Diffusion welding. [heat treatment of nickel alloys following single step vacuum welding process

NASA Technical Reports Server (NTRS)

Holko, K. H. (Inventor)

1974-01-01

Dispersion-strengthened nickel alloys are sanded on one side and chemically polished. This is followed by a single-step welding process wherein the polished surfaces are forced into intimate contact at 1,400 F for one hour in a vacuum. Diffusion, recrystallization, and grain growth across the original weld interface are obtained during postheating at 2,150 F for two hours in hydrogen.

Growth mechanisms, polytypism, and real structure of kaolinite microcrystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samotoin, N. D., E-mail: samnik@igem.ru

2008-09-15

The mechanisms of growth of kaolinite microcrystals (0.1-5.0 {mu}m in size) at deposits related to the cluvial weathering crust, as well as to the low-temperature and medium-temperature hydrothermal processes of transformations of minerals in different rocks in Russia, Kazakhstan, Ukraine, Czechia, Vietnam, India, Cuba, and Madagascar, are investigated using transmission electron microscopy and vacuum decoration with gold. It is established that kaolinite microcrystals grow according to two mechanisms: the mechanism of periodic formation of two-dimensional nuclei and the mechanism of spiral growth. The spiral growth of kaolinite microcrystals is dominant and occurs on steps of screw dislocations that differ inmore » sign and magnitude of the Burgers vector along the c axis. The layered growth of kaolinite originates from a widespread source in the form of a step between polar (+ and -) dislocations, i.e., a growth analogue of the Frank-Read dislocation source. The density of growth screw dislocations varies over a wide range and can be as high as {approx}10{sup 9} cm{sup -2}. Layered stepped kaolinite growth pyramids for all mechanisms of growth on the (001) face of kaolinite exhibit the main features of the triclinic 1Tc and real structures of this mineral.« less

Kinetic aspects of chain growth in Fischer-Tropsch synthesis.

PubMed

Filot, Ivo A W; Zijlstra, Bart; Broos, Robin J P; Chen, Wei; Pestman, Robert; Hensen, Emiel J M

2017-04-28

Microkinetics simulations are used to investigate the elementary reaction steps that control chain growth in the Fischer-Tropsch reaction. Chain growth in the FT reaction on stepped Ru surfaces proceeds via coupling of CH and CR surface intermediates. Essential to the growth mechanism are C-H dehydrogenation and C hydrogenation steps, whose kinetic consequences have been examined by formulating two novel kinetic concepts, the degree of chain-growth probability control and the thermodynamic degree of chain-growth probability control. For Ru the CO conversion rate is controlled by the removal of O atoms from the catalytic surface. The temperature of maximum CO conversion rate is higher than the temperature to obtain maximum chain-growth probability. Both maxima are determined by Sabatier behavior, but the steps that control chain-growth probability are different from those that control the overall rate. Below the optimum for obtaining long hydrocarbon chains, the reaction is limited by the high total surface coverage: in the absence of sufficient vacancies the CHCHR → CCHR + H reaction is slowed down. Beyond the optimum in chain-growth probability, CHCR + H → CHCHR and OH + H → H 2 O limit the chain-growth process. The thermodynamic degree of chain-growth probability control emphasizes the critical role of the H and free-site coverage and shows that at high temperature, chain depolymerization contributes to the decreased chain-growth probability. That is to say, during the FT reaction chain growth is much faster than chain depolymerization, which ensures high chain-growth probability. The chain-growth rate is also fast compared to chain-growth termination and the steps that control the overall CO conversion rate, which are O removal steps for Ru.

Ecogeomorphic feedbacks in regrowth of travertine step-pool morphology after dam decommissioning, Fossil Creek, Arizona

NASA Astrophysics Data System (ADS)

Fuller, Brian M.; Sklar, Leonard S.; Compson, Zacchaeus G.; Adams, Kenneth J.; Marks, Jane C.; Wilcox, Andrew C.

2011-03-01

The linkages between fluvial geomorphology and aquatic ecosystems are commonly conceptualized as a one-way causal chain in which geomorphic processes create the physical template for ecological dynamics. In streams with a travertine step-pool morphology, however, biotic processes strongly influence the formation and growth of travertine dams, creating the potential for numerous feedbacks. Here we take advantage of the decommissioning of a hydroelectric project on Fossil Creek, Arizona, where restoration of CaCO 3-rich baseflow has triggered rapid regrowth of travertine dams, to explore the interactions between biotic and abiotic factors in travertine morphodynamics. We consider three conceptual frameworks, where biotic factors independently modulate the rate of physical and chemical processes that produce travertine dams; combine with abiotic factors in a set of feedback loops; and work in opposition to abiotic processes, such that the travertine step-pool morphology reflects a dynamic balance between dominantly-biotic constructive processes and dominantly-abiotic destructive processes. We consider separately three phases of an idealized life cycle of travertine dams: dam formation, growth, and destruction by erosive floods. Dam formation is catalyzed by abiotic factors (e.g. channel constrictions, and bedrock steps) and biotic factors (e.g. woody debris, and emergent vegetation). From measurements of changes over time in travertine thickness on a bedrock step, we find evidence for a positive feedback between flow hydraulics and travertine accrual. Measurements of organic content in travertine samples from this step show that algal growth contributes substantially to travertine accumulation and suggest that growth is most rapid during seasonal algal blooms. To document vertical growth of travertine dams, we embedded 252 magnets into nascent travertine dams, along a 10 km stretch of river. Growth rates are calculated from changes over time in the magnetic field intensity at the dam surface. At each magnet we record a range of hydraulic and travertine composition variables to characterize the dominant mechanism of growth: abiotic precipitation, algal growth, trapping of organic material, or in situ plant growth. We find: (1) rapid growth of travertine dams following flow restoration, averaging more than 2 cm/year; (2) growth rates decline downstream, consistent with loss of dissolved constituents because of upstream travertine deposition, but also parallel to a decline in organic content in dam surface material and a downstream shift in dominant biotic mechanism; (3) biotic mechanisms are associated with faster growth rates; and (4) correlations between hydraulic attributes and growth rates are more consistent with biotic than abiotic controls. We conclude that the strong influence of living organisms on rates of travertine growth, coupled with the beneficial effects of travertine on ecosystem dynamics, demonstrate a positive feedback between biology and geomorphology. During our two-year study period, erosive flood flows occurred causing widespread removal of travertine. The temporal distribution of travertine growth and erosion over the study period is consistent with a bimodal magnitude-frequency relation in which growth dominates except when large, infrequent storms occur. This model may be useful in other systems where biology exerts strong controls on geomorphic processes.

Slow-Injection Growth of Seeded CdSe/CdS Nanorods with Unity Fluorescence Quantum Yield and Complete Shell to Core Energy Transfer.

PubMed

Coropceanu, Igor; Rossinelli, Aurelio; Caram, Justin R; Freyria, Francesca S; Bawendi, Moungi G

2016-03-22

A two-step process has been developed for growing the shell of CdSe/CdS core/shell nanorods. The method combines an established fast-injection-based step to create the initial elongated shell with a second slow-injection growth that allows for a systematic variation of the shell thickness while maintaining a high degree of monodispersity at the batch level and enhancing the uniformity at the single-nanorod level. The second growth step resulted in nanorods exhibiting a fluorescence quantum yield up to 100% as well as effectively complete energy transfer from the shell to the core. This improvement suggests that the second step is associated with a strong suppression of the nonradiative channels operating both before and after the thermalization of the exciton. This hypothesis is supported by the suppression of a defect band, ubiquitous to CdSe-based nanocrystals after the second growth.

The effect of cation:anion ratio in solution on the mechanism of barite growth at constant supersaturation: Role of the desolvation process on the growth kinetics

NASA Astrophysics Data System (ADS)

Kowacz, M.; Putnis, C. V.; Putnis, A.

2007-11-01

The mechanism of barite growth has been investigated in a fluid cell of an Atomic Force Microscope by passing solutions of constant supersaturation ( Ω) but variable ion activity ratio ( r=a/a) over a barite substrate.The observed dependence of step-spreading velocity on solution stoichiometry can be explained by considering non-equivalent attachment frequency factors for the cation and anion. We show that the potential for two-dimensional nucleation changes under a constant thermodynamic driving force due to the kinetics of barium integration into the surface, and that the growth mode changes from preexisting step advancement to island spreading as the cation/anion activity ratio increases. Scanning electron microscopy studies of crystals grown in bulk solutions support our findings that matching the ion ratio in the fluid to that of the crystal lattice does not result in maximum growth and nucleation rates. Significantly more rapid rates correspond to solution stoichiometries where [Ba 2+] is in excess with respect to [ SO42-]. Experiments performed in dilute aqueous solutions of methanol show that even 0.02 molar fraction of organic cosolvent in the growth solution significantly accelerates step growth velocity and nucleation rates (while keeping Ω the same as in the reference solution in water). Our observations suggest that the effect of methanol on barite growth results first of all from reduction of the barrier that prevents the Ba 2+ from reaching the surface and corroborate the hypothesis that desolvation of the cation and of the surface is the rate limiting kinetic process for two-dimensional nucleation and for crystal growth.

Effect of growth pressure on the morphology evolution and doping characteristics in nonpolar a-plane GaN

NASA Astrophysics Data System (ADS)

Song, Keun Man; Kim, Jong Min; Kang, Bong Kyun; Shin, Chan Soo; Ko, Chul Gi; Kong, Bo Hyun; Cho, Hyung Koun; Yoon, Dae Ho; Kim, Hogyoung; Hwang, Sung Min

2012-02-01

Nonpolar a-plane GaN layers grown on r-plane sapphire substrates were examined by using a two-step growth process. The higher initial growth pressure for the nucleation layer resulted in the improved crystalline quality with lower density of both threading dislocations and basal stacking faults. This was attributed to the higher degree of initial roughening and recovery time via a growth mode transition from three-dimensional (3D) to quasi two-dimensional (2D) lateral growth. Using Hall-effect measurements, the overgrown Si doped GaN layers grown with higher initial growth pressure were found to have higher mobility. The scattering mechanism due to the dislocations was dominant especially at low temperature (<200 K) for the lower initial growth pressure, which was insignificant for the higher initial growth pressure. The temperature-dependent Hall-effect measurements for the Mg doped GaN with a higher initial growth pressure yielded the activation energy and the acceptor concentration to be 128 meV and 1.2 × 1019 cm-3, respectively, corresponding to about 3.6% of activation at room temperature. Two-step growth scheme with a higher initial growth pressure is suggested as a potential method to improve the performance of nonpolar a-plane GaN based devices.

Growth and Characterization of Pyrite Thin Films for Photovoltaic Applications

NASA Astrophysics Data System (ADS)

Wertheim, Alex

A series of pyrite thin films were synthesized using a novel sequential evaporation technique to study the effects of substrate temperature on deposition rate and micro-structure of the deposited material. Pyrite was deposited in a monolayer-by-monolayer fashion using sequential evaporation of Fe under high vacuum, followed by sulfidation at high S pressures (typically > 1 mTorr to 1 Torr). Thin films were synthesized using two different growth processes; a one-step process in which a constant growth temperature is maintained throughout growth, and a three-step process in which an initial low temperature seed layer is deposited, followed by a high temperature layer, and then finished with a low temperature capping layer. Analysis methods to analyze the properties of the films included Glancing Angle X-Ray Diffraction (GAXRD), Rutherford Back-scattering Spectroscopy (RBS), Transmission Electron Microscopy (TEM), Secondary Ion Mass Spectroscopy (SIMS), 2-point IV measurements, and Hall effect measurements. Our results show that crystallinity of the pyrite thin film improves and grain size increases with increasing substrate temperature. The sticking coefficient of Fe was found to increase with increasing growth temperature, indicating that the Fe incorporation into the growing film is a thermally activated process.

Supercritical Fluid Atomic Layer Deposition: Base-Catalyzed Deposition of SiO2.

PubMed

Kalan, Roghi E; McCool, Benjamin A; Tripp, Carl P

2016-07-19

An in situ FTIR thin film technique was used to study the sequential atomic layer deposition (ALD) reactions of SiCl4, tetraethyl orthosilicate (TEOS) precursors, and water on nonporous silica powder using supercritical CO2 (sc-CO2) as the solvent. The IR work on nonporous powders was used to identify the reaction sequence for using a sc-CO2-based ALD to tune the pore size of a mesoporous silica. The IR studies showed that only trace adsorption of SiCl4 occurred on the silica, and this was due to the desiccating power of sc-CO2 to remove the adsorbed water from the surface. This was overcome by employing a three-step reaction scheme involving a first step of adsorption of triethylamine (TEA), followed by SiCl4 and then H2O. For TEOS, a three-step reaction sequence using TEA, TEOS, and then water offered no advantage, as the TEOS simply displaced the TEA from the silica surface. A two-step reaction involving the addition of TEOS followed by H2O in a second step did lead to silica film growth. However, higher growth rates were obtained when using a mixture of TEOS/TEA in the first step. The hydrolysis of the adsorbed TEOS was also much slower than that of the adsorbed SiCl4, and this was overcome by using a mixture of water/TEA during the second step. While the three-step process with SiCl4 showed a higher linear growth rate than obtained with two-step process using TEOS/TEA, its use was not practical, as the HCl generated led to corrosion of our sc-CO2 delivery system. However, when applying the two-step ALD reaction using TEOS on an MCM-41 powder, a 0.21 nm decrease in pore diameter was obtained after the first ALD cycle whereas further ALD cycles did not lead to further pore size reduction. This was attributed to the difficulty in removal of the H2O in the pores after the first cycle.

Synchrotron x-ray study of a low roughness and high efficiency K 2 CsSb photocathode during film growth

DOE PAGES

Xie, Junqi; Demarteau, Marcel; Wagner, Robert; ...

2017-04-24

Reduction of roughness to the nm level is critical of achieving the ultimate performance from photocathodes used in high gradient fields. The thrust of this paper is to explore the evolution of roughness during sequential growth, and to show that deposition of multilayer structures consisting of very thin reacted layers results in an nm level smooth photocathode. Synchrotron x-ray methods were applied to study the multi-step growth process of a high efficiency K 2CsSb photocathode. We observed a transition point of the Sb film grown on Si at the film thickness of similar to 40 angstrom with the substrate temperaturemore » at 100 degrees C and the growth rate at 0.1 Å s -1. The final K 2CsSb photocathode exhibits a thickness of around five times that of the total deposited Sb film regardless of how the Sb film was grown. The film surface roughening process occurs first at the step when K diffuses into the crystalline Sb. Furthermore, the photocathode we obtained from the multi-step growth exhibits roughness in an order of magnitude lower than the normal sequential process. X-ray diffraction measurements show that the material goes through two structural changes of the crystalline phase during formation, from crystalline Sb to K 3Sb and finally to K 2CsSb.« less

Synchrotron x-ray study of a low roughness and high efficiency K 2 CsSb photocathode during film growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Junqi; Demarteau, Marcel; Wagner, Robert

Reduction of roughness to the nm level is critical of achieving the ultimate performance from photocathodes used in high gradient fields. The thrust of this paper is to explore the evolution of roughness during sequential growth, and to show that deposition of multilayer structures consisting of very thin reacted layers results in an nm level smooth photocathode. Synchrotron x-ray methods were applied to study the multi-step growth process of a high efficiency K 2CsSb photocathode. We observed a transition point of the Sb film grown on Si at the film thickness of similar to 40 angstrom with the substrate temperaturemore » at 100 degrees C and the growth rate at 0.1 Å s -1. The final K 2CsSb photocathode exhibits a thickness of around five times that of the total deposited Sb film regardless of how the Sb film was grown. The film surface roughening process occurs first at the step when K diffuses into the crystalline Sb. Furthermore, the photocathode we obtained from the multi-step growth exhibits roughness in an order of magnitude lower than the normal sequential process. X-ray diffraction measurements show that the material goes through two structural changes of the crystalline phase during formation, from crystalline Sb to K 3Sb and finally to K 2CsSb.« less

Controlling CH3NH3PbI(3-x)Cl(x) Film Morphology with Two-Step Annealing Method for Efficient Hybrid Perovskite Solar Cells.

PubMed

Liu, Dong; Wu, Lili; Li, Chunxiu; Ren, Shengqiang; Zhang, Jingquan; Li, Wei; Feng, Lianghuan

2015-08-05

The methylammonium lead halide perovskite solar cells have become very attractive because they can be prepared with low-cost solution-processable technology and their power conversion efficiency have been increasing from 3.9% to 20% in recent years. However, the high performance of perovskite photovoltaic devices are dependent on the complicated process to prepare compact perovskite films with large grain size. Herein, a new method is developed to achieve excellent CH3NH3PbI3-xClx film with fine morphology and crystallization based on one step deposition and two-step annealing process. This method include the spin coating deposition of the perovskite films with the precursor solution of PbI2, PbCl2, and CH3NH3I at the molar ratio 1:1:4 in dimethylformamide (DMF) and the post two-step annealing (TSA). The first annealing is achieved by solvent-induced process in DMF to promote migration and interdiffusion of the solvent-assisted precursor ions and molecules and realize large size grain growth. The second annealing is conducted by thermal-induced process to further improve morphology and crystallization of films. The compact perovskite films are successfully prepared with grain size up to 1.1 μm according to SEM observation. The PL decay lifetime, and the optic energy gap for the film with two-step annealing are 460 ns and 1.575 eV, respectively, while they are 307 and 327 ns and 1.577 and 1.582 eV for the films annealed in one-step thermal and one-step solvent process. On the basis of the TSA process, the photovoltaic devices exhibit the best efficiency of 14% under AM 1.5G irradiation (100 mW·cm(-2)).

EFFECT OF PRE-ANNEALING TEMPERATURE ON THE GROWTH OF ALIGNED α-Fe2O3 NANOWIRES VIA A TWO-STEP THERMAL OXIDATION

NASA Astrophysics Data System (ADS)

Rashid, Norhana Mohamed; Kishi, Naoki; Soga, Tetsuo

2016-03-01

Pre-annealing as part of a two-step thermal oxidation process has a significant effect on the growth of hematite (α-Fe2O3) nanowires on Fe foil. High-density aligned nanowires were obtained on iron foils pre-annealed at 300∘C under a dry air flow for 30min. The X-ray diffraction (XRD) patterns indicate that the nanowires are transformed from the small α-Fe2O3 grains and uniquely grow in the (110) direction. The formation of a high-density of small grains by pre-annealing improved the alignment and density of the α-Fe2O3 nanowires.

Platelet-rich plasma differs according to preparation method and human variability.

PubMed

Mazzocca, Augustus D; McCarthy, Mary Beth R; Chowaniec, David M; Cote, Mark P; Romeo, Anthony A; Bradley, James P; Arciero, Robert A; Beitzel, Knut

2012-02-15

Varying concentrations of blood components in platelet-rich plasma preparations may contribute to the variable results seen in recently published clinical studies. The purposes of this investigation were (1) to quantify the level of platelets, growth factors, red blood cells, and white blood cells in so-called one-step (clinically used commercial devices) and two-step separation systems and (2) to determine the influence of three separate blood draws on the resulting components of platelet-rich plasma. Three different platelet-rich plasma (PRP) separation methods (on blood samples from eight subjects with a mean age [and standard deviation] of 31.6 ± 10.9 years) were used: two single-spin processes (PRPLP and PRPHP) and a double-spin process (PRPDS) were evaluated for concentrations of platelets, red and white blood cells, and growth factors. Additionally, the effect of three repetitive blood draws on platelet-rich plasma components was evaluated. The content and concentrations of platelets, white blood cells, and growth factors for each method of separation differed significantly. All separation techniques resulted in a significant increase in platelet concentration compared with native blood. Platelet and white blood-cell concentrations of the PRPHP procedure were significantly higher than platelet and white blood-cell concentrations produced by the so-called single-step PRPLP and the so-called two-step PRPDS procedures, although significant differences between PRPLP and PRPDS were not observed. Comparing the results of the three blood draws with regard to the reliability of platelet number and cell counts, wide variations of intra-individual numbers were observed. Single-step procedures are capable of producing sufficient amounts of platelets for clinical usage. Within the evaluated procedures, platelet numbers and numbers of white blood cells differ significantly. The intra-individual results of platelet-rich plasma separations showed wide variations in platelet and cell numbers as well as levels of growth factors regardless of separation method.

Mesoscopic homogenization of semi-insulating GaAs by two-step post growth annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffmann, B.; Jurisch, M.; Koehler, A.

1996-12-31

Mesoscopic homogenization of the electrical properties of s.i. LEC-GaAs is commonly realized by thermal treatment of the crystals including the steps of dissolution of arsenic precipitates, homogenization of excess As and re-precipitation by creating a controlled supersaturation. Caused by the inhomogeneous distribution of dislocations and the corresponding cellular structure along and across LEC-grown crystals a proper choice of the time-temperature program is necessary to minimize fluctuations of mesoscopic homogeneity. A modified two-step ingot annealing process is demonstrated to ensure the homogeneous distribution of mesoscopic homogeneity.

Miscut dependent surface evolution in the process of N-polar GaN(000 1 bar) growth under N-rich condition

NASA Astrophysics Data System (ADS)

Krzyżewski, Filip; Załuska-Kotur, Magdalena A.; Turski, Henryk; Sawicka, Marta; Skierbiszewski, Czesław

2017-01-01

The evolution of surface morphology during the growth of N-polar (000 1 bar) GaN under N-rich conditions is studied by kinetic Monte Carlo (kMC) simulations for two substrates miscuts 2° and 4°. The results are compared with experimentally observed surface morphologies of (000 1 bar) GaN layers grown by plasma-assisted molecular beam epitaxy. The proposed kMC two-component model of GaN(000 1 bar) surface where both types of atoms, nitrogen and gallium, attach to the surface and diffuse independently shows that at relatively high rates of the step flow (miscut angle < 2 °) the low mobility of gallium adatoms causes surface instabilities and leads to experimentally observed roughening while for low rates of the step flow (miscut 4°), smooth surface can be obtained. In the presence of almost immobile nitrogen atoms under N-rich conditions crystal growth is realized by the process of two-dimensional island nucleation and coalescence. Larger crystal miscut, lower growth rate or higher temperature results in similar effect of the surface smoothening. We show that the surface also smoothens for the growth conditions with very high N-excess. In the presence of large number of nitrogen atoms the mobility of gallium atoms changes locally thus providing easier coalescence of separated island.

Analysis of Dibenzothiophene Desulfurization in a Recombinant Pseudomonas putida Strain▿

PubMed Central

Calzada, Javier; Zamarro, María T.; Alcón, Almudena; Santos, Victoria E.; Díaz, Eduardo; García, José L.; Garcia-Ochoa, Felix

2009-01-01

Biodesulfurization was monitored in a recombinant Pseudomonas putida CECT5279 strain. DszB desulfinase activity reached a sharp maximum at the early exponential phase, but it rapidly decreased at later growth phases. A model two-step resting-cell process combining sequentially P. putida cells from the late and early exponential growth phases was designed to significantly increase biodesulfurization. PMID:19047400

Monotonic entropy growth for a nonlinear model of random exchanges.

PubMed

Apenko, S M

2013-02-01

We present a proof of the monotonic entropy growth for a nonlinear discrete-time model of a random market. This model, based on binary collisions, also may be viewed as a particular case of Ulam's redistribution of energy problem. We represent each step of this dynamics as a combination of two processes. The first one is a linear energy-conserving evolution of the two-particle distribution, for which the entropy growth can be easily verified. The original nonlinear process is actually a result of a specific "coarse graining" of this linear evolution, when after the collision one variable is integrated away. This coarse graining is of the same type as the real space renormalization group transformation and leads to an additional entropy growth. The combination of these two factors produces the required result which is obtained only by means of information theory inequalities.

Monotonic entropy growth for a nonlinear model of random exchanges

NASA Astrophysics Data System (ADS)

Apenko, S. M.

2013-02-01

We present a proof of the monotonic entropy growth for a nonlinear discrete-time model of a random market. This model, based on binary collisions, also may be viewed as a particular case of Ulam's redistribution of energy problem. We represent each step of this dynamics as a combination of two processes. The first one is a linear energy-conserving evolution of the two-particle distribution, for which the entropy growth can be easily verified. The original nonlinear process is actually a result of a specific “coarse graining” of this linear evolution, when after the collision one variable is integrated away. This coarse graining is of the same type as the real space renormalization group transformation and leads to an additional entropy growth. The combination of these two factors produces the required result which is obtained only by means of information theory inequalities.

Step and Kink Dynamics in Inorganic and Protein Crystallization

NASA Technical Reports Server (NTRS)

Chernov, A. A.; Rashkovich, L. N.; Vekilov, P. G.; DeYoreo, J. J.

2004-01-01

Behavior of low-kink-density steps in solution growth and consequences for general understanding of spiral crystal growth processes will be overviewed. Also, influence of turbulence on step bunching and possibility to diminish this bunching will be presented.

Molecular-Scale Structural Controls on Nanoscale Growth Processes: Step-Specific Regulation of Biomineral Morphology

NASA Astrophysics Data System (ADS)

Dove, P. M.; Davis, K. J.; De Yoreo, J. J.; Orme, C. A.

2001-12-01

Deciphering the complex strategies by which organisms produce nanocrystalline materials with exquisite morphologies is central to understanding biomineralizing systems. One control on the morphology of biogenic nanoparticles is the specific interactions of their surfaces with the organic functional groups provided by the organism and the various inorganic species present in the ambient environment. It is now possible to directly probe the microscopic structural controls on crystal morphology by making quantitative measurements of the dynamic processes occurring at the mineral-water interface. These observations can provide crucial information concerning the actual mechanisms of growth that is otherwise unobtainable through macroscopic techniques. Here we use in situ molecular-scale observations of step dynamics and growth hillock morphology to directly resolve roles of principal impurities in regulating calcite surface morphologies. We show that the interactions of certain inorganic as well as organic impurities with the calcite surface are dependent upon the molecular-scale structures of step-edges. These interactions can assume a primary role in directing crystal morphology. In calcite growth experiments containing magnesium, we show that growth hillock structures become modified owing to the preferential inhibition of step motion along directions approximately parallel to the [010]. Compositional analyses have shown that Mg incorporates at different levels into the two types of nonequivalent steps, which meet at the hillock corner parallel to [010]. A simple calculation of the strain caused by this difference indicates that we should expect a significant retardation at this corner, in agreement with the observed development of [010] steps. If the low-energy step-risers produced by these [010] steps is perpendicular to the c-axis as seems likely from crystallographic considerations, this effect provides a plausible mechanism for the elongated calcite crystal habits found in natural environments that contain magnesium. In a separate study, step-specific interactions are also found between chiral aspartate molecules and the calcite surface. The L and D- aspartate enantiomers exhibit structure preferences for the different types of step-risers on the calcite surface. These site-specific interactions result in the transfer of asymmetry from the organic molecule to the crystal surface through the formation of chiral growth hillocks and surface morphologies. These studies yield direct experimental insight into the molecular-scale structural controls on nanocrystal morphology in biomineralizing systems.

Dynamic Scaling and Island Growth Kinetics in Pulsed Laser Deposition of SrTiO 3

DOE PAGES

Eres, Gyula; Tischler, J. Z.; Rouleau, C. M.; ...

2016-11-11

We use real-time diffuse surface x-ray diffraction to probe the evolution of island size distributions and its effects on surface smoothing in pulsed laser deposition (PLD) of SrTiO 3. In this study, we show that the island size evolution obeys dynamic scaling and two distinct regimes of island growth kinetics. Our data show that PLD film growth can persist without roughening despite thermally driven Ostwald ripening, the main mechanism for surface smoothing, being shut down. The absence of roughening is concomitant with decreasing island density, contradicting the prevailing view that increasing island density is the key to surface smoothing inmore » PLD. We also report a previously unobserved crossover from diffusion-limited to attachment-limited island growth that reveals the influence of nonequilibrium atomic level surface transport processes on the growth modes in PLD. We show by direct measurements that attachment-limited island growth is the dominant process in PLD that creates step flowlike behavior or quasistep flow as PLD “self-organizes” local step flow on a length scale consistent with the substrate temperature and PLD parameters.« less

Dynamic Scaling and Island Growth Kinetics in Pulsed Laser Deposition of SrTiO 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eres, Gyula; Tischler, J. Z.; Rouleau, C. M.

We use real-time diffuse surface x-ray diffraction to probe the evolution of island size distributions and its effects on surface smoothing in pulsed laser deposition (PLD) of SrTiO 3. In this study, we show that the island size evolution obeys dynamic scaling and two distinct regimes of island growth kinetics. Our data show that PLD film growth can persist without roughening despite thermally driven Ostwald ripening, the main mechanism for surface smoothing, being shut down. The absence of roughening is concomitant with decreasing island density, contradicting the prevailing view that increasing island density is the key to surface smoothing inmore » PLD. We also report a previously unobserved crossover from diffusion-limited to attachment-limited island growth that reveals the influence of nonequilibrium atomic level surface transport processes on the growth modes in PLD. We show by direct measurements that attachment-limited island growth is the dominant process in PLD that creates step flowlike behavior or quasistep flow as PLD “self-organizes” local step flow on a length scale consistent with the substrate temperature and PLD parameters.« less

Preparation and Optical Properties of CuS Nanofilms by a Facile Two-Step Process

NASA Astrophysics Data System (ADS)

Cui, Zhankui; Zhou, Junqiang; Ge, Suxiang; Zhao, Hongxiao

CuS nanofilms were prepared by a facile two-step process including chemical bath deposition of Cu nanofilms first and the subsequent thermal sulfuration step. The composition and structure of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Raman spectroscopy. The optical properties of CuS nanofilms were determined by Ultraviolet-visible (UV-Vis) technique. The results show that the nanofilms composed by Cu spherical nanoparticles were completely transformed to the nanofilms composed by CuS nanosheets when the sulfuration temperature was 350∘C. The light absorption edges of CuS nanofilms exhibit red shift when sulfuration occurred at lower temperature. A plausible growth mechanism related with gas phase reaction for formation of CuS nanofilms was also proposed.

Polarized Growth in the Absence of F-Actin in Saccharomyces cerevisiae Exiting Quiescence

PubMed Central

Sahin, Annelise; Daignan-Fornier, Bertrand; Sagot, Isabelle

2008-01-01

Background Polarity establishment and maintenance are crucial for morphogenesis and development. In budding yeast, these two intricate processes involve the superposition of regulatory loops between polarity landmarks, RHO GTPases, actin-mediated vesicles transport and endocytosis. Deciphering the chronology and the significance of each molecular step of polarized growth is therefore very challenging. Principal Findings We have taken advantage of the fact that yeast quiescent cells display actin bodies, a non polarized actin structure, to evaluate the role of F-actin in bud emergence. Here we show that upon exit from quiescence, actin cables are not required for the first steps of polarized growth. We further show that polarized growth can occur in the absence of actin patch-mediated endocytosis. We finally establish, using latrunculin-A, that the first steps of polarized growth do not require any F-actin containing structures. Yet, these structures are required for the formation of a bona fide daughter cell and cell cycle completion. We propose that upon exit from quiescence in the absence of F-actin, secretory vesicles randomly reach the plasma membrane but preferentially dock and fuse where polarity cues are localized, this being sufficient to trigger polarized growth. PMID:18596916

One-pot growth of two-dimensional lateral heterostructures via sequential edge-epitaxy

NASA Astrophysics Data System (ADS)

Sahoo, Prasana K.; Memaran, Shahriar; Xin, Yan; Balicas, Luis; Gutiérrez, Humberto R.

2018-01-01

Two-dimensional heterojunctions of transition-metal dichalcogenides have great potential for application in low-power, high-performance and flexible electro-optical devices, such as tunnelling transistors, light-emitting diodes, photodetectors and photovoltaic cells. Although complex heterostructures have been fabricated via the van der Waals stacking of different two-dimensional materials, the in situ fabrication of high-quality lateral heterostructures with multiple junctions remains a challenge. Transition-metal-dichalcogenide lateral heterostructures have been synthesized via single-step, two-step or multi-step growth processes. However, these methods lack the flexibility to control, in situ, the growth of individual domains. In situ synthesis of multi-junction lateral heterostructures does not require multiple exchanges of sources or reactors, a limitation in previous approaches as it exposes the edges to ambient contamination, compromises the homogeneity of domain size in periodic structures, and results in long processing times. Here we report a one-pot synthetic approach, using a single heterogeneous solid source, for the continuous fabrication of lateral multi-junction heterostructures consisting of monolayers of transition-metal dichalcogenides. The sequential formation of heterojunctions is achieved solely by changing the composition of the reactive gas environment in the presence of water vapour. This enables selective control of the water-induced oxidation and volatilization of each transition-metal precursor, as well as its nucleation on the substrate, leading to sequential edge-epitaxy of distinct transition-metal dichalcogenides. Photoluminescence maps confirm the sequential spatial modulation of the bandgap, and atomic-resolution images reveal defect-free lateral connectivity between the different transition-metal-dichalcogenide domains within a single crystal structure. Electrical transport measurements revealed diode-like responses across the junctions. Our new approach offers greater flexibility and control than previous methods for continuous growth of transition-metal-dichalcogenide-based multi-junction lateral heterostructures. These findings could be extended to other families of two-dimensional materials, and establish a foundation for the development of complex and atomically thin in-plane superlattices, devices and integrated circuits.

[Influence on microstructure of dental zirconia ceramics prepared by two-step sintering].

PubMed

Jian, Chao; Li, Ning; Wu, Zhikai; Teng, Jing; Yan, Jiazhen

2013-10-01

To investigate the microstructure of dental zirconia ceramics prepared by two-step sintering. Nanostructured zirconia powder was dry compacted, cold isostatic pressed, and pre-sintered. The pre-sintered discs were cut processed into samples. Conventional sintering, single-step sintering, and two-step sintering were carried out, and density and grain size of the samples were measured. Afterward, T1 and/or T2 of two-step sintering ranges were measured. Effects on microstructure of different routes, which consisted of two-step sintering and conventional sintering were discussed. The influence of T1 and/or T2 on density and grain size were analyzed as well. The range of T1 was between 1450 degrees C and 1550 degrees C, and the range of T2 was between 1250 degrees C and 1350 degrees C. Compared with conventional sintering, finer microstructure of higher density and smaller grain could be obtained by two-step sintering. Grain growth was dependent on T1, whereas density was not much related with T1. However, density was dependent on T2, and grain size was minimally influenced. Two-step sintering could ensure a sintering body with high density and small grain, which is good for optimizing the microstructure of dental zirconia ceramics.

Effect of selenization time on the structural and morphological properties of Cu(In,Ga)Se2 thin films absorber layers using two step growth process

NASA Astrophysics Data System (ADS)

Korir, Peter C.; Dejene, Francis B.

2018-04-01

In this work two step growth process was used to prepare Cu(In, Ga)Se2 thin film for solar cell applications. The first step involves deposition of Cu-In-Ga precursor films followed by the selenization process under vacuum using elemental selenium vapor to form Cu(In,Ga)Se2 film. The growth process was done at a fixed temperature of 515 °C for 45, 60 and 90 min to control film thickness and gallium incorporation into the absorber layer film. The X-ray diffraction (XRD) pattern confirms single-phase Cu(In,Ga)Se2 film for all the three samples and no secondary phases were observed. A shift in the diffraction peaks to higher 2θ (2 theta) values is observed for the thin films compared to that of pure CuInSe2. The surface morphology of the resulting film grown for 60 min was characterized by the presence of uniform large grain size particles, which are typical for device quality material. Photoluminescence spectra show the shifting of emission peaks to higher energies for longer duration of selenization attributed to the incorporation of more gallium into the CuInSe2 crystal structure. Electron probe microanalysis (EPMA) revealed a uniform distribution of the elements through the surface of the film. The elemental ratio of Cu/(In + Ga) and Se/Cu + In + Ga strongly depends on the selenization time. The Cu/In + Ga ratio for the 60 min film is 0.88 which is in the range of the values (0.75-0.98) for best solar cell device performances.

Persistent Step-Flow Growth of Strained Films on Vicinal Substrates

NASA Astrophysics Data System (ADS)

Hong, Wei; Lee, Ho Nyung; Yoon, Mina; Christen, Hans M.; Lowndes, Douglas H.; Suo, Zhigang; Zhang, Zhenyu

2005-08-01

We propose a model of persistent step flow, emphasizing dominant kinetic processes and strain effects. Within this model, we construct a morphological phase diagram, delineating a regime of step flow from regimes of step bunching and island formation. In particular, we predict the existence of concurrent step bunching and island formation, a new growth mode that competes with step flow for phase space, and show that the deposition flux and temperature must be chosen within a window in order to achieve persistent step flow. The model rationalizes the diverse growth modes observed in pulsed laser deposition of SrRuO3 on SrTiO3.

Effect of Two-Step Metal Organic Chemical Vapor Deposition Growth on Quality, Diameter and Density of InAs Nanowires on Si (111) Substrate

NASA Astrophysics Data System (ADS)

Yu, Hung Wei; Anandan, Deepak; Hsu, Ching Yi; Hung, Yu Chih; Su, Chun Jung; Wu, Chien Ting; Kakkerla, Ramesh Kumar; Ha, Minh Thien Huu; Huynh, Sa Hoang; Tu, Yung Yi; Chang, Edward Yi

2018-02-01

High-density (˜ 80/um2) vertical InAs nanowires (NWs) with small diameters (˜ 28 nm) were grown on bare Si (111) substrates by means of two-step metal organic chemical vapor deposition. There are two critical factors in the growth process: (1) a critical nucleation temperature for a specific In molar fraction (approximately 1.69 × 10-5 atm) is the key factor to reduce the size of the nuclei and hence the diameter of the InAs NWs, and (2) a critical V/III ratio during the 2nd step growth will greatly increase the density of the InAs NWs (from 45 μm-2 to 80 μm-2) and at the same time keep the diameter small. The high-resolution transmission electron microscopy and selected area diffraction patterns of InAs NWs grown on Si exhibit a Wurtzite structure and no stacking faults. The observed longitudinal optic peaks in the Raman spectra were explained in terms of the small surface charge region width due to the small NW diameter and the increase of the free electron concentration, which was consistent with the TCAD program simulation of small diameter (< 40 nm) InAs NWs.

Sol-gel preparation of hydrophobic silica antireflective coatings with low refractive index by base/acid two-step catalysis.

PubMed

Cai, Shuang; Zhang, Yulu; Zhang, Hongli; Yan, Hongwei; Lv, Haibing; Jiang, Bo

2014-07-23

Hydrophobic antireflective coatings with a low refractive index were prepared via a base/acid-catalyzed two-step sol-gel process using tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) as precursors, respectively. The base-catalyzed hydrolysis of TEOS leads to the formation of a sol with spherical silica particles in the first step. In the second step, the acid-catalyzed MTES hydrolysis and condensation occur at the surface of the initial base-catalyzed spherical silica particles, which enlarge the silica particle size from 12.9 to 35.0 nm. By a dip-coating process, this hybrid sol gives an antireflective coating with a refractive index of about 1.15. Moreover, the water contact angles of the resulted coatings increase from 22.4 to 108.7° with the increases of MTES content, which affords the coatings an excellent hydrophobicity. A "core-shell" particle growth mechanism of the hybrid sol was proposed and the relationship between the microstructure of silica sols and the properties of AR coatings was investigated.

Fundamental Studies on High Temperature Deformation, Recrystallization, and Grain Growth of Two-Phase Materials.

DTIC Science & Technology

1987-02-18

17 ml) Benzalkonium Chloride (50%) 4 35 ml Ethanol The Ti-V alloys were etched with the following ethant for about 10 sec. 4% HNO 3 2% HF Bal. H 0 2...that in the last *step all the alloys were processed in the ax+ 6 field from 973 0K L 0 (700 C). The amount of work given in this step (60% reduction in...interfaces (29). The interfaces move by random jumping of atoms from grain to grain, the driving force for the process being the reduction of free

STIR: Tailored Interfaces for High Strength Composites Across Strain Rates

DTIC Science & Technology

2013-09-02

following by the nanowire growth . For the seeding process, the fibers were dipped into a colloidal solution of ZnO nanoparticles (2nm diameter) that was...to the fabric prior to nanowire growth . The synthesis of ZnO nanowire on Kevlar fabric surface was conducted in two steps; initial seeding and...Patterson, Mohammad H. Malakooti, Henry A. Sodano. Modification of Pullout Behavior of Kevlar Fabric by Zinc Oxide Nanowire Reinforcement, Proceedings of

Conversion treatment of thin titanium layer deposited on carbon steel

NASA Astrophysics Data System (ADS)

Benarioua, Younes; Wendler, Bogdan; Chicot, Didier

2018-05-01

The present study has been conducted in order to obtain titanium carbide layer using a conversion treatment consisting of two main steps. In the first step a thin pure titanium layer was deposited on 120C4 carbon steel by PVD. In the second step, the carbon atoms from the substrate diffuse to the titanium coating due to a vacuum annealing treatment and the Ti coating transforms into titanium carbide. Depending on the annealing temperature a partial or complete conversion into TiC is obtained. The hardness of the layer can be expected to differ depending on the processing temperatures. By a systematic study of the hardness as a function of the applied load, we confirm the process of growth of the layer.

Controllable 3D architectures of aligned carbon nanotube arrays by multi-step processes

NASA Astrophysics Data System (ADS)

Huang, Shaoming

2003-06-01

An effective way to fabricate large area three-dimensional (3D) aligned CNTs pattern based on pyrolysis of iron(II) phthalocyanine (FePc) by two-step processes is reported. The controllable generation of different lengths and selective growth of the aligned CNT arrays on metal-patterned (e.g., Ag and Au) substrate are the bases for generating such 3D aligned CNTs architectures. By controlling experimental conditions 3D aligned CNT arrays with different lengths/densities and morphologies/structures as well as multi-layered architectures can be fabricated in large scale by multi-step pyrolysis of FePc. These 3D architectures could have interesting properties and be applied for developing novel nanotube-based devices.

Atomistics of vapour–liquid–solid nanowire growth

PubMed Central

Wang, Hailong; Zepeda-Ruiz, Luis A.; Gilmer, George H.; Upmanyu, Moneesh

2013-01-01

Vapour–liquid–solid route and its variants are routinely used for scalable synthesis of semiconducting nanowires, yet the fundamental growth processes remain unknown. Here we employ atomic-scale computations based on model potentials to study the stability and growth of gold-catalysed silicon nanowires. Equilibrium studies uncover segregation at the solid-like surface of the catalyst particle, a liquid AuSi droplet, and a silicon-rich droplet–nanowire interface enveloped by heterogeneous truncating facets. Supersaturation of the droplets leads to rapid one-dimensional growth on the truncating facets and much slower nucleation-controlled two-dimensional growth on the main facet. Surface diffusion is suppressed and the excess Si flux occurs through the droplet bulk which, together with the Si-rich interface and contact line, lowers the nucleation barrier on the main facet. The ensuing step flow is modified by Au diffusion away from the step edges. Our study highlights key interfacial characteristics for morphological and compositional control of semiconducting nanowire arrays. PMID:23752586

Determining the Molecular Growth Mechanisms of Protein Crystal faces by Atomic Force Microscopy

NASA Technical Reports Server (NTRS)

Li, Huayu; Nadarajah, Arunan; Pusey, Marc L.

1998-01-01

A high resolution atomic force microscopy (AFM) study had shown that the molecular packing on the tetragonal lysozyme (110) face corresponded to only one of two possible packing arrangements, suggesting that growth layers on this face were of bimolecular height (Li et al., 1998). Theoretical analyses of the packing had also indicated that growth of this face should proceed by the addition of growth units of at least tetramer size corresponding to the 43 helices in the crystal. In this study an AFM linescan technique was devised to measure the dimensions of individual growth units on protein crystal faces. The growth process of tetragonal lysozyme crystals was slowed down by employing very low supersaturations. As a result images of individual growth events on the (110) face were observed, shown by jump discontinuities in the growth step in the linescan images. The growth unit dimension in the scanned direction was obtained by suitably averaging these images. A large number of scans in two directions on the (110) face were performed and the distribution of lysozyme aggregate sizes were obtained. A variety of growth units, all of which were 43 helical lysozyme aggregates, were shown to participate in the growth process with a 43 tetramer being the minimum observed size. This technique represents a new application for AFM allowing time resolved studies of molecular process to be carried out.

In Vitro Characterization of the Two-Stage Non-Classical Reassembly Pathway of S-Layers

PubMed Central

Breitwieser, Andreas; Iturri, Jagoba; Toca-Herrera, Jose-Luis; Sleytr, Uwe B.; Pum, Dietmar

2017-01-01

The recombinant bacterial surface layer (S-layer) protein rSbpA of Lysinibacillus sphaericus CCM 2177 is an ideal model system to study non-classical nucleation and growth of protein crystals at surfaces since the recrystallization process may be separated into two distinct steps: (i) adsorption of S-layer protein monomers on silicon surfaces is completed within 5 min and the amount of bound S-layer protein sufficient for the subsequent formation of a closed crystalline monolayer; (ii) the recrystallization process is triggered—after washing away the unbound S-layer protein—by the addition of a CaCl2 containing buffer solution, and completed after approximately 2 h. The entire self-assembly process including the formation of amorphous clusters, the subsequent transformation into crystalline monomolecular arrays, and finally crystal growth into extended lattices was investigated by quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM). Moreover, contact angle measurements showed that the surface properties of S-layers change from hydrophilic to hydrophobic as the crystallization proceeds. This two-step approach is new in basic and application driven S-layer research and, most likely, will have advantages for functionalizing surfaces (e.g., by spray-coating) with tailor-made biological sensing layers. PMID:28216572

Methods for growth of relatively large step-free SiC crystal surfaces

NASA Technical Reports Server (NTRS)

Neudeck, Philip G. (Inventor); Powell, J. Anthony (Inventor)

2002-01-01

A method for growing arrays of large-area device-size films of step-free (i.e., atomically flat) SiC surfaces for semiconductor electronic device applications is disclosed. This method utilizes a lateral growth process that better overcomes the effect of extended defects in the seed crystal substrate that limited the obtainable step-free area achievable by prior art processes. The step-free SiC surface is particularly suited for the heteroepitaxial growth of 3C (cubic) SiC, AlN, and GaN films used for the fabrication of both surface-sensitive devices (i.e., surface channel field effect transistors such as HEMT's and MOSFET's) as well as high-electric field devices (pn diodes and other solid-state power switching devices) that are sensitive to extended crystal defects.

One-step aluminium-assisted crystallization of Ge epitaxy on Si by magnetron sputtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Ziheng, E-mail: ziheng.liu@unsw.edu.au; Hao, Xiaojing; Ho-Baillie, Anita

In this work, one-step aluminium-assisted crystallization of Ge on Si is achieved via magnetron sputtering by applying an in-situ low temperature (50 °C to 150 °C) heat treatment in between Al and Ge depositions. The effect of heat treatment on film properties and the growth mechanism of Ge epitaxy on Si are studied via X-ray diffraction, Raman and transmission electron microscopy analyses. Compared with the conventional two-step process, the one-step aluminium-assisted crystallization requires much lower thermal budget and results in pure Ge epitaxial layer, which may be suitable for use as a virtual substrate for the fabrication of III-V solar cells.

Unsteady Crystal Growth Due to Step-Bunch Cascading

NASA Technical Reports Server (NTRS)

Vekilov, Peter G.; Lin, Hong; Rosenberger, Franz

1997-01-01

Based on our experimental findings of growth rate fluctuations during the crystallization of the protein lysozym, we have developed a numerical model that combines diffusion in the bulk of a solution with diffusive transport to microscopic growth steps that propagate on a finite crystal facet. Nonlinearities in layer growth kinetics arising from step interaction by bulk and surface diffusion, and from step generation by surface nucleation, are taken into account. On evaluation of the model with properties characteristic for the solute transport, and the generation and propagation of steps in the lysozyme system, growth rate fluctuations of the same magnitude and characteristic time, as in the experiments, are obtained. The fluctuation time scale is large compared to that of step generation. Variations of the governing parameters of the model reveal that both the nonlinearity in step kinetics and mixed transport-kinetics control of the crystallization process are necessary conditions for the fluctuations. On a microscopic scale, the fluctuations are associated with a morphological instability of the vicinal face, in which a step bunch triggers a cascade of new step bunches through the microscopic interfacial supersaturation distribution.

Growth of carbon nanofibers using resol-type phenolic resin and cobalt(II) catalyst.

PubMed

Kim, Taeyun; Mees, Karina; Park, Ho-Seon; Willert-Porada, Monika; Lee, Chang-Seop

2013-11-01

This study investigated carbon nanofibers (CNFs) grown on reticulated vitreous carbon (RVC) foam through catalytic deposition of ethylene. Before growing the CNFs, Co(II) on the RVC foam was expected to act as a catalyst by deposition. The preparation of the CNFs was a two-step process. The first step was preparing the RVC from polyurethane (PU) foam. Changes in weight over time were evaluated using two kinds of resol. The change in the mass and state of the sample with the change in temperature was studied during the carbonization process. The second step was to prepare the CNFs. An OH group was attached by the oxidation of the RVC foam. A change in the shape and mass of the sample was observed due to a change in nitric acid concentration and oxidation time. Then, cobalt was deposited to grow CNFs on the RVC foam. Hydrolysis helped to deposit the Co(ll) on the RVC foam. The appropriate time and temperature were investigated for the reduction process. In the last step, CNFs were prepared by the introducing ethylene gas. The resulting samples were analyzed using scanning electron microscopy, energy dispersive spectroscopy, N2-sorption, and X-ray photoelectron spectroscopy.

Viral capsomere structure, surface processes and growth kinetics in the crystallization of macromolecular crystals visualized by in situ atomic force microscopy

NASA Astrophysics Data System (ADS)

Malkin, A. J.; Kuznetsov, Yu. G.; McPherson, A.

2001-11-01

In situ atomic force microscopy (AFM) was used to investigate surface evolution during the growth of single crystals of turnip yellow mosaic virus (TYMV), cucumber mosaic virus (CMV) and glucose isomerase. Growth of these crystals proceeded by two-dimensional (2D) nucleation. For glucose isomerase, from supersaturation dependencies of tangential step rates and critical step length, the kinetic coefficients of the steps and the surface free energy of the step edge were calculated for different crystallographic directions. The molecular structure of the step edges, the adsorption of individual virus particles and their aggregates, and the initial stages of formation of 2D nuclei on the surfaces of TYMV and CMV crystals were recorded. The surfaces of individual TYMV virions within crystals were visualized, and hexameric and pentameric capsomers of the T=3 capsids were clearly resolved. This, so far as we are aware, is the first direct visualization of the capsomere structure of a virus by AFM. In the course of recording the in situ development of the TYMV crystals, a profound restructuring of the surface arrangement was observed. This transformation was highly cooperative in nature, but the transitions were unambiguous and readily explicable in terms of an organized loss of classes of virus particles from specific lattice positions.

Growth mechanism changes in pseudo-dewetted monolayer poly(ethylene oxide) crystallization

NASA Astrophysics Data System (ADS)

Zhu, Dun-Shen; Chen, Er-Qiang; Shi, An-Chang; Cheng, Stephen

2006-03-01

Crystal growth mechanism changes have been observed in pseudo-dewetted monolayers of low molecular weight (LMW) (PEO) on freshly cleaved hydrophilic mica surfaces [HPEO(4250) which have -OH groups at both ends and MHPEO(4700) which has one -OH and one -OCH3 as end groups]. X-ray scattering reflectivity measurements show a wetted monolayer of molten PEO with a thickness of ˜ 4.5 nm on the mica surface. Non-adsorbed PEO droplets sit on top of the wetted monolayer. A two-step process for PEO single crystal growth under isothermal conditions was identified utilizing in-situ atomic force microscopy at different crystallization temperatures (Tx). In the first step, the crystal grows within the droplet which supplies the molten PEO that participates in the crystal formation. In this second-step, the wetted monolayer at the growth front is depleted by about 1.5 - 2.5 nm. The growing crystal lateral sizes obey a power law of t^α (t: time). At a high Tx of 63 C for MHPEO(4700), the growth behavior obeys r t (α = 1). While in the case of HPEO(4250), its growth behavior follows r t^0.5 (α = 0.5) in the whole Tx range. With decreasing Tx, the growth of MHPEO(4700) falls into a scaling law of r t^α (0.5 < α < 1).

Mushroom-free selective epitaxial growth of Si, SiGe and SiGe:B raised sources and drains

NASA Astrophysics Data System (ADS)

Hartmann, J. M.; Benevent, V.; Barnes, J. P.; Veillerot, M.; Lafond, D.; Damlencourt, J. F.; Morvan, S.; Prévitali, B.; Andrieu, F.; Loubet, N.; Dutartre, D.

2013-05-01

We have evaluated various Cyclic Selective Epitaxial Growth/Etch (CSEGE) processes in order to grow "mushroom-free" Si and SiGe:B Raised Sources and Drains (RSDs) on each side of ultra-short gate length Extra-Thin Silicon-On-Insulator (ET-SOI) transistors. The 750 °C, 20 Torr Si CSEGE process we have developed (5 chlorinated growth steps with four HCl etch steps in-between) yielded excellent crystalline quality, typically 18 nm thick Si RSDs. Growth was conformal along the Si3N4 sidewall spacers, without any poly-Si mushrooms on top of unprotected gates. We have then evaluated on blanket 300 mm Si(001) wafers the feasibility of a 650 °C, 20 Torr SiGe:B CSEGE process (5 chlorinated growth steps with four HCl etch steps in-between, as for Si). As expected, the deposited thickness decreased as the total HCl etch time increased. This came hands in hands with unforeseen (i) decrease of the mean Ge concentration (from 30% down to 26%) and (ii) increase of the substitutional B concentration (from 2 × 1020 cm-3 up to 3 × 1020 cm-3). They were due to fluctuations of the Ge concentration and of the atomic B concentration [B] in such layers (drop of the Ge% and increase of [B] at etch step locations). Such blanket layers were a bit rougher than layers grown using a single epitaxy step, but nevertheless of excellent crystalline quality. Transposition of our CSEGE process on patterned ET-SOI wafers did not yield the expected results. HCl etch steps indeed helped in partly or totally removing the poly-SiGe:B mushrooms on top of the gates. This was however at the expense of the crystalline quality and 2D nature of the ˜45 nm thick Si0.7Ge0.3:B recessed sources and drains selectively grown on each side of the imperfectly protected poly-Si gates. The only solution we have so far identified that yields a lesser amount of mushrooms while preserving the quality of the S/D is to increase the HCl flow during growth steps.

Numerical Simulation of Nanostructure Growth

NASA Technical Reports Server (NTRS)

Hwang, Helen H.; Bose, Deepak; Govindan, T. R.; Meyyappan, M.

2004-01-01

Nanoscale structures, such as nanowires and carbon nanotubes (CNTs), are often grown in gaseous or plasma environments. Successful growth of these structures is defined by achieving a specified crystallinity or chirality, size or diameter, alignment, etc., which in turn depend on gas mixture ratios. pressure, flow rate, substrate temperature, and other operating conditions. To date, there has not been a rigorous growth model that addresses the specific concerns of crystalline nanowire growth, while demonstrating the correct trends of the processing conditions on growth rates. Most crystal growth models are based on the Burton, Cabrera, and Frank (BCF) method, where adatoms are incorporated into a growing crystal at surface steps or spirals. When the supersaturation of the vapor is high, islands nucleate to form steps, and these steps subsequently spread (grow). The overall bulk growth rate is determined by solving for the evolving motion of the steps. Our approach is to use a phase field model to simulate the growth of finite sized nanowire crystals, linking the free energy equation with the diffusion equation of the adatoms. The phase field method solves for an order parameter that defines the evolving steps in a concentration field. This eliminates the need for explicit front tracking/location, or complicated shadowing routines, both of which can be computationally expensive, particularly in higher dimensions. We will present results demonstrating the effect of process conditions, such as substrate temperature, vapor supersaturation, etc. on the evolving morphologies and overall growth rates of the nanostructures.

Introduction to Polymer Chemistry.

ERIC Educational Resources Information Center

Harris, Frank W.

1981-01-01

Reviews the physical and chemical properties of polymers and the two major methods of polymer synthesis: addition (chain, chain-growth, or chain-reaction), and condensation (step-growth or step-reaction) polymerization. (JN)

Reflection high energy electron diffraction observation of surface mass transport at the two- to three-dimensional growth transition of InAs on GaAs(001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patella, F.; Arciprete, F.; Fanfoni, M.

2005-12-19

We have followed by reflection high-energy electron diffraction the nucleation of InAs quantum dots on GaAs(001), grown by molecular-beam epitaxy with growth interruptions. Surface mass transport gives rise, at the critical InAs thickness, to a huge nucleation of three-dimensional islands within 0.2 monolayers (ML). Such surface mass diffusion has been evidenced by observing the transition of the reflection high-energy electron diffraction pattern from two- to three-dimensional during the growth interruption after the deposition of 1.59 ML of InAs. It is suggested that the process is driven by the As{sub 2} adsorption-desorption process and by the lowering of the In bindingmore » energy due to compressive strain. The last condition is met first in the region surrounding dots at step edges where nucleation predominantly occurs.« less

Synthesis of Novel Double-Layer Nanostructures of SiC–WOxby a Two Step Thermal Evaporation Process

PubMed Central

2009-01-01

A novel double-layer nanostructure of silicon carbide and tungsten oxide is synthesized by a two-step thermal evaporation process using NiO as the catalyst. First, SiC nanowires are grown on Si substrate and then high density W18O49nanorods are grown on these SiC nanowires to form a double-layer nanostructure. XRD and TEM analysis revealed that the synthesized nanostructures are well crystalline. The growth of W18O49nanorods on SiC nanowires is explained on the basis of vapor–solid (VS) mechanism. The reasonably better turn-on field (5.4 V/μm) measured from the field emission measurements suggest that the synthesized nanostructures could be used as potential field emitters. PMID:20596292

Determining the Molecular Growth Mechanisms of Protein Crystal Faces by Atomic Force Microscopy

NASA Technical Reports Server (NTRS)

Nadarajah, Arunan; Li, Huayu; Pusey, Marc L.

1999-01-01

A high resolution atomic force microscopy (AFM) study had shown that the molecular packing on the tetragonal lysozyme (110) face corresponded to only one of two possible packing arrangements, suggesting that growth layers on this face were of bimolecular height. Theoretical analyses of the packing also indicated that growth of this face should proceed by the addition of growth units of at least tetramer size corresponding to the 43 helices in the crystal. In this study an AFM linescan technique was devised to measure the dimensions of individual growth units on protein crystal faces as they were being incorporated into the lattice. Images of individual growth events on the (110) face of tetragonal lysozyme crystals were observed, shown by jump discontinuities in the growth step in the linescan images as shown in the figure. The growth unit dimension in the scanned direction was obtained from these images. A large number of scans in two directions on the (110) face were performed and the distribution of lysozyme growth unit sizes were obtained. A variety of unit sizes corresponding to 43 helices, were shown to participate in the growth process, with the 43 tetramer being the minimum observed size. This technique represents a new application for AFM allowing time resolved studies of molecular process to be carried out.

Low Temperature Metal Free Growth of Graphene on Insulating Substrates by Plasma Assisted Chemical Vapor Deposition

PubMed Central

Muñoz, R.; Munuera, C.; Martínez, J. I.; Azpeitia, J.; Gómez-Aleixandre, C.; García-Hernández, M.

2016-01-01

Direct growth of graphene films on dielectric substrates (quartz and silica) is reported, by means of remote electron cyclotron resonance plasma assisted chemical vapor deposition r-(ECR-CVD) at low temperature (650°C). Using a two step deposition process- nucleation and growth- by changing the partial pressure of the gas precursors at constant temperature, mostly monolayer continuous films, with grain sizes up to 500 nm are grown, exhibiting transmittance larger than 92% and sheet resistance as low as 900 Ω·sq-1. The grain size and nucleation density of the resulting graphene sheets can be controlled varying the deposition time and pressure. In additon, first-principles DFT-based calculations have been carried out in order to rationalize the oxygen reduction in the quartz surface experimentally observed. This method is easily scalable and avoids damaging and expensive transfer steps of graphene films, improving compatibility with current fabrication technologies. PMID:28070341

Interaction of tetraethoxysilane with OH-terminated SiO2 (0 0 1) surface: A first principles study

NASA Astrophysics Data System (ADS)

Deng, Xiaodi; Song, Yixu; Li, Jinchun; Pu, Yikang

2014-06-01

First principles calculates have been performed to investigate the surface reaction mechanism of tetraethoxysilane (TEOS) with fully hydroxylated SiO2(0 0 1) substrate. In semiconductor industry, this is the key step to understand and control the SiO2 film growth in chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes. During the calculation, we proposed a model which breaks the surface dissociative chemisorption into two steps and we calculated the activation barriers and thermochemical energies for each step. Our calculation result for step one shows that the first half reaction is thermodynamically favorable. For the second half reaction, we systematically studied the two potential reaction pathways. The comparing result indicates that the pathway which is more energetically favorable will lead to formation of crystalline SiO2 films while the other will lead to formation of disordered SiO2 films.

Bioenergetic Strategy for the Biodegradation of p-Cresol by the Unicellular Green Alga Scenedesmus obliquus

PubMed Central

Papazi, Aikaterini; Assimakopoulos, Konstantinos; Kotzabasis, Kiriakos

2012-01-01

Cultures from the unicellular green alga Scenedesmus obliquus biodegrade the toxic p-cresol (4-methylphenol) and use it as alternative carbon/energy source. The biodegradation procedure of p-cresol seems to be a two-step process. HPLC analyses indicate that the split of the methyl group (first step) that is possibly converted to methanol (increased methanol concentration in the growth medium), leading, according to our previous work, to changes in the molecular structure and function of the photosynthetic apparatus and therefore to microalgal biomass increase. The second step is the fission of the intermediately produced phenol. A higher p-cresol concentration results in a higher p-cresol biodegradation rate and a lower total p-cresol biodegradability. The first biodegradation step seems to be the most decisive for the effectiveness of the process, because methanol offers energy for the further biodegradation reactions. The absence of LHCII from the Scenedesmus mutant wt-lhc stopped the methanol effect and significantly reduced the p-cresol biodegradation (only 9%). The present contribution deals with an energy distribution between microalgal growth and p-cresol biodegradation, activated by p-cresol concentration. The simultaneous biomass increase with the detoxification of a toxic phenolic compound (p-cresol) could be a significant biotechnological aspect for further applications. PMID:23251641

Two-step growth of two-dimensional WSe 2/MoSe 2 heterostructures

DOE PAGES

Gong, Yongji; Lei, Sidong; Lou, Jun; ...

2015-08-03

Two dimensional (2D) materials have attracted great attention due to their unique properties and atomic thickness. Although various 2D materials have been successfully synthesized with different optical and electrical properties, a strategy for fabricating 2D heterostructures must be developed in order to construct more complicated devices for practical applications. Here we demonstrate for the first time a two-step chemical vapor deposition (CVD) method for growing transition-metal dichalcogenide (TMD) heterostructures, where MoSe 2 was synthesized first and followed by an epitaxial growth of WSe 2 on the edge and on the top surface of MoSe 2. Compared to previously reported one-stepmore » growth methods, this two-step growth has the capability of spatial and size control of each 2D component, leading to much larger (up to 169 μm) heterostructure size, and cross-contamination can be effectively minimized. Furthermore, this two-step growth produces well-defined 2H and 3R stacking in the WSe 2/MoSe 2 bilayer regions and much sharper in-plane interfaces than the previously reported MoSe 2/WSe 2 heterojunctions obtained from one-step growth methods. The resultant heterostructures with WSe 2/MoSe 2 bilayer and the exposed MoSe 2 monolayer display rectification characteristics of a p-n junction, as revealed by optoelectronic tests, and an internal quantum efficiency of 91% when functioning as a photodetector. As a result, a photovoltaic effect without any external gates was observed, showing incident photon to converted electron (IPCE) efficiencies of approximately 0.12%, providing application potential in electronics and energy harvesting.« less

NANOELECTRONICS. Epitaxial growth of a monolayer WSe2-MoS2 lateral p-n junction with an atomically sharp interface.

PubMed

Li, Ming-Yang; Shi, Yumeng; Cheng, Chia-Chin; Lu, Li-Syuan; Lin, Yung-Chang; Tang, Hao-Lin; Tsai, Meng-Lin; Chu, Chih-Wei; Wei, Kung-Hwa; He, Jr-Hau; Chang, Wen-Hao; Suenaga, Kazu; Li, Lain-Jong

2015-07-31

Two-dimensional transition metal dichalcogenides (TMDCs) such as molybdenum sulfide MoS2 and tungsten sulfide WSe2 have potential applications in electronics because they exhibit high on-off current ratios and distinctive electro-optical properties. Spatially connected TMDC lateral heterojunctions are key components for constructing monolayer p-n rectifying diodes, light-emitting diodes, photovoltaic devices, and bipolar junction transistors. However, such structures are not readily prepared via the layer-stacking techniques, and direct growth favors the thermodynamically preferred TMDC alloys. We report the two-step epitaxial growth of lateral WSe2-MoS2 heterojunction, where the edge of WSe2 induces the epitaxial MoS2 growth despite a large lattice mismatch. The epitaxial growth process offers a controllable method to obtain lateral heterojunction with an atomically sharp interface. Copyright © 2015, American Association for the Advancement of Science.

Growth of hierarchical GaN nanowires for optoelectronic device applications

NASA Astrophysics Data System (ADS)

Raj, Rishabh; Vignesh, Veeramuthu; Ra, Yong-Ho; Nirmala, Rajkumar; Lee, Cheul-Ro; Navamathavan, Rangaswamy

2017-01-01

Gallium nitride nanostructures have been receiving considerable attention as building blocks for nanophotonic technologies due to their unique high aspect ratios, promising the realization of photonic and biological nanodevices such as blue light emitting diodes (LEDs), short-wavelength ultraviolet nanolasers, and nanofluidic biochemical sensors. We report on the growth of hierarchical GaN nanowires (NWs) by dynamically adjusting the growth parameters using the pulsed flow metal-organic chemical vapor deposition technique. We carried out two step growth processes to grow hierarchical GaN NWs. In the first step, the GaN NWs were grown at 950°C, and in the second, we suitably decreased the growth temperature to 630°C and 710°C to grow the hierarchical structures. The surface morphology and optical characterization of the grown GaN NWs were studied by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, photoluminescence, and cathodoluminescence measurements. These kinds of hierarchical GaN NWs are promising for allowing flat band quantum structures that are shown to improve the efficiency of LEDs.

Site-discrimination by molecular imposters at dissymmetric molecular crystal surfaces

NASA Astrophysics Data System (ADS)

Poloni, Laura N.

The organization of atoms and molecules into crystalline forms is ubiquitous in nature and has been critical to the development of many technologies on which modern society relies. Classical crystal growth theory can describe atomic crystal growth, however, a description of molecular crystal growth is lacking. Molecular crystals are often characterized by anisotropic intermolecular interactions and dissymmetric crystal surfaces with anisotropic growth rates along different crystallographic directions. This thesis describes combination of experimental and computational techniques to relate crystal structure to surface structure and observed growth rates. Molecular imposters, also known as tailor-made impurities, can be used to control crystal growth for practical applications such as inhibition of pathological crystals, but can also be used to understand site specificity at crystal growth surfaces. The first part of this thesis builds on previous real-time in situ atomic force microscopy (AFM) observations of dislocation-actuated growth on the morphologically significant face of hexagonal L-cystine crystals, which aggregate in vivo to form kidney stones in patients suffering from cystinuria. The inhibitory effect of various L-cystine structural mimics (a.k.a. molecular imposters) was investigated through experimental and computational methods to identify the key structural factors responsible for molecular recognition between molecular imposters and L-cystine crystal surface sites. The investigation of L-cystine crystal growth in the presence of molecular imposters through a combination of kinetic analysis using in situ AFM, morphology analysis and birefringence measurements of bulk crystals, and molecular modeling of imposter binding to energetically inequivalent surface sites revealed that different molecular imposters inhibited crystal growth by a Cabrera-Vermilyea pinning mechanism and that imposters bind to a single binding site on the dissymmetric {1000} L-cystine surfaces. Collectively, these findings identify the key structural factors responsible for molecular recognition between molecular imposters and L-cystine crystal step sites, thereby articulating a strategy for stone prevention based on molecular design. The second part of this thesis describes the crystal growth and inhibition of a P2X3 receptor antagonist, denoted as DAPSA, recently reported as a non-opioid treatment of chronic pain. The low solubility of this compound results in the formation of drug-induced renal calculi (a.k.a. xenostones). in situ AFM of the morphologically significant (011) DAPSA surface revealed dislocation-actuated growth spirals with an anisotropic morphology, behavior that can be attributed to the non-uniform rate of solute attachment to eight crystallographically unique steps of the spiral, a direct consequence of the dissymmetry of this crystal surface. Eighteen molecular imposters were selected from the screening library to systematically investigate the roles of imposter substitute position, size, and functionality on the step velocities along the eight unique crystallographic directions. A non-uniform reduction in step velocities was observed, signaling site discrimination of imposter binding that can be attributed to stereochemical recognition of the imposters at specific crystal sites. The anisotropy of growth inhibition observed in the presence of the various imposters is consistent with binding energies calculated for the thirty-two crystallographically unique kink sites on steps advancing along predominant growth directions. These results provide insight to the design of growth inhibitors for molecular crystalline solids with complex and dissymmetric surfaces, while also suggesting a strategy for formulations containing congeners that can prevent harmful crystal growth in human renal structures. The last two crystalline systems discussed in this thesis are two isomorphous crystal systems that are ideal for the study of impurity incorporation at dissymmetric surfaces because their morphology is dominated by dissymmetric {101} growth faces. Growth processes on the dissymmetric (101) surfaces of these crystalline systems were investigated using metadynamics simulations to determine the free energy of adsorption for solute and impurity attachment to different flat, stepped, and kinked (101) surface terminations. Results suggest that growth occurs via a non-Kossel crystal growth mechanism, and highlights the need for dissymmetric surface structures (i.e. steps and kinks) for a higher fidelity in the orientation of adsorbed molecules. Overall, the results presented in this thesis suggest that growth of molecular crystals, particularly at dissymmetric surfaces, is complex and requires the combination of several experimental and computational techniques to decipher the mechanisms responsible for growth phenomena. The use of molecular imposters to inhibit growth can be useful for the development of therapeutics for pathological crystals, but can also inform processes by which crystal growth occurs at complex surfaces as a result of their site selectivity.

CH3NH3PbI3 grain growth and interfacial properties in meso-structured perovskite solar cells fabricated by two-step deposition

PubMed Central

Yao, Zhibo; Wang, Wenli; Shen, Heping; Zhang, Ye; Luo, Qiang; Yin, Xuewen; Dai, Xuezeng; Li, Jianbao; Lin, Hong

2017-01-01

Abstract Although the two-step deposition (TSD) method is widely adopted for the high performance perovskite solar cells (PSCs), the CH3NH3PbI3 perovskite crystal growth mechanism during the TSD process and the photo-generated charge recombination dynamics in the mesoporous-TiO2 (mp-TiO2)/CH3NH3PbI3/hole transporting material (HTM) system remains unexploited. Herein, we modified the concentration of PbI2 (C (PbI2)) solution to control the perovskite crystal properties, and observed an abnormal CH3NH3PbI3 grain growth phenomenon atop mesoporous TiO2 film. To illustrate this abnormal grain growth mechanism, we propose that a grain ripening process is taking place during the transformation from PbI2 to CH3NH3PbI3, and discuss the PbI2 nuclei morphology, perovskite grain growing stage, as well as Pb:I atomic ratio difference among CH3NH3PbI3 grains with different morphology. These C (PbI2)-dependent perovskite morphologies resulted in varied charge carrier transfer properties throughout the mp-TiO2/CH3NH3PbI3/HTM hybrid, as illustrated by photoluminescence measurement. Furthermore, the effect of CH3NH3PbI3 morphology on light absorption and interfacial properties is investigated and correlated with the photovoltaic performance of PSCs. PMID:28458747

CH3NH3PbI3 grain growth and interfacial properties in meso-structured perovskite solar cells fabricated by two-step deposition

NASA Astrophysics Data System (ADS)

Yao, Zhibo; Wang, Wenli; Shen, Heping; Zhang, Ye; Luo, Qiang; Yin, Xuewen; Dai, Xuezeng; Li, Jianbao; Lin, Hong

2017-12-01

Although the two-step deposition (TSD) method is widely adopted for the high performance perovskite solar cells (PSCs), the CH3NH3PbI3 perovskite crystal growth mechanism during the TSD process and the photo-generated charge recombination dynamics in the mesoporous-TiO2 (mp-TiO2)/CH3NH3PbI3/hole transporting material (HTM) system remains unexploited. Herein, we modified the concentration of PbI2 (C(PbI2)) solution to control the perovskite crystal properties, and observed an abnormal CH3NH3PbI3 grain growth phenomenon atop mesoporous TiO2 film. To illustrate this abnormal grain growth mechanism, we propose that a grain ripening process is taking place during the transformation from PbI2 to CH3NH3PbI3, and discuss the PbI2 nuclei morphology, perovskite grain growing stage, as well as Pb:I atomic ratio difference among CH3NH3PbI3 grains with different morphology. These C(PbI2)-dependent perovskite morphologies resulted in varied charge carrier transfer properties throughout the mp-TiO2/CH3NH3PbI3/HTM hybrid, as illustrated by photoluminescence measurement. Furthermore, the effect of CH3NH3PbI3 morphology on light absorption and interfacial properties is investigated and correlated with the photovoltaic performance of PSCs.

CH3NH3PbI3 grain growth and interfacial properties in meso-structured perovskite solar cells fabricated by two-step deposition.

PubMed

Yao, Zhibo; Wang, Wenli; Shen, Heping; Zhang, Ye; Luo, Qiang; Yin, Xuewen; Dai, Xuezeng; Li, Jianbao; Lin, Hong

2017-01-01

Although the two-step deposition (TSD) method is widely adopted for the high performance perovskite solar cells (PSCs), the CH 3 NH 3 PbI 3 perovskite crystal growth mechanism during the TSD process and the photo-generated charge recombination dynamics in the mesoporous-TiO 2 (mp-TiO 2 )/CH 3 NH 3 PbI 3 /hole transporting material (HTM) system remains unexploited. Herein, we modified the concentration of PbI 2 ( C (PbI2) ) solution to control the perovskite crystal properties, and observed an abnormal CH 3 NH 3 PbI 3 grain growth phenomenon atop mesoporous TiO 2 film. To illustrate this abnormal grain growth mechanism, we propose that a grain ripening process is taking place during the transformation from PbI 2 to CH 3 NH 3 PbI 3 , and discuss the PbI 2 nuclei morphology, perovskite grain growing stage, as well as Pb:I atomic ratio difference among CH 3 NH 3 PbI 3 grains with different morphology. These C (PbI2) -dependent perovskite morphologies resulted in varied charge carrier transfer properties throughout the mp-TiO 2 /CH 3 NH 3 PbI 3 /HTM hybrid, as illustrated by photoluminescence measurement. Furthermore, the effect of CH 3 NH 3 PbI 3 morphology on light absorption and interfacial properties is investigated and correlated with the photovoltaic performance of PSCs.

