Steady-state Growth Research Articles

Intermolecular interactions involving an acidic patch on immunoglobulin variable domain and the γ2 constant region mediate crystalline inclusion body formation in the endoplasmic reticulum.

Full-length immunoglobulins (Igs) are widely considered difficult to crystallize because of their large size, N-linked glycosylation, and flexible hinge region. However, numerous cases of intracellular Ig crystallization are reported in plasma cell dyscrasias. What makes some Ig clones more prone to crystallize during biosynthesis as well as the biochemical and cell biological requirements for this cryptic event are poorly understood. To investigate the underlying process of intracellular Ig crystallization we searched for model IgGs that can induce crystalline inclusions during recombinant overexpression. By testing various subunit combinations through mixing and matching of individual subunit chains derived from a panel of human IgG clones, we identified one secretion competent IgG2λ that induced needle-like crystalline inclusions in transfected HEK293 cells. Ig crystallization rarely occurred at steady-state cell growth conditions but was easily induced when ER-to-Golgi transport was pharmacologically blocked. Homology modeling revealed the presence of a prominent negatively-charged patch on the variable domain surface. The patch was composed of eight aspartic acids, of which five were in the heavy chain variable region and three were in the light chain. Crystallization occurred only when the two subunits were co-transfected and the intracellular crystals co-localized with ER resident proteins. Furthermore, subtype switching from IgG2 to IgG1 and stepwise neutralization of the acidic patch independently abrogated Ig crystallization events. The evidence supported that the formation of needle-like crystalline inclusions in the ER was underscored by multivalent intermolecular interactions between the acidic patch and undefined determinants present on the γ2 subunit constant region.

Ultra-large-scale phase-field simulation study of ideal grain growth

Grain growth, a competitive growth of crystal grains accompanied by curvature-driven boundary migration, is one of the most fundamental phenomena in the context of metallurgy and other scientific disciplines. However, the true picture of grain growth is still controversial, even for the simplest (or ‘ideal’) case. This problem can be addressed only by large-scale numerical simulation. Here, we analyze ideal grain growth via ultra-large-scale phase-field simulations on a supercomputer for elucidating the corresponding authentic statistical behaviors. The performed simulations are more than ten times larger in time and space than the ones previously considered as the largest; this computational scale gives a strong indication of the achievement of true steady-state growth with statistically sufficient number of grains. Moreover, we provide a comprehensive theoretical description of ideal grain growth behaviors correctly quantified by the present simulations. Our findings provide conclusive knowledge on ideal grain growth, establishing a platform for studying more realistic growth processes.

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

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.

Generation and Characterization of Acid Tolerant Fibrobacter succinogenes S85

Microorganisms are key components for plant biomass breakdown within rumen environments. Fibrobacter succinogenes have been identified as being active and dominant cellulolytic members of the rumen. In this study, F. succinogenes type strain S85 was adapted for steady state growth in continuous culture at pH 5.75 and confirmed to grow in the range of pH 5.60–5.65, which is lower than has been reported previously. Wild type and acid tolerant strains digested corn stover with equal efficiency in batch culture at low pH. RNA-seq analysis revealed 268 and 829 genes were differentially expressed at pH 6.10 and 5.65 compared to pH 6.70, respectively. Resequencing analysis identified seven single nucleotide polymorphisms (SNPs) in the sufD, yidE, xylE, rlmM, mscL and dosC genes of acid tolerant strains. Due to the absence of a F. succinogenes genetic system, homologues in Escherichia coli were mutated and complemented and the resulting strains were assayed for acid survival. Complementation with wild-type or acid tolerant F. succinogenes sufD restored E. coli wild-type levels of acid tolerance, suggesting a possible role in acid homeostasis. Recent genetic engineering developments need to be adapted and applied in F. succinogenes to further our understanding of this bacterium.

