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

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

J. Appl. Cryst.の発刊に際して

On the significance of the H/E ratio in wear control: a nanocomposite coating approach to optimised tribological behaviour

Characterization of tribo-layers on self-lubricating plasma-assisted chemical-vapor-deposited TiN coatings

Thin films (≊2 μm) of boron nitride, titanium boron nitride, and titanium aluminum boron nitride have been grown on molybdenum, niobium, and cemented carbide substrates employing nonreactive as well as reactive rf magnetron sputter deposition from either a BN, a TiN‐BN, or a TiN–AlN–BN target. Substrates have been rf biased, with dc potentials up to −200 V. By means of nonreactive sputtering mixed‐phase structures with dominant phases B48B2N2 (using a BN target), or B48B2N2 and hexagonal Ti–B–N (using a TiN–BN or a TiN–AlN–BN target) are formed. Reactive deposition leads to the existence of hexagonal BN in all deposition modes. In the cases of Ti–B–N and Ti–Al–B–N films this phase is accompanied by fcc Ti–B–N. SEM cross sections revealed very fine grained to fracture‐amorphous film structures. Hardness measurements gave the following maximum HV 0.02 values: B–N films 2800, Ti–B–N films 2750, and Ti–Al–B–N films 1650.

Radio-frequency sputter deposition of boron nitride based thin films

This study demonstrates the successful synthesis of hard and wear resistant nanocomposite Ti–B–N coatings by high-rate reactive arc-evaporation from Ti/B compound targets in a commercial industrial-sized deposition chamber. Morphological investigations by profilometry and scanning electron microscopy indicate that the coatings exhibit a lower droplet density as compared to a TiN reference as well as a compositionally graded multilayer structure. These results will be related to the previously reported microstructural characterization, which revealed a highly stressed nanocrystalline TiBN solid solution formed at lower N2 fractions and a stable TiN/(amorphous) BN dual-phase structure obtained at higher N2 partial pressures. Emphasis is further laid on mechanical and tribological characterization. A maximum hardness of 34.5 GPa is detected for the TiBN solid solution decreasing to 24 GPa for the coatings containing approximately 30–40 vol.% amorphous BN. The maximum in hardness coincides with the minimum in wear, while the coefficient of friction is fairly constant at 0.7–0.8.

Structure–property–performance relations of high-rate reactive arc-evaporated Ti–B–N nanocomposite coatings

The article reports on thermal stability of the structure and mechanical properties of Zr–Si–N films with a high (≥ 25 at.%) Si content deposited from a ceramic ZrSi 2 target by reactive magnetron sputtering. The annealed films were characterized using X-ray diffraction, microhardness and macrostress measurements, and differential scanning calorimetry. Special attention was devoted to the influence of the annealing temperature (up to 1600 °C), annealing environment and presence of the substrate. It was found that the phase composition of the films strongly influences its thermal stability. Furthermore, (i) microhardness of the Zr–Si–N films sputtered under conditions used in our experiments is determined by their structure and not by the macrostress, (ii) crystallization of the X-ray amorphous films strongly depends on its phase composition, the ambient atmosphere and the incorporation of the substrate elements into the film due to interdiffusion during annealing, and (iii) X-ray amorphous Zr–Si–N films containing a high (≥ 50 vol.%) content of the Si 3 N 4 phase exhibit the highest thermal stability considerably exceeding 1000 °C.

Thermal stability of magnetron sputtered Zr–Si–N films

The article reports on structure and mechanical properties of Ti-B alloy films sputter deposited from a sintered TiB 2 target using an unbalanced dc magnetron. We present results of a systematic investigation of the effect of negative substrate bias, U s , substrate ion current density i s , and substrate temperature, T s , on properties of Ti-B films. The X-ray diffraction (XRD) analysis shows that the Ti-B films consist of the hexagonal TiB 2 phase with the typical (0001) texture only. The TiB x films are over-stoichiometric with the ratio x=B/Ti=2.4. All Ti-B films sputter ion plated in argon magnetron discharge are superhard films with hardness H>40 GPa and exhibit high values of (i) effective Young's modulus E*=E/(1 - v 2 ) up to approximately 600 GPa and (ii) elastic recovery, W e , up to approximately 82%; here E and v are the Young's modulus and the Poisson's ratio, respectively. Besides, it was found that the value of the Bragg's angle 20 of the (0001) reflection line can be easily controlled by the energy delivered to the film during its growth by (I) the substrate heating T s and (2) ion bombardment (U s , i s ). The angle 20 of the (0001) reflection increases with increasing T s from 300 to 550 °C and decreasing U s from -150 to -50 V. In this range of process parameters, the energy E p delivered to the growing film per condensing atom by ion bombardment can be adjusted to a value, at which the (0001) reflection from sputtered films is close to that of the TiB 2 (0001) powder standard. These films exhibit a low macrostress, which approaches to zero. It enables to sputter thick (up to 8 μm) superhard (H>40 GPa) Ti-B films. The optimum value of E p is achieved when the Ti-B film is sputtered at U s =-50 V, i s = 1 mA/cm 2 , T s =550 °C with a deposition rate a D =52 nm/min. The Ti-B film prepared under these conditions exhibits a maximum hardness of H77 GPa, measured using a computer controlled microhardness tester Fischerscope H100 at the Vickers diamond indenter load L=50 mN.

Christian Mitterer

Papers

Characterization of tribo-layers on self-lubricating plasma-assisted chemical-vapor-deposited TiN coatings

Radio-frequency sputter deposition of boron nitride based thin films

Structure–property–performance relations of high-rate reactive arc-evaporated Ti–B–N nanocomposite coatings

Thermal stability of magnetron sputtered Zr–Si–N films

Low-stress superhard Ti-B films prepared by magnetron sputtering