Complex Phase Transitions Research Articles

Time-Resolved Infrared Vibrational Spectroscopy of the Photoinduced Phase Transition of Pd(dmit)2 Salts Having Different Orders of Phase Transition

To clarify the mechanism of the later process of photoinduced phase transition (PIPT) in organic charge-transfer complexes, we examined by time-resolved infrared vibrational spectroscopy two dimeric anion radical salts, Et2Me2Sb[Pd(dmit)2]2 (Et2Me2Sb salt) and Cs[Pd(dmit)2]2 (Cs salt) (Et, Me, and dmit are C2H5, CH3, and 1,3-dithiol-2-thione-4,5-dithiolate, respectively), having similar characteristics except for the order of their phase transitions at thermal equilibrium. The phase transition is first order for the Et2Me2Sb salt and second order for the Cs salt at thermal equilibrium. Although both salts exhibit a high-temperature phase at later delay times (>100 ps) after the photoexcitation of the low-temperature phase, the time required for the emergence of the high-temperature phase was significantly different: 70 ps for the Et2Me2Sb salt and <0.1 ps for the Cs salt. The slow emergence of the high-temperature phase in the PIPT of the Et2Me2Sb salt presumably has an origin similar to that recognized for the first-order thermal phase transition, that is, steric effects of the Et2Me2Sb cation when the phase transitions occur.

Low Temperature Structural Instability of Tetragonal Spinel Mn3O4

Tetragonal ferrimagnetic spinel Mn3O4 shows complex magnetic phase transitions due to competing anti ferromagnetic interactions involving Mn2+/3+ ions with difference valences. Using magnetization and neutron diffraction measurements, we propose that its tetragonal lattice possesses an instability towards orthorhombic distortion in zero field well below \(T_{\text{N}}\). The direction of the observed instability suggests that the anomaly is related to lifting of the persistent geometrical frustration via spin–lattice coupling.

Dynamical Movement Primitives: Learning Attractor Models for Motor Behaviors

Nonlinear dynamical systems have been used in many disciplines to model complex behaviors, including biological motor control, robotics, perception, economics, traffic prediction, and neuroscience. While often the unexpected emergent behavior of nonlinear systems is the focus of investigations, it is of equal importance to create goal-directed behavior (e.g., stable locomotion from a system of coupled oscillators under perceptual guidance). Modeling goal-directed behavior with nonlinear systems is, however, rather difficult due to the parameter sensitivity of these systems, their complex phase transitions in response to subtle parameter changes, and the difficulty of analyzing and predicting their long-term behavior; intuition and time-consuming parameter tuning play a major role. This letter presents and reviews dynamical movement primitives, a line of research for modeling attractor behaviors of autonomous nonlinear dynamical systems with the help of statistical learning techniques. The essence of our approach is to start with a simple dynamical system, such as a set of linear differential equations, and transform those into a weakly nonlinear system with prescribed attractor dynamics by means of a learnable autonomous forcing term. Both point attractors and limit cycle attractors of almost arbitrary complexity can be generated. We explain the design principle of our approach and evaluate its properties in several example applications in motor control and robotics.

Stacking of Short DNA Induces the Gyroid Cubic-to-Inverted Hexagonal Phase Transition in Lipid-DNA Complexes.

Lyotropic phases of amphiphiles are a prototypical example of self-assemblies. Their structure is generally determined by amphiphile shape and their phase transitions are primarily governed by composition. In this paper, we demonstrate a new paradigm for membrane shape control where the electrostatic coupling of charged membranes to short DNA (sDNA), with tunable temperature-dependent end-to-end stacking interactions, enables switching between the inverted gyroid cubic structure (QIIG) and the inverted hexagonal phase (HIIC). We investigated the structural shape transitions induced in the QIIG phase upon complexation with a series of sDNAs (5, 11, 24, and 48 bp) with three types of end structure ("sticky" adenine (A)-thymine (T) (dAdT) overhangs, no overhang (blunt), and "nonsticky" dTdT overhangs) using synchrotron small-angle X-ray scattering. Very short 5 bp sDNA with dAdT overhangs and blunt ends induce coexistence of the QIIG and the HIIC phase, with the fraction of QIIG increasing with temperature. Phase coexistence for blunt 5 bp sDNA is observed from 27 °C to about 65 °C, where the HIIC phase disappears and the temperature dependence of the lattice spacing of the QIIG phase indicates that the sDNA duplexes melt into single strands. The only other sDNA for which melting is observed is 5 bp sDNA with dTdT overhangs, which forms the QIIG phase throughout the studied range of temperature (27 °C to 85.2 °C). The longer 11 bp sDNA forms coexisting QIIG and HIIC phases (with the fraction of QIIG again increasing with temperature) only for "nonsticky" dTdT overhangs, while dAdT overhangs and blunt ends exclusively template the HIIC phase. For 24 and 48 bp sDNAs the HIIC phase replaces the QIIG phase at all investigated temperatures, independent of sDNA end structure. Our work demonstrates how the combined effects of sDNA length and end structure (which determine the temperature-dependent stacking length) tune the phase behavior of the complexes. These findings are consistent with the hypothesis that sDNAs and sDNA stacks with lengths comparable to or larger than the cubic unit cell length disfavor the highly curved channels present in the QIIG phase, thus driving the QIIG-to-HIIC phase transition. As the temperature is increased, the breaking of stacks due to thermal fluctuations restores increasing percentages of the QIIG phase.

