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free-energy principle

Sanat K Singha, Prasanta K Das, Biswajit Maiti
The effect of contact line pinning on nucleation is reported using continuum thermodynamics. Based on the principle of the free-energy maximization, closed-form expressions in the dimensionless form for the free-energy of the three-phase metastable system and the thermodynamic barrier are formulated with respect to the system geometry and the substrate wettability. The condition of maximality limits the dynamic contact angle within the cluster-phase-phobic regime. The dimensionless nucleation barrier or the potency factor can be divided into two components related to the system geometry and the pinning effect...
June 21, 2017: Journal of Chemical Physics
Paco Calvo, Karl Friston
In this article we account for the way plants respond to salient features of their environment under the free-energy principle for biological systems. Biological self-organization amounts to the minimization of surprise over time. We posit that any self-organizing system must embody a generative model whose predictions ensure that (expected) free energy is minimized through action. Plants respond in a fast, and yet coordinated manner, to environmental contingencies. They pro-actively sample their local environment to elicit information with an adaptive value...
June 2017: Journal of the Royal Society, Interface
Raquel Lizárraga, Fan Pan, Lars Bergqvist, Erik Holmström, Zsolt Gercsi, Levente Vitos
Identifying the forces that drive a phase transition is always challenging. The hcp-fcc phase transition that occurs in cobalt at ~700 K has not yet been fully understood, although early theoretical studies have suggested that magnetism plays a main role in the stabilization of the fcc phase at high temperatures. Here, we perform a first principles study of the free energies of these two phases, which we break into contributions arising from the vibration of the lattice, electronic and magnetic systems and volume expansion...
June 19, 2017: Scientific Reports
Manoj Ducher, Fabio Pietrucci, Etienne Balan, Guillaume Ferlat, Lorenzo Paulatto, Marc Blanchard
Many properties of aqueous cations depend on their coordination state. However, the lack of long-range order and the dynamic character of aqueous solutions make it difficult to obtain information beyond average coordination parameters. A thorough understanding of the molecular scale environment of aqueous cations usually requires a combination of experimental and theoretical approaches. In the case of Zn(2+), significant discrepancies occur among theoretical investigations based on first-principles molecular-dynamics (FPMD) or free-energy calculations, although experimental data consistently point to a dominant hexaaquo-zinc complex (Zn[H2O]6)(2+) in pure water...
June 16, 2017: Journal of Chemical Theory and Computation
Robert A Evarestov, Andrei V Bandura, Vitaly V Porsev, Alexey V Kovalenko
Hybrid density functional theory calculations were performed for the first time on structure, stability, phonon frequencies, and thermodynamic functions of hafnia-based single-wall nanotubes. The nanotubes were rolled up from the thin free layers of cubic and tetragonal phases of HfO2 . It was shown that the most stable HfO2 single-wall nanotubes can be obtained from hexagonal (111) layer of the cubic phase. Phonon frequencies have been calculated for different HfO2 nanolayers and nanotubes to prove the local stability and to find the thermal contributions to their thermodynamic functions...
June 15, 2017: Journal of Computational Chemistry
Prabu Manoharan, Nanda Ghoshal
Traditional structure-based virtual screening method to identify drug-like small molecules for BACE1 is so far unsuccessful. Location of BACE1, poor Blood Brain Barrier permeability and P-glycoprotein (Pgp) susceptibility of the inhibitors make it even more difficult. Fragment-based drug design method is suitable for efficient optimization of initial hit molecules for target like BACE1. We have developed a fragment-based virtual screening approach to identify/optimize the fragment molecules as a starting point...
June 15, 2017: Journal of Biomolecular Structure & Dynamics
Kyle Daniel Gilroy, Joël Puibasset, Madeline Vara, Younan Xia
This work demonstrates a new strategy for controlling the evolution of twin defects in metal nanocrystals by simply following thermodynamic principles. With Ag nanocrystals supported on amorphous SiO2 as a typical example, we establish that twin defects can be rationally generated by equilibrating nanoparticles of different sizes through heating and then cooling. We validate that Ag nanocrystals with icosahedral, decahedral, and single-crystal structures are favored at sizes below 7 nm, between 7 and 11 nm, and greater than 11 nm, respectively...