Engineered Multifunctional Surfaces for Fluid Handling

NASA Technical Reports Server (NTRS)

Thomas, Chris; Ma, Yonghui; Weislogel, Mark

2012-01-01

Designs incorporating variations in capillary geometry and hydrophilic and/or antibacterial surface properties have been developed that are capable of passive gas/liquid separation and passive water flow. These designs can incorporate capillary grooves and/or surfaces arranged to create linear and circumferential capillary geometry at the micro and macro scale, radial fin configurations, micro holes and patterns, and combinations of the above. The antibacterial property of this design inhibits the growth of bacteria or the development of biofilm. The hydrophilic property reduces the water contact angle with a treated substrate such that water spreads into a thin layer atop the treated surface. These antibacterial and hydrophilic properties applied to a thermally conductive surface, combined with capillary geometry, create a novel heat exchanger capable of condensing water from a humid, two-phase water and gas flow onto the treated heat exchanger surfaces, and passively separating the condensed water from the gas flow in a reduced gravity application. The overall process to generate the antibacterial and hydrophilic properties includes multiple steps to generate the two different surface properties, and can be divided into two major steps. Step 1 uses a magnetron-based sputtering technique to implant the silver atoms into the base material. A layer of silver is built up on top of the base material. Completion of this step provides the antibacterial property. Step 2 uses a cold-plasma technique to generate the hydrophilic surface property on top of the silver layer generated in Step 1. Completion of this step provides the hydrophilic property in addition to the antibacterial property. Thermally conductive materials are fabricated and then treated to create the antibacterial and hydrophilic surface properties. The individual parts are assembled to create a condensing heat exchanger with antibacterial and hydrophilic surface properties and capillary geometry, which is capable of passive phase separation in a reduced gravity application. The plasma processes for creating antibacterial and hydrophilic surface properties are suitable for applications where water is present on an exposed surface for an extended time, such that bacteria or biofilms could form, and where there is a need to manage the water on the surface. The processes are also suitable for applications where only the hydrophilic property is needed. In particular, the processes are applicable to condensing heat exchangers (CHXs), which benefit from the antibacterial properties as well as the hydrophilic properties. Water condensing onto the control surfaces of the CHX will provide the moist conditions necessary for the growth of bacteria and the formation of biofilms. The antibacterial properties of the base layer (silver) will mitigate and prevent the growth of bacteria and formation of biofilms that would otherwise reduce the CHX performance. In addition, the hydrophilic properties reduce the water contact angle and prevent water droplets from bridging between control surfaces. Overall, the hydrophilic properties reduce the pressure drop across the CHX.

Catalyst Interface Engineering for Improved 2D Film Lift-Off and Transfer

PubMed Central

2016-01-01

The mechanisms by which chemical vapor deposited (CVD) graphene and hexagonal boron nitride (h-BN) films can be released from a growth catalyst, such as widely used copper (Cu) foil, are systematically explored as a basis for an improved lift-off transfer. We show how intercalation processes allow the local Cu oxidation at the interface followed by selective oxide dissolution, which gently releases the 2D material (2DM) film. Interfacial composition change and selective dissolution can thereby be achieved in a single step or split into two individual process steps. We demonstrate that this method is not only highly versatile but also yields graphene and h-BN films of high quality regarding surface contamination, layer coherence, defects, and electronic properties, without requiring additional post-transfer annealing. We highlight how such transfers rely on targeted corrosion at the catalyst interface and discuss this in context of the wider CVD growth and 2DM transfer literature, thereby fostering an improved general understanding of widely used transfer processes, which is essential to numerous other applications. PMID:27934130

Observations of the Growth of an Active Region Filament

NASA Astrophysics Data System (ADS)

Yang, Bo

2017-04-01

We present observations of the growth of an active region filament caused by magnetic interactions among the filament and its adjacent superpenumbral filament (SF) and dark thread-like structures (T). Multistep reconnections are identified during the whole growing process. Magnetic flux convergence and cancellation occurring at the positive footpoint region of the filament is the first step reconnection, which resulted in the filament bifurcating into two sets of intertwined threads. One set anchored in situ, while the other set moved toward and interacted with the SF and part of T. This indicates the second step reconnection, which gave rise to the disappearance of the SF and the formation of a long thread-like structure that connects the far ends of the filament and T. The long thread-like structure further interacted with the T and then separated into two parts, representing the third step reconnection. Finally, another similar long thread-like structure, which intertwined with the fixed filament threads, appeared. Hαobservations show that this twisted structure is a longer sinistral filament. Based on the observed photospheric vector magnetograms, we performed a non-linear force-free field extrapolation to reconstruct the magnetic fields above the photosphere and found that the coronal magnetic field lines associated with the filament consists of two twisted flux ropes winding around each other. These results suggest that magnetic interactions among filaments and their adjacent SFs and T could lead to the growth of the filaments, and the filament is probably supported in a flux rope.

Gene co-expression analysis identifies gene clusters associated with isotropic and polarized growth in Aspergillus fumigatus conidia.

PubMed

Baltussen, Tim J H; Coolen, Jordy P M; Zoll, Jan; Verweij, Paul E; Melchers, Willem J G

2018-04-26

Aspergillus fumigatus is a saprophytic fungus that extensively produces conidia. These microscopic asexually reproductive structures are small enough to reach the lungs. Germination of conidia followed by hyphal growth inside human lungs is a key step in the establishment of infection in immunocompromised patients. RNA-Seq was used to analyze the transcriptome of dormant and germinating A. fumigatus conidia. Construction of a gene co-expression network revealed four gene clusters (modules) correlated with a growth phase (dormant, isotropic growth, polarized growth). Transcripts levels of genes encoding for secondary metabolites were high in dormant conidia. During isotropic growth, transcript levels of genes involved in cell wall modifications increased. Two modules encoding for growth and cell cycle/DNA processing were associated with polarized growth. In addition, the co-expression network was used to identify highly connected intermodular hub genes. These genes may have a pivotal role in the respective module and could therefore be compelling therapeutic targets. Generally, cell wall remodeling is an important process during isotropic and polarized growth, characterized by an increase of transcripts coding for hyphal growth and cell cycle/DNA processing when polarized growth is initiated. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

Lanthanide (Nd, Gd) compounds with garnet and monazite structures. Powders synthesis by "wet" chemistry to sintering ceramics by Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Potanina, Ekaterina; Golovkina, Ludmila; Orlova, Albina; Nokhrin, Aleksey; Boldin, Maksim; Sakharov, Nikita

2016-05-01

Complex oxide Y2.5Nd0.5Al5O12 with garnet structure and phosphates NdPO4 and GdPO4 with monazite structure were obtained by using precipitation methods. Ceramics Y2.5Nd0.5Al5O12 and NdPO4 were processed by Spark Plasma Sintering (SPS). Relative density more 98%, sintering time did not exceed 8 min, sintering temperature 1330-1390 °C. Leaching rates of elements from ceramics were 10-6-10-7 g/(cm2 d). The process of ceramics sintering has two-stage character: the first step of sintering-compaction process is related to the plastic flow of the material, the second step-to the process of grain boundary diffusion and grain growth.

Combined angle-resolved X-ray photoelectron spectroscopy, density functional theory and kinetic study of nitridation of gallium arsenide

NASA Astrophysics Data System (ADS)

Mehdi, H.; Monier, G.; Hoggan, P. E.; Bideux, L.; Robert-Goumet, C.; Dubrovskii, V. G.

2018-01-01

The high density of interface and surface states that cause the strong Fermi pinning observed on GaAs surfaces can be reduced by depositing GaN ultra-thin films on GaAs. To further improve this passivation, it is necessary to investigate the nitridation phenomena by identifying the distinct steps occurring during the process and to understand and quantify the growth kinetics of GaAs nitridation under different conditions. Nitridation of the cleaned GaAs substrate was performed using N2 plasma source. Two approaches have been combined. Firstly, an AR-XPS (Angle Resolved X-ray Photoelectron Spectroscopy) study is carried out to determine the chemical environments of the Ga, As and N atoms and the composition depth profile of the GaN thin film which allow us to summarize the nitridation process in three steps. Moreover, the temperature and time treatment have been investigated and show a significant impact on the formation of the GaN layer. The second approach is a refined growth kinetic model which better describes the GaN growth as a function of the nitridation time. This model clarifies the exchange mechanism of arsenic with nitrogen atoms at the GaN/GaAs interface and the phenomenon of quasi-saturation of the process observed experimentally.

The Effect of Growth Environment on the Morphological and Extended Defect Evolution in GaN Grown by Metalorganic Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Fini, P.; Wu, X.; Tarsa, E.; Golan, Y.; Srikant, V.; Keller, S.; Denbaars, S.; Speck, J.

1998-08-01

The evolution of morphology and associated extended defects in GaN thin films grown on sapphire by metalorganic chemical vapor deposition (MOCVD) are shown to depend strongly on the growth environment. For the commonly used two-step growth process, a change in growth parameter such as reactor pressure influences the initial high temperature (HT) GaN growth mechanism. By means of transmission electron microscopy (TEM), atomic force microscopy (AFM), and high resolution X-ray diffraction (HRXRD) measurements, it is shown that the initial density of HT islands on the nucleation layer (NL) and subsequently the threading dislocation density in the HT GaN film may be directly controlled by tailoring the initial HT GaN growth conditions.

Neuronal differentiation of human mesenchymal stem cells in response to the domain size of graphene substrates.

PubMed

Lee, Yoo-Jung; Seo, Tae Hoon; Lee, Seula; Jang, Wonhee; Kim, Myung Jong; Sung, Jung-Suk

2018-01-01

Graphene is a noncytotoxic monolayer platform with unique physical, chemical, and biological properties. It has been demonstrated that graphene substrate may provide a promising biocompatible scaffold for stem cell therapy. Because chemical vapor deposited graphene has a two dimensional polycrystalline structure, it is important to control the individual domain size to obtain desirable properties for nano-material. However, the biological effects mediated by differences in domain size of graphene have not yet been reported. On the basis of the control of graphene domain achieved by one-step growth (1step-G, small domain) and two-step growth (2step-G, large domain) process, we found that the neuronal differentiation of bone marrow-derived human mesenchymal stem cells (hMSCs) highly depended on the graphene domain size. The defects at the domain boundaries in 1step-G graphene was higher (×8.5) and had a relatively low (13% lower) contact angle of water droplet than 2step-G graphene, leading to enhanced cell-substrate adhesion and upregulated neuronal differentiation of hMSCs. We confirmed that the strong interactions between cells and defects at the domain boundaries in 1step-G graphene can be obtained due to their relatively high surface energy, which is stronger than interactions between cells and graphene surfaces. Our results may provide valuable information on the development of graphene-based scaffold by understanding which properties of graphene domain influence cell adhesion efficacy and stem cell differentiation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 43-51, 2018. © 2017 Wiley Periodicals, Inc.

Abnormal Grain Growth Suppression in Aluminum Alloys

NASA Technical Reports Server (NTRS)

Hales, Stephen J. (Inventor); Claytor, Harold Dale (Inventor); Alexa, Joel A. (Inventor)

2015-01-01

The present invention provides a process for suppressing abnormal grain growth in friction stir welded aluminum alloys by inserting an intermediate annealing treatment ("IAT") after the welding step on the article. The IAT may be followed by a solution heat treatment (SHT) on the article under effectively high solution heat treatment conditions. In at least some embodiments, a deformation step is conducted on the article under effective spin-forming deformation conditions or under effective superplastic deformation conditions. The invention further provides a welded article having suppressed abnormal grain growth, prepared by the process above. Preferably the article is characterized with greater than about 90% reduction in area fraction abnormal grain growth in any friction-stir-welded nugget.

Development of processes for the production of low cost silicon dendritic web for solar cells

NASA Technical Reports Server (NTRS)

Duncan, C. S.; Seidensticker, R. G.; Mchugh, J. P.; Hopkins, R. H.; Skutch, M. E.; Driggers, J. M.; Hill, F. E.

1980-01-01

High area output rates and continuous, automated growth are two key technical requirements for the growth of low-cost silicon ribbons for solar cells. By means of computer-aided furnace design, silicon dendritic web output rates as high as 27 sq cm/min have been achieved, a value in excess of that projected to meet a $0.50 per peak watt solar array manufacturing cost. The feasibility of simultaneous web growth while the melt is replenished with pelletized silicon has also been demonstrated. This step is an important precursor to the development of an automated growth system. Solar cells made on the replenished material were just as efficient as devices fabricated on typical webs grown without replenishment. Moreover, web cells made on a less-refined, pelletized polycrystalline silicon synthesized by the Battelle process yielded efficiencies up to 13% (AM1).

Kinetic Monte Carlo simulations of GaN homoepitaxy on c- and m-plane surfaces

DOE PAGES

Xu, Dongwei; Zapol, Peter; Stephenson, G. Brian; ...

2017-04-12

The surface orientation can have profound effects on the atomic-scale processes of crystal growth and is essential to such technologies as GaN-based light-emitting diodes and high-power electronics. We investigate the dependence of homoepitaxial growth mechanisms on the surface orientation of a hexagonal crystal using kinetic Monte Carlo simulations. To model GaN metal-organic vapor phase epitaxy, in which N species are supplied in excess, only Ga atoms on a hexagonal close-packed (HCP) lattice are considered. The results are thus potentially applicable to any HCP material. Growth behaviors on c-plane (0001) and m-plane (011¯0) surfaces are compared. We present a reciprocal spacemore » analysis of the surface morphology, which allows extraction of growth mode boundaries and direct comparison with surface X-ray diffraction experiments. For each orientation, we map the boundaries between 3-dimensional, layer-by-layer, and step flow growth modes as a function of temperature and growth rate. Two models for surface diffusion are used, which produce different effective Ehrlich-Schwoebel step-edge barriers and different adatom diffusion anisotropies on m-plane surfaces. Simulation results in agreement with observed GaN island morphologies and growth mode boundaries are obtained. These indicate that anisotropy of step edge energy, rather than adatom diffusion, is responsible for the elongated islands observed on m-plane surfaces. As a result, island nucleation spacing obeys a power-law dependence on growth rate, with exponents of –0.24 and –0.29 for the m- and c-plane, respectively.« less

Kinetic Monte Carlo simulations of GaN homoepitaxy on c- and m-plane surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Dongwei; Zapol, Peter; Stephenson, G. Brian

The surface orientation can have profound effects on the atomic-scale processes of crystal growth and is essential to such technologies as GaN-based light-emitting diodes and high-power electronics. We investigate the dependence of homoepitaxial growth mechanisms on the surface orientation of a hexagonal crystal using kinetic Monte Carlo simulations. To model GaN metal-organic vapor phase epitaxy, in which N species are supplied in excess, only Ga atoms on a hexagonal close-packed (HCP) lattice are considered. The results are thus potentially applicable to any HCP material. Growth behaviors on c-plane (0001) and m-plane (011¯0) surfaces are compared. We present a reciprocal spacemore » analysis of the surface morphology, which allows extraction of growth mode boundaries and direct comparison with surface X-ray diffraction experiments. For each orientation, we map the boundaries between 3-dimensional, layer-by-layer, and step flow growth modes as a function of temperature and growth rate. Two models for surface diffusion are used, which produce different effective Ehrlich-Schwoebel step-edge barriers and different adatom diffusion anisotropies on m-plane surfaces. Simulation results in agreement with observed GaN island morphologies and growth mode boundaries are obtained. These indicate that anisotropy of step edge energy, rather than adatom diffusion, is responsible for the elongated islands observed on m-plane surfaces. As a result, island nucleation spacing obeys a power-law dependence on growth rate, with exponents of –0.24 and –0.29 for the m- and c-plane, respectively.« less

Metalorganic chemical vapor deposition growth of high-mobility AlGaN/AlN/GaN heterostructures on GaN templates and native GaN substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Jr-Tai, E-mail: jrche@ifm.liu.se; Hsu, Chih-Wei; Forsberg, Urban

2015-02-28

Severe surface decomposition of semi-insulating (SI) GaN templates occurred in high-temperature H{sub 2} atmosphere prior to epitaxial growth in a metalorganic chemical vapor deposition system. A two-step heating process with a surface stabilization technique was developed to preserve the GaN template surface. Utilizing the optimized heating process, a high two-dimensional electron gas mobility ∼2000 cm{sup 2}/V·s was obtained in a thin AlGaN/AlN/GaN heterostructure with an only 100-nm-thick GaN spacer layer homoepitaxially grown on the GaN template. This technique was also demonstrated viable for native GaN substrates to stabilize the surface facilitating two-dimensional growth of GaN layers. Very high residual silicon andmore » oxygen concentrations were found up to ∼1 × 10{sup 20 }cm{sup −3} at the interface between the GaN epilayer and the native GaN substrate. Capacitance-voltage measurements confirmed that the residual carbon doping controlled by growth conditions of the GaN epilayer can be used to successfully compensate the donor-like impurities. State-of-the-art structural properties of a high-mobility AlGaN/AlN/GaN heterostructure was then realized on a 1 × 1 cm{sup 2} SI native GaN substrate; the full width at half maximum of the X-ray rocking curves of the GaN (002) and (102) peaks are only 21 and 14 arc sec, respectively. The surface morphology of the heterostructure shows uniform parallel bilayer steps, and no morphological defects were noticeable over the entire epi-wafer.« less

Density functional study of the decomposition pathways of SiH₃ and GeH₃ at the Si(100) and Ge(100) surfaces.

PubMed

Ceriotti, M; Montalenti, F; Bernasconi, M

2012-03-14

By means of first-principles calculations we studied the decomposition pathways of SiH₃ on Ge(100) and of GeH₃ on Si(100), of interest for the growth of crystalline SiGe alloys and Si/Ge heterostructures by plasma-enhanced chemical vapor deposition. We also investigated H desorption via reaction of two adsorbed SiH₂/GeH₂ species (β₂ reaction) or via Eley-Rideal abstraction of surface H atoms from the impinging SiH₃ and GeH₃ species. The calculated activation energies for the different processes suggest that the rate-limiting step for the growth of Si/Ge systems is still the β₂ reaction of two SiH₂ as in the growth of crystalline Si.

Effect of Microstructure on Time Dependent Fatigue Crack Growth Behavior In a P/M Turbine Disk Alloy

NASA Technical Reports Server (NTRS)

Telesman, Ignacy J.; Gabb, T. P.; Bonacuse, P.; Gayda, J.

2008-01-01

A study was conducted to determine the processes which govern hold time crack growth behavior in the LSHR disk P/M superalloy. Nineteen different heat treatments of this alloy were evaluated by systematically controlling the cooling rate from the supersolvus solutioning step and applying various single and double step aging treatments. The resulting hold time crack growth rates varied by more than two orders of magnitude. It was shown that the associated stress relaxation behavior for these heat treatments was closely correlated with the crack growth behavior. As stress relaxation increased, the hold time crack growth resistance was also increased. The size of the tertiary gamma' in the general microstructure was found to be the key microstructural variable controlling both the hold time crack growth behavior and stress relaxation. No relationship between the presence of grain boundary M23C6 carbides and hold time crack growth was identified which further brings into question the importance of the grain boundary phases in determining hold time crack growth behavior. The linear elastic fracture mechanics parameter, Kmax, is unable to account for visco-plastic redistribution of the crack tip stress field during hold times and thus is inadequate for correlating time dependent crack growth data. A novel methodology was developed which captures the intrinsic crack driving force and was able to collapse hold time crack growth data onto a single curve.

Advantages of InGaN/GaN multiple quantum wells with two-step grown low temperature GaN cap layers

NASA Astrophysics Data System (ADS)

Zhu, Yadan; Lu, Taiping; Zhou, Xiaorun; Zhao, Guangzhou; Dong, Hailiang; Jia, Zhigang; Liu, Xuguang; Xu, Bingshe

2017-11-01

Two-step grown low temperature GaN cap layers (LT-cap) are employed to improve the optical and structural properties of InGaN/GaN multiple quantum wells (MQWs). The first LT-cap layer is grown in nitrogen atmosphere, while a small hydrogen flow is added to the carrier gas during the growth of the second LT-cap layer. High-resolution X-ray diffraction results indicate that the two-step growth method can improve the interface quality of MQWs. Room temperature photoluminescence (PL) tests show about two-fold enhancement in integrated PL intensity, only 25 meV blue-shift in peak energy and almost unchanged line width. On the basis of temperature-dependent PL characteristics analysis, it is concluded that the first and the second LT-cap layer play a different role during the growth of MQWs. The first LT-cap layer acts as a protective layer, which protects quantum well from serious indium loss and interface roughening resulting from the hydrogen over-etching. The hydrogen gas employed in the second LT-cap layer is in favor of reducing defect density and indium segregation. Consequently, interface/surface and optical properties are improved by adopting the two-step growth method.

Superthermostability of nanoscale TIC-reinforced copper alloys manufactured by a two-step ball-milling process

NASA Astrophysics Data System (ADS)

Wang, Fenglin; Li, Yunping; Xu, Xiandong; Koizumi, Yuichiro; Yamanaka, Kenta; Bian, Huakang; Chiba, Akihiko

2015-12-01

A Cu-TiC alloy, with nanoscale TiC particles highly dispersed in the submicron-grained Cu matrix, was manufactured by a self-developed two-step ball-milling process on Cu, Ti and C powders. The thermostability of the composite was evaluated by high-temperature isothermal annealing treatments, with temperatures ranging from 727 to 1273 K. The semicoherent nanoscale TiC particles with Cu matrix, mainly located along the grain boundaries, were found to exhibit the promising trait of blocking grain boundary migrations, which leads to a super-stabilized microstructures up to approximately the melting point of copper (1223 K). Furthermore, the Cu-TiC alloys after annealing at 1323 K showed a slight decrease in Vickers hardness as well as the duplex microstructure due to selective grain growth, which were discussed in terms of hardness contributions from various mechanisms.

Overview of TANGENT (Tandem Aerosol Nucleation and Growth ENvironment Tube) 2017 IOP Study

NASA Astrophysics Data System (ADS)

Tiszenkel, L.

2017-12-01

New particle formation consists of two steps: nucleation and growth of nucleated particles. However, most laboratory studies have been conducted under conditions where these two processes are convoluted together, thereby hampering the detailed understanding of the effect of chemical species and atmospheric conditions on two processes. The objective of the Tandem Aerosol Nucleation and Growth ENvironment Tube (TANGENT) laboratory study is to investigate aerosol nucleation and growth properties independently by separating these two processes in two different flow tubes. This research is a collaboration between the University of Alabama in Huntsville and the University of Delaware. In this poster we will present the experimental setup of TANGENT and summarize the key results from the first IOP (intense observation period) experiments undertaken during Summer 2017. Nucleation takes place in a temperature- and RH-controlled fast flow reactor (FT-1) where sulfuric acid forms from OH radicals and sulfur dioxide. Sulfuric acid and impurity base compounds are detected with chemical ionization mass spectrometers (CIMS). Particle sizes and number concentrations of newly nucleated particles are measured with a scanning mobility particle sizer (SMPS) and particle size magnifier (PSM), providing concentrations of particles between 1-100 nm. The nucleation particles are transferred directly to the growth tube (FT-2) where oxidants and biogenic organic precursors are added to grow nucleated nanoparticles. Sizes of particles after growth are analyzed with an additional SMPS and elemental chemical composition of 50 nm and above particles detected with a nano-aerosol mass spectrometer (NAMS). TANGENT provides the unique ability to conduct experiments that can monitor and control reactant concentrations, aerosol size and aerosol chemical composition during nucleation and growth. Experiments during this first IOP study have elucidated the effects of sulfur dioxide, particle size, relative humidity, temperature, oxidants and biogenic organics on nanoparticle formation and growth. In another 3 companion posters, we will discuss findings of these results in detail.

Two-Dimensional Nucleation on the Terrace of Colloidal Crystals with Added Polymers.

PubMed

Nozawa, Jun; Uda, Satoshi; Guo, Suxia; Hu, Sumeng; Toyotama, Akiko; Yamanaka, Junpei; Okada, Junpei; Koizumi, Haruhiko

2017-04-04

Understanding nucleation dynamics is important both fundamentally and technologically in materials science and other scientific fields. Two-dimensional (2D) nucleation is the predominant growth mechanism in colloidal crystallization, in which the particle interaction is attractive, and has recently been regarded as a promising method to fabricate varieties of complex nanostructures possessing innovative functionality. Here, polymers are added to a colloidal suspension to generate a depletion attractive force, and the detailed 2D nucleation process on the terrace of the colloidal crystals is investigated. In the system, we first measured the nucleation rate at various area fractions of particles on the terrace, ϕ area . In situ observations at single-particle resolution revealed that nucleation behavior follows the framework of classical nucleation theory (CNT), such as single-step nucleation pathway and existence of critical size. Characteristic nucleation behavior is observed in that the nucleation and growth stage are clearly differentiated. When many nuclei form in a small area of the terrace, a high density of kink sites of once formed islands makes growth more likely to occur than further nucleation because nucleation has a higher energy barrier than growth. The steady-state homogeneous 2D nucleation rate, J, and the critical size of nuclei, r*, are measured by in situ observations based on the CNT, which enable us to obtain the step free energy, γ, which is an important parameter for characterizing the nucleation process. The γ value is found to change according to the strength of attraction, which is tuned by the concentration of the polymer as a depletant.

Modeling Growth of Nanostructures in Plasmas

NASA Technical Reports Server (NTRS)

Hwang, Helen H.; Bose, Deepak; Govindan, T. R.; Meyyappan, M.

2004-01-01

As semiconductor circuits shrink to CDs below 0.1 nm, it is becoming increasingly critical to replace and/or enhance existing technology with nanoscale structures, such as nanowires for interconnects. Nanowires grown in plasmas are strongly dependent on processing conditions, such as gas composition and substrate temperature. Growth occurs at specific sites, or step-edges, with the bulk growth rate of the nanowires determined from the equation of motion of the nucleating crystalline steps. Traditional front-tracking algorithms, such as string-based or level set methods, suffer either from numerical complications in higher spatial dimensions, or from difficulties in incorporating surface-intense physical and chemical phenomena. Phase field models have the robustness of the level set method, combined with the ability to implement surface-specific chemistry that is required to model crystal growth, although they do not necessarily directly solve for the advancing front location. We have adopted a phase field approach and will present results of the adatom density and step-growth location in time as a function of processing conditions, such as temperature and plasma gas composition.

Simultaneous saccharification and bioethanol production from corn cobs: Process optimization and kinetic studies.

PubMed

Sewsynker-Sukai, Yeshona; Gueguim Kana, E B

2018-08-01

This study investigates the simultaneous saccharification and fermentation (SSF) process for bioethanol production from corn cobs with prehydrolysis (PSSF) and without prehydrolysis (OSSF). Two response surface models were developed with high coefficients of determination (>0.90). Process optimization gave high bioethanol concentrations and bioethanol conversions for the PSSF (36.92 ± 1.34 g/L and 62.36 ± 2.27%) and OSSF (35.04 ± 0.170 g/L and 58.13 ± 0.283%) models respectively. Additionally, the logistic and modified Gompertz models were used to study the kinetics of microbial cell growth and ethanol formation under microaerophilic and anaerobic conditions. Cell growth in the OSSF microaerophilic process gave the highest maximum specific growth rate (µ max ) of 0.274 h -1 . The PSSF microaerophilic bioprocess gave the highest potential maximum bioethanol concentration (P m ) (42.24 g/L). This study demonstrated that microaerophilic rather than anaerobic culture conditions enhanced cell growth and bioethanol production, and that additional prehydrolysis steps do not significantly impact on the bioethanol concentration and conversion in SSF process. Copyright © 2018 Elsevier Ltd. All rights reserved.

OBSERVATIONS OF THE GROWTH OF AN ACTIVE REGION FILAMENT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Bo; Jiang, Yunchun; Yang, Jiayan

We present observations of the growth of an active region filament caused by magnetic interactions among the filament and its adjacent superpenumbral filament (SF) and dark thread-like structures (T). Multistep reconnections are identified during the whole growing process. Magnetic flux convergence and cancellation occurring at the positive footpoint region of the filament is the first step reconnection, which resulted in the filament bifurcating into two sets of intertwined threads. One set anchored in situ, while the other set moved toward and interacted with the SF and part of T. This indicates the second step reconnection, which gave rise to themore » disappearance of the SF and the formation of a long thread-like structure that connects the far ends of the filament and T. The long thread-like structure further interacted with the T and then separated into two parts, representing the third step reconnection. Finally, another similar long thread-like structure, which intertwined with the fixed filament threads, appeared. H {sub α} observations show that this twisted structure is a longer sinistral filament. Based on the observed photospheric vector magnetograms, we performed a non-linear force-free field extrapolation to reconstruct the magnetic fields above the photosphere and found that the coronal magnetic field lines associated with the filament consists of two twisted flux ropes winding around each other. These results suggest that magnetic interactions among filaments and their adjacent SFs and T could lead to the growth of the filaments, and the filament is probably supported in a flux rope.« less

Metalorganic Vapor-Phase Epitaxy Growth Parameters for Two-Dimensional MoS2

NASA Astrophysics Data System (ADS)

Marx, M.; Grundmann, A.; Lin, Y.-R.; Andrzejewski, D.; Kümmell, T.; Bacher, G.; Heuken, M.; Kalisch, H.; Vescan, A.

2018-02-01

The influence of the main growth parameters on the growth mechanism and film formation processes during metalorganic vapor-phase epitaxy (MOVPE) of two-dimensional MoS2 on sapphire (0001) have been investigated. Deposition was performed using molybdenum hexacarbonyl and di- tert-butyl sulfide as metalorganic precursors in a horizontal hot-wall MOVPE reactor from AIXTRON. The structural properties of the MoS2 films were analyzed by atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. It was found that a substrate prebake step prior to growth reduced the nucleation density of the polycrystalline film. Simultaneously, the size of the MoS2 domains increased and the formation of parasitic carbonaceous film was suppressed. Additionally, the influence of growth parameters such as reactor pressure and surface temperature is discussed. An upper limit for these parameters was found, beyond which strong parasitic deposition or incorporation of carbon into MoS2 took place. This carbon contamination became significant at reactor pressure above 100 hPa and temperature above 900°C.

Low-temperature plasma-deposited silicon epitaxial films: Growth and properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Demaurex, Bénédicte, E-mail: benedicte.demaurex@epfl.ch; Bartlome, Richard; Seif, Johannes P.

2014-08-07

Low-temperature (≤200 °C) epitaxial growth yields precise thickness, doping, and thermal-budget control, which enables advanced-design semiconductor devices. In this paper, we use plasma-enhanced chemical vapor deposition to grow homo-epitaxial layers and study the different growth modes on crystalline silicon substrates. In particular, we determine the conditions leading to epitaxial growth in light of a model that depends only on the silane concentration in the plasma and the mean free path length of surface adatoms. For such growth, we show that the presence of a persistent defective interface layer between the crystalline silicon substrate and the epitaxial layer stems not only frommore » the growth conditions but also from unintentional contamination of the reactor. Based on our findings, we determine the plasma conditions to grow high-quality bulk epitaxial films and propose a two-step growth process to obtain device-grade material.« less

Low-temperature plasma-deposited silicon epitaxial films: Growth and properties

DOE PAGES

Demaurex, Bénédicte; Bartlome, Richard; Seif, Johannes P.; ...

2014-08-05

Low-temperature (≤ 180 °C) epitaxial growth yields precise thickness, doping, and thermal-budget control, which enables advanced-design semiconductor devices. In this paper, we use plasma-ehanced chemical vapor deposition to grow homo-epitaxial layers and study the different growth modes on crystalline silicon substrates. In particular, we determine the conditions leading to epitaxial growth in light of a model that depends only on the silane concentration in the plasma and the mean free path length of surface adatoms. For such growth, we show that the presence of a persistent defective interface layer between the crystalline silicon substrate and the epitaxial layer stems notmore » only from the growth conditions but also from unintentional contamination of the reactor. As a result of our findings, we determine the plasma conditions to grow high-quality bulk epitaxial films and propose a two-step growth process to obtain device-grade material.« less

Atomic force microscopy study on crystal growth of Cu 2+-doped L-arginine phosphate monohydrate crystals

NASA Astrophysics Data System (ADS)

Geng, Y. L.; Xu, D.; Wang, Y. L.; Du, W.; Liu, H. Y.; Zhang, G. H.; Wang, X. Q.; Sun, D. L.

2005-01-01

Sub-steps and defects of the {1 0 0} planes of Cu 2+-doped L-arginine phosphate monohydrate (LAP) crystals are observed by atomic force microscopy. Formation of sub-steps is not due to the stacking faults but a result of single LAP: Cu 2+ molecule acting as growth unit. Two-dimensional (2D) nuclei with the same height as sub-steps occur on the step-edges. Impurities of Cu 2+ ions cause steps bunch and macrosteps formation. Liquid inclusions in the form of long channels form when the macrosteps lose their stability. Numerous small 3D growth hillocks are found in the channels. The extra stress induced by the 3D islands can result in dislocations and steps mismatches.

Role of hydrogen in the chemical vapor deposition growth of MoS2 atomic layers

NASA Astrophysics Data System (ADS)

Li, Xiao; Li, Xinming; Zang, Xiaobei; Zhu, Miao; He, Yijia; Wang, Kunlin; Xie, Dan; Zhu, Hongwei

2015-04-01

Hydrogen plays a crucial role in the chemical vapor deposition (CVD) growth of graphene. Here, we have revealed the roles of hydrogen in the two-step CVD growth of MoS2. Our study demonstrates that hydrogen acts as the following: (i) an inhibitor of the thermal-induced etching effect in the continuous film growth process; and (ii) a promoter of the desulfurization reaction by decreasing the S/Mo atomic ratio and the oxidation reaction of the obtained MoSx (0 < x < 2) films. A high hydrogen content of more than 100% in argon forms nano-sized circle-like defects and damages the continuity and uniformity of the film. Continuous MoS2 films with a high crystallinity and a nearly perfect S/Mo atomic ratio were finally obtained after sulfurization annealing with a hydrogen content in the range of 20%-80%. This insightful understanding reveals the crucial roles of hydrogen in the CVD growth of MoS2 and paves the way for the controllable synthesis of two-dimensional materials.Hydrogen plays a crucial role in the chemical vapor deposition (CVD) growth of graphene. Here, we have revealed the roles of hydrogen in the two-step CVD growth of MoS2. Our study demonstrates that hydrogen acts as the following: (i) an inhibitor of the thermal-induced etching effect in the continuous film growth process; and (ii) a promoter of the desulfurization reaction by decreasing the S/Mo atomic ratio and the oxidation reaction of the obtained MoSx (0 < x < 2) films. A high hydrogen content of more than 100% in argon forms nano-sized circle-like defects and damages the continuity and uniformity of the film. Continuous MoS2 films with a high crystallinity and a nearly perfect S/Mo atomic ratio were finally obtained after sulfurization annealing with a hydrogen content in the range of 20%-80%. This insightful understanding reveals the crucial roles of hydrogen in the CVD growth of MoS2 and paves the way for the controllable synthesis of two-dimensional materials. Electronic supplementary information (ESI) available: Low-magnification optical images; Raman spectra of 0% and 5% H2 samples; AFM characterization; Schematic of the film before and after sulfurization annealing; Schematic illustrations of two typical Raman-active phonon modes (E12g, A1g); Raman (mapping) spectra for 40% and 80% H2 samples before and after sulfurization annealing; PL spectra. See DOI: 10.1039/c5nr00904a

Novel Cyclosilazane-Type Silicon Precursor and Two-Step Plasma for Plasma-Enhanced Atomic Layer Deposition of Silicon Nitride.

PubMed

Park, Jae-Min; Jang, Se Jin; Lee, Sang-Ick; Lee, Won-Jun

2018-03-14

We designed cyclosilazane-type silicon precursors and proposed a three-step plasma-enhanced atomic layer deposition (PEALD) process to prepare silicon nitride films with high quality and excellent step coverage. The cyclosilazane-type precursor, 1,3-di-isopropylamino-2,4-dimethylcyclosilazane (CSN-2), has a closed ring structure for good thermal stability and high reactivity. CSN-2 showed thermal stability up to 450 °C and a sufficient vapor pressure of 4 Torr at 60 °C. The energy for the chemisorption of CSN-2 on the undercoordinated silicon nitride surface as calculated by density functional theory method was -7.38 eV. The PEALD process window was between 200 and 500 °C, with a growth rate of 0.43 Å/cycle. The best film quality was obtained at 500 °C, with hydrogen impurity of ∼7 atom %, oxygen impurity less than 2 atom %, low wet etching rate, and excellent step coverage of ∼95%. At 300 °C and lower temperatures, the wet etching rate was high especially at the lower sidewall of the trench pattern. We introduced the three-step PEALD process to improve the film quality and the step coverage on the lower sidewall. The sequence of the three-step PEALD process consists of the CSN-2 feeding step, the NH 3 /N 2 plasma step, and the N 2 plasma step. The H radicals in NH 3 /N 2 plasma efficiently remove the ligands from the precursor, and the N 2 plasma after the NH 3 plasma removes the surface hydrogen atoms to activate the adsorption of the precursor. The films deposited at 300 °C using the novel precursor and the three-step PEALD process showed a significantly improved step coverage of ∼95% and an excellent wet etching resistance at the lower sidewall, which is only twice as high as that of the blanket film prepared by low-pressure chemical vapor deposition.

Selected Topics on the Synthesis, Properties and Applications of Multiwalled Carbon Nanotubes

PubMed Central

Stoner, B.R.; Brown, B.; Glass, J.T.

2014-01-01

Summary In summary, MWCNTs have been examined for a variety of electronic applications due to their unique structure and chemistry. Electrodes for field emission, energy and sensor applications hold particular interest. MWCNTs provide a very high surface area, relatively easy methods of surface modification, controllable and high concentration of reactive surface sites, and high specific capacitance. Combining MWCNTs with graphene structures, oxide and metal nanoparticles and certain polymers extends their performance and functionality. Such hybrid structures have been produced in situ during CNT growth and in two-step processes. Excellent progress on understanding the mechanisms of CNT growth has enabled numerous growth methods to all yield MWCNT structures in a variety of morphologies. PMID:24910503

Curriculum Redesign in Veterinary Medicine: Part I.

PubMed

Chaney, Kristin P; Macik, Maria L; Turner, Jacqueline S; Korich, Jodi A; Rogers, Kenita S; Fowler, Debra; Scallan, Elizabeth M; Keefe, Lisa M

Curricular review is considered a necessary component for growth and enhancement of academic programs and requires time, energy, creativity, and persistence from both faculty and administration. At Texas A&M College of Veterinary Medicine & Biomedical Sciences (TAMU), the faculty and administration partnered with the university's Center for Teaching Excellence to create a faculty-driven, data-enhanced curricular redesign process. The 8-step process begins with the formation of a dedicated faculty curriculum design team to drive the redesign process and to support the college curriculum committee. The next steps include defining graduate outcomes and mapping the current curriculum to identify gaps and redundancies across the curriculum. Data are collected from internal and external stakeholders including veterinary students, faculty, alumni, and employers of graduates. Data collected through curriculum mapping and stakeholder engagement substantiate the curriculum redesign. The guidelines, supporting documents, and 8-step process developed at TAMU are provided to assist other veterinary schools in successful curricular redesign. This is the first of a two-part report that provides the background, context, and description of the process for charting the course for curricular change. The process involves defining expected learning outcomes for new graduates, conducting a curriculum mapping exercise, and collecting stakeholder data for curricular evaluation (steps 1-4). The second part of the report describes the development of rubrics that were applied to the graduate learning outcomes (steps 5-8) and engagement of faculty during the implementation phases of data-driven curriculum change.

Hyperthermophilic Archaeon Thermococcus kodakarensis Utilizes a Four-Step Pathway for NAD+ Salvage through Nicotinamide Deamination.

PubMed

Hachisuka, Shin-Ichi; Sato, Takaaki; Atomi, Haruyuki

2018-06-01

Many organisms possess pathways that regenerate NAD + from its degradation products, and two pathways are known to salvage NAD + from nicotinamide (Nm). One is a four-step pathway that proceeds through deamination of Nm to nicotinic acid (Na) by Nm deamidase and phosphoribosylation to nicotinic acid mononucleotide (NaMN), followed by adenylylation and amidation. Another is a two-step pathway that does not involve deamination and directly proceeds with the phosphoribosylation of Nm to nicotinamide mononucleotide (NMN), followed by adenylylation. Judging from genome sequence data, the hyperthermophilic archaeon Thermococcus kodakarensis is supposed to utilize the four-step pathway, but the fact that the adenylyltransferase encoded by TK0067 recognizes both NMN and NaMN also raises the possibility of a two-step salvage mechanism. Here, we examined the substrate specificity of the recombinant TK1676 protein, annotated as nicotinic acid phosphoribosyltransferase. The TK1676 protein displayed significant activity toward Na and phosphoribosyl pyrophosphate (PRPP) and only trace activity with Nm and PRPP. We further performed genetic analyses on TK0218 (quinolinic acid phosphoribosyltransferase) and TK1650 (Nm deamidase), involved in de novo biosynthesis and four-step salvage of NAD + , respectively. The ΔTK0218 mutant cells displayed growth defects in a minimal synthetic medium, but growth was fully restored with the addition of Na or Nm. The ΔTK0218 ΔTK1650 mutant cells did not display growth in the minimal medium, and growth was restored with the addition of Na but not Nm. The enzymatic and genetic analyses strongly suggest that NAD + salvage in T. kodakarensis requires deamination of Nm and proceeds through the four-step pathway. IMPORTANCE Hyperthermophiles must constantly deal with increased degradation rates of their biomolecules due to their high growth temperatures. Here, we identified the pathway that regenerates NAD + from nicotinamide (Nm) in the hyperthermophilic archaeon Thermococcus kodakarensis The organism utilizes a four-step pathway that initially hydrolyzes the amide bond of Nm to generate nicotinic acid (Na), followed by phosphoribosylation, adenylylation, and amidation. Although the two-step pathway, consisting of only phosphoribosylation of Nm and adenylylation, seems to be more efficient, Nm mononucleotide in the two-step pathway is much more thermolabile than Na mononucleotide, the corresponding intermediate in the four-step pathway. Although NAD + itself is thermolabile, this may represent an example of a metabolism that has evolved to avoid the use of thermolabile intermediates. Copyright © 2018 American Society for Microbiology.

Microstructure stability of ultra-fine grained magnesium alloy AZ31 processed by extrusion and equal-channel angular pressing (EX–ECAP)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stráská, Jitka, E-mail: straska.jitka@gmail.com; Janeček, Miloš, E-mail: janecek@met.mff.cuni.cz; Čížek, Jakub, E-mail: jcizek@mbox.troja.mff.cuni.cz

Thermal stability of the ultra-fine grained (UFG) microstructure of magnesium AZ31 alloy was investigated. UFG microstructure was achieved by a combined two-step severe plastic deformation process: the extrusion (EX) and subsequent equal-channel angular pressing (ECAP). This combined process leads to refined microstructure and enhanced microhardness. Specimens with UFG microstructure were annealed isochronally at temperatures 150–500 °C for 1 h. The evolution of microstructure, mechanical properties and dislocation density was studied by electron backscatter diffraction (EBSD), microhardness measurements and positron annihilation spectroscopy (PAS). The coarsening of the fine-grained structure at higher temperatures was accompanied by a gradual decrease of the microhardnessmore » and decrease of dislocation density. Mechanism of grain growth was studied by general equation for grain growth and Arrhenius equation. Activation energies for grain growth were calculated to be 115, 33 and 164 kJ/mol in temperature ranges of 170–210 °C, 210–400 °C and 400–500 °C (443–483 K, 483–673 K and 673–773 K), respectively. - Highlights: • Microhardness of UFG AZ31 alloy decreases with increasing annealing temperature. • This fact has two reasons: dislocation annihilations and/or grain growth. • The activation energies for grain growth were calculated for all temperature ranges.« less

Individual tree-diameter growth model for the Northeastern United States

Treesearch

Richard M. Teck; Donald E. Hilt

1991-01-01

Describes a distance-independent individual-tree diameter growth model for the Northeastern United States. Diameter growth is predicted in two steps using a two parameter, sigmoidal growth function modified by a one parameter exponential decay function with species-specific coefficients. Coefficients are presented for 28 species groups. The model accounts for...

Synthesis of highly uniform Cu2O spheres by a two-step approach and their assembly to form photonic crystals with a brilliant color.

PubMed

Su, Xin; Chang, Jie; Wu, Suli; Tang, Bingtao; Zhang, Shufen

2016-03-21

Monodisperse semiconductor colloidal spheres with a high refractive index hold great potential for building photonic crystals with a strong band gap, but the difficulty in separating the nucleation and growth processes makes it challenging to prepare highly uniform semiconductor colloidal spheres. Herein, real monodisperse Cu2O spheres were prepared via a hot-injection & heating-up two-step method using diethylene glycol as a milder reducing agent. The diameter of the as prepared Cu2O spheres can be tuned from 90 nm to 190 nm precisely. The SEM images reveal that the obtained Cu2O spheres have a narrow size distribution, which permits their self-assembly to form photonic crystals. The effects of precursor concentration and heating rates on the size and morphology of the Cu2O spheres were investigated in detail. The results indicate that the key points of the method include the burst nucleation to form seeds at a high temperature followed by rapid cooling to prevent agglomeration, and appropriate precursor concentration as well as a moderate growth rate during the further growth process. Importantly, photonic crystal films exhibiting a brilliant structural color were fabricated with the obtained monodisperse Cu2O spheres as building blocks, proving the possibility of making photonic crystals with a strong band gap. The developed method was also successfully applied to prepare monodisperse CdS spheres with diameters in the range from 110 nm to 210 nm.

[Effect of excess ethanol on the growth of yeasts of the genus Candida during continuous cultivation].

PubMed

Shkidchenko, A N; Shul'ga, A V; Gurina, L V

1988-01-01

The effect of flow rates and a specific ethanol load on the growth of Candida utilis and Candida krusei was studied in the process of one-step and three-step cultivation. The productive capacity of fermenters and the economic coefficient of yeast biomass production were shown to depend on the ability of microbial populations to assimilate a certain quantity of a carbon substrate per unit time. When a specific ethanol load exceeds the optimal one, the respiratory activity of a population and the economic coefficient of growth fall down whereas the accumulation of metabolites in the cultural broth increases. The steady state of biomass can be maintained in the process of continuous cultivation by inhibiting the yeast growth with an excess of ethanol.

A Three-Step Atomic Layer Deposition Process for SiN x Using Si2Cl6, CH3NH2, and N2 Plasma.

PubMed

Ovanesyan, Rafaiel A; Hausmann, Dennis M; Agarwal, Sumit

2018-06-06

We report a novel three-step SiN x atomic layer deposition (ALD) process using Si 2 Cl 6 , CH 3 NH 2 , and N 2 plasma. In a two-step process, nonhydrogenated chlorosilanes such as Si 2 Cl 6 with N 2 plasmas lead to poor-quality SiN x films that oxidize rapidly. The intermediate CH 3 NH 2 step was therefore introduced in the ALD cycle to replace the NH 3 plasma step with a N 2 plasma, while using Si 2 Cl 6 as the Si precursor. This three-step process lowers the atomic H content and improves the film conformality on high-aspect-ratio nanostructures as Si-N-Si bonds are formed during a thermal CH 3 NH 2 step in addition to the N 2 plasma step. During ALD, the reactive surface sites were monitored using in situ surface infrared spectroscopy. Our infrared spectra show that, on the post-N 2 plasma-treated SiN x surface, Si 2 Cl 6 reacts primarily with the surface -NH 2 species to form surface -SiCl x ( x = 1, 2, or 3) bonds, which are the reactive sites during the CH 3 NH 2 cycle. In the N 2 plasma step, reactive -NH 2 surface species are created because of the surface H available from the -CH 3 groups. At 400 °C, the SiN x films have a growth per cycle of ∼0.9 Å with ∼12 atomic percent H. The films grown on high-aspect-ratio nanostructures have a conformality of ∼90%.

Hybrid C-nanotubes/Si 3D nanostructures by one-step growth in a dual-plasma reactor

NASA Astrophysics Data System (ADS)

Toschi, Francesco; Orlanducci, Silvia; Guglielmotti, Valeria; Cianchetta, Ilaria; Magni, Corrado; Terranova, Maria Letizia; Pasquali, Matteo; Tamburri, Emanuela; Matassa, Roberto; Rossi, Marco

2012-06-01

Hybrid nanostructures consisting of Si polycrystalline nanocones, with an anemone-like termination coated with C-nanotubes bundles, have been generated on a (1 0 0) Si substrate in a dual mode microwave/radio-frequency plasma reactor. The substrate is both heated and bombarded by energetic H ions during the synthesis process. The nanocones growth is explained considering pull of the growing Si nanocrystalline phase along the lines of the electrical field, likely via a molten/recrystallization mechanism. The one-step building of the achieved complex 3D architectures is described in terms of dynamic competition between Si and C nanotubes growth under the peculiar conditions of kinetically driven processes.

A Two-Step Absorber Deposition Approach To Overcome Shunt Losses in Thin-Film Solar Cells: Using Tin Sulfide as a Proof-of-Concept Material System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steinmann, Vera; Chakraborty, Rupak; Rekemeyer, Paul H.

2016-08-31

As novel absorber materials are developed and screened for their photovoltaic (PV) properties, the challenge remains to reproducibly test promising candidates for high-performing PV devices. Many early-stage devices are prone to device shunting due to pinholes in the absorber layer, producing 'false-negative' results. Here, we demonstrate a device engineering solution toward a robust device architecture, using a two-step absorber deposition approach. We use tin sulfide (SnS) as a test absorber material. The SnS bulk is processed at high temperature (400 degrees C) to stimulate grain growth, followed by a much thinner, low-temperature (200 degrees C) absorber deposition. At a lowermore » process temperature, the thin absorber overlayer contains significantly smaller, densely packed grains, which are likely to provide a continuous coating and fill pinholes in the underlying absorber bulk. We compare this two-step approach to the more standard approach of using a semi-insulating buffer layer directly on top of the annealed absorber bulk, and we demonstrate a more than 3.5x superior shunt resistance Rsh with smaller standard error ..sigma..Rsh. Electron-beam-induced current (EBIC) measurements indicate a lower density of pinholes in the SnS absorber bulk when using the two-step absorber deposition approach. We correlate those findings to improvements in the device performance and device performance reproducibility.« less

Comparison of machinability of manganese alloyed austempered ductile iron produced using conventional and two step austempering processes

NASA Astrophysics Data System (ADS)

Hegde, Ananda; Sharma, Sathyashankara

2018-05-01

Austempered Ductile Iron (ADI) is a revolutionary material with high strength and hardness combined with optimum ductility and toughness. The discovery of two step austempering process has lead to the superior combination of all the mechanical properties. However, because of the high strength and hardness of ADI, there is a concern regarding its machinability. In the present study, machinability of ADI produced using conventional and two step heat treatment processes is assessed using tool life and the surface roughness. Speed, feed and depth of cut are considered as the machining parameters in the dry turning operation. The machinability results along with the mechanical properties are compared for ADI produced using both conventional and two step austempering processes. The results have shown that two step austempering process has produced better toughness with good hardness and strength without sacrificing ductility. Addition of 0.64 wt% manganese did not cause any detrimental effect on the machinability of ADI, both in conventional and two step processes. Marginal improvement in tool life and surface roughness were observed in two step process compared to that with conventional process.

Gold biorecovery from e-waste: An improved strategy through spent medium leaching with pH modification.

PubMed

Natarajan, Gayathri; Ting, Yen-Peng

2015-10-01

Rapid technological advancement and relatively short life time of electronic goods have resulted in an alarming growth rate of electronic waste which often contains significant quantities of toxic and precious metals. Compared to conventional recovery methods, bioleaching is an environmentally friendly process for metal extraction. Gold was bioleached from electronic scrap materials (ESM) via gold-cyanide complexation using cyanide produced from pure and mixed cultures of cyanogenic bacteria Chromobacterium violaceum, Pseudomonas aeruginosa and Pseudomonas fluorescens. As ESM was toxic to the bacteria, a two-step bioleaching approach was adopted where the solid waste was added to the bacterial culture after it has reached maximum growth and cyanide production during early stationary phase. Pure culture of C. violaceum showed the highest cyanide production, yielding maximum gold recovery of 11.3% at 0.5% w/v pulp density of ESM in two-step bioleaching. At the same pulp density of ESM, spent medium bioleaching using bacterial cell-free metabolites achieved gold recovery of 18%. Recovery increased to 30% when the pH of the spent medium was increased to shift the equilibrium in favor of cyanide ions production. It is demonstrated for the first time that pH modification of spent medium further improved metal solubilization and yielded higher metal recovery (compared to two-step bioleaching). Copyright © 2015 Elsevier Ltd. All rights reserved.

Optimal growth trajectories with finite carrying capacity.

PubMed

Caravelli, F; Sindoni, L; Caccioli, F; Ududec, C

2016-08-01

We consider the problem of finding optimal strategies that maximize the average growth rate of multiplicative stochastic processes. For a geometric Brownian motion, the problem is solved through the so-called Kelly criterion, according to which the optimal growth rate is achieved by investing a constant given fraction of resources at any step of the dynamics. We generalize these finding to the case of dynamical equations with finite carrying capacity, which can find applications in biology, mathematical ecology, and finance. We formulate the problem in terms of a stochastic process with multiplicative noise and a nonlinear drift term that is determined by the specific functional form of carrying capacity. We solve the stochastic equation for two classes of carrying capacity functions (power laws and logarithmic), and in both cases we compute the optimal trajectories of the control parameter. We further test the validity of our analytical results using numerical simulations.

Optimal growth trajectories with finite carrying capacity

NASA Astrophysics Data System (ADS)

Caravelli, F.; Sindoni, L.; Caccioli, F.; Ududec, C.

2016-08-01

We consider the problem of finding optimal strategies that maximize the average growth rate of multiplicative stochastic processes. For a geometric Brownian motion, the problem is solved through the so-called Kelly criterion, according to which the optimal growth rate is achieved by investing a constant given fraction of resources at any step of the dynamics. We generalize these finding to the case of dynamical equations with finite carrying capacity, which can find applications in biology, mathematical ecology, and finance. We formulate the problem in terms of a stochastic process with multiplicative noise and a nonlinear drift term that is determined by the specific functional form of carrying capacity. We solve the stochastic equation for two classes of carrying capacity functions (power laws and logarithmic), and in both cases we compute the optimal trajectories of the control parameter. We further test the validity of our analytical results using numerical simulations.

Twins and their boundaries during homoepitaxy on Ir(111)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bleikamp, Sebastian; Michely, Thomas; Coraux, Johann

2011-02-01

The growth and annealing behavior of strongly twinned homoepitaxial films on Ir(111) have been investigated by scanning tunneling microscopy, low-energy electron diffraction, and surface x-ray diffraction. In situ surface x-ray diffraction during and after film growth turned out to be an efficient tool for the determination of twin fractions in multilayer films and to unravel the nature of lateral twin crystallite boundaries. The annealing of the twin structures is shown to take place in a two-step process; first, the length of the lateral twin crystallite boundaries is reduced, without affecting the amount of twinned material, and then, at much highermore » temperatures, the twins themselves anneal. Within moderately annealed films lateral twin crystallite boundaries are visible at the film surface as fractional steps from which strain fields extend. The nature of these boundaries is discussed.« less

Synthesis and Characterization of Antireflective ZnO Nanoparticles Coatings Used for Energy Improving Efficiency of Silicone Solar Cells

NASA Astrophysics Data System (ADS)

Pîslaru-Dănescu, Lucian; Chitanu, Elena; El-Leathey, Lucia-Andreea; Marinescu, Virgil; Marin, Dorian; Sbârcea, Beatrice-Gabriela

2018-05-01

The paper proposes a new and complex process for the synthesis of ZnO nanoparticles for antireflective coating corresponding to silicone solar cells applications. The process consists of two major steps: preparation of seed layer and hydrothermal growth of ZnO nanoparticles. Due to the fact that the seed layer morphology influences the ZnO nanoparticles proprieties, the process optimization of the seed layer preparation is necessary. Following the hydrothermal growth of the ZnO nanoparticles, antireflective coating of silicone solar cells is achieved. After determining the functional parameters of the solar cells provided either with glass or with ZnO, it is concluded that all the parameters values are superior in the case of solar cells with ZnO antireflection coating and are increasing along with the solar irradiance.

A generalized theory of thin film growth

NASA Astrophysics Data System (ADS)

Du, Feng; Huang, Hanchen

2018-03-01

This paper reports a theory of thin film growth that is generalized for arbitrary incidence angle during physical vapor deposition in two dimensions. The accompanying kinetic Monte Carlo simulations serve as verification. A special theory already exists for thin film growth with zero incidence angle, and another theory also exists for nanorod growth with a glancing angle. The theory in this report serves as a bridge to describe the transition from thin film growth to nanorod growth. In particular, this theory gives two critical conditions in analytical form of critical coverage, ΘI and ΘII. The first critical condition defines the onset when crystal growth or step dynamics stops following the wedding cake model for thin film growth. The second critical condition defines the onset when multiple-layer surface steps form to enable nanorod growth. Further, this theory also reveals a critical incidence angle, below which nanorod growth is impossible. The critical coverages, together with the critical incidence angle, defines a phase diagram of thin growth versus nanorod growth.

Structural properties of templated Ge quantum dot arrays: impact of growth and pre-pattern parameters

NASA Astrophysics Data System (ADS)

Tempeler, J.; Danylyuk, S.; Brose, S.; Loosen, P.; Juschkin, L.

2018-07-01

In this study we analyze the impact of process and growth parameters on the structural properties of germanium (Ge) quantum dot (QD) arrays. The arrays were deposited by molecular-beam epitaxy on pre-patterned silicon (Si) substrates. Periodic arrays of pits with diameters between 120 and 20 nm and pitches ranging from 200 nm down to 40 nm were etched into the substrate prior to growth. The structural perfection of the two-dimensional QD arrays was evaluated based on SEM images. The impact of two processing steps on the directed self-assembly of Ge QD arrays is investigated. First, a thin Si buffer layer grown on a pre-patterned substrate reshapes the pre-pattern pits and determines the nucleation and initial shape of the QDs. Subsequently, the deposition parameters of the Ge define the overall shape and uniformity of the QDs. In particular, the growth temperature and the deposition rate are relevant and need to be optimized according to the design of the pre-pattern. Applying this knowledge, we are able to fabricate regular arrays of pyramid shaped QDs with dot densities up to 7.2 × 1010 cm‑2.

Structural properties of templated Ge quantum dot arrays: impact of growth and pre-pattern parameters.

PubMed

Tempeler, J; Danylyuk, S; Brose, S; Loosen, P; Juschkin, L

2018-07-06

In this study we analyze the impact of process and growth parameters on the structural properties of germanium (Ge) quantum dot (QD) arrays. The arrays were deposited by molecular-beam epitaxy on pre-patterned silicon (Si) substrates. Periodic arrays of pits with diameters between 120 and 20 nm and pitches ranging from 200 nm down to 40 nm were etched into the substrate prior to growth. The structural perfection of the two-dimensional QD arrays was evaluated based on SEM images. The impact of two processing steps on the directed self-assembly of Ge QD arrays is investigated. First, a thin Si buffer layer grown on a pre-patterned substrate reshapes the pre-pattern pits and determines the nucleation and initial shape of the QDs. Subsequently, the deposition parameters of the Ge define the overall shape and uniformity of the QDs. In particular, the growth temperature and the deposition rate are relevant and need to be optimized according to the design of the pre-pattern. Applying this knowledge, we are able to fabricate regular arrays of pyramid shaped QDs with dot densities up to 7.2 × 10 10 cm -2 .

Minimization of diauxic growth lag-phase for high-efficiency biogas production.

PubMed

Kim, Min Jee; Kim, Sang Hun

2017-02-01

The objective of this study was to develop a minimization method of a diauxic growth lag-phase for the biogas production from agricultural by-products (ABPs). Specifically, the effects of proximate composition on the biogas production and degradation rates of the ABPs were investigated, and a new method based on proximate composition combinations was developed to minimize the diauxic growth lag-phase. Experiments were performed using biogas potential tests at a substrate loading of 2.5 g VS/L and feed to microorganism ratio (F/M) of 0.5 under the mesophilic condition. The ABPs were classified based on proximate composition (carbohydrate, protein, and fat etc.). The biogas production patterns, lag phase, and times taken for 90% biogas production (T90) were used for the evaluation of the biogas production with biochemical methane potential (BMP) test. The high- or medium-carbohydrate and low-fat ABPs (cheese whey, cabbage, and skim milk) showed a single step digestion process and low-carbohydrate and high-fat ABPs (bean curd and perilla seed) showed a two-step digestion process. The mixture of high-fat ABPs and high-carbohydrate ABPs reduced the lag-phase and increased the biogas yield more than that from single ABP by 35-46%. Copyright © 2016 Elsevier Ltd. All rights reserved.

A benchmark of co-flow and cyclic deposition/etch approaches for the selective epitaxial growth of tensile-strained Si:P

NASA Astrophysics Data System (ADS)

Hartmann, J. M.; Veillerot, M.; Prévitali, B.

2017-10-01

We have compared co-flow and cyclic deposition/etch processes for the selective epitaxial growth of Si:P layers. High growth rates, relatively low resistivities and significant amounts of tensile strain (up to 10 nm min-1, 0.55 mOhm cm and a strain equivalent to 1.06% of substitutional C in Si:C layers) were obtained at 700 °C, 760 Torr with a co-flow approach and a SiH2Cl2 + PH3 + HCl chemistry. This approach was successfully used to thicken the sources and drains regions of n-type fin-shaped Field Effect Transistors. Meanwhile, the (Si2H6 + PH3/HCl + GeH4) CDE process evaluated yielded at 600 °C, 80 Torr even lower resistivities (0.4 mOhm cm, typically), at the cost however of the tensile strain which was lost due to (i) the incorporation of Ge atoms (1.5%, typically) into the lattice during the selective etch steps and (ii) a reduction by a factor of two of the P atomic concentration in CDE layers compared to that in layers grown in a single step (5 × 1020 cm-3 compared to 1021 cm-3).

Enhancement of soil retention for phenanthrene in binary cationic gemini and nonionic surfactant mixtures: characterizing two-step adsorption and partition processes through experimental and modeling approaches.

PubMed

Zhao, Shan; Huang, Gordon; An, Chunjiang; Wei, Jia; Yao, Yao

2015-04-09

The enhancement of soil retention for phenanthrene (PHE) through the addition of a binary mixture of cationic gemini (12-2-12) and nonionic surfactants (C12E10) was investigated. The maximum apparent sorption coefficient Kd(*) reached 4247.8 mL/g through the addition of mixed 12-2-12 gemini and C12E10 surfactants, which was markedly higher than the summed individual results in the presence of individual 12-2-12 gemini (1148.6 mL/g) or C12E10 (210.0 mL/g) surfactant. However, the sorption of 12-2-12 gemini was inhibited by the increasing C12E10 dose; and a higher initial 12-2-12 gemini dose showed a higher "desorption" rate. The present study also addressed the sorption behavior of the single 12-2-12 gemini surfactant at the soil/aqueous interface. The sorption isotherm was divided into two steps to elucidate the sorption process; and the sorption schematics were proposed to elaborate the growth of surfactant aggregates corresponding to the various steps of the sorption isotherm. Finally, a two-step adsorption and partition model (TAPM) was developed to simulate the sorption process. Analysis of the equilibrium data indicated that the sorption isotherms of 12-2-12 gemini fitted the TAPM model better. Thermodynamic calculations confirmed that the 12-2-12 gemini sorption at the soil/aqueous interface was spontaneous and exothermic from 288 to 308K. Copyright © 2014 Elsevier B.V. All rights reserved.

Perfusion mammalian cell culture for recombinant protein manufacturing - A critical review.

PubMed

Bielser, Jean-Marc; Wolf, Moritz; Souquet, Jonathan; Broly, Hervé; Morbidelli, Massimo

The manufacturing of recombinant protein is traditionally divided in two main steps: upstream (cell culture and synthesis of the target protein) and downstream (purification and formulation of the protein into a drug substance or drug product). Today, cost pressure, market uncertainty and market growth, challenge the existing manufacturing technologies. Leaders in the field are active in designing the process of the future and continuous manufacturing is recurrently mentioned as a potential solution to address some of the current limitations. This review focuses on the application of continuous processing to the first step of the manufacturing process. Enabling technologies and operation modes are described in the first part. In the second part, recent advances in the field that have the potential to support its successful future development are critically discussed. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

Studies of carbon incorporation on the diamond [100] surface during chemical vapor deposition using density functional theory.

PubMed

Cheesman, Andrew; Harvey, Jeremy N; Ashfold, Michael N R

2008-11-13

Accurate potential energy surface calculations are presented for many of the key steps involved in diamond chemical vapor deposition on the [100] surface (in its 2 x 1 reconstructed and hydrogenated form). The growing diamond surface was described by using a large (approximately 1500 atoms) cluster model, with the key atoms involved in chemical steps being described by using a quantum mechanical (QM, density functional theory, DFT) method and the bulk of the atoms being described by molecular mechanics (MM). The resulting hybrid QM/MM calculations are more systematic and/or at a higher level of theory than previous work on this growth process. The dominant process for carbon addition, in the form of methyl radicals, is predicted to be addition to a surface radical site, opening of the adjacent C-C dimer bond, insertion, and ultimate ring closure. Other steps such as insertion across the trough between rows of dimer bonds or addition to a neighboring dimer leading to formation of a reconstruction on the next layer may also contribute. Etching of carbon can also occur; the most likely mechanism involves loss of a two-carbon moiety in the form of ethene. The present higher-level calculations confirm that migration of inserted carbon along both dimer rows and chains should be relatively facile, with barriers of approximately 150 kJ mol (-1) when starting from suitable diradical species, and that this step should play an important role in establishing growth of smooth surfaces.

A parallel algorithm for step- and chain-growth polymerization in molecular dynamics.

PubMed

de Buyl, Pierre; Nies, Erik

2015-04-07

Classical Molecular Dynamics (MD) simulations provide insight into the properties of many soft-matter systems. In some situations, it is interesting to model the creation of chemical bonds, a process that is not part of the MD framework. In this context, we propose a parallel algorithm for step- and chain-growth polymerization that is based on a generic reaction scheme, works at a given intrinsic rate and produces continuous trajectories. We present an implementation in the ESPResSo++ simulation software and compare it with the corresponding feature in LAMMPS. For chain growth, our results are compared to the existing simulation literature. For step growth, a rate equation is proposed for the evolution of the crosslinker population that compares well to the simulations for low crosslinker functionality or for short times.

A parallel algorithm for step- and chain-growth polymerization in molecular dynamics

NASA Astrophysics Data System (ADS)

de Buyl, Pierre; Nies, Erik

2015-04-01

Classical Molecular Dynamics (MD) simulations provide insight into the properties of many soft-matter systems. In some situations, it is interesting to model the creation of chemical bonds, a process that is not part of the MD framework. In this context, we propose a parallel algorithm for step- and chain-growth polymerization that is based on a generic reaction scheme, works at a given intrinsic rate and produces continuous trajectories. We present an implementation in the ESPResSo++ simulation software and compare it with the corresponding feature in LAMMPS. For chain growth, our results are compared to the existing simulation literature. For step growth, a rate equation is proposed for the evolution of the crosslinker population that compares well to the simulations for low crosslinker functionality or for short times.

Modeling and simulation of the deposition/relaxation processes of polycrystalline diatomic structures of metallic nitride films

NASA Astrophysics Data System (ADS)

García, M. F.; Restrepo-Parra, E.; Riaño-Rojas, J. C.

2015-05-01

This work develops a model that mimics the growth of diatomic, polycrystalline thin films by artificially splitting the growth into deposition and relaxation processes including two stages: (1) a grain-based stochastic method (grains orientation randomly chosen) is considered and by means of the Kinetic Monte Carlo method employing a non-standard version, known as Constant Time Stepping, the deposition is simulated. The adsorption of adatoms is accepted or rejected depending on the neighborhood conditions; furthermore, the desorption process is not included in the simulation and (2) the Monte Carlo method combined with the metropolis algorithm is used to simulate the diffusion. The model was developed by accounting for parameters that determine the morphology of the film, such as the growth temperature, the interacting atomic species, the binding energy and the material crystal structure. The modeled samples exhibited an FCC structure with grain formation with orientations in the family planes of < 111 >, < 200 > and < 220 >. The grain size and film roughness were analyzed. By construction, the grain size decreased, and the roughness increased, as the growth temperature increased. Although, during the growth process of real materials, the deposition and relaxation occurs simultaneously, this method may perhaps be valid to build realistic polycrystalline samples.

High resolution electron microscopy study of crystal growth mechanisms in chicken bone composites

NASA Astrophysics Data System (ADS)

Cuisinier, F. J. G.; Steuer, P.; Brisson, A.; Voegel, J. C.

1995-12-01

The present study describes the early stages of chicken bone crystal growth, followed by high resolution electron microscopy (HREM). We have developed an original analysis procedure to determine the crystal structure. Images were first digitalized and selected areas were fast Fourier transformed. Numerical masks were selected around the most intense spots and the filtered signal was retransformed back to real space. The filtered images were then compared to computer calculated images to identify the inorganic mineral phase. Nanometer-sized particles were observed on amorphous areas. These particles have a structure loosely related to hydroxyapatite (HA) and a specific orientation. In a more advanced situation, the nanoparticles appeared to grow in two dimensions and to form plate-like crystals. These crystals seem, in a last growth step, to fuse by their (100) faces. These experimental observations allowed us to propose a four-step model for the development and growth of chicken bone crystals. The two initial stages are the ionic adsorption onto the organic substrate followed by the nucleation of nanometer-sized particles. The two following steps, i.e. two-dimensional growth of the nanoparticles leading to the formation of needle-like crystals, and the lateral fusion of these crystals by their (100) faces, are controlled only by spatial constraints inside the extracellular organic matrix.

Site-Controlled Growth of Monolithic InGaAs/InP Quantum Well Nanopillar Lasers on Silicon.

PubMed

Schuster, Fabian; Kapraun, Jonas; Malheiros-Silveira, Gilliard N; Deshpande, Saniya; Chang-Hasnain, Connie J

2017-04-12

In this Letter, we report the site-controlled growth of InP nanolasers on a silicon substrate with patterned SiO 2 nanomasks by low-temperature metal-organic chemical vapor deposition, compatible with silicon complementary metal-oxide-semiconductor (CMOS) post-processing. A two-step growth procedure is presented to achieve smooth wurtzite faceting of vertical nanopillars. By incorporating InGaAs multiquantum wells, the nanopillar emission can be tuned over a wide spectral range. Enhanced quality factors of the intrinsic InP nanopillar cavities promote lasing at 0.87 and 1.21 μm, located within two important optical telecommunication bands. This is the first demonstration of a site-controlled III-V nanolaser monolithically integrated on silicon with a silicon-transparent emission wavelength, paving the way for energy-efficient on-chip optical links at typical telecommunication wavelengths.

Calculation of trajectories and the rate of growth of curvilinear fatigue cracks in isotropic and composite plates

NASA Astrophysics Data System (ADS)

Pokhmurska, H.; Maksymovych, O.; Dzyubyk, A.; Dzyubyk, L.

2018-06-01

The methods of calculating the trajectories and the rate of growth of curvilinear fatigue cracks in isotropic and composite plate structure elements during cyclic loading along straight or curvilinear trajectories are developed. For isotropic and anisotropic materials, the methodes are developed on the basis of the force criterion of destruction with the additional application of the fatigue fracture diagrams. To find the change in the shape of the cracks in the loading process, the step-by-step method was used. At each stage, the direction of the growth of all vertices of cracks and the lengths of their arcs was found on the basis of determining the intensity coefficients of stresses by the method of singular integral equations. The results of calculations of the cracks system growth process are presented.

Image analysis for skeletal evaluation of carpal bones

NASA Astrophysics Data System (ADS)

Ko, Chien-Chuan; Mao, Chi-Wu; Lin, Chi-Jen; Sun, Yung-Nien

1995-04-01

The assessment of bone age is an important field to the pediatric radiology. It provides very important information for treatment and prediction of skeletal growth in a developing child. So far, various computerized algorithms for automatically assessing the skeletal growth have been reported. Most of these methods made attempt to analyze the phalangeal growth. The most fundamental step in these automatic measurement methods is the image segmentation that extracts bones from soft-tissue and background. These automatic segmentation methods of hand radiographs can roughly be categorized into two main approaches that are edge and region based methods. This paper presents a region-based carpal-bone segmentation approach. It is organized into four stages: contrast enhancement, moment-preserving thresholding, morphological processing, and region-growing labeling.

High-Energy Faceted SnO₂-Coated TiO₂ Nanobelt Heterostructure for Near-Ambient Temperature-Responsive Ethanol Sensor.

PubMed

Chen, Guohui; Ji, Shaozheng; Li, Haidong; Kang, Xueliang; Chang, Sujie; Wang, Yana; Yu, Guangwei; Lu, Jianren; Claverie, Jerome; Sang, Yuanhua; Liu, Hong

2015-11-11

A SnO2 gas sensor was prepared by a two-step oxidation process whereby a Sn(II) precursor was partially oxidized by a hydrothermal process and the resulting Sn3O4 nanoplates were thermally oxidized to yield SnO2 nanoplates. The SnO2 sensor was selective and responsive toward ethanol at a temperature as low as 43 °C. This low sensing temperature stems from the rapid charge transport within SnO2 and from the presence of high-energy (001) facets available for oxygen chemisorption. SnO2/TiO2 nanobelt heterostructures were fabricated by a similar two-step process in which TiO2 nanobelts acted as support for the epitaxial growth of intermediate Sn3O4. At temperatures ranging from 43 to 276 °C, the response of these branched nanobelts is more than double the response of SnO2 for ethanol detection. Our observations demonstrate the potential of low-cost SnO2-based sensors with controlled morphology and reactive facets for detecting gases around room temperature.

From globules to crystals: a spectral study of poly(2-isopropyl-2-oxazoline) crystallization in hot water.