Did CNBC Contribute to the Great Moderation or the Great Recession?

We construct a multi-agent system (MAS) model of cyclical growth in which aggregate fluctuations result from variations in activity at firm level. The latter, in turn, result from changes in the state of long run expectations (SOLE) or “animal spirits” and their effect on firms’ investment behaviour. We focus on the impact of a common source of information – analogous to the mass media – on the amplitude of aggregate fluctuations. Our results suggest that the amplitude of growth cycles is reduced by extremes of attention or inattention to aggregate economic performance, but that this relationship is subject to complicated (and possibly complex) phase transitions.

Structural Dynamics of Polycrystals under Shock Compression Observed via Nanosecond Time-resolved X-ray Diffraction

ABSTRACTDynamics of structural phase transition in polycrystalline samples (tetragonal stabilized zirconia and bismuth) under laser-shock compression has been studied using nanosecond time-resolved X-ray diffraction technique based on synchrotron radiation. Tetragonal zirconia shows the structural phase transition to the monoclinic phase within 20 ns during shock compression without any intermediate and reverts back to the tetragonal phase during pressure release. Bismuth shows more complex phase transition dynamics. The Bi-I phase, which is the stable phase at ambient pressure and temperature, transfers to Bi-V phase within 4 ns under shock compression and gradually reverts back following the path of Bi-V →Bi-III → Bi-II → Bi-I within 30 ns during pressure release.

Crystal‐to‐Crystal Transformations in a Seven‐Coordinated Scandium Complex

AbstractAquatris(3‐cyanopentane‐2, 4‐dionato)scandium(III) undergoes two transformations which can be monitored by X‐ray diffraction as well as solid‐state NMR spectroscopy: At 145 K, the mononuclear complex shows a reversible phase transition; in agreement with the symmetry principle, this transition of the t2 type proceeds from the monoclinic room temperature phase to triclinic twins at low temperature, the twin law corresponding to a twofold rotation. Under vacuum at room temperature, the aqua ligand of the complex is irreversibly eliminated and the structure rearranges, forming a 1D chain polymer. In both phases of the mononuclear complex as well as in the polymer, the coordination polyhedra around the ScIII atom represent distorted capped trigonal prisms. Solid‐state 45Sc NMR spectroscopic investigations on powder samples reveal a reversible phase transition of the monoclinic complex at low temperatures. Changes of the NMR signal line shapes for the room and low temperature complex as well as the 1D chain polymer are a fingerprint for different scandium bonding situations.

Complex structural phase transitions in slightly Ca modified Na0.5Bi0.5TiO3

A temperature dependent neutron powder diffraction study, in conjunction with dielectric and ferroelectric characterization, of slightly Ca modified Na0.5Bi0.5TiO3 (NBT) revealed an instability with regard to a non-polar orthorhombic (Pbnm) distortion above room temperature. This intermediate orthorhombic phase has earlier been reported for unmodified NBT by electron diffraction studies, but has never been captured by global (x-ray/neutron) diffraction techniques. Calcium substitution seems to amplify the magnitude of this intermediate orthorhombic distortion thereby making the corresponding superlattice reflections become visible in the neutron diffraction pattern. The study revealed the following sequence of very complex structural evolution with temperature: .

Dynamic light scattering study of phase transitions in three-dimensional complex plasmas

The phase transitions of a three-dimensional complex (dusty) plasma under gravity are studied by means of the dynamic light scattering technique. The thermal energy of the dust component is determined during the phase transition to characterize the phase state. Detailed parametric studies are performed to examine the impact of the main plasma parameters on phase transitions. The results are found to be in good agreement with the predictions of a theoretical description of phase transitions that considers plasma instabilities to be the main heating mechanism. The distribution of energy in the system is strongly anisotropic. In the melted state, the dust particle movement in the vertical direction has much higher thermal energies than in the horizontal plane. The ratio of the two energies is constant and in particular independent of all the plasma parameters studied. Furthermore, the phase transition of the dust component is a gradual process. A transition front moves through the system in the vertical direction until the whole system reaches the new phase state. The velocities of energy fronts for the horizontal and vertical components of particle motion are very different. In particular, the melted state is a strongly inhomogeneous and anisotropic state in terms of energy transport.

