Unstable Phase Research Articles

Symbiotic Ni3Se4/Ni heterostructure induced by unstable NiSe2 for enhanced hydrogen generation

Creating dual-site catalysts that can separately provide good OH and H interaction sites for water dissociation and hydrogen adsorption is proved to be an effective strategy for improving the activity of hydrogen generation in alkaline medium. However, there is still great challenge to construct a robust dual-site catalyst with multiple and efficient interfaces. Herein, taking thermodynamically unstable cubic NiSe2 phase as a self-sacrificial template, a symbiotic Ni3Se4/Ni heterostructure is successfully synthesized via in-situ electrochemical reduction of Ni3Se4/NiSe2 precatalyst. Density functional theory calculation suggests that the d-band center and electronic state of Ni sites are well optimized after forming the Ni3Se4/Ni heterostructure, which is favorable for the proper hydrogen adsorption. Benefiting from the good electrical conductivity, large electrochemical surface area, and distinct sites for water dissociation, Ni3Se4/Ni exhibits a low overpotential of 106 mV at −10 mA cm−2 for hydrogen generation in 1 M KOH.

Formulation Characterization and Pharmacokinetic Evaluation of Amorphous Solid Dispersions of Dasatinib.

The aim of this study was to improve the physicochemical properties and oral bioavailability of dasatinib (DST) by the amorphous solid dispersion (ASD) approach using cellulose acetate butyrate (CAB) as a carrier. Various formulations of ASD (DST:CAB 1:1 to 1:5) were prepared by the solvent evaporation method. ASDs were characterized for physicochemical attributes, stability and pharmacokinetics. Scanning electron microscopy, Fourier transformed infrared, X-ray powder diffraction, and differential scanning calorimetry confirmed the transformation of the crystalline drug into amorphous phase. ASD formation resulted in a 3.7-4.9 fold increase in dissolution compared to DST or physical mixture. The ASDs formulation exhibited relative stability against transformation from the unstable amorphous phase to a stable crystalline phase that was indicated by spectral and X-ray powder diffraction data, and insignificant (p > 0.05) decrease in dissolution. Tmax, Cmax and AUC0-∞ of ASD were 4.3-fold faster and 2.0 and 1.5 fold higher than the corresponding physical mixture. In conclusion, the ASD of DST significantly improved dissolution and oral bioavailability which may be translated into a reduction in dose and adverse events.

Supercritical hydrothermal synthesis of zirconia nanoparticles from zirconium basic carbonate

Zirconia nanoparticles were synthesized by using the supercritical hydrothermal method from zirconium basic carbonate, which is insoluble in water at ambient temperature. The diameters of these nanoparticles were 10–20 nm. They contained both tetragonal and monoclinic phases. A long treatment in supercritical water induced the phase transition from the tetragonal phase to the monoclinic phase with the desorption of carbonate ions. These results indicated that the carbonate ions absorbed on the surface works as a stabilizer of the unstable tetragonal phase. The process developed here allows us to bypass wastewater treatment along with the product refining because byproducts are only water and carbon dioxide.

Phase-resolved spectroscopic analysis of the eclipsing black hole X-ray binary M33 X-7: System properties, accretion, and evolution

M33 X-7 is the only known eclipsing black hole high mass X-ray binary. The system is reported to contain a very massive O supergiant donor and a massive black hole in a short orbit. The high X-ray luminosity and its location in the metal-poor galaxy M33 make it a unique laboratory for studying the winds of metal-poor donor stars with black hole companions and it helps us to understand the potential progenitors of black hole mergers. Using phase-resolved simultaneous HST- and XMM-Newton-observations, we traced the interaction of the stellar wind with the black hole. We observed a strong Hatchett-McCray effect in M33 X-7 for the full range of wind velocities. Our comprehensive spectroscopic investigation of the donor star (X-ray+UV+optical) yields new stellar and wind parameters for the system that differ significantly from previous estimates. In particular, the masses of the components are considerably reduced to ≈38 M⊙ for the O-star donor and ≈11.4 M⊙ for the black hole. The O giant is overfilling its Roche lobe and shows surface He enrichment. The donor shows a densely clumped wind with a mass-loss rate that matches theoretical predictions. An extended ionization zone is even present during the eclipse due to scattered X-ray photons. The X-ray ionization zone extends close to the photosphere of the donor during inferior conjunction. We investigated the wind-driving contributions from different ions and the changes in the ionization structure due to X-ray illumination. Toward the black hole, the wind is strongly quenched due to strong X-ray illumination. For this system, the standard wind-fed accretion scenario alone cannot explain the observed X-ray luminosity, pointing toward an additional mass overflow, which is in line with our acceleration calculations. The X-ray photoionization creates an He II emission region around the system emitting ∼1047 ph s−1. We computed binary evolutionary tracks for the system using MESA. Currently, the system is transitioning toward an unstable mass transfer phase, possibly resulting in a common envelope of the black hole and the O-star donor. Since the mass ratio is q ≳ 3.3 and the period is short, the system is unlikely to survive the common envelope, but will rather merge.

