10 years of Cassini/VIMS observations at Titan

NASA Astrophysics Data System (ADS)

Sotin, C.; Brown, R. H.; Baines, K. H.; Barnes, J.; Buratti, B. J.; Clark, R. N.; Jaumann, R.; LeMouelic, S.; Nicholson, P. D.; Rodriguez, S.; Soderblom, J.; Soderblom, L.; Stephan, K.

2014-04-01

The interplanetary space probe Cassini/Huygens reached Saturn in July 2004 after seven years of cruise phase. Today, the German-lead Cosmic Dust Analyser (CDA) is operated continuously for 10 years in orbit around Saturn. During the cruise phase CDA measured the interstellar dust flux at one AU distance from the Sun, the charge and composition of interplanetary dust grains and the composition of the Jovian nanodust streams. The first discovery of CDA related to Saturn was the measurement of nanometer sized dust particles ejected by its magnetosphere to interplanetary space with speeds higher than 100 km/s. Their origin and composition was analysed and an their dynamical studies showed a strong link to the conditions of the solar wind plasma flow. A recent surprising result was, that stream particles stem from the interior of Enceladus. Since 2004 CDA measured millions of dust impacts characterizing the dust environment of Saturn. The instrument showed strong evidence for ice geysers located at the south pole of Saturn's moon Enceladus in 2005. Later, a detailed compositional analysis of the salt-rich water ice grains in Saturn's E ring system lead to the discovery of liquid water below the icy crust connected to an ocean at depth feeding the icy jets. CDA was even capable to derive a spatially resolved compositional profile of the plume during close Enceladus flybys. A determination of the dust-magnetosphere interaction and the discovery of the extended E ring allowed the definition of a dynamical dust model of Saturn's E ring describing the observed properties. The measured dust density profiles in the dense E ring revealed geometric asymmetries. Cassini performed shadow crossings in the ring plane and dust grain charges were measured in shadow regions delivering important data for dust-plasma interaction studies. In the last years, dedicated measurement campaigns were executed by CDA to monitor the flux of interplanetary and interstellar dust particles reaching Saturn. Currently, the composition of interstellar grains and the meteoroid flux into the Saturnian system are in analysis.

Nitrogen Isotopic Anomalies in a Hydrous Interplanetary Dust Particle

NASA Technical Reports Server (NTRS)

Smith, J. B.; Dai, Z. R.; Weber, P. K.; Graham, G. A.; Hutcheon, I. D.; Bajt, S.; Ishii, H.; Bradley, J. P.

2005-01-01

Interplanetary dust particles (IDPs) collected in the stratosphere are the fine-grained end member (5 - 50 microns in size) of the meteoritic material available for investigation in the laboratory. IDPs are derived from either cometary or asteroidal sources. Some IDPs contain cosmically primitive materials with isotopic signatures reflecting presolar origins. Recent detailed studies using the NanoSIMS have shown there is a wide variation of isotopic signatures within individual IDPs; grains with a presolar signature have been observed surrounded by material with a solar isotopic composition. The majority of IDPs studied have been anhydrous. We report here results from integrated NanoSIMS/FIB/TEM/Synchrotron IR studies of a hydrous IDP, focused on understanding the correlations between the isotopic, mineralogical and chemical compositions of IDPs.

Extracting lunar dust parameters from image charge signals produced by the Lunar Dust Experiment

NASA Astrophysics Data System (ADS)

Stanley, J.; Kempf, S.; Horanyi, M.; Szalay, J.

2015-12-01

The Lunar Dust Experiment (LDEX) onboard the Lunar Atmosphere and Dust Environment Explorer (LADEE) is an impact ionization dust detector used to characterize the lunar dust exosphere generated by the impacts of large interplanetary particles and meteor streams (Horanyi et al., 2015). In addition to the mass and speed of these lofted particles, LDEX is sensitive to their charge. The resulting signatures of impact events therefore provide valuable information about not only the ambient plasma environment, but also the speed vectors of these dust grains. Here, impact events produced from LDEX's calibration at the Dust Accelerator Laboratory are analyzed using an image charge model derived from the electrostatic simulation program, Coulomb. We show that parameters such as dust grain speed, size, charge, and position of entry into LDEX can be recovered and applied to data collected during LADEE's seven-month mission.

Synchrotron FTIR Examination of Interplanetary Dust Particles: An Effort to Determine the Compounds and Minerals in Interstellar and Circumstellar Dust

NASA Technical Reports Server (NTRS)

Flynn, G. J.; Keller, L. P.

2002-01-01

Some interplanetary dust particles (IDPs), collected by NASA from the Earth's stratosphere, are the most primitive extraterrestrial material available for laboratory analysis. Many exhibit isotopic anomalies in H, N, and O, suggesting they contain preserved interstellar matter. We report the preliminary results of a comparison of the infrared absorption spectra of subunits of the IDPs with astronomical spectra of interstellar grains.

Euhedral metallic-Fe-Ni grains in extraterrestrial samples

NASA Technical Reports Server (NTRS)

Rubin, Alan E.

1993-01-01

Metallic Fe-Ni is rare in terrestrial rocks, being largely restricted to serpentinized peridotites and volcanic rocks that assimilated carbonaceous material. In contrast, metallic Fe-Ni is nearly ubiquitous among extraterrestrial samples (i.e., meteorites, lunar rocks, and interplanetary dust particles). Anhedral grains are common. For example, in eucrites and lunar basalts, most of the metallic Fe-Ni occurs interstitially between silicate grains and thus tends to have irregular morphologies. In many porphyritic chondrules, metallic Fe-Ni and troilite form rounded blebs in the mesostasis because their precursors were immiscible droplets. In metamorphosed ordinary chondrites, metallic Fe-Ni and troilite form coarse anhedral grains. Some of the metallic Fe-Ni and troilite grains has also been mobilized and injected into fractures in adjacent silicate grains where local shock-reheating temperatures reached the Fe-FeS eutectic (988 C). In interplanetary dust particles metallic Fe-Ni most commonly occurs along with sulfide as spheroids and fragments. Euhedral metallic Fe-Ni grains are extremely rare. Several conditions must be met before such grains can form: (1) grain growth must occur at free surfaces, restricting euhedral metallic Fe-Ni grains to systems that are igneous or undergoing vapor-deposition; (2) the metal (+/-) sulfide assemblage must have an appropriate bulk composition so that taenite is the liquidus phase in igneous systems or the stable condensate phase in vapor-deposition systems; and (3) metallic Fe-Ni grains must remain underformed during subsequent compaction, thermal metamorphism, and shock. Because of these restrictions, the occurrence of euhedral metallic Fe-Ni grains in an object can potentially provide important petrogenetic information. Despite its rarity, euhedral metallic Fe-Ni occurs in a wide variety of extraterrestrial materials. Some of these materials formed in the solar nebula; others formed on parent body surfaces by meteoroid impacts.

Mineralogy of interplanetary dust particles from the 'olivine' infrared class

NASA Technical Reports Server (NTRS)

Christoffersen, R.; Buseck, P. R.

1986-01-01

Analytical electron microscopy observations establish that olivine is abundant and the predominant silicate phase in three interplanetary dust particles (IDPs) from the 'olivine' infrared spectra category. Two of the particles have microstructures resembling those of most nonhydrous chondritic IDPs, consisting of micron to submicron grains together with a matrix composed of amorphous carbonaceous material and sub-500 A grains. In addition to olivine these particles respectively contain enstatite and magnetite, and pentlandite plus Ca-rich clinopyroxene. The third IDP consists mostly of olivine and pyrrhotite with little or no matrix material. Olivine grains in this particle contain prominent solar-flare ion tracks with densities corresponding to a space-exposure age between 1000 to 100,000 years. Although the three particles have olivine-rich mineralogies in common, other aspects of their mineralogies and microstructures suggest that they experienced different formation histories. The differences between the particles indicate that the olivine infrared spectral category is a diverse collection of IDPs that probably incorporates several genetic groups.

Interplanetary Program to Optimize Simulated Trajectories (IPOST). Volume 3: Programmer's manual

NASA Technical Reports Server (NTRS)

Hong, P. E.; Kent, P. D.; Olson, D. W.; Vallado, C. A.

1992-01-01

The Interplanetary Program to Optimize Space Trajectories (IPOST) is intended to support many analysis phases, from early interplanetary feasibility studies through spacecraft development and operations. Here, information is given on the IPOST code.

Cometary and interstellar dust grains - Analysis by ion microprobe mass spectrometry and other techniques

NASA Technical Reports Server (NTRS)

Zinner, Ernst

1991-01-01

A survey of microanalytical measurements on interplanetary dust particles (IDPs) and interstellar dust grains from primitive meteorites is presented. Ion-microprobe mass spectrometry with its capability to determine isotopic compositions of many elements on a micron spatial scale has played a special role. Examples are measurements of H, N, and O isotopes and refractory trace elements in IDPs; C, N, Mg, and Si isotopes in interstellar SiC grains; and C and N isotopes and H, N, Al, and Si concentrations in interstellar graphite grains.

Origins of GEMS Grains

NASA Technical Reports Server (NTRS)

Messenger, S.; Walker, R. M.

2012-01-01

Interplanetary dust particles (IDPs) collected in the Earth s stratosphere contain high abundances of submicrometer amorphous silicates known as GEMS grains. From their birth as condensates in the outflows of oxygen-rich evolved stars, processing in interstellar space, and incorporation into disks around new stars, amorphous silicates predominate in most astrophysical environments. Amorphous silicates were a major building block of our Solar System and are prominent in infrared spectra of comets. Anhydrous interplanetary dust particles (IDPs) thought to derive from comets contain abundant amorphous silicates known as GEMS (glass with embedded metal and sulfides) grains. GEMS grains have been proposed to be isotopically and chemically homogenized interstellar amorphous silicate dust. We evaluated this hypothesis through coordinated chemical and isotopic analyses of GEMS grains in a suite of IDPs to constrain their origins. GEMS grains show order of magnitude variations in Mg, Fe, Ca, and S abundances. GEMS grains do not match the average element abundances inferred for ISM dust containing on average, too little Mg, Fe, and Ca, and too much S. GEMS grains have complementary compositions to the crystalline components in IDPs suggesting that they formed from the same reservoir. We did not observe any unequivocal microstructural or chemical evidence that GEMS grains experienced prolonged exposure to radiation. We identified four GEMS grains having O isotopic compositions that point to origins in red giant branch or asymptotic giant branch stars and supernovae. Based on their O isotopic compositions, we estimate that 1-6% of GEMS grains are surviving circumstellar grains. The remaining 94-99% of GEMS grains have O isotopic compositions that are indistinguishable from terrestrial materials and carbonaceous chondrites. These isotopically solar GEMS grains either formed in the Solar System or were completely homogenized in the interstellar medium (ISM). However, the chemical compositions of GEMS grains are extremely heterogeneous and seem to rule out this possibility. Based on their solar isotopic compositions and their non-solar elemental compositions we propose that most GEMS grains formed in the nebula as late-stage non-equilibrium condensates.

Highlights and discoveries of the Cosmic Dust Analyser (CDA) during its 15 years of exploration

NASA Astrophysics Data System (ADS)

Srama, R.; Moragas-Klostermeyer, G.; Kempf, S.; Postberg, F.; Albin, T.; Auer, S.; Altobelli, N.; Beckmann, U.; Bugiel, S.; Burton, M.; Economou, T.; Fliege, K.; Grande, M.; Gruen, E.; Guglielmino, M.; Hillier, J. K.; Schilling, A.; Schmidt, J.; Seiss, M.; Spahn, F.; Sterken, V.; Trieloff, M.

2014-04-01

The interplanetary space probe Cassini/Huygens reached Saturn in July 2004 after seven years of cruise phase. Today, the German-lead Cosmic Dust Analyser (CDA) is operated continuously for 10 years in orbit around Saturn. During the cruise phase CDA measured the interstellar dust flux at one AU distance from the Sun, the charge and composition of interplanetary dust grains and the composition of the Jovian nanodust streams. The first discovery of CDA related to Saturn was the measurement of nanometer sized dust particles ejected by its magnetosphere to interplanetary space with speeds higher than 100 km/s. Their origin and composition was analysed and an their dynamical studies showed a strong link to the conditions of the solar wind plasma flow. A recent surprising result was, that stream particles stem from the interior of Enceladus. Since 2004 CDA measured millions of dust impacts characterizing the dust environment of Saturn. The instrument showed strong evidence for ice geysers located at the south pole of Saturn's moon Enceladus in 2005. Later, a detailed compositional analysis of the salt-rich water ice grains in Saturn's E ring system lead to the discovery of liquid water below the icy crust connected to an ocean at depth feeding the icy jets. CDA was even capable to derive a spatially resolved compositional profile of the plume during close Enceladus flybys. A determination of the dust-magnetosphere interaction and the discovery of the extended E ring allowed the definition of a dynamical dust model of Saturn's E ring describing the observed properties. The measured dust density profiles in the dense E ring revealed geometric asymmetries. Cassini performed shadow crossings in the ring plane and dust grain charges were measured in shadow regions delivering important data for dust-plasma interaction studies. In the last years, dedicated measurement campaigns were executed by CDA to monitor the flux of interplanetary and interstellar dust particles reaching Saturn. Currently, the composition of interstellar grains and the meteoroid flux into the Saturnian system are in analysis.

MHD Simulation of the Interplanetary Environment in the Ecliptic Plane during the 3-9 February 1986 Solar and Geomagnetic Activity.

DTIC Science & Technology

1986-09-01

AD-R173 822 MWD SIMULATION OF THE INTERPLANETARY ENVIRONMENT IN THE 1/1 ECLIPTIC PLRNE DU (U) AIR FORCE GEOPHYSICS LAS HANSCOM AFB MA M DRYER ET AL...RESOLUTION TEST CHART M4rtqOAI RIM) Of STANDARMS 96I-A AFGL-TR-86-0189 M Simulation of the Interplanetary Environment in the Ecliptic Plane During the 3-9...CLASSIFICATION OF THIS PAGE Cant of Block 11: in the Ecliptic Plane During the 3-9 February 1986 Solar and Geomagnetic Activity Cant of Block 19 (ABSTRACT

In situ 3-D mapping of pore structures and hollow grains of interplanetary dust particles with phase contrast X-ray nanotomography

NASA Astrophysics Data System (ADS)

Hu, Z. W.; Winarski, R. P.

2016-09-01

Unlocking the 3-D structure and properties of intact chondritic porous interplanetary dust particles (IDPs) in nanoscale detail is challenging, which is also complicated by atmospheric entry heating, but is important for advancing our understanding of the formation and origins of IDPs and planetary bodies as well as dust and ice agglomeration in the outer protoplanetary disk. Here, we show that indigenous pores, pristine grains, and thermal alteration products throughout intact particles can be noninvasively visualized and distinguished morphologically and microstructurally in 3-D detail down to ~10 nm by exploiting phase contrast X-ray nanotomography. We have uncovered the surprisingly intricate, submicron, and nanoscale pore structures of a ~10-μm-long porous IDP, consisting of two types of voids that are interconnected in 3-D space. One is morphologically primitive and mostly submicron-sized intergranular voids that are ubiquitous; the other is morphologically advanced and well-defined intragranular nanoholes that run through the approximate centers of ~0.3 μm or lower submicron hollow grains. The distinct hollow grains exhibit complex 3-D morphologies but in 2-D projections resemble typical organic hollow globules observed by transmission electron microscopy. The particle, with its outer region characterized by rough vesicular structures due to thermal alteration, has turned out to be an inherently fragile and intricately submicron- and nanoporous aggregate of the sub-μm grains or grain clumps that are delicately bound together frequently with little grain-to-grain contact in 3-D space.

Interrelationships between interstellar and interplanetary grains

NASA Technical Reports Server (NTRS)

Clayton, D. D.

1986-01-01

The relationship between solar system dust (SSD) and interstellar dust particles (ISMD) is being reconsidered because of the discovery of isotopic anomalies in meteorites. Meteoritic, circumstellar/meteoritic, interstellar/meteoritic, planetary, and cometary data are reviewed.

STEREO SECCHI and S/WAVES Observations of Spacecraft Debris Caused by Micron-Size Interplanetary Dust Impacts

NASA Astrophysics Data System (ADS)

St. Cyr, O. C.; Kaiser, M. L.; Meyer-Vernet, N.; Howard, R. A.; Harrison, R. A.; Bale, S. D.; Thompson, W. T.; Goetz, K.; Maksimovic, M.; Bougeret, J.-L.; Wang, D.; Crothers, S.

2009-05-01

Early in the STEREO mission observers noted that the white-light instruments of the SECCHI suite were detecting significantly more spacecraft-related “debris” than any previously flown coronagraphic instruments. Comparison of SECCHI “debris storms” with S/WAVES indicates that almost all are coincident with the most intense transient emissions observed by the radio and plasma waves instrument. We believe the debris is endogenous ( i.e., from the spacecraft thermal blanketing), and the storms appear to be caused by impacts of large interplanetary dust grains that are detected by S/WAVES. Here we report the observations, compare them to interplanetary dust distributions, and document a reminder for future spacebased coronagraphic instrument builders.

Bioastrophysical aspects of low energy ion irradiation of frozen anthracene containing water.

PubMed

Tuleta, M; Gabła, L; Madej, J

2001-08-13

The origin of life on Earth remains a fascinating mystery in spite of many theories existing on this subject. However, it seems that simple prebiotic molecules could play an essential role in the formation of more complex organisms. In our experiment, we synthesized a class of these molecules (quinones) bombarding frozen anthracene containing water with low energy hydrogen ions. This experiment roughly simulated the astrophysical conditions which one can find in the solar system. Thus, we can hypothesize that prebiotic molecules could be created by interaction of the solar wind with interplanetary dust grains. The delivery of these molecules to early Earth may have contributed to the generation of life on our planet.

The electric potential of particles in interstellar space released from a nuclear waste payload

NASA Technical Reports Server (NTRS)

Williams, A. C.

1980-01-01

Mechanisms for charging a grain in the interplanetary medium include: (1) capture of solar wind electrons; (2) capture of solar wind protons; (3) ejection of electrons through the photoelectric effect due to the solar radiation; (4) escape of beta particles from beta emitters in the grain; and (5) escape of alpha particles from alpha emitters in the grain. The potentials on both nonradioactive and radioactive grains are considered with relation to particle size and time, and the distance from the Sun. Numerical results are presented where the waste mix is assumed to be PW-4b.

Flux rope evolution in interplanetary coronal mass ejections: the 13 May 2005 event

NASA Astrophysics Data System (ADS)

Manchester, W. B., IV; van der Holst, B.; Lavraud, B.

2014-06-01

Coronal mass ejections (CMEs) are a dramatic manifestation of solar activity that release vast amounts of plasma into the heliosphere, and have many effects on the interplanetary medium and on planetary atmospheres, and are the major driver of space weather. CMEs occur with the formation and expulsion of large-scale magnetic flux ropes from the solar corona, which are routinely observed in interplanetary space. Simulating and predicting the structure and dynamics of these interplanetary CME magnetic fields are essential to the progress of heliospheric science and space weather prediction. We discuss the simulation of the 13 May 2005 CME event in which we follow the propagation of a flux rope from the solar corona to beyond Earth orbit. In simulating this event, we find that the magnetic flux rope reconnects with the interplanetary magnetic field, to evolve to an open configuration and later reconnects to reform a twisted structure sunward of the original rope. Observations of the 13 May 2005 CME magnetic field near Earth suggest that such a rearrangement of magnetic flux by reconnection may have occurred.

Principal components - Petrology and chemistry of polyphase units in chondritic porous interplanetary dust particles

NASA Astrophysics Data System (ADS)

Rietmeijer, Frans J. M.

1997-03-01

Chondritic porous (CP) interplanetary dust particles (IDPs) can be described as 'cosmic sediments'. It should be possible to recognize in these IDPs the 4500 Myrs old solar nebula dusts. The studies of unaltered chondritic IDPs show that their matrices are a mixture of three different principal components (PCs) that also describe variable C/Si ratios of chondritic IDPs. Among others, PCs include polyphase units (PUs) that are amorphous to holocrystalline, both ultrafine- and coarse-grained, ferromagnesiosilica(te) materials with minor Al and Ca. The properties of PCs and their alteration products define the physical and chemical processes that produced and altered these components. PCs are also cornerstones of IDP classification. For example, the bulk composition of ultrafine-grained PCs can be reconstructed using the 'butterfly method' and also allows an evaluation of the metamorphic signatures, (e.g., dynamic pyrometamorphism), in chondritic IDPs.

A new method to generate dust with astrophysical properties

NASA Astrophysics Data System (ADS)

Hansen, J. F.; van Breugel, W.; Bringa, E. M.; Eberly, B.; Graham, G. A.; Remington, B. A.; Taylor, E. A.; Tielens, A. G. G. M.

2011-05-01

To model the size distribution and composition of interstellar and interplanetary dust grains, and their effect on a wide range of phenomena, it is vital to understand the mechanism of dust-shock interaction. We demonstrate a new laser experiment that subjects dust grains to pressure spikes similar to those of colliding astrophysical dust, and that accelerates the grains to astrophysical velocities. This new method generates much larger data sets than earlier methods; we show how large quantities (thousands) of grains are accelerated at once, rather than accelerating individual grains, as is the case of earlier methods using electric fields. We also measure the in-flight velocity ( ~ 4.5km/s) of hundreds of grains simultaneously by use of a particle image velocimetry (PIV) technique.

What can meteorites tell us about comets?

NASA Technical Reports Server (NTRS)

Anders, Edward

1986-01-01

Cometary silicates, carbon, and volatiles are reviewed using data from the Halley probes, interplanetary dust particles, and cometary spectra. The origins of anhydrous Fe(2+)-bearing silicates; whether hydrated silicates, if present, were made by gaseous or liquid H2O3; sources of organic compounds: ion-molecule reactions, photochemistry, grain catalysis; sources of CO2 and of organic polymers; and interstellar molecules and grains in comets are discussed.

Identification of a Compound Spinel and Silicate Presolar Grain in a Chondritic Interplanetary Dust Particle

NASA Technical Reports Server (NTRS)

Nguyen, A. N.; Nakamura-Messenger, K.; Messenger, S.; Keller, L. P.; Kloeck, W.

2014-01-01

Anhydrous chondritic porous interplanetary dust particles (CP IDPs) have undergone minimal parent body alteration and contain an assemblage of highly primitive materials, including molecular cloud material, presolar grains, and material that formed in the early solar nebula [1-3]. The exact parent bodies of individual IDPs are not known, but IDPs that have extremely high abundances of presolar silicates (up to 1.5%) most likely have cometary origins [1, 4]. The presolar grain abundance among these minimally altered CP IDPs varies widely. "Isotopically primitive" IDPs distinguished by anomalous bulk N isotopic compositions, numerous 15N-rich hotspots, and some C isotopic anomalies have higher average abundances of presolar grains (375 ppm) than IDPs with isotopically normal bulk N (<10 ppm) [5]. Some D and N isotopic anomalies have been linked to carbonaceous matter, though this material is only rarely isotopically anomalous in C [1, 5, 6]. Previous studies of the bulk chemistry and, in some samples, the mineralogy of select anhydrous CP IDPs indicate a link between high C abundance and pyroxene-dominated mineralogy [7]. In this study, we conduct coordinated mineralogical and isotopic analyses of samples that were analyzed by [7] to characterize isotopically anomalous materials and to establish possible correlations with C abundance.

Stardust in meteorites.

PubMed

Davis, Andrew M

2011-11-29

Primitive meteorites, interplanetary dust particles, and comets contain dust grains that formed around stars that lived their lives before the solar system formed. These remarkable objects have been intensively studied since their discovery a little over twenty years ago and they provide samples of other stars that can be studied in the laboratory in exquisite detail with modern analytical tools. The properties of stardust grains are used to constrain models of nucleosynthesis in red giant stars and supernovae, the dominant sources of dust grains that are recycled into the interstellar medium by stars.

Stardust in meteorites

PubMed Central

Davis, Andrew M.

2011-01-01

Primitive meteorites, interplanetary dust particles, and comets contain dust grains that formed around stars that lived their lives before the solar system formed. These remarkable objects have been intensively studied since their discovery a little over twenty years ago and they provide samples of other stars that can be studied in the laboratory in exquisite detail with modern analytical tools. The properties of stardust grains are used to constrain models of nucleosynthesis in red giant stars and supernovae, the dominant sources of dust grains that are recycled into the interstellar medium by stars. PMID:22106261

Radio Emmision during the interaction of two Interplanetary Coronal Mass Ejections

NASA Astrophysics Data System (ADS)

Lara, Alejandro; Niembro, Tatiana; González, Ricardo

2016-07-01

We show that some sporadic radio emission observed by the WIND/WAVES experiment in the decametric/kilometric bands are due to the interaction of two interplanetary Coronal Mass Ejections. We have performed hydrodynamic simulations of the evolution of two consecutive Coronal Mass ejections in the interplanetary medium. With these simulations it is possible to follow the density evolution of the merged structure, and therefore, compute the frequency limits of the possible plasma emission. We study four well documented ICME interaction events, and found radio emission at the time and frequencies predicted by the simulations. This emission may help to anticipate the complexity of the merged region before it reaches one AU.

Laboratory Studies of the Optical Properties and Condensation Processes of Cosmic Dust Grains

NASA Technical Reports Server (NTRS)

Abbas, M. M.; Craven, P. D.; Spann, J. F.; Tankosic, D.; LeClair, A.; West, E.; Sheldon, R.; Witherow, W. K.; Gallagher, D. L.; Adrian, M. L.

2002-01-01

A laboratory facility for conducting a variety of experiments on single isolated dust particles of astrophysical interest levitated in an electrodynamics balance has been developed at NASA/Marshall Space Flight Center. The objective of the research is to employ this experimental technique for studies of the physical and optical properties of individual cosmic dust grains of 0.1-100 micron size in controlled pressure/temperatures environments simulating astrophysical conditions. The physical and optical properties of the analogs of interstellar and interplanetary dust grains of known composition and size distribution will be investigated by this facility. In particular, we will carry out three classes of experiments to study the micro-physics of cosmic dust grains. (1) Charge characteristics of micron size single dust grains to determine the photoelectric efficiencies, yields, and equilibrium potentials when exposed to UV radiation. (2) Infrared optical properties of dust particles (extinction coefficients and scattering phase functions) in the 1-30 micron region using infrared diode lasers and measuring the scattered radiation. (3) Condensation experiments to investigate the condensation of volatile gases on colder nucleated particles in dense interstellar clouds and lower planetary atmospheres. The condensation experiments will involve levitated nucleus dust grains of known composition and initial mass (or m/q ratio), cooled to a temperature and pressure (or scaled pressure) simulating the astrophysical conditions, and injection of a volatile gas at a higher temperature from a controlled port. The increase in the mass due to condensation on the particle will be monitored as a function of the dust particle temperature and the partial pressure of the injected volatile gas. The measured data will permit determination of the sticking coefficients of volatile gases and growth rates of dust particles of astrophysical interest. Some preliminary results based on measurements of photoelectric emission and radiation pressure on single isolated 0.2 to 6.6 micron size silica particles exposed to UV radiation at 120-200 nm and green laser light at 532 nm are presented.

Analysis of organic grain coatings in primitive interplanetary dust particles: Implications for the origin of Solar System organic matter

NASA Astrophysics Data System (ADS)

Flynn, George

Analysis of organic grain coatings in primitive interplanetary dust particles: Implications for the origin of Solar System organic matter Chondritic, porous interplanetary dust particles (CP IDPs), the most primitive samples of extraterrestrial material available for laboratory analysis [1], are unequilibrated aggregates of mostly submicron, anhydrous grains of a diverse mineralogy. They contain organic matter not produced by parent body aqueous processing [2], some carrying H and N isotopic anomalies consistent with molecular cloud or outer Solar System material [3]. Scanning Transmission X-Ray Microscope (STXM) imaging at the C K-edge shows the individual grains in 10 micron aggregate CP IDPs are coated by a layer of carbonaceous material 100 nm thick. This structure implies a three-step formation sequence. First, individual grains condensed from the cooling nebular gas. Then complex, refractory organic molecules covered the surfaces of the grains either by deposition, formation in-situ, or a combination of both processes. Finally, the grains collided and stuck together forming the first dust-size material in the Solar System. Ultramicrotome sections, 70 to 100 nm thick were cut from several CP IDPs, embedded in elemental S to avoid exposure to C-based embedding media. X-ray Absorption Near Edge Structure (XANES) spectra were derived from image stacks obtained using a STXM. "Cluster analysis" was used to compare the C-XANES spectra from each of the pixels in an image stack and identify pixels exhibiting similar spectra. When applied to a CP IDP, cluster analysis identifies most carbonaceous grain coatings in a particle as having similar C-XANES spectra. Two processes are commonly suggested in the literature for production of organic grain coatings. The similarity in thickness and C-XANES spectra of the coatings on different minerals in the same IDP indicates the first, mineral specific catalysis, was not the process that produced these organic rims. Our results are consistent with this primitive organic matter being produced by the alternative process of condensation of C-bearing ices onto the grain surfaces and production of refractory organic matter by UV or other ionizing radiation bombardment of the ices [4]. The processes by which primitive grains aggregate to form the first dust of our Solar System are not well understood. Collision experiments indicate that bare rocky grains bounce apart at collision speeds ¡30 to 50 m/s and shatter at larger speeds [5]. However, experiments indicate grains coated with organic matter stick quite easily, even at speeds up to 5 m/s -an order of magnitude higher than the speed at which silicate grains accrete [6]. Thus the organic grain coatings we identified likely played a critical role in dust aggregation in the early Solar System. References: [1] Ishii, H. et al. Science 2009. [2] Flynn, G. J. et al. (2003) Geochim. Cosmochim. Acta, 67, 4791-4806. [3] Keller L. P. et al. GCA (2004) Geochim. Cosmochim. Acta, 68, 2577-2589. [4] Bernstein, M. P. et al. (1995) Astrophys. J., 454, 327-344. [5] Hartmann, W. K. (1978) Icarus, 33, 50-61. [6] Kudo, T. et al. (2002) Meteoritics Planet. Sci., 37, 1975-1983.

CM-like Interplanetary Dust Particles in Lower Stratosphere During 1989 October and 1991 June/July

NASA Technical Reports Server (NTRS)

Rietmeijer, Frans J. M.

1996-01-01

The stratospheric interplanetary dust particles L2005T12 and L2011O3 are linked to CM chondrite matrix. Particle L2005T12 is dominated by tabular grains of partially dehydrated greenalite-rich serpentine. Its amorphous matrix contains abundant smectite nanocrystals and annular Fe,Ni,S units. A uniquely stratified (partial) maghemite rim occurs only on S-rich parts of the matrix. Formation of this rim and Mg depletions in the matrix occurred during atmospheric entry heating of this particle. Particle L2011O3 has large iron sulfide and magnesiowustite grains in an amorphous low-Al, ferromagnesiosilica matrix. Hydrous crystallisation of this matrix produced ultrafine-grained smectites and disseminated iron sulfides. Atmospheric entry heating of both particles is indicated by the partial iron oxide rim, vesicular sulfides, and the scatter of matrix compositions due to loss of Mg. While many uncertainties remain, the high incidence of chondritic rough particles, which include an unknown amount of CM-like particles, in the lower stratosphere during 1984, 1989, and 1991 suggests annual variations in their abundances. The timing of lower stratospheric dust samplings is critical to collect these particles.

Preliminary Examination of Impact Craters on Al Foil from the Stardust Interstellar Dust Collector

NASA Astrophysics Data System (ADS)

Stroud, R.; Stardust Interstellar Preliminary Examination Team; 29,000 Stardust@home Dusters

2011-12-01

The Interstellar Dust Collector from the NASA Stardust mission provides an unprecedented opportunity for direct laboratory study of particles from the contemporary interstellar dust (ISD) stream in order to obtain such information as grain composition and microstructure. The collector is comprised of two collection media: silica aerogel tiles and Al foil strips. Preliminary examination (PE) of particles captured in each medium is on-going. To-date, four grains analyzed in situ in aerogel with synchrotron X-ray techniques show track trajectories and elemental composition that indicate a probable interstellar origin. In addition, we report here the discovery of one crater on an Al foil for which the residue elemental composition and crater shape are consistent with the impact of a grain of interstellar origin, although an interplanetary origin has not been ruled out. Automated mapping by SEM is the primary tool for identifi-cation of craters on the Al foils. A complete map of each foil requires collection of several thousand images at a resolution of ~ 50 nm/px. Automated software has been developed to identify crater candidates, but so far it has not replaced manual efforts. Identified candidates are then re-imaged at ~ 15 nm/px, for confirmation as impact craters. Fifteen foils have been imaged; crater identification is complete for eight, yielding 32 craters. The average areal density of craters is 9.7 cm-2, which extrapolates to ~1500 craters on the total foil collection area. Initial elemental analysis of residues in six craters has been performed with a combination of Auger spectroscopy, conventional, off-axis energy dispersive X-ray spectroscopy (EDX), on-axis, silicon drift-detector EDX. Additional analysis by TEM of the residue composition and crater morphology was obtained on FIB cross-sections of four of the craters. All craters contained detectable levels of Si and O. One crater was found to contain Mg, Si, O, Fe, Ni, S, Ca and Cr, indicative of an interstellar or interplanetary origin. The shape of this crater is consistent with the impact of a fluffy aggregate grain at < 10 km/s, similar to three of the four ISD candidates identified in the aerogel, and slower than expected for an interplanetary dust grain. In three cases the impacting grain was determined by detection of additional Ce, Zn, Ti, K, or Na to be a fragment of the solar cell cover glass.

Interplanetary dust. [survey of last four years' research

NASA Technical Reports Server (NTRS)

Brownlee, D. E.

1979-01-01

Progress in the study of interplanetary dust during the past four years is reviewed. Attention is given to determinations of the relative contributions of interstellar dust grains, collisional debris from the asteroid belt and short-period comets to the interplanetary dust cloud. Effects of radiation pressure and collisions on particle dynamics are discussed, noting the discovery of the variation of the orbital parameters of dust particles at 1 AU with size and in situ measurements of dust density between 0.3 and 5 AU by the Helios and Pioneer spacecraft. The interpretation of the zodiacal light as produced by porous absorbing particles 10 to 100 microns in size is noted, and measurements of the Doppler shift, light-producing-particle density, UV spectrum, photometric axis and angular scattering function of the zodiacal light are reported. Results of analyses of lunar rock microcraters as to micrometeoroid density, flux rate, size distribution and composition are indicated and interplanetary dust particles collected from the stratosphere are discussed. Findings concerning the composition of fragile meteoroid types found as cosmic spherules in deep sea sediments are also presented.

Stardust from Supernovae and Its Isotopes

NASA Astrophysics Data System (ADS)

Hoppe, Peter

Primitive solar system materials, namely, meteorites, interplanetary dust particles, and cometary matter contain small quantities of nanometer- to micrometer-sized refractory dust grains that exhibit large isotopic abundance anomalies. These grains are older than our solar system and have been named "presolar grains." They formed in the winds of red giant and asymptotic giant stars and in the ejecta of stellar explosions, i.e., represent a sample of stardust that can be analyzed in terrestrial laboratories for isotopic compositions and other properties. The inventory of presolar grains is dominated by grains from red giant and asymptotic giant branch stars. Presolar grains from supernovae form a minor but important subpopulation. Supernova (SN) minerals identified to date include silicon carbide, graphite, silicon nitride, oxides, and silicates. Isotopic studies of major, minor, and trace elements in these dust grains have provided detailed insights into nucleosynthetic and mixing processes in supernovae and how dust forms in these violent environments.

The interplanetary electric field, cleft currents and plasma convection in the polar caps

NASA Technical Reports Server (NTRS)

Banks, P. M.; Clauer, C. R.; Araki, T.; St. Maurice, J. P.; Foster, J. C.

1984-01-01

The relationship between the pattern of plasma convection in the polar cleft and the dynamics of the interplanetary electric field (IEF) is examined theoretically. It is shown that owing to the geometrical properties of the magnetosphere, the East-West component of the IEF will drive field-aligned currents which connect to the ionosphere at points lying on either side of noon, while currents associated with the North-South component of the IEF will connect the two polar caps as sheet currents, also centered at 12 MLT. In order to describe the consequences of the Interplanetary Magnetic Field (IMF) effects upon high-latitude electric fields and convection patterns, a series of numerical simulations was carried out. The simulations were based on a solution to the steady-state equation of current continuity in a height-integrated ionospheric current. The simulations demonstrate that a simple hydrodynamical model can account for the narrow 'throats' of strong dayside antisunward convection observed during periods of southward interplanetary IMF drift, as well as the sunward convection observed during periods of strongly northward IMF drift.

SpaceNet: Modeling and Simulating Space Logistics

NASA Technical Reports Server (NTRS)

Lee, Gene; Jordan, Elizabeth; Shishko, Robert; de Weck, Olivier; Armar, Nii; Siddiqi, Afreen

2008-01-01

This paper summarizes the current state of the art in interplanetary supply chain modeling and discusses SpaceNet as one particular method and tool to address space logistics modeling and simulation challenges. Fundamental upgrades to the interplanetary supply chain framework such as process groups, nested elements, and cargo sharing, enabled SpaceNet to model an integrated set of missions as a campaign. The capabilities and uses of SpaceNet are demonstrated by a step-by-step modeling and simulation of a lunar campaign.

Dust arcs in the region of Jupiter's Trojan asteroids

NASA Astrophysics Data System (ADS)

Liu, Xiaodong; Schmidt, Jürgen

2018-01-01

Aims: The surfaces of the Trojan asteroids are steadily bombarded by interplanetary micrometeoroids, which releases ejecta of small dust particles. These particles form the faint dust arcs that are associated with asteroid clouds. Here we analyze the particle dynamics and structure of the arc in the region of the L4 Trojan asteroids. Methods: We calculate the total cross section of the L4 Trojan asteroids and the production rate of dust particles. The motion of the particles is perturbed by a variety of forces. We simulate the dynamical evolution of the dust particles, and explore the overall features of the Trojan dust arc. Results: The simulations show that the arc is mainly composed of grains in the size range 4-10 microns. Compared to the L4 Trojan asteroids, the dust arc is distributed more widely in the azimuthal direction, extending to a range of [30, 120] degrees relative to Jupiter. The peak number density does not develop at L4. There exist two peaks that are azimuthally displaced from L4.

Occurrence and possible significance of rare Ti oxides (Magneli phases) in carbonaceous chondrite matrices

NASA Technical Reports Server (NTRS)

Brearley, Adrian J.

1993-01-01

Rare, ultrafine-grained Ti oxides (Ti3O5 and the Magneli phases, Ti5O9 and Ti8O15) have been identified by TEM in the CM2 carbonaceous chondrite, Bells, and a carbonaceous chondrite matrix clast from the Nilpena polymict ureilite. In both meteorites the Ti oxides occur in the matrix as isolated grains and clusters of two or more grains. They are euhedral in shape and have grain sizes of 0.05-0.3 micron. Magneli phases have been recently shown to be a common component in some interplanetary dust particles, but this is the first reported occurrence in a meteorite. The morphological properties and grain size of the Ti oxides are consistent with formation by vapor phase condensation either within the solar nebula or possibly in a presolar environment.

Chemically anomalous, pre-accretionally irradiated grains in interplanetary dust -- interstellar grains?. [Abstract only

NASA Technical Reports Server (NTRS)

Bradley, J. P.

1994-01-01

Ultrafine-grained matrix is a unique and fundamental building block of chondritic porous (CP) interplanetary dust particles. Most IDPs so far determined to be of cometary origin belong to the CP class. The matrix in CP IDPs is not homogeneous but rather a loose mixture of discrete single crystals (e.g., olivine, pyroxene, Fe sulfides) and polyphase grains. The petrographic diversity observed among the polyphase grains suggest that they were formed under variable physiochemical conditions. One particular class of polyphase grains are a dominant component in cometary IDPs. Although their occurrence is well documented, the terminology used to describe them is confused. They have been called many names. Here they are simply called GEMS (Glass with Embedded Metal and Sulfides). The bulk compositions of GEMS are within a factor of 3 chondritic (solar) for all major elements except C. Quantitative thin-film X-ray (EDS) analyses have shown that GEMS are systematically depleted in Mg and Si, enriched in S, Fe, and Ni, and stoichiometrically enriched in O. Electron energy-loss spectroscopy (EELS) suggests that the excess O is present as hydroxyl (-OH) groups. These same chemical 'anomalies' were observed in solar-wind-irradiated amorphous rims on the surfaces of IDPs, suggesting that the compositions of GEMS reflect prior exposure to ionizing radiation. In order to test this hypothesis, a sample of Allende (CV3) matrix was exposed to proton flux. Radiation-damaged amorphous rims on olivine and pyroxene crystals in the Allende sample were found to be depleted in Mg and Ca, enriched in S, Fe, and Ni, and stoichiometrically enriched in O. Thus, the compositions of GEMS are indeed consistent with exposure to ionizing radiation. This study suggests that chemical as well as isotopic anomalies may be used to identify presolar interstellar grains in primitive meteoritic materials.

Modeling solar wind with boundary conditions from interplanetary scintillations

DOE PAGES

Manoharan, P.; Kim, T.; Pogorelov, N. V.; ...

2015-09-30

Interplanetary scintillations make it possible to create three-dimensional, time- dependent distributions of the solar wind velocity. Combined with the magnetic field observations in the solar photosphere, they help perform solar wind simulations in a genuinely time-dependent way. Interplanetary scintillation measurements from the Ooty Radio Astronomical Observatory in India provide directions to multiple stars and may assure better resolution of transient processes in the solar wind. In this paper, we present velocity distributions derived from Ooty observations and compare them with those obtained with the Wang-Sheeley-Arge (WSA) model. We also present our simulations of the solar wind flow from 0.1 AUmore » to 1 AU with the boundary conditions based on both Ooty and WSA data.« less

Cosmic dust synthesis by accretion and coagulation

NASA Technical Reports Server (NTRS)

Praburam, G.; Goree, J.

1995-01-01

The morphology of grains grown by accretion and coagulation is revaled by a new laboratory method of synthesizing cosmic dust analogs. Submicron carbon particles, grown by accretion of carbon atoms from a gas, have a spherical shape with a cauliflower-like surface and an internal micro-structure of radial columns. This shape is probably common for grains grown by accretion at a temperature well below the melting point. Coagulated grains, consisting of spheres that collided to form irregular strings, were also synthesized. Another shape we produced had a bumpy non- spherical morphology, like an interplanetary particle collected in the terrestrial stratosphere. Besides these isolated grains, large spongy aggregates of nanometer-size particles were also found for various experimental conditions. Grains were synthesized using ions to sputter a solid target, producing an atomic vapor at a low temperature. The ions were provided by a plasma, which also provided electrostatic levitation of the grains during their growth. The temporal development of grain growth was studied by extinguishing the plasma after various intervals.

Analytical electron microscopy of fine-grained phases in primitive interplanetary dust particles and carbonaceous chondrites

NASA Technical Reports Server (NTRS)

Mackinnon, Ian D. R.; Rietmeijer, Frans J. M.; Mckay, David S.

1987-01-01

In order to describe the total mineralogical diversity within primitive extraterrestrial materials, individual interplanetary dust particles (IDPs) collected from the stratosphere as part of the JSC Cosmic Dust Curatorial Program were analyzed using a variety of AEM techniques. Identification of over 250 individual grains within one chondritic porous (CP) IDP shows that most phases could be formed by low temperature processes and that heating of the IDP during atmospheric entry is minimal and less than 600 C. In a review of the mineralogy of IDPs, it was suggested that the occurrence of other silicates such as enstatite whiskers is consistent with the formation in an early turbulent period of the solar nebula. Experimental confirmation of fundamental chemical and physical processes in a stellar environment, such as vapor phase condensation, nucleation, and growth by annealing, is an important aspect of astrophysical models for the evolution of the Solar System. A detailed comparison of chondritic IDP and carbonaceous chondrite mineralogies shows significant differences between the types of silicate minerals as well as the predominant oxides.

Interplanetary dust in the transmission electron microscope - Diverse materials from the early solar system

NASA Technical Reports Server (NTRS)

Fraundorf, P.

1981-01-01

An analytical electron microscope study of dispersed interplanetary dust aggregates collected in the earth's stratosphere shows that, in spite of their similarities, the aggregates exhibit significant differences in composition, internal morphology, and mineralogy. Of 11 chondritic particles examined, two consist mostly of a noncrystalline chondritic material with an atomic S/Fe ratio equal to or greater than 2 in places, one consists of submicron metal and reduced silicate 'microchondrules' and sulfide grains embedded in a carbonaceous matrix, and another consists of submicron magnetic-decorated unequilibrated silicate and sulfide grains with thick low-Z coatings. Although the particles are unmetamorphosed by criteria commonly applied for chondritic meteorites, the presence of reduced chemistries and the ubiquity of mafic, instead of hydrated, silicates confirm that they are not simply C1 or C2 chondrite matrix material. The observations indicate that portions of some particles have not been significantly altered by thermal or radiation processes since their assembly, and that the particles probably contain fine debris from diverse processes in the early solar system.

Simulating Autonomous Telecommunication Networks for Space Exploration

NASA Technical Reports Server (NTRS)

Segui, John S.; Jennings, Esther H.

2008-01-01

Currently, most interplanetary telecommunication systems require human intervention for command and control. However, considering the range from near Earth to deep space missions, combined with the increase in the number of nodes and advancements in processing capabilities, the benefits from communication autonomy will be immense. Likewise, greater mission science autonomy brings the need for unscheduled, unpredictable communication and network routing. While the terrestrial Internet protocols are highly developed their suitability for space exploration has been questioned. JPL has developed the Multi-mission Advanced Communications Hybrid Environment for Test and Evaluation (MACHETE) tool to help characterize network designs and protocols. The results will allow future mission planners to better understand the trade offs of communication protocols. This paper discusses various issues with interplanetary network and simulation results of interplanetary networking protocols.

Astrophysics with Presolar Stardust

NASA Astrophysics Data System (ADS)

Clayton, Donald D.; Nittler, Larry R.

2004-09-01

Meteorites and interplanetary dust particles contain presolar stardust grains: solid samples of stars that can be studied in the laboratory. The stellar origin of the grains is indicated by enormous isotopic ratio variations compared with Solar System materials, explainable only by nuclear reactions occurring in stars. Known presolar phases include diamond, SiC, graphite, Si3N4, Al2O3, MgAl2O4, CaAl12O19, TiO2, Mg(Cr,Al)2O4, and most recently, silicates. Subgrains of refractory carbides (e.g., TiC), and Fe-Ni metal have also been observed within individual presolar graphite grains. We review the astrophysical implications of these grains for the sciences of nucleosynthesis, stellar evolution, grain condensation, and the chemical and dynamic evolution of the Galaxy. Unique scientific information derives primarily from the high precision (in some cases <1%) of the measured isotopic ratios of large numbers of elements in single stardust grains. Stardust science is just now reaching maturity and will play an increasingly important role in nucleosynthesis applications.

What does the fine-scale petrography of IDPs reveal about grain formation and evolution in the early solar system?

NASA Technical Reports Server (NTRS)

Bradley, John

1994-01-01

The 'pyroxene' interplanetary dust particles (IDP's) may be the best samples for investigation of primordial grain-forming reactions because they appear to have experienced negligible post-accretional alteration. They are likely to continue to yield information about gas-to-solid condensation and other grain-forming reactions that may have occurred either in the solar nebular or presolar interstellar environments. An immediate challenge lies in understanding the nanometer-scale petrography of the ultrafine-grained aggregates in 'pyroxene' IDP's. Whether these aggregates contain components from diverse grain-forming environments may ultimately be answered by systematic petrographic studies using electron microscopes capable of high spatial resolution microanalysis. It may be more difficult to decipher evidence of grain formation and evolution in 'olivine' and 'layer silicate' IDP's because they appear to have experienced post-accretional alteration. Most of the studied 'olivine' IDPs have been subjected to heating and equilibration, perhaps during atmospheric entry, while the 'layer silicate' IDP's have experienced aqueous alteration.

Interplanetary program to optimize simulated trajectories (IPOST). Volume 4: Sample cases

NASA Technical Reports Server (NTRS)

Hong, P. E.; Kent, P. D; Olson, D. W.; Vallado, C. A.

1992-01-01

The Interplanetary Program to Optimize Simulated Trajectories (IPOST) is intended to support many analysis phases, from early interplanetary feasibility studies through spacecraft development and operations. The IPOST output provides information for sizing and understanding mission impacts related to propulsion, guidance, communications, sensor/actuators, payload, and other dynamic and geometric environments. IPOST models three degree of freedom trajectory events, such as launch/ascent, orbital coast, propulsive maneuvering (impulsive and finite burn), gravity assist, and atmospheric entry. Trajectory propagation is performed using a choice of Cowell, Encke, Multiconic, Onestep, or Conic methods. The user identifies a desired sequence of trajectory events, and selects which parameters are independent (controls) and dependent (targets), as well as other constraints and the cost function. Targeting and optimization are performed using the Standard NPSOL algorithm. The IPOST structure allows sub-problems within a master optimization problem to aid in the general constrained parameter optimization solution. An alternate optimization method uses implicit simulation and collocation techniques.

The MHD simulation of interplanetary space and heliosphere by using the boundary conditions of time-varying magnetic field and IPS-based plasma

NASA Astrophysics Data System (ADS)

Hayashi, K.; Tokumaru, M.; Kojima, M.; Fujiki, K.

2008-12-01

We present our new boundary treatment to introduce the temporal variation of the observation-based magnetic field and plasma parameters on the inner boundary sphere (at 30 to 50 Rs) to the MHD simulation of the interplanetary space and the simulation results. The boundary treatment to induce the time-variation of the magnetic field including the radial component is essentially same as shown in our previous AGU meetings and newly modified so that the model can also include the variation of the plasma variables detected by IPS (interplanetary scintillation) observation, a ground-based remote sensing technique for the solar wind plasma. We used the WSO (Wilcox Solar Observatory at Stanford University) for the solar magnetic field input. By using the time-varying boundary condition, smooth variations of heliospheric MHD variables during the several Carrington solar rotation period are obtained. The simulation movie will show how the changes in the inner heliosphere observable by the ground-based instrument propagate outward and affects the outer heliosphere. The simulated MHD variables are compared with the Ulysses in-situ measurement data including ones made during its travel from the Earth to Jupiter for validation, and we obtain better agreements than with the simulation with fixed boundary conditions.

Interplanetary laser ranging - an emerging technology for planetary science missions

NASA Astrophysics Data System (ADS)

Dirkx, D.; Vermeersen, L. L. A.

2012-09-01

Interplanetary laser ranging (ILR) is an emerging technology for very high accuracy distance determination between Earth-based stations and spacecraft or landers at interplanetary distances. It has evolved from laser ranging to Earth-orbiting satellites, modified with active laser transceiver systems at both ends of the link instead of the passive space-based retroreflectors. It has been estimated that this technology can be used for mm- to cm-level accuracy range determination at interplanetary distances [2, 7]. Work is being performed in the ESPaCE project [6] to evaluate in detail the potential and limitations of this technology by means of bottom-up laser link simulation, allowing for a reliable performance estimate from mission architecture and hardware characteristics.

The Abundance and Distribution of Presolar Materials in Cluster IDPS

NASA Technical Reports Server (NTRS)

Messenger, Scott; Keller, Lindsay; Nakamura-Messenger, Keiko; Ito, Motoo

2007-01-01

Presolar grains and remnants of interstellar organic compounds occur in a wide range of primitive solar system materials, including meteorites, interplanetary dust particles (IDPs), and comet Wild-2 samples. Among the most abundant presolar phases are silicate stardust grains and molecular cloud material. However, these materials have also been susceptible to destruction and alteration during parent body and nebular processing. In addition to their importance as direct samples of remote and ancient astrophysical environments, presolar materials thus provide a measure of how well different primitive bodies have preserved the original solar system starting materials.

Coordinated Analyses of Mineral-organic Matter Associations in Interplanetary Dust Particles

NASA Technical Reports Server (NTRS)

Nakamura-Messenger, K.; Herzog, G. F.; Smith, T.; Keller, L. P.; Flynn, G. J.; Khodja, H.; Taylor, S.; Wirick, S.; Messenger, S.

2012-01-01

Little is known about the timing and processes involved in the incorporation of organic matter with inorganic materials in early Solar System bodies. Recently, X-ray absorption near-edge spectroscopy (XANES) studies showed carbon-rich rims surrounding individual mineral grains in anhydrous IDPs [1,2]. These carbonaceous rims are believed to have formed prior to parent body formation and likely served to bond mineral grains during accretion into larger aggregates. We are exploring the nature of these carbonaceous rims through coordinated analyses of their chemistry, mineralogy, spectroscopy and isotopic characteristics. Here we report our preliminary mineralogical observations.

Laboratory simulation of interplanetary ultraviolet radiation (broad spectrum) and its effects on Deinococcus radiodurans

NASA Astrophysics Data System (ADS)

Paulino-Lima, Ivan Gláucio; Pilling, Sérgio; Janot-Pacheco, Eduardo; de Brito, Arnaldo Naves; Barbosa, João Alexandre Ribeiro Gonçalves; Leitão, Alvaro Costa; Lage, Claudia de Alencar Santos

2010-08-01

The radiation-resistant bacterium Deinococcus radiodurans was exposed to a simulated interplanetary UV radiation at the Brazilian Synchrotron Light Laboratory (LNLS). Bacterial samples were irradiated on different substrates to investigate the influence of surface relief on cell survival. The effects of cell multi-layers were also investigated. The ratio of viable microorganisms remained virtually the same (average 2%) for integrated doses from 1.2 to 12 kJ m -2, corresponding to 16 h of irradiation at most. The asymptotic profiles of the curves, clearly connected to a shielding effect provided by multi-layering cells on a cavitary substrate (carbon tape), means that the inactivation rate may not change significantly along extended periods of exposure to radiation. Such high survival rates reinforce the possibility of an interplanetary transfer of viable microbes.

Laboratory measurements for the wavelength dependence of the linear polarization with the PROGRA2 instruments

NASA Astrophysics Data System (ADS)

Renard, Jean-Baptiste; Hadamcik, Edith; Levasseur-Regourd, Anny-Chantal; Carrasco, Nathalie; Couté, Benoit; Duverger, Vincent; Guerrini, Vincent

2017-04-01

Clouds of solid particles are present in many regions of the Solar System (comets, interplanetary dust cloud, planetary atmospheres). These clouds can be remotely studied by the light they scatter. There is a need for a data base of the light scattered by a large variety of samples at different wavelengths to interpret such measurements. The PROGRA2 instruments are used for this purpose. The PROGRA2 instruments, PROGRA2-VIS and PROGRA2-IR, are imaging polarimeters with a rotating arm to change the phase angle (angle between directions of illumination and observation). They allow to retrieve the complete polarization phase function between 10° and 165°. The light sources are at around 550 and 650 nm for PROGRA2-VIS, and 1000 and 1500 nm for PROGRA2-IR. The detectors are cameras, with a spatial resolution between 20 and 40 micrometers per pixel (PROGRA2-IR uses now new high sensitivity cameras). Measurements are conducted in the laboratory by an air draught technique for grains smaller than about 20 micrometers (which can be included in porous aggregates), and during parabolic flights on-board the A300 ZeroG and now the A310 ZeroG for larger grains; these flights campaigns are funded by the French and European Space Agencies. Hundreds of scattering phase functions have been obtained since 20 years, for a large number of samples (sands, silicon carbide, basalt, volcanic ashes, lunar and Martian simulants, tholins, meteoritic material, black carbon, carbonaceous compounds, …); the main results are available at www.icare.univ-lille1.fr/progra2/. Several samples have been already studied by the two instruments, showing a large diversity of wavelength dependences, from close-to-zero dependence for yellow and ocher sand grains to high dependence for silicon carbide and anthracite grains. These variations should be related to the wavelength dependence of the real and imaginary parts of the refractive index of the particles. We present a summary of the main results of the wavelength dependence of polarization already obtained with PROGRA2. We present also the interest of conducting new measurements for meteoritic material, tholins, and carbonaceous particles that can be analogues of the cometary and interplanetary grains. Since PROGRA2 is well adapted to study the large (porous) particles, as those detected by Rosetta, these new measurements will be useful to tentatively relate the wavelength dependence of linear polarization detected within several cometary comae with the main composition and nature of the particles. References : Renard et al., JQSRT, 146, 424-430, 2014 ; Hadamcik et al., Earth Planets Space, 65, 1175-1184, 2013.

Mineralogical Studies of a Highly O-17-Depleted and an O-17-Rich Presolar Grain from the Acfer 094 Meteorite

NASA Technical Reports Server (NTRS)

Nguyen, A. N.; Keller, L. P.; Rahman, Z.; Messenger, S.

2012-01-01

Silicate grains are the most abundant condensate around O-rich evolved stars, including red giants, supernovae (SNe) and binary systems. These grains have been identified in abundance in primitive meteorites and interplanetary dust particles [1,2]. Astronomical observations of the silicate spectroscopic features around circumstellar disks indicate that most silicates are amorphous olivine-like grains, though some sources show a large crystalline portion [3]. Fewer astronomical observations of SN and nova silicates exist, but amorphous Mg-rich grains predominate [4,5]. The laboratory analysis of presolar silicates by transmission electron microscopy (TEM) offers more details on the structure and chemistry of individual grains. These studies provide information on the physical and chemical conditions of the parent stellar atmosphere during grain condensation. Moreover, be-cause silicates are susceptible to secondary alteration, processing events succeeding condensation can be traced. Thus far, similar microstructures have been observed for silicates that condensed in SN outflows and in the envelopes of asymptotic giant branch (AGB) stars, but not as many of the comparatively rare SN grains have been analyzed. Here we examine the mineralogies of two presolar silicate grains having different origins.

The Acceleration of Thermal Protons and Minor Ions at a Quasi-Parallel Interplanetary Shock

NASA Astrophysics Data System (ADS)

Giacalone, J.; Lario, D.; Lepri, S. T.

2017-12-01

We compare the results from self-consistent hybrid simulations (kinetic ions, massless fluid electrons) and spacecraft observations of a strong, quasi-parallel interplanetary shock that crossed the Advanced Composition Explorer (ACE) on DOY 94, 2001. In our simulations, the un-shocked plasma-frame ion distributions are Maxwellian. Our simulations include protons and minor ions (alphas, 3He++, and C5+). The interplanetary shock crossed both the ACE and the Wind spacecraft, and was associated with significant increases in the flux of > 50 keV/nuc ions. Our simulation uses parameters (ion densities, magnetic field strength, Mach number, etc.) consistent with those observed. Acceleration of the ions by the shock, in a manner similar to that expected from diffusive shock acceleration theory, leads to a high-energy tail in the distribution of the post-shock plasma for all ions we considered. The simulated distributions are directly compared to those observed by ACE/SWICS, EPAM, and ULEIS, and Wind/STICS and 3DP, covering the energy range from below the thermal peak to the suprathermal tail. We conclude from our study that the solar wind is the most significant source of the high-energy ions for this event. Our results have important implications for the physics of the so-called `injection problem', which will be discussed.

Interplanetary Program to Optimize Simulated Trajectories (IPOST). Volume 2: Analytic manual

NASA Technical Reports Server (NTRS)

Hong, P. E.; Kent, P. D.; Olson, D. W.; Vallado, C. A.

1992-01-01

The Interplanetary Program to Optimize Space Trajectories (IPOST) is intended to support many analysis phases, from early interplanetary feasibility studies through spacecraft development and operations. The IPOST output provides information for sizing and understanding mission impacts related to propulsion, guidance, communications, sensor/actuators, payload, and other dynamic and geometric environments. IPOST models three degree of freedom trajectory events, such as launch/ascent, orbital coast, propulsive maneuvering (impulsive and finite burn), gravity assist, and atmospheric entry. Trajectory propagation is performed using a choice of Cowell, Encke, Multiconic, Onestep, or Conic methods. The user identifies a desired sequence of trajectory events, and selects which parameters are independent (controls) and dependent (targets), as well as other constraints and the cost function. Targeting and optimization is performed using the Stanford NPSOL algorithm. IPOST structure allows subproblems within a master optimization problem to aid in the general constrained parameter optimization solution. An alternate optimization method uses implicit simulation and collocation techniques.

Water and organics in interplanetary dust particles

NASA Astrophysics Data System (ADS)

Bradley, John

Interplanetary dust particles (IDPs) and larger micrometeorites (MMs) impinge on the upper atmosphere where they decelerate at 90 km altitude and settle to the Earths surface. Comets and asteroids are the major sources and the flux, 30,000-40,000 tons/yr, is comparable to the mass of larger meteorites impacting the Earths surface. The sedimentary record suggests that the flux was much higher on the early Earth. The chondritic porous (CP) subset of IDPs together with their larger counterparts, ultracarbonaceous micrometeorites (UCMMs), appear to be unique among known meteoritic materials in that they are composed almost exclusively of anhydrous minerals, some of them contain >> 50% organic carbon by volume as well as the highest abundances of presolar silicate grains including GEMS. D/H and 15N abundances implicate the Oort Cloud or presolar molecular cloud as likely sources of the organic carbon. Prior to atmospheric entry, IDPs and MMs spend 104-105 year lifetimes in solar orbit where their surfaces develop amorphous space weathered rims from exposure to the solar wind (SW). Similar rims are observed on lunar soil grains and on asteroid Itokawa regolith grains. Using valence electron energy-loss spectroscopy (VEELS) we have detected radiolytic water in the rims on IDPs formed by the interaction of solar wind protons with oxygen in silicate minerals. Therefore, IDPs and MMs continuously deliver both water and organics to the earth and other terrestrial planets. The interaction of protons with oxygen-rich minerals to form water is a universal process.

The Ultrafine Mineralogy of a Molten Interplanetary Dust Particle as an Example of the Quench Regime of Atmospheric Entry Heating

NASA Technical Reports Server (NTRS)

Rietmeijer, Frans J. M.

