Stability Range Research Articles

Attractors and bifurcation diagrams in complex climate models.

The climate is a complex nonequilibrium dynamical system that relaxes toward a steady state under the continuous input of solar radiation and dissipative mechanisms. The steady state is not necessarily unique. A useful tool to describe the possible steady states under different forcing is the bifurcation diagram, which reveals the regions of multistability, the position of tipping points, and the range of stability of each steady state. However, its construction is highly time consuming in climate models with a dynamical deep ocean, whose relaxation time is of the order of thousand years, or other feedback mechanisms that act on even longer time scales, like continental ice or carbon cycle. Using a coupled setup of the MIT general circulation model, we test two techniques for the construction of bifurcation diagrams with complementary advantages and reduced execution time. The first is based on the introduction of random fluctuations in the forcing and permits to explore a wide part of phase space. The second reconstructs the stable branches using estimates of the internal variability and of the surface energy imbalance on each attractor, and is more precise in finding the position of tipping points.

Green water-etching synthesized La-MIL-101(Fe)-NH2@SiO2 yolk-shell nanocomposites with superior pH stability for efficient and selective phosphorus recovery

Although MIL-101(Fe) has a homogeneous distribution of active metal sites, the relatively low stability of its coordination bonds limits its potential for application, especially in harsh environments. Here, a novel lanthanum-doped MIL-101(Fe)-NH2@mesoporous SiO2 yolk-shell (LMFN-YS) material, synthesized by green water-etching, has effectively improved the adsorption capacity and stability of MIL-101(Fe)-NH2. Compared to traditional acid-base etching methods, water etching offered a more co-friendly and cost-effective approach to producing yolk-shell structures. Due to the mesoporous protective shell of mesoporous SiO2 and more exposed active sites, the yolk-shell materials showed a faster adsorption rate (30 min) and a larger uptake capacity (240.0 mg P/g) than those of MIL-101. The material also exhibited broad range of pH stability from 2 to 10 and displayed good cyclic regeneration ability, with a removal efficiency of 75.9 % after three cycles. Additionally, it demonstrated excellent selectivity towards various coexisting anions such as Cl−, NO3−, SO42−, CO32− and HCO3− at diverse ionic strengths ranging from 0.001 to 1 M. The superior performance of L1MFN-YS (yolk-shell materials of La: Fe = 1:1) was attributed to a combination of factors, including ligand exchange between La(Fe)-OH and phosphates, Lewis acid-base interaction and electrostatic attraction. Additionally, high phosphate removal performance was observed in the real petrochemical wastewater (initial concentrations of 5.48 mg P/g) with a residual effluent concentration of 0.05 mg P/L, which was below the A-level standard of phosphate effluent in China (0.5 mg/L). This work provides a green method for preparing yolk-shell materials with improved ability to treat phosphate wastewater.

Comparison of combustion characteristics of MILD model combustor and multi-nozzle array model combustor fueled hydrogen-methane mixtures

Key issues facing the development of hydrogen gas turbines include achieving low NOx emissions on hydrogen-enriched fuels, prevention of flashback and thermoacoustic instability. The present experimental investigation shows the fuel feasibility of MILD combustion and multi-nozzle array combustion with hydrogen-enriched fuels. The combustion characteristics, such as the range of combustion stability, NOx/CO emissions, and reaction zone distribution, have been determined for hydrogen contents ranging from 0% to 50% by volume. Compared to the MILD model combustor, the multi-nozzle array model combustor can achieve a broader range of stable combustion up to 40% by volume. As the hydrogen content increases from 0% to 40% by volume, the lean blowout (LBO) temperature of the multi-nozzle array model combustor decreases from 1600 K to 1400 K. When the hydrogen content reaches 50% of the volume, both the MILD model combustor and the multi-nozzle array model combustor exhibit thermoacoustic instability at high equivalence ratios. For the multi-nozzle array model combustor, NOx emissions are less than 20 ppm@15% O2 and CO emissions are less than 30 ppm@15% O2 in the adiabatic temperature range of 1400 K–2100 K. NOx emissions of the multi-nozzle array combustor are higher than that of the MILD combustor, but remain ultra-low due to the flue gas recirculation ratio. With increasing hydrogen content, the reaction zone becomes more concentrated along the axial and radial directions. The lift-off height of the reaction zone is 1.6 nozzle diameters at 40% by volume hydrogen content, which ensures the safety of the nozzles and prevent flashback.

