Stability In Presence Research Articles

Heat and cold denaturation of yeast frataxin: The effect of pressure

Yfh1 is a yeast protein with the peculiar characteristic to undergo, in the absence of salt, cold denaturation at temperatures above the water freezing point. This feature makes the protein particularly interesting for studies aiming at understanding the rules that determine protein fold stability. Here, we present the phase diagram of Yfh1 unfolding as a function of pressure (0.1–500 MPa) and temperature 278–313 K (5–40°C) both in the absence and in the presence of stabilizers using Trp fluorescence as a monitor. The protein showed a remarkable sensitivity to pressure: at 293 K, pressures around 10 MPa are sufficient to cause 50% of unfolding. Higher pressures were required for the unfolding of the protein in the presence of stabilizers. The phase diagram on the pressure-temperature plane together with a critical comparison between our results and those found in the literature allowed us to draw conclusions on the mechanism of the unfolding process under different environmental conditions.

Anisotropic growth of gold nanocrystals induced by concerted adsorption using a photochemical approach

Photochemical reduction of noble metal ions in the presence of stabilizers that selectively adsorb on different crystal planes is a fascinating method for synthesizing shape-controlled metal nanocrystals (NCs). In this study, we demonstrate the photoreduction of Au3+ ions in the presence of polyvinylpyrrolidone (PVP) and Br− ions, that are classified into different categories of protective agents. Au nanoplates with atomically flat surfaces are obtained by the photoirradiation of an aqueous solution containing Au3+, PVP and Br−. Notably, PVP preferentially adsorbs along the perimeter, while Br− ions tend to adsorb on the flat top and bottom (111) faces. The selective adsorption of these structurally distinct stabilizers promotes two-dimensional growth of the Au nanoplates. PVP serves not only as a protective agent but also as a reduction agent in the photoreduction process. At high concentrations of Br− ions, the adsorption of the Br− ions also occurs at the perimeter, which kinetically traps the side growth of the nanoplates and leads to the formation of polygonal Au nanoplates. In other words, competitive adsorption of PVP and Br− at the facets and their density kinetically affect the shape of the formed Au NCs. This concept was successfully applied to control the photoreduction of Au3+ ions into icosahedral Au nanoparticles.

Topical noninvasive retinal drug delivery of a tyrosine kinase inhibitor: 3% cediranib maleate cyclodextrin nanoparticle eye drops in the rabbit eye.

Tyrosine kinase inhibitors inhibit VEGF receptors. If delivered to the retina, they might inhibit oedema and neovascularization such as in age-related macular degeneration and diabetic retinopathy. The aim of this study was to formulate cediranib maleate, a potent VEGF inhibitor, as γ-cyclodextrin nanoparticle eye drops and measure the retinal delivery and overall ocular pharmacokinetics after a single-dose administration in rabbits. A novel formulation technology with 3% cediranib maleate as γ-cyclodextrin micro-suspension was prepared by autoclaving method. Suitable stabilizers were tested for heat-stable eye drops. The ophthalmic formulation was topically applied to one eye in rabbits. The pharmacokinetics in ocular tissues, tear film and blood samples were studied at 1, 3 and 6 hr after administration. γ-cyclodextrin formed complex with cediranib maleate. The formation of γ-cyclodextrin nanoparticles occurred in concentrated complexing media. Combined stabilizers prevented the degradation of drug during the autoclaving process. Three hours after administration of the eye drops, treated eyes showed cediranib levels of 737 ± 460 nM (mean ± SD) in the retina and 10 ± 6 nM in the vitreous humour. Cediranib maleate in γ-cyclodextrin nanoparticles were stable to heat in presence of stabilizers. The drug as eye drops reached the retina in concentrations that are more than 100 times higher than the 0.4 nM IC50 value reported for the VEGF type-II receptor and thus, presumably, above therapeutic level. These results suggest that γ-cyclodextrin-based cediranib maleate eye drops deliver effective drug concentrations to the retina in rabbits after a single-dose administration.

Stability and operation limits of power systems with high penetration of power electronics

Modern power systems are facing a number of challenges related to stability when integrating large amounts of power electronics, which is present in renewable generation, energy storage, flexible AC transmission systems or high voltage DC links. This paper analyses the stability and operation limits in power systems with high penetration of power electronics. In particular, steady-state, small-signal and transient analysis have been carried out to examine the minimum synchronous generation required to ensure stability in presence of an HVDC link based on a VSC operating in grid-following control. These analysis are based on performance indices, which evaluate the main magnitudes of the system, such as the grid frequency and voltage, but also the particular magnitudes of the system elements, mainly generators and VSCs. The use of these indices provides a fast overview of the system performance that could lead to save analysis time of power system engineers in the task of identifying critical cases for the system.