1996-01-01

Melting and degassing of interplanetary dust particle L2005B22 at approx. 1200 C was due to flash heating during atmospheric entry. Preservation of the porous particle texture supports rapid quenching from the peak heating temperature whereby olivine and pyroxene nanocrystals (3 nm-26 nm) show partial devitrification of the quenched melt at T approx. = 450 C - 740 C. The implied ultrahigh cooling rates are calculated at approx. 105 C/h-106 C/h, which is consistent with quench rates inferred from the temperature-time profiles based on atmospheric entry heating models. A vesicular rim on a nonstoichiometric relic forsterite grain in this particle represents either evaporative magnesium loss during flash heating or thermally annealed ion implantation texture.

Inferring Sources in the Interplanetary Dust Cloud, from Observations and Simulations of Zodiacal Light and Thermal Emission

NASA Technical Reports Server (NTRS)

Levasseur-Regourd, A. C.; Lasue, J.

2011-01-01

Interplanetary dust particles physical properties may be approached through observations of the solar light they scatter, specially its polarization, and of their thermal emission. Results, at least near the ecliptic plane, on polarization phase curves and on the heliocentric dependence of the local spatial density, albedo, polarization and temperature are summarized. As far as interpretations through simulations are concerned, a very good fit of the polarization phase curve near 1.5 AU is obtained for a mixture of silicates and more absorbing organics material, with a significant amount of fluffy aggregates. In the 1.5-0.5 AU solar distance range, the temperature variation suggests the presence of a large amount of absorbing organic compounds, while the decrease of the polarization with decreasing solar distance is indeed compatible with a decrease of the organics towards the Sun. Such results are in favor of the predominance of dust of cometary origin in the interplanetary dust cloud, at least below 1.5 AU. The implication of these results on the delivery of complex organic molecules on Earth during the LHB epoch, when the spatial density of the interplanetary dust cloud was orders of magnitude greater than today, is discussed.

The Ambient and Perturbed Solar Wind: From the Sun to 1 AU

NASA Technical Reports Server (NTRS)

Steinolfson, R. S.

1997-01-01

The overall objective of the proposed research was to use numerical solutions of the magnetohydrodynamic (MHD) equations along with comparisons of the computed results with observations to study the following topics: (1) ambient solar wind solutions that extend from the solar surface to 1 astronomical unit (AU), contain closed magnetic structures near the Sun, and are consistent with observed values; (2) magnetic and plasma structures in coronal mass ejections (CMES) as they propagate to the interplanetary medium; (3) relation of MHD shocks to CMEs in the interplanetary medium; (4) interaction of MHD shocks with structures (such as other shocks, corotating interaction regions, current sheets) in the interplanetary plasma; and (5) simulations of observed interplanetary structures. A planned close collaboration with data analysts served to make the model more relevant to the data. The outcome of this research program is an improved understanding of the physical processes occurring in solar-generated disturbances in the interplanetary medium between the Sun and 1 AU.

The Cassini Cosmic Dust Analyser CDA - A 10 year exploration of Saturn's dust environment

NASA Astrophysics Data System (ADS)

Srama, Ralf

2014-05-01

The interplanetary space probe Cassini/Huygens reached Saturn in July 2004 after seven years of cruise phase. Since then, the German-lead Cosmic Dust Analyser (CDA) was operated continuously for 10 years in orbit around Saturn. The first discovery of CDA related to Saturn was the measurement of nanometer sized dust particles ejected by its magnetosphere to interplanetary space with speeds higher than 100 km/s. Their origin and composition was analysed and an their dynamical studies showed a strong link to the conditions of the solar wind plasma flow. A recent surprising result was, that stream particles stem from the interior of Enceladus. Since 2004 CDA measured millions of dust impacts characterizing the dust environment of Saturn. The instrument showed strong evidence for ice geysers located at the south pole of Saturn's moon Enceladus in 2005. Later, a detailed compositional analysis of the salt-rich water ice grains in Saturn's E ring system lead to the discovery of liquid water below the crust connected to an ocean at depth feeding the icy jets. CDA was even capable to derive a spatially resolved compositional profile of the plume during close Enceladus flybys. A determination of the dust-magnetosphere interaction and the discovery of the extended E ring (at least twice as large as previously known) allowed the definition of a dynamical dust model of Saturns E ring describing the observed properties. Cassini performed shadow crossings in the ring plane and dust grain charges were measured in shadow regions delivering important data for dust-plasma interaction studies. In the last years, dedicated measurement campaigns were executed by CDA to monitor the flux of interplanetary and interstellar dust particles reaching Saturn.

Low-thrust solar electric propulsion navigation simulation program

NASA Technical Reports Server (NTRS)

Hagar, H. J.; Eller, T. J.

1973-01-01

An interplanetary low-thrust, solar electric propulsion mission simulation program suitable for navigation studies is presented. The mathematical models for trajectory simulation, error compensation, and tracking motion are described. The languages, input-output procedures, and subroutines are included.

Computer Aided Design of Ka-Band Waveguide Power Combining Architectures for Interplanetary Spacecraft

NASA Technical Reports Server (NTRS)

Vaden, Karl R.

2006-01-01

Communication systems for future NASA interplanetary spacecraft require transmitter power ranging from several hundred watts to kilowatts. Several hybrid junctions are considered as elements within a corporate combining architecture for high power Ka-band space traveling-wave tube amplifiers (TWTAs). This report presents the simulated transmission characteristics of several hybrid junctions designed for a low loss, high power waveguide based power combiner.

Photoelectric Emission Measurements on the Analogs of Individual Cosmic Dust Grains

NASA Technical Reports Server (NTRS)

Abbas, M. M.; Tankosic, D.; Craven, P. D.; Spann, J. F.; LeClair, A.; West, E. A.; Weingartner, J. C.; Tielens, A. G. G. M.; Nuth, J. a.; Camata, R. P.

2006-01-01

The photoelectric emission process is considered to be the dominant mechanism for charging of cosmic dust grains in many astrophysical environments. The grain charge and equilibrium potentials play an important role in the dynamical and physical processes that include heating of the neutral gas in the interstellar medium, coagulation processes in the dust clouds, and levitation and dynamical processes in the interplanetary medium and planetary surfaces and rings. An accurate evaluation of photoelectric emission processes requires knowledge of the photoelectric yields of individual dust grains of astrophysical composition as opposed to the values obtained from measurements on flat surfaces of bulk materials, as it is generally assumed on theoretical considerations that the yields for the small grains are much different from the bulk values. We present laboratory measurements of the photoelectric yields of individual dust grains of silica, olivine, and graphite of approx. 0.09-5 micrometer radii levitated in an electrodynamic balance and illuminated with ultraviolet radiation at 120-160 nm wavelengths. The measured yields are found to be substantially higher than the bulk values given in the literature and indicate a size dependence with larger particles having order-of-magnitude higher values than for submicron-size grains.

Star Formation and the Solar System

NASA Technical Reports Server (NTRS)

Bally, John; Boss, Alan; Papanastassiou, Dimitri; Sandford, Scott; Sargent, Anneila

1988-01-01

We have seen that studies of nearby star-forming regions are beginning to reveal the first signs of protoplanetary disks. Studies of interstellar and interplanetary grains are starting to provide clues about the processing and incorporation of matter into the Solar System. Studies of meteorites have yielded isotopic anomalies which indicate that some of the grains and inclusions in these bodies are very primitive. Although we have not yet detected a true interstellar grain, some of these materials have not been extensively modified since their removal from the ISM. We are indeed close to seeing our interstellar heritage. The overlap between astronomical and Solar System studies is in its infancy. What future experiments, observations, and missions can be performed in the near future that will greatly enhance our understanding of star formation and the formation of the Solar System?

The measurement of trace elements in interplanetary dust and cometary particles by ultra-high sensitivity INAA

NASA Technical Reports Server (NTRS)

Zolensky, M. E.; Lindstrom, David J.; Lindstrom, Richard M.; Lindstrom, M. M.

1989-01-01

Today the major elemental composition of interplanetary dust particles (IDPs) is routinely determined in many laboratories. These and mineralogical studies have revealed the presence of at least two major types of IDPs, chondritic and refractory. Preliminary results of a successful attempt to determine abundances of a large suite of trace elements from both chondritic and refractory IDPs are reported. The analytical procedure can be used in the grain-by-grain analysis of returned cometary samples. Chondritic and refractory IDPs are characterized by standard scanning electron microscopy and energy dispersive x ray spectroscopy (SEM-EDX) techniques. With this system, detection limits for many elements are well below picogram levels, and some approach femtogram levels. This technique is non-destructive, although some sample handling is required, so particles can be analyzed by other techniques after instrument neutron activation analysis (INAA) is completed. Data is presently being reduced from the analyses of 7 IDPs. These are U2015E10, U2015F1, W7029-A2, W7029-A3, W7013A8, LACl (all chondritic) and 705 (refractory). So far, 17 different major and trace elements were detected and measured in these particles, including rare earths and some very volatile elements (Br and Zn).

Numerical Simulation on a Possible Formation Mechanism of Interplanetary Magnetic Cloud Boundaries

NASA Astrophysics Data System (ADS)

Fan, Quan-Lin; Wei, Feng-Si; Feng, Xue-Shang

2003-08-01

The formation mechanism of the interplanetary magnetic cloud (MC) boundaries is numerically investigated by simulating the interactions between an MC of some initial momentum and a local interplanetary current sheet. The compressible 2.5D MHD equations are solved. Results show that the magnetic reconnection process is a possible formation mechanism when an MC interacts with a surrounding current sheet. A number of interesting features are found. For instance, the front boundary of the MCs is a magnetic reconnection boundary that could be caused by a driven reconnection ahead of the cloud, and the tail boundary might be caused by the driving of the entrained flow as a result of the Bernoulli principle. Analysis of the magnetic field and plasma data demonstrates that at these two boundaries appear large value of the plasma parameter β, clear increase of plasma temperature and density, distinct decrease of magnetic magnitude, and a transition of magnetic field direction of about 180 degrees. The outcome of the present simulation agrees qualitatively with the observational results on MC boundary inferred from IMP-8, etc. The project supported by National Natural Science Foundation of China under Grant Nos. 40104006, 49925412, and 49990450

Cruise Stage Testing for Mars Science Laboratory

NASA Image and Video Library

2010-09-02

Testing of the cruise stage for NASA Mars Science Laboratory in August 2010 included a session in a facility that simulates the environment found in interplanetary space. Spacecraft technicians at JPL prepare a space-simulation test.

Modeling Nucleation and Grain Growth in the Solar Nebula: Initial Progress Report

NASA Technical Reports Server (NTRS)

Nuth, Joseph A.; Paquette, J. A.; Ferguson, F. T.

2010-01-01

The primitive solar nebula was a violent and chaotic environment where high energy collisions, lightning, shocks and magnetic re-connection events rapidly vaporized some fraction of nebular dust, melted larger particles while leaving the largest grains virtually undisturbed. At the same time, some tiny grains containing very easily disturbed noble gas signatures (e.g., small, pre-solar graphite or SiC particles) never experienced this violence, yet can be found directly adjacent to much larger meteoritic components (chondrules or CAIs) that did. Additional components in the matrix of the most primitive carbonaceous chondrites and in some chondritic porous interplanetary dust particles include tiny nebular condensates, aggregates of condensates and partially annealed aggregates. Grains formed in violent transient events in the solar nebula did not come to equilibrium with their surroundings. To understand the formation and textures of these materials as well as their nebular abundances we must rely on Nucleation Theory and kinetic models of grain growth, coagulation and annealing. Such models have been very uncertain in the past: we will discuss the steps we are taking to increase their reliability.

Modeling of ion acceleration through drift and diffusion at interplanetary shocks

NASA Technical Reports Server (NTRS)

Decker, R. B.; Vlahos, L.

1986-01-01

A test particle simulation designed to model ion acceleration through drift and diffusion at interplanetary shocks is described. The technique consists of integrating along exact particle orbits in a system where the angle between the shock normal and mean upstream magnetic field, the level of magnetic fluctuations, and the energy of injected particles can assume a range of values. The technique makes it possible to study time-dependent shock acceleration under conditions not amenable to analytical techniques. To illustrate the capability of the numerical model, proton acceleration was considered under conditions appropriate for interplanetary shocks at 1 AU, including large-amplitude transverse magnetic fluctuations derived from power spectra of both ambient and shock-associated MHD waves.

Phototelectric Emission Measurements on the Analogs of Individual Cosmic Dust Grains

NASA Technical Reports Server (NTRS)

Abbas, Mian M.; Tankosic, D.; Craven, P. D.; Spann, J. F.; LeClair, A.; West, E. A.; Weingartner, J. C.; Tielens, A. G. G. M.; Nuth, J. A.; Camata, R. P.;

Secondary electron emission and its role in the space environment

NASA Astrophysics Data System (ADS)

Němeček, Z.; Pavlů, J.; Richterová, I.; Šafránková, J.; Vaverka, J.

2018-01-01

The role of dust in the space environment is of increasing interest in recent years and also the fast development of fusion devices with a magnetic confinement brought new issues in the plasma-surface interaction. Among other processes, secondary electron emission plays an important role for dust charging in interplanetary space and its importance increases at and above the surfaces of airless bodies like planets, moons, comets or asteroids. A similar situation can be found in many industrial applications where the dust is a final product or an unintentional impurity. The present paper reviews the progress in laboratory investigations of the secondary emission process as well as an evolution of the modeling of the interaction of energetic electrons with dust grains of different materials and sizes. The results of the model are discussed in view of latest laboratory simulations and they are finally applied on the estimation of an interaction of the solar wind and magnetospheric plasmas with the dust attached to or levitating above the lunar surface.

The role of Mab as a source for the μ ring of Uranus

NASA Astrophysics Data System (ADS)

Sfair, R.; Giuliatti Winter, S. M.

2012-07-01

Context. We previously analysed how the solar radiation force combined with the planetary oblateness changes the orbital evolution of a sample of dust particles located at the secondary ring system of Uranus. Both effects combined with the gravitational perturbations of the close satellites lead to the depletion of these dust particles through collisions on the surfaces of these satellites on a timescale of hundreds of years. Aims: In this work we investigate if the impacts of interplanetary dust particles (IDPs) onto Mab's surface can produce sufficient particles to replenish the μ ring population. Methods: We first analysed through numerical simulations the evolution of a sample of particles ejected from the surface of Mab and computed the lifetime of the grains when the effects of the solar radiation pressure and the planetary oblateness are taken into account. Then we estimated the mass production rate due to the impacts of IDPs following a previously established algorithm, and used this value to determine the time necessary to accumulate an amount of particles comparable with the mass of the μ ring. Results: Based on an estimate of the flux of interplanetary particles and on the surface properties of Mab it is expected that the satellite supplies material to the ring at a rate of ~3 g/s. Meanwhile, our numerical model showed that the ejected particles are removed from the system through collisions with the satellite, and the mean lifetime of the grains may vary from 320 to 1500 years, depending on the radius of the particle. Conclusions: The time necessary to accumulate the mass of the μ ring via ejection from Mab is much shorter than the mean lifetime of the particles, and a stationary regime is not reached. If the ring is kept in a steady state, other effects such as the electromagnetic force and/or the existence of additional bodies may play a significant role in the dust balance, but the current lack of information about the environment renders modelling these effects unfeasible.

Unusual olivine and pyroxene composition in interplanetary dust and unequilibrated ordinary chondrites

NASA Technical Reports Server (NTRS)

Klock, W.; Mckay, D. S.; Thomas, K. L.; Palme, H.

1989-01-01

The presence, in both a number of interplanetary dust particles (IDPs) and in meteorite matrices, of olivine and orthopyroxene grains, low in FeO but containing up to 5 wt pct MnO, is reported. The majority of olivines and pyroxenes in meteorites contain less than 0.5 wt pct MnO. The presence of these low-iron, manganese-enriched (LIME) olivines and pyroxenes in IDPs and meteorites may indicate a link between the origin and history of IDPs and the matrix material of primitive meteorites. The origin of the LIME silicates could be explained by condensation from a gas of solar composition. Forsterite is the first major silicate phase to condense from a solar nebula gas, and Mn, which is not stable as a metal under solar nebula conditions, would condense at about 1100 K as Mn2SiO4 in solid solution with forsterite.

Infrared Spectroscopy of Anhydrous Interplanetary Dust Particles

NASA Technical Reports Server (NTRS)

Keller, L. P.; Flynn, G. J.

2003-01-01

Infrared (IR) spectroscopy is the primary means of mineralogical analysis of materials outside our solar system. The identity and properties of circumstellar grains are inferred from spectral comparisons between astronomical observations and laboratory data from natural and synthetic materials. These comparisons have been facilitated by the Infrared Space Observatory (ISO), which obtained IR spectra from numerous astrophysical objects over a wide spectral range (out to 50/cm) where crystalline silicates and other phases have distinct features. The anhydrous interplanetary dust particles (IDPs) are particularly important comparison materials because some IDPs contain carbonaceous material with non-solar D/H and N-15/N-14 ratios and amorphous and crystalline silicates with non-solar 0- isotopic ratios, demonstrating that these IDPs contain preserved interstellar material. Here, we report on micro- Fourier transform (FT) IR spectrometry of IDPs, focusing on the inorganic components of primitive IDPs (FTIR spectra from the organic/carbonacecous materials in IDPs are described elsewhere).

Physical processes in comets

NASA Technical Reports Server (NTRS)

Whipple, F. L.; Huebner, W. F.

1976-01-01

The paper discusses physical processes in comets which involve solar and nuclear radial forces that affect the motions of gases and icy grains, gas-phase chemistry very close to the nuclei of large comets near the sun, sublimation of icy grains, dissociation of parent molecules into radicals and of radicals into atoms, and ionization by sunlight and collisions. The composition and dimensions of nuclei are examined along with variations in intrinsic brightness, the nature of volatiles, gas production rates in the coma, characteristics of icy grains in the coma, and the structure of streamers, ion tails, and dust tails. The structure of the coma is described in detail on the basis of spectroscopic observations of several comets. The origin of comets is briefly reviewed together with the relation of comets to earth, the interplanetary complex, and the interstellar medium. Desirable future observations are noted, especially by space missions to comets.

Remote comets and related bodies - VJHK colorimetry and surface materials

NASA Technical Reports Server (NTRS)

Hartmann, W. K.; Cruikshank, D. P.; Degewij, J.

1982-01-01

VJHK colors for a number of asteroids and eight comets at various solar distances and levels of activity were obtained, and the observations are interpreted in terms of a two-component mixing model in which outer solar system interplanetary bodies are viewed as mixtures of ice and dark carbonaceous-type (RD and C) dirt. It is inferred that the observed comets have comae, and perhaps surfaces, of dirty ice or ice dirt grains colored by an RD-dirt component. This inference is supported by systematics of an 'alpha index' based on VJHK colors and empirically correlated with albedo and ice/dirt ratio. Among comets the alpha index correlates with solar distance in a way that suggests comets emit dirty ice grains which are stable at large solar distance but from which the ice component sublimes and leaves dirt grains at small solar distance.

Simulated trajectories error analysis program, version 2. Volume 2: Programmer's manual

NASA Technical Reports Server (NTRS)

Vogt, E. D.; Adams, G. L.; Working, M. M.; Ferguson, J. B.; Bynum, M. R.

1971-01-01

A series of three computer programs for the mathematical analysis of navigation and guidance of lunar and interplanetary trajectories was developed. All three programs require the integration of n-body trajectories for both interplanetary and lunar missions. The virutal mass technique is used in all three programs. The user's manual contains the information necessary to operate the programs. The input and output quantities of the programs are described. Sample cases are given and discussed.

Origin of coronal mass ejection and magnetic cloud: Thermal or magnetic driven?

NASA Technical Reports Server (NTRS)

Zhang, Gong-Liang; Wang, Chi; He, Shuang-Hua

1995-01-01

A fundamental problem in Solar-Terrestrial Physics is the origin of the solar transient plasma output, which includes the coronal mass ejection and its interplanetary manifestation, e.g. the magnetic cloud. The traditional blast wave model resulted from solar thermal pressure impulse has faced with challenge during recent years. In the MHD numerical simulation study of CME, the authors find that the basic feature of the asymmetrical event on 18 August 1980 can be reproduced neither by a thermal pressure nor by a speed increment. Also, the thermal pressure model fails in simulating the interplanetary structure with low thermal pressure and strong magnetic field strength, representative of a typical magnetic cloud. Instead, the numerical simulation results are in favor of the magnetic field expansion as the likely mechanism for both the asymmetrical CME event and magnetic cloud.

The use of x-ray pulsar-based navigation method for interplanetary flight

NASA Astrophysics Data System (ADS)

Yang, Bo; Guo, Xingcan; Yang, Yong

2009-07-01

As interplanetary missions are increasingly complex, the existing unique mature interplanetary navigation method mainly based on radiometric tracking techniques of Deep Space Network can not meet the rising demands of autonomous real-time navigation. This paper studied the applications for interplanetary flights of a new navigation technology under rapid development-the X-ray pulsar-based navigation for spacecraft (XPNAV), and valued its performance with a computer simulation. The XPNAV is an excellent autonomous real-time navigation method, and can provide comprehensive navigation information, including position, velocity, attitude, attitude rate and time. In the paper the fundamental principles and time transformation of the XPNAV were analyzed, and then the Delta-correction XPNAV blending the vehicles' trajectory dynamics with the pulse time-of-arrival differences at nominal and estimated spacecraft locations within an Unscented Kalman Filter (UKF) was discussed with a background mission of Mars Pathfinder during the heliocentric transferring orbit. The XPNAV has an intractable problem of integer pulse phase cycle ambiguities similar to the GPS carrier phase navigation. This article innovatively proposed the non-ambiguity assumption approach based on an analysis of the search space array method to resolve pulse phase cycle ambiguities between the nominal position and estimated position of the spacecraft. The simulation results show that the search space array method are computationally intensive and require long processing time when the position errors are large, and the non-ambiguity assumption method can solve ambiguity problem quickly and reliably. It is deemed that autonomous real-time integrated navigation system of the XPNAV blending with DSN, celestial navigation, inertial navigation and so on will be the development direction of interplanetary flight navigation system in the future.

Interplanetary Type III Bursts and Electron Density Fluctuations in the Solar Wind

NASA Astrophysics Data System (ADS)

Krupar, V.; Maksimovic, M.; Kontar, E. P.; Zaslavsky, A.; Santolik, O.; Soucek, J.; Kruparova, O.; Eastwood, J. P.; Szabo, A.

2018-04-01

Type III bursts are generated by fast electron beams originated from magnetic reconnection sites of solar flares. As propagation of radio waves in the interplanetary medium is strongly affected by random electron density fluctuations, type III bursts provide us with a unique diagnostic tool for solar wind remote plasma measurements. Here, we performed a statistical survey of 152 simple and isolated type III bursts observed by the twin-spacecraft Solar TErrestrial RElations Observatory mission. We investigated their time–frequency profiles in order to retrieve decay times as a function of frequency. Next, we performed Monte Carlo simulations to study the role of scattering due to random electron density fluctuations on time–frequency profiles of radio emissions generated in the interplanetary medium. For simplification, we assumed the presence of isotropic electron density fluctuations described by a power law with the Kolmogorov spectral index. Decay times obtained from observations and simulations were compared. We found that the characteristic exponential decay profile of type III bursts can be explained by the scattering of the fundamental component between the source and the observer despite restrictive assumptions included in the Monte Carlo simulation algorithm. Our results suggest that relative electron density fluctuations < δ {n}{{e}}> /{n}{{e}} in the solar wind are 0.06–0.07 over wide range of heliospheric distances.

Outer Radiation Belt Dropout Dynamics Following the Arrival of Two Interplanetary Coronal Mass Ejections

NASA Technical Reports Server (NTRS)

Alves, L. R.; Da Silva, L. A.; Souza, V. M.; Sibeck, D. G.; Jauer, P. R.; Vieira, L. E. A.; Walsh, B. M.; Silveira, M. V. D.; Marchezi, J. P.; Rockenbach, M.;

Volatiles in interplanetary dust particles: A comparison with CI and CM chondrites

NASA Technical Reports Server (NTRS)

Bustin, Roberta

1992-01-01

In an effort to classify and determine the origin of interplanetary dust particles (IDPs), 14 of these particles were studied using a laser microprobe/mass spectrometer. The mass spectra for these particles varied dramatically. Some particles released hydroxide or water which probably originated in hydroxide-bearing minerals or hydrates. Others produced spectra which included a number of hydrocarbons and resembled meteorite spectra. However, none of the individual IDPs gave spectra which could be matched identically with a particular meteorite type such as a CI or CM carbonaceous chondrite. We believe this was due to the fact that 10-20 micron size IDPs are too small to be representative of the parent body. To verify that the diversity was due primarily to the small particle sizes, small grains of approximately the same size range as the IDPs were obtained from two primitive meteorites, Murchison and Orgueil, and these small meteorite particles were treated exactly like the IDPs. Considerable diversity was observed among individual grains, but a composite spectrum of all the grains from one meteorite closely resembled the spectrum obtained from a much larger sample of that meteorite. A composite spectrum of the 14 IDPs also resembled the spectra of the CM and CI meteorites, pointing to a possible link between IDPs and carbonaceous chondrites. This also illustrates that despite the inherent diversity in particles as small as 10-20 micron, conclusions can be drawn about the possible origin and overall composition of such particles by looking not only at results from individual particles but also by including many particles in a study and basing conclusions on some kind of composite data.

Gravity-Assist Mechanical Simulator for Outreach

NASA Technical Reports Server (NTRS)

Doody, David F.; White, Victor E.; Schaff, Mitch D.

2012-01-01

There is no convenient way to demonstrate mechanically, as an outreach (or inreach) topic, the angular momentum trade-offs and the conservation of angular momentum associated with gravityassist interplanetary trajectories. The mechanical concepts that underlie gravity assist are often misunderstood or confused, possibly because there is no mechanical analog to it in everyday experience. The Gravity Assist Mech - anical Simulator is a hands-on solution to this longstanding technical communications challenge. Users intuitively grasp the concepts, meeting specific educational objectives. A manually spun wheel with high angular mass and low-friction bearings supplies momentum to an attached spherical neodymium magnet that represents a planet orbiting the Sun. A steel bearing ball following a trajectory across a glass plate above the wheel and magnet undergoes an elastic collision with the revolving magnet, illustrating the gravitational elastic collision between spacecraft and planet on a gravity-assist interplanetary trajectory. Manually supplying the angular momentum for the elastic collision, rather than observing an animation, intuitively conveys the concepts, meeting nine specific educational objectives. Many NASA and JPL interplanetary missions are enabled by the gravity-assist technique.

Iron, magnesium, and silicon in dust from Comet Halley

NASA Technical Reports Server (NTRS)

Lawler, Mark E.; Brownlee, Donald E.; Temple, Scott; Wheelock, Maya M.

1989-01-01

The highest-quality impact mass spectrometer data from the Vega-1 and Giotto spacecraft are presently used to study the Mg, Si, and Fe composition of dust grains in Comet Halley. The results thus obtained are in general agreement with previously reported data, but differ with respect to ion ratio dispersions. A lack of sharp clustering in the data indicates that none of the detected particles can be characterized as single mineral grains; an abundant glass content in the solids may be indicated. The best match of the distribution of Fe/(Fe+Mg) is with interplanetary particles containing high temperature, Mg-rich silicates dominated by anhydrous minerals, so that Comet Halley may be a mixture of ice and high-temperature anhydrous minerals.

Link between interplanetary & cometary dust: Polarimetric observations and space studies with Rosetta & Eye-Sat

NASA Astrophysics Data System (ADS)

Levasseur-Regourd, Anny-Chantal; Gaboriaud, Alain; Buil, Christian; Ressouche, Antoine; Lasue, J.; Palun, Adrien; Apper, Fabien; Elmaleh, Marc

Intensity and linear polarization observations of the solar light scattered by interplanetary dust, the so-called zodiacal light, provide information on properties of the dust particles, such as their spatial density, local changes, morphology and albedo. Earth-based polarimetric observations, with a resolution of 5° or more, have been used to derive the polarization phase curve of interplanetary dust particles and to establish that the polarization at 90° phase angle increases with increasing solar distance, at least up to 1.5 au in the ecliptic, while the albedo decreases [1, 2]. Analysis of such studies will be revisited. Numerical simulations of the polarimetric behavior of interplanetary dust particles strongly suggest that, in the inner solar system, interplanetary dust particles consist of absorbing (e.g., organic compounds) and less absorbing (e.g., silicates) materials, that radial changes originate in a decrease of organics with decreasing solar distance (probably due to alteration processes), and that a significant fraction of the interplanetary dust is of cometary origin, in agreement with dynamical studies [3, 4]. The polarimetric behaviors of interplanetary dust and cometary dust particles seem to present striking similarities. The properties of cometary dust particles, as derived from remote polarimetric observations of comets including 67P/Churyumov-Gerasimenko, the target of the Rosetta rendezvous mission, at various wavelengths, will be summarized [5, 6]. The ground truth expected from Rosetta dust experiments, i.e., MIDAS, COSIMA, GIADA, about dust particles’ morphology, composition, and evolution (with distance to the nucleus before Philae release and with distance to the Sun before and after perihelion passage) over the year and a half of nominal mission, will be discussed. Finally, the Eye-Sat nanosatellite will be presented. This triple cubesat, developed by students from engineering schools working as interns at CNES, is to be launched in 2016 [7]. Its main purpose is to study the zodiacal light intensity and polarization from a Sun-synchronous orbit, for the first time at the high spatial resolution of 1° over a wide portion of the sky and at four different wavelengths (in the visible and near-IR domains). The instrumental choices and new on-board technologies will be summarized, together with the results that may be expected on local properties of the interplanetary dust particles and thus on their similarities and differences with cometary dust particles. Support from CNES is warmly acknowledged. [1] Leinert, C., Bowyer, S., Haikala, L.K., et al. The 1997 reference of diffuse night sky brightness, Astron. Astrophys. Supp., 127, 1-99, 1998. [2] Levasseur-Regourd, A.C., Mann, I., Dumont, R., et al. Optical and thermal properties of interplanetary dust. In Interplanetary dust (Grün, E. et al. Eds), 57-94, Springer-Verlag, Berlin, 2001. [3] Lasue, J., Levasseur-Regourd, A.C., Fray, N., et al. Inferring the interplanetary dust properties from remote observations and simulations, Astron. Astrophys., 473, 641-649, 2007. [4] Nesvorny, D., Jenniskens, P., Levison, H.F., et al. Cometary origin of the zodiacal cloud and carbonaceous micrometeorites: implications for hot debris disks. Astrophys. J. 713, 816-836, 2010. [5] Levasseur-Regourd, A.C., Mukai, T., Lasue, J., et al. Physical properties of cometary and interplanetary dust, Planet. Space Sci., 55, 1010-1020, 2007. [6] Hadamcik, E., Sen, A.K., Levasseur-Regourd, A.C., et al., Astron. Astrophys., 517, A86, 2010. [7] CNES internal report. Eye-Sat end of phase A internal review, EYESAT-PR-0-022-CNES, 2013.

High-Nickel Iron-Sulfides in Anhydrous, Gems-Rich CP IDPs

NASA Technical Reports Server (NTRS)

FLynn, G. J.; Keller, L. P.; Wirick, S.; Hu, W.; Li, L.; Yan, H.; Huang, X.; Nazaretski, E.; Lauer, K.; Chu, Y. S.

2016-01-01

Chondritic porous interplanetary dust particles (CP IDPs) that were not severly heated during atmospheric deceleration are the best preserved samples of the solids that condensed from the Solar protoplanetary disk, as well as pre-Solar grains thatr survived incorporation into the disk, currently available for laboratory analysis [1]. These CP IDPs never experienced the aqueous and/or thermal processing, gravitational compaction, and shock effects that overprinted the record of Solar nebula processes in meteorites.

Assemblage of Presolar Materials and Early Solar System Condensates in Chondritic Porous Interplanetary Dust Particles

NASA Technical Reports Server (NTRS)

Nguyen, A. N.; Nakamura-Messenger, K.; Messenger, S.; Keller, L. P.; Kloeck, W.

2015-01-01

Anhydrous chondritic porous inter-planetary dust particles (CP IDPs) contain an assortment of highly primitive solar system components, molecular cloud matter, and presolar grains. These IDPs have largely escaped parent body processing that has affected meteorites, advocating cometary origins. Though the stardust abundance in CP IDPs is generally greater than in primitive meteorites, it can vary widely among individual CP IDPs. The average abundance of silicate stardust among isotopically primitive IDPs is approx. 375 ppm while some have extreme abundances up to approx. 1.5%. H and N isotopic anomalies are common in CP IDPs and the carrier of these anomalies has been traced to organic matter that has experienced chemical reactions in cold molecular clouds or the outer protosolar disk. Significant variations in these anomalies may reflect different degrees of nebular processing. Refractory inclusions are commonly observed in carbonaceous chondrites. These inclusions are among the first solar system condensates and display 16O-rich isotopic compositions. Refractory grains have also been observed in the comet 81P/Wild-2 samples re-turned from the Stardust Mission and in CP IDPs, but they occur with much less frequency. Here we conduct coordinated mineralogical and isotopic analyses of CP IDPs that were characterized for their bulk chemistry by to study the distribution of primitive components and the degree of nebular alteration incurred.

Diagnostic Imaging in the Medical Support of the Future Missions to the Moon

NASA Technical Reports Server (NTRS)

Sargsyan, Ashot E.; Jones, Jeffrey A.; Hamilton, Douglas R.; Dulchavsky, Scott A.; Duncan, J. Michael

2007-01-01

This viewgraph presentation is a course that reviews the diagnostic imaging techniques available for medical support on the future moon missions. The educational objectives of the course are to: 1) Update the audience on the curreultrasound imaging in space flight; 2) Discuss the unique aspects of conducting ultrasound imaging on ISS, interplanetary transit, ultrasound imaging on ISS, interplanetary transit, and lunar surface operations; and 3) Review preliminary data obtained in simulations of medical imaging in lunar surface operations.

Simulation of ASTROD I test mass charging due to solar energetic particles and interplanetary electrons

NASA Astrophysics Data System (ADS)

Liu, L.; Dong, Y.; Bao, G.; Ni, W.-T.; Shaul, D. N. A.

2010-01-01

As ASTROD I travels through space, its test mass will accrue charge due to exposure of the spacecraft to high-energy particles. This test mass charge will result in Coulomb forces between the test mass and the surrounding electrodes. In earlier work, we have used the GEANT 4 toolkit to simulate charging of the ASTROD test mass due to cosmic-ray protons of energies between 0.1 and 1000 GeV at solar maximum and at solar minimum. Here we use GEANT 4 to simulate the charging process due to solar energetic particle events and interplanetary electrons. We then estimate the test mass acceleration noise due to these fluxes. The predicted charging rates range from 2247 e+/s to 47,055 e+/s, at peak intensity, for the four largest SEP events in September and October 1989. Although the noise due to charging exceeds the ASTROD I budget for the two larger events, it can be suppressed through continuous discharging. The acceleration noise during the two small events is well below the design target. The charging rate of the ASTROD I test mass due to interplanetary electrons in this simulation is about -11% of the cosmic-ray protons at solar minimum, and over -37% at solar maximum. In addition to the Monte Carlo uncertainty, an error of ±30% in the net charging rates should be added to account for uncertainties in the spectra, physics models and geometry implementations.

Global MHD simulations driven by idealized Alfvenic fluctuations in the solar wind

NASA Astrophysics Data System (ADS)

Claudepierre, S. G.

2017-12-01

High speed solar wind streams (HSSs) and corotating interaction regions (CIRs) often lead to MeV electron flux enhancements the Earth's outer radiation belt. The relevant physical processes responsible for these enhancements are not entirely understood. We investigate the potential role that solar wind Alfvenic fluctuations, intrinsic structures embedded in the HSS/CIRs, play in radiation belt dynamics. In particular, we explore the hypothesis that magnetospheric ultra-low frequency (ULF) pulsations driven by interplanetary magnetic field fluctuations are the intermediary mechanism responsible for the pronounced effect that HSS/CIRs have on the outer electron radiation belt. We examine these effects using global, three-dimensional magnetohydrodynamic (MHD) simulations driven by idealized interplanetary Alfvenic fluctuations, both monochromatic and broadband noise (Kolmogorov turbulence).

Testing model for prediction system of 1-AU arrival times of CME-associated interplanetary shocks

NASA Astrophysics Data System (ADS)

Ogawa, Tomoya; den, Mitsue; Tanaka, Takashi; Sugihara, Kohta; Takei, Toshifumi; Amo, Hiroyoshi; Watari, Shinichi

We test a model to predict arrival times of interplanetary shock waves associated with coronal mass ejections (CMEs) using a three-dimensional adaptive mesh refinement (AMR) code. The model is used for the prediction system we develop, which has a Web-based user interface and aims at people who is not familiar with operation of computers and numerical simulations or is not researcher. We apply the model to interplanetary CME events. We first choose coronal parameters so that property of background solar wind observed by ACE space craft is reproduced. Then we input CME parameters observed by SOHO/LASCO. Finally we compare the predicted arrival times with observed ones. We describe results of the test and discuss tendency of the model.

Microcrystals and Amorphous Material in Comets and Primitive Meteorites: Keys to Understanding Processes in the Early Solar System

NASA Technical Reports Server (NTRS)

Nuth, J. A.; Brearley, A. J.; Scott, E. R. D.

2004-01-01

Comets, fine-grained matrices of chondrites, and chondritic interplanetary dust particles (IDPs) are each composed of both crystalline and amorphous silicates. The primitive solar nebula, in which comets and asteroids accreted, was formed from the collapsed core of a Giant Molecular Cloud, that, in turn, condensed from materials present in the interstellar medium (ISM). Despite observations that reveal the presence of crystalline magnesium silicate minerals in the shells of very high mass-loss-rate stars [1,2], typical silicate grains in the ISM are most likely to be amorphous, given their relatively long residence time in such a high radiation environment. An upper limit of 3% crystalline grains can be derived from their non-detection in spectra of ISM solids [3]. If the vast majority of grains that enter the primitive solar nebula are amorphous, then the observation of crystalline dust in comets and primitive chondrite matrices indicates the action of specific processes required to transform the amorphous starting materials into the crystals that are observed.

Swarms of Micron-Sized Sensors

NASA Technical Reports Server (NTRS)

Quadrelli, Marco

2003-01-01

A paper presents the concept of swarms of micron-sized and smaller carriers of sensing equipment, denoted generally as controllable granular matter, to be used in exploring remote planets and interplanetary space. The design and manufacture of controllable granular matter would exploit advances in microelectromechanical systems and nanotechnology. Depending on specific designs and applications, controllable granular matter could have characteristics like those of powders, sands, or aerosols, which would be dispersed into the environments to be explored: For example, sensory grains could be released into orbit around a planet, spread out over ground, or dispersed into wind or into a body of liquid. The grains would thus become integral parts of multiphase environments, where they would function individually and/or collectively to gather information about the environments. In cases of clouds of grains dispersed in outer space, it may be feasible to use laser beams to shape the clouds to perform specific functions. To enable the full utilization of controllable granular matter, it is necessary to advance the knowledge of the dynamics and controllable characteristics of both individual grains and the powders, sands, or aerosols of which they are parts.

Investigations of the Formation of Carbon Grains in Circumstellar Outflows

NASA Technical Reports Server (NTRS)

Contreras, Cesar; Salama, Farid

2013-01-01

The study of formation and destruction processes of cosmic dust is essential to understand and to quantify the budget of extraterrestrial organic molecules. Although dust with all its components plays an important role in the evolution of interstellar chemistry and in the formation of organic molecules, little is known on the formation and destruction processes of carbonaceous dust. PAHs are important chemical building blocks of interstellar dust. They are detected in interplanetary dust particles and in meteoritic samples. Additionally, observational, laboratory, and theoretical studies have shown that PAHs, in their neutral and ionized forms, are an important, ubiquitous component of the interstellar medium. Also, the formation of PAHs from smaller molecules has not been extensively studied. Therefore, it is imperative that laboratory experiments be conducted to study the dynamic processes of carbon grain formation from PAH precursors. Studies of interstellar dust analogs formed from a variety of PAH and hydrocarbon precursors as well as species that include the atoms O, N, and S, have recently been performed in our laboratory under conditions that simulate interstellar and circumstellar environments. The species formed in the pulsed discharge nozzle (PDN) plasma source are detected and characterized with a high-sensitivity cavity ringdown spectrometer (CRDS) coupled to a Reflectron time-of-flight mass spectrometer (ReTOF-MS), thus providing both spectroscopic and ion mass information in-situ. We report the first set of measurements obtained in these experiments and identify the species present in the experiments and the ions that are formed in the plasma process. From these unique measurements, we derive information on the size and the structure of interstellar dust grain particles, the growth and the destruction processes of interstellar dust and the resulting budget of extraterrestrial organic molecules.

Laboratory Studies of the Optical Properties and Condensation Processes of Cosmic Dust Particles

NASA Technical Reports Server (NTRS)

Abbas, Mian M.; Craven, Paul D.; Spann, James F.; Tankosic, Dragana; Six, N. Frank (Technical Monitor)

2002-01-01

A laboratory facility for levitating single isolated dust particles in an electrodynamics balance has been developing at NASA/Marshall Space Flight Center for conducting a variety of experimental, of astrophysical interest. The objective of this research is to employ this innovative experimental technique for studies of the physical and optical properties of the analogs of cosmic grains of 0.2-10 micron size in a chamber with controlled pressure/temperatures simulating astrophysical environments. In particular, we will carry out three classes of experiments to investigate the microphysics of the analogs of interstellar and interplanetary dust grains. (1) Charge characteristics of micron size single dust grains to determine the photoelectric efficiencies, yields, and equilibrium potentials when exposed to UV radiation. These measurements will provide the much-needed photoelectric emission data relating to individual particles as opposed to that for the bulk materials available so far. (2) Infrared optical properties of dust particles obtained by irradiating the particles with radiation from tunable infrared diode lasers and measuring the scattered radiation. Specifically, the complex refractive indices, the extinction coefficients, the scattering phase functions, and the polarization properties of single dust grains of interest in interstellar environments, in the 1-25 micron spectral region will be determined. (3) Condensation experiments to investigate the deposition of volatile gases on colder nucleated particles in dense interstellar clouds and lower planetary atmospheres. The increase in the mass or m/q ratio due to condensation on the particle will be monitored as a function of the dust particle temperature and the partial pressure of the injected volatile gas. The measured data wild permit determination of the sticking efficiencies of volatile gases of astrophysical interest. Preliminary results based on photoelectric emission experiments on 0.2-6.6 micron size silica particles exposed to UV radiation in the 120-200 nm spectral region will be presented.

Integrated Vehicle and Trajectory Design of Small Spacecraft with Electric Propulsion for Earth and Interplanetary Missions

NASA Technical Reports Server (NTRS)

Spangelo, Sara; Dalle, Derek; Longmier, Benjamin

2015-01-01

This paper investigates the feasibility of Earth-transfer and interplanetary mission architectures for miniaturized spacecraft using emerging small solar electric propulsion technologies. Emerging small SEP thrusters offer significant advantages relative to existing technologies and will enable U-class systems to perform trajectory maneuvers with significant Delta V requirements. The approach in this paper is unique because it integrates trajectory design with vehicle sizing and accounts for the system and operational constraints of small U-class missions. The modeling framework includes integrated propulsion, orbit, energy, and external environment dynamics and systems-level power, energy, mass, and volume constraints. The trajectory simulation environment models orbit boosts in Earth orbit and flyby and capture trajectories to interplanetary destinations. A family of small spacecraft mission architectures are studied, including altitude and inclination transfers in Earth orbit and trajectories that escape Earth orbit and travel to interplanetary destinations such as Mercury, Venus, and Mars. Results are presented visually to show the trade-offs between competing performance objectives such as maximizing available mass and volume for payloads and minimizing transfer time. The results demonstrate the feasibility of using small spacecraft to perform significant Earth and interplanetary orbit transfers in less than one year with reasonable U-class mass, power, volume, and mission durations.

Mineralogy of chondritic interplanetary dust particle impact residues from LDEF

NASA Technical Reports Server (NTRS)

Barrett, R. A.; Zolensky, M. E.; Bernhard, R.

1993-01-01

A detailed structural and compositional analysis of several impactor residues was performed utilizing transmission electron microscopy, energy dispersive spectroscopy, and electron diffraction. Residues from the interior of several craters in gold surfaces were removed with a tungsten needle, mounted in EMBED-812 epoxy, and ultramicrotomed. The presence in these residues of equilibrated ferromagnesian minerals, recrystallization textures, glass, and melted metal and sulfide bodies decorating grain boundaries is indicative of varying degrees of shock metamorphism in all impact residues we have characterized.

Surface materials on unusual planetary object Chiron

NASA Technical Reports Server (NTRS)

Hartmann, W. K.; Cruikshank, D. P.; Degewij, J.; Capps, R. W.

1981-01-01

JHK near-infrared colorimetry of the surface of the planetary object 2060 Chiron has yielded colors consistent with those of outer solar system asteroids, which have: (1) albedos of only a few percent, (2) C-, RD-, or DM-type spectra, and (3) no known H2O ice absorption features. The colors are also in keeping with theoretical colors for certain size distributions of dirty ice grains. Along with VJHK colorimetric data, results suggest that the spectrally dominant surface is probably dark, carbonaceous-like silicate dust with a possible, microscale admixture of ice grains. It is concluded that, if Chiron has the low albedo common to such materials on known interplanetary bodies, its diameter may lie in the 310-400 km range and therefore place it among the eight largest asteroids.

Are the stratospheric dust particles meteor ablation debris or interplanetary dust?

NASA Technical Reports Server (NTRS)

Blanchard, M. B.; Kyte, F. T.

1978-01-01

Natural and laboratory created fusion crusts and debris from artificial meteor samples were used to develop criteria for recognizing meteor ablation debris in a collection of 5 to 50 micron particles from the stratosphere. These laboratory studies indicate that meteor ablation debris from nickel-iron meteoroids produce spherules containing taenite, wuestite, magnetite, and hematite. These same studies also indicate that ablation debris from chondritic meteoroids produce spheres and fragmentary debris. The spheres may be either silicate rich, containing zoned olivine, magnetite, and glass, or sulfide rich, containing iron oxides (e.g., magnetite, wuestite) and iron sulfides (e.g., pyrrhotite, pentlandite). The fragmentary debris may be either fine-grained aggregates of olivine, magnetite, pyroxene, and occasionally pyrrhotite (derived from the meteorite matrix) or individual olivine and pyroxene grains (derived from meteorite inclusions).

Characterization of biogenic elements in interplanetary dust particles

NASA Technical Reports Server (NTRS)

Bunch, T. E.

1986-01-01

Those particles that were designated cometary are aggregates of amorphous materials including carbon, iron-magnesium silicates, sulfides, metal and trace amounts of unusual phases. Most aggregates are carbon-rich with major and minor element abundances similar to a fine grained matrix of carbonaceous chondrites. Several particles were analyzed by a laser microprobe. The negative ionic species identified to date include carbon clusters, protonated carbon clusters, CN-, HCN-, CNO-, PO2-, PO3-, S-, S2- asnd OH-. These species are similar to those observed in cometary spectra and they support the assumption that organic materials are present. The occurance of phosphate ions suggests the presence of apatite or whitlockite. Cometary particle characteristics may indicate that the component grains represent primitive unaltered dust whose overall properties are extremely similar to altered primitive dust in carbonaceous chondrites.

Complex Role of Secondary Electron Emissions in Dust Grain Charging in Space Environments: Measurements on Apollo 11 and 17 Dust Grains

NASA Technical Reports Server (NTRS)

Abbas, M. M.; Tankosic, D.; Spann, J. F.; LeClair, A. C.

2010-01-01

Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with radiation from nearby sources, or by electron/ion collisions by sticking or secondary electron emissions. Knowledge of the dust grain charges and equilibrium potentials is important for understanding of a variety of physical and dynamical processes in the interstellar medium (ISM), and heliospheric, interplanetary, planetary, and lunar environments. The high vacuum environment on the lunar surface leads to some unusual physical and dynamical phenomena involving dust grains with high adhesive characteristics, and levitation and transportation over long distances. It has been well recognized that the charging properties of individual micron/submicron size dust grains are expected to be substantially different from the corresponding values for bulk materials and theoretical models. In this paper we present experimental results on charging of individual dust grains selected from Apollo 11 and Apollo 17 dust samples by exposing them to mono-energetic electron beams in the 10- 400 eV energy range. The charging rates of positively and negatively charged particles of approximately 0.2 to 13 microns diameters are discussed in terms of the secondary electron emission (SEE) process, which is found to be a complex charging process at electron energies as low as 10-25 eV, with strong particle size dependence. The measurements indicate substantial differences between dust charging properties of individual small size dust grains and of bulk materials.

Prediction system of the 1-AU arrival times of CME-associated interplanetary shocks using three-dimensional simulations

NASA Astrophysics Data System (ADS)

den, Mitsue; Amo, Hiroyoshi; Sugihara, Kohta; Takei, Toshifumi; Ogawa, Tomoya; Tanaka, Takashi; Watari, Shinichi

We describe prediction system of the 1-AU arrival times of interplanetary shock waves associated with coromal mass ejections (CMEs). The system is based on modeling of the shock propagation using a three-dimensional adaptive mesh refinement (AMR) code. Once a CME is observed by LASCO/SOHO, firstly ambient solar wind is obtained by numerical simulation, which reproduces the solar wind parameters at that time observed by ACE spacecraft. Then we input the expansion speed and occurrence position data of that CME as initial condtions for an CME model, and 3D simulation of the CME and the shock propagation is perfomed until the shock wave passes the 1-AU. Input the parameters, execution of simulation and output of the result are available on Web, so a person who is not familiar with operation of computer or simulations or is not a researcher can use this system to predict the shock passage time. Simulated CME and shock evolution is visuallized at the same time with simulation and snap shots appear on the web automatically, so that user can follow the propagation. This system is expected to be useful for forecasters of space weather. We will describe the system and simulation model in detail.

The nature of cometary dust as determined from infrared observations

NASA Technical Reports Server (NTRS)

Swamy, K. S. Krishna; Sandford, Scott A.; Allamandola, Louis J.; Witteborn, Fred C.; Bregman, Jesse D.

1989-01-01

The infrared measurements of comets, the compositional information available from interplanetary dust particles (IDPs), and the recent results of flybys to Comet Halley can help in restricting the nature and composition of cometary dust models (c.f., Proceedings of the 20th ESLAB Symposium on Exploration of Halley's Comet, 1986). Researchers tried to incorporate some of these results into a coherent model to account for the observed cometary infrared emission. The presence of 10 and 3.4 micron features in Comet Halley (c.f. Bregman et al. 1987; Wickramasinghe and Allen 1986) indicated the presence of at least two components in the grain material, namely silicates and some form of amorphous carbon. These two components could reside in separate grains or may be parts of composite particles. Both these cases have been considered (see Krishna Swamy el a. 1988a, 1988b). In the absence of refractive index data for cometary analogs, the authors used the optical constants of olivine-rich lunar material 12009.48 (Perry et al. 1972) for the infrared region and that of alpha:C-H film for amorphous carbon (angus et al. 1986). For the visible region, a value of m = 1.38-0.39i was used for the silicates, and values published by Arakawa et al. (1985) were used for the amorphous carbon. These materials should give a representative behavior of the expected results. The model results were compared to observational data. The strength of the 3.4 micron and 10 micron features relative to the adjacent continuum, as well as the slope of the continuum between 2500 and 1250 cm(exp -1) (4 to 8 microns), were used as criteria for comparison. Model calculations with alpha approx. equals -3.5, and also the size distribution function inferred for Comet Halley, with a mass fraction (X) of silicate to amorphous carbon grains of about 40 to 1 can fit the data. A good match is obtained for the infrared spectra of Comets Halley and West from a 40 to 1 mixture of silicate and amorphous carbon grains with a a(exp -3.5) size distribution function. The results are consistent with compositional constraints provided by interplanetary dust particles (IPDs) and Halley flyby data. The variation of grain temperature with heliocentric distance appears to account for the major changes observed in cometary spectra.

The effect of interplanetary trajectory options on a manned Mars aerobrake configuration

NASA Technical Reports Server (NTRS)

Braun, Robert D.; Powell, Richard W.; Hartung, Lin C.

1990-01-01

Manned Mars missions originating in low Earth orbit (LEO) in the time frame 2010 to 2025 were analyzed to identify preferred mission opportunities and their associated vehicle and trajectory characteristics. Interplanetary and Mars atmospheric trajectory options were examined under the constraints of an initial manned exploration scenario. Two chemically propelled vehicle options were considered: (1) an all propulsive configuration, and (2) a configuration which employs aerobraking at Earth and Mars with low lift/drag (L/D) shapes. Both the interplanetary trajectory options as well as the Mars atmospheric passage are addressed to provide a coupled trajectory simulation. Direct and Venus swingby interplanetary transfers with a 60 day Mars stopover are considered. The range and variation in both Earth and Mars entry velocity are also defined. Two promising mission strategies emerged from the study: (1) a 1.0 to 2.0 year Venus swingby mission, and (2) a 2.0 to 2.5 year direct mission. Through careful trajectory selection, 11 mission opportunities are identified in which the Mars entry velocity is between 6 and 10 km/sec and Earth entry velocity ranges from 11.5 to 12.5 km/sec. Simulation of the Earth return aerobraking maneuver is not performed. It is shown that a low L/D configuration is not feasible for Mars aerobraking without substantial improvements in the interplanetary navigation system. However, even with an advanced navigation system, entry corridor and aerothermal requirements restrict the number of potential mission opportunities. It is also shown that for a large blunt Mars aerobrake configuration, the effects of radiative heating can be significant at entry velocities as low as 6.2 km/sec and will grow to dominate the aerothermal environment at entry velocities above 8.5 km/sec. Despite the additional system complexity associated with an aerobraking vehicle, the use of aerobraking was shown to significantly lower the required initial LEO weight. In comparison with an all propulsive mission, savings between 19 and 59 percent were obtained depending upon launch date.

Organic and inorganic correlations for Northwest Africa 852 by synchrotron-based Fourier transform infrared microspectroscopy

NASA Astrophysics Data System (ADS)

Yesiltas, Mehmet; Peale, Robert E.; Unger, Miriam; Sedlmair, Julia; Hirschmugl, Carol J.

2015-10-01

Relationships between organic molecules and inorganic minerals are investigated in a single 34 μm diameter grain of the CR2 chondrite Northwest Africa 852 (NWA) 852 with submicron spatial resolution using synchrotron-based imaging micro-FTIR spectroscopy. Correlations based on absorption strength for the various constituents are determined using statistical correlation analysis. The silicate band is found to be correlated with the hydration band, and the latter is highly correlated with stretching modes of aliphatic hydrocarbons. Spatial distribution maps show that water+organic combination, silicate, OH, and C-H distributions overlap, suggesting a possible catalytic role of phyllosilicates in the formation of organics. In contrast, the carbonate band is anticorrelated with water+organic combination, however uncorrelated with any other spectral feature. The average ratio of asymmetric CH2 and CH3 band strengths (CH2/CH3 = 2.53) for NWA 852 is similar to the average ratio of interplanetary dust particles (~2.40) and Wild 2 cometary dust particles (2.50), but it significantly exceeds that of interstellar medium objects (~1.00) and several aqueously altered carbonaceous chondrites (~1.40). This suggests organics of similar length/branching, and perhaps similar formation regions, for NWA 852, Wild 2 dust particles, and interplanetary dust particles. The heterogeneous spatial distribution of ratio values indicates the presence of a mixture of aliphatic organic material with different length/branching, and thus a wide range of parent body processes, which occurred before the considered grain was formed.

Investigations of Wind/WAVES Dust Impacts

NASA Astrophysics Data System (ADS)

St Cyr, O. C.; Wilson, L. B., III; Rockcliffe, K.; Mills, A.; Nieves-Chinchilla, T.; Adrian, M. L.; Malaspina, D.

2017-12-01

The Wind spacecraft launched in November 1994 with a primary goal to observe and understand the interaction between the solar wind and Earth's magnetosphere. The waveform capture detector, TDS, of the radio and plasma wave investigation, WAVES [Bougeret et al., 1995], onboard Wind incidentally detected micron-sized dust as electric field pulses from the recollection of the impact plasma clouds (an unintended objective). TDS has detected over 100,000 dust impacts spanning almost two solar cycles; a dataset of these impacts has been created and was described in Malaspina & Wilson [2016]. The spacecraft continues to collect data about plasma, energetic particles, and interplanetary dust impacts. Here we report on two investigations recently conducted on the Wind/WAVES TDS database of dust impacts. One possible source of dust particles is the annually-recurring meteor showers. Using the nine major showers defined by the American Meteor Society, we compared dust count rates before, during, and after the peak of the showers using averaging windows of varying duration. However, we found no statistically significant change in the dust count rates due to major meteor showers. This appears to be an expected result since smaller grains, like the micron particles that Wind is sensitive to, are affected by electromagnetic interactions and Poynting-Robertson drag, and so are scattered away from their initial orbits. Larger grains tend to be more gravitationally dominated and stay on the initial trajectory of the parent body so that only the largest dust grains (those that create streaks as they burn up in the atmosphere) are left in the orbit of the parent body. Ragot and Kahler [2003] predicted that coronal mass ejections (CMEs) near the Sun could effectively scatter dust grains of comparable size to those observed by Wind. Thus, we examined the dust count rates immediately before, during, and after the passage of the 350 interplanetary CMEs observed by Wind over its 20+ year lifetime. We found a statistically significant and consistent trend of count rate deficits during the ICMEs compared to the periods immediately before and after the ICMEs. These preliminary results suggest that ICMEs may scatter micron-sized dust, or that they may exclude it during their initiation.

Were micrometeorites a source of prebiotic molecules on the early Earth?

PubMed

Maurette, M; Brack, A; Kurat, G; Perreau, M; Engrand, C

1995-03-01

"Interplanetary Dust Particles" with sizes approximately 10 micrometers collected in the stratosphere (IDPs), as well as much larger "giant" micrometeorites retrieved from Antarctic ice melt water (AMMs), are mostly composed of unequilibrated assemblages of minerals, thus being related to primitive unequilibrated meteorites. Two independent evaluations of the mass flux of micrometeorites measuring approximately 50 micrometers to approximately 200 micrometers, recovered from either the Greenland or the Antarctic ice sheets have been reported (approximately 20,000 tons/a). A comparison with recent evaluation of the flux of meteorites reaching the Earth's surface (up to masses of 10,000 tons), indicates that micrometeorites represent about 99.5% of the extraterrestrial material falling on the Earth's surface each year. As they show carbon concentrations exceeding that of the most C-rich meteorite (Orgueil), they are the major contributors of extraterrestrial C-rich matter accreting to the Earth today. Moreover they are complex microstructured aggregates of grains. They contain not only a variety of C-rich matter, such as a new "dirty" magnetite phase enriched in P, S, and minor elements, but also a diversity of potential catalysts (hydrous silicates, oxides, sulfides and metal grains of Fe/Ni composition, etc.). They could have individually functioned on the early Earth, as "micro-chondritic-reactors" for the processing of prebiotic organic molecules in liquid water. Future progress requires the challenging development of meaningful laboratory simulation experiments, and a better understanding of the partial reprocessing of micrometeorites in the atmosphere.

Fluid-induced organic synthesis in the solar nebula recorded in extraterrestrial dust from meteorites.

PubMed

Vollmer, Christian; Kepaptsoglou, Demie; Leitner, Jan; Busemann, Henner; Spring, Nicole H; Ramasse, Quentin M; Hoppe, Peter; Nittler, Larry R

2014-10-28

Isotopically anomalous carbonaceous grains in extraterrestrial samples represent the most pristine organics that were delivered to the early Earth. Here we report on gentle aberration-corrected scanning transmission electron microscopy investigations of eight (15)N-rich or D-rich organic grains within two carbonaceous Renazzo-type (CR) chondrites and two interplanetary dust particles (IDPs) originating from comets. Organic matter in the IDP samples is less aromatic than that in the CR chondrites, and its functional group chemistry is mainly characterized by C-O bonding and aliphatic C. Organic grains in CR chondrites are associated with carbonates and elemental Ca, which originate either from aqueous fluids or possibly an indigenous organic source. One distinct grain from the CR chondrite NWA 852 exhibits a rim structure only visible in chemical maps. The outer part is nanoglobular in shape, highly aromatic, and enriched in anomalous nitrogen. Functional group chemistry of the inner part is similar to spectra from IDP organic grains and less aromatic with nitrogen below the detection limit. The boundary between these two areas is very sharp. The direct association of both IDP-like organic matter with dominant C-O bonding environments and nanoglobular organics with dominant aromatic and C-N functionality within one unique grain provides for the first time to our knowledge strong evidence for organic synthesis in the early solar system activated by an anomalous nitrogen-containing parent body fluid.

Novel Experimental Simulations of the Atmospheric Injection of Meteoric Metals

NASA Astrophysics Data System (ADS)

Gómez Martín, J. C.; Bones, D. L.; Carrillo-Sánchez, J. D.; James, A. D.; Trigo-Rodríguez, J. M.; Fegley, B., Jr.; Plane, J. M. C.

2017-02-01

A newly developed laboratory, Meteoric Ablation Simulator (MASI), is used to test model predictions of the atmospheric ablation of interplanetary dust particles (IDPs) with experimental Na, Fe, and Ca vaporization profiles. MASI is the first laboratory setup capable of performing time-resolved atmospheric ablation simulations, by means of precision resistive heating and atomic laser-induced fluorescence detection. Experiments using meteoritic IDP analogues show that at least three mineral phases (Na-rich plagioclase, metal sulfide, and Mg-rich silicate) are required to explain the observed appearance temperatures of the vaporized elements. Low melting temperatures of Na-rich plagioclase and metal sulfide, compared to silicate grains, preclude equilibration of all the elemental constituents in a single melt. The phase-change process of distinct mineral components determines the way in which Na and Fe evaporate. Ca evaporation is dependent on particle size and on the initial composition of the molten silicate. Measured vaporized fractions of Na, Fe, and Ca as a function of particle size and speed confirm differential ablation (I.e., the most volatile elements such as Na ablate first, followed by the main constituents Fe, Mg, and Si, and finally the most refractory elements such as Ca). The Chemical Ablation Model (CABMOD) provides a reasonable approximation to this effect based on chemical fractionation of a molten silicate in thermodynamic equilibrium, even though the compositional and geometric description of IDPs is simplistic. Improvements in the model are required in order to better reproduce the specific shape of the elemental ablation profiles.

