Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session S26: Focus Session: Materials in Extremes |
Hide Abstracts |
Sponsoring Units: GSCCM DCOMP DMP Chair: Marc Cawkwell, Los Alamos National Laboratory Room: 502 |
Thursday, March 6, 2014 8:00AM - 8:12AM |
S26.00001: Unusual magnetic fields of Uranus and Neptune William Nellis Voyager 2 measured spatial distributions of the magnetic fields of Uranus and Neptune (U/N) in the 1980s. Prior to Voyager 2 known planetary magnetic fields were dipolar with dipole axis aligned closely with the axis of rotation. Surprisingly, the fields of U/N are non-dipolar and non-axisymetric. If those field geometries are force-fit to dipoles, the dipole axes are tilted $\sim$45 deg. from the axes of rotation and off-centered by 30\% of planet radii. Stanley and Bloxham developed a 3D thin-shell dynamo model that matches measured field geometries, assuming fluid metal at radii below the inner radius of the thin shell is stably stratified [1]. Pressures and temperatures exceed $\sim$300 GPa and several 1000 K in that region. Consideration of measured electrical conductivities of metallic fluid H, N, O and of ionic water and SU (a representative Ice mixture) up to 180 GPa, a theoretical prediction of metallization of water at 300 GPa and several 1000 K, condensed matter physics of electrical conduction in disordered systems, and likely mutual solubilities suggests it is reasonable to expect stable stratification in the deep interiors of U/N, as assumed by Stanley and Bloxham. \\[4pt] [1] S. Stanley and J. Bloxham, Nature 248, 151 (2004). [Preview Abstract] |
Thursday, March 6, 2014 8:12AM - 8:24AM |
S26.00002: Structure at the bottom of an accreted neutron star crust, and at the top of a magnetized crust Tyler Engstrom, Noah Yoder, Vincent Crespi, Benjamin Owen, James Brannick, Xiaozhe Hu Neutron star crusts play a role in a growing list of observable phenomena. These include cooling and thermal structure of the star, gravitational wave emission, and quasi-periodic oscillations in the tails of magnetar flares. Below neutron drip density $4\times 10^{11}$ g/cc, an accreted crust contains a variety of nuclear species embedded in a relativistic, degenerate electron gas. We model interactions with Yukawa pair potentials, and carry out extensive structure searches using a genetic algorithm. The search results are used to calculate equilibrium phase diagrams for representative ternary systems. Pulsars are magnetic neutron stars with surface fields $\sim 10^{12}$ gauss. The outermost several meters of pulsar crust is a good candidate for description with the magnetic Thomas-Fermi model. We introduce a novel domain decomposition method for solving the nonlinear, periodized version of this model, and calculate the single-component phase diagram, equation of state, and other properties. Connections to astrophysical observables will be discussed. [Preview Abstract] |
Thursday, March 6, 2014 8:24AM - 8:36AM |
S26.00003: Nonlocal orbital-free density functional theory for warm dense matter Travis Sjostrom Accurate simulations of warm dense matter remain challenging in current research, while being motivated further as recent experiments probe more accurately into this regime. While the \textit{de facto} standard is quantum molecular dynamics using Kohn-Sham DFT, this methods scales significantly with temperature due to the orbital dependence. From the other side, the orbital-free Thomas-Fermi approximation works well for hot dense systems, but loses accuracy at lower temperatures. Recently developed nonlocal orbital-free functionals for the noninteracting free energy [Phys. Rev. B 88, 195103], which show near Kohn-Sham accuracy for broad ranges of temperature and density are presented. The application of which are detailed in regards to pseudopotentials and molecular dynamics for various systems. Comparisons with local orbital-free methods as well as orbital-dependent Kohn-Sham calculations, including accuracy and computational cost are made. [Preview Abstract] |
Thursday, March 6, 2014 8:36AM - 8:48AM |