June 13, 2017: Angewandte Chemie
Foteini A Kappi, George A Papadopoulos, George Z Tsogas, Dimosthenis L Giokas
This work describes a new approach for the determination of free biothiols in biological fluids that exploits some of the basic principles of early photographic chemistry - that was based on silver-halide recording materials - and uses broadly-available imaging devices (i.e. flatbed scanners) as detectors. Specifically, the proposed approach relies on the ability of biothiols to bind to silver ions and dissociate the silver halide crystals thus changing the photosensitivity of silver halide crystal suspension...
September 1, 2017: Talanta
Kyoung-Whan Kim, Kyung-Jin Lee, Hyun-Woo Lee, M D Stiles
We compute the magnetocrystalline anisotropy energy within two-dimensional Rashba models. For a ferromagnetic free-electron Rashba model, the magnetic anisotropy is exactly zero regardless of the strength of the Rashba coupling, unless only the lowest band is occupied. For this latter case, the model predicts in-plane anisotropy. For a more realistic Rashba model with finite band width, the magnetic anisotropy evolves from in-plane to perpendicular and back to in-plane as bands are progressively filled. This evolution agrees with first-principles calculations on the interfacial anisotropy, suggesting that the Rashba model captures energetics leading to anisotropy originating from the interface provided that the model takes account of the finite Brillouin zone...
November 2016: Physical Review. B
Achim Peters, Bruce S McEwen, Karl Friston
The term 'stress' - coined in 1936 - has many definitions, but until now has lacked a theoretical foundation. Here we present an information-theoretic approach - based on the 'free energy principle' - defining the essence of stress; namely, uncertainty. We address three questions: What is uncertainty? What does it do to us? What are our resources to master it? Mathematically speaking, uncertainty is entropy or 'expected surprise'. The 'free energy principle' rests upon the fact that self-organizing biological agents resist a tendency to disorder and must therefore minimize the entropy of their sensory states...
May 30, 2017: Progress in Neurobiology
M A Beckwith, S Jiang, A Schropp, A Fernandez-Pañella, H G Rinderknecht, S C Wilks, K B Fournier, E C Galtier, Z Xing, E Granados, E Gamboa, S H Glenzer, P Heimann, U Zastrau, B I Cho, J H Eggert, G W Collins, Y Ping
Tuning the energy of an x-ray probe to an absorption line or edge can provide material-specific measurements that are particularly useful for interfaces. Simulated hard x-ray images above the Fe K-edge are presented to examine ion diffusion across an interface between Fe2O3 and SiO2 aerogel foam materials. The simulations demonstrate the feasibility of such a technique for measurements of density scale lengths near the interface with submicron spatial resolution. A proof-of-principle experiment is designed and performed at the Linac coherent light source facility...
May 2017: Review of Scientific Instruments
A Moyassari, M Unge, M S Hedenqvist, U W Gedde, F Nilsson
In order to increase our fundamental knowledge about high-voltage cable insulation materials, realistic polyethylene (PE) structures, generated with a novel molecular modeling strategy, have been analyzed using first principle electronic structure simulations. The PE structures were constructed by first generating atomistic PE configurations with an off-lattice Monte Carlo method and then equilibrating the structures at the desired temperature and pressure using molecular dynamics simulations. Semicrystalline, fully crystalline and fully amorphous PE, in some cases including crosslinks and short-chain branches, were analyzed...
May 28, 2017: Journal of Chemical Physics
G Rosi, G D'Amico, L Cacciapuoti, F Sorrentino, M Prevedelli, M Zych, Č Brukner, G M Tino
The Einstein equivalence principle (EEP) has a central role in the understanding of gravity and space-time. In its weak form, or weak equivalence principle (WEP), it directly implies equivalence between inertial and gravitational mass. Verifying this principle in a regime where the relevant properties of the test body must be described by quantum theory has profound implications. Here we report on a novel WEP test for atoms: a Bragg atom interferometer in a gravity gradiometer configuration compares the free fall of rubidium atoms prepared in two hyperfine states and in their coherent superposition...
June 1, 2017: Nature Communications
Sippakorn Wannakao, Watthanachai Jumpathong, Kanokwan Kongpatpanich
The electrocatalytic reduction of carbon dioxide (CO2ER) is a great challenge within the field of energy and environmental research. Competing reactions, including hydrogen evolution reactions (HER) and surface oxidation, limit the conversion of CO2ER at low overpotentials. This is because these competing reactions produce intermediates (adsorbed H and OH) with chemical bonds similar to those formed in CO2ER (adsorbed COOH and OCHO). Here, we report the adsorption free energies of CO2ER and competitive intermediates within H-bonding functionalized metalloporphyrin frameworks using first-principles calculations...
