Stability Matrix Research Articles

Quantification of ceftazidime/avibactam in human plasma and dried blood spots: Implications on stability and sample transport

Ceftazidime is an established third-generation cephalosporin antibiotic frequently administered to intensive care patients. To overcome drug resistance of pathogens, it is combined with the newly developed non-ß-lactam ß-lactamase inhibitor avibactam under the brand name Zavicefta®. To facilitate therapeutic drug monitoring (TDM), we developed a method for the simultaneous quantification of these substances by LC-MS/MS. A problem for TDM is the low stability of the analytes in plasma, requiring transport times of less than 6 h at 23 °C. Thus, we evaluated dried blood spots (DBS) as matrix for better stability. For both analytes, stable isotope labelled internal standards were applied. Plasma samples were prepared by protein precipitation, DBS by liquid extraction. The chromatographic separation took place on a polar-modified C18 column, and detection was achieved by tandem mass spectrometry with ESI ionization in positive mode for ceftazidime and negative mode for avibactam. Calibration was linear in the ranges of 5 – 100 µg/mL for ceftazidime and 1.25 – 25 µg/mL for avibactam in plasma and 2.5 – 50 µg/mL and 0.625 – 12.5 µg/mL in DBS, respectively. Precision was better than 7 % and accuracy better than 10% for plasma as well as for DBS. The stability of ceftazidime and avibactam was better in DBS than in plasma or full blood, extending maximal transport times at 23 °C from 6 h in plasma or full blood to 24 h for DBS samples. However, robust estimation of plasma concentrations from DBS measurements requires validation by future clinical studies.

Stability-Oriented Minimum Switching/Sampling Frequency for Cyber-Physical Systems: Grid-Connected Inverters Under Weak Grid

Although the cyber-physical system stability is widely studied, scholars focus more on system stability with communication time delay. Therein, grid-connected inverters with the digital control system are regarded as one simplest and typical cyber-physical system. Meanwhile, the switching/sampling frequency of the inverter is always selected as low as possible from an efficiency viewpoint, resulting in unavoidable delay time. This delay time is apt to cause the system instability, which is more prone to severity under weak grid. To this end, this paper provides a minimum switching/sampling frequency for grid-connected inverters. Firstly, the system impedance model with equivalent delay time is constructed, which is based on padé approximate approach. This equivalent delay time consists of three parts, i.e., sampling delay time in cyber/physical level, calculation delay time in cyber level and pulsewidth modulation delay time in physical level, which reflects the cyber-physical interaction impact. Furthermore, the stability forbidden criterion is applied to make the switching/sampling frequency solving process become Hurwitz matrix identification problem through space mappings. Based on these space mappings, an adaptive step search approach is adopted to obtain the minimum switching/sampling frequency. Finally, the proposed approach can well evaluate the system stability under different frequencies through simulation and experiment.

The behavior of iodine in stabilized granular activated carbon and silver mordenite in cementitious waste forms

Both granular activated carbon (GAC) and silver mordenite (AgM) are utilized for the removal of contaminants and radionuclides (e.g., radioiodine) from off-gas streams in nuclear fuel reprocessing and high temperature immobilization of nuclear waste. Following their service lifetimes, the GAC and AgM contain an inventory of contaminants and radionuclides and require stabilization in a matrix for disposal. GAC and AgM are referred to as solid secondary waste (SSW) materials. Cementitious waste forms can be used as the stabilization matrix for SSW, however, for successful stabilization, the inclusion of GAC and AgM should not negatively impact the physical behavior of the cementitious waste form or increase release of the contaminants/radionuclides compared to the baseline case without stabilization. The present work focuses on evaluation of cement formulations, with and without slag, for the stabilization of iodine-loaded GAC or AgM. The results showed that both a slag-containing and slag-free formulations were able to stabilize GAC and AgM, up to 30 vol%, without deleterious impacts on the bulk physical properties of the encapsulating matrix. When monolithic samples of the GAC or AgM containing cement formulations were subjected to leach tests, it was observed that iodide leached from the SSW) had limited sorption to either of the cement matrices. Nonetheless, the iodine can interact with the SSW materials themselves. Specifically, iodine retention within monolithic samples containing the iodine-loaded GAC or AgM was improved for AgM containing waste forms while no improvement was observed for the GAC containing waste forms. The improvement for the AgM containing waste forms was likely due to an enrichment of Ag at the interface between the AgM particles and the cement matrix that can impede iodine migration out from the waste form. The results are significant in highlighting the potential for long-term retention of iodine in specific cementitious waste forms.

