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

▪ Abstract This review surveys the observed properties of interstellar dust grains: the wavelength-dependent extinction of starlight, including absorption features, from UV to infrared; optical lum...

https://www.ifa.hawaii.edu/users/reipurth/reviews/draine.pdf

Interstellar dust grains

IR emission spectra are calculated for dust heated by starlight, for mixtures of amorphous silicate and graphitic grains, including varying amounts of PAH particles. The models are constrained to reproduce the average Milky Way extinction curve. The calculations include the effects of single-photon heating. Updated IR absorption properties for the PAHs are presented that are consistent with observed emission spectra, including those newly obtained by Spitzer. We find a size distribution for the PAHs giving emission band ratios consistent with the observed spectra of the Milky Way and other galaxies. Emission spectra are presented for a wide range of starlight intensities. We calculate how the efficiency of emission into different IR bands depends on PAH size; the strong 7.7 μm emission feature is produced mainly by PAH particles containing Umin. We present graphical procedures using Spitzer IRAC and MIPS photometry to estimate the parameters qPAH, Umin, and γ, the fraction fPDR of the dust luminosity coming from photodissociation regions with U > 100, and the total dust mass Mdust.

https://iopscience.iop.org/article/10.1086/511055/pdf

Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era

Large polycyclic aromatic hydrocarbon (PAH) molecules carry the infrared (IR) emission features that dominate the spectra of most galactic and extragalactic sources. This review surveys the observed mid-IR characteristics of these emission features and summarizes laboratory and theoretical studies of the spectral characteristics of PAHs and the derived intrinsic properties of emitting interstellar PAHs. Dedicated experimental studies have provided critical input for detailed astronomical models that probe the origin and evolution of interstellar PAHs and their role in the universe. The physics and chemistry of PAHs are discussed, emphasizing the contribution of these species to the photoelectric heating and the ionization balance of the interstellar gas and to the formation of small hydrocarbon radicals and carbon chains. Together, these studies demonstrate that PAHs are abundant, ubiquitous, and a dominant force in the interstellar medium of galaxies.

Interstellar Polycyclic Aromatic Hydrocarbon Molecules

We present a quantitative model for the infrared emission from dust in the diffuse interstellar medium. The model consists of a mixture of amorphous silicate grains and carbonaceous grains, each with a wide size distribution ranging from molecules containing tens of atoms to large grains 1 μm in diameter. We assume that the carbonaceous grains have properties like polycyclic aromatic hydrocarbons (PAHs) at very small sizes and graphitic properties for radii a 50 A. On the basis of recent laboratory studies and guided by astronomical observations, we propose astronomical absorption cross sections for use in modeling neutral and ionized PAHs from the far-ultraviolet to the far-infrared. We also propose modifications to the far-infrared emissivity of astronomical silicate. We calculate energy distribution functions for small grains undergoing temperature spikes caused by stochastic absorption of starlight photons using realistic heat capacities and optical properties. Using a grain-size distribution consistent with the observed interstellar extinction, we are able to reproduce the near-IR to submillimeter emission spectrum of the diffuse interstellar medium, including the PAH emission features at 3.3, 6.2, 7.7, 8.6, and 11.3 μm. The model is compared with the observed emission at high Galactic latitudes as well as in the Galactic plane, as measured by the COBE/DIRBE, COBE/FIRAS, IRTS/MIRS, and IRTS/NIRS instruments. The model has 60 × 10-6 of C (relative to H) locked up in PAHs, with 45 × 10-6 of C in a component peaking at ~6 A (NC ≈ 100 carbon atoms) to account for the PAH emission features and with 15 × 10-6 of C in a component peaking at ~50 A to account for the 60 μm flux. The total infrared emission is in excellent agreement with COBE/DIRBE observations at high Galactic latitudes, just as the albedo for our grain model is in accord with observations of the diffuse Galactic light. The aromatic absorption features at 3.3 and 6.2 μm predicted by our dust model are consistent with observations. We calculate infrared emission spectra for our dust model heated by a range of starlight intensities, from 0.3 to 104 times the local interstellar radiation field, and we tabulate the intensities integrated over the SIRTF/IRAC and MIPS bands. We also provide dust opacities tabulated from the extreme-ultraviolet to submillimeter wavelengths.

