Formation Of Doublets Research Articles

Rayleigh scattering of whispering gallery modes of microspheres due to a single dipole scatterer

The interaction of whispering gallery modes (WGM) of optical microresonators with subwavelength imperfections has been studied both experimentally and theoretically. This interaction is responsible for the formation of spectral doublets in place of single resonance peaks, and for degrading of Q-factors of the resonances. Within the currently accepted framework the spectral doublets are explained as a result of degeneracy removal of clockwise and counterclockwise WGMs due to their coupling caused by defect-induced backscattering, while the degrading of the Q-factor is described phenomenologically as an additional contribution to the overall decay rate of WGM due to coupling between WGM and radiative modes. Here we show that the existing understanding of this phenomenon is conceptually wrong and develop an exact theory of WGM interaction with a single defect, which provides a unified treatment for both aspects of this interaction explaining existing experiments and predicting new phenomena.

El español hablado en Cuba : préstamos vigentes, lexicogénesis y variación lingüística

The variety of Spanish spoken in Cuba, which is a Caribbean Spanish dialect, features at the lexical level an abundance of loan words from various etymological origins (indigenisms, afroamericanisms, anglicisms, gallicisms, among others). In the present research we offer an exhaustive sampling of words of this kind and a taxonomy of the phenomena that motivate their integration into the system that has borrowed them. Among such phenomena, which are proof of the morphological and socio-semantic productiveness of these loan words, we have morphological hybridization through derivation, lexicalization, semantic change, and the formation of semantic doublets through the influence of diatopic and diaphasic variation.

Controlled reduction of LaFe xMn yMo zO3/Al2O3 composites to produce highly dispersed and stable Fe0 catalysts: a Mössbauer investigation

In this work, controlled reduction of perovskites supported on Al2O3 was used to prepare thermally stable nanodispersed iron catalysts based on Fe0/La2O3/Al2O3. The perovskites composites LaFe0.90Mn0.08Mo0.02O3(25, 33 and 50 wt (%)) /Al2O3 and LaFe0.90Mn0.1O3(25 wt (%)) /Al2O3 were prepared and characterized by XRD, BET, TPR, SEM and Mössbauer spectroscopy. XRD for unsupported perovskite showed the formation of a single phase perovskite structure. The Mössbauer spectra of the perovskites were fitted with hyperfine field distribution model for the perovskite. Supported perovskites on Al2O3 showed a decrease of the hyperfine field in respect to unsupported perovskite, due to decrease of particle size and dispersion of the Fe3+ specimens on the support. Also showed broaden lines and relaxation effects due to the small particle size. To produce the Fe0 catalyst, the composite perovskite(25%)/Al2O3 was reduced with H2 at 900, 1000 and 1100 °C for 1 hour. XRD data indicated the formation of Fe0 catalyst with particles sizes of ca. 35 nm. The Mössbauer spectrum showed the formation of metallic iron and doublets corresponding to species of octahedric Fe2+ and Fe3+ sites dispersed on Al2O3. These catalysts showed improved stability towards sintering even upon treatment at 1000 and 1100 °C under H2.

Diffraction effects in X-ray diffraction patterns of the equiatomic alloy CuAu preceding the formation of tetragonality-induced doublets during the crystal-lattice rearrangement in the course of low-temperature ordering

A spatial scheme is suggested which makes it possible to explain diffraction effects observed at the incomplete stage of ordering in angular ranges corresponding to a tetragonality-induced splitting of fundamental X-ray diffraction lines (200) and (220) of the parent cubic phase.