S26.00004: Optical Response of Warm Dense Matter Using Real-Time Electron Dynamics Andrew Baczewski, Luke Shulenburger, Michael Desjarlais, Rudolph Magyar The extreme temperatures and solid-like densities in warm dense matter present a unique challenge for theory, wherein neither conventional models from condensed matter nor plasma physics capture all of the relevant phenomenology. While Kubo-Greenwood DFT calculations have proven capable of reproducing optical properties of WDM, they require a significant number of virtual orbitals to reach convergence due to their perturbative nature. Real-time TDDFT presents a complementary framework with a number of computationally favorable properties, including reduced cost complexity and better scalability, and has been used to reproduce the optical response of finite and ordered extended systems. We will describe the use of Ehrenfest-TDDFT to evolve coupled electron-nuclear dynamics in WDM systems, and the subsequent evaluation of optical response functions from the real-time electron dynamics. The advantages and disadvantages of this approach will be discussed relative to the current state-of-the-art. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Thursday, March 6, 2014 8:48AM - 9:00AM |
S26.00005: \textit{Ab initio} calculations of the electron momentum distribution function for ordered and disordered warm dense matter (WDM) E. Klevak, B.A. Mattern, J.J. Kas, J.J. Rehr, G.T. Seidler We report new calculations of the electron momentum distribution $n(p)$ for ordered and disordered materials of interest for warm dense matter research. The central role of the electron-ion interaction and the need to orthogonalize the valence-electron and core-electron wave functions has often been ignored in the interpretation of x-ray Thomson scattering studies of WDM.\footnote{Mattern, B.~A. et al. arXiv:\textbf{1308.2990} (2013)} This has led to substantial uncertainty in the inferred temperatures and ionization states in laser-shock generated dense plasmas. Real space Green's function calculations as a function of density and disorder are used to evaluate the possibility of a broadly applicable universal rescaling of the free-electron $n(p)$ by an effective volume and effective temperature to approximate the effects of valence-core orthogonalization. [Preview Abstract] |
Thursday, March 6, 2014 9:00AM - 9:12AM |
S26.00006: ABSTRACT WITHDRAWN |
Thursday, March 6, 2014 9:12AM - 9:24AM |
S26.00007: Controlling shock wave propagation in individual nanoplasmas: experiment and hydrodynamic simulations Daniel Hickstein, Wei Xiong, Franklin Dollar, Jennifer Ellis, Ellen Keister, Chengyuan Ding, Henry Kapteyn, Margaret Murnane, Jim Gaffney, Mark Foord, Stephen Libby, Brett Palm, Jose Jimenez, George Petrov By coupling a velocity-map-imaging spectrometer with a nanoparticle aerosol source, we present the first observations of individual nanoscale plasmas (nanoplasmas) generated from isolated nanoparticles. We show that short (40 fs) infrared (800 nm) laser pulses at a relatively low intensity (10$^{\mathrm{14}}$ W/cm$^{\mathrm{2}})$ are capable of driving shock waves in the expanding nanoplasma, providing a new method for studying shock physics in a relatively unexplored regime of dense, low-temperature, nanoplasmas. We demonstrate control of the shock waves by using a 400-nm heating pulse to pre-expand the plasma on a picosecond timescale, providing a significant enhancement in the intensity of the shock wave. Numerical hydrodynamic calculations using the HYDRA software reveal the mechanism for shock formation and suggest how the energy and intensity of the shocks can be tailored by adjusting the laser parameters. In addition, we generate nanoplasmas from various dielectric and conducting nanomaterials, and demonstrate that the direction of ion ejection can be controlled by changing the geometric shape of metal nanostructures. [Preview Abstract] |
Thursday, March 6, 2014 9:24AM - 9:36AM |
S26.00008: Atomistic simulation of systems driven through phase transitions by hot electron distributions Xukun Xiang, Jenni Portman, Faran Zhou, Chong-yu Ruan, Frederique Pellemoine, Don Morelli, Phillip Duxbury A variety of pump-probe experiments are emerging to monitor the ultrafast structural response of materials. Typically a hot electron distribution is generated by an ultrafast laser pulse or by high energy particle beams, such as swift heavy ions. The hot electron distribution then thermalizes relatively quickly, on timescales in the 100fs range, while the lattice response is slower. Structural probes such as ultrafast electron diffraction or ultrafast x-ray diffraction, are able to image the structural response typically on timescales of 100fs to nanoseconds. In this presentation we discuss the results of simulations to elucidate this ultrafast structural response when materials are driven through a phase transition. Results for titanium, graphite and phase-change materials (such as Ge$_2$Sb$_2$Se$_5$) will be presented. [Preview Abstract] |
Thursday, March 6, 2014 9:36AM - 9:48AM |