MCNPX Cosmic Ray Shielding Calculations with the NORMAN Phantom Model

NASA Technical Reports Server (NTRS)

James, Michael R.; Durkee, Joe W.; McKinney, Gregg; Singleterry Robert

2008-01-01

The United States is planning manned lunar and interplanetary missions in the coming years. Shielding from cosmic rays is a critical aspect of manned spaceflight. These ventures will present exposure issues involving the interplanetary Galactic Cosmic Ray (GCR) environment. GCRs are comprised primarily of protons (approx.84.5%) and alpha-particles (approx.14.7%), while the remainder is comprised of massive, highly energetic nuclei. The National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) has commissioned a joint study with Los Alamos National Laboratory (LANL) to investigate the interaction of the GCR environment with humans using high-fidelity, state-of-the-art computer simulations. The simulations involve shielding and dose calculations in order to assess radiation effects in various organs. The simulations are being conducted using high-resolution voxel-phantom models and the MCNPX[1] Monte Carlo radiation-transport code. Recent advances in MCNPX physics packages now enable simulated transport over 2200 types of ions of widely varying energies in large, intricate geometries. We report here initial results obtained using a GCR spectrum and a NORMAN[3] phantom.

COORDINATED ANALYSES OF PRESOLAR GRAINS IN THE ALLAN HILLS 77307 AND QUEEN ELIZABETH RANGE 99177 METEORITES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Ann N.; Nittler, Larry R.; Alexander, Conel M. O'D.

2010-08-10

We report the identification of presolar silicates ({approx}177 ppm), presolar oxides ({approx}11 ppm), and one presolar SiO{sub 2} grain in the Allan Hills (ALHA) 77307 chondrite. Three grains having Si-isotopic compositions similar to SiC X and Z grains were also identified, though the mineral phases are unconfirmed. Similar abundances of presolar silicates ({approx}152 ppm) and oxides ({approx}8 ppm) were also uncovered in the primitive CR chondrite Queen Elizabeth Range (QUE) 99177, along with 13 presolar SiC grains and one presolar silicon nitride. The O-isotopic compositions of the presolar silicates and oxides indicate that most of the grains condensed in low-massmore » red giant and asymptotic giant branch stars. Interestingly, unlike presolar oxides, few presolar silicate grains have isotopic compositions pointing to low-metallicity, low-mass stars (Group 3). The {sup 18}O-rich (Group 4) silicates, along with the few Group 3 silicates that were identified, likely have origins in supernova outflows. This is supported by their O- and Si-isotopic compositions. Elemental compositions for 74 presolar silicate grains were determined by scanning Auger spectroscopy. Most of the grains have non-stoichiometric elemental compositions inconsistent with pyroxene or olivine, the phases commonly used to fit astronomical spectra, and have comparable Mg and Fe contents. Non-equilibrium condensation and/or secondary alteration could produce the high Fe contents. Transmission electron microscopic analysis of three silicate grains also reveals non-stoichiometric compositions, attributable to non-equilibrium or multistep condensation, and very fine scale elemental heterogeneity, possibly due to subsequent annealing. The mineralogies of presolar silicates identified in meteorites thus far seem to differ from those in interplanetary dust particles.« less

Dynamics of aspherical dust grains in a cometary atmosphere: I. axially symmetric grains in a spherically symmetric atmosphere

NASA Astrophysics Data System (ADS)

Ivanovski, S. L.; Zakharov, V. V.; Della Corte, V.; Crifo, J.-F.; Rotundi, A.; Fulle, M.

2017-01-01

In-situ measurements of individual dust grain parameters in the immediate vicinity of a cometary nucleus are being carried by the Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko. For the interpretations of these observational data, a model of dust grain motion as realistic as possible is requested. In particular, the results of the Stardust mission and analysis of samples of interplanetary dust have shown that these particles are highly aspherical, which should be taken into account in any credible model. The aim of the present work is to study the dynamics of ellipsoidal shape particles with various aspect ratios introduced in a spherically symmetric expanding gas flow and to reveal the possible differences in dynamics between spherical and aspherical particles. Their translational and rotational motion under influence of the gravity and of the aerodynamic force and torque is numerically integrated in a wide range of physical parameters values including those of comet 67P/Churyumov-Gerasimenko. The main distinctions of the dynamics of spherical and ellipsoidal particles are discussed. The aerodynamic characteristics of the ellipsoidal particles, and examples of their translational and rotational motion in the postulated gas flow are presented.

A Magnetohydrodynamic Modeling of the Interchange Cycle for Oblique Northward Interplanetary Magnetic Field

NASA Astrophysics Data System (ADS)

Watanabe, Masakazu; Fujita, Shigeru; Tanaka, Takashi; Kubota, Yasubumi; Shinagawa, Hiroyuki; Murata, Ken T.

2018-01-01

We perform numerical modeling of the interchange cycle in the magnetosphere-ionosphere convection system for oblique northward interplanetary magnetic field (IMF). The interchange cycle results from the coupling of IMF-to-lobe reconnection and lobe-to-closed reconnection. Using a global magnetohydrodynamic simulation code, for an IMF clock angle of 20° (measured from due north), we successfully reproduced the following features of the interchange cycle. (1) In the ionosphere, for each hemisphere, there appears a reverse cell circulating exclusively in the closed field line region (the reciprocal cell). (2) The topology transition of the magnetic field along a streamline near the equatorial plane precisely represents the magnetic flux reciprocation during the interchange cycle. (3) Field-aligned electric fields on the interplanetary-open separatrix and on the open-closed separatrix are those that are consistent with IMF-to-lobe reconnection and lobe-to-closed reconnection, respectively. These three features prove the existence of the interchange cycle in the simulated magnetosphere-ionosphere system. We conclude that the interchange cycle does exist in the real solar wind-magnetosphere-ionosphere system. In addition, the simulation revealed that the reciprocal cell described above is not a direct projection of the diffusion region as predicted by the "vacuum" model in which diffusion is added a priori to the vacuum magnetic topology. Instead, the reciprocal cell is a consequence of the plasma convection system coupled to the so-called NBZ ("northward Bz") field-aligned current system.

Time-dependent radiation dose simulations during interplanetary space flights

NASA Astrophysics Data System (ADS)

Dobynde, Mikhail; Shprits, Yuri; Drozdov, Alexander; Hoffman, Jeffrey; Li, Ju

2016-07-01

Space radiation is one of the main concerns in planning long-term interplanetary human space missions. There are two main types of hazardous radiation - Solar Energetic Particles (SEP) and Galactic Cosmic Rays (GCR). Their intensities and evolution depend on the solar activity. GCR activity is most enhanced during solar minimum, while the most intense SEPs usually occur during the solar maximum. SEPs are better shielded with thick shields, while GCR dose is less behind think shields. Time and thickness dependences of the intensity of these two components encourage looking for a time window of flight, when radiation intensity and dose of SEP and GCR would be minimized. In this study we combine state-of-the-art space environment models with GEANT4 simulations to determine the optimal shielding, geometry of the spacecraft, and launch time with respect to the phase of the solar cycle. The radiation environment was described by the time-dependent GCR model, and the SEP spectra that were measured during the period from 1990 to 2010. We included gamma rays, electrons, neutrons and 27 fully ionized elements from hydrogen to nickel. We calculated the astronaut's radiation doses during interplanetary flights using the Monte-Carlo code that accounts for the primary and the secondary radiation. We also performed sensitivity simulations for the assumed spacecraft size and thickness to find an optimal shielding. In conclusion, we present the dependences of the radiation dose as a function of launch date from 1990 to 2010, for flight durations of up to 3 years.

Thin-sectioning and analysis of fine-grained meteoritic materials

NASA Technical Reports Server (NTRS)

Brooks, Donald A. (Editor); Bradley, John P.

1992-01-01

The overall theme of the work was the identification of the sources and formation/aggregation mechanisms of the various classes of interplanetary dust particles (IDP's) and to clarify the relationship between IDP's and conventional meteorites. IDP's are believed to be derived from a much broader range of parent bodies than conventional meteorites. Some of these parent bodies (e.g., comets) have escaped that post accretional processing that has affected the parent bodies of meteorites. Therefore, IDP's are likely to preserve a record of early solar system and possibly presolar grain forming reactions. Using analytical electron microscopy (AEM) and more recently micro-infrared (IR) microspectroscopy to examine ultramicrotomed thin sections, we have addressed the questions of IDP formation mechanisms, sources, and their relationship to conventional meteorites. The following sections describe specific findings resulting from these studies.

Electrostatic charge on a dust size distribution in a plasma. [in interplanetary space

NASA Technical Reports Server (NTRS)

Houpis, Harry L. F.; Whipple, Elden C., Jr.

1987-01-01

The capacitance of a grain immersed in a steady state plasma containing a size distribution of dust particles is studied. The grain charge is determined by assuming the equilibrium potential has been obtained by a simple balance of electron and ion collection currents. It is shown that the validity of the analytical treatment given here for the linearized Poisson equation is confined to a certain region of space. Within this region and starting at very small plasma Debye length lambda(D), the capacitance at first exhibits a monotonic increase with increasing lambda(D). The capacitance eventually reaches a maximum, followed by a monotonic decrease. The charge density of the dust in the plasma is found to be only a function of the lambda(D); there is no significant dependence on the interparticle spacing.

Creation of fully vectorized FORTRAN code for integrating the movement of dust grains in interplanetary environments

NASA Technical Reports Server (NTRS)

Colquitt, Walter

1989-01-01

The main objective is to improve the performance of a specific FORTRAN computer code from the Planetary Sciences Division of NASA/Johnson Space Center when used on a modern vectorizing supercomputer. The code is used to calculate orbits of dust grains that separate from comets and asteroids. This code accounts for influences of the sun and 8 planets (neglecting Pluto), solar wind, and solar light pressure including Poynting-Robertson drag. Calculations allow one to study the motion of these particles as they are influenced by the Earth or one of the other planets. Some of these particles become trapped just beyond the Earth for long periods of time. These integer period resonances vary from 3 orbits of the Earth and 2 orbits of the particles to as high as 14 to 13.

Atomistic simulations of dislocation pileup: Grain boundaries interaction

DOE PAGES

Wang, Jian

2015-05-27

Here, using molecular dynamics (MD) simulations, we studied the dislocation pileup–grain boundary (GB) interactions. Two Σ11 asymmetrical tilt grain boundaries in Al are studied to explore the influence of orientation relationship and interface structure on dislocation activities at grain boundaries. To mimic the reality of a dislocation pileup in a coarse-grained polycrystalline, we optimized the dislocation population in MD simulations and developed a predict-correct method to create a dislocation pileup in MD simulations. MD simulations explored several kinetic processes of dislocations–GB reactions: grain boundary sliding, grain boundary migration, slip transmission, dislocation reflection, reconstruction of grain boundary, and the correlation ofmore » these kinetic processes with the available slip systems across the GB and atomic structures of the GB.« less

LUNAR DUST GRAIN CHARGING BY ELECTRON IMPACT: COMPLEX ROLE OF SECONDARY ELECTRON EMISSIONS IN SPACE ENVIRONMENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abbas, M. M.; Craven, P. D.; LeClair, A. C.

2010-08-01

Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with radiation from nearby sources, or by electron/ion collisions by sticking or secondary electron emissions (SEEs). The high vacuum environment on the lunar surface leads to some unusual physical and dynamical phenomena involving dust grains with high adhesive characteristics, and levitation and transportation over long distances. Knowledge of the dust grain charges and equilibrium potentials is important for understanding a variety of physical and dynamical processes in the interstellar medium, and heliospheric, interplanetary/planetary, and lunar environments. It has been well recognized that the charging properties of individualmore » micron-/submicron-size dust grains are expected to be substantially different from the corresponding values for bulk materials. In this paper, we present experimental results on the charging of individual 0.2-13 {mu}m size dust grains selected from Apollo 11 and 17 dust samples, and spherical silica particles by exposing them to mono-energetic electron beams in the 10-200 eV energy range. The dust charging process by electron impact involving the SEEs discussed is found to be a complex charging phenomenon with strong particle size dependence. The measurements indicate substantial differences between the polarity and magnitude of the dust charging rates of individual small-size dust grains, and the measurements and model properties of corresponding bulk materials. A more comprehensive plan of measurements of the charging properties of individual dust grains for developing a database for realistic models of dust charging in astrophysical and lunar environments is in progress.« less

Lunary Dust Grain Charging by Electron Impact: Complex Role of Secondary Electron Emissions in Space Environments

NASA Technical Reports Server (NTRS)

Abbas, M. M.; Tankosic, D.; Crave, P. D.; LeClair, A.; Spann, J. F.

2010-01-01

Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with radiation from nearby sources, or by electron/ion collisions by sticking or secondary electron emissions (SEES). The high vacuum environment on the lunar surface leads to some unusual physical and dynamical phenomena involving dust grains with high adhesive characteristics, and levitation and transportation over long distances. Knowledge of the dust grain charges and equilibrium potentials is important for understanding a variety of physical and dynamical processes in the interstellar medium, and heliospheric, interplanetary/ planetary, and lunar environments. It has been well recognized that the charging properties of individual micron-/submicron-size dust grains are expected to be substantially different from the corresponding values for bulk materials. In this paper, we present experimental results on the charging of individual 0.2-13 m size dust grains selected from Apollo 11 and 17 dust samples, and spherical silica particles by exposing them to mono-energetic electron beams in the 10-200 eV energy range. The dust charging process by electron impact involving the SEES discussed is found to be a complex charging phenomenon with strong particle size dependence. The measurements indicate substantial differences between the polarity and magnitude of the dust charging rates of individual small-size dust grains, and the measurements and model properties of corresponding bulk materials. A more comprehensive plan of measurements of the charging properties of individual dust grains for developing a database for realistic models of dust charging in astrophysical and lunar environments is in progress.

Mineralogy of dark clasts in primitive versus differentiated meteorites

NASA Technical Reports Server (NTRS)

Zolensky, M. E.; Weisberg, M. K.; Barrett, R. A.; Prinz, M.

1993-01-01

The presence of dark lithic clasts within meteorites can provide information concerning asteroidal regolith processes, the extent of interactions between asteroids, and the relationship between meteorite types, micrometeorites, and interplanetary dust particles. Accordingly, we have been seeking and characterizing dark clasts found within carbonaceous chondrites, unequilibrated ordinary chondrites, howardites, and eucrites. We find that unequilibrated chondrites in this study contain fine-grained, anhydrous unequilibrated inclusions, while the howardites often contain inclusions from geochemically processed, hydrous asteroids (type 1 and 2 carbonaceous chondrites). Eucrites and howardities contain unusual clasts, not easily classified.

What if chondritic porous interplanetary dust particles are not the real McCoy

NASA Astrophysics Data System (ADS)

Rietmeijer, Frans J. M.

To select a target comet for a Comet Nucleus Sample Return Mission (CNSRM) it is necessary to have an experimental data base to evaluate the extent of diversity and similarity of comets. For example, the physical properties (e.g., low density) of chondritic porous (CP) interplanetary dust particles (IDPs) are believed to resemble these properties of cometary dust although it is yet to be demonstrated that the porous structure of CP IDPs is inherent to presolar dust particles stored in comet nuclei. Porous structures of IDPs could conceivably form during sublimation at the surface of active comet nuclei. Porous structures are also obtained during annealing of amorphous Mg-SiO smokes which initially forms porous aggregates of olivine + platey tridymite and which, upon continued annealing, react to fluffy enstatite aggregates. It is therefore uncertain that CP IDPs are entirely composed of unmetamorphosed presolar dust. Conceivably, new minerals and textures may form in situ in nuclei of active comets as a function of their individual thermal history. Unmetamorphosed comet dust is probably structurally amorphous. Thermal annealing of this dust can produce ultra fine-grained minerals and this ultrafine grain size of CP IDPs should be considered in assessments of aqueous alterations that could affect presolar dust in comet nuclei between 200 and 400 K. Devitrification and hydration may occur in situ in ice-dust mixtures and the mantle of active comet nuclei. Devitrification, or uncontrolled crystallization, of amorphous precursor dust can produce a range of chemical compositions of ultrafine-grained minerals and (non-equilibrium) mineral assemblages and textures in dust contained in comet nuclei as a function of period and trajectory of orbit and number of perihelion passages (not considering internal heating). Thus, experimental data on relevant processes and reaction rates between 200 and 400 K are needed in order to evaluate comet selection, penetration depth for sampling device and curation of samples for CNSRM.

What if chondritic porous interplanetary dust particles are not the real McCoy

NASA Technical Reports Server (NTRS)

Rietmeijer, Frans J. M.

1989-01-01

To select a target comet for a Comet Nucleus Sample Return Mission (CNSRM) it is necessary to have an experimental data base to evaluate the extent of diversity and similarity of comets. For example, the physical properties (e.g., low density) of chondritic porous (CP) interplanetary dust particles (IDPs) are believed to resemble these properties of cometary dust although it is yet to be demonstrated that the porous structure of CP IDPs is inherent to presolar dust particles stored in comet nuclei. Porous structures of IDPs could conceivably form during sublimation at the surface of active comet nuclei. Porous structures are also obtained during annealing of amorphous Mg-SiO smokes which initially forms porous aggregates of olivine + platey tridymite and which, upon continued annealing, react to fluffy enstatite aggregates. It is therefore uncertain that CP IDPs are entirely composed of unmetamorphosed presolar dust. Conceivably, new minerals and textures may form in situ in nuclei of active comets as a function of their individual thermal history. Unmetamorphosed comet dust is probably structurally amorphous. Thermal annealing of this dust can produce ultra fine-grained minerals and this ultrafine grain size of CP IDPs should be considered in assessments of aqueous alterations that could affect presolar dust in comet nuclei between 200 and 400 K. Devitrification and hydration may occur in situ in ice-dust mixtures and the mantle of active comet nuclei. Devitrification, or uncontrolled crystallization, of amorphous precursor dust can produce a range of chemical compositions of ultrafine-grained minerals and (non-equilibrium) mineral assemblages and textures in dust contained in comet nuclei as a function of period and trajectory of orbit and number of perihelion passages (not considering internal heating). Thus, experimental data on relevant processes and reaction rates between 200 and 400 K are needed in order to evaluate comet selection, penetration depth for sampling device and curation of samples for CNSRM.

Water and organics in interplanetary dust particles

NASA Astrophysics Data System (ADS)

Bradley, John P.

2015-08-01

Interplanetary dust particles (IDPs) and larger micrometeorites (MMs) impinge on the upper atmosphere where they decelerate at ~90 km altitude and settle to the Earth’s surface. Comets and asteroids are the major sources and the flux, 30,000-40,000 tons/yr, is comparable to the mass of larger meteorites impacting the Earth’s surface. The sedimentary record suggests that the flux was much higher on the early Earth. The chondritic porous (CP) subset of IDPs together with their larger counterparts, ultracarbonaceous micrometeorites (UCMMs), appear to be unique among known meteoritic materials in that they are composed almost exclusively of anhydrous minerals, some of them contain >> 50% organic carbon by volume as well as the highest abundances of presolar silicate grains including GEMS. D/H and 15N abundances implicate the Oort Cloud or presolar molecular cloud as likely sources of the organic carbon. Prior to atmospheric entry, IDPs and MMs spend ~104-105 year lifetimes in solar orbit where their surfaces develop amorphous space weathered rims from exposure to the solar wind (SW). Similar rims are observed on lunar soil grains and on asteroid Itokawa regolith grains. Using valence electron energy-loss spectroscopy (VEELS) we have detected radiolytic water in the rims on IDPs formed by the interaction of solar wind protons with oxygen in silicate minerals. Therefore, IDPs and MMs continuously deliver both water and organics to the earth and other terrestrial planets. The interaction of protons with oxygen-rich minerals to form water is a universal process.Affiliations:a University of Hawaii at Manoa, Hawaii Institute of Geophysics and Planetology, 1680 East-West Road, Honolulu, HI 96822, USA.b National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.c Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.d Department of Materials Science & Engineering, University of California, Berkeley, CA 94720, USA.e Advanced Light Source Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.

Analysis of Voyager Observed High-Energy Electron Fluxes in the Heliosheath Using MHD Simulations

NASA Technical Reports Server (NTRS)

Washimi, Haruichi; Webber, W. R.; Zank, Gary P.; Hu, Qiang; Florinski, Vladimir; Adams, James; Kubo, Yuki

2011-01-01

The Voyager spacecraft (V1 and V2) observed electrons of 6-14 MeV in the heliosheath which showed several incidences of flux variation relative to a background of gradually increasing flux with distance from the Sun. The increasing flux of background electrons is thought to result from inward radial diffusion. We compare the temporal electron flux variation with dynamical phenomena in the heliosheath that are obtained from our MHD simulations. Because our simulation is based on V2 observed plasma data before V2 crossed the termination shock, this analysis is effective up to late 2008, i.e., about a year after the V2-crossing, during which disturbances, driven prior to the crossing time, survived in the heliosheath. Several electron flux variations correspond to times directly associated with interplanetary shock events. One noteworthy example corresponds to various times associated with the March 2006 interplanetary shock, these being the collision with the termination shock, the passage past the V1 spacecraft, and the collision with the region near the heliopause, as identified by W.R. Webber et al. for proton/helium of 7-200 MeV. Our simulations indicate that all other electron flux variations, except one, correspond well to the times when a shock-driven magneto-sonic pulse and its reflection in the heliosheath either passed across V1/V2, or collided with the termination shock or with the plasma sheet near the heliopause. This result suggests that variation in the electron flux should be due to either direct or indirect effects of magnetosonic pulses in the heliosheath driven by interplanetary shocks

Light scattering by dust particles (PROGRA2 experiment): size and structure effects for transparent and absorbing materials

NASA Astrophysics Data System (ADS)

Hadamcik, E.; Renard, J.-B.; Lasue, J.; Levasseur-Regourd, A. C.

2007-08-01

1- Introduction Cometary and possibly interplanetary dust particles seem to be mainly made of agglomerates of submicron and micron-sized grains. These particles are among the most primitive in our solar system. Regoliths on asteroidal and planetary surfaces seem to be loose materials produced by impinging meteorites on the surface of small bodies. Comparing their physical properties is thus fundamental to understand their evolution. To interpret remote observations of solar light scattered by dust particles and regoliths, it is necessary to use numerical and experimental simulations [1,2,3]. 2- PROGRA2 experiment PROGRA2 instruments are polarimeters; the light sources are two randomly polarized lasers (632.8 nm and 543.5 nm). Levitating particles (in microgravity or lifted by an air-draught) are studied by imaging polarimetry. Details on the instruments can be found in [4,5]. 3- Samples Two kinds of samples are studied: compact particles in the (1-400) micrometer size range and fluffy aggregates in the same size range, made from submicron and micronsized grains. The materials are transparent silica and absorbing carbon. Some deposited particles are huge agglomerates of micron-sized grains produced by random ballistic deposition of single grains [6,7] or produced by evaporation of mixtures in alcohol of fluffy aggregates of submicron-sized grains. Two samples are made of silica spheres coated by a carbonaceous black compound. Cometary analogues are mixtures of silica and amorphous carbon or Mg-Fe silicates mixed with amorphous carbon. 4- Results Phase curves and their main parameters (negative polarization at small phase angles and maximum polarization, Pmax, at 90-100° phase angle) for the different materials will be compared and related to the physical properties. For example, it is well known by numerical simulations and/or by experiments that the maximum polarization decreases when the size (submicrometer range) of the grains increases [2,8,9]. An inverse rule is found for compact grains, larger than the wavelength. Mixtures of fluffy silica and fined grained amorphous carbon or better Mg-Fe silicates with amorphous carbon are excellent cometary particles analogues (as light scattering is concerned) if they are mixed with some compact micron-sized grains [9]. Nevertheless the structure of the aggregates seems to play a major role to obtain the negative branch found on the polarimetric phase curves for comets [10]. 5- Discussion and conclusions The experiments purpose is to help to disentangle the different physical properties of dust particles that can be deduced from remote observations (cometary dust, regoliths). Differences between the main parameters influencing the variations of Pmax and the presence of a negative branch on the polarimetric phase curves for lifted and deposited particles (in huge agglomerates or not) will be discussed. Acknowledgments: Technische Universität Carolo-Wilhelmina, Braunschweig, Deutschland (Pr Blum, Dr Schräpler); University of New Mexico, Albuquerque, USA (Pr Rietmeijer); NASA Goddard Space Flight Center, Maryland, USA (Dr Nuth) References [1] A.C. Levasseur-Regourd, E. Hadamcik, JQSRT 79-80, 903 (2003) [2] J. Lasue, A.C. Levasseur-Regourd, JQSRT 100, 220 (2006) [3] J.-B. Renard et al., ASR 31, 2511 (2003) [4] J.-B. Renard et al., Appl. Opt. 91, 609 (2002) [5] E. Hadamcik et al., JQSRT 106, 74 (2007) [6] J. Blum, R. Schreapler, Phys. Rev Let 93:115031 (2004) [7] J. Blum et al., Astrophys J 652, 1768 (2006) [8] R. West, Appl. Opt. 30, 5216 (1991) [9] E. Hadamcik et al., JQSRT 100, 143 (2006) [10] E. Hadamcik et al., Icarus, in press (2007)

Particle acceleration due to shocks in the interplanetary field: High time resolution data and simulation results

NASA Technical Reports Server (NTRS)

Kessel, R. L.; Armstrong, T. P.; Nuber, R.; Bandle, J.

1985-01-01

Data were examined from two experiments aboard the Explorer 50 (IMP 8) spacecraft. The Johns Hopkins University/Applied Lab Charged Particle Measurement Experiment (CPME) provides 10.12 second resolution ion and electron count rates as well as 5.5 minute or longer averages of the same, with data sampled in the ecliptic plane. The high time resolution of the data allows for an explicit, point by point, merging of the magnetic field and particle data and thus a close examination of the pre- and post-shock conditions and particle fluxes associated with large angle oblique shocks in the interplanetary field. A computer simulation has been developed wherein sample particle trajectories, taken from observed fluxes, are allowed to interact with a planar shock either forward or backward in time. One event, the 1974 Day 312 shock, is examined in detail.

Interplanetary Program to Optimize Simulated Trajectories (IPOST). Volume 1: User's guide

NASA Technical Reports Server (NTRS)

Hong, P. E.; Kent, P. D.; Olson, D. W.; Vallado, C. A.

1992-01-01

IPOST is intended to support many analysis phases, from early interplanetary feasibility studies through spacecraft development and operations. The IPOST output provides information for sizing and understanding mission impacts related to propulsion, guidance, communications, sensor/actuators, payload, and other dynamic and geometric environments. IPOST models three degree of freedom trajectory events, such as launch/ascent, orbital coast, propulsive maneuvering (impulsive and finite burn), gravity assist, and atmospheric entry. Trajectory propagation is performed using a choice of Cowell, Encke, Multiconic, Onestep, or Conic methods. The user identifies a desired sequence fo trajectory events, and selects which parameters are independent (controls) and dependent (targets), as well as other constraints and the coat function. Targeting and optimization is performed using the Stanford NPSOL algorithm. IPOST structure allows sub-problems within a master optimization problem to aid in the general constrained parameter optimization solution. An alternate optimization method uses implicit simulation and collocation techniques.

Lunar dust simulant charging and transport under UV irradiation in vacuum: Experiments and numerical modeling

NASA Astrophysics Data System (ADS)

Champlain, A.; Matéo-Vélez, J.-C.; Roussel, J.-F.; Hess, S.; Sarrailh, P.; Murat, G.; Chardon, J.-P.; Gajan, A.

2016-01-01

Recent high-altitude observations, made by the Lunar Dust Experiment (LDEX) experiment on board LADEE orbiting the Moon, indicate that high-altitude (>10 km) dust particle densities are well correlated with interplanetary dust impacts. They show no evidence of high dust density suggested by Apollo 15 and 17 observations and possibly explained by electrostatic forces imposed by the plasma environment and photon irradiation. This paper deals with near-surface conditions below the domain of observation of LDEX where electrostatic forces could clearly be at play. The upper and lower limits of the cohesive force between dusts are obtained by comparing experiments and numerical simulations of dust charging under ultraviolet irradiation in the presence of an electric field and mechanical vibrations. It is suggested that dust ejection by electrostatic forces is made possible by microscopic-scale amplifications due to soil irregularities. At low altitude, this process may be complementary to interplanetary dust impacts.

Time-dependent MHD simulations of the solar wind outflow using interplanetary scintillation observations

DOE PAGES

Kim, Tae K.; Pogorelov, Nikolai V.; Borovikov, Sergey N.; ...

2012-11-20

Numerical modeling of the heliosphere is a critical component of space weather forecasting. The accuracy of heliospheric models can be improved by using realistic boundary conditions and confirming the results with in situ spacecraft measurements. To accurately reproduce the solar wind (SW) plasma flow near Earth, we need realistic, time-dependent boundary conditions at a fixed distance from the Sun. We may prepare such boundary conditions using SW speed and density determined from interplanetary scintillation (IPS) observations, magnetic field derived from photospheric magnetograms, and temperature estimated from its correlation with SW speed. In conclusion, we present here the time-dependent MHD simulationmore » results obtained by using the 2011 IPS data from the Solar-Terrestrial Environment Laboratory as time-varying inner boundary conditions and compare the simulated data at Earth with OMNI data (spacecraft-interspersed, near-Earth solar wind data).« less

The problems of cosmic ray particle simulation for the near-Earth orbital and interplanetary flight conditions.

PubMed

Nymmik, R A

1999-10-01

A wide range of the galactic cosmic ray and SEP event flux simulation problems for the near-Earth satellite and manned spacecraft orbits and for the interplanetary mission trajectories are discussed. The models of the galactic cosmic ray and SEP events in the Earth orbit beyond the Earth's magnetosphere are used as a basis. The particle fluxes in the near-Earth orbits should be calculated using the transmission functions. To calculate the functions, the dependences of the cutoff rigidities on the magnetic disturbance level and on magnetic local time have to be known. In the case of space flights towards the Sun and to the boundary of the solar system, particular attention is paid to the changes in the SEP event occurrence frequency and size. The particle flux gradients are applied in this case to galactic cosmic ray fluxes.

Fluid-induced organic synthesis in the solar nebula recorded in extraterrestrial dust from meteorites

PubMed Central

Vollmer, Christian; Kepaptsoglou, Demie; Leitner, Jan; Busemann, Henner; Spring, Nicole H.; Ramasse, Quentin M.; Hoppe, Peter; Nittler, Larry R.

2014-01-01

Isotopically anomalous carbonaceous grains in extraterrestrial samples represent the most pristine organics that were delivered to the early Earth. Here we report on gentle aberration-corrected scanning transmission electron microscopy investigations of eight 15N-rich or D-rich organic grains within two carbonaceous Renazzo-type (CR) chondrites and two interplanetary dust particles (IDPs) originating from comets. Organic matter in the IDP samples is less aromatic than that in the CR chondrites, and its functional group chemistry is mainly characterized by C–O bonding and aliphatic C. Organic grains in CR chondrites are associated with carbonates and elemental Ca, which originate either from aqueous fluids or possibly an indigenous organic source. One distinct grain from the CR chondrite NWA 852 exhibits a rim structure only visible in chemical maps. The outer part is nanoglobular in shape, highly aromatic, and enriched in anomalous nitrogen. Functional group chemistry of the inner part is similar to spectra from IDP organic grains and less aromatic with nitrogen below the detection limit. The boundary between these two areas is very sharp. The direct association of both IDP-like organic matter with dominant C–O bonding environments and nanoglobular organics with dominant aromatic and C–N functionality within one unique grain provides for the first time to our knowledge strong evidence for organic synthesis in the early solar system activated by an anomalous nitrogen-containing parent body fluid. PMID:25288736

New Manganese Silicide Mineral Phase in an Interplanetary Dust Particle

NASA Technical Reports Server (NTRS)

Nakamura-Messenger, K.; Keller, L. P.; Clemett, S. J.; Jones, J. H.; Palma, R. L.; Pepin, R. O.; Kloeck, W.; Zolensky, M. E.; Messenger, S.

2008-01-01

Comet 26P/Grigg-Skjellerup was identified as a source of an Earth-crossing dust stream with low Earth-encounter velocities, with peak anticipated fluxes during April in 2003 and 2004 [1]. In response to this prediction, NASA performed dedicated stratospheric dust collections using high altitude aircraft to target potential interplanetary dust particles (IDPs) from this comet stream in April 2003. Several IDPs from this collection have shown unusually low noble gas abundances [2] consistent with the predicted short space exposure ages of Grigg-Skjellerup dust particles [1]. High abundances of large D enrichments [3] and presolar grains [4] in IDPs from this collection are also consistent with an origin from the comet Grigg-Skjellerup. Here we report a new mineral from one of the cluster IDPs of the "Grigg-Skjellerup" collection, L2055. Our report focuses on an unusual manganese-iron-chromium silicide phase that, to our knowledge, has not been observed previously in nature. This unique phase may also shed light on the genesis of the enigmatic low-Fe,Mn-enriched (LIME) olivine that has been previously reported in IDPs and meteorites [5].

A new technique for observationally derived boundary conditions for space weather

NASA Astrophysics Data System (ADS)

Pagano, Paolo; Mackay, Duncan Hendry; Yeates, Anthony Robinson

2018-04-01

Context. In recent years, space weather research has focused on developing modelling techniques to predict the arrival time and properties of coronal mass ejections (CMEs) at the Earth. The aim of this paper is to propose a new modelling technique suitable for the next generation of Space Weather predictive tools that is both efficient and accurate. The aim of the new approach is to provide interplanetary space weather forecasting models with accurate time dependent boundary conditions of erupting magnetic flux ropes in the upper solar corona. Methods: To produce boundary conditions, we couple two different modelling techniques, MHD simulations and a quasi-static non-potential evolution model. Both are applied on a spatial domain that covers the entire solar surface, although they extend over a different radial distance. The non-potential model uses a time series of observed synoptic magnetograms to drive the non-potential quasi-static evolution of the coronal magnetic field. This allows us to follow the formation and loss of equilibrium of magnetic flux ropes. Following this a MHD simulation captures the dynamic evolution of the erupting flux rope, when it is ejected into interplanetary space. Results.The present paper focuses on the MHD simulations that follow the ejection of magnetic flux ropes to 4 R⊙. We first propose a technique for specifying the pre-eruptive plasma properties in the corona. Next, time dependent MHD simulations describe the ejection of two magnetic flux ropes, that produce time dependent boundary conditions for the magnetic field and plasma at 4 R⊙ that in future may be applied to interplanetary space weather prediction models. Conclusions: In the present paper, we show that the dual use of quasi-static non-potential magnetic field simulations and full time dependent MHD simulations can produce realistic inhomogeneous boundary conditions for space weather forecasting tools. Before a fully operational model can be produced there are a number of technical and scientific challenges that still need to be addressed. Nevertheless, we illustrate that coupling quasi-static and MHD simulations in this way can significantly reduce the computational time required to produce realistic space weather boundary conditions.

The Butterflies of Principal Components: A Case of Ultrafine-Grained Polyphase Units

NASA Astrophysics Data System (ADS)

Rietmeijer, F. J. M.

1996-03-01

Dusts in the accretion regions of chondritic interplanetary dust particles [IDPs] consisted of three principal components: carbonaceous units [CUs], carbon-bearing chondritic units [GUs] and carbon-free silicate units [PUs]. Among others, differences among chondritic IDP morphologies and variable bulk C/Si ratios reflect variable mixtures of principal components. The spherical shapes of the initially amorphous principal components remain visible in many chondritic porous IDPs but fusion was documented for CUs, GUs and PUs. The PUs occur as coarse- and ultrafine-grained units that include so called GEMS. Spherical principal components preserved in an IDP as recognisable textural units have unique proporties with important implications for their petrological evolution from pre-accretion processing to protoplanet alteration and dynamic pyrometamorphism. Throughout their lifetime the units behaved as closed-systems without chemical exchange with other units. This behaviour is reflected in their mineralogies while the bulk compositions of principal components define the environments wherein they were formed.

Carbonate in Comets: A Comparison of Comets 1P/Halley, 9P/Temple 1, and 81P/Wild 2

NASA Technical Reports Server (NTRS)

Flynn, G. J.; Leroux, H.; Tomeoka, K.; Tomioka, N.; Ohnishi, I.; Mikouchi, T.; Wirick, S.; Keller, L. P.; Jacobsen, C.; Sanford, S. A.

2008-01-01

Comets are generally believed to have formed in a cold region, trapping in the cometary ices the original low-temperature condensate grains of our Solar System. These grains would have been preserved in cold-storage, at a temperature below the freezing point of CO2, for the last 4.5+ billion years. Carbonates are common in hydrous meteorites and hydrous interplanetary dust particles (IDPs), where they are believed to have formed by parent-body aqueous processing. Since simple models of cometary evolution involve no aqueous processing, carbonates were generally presumed not to occur in comets. However, Toppani et al. [1] have performed experiments that indicate carbonate can be formed by non-equilibrium condensation in circumstellar environments where water is present as a vapor, not as a liquid. This suggests carbonate might have condensed in cold regions of the Solar Nebula, and might be present in comets.

The solar ionisation rate deduced from Ulysses measurements and its implications to interplanetary Lyman alpha-intensity

NASA Technical Reports Server (NTRS)

Summanen, T.; Kyroelae, E.

1995-01-01

We have developed a computer code which can be used to study 3-dimensional and time-dependent effects of the solar cycle on the interplanetary (IP) hydrogen distribution. The code is based on the inverted Monte Carlo simulation. In this work we have modelled the temporal behaviour of the solar ionisation rate. We have assumed that during the most of the time of the solar cycle there is an anisotopic latitudinal structure but right at the solar maximum the anisotropy disappears. The effects of this behaviour will be discussed both in regard to the IP hydrogen distribution and IP Lyman a a-intensity.

Preliminary performance analysis of an interplanetary navigation system using asteroid based beacons

NASA Technical Reports Server (NTRS)

Jee, J. Rodney; Khatib, Ahmad R.; Muellerschoen, Ronald J.; Williams, Bobby G.; Vincent, Mark A.

1988-01-01

A futuristic interplanetary navigation system using transmitters placed on selected asteroids is introduced. This network of space beacons is seen as a needed alternative to the overly burdened Deep Space Network. Covariance analyses on the potential performance of these space beacons located on a candidate constellation of eight real asteroids are initiated. Simplified analytic calculations are performed to determine limiting accuracies attainable with the network for geometric positioning. More sophisticated computer simulations are also performed to determine potential accuracies using long arcs of range and Doppler data from the beacons. The results from these computations show promise for this navigation system.

Dust in the Solar System - Properties and Origins

NASA Technical Reports Server (NTRS)

Messenger, Scott; Keller, Lindsay; Nakamura-Messenger, Keiko

2013-01-01

Interplanetary dust pervades the inner Solar System, giving rise to a prominent glow above the horizon at sunrise and sunset known as the zodiacal light. This dust derives from the disintegration of comets as they approach the Sun and from collisions among main-belt asteroids. The Earth accretes roughly 4x10(exp 6) kg/year of 1 - 1,000 micron dust particles as they spiral into the Sun under the influence of Poynting-Robertson drag and solar wind drag. Samples of these grains have been collected from deep sea sediments, Antarctic ice and by high-altitude aircraft and balloon flights. Interplanetary dust particles (IDPs) collected in the stratosphere have been classified by their IR spectra into olivine, pyroxene, and hydrated silicate-dominated classes. Most IDPs have bulk major and minor element abundances that are similar to carbonaceous chondrite meteorites. Hydrated silicate-rich IDPs are thought to derive from asteroids based on their mineralogy and low atmospheric entry velocities estimated from peak temperatures reached during atmospheric entry. Anhydrous IDPs are typically aggregates of 0.1 - approx. 1 micron Mg-rich olivine and pyroxene, amorphous silicates (GEMS), Fe, Nisulfides and rare spinel and oxides bound together by carbonaceous material. These IDPs are often argued to derive from comets based on compositional similarities and high atmospheric entry velocities that imply high eccentricity orbits. Infrared spectra obtained from anhydrous IDPs closely match remote IR spectra obtained from comets. The most primitive (anhydrous) IDPs appear to have escaped the parent-body thermal and aqueous alteration that has affected meteorites. These samples thus consist entirely of grains that formed in the ancient solar nebula and pre-solar interstellar and circumstellar environments. Isotopic studies of IDPs have identified silicate stardust grains that formed in the outflows of red giant and asymptotic giant branch stars and supernovae]. These stardust grains include both amorphous and crystalline silicates. The organic matter in these samples also exhibits highly anomalous H, C, and N isotopic compositions that are consistent with formation in low temperature environments at the outermost regions of the solar nebula or presolar cold molecular cloud. The scientific frontiers for these samples include working toward a better understanding of the origins of the solar system amorphous and crystalline grains in IDPs and the very challenging task of determining the chemical composition of sub-micron organic grains. Laboratory studies of ancient and present-day dust in the Solar System thus reveal in exquisite detail the chemistry, mineralogy and isotopic properties of materials that derive from a range of astrophysical environments. These studies are an important complement to astronomical observations that help to place the laboratory observations into broader context.

Analysis of an Interplanetary Coronal Mass Ejection by a Spacecraft Radio Signal: A Case Study

NASA Astrophysics Data System (ADS)

Molera Calvés, G.; Kallio, E.; Cimo, G.; Quick, J.; Duev, D. A.; Bocanegra Bahamón, T.; Nickola, M.; Kharinov, M. A.; Mikhailov, A. G.

2017-11-01

Tracking radio communication signals from planetary spacecraft with ground-based telescopes offers the possibility to study the electron density and the interplanetary scintillation of the solar wind. Observations of the telemetry link of planetary spacecraft have been conducted regularly with ground antennae from the European Very Long Baseline Interferometry Network, aiming to study the propagation of radio signals in the solar wind at different solar elongations and distances from the Sun. We have analyzed the Mars Express spacecraft radio signal phase fluctuations while, based on a 3-D heliosphere plasma simulation, an interplanetary coronal mass ejection (ICME) crossed the radio path during one of our observations on 6 April 2015. Our measurements showed that the phase scintillation indices increased by a factor of 4 during the passage of the ICME. The method presented here confirms that the phase scintillation technique based on spacecraft signals provides information of the properties and propagation of the ICMEs in the heliosphere.

Inter-Hemispheric Comparisons of the Ground Magnetic Response to an Interplanetary Shock

NASA Astrophysics Data System (ADS)

Hartinger, M.; Xu, Z.; Clauer, C. R.; Yu, Y.; Weimer, D. R.; Kim, H.; Pilipenko, V.; Welling, D. T.; Behlke, R.; Willer, A. N.

2016-12-01

Models predict that hemispheric differences in ionospheric conductivity affect the high-latitude ground magnetic response during interplanetary shock events. Using ground magnetometer observations from dense north-south chains in both the Northern (Greenland) and Southern (East Antarctic Plateau) hemispheres, we show an event study where that is not the case: nearly the same magnetic response is observed in both hemispheres, despite near-solstice conditions when hemispheric conductivity differences should be large. We compare observations to virtual ground magnetometer output from global magnetohydrodynamic (MHD) simulations with the same driving conditions but different ionospheric conductivity profiles: (1) uniform conductivity, (2) variable conductivity appropriate for solar illumination during solstice, (3) the same as 2 but with additional conductivity contributions from auroral precipitation. There are major quantitative differences between simulations, with simulation 3 exhibiting the best agreement with data. Our results demonstrate the importance of constraining ionospheric conductivity - especially contributions from auroral precipitation - before interpreting hemispheric differences in ground magnetic perturbation amplitude. We discuss the application of these results to techniques that relate high-latitude ground magnetometer observations to current or voltage generators.

Novel Experimental Simulations of the Atmospheric Injection of Meteoric Metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gómez Martín, J. C.; Bones, D. L.; Carrillo-Sánchez, J. D.

2017-02-20

A newly developed laboratory, Meteoric Ablation Simulator (MASI), is used to test model predictions of the atmospheric ablation of interplanetary dust particles (IDPs) with experimental Na, Fe, and Ca vaporization profiles. MASI is the first laboratory setup capable of performing time-resolved atmospheric ablation simulations, by means of precision resistive heating and atomic laser-induced fluorescence detection. Experiments using meteoritic IDP analogues show that at least three mineral phases (Na-rich plagioclase, metal sulfide, and Mg-rich silicate) are required to explain the observed appearance temperatures of the vaporized elements. Low melting temperatures of Na-rich plagioclase and metal sulfide, compared to silicate grains, precludemore » equilibration of all the elemental constituents in a single melt. The phase-change process of distinct mineral components determines the way in which Na and Fe evaporate. Ca evaporation is dependent on particle size and on the initial composition of the molten silicate. Measured vaporized fractions of Na, Fe, and Ca as a function of particle size and speed confirm differential ablation (i.e., the most volatile elements such as Na ablate first, followed by the main constituents Fe, Mg, and Si, and finally the most refractory elements such as Ca). The Chemical Ablation Model (CABMOD) provides a reasonable approximation to this effect based on chemical fractionation of a molten silicate in thermodynamic equilibrium, even though the compositional and geometric description of IDPs is simplistic. Improvements in the model are required in order to better reproduce the specific shape of the elemental ablation profiles.« less

Dust coagulation in ISM

NASA Technical Reports Server (NTRS)

Chokshi, Arati; Tielens, Alexander G. G. M.; Hollenbach, David

1989-01-01

Coagulation is an important mechanism in the growth of interstellar and interplanetary dust particles. The microphysics of the coagulation process was theoretically analyzed as a function of the physical properties of the coagulating grains, i.e., their size, relative velocities, temperature, elastic properties, and the van der Waal interaction. Numerical calculations of collisions between linear chains provide the wave energy in individual particles and the spectrum of the mechanical vibrations set up in colliding particles. Sticking probabilities are then calculated using simple estimates for elastic deformation energies and for the attenuation of the wave energy due to absorption and scattering processes.

Comparison of the orbital properties of Jupiter Trojan asteroids and Trojan dust

NASA Astrophysics Data System (ADS)

Liu, Xiaodong; Schmidt, Jrgen

2018-06-01

In a previous paper we simulated the orbital evolution of dust particles from the Jupiter Trojan asteroids ejected by the impacts of interplanetary particles, and evaluated their overall configuration in the form of dust arcs. Here we compare the orbital properties of these Trojan dust particles and the Trojan asteroids. Both Trojan asteroids and most of the dust particles are trapped in the Jupiter 1:1 resonance. However, for dust particles, this resonance is modified because of the presence of solar radiation pressure, which reduces the peak value of the semi-major axis distribution. We find also that some particles can be trapped in the Saturn 1:1 resonance and higher order resonances with Jupiter. The distributions of the eccentricity, the longitude of pericenter, and the inclination for Trojans and the dust are compared. For the Trojan asteroids, the peak in the longitude of pericenter distribution is about 60 degrees larger than the longitude of pericenter of Jupiter; in contrast, for Trojan dust this difference is smaller than 60 degrees, and it decreases with decreasing grain size. For the Trojan asteroids and most of the Trojan dust, the Tisserand parameter is distributed in the range of two to three.

Evolution of magnetic flux ropes associated with flux transfer events and interplanetary magnetic clouds

NASA Technical Reports Server (NTRS)

Wei, C. Q.; Lee, L. C.; Wang, S.; Akasofu, S.-I.

1991-01-01

Spacecraft observations suggest that flux transfer events and interplanetary magnetic clouds may be associated with magnetic flux ropes which are magnetic flux tubes containing helical magnetic field lines. In the magnetic flux ropes, the azimuthal magnetic field is superposed on the axial field. The time evolution of a localized magnetic flux rope is studied. A two-dimensional compressible MHD simulation code with a cylindrical symmetry is developed to study the wave modes associated with the evolution of flux ropes. It is found that in the initial phase both the fast magnetosonic wave and the Alfven wave are developed in the flux rope. After this initial phase, the Alfven wave becomes the dominant wave mode for the evolution of the magnetic flux rope and the radial expansion velocity of the flux rope is found to be negligible. Numerical results further show that even for a large initial azimuthal component of the magnetic field, the propagation velocity along the axial direction of the flux rope remains the Alfven velocity. It is also found that the localized magnetic flux rope tends to evolve into two separate magnetic ropes propagating in opposite directions. The simulation results are used to study the evolution of magnetic flux ropes associated with flux transfer events observed at the earth's dayside magnetopause and magnetic clouds in the interplanetary space.

Mimicking coarse-grained simulations without coarse-graining: enhanced sampling by damping short-range interactions.

PubMed

Wei, Dongshan; Wang, Feng

2010-08-28

The damped-short-range-interaction (DSRI) method is proposed to mimic coarse-grained simulations by propagating an atomistic scale system on a smoothed potential energy surface. The DSRI method has the benefit of enhanced sampling provided by a typical coarse-grained simulation without the need to perform coarse-graining. Our method was used to simulate liquid water, alanine dipeptide folding, and the self-assembly of dimyristoylphosphatidylcholine lipid. In each case, our method appreciably accelerated the dynamics without significantly changing the free energy surface. Additional insights from DSRI simulations and the promise of coupling our DSRI method with Hamiltonian replica-exchange molecular dynamics are discussed.

Mimicking coarse-grained simulations without coarse-graining: Enhanced sampling by damping short-range interactions

NASA Astrophysics Data System (ADS)

Wei, Dongshan; Wang, Feng

2010-08-01

The damped-short-range-interaction (DSRI) method is proposed to mimic coarse-grained simulations by propagating an atomistic scale system on a smoothed potential energy surface. The DSRI method has the benefit of enhanced sampling provided by a typical coarse-grained simulation without the need to perform coarse-graining. Our method was used to simulate liquid water, alanine dipeptide folding, and the self-assembly of dimyristoylphosphatidylcholine lipid. In each case, our method appreciably accelerated the dynamics without significantly changing the free energy surface. Additional insights from DSRI simulations and the promise of coupling our DSRI method with Hamiltonian replica-exchange molecular dynamics are discussed.

Rapid acceleration of outer radiation belt electrons associated with solar wind pressure pulse: Simulation study with Arase and Van Allen Probe observations

NASA Astrophysics Data System (ADS)

Hayashi, M.; Yoshizumi, M.; Saito, S.; Matsumoto, Y.; Kurita, S.; Teramoto, M.; Hori, T.; Matsuda, S.; Shoji, M.; Machida, S.; Amano, T.; Seki, K.; Higashio, N.; Mitani, T.; Takashima, T.; Kasahara, Y.; Kasaba, Y.; Yagitani, S.; Ishisaka, K.; Tsuchiya, F.; Kumamoto, A.; Matsuoka, A.; Shinohara, I.; Blake, J. B.; Fennell, J. F.; Claudepierre, S. G.

2017-12-01

Relativistic electron fluxes of the outer radiation belt rapidly change in response to solar wind variations. One of the shortest acceleration processes of electrons in the outer radiation belt is wave-particle interactions between drifting electrons and fast-mode waves induced by compression of the dayside magnetopause caused by interplanetary shocks. In order to investigate this process by a solar wind pressure pulse, we perform a code-coupling simulation using the GEMSIS-RB test particle simulation (Saito et al., 2010) and the GEMSIS-GM global MHD magnetosphere simulation (Matsumoto et al., 2010). As a case study, an interplanetary pressure pulse with the enhancement of 5 nPa is used as the up-stream condition. In the magnetosphere, the fast mode waves with the azimuthal electric field ( negative 𝐸𝜙 : |𝐸&;#120601;| 10 mV/m, azimuthal mode number : m ≤ 2) propagates from the dayside to nightside, interacting with electrons. From the simulation results, we derived effective acceleration model and condition : The electrons whose drift velocities vd ≥ (π/2)Vfast are accelerated efficiently. On December 20, 2016, the Arase (ERG) satellite was launched , allowing more accurate multi-point simultaneous observation with other satellites. We will compare our simulation results with observations from Arase and Van Allen Probes, and investigate the acceleration condition of relativistic electrons associated with storm sudden commencement (SSC).

Evaluation of the Interplanetary Magnetic Field Strength Using the Cosmic-Ray Shadow of the Sun

NASA Astrophysics Data System (ADS)

Amenomori, M.; Bi, X. J.; Chen, D.; Chen, T. L.; Chen, W. Y.; Cui, S. W.; Danzengluobu, Ding, L. K.; Feng, C. F.; Feng, Zhaoyang; Feng, Z. Y.; Gou, Q. B.; Guo, Y. Q.; He, H. H.; He, Z. T.; Hibino, K.; Hotta, N.; Hu, Haibing; Hu, H. B.; Huang, J.; Jia, H. Y.; Jiang, L.; Kajino, F.; Kasahara, K.; Katayose, Y.; Kato, C.; Kawata, K.; Kozai, M.; Labaciren, Le, G. M.; Li, A. F.; Li, H. J.; Li, W. J.; Liu, C.; Liu, J. S.; Liu, M. Y.; Lu, H.; Meng, X. R.; Miyazaki, T.; Mizutani, K.; Munakata, K.; Nakajima, T.; Nakamura, Y.; Nanjo, H.; Nishizawa, M.; Niwa, T.; Ohnishi, M.; Ohta, I.; Ozawa, S.; Qian, X. L.; Qu, X. B.; Saito, T.; Saito, T. Y.; Sakata, M.; Sako, T. K.; Shao, J.; Shibata, M.; Shiomi, A.; Shirai, T.; Sugimoto, H.; Takita, M.; Tan, Y. H.; Tateyama, N.; Torii, S.; Tsuchiya, H.; Udo, S.; Wang, H.; Wu, H. R.; Xue, L.; Yamamoto, Y.; Yamauchi, K.; Yang, Z.; Yuan, A. F.; Yuda, T.; Zhai, L. M.; Zhang, H. M.; Zhang, J. L.; Zhang, X. Y.; Zhang, Y.; Zhang, Yi; Zhang, Ying; Zhaxisangzhu, Zhou, X. X.; Tibet AS γ Collaboration

2018-01-01

We analyze the Sun's shadow observed with the Tibet-III air shower array and find that the shadow's center deviates northward (southward) from the optical solar disk center in the "away" ("toward") interplanetary magnetic field (IMF) sector. By comparing with numerical simulations based on the solar magnetic field model, we find that the average IMF strength in the away (toward) sector is 1.54 ±0.21stat±0.20syst (1.62 ±0.15stat±0.22syst ) times larger than the model prediction. These demonstrate that the observed Sun's shadow is a useful tool for the quantitative evaluation of the average solar magnetic field.

Evaluation of the Interplanetary Magnetic Field Strength Using the Cosmic-Ray Shadow of the Sun.

PubMed

Amenomori, M; Bi, X J; Chen, D; Chen, T L; Chen, W Y; Cui, S W; Danzengluobu; Ding, L K; Feng, C F; Feng, Zhaoyang; Feng, Z Y; Gou, Q B; Guo, Y Q; He, H H; He, Z T; Hibino, K; Hotta, N; Hu, Haibing; Hu, H B; Huang, J; Jia, H Y; Jiang, L; Kajino, F; Kasahara, K; Katayose, Y; Kato, C; Kawata, K; Kozai, M; Labaciren; Le, G M; Li, A F; Li, H J; Li, W J; Liu, C; Liu, J S; Liu, M Y; Lu, H; Meng, X R; Miyazaki, T; Mizutani, K; Munakata, K; Nakajima, T; Nakamura, Y; Nanjo, H; Nishizawa, M; Niwa, T; Ohnishi, M; Ohta, I; Ozawa, S; Qian, X L; Qu, X B; Saito, T; Saito, T Y; Sakata, M; Sako, T K; Shao, J; Shibata, M; Shiomi, A; Shirai, T; Sugimoto, H; Takita, M; Tan, Y H; Tateyama, N; Torii, S; Tsuchiya, H; Udo, S; Wang, H; Wu, H R; Xue, L; Yamamoto, Y; Yamauchi, K; Yang, Z; Yuan, A F; Yuda, T; Zhai, L M; Zhang, H M; Zhang, J L; Zhang, X Y; Zhang, Y; Zhang, Yi; Zhang, Ying; Zhaxisangzhu; Zhou, X X

2018-01-19

We analyze the Sun's shadow observed with the Tibet-III air shower array and find that the shadow's center deviates northward (southward) from the optical solar disk center in the "away" ("toward") interplanetary magnetic field (IMF) sector. By comparing with numerical simulations based on the solar magnetic field model, we find that the average IMF strength in the away (toward) sector is 1.54±0.21_{stat}±0.20_{syst} (1.62±0.15_{stat}±0.22_{syst}) times larger than the model prediction. These demonstrate that the observed Sun's shadow is a useful tool for the quantitative evaluation of the average solar magnetic field.

Carbonaceous Components in the Comet Halley Dust

NASA Technical Reports Server (NTRS)

Fomenkova, M. N.; Chang, S.; Mukhin, L. M.

1994-01-01

Cometary grains containing large amounts of carbon and/or organic matter (CHON) were discovered by in situ measurements of comet Halley dust composition during VEGA and GIOTTO flyby missions. In this paper, we report the classification of these cometary, grains by means of cluster analysis, discuss the resulting compositional groups, and compare them with substances observed or hypothesized in meteorites, interplanetary dust particles, and the interstellar medium. Grains dominated by carbon and/or organic matter (CHON grains) represent approx. 22% of the total population of measured cometary dust particles. They, usually contain a minor abundance of rock-forming elements as well. Grains having organic material are relatively more abundant in the vicinity of the nucleus than in the outer regions of the coma, which suggests decomposition of the organics in the coma environment. The majority of comet Halley organic particles are multicomponent mixtures of carbon phases and organic compounds. Possibly, the cometary CHON grains may be related to kerogen material of an interstellar origin in carbonaceous meteorites. Pure carbon grains, hydrocarbons and polymers of cyanopolyynes, and multi-carbon monoxides are present in cometary dust as compositionally simple and distinctive components among a variety of others. There is no clear evidence of significant presence of pure formaldehyde or HCN polymers in Halley dust particles. The diversity of types of cometary organic compounds is consistent with the inter-stellar dust model of comets and probably reflects differences in composition of precursor dust. Preservation of this heterogeneity among submicron particles suggest the gentle formation of cometary, nucleus by aggregation of interstellar dust in the protosolar nebula without complete mixing or chemical homogenization at the submicron level.

Interstellar and Solar System Organic Matter Preserved in Interplanetary Dust

NASA Technical Reports Server (NTRS)

Messenger, Scott; Nakamura-Messenger, Keiko

2015-01-01

Interplanetary dust particles (IDPs) collected in the Earth's stratosphere derive from collisions among asteroids and by the disruption and outgassing of short-period comets. Chondritic porous (CP) IDPs are among the most primitive Solar System materials. CP-IDPs have been linked to cometary parent bodies by their mineralogy, textures, C-content, and dynamical histories. CP-IDPs are fragile, fine-grained (less than um) assemblages of anhydrous amorphous and crystalline silicates, oxides and sulfides bound together by abundant carbonaceous material. Ancient silicate, oxide, and SiC stardust grains exhibiting highly anomalous isotopic compositions are abundant in CP-IDPs, constituting 0.01 - 1 % of the mass of the particles. The organic matter in CP-IDPs is isotopically anomalous, with enrichments in D/H reaching 50x the terrestrial SMOW value and 15N/14N ratios up to 3x terrestrial standard compositions. These anomalies are indicative of low T (10-100 K) mass fractionation in cold molecular cloud or the outermost reaches of the protosolar disk. The organic matter shows distinct morphologies, including sub-um globules, bubbly textures, featureless, and with mineral inclusions. Infrared spectroscopy and mass spectrometry studies of organic matter in IDPs reveals diverse species including aliphatic and aromatic compounds. The organic matter with the highest isotopic anomalies appears to be richer in aliphatic compounds. These materials also bear similarities and differences with primitive, isotopically anomalous organic matter in carbonaceous chondrite meteorites. The diversity of the organic chemistry, morphology, and isotopic properties in IDPs and meteorites reflects variable preservation of interstellar/primordial components and Solar System processing. One unifying feature is the presence of sub-um isotopically anomalous organic globules among all primitive materials, including IDPs, meteorites, and comet Wild-2 samples returned by the Stardust mission.

Dust ablation on the giant planets: Consequences for stratospheric photochemistry

NASA Astrophysics Data System (ADS)

Moses, Julianne I.; Poppe, Andrew R.

2017-11-01

Ablation of interplanetary dust supplies oxygen to the upper atmospheres of Jupiter, Saturn, Uranus, and Neptune. Using recent dynamical model predictions for the dust influx rates to the giant planets (Poppe et al., 2016), we calculate the ablation profiles and investigate the subsequent coupled oxygen-hydrocarbon neutral photochemistry in the stratospheres of these planets. We find that dust grains from the Edgeworth-Kuiper Belt, Jupiter-family comets, and Oort-cloud comets supply an effective oxygen influx rate of 1.0-0.7+2.2 ×107 O atoms cm-2 s-1 to Jupiter, 7.4-5.1+16 ×104 cm-2 s-1 to Saturn, 8.9-6.1+19 ×104 cm-2 s-1 to Uranus, and 7.5-5.1+16 ×105 cm-2 s-1 to Neptune. The fate of the ablated oxygen depends in part on the molecular/atomic form of the initially delivered products, and on the altitude at which it was deposited. The dominant stratospheric products are CO, H2O, and CO2, which are relatively stable photochemically. Model-data comparisons suggest that interplanetary dust grains deliver an important component of the external oxygen to Jupiter and Uranus but fall far short of the amount needed to explain the CO abundance currently seen in the middle stratospheres of Saturn and Neptune. Our results are consistent with the theory that all of the giant planets have experienced large cometary impacts within the last few hundred years. Our results also suggest that the low background H2O abundance in Jupiter's stratosphere is indicative of effective conversion of meteoric oxygen to CO during or immediately after the ablation process - photochemistry alone cannot efficiently convert the H2O into CO on the giant planets.