Initial and steady-state Ru growth by atomic layer deposition studied by in situ Angle Resolved X-ray Photoelectron Spectroscopy

The clear substrate-dependent growth and delayed film continuity are essential challenges of Ru atomic layer deposition (ALD) demanding adequate and versatile approaches for their study. Here, we report on the application of in situ Angle Resolved X-ray Phototelectron Spectroscopy (ARXPS) for investigation of initial and steady-state ALD growth of Ru using Ru(EtCp)2 and O2 as precursors. Using ARXPS surface analysis technique we determine such parameters of Ru ALD initial growth as incubation period, fractional coverage and the thickness of islands/film depending on the substrate chemical state, governed by the presence/absence of NH3/Ar plasma pretreatment. It was demonstrated that NH3/Ar plasma pretreatment allows to obtain the lowest incubation period (∼7 ALD cycles) resulting in a continuous ultrathin (∼20Å) and smooth Ru films after 70 ALD cycles. In situ XPS at UHV was used at steady state Ru growth for analysis of half-cycle reactions that revealed formation of RuOx (x≈2) layer with thickness of ∼8Å after O2 pulse (first half-cycle). It was also shown that oxygen of RuOx layer combusts Ru(EtCp)2 ligands in the second half-cycle reaction and the observed Ru growth of ∼0.34Å per cycle is in a good agreement with the amount of oxygen in the RuOx layer.

Virtual trade between separated time zones and growth

AbstractThe purpose of this paper is to propose a model where trade has a direct and positive impact on growth rate of two trading nations beyond the level effect. We use the idea of virtual trade in intermediates induced by non‐overlapping time zones and show how trade can increase the equilibrium optimal rate of growth. In this structure the trade impact goes beyond the level effect and directly causes growth. Typically standard models of trade cannot generate an automatic growth impact. Virtual trade may allow production to continue uninterrupted in separated time zones such as between the USA and India, and that can lead to higher growth for both countries. Later we extend the model to incorporate the accumulation of skills which becomes necessary for sustaining steady state growth.

Dynamics of spacing adjustment and recovery mechanisms of ABAC-type growth pattern in ternary eutectic systems

In directionally solidified 2D samples at ternary eutectic compositions, the stable three-phase pattern is established to be lamellar structure with ABAC stacking, where A, B, and C are crystalline phases. Beyond the stability limits of the ABAC pattern, the system uses various spacing adjustment mechanisms to revert to the stable regime.In this study, the dynamics of spacing adjustment and recovery mechanisms of isotropic ABAC patterns were investigated using three-phase In–Bi–Sn alloy. Unidirectional solidification experiments were performed on 23.0 and 62.7µm-thick samples, where solidification front was monitored in real-time from both sides of the sample using a particular microscopy system. At these thicknesses, the pattern was found to be 2D during steady-state growth, i.e. both top and bottom microstructures were the same. However, during spacing adjustment and recovery mechanisms, 3D features were observed. Dynamics of two major instabilities, lamellae branching and elimination, were quantified. After these instabilities, two key ABAC pattern recovery mechanisms, namely, phase invasion and phase exchange processes, were identified and analyzed. After elimination, ABAC pattern is recovered by either continuous eliminations of all phases or by phase exchange. After branching, the recovery mechanisms are established to be phase invasion and phase exchange.

A relaxation time of secondary dendritic branches to their steady-state growth

In the present article, we use the selection theory to estimate the non-stationarity time of evolving dendrites to their steady-state growth.

Increased dosage of AOX1 promoter-regulated expression cassettes leads to transcription attenuation of the methanol metabolism in Pichia pastoris

The methanol-regulated alcohol oxidase promoter (PAOX1) of Pichia pastoris is one of the strongest promoters for heterologous gene expression in this methylotrophic yeast. Although increasing gene dosage is one of the most common strategies to increase recombinant protein productivities, the increase of gene dosage of Rhizopus oryzae lipase (ROL) in P. pastoris has been previously shown to reduce cell growth, lipase production and substrate consumption in high-copy strains. To better assess that physiological response, transcriptomics analysis was performed of a subset of strains with 1 to 15 ROL copies. The macroscopic physiological parameters confirm that growth yield and carbon uptake rate are gene dosage dependent, and were supported by the transcriptomic data, showing the impact of increased dosage of AOX1 promoter-regulated expression cassettes on P. pastoris physiology under steady methanolic growth conditions. Remarkably, increased number of cassettes led to transcription attenuation of the methanol metabolism and peroxisome biogenesis in P. pastoris, concomitant with reduced secretion levels of the heterologous product. Moreover, our data also point to a block in ROL mRNA translation in the higher ROL-copies constructs, while the low productivities of multi-copy strains under steady growth conditions do not appear to be directly related to UPR and ERAD induction.

