Unstable Phase Research Articles

Progenitors of low-mass binary black-hole mergers in the isolated binary evolution scenario

Context. The formation history, progenitor properties, and expected rates of the binary black holes discovered by the LIGO-Virgo collaboration via the gravitational-wave emission during their coalescence are a topic of active research. Aims. We aim to study the progenitor properties and expected rates of the two lowest-mass binary black hole mergers, GW151226 and GW170608, detected within the first two Advanced LIGO-Virgo observing runs, in the context of the classical isolated binary-evolution scenario. Methods. We used the publicly available 1D-hydrodynamic stellar-evolution code MESA, which we adapted to include the black-hole formation and the unstable mass transfer developed during the so-called common-envelope phase. Using more than 60 000 binary simulations, we explored a wide parameter space for initial stellar masses, separations, metallicities, and mass-transfer efficiencies. We obtained the expected distributions for the chirp mass, mass ratio, and merger time delay by accounting for the initial stellar binary distributions. We predicted the expected merger rates and compared them with those of the detected gravitational-wave events. We studied the dependence of our predictions with respect to the (as yet) unconstrained parameters inherent to binary stellar evolution. Results. Our simulations for both events show that while the progenitors we obtained are compatible over the entire range of explored metallicities, they show a strong dependence on the initial masses of the stars, according to stellar winds. All the progenitors we found follow a similar evolutionary path, starting from binaries with initial separations in the 30−200 R⊙ range experiencing a stable mass transfer interaction before the formation of the first black hole, followed by a second unstable mass-transfer episode leading to a common-envelope ejection that occurs either when the secondary star crosses the Hertzsprung gap or when it is burning He in its core. The common-envelope phase plays a fundamental role in the considered low-mass range: only progenitors experiencing such an unstable mass-transfer phase are able to merge in less than a Hubble time. Conclusions. We find integrated merger-rate densities in the range 0.2–5.0 yr−1 Gpc−3 in the Local Universe for the highest mass-transfer efficiencies explored here. The highest rate densities lead to detection rates of 1.2–3.3 yr−1, which are compatible with the observed rates. The common-envelope efficiency αCE has a strong impact on the progenitor populations. A high-efficiency scenario with αCE = 2.0 is favoured when comparing the expected rates with the observations.

Thermodynamics of AdS black holes from deflection angle formalism

We explore a link between AdS black hole thermodynamics and the deflection angle variation. Using the elliptic function analysis, we first study the phase structure of RN-AdS solutions in terms of optical aspects. Precisely, we find that the stable and the unstable phases can be derived from thermal variations of the deflection angle. Then, we investigate the Hawking-Page transition from the Gibbs energy optical dependence. Among others, we reveal that the large black hole/small black hole transition occurs at a specific value of the deflection angle. The finding results, being confirmed by the help of the Ruppeiner metric of the phase state space, indicate that the deflection angle can be exploited to unveil data on thermodynamics of AdS black holes.

Enhanced mechanical properties of as-cast Mg-Al-Ca magnesium alloys by friction stir processing

Friction stir processing (FSP) of as-cast Mg-7Al, Mg-4Al-3Ca (AX43), and Mg-2Al-5Ca (AX25) magnesium alloys led to the remarkable grain refinement and enhancement of mechanical properties. This is due to the replacement of the interconnected, brittle constituents with uniformly dispersed fine particles after FSP. Due to the presence of thermally-stable Al-Ca intermetallics, the calcium-containing alloys showed more intense grain refinement compared to the Mg-7Al alloy with unstable Mg17Al12 phase. The friction stir processed AX43 alloy with a grain size of 1.7 μm exhibited the best tensile properties.