OUTWARD MOTION OF POROUS DUST AGGREGATES BY STELLAR RADIATION PRESSURE IN PROTOPLANETARY DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tazaki, Ryo; Nomura, Hideko, E-mail: rtazaki@kusastro.kyoto-u.ac.jp

2015-02-01

We study the dust motion at the surface layer of protoplanetary disks. Dust grains in the surface layer migrate outward owing to angular momentum transport via gas-drag force induced by the stellar radiation pressure. In this study we calculate the mass flux of the outward motion of compact grains and porous dust aggregates by the radiation pressure. The radiation pressure force for porous dust aggregates is calculated using the T-Matrix Method for the Clusters of Spheres. First, we confirm that porous dust aggregates are forced by strong radiation pressure even if they grow to be larger aggregates, in contrast tomore » homogeneous and spherical compact grains, for which radiation pressure efficiency becomes lower when their sizes increase. In addition, we find that the outward mass flux of porous dust aggregates with monomer size of 0.1 μm is larger than that of compact grains by an order of magnitude at the disk radius of 1 AU, when their sizes are several microns. This implies that large compact grains like calcium-aluminum-rich inclusions are hardly transported to the outer region by stellar radiation pressure, whereas porous dust aggregates like chondritic-porous interplanetary dust particles are efficiently transported to the comet formation region. Crystalline silicates are possibly transported in porous dust aggregates by stellar radiation pressure from the inner hot region to the outer cold cometary region in the protosolar nebula.« less

Program manual for HILTOP, a heliocentric interplanetary low thrust trajectory optimization program. Part 1: User's guide

NASA Technical Reports Server (NTRS)

Mann, F. I.; Horsewood, J. L.

1974-01-01

A performance-analysis computer program, that was developed explicitly to generate optimum electric propulsion trajectory data for missions of interest in the exploration of the solar system is presented. The program was primarily designed to evaluate the performance capabilities of electric propulsion systems, and in the simulation of a wide variety of interplanetary missions. A numerical integration of the two-body, three-dimensional equations of motion and the Euler-Lagrange equations was used in the program. Transversality conditions which permit the rapid generation of converged maximum-payload trajectory data, and the optimization of numerous other performance indices for which no transversality conditions exist are included. The ability to simulate constrained optimum solutions, including trajectories having specified propulsion time and constant thrust cone angle, is also in the program. The program was designed to handle multiple-target missions with various types of encounters, such as rendezvous, stopover, orbital capture, and flyby. Performance requirements for a variety of launch vehicles can be determined.

Lunar far side surface navigation using Linked Autonomous Interplanetary Satellite Orbit Navigation (LiAISON)

NASA Astrophysics Data System (ADS)

Hesar, Siamak G.; Parker, Jeffrey S.; Leonard, Jason M.; McGranaghan, Ryan M.; Born, George H.

2015-12-01

We study the application of Linked Autonomous Interplanetary Satellite Orbit Navigation (LiAISON) to track vehicles on the far side of the lunar surface. The LiAISON architecture is demonstrated to achieve accurate orbit determination solutions for various mission scenarios in the Earth-Moon system. Given the proper description of the force field, LiAISON is capable of producing absolute orbit determination solutions using relative satellite-to-satellite tracking observations alone. The lack of direct communication between Earth-based tracking stations and the far side of the Moon provides an ideal opportunity for implementing LiAISON. This paper presents a novel approach to use the LiAISON architecture to perform autonomous navigation of assets on the lunar far side surface. Relative measurements between a spacecraft placed in an EML-2 halo orbit and lunar surface asset(s) are simulated and processed. Comprehensive simulation results show that absolute states of the surface assets are observable with an achieved accuracy of the position estimate on the order of tens of meters.

Structure of High Latitude Currents in Magnetosphere-Ionosphere Models

NASA Astrophysics Data System (ADS)

Wiltberger, M.; Rigler, E. J.; Merkin, V.; Lyon, J. G.

2017-03-01

Using three resolutions of the Lyon-Fedder-Mobarry global magnetosphere-ionosphere model (LFM) and the Weimer 2005 empirical model we examine the structure of the high latitude field-aligned current patterns. Each resolution was run for the entire Whole Heliosphere Interval which contained two high speed solar wind streams and modest interplanetary magnetic field strengths. Average states of the field-aligned current (FAC) patterns for 8 interplanetary magnetic field clock angle directions are computed using data from these runs. Generally speaking the patterns obtained agree well with results obtained from the Weimer 2005 computing using the solar wind and IMF conditions that correspond to each bin. As the simulation resolution increases the currents become more intense and narrow. A machine learning analysis of the FAC patterns shows that the ratio of Region 1 (R1) to Region 2 (R2) currents decreases as the simulation resolution increases. This brings the simulation results into better agreement with observational predictions and the Weimer 2005 model results. The increase in R2 current strengths also results in the cross polar cap potential (CPCP) pattern being concentrated in higher latitudes. Current-voltage relationships between the R1 and CPCP are quite similar at the higher resolution indicating the simulation is converging on a common solution. We conclude that LFM simulations are capable of reproducing the statistical features of FAC patterns.

Structure of high latitude currents in global magnetospheric-ionospheric models

USGS Publications Warehouse

Wiltberger, M; Rigler, E. J.; Merkin, V; Lyon, J. G

2016-01-01

Using three resolutions of the Lyon-Fedder-Mobarry global magnetosphere-ionosphere model (LFM) and the Weimer 2005 empirical model we examine the structure of the high latitude field-aligned current patterns. Each resolution was run for the entire Whole Heliosphere Interval which contained two high speed solar wind streams and modest interplanetary magnetic field strengths. Average states of the field-aligned current (FAC) patterns for 8 interplanetary magnetic field clock angle directions are computed using data from these runs. Generally speaking the patterns obtained agree well with results obtained from the Weimer 2005 computing using the solar wind and IMF conditions that correspond to each bin. As the simulation resolution increases the currents become more intense and narrow. A machine learning analysis of the FAC patterns shows that the ratio of Region 1 (R1) to Region 2 (R2) currents decreases as the simulation resolution increases. This brings the simulation results into better agreement with observational predictions and the Weimer 2005 model results. The increase in R2 current strengths also results in the cross polar cap potential (CPCP) pattern being concentrated in higher latitudes. Current-voltage relationships between the R1 and CPCP are quite similar at the higher resolution indicating the simulation is converging on a common solution. We conclude that LFM simulations are capable of reproducing the statistical features of FAC patterns.

Submicrometer Organic Grains: Widespread Constituents of the Early Solar System

NASA Technical Reports Server (NTRS)

Messenger, Scott; Nakamuri-Messenger, Keiko; Keller, Lindsay; Matrajt, Graciela; Clemett, Simon; Ito, Motoo

2007-01-01

Primitive meteorites and interplanetary dust particles (IDPs) contain remants of interstellar organic matter, marked by anomalous H and N isotopic ratios. These isotopic anomalies are attributed to mass fractionation during chemical reactions at cryogenic temperatures (10-100K) in a cold molecular cloud. Significant variations in the chemistry and isotopic compositions of organic compounds within and between these samples suggest varying histories of alteration and dilution of the presolar components. Recent studies have reported large H and N isotopic anomalies preserved in sub-m organic inclusions in both meteorites and IDPs. In the Tagish Lake meteorite, the largest H and N isotopic anomalies are associated with sub-m, hollow organic globules. The common physical, chemical, and isotopic characteristics of these globules suggest that they formed before being incorporated into their parent meteorite. These organic globules probably originated as organic ice coatings that formed on preexisting ice or mineral grains in a cold molecular cloud. Radiation driven photochemistry may have processed them into refractory organic grains. This model implies that submicrometer organic grains were widely distributed throughout the solar nebula during the epoch of planet formation. Submicrometer organic particles were detected by the Giotto and Vega encounters with comet Halley, termed CHON particles based on their major element chemistry. The first direct samples of cometary dust (comet Wild-2) were returned by the Stardust spacecraft in January 2006. These samples exhibit widely varying, fine grained mineralogy similar to anhydrous IDPs, including submicrometer carbonaceous grains. The submicrometer organic grains from comet Wild-2 exhibit H and N isotopic anomalies of similar magnitude to those commonly observed in primitive meteorites and IDPs. Isotopically anomalous, submicrometer organic grains have now been observed in meteorites, IDPs, the Oort-cloud comet Halley, and the Kuiper-belt comet Wild-2, suggesting that such grains were prevalent throughout the protoplanetary disk.

Hyperdust : An advanced in-situ detection and chemical analysis of microparticles in space

NASA Astrophysics Data System (ADS)

Sternovsky, Z.; Gruen, E.; Horanyi, M.; Kempf, S.; Maute, K.; Srama, R.

2014-12-01

Interplanetary dust that originates from comets and asteroids may be in different stages of Solar System evolution. Atmosphereless planetary bodies, e.g., planetary satellites, asteroids, or Kuiper belt objects are enshrouded in clouds of dust released by meteoroid impacts or by volcanism. The ejecta grains are samples from the surface of these objects and their analysis can be performed from orbit or flyby to determine the surface composition, interior structure and ongoing geochemical processes. Early dust mass spectrometers on the Halley missions had sufficient mass resolution in order to provide important cosmochemical information in the near-comet high dust flux environment. The Ulysses dust detector discovered interstellar grains within the planetary system (Gruen et al. A&A, 1994) and its twin detector on Galileo discovered the tenuous dust clouds around the Galilean satellites (Krueger et al., Icarus, 2003). The similar-sized Cosmic Dust Analyzer onboard the Cassini mission combined a highly sensitive dust detector with a low-mass resolution mass spectrometer. Compositional dust measurements from this instrument probed the deep interior of Saturn's Enceladus satellite (Postberg et al., Nature, 2009). Based on this experience new instrumentation was developed that combined the best attributes of all these predecessors and exceeded their capabilities in accurate trajectory determination. The Hyperdust instrument is a combination of a Dust Trajectory Sensor (DTS) together with an analyzer for the chemical composition of dust particles in space. Dust particles' trajectories are determined by the measurement of induced electric signals. Large area chemical analyzers of 0.1 m2 sensitive area have been tested at a dust accelerator and it was demonstrated that they have sufficient mass resolution to resolve ions with atomic mass number >100. The Hyperdust instrument is capable of distinguishing interstellar and interplanetary grains based on their trajectory composition information. In orbit or flyby near airless planetary bodies the instrument can map the surface compositional down to a spatial resolution of ~10 km. The Hyperdust instrument is currently being developed to TRL 6 funded by NASA's MatISSE program to be a low-mass, high performance instrument for future in-situ exploration.

A Database of Interplanetary and Interstellar Dust Detected by the Wind Spacecraft

NASA Technical Reports Server (NTRS)

Malaspina, David M.; Wilson, Lynn B., III

2016-01-01

It was recently discovered that the WAVES instrument on the Wind spacecraft has been detecting, in situ, interplanetary and interstellar dust of approximately 1 micron radius for the past 22 years. These data have the potential to enable advances in the study of cosmic dust and dust-plasma coupling within the heliosphere due to several unique properties: the Wind dust database spans two full solar cycles; it contains over 107,000 dust detections; it contains information about dust grain direction of motion; it contains data exclusively from the space environment within 350 Earth radii of Earth; and it overlaps by 12 years with the Ulysses dust database. Further, changes to the WAVES antenna response and the plasma environment traversed by Wind over the lifetime of the Wind mission create an opportunity for these data to inform investigations of the physics governing the coupling of dust impacts on spacecraft surfaces to electric field antennas. A Wind dust database has been created to make the Wind dust data easily accessible to the heliophysics community and other researchers. This work describes the motivation, methodology, contents, and accessibility of the Wind dust database.

Wind Observations of Wave Heating and/or Particle Energization at Supercritical Interplanetary Shocks

NASA Technical Reports Server (NTRS)

Wilson, Lynn Bruce, III; Szabo, Adam; Koval, Andriy; Cattell, Cynthia A.; Kellogg, Paul J.; Goetz, Keith; Breneman, Aaron; Kersten, Kris; Kasper, Justin C.; Pulupa, Marc

2011-01-01

We present the first observations at supercritical interplanetary shocks of large amplitude (> 100 mV/m pk-pk) solitary waves, approx.30 mV/m pk-pk waves exhibiting characteristics consistent with electron Bernstein waves, and > 20 nT pk-pk electromagnetic lower hybrid-like waves, with simultaneous evidence for wave heating and particle energization. The solitary waves and the Bernstein-like waves were likely due to instabilities driven by the free energy provided by reflected ions [Wilson III et al., 2010]. They were associated with strong particle heating in both the electrons and ions. We also show a case example of parallel electron energization and perpendicular ion heating due to a electromagnetic lower hybrid-like wave. Both studies provide the first experimental evidence of wave heating and/or particle energization at interplanetary shocks. Our experimental results, together with the results of recent Vlasov [Petkaki and Freeman, 2008] and PIC [Matsukyo and Scholer, 2006] simulations using realistic mass ratios provide new evidence to suggest that the importance of wave-particle dissipation at shocks may be greater than previously thought.

Probing interferometric parallax with interplanetary spacecraft

NASA Astrophysics Data System (ADS)

Rodeghiero, G.; Gini, F.; Marchili, N.; Jain, P.; Ralston, J. P.; Dallacasa, D.; Naletto, G.; Possenti, A.; Barbieri, C.; Franceschini, A.; Zampieri, L.

2017-07-01

We describe an experimental scenario for testing a novel method to measure distance and proper motion of astronomical sources. The method is based on multi-epoch observations of amplitude or intensity correlations between separate receiving systems. This technique is called Interferometric Parallax, and efficiently exploits phase information that has traditionally been overlooked. The test case we discuss combines amplitude correlations of signals from deep space interplanetary spacecraft with those from distant galactic and extragalactic radio sources with the goal of estimating the interplanetary spacecraft distance. Interferometric parallax relies on the detection of wavefront curvature effects in signals collected by pairs of separate receiving systems. The method shows promising potentialities over current techniques when the target is unresolved from the background reference sources. Developments in this field might lead to the construction of an independent, geometrical cosmic distance ladder using a dedicated project and future generation instruments. We present a conceptual overview supported by numerical estimates of its performances applied to a spacecraft orbiting the Solar System. Simulations support the feasibility of measurements with a simple and time-saving observational scheme using current facilities.

Are Polar Field Magnetic Flux Concentrations Responsible for Missing Interplanetary Flux?

NASA Astrophysics Data System (ADS)

Linker, Jon A.; Downs, C.; Mikic, Z.; Riley, P.; Henney, C. J.; Arge, C. N.

2012-05-01

Magnetohydrodynamic (MHD) simulations are now routinely used to produce models of the solar corona and inner heliosphere for specific time periods. These models typically use magnetic maps of the photospheric magnetic field built up over a solar rotation, available from a number of ground-based and space-based solar observatories. The line-of-sight field at the Sun's poles is poorly observed, and the polar fields in these maps are filled with a variety of interpolation/extrapolation techniques. These models have been found to frequently underestimate the interplanetary magnetic flux (Riley et al., 2012, in press, Stevens et al., 2012, in press) near the minimum part of the cycle unless mitigating correction factors are applied. Hinode SOT observations indicate that strong concentrations of magnetic flux may be present at the poles (Tsuneta et al. 2008). The ADAPT flux evolution model (Arge et al. 2010) also predicts the appearance of such concentrations. In this paper, we explore the possibility that these flux concentrations may account for a significant amount of magnetic flux and alleviate discrepancies in interplanetary magnetic flux predictions. Research supported by AFOSR, NASA, and NSF.

Comparison of Meteoroid Flux Models for Near Earth Space

NASA Technical Reports Server (NTRS)

Drolshagen, G.; Liou, J.-C.; Dikarev, V.; Landgraf, M.; Krag, H.; Kuiper, W.

2007-01-01

Over the last decade several new models for the sporadic interplanetary meteoroid flux have been developed. These include the Meteoroid Engineering Model (MEM), the Divine-Staubach model and the Interplanetary Meteoroid Engineering Model (IMEM). They typically cover mass ranges from 10-12 g (or lower) to 1 g and are applicable for model specific sun distance ranges between 0.2 A.U. and 10 A.U. Near 1 A.U. averaged fluxes (over direction and velocities) for all these models are tuned to the well established interplanetary model by Gr?n et. al. However, in many respects these models differ considerably. Examples are the velocity and directional distributions and the assumed meteoroid sources. In this paper flux predictions by the various models to Earth orbiting spacecraft are compared. Main differences are presented and analysed. The persisting differences even for near Earth space can be seen as surprising in view of the numerous ground based (optical, radar) and in-situ (captured IDPs, in-situ detectors and analysis of retrieved hardware) measurements and simulations. Remaining uncertainties and potential additional studies to overcome the existing model discrepancies are discussed.

Observation and Numerical Simulation of Cavity Mode Oscillations Excited by an Interplanetary Shock

NASA Astrophysics Data System (ADS)

Takahashi, Kazue; Lysak, Robert; Vellante, Massimo; Kletzing, Craig A.; Hartinger, Michael D.; Smith, Charles W.

2018-03-01

Cavity mode oscillations (CMOs) are basic magnetohydrodynamic eigenmodes in the magnetosphere predicted by theory and are expected to occur following the arrival of an interplanetary shock. However, observational studies of shock-induced CMOs have been sparse. We present a case study of a dayside ultralow-frequency wave event that exhibited CMO properties. The event occurred immediately following the arrival of an interplanetary shock at 0829 UT on 15 August 2015. The shock was observed in the solar wind by the Time History of Events and Macroscale Interactions during Substorms-B and -C spacecraft, and magnetospheric ultralow-frequency waves were observed by multiple spacecraft including the Van Allen Probe-A and Van Allen Probe-B spacecraft, which were located in the dayside plasmasphere at L ˜1.4 and L ˜ 2.4, respectively. Both Van Allen Probes spacecraft detected compressional poloidal mode oscillations at ˜13 mHz (fundamental) and ˜26 mHz (second harmonic). At both frequencies, the azimuthal component of the electric field (Eϕ) lagged behind the compressional component of the magnetic field (Bμ) by ˜90°. The frequencies and the Eϕ-Bμ relative phase are in good agreement with the CMOs generated in a dipole magnetohydrodynamic simulation that incorporates a realistic plasma mass density distribution and ionospheric boundary condition. The oscillations were also detected on the ground by the European quasi-Meridional Magnetometer Array, which was located near the magnetic field footprints of the Van Allen Probes spacecraft.

SEM and TEM Observation of the Surfaces of the Fine-Grained Particles Retrieved from the Muses-C Regio on the Asteroid 25413 Itokawa

NASA Technical Reports Server (NTRS)

Noguchi, T.; Nakamura, T.; Zolensky, Michael E.; Tanaka, M.; Hashimoto, T.; Konno, M.; Nakato, A.; Ogami, T.; Fujimura, A.; Abe, M.;

Si Isotopes of Brownleeite

NASA Technical Reports Server (NTRS)

Nakamura-Messenger, K.; Messenger, Scott R.; Ito, M.; Keller, L. P.; Clemett, S. J.; Jones, J. H.; Tatsuoka, H.; Zolensky, M. E.; Tatsuoka, H.

2010-01-01

Brownleeite is a manganese silicide, ideally stoichiometric MnSi, not previously observed in nature until its discovery within an interplanetary dust particle (IDP) that likely originated from a comet [1]. Three discrete brownleeite grains in the IDP L2055 I3 (4 microns in size, hereafter IDP I3) were identified with maximum dimensions of 100, 250 and 600 nm and fully analyzed using scanning-transmission electron microscopy (STEM) [1]. One of the grains (100 nm in size) was poikilitically enclosed by low-Fe, Mn-enriched (LIME) olivine. LIME olivine is epitaxial to the brownleeite with the brownleeite (200) parallel to the olivine c* [1]. LIME olivine is an enigmatic phase first reported from chondritic porous IDPs and some unequilibrated ordinary chondrites [ 2], that is commonly observed in chondritic-porous IDPs. Recently, LIME olivine has been also found in comet Wild-2 (Stardust) samples [3], indicating that LIME olivine is a common mineral component of comets. LIME olivine has been proposed to form as a high temperature condensate in the protosolar nebula [2]. Brownleeite grains also likely formed as high-temperature condensates either in the early Solar System or in the outflow of an evolved star or supernova explosion [1]. The isotopic composition of the brownleeite grains may strongly constrain their ultimate source. To test this hypothesis, we performed isotopic analyses of the brownleeite and the associated LIME olivine, using the NASA/JSC NanoSIMS 50L ion microprobe.

Pre-accretional sorting of grains in the outer solar nebula

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wozniakiewicz, P. J.; Bradley, J. P.; Ishii, H. A.

2013-12-20

Despite their micrometer-scale dimensions and nanogram masses, chondritic porous interplanetary dust particles (CP IDPs) are an important class of extraterrestrial material since their properties are consistent with a cometary origin and they show no evidence of significant post-accretional parent body alteration. Consequently, they can provide information about grain accretion in the comet-forming region of the outer solar nebula. We have previously reported our comparative study of the sizes and size distributions of crystalline silicate and sulfide grains in CP IDPs, in which we found these components exhibit a size-density relationship consistent with having been sorted together prior to accretion. Heremore » we extend our data set and include GEMS (glass with embedded metal and sulfide), the most abundant amorphous silicate phase observed in CP IDPs. We find that while the silicate and sulfide sorting trend previously observed is maintained, the GEMS size data do not exhibit any clear relationship to these crystalline components. Therefore, GEMS do not appear to have been sorted with the silicate and sulfide crystals. The disparate sorting trends observed in GEMS and the crystalline grains in CP IDPs present an interesting challenge for modeling early transport and accretion processes. They may indicate that several sorting mechanisms operated on these CP IDP components, or alternatively, they may simply be a reflection of different source environments.« less

Clay minerals in primitive meteorites and interplanetary dust 2. Smectites and micas

NASA Technical Reports Server (NTRS)

Keller, L. P.; Zolensky, M. E.

1991-01-01

The classification is briefly summarized of stony meteorites and cosmic dust, and the mineralogy and chemistry is described of serpentine group minerals. The occurrence of smectites and micas in extraterrestrial materials is examined. The characterization of fine grained minerals in meteorites and IDPs relies heavily on electron beam instruments, especially the transmission electron microscope (TEM). Typically, phyllosilicates are identified by a combination of high resolution imaging of basal spacings, electron diffraction, and chemical analysis. Smectites can be difficult to differentiate from micas because the smectites lose their interlayer water and the interlayer partly collapse in the high vacuum of the TEM.

Simulation and Experimental Studies on Grain Selection and Structure Design of the Spiral Selector for Casting Single Crystal Ni-Based Superalloy.

PubMed

Zhang, Hang; Xu, Qingyan

2017-10-27

Grain selection is an important process in single crystal turbine blades manufacturing. Selector structure is a control factor of grain selection, as well as directional solidification (DS). In this study, the grain selection and structure design of the spiral selector were investigated through experimentation and simulation. A heat transfer model and a 3D microstructure growth model were established based on the Cellular automaton-Finite difference (CA-FD) method for the grain selector. Consequently, the temperature field, the microstructure and the grain orientation distribution were simulated and further verified. The average error of the temperature result was less than 1.5%. The grain selection mechanisms were further analyzed and validated through simulations. The structural design specifications of the selector were suggested based on the two grain selection effects. The structural parameters of the spiral selector, namely, the spiral tunnel diameter ( d w ), the spiral pitch ( h b ) and the spiral diameter ( h s ), were studied and the design criteria of these parameters were proposed. The experimental and simulation results demonstrated that the improved selector could accurately and efficiently produce a single crystal structure.

Simulation and Experimental Studies on Grain Selection and Structure Design of the Spiral Selector for Casting Single Crystal Ni-Based Superalloy

PubMed Central

Zhang, Hang; Xu, Qingyan

2017-01-01

Grain selection is an important process in single crystal turbine blades manufacturing. Selector structure is a control factor of grain selection, as well as directional solidification (DS). In this study, the grain selection and structure design of the spiral selector were investigated through experimentation and simulation. A heat transfer model and a 3D microstructure growth model were established based on the Cellular automaton-Finite difference (CA-FD) method for the grain selector. Consequently, the temperature field, the microstructure and the grain orientation distribution were simulated and further verified. The average error of the temperature result was less than 1.5%. The grain selection mechanisms were further analyzed and validated through simulations. The structural design specifications of the selector were suggested based on the two grain selection effects. The structural parameters of the spiral selector, namely, the spiral tunnel diameter (dw), the spiral pitch (hb) and the spiral diameter (hs), were studied and the design criteria of these parameters were proposed. The experimental and simulation results demonstrated that the improved selector could accurately and efficiently produce a single crystal structure. PMID:29077067

STOCK: Structure mapper and online coarse-graining kit for molecular simulations

DOE PAGES

Bevc, Staš; Junghans, Christoph; Praprotnik, Matej

2015-03-15

We present a web toolkit STructure mapper and Online Coarse-graining Kit for setting up coarse-grained molecular simulations. The kit consists of two tools: structure mapping and Boltzmann inversion tools. The aim of the first tool is to define a molecular mapping from high, e.g. all-atom, to low, i.e. coarse-grained, resolution. Using a graphical user interface it generates input files, which are compatible with standard coarse-graining packages, e.g. VOTCA and DL_CGMAP. Our second tool generates effective potentials for coarse-grained simulations preserving the structural properties, e.g. radial distribution functions, of the underlying higher resolution model. The required distribution functions can be providedmore » by any simulation package. Simulations are performed on a local machine and only the distributions are uploaded to the server. The applicability of the toolkit is validated by mapping atomistic pentane and polyalanine molecules to a coarse-grained representation. Effective potentials are derived for systems of TIP3P (transferable intermolecular potential 3 point) water molecules and salt solution. The presented coarse-graining web toolkit is available at http://stock.cmm.ki.si.« less

Particle models for discrete element modeling of bulk grain properties of wheat kernels

USDA-ARS?s Scientific Manuscript database

Recent research has shown the potential of discrete element method (DEM) in simulating grain flow in bulk handling systems. Research has also revealed that simulation of grain flow with DEM requires establishment of appropriate particle models for each grain type. This research completes the three-p...

Computer simulation of a geomagnetic substorm

NASA Technical Reports Server (NTRS)

Lyon, J. G.; Brecht, S. H.; Huba, J. D.; Fedder, J. A.; Palmadesso, P. J.

1981-01-01

A global two-dimensional simulation of a substormlike process occurring in earth's magnetosphere is presented. The results are consistent with an empirical substorm model - the neutral-line model. Specifically, the introduction of a southward interplanetary magnetic field forms an open magnetosphere. Subsequently, a substorm neutral line forms at about 15 earth radii or closer in the magnetotail, and plasma sheet thinning and plasma acceleration occur. Eventually the substorm neutral line moves tailward toward its presubstorm position.

Stress Distribution During Deformation of Polycrystalline Aluminum by Molecular-Dynamics and Finite-Element Modeling

NASA Technical Reports Server (NTRS)

Yamakov, V.; Saether, E.; Phillips, D.; Glaessgen, E. H.

2004-01-01

In this paper, a multiscale modelling strategy is used to study the effect of grain-boundary sliding on stress localization in a polycrystalline microstructure with an uneven distribution of grain size. The development of the molecular dynamics (MD) analysis used to interrogate idealized grain microstructures with various types of grain boundaries and the multiscale modelling strategies for modelling large systems of grains is discussed. Both molecular-dynamics and finite-element (FE) simulations for idealized polycrystalline models of identical geometry are presented with the purpose of demonstrating the effectiveness of the adapted finite-element method using cohesive zone models to reproduce grain-boundary sliding and its effect on the stress distribution in a polycrystalline metal. The yield properties of the grain-boundary interface, used in the FE simulations, are extracted from a MD simulation on a bicrystal. The models allow for the study of the load transfer between adjacent grains of very different size through grain-boundary sliding during deformation. A large-scale FE simulation of 100 grains of a typical microstructure is then presented to reveal that the stress distribution due to grain-boundary sliding during uniform tensile strain can lead to stress localization of two to three times the background stress, thus suggesting a significant effect on the failure properties of the metal.

Low-temperature crystallization of silicate dust in circumstellar disks.

PubMed

Molster, F J; Yamamura, I; Waters, L B; Tielens, A G; de Graauw, T; de Jong, T; de Koter, A; Malfait, K; van den Ancker, M E; van Winckel, H; Voors, R H; Waelkens, C

1999-10-07

Silicate dust in the interstellar medium is observed to be amorphous, yet silicate dust in comets and interplanetary dust particles is sometimes partially crystalline. The dust in disks that are thought to be forming planets around some young stars also appears to be partially crystalline. These observations suggest that as the dust goes from the precursor clouds to a planetary system, it must undergo some processing, but the nature and extent of this processing remain unknown. Here we report observations of highly crystalline silicate dust in the disks surrounding binary red-giant stars. The dust was created in amorphous form in the outer atmospheres of the red giants, and therefore must be processed in the disks to become crystalline. The temperatures in these disks are too low for the grains to anneal; therefore, some low-temperature process must be responsible. As the physical properties of the disks around young stars and red giants are similar, our results suggest that low-temperature crystallization of silicate grains also can occur in protoplanetary systems.

Aerospace Medicine and Biology: A Continuing Bibliography with Indexes, Supplement 194

NASA Technical Reports Server (NTRS)

1979-01-01

Articles on the biological, physiological, psychological, and environmental effects to which man is subjected to during and following simulated or actual flight in the earth's atmosphere or in interplanetary space are presented. The emphasis is on applied research more than fundamental studies or theoretical principles.

Multiscale Modeling of Grain-Boundary Fracture: Cohesive Zone Models Parameterized From Atomistic Simulations

NASA Technical Reports Server (NTRS)

Glaessgen, Edward H.; Saether, Erik; Phillips, Dawn R.; Yamakov, Vesselin

2006-01-01

A multiscale modeling strategy is developed to study grain boundary fracture in polycrystalline aluminum. Atomistic simulation is used to model fundamental nanoscale deformation and fracture mechanisms and to develop a constitutive relationship for separation along a grain boundary interface. The nanoscale constitutive relationship is then parameterized within a cohesive zone model to represent variations in grain boundary properties. These variations arise from the presence of vacancies, intersticies, and other defects in addition to deviations in grain boundary angle from the baseline configuration considered in the molecular dynamics simulation. The parameterized cohesive zone models are then used to model grain boundaries within finite element analyses of aluminum polycrystals.

Coordinated STEM/FIB/NanoSIMS Analyses of Presolar Silicates in Comet Dust and Primitive Meteorites

NASA Technical Reports Server (NTRS)

Keller, Lindsay; Nguyen, A.; Rahman, Z.; Messenger, S.

2012-01-01

Silicate grains were among the most abundant mineralogical building blocks of our Solar System. These grains were the detritus from earlier generations of stars that have been recycled in the early solar nebula. Rare sub-micrometer survivors of this processing have been identified in meteorites, micrometeorites and interplanetary dust particles (IDPs). These silicate grains are recognized as presolar in origin because of their extremely anomalous isotopic compositions that reflect nucleosynthetic processes in their stellar sources (evolved stars, novae and supernovae). We perform coordinated chemical, mineralogical and isotopic studies of these grains to determine their origins and histories. We examine the complex mineralogy and petrography of presolar silicates using imaging, diffraction and chemical data obtained from thin sections with the JSC JEOL 2500 field-emission STEM equipped with a Noran thin window energy dispersive x-ray (EDX) spectrometer and a Gatan Tridiem GIF. Quantitative element x-ray maps (spectrum images) are acquired by rastering a 4 nm incident probe whose dwell time is minimized to avoid beam damage and element diffusion during mapping. Successive image layers are acquired and combined in order to achieve approx 1% counting statistics for major elements. The IDP samples are prepared by ultramicrotomy of particles embedded in epoxy or elemental sulfur. After EDX mapping, the sections are subjected to C, N, and O isotopic imaging with the JSC NanoSIMS 50L ion microprobe. We prepare sections of some meteorite grains using the JSC FEI Quanta 3D focused ion beam (FIB) instrument. The specimen surface is protected from the FIB milling process by layers of electron beam-deposited C and Pt followed by an ion-deposited Pt layer. We also use the FIB to preferentially remove surrounding grains to reduce the background in subsequent NanoSIMS measurements. For mineralogical studies, we again employ the FIB instrument to deposit a protective cap over the grain of interest and then extract the grain and thin it to electron transparency for TEM analysis.

High abundances of presolar grains and 15N-rich organic matter in CO3.0 chondrite Dominion Range 08006

NASA Astrophysics Data System (ADS)

Nittler, Larry R.; Alexander, Conel M. O'D.; Davidson, Jemma; Riebe, My E. I.; Stroud, Rhonda M.; Wang, Jianhua

2018-04-01

NanoSIMS C-, N-, and O-isotopic mapping of matrix in CO3.0 chondrite Dominion Range (DOM) 08006 revealed it to have in its matrix the highest abundance of presolar O-rich grains (257 +76/-96 ppm, 2σ) of any meteorite. It also has a matrix abundance of presolar SiC of 35 (+25/-17, 2σ) ppm, similar to that seen across primitive chondrite classes. This provides additional support to bulk isotopic and petrologic evidence that DOM 08006 is the most primitive known CO meteorite. Transmission electron microscopy of five presolar silicate grains revealed one to have a composite mineralogy similar to larger amoeboid olivine aggregates and consistent with equilibrium condensation, two non-stoichiometric amorphous grains, and two olivine grains, though one is identified as such solely based on its composition. We also found insoluble organic matter (IOM) to be present primarily as sub-micron inclusions with ranges of C- and N-isotopic anomalies similar to those seen in primitive CR chondrites and interplanetary dust particles. In contrast to other primitive extraterrestrial materials, H isotopic imaging showed normal and homogeneous D/H. Most likely, DOM 08006 and other CO chondrites accreted a similar complement of primitive and isotopically anomalous organic matter to that found in other chondrite classes and IDPs, but the very limited amount of thermal metamorphism experienced by DOM 08006 has caused loss of D-rich organic moieties, while not substantially affecting either the molecular carriers of C and N anomalies or most inorganic phases in the meteorite. One C-rich grain that was highly depleted in 13C and 15N was identified; we propose it originated in the Sun's parental molecular cloud.

Multiple generations of grain aggregation in different environments preceded solar system body formation.

PubMed

Ishii, Hope A; Bradley, John P; Bechtel, Hans A; Brownlee, Donald E; Bustillo, Karen C; Ciston, James; Cuzzi, Jeffrey N; Floss, Christine; Joswiak, David J

2018-06-26

The solar system formed from interstellar dust and gas in a molecular cloud. Astronomical observations show that typical interstellar dust consists of amorphous ( a -) silicate and organic carbon. Bona fide physical samples for laboratory studies would yield unprecedented insight about solar system formation, but they were largely destroyed. The most likely repositories of surviving presolar dust are the least altered extraterrestrial materials, interplanetary dust particles (IDPs) with probable cometary origins. Cometary IDPs contain abundant submicron a- silicate grains called GEMS (glass with embedded metal and sulfides), believed to be carbon-free. Some have detectable isotopically anomalous a- silicate components from other stars, proving they are preserved dust inherited from the interstellar medium. However, it is debated whether the majority of GEMS predate the solar system or formed in the solar nebula by condensation of high-temperature (>1,300 K) gas. Here, we map IDP compositions with single nanometer-scale resolution and find that GEMS contain organic carbon. Mapping reveals two generations of grain aggregation, the key process in growth from dust grains to planetesimals, mediated by carbon. GEMS grains, some with a- silicate subgrains mantled by organic carbon, comprise the earliest generation of aggregates. These aggregates (and other grains) are encapsulated in lower-density organic carbon matrix, indicating a second generation of aggregation. Since this organic carbon thermally decomposes above ∼450 K, GEMS cannot have accreted in the hot solar nebula, and formed, instead, in the cold presolar molecular cloud and/or outer protoplanetary disk. We suggest that GEMS are consistent with surviving interstellar dust, condensed in situ, and cycled through multiple molecular clouds. Copyright © 2018 the Author(s). Published by PNAS.

Laboratory Analysis of Silicate Stardust Grains of Diverse Stellar Origins

NASA Technical Reports Server (NTRS)

Nguyen, Ann N.; Keller, Lindsay P.; Nakamura-Messenger, Keiko

2016-01-01

Silicate dust is ubiquitous in a multitude of environments across the cosmos, including evolved oxygen-rich stars, interstellar space, protoplanetary disks, comets, and asteroids. The identification of bona fide silicate stardust grains in meteorites, interplanetary dust particles, micrometeorites, and dust returned from comet Wild 2 by the Stardust spacecraft has revolutionized the study of stars, interstellar space, and the history of dust in the Galaxy. These stardust grains have exotic isotopic compositions that are records of nucleosynthetic processes that occurred in the depths of their now extinct parent stars. Moreover, the chemical compositions and mineralogies of silicate stardust are consequences of the physical and chemical nature of the stellar condensation environment, as well as secondary alteration processes that can occur in interstellar space, the solar nebula, and on the asteroid or comet parent body in which they were incorporated. In this talk I will discuss our use of advanced nano-scale instrumentation in the laboratory to conduct coordinated isotopic, chemical, and mineralogical analyses of silicate stardust grains from AGB stars, supernovae, and novae. By analyzing the isotopic compositions of multiple elements in individual grains, we have been able to constrain their stellar sources, explore stellar nucleosynthetic and mixing processes, and Galactic chemical evolution. Through our mineralogical studies, we have found these presolar silicate grains to have wide-ranging chemical and mineral characteristics. This diversity is the result of primary condensation characteristics and in some cases secondary features imparted by alteration in space and in our Solar System. The laboratory analysis of actual samples of stars directly complements astronomical observations and astrophysical models and offers an unprecedented level of detail into the lifecycles of dust in the Galaxy.

Cohesion of Mm- to Cm-Sized Asteroid Simulant Grains: An Experimental Study

NASA Astrophysics Data System (ADS)

Brisset, Julie; Colwell, Joshua E.; Dove, Adrienne; Jarmak, Stephanie; Anderson, Seamus

2017-10-01

The regolith covering the surfaces of asteroids and planetary satellites is very different from terrestrial soil particles and subject to environmental conditions very different from what is found on Earth. The loose, unconsolidated granular material has angular-shaped grains and a broad size distribution. On small and airless bodies (<10 km), the solar wind leads to a depletion of fine grains (<100µm) on the surface. Ground observations of the two asteroids currently targeted by spacecraft, Ryugu (Hayabusa-2) and Bennu (OSIRIS-REx), indicate that their surfaces could be covered in mm- to cm-sized regolith grains. As these small bodies have surface gravity levels below 10-5g, g being the Earth surface gravity, the cohesion behavior of the regolith grains will dictate the asteroid’s surface morphology and its response to impact or spacecraft contact.Previous laboratory experiments on low-velocity impacts into regolith simulant with grain sizes <250 µm have revealed a transition of the grain behavior from a gravity-dominated regime to a cohesion-dominated regime when the local gravity level reaches values below 10-3g. This is in good agreement with analytical and simulation studies for these grain sizes. From the expected grain sizes at the surfaces of Ryugu and Bennu, we have now focused on larger grain sizes ranging from mm to cm. We have carried out a series of experiments to study the cohesion behavior of such larger grains of asteroid regolith simulant. The simulant used was CI Orgueil of Deep Space Industries. Experiments included laboratory tabletop avalanching, compression and shear force measurements, as well as low-velocity impacts under microgravity.Our goal is to determine if the grain size distribution has an influence on the cohesion behavior of the regolith and if we can validate numerical simulation results with experimental measurements. We will discuss the implications of our results for sample return or landing missions to small bodies such as asteroids or Martian moons.

Effect of Strain Restored Energy on Abnormal Grain Growth in Mg Alloy Simulated by Phase Field Methods

NASA Astrophysics Data System (ADS)

Wu, Yan; Huang, Yuan-yuan

2018-03-01

Abnormal grain growth of single phase AZ31 Mg alloy in the spatio-temporal process has been simulated by phase field models, and the influencing factors of abnormal grain growth are studied in order to find the ways to control secondary recrystallization in the microstructure. The study aims to find out the mechanisms for abnormal grain growth in real alloys. It is shown from the simulated results that the abnormal grain growth can be controlled by the strain restored energy. Secondary recrystallization after an annealing treatment can be induced if there are grains of a certain orientation in the microstructure with local high restored energy. However, if the value of the local restored energy at a certain grain orientation is not greater than 1.1E 0, there may be no abnormal grain growth in the microstructure.

Orientation influence on grain size-effects in ultrafine-grained magnesium

DOE PAGES

Fan, Haidong; Aubry, Sylvie; Arsenlis, A.; ...

2014-11-08

The mechanical behavior of ultrafine-grained magnesium was studied by discrete dislocation dynamics (DDD) simulations. Our results show basal slip yields a strong size effect, while prismatic and pyramidal slips produce a weak one. We developed a new size-strength model that considers dislocation transmission across grain boundaries. Good agreement between this model, current DDD simulations and previous experiments is observed. These results reveal that the grain size effect depends on 3 factors: Peierls stress, dislocation source strength and grain boundary strength.

Diffusion-coupled cohesive interface simulations of stress corrosion intergranular cracking in polycrystalline materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pu, Chao; Gao, Yanfei; Wang, Yanli

To study the stress corrosion intergranular cracking mechanism, a diffusion-coupled cohesive zone model (CZM) is proposed for the simulation of the stress-assisted diffusional process along grain boundaries and the mechanical response of grain boundary sliding and separation. This simulation methodology considers the synergistic effects of impurity diffusion driven by pressure gradient and degradation of grain boundary strength by impurity concentration. The diffusion-coupled CZM is combined with crystal plasticity finite element model (CPFEM) to simulate intergranular fracture of polycrystalline material under corrosive environment. Significant heterogeneity of the stress field and extensive impurity accumulation is observed at grain boundaries and junction points.more » Deformation mechanism maps are constructed with respect to the grain boundary degradation factor and applied strain rate, which dictate the transition from internal to near-surface intergranular fracture modes under various strain amplitudes and grain sizes.« less

The Mineralogy of Circumstellar Silicates Preserved in Cometary Dust

NASA Technical Reports Server (NTRS)

Keller, L. P.; Messenger, S.

2010-01-01

Interplanetary dust particles (IDPs) contain a record of the building blocks of the solar system including presolar grains, molecular cloud material, and materials formed in the early solar nebula. Cometary IDPs have remained relatively unaltered since their accretion because of the lack of parent body thermal and aqueous alteration. We are using coordinated transmission electron microscope (TEM) and ion microprobe studies to establish the origins of the various components within cometary IDPs. Of particular interest is the nature and abundance of presolar silicates in these particles because astronomical observations suggest that crystalline and amorphous silicates are the dominant grain types produced in young main sequence stars and evolved O-rich stars. Five circumstellar grains have been identified including three amorphous silicate grains and two polycrystalline aggregates. All of these grains are between 0.2 and 0.5 micrometers in size. The isotopic compositions of all five presolar silicate grains fall within the range of presolar oxides and silicates, having large (17)O-enrichments and normal (18)O/(16)O ratios (Group 1 grains from AGB and RG stars). The amorphous silicates are chemically heterogeneous and contain nanophase FeNi metal and FeS grains in a Mg-silicate matrix. Two of the amorphous silicate grains are aggregates with subgrains showing variable Mg/Si ratios in chemical maps. The polycrystalline grains show annealed textures (equilibrium grains boundaries, uniform Mg/Fe ratios), and consist of 50-100 nm enstatite and pyrrhotite grains with lesser forsterite. One of the polycrystalline aggregates contains a subgrain of diopside. The polycrystalline aggregates form by subsolidus annealing of amorphous precursors. The bulk compositions of the five grains span a wide range in Mg/Si ratios from 0.4 to 1.2 (avg. 0.86). The average Fe/Si (0.40) and S/Si (0.21) ratios show a much narrower range of values and are approximately 50% of their solar abundances. The latter observation may indicate a decoupling of the silicate and sulfide components in grains that condense in stellar outflows. The amorphous silicate grains described here were not extensively affected by irradiation, sputtering, or thermal processing and may represent relatively pristine circumstellar grains. They are strong candidates for the "dirty silicates" in astronomical observations of circumstellar dust shells. The polycrystalline grains were originally amorphous silicate grains that were likely annealed in the early solar nebula but the processing was not sufficient to erase their anomalous oxygen isotopic compositions.

H ATOM IRRADIATION OF CARBON GRAINS UNDER SIMULATED DENSE INTERSTELLAR MEDIUM CONDITIONS: THE EVOLUTION OF ORGANICS FROM DIFFUSE INTERSTELLAR CLOUDS TO THE SOLAR SYSTEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mennella, Vito, E-mail: mennella@na.astro.i

2010-08-01

We present the results of experiments aimed at studying the interaction of hydrogen atoms at 80 K with carbon grains covered with a water ice layer at 12 K. The effects of H processing have been analyzed, using IR spectroscopy, as a function of the water ice layer. The results confirm that exposure of the samples to H atoms induces the activation of the band at 3.47 {mu}m with no evidence for the formation of aromatic and aliphatic C-H bonds in the CH{sub 2} and CH{sub 3} functional groups. The formation cross section of the 3.47 {mu}m band has beenmore » estimated from the increase of its integrated optical depth as a function of the H atom fluence. The cross section decreases with increasing thickness of the water ice layer, indicating an increase of adsorption of H atoms in the water ice layer. A penetration depth of 100 nm has been estimated for H atoms in the porous water ice covering carbon grains. Sample warm-up at room temperature causes the activation of the IR features due to the vibrations of the CH{sub 2} and CH{sub 3} aliphatic functional groups. The evolution of the 3.47 {mu}m band carrier has been evaluated for dense and diffuse interstellar clouds, using the estimated formation cross section and assuming that the destruction cross section by energetic processing is the same as that derived for the 3.4 {mu}m band. In both environments, the presence of the 3.47 {mu}m band carrier is compatible with the evolutionary timescale limit imposed by fast cycling of materials between dense and diffuse regions of the interstellar medium. In diffuse regions the formation of the CH{sub 2} and CH{sub 3} aliphatic bands, inhibited in dense regions, takes place, masking the 3.47 {mu}m band. The activation of the CH{sub 2} and CH{sub 3} aliphatic vibrational modes at the end of H processing after sample warm-up represents the first experimental evidence supporting an evolutionary connection between the interstellar carbon grain population, which is responsible for the 3.4 {mu}m band (diffuse regions) and contributes to the absorption at 3.47 {mu}m (dense regions), and the organics observed in interplanetary dust particles and cometary Stardust grains.« less

Structure of high latitude currents in magnetosphere-ionosphere models

NASA Astrophysics Data System (ADS)

Wiltberger, M. J.; Lyon, J.; Merkin, V. G.; Rigler, E. J.

2016-12-01

Using three resolutions of the Lyon-Fedder-Mobarry global magnetosphere-ionosphere model (LFM) and the Weimer 2005 empirical model the structure of the high latitude field-aligned current patterns is examined. Each LFM resolution was run for the entire Whole Heliosphere Interval (WHI), which contained two high-speed solar wind streams and modest interplanetary magnetic field strengths. Average states of the field-aligned current (FAC) patterns for 8 interplanetary magnetic field clock angle directions are computed using data from these runs. Generally speaking the patterns obtained agree well with results from the Weimer 2005 computed using the solar wind and IMF conditions that correspond to each bin. As the simulation resolution increases the currents become more intense and confined. A machine learning analysis of the FAC patterns shows that the ratio of Region 1 (R1) to Region 2 (R2) currents decreases as the simulation resolution increases. This brings the simulation results into better agreement with observational predictions and the Weimer 2005 model results. The increase in R2 current strengths in the model also results in a better shielding of mid- and low-latitude ionosphere from the polar cap convection, also in agreement with observations. Current-voltage relationships between the R1 strength and the cross-polar cap potential (CPCP) are quite similar at the higher resolutions indicating the simulation is converging on a common solution. We conclude that LFM simulations are capable of reproducing the statistical features of FAC patterns.

Mechanical response of two polyimides through coarse-grained molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Sudarkodi, V.; Sooraj, K.; Nair, Nisanth N.; Basu, Sumit; Parandekar, Priya V.; Sinha, Nishant K.; Prakash, Om; Tsotsis, Tom

2018-03-01

Coarse-grained molecular dynamics (MD) simulations allow us to predict the mechanical responses of polymers, starting merely with a description of their molecular architectures. It is interesting to ask whether, given two competing molecular architectures, coarse-grained MD simulations can predict the differences that can be expected in their mechanical responses. We have studied two crosslinked polyimides PMR15 and HFPE52—both used in high- temperature applications—to assess whether the subtle differences in their uniaxial stress-strain responses, revealed by experiments, can be reproduced by carefully coarse-grained MD models. The coarse graining procedure for PMR15 is outlined in this work, while the coarse grain forcefields for HFPE52 are borrowed from an earlier one (Pandiyan et al 2015 Macromol. Theory Simul. 24 513-20). We show that the stress-strain responses of both these polyimides are qualitatively reproduced, and important insights into their deformation and failure mechanisms are obtained. More importantly, the differences in the molecular architecture between the polyimides carry over to the differences in the stress-strain responses in a manner that parallels the experimental results. A critical assessment of the successes and shortcomings of predicting mechanical responses through coarse-grained MD simulations has been made.

A Cosmic Dust Sensor Based on an Array of Grid Electrodes

NASA Astrophysics Data System (ADS)

Li, Y. W.; Bugiel, S.; Strack, H.; Srama, R.

2014-04-01

We described a low mass and high sensitivity cosmic dust trajectory sensor using a array of grid segments[1]. the sensor determines the particle velocity vector and the particle mass. An impact target is used for the detection of the impact plasma of high speed particles like interplanetary dust grains or high speed ejecta. Slower particles are measured by three planes of grid electrodes using charge induction. In contrast to conventional Dust Trajectory Sensor based on wire electrodes, grid electrodes a robust and sensitive design with a trajectory resolution of a few degree. Coulomb simulation and laboratory tests were performed in order to verify the instrument design. The signal shapes are used to derive the particle plane intersection points and to derive the exact particle trajectory. The accuracy of the instrument for the incident angle depends on the particle charge, the position of the intersection point and the signal-to-noise of the charge sensitive amplifier (CSA). There are some advantages of this grid-electrodes based design with respect to conventional trajectory sensor using individual wire electrodes: the grid segment electrodes show higher amplitudes (close to 100%induced charge) and the overall number of measurement channels can be reduced. This allows a compact instrument with low power and mass requirements.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Floss, Christine; Stadermann, Frank J.; Ong, W. J.

We carried out hypervelocity impact experiments in order to test the possibility that presolar grains are preferentially destroyed during impact of the comet 81P/Wild 2 samples into the Stardust Al foil collectors. Powdered samples of the ungrouped carbonaceous chondrite Acfer 094 were shot at 6 km s{sup -1} into Stardust flight spare Al foil. Craters from the Acfer 094 test shots, as well as ones from the actual Stardust cometary foils, were analyzed by NanoSIMS ion imaging to search for presolar grains. We found two O-rich presolar grains and two presolar SiC grains in the Acfer 94 test shots, withmore » measured abundances in the foils of 4 and 5 ppm, respectively, significantly lower than the amount of presolar grains actually present in this meteorite. Based on known abundances of these phases in Acfer 094, we estimate a loss of over 90% of the O-rich presolar grains; the fraction of SiC lost is lower, reflecting its higher resistance to destruction. In the Stardust cometary foils, we identified four O-rich presolar grains in 5000 {mu}m{sup 2} of crater residue. Including a presolar silicate grain found by Leitner et al., the overall measured abundance of O-rich presolar grains in Wild 2 is {approx}35 ppm. No presolar SiC has been found in the foil searches, although one was identified in the aerogel samples. Based on the known abundances of presolar silicates and oxides in Acfer 094, we can calculate the pre-impact abundances of these grains in the Stardust samples. Our calculations indicate initial abundances of 600-830 ppm for O-rich presolar grains. Assuming a typical diameter of {approx}300 nm for SiC suggests a presolar SiC abundance of {approx}45 ppm. Analyses of the Stardust samples indicated early on that recognizable presolar components were not particularly abundant, an observation that was contrary to expectations that the cometary material would, like interplanetary dust particles, be dominated by primitive materials from the early solar system (including abundant presolar grains), which had remained essentially unaltered over solar system history in the cold environment of the Kuiper Belt. Our work shows that comet Wild 2, in fact, does contain more presolar grains than measurements on the Stardust samples suggest, with abundances similar to those observed in primitive IDPs.« less

Sticking properties of ice grains

NASA Astrophysics Data System (ADS)

Jongmanns, M.; Kumm, M.; Wurm, G.; Wolf, D. E.; Teiser, J.

2017-06-01

We study the size dependence of pull-off forces of water ice in laboratory experiments and numerical simulations. To determine the pull-off force in our laboratory experiments, we use a liquid nitrogen cooled centrifuge. Depending on its rotation frequency, spherical ice grains detach due to the centrifugal force which is related to the adhesive properties. Numerical simulations are conducted by means of molecular dynamics simulations of hexagonal ice using a standard coarse-grained water potential. The pull-off force of a single contact between two spherical ice grains is measured due to strain controlled simulations. Both, the experimental study and the simulations reveal a dependence between the pull-off force and the (reduced) particle radii, which differ significantly from the linear dependence of common contact theories.

Formation of fivefold deformation twins in nanocrystalline face-centered-cubic copper based on molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, A. J.; Wei, Y. G.

2006-07-24

Fivefold deformation twins were reported recently to be observed in the experiment of the nanocrystalline face-centered-cubic metals and alloys. However, they were not predicted previously based on the molecular dynamics (MD) simulations and the reason was thought to be a uniaxial tension considered in the simulations. In the present investigation, through introducing pretwins in grain regions, using the MD simulations, the authors predict out the fivefold deformation twins in the grain regions of the nanocrystal grain cell, which undergoes a uniaxial tension. It is shown in their simulation results that series of Shockley partial dislocations emitted from grain boundaries providemore » sequential twining mechanism, which results in fivefold deformation twins.« less

Deformation Twins in Nanocrystalline Body-Centered Cubic Mo as Predicted by Molecular Dynamics Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michael Tonks; Bulent biner; Yongfeng Zhang

2012-10-01

This work studies deformation twins in nanocrystalline body-centered cubic Mo, including the nucleation and growth mechanisms as well as their effects on ductility, through molecular dynamics simulations. The deformation processes of nanocrystalline Mo are simulated using a columnar grain model with three different orientations. The deformation mechanisms identified, including dislocation slip, grain-boundary-mediated plasticity, deformation twins and martensitic transformation, are in agreement with previous studies. In (1 1 0) columnar grains, the deformation is dominated by twinning, which nucleates primarily from the grain boundaries by successive emission of twinning partials and thickens by jog nucleation in the grain interiors. Upon arrestmore » by a grain boundary, the twin may either produce continuous plastic strain across the grain boundary by activating compatible twinning/slip systems or result in intergranular failure in the absence of compatible twinning/slip systems in the neighboring grain. Multiple twinning systems can be activated in the same grain, and the competition between them favors those capable of producing continuous deformation across the grain boundary.« less

HILTOP supplement: Heliocentric interplanetary low thrust trajectory optimization program, supplement 1

NASA Technical Reports Server (NTRS)

Mann, F. I.; Horsewood, J. L.

1974-01-01

Modifications and improvements are described that were made to the HILTOP electric propulsion trajectory optimization computer program during calendar years 1973 and 1974. New program features include the simulation of power degradation, housekeeping power, launch asymptote declination optimization, and powered and unpowered ballistic multiple swingby missions with an optional deep space burn.

The Deep Impact Network Experiment Operations Center Monitor and Control System

NASA Technical Reports Server (NTRS)

Wang, Shin-Ywan (Cindy); Torgerson, J. Leigh; Schoolcraft, Joshua; Brenman, Yan

2009-01-01

The Interplanetary Overlay Network (ION) software at JPL is an implementation of Delay/Disruption Tolerant Networking (DTN) which has been proposed as an interplanetary protocol to support space communication. The JPL Deep Impact Network (DINET) is a technology development experiment intended to increase the technical readiness of the JPL implemented ION suite. The DINET Experiment Operations Center (EOC) developed by JPL's Protocol Technology Lab (PTL) was critical in accomplishing the experiment. EOC, containing all end nodes of simulated spaces and one administrative node, exercised publish and subscribe functions for payload data among all end nodes to verify the effectiveness of data exchange over ION protocol stacks. A Monitor and Control System was created and installed on the administrative node as a multi-tiered internet-based Web application to support the Deep Impact Network Experiment by allowing monitoring and analysis of the data delivery and statistics from ION. This Monitor and Control System includes the capability of receiving protocol status messages, classifying and storing status messages into a database from the ION simulation network, and providing web interfaces for viewing the live results in addition to interactive database queries.

Numerical analysis of orbital transfers to Mars using solar sails and attitude control

NASA Astrophysics Data System (ADS)

Pereira, M. C.; de Melo, C. F.; Meireles, L. G.

2017-10-01

Solar sails present a promising alternative method of propulsion for the coming phases of the space exploration. With the recent advances in materials engineering, the construction of lighter and more resistant materials capable of impelling spaceships with the use of solar radiation pressure has become increasingly viable technologically and economically. The studies, simulations and analysis of orbital transfers from Earth to Mars proposed in this work were implemented considering the use of a flat solar sail. Maneuvers considering the delivery of a sailcraft from a Low Earth Orbit to the border of the Earth’s sphere of influence and interplanetary trajectories to Mars were investigated. A set of simulations were implemented varying the attitude of the sail relative to the Sun. Results show that a sailcraft can carry out transfers with final velocity with respect to Mars smaller than the interplanetary Patched-conic approximation, although this requires a longer time of transfers, provided the attitude of the sailcraft relative to the Sun can be controlled in some points of the trajectories.

Interplanetary Magnetic Field Control of the Entry of Solar Energetic Particles into the Magnetosphere

NASA Technical Reports Server (NTRS)

Richard, R. L.; El-Alaoui, M.; Ashour-Abdalla, M.; Walker, R. J.

2002-01-01

We have investigated the entry of energetic ions of solar origin into the magnetosphere as a function of the interplanetary magnetic field orientation. We have modeled this entry by following high energy particles (protons and 3 He ions) ranging from 0.1 to 50 MeV in electric and magnetic fields from a global magnetohydrodynamic (MHD) model of the magnetosphere and its interaction with the solar wind. For the most part these particles entered the magnetosphere on or near open field lines except for some above 10 MeV that could enter directly by crossing field lines due to their large gyroradii. The MHD simulation was driven by a series of idealized solar wind and interplanetary magnetic field (IMF) conditions. It was found that the flux of particles in the magnetosphere and transport into the inner magnetosphere varied widely according to the IMF orientation for a constant upstream particle source, with the most efficient entry occurring under southward IMF conditions. The flux inside the magnetosphere could approach that in the solar wind implying that SEPs can contribute significantly to the magnetospheric energetic particle population during typical SEP events depending on the state of the magnetosphere.

Enhancing the Scientific Return from HST Imaging of Debris Disks

NASA Astrophysics Data System (ADS)

Weinberger, Alycia

2016-10-01

We propose realistic modeling of scattering of light by small aggregate dust grains that will enable us to interpret visible to near-infrared imaging of debris disks. We will determine if disk colors, phase functions, and polarizations place unique constraints on the composition of debris dust. Ongoing collisions of planetesimals generate dust; therefore, the dust provides unique information on compositions of the parent bodies. These exosolar analogs of asteroids and comets can bear clues to the history of a planetary system including migration and thermal processing. Because directly imaged debris disks are cold, they have no solid state emission features. Grain scattering properties as a function of wavelength are our only tool to reveal their compositions. Solar system interplanetary dust particles are fluffy aggregates, but most previous work on debris disk composition relied on Mie theory, i.e. assumed compact spherical grains. Mie calculations do not reproduce the observed colors and phase functions observed from debris disks. The few more complex calculations that exist do not explore the range of compositions and sizes relevant to debris disk dust. In particular, we expect porosity to help distinguish between cometary-like parent bodies, which are fluffy due to high volatile content and low collisional velocities, and asteroidal-like parent bodies that are compacted.

Lunar and Planetary Surface Dynamics and Early History

NASA Technical Reports Server (NTRS)

2003-01-01

This document, submitted as part of this proposal renewal represents the Final Report required by NASA for Grant NAGS-9442. It should be emphasized that, while this work statement in the original proposal outlined anticipated directions of our research, the specific activities we carried out during this period differed slightly from those proposed, capitalizing on new unexpected results and new advances in analytical capability. The thrust of all the work we completed were completely within the stated research goals of the proposal and significantly advanced our knowledge of planetary processes and our understanding of the early solar system. The following summary outlines our achievements in the different areas of research. These include: A) Early solar system processes and time scales using I-Xe chronometry; B) The Active Capture of Volatiles: A new mechanism for the capture of heavy noble gases, possible implications for phase Q and planetary heavy noble gases; C) Separation of Xe-L from Xe-H: Physically selective experiments; D) Abundances of Presolar grains; E) Studies of Neon and Helium from single interstellar SiC and graphite grains; F) Pre-compaction exposure of meteoritic grains and chondrules; G) Geochemically Measured Half-Lives: Double beta-decay of Te and Ba isotopes; H) Noble gases in stratospheric interplanetary dust particles; I) New Analytical Instrument.