Friendship during patients’ stable and unstable phases of incurable cancer: a qualitative interview study

ObjectivesLittle is known about the added value of friendship during the care of intensive cancer disease trajectories. Friends, however, can play an important (caring-)role to increase their friends’ (mental) well-being....

Symptoms, performance status and phase of illness in advanced cancer: multicentre cross-sectional study of palliative care unit admissions

ObjectivesTo clarify the relationship between Phase of Illness at the time of admission to palliative care units and symptoms of patients with advanced cancer.MethodsThis study was a secondary analysis of...

Classification of progressive failure and mechanical behavior of dissimilar material hybrid joints at varying temperatures

This research illustrates the progressive failure mechanisms and variation in the mechanical behavior of dissimilar materials hybrid joints at elevated temperatures. For this purpose, a novel in-situ data fusion scheme was developed from experimental analysis which was validated through a coupled computational approach. The hybrid joint consisted of CFRP/Al worksheets joined through a steel bolt. The experimental analysis revealed distinct failure mechanisms in worksheets, i.e., yielding in Al sheet and a mixed failure mode in CFRP sheet while no signs of failure were observed in the steel bolt. Further, the progressive damage in the CFRP sheet was classified as a three-staged process which comprised elastic strain phase, crack initiation and progressive damage phase, and unstable fracture phase by correlating the temperature (Infrared Thermography) and strain variations (Digital Image Correlation). Further, degradation in mechanical behavior from room temperature was evaluated at three elevated temperatures, i.e., 50 °C, 75 °C, and 100 °C. A significant drop in mechanical properties (maximum strength and nominal stiffness) was noticed at high temperatures while a transition in failure mode was also evident (ply bending and pronounced fiber breakage) in comparison to the joints tested at room temperature. In computational analysis, Tsai–Wu, Maximum Stress, and Puck’s static failure criteria were coupled with the element deletion model to ascertain the critical ply and progressive damage in the joint. The experimental results were found in good agreement with the computational results in terms of critical ply and load-carrying behavior. In summary, this research helps to understand the progressive failure and variation in mechanical behavior about high temperatures in hybrid joints which can be extended to other dissimilar materials configurations as well.

On the understanding of a cryogenic two-phase LOX/GH2 flame: Parametric sensitivity, characteristic scaling and phase instability

This study concerns the cryogenic hydrogen combustion in subcritical pressure conditions, with practical relevance to rocket engine applications. A cryogenic two-phase flame in the counterflow configuration is calculated and analyzed with the consideration of real-fluid effects and heat/mass transfer across the liquid-gas interface. The effects of pressure, strain rate, fuel inlet temperature, and heat loss on the flame characteristic behaviors are examined. It is found that the vaporization rate of liquid oxidizer scales with the square-root of pressure (p) times strain rate (ast), and is not a limiting factor for combustion. The total heat release scales with past at lower strain rates while with p4/5ast1/3 at higher strain rates. The significant results on the phase-stability of cryogenic flame are also established. It is found that the unstable phase, in terms of vapor-liquid equilibrium, arises in the vicinity of the liquid-gas interface; however, all unstable-phase states still stay in the metastable region of the phase diagram. For all the flame solutions considered in this study, no thermochemical state enters the spinodal region.

Mathematical modelling and simulation investigation of the dynamic behaviour of a compliant 2-R robot by using N-E method Via Matlab/Simulink

This paper presents a mathematical modeling and simulation investigation on the effect of the equilibrium position on the stability and the energy provided by the robot by proposing four simulation cases. No closed solution for this critical study has been reported. An explicit elbow down model of a 2-R robot has been modelled by adding passive springs. The authors in this paper develop the dynamic of a compliant 2-R robot by using the extended Newton-Euler (N-E) method. The dynamic simulation is investigated by using Matlab/Simulink based on motion with jerk zero at the start-stop path, which guarantees less vibration to the robot’s articulations. The simulation of trajectory is realized by SolidWorks to import the results to Matlab/Simulink for the dynamical simulation. The simulation results show that the energy-saving and good robot stability can be achieved whenever the equilibrium position is close from the beginning of motion with avoiding the unstable phase of the robot during working.