Robust Fractional Order Attitude Controller for Launch Vehicle with Flexible Dynamics

The importance of Fractional Order Proportional Integral Differential (FOPID) controller is increased due to the presence of two design parameters more than the conventional PID controller. This paper uses of these additional degrees of freedom in designing the attitude controller for launch vehicle system with unstable rigid body dynamics and flexible dynamics. The parameters of the controller are designed to meet time domain specifications by optimizing the performance indices using genetic algorithms. The proposed tracking controller exhibits the robustness property to the parameter variations during highly unstable atmospheric phase of the attitude controller. The tracking performance of the controller is analysed with flexible vehicle dynamics in presence of two bending modes. The proposed controller can reduce the steady state error by 30% and the settling time is reduced by 50%. The time domain analysis confirms the effectiveness of the proposed controller even in the presence of unmodelled dynamics and wind disturbance without losing stability of launch vehicle. In order to assure the robustness property of the proposed controller, the plant parameters such as control moment coefficient and aerodynamic coefficients are varied by 25%. The tracking performance with these off nominal parameters shows only 1% deviation from the response of plant with nominal parameters.

Phase Diagrams of Ternary π-Conjugated Polymer Solutions for Organic Photovoltaics.

Phase diagrams of ternary conjugated polymer solutions were constructed based on Flory-Huggins lattice theory with a constant interaction parameter. For this purpose, the poly(3-hexylthiophene-2,5-diyl) (P3HT) solution as a model system was investigated as a function of temperature, molecular weight (or chain length), solvent species, processing additives, and electron-accepting small molecules. Then, other high-performance conjugated polymers such as PTB7 and PffBT4T-2OD were also studied in the same vein of demixing processes. Herein, the liquid-liquid phase transition is processed through the nucleation and growth of the metastable phase or the spontaneous spinodal decomposition of the unstable phase. Resultantly, the versatile binodal, spinodal, tie line, and critical point were calculated depending on the Flory-Huggins interaction parameter as well as the relative molar volume of each component. These findings may pave the way to rationally understand the phase behavior of solvent-polymer-fullerene (or nonfullerene) systems at the interface of organic photovoltaics and molecular thermodynamics.

Optically Unstable Phase from Ion-Ion Interactions in an Erbium-Doped Crystal.

Optical many-body systems naturally possess strong light-matter interactions and are thus of central importance for photonic applications. However, these applications are so far limited within the regime of intrinsic dynamically stable phases, and the possibility of unstable phases remains unidentified. Here we experimentally revealed a new dynamical phase of intrinsic optical instability by using a continuous-wave laser to drive an erbium-doped crystal. The transmission through the sample became unstable for intense laser inputs, and transient net gain was observed if the light passed the sample twice. The phase transition, between states in and out of a dynamical equilibrium, was induced by the dipole-dipole interactions between nearby erbium ions.

Study of Ageostrophy during Strong, Nonlinear Eddy-Front Interaction in the Gulf of Mexico

AbstractThe Loop Current (LC) system has long been assumed to be close to geostrophic balance despite its strong flow and the development of large meanders and strong frontal eddies during unstable phases. The region between the LC meanders and its frontal eddies was shown to have high Rossby numbers indicating nonlinearity; however, the effect of the nonlinear term on the flow has not been studied so far. In this study, the ageostrophy of the LC meanders is assessed using a high-resolution numerical model and geostrophic velocities from altimetry. A formula to compute the radius of curvature of the flow from the velocity field is also presented. The results indicate that during strong meandering, especially before and during LC shedding and in the presence of frontal eddies, the centrifugal force becomes as important as the Coriolis force and the pressure gradient force: LC meanders are in gradient-wind balance. The centrifugal force modulates the balance and modifies the flow speed, resulting in a subgeostrophic flow in the LC meander trough around the LC frontal eddies and supergeostrophic flow in the LC meander crest. The same pattern is found when correcting the geostrophic velocities from altimetry to account for the centrifugal force. The ageostrophic percentage in the cyclonic and anticyclonic meanders is 47% ± 1% and 78% ± 8% in the model and 31% ± 3% and 78% ± 29% in the altimetry dataset, respectively. Thus, the ageostrophic velocity is an important component of the LC flow and cannot be neglected when studying the LC system.