Meso-scale Computational Investigation of Polyurea Microstructure and Its Role in Shockwave Attenuation/dispersion

DTIC Science & Technology

2015-07-01

grained simulations of the formation of meso-segregated microstructure and its interaction with the shockwave is analyzed in the present work. It is...help identify these phenomena and processes, meso-scale coarse-grained simulations of the formation of meso-segregated microstructure and its...of shockwave-induced hard-domain densification. Keywords: Polyurea; Meso-scale; Coarse-grained simulations ; Shockwave attenuation; shockwave

Dynamics of nanoparticules detected at 1 AU by S/WAVES onboard STEREO spacecraft

NASA Astrophysics Data System (ADS)

Belheouane, Soraya; Issautier, Karine; Meyer-Vernet, Nicole; Le Chat, Gaétan; Czechowski, Andrzej; Zaslavsky, Arnaud; Zouganelis, Yannis; Mann, Ingrid

In order to interpret in detail the S/WAVES data on the interplanetary nanodust discovered by STEREO at 1 AU [Meyer-Vernet et al., 2009], we study the dynamics of nanoparticles in the inner interplanetary medium as well as the distribution of their velocities and directions of arrival, with a model based on [Czechowski and Mann, 2012]. We deduce the charges released by their impacts on the STEREO spacecraft at 1 AU and their dependence on the position of the spacecraft on their orbits. The model studies nanoparticles of size equal or smaller than about 70 nm, assumed to be created via collisional fragmentation of dust grains of larger size moving on keplerian orbits, and sublimation of dust, meteoroids and comets. The nanoparticles are released near the Sun with initial velocities close to keplerian, and mainly subjected to the Lorentz force calculated with a simple solar wind model. A part of the nanoparticles is accelerated to high speeds of the order of 300 km/s, thereby providing impact charges between 10(-14) and 10(-11) Cb [Belheouane, 2014] which enable them to be detected by S/WAVES, whereas another part is trapped within about 0.2 AU from the Sun. We discuss how the fluxes and direction of arrival at 1 AU are expected to change in function of the solar cycle. These results enable us to interpret in detail the STEREO/WAVES observations [Zaslavsky et al., 2012]; [Pantellini et al., 2013]; [Le Chat et al., 2013]. Belheouane, S. (2014). Nanoparticules dans le vent solaire, observations spatiales et theorie. PhD thesis, Pierre and Marie Curie University UPMC. Czechowski, A. and Mann, I. (2012). Nanodust Dynamics in Interplanetary Space, chapter Nanodust Dynamics in Interplanetary Space. Springer Berlin Heidelberg. Le Chat, G., Zaslavsky, A., Meyer-Vernet, N., Issautier, K., Belheouane, S., Pantellini, F., Maksimovic, M., Zouganelis, I., Bale, S., and Kasper, J. (2013). Interplanetary Nanodust Detection by the Solar Terrestrial Relations Observatory/WAVES Low Frequency Receiver. Solar Physics, 286(2):549-559. Meyer-Vernet, N., Maksimovic, M., Czechowski, A., Mann, I., Zouganelis, I., Goetz, K., Kaiser, M., Cyr, O. S., Bougeret, J.-L., and Bale, S. (2009). Dust Detection by the Wave Instrument on STEREO : Nanoparticles Picked up by the Solar Wind? Solar Phys, 256:463-474. Pantellini, F., Le Chat, G., Belheouane, S., Meyer-Vernet, N., and Zaslavsky, A. (2013). On the detection of nano dust using spacecraft based boom antennas. Solar Wind 13: Proceedings of the Thirteenth International Solar Wind Conference, 1539:414-417. Zaslavsky, A., Meyer-Vernet, N., Mann, I., Czechowski, A., Issautier, K., Le Chat, G., Pantellini, F., Goetz, K., Maksimovic, M., Bale, S. D., and Kasper, J. K. (2012). Interplanetary dust detection by radio antennas: Mass calibration and fluxes measured by STEREO/WAVES. J. Geophys. Res., 117.

Geochemical evidence for a comet shower in the late Eocene

USGS Publications Warehouse

Farley, K.A.; Montanari, A.; Shoemaker, E.M.; Shoemaker, C.S.

1998-01-01

Analyses of pelagic limestones indicate that the flux of extraterrestrial helium-3 to Earth was increased for a 2.5-million year (My) period in the late Eocene. The enhancement began ~1 My before and ended ~1.5 My after the major impact events that produced the large Popigai and Chesapeake Bay craters ~36 million years ago. The correlation between increased concentrations of helium-3, a tracer of fine-grained interplanetary dust, and large impacts indicates that the abundance of Earth-crossing objects and dustiness in the inner solar system were simultaneously but only briefly enhanced. These observations provide evidence for a comet shower triggered by an impulsive perturbation of the Oort cloud.

CCSDS Advanced Orbiting Systems Virtual Channel Access Service for QoS MACHETE Model

NASA Technical Reports Server (NTRS)

Jennings, Esther H.; Segui, John S.

2011-01-01

To support various communications requirements imposed by different missions, interplanetary communication protocols need to be designed, validated, and evaluated carefully. Multimission Advanced Communications Hybrid Environment for Test and Evaluation (MACHETE), described in "Simulator of Space Communication Networks" (NPO-41373), NASA Tech Briefs, Vol. 29, No. 8 (August 2005), p. 44, combines various tools for simulation and performance analysis of space networks. The MACHETE environment supports orbital analysis, link budget analysis, communications network simulations, and hardware-in-the-loop testing. By building abstract behavioral models of network protocols, one can validate performance after identifying the appropriate metrics of interest. The innovators have extended the MACHETE model library to include a generic link-layer Virtual Channel (VC) model supporting quality-of-service (QoS) controls based on IP streams. The main purpose of this generic Virtual Channel model addition was to interface fine-grain flow-based QoS (quality of service) between the network and MAC layers of the QualNet simulator, a commercial component of MACHETE. This software model adds the capability of mapping IP streams, based on header fields, to virtual channel numbers, allowing extended QoS handling at link layer. This feature further refines the QoS v existing at the network layer. QoS at the network layer (e.g. diffserv) supports few QoS classes, so data from one class will be aggregated together; differentiating between flows internal to a class/priority is not supported. By adding QoS classification capability between network and MAC layers through VC, one maps multiple VCs onto the same physical link. Users then specify different VC weights, and different queuing and scheduling policies at the link layer. This VC model supports system performance analysis of various virtual channel link-layer QoS queuing schemes independent of the network-layer QoS systems.

The Abundance and Distribution of Presolar Materials in Cluster IDPS

NASA Technical Reports Server (NTRS)

Messenger, Scott; Keller, Lindsay; Nakamura-Messenger, Keiko; Ito, Motoo

2007-01-01

Presolar grains and remnants of interstellar organic compounds occur in a wide range of primitive solar system materials, including meteorites, interplanetary dust particles (IDPs), and comet Wild-2 samples. Among the most abundant presolar phases are silicate stardust grains and molecular cloud material. However, these materials have also been susceptible to destruction and alteration during parent body and nebular processing. In addition to their importance as direct samples of remote and ancient astrophysical environments, presolar materials thus provide a measure of how well different primitive bodies have preserved the original solar system starting materials. The matrix normalized abundances of presolar silicate grains in meteorites range from 20 ppm in Semarkona and Bishunpur to 170 ppm for Acfer 094. The lower abundances of presolar silicates in Bishunpur and Semarkona has been ascribed to the destruction of presolar silicates during aqueous processes. Presolar silicates appear to be significantly more abundant in anhydrous IDPs, possibly because these materials did not experience parent body hydrothermal alteration. Among IDPs the estimated abundances of presolar silicates vary by more than an order of magnitude, from 480 to 5500 ppm. The wide disparity in the abundances of presolar silicates of IDPs may be a consequence of the relatively small total area analyzed in those studies and the fine grain sizes of the IDPs. Alternatively, there may be a wide range in presolar silicate abundances between different IDPs. This view is supported by the observation that 15N-rich IDPs have higher presolar silicate abundances than those with isotopically normal N.

Lennard-Jones type pair-potential method for coarse-grained lipid bilayer membrane simulations in LAMMPS

NASA Astrophysics Data System (ADS)

Fu, S.-P.; Peng, Z.; Yuan, H.; Kfoury, R.; Young, Y.-N.

2017-01-01

Lipid bilayer membranes have been extensively studied by coarse-grained molecular dynamics simulations. Numerical efficiencies have been reported in the cases of aggressive coarse-graining, where several lipids are coarse-grained into a particle of size 4 ∼ 6 nm so that there is only one particle in the thickness direction. Yuan et al. proposed a pair-potential between these one-particle-thick coarse-grained lipid particles to capture the mechanical properties of a lipid bilayer membrane, such as gel-fluid-gas phase transitions of lipids, diffusion, and bending rigidity Yuan et al. (2010). In this work we implement such an interaction potential in LAMMPS to simulate large-scale lipid systems such as a giant unilamellar vesicle (GUV) and red blood cells (RBCs). We also consider the effect of cytoskeleton on the lipid membrane dynamics as a model for RBC dynamics, and incorporate coarse-grained water molecules to account for hydrodynamic interactions. The interaction between the coarse-grained water molecules (explicit solvent molecules) is modeled as a Lennard-Jones (L-J) potential. To demonstrate that the proposed methods do capture the observed dynamics of vesicles and RBCs, we focus on two sets of LAMMPS simulations: 1. Vesicle shape transitions with enclosed volume; 2. RBC shape transitions with different enclosed volume. Finally utilizing the parallel computing capability in LAMMPS, we provide some timing results for parallel coarse-grained simulations to illustrate that it is possible to use LAMMPS to simulate large-scale realistic complex biological membranes for more than 1 ms.

Atomistic Simulations of Grain Boundary Pinning in CuFe Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zepeda-Ruiz, L A; Gilmer, G H; Sadigh, B

2005-05-22

The authors apply a hybrid Monte Carlo-molecular dynamics code to the study of grain boundary motion upon annealing of pure Cu and Cu with low concentrations of Fe. The hybrid simulations account for segregation and precipitation of the low solubility Fe, together with curvature driven grain boundary motion. Grain boundaries in two different systems, a {Sigma}7+U-shaped half-loop grain and a nanocrystalline sample, were found to be pinned in the presence of Fe concentrations exceeding 3%.

Magnetic flux ropes at the high-latitude magnetopause

NASA Technical Reports Server (NTRS)

Berchem, Jean; Raeder, Joachim; Ashour-Abdalla, Maha

1995-01-01

We examine the consequences of magnetic reconnection at the high-latitude magnetopause using a three-dimensional global magnetohydrodynamic simulation of the solar wind interaction with the Earth's magnetosphere. Magnetic field lines from the simulation reveal the formation of magnetic flux ropes during periods with northward interplanetary magnetic field. These flux ropes result from multiple reconnection processes between the lobes field lines and draped magnetosheath field lines that are convected around the flank of the magnetosphere. The flux ropes identified in the simulation are consistent with features observed in the magnetic field measured by Hawkeye-1 during some high-latitude magnetopause crossings.

Testing the responses of four wheat crop models to heat stress at anthesis and grain filling.

PubMed

Liu, Bing; Asseng, Senthold; Liu, Leilei; Tang, Liang; Cao, Weixing; Zhu, Yan

2016-05-01

Higher temperatures caused by future climate change will bring more frequent heat stress events and pose an increasing risk to global wheat production. Crop models have been widely used to simulate future crop productivity but are rarely tested with observed heat stress experimental datasets. Four wheat models (DSSAT-CERES-Wheat, DSSAT-Nwheat, APSIM-Wheat, and WheatGrow) were evaluated with 4 years of environment-controlled phytotron experimental datasets with two wheat cultivars under heat stress at anthesis and grain filling stages. Heat stress at anthesis reduced observed grain numbers per unit area and individual grain size, while heat stress during grain filling mainly decreased the size of the individual grains. The observed impact of heat stress on grain filling duration, total aboveground biomass, grain yield, and grain protein concentration (GPC) varied depending on cultivar and accumulated heat stress. For every unit increase of heat degree days (HDD, degree days over 30 °C), grain filling duration was reduced by 0.30-0.60%, total aboveground biomass was reduced by 0.37-0.43%, and grain yield was reduced by 1.0-1.6%, but GPC was increased by 0.50% for cv Yangmai16 and 0.80% for cv Xumai30. The tested crop simulation models could reproduce some of the observed reductions in grain filling duration, final total aboveground biomass, and grain yield, as well as the observed increase in GPC due to heat stress. Most of the crop models tended to reproduce heat stress impacts better during grain filling than at anthesis. Some of the tested models require improvements in the response to heat stress during grain filling, but all models need improvements in simulating heat stress effects on grain set during anthesis. The observed significant genetic variability in the response of wheat to heat stress needs to be considered through cultivar parameters in future simulation studies. © 2016 John Wiley & Sons Ltd.

On the applicability of density dependent effective interactions in cluster-forming systems

NASA Astrophysics Data System (ADS)

Montes-Saralegui, Marta; Kahl, Gerhard; Nikoubashman, Arash

2017-02-01

We systematically studied the validity and transferability of the force-matching algorithm for computing effective pair potentials in a system of dendritic polymers, i.e., a particular class of ultrasoft colloids. We focused on amphiphilic dendrimers, macromolecules which can aggregate into clusters of overlapping particles to minimize the contact area with the surrounding implicit solvent. Simulations were performed for both the monomeric and coarse-grained models in the liquid phase at densities ranging from infinite dilution up to values close to the freezing point. The effective pair potentials for the coarse-grained simulations were computed from the monomeric simulations both in the zero-density limit (Φeff0) and at each investigated finite density (Φeff). Conducting the coarse-grained simulations with Φeff0 at higher densities is not appropriate as they failed at reproducing the structural properties of the monomeric simulations. In contrast, we found excellent agreement between the spatial dendrimer distributions obtained from the coarse-grained simulations with Φeff and the microscopically detailed simulations at low densities, where the macromolecules were distributed homogeneously in the system. However, the reliability of the coarse-grained simulations deteriorated significantly as the density was increased further and the cluster occupation became more polydisperse. Under these conditions, the effective pair potential of the coarse-grained model can no longer be computed by averaging over the whole system, but the local density needs to be taken into account instead.

CAMELOT: A machine learning approach for coarse-grained simulations of aggregation of block-copolymeric protein sequences

PubMed Central

Ruff, Kiersten M.; Harmon, Tyler S.; Pappu, Rohit V.

2015-01-01

We report the development and deployment of a coarse-graining method that is well suited for computer simulations of aggregation and phase separation of protein sequences with block-copolymeric architectures. Our algorithm, named CAMELOT for Coarse-grained simulations Aided by MachinE Learning Optimization and Training, leverages information from converged all atom simulations that is used to determine a suitable resolution and parameterize the coarse-grained model. To parameterize a system-specific coarse-grained model, we use a combination of Boltzmann inversion, non-linear regression, and a Gaussian process Bayesian optimization approach. The accuracy of the coarse-grained model is demonstrated through direct comparisons to results from all atom simulations. We demonstrate the utility of our coarse-graining approach using the block-copolymeric sequence from the exon 1 encoded sequence of the huntingtin protein. This sequence comprises of 17 residues from the N-terminal end of huntingtin (N17) followed by a polyglutamine (polyQ) tract. Simulations based on the CAMELOT approach are used to show that the adsorption and unfolding of the wild type N17 and its sequence variants on the surface of polyQ tracts engender a patchy colloid like architecture that promotes the formation of linear aggregates. These results provide a plausible explanation for experimental observations, which show that N17 accelerates the formation of linear aggregates in block-copolymeric N17-polyQ sequences. The CAMELOT approach is versatile and is generalizable for simulating the aggregation and phase behavior of a range of block-copolymeric protein sequences. PMID:26723608

Gas-Grain Simulation Facility: Fundamental studies of particle formation and interactions. Volume 1: Executive summary and overview

NASA Technical Reports Server (NTRS)

Fogleman, Guy (Editor); Huntington, Judith L. (Editor); Schwartz, Deborah E. (Editor); Fonda, Mark L. (Editor)

1989-01-01

An overview of the Gas-Grain Simulation Facility (GGSF) project and its current status is provided. The proceedings of the Gas-Grain Simulation Facility Experiments Workshop are recorded. The goal of the workshop was to define experiments for the GGSF--a small particle microgravity research facility. The workshop addressed the opportunity for performing, in Earth orbit, a wide variety of experiments that involve single small particles (grains) or clouds of particles. The first volume includes the executive summary, overview, scientific justification, history, and planned development of the Facility.

On the role of the grain size in the magnetic behavior of sintered permanent magnets

NASA Astrophysics Data System (ADS)

Efthimiadis, K. G.; Ntallis, N.

2018-02-01

In this work the finite elements method is used to simulate, by micromagnetic modeling, the magnetic behavior of sintered anisotropic magnets. Hysteresis loops were simulated for different grain sizes in an oriented multigrain sample. By keeping out other parameters that contribute to the magnetic microstructure, such as the sample size, the grain morphology and the grain boundaries mismatch, it has been found that the grain size affects the magnetic properties only if the grains are exchange-decoupled. In this case, as the grain size decreases, a decrease in the nucleation field of a reverse magnetic domain is observed and an increase in the coercive field due to the pinning of the magnetic domain walls at the grain boundaries.

Coarse-grained stochastic processes and kinetic Monte Carlo simulators for the diffusion of interacting particles

NASA Astrophysics Data System (ADS)

Katsoulakis, Markos A.; Vlachos, Dionisios G.

2003-11-01

We derive a hierarchy of successively coarse-grained stochastic processes and associated coarse-grained Monte Carlo (CGMC) algorithms directly from the microscopic processes as approximations in larger length scales for the case of diffusion of interacting particles on a lattice. This hierarchy of models spans length scales between microscopic and mesoscopic, satisfies a detailed balance, and gives self-consistent fluctuation mechanisms whose noise is asymptotically identical to the microscopic MC. Rigorous, detailed asymptotics justify and clarify these connections. Gradient continuous time microscopic MC and CGMC simulations are compared under far from equilibrium conditions to illustrate the validity of our theory and delineate the errors obtained by rigorous asymptotics. Information theory estimates are employed for the first time to provide rigorous error estimates between the solutions of microscopic MC and CGMC, describing the loss of information during the coarse-graining process. Simulations under periodic boundary conditions are used to verify the information theory error estimates. It is shown that coarse-graining in space leads also to coarse-graining in time by q2, where q is the level of coarse-graining, and overcomes in part the hydrodynamic slowdown. Operation counting and CGMC simulations demonstrate significant CPU savings in continuous time MC simulations that vary from q3 for short potentials to q4 for long potentials. Finally, connections of the new coarse-grained stochastic processes to stochastic mesoscopic and Cahn-Hilliard-Cook models are made.

Design of Energetic Ionic Liquids (Preprint)

DTIC Science & Technology

2008-05-07

mesoscale-level simulations of bulk ionic liquids based upon multiscale coarse graining techniques. 15. SUBJECT TERMS 16. SECURITY...simulations utilizing polarizable force fields, and mesoscale-level simulations of bulk ionic liquids based upon multiscale coarse graining...Simulations of the Energetic Ionic Liquid 1-hydroxyethyl-4-amino-1, 2, 4- triazolium Nitrate (HEATN): Molecular dynamics (MD) simulations have been

Interplanetary double-shock ensembles with anomalous electrical conductivity

NASA Technical Reports Server (NTRS)

Dryer, M.

1972-01-01

Similarity theory is applied to the case of constant velocity, piston-driven, shock waves. This family of solutions, incorporating the interplanetary magnetic field for the case of infinite electric conductivity, represents one class of experimentally observed, flare-generated shock waves. This paper discusses the theoretical extension to flows with finite conductivity (presumably caused by unspecified modes of wave-particle interactions). Solutions, including reverse shocks, are found for a wide range of magnetic Reynolds numbers from one to infinity. Consideration of a zero and nonzero ambient flowing solar wind (together with removal of magnetic considerations) enables the recovery of earlier similarity solutions as well as numerical simulations. A limited comparison with observations suggests that flare energetics can be reasonably estimated once the shock velocity, ambient solar wind velocity and density, and ambient azimuthal Alfven Mach number are known.

A simple phenomenological model for grain clustering in turbulence

NASA Astrophysics Data System (ADS)

Hopkins, Philip F.

2016-01-01

We propose a simple model for density fluctuations of aerodynamic grains, embedded in a turbulent, gravitating gas disc. The model combines a calculation for the behaviour of a group of grains encountering a single turbulent eddy, with a hierarchical approximation of the eddy statistics. This makes analytic predictions for a range of quantities including: distributions of grain densities, power spectra and correlation functions of fluctuations, and maximum grain densities reached. We predict how these scale as a function of grain drag time ts, spatial scale, grain-to-gas mass ratio tilde{ρ }, strength of turbulence α, and detailed disc properties. We test these against numerical simulations with various turbulence-driving mechanisms. The simulations agree well with the predictions, spanning ts Ω ˜ 10-4-10, tilde{ρ }˜ 0{-}3, α ˜ 10-10-10-2. Results from `turbulent concentration' simulations and laboratory experiments are also predicted as a special case. Vortices on a wide range of scales disperse and concentrate grains hierarchically. For small grains this is most efficient in eddies with turnover time comparable to the stopping time, but fluctuations are also damped by local gas-grain drift. For large grains, shear and gravity lead to a much broader range of eddy scales driving fluctuations, with most power on the largest scales. The grain density distribution has a log-Poisson shape, with fluctuations for large grains up to factors ≳1000. We provide simple analytic expressions for the predictions, and discuss implications for planetesimal formation, grain growth, and the structure of turbulence.

Coarse-grained hydrodynamics from correlation functions

NASA Astrophysics Data System (ADS)

Palmer, Bruce

2018-02-01

This paper will describe a formalism for using correlation functions between different grid cells as the basis for determining coarse-grained hydrodynamic equations for modeling the behavior of mesoscopic fluid systems. Configurations from a molecular dynamics simulation or other atomistic simulation are projected onto basis functions representing grid cells in a continuum hydrodynamic simulation. Equilibrium correlation functions between different grid cells are evaluated from the molecular simulation and used to determine the evolution operator for the coarse-grained hydrodynamic system. The formalism is demonstrated on a discrete particle simulation of diffusion with a spatially dependent diffusion coefficient. Correlation functions are calculated from the particle simulation and the spatially varying diffusion coefficient is recovered using a fitting procedure.

Electron Beam Analysis of Micrometeoroids Captured in Aerogel as Stardust Analogues

NASA Technical Reports Server (NTRS)

Graham, G. A.; Sheffield-Parker, J.; Bradley, P.; Kearsley, A. T.; Dai, Z. R.; Mayo, S. C.; Teslich, N.; Snead, C.; Westphal, A. J.; Ishii, H.

2005-01-01

In January 2004, NASA s Stardust spacecraft passed through the tail of Comet 81P/Wild-2. The on-board dust flux monitor instrument indicated that numerous micro- and nano-meter sized cometary dust particles were captured by the dedicated silica aerogel capture cell. The collected cometary particles will be returned to Earth in January 2006. Current Stardust analogues are: (i) Light-gas-gun accelerated individual mineral grains and carbonaceous meteoritic material in aerogels at the Stardust encounter velocity ca.approximately 6 kilometers per second. (ii) Aerogels exposed in low-Earth orbit (LEO) containing preserved cosmic dust grains. Studies of these impacts offer insight into the potential state of the captured cometary dust by Stardust and the suitability of various analytical techniques. A number of papers have discussed the application of sophisticated synchrotron analytical techniques to analyze Stardust particles. Yet much of the understanding gained on the composition and mineralogy of interplanetary dust particles (IDPs) has come from electron microscopy studies. Here we discuss the application of scanning electron microscopy (SEM) for Stardust during the preliminary phase of post-return investigations.

Shear-Coupled Grain Growth and Texture Development in a Nanocrystalline Ni-Fe Alloy during Cold Rolling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Li; Ungár, Tamás; Toth, Laszlo S.

The evolution of texture, grain size, grain shape, dislocation and twin density has been determined by synchrotron X-ray diffraction and line profile analysis in a nanocrystalline Ni- Fe alloy after cold rolling along different directions related to the initial fiber and the long axis of grains. The texture evolution has been simulated by the Taylor-type relaxed constraints viscoplastic polycrystal model. The simulations were based on the activity of partial dislocations in correlation with the experimental results of dislocation density determination. The concept of stress-induced shear-coupling is supported and strengthened by both the texture simulations and the experimentally determined evolution ofmore » the microstructure parameters. Grain-growth and texture evolution are shown to proceed by the shear-coupling mechanism supported by dislocation activity as long as the grain size is not smaller than about 20 nm.« less

Molecular dynamics simulations investigating consecutive nucleation, solidification and grain growth in a twelve-million-atom Fe-system

NASA Astrophysics Data System (ADS)

Okita, Shin; Verestek, Wolfgang; Sakane, Shinji; Takaki, Tomohiro; Ohno, Munekazu; Shibuta, Yasushi

2017-09-01

Continuous processes of homogeneous nucleation, solidification and grain growth are spontaneously achieved from an undercooled iron melt without any phenomenological parameter in the molecular dynamics (MD) simulation with 12 million atoms. The nucleation rate at the critical temperature is directly estimated from the atomistic configuration by cluster analysis to be of the order of 1034 m-3 s-1. Moreover, time evolution of grain size distribution during grain growth is obtained by the combination of Voronoi and cluster analyses. The grain growth exponent is estimated to be around 0.3 from the geometric average of the grain size distribution. Comprehensive understanding of kinetic properties during continuous processes is achieved in the large-scale MD simulation by utilizing the high parallel efficiency of a graphics processing unit (GPU), which is shedding light on the fundamental aspects of production processes of materials from the atomistic viewpoint.

A Microstructure-Based Constitutive Model for Superplastic Forming

NASA Astrophysics Data System (ADS)

Jafari Nedoushan, Reza; Farzin, Mahmoud; Mashayekhi, Mohammad; Banabic, Dorel

2012-11-01

A constitutive model is proposed for simulations of hot metal forming processes. This model is constructed based on dominant mechanisms that take part in hot forming and includes intergranular deformation, grain boundary sliding, and grain boundary diffusion. A Taylor type polycrystalline model is used to predict intergranular deformation. Previous works on grain boundary sliding and grain boundary diffusion are extended to drive three-dimensional macro stress-strain rate relationships for each mechanism. In these relationships, the effect of grain size is also taken into account. The proposed model is first used to simulate step strain-rate tests and the results are compared with experimental data. It is shown that the model can be used to predict flow stresses for various grain sizes and strain rates. The yield locus is then predicted for multiaxial stress states, and it is observed that it is very close to the von Mises yield criterion. It is also shown that the proposed model can be directly used to simulate hot forming processes. Bulge forming process and gas pressure tray forming are simulated, and the results are compared with experimental data.

Heterogeneity in homogeneous nucleation from billion-atom molecular dynamics simulation of solidification of pure metal.

PubMed

Shibuta, Yasushi; Sakane, Shinji; Miyoshi, Eisuke; Okita, Shin; Takaki, Tomohiro; Ohno, Munekazu

2017-04-05

Can completely homogeneous nucleation occur? Large scale molecular dynamics simulations performed on a graphics-processing-unit rich supercomputer can shed light on this long-standing issue. Here, a billion-atom molecular dynamics simulation of homogeneous nucleation from an undercooled iron melt reveals that some satellite-like small grains surrounding previously formed large grains exist in the middle of the nucleation process, which are not distributed uniformly. At the same time, grains with a twin boundary are formed by heterogeneous nucleation from the surface of the previously formed grains. The local heterogeneity in the distribution of grains is caused by the local accumulation of the icosahedral structure in the undercooled melt near the previously formed grains. This insight is mainly attributable to the multi-graphics processing unit parallel computation combined with the rapid progress in high-performance computational environments.Nucleation is a fundamental physical process, however it is a long-standing issue whether completely homogeneous nucleation can occur. Here the authors reveal, via a billion-atom molecular dynamics simulation, that local heterogeneity exists during homogeneous nucleation in an undercooled iron melt.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Linyun; Mei, Zhi-Gang; Yacout, Abdellatif M.

We have developed a mesoscale phase-field model for studying the effect of recrystallization on the gas-bubble-driven swelling in irradiated U-Mo alloy fuel. The model can simulate the microstructural evolution of the intergranular gas bubbles on the grain boundaries as well as the recrystallization process. Our simulation results show that the intergranular gas-bubble-induced fuel swelling exhibits two stages: slow swelling kinetics before recrystallization and rapid swelling kinetics with recrystallization. We observe that the recrystallization can significantly expedite the formation and growth of gas bubbles at high fission densities. The reason is that the recrystallization process increases the nucleation probability of gasmore » bubbles and reduces the diffusion time of fission gases from grain interior to grain boundaries by increasing the grain boundary area and decreasing the diffusion distance. The simulated gas bubble shape, size distribution, and density on the grain boundaries are consistent with experimental measurements. We investigate the effect of the recrystallization on the gas-bubble-driven fuel swelling in UMo through varying the initial grain size and grain aspect ratio. We conclude that the initial microstructure of fuel, such as grain size and grain aspect ratio, can be used to effectively control the recrystallization and therefore reduce the swelling in U-Mo fuel.« less

Temporal acceleration of spatially distributed kinetic Monte Carlo simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chatterjee, Abhijit; Vlachos, Dionisios G.

The computational intensity of kinetic Monte Carlo (KMC) simulation is a major impediment in simulating large length and time scales. In recent work, an approximate method for KMC simulation of spatially uniform systems, termed the binomial {tau}-leap method, was introduced [A. Chatterjee, D.G. Vlachos, M.A. Katsoulakis, Binomial distribution based {tau}-leap accelerated stochastic simulation, J. Chem. Phys. 122 (2005) 024112], where molecular bundles instead of individual processes are executed over coarse-grained time increments. This temporal coarse-graining can lead to significant computational savings but its generalization to spatially lattice KMC simulation has not been realized yet. Here we extend the binomial {tau}-leapmore » method to lattice KMC simulations by combining it with spatially adaptive coarse-graining. Absolute stability and computational speed-up analyses for spatial systems along with simulations provide insights into the conditions where accuracy and substantial acceleration of the new spatio-temporal coarse-graining method are ensured. Model systems demonstrate that the r-time increment criterion of Chatterjee et al. obeys the absolute stability limit for values of r up to near 1.« less

Modeling of Grain Size Distribution of Tsunami Sand Deposits in V-shaped Valley of Numanohama During the 2011 Tohoku Tsunami

NASA Astrophysics Data System (ADS)

Gusman, A. R.; Satake, K.; Goto, T.; Takahashi, T.

2016-12-01

Estimating tsunami amplitude from tsunami sand deposit has been a challenge. The grain size distribution of tsunami sand deposit may have correlation with tsunami inundation process, and further with its source characteristics. In order to test this hypothesis, we need a tsunami sediment transport model that can accurately estimate grain size distribution of tsunami deposit. Here, we built and validate a tsunami sediment transport model that can simulate grain size distribution. Our numerical model has three layers which are suspended load layer, active bed layer, and parent bed layer. The two bed layers contain information about the grain size distribution. This numerical model can handle a wide range of grain sizes from 0.063 (4 ϕ) to 5.657 mm (-2.5 ϕ). We apply the numerical model to simulate the sedimentation process during the 2011 Tohoku earthquake in Numanohama, Iwate prefecture, Japan. The grain size distributions at 15 sample points along a 900 m transect from the beach are used to validate the tsunami sediment transport model. The tsunami deposits are dominated by coarse sand with diameter of 0.5 - 1 mm and their thickness are up to 25 cm. Our tsunami model can well reproduce the observed tsunami run-ups that are ranged from 16 to 34 m along the steep valley in Numanohama. The shapes of the simulated grain size distributions at many sample points located within 300 m from the shoreline are similar to the observations. The differences between observed and simulated peak of grain size distributions are less than 1 ϕ. Our result also shows that the simulated sand thickness distribution along the transect is consistent with the observation.

Coarse-Grained Molecular Dynamics Simulation of Ionic Polymer Networks

DTIC Science & Technology

2008-07-01

AFRL-RX-WP-TP-2009-4198 COARSE-GRAINED MOLECULAR DYNAMICS SIMULATION OF IONIC POLYMER NETWORKS (Postprint) T.E. Dirama, V. Varshney, K.L...GRAINED MOLECULAR DYNAMICS SIMULATION OF IONIC POLYMER NETWORKS (Postprint) 5a. CONTRACT NUMBER FA8650-05-D-5807-0052 5b. GRANT NUMBER 5c...We studied two types of networks which differ only by one containing ionic pairs that amount to 7% of the total number of bonds present. The stress

Possible survival of simple amino acids to X-ray irradiation in ice: the case of glycine

NASA Astrophysics Data System (ADS)

Pernet, A.; Pilmé, J.; Pauzat, F.; Ellinger, Y.; Sirotti, F.; Silly, M.; Parent, Ph.; Laffon, C.

2013-04-01

Context. Glycine, the simplest of amino acids, has been found in several carbonaceous meteorites collected on Earth, though its presence in the interstellar medium (ISM) has never been confirmed as of today. It is now considered that its synthesis took place in the icy mantles of interstellar grains, but it remains unclear how glycine, once synthesized and trapped in interplanetary particles, survives during the transfer to the Earth. Aims: Assuming that glycine was effectively formed in the ice, we address the question of its resistance to a solar-like radiation field and look for the possible molecular remnants that would be useful tracers of its former existence. Methods: The search was conducted using an interdisciplinary approach that mixes, on the one hand, irradiations in ultra high vacuum at 30 K on the TEMPO beam line of the synchrotron SOLEIL, simultaneously with near-edge X-ray absorption spectroscopy (NEXAFS) measurements, and on the other hand, quantum calculations to determine the energetics of the fragmentations and the relative stability of the different byproducts. The last points were addressed by means of density functional theory (DFT) simulations followed by high-level post Hartree-Fock calculations when more accurate relative energies were necessary. The constraints of an icy environment deserved special attention and the ice was modeled by a polarizable continuum medium that relies on the dielectric constant of water ice at 10-50 K. Results: Destruction of glycine is observed in the first seconds of irradiation, and carbon dioxide (CO2) and methylamine (CH3NH2) are formed. Carbon monoxide (CO), methanimine (CH2NH) and hydrogen cyanide (HCN) are also produced in secondary reactions. The amino acid destruction is the same for pure glycine and glycine in ice, indicating that the OH radicals released by the water matrix is barely involved in the photolytic process; however, these radicals are involved in the production of the secondary byproducts through dehydrogenation reactions as shown by ab initio quantum chemical simulation presented in this article along with the experimental results. Conclusions: The experiments show that glycine is only partially destroyed. Its abundance is found to stay at a level of ~30% of the initial concentration, for an irradiation dose equivalent to three years of solar radiation (at a distance of one astronomical unit). This result supports the hypothesis that, if trapped in protected icy environments and/or in the interior of interplanetary particles and meteorites, glycine may partly resist the radiation field to which it is submitted and, accordingly, survives its journey to the Earth.

Comparison of the Mineralogy of Comet Wild 2 Coma Grains to Other Astromaterials

NASA Technical Reports Server (NTRS)

Frank, David; Zolensky, Michael

2010-01-01

We propose that Kuiper Belt samples (in this case comet coma grains from the Jupiter family comet Wild 2) are recognizably different from the bulk of materials in outer belt asteroids, because of their different formation positions and times in the early solar system. We believe this despite similarities found between some Wild 2 grains and components of carbonaceous chondrites (i.e. some CAI and chondrules). Kuiper Belt samples must preserve measurable mineralogical and compositional evidence of formation at unique positions and times in the early solar nebula, and these formational differences must have imparted recognizable special characteristics. We hypothesize that these characteristics include: (1) Unique major element compositional ranges of common astromaterial minerals, especially olivine and pyroxene; (2) Unique minor element compositions of major silicate phases, especially olivine and low-Ca pyroxene; (3) Degree and effects of radiation processing -- including amorphous rims, metal coatings, and Glass with Embedded Metal and Sulfides (GEMS); (4) Presence of abundant presolar silicate grains as recognized by anomalous oxygen in silicates; (5) Oxidation state of the mineral assemblage. We are working our way through all available Wild 2 samples, selecting 1-2 non-consecutive viable TEM grids from each possible extracted Wild 2 grain. We especially prefer TEM grids from grains for which complete mineralogical details have not been published (which is to say the majority of the extracted grains). We are performing a basic mineralogic survey by E-beam techniques, to establish the essential features of the extracted Wild 2 grains. We are making a particular effort to carefully and accurately measure minor elements of olivine and pyroxene, as these minerals are widespread in astromaterials, and comparisons of their compositions will serve to place the Wild 2 silicates in contact with asteroids, meteorites and chondritic interplanetary dust particles processing. We are also making a special effort to search for mineralogical products of aqueous alteration, since their presence would reveal that Wild 2 was once internally heated, a result with dramatic implications for models of early solar system primitive bodies. Thus far carbonates are the only potential evidence for aqueous alteration for Wild 2.

Understanding the Effect of Grain Boundary Character on Dynamic Recrystallization in Stainless Steel 316L

NASA Astrophysics Data System (ADS)

Beck, Megan; Morse, Michael; Corolewski, Caleb; Fritchman, Koyuki; Stifter, Chris; Poole, Callum; Hurley, Michael; Frary, Megan

2017-08-01

Dynamic recrystallization (DRX) occurs during high-temperature deformation in metals and alloys with low to medium stacking fault energies. Previous simulations and experimental research have shown the effect of temperature and grain size on DRX behavior, but not the effect of the grain boundary character distribution. To investigate the effects of the distribution of grain boundary types, experimental testing was performed on stainless steel 316L specimens with different initial special boundary fractions (SBF). This work was completed in conjunction with computer simulations that used a modified Monte Carlo method which allowed for the addition of anisotropic grain boundary energies using orientation data from electron backscatter diffraction (EBSD). The correlation of the experimental and simulation work allows for a better understanding of how the input parameters in the simulations correspond to what occurs experimentally. Results from both simulations and experiments showed that a higher fraction of so-called "special" boundaries ( e.g., Σ3 twin boundaries) delayed the onset of recrystallization to larger strains and that it is energetically favorable for nuclei to form on triple junctions without these so-called "special" boundaries.

High energy electron sintering of icy regoliths: Formation of the PacMan thermal anomalies on the icy Saturnian moons

NASA Astrophysics Data System (ADS)

Schaible, M. J.; Johnson, R. E.; Zhigilei, L. V.; Piqueux, S.

2017-03-01

The so-called 'PacMan' features on the leading hemispheres of the icy Saturnian moons of Mimas, Tethys and Dione were initially identified as anomalous optical discolorations and subsequently shown to have greater thermal inertia than the surrounding regions. The shape of these regions matches calculated deposition contours of high energy plasma electrons moving opposite to the moon's orbital direction, thus suggesting that electron interactions with the grains produce the observed anomalies. Here, descriptions of radiation-induced diffusion processes are given, and various sintering models are considered to calculate the rate of increase in the contact volume between grains in an icy regolith. Estimates of the characteristic sintering timescale, i.e. the time necessary for the thermal inertia to increase from that measured outside the anomalous regions to that within, are given for each of the moons. Since interplanetary dust particle (IDP) impact gardening and E-ring grain infall would be expected to mix the regolith and obscure the effects of high energy electrons, sintering rates are compared to rough estimates of the impact-induced resurfacing rates. Estimates of the sintering timescale determined by extrapolating laboratory measurements are below ∼0.03 Myr, while the regolith renewal timescales are larger than ∼0.1 Myr, thus indicating that irradiation by the high energy electrons should be sufficient to form stable thermal anomalies. More detailed models developed for sintering of spherical grains are able to account for the radiation-induced anomalies on Mimas and Tethys only if the regoliths on those bodies are relatively compact and composed of small (≲ 5 μm) grains or grain aggregates, and/or the grains are highly non-spherical with surface defect densities in the inter-grain contact regions that are much higher than expected for crystalline water ice grains at thermal equilibrium. These results are consistent with regolith thermal conductivity models which can only be reconciled with spacecraft observations if the contacts between grains are assumed to have much lower thermal conductance than predicted for idealized grains. The strength of the anomalies on Tethys and Dione appear to be limited by E-ring grain infall, while on Mimas IDP gardening limits the strength of the anomaly. The smaller flux of more deeply penetrating high energy (>1 MeV) electrons on Dione can account for the small thermal inertia differences measured there. Determining regolith sintering rates and the corresponding effect on thermal conductivity can, in principle, provide an independent constraint on the regolith grain geometries and exposure timescales for icy bodies.

Resolution-Adapted All-Atomic and Coarse-Grained Model for Biomolecular Simulations.

PubMed

Shen, Lin; Hu, Hao

2014-06-10

We develop here an adaptive multiresolution method for the simulation of complex heterogeneous systems such as the protein molecules. The target molecular system is described with the atomistic structure while maintaining concurrently a mapping to the coarse-grained models. The theoretical model, or force field, used to describe the interactions between two sites is automatically adjusted in the simulation processes according to the interaction distance/strength. Therefore, all-atomic, coarse-grained, or mixed all-atomic and coarse-grained models would be used together to describe the interactions between a group of atoms and its surroundings. Because the choice of theory is made on the force field level while the sampling is always carried out in the atomic space, the new adaptive method preserves naturally the atomic structure and thermodynamic properties of the entire system throughout the simulation processes. The new method will be very useful in many biomolecular simulations where atomistic details are critically needed.

Local-feature analysis for automated coarse-graining of bulk-polymer molecular dynamics simulations.

PubMed

Xue, Y; Ludovice, P J; Grover, M A

2012-12-01

A method for automated coarse-graining of bulk polymers is presented, using the data-mining tool of local feature analysis. Most existing methods for polymer coarse-graining define superatoms based on their covalent bonding topology along the polymer backbone, but here superatoms are defined based only on their correlated motions, as observed in molecular dynamics simulations. Correlated atomic motions are identified in the simulation data using local feature analysis, between atoms in the same or in different polymer chains. Groups of highly correlated atoms constitute the superatoms in the coarse-graining scheme, and the positions of their seed coordinates are then projected forward in time. Based on only the seed positions, local feature analysis enables the full reconstruction of all atomic positions. This reconstruction suggests an iterative scheme to reduce the computation of the simulations to initialize another short molecular dynamic simulation, identify new superatoms, and again project forward in time.

Influence of the solar wind and IMF on Jupiter's magnetosphere: Results from global MHD simulations

NASA Astrophysics Data System (ADS)

Sarkango, Y.; Jia, X.; Toth, G.; Hansen, K. C.

2017-12-01

Due to its large size, rapid rotation and presence of substantial internal plasma sources, Jupiter's magnetosphere is fundamentally different from that of the Earth. How and to what extent do the external factors, such as the solar wind and interplanetary magnetic field (IMF), influence the internally-driven magnetosphere is an open question. In this work, we solve the 3D semi-relativistic magnetohydrodynamic (MHD) equations using a well-established code, BATSRUS, to model the Jovian magnetosphere and study its interaction with the solar wind. Our global model adopts a non-uniform mesh covering the region from 200 RJ upstream to 1800 RJ downstream with the inner boundary placed at a radial distance of 2.5 RJ. The Io plasma torus centered around 6 RJ is generated in our model through appropriate mass-loading terms added to the set of MHD equations. We perform systematic numerical experiments in which we vary the upstream solar wind properties to investigate the impact of solar wind events, such as interplanetary shock and IMF rotation, on the global magnetosphere. From our simulations, we extract the location of the magnetopause boundary, the bow shock and the open-closed field line boundary (OCB), and determine their dependence on the solar wind properties and the IMF orientation. For validation, we compare our simulation results, such as density, temperature and magnetic field, to published empirical models based on in-situ measurements.

Design of the VISITOR Tool: A Versatile ImpulSive Interplanetary Trajectory OptimizeR

NASA Technical Reports Server (NTRS)

Corpaccioli, Luca; Linskens, Harry; Komar, David R.

2014-01-01

The design of trajectories for interplanetary missions represents one of the most complex and important problems to solve during conceptual space mission design. To facilitate conceptual mission sizing activities, it is essential to obtain sufficiently accurate trajectories in a fast and repeatable manner. To this end, the VISITOR tool was developed. This tool modularly augments a patched conic MGA-1DSM model with a mass model, launch window analysis, and the ability to simulate more realistic arrival and departure operations. This was implemented in MATLAB, exploiting the built-in optimization tools and vector analysis routines. The chosen optimization strategy uses a grid search and pattern search, an iterative variable grid method. A genetic algorithm can be selectively used to improve search space pruning, at the cost of losing the repeatability of the results and increased computation time. The tool was validated against seven flown missions: the average total mission (Delta)V offset from the nominal trajectory was 9.1%, which was reduced to 7.3% when using the genetic algorithm at the cost of an increase in computation time by a factor 5.7. It was found that VISITOR was well-suited for the conceptual design of interplanetary trajectories, while also facilitating future improvements due to its modular structure.

KSC-04PD-2554

NASA Technical Reports Server (NTRS)

2004-01-01

KENNEDY SPACE CENTER, FLA. Andy Schuerger, a research assistant professor with the University of Florida, demonstrates the Mars Simulation Chamber at the Space Life Sciences Lab during a tour of the facility for members of the news media. Schuerger is studying the effects of interplanetary space and Mars surface conditions on the survival, growth, and potential adaption of terrestrial microbes to the martian surface.

Dust in the Outer Solar System as measured by Cassini-CDA: KBOs, Centaurs and TNOs as parent bodies?

NASA Astrophysics Data System (ADS)

Altobelli, N.; Kempf, S.; Srama, R.

2017-09-01

We analyse 13 years of data acquired by the Cosmic Dust Analyser (CDA)-Entrance Grid (EG) subsystem on-board the Cassini spacecraft around Saturn. We confirm the presence of exogenous dust, originating from the interplanetary space and permanently crossing the Saturnian system. We analyse the range of possible heliocentric orbital elements in order to identify their possible origin. We observe particles whose dynamics is compatible with 'old' collisional debris from the Kuiper-Belt, migrating inward the Solar System under influence of the Poynting-Robertson drag, or relatively fresh grains from recently discovered cometary activity of Centaurs. A population of particles entering the Saturn's system with high velocities can be linked to Halley-type comets as parent bodies.

NEAMS FPL M2 Milestone Report: Development of a UO₂ Grain Size Model using Multicale Modeling and Simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tonks, Michael R; Zhang, Yongfeng; Bai, Xianming

2014-06-01

This report summarizes development work funded by the Nuclear Energy Advanced Modeling Simulation program's Fuels Product Line (FPL) to develop a mechanistic model for the average grain size in UO₂ fuel. The model is developed using a multiscale modeling and simulation approach involving atomistic simulations, as well as mesoscale simulations using INL's MARMOT code.

Pristine Samples of Silicon Carbide Separated From the Canyon Diablo Meteorite

NASA Astrophysics Data System (ADS)

Leung, I. S.; Winston, R.

2008-12-01

The Canyon Diablo is an iron meteorite whose collision with Earth created Meteor Crater in Arizona. In a study of a large block (53 kg) of this meteorite, Henri Moissan reported his findings of green, hexagonal crystals of silicon carbide (SiC) which was given the name moissanite the following year by George Kunz (1905). Moissan did not report finding the cubic form of SiC. Subsequently, many erroneous reports appeared when the polishing compound (synthetic SiC) was mistakenly considered by researchers as a natural mineral associated with, rather than a contaminant of many rock types. Hence, the occurrence of SiC in the Canyon Diablo remains in doubt, and any proposal to investigate this problem was discouraged and regarded as predictably unproductive. This notion hampered further work on abundant materials housed in museums. SiC grains have been found in primitive meteorites and interplanetary dust particles. Some have been identified as presolar grains. The significance of SiC in the Canyon Diablo cannot be revealed unless we have abundant data from pristine samples, enough for us to classify them into presolar or other types. We report here a simple method we used to separate SiC crystals from the meteorite. We chose samples containing a carbon nodule composed of graphite, diamond-lonsdaleite, and SiC grains in the iron matrix. We broke up the carbon nodule with a sharp tungsten carbide chisel and hammer. After removing the large metal fragments, we put a small amount of the fine black grains in a Petri dish with acetone, then swerved the dish to scatter the grains sparingly on the bottom of the dish. Under a binocular microscope, SiC crystals can be spotted easily by their adamantine luster, color (blue, green, beige, etc.), and high birefringence when placed between crossed polarizers of a petrographic microscope. We also X-rayed individual grains, and have identified several hexagonal polytype structures as well as the cubic form (3C polytype).

Complete Tem-Tomography: 3D Structure of Gems Cluster

NASA Technical Reports Server (NTRS)

Matsuno, J.; Miyake, A.; Tsuchiyama, A.; Messenger, S.; Nakamura-Messenger, K.

2015-01-01

GEMS (glass with embedded metal and sulfide) grains in interplanetary dust particles (IDPs) are considered to be one of the ubiquitous and fundamental building blocks of solids in the Solar System. They have been considered to be interstellar silicate dust that survived various metamorphism or alteration processes in the protoplanetary disk but the elemental and isotopic composition measurements suggest that most of them have been formed in the protoplanetary disk as condensates from high temperature gas. This formation model is also supported by the formation of GEMS-like grains with respect to the size, mineral assemblage, texture and infrared spectrum by condensation experiments from mean GEMS composition materials. Previous GEMS studies were performed only with 2D observation by transmission electron microscopy (TEM) or scanning TEM (STEM). However, the 3D shape and structure of GEMS grains and the spatial distribution of Fe/FeS's has critical information about their formation and origin. Recently, the 3D structure of GEMS grains in ultrathin sections of cluster IDPs was revealed by electron tomography using a TEM/STEM (JEM-2100F, JEOL). However, CT images of thin sections mounted on Cu grids acquired by conventional TEM-tomography are limited to low tilt angles (e. g., less than absolute value of 75 deg. In fact, previous 3D TEM observations of GEMS were affected by some artifacts related to the limited tilt range in the TEM used. Complete tomographic images should be acquired by rotating the sample tilt angle over a range of more than absolute value of 80 deg otherwise the CT images lose their correct structures. In order to constrain the origin and formation process of GEMS grains more clearly, we performed complete electron tomography for GEMS grains. Here we report the sample preparation method we have developed for this study, and the preliminary results.

Effect of Time-Dependent Pinning Pressure on Abnormal Grain Growth: Phase Field Simulation

NASA Astrophysics Data System (ADS)

Kim, Jeong Min; Min, Guensik; Shim, Jae-Hyeok; Lee, Kyung Jong

2018-05-01

The effect of the time-dependent pinning pressure of precipitates on abnormal grain growth has been investigated by multiphase field simulation with a simple precipitation model. The application of constant pinning pressure is problematic because it always induces abnormal grain growth or no grain growth, which is not reasonable considering the real situation. To produce time-dependent pinning pressure, both precipitation kinetics and precipitate coarsening kinetics have been considered with two rates: slow and fast. The results show that abnormal grain growth is suppressed at the slow precipitation rate. At the slow precipitation rate, the overall grain growth caused by the low pinning pressure in the early stage indeed plays a role in preventing abnormal grain growth by reducing the mobility advantage of abnormal grains. In addition, the fast precipitate coarsening rate tends to more quickly transform abnormal grain growth into normal grain growth by inducing the active growth of grains adjacent to the abnormal grains in the early stage. Therefore, the present study demonstrates that the time dependence of the pinning pressure of precipitates is a critical factor that determines the grain growth mode.

Effect of Time-Dependent Pinning Pressure on Abnormal Grain Growth: Phase Field Simulation

NASA Astrophysics Data System (ADS)

Kim, Jeong Min; Min, Guensik; Shim, Jae-Hyeok; Lee, Kyung Jong

2018-03-01

The effect of the time-dependent pinning pressure of precipitates on abnormal grain growth has been investigated by multiphase field simulation with a simple precipitation model. The application of constant pinning pressure is problematic because it always induces abnormal grain growth or no grain growth, which is not reasonable considering the real situation. To produce time-dependent pinning pressure, both precipitation kinetics and precipitate coarsening kinetics have been considered with two rates: slow and fast. The results show that abnormal grain growth is suppressed at the slow precipitation rate. At the slow precipitation rate, the overall grain growth caused by the low pinning pressure in the early stage indeed plays a role in preventing abnormal grain growth by reducing the mobility advantage of abnormal grains. In addition, the fast precipitate coarsening rate tends to more quickly transform abnormal grain growth into normal grain growth by inducing the active growth of grains adjacent to the abnormal grains in the early stage. Therefore, the present study demonstrates that the time dependence of the pinning pressure of precipitates is a critical factor that determines the grain growth mode.

Predicting mesoscale microstructural evolution in electron beam welding

DOE PAGES

Rodgers, Theron M.; Madison, Jonathan D.; Tikare, Veena; ...

2016-03-16

Using the kinetic Monte Carlo simulator, Stochastic Parallel PARticle Kinetic Simulator, from Sandia National Laboratories, a user routine has been developed to simulate mesoscale predictions of a grain structure near a moving heat source. Here, we demonstrate the use of this user routine to produce voxelized, synthetic, three-dimensional microstructures for electron-beam welding by comparing them with experimentally produced microstructures. When simulation input parameters are matched to experimental process parameters, qualitative and quantitative agreement for both grain size and grain morphology are achieved. The method is capable of simulating both single- and multipass welds. As a result, the simulations provide anmore » opportunity for not only accelerated design but also the integration of simulation and experiments in design such that simulations can receive parameter bounds from experiments and, in turn, provide predictions of a resultant microstructure.« less

Simulation study of entropy production in the one-dimensional Vlasov system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dai, Zongliang, E-mail: liangliang1223@gmail.com; Wang, Shaojie

2016-07-15

The coarse-grain averaged distribution function of the one-dimensional Vlasov system is obtained by numerical simulation. The entropy productions in cases of the random field, the linear Landau damping, and the bump-on-tail instability are computed with the coarse-grain averaged distribution function. The computed entropy production is converged with increasing length of coarse-grain average. When the distribution function differs slightly from a Maxwellian distribution, the converged value agrees with the result computed by using the definition of thermodynamic entropy. The length of the coarse-grain average to compute the coarse-grain averaged distribution function is discussed.

Process simulation of modified dry grind ethanol plant with recycle of pretreated and enzymatically hydrolyzed distillers' grains.

PubMed

Kim, Youngmi; Mosier, Nathan; Ladisch, Michael R

2008-08-01

Distillers' grains (DG), a co-product of a dry grind ethanol process, is an excellent source of supplemental proteins in livestock feed. Studies have shown that, due to its high polymeric sugar contents and ease of hydrolysis, the distillers' grains have potential as an additional source of fermentable sugars for ethanol fermentation. The benefit of processing the distillers' grains to extract fermentable sugars lies in an increased ethanol yield without significant modification in the current dry grind technology. Three different potential configurations of process alternatives in which pretreated and hydrolyzed distillers' grains are recycled for an enhanced overall ethanol yield are proposed and discussed in this paper based on the liquid hot water (LHW) pretreatment of distillers' grains. Possible limitations of each proposed process are also discussed. This paper presents a compositional analysis of distillers' grains, as well as a simulation of the modified dry grind processes with recycle of distillers' grains. Simulated material balances for the modified dry grind processes are established based on the base case assumptions. These balances are compared to the conventional dry grind process in terms of ethanol yield, compositions of its co-products, and accumulation of fermentation inhibitors. Results show that 14% higher ethanol yield is achievable by processing and hydrolyzing the distillers' grains for additional fermentable sugars, as compared to the conventional dry grind process. Accumulation of fermentation by-products and inhibitory components in the proposed process is predicted to be 2-5 times higher than in the conventional dry grind process. The impact of fermentation inhibitors is reviewed and discussed. The final eDDGS (enhanced dried distillers' grains) from the modified processes has 30-40% greater protein content per mass than DDGS, and its potential as a value-added process is also analyzed. While the case studies used to illustrate the process simulation are based on LHW pretreated DG, the process simulation itself provides a framework for evaluation of the impact of other pretreatments.

Interplanetary Physics Laboratory (IPL): A concept for an interplanetary mission in the mid-eighties

NASA Technical Reports Server (NTRS)

Burlaga, L. F.; Ogilvie, K. W.; Feldman, W.

1977-01-01

A concept for a near-earth interplanetary mission in the mid-eighties is described. The proposed objectives would be to determine the composition of the interplanetary constituents and its dependence on source-conditions and to investigate energy and momentum transfer processes in the interplanetary medium. Such a mission would accomplish three secondary objectives: (1) provide a baseline for deep space missions, (2) investigate variations of the solar wind with solar activity, and (3) provide input functions for magnetospheric studies.

Revealing Grain Boundary Sliding from Textures of a Deformed Nanocrystalline Pd–Au Alloy

PubMed Central

Skrotzki, Werner; Zhao, Yajun; Pukenas, Aurimas; Birringer, Rainer

2018-01-01

Employing a recent modeling scheme for grain boundary sliding [Zhao et al. Adv. Eng. Mater. 2017, doi:10.1002/adem.201700212], crystallographic textures were simulated for nanocrystalline fcc metals deformed in shear compression. It is shown that, as grain boundary sliding increases, the texture strength decreases while the signature of the texture type remains the same. Grain boundary sliding affects the texture components differently with respect to intensity and angular position. A comparison of a simulation and an experiment on a Pd–10 atom % Au alloy with a 15 nm grain size reveals that, at room temperature, the predominant deformation mode is grain boundary sliding contributing to strain by about 60%. PMID:29370130

The mechanical behavior of metal alloys with grain size distribution in a wide range of strain rates

NASA Astrophysics Data System (ADS)

Skripnyak, V. A.; Skripnyak, V. V.; Skripnyak, E. G.

2017-12-01

The paper discusses a multiscale simulation approach for the construction of grain structure of metals and alloys, providing high tensile strength with ductility. This work compares the mechanical behavior of light alloys and the influence of the grain size distribution in a wide range of strain rates. The influence of the grain size distribution on the inelastic deformation and fracture of aluminium and magnesium alloys is investigated by computer simulations in a wide range of strain rates. It is shown that the yield stress depends on the logarithm of the normalized strain rate for light alloys with a bimodal grain distribution and coarse-grained structure.

Interplanetary field and plasma during initial phase of geomagnetic storms

NASA Technical Reports Server (NTRS)

Patel, V. L.; Wiskerchen, M. J.

1975-01-01

A study has been conducted of a large number of geomagnetic storms occurring during the period from 1966 to 1970. Questions of data selection are discussed and the large-scale interplanetary magnetic field during the initial phase is examined. Small-scale interplanetary fields during the initial phase are also considered, taking into account important features of small-scale variations in the interplanetary field and plasma for three storms. Details concerning 23 geomagnetic storms and the interplanetary magnetic field are presented in a table. A study of the initial phase of these storms indicates that in most of these events, the solar-ecliptic Z component of the interplanetary magnetic field turns southward when the main phase decrease begins.

A likely detection of a local interplanetary dust cloud passing near the Earth in the AKARI mid-infrared all-sky map

NASA Astrophysics Data System (ADS)

Ishihara, D.; Kondo, T.; Kaneda, H.; Suzuki, T.; Nakamichi, K.; Takaba, S.; Kobayashi, H.; Masuda, S.; Ootsubo, T.; Pyo, J.; Onaka, T.

2017-07-01

Context. We are creating the AKARI mid-infrared all-sky diffuse maps. Through a foreground removal of the zodiacal emission, we serendipitously detected a bright residual component whose angular size is about 50° × 20° at a wavelength of 9 μm. Aims: We investigate the origin and the physical properties of the residual component. Methods: We measured the surface brightness of the residual component in the AKARI mid-infrared all-sky maps. Results: The residual component was significantly detected only in 2007 January, even though the same region was observed in 2006 July and 2007 July, which shows that it is not due to the Galactic emission. We suggest that this may be a small cloud passing near the Earth. By comparing the observed intensity ratio of I9 μm/I18 μm with the expected intensity ratio assuming thermal equilibrium of dust grains at 1 AU for various dust compositions and sizes, we find that dust grains in the moving cloud are likely to be much smaller than typical grains that produce the bulk of the zodiacal light. Conclusions: Considering the observed date and position, it is likely that it originates in the solar coronal mass ejection (CME) which took place on 2007 January 25.

A Coordinated Focused Ion Beam/Ultramicrotomy Technique for Serial Sectioning of Hayabusa Particles and Other Returned Samples

NASA Technical Reports Server (NTRS)

Berger, E. L.; Keller, L. P.

2014-01-01

Recent sample return missions, such as NASA's Stardust mission to comet 81P/Wild 2 and JAXA's Hayabusa mission to asteroid 25143 Itokawa, have returned particulate samples (typically 5-50 µm) that pose tremendous challenges to coordinated analysis using a variety of nano- and micro-beam techniques. The ability to glean maximal information from individual particles has become increasingly important and depends critically on how the samples are prepared for analysis. This also holds true for other extraterrestrial materials, including interplanetary dust particles, micrometeorites and lunar regolith grains. Traditionally, particulate samples have been prepared using microtomy techniques (e.g., [1]). However, for hard mineral particles ?20 µm, microtome thin sections are compromised by severe chatter and sample loss. For these difficult samples, we have developed a hybrid technique that combines traditional ultramicrotomy with focused ion beam (FIB) techniques, allowing for the in situ investigation of grain surfaces and interiors. Using this method, we have increased the number of FIB-SEM prepared sections that can be recovered from a particle with dimensions on the order of tens of µms. These sections can be subsequently analyzed using a variety of electron beam techniques. Here, we demonstrate this sample preparation technique on individual lunar regolith grains in order to study their space-weathered surfaces. We plan to extend these efforts to analyses of individual Hayabusa samples.

Large-scale properties of the interplanetary magnetic field

NASA Technical Reports Server (NTRS)

Schatten, K. H.

1972-01-01

Early theoretical work of Parker is presented along with the observational evidence supporting his Archimedes spiral model. Variations present in the interplanetary magnetic field from the spiral angle are related to structures in the solar wind. The causes of these structures are found to be either nonuniform radial solar wind flow or the time evolution of the photospheric field. Coronal magnetic models are related to the connection between the solar magnetic field and the interplanetary magnetic field. Direct extension of the solar field-magnetic nozzle controversy is discussed along with the coronal magnetic models. Effects of active regions on the interplanetary magnetic field is discussed with particular reference to the evolution of interplanetary sectors. Interplanetary magnetic field magnitude variations are shown throughout the solar cycle. The percentage of time the field magnitude is greater than 10 gamma is shown to closely parallel sunspot number. The sun's polar field influence on the interplanetary field and alternative views of the magnetic field structure out of the ecliptic plane are presented. In addition, a variety of significantly different interplanetary field structures are discussed.