Topology of critical points and Hawking-Page transition

Using the Bragg-Williams construction of an off-shell free energy we compute the topological charge of the Hawking-Page transition point for black holes in AdS. A computation following from a related off-shell effective potential in the boundary gauge dual matches the value of topological charge obtained in the bulk. We also compute the topological charges of the equilibrium phases of these systems, which follow from the saddle points of the appropriate free energy. The locally stable and unstable phases turn out to have topological charges opposite to each other, with the total being zero, in agreement with the result obtained from a related construction [arXiv:2208.01932].

Black holes surrounded by modified Chaplygin gas in Lovelock theory of gravity

The Lovelock theory of gravity is a natural extension of the Einstein’s theory of general relativity to higher dimensions, which presents the criteria of general covariance and is free of ghosts. In this work, we consider a model that static spherically-symmetric black hole is surrounded by the modified Chaplygin gas with equation of state p=Aρ−B/ρα. We find that the energy density of the modified Chaplygin gas can be characterized by four parameters. The black hole thermodynamical quantities, consisting of gravitational mass, temperature, entropy and heat capacity, as functions of horizon radius, are calculated. Concerning the thermodynamical stability of the black holes, we consider the third-order Lovelock gravity as a specific case and show in figures the heat capacity versus the horizon radius, observing that there exist a phase of thermodynamically stable small black hole and a phase of thermodynamically unstable large black hole for D=7, while an additional intermediate local unstable phase as well as an intermediate local stable phase appear for D=8 with configuring properly the model parameters. The effects of the modified Chaplygin gas and Lovelock gravity on thermodynamical stability of the black holes are discussed.

Enhanced Energy Density and Efficiency in Lead‐Free Sodium Niobate‐Based Relaxor Antiferroelectric Ceramics for Electrostatic Energy Storage Application

AbstractAntiferroelectric ceramics are recently, a research hotspot for electrostatic energy storage because of their large electric‐field induced polarization. Lead‐free sodium niobate (NaNbO3)‐based ceramics are one of the emerging antiferroelectric counterparts. However, the unstable antiferroelectric phase seriously restricts the further improvement of energy density and efficiency. In this work, by introducing binary perovskite end‐member BiFeO3–BaTiO3 with lower tolerance factor and average electronegativity into NaNbO3 ceramics, the stablized antiferroelectric phase with improved relaxation characteristic is identified by slim double‐like polarization‐electric field (P–E) loops and four‐peak current–electric field (I–E) curves. Meanwhile, the antiferroelectric P to R phase transition is verified through Raman spectra, X‐ray diffraction (XRD) patterns, and dielectric performance. In particular, the enhanced electric breakdown strength Eb is achieved by synergic contributions from ultralow dielectric loss, reduced grain size, and so on. Consequently, the sample with optimized composition displays ultrahigh recoverable energy storage density (Wrec) of 14.5 J cm−3 and satisfied efficiency (η) of 83.9%, which shows the superiority in the state‐of‐the‐art dielectric ceramics. These results provide a feasible route by regulating the relationship between antiferroelectric structure and properties to explore high‐performance dielectrics for electrostatic energy storage applications.

Tuning the melting point and phase stability of rare-earth oxides to facilitate their crystal growth from the melt

The challenge of growing rare-earth (RE) sesquioxide crystals can be overcome by tailoring their structural stability and melting point via composition engineering. This work contributes to the advancement of the field of crystal growth of high-entropy oxides. A compound with only small REs (Lu,Y,Ho,Yb,Er)2O3 maintains a cubic C-type structure upon cooling from the melt, as observed via in-situ high-temperature neutron diffraction on aerodynamically levitated samples. On the other hand, a compound with a mixture of small and large REs (Lu,Y,Ho,Nd,La)2O3 crystallizes as a mixture of a primary C-type phase with an unstable secondary phase. Crystals of compositions (Lu,Y,Ho,Nd,La)2O3 and (Lu,Y,Gd,Nd,La)2O3 were grown by the micro-pulling-down (mPD) method with a single monoclinic B-type phase, while a powder of (Lu,Y,Ho,Yb,Er)2O3 did not melt at the maximum operating temperature of an iridium-rhenium crucible. The minimization of the melting point of the two grown crystals is attributed to the mismatch in cation sizes. The electron probe microanalysis reveals that the general element segregation behavior in the crystals depends on the composition.

