Formation Of Depletion Zones Research Articles

Linear Electro-optic Effect in Silicon Nitride Waveguides Enabled by Electric-Field Poling.

Stoichiometric silicon nitride (Si3N4) is one of the most mature integrated photonic platforms for linear and nonlinear optical applications on-chip. However, because it is a centrosymmetric material, second-order nonlinear processes are inherently not available in Si3N4, limiting its use for multiple classical and quantum applications. In this work, we implement thermally assisted electric-field poling, which allows charge carrier separation in the waveguide core, leading to a depletion zone formation and the inscription of a strong electric field reaching 20 V/μm. The latter results in an effective second-order susceptibility (χ(2)) inside the Si3N4 waveguide, making linear electro-optic modulation accessible on the platform for the first time. We develop a numerical model for simulating the poling process inside the waveguide and use it to calculate the diffusion coefficient and the concentration of the charge carriers responsible for the field formation. The charge carrier concentration, as well as the waveguide core size, is found to play a significant role in determining the achievable effective nonlinearity experienced by the optical mode inside the waveguide. Current findings establish a strong groundwork for further advancement of χ(2)-based devices on Si3N4.

Regulating solute partitioning utilized to decorate grain boundary for improving corrosion resistance in a model Al-Cu-Mg alloy

The precise manipulation of grain boundary microstructure, including interfacial solute partition and precipitate distribution, is crucial for regulating the corrosion resistance of age-hardening aluminum alloys. In this study, we explored a novel manipulation pathway, the pulsed electric field (PEC), to regulate solute segregation to grain boundary to form a specific grain boundary structure. The calculated atomic diffusion results reveal that the PEC can stimulate atomic diffusion by decreasing the energy required for diffusion, through which the continuous distribution of grain boundary precipitates and solute depletion zone formation can be inhibited. Hence, the corrosion resistance is significantly improved.

Controlling ionic current through a nanopore by tuning pH: a local equilibrium Monte Carlo study

ABSTRACTThe purpose of this work is to create a model of a nanofluidic transistor which is able to mimic the effects of pH on nanopore conductance. The pH of the electrolyte is an experimentally controllable parameter through which the charge pattern can be tuned: pH affects the ratio of the protonated/deprotonated forms of the functional groups anchored to the surface of the nanopore (for example, amino and carboxyl groups). Thus, the behaviour of the bipolar transistor changes as it becomes ion selective in acidic/basic environments. We relate the surface charge to pH and perform particle simulations (Local Equilibrium Monte Carlo) with different nanopore geometries (cylindrical and double conical). The simulations form a self consistent system with the Nernst–Planck equation with which we compute ionic flux. We discuss the mechanism behind pH-control of ionic current: formation of depletion zones.

Experimental and first principle calculation study on titanium, zirconium and aluminum oxides in promoting ferrite nucleation

Double thermal diffusion bonding experiment, electron probe microstructure analysis and first principle calculation were used to investigate the potency of titanium, zirconium and aluminum oxides in steels in promoting ferrite formation. Oxides studied here include TiO, Ti2O3, Ti3O5 and TiO2 as well as ZrO2 and Al2O3. During thermal diffusion bonding experiment, the specimen was first held at 1200 °C for 10 min and then rapidly cooled to the dual phase region of the matrix steels for isothermal holding, followed by direct quenching to room temperature. The potency and/or efficiency of the oxides in promoting ferrite nucleation was differentiated by the choice of different matrix, the austenization temperature and the isothermal holding temperature within the dual phase region. Mn was found in the interior of all the oxides except TiO with Fe-C-Mn steel as the matrix. Ni was not found in the interior of all the oxides with Fe-C-Ni steel as the matrix. The promoting ferrite nucleation induced by Ti2O3 and Ti3O5 is explained by Mn-depletion zone formation. The promoting ferrite nucleation induced by TiO2 and ZrO2 can be explained by Mn and/or C-depletion zone formation. The promoting ferrite nucleation by Al2O3 can be explained by Mn depletion zone formation and/or lower interfacial energy theory.

Protein Gradients on the Nucleoid Position the Carbon-Fixing Organelles of Cyanobacteria

Carboxysomes are protein-based bacterial organelles that encapsulate a key enzyme of the Calvin-Benson-Bassham cycle. Previous work has implicated a ParA-like protein (hereafter McdA) as important for spatially organizing carboxysomes along the longitudinal axis of the model cyanobacterium Synechococcus elongatus PCC 7942. Yet, how self-organization of McdA emerges and contributes to carboxysome positioning is unknown. Here, we show that a small protein, termed McdB, localizes to carboxysomes through interactions with carboxysome shell proteins to drive emergent oscillatory patterning of McdA on the nucleoid. Our results demonstrate that McdB directly interacts to stimulate McdA ATPase activity, and indicate that carboxysome-dependent McdA depletion zone formation on the nucleoid is required for directed motion of carboxysomes towards increased concentrations of McdA. We propose that McdA and McdB are a new class of self-organizing proteins that follow a Brownian-ratchet mechanism, challenging the cytoskeletal model of organelle transport, for equidistant positioning of carboxysomes in cyanobacteria. These results have broader implications for understanding spatial organization of protein mega-complexes and organelles in bacteria more broadly.