Approximate Synchronization of Complex Network Consisting of Nodes With Minimum-Phase Zero Dynamics and Uncertainties

A synchronization algorithm of nonlinear complex networks composed of nonlinear nodes is designed. The main idea is to apply the exact feedback linearization of every node first, then applying methods for synchronization of linear complex networks. The nodes need not admit full exact feedback linearization, however, they are supposed to be minimum-phase systems. To achieve the synchronization of the observable parts of the nodes, an algorithm based on the convex optimization (to be specific, on linear matrix inequalities) is proposed. Then, it is demonstrated that, using the minimum-phase assumption, the non-observable part of the nodes is synchronized as well. The algorithm for synchronization of the observable parts of the nodes can be used to design a control law that is capable of maintaining stability in presence of certain variations of the control gain. Uncertainties in the parameters are also taken into account. Two examples illustrate the control design.

Nanoviricides Platform Technology Based NV-387 Polymer Protects Remdesivir from Plasma-Mediated Catabolism In vitro: Importance of its Increased Lifetime for In vivo Action

As of today, seven coronaviruses were identified to infect humans, out of which only 4 of them belongs to beta family of coronavirus, like HCoV-HKU1, SARS-CoV-2, MERS-CoV and SARS-CoV. SARS family of viruses were known to cause severe respiratory disease in humans. SARS-CoV-2 infection causes pandemic COVID-19 disease with high morbidity and mortality. Remdesivir (RDV) is the only antiviral drug so far approved for COVID-19 therapy by FDA. However, it’s efficacy is limited in vivo due to its low stability in presence of Plasma. Here we show the stability of RDV encapsulated with our platform technology based polymer NV-387 (NV-CoV- 2-R), in presence of Plasma in vitro in comparison to naked RDV when incubated in plasma. The potential use of this polymer in vivo will be discussed, here.

A small gain theorem for finite-time input-to-state stability of infinite networks and its applications

We prove a small-gain sufficient condition for (global) finite-time input-to-state stability (FTISS) of infinite networks. The network under consideration is composed of a countable set of finite-dimensional subsystems of ordinary differential equations, each of which is interconnected with a finite number of its “neighbors” only and is affected by some external disturbances. We assume that each node (subsystem) of our network is finite-time input-to-state stable (FTISS) with respect to its finite-dimensional inputs produced by this finite set of the neighbors and with respect to the corresponding external disturbance. As an application we obtain a new theorem on decentralized finite-time input-to-state stabilization with respect to external disturbances for infinite networks composed of a countable set of strict-feedback form systems of ordinary differential equations. For this we combine our small-gain theorem proposed in the current work with the controllers design developed by S. Pavlichkov and C. K. Pang (NOLCOS-2016) for the gain assignment of the strict-feedback form systems in the case of finite networks. The current results address the finite-time input-to-state stability and decentralized finite-time input-to-state stabilization and redesign the technique proposed in recent work S. Dashkovskiy and S. Pavlichkov, Stability conditions for infinite networks of nonlinear systems and their application for stabilization, Automatica. – 2020. – 112. – 108643, in which the case of $\ell_{\infty}$-ISS of infinite networks was investigated. The current paper extends and generalizes its conference predecessor to the case of finite-time ISS stability and decentralized stabilization in presence of external disturbance inputs and with respect to these disturbance inputs. In the special case when all these external disturbances are zeroes (i.e. are abscent), we just obtain finite-time stability and finite-time decentralized stabilization of infinite networks accordingly.

Observer-Based Stabilization of Linear Discrete Time-VaryingDelay Systems

Abstract This paper presents the design of an observer-based stabilizing controller for linear discrete-time systems subject to interval time-varying state-delay. In this work, the problem has been formulated in convex optimization framework by constructing a new Lyapunov–Krasovskii (LK) functional to derive delay-dependent stabilization criteria. The summation inequality and the extended reciprocally convex inequality are exploited to obtain a less conservative delay upper bound in linear matrix inequality (LMI) framework. The derived stability conditions are delay-dependent and thus ensure global asymptotic stability in presence of any time-delay less than the obtained delay upper bound. Numerical examples are included to demonstrate the usefulness of the developed results.