PubMed

Sun, Shengtong; Wu, Peiyi

2015-12-28

One easy strategy to comprehend the complex folding/crystallization behaviors of proteins is to study the self-assembly process of their synthetic polymeric analogues with similar properties owing to their simple structures and easy access to molecular design. Poly(2-isopropyl-2-oxazoline) (PIPOZ) is often regarded as an ideal pseudopeptide with similar two-step crystallization behavior to proteins, whose aqueous solution experiences successive lower critical solution temperature (LCST)-type liquid-liquid phase separation upon heating and irreversible crystallization when annealed above LCST for several hours. In this paper, by microscopic observations, IR and Raman spectroscopy in combination with 2D correlation analysis, we show that the second step of PIPOZ crystallization in hot water can be further divided into two apparent stages, i.e., nucleation and crystal growth, and perfect crystalline PIPOZ chains are found to only develop in the second stage. While all the groups exhibit changes in initial nucleation, only methylene groups on the backbone participate in the crystal growth stage. During nucleation, a group motion transfer is found from the side chain to the backbone, and nucleation is assumed to be mainly driven by the cleavage of bridging C=O···D-O-D···O=C hydrogen bonds followed by chain arrangement due to amide dipolar orientation. Nevertheless, during crystal growth, a further chain ordering process occurs resulting in the final formation of crystalline PIPOZ chains with partial trans conformation of backbones and alternative side chains on the two sides. The underlying crystallization mechanism of PIPOZ in hot water we present here may provide very useful information for understanding the crystallization of biomacromolecules in biological systems.

Mechanisms of nuclear pore complex assembly - two different ways of building one molecular machine.

PubMed

Otsuka, Shotaro; Ellenberg, Jan

2018-02-01

The nuclear pore complex (NPC) mediates all macromolecular transport across the nuclear envelope. In higher eukaryotes that have an open mitosis, NPCs assemble at two points in the cell cycle: during nuclear assembly in late mitosis and during nuclear growth in interphase. How the NPC, the largest nonpolymeric protein complex in eukaryotic cells, self-assembles inside cells remained unclear. Recent studies have started to uncover the assembly process, and evidence has been accumulating that postmitotic and interphase NPC assembly use fundamentally different mechanisms; the duration, structural intermediates, and regulation by molecular players are different and different types of membrane deformation are involved. In this Review, we summarize the current understanding of these two modes of NPC assembly and discuss the structural and regulatory steps that might drive the assembly processes. We furthermore integrate understanding of NPC assembly with the mechanisms for rapid nuclear growth in embryos and, finally, speculate on the evolutionary origin of the NPC implied by the presence of two distinct assembly mechanisms. © 2017 The Authors. FEBS Letters published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.

Influence of processing steps in cold-smoked salmon production on survival and growth of persistent and presumed non-persistent Listeria monocytogenes.

PubMed

Porsby, Cisse Hedegaard; Vogel, Birte Fonnesbech; Mohr, Mona; Gram, Lone

2008-03-20

Cold-smoked salmon is a ready-to-eat product in which Listeria monocytogenes sometimes can grow to high numbers. The bacterium can colonize the processing environment and it is believed to survive or even grow during the processing steps. The purpose of the present study was to determine if the steps in the processing of cold-smoked salmon affect survival and subsequent growth of a persistent strain of L. monocytogenes to a lesser degree than presumed non-persistent strains. We used a sequence of experiments increasing in complexity: (i) small salmon blocks salted, smoked or dried under model conditions, (ii) fillets of salmon cold-smoked in a pilot plant and finally, (iii) assessment of the bacterial levels before and after processing during commercial scale production. L. monocytogenes proliferated on salmon blocks that were brined or dipped in liquid smoke and left at 25 degrees C in a humidity chamber for 24 h. However, combining brining and liquid smoke with a drying (25 degrees C) step reduced the bacterium 10-100 fold over a 24 h period. Non-salted, brine injected or dry salted salmon fillets were surface inoculated with L. monocytogenes and cold-smoked in a pilot plant. L. monocytogenes was reduced from 10(3) to 10-10(2) CFU/cm(2) immediately after cold-smoking. The greatest reductions were observed in dry salted and brine injected fillets as compared to cold-smoking of non-salted fresh fillets. Levels of L. monocytogenes decreased further when the cold-smoked fish was vacuum-packed and stored at 5 degrees C. A similar decline was seen when inoculating brine injected fillets after cold-smoking. High phenol concentrations are a likely cause of this marked growth inhibition. In a commercial production facility, the total viable count of salmon fillets was reduced 10-1000 fold by salting, cold-smoking and process-freezing (a freezing step after smoking and before slicing). The prevalence of L. monocytogenes in the commercial production facility was too low to determine any quantitative effects, however, one of nine samples was positive before processing and none after. Taken together, the processing steps involved in cold-smoking of salmon are bactericidal and reduce, but do not eliminate L. monocytogenes. A persistent strain was no less sensitive to the processing steps than a clinical strain or strain EGD.

Computer simulation of phase separation under a double temperature quench.

PubMed

Podariu, Iulia; Chakrabarti, Amitabha

2007-04-21

The authors numerically study a two-step quench process in an asymmetric binary mixture. The mixture is first quenched to an unstable state in the two-phase region. After a large phase-separated structure is formed, the authors again quench the system deeper. The second quench induces the formation of small secondary droplets inside the large domains created by the first quench. The authors characterize this secondary droplet growth in terms of the temperature of the first quench as well as the depth of the second one.

Effect of preparation conditions on the properties of Cu3BiS3 thin films grown by a two - step process

NASA Astrophysics Data System (ADS)

Mesa, F.; Gordillo, G.

2009-05-01

Cu3BiS3 thin films were prepared on soda-lime glass substrates by co-evaporation of the precursors in a two-step process; for that, the metallic precursors were evaporated from a tungsten boat in presence of elemental sulfur evaporated from a tantalum effusion cell. The films were characterized by spectral transmittance, atomic force microscopy AFM and x-ray diffraction (XRD) measurements to investigate the effect of the growth conditions on the optical, morphological and structural properties. The results revealed that, independently of the deposition conditions, the films grow only in the orthorhombic Cu3BiS3 phase. It was also found that the Cu3BiS3 films present p-type conductivity, a high absorption coefficient (greater than 104 cm-1) and an energy band gap Eg of about 1.41 eV, indicating that this compound has good properties to perform as absorbent layer in thin film solar cells.

Ground Based Program for the Physical Analysis of Macromolecular Crystal Growth

NASA Technical Reports Server (NTRS)

Malkin, Alexander J.

1998-01-01

During the past year we have focused on application of in situ Atomic Force Microscopy (AFM) for studies of the growth mechanisms and kinetics of crystallization for different macromolecular systems. Mechanisms of macrostep formation and their decay, which are important in understanding of defect formation, were studied on the surfaces of thaumatin, catalase, canavalin and lysozyme crystals. Experiments revealed that step bunching on crystalline surfaces occurred either due to two- or three-dimensional nucleation on the terraces of vicinal slopes or as a result of uneven step generation by complex dislocation sources. No step bunching arising from interaction of individual steps in the course of the experiment was observed. The molecular structure of the growth steps for thaumatin and lipase crystals were deduced. It was further shown that growth step advance occurs by incorporation of single protein molecules. In singular directions growth steps move by one-dimensional nucleation on step edges followed by lateral growth. One-dimensional nuclei have different sizes, less then a single unit cell, varying for different directions of step movement. There is no roughness due to thermal fluctuations, and each protein molecule which incorporated into the step remained. Growth kinetics for catalase crystals was investigated over wide supersaturation ranges. Strong directional kinetic anisotropy in the tangential step growth rates in different directions was seen. The influence of impurities on growth kinetics and cessation of macromolecular crystals was studied. Thus, for catalase, in addition to pronounced impurity effects on the kinetics of crystallization, we were also able to directly observe adsorption of some impurities. At low supersaturation we repeatedly observed filaments which formed from impurity molecules sedimenting on the surfaces. Similar filaments were observed on the surfaces of thaumatin, canavalin and STMV crystals as well, but the frequency was low compared with catalase crystallization. Cessation of growth of xylanase and lysozyme crystals was also observed and appeared to be a consequence of the formation of dense impurity adsorption layers. Attachment: "An in situ AFM investigation of catalase crystallization", "Atomic force microscopy studies of living cells: visualization of motility, division, aggregation, transformation, and apoptosis", AFM studies on mechanisms of nucleation and growth of macromolecular crystals", and "In situ atomic force microscopy studies of surface morphology, growth kinetics, defect structure and dissolution in macromolecular crystallization".

Two-Step Vapor/Liquid/Solid Purification

NASA Technical Reports Server (NTRS)

Holland, L. R.

1986-01-01

Vertical distillation system combines in single operation advantages of multiple zone refining with those of distillation. Developed specifically to load Bridgman-Stockbarger (vertical-solidification) growth ampoules with ultrapure tellurium and cadmium, system, with suitable modifications, serves as material refiner. In first phase of purification process, ampoule heated to drive off absorbed volatiles. Second phase, evaporator heated to drive off volatiles in charge. Third phase, slowly descending heater causes distillation from evaporator to growing crystal in ampoule.

Mechanisms of protein and virus crystal growth: An atomic force microscopy study of canavalin and STMV crystallization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Land, T.A.; De Yoreo, J.J.; Malkin, A.J.

1996-05-01

The evolution of surface morphology and step dynamics during growth of rhombohedral crystals of the protein canavalin and crystals of the cubic satellite tobacco mosaic virus (STMV) have been investigated for the first time by in situ atomic force microscopy. These two crystals were observed to grow by very different mechanisms. Growth of canavalin occurs on complex vicinal hillocks formed by multiple, independently acting screw dislocations. Small clusters were observed on the terraces. STMV on the other hand, was observed to grow by 2D nucleation of islands. No dislocations were found on the crystal. The results are used to determinemore » the growth mechanisms and estimate the fundamental materials parameters. The images also illustrate the important mechanism of defect incorporation and provide insight to the processes that limit the growth rate and uniformity of these crystals.« less

Two steps hydrothermal growth and characterisations of BaTiO3 films composed of nanowires

NASA Astrophysics Data System (ADS)

Zawawi, Che Zaheerah Najeehah Che Mohd; Salleh, Shahril; Oon Jew, Lee; Tufail Chaudhary, Kashif; Helmi, Mohamad; Safwan Aziz, Muhammad; Haider, Zuhaib; Ali, Jalil

2018-05-01

Barium titanate (BaTiO3) films composed of nanowires have gained considerable research interest due to their lead-free composition and strong energy conversion efficiency. BaTiO3 films can be developed with a simple two steps hydrothermal reactions, which are low cost effective. In this research, BaTiO3 films were fabricated on titanium foil through two steps hydrothermal method namely, the growth of TiO2 and followed by BaTiO3 films. The structural evolutions and the dielectric properties of the films were investigated as well. The structural evolutions of titanium dioxide (TiO2) and BaTiO3 nanowires were characterized using X-ray diffraction and scanning electron microscopy. First step of hydrothermal reaction, TiO2 nanowires were prepared in varied temperatures of 160 °C, 200 °C and 250 °C respectively. Second step of hydrothermal reaction was performed to produce a layer of BaTiO3 films.

Synthesis of porous carbon nanofiber with bamboo-like carbon nanofiber branches by one-step carbonization process

NASA Astrophysics Data System (ADS)

Yoo, Seung Hwa; Joh, Han-Ik; Lee, Sungho

2017-04-01

Porous carbon nanofibers (PCNFs) with CNF branches (PCNF/bCNF) were synthesized by a simple heat treatment method. Conventional methods to synthesize this unique structure usually follow a typical route, which consists of CNF preparation, catalyst deposition, and secondary CNF growth. In contrast, our method utilized a one-step carbonization process of polymer nanofibers, which were electrospun from a one-pot solution consisted of polyacrylonitrile, polystyrene (PS), and iron acetylacetonate. Various structures of PCNF/CNF were synthesized by changing the solution composition and molecular weight of PS. It was verified that the content and molecular weight of PS were critical for the growth of catalyst particles and subsequent growth of CNF branches. The morphology, phase of catalyst, and carbon structure of PCNF/bCNF were analyzed at different temperature steps during carbonization. It was found that pores were generated by the evaporation of PS and the catalyst particles were formed on the surface of PCNF at 700 °C. The gases originated from the evaporation of PS acted as a carbon source for the growth of CNF branches that started at 900 °C. Finally, when the carbonization process was finished at 1200 °C, uniform and abundant CNF branches were formed on the surface of PCNF.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, Xiang; Zhang, Shuai; Jiao, Fang

Two-step nucleation pathways in which disordered, amorphous, or dense liquid states precede appearance of crystalline phases have been reported for a wide range of materials, but the dynamics of such pathways are poorly understood. Moreover, whether these pathways are general features of crystallizing systems or a consequence of system-specific structural details that select for direct vs two-step processes is unknown. Using atomic force microscopy to directly observe crystallization of sequence-defined polymers, we show that crystallization pathways are indeed sequence dependent. When a short hydrophobic region is added to a sequence that directly forms crystalline particles, crystallization instead follows a two-stepmore » pathway that begins with creation of disordered clusters of 10-20 molecules and is characterized by highly non-linear crystallization kinetics in which clusters transform into ordered structures that then enter the growth phase. The results shed new light on non-classical crystallization mechanisms and have implications for design of self-assembling polymer systems.« less

In Situ μGISAXS: II. Thaumatin Crystal Growth Kinetic

PubMed Central

Gebhardt, Ronald; Pechkova, Eugenia; Riekel, Christian; Nicolini, Claudio

2010-01-01

The formation of thaumatin crystals by Langmuir-Blodgett (LB) film nanotemplates was studied by the hanging-drop technique in a flow-through cell by synchrotron radiation micrograzing-incidence small-angle x-ray scattering. The kinetics of crystallization was measured directly on the interface of the LB film crystallization nanotemplate. The evolution of the micrograzing-incidence small-angle x-ray scattering patterns suggests that the increase in intensity in the Yoneda region is due to protein incorporation into the LB film. The intensity variation suggests several steps, which were modeled by system dynamics based on first-order differential equations. The kinetic data can be described by two processes that take place on the LB film, a first, fast, process, attributed to the crystal growth and its detachment from the LB film, and a second, slower process, attributed to an unordered association and conversion of protein on the LB film. PMID:20713011

High Yield Chemical Vapor Deposition Growth of High Quality Large-Area AB Stacked Bilayer Graphene

PubMed Central

Liu, Lixin; Zhou, Hailong; Cheng, Rui; Yu, Woo Jong; Liu, Yuan; Chen, Yu; Shaw, Jonathan; Zhong, Xing; Huang, Yu; Duan, Xiangfeng

2012-01-01

Bernal stacked (AB stacked) bilayer graphene is of significant interest for functional electronic and photonic devices due to the feasibility to continuously tune its band gap with a vertical electrical field. Mechanical exfoliation can be used to produce AB stacked bilayer graphene flakes but typically with the sizes limited to a few micrometers. Chemical vapor deposition (CVD) has been recently explored for the synthesis of bilayer graphene but usually with limited coverage and a mixture of AB and randomly stacked structures. Herein we report a rational approach to produce large-area high quality AB stacked bilayer graphene. We show that the self-limiting effect of graphene growth on Cu foil can be broken by using a high H2/CH4 ratio in a low pressure CVD process to enable the continued growth of bilayer graphene. A high temperature and low pressure nucleation step is found to be critical for the formation of bilayer graphene nuclei with high AB stacking ratio. A rational design of a two-step CVD process is developed for the growth of bilayer graphene with high AB stacking ratio (up to 90 %) and high coverage (up to 99 %). The electrical transport studies demonstrated that devices made of the as-grown bilayer graphene exhibit typical characteristics of AB stacked bilayer graphene with the highest carrier mobility exceeding 4,000 cm2/V·s at room temperature, comparable to that of the exfoliated bilayer graphene. PMID:22906199

Two-Step Plasma Process for Cleaning Indium Bonding Bumps

NASA Technical Reports Server (NTRS)

Greer, Harold F.; Vasquez, Richard P.; Jones, Todd J.; Hoenk, Michael E.; Dickie, Matthew R.; Nikzad, Shouleh

2009-01-01

A two-step plasma process has been developed as a means of removing surface oxide layers from indium bumps used in flip-chip hybridization (bump bonding) of integrated circuits. The two-step plasma process makes it possible to remove surface indium oxide, without incurring the adverse effects of the acid etching process.

Computational modeling of soot nucleation

NASA Astrophysics Data System (ADS)

Chung, Seung-Hyun

Recent studies indicate that soot is the second most significant driver of climate change---behind CO2, but ahead of methane---and increased levels of soot particles in the air are linked to health hazards such as heart disease and lung cancer. Within the soot formation process, soot nucleation is the least understood step, and current experimental findings are still limited. This thesis presents computational modeling studies of the major pathways of the soot nucleation process. In this study, two regimes of soot nucleation---chemical growth and physical agglomeration---were evaluated and the results demonstrated that combustion conditions determine the relative importance of these two routes. Also, the dimerization process of polycyclic aromatic hydrocarbons, which has been regarded as one of the most important physical agglomeration processes in soot formation, was carefully examined with a new method for obtaining the nucleation rate using molecular dynamics simulation. The results indicate that the role of pyrene dimerization, which is the commonly accepted model, is expected to be highly dependent on various flame temperature conditions and may not be a key step in the soot nucleation process. An additional pathway, coronene dimerization in this case, needed to be included to improve the match with experimental data. The results of this thesis provide insight on the soot nucleation process and can be utilized to improve current soot formation models.

Uncovering molecular details of urea crystal growth in the presence of additives.

PubMed

Salvalaglio, Matteo; Vetter, Thomas; Giberti, Federico; Mazzotti, Marco; Parrinello, Michele

2012-10-17

Controlling the shape of crystals is of great practical relevance in fields like pharmacology and fine chemistry. Here we examine the paradigmatic case of urea which is known to crystallize from water with a needle-like morphology. To prevent this undesired effect, inhibitors that selectively favor or discourage the growth of specific crystal faces can be used. In urea the most relevant faces are the {001} and the {110} which are known to grow fast and slow, respectively. The relevant growth speed difference between these two crystal faces is responsible for the needle-like structure of crystals grown in water solution. To prevent this effect, additives are used to slow down the growth of one face relative to another, thus controlling the shape of the crystal. We study the growth of fast {001} and slow {110} faces in water solution and the effect of shape controlling inhibitors like biuret. Extensive sampling through molecular dynamics simulations provides a microscopic picture of the growth mechanism and of the role of the additives. We find a continuous growth mechanism on the {001} face, while the slow growing {110} face evolves through a birth and spread process, in which the rate-determining step is the formation on the surface of a two-dimensional crystalline nucleus. On the {001} face, growth inhibitors like biuret compete with urea for the adsorption on surface lattice sites; on the {110} face instead additives cannot interact specifically with surface sites and play a marginal sterical hindrance of the crystal growth. The free energies of adsorption of additives and urea are evaluated with advanced simulation methods (well-tempered metadynamics) allowing a microscopic understanding of the selective effect of additives. Based on this case study, general principles for the understanding of the anisotropic growth of molecular crystals from solutions are laid out. Our work is a step toward a rational development of novel shape-affecting additives.

A comparative study of one-step and two-step approaches for MAPbI3 perovskite layer and its influence on the performance of mesoscopic perovskite solar cell

NASA Astrophysics Data System (ADS)

Wang, Minhuan; Feng, Yulin; Bian, Jiming; Liu, Hongzhu; Shi, Yantao

2018-01-01

The mesoscopic perovskite solar cells (M-PSCs) were synthesized with MAPbI3 perovskite layers as light harvesters, which were grown with one-step and two-step solution process, respectively. A comparative study was performed through the quantitative correlation of resulting device performance and the crystalline quality of perovskite layers. Comparing with the one-step counterpart, a pronounced improvement in the steady-state power conversion efficiencies (PCEs) by 56.86% was achieved with two-step process, which was mainly resulted from the significant enhancement in fill factor (FF) from 48% to 77% without sacrificing the open circuit voltage (Voc) and short circuit current (Jsc). The enhanced FF was attributed to the reduced non-radiative recombination channels due to the better crystalline quality and larger grain size with the two-step processed perovskite layer. Moreover, the superiority of two-step over one-step process was demonstrated with rather good reproducibility.

Simultaneous methanogenesis and denitrification of pretreated effluents from a fish canning industry.

PubMed

Mosquera-Corral, A; Sánchez, M; Campos, J L; Méndez, R; Lema, J M

2001-02-01

A lab-scale hybrid upflow sludge bed-filter (USBF) reactor was employed to carry out methanogenesis and denitrification of the effluent from an anaerobic industrial reactor (EAIR) in a fish canning industry. The reactor was initially inoculated with methanogenic sludge and there were two different operational steps. During the first step (Step I: days 1-61), the methanogenic process was carried out at organic loading rates (OLR) of 1.0-1.25 g COD l-1 d-1 reaching COD removal percentages of 80%. During the second step (Step II: days 62-109) nitrate was added as KNO3 to the industrial effluent and the OLR was varied between 1.0 and 1.25 g COD l-1 d-1. Two different nitrogen loads of 0.10 and 0.22 g NO3(-)-N l-1 d-1 were applied and these led to nitrogen removal percentages of around 100% in both cases and COD removal percentages of around 80%. Carbon to nitrogen ratio (C:N) in the influent was maintained at 2.0 and eventually it was increased to 3.0, by means of glucose addition, to control the denitrification process. From these results it is possible to establish that wastewater produced in a fish canning industry can be used as a carbon source for denitrification and that denitrifying microorganisms were present in the initially methanogenic sludge. Biomass productions of 0.23 and 0.61 g VSS:g TOC fed for Steps I and II, respectively, were calculated from carbon global balances, showing an increase in biomass growth due to denitrification.

Preparation of clinical-grade 89Zr-panitumumab as a positron emission tomography biomarker for evaluating epidermal growth factor receptor-targeted therapy

PubMed Central

Wei, Ling; Shi, Jianfeng; Afari, George; Bhattacharyya, Sibaprasad

2014-01-01

Panitumumab is a fully human monoclonal antibody approved for the treatment of epidermal growth factor receptor (EGFR) positive colorectal cancer. Recently, panitumumab has been radiolabeled with 89Zr and evaluated for its potential to be used as immuno-positron emission tomography (PET) probe for EGFR positive cancers. Interesting preclinical results published by several groups of researchers have prompted us to develop a robust procedure for producing clinical-grade 89Zr-panitumumab as an immuno-PET probe to evaluate EGFR-targeted therapy. In this process, clinical-grade panitumumab is bio-conjugated with desferrioxamine chelate and subsequently radiolabeled with 89Zr resulting in high radiochemical yield (>70%, n=3) and purity (>98%, n=3). All quality control (QC) tests were performed according to United States Pharmacopeia specifications. QC tests showed that 89Zr-panitumumab met all specifications for human injection. Herein, we describe a step-by-step method for the facile synthesis and QC tests of 89Zr-panitumumab for medical use. The entire process of bioconjugation, radiolabeling, and all QC tests will take about 5h. Because the synthesis is fully manual, two rapid, in-process QC tests have been introduced to make the procedure robust and error free. PMID:24448743

Plasma-Assisted Growth of Silicon Nanowires by Sn Catalyst: Step-by-Step Observation

NASA Astrophysics Data System (ADS)

Tang, Jian; Maurice, Jean-Luc; Chen, Wanghua; Misra, Soumyadeep; Foldyna, Martin; Johnson, Erik V.; Roca i Cabarrocas, Pere

2016-10-01

A comprehensive study of the silicon nanowire growth process has been carried out. Silicon nanowires were grown by plasma-assisted-vapor-solid method using tin as a catalyst. We have focused on the evolution of the silicon nanowire density, morphology, and crystallinity. For the first time, the initial growth stage, which determines the nanowire (NW) density and growth direction, has been observed step by step. We provide direct evidence of the merging of Sn catalyst droplets and the formation of Si nanowires during the first 10 s of growth. We found that the density of Sn droplets decreases from 9000 Sn droplets/μm2 to 2000 droplets/μm2 after just 10 s of growth. Moreover, the long and straight nanowire density decreases from 170/μm2 after 2 min of growth to less than 10/μm2 after 90 min. This strong reduction in nanowire density is accompanied by an evolution of their morphology from cylindrical to conical, then to bend conical, and finally, to a bend inverted conical shape. Moreover, the changes in the crystalline structure of nanowires are from (i) monocrystalline to (ii) monocrystalline core/defective crystalline shell and then to (iii) monocrystalline core/defective crystalline shell/amorphous shell. The evolutions of NW properties have been explained in detail.

Crystal growth of YBCO coated conductors by TFA MOD method

NASA Astrophysics Data System (ADS)

Yoshizumi, M.; Nakanishi, T.; Matsuda, J.; Nakaoka, K.; Sutoh, Y.; Izumi, T.; Shiohara, Y.

2008-09-01

The crystal growth mechanism of TFA (trifluoroacetates)-MOD (metal organic deposition) derived YBa 2Cu 3O y has been investigated to understand the process for higher production rates of the conversion process. YBCO films were prepared by TFA-MOD on CeO 2/Gd 2Zr 2O 7/Hastelloy C276 substrates. The growth rates of YBCO derived from Y:Ba:Cu = 1:2:3 and 1:1.5:3 starting solutions were investigated by XRD and TEM analyses. YBCO growth proceeds in two steps of the epitaxial one from the substrate and solid state reaction. The overall growth rate estimated from the residual amounts of BaF 2 with time measured by XRD is proportional to a square root of P(H 2O). The trend was independent of the composition of starting solutions, however, the growth rate obtained from the 1:1.5:3 starting solutions was high as twice as that of 1:2:3, which could not be explained by the composition of BaF 2 included in the precursor films. On the other hand, the growth rate measured from the thickness of the YBCO quenched film at the same process time showed no difference between the samples of 1:2:3 and 1:1.5:3. The epitaxial growth rate of 1:1.5:3 was also the same as the overall growth rate of that, which means there was no solid state reaction to form YBCO after the epitaxial growth. The YBCO growth mechanism was found to be as follows; YBCO crystals nucleate at the surface of the substrate and epitaxially grow into the precursor by layer-by-layer by a manner with trapping unreacted particles. The amounts of YBCO and the unreacted particles trapped in the YBCO film are independent of the composition of the starting solution in this step. Unreacted particles react with each other to form YBCO and pores by solid state reaction as long as there is BaF 2 left in the film. The Ba-poor starting solution gives little BaF 2 left in the film and so the solid state reaction is completed within a short time, resulting in the fast overall growth rate.

Improved performance of mesostructured perovskite solar cells via an anti-solvent method

NASA Astrophysics Data System (ADS)

Hao, Jiabin; Hao, Huiying; Cheng, Feiyu; Li, Jianfeng; Zhang, Haiyu; Dong, Jingjing; Xing, Jie; Liu, Hao; Wu, Jian

2018-06-01

One-step solution process is a facile and widely used procedure to prepare organic-inorganic perovskite materials. However, the poor surface morphology of the films attributed to the uncontrollable nucleation and crystal growth in the process is unfavorable to solar cells. In this study, an anti-solvent treatment during the one-step solution process, in which ethyl acetate (EA) was dropped on the sample during spinning the precursor solution containing CH3NH3Cl, was adopted to fabricate perovskite materials and solar cells. It was found that the morphology of the perovskite film was significantly improved due to the rapid nucleation and slow crystal growth process. The modified process enabled us to fabricate the mesoporous solar cell with power conversion efficiency of 14%, showing an improvement of 40% over the efficiency of 9.7% of the device prepared by conventional one-step method. The controlling effect of annealing time on the morphology, crystal structure and transport properties of perovskite layer as well as the performance of device fabricated by the anti-solvent method were investigated and the possible mechanism was discussed.

Strained-layer indium gallium arsenide-gallium arsenide- aluminum galium arsenide photonic devices by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Osowski, Mark Louis

With the arrival of advanced growth technologies such as molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD), research in III-V compound semiconductor photonic devices has flourished. Advances in fabrication processes have allowed the realization of high-performance quantum well lasers which emit over a wide spectral range and operate with low threshold currents. As a result, semiconductor lasers are presently employed in a wide variety of applications, including fiber-optic telecommunications, optical spectroscopy, solid-state laser pumping, and photonic integrated circuits. The work in this dissertation addresses three photonic device structures which are currently receiving a great deal of attention in the research community: integrable quantum well laser devices, distributed feedback (DFB) laser devices, and quantum wire arrays. For the realization of the integrable and integrated photonic devices described-in Chapter 2, a three-step selective-area growth technique was utilized. The selective epitaxy process was used to produce discrete buried-heterostructure Fabry Perot lasers with threshold currents as low as 2.6 mA. Based on this process, broad- spectrum edge-emitting superluminescent diodes are demonstrated which display spectral widths of over 80 nm. In addition, the monolithic integration of a multiwavelength emitter is demonstrated in which two distinct laser sources are coupled into a single output waveguide. The dissertation also describes the development of a single-growth-step ridge waveguide DFB laser. The DFB laser utilizes an asymmetric cladding waveguide structure to enhance the interaction of the optical mode with the titanium surface metal to promote single frequency emission via gain coupling. These lasers exhibit low threshold currents (11 mA), high side mode suppression ratios (50 dB), and narrow linewidths (45 kHz). In light of the substantial performance advantages of quantum well lasers relative to double heterostructure lasers, extensive efforts have been directed toward producing quantum wire systems. In view of this, the final subject of this dissertation details the fabrication and characterization of quantum wire arrays by selective-area MOCVD. The method employs a silicon dioxide grating mask with sub-micron oxide dimensions to achieve selective deposition of high-quality buried layers in the open areas of the patterned substrate. This allows the fabrication of embedded nanostructures in a single growth step, and the crystallographic nature of the growth allows for control of their lateral size. Using this process, the growth of strained InGaAs wires with a lateral dimension of less than 50 nm are obtained. Subsequent characterization by photoluminescence, scanning electron microscopy and transmission electron microscopy is also presented.

Vertical epitaxial wire-on-wire growth of Ge/Si on Si(100) substrate.

PubMed

Shimizu, Tomohiro; Zhang, Zhang; Shingubara, Shoso; Senz, Stephan; Gösele, Ulrich

2009-04-01

Vertically aligned epitaxial Ge/Si heterostructure nanowire arrays on Si(100) substrates were prepared by a two-step chemical vapor deposition method in anodic aluminum oxide templates. n-Butylgermane vapor was employed as new safer precursor for Ge nanowire growth instead of germane. First a Si nanowire was grown by the vapor liquid solid growth mechanism using Au as catalyst and silane. The second step was the growth of Ge nanowires on top of the Si nanowires. The method presented will allow preparing epitaxially grown vertical heterostructure nanowires consisting of multiple materials on an arbitrary substrate avoiding undesired lateral growth.

From monoscale to multiscale modeling of fatigue crack growth: Stress and energy density factor

NASA Astrophysics Data System (ADS)

Sih, G. C.

2014-01-01

The formalism of the earlier fatigue crack growth models is retained to account for multiscaling of the fatigue process that involves the creation of macrocracks from the accumulation of micro damage. The effects of at least two scales, say micro to macro, must be accounted for. The same data can thus be reinterpreted by the invariancy of the transitional stress intensity factors such that the microcracking and macrocracking data would lie on a straight line. The threshold associated with the sigmoid curve disappears. Scale segmentation is shown to be a necessity for addressing multiscale energy dissipative processes such as fatigue and creep. Path independency and energy release rate are monoscale criteria that can lead to unphysical results, violating the first principles. Application of monoscale failure or fracture criteria to nanomaterials is taking toll at the expense of manufacturing super strength and light materials and structural components. This brief view is offered in the spirit of much needed additional research for the reinforcement of materials by creating nanoscale interfaces with sustainable time in service. The step by step consideraton at the different scales may offer a better understanding of the test data and their limitations with reference to space and time.

Crystal growth kinetics of triblock Janus colloids

NASA Astrophysics Data System (ADS)

Reinhart, Wesley F.; Panagiotopoulos, Athanassios Z.

2018-03-01

We measure the kinetics of crystal growth from a melt of triblock Janus colloids using non-equilibrium molecular dynamics simulations. We assess the impact of interaction anisotropy by systematically varying the size of the attractive patches from 40% to 100% coverage, finding substantially different growth behaviors in the two limits. With isotropic particles, the interface velocity is directly proportional to the subcooling, in agreement with previous studies. With highly anisotropic particles, the growth curves are well approximated by using a power law with exponent and prefactor that depend strongly on the particular surface geometry and patch fraction. This nonlinear growth appears correlated to the roughness of the solid-liquid interface, with the strongest growth inhibition occurring for the smoothest crystal faces. We conclude that crystal growth for patchy particles does not conform to the typical collision-limited mechanism, but is instead an activated process in which the rate-limiting step is the collective rotation of particles into the proper orientation. Finally, we show how differences in the growth kinetics could be leveraged to achieve kinetic control over polymorph growth, either enhancing or suppressing metastable phases near solid-solid coexistence lines.

Wide-bandgap III-Nitride based Second Harmonic Generation

DTIC Science & Technology

2014-10-02

fabrication process for a GaN LPS. Fig. 1: 3-step Fabrication process of a GaN based lateral polar structure. ( a ) Growth of a 20 nm AlN buffer layer...etching of the LT-AlN stripes. This results are shown in Fig. 2 ( a ) and (b). Fig. 2: AFM images of KOH ( a ) and RIE (b) patterned templates for lateral ...was varied between 0.6 - 1.0. FIG. 3: Growth process of AlGaN based Lateral Polar Structures. ( a ) RIE patterning. (b) Growth of HT- AlN. (c

A combined optical, SEM and STM study of growth spirals on the polytypic cadmium iodide crystals

NASA Astrophysics Data System (ADS)

Singh, Rajendra; Samanta, S. B.; Narlikar, A. V.; Trigunayat, G. C.

2000-05-01

Some novel results of a combined sequential study of growth spirals on the basal surface of the richly polytypic CdI 2 crystals by optical microscopy, scanning electron microscopy (SEM) and scanning tunneling microscopy (STM) are presented and discussed. Under the high resolution and magnification achieved in the scanning electron microscope, the growth steps of large heights seen in the optical micrographs are found to have a large number of additional steps of smaller heights existing between any two adjacent large height growth steps. When further seen by a scanning tunneling microscope, which provides still higher resolution, sequences of unit substeps, each of height equal to the unit cell height of the underlying polytype, are revealed to exist on the surface. Several large steps also lie between the unit steps, with heights equal to an integral multiple of either the unit cell height of the underlying polytype or the thickness of a molecular sheet I-Cd-I. It is suggested that initially a giant screw dislocation may form by brittle fracture of the crystal platelet, which may gradually decompose into numerous unit dislocations during subsequent crystal growth.

On the formation of well-aligned ZnO nanowall networks by catalyst-free thermal evaporation method

NASA Astrophysics Data System (ADS)

Yin, Zhigang; Chen, Nuofu; Dai, Ruixuan; Liu, Lei; Zhang, Xingwang; Wang, Xiaohui; Wu, Jinliang; Chai, Chunlin

2007-07-01

Two-dimensional ZnO nanowall networks were grown on ZnO-coated silicon by thermal evaporation at low temperature without catalysts or additives. All of the results from scanning electronic spectroscope, X-ray diffraction and Raman scattering confirmed that the ZnO nanowalls were vertically aligned and c-axis oriented. The room-temperature photoluminescence spectra showed a dominated UV peak at 378 nm, and a much suppressed orange emission centered at ˜590 nm. This demonstrates fairly good crystal quality and optical properties of the product. A possible three-step, zinc vapor-controlled process was proposed to explain the growth of well-aligned ZnO nanowall networks. The pre-coated ZnO template layer plays a key role during the synthesis process, which guides the growth direction of the synthesized products.

Initial growth and topography of 4,4'-biphenyldicarboxylic acid on Cu(001)

NASA Astrophysics Data System (ADS)

Poelsema, Bene; Schwarz, Daniel; van Gastel, Raoul; Zandvliet, Harold J. W.

2013-03-01

We have investigated nucleation and initial growth of BDA on Cu(001) at 300 - 410K, using LEEM and μLEED. BDA condenses in a 2D supramolecular c(8 ×8) network of lying molecules. The dehydrogenated molecules form hydrogen bonds with perpendicular adjacent ones. First, the adsorbed BDA molecules form a disordered dilute phase and at a sufficiently high density, the c(8 ×8) crystalline phase nucleates. From the equilibrium densities at different temperatures we obtain the 2D phase diagram. The phase coexistence line provides a cohesive energy of 0.35 eV. LEEM allows a detailed study of nucleation and growth of BDA on Cu(001) at low supersaturation. The real time microscopic information allows a direct visualization of near-critical nuclei. At 332 K and a deposition rate of 1.4 x 10-6ML/s we find a critical nucleus size about 600 nm2. The corresponding value obtained from classic nucleation theory corresponds nicely with this direct result. We estimate the Gibbs free energy for nucleation under these conditions at 4 eV. The size fluctuations are an order of magnitude stronger than expected. At 410 K the influence of steps on the growth process becomes evident: domain growth is terminated by steps even when they are permeable for individual molecules. This leads to a novel Mullins-Sekerka type of growth instability: the growth is very fast along the steps and less fast perpendicular to the steps. The large solid angle at the advancing edge of the condensate dictates the high growth rate along the step.

Surface-interface exploration of Mg deposited on Si(100) and oxidation effect on interfacial layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sarpi, B.; Daineche, R.; Girardeaux, C.

Using scanning tunneling microscopy and spectroscopy, Auger electron spectroscopy, and low energy electron diffraction, we have studied the growth of Mg deposited on Si(100)-(2 × 1). Coverage from 0.05 monolayer (ML) to 3 ML was investigated at room temperature. The growth mode of the magnesium is a two steps process. At very low coverage, there is formation of an amorphous ultrathin silicide layer with a band gap of 0.74 eV, followed by a layer-by-layer growth of Mg on top of this silicide layer. Topographic images reveal that each metallic Mg layer is formed by 2D islands coalescence process on top of the silicidemore » interfacial layer. During oxidation of the Mg monolayer, the interfacial silicide layer acts as diffusion barrier for the oxygen atoms with a decomposition of the silicide film to a magnesium oxide as function of O{sub 2} exposure.« less

Investigation to biodiesel production by the two-step homogeneous base-catalyzed transesterification.

PubMed

Ye, Jianchu; Tu, Song; Sha, Yong

2010-10-01

For the two-step transesterification biodiesel production made from the sunflower oil, based on the kinetics model of the homogeneous base-catalyzed transesterification and the liquid-liquid phase equilibrium of the transesterification product, the total methanol/oil mole ratio, the total reaction time, and the split ratios of methanol and reaction time between the two reactors in the stage of the two-step reaction are determined quantitatively. In consideration of the transesterification intermediate product, both the traditional distillation separation process and the improved separation process of the two-step reaction product are investigated in detail by means of the rigorous process simulation. In comparison with the traditional distillation process, the improved separation process of the two-step reaction product has distinct advantage in the energy duty and equipment requirement due to replacement of the costly methanol-biodiesel distillation column. Copyright 2010 Elsevier Ltd. All rights reserved.

Validation of mathematical model for CZ process using small-scale laboratory crystal growth furnace

NASA Astrophysics Data System (ADS)

Bergfelds, Kristaps; Sabanskis, Andrejs; Virbulis, Janis

2018-05-01

The present material is focused on the modelling of small-scale laboratory NaCl-RbCl crystal growth furnace. First steps towards fully transient simulations are taken in the form of stationary simulations that deal with the optimization of material properties to match the model to experimental conditions. For this purpose, simulation software primarily used for the modelling of industrial-scale silicon crystal growth process was successfully applied. Finally, transient simulations of the crystal growth are presented, giving a sufficient agreement to experimental results.

Platinum and rhenium extraction from a spent refinery catalyst using Bacillus megaterium as a cyanogenic bacterium: statistical modeling and process optimization.

PubMed

Motaghed, M; Mousavi, S M; Rastegar, S O; Shojaosadati, S A

2014-11-01

The present study evaluated the potential of Bacillus megaterium as a cyanogenic bacterium to produce cyanide for solubilization of platinum and rhenium from a spent refinery catalyst. Response surface methodology was applied to study the effects and interaction between two main effective parameters including initial glycine concentration and pulp density. Maximum Pt and Re recovery was obtained 15.7% and 98%, respectively, under optimum conditions of 12.8 g/l initial glycine concentration and 4% (w/v) pulp density after 7 days. Increasing the free cyanide concentration to 3.6 mg/l, varying the pH from 6.7 to 9, and increasing the dissolved oxygen from 2 to 5mg/l demonstrated the growth characteristics of B. megaterium during bioleaching process. The modified shrinking core model was used to determine the rate limiting step of the process. It was found that diffusion through the product layer is the rate controlling step. Copyright © 2014 Elsevier Ltd. All rights reserved.

A systematic study of atmospheric pressure chemical vapor deposition growth of large-area monolayer graphene.

PubMed

Liu, Lixin; Zhou, Hailong; Cheng, Rui; Chen, Yu; Lin, Yung-Chen; Qu, Yongquan; Bai, Jingwei; Ivanov, Ivan A; Liu, Gang; Huang, Yu; Duan, Xiangfeng

2012-01-28

Graphene has attracted considerable interest as a potential material for future electronics. Although mechanical peel is known to produce high quality graphene flakes, practical applications require continuous graphene layers over a large area. The catalyst-assisted chemical vapor deposition (CVD) is a promising synthetic method to deliver wafer-sized graphene. Here we present a systematic study on the nucleation and growth of crystallized graphene domains in an atmospheric pressure chemical vapor deposition (APCVD) process. Parametric studies show that the mean size of the graphene domains increases with increasing growth temperature and CH 4 partial pressure, while the density of domains decreases with increasing growth temperature and is independent of the CH 4 partial pressure. Our studies show that nucleation of graphene domains on copper substrate is highly dependent on the initial annealing temperature. A two-step synthetic process with higher initial annealing temperature but lower growth temperature is developed to reduce domain density and achieve high quality full-surface coverage of monolayer graphene films. Electrical transport measurements demonstrate that the resulting graphene exhibits a high carrier mobility of up to 3000 cm 2 V -1 s -1 at room temperature.

Ultrafast Formation of ZnO Nanorods via Seed-Mediated Microwave Assisted Hydrolysis Process

NASA Astrophysics Data System (ADS)

Tan, S. T.; Umar, A. A.; Yahaya, M.; Yap, C. C.; Salleh, M. M.

2013-04-01

One dimensional (1D) zinc oxide, ZnO nanostructures have shown promising results for usage in photodiode and optoelectronic device due to their high surface area. Faster and conventional method for synthesis ZnO nanorods has become an attention for researcher today. In this paper, ZnO nanorods have been successfully synthesized via two-step process, namely alcothermal seeding and seed-mediated microwave hydrolysis process. In typical process, the ZnO nanoseeds were grown in the growth solution that contained equimolar (0.04 M) of zinc nitrate hexahydrate, Zn (NO3).6H2O and hexamethylenetetramine, HMT. The growth process was carried inside the inverted microwave within 5- 20 s. The effect of growth parameters (i.e. concentration, microwave power, time reaction) upon the modification of ZnO morphology was studied. ZnO nanostructures were characterized by Field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). The densities of nanorods were evaluated by the Image J analysis. It was found that the morphology (e.g. shape and size) of nanostructures has changed drastically with the increment of growth solution concentration. The density of ZnO nanorods was proven to increase with the increasing of reaction time and microwave power. We hypothesize that the microwave power might enhance the rate of nucleation and promote the faster nanostructure growth as compared with the normal heating condition due to the superheating phenomenon. This method might promote a new and faster alternative way in nanostructure growth which can be applied in currently existing application.

Deregulation of cell growth and malignant transformation.

PubMed

Sulić, Sanda; Panić, Linda; Dikić, Ivan; Volarević, Sinisa

2005-08-01

Cell growth and cell division are fundamental aspects of cell behavior in all organisms. Recent insights from many model organisms have shed light on the molecular mechanisms that control cell growth and cell division. A significant body of evidence has now been accumulated, showing a direct link between deregulation of components of cell cycle machinery and cancer. In addition, defects in one or more steps that control growth are important for malignant transformation, as many tumor suppressors and proto-oncogenes have been found to regulate cell growth. The importance of cell growth in tumor development is further supported by the discovery that rapamycin, an effective anticancer drug, inhibits a key regulator of protein synthetic machinery and cell growth, mammalian target of rapamycin (mTOR). In most cases, cell growth and cell division are coupled, thereby maintaining cell size within physiological limits. We believe that, in a long-term perspective, understanding how these two processes are coordinated in vivo and how their interplay is deregulated in a number of diseases, including cancer, may have a direct impact on the efficiency of modern therapeutics.

Fundamental Study on the Fabrication of Inverted Planar Perovskite Solar Cells Using Two-Step Sequential Substrate Vibration-Assisted Spray Coating (2S-SVASC).

PubMed

Zabihi, Fatemeh; Ahmadian-Yazdi, Mohammad-Reza; Eslamian, Morteza

2016-12-01

In this paper, a scalable and fast process is developed and employed for the fabrication of the perovskite light harvesting layer in inverted planar heterojunction solar cell (FTO/PEDOT:PSS/CH3NH3PbI3-x Cl x /PCBM/Al). Perovskite precursor solutions are sprayed onto an ultrasonically vibrating substrate in two sequential steps via a process herein termed as the two-step sequential substrate vibration-assisted spray coating (2S-SVASC). The gentle imposed ultrasonic vibration on the substrate promotes droplet spreading and coalescence, surface wetting, evaporation, mixing of reagents, and uniform growth of perovskite nanocrystals. The role of the substrate temperature, substrate vibration intensity, and the time interval between the two sequential sprays are studied on the roughness, coverage, and crystalline structure of perovskite thin films. We demonstrate that a combination of a long time interval between spraying of precursor solutions (15 min), a high substrate temperature (120 °C), and a mild substrate vibration power (5 W) results in a favorable morphology and surface quality. The characteristics and performance of prepared perovskite thin films made via the 2S-SVASC technique are compared with those of the co-sprayed perovskite thin films. The maximum power conversion efficiency of 5.08 % on a 0.3-cm(2) active area is obtained for the device made via the scalable 2S-SVASC technique.

Free energy of steps using atomistic simulations

NASA Astrophysics Data System (ADS)

Freitas, Rodrigo; Frolov, Timofey; Asta, Mark

The properties of solid-liquid interfaces are known to play critical roles in solidification processes. Particularly special importance is given to thermodynamic quantities that describe the equilibrium state of these surfaces. For example, on the solid-liquid-vapor heteroepitaxial growth of semiconductor nanowires the crystal nucleation process on the faceted solid-liquid interface is influenced by the solid-liquid and vapor-solid interfacial free energies, and also by the free energies of associated steps at these faceted interfaces. Crystal-growth theories and mesoscale simulation methods depend on quantitative information about these properties, which are often poorly characterized from experimental measurements. In this work we propose an extension of the capillary fluctuation method for calculation of the free energy of steps on faceted crystal surfaces. From equilibrium atomistic simulations of steps on (111) surfaces of Copper we computed accurately the step free energy for different step orientations. We show that the step free energy remains finite at all temperature up to the melting point and that the results obtained agree with the more well established method of thermodynamic integration if finite size effects are taken into account. The research of RF and MA at UC Berkeley were supported by the US National Science Foundation (Grant No. DMR-1105409). TF acknowledges support through a postdoctoral fellowship from the Miller Institute for Basic Research in Science.

Scanning tunneling microscope study of GaAs(001) surfaces grown by migration enhanced epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, J.; Gallagher, M.C.; Willis, R.F.

We report an investigation of the morphology of p-type GaAs(001) surfaces using scanning tunneling microscopy (STM). The substrates were prepared using two methods: migration enhanced epitaxy (MEE) and standard molecular-beam epitaxy (MBE). The STM measurements were performed ex situ using As decapping. Analysis indicates that the overall step density of the MEE samples decreases as the growth temperature is increased. Nominally flat samples grown at 300{degrees}C exhibited step densities of 10.5 steps/1000 {Angstrom} along [ 110] dropping to 2.5 steps at 580{degrees}C. MEE samples exhibited a lower step density than MBE samples. However as-grown surfaces exhibited a larger distribution ofmore » step heights. Annealing the samples reduced the step height distribution exposing fewer atomic layers. Samples grown by MEE at 580{degrees}C and annealed for 2 min displayed the lowest step density and the narrowest step height distribution. All samples displayed an anisotropic step density. We found a ratio of A-type to B-type steps of between 2 and 3 which directly reflects the difference in the incorporation energy at steps. The aspect ratio increased slightly with growth temperature. We found a similar aspect ratio on samples grown by MBE. This indicates that anisotropic growth during MEE, like MBE, is dominated by incorporation kinetics. MEE samples grown at 580{degrees}C and capped immediately following growth exhibited a number of {open_quotes}holes{close_quotes} in the surface. The holes could be eliminated by annealing the surface prior to quenching. 20 refs., 3 figs., 1 tab.« less

Effects of Complex Structured Anodic Oxide Dielectric Layer Grown in Pore Matrix for Aluminum Capacitor.

PubMed

Shin, Jin-Ha; Yun, Sook Young; Lee, Chang Hyoung; Park, Hwa-Sun; Suh, Su-Jeong

2015-11-01

Anodization of aluminum is generally divided up into two types of anodic aluminum oxide structures depending on electrolyte type. In this study, an anodization process was carried out in two steps to obtain high dielectric strength and break down voltage. In the first step, evaporated high purity Al on Si wafer was anodized in oxalic acidic aqueous solution at various times at a constant temperature of 5 degrees C. In the second step, citric acidic aqueous solution was used to obtain a thickly grown sub-barrier layer. During the second anodization process, the anodizing potential of various ranges was applied at room temperature. An increased thickness of the sub-barrier layer in the porous matrix was obtained according to the increment of the applied anodizing potential. The microstructures and the growth of the sub-barrier layer were then observed with an increasing anodizing potential of 40 to 300 V by using a scanning electron microscope (SEM). An impedance analyzer was used to observe the change of electrical properties, including the capacitance, dissipation factor, impedance, and equivalent series resistance (ESR) depending on the thickness increase of the sub-barrier layer. In addition, the breakdown voltage was measured. The results revealed that dielectric strength was improved with the increase of sub-barrier layer thickness.

The role of impurities on the process of growing potassium hydrogen phthalate crystals from solution; A quantitative approach

NASA Astrophysics Data System (ADS)

Hottenhuis, M. H. J.; Lucasius, C. B.

1988-09-01

Quantitative information about the influence of impurities on the crystal growth process of potassium hydrogen phthalate from its aqueous solution was obtained at two levels: microscopic and macroscopic. At the microscopic level, detailed in situ observations of spiral steps at the (010) face were performed. The velocity of these steps was measured, as well in a "clean" as in a contaminated solution, where the influence of a number of different impurities was investigated. This resulted in a measure of effectiveness of step retardation for each of these impurities. From the same microscopic observations it was observed how these effectiveness factors were influenced by the supersaturation σ, the saturation temperature Ts of the solution and the concentration cimp of the impurity that w as used. At the macroscopic level, ICP (inductively coupled plasma) measurements were carried out in order to determine the distribution coefficient of the same impurities. In these measurements again the influence of the impurity concentration and the supersaturation on the distribution coefficient kD was determined.

Assessment of an improved bone washing protocol for deceased donor human bone.

PubMed

Eagle, M J; Man, J; Rooney, P; Hogg, P; Kearney, J N

2015-03-01

NHSBT Tissue Services issues bone to surgeons in the UK in two formats, fresh-frozen unprocessed bone from living donors and processed bone from deceased donors. Processed bone may be frozen or freeze dried and all processed bone is currently subjected to a washing protocol to remove blood and bone marrow. In this study we have improved the current bone washing protocol for cancellous bone and assessed the success of the protocol by measuring the removal of the bone marrow components: soluble protein, DNA and haemoglobin at each step in the process, and residual components in the bone at the end of the process. The bone washing protocol is a combination of sonication, warm water washes, centrifugation and chemical (ethanol and hydrogen peroxide) treatments. We report that the bone washing protocol is capable of removing up to 99.85 % soluble protein, 99.95 % DNA and 100 % of haemoglobin from bone. The new bone washing protocol does not render any bone cytotoxic as shown by contact cytotoxicity assays. No microbiological cell growth was detected in any of the wash steps. This process is now in use for processed cancellous bone issued by NHSBT.

Atomistic Simulations of Graphene Growth: From Kinetics to Mechanism.

PubMed

Qiu, Zongyang; Li, Pai; Li, Zhenyu; Yang, Jinlong

2018-03-20

Epitaxial growth is a promising strategy to produce high-quality graphene samples. At the same time, this method has great flexibility for industrial scale-up. To optimize growth protocols, it is essential to understand the underlying growth mechanisms. This is, however, very challenging, as the growth process is complicated and involves many elementary steps. Experimentally, atomic-scale in situ characterization methods are generally not feasible at the high temperature of graphene growth. Therefore, kinetics is the main experimental information to study growth mechanisms. Theoretically, first-principles calculations routinely provide atomic structures and energetics but have a stringent limit on the accessible spatial and time scales. Such gap between experiment and theory can be bridged by atomistic simulations using first-principles atomic details as input and providing the overall growth kinetics, which can be directly compared with experiment, as output. Typically, system-specific approximations should be applied to make such simulations computationally feasible. By feeding kinetic Monte Carlo (kMC) simulations with first-principles parameters, we can directly simulate the graphene growth process and thus understand the growth mechanisms. Our simulations suggest that the carbon dimer is the dominant feeding species in the epitaxial growth of graphene on both Cu(111) and Cu(100) surfaces, which enables us to understand why the reaction is diffusion limited on Cu(111) but attachment limited on Cu(100). When hydrogen is explicitly considered in the simulation, the central role hydrogen plays in graphene growth is revealed, which solves the long-standing puzzle into why H 2 should be fed in the chemical vapor deposition of graphene. The simulation results can be directly compared with the experimental kinetic data, if available. Our kMC simulations reproduce the experimentally observed quintic-like behavior of graphene growth on Ir(111). By checking the simulation results, we find that such nonlinearity is caused by lattice mismatch, and the induced growth front inhomogeneity can be universally used to predict growth behaviors in other heteroepitaxial systems. Notably, although experimental kinetics usually gives useful insight into atomic mechanisms, it can sometimes be misleading. Such pitfalls can be avoided via atomistic simulations, as demonstrated in our study of the graphene etching process. Growth protocols can be designed theoretically with computational kinetic and mechanistic information. By contrasting the different activation energies involved in an atom-exchange-based carbon penetration process for monolayer and bilayer graphene, we propose a three-step strategy to grow high-quality bilayer graphene. Based on first-principles parameters, a kinetic pathway toward the high-density, ordered N doping of epitaxial graphene on Cu(111) using a C 5 NCl 5 precursor is also identified. These studies demonstrate that atomistic simulations can unambiguously produce or reproduce the kinetic information on graphene growth, which is pivotal to understanding the growth mechanism and designing better growth protocols. A similar strategy can be used in growth mechanism studies of other two-dimensional atomic crystals.

Fish scale terrace GaInN/GaN light-emitting diodes with enhanced light extraction

NASA Astrophysics Data System (ADS)

Stark, Christoph J. M.; Detchprohm, Theeradetch; Zhao, Liang; Paskova, Tanya; Preble, Edward A.; Wetzel, Christian

2012-12-01

Non-planar GaInN/GaN light-emitting diodes were epitaxially grown to exhibit steps for enhanced light emission. By means of a large off-cut of the epitaxial growth plane from the c-plane (0.06° to 2.24°), surface morphologies of steps and inclined terraces that resemble fish scale patterns could controllably be achieved. These patterns penetrate the active region without deteriorating the electrical device performance. We find conditions leading to a large increase in light-output power over the virtually on-axis device and over planar sapphire references. The process is found suitable to enhance light extraction even without post-growth processing.

Coupling of Spinosad Fermentation and Separation Process via Two-Step Macroporous Resin Adsorption Method.

PubMed

Zhao, Fanglong; Zhang, Chuanbo; Yin, Jing; Shen, Yueqi; Lu, Wenyu

2015-08-01

In this paper, a two-step resin adsorption technology was investigated for spinosad production and separation as follows: the first step resin addition into the fermentor at early cultivation period to decrease the timely product concentration in the broth; the second step of resin addition was used after fermentation to adsorb and extract the spinosad. Based on this, a two-step macroporous resin adsorption-membrane separation process for spinosad fermentation, separation, and purification was established. Spinosad concentration in 5-L fermentor increased by 14.45 % after adding 50 g/L macroporous at the beginning of fermentation. The established two-step macroporous resin adsorption-membrane separation process got the 95.43 % purity and 87 % yield for spinosad, which were both higher than that of the conventional crystallization of spinosad from aqueous phase that were 93.23 and 79.15 % separately. The two-step macroporous resin adsorption method has not only carried out the coupling of spinosad fermentation and separation but also increased spinosad productivity. In addition, the two-step macroporous resin adsorption-membrane separation process performs better in spinosad yield and purity.

Differential Actions of the Endocytic Collagen Receptor uPARAP/Endo180 and the Collagenase MMP-2 in Bone Homeostasis

PubMed Central

Madsen, Daniel H.; Jürgensen, Henrik J.; Ingvarsen, Signe; Melander, Maria C.; Albrechtsen, Reidar; Hald, Andreas; Holmbeck, Kenn; Bugge, Thomas H.; Behrendt, Niels; Engelholm, Lars H.

2013-01-01

A well-coordinated remodeling of uncalcified collagen matrices is a pre-requisite for bone development and homeostasis. Collagen turnover proceeds through different pathways, either involving extracellular reactions exclusively, or being dependent on endocytic processes. Extracellular collagen degradation requires the action of secreted or membrane attached collagenolytic proteases, whereas the alternative collagen degradation pathway proceeds intracellularly after receptor-mediated uptake and delivery to the lysosomes. In this study we have examined the functional interplay between the extracellular collagenase, MMP-2, and the endocytic collagen receptor, uPARAP, by generating mice with combined deficiency of both components. In both uPARAP-deficient and MMP-2-deficient adult mice the length of the tibia and femur was decreased, along with a reduced bone mineral density and trabecular bone quality. An additional decrease in bone length was observed when combining the two deficiencies, pointing to both components being important for the remodeling processes in long bone growth. In agreement with results found by others, a different effect of MMP-2 deficiency was observed in the distinct bone structures of the calvaria. These membranous bones were found to be thickened in MMP-2-deficient mice, an effect likely to be related to an accompanying defect in the canalicular system. Surprisingly, both of the latter defects in MMP-2-deficient mice were counteracted by concurrent uPARAP deficiency, demonstrating that the collagen receptor does not support the same matrix remodeling processes as the MMP in the growth of the skull. We conclude that both uPARAP and MMP-2 take part in matrix turnover processes important for bone growth. However, in some physiological situations, these two components do not support the same step in the growth process. PMID:23940733

Monte Carlo grain growth modeling with local temperature gradients

NASA Astrophysics Data System (ADS)

Tan, Y.; Maniatty, A. M.; Zheng, C.; Wen, J. T.

2017-09-01

This work investigated the development of a Monte Carlo (MC) simulation approach to modeling grain growth in the presence of non-uniform temperature field that may vary with time. We first scale the MC model to physical growth processes by fitting experimental data. Based on the scaling relationship, we derive a grid site selection probability (SSP) function to consider the effect of a spatially varying temperature field. The SSP function is based on the differential MC step, which allows it to naturally consider time varying temperature fields too. We verify the model and compare the predictions to other existing formulations (Godfrey and Martin 1995 Phil. Mag. A 72 737-49 Radhakrishnan and Zacharia 1995 Metall. Mater. Trans. A 26 2123-30) in simple two-dimensional cases with only spatially varying temperature fields, where the predicted grain growth in regions of constant temperature are expected to be the same as for the isothermal case. We also test the model in a more realistic three-dimensional case with a temperature field varying in both space and time, modeling grain growth in the heat affected zone of a weld. We believe the newly proposed approach is promising for modeling grain growth in material manufacturing processes that involves time-dependent local temperature gradient.

Tying Resource Allocation and TQM into Planning and Assessment Efforts.

ERIC Educational Resources Information Center

Mullendore, Richard H.; Wang, Li-Shing

1996-01-01

Describes the evolution of a model, developed by student affairs officials, which outlines a planning process for implementing Total Quality Management. Presents step-by-step instructions for the model's deployment and discusses such issues as transitions, planning forms, goals, and professional and personal growth needs. (RJM)

Nucleation and growth of a bacterial functional amyloid at single fiber resolution

PubMed Central

Feuillie, Cécile; Jonckheere, Wim; Valotteau, Claire; Dufrêne, Yves F.; Remaut, Han

2017-01-01

Curli are functional amyloids produced by proteobacteria like Escherichia coli, as part of the extracellular matrix that holds cells together into biofilms. The molecular events during curli nucleation and fiber extension remain largely unknown. Combining observations from curli amyloidogenesis in bulk solutions with real-time in situ nanoscopic imaging at the single fiber level, we show that curli display polar growth, and detect two kinetic regimes of fiber elongation. Single fibers exhibit stop-and-go dynamics characterized by bursts of steady-state growth alternated with periods of stagnation. At high subunit concentrations fibers show constant, unperturbed burst growth. Curli follow a one-step nucleation process, where monomers contemporaneously fold and oligomerize into minimal fiber units that have growth characteristics identical to the mature fibrils. Kinetic data and interaction studies of curli fibrillation in the presence of the natural inhibitor CsgC show the inhibitor binds curli fibers and predominantly acts at the level of fiber elongation. PMID:28628096

Incorporation of water-in-oil-in-water (W1/O/W2) double emulsion in a set-type yogurt model.

PubMed

Lalou, Sofia; Kadri, Hani El; Gkatzionis, Konstantinos

2017-10-01

The effect of W 1 /O/W 2 emulsion incorporation in set-type yogurt on the acidification process, physicochemical properties, bacterial growth kinetics and structural characteristics was investigated. The W 1 /O/W 2 emulsion was formed by using a two-step homogenisation process and milk as the W 1 and W 2 phases, and stability was monitored with optical microscopy and cryo-SEM. Adding the W 1 /O/W 2 emulsions reduced the acidification rate, viscosity and water retention capacity. Texture (adhesiveness, cohesiveness, hardness, and gumminess) differed in yogurts containing W 1 /O/W 2 emulsion compared to controls during the acidification process, however, trends became stable during storage. The growth of S. thermophilus during the acidification process of yogurt was reduced in the presence of W 1 /O/W 2 emulsion while L. bulgaricus trended higher during storage. This study shows that yogurts containing W 1 /O/W 2 emulsion are feasible subject to processing modification. Copyright © 2017 Elsevier Ltd. All rights reserved.

Atomically Flat Surfaces Developed for Improved Semiconductor Devices

NASA Technical Reports Server (NTRS)

Powell, J. Anthony

2001-01-01

New wide bandgap semiconductor materials are being developed to meet the diverse high temperature, -power, and -frequency demands of the aerospace industry. Two of the most promising emerging materials are silicon carbide (SiC) for high-temperature and high power applications and gallium nitride (GaN) for high-frequency and optical (blue-light-emitting diodes and lasers) applications. This past year Glenn scientists implemented a NASA-patented crystal growth process for producing arrays of device-size mesas whose tops are atomically flat (i.e., step-free). It is expected that these mesas can be used for fabricating SiC and GaN devices with major improvements in performance and lifetime. The promising new SiC and GaN devices are fabricated in thin-crystal films (known as epi films) that are grown on commercial single-crystal SiC wafers. At this time, no commercial GaN wafers exist. Crystal defects, known as screw defects and micropipes, that are present in the commercial SiC wafers propagate into the epi films and degrade the performance and lifetime of subsequently fabricated devices. The new technology isolates the screw defects in a small percentage of small device-size mesas on the surface of commercial SiC wafers. This enables atomically flat surfaces to be grown on the remaining defect-free mesas. We believe that the atomically flat mesas can also be used to grow GaN epi films with a much lower defect density than in the GaN epi films currently being grown. Much improved devices are expected from these improved low-defect epi films. Surface-sensitive SiC devices such as Schottky diodes and field effect transistors should benefit from atomically flat substrates. Also, we believe that the atomically flat SiC surface will be an ideal surface on which to fabricate nanoscale sensors and devices. The process for achieving atomically flat surfaces is illustrated. The surface steps present on the "as-received" commercial SiC wafer is also illustrated. because of the small tilt angle between the crystal "basal" plane and the polished wafer surface. These steps are used in normal SiC epi film growth in a process known as stepflow growth to produce material for device fabrication. In the new process, the first step is to etch an array of mesas on the SiC wafer top surface. Then, epi film growth is carried out in the step flow fashion until all steps have grown themselves out of existence on each defect-free mesa. If the size of the mesas is sufficiently small (about 0.1 by 0.1 mm), then only a small percentage of the mesas will contain an undesired screw defect. Mesas with screw defects supply steps during the growth process, allowing a rough surface with unwanted hillocks to form on the mesa. The improvement in SiC epi surface morphology achievable with the new technology is shown. An atomic force microscope image of a typical SiC commercial epilayer surface is also shown. A similar image of an SiC atomically flat epi surface grown in a Glenn laboratory is given. With the current screw defect density of commercial wafers (about 5000 defects/cm2), the yield of atomically free 0.1 by 0.l mm mesas is expected to be about 90 percent. This is large enough for many types of electronic and optical devices. The implementation of this new technology was recently published in Applied Physics Letters. This work was initially carried out in-house under a Director's Discretionary Fund project and is currently being further developed under the Information Technology Base Program.

Efficient suppression of nanograss during porous anodic TiO2 nanotubes growth

NASA Astrophysics Data System (ADS)

Gui, Qunfang; Yu, Dongliang; Li, Dongdong; Song, Ye; Zhu, Xufei; Cao, Liu; Zhang, Shaoyu; Ma, Weihua; You, Shiyu

2014-09-01

When Ti foil was anodized in fluoride-containing electrolyte for a long time, undesired etching-induced "nanograss" would inevitably generate on the top of porous anodic TiO2 nanotubes (PATNTs). The nanograss will hinder the ions transport and in turn yield depressed (photo) electrochemical performance. In order to obtain nanograss-free nanotubes, a modified three-step anodization and two-layer nanostructure of PATNTs were designed to avoid the nanograss. The first layer (L1) nanotubes were obtained by the conventional two-step anodization. After washing and drying processes, the third-step anodization was carried out with the presence of L1 nanotubes. The L1 nanotubes, serving as a sacrificed layer, was etched and transformed into nanograss, while the ultralong nanotubes (L2) were maintained underneath the L1. The bi-layer nanostructure of the nanograss/nanotubes (L1/L2) was then ultrasonically rinsed in deionized water to remove the nanograss (L1 layer). Then much longer nanotubes (L2 layer) with intact nanotube mouths could be obtained. Using this novel approach, the ultralong nanotubes without nanograss can be rationally controlled by adjusting the anodizing times of two layers.

An integrated biodesulfurization process, including inoculum preparation, desulfurization and sulfate removal in a single step, for removing sulfur from oils.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tangaromsuk, Jantana; Borole, Abhijeet P; Kruatrachue, Maleeya

2008-01-01

BACKGROUND: A single-stage reactor, in which the growth of bacterial culture, induction of desulfurizing enzymes, and desulfurization reaction are carried out in a single step, was adopted to investigate desulfurization of DBT at high cell densities. IGTS8 was used as the biocatalyst. Optimal condition for the bacterial growth and DBT desulfurization were also investigated. RESULTS: Optimization of fermentation conditions was necessary to obtain high cell densities including controlling accumulation of acetate. Under optimal operating conditions, the maximum OD600 was measured to be 26.6 at 118 h of cultivation. When biodesulfurization of DBT in model oil with a high cell densitymore » culture of IGTS8 was investigated, accumulation of sulfate was found to limit the extent of desulfurization. A sulfate removal step was added to obtain a single-stage integrated biodesulfurization process. Sulfate removal was achieved via an aqueous bleed stream and use of a separation unit to recycle the organic phase. CONCLUSION : A proof of principle of a complete system capable of biocatalyst growth, induction, desulfurization and by-product separation was demonstrated. This system enables simplification of the biodesulfurization process and has potential to lower the operating cost of the bioprocess.« less

Cross-Linking Studies of Lysozyme Nucleation

NASA Technical Reports Server (NTRS)

Forsythe, Elizabeth; Pusey, Marc

2000-01-01

Tetragonal chicken egg white crystals consist of 4(sub 3) helices running in alternating directions, the helix rows having a two fold symmetry with each other. The unit cell consists of one complete tetrameric turn from each of two adjacent helices (an octamer). PBC analysis indicates that the helix intermolecular bonds are the strongest in the crystal, therefore likely formed first. AFM analysis of the (110) surface shows only complete helices, no half steps or bisected helices being found, while AFM line scans to measure the growth step increments show that they are multiples of the 4(sub 3) helix tetramer dimensions. This supports our thesis that the growth units are in fact multiples of the four molecule 4(sub 3) helix unit, the "average" growth unit size for the (110) face being an octamer (two turns about the helix) and the (101) growth unit averaging about the size of a hexamer. In an effort to better understand the species involved in the crystal nucleation and growth process, we have initiated an experimental program to study the species formed in solution compared to what is found in the crystal through covalent cross-linking studies. These experiments use the heterobifunctional cross-linking agent aminoethyl-4-azidonitroanaline (AEANA). An aliphatic amine at one end is covalently attached to the protein by a carbodiimide-mediated reaction, and a photo reactive group at the other can be used to initiate crosslinking. Modifications to the parent structure can be used to alter the distance between the two reactive groups and thus the cross-linking agents "reach". In practice, the cross-linking agent is first coupled to the asp101 side chain through the amine group. Asp101 lies within the active site cleft, and previous work with fluorescent probes had shown that derivatives at this site still crystallize in the tetragonal space group. This was also found to be the case with the AEANA derivative, which gave red tetragonal crystals. The protein now has a reactive group that can be photoactivated at a specific point in the nucleation or crystal growth process to "capture" protein molecules bound within reach of the crosslinking agent. If those bound protein molecules have a defined geometric relationship with the capturing molecule, such as would be found in a crystal, then the photoreacted cross-linking site should be consistent. Random protein interactions, typical of an amorphous precipitate or interaction, would show a random cross-linking reaction. The results of these and other experiments will be presented.

Optimization of experimental conditions for the monitoring of nucleation and growth of racemic Diprophylline from the supercooled melt

NASA Astrophysics Data System (ADS)

Lemercier, Aurélien; Viel, Quentin; Brandel, Clément; Cartigny, Yohann; Dargent, Eric; Petit, Samuel; Coquerel, Gérard

2017-08-01

Since more and more pharmaceutical substances are developed as amorphous forms, it is nowadays of major relevance to get insights into the nucleation and growth mechanisms from supercooled melts (SCM). A step-by-step approach of recrystallization from a SCM is presented here, designed to elucidate the impact of various experimental parameters. Using the bronchodilator agent Diprophylline (DPL) as a model compound, it is shown that optimal conditions for informative observations of the crystallization behaviour from supercooled racemic DPL require to place samples between two cover slides with a maximum sample thickness of 20 μm, and to monitor recrystallization during an annealing step of 30 min at 70 °C, i.e. about 33 °C above the temperature of glass transition. In these optimized conditions, it could be established that DPL crystallization proceeds in two steps: spontaneous nucleation and growth of large and well-faceted particles of a new crystal form (primary crystals: PC) and subsequent crystallization of a previously known form (RII) that develops from specific surfaces of PC. The formation of PC particles therefore constitutes the key-step of the crystallization events and is shown to be favoured by at least 2.33 wt% of the major chemical impurity, Theophylline.

Facilitating a More Efficient Commercial Review Process for Pediatric Drugs and Biologics

PubMed Central

Rykhus, Ryan D.; Shepard, Zachary V.; Young, Alix; Frisby, Hadley; Calder, Kailee A.; Coon, Collin M.; Falk, Justin A.; McAndrews, Sydney R.; Turner, Aspen; Chang, Christina; Michelsohn, Johanna; Petch, Raegan; Dieker, Sarah M.; Markworth, Benjamin H.; Alamo-Perez, Kevin; Hosack, Aaron J.; Berg, Jacob M.; Schmidt, Christian; Storsberg, Joachim; Brown, Mark A.

Over the past two decades, the biopharmaceutical industry has seen unprecedented expansion and innovation in concert with significant technological advancements. While the industry has experienced marked growth, the regulatory system in the United States still operates at a capacity much lower than the influx of new drug and biologic candidates. As a result, it has become standard for months or even years of waiting for commercial approval by the U.S. Food and Drug Administration. These regulatory delays have generated a system that stifles growth and innovation due to the exorbitant costs associated with awaiting approval from the nation’s sole regulatory agency. The recent re-emergence of diseases that impact pediatric demographics represents one particularly acute reason for developing a regulatory system that facilitates a more efficient commercial review process. Herein, we present a range of initiatives that could represent early steps toward alleviating the delays in approving life-saving therapeutics. PMID:29271878

Surface studies relevant to silicon carbide chemical vapor deposition

NASA Technical Reports Server (NTRS)

Stinespring, C. D.; Wormhoudt, J. C.

1989-01-01

Reactions of C2H4, C3H8, and CH4 on the Si(111) surface and C2H4 on the Si(100) surface were investigated for surface temperatures in the range of 1062-1495 K. Results led to the identification of the reaction products, a characterization of the solid-state transport process, a determination of the nucleation mechanism and growth kinetics, and an assessment of orientation effects. Based on these results and on the modeling studies of Stinespring and Wormhoudt (1988) on the associated gas phase chemistry, a physical model for the two-step beta-SiC CVD process is proposed.

Experimental simulation and morphological quantification of volcano growth

NASA Astrophysics Data System (ADS)

Grosse, Pablo; Kervyn, Matthieu; Gallland, Olivier; Delcamp, Audray; Poppe, Sam

2016-04-01

Volcanoes display very diverse morphologies as a result of a complex interplay of several constructive and destructive processes. Here the role played by the spatial distribution of eruption centre and by an underlying strike-slip fault in controlling the long term growth of volcanoes is investigated with analogue models. Volcano growth was simulated by depositing loads of granular material (sand-kaolin mixtures) from a point source. An individual load deposited at a fixed location produces a simple symmetrical cone with flank slopes at the angle of repose of the granular material (~33°) that can be considered as the building-block for the experiments. Two sets of experiments were undertaken: (1) the location of deposition of the granular material (i.e. the volcano growth location) was shifted with time following specific probability density functions simulating shifts or migrations in vent location; (2) the location of deposition was kept fixed, but the deposition rate (i.e. the volcano growth rate) was varied coupled with the movement of a basal plate attached to a step-motor simulating a strike-slip displacement under the growing cone (and hence deformation of the cone). During the progression of the experiments, the models were photographed at regular time intervals using four digital cameras positioned at slightly different angles over the models. The photographs were used to generate synthetic digital elevation models (DEMs) with 0.2 mm spatial resolution of each step of the models by applying the MICMAC digital stereo-photogrammetry software. Morphometric data were extracted from the DEMs by applying two IDL-language algorithms: NETVOLC, used to automatically calculate the volcano edifice basal outline, and MORVOLC, used to extract a set of morphometric parameters that characterize the volcano edifice in terms of size, plan shape, profile shape and slopes. Analysis of the DEM-derived morphometric parameters allows to quantitatively characterize the growth evolution of the volcano models in terms of vent distribution and growth rate-deformation rate ratios.