Local piezoelectric effect on single crystal ZnO microbelt transverse I-V characteristics

One-dimensional ZnO microbelts were prepared by chemical vapor deposition on Si substrates with sputtered Pt film. Using Pt-coated atomic force microscope (AFM) tip, the belts’ transverse I-V characteristics were measured under varying applied elastic loads. ZnO microbelt conductivity reduced with load, but gradually increased upon unloading. Transverse electrical conductivity decrease at higher loads is attributed to the depletion zone formation induced by local piezoelectric effect in ZnO single crystal belt with (0001¯) top surface indented by the AFM tip. The observed effect can be utilized in a nanoforce sensor device.

Absence of depletion zone effects for the trapping reaction in complex networks

In the present work we examine in detail the formation of a depletion zone in the trapping reaction in networks, with a single perfect trap. We monitor the particle density rho(r) with respect to the distance r from the trap. We show using Monte Carlo simulations that the depletion zone is absent in regular, Erdos-Renyi (ER), and scale-free (SF) networks. The density profiles show significant differences for these cases. The particles are homogeneously distributed in regular and ER networks with the depletion effect appearing in very sparse ER networks. In SF networks we reveal the important role of the hubs, which due to their high random walk centrality are critical in the trapping reaction. In addition, the degree distribution plays a significant role in the distribution of the particles recovering the depletion zone formation for high gamma values. The mean connectivity of the network is found to play a significant role in both ER and SF networks.

Intergranular corrosion of Ti-stabilized 11 wt% Cr ferritic stainless steel for automotive exhaust systems

Intergranular corrosion (IGC) of type 409L ferritic stainless steel (FSS) was investigated. A free-exposure corrosion and a double loop electrochemical potentiokinetic reactivation (DL-EPR) tests were conducted to examine IGC of the FSS. IGC occurred in the specimens aged at the temperature range of 400–600 °C that has the sensitization nose located around 600 °C. The critical I r/ I a value was determined to be about 0.03 above which IGC occurred. Based on the analysis of the intergranular precipitates by an energy dispersive spectroscopy (EDS) and a transmission electron microscopy (TEM), IGC was induced by the Cr depletion zone formation due to Cr segregation around intergranular TiC.

Numerical Analysis of the Depletion Zone Formation Around a Growing Protein Crystal

It is expected that a protein depletion zone and an impurity depletion zone are formed around a crystal during protein crystal growth if the diffusion field around the crystal is not disturbed. The growth rate of the crystal may be decreased and the impurity uptake may be suppressed to result in highly ordered crystals if these zones are not disturbed. It is well known that a microgravity environment can reduce convective fluid motion, and this is thought to disturb the depletion zones. Therefore, we expect that crystals grown in space can attain better quality than those grown on the ground. In this study, we estimate the depletion zone formation numerically and discuss the results of crystallization in space experiments. In case of alpha-amylase, most of the crystals form a cluster-like morphology on the ground using PEG 8000 as a precipitant. However, in space, we have obtained a single and high-quality crystal grown from the same sample compositions. We have measured the viscosity of the solution, the diffusion coefficient, and the growth rate of protein crystals on the ground. Applying numerical analysis to these values a significant depletion zone was expected to form mainly due to higher values of the viscosity. This might be one of the main reasons for better quality single crystals grown in space, where the depletion zone is thought to remain undisturbed. For protein crystallization experiments, salts are widely used as a precipitant. However, in that case, reduced concentration depletion zone effects can be expected because of a low viscosity. Therefore, if it is possible to increase the viscosity of the protein solution by means of an additive, the depletion zone formation effect would be enhanced to provide a technique that would be especially effective in space.

Experimental study of a ternaryA+2B→Creaction-diffusion system with a propagating reaction front: Scaling exponents

We study experimentally the $A+2B\ensuremath{\rightarrow}C$ reaction-diffusion process with initially separated reagents in a capillary using an inorganic chemical reaction. We measure and compare with theory the dynamic quantities that characterize the kinetic behavior of the system: the global reaction rate $R(t),$ the location of the reaction center ${x}_{f}(t),$ the front's width $w(t),$ and the local production rate ${R(x}_{f},t).$ We demonstrate the nonclassical phenomena of reactant segregation and depletion-zone formation for this reaction-diffusion process. The experimental results are in good agreement with theory and simulation and quite different from the exponents for the elementary binary $A+B\ensuremath{\rightarrow}C$ reaction. The time exponents are 0.27 for the width, -0.48 for the global reaction rate, and -0.75 for the local reaction rate, compared to theoretical values of 0.25, -0.5, and -0.75, respectively.