Non-linear Boltzmann equation on hybrid-unstructured non-conforming multi-domains

Adaptivity is crucial for addressing practical challenges of the next decades. In this regard, recent surveys [117] highlight that it continues to be a major bottleneck in computational fluid dynamics workflow. We introduce mixed non-conforming discontinuous Galerkin discretization for the full Boltzmann equation in 2D/3D. These schemes have been designed for efficiency — motivated in part by spectral and isogeometric weighted collocation methods — and retain an optimal O(p+1) convergence for a p order approximation for non-linear kinetic systems on non-orthogonal grids. In this setting, it is possible to analyze highly complex problems of industrial strength i.e., structured, unstructured, mixed, irregular, multi-domain (multi-block) adaptive geometries at massively parallel scale (ten thousand cores or beyond). Mixed domains permit flexible mesh generation, whereas local nature of discontinuous Galerkin permits construction of adaptive numerical schemes that scale well. To address flows in mixing regime (low/high rarefaction), we couple the scheme with an asymptotic preserving implicit-explicit time discretization. These schemes are iteration free and applicable for a wide range of rarefied flows from free-molecular to continuum. To ensure stability in presence of shocks, we describe a method of constructing limiters on non-conforming grids. Finally, we show that the computational overhead for solving kinetic equations on non-conforming structured/unstructured domains is negligible relative to conforming domains. So, there is no reason to not prefer non-conforming unstructured domains.

Enhancing the Stabilization Potential of Lyophilization for Extracellular Vesicles.

Extracellular vesicles (EV) are an emerging technology as immune therapeutics and drug delivery vehicles. However, EVs are usually stored at -80°C which limits potential clinical applicability. Freeze-drying of EVs striving for long-term stable formulations is therefore studied. The most appropriate formulation parameters are identified in freeze-thawing studies with two different EV types. After a freeze-drying feasibility study, four lyophilized EV formulations are tested for storage stability for up to 6 months. Freeze-thawing studies revealed improved colloidal EV stability in presence of sucrose or potassium phosphate buffer instead of sodium phosphate buffer or phosphate-buffered saline. Less aggregation and/or vesicle fusion occurred at neutral pH compared to slightly acidic or alkaline pH. EVs colloidal stability can be most effectively preserved by addition of low amounts of poloxamer 188. Polyvinyl pyrrolidone failed to preserve EVs upon freeze-drying. Particle size and concentration of EVs are retained over 6 months at 40°C in lyophilizates containing 10mm K- or Na-phosphate buffer, 0.02% poloxamer 188, and 5% sucrose. The biological activity of associated beta-glucuronidase is maintained for 1month, but decreased after 6 months. Here optimized parameters for lyophilization of EVs that contribute to generate long-term stable EV formulations are presented.

Influence of critical parameters on nanoparticles-surfactant stabilized CO2 foam stability at sub-critical and supercritical conditions

The stability of CO2-foam stabilized via the synergy of nanoparticles and surfactants at downhole conditions is strongly affected by different process parameters such as temperature, CO2 state, nanoparticles concentration, as well as resident brine and oil in the reservoir. Influence of critical parameters on static and dynamic stability of nanoparticles-surfactant stabilized CO2-foam at sub-critical and super-critical conditions was investigated in this study. Firstly, extensive static and dynamic foam stability experiments were conducted at 80 °C and presence of 30 vol% hexadecane oil using formulation turbiscan, to screen different surfactants and nanoparticles. The best performing nanoparticles and surfactant were then selected at the screening stage for further foam stability tests to compare the performance of CO2 foam at sub-critical and super-critical conditions. The foam stabilized by SiO2 and sodium dodecyl sulfate (SDS) demonstrated consistent static and dynamic stability, with least spreading coefficient (-5.28 mN/m) and favourable Lamellae number (0.71). Increasing nanoparticles concentration increased the stability of sub-critical CO2 foam whereas an optimum nanoparticles concentration for maximum stability of the supercritical CO2 foam was obtained as 0.5 wt% SiO2. The static stability of sub-critical and supercritical CO2 foam increased with increased sodium chloride (NaCl) concentrations until 2 wt%. However, the super-critical CO2 foam demonstrated increasing pressure drop and lowest reduction in mobility with increasing NaCl concentration until 10 wt%. Highly durable foams were generated when oil with high viscosity, high density and high molecular weight oil was added into the foaming dispersions. Mechanistic investigation of foam stabilization revealed that thickness of pseudo-emulsion films, as well as particles adsorption and orientation at gas–liquid and liquid–liquid interface, are key controlling parameters of foam static and dynamic stability in presence of oil, brine and at high temperature.

