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Zhihao Lan, Merlijn van Horssen, Stephen Powell, Juan P Garrahan
One of the general mechanisms that give rise to the slow cooperative relaxation characteristic of classical glasses is the presence of kinetic constraints in the dynamics. Here we show that dynamical constraints can similarly lead to slow thermalization and metastability in translationally invariant quantum many-body systems. We illustrate this general idea by considering two simple models: (i) a one-dimensional quantum analogue to classical constrained lattice gases where excitation hopping is constrained by the state of neighboring sites, mimicking excluded-volume interactions of dense fluids; and (ii) fully packed quantum dimers on the square lattice...
July 27, 2018: Physical Review Letters
Nikhil Karthik, Rajamani Narayanan
We study three-dimensional noncompact QED with a single two-component massless fermion and two infinitely massive regulator fermions of half the charge using the lattice overlap formalism. The parity anomaly is expected to cancel exactly between the massless and regulator fermions in the continuum, but this cancellation is inexact on a lattice akin to lattice chiral gauge theories. We show nonperturbatively that parity-breaking terms vanish in the continuum limit at any finite volume. We present numerical evidence that the resulting parity-invariant theory spontaneously breaks parity in the infinite volume limit...
July 27, 2018: Physical Review Letters
Wen-Yu He, Xiao Yan Xu, Gang Chen, K T Law, Patrick A Lee
1T-TaS_{2} is a cluster Mott insulator on the triangular lattice with 13 Ta atoms forming a star of David cluster as the unit cell. We derive a two-dimensional XXZ spin-1/2 model with a four-spin ring exchange term to describe the effective low energy physics of a monolayer 1T-TaS_{2}, where the effective spin-1/2 degrees of freedom arises from the Kramers degenerate spin-orbital states on each star of David. A large scale density matrix renormalization group simulation is further performed on this effective model and we find a gapless spin liquid phase with a spinon Fermi surface at a moderate to large strength region of the four-spin ring exchange term...
July 27, 2018: Physical Review Letters
Ting Jiang, Fang Wang, Anyang Cui, Shuang Guo, Kai Jiang, Liyan Shang, Zhigao Hu, Junhao Chu
The mutual interaction of the type II heterointerface can be very susceptible to the variation of electrons states, bringing into the band structure and the band alignment difference comparing with their pristine states. Here, the thermal evolution of exciton transition and electronic properties inside the covalently bonded type II interface of the atomically planar WSe$_{2}$-WS$_{2}$ lateral heterojunction has been studied. With the aid of luminescence and electronic evolution, it is found that the coupling at the heterointerface is strong, for that the change of photon-electron transition with temperature is weak...
August 10, 2018: Nanotechnology
Pai Li, Zhenyu Li, Jinlong Yang
Alkali metal atom adsorption energy is an important descriptor for anode material design. In this study, an energy decomposition model is developed to provide valuable insights in understanding how the adsorption behavior can be tuned. As an example, Li adsorption on graphene enhanced by a tensile strain is analyzed based on this model. Such an analysis then motivates us to find a system with similar electronic structure but larger lattice parameter compared to graphene as an anode material. Our first principles calculations indicate that B2S, as an isoelectronic system of graphene, is a good candidate...
August 10, 2018: Journal of Physical Chemistry Letters
Mani Sakthivel, Ramaraj Sukanya, Shen-Ming Chen
The electronic conductivity and electrocatalytic activity of metal chalcogenides are normally enhanced by following the ideal strategies such as substitution/doping of heterogeneous atoms and hybridization of highly conductive carbon supportive materials. Here, a rare earth element (samarium) was substituted with MoSe2 by using the simple hydrothermal method. The lattice distortion due to the substitution of Sm3+ with MoSe2 was clearly observed by using HRTEM analysis. As a consequence, the prepared SmMoSe2 nanorod was encapsulated with graphene oxide sheets (GO) using ultrasonication process...
August 10, 2018: ACS Applied Materials & Interfaces
Christina A Gatsiou, Claire S Adjiman, Constantinos C Pantelides
In lattice energy models that combine ab initio and empirical components, it is important to ensure consistency between these components so that meaningful quantitative results are obtained. A method for deriving parameters of atom-atom repulsion dispersion potentials for crystals, tailored to different ab initio models, is presented. It is based on minimization of the sum of squared deviations between experimental and calculated structures and energies. The solution algorithm is designed to avoid convergence to local minima in the parameter space by combining a deterministic low-discrepancy sequence for the generation of multiple initial parameter guesses with an efficient local minimization algorithm...