Valvular interstitial cell mechanobiology: effects of substrate stiffness

During inflammation, neutrophil capture by vascular endothelial cells is dependent on L-selectin and β2-integrin adhesion receptors. One of us (S.I.S.) previously demonstrated that homotypic neutrophil aggregation is analogous to this process in that it is also mediated by these receptors, thus providing a model for studying the dynamics of neutrophil adhesion. In the present work, we set out to confirm the hypothesis that cell–cell adhesion via selectins serves to increase the lifetimes of neutrophil doublets formed through shear-induced two-body collisions. In turn, this would facilitate the engagement of more stable β2-integrin bonds and thus increase the two-body collision efficiency (fraction of collisions resulting in the formation of nonseparating doublets). To this end, suspensions of unstimulated neutrophils were subjected to a uniform shear field in a transparent counter-rotating cone and plate rheoscope, and the formation of doublets and growth of aggregates recorded using high-speed videomicroscopy. The dependence of neutrophil doublet lifetime and two-body collision-capture efficiency on shear rate, G, from 14 to 220 s−1 was investigated. Bond formation during a two-body collision was indicated by doublets rotating well past the orientation predicted for break-up of doublets of inert spheres. A striking dependence of doublet lifetime on shear rate was observed. At low shear (G = 14 s−1), no collision capture occurred, and doublet lifetimes were no different from those of neutrophils pretreated with a blocking antibody to L-selectin, or in Ca++-depleted EDTA buffers. At G ≥ 66 s−1, doublet lifetimes increased, with increasing G reaching values twice those for the L-selectin-blocked controls. This correlated with capture efficiencies in excess of 20%, and, at G ≥ 110 s−1, led to the rapid formation of large aggregates, and this in the absence of exogenous chemotactic stimuli. Moreover, the aggregates almost completely broke up when the shear rate was reduced below 66 s−1. Partial inhibition of aggregate formation was achieved by blocking β2-integrin receptors with antibody. By direct observation of the shear-induced interactions between neutrophils, these data reveal that steady application of a threshold level of shear rate is sufficient to support homotypic neutrophil aggregation.

Theory of the spatial-harmonic magnetron: an equivalent network approach

The spatial-harmonic magnetron (SHM) is an effective source of millimeter-wave radiation. A theory, based on an equivalent network approach, is proposed for self-consistent modeling of such magnetrons. The theory accounts for multimode interactions, formation of doublets, and transient processes. Simulation results are presented to illustrate main features of both transient and steady-state magnetron behavior. These results are compared with experimental data for an 8-mm wave SHM with cold secondary-emission cathode.

Dynamics of Neutrophil Aggregation in Couette Flow Revealed by Videomicroscopy: Effect of Shear Rate on Two-Body Collision Efficiency and Doublet Lifetime

During inflammation, neutrophil capture by vascular endothelial cells is dependent on L-selectin and β 2-integrin adhesion receptors. One of us (S.I.S.) previously demonstrated that homotypic neutrophil aggregation is analogous to this process in that it is also mediated by these receptors, thus providing a model for studying the dynamics of neutrophil adhesion. In the present work, we set out to confirm the hypothesis that cell–cell adhesion via selectins serves to increase the lifetimes of neutrophil doublets formed through shear-induced two-body collisions. In turn, this would facilitate the engagement of more stable β 2-integrin bonds and thus increase the two-body collision efficiency (fraction of collisions resulting in the formation of nonseparating doublets). To this end, suspensions of unstimulated neutrophils were subjected to a uniform shear field in a transparent counter-rotating cone and plate rheoscope, and the formation of doublets and growth of aggregates recorded using high-speed videomicroscopy. The dependence of neutrophil doublet lifetime and two-body collision-capture efficiency on shear rate, G, from 14 to 220 s −1 was investigated. Bond formation during a two-body collision was indicated by doublets rotating well past the orientation predicted for break-up of doublets of inert spheres. A striking dependence of doublet lifetime on shear rate was observed. At low shear ( G = 14 s −1), no collision capture occurred, and doublet lifetimes were no different from those of neutrophils pretreated with a blocking antibody to L-selectin, or in Ca ++-depleted EDTA buffers. At G ≥ 66 s −1, doublet lifetimes increased, with increasing G reaching values twice those for the L-selectin-blocked controls. This correlated with capture efficiencies in excess of 20%, and, at G ≥ 110 s −1, led to the rapid formation of large aggregates, and this in the absence of exogenous chemotactic stimuli. Moreover, the aggregates almost completely broke up when the shear rate was reduced below 66 s −1. Partial inhibition of aggregate formation was achieved by blocking β 2-integrin receptors with antibody. By direct observation of the shear-induced interactions between neutrophils, these data reveal that steady application of a threshold level of shear rate is sufficient to support homotypic neutrophil aggregation.

