Metastable Conditions Research Articles

(Re) framing the politics of climate change: resilience, reparative critique and affective life in situations of extreme heat

ABSTRACT One of the ways we know climate change is through the emergencies that make it present. But how does the connection between singular events (emergencies) and a meta-stable condition (climate change) become perceivable to us? Through what knowledges? And with what political implications? In this paper I apply these questions to deepen critical understanding of government-orchestrated efforts to enhance climate resilience. Pursuing an alternative pathway to critiques that reduce resilience to neoliberalism, I bring resilience into dialogue with Lauren Berlant’s concept of situations. The importance of situations rests in its ability to diversify our understanding of the emergencies to which resilience responds. Initially, situations prompt us to explore emergencies fundamentally as ruptures in people’s ongoing affective encounter with the world. They also capture how our experience of emergencies is colored by the broader historical significance they hold as critical events that change collective life. And, as with all events read through affect, situations are also an object of mediation. Thinking with situations, I demonstrate how, through resilience, government actors mediate our sense of the relationship between emergencies, on one hand, and climate change as an epochal condition, on the other. By distributing responsibility, resilience allows a wide catalogue of voices to influence common perceptions of this relationship and, consequently, evidences potential to integrate what Eve Kosofsky-Sedgwick calls reparative critique into climate consciousness by highlighting the ramifications climate-related emergencies have on specific communities because of environmental harms visited upon them over time and orienting future action towards attending to these harms. I make this argument through research into the US’ Environmental Protection Agency’s attempts to raise situational awareness of extreme heat risk. While seeking to mobilize people’s embodied knowledges in sensing imminent danger, these practices push concurrently for understanding, and acting upon, climate change vulnerability by its entanglement with violent processes that underpinned the modernization projects fundamental to American life now.

Ice nucleation in supercooled water under shear

Classical nucleation theory (CNT) provides a good framework for understanding the nucleation phenomenon in metastable conditions. However, there is still no satisfactory understanding of the shear effect. Here, we propose an ice nucleation model considering the rebounded deformation energy to analyze the ice nucleation rate. It is concluded that: (1) The effect is more pronounced by changing the contact angle to regulate the free energy when both the supercooled degree and the shear rate are small. (2) The variation trend of the nucleation ratio Jhet,sh/Jhet,no increases at first but it may decrease when the contact angle is small, or keeps increasing when the contact angle is large. (3) The probability of the shear nucleation is about several ten orders of magnitude to that of static nucleation. (4) The key factor in the acceleration of the supercooled liquid nucleation is the released deformation energy after encountering the obstruction.

Enhanced connectivity and mobility in liquid water: Implications for the high density liquid structure and its onset

In this work, we investigate simulated liquid water at ambient pressure in both stable and metastable supercooled conditions by means of a new order parameter we recently proposed, namely the node total communicability (NTC), based on graph theory concepts. We show that this order parameter is able to identify the two liquid states differing in density, the LDL- and HDL-like states, in simulation conditions at which both states coexist. We also show that NTC is able to capture both the structural and dynamic differences between the two states, being correlated with both the local density and the mobility of water molecules within the network. In addition, we further investigate the high connectivity patches we previously identified as characteristic of the HDL-like state. We show that these extended patches are composed of molecules with an increased local density and mobility, packed in a highly connected network. The formation of these highly connected networks is characterized by a fast dynamics, with mobile molecules entering and exiting the patches. Interestingly, we observe small highly connected patches also at low temperatures, where the prevailing state is LDL-like. We show that the small-to-large patches transition is related to the Widom line crossing and we suggest that the small highly connected patches at low temperatures might function as initial sites for the formation of extended HDL-like regions characteristic of the highest temperatures.