Effect of starting powders on the sintering of nanostructured ZrO2 ceramics by colloidal processing

NASA Astrophysics Data System (ADS)

Suárez, Gustavo; Sakka, Yoshio; Suzuki, Tohru S.; Uchikoshi, Tetsuo; Zhu, Xinwen; Aglietti, Esteban F.

2009-04-01

The effect of starting powders on the sintering of nanostructured tetragonal zirconia was evaluated. Suspensions were prepared with a concentration of 10 vol.% by mixing a bicomponent mixture of commercial powders (97 mol.% monoclinic zirconia with 3 mol.% yttria) and by dispersing commercially available tetragonal zirconia (3YTZ, Tosoh). The preparation of the slurry by bead-milling was optimized. Colloidal processing using 50 μm zirconia beads at 4000 rpm generated a fully deagglomerated suspension leading to the formation of high-density consolidated compacts (62% of the theoretical density (TD) for the bicomponent suspension). Optimum colloidal processing of the bicomponent suspension followed by the sintering of yttria and zirconia allowed us to obtain nanostructured tetragonal zirconia. Three different sintering techniques were investigated: normal sintering, two-step sintering and spark plasma sintering. The inhibition of grain growth in the bicomponent mixed powders in comparison with 3YTZ was demonstrated. The inhibition of the grain growth may have been caused by inter-diffusion of cations during the sintering.

Intracellular processing of epidermal growth factor. I. Acidification of 125I-epidermal growth factor in intracellular organelles.

PubMed

Matrisian, L M; Planck, S R; Magun, B E

1984-03-10

We previously reported that 125I-labeled epidermal growth factor is processed intracellularly to acidic macromolecules in Rat-1 fibroblasts. The present study defines the precursor-product relationship and localization of the processing steps to subcellular organelles by the use of a single isoelectric species of 125I-epidermal growth factor and Percoll gradient fractionation. The native pI 4.55 125I-epidermal growth factor was rapidly processed to a pI 4.2 species on or near the cell surface and in organelles corresponding to clathrin-coated vesicles, Golgi, and endoplasmic reticulum. This species was then processed to a pI 4.35 species in similar organelles. The pI 4.2 and 4.35 species were converted to a pI 4.0 species in dense, lysosome-like organelles. This species was ultimately degraded and exocytosed from the cell as low molecular weight products.

Growth of group II-VI semiconductor quantum dots with strong quantum confinement and low size dispersion

NASA Astrophysics Data System (ADS)

Pandey, Praveen K.; Sharma, Kriti; Nagpal, Swati; Bhatnagar, P. K.; Mathur, P. C.

2003-11-01

CdTe quantum dots embedded in glass matrix are grown using two-step annealing method. The results for the optical transmission characterization are analysed and compared with the results obtained from CdTe quantum dots grown using conventional single-step annealing method. A theoretical model for the absorption spectra is used to quantitatively estimate the size dispersion in the two cases. In the present work, it is established that the quantum dots grown using two-step annealing method have stronger quantum confinement, reduced size dispersion and higher volume ratio as compared to the single-step annealed samples. (

Defect mediated van der Waals epitaxy of hexagonal boron nitride on graphene

NASA Astrophysics Data System (ADS)

Heilmann, M.; Bashouti, M.; Riechert, H.; Lopes, J. M. J.

2018-04-01

Van der Waals heterostructures comprising of hexagonal boron nitride and graphene are promising building blocks for novel two-dimensional devices such as atomically thin transistors or capacitors. However, demonstrators of those devices have been so far mostly fabricated by mechanical assembly, a non-scalable and time-consuming method, where transfer processes can contaminate the surfaces. Here, we investigate a direct growth process for the fabrication of insulating hexagonal boron nitride on high quality epitaxial graphene using plasma assisted molecular beam epitaxy. Samples were grown at varying temperatures and times and studied using atomic force microscopy, revealing a growth process limited by desorption at high temperatures. Nucleation was mostly commencing from morphological defects in epitaxial graphene, such as step edges or wrinkles. Raman spectroscopy combined with x-ray photoelectron measurements confirm the formation of hexagonal boron nitride and prove the resilience of graphene against the nitrogen plasma used during the growth process. The electrical properties and defects in the heterostructures were studied with high lateral resolution by tunneling current and Kelvin probe force measurements. This correlated approach revealed a nucleation apart from morphological defects in epitaxial graphene, which is mediated by point defects. The presented results help understanding the nucleation and growth behavior during van der Waals epitaxy of 2D materials, and point out a route for a scalable production of van der Waals heterostructures.

Processing of zero-derived words in English: an fMRI investigation.

PubMed

Pliatsikas, Christos; Wheeldon, Linda; Lahiri, Aditi; Hansen, Peter C

2014-01-01

Derivational morphological processes allow us to create new words (e.g. punish (V) to noun (N) punishment) from base forms. The number of steps from the basic units to derived words often varies (e.g., nationalitybridge-V) i.e., zero-derivation (Aronoff, 1980). We compared the processing of one-step (soaking

Effect of TiO2 Addition on Grain Growth, Anodic Bubble Evolution and Anodic Overvoltage of NiFe2O4-Based Composite Inert Anodes

NASA Astrophysics Data System (ADS)

Wang, Bin; Du, Jinjing; Liu, Yihan; Fang, Zhao; Hu, Ping

2017-11-01

A two-step powder compaction and sintering process was employed to fabricate TiO2-doped NiFe2O4 ceramic-based inert anodes. Grain growth during isothermal sintering was analyzed using Brook grain growth model. The bubble behavior of NiFe2O4 ceramic-based inert anodes was investigated in a two-compartment see-through quartz cell for aluminum electrolysis process. Anodic overvoltage and potential decay curves of the inert anodes were measured by using the steady state and current interruption technique. The results showed that the kinetic index of grain growth decreased with an increase in temperature. The average activation energy of grain growth for 1.0 wt.% TiO2-doped NiFe2O4 ceramic samples with a sintering temperature range from 1373 to 1673 K dropped from 675.30 to 183.47 kJ/mol. The diameter size of bubbles before releasing from the bottom surface of the anodes was reduced with increasing the current density, and the larger average releasing bubble size for carbon anode at the same current density could be obtained, which was compared to the NiFe2O4 inert anodes. Besides, the cell voltage of carbon anodes fluctuated much more violently under the same experimental conditions. After adding small amount of TiO2, a minor reduction in anodic overvoltage of NiFe2O4-based anodes can be observed.

A drift-diffusion checkpoint model predicts a highly variable and growth-factor-sensitive portion of the cell cycle G1 phase.

PubMed

Jones, Zack W; Leander, Rachel; Quaranta, Vito; Harris, Leonard A; Tyson, Darren R

2018-01-01

Even among isogenic cells, the time to progress through the cell cycle, or the intermitotic time (IMT), is highly variable. This variability has been a topic of research for several decades and numerous mathematical models have been proposed to explain it. Previously, we developed a top-down, stochastic drift-diffusion+threshold (DDT) model of a cell cycle checkpoint and showed that it can accurately describe experimentally-derived IMT distributions [Leander R, Allen EJ, Garbett SP, Tyson DR, Quaranta V. Derivation and experimental comparison of cell-division probability densities. J. Theor. Biol. 2014;358:129-135]. Here, we use the DDT modeling approach for both descriptive and predictive data analysis. We develop a custom numerical method for the reliable maximum likelihood estimation of model parameters in the absence of a priori knowledge about the number of detectable checkpoints. We employ this method to fit different variants of the DDT model (with one, two, and three checkpoints) to IMT data from multiple cell lines under different growth conditions and drug treatments. We find that a two-checkpoint model best describes the data, consistent with the notion that the cell cycle can be broadly separated into two steps: the commitment to divide and the process of cell division. The model predicts one part of the cell cycle to be highly variable and growth factor sensitive while the other is less variable and relatively refractory to growth factor signaling. Using experimental data that separates IMT into G1 vs. S, G2, and M phases, we show that the model-predicted growth-factor-sensitive part of the cell cycle corresponds to a portion of G1, consistent with previous studies suggesting that the commitment step is the primary source of IMT variability. These results demonstrate that a simple stochastic model, with just a handful of parameters, can provide fundamental insights into the biological underpinnings of cell cycle progression.

Nonlinear Response of Layer Growth Dynamics in the Mixed Kinetics-Bulk-Transport Regime

NASA Technical Reports Server (NTRS)

Vekilov, Peter G.; Alexander, J. Iwan D.; Rosenberger, Franz

1996-01-01

In situ high-resolution interferometry on horizontal facets of the protein lysozyme reveal that the local growth rate R, vicinal slope p, and tangential (step) velocity v fluctuate by up to 80% of their average values. The time scale of these fluctuations, which occur under steady bulk transport conditions through the formation and decay of step bunches (macrosteps), is of the order of 10 min. The fluctuation amplitude of R increases with growth rate (supersaturation) and crystal size, while the amplitude of the v and p fluctuations changes relatively little. Based on a stability analysis for equidistant step trains in the mixed transport-interface-kinetics regime, we argue that the fluctuations originate from the coupling of bulk transport with nonlinear interface kinetics. Furthermore, step bunches moving across the interface in the direction of or opposite to the buoyancy-driven convective flow increase or decrease in height, respectively. This is in agreement with analytical treatments of the interaction of moving steps with solution flow. Major excursions in growth rate are associated with the formation of lattice defects (striations). We show that, in general, the system-dependent kinetic Peclet number, Pe(sub k) , i.e., the relative weight of bulk transport and interface kinetics in the control of the growth process, governs the step bunching dynamics. Since Pe(sub k) can be modified by either forced solution flow or suppression of buoyancy-driven convection under reduced gravity, this model provides a rationale for the choice of specific transport conditions to minimize the formation of compositional inhomogeneities under steady bulk nutrient crystallization conditions.

Design and development of SiGe based near-infrared photodetectors

NASA Astrophysics Data System (ADS)

Zeller, John W.; Puri, Yash R.; Sood, Ashok K.; McMahon, Shane; Efsthadiatis, Harry; Haldar, Pradeep; Dhar, Nibir K.

2014-10-01

Near-infrared (NIR) sensors operating at room temperatures are critical for a variety of commercial and military applications including detecting mortar fire and muzzle flashes. SiGe technology offers a low-cost alternative to conventional IR sensor technologies such as InGaAs, InSb, and HgCdTe for developing NIR micro-sensors that will not require any cooling and can operate with high bandwidths and comparatively low dark currents. Since Ge has a larger thermal expansion coefficient than Si, tensile strain may be incorporated into detector devices during the growth process, enabling an extended operating wavelength range above 1600 nm. SiGe based pin photodetectors have advantages of high stability, low noise, and high responsivity compared to metal-semiconductor-metal (MSM) devices. We have developed a process flow and are fabricating SiGe detector devices on 12" (300 mm) silicon wafers in order to take advantage of high throughput, large-area leading-edge silicon based CMOS technology that provides small feature sizes with associated device cost/density scaling advantages. The fabrication of the detector devices is facilitated by a two-step growth process incorporating initial low temperature growth of Ge/SiGe to form a thin strain-relaxed layer, followed by high temperature growth to deposit a thicker absorbing film, and subsequent high temperature anneal. This growth process is designed to effectively reduce dark current and enhance detector performance by reducing the number of defects and threading dislocations which form recombination centers during the growth process. Various characterization techniques have been employed to determine the properties of the epitaxially deposited Ge/SiGe layers, and the corresponding results are discussed.

Early and transient stages of Cu oxidation: Atomistic insights from theoretical simulations and in situ experiments

NASA Astrophysics Data System (ADS)

Zhu, Qing; Zou, Lianfeng; Zhou, Guangwen; Saidi, Wissam A.; Yang, Judith C.

2016-10-01

Understanding of metal oxidation is critical to corrosion control, catalysis synthesis, and advanced materials engineering. Although, metal oxidation process is rather complicated, different processes, many of them coupled, are involved from the onset of reaction. Since first introduced, there has been great success in applying heteroepitaxial theory to the oxide growth on a metal surface as demonstrated in the Cu oxidation experiments. In this paper, we review the recent progress in experimental findings on Cu oxidation as well as the advances in the theoretical simulations of the Cu oxidation process. We focus on the effects of defects such as step edges, present on realistic metal surfaces, on the oxide growth dynamics. We show that the surface steps can change the mass transport of both Cu and O atoms during oxide growth, and ultimately lead to the formation of different oxide morphology. We also review the oxidation of Cu alloys and explore the effect of a secondary element to the oxide growth on a Cu surface. From the review of the work on Cu oxidation, we demonstrate the correlation of theoretical simulations at multiple scales with various experimental techniques.

Dual-step synthesis of 3-dimensional niobium oxide - Zinc oxide

NASA Astrophysics Data System (ADS)

Rani, Rozina Abdul; Zoolfakar, Ahmad Sabirin; Rusop, M.

2018-05-01

A facile fabrication process for constructing 3-dimensional (3D) structure of Niobium oxide - Zinc oxide (Nb2O5-ZnO) consisting of branched ZnO microrods on top of nanoporous Nb2O5 films was developed based on dual-step synthesis approach. The preliminary procedure was anodization of sputtered niobium metal on Fluorine doped Tin Oxide (FTO) to produce nanoporous Nb2O5, and continued with the growth of branched microrods of ZnO by hydrothermal process. This approach offers insight knowledge on the development of novel 3D metal oxide films via dual-step synthesis process, which might potentially use for multi-functional applications ranging from sensing to photoconversion.

The Effect of Surfactant and Compatibilizer on Inorganic Loading and Properties of PPO-based EPMM Membranes

NASA Astrophysics Data System (ADS)

Bissadi, Golnaz

Hybrid membranes represent a promising alternative to the limitations of organic and inorganic materials for high productivity and selectivity gas separation membranes. In this study, the previously developed concept of emulsion-polymerized mixed matrix (EPMM) membranes was further advanced by investigating the effects of surfactant and compatibilizer on inorganic loading in poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)-based EPMM membranes, in which inorganic part of the membranes originated from tetraethylorthosilicate (TEOS). The polymerization of TEOS, which consists of hydrolysis of TEOS and condensation of the hydrolyzed TEOS, was carried out as (i) one- and (ii) two-step processes. In the one-step process, the hydrolysis and condensation take place in the same environment of a weak acid provided by the aqueous solution of aluminum hydroxonitrate and sodium carbonate. In the two-step process, the hydrolysis takes place in the environment of a strong acid (solution of hydrochloric acid), whereas the condensation takes place in weak base environment obtained by adding excess of the ammonium hydroxide solution to the acidic solution of the hydrolyzed TEOS. For both one- and two-step processes, the emulsion polymerization of TEOS was carried out in two types of emulsions made of (i) pure trichloroethylene (TCE) solvent, and (ii) 10 w/v% solution of PPO in TCE, using different combinations of the compatibilizer (ethanol) and the surfactant (n-octanol). The experiments with pure TCE, which are referred to as a gravimetric powder method (GPM) allowed assessing the effect of different experimental parameters on the conversion of TEOS. The GPM tests also provided a guide for the synthesis of casting emulsions containing PPO, from which the EPMM membranes were prepared using a spin coating technique. The synthesized EPMM membranes were characterized using 29Si nuclear magnetic resonance (29Si NMR), differential scanning calorimetry (DSC), inductively coupled plasma mass spectrometry (ICP-MS), and gas permeation measurements carried out in a constant pressure (CP) system. The 29Si NMR analysis verified polymerization of TEOS in the emulsions made of pure TCE, and the PPO solution in TCE. The conversions of TEOS in the two-step process in the two types of emulsions were very close to each other. In the case of the one-step process, the conversions in the TCE emulsion were significantly greater than those in the emulsion of the PPO solution in TCE. Consequently, the conversions of TEOS in the EPMM membranes made in the two-step process were greater than those in the EPMM membranes made in the one-step process. The latter ranged between 10 - 20%, while the highest conversion in the two-step process was 74% in the presence of pure compatibilizer with no surfactant. Despite greater conversions and hence the greater inorganic loadings, the EPMM membranes prepared in the two-step process had glass transition temperatures (Tg) only slightly greater than the reference PPO membranes. In contrast, despite relatively low inorganic loadings, the EPMM membranes prepared in the one-step process had Tgs markedly greater than PPO, and showed the expected trend of an increase in Tg with the inorganic loading. These results indicate that in the case of the one-step process the polymerized TEOS was well integrated with the PPO chains and the interactions between the two phases lead to high Tgs. On the other hand, this was not the case for the EPMM membranes prepared in the two-step process, suggesting possible phase separation between the polymerized TEOS and the organic phase. The latter was confirmed by detecting no selectivity in the EPMM membranes prepared by the two-step process. In contrast, the EPMM membranes prepared in the one-step process in the presence of the compatibilizer and no surfactant showed 50% greater O2 permeability coefficient and a slightly greater O2/N2 permeability ratio compared to the reference PPO membranes.

A reusable microfluidic plate with alternate-choice architecture for assessing growth preference in tissue culture.

PubMed

Wittig, John H; Ryan, Allen F; Asbeck, Peter M

2005-05-15

We present the design of a chamber to evaluate in vitro how species and concentrations of soluble molecules control features of cell growth-potentially including cell proliferation, cell motility, process extension, and process termination. We have created a reusable cell culture plate that integrates a microfluidic media delivery network with standard cell culture environment. The microfluidic network delivers a stream of cell culture media with a step-like concentration gradient down a 50-100 microm wide microchannel called the presentation region. Migrating cells or growing cell processes freely choose between the two distinct chemical environments in the presentation region, but they are forced to exclusively choose either one environment or the other when they grow past a physical barrier acting as a decision point. Our fabrication technique requires little specialized equipment, and can be carried out in approximately 4 days per plate. We demonstrate the effectiveness of our plates as neurites from spiral ganglion explants preferentially grow in media containing neurotrophin-3 (NT-3) as opposed to media without NT-3. Our design could be used without modification to study dissociated cell responses to soluble growth cues, and for behavioral screening of small motile organisms.

Patterned growth of carbon nanotubes on Si substrates without predeposition of metal catalysts

NASA Astrophysics Data System (ADS)

Chen, Y.; Yu, J.

2005-07-01

Aligned carbon nanotubes (CNTs) can be readily synthesized on quartz or silicon-oxide-coated Si substrates using a chemical vapor deposition method, but it is difficult to grow them on pure Si substrates without predeposition of metal catalysts. We report that aligned CNTs were grown by pyrolysis of iron phthalocyanine at 1000°C on the templates created on Si substrates with simple mechanical scratching. Scanning electron microscopy and x-ray energy spectroscopy analysis revealed that the trenches and patterns created on the surface of Si substrates were preferred nucleation sites for nanotube growth due to a high surface energy, metastable surface structure, and possible capillarity effect. A two-step pyrolysis process maintained Fe as an active catalyst.

Antagonism of Trichoderma harzianum ETS 323 on Botrytis cinerea mycelium in culture conditions.

PubMed

Cheng, Chi-Hua; Yang, Chia-Ann; Peng, Kou-Cheng

2012-11-01

ABSTRACT Previous studies have shown that the extracellular proteins of Trichoderma harzianum ETS 323 grown in the presence of deactivated Botrytis cinerea in culture include a putative l-amino acid oxidase and have suggested the involvement of this enzyme in the antagonistic mechanism. Here, we hypothesized that the mycoparasitic process of Trichoderma spp. against B. cinerea involves two steps; that is, an initial hyphal coiling stage and a subsequent hyphal coiling stage, with different coiling rates. The two-step antagonism of T. harzianum ETS 323 against B. cinerea during the mycoparasitic process in culture was evaluated using a biexponential equation. In addition, an l-amino acid oxidase (Th-l-AAO) was identified from T. harzianum ETS 323. The secretion of Th-l-AAO was increased when T. harzianum ETS 323 was grown with deactivated hyphae of B. cinerea. Moreover, in vitro assays indicated that Th-l-AAO effectively inhibited B. cinerea hyphal growth, caused cytosolic vacuolization in the hyphae, and led to hyphal lysis. Th-l-AAO also showed disease control against the development of B. cinerea on postharvest apple fruit and tobacco leaves. Furthermore, an apoptosis-like response, including the generation of reactive oxygen species, was observed in B. cinerea after treatment with Th-l-AAO, suggesting that Th-l-AAO triggers programmed cell death in B. cinerea. This may be associated with the two-step antagonism of T. harzianum ETS 323 against B. cinerea.

Role of boundary layer diffusion in vapor deposition growth of chalcogenide nanosheets: the case of GeS.

PubMed

Li, Chun; Huang, Liang; Snigdha, Gayatri Pongur; Yu, Yifei; Cao, Linyou

2012-10-23

We report a synthesis of single-crystalline two-dimensional GeS nanosheets using vapor deposition processes and show that the growth behavior of the nanosheet is substantially different from those of other nanomaterials and thin films grown by vapor depositions. The nanosheet growth is subject to strong influences of the diffusion of source materials through the boundary layer of gas flows. This boundary layer diffusion is found to be the rate-determining step of the growth under typical experimental conditions, evidenced by a substantial dependence of the nanosheet's size on diffusion fluxes. We also find that high-quality GeS nanosheets can grow only in the diffusion-limited regime, as the crystalline quality substantially deteriorates when the rate-determining step is changed away from the boundary layer diffusion. We establish a simple model to analyze the diffusion dynamics in experiments. Our analysis uncovers an intuitive correlation of diffusion flux with the partial pressure of source materials, the flow rate of carrier gas, and the total pressure in the synthetic setup. The observed significant role of boundary layer diffusions in the growth is unique for nanosheets. It may be correlated with the high growth rate of GeS nanosheets, ~3-5 μm/min, which is 1 order of magnitude higher than other nanomaterials (such as nanowires) and thin films. This fundamental understanding of the effect of boundary layer diffusions may generally apply to other chalcogenide nanosheets that can grow rapidly. It can provide useful guidance for the development of general paradigms to control the synthesis of nanosheets.

Apoptosis: its role in pituitary development and neoplastic pituitary tissue.

PubMed

Guzzo, M F; Carvalho, L R S; Bronstein, M D

2014-04-01

Apoptosis, also known as programmed cell death, is a phenomenon in which different stimuli trigger cellular mechanisms that culminate in death, in the absence of inflammatory cell response. Two different activation pathways are known, the intrinsic pathway (or mitochondrial) and extrinsic (or death-receptor pathway), both pathways trigger enzymatic reactions that lead cells to break up and be phagocytized by neighboring cells. This process is a common occurrence in physiological and pathological states, participating in the control of cell proliferation, differentiation and remodeling of organs. In the early steps of pituitary gland formation, numerous apoptotic cells are detected in the separation of Rathke's pouch from the roof of oral ectoderm. In the distal part of the gland, which will form the adenohypophysis, the ratio of apoptosis was significantly lower. However, there is evidence that neoplastic pituitary cells undergo unbalance in genes that control apoptosis leading to uncontrolled cell growth. No direct evidence of apoptosis was found in the drugs used for tumors producing prolactin and growth hormone. In conclusion, an unbalancing in the apoptosis process is the boundary between development and tumor growth.

Direct growth of freestanding GaN on C-face SiC by HVPE.

PubMed

Tian, Yuan; Shao, Yongliang; Wu, Yongzhong; Hao, Xiaopeng; Zhang, Lei; Dai, Yuanbin; Huo, Qin

2015-06-02

In this work, high quality GaN crystal was successfully grown on C-face 6H-SiC by HVPE using a two steps growth process. Due to the small interaction stress between the GaN and the SiC substrate, the GaN was self-separated from the SiC substrate even with a small thickness of about 100 μm. Moreover, the SiC substrate was excellent without damage after the whole process so that it can be repeatedly used in the GaN growth. Hot phosphoric acid etching (at 240 °C for 30 min) was employed to identify the polarity of the GaN layer. According to the etching results, the obtained layer was Ga-polar GaN. High-resolution X-ray diffraction (HRXRD) and electron backscatter diffraction (EBSD) were done to characterize the quality of the freestanding GaN. The Raman measurements showed that the freestanding GaN film grown on the C-face 6H-SiC was stress-free. The optical properties of the freestanding GaN layer were determined by photoluminescence (PL) spectra.

Nanoscale dissolution and growth on anhydrite cleavage faces

NASA Astrophysics Data System (ADS)

Pina, Carlos M.

2009-12-01

In situ atomic force microscopy (AFM) was used to study the molecular-scale reactivity of anhydrite (1 0 0), (0 1 0), and (0 0 1) faces exposed to water and CaSO 4 aqueous solutions at room temperature. In pure water, dissolution occurs by step retreat and etch pit nucleation and growth. Both the kinetics of the step retreat and the shape of the etch pits are surface-specific and crystallographically controlled. In CaSO 4 aqueous solutions with concentrations ranging from 0.030 mol/l to 0.075 mol/l, the growth kinetics on anhydrite (1 0 0) and (0 1 0) faces was studied. Growth is also strongly controlled by crystallographic constraints and occurs exclusively from pre-existing step edges by highly anisotropic spreading of monolayers (˜3.5 Å in height). The AFM observations demonstrate that monolayer growth can occur on anhydrite (0 1 0) and (1 0 0) faces even from slightly supersaturated solutions. In addition, the comparison of the step kinetics on anhydrite faces shows that the mechanisms of step dissolution and growth are essentially the same, with the direction of migration of crystal building units being reversed at the anhydrite saturation point. Moreover, the analysis of both high resolution AFM images and lateral force microscopy (LFM) images confirms that the newly-formed monolayers are anhydrite growing in structural continuity with the original (1 0 0) and (0 1 0) surfaces. However, the formation of the first monolayers is metastable and two-dimensional nucleation and further multilayer growth of anhydrite are strongly inhibited even at high supersaturations.

Laser-zone growth in a Ribbon-To-Ribbon (RTR) process. Silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project

NASA Technical Reports Server (NTRS)

Gurtler, R. W.; Baghdadi, A.; Legge, R.; Sopori, B.; Ellis, R. J.

1977-01-01

The Ribbon-to-Ribbon (RTR) approach to silicon ribbon growth is investigated. An existing RTR apparatus is to be upgraded to its full capabilities and operated routinely to investigate and optimize the effects of various growth parameters on growth results. A new RTR apparatus was constructed to incorporate increased capabilities and improvements over the first apparatus and to be capable of continuous growth. New high power lasers were implemented and this led to major improvements in growth velocity -- 4 inch/min. growth has been demonstrated. A major step in demonstration of the full feasibility of the RTR process is reported in the demonstration of RTR growth from CVD polyribbon rather than sliced polyribbon ingots. Average solar cell efficiencies of greater than 9% and a best cell efficiency of 11.7% are reported. Processing was shown to provide a substantial improvement in material minority carrier diffusion length. An economic analysis is reported which treats both the polyribbon fabrication and RTR processes.

Development and Application of a Two-Tier Diagnostic Test for High School Students' Understanding of Flowering Plant Growth and Development

ERIC Educational Resources Information Center

Lin, Sheau-Wen

2004-01-01

This study involved the development and application of a two-tier diagnostic test measuring students' understanding of flowering plant growth and development. The instrument development procedure had three general steps: defining the content boundaries of the test, collecting information on students' misconceptions, and instrument development.…

Growth temperature optimization of GaAs-based In0.83Ga0.17As on InxAl1-xAs buffers

NASA Astrophysics Data System (ADS)

Chen, X. Y.; Gu, Y.; Zhang, Y. G.; Ma, Y. J.; Du, B.; Zhang, J.; Ji, W. Y.; Shi, Y. H.; Zhu, Y.

2018-04-01

Improved quality of gas source molecular beam epitaxy grown In0.83Ga0.17As layer on GaAs substrate was achieved by adopting a two-step InxAl1-xAs metamorphic buffer at different temperatures. With a high-temperature In0.83Al0.17As template following a low-temperature composition continuously graded InxAl1-xAs (x = 0.05-0.86) buffer, better structural, optical and electrical properties of succeeding In0.83Ga0.17As were confirmed by atomic force microscopy, photoluminescence and Hall-effect measurements. Cross-sectional transmission electron microscopy revealed significant effect of the two-step temperature grown InAlAs buffer layers on the inhibition of threading dislocations due to the deposition of high density nuclei on GaAs substrate at the low growth temperature. The limited reduction for the dark current of GaAs-based In0.83Ga0.17As photodetectors on the two-step temperature grown InxAl1-xAs buffer layers was ascribed to the contribution of impurities caused by the low growth temperature of InAlAs buffers.

Correlation of surface site formation to nanoisland growth in the electrochemical roughening of Pt(111)

NASA Astrophysics Data System (ADS)

Jacobse, Leon; Huang, Yi-Fan; Koper, Marc T. M.; Rost, Marcel J.

2018-03-01

Platinum plays a central role in a variety of electrochemical devices and its practical use depends on the prevention of electrode degradation. However, understanding the underlying atomic processes under conditions of repeated oxidation and reduction inducing irreversible surface structure changes has proved challenging. Here, we examine the correlation between the evolution of the electrochemical signal of Pt(111) and its surface roughening by simultaneously performing cyclic voltammetry and in situ electrochemical scanning tunnelling microscopy (EC-STM). We identify a `nucleation and early growth' regime of nanoisland formation, and a `late growth' regime after island coalescence, which continues up to at least 170 cycles. The correlation analysis shows that each step site that is created in the `late growth' regime contributes equally strongly to both the electrochemical and the roughness evolution. In contrast, in the `nucleation and early growth' regime, created step sites contribute to the roughness, but not to the electrochemical signal.

Improving the two-step remediation process for CCA-treated wood. Part I, Evaluating oxalic acid extraction

Treesearch

Carol Clausen

2004-01-01

In this study, three possible improvements to a remediation process for chromated-copper-arsenate (CCA) treated wood were evaluated. The process involves two steps: oxalic acid extraction of wood fiber followed by bacterial culture with Bacillus licheniformis CC01. The three potential improvements to the oxalic acid extraction step were (1) reusing oxalic acid for...

Effect of Chemical and Physical Properties on the In Vitro Degradation of 3D Printed High Resolution Poly(propylene fumarate) Scaffolds.

PubMed

Walker, Jason M; Bodamer, Emily; Krebs, Olivia; Luo, Yuanyuan; Kleinfehn, Alex; Becker, Matthew L; Dean, David

2017-04-10

Two distinct molecular masses of poly(propylene fumarate) (PPF) are combined with an additive manufacturing process to fabricate highly complex scaffolds possessing controlled chemical properties and porous architecture. Scaffolds were manufactured with two polymer molecular masses and two architecture styles. Degradation was assessed in an accelerated in vitro environment. The purpose of the degradation study is not to model or mimic in vivo degradation, but to efficiently compare the effect of modulating scaffold properties. This is the first study addressing degradation of chain-growth synthesized PPF, a process that allows for considerably more control over molecular mass distribution. It demonstrates that, with greater process control, not only is scaffold fabrication reproducible, but the mechanical properties and degradation kinetics can be tailored by altering the physical properties of the scaffold. This is a clear step forward in using PPF to address unmet medical needs while meeting regulatory demands and ultimately obtaining clinical relevancy.

The Effects of Impurities on Protein Crystal Growth and Nucleation: A Preliminary Study

NASA Technical Reports Server (NTRS)

Schall, Constance A.

1998-01-01

Kubota and Mullin (1995) devised a simple model to account for the effects of impurities on crystal growth of small inorganic and organic molecules in aqueous solutions. Experimentally, the relative step velocity and crystal growth of these molecules asymptotically approach zero or non-zero values with increasing concentrations of impurities. Alternatively, the step velocity and crystal growth can linearly approach zero as the impurity concentration increases. The Kubota-Mullin model assumes that the impurity exhibits Langmuirian adsorption onto the crystal surface. Decreases in step velocities and subsequent growth rates are related to the fractional coverage (theta) of the crystal surface by adsorbed impurities; theta = Kx / (I +Kx), x = mole fraction of impurity in solution. In the presence of impurities, the relative step velocity, V/Vo, and the relative growth rate of a crystal face, G/Go, are proposed to conform to the following equations: V/Vo approx. = G/Go = 1 - (alpha)(theta). The adsorption of impurity is assumed to be rapid and in quasi-equilibrium with the crystal surface sites available. When the value of alpha, an effectiveness factor, is one the growth will asymptotically approach zero with increasing concentrations of impurity. At values less than one, growth approaches a non-zero value asymptotically. When alpha is much greater than one, there will be a linear relationship between impurity concentration and growth rates. Kubota and Mullin expect alpha to decrease with increasing supersaturation and shrinking size of a two dimensional nucleus. It is expected that impurity effects on protein crystal growth will exhibit behavior similar to that of impurities in small molecule growth. A number of proteins were added to purified chicken egg white lysozyme, the effect on crystal nucleation and growth assessed.

Study on the mechanism of Si-glass-Si two step anodic bonding process

NASA Astrophysics Data System (ADS)

Hu, Lifang; Wang, Hao; Xue, Yongzhi; Shi, Fangrong; Chen, Shaoping

2018-04-01

Si-glass-Si was successfully bonded together through a two-step anodic bonding process. The bonding current in each step of the two-step bonding process was investigated, and found to be quite different. The first bonding current decreased quickly to a relatively small value, but for the second bonding step, there were two current peaks; the current first decreased, then increased, and then decreased again. The second current peak occurred earlier with higher temperature and voltage. The two-step anodic bonding process was investigated in terms of bonding current. SEM and EDS tests were conducted to investigate the interfacial structure of the Si-glass-Si samples. The two bonding interfaces were almost the same, but after an etching process, transitional layers could be found in the bonding interface and a deeper trench with a thickness of ~1.5 µm could be found in the second bonding interface. Atomic force microscopy mapping results indicated that sodium precipitated from the back of the glass, which makes the roughness of the surface become coarse. Tensile tests indicated that the fracture occurred at the glass substrate and that the bonding strength increased with the increment of bonding temperature and voltage with the maximum strength of 6.4 MPa.

Phase Shift Interferometer and Growth Set Up to Step Pattern Formation During Growth From Solutions. Influence of the Oscillatory solution Flow on Stability

NASA Technical Reports Server (NTRS)

Chernov, Alex A.; Booth, N. A.; Vekilov, P. G.; Murray, B. T.; McFadden, G. B.

2000-01-01

We have assembled an experimental setup based on Michelson interferometry with the growing crystal surface as one of the reflective surfaces. The crystallization part of the device allows optical monitoring of a face of a crystal growing at temperature stable within 0.05 C in a flow of solution of controlled direction and speed. The reference arm of the interferometer contains a liquid crystal element that allows controlled shifts of the phase of the interferograms. We employ an image-processing algorithm, which combines five images with a pi/2 phase difference between each pair of images. The images are transferred to a computer by a camera capable of capturing 60 frames per second. The device allows data collection on surface morphology and kinetics during the face layers growth over a relatively large area (approximately 4 sq. mm) in situ and in real time during growth. The estimated depth resolution of the phase shifting interferometry is approximately 50 Angstroms. The data will be analyzed in order to reveal and monitor step bunching during the growth process. The crystal chosen as a model for study in this work is KH2PO4 (KDP). This optically non-linear material is widely used in frequency doubling applications. There have been a number of studies of the kinetics of KDP crystallization that can serve as a benchmark for our investigations. However, so far, systematic quantitative characteristics of step interaction and bunching are missing. We intend to present our first quantitative results on the onset, initial stages and development of instabilities in moving step trains on vicinal crystal surfaces at varying supersaturation, flow rate, and flow direction. Behavior of a vicinal face growing from solution flowing normal to the steps and periodically changing its direction in time was considered theoretically. It was found that this oscillating flow reduces both stabilization and destabilization effects resulted from the unidirectional solution flow directed up the step stream and down the step stream. This reduction of stabilization and destabilization comes from effective mixing which entangles the phase shifts between the spatially periodic interface perturbation and the concentration wave induced by this perturbation. Numerical results and simplified mixing criterion will be discussed.

Unlocking the coral calcification process: Insights from boron isotope measurements and a skeletal growth model

NASA Astrophysics Data System (ADS)

Mollica, N. R.; Guo, W.; Cohen, A. L.; Huang, K. F.; Foster, G. L.; Donald, H.; Solow, A.

2017-12-01

Carbonate skeletons of scleractinian corals are important archives of ocean climate and environmental change. However, corals don't accrete their skeletons directly from ambient seawater, but from a calcifying fluid whose composition is strongly regulated. There is mounting evidence that the carbonate chemistry of this calcifying fluid significantly impacts the amount of carbonate the coral can precipitate, which in turn affects the geochemical composition of the skeleton produced. However the mechanistic link between calcifying fluid (cf) chemistry, particularly the up-regulation of pHcf and thereby aragonite saturation state (Ωcf), and coral calcification is not well understood. We explored this link by combining boron isotope measurements with in situ measurements of seawater temperature, salinity, and DIC to estimate Ωcf of nine Porites corals from four Pacific reefs. Associated calcification rates were quantified for each core via CT scanning. We do not observe a relationship between calcification rates and Ωcf or Ωsw. Instead, when we deconvolve calcification into linear extension and skeletal density, a significant correlation is observed between density and Ωcf, and also Ωsw while extension does not correlate with either. These observations are consistent with the two-step model of coral calcification, in which skeleton is secreted in two distinct phases: vertical extension creating new skeletal elements, followed by lateral thickening of existing elements that are covered by living tissue. We developed a numerical model of Porites skeletal growth that builds on this two-step model and links skeletal density with the external seawater environment via its influence on the chemistry of coral calcifying fluid. We validated the model using existing coral skeletal datasets from six Porites species collected across five reef sites, and quantified the effects of each seawater parameter (e.g. temperature, pH, DIC) on skeletal density. Our findings illustrate the sensitivity of the second phase of coral calcification to the carbonate chemistry of the calcifying fluid, and support previous coral proxy system modelling efforts by validating the two-step growth model on annual and seasonal scales.

Growth kinetics and island evolution during double-pulsed molecular beam epitaxy of InN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kraus, A.; Hein, C.; Bremers, H.

The kinetic processes of InN growth using alternating source fluxes with sub-monolayer In pulses in plasma-assisted molecular beam epitaxy have been investigated. Growth at various temperatures reveals the existence of two growth regimes. While growth at low temperatures is solely governed by surface diffusion, a combination of decomposition, desorption, and diffusion becomes decisive at growth temperatures of 470 °C and above. At this critical temperature, the surface morphology changes from a grainy structure to a structure made of huge islands. The formation of those islands is attributed to the development of an indium adlayer, which can be observed via reflection highmore » energy electron diffraction monitoring. Based on the growth experiments conducted at temperatures below T{sub Growth} = 470 °C, an activation energy for diffusion of 0.54 ± 0.02 eV has been determined from the decreasing InN island density. A comparison between growth on metalorganic vapor phase epitaxy GaN templates and pseudo bulk GaN indicates that step edges and dislocations are favorable nucleation sites. Based on the results, we developed a growth model, which describes the main mechanisms of the growth.« less

Enhanced performance of wearable piezoelectric nanogenerator fabricated by two-step hydrothermal process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiu, Yu; Lei, Jixue; Yin, Bing

2014-03-17

A simple two-step hydrothermal process was proposed for enhancing the performance of the nanogenerator on flexible and wearable terylene-fabric substrate. With this method, a significant enhancement in output voltage of the nanogenerator from ∼10 mV to 7 V was achieved, comparing with the one by conventional one-step process. In addition, another advantage with the devices synthesized by two-step hydrothermal process was that their output voltages are only sensitive to strain rather than strain rate. The devices with a high output voltage have the ability to power common electric devices and will have important applications in flexible electronics and wearable devices.

Crystallization process of zeolite rho prepared by hydrothermal synthesis using 18-crown-6 ether as organic template.

PubMed

Araki, Sadao; Kiyohara, Yasato; Tanaka, Shunsuke; Miyake, Yoshikazu

2012-06-15

There are many viewpoints on the formation mechanisms for zeolites, but the details are not clear. An understanding of the elementary steps for their formation is important for the development of large-scale membranes and efficient manufacturing processes. In this study, the effects of silicon, aluminum, and the incorporation of 18-crown-6 (18C6) ether, on the formation of zeolite rho, using 18C6 as the structure directing agent (SDA) have been investigated by using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray fluorescence spectrometry (EDX), nuclear magnetic resonance spectroscopy (NMR), thermo gravimetric analysis (TGA), and the pH measurement. These results suggested that a zeolite rho has four synthesis steps; (1) 0-3 h, the dehydration and condensation reaction between the silica and alumina to form amorphous aluminosilicates; (2) 3-20 h, the particle growth and aggregation process for the amorphous aluminosilicates; (3) 20-48 h, the crystallization and crystal growth of zeolite rho, with the incorporation of 18C6; and (4) 48-96 h, gentle growth with an increase in Na/Si ratio and a change in rate for the bounding state between the silica- and the alumina-based species. We consider the above to reflect the four steps for the formation of zeolite rho. Copyright © 2012 Elsevier Inc. All rights reserved.

Letter-Sound Reading: Teaching Preschool Children Print-to-Sound Processing

ERIC Educational Resources Information Center

Wolf, Gail Marie

2016-01-01

This intervention study investigated the growth of letter sound reading and growth of consonant-vowel-consonant (CVC) word decoding abilities for a representative sample of 41 US children in preschool settings. Specifically, the study evaluated the effectiveness of a 3-step letter-sound teaching intervention in teaching preschool children to…

One-step growth of thin film SnS with large grains using MOCVD.

PubMed

Clayton, Andrew J; Charbonneau, Cecile M E; Tsoi, Wing C; Siderfin, Peter J; Irvine, Stuart J C

2018-01-01

Thin film tin sulphide (SnS) films were produced with grain sizes greater than 1 μm using a one-step metal organic chemical vapour deposition process. Tin-doped indium oxide (ITO) was used as the substrate, having a similar work function to molybdenum typically used as the back contact, but with potential use of its transparency for bifacial illumination. Tetraethyltin and ditertiarybutylsulphide were used as precursors with process temperatures 430-470 °C to promote film growth with large grains. The film stoichiometry was controlled by varying the precursor partial pressure ratios and characterised with energy dispersive X-ray spectroscopy to optimise the SnS composition. X-ray diffraction and Raman spectroscopy were used to determine the phases that were present in the film and revealed that small amounts of ottemannite Sn 2 S 3 was present when SnS was deposited on to the ITO using optimised growth parameters. Interaction at the SnS/ITO interface to form Sn 2 S 3 was deduced to have resulted for all growth conditions.

Letter-Sound Reading: Teaching Preschool Children Print-to-Sound Processing

PubMed Central

2015-01-01

This intervention study investigated the growth of letter sound reading and growth of consonant–vowel–consonant (CVC) word decoding abilities for a representative sample of 41 US children in preschool settings. Specifically, the study evaluated the effectiveness of a 3-step letter-sound teaching intervention in teaching pre-school children to decode, or read, single letters. The study compared a control group, which received the preschool’s standard letter-sound instruction, to an intervention group which received a 3-step letter-sound instruction intervention. The children’s growth in letter-sound reading and CVC word decoding abilities were assessed at baseline and 2, 4, 6 and 8 weeks. When compared to the control group, the growth of letter-sound reading ability was slightly higher for the intervention group. The rate of increase in letter-sound reading was significantly faster for the intervention group. In both groups, too few children learned to decode any CVC words to allow for analysis. Results of this study support the use of the intervention strategy in preschools for teaching children print-to-sound processing. PMID:26839494

Process of Infection with Bacteriophage φX174

PubMed Central

Dalgarno, L.; Sinsheimer, Robert L.

1968-01-01

A group of temperature-sensitive mutants of φX174 has been isolated which can go through a single, normal one-step growth cycle at 40 C but fail to form plaques at this temperature. Such mutants fail to initiate a second cycle at 40 C; however they can gain the capacity to infect at 40 C, upon incubation for 10 min in broth at 30 C. In regaining the ability to infect, the phage appear to undergo a temperature-dependent conformational alteration. The inverse process, a reversible loss of ability to infect at 40 C, is observed when such phage produced at 30 C are incubated for 2 hr at 40 C. The defect in initiation of a second cycle of infection appears to be in the injection of viral deoxyribonucleic acid. A two-step complementation test has been used to identify the cistron coding for the affected function. Such mutants are also unusually sensitive to an irreversible thermal inactivation when incubated at 40 C. PMID:4883013

Growth of Defect-Free 3C-SiC on 4H- and 6H-SiC Mesas Using Step-Free Surface Heteroepitaxy

NASA Technical Reports Server (NTRS)

Neudeck, Philip G.; Powell, J. Anthony; Trunek, Andrew J.; Huang, Xianrong R.; Dudley, Michael

2001-01-01

A new growth process, herein named step-free surface heteroepitaxy, has achieved 3CSiC films completely free of double positioning boundaries and stacking faults on 4H-SiC and 6H-SiC substrate mesas. The process is based upon the initial 2-dimensional nucleation and lateral expansion of a single island of 3C-SiC on a 4H- or 6H-SiC mesa surface that is completely free of bilayer surface steps. Our experimental results indicate that substrate-epilayer in-plane lattice mismatch (delta a/a = 0.0854% for 3C/4H) is at least partially relieved parallel to the interface in the initial bilayers of the heterofilm, producing an at least partially relaxed 3C-SiC film without dislocations that undesirably thread through the thickness of the epilayer. This result should enable realization of improved 3C-SiC devices.

Study of mesoporous CdS-quantum-dot-sensitized TiO2 films by using X-ray photoelectron spectroscopy and AFM

PubMed Central

Wojcieszak, Robert; Raj, Gijo

2014-01-01

Summary CdS quantum dots were grown on mesoporous TiO2 films by successive ionic layer adsorption and reaction processes in order to obtain CdS particles of various sizes. AFM analysis shows that the growth of the CdS particles is a two-step process. The first step is the formation of new crystallites at each deposition cycle. In the next step the pre-deposited crystallites grow to form larger aggregates. Special attention is paid to the estimation of the CdS particle size by X-ray photoelectron spectroscopy (XPS). Among the classical methods of characterization the XPS model is described in detail. In order to make an attempt to validate the XPS model, the results are compared to those obtained from AFM analysis and to the evolution of the band gap energy of the CdS nanoparticles as obtained by UV–vis spectroscopy. The results showed that XPS technique is a powerful tool in the estimation of the CdS particle size. In conjunction with these results, a very good correlation has been found between the number of deposition cycles and the particle size. PMID:24605274

Incubation behavior of silicon nanowire growth investigated by laser-assisted rapid heating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryu, Sang-gil; Kim, Eunpa; Grigoropoulos, Costas P., E-mail: cgrigoro@berkeley.edu

2016-08-15

We investigate the early stage of silicon nanowire growth by the vapor-liquid-solid mechanism using laser-localized heating combined with ex-situ chemical mapping analysis by energy-filtered transmission electron microscopy. By achieving fast heating and cooling times, we can precisely determine the nucleation times for nanowire growth. We find that the silicon nanowire nucleation process occurs on a time scale of ∼10 ms, i.e., orders of magnitude faster than the times reported in investigations using furnace processes. The rate-limiting step for silicon nanowire growth at temperatures in the vicinity of the eutectic temperature is found to be the gas reaction and/or the silicon crystalmore » growth process, whereas at higher temperatures it is the rate of silicon diffusion through the molten catalyst that dictates the nucleation kinetics.« less

Development of a Novel Approach for Fatigue Life Prediction of Structural Materials

DTIC Science & Technology

2008-12-01

applied when the crack length was 8.45 mm and 14.96 mm, respectively, on these two specimens. A third specimen was subjected to a constant amplitude...The crack growth rate at the middle point (the third point) was determined from the derivative of the parabola. The stress intensity factor for...minimum load was identical in the two loading steps (Fig. 32(b)). The third specimen experienced two-step loading with identical /?-ratio in the two

Enhancement of cell growth on honeycomb-structured polylactide surface using atmospheric-pressure plasma jet modification

NASA Astrophysics Data System (ADS)

Cheng, Kuang-Yao; Chang, Chia-Hsing; Yang, Yi-Wei; Liao, Guo-Chun; Liu, Chih-Tung; Wu, Jong-Shinn

2017-02-01

In this paper, we compare the cell growth results of NIH-3T3 and Neuro-2A cells over 72 h on flat and honeycomb structured PLA films without and with a two-step atmospheric-pressure nitrogen-based plasma jet treatment. We developed a fabrication system used for forming of a uniform honeycomb structure on PLA surface, which can produce two different pore sizes, 3-4 μm and 7-8 μm, of honeycomb pattern. We applied a previously developed nitrogen-based atmospheric-pressure dielectric barrier discharge (DBD) jet system to treat the PLA film without and with honeycomb structure. NIH-3T3 and a much smaller Neuro-2A cells were cultivated on the films under various surface conditions. The results show that the two-step plasma treatment in combination with a honeycomb structure can enhance cell growth on PLA film, should the cell size be not too smaller than the pore size of honeycomb structure, e.g., NIH-3T3. Otherwise, cell growth would be better on flat PLA film, e.g., Neuro-2A.

Strongly reduced Ehrlich-Schwoebel barriers at the Cu (111) stepped surface with In and Pb surfactants

NASA Astrophysics Data System (ADS)

Hao, Jialei; Zhang, Lixin

2018-01-01

A surfactant can modify the properties of the surface and induce different mode of epitaxy growth. The atomistic mechanism is not fully understood yet. In this first-principles study, taking Cu homoepitaxy along (111) direction as an example, we show that the distribution of the surfactant atoms on the surface is the key. For In and Pb, they prefer to locate at the step edges and remain isolated. Once the growth is started, the distribution can be further modified by Cu adatoms. The uniquely decorated step edges have much lowered Ehrlich-Schwoebel (ES) barriers than that of the clean edges, thus the two dimensional growth on Cu (111) surface is promoted significantly. On the other hand, for Rh, Ir, and Au, these atoms are not favored at the step edges. The ES barriers can't be affected and these metals are not surfactants. The result is very helpful for searching of the optimal surfactants in metal homoepitaxy.

Two-step rapid sulfur capture. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

NONE

1994-04-01

The primary goal of this program was to test the technical and economic feasibility of a novel dry sorbent injection process called the Two-Step Rapid Sulfur Capture process for several advanced coal utilization systems. The Two-Step Rapid Sulfur Capture process consists of limestone activation in a high temperature auxiliary burner for short times followed by sorbent quenching in a lower temperature sulfur containing coal combustion gas. The Two-Step Rapid Sulfur Capture process is based on the Non-Equilibrium Sulfur Capture process developed by the Energy Technology Office of Textron Defense Systems (ETO/TDS). Based on the Non-Equilibrium Sulfur Capture studies the rangemore » of conditions for optimum sorbent activation were thought to be: activation temperature > 2,200 K for activation times in the range of 10--30 ms. Therefore, the aim of the Two-Step process is to create a very active sorbent (under conditions similar to the bomb reactor) and complete the sulfur reaction under thermodynamically favorable conditions. A flow facility was designed and assembled to simulate the temperature, time, stoichiometry, and sulfur gas concentration prevalent in the advanced coal utilization systems such as gasifiers, fluidized bed combustors, mixed-metal oxide desulfurization systems, diesel engines, and gas turbines.« less

Employability Project: The Employment of Persons with Developmental Disabilities.

ERIC Educational Resources Information Center

Watson, Marge

The paper describes the efforts of Stepping Stones Growth Center, a vocational training organization which places persons with developmental disabilities into competitive employment. Two programs within Stepping Stones feature training for boat maintenance and janitorial and grounds maintenance. Placement preparation is described in terms of its…

Incidence, populations and diversity of fungi from raw materials, final products and air of processing environment of multigrain whole meal bread.

PubMed

Santos, Juliana Lane Paixão Dos; Bernardi, Angélica Olivier; Pozza Morassi, Letícia L; Silva, Beatriz S; Copetti, Marina Venturini; S Sant'Ana, Anderson

2016-09-01

This study aimed to assess the incidence, to quantify and to assess the diversity of fungi in a multigrain whole meal bread processing plant. Two hundred and eight one (n=281) samples were analyzed, including raw materials (n=120), air samples (n=136) and multigrain breads (n=25). Among the raw materials, the whole corn flour showed the highest counts of fungi (4.8logCFU/g), followed by whole-wheat flour (3.1logCFU/g). The counts of fungi in the air of processing environment were higher in post-baking steps (oven output, cooling, slicing, packaging) than in pre-baking steps (weighing and mixer) (p<0.05). Species of fungi isolated from spoiled bread samples stored at 5, 20, 25 and 30, and 40°C corresponded mostly to Penicillium paneum and Penicillium polonicum isolated from 20 and 24% of samples, respectively. These species were also isolated from raw materials (P. paneum and P. polonicum) and air collected at different processing sampling points (P. polonicum). The high counts of filamentous fungi in raw materials and air samples in processing steps such as cooling, slicing, and packaging, suggest that contamination that may occur in these steps can be critical for the shelf life of breads. The results of this study highlight that the prevention of contamination of breads by fungal spores is still a challenge for bakery industries and that other strategies such as control of germination and growth of spoilage fungi through the development of more stable formulations have to be developed. Copyright © 2016 Elsevier Ltd. All rights reserved.

Temperature dependence of needle and shoot elongation before bud break in Scots pine.

PubMed

Schiestl-Aalto, Pauliina; Mäkelä, Annikki

2017-03-01

Knowledge about the early part of needle growth is deficient compared with what is known about shoot growth. It is however important to understand growth of different organs to be able to estimate the changes in whole tree growth in a changing environment. The onset of growth in spring has been observed to occur over some certain threshold value of momentary temperature or temperature accumulation. We measured the length growth of Scots pine (Pinus sylvestris L.) needles and shoots from March until bud break over 3 years. We first compared needle growth with concurrent shoot growth. Then, we quantified threshold temperature of growth (i) with a logistic regression based on momentary temperatures and (ii) with the temperature sum accumulation method. Temperature sum was calculated with combinations of various time steps, starting dates and threshold temperature values. Needle elongation began almost concurrently with shoot elongation and proceeded linearly in relation to shoot growth until bud break. When studying the threshold temperature for growth, the method with momentary temperature effect on growth onset yielded ambiguous results in our conditions. The best fit of an exponential regression between needle growth or length and temperature sum was obtained with threshold temperatures -1 to +2 °C, with several combinations of starting date and time step. We conclude that although growth onset is a momentary event the process leading to it is a long-term continuum where past time temperatures have to be accounted for, rather than a sudden switch from quiescence to active growth. Further, our results indicate that lower temperatures than the commonly used +5 °C are sufficient for actuating the growth process. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Perceived Growth versus Actual Growth in Executive Leadership Competencies: An Application of the Stair-Step Behaviorally Anchored Evaluation Approach

ERIC Educational Resources Information Center

McCormick, Michael J.; Dooley, Kim E.; Lindner, James R.; Cummins, Richard L.

2007-01-01

The purpose of this study was to describe student learning in executive leadership core competencies after being engaged in a two-semester leadership education sequence. The researchers used evaluative research techniques to compare perceived and actual growth in learning of executive leadership competencies. Data collection consisted of a…

Step-by-step seeding procedure for preparing HKUST-1 membrane on porous α-alumina support.

PubMed

Nan, Jiangpu; Dong, Xueliang; Wang, Wenjin; Jin, Wanqin; Xu, Nanping

2011-04-19

Metal-organic framework (MOF) membranes have attracted considerable attention because of their striking advantages in small-molecule separation. The preparation of an integrated MOF membrane is still a major challenge. Depositing a uniform seed layer on a support for secondary growth is a main route to obtaining an integrated MOF membrane. A novel seeding method to prepare HKUST-1 (known as Cu(3)(btc)(2)) membranes on porous α-alumina supports is reported. The in situ production of the seed layer was realized in step-by-step fashion via the coordination of H(3)btc and Cu(2+) on an α-alumina support. The formation process of the seed layer was observed by ultraviolet-visible absorption spectroscopy and atomic force microscopy. An integrated HKUST-1 membrane could be synthesized by the secondary hydrothermal growth on the seeded support. The gas permeation performance of the membrane was evaluated. © 2011 American Chemical Society

Steady-state solution growth of microcrystalline silicon on nanocrystalline seed layers on glass

NASA Astrophysics Data System (ADS)

Bansen, R.; Ehlers, C.; Teubner, Th.; Boeck, T.

2016-09-01

The growth of polycrystalline silicon layers on glass from tin solutions at low temperatures is presented. This approach is based on the steady-state solution growth of Si crystallites on nanocrystalline seed layers, which are prepared in a preceding process step. Scanning electron microscopy and atomic force microscopy investigations reveal details about the seed layer surfaces, which consist of small hillocks, as well as about Sn inclusions and gaps along the glass substrate after solution growth. The successful growth of continuous microcrystalline Si layers with grain sizes up to several ten micrometers shows the feasibility of the process and makes it interesting for photovoltaics. Project supported by the German Research Foundation (DFG) (No. BO 1129/5-1).

Evaluation of two platelet-rich plasma processing methods and two platelet-activation techniques for use in llamas and alpacas.

PubMed

Semevolos, Stacy A; Youngblood, Cori D; Grissom, Stephanie K; Gorman, M Elena; Larson, Maureen K

2016-11-01

OBJECTIVE To evaluate 2 processing methods (commercial kit vs conical tube centrifugation) for preparing platelet rich plasma (PRP) for use in llamas and alpacas. SAMPLES Blood samples (30 mL each) aseptically collected from 6 healthy llamas and 6 healthy alpacas. PROCEDURES PRP was prepared from blood samples by use of a commercial kit and by double-step conical tube centrifugation. A CBC was performed for blood and PRP samples. Platelets in PRP samples were activated by means of a freeze-thaw method with or without 23mM CaCl 2 , and concentrations of platelet-derived growth factor-BB and transforming growth factor-β 1 were measured. Values were compared between processing methods and camelid species. RESULTS Blood CBC values for llamas and alpacas were similar. The commercial kit yielded a significantly greater degree of platelet enrichment (mean increase, 8.5 fold vs 2.8 fold) and WBC enrichment (mean increase, 3.7 fold vs 1.9 fold) than did conical tube centrifugation. Llamas had a significantly greater degree of platelet enrichment than alpacas by either processing method. No difference in WBC enrichment was identified between species. Concentrations of both growth factors were significantly greater in PRP samples obtained by use of the commercial kit versus those obtained by conical tube centrifugation. CONCLUSIONS AND CLINICAL RELEVANCE For blood samples from camelids, the commercial kit yielded a PRP product with a higher platelet and WBC concentration than achieved by conical tube centrifugation. Optimal PRP platelet and WBC concentrations for various applications need to be determined for llamas and alpacas.

Unstable vicinal crystal growth from cellular automata

NASA Astrophysics Data System (ADS)

Krasteva, A.; Popova, H.; KrzyŻewski, F.; Załuska-Kotur, M.; Tonchev, V.

2016-03-01

In order to study the unstable step motion on vicinal crystal surfaces we devise vicinal Cellular Automata. Each cell from the colony has value equal to its height in the vicinal, initially the steps are regularly distributed. Another array keeps the adatoms, initially distributed randomly over the surface. The growth rule defines that each adatom at right nearest neighbor position to a (multi-) step attaches to it. The update of whole colony is performed at once and then time increases. This execution of the growth rule is followed by compensation of the consumed particles and by diffusional update(s) of the adatom population. Two principal sources of instability are employed - biased diffusion and infinite inverse Ehrlich-Schwoebel barrier (iiSE). Since these factors are not opposed by step-step repulsion the formation of multi-steps is observed but in general the step bunches preserve a finite width. We monitor the developing surface patterns and quantify the observations by scaling laws with focus on the eventual transition from diffusion-limited to kinetics-limited phenomenon. The time-scaling exponent of the bunch size N is 1/2 for the case of biased diffusion and 1/3 for the case of iiSE. Additional distinction is possible based on the time-scaling exponents of the sizes of multi-step Nmulti, these are 0.36÷0.4 (for biased diffusion) and 1/4 (iiSE).

Manipulating the assembly of perovskites onto soft nanoimprinted titanium dioxide templates.

PubMed

Baca, Alfred J; Roberts, M Joseph; Stenger-Smith, John; Baldwin, Lawrence

2018-06-22

Soft nanoimprinted titanium dioxide (TiO 2 ) substrates decorated with methylammonium lead halide perovskite (MAPbI 3 ) crystals were fabricated by controlling the perovskite precursor concentration and volume during spin coat processing combined with the use of hydrophobic TiO 2 templates. The patterned growth was demonstrated with different perovskite crystallization methods. We investigated and successfully demonstrated the controlled assembly of two MAPbI 3 nanomaterials, one a nanocomposite formed between the perovskite and a hole conducting polymer poly(2,5-bis(N-methyl-N-hexylamino)phenylene vinylene) (BAMPPV), and a second formed from perovskite crystals using common solution based MAPbI 3 growth methods (1-step and 2-step processing). Both types of MAPbI 3 crystals were fabricated on hydrophobic TiO 2 nanotemplates composed of nanowells or grating patterns. Patterned areas as large as 100 μm × 100 μm were achieved. We examined and characterized the substrates using atomic force microscopy, scanning electron microscopy, x-ray diffraction, and energy dispersive spectroscopy. We present the optical properties (i.e. fluorescence and transmission) of soft nanoimprinted nanowells decorated with perovskites demonstrating the successful synthesis of MAPbI 3 perovskite nanocrystals. As an example of their use, we demonstrate a two terminal device and show photocurrent response of a perovskite patterned micro-grating. Our method is a nondestructive approach to nanopatterning perovskites, and produces patterned arrays that maintain their photo-electric properties. The results presented herein suggests an attractive route to developing nanopatterned and small area perovskite substrates for applications in photovoltaics, x-ray sensing/detection, image sensor arrays, and others.

Manipulating the assembly of perovskites onto soft nanoimprinted titanium dioxide templates

NASA Astrophysics Data System (ADS)

Baca, Alfred J.; Roberts, M. Joseph; Stenger-Smith, John; Baldwin, Lawrence

2018-06-01

Soft nanoimprinted titanium dioxide (TiO2) substrates decorated with methylammonium lead halide perovskite (MAPbI3) crystals were fabricated by controlling the perovskite precursor concentration and volume during spin coat processing combined with the use of hydrophobic TiO2 templates. The patterned growth was demonstrated with different perovskite crystallization methods. We investigated and successfully demonstrated the controlled assembly of two MAPbI3 nanomaterials, one a nanocomposite formed between the perovskite and a hole conducting polymer poly(2,5-bis(N-methyl-N-hexylamino)phenylene vinylene) (BAMPPV), and a second formed from perovskite crystals using common solution based MAPbI3 growth methods (1-step and 2-step processing). Both types of MAPbI3 crystals were fabricated on hydrophobic TiO2 nanotemplates composed of nanowells or grating patterns. Patterned areas as large as 100 μm × 100 μm were achieved. We examined and characterized the substrates using atomic force microscopy, scanning electron microscopy, x-ray diffraction, and energy dispersive spectroscopy. We present the optical properties (i.e. fluorescence and transmission) of soft nanoimprinted nanowells decorated with perovskites demonstrating the successful synthesis of MAPbI3 perovskite nanocrystals. As an example of their use, we demonstrate a two terminal device and show photocurrent response of a perovskite patterned micro-grating. Our method is a nondestructive approach to nanopatterning perovskites, and produces patterned arrays that maintain their photo-electric properties. The results presented herein suggests an attractive route to developing nanopatterned and small area perovskite substrates for applications in photovoltaics, x-ray sensing/detection, image sensor arrays, and others.

Advanced imaging programs: maximizing a multislice CT investment.

PubMed

Falk, Robert

2008-01-01

Advanced image processing has moved from a luxury to a necessity in the practice of medicine. A hospital's adoption of sophisticated 3D imaging entails several important steps with many factors to consider in order to be successful. Like any new hospital program, 3D post-processing should be introduced through a strategic planning process that includes administrators, physicians, and technologists to design, implement, and market a program that is scalable-one that minimizes up front costs while providing top level service. This article outlines the steps for planning, implementation, and growth of an advanced imaging program.

DEVELOPMENT OF PERMANENT MECHANICAL REPAIR SLEEVE FOR PLASTIC PIPE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hitesh Patadia

2005-04-29

The report presents a comprehensive summary of the prototype development process utilized towards the development of a permanent mechanical repair fitting intended to be installed on damaged PE mains under blowing gas conditions. Specifically, the step by step construction approach is presented and the experimental data to support the mitigation of ensuing slow crack growth (SCG) of the damage area.

In situ observation of dynamic electrodeposition processes by soft x-ray fluorescence microspectroscopy and keyhole coherent diffractive imaging

NASA Astrophysics Data System (ADS)

Bozzini, Benedetto; Kourousias, George; Gianoncelli, Alessandra

2017-03-01

This paper describes two novel in situ microspectroscopic approaches to the dynamic study of electrodeposition processes: x-ray fluorescence (XRF) mapping with submicrometric space resolution and keyhole coherent diffractive imaging (kCDI) with nanometric lateral resolution. As a case study, we consider the pulse-plating of nanocomposites with polypyrrole matrix and Mn x Co y O z dispersoids, a prospective cathode material for zinc-air batteries. This study is centred on the detailed measurement of the elemental distributions developing in two representative subsequent growth steps, based on the combination of in situ identical-location XRF microspectroscopy—accompanied by soft-x ray absorption microscopy—and kCDI. XRF discloses space and time distributions of the two electrodeposited metals and kCDI on the one hand allows nanometric resolution and on the other hand provides complementary absorption as well as phase contrast modes. The joint information derived from these two microspectroscopies allows measurement of otherwise inaccessible observables that are a prerequisite for electrodeposition modelling and control accounting for dynamic localization processes.

Localized synthesis, assembly and integration of silicon nanowires

NASA Astrophysics Data System (ADS)

Englander, Ongi

Localized synthesis, assembly and integration of one-dimensional silicon nanowires with MEMS structures is demonstrated and characterized in terms of local synthesis processes, electric-field assisted self-assembly, and a proof-of-concept nanoelectromechanical system (HEMS) demonstration. Emphasis is placed on the ease of integration, process control strategies, characterization techniques and the pursuit of integrated devices. A top-down followed by a bottom-up integration approach is utilized. Simple MEMS heater structures are utilized as the microscale platforms for the localized, bottom-up synthesis of one-dimensional nanostructures. Localized heating confines the high temperature region permitting only localized nanostructure synthesis and allowing the surroundings to remain at room temperature thus enabling CMOS compatible post-processing. The vapor-liquid-solid (VLS) process in the presence of a catalytic nanoparticle, a vapor phase reactant, and a specific temperature environment is successfully employed locally. Experimentally, a 5nm thick gold-palladium layer is used as the catalyst while silane is the vapor phase reactant. The current-voltage behavior of the MEMS structures can be correlated to the approximate temperature range required for the VLS reaction to take place. Silicon nanowires averaging 45nm in diameter and up to 29mum in length synthesized at growth rates of up to 1.5mum/min result. By placing two MEMS structures in close proximity, 4--10mum apart, localized silicon nanowire growth can be used to link together MEMS structures to yield a two-terminal, self-assembled micro-to-nano system. Here, one MEMS structure is designated as the hot growth structure while a nearby structure is designated as the cold secondary structure, whose role is to provide a natural stopping point for the VLS reaction. The application of a localized electric-field, 5 to 13V/mum in strength, during the synthesis process, has been shown to improve nanowire organization, alignment, and assembly. The integrated nanoelectrormechanical system was found to be mechanically resilient as it proved to successfully withstand a wide variety of post-processing steps, including manipulations and examinations under scanning and transmission electron microscopes and aqueous processing, although a super critical drying step is necessary to preserve the integrated system during the drying process. Electrical characterization of the system proved challenging due to low carrier concentration and possible transport issues at the nano-micro interface. Nonetheless, in a proof-of-concept demonstration, the system was functionalized and tested for a hydrogen sensing application.

Analytical and numerical analysis of frictional damage in quasi brittle materials

NASA Astrophysics Data System (ADS)

Zhu, Q. Z.; Zhao, L. Y.; Shao, J. F.

2016-07-01

Frictional sliding and crack growth are two main dissipation processes in quasi brittle materials. The frictional sliding along closed cracks is the origin of macroscopic plastic deformation while the crack growth induces a material damage. The main difficulty of modeling is to consider the inherent coupling between these two processes. Various models and associated numerical algorithms have been proposed. But there are so far no analytical solutions even for simple loading paths for the validation of such algorithms. In this paper, we first present a micro-mechanical model taking into account the damage-friction coupling for a large class of quasi brittle materials. The model is formulated by combining a linear homogenization procedure with the Mori-Tanaka scheme and the irreversible thermodynamics framework. As an original contribution, a series of analytical solutions of stress-strain relations are developed for various loading paths. Based on the micro-mechanical model, two numerical integration algorithms are exploited. The first one involves a coupled friction/damage correction scheme, which is consistent with the coupling nature of the constitutive model. The second one contains a friction/damage decoupling scheme with two consecutive steps: the friction correction followed by the damage correction. With the analytical solutions as reference results, the two algorithms are assessed through a series of numerical tests. It is found that the decoupling correction scheme is efficient to guarantee a systematic numerical convergence.

Lactate production as representative of the fermentation potential of Corynebacterium glutamicum 2262 in a one-step process.

PubMed

Khuat, Hoang Bao Truc; Kaboré, Abdoul Karim; Olmos, Eric; Fick, Michel; Boudrant, Joseph; Goergen, Jean-Louis; Delaunay, Stéphane; Guedon, Emmanuel

2014-01-01

The fermentative properties of thermo-sensitive strain Corynebacterium glutamicum 2262 were investigated in processes coupling aerobic cell growth and the anaerobic fermentation phase. In particular, the influence of two modes of fermentation on the production of lactate, the fermentation product model, was studied. In both processes, lactate was produced in significant amount, 27 g/L in batch culture, and up to 55.8 g/L in fed-batch culture, but the specific production rate in the fed-batch culture was four times lower than that in the batch culture. Compared to other investigated fermentation processes, our strategy resulted in the highest yield of lactic acid from biomass. Lactate production by C. glutamicum 2262 thus revealed the capability of the strain to produce various fermentation products from pyruvate.

Phase-field crystal modeling of heteroepitaxy and exotic modes of crystal nucleation

NASA Astrophysics Data System (ADS)

Podmaniczky, Frigyes; Tóth, Gyula I.; Tegze, György; Pusztai, Tamás; Gránásy, László

2017-01-01

We review recent advances made in modeling heteroepitaxy, two-step nucleation, and nucleation at the growth front within the framework of a simple dynamical density functional theory, the Phase-Field Crystal (PFC) model. The crystalline substrate is represented by spatially confined periodic potentials. We investigate the misfit dependence of the critical thickness in the StranskiKrastanov growth mode in isothermal studies. Apparently, the simulation results for stress release via the misfit dislocations fit better to the PeopleBean model than to the one by Matthews and Blakeslee. Next, we investigate structural aspects of two-step crystal nucleation at high undercoolings, where an amorphous precursor forms in the first stage. Finally, we present results for the formation of new grains at the solid-liquid interface at high supersaturations/supercoolings, a phenomenon termed Growth Front Nucleation (GFN). Results obtained with diffusive dynamics (applicable to colloids) and with a hydrodynamic extension of the PFC theory (HPFC, developed for simple liquids) will be compared. The HPFC simulations indicate two possible mechanisms for GFN.

Simple processing of back-contacted silicon heterojunction solar cells using selective-area crystalline growth

NASA Astrophysics Data System (ADS)

Tomasi, Andrea; Paviet-Salomon, Bertrand; Jeangros, Quentin; Haschke, Jan; Christmann, Gabriel; Barraud, Loris; Descoeudres, Antoine; Seif, Johannes Peter; Nicolay, Sylvain; Despeisse, Matthieu; de Wolf, Stefaan; Ballif, Christophe

2017-04-01

For crystalline-silicon solar cells, voltages close to the theoretical limit are nowadays readily achievable when using passivating contacts. Conversely, maximal current generation requires the integration of the electron and hole contacts at the back of the solar cell to liberate its front from any shadowing loss. Recently, the world-record efficiency for crystalline-silicon single-junction solar cells was achieved by merging these two approaches in a single device; however, the complexity of fabricating this class of devices raises concerns about their commercial potential. Here we show a contacting method that substantially simplifies the architecture and fabrication of back-contacted silicon solar cells. We exploit the surface-dependent growth of silicon thin films, deposited by plasma processes, to eliminate the patterning of one of the doped carrier-collecting layers. Then, using only one alignment step for electrode definition, we fabricate a proof-of-concept 9-cm2 tunnel-interdigitated back-contact solar cell with a certified conversion efficiency >22.5%.

The Design Process of Corporate Universities: A Stakeholder Approach

ERIC Educational Resources Information Center

Patrucco, Andrea Stefano; Pellizzoni, Elena; Buganza, Tommaso

2017-01-01

Purpose: Corporate universities (CUs) have been experiencing tremendous growth during the past years and can represent a real driving force for structured organizations. The paper aims to define the process of CU design shaped around company strategy. For each step, the authors propose specific roles, activities and methods.…

Hexagonal Nanopyramidal Prisms of Nearly Intrinsic InN on Patterned GaN Nanowire Arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Golam Sarwar, A. T. M.; Leung, Benjamin; Wang, George T.

By using multiple growth steps that separate the nucleation and growth processes, we show that nearly intrinsic InN single nanocrystals of high optical quality can be formed on patterned GaN nanowire arrays by molecular beam epitaxy. The InN nanostructures form into well-defined hexagonal prisms with pyramidal tops. Micro-photoluminescence (μ-PL) is carried out at low temperature (LT: 28.2 K) and room temperature (RT: 285 K) to gauge the relative material quality of the InN nanostructures. Nanopyramidal prisms grown using a three-step growth method are found to show superior quantum efficiency. In conclusion, excitation and temperature dependent μ-PL demonstrates the very highmore » quality and nearly intrinsic nature of the ordered InN nanostructure arrays.« less

Hexagonal Nanopyramidal Prisms of Nearly Intrinsic InN on Patterned GaN Nanowire Arrays

DOE PAGES

Golam Sarwar, A. T. M.; Leung, Benjamin; Wang, George T.; ...