Sticking of protein-coated particles in a shear field

The shear-driven formation of particle doublets at a wall, of latex and emulsion systems, has been studied using a colloidal particle scattering apparatus. In this technique, one particle is fixed on the wall while a second, mobile free particle is made to collide with the fixed particle by the application of the shear field. The effects of pH (in the range 5.5–4.8) and ionic strength (in the range 0.01–0.5 mol dm −3) on the efficiency of irreversible sticking (capture) of the mobile particle to the fixed particle have been studied for systems stabilised by adsorbed films of sodium caseinate, pure α s1-casein or pure β-casein. At low ionic strength (≤0.2 mol dm −3), the efficiency of capture increases with decreasing pH and increasing ionic strength in ways that are consistent with decreasing net charge on the protein and increased screening of the electrostatic repulsion between the particles. The increase in capture efficiency also agrees well with a previously observed increase in viscoelasticity of the corresponding concentrated protein-stabilised emulsions. However, a pronounced drop in the capture efficiency was found at higher ionic strength (0.5 mol dm −3). This effect at high ionic strength, combined with qualitative visual assessment of the behaviour of particles during collisions, conforms to the additional role of tangential interparticle forces in determining the sticking behaviour. It seems that, if the adsorbed protein layer becomes sufficiently thick, even if it has a very low net charge, then particle sticking can be prevented. The sticking phenomenon probably depends on entanglement of the adsorbed layers and on the strength of the protein–protein attractive interactions, as well as on the net particle charge.

Evidence of stress transfer and formation of fracture clusters in carbon nanotube-based composites

We report the first observation of the formation of damage doublets in adjacent carbon nanotubes embedded in a polymer matrix. Such damage clusters are comparable to those arising in fiber-reinforced composite materials as a result of the redistribution of stress from a failed fiber to its unfailed adjacent neighbors. This observation may help shed light on fracture nucleation and growth in nanotube-based composites.

Probabilistic Modeling of Shear-Induced Formation and Breakage of Doublets Cross-Linked by Receptor-Ligand Bonds

A model was constructed to describe previously published experiments of shear-induced formation and breakage of doublets of red cells and of latexes cross-linked by receptor-ligand bonds (Tees et al. 1993. Biophys. J. 65:1318–1334; Tees and Goldsmith. 1996. Biophys. J. 71:1102–1114; Kwong et al. 1996. Biophys. J. 71:1115–1122). The model, based on McQuarrie’s master equations (1963. J. Phys. Chem. 38:433–436), provides unifying treatments for three distinctive time periods in the experiments of particles in a Couette flow in which a doublet undergoes 1) formation upon two-body collision between singlets; 2) evolution of bonds at low shear rate; and 3) break-up at high shear rate. Neglecting the applied force at low shear rate, the probability of forming a doublet per collision as well as the evolution of probability distribution of bonds in a preformed doublet were solved analytically and found to be in quite good agreement with measurements. At high shear rate with significant force acting to accelerate bond dissociation, the predictions for break-up of doublets were obtained numerically and compared well with data in both individual and population studies. These comparisons enabled bond kinetic parameters for three types of particles cross-linked by two receptor-ligand systems to be calculated, which agreed well with those computed from Monte Carlo simulations. This work can be extended to analyze kinetics of receptor-ligand binding in cell aggregates, such as those of neutrophils and platelets in the circulation.