Diffeomorphically Learning Stable Koopman Operators

System representations inspired by the infinite-dimensional Koopman operator (generator) are increasingly considered for predictive modeling. Due to the operator’s linearity, a range of nonlinear systems admit linear predictor representations -allowing for simplified prediction, analysis and control. However, finding meaningful finite-dimensional representations for prediction is difficult as it involves determining features that are both Koopman-invariant (evolve linearly under the dynamics) as well as relevant (spanning the original state) – a generally unsupervised problem. In this work, we present Koopmanizing Flows -a novel continuous-time framework for supervised learning of linear predictors for a class of nonlinear dynamics. In our model construction a latent diffeomorphically related linear system unfolds into a linear predictor through the composition with a monomial basis. The lifting, its linear dynamics and state reconstruction are learned simultaneously, while an unconstrained parameterization of Hurwitz matrices ensures asymptotic stability regardless of the operator approximation accuracy. The superior efficacy of Koopmanizing Flows is demonstrated in comparison to a state-of-the-art method on the well-known LASA handwriting benchmark.

Математическое моделирование нестационарности биотехнологического получения молочной кислоты: устойчивость

The article presents the calculated ratios of indicators determining the stationary states of the lactic acid production process. Three technologies that are most often mentioned in scientific publications are identified: the technology of using strains of microorganisms to produce biomass is a technology that is extremely rarely used; the fairly common technology of using strains of microorganisms to produce lactic acid with the consumption of the main substrate (most often glucose); the promising technology of obtaining lactic acid using, in addition to the main substrate, a component that reproduces the main substrate in the synthesis process. For each technology, the equations of material balance for stationary and non-stationary conditions, a generalized differential equation for non-stationary conditions, and a characteristic equation are given. The formulas for estimating the coefficients of differential equations and the coefficients of the characteristic equation are also given. The equations for non-stationary conditions according to the last two technologies are based on the use of the Taylor series expansion of functions with the preservation of only the first terms of the expansion, i. e. deviations from stationarity in small. The characteristic equation is formed using the eigenvalues . The methodology for all three technologies is given, which allows us to assess the stability of the considered stationary state – the Hurwitz method. For all three technologies, numerical results are obtained for estimating the coefficients of the characteristic equations Pi. Tabular values of the coefficients are given, according to which stability estimates for the dilution rate of 0.1 h–1, 0.2 h–1, 0.3 h–1 are obtained using determinants according to the Hurwitz matrix. The results of numerical estimates for the stability of stationary states for all three technologies are presented. The estimates were based on the indicators of constants published in scientific studies.

Robust fixed‐time connectivity preserving consensus of nonlinear multi‐agent systems with disturbance

AbstractThis article studies the fixed‐time tracking consensus of second‐order nonlinear multi‐agent systems with disturbance. To make the fixed‐time tracking consensus, a consensus protocol based on the integral sliding mode surface is proposed, which can ensure the adjacent agents remain within a limited communication range in the communication process. By adopting Lyapunov stability theory and matrix theory, sufficient conditions for the fixed‐time tracking consensus are given, and a bound of the settling time is obtained. Finally, a simulation example is presented to verify the potential correctness of the obtained results.

Analysis of Asymptotic and Transient Behaviors of Stochastic Ratio-Dependent Predator–Prey Model

In this paper, we focus on the asymptotic and transient dynamics of the studied ecosystem and measure the response to perturbation of the stochastic ratio-dependent predator–prey model. The method we use is mainly based on the Kronecker product and numerical simulation. Firstly, the mean-square stability matrix can be calculated from the Kronecker product, so as to compute three indicators (root-mean-square resilience, root-mean-square reactivity and root-mean-square amplification envelope) of the response to perturbation for the studied ecosystem. Since the above-measured amounts cannot be obtained explicitly, we use numerical simulation to draw the changing figures within the appropriate parameter range. Then we obtain some conclusions by comparing the numerical results. When perturbing any populations, increasing the disturbance intensity will reduce the mean-square stable area of the system. Ecologists can manage the ecosystem, reduce losses and maximize benefits according to the numerical results of the root-mean-square amplification envelope.

