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

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

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

A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Using the laser-based technique of cavity ring-down spectroscopy extinction measurements have been performed in various gases straightforwardly resulting in cross sections for Rayleigh scattering. For Ar and N 2 measurements are performed in the range 470–490 nm, while for CO 2 cross sections are determined in the wider range 470–570 nm. In addition to these gases also for N 2 O, CH 4 , CO, and SF 6 the scattering cross section is determined at 532 nm, a wavelength of importance for lidar applications and combustion laser diagnostics. In O 2 the cross section at 532 nm is found to depend on pressure due to collision-induced light absorption. The obtained cross sections validate the cross sections for Rayleigh scattering as derived from refractive indices and depolarization ratios through Rayleigh's theory at the few %-level, although somewhat larger discrepancies are found for CO, N 2 O and CH 4 .

http://nat.vu.nl/en/sec/atom/Publications/pdf/Rayleigh-2005.pdf

Direct measurement of the Rayleigh scattering cross section in various gases

Based on highly accurate laboratory measurements of Lyman bands of ${\mathrm{H}}_{2}$ and an updated representation of the structure of the ground $X\text{ }^{1}\ensuremath{\Sigma}_{g}^{+}$ and excited $B\text{ }^{1}\ensuremath{\Sigma}_{u}^{+}$ and $C\text{ }^{1}\ensuremath{\Pi}_{u}$ states, a new set of sensitivity coefficients ${\mathrm{K}}_{\mathrm{i}}$ is derived for all lines in the ${\mathrm{H}}_{2}$ spectrum, representing the dependence of their transition wavelengths on a possible variation of the proton-electron mass ratio $\ensuremath{\mu}={m}_{\mathrm{p}}/{m}_{\mathrm{e}}$. Included are local perturbation effects between $B$ and $C$ levels and adiabatic corrections. The new wavelengths and ${\mathrm{K}}_{\mathrm{i}}$ factors are used to compare with a recent set of highly accurate ${\mathrm{H}}_{2}$ spectral lines observed in the Q 0347-383 and Q 0405-443 quasars, yielding a fractional change in the mass ratio of $\ensuremath{\Delta}\ensuremath{\mu}/\ensuremath{\mu}=(2.4\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ for a weighted fit and $\ensuremath{\Delta}\ensuremath{\mu}/\ensuremath{\mu}=(2.0\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ for an unweighted fit. This result indicates, at a $3.5\ensuremath{\sigma}$ confidence level, that $\ensuremath{\mu}$ could have decreased in the past 12 Gyr.

/pdf/indication-of-a-cosmological-variation-of-the-proton-3abupyr5q4.pdf

Indication of a Cosmological Variation of the Proton-Electron Mass Ratio Based on Laboratory Measurement and Reanalysis of H~2 Spectra

Synchrotron vacuum ultraviolet radiation studies of the D-1 Pi(u) state of H-2 (Correction of vol 133, 144317, 2010)

The transition wave number from the EF Σ1g+(v=0,N=1) energy level of ortho-H2 to the 54p11(0) Rydberg state below the X+ Σ2g+(v+=0,N+=1) ground state of ortho-H2+ has been measured to be 25 209.997 56±(0.000 22)statistical±(0.000 07)systematic cm−1. Combining this result with previous experimental and theoretical results for other energy level intervals, the ionization and dissociation energies of the hydrogen molecule have been determined to be 124 417.491 13(37) and 36 118.069 62(37) cm−1, respectively, which represents a precision improvement over previous experimental and theoretical results by more than one order of magnitude. The new value of the ionization energy can be regarded as the most precise and accurate experimental result of this quantity, whereas the dissociation energy is a hybrid experimental-theoretical determination.

/pdf/determination-of-the-ionization-and-dissociation-energies-of-39a6umn1sq.pdf

Determination of the ionization and dissociation energies of the hydrogen molecule.

We demonstrate a noncollinear optical parametric chirped pulse amplifier system that produces 7.6 fs pulses with a peak power of 2 terawatt at 30 Hz repetition rate. Using an ultra-broadband Ti:Sapphire seed oscillator and grating-based stretching and compression combined with an LCD phase-shaper, we amplify a 310 nm wide spectrum with a total gain of 3×107, and compress it within 5% of its Fourier limit. The total integrated parametric fluorescence is kept below 0.2%, leading to a pre-pulse contrast of 2×10-8 on picosecond timescales.

Wim Ubachs

Papers

Direct measurement of the Rayleigh scattering cross section in various gases

Indication of a Cosmological Variation of the Proton-Electron Mass Ratio Based on Laboratory Measurement and Reanalysis of H~2 Spectra

Synchrotron vacuum ultraviolet radiation studies of the D-1 Pi(u) state of H-2 (Correction of vol 133, 144317, 2010)

Determination of the ionization and dissociation energies of the hydrogen molecule.

A source of 2 terawatt, 2.7 cycle laser pulses based on noncollinear optical parametric chirped pulse amplification.