Optimization of operation mode and design parameters of a finely-dispersed metallic liquid-alloy generator

During the process of designing new devices for the high-speed metallization process, there appears the necessity to define the stable operation range and search for the optimum values of the operation mode and design parameters. This paper describes a process of optimization of a device made for depositing low-melting metal coatings, based on the rocket chamber operation principle. The paper presents an analysis of the objective function surface response metallizer operation performance. On the basis of this analysis the optimal values of fuel mass flow rate and excess oxidant ratio were determined. The choice of fuel and oxidizer throttling orifice cross-section areas was substantiated, the value of the throat cross-section for the metallizer flow-path was found. The expected performance of the designed device was also determined.

Probing structural evolutions in GdVO4 under extreme thermodynamic conditions

Externally applied Pressure and temperature parametres can influence the stability of any material and can also elucidate the stability range of material. The present manuscript reports pressure and temperature-induced structural phase progression/stability in GdVO4, a rare-earth vanadate synthesized using a solid-state reaction. The synthesized sample had a zircon crystalline structure and the expected phonon/vibrational modes. High-pressure XRD studies up to 27.1 GPa revealed a structural transition from ambient zircon to scheelite phase which was found to be initiated at about 0.4 GPa and completed at 12.2 GPa. The pressure induced changes in the lattice parameters as well as unit cell volumes were deduced and the third order Birch-Murngahan equation was used to fit the pressure-volume data. The bulk modulus of zircon and scheelite phases was found to be 85.1 GPa and 145.2 GPa respectively. The temperature-dependent Raman measurements reveal good structural phase stability of zircon structure in the temperature range of 80–440 K. All the phonon modes except one, showed phonon softening with an increase in temperature. Finally, the anharmonic contributions associated with temperature dependent shifts in a few of the Raman modes are calculated in terms of the anharmonic constants.

Laser written mirror profiles for open-access fiber Fabry-Perot microcavities.

We demonstrate laser-written concave hemispherical structures produced on the endfacets of optical fibers that serve as mirror substrates for tunable open-access microcavities. We achieve finesse values of up to 200, and a mostly constant performance across the entire stability range. This enables cavity operation also close to the stability limit, where a peak quality factor of 1.5 × 104 is reached. Together with a small mode waist of 2.3 µm, the cavity achieves a Purcell factor of C ∼ 2.5, which is useful for experiments that require good lateral optical access or otherwise large separation of the mirrors. Laser-written mirror profiles can be produced with a tremendous flexibility in shape and on various surfaces, opening new possibilities for microcavities.

Rock fragmentation and drilling experiment of electric impulse drilling and structural optimization of electrode bit

Due to the low rate of penetration (ROP) and high cost of natural resource development projects such as oil and gas, and mining, it's urgent to explore some new rock-breaking methods with subversive characteristics for rising ROP. Electric impulse drilling (EID) has attracted widespread attention due to its unique advantages, but its rock-breaking effect is affected by various factors such as the structures of electrode bits, pulse voltage characteristics, liquid medium type, rock type, circulation conditions, and the contact between electrode bit and rocks, etc, leading to the lack of theoretical basis for the design of the electrode bit. Therefore, to more truly reflect the interaction among electrode bits, rocks, and liquid media of EID, this study carried out rock fragmentation and drilling experiment of EID on red sandstone. Firstly, an electrical impulse generator (EIG) with a stable frequency range of 1–5 Hz and a pulse voltage of about 0–80 kV at the load terminal was developed. And an indoor EID and rock fragmentation experimental system was built, then three kinds of electrode bits with typical structures: petal-type (H type), cross-type (S type) and, coaxial type (T type) were designed. Subsequently, the rock fragmentation and drilling experiment of EID was carried out on red sandstone in three liquid media (tap water, deionized water, and hydraulic oil) under the capacitors' charging voltage of 13–17 kV (the load terminal voltage was about 45–60 kV). The general influence law of electrode bit structure, liquid medium type, circulation condition, and pulse voltage on EID was studied. Finally, the electrode bits used in the experiment were evaluated, and suggestions for structural optimization of the electrode bit were put forward based on the experiment. This study is expected to further promote the design of electrode bits and the development of EID technology.