Occurrence and timely management of problems requiring prompt intervention among Indigenous compared with non-Indigenous Australian palliative care patients: a multijurisdictional cohort study

ObjectivesAnticipation and prompt relief of symptoms among patients with a life-limiting illness is a core element of palliative care. Indigenous Australians commonly encounter cultural barriers in healthcare that may impair...

Research and Analysis of Generalized Predictive Identification Algorithm Based On Nonlinear System in Control Field of Hydropower Industry

Due to the uncertainties, constraints, nonlinearity and the correlation among variables in the control of hydropower industry, it is difficult to obtain the accurate mathematical model. In this paper, a generalized predictive identification algorithm based on the nonlinear system in the control field of hydropower industry is presented, and a model of the generalized predictive identification algorithm based on the nonlinear system in the control field of hydropower industry is established AB simulation. The simulation results show that the algorithm is robust, can effectively overcome the system delay, and can be applied to the open-loop unstable non minimum phase system. It has strong applicability in the field of electric industry control and can produce good economic benefits.

Autowave Description of Plasticity of Materials with an Unstable Phase Structure at the Macroscale Level

We consider the regularities of a plastic flow in materials with strain-induced phase transformation in titanium nickelide and trip steel as examples. The experimental analysis of plastic deformation processes has been carried out using the technique of digital correction of speckle images, which makes it possible to describe quantitatively the behavior of plasticity fronts associated with phase transformation in the given materials. The mechanisms of formation of the Luders fronts as well as the Portevin–Le Chatelier fronts at different stages of the plastic flow are considered.

WOCS 5379: Detailed Analysis of the Evolution of a Post-mass-transfer Blue Straggler

Abstract The blue straggler binary WOCS 5379 is a member of the old (6–7 Gyr) open cluster NGC 188. WOCS 5379 comprises a blue straggler star with a white dwarf companion in a 120 day eccentric orbit. Combined with the orbital period, this helium white dwarf is evidence of previous mass transfer by a red giant. Detailed models of the system evolution from a progenitor main-sequence binary, including mass transfer, are made using the Modules for Experiments in Stellar Astrophysics. Both of the progenitor stars are evolved in the simulation. WOCS 5379 is well reproduced with a primary star of initial mass 1.19 M ⊙, whose core becomes the white dwarf. The secondary star initially is 1.01 M ⊙. The secondary finished receiving mass from the donor 300 Myr ago, having moved beyond the NGC 188 turnoff as a 1.20 M ⊙ blue straggler. The successful model has a mass-transfer efficiency of 22%. This nonconservative mass transfer is key to expanding the orbit fast enough to permit stable mass transfer. Even so, the mass transfer begins with a short unstable phase, during which half of the accreted mass is transferred. With increasing mass, the secondary evolves from a radiative core to a convective core. The final blue straggler interior is remarkably similar to a 2.1 Gyr old 1.21 M ⊙ main-sequence star at the same location in the H-R diagram. The white dwarf effective temperature is also reproduced, but the modeled white dwarf mass of 0.33 M ⊙ is smaller than the measured mass of 0.42 M ⊙.

M/M/Infinity Birth-Death Processes - A Quantitative Representational Framework to Summarize and Explain Phase Singularity and Wavelet Dynamics in Atrial Fibrillation.

