parts of the germ band. The results are discussed with respect to old and new data concerning the number of head segments and origin of the compound eye in insects.

The spatial organization of epidermal structures: hairy establishes the geometrical pattern of Drosophila leg bristles by delimiting the domains of achaete expression

The spatial organization of Drosophila melanogaster epidermal structures in embryos and adults constitutes a classic model system for understanding how the two dimensional arrangement of particular cell types is generated. For example, the legs of the Drosophila melanogaster adult are covered with bristles, which in most segments are arranged in longitudinal rows. Here we elucidate the key roles of two regulatory genes, hairy and achaete, in setting up this periodic bristle pattern. We show that achaete is expressed during pupal leg development in a dynamic pattern which changes, by approximately 6 hours after puparium formation, into narrow longitudinal stripes of 3-4 cells in width, each of which represents a field of cells (proneural field) from which bristle precursor cells are selected. This pattern of gene expression foreshadows the adult bristle pattern and is established in part through the function of the hairy gene, which also functions in patterning other adult sense organs. In pupal legs, hairy is expressed in four longitudinal stripes, located between every other pair of achaete stripes. We show that in the absence of hairy function achaete expression expands into the interstripe regions that normally express hairy, fusing the two achaete stripes and resulting in extra-wide stripes of achaete expression. This misexpression of achaete, in turn, alters the fields of potential bristle precursor cells which leads to the misalignment of bristle rows in the adult. This function of hairy in patterning achaete expression is distinct from that in the wing in which hairy suppresses late expression of achaete but has no effect on the initial patterning of achaete expression. Thus, the leg bristle pattern is apparently regulated at two levels: a global regulation of the hairy and achaete expression patterns which partitions the leg epidermis into striped zones (this study) and a local regulation (inferred from other studies on the selection of neural precursor cells) that involves refinement steps which may control the alignment and spacing of bristle cells within these zones.

A Xenopus homebox gene defines dorsal-ventral domains in the developing brain.

One of the distinguishing features of vertebrate development is the elaboration of the anterior neural plate into forebrain and midbrain, yet little is known about the early tissue interactions that regulate pattern formation in this region or the genes that mediate these interactions. As an initial step toward analyzing the process of regionalization in the anterior-most region of the brain, we have screened an anterior neural cDNA library for homeobox clones and have identified one which we have called XeNK-2 (Xenopus NK-2) because of its homology to the NK-2 family of homeobox genes. From neurula stages, when XeNK-2 is first detectable, through hatching stages, XeNK-2 mRNA is expressed primarily in the anterior region of the brain. By swimming tadpole stages, XeNK-2 expression resolves into a set of bands positioned at the forebrain-midbrain and the midbrain-hindbrain boundaries, after which XeNK-2 transcripts are no longer detectable. In addition to localized expression along the anterior-posterior axis, XeNK-2 may also play a role in the process of regionalization along the dorsal-ventral axis of the developing brain. At all stages examined, XeNK-2 mRNA is restricted to a pair of stripes that are bilaterally symmetrical in the ventral-lateral region of the brain. To begin to identify the tissue interactions that are required for the proper spatial and temporal localization of XeNK-2, we have performed a series of explant experiments. Consistent with earlier work showing that the A/P axis is not fixed at mid-gastrula stages, we show that XeNK-2 expression is activated when assayed in gastrula stage explants taken from any region along the entire A/P axis and that the tissue interactions necessary to localize XeNK-2 along the A/P axis are not completed until later neurula stages.

Analysis of the cross-coupled lateral mode in a twin-stripe four-contact laser with diagonal current injection

Cross-coupled resonant lateral modes in a twin-stripe four-contact laser are analyzed by coupled-mode theory for conditions in which the current injection into each diagonal pair of stripes is equal. The dependence of the optical power distribution on the laser length and on the carrier-density or the current-density distribution is investigated. The most interesting result is that the highest optical power interesting result is that the highest optical power appears in the waveguide with the lowest carrier density when the carrier-density difference between the adjacent waveguides is small and the laser is shorter than the coupling length. This makes it possible to show that a cross-coupled mode can be supported even in a two-contact twin-stripe laser and that bistable switching between the mode and its mirror image is possible. >

Architecture of the sarcomere matrix of skeletal muscle: immunoelectron microscopic evidence that suggests a set of parallel inextensible nebulin filaments anchored at the Z line.