Structure and Bonding in Amorphous Red Phosphorus.

Amorphous red phosphorus (a-P) is one of the remaining puzzling cases in the structural chemistry of the elements. Here, we elucidate the structure, stability, and chemical bonding in a-P from first principles, combining machine-learning and density-functional theory (DFT) methods. We show that a-P structures exist with a range of energies slightly higher than those of phosphorus nanorods, to which they are closely related, and that the stability of a-P is linked to the degree of structural relaxation and medium-range order. We thus complete the stability range of phosphorus allotropes [Angew. Chem. Int. Ed. 2014, 53, 11629] by now including the previously poorly understood amorphous phase, and we quantify the covalent and van der Waals interactions in all main phases of phosphorus. We also study the electronic densities of states, including those of hydrogenated a-P. Beyond the present study, our structural models are expected to enable wider-ranging first-principles investigations-for example, of a-P-based battery materials.

Struktur und Bindung im amorphen roten Phosphor**

AbstractAmorpher roter Phosphor (a‐P) stellt eine der verbleibenden Herausforderungen in der Strukturchemie der Elemente dar. In diesem Beitrag klären wir Struktur, Stabilität und chemische Bindung im a‐P auf Grundlage voraussetzungsfreier Rechnungen auf, indem wir maschinelles Lernen und dichtefunktionaltheoretische (DFT‐) Methoden kombinieren. Wir zeigen, dass die Energien von a‐P‐Strukturen leicht höher liegen als jene von Phosphor‐Nanostäben, mit denen sie eng verwandt sind, und dass die Stabilität von a‐P mit dem Grad an struktureller Relaxation und mittelreichweitiger Ordnung verknüpft ist. Wir vervollständigen damit die Stabilitätsreihe der Phosphorallotrope [Angew. Chem. Int. Ed. 2014, 53, 11629], indem wir die bislang unvollständig verstandene amorphe Phase hinzufügen, und wir quantifizieren die kovalenten und van‐der‐Waals‐Wechselwirkungen in allen wichtigen Phasen des Phosphors. Wir untersuchen darüberhinaus die elektronische Zustandsdichte, einschließlich jener des wasserstoffhaltigen a‐P. Über die vorliegende Arbeit hinaus erwarten wir, dass unsere Strukturmodelle weiterführende voraussetzungsfreie Untersuchungen ermöglichen werden – beispielsweise zu a‐P‐basierten Batteriematerialien.

Experimental study on combustion and thermal characteristics of impinging premixed flames for low heating value gas (LHVG) fuels

The combustion and thermal characteristics of impinging premixed flames for low heating value gases (LHVGs) composed of methane, propane, and nitrogen are experimentally investigated. For the experiment, a combustor with an impingement plate is used to study the flame stability regions based on flame shapes and visualize OH radical distribution. The OH radical distribution is observed via OH* chemiluminescence and OH planar laser-induced fluorescence (OH-PLIF). Thermal characteristics are investigated by measuring the temperature distribution of the plate and the heat transfer rate into the cooling water. The results show that the flame stability region narrows as the heating value of the fuels decreases. Also, as the equivalence ratio increases (i.e., »1), the flame stability region is expanded. The OH radical intensity of LHVGs is observed to be lower than that of methane. The OH-PLIF images show where OH radicals are more distributed in the flame. The temperature distribution of the plate is determined by the flame shape according to the heating value, and the heat transfer rate into the water has a linear tendency to the fuel's thermal power. Based on these findings, LHVGs can be utilized without system improvement within the flame stability range in the impinging flame system.

Design of Folate-Containing Liposomal Nucleic Acid Delivery Systems for Antitumor Therapy.