Chemical Processes Involved in Atomic Layer Deposition of Gallium Sulfide: Insights from Theory

Growth characteristics of atomic layer deposition (ALD) of gallium sulfide (GaxS) from tris(dimethylamino)gallium (Ga(NMe2)3) and hydrogen sulfide (H2S) have been investigated by density functional theory. The steady-state film growth during one ALD cycle was modeled by studying the energetics of a large set of reactions taking place on a surface described as a SH-terminated gallium sulfide (Ga2S3) cluster. The opportunity of using gas-phase cluster calculations to compute entropic contributions is discussed. Detailed reaction mechanisms are provided, along with free energy profiles and a large reaction network emerges. It confirms a ligand loss/exchange mechanism, and various aspects of the growth are explored (fate of the precursor and co-reactant, self-saturation of the surface, crawling and cooperative effects, role of the amido ligand, of the impurities, etc.) and confronted to experimental observations. All the key reaction steps are facile and thermodynamically favorable, while undesired side react...

Steady-state EB cap size fluctuations are determined by stochastic microtubule growth and maturation

Growing microtubules are protected from depolymerization by the presence of a GTP or GDP/Pi cap. End-binding proteins of the EB1 family bind to the stabilizing cap, allowing monitoring of its size in real time. The cap size has been shown to correlate with instantaneous microtubule stability. Here we have quantitatively characterized the properties of cap size fluctuations during steady-state growth and have developed a theory predicting their timescale and amplitude from the kinetics of microtubule growth and cap maturation. In contrast to growth speed fluctuations, cap size fluctuations show a characteristic timescale, which is defined by the lifetime of the cap sites. Growth fluctuations affect the amplitude of cap size fluctuations; however, cap size does not affect growth speed, indicating that microtubules are far from instability during most of their time of growth. Our theory provides the basis for a quantitative understanding of microtubule stability fluctuations during steady-state growth.

Probing the Interfacial Chemistry of Ultrathin ALD-Grown TiO2 Films: An In-Line XPS Study

Ultrathin TiO2 films received renewed attention in the field of photoelectrochemical water splitting as corrosion protection layers for unstable, small-bandgap semiconductors. Because nucleation on the substrate can differ from steady-state growth of the film itself, it is important to understand the nucleation behavior on a specific surface. In this work, we studied the nucleation mechanism of atomic layer deposition-grown TiO2 from TiCl4 and H2O on as-received silicon by means of in-line X-ray photoelectron spectroscopy. Within a region of ∼0.4 nm of the SiO2/TiO2 interface, the presence of Ti3+ states are detected. In this region, the Ti, O, and Cl species are found to be more strongly bonded. At the initial stages of film growth, prolonged TiCl4 exposure is necessary to reach a saturated surface chemistry, which is in contrast to the outcome of growth per cycle saturation curve analysis. A prolonged water exposure experiment suggests that residual chlorine impurities can be prevented by using a suffic...

Core–shell formation in self-induced InAlN nanorods

We have examined the early stages of self-induced InAlN core–shell nanorod (NR) formation processes on amorphous carbon substrates in plan-view geometry by means of transmission electron microscopy methods. The results show that the grown structure phase separates during the initial moments of deposition into a majority of Al-rich InAlN and a minority of In-enriched InAlN islands. The islands possess polygonal shapes and are mainly oriented along a crystallographic c-axis. The growth proceeds with densification and coalescence of the In-enriched islands, resulting in a base for the In-enriched NR cores with shape transformation to hexagonal. The Al-rich shell formation around such early cores is observed at this stage. The matured core–shell structure grows axially and radially, eventually reaching a steady growth state which is dominated by the axial NR growth. We discuss the NR formation mechanism by considering the adatom surface kinetics, island surface energy, phase separation of InAlN alloys, and incoming flux directions during dual magnetron sputter epitaxy.