2018-01-04

By using multiple growth steps that separate the nucleation and growth processes, we show that nearly intrinsic InN single nanocrystals of high optical quality can be formed on patterned GaN nanowire arrays by molecular beam epitaxy. The InN nanostructures form into well-defined hexagonal prisms with pyramidal tops. Micro-photoluminescence (μ-PL) is carried out at low temperature (LT: 28.2 K) and room temperature (RT: 285 K) to gauge the relative material quality of the InN nanostructures. Nanopyramidal prisms grown using a three-step growth method are found to show superior quantum efficiency. In conclusion, excitation and temperature dependent μ-PL demonstrates the very highmore » quality and nearly intrinsic nature of the ordered InN nanostructure arrays.« less

Full-Process Computer Model of Magnetron Sputter, Part I: Test Existing State-of-Art Components

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walton, C C; Gilmer, G H; Wemhoff, A P

2007-09-26

This work is part of a larger project to develop a modeling capability for magnetron sputter deposition. The process is divided into four steps: plasma transport, target sputter, neutral gas and sputtered atom transport, and film growth, shown schematically in Fig. 1. Each of these is simulated separately in this Part 1 of the project, which is jointly funded between CMLS and Engineering. The Engineering portion is the plasma modeling, in step 1. The plasma modeling was performed using the Object-Oriented Particle-In-Cell code (OOPIC) from UC Berkeley [1]. Figure 2 shows the electron density in the simulated region, using magneticmore » field strength input from experiments by Bohlmark [2], where a scale of 1% is used. Figures 3 and 4 depict the magnetic field components that were generated using two-dimensional linear interpolation of Bohlmark's experimental data. The goal of the overall modeling tool is to understand, and later predict, relationships between parameters of film deposition we can change (such as gas pressure, gun voltage, and target-substrate distance) and key properties of the results (such as film stress, density, and stoichiometry.) The simulation must use existing codes, either open-source or low-cost, not develop new codes. In part 1 (FY07) we identified and tested the best available code for each process step, then determined if it can cover the size and time scales we need in reasonable computation times. We also had to determine if the process steps are sufficiently decoupled that they can be treated separately, and identify any research-level issues preventing practical use of these codes. Part 2 will consider whether the codes can be (or need to be) made to talk to each other and integrated into a whole.« less

Optimization of hetero-epitaxial growth for the threading dislocation density reduction of germanium epilayers

NASA Astrophysics Data System (ADS)

Chong, Haining; Wang, Zhewei; Chen, Chaonan; Xu, Zemin; Wu, Ke; Wu, Lan; Xu, Bo; Ye, Hui

2018-04-01

In order to suppress dislocation generation, we develop a "three-step growth" method to heteroepitaxy low dislocation density germanium (Ge) layers on silicon with the MBE process. The method is composed of 3 growth steps: low temperature (LT) seed layer, LT-HT intermediate layer as well as high temperature (HT) epilayer, successively. Threading dislocation density (TDD) of epitaxial Ge layers is measured as low as 1.4 × 106 cm-2 by optimizing the growth parameters. The results of Raman spectrum showed that the internal strain of heteroepitaxial Ge layers is tensile and homogeneous. During the growth of LT-HT intermediate layer, TDD reduction can be obtained by lowering the temperature ramping rate, and high rate deposition maintains smooth surface morphology in Ge epilayer. A mechanism based on thermodynamics is used to explain the TDD and surface morphological dependence on temperature ramping rate and deposition rate. Furthermore, we demonstrate that the Ge layer obtained can provide an excellent platform for III-V materials integrated on Si.

Calculation tool for transported geothermal energy using two-step absorption process

DOE Data Explorer

Kyle Gluesenkamp

2016-02-01

This spreadsheet allows the user to calculate parameters relevant to techno-economic performance of a two-step absorption process to transport low temperature geothermal heat some distance (1-20 miles) for use in building air conditioning. The parameters included are (1) energy density of aqueous LiBr and LiCl solutions, (2) transportation cost of trucking solution, and (3) equipment cost for the required chillers and cooling towers in the two-step absorption approach. More information is available in the included public report: "A Technical and Economic Analysis of an Innovative Two-Step Absorption System for Utilizing Low-Temperature Geothermal Resources to Condition Commercial Buildings"

The autumn effect: timing of physical dormancy break in seeds of two winter annual species of Geraniaceae by a stepwise process

PubMed Central

Gama-Arachchige, N. S.; Baskin, J. M.; Geneve, R. L.; Baskin, C. C.

2012-01-01

Background and Aims The involvement of two steps in the physical dormancy (PY)-breaking process previously has been demonstrated in seeds of Fabaceae and Convolvulaceae. Even though there is a claim for a moisture-controlled stepwise PY-breaking in some species of Geraniaceae, no study has evaluated the role of temperature in the PY-breaking process in this family. The aim of this study was to determine whether a temperature-controlled stepwise PY-breaking process occurs in seeds of the winter annuals Geranium carolinianum and G. dissectum. Methods Seeds of G. carolinianum and G. dissectum were stored under different temperature regimes to test the effect of storage temperature on PY-break. The role of temperature and moisture regimes in regulating PY-break was investigated by treatments simulating natural conditions. Greenhouse (non-heated) experiments on seed germination and burial experiments (outdoors) were carried out to determine the PY-breaking behaviour in the natural habitat. Key Results Irrespective of moisture conditions, sensitivity to the PY-breaking step in seeds of G. carolinianum was induced at temperatures ≥20 °C, and exposure to temperatures ≤20 °C made the sensitive seeds permeable. Sensitivity of seeds increased with time. In G. dissectum, PY-break occurred at temperatures ≥20 °C in a single step under constant wet or dry conditions and in two steps under alternate wet–dry conditions if seeds were initially kept wet. Conclusions Timing of seed germination with the onset of autumn can be explained by PY-breaking processes involving (a) two temperature-dependent steps in G. carolinianum and (b) one or two moisture-dependent step(s) along with the inability to germinate under high temperatures in G. dissectum. Geraniaceae is the third of 18 families with PY in which a two-step PY-breaking process has been demonstrated. PMID:22684684

Comparison of single-step and two-step purified coagulants from Moringa oleifera seed for turbidity and DOC removal.

PubMed

Sánchez-Martín, J; Ghebremichael, K; Beltrán-Heredia, J

2010-08-01

The coagulant proteins from Moringa oleifera purified with single-step and two-step ion-exchange processes were used for the coagulation of surface water from Meuse river in The Netherlands. The performances of the two purified coagulants and the crude extract were assessed in terms of turbidity and DOC removal. The results indicated that the optimum dosage of the single-step purified coagulant was more than two times higher compared to the two-step purified coagulant in terms of turbidity removal. And the residual DOC in the two-step purified coagulant was lower than in single-step purified coagulant or crude extract. (c) 2010 Elsevier Ltd. All rights reserved.

Adsorption process to recover hydrogen from feed gas mixtures having low hydrogen concentration

DOEpatents

Golden, Timothy Christopher; Weist, Jr., Edward Landis; Hufton, Jeffrey Raymond; Novosat, Paul Anthony

2010-04-13

A process for selectively separating hydrogen from at least one more strongly adsorbable component in a plurality of adsorption beds to produce a hydrogen-rich product gas from a low hydrogen concentration feed with a high recovery rate. Each of the plurality of adsorption beds subjected to a repetitive cycle. The process comprises an adsorption step for producing the hydrogen-rich product from a feed gas mixture comprising 5% to 50% hydrogen, at least two pressure equalization by void space gas withdrawal steps, a provide purge step resulting in a first pressure decrease, a blowdown step resulting in a second pressure decrease, a purge step, at least two pressure equalization by void space gas introduction steps, and a repressurization step. The second pressure decrease is at least 2 times greater than the first pressure decrease.

The Role of Pressure to Quantify the Defects and its Effect on the Morphology of Graphene Layers

NASA Astrophysics Data System (ADS)

Amit, Kumar; Sharma, Rishi

The work reports the traces of graphene synthesized by Thermal-CVD technique over oxidized silicon substrates coated with nickel and cobalt catalysts under different pressures. Other process parameters like temperature, gas composition and time are kept constant during the growth. Effect of pressure on the nature of defects and structure of the graphene has been analyzed by Raman spectra. Effect of pressure on morphology has also been studied. It has been observed that the variation of pressure is responsible for any change in the structure and morphology of the graphene for a given catalyst. Formation of graphene and its defects has been explained with the help of two-step diffusion process.

Alternate Spray-coating for the Direct Fabrication of Hydroxyapatite Films without Crystal Growth Step in Solution.

PubMed

Watanabe, Satoshi; Kashiwagi, Rei; Matsumoto, Mutsuyoshi

2017-03-01

We discuss an alternate spray-coating technique for the direct fabrication of hydroxyapatite films using metal masks, suction-type spray nozzles and two calcification solutions of calcium hydroxide and phosphoric acid aqueous solutions. Hydroxyapatite films were formed only on the hydrophobic surface of the substrates. Scanning electron microscopy and energy dispersive X-ray spectroscopy showed that the spray-coated films consisted of hydroxyapatite nanoparticles. The Ca/P ratio was estimated to be about 1.26. X-ray diffraction patterns of the spray-coated films almost coincided with those of the hydroxyapatite powders, showing that the spray-coated films consisted of hydroxyapatite nanoparticles. Dot arrays of hydroxyapatite films at a diameter of 100 μm were formed by tuning the concentrations of calcium hydroxide and phosphoric acid aqueous solutions. This technique allows for the direct fabrication of the hydroxyapatite films without crystal growth process in hydroxyapatite precursors, the scaffolds of crystal growth such as biocompatibility SiO 2 -CaO glasses, or electrophoresis processes. By using this technique, large-area ceramic films with biocompatibility will be micropatterned with minimized material consumption, short fabrication time, and reduced equipment investments.

The Selective Epitaxy of Silicon at Low Temperatures.

NASA Astrophysics Data System (ADS)

Lou, Jen-Chung

1991-01-01

This dissertation has developed a process for the selective epitaxial growth (SEG) of silicon at low temperatures using a dichlorosilane-hydrogen mixture in a hot-wall low pressure chemical vapor deposition (LPCVD) reactor. Some basic issues concerning the quality of epilayers --substrate preparation, ex-situ and in-situ cleaning, and deposition cycle, have been studied. We find it necessary to use a plasma etch to open epitaxial windows for the SEG of Si. A cycled plasma etch, a thin sacrificial oxide growth, and an oxide etching step can completely remove plasma-etch-induced surface damage and contaminants, which result in high quality epilayers. A practical wafer cleaning step is developed for low temperature Si epitaxial growth. An ex-situ HF vapor treatment can completely remove chemical oxide from the silicon surface and retard the reoxidation of the silicon surface. An in-situ low-concentration DCS cycle can aid in decomposition of surface oxide during a 900 ^circC H_2 prebake step. An HF vapor treatment combined with a low-concentration of DCS cycle consistently achieves defect-free epilayers at 850^circC and lower temperatures. We also show that a BF_sp{2}{+ } or F^+ ion implantation is a potential ex-situ wafer cleaning process for SEG of Si at low temperatures. The mechanism for the formation of surface features on Si epilayers is also discussed. Based on O ^+ ion implantation, we showed that the oxygen incorporation in silicon epilayers suppresses the Si growth rate. Therefore, we attribute the formation of surface features to the local reduction of the Si growth rate due to the dissolution of oxide islands at the epi/substrate interface. Finally, with this developed process for the SEG of silicon, defect-free overgrown epilayers are also obtained. This achievement demonstrates the feasibility for the future silicon-on-oxide (SOI) manufacturing technology.

A mathematical model for the effects of radiation to the induced cancer in mice

NASA Astrophysics Data System (ADS)

Wada, Takahiro; Manabe, Yuichiro; Bando, Masako

We have been studying biological effects of radiation in terms of mathematical models. There are two main objects that we need to study: mutation and cancer. We proposed the Whack-A-Mole (WAM) model which takes account of the repair effects to study radiation induced mutations. We applied it to the mutation of several species including Drosophila and mice, and succeeded to reproduce the dose and dose-rate dependence of the mutation rates. Here, as a next step, we study the effects of low dose-rate radiation to an induced cancer in mice. In the experiment, they divided their mice in four groups and kept them under constant gamma-ray radiations with different dose rate for each group since the birth. On the 35th day, chemical carcinogen was given to each mouse and they observed the occurrence and the growth of cancer for one year. Our mathematical model consists of two stages. The first stage describes a multiple-step carcinogenesis and the second stage describes its growth. We assume that the carcinogenesis starts with the chemical carcinogen and that the rate of the following processes depends on the dose rate as it does in the WAM model. We found some irregularities in the data, however, the overall fit is satisfactory. This work was supported by JSPS KAKENHI Grant Number JP16H04637.

Ion/proton-conducting apparatus and method

DOEpatents

Yates, Matthew; Xue, Wei

2014-12-23

A c-axis-oriented HAP thin film synthesized by seeded growth on a palladium hydrogen membrane substrate. An exemplary synthetic process includes electrochemical seeding on the substrate, and secondary and tertiary hydrothermal treatments under conditions that favor growth along c-axes and a-axes in sequence. By adjusting corresponding synthetic conditions, an HAP this film can be grown to a controllable thickness with a dense coverage on the underlying substrate. The thin films have relatively high proton conductivity under hydrogen atmosphere and high temperature conditions. The c-axis oriented films may be integrated into fuel cells for application in the intermediate temperature range of 200-600.degree. C. The electrochemical-hydrothermal deposition technique may be applied to create other oriented crystal materials having optimized properties, useful for separations and catalysis as well as electronic and electrochemical applications, electrochemical membrane reactors, and in chemical sensors. Additional high-density and gas-tight HAP film compositions may be deposited using a two-step deposition method that includes an electrochemical deposition method followed by a hydrothermal deposition method. The two-step method uses a single hydrothermal deposition solution composition. The method may be used to deposit HAP films including but not limited to at least doped HAP films, and more particularly including carbonated HAP films. In addition, the high-density and gas-tight HAP films may be used in proton exchange membrane fuel cells.

Diffusion-controlled growth of molecular heterostructures: fabrication of two-, one-, and zero-dimensional C(60) nanostructures on pentacene substrates.

PubMed

Breuer, Tobias; Witte, Gregor

2013-10-09

A variety of low dimensional C60 structures has been grown on supporting pentacene multilayers. By choice of substrate temperature during growth the effective diffusion length of evaporated fullerenes and their nucleation at terraces or step edges can be precisely controlled. AFM and SEM measurements show that this enables the fabrication of either 2D adlayers or solely 1D chains decorating substrate steps, while at elevated growth temperature continuous wetting of step edges is prohibited and instead the formation of separated C60 clusters pinned at the pentacene step edges occurs. Remarkably, all structures remain thermally stable at room temperature once they are formed. In addition the various fullerene structures have been overgrown by an additional pentacene capping layer. Utilizing the different probe depth of XRD and NEXAFS, we found that no contiguous pentacene film is formed on the 2D C60 structure, whereas an encapsulation of the 1D and 0D structures with uniformly upright oriented pentacene is achieved, hence allowing the fabrication of low dimensional buried organic heterostructures.

Turning the undesired voids in silicon into a tool: In-situ fabrication of free-standing 3C-SiC membranes

NASA Astrophysics Data System (ADS)

Khazaka, Rami; Michaud, Jean François; Vennéguès, Philippe; Alquier, Daniel; Portail, Marc

2017-02-01

In this contribution, we present a method to form free-standing cubic silicon carbide (3C-SiC) membranes in-situ during the growth stage. To do so, we exploit the presence of voids in the silicon (Si) epilayer underneath the 3C-SiC membrane, in stark contrast to the conventional view of voids as defects. The shape and the size of the 3C-SiC membranes can be controlled by a preceding patterning step of the Si epilayer. Afterwards, by controlling the expansion of voids in Si, the structured sacrificial layer is consumed during the 3C-SiC growth step. Consequently, the membranes are grown and released simultaneously in a single step process. This straightforward technique is expected to markedly simplify the fabrication process of membranes by reducing the fabrication duration and cost. Furthermore, it helps to overcome several technical issues and presents the cornerstone for micro and nano-electromechanical systems applications, profiting from the outstanding properties of cubic silicon carbide.

Coherent blue emission generated by Rb two-photon excitation using diode and femtosecond lasers

NASA Astrophysics Data System (ADS)

Lopez, Jesus P.; Moreno, Marco P.; de Miranda, Marcio H. G.; Vianna, Sandra S.

2017-04-01

The coherent blue light generated in rubidium vapor due to the combined action of an ultrashort pulse train and a continuous wave diode laser is investigated. Each step of the two-photon transition 5S-5P{}3/2-5D is excited by one of the lasers, and the induced coherence between the 5S and 6P{}3/2 states is responsible for generating the blue beam. Measurements of the excitation spectrum reveal the frequency comb structure and allow us to identify the resonant modes responsible for inducing the nonlinear process. Further, each resonant mode excites a different group of atoms, making the process selective in atomic velocity. The signal dependency on the atomic density is characterized by a sharp growth and a rapid saturation. We also show that for high intensity of the diode laser, the Stark shift at resonance causes the signal suppression observed at low atomic density.

Growth of biaxially textured template layers using ion beam assisted deposition

NASA Astrophysics Data System (ADS)

Park, Seh-Jin

A two-step IBAD (ion beam assisted deposition) method is investigated, and compared to the conventional IBAD methods. The two step method uses surface energy anisotropy to achieve uniaxial texture and ion beam irradiation for biaxial texture. The biaxial texture was achieved by selective surface etching and enhanced by grain overgrowth. In this method, biaxial texture alignment is performed on a (001) uniaxially textured buffer layer. The material selected for achieving uniaxial texture, YBCO (YBa2Cu3O7-x), has strong surface energy anisotropy. YBCO is chemically susceptible to the reaction with the adjacent layer. Yttria stabilized zirconia (YSZ) was used to prevent the reaction between YBCO and the substrates (polycrystalline Ni alloy [Hastelloy] and amorphous SiNx/Si). A SrTiO3 layer was deposited on the uniaxially textured YBCO layer to retard stoichiometry change with subsequent processing. STO is well lattice matched with YBCO. A top layer of Ni was then deposited. The Ni layer was used for studying the effect of grain overgrowth. The obtained uniaxial Ni films were used for subsequent ion beam processing. Ar ion beam irradiation onto the uniaxially textured Ni film was used to study the effect of selective grain etching in achieving in-plane aligned Ni grains. Additional Ni deposition induces the overgrowth of the in-plane aligned Ni grains and, finally, the overall in-plane alignment. The in-plane alignment is examined with XRD phi scan. The effect of surface polarity of insulating oxide substrates on the epitaxial growth behavior was investigated. The lattice strain energy was the most important factor for determining the orientation of Ni films on a non-polar surface. However, for a polar surface, the surface energy plays an important role in determining the final orientation of the Ni films based on the experimental and theoretical results. Y2O3 growth behavior was also studied. The lattice strain energy is the most important factor for Y2O3 growth on single crystalline substrates. The surface energy anisotropy is the most important factor for the growth on amorphous substrates. The XRD phi scan study shows that Ar ion beam irradiation with favorable angle of incidence enhances the in-plane alignment of Y2O3 films grown on randomly oriented substrates due to the ion channeling.

Direct Growth of Graphene on Silicon by Metal-Free Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Tai, Lixuan; Zhu, Daming; Liu, Xing; Yang, Tieying; Wang, Lei; Wang, Rui; Jiang, Sheng; Chen, Zhenhua; Xu, Zhongmin; Li, Xiaolong

2018-06-01

The metal-free synthesis of graphene on single-crystal silicon substrates, the most common commercial semiconductor, is of paramount significance for many technological applications. In this work, we report the growth of graphene directly on an upside-down placed, single-crystal silicon substrate using metal-free, ambient-pressure chemical vapor deposition. By controlling the growth temperature, in-plane propagation, edge-propagation, and core-propagation, the process of graphene growth on silicon can be identified. This process produces atomically flat monolayer or bilayer graphene domains, concave bilayer graphene domains, and bulging few-layer graphene domains. This work would be a significant step toward the synthesis of large-area and layer-controlled, high-quality graphene on single-crystal silicon substrates. [Figure not available: see fulltext.

Quantitative measurement of the growth rate of the PHA-producing photosynthetic bacterium Rhodocyclus gelatinous CBS-2[PolyHydroxyAlkanoate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wolfrum, E.J.; Weaver, P.F.

Researchers at the National Renewable Energy Laboratory (NREL) have been investigating the use of model photosynthetic microorganisms that use sunlight and two-carbon organic substrates (e.g., ethanol, acetate) to produce biodegradable polyhydroxyalkanoate (PHA) copolymers as carbon storage compounds. Use of these biological PHAs in single-use plastics applications, followed by their post-consumer composting or anaerobic digestion, could impact petroleum consumption as well as the overloading of landfills. The large-scale production of PHA polymers by photosynthetic bacteria will require large-scale reactor systems utilizing either sunlight or artificial illumination. The first step in the scale-up process is to quantify the microbial growth rates andmore » the PHA production rates as a function of reaction conditions such as nutrient concentration, temperature, and light quality and intensity.« less

High-speed growth of TiO2 nanotube arrays with gradient pore diameter and ultrathin tube wall under high-field anodization

NASA Astrophysics Data System (ADS)

Yuan, Xiaoliang; Zheng, Maojun; Ma, Li; Shen, Wenzhong

2010-10-01

Highly ordered TiO2 nanotubular arrays have been prepared by two-step anodization under high field. The high anodizing current densities lead to a high-speed film growth (0.40-1.00 µm min - 1), which is nearly 16 times faster than traditional fabrication of TiO2 at low field. It was found that an annealing process of Ti foil is an effective approach to get a monodisperse and double-pass TiO2 nanotubular layer with a gradient pore diameter and ultrathin tube wall (nearly 10 nm). A higher anodic voltage and longer anodization time are beneficial to the formation of ultrathin tube walls. This approach is simple and cost-effective in fabricating high-quality ordered TiO2 nanotubular arrays for practical applications.

High-speed growth of TiO2 nanotube arrays with gradient pore diameter and ultrathin tube wall under high-field anodization.

PubMed

Yuan, Xiaoliang; Zheng, Maojun; Ma, Li; Shen, Wenzhong

2010-10-08

Highly ordered TiO(2) nanotubular arrays have been prepared by two-step anodization under high field. The high anodizing current densities lead to a high-speed film growth (0.40-1.00 microm min(-1)), which is nearly 16 times faster than traditional fabrication of TiO(2) at low field. It was found that an annealing process of Ti foil is an effective approach to get a monodisperse and double-pass TiO(2) nanotubular layer with a gradient pore diameter and ultrathin tube wall (nearly 10 nm). A higher anodic voltage and longer anodization time are beneficial to the formation of ultrathin tube walls. This approach is simple and cost-effective in fabricating high-quality ordered TiO(2) nanotubular arrays for practical applications.

Process for fabrication of large titanium diboride ceramic bodies

DOEpatents

Moorhead, Arthur J.; Bomar, E. S.; Becher, Paul F.

1989-01-01

A process for manufacturing large, fully dense, high purity TiB.sub.2 articles by pressing powders with a sintering aid at relatively low temperatures to reduce grain growth. The process requires stringent temperature and pressure applications in the hot-pressing step to ensure maximum removal of sintering aid and to avoid damage to the fabricated article or the die.

Single-Step Seeded-Growth of Graphene Nanoribbons (GNRs) via Plasma-Enhanced Chemical Vapor Deposition (PECVD)

NASA Astrophysics Data System (ADS)

Hsu, C.-C.; Yang, K.; Tseng, W.-S.; Li, Yiliang; Li, Yilun; Tour, J. M.; Yeh, N.-C.

One of the main challenges in the fabrication of GNRs is achieving large-scale low-cost production with high quality. Current techniques, including lithography and unzipped carbon nanotubes, are not suitable for mass production. We have recently developed a single-step PECVD growth process of high-quality graphene sheets without any active heating. By adding some substituted aromatic as seeding molecules, we are able to rapidly grow GNRs vertically on various transition-metal substrates. The morphology and electrical properties of the GNRs are dependent on the growth parameters such as the growth time, gas flow and species of the seeding molecules. On the other hand, all GNRs exhibit strong infrared and optical absorption. From studies of the Raman spectra, scanning electron microscopic images, and x-ray/ultraviolet photoelectron spectra of these GNRs as functions of the growth parameters, we propose a model for the growth mechanism. Our findings suggest that our approach opens up a pathway to large-scale, inexpensive production of GNRs for applications to supercapacitors and solar cells. This work was supported by the Grubstake Award and NSF through IQIM at Caltech.

Purification and Refolding of Overexpressed Human Basic Fibroblast Growth Factor in Escherichia coli

PubMed Central

Alibolandi, Mona; Mirzahoseini, Hasan

2011-01-01

This work describes the integration of expanded bed adsorption (EBA) and adsorptive protein refolding operations used to recover purified and biologically active human basic fibroblast growth factor from inclusion bodies expressed in E. coli. Insoluble overexpressed human basic fibroblast growth factor has been purified on CM Hyper Z matrix by expanded bed adsorption after isolation and solubilization in 8 M urea. The adsorption was made in expanded bed without clarification steps such as centrifugation. Column refolding was done by elimination of urea and elution with NaCl. The human basic fibroblast growth factor was obtained as a highly purified soluble monomer form with similar behavior in circular dichroism and fluorescence spectroscopy as native protein. A total of 92.52% of the available human basic fibroblast growth factor was recovered as biologically active and purified protein using the mentioned purification and refolding process. This resulted in the first procedure describing high-throughput purification and refolding of human basic fibroblast growth factor in one step and is likely to have the greatest benefit for proteins that tend to aggregate when refolded by dilution. PMID:21837279

Flg22-Triggered Immunity Negatively Regulates Key BR Biosynthetic Genes.

PubMed

Jiménez-Góngora, Tamara; Kim, Seong-Ki; Lozano-Durán, Rosa; Zipfel, Cyril

2015-01-01

In plants, activation of growth and activation of immunity are opposing processes that define a trade-off. In the past few years, the growth-promoting hormones brassinosteroids (BR) have emerged as negative regulators of pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI), promoting growth at the expense of defense. The crosstalk between BR and PTI signaling was described as negative and unidirectional, since activation of PTI does not affect several analyzed steps in the BR signaling pathway. In this work, we describe that activation of PTI by the bacterial PAMP flg22 results in the reduced expression of BR biosynthetic genes. This effect does not require BR perception or signaling, and occurs within 15 min of flg22 treatment. Since the described PTI-induced repression of gene expression may result in a reduction in BR biosynthesis, the crosstalk between PTI and BR could actually be negative and bidirectional, a possibility that should be taken into account when considering the interaction between these two pathways.

Molecular beam epitaxy of quasi-freestanding transition metal disulphide monolayers on van der Waals substrates: a growth study

NASA Astrophysics Data System (ADS)

Hall, Joshua; Pielić, Borna; Murray, Clifford; Jolie, Wouter; Wekking, Tobias; Busse, Carsten; Kralj, Marko; Michely, Thomas

2018-04-01

Based on an ultra-high vacuum compatible two-step molecular beam epitaxy synthesis with elemental sulphur, we grow clean, well-oriented, and almost defect-free monolayer islands and layers of the transition metal disulphides MoS2, TaS2 and WS2. Using scanning tunneling microscopy and low energy electron diffraction we investigate systematically how to optimise the growth process, and provide insight into the growth and annealing mechanisms. A large band gap of 2.55 eV and the ability to move flakes with the scanning tunneling microscope tip both document the weak interaction of MoS2 with its substrate consisting of graphene grown on Ir(1 1 1). As the method works for the synthesis of a variety of transition metal disulphides on different substrates, we speculate that it could be of great use for providing hitherto unattainable high quality monolayers of transition metal disulphides for fundamental spectroscopic investigations.

Watching adsorption and electron beam induced decomposition on the model system Mo(CO)6/Cu(1 1 1) by X-ray absorption and photoemission spectroscopies

NASA Astrophysics Data System (ADS)

Paufert, Pierre; Fonda, Emiliano; Li, Zheshen; Domenichini, Bruno; Bourgeois, Sylvie

2013-11-01

An in-depth study of the first steps of electron beam assisted growth of Mo from molybdenum hexacarbonyl on Cu(1 1 1) has been carried out exploiting the complementarity of X-ray photoemission and X-ray absorption spectroscopies. Frank van der Merwe (2D) growth mode has been observed for the completion of the two first monolayers of adsorbed molecules through a simple physisorption process. Irradiation of the Mo(CO)6 deposit by 1 keV electron beam induces a modification of molybdenum coordination, the average number of C-neighbors decreasing from 6 to 3. Decomposed molecules remain on the surface after annealing at 520 K and organize themselves, the molybdenum atoms moving in Cu(1 1 1) surface fcc hollow sites. After annealing at 670 K, metallic molybdenum growth begins, if the total amount of adsorbed Mo atoms exceeds 1.2 monolayers.

Steps in Solution Growth: Revised Gibbs-Thomson Law, Turbulence and Morphological Stability

NASA Technical Reports Server (NTRS)

Chernov, A. A.; Rashkovich, L. N.; Vekilov, P. G.

2004-01-01

Two groups of new phenomena revealed by AFM and high resolution optical interferometry on crystal faces growing from solutions will be discussed. 1. Spacing between strongly polygonized spiral steps with low less than 10(exp -2) kink density on lysozyme and K- biphtalate do not follow the Burton-cabrera-Frank theory. The critical length of the yet immobile first Short step segment adjacent to a pinning defect (dislocation, stacking fault) is many times longer than that following from the step free energy. The low-kink density steps are typical of many growth conditions and materials, including low temperature gas phase epitaxy and MBE. 2. The step bunching pattern on the approx. 1 cm long { 110) KDP face growing from the turbulent solution flow (Re (triple bonds) 10(exp 4), solution flow rate approx. 1 m/s) suggests that the step bunch height does not increase infinitely as the bunch path on the crystal face rises, as is usually observed on large KDP crystals. The mechanism controlling the maximal bunch width and height is based on the drag of the solution depleted by the step bunch down thc solution stream. It includes splitting, coagulation and interlacing of bunches

Long-wave model for strongly anisotropic growth of a crystal step.

PubMed

Khenner, Mikhail

2013-08-01

A continuum model for the dynamics of a single step with the strongly anisotropic line energy is formulated and analyzed. The step grows by attachment of adatoms from the lower terrace, onto which atoms adsorb from a vapor phase or from a molecular beam, and the desorption is nonnegligible (the "one-sided" model). Via a multiscale expansion, we derived a long-wave, strongly nonlinear, and strongly anisotropic evolution PDE for the step profile. Written in terms of the step slope, the PDE can be represented in a form similar to a convective Cahn-Hilliard equation. We performed the linear stability analysis and computed the nonlinear dynamics. Linear stability depends on whether the stiffness is minimum or maximum in the direction of the step growth. It also depends nontrivially on the combination of the anisotropy strength parameter and the atomic flux from the terrace to the step. Computations show formation and coarsening of a hill-and-valley structure superimposed onto a long-wavelength profile, which independently coarsens. Coarsening laws for the hill-and-valley structure are computed for two principal orientations of a maximum step stiffness, the increasing anisotropy strength, and the varying atomic flux.

The impact of a public health department's expansion from a one-step to a two-step refugee screening process on the detection and initiation of treatment of latent tuberculosis.

PubMed

Einterz, E M; Younge, O; Hadi, C

2018-06-01

To determine, subsequent to the expansion of a county health department's refugee screening process from a one-step to a two-step process, the change in early loss to follow-up and time to initiation of treatment of new refugees with latent tuberculosis infection (LTBI). Quasi-experimental, quantitative. Review of patient medical records. Among 384 refugees who met the case definition of LTBI without prior tuberculosis (TB) classification, the number of cases lost to early follow-up fell from 12.5% to 0% after expansion to a two-step screening process. The average interval between in-country arrival and initiation of LTBI treatment was shortened by 41.4%. The addition of a second step to the refugee screening process was correlated with significant improvements in the county's success in tracking and treating cases of LTBI in refugees. Given the disproportionate importance of foreign-born cases of LTBI to the incidence of TB disease in low-incidence countries, these improvements could have a substantial impact on overall TB control, and the process described could serve as a model for other local health department refugee screening programs. Copyright © 2018 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.

Modeling dust growth in protoplanetary disks: The breakthrough case

NASA Astrophysics Data System (ADS)

Drążkowska, J.; Windmark, F.; Dullemond, C. P.

2014-07-01

Context. Dust coagulation in protoplanetary disks is one of the initial steps toward planet formation. Simple toy models are often not sufficient to cover the complexity of the coagulation process, and a number of numerical approaches are therefore used, among which integration of the Smoluchowski equation and various versions of the Monte Carlo algorithm are the most popular. Aims: Recent progress in understanding the processes involved in dust coagulation have caused a need for benchmarking and comparison of various physical aspects of the coagulation process. In this paper, we directly compare the Smoluchowski and Monte Carlo approaches to show their advantages and disadvantages. Methods: We focus on the mechanism of planetesimal formation via sweep-up growth, which is a new and important aspect of the current planet formation theory. We use realistic test cases that implement a distribution in dust collision velocities. This allows a single collision between two grains to have a wide range of possible outcomes but also requires a very high numerical accuracy. Results: For most coagulation problems, we find a general agreement between the two approaches. However, for the sweep-up growth driven by the "lucky" breakthrough mechanism, the methods exhibit very different resolution dependencies. With too few mass bins, the Smoluchowski algorithm tends to overestimate the growth rate and the probability of breakthrough. The Monte Carlo method is less dependent on the number of particles in the growth timescale aspect but tends to underestimate the breakthrough chance due to its limited dynamic mass range. Conclusions: We find that the Smoluchowski approach, which is generally better for the breakthrough studies, is sensitive to low mass resolutions in the high-mass, low-number tail that is important in this scenario. To study the low number density features, a new modulation function has to be introduced to the interaction probabilities. As the minimum resolution needed for breakthrough studies depends strongly on setup, verification has to be performed on a case by case basis.

Impurity effects in crystal growth from solutions: Steady states, transients and step bunch motion

NASA Astrophysics Data System (ADS)

Ranganathan, Madhav; Weeks, John D.

2014-05-01

We analyze a recently formulated model in which adsorbed impurities impede the motion of steps in crystals grown from solutions, while moving steps can remove or deactivate adjacent impurities. In this model, the chemical potential change of an atom on incorporation/desorption to/from a step is calculated for different step configurations and used in the dynamical simulation of step motion. The crucial difference between solution growth and vapor growth is related to the dependence of the driving force for growth of the main component on the size of the terrace in front of the step. This model has features resembling experiments in solution growth, which yields a dead zone with essentially no growth at low supersaturation and the motion of large coherent step bunches at larger supersaturation. The transient behavior shows a regime wherein steps bunch together and move coherently as the bunch size increases. The behavior at large line tension is reminiscent of the kink-poisoning mechanism of impurities observed in calcite growth. Our model unifies different impurity models and gives a picture of nonequilibrium dynamics that includes both steady states and time dependent behavior and shows similarities with models of disordered systems and the pinning/depinning transition.

From fatalism to resilience: reducing disaster impacts through systematic investments.

PubMed

Hill, Harvey; Wiener, John; Warner, Koko

2012-04-01

This paper describes a method for reducing the economic risks associated with predictable natural hazards by enhancing the resilience of national infrastructure systems. The three-step generalised framework is described along with examples. Step one establishes economic baseline growth without the disaster impact. Step two characterises economic growth constrained by a disaster. Step three assesses the economy's resilience to the disaster event when it is buffered by alternative resiliency investments. The successful outcome of step three is a disaster-resistant core of infrastructure systems and social capacity more able to maintain the national economy and development post disaster. In addition, the paper considers ways to achieve this goal in data-limited environments. The method provides a methodology to address this challenge via the integration of physical and social data of different spatial scales into macroeconomic models. This supports the disaster risk reduction objectives of governments, donor agencies, and the United Nations International Strategy for Disaster Reduction. © 2012 The Author(s). Disasters © Overseas Development Institute, 2012.

Complete nitrification by Nitrospira bacteria

PubMed Central

Daims, Holger; Lebedeva, Elena V.; Pjevac, Petra; Han, Ping; Herbold, Craig; Albertsen, Mads; Jehmlich, Nico; Palatinszky, Marton; Vierheilig, Julia; Bulaev, Alexandr; Kirkegaard, Rasmus H.; von Bergen, Martin; Rattei, Thomas; Bendinger, Bernd; Nielsen, Per H.; Wagner, Michael

2016-01-01

Nitrification, the oxidation of ammonia via nitrite to nitrate, has always been considered as a two-step process catalyzed by chemolithoautotrophic microorganisms oxidizing either ammonia or nitrite. No known nitrifier carries out both steps, although complete nitrification should be energetically advantageous. This functional separation has puzzled microbiologists for a century. Here we report on the discovery and cultivation of a completely nitrifying bacterium from the genus Nitrospira, a globally distributed group of nitrite oxidizers. The genome of this chemolithoautotrophic organism encodes both the pathways for ammonia and nitrite oxidation, which are concomitantly expressed during growth by ammonia oxidation to nitrate. Genes affiliated with the phylogenetically distinct ammonia monooxygenase and hydroxylamine dehydrogenase genes of Nitrospira are present in many environments and were retrieved on Nitrospira-contigs in new metagenomes from engineered systems. These findings fundamentally change our picture of nitrification and point to completely nitrifying Nitrospira as key components of nitrogen-cycling microbial communities. PMID:26610024

Assay Methods for ACS Activity and ACS Phosphorylation by MAP Kinases In Vitro and In Vivo.

PubMed

Han, Xiaomin; Li, Guojing; Zhang, Shuqun

2017-01-01

Ethylene, a gaseous phytohormone, has profound effects on plant growth, development, and adaptation to the environment. Ethylene-regulated processes begin with the induction of ethylene biosynthesis. There are two key steps in ethylene biosynthesis. The first is the biosynthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) from S-Adenosyl-Methionine (SAM), a common precursor in many metabolic pathways, which is catalyzed by ACC synthase (ACS). The second is the oxidative cleavage of ACC to form ethylene under the action of ACC oxidase (ACO). ACC biosynthesis is the committing and generally the rate-limiting step in ethylene biosynthesis. As a result, characterizing the cellular ACS activity and understanding its regulation are important. In this chapter, we detail the methods used to measure, (1) the enzymatic activity of both recombinant and native ACS proteins, and (2) the phosphorylation of ACS protein by mitogen-activated protein kinases (MAPKs) in vivo and in vitro.

Effects of the voltage and time of anodization on modulation of the pore dimensions of AAO films for nanomaterials synthesis

NASA Astrophysics Data System (ADS)

Chahrour, Khaled M.; Ahmed, Naser M.; Hashim, M. R.; Elfadill, Nezar G.; Maryam, W.; Ahmad, M. A.; Bououdina, M.

2015-12-01

Highly-ordered and hexagonal-shaped nanoporous anodic aluminum oxide (AAO) of 1 μm thickness of Al pre-deposited onto Si substrate using two-step anodization was successfully fabricated. The growth mechanism of the porous AAO film was investigated by anodization current-time behavior for different anodizing voltages and by visualizing the microstructural procedure of the fabrication of AAO film by two-step anodization using cross-sectional and top view of FESEM imaging. Optimum conditions of the process variables such as annealing time of the as-deposited Al thin film and pore widening time of porous AAO film were experimentally determined to obtain AAO films with uniformly distributed and vertically aligned porous microstructure. Pores with diameter ranging from 50 nm to 110 nm and thicknesses between 250 nm and 1400 nm, were obtained by controlling two main influential anodization parameters: the anodizing voltage and time of the second-step anodization. X-ray diffraction analysis reveals amorphous-to-crystalline phase transformation after annealing at temperatures above 800 °C. AFM images show optimum ordering of the porous AAO film anodized under low voltage condition. AAO films may be exploited as templates with desired size distribution for the fabrication of CuO nanorod arrays. Such nanostructured materials exhibit unique properties and hold high potential for nanotechnology devices.

Pin-Hole Free Perovskite Film for Solar Cells Application Prepared by Controlled Two-Step Spin-Coating Method

NASA Astrophysics Data System (ADS)

Bahtiar, A.; Rahmanita, S.; Inayatie, Y. D.

2017-05-01

Morphology of perovskite film is a key important for achieving high performance perovskite solar cells. Perovskite films are commonly prepared by two-step spin-coating method. However, pin-holes are frequently formed in perovskite films due to incomplete conversion of lead-iodide (PbI2) into perovskite CH3NH3PbI3. Pin-holes in perovskite film cause large hysteresis in current-voltage curve of solar cells due to large series resistance between perovskite layer-hole transport material. Moreover, crystal structure and grain size of perovskite crystal are also other important parameters for achieving high performance solar cells, which are significantly affected by preparation of perovskite film. We studied the effect of preparation of perovskite film using controlled spin-coating parameters on crystal structure and morphological properties of perovskite film. We used two-step spin-coating method for preparation of perovskite film with varied spinning speed, spinning time and temperature of spin-coating process to control growth of perovskite crystal aimed to produce high quality perovskite crystal with pin-hole free and large grain size. All experiment was performed in air with high humidity (larger than 80%). The best crystal structure, pin-hole free with large grain crystal size of perovskite film was obtained from film prepared at room temperature with spinning speed 1000 rpm for 20 seconds and annealed at 100°C for 300 seconds.

Microcrystalline silicon thin films deposited by matrix-distributed electron cyclotron resonance plasma enhanced chemical vapor deposition using an SiF4 /H2 chemistry

NASA Astrophysics Data System (ADS)

Wang, Junkang; Bulkin, Pavel; Florea, Ileana; Maurice, Jean-Luc; Johnson, Erik

2016-07-01

For the growth of hydrogenated microcrystalline silicon (μc-Si:H) thin films by low temperature plasma-enhanced chemical vapor deposition (PECVD), silicon tetrafluoride (SiF4) has recently attracted interest as a precursor due to the resilient optoelectronic performance of the resulting material and devices. In this work, μc-Si:H films are deposited at high rates (7 Å s-1) from a SiF4 and hydrogen (H2) gas mixture by matrix-distributed electron cyclotron resonance PECVD (MDECR-PECVD). Increased substrate temperature and moderate ion bombardment energy (IBE) are demonstrated to be of vital importance to achieve high quality μc-Si:H films under such low process pressure and high plasma density conditions, presumably due to thermally-induced and ion-induced enhancement of surface species migration. Two well-defined IBE thresholds at 12 eV and 43 eV, corresponding respectively to SiF+ ion-induced surface and bulk atomic displacement, are found to be determinant to the final film properties, namely the surface roughness, feature size and crystalline content. Moreover, a study of the growth dynamics shows that the primary challenge to producing highly crystallized μc-Si:H films by MDECR-PECVD appears to be the nucleation step. By employing a two-step method to first prepare a highly crystallized seed layer, μc-Si:H films lacking any amorphous incubation layer have been obtained. A crystalline volume fraction of 68% is achieved with a substrate temperature as low as 120 °C, which is of great interest to broaden the process window for solar cell applications.

On the driving force of PAH production

NASA Technical Reports Server (NTRS)

Frenklach, Michael

1989-01-01

The kinetic factors affecting the production of polycyclic aromatic hydrocarbons (PAH) in high-temperature pyrolysis and combustion environments are analyzed. A lumped kinetic model representing polymerization-type growth by one irreversible step and two reversible steps is considered. It is shown that at high temperatures, PAH growth is controlled by the superequilibrium of hydrogen atoms; at low temperatures and low H2 concentrations, the PAH growth rate is proportional to the rate of the H-abstraction of a hydrogen atom from aromatic molecules; while at low temperatures and high H2 concentrations, it is controlled by the thermodynamics of the H-abstraction and the kinetics of acetylene addition to aromatic radicals. The presence of oxygen mainly affects the small-molecule reactions during the induction period.

Isothermal reduction kinetics of Panzhihua ilmenite concentrate under 30vol% CO-70vol% N2 atmosphere

NASA Astrophysics Data System (ADS)

Zhang, Ying-yi; Lü, Wei; Lü, Xue-wei; Li, Sheng-ping; Bai, Chen-guang; Song, Bing; Han, Ke-xi

2017-03-01

The reduction of ilmenite concentrate in 30vol% CO-70vol% N2 atmosphere was characterized by thermogravimetric and differential thermogravimetric (TG-DTG) analysis methods at temperatures from 1073 to 1223 K. The isothermal reduction results show that the reduction process comprised two stages; the corresponding apparent activation energy was obtained by the iso-conversional and model-fitting methods. For the first stage, the effect of temperature on the conversion degree was not obvious, the phase boundary chemical reaction was the controlling step, with an apparent activation energy of 15.55-40.71 kJ·mol-1. For the second stage, when the temperatures was greater than 1123 K, the reaction rate and the conversion degree increased sharply with increasing temperature, and random nucleation and subsequent growth were the controlling steps, with an apparent activation energy ranging from 182.33 to 195.95 kJ·mol-1. For the whole reduction process, the average activation energy and pre-exponential factor were 98.94-118.33 kJ·mol-1 and 1.820-1.816 min-1, respectively.

Spectral phasor analysis of LAURDAN fluorescence in live A549 lung cells to study the hydration and time evolution of intracellular lamellar body-like structures.

PubMed

Malacrida, Leonel; Astrada, Soledad; Briva, Arturo; Bollati-Fogolín, Mariela; Gratton, Enrico; Bagatolli, Luis A

2016-11-01

Using LAURDAN spectral imaging and spectral phasor analysis we concurrently studied the growth and hydration state of subcellular organelles (lamellar body-like, LB-like) from live A549 lung cancer cells at different post-confluence days. Our results reveal a time dependent two-step process governing the size and hydration of these intracellular LB-like structures. Specifically, a first step (days 1 to 7) is characterized by an increase in their size, followed by a second one (days 7 to 14) where the organelles display a decrease in their global hydration properties. Interestingly, our results also show that their hydration properties significantly differ from those observed in well-characterized artificial lamellar model membranes, challenging the notion that a pure lamellar membrane organization is present in these organelles at intracellular conditions. Finally, these LB-like structures show a significant increase in their hydration state upon secretion, suggesting a relevant role of entropy during this process. Copyright © 2016 Elsevier B.V. All rights reserved.

Optimization of processing parameters on the controlled growth of ZnO nanorod arrays for the performance improvement of solid-state dye-sensitized solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Yi-Mu, E-mail: ymlee@nuu.edu.t; Yang, Hsi-Wen

2011-03-15

High-transparency and high quality ZnO nanorod arrays were grown on the ITO substrates by a two-step chemical bath deposition (CBD) method. The effects of processing parameters including reaction temperature (25-95 {sup o}C) and solution concentration (0.01-0.1 M) on the crystal growth, alignment, optical and electrical properties were systematically investigated. It has been found that these process parameters are critical for the growth, orientation and aspect ratio of the nanorod arrays, showing different structural and optical properties. Experimental results reveal that the hexagonal ZnO nanorod arrays prepared under reaction temperature of 95 {sup o}C and solution concentration of 0.03 M possessmore » highest aspect ratio of {approx}21, and show the well-aligned orientation and optimum optical properties. Moreover the ZnO nanorod arrays based heterojunction electrodes and the solid-state dye-sensitized solar cells (SS-DSSCs) were fabricated with an improved optoelectrical performance. -- Graphical abstract: The ZnO nanorod arrays demonstrate well-alignment, high aspect ratio (L/D{approx}21) and excellent optical transmittance by low-temperature chemical bath deposition (CBD). Display Omitted Research highlights: > Investigate the processing parameters of CBD on the growth of ZnO nanorod arrays. > Optimization of CBD process parameters: 0.03 M solution concentration and reaction temperature of 95 {sup o}C. > The prepared ZnO samples possess well-alignment and high aspect ratio (L/D{approx}21). > An n-ZnO/p-NiO heterojunction: great rectifying behavior and low leakage current. > SS-DSSC has J{sub SC} of 0.31 mA/cm{sup 2} and V{sub OC} of 590 mV, and an improved {eta} of 0.059%.« less

Atomic force microscopic study of step bunching and macrostep formation during the growth of L-arginine phosphate monohydrate single crystals

NASA Astrophysics Data System (ADS)

Sangwal, K.; Torrent-Burgues, J.; Sanz, F.; Gorostiza, P.

1997-02-01

The experimental results of the formation of step bunches and macrosteps on the {100} face of L-arginine phosphate monohydrate crystals grown from aqueous solutions at different supersaturations studied by using atomic force microscopy are described and discussed. It was observed that (1) the step height does not remain constant with increasing time but fluctuates within a particular range of heights, which depends on the region of step bunches, (2) the maximum height and the slope of bunched steps increases with growth time as well as supersaturation used for growth, and that (3) the slope of steps of relatively small heights is usually low with a value of about 8° and does not depend on the region of formation of step bunches, but the slope of steps of large heights is up to 21°. Analysis of the experimental results showed that (1) at a particular value of supersaturation the ratio of the average step height to the average step spacing is a constant, suggesting that growth of the {100} face of L-arginine phosphate monohydrate crystals occurs by direct integration of growth entities to growth steps, and that (2) the formation of step bunches and macrosteps follows the dynamic theory of faceting, advanced by Vlachos et al.

Fabrication of selective-area growth InGaN LED by mixed-source hydride vapor-phase epitaxy

NASA Astrophysics Data System (ADS)

Bae, Sung Geun; Jeon, Injun; Jeon, Hunsoo; Kim, Kyoung Hwa; Yang, Min; Yi, Sam Nyung; Lee, Jae Hak; Ahn, Hyung Soo; Yu, Young Moon; Sawaki, Nobuhiko; Kim, Suck-Whan

2018-01-01

We prepared InGaN light-emitting diodes (LEDs) with the active layers grown from a mixed source of Ga-In-N materials on an n-type GaN substrate by a selective-area growth method and three fabrication steps: photolithography, epitaxial layer growth, and metallization. The preparation followed a previously developed experimental process using apparatus for mixed-source hydride vapor-phase epitaxy (HVPE), which consisted of a multi-graphite boat, for insulating against the high temperature and to control the growth rate of epilayers, filled with the mixed source on the inside and a radio-frequency (RF) heating coil for heating to a high temperature (T > 900 °C) and for easy control of temperature outside the source zone. Two types of LEDs were prepared, with In compositions of 11.0 and 6.0% in the InGaN active layer, and room-temperature electroluminescence measurements exhibited a main peak corresponding to the In composition at either 420 or 390 nm. The consecutive growth of InGaN LEDs by the mixed-source HVPE method provides a technique for the production of LEDs with a wide range of In compositions in the active layer.

Morphological evolution of TiO2 nanotube arrays with lotus-root-shaped nanostructure

NASA Astrophysics Data System (ADS)

Yu, Dongliang; Song, Ye; Zhu, Xufei; Yang, Ruiquan; Han, Aijun

2013-07-01

TiO2 nanotube arrays (TNAs) with lotus-root-shaped nanostructure have been fabricated by a modified two-step electrochemical anodization method. In the present work, different morphologies formed under different anodizing voltages are investigated in detail by field-emission scanning electron microscope. The results show that the concaves left by the first-step anodization can guide the uniform growth of TNAs in some degree as the second-step anodizing voltage is the same with that in the first step, however, when lower voltages are adopted in the second-step anodization, no guidance can be achieved, and different morphological TNAs with lotus-root-shaped nanostructure are fabricated. And we find that the nanotube diameters are directly proportional to the applied voltage in the second-step anodization. Furthermore, a possible mechanism for the growth of the TiO2 nanotubes with the special morphology is proposed for the first time, which depends on both the oxygen bubble mold and the viscous flow of the barrier oxide from the pore base to the pore wall.

Biodiesel from Citrullus colocynthis Oil: Sulfonic-Ionic Liquid-Catalyzed Esterification of a Two-Step Process

PubMed Central

Ali Elsheikh, Yasir; Hassan Akhtar, Faheem

2014-01-01

Biodiesel was prepared from Citrullus colocynthis oil (CCO) via a two-step process. The first esterification step was explored in two ionic liquids (ILs) with 1,3-disulfonic acid imidazolium hydrogen sulfate (DSIMHSO4) and 3-methyl-1-sulfonic acid imidazolium hydrogen sulfate (MSIMHSO4). Both ILs appeared to be good candidates to replace hazardous acidic catalyst due to their exceptional properties. However, the two sulfonic chains existing in DSIMHSO4 were found to increase the acidity to the IL than the single sulfonic chain in MSIMHSO4. Based on the results, 3.6 wt% of DSIMHSO4, methanol/CCO molar ratio of 12 : 1, and 150°C offered a final FFA conversion of 95.4% within 105 min. A 98.2% was produced via second KOH-catalyzed step in 1.0%, 6 : 1 molar ratio, 600 rpm, and 60°C for 50 min. This new two-step catalyzed process could solve the corrosion and environmental problems associated with the current acidic catalysts. PMID:24987736

Temporal consistency of spatial pattern in growth of the mussel, Mytilus edulis: Implications for predictive modelling

NASA Astrophysics Data System (ADS)

Bergström, Per; Lindegarth, Susanne; Lindegarth, Mats

2013-10-01

Human pressures on coastal seas are increasing and methods for sustainable management, including spatial planning and mitigative actions, are therefore needed. In coastal areas worldwide, the development of mussel farming as an economically and ecologically sustainable industry requires geographic information on the growth and potential production capacity. In practice this means that coherent maps of temporally stable spatial patterns of growth need to be available in the planning process and that maps need to be based on mechanistic or empirical models. Therefore, as a first step towards development of models of growth, we assessed empirically the fundamental requirement that there are temporally consistent spatial patterns of growth in the blue mussel, Mytilus edulis. Using a pilot study we designed and dimensioned a transplant experiment, where the spatial consistency in the growth of mussels was evaluated at two resolutions. We found strong temporal and scale-dependent spatial variability in growth but patterns suggested that spatial patterns were uncoupled between growth of shell and that of soft tissue. Spatial patterns of shell growth were complex and largely inconsistent among years. Importantly, however, the growth of soft tissue was qualitatively consistent among years at the scale of km. The results suggest that processes affecting the whole coastal area cause substantial differences in growth of soft tissue among years but that factors varying at the scale of km create strong and persistent spatial patterns of growth, with a potential doubling of productivity by identifying the most suitable locations. We conclude that the observed spatial consistency provides a basis for further development of predictive modelling and mapping of soft tissue growth in these coastal areas. Potential causes of observed patterns, consequences for mussel-farming as a tool for mitigating eutrophication, aspects of precision of modelling and sampling of mussel growth as well as ecological functions in general are discussed.

Influence of MBE growth modes and conditions on spontaneous formation of metallic In nanoparticles and electrical properties of InN matrix

NASA Astrophysics Data System (ADS)

Komissarova, T. A.; Wang, P.; Paturi, P.; Wang, X.; Ivanov, S. V.

2017-11-01

Influence of the molecular beam epitaxy (MBE) growth conditions on the electrical properties of the InN epilayers in terms of minimization of the effect of spontaneously formed In nanoparticles was studied. A three-step growth sequence was used, including direct MBE growth of an InN nucleation layer, migration enhanced epitaxy (MEE) of an InN buffer layer, and In-rich MBE growth of the main InN layer, utilizing the droplet elimination by radical-beam irradiation (DERI) technique. The three-step growth regime was found to lead to decreasing the relative amount of In nanoparticles to 4.8% and 3.8% in In-rich and near-stoichiometric conditions, respectively, whereas the transport properties are better for the In-rich growth. Further reduction of the metallic indium inclusions in the InN films, while keeping simultaneously satisfactory transport parameters, is hardly possible due to fundamental processes of InN thermal decomposition and formation of the nitrogen vacancy conglomerates in the InN matrix. The In inclusions are shown to dominate the electrical conductivity of the InN films even at their minimum amount.

In Situ Graphene Growth Dynamics on Polycrystalline Catalyst Foils

PubMed Central

2016-01-01

The dynamics of graphene growth on polycrystalline Pt foils during chemical vapor deposition (CVD) are investigated using in situ scanning electron microscopy and complementary structural characterization of the catalyst with electron backscatter diffraction. A general growth model is outlined that considers precursor dissociation, mass transport, and attachment to the edge of a growing domain. We thereby analyze graphene growth dynamics at different length scales and reveal that the rate-limiting step varies throughout the process and across different regions of the catalyst surface, including different facets of an individual graphene domain. The facets that define the domain shapes lie normal to slow growth directions, which are determined by the interfacial mobility when attachment to domain edges is rate-limiting, as well as anisotropy in surface diffusion as diffusion becomes rate-limiting. Our observations and analysis thus reveal that the structure of CVD graphene films is intimately linked to that of the underlying polycrystalline catalyst, with both interfacial mobility and diffusional anisotropy depending on the presence of step edges and grain boundaries. The growth model developed serves as a general framework for understanding and optimizing the growth of 2D materials on polycrystalline catalysts. PMID:27576749

Step Permeability on the Pt(111) Surface

NASA Astrophysics Data System (ADS)

Altman, Michael

2005-03-01

Surface morphology will be affected, or even dictated, by kinetic limitations that may be present during growth. Asymmetric step attachment is recognized to be an important and possibly common cause of morphological growth instabilities. However, the impact of this kinetic limitation on growth morphology may be hindered by other factors such as the rate limiting step and step permeability. This strongly motivates experimental measurements of these quantities in real systems. Using low energy electron microscopy, we have measured step flow velocities in growth on the Pt(111) surface. The dependence of step velocity upon adjacent terrace width clearly shows evidence of asymmetric step attachment and step permeability. Step velocity is modeled by solving the diffusion equation simultaneously on several adjacent terraces subject to boundary conditions at intervening steps that include asymmetric step attachment and step permeability. This analysis allows a quantitative evaluation of step permeability and the kinetic length, which characterizes the rate limiting step continuously between diffusion and attachment-detachment limited regimes. This work provides information that is greatly needed to set physical bounds on the parameters that are used in theoretical treatments of growth. The observation that steps are permeable even on a simple metal surface should also stimulate more experimental measurements and theoretical treatments of this effect.

Using the Binary Phase-Field Crystal Model to Describe Non-Classical Nucleation Pathways in Gold Nanoparticles

NASA Astrophysics Data System (ADS)

Smith, Nathan; Provatas, Nikolas

Recent experimental work has shown that gold nanoparticles can precipitate from an aqueous solution through a non-classical, multi-step nucleation process. This multi-step process begins with spinodal decomposition into solute-rich and solute-poor liquid domains followed by nucleation from within the solute-rich domains. We present a binary phase-field crystal theory that shows the same phenomology and examine various cross-over regimes in the growth and coarsening of liquid and solid domains. We'd like to the thank Canada Research Chairs (CRC) program for funding this work.

Aging Optimization of Aluminum-Lithium Alloy C458 for Application to Cryotank Structures

NASA Technical Reports Server (NTRS)

Sova, B. J.; Sankaran, K. K.; Babel, H.; Farahmand, B.; Rioja, R.

2003-01-01

Compared with aluminum alloys such as 2219, which is widely used in space vehicle for cryogenic tanks and unpressurized structures, aluminum-lithium alloys possess attractive combinations of lower density and higher modulus along with comparable mechanical properties. These characteristics have resulted in the successful use of the aluminum-lithium alloy 2195 (Al-1.0 Li-4.0 Cu-0.4 Mg-0.4 Ag-0.12 Zr) for the Space Shuttle External Tank, and the consideration of newer U.S. aluminum-lithium alloys such as L277 and C458 for future space vehicles. These newer alloys generally have lithium content less than 2 wt. % and their composition and processing have been carefully tailored to increase the toughness and reduce the mechanical property anisotropy of the earlier generation alloys such 2090 and 8090. Alloy processing, particularly the aging treatment, has a significant influence on the strength-toughness combinations and their dependence on service environments for aluminum-lithium alloys. Work at NASA Marshall Space Flight Center on alloy 2195 has shown that the cryogenic toughness can be improved by employing a two-step aging process. This is accomplished by aging at a lower temperature in the first step to suppress nucleation of the strengthening precipitate at sub-grain boundaries while promoting nucleation in the interior of the grains. Second step aging at the normal aging temperature results in precipitate growth to the optimum size. A design of experiments aging study was conducted for plate. To achieve the T8 temper, Alloy C458 (Al-1.8 Li-2.7 Cu-0.3 Mg-0.08 Zr-0.3 Mn-0.6 Zn) is typically aged at 300F for 24hours. In this study, a two-step aging treatment was developed through a comprehensive 2(exp 4) full factorial design of experiments study and the typical one-step aging used as a reference. Based on the higher lithium content of C458 compared with 2195, the first step aging temperature was varied between 175F and 250F. The second step aging temperatures was varied between 275F and 325F, which is in the range of the single-step aging temperature. The results of the design of experiments used for the T8 temper as well as a smaller set of experiments for the T6 temper will be presented. The process of selecting the optimum aging treatment, based on the measured mechanical properties at room and cryogenic temperature as well as the observed deformation mechanisms, will be presented in detail. The implications for the use of alloy C458 in cryotanks will be discussed.

Aging Optimization of Aluminum-Lithium Alloy C458 for Application to Cryotank Structures

NASA Technical Reports Server (NTRS)

Sova, B. J.; Sankaran, K. K.; Babel, H.; Farahmand, B.; Rioja, R.

2003-01-01

Compared with aluminum alloys such as 2219, which is widely used in space vehicle for cryogenic tanks and unpressurized structures, aluminum-lithium alloys possess attractive combinations of lower density and higher modulus along with comparable mechanical properties. These characteristics have resulted in the successful use of the aluminum-lithium alloy 2195 (Al-1.0 Li-4.0 Cu-0.4 Mg-0.4 Ag-0.12 Zr) for the Space Shuttle External Tank, and the consideration of newer U.S. aluminum-lithium alloys such as L277 and C458 for future space vehicles. These newer alloys generally have lithium content less than 2 wt. % and their composition and processing have been carefully tailored to increase the toughness and reduce the mechanical property anisotropy of the earlier generation alloys such 2090 and 8090. Alloy processing, particularly the aging treatment, has a significant influence on the strength-toughness combinations and their dependence on service environments for aluminum-lithium alloys. Work at NASA Marshall Space Flight Center on alloy 2195 has shown that the cryogenic toughness can be improved by employing a two-step aging process. This is accomplished by aging at a lower temperature in the first step to suppress nucleation of the strengthening precipitate at sub-grain boundaries while promoting nucleation in the interior of the grains. Second step aging at the normal aging temperature results in precipitate growth to the optimum size. A design of experiments aging study was conducted for plate. To achieve the T8 temper, Alloy C458 (Al-1.8 Li-2.7 Cu-0.3 Mg- 0.08 Zr-0.3 Mn-0.6 Zn) is typically aged at 300 F for 24 hours. In this study, a two-step aging treatment was developed through a comprehensive 24 full factorial design of experiments study and the typical one-step aging used as a reference. Based on the higher lithium content of C458 compared with 2195, the first step aging temperature was varied between 175 F and 250 F. The second step aging temperatures was varied between 275 F and 325 F, which is in the range of the single-step aging temperature. The results of the design of experiments used for the T8 temper as well as a smaller set of experiments for the T6 temper will be presented. The process of selecting the optimum aging treatment, based on the measured mechanical properties at room and cryogenic temperature as well as the observed deformation mechanisms, will be presented in detail. The implications for the use of alloy C458 in cryotanks will be discussed.

[Investigation of stages of chemical leaching and biooxidation during the extraction of gold from sulfide concentrates].

PubMed

Murav'ev, M I; Fomchenko, N V; Kondrat'eva, T V

2015-01-01

We examined the chemical leaching and biooxidation stages in a two-stage biooxidation process of an auriferous sulfide concentrate containing pyrrhotite, arsenopyrite and pyrite. Chemical leaching of the concentrate (slurry density at 200 g/L) by ferric sulfate biosolvent (initial concentration at 35.6 g/L), which was obtained by microbial oxidation of ferrous sulfate for 2 hours at 70°C at pH 1.4, was allowed to oxidize 20.4% ofarsenopyrite and 52.1% of sulfur. The most effective biooxidation of chemically leached concentrate was observed at 45°C in the presence of yeast extract. Oxidation of the sulfide concentrate in a two-step process proceeded more efficiently than in one-step. In a two-step mode, gold extraction from the precipitate was 10% higher and the content of elemental sulfur was two times lower than in a one-step process.

Boron-doped few-walled carbon nanotubes: novel synthesis and properties

NASA Astrophysics Data System (ADS)

Preston, Colin; Song, Da; Taillon, Josh; Cumings, John; Hu, Liangbing

2016-11-01

Few-walled carbon nanotubes offer a unique marriage of graphitic quality and robustness to ink-processing; however, doping procedures that may alter the band structure of these few-walled nanotubes are still lacking. This report introduces a novel solution-injected chemical vapor deposition growth process to fabricate the first boron-doped few-walled carbon nanotubes (B-FWNTs) reported in literature, which may have extensive applications in battery devices. A comprehensive characterization of the as-grown B-FWNTs confirms successful boron substitution in the graphitic lattice, and reveals varying growth parameters impact the structural properties of B-FWNT yield. An investigation into the optimal growth purification parameters and ink-making procedures was also conducted. This study introduces the first process technique to successfully grow intrinsically p-doped FWNTs, and provides the first investigation into the impact factors of the growth parameters, purification steps, and ink-making processes on the structural properties of the B-FWNTs and the electrical properties of the resulting spray-coated thin-film electrodes.

A theory of growing crystalline nanorods - Mode I

NASA Astrophysics Data System (ADS)

Du, Feng; Huang, Hanchen

2018-08-01

Nanorods grow in two possible modes during physical vapor deposition (PVD). In mode I, monolayer surface steps dictate the diameter of nanorods. In mode II, multiple-layer surface steps dictate the diameter, which is the smallest possible under physical vapor deposition [5,10]. This paper reports closed-form theories of terrace lengths and nanorod diameter during the growth in mode I, as a function of deposition conditions. The accompanying lattice kinetic Monte Carlo simulations verify these theories. This study reveals that (1) quasi-steady growth exists for each set of nanorod growth conditions, and (2) the characteristic length scales, including terrace lengths and nanorod diameter at the quasi-steady state, depend on the deposition conditions - deposition rate F, substrate temperature T, and incidence angle θ - only as a function of l2D/tan θ, with l2 D = 2(v2 D/Fcosθ) 1/3 as a diffusion-limited length scale and v2D as the atomic diffusion jump rate over monolayer surface steps.

Synthesis of nanogranular Fe3O4/biomimetic hydroxyapatite for potential applications in nanomedicine: structural and magnetic characterization

NASA Astrophysics Data System (ADS)

Del Bianco, L.; Lesci, I. G.; Fracasso, G.; Barucca, G.; Spizzo, F.; Tamisari, M.; Scotti, R.; Ciocca, L.

2015-06-01

We realized the synthesis of a novel nanogranular system consisting of magnetite nanoparticles embedded in biomimetic carbonate hydroxyapatite (HA), for prospective uses in bone tissue engineering. An original two-step method was implemented: in the first step, magnetite nanoparticles are prepared by refluxing an aqueous solution of Fe(SO4) and Fe2(SO4)3 in an excess of tetrabutilammonium hydroxide acting as surfactant; then, the magnetite nanoparticles are coated with a Ca(OH)2 layer, to induce the growth of HA directly on their surface, by reaction of Ca(OH)2 with HPO42-. Two nanogranular samples were collected with magnetite content ˜0.8 and ˜4 wt%. The magnetite nanoparticles and the composite material were investigated by x-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. These analyses provided information on the structure of the nanoparticles (mean size ˜6 nm) and revealed the presence of surface hydroxyl groups, which promoted the subsequent growth of the HA phase, featuring a nanocrystalline lamellar structure. The magnetic study, by a superconducting quantum interference device magnetometer, has shown that both the as-prepared and the HA-coated magnetite nanoparticles are superparamagnetic at T = 300 K, but the magnetization relaxation process is dominated by dipolar magnetic interactions of comparable strength. In the three samples, a collective frozen magnetic regime is established below T ˜ 20 K. These results indicate that the magnetite nanoparticles tend to form agglomerates in the as-prepared state, which are not substantially altered by the HA growth, coherently with the creation of electrostatic hydrogen bonds among the surface hydroxyl groups.

Starting a new residency program: a step-by-step guide for institutions, hospitals, and program directors

PubMed Central

Barajaz, Michelle; Turner, Teri

2016-01-01

Although our country faces a looming shortage of doctors, constraints of space, funding, and patient volume in many existing residency programs limit training opportunities for medical graduates. New residency programs need to be created for the expansion of graduate medical education training positions. Partnerships between existing academic institutions and community hospitals with a need for physicians can be a very successful means toward this end. Baylor College of Medicine and The Children's Hospital of San Antonio were affiliated in 2012, and subsequently, we developed and received accreditation for a new categorical pediatric residency program at that site in 2014. We share below a step-by-step guide through the process that includes building of the infrastructure, educational development, accreditation, marketing, and recruitment. It is our hope that the description of this process will help others to spur growth in graduate medical training positions. PMID:27507541

Preparation, characterization and dissolution of passive oxide film on the 400 series stainless steel surfaces

NASA Astrophysics Data System (ADS)

Sathyaseelan, V. S.; Rufus, A. L.; Chandramohan, P.; Subramanian, H.; Velmurugan, S.

2015-12-01

Full system decontamination of Primary Heat Transport (PHT) system of Pressurised Heavy Water Reactors (PHWRs) resulted in low decontamination factors (DF) on stainless steel (SS) surfaces. Hence, studies were carried out with 403 SS and 410 SS that are the material of construction of "End-Fitting body" and "End-Fitting Liner tubes". Three formulations were evaluated for the dissolution of passive films formed over these alloys viz., i) Two-step process consisting of oxidation and reduction reactions, ii) Dilute Chemical Decontamination (DCD) and iii) High Temperature Process. The two-step and high temperature processes could dissolve the oxide completely while the DCD process could remove only 60%. Various techniques like XRD, Raman spectroscopy and SEM-EDX were used for assessing the dissolution process. The two-step process is time consuming, laborious while the high temperature process is less time consuming and is recommended for SS decontamination.

Enhancement of neutral lipid productivity in the microalga Isochrysis affinis Galbana (T-Iso) by a mutation-selection procedure.

PubMed

Bougaran, Gaël; Rouxel, Catherine; Dubois, Nolwenn; Kaas, Raymond; Grouas, Sophie; Lukomska, Ewa; Le Coz, Jean-René; Cadoret, Jean-Paul

2012-11-01

Microalgae offer a high potential for energetic lipid storage as well as high growth rates. They are therefore considered promising candidates for biofuel production, with the selection of high lipid-producing strains a major objective in projects on the development of this technology. We developed a mutation-selection method aimed at increasing microalgae neutral lipid productivity. A two step method, based on UVc irradiation followed by flow cytometry selection, was applied to a set of strains that had an initial high lipid content and improvement was assessed by means of Nile-red fluorescence measurements. The method was first tested on Isochrysis affinis galbana (T-Iso). Following a first round of mutation-selection, the total fatty acid content had not increased significantly, being 262 ± 21 mgTFA (gC)-1 for the wild type (WT) and 269 ± 49 mgTFA (gC)-1 for the selected population (S1M1). Conversely, fatty acid distribution among the lipid classes was affected by the process, resulting in a 20% increase for the fatty acids in the neutral lipids and a 40% decrease in the phospholipids. After a second mutation-selection step (S2M2), the total fatty acid content reached 409 ± 64 mgTFA (gC)-1 with a fatty acid distribution similar to the S1M1 population. Growth rate remained unaffected by the process, resulting in a 80% increase for neutral lipid productivity. Copyright © 2012 Wiley Periodicals, Inc.

Vanadium doped Sb{sub 2}Te{sub 3} material with modified crystallization mechanism for phase-change memory application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ji, Xinglong; Zheng, Yonghui; Zhou, Wangyang

2015-06-15

In this paper, V{sub 0.21}Sb{sub 2}Te{sub 3} (VST) has been proposed for phase-change memory applications. With vanadium incorporating, VST has better thermal stability than Sb{sub 2}Te{sub 3} and can maintain in amorphous phase at room temperature. Two resistance steps were observed in temperature dependent resistance measurements. By real-time observing the temperature dependent lattice structure evolution, VST presents as a homogenous phase throughout the whole thermal process. Combining Hall measurement and transmission electron microscopy results, we can ascribe the two resistance steps to the unique crystallization mechanism of VST material. Then, the amorphous thermal stability enhancement can also be rooted inmore » the suppression of the fast growth crystallization mechanism. Furthermore, the applicability of VST is demonstrated by resistance-voltage measurement, and the phase transition of VST can be triggered by a 15 ns electric pulse. In addition, endurance up to 2.7×10{sup 4} cycles makes VST a promising candidate for phase-change memory applications.« less

Representation of Nucleation Mode Microphysics in a Global Aerosol Model with Sectional Microphysics

NASA Technical Reports Server (NTRS)

Lee, Y. H.; Pierce, J. R.; Adams, P. J.

2013-01-01

In models, nucleation mode (1 nm

Comparability of automated human induced pluripotent stem cell culture: a pilot study.

PubMed

Archibald, Peter R T; Chandra, Amit; Thomas, Dave; Chose, Olivier; Massouridès, Emmanuelle; Laâbi, Yacine; Williams, David J

2016-12-01

Consistent and robust manufacturing is essential for the translation of cell therapies, and the utilisation automation throughout the manufacturing process may allow for improvements in quality control, scalability, reproducibility and economics of the process. The aim of this study was to measure and establish the comparability between alternative process steps for the culture of hiPSCs. Consequently, the effects of manual centrifugation and automated non-centrifugation process steps, performed using TAP Biosystems' CompacT SelecT automated cell culture platform, upon the culture of a human induced pluripotent stem cell (hiPSC) line (VAX001024c07) were compared. This study, has demonstrated that comparable morphologies and cell diameters were observed in hiPSCs cultured using either manual or automated process steps. However, non-centrifugation hiPSC populations exhibited greater cell yields, greater aggregate rates, increased pluripotency marker expression, and decreased differentiation marker expression compared to centrifugation hiPSCs. A trend for decreased variability in cell yield was also observed after the utilisation of the automated process step. This study also highlights the detrimental effect of the cryopreservation and thawing processes upon the growth and characteristics of hiPSC cultures, and demonstrates that automated hiPSC manufacturing protocols can be successfully transferred between independent laboratories.

Growth Mechanism of Transition Metal Dichalcogenide Monolayers: The Role of Self-Seeding Fullerene Nuclei.