The delivery of therapeutic nucleic acids is a prospective method for the treatment of both inherited and acquired diseases including cancer. To achieve maximal delivery efficiency and selectivity, nucleic acids should be targeted to the cells of interest. In the case of cancer, such targeting may be provided through folate receptors overexpressed in many tumor cells. For this purpose, folic acid and its lipoconjugates are used. Compared to other targeting ligands, folic acid provides low immunogenicity, rapid tumor penetration, high affinity to a wide range of tumors, chemical stability, and easy production. Different delivery systems can utilize targeting by folate ligand including liposomal forms of anticancer drugs, viruses, and lipid and polymer nanoparticles. This review focuses on the liposomal gene delivery systems that provide targeted nucleic acid transport into tumor cells due to folate lipoconjugates. Moreover, important development step, such as rational design of lipoconjugates, folic acid content, size, and ζ-potential of lipoplexes are discussed.

Abstract 644: Angiogenic Blood Vessels Reconfigure/ Attenuate Hypoxic Tumor Microenvironments In A Quantitative In Vitro Model

Introduction: Angiogenesis is crucial in the spread of cancer cells, and hypoxic tumor microenvironment (TME) plays a vital role in its initiation. Hypoxia stimulates the release of pro-angiogenic factors, promoting the growth of new blood vessels towards the tumor, which further alters the TME. The variation of in vivo hypoxic TME have been studied recently. However, due to technical limitations such as highly invasive procedure, high cost, tedious process, and poor signal-to-noise ratio, it is challenging to perform quantitative oxygen sensing. Here we develop an advanced in vitro model directly investigating the interaction between a solid tumor and blood vessels for an extended period. Hypothesis: The angiogenic blood vessels can reconfigure and attenuate the hypoxic TME, which can be directly measured Methods: The model is built using a microfluidic device with a sealed microwell for 3D tumor spheroid culture (human colon cancer cell line, HCT116), and a microfluidic channel beneath the microwell for endothelium formation (human umbilical vein endothelial cell, HUVEC), connected by a small hole for interaction between the cell types. Oxygen sensitive fluorescence particles are distributed in the hydrogel matrix, and the widefield frequency domain fluorescence lifetime imaging microscopy (FD-FLIM) is exploited to reliably characterize the oxygen tension around the tumor spheroid with minimal sensitivity to ambient optical noise. Results: The oxygen tension of TME around the tumor spheroid within the distance of 0 to 0.7 mm rapidly decreases during tumor growth, from 15% at day 1 to less than 6% at day 14. The presence of endothelial cells slows down this decreasing rate and maintains it in a stable range, from 16% to 14%. The average oxygen tension difference between the two experiments, with and without co-culture of endothelial cells, is statistically significant after 5 days of observation (p<0.01). Conclusions: We develop a quantitative in vitro method to study the hypoxic TME for its dynamic pattern and as a target for cancer treatment. By observing the effect of angiogenesis on it, this method can aid in exploring optimal cancer management strategies, such as chemotherapy, immunotherapy, tailored anti-angiogenic agents and other targeted therapies.

On the analyticity of the pressure for a non-ideal gas with high density boundary conditions

We consider a continuous system of classical particles confined in a cubic box Λ interacting through a stable and finite range pair potential with an attractive tail. We study the Mayer series of the grand canonical pressure of the system pΛω(β,λ) at inverse temperature β and fugacity λ in the presence of boundary conditions ω belonging to a very large class of locally finite particle configurations. This class of allowed boundary conditions is the basis for any probability measure on the space of locally finite particle configurations satisfying the Ruelle estimates. We show that the pΛω(β,λ) can be written as the sum of two terms. The first term, which is analytic and bounded as the fugacity λ varies in a Λ-independent and ω-independent disk, coincides with the free-boundary-condition pressure in the thermodynamic limit. The second term, analytic in a ω-dependent convergence radius, goes to zero in the thermodynamic limit. As far as we know, this is the first rigorous analysis of the behavior of the Mayer series of a non-ideal gas subjected to non-free and non-periodic boundary conditions in the low-density/high-temperature regime when particles interact through a non-purely repulsive pair potential.