https://iopscience.iop.org/article/10.1086/323147/pdf

Infrared Emission from Interstellar Dust. II. The Diffuse Interstellar Medium

/pdf/the-infrared-spectrum-of-interstellar-dust-surface-c4bs5fjezn.pdf

The infrared spectrum of interstellar dust: Surface functional groups on carbon

1 Lasers and Laser Radiation.- 1.1. Introduction.- 1.2. Laser Sources.- 1.2.1. Ruby Laser.- 1.2.2. Nd-YAG Laser.- 1.2.3. Nd-Glass Laser.- 1.2.4. Tunable Infrared Diode Lasers.- 1.2.5. Helium-Neon Laser.- 1.2.6. Argon and Krypton Ion Lasers.- 1.2.7. Helium-Cadmium Laser.- 1.2.8. CO2 Laser.- 1.2.9. Rare Gas Halide Lasers.- 1.2.10. Dye Lasers.- 1.2.11. Stimulated Raman Scattering.- 1.3. Laser Radiation.- 1.3.1. Monochromaticity.- 1.3.2. Beam Shape.- 1.3.3. Beam Divergence.- 1.3.4. Brightness.- 1.3.5. Focusing of Laser Radiation.- 1.3.6. Coherence.- 1.4. Lens Aberrations.- 1.4.1. Spherical Aberration.- 1.4.2. Coma.- 1.4.3. Astigmatism.- 1.4.4. Field Curvature.- 1.4.5. Distortion.- 1.5. Window Materials.- 1.6. Mirrors and Polarizers.- 1.7. Q-Switching.- 1.7.1. Acousto-Optical Q-Switches.- 1.7.2. Electro-Optical Q-Switches.- 1.7.3. Passive Q-Switching.- 1.8. Frequency Conversion.- 1.9. Mode Locking.- 1.10. Detectors and Power Meters.- 1.10.1. Power Meters.- 1.10.2. Radiation Detectors.- 2. Materials Processing.- 2.1. Absorption of Laser Radiation by Metals.- 2.2. Absorption of Laser Radiation by Semiconductors and Insulators.- 2.3. Thermal Constants.- 2.4. Laser Drilling: Heat Transfer.- 2.4.1. Heating without Change of Phase.- 2.4.2. Heating with Change of Phase.- 2.4.3. Experimental.- 2.5. Welding.- 2.5.1. Heat Transfer-Penetration Welding.- 2.5.2. Heat Transfer-Conduction Welding.- 2.5.3. Welding with Multikilowatt Lasers.- 2.5.4. Welding with Low-Power Lasers.- 2.5.5. Laser Spot Welding.- 2.6. Cutting.- 2.6.1. Heat Transfer.- 2.6.2. Cutting Metals.- 2.6.3. Cutting Nonmetals.- 2.6.4. Scribing and Controlled Fracture.- 2.7. Micromachining.- 2.7.1. Resistor Trimming.- 2.7.2. Machining of Conductor Patterns.- 2.7.3. Fabrication of Gap Capacitors.- 2.7.4. Image Recording.- 2.7.5. Laser Marking.- 2.7.6. Micromachining-Thermal Considerations.- 2.8. Surface Hardening.- 2.9. Surface Melting, Alloying, and Cladding.- 2.10. Surface Cleaning.- 2.11. Crystal Growth.- 2.12. Optical Fiber Splicing.- 2.12.1. Optical Fiber-End Preparation.- 2.12.2. Optical Fiber-Drawing.- 2.13. Laser Deposition of Thin Films.- 2.13.1. Evaporation.- 2.13.2. Electroplating.- 2.13.3. Chemical Vapor Deposition.- 2.13.4. Photodeposition and Photoetching.- 3 Laser Processing of Semiconductors.- 3.1. Introduction.- 3.2. Annealing.- 3.3. Annealing-CW Lasers.- 3.4. Recrystallization.- 3.5. Silicide Formation.- 3.6. Ohmic Contacts and Junction Formation.- 3.7. Device Fabrication.- 3.8. Electrical Connections on Integrated Circuits.- 3.9. Monolithic Displays.- 4 Chemical Processing.- 4.1. Introduction.- 4.2. Schemes for Laser Isotope Separation.- 4.3. The Enrichment Factor.- 4.4. Laser-Induced Reaction.- 4.5. Single-Photon Predissociation.- 4.6. Two-Photon Dissociation.- 4.7. Photoisomerization.- 4.8. Two-Step Photoionization.- 4.9. Photodeflection.- 4.10. Multiphoton Dissociation.- 4.10.1. Deuterium.- 4.10.2. Boron.- 4.10.3. Carbon.- 4.10.4. Silicon.- 4.10.5. Sulfur.- 4.10.6. Chlorine.- 4.10.7. Molybdenum.- 4.10.8. Osmium.- 4.10.9. Uranium.- 4.11. Selective Raman Excitation.- 4.12. Economics of Laser Isotope Separation.- 4.13. Laser-Induced Reactions.- 4.13.1. Infrared Photochemistry-Basic Mechanisms.- 4.13.2. Vibrationally Enhanced Chemical Reactions.- 4.13.3. Vibrationally Induced Decomposition.- 4.14. Isomerization.- 4.15. Lasers in Catalysis.- 4.16. Laser-Induced Reactions: UV-VIS Excitation.- 4.17. Processing via Thermal Heating.- 4.18. Polymerization.- 5 Lasers in Chemical Analysis.- 5.1. Introduction.- 5.2. Absorption Spectroscopy.- 5.2.1. Absorption vs. Other Techniques.- 5.2.2. Intracavity Absorption.- 5.3. Laser-Induced Fluorescence.- 5.3.1. Laser-Induced Fluorescence: Theory.- 5.3.2. Laser-Excited Atomic Flame Fluorescence.- 5.3.3. Laser-Excited Molecular Flame Fluorescence.- 5.3.4. Beam Diagnostics.- 5.3.5. Fluorimetry and Phosphorimetry.- 5.3.6. Selective Excitation of Probe Ion Luminescence.- 5.4. Laser-Enhanced Ionization Spectroscopy.- 5.5. Multiphoton Ionization.- 5.6. Raman Spectroscopy.- 5.6.1. Theory and Physical Principles.- 5.6.2. Experimental Techniques.- 5.6.3. Experimental Results.- 5.6.4. Coherent Anti-Stokes Raman Spectroscopy.- 5.7. Laser Magnetic Resonance.- 5.8. Laser Photoacoustic Spectroscopy.- 5.8.1. LPS of Gases.- 5.8.2. LPS of Liquids and Solids.- 5.8.3. Photoacoustic Imaging.- 5.9. Laser Microprobe.- 5.10. Atomic Absorption Spectrometry.- 5.11. Laser Microprobe Mass Spectrometer.- 5.12. Laser Raman Microprobe.- 5.13. Lasers in Chromatography.- 6 Lasers in Environmental Analysis.- 6.1. Propagation of Laser Radiation through the Atmosphere.- 6.2. Laser Remote Sensing of the Atmosphere.- 6.2.1. Absorption Measurements.- 6.2.2. LIDAR.- 6.2.3. Laser Remote Sensing of Wind Velocity.- 6.2.4. Raman LIDAR.- 6.2.5. Differential Absorption LIDAR (DIAL).- 6.2.6. Resonance Fluorescence.- 6.2.7. Heterodyne Detection.- 6.3. Laser Sampling of Aerosols.- 6.3.1. Particle Size and Distribution.- 6.3.2. Particle Composition.- 6.3.3. Interaction of High-Power Laser Radiation with Aerosol Particles.- 6.4. Laser Remote Sensing of Water Quality.- References.- Materials Index.