Phase‐Coherent Optical Frequency Up‐Conversion with Millimeter‐Size Zn(3‐ptz)2 Metal‐Organic Framework Single Crystals

AbstractMetal‐organic frameworks (MOFs) have emerged as candidate materials for nonlinear optics due to their enhanced optical and chemical stability in comparison with conventional organic crystals. However, producing large single crystals that support perfect phase matching conditions for frequency conversion is a long‐standing challenge due to the highly metastable conditions in which MOF crystals tend to self‐assemble in solution. By modulating the synthesis and growth conditions, this limitation is overcome to produce millimeter–sized Zn(3‐ptz)2 uniaxial MOF single crystals. Optimized MOF crystals with large birefringence in the visible Δn ≈ −0.3 and high transparency allow for the observation of strong second‐harmonic (SHG) and third‐harmonic generation (THG) signals for the first time, using femtosecond near‐infrared pump pulses. For conditions of type‐I SHG phase‐matching, the measured effective nonlinear coefficient of Zn(3‐ptz)2 is deff ≈ 0.10 pm V−1, the largest measured nonlinearity for MOF materials to date. The experiments quantitatively agree with first‐principles simulations based on the crystal lattice structure. The damage threshold is estimated on the order of 0.2 TW cm−2 for raw single crystals, which can be further increased with additional crystal engineering steps. The demonstration of efficient frequency up‐conversion of light with long‐range phase coherence establishes MOF single crystals as promising materials for nonlinear optical devices.

Metastable Conditions in a Three-Wheeled Bicycle with Variable Front Wheel Spacing

Abstract The article concerns the problem of lateral stabilization of a tricycle with variable front wheel track. The vehicle can operate in two modes: with the front wheels folded out and connected. A bicycle designed for people with special needs. The element that requires elaboration is the stabilization while driving with the front wheels unfolded. In this mode, a metastable state is created. When the lateral angle of the slope exceeds the limit value, the lateral force causes the lateral tilt. This phenomenon should be treated as a disadvantage as it makes it difficult to smoothly tilt the bicycle, which can lead to disorientation of the rider and difficulty in maintaining balance. The article presents mathematical simulations that allow for the analysis of factors influencing the discussed phenomenon.

Axial cyclic loading of piles in low-to-medium-density chalk

Comprehensive field investigations into the axial cyclic loading behaviour of open steel pipe piles driven and aged in low-to-medium-density chalk identify the conditions under which behaviour is stable, unstable or metastable. Post-cycling monotonic tests confirmed that stable cycling enhanced pile capacity marginally, while unstable cases suffered potentially large losses of shaft capacity. Metastable conditions led to intermediate outcomes. The patterns by which axial deflections grew under cyclic loading varied systematically with the normalised loading parameters and could be captured by simple fitting expressions. Cyclic stiffnesses also varied with loading conditions, with the highest operational shear stiffnesses falling far below the in situ seismic test values. The monotonic and cyclic axial responses of the test piles were controlled by the behaviour of, and conditions within, the reconsolidated, de-structured, chalk putty annuli formed around pile shafts during driving. Fibre-optic strain gauges identified progressive failure from the pile tip upwards. Large factors of safety were required for piles to survive repetitive loading under high-level, two-way conditions involving low mean loads, while low-amplitude one-way cycling had little impact. A simple ‘global’ prediction procedure employing interface shear and cyclic triaxial tests is shown to provide broadly representative predictions for field behaviour.

First-Principles Insights into the Relative Stability, Physical Properties, and Chemical Properties of MoSe2.

A fascinating transition-metal dichalcogenide (TMDC) compound, MoSe2, has attracted a lot of interest in electrochemical, photocatalytic, and optoelectronic systems. However, detailed studies on the structural stability of the various MoSe2 polymorphs are still lacking. For the first time, the relative stability of 11 different MoSe2 polymorphs (1H, 2H, 3Ha, 3Hb, 2T, 4T, 2R1, 1T1, 1T2, 3T, and 2R2) is proposed, and a detailed analysis of these polymorphs is carried out by employing the first-principles calculations based on density functional theory (DFT). We computed the physical properties of the polymorphs such as band structure, phonon, and elastic constants to examine the viability for real-world applications. The electronic properties of the involved polymorphs were calculated by employing the hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE06). The energy band gap of the polymorphs (1H, 2H, 3Ha, 3Hb, 2T, 4T, and 2R1) is in the range of 1.6-1.8 eV, coinciding with the experimental value for the polymorph 2H. The covalent bonding nature of MoSe2 is analyzed from the charge density, charge transfer, and electron localization function. Among the 11 polymorphs, 1H, 2H, 2T, and 3Hb polymorphs are predicted as stable polymorphs based on the calculation of the mechanical and dynamical properties. Even though the 4T and 3Ha polymorphs' phonons are stable, they are mechanically unstable; hence, they are considered to be under a metastable condition. Additionally, we computed the direction-dependent elastic moduli and isotropic factors for both mechanically and dynamically stable polymorphs. Stable polymorphs are analyzed spectroscopically using IR and Raman spectra. The thermal stability of the polymorphs is also studied.