Mechanism study on the effect of self-circulating casing treatment with different circumferential coverage ratios on the axial compressor stability

To reveal the mechanisms underlying the effect of self-circulating casing treatment with different circumferential coverage ratios on the stability of the axial compressor, a three-dimensional unsteady numerical was hereby conducted on Rotor 35. The circumferential coverage ratios of self-circulating casing of 20%, 40%, 60%, and 80% were designed, respectively. The calculated results point out that all the schemes effectively expand the stable working range of the compressor and that the expansion effect is positively correlated with the circumferential coverage ratio. The self-circulating casing with an 80% circumferential coverage ratio exhibits the highest stall margin improvement at 14.83%. The internal flow field analysis shows that the underlying mechanism for the compressor stability increasing with the increase in the circumferential coverage ratio is that after the flows with a higher circumferential speed component enter the self-circulating casing suction port, sufficient circumferential space is required to complete the transformation in the flow direction, so that the flows can smoothly enter the self-circulating casing and subsequent development can be carried out. The larger circumferential size of the self-circulating casing creates favorable conditions for more airflows to enter the self-circulating casing. With the increase in the circumferential coverage ratio, the suction effect of self-circulating casing on low-speed fluid at the blade tip and the bleeding mass flow rate is larger, and a better compressor expansion effect is thereby achieved.

Intelligent control chamber for plasma-enhanced combustion

At present, there are some problems with aero-engine, such as insufficient high-altitude point/flameout boundary, smoke in large conditions, and easy flameout in slow trains with poor oil, which seriously threaten flight safety. Aiming at the problem of insufficient high altitude stable combustion range, an intelligent control combustor of plasma-enhanced combustion is proposed in this paper. The sliding arc exciter is perfectly combined with the combustor head and the pre-burning sliding arc jet igniter is used as the technical basis of the enhanced combustion. Based on the working environment and service state of the engine, a set of the control system is designed for active control. The influence of the installation of the exciter on the combustion flow field is explored, and the feasibility of the exciter for widening the point flameout boundary and improving the combustion efficiency is verified. A set of the control scheme is proposed. The research shows that: the exciter can realize the integration of ignition and combustion support in the combustion chamber. After the exciter is started, the ignition boundary is widened by about 17.6% on average, and the flameout boundary is widened by about 45.3% on average. The combustion efficiency can be increased by 9.28%, which indicates the feasibility of the combustion chamber.

Grain structure influence on synchronized two-dimensional spin-Hall nano-oscillators

Nanoconstriction spin-Hall nano-oscillators (NC-SHNOs) are excellent devices for a wide variety of applications, from RF communication to bio-inspired computing. NC-SHNOs are easy to fabricate in large arrays, are CMOS compatible, and feature a narrow linewidth and high output power. However, in order to take full advantage of the device capabilities, a systematic analysis of the array behavior with respect to the number and dimensions of oscillators, the temperature of operation, and the influence of layer quality is needed. Here, we focus on micromagnetic simulations of 2 × 2 and 4 × 4 NC-SHNO arrays with single oscillators separated by up to 300 nm. We observe a synchronization scheme that allows for column-wise selection of the oscillation frequency for a larger pitch. However, for smaller pitches, a coherent oscillation volume was observed, and this volume included both the constrictions and extended beyond that region. A local variation in the exchange coupling in the active oscillator region was investigated by placing physical grains in the free magnetic layer, and it was shown to influence both the stable current range and the resulting frequency and output power. De-coupling the oscillators along rows or columns could provide higher power due to more favorable phase shifts between oscillators. Our investigation helps in achieving a deeper understanding of the intrinsic working principles of NC-SHNO arrays and how they reach fully synchronized states, and this will help to expand non-conventional computing capabilities.