Phase stabilisation, chemical behaviour and protonic conductivity of vanadium doped Barium Indate for ITSOFC application

Barium indate (Ba2In2O5) is known to be a good proton conducting oxide at moderate temperatures. Vanadium substituted barium indate, Ba2In2‐xVxO5+xsolid solutions were synthesized by ceramic route and their hydrated samples were prepared to evaluate their stability in presence of moisture. Partial substitution for In3+ by V5+ led to the stabilization of the Ba2In2O5 cubic form at lower temperatures. Their thermal as well chemical stability was studied using thermogravimetry and x-ray diffraction techniques. At high temperature, in presence of moisture indium leached out as In(OH)3, whereas in presence of CO2 barium comes out as BaCO3 from Ba2In2O5. The effect of vanadium substitution in Ba2In2O5on its chemical stability was demonstrated. As vanadium content increases the hydrated composition of the above oxides exhibit enhanced stability.

Absence of the CXCR4 antagonist EPI-X4 from pharmaceutical human serum albumin preparations

BackgroundEndogenous Peptide Inhibitor of CXCR4 (EPI-X4) is a natural antagonist of the CXC chemokine receptor 4 (CXCR4). EPI-X4 is a 16-mer peptide that is released from human serum albumin (HSA) by acidic aspartic proteases such as Cathepsin D and E. Since human serum albumin (HSA) is an important medicinal substance we asked whether different pharmaceutical HSA products contain EPI-X4 which could have been generated during manufacturing and whether HSA can serve as a substrate for cathepsins despite of the presence of stabilizers like caprylate.MethodsEight pharmaceutical HSA preparations representing all currently used fractionation technologies were analyzed. The previously described specific EPI-X4 ELISA was used for quantification; in vitro EPI-X4 generation by acidification in the presence or absence of cathepsins was followed by quantification with ELISA.ResultsNone of the pharmaceutical HSA preparations tested contained EPI-X4. Acidification of HSA did not generate EPI-X4. Addition of cathepsins D and E to acidified HSA yielded high concentrations of EPI-X4 in all HSA preparations, indistinguishable between individual products.ConclusionMedicinal HSA preparations per se do not contain EPI-X4, but will replenish its precursor which can be cleaved to EPI-X4 in vivo, environmental conditions permitting.

Numerical modeling of a high power triode-based self-excited oscillator: a path forward more efficient designs and a better frequency stability of low cost high power RF sources

Triode-based circuits are still the less expensive and more reliable high power sources for industrial applications between 13.56 and 40.68 Mhz. Among them, self-excited oscillators feature the lower cost but with a frequency stability preventing them to address all ISM frequencies and applications. This article demonstrates the possibility to model numerically self-excited oscillators with power triodes using a class-C practical circuit. Advantages over existing analytical calculations and graphical derivations are shown. A method is proposed to evaluate the frequency stability in presence of internal imperfections and external perturbations. These tools offer the possibility to design and analyze more efficiently this family of oscillators especially for demanding applications regarding frequency stability.

Ideal internal kink stability in presence of plasma flow and neoclassical toroidal viscosity due to energetic particles

The influence of energetic particles (EPs) on the ideal internal kink mode, in rotating tokamak plasmas, is numerically investigated by simultaneously solving MHD-kinetic hybrid equations together with a toroidal momentum balance equation utilizing the MARS-Q code (Liu et al 2013 Phys. Plasmas 20 042503). The neoclassical toroidal viscous (NTV) torque, induced by precessional drift resonances of trapped energetic particles, acts as the momentum sink term to damp the plasma flow. Quasi-linear initial value simulations show local reduction of the flow amplitude and enhancement of the flow shear near the q = 1 rational surface (q is the safety factor) due to EP induced NTV. Both effects in turn destabilize the internal kink mode. These numerical findings are robust against the initial linear stability of internal kink, the initial plasma flow profile, as well as the equilibrium distribution model for EPs.

Effect of random anisotropy in stabilization of skyrmions and antiskyrmions

Ever increasing demand of skyrmion manipulation in nanodevices has brought up interesting research to understand the stabilization of these topologically protected chiral structures. To understand the actual shape and size of skyrmions and antiskyrmions observed experimentally, we have performed micromagnetic simulations to investigate their stabilization in presence of random anisotropy in magnetic thin film system. Previous experimental reports of skyrmion imaging in thin films depicts that the skyrmion shape is not perfectly circular. Here we show via simulations that the shape of a skyrmion and an antiskyrmion can get distorted due to the presence of different local anisotropy energy. The values of uniaxial anisotropy constant (Ku) and random aniostropy constant (Kr) are varied to understand the change in shape and size of a skyrmion and an antiskyrmion stabilized in a square magnetic nanoelement. The skyrmion or antiskyrmion shape gets distorted with the presence of random anisotropy energy in the system.