On the enhanced dielectric and magnetic properties of BiFeO3 ceramics sintered under meta-stable conditions

Multiferroic BiFeO3 (BFO) ceramics are synthesized by non-thermodynamically stable methods, such as fast firing, cryomilling and Spark Plasma Sintering (SPS) with applied pressure of 60 MPa and high heating rate of 150 K/min. We obtained BFO ceramics and powders that present enhanced magnetic and electrical properties. The observed enhancements are caused by the chosen routes, such as cryomilling, which causes a significant reduction of crystallite size, reaching 23 nm, and a high micro-strain level, reaching 1.2%. This is reflected in the magnetic curve which is changed from antiferromagnetic-like to weak-ferromagnetic-like, with an increased maximum magnetization from 0.085 emu/g to 0.369 emu/g. The dielectric constant reached a high value, close to Ɛ’= 102 coupled with low dielectric loss (tan δ ∼ 0.019) over a wide range of frequencies (1 kHz to 2 MHz), reaching values close to 0.005 near 2 MHz. Such dielectric constant (dielectric loss) values are generally present for highly resistive ceramics. By equivalent circuit fitting we managed to separate the grain and grain boundary contributions. These results and those from XRD diffraction and Mössbauer spectroscopy indicate a migration of defects to the surface of the grains. In summary, we managed to consolidate this sintering method as a powerful method to obtain BFO ceramics with enhanced electrical and magnetic properties. Such improvements, especially the high resistivity and low tangent losses, can open new avenues for future technological applications of BiFeO3 nanostructured ceramics, such as ferroelectric memories and the magnetic enhancements for spintronic based devices.

Liquid-liquid phase separation in supercooled water from ultrafast heating of low-density amorphous ice

Recent experiments continue to find evidence for a liquid-liquid phase transition (LLPT) in supercooled water, which would unify our understanding of the anomalous properties of liquid water and amorphous ice. These experiments are challenging because the proposed LLPT occurs under extreme metastable conditions where the liquid freezes to a crystal on a very short time scale. Here, we analyze models for the LLPT to show that coexistence of distinct high-density and low-density liquid phases may be observed by subjecting low-density amorphous (LDA) ice to ultrafast heating. We then describe experiments in which we heat LDA ice to near the predicted critical point of the LLPT by an ultrafast infrared laser pulse, following which we measure the structure factor using femtosecond x-ray laser pulses. Consistent with our predictions, we observe a LLPT occurring on a time scale < 100 ns and widely separated from ice formation, which begins at times >1 μs.

Modelling of two-phase expansion in a reciprocating expander

Two-phase expansion devices can be applied in a multitude of cycles which allow for an increase of the overall system efficiency in currently used heat and power cycles. The expanders that are mainly investigated for the purpose of two-phase expansion are the Lysholm and the reciprocating expanders. From these two, the reciprocating expander is challenging to model as there is a need to describe the non-equilibrium state of the phases during the expansion process. This study aims to fill the knowledge gap that exists for two-phase reciprocating expanders, by constructing a predictive model to describe the expansion process and the non-equilibrium phenomena occurring. The simulation framework makes use of a modified homogeneous relaxation model to describe the thermal non-equilibrium between the phases within the isolated working chamber. The model results are verified and compared to experimental data in literature with water as working fluid. Subsequently, Cyclopentane is selected as a more suitable candidate and a thorough analysis is presented. The simulation results predict a 15% lower work and a 10% higher mass intake per stroke of the expander compared to equilibrium working conditions. • A model is constructed to predict the evaporation rate of a two-phase mixture in a reciprocating expander. • The homogeneous relaxation model is applied and compared to the homogeneous equilibrium model. • The evaporation rate in a reciprocating expander is lower than expected, resulting in metastable conditions during the process. • The updated disequilibrium model predicts around 25% more mass intake and 8% lower work compared to the equilibrium model.