Small Spacecraft System-Level Design and Optimization for Interplanetary Trajectories

NASA Technical Reports Server (NTRS)

Spangelo, Sara; Dalle, Derek; Longmier, Ben

2014-01-01

The feasibility of an interplanetary mission for a CubeSat, a type of miniaturized spacecraft, that uses an emerging technology, the CubeSat Ambipolar Thruster (CAT) is investigated. CAT is a large delta-V propulsion system that uses a high-density plasma source that has been miniaturized for small spacecraft applications. An initial feasibility assessment that demonstrated escaping Low Earth Orbit (LEO) and achieving Earth-escape trajectories with a 3U CubeSat and this thruster technology was demonstrated in previous work. We examine a mission architecture with a trajectory that begins in Earth orbits such as LEO and Geostationary Earth Orbit (GEO) which escapes Earth orbit and travels to Mars, Jupiter, or Saturn. The goal was to minimize travel time to reach the destinations and considering trade-offs between spacecraft dry mass, fuel mass, and solar power array size. Sensitivities to spacecraft dry mass and available power are considered. CubeSats are extremely size, mass, and power constrained, and their subsystems are tightly coupled, limiting their performance potential. System-level modeling, simulation, and optimization approaches are necessary to find feasible and optimal operational solutions to ensure system-level interactions are modeled. Thus, propulsion, power/energy, attitude, and orbit transfer models are integrated to enable systems-level analysis and trades. The CAT technology broadens the possible missions achievable with small satellites. In particular, this technology enables more sophisticated maneuvers by small spacecraft such as polar orbit insertion from an equatorial orbit, LEO to GEO transfers, Earth-escape trajectories, and transfers to other interplanetary bodies. This work lays the groundwork for upcoming CubeSat launch opportunities and supports future development of interplanetary and constellation CubeSat and small satellite mission concepts.

Characterization of high-intensity, long-duration continuous auroral activity (HILDCAA) events using recurrence quantification analysis

NASA Astrophysics Data System (ADS)

Mendes, Odim; Oliveira Domingues, Margarete; Echer, Ezequiel; Hajra, Rajkumar; Everton Menconi, Varlei

2017-08-01

Considering the magnetic reconnection and the viscous interaction as the fundamental mechanisms for transfer particles and energy into the magnetosphere, we study the dynamical characteristics of auroral electrojet (AE) index during high-intensity, long-duration continuous auroral activity (HILDCAA) events, using a long-term geomagnetic database (1975-2012), and other distinct interplanetary conditions (geomagnetically quiet intervals, co-rotating interaction regions (CIRs)/high-speed streams (HSSs) not followed by HILDCAAs, and events of AE comprised in global intense geomagnetic disturbances). It is worth noting that we also study active but non-HILDCAA intervals. Examining the geomagnetic AE index, we apply a dynamics analysis composed of the phase space, the recurrence plot (RP), and the recurrence quantification analysis (RQA) methods. As a result, the quantification finds two distinct clusterings of the dynamical behaviours occurring in the interplanetary medium: one regarding a geomagnetically quiet condition regime and the other regarding an interplanetary activity regime. Furthermore, the HILDCAAs seem unique events regarding a visible, intense manifestations of interplanetary Alfvénic waves; however, they are similar to the other kinds of conditions regarding a dynamical signature (based on RQA), because it is involved in the same complex mechanism of generating geomagnetic disturbances. Also, by characterizing the proper conditions of transitions from quiescent conditions to weaker geomagnetic disturbances inside the magnetosphere and ionosphere system, the RQA method indicates clearly the two fundamental dynamics (geomagnetically quiet intervals and HILDCAA events) to be evaluated with magneto-hydrodynamics simulations to understand better the critical processes related to energy and particle transfer into the magnetosphere-ionosphere system. Finally, with this work, we have also reinforced the potential applicability of the RQA method for characterizing nonlinear geomagnetic processes related to the magnetic reconnection and the viscous interaction affecting the magnetosphere.

Enforcing dust mass conservation in 3D simulations of tightly coupled grains with the PHANTOM SPH code

NASA Astrophysics Data System (ADS)

Ballabio, G.; Dipierro, G.; Veronesi, B.; Lodato, G.; Hutchison, M.; Laibe, G.; Price, D. J.

2018-06-01

We describe a new implementation of the one-fluid method in the SPH code PHANTOM to simulate the dynamics of dust grains in gas protoplanetary discs. We revise and extend previously developed algorithms by computing the evolution of a new fluid quantity that produces a more accurate and numerically controlled evolution of the dust dynamics. Moreover, by limiting the stopping time of uncoupled grains that violate the assumptions of the terminal velocity approximation, we avoid fatal numerical errors in mass conservation. We test and validate our new algorithm by running 3D SPH simulations of a large range of disc models with tightly and marginally coupled grains.

A highly efficient 3D level-set grain growth algorithm tailored for ccNUMA architecture

NASA Astrophysics Data System (ADS)

Mießen, C.; Velinov, N.; Gottstein, G.; Barrales-Mora, L. A.

2017-12-01

A highly efficient simulation model for 2D and 3D grain growth was developed based on the level-set method. The model introduces modern computational concepts to achieve excellent performance on parallel computer architectures. Strong scalability was measured on cache-coherent non-uniform memory access (ccNUMA) architectures. To achieve this, the proposed approach considers the application of local level-set functions at the grain level. Ideal and non-ideal grain growth was simulated in 3D with the objective to study the evolution of statistical representative volume elements in polycrystals. In addition, microstructure evolution in an anisotropic magnetic material affected by an external magnetic field was simulated.

Prediction of the Grain-Microstructure Evolution Within a Friction Stir Welding (FSW) Joint via the Use of the Monte Carlo Simulation Method

NASA Astrophysics Data System (ADS)

Grujicic, M.; Ramaswami, S.; Snipes, J. S.; Avuthu, V.; Galgalikar, R.; Zhang, Z.

2015-09-01

A thermo-mechanical finite element analysis of the friction stir welding (FSW) process is carried out and the evolution of the material state (e.g., temperature, the extent of plastic deformation, etc.) monitored. Subsequently, the finite-element results are used as input to a Monte-Carlo simulation algorithm in order to predict the evolution of the grain microstructure within different weld zones, during the FSW process and the subsequent cooling of the material within the weld to room temperature. To help delineate different weld zones, (a) temperature and deformation fields during the welding process, and during the subsequent cooling, are monitored; and (b) competition between the grain growth (driven by the reduction in the total grain-boundary surface area) and dynamic-recrystallization grain refinement (driven by the replacement of highly deformed material with an effectively "dislocation-free" material) is simulated. The results obtained clearly revealed that different weld zones form as a result of different outcomes of the competition between the grain growth and grain refinement processes.

Experimental and simulation studies on grain growth in TiC and WC-based cermets during liquid phase sintering

NASA Astrophysics Data System (ADS)

Shin, Soon-Gi

2000-06-01

The grain growth behaviors of TiC and WC particles in TiC-Ni, TiC-Mo2C-Ni, WC-Co and WC-VC-Co alloys during liquid phase sintering were investigated for different Ni or Co contents and compared with the results of Monte Carlo simulations. In the experimental study, TiC-Ni and WC-Co alloys had a maximum grain size at a certain liquid volume fraction, while the grain size in TiC-Mo2C-Ni and WC-VC-Co alloys increased monotonically with an increasing liquid volume fraction. These results mean that the grain growth of these alloys cannot be explained by the conventional mechanisms for Ostwald ripening, namely diffusion or reaction controlled processes. Monte Carlo simulations with different energy relationships between solidliquid interfaces predicted the effect of the liquid volume fraction on grain size similar to the experimental results. The contiguous boundaries between solid (carbide) particles appear to influence the grain growth behavior in TiC- and WC-based alloys during liquid phase sintering.

Magnetization reversal mechanism and coercivity enhancement in three-dimensional granular Nd-Fe-B magnets studied by micromagnetic simulations

NASA Astrophysics Data System (ADS)

Lee, Jae-Hyeok; Choe, Jinhyeok; Hwang, Shinwon; Kim, Sang-Koog

2017-08-01

We studied the mechanism of magnetization reversals and coercivity enhancements in three-dimensional (3D) granular Nd-Fe-B permanent magnets using finite-element micromagnetic simulations. The magnetization reversals in the hard magnets consisting of hard-phase grains separated by relatively soft-phase grain boundaries were analyzed with reference to the simulation results for the magnetic field-dependent distributions of the local magnetizations. The saturation magnetization of the grain-boundary phase plays a crucial role in the transition between nucleation- and domain-wall-propagation-controlled reversal processes. The smaller the saturation magnetization of the grain-boundary phase is, the more preferable is the nucleation-controlled process, which results in a larger coercivity. The exchange stiffness of the grain-boundary phase determines the preferred paths of domain-wall propagations, whether inward into grains or along the grain boundaries for relatively small and large exchange stiffness, respectively. However, the exchange stiffness of the grain-boundary phase alone does not significantly contribute to coercivity enhancement in cases where the size of hard-phase grains is much greater than the exchange length. This work paves the way for the design of high-performance hard magnets of large coercivity and maximum-energy-product values.

Global Effects of Transmitted Shock Wave Propagation Through the Earth's Inner Magnetosphere: First Results from 3-D Hybrid Kinetic Modeling

NASA Technical Reports Server (NTRS)

Lipatov, A. S.; Sibeck, D. G.

2016-01-01

We use a new hybrid kinetic model to simulate the response of ring current, outer radiation belt, and plasmaspheric particle populations to impulsive interplanetary shocks. Since particle distributions attending the interplanetary shock waves and in the ring current and radiation belts are non-Maxwellian, waveparticle interactions play a crucial role in energy transport within the inner magnetosphere. Finite gyroradius effects become important in mass loading the shock waves with the background plasma in the presence of higher energy ring current and radiation belt ions and electrons. Initial results show that shocks cause strong deformations in the global structure of the ring current, radiation belt, and plasmasphere. The ion velocity distribution functions at the shock front, in the ring current, and in the radiation belt help us determine energy transport through the Earth's inner magnetosphere.

Grain dissection as a grain size reducing mechanism during ice microdynamics

NASA Astrophysics Data System (ADS)

Steinbach, Florian; Kuiper, Ernst N.; Eichler, Jan; Bons, Paul D.; Drury, Martin R.; Griera, Albert; Pennock, Gill M.; Weikusat, Ilka

2017-04-01

Ice sheets are valuable paleo-climate archives, but can lose their integrity by ice flow. An understanding of the microdynamic mechanisms controlling the flow of ice is essential when assessing climatic and environmental developments related to ice sheets and glaciers. For instance, the development of a consistent mechanistic grain size law would support larger scale ice flow models. Recent research made significant progress in numerically modelling deformation and recrystallisation mechanisms in the polycrystalline ice and ice-air aggregate (Llorens et al., 2016a,b; Steinbach et al., 2016). The numerical setup assumed grain size reduction is achieved by the progressive transformation of subgrain boundaries into new high angle grain boundaries splitting an existing grain. This mechanism is usually termed polygonisation. Analogue experiments suggested, that strain induced grain boundary migration can cause bulges to migrate through the whole of a grain separating one region of the grain from another (Jessell, 1986; Urai, 1987). This mechanism of grain dissection could provide an alternative grain size reducing mechanism, but has not yet been observed during ice microdynamics. In this contribution, we present results using an updated numerical approach allowing for grain dissection. The approach is based on coupling the full field theory crystal visco-plasticity code (VPFFT) of Lebensohn (2001) to the multi-process modelling platform Elle (Bons et al., 2008). VPFFT predicts the mechanical fields resulting from short strain increments, dynamic recrystallisation process are implemented in Elle. The novel approach includes improvements to allow for grain dissection, which was topologically impossible during earlier simulations. The simulations are supported by microstructural observations from NEEM (North Greenland Eemian Ice Drilling) ice core. Mappings of c-axis orientations using the automatic fabric analyser and full crystallographic orientations using electron backscatter diffraction (EBSD) are presented. Numerical simulations predict and resolve the microstructural evolution over strain and time. The occurrence of processes such as grain dissection can only be proven using such time resolved movies of microstructure evolution. We will present movies that show grain dissection as a common process during the simulations. Microstructures obtained from NEEM ice core support the observations and we provide evidence for grain dissection in natural ice. Grain dissection is observed to be most efficient relative to polygonisation, when the microstructure approaches steady state grain sizes. This is consistent with analogue experiments observing grain dissection by Jessell (1986) and Urai (1987). Our research suggests a novel grain size reducing mechanisms in ice microdynamics that should be considered when developing a consistent grain size law.

Brownian dynamics simulations of lipid bilayer membrane with hydrodynamic interactions in LAMMPS

NASA Astrophysics Data System (ADS)

Fu, Szu-Pei; Young, Yuan-Nan; Peng, Zhangli; Yuan, Hongyan

2016-11-01

Lipid bilayer membranes have been extensively studied by coarse-grained molecular dynamics simulations. Numerical efficiencies have been reported in the cases of aggressive coarse-graining, where several lipids are coarse-grained into a particle of size 4 6 nm so that there is only one particle in the thickness direction. Yuan et al. proposed a pair-potential between these one-particle-thick coarse-grained lipid particles to capture the mechanical properties of a lipid bilayer membrane (such as gel-fluid-gas phase transitions of lipids, diffusion, and bending rigidity). In this work we implement such interaction potential in LAMMPS to simulate large-scale lipid systems such as vesicles and red blood cells (RBCs). We also consider the effect of cytoskeleton on the lipid membrane dynamics as a model for red blood cell (RBC) dynamics, and incorporate coarse-grained water molecules to account for hydrodynamic interactions. The interaction between the coarse-grained water molecules (explicit solvent molecules) is modeled as a Lennard-Jones (L-J) potential. We focus on two sets of LAMMPS simulations: 1. Vesicle shape transitions with varying enclosed volume; 2. RBC shape transitions with different enclosed volume. This work is funded by NSF under Grant DMS-1222550.

Brownian dynamics simulations of lipid bilayer membrane with hydrodynamic interactions in LAMMPS

NASA Astrophysics Data System (ADS)

Fu, Szu-Pei; Young, Yuan-Nan; Peng, Zhangli; Yuan, Hongyan

Lipid bilayer membranes have been extensively studied by coarse-grained molecular dynamics simulations. Numerical efficiency has been reported in the cases of aggressive coarse-graining, where several lipids are coarse-grained into a particle of size 4 6 nm so that there is only one particle in the thickness direction. Yuan et al. proposed a pair-potential between these one-particle-thick coarse-grained lipid particles to capture the mechanical properties of a lipid bilayer membrane (such as gel-fluid-gas phase transitions of lipids, diffusion, and bending rigidity). In this work we implement such interaction potential in LAMMPS to simulate large-scale lipid systems such as vesicles and red blood cells (RBCs). We also consider the effect of cytoskeleton on the lipid membrane dynamics as a model for red blood cell (RBC) dynamics, and incorporate coarse-grained water molecules to account for hydrodynamic interactions. The interaction between the coarse-grained water molecules (explicit solvent molecules) is modeled as a Lennard-Jones (L-J) potential. We focus on two sets of LAMMPS simulations: 1. Vesicle shape transitions with varying enclosed volume; 2. RBC shape transitions with different enclosed volume.

Dynamics of basaltic glass dissolution - Capturing microscopic effects in continuum scale models

NASA Astrophysics Data System (ADS)

Aradóttir, E. S. P.; Sigfússon, B.; Sonnenthal, E. L.; Björnsson, G.; Jónsson, H.

2013-11-01

The method of 'multiple interacting continua' (MINC) was applied to include microscopic rate-limiting processes in continuum scale reactive transport models of basaltic glass dissolution. The MINC method involves dividing the system up to ambient fluid and grains, using a specific surface area to describe the interface between the two. The various grains and regions within grains can then be described by dividing them into continua separated by dividing surfaces. Millions of grains can thus be considered within the method without the need to explicity discretizing them. Four continua were used for describing a dissolving basaltic glass grain; the first one describes the ambient fluid around the grain, while the second, third and fourth continuum refer to a diffusive leached layer, the dissolving part of the grain and the inert part of the grain, respectively. The model was validated using the TOUGHREACT simulator and data from column flow through experiments of basaltic glass dissolution at low, neutral and high pH values. Successful reactive transport simulations of the experiments and overall adequate agreement between measured and simulated values provides validation that the MINC approach can be applied for incorporating microscopic effects in continuum scale basaltic glass dissolution models. Equivalent models can be used when simulating dissolution and alteration of other minerals. The study provides an example of how numerical modeling and experimental work can be combined to enhance understanding of mechanisms associated with basaltic glass dissolution. Column outlet concentrations indicated basaltic glass to dissolve stoichiometrically at pH 3. Predictive simulations with the developed MINC model indicated significant precipitation of secondary minerals within the column at neutral and high pH, explaining observed non-stoichiometric outlet concentrations at these pH levels. Clay, zeolite and hydroxide precipitation was predicted to be most abundant within the column.

Sun-to-Earth simulations of geo-effective Coronal Mass Ejections with EUHFORIA: a heliospheric-magnetospheric model chain approach

NASA Astrophysics Data System (ADS)

Scolini, C.; Verbeke, C.; Gopalswamy, N.; Wijsen, N.; Poedts, S.; Mierla, M.; Rodriguez, L.; Pomoell, J.; Cramer, W. D.; Raeder, J.

2017-12-01

Coronal Mass Ejections (CMEs) and their interplanetary counterparts are considered to be the major space weather drivers. An accurate modelling of their onset and propagation up to 1 AU represents a key issue for more reliable space weather forecasts, and predictions about their actual geo-effectiveness can only be performed by coupling global heliospheric models to 3D models describing the terrestrial environment, e.g. magnetospheric and ionospheric codes in the first place. In this work we perform a Sun-to-Earth comprehensive analysis of the July 12, 2012 CME with the aim of testing the space weather predictive capabilities of the newly developed EUHFORIA heliospheric model integrated with the Gibson-Low (GL) flux rope model. In order to achieve this goal, we make use of a model chain approach by using EUHFORIA outputs at Earth as input parameters for the OpenGGCM magnetospheric model. We first reconstruct the CME kinematic parameters by means of single- and multi- spacecraft reconstruction methods based on coronagraphic and heliospheric CME observations. The magnetic field-related parameters of the flux rope are estimated based on imaging observations of the photospheric and low coronal source regions of the eruption. We then simulate the event with EUHFORIA, testing the effect of the different CME kinematic input parameters on simulation results at L1. We compare simulation outputs with in-situ measurements of the Interplanetary CME and we use them as input for the OpenGGCM model, so to investigate the magnetospheric response to solar perturbations. From simulation outputs we extract some global geomagnetic activity indexes and compare them with actual data records and with results obtained by the use of empirical relations. Finally, we discuss the forecasting capabilities of such kind of approach and its future improvements.

Linear polarization of light scattered by cometary analogs: New samples

NASA Astrophysics Data System (ADS)

Hadamcik, E.; Renard, J.; Buch, A.; Carrasco, N.; Johnson, N.; Nuth, J.

2014-07-01

Mixtures of silicates (Mg and Fe) with carbonaceous compounds (carbon and/or organics) are currently proposed as cometary analogs. The particles are fluffy aggregates of submicron-sized constituent grains and compact grains (tens of micrometers), similar to those captured in the Earth's stratosphere (interplanetary dust particles or IDPs) and deduced from the Stardust results. They are lifted or in microgravity or levitated by an air-draught. The light source is unpolarized. The linear polarization of the scattered light floating in the beam is studied as a function of the phase angle. In previous experiments with the PROGRA2 instrument (Hadamcik et al., 2011), the general shape of the cometary polarimetric phase curves is reproduced with a shallow negative branch and a more developed positive branch (maximum polarization around 20--30 %) depending on the size distributions of the particles (compact and/or aggregates) and their constituent grains. To observe the increase of polarization with wavelength, the organic materials were necessary. When fluffy aggregates (silicates and carbon black mixtures) and compact silicate grains of tens of micrometers are present, the whole cometary coma polarization phase curve is well fitted by the phase curves obtained. The maximum polarization value decreases when the ratio of compact silicates to fluffy aggregates increases. The observed differences in polarization between different coma regions may be also simulated. When only fluffy aggregates are used, the maximum polarization corresponds to the polarization in jets of 'high polarization' active comets (Hadamcik and Levasseur-Regourd, 2003). A high polarization region may exist in some 'low polarization' comets, with large slowly moving particles; using the experimental results, we suggest the presence of dark relatively compact particles larger than 20 micrometers (Hadamcik et al., 2007; 2011). When not hidden by jets, a polarimetric halo is sometimes observed in the inner coma. The negative branch can be as deep as -6% and the positive branch is smaller as compared to the whole coma (Hadamcik et al., 2003). Zubko et al. (2012) have proposed an increased fraction of silicates. From the experiments, we suggest some carbonaceous compounds with refractive indices close to those of silicates (relatively transparent). This material, if heated by the Sun after ejection, should be darker as observed when these materials are heated to 200--300°C. We are working on new analogs with mixtures of silicates and organics (not only carbon), silicates coated by organics (Johnson et al., 2004), or organics heated or not and with different elemental compositions (N/C ratios).

Computational Investigation of Effects of Grain Size on Ballistic Performance of Copper

NASA Astrophysics Data System (ADS)

He, Ge; Dou, Yangqing; Guo, Xiang; Liu, Yucheng

2018-01-01

Numerical simulations were conducted to compare ballistic performance and penetration mechanism of copper (Cu) with four representative grain sizes. Ballistic limit velocities for coarse-grained (CG) copper (grain size ≈ 90 µm), regular copper (grain size ≈ 30 µm), fine-grained (FG) copper (grain size ≈ 890 nm), and ultrafine-grained (UG) copper (grain size ≈ 200 nm) were determined for the first time through the simulations. It was found that the copper with reduced grain size would offer higher strength and better ductility, and therefore renders improved ballistic performance than the CG and regular copper. High speed impact and penetration behavior of the FG and UG copper was also compared with the CG coppers strengthened by nanotwinned (NT) regions. The comparison results showed the impact and penetration resistance of UG copper is comparable to the CG copper strengthened by NT regions with the minimum twin spacing. Therefore, besides the NT-strengthened copper, the single phase copper with nanoscale grain size could also be a strong candidate material for better ballistic protection. A computational modeling and simulation framework was proposed for this study, in which Johnson-Cook (JC) constitutive model is used to predict the plastic deformation of Cu; the JC damage model is to capture the penetration and fragmentation behavior of Cu; Bao-Wierzbicki (B-W) failure criterion defines the material's failure mechanisms; and temperature increase during this adiabatic penetration process is given by the Taylor-Quinney method.

Principal Components Constrain Dynamic Pyrometamorphism in a Partially Melted Interplanetary Dust Particle

NASA Astrophysics Data System (ADS)

Rietmeijer, F. J. M.

1996-03-01

All interplanetary dust particles [IDPs] that decelerate in the Earth's atmosphere experience flash heating whereby their orbital velocity (km s^-1) is reduced to cm s^-1. Iron-oxide rims that may either be continuous on the particle surface, or discontinuous along its perimeter, occur on many IDPs. It is the most conspicuous mineralogical indicator of dynamic pyrometamorphism and its formation is interpreted as 'intense' IDP heating. It appears that the formation of these magnetite and maghemite rims is intimately linked to the presence of Fe,Ni-sulfides in the pre-entry particle. In this regard chondritic porous (CP) IDP L2011K7 may be an unusual particle. This porous aggregate consists of S-free polyphase units (PUs), nonstoichiometric diopside and Mg-rich wollastonite single-crystals and small, accessory Fe,Ni-sulfide grains. Only a few Fe-oxide nanograins are present along its perimeter. The nonstoichiometry of its Ca,Mg-clinopyroxenes indicates incongruent melting or vaporization that was experimentally determined at 1300 degrees-1400 degrees C. The CP IDP L2011K7 is probably of cometary origin since active comet nuclei are the most likely sources for uncompacted aggregate IDPs whereby their low density (< 1 g cm^-3) enhances atmospheric entry survival of large particles. In addition, the fluffy texture which inhibits chemical exchange among its components further enhances their survival unless compaction occurs during deceleration in the Earth's atmosphere.

Comparison of the oxidation state of Fe in comet 81P/Wild 2 and chondritic-porous interplanetary dust particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogliore, Ryan C.; Butterworth, Anna L.; Fakra, Sirine C.

2010-07-16

The fragile structure of chondritic-porous interplanetary dust particles (CP-IDPs) and their minimal parent-body alteration have led researchers to believe these particles originate in comets rather than asteroids where aqueous and thermal alterations have occurred. The solar elemental abundances and atmospheric entry speed of CP-IDPs also suggest a cometary origin. With the return of the Stardust samples from Jupiter-family comet 81P/Wild 2, this hypothesis can be tested. We have measured the Fe oxidation state of 15 CP-IDPs and 194 Stardust fragments using a synchrotron-based x-ray microprobe. We analyzed {approx}300 ng of Wild 2 material - three orders of magnitude more materialmore » than other analyses comparing Wild 2 and CP-IDPs. The Fe oxidation state of these two samples of material are > 2{sigma} different: the CP-IDPs are more oxidized than the Wild 2 grains. We conclude that comet Wild 2 contains material that formed at a lower oxygen fugacity than the parent-body, or parent bodies, of CP-IDPs. If all Jupiter-family comets are similar, they do not appear to be consistent with the origin of CP-IDPs. However, comets that formed from a different mix of nebular material and are more oxidized than Wild 2 could be the source of CP-IDPs.« less

Wave-Particle Interactions and Particle Acceleration in Turbulent Plasmas: Hybrid Simulations

NASA Astrophysics Data System (ADS)

Kucharek, Harald; Pogorelov, Nikolai; Mueller, Hans; Gamayunov, Konstantin; Farrugia, Charles

2015-04-01

Wave-particle interactions and acceleration processes are present in all key regions inside and outside of the heliosphere. Spacecraft observations measure ion distributions and accelerated ion populations, which are the result of one or several processes. For instance STEREO measures energetic particles associated with interplanetary discontinuities and in the solar wind. Voyager and IBEX provide unique data of energetic particles from the termination shock and the inner and outer heliopause. The range of plasma conditions covered by observations is enormous. However, the physical processes causing particle acceleration and wave-particle interaction and determining the particle distributions are still unknown. Currently two mechanisms, the so-called pumping mechanism (Fisk and Gloeckler, 2010) and merging/contracting island (Fermo, Drake & Swisdak, 2010) are discussed as promising models. In order to determine these individual processes, numerical models or theoretical considerations are needed. Hybrid simulations, which include all kinetic processes self-consistently on the ion level, are a very proven, powerful tool to investigate wave-particle interaction, turbulence, and phase-space evolution of pickup and solar wind ions. In the framework of this study we performed 3D multi-species hybrid simulations for an ion/ion beam instability to study the temporal evolution of ion distributions, their stability, and the influence of self-generated waves. We investigated the energization of ions downstream of interplanetary discontinuities and shocks and downstream of the termination shock, the turbulence, and growth rate of instabilities and compared the results with theoretical predictions. The simulations show that ions can be accelerated downstream of collisionless shocks by trapping of charged particles in coherent wave fronts.

Influence of deep defects on device performance of thin-film polycrystalline silicon solar cells

NASA Astrophysics Data System (ADS)

Fehr, M.; Simon, P.; Sontheimer, T.; Leendertz, C.; Gorka, B.; Schnegg, A.; Rech, B.; Lips, K.

2012-09-01

Employing quantitative electron-paramagnetic resonance analysis and numerical simulations, we investigate the performance of thin-film polycrystalline silicon solar cells as a function of defect density. We find that the open-circuit voltage is correlated to the density of defects, which we assign to coordination defects at grain boundaries and in dislocation cores. Numerical device simulations confirm the observed correlation and indicate that the device performance is limited by deep defects in the absorber bulk. Analyzing the defect density as a function of grain size indicates a high concentration of intra-grain defects. For large grains (>2 μm), we find that intra-grain defects dominate over grain boundary defects and limit the solar cell performance.

Effect of irradiation on mechanical properties of symmetrical grain boundaries investigated by atomic simulations

NASA Astrophysics Data System (ADS)

Wang, X. Y.; Gao, N.; Setyawan, W.; Xu, B.; Liu, W.; Wang, Z. G.

2017-08-01

Tensile response of irradiated symmetric grain boundaries to the externally applied strain has been studied using atomic simulation methods. The absorption of irradiation induced defects by grain boundaries has been confirmed to degrade the mechanical properties of grain boundaries through the change of its undertaken deformation mechanism. Atomic rearrangement, the formations of a stress accumulation region and vacancy-rich zone and the nucleation and movement of dislocations under stress effect have been observed after the displacement cascades in grain boundaries, which are considered as main reasons to induce above degradation. These results suggest the necessity of considering both trapping efficiency to defects and the mechanical property change of irradiated grain boundaries for further development of radiation resistant materials.

Coarse-grained hydrodynamics from correlation functions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palmer, Bruce

This paper will describe a formalism for using correlation functions between different grid cells as the basis for determining coarse-grained hydrodynamic equations for modeling the behavior of mesoscopic fluid systems. Configuration from a molecular dynamics simulation are projected onto basis functions representing grid cells in a continuum hydrodynamic simulation. Equilbrium correlation functions between different grid cells are evaluated from the molecular simulation and used to determine the evolution operator for the coarse-grained hydrodynamic system. The formalism is applied to some simple hydrodynamic cases to determine the feasibility of applying this to realistic nanoscale systems.

On the twists of interplanetary magnetic flux ropes observed at 1 AU

NASA Astrophysics Data System (ADS)

Wang, Yuming; Zhuang, Bin; Hu, Qiang; Liu, Rui; Shen, Chenglong; Chi, Yutian

2016-10-01

Magnetic flux ropes (MFRs) are one kind of fundamental structures in the solar/space physics and involved in various eruption phenomena. Twist, characterizing how the magnetic field lines wind around a main axis, is an intrinsic property of MFRs, closely related to the magnetic free energy and stableness. Although the effect of the twist on the behavior of MFRs had been widely studied in observations, theory, modeling, and numerical simulations, it is still unclear how much amount of twist is carried by MFRs in the solar atmosphere and in heliosphere and what role the twist played in the eruptions of MFRs. Contrasting to the solar MFRs, there are lots of in situ measurements of magnetic clouds (MCs), the large-scale MFRs in interplanetary space, providing some important information of the twist of MFRs. Thus, starting from MCs, we investigate the twist of interplanetary MFRs with the aid of a velocity-modified uniform-twist force-free flux rope model. It is found that most of MCs can be roughly fitted by the model and nearly half of them can be fitted fairly well though the derived twist is probably overestimated by a factor of 2.5. By applying the model to 115 MCs observed at 1 AU, we find that (1) the twist angles of interplanetary MFRs generally follow a trend of about 0.6l/R radians, where l/R is the aspect ratio of a MFR, with a cutoff at about 12π radians AU-1, (2) most of them are significantly larger than 2.5π radians but well bounded by 2l/R radians, (3) strongly twisted magnetic field lines probably limit the expansion and size of MFRs, and (4) the magnetic field lines in the legs wind more tightly than those in the leading part of MFRs. These results not only advance our understanding of the properties and behavior of interplanetary MFRs but also shed light on the formation and eruption of MFRs in the solar atmosphere. A discussion about the twist and stableness of solar MFRs are therefore given.

Advanced Polymer Network Structures

DTIC Science & Technology

2016-02-01

double networks in a single step was identified from coarse-grained molecular dynamics simulations of polymer solvents bearing rigid side chains dissolved...in a polymer network. Coarse-grained molecular dynamics simulations also explored the mechanical behavior of traditional double networks and...DRI), polymer networks, polymer gels, molecular dynamics simulations , double networks 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

Electromagnetic Simulations for an Axisymmetric Gregorian Reflector System for a Space Deployed Inflatable Antenna

DTIC Science & Technology

2016-01-22

Q. J. Wei, S. Pan, S. Mohan, and S. Seager, Inflatable antenna for CubeSat : fabrication, deployment and results of experimental tests, 2014 IEEE...Aerospace Conference, pp. 1- 12. [8] A. Babuscia, T. Choi, C. Lee, and K-M. Cheung, Inflatable antennas and arrays for interplanetary communication using CubeSats and SmallSats, 2015 IEEE Aerospace Conference, pp. 1-9.

Interplanetary travel: Is gravity needed to close the loop

NASA Technical Reports Server (NTRS)

Vernikos-Danellis, Joan

1988-01-01

Evidence has been accumulating from spaceflight and ground simulation studies suggesting that the normal relationship between neuroendocrine driving mechanisms and their respective target organs may become uncoupled; and that the sensitivity of the various components of the closed-loop systems may be altered. Changes in the regulation of the pituitary-adrenal system and the angioten-sinaldosterone system is discussed in support of this thesis.

Simulating galactic dust grain evolution on a moving mesh

NASA Astrophysics Data System (ADS)

McKinnon, Ryan; Vogelsberger, Mark; Torrey, Paul; Marinacci, Federico; Kannan, Rahul

2018-05-01

Interstellar dust is an important component of the galactic ecosystem, playing a key role in multiple galaxy formation processes. We present a novel numerical framework for the dynamics and size evolution of dust grains implemented in the moving-mesh hydrodynamics code AREPO suited for cosmological galaxy formation simulations. We employ a particle-based method for dust subject to dynamical forces including drag and gravity. The drag force is implemented using a second-order semi-implicit integrator and validated using several dust-hydrodynamical test problems. Each dust particle has a grain size distribution, describing the local abundance of grains of different sizes. The grain size distribution is discretised with a second-order piecewise linear method and evolves in time according to various dust physical processes, including accretion, sputtering, shattering, and coagulation. We present a novel scheme for stochastically forming dust during stellar evolution and new methods for sub-cycling of dust physics time-steps. Using this model, we simulate an isolated disc galaxy to study the impact of dust physical processes that shape the interstellar grain size distribution. We demonstrate, for example, how dust shattering shifts the grain size distribution to smaller sizes resulting in a significant rise of radiation extinction from optical to near-ultraviolet wavelengths. Our framework for simulating dust and gas mixtures can readily be extended to account for other dynamical processes relevant in galaxy formation, like magnetohydrodynamics, radiation pressure, and thermo-chemical processes.

Adiabatic coarse-graining and simulations of stochastic biochemical networks

PubMed Central

Sinitsyn, N. A.; Hengartner, Nicolas; Nemenman, Ilya

2009-01-01

We propose a universal approach for analysis and fast simulations of stiff stochastic biochemical networks, which rests on elimination of fast chemical species without a loss of information about mesoscopic, non-Poissonian fluctuations of the slow ones. Our approach is similar to the Born–Oppenheimer approximation in quantum mechanics and follows from the stochastic path integral representation of the cumulant generating function of reaction events. In applications with a small number of chemical reactions, it produces analytical expressions for cumulants of chemical fluxes between the slow variables. This allows for a low-dimensional, interpretable representation and can be used for high-accuracy, low-complexity coarse-grained numerical simulations. As an example, we derive the coarse-grained description for a chain of biochemical reactions and show that the coarse-grained and the microscopic simulations agree, but the former is 3 orders of magnitude faster. PMID:19525397

Grain size effects on dislocation and twinning mediated plasticity in magnesium

DOE PAGES

Fan, Haidong; Aubry, Sylvie; Arsenlis, Athanasios; ...

2015-09-20

Grain size effects on the competition between dislocation slip and {101¯2} -twinning in magnesium are investigated using discrete dislocation dynamics simulations. These simulations account for dislocation–twin boundary interactions and twin boundary migration through the glide of twinning dislocations. It is shown that twinning deformation exhibits a strong grain size effect; while dislocation mediated slip in untwinned polycrystals displays a weak one. In conclusion, this leads to a critical grain size at 2.7 μm, above which twinning dominates, and below which dislocation slip dominates.

Planting Patterns and Deficit Irrigation Strategies to Improve Wheat Production and Water Use Efficiency under Simulated Rainfall Conditions

PubMed Central

Ali, Shahzad; Xu, Yueyue; Ma, Xiangcheng; Ahmad, Irshad; Kamran, Muhammad; Dong, Zhaoyun; Cai, Tie; Jia, Qianmin; Ren, Xiaolong; Zhang, Peng; Jia, Zhikuan

2017-01-01

The ridge furrow (RF) rainwater harvesting system is an efficient way to enhance rainwater accessibility for crops and increase winter wheat productivity in semi-arid regions. However, the RF system has not been promoted widely in the semi-arid regions, which primarily exist in remote hilly areas. To exploit its efficiency on a large-scale, the RF system needs to be tested at different amounts of simulated precipitation combined with deficit irrigation. Therefore, in during the 2015–16 and 2016–17 winter wheat growing seasons, we examined the effects of two planting patterns: (1) the RF system and (2) traditional flat planting (TF) with three deficit irrigation levels (150, 75, 0 mm) under three simulated rainfall intensity (1: 275, 2: 200, 3: 125 mm), and determined soil water storage profile, evapotranspiration rate, grain filling rate, biomass, grain yield, and net economic return. Over the two study years, the RF treatment with 200 mm simulated rainfall and 150 mm deficit irrigation (RF2150) significantly (P < 0.05) increased soil water storage in the depth of (200 cm); reduced ET at the field scale by 33%; increased total dry matter accumulation per plant; increased the grain-filling rate; and improved biomass (11%) and grain (19%) yields. The RF2150 treatment thus achieved a higher WUE (76%) and RIWP (21%) compared to TF. Grain-filling rates, grain weight of superior and inferior grains, and net economic profit of winter wheat responded positively to simulated rainfall and deficit irrigation under both planting patterns. The 200 mm simulated rainfall amount was more economical than other precipitation amounts, and led to slight increases in soil water storage, total dry matter per plant, and grain yield; there were no significant differences when the simulated rainfall was increased beyond 200 mm. The highest (12,593 Yuan ha−1) net income profit was attained using the RF system at 200 mm rainfall and 150 mm deficit irrigation, which also led to significantly higher grain yield, WUE, and RIWP than all other treatments. Thus, we recommend the RF2150 treatment for higher productivity, income profit, and improve WUE in the dry-land farming system of China. PMID:28878787

Gas-Grain Simulation Facility: Fundamental studies of particle formation and interactions. Volume 2: Abstracts, candidate experiments and feasibility study

NASA Technical Reports Server (NTRS)

Fogleman, Guy (Editor); Huntington, Judith L. (Editor); Schwartz, Deborah E. (Editor); Fonda, Mark L. (Editor)

1989-01-01

An overview of the Gas-Grain Simulation Facility (GGSF) project and its current status is provided. The proceedings of the Gas-Grain Simulation Facility Experiments Workshop are recorded. The goal of the workshop was to define experiments for the GGSF--a small particle microgravity research facility. The workshop addressed the opportunity for performing, in Earth orbit, a wide variety of experiments that involve single small particles (grains) or clouds of particles. Twenty experiments from the fields of exobiology, planetary science, astrophysics, atmospheric science, biology, physics, and chemistry were described at the workshop and are outlined in Volume 2. Each experiment description included specific scientific objectives, an outline of the experimental procedure, and the anticipated GGSF performance requirements. Since these experiments represent the types of studies that will ultimately be proposed for the facility, they will be used to define the general science requirements of the GGSF. Also included in the second volume is a physics feasibility study and abstracts of example Gas-Grain Simulation Facility experiments and related experiments in progress.

Proceedings of the Symposium on the Study of the Sun and Interplanetary Medium in Three Dimensions. [space mission planning and interplanetary trajectories by NASA and ESA to better observe the sun and solar system

NASA Technical Reports Server (NTRS)

Fisk, L. A. (Editor); Axford, W. I. (Editor)

1976-01-01

A series of papers are presented from a symposium attended by over 200 European and American scientists to examine the importance of exploring the interplanetary medium and the sun by out-of-the-ecliptic space missions. The likely scientific returns of these missions in the areas of solar, interplanetary, and cosmic ray physics is examined. Theoretical models of the solar wind and its interaction with interplanetary magnetic fields are given.

Magnetohydrodynamic Modeling of the Jovian Magnetosphere

NASA Technical Reports Server (NTRS)

Walker, Raymond

2005-01-01

Under this grant we have undertaken a series of magnetohydrodynamic (MHD) simulation and data analysis studies to help better understand the configuration and dynamics of Jupiter's magnetosphere. We approached our studies of Jupiter's magnetosphere in two ways. First we carried out a number of studies using our existing MHD code. We carried out simulation studies of Jupiter s magnetospheric boundaries and their dependence on solar wind parameters, we studied the current systems which give the Jovian magnetosphere its unique configuration and we modeled the dynamics of Jupiter s magnetosphere following a northward turning of the interplanetary magnetic field (IMF). Second we worked to develop a new simulation code for studies of outer planet magnetospheres.

Effect of stochastic grain heating on cold dense clouds chemistry

NASA Astrophysics Data System (ADS)

Chen, Long-Fei; Chang, Qiang; Xi, Hong-Wei

2018-06-01

The temperatures of dust grains play important roles in the chemical evolution of molecular clouds. Unlike large grains, the temperature fluctuations of small grains induced by photons may be significant. Therefore, if the grain size distribution is included in astrochemical models, the temperatures of small dust grains may not be assumed to be constant. We simulate a full gas-grain reaction network with a set of dust grain radii using the classical MRN grain size distribution and include the temperature fluctuations of small dust grains. Monte Carlo method is used to simulate the real-time dust grain's temperature fluctuations which is caused by the external low energy photons and the internal cosmic ray induced secondary photons. The increase of dust grains radii as ice mantles accumulate on grain surfaces is also included in our models. We found that surface CO2 abundances in models with grain size distribution and temperature fluctuations are more than one order of magnitude larger than those with single grain size. Small amounts of terrestrial complex organic molecules (COMs) can also be formed on small grains due to the temperature spikes induced by external low energy photons. However, cosmic ray induced secondary photons overheat small grains so that surface CO sublime and less radicals are formed on grains surfaces, thus the production of surface CO2 and COMs decreases by about one order of magnitude. The overheating of small grains can be offset by grain growth so that the formation of surface CO2 and COMs becomes more efficient.

Hierarchical coarse-graining strategy for protein-membrane systems to access mesoscopic scales

PubMed Central

Ayton, Gary S.; Lyman, Edward

2014-01-01

An overall multiscale simulation strategy for large scale coarse-grain simulations of membrane protein systems is presented. The protein is modeled as a heterogeneous elastic network, while the lipids are modeled using the hybrid analytic-systematic (HAS) methodology, where in both cases atomistic level information obtained from molecular dynamics simulation is used to parameterize the model. A feature of this approach is that from the outset liposome length scales are employed in the simulation (i.e., on the order of ½ a million lipids plus protein). A route to develop highly coarse-grained models from molecular-scale information is proposed and results for N-BAR domain protein remodeling of a liposome are presented. PMID:20158037

Continuum understanding of twin formation near grain boundaries of FCC metals with low stacking fault energy

NASA Astrophysics Data System (ADS)

Jung, Jaimyun; Yoon, Jae Ik; Kim, Jung Gi; Latypov, Marat I.; Kim, Jin You; Kim, Hyoung Seop

2017-12-01

Deformation twinning from grain boundaries is often observed in face-centered cubic metals with low stacking fault energy. One of the possible factors that contribute to twinning origination from grain boundaries is the intergranular interactions during deformation. Nonetheless, the influence of mechanical interaction among grains on twin evolution has not been fully understood. In spite of extensive experimental and modeling efforts on correlating microstructural features with their twinning behavior, a clear relation among the large aggregate of grains is still lacking. In this work, we characterize the micromechanics of grain-to-grain interactions that contribute to twin evolution by investigating the mechanical twins near grain boundaries using a full-field crystal plasticity simulation of a twinning-induced plasticity steel deformed in uniaxial tension at room temperature. Microstructures are first observed through electron backscatter diffraction technique to obtain data to reconstruct a statistically equivalent microstructure through synthetic microstructure building. Grain-to-grain micromechanical response is analyzed to assess the collective twinning behavior of the microstructural volume element under tensile deformation. Examination of the simulated results reveal that grain interactions are capable of changing the local mechanical behavior near grain boundaries by transferring strain across grain boundary or localizing strain near grain boundary.

Photovoltaic effect in ferroelectric ceramics

NASA Technical Reports Server (NTRS)

Epstein, D. J.; Linz, A.; Jenssen, H. P.

1982-01-01

The ceramic structure was simulated in a form that is more tractable to correlation between experiment and theory. Single crystals (of barium titanate) were fabricated in a simple corrugated structure in which the pedestals of the corrugation simulated the grain while the intervening cuts could be filled with materials simulating the grain boundaries. The observed photovoltages were extremely small (100 mv).

Effect of irradiation on mechanical properties of symmetrical grain boundaries investigated by atomic simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, X. Y.; Gao, N.; Setyawan, W.

Tensile response of irradiated symmetric grain boundaries to externally applied strain has been studied using atomic simulation methods. The absorption of irradiation induced defects by grain boundaries has been confirmed to degrade the mechanical properties of grain boundaries through the change of its under- taken deformation mechanism. Atomic rearrangement, the formations of a stress accumulation region and vacancy-rich zone and the nucleation and movement of dislocations under stress effect have been observed after the displacement cascades in grain boundaries, which are considered as main reasons to induce above degradation. These results suggest the necessity of considering both trap- ping efficiencymore » to defects and the mechanical property change of irradiated grain boundaries for further development of radiation resistant materials.« less

An Analysis of Hole Trapping at Grain Boundary or Poly-Si Floating-Body MOSFET.

PubMed

Jang, Taejin; Baek, Myung-Hyun; Kim, Hyungjin; Park, Byung-Gook

2018-09-01

In this paper, we demonstrate the characteristics of the floating body effect of poly-silicon with grain boundary by SENTAURUS™ TCAD simulation. As drain voltage increases, impact ionization occurs at the drain-channel junction. And these holes created by impact ionization are deposited on the bottom of the body to change the threshold voltage. This feature, the kink effect, is also observed in fully depleted silicon on insulator because grain boundary of the poly-silicon serve as a storage to trap the holes. We simulate the transfer curve depending on the density and position of the grain boundary. The trap density of the grain boundary affects the device characteristics significantly. However similar properties appear except where the grain boundary is located on the drain side.

Mechanistic Study of Delamination Fracture in Al-Li Alloy C458 (2099)

NASA Technical Reports Server (NTRS)

Tayon, W. A.; Crooks, R. E.; Domack, M. S.; Wagner, J. A.; Beaudoin, A. J.; McDonald, R. J.

2009-01-01

Delamination fracture has limited the use of lightweight Al-Li alloys. In the present study, electron backscattered diffraction (EBSD) methods were used to characterize crack paths in Al-Li alloy C458 (2099). Secondary delamination cracks in fracture toughness samples showed a pronounced tendency for fracture between grain variants of the same deformation texture component. These results were analyzed by EBSD mapping methods and simulated with finite element analyses. Simulation procedures include a description of material anisotropy, local grain orientations, and fracture utilizing crystal plasticity and cohesive zone elements. Taylor factors computed for each grain orientation subjected to normal and shear stresses indicated that grain pairs with the largest Taylor factor differences were adjacent to boundaries that failed by delamination. Examination of matching delamination fracture surface pairs revealed pronounced slip bands in only one of the grains bordering the delamination. These results, along with EBSD studies, plasticity simulations, and Auger electron spectroscopy observations support a hypothesis that delamination fracture occurs due to poor slip accommodation along boundaries between grains with greatly differing plastic response.

Testing thermal gradient driving force for grain boundary migration using molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai, Xian-Ming; Zhang, Yongfeng; Tonks, Michael R.

2015-02-01

Strong thermal gradients in low-thermal-conductivity ceramics may drive extended defects, such as grain boundaries and voids, to migrate in preferential directions. In this work, molecular dynamics simulations are conducted to study thermal gradient driven grain boundary migration and to verify a previously proposed thermal gradient driving force equation, using uranium dioxide as a model system. It is found that a thermal gradient drives grain boundaries to migrate up the gradient and the migration velocity increases under a constant gradient owing to the increase in mobility with temperature. Different grain boundaries migrate at very different rates due to their different intrinsicmore » mobilities. The extracted mobilities from the thermal gradient driven simulations are compared with those calculated from two other well-established methods and good agreement between the three different methods is found, demonstrating that the theoretical equation of the thermal gradient driving force is valid, although a correction of one input parameter should be made. The discrepancy in the grain boundary mobilities between modeling and experiments is also discussed.« less

Deformation-mechanism map for nanocrystalline metals by molecular-dynamics simulation.

PubMed

Yamakov, V; Wolf, D; Phillpot, S R; Mukherjee, A K; Gleiter, H

2004-01-01

Molecular-dynamics simulations have recently been used to elucidate the transition with decreasing grain size from a dislocation-based to a grain-boundary-based deformation mechanism in nanocrystalline f.c.c. metals. This transition in the deformation mechanism results in a maximum yield strength at a grain size (the 'strongest size') that depends strongly on the stacking-fault energy, the elastic properties of the metal, and the magnitude of the applied stress. Here, by exploring the role of the stacking-fault energy in this crossover, we elucidate how the size of the extended dislocations nucleated from the grain boundaries affects the mechanical behaviour. Building on the fundamental physics of deformation as exposed by these simulations, we propose a two-dimensional stress-grain size deformation-mechanism map for the mechanical behaviour of nanocrystalline f.c.c. metals at low temperature. The map captures this transition in both the deformation mechanism and the related mechanical behaviour with decreasing grain size, as well as its dependence on the stacking-fault energy, the elastic properties of the material, and the applied stress level.

Nebular and Interstellar Materials in a Giant Cluster IDP of Probable Cometary Origin

NASA Technical Reports Server (NTRS)

Messenger, S.; Brownlee, D. E.; Joswiak, D. J.; Nguyen, A. N.

2015-01-01

Comets contain a complex mixture of materials with presolar and Solar System origins. Chondritic porous interplanetary dust particles (CP-IDPs) are associated with comets by their fragile nature, unequilibrated anhydrous mineralogy and high abundances of circumstellar grains and isotopically anomalous organic materials. Comet 81P/Wild 2 samples returned by the Stardust spacecraft contain presolar materials as well as refractory 16O-rich Ca-Al-rich inclusion- (CAI), chondrule-, and AOA-like materials. We are conducting coordinated chemical, mineralogical, and isotopic studies of a giant cluster CP-IDP (U2-20-GCA) to determine the proportions of inner Solar System and interstellar materials. We previously found that this IDP contains abundant presolar silicates (approx. 1,800 ppm) and 15N-rich hotspots [6].

Densities of 5-15 micron interplanetary dust particles

NASA Technical Reports Server (NTRS)

Love, S. G.; Joswiak, D. J.; Brownlee, D. E.

1993-01-01

We have measured the densities of about 100 5-15 micron stratospheric IDPs. Great care was taken to minimize selection bias in the sample population. Masses were determined using an absolute x-ray analysis technique with a transmission electron microscope, and volumes were found using scanning electron microscope imagery. Unmelted chondritic particles have densities between 0.5 and 6.0 g/cc. Roughly half of the particles have densities below 2 g/cc, indicating appreciable porosity, but porosities greater than about 70 percent are rare. IDPs with densities above 3.5 g/cc usually contain large sulfide grains. We find no evidence of bimodality in the unmelted particle density distribution. Chondritic spherules (melted particles) have densities near 3.5 g/cc, consistent with previous results for deep sea spherules.

Time-dependent Processes in the Sheath Between the Heliospheric Termination Shock and the Heliopause

NASA Astrophysics Data System (ADS)

Pogorelov, N. V.; Borovikov, S. N.; Heerikhuisen, J.; Kim, T. K.; Zank, G. P.

2014-09-01

In this paper, we present the results of our numerical simulation of the solar wind (SW) interaction with the local interstellar medium (LISM). In particular, a solar cycle model based on Ulysses measurements allowed us to estimate the interrelationship between heliospheric asymmetries due to the action of the interstellar magnetic field and the decrease in the solar wind ram pressure. We evaluate the possibility to develop an improved approach to derive SW boundary conditions from interplanetary scintillation data. It is shown that solar cycle affects stability of the heliopause in a way favorable for the interpretation of Voyager 1 “early” penetration into the local interstellar medium. We also show that the heliotail is always a subject of violent Kelvin-Helmholtz instability, which ultimately should make the heliotail indistinguishable from the LISM. Numerical results are obtained with a Multi-Scale Fluid-Kinetic Simulation Suite (MS-FLUKSS), which is a package of numerical codes capable of performing adaptive mesh refinement simulations of complex plasma flows in the presence of discontinuities and charge exchange between ions and neutral atoms. The flow of the ionized component is described with the ideal MHD equations, while the transport of atoms is governed either by the Boltzmann equation or multiple Euler gas dynamics equations. We have enhanced the code with additional physical treatments for the transport of turbulence and acceleration of pickup ions in interplanetary space and at the termination shock.

Design and simulation of betavoltaic battery using large-grain polysilicon.

PubMed

Yao, Shulin; Song, Zijun; Wang, Xiang; San, Haisheng; Yu, Yuxi

2012-10-01

In this paper, we present the design and simulation of a p-n junction betavoltaic battery based on large-grain polysilicon. By the Monte Carlo simulation, the average penetration depth were obtained, according to which the optimal depletion region width was designed. The carriers transport model of large-grain polysilicon is used to determine the diffusion length of minority carrier. By optimizing the doping concentration, the maximum power conversion efficiency can be achieved to be 0.90% with a 10 mCi/cm(2) Ni-63 source radiation. Copyright © 2012 Elsevier Ltd. All rights reserved.

Stability of nanocrystalline Ni-based alloys: coupling Monte Carlo and molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Waseda, O.; Goldenstein, H.; Silva, G. F. B. Lenz e.; Neiva, A.; Chantrenne, P.; Morthomas, J.; Perez, M.; Becquart, C. S.; Veiga, R. G. A.

2017-10-01

The thermal stability of nanocrystalline Ni due to small additions of Mo or W (up to 1 at%) was investigated in computer simulations by means of a combined Monte Carlo (MC)/molecular dynamics (MD) two-steps approach. In the first step, energy-biased on-lattice MC revealed segregation of the alloying elements to grain boundaries. However, the condition for the thermodynamic stability of these nanocrystalline Ni alloys (zero grain boundary energy) was not fulfilled. Subsequently, MD simulations were carried out for up to 0.5 μs at 1000 K. At this temperature, grain growth was hindered for minimum global concentrations of 0.5 at% W and 0.7 at% Mo, thus preserving most of the nanocrystalline structure. This is in clear contrast to a pure Ni model system, for which the transformation into a monocrystal was observed in MD simulations within 0.2 μs at the same temperature. These results suggest that grain boundary segregation of low-soluble alloying elements in low-alloyed systems can produce high-temperature metastable nanocrystalline materials. MD simulations carried out at 1200 K for 1 at% Mo/W showed significant grain boundary migration accompanied by some degree of solute diffusion, thus providing additional evidence that solute drag mostly contributed to the nanostructure stability observed at lower temperature.

Coarse-grained Simulations of Conformational Changes in Multidrug Resistance Transporters

NASA Astrophysics Data System (ADS)

Jewel, S. M. Yead; Dutta, Prashanta; Liu, Jin

2016-11-01

The overexpression of multidrug resistance (MDR) systems on the gram negative bacteria causes serious problems for treatment of bacterial infectious diseases. The system effectively pumps the antibiotic drugs out of the bacterial cells. During the pumping process one of the MDR components, AcrB undergoes a series of large-scale conformational changes which are responsible for drug recognition, binding and expelling. All-atom simulations are unable to capture those conformational changes because of computational cost. Here, we implement a hybrid coarse-grained force field that couples the united-atom protein models with the coarse-grained MARTINI water/lipid, to investigate the proton-dependent conformational changes of AcrB. The simulation results in early stage ( 100 ns) of proton-dependent conformational changes agree with all-atom simulations, validating the coarse-grained model. The coarse-grained force field allows us to explore the process in microsecond simulations. Starting from the crystal structures of Access(A)/Binding(B)/Extrusion(E) monomers in AcrB, we find that deprotonation of Asp407 and Asp408 in monomer E causes a series of large-scale conformational changes from ABE to AAA in absence of drug molecules, which is consistent with experimental findings. This work is supported by NIH Grant: 1R01GM122081-01.

Direct numerical simulations in solid mechanics for quantifying the macroscale effects of microstructure and material model-form error

DOE PAGES

Bishop, Joseph E.; Emery, John M.; Battaile, Corbett C.; ...

2016-03-16

Two fundamental approximations in macroscale solid-mechanics modeling are (1) the assumption of scale separation in homogenization theory and (2) the use of a macroscopic plasticity material model that represents, in a mean sense, the multitude of inelastic processes occurring at the microscale. With the goal of quantifying the errors induced by these approximations on engineering quantities of interest, we perform a set of direct numerical simulations (DNS) in which polycrystalline microstructures are embedded throughout a macroscale structure. The largest simulations model over 50,000 grains. The microstructure is idealized using a randomly close-packed Voronoi tessellation in which each polyhedral Voronoi cellmore » represents a grain. An face centered cubic crystal-plasticity model is used to model the mechanical response of each grain. The overall grain structure is equiaxed, and each grain is randomly oriented with no overall texture. The detailed results from the DNS simulations are compared to results obtained from conventional macroscale simulations that use homogeneous isotropic plasticity models. The macroscale plasticity models are calibrated using a representative volume element of the idealized microstructure. Furthermore, we envision that DNS modeling will be used to gain new insights into the mechanics of material deformation and failure.« less

Lunar and Planetary Science Conference, 18th, Houston, TX, Mar. 16-20, 1987, Proceedings

NASA Technical Reports Server (NTRS)

Ryder, Graham (Editor)

1988-01-01

Papers on lunar and planetary science are presented, including petrogenesis and chemistry of lunar samples, geology and petrogenesis of the Apollo 15 landing site, lunar geology and applications, cratering records and cratering effects, differentiated meteorites, chondritic meteorites and asteroids, extraterrestrial grains, Venus, Mars, and icy satellites. The importance of lunar granite and KREEP in very high potassium basalt petrogenesis, indentifying parent plutonic rocks from lunar breccia and soil fragments, glasses in ancient and young Apollo 16 regolith breccias, the formation of the Imbrium basin, the chemistry and petrology of the Apennine Front, lunar mare ridges, studies of Rima Mozart, electromagnetic energy applications in lunar resource mining and construction, detecting a periodic signal in the terrestrial cratering record, and a search for water on the moon, are among the topics discussed. Other topics include the bidirectional reflectance properties of Fe-Ni meteorites, the nature and origin of C-rich ordinary chondrites and chondritic clasts, the dehydration kinetics of shocked serpentine, characteristics of Greenland Fe/Ni cosmic grains, electron microscopy of a hydrated interplanetary dust particle, trapping Ne, Ar, Kr, and Xe in Si2O3 smokes, gossans on Mars, and a model of the porous structure of icy satellites.

Grain growth in U–7Mo alloy: A combined first-principles and phase field study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mei, Zhi-Gang; Liang, Linyun; Kim, Yeon Soo

2016-05-01

Grain size is an important factor in controlling the swelling behavior in irradiated U-Mo dispersion fuels. Increasing the grain size in UeMo fuel particles by heat treatment is believed to delay the fuel swelling at high fission density. In this work, a multiscale simulation approach combining first-principles calculation and phase field modeling is used to investigate the grain growth behavior in U-7Mo alloy. The density functional theory based first-principles calculations were used to predict the material properties of U-7Mo alloy. The obtained grain boundary energies were then adopted as an input parameter for mesoscale phase field simulations. The effects ofmore » annealing temperature, annealing time and initial grain structures of fuel particles on the grain growth in U-7Mo alloy were examined. The predicted grain growth rate compares well with the empirical correlation derived from experiments. (C) 2016 Elsevier B.V. All rights reserved.« less

Stardust in STARDUST - the C, N, and O Isotopic Compositions of Wild 2 Cometary Matter in Al Foil Impacts

NASA Technical Reports Server (NTRS)

Stadermann, Frank J.; Hoppe, Peter; Floss, Christine; Heck, Philipp R.; Hoerz, Friedrich; Huth, Joachim; Kearsley, Anton T.; Leitner, Jan; Marhas, Kuljeet K.; McKeegan, Kevin D.;

Stardust in STARDUST - the C, N, and O Isotopic Compositions of Wild 2 Cometary Matter in Al foil Impacts

NASA Technical Reports Server (NTRS)

Stadermann, Frank J.; Hoppe, Peter; Floss, Christine; Hoerz, Friedrich; Huth, Joachim; Kearsley, Anton T.; Leitner, Jan; Marhas, Kuljeet K.; McKeegan, Kevin D.; Stephan, Thomas;

Stardust@home: A Massively Distributed Public Search for Interstellar Dust in the Stardust Interstellar Dust Collector

NASA Technical Reports Server (NTRS)

Westphal, Andrew J.; Butterworth, Anna L.; Snead, Christopher J.; Craig, Nahide; Anderson, David; Jones, Steven M.; Brownlee, Donald E.; Farnsworth, Richard; Zolensky, Michael E.

2005-01-01

In January 2006, the Stardust mission will return the first samples from a solid solar system body beyond the Moon. Stardust was in the news in January 2004, when it encountered comet Wild2 and captured a sample of cometary dust. But Stardust carries an equally important payload: the first samples of contemporary interstellar dust ever collected. Although it is known that interstellar (IS) dust penetrates into the inner solar system [2, 3], to date not even a single contemporary interstellar dust particle has been captured and analyzed in the laboratory. Stardust uses aerogel collectors to capture dust samples. Identification of interstellar dust impacts in the Stardust Interstellar Dust Collector probably cannot be automated, but will require the expertise of the human eye. However, the labor required for visual scanning of the entire collector would exceed the resources of any reasonably-sized research group. We are developing a project to recruit the public in the search for interstellar dust, based in part on the wildly popular SETI@home project, which has five million subscribers. We call the project Stardust@home. Using sophisticated chemical separation techniques, certain types of refractory ancient IS particles (so-called presolar grains) have been isolated from primitive meteorites (e.g., [4] ). Recently, presolar grains have been identified in Interplanetary Dust Particles[6]. Because these grains are not isolated chemically, but are recognized only by their unusual isotopic compositions, they are probably less biased than presolar grains isolated from meteorites. However, it is entirely possible that the typical interstellar dust particle is isotopically solar in composition. The Stardust collection of interstellar dust will be the first truly unbiased one.