Part I: Experimental

Perikinetic coagulation experiments are reported which were performed under 1gand μgconditions during a flight in a sounding rocket, for dispersions of polystyrene, quartz, and amorphous silica particles. Coagulation rates for dispersions of polystyrene, quartz, and amorphous silica are found to increase significantly under μgconditions compared to 1gconditions. Another set of experiments was performed at 1g,2g,4g,and 7g,with different densities of the continuous phase; also a mixture of two different polystyrene latices was used. The most pronounced effect of gravity on coagulation rate is found for dispersions with a small density difference, on going from 1gto 2g.In this regime a significant decrease in coagulation rates is observed. For the latex mixture at pronounced density differences, gravity-induced coagulation was observed; however, the aggregates formed did not have a lasting contact. The rate constant calculated under μgconditions approaches the theoretical value of von Smoluchowski. By means of a video analysis of the perikinetic coagulation process, the formation of doublets was studied. The “interaction time” for two particles was found to be longer for the density-matched dispersion. Doublets of particles are easily disrupted, and at 1g,free convection currents were observed even at small temperature differences in the system.

Micro and nano layered polymers

AbstractThe crazing behavior of coextruded microlayer sheets consisting of alternating layers of polycarbonate (PC) and styreneacrylonitrile copolymer (SAN) was investigated as a function of PC and SAN layer thicknesses. In this study, the total sheet thickness remained essentially constant and the PC and SAN layer thicknesses were changed by varying both the total number of layers from 49 to 1857 and the PC/SAN volume ratio.[1,2] Photographs of the deformation processes were obtained when microspecimens were deformed under an optical microscope. Three different types of crazing behavior were identified: single crazes randomly distributed in the SAN layers, doublets consisting of two aligned crazes in neighboring SAN layers, and craze arrays with many aligned crazes in neighboring SAN layers. The transition from single crazes to doublets was observed when the PC layer thickness was decreased to 6 microns. Craze array development was prevalent in composites with PC layer thickness less than 1.3 microns. It was concluded that SAN layer thickness was not a factor in formation of arrays and doublets; formation of craze doublets and craze arrays was dependent only upon PC layer thickness.

Ultrastructural localization of adhalin in normal murine skeletal myofiber.

The ultrastructural localization of adhalin and its relations to dystrophin, beta-dystroglycan, and beta-spectrin were studied in normal murine skeletal myofibers. The C-terminal peptides of adhalin and beta-dystroglycan were synthesized based on their cDNAs, and the affinity-purified antibodies against these peptides were produced. Single-immunolabeling electron microscopy showed that the adhalin was located just inside the muscle plasma membrane or inside the myofiber a short distance from the plasma membrane. The adhalin signal was also noted at the sarcoplasmic side of plasmalemmal invaginations or at vesicular structures in subsarcolemmal areas. Double-immunogold-labeling electron microscopy disclosed a similar localization of dystrophin, beta-dystroglycan, and beta-spectrin. The close association of adhalin with dystrophin or beta-dystroglycan was demonstrated by formation of doublets by signals of antibodies of adhalin with those of dystrophin or beta-dystroglycan and was confirmed by statistical analyses. This study demonstrated that the location of adhalin is close to that of dystrophin and beta-dystroglycan at the muscle plasma membrane.

Colloidal Stability and Titania Precipitate Morphology: Influence of Short‐Range Repulsions

For a wide range of reagent concentrations, particles formed from the hydrolysis of tetraethyl orthotitanate in aqueous ethanol solutions fall into two morphological types. In the first, the particles are composed of uniform spheres, while in the second, the precipitate consists of agglomerates of discrete particles which have been fused together by further reaction products. To explain this observation, we develop a growth mechanism where colloidal stability is imparted to the growing particles through a combination of electrostatic and short‐range repulsions giving rise to a shallow secondary minimum which develops for certain particle sizes and results in the formation of doublets that can be fused together. If the particle surface potential is of sufficient magnitude, the secondary minimum is no longer accessible by Brownian motion and uniform precipitates result. The effects of particle surface potential and reaction medium ionic strength are discussed.