Experimental study of a crossover from nonclassical to classical chemical kinetics: An elementary and reversible A+B C reaction-diffusion process in a capillary.

We study an elementary and reversible A+B\ensuremath{\leftrightarrows}C reaction-diffusion process with initially separated reagents, in a convectionless capillary, using an inorganic chemical reaction. We show that the dynamics of the system can be described in terms of a crossover between an ``irreversible regime'' and a ``reversible regime.'' We measured the critical exponents in both regimes. In the irreversible regime we demonstrate the nonclassical phenomena of reactant segregation and depletion-zone formation. In the reversible regime we observed the effect of a local equilibrium where the classical prediction is confirmed. The experimental results are in good agreement with values predicted by theory and simulation. \textcopyright{} 1996 The American Physical Society.

Virus and protein crystal growth on earth and in microgravity

Protein and virus crystals commonly grown in the laboratory on earth have also been grown in a microgravity environment on the US Space Shuttle. Two techniques for growth of the crystals were investigated: vapour diffusion and direct liquid-liquid diffusion. Crystals produced in microgravity, although generally isomorphous with earth-grown crystals, frequently show positive changes in habit, size and degree of perfection. X-ray diffusion analyses of crystals grown free from gravity usually show an improvement in the intensity-to-background ratio for all resolution ranges, and in some cases an extension of the resolution of the diffraction patterns to a higher limit. Both findings suggest an overall improvement in the quality of macromolecular crystals grown in space. A possible source of this improvement is the formation of depletion zones around crystals growing in microgravity that remain stable in the absence of convection and thereby allow more self-regulated growth. This in turn may be manifested as a more uniform and general ordering of the molecules in the crystal lattice and/or a reduction in gross crystal imperfections. Some illustrative results obtained in two kinds of macromolecular crystal growth experiments on International Microgravity Laboratory-1 are described.

CONVECTIVE TRANSPORT IN VAPOR CRYSTAL GROWTH AMPULS

Annals of the New York Academy of SciencesVolume 404, Issue 1 p. 276-276 CONVECTIVE TRANSPORT IN VAPOR CRYSTAL GROWTH AMPULS Franz Rosenberger, Franz Rosenberger Departments of Physics and Materials Science University of Utah Salt Lake City, Utah 84112Search for more papers by this authorGerhard H. Schiroky, Gerhard H. Schiroky Departments of Physics and Materials Science University of Utah Salt Lake City, Utah 84112Search for more papers by this author Franz Rosenberger, Franz Rosenberger Departments of Physics and Materials Science University of Utah Salt Lake City, Utah 84112Search for more papers by this authorGerhard H. Schiroky, Gerhard H. Schiroky Departments of Physics and Materials Science University of Utah Salt Lake City, Utah 84112Search for more papers by this author First published: May 1983 https://doi.org/10.1111/j.1749-6632.1983.tb19476.xAboutRelatedInformationPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessClose modalShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume404, Issue1Fourth International Conference on Physicochemical HydrodynamicsMay 1983Pages 276-276 RelatedInformation RecommendedVapor Transport Growth of Organic Solids in Microgravity and Unit GravityMARIA ITTU ZUGRAV, WILLIAM E. CARSWELL, GLEN B. HAULENBEEK, MOHAN SANGHADASA, SUE K. O'BRIEN, BOGDAN C. GHITA, WILLIAM E. GATHINGS, Annals of the New York Academy of SciencesConjugate Problems of Transport Phenomena under Quasi‐steady Microaccelerations in Realistic SpaceflightV. I. Polezhaev, S. A. Nikitin, Annals of the New York Academy of SciencesGrowth and Characterization of High‐quality Protein Crystals for X‐ray CrystallographyAbel Moreno, Fabiano Yokaichiya, Elaine Dimasi, Vivian Stojanoff, Annals of the New York Academy of SciencesNumerical Analysis of the Depletion Zone Formation Around a Growing Protein CrystalHIROAKI TANAKA, KOJI INAKA, SHIGERU SUGIYAMA, SACHIKO TAKAHASHI, SATOSHI SANO, MASARU SATO, SUSUMU YOSHITOMI, Annals of the New York Academy of SciencesDeveloping Quantitative, Multiscale Models for Microgravity Crystal GrowthJEFFREY J. DERBY, YONG-Il KWON, ARUN PANDY, PAUL SONDA, ANDREW YECKEL, THOMAS JUNG, AND GEORG MÜLLER, Annals of the New York Academy of Sciences