S26.00009: Propagation in atmosphere of ablated material from femtosecond laser machining of fused silica Trevor Bowman, Brian Canfield, Lloyd Davis Femtosecond laser pulses provide a means to machine structures with small heat-affected areas through highly non-linear mechanisms that enable direct writing of nanoscale features, which can be applied for fabricating a range of devices, including micro-optics and micro-fluidics. A single, tightly focused ultrashort pulse induces extreme conditions on sub-picosecond time-scales and forms a region of expanding plasma beyond the focal region. This plasma, which typically limits the depth of the nanoscale features to create shallow craters, results in the ejection of micro/nano-particles. The generation and use of these particles have a large range of applications in nanotechnology. We have studied the propagation, in atmosphere, of micro/nano particles ejected using single pulses from a 100 fs, 800 nm laser tightly focused with either a line or spot profile near the back surface of a fused silica substrate. The substrate was translated such that a fresh portion was ablated with each pulse. Time-gated images of the ejected material were taken using an intensified charged coupled device camera with additional illumination along the axial direction. Physical mechanisms and experimental results to date will be discussed. [Preview Abstract] |
Thursday, March 6, 2014 9:48AM - 10:00AM |
S26.00010: Exceptionally high aspect ratio micromachining with single femtosecond laser pulses Brian K. Canfield, Trevor S. Bowman, Alexander Terekhov, Lino Costa, Deepak Rajput, William H. Hofmeister, Lloyd M. Davis Traditional microchannel laser machining techniques involve overlapping focal spots from many laser pulses by scanning the substrate. However, this procedure is both time-consuming and allows thermal and mechanical damage to accumulate, degrading the quality of the channel profile and surrounding substrate. We have developed an alternate means of machining a very long microchannel in fused silica with a single pulse, using combinations of cylindrical lenses and an aspheric lens to reshape a near-Gaussian beam into a tight line focus. For microfluidic applications, channels should possess near diffraction-limited cross-sections just a few microns deep while being up to 2 mm long. However, depending on the pulse energy, the extremely high peak fluences can induce nonlinear effects such as filamentation and self-focusing. These effects mayproduce unexpected features, including beam-path bifurcations and multiple foci that sometimes blend into exceptionally deep channel profiles. We demonstrate microchannels that range from 5 microns to more than 30 microns deep but are only about 1 micron wide along the entire channel length. We explore the underlying extreme physical processes that might yield such extraordinary results. [Preview Abstract] |
Thursday, March 6, 2014 10:00AM - 10:12AM |
S26.00011: Efficient ab-initio thermodynamic calculations at high pressure and temperature Hugh Wilson Prediction of solubility properties and phase diagrams under conditions of high temperature and pressure requires the computation of the Gibbs free energies of materials, a property not directly accessible from molecular dynamics trajectories. Two-step coupling constant integration methods have previously achieved success in the computation of free energies of fluid, solid, and superionic phases of materials by connecting the ab-initio system of interest to a non-interacting reference system via a series of thermodynamic integration steps. These methods, however, require a series of time-consuming and computationally awkward integrations over molecular dynamics trajectories, limiting the utility of the method. Here we propose and demonstrate a method for more efficiently carrying out the same thermodynamic integration without the need for separate molecular dynamics runs, and show how it may be used to carry out the integration up to an order of magnitude more efficiently, in a massively parallel manner, and without the need for code modification. Applications of thermodynamic integration including core solubility in Jupiter and Saturn, and superionic-to-superionic phase transitions in Uranus and Neptune, will be discussed. [Preview Abstract] |
Thursday, March 6, 2014 10:12AM - 10:24AM |