Thermal fluctuations in metastable fluids

In this work, the thermal fluctuations of fluid in metastable conditions have been theoretically investigated. The fluid is described with a diffuse interface approach based on the Van der Waals squared-gradient theory (SGT), where the free energy is augmented by a density square gradient term to take into account capillary effects. By averaging physical observables on coarse-graining cells, it is found that capillarity strongly modifies the fluctuation statistics when increasing fluid metastability. A remarkable difference with respect to simple fluid description is also detected when approaching nanoscopic scales. Peculiarly, near spinodal loci, the classical theory envisages a divergent behavior of density fluctuations intensity, while the SGT provides a finite variance of the density field. The scaling behavior of density fluctuations near spinodal lines is analytically derived and discussed. Finally, the correlation length of the capillary system is identified for different metastabilities. Also in the latter case, the critical exponents are theoretically calculated. The theoretical results are corroborated by Landau–Lifshitz–Navier–Stokes fluctuating hydrodynamics simulations.

Meta-stable initial condition for improving the switching probability in azobenzene derivatives on surface

The trans isomer of azobenzene (AB) and its derivatives is the most abundant isomer at thermodynamic equilibrium and is known to switch between its trans and cis isomers when triggered by light, electrons/holes and electrical field in adlayers on surfaces. However, the equilibrium initial condition limits the operation of molecular switches on surface due to large activation barrier for switching (trans to cis), hence the switching probability is very low. We show in this article, condensation of meta-stable (non-equilibrium) cis state of azobenzene derivatives on graphite. When electrons/holes induced switching is performed on these molecular switches from the meta-stable initial condition, the switching probability is enhanced by several folds. The molecules are switching between two associated cis states, instead of trans–cis switching. The switching between the cis states has relatively low energy barrier as revealed by density functional theory (DFT) calculations is at the origin of the enhanced switching probability. We also observe that reversible trans–cis and cis–cis’ switching on graphite is mediated through a stable charged intermediate state, leading to a low threshold voltage for switching compared to neutral molecules.

Stable, metastable and unstable states of the mixed spin (1, 3/2) Ising model in the absence and presence of constant magnetic fields

Stable, metastable and unstable states of the mixed spin (1, 3/2) Ising system in the absence and presence of constant external magnetic fields (CEMFs) were investigated both by the cluster variation method (CVM) and the path probability method (PPM). First, we examine the thermal behavior of the magnetizations by using the CVM and search the metastable and unstable branches of magnetizations in addition to the stable branches. We present the metastable phase diagrams besides to equilibrium phase diagrams in the absence of the CEMFs. We also constructed only the metastable phase diagram under the presence of CEMFs. Since the metastability is a stable state of a dynamical system, we used the PPM on the model and found the dynamic equations. Dynamic equations were solved by means of the flow diagrams (FDs). The FDs clearly display the stable, metastable and unstable states in which also obtained within the CVM. The FDs display the role of the metastable, unstable states and initial conditions as well as how the system trapped into the metastable state. Some properties of the metastable states were observed from the FDs. These studies were made both for the ferrimagnetic and antiferrimagnetic cases.PACS: 05.50. + q, 05.70.Fh, 05.70.Ln, 64.60.Cn, 64.60. My, 75.10.Hk

End-to-End Prediction of Lightning Events from Geostationary Satellite Images

While thunderstorms can pose severe risks to property and life, forecasting remains challenging, even at short lead times, as these often arise in meta-stable atmospheric conditions. In this paper, we examine the question of how well we could perform short-term (up to 180 min) forecasts using exclusively multi-spectral satellite images and past lighting events as data. We employ representation learning based on deep convolutional neural networks in an “end-to-end” fashion. Here, a crucial problem is handling the imbalance of the positive and negative classes appropriately in order to be able to obtain predictive results (which is not addressed by many previous machine-learning-based approaches). The resulting network outperforms previous methods based on physically based features and optical flow methods (similar to operational prediction models) and generalizes across different years. A closer examination of the classifier performance over time and under masking of input data indicates that the learned model actually draws most information from structures in the visible spectrum, with infrared imaging sustaining some classification performance during the night.