Arrested development – a comparative analysis of multilayer corona textures in high-grade metamorphic rocks

Abstract. Coronas, including symplectites, provide vital clues to the presence of arrested reaction and preservation of partial equilibrium in metamorphic and igneous rocks. Compositional zonation across such coronas is common, indicating the persistence of chemical potential gradients and incomplete equilibration. Major controls on corona mineralogy include prevailing pressure (P), temperature (T) and water activity (aH2O) during formation, reaction duration (t) single-stage or sequential corona layer growth; reactant bulk compositions (X) and the extent of metasomatic exchange with the surrounding rock; relative diffusion rates for major components; and/or contemporaneous deformation and strain. High-variance local equilibria in a corona and disequilibrium across the corona as a whole preclude the application of conventional thermobarometry when determining P–T conditions of corona formation, and zonation in phase composition across a corona should not be interpreted as a record of discrete P–T conditions during successive layer growth along the P–T path. Rather, the local equilibria between mineral pairs in corona layers more likely reflect compositional partitioning of the corona domain during steady-state growth at constant P and T. Corona formation in pelitic and mafic rocks requires relatively dry, residual bulk rock compositions. Since most melt is lost along the high-T prograde to peak segment of the P–T path, only a small fraction of melt is generally retained in the residual post-peak assemblage. Reduced melt volumes with cooling limit length scales of diffusion to the extent that diffusion-controlled corona growth occurs. On the prograde path, the low melt (or melt-absent) volumes required for diffusion-controlled corona growth are only commonly realized in mafic igneous rocks, owing to their intrinsic anhydrous bulk composition, and in dry, residual pelitic compositions that have lost melt in an earlier metamorphic event. Experimental work characterizing rate-limiting reaction mechanisms and their petrogenetic signatures in increasingly complex, higher-variance systems has facilitated the refinement of chemical fractionation and partial equilibration diffusion models necessary to more fully understand corona development. Through the application of quantitative physical diffusion models of coronas coupled with phase equilibria modelling utilizing calculated chemical potential gradients, it is possible to model the evolution of a corona through P–T–X–t space by continuous, steady-state and/or sequential, episodic reaction mechanisms. Most coronas in granulites form through a combination of these endmember reaction mechanisms, each characterized by distinct textural and chemical potential signatures with very different petrogenetic implications. An understanding of the inherent petrogenetic limitations of a reaction mechanism model is critical if an appropriate interpretation of P–T evolution is to be inferred from a corona. Since corona modelling employing calculated chemical potential gradients assumes nothing about the sequence in which the layers form and is directly constrained by phase compositional variation within a layer, it allows far more nuanced and robust understanding of corona evolution and its implications for the path of a rock in P–T–X space.

Effect of self-ion irradiation on the microstructural changes of alloy EK-181 in annealed and severely deformed conditions

EK-181 is a low-activation ferritic/martensitic steel that is an attractive candidate for in-core component materials for both fast reactors and fusion reactors. To assess the effect of microstructural engineering on radiation response, two variants of EK-181 were studied: one in an annealed condition and the other subject to severe plastic deformation. These specimens were irradiated with 3.5 MeV Fe self-ions up to 400 peak displacements per atom (dpa) at temperatures ranging from 400 °C to 500 °C. The deformation did not suppress swelling over the whole irradiated region. Instead, deformed samples showed higher swelling in the near-surface region. Void swelling was found to be correlated with grain boundary instability. Significant grain growth occurred when steady-state void growth started.

Dynamic modeling reveals a three-step response of Saccharomyces cerevisiae to high CO2 levels accompanied by increasing ATP demands.