Nebulin, a giant myofibrillar protein (600-800 kD) that is abundant (3%) in the sarcomere of a wide range of skeletal muscles, has been proposed as a component of a cytoskeletal matrix that coexists with actin and myosin filaments within the sarcomere. Immunoblot analysis indicates that although polypeptides of similar size are present in cardiac and smooth muscles at low abundance, those proteins show no immunological cross-reactivity with skeletal muscle nebulin. Gel analysis reveals that nebulins in various skeletal muscles of rabbit belong to at least two classes of size variants. A monospecific antibody has been used to localize nebulin by immunoelectron microscopy in a mechanically split rabbit psoas muscle fiber preparation. Labeled split fibers exhibit six pairs of stripes of antibody-imparted transverse densities spaced at 0.1-1.0 micron from the Z line within each sarcomere. These epitopes maintain a fixed distance to the Z line irrespective of sarcomere length and do not exhibit the characteristic elastic stretch-response of titin epitopes within the I band domain. It is proposed that nebulin constitutes a set of inextensible filaments attached at one end to the Z line and that nebulin filaments are in parallel, and not in series, with titin filaments. Thus the skeletal muscle sarcomere may have two sets of nonactomyosin filaments: a set of I segment-linked nebulin filaments and a set of A segment-linked titin filaments. This four-filament sarcomere model raises the possibility that nebulin and titin might act as organizing templates and length-determining factors for actin and myosin respectively.

The organization of titin filaments in the half-sarcomere revealed by monoclonal antibodies in immunoelectron microscopy: a map of ten nonrepetitive epitopes starting at the Z line extends close to the M line.

mAbs specific for titin or nebulin were characterized by immunoblotting and fluorescence microscopy. Immunoelectron microscopy on relaxed chicken breast muscle revealed unique transverse striping patterns. Each of the 10 distinct titin antibodies provided a pair of delicate decoration lines per sarcomere. The position of these pairs was centrally symmetric to the M line and was antibody dependent. The results provided a linear epitope map, which starts at the Z line (antibody T20), covers five distinct positions along the I band (T21, T12, T4, T1, T11), the A-I junction (T3), and three distinct positions within the A band (T10, T22, T23). The epitope of T23 locates 0.2 micron before the M line. In immunoblots, the two antibodies decorating at or just before the Z line (T20, T21) specifically recognized the insoluble titin TI component but did not recognize TII, a proteolytic derivative. All other titin antibodies recognized TI and TII. Thus titin molecules appear as polar structures lacking over large regions repetitive epitopes. One physical end seems related to Z line anchorage, while the other may bind close to the M line. Titin epitopes influenced by the contractional state of the sarcomere locate between the N1 line and the A-I junction (T4, T1, T11). We discuss the results in relation to titin molecules having half-sarcomere lengths. The three nebulin antibodies so far characterized again give rise to distinct pairs of stripes. These locate close to the N2 line.

The complete pattern of ocular dominance stripes in the striate cortex and visual field of the macaque monkey

Ocular dominance stripes in the striate cortex of a macaque monkey were labeled by autoradiography after injection of [3H]proline into one eye. The stripes were reconstructed on a representation of the flattened cortical surface by two independent techniques: one used computer graphics, and the other was the manual unfolding procedure of Van Essen and Maunsell (VanEssen, D. C., and J. H. R. Maunsell (1980) J. Comp. Neurol. 191: 255-281). The two reconstructions differed in many details of the pattern but were in agreement on its general features. As described in earlier studies, the stripes formed a system of parallel bands, with numerous branches and islands. They were roughly orthogonal to the V1/V2 border throughout the binocular segment of the cortex. In the lateral part of the operculum, where the fovea is represented, the stripes were less orderly than elsewhere. In the calcarine fissure the stripes ran directly across the striate cortex from its dorsal to its ventral margin. In the far periphery the stripes for the ipsilateral eye became progressively narrower, eventually fragmenting into small islands at the edge of the monocular segment. The overall periodicity (width of a left- plus right-eye pair of stripes) averaged 0.88 mm but decreased by a factor of about 2 from center to periphery. This decrease was not accounted for solely by shrinkage of the ipsilateral eye stripes. The flattened cortical reconstruction was transformed back into visual field coordinates, using information about visual field topography obtained from the detailed mapping study of Van Essen et al. (Van Essen, D.C., W.T. Newsome, and J.H.R. Maunsell (1984) Vision Res. 24: 429-448), as well as from more limited mapping done in the same monkey that was used for the reconstruction. In the transformed map, the stripes increased in width about 40-fold from the fovea to the far periphery. As deduced previously (LeVay, S., D. H. Hubel, and T. N. Wiesel (1975) J. Comp. Neurol. 159: 559-576; Hubel, D. H., and D. C., Freeman (1977) Brain Res. 122: 336-343), there were portions of the map in which the stripes followed curves approximating isoeccentricity lines, but this relationship was not very exact or consistent. The pattern of stripes appears to be more meaningfully related to the geometry of the cortical surface. This has significant implications for understanding the developmental mechanisms involved in stripe formation.