Numerical investigation of flashing of propane (R-290) in a helical capillary tube

The present study addresses the expansion of pressurized liquid R-290 through a diameter capillary tube and its subsequent motion through a metastable condition entailing a change of phase through flashing phenomenon. The expansion of R-290 through a helical capillary tube is numerically simulated using a finite volume-based mixture model. For the simulation of the flashing phenomena, a homogeneous equilibrium approach is used. The Zwart–Gerber–Belamri model is deployed to represent mass transfer during flashing. ANSYS Fluent 2021 R2 software has been used for the numerical simulations. A series of UDF (user defined functions) are developed to read the recorded database of R-290 and perform the cavitation modeling. Bilinear interpolation is performed for determining the fluid properties at the corresponding pressure and temperature. The developed numerical model has been validated against the available numerical and experimental results. For the simulations, tubes with lengths of and have been considered, and the impacts of increasing length on the flow characteristics at the outlet have been determined. In this investigation, the R-290 refrigerant expands from three different condenser pressures of 16, 14, and 12 bar. Evaporator pressure is adjusted from 2 bar to 8 bar to investigate its influence on flow characteristics. The fall in evaporator pressure brings about a flow transition from subsonic to supersonic. The effects of tube length, condenser, and evaporator pressures on mass transfer rate, evaporator entry temperature, mixture quality at the evaporator entrance, and available refrigeration effects have been analyzed.

Migration of Salt Ions in Frozen Hydrate-Saturated Sediments: Temperature and Chemistry Constraints

Migration of dissolved salts from natural (cryopeg brines, seawater, etc.), or artificial sources can destabilize intrapermafrost gas hydrates. Salt transport patterns vary as a function of gas pressure, temperature, salinity, etc. The sensitivity of the salt migration and hydrate dissociation processes to ambient temperature and to the concentration and chemistry of saline solutions is investigated experimentally on frozen sand samples at a constant negative temperature (−6 °C). The experiments show that the ambient temperature and the solution chemistry control the critical salt concentration required for complete gas hydrate dissociation. Salt ions migrate faster from more saline solutions at higher temperatures, and the pore moisture can reach the critical salinity in a shorter time. The flux density and contents of different salt ions transported to the samples increase in the series Na2SO4–KCl–CaCl2–NaCl–MgCl2. A model is suggested to account for phase transitions of pore moisture in frozen hydrate-saturated sediments exposed to contact with concentrated saline solutions at pressures above and below the thermodynamic equilibrium, in stable and metastable conditions of gas hydrates, respectively.

Engineering the nature of polarization dynamics in lead-free relaxors based on (Bi1/2Na1/2)TiO3

(Bi1/2Na1/2)TiO3 (BNT) is a lead-free ferroelectric material, which has shown promising electromechanical properties and energy storage capacities. These attractive functionalities and property performances are attributed to the relaxor behavior of BNT. However, the nature of the dielectric relaxation is not well understood in these materials, and the physical meaning of some important parameters associated with the permittivity is still under debate. In this Letter, we focus on the dielectric “shoulder,” Ts, that is readily seen in the ε′–T curve of every BNT-based relaxor. It is found that the Ts is controlled by not only the typical compositional engineering but also by the thermal, electrical, or mechanical history. From a moderate temperature (≤250 °C), a sample can be rapidly cooled to room temperature or slowly cooled under an electrical bias or a mechanical bias in the form of a compressive stress. All three treatments lead to a nearly identical effect, which is to alter the Ts with respect to rest of the ε′–T curve that remains unperturbed. Therefore, the internal stress is identified to be a general perturbance to the polarization dynamics. Finally, the “breathing” model is revisited to interpret the physical meaning of Ts for these BNT materials under these metastable conditions.