PubMed

Cain, Jeffrey D; Shi, Fengyuan; Wu, Jinsong; Dravid, Vinayak P

2016-05-24

Due to their unique optoelectronic properties and potential for next generation devices, monolayer transition metal dichalcogenides (TMDs) have attracted a great deal of interest since the first observation of monolayer MoS2 a few years ago. While initially isolated in monolayer form by mechanical exfoliation, the field has evolved to more sophisticated methods capable of direct growth of large-area monolayer TMDs. Chemical vapor deposition (CVD) is the technique used most prominently throughout the literature and is based on the sulfurization of transition metal oxide precursors. CVD-grown monolayers exhibit excellent quality, and this process is widely used in studies ranging from the fundamental to the applied. However, little is known about the specifics of the nucleation and growth mechanisms occurring during the CVD process. In this study, we have investigated the nucleation centers or "seeds" from which monolayer TMDs typically grow. This was accomplished using aberration-corrected scanning transmission electron microscopy to analyze the structure and composition of the nuclei present in CVD-grown MoS2-MoSe2 alloys. We find that monolayer growth proceeds from nominally oxi-chalcogenide nanoparticles which act as heterogeneous nucleation sites for monolayer growth. The oxi-chalcogenide nanoparticles are typically encased in a fullerene-like shell made of the TMD. Using this information, we propose a step-by-step nucleation and growth mechanism for monolayer TMDs. Understanding this mechanism may pave the way for precise control over the synthesis of 2D materials, heterostructures, and related complexes.

Bifurcation analysis of a discrete-time ratio-dependent predator-prey model with Allee Effect

NASA Astrophysics Data System (ADS)

Cheng, Lifang; Cao, Hongjun

2016-09-01

A discrete-time predator-prey model with Allee effect is investigated in this paper. We consider the strong and the weak Allee effect (the population growth rate is negative and positive at low population density, respectively). From the stability analysis and the bifurcation diagrams, we get that the model with Allee effect (strong or weak) growth function and the model with logistic growth function have somewhat similar bifurcation structures. If the predator growth rate is smaller than its death rate, two species cannot coexist due to having no interior fixed points. When the predator growth rate is greater than its death rate and other parameters are fixed, the model can have two interior fixed points. One is always unstable, and the stability of the other is determined by the integral step size, which decides the species coexistence or not in some extent. If we increase the value of the integral step size, then the bifurcated period doubled orbits or invariant circle orbits may arise. So the numbers of the prey and the predator deviate from one stable state and then circulate along the period orbits or quasi-period orbits. When the integral step size is increased to a critical value, chaotic orbits may appear with many uncertain period-windows, which means that the numbers of prey and predator will be chaotic. In terms of bifurcation diagrams and phase portraits, we know that the complexity degree of the model with strong Allee effect decreases, which is related to the fact that the persistence of species can be determined by the initial species densities.

Effect of production management on semen quality during long-term storage in different European boar studs.

PubMed

Schulze, M; Kuster, C; Schäfer, J; Jung, M; Grossfeld, R

2018-03-01

The processing of ejaculates is a fundamental step for the fertilizing capacity of boar spermatozoa. The aim of the present study was to identify factors that affect quality of boar semen doses. The production process during 1 day of semen processing in 26 European boar studs was monitored. In each boar stud, nine to 19 randomly selected ejaculates from 372 Pietrain boars were analyzed for sperm motility, acrosome and plasma membrane integrity, mitochondrial activity and thermo-resistance (TRT). Each ejaculate was monitored for production time and temperature for each step in semen processing using the special programmed software SEQU (version 1.7, Minitüb, Tiefenbach, Germany). The dilution of ejaculates with a short-term extender was completed in one step in 10 AI centers (n = 135 ejaculates), in two steps in 11 AI centers (n = 158 ejaculates) and in three steps in five AI centers (n = 79 ejaculates). Results indicated there was a greater semen quality with one-step isothermal dilution compared with the multi-step dilution of AI semen doses (total motility TRT d7: 71.1 ± 19.2%, 64.6 ± 20.0%, 47.1 ± 27.1%; one-step compared with two-step compared with the three-step dilution; P < .05). There was a marked advantage when using the one-step isothermal dilution regarding time management, preservation suitability, stability and stress resistance. One-step dilution caused significant lower holding times of raw ejaculates and reduced the possible risk of making mistakes due to a lower number of processing steps. These results lead to refined recommendations for boar semen processing. Copyright © 2018 Elsevier B.V. All rights reserved.

Thermodynamics versus Kinetics Dichotomy in the Linear Self-Assembly of Mixed Nanoblocks.

PubMed

Ruiz, L; Keten, S

2014-06-05

We report classical and replica exchange molecular dynamics simulations that establish the mechanisms underpinning the growth kinetics of a binary mix of nanorings that form striped nanotubes via self-assembly. A step-growth coalescence model captures the growth process of the nanotubes, which suggests that high aspect ratio nanostructures can grow by obeying the universal laws of self-similar coarsening, contrary to systems that grow through nucleation and elongation. Notably, striped patterns do not depend on specific growth mechanisms, but are governed by tempering conditions that control the likelihood of depropagation and fragmentation.

Effect of Temperature and Fluid Flow on Dendrite Growth During Solidification of Al-3 Wt Pct Cu Alloy by the Two-Dimensional Cellular Automaton Method

NASA Astrophysics Data System (ADS)

Gu, Cheng; Wei, Yanhong; Liu, Renpei; Yu, Fengyi

2017-12-01

A two-dimensional cellular automaton-finite volume model was developed to simulate dendrite growth of Al-3 wt pct Cu alloy during solidification to investigate the effect of temperature and fluid flow on dendrite morphology, solute concentration distribution, and dendrite growth velocity. Different calculation conditions that may influence the results of the simulation, including temperature and flow, were considered. The model was also employed to study the effect of different undercoolings, applied temperature fields, and forced flow velocities on solute segregation and dendrite growth. The initial temperature and fluid flow have a significant impact on the dendrite morphologies and solute profiles during solidification. The release of energy is operated with solidification and results in the increase of temperature. A larger undercooling leads to larger solute concentration near the solid/liquid interface and solute concentration gradient at the same time-step. Solute concentration in the solid region tends to increase with the increase of undercooling. Four vortexes appear under the condition when natural flow exists: the two on the right of the dendrite rotate clockwise, and those on the left of the dendrite rotate counterclockwise. With the increase of forced flow velocity, the rejected solute in the upstream region becomes easier to be washed away and enriched in the downstream region, resulting in acceleration of the growth of the dendrite in the upstream and inhibiting the downstream dendrite growth. The dendrite perpendicular to fluid flow shows a coarser morphology in the upstream region than that of the downstream. Almost no secondary dendrite appears during the calculation process.

An atomistic simulation scheme for modeling crystal formation from solution.

PubMed

Kawska, Agnieszka; Brickmann, Jürgen; Kniep, Rüdiger; Hochrein, Oliver; Zahn, Dirk

2006-01-14

We present an atomistic simulation scheme for investigating crystal growth from solution. Molecular-dynamics simulation studies of such processes typically suffer from considerable limitations concerning both system size and simulation times. In our method this time-length scale problem is circumvented by an iterative scheme which combines a Monte Carlo-type approach for the identification of ion adsorption sites and, after each growth step, structural optimization of the ion cluster and the solvent by means of molecular-dynamics simulation runs. An important approximation of our method is based on assuming full structural relaxation of the aggregates between each of the growth steps. This concept only holds for compounds of low solubility. To illustrate our method we studied CaF2 aggregate growth from aqueous solution, which may be taken as prototypes for compounds of very low solubility. The limitations of our simulation scheme are illustrated by the example of NaCl aggregation from aqueous solution, which corresponds to a solute/solvent combination of very high salt solubility.

Growth process for gallium nitride porous nanorods

DOEpatents

Wildeson, Isaac Harshman; Sands, Timothy David

2015-03-24

A GaN nanorod and formation method. Formation includes providing a substrate having a GaN film, depositing SiN.sub.x on the GaN film, etching a growth opening through the SiN.sub.x and into the GaN film, growing a GaN nanorod through the growth opening, the nanorod having a nanopore running substantially through its centerline. Focused ion beam etching can be used. The growing can be done using organometallic vapor phase epitaxy. The nanopore diameter can be controlled using the growth opening diameter or the growing step duration. The GaN nanorods can be removed from the substrate. The SiN.sub.x layer can be removed after the growing step. A SiO.sub.x template can be formed on the GaN film and the GaN can be grown to cover the SiO.sub.x template before depositing SiN.sub.x on the GaN film. The SiO.sub.x template can be removed after growing the nanorods.

Competing growth processes induced by next-nearest-neighbor interactions: Effects on meandering wavelength and stiffness

NASA Astrophysics Data System (ADS)

Blel, Sonia; Hamouda, Ajmi BH.; Mahjoub, B.; Einstein, T. L.

2017-02-01

In this paper we explore the meandering instability of vicinal steps with a kinetic Monte Carlo simulations (kMC) model including the attractive next-nearest-neighbor (NNN) interactions. kMC simulations show that increase of the NNN interaction strength leads to considerable reduction of the meandering wavelength and to weaker dependence of the wavelength on the deposition rate F. The dependences of the meandering wavelength on the temperature and the deposition rate obtained with simulations are in good quantitative agreement with the experimental result on the meandering instability of Cu(0 2 24) [T. Maroutian et al., Phys. Rev. B 64, 165401 (2001), 10.1103/PhysRevB.64.165401]. The effective step stiffness is found to depend not only on the strength of NNN interactions and the Ehrlich-Schwoebel barrier, but also on F. We argue that attractive NNN interactions intensify the incorporation of adatoms at step edges and enhance step roughening. Competition between NNN and nearest-neighbor interactions results in an alternative form of meandering instability which we call "roughening-limited" growth, rather than attachment-detachment-limited growth that governs the Bales-Zangwill instability. The computed effective wavelength and the effective stiffness behave as λeff˜F-q and β˜eff˜F-p , respectively, with q ≈p /2 .

Different growth regimes in InP nanowire growth mediated by Ag nanoparticles.

PubMed

Oliveira, D S; Zavarize, M; Tizei, L H G; Walls, M; Ospina, C A; Iikawa, F; Ugarte, D; Cotta, M A

2017-12-15

We report on the existence of two different regimes in one-step Ag-seeded InP nanowire growth. The vapor-liquid-solid-mechanism is present at larger In precursor flows and temperatures, ∼500 °C, yielding high aspect ratio and pure wurtzite InP nanowires with a semi-spherical metal particle at the thin apex. Periodic diameter oscillations can be achieved under extreme In supersaturations at this temperature range, showing the presence of a liquid catalyst. However, under lower temperatures and In precursor flows, large diameter InP nanowires with mixed wurtzite/zincblende segments are obtained, similarly to In-assisted growth. Chemical composition analysis suggest that In-rich droplet formation is catalyzed at the substrate surface via Ag nanoparticles; this process might be facilitated by the sulfur contamination detected in these nanoparticles. Furthermore, part of the original Ag nanoparticle remains solid and is embedded inside the actual catalyst, providing an in situ method to switch growth mechanisms upon changing In precursor flow. Nevertheless, our Ag-seeded InP nanowires exhibit overall optical emission spectra consistent with the observed structural properties and similar to Au-catalyzed InP nanowires. We thus show that Ag nanoparticles may be a suitable replacement for Au in InP nanowire growth.

Sol-gel chemistry by ring-opening polymerization

DOE Office of Scientific and Technical Information (OSTI.GOV)

RAHIMIAN,KAMYAR; LOY,DOUGLAS A.

2000-02-07

Sol-gel processing of materials is plagued by shrinkage during polymerization of the alkoxide monomers and processing (aging and drying) of the resulting gels. The authors have developed a new class of hybrid organic-inorganic materials based on the solventless ring-opening polymerization (ROP) of monomers bearing the 2,2,5,5-tetramethyl-2,5-disilaoxacyclopentyl group, which permits them to drastically reduce shrinkage in sol-gel processed materials. Because the monomers are polymerized through a chain growth mechanism catalyzed by base rather than the step growth mechanism normally used in sol-gel systems, hydrolysis and condensation products are entirely eliminated. Furthermore, since water is not required for hydrolysis, an alcohol solventmore » is not necessary. Monomers with two disilaoxacyclopentyl groups, separated by a rigid phenylene group or a more flexible alkylene group, were prepared through disilylation of the corresponding diacetylenes, followed by ring closure and hydrogenation. Anionic polymerization of these materials, either neat or with 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane as a copolymer, affords thermally stable transparent gels with no visible shrinkage. These materials provide an easy route to the introduction of sol-gel type materials in encapsulation of microelectronics, which they have successfully demonstrated.« less

Epitaxy of Polar Oxides and Semiconductors

NASA Astrophysics Data System (ADS)

Shelton, Christopher Tyrel

Integrating polar oxide materials with wide-bandgap nitride semiconductors offers the possibility of a tunable 2D carrier gas (2DCG) - provided defect densities are low and interfaces are abrupt. This dissertation investigates a portion of the synthesis science necessary to produce a "semiconductor-grade" interface between these highly dissimilar materials. A significant portion of this work is aligned with efforts to engineer a step-free GaN substrate to produce single in-plane oriented rocksalt oxide films. Initially, we explore the homoepitaxial MOCVD growth conditions necessary to produce highquality GaN films on ammonothermally grown substrates. Ammono substrates are only recently available for purchase and are the market leader in low-dislocation density material. Their novelty requires development of an understanding of morphology trade-offs in processing space. This includes preservation of the epi-polished surface in aggressive MOCVD environments and an understanding of the kinetic barriers affecting growth morphologies. Based on several factors, it was determined that GaN exhibits an 'uphill' diffusion bias that may likely be ascribed to a positive Ehrlich-Schwoebel (ES) barrier. This barrier should have a stabilizing effect against step-bunching but, for many growth conditions, regular step bunching was observed. One possible explanation for the step-bunching instability is the presence of impurities. Experimentally, conditions which incorporate more carbon into GaN homoepitaxial layers are correlated with step-bunching while conditions that suppress carbon produce bilayer stepped morphologies. These observations lead us to the conclusion that GaN homoepitaxial morphology is a competition between impurity induced step-bunching and a stabilizing diffusion bias due to a positive ES barrier. Application of the aforementioned homoepitaxial growth techniques to discrete substrate regions using selected- and confined area epitaxy (SAE,CAE) produces some remarkable surface morphologies. This work represents the first effort to extend SAE and CAE to true bulk single-crystal GaN substrates. By carefully controlling supersaturation during growth it is possible to prepare confined areas with a range of step densities, including surfaces that are entirely step-free. Single terrace GaN mesas up to 100 m in size have been observed, however the potential exists, due to the extremely low dislocation density of the substrate, to further extend the dimensions of these regions. Step-free GaN templates are ideal substrates for rocksalt heteroepitaxy and solve a long-standing challenge related to the integration of cubic and hexagonal materials. It has been previously observed that the origin of the two in-plane orientations in rocksalts grown on III-nitrides is a consequence of the stepped GaN surface. By using a substrate that is effectively step-free across a 100 m region, it is possible to prepare a rocksalt // GaN film with a single in-plane orientation. Heterojunctions of this type are disclination defect free and highly crystalline. The ability to locally prepare a single orientation rocksalt film, coupled with commensurate 2D layer-by-layer growth techniques, allows growth, for the first time, of a truly 'semiconductor-grade' oxide-nitride interface. To study the transport properties of oxide-nitride heterostructures, a series of experiments on standard GaN // sapphire template layers were conducted. Devices that allowed contact to the buried oxide-nitride interface were prepared and characterized using low-temperature Hall measurements. Although a high mobility 2DEG was not observed in these samples, a conduction path at the lattice matched Mg0.52Ca0.48O // GaN interface did appear. If confirmed, this finding could represent the first evidence for interfacial polar coupling between an oxide and a nitride. Overcoming the significant symmetry, chemistry and bonding environment barriers to forming a structurally perfect oxide-nitride interface has required many innovations and the development of several new technologies. It is encouraging, however, that a path around such challenging obstacles exists. We believe the techniques and findings presented in this work are general to many systems, offering hope for a future 'materials functionality' based integration strategy. (Abstract shortened by ProQuest.).

Finite-difference fluid dynamics computer mathematical models for the design and interpretation of experiments for space flight. [atmospheric general circulation experiment, convection in a float zone, and the Bridgman-Stockbarger crystal growing system

NASA Technical Reports Server (NTRS)

Roberts, G. O.; Fowlis, W. W.; Miller, T. L.

1984-01-01

Numerical methods are used to design a spherical baroclinic flow model experiment of the large scale atmosphere flow for Spacelab. The dielectric simulation of radial gravity is only dominant in a low gravity environment. Computer codes are developed to study the processes at work in crystal growing systems which are also candidates for space flight. Crystalline materials rarely achieve their potential properties because of imperfections and component concentration variations. Thermosolutal convection in the liquid melt can be the cause of these imperfections. Such convection is suppressed in a low gravity environment. Two and three dimensional finite difference codes are being used for this work. Nonuniform meshes and implicit iterative methods are used. The iterative method for steady solutions is based on time stepping but has the options of different time steps for velocity and temperature and of a time step varying smoothly with position according to specified powers of the mesh spacings. This allows for more rapid convergence. The code being developed for the crystal growth studies allows for growth of the crystal as the solid-liquid interface. The moving interface is followed using finite differences; shape variations are permitted. For convenience in applying finite differences in the solid and liquid, a time dependent coordinate transformation is used to make this interface a coordinate surface.

Metastasis Suppressor Genes: At the Interface Between the Environment and Tumor Cell Growth

PubMed Central

Hurst, Douglas R.; Welch, Danny R.

2013-01-01

The molecular mechanisms and genetic programs required for cancer metastasis are sometimes overlapping, but components are clearly distinct from those promoting growth of a primary tumor. Every sequential, rate-limiting step in the sequence of events leading to metastasis requires coordinated expression of multiple genes, necessary signaling events, and favorable environmental conditions or the ability to escape negative selection pressures. Metastasis suppressors are molecules that inhibit the process of metastasis without preventing growth of the primary tumor. The cellular processes regulated by metastasis suppressors are diverse and function at every step in the metastatic cascade. As we gain knowledge into the molecular mechanisms of metastasis suppressors and cofactors with which they interact, we learn more about the process, including appreciation that some are potential targets for therapy of metastasis, the most lethal aspect of cancer. Until now, metastasis suppressors have been described largely by their function. With greater appreciation of their biochemical mechanisms of action, the importance of context is increasingly recognized especially since tumor cells exist in myriad microenvironments. In this review, we assemble the evidence that selected molecules are indeed suppressors of metastasis, collate the data defining the biochemical mechanisms of action, and glean insights regarding how metastasis suppressors regulate tumor cell communication to–from microenvironments. PMID:21199781

Computer control of a microgravity mammalian cell bioreactor

NASA Technical Reports Server (NTRS)

Hall, William A.

1987-01-01

The initial steps taken in developing a completely menu driven and totally automated computer control system for a bioreactor are discussed. This bioreactor is an electro-mechanical cell growth system cell requiring vigorous control of slowly changing parameters, many of which are so dynamically interactive that computer control is a necessity. The process computer will have two main functions. First, it will provide continuous environmental control utilizing low signal level transducers as inputs and high powered control devices such as solenoids and motors as outputs. Secondly, it will provide continuous environmental monitoring, including mass data storage and periodic data dumps to a supervisory computer.

Deposition of thin silicon layers on transferred large area graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lupina, Grzegorz, E-mail: lupina@ihp-microelectronics.com; Kitzmann, Julia; Lukosius, Mindaugas

2013-12-23

Physical vapor deposition of Si onto transferred graphene is investigated. At elevated temperatures, Si nucleates preferably on wrinkles and multilayer graphene islands. In some cases, however, Si can be quasi-selectively grown only on the monolayer graphene regions while the multilayer islands remain uncovered. Experimental insights and ab initio calculations show that variations in the removal efficiency of carbon residuals after the transfer process can be responsible for this behavior. Low-temperature Si seed layer results in improved wetting and enables homogeneous growth. This is an important step towards realization of electronic devices in which graphene is embedded between two Si layers.

Optimization of cooling strategy and seeding by FBRM analysis of batch crystallization

NASA Astrophysics Data System (ADS)

Zhang, Dejiang; Liu, Lande; Xu, Shijie; Du, Shichao; Dong, Weibing; Gong, Junbo

2018-03-01

A method is presented for optimizing the cooling strategy and seed loading simultaneously. Focused beam reflectance measurement (FBRM) was used to determine the approximating optimal cooling profile. Using these results in conjunction with constant growth rate assumption, modified Mullin-Nyvlt trajectory could be calculated. This trajectory could suppress secondary nucleation and has the potential to control product's polymorph distribution. Comparing with linear and two step cooling, modified Mullin-Nyvlt trajectory have a larger size distribution and a better morphology. Based on the calculating results, the optimized seed loading policy was also developed. This policy could be useful for guiding the batch crystallization process.

The heavy metal ions (Cu2+, Zn2+, Cd+) toxic compounds influence on triticale plants growth

NASA Astrophysics Data System (ADS)

Brezoczki, V. M.; Filip, G. M.

2017-05-01

The presence of the heavy metals toxic compounds (CuSO4 · 5H2O, ZnSO4 · 7H2O and 3CdSO4·8H2O) in water and soil can be observed by their negative effects on the germination and growth process for different vegetable (barley, oat, maize) who are used for human and animal consumption. This paper it aims the determination of germination and growth inhibition negative effects for triticale plants in the heavy metals ions presence by ecotoxicological laboratory tests. The triticale plants was chosen for their different characteristics to the other grasses respectively: a very good resistance for a wide range of diseases, an accelerated growth and a very good tolerance for aluminum ions presents in acid soils. The determinations were conducted step by step, first, we put the triticale grains in contact with the heavy metal solutions with different concentration then for 3 days we noticed the triticale germination inhibition effects and finally we noticed the growth inhibition process for triticale plants respectively in 7th and 9th day from the start of the experiment. At the end of the tests we can conclude that the triticale roots have a very great sensibility to a CuSO4 solutions compared to the effects for their stalks. A positive effect for triticale stalks we can see for low CuSO4 solution concentrations thus for 5 mg Cu/l the growth is 19,44%. A positive effect for triticale roots it can see for low ZnSO4 solution concentrations so for 5 - 15 mg Zn/l the growth is 24,4%. In the presence of the CdSO4 solution all the processes are inhibited (germination and growth for triticale plants) even for a low concentrations for this toxic.

Fibrosis of Two: Epithelial Cell-Fibroblast Interactions in Pulmonary Fibrosis

PubMed Central

Sakai, Norihiko; Tager, Andrew M.

2013-01-01

Idiopathic pulmonary fibrosis (IPF) is characterized by the progressive and ultimately fatal accumulation of fibroblasts and extracellular matrix in the lung that distorts its architecture and compromises its function. IPF is now thought to result from wound-healing processes that, although initiated to protect the host from injurious environmental stimuli, lead to pathological fibrosis due to these processes becoming aberrant or over-exuberant. Although the environmental stimuli that trigger IPF remain to be identified, recent evidence suggests that they initially injure the alveolar epithelium. Repetitive cycles of epithelial injury and resultant alveolar epithelial cell death provoke the migration, proliferation, activation and myofibroblast differentiation of fibroblasts, causing the accumulation of these cells and the extracellular matrix that they synthesize. In turn, these activated fibroblasts induce further alveolar epithelial cell injury and death, thereby creating a vicious cycle of pro-fibrotic epithelial cell-fibroblast interactions. Though other cell types certainly make important contributions, we focus here on the “pas de deux” (steps of two), or perhaps more appropriate to IPF pathogenesis, the “folie à deux” (madness of two) of epithelial cells and fibroblasts that drives the progression of pulmonary fibrosis. We describe the signaling molecules that mediate the interactions of these cell types in their “fibrosis of two”, including transforming growth factor-β, connective tissue growth factor, sonic hedgehog, prostaglandin E2, angiotensin II and reactive oxygen species. PMID:23499992

Heterogeneous nucleation of pits via step pinning during Si(100) homoepitaxy

NASA Astrophysics Data System (ADS)

Yitamben, E. N.; Butera, R. E.; Swartzentruber, B. S.; Simonson, R. J.; Misra, S.; Carroll, M. S.; Bussmann, E.

2017-11-01

Using scanning tunneling microscopy (STM), we investigate oxide-induced growth pits in Si thin films deposited by molecular beam epitaxy. In the transition temperature range from 2D adatom islanding to step-flow growth, systematic controlled air leaks into the growth chamber induce pits in the growth surface. We show that pits are also correlated with oxygen-contaminated flux from Si sublimation sources. From a thermodynamic standpoint, multilayer growth pits are unexpected in relaxed homoepitaxial growth, whereas oxidation is a known cause for step pinning, roughening, and faceting on elemental surfaces, both with and without growth flux. Not surprisingly, pits are thermodynamically metastable and heal by annealing to recover a smooth periodic step arrangement. STM reveals new details about the pits’ atomistic origins and growth dynamics. We give a model for heterogeneous nucleation of pits by preferential adsorption of Å-sized oxide nuclei at intrinsic growth antiphase boundaries, and subsequent step pinning and bunching around the nuclei.

Heterogeneous nucleation of pits via step pinning during Si(100) homoepitaxy

DOE PAGES

Yitamben, Esmeralda; Butera, Robert E.; Swartzentruber, Brian S.; ...

2017-10-16

Using scanning tunneling microscopy (STM), we investigate oxide-induced growth pits in Si thin films deposited by molecular beam epitaxy. In the transition temperature range from 2D adatom islanding to step-flow growth, systematic controlled air leaks into the growth chamber induce pits in the growth surface. We show that pits are also correlated with oxygen-contaminated flux from Si sublimation sources. From a thermodynamic standpoint, multilayer growth pits are unexpected in relaxed homoepitaxial growth, whereas oxidation is a known cause for step-pinning, roughening, and faceting on elemental surfaces, both with and without growth flux. Not surprisingly, pits are thermodynamically metastable and healmore » by annealing to recover a smooth periodic step arrangement. STM reveals new details about the pits' atomistic origins and growth dynamics. Here, we give a model for heterogeneous nucleation of pits by preferential adsorption of Å-sized oxide nuclei at intrinsic growth antiphase boundaries, and subsequent step pinning and bunching around the nuclei.« less

Temporally distinct transcriptional regulation of myocyte dedifferentiation and Myofiber growth during muscle regeneration.

PubMed

Louie, Ke'ale W; Saera-Vila, Alfonso; Kish, Phillip E; Colacino, Justin A; Kahana, Alon

2017-11-09

Tissue regeneration requires a series of steps, beginning with generation of the necessary cell mass, followed by cell migration into damaged area, and ending with differentiation and integration with surrounding tissues. Temporal regulation of these steps lies at the heart of the regenerative process, yet its basis is not well understood. The ability of zebrafish to dedifferentiate mature "post-mitotic" myocytes into proliferating myoblasts that in turn regenerate lost muscle tissue provides an opportunity to probe the molecular mechanisms of regeneration. Following subtotal excision of adult zebrafish lateral rectus muscle, dedifferentiating residual myocytes were collected at two time points prior to cell cycle reentry and compared to uninjured muscles using RNA-seq. Functional annotation (GAGE or K-means clustering followed by GO enrichment) revealed a coordinated response encompassing epigenetic regulation of transcription, RNA processing, and DNA replication and repair, along with protein degradation and translation that would rewire the cellular proteome and metabolome. Selected candidate genes were phenotypically validated in vivo by morpholino knockdown. Rapidly induced gene products, such as the Polycomb group factors Ezh2 and Suz12a, were necessary for both efficient dedifferentiation (i.e. cell reprogramming leading to cell cycle reentry) and complete anatomic regeneration. In contrast, the late activated gene fibronectin was important for efficient anatomic muscle regeneration but not for the early step of myocyte cell cycle reentry. Reprogramming of a "post-mitotic" myocyte into a dedifferentiated myoblast requires a complex coordinated effort that reshapes the cellular proteome and rewires metabolic pathways mediated by heritable yet nuanced epigenetic alterations and molecular switches, including transcription factors and non-coding RNAs. Our studies show that temporal regulation of gene expression is programmatically linked to distinct steps in the regeneration process, with immediate early expression driving dedifferentiation and reprogramming, and later expression facilitating anatomical regeneration.

Removal of ion-implanted photoresists on GaAs using two organic solvents in sequence

NASA Astrophysics Data System (ADS)

Oh, Eunseok; Na, Jihoon; Lee, Seunghyo; Lim, Sangwoo

2016-07-01

Organic solvents can effectively remove photoresists on III-V channels without damage or etching of the channel material during the process. In this study, a two-step sequential photoresist removal process using two different organic solvents was developed to remove implanted ArF and KrF photoresists at room temperature. The effects of organic solvents with either low molar volumes or high affinities for photoresists were evaluated to find a proper combination that can effectively remove high-dose implanted photoresists without damaging GaAs surfaces. The performance of formamide, acetonitrile, nitromethane, and monoethanolamine for the removal of ion-implanted ArF and KrF photoresists were compared using a two-step sequential photoresist removal process followed by treatment in dimethyl sulfoxide (DMSO). Among the various combinations, the acetonitrile + DMSO two-step sequence exhibited the best removal of photoresists that underwent ion implantation at doses of 5 × 1013-5 × 1015 atoms/cm2 on both flat and trench-structured GaAs surfaces. The ability of the two-step process using organic solvents to remove the photoresists can be explained by considering the affinities of solvents for a polymer and its permeability through the photoresist.

Efficiency improvement of silicon solar cells enabled by ZnO nanowhisker array coating

PubMed Central

2012-01-01

An efficient antireflection coating is critical for the improvement of silicon solar cell performance via increased light coupling. Here, we have grown well-aligned ZnO nanowhisker (NW) arrays on Czochralski silicon solar cells by a seeding-growth two-step process. It is found that the ZnO NWs have a great effect on the macroscopic antireflection effect and, therefore, improves the solar cell performance. The ZnO NW array-coated solar cells display a broadband reflection suppression from 500 to 1,100 nm, and the minimum reflectance smaller than 3% can easily be achieved. By optimizing the time of ZnO NW growth, it has been confirmed that an increase of 3% relatively in the solar cell efficiency can be obtained. These results are quite interesting for the application of ZnO nanostructure in the fabrication of high-efficiency silicon solar cells. PMID:22704578

Heterointerface study of InAs/GaSb nanoridge heterostructures grown by metal organic chemical vapor deposition on V-grooved Si (0 0 1) substrates

NASA Astrophysics Data System (ADS)

Lai, Billy; Li, Qiang; Lau, Kei May

2018-02-01

InAs/GaSb nanoridge heterostructures were grown on V-grooved (0 0 1) Si by metal organic chemical vapor deposition. Combining the aspect ratio trapping process and a low temperature GaAs buffer, we demonstrated high quality GaSb nanoridge templates for InAs/GaSb heterostructure growth. Two different interfaces, a transitional GaAsSb and an InSb-like interface, were investigated when growing these heterostructures. A 500 °C growth temperature in conjunction with a GaAsSb interface was determined to produce the optimal interface, properly compensating for the tensile strain accumulated when growing InAs on GaSb. Without the need for a complicated switching sequence, this GaAsSb-like interface utilized at the optimized temperature is the initial step towards InAs/GaSb type II superlattice and other device structures integrated onto Si.

Role of codeposited impurities during growth. II. Dependence of morphology on binding and barrier energies

NASA Astrophysics Data System (ADS)

Sathiyanarayanan, Rajesh; Hamouda, Ajmi Bh.; Pimpinelli, A.; Einstein, T. L.

2011-01-01

In an accompanying article we showed that surface morphologies obtained through codeposition of a small quantity (2%) of impurities with Cu during growth (step-flow mode, θ = 40 ML) significantly depends on the lateral nearest-neighbor binding energy (ENN) to Cu adatom and the diffusion barrier (Ed) of the impurity atom on Cu(0 0 1). Based on these two energy parameters, ENN and Ed, we classify impurity atoms into four sets. We study island nucleation and growth in the presence of codeposited impurities from different sets in the submonolayer (θ⩽ 0.7 ML) regime. Similar to growth in the step-flow mode, we find different nucleation and growth behavior for impurities from different sets. We characterize these differences through variations of the number of islands (Ni) and the average island size with coverage (θ). Further, we compute the critical nucleus size (i) for all of these cases from the distribution of capture-zone areas using the generalized Wigner distribution.

Behavior of Different Shiga Toxin-Producing Escherichia coli Serotypes in Various Experimentally Contaminated Raw-Milk Cheeses

PubMed Central

Miszczycha, Stéphane D.; Perrin, Frédérique; Ganet, Sarah; Jamet, Emmanuel; Tenenhaus-Aziza, Fanny; Montel, Marie-Christine

2013-01-01

Shiga toxin-producing Escherichia coli (STEC) is an important cause of food-borne illness. The public health implication of the presence of STEC in dairy products remains unclear. Knowledge of STEC behavior in cheeses would help to evaluate the human health risk. The aim of our study was to observe the growth and survival of experimentally inoculated STEC strains in raw-milk cheeses manufactured and ripened according to five technological schemes: blue-type cheese, uncooked pressed cheese with long ripening and with short ripening steps, cooked cheese, and lactic cheese. Cheeses were contaminated with different STEC serotypes (O157:H7, O26:H11, O103:H2, and O145:H28) at the milk preparation stage. STEC growth and survival were monitored on selective media during the entire manufacturing process. STEC grew (2 to 3 log10 CFU · g−1) in blue-type cheese and the two uncooked pressed cheeses during the first 24 h of cheese making. Then, STEC levels progressively decreased in cheeses that were ripened for more than 6 months. In cooked cheese and in lactic cheese with a long acidic coagulation step (pH < 4.5), STEC did not grow. Their levels decreased after the cooking step in the cooked cheese and after the coagulation step in the lactic cheese, but STEC was still detectable at the end of ripening and storage. A serotype effect was found: in all cheeses studied, serotype O157:H7 grew less strongly and was less persistent than the others serotypes. This study improves knowledge of the behavior of different STEC serotypes in various raw-milk cheeses. PMID:23087038

Studies of the Initial Stages of Epitaxial Growth of Germanium on Silicon

NASA Astrophysics Data System (ADS)

Krishnamurthy, Mohan

The epitaxial growth of ultra-thin films (< 1nm thick) of Ge on Si(100) has been studied in -situ in an Ultra High Vacuum-Scanning Transmission Electron Microscope. Ge was deposited on clean Si(100) using molecular beam techniques to study two types of growth processes, Molecular Beam Epitaxy (MBE) and Solid Phase MBE. Ge grows in the Stranski-Krastanov growth mode, forming islands after initial layer growth. This islanding transition has been studied with high spatial resolution biassed Secondary Electron Imaging and Auger spectroscopy and imaging. Ex -situ Transmission Electron Microscopy (TEM) and Reflection High Energy Diffraction (RHEED) were also used to characterize the transition. The islanding process and its subsequent evolution was monitored with the help of island size distributions, sensitive to islands above 2nm in size. The studies indicate that Ge forms islands in equilibrium with a 3 monolayer (ML) thick intermediate layer. These islands may initially grow coherently strained (dislocation free) with radii usually below 10nm under the conditions. The strain in these islands reduces the adatom sticking coefficient and strongly influences the microstructural evolution. The intermediate layer may grow metastably under certain conditions to as much as 7 ML before collapsing to its equilibrium form. The influence of three types of adatom sinks--strained islands, dislocated islands and contaminant particles have been studied. The contaminant particles are the strongest sinks, followed by dislocated islands and strained islands. Stepped (vicinal) surfaces (1^circ and 5 ^circ toward {110 }) had no significant influence possibly due to the steps being weak adatom sinks. The coarsening of Ge islands does not follow the Ostwald ripening model at the early stages and is influenced by the supersaturation in the intermediate layer and the strain in the coherent islands. A novel mechanism has been observed, where the larger (dislocated) islands grow at the expense of the unstable intermediate layer while the distribution of smaller (strained) islands is constant. This is possibly due to the lower sticking coefficient at the strained islands.

Optical properties of m-plane GaN grown on patterned Si(112) substrates by MOCVD using a two-step approach

NASA Astrophysics Data System (ADS)

Izyumskaya, N.; Okur, S.; Zhang, F.; Monavarian, M.; Avrutin, V.; Özgür, Ü.; Metzner, S.; Karbaum, C.; Bertram, F.; Christen, J.; Morkoç, H.

2014-03-01

Nonpolar m-plane GaN layers were grown on patterned Si (112) substrates by metal-organic chemical vapor deposition (MOCVD). A two-step growth procedure involving a low-pressure (30 Torr) first step to ensure formation of the m-plane facet and a high-pressure step (200 Torr) for improvement of optical quality was employed. The layers grown in two steps show improvement of the optical quality: the near-bandedge photoluminescence (PL) intensity is about 3 times higher than that for the layers grown at low pressure, and deep emission is considerably weaker. However, emission intensity from m-GaN is still lower than that of polar and semipolar (1 100 ) reference samples grown under the same conditions. To shed light on this problem, spatial distribution of optical emission over the c+ and c- wings of the nonpolar GaN/Si was studied by spatially resolved cathodoluminescence and near-field scanning optical microscopy.

Atomic Resolution in Situ Imaging of a Double-Bilayer Multistep Growth Mode in Gallium Nitride Nanowires

DOE PAGES

Gamalski, A. D.; Tersoff, J.; Stach, E. A.

2016-04-13

We study the growth of GaN nanowires from liquid Au–Ga catalysts using environmental transmission electron microscopy. GaN wires grow in either (11¯20) or (11¯00) directions, by the addition of {11¯00} double bilayers via step flow with multiple steps. Step-train growth is not typically seen with liquid catalysts, and we suggest that it results from low step mobility related to the unusual double-height step structure. Finally, the results here illustrate the surprising dynamics of catalytic GaN wire growth at the nanoscale and highlight striking differences between the growth of GaN and other III–V semiconductor nanowires.

Controlled epitaxial graphene growth within removable amorphous carbon corrals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palmer, James; Hu, Yike; Hankinson, John

2014-07-14

We address the question of control of the silicon carbide (SiC) steps and terraces under epitaxial graphene on SiC and demonstrate amorphous carbon (aC) corrals as an ideal method to pin SiC surface steps. aC is compatible with graphene growth, structurally stable at high temperatures, and can be removed after graphene growth. For this, aC is first evaporated and patterned on SiC, then annealed in the graphene growth furnace. There at temperatures above 1200 °C, mobile SiC steps accumulate at the aC corral that provide effective step flow barriers. Aligned step free regions are thereby formed for subsequent graphene growth atmore » temperatures above 1330 °C. Atomic force microscopy imaging supports the formation of step-free terraces on SiC with the step morphology aligned to the aC corrals. Raman spectroscopy indicates the presence of good graphene sheets on the step-free terraces.« less

A comparison between atmospheric/humidity and vacuum cyanoacrylate fuming of latent fingermarks.

PubMed

Farrugia, Kevin J; Fraser, Joanna; Friel, Lauren; Adams, Duncan; Attard-Montalto, Nicola; Deacon, Paul

2015-12-01

A number of pseudo-operational trials were set up to compare the atmospheric/humidity and vacuum cyanoacrylate fuming processes on plastic carrier bags. The fuming processes were compared using two-step cyanoacrylate fuming with basic yellow 40 (BY40) staining and a one-step fluorescent cyanoacrylate fuming, Lumicyano 4%. Preliminary work using planted fingermarks and split depletions were performed to identify the optimum vacuum fuming conditions. The first pseudo-operational trial compared the different fuming conditions (atmospheric/humidity vs. vacuum) for the two-step process where an additional 50% more marks were detected with the atmospheric/humidity process. None of the marks by the vacuum process could be observed visually; however, a significant number of marks were detected by fluorescence after BY40 staining. The second trial repeated the same work in trial 1 using the one-step cyanoacrylate process, Lumicyano at a concentration of 4%. Trial 2 provided comparable results to trial 1 and all the items were then re-treated with Lumicyano 4% at atmospheric/humidity conditions before dyeing with BY40 to provide the sequences of process A (Lumicyano 4% atmospheric-Lumicyano 4% atmospheric-BY40) and process B (Lumicyano 4% vacuum-Lumicyano 4% atmospheric-BY40). The number of marks (visual and fluorescent) was counted after each treatment with a substantial increase in the number of detected marks in the second and third treatments of the process. The increased detection rate after the double Lumicyano process was unexpected and may have important implications. Trial 3 was performed to investigate whether the amount of cyanoacrylate and/or fuming time had an impact on the results observed in trial 2 whereas trial 4 assessed if the double process using conventional cyanoacrylate, rather than Lumicyano 4%, provided an increased detection rate. Trials 3 and 4 confirmed that doubling the amount of Lumicyano 4% cyanoacrylate and fuming time produced a lower detection rate than the double process with Lumicyano 4%. Furthermore, the double process with conventional cyanoacrylate did not provide any benefit. Scanning electron microscopy was also performed to investigate the morphology of the cyanoacrylate polymer under different conditions. The atmospheric/humidity process appears to be superior to the vacuum process for both the two-step and one-step cyanoacrylate fuming, although the two-step process performed better in comparison to the one-step process under vacuum conditions. Nonetheless, the use of vacuum cyanoacrylate fuming may have certain operational advantages and its use does not adversely affect subsequent cyanoacrylate fuming with atmospheric/humidity conditions. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Fungi and mycotoxins in cocoa: from farm to chocolate.

PubMed

Copetti, Marina V; Iamanaka, Beatriz T; Pitt, John I; Taniwaki, Marta H

2014-05-16

Cocoa is an important crop, as it is the raw material from which chocolate is manufactured. It is grown mainly in West Africa although significant quantities also come from Asia and Central and South America. Primary processing is carried out on the farm, and the flavour of chocolate starts to develop at that time. Freshly harvested pods are opened, the beans, piled in heaps or wooden boxes, are fermented naturally by yeasts and bacteria, then dried in the sun on wooden platforms or sometimes on cement or on the ground, where a gradual reduction in moisture content inhibits microbial growth. Beans are then bagged and marketed. In processing plants, the dried fermented beans are roasted, shelled and ground, then two distinct processes are used, to produce powdered cocoa or chocolate. Filamentous fungi may contaminate many stages in cocoa processing, and poor practices may have a strong influence on the quality of the beans. Apart from causing spoilage, filamentous fungi may also produce aflatoxins and ochratoxin A. This review deals with the growth of fungal species and formation of mycotoxins during the various steps in cocoa processing, as well as reduction of these contaminants by good processing practices. Methodologies for fungal and mycotoxin detection and quantification are discussed while current data about dietary exposure and regulation are also presented. Copyright © 2014 Elsevier B.V. All rights reserved.

Characteristics of MAO coating obtained on ZK60 Mg alloy under two and three steps voltage-increasing modes in dual electrolyte

NASA Astrophysics Data System (ADS)

Yang, Jun; Wang, Ze-Xin; Lu, Sheng; Lv, Wei-gang; Jiang, Xi-zhi; Sun, Lei

2017-03-01

The micro-arc oxidation process was conducted on ZK60 Mg alloy under two and three steps voltage-increasing modes by DC pulse electrical source. The effect of each mode on current-time responses during MAO process and the coating characteristic were analysed and discussed systematically. The microstructure, thickness and corrosion resistance of MAO coatings were evaluated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), microscope with super-depth of field and electrochemical impedance spectroscopy (EIS). The results indicate that two and three steps voltage-increasing modes can improve weak spark discharges with insufficient breakdown strength in later period during the MAO process. Due to higher value of voltage and voltage increment, the coating with maximum thickness of about 20.20μm formed under two steps voltage-increasing mode shows the best corrosion resistance. In addition, the coating fabricated under three steps voltage-increasing mode shows a smoother coating with better corrosion resistance due to the lower amplitude of voltage-increasing.

Unexpected Reaction Pathway for butyrylcholinesterase-catalyzed inactivation of “hunger hormone” ghrelin

NASA Astrophysics Data System (ADS)

Yao, Jianzhuang; Yuan, Yaxia; Zheng, Fang; Zhan, Chang-Guo

2016-02-01

Extensive computational modeling and simulations have been carried out, in the present study, to uncover the fundamental reaction pathway for butyrylcholinesterase (BChE)-catalyzed hydrolysis of ghrelin, demonstrating that the acylation process of BChE-catalyzed hydrolysis of ghrelin follows an unprecedented single-step reaction pathway and the single-step acylation process is rate-determining. The free energy barrier (18.8 kcal/mol) calculated for the rate-determining step is reasonably close to the experimentally-derived free energy barrier (~19.4 kcal/mol), suggesting that the obtained mechanistic insights are reasonable. The single-step reaction pathway for the acylation is remarkably different from the well-known two-step acylation reaction pathway for numerous ester hydrolysis reactions catalyzed by a serine esterase. This is the first time demonstrating that a single-step reaction pathway is possible for an ester hydrolysis reaction catalyzed by a serine esterase and, therefore, one no longer can simply assume that the acylation process must follow the well-known two-step reaction pathway.

Electrical property of macroscopic graphene composite fibers prepared by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Sun, Haibin; Fu, Can; Gao, Yanli; Guo, Pengfei; Wang, Chunlei; Yang, Wenchao; Wang, Qishang; Zhang, Chongwu; Wang, Junya; Xu, Junqi

2018-07-01

Graphene fibers are promising candidates in portable and wearable electronics due to their tiny volume, flexibility and wearability. Here, we successfully synthesized macroscopic graphene composite fibers via a two-step process, i.e. first electrospinning and then chemical vapor deposition (CVD). Briefly, the well-dispersed PAN nanofibers were sprayed onto the copper surface in an electrified thin liquid jet by electrospinning. Subsequently, CVD growth process induced the formation of graphene films using a PAN-solid source of carbon and a copper catalyst. Finally, crumpled and macroscopic graphene composite fibers were obtained from carbon nanofiber/graphene composite webs by self-assembly process in the deionized water. Temperature-dependent conduct behavior reveals that electron transport of the graphene composite fibers belongs to hopping mechanism and the typical electrical conductivity reaches 4.59 × 103 S m‑1. These results demonstrated that the graphene composite fibers are promising for the next-generation flexible and wearable electronics.

A Functional Study of AUXILIN-LIKE1 and 2, Two Putative Clathrin Uncoating Factors in Arabidopsis[OPEN

PubMed Central

Adamowski, Maciek; Kania, Urszula

2018-01-01

Clathrin-mediated endocytosis (CME) is a cellular trafficking process in which cargoes and lipids are internalized from the plasma membrane into vesicles coated with clathrin and adaptor proteins. CME is essential for many developmental and physiological processes in plants, but its underlying mechanism is not well characterized compared with that in yeast and animal systems. Here, we searched for new factors involved in CME in Arabidopsis thaliana by performing tandem affinity purification of proteins that interact with clathrin light chain, a principal component of the clathrin coat. Among the confirmed interactors, we found two putative homologs of the clathrin-coat uncoating factor auxilin previously described in non-plant systems. Overexpression of AUXILIN-LIKE1 and AUXILIN-LIKE2 in Arabidopsis caused an arrest of seedling growth and development. This was concomitant with inhibited endocytosis due to blocking of clathrin recruitment after the initial step of adaptor protein binding to the plasma membrane. By contrast, auxilin-like1/2 loss-of-function lines did not present endocytosis-related developmental or cellular phenotypes under normal growth conditions. This work contributes to the ongoing characterization of the endocytotic machinery in plants and provides a robust tool for conditionally and specifically interfering with CME in Arabidopsis. PMID:29511054

Reduction of structural defects in thick 4H-SiC epitaxial layers grown on 4° off-axis substrates

NASA Astrophysics Data System (ADS)

Yazdanfar, M.; Ivanov, I. G.; Pedersen, H.; Kordina, O.; Janzén, E.

2013-06-01

By carefully controlling the surface chemistry of the chemical vapor deposition process for silicon carbide (SiC), 100 μm thick epitaxial layers with excellent morphology were grown on 4° off-axis SiC substrates at growth rates exceeding 100 μm/h. In order to reduce the formation of step bunching and structural defects, mainly triangular defects, the effect of varying parameters such as growth temperature, C/Si ratio, Cl/Si ratio, Si/H2 ratio, and in situ pre-growth surface etching time are studied. It was found that an in-situ pre growth etch at growth temperature and pressure using 0.6% HCl in hydrogen for 12 min reduced the structural defects by etching preferentially on surface damages of the substrate surface. By then applying a slightly lower growth temperature of 1575 °C, a C/Si ratio of 0.8, and a Cl/Si ratio of 5, 100 μm thick, step-bunch free epitaxial layer with a minimum triangular defect density and excellent morphology could be grown, thus enabling SiC power device structures to be grown on 4° off axis SiC substrates.

NaCl-assisted one-step growth of MoS2-WS2 in-plane heterostructures

NASA Astrophysics Data System (ADS)

Wang, Zhan; Xie, Yong; Wang, Haolin; Wu, Ruixue; Nan, Tang; Zhan, Yongjie; Sun, Jing; Jiang, Teng; Zhao, Ying; Lei, Yimin; Yang, Mei; Wang, Weidong; Zhu, Qing; Ma, Xiaohua; Hao, Yue

2017-08-01

Transition metal dichalcogenides (TMDs) have attracted considerable interest for exploration of next-generation electronics and optoelectronics in recent years. Fabrication of in-plane lateral heterostructures between TMDs has opened up excellent opportunities for engineering two-dimensional materials. The creation of high quality heterostructures with a facile method is highly desirable but it still remains challenging. In this work, we demonstrate a one-step growth method for the construction of high-quality MoS2-WS2 in-plane heterostructures. The synthesis was carried out using ambient pressure chemical vapor deposition (APCVD) with the assistance of sodium chloride (NaCl). It was found that the addition of NaCl played a key role in lowering the growth temperatures, in which the Na-containing precursors could be formed and condensed on the substrates to reduce the energy of the reaction. As a result, the growth regimes of MoS2 and WS2 are better matched, leading to the formation of in-plane heterostructures in a single step. The heterostructures were proved to be of high quality with a sharp and clear interface. This newly developed strategy with the assistance of NaCl is promising for synthesizing other TMDs and their heterostructures.

Growth factors delivery from hybrid PCL-starch scaffolds processed using supercritical fluid technology.

PubMed

Diaz-Gomez, Luis; Concheiro, Angel; Alvarez-Lorenzo, Carmen; García-González, Carlos A

2016-05-20

Synthetic polymeric scaffolds to be used as surrogates of autologous bone grafts should not only have suitable physicochemical and mechanical properties, but also contain bioactive agents such as growth factors (GFs) to facilitate the tissue growth. For this purpose, cost-effective and autologous GFs sources are preferred to avoid some post-surgery complications after implantation, like immunogenicity or disease transmission, and the scaffolds should be processed using methods able to preserve GFs activity. In this work, poly(ɛ-caprolactone) (PCL) scaffolds incorporating GFs were processed using a green foaming process based on supercritical fluid technology. Preparation rich in growth factors (PRGF), a natural and highly available cocktail of GFs obtained from platelet rich plasma (PRP), was used as GF source. PCL:starch:PRGF (85:10:5 weight ratio) porous solid scaffolds were obtained by a supercritical CO2-assisted foaming process at 100 bar and 37 °C with no need of post-processing steps. Bioactivity of GFs after processing and scaffold cytocompatibility were confirmed using mesenchymal stem cells. The performance of starch as GF control release component was shown to be dependent on starch pre-gelification conditions. Copyright © 2016 Elsevier Ltd. All rights reserved.

Colony patterning and collective hyphal growth of filamentous fungi

NASA Astrophysics Data System (ADS)

Matsuura, Shu

2002-11-01

Colony morphology of wild and mutant strains of Aspergillus nidulans at various nutrient and agar levels was investigated. Two types of colony patterning were found for these strains. One type produced uniform colonies at all nutrient and agar levels tested, and the other exhibited morphological change into disordered ramified colonies at low nutrient levels. Both types showed highly condensed compact colonies at high nutrient levels on low agar media that was highly diffusive. Disordered colonies were found to develop with low hyphal extension rates at low nutrient levels. To understand basic pattern selection rules, a colony model with three parameters, i.e., the initial nutrient level and the step length of nutrient random walk as the external parameters, and the frequency of nutrient uptake as an internal parameter, was constructed. At low nutrient levels, with decreasing nutrient uptake frequency under diffusive conditions, the model colony exhibited onsets of disordered ramification. Further, in the growth process of A. nidulans, reduction of hyphal extension rate due to a population effect of hyphae was found when hyphae form three-dimensional dense colonies, as compared to the case in which hyphal growth was restricted into two-dimensional space. A hyphal population effect was introduced in the colony model. Thickening of colony periphery due to the population effect became distinctive as the nutrient diffusion effect was raised at high nutrient levels with low hyphal growth rate. It was considered that colony patterning and onset of disorder were strongly governed by the combination of nutrient diffusion and hyphal growth rate.

Method for producing damage resistant optics

DOEpatents

Hackel, Lloyd A.; Burnham, Alan K.; Penetrante, Bernardino M.; Brusasco, Raymond M.; Wegner, Paul J.; Hrubesh, Lawrence W.; Kozlowski, Mark R.; Feit, Michael D.

2003-01-01

The present invention provides a system that mitigates the growth of surface damage in an optic. Damage to the optic is minimally initiated. In an embodiment of the invention, damage sites in the optic are initiated, located, and then treated to stop the growth of the damage sites. The step of initiating damage sites in the optic includes a scan of the optic using a laser to initiate defects. The exact positions of the initiated sites are identified. A mitigation process is performed that locally or globally removes the cause of subsequent growth of the damaged sites.

Two-step growth mechanism of supported Co3O4-based sea-urchin like hierarchical nanostructures

NASA Astrophysics Data System (ADS)

Maurizio, Chiara; Edla, Raju; Michieli, Niccolo'; Orlandi, Michele; Trapananti, Angela; Mattei, Giovanni; Miotello, Antonio

2018-05-01

Supported 3D hierarchical nanostructures of transition metal oxides exhibit enhanced photocatalytic performances and long-term stability under working conditions. The growth mechanisms crucially determine their intimate structure, that is a key element to optimize their properties. We report on the formation mechanism of supported Co3O4 hierarchical sea urchin-like nanostructured catalyst, starting from Co-O-B layers deposited by Pulsed Laser Deposition (PLD). The particles deposited on the layer surface, that constitute the seeds for the urchin formation, have been investigated after separation from the underneath deposited layer, by X-ray diffraction, X-ray absorption spectroscopy and scanning electron microscopy. The comparison with PLD deposited layers without O and/or B indicates a crucial role of B for the urchin formation that (i) limits Co oxidation during the deposition process and (ii) induces a chemical reduction of Co, especially in the particle core, in the first step of air annealing (2 h, 500 °C). After 2 h heating Co oxidation proceeds and Co atoms outdiffuse from the Co fcc particle core likely through fast diffusion channel present in the shell and form Co3O4 nano-needles. The growth of nano-needles from the layer beneath the particles is prevented by a faster Co oxidation and a minimum fraction of metallic Co. This investigation shows how diffusion mechanisms and chemical effects can be effectively coupled to obtain hierarchical structures of transition metal oxides.

Modelling uveal melanoma

PubMed Central

Foss, A.; Cree, I.; Dolin, P.; Hungerford, J.

1999-01-01

BACKGROUND/AIM—There has been no consistent pattern reported on how mortality for uveal melanoma varies with age. This information can be useful to model the complexity of the disease. The authors have examined ocular cancer trends, as an indirect measure for uveal melanoma mortality, to see how rates vary with age and to compare the results with their other studies on predicting metastatic disease.
METHODS—Age specific mortality was examined for England and Wales, the USA, and Canada. A log-log model was fitted to the data. The slopes of the log-log plots were used as measure of disease complexity and compared with the results of previous work on predicting metastatic disease.
RESULTS—The log-log model provided a good fit for the US and Canadian data, but the observed rates deviated for England and Wales among people over the age of 65 years. The log-log model for mortality data suggests that the underlying process depends upon four rate limiting steps, while a similar model for the incidence data suggests between three and four rate limiting steps. Further analysis of previous data on predicting metastatic disease on the basis of tumour size and blood vessel density would indicate a single rate limiting step between developing the primary tumour and developing metastatic disease.
CONCLUSIONS—There is significant underreporting or underdiagnosis of ocular melanoma for England and Wales in those over the age of 65 years. In those under the age of 65, a model is presented for ocular melanoma oncogenesis requiring three rate limiting steps to develop the primary tumour and a fourth rate limiting step to develop metastatic disease. The three steps in the generation of the primary tumour involve two key processes—namely, growth and angiogenesis within the primary tumour. The step from development of the primary to development of metastatic disease is likely to involve a single rate limiting process.

 PMID:10216060

InGaP/GaAs Inverted Dual Junction Solar Cells For CPV Applications Using Metal-Backed Epitaxial Lift-Off

NASA Astrophysics Data System (ADS)

Bauhuis, Gerard J.; Mulder, Peter; Haverkamp, Erik J.; Schermer, John J.; Nash, Lee J.; Fulgoni, Dominic J. F.; Ballard, Ian M.; Duggan, Geoffrey

2010-10-01

The epitaxial lift-off (ELO) technique has been combined with inverted III-V PV cell epitaxial growth with the aim of employing thin film PV cells in HCPV systems. In a stepwise approach to the realization of an inverted triple junction on a MELO platform we have first grown a GaAs single junction PV cell to establish the basic layer release process and cell processing steps followed by the growth, fabrication and test of an inverted InGaP/GaAs dual junction structure.

Intermediate surface structure between step bunching and step flow in SrRuO3 thin film growth

NASA Astrophysics Data System (ADS)

Bertino, Giulia; Gura, Anna; Dawber, Matthew

We performed a systematic study of SrRuO3 thin films grown on TiO2 terminated SrTiO3 substrates using off-axis magnetron sputtering. We investigated the step bunching formation and the evolution of the SRO film morphology by varying the step size of the substrate, the growth temperature and the film thickness. The thin films were characterized using Atomic Force Microscopy and X-Ray Diffraction. We identified single and multiple step bunching and step flow growth regimes as a function of the growth parameters. Also, we clearly observe a stronger influence of the step size of the substrate on the evolution of the SRO film surface with respect to the other growth parameters. Remarkably, we observe the formation of a smooth, regular and uniform ``fish skin'' structure at the transition between one regime and another. We believe that the fish skin structure results from the merging of 2D flat islands predicted by previous models. The direct observation of this transition structure allows us to better understand how and when step bunching develops in the growth of SrRuO3 thin films.

Raising Butterflies from Your Own Garden.

ERIC Educational Resources Information Center

Howley-Pfeifer, Patricia

2002-01-01

Describes how raising monarch, black swallowtail, and mourning cloak butterflies in a kindergarten class garden can provide opportunities for observation experiences. Includes detailed steps for instruction and describes stages of growth. Excerpts children's journal dictations to illustrate ways to support the discovery process. Describes related…

Bacterial Stressors in Minimally Processed Food

PubMed Central

Capozzi, Vittorio; Fiocco, Daniela; Amodio, Maria Luisa; Gallone, Anna; Spano, Giuseppe

2009-01-01

Stress responses are of particular importance to microorganisms, because their habitats are subjected to continual changes in temperature, osmotic pressure, and nutrients availability. Stressors (and stress factors), may be of chemical, physical, or biological nature. While stress to microorganisms is frequently caused by the surrounding environment, the growth of microbial cells on its own may also result in induction of some kinds of stress such as starvation and acidity. During production of fresh-cut produce, cumulative mild processing steps are employed, to control the growth of microorganisms. Pathogens on plant surfaces are already stressed and stress may be increased during the multiple mild processing steps, potentially leading to very hardy bacteria geared towards enhanced survival. Cross-protection can occur because the overlapping stress responses enable bacteria exposed to one stress to become resistant to another stress. A number of stresses have been shown to induce cross protection, including heat, cold, acid and osmotic stress. Among other factors, adaptation to heat stress appears to provide bacterial cells with more pronounced cross protection against several other stresses. Understanding how pathogens sense and respond to mild stresses is essential in order to design safe and effective minimal processing regimes. PMID:19742126

Modified Gompertz equation for electrotherapy murine tumor growth kinetics: predictions and new hypotheses.

PubMed

Cabrales, Luis E Bergues; Nava, Juan J Godina; Aguilera, Andrés Ramírez; Joa, Javier A González; Ciria, Héctor M Camué; González, Maraelys Morales; Salas, Miriam Fariñas; Jarque, Manuel Verdecia; González, Tamara Rubio; Mateus, Miguel A O'Farril; Brooks, Soraida C Acosta; Palencia, Fabiola Suárez; Zamora, Lisset Ortiz; Quevedo, María C Céspedes; Seringe, Sarah Edward; Cuitié, Vladimir Crombet; Cabrales, Idelisa Bergues; González, Gustavo Sierra

2010-10-28

Electrotherapy effectiveness at different doses has been demonstrated in preclinical and clinical studies; however, several aspects that occur in the tumor growth kinetics before and after treatment have not yet been revealed. Mathematical modeling is a useful instrument that can reveal some of these aspects. The aim of this paper is to describe the complete growth kinetics of unperturbed and perturbed tumors through use of the modified Gompertz equation in order to generate useful insight into the mechanisms that underpin this devastating disease. The complete tumor growth kinetics for control and treated groups are obtained by interpolation and extrapolation methods with different time steps, using experimental data of fibrosarcoma Sa-37. In the modified Gompertz equation, a delay time is introduced to describe the tumor's natural history before treatment. Different graphical strategies are used in order to reveal new information in the complete kinetics of this tumor type. The first stage of complete tumor growth kinetics is highly non linear. The model, at this stage, shows different aspects that agree with those reported theoretically and experimentally. Tumor reversibility and the proportionality between regions before and after electrotherapy are demonstrated. In tumors that reach partial remission, two antagonistic post-treatment processes are induced, whereas in complete remission, two unknown antitumor mechanisms are induced. The modified Gompertz equation is likely to lead to insights within cancer research. Such insights hold promise for increasing our understanding of tumors as self-organizing systems and, the possible existence of phase transitions in tumor growth kinetics, which, in turn, may have significant impacts both on cancer research and on clinical practice.

The influence of MOVPE growth conditions on the shell of core-shell GaN microrod structures

NASA Astrophysics Data System (ADS)

Schimpke, Tilman; Avramescu, Adrian; Koller, Andreas; Fernando-Saavedra, Amalia; Hartmann, Jana; Ledig, Johannes; Waag, Andreas; Strassburg, Martin; Lugauer, Hans-Jürgen

2017-05-01

A core-shell geometry is employed for most next-generation, three-dimensional opto-electric devices based on III-V semiconductors and grown by metal organic vapor phase epitaxy (MOVPE). Controlling the shape of the shell layers is fundamental for device optimization, however no detailed analysis of the influence of growth conditions has been published to date. We study homogeneous arrays of gallium nitride core-shell microrods with height and diameter in the micrometer range and grown in a two-step selective area MOVPE process. Changes in shell shape and homogeneity effected by deliberately altered shell growth conditions were accurately assessed by digital analysis of high-resolution scanning electron microscope images. Most notably, two temperature regimes could be established, which show a significantly different behavior with regard to material distribution. Above 900 °C of wafer carrier temperature, the shell thickness along the growth axis of the rods was very homogeneous, however variations between vicinal rods increase. In contrast, below 830 °C the shell thickness is higher close to the microrod tip than at the base of the rods, while the lateral homogeneity between neighboring microrods is very uniform. This temperature effect could be either amplified or attenuated by changing the remaining growth parameters such as reactor pressure, structure distance, gallium precursor, carrier gas composition and dopant materials. Possible reasons for these findings are discussed with respect to GaN decomposition as well as the surface and gas phase diffusion of growth species, leading to an improved control of the functional layers in next-generation 3D V-III devices.

Surfactant-controlled polymerization of semiconductor clusters to quantum dots through competing step-growth and living chain-growth mechanisms.

PubMed

Evans, Christopher M; Love, Alyssa M; Weiss, Emily A

2012-10-17

This article reports control of the competition between step-growth and living chain-growth polymerization mechanisms in the formation of cadmium chalcogenide colloidal quantum dots (QDs) from CdSe(S) clusters by varying the concentration of anionic surfactant in the synthetic reaction mixture. The growth of the particles proceeds by step-addition from initially nucleated clusters in the absence of excess phosphinic or carboxylic acids, which adsorb as their anionic conjugate bases, and proceeds indirectly by dissolution of clusters, and subsequent chain-addition of monomers to stable clusters (Ostwald ripening) in the presence of excess phosphinic or carboxylic acid. Fusion of clusters by step-growth polymerization is an explanation for the consistent observation of so-called "magic-sized" clusters in QD growth reactions. Living chain-addition (chain addition with no explicit termination step) produces QDs over a larger range of sizes with better size dispersity than step-addition. Tuning the molar ratio of surfactant to Se(2-)(S(2-)), the limiting ionic reagent, within the living chain-addition polymerization allows for stoichiometric control of QD radius without relying on reaction time.

Sandwich-structured C/C-SiC composites fabricated by electromagnetic-coupling chemical vapor infiltration.

PubMed

Hu, Chenglong; Hong, Wenhu; Xu, Xiaojing; Tang, Sufang; Du, Shanyi; Cheng, Hui-Ming

2017-10-13

Carbon fiber (CF) reinforced carbon-silicon carbide (C/C-SiC) composites are one of the most promising lightweight materials for re-entry thermal protection, rocket nozzles and brake discs applications. In this paper, a novel sandwich-structured C/C-SiC composite, containing two exterior C/SiC layers, two gradient C/C-SiC layers and a C/C core, has been designed and fabricated by two-step electromagnetic-coupling chemical vapor infiltration (E-CVI) for a 20-hour deposition time. The cross-section morphologies, interface microstructures and SiC-matrix growth characteristics and compositions of the composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), respectively. Microstructure characterization indicates that the SiC growth includes an initial amorphous SiC zone, a gradual crystallization of SiC and grow-up of nano-crystal, and a columnar grain region. The sandwich structure, rapid deposition rate and growth characteristics are attributed to the formation of thermal gradient and the establishment of electromagnetic field in the E-CVI process. The composite possesses low density of 1.84 g/cm 3 , high flexural strength of 325 MPa, and low linear ablation rate of 0.38 μm/s under exposure to 5-cycle oxyacetylene flame for 1000 s at ~1700 °C.

Stabilization of miscible viscous fingering by a step-growth polymerization reaction

NASA Astrophysics Data System (ADS)

Bunton, Patrick; Stewart, Simone; Marin, Daniela; Tullier, Michael; Meiburg, Eckart; Pojman, John

2017-11-01

Viscous fingering is a hydrodynamic instability that occurs when a more mobile fluid displaces a fluid of lower mobility. Viscous fingering is often undesirable in industrial processes such as secondary petroleum recovery where it limits resource recovery. Linear stability analysis by Hejazi et al. (2010) has predicted that a non-monotonic viscosity profile at an otherwise unstable interface can in some instances stabilize the flow. We use step-growth polymerization at the interface between two miscible monomers as a model system. A dithiol monomer displacing a diacrylate react to form a linear polymer that behaves as a Newtonian fluid. Viscous fingering was imaged in a horizontal Hele-Shaw cell via Schlieren, which is sensitive to polymer conversion. By varying reaction rate via initiator concentration along with flow rate, we demonstrated increasing stabilization of the flow with increasing Damkohler number (ratio of the reaction rate to the flow rate). Results were compared with regions of predicted stability from the results of Hejazi et al. (2010). When the advection outran the reaction, viscous fingering occurred as usual. However, when the reaction was able to keep pace with the advection, the increased viscosity at the interface stabilized the flow. We acknowledge support from NSF CBET-1335739 and NSF CBET 1511653.

Sliding wear and corrosion behaviour of alloyed austempered ductile iron subjected to novel two step austempering treatment

NASA Astrophysics Data System (ADS)

Sethuram, D.; Srisailam, Shravani; Rao Ponangi, Babu

2018-04-01

Austempered Ductile Iron(ADI) is an exciting alloy of iron which offers the design engineers the best combination high strength-to-weight ratio, low cost design flexibility, good toughness, wear resistance along with fatigue strength. The two step austempering procedure helps in simultaneously improving the tensile strength as-well as the ductility to more than that of the conventional austempering process. Extensive literature survey reveals that it’s mechanical and wear behaviour are dependent on heat treatment and alloy additions. Current work focuses on characterizing the two-step ADI samples (TSADI) developed by novel heat treatment process for resistance to corrosion and wear. The samples of Ductile Iron were austempered by the two-Step Austempering process at temperatures 300°C to 450°C in the steps of 50°C.Temperaturesare gradually increased at the rate of 14°C/Hour. In acidic medium (H2SO4), the austempered samples showed better corrosive resistance compared to conventional ductile iron. It has been observed from the wear studies that TSADI sample at 350°C is showing better wear resistance compared to ductile iron. The results are discussed in terms of fractographs, process variables and microstructural features of TSADI samples.

Competing Classical and Quantum Effects in Shape Relaxation of a Metallic Nanostructure

NASA Technical Reports Server (NTRS)

Chen, Dongmin; Okamoto, Hiroshi; Yamada, Toshishi; Biegel, Bryan (Technical Monitor)

2003-01-01

We demonstrate for the first time that the quantum size effect (QSE) plays a competing role along side the classical thermodynamic effect in the shape relaxation of a small metallic island. Together, these effects transforms a lead(Pb) island grown on Si(111) substrate from its initially flattop faceted morphology to a peculiar ring-shape island, a process catalysed by the tip electric field of a scanning tunnelling microscope (STM). We shall show for the first time how QSE affects the relaxation process dynamically. In particular, it leads to a novel strip-flow growth and double-step growth on selective strips of a plateau inside the ring, defined by the substrate steps more than 60?0?3 below. It appears that atoms diffusing on the plateau can clearly (sub i)(deg)sense(sub i)+/- the quantized energy states inside the island and have preferentially attached to regions that further reduces the surface energy as a result of the QSE, limiting its own growth and stabilizing the ring shape. The mechanism proposed here offers a sound explanation for ring shape metal and semiconductor islands observed in other systems as well.

Surface Modified Particles By Multi-Step Addition And Process For The Preparation Thereof

DOEpatents

Cook, Ronald Lee; Elliott, Brian John; Luebben, Silvia DeVito; Myers, Andrew William; Smith, Bryan Matthew

2006-01-17

The present invention relates to a new class of surface modified particles and to a multi-step surface modification process for the preparation of the same. The multi-step surface functionalization process involves two or more reactions to produce particles that are compatible with various host systems and/or to provide the particles with particular chemical reactivities. The initial step comprises the attachment of a small organic compound to the surface of the inorganic particle. The subsequent steps attach additional compounds to the previously attached organic compounds through organic linking groups.

Anaerobic digestion of sulfate-acidified cattle slurry: One-stage vs. two-stage.

PubMed

Moset, Veronica; Ottosen, Lars Ditlev Mørck; Xavier, Cristiane de Almeida Neves; Møller, Henrik Bjarne

2016-05-15

Two strategies to include acidified cattle manure (AcCM) in co-digestion with normal cattle manure (CM) are presented in this work. The strategies are a single thermophilic (50 °C) continuous stirred tank reactor (CSTR) anaerobic digestion and a two-step (65 °C + 50 °C) CSTR process. In both strategies, two different inclusion levels of H2SO4-acidified CM (10% and 20%) in co-digestion with normal CM were tested and compared with a control CSTR fed only CM. Important enhancement of methane (CH4) yield and solid reductions were observed in the thermophilic one-step CSTR working with 10% AcCM. However, a higher inclusion level of AcCM (20%) caused volatile fatty acid accumulation in the reactor and a more than 30% reduction in CH4 production. In terms of CH4 production, when 10% of AcCM was co-digested with 90% of CM, the two-step anaerobic co-digestion yielded less than the single step. During the first step of the two-step CSTR process, acidogenesis and a partial sulfate reduction were achieved. However, sulfide stripping between the first and the second step must be promoted in order to advance this technology. Copyright © 2016 Elsevier Ltd. All rights reserved.

One-Step Printable Perovskite Films Fabricated under Ambient Conditions for Efficient and Reproducible Solar Cells.

PubMed

Jung, Yen-Sook; Hwang, Kyeongil; Heo, Youn-Jung; Kim, Jueng-Eun; Lee, Donmin; Lee, Cheol-Ho; Joh, Han-Ik; Yeo, Jun-Seok; Kim, Dong-Yu

2017-08-23

Despite the potential of roll-to-roll processing for the fabrication of perovskite films, the realization of highly efficient and reproducible perovskite solar cells (PeSCs) through continuous coating techniques and low-temperature processing is still challenging. Here, we demonstrate that efficient and reliable CH 3 NH 3 PbI 3 (MAPbI 3 ) films fabricated by a printing process can be achieved through synergetic effects of binary processing additives, N-cyclohexyl-2-pyrrolidone (CHP) and dimethyl sulfoxide (DMSO). Notably, these perovskite films are deposited from premixed perovskite solutions for facile one-step processing under a room-temperature and ambient atmosphere. The CHP molecules result in the uniform and homogeneous perovskite films even in the one-step slot-die system, which originate from the high boiling point and low vapor pressure of CHP. Meanwhile, the DMSO molecules facilitate the growth of perovskite grains by forming intermediate states with the perovskite precursor molecules. Consequently, fully printed PeSC based on the binary additive system exhibits a high PCE of 12.56% with a high reproducibility.

Illusory spirals and loops in crystal growth

PubMed Central

Shtukenberg, Alexander G.; Zhu, Zina; Bhandari, Misha; Song, Pengcheng; Kahr, Bart; Ward, Michael D.

2013-01-01

The theory of dislocation-controlled crystal growth identifies a continuous spiral step with an emergent lattice displacement on a crystal surface; a mechanistic corollary is that closely spaced, oppositely winding spirals merge to form concentric loops. In situ atomic force microscopy of step propagation on pathological l-cystine crystals did indeed show spirals and islands with step heights of one lattice displacement. We show by analysis of the rates of growth of smaller steps only one molecule high that the major morphological spirals and loops are actually consequences of the bunching of the smaller steps. The morphology of the bunched steps actually inverts the predictions of the theory: Spirals arise from pairs of dislocations, loops from single dislocations. Only through numerical simulation of the growth is it revealed how normal growth of anisotropic layers of molecules within the highly symmetrical crystals can conspire to create features in apparent violation of the classic theory. PMID:24101507

Large scale crystallization of protein pharmaceuticals in microgravity via temperature change

NASA Technical Reports Server (NTRS)

Long, Marianna M.