Magneto-optic observation of Bloch lines

We report the first visual observation of Bloch lines in thin garnet films without the perturbing influence of magnetic particles in suspension (Bitter solution). A second-order magneto-optic effect reveals the Bloch line position and the signs and positions of the domain wall segments lying adjacent to it. The present study is limited to Neel walls that separate in-plane domains aligned along [110] ‘‘easy’’ magnetic axes in a (100) garnet film 0.8 μm thick with large in-plane uniaxial anisotropy (Ku≪0). Images are viewed using normally incident laser illumination and crossed polarizers in a polarizing microscope also having an adjustable optical phase compensator. The contrast image for 180° walls with incident light vector E∥ polarized parallel to the wall is an adjacent pair of dark and light stripes. The usual first-order Faraday effect (magnetic circular birefringence) is excluded because all components of M are perpendicular to the beam. The quadratic dependence on M is verified, outside the wall at least, in domain contrast studies, e.g., by the lack of contrast between two opposing 180° domains. Within the wall magnetic linear birefringence would cause incident light E∥ to emerge as right- or left-handed elliptically polarized light according to the quadrants of the orientation of M wall in the E∥−E⊥ plane. Thus, the observed ordering of black/white or white/black stripes in the image reflects the sign of twist in M wall when the transmitted light is viewed through a compensator and analyser. The Bloch-line position is delineated by a discontinuous reversal in the black/white ordering.

On Seeing Reddish Green and Yellowish Blue

Four color names-red, yellow, green, and blue-can be used singly or combined in pairs to describe all other colors. Orange, for example, can be described as a reddish yellow, cyan as a bluish green, and purple as a reddish blue. Some dyadic color names (such as reddish green and bluish yellow) describe colors that are not normally realizable. By stabilizing the retinal image of the boundary between a pair of red and green stripes (or a pair of yellow and blue stripes) but not their outer edges, however, the entire region can be perceived simultaneously as both red and green (or yellow and blue).

Responsiveness in newborn infants of overweight and normal weight parents

In exploration of the relation between obesity and heightened responsiveness to prominent stimuli, an examination was made of the visual and taste responsiveness of 1–3 day old babies whose parents were both overweight or were both of normal weight. Twelve infants of overweight parentage (OP) and 12 infants of normal weight parentage (NP) were presented with three trials with a pair of red stripes, and with three different concentrations of a glucose solution followed by sterile water. Results indicated differences in visual and taste responsiveness between NP and OP babies. OP babies' average responses to water following glucose were lower than those of NP babies. Presented with two stripes in the visual field, OP babies shifted their gaze significantly more often and with greater magnitude than NP babies did. NP and OP babies did not differ significantly on a variety of physical and developmental measures; estimated gestational age, firthweight, skinfold thickness (SFT), and weight/length2 (BMI) were similar for the two groups. Supplemental analyses of the taste data, classifying babies according to SFT and BMI, however, indicated that while most babies preferred glucose solutions of increasing concentration, “thin” babies did not.

Optical Observation of Domain Motion in Ferroelectric BaTiO3

AbstractMicroscopic observations are made of a BaTiO3 crystal cut in parallel to the ferroelectric axis. Besides nucleating and forward growth of antiparallel domains, sidewards motion of the expanding domains is clearly observed. The fine structure of a nucleating domain is found to consist of a pair of bright stripes in the microscopic view at the point of extinction. The visibility of the antiparallel domains is explained.

Polymorphism in the Spider, Theridion ovatum

REFERENCE has often been made1–3 to the colour varieties of Theridion ovatum. According to Locket and Millidge4, the abdomen may have one of three colour patterns: Clerk's lineatum, abdomen creamy white; Clerk's redimitum, abdomen with a pair of wide longitudinal carmine stripes; Clerk's ovatum, abdomen dorsally covered with carmine. Field observations confirm that these varieties are polymorphic, in accordance with the accepted definition5 for genetic polymorphism.

THREE NEW GOMPHINES

Herewith I offer descriptions of three new species of dragon-flies of the subfamily Gomphinæ of Odonata. Figures of the appendages of all will appear in my forthcoming handbook of the dragon-flies of North America.Gromphus lentulus, n. sp.Colours obscure (due in part to fading of specimen); face obscure yellowish, shining; frons above and occiput and the ridges above the lateral ocelli yellow, the remainder of the vertex brownish. Prothorax brownish, with a double median spot of yellow on the dorsum. Thorax obscure yellowish, with a faint indication of a pair of narrow stripes of brown beside the middorsal carina, and of broader antehumeral and humeral stripes; a brown pale line on the third lateral suture.