A proteomics analysis of neointima formation on decellularized vascular grafts reveals regenerative alterations in protein signature running head: Proteomics analysis of neointima formation.

Background: Neointima formation contributes to vascular grafts stenosis and thrombosis. It is a complex reaction that plays a significant role in the performance of vascular grafts. Despite its critical implications, little is known about the mechanisms underlying neointima formation. This study compares neointima proteome in different stages and plasma samples. Methods: Heterogenous acellular native arteries were implanted as abdominal aortic interposition grafts in a rabbit model. Grafts were harvested at 0.5, 1, 4, 6, 7, 14, 21, and 28days post-surgery for histological and proteomic analysis of the neointima. Results: Histological examination showed a transformed morphological pattern and components, including serum proteins, inflammatory cells, and regenerative cells. Proteomics analysis of the neointima showed distinct characteristics after 14days of implantation compared to early implantation. Early changes in the neointima samples were proteins involved in acute inflammation and thrombosis, followed by the accumulation of extracellular matrix (ECM) proteins. A total of 110 proteins were found to be differentially expressed in later samples of neointima compared to early controls. The enriched pathways were mainly protein digestion and adsorption, focal adhesion, PI3K-Akt signaling pathway, and ECM-receptor interaction in the late stage. All distributions of proteins in the neointima are different compared to plasma. Conclusion: The biological processes of neointima formation at different stages identified with proteome found developmental characteristics of vascular structure on a decellularized small vascular graft, and significant differences were identified by proteomics in the neointima of early-stage and late-stage after implantation. In the acute unstable phase, the loose and uniform neointima was mainly composed of plasma proteins and inflammatory cells. However, in the relatively stable later stage, the most notable results were an up-regulation of ECM components. The present study demonstrates an interaction between biological matter and vascular graft, provides insights into biological process changes of neointima and facilitates the construction of a functional bioengineered small vascular graft for future clinical applications.

Superior high-temperature piezoelectric performances in BF-PT-BT ceramics via electric field constructed phase boundary

Owing to the mutual restriction between piezoelectric coefficient (d33) and Curie temperature (Tc), the discovery of high-temperature piezoceramics with large d33 is highly desirable but challenging. Here, BiFeO3-BaTiO3-PbTiO3 (BF-BT-PT) ternary system is redesigned by combining the low lattice distortion of BF-BT perovskites and rhombohedral-tetragonal coexistence of BF-PT phase boundary. As a result, excellent comprehensive piezoelectric properties with a large d33 of ∼380 pC/N and a high Tc of ∼483 °C are obtained in a tetragonal composition close to the triple point. Interestingly, even though a c/a ratio as large as 1.04 can be detected in the virgin sample, hierarchical domains that macrodomains composed of nanosized stripe domains can be found. The tetragonal phase could partly transform into a monoclinic phase under electric field according to in-situ high-energy synchrotron X-ray diffraction measurement, constructing a field-induced morphotropic phase boundary. The large lattice distortion and unstable phase structure simultaneously contribute to the high Tc, and large d33 for the studied BF-BT-PT ceramics, respectively, showing great potential for high-temperature sensors and transducers.

Nonlinear dynamic behavior analysis of bridge pier impacted by a moving barge

The contradiction between ships and bridges is becoming increasingly prominent, and ship-bridge collision accidents occur frequently. However, the existing researches focus on the impact force, the bridge will be simplified to a single pier, but the single pier collision model cannot accurately reflect the dynamic behaviors and damage evolution process of collision. In order to solve this problem, a refined barge-whole bridge collision finite element model is established. This model can be used to analyze the dynamic characteristics of barge and whole bridge collision. According to finite element results, the impact force can be divided into four phases: (1) Linear elastic phase, (2) Buckling unstable phase, (3) Plastic deformation phase and (4) Unloading phase. The impact velocity and barge mass change the initial kinetic energy of the barge, which is positively correlated with the peak impact force and the duration of the impact force. Compared with the barge-single pier collision model, the barge-whole bridge collision model is more systematic and comprehensive in reflecting the dynamic behavior of collision. In this paper, the research of barge-bridge collision provides a scientific basic theoretical basis for the design of anti-collision facilities, the proposal of post-collision damage assessment techniques and the development of bridge post-collision warning system.