Efficacy of Hinged Ankle–Foot Orthosis on Gait Improvement of Children with Spastic Diplegic Cerebral Palsy: A Literature Review

Purpose: The purpose is to study the effect of hinged ankle–foot orthosis (HAFO) on gait kinematics and temporospatial parameters of children with diplegic cerebral palsy. Methods: A literature search has been conducted from 2005 to 2022 to find the studies measuring the effect of HAFO on children with diplegic spastic cerebral palsy (CP) during gait through various bibliographic databases: PubMed, Scopus, EMBASE, O and P Virtual Library and Google Scholar. Results: We found 96 pieces of potentially relevant literature from which only six studies met the inclusion criteria were included. One hundred and fifty-three participants, with a mean age of 8.6 years (4–17 years), were investigated, of which 128 were spastic diplegic CP. Among spastic diplegic, 45 individuals were identified as walking with true equinus gait and 34 with jump gait. Gait parameters of participants were evaluated with ankle–foot orthoses (AFO) (hinged, solid and supramalleolar orthosis), and barefoot walking conditions showed improvement in some kinematic and spatial-temporal parameters, making their gait closer to that of typically developing children. Conclusion: HAFO was found very satisfactory, as it improves dynamic stability and ankle range of motion resulting in a more natural gait in children with spastic diplegic CP.

Nonlinear stability of two dusty magnetic liquids surrounded via a cylindrical surface: impact of mass and heat spread

The current article examines a nonlinear axisymmetric streaming flow obeying the Rivlin–Ericksen viscoelastic model and overloaded by suspended dust particles. The fluids are separated by an infinite vertical cylindrical interface. A uniform axial magnetic field as well as mass and heat transmission (MHT) act everywhere the cylindrical flows. For the sake of simplicity, the viscous potential theory (VPT) is adopted to ease the analysis. The study finds its significance in wastewater treatment, petroleum transport as well as various practical engineering applications. The methodology of the nonlinear approach is conditional primarily on utilizing the linear fundamental equations of motion along with the appropriate nonlinear applicable boundary conditions (BCs). A dimensionless procedure reveals a group of physical dimensionless numerals. The linear stability requirements are estimated by means of the Routh–Hurwitz statement. The application of Taylor’s theory with the multiple time scales provides a Ginzburg–Landau equation, which regulates the nonlinear stability criterion. Therefore, the theoretical nonlinear stability standards are determined. A collection of graphs is drawn throughout the linear as well as the nonlinear approaches. In light of the Homotopy perturbation method (HPM), an estimated uniform solution to the surface displacement is anticipated. This solution is verified by means of a numerical approach. The influence of different natural factors on the stability configuration is addressed. When the density number of the suspended inner dust particles is less than the density number of the suspended outer dust particles, and vice versa, it is found that the structure is reflected to be stable. Furthermore, as the pure outer viscosity of the liquid increases, the stable range contracts, this means that this parameter has a destabilizing effect. Additionally, the magnetic field and the transfer of heat don’t affect the nature of viscoelasticity.

Stability and Esterification Activity of Candida rugosa Lipase Immobilized on Celite with Acetone Solvent

Candida rugosa lipase (CRL) is an enzyme that is widely used in biopharmaceutical and biopesticide industries due to its high catalytic ability and reusability. However, conditions from industrial processes that are often outside CRL stability range may cause denaturation or destabilization of the enzyme, causing it to be not reusable, hence lowering its economic value. To increase its catalytic activity, stability, and reusability, CRL enzyme can be immobilized in a matrix. In this study, the CRL was physically adsorbed onto Celite-545. The immobilization process was done using buffer solution with the addition of acetone. The influence of initial enzyme concentration and immobilization condition (time, temperature, and pH) were optimized using OFAT method. The data were taken in terms of esterification activity, thermal stability, and protein content. The result showed good thermal stability of the immobilized biocatalysts and an increase in esterification activity at optimum conditions that supported the efficiency of Celite-545 as lipase immobilization supports.

Critical review of a paper about limits of stability of carbon dioxide in terms of temperature up to 1000 ℃ and pressure up to 100 atm

The thermal decomposition of carbon dioxide (CO2) has been dealt by many authors to determine the necessary conditions to break down the molecules of CO2, generally at very high temperature (more than 1000 K) or/and with a catalyst and at atmospheric pressure. The goal of our work was to investigate the stability range of CO2 molecule as a function of temperature (less than 1000 °C) and pressure (up to 100 atm), to estimate if the CO2 is a good candidate for thermal compression. The only work about thermal stability of CO2 was published by M. H. LIETZKE and C. MULLINS in 1981. Our results did not match theirs. Therefore, the stability range of CO2 remains unknow.