Robust control design for delayed periodic piecewise time-varying systems with actuator faults

This paper is mainly focused on the stabilization problem of uncertain delayed periodic piecewise time-varying systems inclusive of disturbances and faults in actuators. More specifically, the considered system is encompassed of periodic dynamics, which exhibits the nature of switched systems with fixed switching sequence and dwell time. The control protocol is configured in the form of both the present and past state information of the addressed system with passive performance. Moreover, the proposed control approach discloses the stabilization issue mainly by resolving the effect of faults in actuator components. Precisely, the desired periodic gain matrices of the developed controller are calculated by way of solving some matrix inequalities which are derived by making use of Lyapunov stability theory and matrix polynomial approach. As a result, the asymptotic stability of the considered system is ensured in conjunction with satisfied disturbance attenuation index. Conclusively, the simulation results of two numerical examples including mass-spring damping system are presented for validating the theoretical result.

Homoclinic Renormalization Group Flows, or When Relevant Operators Become Irrelevant.

We study an N=1 supersymmetric quantum field theory with O(M)×O(N) symmetry. Working in 3-ε dimensions, we calculate the beta functions up to second loop order and analyze in detail the renormalization group (RG) flow and its fixed points. We allow N and M to assume general real values, which results in them functioning as bifurcation parameters. In studying the behavior of the model in the space of M and N, we demarcate the region where the RG flow is nonmonotonic and determine curves along which Hopf bifurcations take place. At a number of points in the space of M and N we find that the model exhibits an interesting phenomenon: at these points the RG flow possesses a fixed point located at real values of the coupling constants g_{i} but with a stability matrix (∂β_{i}/∂g_{j}) that is not diagonalizable and has a Jordan block of size two with zero eigenvalue. Such points correspond to logarithmic conformal field theories and represent Bogdanov-Takens bifurcations, a type of bifurcation known to give rise to a nearby homoclinic orbit-an RG flow that originates and terminates at the same fixed point. In the present example, we are able to employ analytic and numeric evidence to display the existence of the homoclinic RG flow.

Guaranteed‐cost finite‐time consensus of multi‐agent systems via intermittent control

The guaranteed‐cost finite‐time consensus control problem for a class of nonlinear multi‐agent systems with uncertain parameters was investigated. For a class of nonlinear multi‐agent systems with uncertain parameters, a periodic intermittent control strategy and a continuous feedback control strategy were designed, and the guaranteed‐cost consensus control of the system was investigated using Lyapunov stability theory and matrix inequality technology. Several sufficient conditions to achieve the guaranteed‐cost finite‐time consensus were obtained. It was demonstrated that the multi‐agent system could achieve consensus in a finite time under certain conditions, and the upper bound of the time was given to make the system achieve consensus in finite time. The upper bound of the guaranteed‐cost function was also obtained. Finally, simulations were provided to verify the effectiveness of the proposed method.

Moisture-induced autonomous surface potential oscillations for energy harvesting

A variety of autonomous oscillations in nature such as heartbeats and some biochemical reactions have been widely studied and utilized for applications in the fields of bioscience and engineering. Here, we report a unique phenomenon of moisture-induced electrical potential oscillations on polymers, poly([2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide-co-acrylic acid), during the diffusion of water molecules. Chemical reactions are modeled by kinetic simulations while system dynamic equations and the stability matrix are analyzed to show the chaotic nature of the system which oscillates with hidden attractors to induce the autonomous surface potential oscillation. Using moisture in the ambient environment as the activation source, this self-excited chemoelectrical reaction could have broad influences and usages in surface-reaction based devices and systems. As a proof-of-concept demonstration, an energy harvester is constructed and achieved the continuous energy production for more than 15,000 seconds with an energy density of 16.8 mJ/cm2. A 2-Volts output voltage has been produced to power a liquid crystal display toward practical applications with five energy harvesters connected in series.

Global quasi-synchronization of complex-valued recurrent neural networks with time-varying delay and interaction terms

In this article, the global quasi-synchronization of complex-valued recurrent neural networks (CVRNNs) with time-varying delays and interaction terms has been investigated. It is based on the standard Lyapunov stability theory and matrix measure method employed with the nonlinear Lipschitz activation functions. A sufficient condition for global quasi-synchronization of the complex-valued recurrent neural network model is shown in an effective way through a proper description of Lyapunov-stability technique. This article provides quite a new result for the CVRNNs having time-varying delays and interaction terms. Finally, a numerical example is considered to show the viability and unwavering quality of our theoretical results under several conditions.

