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Materials in metastable states, such as amorphous ice and supercooled condensed matter, often exhibit exotic phenomena. To date, achieving metastability is usually accomplished by rapid quenching through a thermodynamic path function, namely, heating−cooling cycles. However, heat can be detrimental to organic-containing materials because it can induce degradation. Alternatively, the application of pressure can be used to achieve metastable states that are inaccessible via heating−cooling cycles. Here we report metastable states of 2D organic−inorganic hybrid perovskites reached through structural amorphization under compression followed by recrystallization via decompression. Remarkably, such pressure-derived metastable states in 2D hybrid perovskites exhibit enduring bandgap narrowing by as much as 8.2% with stability under ambient conditions. The achieved metastable states in 2D hybrid perovskites via compression−decompression cycles offer an alternative pathway toward manipulating the properties of these “soft” materials.

Perhaps the most iconic feature of melting Arctic sea ice is the distinctive ponds that form on its surface. The geometrical patterns describing how melt water is distributed over the surface largely determine the solar reflectance and transmittance of the sea ice cover, which are key parameters in climate modeling and upper ocean ecology. In order to help develop a predictive theoretical approach to studying melting sea ice, and the resulting patterns of light and dark regions on its surface in particular, we look to the statistical mechanics of phase transitions and introduce a two-dimensional random field Ising model which accounts for only the most basic physics in the system. The ponds are identified as metastable states in the model, where the binary spin variable corresponds to the presence of melt water or ice on the sea ice surface. With the lattice spacing determined by snow topography data as the only measured parameter input into the model, energy minimization drives the system toward realistic pond configurations from an initially random state. The model captures the essential mechanism of pattern formation of Arctic melt ponds, with predictions that agree very closely with observed scaling of pond sizes and transition in pond fractal dimension.

Noninvasive ultrasound is more convenient and easily accessible for controlled drug delivery of polymeric nanoparticles than many other stimuli. However, controlled ultrasound responsiveness is rather challenging as the mechanism is still unclear. In this article, we disclose the origin and the key regulating factors of ultrasound responsiveness of block copolymer nanoparticles such as simple vesicles, framboidal vesicles, lamellae, beads-like micelles and complex micelles that are self-assembled from a range of poly(ethylene oxide)- b -polymethacrylates based model copolymers. We discover that the intrinsic ultrasound responsiveness of block copolymer nanoparticles thermodynamically originates from their metastable states, and its expression kinetically relates to the mobility of the hydrophobic segments of block copolymers. Specifically, the self-assembly temperature ( T s ) that has been usually considered as a less important factor in most of macromolecular self-assembly systems, and the solvents for the selfassembly are two dominant regulating factors of the ultrasound responsiveness because they determine the thermodynamic state (metastable or stable) of nanoparticles. For example, simple vesicles with good or excellent ultrasound responsiveness can be prepared in THF/water when the T s is around or slightly below the glass transition temperature ( T g ) of the hydrophobic segment of the block copolymer because the combination of this solvent with this T s facilitates the formation of metastable vesicles. By contrast, thermodynamically stable solid nanoparticles such as spherical micelles and lamellae (mainly formed in DMF/water) are not sensitive to ultrasound at all, neither are the vesicles in THF/water at stable states when the T s is highly above T g . In addition, we unravel that the responsive rate is highly dependent on the sonication temperature ( T u ), i.e., the higher the T u , the faster the rate. Overall, the above important findings provide us with a fresh insight into how to design ultrasound-responsive nanoparticles and may open new avenues for synthesizing translational noninvasively responsive drug carriers.

We study the statistical underpinnings of life, in particular its increase in order and complexity over evolutionary time. We question some common assumptions about the thermodynamics of life. We recall that contrary to widespread belief, even in a closed system entropy growth can accompany an increase in macroscopic order. We view metabolism in living things as microscopic variables directly driven by the second law of thermodynamics, while viewing the macroscopic variables of structure, complexity and homeostasis as mechanisms that are entropically favored because they open channels for entropy to grow via metabolism. This perspective reverses the conventional relation between structure and metabolism, by emphasizing the role of structure for metabolism rather than the converse. Structure extends in time, preserving information along generations, particularly in the genetic code, but also in human culture. We argue that increasing complexity is an inevitable tendency for systems with these dynamics and explain this with the notion of metastable states, which are enclosed regions of the phase-space that we call “bubbles,” and channels between these, which are discovered by random motion of the system. We consider that more complex systems inhabit larger bubbles (have more available states), and also that larger bubbles are more easily entered and less easily exited than small bubbles. The result is that the system entropically wanders into ever-larger bubbles in the foamy phase space, becoming more complex over time. This formulation makes intuitive why the increase in order/complexity over time is often stepwise and sometimes collapses catastrophically, as in biological extinction.

