Dependent Scattering of Acoustic Phonons From Particles Embedded in an Anisotropic Medium

2007 ◽  
Author(s):  
Neil Zuckerman ◽  
Jennifer R. Lukes
Keyword(s):  
Cross Sections ◽  
Phonon Scattering ◽  
Elastic Anisotropy ◽  
Mode Conversion ◽  
Three Dimensional ◽  
Atomic Scale ◽  
Dynamics Simulation ◽  
Nanometer Scale ◽  
Acoustic Phonons ◽  
Scale Granularity

Dependent scattering of acoustic phonons by multiple nanometer-scale inclusions in anisotropic media is investigated using a new molecular dynamics simulation technique. The spectral-directional characteristics of the scattering are found by calculation of three-dimensional scattering phase functions and cross sections for inclusions of varying sizes in various spatial arrangements. The technique enables computation of the effects of reflected wave interference and sequential scattering, mode conversion, lattice strain, elastic anisotropy, and atomic-scale granularity on acoustic phonon scattering from structured inclusions. The results will improve understanding and prediction of heat transfer in quantum-dot superlattices and other engineered thermal materials with nanometer-scale structures.

Molecular Dynamics Simulation of a Rigid Sphere Indenting a Copper Substrate

2012 ◽  
Author(s):  
Ding Jia ◽  
Longqiu Li ◽  
Andrey Ovcharenko ◽  
Wenping Song ◽  
Guangyu Zhang
Keyword(s):  
Molecular Dynamics ◽  
Md Simulation ◽  
Copper Substrate ◽  
Three Dimensional ◽  
Atomic Scale ◽  
Dynamics Simulation ◽  
Rigid Sphere ◽  
Displacement Curve ◽  
Loading And Unloading ◽  
Force Displacement

Three-dimensional molecular dynamics (MD) simulation is used to study the atomic-scale indentation process of a spherical diamond tip in contact with a copper substrate. In the indentation simulations, the force-displacement curve is obtained and compared with a modified elastic solution of Hertz. The contact area under different indentation depths is also investigated. The force-displacement curve under different maximum indentation depths is obtained to investigate elastic-plastic deformation during the loading and unloading processes.

Synthetic seismic sections of typical petroleum traps

Geophysics ◽  
1978 ◽  
Vol 43 (6) ◽  
pp. 1119-1147 ◽  
Author(s):  
Bruce T. May ◽  
Franta Hron
Keyword(s):  
Cross Sections ◽  
Structural Information ◽  
Mode Conversion ◽  
Three Dimensional ◽  
Fundamental Principle ◽  
Seismic Exploration ◽  
Complex Behavior ◽  
P Waves ◽  
Seismic Sections ◽  
Zero Offset

Interpretation of seismic reflections remains a key problem in seismic exploration because reflections have complex behavior, especially near geologic structures. One method to gain an understanding of this complex behavior is to study synthetic seismic sections of models of typical petroleum traps as computed by zero‐offset ray tracing for primary P‐waves only. These synthetic sections have features of significant interpretative value to the practicing geophysicist, such as variations in reflection amplitudes and complexities in reflection‐time geometries. Asymptotic ray theory was applied to calculate reflection amplitudes, accounting for mode conversion and three‐dimensional geometric divergence of ray tubes in the presence of curvilinear interfaces. This suite of synthetic seismic sections illustrates the difficulties in making correct seismic interpretations of geologic structures and suggests three conclusions: (1) The customary assumption that seismic sections are simple images of geologic cross‐sections is an oversimplification and can lead to erroneous interpretations. (2) Variations in overlying strata produce marked disturbances in reflection amplitude and traveltime. (3) Critical reflections that provide key structural information are often difficult to recognize and are apt to be ignored, or misidentified, especially if trace processing has been cursory. A fundamental principle of interpretation is underscored by this study: CDP stacked seismic sections must be interpreted so as to be consistent with structural depth models because stacked sections are not simple images of geologic structures.

