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free-energy principle

I A Nedospasov, V G Mozhaev, I E Kuznetsova
It is found that leaky backward Lamb waves, i.e. waves with negative energy-flux velocity, propagating in a plate submerged in a liquid possess extraordinary energy properties distinguishing them from any other type of waves in isotropic media. Namely, the total time-averaged energy flux along the waveguide axis is equal to zero for these waves due to opposite directions of the longitudinal energy fluxes in the adjacent media. This property gives rise to the fundamental question of how to define and calculate correctly the energy velocity in such an unusual case...
February 1, 2017: Ultrasonics
Li-Qiang Xie, Liang Chen, Zi-Ang Nan, Hai-Xin Lin, Tan Wang, Dongping Zhan, Jia-Wei Yan, Bing-Wei Mao, Zhong-Qun Tian
The spontaneous α-to-δ phase transition of the Formamidinium-based (FA) lead halide perovskite hinders its large scale application in solar cells. Though this phase transition can be inhibited by alloying with Methylammonium-based (MA) perovskite, the underlying mechanism is largely unexplored. In this communication, we grow high quality mixed cations and halides perovskite single crystals (FAPbI3)1-x(MAPbBr3)x to understand the principles for maintaining pure perovskite phase, which is essential to device optimization...
February 17, 2017: Journal of the American Chemical Society
Hossein Ahmadzadeh, Marie R Webster, Reeti Behera, Angela M Jimenez Valencia, Denis Wirtz, Ashani T Weeraratna, Vivek B Shenoy
Cancer cell invasion from primary tumors is mediated by a complex interplay between cellular adhesions, actomyosin-driven contractility, and the physical characteristics of the extracellular matrix (ECM). Here, we incorporate a mechanochemical free-energy-based approach to elucidate how the two-way feedback loop between cell contractility (induced by the activity of chemomechanical interactions such as Ca(2+) and Rho signaling pathways) and matrix fiber realignment and strain stiffening enables the cells to polarize and develop contractile forces to break free from the tumor spheroids and invade into the ECM...
February 14, 2017: Proceedings of the National Academy of Sciences of the United States of America
Alexei V Finkelstein, Azat J Badretdin, Oxana V Galzitskaya, Dmitry N Ivankov, Natalya S Bogatyreva, Sergiy O Garbuzynskiy
The ability of protein chains to spontaneously form their spatial structures is a long-standing puzzle in molecular biology. Experimentally measured folding times of single-domain globular proteins range from microseconds to hours: the difference (10-11 orders of magnitude) is the same as that between the life span of a mosquito and the age of the universe. This review describes physical theories of rates of overcoming the free-energy barrier separating the natively folded (N) and unfolded (U) states of protein chains in both directions: "U-to-N" and "N-to-U"...
January 27, 2017: Physics of Life Reviews
Arthur C Reber, Shiv N Khanna
The relative role of electronic and geometric effects on the stability of clusters has been a contentious topic for quite some time, with the focus on electronic structure generally gaining the upper hand. In this Account, we hope to demonstrate that both electronic shell filling and geometric shell filling are necessary concepts for an intuitive understanding of the reactivity of metal clusters. This work will focus on the reactivity of aluminum based clusters, although these concepts may be applied to clusters of different metals and ligand protected clusters...
February 9, 2017: Accounts of Chemical Research
Jarrod Milshtein, Sydney Fisher, Tanya Breault, Levi Thompson, Fikile Brushett
Non-aqueous redox flow batteries (NAqRFBs) are promising devices for grid-scale energy storage, however, high projected prices could limit commercial prospects. One price reduction route is to minimize or eliminate the expensive supporting salts typically employed in NAqRFBs. We demonstrate the feasibility of a flow cell operating in the absence of supporting salt, utilizing ionic active species. These ionic species possess high conductivities in acetonitrile (12 - 19 mS cm-1), and cycle at 20 mA cm-2 with energy efficiencies (> 75%) comparable to state-of-the-art NAqRFBs employing high concentrations of supporting salt...
February 8, 2017: ChemSusChem
Jan Wrobel, Duc Nguyen-Manh, Sergei Dudarev, Krzysztof Kurzydłowski
The occurrence of segregation in dilute alloys under irradiation is a highly unusual phenomenon that has recently attracted attention, simulated by the interest in the fundamental properties of alloys as well as by applications. The fact that solute atoms segregate in alloys that, according to equilibrium thermodynamics, should exhibit full solubility, has significant practical implications, as the formation of precipitates strongly affects physical and mechanical properties. A lattice Hamiltonian model, generalizing so-called "ABV" Ising model and including collective many-body inter-atomic interactions, has been developed to treat rhenium solute atoms and vacancies in tungsten as components of a ternary alloy...