Crazing phenomena in PC/SAN microlayer composites

AbstractThe crazing behavior of coextruded microlayer sheets consisting of alternating layers of polycarbonate (PC) and styrene–acrylonitrile copolymer (SAN) was investigated as a function of PC and SAN layer thicknesses. In this study, the total sheet thickness remained essentially constant and the PC and SAN layer thicknesses were changed by varying both the total number of layers from 49 to 1857 and the PC/SAN volume ratio. Photographs of the deformation processes were obtained when microspecimens were deformed under an optical microscope. Three different types of crazing behavior were identified: single crazes randomly distributed in the SAN layers, doublets consisting of two aligned crazes in neighboring SAN layers, and craze arrays with many aligned crazes in neighboring SAN layers. The transition from single crazes to doublets was observed when the PC layer thickness was decreased to 6 microns. Craze array development was prevalent in composites with PC layer thickness less than 1.3 microns. It was concluded that SAN layer thickness was not a factor in formation of arrays and doublets; formation of craze doublets and craze arrays was dependent only upon PC layer thickness. © 1994 John Wiley & Sons, Inc.

Mechanisms of interactive crazing in PC/SAN microlayer composites

AbstractMechanisms are proposed for the two types of interactive crazing that have been observed in PC/SAN microlayer composites when the PC layer thickness is on the micron‐size scale. It is demonstrated that when the PC layer is thin enough the deformation zone that forms at a craze tip can interact with the next‐neighboring SAN layer. By measuring the dimensions of the craze tip in scanning electron micrographs, it was found that the craze‐tip opening does not depend on the SAN layer thickness, i.e., the length of the SAN craze. Consequently, the size and shape of the resulting plastic zone in the PC layer are also independent of layer thickness. The zone that forms in the PC layer consists of a colinear plastic zone together with a pair of micro‐shearbands that grow at an angle of about 45°. When the PC layer is less than 6 μm, the elastic stress concentration from the colinear plastic zone increases the probability of crazing in the neighboring SAN layer with the formation of craze doublets that consist of two aligned crazes in neighboring SAN layers. By taking into consideration the Weibull distribution of crazing, a craze doublet fraction comparable to the 30% observed experimentally was predicted with a stress intensification factor in the range of 1.03–1.05. When the PC layer thickness is less than 1.3 μm, the length of the colinear plastic zone is comparable to the PC layer thickness. Formation of a craze at the point of impingement of the plastic zone on the neighboring SAN layer leads to craze arrays with many aligned crazes in neighboring SAN layers. At higher strains, the micro‐shearbands grow through the PC layers and extend into several adjacent SAN and PC layers. This produces a change in deformation mechanism in the SAN layers at the yield instability, from craze opening to shear yielding. © 1994 John Wiley & Sons, Inc.

Array of doublets: A branch of cellular solutions in directional solidification.

In directional solidification of alloys, the interface pattern assumes a cellular structure, with a periodic array of cells, when the velocity is increased beyond the threshold of planar interface instability. A detailed experimental study in the succinonitrile-acetone system has revealed a branch of cellular structure in which the interface pattern consists of a periodic array of coupled cells or doublets. This doublet interface evolves with two characteristic length scales at the advancing front: a small intraspacing between the cells in a doublet, whose selection is sharp, and a larger interspacing corresponding to the distance between cells in adjoining doublets, whose selection is weak. The dynamics of the time-dependent evolution of a doublet interface is investigated by statistical analysis of tip spacings, by using a Fourier transform of the interface shape and through the study of the variation of shape parameters with time. These dynamical studies have confirmed the selection of doublet interface as a stable solution of the cellular pattern formation. A range of stable regime for an array with doublets is determined and the key factor that controls the formation of regular cells or doublets in an array is discussed. When doublets are unstable, time dependency may follow due to a source mechanism at grain boundaries, which induces strong spatiotemporal chaos.