RationaleA quantitative framework to summarize and explain the quasi-stationary population dynamics of unstable phase singularities (PS) and wavelets in human atrial fibrillation (AF) is at present lacking. Building on recent evidence showing that the formation and destruction of PS and wavelets in AF can be represented as renewal processes, we sought to establish such a quantitative framework, which could also potentially provide insight into the mechanisms of spontaneous AF termination.ObjectivesHere, we hypothesized that the observed number of PS or wavelets in AF could be governed by a common set of renewal rate constants λf (for PS or wavelet formation) and λd (PS or wavelet destruction), with steady-state population dynamics modeled as an M/M/∞ birth–death process. We further hypothesized that changes to the M/M/∞ birth–death matrix would explain spontaneous AF termination.Methods and ResultsAF was studied in in a multimodality, multispecies study in humans, animal experimental models (rats and sheep) and Ramirez-Nattel-Courtemanche model computer simulations. We demonstrated: (i) that λf and λd can be combined in a Markov M/M/∞ process to accurately model the observed average number and population distribution of PS and wavelets in all systems at different scales of mapping; and (ii) that slowing of the rate constants λf and λd is associated with slower mixing rates of the M/M/∞ birth–death matrix, providing an explanation for spontaneous AF termination.ConclusionM/M/∞ birth–death processes provide an accurate quantitative representational architecture to characterize PS and wavelet population dynamics in AF, by providing governing equations to understand the regeneration of PS and wavelets during sustained AF, as well as providing insight into the mechanism of spontaneous AF termination.

Effect of Phosphorus Content and Heat Treatment Temperature on Microstructure and Corrosion Resistance of Ni–(X)P–GO Nanocomposite Coating on AZ31D Alloy

In the present study, a nanocomposite coating of nickel–Phosphor–graphene nano-oxide with three different phosphor content was applied on the surface of AZ31D magnesium-based alloy by the use of electroless method. Structural studies by scanning electron microscope (SEM) and X-ray diffraction (XRD) showed that a coating with a semi-amorphous structure and a cauliflower morphology is formed on the substrate surface. This is in such a way that as the phosphor content of the coating increases along with the crystallinity of the coating, GO absorption increases up to 4.5%. The obtained coatings are heat treated in argon-gas shielding atmosphere at three different temperatures of 300 °C, 400 °C, and 500 °C for 1 h. SEM results showed that by annealing, the cauliflower morphology of the coating is omitted. By heat treatment, all of the coatings were crystallized and Ni2P and Ni3P intermetallic compounds appeared in the structure in such a way that as heat treatment temperature increased, Ni2P transformed to Ni3P. By increasing heat treatment temperature and phosphor content, suitable conditions were provided for the precipitation of Ni5P2 and Ni8P3 unstable phases. Polarization corrosion test results showed that coating results in higher corrosion resistance in the substrate; as the phosphor content of the coating increases, corrosion resistance is improved. Moreover, the increase in the heat treatment temperature enhances the decreasing trend in corrosion resistance. However, corrosion resistance of the coating is higher than that of the substrate.

Structural, electronic, mechanical, and dynamical properties of scandium carbide

We report results of first-principles calculations for the structural, mechanical, dynamical and electronic properties of Scandium Carbide (ScC) compound, using a Full-Potential Linearized-Augmented Plane Wave (FP-LAPW) method based on density functional theory, within the generalized gradient approximation (GGA). The computed ground states properties; lattice constants, bulk modulus and the pressure derivative of the bulk modulus (a0, B and B') are in good agreement with former works. The calculated transition pressures from the rocksalt (NaCl) structure to the CsCl structure and from the NiAs to CsCl are found to be 111.0 GPa and 27.15GPa, respectively. It was found, that NaCl and NiAs are mechanically and dynamically the stable phases, with NaCl considered as the ground state phase. In contrast, the Zincblende (ZB) and CsCl are both unstable phases mechanically and dynamically. Wurtzite (WZ) phase was found mechanically stable and dynamically not, which might be a possible indication for a metastable phase. The electronic structures reveal that all the considered structures have a metallic character. Upon our best knowledge, for the first time, the mechanical and dynamical properties of the studied structures beside NaCl were calculated.

