There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Lithium (Li)-ion batteries (LIB) have governed the current worldwide rechargeable battery market due to their outstanding energy and power capability. In particular, the LIB's role in enabling electric vehicles (EVs) has been highlighted to replace the current oil-driven vehicles in order to reduce the usage of oil resources and generation of CO2 gases. Unlike Li, sodium is one of the more abundant elements on Earth and exhibits similar chemical properties to Li, indicating that Na chemistry could be applied to a similar battery system. In the 1970s-80s, both Na-ion and Li-ion electrodes were investigated, but the higher energy density of Li-ion cells made them more applicable to small, portable electronic devices, and research efforts for rechargeable batteries have been mainly concentrated on LIB since then. Recently, research interest in Na-ion batteries (NIB) has been resurrected, driven by new applications with requirements different from those in portable electronics, and to address the concern on Li abundance. In this article, both negative and positive electrode materials in NIB are briefly reviewed. While the voltage is generally lower and the volume change upon Na removal or insertion is larger for Na-intercalation electrodes, compared to their Li equivalents, the power capability can vary depending on the crystal structures. It is concluded that cost-effective NIB can partially replace LIB, but requires further investigation and improvement.

/pdf/electrode-materials-for-rechargeable-sodium-ion-batteries-1cf2yiiw7z.pdf

Electrode Materials for Rechargeable Sodium-Ion Batteries: Potential Alternatives to Current Lithium-Ion Batteries

Incorporation of alkaline-earth cations into the zircon-type lattice of Ce1−xAxVO4+δ (A=Ca, Sr; x=0−0.2) was found to significantly increase the p-type electronic conductivity and to decrease the Seebeck coefficient, which becomes negative at x≥0.1. The oxygen ionic conductivity is essentially unaffected by doping. The ion transference numbers of Ce1−xAxVO4+δ in air, determined by the faradaic efficiency measurements, are in the range from 2×10−4 to 6×10−3 at 973–1223 K, increasing when temperature increases or alkaline-earth cation content decreases. The results on the partial conductivities and Seebeck coefficient suggest the presence of hyperstoichiometric oxygen, responsible for ionic transport, in the lattice of doped cerium vanadates. The activation energies for the electron-hole and ionic conduction both decrease on doping and vary in the ranges 39–45 kJ/mol and 87–112 kJ/mol, respectively.

/pdf/mixed-conductivity-of-zircon-type-ce1-xaxvo4-d-a-ca-sr-11uuasdvao.pdf

Mixed conductivity of zircon-type Ce1−xAxVO4±δ (A=Ca, Sr)

The Na + -conducting ceramics of layered Na 0 . 8 Ni 0 . 4 Ti 0 . 6 O 2 , Na 0 . 8 Fe 0 . 8 Ti 0 . 2 O 2 , Na 0 . 8 Ni 0 . 6 Sb 0 . 4 O 2 (structural type 03) and Na 0 . 6 8 Ni 0 . 3 4 Ti 0 . 6 6 O 2 (P2 type) with density higher than 91% were prepared via the standard solid-state synthesis route and characterized by the impedance spectroscopy, thermal analysis, scanning electron microscopy, structure refinement using X-ray powder diffraction data, measurements of Na + concentration cell e.m.f., and dilatometry. The conductivity of antimonate Na 0 . 8 Ni 0 . 6 Sb 0 . 4 O 2 , synthesized first time, was found lower than that of isostructural Na 0 . 8 Ni 0 . 4 Ti 0 . 6 O 2 due to larger ion jump distance between Na + sites. At temperatures above 420 K, transport properties of sodium cation-conducting materials are essentially independent of partial water vapor pressure. In the low-temperature range, the conductivity reversibly increases with water vapor pressure varied in the range from approximately 0 (dry air) up to 0.46 atm. The sensitivity to air humidity is influenced by the ceramic microstructure, being favored by increasing boundary area. The average thermal expansion coefficients of layered materials at 300-1173 K are in the range (13.7-16.0)×10 - 6 K - 1 .