Orientation and phase transition dependence of the electrocaloric effect in 0.71PbMg1/3Nb2/3O3-0.29PbTiO3 single crystal

In this letter, the electrocaloric effect (ECE) of 〈111〉- and 〈001〉-oriented 0.71PbMg1/3Nb2/3O3-0.29PbTiO3 (0.71PMN-0.29PT) single crystals is investigated with emphasis on the effects of phase transitions and their dependence on electric field. We show that crystal orientation and more specifically the complex phase transitions taking place in the specific composition above have large effects on the maximum ECE temperature, ΔTmax, its peak temperature, TEC, and the width of the ECE peak of the ΔT(T) curve. The investigation shows that ECE may be tuned by a proper choice of 0.71PMN-0.29PT crystal orientations.

Bridging Lattice-Scale Physics and Continuum Field Theory with Quantum Monte Carlo Simulations

We discuss designer Hamiltonians—lattice models tailored to be free from sign problems (“de-signed”) when simulated with quantum Monte Carlo (QMC) methods but which still host complex many-body states and quantum phase transitions of interest in condensed matter physics. We focus on quantum spin systems in which competing interactions lead to nonmagnetic ground states. These states and the associated quantum phase transitions can be studied in great detail, enabling direct access to universal properties and connections with low-energy effective quantum field theories. As specific examples, we discuss the transition from a Néel antiferromagnet to either a uniform quantum paramagnet or a spontaneously symmetry-broken valence-bond solid (VBS) in SU(2) and SU(N) invariant spin models. We also discuss anisotropic (XXZ) systems harboring topological Z2 spin liquids and the XY* transition. We briefly review recent progress on QMC algorithms, including ground-state projection in the valence-bond basis and direct computation of the Renyi variants of the entanglement entropy.

Discontinuous Changes in Ionic Conductivity of a Block Copolymer Electrolyte through an Order-Disorder Transition.

The ionic conductivity of a block copolymer electrolyte was measured in an in situ small-angle X-ray scattering experiment as it transitioned from an ordered lamellar structure to a disordered phase. The ionic conductivity increases discontinuously as the electrolyte transitions from order to disorder. A simple framework for quantifying the magnitude of the discontinuity is presented. This study lays the groundwork for understanding the effect of more complex phase transitions such as order-order transitions on ion transport.

Multiphase equation of states of solid and liquid phases for bismuth

Element bismuth (Bi) will experience complex phase transitions under high temperature and high pressure, which means significant changes in physical properties, such as density, energy, etc. Multiphase equations of states (EOSs) of both solid and liquid phases for Bi are presented. The EOSs are based on the three-term expression for Helmholtz free energy, where the ion vibration free energy is evaluated from the mean field potential model we recently proposed. The calculated results show that our multiphase EOSs can well reproduce the experimental data, including phase diagram, isotherms of solid phases, density measurements of liquid phase and shock-wave compression data, which proves the rationality of the parameter values and the universal nature of this model.

CFD Simulation of Mixing Effects in Gas-Liquid-Solid Stirred Reactor

In order to analyze the complex phase transition in the gas-liquid-solid three-phase mixing systems and to predict gas-liquid-solid multiphase mixing time, a novel method combined image processing technology, computational homology and CFD (Computational Fluid Dynamics) numerical simulation is introduced in this study. Firstly, the volume of fluid (VOF) multiphase flow model in FLUENT software is used for the simulation of fluid characteristics. Secondly the patterns produced by phase transition in the stirred tank are binaryzed. Finally evolution profile of the zeroth dimensional Betti numbers and the first dimensional Betti numbers in time series are obtained separately. In fact,some aggregates still remain in the tank after the homogeneous mixing.Comparing with the fractal method to characterize the mixing time, the result shows that this method not only can predict the gas-liquid-solid mixing time by the zeroth dimenstional Betti numbers, but also can predict the amount of these aggregates in the stired tank by the first dimenstional Betti numbers, leading to a useful parameter to characterize the non-uniformity of gas-liquid-solid mixing.

Pseudogap and charge ordering in a large-bandwidth electron-doped manganite

We study the origin of complex phase transitions in an electron-doped manganite, La${}_{0.2}$Sr${}_{0.8}$MnO${}_{3}$, using high-resolution photoemission spectroscopy and transmission electron microscopy. The results reveal evidence of phase coexistence and charge ordering in an intermediate temperature range unexpected in this high bandwidth system. The charge ordering nucleates above the phase transition temperature of 265 K, indicating a precursor effect. The high-resolution photoemission spectra exhibit unusual chemical potential shift and persistence of quasiparticles within the insulating phase below 265 K, where the charge-ordered phase dominates and hysteresis is observed in the resistivity. These results provide insight in the study of correlated electron systems exhibiting complex behaviors.