August 10, 2018: Faraday Discussions
L Straka, J Drahokoupil, P Veřtát, M Zelený, J Kopeček, A Sozinov, O Heczko
We have found low temperature a/b nanotwins having (110) twinning plane in a five-layered modulated martensite phase of Ni50 Mn25+x Ga25-x (at. %) Heusler alloys and identified the particular region in phase diagram where the nanotwinning occurs. Evolution of the structure with decreasing temperature was studied by X-ray diffraction using single crystals exhibiting magnetic shape memory effect. The merging of (400) and (040) lines upon cooling for 2.6 < x < 3.5 indicated a/b nanotwinning originating from the refinement of initially coarse a/b twins...
August 9, 2018: Scientific Reports
Aniruddha Mitra, Felix Ruhnow, Salvatore Girardo, Stefan Diez
Kinesin-8 motors, which move in a highly processive manner toward microtubule plus ends where they act as depolymerases, are essential regulators of microtubule dynamics in cells. To understand their navigation strategy on the microtubule lattice, we studied the 3D motion of single yeast kinesin-8 motors, Kip3, on freely suspended microtubules in vitro. We observed short-pitch, left-handed helical trajectories indicating that kinesin-8 motors frequently switch protofilaments in a directionally biased manner...
August 9, 2018: Proceedings of the National Academy of Sciences of the United States of America
P Barmpalexis, A Karagianni, I Nikolakakis, K Kachrimanis
The aim of the present study was to evaluate the thermodynamic properties of in-situ formation of cocrystal formulations by the melt-mixing method. Specifically, the thermodynamic mixing behaviour of carbamazepine-nicotinamide and ibuprofen-nicotinamide cocrystals prepared with the aid of Soluplus® (SOL) were evaluated using thermodynamic lattice-based solution theories. Thermodynamic miscibility of both cocrystals with SOL was predicted by calculating Gibb's free energy based on the Flory-Huggins (FH) interaction parameter (χ), while the activity coefficient of cocrystals estimated with the aid of solid-liquid equilibrium equation and FH lattice theory, showed good thermodynamic miscibility of the components at elevated temperatures used normally during melt-mixing based processes...
August 6, 2018: European Journal of Pharmaceutics and Biopharmaceutics
Ryusuke Uchida, Silvia Binet, Neha Arora, Gwenole Jacopin, Mohammad Hayal Alotaibi, Andreas Taubert, Shaik M Zakeeruddin, M Ibrahim Dar, Michael Graetzel
Efficiencies >20% are obtained from the perovskite solar cells (PSCs) employing Cs+ and Rb+ based perovskite compositions; therefore, it is important to understand the effect of these inorganic cations specifically Rb+ on the properties of perovskite structures. Here the influence of Cs+ and Rb+ is elucidated on the structural, morphological, and photophysical properties of perovskite structures and the photovoltaic performances of resulting PSCs. Structural, photoluminescence (PL), and external quantum efficiency studies establish the incorporation of Cs+ (x < 10%) but amply rule out the possibility of Rb-incorporation into the MAPbI3 (MA = CH3 NH3 + ) lattice...
August 9, 2018: Small
Kazuaki Z Takahashi, Takuma Nozawa, Kenji Yasuoka
An isotropic periodic sum (IPS) is a powerful technique to reasonably calculate intermolecular interactions for wide range of molecular systems under periodic boundary conditions. A linear-combination-based IPS (LIPS) has been developed to attain computational accuracy close to an exact lattice sum, such as the Ewald sum. The algorithm of the original LIPS method has a high computational cost because it needs long-range interaction calculations in real space. This becomes a performance bottleneck for long-time molecular simulations...
August 8, 2018: Scientific Reports
Kamil F Dziubek, Martin Ende, Demetrio Scelta, Roberto Bini, Mohamed Mezouar, Gaston Garbarino, Ronald Miletich
Carbon dioxide is a widespread simple molecule in the Universe. In spite of its simplicity it has a very complex phase diagram, forming both amorphous and crystalline extended phases above 40 GPa. The stability range and nature of these phases are still debated, especially in view of their possible role within the deep carbon cycle. Here, we report static synchrotron X-ray diffraction and Raman high-pressure experiments in the megabar range providing evidence for the stability of the polymeric phase V at pressure-temperature conditions relevant to the Earth's lowermost mantle...
August 8, 2018: Nature Communications
Robin P Forslund, William G Hardin, Xi Rong, Artem M Abakumov, Dmitry Filimonov, Caleb T Alexander, J Tyler Mefford, Hrishikesh Iyer, Alexie M Kolpak, Keith P Johnston, Keith J Stevenson
The electrolysis of water is of global importance to store renewable energy and the methodical design of next-generation oxygen evolution catalysts requires a greater understanding of the structural and electronic contributions that give rise to increased activities. Herein, we report a series of Ruddlesden-Popper La0.5 Sr1.5 Ni1-x Fex O4±δ oxides that promote charge transfer via cross-gap hybridization to enhance electrocatalytic water splitting. Using selective substitution of lanthanum with strontium and nickel with iron to tune the extent to which transition metal and oxygen valence bands hybridize, we demonstrate remarkable catalytic activity of 10 mA cm-2 at a 360 mV overpotential and mass activity of 1930 mA mg-1 ox at 1...