Laser processing and analysis of materials

Interstellar chemistry

Most state-of-the-art electronic wearable sensors are powered by batteries that require regular charging and eventual replacement, which would cause environmental issues and complex management problems. Here, a device concept is reported that can break this paradigm in ambient moisture monitoring-a new class of simple sensors themselves can generate moisture-dependent voltage that can be used to determine the ambient humidity level directly. It is demonstrated that a moisture-driven electrical generator, based on the diffusive flow of water in titanium dioxide (TiO2 ) nanowire networks, can yield an output power density of up to 4 µW cm-2 when exposed to a highly moist environment. This performance is two orders of magnitude better than that reported for carbon-black generators. The output voltage is strongly dependent on humidity of ambient environment. As a big breakthrough, this new type of device is successfully used as self-powered wearable human-breathing monitors and touch pads, which is not achievable by any existing moisture-induced-electricity technology. The availability of high-output self-powered electrical generators will facilitate the design and application of a wide range of new innovative flexible electronic devices.

Self-Powered Wearable Electronics Based on Moisture Enabled Electricity Generation.

We describe a rapid, simple, room-temperature technique for the production of large-scale metallic thin films with tunable plasmonic properties assembled from size-selected silver nanoplates (SNPs). We outline the properties of a series of ultrathin monolayer metallic films (8-20 nm) self-assembled on glass substrates in which the localized surface plasmon resonance can be tuned over a range from 500 to 800 nm. It is found that the resonance peaks of the films are strongly dependent on the size of the nanoplates and the refractive index of the surrounding dielectric. It is also shown that the bandwidth and the resonance peak of the plasmon resonance spectrum of the metallic films can be engineered by simply controlling aggregation of the SNP. A three-dimensional finite element method was used to investigate the plasmon resonance properties for individual SNPs in different dielectrics and plasmon coupling in SNP aggregates. A 5-17 times enhancement of scattering from these SNP films has been observed experimentally. Our experimental results, together with numerical simulations, indicate that this self-assembly method shows great promise in the production of nanoscale metallic films with enormous electric-field enhancements at visible and near-infrared wavelengths. These may be utilized in biochemical sensing, solar photovoltaic, and optical processing applications.

/pdf/self-assembly-of-large-scale-and-ultrathin-silver-nanoplate-1mxcrcgjul.pdf

Walter W. Duley

Papers

The infrared spectrum of interstellar dust: Surface functional groups on carbon

Laser processing and analysis of materials

Interstellar chemistry

Self-Powered Wearable Electronics Based on Moisture Enabled Electricity Generation.

Self-Assembly of Large-Scale and Ultrathin Silver Nanoplate Films with Tunable Plasmon Resonance Properties