June 1, 2017: Inorganic Chemistry
Jing Chen, Zhixun Luo, Hongbing Fu, Jiannian Yao
The newly built 177 nm all-solid-state deep ultraviolet (DUV) laser photoionization mass spectrometer finds a unique advantage to identify porphyrins that bear ionization energies close to 7.0 eV. We observed dramatic selectivity of tetraphenylporphyrins (TPPs) pertaining to varied photochemical processes initiated by the DUV laser excitation. Single-photon ionization was found dominant for 2H-TPP resulting in a fragmentation-free mass spectrum; photoinduced dehydrogenation was observed for zinc TPP, but both dehydrogenation and demetalation are noted for copper TPP...
June 7, 2017: Journal of Physical Chemistry. A
Bin Xu, Jorge Íñiguez, L Bellaiche
Dielectric capacitors, although presenting faster charging/discharging rates and better stability compared with supercapacitors or batteries, are limited in applications due to their low energy density. Antiferroelectric (AFE) compounds, however, show great promise due to their atypical polarization-versus-electric field curves. Here we report our first-principles-based theoretical predictions that Bi1-xRxFeO3 systems (R being a lanthanide, Nd in this work) can potentially allow high energy densities (100-150 J cm(-3)) and efficiencies (80-88%) for electric fields that may be within the range of feasibility upon experimental advances (2-3 MV cm(-1))...
May 30, 2017: Nature Communications
David Rudrauf, Daniel Bennequin, Isabela Granic, Gregory Landini, Karl Friston, Kenneth Williford
We introduce a mathematical model of embodied consciousness, the Projective Consciousness Model (PCM), which is based on the hypothesis that the spatial field of consciousness (FoC) is structured by a projective geometry and under the control of a process of active inference. The FoC in the PCM combines multisensory evidence with prior beliefs in memory, and frames them by selecting points of view and perspectives according to preferences. The choice of projective frames governs how expectations are transformed by consciousness...
May 26, 2017: Journal of Theoretical Biology
Alessandra S Oliveira, Flávia M Dalla Nora, Renius O Mello, Paola A Mello, Bruna Tischer, Adilson B Costa, Juliano S Barin
A simple and fast method is proposed for determining the alcoholic content of distilled beverages by thermal infrared enthalpimetry (TIE), in which purified water is added directly and the temperature rise caused by the heat of dilution is monitored using an infrared camera. A calibration curve was constructed with hydroalcoholic reference solutions to determine the alcoholic content of vodka, whisky, and cachaça. The influence of the total volume of solutions in the reactor, the stirring speed, the dispensing rate, and the ratio between hydroalcoholic samples and water were evaluated to reach an optimum mixture and provide low variation among measurements...
August 15, 2017: Talanta
Ali Kachmar, Marcelo Carignano, Teodoro Laino, Marcella Iannuzzi, Jürg Hutter
The understanding of lithium solvation and transport in ionic liquids is important due to the possible applications in electrochemical devices. Using first principles simulations aided with the metadynamics approach we study the free energy landscape for lithium at infinite dilution conditions in ethylammonium nitrate, a protic ionic liquid. We analyze the local structure of the liquid around the lithium cation and find a quantitative picture in agreement with experimental findings. Our simulations show that the lowest two free energy minima correspond to conformations with the lithium solvated either by 3 or 4 nitrates ions with a transition barrier between them of 0...
May 26, 2017: ChemSusChem
Bingcheng Luo, Xiaohui Wang, Enke Tian, Hongzhou Song, Hongxian Wang, Longtu Li
A novel lead-free (1 - x)CaTiO3-xBiScO3 linear dielectric ceramic with enhanced energy-storage density was fabricated. With the composition of BiScO3 increasing, the dielectric constant of (1 - x)CaTiO3-xBiScO3 ceramics first increased and then decreased after the composition x > 0.1, while the dielectric loss decreased first and increased. For the composition x = 0.1, the polarization was increased into 12.36 μC/cm(2), 4.6 times higher than that of the pure CaTiO3. The energy density of 0.9CaTiO3-0.1BiScO3 ceramic was 1...
May 31, 2017: ACS Applied Materials & Interfaces
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