February 8, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
A V Potemkin, M A Grishina, V A Potemkin
BACKGROUND: In 1979, R.D.Cramer and M.Milne made a first realization of the above mentioned principles attempting to compare molecules by aligning them in space and by mapping their molecular fields to a 3D grid. Further, this approach was developed as the DYLOMMS (DYnamic Lattice-Oriented Molecular Modelling System) approach. In 1984, H.Wold and S.Wold proposed the use of partial least squares (PLS) analysis, instead of principal component analysis, to correlate the field values with biological activities...
February 7, 2017: Current Drug Discovery Technologies
Paul B Badcock, Christopher G Davey, Sarah Whittle, Nicholas B Allen, Karl J Friston
Major depression is a debilitating condition characterised by diverse neurocognitive and behavioural deficits. Nevertheless, our species-typical capacity for depressed mood implies that it serves an adaptive function. Here we apply an interdisciplinary theory of brain function to explain depressed mood and its clinical manifestations. Combining insights from the free-energy principle (FEP) with evolutionary theorising in psychology, we argue that depression reflects an adaptive response to perceived threats of aversive social outcomes (e...
February 1, 2017: Trends in Cognitive Sciences
Paul Maguire, David Rutherford, Manuel Macias-Montero, Charles Mahony, Colin Kelsey, Mark Tweedie, Fátima Pérez-Martin, Harold McQuaid, Declan Diver, Davide Mariotti
We demonstrate an entirely new method of nanoparticle chemical synthesis based on liquid droplet irradiation with ultralow (<0.1 eV) energy electrons. While nanoparticle formation via high energy radiolysis or transmission electron microscopy-based electron bombardment is well-understood, we have developed a source of electrons with energies close to thermal which leads to a number of important and unique benefits. The charged species, including the growing nanoparticles, are held in an ultrathin surface reaction zone which enables extremely rapid precursor reduction...
January 31, 2017: Nano Letters
Wenhao Sun, Stephen T Dacek, Shyue Ping Ong, Geoffroy Hautier, Anubhav Jain, William D Richards, Anthony C Gamst, Kristin A Persson, Gerbrand Ceder
The space of metastable materials offers promising new design opportunities for next-generation technological materials, such as complex oxides, semiconductors, pharmaceuticals, steels, and beyond. Although metastable phases are ubiquitous in both nature and technology, only a heuristic understanding of their underlying thermodynamics exists. We report a large-scale data-mining study of the Materials Project, a high-throughput database of density functional theory-calculated energetics of Inorganic Crystal Structure Database structures, to explicitly quantify the thermodynamic scale of metastability for 29,902 observed inorganic crystalline phases...
November 2016: Science Advances
Andrey A Kistanov, Yongqing Cai, Yong-Wei Zhang, Sergey V Dmitriev, Kun Zhou
By using first-principles calculations, the electronic structure of planar and strained in-plane graphene/silicene heterostructure is studied. The heterostructure is found to be metallic in a strain range from  -7% (compression) to  +7% (tension). The effect of compressive/tensile strain on the chemical activity of the in-plane graphene/silicene heterostructure is examined by studying its interaction with the H2O molecule. It shows that compressive/tensile strain is able to increase the binding energy of H2O compared with the adsorption on a planar surface, and the charge transfer between the water molecule and the graphene/silicene sheet can be modulated by strain...
March 8, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Jing Li, Yang Su, Wei Xia, Yan Qin, Martin J Humphries, Dietmar Vestweber, Carlos Cabañas, Chafen Lu, Timothy A Springer
We show that the three conformational states of integrin α5β1 have discrete free energies and define activation by measuring intrinsic affinities for ligand of each state and the equilibria linking them. The 5,000-fold higher affinity of the extended-open state than the bent-closed and extended-closed states demonstrates profound regulation of affinity. Free energy requirements for activation are defined with protein fragments and intact α5β1 On the surface of K562 cells, α5β1 is 99.8% bent-closed. Stabilization of the bent conformation by integrin transmembrane and cytoplasmic domains must be overcome by cellular energy input to stabilize extension...