A Review on Flow Characteristics of the Straight and Coiled Capillary Tubes

A detailed literature review on the flow characterization of the capillary tubes is presented in this paper. The flow behavior is reviewed for straight, helically, and spirally coiled capillary tubes at different operating and geometric conditions by considering various aspects in the tube. This paper summarizes experimental and numerical study on the adiabatic and nonadiabatic straight and coiled capillary tubes at different geometries conditions. The vital information of the range of the tube geometry and operating conditions are discussed, which can be utilized for further studies on the capillary tube. Various methodologies with generalized correlations are indicated. It has been observed that there are even more studies need to do with environmentally friendly refrigerants with various practical aspects in the capillary tube. It would be interesting to find the coiling effect on the design and simulation of the capillary tube. In addition to that more experimental and numerical studies need to explore the nonadiabatic coiled capillary tube. It would be fascinating to study the metastable condition in the capillary tube and set suitable relations to present its effect on the mass flow rate.

On the inverse quenching technique applied to gelatin solutions

Gelatin gels are known to be nonequilibrium systems, because of the continuous growth and rearrangements of physical junctions, even in the solidlike state. Establishing a relationship between the relative degree of cross-linking and macroscopic elasticity would be crucial in understanding, modeling, and predicting the transformation processes of gelatin solutions. Performing rheological experiments on a distinct gel structure, with a definite number of cross-links, is, however, a challenging task. In isothermal conditions, indeed, the density of physical cross-links changes indefinitely, and network evolution cannot be arrested. Inspired by the inverse quenching technique applied in the past to semicrystalline polymers, we here apply an unusual thermal history to an aqueous solution of gelatin in the semiconcentrated regime (6.67%w pig-skin gelatin), in order to freeze the system in a metastable condition for a time sufficiently long to perform a rheological characterization. The solution, initially kept in the sol state at 60°C, is rapidly cooled below gelation temperature, and isothermal gelation is started at 10°C. After soaking at this low temperature for a given time, the sample is rapidly heated (inverse quenching) up to a value in the range 24–29 °C, where kinetics is monitored. If the waiting time at low temperature and the inverse quenching temperature are suitably chosen, sample elasticity will remain stationary for a relatively large time window, and rheological experiments can then be reliably performed.

A15 Nb3Si: a ‘high’ T c superconductor synthesized at a pressure of one megabar and metastable at ambient conditions

A15 Nb3Si is, until now, the only ‘high’ temperature superconductor produced at high pressure (∼110 GPa) that has been successfully brought back to room pressure conditions in a metastable condition. Based on the current great interest in trying to create metastable-at-room-pressure high temperature superconductors produced at high pressure, we have restudied explosively compressed A15 Nb3Si and its production from tetragonal Nb3Si. First, diamond anvil cell pressure measurements up to 88 GPa were performed on explosively compressed A15 Nb3Si material to trace T c as a function of pressure. T c is suppressed to ∼5.2 K at 88 GPa. Then, using these T c (P) data for A15 Nb3Si, pressures up to 92 GPa were applied at room temperature (which increased to 120 GPa at 5 K) on tetragonal Nb3Si. Measurements of the resistivity gave no indication of any A15 structure production, i.e. no indications of the superconductivity characteristic of A15 Nb3Si. This is in contrast to the explosive compression (up to P ∼ 110 GPa) of tetragonal Nb3Si, which produced 50%–70% A15 material, T c = 18 K at ambient pressure, in a 1981 Los Alamos National Laboratory experiment. This implies that the accompanying high temperature (1000 °C) caused by explosive compression is necessary to successfully drive the reaction kinetics of the tetragonal → A15 Nb3Si structural transformation. Our theoretical calculations show that A15 Nb3Si has an enthalpy vs the tetragonal structure that is 70 meV atom−1 smaller at 100 GPa, while at ambient pressure the tetragonal phase enthalpy is lower than that of the A15 phase by 90 meV atom−1. The fact that ‘annealing’ the A15 explosively compressed material at room temperature for 39 years has no effect shows that slow kinetics can stabilize high pressure metastable phases at ambient conditions over long times even for large driving forces of 90 meV atom−1.