S26.00012: The confinement effect of inert materials on insensitive high explosives Yutao Sun, Ming Yu, Li Tang The paper aims at investing the confinement effect of inert materials on insensitive high explosives by means of shock polar curve and phenomenological reaction model. The confinement types are categorized by the shock polar theory, which built on the leading shock wave based on the detonation ZND model. If the sonic velocity of the confinement material is less than the CJ velocity of an explosive, the shock polar theory can be utilized. In general, there are several types of interactions that give a ?match? of the pressure and streamline-deflection across the interface between IHE and confinement material. A two-dimensional Lagrangian hydrodynamic method with three-term Lee-Tarver rate law is used to numerically simulate all types of confinement interactions. The important character of confinement material include: compressibility, thickness, the representative assembled layers, such as bakelite-iron and iron-beryllium. An improved detonation model is established to simulate the pre-compression effect on unreact explosive. [Preview Abstract] |
Thursday, March 6, 2014 10:24AM - 10:36AM |
S26.00013: Effect of slow energy releasing on divergent detonation of Insensitive High Explosives Xiaomian Hu, Hao Pan, Yong Huang, Zihui Wu There exists a slow energy releasing (SER) process in the slow reaction zone located behind the detonation wave due to the carbon cluster in the detonation products of Insensitive High Explosives (IHEs), and the process will affect the divergent detonation wave's propagation and the driving process of the explosives. To study the potential effect, a new artificial burn model including the SER process based on the programmed burn model is proposed in the paper. Quasi-steady analysis of the new model indicates that the nonlinearity of the detonation speed as a function of front curvature owes to the significant change of the reaction rate and the reaction zone length at the sonic state. What's more, in simulating the detonation of IHE JB-9014, the new model including the slow reaction can predict a slower jump-off velocity, in good agreement with the result of the test. [Preview Abstract] |
Thursday, March 6, 2014 10:36AM - 10:48AM |
S26.00014: Study on the Mechanism of the Deflagration to Detonation Transition Process of Explosive Yangjun Ying, Xiaomian Hu, Lan Wei In this paper we presented a numerical study of the mechanisms of the deflagration to detonation transition (DDT) process of explosives to assess its thermal stability. We treated the modeling system as a mixture of solid explosives and gaseous reaction products. We utilized a one-dimensional two-phase flow modeling approach with space-time conservation element and solution element (CE/SE) method. Simulation results show a plug area of high density with relatively slow chemical reactions, whose forward boundary is the fast running shock wave, and rearward boundary is the burning wave.We identified a criterion of steady detonation through a detailed analysis of the characteristics of the reaction process: steady detonation occurs at locations where different physical quantities, such as pressure, density, temperature and velocity, reach peak values simultaneously.We also simulated the high temperature DDT tube experiments of HMX-based high explosive. We found good agreement between the simulation results of detonation velocity and run length determined by the above criterion and the experimental results. [Preview Abstract] |
Thursday, March 6, 2014 10:48AM - 11:00AM |
S26.00015: PETN, RDX, HMX, TATB: band gap dependence on pressure under hydrostatic compression from DFT with GW and vdW corrections Andrei Mukhanov, Alexei Yanilkin In the middle of 1990s Gilman (Gilman J. J. 1995 Phil. Mag. B, 71:6, 1057) proposed the idea that explosives transit from insulator to conductor state with following adiabatic expansion of free electrons in shockwave. One of the reasons of such a behavior of electrons is narrowing or disappearing of the fundamental band gap in explosive single crystal. It is well known that similar behavior can be simulated by DFT. But there is a severe problem of lowering the value of gap by DFT. So for quantitative prediction of narrowing of gap under pressure it is necessary to use more complicated methods like GW. From first principle calculations we determined elastic moduli for ideal crystals of PETN, RDX, HMX, and TATB. Accounting for those moduli we simulated the 0 K isotherms for hydrostatic compression of single crystal. Due to the essential role of van der Waals interaction in such materials the vdW corrections to DFT in Grimme's form was used. We obtained the dependencies for band gap on pressure under hydrostatic compression. Our preliminary results on GW calculations show that for TATB at initial uncompressed volume we have the value of gap twice a bigger in GW than in DFT. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700