Effects of the fluorescence dye DAPI on microtuble structure in vitro: Formation of novel types of tubulin assembly products

It has been found that the DNA fluorescence dye 4',6-diamidino-2-phenylindole (DAPI) is able to stain also microtubules. However, electron microscopy revealed that DAPI changed microtubule structure and induced the formation of a broad spectrum of polymorphic tubulin assembly products. Upon addition of DAPI to microtubules assembled from 10 to 15 mumol tubulin (molar DAPI/tubulin ratios of 10 to 40) in the presence of microtubule-associated proteins, most of the microtubules were decorated with additional protofilaments usually running parallel to the protofilaments of the microtubule wall (microtubule-protofilament complexes). When DAPI was already present during assembly, curved C- and S-shaped protofilament ribbons and microtubule-ribbon complexes with 6-shaped profiles were the most prominent products, beside microtubules. Additionally, protofilament bundles, some flat sheets, and hoops occurred. Electrophoresis revealed that DAPI lowered the amount of associated proteins, especially of tau-proteins, bound to the assembly products. Nevertheless, DAPI stimulated the assembly, enabled pure tubulin to assemble even at concentrations as low as 10 mumol, and stabilized the assembly products against cold. The microtubule-protofilament complexes, observed for the first time, are interpreted as the result of DAPI-induced protofilament linking as well as of activation of an additional tubulin-tubulin binding site which is possibly identical to that involved in the formation of microtubule doublets.

Further physicochemical characterization of the novel human brain protein h3.

Recently we reported the isolation and partial biochemical characterization of the novel polypeptide h3 from human brain and liver. In this report, the physicochemical characterization is further established by the use of several analytical methods. The following results were obtained: the ultraviolet absorption spectrum is not influenced by pH, and the circular dichroism (CD) spectrum reveals that this protein has no alpha-helices, whereas approximately 25% of the polypeptide chain is found to be folded as a beta-pleated sheet structure. Neither the conformation of h3 as assessed by CD nor the titration kinetics of sulfhydryl groups with Ellman's reagent are affected by the presence of the ions K+, Na+, Ca2+, and Mg2+. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in a beta-mercaptoethanol gradient and Cleveland sequential SDS-PAGE showed that the frequent formation of h3 polymers and doublets, as observed earlier, is almost exclusively due to disulfide bonding.

Maintenance and regulation of cellular handedness in Tetrahymena

The left-handed phenotype of Tetrahymena thermophila (LH) is a global mirror image of its right-handed counterpart (RH). LH cells are 'wound' in the opposite direction from that of RH cells with respect to the placement of all structures that are asymmetrically disposed on the cell circumference. However, the local geometry of ciliary rows, including the asymmetrically placed microtubule bands and other accessory structures, is identical in RH and LH cells. Populations of LH cells grow more slowly than those of RH cells, probably because of nutritional problems due to faulty construction of the cell mouth. LH cells, like RH cells, conjugate in a homopolar configuration, while LH cells mate with RH cells in a heteropolar union which suffices to initiate the conjugal nuclear events but is insufficient to allow survival of progeny. Subclonal analyses indicate that reversion of the LH to the RH form is relatively rare. However, the frequency of reversion is greatly increased by conditions that promote the formation of doublets by fission arrest. An analysis of intermediate doublet forms in such cultures strongly suggests that reversion takes place through a specific pathway, with LH-LH doublets regulating to LH-RH forms that then may give rise to RH singlets. The origin and fate of the LH-RH intermediate forms can be explained by applying a modified polar coordinate model of positional information with the proviso that there is a preferred direction for the intercalation of new positional values.