/pdf/sintesis-y-caracterizacion-del-conductor-cationico-de-sodio-304o2evv1n.pdf

Síntesis y caracterización del conductor catiónico de sodio Nax(MyL1-y)O2 (M = Ni2+, Fe3+; L = Ti4+, Sb5+)

Cr and Mg codoped bismuth tantalate pyrochlores: Thermal expansion and stability, crystal structure, electrical and optical properties, NEXAFS and XPS study

The effect of Fe and Mg-codoping on the crystal structure, optical and dielectric properties of bismuth tantalate-based pyrochlores has been studied. Samples of Bi2MgxFe1−xTa2O9.5−Δ (x ≤ 0.7) are characterized by a porous dendrite-like microstructure. Fe,Mg-codoped bismuth tantalate pyrochlores are thermally stable up to a temperature of 1140 °C (x = 1). The Bi2Mg0.5Fe0.5Ta2O9.5−Δ thermal expansion coefficient increases uniformly and weakly from 3.6 to 9.3 × 10−6 °C−1 (30–1050 °C). The unit cell parameter of solid solutions increases uniformly from 10.5009(1) Å (x = 0.3) up to 10.5225(7) Å (x = 0.7). The structural parameters of disordered pyrochlore are determined by the Rietveld method (sp. gr. Fd3¯m:2 (227), Z = 8). According to near edge X-ray absorption fine structure and X-ray photoelectron spectroscopy data, ions in solid solutions are in the charge states Bi (+3), Mg (+2), Fe (+3), Ta (+5-δ). The Mössbauer spectrum is represented by a symmetric doublet with parameters IS = 0.365 ± 0.0020 mm/s, QS = 0.604 ± 0.034 mm/s, related to Fe3+ ions in regular axial octahedral positions. The samples exhibit the properties of dielectrics. The permittivity and the tangent of dielectric losses at 20 °C increases with the growth of iron content in the samples in the range of 28.5–30.5 and 0.001 (1 MHz). The width of the band gap of the obtained materials for direct allowed electronic transitions is in the range of 2.16(5)–2.41(5) eV. The studied samples satisfy the condition of efficient conversion of solar energy into an electrical one and are promising as catalysts and light-absorbing elements for solar panels.

/pdf/fe-mg-codoped-bismuth-tantalate-pyrochlores-crystal-1jagyc0u.pdf

Fe,Mg-Codoped Bismuth Tantalate Pyrochlores: Crystal Structure, Thermal Stability, Optical and Electrical Properties, XPS, NEXAFS, ESR, and 57Fe Mössbauer Spectroscopy Study

Mixed perovskite-like oxides based on strontium cobaltate exhibit high oxygen conductivity superimposed over the much higher electronic conductivity and are, therefore, promising materials for producing different high-temperature electrochemical devices. The maximum oxygen conductivity was found in SrCo{sub 1-x}Fe{sub x}O{sub 3-{delta}} solid solutions with x = 0.2-0.3. The high ionic conductivity of strontium cobaltate ferrites is likely to arise from both the stabilization of the cubic perovskite structure of strontium cobaltate and the relatively low iron-oxygen bond energy. The cubic perovskite structure ABO{sub 3} can be stabilized by substitution of larger cations at the A site. In this paper, the authors report studies on the physicochemical properties of Ba-substituted strontium cobaltate.

Vladislav V. Kharton

Papers

Mixed conductivity of zircon-type Ce1−xAxVO4±δ (A=Ca, Sr)

Síntesis y caracterización del conductor catiónico de sodio Nax(MyL1-y)O2 (M = Ni2+, Fe3+; L = Ti4+, Sb5+)

Cr and Mg codoped bismuth tantalate pyrochlores: Thermal expansion and stability, crystal structure, electrical and optical properties, NEXAFS and XPS study

Fe,Mg-Codoped Bismuth Tantalate Pyrochlores: Crystal Structure, Thermal Stability, Optical and Electrical Properties, XPS, NEXAFS, ESR, and 57Fe Mössbauer Spectroscopy Study

Ionic transport in Sr(Ba)CoO{sub 3-{delta}} solid solutions