On Einstein-non linear-Maxwell-Yukawa de-Sitter black hole thermodynamics

We investigate the thermodynamics of the Einstein-non linear-Maxwell-Yukawa black hole solution in de Sitter spacetime. After presenting the black hole solution and its horizons, we use different thermodynamical points of view to probe the phase structure of such a black hole, ranging from local, global thermodynamics to effective thermodynamical formalism with two horizons. Our analysis showed that the black hole can undergo a thermal phase transition between an unstable phase and stable phase. These results are consolidated by our proposal of generalizing effective thermodynamics to three horizons. As a remarkable byproduct, we find that the effective temperatures behave as an association of ohmic resistances in an electric circuit, which may reveal a possible analogy between the electric and thermodynamic systems.

Mg‐Pillared LiCoO2: Towards Stable Cycling at 4.6 V

AbstractLiCoO2 is used as a cathode material for lithium‐ion batteries, however, cationic/anodic‐redox‐induced unstable phase transitions, oxygen escape, and side reactions with electrolytes always occur when charging LiCoO2 to voltages higher than 4.35 V, resulting in severe capacity fade. Reported here is Mg‐pillared LiCoO2. Dopant Mg ions, serving as pillars in the Li‐slab of LiCoO2, prevent slab sliding in a delithiated state, thereby suppressing unfavorable phase transitions. Moreover, the resulting Li‐Mg mixing structure at the surface of Mg‐pillared LiCoO2 is beneficial for eliminating the cathode‐electrolyte interphase overgrowth and phase transformation in the close‐to‐surface region. Mg‐pillared LiCoO2 exhibits a high capacity of 204 mAh g−1 at 0.2 C and an enhanced capacity retention of 84 % at 1.0 C over 100 cycles within the voltage window of 3.0–4.6 V. In contrast, pristine LiCoO2 has a capacity retention of 14 % within the same voltage window.

Mg-Pillared LiCoO2 : Towards Stable Cycling at 4.6 V.

LiCoO2 is used as a cathode material for lithium-ion batteries, however, cationic/anodic-redox-induced unstable phase transitions, oxygen escape, and side reactions with electrolytes always occur when charging LiCoO2 to voltages higher than 4.35 V, resulting in severe capacity fade. Reported here is Mg-pillared LiCoO2 . Dopant Mg ions, serving as pillars in the Li-slab of LiCoO2 , prevent slab sliding in a delithiated state, thereby suppressing unfavorable phase transitions. Moreover, the resulting Li-Mg mixing structure at the surface of Mg-pillared LiCoO2 is beneficial for eliminating the cathode-electrolyte interphase overgrowth and phase transformation in the close-to-surface region. Mg-pillared LiCoO2 exhibits a high capacity of 204 mAh g-1 at 0.2 C and an enhanced capacity retention of 84 % at 1.0 C over 100 cycles within the voltage window of 3.0-4.6 V. In contrast, pristine LiCoO2 has a capacity retention of 14 % within the same voltage window.

Effect of thermal fluctuation on the thermodynamics of GMGHS black hole

In present paper we discuss the effect of higher order corrections of entropy on the thermodynamic fluctuation of the Gibbons-Maeda-Garfinkle-Horowitz-Strominger black hole (GMGHS), i.,e. charged diatonic black hole. By investigating the thermodynamic property functions, such as the internal energy, the enthalpy, the Helmholtz free energy, the Gibbs free energy and the heat capacity, we find that the correction from the thermodynamic fluctuation is very important for small black hole case and one can neglect the correction for large black hole case. We also find that when there is no thermal fluctuation, this black hole thermodynamic system acts as an ideal gas state. However when we consider the thermal fluctuation, we can see the Van der waals type behavior in GMGHS black hole system. Finally, we discuss the stability of GMGHS black hole by investigating the behaviour of heat capacity under effect of thermal fluctuation, we find that, without any thermal fluctuation, we get the completely unstable black hole. However, with the presence of thermal fluctuation, the black hole becomes stable at smaller value of horizon radius, also there is a stable to unstable phase transition from the corrected specific heat.