Preparation of Polymer Bitumen Binder in the Presence of a Stabilizer

The article presents the results of research on the production of polymer-bitumen binder (PBB) based on mixtures of non-oxidized and oxidized petroleum products, namely high-viscosity tar, darkened vacuum distillate, and oxidized petroleum bitumen 70/100, obtained at technological installations of Limited Liability Partnership (LLP) “JV Caspi Bitum’’ and styrene-butadiene-styrene (SBS) block copolymer brand L 30-01A modifier in the presence of a stabilizer. The results obtained show that the introduction of the SBS modifier in the presence of a sulfur stabilizer improves the performance characteristics of PBB, such as elasticity, ductility, softening temperature, penetration, and brittleness temperature.

Gold nanoparticles obtained by ns-pulsed laser ablation in liquids (ns-PLAL) are arranged in the form of fractal clusters

Gold nanoparticles (AuNPs), synthesized by ns-pulsed laser ablation in liquid (ns-PLAL) in the absence of any capping agents, are potential model systems to study the interactions with biological structures unencumbered by interference from the presence of stabilizers and capping agents. However, several aspects of the physics behind these AuNPs solutions deserve a detailed investigation. The structure in solution of ns-PLAL-synthesized AuNPs was investigated in solution by means of small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS). Furthermore, the (dried) NPs have been examined using TEM. The analysis of the SAXS curve shows the presence of a large number of small aggregates with a fractal structure stabilized by strong long-range repulsive interactions. Fitting of the SAXS curve to a suitable “fractal model” allows the estimation of the features of the fractal including the fractal dimension d = 1.9. The latter allows to estimate the fraction of light scattered by fractals of different sizes and thus permits a fair comparison between the DLS and TEM data. Here, a stable abundant population of fractal clusters is reported reflecting a mechanism where primary AuNPs (size 7.6 nm) are forced to aggregate forming clusters during the collapse of the cavitation bubble. When these clusters are released in the aqueous phase, their large negative charge builds up repulsive interactions that prevent cluster-cluster aggregation imparting colloidal stability.

Plant miR171 modulates mTOR pathway in HEK293 cells by targeting GNA12.

Plant microRNAs have shown the capacity to regulate mammalian systems. The potential bioactivity of miR171vr, an isoform of the plant miR171, on human embryonic kidney 293 (HEK293) cells was investigated. Bioinformatics simulations revealed that human G protein subunit alpha 12 (GNA12) transcript could represent an excellent target for miR171vr. To confirm this prediction, in vitro experiments were performed using a synthetic microRNA designed on miR171vr sequence. MiR-treated cells showed a significant decrease of GNA12 mRNA and protein levels, confirming the putative cross-kingdom interaction. In addition, miR171vr determined the modulation of GNA12 downstream signaling factors, including mTOR, as expected. Finally, the effect of the plant miRNA on HEK293 cell growth and its stability in presence of several stressors, such as those miming digestive processes and procedures for preparing food, were evaluated. All this preliminary evidence would suggest that miR171vr, introduced by diet or as supplement in gene therapies, could potentially influence human gene expression, especially for treating disorders where GNA12 is over-expressed (i.e. oral cancer, breast and prostate adenocarcinoma) or mTOR kinase is down-regulated (e.g. obesity, type 2 diabetes, neurodegeneration).

Metal-Organic Frameworks: Screening M-MOF-74 (M = Co, Cr, Cu, Fe, Mg, Mn, Ni, Ti, and Zn) Based for Carbon Dioxide Adsorption

The release of carbon dioxide in the environment is increasing yearly due to human activities and it will affect greenhouse gas. To overcome this issue, adsorption technology found to be the best candidate due to its performance to capture high CO2 with lower capital cost. Much attention has focused on metal-organic framework (MOF) due to high potential of CO2 capture compared with conventional adsorbents. More research has been done on MOF-74 due to presence of the open-metal site that favors CO2 binding. The presence of metal in MOF-74 able to give higher surface area and porosity of the molecules thus result in higher adsorption of CO2. However, there is limited research related to metal in MOF-74 where most focused on the Mg-MOF-74 due to its ability to adsorb twice of CO2 compared with zeolites. Yet, Mg-MOF-74 found to lose stability in presence of water where it's only able to recover 15% from initial adsorption. Synthesizing MOF-74 requires high cost and providing not a promising result for each synthesizes. Thus, this paper introduces to screen MOF-74 for different metal centers using modeling approach by Material Studio. As result, Ni-MOF-74 shows the highest adsorption of CO2 with 12.35mmol/g compared to other metals.