1992-01-01

The major objective of this research effort is the temperature driven growth of protein crystals in large batches in the microgravity environment of space. Pharmaceutical houses are developing protein products for patient care, for example, human insulin, human growth hormone, interferons, and tissue plasminogen activator or TPA, the clot buster for heart attack victims. Except for insulin, these are very high value products; they are extremely potent in small quantities and have a great value per gram of material. It is feasible that microgravity crystallization can be a cost recoverable, economically sound final processing step in their manufacture. Large scale protein crystal growth in microgravity has significant advantages from the basic science and the applied science standpoints. Crystal growth can proceed unhindered due to lack of surface effects. Dynamic control is possible and relatively easy. The method has the potential to yield large quantities of pure crystalline product. Crystallization is a time honored procedure for purifying organic materials and microgravity crystallization could be the final step to remove trace impurities from high value protein pharmaceuticals. In addition, microgravity grown crystals could be the final formulation for those medicines that need to be administered in a timed release fashion. Long lasting insulin, insulin lente, is such a product. Also crystalline protein pharmaceuticals are more stable for long-term storage. Temperature, as the initiation step, has certain advantages. Again, dynamic control of the crystallization process is possible and easy. A temperature step is non-invasive and is the most subtle way to control protein solubility and therefore crystallization. Seeding is not necessary. Changes in protein and precipitant concentrations and pH are not necessary. Finally, this method represents a new way to crystallize proteins in space that takes advantage of the unique microgravity environment. The results from two flights showed that the hardware performed perfectly, many crystals were produced, and they were much larger than their ground grown controls. Morphometric analysis was done on over 4,000 crystals to establish crystal size, size distribution, and relative size. Space grown crystals were remarkably larger than their earth grown counterparts and crystal size was a function of PCF volume. That size distribution for the space grown crystals was a function of PCF volume may indicate that ultimate size was a function of temperature gradient. Since the insulin protein concentration was very low, 0.4 mg/ml, the size distribution could also be following the total amount of protein in each of the PCF's. X-ray analysis showed that the bigger space grown insulin crystals diffracted to higher resolution than their ground grown controls. When the data were normalized for size, they still indicated that the space crystals were better than the ground crystals.

Internal and external atomic steps in graphite exhibit dramatically different physical and chemical properties.

PubMed

Lee, Hyunsoo; Lee, Han-Bo-Ram; Kwon, Sangku; Salmeron, Miquel; Park, Jeong Young

2015-04-28

We report on the physical and chemical properties of atomic steps on the surface of highly oriented pyrolytic graphite (HOPG) investigated using atomic force microscopy. Two types of step edges are identified: internal (formed during crystal growth) and external (formed by mechanical cleavage of bulk HOPG). The external steps exhibit higher friction than the internal steps due to the broken bonds of the exposed edge C atoms, while carbon atoms in the internal steps are not exposed. The reactivity of the atomic steps is manifested in a variety of ways, including the preferential attachment of Pt nanoparticles deposited on HOPG when using atomic layer deposition and KOH clusters formed during drop casting from aqueous solutions. These phenomena imply that only external atomic steps can be used for selective electrodeposition for nanoscale electronic devices.

Controllable Magnetization Processes Induced by Nucleation Sites in Permalloy Rings

NASA Astrophysics Data System (ADS)

Chen, Ying-Jiun; Hsu, Chia-Jung; Liao, Chun-Neng; Huang, Hao-Ting; Lee, Chiun-Peng; Chiu, Yi-Hsun; Tung, Tzu-Yun; Lai, Mei-Feng

2010-02-01

Different arrangements of notches as nucleation sites are demonstrated experimentally and numerically to effectively control the magnetization processes of permalloy rings. In the ring with notches at the same side with respect to field direction, two same-helicity vortex domain walls in the onion state lead to two-step switching going through flux-closure state; in the ring with diagonal notches two opposite-helicity vortex domain walls lead to one-step switching skipping flux-closure state. The switching processes are repeatable in contrast to rings without notches where helicites of two vortex domain walls are random so the switching processes can not be controlled.

An atomistic mechanism study of GaN step-flow growth in vicinal m-plane orientations

DOE PAGES

Liu, Zhun; Wang, Ru-Zhi; Zapol, Peter

2016-10-12

We present elucidation of homoepitaxial growth mechanisms on vicinal non-polar surfaces of GaN that is highly important for gaining an understanding of and control thin film surface morphology and properties. Using first-principles calculations, we study the step-flow growth in m-plane GaN based on atomic row nucleation and kink propagation kinetics. Ga–N dimer adsorption onto the m-plane is energetically more favorable than that of Ga and N isolated adatoms. Therefore, we have treated the dimers as the dominant growth species attached to the step edges. By calculating the free energies of sequentially attached Ga–N dimers, we have elucidated that the a-stepmore » edge kink growth proceeds by parallel attachment rather than by across the step edge approach. We found a series of favorable configurations of kink propagation and calculated the free energy and nucleation barriers for kink evolution on five types of step edges (a, +c, -c, +a + c, and -a - c). By changing the chemical potential μGa and the excess chemical potential Δμ, the growth velocities at the five types of edges are controlled by the corresponding kink pair nucleation barrier E* in their free energy profiles. To explore the kink-flow growth instability observed at different Ga/N flux ratios, calculations of kink pairs on the incompact -c and +c-step edges are further performed to study their formation energies. Variations of these step edge morphologies with a tuned chemical environment are consistent with previous experimental observations, including stable diagonal ±a ± c-direction steps. In conclusion, our work provides a first-principles approach to explore step growth and surface morphology of the vicinal m-plane GaN, which is applicable to analyze and control the step-flow growth of other binary thin films.« less

Low temperature synthesis of nano alpha-alumina powder by two-step hydrolysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Ting; Guo, Xiaode, E-mail: guoxiaodenj@sina.com; Zhang, Xiang

Highlights: • The nano α-Al{sub 2}O{sub 3} with good dispersion was prepared by two-step hydrolysis. • α-Al{sub 2}O{sub 3} powders were added as seed particles in the hydrolysis. • This article indicated that the glucose could impel the γ-Al{sub 2}O{sub 3} transformed to α-Al{sub 2}O{sub 3} directly. • This article indicated that the addictive of α-Al{sub 2}O{sub 3} seed could improve the phase transformation rate of γ-Al{sub 2}O{sub 3} to α-Al{sub 2}O{sub 3}. • In this article, the pure α-Al{sub 2}O{sub 3} could be obtained by calcining at 1000 °C for 1.5 h. - Abstract: The ultral fine alpha-alumina powdermore » has been successfully synthesized via two-step hydrolysis of aluminum isopropoxide. Glucose and polyvinyl pyrrolidone were used as surfactants during the appropriate processing step. The alpha-alumina powder was used as seed particles. Several synthesis parameters, such as the amount of seeds, surfactants, and calcination temperature, were studied by X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), Thermogravimetry-differential scanning calorimetry (TG-DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results showed that glucose greatly lower the phase transformation temperature of alpha-alumina by impelling the gamma-alumina transformed to alpha-alumina directly, and the seed could improve the phase transformation rate of alpha-alumina, the polyvinylpyrrolidone have an effect on preventing excessive grain growth and agglomeration of alpha-alumina powder. Comparatively well dispersed alpha-alumina powder with particle size less than 50 nm can be synthesized through this method after calcinations at 1000 °C for 2 h.« less

Simulation of dendritic growth reveals necessary and sufficient parameters to describe the shapes of dendritic trees

NASA Astrophysics Data System (ADS)

Trottier, Olivier; Ganguly, Sujoy; Bowne-Anderson, Hugo; Liang, Xin; Howard, Jonathon

For the last 120 years, the development of neuronal shapes has been of great interest to the scientific community. Over the last 30 years, significant work has been done on the molecular processes responsible for dendritic development. In our ongoing research, we use the class IV sensory neurons of the Drosophila melanogaster larva as a model system to understand the growth of dendritic arbors. Our main goal is to elucidate the mechanisms that the neuron uses to determine the shape of its dendritic tree. We have observed the development of the class IV neuron's dendritic tree in the larval stage and have concluded that morphogenesis is defined by 3 distinct processes: 1) branch growth, 2) branching and 3) branch retraction. As the first step towards understanding dendritic growth, we have implemented these three processes in a computational model. Our simulations are able to reproduce the branch length distribution, number of branches and fractal dimension of the class IV neurons for a small range of parameters.

Surface Modifications of Materials by Electrochemical Methods to Improve the Properties for Industrial and Medical Applications

NASA Astrophysics Data System (ADS)

Benea, Lidia

2018-06-01

There are two applied electrochemical methods in our group in order to obtain advanced functional surfaces on materials: (i) direct electrochemical synthesis by electro-codeposition process and (ii) anodization of materials to form nanoporous oxide layers followed by electrodeposition of hydroxyapatite or other bioactive molecules and compounds into porous film. Electrodeposition is a process of low energy consumption, and therefore very convenient for the surface modification of various types of materials. Electrodeposition is a powerful method compared with other methods, which led her to be adopted and spread rapidly in nanotechnology to obtain nanostructured layers and films. Nanoporous thin oxide layers on titanum alloys as support for hydroxyapatite or other biomolecules electrodeposition in view of biomedical applications could be obtained by electrochemical methods. For surface modification of titanium or titanium alloys to improve the biocompatibility or osseointegration, the two steps must be fulfilled; the first is controlled growth of oxide layer followed by second being biomolecule electrodeposition into nanoporous formed titanium oxide layer.

A Direct Cell Quenching Method for Cell-Culture Based Metabolomics

EPA Science Inventory

A crucial step in metabolomic analysis of cellular extracts is the cell quenching process. The conventional method first uses trypsin to detach cells from their growth surface. This inevitably changes the profile of cellular metabolites since the detachment of cells from the extr...

Method for extracting relevant electrical parameters from graphene field-effect transistors using a physical model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boscá, A., E-mail: alberto.bosca@upm.es; Dpto. de Ingeniería Electrónica, E.T.S.I. de Telecomunicación, Universidad Politécnica de Madrid, Madrid 28040; Pedrós, J.

2015-01-28

Due to its intrinsic high mobility, graphene has proved to be a suitable material for high-speed electronics, where graphene field-effect transistor (GFET) has shown excellent properties. In this work, we present a method for extracting relevant electrical parameters from GFET devices using a simple electrical characterization and a model fitting. With experimental data from the device output characteristics, the method allows to calculate parameters such as the mobility, the contact resistance, and the fixed charge. Differentiated electron and hole mobilities and direct connection with intrinsic material properties are some of the key aspects of this method. Moreover, the method outputmore » values can be correlated with several issues during key fabrication steps such as the graphene growth and transfer, the lithographic steps, or the metalization processes, providing a flexible tool for quality control in GFET fabrication, as well as a valuable feedback for improving the material-growth process.« less

Production of functional human insulin-like growth factor binding proteins (IGFBPs) using recombinant expression in HEK293 cells.

PubMed

Wanscher, Anne Sofie Molsted; Williamson, Michael; Ebersole, Tasja Wainani; Streicher, Werner; Wikström, Mats; Cazzamali, Giuseppe

2015-04-01

Insulin-like growth factor binding proteins (IGFBPs) display many functions in humans including regulation of the insulin-like growth factor (IGF) signaling pathway. The various roles of human IGFBPs make them attractive protein candidates in drug discovery. Structural and functional knowledge on human proteins with therapeutic relevance is needed to design and process the next generation of protein therapeutics. In order to conduct structural and functional investigations large quantities of recombinant proteins are needed. However, finding a suitable recombinant production system for proteins such as full-length human IGFBPs, still remains a challenge. Here we present a mammalian HEK293 expression method suitable for over-expression of secretory full-length human IGFBP-1 to -7. Protein purification of full-length human IGFBP-1, -2, -3 and -5 was conducted using a two-step chromatography procedure and the final protein yields were between 1 and 12mg protein per liter culture media. The recombinant IGFBPs contained PTMs and exhibited high-affinity interactions with their natural ligands IGF-1 and IGF-2. Copyright © 2014 Elsevier Inc. All rights reserved.

Thermal quenching effect of an infrared deep level in Mg-doped p-type GaN films

NASA Astrophysics Data System (ADS)

Kim, Keunjoo; Chung, Sang Jo

2002-03-01

The thermal quenching of an infrared deep level of 1.2-1.5 eV has been investigated on Mg-doped p-type GaN films, using one- and two-step annealing processes and photocurrent measurements. The deep level appeared in the one-step annealing process at a relatively high temperature of 900 °C, but disappeared in the two-step annealing process with a low-temperature step and a subsequent high-temperature step. The persistent photocurrent was residual in the sample including the deep level, while it was terminated in the sample without the deep level. This indicates that the deep level is a neutral hole center located above a quasi-Fermi level, estimated with an energy of EpF=0.1-0.15 eV above the valence band at a hole carrier concentration of 2.0-2.5×1017/cm3.

The Role of Moist Processes in the Intrinsic Predictability of Indian Ocean Cyclones

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taraphdar, Sourav; Mukhopadhyay, P.; Leung, Lai-Yung R.

The role of moist processes and the possibility of error cascade from cloud scale processes affecting the intrinsic predictable time scale of a high resolution convection permitting model within the environment of tropical cyclones (TCs) over the Indian region are investigated. Consistent with past studies of extra-tropical cyclones, it is demonstrated that moist processes play a major role in forecast error growth which may ultimately limit the intrinsic predictability of the TCs. Small errors in the initial conditions may grow rapidly and cascades from smaller scales to the larger scales through strong diabatic heating and nonlinearities associated with moist convection.more » Results from a suite of twin perturbation experiments for four tropical cyclones suggest that the error growth is significantly higher in cloud permitting simulation at 3.3 km resolutions compared to simulations at 3.3 km and 10 km resolution with parameterized convection. Convective parameterizations with prescribed convective time scales typically longer than the model time step allows the effects of microphysical tendencies to average out so convection responds to a smoother dynamical forcing. Without convective parameterizations, the finer-scale instabilities resolved at 3.3 km resolution and stronger vertical motion that results from the cloud microphysical parameterizations removing super-saturation at each model time step can ultimately feed the error growth in convection permitting simulations. This implies that careful considerations and/or improvements in cloud parameterizations are needed if numerical predictions are to be improved through increased model resolution. Rapid upscale error growth from convective scales may ultimately limit the intrinsic mesoscale predictability of the TCs, which further supports the needs for probabilistic forecasts of these events, even at the mesoscales.« less

Towards a seascape typology. I. Zipf versus Pareto laws

NASA Astrophysics Data System (ADS)

Seuront, Laurent; Mitchell, James G.

Two data analysis methods, referred to as the Zipf and Pareto methods, initially introduced in economics and linguistics two centuries ago and subsequently used in a wide range of fields (word frequency in languages and literature, human demographics, finance, city formation, genomics and physics), are described and proposed here as a potential tool to classify space-time patterns in marine ecology. The aim of this paper is, first, to present the theoretical bases of Zipf and Pareto laws, and to demonstrate that they are strictly equivalent. In that way, we provide a one-to-one correspondence between their characteristic exponents and argue that the choice of technique is a matter of convenience. Second, we argue that the appeal of this technique is that it is assumption-free for the distribution of the data and regularity of sampling interval, as well as being extremely easy to implement. Finally, in order to allow marine ecologists to identify and classify any structure in their data sets, we provide a step by step overview of the characteristic shapes expected for Zipf's law for the cases of randomness, power law behavior, power law behavior contaminated by internal and external noise, and competing power laws illustrated on the basis of typical ecological situations such as mixing processes involving non-interacting and interacting species, phytoplankton growth processes and differential grazing by zooplankton.

MELiSSA third compartment: Nitrosomonas europaea and Nitrobacter winogradskyi axenic cultures in bioreactors

NASA Astrophysics Data System (ADS)

Cruvellier, Nelly; Lasseur, Christophe; Poughon, Laurent; Creuly, Catherine; Dussap, Gilles

Nitrogen is a key element for the life and its balance on Earth is regulated by the nitrogen cycle. This loop includes several steps among which nitrification that permits the transformation of the ammonium into nitrate. The MELiSSA loop is an artificial ecosystem designed for life support systems (LSS). It is based on the carbon and nitrogen cycles and the recycling of the non-edible part of the higher plants and the waste produced by the crew. In this order, all the wastes are collected in the first compartment to degrade them into organic acids and CO2. These compounds are joining the second compartment which is a photoheterotrophic compartment where at the outlet an organic-free medium containing ammonium is produced. This solution will be the substrate of the third compartment where nitrification is done. This compartment has to oxidize the ammonium into nitrate, and this biological reaction needs two steps. In the MELiSSA loop, the nitrification is carried out by two bacteria: Nitrosomonas europaea ATCC® 19718™ which is oxidizing ammonia into nitrite and Nitrobacter winogradskyi ATCC® 25391™ which is producing nitrate from nitrite in the third compartment. These two bacteria are growing in axenic conditions on a fixed bed bioreactor filled with Biostyr® beads. The nitrogen compounds are controlled by Ionic Chromatography and colorimetric titration for each sample. The work presented here deals with the culture of both bacteria in pure cultures and mixed cultures in stirred and aerated bioreactors of different volumes. The first aim of our work is the characterization of the bacteria growth in bioreactors and in the nitrifying fixed-bed column. The experimental results confirm that the growth is slow; the maximal growth rate in suspended cultures is 0.054h-1 for Nitrosomonas europaea and 0.022h-1 for Nitrobacter winogradskyi. Mixed cultures are difficult to control and operate but one could be done for more than 500 hours. The characterization of the bacteria will be used to calibrate the nitrification model which will be the basis of the control model for managing the nitrification process in the MELiSSA loop. The experimental results highlighted the use of online measurement of base addition and oxygen consumption as possible parameters for the control of the nitrification process. Keywords: Nitrosomonas europaea, Nitrobacter winogradskyi, MELiSSA, bioreactor

Polycrystalline semiconductor processing

DOEpatents

Glaeser, Andreas M.; Haggerty, John S.; Danforth, Stephen C.

1983-01-01

A process for forming large-grain polycrystalline films from amorphous films for use as photovoltaic devices. The process operates on the amorphous film and uses the driving force inherent to the transition from the amorphous state to the crystalline state as the force which drives the grain growth process. The resultant polycrystalline film is characterized by a grain size that is greater than the thickness of the film. A thin amorphous film is deposited on a substrate. The formation of a plurality of crystalline embryos is induced in the amorphous film at predetermined spaced apart locations and nucleation is inhibited elsewhere in the film. The crystalline embryos are caused to grow in the amorphous film, without further nucleation occurring in the film, until the growth of the embryos is halted by imgingement on adjacently growing embryos. The process is applicable to both batch and continuous processing techniques. In either type of process, the thin amorphous film is sequentially doped with p and n type dopants. Doping is effected either before or after the formation and growth of the crystalline embryos in the amorphous film, or during a continuously proceeding crystallization step.

Polycrystalline semiconductor processing

DOEpatents

Glaeser, A.M.; Haggerty, J.S.; Danforth, S.C.

1983-04-05

A process is described for forming large-grain polycrystalline films from amorphous films for use as photovoltaic devices. The process operates on the amorphous film and uses the driving force inherent to the transition from the amorphous state to the crystalline state as the force which drives the grain growth process. The resultant polycrystalline film is characterized by a grain size that is greater than the thickness of the film. A thin amorphous film is deposited on a substrate. The formation of a plurality of crystalline embryos is induced in the amorphous film at predetermined spaced apart locations and nucleation is inhibited elsewhere in the film. The crystalline embryos are caused to grow in the amorphous film, without further nucleation occurring in the film, until the growth of the embryos is halted by impingement on adjacently growing embryos. The process is applicable to both batch and continuous processing techniques. In either type of process, the thin amorphous film is sequentially doped with p and n type dopants. Doping is effected either before or after the formation and growth of the crystalline embryos in the amorphous film, or during a continuously proceeding crystallization step. 10 figs.

Development of metallization process. FSA project, cell and module formation research area

NASA Technical Reports Server (NTRS)

Garcia, A., III

1984-01-01

New pastes were evaluated that contained additives to aid in the silicon-to-metallization contact. None were completely successful. A reevaluation of the molybdenum oxide paste and the two-step screen printing process was done. The oxide paste did not show promise. The two-step process enabled soldering of the cells but the cells still had a high series resistance. Pastes are on order from a different manufacturer.

Movement patterns and the medium-sized city. Tenants on the move in Gweru, Zimbabwe.

PubMed

Grant, M

1995-01-01

During 1965-79, urban growth rates accelerated and continued after Zimbabwe's independence in 1980. For 1960-80, the estimated urban growth rate was 5.6% as compared with the natural growth rate of 3.5% and urban growth rate of 5.0% to 8.1% for the period 1982-92. Gweru, Zimbabwe, had a population of 110,000 in 1990, and as the provincial capital it is an important destination for rural and interurban migrants. Between 1982 and 1990 there was a 4.9% growth rate, resulting in the municipal waiting list for housing to exceed 14,000 in mid-1990. In a large study on migration and rental shelter, 188 tenants were interviewed in high, low-medium density, and periurban areas of the city with the intent of tracing respondents and the nature of migration streams. Regarding origins and connections, only one-fifth of the migrants were born in Gweru, more than half were born in rural areas, and the rest in other urban areas. More than 90% still had rural homes. Two-thirds made rural home visits six times or less a year and one-fourth visited seven times a year to once a month. 40% of the migrants to Gweru originated in larger cities, 24% in smaller urban areas, and 36% in rural areas. 58% moved to high density areas, 34% to low-medium, and 8% to peri-urban areas. The dominant motive was the search for employment and direct transfers, thus economic factors dominated over social factors. Three groups were distinguished according to length of stay: 1) 5 years or less who lived mainly in high and low-medium density housing; 2) 6-15 years; and 3) more than 15 years who lived in low density and high density areas. Regarding the previous two migrations, two-thirds stayed at the previous place for 5 years of less. The reasons for migration were overcrowding, family, and employment. Within Gweru high mobility was typical: one-third initiated one step, 43% initiated two steps, and 27% initiated three steps. Lodgers were the most mobile since one-third were moving three times.

Growth and Characterization of 3C-SiC and 2H-AIN/GaN Films and Devices Produced on Step-Free 4H-SiC Mesa Substrates

NASA Technical Reports Server (NTRS)

Neudeck, P. G.; Du, H.; Skowronski, M.; Spry, D. J.; Trunek, A. J.

2007-01-01

While previously published experimental results have shown that the step-free (0 0 0 1) 4H-SiC mesa growth surface uniquely enables radical improvement of 3C-SiC and 2H-AlN/GaN heteroepitaxial film quality (greater than 100-fold reduction in extended defect densities), important aspects of the step-free mesa heterofilm growth processes and resulting electronic device benefits remain to be more fully elucidated. This paper reviews and updates recent ongoing studies of 3C-SiC and 2H-AlN/GaN heteroepilayers grown on top of 4H-SiC mesas. For both 3C-SiC and AlN/GaN films nucleated on 4H-SiC mesas rendered completely free of atomic-scale surface steps, TEM studies reveal that relaxation of heterofilm strain arising from in-plane film/substrate lattice constant mismatch occurs in a remarkably benign manner that avoids formation of threading dislocations in the heteroepilayer. In particular, relaxation appears to occur via nucleation and inward lateral glide of near-interfacial dislocation half-loops from the mesa sidewalls. Preliminary studies of homojunction diodes implemented in 3C-SiC and AlN/GaN heterolayers demonstrate improved electrical performance compared with much more defective heterofilms grown on neighbouring stepped 4H-SiC mesas. Recombination-enhanced dislocation motion known to degrade forward-biased 4H-SiC bipolar diodes has been completely absent from our initial studies of 3C-SiC diodes, including diodes implemented on defective 3C-SiC heterolayers grown on stepped 4H-SiC mesas.

[Clinical and etiopathogenetic role of plasminogen and metaloproteinase systems in the tumor growth. Pericellular proteolysis of extracellular matrix and tumor growth].

PubMed

Cosić, Sanda Jelisavac; Kovac, Zdenko

2011-01-01

Pericellular proteolysis is a cascade process involved in degradation of extracellular matrix. This process is included in various physiological and pathological processes. Pericellullar proteolysis has major functions like degradation of tissue stroma and weakening of intercellular connections but it also has a function in the synthesis of bioactive molecules (cytokines, growth factors and inhibitory factors). Plasminogen system is involved in fibrinolysis and starts metalloproteinase activation. Activity of proteolytic molecules is controlled by the rate of zymogenic activation, half-life of molecules, and action of inhibitory molecules. Inhibition is achieved through direct binding of inhibitor and enzyme and takes a few steps. Pericellular proteolysis is involved in tumor invasion and metastasis, inflammatory reaction, degenerative diseases and other diseases. Pathophysiological regulation of pericellular proteolysis in mentioned diseases contributes to clinical properties of diseases and has diagnostic and therapeutic importance.

A Vertically Lagrangian Finite-Volume Dynamical Core for Global Models

NASA Technical Reports Server (NTRS)

Lin, Shian-Jiann

2003-01-01

A finite-volume dynamical core with a terrain-following Lagrangian control-volume discretization is described. The vertically Lagrangian discretization reduces the dimensionality of the physical problem from three to two with the resulting dynamical system closely resembling that of the shallow water dynamical system. The 2D horizontal-to-Lagrangian-surface transport and dynamical processes are then discretized using the genuinely conservative flux-form semi-Lagrangian algorithm. Time marching is split- explicit, with large-time-step for scalar transport, and small fractional time step for the Lagrangian dynamics, which permits the accurate propagation of fast waves. A mass, momentum, and total energy conserving algorithm is developed for mapping the state variables periodically from the floating Lagrangian control-volume to an Eulerian terrain-following coordinate for dealing with physical parameterizations and to prevent severe distortion of the Lagrangian surfaces. Deterministic baroclinic wave growth tests and long-term integrations using the Held-Suarez forcing are presented. Impact of the monotonicity constraint is discussed.

Cyanide Degradation under Alkaline Conditions by a Strain of Fusarium solani Isolated from Contaminated Soils

PubMed Central

Dumestre, A.; Chone, T.; Portal, J.; Gerard, M.; Berthelin, J.

1997-01-01

Several cyanide-tolerant microorganisms have been selected from alkaline wastes and soils contaminated with cyanide. Among them, a fungus identified as Fusarium solani IHEM 8026 shows a good potential for cyanide biodegradation under alkaline conditions (pH 9.2 to 10.7). Results of K(sup14)CN biodegradation studies show that fungal metabolism seems to proceed by a two-step hydrolytic mechanism: (i) the first reaction involves the conversion of cyanide to formamide by a cyanide-hydrolyzing enzyme, cyanide hydratase (EC 4.2.1.66); and (ii) the second reaction consists of the conversion of formamide to formate, which is associated with fungal growth. No growth occurred during the first step of cyanide degradation, suggesting that cyanide is toxic to some degree even in cyanide-degrading microorganisms, such as F. solani. The presence of organic nutrients in the medium has a major influence on the occurrence of the second step. Addition of small amounts of yeast extract led to fungal growth, whereas no growth was observed in media containing cyanide as the sole source of carbon and nitrogen. The simple hydrolytic detoxification pathway identified in the present study could be used for the treatment of many industrial alkaline effluents and wastes containing free cyanide without a prior acidification step, thus limiting the risk of cyanhydric acid volatilization; this should be of great interest from an environmental and health point of view. PMID:16535647

Novel growth techniques for the deposition of high-quality perovskite thin films

NASA Astrophysics Data System (ADS)

Ng, Annie; Ren, Zhiwei; Li, Gang; Djurišić, Aleksandra B.; Surya, Charles

2018-02-01

We present investigations on the growth of high quality CH3NH3PbI3 (MAPI) thin films using both vapor and solution techniques. Recent work on perovskite film growth indicates critical dependencies of the film quality on the nucleation and crystallization steps requiring: i.) uniform distribution of nucleation sites; and ii.) optimal crystallization rate that facilitates the growth of a compact, continuous film with low density of pinholes. Our work shows that the hybrid chemical vapor deposition technique (HCVD) technique is well suited for the deposition of evenly distributed nucleation sites and the optimization of the crystallization rate of the film through detailed monitoring of the thermal profile of the growth process. Signficant reduction in the defect states is recorded by annealing the perovskite films in O2. The results are consistent with theoretical studies by Yin et al. 1 on O and Cl passivation of the shallow states at the grain boundary of MAPI. Their work provides the theoretical basis for our experimental observations on the passivation of shallow states by oxygen annealing. High quality films were achieved through detailed management of the carrier gas composition and the thermal profile of the nucleation and crystallization steps.

Hierarchical Oriented Anatase TiO2 Nanostructure arrays on Flexible Substrate for Efficient Dye-sensitized Solar Cells

PubMed Central

Wu, Wu-Qiang; Rao, Hua-Shang; Xu, Yang-Fan; Wang, Yu-Fen; Su, Cheng-Yong; Kuang, Dai-Bin

2013-01-01

The vertically oriented anatase single crystalline TiO2 nanostructure arrays (TNAs) consisting of TiO2 truncated octahedrons with exposed {001} facets or hierarchical TiO2 nanotubes (HNTs) consisting of numerous nanocrystals on Ti-foil substrate were synthesized via a two-step hydrothermal growth process. The first step hydrothermal reaction of Ti foil and NaOH leads to the formation of H-titanate nanowire arrays, which is further performed the second step hydrothermal reaction to obtain the oriented anatase single crystalline TiO2 nanostructures such as TiO2 nanoarrays assembly with truncated octahedral TiO2 nanocrystals in the presence of NH4F aqueous or hierarchical TiO2 nanotubes with walls made of nanocrystals in the presence of pure water. Subsequently, these TiO2 nanostructures were utilized to produce dye-sensitized solar cells in a backside illumination pattern, yielding a significant high power conversion efficiency (PCE) of 4.66% (TNAs, JSC = 7.46 mA cm−2, VOC = 839 mV, FF = 0.75) and 5.84% (HNTs, JSC = 10.02 mA cm−2, VOC = 817 mV, FF = 0.72), respectively. PMID:23715529

Apparatus for mixing solutions in low gravity environments

NASA Technical Reports Server (NTRS)

Carter, Daniel C. (Inventor); Broom, Mary B. (Inventor)

1990-01-01

An apparatus is disclosed for allowing mixing of solutions in low gravity environments so as to carry out crystallization of proteins and other small molecules or other chemical syntheses, under conditions that maximize crystal growth and minimize disruptive turbulent effects. The apparatus is comprised of a housing, a plurality of chambers, and a cylindrical rotatable valve disposed between at least two of the chambers, said valve having an internal passageway so as to allow fluid movement between the chambers by rotation of the valve. In an alternate embodiment of the invention, a valve is provided having an additional internal passage way so that fluid from a third chamber can be mixed with the fluids of the first two chambers. This alternate embodiment of the invention is particularly desirable when it is necessary to provide a termination step to the crystal growth, or if a second synthetic step is required.

Observation of Charge Generation and Transfer during CVD Growth of Carbon Nanotubes.

PubMed

Wang, Jiangtao; Liu, Peng; Xia, Bingyu; Wei, Haoming; Wei, Yang; Wu, Yang; Liu, Kai; Zhang, Lina; Wang, Jiaping; Li, Qunqing; Fan, Shoushan; Jiang, Kaili

2016-07-13

Carbon nanotube (CNT) is believed to be the most promising material for next generation IC industries with the prerequisite of chirality specific growth. For various approaches to controlling the chiral indices of CNTs, the key is to deepen the understanding of the catalytic growth mechanism in chemical vapor deposition (CVD). Here we show our discovery that the as-grown CNTs are all negatively charged after Fe-catalyzed CVD process. The extra electrons come from the charge generation and transfer during the growth of CNTs, which indicates that an electrochemical process happens in the surface reaction step. We then designed an in situ measurement equipment, verifying that the CVD growth of CNTs can be regarded as a primary battery system. Furthermore, we found that the variation of the Fermi level in Fe catalysts have a significant impact on the chirality of CNTs when different external electric fields are applied. These findings not only provide a new perspective on the growth of CNTs but also open up new possibilities for controlling the growth of CNTs by electrochemical methods.

Effects of acute alcohol intoxication on automated processing: evidence from the double-step paradigm.

PubMed

Vorstius, Christian; Radach, Ralph; Lang, Alan R

2012-02-01

Reflexive and voluntary levels of processing have been studied extensively with respect to possible impairments due to alcohol intoxication. This study examined alcohol effects at the 'automated' level of processing essential to many complex visual processing tasks (e.g., reading, visual search) that involve ongoing modifications or reprogramming of well-practiced routines. Data from 30 participants (16 male) were collected in two counterbalanced sessions (alcohol vs. no-alcohol control; mean breath alcohol concentration = 68 mg/dL vs. 0 mg/dL). Eye movements were recorded during a double-step task where 75% of trials involved two target stimuli in rapid succession (inter-stimulus interval [ISI]=40, 70, or 100 ms) so that they could elicit two distinct saccades or eye movements (double steps). On 25% of trials a single target appeared. Results indicated that saccade latencies were longer under alcohol. In addition, the proportion of single-step responses and the mean saccade amplitude (length) of primary saccades decreased significantly with increasing ISI. The key novel finding, however, was that the reprogramming time needed to cancel the first saccade and adjust saccade amplitude was extended significantly by alcohol. The additional time made available by prolonged latencies due to alcohol was not utilized by the saccade programming system to decrease the number of two-step responses. These results represent the first demonstration of specific alcohol-induced programming deficits at the automated level of oculomotor processing.

Dissolution Processes at Step Edges of Calcite in Water Investigated by High-Speed Frequency Modulation Atomic Force Microscopy and Simulation.

PubMed

Miyata, Kazuki; Tracey, John; Miyazawa, Keisuke; Haapasilta, Ville; Spijker, Peter; Kawagoe, Yuta; Foster, Adam S; Tsukamoto, Katsuo; Fukuma, Takeshi

2017-07-12

The microscopic understanding of the crystal growth and dissolution processes have been greatly advanced by the direct imaging of nanoscale step flows by atomic force microscopy (AFM), optical interferometry, and X-ray microscopy. However, one of the most fundamental events that govern their kinetics, namely, atomistic events at the step edges, have not been well understood. In this study, we have developed high-speed frequency modulation AFM (FM-AFM) and enabled true atomic-resolution imaging in liquid at ∼1 s/frame, which is ∼50 times faster than the conventional FM-AFM. With the developed AFM, we have directly imaged subnanometer-scale surface structures around the moving step edges of calcite during its dissolution in water. The obtained images reveal that the transition region with typical width of a few nanometers is formed along the step edges. Building upon insight in previous studies, our simulations suggest that the transition region is most likely to be a Ca(OH) 2 monolayer formed as an intermediate state in the dissolution process. On the basis of this finding, we improve our understanding of the atomistic dissolution model of calcite in water. These results open up a wide range of future applications of the high-speed FM-AFM to the studies on various dynamic processes at solid-liquid interfaces with true atomic resolution.

Efficient differentiation of mouse embryonic stem cells into motor neurons.

PubMed

Wu, Chia-Yen; Whye, Dosh; Mason, Robert W; Wang, Wenlan

2012-06-09

Direct differentiation of embryonic stem (ES) cells into functional motor neurons represents a promising resource to study disease mechanisms, to screen new drug compounds, and to develop new therapies for motor neuron diseases such as spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS). Many current protocols use a combination of retinoic acid (RA) and sonic hedgehog (Shh) to differentiate mouse embryonic stem (mES) cells into motor neurons. However, the differentiation efficiency of mES cells into motor neurons has only met with moderate success. We have developed a two-step differentiation protocol that significantly improves the differentiation efficiency compared with currently established protocols. The first step is to enhance the neuralization process by adding Noggin and fibroblast growth factors (FGFs). Noggin is a bone morphogenetic protein (BMP) antagonist and is implicated in neural induction according to the default model of neurogenesis and results in the formation of anterior neural patterning. FGF signaling acts synergistically with Noggin in inducing neural tissue formation by promoting a posterior neural identity. In this step, mES cells were primed with Noggin, bFGF, and FGF-8 for two days to promote differentiation towards neural lineages. The second step is to induce motor neuron specification. Noggin/FGFs exposed mES cells were incubated with RA and a Shh agonist, Smoothened agonist (SAG), for another 5 days to facilitate motor neuron generation. To monitor the differentiation of mESs into motor neurons, we used an ES cell line derived from a transgenic mouse expressing eGFP under the control of the motor neuron specific promoter Hb9. Using this robust protocol, we achieved 51 ± 0.8% of differentiation efficiency (n = 3; p < 0.01, Student's t-test). Results from immunofluorescent staining showed that GFP+ cells express the motor neuron specific markers, Islet-1 and choline acetyltransferase (ChAT). Our two-step differentiation protocol provides an efficient way to differentiate mES cells into spinal motor neurons.

Ca. 400 Ma Recrystallization of Norwegian Ultrahigh-pressure Eclogites: an ion Microprobe and Chemical Abrasion Study

NASA Astrophysics Data System (ADS)

Root, D. B.; Mattinson, J. M.; Hacker, B. R.; Wooden, J. L.

2002-12-01

Understanding the formation and exhumation of the ultrahigh-pressure (UHP) rocks of western Norway hinges on precise determination of the time of eclogite recrystallization. Our study consists of SHRIMP analysis, in conjunction with CL imagery, of zircon from four UHP and high-pressure (HP) eclogites; and detailed TIMS analysis of zircon from two samples subjected to combined thermal annealing and multi-step chemical abrasion (CA). SHRIMP analyses of the Otnheim and Langenes eclogites yield Caledonian spot ages of ca. 400 Ma from zircon rims. CL imagery and Th/U ratios from the Langenes eclogite indicate formation of rims by recrystallization of inherited zircon. SHRIMP analysis of the UHP Flatraket eclogite yielded a broad range of apparently concordant Caledonian ages. CA analyses of two fractions yielded moderate Pb loss from the first (lowest T) steps; possible minor Pb loss or minor growth at 400 Ma from the second steps; and a 407-404 Ma cluster of slightly discordant 206Pb/238U ages, most likely free from Pb loss, from the remaining steps. We interpret the latter to reflect recrystallization of inherited zircon, with possible new growth, at ca. 400-395 Ma. Alternatively, the high-temperature CA steps could represent growth at 407-404 Ma, with apparent discordance due to intermediate daughter product effects. HP/UHP zircon recrystallization in the Flatraket eclogite is inferred from three lines of evidence: i) zircon occurs as inclusions in garnet, omphacite, breunnerite, dolomite, and quartz, as well as in symplectites after phengite and omphacite; ii) association of zircon with rutile implies zircon formation during HP breakdown of Zr-ilmenite; and iii) chondrite-normalized ICP-MS analyses of the CA steps reveal small Eu anomalies and shallow HREE profiles, indicating zircon recrystallization in the presence of garnet. CA analysis of the Verpeneset eclogite yielded distinctly discordant step ages from two steps comprising <90% of the sample, with 206Pb/238U ages of 408 and 414 Ma. CL imagery indicates incomplete recrystallization of inherited igneous zircon, in keeping with steep HREE profiles determined from chondrite-normalized ICP-MS analyses. Our zircon age of ca. 400-395 Ma for the Flatraket eclogite is significantly younger than the 425 Ma age often cited for western Norway eclogite recrystallization, implying, in conjunction with 390-385 Ma 40Ar/39Ar white mica cooling ages, faster rates of exhumation (ca. 15 km/m.y.), and weakening the link between UHP metamorphism and ophiolite emplacement at 430-425 Ma.

Modeling the Growth Rates of Tetragonal Lysozyme Crystal Faces

NASA Technical Reports Server (NTRS)

Li, Meirong; Nadarajah, Arunan; Pusey, Marc L.

1998-01-01

The measured macroscopic growth rates of the (110) and (101) faces of tetragonal lysozyme show an unexpectedly complex dependence on the supersaturation. The growth rates decay asymptotically to zero when the supersaturation is lowered to zero and increase rapidly when the supersaturation is increased. When supersaturations are increased still further the growth rates attain a maximum before starting to decrease. However, growth of these crystals is known to proceed by the classical dislocation and 2D nucleation growth mechanisms. This anomaly can be explained if growth is assumed to occur not by monomer units but by lysozyme aggregates. Analysis of the molecular packing of these crystals revealed that they were constructed of strongly bonded 4(sub 3) helices, while weaker bonds were responsible for binding the helices to each other. It follows that during crystal growth the stronger bonds are formed before the weaker ones. Thus, the growth of these crystals could be viewed as a two step process: aggregate growth units corresponding to the 4(sub 3) helix are first formed in the bulk solution by stronger intermolecular bonds and then attached to the crystal face by weaker bonds on dislocation hillocks or 2D islands. This will lead to a distribution of aggregates in the solution with monomers and lower order aggregates being predominant at low supersaturations and higher order aggregates being predominant at high supersaturations. If the crystal grows mostly by higher order aggregates, such as tetramers and octamers, it would explain the anomalous dependence of the growth rates on the supersaturation. Besides the analysis of molecular packing, a comprehensive analysis of the measured (110) and (101) growth rates was also undertaken in this study. The distribution of aggregates in lysozyme nutrient solutions at various solution conditions were determined from reversible aggregation reactions at equilibrium. The supersaturation was defined for each aggregate species with respect to its concentration at saturation in order to apply growth rate models to this process. The measured growth rates were then compared with the predicted ones from several dislocation and 2D nucleation growth models, employing tetramer and octamer growth units in polydisperse solutions and monomer units in monodisperse solutions. For the (110) face, the calculations consistently showed that the measured growth rates followed the expected model relations with octamer growth units. For the (101) face, it is not possible to obtain a clear agreement between the predicted and measured growth rates for a single growth unit as done for the (110) face. However, the calculations do indicate that the average size of the growth unit is between a tetramer and an octamer. This suggests that tetramers, octamers and other intermediate size growth units all participate in the growth process for this face. These calculations show that it is possible to model the macroscopic protein crystal growth rates if the molecular level processes can be account for, particularly protein aggregation processes in the bulk solution. Our recent investigations of tetragonal lysozyme crystals employing high resolution atomic force microscopy scans have further confirmed the growth of these crystals by aggregate growth units corresponding to 4(sub 3) helices.

Dynamic Emotional Processing in Experiential Therapy: Two Steps Forward, One Step Back

ERIC Educational Resources Information Center

Pascual-Leone, Antonio

2009-01-01

The study of dynamic and nonlinear change has been a valuable development in psychotherapy process research. However, little advancement has been made in describing how moment-by-moment affective processes contribute to larger units of change. The purpose of this study was to examine observable moment-by-moment sequences in emotional processing as…

Vertical heterostructures of MoS2 and graphene nanoribbons grown by two-step chemical vapor deposition for high-gain photodetectors.

PubMed

Yunus, Rozan Mohamad; Endo, Hiroko; Tsuji, Masaharu; Ago, Hiroki

2015-10-14

Heterostructures of two-dimensional (2D) layered materials have attracted growing interest due to their unique properties and possible applications in electronics, photonics, and energy. Reduction of the dimensionality from 2D to one-dimensional (1D), such as graphene nanoribbons (GNRs), is also interesting due to the electron confinement effect and unique edge effects. Here, we demonstrate a bottom-up approach to grow vertical heterostructures of MoS2 and GNRs by a two-step chemical vapor deposition (CVD) method. Single-layer GNRs were first grown by ambient pressure CVD on an epitaxial Cu(100) film, followed by the second CVD process to grow MoS2 over the GNRs. The MoS2 layer was found to grow preferentially on the GNR surface, while the coverage could be further tuned by adjusting the growth conditions. The MoS2/GNR nanostructures show clear photosensitivity to visible light with an optical response much higher than that of a 2D MoS2/graphene heterostructure. The ability to grow a novel 1D heterostructure of layered materials by a bottom-up CVD approach will open up a new avenue to expand the dimensionality of the material synthesis and applications.

Simultaneous Silencing of Two Arginine Decarboxylase Genes Alters Development in Arabidopsis

PubMed Central

Sánchez-Rangel, Diana; Chávez-Martínez, Ana I.; Rodríguez-Hernández, Aída A.; Maruri-López, Israel; Urano, Kaoru; Shinozaki, Kazuo; Jiménez-Bremont, Juan F.

2016-01-01

Polyamines (PAs) are small aliphatic polycations that are found ubiquitously in all organisms. In plants, PAs are involved in diverse biological processes such as growth, development, and stress responses. In Arabidopsis thaliana, the arginine decarboxylase enzymes (ADC1 and 2) catalyze the first step of PA biosynthesis. For a better understanding of PA biological functions, mutants in PA biosynthesis have been generated; however, the double adc1/adc2 mutant is not viable in A. thaliana. In this study, we generated non-lethal A. thaliana lines through an artificial microRNA that simultaneously silenced the two ADC genes (amiR:ADC). The generated transgenic lines (amiR:ADC-L1 and -L2) showed reduced AtADC1 and AtADC2 transcript levels. For further analyses the amiR:ADC-L2 line was selected. We found that the amiR:ADC-L2 line showed a significant decrease of their PA levels. The co-silencing revealed a stunted growth in A. thaliana seedlings, plantlets and delay in its flowering rate; these phenotypes were reverted with PA treatment. In addition, amiR:ADC-L2 plants displayed two seed phenotypes, such as yellow and brownish seeds. The yellow mutant seeds were smaller than adc1, adc2 mutants and wild type seeds; however, the brownish were the smallest seeds with arrested embryos at the torpedo stage. These data reinforce the importance of PA homeostasis in the plant development processes. PMID:27014322

Simulation of clustering and anisotropy due to Co step-edge segregation in vapor-deposited CoPt3

NASA Astrophysics Data System (ADS)

Maranville, B. B.; Schuerman, M.; Hellman, F.

2006-03-01

An atomistic mechanism is proposed for the creation of structural anisotropy and consequent large perpendicular magnetic anisotropy in vapor-deposited films of CoPt3 . Energetic considerations of bonding in Co-Pt suggest that Co segregates to step edges due to their low coordination, for all film orientations, while Pt segregates to the two low index surfaces. Coalescence of islands during growth cause these Co-rich step edges to become flat thin Co platelets in a Pt rich matrix, giving rise to the experimentally observed magnetic anisotropy. This proposed model is tested with kinetic Monte Carlo simulation of the vapor deposition growth. A tight-binding, second-moment approximation to the interatomic potential is used to calculate the probability of an atom hopping from one surface site to another, assuming an Arrhenius-like activation model of surface motion. Growth is simulated by allowing many hopping events per adatom. The simulated as-grown films show an asymmetry in Co-Co bonding between the in-plane and out-of-plane directions, in good agreement with experimental data. The growth temperature dependence found in the simulations is strong and similar to that seen in experiments, and an increase in Co edge segregation with increasing temperature is also observed.

Theoretical studies of growth processes and electronic properties of nanostructures on surfaces

NASA Astrophysics Data System (ADS)

Mo, Yina

Low dimensional nanostructures have been of particular interest because of their potential applications in both theoretical studies and industrial use. Although great efforts have been put into obtaining better understanding of the formation and properties of these materials, many questions still remain unanswered. This thesis work has focused on theoretical studies of (1) the growth processes of magnetic nanowires on transition-metal surfaces, (2) the dynamics of pentacene thin-film growth and island structures on inert surfaces, and (3) our proposal of a new type of semiconducting nanotube. In the first study, we elucidated a novel and intriguing kinetic pathway for the formation of Fe nanowires on the upper edge of a monatomic-layer-high step on Cu(111) using first-principles calculations. The identification of a hidden fundamental Fe basal line within the Cu steps prior to the formation of the apparent upper step edge Fe wire produces a totally different view of step-decorating wire structures and offers new possibilities for the study of the properties of these wires. Subsequent experiments with scanning tunneling microscopy unambiguously established the essential role of embedded Fe atoms as precursors to monatomic wire growth. A more general study of adatom behavior near transition-metal step edges illustrated a systematic trend in the adatom energetics and kinetics, resulted from the electronic interactions between the adatom and the surfaces. This work opens the possibility of controlled manufacturing of one-dimensional nanowires. In the second study, we investigated pentacene thin-films on H-diamond, H-silica and OH-silica surfaces via force field molecular dynamics simulations. Pentacene island structures on these surfaces were identified and found to have a 90-degree rotation relative to the structure proposed by some experimental groups. Our work may facilitate the design and control of experimental pentacene thin-film growth, and thus the development of organic thin-film transistors. Finally, in our third study, we proposed a new type of structurally simple and energetically stable cyanide transition metal nanotube, based on the planar structure of M(CN)2, (M = Ni, Pd, Pt). These nanotubes have semiconducting character with large band gaps (2--3 eV), which are insensitive to the chirality and diameter. We have investigated the energetic, electronic, and mechanical properties of these materials in both planar and tubular forms through first-principles density functional calculations. These calculations reveal interesting multi-center bonding features that should lead to preferential growth of tubes of a particular chirality. The unique features of these nanotubes should make them capable of being mass-produced, which is one of the most significant shortcomings of semiconducting carbon nanotubes.

A flow-free droplet-based device for high throughput polymorphic crystallization.

PubMed

Yang, Shih-Mo; Zhang, Dapeng; Chen, Wang; Chen, Shih-Chi

2015-06-21

Crystallization is one of the most crucial steps in the process of pharmaceutical formulation. In recent years, emulsion-based platforms have been developed and broadly adopted to generate high quality products. However, these conventional approaches such as stirring are still limited in several aspects, e.g., unstable crystallization conditions and broad size distribution; besides, only simple crystal forms can be produced. In this paper, we present a new flow-free droplet-based formation process for producing highly controlled crystallization with two examples: (1) NaCl crystallization reveals the ability to package saturated solution into nanoliter droplets, and (2) glycine crystallization demonstrates the ability to produce polymorphic crystallization forms by controlling the droplet size and temperature. In our process, the saturated solution automatically fills the microwell array powered by degassed bulk PDMS. A critical oil covering step is then introduced to isolate the saturated solution and control the water dissolution rate. Utilizing surface tension, the solution is uniformly packaged in the form of thousands of isolating droplets at the bottom of each microwell of 50-300 μm diameter. After water dissolution, individual crystal structures are automatically formed inside the microwell array. This approach facilitates the study of different glycine growth processes: α-form generated inside the droplets and γ-form generated at the edge of the droplets. With precise temperature control over nanoliter-sized droplets, the growth of ellipsoidal crystalline agglomerates of glycine was achieved for the first time. Optical and SEM images illustrate that the ellipsoidal agglomerates consist of 2-5 μm glycine clusters with inner spiral structures of ~35 μm screw pitch. Lastly, the size distribution of spherical crystalline agglomerates (SAs) produced from microwells of different sizes was measured to have a coefficient variation (CV) of less than 5%, showing crystal sizes can be precisely controlled by microwell sizes with high uniformity. This new method can be used to reliably fabricate monodispersed crystals for pharmaceutical applications.

Drastic changes of (p,t) analyzing powers for the isotopes /sup 58,60,62,64/Ni and marked incident-energy dependence of the analyzing powers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Toba Y.; Yagi, K.

1984-01-01

Drastic changes of (p,t) analyzing powers for the four Ni isotopes in ground-state transitions were observed. The changes are not explained by direct one-step processes but are interpreted by including strong two-step (p,d) (d,t) processes. Interference between the two processes of comparable intensities is essential. Marked incident-energy dependence of the analyzing powers is interpreted similarly.

Interdependence of endomembrane trafficking and actin dynamics during polarized growth of Arabidopsis pollen tubes

USDA-ARS?s Scientific Manuscript database

During polarized growth of pollen tubes, endomembrane trafficking and actin polymerization are two critical processes that establish membrane/wall homeostasis and maintain growth polarity. Fine-tuned interactions between these two processes are therefore necessary but poorly understood. To better un...

Controlling Catalyst Bulk Reservoir Effects for Monolayer Hexagonal Boron Nitride CVD.

PubMed

Caneva, Sabina; Weatherup, Robert S; Bayer, Bernhard C; Blume, Raoul; Cabrero-Vilatela, Andrea; Braeuninger-Weimer, Philipp; Martin, Marie-Blandine; Wang, Ruizhi; Baehtz, Carsten; Schloegl, Robert; Meyer, Jannik C; Hofmann, Stephan

2016-02-10

Highly controlled Fe-catalyzed growth of monolayer hexagonal boron nitride (h-BN) films is demonstrated by the dissolution of nitrogen into the catalyst bulk via NH3 exposure prior to the actual growth step. This "pre-filling" of the catalyst bulk reservoir allows us to control and limit the uptake of B and N species during borazine exposure and thereby to control the incubation time and h-BN growth kinetics while also limiting the contribution of uncontrolled precipitation-driven h-BN growth during cooling. Using in situ X-ray diffraction and in situ X-ray photoelectron spectroscopy combined with systematic growth calibrations, we develop an understanding and framework for engineering the catalyst bulk reservoir to optimize the growth process, which is also relevant to other 2D materials and their heterostructures.

Probability of Two-Step Photoexcitation of Electron from Valence Band to Conduction Band through Doping Level in TiO2.

PubMed

Nishikawa, Masami; Shiroishi, Wataru; Honghao, Hou; Suizu, Hiroshi; Nagai, Hideyuki; Saito, Nobuo

2017-08-17

For an Ir-doped TiO 2 (Ir:TiO 2 ) photocatalyst, we examined the most dominant electron-transfer path for the visible-light-driven photocatalytic performance. The Ir:TiO 2 photocatalyst showed a much higher photocatalytic activity under visible-light irradiation than nondoped TiO 2 after grafting with the cocatalyst of Fe 3+ . For the Ir:TiO 2 photocatalyst, the two-step photoexcitation of an electron from the valence band to the conduction band through the Ir doping level occurred upon visible-light irradiation, as observed by electron spin resonance spectroscopy. The two-step photoexcitation through the doping level was found to be a more stable process with a lower recombination rate of hole-electron pairs than the two-step photoexcitation process through an oxygen vacancy. Once electrons are photoexcited to the conduction band by the two-step excitation, the electrons can easily transfer to the surface because the conduction band is a continuous electron path, whereas the electrons photoexcited at only the doping level could not easily transfer to the surface because of the discontinuity of this path. The observed two-step photoexcitation from the valence band to the conduction band through the doping level significantly contributes to the enhancement of the photocatalytic performance.

Highly efficient enzymatic synthesis of 2-monoacylglycerides and structured lipids and their production on a technical scale.

PubMed

Pfeffer, Jan; Freund, Andreas; Bel-Rhlid, Rachid; Hansen, Carl-Erik; Reuss, Matthias; Schmid, Rolf D; Maurer, Steffen C

2007-10-01

We report here a two-step process for the high-yield enzymatic synthesis of 2-monoacylglycerides (2-MAG) of saturated as well as unsaturated fatty acids with different chain lengths. The process consists of two steps: first the unselective esterification of fatty acids and glycerol leading to a triacylglyceride followed by an sn1,3-selective alcoholysis reaction yielding 2-monoacylglycerides. Remarkably, both steps can be catalyzed by lipase B from Candida antarctica (CalB). The whole process including esterification and alcoholysis was scaled up in a miniplant to a total volume of 10 l. With this volume, a two-step process catalyzed by CalB for the synthesis of 1,3-oleoyl-2-palmitoylglycerol (OPO) using tripalmitate as starting material was established. On a laboratory scale, we obtained gram quantities of the synthesized 2-monoacylglycerides of polyunsaturated fatty acids such as arachidonic-, docosahexaenoic- and eicosapentaenoic acids and up to 96.4% of the theoretically possible yield with 95% purity. On a technical scale (>100 g of product, >5 l of reaction volume), 97% yield was reached in the esterification and 73% in the alcoholysis and a new promising process for the enzymatic synthesis of OPO was established.

Comparison of microbial community shifts in two parallel multi-step drinking water treatment processes.

PubMed

Xu, Jiajiong; Tang, Wei; Ma, Jun; Wang, Hong

2017-07-01

Drinking water treatment processes remove undesirable chemicals and microorganisms from source water, which is vital to public health protection. The purpose of this study was to investigate the effects of treatment processes and configuration on the microbiome by comparing microbial community shifts in two series of different treatment processes operated in parallel within a full-scale drinking water treatment plant (DWTP) in Southeast China. Illumina sequencing of 16S rRNA genes of water samples demonstrated little effect of coagulation/sedimentation and pre-oxidation steps on bacterial communities, in contrast to dramatic and concurrent microbial community shifts during ozonation, granular activated carbon treatment, sand filtration, and disinfection for both series. A large number of unique operational taxonomic units (OTUs) at these four treatment steps further illustrated their strong shaping power towards the drinking water microbial communities. Interestingly, multidimensional scaling analysis revealed tight clustering of biofilm samples collected from different treatment steps, with Nitrospira, the nitrite-oxidizing bacteria, noted at higher relative abundances in biofilm compared to water samples. Overall, this study provides a snapshot of step-to-step microbial evolvement in multi-step drinking water treatment systems, and the results provide insight to control and manipulation of the drinking water microbiome via optimization of DWTP design and operation.

3D-printed microfluidic chips with patterned, cell-laden hydrogel constructs.

PubMed

Knowlton, Stephanie; Yu, Chu Hsiang; Ersoy, Fulya; Emadi, Sharareh; Khademhosseini, Ali; Tasoglu, Savas

2016-06-20

Three-dimensional (3D) printing offers potential to fabricate high-throughput and low-cost fabrication of microfluidic devices as a promising alternative to traditional techniques which enables efficient design iterations in the development stage. In this study, we demonstrate a single-step fabrication of a 3D transparent microfluidic chip using two alternative techniques: a stereolithography-based desktop 3D printer and a two-step fabrication using an industrial 3D printer based on polyjet technology. This method, compared to conventional fabrication using relatively expensive materials and labor-intensive processes, presents a low-cost, rapid prototyping technique to print functional 3D microfluidic chips. We enhance the capabilities of 3D-printed microfluidic devices by coupling 3D cell encapsulation and spatial patterning within photocrosslinkable gelatin methacryloyl (GelMA). The platform presented here serves as a 3D culture environment for long-term cell culture and growth. Furthermore, we have demonstrated the ability to print complex 3D microfluidic channels to create predictable and controllable fluid flow regimes. Here, we demonstrate the novel use of 3D-printed microfluidic chips as controllable 3D cell culture environments, advancing the applicability of 3D printing to engineering physiological systems for future applications in bioengineering.

Synthesis, Characterization, and Properties of the Two-Dimensional Chalcogenides: Monolayers, Alloys, and Heterostructures

NASA Astrophysics Data System (ADS)

Cain, Jeffrey D.

Inspired by the triumphs of graphene, and motivated by its limitations, the science and engineering community is rapidly exploring the landscape of other layered materials in their atomically-thin forms. Dominating this landscape are the layered chalcogenides; diverse in chemistry, crystal structure, and properties, there are well over 100 primary members of this material family. Driven by quantum confinement, single layers (or few, in some cases) of these materials exhibit electronic, optical, and mechanical properties that diverge dramatically from their bulk counterparts. While initially isolated in monolayer form via mechanical exfoliation, the field of two-dimensional (2D) materials is being forced evolve to more scalable and reliable methods. Focusing on the chalcogenides (e.g. MoS2, Bi 2Se3, etc.), this dissertation introduces and mechanistically examines multiple novel synthetic approaches for the direct growth of monolayers, heterostructures, and alloys with the desired quality, reproducibility and generality. The first methods described in this thesis are physical vapor transport (PVT) and evaporative thinning (ET): a facile, top-down synthesis approach for creating ultrathin specimens of layered materials down to the two-dimensional limit. Evaporative thinning, applied in this study to the fabrication of A2X3 (Bi2Se3 and Sb2Te3) monolayers, is based on the controlled evaporation of material from initially thick specimens until the 2D limit is reached. The resultant flakes are characterized with a suite of imaging and spectroscopic techniques and the mechanism of ET is investigated via in-situ heating within a transmission electron microscope. Additionally, the basic transport properties of the resultant flakes are probed. The growth of ultrathin GeSe flakes is explored using PVT and the material's basic structure, properties, and stability are addressed. Second, oxide precursor based chemical vapor deposition (CVD) is presented for the direct growth of monolayer transition metal dichalcogenides materials (TMDs), MX2. Specifically, synthetic protocols for monolayers of the semiconducting TMDs, MoS2, WS2, and MoSe2, are presented and the layers are completely characterized with a full suite of techniques including scanning/transmission electron microscopy, scanning probe microscopy, and photo-spectroscopy (photoluminescence, Raman scattering) among others. Furthermore, the nucleation and growth processes in CVD grown TMD monolayers is investigated using aberration-corrected scanning transmission electron microscopy and a step-by-step nucleation and growth mechanism for monolayer TMDs is elucidated. Third, the use of monolayers as building blocks for more complex structures is explored and a predictive approach for the synthesis of van der Waals heterostructures and monolayer alloys is designed. This is accomplished using an intellectual framework analogous to the Time-Temperature-Transformation (TTT) diagrams that are ubiquitous in traditional materials science and metallurgy. These are called Time-Temperature-Architecture (TTA) diagrams, wherein the term "architecture" defines the specific conformation of the 2D components. These diagrams provide process guidance to synthesize a library of heterostructures with a range of morphologies and monolayer alloys within both the transition metal sulfide and selenide systems. Lastly, some next steps for future research are outlined. An appendix of summaries of collaborative studies of the optical and electronic properties of CVD grown monolayers TMDs is appended.

Understanding the barriers to crystal growth: dynamical simulation of the dissolution and growth of urea from aqueous solution.

PubMed

Piana, Stefano; Gale, Julian D

2005-02-16

Both the dissolution and growth of a molecular crystalline material, urea, has been studied using dynamical atomistic simulation. The kinetic steps of dissolution and growth are clearly identified, and the activation energies for each possible step are calculated. Our molecular dynamics simulations indicate that crystal growth on the [001] face is characterized by a nucleation and growth mechanism. Nucleation on the [001] urea crystal face is predicted to occur at a very high rate, followed by rapid propagation of the steps. The rate-limiting step for crystallization is actually found to be the removal of surface defects, rather than the initial formation of the next surface layer. Through kinetic Monte Carlo modeling of the surface growth, it is found that this crystal face evolves via a rough surface topography, rather than a clean layer-by-layer mechanism.

Carbothermal Reduction of Quartz with Carbon from Natural Gas

NASA Astrophysics Data System (ADS)

Li, Fei; Tangstad, Merete

2017-04-01

Carbothermal reaction between quartz and two different carbons originating from natural gas were investigated in this paper. One of two carbons is the commercial carbon black produced from natural gas in a medium thermal production process. The other carbon is obtained from natural gas cracking at 1273 K (1000 °C) deposited directly on the quartz pellet. At the 1923 K (1650 °C) and CO atmosphere, the impact of carbon content, pellet structure, gas transfer, and heating rate are investigated in a thermo-gravimetric furnace. The reaction process can be divided into two steps: an initial SiC-producing step followed by a SiO-producing step. Higher carbon content and increased gas transfer improves the reaction rate of SiC-producing step, while the thicker carbon coating in carbon-deposited pellet hinders reaction rate. Better gas transfer of sample holder improves reaction rate but causes more SiO loss. Heating rate has almost no influence on reaction. Mass balance analysis shows that mole ratios between SiO2, free carbon, and SiC in the SiC-producing step and SiO-producing step in CO and Ar fit the reaction SiO2(s) + 3 C(s) = SiC(s) + 2 CO(g). SiC-particle and SiC-coating formation process in mixed pellet and carbon-deposited pellet are proposed. SiC whiskers formed in the voids of these two types of pellets.

Amino Acids Regulate mTORC1 by an Obligate Two-step Mechanism*

PubMed Central

Dyachok, Julia; Earnest, Svetlana; Iturraran, Erica N.; Cobb, Melanie H.

2016-01-01

The mechanistic target of rapamycin complex 1 (mTORC1) coordinates cell growth with its nutritional, hormonal, energy, and stress status. Amino acids are critical regulators of mTORC1 that permit other inputs to mTORC1 activity. However, the roles of individual amino acids and their interactions in mTORC1 activation are not well understood. Here we demonstrate that activation of mTORC1 by amino acids includes two discrete and separable steps: priming and activation. Sensitizing mTORC1 activation by priming amino acids is a prerequisite for subsequent stimulation of mTORC1 by activating amino acids. Priming is achieved by a group of amino acids that includes l-asparagine, l-glutamine, l-threonine, l-arginine, l-glycine, l-proline, l-serine, l-alanine, and l-glutamic acid. The group of activating amino acids is dominated by l-leucine but also includes l-methionine, l-isoleucine, and l-valine. l-Cysteine predominantly inhibits priming but not the activating step. Priming and activating steps differ in their requirements for amino acid concentration and duration of treatment. Priming and activating amino acids use mechanisms that are distinct both from each other and from growth factor signaling. Neither step requires intact tuberous sclerosis complex of proteins to activate mTORC1. Concerted action of priming and activating amino acids is required to localize mTORC1 to lysosomes and achieve its activation. PMID:27587390

Short term storage stability at room temperature of two different platelet-rich plasma preparations from equine donors and potential impact on growth factor concentrations.

PubMed

Hauschild, Gregor; Geburek, Florian; Gosheger, Georg; Eveslage, Maria; Serrano, Daniela; Streitbürger, Arne; Johannlükens, Sara; Menzel, Dirk; Mischke, Reinhard

2017-01-05

The increasing interest in platelet-rich plasma (PRP) based therapies is as yet accompanied by inconsistent information regarding nearly all aspects of handling and application. Among these storage stability of processed platelet-rich products may be the basis for a more flexible application mode. The objective of this study was (1) to estimate the storage stability of growth factors platelet derived growth factor BB (PDGF-BB) and transforming growth factor ß1 (TGF-ß1) in both, a single-step softspin centrifugation-based pure-PRP (P-PRP, ACP®), and a gravity filtration system-based leukocyte-rich-PRP (L-PRP, E-PET), over a six hours time span after preparation at room temperature and (2) to identify possible factors influencing these growth factor concentrations in an equine model. Growth factor concentrations remained stable over the entire investigation period in L-PRP as well as P-PRP preparations revealing a mean of 3569 pg/ml PDGF-BB for E-PET and means of 1276 pg/ml PDGF-BB and 5086 pg/ml TGF-ß1 for ACP®. Pearson correlations yielded no significant impact of whole blood platelet (PLT), white blood cell (WBC) and red blood cell (RBC) counts on resulting cytokine values. In case of ACP® no significant dependencies between PLT, WBC and RBC counts of the processed platelet-rich product and resulting cytokine content occurred with exception of TGF-ß1 concentrations showing a strong correlation with the WBC content. PDGF-BB content of E-PET preparations showed a strong positive correlation with PLT and a strong negative with WBC of these preparations but not with RBC. L-PRP ad modum E-PET and P-PRP ad modum ACP® are applicable over at least a six hours time span at room temperature without loss of growth factor content. Based on the results of this study factors influencing the resulting growth factor concentrations still remain questionable. Additional studies implicating a further standardization of preparation protocols are necessary to identify consistent impact on cytokine content after PRP processing.

Simple design for DNA nanotubes from a minimal set of unmodified strands: rapid, room-temperature assembly and readily tunable structure.

PubMed

Hamblin, Graham D; Hariri, Amani A; Carneiro, Karina M M; Lau, Kai L; Cosa, Gonzalo; Sleiman, Hanadi F

2013-04-23

DNA nanotubes have great potential as nanoscale scaffolds for the organization of materials and the templation of nanowires and as drug delivery vehicles. Current methods for making DNA nanotubes either rely on a tile-based step-growth polymerization mechanism or use a large number of component strands and long annealing times. Step-growth polymerization gives little control over length, is sensitive to stoichiometry, and is slow to generate long products. Here, we present a design strategy for DNA nanotubes that uses an alternative, more controlled growth mechanism, while using just five unmodified component strands and a long enzymatically produced backbone. These tubes form rapidly at room temperature and have numerous, orthogonal sites available for the programmable incorporation of arrays of cargo along their length. As a proof-of-concept, cyanine dyes were organized into two distinct patterns by inclusion into these DNA nanotubes.

Multiscale Simulation and Modeling of Multilayer Heteroepitactic Growth of C60 on Pentacene.

PubMed

Acevedo, Yaset M; Cantrell, Rebecca A; Berard, Philip G; Koch, Donald L; Clancy, Paulette

2016-03-29

We apply multiscale methods to describe the strained growth of multiple layers of C60 on a thin film of pentacene. We study this growth in the presence of a monolayer pentacene step to compare our simulations to recent experimental studies by Breuer and Witte of submonolayer growth in the presence of monolayer steps. The molecular-level details of this organic semiconductor interface have ramifications on the macroscale structural and electronic behavior of this system and allow us to describe several unexplained experimental observations for this system. The growth of a C60 thin film on a pentacene surface is complicated by the differing crystal habits of the two component species, leading to heteroepitactical growth. In order to probe this growth, we use three computational methods that offer different approaches to coarse-graining the system and differing degrees of computational efficiency. We present a new, efficient reaction-diffusion continuum model for 2D systems whose results compare well with mesoscale kinetic Monte Carlo (KMC) results for submonolayer growth. KMC extends our ability to simulate multiple layers but requires a library of predefined rates for event transitions. Coarse-grained molecular dynamics (CGMD) circumvents KMC's need for predefined lattices, allowing defects and grain boundaries to provide a more realistic thin film morphology. For multilayer growth, in this particularly suitable candidate for coarse-graining, CGMD is a preferable approach to KMC. Combining the results from these three methods, we show that the lattice strain induced by heteroepitactical growth promotes 3D growth and the creation of defects in the first monolayer. The CGMD results are consistent with experimental results on the same system by Conrad et al. and by Breuer and Witte in which C60 aggregates change from a 2D structure at low temperature to 3D clusters along the pentacene step edges at higher temperatures.

Electrochemistry and the mechanisms of nucleation and growth of neodymium during electroreduction from LiCl-KCl eutectic salts on Mo substrate

NASA Astrophysics Data System (ADS)

Tang, Hao; Pesic, Batric

2015-03-01

The electrochemical behavior of NdCl3 was studied on a Mo electrode in molten LiCl-KCl eutectic salts. The electroreduction of Nd(III)/Nd(0) involved two reaction steps, as confirmed by three different electrochemical techniques. In the first reaction step, Nd(III) is converted into soluble Nd(II), which undergoes further reduction into metallic Nd(0) in the second reaction step. The standard reaction rate constants for each reaction step were determined by Nicholson method. The rate constant values were used in Matsuda-Ayabe's criteria for testing the electrochemical reversibility. Accordingly, both reaction steps were quasi-reversible redox reactions. The nucleation mechanisms of neodymium metal deposited on a Mo substrate were predicted by using Scharifker-Hill model, and tested for the first time by scanning electron microscopy (SEM) studies of the electrode surface. The SEM studies confirmed that for the low initial concentration of NdCl3, neodymium nucleates and grows progressively, while for higher NdCl3 concentrations, the related mechanism is instantaneous. Both are governed by the aggregative growth mechanisms based on surface mobility of formed nanoclusters.

Analysing growth and development of plants jointly using developmental growth stages

PubMed Central

Dambreville, Anaëlle; Lauri, Pierre-Éric; Normand, Frédéric; Guédon, Yann

2015-01-01

Background and Aims Plant growth, the increase of organ dimensions over time, and development, the change in plant structure, are often studied as two separate processes. However, there is structural and functional evidence that these two processes are strongly related. The aim of this study was to investigate the co-ordination between growth and development using mango trees, which have well-defined developmental stages. Methods Developmental stages, determined in an expert way, and organ sizes, determined from objective measurements, were collected during the vegetative growth and flowering phases of two cultivars of mango, Mangifera indica. For a given cultivar and growth unit type (either vegetative or flowering), a multistage model based on absolute growth rate sequences deduced from the measurements was first built, and then growth stages deduced from the model were compared with developmental stages. Key Results Strong matches were obtained between growth stages and developmental stages, leading to a consistent definition of integrative developmental growth stages. The growth stages highlighted growth asynchronisms between two topologically connected organs, namely the vegetative axis and its leaves. Conclusions Integrative developmental growth stages emphasize that developmental stages are closely related to organ growth rates. The results are discussed in terms of the possible physiological processes underlying these stages, including plant hydraulics, biomechanics and carbohydrate partitioning. PMID:25452250

Single-step ambient-air synthesis of graphene from renewable precursors as electrochemical genosensor.

PubMed

Seo, Dong Han; Pineda, Shafique; Fang, Jinghua; Gozukara, Yesim; Yick, Samuel; Bendavid, Avi; Lam, Simon Kwai Hung; Murdock, Adrian T; Murphy, Anthony B; Han, Zhao Jun; Ostrikov, Kostya Ken

2017-01-30

Thermal chemical vapour deposition techniques for graphene fabrication, while promising, are thus far limited by resource-consuming and energy-intensive principles. In particular, purified gases and extensive vacuum processing are necessary for creating a highly controlled environment, isolated from ambient air, to enable the growth of graphene films. Here we exploit the ambient-air environment to enable the growth of graphene films, without the need for compressed gases. A renewable natural precursor, soybean oil, is transformed into continuous graphene films, composed of single-to-few layers, in a single step. The enabling parameters for controlled synthesis and tailored properties of the graphene film are discussed, and a mechanism for the ambient-air growth is proposed. Furthermore, the functionality of the graphene is demonstrated through direct utilization as an electrode to realize an effective electrochemical genosensor. Our method is applicable to other types of renewable precursors and may open a new avenue for low-cost synthesis of graphene films.

Formation of Stone-Wales edge: Multistep reconstruction and growth mechanisms of zigzag nanographene.

PubMed

Dang, Jing-Shuang; Wang, Wei-Wei; Zheng, Jia-Jia; Nagase, Shigeru; Zhao, Xiang

2017-10-05

Although the existence of Stone-Wales (5-7) defect at graphene edge has been clarified experimentally, theoretical study on the formation mechanism is still imperfect. In particular, the regioselectivity of multistep reactions at edge (self-reconstruction and growth with foreign carbon feedstock) is essential to understand the kinetic behavior of reactive boundaries but investigations are still lacking. Herein, by using finite-sized models, multistep reconstructions and carbon dimer additions of a bared zigzag edge are introduced using density functional theory calculations. The zigzag to 5-7 transformation is proved as a site-selective process to generate alternating 5-7 pairs sequentially and the first step with largest barrier is suggested as the rate-determining step. Conversely, successive C 2 insertions on the active edge are calculated to elucidate the formation of 5-7 edge during graphene growth. A metastable intermediate with a triple sequentially fused pentagon fragment is proved as the key structure for 5-7 edge formation. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Single-step ambient-air synthesis of graphene from renewable precursors as electrochemical genosensor

NASA Astrophysics Data System (ADS)

Seo, Dong Han; Pineda, Shafique; Fang, Jinghua; Gozukara, Yesim; Yick, Samuel; Bendavid, Avi; Lam, Simon Kwai Hung; Murdock, Adrian T.; Murphy, Anthony B.; Han, Zhao Jun; Ostrikov, Kostya (Ken)

2017-01-01

Thermal chemical vapour deposition techniques for graphene fabrication, while promising, are thus far limited by resource-consuming and energy-intensive principles. In particular, purified gases and extensive vacuum processing are necessary for creating a highly controlled environment, isolated from ambient air, to enable the growth of graphene films. Here we exploit the ambient-air environment to enable the growth of graphene films, without the need for compressed gases. A renewable natural precursor, soybean oil, is transformed into continuous graphene films, composed of single-to-few layers, in a single step. The enabling parameters for controlled synthesis and tailored properties of the graphene film are discussed, and a mechanism for the ambient-air growth is proposed. Furthermore, the functionality of the graphene is demonstrated through direct utilization as an electrode to realize an effective electrochemical genosensor. Our method is applicable to other types of renewable precursors and may open a new avenue for low-cost synthesis of graphene films.