August 8, 2018: Nature Communications
Sanela Rankovic, Ruben Ramalho, Christopher Aiken, Itay Rousso
The RNA genome of human immunodeficiency virus type 1 (HIV-1) is enclosed in a cone-shaped capsid shell that disassembles following cell entry via a process known as uncoating. During HIV-1 infection, the capsid is important for reverse transcription and entry of the virus into the target cell nucleus. The small molecule PF74 inhibits HIV-1 infection at early stages by binding to the capsid and perturbing uncoating. However, the mechanism by which PF74 alters capsid stability and reduces viral infection is presently unknown...
August 8, 2018: Journal of Virology
Ram M Adar, Tomer Markovich, Amir Levy, Henri Orland, David Andelman
The dielectric constant of ionic solutions is known to reduce with increasing ionic concentrations. However, the origin of this effect has not been thoroughly explored. In this paper, we study two such possible sources: long-range Coulombic correlations and solvent excluded-volume. Correlations originate from fluctuations of the electrostatic potential beyond the mean-field Poisson-Boltzmann theory, evaluated by employing a field-theoretical loop expansion of the free energy. The solvent excluded-volume, on the other hand, stems from the finite ion size, accounted for via a lattice-gas model...
August 7, 2018: Journal of Chemical Physics
Paulo F Almeida, Faith E Carter, Katie M Kilgour, Matthew H Raymonda, Emmanuel Tejada
The excess heat capacity (Δ C p ) of mixtures of dipalmitoylphosphatidylcholine (DPPC) and cholesterol (Chol) is examined in detail in large unilamellar vesicles (LUVs), both experimentally, using differential scanning calorimetry (DSC), and theoretically, using a three-state Ising model. The model postulates that DPPC can access three conformational states: gel, liquid-disordered (Ld ), and liquid-ordered (Lo ). The Lo state, however, is only available if coupled with interaction with an adjacent Chol. Δ C p was calculated using Monte Carlo simulations on a lattice and compared to experiment...
August 8, 2018: Langmuir: the ACS Journal of Surfaces and Colloids
Xuemei Zhou, Ning Liu, Tadahiro Yokosawa, Andres Osvet, Matthias E Miehlich, Karsten Meyer, Erdmann Spiecker, Patrik Schmuki
Noble metal co-catalysts are conventionally a crucial factor in oxide-semiconductor based photocatalytic hydrogen generation. In the present work we show that optimized high-temperature hydrogenation of commercially available strontium titanate (SrTiO3) powder can be used to engineer an intrinsic co-catalytic shell around nanoparticles that can create a photocatalyst that is highly effective without the use of any additional co-catalyst for hydrogen generation from neutral aqueous methanol solutions. This intrinsic activation effect can also be observed for SrTiO3 [100] single crystal as well as Nb-doped SrTiO3 [100] single crystal...
August 8, 2018: ACS Applied Materials & Interfaces
Shao-Hai Li, Nan Zhang, Xiuqiang Xie, Rafael Luque, Yi-Jun Xu
Ultrathin two-dimensional (2D) nanostructures have attracted increasing research interest in energy storage and conversion. However, tackling the key problem of lattice mismatch inducing the instability of ultrathin nanostructures during phase transformation is still a critical challenge. Herein, we have developed a facile and scalable strategy for the growth of ultrathin nickel phosphide (Ni2P) nanosheets (NSs) with exposed (001) facets. The results reveal that single-layer functionalized graphene with residual oxygen containing groups and large lateral size contributes to releasing the lattice strain during phosphorization...
August 8, 2018: Angewandte Chemie
Leon Zwiener, Frank Girgsdies, Robert Schlögl, Elias Frei
The existence of a limited solid solution series in the Cu/Zn binary metal oxalate system is reported. Co-precipitation was applied for the preparation of a comprehensive set of mixed Cu/Zn oxalate samples. Rietveld refinement of the diffraction data (XRD) revealed the formation of mixed metal oxalate single phases at the compositional peripheries. Accordingly, the isomorphous substitution of ZnII into CuII oxalate takes place at a Zn content ≤6.6 and ≥79.1 at.-%. The Zn incorporation leads to a pronounced unit-cell contraction accompanied by Vegard-type trends for the lattice parameters...
August 8, 2018: Chemistry: a European Journal
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