Correlation on precipitation parameters towards ferromagnetism and stabilization of the magnetite nanoparticles

The conventional synthesis methods of magnetite nanoparticles by hydrothermal required high temperature and aging process, which results in an unstable magnetite phase. In this work, the focus is on producing magnetite nanoparticles by simple and sustainable titration methods with the variable in parameters on the precipitate growth rate and structure of iron oxide nanoparticles utilizing a single sulphate precursor. Iron salt precursor hydrolysis was faster at temperatures of 30 ​°C and 45 ​°C; hence the number of hydroxyl ions (OH−) needed to reach the equivalence point for the precipitate to form is lower, creating the highest percentage of magnetite nanoparticles. However, at 45 ​°C, larger magnetite nanoparticles were obtained hence higher magnetization through lower coercivity. Precipitating agent rate of addition increase leads to reaction sequence delay, favoring goethite nanoparticle formation and lower magnetization. The novel understanding of precipitation parameter synergistic effect has resulted in promising ferromagnetic and stabilization properties of magnetite nanoparticle synthesis.

Hawking evaporation, shadow images, and thermodynamics of black holes through deflection angle

We study the Hawking evaporation process of the exact black hole with nonlinear electrodynamics for positive and negative coupling constant zeta . We provide a new perspective to study the thermodynamics of exact black hole through deflection angle formalism. We also evaluate the shadow images in the presence of deflection images for this black hole. Moreover, we consider the Gibbs energy optical dependence to investigate the Hawking-Page transition. We observe that evaporation rate depends upon zeta and black hole evaporates more quickly for positive zeta as compared to negative zeta . For the case zeta =-1, the black hole’s lifetime become infinite, which makes the black hole a remnant and the third law of black hole thermodynamics holds in this scenario. We show that the thermal variations in the deflection angle can be used to determine the stable and unstable phases of the black hole. Our findings show that large and small phase transitions of black hole occur at a specific value of the deflection angle.

Ancient acid rains in the Ediacaran period – An alternative story for sulfate sedimentation

Vast deposits of anhydrite and magnesite are widely distributed in the Ediacaran strata of East Siberia near the Riphean unconformity. Anhydrite-rich rocks are likely not of evaporitic origin and mostly occur in the forms of nodules, the layers of chicken-wire structures otherwise disseminated as tiny sulfatic forms amongst the terrigenous rocks. Here, we propose an alternative point of view for anhydrite origin: the enrichment and increase of sulfur content in the Ediacaran atmosphere is due to high volcanic activity. It is suggested that the ancient Earth's atmosphere could have also been influenced by powerful sulfuric acid rains that eroded the Precambrian dolomites, causing their aggressive degradation. Chemical reactions with dolomite and sulfuric acid showed that an unstable phase of bassanite occurred in the early stages, which later stabilised as anhydrite after heating as an analogue of ageing. Aggressive acids have caused global dolomite karstification of the Siberian craton with the appearance of Ediacaran strata in addition to sulfate phases, including magnesite and sulfurous phases of pyrite and barite.

A novel [formula omitted] adaptive-hybrid control with guaranteed stability for a class of uncertain nonlinear systems: A case study on SA330 Puma

The helicopter is a highly unstable nonlinear non-minimum phase multiple-input multiple-output (MIMO) system with strong coupling between degrees of freedom. Therefore, its modeling will cause many problems such as control complexity. In addition, hover and forward flight modes are one of the most widely used helicopter flight modes used in many operations. To achieve and stay in these situations, you need very precise settings and timely manual control of the bird. This paper seeks to provide an L1 adaptive-hybrid control method to solve helicopter control problems in the Koppler system. In this regard, three channels in the coupler system are considered for the design of this controller. The proposed controller also proves the stability of the system during switching between channels. The helicopter that is modeled in this research and its data is used to implement and simulate the Coupler system control is the SA330 Puma helicopter, which is a medium-sized twin-engine support helicopter, in the category of 6 tons, built by Eurocopter France (ECF), and is in service several domestic operators and the armed forces, including the British Air Force. This device is a completely unstable dynamic system. In addition to the inherent instability of this bird, by adding an external load hanging to this system, the challenge of controlling this system is doubled hence, it is necessary to maintain its stability by using a suitable control system. In the meantime, the modeling of the hanging load should be done in three dimensions and two planes, and like most of the work done, only the movement of the plane should not be considered. For this purpose, an L1 adaptive-hybrid control method is proposed and fully developed in the paper, then it is properly designed for the Coupler system, which contains three channels: Pitch, Roll, and Collective, taking into account the load hanging on the helicopter. Finally, by simulating the results, it can be seen that the main goals, even in the presence of various disturbances, have the desired, efficient, and very good performance.