Antisymmetric vortex interactions in the wake behind a step cylinder

NASA Astrophysics Data System (ADS)

Tian, Cai; Jiang, Fengjian; Pettersen, Bjørnar; Andersson, Helge I.

2017-10-01

Flow around a step cylinder at the Reynolds number 150 was simulated by directly solving the full Navier-Stokes equations. The configuration was adopted from the work of Morton and Yarusevych ["Vortex shedding in the wake of a step cylinder," Phys. Fluids 22, 083602 (2010)], in which the wake dynamics were systematically described. A more detailed investigation of the vortex dislocation process has now been performed. Two kinds of new loop vortex structures were identified. Additionally, antisymmetric vortex interactions in two adjacent vortex dislocation processes were observed and explained. The results in this letter serve as a supplement for a more thorough understanding of the vortex dynamics in the step cylinder wake.

Tuning the surface morphology of aluminium doped zinc oxide thin films by arrayed nanorods through chemical growth process

NASA Astrophysics Data System (ADS)

Devasia, Sebin; Anila, E. I.

2018-04-01

Here we report the growth and characterization of chemically grown aluminium doped zinc oxide nanorods on seed layers. The seed layers were prepared by chemical spray pyrolysis which acted as the growth centers. The growth duration of nanorods were varied from 3h to 12h in steps of 3h. Further, investigations on their structural, morphological, electrical and optical properties. The SEM images confirmed the hexagonal shaped nanorod arrays grown on the seed layers. Later, the x-ray diffraction measurements revealed the pure zinc oxide phase of the samples. Photoluminescence and photoconductivity studies were carried out to analyze the potential of its optoelectronic properties.

Modified Gompertz equation for electrotherapy murine tumor growth kinetics: predictions and new hypotheses

PubMed Central

2010-01-01

Background Electrotherapy effectiveness at different doses has been demonstrated in preclinical and clinical studies; however, several aspects that occur in the tumor growth kinetics before and after treatment have not yet been revealed. Mathematical modeling is a useful instrument that can reveal some of these aspects. The aim of this paper is to describe the complete growth kinetics of unperturbed and perturbed tumors through use of the modified Gompertz equation in order to generate useful insight into the mechanisms that underpin this devastating disease. Methods The complete tumor growth kinetics for control and treated groups are obtained by interpolation and extrapolation methods with different time steps, using experimental data of fibrosarcoma Sa-37. In the modified Gompertz equation, a delay time is introduced to describe the tumor's natural history before treatment. Different graphical strategies are used in order to reveal new information in the complete kinetics of this tumor type. Results The first stage of complete tumor growth kinetics is highly non linear. The model, at this stage, shows different aspects that agree with those reported theoretically and experimentally. Tumor reversibility and the proportionality between regions before and after electrotherapy are demonstrated. In tumors that reach partial remission, two antagonistic post-treatment processes are induced, whereas in complete remission, two unknown antitumor mechanisms are induced. Conclusion The modified Gompertz equation is likely to lead to insights within cancer research. Such insights hold promise for increasing our understanding of tumors as self-organizing systems and, the possible existence of phase transitions in tumor growth kinetics, which, in turn, may have significant impacts both on cancer research and on clinical practice. PMID:21029411

Protein complexing in a methanogen suggests electron bifurcation and electron delivery from formate to heterodisulfide reductase.

PubMed

Costa, Kyle C; Wong, Phoebe M; Wang, Tiansong; Lie, Thomas J; Dodsworth, Jeremy A; Swanson, Ingrid; Burn, June A; Hackett, Murray; Leigh, John A

2010-06-15

In methanogenic Archaea, the final step of methanogenesis generates methane and a heterodisulfide of coenzyme M and coenzyme B (CoM-S-S-CoB). Reduction of this heterodisulfide by heterodisulfide reductase to regenerate HS-CoM and HS-CoB is an exergonic process. Thauer et al. [Thauer, et al. 2008 Nat Rev Microbiol 6:579-591] recently suggested that in hydrogenotrophic methanogens the energy of heterodisulfide reduction powers the most endergonic reaction in the pathway, catalyzed by the formylmethanofuran dehydrogenase, via flavin-based electron bifurcation. Here we present evidence that these two steps in methanogenesis are physically linked. We identify a protein complex from the hydrogenotrophic methanogen, Methanococcus maripaludis, that contains heterodisulfide reductase, formylmethanofuran dehydrogenase, F(420)-nonreducing hydrogenase, and formate dehydrogenase. In addition to establishing a physical basis for the electron-bifurcation model of energy conservation, the composition of the complex also suggests that either H(2) or formate (two alternative electron donors for methanogenesis) can donate electrons to the heterodisulfide-H(2) via F(420)-nonreducing hydrogenase or formate via formate dehydrogenase. Electron flow from formate to the heterodisulfide rather than the use of H(2) as an intermediate represents a previously unknown path of electron flow in methanogenesis. We further tested whether this path occurs by constructing a mutant lacking F(420)-nonreducing hydrogenase. The mutant displayed growth equal to wild-type with formate but markedly slower growth with hydrogen. The results support the model of electron bifurcation and suggest that formate, like H(2), is closely integrated into the methanogenic pathway.

Uncertainty quantification methodologies development for stress corrosion cracking of canister welds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dingreville, Remi Philippe Michel; Bryan, Charles R.

2016-09-30

This letter report presents a probabilistic performance assessment model to evaluate the probability of canister failure (through-wall penetration) by SCC. The model first assesses whether environmental conditions for SCC – the presence of an aqueous film – are present at canister weld locations (where tensile stresses are likely to occur) on the canister surface. Geometry-specific storage system thermal models and weather data sets representative of U.S. spent nuclear fuel (SNF) storage sites are implemented to evaluate location-specific canister surface temperature and relative humidity (RH). As the canister cools and aqueous conditions become possible, the occurrence of corrosion is evaluated. Corrosionmore » is modeled as a two-step process: first, pitting is initiated, and the extent and depth of pitting is a function of the chloride surface load and the environmental conditions (temperature and RH). Second, as corrosion penetration increases, the pit eventually transitions to a SCC crack, with crack initiation becoming more likely with increasing pit depth. Once pits convert to cracks, a crack growth model is implemented. The SCC growth model includes rate dependencies on both temperature and crack tip stress intensity factor, and crack growth only occurs in time steps when aqueous conditions are predicted. The model suggests that SCC is likely to occur over potential SNF interim storage intervals; however, this result is based on many modeling assumptions. Sensitivity analyses provide information on the model assumptions and parameter values that have the greatest impact on predicted storage canister performance, and provide guidance for further research to reduce uncertainties.« less

Rapid low-temperature epitaxial growth using a hot-element assisted chemical vapor deposition process

DOEpatents

Iwancizko, Eugene; Jones, Kim M.; Crandall, Richard S.; Nelson, Brent P.; Mahan, Archie Harvin

2001-01-01

The invention provides a process for depositing an epitaxial layer on a crystalline substrate, comprising the steps of providing a chamber having an element capable of heating, introducing the substrate into the chamber, heating the element at a temperature sufficient to decompose a source gas, passing the source gas in contact with the element; and forming an epitaxial layer on the substrate.

Preparation of Rutile from Ilmenite Concentrate Through Pressure Leaching with Hydrochloric Acid

NASA Astrophysics Data System (ADS)

Xiang, Junyi; Liu, Songli; Lv, Xuewei; Bai, Chenguang

2017-04-01

Take into account the fact that the natural rutile utilized for the production of titanium dioxide pigment through chloride process is desperately lacking worldwide especially in China, an attempt was exploited for extracting synthetic rutile from Yunnan ilmenite concentrate with hydrochloric acid pressure leaching process. The leaching parameters for one step leaching process were investigated. The results shown that the optimum condition is leaching temperature of 413 K (140 °C), acid concentration of 20 pct HCl, leaching time of 4 hours and liquid/solid mass ratio of 8:1. A two steps leaching process was also suggested to reutilize the leaching liquor which with a high content of HCl. The results showed that the content of HCl decreased from 135 to 75 g/L, total iron increased from 44.5 g/L to about 87.6 g/L, and the liquid/solid mass ratio decreased to 5:1 with a two steps leaching process. The leaching product produced through a two steps leaching process shows a pure golden red with a high content of titanium (92.65 pct TiO2), a relatively low content of calcium (0.10 pct CaO) and magnesium (0.12 pct MgO), but high content of silicon (5.72 pct SiO2).

A Co3O4-embedded porous ZnO rhombic dodecahedron prepared using zeolitic imidazolate frameworks as precursors for CO2 photoreduction

NASA Astrophysics Data System (ADS)

Wang, Tao; Shi, Li; Tang, Jing; Malgras, Victor; Asahina, Shunsuke; Liu, Guigao; Zhang, Huabin; Meng, Xianguang; Chang, Kun; He, Jianping; Terasaki, Osamu; Yamauchi, Yusuke; Ye, Jinhua

2016-03-01

Metal-organic frameworks (MOFs) are attracting considerable attention for their use as both the precursor and the template to prepare metal oxides or carbon-based materials. For the first time in this paper, the core-shell ZIF-8@ZIF-67 crystals are thermally converted into porous ZnO@Co3O4 composites by combining a seed-mediated growth process with a two-step calcination. The designed porous ZnO@Co3O4 composites exhibited the highest photocatalytic activity with an excellent stability for the reduction of CO2 among the commonly reported composite photocatalysts. Their superior photocatalytic performance is demonstrated to be resulting from the unique porous structure of ZnO@Co3O4 and the co-catalytic function of Co3O4 which can effectively suppress the photocorrosion of ZnO.Metal-organic frameworks (MOFs) are attracting considerable attention for their use as both the precursor and the template to prepare metal oxides or carbon-based materials. For the first time in this paper, the core-shell ZIF-8@ZIF-67 crystals are thermally converted into porous ZnO@Co3O4 composites by combining a seed-mediated growth process with a two-step calcination. The designed porous ZnO@Co3O4 composites exhibited the highest photocatalytic activity with an excellent stability for the reduction of CO2 among the commonly reported composite photocatalysts. Their superior photocatalytic performance is demonstrated to be resulting from the unique porous structure of ZnO@Co3O4 and the co-catalytic function of Co3O4 which can effectively suppress the photocorrosion of ZnO. Electronic supplementary information (ESI) available: Additional TG and DTA curves, XRD patterns, SEM images, TEM images, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy and GC-MS spectra of the samples. See DOI: 10.1039/c5nr08747c

Improving Human Milk and Breastfeeding Practices in the NICU.

PubMed

Fugate, Karen; Hernandez, Ivonne; Ashmeade, Terri; Miladinovic, Branko; Spatz, Diane L

2015-01-01

To determine if systematic implementation of the Spatz Ten Steps for Promoting and Protecting Breastfeeding for Vulnerable Infants (Ten Steps) would result in an improvement in the percentage of infants receiving mother's own milk (MOM) at initiation of feedings and at hospital discharge. Continuous quality improvement (QI) process. Urban, 82-bed, Level-III NICU. Very- low-birth-weight (VLBW) infants weighing fewer than 1500 grams. The Ten Step method was implemented during a 3-year period. Process measurements included percentage of VLBW infants receiving MOM at initiation of feeds, number of mothers of VLBW infants with hospital-grade electric breast pump at hospital discharge, and number of mothers of VLBW infants initiating pumping within 6 hours of delivery. Outcome measurements included percentage of VLBW infants with any human milk at discharge to home and parent satisfaction with nurses' support of mother's efforts to breastfeed. Balancing measurements included percentage of VLBW infants at less than the third percentile for growth on the Fenton growth chart at discharge and receiving pasteurized donor milk (PDM). Significant improvements were achieved in the percentages of mothers expressing their milk within 6 hours of delivery, infants receiving MOM at initiation of feeds, and mothers with a hospital-grade pump at discharge. Improvements in these processes resulted in increased parent satisfaction with nurses' support of breastfeeding and a 3.1-fold greater odds of the VLBW infant receiving MOM at discharge in 2013 compared to 2010 (odds ratio [OR]= 3.01, 95% confidence interval [CI] [1.75, 5.17], p < .001). Despite an increase in the use of MOM, there was not a significant increase in VLBW infants discharged at less than the third percentile for growth, and initiation of PDM did not negatively affect the percentage of VLBW infants with any human milk at discharge. Implementation of the Ten Steps method using QI methodology resulted in significantly improved rates of use of MOM at initiation of feeds and at hospital discharge. © 2015 AWHONN, the Association of Women's Health, Obstetric and Neonatal Nurses.

Improvements in the Formation of Boron-Doped Diamond Coatings on Platinum Wires Using the Novel Nucleation Process (NNP)

PubMed Central

Fhaner, Mathew; Zhao, Hong; Bian, Xiaochun; Galligan, James J.; Swain, Greg M.

2010-01-01

In order to increase the initial nucleation density for the growth of boron-doped diamond on platinum wires, we employed the novel nucleation process (NNP) originally developed by Rotter et al. and discussed by others [1–3]. This pretreatment method involves (i) the initial formation of a thin carbon layer over the substrate followed by (ii) ultrasonic seeding of this “soft” carbon layer with nanoscale particles of diamond. This two-step pretreatment is followed by the deposition of boron-doped diamond by microwave plasma-assisted CVD. Both the diamond seed particles and sites on the carbon layer itself function as the initial nucleation zones for diamond growth from an H2-rich source gas mixture. We report herein on the characterization of the pre-growth carbon layer formed on Pt as well as boron-doped films grown for 2, 4 and 6 h post NNP pretreatment. Results from scanning electron microscopy, Raman spectroscopy and electrochemical studies are reported. The NNP method increases the initial nucleation density on Pt and leads to the formation of a continuous diamond film in a shorter deposition time than is typical for wires pretreated by conventional ultrasonic seeding. The results indicate that the pregrowth layer itself consists of nanoscopic domains of diamond and functions well to enhance the initial nucleation of diamond without any diamond powder seeding. PMID:21617759

Turbulence, combustion, pollutant, and stability characterization of a premixed, step combustor

NASA Technical Reports Server (NTRS)

Ganji, A. T.; Sawyer, R. F.

1980-01-01

A two dimensional combustion tunnel was constructed to study a lean premixed turbulent propane/air flame stablized behind a rearward facing step. Studied were: (1) the existence and importance of large coherent structures in turbulent reacting and nonreacting free shear layers behind the steps; (2) the effect of inlet temperature and reference velocity on combustion efficiency; (3) CO, NO2 and NO sub x production in the flame; and (4) the blowout and upstream propagation of the flame. In the ranges studied, the large coherent structures dominated both the reacting and the nonreacting free shear layers behind the step. The growth of the vortices and the propagation of the flamer were intimately linked. Vortex pairing was observed to be one of the mechanisms for introduction of fresh reactants into the shear layer and growth of the shear layer. Probe composition measurements of the flame showed that, in the recirculation zone, the reaction was above 99 percent complete, CO and unburnt hydrocarbons were above the equilibrium level NO sub x concentration was far below the equilibrium level and NO2 comprised a negligible fraction of NO sub x.

Nucleation of uniform mono- and bilayer epitaxial graphene on SiC(0001)

NASA Astrophysics Data System (ADS)

Wu, Xiaosong; Zhang, Rui; Dong, Yunliang; Guo, Shuai; Kong, Wenjie; Liao, Zhimin; Yu, Dapeng

2012-02-01

Early stage of epitaxial graphene growth on SiC(0001) has been investigated. Using the confinement controlled sublimation (CCS) method, we has achieved well controlled growth and been able to see the formation of mono- and bilayer graphene islands. The growth features reveal the intriguing growth mechanism. In particular, a new ``stepdown'' growth mode has been identified. Graphene can propagate tens of micrometers across many SiC steps, while, most importantly, step bunching is avoided and the initial regular stepped SiC surface morphology is preserved. The stepdown growth demonstrates a route towards uniform epitaxial graphene in wafer size without sacrificing the initial substrate surface morphology.

Isolation of Salmonella from alfalfa seed and demonstration of impaired growth of heat-injured cells in seed homogenates.

PubMed

Liao, Ching-Hsing; Fett, William F

2003-05-15

Three major foodborne outbreaks of salmonellosis in 1998 and 1999 were linked to the consumption of raw alfalfa sprouts. In this report, an improved method is described for isolation of Salmonella from alfalfa seed lots, which had been implicated in these outbreaks. From each seed lot, eight samples each containing 25 g of seed were tested for the presence of Salmonella by the US FDA Bacteriological Analytical Manual (BAM) procedure and by a modified method applying two successive pre-enrichment steps. Depending on the seed lot, one to four out of eight samples tested positive for Salmonella by the standard procedure and two to seven out of eight samples tested positive by the modified method. Thus, the use of two consecutive pre-enrichment steps led to a higher detection rate than a single pre-enrichment step. This result indirectly suggested that Salmonella cells on contaminated seeds might be injured and failed to fully resuscitate in pre-enrichment broth containing seed components during the first 24 h of incubation. Responses of heat-injured Salmonella cells grown in buffered peptone water (BPW) and in three alfalfa seed homogenates were investigated. For preparation of seed homogenates, 25 g of seeds were homogenized in 200 ml of BPW using a laboratory Stomacher and subsequently held at 37 degrees C for 24 h prior to centrifugation and filtration. While untreated cells grew at about the same rate in BPW and in seed homogenates, heat-injured cells (52 degrees C, 10 min) required approximately 0.5 to 4.0 h longer to resuscitate in seed homogenates than in BPW. This result suggests that the alfalfa seed components or fermented metabolites from native bacteria hinder the repair and growth of heat-injured cells. This study also shows that an additional pre-enrichment step increases the frequency of isolation of Salmonella from naturally contaminated seeds, possibly by alleviating the toxic effect of seed homogenates on repair or growth of injured cells.

A Cellular Automaton / Finite Element model for predicting grain texture development in galvanized coatings

NASA Astrophysics Data System (ADS)

Guillemot, G.; Avettand-Fènoël, M.-N.; Iosta, A.; Foct, J.

2011-01-01

Hot-dipping galvanizing process is a widely used and efficient way to protect steel from corrosion. We propose to master the microstructure of zinc grains by investigating the relevant process parameters. In order to improve the texture of this coating, we model grain nucleation and growth processes and simulate the zinc solid phase development. A coupling scheme model has been applied with this aim. This model improves a previous two-dimensional model of the solidification process. It couples a cellular automaton (CA) approach and a finite element (FE) method. CA grid and FE mesh are superimposed on the same domain. The grain development is simulated at the micro-scale based on the CA grid. A nucleation law is defined using a Gaussian probability and a random set of nucleating cells. A crystallographic orientation is defined for each one with a choice of Euler's angle (Ψ,θ,φ). A small growing shape is then associated to each cell in the mushy domain and a dendrite tip kinetics is defined using the model of Kurz [2]. The six directions of basal plane and the two perpendicular directions develop in each mushy cell. During each time step, cell temperature and solid fraction are then determined at micro-scale using the enthalpy conservation relation and variations are reassigned at macro-scale. This coupling scheme model enables to simulate the three-dimensional growing kinetics of the zinc grain in a two-dimensional approach. Grain structure evolutions for various cooling times have been simulated. Final grain structure has been compared to EBSD measurements. We show that the preferentially growth of dendrite arms in the basal plane of zinc grains is correctly predicted. The described coupling scheme model could be applied for simulated other product or manufacturing processes. It constitutes an approach gathering both micro and macro scale models.

Patient accounting systems: needs and capabilities.

PubMed

Kennedy, O G; Collignon, S

1987-09-01

In the first article of this series, it was stated that most finance executives are not very satisfied with the performance of their current patient accounting systems. What steps can a patient accounting system planner take to help ensure the system selected will garner high ratings from managers and users? Two primarily steps need to be taken. First, the planner needs to perform a thorough evaluation of both near- and long-term patient accounting requirements. He should determine which features and functions are most critical and ensure they are incorporated as selection criteria. The planner should also incorporate institutional planning into that process, such as planned expansion of facilities or services, to ensure that the system selected has the growth potential, interfacing capabilities, and flexibility to respond to the changing environment. Then, once system needs are fully charted, the planner should educate himself about the range of patient accounting system solutions available. The data show that most financial managers lack knowledge about most of the major patient accounting system vendors in the marketplace. Once vendors that offer systems that seemingly could meet needs are identified, the wise system planner will also want to obtain information from users about those vendors, to determine whether the systems perform as described and whether the vendor has been responsive to the needs of its customers. This step is a particularly important part of the planning process, because the data also show that users of some systems are significantly more satisfied than users of other patient accounting systems.

Hydrothermal atomic force microscopy observations of barite step growth rates as a function of the aqueous barium-to-sulfate ratio

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bracco, Jacquelyn N.; Gooijer, Yiscka; Higgins, Steven R.

The rate of growth of ionic minerals from solutions with varying aqueous cation:anion ratios may result in significant errors in mineralization rates predicted by commonly-used affinity-based rate equations. To assess the potential influence of solute stoichiometry on barite growth, step velocities on the barite (001) surface have been measured at 108 °C using hydrothermal atomic force microscopy (HAFM) at moderate supersaturation and as a function of the aqueous barium:sulfate ratio (r). Barite growth hillocks at r ~ 1 were bounded bymore » $$\\langle$$120$$\\rangle$$ steps, however at r < 1, kink site densities increased, steps followed a direction vicinal to $$\\langle$$120$$\\rangle$$, and the [010] steps developed. At r > 1, steps roughened and rounded as the kink site density increased. Step velocities peaked at r = 1 and decreased roughly symmetrically as a function of r, indicating the attachment rates of barium and sulfate ions are similar under these conditions. We hypothesize that the differences in our observations at high and low r arise from differences in the attachment rate constants for the obtuse and acute $$\\langle$$120$$\\rangle$$ steps. Based on results at low r, the data suggests the attachment rate constant for barium ions is similar for obtuse and acute steps. Based on results at high r, the data suggests the attachment rate constant for sulfate is greater for obtuse steps than acute steps. In conclusion, utilizing a step growth model developed by Stack and Grantham (2010) the experimental step velocities as a function of r were readily fit while attempts to fit the data using a model developed by Zhang and Nancollas (1998) were less successful.« less

Hydrothermal atomic force microscopy observations of barite step growth rates as a function of the aqueous barium-to-sulfate ratio

DOE PAGES

Bracco, Jacquelyn N.; Gooijer, Yiscka; Higgins, Steven R.

2016-03-19

The rate of growth of ionic minerals from solutions with varying aqueous cation:anion ratios may result in significant errors in mineralization rates predicted by commonly-used affinity-based rate equations. To assess the potential influence of solute stoichiometry on barite growth, step velocities on the barite (001) surface have been measured at 108 °C using hydrothermal atomic force microscopy (HAFM) at moderate supersaturation and as a function of the aqueous barium:sulfate ratio (r). Barite growth hillocks at r ~ 1 were bounded bymore » $$\\langle$$120$$\\rangle$$ steps, however at r < 1, kink site densities increased, steps followed a direction vicinal to $$\\langle$$120$$\\rangle$$, and the [010] steps developed. At r > 1, steps roughened and rounded as the kink site density increased. Step velocities peaked at r = 1 and decreased roughly symmetrically as a function of r, indicating the attachment rates of barium and sulfate ions are similar under these conditions. We hypothesize that the differences in our observations at high and low r arise from differences in the attachment rate constants for the obtuse and acute $$\\langle$$120$$\\rangle$$ steps. Based on results at low r, the data suggests the attachment rate constant for barium ions is similar for obtuse and acute steps. Based on results at high r, the data suggests the attachment rate constant for sulfate is greater for obtuse steps than acute steps. In conclusion, utilizing a step growth model developed by Stack and Grantham (2010) the experimental step velocities as a function of r were readily fit while attempts to fit the data using a model developed by Zhang and Nancollas (1998) were less successful.« less

Full System Model of Magnetron Sputter Chamber - Proof-of-Principle Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walton, C; Gilmer, G; Zepeda-Ruiz, L

2007-05-04

The lack of detailed knowledge of internal process conditions remains a key challenge in magnetron sputtering, both for chamber design and for process development. Fundamental information such as the pressure and temperature distribution of the sputter gas, and the energies and arrival angles of the sputtered atoms and other energetic species is often missing, or is only estimated from general formulas. However, open-source or low-cost tools are available for modeling most steps of the sputter process, which can give more accurate and complete data than textbook estimates, using only desktop computations. To get a better understanding of magnetron sputtering, wemore » have collected existing models for the 5 major process steps: the input and distribution of the neutral background gas using Direct Simulation Monte Carlo (DSMC), dynamics of the plasma using Particle In Cell-Monte Carlo Collision (PIC-MCC), impact of ions on the target using molecular dynamics (MD), transport of sputtered atoms to the substrate using DSMC, and growth of the film using hybrid Kinetic Monte Carlo (KMC) and MD methods. Models have been tested against experimental measurements. For example, gas rarefaction as observed by Rossnagel and others has been reproduced, and it is associated with a local pressure increase of {approx}50% which may strongly influence film properties such as stress. Results on energies and arrival angles of sputtered atoms and reflected gas neutrals are applied to the Kinetic Monte Carlo simulation of film growth. Model results and applications to growth of dense Cu and Be films are presented.« less

Optimal design of an alignment-free two-DOF rehabilitation robot for the shoulder complex.

PubMed

Galinski, Daniel; Sapin, Julien; Dehez, Bruno

2013-06-01

This paper presents the optimal design of an alignment-free exoskeleton for the rehabilitation of the shoulder complex. This robot structure is constituted of two actuated joints and is linked to the arm through passive degrees of freedom (DOFs) to drive the flexion-extension and abduction-adduction movements of the upper arm. The optimal design of this structure is performed through two steps. The first step is a multi-objective optimization process aiming to find the best parameters characterizing the robot and its position relative to the patient. The second step is a comparison process aiming to select the best solution from the optimization results on the basis of several criteria related to practical considerations. The optimal design process leads to a solution outperforming an existing solution on aspects as kinematics or ergonomics while being more simple.

Crystallographic control of surface structure on the sectoral zoning of iron in a diopside from Orford nickel mine (Quebec), Canada

NASA Astrophysics Data System (ADS)

Paquette, J.; Zangooi, A.; Thornton, K.

2004-05-01

The influence of surface structure on partitioning between mineral and melt (or solution) has been noted by other workers in a handful of minerals, including calcite, dolomite, apatite, topaz and diamond. Each one of these minerals displays at least one crystallographic face where steps present during crystal growth are not equivalent by symmetry. When this is the case, sectors grown at the edge of these steps commonly show differential incorporation of minor or trace elements. In the diopside investigated here, electron probe microanalyses performed on the as-grown (100) surface of several crystals show concentric and sectoral zoning defined by variations in Fe content. Atomic force microscopy (AFM) was used to study the surfaces of the three crystallographic forms present on the diopside crystals, with the goal of relating the compositional zoning to the surface structure of the faces. The dominant {100} faces are covered with growth hillocks consisting of four vicinal faces defined by steps parallel to [010] and [001]. The steps are often bunched into macrosteps and the resulting hillocks are visible optically. The steps along the two crystallographic directions show significant differences in straightness and smoothness that indicate non-equivalent kinetics. The wavier steps correspond to Fe-enriched areas within the {100} sectors. The {010} faces, next in morphological importance, are dominated by a single step orientation and show no differential incorporation. They display topography related to polysynthetic twinning. The {110} faces are much smaller and very few show resolvable steps. Sector zoning (i.e. diffential partitioning among non-equivalent crystallographic faces) has been described in the past from pyroxenes. Explanations have invoked either differences in surface structure among non-equivalent faces or their unequal growth rates. This particular occurrence indicates that trace element incorporation is, in fact, highly site-specific and that significant compositioinal zoning can be induced on a single face without invoking the effect of growth rate. The natural diopside crystals from the Orford nickel mine (Brompton, Quebec) show a unusual bladed habit flattened on {100} faces. Exceptional fluid chemistry during crystallization may therefore be required for the persistence of steps responsible for differential incorporation. Nevertheless, whenever this zoning is present, the trace element involved cannot be expected to reflect thermodynamic equilibrium between the solid and the fluid from which it crystallized.

The fiber walk: a model of tip-driven growth with lateral expansion.

PubMed

Bucksch, Alexander; Turk, Greg; Weitz, Joshua S

2014-01-01

Tip-driven growth processes underlie the development of many plants. To date, tip-driven growth processes have been modeled as an elongating path or series of segments, without taking into account lateral expansion during elongation. Instead, models of growth often introduce an explicit thickness by expanding the area around the completed elongated path. Modeling expansion in this way can lead to contradictions in the physical plausibility of the resulting surface and to uncertainty about how the object reached certain regions of space. Here, we introduce fiber walks as a self-avoiding random walk model for tip-driven growth processes that includes lateral expansion. In 2D, the fiber walk takes place on a square lattice and the space occupied by the fiber is modeled as a lateral contraction of the lattice. This contraction influences the possible subsequent steps of the fiber walk. The boundary of the area consumed by the contraction is derived as the dual of the lattice faces adjacent to the fiber. We show that fiber walks generate fibers that have well-defined curvatures, and thus enable the identification of the process underlying the occupancy of physical space. Hence, fiber walks provide a base from which to model both the extension and expansion of physical biological objects with finite thickness.

The Fiber Walk: A Model of Tip-Driven Growth with Lateral Expansion

PubMed Central

Bucksch, Alexander; Turk, Greg; Weitz, Joshua S.

2014-01-01

Tip-driven growth processes underlie the development of many plants. To date, tip-driven growth processes have been modeled as an elongating path or series of segments, without taking into account lateral expansion during elongation. Instead, models of growth often introduce an explicit thickness by expanding the area around the completed elongated path. Modeling expansion in this way can lead to contradictions in the physical plausibility of the resulting surface and to uncertainty about how the object reached certain regions of space. Here, we introduce fiber walks as a self-avoiding random walk model for tip-driven growth processes that includes lateral expansion. In 2D, the fiber walk takes place on a square lattice and the space occupied by the fiber is modeled as a lateral contraction of the lattice. This contraction influences the possible subsequent steps of the fiber walk. The boundary of the area consumed by the contraction is derived as the dual of the lattice faces adjacent to the fiber. We show that fiber walks generate fibers that have well-defined curvatures, and thus enable the identification of the process underlying the occupancy of physical space. Hence, fiber walks provide a base from which to model both the extension and expansion of physical biological objects with finite thickness. PMID:24465607

Stochastic predation events and population persistence in bighorn sheep

PubMed Central

Festa-Bianchet, Marco; Coulson, Tim; Gaillard, Jean-Michel; Hogg, John T; Pelletier, Fanie

2006-01-01

Many studies have reported temporal changes in the relative importance of density-dependence and environmental stochasticity in affecting population growth rates, but they typically assume that the predominant factor limiting growth remains constant over long periods of time. Stochastic switches in limiting factors that persist for multiple time-steps have received little attention, but most wild populations may periodically experience such switches. Here, we consider the dynamics of three populations of individually marked bighorn sheep (Ovis canadensis) monitored for 24–28 years. Each population experienced one or two distinct cougar (Puma concolor) predation events leading to population declines. The onset and duration of predation events were stochastic and consistent with predation by specialist individuals. A realistic Markov chain model confirms that predation by specialist cougars can cause extinction of isolated populations. We suggest that such processes may be common. In such cases, predator–prey equilibria may only occur at large geographical and temporal scales, and are unlikely with increasing habitat fragmentation. PMID:16777749

Primary Dendrite Array Morphology: Observations from Ground-based and Space Station Processed Samples

NASA Technical Reports Server (NTRS)

Tewari, Surendra; Rajamure, Ravi; Grugel, Richard; Erdmann, Robert; Poirier, David

2012-01-01

Influence of natural convection on primary dendrite array morphology during directional solidification is being investigated under a collaborative European Space Agency-NASA joint research program, "Microstructure Formation in Castings of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions (MICAST)". Two Aluminum-7 wt pct Silicon alloy samples, MICAST6 and MICAST7, were directionally solidified in microgravity on the International Space Station. Terrestrially grown dendritic monocrystal cylindrical samples were remelted and directionally solidified at 18 K/cm (MICAST6) and 28 K/cm (MICAST7). Directional solidification involved a growth speed step increase (MICAST6-from 5 to 50 micron/s) and a speed decrease (MICAST7-from 20 to 10 micron/s). Distribution and morphology of primary dendrites is currently being characterized in these samples, and also in samples solidified on earth under nominally similar thermal gradients and growth speeds. Primary dendrite spacing and trunk diameter measurements from this investigation will be presented.

Primary Dendrite Array: Observations from Ground-Based and Space Station Processed Samples

NASA Technical Reports Server (NTRS)

Tewari, Surendra N.; Grugel, Richard N.; Erdman, Robert G.; Poirier, David R.

2012-01-01

Influence of natural convection on primary dendrite array morphology during directional solidification is being investigated under a collaborative European Space Agency-NASA joint research program, Microstructure Formation in Castings of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions (MICAST). Two Aluminum-7 wt pct Silicon alloy samples, MICAST6 and MICAST7, were directionally solidified in microgravity on the International Space Station. Terrestrially grown dendritic monocrystal cylindrical samples were remelted and directionally solidified at 18 K per centimeter (MICAST6) and 28 K per centimeter (MICAST7). Directional solidification involved a growth speed step increase (MICAST6-from 5 to 50 millimeters per second) and a speed decrease (MICAST7-from 20 to 10 millimeters per second). Distribution and morphology of primary dendrites is currently being characterized in these samples, and also in samples solidified on earth under nominally similar thermal gradients and growth speeds. Primary dendrite spacing and trunk diameter measurements from this investigation will be presented.

Flower-like superstructures of AIE-active tetraphenylethylene through solvophobic controlled self-assembly

NASA Astrophysics Data System (ADS)

Salimimarand, Mina; La, Duong Duc; Kobaisi, Mohammad Al; Bhosale, Sheshanath V.

2017-02-01

The development of well-organized structures with high luminescent properties in the solid and aggregated states is of both scientific and technological interest due to their applications in nanotechnology. In this paper we described the synthesis of amphiphilic and dumbbell shaped AIE-active tetraphenylethylene (TPE) derivatives and studied their self-assembly with solvophobic control. Interestingly, both TPE derivatives form a 3D flower-shape supramolecular structure from THF/water solutions at varying water fractions. SEM microscopy was used to visualise step-wise growth of flower-shape assembly. TPE derivatives also show good mechanochromic properties which can be observed in the process of grinding, fuming and heating. These TPE derivative self-assemblies are formed due to two main important properties: (i) the TPE-core along with alkyl chains, optimizing the dispersive interactions within a construct, and (ii) amide-linkage through molecular recognition. We believe such arrangements prevent crystallization and favour the directional growth of flower-shape nanostructures in a 3D fashion.

Crystal Growth and Dissolution of Methylammonium Lead Iodide Perovskite in Sequential Deposition: Correlation between Morphology Evolution and Photovoltaic Performance.

PubMed

Hsieh, Tsung-Yu; Huang, Chi-Kai; Su, Tzu-Sen; Hong, Cheng-You; Wei, Tzu-Chien

2017-03-15

Crystal morphology and structure are important for improving the organic-inorganic lead halide perovskite semiconductor property in optoelectronic, electronic, and photovoltaic devices. In particular, crystal growth and dissolution are two major phenomena in determining the morphology of methylammonium lead iodide perovskite in the sequential deposition method for fabricating a perovskite solar cell. In this report, the effect of immersion time in the second step, i.e., methlyammonium iodide immersion in the morphological, structural, optical, and photovoltaic evolution, is extensively investigated. Supported by experimental evidence, a five-staged, time-dependent evolution of the morphology of methylammonium lead iodide perovskite crystals is established and is well connected to the photovoltaic performance. This result is beneficial for engineering optimal time for methylammonium iodide immersion and converging the solar cell performance in the sequential deposition route. Meanwhile, our result suggests that large, well-faceted methylammonium lead iodide perovskite single crystal may be incubated by solution process. This offers a low cost route for synthesizing perovskite single crystal.

Characterization of 3C-SiC Films Grown on 4H- and 6H-SiC Substrate Mesas During Step-Free Surface Heteroepitaxy

NASA Technical Reports Server (NTRS)

Neudeck, Philip G.; Powel J. Anthony; Spry, David J.; Trunek, Andrew J.; Huang, Xianrong; Vetter, William M.; Dudley, Michael; Skowronski, Marek; Liu, Jinqiang

2002-01-01

This paper reports detailed structural characterization of 3C-SiC heteroepitaxial films grown on 4H- and 6H-SiC mesa surfaces. 3C-SiC heterofilms grown by the "step-free surface heteroepitaxy" process, free of double-positioning boundary (DPB) and stacking-fault (SF) defects, were compared to less-optimized 3C-SiC heterofilms using High Resolution X-ray Diffraction (HRXRD), High Resolution Cross-sectional Transmission Electron Microscopy (HRXTEM), molten potassium hydroxide (KOH) etching, and dry thermal oxidation. The results suggest that step free surface heteroepitaxy enables remarkably benign partial lattice mismatch strain relief during heterofilm growth.

The effects of different preservation processes on the total protein and growth factor content in a new biological product developed from human amniotic membrane.

PubMed

Russo, Alessandra; Bonci, Paola; Bonci, Paolo

2012-06-01

The aim of this work is to quantify the total protein and growth factors content in a tissue-suspension obtained from processed human amniotic membrane (hAM). hAM was collected, frozen, freeze dried, powdered and sterilized by γ-irradiation. At each step of the process, samples were characterized for the total protein amounts by a Bradford protein assay and for the growth factor concentrations by ELISA test of the tissue suspensions. Frozen-hAM samples show higher release of total proteins and specific growth factors in the tissue suspension in comparison with freeze-dried hAM. We observed that even if the protein extraction is hindered once the tissue is dried, the powdering process allows a greater release in the tissue suspension of total proteins and growth factors after tissue re-solubilization in comparison with only the freeze-drying process (+91 ± 13% for EGF, +16 ± 4% for HGF, +11 ± 5% for FGF, +16 ± 9% for TGF-β1), and a greater release of EGF (85 ± 10%) in comparison with only the freezing process, because proteins become much readily solubilized in the solution. According with these results, we describe a protocol to obtain a new sterile biological product from hAM tissue, with well-known effects of thermal, mechanical and physical processes on the total protein and grow factors contents.

Study of the highly ordered TiO2 nanotubes physical properties prepared with two-step anodization

NASA Astrophysics Data System (ADS)

Pishkar, Negin; Ghoranneviss, Mahmood; Ghorannevis, Zohreh; Akbari, Hossein

2018-06-01

Highly ordered hexagonal closely packed titanium dioxide nanotubes (TiO2 NTs) were successfully grown by a two-step anodization process. The TiO2 NTs were synthesized by electrochemical anodization of titanium foils in an ethylene glycol based electrolyte solution containing 0.3 wt% NH4F and 2 vol% deionized (DI) water at constant potential (50 V) for 1 h at room temperature. Physical properties of the TiO2 NTs, which were prepared via one and two-step anodization, were investigated. Atomic Force Microscopy (AFM) analysis revealed that anodization and subsequently peeled off the TiO2 NTs caused to the periodic pattern on the Ti surface. In order To study the nanotubes morphology, Field Emission Scanning Electron Microscopy (FESEM) was used, which was revealed that the two-step anodization resulted highly ordered hexagonal TiO2 NTs. Crystal structures of the TiO2 NTs were mainly anatase, determined by X-ray diffraction analysis. Optical studies were performed by Diffuse Reflection Spectra (DRS) and Photoluminescence (PL) analysis showed that the band gap of TiO2 NTs prepared via two-step anodization was lower than the band gap of samples prepared by one-step anodization process.

Direct synthesis of graphene on silicon oxide by low temperature plasma enhanced chemical vapor deposition.

PubMed

Muñoz, Roberto; Martínez, Lidia; López-Elvira, Elena; Munuera, Carmen; Huttel, Yves; García-Hernández, Mar

2018-06-27

Direct graphene growth on silicon with a native oxide using plasma enhanced chemical vapour deposition at low temperatures [550 °C-650 °C] is demonstrated for the first time. It is shown that the fine-tuning of a two-step synthesis with gas mixtures C2H2/H2 yields monolayer and few layer graphene films with a controllable domain size from 50 nm to more than 300 nm and the sheet resistance ranging from 8 kΩ sq-1 to less than 1.8 kΩ sq-1. Differences are understood in terms of the interaction of the plasma species - chiefly atomic H - with the deposited graphene and the native oxide layer. The proposed low temperature direct synthesis on an insulating substrate does not require any transfer processes and improves the compatibility with the current industrial processes.

Elemental Anisotropic Growth and Atomic-Scale Structure of Shape-Controlled Octahedral Pt-Ni-Co Alloy Nanocatalysts.

PubMed

Arán-Ais, Rosa M; Dionigi, Fabio; Merzdorf, Thomas; Gocyla, Martin; Heggen, Marc; Dunin-Borkowski, Rafal E; Gliech, Manuel; Solla-Gullón, José; Herrero, Enrique; Feliu, Juan M; Strasser, Peter

2015-11-11

Multimetallic shape-controlled nanoparticles offer great opportunities to tune the activity, selectivity, and stability of electrocatalytic surface reactions. However, in many cases, our synthetic control over particle size, composition, and shape is limited requiring trial and error. Deeper atomic-scale insight in the particle formation process would enable more rational syntheses. Here we exemplify this using a family of trimetallic PtNiCo nanooctahedra obtained via a low-temperature, surfactant-free solvothermal synthesis. We analyze the competition between Ni and Co precursors under coreduction "one-step" conditions when the Ni reduction rates prevailed. To tune the Co reduction rate and final content, we develop a "two-step" route and track the evolution of the composition and morphology of the particles at the atomic scale. To achieve this, scanning transmission electron microscopy and energy dispersive X-ray elemental mapping techniques are used. We provide evidence of a heterogeneous element distribution caused by element-specific anisotropic growth and create octahedral nanoparticles with tailored atomic composition like Pt1.5M, PtM, and PtM1.5 (M = Ni + Co). These trimetallic electrocatalysts have been tested toward the oxygen reduction reaction (ORR), showing a greatly enhanced mass activity related to commercial Pt/C and less activity loss than binary PtNi and PtCo after 4000 potential cycles.

Simulation of wheat growth and development based on organ-level photosynthesis and assimilate allocation.

PubMed

Evers, J B; Vos, J; Yin, X; Romero, P; van der Putten, P E L; Struik, P C

2010-05-01

Intimate relationships exist between form and function of plants, determining many processes governing their growth and development. However, in most crop simulation models that have been created to simulate plant growth and, for example, predict biomass production, plant structure has been neglected. In this study, a detailed simulation model of growth and development of spring wheat (Triticum aestivum) is presented, which integrates degree of tillering and canopy architecture with organ-level light interception, photosynthesis, and dry-matter partitioning. An existing spatially explicit 3D architectural model of wheat development was extended with routines for organ-level microclimate, photosynthesis, assimilate distribution within the plant structure according to organ demands, and organ growth and development. Outgrowth of tiller buds was made dependent on the ratio between assimilate supply and demand of the plants. Organ-level photosynthesis, biomass production, and bud outgrowth were simulated satisfactorily. However, to improve crop simulation results more efforts are needed mechanistically to model other major plant physiological processes such as nitrogen uptake and distribution, tiller death, and leaf senescence. Nevertheless, the work presented here is a significant step forwards towards a mechanistic functional-structural plant model, which integrates plant architecture with key plant processes.

The Nucleation and Growth of Protein Crystals

NASA Technical Reports Server (NTRS)

Pusey, Marc

2004-01-01

Obtaining crystals of suitable size and high quality continues to be a major bottleneck in macromolecular crystallography. Currently, structural genomics efforts are achieving on average about a 10% success rate in going from purified protein to a deposited crystal structure. Growth of crystals in microgravity was proposed as a means of overcoming size and quality problems, which subsequently led to a major NASA effort in microgravity crystal growth, with the agency also funding research into understanding the process. Studies of the macromolecule crystal nucleation and growth process were carried out in a number of labs in an effort to understand what affected the resultant crystal quality on Earth, and how microgravity improved the process. Based upon experimental evidence, as well as simple starting assumptions, we have proposed that crystal nucleation occurs by a series of discrete self assembly steps, which 'set' the underlying crystal symmetry. This talk will review the model developed, and its origins, in our laboratory for how crystals nucleate and grow, and will then present, along with preliminary data, how we propose to use this model to improve the success rate for obtaining crystals from a given protein.

Functional analysis of the interactions between reovirus particles and various proteases in vitro

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sargent, M.D.; Long, D.G.; Borsa, J.

1977-01-01

The digestion of purified reovirus particles by various proteases including chymotrypsin, trypsin, pronase, papain, bromelain, proteinase K, and fibrinolysin has been examined as it relates to virion transcriptase activation and alteration of infectivity. In every case uncoating to the level of active transcriptase proceeds via two mechanistically distinct steps. All the proteases tested serve to mediate only the first of the two steps, converting intact virions to intermediate subviral particles (ISVP) in which the transcriptase is retained in a latent state. The second step of the uncoating process is mediated by a K/sup +/ ion-triggered, endogenous mechanism and results inmore » conversion of ISVP to cores, concomitant with transcriptase activation and loss of infectivity. All of the tested enzymes, except trypsin, reversibly block the second step of uncoating. These results indicate the generality, with respect to protease employed, of the two-step process for reovirus uncoating and transcriptase activation demonstrated previously with chymotrypsin.« less

Electrical property of macroscopic graphene composite fibers prepared by chemical vapor deposition.

PubMed

Sun, Haibin; Fu, Can; Gao, Yanli; Guo, Pengfei; Wang, Chunlei; Yang, Wenchao; Wang, Qishang; Zhang, Chongwu; Wang, Junya; Xu, Junqi

2018-07-27

Graphene fibers are promising candidates in portable and wearable electronics due to their tiny volume, flexibility and wearability. Here, we successfully synthesized macroscopic graphene composite fibers via a two-step process, i.e. first electrospinning and then chemical vapor deposition (CVD). Briefly, the well-dispersed PAN nanofibers were sprayed onto the copper surface in an electrified thin liquid jet by electrospinning. Subsequently, CVD growth process induced the formation of graphene films using a PAN-solid source of carbon and a copper catalyst. Finally, crumpled and macroscopic graphene composite fibers were obtained from carbon nanofiber/graphene composite webs by self-assembly process in the deionized water. Temperature-dependent conduct behavior reveals that electron transport of the graphene composite fibers belongs to hopping mechanism and the typical electrical conductivity reaches 4.59 × 10 3 S m -1 . These results demonstrated that the graphene composite fibers are promising for the next-generation flexible and wearable electronics.

Production of Biodiesel from Lipid of Phytoplankton Chaetoceros calcitrans through Ultrasonic Method

PubMed Central

Kwangdinata, Raymond; Raya, Indah; Zakir, Muhammad

2014-01-01

A research on production of biodiesel from lipid of phytoplankton Chaetoceros calcitrans through ultrasonic method has been done. In this research, we carried out a series of phytoplankton cultures to determine the optimum time of growth and biodiesel synthesis process from phytoplankton lipids. Process of biodiesel synthesis consists of two steps, that is, isolation of phytoplankton lipids and biodiesel synthesis from those lipids. Oil isolation process was carried out by ultrasonic extraction method using ethanol 96%, while biodiesel synthesis was carried out by transesterification reaction using methanol and KOH catalyst under sonication. Weight of biodiesel yield per biomass Chaetoceros calcitrans is 35.35%. Characterization of biodiesel was well carried out in terms of physical properties which are density and viscosity and chemical properties which are FFA content, saponification value, and iodine value. These values meet the American Society for Testing and Materials (ASTM D6751) standard levels, except for the viscosity value which was 1.14 g·cm−3. PMID:24688372

Modeling of the HiPco process for carbon nanotube production. I. Chemical kinetics

NASA Technical Reports Server (NTRS)

Dateo, Christopher E.; Gokcen, Tahir; Meyyappan, M.

2002-01-01

A chemical kinetic model is developed to help understand and optimize the production of single-walled carbon nanotubes via the high-pressure carbon monoxide (HiPco) process, which employs iron pentacarbonyl as the catalyst precursor and carbon monoxide as the carbon feedstock. The model separates the HiPco process into three steps, precursor decomposition, catalyst growth and evaporation, and carbon nanotube production resulting from the catalyst-enhanced disproportionation of carbon monoxide, known as the Boudouard reaction: 2 CO(g)-->C(s) + CO2(g). The resulting detailed model contains 971 species and 1948 chemical reactions. A second model with a reduced reaction set containing 14 species and 22 chemical reactions is developed on the basis of the detailed model and reproduces the chemistry of the major species. Results showing the parametric dependence of temperature, total pressure, and initial precursor partial pressures are presented, with comparison between the two models. The reduced model is more amenable to coupled reacting flow-field simulations, presented in the following article.

Photopolymerization Of Levitated Droplets

NASA Technical Reports Server (NTRS)

Rembaum, Alan; Rhim, Won-Kyu; Hyson, Michael T.; Chang, Manchium

1989-01-01

Experimental containerless process combines two established techniques to make variety of polymeric microspheres. In single step, electrostatically-levitated monomer droplets polymerized by ultraviolet light. Faster than multiple-step emulsion polymerization process used to make microspheres. Droplets suspended in cylindrical quadrupole electrostatic levitator. Alternating electrostatic field produces dynamic potential along axis. Process enables tailoring of microspheres for medical, scientific, and industrial applications.

Sporulation during Growth in a Gut Isolate of Bacillus subtilis

PubMed Central

Serra, Cláudia R.; Earl, Ashlee M.; Barbosa, Teresa M.; Kolter, Roberto

2014-01-01

Sporulation by Bacillus subtilis is a cell density-dependent response to nutrient deprivation. Central to the decision of entering sporulation is a phosphorelay, through which sensor kinases promote phosphorylation of Spo0A. The phosphorelay integrates both positive and negative signals, ensuring that sporulation, a time- and energy-consuming process that may bring an ecological cost, is only triggered should other adaptations fail. Here we report that a gastrointestinal isolate of B. subtilis sporulates with high efficiency during growth, bypassing the cell density, nutritional, and other signals that normally make sporulation a post-exponential-phase response. Sporulation during growth occurs because Spo0A is more active per cell and in a higher fraction of the population than in a laboratory strain. This in turn, is primarily caused by the absence from the gut strain of the genes rapE and rapK, coding for two aspartyl phosphatases that negatively modulate the flow of phosphoryl groups to Spo0A. We show, in line with recent results, that activation of Spo0A through the phosphorelay is the limiting step for sporulation initiation in the gut strain. Our results further suggest that the phosphorelay is tuned to favor sporulation during growth in gastrointestinal B. subtilis isolates, presumably as a form of survival and/or propagation in the gut environment. PMID:25225273

Domain growth of carbon nanotubes assisted by dewetting of thin catalyst precursor films

NASA Astrophysics Data System (ADS)

Srivastava, Alok Kumar; Sachan, Priyanka; Samanta, Chandan; Mukhopadhyay, Kingsuk; Sharma, Ashutosh

2014-01-01

We explore self-organized dewetting of ultrathin films of a novel metal complex as a one step surface patterning method to create nanoislands of iron, using which spatially separated carbon nanostructures were synthesized. Dewetting of ultrathin metal complex films was induced by two different methods: liquid solvent exposure and thermal annealing to engender surface patterning. For thermal dewetting, thin films of the iron oleate complex were dewetted at high temperature. In the case of liquid solvent assisted dewetting, the metal complex, mixed with a sacrificial polymer (polystyrene) was spin coated as thin films (<40 nm) and then dewetted under an optimal solution mixture consisting of methyl ethyl ketone, acetone and water. The carrier polymer was then selectively removed to produce the iron metal islands. These metal islands were used for selective growth of discrete patches of multiwall CNTs and CNFs by a chemical vapor deposition (CVD) process. Solvent induced dewetting showed clear advantages over thermal dewetting owing to reduced size of catalyst domains formed by dewetting, an improved control over CNT growth as well as in its ability to immobilize the seed particles. The generic solution mediated dewetting and pattern generation in thin films of various catalytic precursors can thus be a powerful method for selective domain growth of a variety of functional nanomaterials.

Oriented Growth of α-MnO2 Nanorods Using Natural Extracts from Grape Stems and Apple Peels

PubMed Central

Sanchez-Botero, Lina; Herrera, Adriana P.; Hinestroza, Juan P.

2017-01-01

We report on the synthesis of alpha manganese dioxide (α-MnO2) nanorods using natural extracts from Vitis vinifera grape stems and Malus domestica ‘Cortland’ apple peels. We used a two-step method to produce highly crystalline α-MnO2 nanorods: (1) reduction of KMnO4 in the presence of natural extracts to initiate the nucleation process; and (2) a thermal treatment to enable further solid-state growth of the nuclei. Transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) images provided direct evidence of the morphology of the nanorods and these images were used to propose nucleation and growth mechanisms. We found that the α-MnO2 nanorods synthesized using natural extracts exhibit structural and magnetic properties similar to those of nanoparticles synthesized via traditional chemical routes. Furthermore, Fourier transform infrared (FTIR) shows that the particle growth of the α-MnO2 nanorods appears to be controlled by the presence of natural capping agents during the thermal treatment. We also evaluated the catalytic activity of the nanorods in the degradation of aqueous solutions of indigo carmine dye, highlighting the potential use of these materials to clean dye-polluted water. PMID:28531147

Modeling Tetragonal Lysozyme Crystal Growth Rates

NASA Technical Reports Server (NTRS)

Gorti, Sridhar; Forsythe, Elizabeth L.; Pusey, Marc L.

2003-01-01

Tetragonal lysozyme 110 face crystal growth rates, measured over 5 orders of magnitude in range, can be described using a model where growth occurs by 2D nucleation on the crystal surface for solution supersaturations of c/c(sub eq) less than or equal to 7 +/- 2. Based upon the model, the step energy per unit length, beta was estimated to be approx. 5.3 +/- 0.4 x 10(exp -7) erg/mol-cm, which for a step height of 56 A corresponds to barrier of approx. 7 +/- 1 k(sub B)T at 300 K. For supersaturations of c/c(sub eq) > 8, the model emphasizing crystal growth by 2D nucleation not only could not predict, but also consistently overestimated, the highest observable crystal growth rates. Kinetic roughening is hypothesized to occur at a cross-over supersaturation of c/c(sub eq) > 8, where crystal growth is postulated to occur by a different process such as adsorption. Under this assumption, all growth rate data indicated that a kinetic roughening transition and subsequent crystal growth by adsorption for all solution conditions, varying in buffer pH, temperature and precipitant concentration, occurs for c/c(sub eq)(T, pH, NaCl) in the range between 5 and 10, with an energy barrier for adsorption estimated to be approx. 20 k(sub B)T at 300 K. Based upon these and other estimates, we determined the size of the critical surface nucleate, at the crossover supersaturation and higher concentrations, to range from 4 to 10 molecules.

Systematic study on dynamic atomic layer epitaxy of InN on/in +c-GaN matrix and fabrication of fine-structure InN/GaN quantum wells: Role of high growth temperature

NASA Astrophysics Data System (ADS)

Yoshikawa, Akihiko; Kusakabe, Kazuhide; Hashimoto, Naoki; Hwang, Eun-Sook; Imai, Daichi; Itoi, Takaomi

2016-12-01

The growth kinetics and properties of nominally 1-ML (monolayer)-thick InN wells on/in +c-GaN matrix fabricated using dynamic atomic layer epitaxy (D-ALEp) by plasma-assisted molecular beam epitaxy were systematically studied, with particular attention given to the effects of growth temperature. Attention was also given to how and where the ˜1-ML-thick InN layers were frozen or embedded on/in the +c-GaN matrix. The D-ALEp of InN on GaN was a two-stage process; in the 1st stage, an "In+N" bilayer/monolayer was formed on the GaN surface, while in the 2nd, this was capped by a GaN barrier layer. Each process was monitored in-situ using spectroscopic ellipsometry. The target growth temperature was above 620 °C and much higher than the upper critical epitaxy temperature of InN (˜500 °C). The "In+N" bilayer/monolayer tended to be an incommensurate phase, and the growth of InN layers was possible only when they were capped with a GaN layer. The InN layers could be coherently inserted into the GaN matrix under self-organizing and self-limiting epitaxy modes. The growth temperature was the most dominant growth parameter on both the growth process and the structure of the InN layers. Reflecting the inherent growth behavior of D-ALEp grown InN on/in +c-GaN at high growth temperature, the embedded InN layers in the GaN matrix were basically not full-ML in coverage, and the thickness of sheet-island-like InN layers was essentially either 1-ML or 2-ML. It was found that these InN layers tended to be frozen at the step edges on the GaN and around screw-type threading dislocations. The InN wells formed type-I band line-up heterostructures with GaN barriers, with exciton localization energies of about 300 and 500 meV at 15 K for the 1-ML and 2-ML InN wells, respectively.

Influence of ageing on self-etch adhesives: one-step vs. two-step systems.

PubMed

Marchesi, Giulio; Frassetto, Andrea; Visintini, Erika; Diolosà, Marina; Turco, Gianluca; Salgarello, Stefano; Di Lenarda, Roberto; Cadenaro, Milena; Breschi, Lorenzo

2013-02-01

The aim of this study was to evaluate microtensile bond strength (μTBS) to dentine, interfacial nanoleakage expression, and stability after ageing, of two-step vs. one-step self-etch adhesives. Human molars were cut to expose middle/deep dentine, assigned to groups (n = 15), and treated with the following bonding systems: (i) Optibond XTR (a two-step self-etch adhesive; Kerr), (ii) Clearfil SE Bond (a two-step self-etch adhesive; Kuraray), (iii) Adper Easy Bond (a one-step self-etch adhesive; 3M ESPE), and (iv) Bond Force (a one-step self-etch adhesive; Tokuyama). Specimens were processed for μTBS testing after 24 h, 6 months, or 1 yr of storage in artificial saliva at 37°C. Nanoleakage expression was examined in similarly processed additional specimens. At baseline the μTBS results ranked in the following order: Adper Easy Bond = Optibond XTR ≥Clearfil SE = Bond Force, and interfacial nanoleakage analysis showed Clearfil SE Bond = Adper Easy Bond = Optibond XTR> Bond Force. After 1 yr of storage, Optibond XTR, Clearfil SE Bond, and Adper Easy Bond showed higher μTBS and lower interfacial nanoleakage expression compared with Bond Force. In conclusion, immediate bond strength, nanoleakage expression, and stability over time were not related to the number of steps of the bonding systems, but to their chemical formulations. © 2012 Eur J Oral Sci.

Analysing growth and development of plants jointly using developmental growth stages.

PubMed

Dambreville, Anaëlle; Lauri, Pierre-Éric; Normand, Frédéric; Guédon, Yann

2015-01-01

Plant growth, the increase of organ dimensions over time, and development, the change in plant structure, are often studied as two separate processes. However, there is structural and functional evidence that these two processes are strongly related. The aim of this study was to investigate the co-ordination between growth and development using mango trees, which have well-defined developmental stages. Developmental stages, determined in an expert way, and organ sizes, determined from objective measurements, were collected during the vegetative growth and flowering phases of two cultivars of mango, Mangifera indica. For a given cultivar and growth unit type (either vegetative or flowering), a multistage model based on absolute growth rate sequences deduced from the measurements was first built, and then growth stages deduced from the model were compared with developmental stages. Strong matches were obtained between growth stages and developmental stages, leading to a consistent definition of integrative developmental growth stages. The growth stages highlighted growth asynchronisms between two topologically connected organs, namely the vegetative axis and its leaves. Integrative developmental growth stages emphasize that developmental stages are closely related to organ growth rates. The results are discussed in terms of the possible physiological processes underlying these stages, including plant hydraulics, biomechanics and carbohydrate partitioning. © The Author 2014. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Ultrahigh vacuum process for the deposition of nanotubes and nanowires

DOEpatents

Das, Biswajit; Lee, Myung B

2015-02-03

A system and method A method of growing an elongate nanoelement from a growth surface includes: a) cleaning a growth surface on a base element; b) providing an ultrahigh vacuum reaction environment over the cleaned growth surface; c) generating a reactive gas of an atomic material to be used in forming the nanoelement; d) projecting a stream of the reactive gas at the growth surface within the reactive environment while maintaining a vacuum of at most 1.times.10.sup.-4 Pascal; e) growing the elongate nanoelement from the growth surface within the environment while maintaining the pressure of step c); f) after a desired length of nanoelement is attained within the environment, stopping direction of reactive gas into the environment; and g) returning the environment to an ultrahigh vacuum condition.

Magnetoresistance measurement of permalloy thin film rings with triangular fins

NASA Astrophysics Data System (ADS)

Lai, Mei-Feng; Hsu, Chia-Jung; Liao, Chun-Neng; Chen, Ying-Jiun; Wei, Zung-Hang

2010-01-01

Magnetization reversals in permalloy rings controlled by nucleation sites using triangular fins at the same side and diagonal with respect to the field direction are demonstrated by magnetoresistance measurement and micromagnetic simulation. In the ring with triangular fins at the same side, there exists two-step reversal from onion to flux-closure state (or vortex state) and then from flux-closure (or vortex state) to reverse onion state; in the ring with diagonal triangular fins, one-step reversal occurs directly from onion to reverse onion state. The reversal processes are repeatable and controllable in contrast to an ideal ring without triangular fins where one-step and two-step reversals occur randomly in sweep-up and sweep-down processes.

Hydrocarbons from spirulina pyrolysis bio-oil using one-step hydrotreating and aqueous extraction of heteroatom compounds

USDA-ARS?s Scientific Manuscript database

Biomass feedstocks such as algae and cyanobacteria are highly sought after due to their high reproduction rates and growth densities, but their high concentrations of O and N heteroatoms are problematic for biofuels applications. The development of mild upgrading processes is necessary for producing...

China's Population Program at the Grassroots Level: Report on a Field Trip, Summer 1972.

ERIC Educational Resources Information Center

Chen, Pi-chao

The goals of the Caltech Population Program are to increase understanding of the interrelationships between population growth and socioeconomic and cultural patterns throughout the world and to communicate this understanding. This series of occasional papers is one step in the process of communicating research results. The papers deal primarily…

New Beginnings. A Manual for Facilitating Growth for Displaced Homemakers.

ERIC Educational Resources Information Center

Burnside, Nancy; And Others

This resource manual shares ideas and exercises with those persons interested in and working with the specific concerns of displaced homemakers. Sections correspond to steps in an adjustment process leading to job search. An introduction overviews the manual and provides helpful hints for use by peer counselors, professional therapists, and group…

Atomic Scale Imaging of Nucleation and Growth Trajectories of an Interfacial Bismuth Nanodroplet.

PubMed

Li, Yingxuan; Bunes, Benjamin R; Zang, Ling; Zhao, Jie; Li, Yan; Zhu, Yunqing; Wang, Chuanyi

2016-02-23

Because of the lack of experimental evidence, much confusion still exists on the nucleation and growth dynamics of a nanostructure, particularly of metal. The situation is even worse for nanodroplets because it is more difficult to induce the formation of a nanodroplet while imaging the dynamic process with atomic resolution. Here, taking advantage of an electron beam to induce the growth of Bi nanodroplets on a SrBi2Ta2O9 platelet under a high resolution transmission electron microscope (HRTEM), we directly observed the detailed growth pathways of Bi nanodroplets from the earliest stage of nucleation that were previously inaccessible. Atomic scale imaging reveals that the dynamics of nucleation involves a much more complex trajectory than previously predicted based on classical nucleation theory (CNT). The monatomic Bi layer was first formed in the nucleation process, which induced the formation of the prenucleated clusters. Following that, critical nuclei for the nanodroplets formed both directly from the addition of atoms to the prenucleated clusters by the classical growth process and indirectly through transformation of an intermediate liquid film based on the Stranski-Krastanov growth mode, in which the liquid film was induced by the self-assembly of the prenucleated clusters. Finally, the growth of the Bi nanodroplets advanced through the classical pathway and sudden droplet coalescence. This study allows us to visualize the critical steps in the nucleation process of an interfacial nanodroplet, which suggests a revision of the perspective of CNT.

Free energy landscape of dissociative adsorption of methane on ideal and defected graphene from ab initio simulations

NASA Astrophysics Data System (ADS)

Wlazło, M.; Majewski, J. A.

2018-03-01

We study the dissociative adsorption of methane at the surface of graphene. Free energy profiles, which include activation energies for different steps of the reaction, are computed from constrained ab initio molecular dynamics. At 300 K, the reaction barriers are much lower than experimental bond dissociation energies of gaseous methane, strongly indicating that the graphene surface acts as a catalyst of methane decomposition. On the other hand, the barriers are still much higher than on the nickel surface. Methane dissociation therefore occurs at a higher rate on nickel than on graphene. This reaction is a prerequisite for graphene growth from a precursor gas. Thus, the growth of the first monolayer should be a fast and efficient process while subsequent layers grow at a diminished rate and in a more controllable manner. Defects may also influence reaction energetics. This is evident from our results, in which simple defects (Stone-Wales defect and nitrogen substitution) lead to different free energy landscapes at both dissociation and adsorption steps of the process.

Polygonum sachalinense alters the balance between capacities of regeneration and carboxylation of ribulose-1,5-bisphosphate in response to growth CO2 increment but not the nitrogen allocation within the photosynthetic apparatus.

PubMed

Akita, Risako; Kamiyama, Chiho; Hikosaka, Kouki

2012-12-01

The limiting step of photosynthesis changes depending on CO(2) concentration and, in theory, photosynthetic nitrogen use efficiency at a respective CO(2) concentration is maximized if nitrogen is redistributed from non-limiting to limiting processes. It has been shown that some plants increase the capacity of ribulose-1,5-bisphoshate (RuBP) regeneration (evaluated as J(max) ) relative to the RuBP carboxylation capacity (evaluated as V(cmax) ) at elevated CO(2) , which is in accord with the theory. However, there is no study that tests whether this change is accompanied by redistribution of nitrogen in the photosynthetic apparatus. We raised a perennial plant, Polygonum sachalinense, at two nutrient availabilities under two CO(2) concentrations. The J(max) to V(cmax) ratio significantly changed with CO(2) increment but the nitrogen allocation among the photosynthetic apparatus did not respond to growth CO(2) . Enzymes involved in RuBP regeneration might be more activated at elevated CO(2) , leading to the higher J(max) to V(cmax) ratio. Our result suggests that nitrogen partitioning is not responsive to elevated CO(2) even in species that alters the balance between RuBP regeneration and carboxylation. Nitrogen partitioning seems to be conservative against changes in growth CO(2) concentration. Copyright © Physiologia Plantarum 2012.

Rice growth monitoring using simulated compact polarimetric C band SAR

NASA Astrophysics Data System (ADS)

Yang, Zhi; Li, Kun; Liu, Long; Shao, Yun; Brisco, Brian; Li, Weiguo

2014-12-01

In this study, a set of nine compact polarimetric (CP) images were simulated from polarimetric RADARSAT-2 data acquired over a test site containing two types of rice field in Jiangsu province, China. The types of rice field in the test site were (1) transplanted hybrid rice fields, and (2) direct-sown japonica rice fields. Both types have different yields and phenological stages. As a first step, the two types of rice field were distinguished with 94% and 86% accuracy respectively through analyzing CP synthetic aperture radar (SAR) observations and their behavior in terms of scattering mechanisms during the rice growth season. The focus was then on phenology retrieval for each type of rice field. A decision tree (DT) algorithm was built to fulfill the precise retrieval of rice phenological stages, in which seven phenological stages were discriminated. The key criterion for each phenological stage was composed of 1-4 CP parameters, some of which were first used for rice phenology retrieval and found to be very sensitive to rice phenological changes. The retrieval results were verified at parcel level for a set of 12 stands of rice and up to nine observation dates per stand. This gave an accuracy of 88-95%. Throughout the phenology retrieval process, only simulated CP data were used, without any auxiliary data. These results demonstrate the potential of CP SAR for rice growth monitoring applications.

Enzymatic enrichment of egg-yolk phosphatidylcholine with alpha-linolenic acid.

PubMed

Chojnacka, A; Gładkowski, W; Kiełbowicz, G; Wawrzeńczyk, C

2009-05-01

alpha-Linolenic acid (ALA) was incorporated at 28% into the sn-1 position of egg-yolk phospatidylcholine using Novozyme 435 in one-step transesterification process. Using phospholipase A(2) in a two-step process gave 25% incorporation of ALA into the sn-2 position.

One-Step Real-Image Reflection Holograms

ERIC Educational Resources Information Center

Buah-Bassuah, Paul K.; Vannoni, Maurizio; Molesini, Giuseppe

2007-01-01

A holographic process is presented where the object is made of the real image produced by a two-mirror system. Single-step reflection hologram recording is achieved. Details of the process are given, optics concepts are outlined and demonstrative results are presented. (Contains 6 figures and 2 footnotes.)

Nonclassical nucleation pathways in protein crystallization

NASA Astrophysics Data System (ADS)

Zhang, Fajun

2017-11-01

Classical nucleation theory (CNT), which was established about 90 years ago, has been very successful in many research fields, and continues to be the most commonly used theory in describing the nucleation process. For a fluid-to-solid phase transition, CNT states that the solute molecules in a supersaturated solution reversibly form small clusters. Once the cluster size reaches a critical value, it becomes thermodynamically stable and favored for further growth. One of the most important assumptions of CNT is that the nucleation process is described by one reaction coordinate and all order parameters proceed simultaneously. Recent studies in experiments, computer simulations and theory have revealed nonclassical features in the early stage of nucleation. In particular, the decoupling of order parameters involved during a fluid-to-solid transition leads to the so-called two-step nucleation mechanism, in which a metastable intermediate phase (MIP) exists between the initial supersaturated solution and the final crystals. Depending on the exact free energy landscapes, the MIPs can be a high density liquid phase, mesoscopic clusters, or a pre-ordered state. In this review, we focus on the studies of nonclassical pathways in protein crystallization and discuss the applications of the various scenarios of two-step nucleation theory. In particular, we focus on protein solutions in the presence of multivalent salts, which serve as a model protein system to study the nucleation pathways. We wish to point out the unique features of proteins as model systems for further studies.

Nonclassical nucleation pathways in protein crystallization.

PubMed

Zhang, Fajun

2017-11-08

Classical nucleation theory (CNT), which was established about 90 years ago, has been very successful in many research fields, and continues to be the most commonly used theory in describing the nucleation process. For a fluid-to-solid phase transition, CNT states that the solute molecules in a supersaturated solution reversibly form small clusters. Once the cluster size reaches a critical value, it becomes thermodynamically stable and favored for further growth. One of the most important assumptions of CNT is that the nucleation process is described by one reaction coordinate and all order parameters proceed simultaneously. Recent studies in experiments, computer simulations and theory have revealed nonclassical features in the early stage of nucleation. In particular, the decoupling of order parameters involved during a fluid-to-solid transition leads to the so-called two-step nucleation mechanism, in which a metastable intermediate phase (MIP) exists between the initial supersaturated solution and the final crystals. Depending on the exact free energy landscapes, the MIPs can be a high density liquid phase, mesoscopic clusters, or a pre-ordered state. In this review, we focus on the studies of nonclassical pathways in protein crystallization and discuss the applications of the various scenarios of two-step nucleation theory. In particular, we focus on protein solutions in the presence of multivalent salts, which serve as a model protein system to study the nucleation pathways. We wish to point out the unique features of proteins as model systems for further studies.

Three-Dimensional Conformation of Folded Polymers in Single Crystals

NASA Astrophysics Data System (ADS)

Hong, You-lee; Yuan, Shichen; Li, Zhen; Ke, Yutian; Nozaki, Koji; Miyoshi, Toshikazu

2015-10-01

The chain-folding mechanism and structure of semicrystalline polymers have long been controversial. Solid-state NMR was applied to determine the chain trajectory of 13C CH3 -labeled isotactic poly(1-butene) (i PB 1 ) in form III chiral single crystals blended with nonlabeled i PB 1 crystallized in dilute solutions under low supercooling. An advanced 13C - 13C double-quantum NMR technique probing the spatial proximity pattern of labeled 13C nuclei revealed that the chains adopt a three-dimensional (3D) conformation in single crystals. The determined results indicate a two-step crystallization process of (i) cluster formation via self-folding in the precrystallization stage and (ii) deposition of the nanoclusters as a building block at the growth front in single crystals.

Interface coupling and growth rate measurements in multilayer Rayleigh-Taylor instabilities

NASA Astrophysics Data System (ADS)

Adkins, Raymond; Shelton, Emily M.; Renoult, Marie-Charlotte; Carles, Pierre; Rosenblatt, Charles

2017-06-01

Magnetic levitation was used to measure the growth rate Σ vs wave vector k of a Rayleigh-Taylor instability in a three-layer fluid system, a crucial step in the elucidation of interface coupling in finite-layer instabilities. For a three-layer (low-high-low density) system, the unstable mode growth rate decreases as both the height h of the middle layer and k are reduced, consistent with an interface coupling ∝e-k h . The ratios of the three-layer to the established two-layer growth rates are in good agreement with those of classic linear stability theory, which has long resisted verification in that configuration.

Quantitative microbiological risk assessment in food industry: Theory and practical application.

PubMed

Membré, Jeanne-Marie; Boué, Géraldine

2018-04-01

The objective of this article is to bring scientific background as well as practical hints and tips to guide risk assessors and modelers who want to develop a quantitative Microbiological Risk Assessment (MRA) in an industrial context. MRA aims at determining the public health risk associated with biological hazards in a food. Its implementation in industry enables to compare the efficiency of different risk reduction measures, and more precisely different operational settings, by predicting their effect on the final model output. The first stage in MRA is to clearly define the purpose and scope with stakeholders, risk assessors and modelers. Then, a probabilistic model is developed; this includes schematically three important phases. Firstly, the model structure has to be defined, i.e. the connections between different operational processing steps. An important step in food industry is the thermal processing leading to microbial inactivation. Growth of heat-treated surviving microorganisms and/or post-process contamination during storage phase is also important to take into account. Secondly, mathematical equations are determined to estimate the change of microbial load after each processing step. This phase includes the construction of model inputs by collecting data or eliciting experts. Finally, the model outputs are obtained by simulation procedures, they have to be interpreted and communicated to targeted stakeholders. In this latter phase, tools such as what-if scenarios provide an essential added value. These different MRA phases are illustrated through two examples covering important issues in industry. The first one covers process optimization in a food safety context, the second one covers shelf-life determination in a food quality context. Although both contexts required the same methodology, they do not have the same endpoint: up to the human health in the foie gras case-study illustrating here a safety application, up to the food portion in the brioche case-study illustrating here a quality application. Copyright © 2017 Elsevier Ltd. All rights reserved.