TAFONOMÍA DE LOS CARBONATOS TEMPLADOS PLIOCENOS DE LA CUENCA DE ALMAYATE (MÁLAGA, S DE ESPAÑA)

Se analizan los procesos tafonómicos que afectan a las asociaciones de fósiles de los carbonatos templados del Plioceno que afloran en la Cuenca de Almayate (Málaga, S de España). El estudio tafonómico se ha realizado cuantificando varias propiedades tafonómicas. Los valores obtenidos han servido para realizar un análisis multivariante de agrupamiento de muestras, con objeto de establecer modelos de tafofacies. Los resultados obtenidos indican unas condiciones de depósito de alta energía donde los restos esqueléticos permanecieron durante prolongados períodos de tiempo en la zona tafonómicamente activa. En este contexto, durante los periodos de sedimentación normal se produjo un efecto combinado de destrucción tafonómica: 1) destrucción física, como consecuencia de la alta energía, 2) destrucción biológica, debido al efecto de los organismos bioperforadores, y 3) destrucción química, por disolución de las fases inestables del carbonato cálcico. Estos procesos tafonómicos son los que de forma habitual afectan a los carbonatos templados. Además de estos procesos normales, la acción esporádica de tormentas dejó señales sedimentológicas (presencia de niveles de tempestitas) y tafonómicas propias. En este sentido, el análisis cluster individualiza un conjunto de muestras tomadas en niveles de tempestitas. Finalmente, el análisis cluster separa un tercer grupo de muestras donde domina la presencia de moldes de organismos originalmente aragoníticos sobre restos que mantienen la mineralogía original de la concha. Una cementación temprana debió jugar un papel decisivo en la formación de esta asociación.

Modeling the hydrothermal impact on the Jurassic deposits of the West Siberian sedimentary basin (series with H2O and H2O2)

The results of hydrothermal modeling of the formation of epigenetic mineral associations and secondary reservoirs in various types of sedimentary rocks of the Jurassic age in Western Siberia in the H2O-H2O2 system are considered. The experiments were carried out at a temperature of 390°C, a pressure of 70 MPa and H2O2 concentrations varying from 0 to 37.5%. The duration of the experiments was 10 days. In all experiments, a pyrite mixture was added as a buffer. It was found that in experiments in which there was no H2O2, that is, the hydrothermal fluid consisted only of water, there was an intense formation of bitumen and volatile components from the organic matter present in the initial samples. The process of generation of bitumen and volatile components was accompanied by fluid fracturing of rocks and the formation of secondary porosity. Under these conditions, carbonates (calcite, siderite), plagioclases, and kaolinite turned out to be unstable. On the contrary, the formation of hydrothermal ferruginous chlorite was noted. Dissolution of unstable mineral phases by hydrothermal fluid led to the formation of additional secondary porosity. As the concentration of H2O2 and, accordingly, oxygen in the composition of the hydrothermal fluid increased, more and more complete oxidation of the organic matter present in the composition of the sediments was noted until its complete disappearance. With an increase in the oxygen concentration in the composition of the hydrothermal fluid, the appearance of first magnetite and then hematite, native sulfur, and anhydrite was observed. Under hydrothermal conditions with a maximum oxygen concentration, the formation of kaolinite and various sulfates in addition to anhydrite, represented by millosevichite, alum, as well as phases with the participation of elements that make up autoclaves, nickel and chromium sulfates, was noted. Intensive silicification of the sample surface is noted, as well as the constant presence of amorphous silica, which, along with various sulfates, is a quenching phase. These mineral phases are separated from the supersaturated hydrothermal fluid due to its rapid cooling and do not have time to form well-faceted crystals, but are present in the form of loose microporous aggregates. Along with kaolinite, the formation of hydrothermal film illite is noted. The results obtained indicate that the presence of bitumen in the Jurassic sediments is an important exploratory feature, indicating that in this place they were subjected to hydrothermal action, which means, firstly, secondary reservoirs with high filtration and capacity properties were formed, and second, there was an intensive generation of hydrocarbons and, as a consequence, the formation of hydrocarbon deposits.