First-Principles and Genetic Modelling of Precipitation Sequences in Aluminium Alloys

Aluminium alloys display complex phase transitions to achieve their desired properties.Many of these involve elaborated precipitation sequences where the main role is not played by ther-modynamically stable species, but by metastable precipitates instead. An interplay between phasestability, crystal symmetry, diffusion, volume and particle/matrix interfaces sets the pace for the ki-netics. Thermodynamic modelling, which focuses on stable precipitates, is not an aid in describingsuch processes, as it is usually transitional phases that achieve the desired properties. The model pre-sented here combines first--principles to obtain the transition precipitate energetics (both at the bulkand at the interface with the matrix) with thermochemical databases to describe the overall kineticsof stable precipitates. Precipitate size and number density are captured via the Kampmann--Wagnernumerical approach, which is embedded in a genetic algorithm to obtain optimal compositional andheat treatment scenarios for the optimisation of the mechanical properties in aluminium alloys of the 7000 series.

Exotic high pressure behavior of light alkali metals, lithium and sodium

At ambient conditions, lithium and sodium behave as free-electron metals and adopt highly symmetric close-packed structures. Under high pressure, however, these simple metals undergo a series of complex phase transitions to structures of lower symmetry, along with significant changes of their physical properties. In this review we provide a comprehensive description of these light alkali metals, with a focus on the structural and electronic properties under pressure.

Observations on PVP-protected noble metallic nanoparticle deposits upon heating via in situ synchrotron radiation X-ray diffraction

Through monitoring the evolution of the X-ray diffraction peaks, the phase transformation of PVP-protected Ag and Au nanoparticle deposits (NPDs) on electronic substrates of Cu and Ni upon heating in air was investigated via in situ synchrotron radiation X-ray diffraction. With an increasing temperature, the broad diffraction peak of nano-sized Ag and Au particles with the original average diameters of 4.2 nm and 9.6 nm, respectively, became sharp because of particle coarsening and coalescence. Complex phase transitions among Au, Cu, AuCu(3) and CuO(x) were observed, mainly due to the negative enthalpy of mixing between Au and Cu. The interactions between NPDs and the substrates affected the shift of diffraction peaks to lower angles, caused by thermal expansion and also the temperature for the oxide formation. Compared to Au, Ag NPDs did not form intermetallic compounds with Cu and the formation of copper oxides can also be retarded mainly due to the phase separation feature of the Ag-Cu system.

Low temperature phase transitions as a representation of structural flexibility of alkaline earth mixed ligand β-diketonates

The low temperature phase transitions of mixed ligand complexes [Ca(hfa) 2(diglyme)(H 2O)] ( I), [Sr(hfa) 2(diglyme)(H 2O)] ( II) and [Ba(hfa) 2(diglyme) 2] ( III) (Hhfa = hexafluoroacetylacetone, diglyme = 2,5,8-trioxanonane) have been detected by differential scanning calorimetry and X-ray diffraction. A comparison of the single-crystal XRD data collected at low and room temperatures shows that these transitions occur due to conformational and positional changes of the ligands in the coordination polyhedra of the central alkaline earth ions, and represent the structural flexibility of I–III. The revealed effects influence the lattice energy of alkaline earth complexes with a structural flexible coordination polyhedron and should be taken into account during theoretical estimation of the thermodynamic properties based on low temperature crystallographic data.

Challenges in the development of hydrate phases as active pharmaceutical ingredients – An example

The challenges during pilot plant scale-up of the SAR474832 API (active pharmaceutical ingredient) production in view of crystallization, isolation, drying and micronization are reported. A variety of different solid-state analytical and spectroscopic techniques (also coupled methods) were applied in order to understand the complex phase transition behaviour of the crystallographic phase (form 1) chosen for development: a partially non-stoichiometric channel-hydrate ( x (1 + 1.25) H 2O) crystallizing from pure water in the crystal habit of fine needles, which tend to agglomerate upon isolation and drying. Processes have been developed for drying, sieving and micronization by jetmilling to avoid non-desired phase transitions (overdrying effects) into other hydrate forms. Special methods have been established to minimize, monitor and control the formation of amorphous content during the particle size reduction steps. By optimizing all production parameters it was possible to produce API batches in 10 kg scale with physical quality suitable for oral formulations (e.g. particle size d90 value < 20 μm, water content and crystallographic phase corresponding to desired form 1 of SAR474832).