Saccharomyces cerevisiae is often applied in large-scale bioreactors where gradients of dissolved CO2 exist. Under high CO2 pressure, the dissolved gas enters the microbe, causing multifold intracellular responses such as decrease of pH, increase of HCO3- and changes of ion balance. Effects of varying CO2 concentrations are multifold, hard to scale and hardly investigated. Hence, the multi-level response to CO2 shifts was summarized in a predicting ODE model with mass action kinetics, balancing electrochemical charges in steady-state growth conditions. Compared to experimental observations, the simulated dynamics of ion concentrations were found to be consistent. During CO2 shifts, the model predicts the initial depolarization of the membrane potential, the temporal pH drop and the activation of countermeasures such as Pma1-mediated H+ export and Trk1,2-mediated K+ import. In conclusion, extracellular cation concentrations and the cellular pH regulation are critical factors that determine physiology and cellular energy management. Consequently, pressure-induced CO2 gradients cause peaks of ATP demand which may occur in cells circulating in large-scale industrial bioreactors.

Steady State Morphologies of Paracetamol Crystal from Different Solvents

Nowadays, mastering crystal growth from different points of view is becoming an essential technique, with the continuous development of pharmaceutical industries and scientific research. Paracetamol (acetaminophen), a medication used to treat pain and fever, is often at a steady state growth shape but has a complex crystal habit. Because of its non-centrosymmetric structure, paracetamol has multiple types of kink sites on each edge of each face, which brings more difficulties in growth predicting for crystal morphology designers. Therefore, accurate analysis of paracetamol crystal structure and the ability to design its crystal shapes from as many solvents as possible are of significant meaning and interest. Here, a general mechanistic spiral growth model is introduced to predict the steady state morphologies of paracetamol crystal grown from 30 different solvents. An upgraded kink rate expression and a kink density expression are proposed to describe how the growth units associated with the kink, step, e...

Demand-Led Growth and Accommodating Supply

We model demand-led growth with endogenous adjustment of labor supply and productivity to accommodate the demand-led path, reconciling Harrod’s warranted rate of demand growth with supply. The model delivers a range of growth paths and unemployment rates rather than a single “natural rate.” Theoretically, the steady-state growth path may be dynamically stable or unstable, but a detailed empirical calibration favors stability. We show analytically that if demand dynamics are stable, supply will converge to demand. While a minimum unemployment rate ultimately imposes a supply constraint on growth, empirical results show that a wide range of steady-state growth rates are feasible across different demand regimes. The results explain how economies can become trapped with low growth due to weak demand or fiscal austerity and suggest policy responses to stagnant demand

Steady-state crack growth in single crystals under Mode I loading

The active plastic zone that surrounds the tip of a sharp crack growing under plane strain Mode I loading conditions at a constant velocity in a single crystal is studied. Both the characteristics of the plastic zone and its effect on the macroscopic toughness is investigated in terms of crack tip shielding due to plasticity (quantified by employing the Suo, Shih, and Varias set-up). Three single crystals (FCC, BCC, HCP) are modelled in a steady-state elastic visco-plastic framework, with emphasis on the influence of rate-sensitivity and crystal structures. Distinct velocity discontinuities at the crack tip predicted by Rice [Rice J.R., 1987. Tensile crack tip fields in elastic-ideally plastic crystals. Mech. Mater. 6, pp. 317–335] for quasi-static crack growth are confirmed through the numerical simulations and highly refined details are revealed. Through a detailed study, it is demonstrated that the largest shielding effect develops in HCP crystals, while the lowest shielding exists for FCC crystals. Rate-sensitivity is found to affect the plastic zone size, but the characteristics overall remain similar for each individual crystal structure. An increasing rate-sensitivity at low crack velocities monotonically increases the crack tip shielding, whereas the opposite behaviour is observed at high velocities. This observation leads to the existence of a characteristic velocity at which the crack tip shielding becomes independent of the rate-sensitivity.

Growth and Welfare Under Endogenous Lifetime

We develop a perpetual youth model to investigate how longevity affects economic growth and welfare. Life expectancy is determined by individuals’ investments in healthcare. We find that improvements in the healthcare technology always increase the steady state growth rate. Although the effect is small, even for large increases in longevity, welfare gains may be substantial depending on the type of the technological improvement. We identify two externalities associated with healthcare investments and provide a condition when healthcare expenditures are inefficiently low in the market equilibrium. Finally, we discuss our results with respect to alternative spillover specifications in the production sector.