Hydrogen generation via cross-linked glucomannan supported cobalt nano catalyst

Hydrogen generation through hydrolysis of sodium borohydride was examined over a series of supported cobalt nano particles as novel catalysts. For the first time extracted Glucomannan from Orchis Mascula used as a suitable matrix for preparation and stabilization of cobalt catalysts. Insoluble glucomannan obtained by polymerization reaction in the presence of MBA cross-linker and MAA monomer. Size, morphology and hydrogen generation activity of Co-glucomannan powders are studied by varying MAA/MBA ratios. XRD, XPS, FE-SEM and TEM techniques were used to characterization of obtained catalysts. All nano catalysts are formed in amorphous phase. Electron microscopic images confirmed that almost all particles are less than 10 nm. It is shown, cobalt particles are dispersed on the surface of glucomannan polymer without agglomeration. Catalytic activity of obtained Co-glucomannan are tested on hydrogen generation over hydrolysis of sodium borohydride reaction. Kinetic studies were applied to determine partial order respect to catalyst dosage and initial concentration of sodium borohydride. Finally, Arrhenius equation was used to find activation energy of hydrolysis sodium borohydride reaction over Co-glucomannan nano catalyst.

Nearest varOmega -stable matrix via Riemannian optimization

We study the problem of finding the nearest varOmega -stable matrix to a certain matrix A, i.e., the nearest matrix with all its eigenvalues in a prescribed closed set varOmega . Distances are measured in the Frobenius norm. An important special case is finding the nearest Hurwitz or Schur stable matrix, which has applications in systems theory. We describe a reformulation of the task as an optimization problem on the Riemannian manifold of orthogonal (or unitary) matrices. The problem can then be solved using standard methods from the theory of Riemannian optimization. The resulting algorithm is remarkably fast on small-scale and medium-scale matrices, and returns directly a Schur factorization of the minimizer, sidestepping the numerical difficulties associated with eigenvalues with high multiplicity.

Effect of sterilization methods on the mechanical stability and extracellular matrix constituents of decellularized brain tissues

The cell and matrix content in the central nervous system (CNS) regulates a number of fundamental neural processes and decellularized brain matrices have drawn attention for biomedical applications. However, the effect of sterilization methods on the structural/mechanical stability and cell/matrix contents have yet to be addressed. In this study, supercritical carbon dioxide (SC-CO2), ultraviolet (UV) irradiation and ethylene oxide (EtO) sterilizations were applied to SDS-decellularized sheep brain cortical slices, then subjected to mechanical test, quantification of DNA and extracellular matrix (ECM) protein contents. The cell and matrix morphology were quantitatively analyzed at light and scanning electron microscopical levels. The optimum parameters for SC-CO2 sterilization were 150 bar, 37 °C and 60 min, which ensured complete sterility along with EtO sterilization unlike UV treatment. Although histomorphometry revealed no significant alterations on cellular nuclear content of decellularized matrices, SC-CO2 entrained with 6% ethanol yielded better results with respect to preservation of ECM proteins.

Infliximab formulation strategy for a stable ileo-colonic targeted oral dosage form intended for the topical treatment of inflammatory bowel disease

Research shows that topically active infliximab therapy may be efficacious in the treatment of inflammatory bowel disease (IBD) with expected fewer side effects related to systemic exposure. Oral administration of infliximab with site-specific delivery could enable such therapy. In the present study, infliximab was incorporated in a sugar glass matrix (IFX-I) for additional stability and compounding flexibility after which IFX-I was compounded to ileo-colonic-targeted tablets containing 5 mg infliximab (ColoPulse-IFX). Potential critical steps in the production process that may decrease the formulation stability were identified and investigated. Furthermore, the long-term stability of IFX-I (6 months) and ColoPulse-IFX (12 months) stored either at room temperature (25 °C ± 2 °C/60% RH ± 5% RH) or refrigerated (5 °C ± 3 °C) was investigated according to ICH guidelines. Size-exclusion chromatography, fluorescence spectroscopy, and ELISA analyses were used to investigate the infliximab stability, content, tertiary protein structure, and potency at t0, t3, t6, t9, and t12 months. The coating performance of ColoPulse-IFX was investigated in a gastrointestinal simulation system at t0 and t12 months. All the analyses showed that IFX-I and ColoPulse-IFX were stable, potent, and that the coating performance was maintained during the entire storage period at both storage conditions. Thus, IFX-I is a stable dry-powder formulation and ColoPulse-IFX is a promising oral dosage form for the topical treatment of ileo-colonic IBD. This formulation strategy may serve as a new platform for the development of oral peptide or protein formulations that are targeted to the ileo-colonic region in IBD.