Temperature and Size Effects on the Extremely Low Thermal Conductivity of Self-assembled Germanium Quantum-dot Supercrystals in Silicon

2010 ◽  
Vol 1267 ◽  
Author(s):  
Jean-Numa Gillet
Keyword(s):  
Thermal Conductivity ◽  
Quantum Dot ◽  
Phonon Scattering ◽  
Lattice Mismatch ◽  
Average Distance ◽  
Near Field ◽  
Phononic Crystal ◽  
Three Dimensional ◽  
Atomic Scale ◽  
Self Assembled

AbstractDesign of semiconducting nanomaterials with an indirect electronic bandgap is currently one of the major areas of research to obtain a high thermoelectric yield by lowering their lattice thermal conductivity. Intensive investigations on superlattices were performed to achieve this goal. However, like one-dimensional nanowires, they decrease heat transport in only one propagation direction of the phonons. Moreover, they often lead to dislocations since they are composed of layered materials with a lattice mismatch. Design of superlattices with a thermoelectric figure of merit ZT higher than unity is therefore hazardous. Self-assembly of epitaxial layers on silicon has been used for bottom-up synthesis of three-dimensional (3D) Ge quantum-dot (QD) arrays in Si for quantum-device and solar-energy applications. Using the atomic-scale 3D phononic crystal model, it is predicted that high-density 3D arrays of self-assembled Ge QDs in Si can as well show an extreme reduction of the thermal transport. 3D supercrystals of Ge QDs in Si present a thermal conductivity that can be as tiny as that of air. These extremely low values of the thermal conductivity are computed for a number of Ge filling ratios and size parameters of the 3D Si-Ge supercrystal. Owing to incoherent phonon scattering with predominant near-field effects, the same conclusion holds for supercrystals with moderate QD disordering. As a result, design of highly-efficient CMOS-compatible thermoelectric devices with ZT possibly much higher than unity might be possible. In this theoretical study, simultaneous evolution of both temperature and average distance between the Ge QDs is analyzed for a non-variable Ge filling ratio to obtain thermal-conductivity values as low as that of air (+/- 0.025 W/m/K).

Molecular Dynamics Simulation of Rubbing Phenomena in Ultra-Precision Abrasive Machining

2010 ◽  
Vol 443 ◽  
pp. 417-422
Author(s):  
Jun Shimizu ◽  
Li Bo Zhou ◽  
Takeyuki Yamamoto ◽  
Han Huang
Keyword(s):  
Molecular Dynamics ◽  
Normal Load ◽  
Three Dimensional ◽  
Copper Surface ◽  
Atomic Scale ◽  
Dynamics Simulation ◽  
Abrasive Machining ◽  
Stick Slip ◽  
Abrasive Grain ◽  
The One

This study aims to clarify the friction and wear phenomena, which are of great importance in abrasive machining with atomic-scale material removal, such as polishing of magnetic disk substrates and CMP of semiconductor substrates. Various phenomena that occurred when a well-defined copper surface rubbed by an extremely fine rigid diamond abrasive, such asthe sliding without removal and the atomic-scale wear, were analyzed using a molecular dynamics model, in which the abrasive grain was connected to a three-dimensional spring and the holding rigidity of the abrasive grain was taken into account. A series of simulations using different indentation depths clarified that the one- or two-dimensional atomic-scale stick-slip phenomenon in proportion to the period of atomic arrays of workpiece surface occurred in the sliding processes without atomic removal. The results also demonstrated that the period and amplitude of the fundamental stick-slip wave varied when accompanied with atomic removal due to the increase in normal load.

Geological Field Sketches and Illustrations

2019 ◽  
Author(s):  
Matthew J. Genge
Keyword(s):  
Cross Sections ◽  
Earth Science ◽  
Three Dimensional ◽  
Worked Examples ◽  
Scientific Publications ◽  
Thin Sections ◽  
Geological Features ◽  
Different Types ◽  
The Subject

Drawings, illustrations, and field sketches play an important role in Earth Science since they are used to record field observations, develop interpretations, and communicate results in reports and scientific publications. Drawing geology in the field furthermore facilitates observation and maximizes the value of fieldwork. Every geologist, whether a student, academic, professional, or amateur enthusiast, will benefit from the ability to draw geological features accurately. This book describes how and what to draw in geology. Essential drawing techniques, together with practical advice in creating high quality diagrams, are described the opening chapters. How to draw different types of geology, including faults, folds, metamorphic rocks, sedimentary rocks, igneous rocks, and fossils, are the subjects of separate chapters, and include descriptions of what are the important features to draw and describe. Different types of sketch, such as drawings of three-dimensional outcrops, landscapes, thin-sections, and hand-specimens of rocks, crystals, and minerals, are discussed. The methods used to create technical diagrams such as geological maps and cross-sections are also covered. Finally, modern techniques in the acquisition and recording of field data, including photogrammetry and aerial surveys, and digital methods of illustration, are the subject of the final chapter of the book. Throughout, worked examples of field sketches and illustrations are provided as well as descriptions of the common mistakes to be avoided.

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