Formation of Glass with Embedded Metal and Sulfides from Shock-accelerated Crystalline Dust in Superbubbles

NASA Astrophysics Data System (ADS)

Westphal, A. J.; Bradley, J. P.

2004-12-01

Interplanetary dust particles (IDPs) contain enigmatic submicron components called GEMS (glass with embedded metal and sulfides). The compositions and structures of GEMS indicate that they have been processed by exposure to ionizing radiation, but details of the actual irradiation environment(s) have remained elusive. Here we propose a mechanism and astrophysical site for GEMS formation that explains for the first time the following key properties of GEMS: they are stoichiometrically enriched in oxygen and systematically depleted in S, Mg, Ca, and Fe (relative to solar abundances); most have normal (solar) oxygen isotopic compositions; they exhibit a strikingly narrow size distribution (0.1-0.5 μm diameter); and some of them contain ``relict'' crystals within their silicate glass matrices. We show that the compositions, size distribution, and survival of relict crystals are inconsistent with amorphization by particles accelerated by diffusive shock acceleration. Instead, we propose that GEMS are formed from crystalline grains that condense in stellar outflows from massive stars in OB associations, are accelerated in encounters with frequent supernova shocks inside the associated superbubble (SB), and are implanted with atoms from the hot gas in the SB interior. We thus reverse the usual roles of target and projectile. Rather than being bombarded at rest by energetic ions, grains are accelerated and bombarded by a nearly monovelocity beam of atoms as viewed in their rest frame. Meyer, Drury, and Ellison have proposed that Galactic cosmic rays (GCRs) originate from ions sputtered from such accelerated dust grains. We suggest that GEMS are surviving members of a population of fast grains that constitute the long-sought source material for GCRs. Thus, representatives of the GCR source material may have been awaiting discovery in cosmic dust labs for the last 30 yr.

Neon isotopes show that Earth was accreted from irradiated material

NASA Astrophysics Data System (ADS)

Moreira, M. A.

2015-12-01

Since the 1980s, the notion that the Earth's mantle has a "solar" isotopic signature for neon has been favoured. Indeed, the 20Ne/22Ne ratio is above 12.5 in the mantle sources of OIB and MORB, close to the solar composition (13.4 for the Sun or 13.8 for the solar wind) and different from both atmospheric and chondritic compositions (Phase Q, Neon A). The most well accepted process invoked to explain this observed solar composition in the mantle is dissolution into a magma ocean of solar gases captured by gravity around the proto-Earth. However, Earth was accreted after gas from the proto-planetary disk had evaporated, suggesting that Earth itself could not have captured such a solar primordial atmosphere. Only planetary embryos were formed when the gas was still present in the disk. However, these planetary embryos with the mass of Mars are not massive enough to capture a solar dense atmosphere able to incorporate enough neon into the mantle. New estimates of the neon isotopic compositions of both the Earth's mantle and of the implanted solar wind into grains suggest that the origin of the neon on Earth is related to solar wind irradiation on μm grains before planetary accretion started and not dissolution. Although incorporation of solar ions by this process is only significant for very volatiles (depleted) elements, the irradiation by x-rays has important consequences for the bulk chemistry of irradiated grains as it has been demonstrated that it produces depletion in Mg and Si, relatively to O (e.g Bradley et al., 1994), a pattern also observed for the Bulk silicate Earth. References Bradley, J. (1994). "Chemically Anomalous, Preaccretionally irradiated Grains in Interplanetary fust from Comets." Science 265: 925-929.

Atom based grain extraction and measurement of geometric properties

NASA Astrophysics Data System (ADS)

Martine La Boissonière, Gabriel; Choksi, Rustum

2018-04-01

We introduce an accurate, self-contained and automatic atom based numerical algorithm to characterize grain distributions in two dimensional Phase Field Crystal (PFC) simulations. We compare the method with hand segmented and known test grain distributions to show that the algorithm is able to extract grains and measure their area, perimeter and other geometric properties with high accuracy. Four input parameters must be set by the user and their influence on the results is described. The method is currently tuned to extract data from PFC simulations in the hexagonal lattice regime but the framework may be extended to more general problems.

Human Factor Studies on a Mars Analogue During Crew 100b International Lunar Exploration Working Group EuroMoonMars Crew: Proposed New Approaches for Future Human Space and Interplanetary Missions.

PubMed

Rai, Balwant; Kaur, Jasdeep

2012-11-01

Knowing the risks, costs, and complexities associated with human missions to Mars, analogue research can be a great (low-risk) tool for exploring the challenges associated with the preparation for living, operating, and undertaking research in interplanetary missions. Short-duration analogue studies, such as those being accomplished at the Mars Desert Research Station (MDRS), offer the chance to study mission operations and human factors in a simulated environment, and therefore contribute to exploration of the Moon and Mars in planned future missions. This article is based upon previously published articles, abstracts, and presentations by a series of independent authors, human factor studies performed on mars analogue station by Crew 100B. The MDRS Crew 100B performed studies over 15 days providing a unique insight into human factor issues in simulated short-duration Mars mission. In this study, 15 human factors were evaluated and analyzed by subjective and objective means, and from the summary of results it was concluded that optimum health of an individual and the crew as a whole is a necessity in order to encourage and maintain high performance and the satisfaction of project goals.

Human Factor Studies on a Mars Analogue During Crew 100b International Lunar Exploration Working Group EuroMoonMars Crew: Proposed New Approaches for Future Human Space and Interplanetary Missions

PubMed Central

Rai, Balwant; Kaur, Jasdeep

2012-01-01

Knowing the risks, costs, and complexities associated with human missions to Mars, analogue research can be a great (low-risk) tool for exploring the challenges associated with the preparation for living, operating, and undertaking research in interplanetary missions. Short-duration analogue studies, such as those being accomplished at the Mars Desert Research Station (MDRS), offer the chance to study mission operations and human factors in a simulated environment, and therefore contribute to exploration of the Moon and Mars in planned future missions. This article is based upon previously published articles, abstracts, and presentations by a series of independent authors, human factor studies performed on mars analogue station by Crew 100B. The MDRS Crew 100B performed studies over 15 days providing a unique insight into human factor issues in simulated short-duration Mars mission. In this study, 15 human factors were evaluated and analyzed by subjective and objective means, and from the summary of results it was concluded that optimum health of an individual and the crew as a whole is a necessity in order to encourage and maintain high performance and the satisfaction of project goals. PMID:23181225

Dynamical Evolution of a Coronal Streamer-Flux Rope System: 2. A Self-Consistent Non-Planar Magnetohydrodynamic Simulation

NASA Technical Reports Server (NTRS)

Wu, S. T.; Guo, W. P.; Dryer, Murray

1996-01-01

The dynamical response of a helmet streamer to a flux rope escape from the sub-photosphere is examined in a physically self-consistent manner within the approximation of axisymmetric three-dimensional magnetohydrodynamics (i.e., so-called '2 1/2 D'). In contrast to the previous planar analyses of Paper 1 (Wu, Guo, and Wang), the present study shows, with the inclusion of out-of-plane components of magnetic and velocity fields, that the magnetic configuration represents a helical flux rope instead of a planar bubble as shown in Paper 1. Because of this more physically-realistic configuration, we are able to examine the dynamical evolution of the helical flux rope's interaction with the helmet streamer. This process leads to the formation of two parts of the solar mass ejection: (i) the expulsion of the helmet dome due to eruption of this flux rope, and (ii) the flux rope's eruption itself. When this two-part feature propagates out to the interplanetary space, it exhibits all the physical characteristics of observed interplanetary magnetic clouds. These numerical simulations also show that the dynamical behavior of the streamer-flux rope system has three distinct states: (i) quasi-equilibrium, (ii) non-equilibrium, and (iii) eruptive state depending on the energy level of the flux rope.

Preparation of Entangled Polymer Melts of Various Architecture for Coarse-Grained Models

DTIC Science & Technology

2011-09-01

Simulator ( LAMMPS ). This report presents a theory overview and a manual how to use the method. 15. SUBJECT TERMS Ammunition, coarse-grained model...polymer builder, LAMMPS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT UU 18. NUMBER OF PAGES 26 19a. NAME OF RESPONSIBLE PERSON...scale Atomic/Molecular Massively Parallel Simulator ( LAMMPS ). Gel is an in house written C program of coarse- grained polymer builder, and LAMMPS is

Interstellar and Cometary Dust

NASA Technical Reports Server (NTRS)

Mathis, John S.

1997-01-01

'Interstellar dust' forms a continuum of materials with differing properties which I divide into three classes on the basis of observations: (a) diffuse dust, in the low-density interstellar medium; (b) outer-cloud dust, observed in stars close enough to the outer edges of molecular clouds to be observed in the optical and ultraviolet regions of the spectrum, and (c) inner-cloud dust, deep within the cores of molecular clouds, and observed only in the infrared by means of absorption bands of C-H, C=O, 0-H, C(triple bond)N, etc. There is a surprising regularity of the extinction laws between diffuse- and outer-cloud dust. The entire mean extinction law from infrared through the observable ultraviolet spectrum can be characterized by a single parameter. There are real deviations from this mean law, larger than observational uncertainties, but they are much smaller than differences of the mean laws in diffuse- and outer-cloud dust. This fact shows that there are processes which operate over the entire distribution of grain sizes, and which change size distributions extremely efficiently. There is no evidence for mantles on grains in local diffuse and outer-cloud dust. The only published spectra of the star VI Cyg 12, the best candidate for showing mantles, does not show the 3.4 micro-m band which appreciable mantles would produce. Grains are larger in outer-cloud dust than diffuse dust because of coagulation, not accretion of extensive mantles. Core-mantle grains favored by J. M. Greenberg and collaborators, and composite grains of Mathis and Whiffen (1989), are discussed more extensively (naturally, I prefer the latter). The composite grains are fluffy and consist of silicates, amorphous carbon, and some graphite in the same grain. Grains deep within molecular clouds but before any processing within the solar system are presumably formed from the accretion of icy mantles on and within the coagulated outer-cloud grains. They should contain a mineral/carbonaceous matrix, without organic refractory mantles, in between the ices. Unfortunately, they may be significantly processed by chemical processes accompanying the warming (over the 10 K of the dark cloud cores) which occurs in the outer solar system. Evidence of this processing is the chemical anomalies present in interplanetary dust particles collected in the stratosphere, which may be the most primitive materials we have obtained to date. The comet return mission would greatly clarify the situation, and probably provide samples of genuine interstellar grains.

Theory and Simulations of Solar System Plasmas

NASA Technical Reports Server (NTRS)

Goldstein, Melvyn L.

2011-01-01

"Theory and simulations of solar system plasmas" aims to highlight results from microscopic to global scales, achieved by theoretical investigations and numerical simulations of the plasma dynamics in the solar system. The theoretical approach must allow evidencing the universality of the phenomena being considered, whatever the region is where their role is studied; at the Sun, in the solar corona, in the interplanetary space or in planetary magnetospheres. All possible theoretical issues concerning plasma dynamics are welcome, especially those using numerical models and simulations, since these tools are mandatory whenever analytical treatments fail, in particular when complex nonlinear phenomena are at work. Comparative studies for ongoing missions like Cassini, Cluster, Demeter, Stereo, Wind, SDO, Hinode, as well as those preparing future missions and proposals, like, e.g., MMS and Solar Orbiter, are especially encouraged.

A Cellular Automaton / Finite Element model for predicting grain texture development in galvanized coatings

NASA Astrophysics Data System (ADS)

Guillemot, G.; Avettand-Fènoël, M.-N.; Iosta, A.; Foct, J.

2011-01-01

Hot-dipping galvanizing process is a widely used and efficient way to protect steel from corrosion. We propose to master the microstructure of zinc grains by investigating the relevant process parameters. In order to improve the texture of this coating, we model grain nucleation and growth processes and simulate the zinc solid phase development. A coupling scheme model has been applied with this aim. This model improves a previous two-dimensional model of the solidification process. It couples a cellular automaton (CA) approach and a finite element (FE) method. CA grid and FE mesh are superimposed on the same domain. The grain development is simulated at the micro-scale based on the CA grid. A nucleation law is defined using a Gaussian probability and a random set of nucleating cells. A crystallographic orientation is defined for each one with a choice of Euler's angle (Ψ,θ,φ). A small growing shape is then associated to each cell in the mushy domain and a dendrite tip kinetics is defined using the model of Kurz [2]. The six directions of basal plane and the two perpendicular directions develop in each mushy cell. During each time step, cell temperature and solid fraction are then determined at micro-scale using the enthalpy conservation relation and variations are reassigned at macro-scale. This coupling scheme model enables to simulate the three-dimensional growing kinetics of the zinc grain in a two-dimensional approach. Grain structure evolutions for various cooling times have been simulated. Final grain structure has been compared to EBSD measurements. We show that the preferentially growth of dendrite arms in the basal plane of zinc grains is correctly predicted. The described coupling scheme model could be applied for simulated other product or manufacturing processes. It constitutes an approach gathering both micro and macro scale models.

Applications of discrete element method in modeling of grain postharvest operations

USDA-ARS?s Scientific Manuscript database

Grain kernels are finite and discrete materials. Although flowing grain can behave like a continuum fluid at times, the discontinuous behavior exhibited by grain kernels cannot be simulated solely with conventional continuum-based computer modeling such as finite-element or finite-difference methods...

Suppression of Twinning and Phase Transformation in an Ultrafine Grained 2 GPa Strong Metastable Austenitic Steel: Experiment and Simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shen, Yongfeng; Jia, Nan; Wang, Y. D.

2015-07-17

An ultrafine-grained 304 austenitic 18 wt.%Cr-8 wt.%Ni stainless steel with a grain size of ~270 nm was synthesized by accumulative rolling (67 % total reduction) and annealing (550 °C, 150s). Uniaxial tensile testing at room temperature reveals an extremely high yield strength of 1890 ± 50MPa and a tensile strength of 2050 ± 30MPa, while the elongation reaches 6 ± 1%. Experimental characterization on samples with different grain sizes between 270 nm and 35 μm indicates that both, deformation twinning and martensitic phase transformation are significantly retarded with increasing grain refinement. A crystal plasticity finite element model incorporating a constitutivemore » law reflecting the grain size-controlled dislocation slip and deformation twinning captures the micromechanical behavior of the steels with different grain sizes. Comparison of simulation and experiment shows that the deformation of ultrafine-grained 304 steels is dominated by the slip of partial dislocations, whereas for coarse-grained steels dislocation slip, twinning and martensite formation jointly contribute to the shape change.« less

Serial sectioning of grain microstructures under junction control: An old problem in a new guise

NASA Astrophysics Data System (ADS)

Zöllner, D.; Streitenberger, P.

2015-04-01

In the present work the importance of 3D and 4D microstructure analyses are shown. To that aim, we study polycrystalline grain microstructures obtained by grain growth under grain boundary, triple line and quadruple point control. The microstructures themselves are obtained by mesoscopic computer simulations, which enjoy a far greater control over the kinetic and thermodynamic parameters affecting grain growth than can be realized experimentally. In extensive simulation studies we find by 3D respectively 4D microstructure analyses that metrical and topological properties of the microstructures depend strongly on the microstructural feature controlling the growth kinetics. However, the differences between the growth kinetics vanish when we look at classical 2D sections of the 3D ensembles making a differentiation of the controlling grain feature near impossible.

Coarse-grained simulations of polyelectrolyte complexes: MARTINI models for poly(styrene sulfonate) and poly(diallyldimethylammonium)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vögele, Martin; Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Frankfurt a. M.; Holm, Christian

2015-12-28

We present simulations of aqueous polyelectrolyte complexes with new MARTINI models for the charged polymers poly(styrene sulfonate) and poly(diallyldimethylammonium). Our coarse-grained polyelectrolyte models allow us to study large length and long time scales with regard to chemical details and thermodynamic properties. The results are compared to the outcomes of previous atomistic molecular dynamics simulations and verify that electrostatic properties are reproduced by our MARTINI coarse-grained approach with reasonable accuracy. Structural similarity between the atomistic and the coarse-grained results is indicated by a comparison between the pair radial distribution functions and the cumulative number of surrounding particles. Our coarse-grained models aremore » able to quantitatively reproduce previous findings like the correct charge compensation mechanism and a reduced dielectric constant of water. These results can be interpreted as the underlying reason for the stability of polyelectrolyte multilayers and complexes and validate the robustness of the proposed models.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bishop, Joseph E.; Emery, John M.; Battaile, Corbett C.

Two fundamental approximations in macroscale solid-mechanics modeling are (1) the assumption of scale separation in homogenization theory and (2) the use of a macroscopic plasticity material model that represents, in a mean sense, the multitude of inelastic processes occurring at the microscale. With the goal of quantifying the errors induced by these approximations on engineering quantities of interest, we perform a set of direct numerical simulations (DNS) in which polycrystalline microstructures are embedded throughout a macroscale structure. The largest simulations model over 50,000 grains. The microstructure is idealized using a randomly close-packed Voronoi tessellation in which each polyhedral Voronoi cellmore » represents a grain. An face centered cubic crystal-plasticity model is used to model the mechanical response of each grain. The overall grain structure is equiaxed, and each grain is randomly oriented with no overall texture. The detailed results from the DNS simulations are compared to results obtained from conventional macroscale simulations that use homogeneous isotropic plasticity models. The macroscale plasticity models are calibrated using a representative volume element of the idealized microstructure. Furthermore, we envision that DNS modeling will be used to gain new insights into the mechanics of material deformation and failure.« less

Adaptive resolution simulation of an atomistic protein in MARTINI water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zavadlav, Julija; Melo, Manuel Nuno; Marrink, Siewert J., E-mail: s.j.marrink@rug.nl

2014-02-07

We present an adaptive resolution simulation of protein G in multiscale water. We couple atomistic water around the protein with mesoscopic water, where four water molecules are represented with one coarse-grained bead, farther away. We circumvent the difficulties that arise from coupling to the coarse-grained model via a 4-to-1 molecule coarse-grain mapping by using bundled water models, i.e., we restrict the relative movement of water molecules that are mapped to the same coarse-grained bead employing harmonic springs. The water molecules change their resolution from four molecules to one coarse-grained particle and vice versa adaptively on-the-fly. Having performed 15 ns long molecularmore » dynamics simulations, we observe within our error bars no differences between structural (e.g., root-mean-squared deviation and fluctuations of backbone atoms, radius of gyration, the stability of native contacts and secondary structure, and the solvent accessible surface area) and dynamical properties of the protein in the adaptive resolution approach compared to the fully atomistically solvated model. Our multiscale model is compatible with the widely used MARTINI force field and will therefore significantly enhance the scope of biomolecular simulations.« less

Adaptive resolution simulation of an atomistic protein in MARTINI water.

PubMed

Zavadlav, Julija; Melo, Manuel Nuno; Marrink, Siewert J; Praprotnik, Matej

2014-02-07

We present an adaptive resolution simulation of protein G in multiscale water. We couple atomistic water around the protein with mesoscopic water, where four water molecules are represented with one coarse-grained bead, farther away. We circumvent the difficulties that arise from coupling to the coarse-grained model via a 4-to-1 molecule coarse-grain mapping by using bundled water models, i.e., we restrict the relative movement of water molecules that are mapped to the same coarse-grained bead employing harmonic springs. The water molecules change their resolution from four molecules to one coarse-grained particle and vice versa adaptively on-the-fly. Having performed 15 ns long molecular dynamics simulations, we observe within our error bars no differences between structural (e.g., root-mean-squared deviation and fluctuations of backbone atoms, radius of gyration, the stability of native contacts and secondary structure, and the solvent accessible surface area) and dynamical properties of the protein in the adaptive resolution approach compared to the fully atomistically solvated model. Our multiscale model is compatible with the widely used MARTINI force field and will therefore significantly enhance the scope of biomolecular simulations.

Grain growth simulation of [001] textured YBCO films grown on (001) substrates with large lattice misfit: Prediction of misorientations of the remaining boundaries

NASA Astrophysics Data System (ADS)

Tsai, Jack W. H.; Ling, Shiun; Rodriguez, Julio C.; Mustapha, Zarina; Chan, Siu-Wai

2001-04-01

We study the effects of (1) the variation of grain boundary energy with misorientation and (2) the large lattice misfit (>3%) between the films and substrates on grain growth in films by method of Monte Carlo simulations. The results from the grain growth simulation in YBa2Cu3O7-x (YBCO) films was found to concur with previous experimental observation of preferred grain orientations for YBCO films deposited on various substrates such as (001) magnesium oxide (MgO) and (001) yttria stabilized zirconia (YSZ). The simulation has helped us to identify three factors influencing the competition of these [001] tilt boundaries. They are: (1) the relative depths of local minima in the boundary energy vs. misorientation curve, (2) the number of combinations of coincidence epitaxy (CE) orientations contributing to the exact misorientation for each of the high-angle-but-low-energy (HABLE) boundaries, and (3) the number of combinations of CE orientations within the angular ranges bracketing each of the exact HABLE boundaries. Hence, these factors can be applied to clarify the origin of special misorientations observed experimentally.

Helium isotopes in ferromanganese crusts from the central Pacific Ocean

USGS Publications Warehouse

Basu, S.; Stuart, F.M.; Klemm, V.; Korschinek, G.; Knie, K.; Hein, J.R.

2006-01-01

Helium isotopes have been measured in samples of two ferromanganese crusts (VA13/2 and CD29-2) from the central Pacific Ocean. With the exception of the deepest part of crust CD29-2 the data can be explained by a mixture of implanted solar- and galactic cosmic ray-produced (GCR) He, in extraterrestrial grains, and radiogenic He in wind-borne continental dust grains. 4He concentrations are invariant and require retention of less than 12% of the in situ He produced since crust formation. Loss has occurred by recoil and diffusion. High 4He in CD29-2 samples older than 42 Ma are correlated with phosphatization and can be explained by retention of up to 12% of the in situ-produced 4He. 3He/4He of VA13/2 samples varies from 18.5 to 1852 Ra due almost entirely to variation in the extraterrestrial He contribution. The highest 3He/4He is comparable to the highest values measured in interplanetary dust particles (IDPs) and micrometeorites (MMs). Helium concentrations are orders of magnitude lower than in oceanic sediments reflecting the low trapping efficiency for in-falling terrestrial and extraterrestrial grains of Fe-Mn crusts. The extraterrestrial 3He concentration of the crusts rules out whole, undegassed 4–40 μm diameter IDPs as the host. Instead it requires that the extraterrestrial He inventory is carried by numerous particles with significantly lower He concentrations, and occasional high concentration GCR-He-bearing particles.

Mars Exploration Rover Terminal Descent Mission Modeling and Simulation

NASA Technical Reports Server (NTRS)

Raiszadeh, Behzad; Queen, Eric M.

2004-01-01

Because of NASA's added reliance on simulation for successful interplanetary missions, the MER mission has developed a detailed EDL trajectory modeling and simulation. This paper summarizes how the MER EDL sequence of events are modeled, verification of the methods used, and the inputs. This simulation is built upon a multibody parachute trajectory simulation tool that has been developed in POST I1 that accurately simulates the trajectory of multiple vehicles in flight with interacting forces. In this model the parachute and the suspended bodies are treated as 6 Degree-of-Freedom (6 DOF) bodies. The terminal descent phase of the mission consists of several Entry, Descent, Landing (EDL) events, such as parachute deployment, heatshield separation, deployment of the lander from the backshell, deployment of the airbags, RAD firings, TIRS firings, etc. For an accurate, reliable simulation these events need to be modeled seamlessly and robustly so that the simulations will remain numerically stable during Monte-Carlo simulations. This paper also summarizes how the events have been modeled, the numerical issues, and modeling challenges.

On Presolar Stardust Grains from CO Classical Novae

NASA Astrophysics Data System (ADS)

Iliadis, Christian; Downen, Lori N.; José, Jordi; Nittler, Larry R.; Starrfield, Sumner

2018-03-01

About 30%–40% of classical novae produce dust 20–100 days after the outburst, but no presolar stardust grains from classical novae have been unambiguously identified yet. Although several studies claimed a nova paternity for certain grains, the measured and simulated isotopic ratios could only be reconciled, assuming that the grains condensed after the nova ejecta mixed with a much larger amount of close-to-solar matter. However, the source and mechanism of this potential post-explosion dilution of the ejecta remains a mystery. A major problem with previous studies is the small number of simulations performed and the implied poor exploration of the large nova parameter space. We report the results of a different strategy, based on a Monte Carlo technique, that involves the random sampling over the most important nova model parameters: the white dwarf composition; the mixing of the outer white dwarf layers with the accreted material before the explosion; the peak temperature and density; the explosion timescales; and the possible dilution of the ejecta after the outburst. We discuss and take into account the systematic uncertainties for both the presolar grain measurements and the simulation results. Only those simulations that are consistent with all measured isotopic ratios of a given grain are accepted for further analysis. We also present the numerical results of the model parameters. We identify 18 presolar grains with measured isotopic signatures consistent with a CO nova origin, without assuming any dilution of the ejecta. Among these, the grains G270_2, M11-334-2, G278, M11-347-4, M11-151-4, and Ag26 have the highest probability of a CO nova paternity.

Supplying materials needed for grain growth characterizations of nano-grained UO 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mo, Kun; Miao, Yinbin; Yun, Di

2015-09-30

This activity is supported by the US Nuclear Energy Advanced Modeling and Simulation (NEAMS) Fuels Product Line (FPL) and aims at providing experimental data for the validation of the mesoscale simulation code MARMOT. MARMOT is a mesoscale multiphysics code that predicts the coevolution of microstructure and properties within reactor fuel during its lifetime in the reactor. It is an important component of the Moose-Bison-Marmot (MBM) code suite that has been developed by Idaho National Laboratory (INL) to enable next generation fuel performance modeling capability as part of the NEAMS Program FPL. In order to ensure the accuracy of the microstructuremore » based materials models being developed within the MARMOT code, extensive validation efforts must be carried out. In this report, we summarize our preliminary synchrotron radiation experiments at APS to determine the grain size of nanograin UO 2. The methodology and experimental setup developed in this experiment can directly apply to the proposed in-situ grain growth measurements. The investigation of the grain growth kinetics was conducted based on isothermal annealing and grain growth characterization as functions of duration and temperature. The kinetic parameters such as activation energy for grain growth for UO 2 with different stoichiometry are obtained and compared with molecular dynamics (MD) simulations.« less

First-principles simulations of electrostatic interactions between dust grains

NASA Astrophysics Data System (ADS)

Itou, H.; Amano, T.; Hoshino, M.

2014-12-01

We investigated the electrostatic interaction between two identical dust grains of an infinite mass immersed in homogeneous plasma by employing first-principles N-body simulations combined with the Ewald method. We specifically tested the possibility of an attractive force due to overlapping Debye spheres (ODSs), as was suggested by Resendes et al. [Phys. Lett. A 239, 181-186 (1998)]. Our simulation results demonstrate that the electrostatic interaction is repulsive and even stronger than the standard Yukawa potential. We showed that the measured electric field acting on the grain is highly consistent with a model electrostatic potential around a single isolated grain that takes into account a correction due to the orbital motion limited theory. Our result is qualitatively consistent with the counterargument suggested by Markes and Williams [Phys. Lett. A 278, 152-158 (2000)], indicating the absence of the ODS attractive force.

Grain-scale modeling and splash parametrization for aeolian sand transport.

PubMed

Lämmel, Marc; Dzikowski, Kamil; Kroy, Klaus; Oger, Luc; Valance, Alexandre

2017-02-01

The collision of a spherical grain with a granular bed is commonly parametrized by the splash function, which provides the velocity of the rebounding grain and the velocity distribution and number of ejected grains. Starting from elementary geometric considerations and physical principles, like momentum conservation and energy dissipation in inelastic pair collisions, we derive a rebound parametrization for the collision of a spherical grain with a granular bed. Combined with a recently proposed energy-splitting model [Ho et al., Phys. Rev. E 85, 052301 (2012)PLEEE81539-375510.1103/PhysRevE.85.052301] that predicts how the impact energy is distributed among the bed grains, this yields a coarse-grained but complete characterization of the splash as a function of the impact velocity and the impactor-bed grain-size ratio. The predicted mean values of the rebound angle, total and vertical restitution, ejection speed, and number of ejected grains are in excellent agreement with experimental literature data and with our own discrete-element computer simulations. We extract a set of analytical asymptotic relations for shallow impact geometries, which can readily be used in coarse-grained analytical modeling or computer simulations of geophysical particle-laden flows.

Solar and interplanetary dynamics; Proceedings of the Symposium, Harvard University, Cambridge, Mass., August 27-31, 1979

NASA Technical Reports Server (NTRS)

Dryer, M. (Editor); Tandberg-Hanssen, E.

1980-01-01

The symposium focuses on solar phenomena as the source of transient events propagating through the solar system, and theoretical and observational assessments of the dynamic processes involved in these events. The topics discussed include the life history of coronal structures and fields, coronal and interplanetary responses to long time scale phenomena, solar transient phenomena affecting the corona and interplanetary medium, coronal and interplanetary responses to short time scale phenomena, and future directions.

The "Approximate 150 Day Quasi-Periodicity" in Interplanetary and Solar Phenomena During Cycle 23

NASA Technical Reports Server (NTRS)

Richardson, I. G.; Cane, H. V.

2004-01-01

A"quasi-periodicity" of approx. 150 days in various solar and interplanetary phenomena has been reported in earlier solar cycles. We suggest that variations in the occurrence of solar energetic particle events, inter-planetary coronal mass ejections, and geomagnetic storm sudden commenceents during solar cycle 23 show evidence of this quasi-periodicity, which is also present in the sunspot number, in particular in the northern solar hemisphere. It is not, however, prominent in the interplanetary magnetic field strength.

The Interplanetary Transport Effects on the Fe/O Ratio of Large Solar Energetic Particle Events

NASA Astrophysics Data System (ADS)

Qin, G.; Wang, Y.

2016-12-01

Mason and coauthors in 2006 invested the intensities of O and Fe in large western solar energetic particle (SEP) events observed by ACE spacecraft. It was found that the Fe/O ratio decreases with time at the same kinetic energy per nucleon during the rising phase of time-intensity profile, and the Fe/O ratio gradually becomes a constant during the decay phase of intensity. However, if the O intensity is compared at a higher kinetic energy with the Fe intensity, the behaviors of intensity profiles of O and Fe are similar. So they concluded that for such kind of events the injection profiles of Fe and O are similar near the Sun, and that scattering effects dominates. With numerical simulations, we find that in order to get such kind of SEPs behavior, Fe and O have to have similar injection profiles near the Sun, and similar diffusion and adiabatic cooling processes in the interplanetary space.

Plasma circulation in Jupiter's magnetosphere

NASA Astrophysics Data System (ADS)

Chané, E.

2017-12-01

We are using our three-dimensional global MHD model of Jupiter's magnetosphere to study the plasma circulation in the magnetodisk. We show that the Iogenic plasma does not travel outward axisymmetrically but rather forms a long spiral arm of high density corotating with the planet. This leads to periodic phenomena in the magnetodisk: for instance, every rotation period, a region of high density is rapidly moving outward on the pre-noon sector. This leads to shearing motions that generate field aligned currents and periodically affect the main oval in this sector.We will also show how the interplanetary magnetic field influences the position of the magnetodisk in our simulations, displacing the current sheet above and below the equatorial plan. We will discuss how this is affecting the depleted flux-tubes returning from the night-side after unloading most of their plasma in the magnetotail (Vasyliunas cycle) and see how they can then move above or below the magnetodisk when arriving at dawn and then reconnect with the interplanetary magnetic field on the day-side.

Transport of solar electrons in the turbulent interplanetary magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ablaßmayer, J.; Tautz, R. C., E-mail: robert.c.tautz@gmail.com; Dresing, N., E-mail: dresing@physik.uni-kiel.de

2016-01-15

The turbulent transport of solar energetic electrons in the interplanetary magnetic field is investigated by means of a test-particle Monte-Carlo simulation. The magnetic fields are modeled as a combination of the Parker field and a turbulent component. In combination with the direct calculation of diffusion coefficients via the mean-square displacements, this approach allows one to analyze the effect of the initial ballistic transport phase. In that sense, the model complements the main other approach in which a transport equation is solved. The major advancement is that, by recording the flux of particles arriving at virtual detectors, intensity and anisotropy-time profilesmore » can be obtained. Observational indications for a longitudinal asymmetry can thus be explained by tracing the diffusive spread of the particle distribution. The approach may be of future help for the systematic interpretation of observations for instance by the solar terrestrial relations observatory (STEREO) and advanced composition explorer (ACE) spacecrafts.« less

An MHD simulation of the effects of the interplanetary magnetic field By component on the interaction of the solar wind with the earth's magnetosphere during southward interplanetary magnetic field

NASA Technical Reports Server (NTRS)

Ogino, T.; Walker, R. J.; Ashour-Abdalla, M.; Dawson, J. M.

1986-01-01

The interaction between the solar wind and the earth's magnetosphere has been studied by using a time-dependent three-dimensional MHD model in which the IMF pointed in several directions between dawnward and southward. When the IMF is dawnward, the dayside cusp and the tail lobes shift toward the morningside in the northern magnetosphere. The plasma sheet rotates toward the north on the dawnside of the tail and toward the south on the duskside. For an increasing southward IMF component, the plasma sheet becomes thinner and subsequently wavy because of patchy or localized tail reconnection. At the same time, the tail field-aligned currents have a filamentary layered structure. When projected onto the northern polar cap, the filamentary field-aligned currents are located in the same area as the region 1 currents, with a pattern similar to that associated with auroral surges. Magnetic reconnection also occurs on the dayside magnetopause for southward IMF.

The Gas-Grain Chemistry of Galactic Translucent Clouds

NASA Astrophysics Data System (ADS)

Maffucci, Dominique M.; Herbst, Eric

2016-01-01

We employ a combination of traditional and modified rate equation approaches to simulate the time-dependent gas-grain chemistry that pertains to molecular species observed in absorption in Galactic translucent clouds towards Sgr B2(N). We solve the kinetic rate laws over a range of relevant physical conditions (gas and grain temperatures, particle density, visual extinction, cosmic ray ionization rate) characteristic of translucent clouds by implementing a new grid module that allows for parallelization of the astrochemical simulations. Gas-phase and grain-surface synthetic pathways, chemical timescales, and associated physical sensitivities are discussed for selected classes of species including the cyanopolyynes, complex cyanides, and simple aldehydes.

Effect of Deformation Parameters on Microstructure and Properties During DIFT of X70HD Pipeline Steel

NASA Astrophysics Data System (ADS)

Wang, Jian; Zhu, Wei; Xiao, Hong; Zhang, Liang-liang; Qin, Hao; Yu, Yue

2018-02-01

Grain refinement is a critical approach to improve the strength of materials without damaging the toughness. The grains of deformation-induced ferrite are considerably smaller than those of proeutectoid ferrite. Grain refinement is crucial to the application of deformation-induced ferrite. The composition of ferrite and bainite or martensite is important in controlling the performance of X70HD pipeline steel, and cooling significantly influences the control of their ratio and grain size. By analyzing the static and dynamic phase-transition points using Gleeble-3800 thermal simulator, thermal simulations were performed through two-stage deformations in the austenite zone. Ferrite transformation rules were studied with thermal simulation tests under different deformation and cooling parameters based on the actual production of cumulative deformation. The influence of deformation parameters on the microstructure transformation was analyzed. Numerous fine-grain deformation-induced ferrites were obtained by regulating various parameters, including deformation temperature, strain rate, cooling rate, final cooling temperature and other parameters. Results of metallographic observation and microtensile testing revealed that the selection of appropriate parameters can refine the grains and improve the performance of the X70HD pipeline steel.

Effect of Secondary Cooling Conditions on Solidification Structure and Central Macrosegregation in Continuously Cast High-Carbon Rectangular Billet

NASA Astrophysics Data System (ADS)

Zeng, Jie; Chen, Weiqing

2015-10-01

Solidification structures of high carbon rectangular billet with a size of 180 mm × 240 mm in different secondary cooling conditions were simulated using cellular automaton-finite element (CAFE) coupling model. The adequacy of the model was compared with the simulated and the actual macrostructures of 82B steel. Effects of the secondary cooling water intensity on solidification structures including the equiaxed grain ratio and the equiaxed grain compactness were discussed. It was shown that the equiaxed grain ratio and the equiaxed grain compactness changed in the opposite direction at different secondary cooling water intensities. Increasing the secondary cooling water intensity from 0.9 or 1.1 to 1.3 L/kg could improve the equiaxed grain compactness and decrease the equiaxed grain ratio. Besides, the industrial test was conducted to investigate the effect of different secondary cooling water intensities on the center carbon macrosegregation of 82B steel. The optimum secondary cooling water intensity was 0.9 L/kg, while the center carbon segregation degree was 1.10. The relationship between solidification structure and center carbon segregation was discussed based on the simulation results and the industrial test.

Coarse graining atomistic simulations of plastically deforming amorphous solids

NASA Astrophysics Data System (ADS)

Hinkle, Adam R.; Rycroft, Chris H.; Shields, Michael D.; Falk, Michael L.

2017-05-01

The primary mode of failure in disordered solids results from the formation and persistence of highly localized regions of large plastic strains known as shear bands. Continuum-level field theories capable of predicting this mechanical response rely upon an accurate representation of the initial and evolving states of the amorphous structure. We perform molecular dynamics simulations of a metallic glass and propose a methodology for coarse graining discrete, atomistic quantities, such as the potential energies of the elemental constituents. A strain criterion is established and used to distinguish the coarse-grained degrees-of-freedom inside the emerging shear band from those of the surrounding material. A signal-to-noise ratio provides a means of evaluating the strength of the signal of the shear band as a function of the coarse graining. Finally, we investigate the effect of different coarse graining length scales by comparing a two-dimensional, numerical implementation of the effective-temperature description in the shear transformation zone (STZ) theory with direct molecular dynamics simulations. These comparisons indicate the coarse graining length scale has a lower bound, above which there is a high level of agreement between the atomistics and the STZ theory, and below which the concept of effective temperature breaks down.

Genesis of Interplanetary Intermittent Turbulence: a Case Study of Rope-Rope Magnetic Reconnection

NASA Technical Reports Server (NTRS)

Chian, Abraham C.- L.; Feng, Heng Q.; Hu, Qiang; Loew, Murray H.; Miranda, Rodrigo A.; Munoz, Pablo R.; Sibeck, David G.; Wu, De J.

2016-01-01

In a recent paper, the relation between current sheet, magnetic reconnection, and turbulence at the leading edge of an interplanetary coronal mass ejection was studied. We report here the observation of magnetic reconnection at the interface region of two interplanetary magnetic flux ropes. The front and rear boundary layers of three interplanetary magnetic flux ropes are identified, and the structures of magnetic flux ropes are reconstructed by the Grad Shafranov method. A quantitative analysis of the reconnection condition and the degree of intermittency reveals that rope-rope magnetic reconnection is the most likely site for genesis of interplanetary intermittency turbulence in this event. The dynamic pressure pulse resulting from this reconnection triggers the onset of a geomagnetic storm.

Physics of interplanetary dust capture via impact into organic polymer foams

NASA Technical Reports Server (NTRS)

Anderson, William W.; Ahrens, Thomas J.

1994-01-01

The physics of hypervelocity impacts into foams is of interest because of the possible application to interplanetary dust particle (IDP) capture by spacecraft. We present a model for the phenomena occurring in such impacts into low-density organic polymer foams. Particles smaller than foam cells behave as if the foam is a series of solid slabs and are fragmented and, at higher velocities, thermally altered. Particles much larger than the foam cells behave as if the foam were a continuum, allowing the use of a continuum mechanics model to describe the effects of drag and ablation. Fragmentation is expected to be a major process, especially for aggregates of small grains. Calculations based on these arguments accurately predict experimental data and, for hypothetical IDPs, indicate that recovery of organic materials will be low for encounter velocities greater than 5 km/s. For an organic particle 100 micrometers in diameter, approx. 35% of the original mass would be collected in an impact at 5 km/s, dropping to approx. 10% at 10 km/s and approx. 0% at 15 km/s. For the same velocities the recovery ratios for troilite (FeS) are approx. 95%, 65%, and 50%, and for olivine (Mg2SiO4) they are approx. 98%, 80%, and 65%, demonstrating that inorganic materials are much more easily collected. The density of the collector material has only a second-order effect, changing the recovered mass by less than 10% of the original mass.

High Precision Oxygen Three Isotope Analysis of Wild-2 Particles and Anhydrous Chondritic Interplanetary Dust Particles

NASA Technical Reports Server (NTRS)

Nakashima, D.; Ushikubo, T.; Zolensky, Michael E.; Weisberg, M. K.; Joswiak, D. J.; Brownlee, D. E.; Matrajt, G.; Kita, N. T.

2011-01-01

One of the most important discoveries from comet Wild-2 samples was observation of crystalline silicate particles that resemble chondrules and CAIs in carbonaceous chondrites. Previous oxygen isotope analyses of crystalline silicate terminal particles showed heterogeneous oxygen isotope ratios with delta(sup 18)O to approx. delta(sup 17)O down to -50% in the CAI-like particle Inti, a relict olivine grain in Gozen-sama, and an olivine particle. However, many Wild-2 particles as well as ferromagnesian silicates in anhydrous interplanetary dust particles (IDPs) showed Delta(sup 17)O values that cluster around -2%. In carbonaceous chondrites, chondrules seem to show two major isotope reservoirs with Delta(sup 17)O values at -5% and -2%. It was suggested that the Delta(sup 17)O = -2% is the common oxygen isotope reservoir for carbonaceous chondrite chondrules and cometary dust, from the outer asteroid belt to the Kuiper belt region. However, a larger dataset with high precision isotope analyses (+/-1-2%) is still needed to resolve the similarities or distinctions among Wild-2 particles, IDPs and chondrules in meteorites. We have made signifi-cant efforts to establish routine analyses of small particles (< or =10micronsm) at 1-2% precision using IMS-1280 at WiscSIMS laboratory. Here we report new results of high precision oxygen isotope analyses of Wild-2 particles and anhydrous chondritic IDPs, and discuss the relationship between the cometary dust and carbonaceous chondrite chondrules.

Fullerenes and interplanetary dust at the Permian-Triassic boundary.

PubMed

Poreda, Robert J; Becker, Luann

2003-01-01

We recently presented new evidence that an impact occurred approximately 250 million years ago at the Permian-Triassic boundary (PTB), triggering the most severe mass extinction in the history of life on Earth. We used a new extraterrestrial tracer, fullerene, a third carbon carrier of noble gases besides diamond and graphite. By exploiting the unique properties of this molecule to trap noble gases inside of its caged structure (helium, neon, argon), the origin of the fullerenes can be determined. Here, we present new evidence for fullerenes with extraterrestrial noble gases in the PTB at Graphite Peak, Antarctica, similar to PTB fullerenes from Meishan, China and Sasayama, Japan. In addition, we isolated a (3)He-rich magnetic carrier phase in three fractions from the Graphite Peak section. The noble gases in this magnetic fraction were similar to zero-age deep-sea interplanetary dust particles (IDPs) and some magnetic grains isolated from the Cretaceous-Tertiary boundary. The helium and neon isotopic compositions for both the bulk Graphite Peak sediments and an isolated magnetic fraction from the bulk material are consistent with solar-type gases measured in zero-age deep-sea sediments and point to a common source, namely, the flux of IDPs to the Earth's surface. In this instance, the IDP noble gas signature for the bulk sediment can be uniquely decoupled from fullerene, demonstrating that two separate tracers are present (direct flux of IDPs for (3)He vs. giant impact for fullerene).

Reconstruction of three-dimensional grain structure in polycrystalline iron via an interactive segmentation method

NASA Astrophysics Data System (ADS)

Feng, Min-nan; Wang, Yu-cong; Wang, Hao; Liu, Guo-quan; Xue, Wei-hua

2017-03-01

Using a total of 297 segmented sections, we reconstructed the three-dimensional (3D) structure of pure iron and obtained the largest dataset of 16254 3D complete grains reported to date. The mean values of equivalent sphere radius and face number of pure iron were observed to be consistent with those of Monte Carlo simulated grains, phase-field simulated grains, Ti-alloy grains, and Ni-based super alloy grains. In this work, by finding a balance between automatic methods and manual refinement, we developed an interactive segmentation method to segment serial sections accurately in the reconstruction of the 3D microstructure; this approach can save time as well as substantially eliminate errors. The segmentation process comprises four operations: image preprocessing, breakpoint detection based on mathematical morphology analysis, optimized automatic connection of the breakpoints, and manual refinement by artificial evaluation.

Defect and grain boundary scattering in tungsten: A combined theoretical and experimental study

NASA Astrophysics Data System (ADS)

Lanzillo, Nicholas A.; Dixit, Hemant; Milosevic, Erik; Niu, Chengyu; Carr, Adra V.; Oldiges, Phil; Raymond, Mark V.; Cho, Jin; Standaert, Theodorus E.; Kamineni, Vimal K.

2018-04-01

Several major electron scattering mechanisms in tungsten (W) are evaluated using a combination of first-principles density functional theory, a Non-Equilibrium Green's Function formalism, and thin film Kelvin 4-point sheet resistance measurements. The impact of grain boundary scattering is found to be roughly an order of magnitude larger than the impact of defect scattering. Ab initio simulations predict average grain boundary reflection coefficients for a number of twin grain boundaries to lie in the range r = 0.47 to r = 0.62, while experimental data can be fit to the empirical Mayadas-Schatzkes model with a comparable but slightly larger value of r = 0.69. The experimental and simulation data for grain boundary resistivity as a function of grain size show excellent agreement. These results provide crucial insights for understanding the impact of scaling of W-based contacts between active devices and back-end-of-line interconnects in next-generation semiconductor technology.

Simulating the probability of grain sorghum maturity before the first frost in northeastern Colorado

USDA-ARS?s Scientific Manuscript database

Expanding grain sorghum [Sorghum bicolor (L.) Moench] production northward from southeastern Colorado is thought to be limited by shorter growing seasons due to lower temperatures and earlier frost dates. This study used a simulation model for predicting crop phenology (PhenologyMMS) to predict the ...

Bacillus subtilis spore survival and expression of germination-induced bioluminescence after prolonged incubation under simulated Mars atmospheric pressure and composition: implications for planetary protection and lithopanspermia

NASA Technical Reports Server (NTRS)

Nicholson, Wayne L.; Schuerger, Andrew C.

2005-01-01

Bacterial endospores in the genus Bacillus are considered good models for studying interplanetary transfer of microbes by natural or human processes. Although spore survival during transfer itself has been the subject of considerable study, the fate of spores in extraterrestrial environments has received less attention. In this report we subjected spores of a strain of Bacillus subtilis, containing luciferase resulting from expression of an sspB-luxAB gene fusion, to simulated martian atmospheric pressure (7-18 mbar) and composition (100% CO(2)) for up to 19 days in a Mars simulation chamber. We report here that survival was similar between spores exposed to Earth conditions and spores exposed up to 19 days to simulated martian conditions. However, germination-induced bioluminescence was lower in spores exposed to simulated martian atmosphere, which suggests sublethal impairment of some endogenous spore germination processes.

Fundamental studies concerning planetary quarantine in space

NASA Astrophysics Data System (ADS)

Koike, J.; Hori, T.; Katahira, Y.; Koike, K. A.; Tanaka, K.; Kobayashi, K.; Kawasaki, Y.

If there is a possibility that the organisms carried from Earth to space can live for a significant period on planets, the contamination of planets should be prevented for the purpose of future life-detection experiments. In connection with quarantine for interplanetary missions, we have examined the survivabilities of terrestrial microorganisms under simulated space conditions /1-8/. In this study, examined the survivabilities of terrestrial organisms under simulated Mars conditions. The Mars conditions were simulated by ultraviolet (UV) and proton irradiation under low temperature, high vacuum, and simulated gaseous conditions. After exposure to the simulated Mars condition, the survivabilities of the organisms were examined. The spores of Bacillus subtilis andAspergillus niger , some anaerobic bacterias and algaes, showed considerably high survivabilities even after UV and proton irradiation corresponding to 200 years on Mars. This subject is not restricted to academic curiosity but concerns problems involving the contamination of Mars with terrestrial organisms carried by space-probes.

Monte Carlo simulations of particle acceleration at oblique shocks: Including cross-field diffusion

NASA Technical Reports Server (NTRS)

Baring, M. G.; Ellison, D. C.; Jones, F. C.

1995-01-01

The Monte Carlo technique of simulating diffusive particle acceleration at shocks has made spectral predictions that compare extremely well with particle distributions observed at the quasi-parallel region of the earth's bow shock. The current extension of this work to compare simulation predictions with particle spectra at oblique interplanetary shocks has required the inclusion of significant cross-field diffusion (strong scattering) in the simulation technique, since oblique shocks are intrinsically inefficient in the limit of weak scattering. In this paper, we present results from the method we have developed for the inclusion of cross-field diffusion in our simulations, namely model predictions of particle spectra downstream of oblique subluminal shocks. While the high-energy spectral index is independent of the shock obliquity and the strength of the scattering, the latter is observed to profoundly influence the efficiency of injection of cosmic rays into the acceleration process.

Interactions of Dust Grains with Coronal Mass Ejections and Solar Cycle Variations of the F-Coronal Brightness

NASA Technical Reports Server (NTRS)

Ragot, B. R.; Kahler, S. W.

2003-01-01

The density of interplanetary dust increases sunward to reach its maximum in the F corona, where its scattered white-light emission dominates that of the electron K corona above about 3 Solar Radius. The dust will interact with both the particles and fields of antisunward propagating coronal mass ejections (CMEs). To understand the effects of the CME/dust interactions we consider the dominant forces, with and without CMEs. acting on the dust in the 3-5 Solar Radius region. Dust grain orbits are then computed to compare the drift rates from 5 to 3 Solar Radius. for periods of minimum and maximum solar activity, where a simple CME model is adopted to distinguish between the two periods. The ion-drag force, even in the quiet solar wind, reduces the drift time by a significant factor from its value estimated with the Poynting-Robertson drag force alone. The ion-drag effects of CMEs result in even shorter drift times of the large (greater than or approx. 3 microns) dust grains. hence faster depletion rates and lower dust-pain densities, at solar maxima. If dominated by thermal emission, the near-infrared brightness will thus display solar cycle variations close to the dust plane of symmetry. While trapping the smallest of the grains, the CME magnetic fields also scatter the grains of intermediate size (0.1-3 microns) in latitude. If light scattering by small grains close to the Sun dominates the optical brightness. the scattering by the CME magnetic fields will result in a solar cycle variation of the optical brightness distribution not exceeding 100% at high latitudes, with a higher isotropy reached at solar maxima. A good degree of latitudinal isotropy is already reached at low solar activity since the magnetic fields of the quiet solar wind so close to the Sun are able to scatter the small (less than or approx. 3 microns) grains up to the polar regions in only a few days or less, producing strong perturbations of their trajectories in less than half their orbital periods. Finally, we consider possible observable consequences of individual CME/dust interactions. We show that the dust grains very likely have no observable effect on the dynamics of CMEs. The effect of an individual CME on the dust grains, however, might serve as a forecasting tool for the directions and amplitudes of the magnetic fields within the CME.

Simulating the Liaison Navigation Concept in a Geo + Earth-Moon Halo Constellation

NASA Technical Reports Server (NTRS)

Fujimoto, K.; Leonard, J. M.; McGranaghan, R. M.; Parker, J. S.; Anderson, R. L.; Born, G. H.

2012-01-01

Linked Autonomous Interplanetary Satellite Orbit Navigation, or LiAISON, is a novel satellite navigation technique where relative radiometric measurements between two or more spacecraft in a constellation are processed to obtain the absolute state of all spacecraft. The method leverages the asymmetry of the gravity field that the constellation exists in. This paper takes a step forward in developing a high fidelity navigation simulation for the LiAISON concept in an Earth-Moon constellation. In particular, we aim to process two-way Doppler measurements between a satellite in GEO orbit and another in a halo orbit about the Earth-Moon L1 point.

Magnetization switching in nanoscale ferromagnetic grains: MFM observables from Monte Carlo simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Richards, H.L.; Sides, S.W.; Novotny, M.A.

1996-12-31

Recently experimental techniques, such as magnetic force microscopy (MFM), have enabled the magnetic state of individual sub-micron particles to be resolved. Motivated by these experimental developments, the authors use Monte Carlo simulations of two-dimensional kinetic Ising ferromagnets to study the magnetic relaxation in a negative applied field of a grain with an initial magnetization m{sub 0} = + 1. They use classical droplet theory to predict the functional forms for some quantities which can be observed by MFM. An example is the probability that the magnetization is positive, which is a function of time, field, grain size, and grain dimensionality.more » The qualitative agreement between experiments and their simulations of switching in individual single-domain ferromagnets indicates that the switching mechanism in such particles may involve local nucleation and subsequent growth of droplets of the stable phase.« less

Mechanical properties and crack growth behavior of polycrystalline copper using molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Qiu, Ren-Zheng; Li, Chi-Chen; Fang, Te-Hua

2017-08-01

This study investigated the mechanical properties and crack propagation behavior of polycrystalline copper using a molecular dynamics simulation. The effects of temperature, grain size, and crack length were evaluated in terms of atomic trajectories, slip vectors, common neighbor analysis, the material’s stress-strain diagram and Young’s modulus. The simulation results show that the grain boundary of the material is more easily damaged at high temperatures and that grain boundaries will combine at the crack tip. From the stress-strain diagram, it was observed that the maximum stress increased as the temperature decreased. In contrast, the maximum stress was reduced by increasing the temperature. With regard to the effect of the grain size, when the grain size was too small, the structure of the sample deformed due to the effect of atomic interactions, which caused the grain boundary structure to be disordered in general. However, when the grain size was larger, dislocations appeared and began to move from the tip of the crack, which led to a new dislocation phenomenon. With regards to the effect of the crack length, the tip of the crack did not affect the sample’s material when the crack length was less than 5 nm. However, when the crack length was above 7.5 nm, the grain boundary was damaged, and twinning structures and dislocations appeared on both sides of the crack tip. This is because the tip of the crack was blunt at first before sharpening due to the dislocation effect.

Structurally detailed coarse-grained model for Sec-facilitated co-translational protein translocation and membrane integration

PubMed Central

Miller, Thomas F.

2017-01-01

We present a coarse-grained simulation model that is capable of simulating the minute-timescale dynamics of protein translocation and membrane integration via the Sec translocon, while retaining sufficient chemical and structural detail to capture many of the sequence-specific interactions that drive these processes. The model includes accurate geometric representations of the ribosome and Sec translocon, obtained directly from experimental structures, and interactions parameterized from nearly 200 μs of residue-based coarse-grained molecular dynamics simulations. A protocol for mapping amino-acid sequences to coarse-grained beads enables the direct simulation of trajectories for the co-translational insertion of arbitrary polypeptide sequences into the Sec translocon. The model reproduces experimentally observed features of membrane protein integration, including the efficiency with which polypeptide domains integrate into the membrane, the variation in integration efficiency upon single amino-acid mutations, and the orientation of transmembrane domains. The central advantage of the model is that it connects sequence-level protein features to biological observables and timescales, enabling direct simulation for the mechanistic analysis of co-translational integration and for the engineering of membrane proteins with enhanced membrane integration efficiency. PMID:28328943

Titanium carbide and titania phases on Antarctic ice particles of probable extraterrrestrial origin

NASA Technical Reports Server (NTRS)

Zolensky, M. E.; Pun, A.; Thomas, K. L.

1989-01-01

Two unique titania-rich particles, found within ancient Antarctic ice have been discovered and characterized, and are believed to be of extraterrestrial origin. Both particles contain abundant submicron-sized crystals of Magneli phases (Ti(n)O(2n-1). In addition, one particle contains a core of TiC. Whereas the Magneli phases would have been stable in the early solar nebula, and so probably formed there, the TiC is more likely to have condensed in the cool, dusty, carbon-rich outer shell of a red giant star. It is suggested that both particles are interplanetary dust particles whose Magneli phases carry a record of the PO2-T conditions of the early solar nebula. It is further suggested that the TiC grain in particle 705 is remnant interstellar dust.

Nitrogen Isotopic Composition of Organic Matter in a Pristine Collection IDP

NASA Technical Reports Server (NTRS)

Messenger, S.; Nakamura-Messenger, K.; Keller, L. P.; Clemett, S. J.; Nguyen, A. N.; Walker, Robert M.

2012-01-01

Anhydrous chondritic porous interplanetary dust particles (CP IDPs) are probable cometary materials that show primitive characteristics, such as unequilibrated mineralogy, fragile structure, and abundant presolar grains and organic matter [1-3]. CP IDPs are richer in aliphatic species and N-bearing aromatic hydrocarbons than meteoritic organics and commonly exhibit highly anomalous H and N isotopic compositions [4,5]. Cometary organic matter is of interest in part because it has escaped the hydrothermal processing experienced by meteorites. However, IDPs are collected using silicon oil that must be removed with strong organic solvents such as hexane. This procedure is likely to have removed some fraction of soluble organic phases in IDPs. We recently reported the first stratospheric collection of IDPs without the use of silicone oil [6]. Here we present initial studies of the carbonaceous material in an IDP from this collection.

Effects of snow grain non-sphericity on climate simulations: Sensitivity tests with the NorESM model

NASA Astrophysics Data System (ADS)

Räisänen, Petri; Makkonen, Risto; Kirkevåg, Alf

2017-04-01

Snow grains are non-spherical and generally irregular in shape. Still, in radiative transfer calculations, they are often treated as spheres. This also applies to the computation of snow albedo in the Snow, Ice, and Aerosol Radiation (SNICAR) model and in the Los Alamos sea ice model, version 4 (CICE4), both of which are employed in the Community Earth System Model and in the Norwegian Earth System Model (NorESM). In this work, we evaluate the effect of snow grain shape on climate simulated by NorESM in a slab ocean configuration of the model. An experiment with spherical snow grains (SPH) is compared with another (NONSPH) in which the snow shortwave single-scattering properties are based on a combination of non-spherical snow grain shapes optimized using measurements of angular scattering by blowing snow. The key difference between these treatments is that the asymmetry parameter is smaller in the non-spherical case (≈ 0.78 in the visible region) than in the spherical case (≈ 0.89). Therefore, for a given snow grain size, the use of non-spherical snow grains yields a higher snow broadband albedo, typically by ≈0.03. Consequently, considering the spherical case as the baseline, the use of non-spherical snow grains results in a negative radiative forcing (RF), with a global-mean top-of-the-model value of ≈ -0.22 W m-2. Although this global-mean RF is modest, it has a rather substantial impact on the climate simulated by NoRESM. In particular, the global annual-mean 2-m air temperature in NONSPH is 1.17 K lower than in SPH, with substantially larger differences at high latitudes. The climatic response is amplified by strong snow and sea ice feedbacks. It is further found that the difference between NONSPH and SPH could be largely "tuned away" by adjusting the snow grain size in the NONSPH experiment by ≈ 70%. The impact of snow grain shape on the radiative effect (RE) of absorbing aerosols in snow (black carbon and mineral dust) is also discussed. For an optically thick snowpack with a given snow grain effective size, the absorbing aerosol RE is smaller for non-spherical than for spherical snow grains. The reason for this is that due to the lower asymmetry parameter of the non-spherical snow grains, solar radiation does not penetrate as deep in snow as in the case of spherical snow grains. However, in a climate model simulation, the RE is sensitive to patterns of aerosol deposition and simulated snow cover. In fact, the global land-area mean absorbing aerosol RE is larger in the NONSPH than SPH experiment (0.193 vs. 0.168 W m-2), owing to later snowmelt in spring.

Model-based software for simulating ultrasonic pulse/echo inspections of metal components

NASA Astrophysics Data System (ADS)

Chiou, Chien-Ping; Margetan, Frank J.; Taylor, Jared L.; McKillip, Matthew; Engle, Brady J.; Roberts, Ronald A.; Barnard, Daniel J.

2017-02-01

Under the sponsorship of the National Science Foundation's Industry/University Cooperative Research Center at Iowa State University, an effort was initiated in 2015 to repackage existing research-grade software into user friendly tools for the rapid estimation of signal-to-noise ratio (S/N) for ultrasonic inspections of metals. The software combines: (1) a Python-based graphical user interface for specifying an inspection scenario and displaying results; and (2) a Fortran-based engine for computing defect signals and backscattered grain noise characteristics. The later makes use the Thompson-Gray Model for the response from an internal defect and the Independent Scatterer Model for backscattered grain noise. This paper provides an overview of the ongoing modeling effort with emphasis on recent developments. These include: treatment of angle-beam inspections, implementation of distance-amplitude corrections, changes in the generation of "invented" calibration signals, efforts to simulate ultrasonic C-scans; and experimental testing of model predictions. The simulation software can now treat both normal and oblique-incidence immersion inspections of curved metal components having equiaxed microstructures in which the grain size varies with depth. Both longitudinal and shear-wave inspections are treated. The model transducer can either be planar, spherically-focused, or bi-cylindrically-focused. A calibration (or reference) signal is required and is used to deduce the measurement system efficiency function. This can be "invented" by the software using center frequency and bandwidth information specified by the user, or, alternatively, a measured calibration signal can be used. Defect types include flat-bottomed-hole reference reflectors, and spherical pores and inclusions. Simulation outputs include estimated defect signal amplitudes, root-mean-squared grain noise amplitudes, and S/N as functions of the depth of the defect within the metal component. At any particular depth, the user can view a simulated A-scan displaying the superimposed defect and grain-noise waveforms. The realistic grain noise signals used in the A-scans are generated from a set of measured "universal" noise signals whose strengths and spectral characteristics are altered to match predicted noise characteristics for the simulation at hand. We present simulation examples demonstrating recent developments, and discuss plans to improve simulator capabilities.