January 25, 2017: EMBO Journal
M Kozák, J McNeur, K J Leedle, H Deng, N Schönenberger, A Ruehl, I Hartl, J S Harris, R L Byer, P Hommelhoff
The temporal resolution of ultrafast electron diffraction and microscopy experiments is currently limited by the available experimental techniques for the generation and characterization of electron bunches with single femtosecond or attosecond durations. Here, we present proof of principle experiments of an optical gating concept for free electrons via direct time-domain visualization of the sub-optical cycle energy and transverse momentum structure imprinted on the electron beam. We demonstrate a temporal resolution of 1...
January 25, 2017: Nature Communications
Nicholas J Borys, Edward S Barnard, Shiyuan Gao, Kaiyuan Yao, Wei Bao, Alexander Buyanin, Yingjie Zhang, Sefaattin Tongay, Changhyun Ko, Joonki Suh, Alexander Weber-Bargioni, Junqiao Wu, Li Yang, P James Schuck
Broadband optoelectronics such as artificial light harvesting technologies necessitate efficient and, ideally, tunable coupling of excited states over a wide range of energies. In monolayer MoS2, a prototypical two-dimensional layered semiconductor, the excited state manifold spans the visible electromagnetic spectrum and is comprised of an interconnected network of excitonic and free-carrier excitations. Here, photoluminescence excitation spectroscopy is used to reveal the energetic and spatial dependence of broadband excited state coupling to the ground-state luminescent excitons of monolayer MoS2...
February 1, 2017: ACS Nano
Fawei Tang, Xiaoyan Song, Haibin Wang, Xuemei Liu, Zuoren Nie
A hybrid model that combines first principles calculations and thermodynamic evaluation was developed to describe the thermal stability of a nanocrystalline solid solution with weak segregation. The dependence of the solute segregation behavior on the electronic structure, solute concentration, grain size and temperature was demonstrated, using the nanocrystalline Cu-Zn system as an example. The modeling results show that the segregation energy changes with the solute concentration in a form of nonmonotonic function...
January 24, 2017: Physical Chemistry Chemical Physics: PCCP
Xin-Gang Zhao, Ji-Hui Yang, Yuhao Fu, Dongwen Yang, Qiaoling Xu, Liping Yu, Su-Huai Wei, Lijun Zhang
Hybrid organic-inorganic halide perovskites with the prototype material of CH3NH3PbI3 have recently attracted intense interest as low-cost and high-performance photovoltaic absorbers. Despite the high power conversion efficiency exceeding 20% achieved by their solar cells, two key issues-the poor device stabilities associated with their intrinsic material instability and the toxicity due to water-soluble Pb(2+)-need to be resolved before large-scale commercialization. Here, we address these issues by exploiting the strategy of cation-transmutation to design stable inorganic Pb-free halide perovskites for solar cells...
February 9, 2017: Journal of the American Chemical Society
J Baumann, C Herzog, M Spanier, D Grötzsch, L Lühl, K Witte, A Jonas, S Günther, F Förste, R Hartmann, M Huth, D Kalok, D Steigenhöfer, M Krämer, T Holz, R Dietsch, L Strüder, B Kanngießer, I Mantouvalou
Grazing incidence and grazing emission X-ray fluorescence spectroscopy (GI/GE-XRF) are techniques that enable nondestructive, quantitative analysis of elemental depth profiles with a resolution in the nanometer regime. A laboratory setup for soft X-ray GEXRF measurements is presented. Reasonable measurement times could be achieved by combining a highly brilliant laser produced plasma (LPP) source with a scanning-free GEXRF setup, providing a large solid angle of detection. The detector, a pnCCD, was operated in a single photon counting mode in order to utilize its energy dispersive properties...
February 7, 2017: Analytical Chemistry
S Herminghaus, M G Mazza
The emergence of patterns and phase separation in many-body systems far from thermal equilibrium is discussed using the example of driven granular gases. It is shown that phase separation follows a similar mechanism as in the systems of active Brownian particles. Depending on the quantities chosen for observation, it may or may not be easy to find functionals analogous to the free energy in equilibrium statistical physics. We argue that although such functionals can always be derived from the dynamics, it is of only limited value for predicting relevant aspects of the nonequilibrium steady state of the system...
February 7, 2017: Soft Matter
Jing Yang, Mostafa Youssef, Bilge Yildiz
We present a multi-scale approach to predict equilibrium defect concentrations across oxide/oxide hetero-interfaces. There are three factors that need to be taken into account simultaneously for computing defect redistribution around the hetero-interfaces: the variation of local bonding environment at the interface as epitomized in defect segregation energies, the band offset at the interface, and the equilibration of the chemical potentials of species and electrons via ionic and electronic drift-diffusion fluxes...
February 1, 2017: Physical Chemistry Chemical Physics: PCCP
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