The search for low-energy antideuterons in cosmic rays allows the addressing of fundamental physics problems testing for the presence of primordial antimatter and the nature of Dark Matter. The PHeSCAMI (Pressurized Helium Scintillating Calorimeter for AntiMatter Identification) project aims to exploit the long-living metastable states of the helium target for the identification of low-energy antideuterons in cosmic rays. A space-based pressurized helium calorimeter would provide a characteristic identification signature based on the coincident detection of a prompt scintillation signal emitted by the antideuteron energy loss during the slowing-down phase in the gas, and the (≈µs) delayed scintillation signal provided by the charged pions produced in the subsequent annihilation. The performance of a high-pressure (200-bar) helium scintillator prototype, tested in the INFN-TIFPA laboratory, will be summarized.

We investigate dissociation in flight of metastable molecular dications formed by ultrashort, intense laser pulses using the cold target recoil ion momentum spectroscopy technique. A method for retrieving the lifetime(s) of the transient metastable state(s) as well as the complete three-dimensional momenta of the dissociating fragments is presented. Specifically, we demonstrate and discuss this approach by focusing on dissociation in flight of the ethylene dication going to the deprotonation channel. Two lifetimes are found to be associated with this process, C2H 4 2 + → C2H3+ + H+: τ 1 = 202 10 ns and τ 2 = 916 40 ns. For the corresponding channel in deuterated ethylene, lifetimes of τ 1 = 269 29 ns and τ 2 = 956 83 ns are obtained.

After reviewing the peculiar thermodynamics and statistical mechanics of self-gravitating systems, we consider the case of a “binary star” consisting of two particles of size a in gravitational interaction in a box of radius R. The caloric curve of this system displays a region of negative specific heat in the microcanonical ensemble, which is replaced by a first-order phase transition in the canonical ensemble. The free energy viewed as a thermodynamic potential exhibits two local minima that correspond to two metastable states separated by an unstable maximum forming a barrier of potential. By introducing a Langevin equation to model the interaction of the particles with the thermal bath, we study the random transitions of the system between a “dilute” state, where the particles are well separated, and a “condensed” state, where the particles are bound together. We show that the evolution of the system is given by a Fokker–Planck equation in energy space and that the lifetime of a metastable state is given by the Kramers formula involving the barrier of free energy. This is a particular case of the theory developed in a previous paper (Chavanis, 2005) for N Brownian particles in gravitational interaction associated with the canonical ensemble. In the case of a binary star (N=2), all the quantities can be calculated exactly analytically. We compare these results with those obtained in the mean field limit N→+∞.

This study investigates the ionization balance of Sn ions in an electron beam ion trap (EBIT). Highly charged Sn ions are produced via collisions with a quasi-monochromatic electron beam, and the charge state distribution is analyzed using a Wien filter. Significant Sn15+ production occurs at electron energies below the ionization potential of Sn14+ (379 eV). Calculations attribute this to electron-impact ionization from metastable Sn14+ states.

From the dynamical point of view, most cognitive phenomena are hierarchical, transient and sequential. Such cognitive spatio-temporal processes can be represented by a set of sequential metastable dynamical states together with their associated transitions: The state is quasi-stationary close to one metastable state before a rapid transition to another state. Hence, we postulate that metastable states are the central players in cognitive information processing. Based on the analogy of quasiparticles as elementary units in physics, we introduce here the quantum of cognitive information dynamics, which we term “cognon”. A cognon, or dynamical unit of thought, is represented by a robust finite chain of metastable neural states. Cognons can be organized at multiple hierarchical levels and coordinate complex cognitive information representations. Since a cognon is an abstract conceptualization, we link this abstraction to brain sequential dynamics that can be measured using common modalities and argue that cognons and brain rhythms form binding spatiotemporal complexes to keep simultaneous dynamical information which relate the ‘what’, ‘where’ and ‘when’.

The authors have given results of experimental study of metastable states of a nonwetting liquid (distilled water) dispersed in the pore space of hydrophobizated silica gel Fluka 100 C 18 under the conditions of partial filling. The results were obtained for 10 and 22°C with a varying degree of filling (11 to 100%) at expectation times from 1 to 1000 s. According to the obtained data, the dependence of the fraction of fast states on the initial degree of filling has been obtained at different temperatures. It has been shown that the increase in temperature and the increase in the initially filled fraction of the volume of nanoporous material lead to a growth in the fraction of fast states with a characteristic time of outflow of the order of several seconds.