Heavy handed quest for fixed points in multiple coupling scalar theories in the \u03b5 expansion

The tensorial equations for non trivial fully interacting fixed points at lowest order in the ε expansion in 4 − ε and 3 − ε dimensions are analysed for N-component fields and corresponding multi-index couplings λ which are symmetric tensors with four or six indices. Both analytic and numerical methods are used. For N = 5, 6, 7 in the four-index case large numbers of irrational fixed points are found numerically where ‖λ‖2 is close to the bound found by Rychkov and Stergiou [1]. No solutions, other than those already known, are found which saturate the bound. These examples in general do not have unique quadratic invariants in the fields. For N ⩾ 6 the stability matrix in the full space of couplings always has negative eigenvalues. In the six index case the numerical search generates a very large number of solutions for N = 5.

Improved Algorithm for Nonlinear Programming with Inequality Constraints Based on Big Data Framework

With the development of network technology and electronic information technology, the nonlinear programming problem (NPP) with inequality constraints in the BD framework has become one of the research hotspots and one of the trends that need improvement. Due to the introduction of BD technology, there is still a lack of research on the situation where the objective function is a NPP. The purpose of this article is to use the analysis and computing power of BD technology to simulate and calulate nonlinear programming (NP) with inequality constraints and improve it. In this paper, with the help of stability conditions, matrix splitting and iteration theory, the alternate direction method is used to solve the NPP with inequality constraints, and the principle of compressed mapping is used to finally prove the convergence of the alternate direction method. Matrix splitting techniques and Gauss-Seidel iterative ideas construct an iterative algorithm for solving linear systems. The iterative format of the alternating direction method for solving NPPs with inequality constraints and the equivalent matrix format are given to prepare for further proof of the convergence of the algorithm. Experimental research shows that the NPP model with inequality constraints designed by the dynamic BP technology error correction GPC algorithm used in this article has faster response time and smaller overshoot, and the control effect is better than 20% of the traditional GPC algorithm.

Combined plasma–coil optimization algorithms

Combined plasma–coil optimization approaches for designing stellarators are discussed and a new method for calculating free-boundary equilibria for multiregion relaxed magnetohydrodynmics (MRxMHD) is proposed. Four distinct categories of stellarator optimization, two of which are novel approaches, are the fixed-boundary optimization, the generalized fixed-boundary optimization, the quasi-free-boundary optimization, and the free-boundary (coil) optimization. These are described using the MRxMHD energy functional, the Biot–Savart integral, the coil-penalty functional and the virtual casing integral and their derivatives. The proposed free-boundary equilibrium calculation differs from existing methods in how the boundary-value problem is posed, and for the new approach it seems that there is not an associated energy minimization principle because a non-symmetric functional arises. We propose to solve the weak formulation of this problem using a spectral-Galerkin method, and this will reduce the free-boundary equilibrium calculation to something comparable to a fixed-boundary calculation. In our discussion of combined plasma–coil optimization algorithms, we emphasize the importance of the stability matrix.

Synthesis of Selenium Sulfide Nanoparticles in Polysaccharide Arabinogalactan and Starch Matrices

New water-soluble SeS2 containing nanocomposites are obtained via ion-exchange interaction between selenous acid and ammonium sulfide in water using natural arabinogalactan and starch polysaccharides as nanoparticle stabilizers. The transmission electron microscopy, X-ray diffraction analysis, and dynamic light scattering data show that nanocomposites are formed as spherical crystalline SeS2 nanoparticles 5–140 nm in size, dispersed in polysaccharide matrices. The type of stabilization matrix and ratio of reactants have a decisive influence on the nanomorphological properties of the materials obtained.