Coarse graining of atactic polystyrene and its derivatives

NASA Astrophysics Data System (ADS)

Agrawal, Anupriya; Perahia, Dvora; Grest, Gary S.

2014-03-01

Capturing large length scales in polymers and soft matter while retaining atomistic properties is imperative to computational studies of dynamic systems. Here we present a new methodology developing coarse-grain model based on atomistic simulation of atactic polystyrene (PS). Similar to previous work by Fritz et al., each monomer is described by two coarse grained beads. In contrast to this earlier work where intramolecular potentials were based on Monte Carlo simulation of both isotactic and syndiotactic single PS molecule to capture stereochemistry, we obtained intramolecular interactions from a single molecular dynamics simulation of an all-atom atactic PS melts. The non-bonded interactions are obtained using the iterative Boltzmann inversion (IBI) scheme. This methodology has been extended to coarse graining of poly-(t-butyl-styrene) (PtBS). An additional coarse-grained bead is used to describe the t-butyl group. Similar to the process for PS, the intramolecular interactions are obtained from a single all atom atactic melt simulation. Starting from the non-bonded interactions for PS, we show that the IBI method for the non-bonded interactions of PtBS converges relatively fast. A generalized scheme for substituted PS is currently in development. We would like to acknowledge Prof. Kurt Kremer for helpful discussions during this work.

Modeling and simulation of the deposition/relaxation processes of polycrystalline diatomic structures of metallic nitride films

NASA Astrophysics Data System (ADS)

García, M. F.; Restrepo-Parra, E.; Riaño-Rojas, J. C.

2015-05-01

This work develops a model that mimics the growth of diatomic, polycrystalline thin films by artificially splitting the growth into deposition and relaxation processes including two stages: (1) a grain-based stochastic method (grains orientation randomly chosen) is considered and by means of the Kinetic Monte Carlo method employing a non-standard version, known as Constant Time Stepping, the deposition is simulated. The adsorption of adatoms is accepted or rejected depending on the neighborhood conditions; furthermore, the desorption process is not included in the simulation and (2) the Monte Carlo method combined with the metropolis algorithm is used to simulate the diffusion. The model was developed by accounting for parameters that determine the morphology of the film, such as the growth temperature, the interacting atomic species, the binding energy and the material crystal structure. The modeled samples exhibited an FCC structure with grain formation with orientations in the family planes of < 111 >, < 200 > and < 220 >. The grain size and film roughness were analyzed. By construction, the grain size decreased, and the roughness increased, as the growth temperature increased. Although, during the growth process of real materials, the deposition and relaxation occurs simultaneously, this method may perhaps be valid to build realistic polycrystalline samples.

GENESIS OF INTERPLANETARY INTERMITTENT TURBULENCE: A CASE STUDY OF ROPE–ROPE MAGNETIC RECONNECTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chian, Abraham C.-L.; Loew, Murray H.; Feng, Heng Q.

In a recent paper, the relation between current sheet, magnetic reconnection, and turbulence at the leading edge of an interplanetary coronal mass ejection was studied. We report here the observation of magnetic reconnection at the interface region of two interplanetary magnetic flux ropes. The front and rear boundary layers of three interplanetary magnetic flux ropes are identified, and the structures of magnetic flux ropes are reconstructed by the Grad–Shafranov method. A quantitative analysis of the reconnection condition and the degree of intermittency reveals that rope–rope magnetic reconnection is the most likely site for genesis of interplanetary intermittency turbulence in this event.more » The dynamic pressure pulse resulting from this reconnection triggers the onset of a geomagnetic storm.« less

DOUBLE POWER LAWS IN THE EVENT-INTEGRATED SOLAR ENERGETIC PARTICLE SPECTRUM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Lulu; Zhang, Ming; Rassoul, Hamid K., E-mail: lzhao@fit.edu

2016-04-10

A double power law or a power law with exponential rollover at a few to tens of MeV nucleon{sup −1} of the event-integrated differential spectra has been reported in many solar energetic particle (SEP) events. The rollover energies per nucleon of different elements correlate with a particle's charge-to-mass ratio (Q/A). The probable causes are suggested as residing in shock finite lifetimes, shock finite sizes, shock geometry, and an adiabatic cooling effect. In this work, we conduct a numerical simulation to investigate a particle's transport process in the inner heliosphere. We solve the focused transport equation using a time-backward Markov stochasticmore » approach. The convection, magnetic focusing, adiabatic cooling effect, and pitch-angle scattering are included. The effects that the interplanetary turbulence imposes on the shape of the resulting SEP spectra are examined. By assuming a pure power-law differential spectrum at the Sun, a perfect double-power-law feature with a break energy ranging from 10 to 120 MeV nucleon{sup −1} is obtained at 1 au. We found that the double power law of the differential energy spectrum is a robust result of SEP interplanetary propagation. It works for many assumptions of interplanetary turbulence spectra that give various forms of momentum dependence of a particle's mean free path. The different spectral shapes in low-energy and high-energy ends are not just a transition from the convection-dominated propagation to diffusion-dominated propagation.« less

Using ACE Observations of Interplanetary Particles and Magnetic Fields as Possible Contributors to Variations Observed at Van Allen Probes during Major events in 2013

NASA Astrophysics Data System (ADS)

Armstrong, T. P.; Manweiler, J. W.; Gerrard, A. J.; Gkioulidou, M.; Lanzerotti, L. J.; Patterson, J. D.

2013-12-01

Observations from ACE EPAM including energy spectra of protons, helium, and oxygen will be prepared for coordinated use in estimating the direct and indirect access of energetic particles to inner and outer geomagnetic trapping zones. Complete temporal coverage from ACE at 12 seconds, 5 minutes, 17 minutes, hourly and daily cadences will be used to catalog interplanetary events arriving at Earth including interplanetary magnetic field sector boundaries, interplanetary shocks, and interplanetary coronal mass ejections, ICMEs. The first 6 months of 2013 have included both highly disturbed times, March 17 and May 22, and extended quiet periods of little or no variations. Among the specific questions that ACE and Van Allen Probes coordinated observations may aid in resolving are: 1. How much, if any, direct capture of interplanetary energetic particles occurs and what conditions account for it? 2. How much influence do interplanetary field and particle variations have on energization and/or loss of geomagnetically trapped populations? The poster will also present important links and describe methods and important details of access to numerically expressed ACE EPAM and Van Allen Probes RBSPICE observations that can be flexibly and easily accessed via the internet for student and senior researcher use.

Static Grain Growth in Contact Metamorphic Calcite: A Cathodoluminescence Study.

NASA Astrophysics Data System (ADS)

Vogt, B.; Heilbronner, R.; Herwegh, M.; Ramseyer, K.

2009-04-01

In the Adamello contact aureole, monomineralic mesozoic limestones were investigated in terms of grain size evolution and compared to results on numerical modeling performed by Elle. The sampled area shows no deformation and therefore represents an appropriate natural laboratory for the study of static grain growth (Herwegh & Berger, 2003). For this purpose, samples were collected at different distances to the contact to the pluton, covering a temperature range between 270 to 630°C. In these marbles, the grain sizes increase with temperature from 5 µm to about 1 cm as one approaches the contact (Herwegh & Berger, 2003). In some samples, photomicrographs show domains of variable cathodoluminescence (CL) intensities, which are interpreted to represent growth zonations. Microstructures show grains that contain cores and in some samples even several growth stages. The cores are usually not centered and the zones not concentric. They may be in touch with grain boundaries. These zonation patterns are consistent within a given aggregate but differ among the samples even if they come from the same location. Relative CL intensities depend on the Mn/Fe ratio. We assume that changes in trace amounts of Mn/Fe must have occurred during the grain size evolution, preserving local geochemical trends and their variations with time. Changes in Mn/Fe ratios can either be explained by (a) locally derived fluids (e.g. hydration reactions of sheet silicate rich marbles in the vicinity) or (b) by the infiltration of the calcite aggregates by externally derived (magmatic?) fluids. At the present stage, we prefer a regional change in fluid composition (b) because the growth zonations only occur at distances of 750-1250 m from the pluton contact (350-450°C). Closer to the contact, neither zonations nor cores were found. At larger distances, CL intensities differ from grain to grain, revealing diagenetic CL patterns that were incompletely recrystallized by grain growth. The role of infiltration of magmatic fluids is also manifest in the vicinity of dikes, where intense zonation patterns are prominent in the marbles. The software Elle was developed to simulate microstructural evolution in rocks. The numerical model with the title "Grain boundary sweeping" was performed by M. Jessell and was found on http://www.materialsknowledge.org/elle. It displays the grain size evolution and the development of growth zonations during grain boundary migration of a 2D foam structure. This simulation was chosen because the driving force is the minimization of isotropic surface energies. It will be compared to the natural microstructures. At the last stage of the simulation the average grain and core sizes have increased. All, even the smallest grains, show growth zonations. Grains can be divided into two groups: (a) initially larger grains, increasing their grain size and maintaining their core size and (b) initially smaller grains with decreasing grain and decreasing core size. Group (a) grains show large areas swept by grain boundaries into the direction of small grains. Grain boundaries between large grains move more slowly. Their cores do not touch any grain boundaries. Cores of group (b) grains are in contact with the grain boundary network and are on the way to be consumed. In the numerical model and in the natural example similar features can be observed: The cores are not necessarily centered, the zonations are not necessarily concentric and some of the cores touch the grain boundary network. In the simulation, grain boundary migration velocity between large grains is smaller than between a large and a small grain. From this we would predict that - given enough time - a well sorted grain size distribution of increased grain size could be generated. But since many small grains occur we infer that this equilibrium has not been obtained. Analytical results of some natural samples that could be analyzed up to now indicate a relatively well sorted grain size distribution suggesting a more mature state of static grain growth. In comparison to the simulation, grain and core boundaries in the marbles are not always straight. For lobate grain boundaries the surface area has not been minimized in respect to the grain size. An explanation for this might be grain boundary pinning or a local dynamic overprint. Some cores and growth zones in the investigated calcites show a continuous change in luminescence. This is interpreted to be an effect of late diffusion within the grain and/or a continuous change of fluid composition and supply. The absence of zonation in samples close to the contact might be explained by fast grain growth due to high temperatures and/or fast fluid transport. Possibly, this is combined with an enhanced component of volume diffusion. Thus concentration variations of Mn/Fe are diminished and not visible in form of a growth zonation. Herwegh M, Berger A (2003) Differences in grain growth of calcite: a field-based modeling approach. Contr. Min. Pet. 145: 600-611

Simulation of Magnetic Cloud Erosion and Deformation During Propagation

NASA Astrophysics Data System (ADS)

Manchester, W.; Kozyra, J. U.; Lepri, S. T.; Lavraud, B.; Jackson, B. V.

2013-12-01

We examine a three-dimensional (3-D) numerical magnetohydrodynamic (MHD) simulation describing a very fast interplanetary coronal mass ejection (ICME) propagating from the solar corona to 1 AU. In conjunction with it's high speed, the ICME evolves in ways that give it a unique appearance at 1AU that does not resemble a typical ICME. First, as the ICME decelerates in the solar wind, filament material at the back of the flux rope pushes its way forward through the flux rope. Second, diverging nonradial flows in front of the filament transport azimuthal flux of the rope to the sides of the ICME. Third, the magnetic flux rope reconnects with the interplanetary magnetic field (IMF). As a consequence of these processes, the flux rope partially unravels and appears to evolve to an entirely open configuration near its nose. At the same time, filament material at the base of the flux rope moves forward and comes in direct contact with the shocked plasma in the CME sheath. We find evidence such remarkable behavior has occurred when we examine a very fast CME that erupted from the Sun on 2005 January 20. In situ observations of this event near 1 AU show very dense cold material impacting the Earth following immediately behind the CME sheath. Charge state analysis shows this dense plasma is filament material, and the analysis of SMEI data provides the trajectory of this dense plasma from the Sun. Consistent with the simulation, we find the azimuthal flux (Bz) to be entirely unbalanced giving the appearance that the flux rope has completely eroded on the anti-sunward side.

Bacterial spores in granite survive hypervelocity launch by spallation: implications for lithopanspermia.

PubMed

Fajardo-Cavazos, Patricia; Langenhorst, Falko; Melosh, H Jay; Nicholson, Wayne L

2009-09-01

Bacterial spores are considered good candidates for endolithic life-forms that could survive interplanetary transport by natural impact processes, i.e., lithopanspermia. Organisms within rock can only embark on an interplanetary journey if they survive ejection from the surface of the donor planet and the associated extremes of compressional shock, heating, and acceleration. Previous simulation experiments have measured each of these three stresses more or less in isolation of one another, and results to date indicate that spores of the model organism Bacillus subtilis can survive each stress applied singly. Few simulations, however, have combined all three stresses simultaneously. Because considerable experimental and theoretical evidence supports a spallation mechanism for launch, we devised an experimental simulation of launch by spallation using the Ames Vertical Gun Range (AVGR). B. subtilis spores were applied to the surface of a granite target that was impacted from above by an aluminum projectile fired at 5.4 km/s. Granite spall fragments were captured in a foam recovery fixture and then recovered and assayed for shock damage by transmission electron microscopy and for spore survival by viability assays. Peak shock pressure at the impact site was calculated to be 57.1 GPa, though recovered spall fragments were only very lightly shocked at pressures of 5-7 GPa. Spore survival was calculated to be on the order of 10(-5), which is in agreement with results of previous static compressional shock experiments. These results demonstrate that endolithic spores can survive launch by spallation from a hypervelocity impact, which lends further evidence in favor of lithopanspermia theory.

Finite element analysis of heat load of tungsten relevant to ITER conditions

NASA Astrophysics Data System (ADS)

Zinovev, A.; Terentyev, D.; Delannay, L.

2017-12-01

A computational procedure is proposed in order to predict the initiation of intergranular cracks in tungsten with ITER specification microstructure (i.e. characterised by elongated micrometre-sized grains). Damage is caused by a cyclic heat load, which emerges from plasma instabilities during operation of thermonuclear devices. First, a macroscopic thermo-mechanical simulation is performed in order to obtain temperature- and strain field in the material. The strain path is recorded at a selected point of interest of the macroscopic specimen, and is then applied at the microscopic level to a finite element mesh of a polycrystal. In the microscopic simulation, the stress state at the grain boundaries serves as the marker of cracking initiation. The simulated heat load cycle is a representative of edge-localized modes, which are anticipated during normal operations of ITER. Normal stresses at the grain boundary interfaces were shown to strongly depend on the direction of grain orientation with respect to the heat flux direction and to attain higher values if the flux is perpendicular to the elongated grains, where it apparently promotes crack initiation.

Structure and transport at grain boundaries in polycrystalline olivine: An atomic-scale perspective

NASA Astrophysics Data System (ADS)

Mantisi, Boris; Sator, Nicolas; Guillot, Bertrand

2017-12-01

Structure and transport properties at grain boundaries in polycrystalline olivine have been investigated at the atomic scale by molecular dynamics simulation (MD) using an empirical ionocovalent interaction potential. On the time scale of the simulation (a few tens of nanoseconds for a system size of ∼650,000 atoms) grain boundaries and grain interior were identified by mapping the atomic displacements along the simulation run. In the investigated temperature range (1300-1700 K) the mean thickness of the grain boundary phase is evaluated between 0.5 and 2 nm, a value which depends on temperature and grain size. The structure of the grain boundary phase is found to be disordered (amorphous-like) and is different from the one exhibited by the supercooled liquid. The self-diffusion coefficients of major elements in the intergranular region range from ∼10-13 to 10-10 m2/s between 1300 and 1700 K (with DSigb < DOgb < DFegb < DMggb) and are only one order of magnitude smaller than those evaluated in the supercooled melt. In using a newly derived expression for the bulk self-diffusion coefficient it is concluded that the latter one is driven by the grain boundary contribution as long as the grain size is smaller than a centimeter. In assuming that the electrical conduction at grain boundaries is purely ionic, the macroscopic grain boundary conductivity is found to be two orders of magnitude lower than in molten olivine, and one order of magnitude higher than the lattice conductivity. A consequence is that the conductivity of the olivine polycrystal is dominated by the grain interior contribution as soon as the grain size is larger than a micrometer or so. The grain boundary viscosity has been evaluated from the Green-Kubo relation expressing the viscosity as function of the stress tensor time correlation function. In spite of a slow convergence of the calculation by MD, the grain boundary viscosity was estimated about ∼105 Pa s at 1500 K, a value in agreement with high-temperature viscoelastic relaxation data. An interesting information gained from MD is that sliding at grain boundaries is essentially controlled by the internal friction between the intergranular phase and the grain edges.

Influences of granular constraints and surface effects on the heterogeneity of elastic, superelastic, and plastic responses of polycrystalline shape memory alloys

DOE PAGES

Paranjape, Harshad M.; Paul, Partha P.; Sharma, Hemant; ...

2017-02-16

Deformation heterogeneities at the microstructural length-scale developed in polycrystalline shape memory alloys (SMAs) during superelastic loading are studied using both experiments and simulations. In situ X-ray diffraction, specifically the far-field high energy diffraction microscopy (ff-HEDM) technique, was used to non-destructively measure the grain-averaged statistics of position, crystal orientation, elastic strain tensor, and volume for hundreds of austenite grains in a superelastically loaded nickel-titanium (NiTi) SMA. These experimental data were also used to create a synthetic microstructure within a finite element model. The development of intragranular stresses were then simulated during tensile loading of the model using anisotropic elasticity. Driving forcesmore » for phase transformation and slip were calculated from these stresses. The grain-average responses of individual austenite crystals examined before and after multiple stress-induced transformation events showed that grains in the specimen interior carry more axial stress than the surface grains as the superelastic response "shakes down". Examination of the heterogeneity within individual grains showed that regions near grain boundaries exhibit larger stress variation compared to the grain interiors. As a result, this intragranular heterogeneity is more strongly driven by the constraints of neighboring grains than the initial stress state and orientation of the individual grains.« less

Influences of granular constraints and surface effects on the heterogeneity of elastic, superelastic, and plastic responses of polycrystalline shape memory alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paranjape, Harshad M.; Paul, Partha P.; Sharma, Hemant

Deformation heterogeneities at the microstructural length-scale developed in polycrystalline shape memory alloys (SMAs) during superelastic loading are studied using both experiments and simulations. In situ X-ray diffraction, specifically the far-field high energy diffraction microscopy (ff-HEDM) technique, was used to non-destructively measure the grain-averaged statistics of position, crystal orientation, elastic strain tensor, and volume for hundreds of austenite grains in a superelastically loaded nickel-titanium (NiTi) SMA. These experimental data were also used to create a synthetic microstructure within a finite element model. The development of intragranular stresses were then simulated during tensile loading of the model using anisotropic elasticity. Driving forcesmore » for phase transformation and slip were calculated from these stresses. The grain-average responses of individual austenite crystals examined before and after multiple stress-induced transformation events showed that grains in the specimen interior carry more axial stress than the surface grains as the superelastic response "shakes down". Examination of the heterogeneity within individual grains showed that regions near grain boundaries exhibit larger stress variation compared to the grain interiors. As a result, this intragranular heterogeneity is more strongly driven by the constraints of neighboring grains than the initial stress state and orientation of the individual grains.« less

Advances in model-based software for simulating ultrasonic immersion inspections of metal components

NASA Astrophysics Data System (ADS)

Chiou, Chien-Ping; Margetan, Frank J.; Taylor, Jared L.; Engle, Brady J.; Roberts, Ronald A.

2018-04-01

Under the sponsorship of the National Science Foundation's Industry/University Cooperative Research Center at ISU, an effort was initiated in 2015 to repackage existing research-grade software into user-friendly tools for the rapid estimation of signal-to-noise ratio (SNR) for ultrasonic inspections of metals. The software combines: (1) a Python-based graphical user interface for specifying an inspection scenario and displaying results; and (2) a Fortran-based engine for computing defect signals and backscattered grain noise characteristics. The later makes use the Thompson-Gray measurement model for the response from an internal defect, and the Thompson-Margetan independent scatterer model for backscattered grain noise. This paper, the third in the series [1-2], provides an overview of the ongoing modeling effort with emphasis on recent developments. These include the ability to: (1) treat microstructures where grain size, shape and tilt relative to the incident sound direction can all vary with depth; and (2) simulate C-scans of defect signals in the presence of backscattered grain noise. The simulation software can now treat both normal and oblique-incidence immersion inspections of curved metal components. Both longitudinal and shear-wave inspections are treated. The model transducer can either be planar, spherically-focused, or bi-cylindrically-focused. A calibration (or reference) signal is required and is used to deduce the measurement system efficiency function. This can be "invented" by the software using center frequency and bandwidth information specified by the user, or, alternatively, a measured calibration signal can be used. Defect types include flat-bottomed-hole reference reflectors, and spherical pores and inclusions. Simulation outputs include estimated defect signal amplitudes, root-mean-square values of grain noise amplitudes, and SNR as functions of the depth of the defect within the metal component. At any particular depth, the user can view a simulated A-, B-, and C-scans displaying the superimposed defect and grain-noise waveforms. The realistic grain noise signals used in the A-scans are generated from a set of measured "universal" noise signals whose strengths and spectral characteristics are altered to match predicted noise characteristics for the simulation at hand.

Impact of grain size evolution on necking and pinch-and-swell formation in calcite layers

NASA Astrophysics Data System (ADS)

Schmalholz, Stefan Markus; Duretz, Thibault

2017-04-01

The formation of necking zones and the associated formation of pinch-and-swell structure is one form of strain localization in extending, competent layers. Natural pinch-and-swell structure in centimetre-thick calcite layers typically shows a reduction of grain size from swell towards pinch. However, the impact of grain size evolution on necking and pinch-and-swell formation is incompletely understood. We perform zero-dimensional (0D) and 2D thermo-mechanical numerical simulations to quantify the impact of grain size evolution on necking for extension rates between 10-12s^-1and10^-14 s-1 and temperatures around 350°C. For a combination of diffusion and dislocation creep we calculate grain size evolution according to the paleowattmeter (grain size is proportional to mechanical work rate) or the paleopiezometer (grain size is proportional to stress). Numerical results fit two observations: (i) grain size reduction from swells towards pinches, and (ii) dislocation creep dominated deformation in swells and significant contribution of diffusion creep in pinches. Modelled grain size in pinches (10 to 60 μm) and swells (70 to 800 μm) is close to observed grain size in pinches (15 to 27 μm) and in swells (250 to 1500 μm). Grain size evolution has only a minor impact on necking suggesting that grain size evolution is a consequence, and not the cause of necking. Viscous shear heating and grain size evolution had a negligible thermal impact in the simulations.

An analytical coarse-graining method which preserves the free energy, structural correlations, and thermodynamic state of polymer melts from the atomistic to the mesoscale.

PubMed

McCarty, J; Clark, A J; Copperman, J; Guenza, M G

2014-05-28

Structural and thermodynamic consistency of coarse-graining models across multiple length scales is essential for the predictive role of multi-scale modeling and molecular dynamic simulations that use mesoscale descriptions. Our approach is a coarse-grained model based on integral equation theory, which can represent polymer chains at variable levels of chemical details. The model is analytical and depends on molecular and thermodynamic parameters of the system under study, as well as on the direct correlation function in the k → 0 limit, c0. A numerical solution to the PRISM integral equations is used to determine c0, by adjusting the value of the effective hard sphere diameter, dHS, to agree with the predicted equation of state. This single quantity parameterizes the coarse-grained potential, which is used to perform mesoscale simulations that are directly compared with atomistic-level simulations of the same system. We test our coarse-graining formalism by comparing structural correlations, isothermal compressibility, equation of state, Helmholtz and Gibbs free energies, and potential energy and entropy using both united atom and coarse-grained descriptions. We find quantitative agreement between the analytical formalism for the thermodynamic properties, and the results of Molecular Dynamics simulations, independent of the chosen level of representation. In the mesoscale description, the potential energy of the soft-particle interaction becomes a free energy in the coarse-grained coordinates which preserves the excess free energy from an ideal gas across all levels of description. The structural consistency between the united-atom and mesoscale descriptions means the relative entropy between descriptions has been minimized without any variational optimization parameters. The approach is general and applicable to any polymeric system in different thermodynamic conditions.

Simulation of fatigue damage in ferroelectric polycrystals under mechanical/electrical loading

NASA Astrophysics Data System (ADS)

Kozinov, S.; Kuna, M.

2018-07-01

The reliability of smart-structures made of ferroelectric ceramics is essentially reduced by the formation of cracks under the action of external electrical and/or mechanical loading. In the current research a numerical model for low-cycle fatigue in ferroelectric mesostructures is proposed. In the finite element simulations a combination of two user element routines is utilized. The first one is used to model a micromechanical ferroelectric domain switching behavior inside the grains. The second one is used to simulate fatigue damage of grain boundaries by a cohesive zone model (EMCCZM) based on an electromechanical cyclic traction-separation law (TSL). For numerical simulations a scanning electron microscope image of the ceramic's grain structure was digitalized and meshed. The response of this mesostructure to cyclic electrical or mechanical loading is systematically analyzed. As a result of the simulations, the distribution of electric potential, field, displacement and polarization as well as mechanical stresses and deformations inside the grains are obtained. At the grain boundaries, the formation and evolution of damage are analyzed until final failure and induced degradation of electric permittivity. It is found that the proposed model correctly mimics polycrystalline behavior during poling processes and progressive damage under cyclic electromechanical loading. To the authors' knowledge, it is the first model and numerical analysis of ferroelectric polycrystals taking into account both domain reorientation and cohesive modeling of intergranular fracture. It can help to understand failure mechanisms taking place in ferroelectrics during fatigue processes.

Coupled Finite Element ? Potts Model Simulations of Grain Growth in Copper Interconnects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radhakrishnan, Balasubramaniam; Gorti, Sarma B

The paper addresses grain growth in copper interconnects in the presence of thermal expansion mismatch stresses. The evolution of grain structure and texture in copper in the simultaneous presence of two driving forces, curvature and elastic stored energy difference, is modeled by using a hybrid Potts model simulation approach. The elastic stored energy is calculated by using the commercial finite element code ABAQUS, where the effect of elastic anisotropy on the thermal mismatch stress and strain distribution within a polycrystalline grain structure is modeled through a user material (UMAT) interface. Parametric studies on the effect of trench width and themore » height of the overburden were carried out. The results show that the grain structure and texture evolution are significantly altered by the presence of elastic strain energy.« less

Simulation and measurement of nanometer-scale resistivity of copper films for interconnect applications

NASA Astrophysics Data System (ADS)

Yarimbiyik, Arif Emre

2007-12-01

A highly versatile simulation program is developed and used to examine how the resistivity of thin metal films and lines increases as their dimensions approach and become smaller than the mean fee path of electrons in metals such as copper (size effect). The simulation program: (1) provides a more accurate calculation of surface scattering effects than that obtained from the usual formulation of Fuchs' theory, (2) calculates grain-boundary effects that are consistent with the theory of Mayadas and Shatzkes, (3) includes the effects of surface and grain-boundary scattering either separately or together, and (4) simulates the effect on resistivity if a surface of a film or line has a different value for the scattering parameter. The increase in resistivity with decreasing thickness of thin, evaporated copper films (approximately 10 nm to 150 nm thick) was determined from sheet resistance and film thickness measurements. Good agreement between the experimental results with those of the simulation program was obtained when the measured mean grain sizes were used by the simulation program. The mean of the grain sizes tend to decrease with decreasing film thickness and thereby increase the impact of grain-boundary scattering on the effective resistivity of the film. Estimates of the mean grain size for each film were determined from using, in combination, the electron backscatter diffraction (EBSD) and the X-ray diffraction (XRD) methods. With values for the measured change in sheet resistance with temperature of these films, it is shown that measurements of the electrical film thickness, using Matthiessen's rule, agreed to within 3 nm of the physical measurements (profilometer) of these films. Hence, Matthiessen's rule can continue to be used to measure the thickness of a copper film and, by inference, the cross-sectional area of a copper line for dimensions well below the mean free path of electrons in copper at room temperature (39 nm).

Correlation of interplanetary-space B sub z field fluctuations and trapped-particle redistribution.

NASA Technical Reports Server (NTRS)

Parks, G. K.; Pellat, R.

1972-01-01

Observations of interplanetary magnetic field fluctuations in correlation with trapped particle fluctuations are discussed. From observations of particle-redistribution effects, properties of the magnetospheric electric field are derived. The obtained results suggest that the interplanetary B(sub z) field fluctuations might represent a strong driving source for particle diffusion.

Radio-scintillation observations of interplanetary disturbances

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watanabe, T.; Kakinuma, T.

1984-01-01

Recent developments in the studies of interplanetary disturbances by scintillation techniques are briefly reviewed. The turbulent postshock region of an interplanetary disturbance produces transient enhancements in the scintillation level and the flow speed in many cases. An empirical method to determine three-dimensional angular distribution of the propagation speed of the disturbance on the basis of interplanetary scintillation measurements of postshock flow speeds is applied to 17 events which took place in 1978-1981. Among them, four representative examples, including two events which were associated with disappearing solar filaments, are described in detail. Several disturbances had oblate configurations the latitudinal extent ismore » smaller than the longitudinal extent. On the average, the angular distribution of the propagation speed at 1-AU heliocentric distance is quasi-isotropic over a longitudinal range of 100 deg centered at the normal of relevant solar phenomenon. The net excess mass and energy in an interplanetary disturbance associated with a disappearing solar filament can be comparable to those of an interplanetary disturbance associated with a large solar flare. 57 references.« less

Aerospace medicine and biology: A continuing bibliography with indexes, supplement 97

NASA Technical Reports Server (NTRS)

1972-01-01

Subject coverage concentrates on the biological, physiological, psychological, and environmental effects to which man is subjected during and following simulated or actual flight in the earth's atmosphere or in interplanetary space. References describing similar effects on biological organisms of lower order are also included. Such related topics as sanitary problems, pharmacology, toxicology, safety and survival, life support systems, exobiology, and personnel factors receive appropriate attention. Each entry consists of a standard citation accompanied by its abstract.

Aerospace medicine and biology: A continuing bibliography with indexes (supplement 94)

NASA Technical Reports Server (NTRS)

1971-01-01

Subject coverage concentrates on the biological, physiological, psychological, and environmental effects to which man is subjected during and following simulated or actual flight in the earth's atmosphere or in interplanetary space. References describing similar effects on biological organisms of lower order are also included. Such related topics as sanitary problems, pharmacology, toxicology, safety and survival, life support systems, exobiology, and personnel factors receive appropriate attention. Each entry consists of a standard citation accompanied by its abstract.

Aerospace medicine and biology: A continuing bibliography with indexes, supplement 96

NASA Technical Reports Server (NTRS)

1971-01-01

Subject coverage concentrates on the biological, physiological, psychological, and environmental effects to which man is subjected during and following simulated or actual flight in the earth's atmosphere or in interplanetary space. References describing similar effects on biological organisms of lower order are also included. Such related topics as sanitary problems, pharmacology, toxicology, safety and survival, life support systems, exobiology, and personnel factors receive appropriate attention. Each entry consists of a standard citation accompanied by its abstract.

Aerospace medicine and biology: A continuing bibliography with indexes, supplement

NASA Technical Reports Server (NTRS)

1972-01-01

Subject coverage concentrates on the biological, physiological, psychological, and environmental effects to which man is subjected during and following simulated or actual flight in the earth's atmosphere or in interplanetary space. References describing similar effects on biological organisms of lower order are also included. Such related topics as sanitary problems, pharmacology, toxicology, safety and survival, life support systems, exobiology, and personnel factors receive appropriate attention. Each entry consists of a standard citation accompanied by its abstract.

Aerospace medicine and biology: A continuing bibliography with indexes (supplement 100)

NASA Technical Reports Server (NTRS)

1972-01-01

Subject coverage concentrates on the biological, physiological, psychological, and environmental effects to which man is subjected during and following simulated or actual flight in the earth's atmosphere or in interplanetary space. Reference describing similar effects on biological organisms of lower order are also included. Such related topics as sanitary problems, pharmacology, toxicology, safety and survival, life support systems, exobiology, and personnel factors receive appropriate attention. Each entry consists of a standard citation accompanied by its abstract.

Optimization of interplanetary trajectories with unpowered planetary swingbys

NASA Technical Reports Server (NTRS)

Sauer, Carl G., Jr.

1988-01-01

A method is presented for calculating and optimizing unpowered planetary swingby trajectories using a patched conic trajectory generator. Examples of unpowered swingby trajectories are given to demonstrate the method. The method, which uses primer vector theory, is not highly accurate, but provides projections for preliminary mission definition studies. Advantages to using a patched conic trajectory simulation for preliminary studies which examine many different and complex missions include calculation speed and adaptability to changes or additions to the formulation.

3D Observation of GEMS by Electron Tomography

NASA Technical Reports Server (NTRS)

Matsuno, Junya; Miyake, Akira; Tsuchiyama, Akira; Nakamura-Messenger, Keiko; Messenger, Scott

2014-01-01

Amorphous silicates in chondritic porous interplanetary dust particles (CP-IDPs) coming from comets are dominated by glass with embedded metal and sulfides (GEMS). GEMS grains are submicron-sized rounded objects (typically 100-500) nm in diameter) with anaometer-sized (10-50 nm) Fe-Ni metal and sulfide grains embedded in an amorphous silicate matrix. Several formation processes for GEMS grains have been proposed so far, but these models are still being debated [2-5]. Bradley et al. proposed that GEMS grains are interstellar silicate dust that survived various metamorphism or alteration processes in the protoplanetary disk and that they are amorphiation products of crystalline silicates in the interstellar medium by sputter-deposition of cosmic ray irradiation, similar to space weathering [2,4]. This consideration is based on the observation of nano-sized crystals (approximately 10 nm) called relict grains in GEMS grains and their shapes are pseudomorphs to the host GEMS grains. On the other hand, Keller and Messenger proposed that most GEMS formed in the protoplanetary disk as condensates from high temperature gas [3,5]. This model is based on the fact that most GEMS grains have solar isotopic compositions and have extremely heterogeneous and non-solar elemental compositions. Keller and Messenger (2011) also reported that amorphous silicates in GEMS grains are surrounded by sulfide grains, which formed as sulfidization of metallic iron grains located on the GEMS surface. The previous studies were performed with 2D observation by using transmission electron microscopy (TEM) or scanning TEM (STEM). In order to understand the structure of GEMS grains described above more clearly, we observed 3D structure of GEMS grains by electron tomography using a TEM/STEM (JEM-2100F, JEOL) at Kyoto University. Electron tomography gives not only 3D structures but also gives higher spatial resolution (approximately a few nm) than that in conventional 2D image, which is restricted by sample thickness ) approx. or greater than 50 nm). Three cluster IDPs (L2036AA5 cluster4, L2009L8 cluster 13 and W726A2) were used for the observations. ID W726A2 was collected without silicon oil, which is ordinary used to collect IDPs, so this sample has no possibility of contaminations caused by silicon oil or solvent to rinse it [6]. The samples were embedded in epoxy risin and sliced into ultrathin sections (50-300 nm) using an ultramicotome. The sections were observed by BF-TEM and HAADF-STEM (high angle annular dark field-scanning TEM) modes. Images were obtained by rotating the sample tilt angle over a range of +/- 65 deg in 1 deg steps. The obtained images were reconstructed to slice images. Mineral phases in the slice images were estimated by comparing with a 2D elemental map obtained by an EDS (energy dispersive X-ray spectroscopy) system equipped in the TEM/STEM. Careful examination of the slice images confirmed that iron grains are embedded in the amorphous silicate matrix of the GEMS grains, but sulfide grains were mainly present on the surface of the amorphous silicate. These results are consistent with the model that GEMS grains formed as condensates [3,5], although more data are needed to conclude the origin of GEMS grains. The present study is the first successful example adapting the electron tomography to the IDPs. This type of analysis will be important for planetary material sciences in the future.

Simulated Prompt Acceleration of Multi-MeV Electrons by the 17 March 2015 Interplanetary Shock

NASA Astrophysics Data System (ADS)

Hudson, Mary; Jaynes, Allison; Kress, Brian; Li, Zhao; Patel, Maulik; Shen, Xiao-Chen; Thaller, Scott; Wiltberger, Michael; Wygant, John

2017-10-01

Prompt enhancement of relativistic electron flux at L = 3-5 has been reported from Van Allen Probes Relativistic Electron Proton Telescope (REPT) measurements associated with the 17 March 2015 interplanetary shock compression of the dayside magnetosphere. Acceleration by ˜1 MeV is inferred on less than a drift timescale as seen in prior shock compression events, which launch a magnetosonic azimuthal electric field impulse tailward. This impulse propagates from the dayside around the flanks accelerating electrons in drift resonance at the dusk flank. Such longitudinally localized acceleration events produce a drift echo signature which was seen at >1 MeV energy on both Van Allen Probe spacecraft, with sustained observations by Probe B outbound at L = 5 at 2100 MLT at the time of impulse arrival, measured by the Electric Fields and Waves instrument. MHD test particle simulations are presented which reproduce drift echo features observed in the REPT measurements at Probe B, including the energy and pitch angle dependence of drift echoes observed. While the flux enhancement was short lived for this event due to subsequent inward motion of the magnetopause, stronger events with larger electric field impulses, as observed in March 1991 and the Halloween 2003 storm, produce enhancements which can be quantified by the inward radial transport and energization determined by the induction electric field resulting from dayside compression.

Solar energetic particle transport and the possibility of wave generation by streaming electrons

NASA Astrophysics Data System (ADS)

Strauss, R. D. T.; le Roux, J. A.

2017-12-01

After being accelerated close to the Sun, solar energetic particles (SEPs) are transported (mainly) along the turbulent interplanetary magnetic field. In this study, we simulate the propagation of 100 keV electrons as they are scattered in the interplanetary medium. A consequence of these wave-particle interactions is the possible modification (either growth or damping) of the background turbulence by anisotropic SEP electron beams. This process was thought to be negligible, and therefore neglected in past modeling approaches. However, recent observations and modeling by Agueda and Lario (2016) suggest that wave generation may be significant and is therefore included and evaluated in our present model. Our results suggest that wave amplification by streaming SEP electrons is indeed possible and may even significantly alter the background turbulent field. However, the simulations show that this process is much too weak to produce observable effects at Earth's orbit, but such effects may well be observed in future by spacecraft closer to the Sun, presenting an intriguing observational opportunity for either the Solar Orbiter or the Parker Solar Probe spacecraft. Lastly, we note that the level of perpendicular diffusion may also play an important role in determining the effectiveness of the wave growth process. Reference: Agueda, N. and Lario, D. Release History and Transport Parameters of Relativistic Solar Electrons Inferred From Near-the-Sun In Situ Observations, ApJ, 829, 131, 2016.

Forced three-dimensional magnetic reconnection due to linkage of magnetic flux tubes

NASA Technical Reports Server (NTRS)

Otto, A.

1995-01-01

During periods of southward interplanetary magnetic field (IMF) orientation the magnetic field geometry at the dayside magnetopause is susceptible to magnetic reconnection. It has been suggested that reconnection may occur in a localized manner at several patches on the magnetopause. A major problem with this picture is the interaction of magnetic flux ropes which are generated by different reconnection processes. An individual flux rope is bent elbowlike where it intersects the magnetopause and the magnetic field changes from magnetospheric to interplanetary magnetic field orientation. Multiple patches of reconnection can lead to the formation of interlinked magnetic flux tubes. Although the corresponding flux is connected to the IMF the northward and southward connected branches are hooked into each other and cannot develop independently. We have studied this problem in the framework of three-dimensional magnetohydrodynamic simulations. The results indicate that a singular current sheet forms at the interface of two interlinked flux tubes if no resistivity is present in the simulation. This current sheet is strongly tilted compared to the original current sheet. In the presence of resistivity the interaction of the two flux tubes forces a fast reconnection process which generates helically twisted closed magnetospheric flux. This linkage induced reconnection generates a boundary layer with layers of open and closed magnetospheric flux and may account for the brightening of auroral arcs poleward of the boundary between open and closed magnetic flux.

Microstructure-sensitive small fatigue crack growth assessment. Effect of strain ratio multiaxial strain state and geometric discontinuities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Castelluccio, Gustavo M.; McDowell, David L.

Fatigue crack initiation in the high cycle fatigue regime is strongly influenced by microstructural features. Research efforts have usually focused on predicting fatigue resistance against crack incubation without considering the early fatigue crack growth after encountering the first grain boundary. However, a significant fraction of the variability of the total fatigue life can be attributed to growth of small cracks as they encounter the first few grain boundaries, rather than crack formation within the first grain. Our paper builds on the framework previously developed by the authors to assess microstructure-sensitive small fatigue crack formation and early growth under complex loadingmore » conditions. Moreover, the scheme employs finite element simulations that explicitly render grains and crystallographic directions along with simulation of microstructurally small fatigue crack growth from grain to grain. The methodology employs a crystal plasticity algorithm in ABAQUS that was previously calibrated to study fatigue crack initiation in RR1000 Ni-base superalloy. Our work present simulations with non-zero applied mean strains and geometric discontinuities that were not previously considered for calibration. Results exhibit trends similar to those found in experiments for multiple metallic materials, conveying a consistent physical description of fatigue damage phenomena.« less

Modeling the total dust production of Enceladus from stochastic charge equilibrium and simulations

NASA Astrophysics Data System (ADS)

Meier, Patrick; Motschmann, Uwe; Schmidt, Jürgen; Spahn, Frank; Hill, Thomas W.; Dong, Yaxue; Jones, Geraint H.; Kriegel, Hendrik

2015-12-01

Negatively and positively charged nano-sized ice grains were detected in the Enceladus plume by the Cassini Plasma Spectrometer (CAPS). However, no data for uncharged grains, and thus for the total amount of dust, are available. In this paper we estimate this population of uncharged grains based on a model of stochastic charging in thermodynamic equilibrium and on the assumption of quasi-neutrality in the plasma-dust system. This estimation is improved upon by combining simulations of the dust component of the plume and simulations for the plasma environment into one self-consistent model. Calibration of this model with CAPS data provides a total dust production rate of about 12 kg s-1, including larger dust grains up to a few microns in size. We find that the fraction of charged grains dominates over that of the uncharged grains. Moreover, our model reproduces densities of both negatively and positively charged nanograins measured by Cassini CAPS. In Enceladus' plume ion densities up to ~104cm-3 are required by the self-consistent model, resulting in an electron depletion of about 50% in the plasma, because electrons are attached to the negatively charged nanograins. These ion densities correspond to effective ionization rates of about 10-7s-1, which are about two orders of magnitude higher than expected.

Microstructure-sensitive small fatigue crack growth assessment. Effect of strain ratio multiaxial strain state and geometric discontinuities

DOE PAGES

Castelluccio, Gustavo M.; McDowell, David L.

2015-09-16

Fatigue crack initiation in the high cycle fatigue regime is strongly influenced by microstructural features. Research efforts have usually focused on predicting fatigue resistance against crack incubation without considering the early fatigue crack growth after encountering the first grain boundary. However, a significant fraction of the variability of the total fatigue life can be attributed to growth of small cracks as they encounter the first few grain boundaries, rather than crack formation within the first grain. Our paper builds on the framework previously developed by the authors to assess microstructure-sensitive small fatigue crack formation and early growth under complex loadingmore » conditions. Moreover, the scheme employs finite element simulations that explicitly render grains and crystallographic directions along with simulation of microstructurally small fatigue crack growth from grain to grain. The methodology employs a crystal plasticity algorithm in ABAQUS that was previously calibrated to study fatigue crack initiation in RR1000 Ni-base superalloy. Our work present simulations with non-zero applied mean strains and geometric discontinuities that were not previously considered for calibration. Results exhibit trends similar to those found in experiments for multiple metallic materials, conveying a consistent physical description of fatigue damage phenomena.« less

Synchrotron characterization of nanograined UO 2 grain growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mo, Kun; Miao, Yinbin; Yun, Di

2015-09-30

This activity is supported by the US Nuclear Energy Advanced Modeling and Simulation (NEAMS) Fuels Product Line (FPL) and aims at providing experimental data for the validation of the mesoscale simulation code MARMOT. MARMOT is a mesoscale multiphysics code that predicts the coevolution of microstructure and properties within reactor fuel during its lifetime in the reactor. It is an important component of the Moose-Bison-Marmot (MBM) code suite that has been developed by Idaho National Laboratory (INL) to enable next generation fuel performance modeling capability as part of the NEAMS Program FPL. In order to ensure the accuracy of the microstructuremore » based materials models being developed within the MARMOT code, extensive validation efforts must be carried out. In this report, we summarize our preliminary synchrotron radiation experiments at APS to determine the grain size of nanograin UO 2. The methodology and experimental setup developed in this experiment can directly apply to the proposed in-situ grain growth measurements. The investigation of the grain growth kinetics was conducted based on isothermal annealing and grain growth characterization as functions of duration and temperature. The kinetic parameters such as activation energy for grain growth for UO 2 with different stoichiometry are obtained and compared with molecular dynamics (MD) simulations.« less

Molecular dynamic simulations of the intergranular films between alumina and silicon nitride crystal grains

NASA Astrophysics Data System (ADS)

Zhang, Shenghong

The intergranular films (IGFs) between the ceramics grains have very important effects on the structure and mechanical properties on the whole ceramics and have been studied for many decades. In the thesis, molecular dynamic (MD) computer simulations were applied to study the IGFs between the alumina and silicon nitride ceramic grains. Preferential adsorption of specific ions from the IGFs to the contacting surfaces of the alumina crystals was observed in the study of calcium-alumino-silicate glassy (CAS) IGFs formed between the combined basal and prism orientations of alpha-Al2O3 crystals. This segregation of specific ions to the interface enables formation of localized, ordered structures between the IGF and the crystals. However, the segregation behavior of the ions is anisotropic, depending on the orientation of the alpha-Al2O 3 crystals. Self-diffusion of calcium ions between these CAS IGFs was also carried out by MD simulations. The results show that the diffusion coefficients adjacent to the interfaces are smaller and the activation energies are much higher than those in the interior of the IGF and in bulk glasses. It was also suggested that Ca transport is mainly though the interior of the IGF and implies that diffusion would be significantly inhibited by sufficiently thin IGFs. The growth of the alumina ceramic grains was simulated in the contacting with IGFs containing high concentrations of aluminum ions. Five different compositions in the IGFs were studied. Results show preferential growth along the [1120] of the (1120) surface in comparison to growth along the [0001] direction on the (0001) surface for compositions near a Ca/Al ratio of 0.5. The simulations also show the mechanism by which Ca ions in the IGF inhibit growth on the basal surface. The simulations provide an atomistic view of attachment onto crystal surfaces, affecting grain growth in alumina. The dissolution of the alumina crystal grains in the silicate melts is another important issue in the application of alumina ceramics. The simulations results showed that alumina grains dissolved into the melts homogeneously at very high temperatures. The orientation of the crystals and the compositions of the melts only take effect at some intermediate temperatures, to make the alumina grains dissolution anisotropic. The fracture phenomena of the pure silica IGFs between the basal silicon nitride crystals were studied by applying the constant tensile strain on the simulated IGF system, as well as for the bulk silica glass for the comparison. The data indicated that the fracture was happened in the interior of the IGFs and the thickness of the IGFs has important effect on the fracture stress/strain relationships.

Self-charging of identical grains in the absence of an external field.

PubMed

Yoshimatsu, R; Araújo, N A M; Wurm, G; Herrmann, H J; Shinbrot, T

2017-01-06

We investigate the electrostatic charging of an agitated bed of identical grains using simulations, mathematical modeling, and experiments. We simulate charging with a discrete-element model including electrical multipoles and find that infinitesimally small initial charges can grow exponentially rapidly. We propose a mathematical Turing model that defines conditions for exponential charging to occur and provides insights into the mechanisms involved. Finally, we confirm the predicted exponential growth in experiments using vibrated grains under microgravity, and we describe novel predicted spatiotemporal states that merit further study.

Self-charging of identical grains in the absence of an external field

NASA Astrophysics Data System (ADS)

Yoshimatsu, R.; Araújo, N. A. M.; Wurm, G.; Herrmann, H. J.; Shinbrot, T.

2017-01-01

We investigate the electrostatic charging of an agitated bed of identical grains using simulations, mathematical modeling, and experiments. We simulate charging with a discrete-element model including electrical multipoles and find that infinitesimally small initial charges can grow exponentially rapidly. We propose a mathematical Turing model that defines conditions for exponential charging to occur and provides insights into the mechanisms involved. Finally, we confirm the predicted exponential growth in experiments using vibrated grains under microgravity, and we describe novel predicted spatiotemporal states that merit further study.

Something from nothing: self-charging of identical grains

NASA Astrophysics Data System (ADS)

Shinbrot, Troy; Yoshimatsu, Ryuta; Nuno Araujo, Nuno; Wurm, Gerhard; Herrmann, Hans

We investigate the electrostatic charging of an agitated bed of identical grains using simulations, mathematical modeling, and experiments. We simulate charging with a discrete-element model including electrical multipoles and find that infinitesimally small initial charges can grow exponentially rapidly. We propose a mathematical Turing model that defines conditions for exponential charging to occur and provides insights into the mechanisms involved. Finally, we confirm the predicted exponential growth in experiments using vibrated grains under microgravity, and we describe novel predicted spatiotemporal states that merit further study. I acknowledge support from NSF/DMR, award 1404792.

Self-charging of identical grains in the absence of an external field

PubMed Central

Yoshimatsu, R.; Araújo, N. A. M.; Wurm, G.; Herrmann, H. J.; Shinbrot, T.

2017-01-01

We investigate the electrostatic charging of an agitated bed of identical grains using simulations, mathematical modeling, and experiments. We simulate charging with a discrete-element model including electrical multipoles and find that infinitesimally small initial charges can grow exponentially rapidly. We propose a mathematical Turing model that defines conditions for exponential charging to occur and provides insights into the mechanisms involved. Finally, we confirm the predicted exponential growth in experiments using vibrated grains under microgravity, and we describe novel predicted spatiotemporal states that merit further study. PMID:28059124

Propagation and Evolution of CMEs in the Interplanetary Medium: Analysis of Remote Sensing and In situ Observations

NASA Technical Reports Server (NTRS)

Figueroa-Vinas, Adolfo; Nieves-Chinchilla, Teresa; Vourlidas, Angelos; Gomez-Herrero, Raul; Malandraki, Olga; Szabo, Adam; Dresing, Nina; Davila, Joseph M.

2010-01-01

EUV disk imagers and white light coronagraphs have provided for many years information on the early formation and evolution of corona) mass ejections (CMEs). More recently, the novel heliospheric imaging instruments aboard the STEREO mission are providing crucial remote sensing information on the interplanetary evolution of these events while in situ instruments complete the overall characterization of the interplanetary CMEs. In this work, we present an analysis of CMEs from the Sun to the interplanetary medium using combined data from THE SOHO, STEREO, WIND, and ACE spacecraft. The events were selected to cover the widest possible spectrum of different ambient solar wind, magnetic field configurations, plasma parameters, etc. to allow uncovering those aspects that are important in understanding the propagation and evolution mechanisms of CMEs in the interplanetary medium.

Interplanetary Coronal Mass Ejections During 1996 - 2007

NASA Technical Reports Server (NTRS)

Richardson, I. G.; Cane, H. V.

2007-01-01

Interplanetary coronal mass ejections, the interplanetary counterparts of coronal mass ejections at the Sun, are the major drivers of interplanetary shocks in the heliosphere, and are associated with modulations of the galactic cosmic ray intensity, both short term (Forbush decreases caused by the passage of the shock, post-shock sheath, and ICME), and possibly with longer term modulation. Using several in-situ signatures of ICMEs, including plasma temperature, and composition, magnetic fields, and cosmic ray modulations, made by near-Earth spacecraft, we have compiled a "comprehensive" list of ICMEs passing the Earth since 1996, encompassing solar cycle 23. We summarize the properties of these ICMEs, such as their occurrence rate, speeds and other parameters, the fraction of ICMEs that are classic magnetic clouds, and their association with solar energetic particle events, halo CMEs, interplanetary shocks, geomagnetic storms, shocks and cosmic ray decreases.

Combined Near and Far Field High Energy Diffraction Microscopy Dataset for Ti-7Al Tensile Specimen Elastically Loaded In Situ

DOE Data Explorer

Turner, Todd J.; Shade, Paul A; Bernier, Joel V.; Li, Shiu Fai; Schuren, Jay C.; Lind, Jonathan F.; Lienert, Ulrich; Kenesei, Peter; Suter, Robert; Blank, Basil; Almer, Jonathan

2016-01-01

We present both near-field HEDM data that maps out the grain morphology and intragranular crystallographic orientations and far-field HEDM data that provides the grain centroid, grain average crystallographic orientation, and grain average elastic strain tensor for each grain. Finally, we provide a finite element mesh that can be utilized to simulate deformation in the volume of this Ti-7Al specimen.

Study of large Forbush decreases in cosmic-ray intensity observed during solar cycle 23 and 24

NASA Astrophysics Data System (ADS)

Kumar, Anand; Badruddin, B.

2016-07-01

Neutron monitors at different geomagnetic latitude and longitude of Earth measure the cosmic-ray intensity with high precision. Sudden decreases in cosmic-ray intensity within few hours and slow recovery to pre-decrease level within a few days (Forbush decreases) are observed in neutron monitor data. We identify large-amplitude Forbush decreases (FDs), using high counting rate neutron monitor data, that occurred during previous solar cycle 23 (1995-2009) and current solar cycle 24 (2010-2015). We then search for the solar sources and the interplanetary structures responsible for these decreases. We attempt to find the relative importance of various interplanetary plasma and field parameters and the physical mechanism(s) responsible for FDs of varying amplitudes. We analyze a number of interplanetary plasma and field parameters, during both the phases (main and recovery) of FDs. The interplanetary plasma and field data analyzed in this study are the solar-wind velocity, the interplanetary magnetic field, its fluctuations, interplanetary electric field and the time variation of interplanetary electric potential. For monitoring the changes in interplanetary plasma/field conditions during the development of FDs, we also utilize plasma density, temperature and plasma beta, dynamic pressure and Mach number during the passage of interplanetary structures responsible for FDs. In addition to their amplitude, we study the recovery of FDs in detail after determining the time constant during their recovery by exponential fit to the data. As the solar magnetic polarity reversed during the maximum phase of solar cycle 23 (in the year 2000), we study the differences in amplitude, time constant of recovery and plasma/field condition to search for the polarity dependent effects, if any, on the amplitude and recovery of FDs due to implication for the models suggested to explain the Forbush decrease phenomena. The implications of these results are discussed.

ESOC's System for Interplanetary Orbit Determination: Implementation and Operational Experience

NASA Astrophysics Data System (ADS)

Budnik, F.; Morley, T. A.; MacKenzie, R. A.

A system for interplanetary orbit determination has been developed at ESOC over the past six years. Today, the system is in place and has been proven to be both reliable and robust by successfully supporting critical operations of ESA's interplanetary spacecraft Rosetta, Mars Express, and SMART-1. To reach this stage a long and challenging way had to be travelled. This paper gives a digest about the journey from the development and testing to the operational use of ESOC's new interplanetary orbit determination system. It presents the capabilities and reflects experiences gained from the performed tests and tracking campaigns.

Reduced grain boundary energies in rare-earth doped MgAl 2O 4 spinel and consequent grain growth inhibition

DOE PAGES

Hasan, Md M.; Dholabhai, Pratik P.; Dey, Sanchita; ...

2017-05-15

In this paper, grain growth inhibition in MgAl 2O 4 spinel nanostructure was achieved by grain boundary (GB) segregation of rare-earth dopants. Microcalorimetric measurements showed that dense spinel compacts doped with 3 mol% of R 2O 3 (R = Y, Gd, and La) had decreased GB energies as compared to the undoped spinel, representing reduction in the driving force for grain growth. Segregation energies of the three dopants to the Σ3 (111) GB were calculated by atomistic simulation. The dopants with higher ionic radius tend to segregate more strongly to GBs. The GB energies were calculated from atomistic simulation and,more » consistent with experiments, a systematic reduction in GB energy with dopant ionic size was found. Finally, high temperature grain growth experiments revealed a significant reduction of grain growth in the doped nanostructures as compared to the undoped one, which was attributed to increased metastability or possibly also a GB dragging originated from the dopant segregation.« less

Nonlinear estimation theory applied to the interplanetary orbit determination problem.

NASA Technical Reports Server (NTRS)

Tapley, B. D.; Choe, C. Y.

1972-01-01

Martingale theory and appropriate smoothing properties of Loeve (1953) have been used to develop a modified Gaussian second-order filter. The performance of the filter is evaluated through numerical simulation of a Jupiter flyby mission. The observations used in the simulation are on-board measurements of the angle between Jupiter and a fixed star taken at discrete time intervals. In the numerical study, the influence of each of the second-order terms is evaluated. Five filter algorithms are used in the simulations. Four of the filters are the modified Gaussian second-order filter and three approximations derived by neglecting one or more of the second-order terms in the equations. The fifth filter is the extended Kalman-Bucy filter which is obtained by neglecting all of the second-order terms.

Ruggedness of 2D code printed on grain tracers for implementing a prospective grain traceability system to the bulk grain delivery system

USDA-ARS?s Scientific Manuscript database

Food-grade tracers were printed with two-dimensional Data Matrix (DM) barcode so that they could carry simulated identifying information about grain as part of a prospective traceability system. The key factor in evaluating the tracers was their ability to be read with a code scanner after being rem...

Comparison of Phase Field Crystal and Molecular Dynamics Simulations for a Shrinking Grain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radhakrishnan, Balasubramaniam; Gorti, Sarma B; Nicholson, Don M

2012-01-01

The Phase-Field Crystal (PFC) model represents the atomic density as a continuous function, whose spatial distribution evolves at diffusional, rather than vibrational time scales. PFC provides a tool to study defect interactions at the atomistic level but over longer time scales than in molecular dynamics (MD). We examine the behavior of the PFC model with the goal of relating the PFC parameters to physical parameters of real systems, derived from MD simulations. For this purpose we model the phenomenon of the shrinking of a spherical grain situated in a matrix. By comparing the rate of shrinking of the central grainmore » using MD and PFC we obtain a relationship between PFC and MD time scales for processes driven by grain boundary diffusion. The morphological changes in the central grain including grain shape and grain rotation are also examined in order to assess the accuracy of the PFC in capturing the evolution path predicted by MD.« less

Resolving Dynamic Properties of Polymers through Coarse-Grained Computational Studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salerno, K. Michael; Agrawal, Anupriya; Perahia, Dvora

2016-02-05

Coupled length and time scales determine the dynamic behavior of polymers and underlie their unique viscoelastic properties. To resolve the long-time dynamics it is imperative to determine which time and length scales must be correctly modeled. In this paper, we probe the degree of coarse graining required to simultaneously retain significant atomistic details and access large length and time scales. The degree of coarse graining in turn sets the minimum length scale instrumental in defining polymer properties and dynamics. Using linear polyethylene as a model system, we probe how the coarse-graining scale affects the measured dynamics. Iterative Boltzmann inversion ismore » used to derive coarse-grained potentials with 2–6 methylene groups per coarse-grained bead from a fully atomistic melt simulation. We show that atomistic detail is critical to capturing large-scale dynamics. Finally, using these models we simulate polyethylene melts for times over 500 μs to study the viscoelastic properties of well-entangled polymer melts.« less

Global Magnetospheric Response to an Interplanetary Shock: THEMIS Observations

NASA Technical Reports Server (NTRS)

Zhang, Hui; Sibeck, David G.; Zong, Q.-G.; McFadden, James P.; Larson, Davin; Glassmeier, K.-H.; Angelopoulos, V.

2011-01-01

We investigate the global response of geospace plasma environment to an interplanetary shock at approx. 0224 UT on May 28, 2008 from multiple THEMIS spacecraft observations in the magnetosheath (THEMIS B and C) and the mid-afternoon (THEMIS A) and dusk magnetosphere (THEMIS D and E). The interaction of the transmitted interplanetary shock with the magnetosphere has global effects. Consequently, it can affect geospace plasma significantly. After interacting with the bow shock, the interplanetary shock transmitted a fast shock and a discontinuity which propagated through the magnetosheath toward the Earth at speeds of 300 km/s and 137 km/s respectively. THEMIS A observations indicate that the plasmaspheric plume changed significantly by the interplanetary shock impact. The plasmaspheric plume density increased rapidly from 10 to 100/ cubic cm in 4 min and the ion distribution changed from isotropic to strongly anisotropic distribution. Electromagnetic ion cyclotron (EMIC) waves observed by THEMIS A are most likely excited by the anisotropic ion distributions caused by the interplanetary shock impact. To our best knowledge, this is the first direct observation of the plasmaspheric plume response to an interplanetary shock's impact. THEMIS A, but not D or E, observed a plasmaspheric plume in the dayside magnetosphere. Multiple spacecraft observations indicate that the dawn-side edge of the plasmaspheric plume was located between THEMIS A and D (or E).

Late Eocene 3He and Ir anomalies associated with ordinary chondritic spinels

NASA Astrophysics Data System (ADS)

Boschi, Samuele; Schmitz, Birger; Heck, Philipp R.; Cronholm, Anders; Defouilloy, Céline; Kita, Noriko T.; Monechi, Simonetta; Montanari, Alessandro; Rout, Surya S.; Terfelt, Fredrik

2017-05-01

During the late Eocene there was an enigmatic enhancement in the flux of extraterrestrial material to Earth. Evidence comes from sedimentary 3He records indicating an increased flux of interplanetary dust during ca. 2 Myr, as well as two very large impact structures, Popigai (100 km diameter) and Chesapeake Bay (40-85 km), that formed within 10-20 kyr at the peak of the 3He delivery. The Massignano section in Italy has one of the best sedimentary records of these events, including a well-defined 3He record, an Ir-rich ejecta bed related to the Popigai impact event, and two smaller Ir anomalies. Recently we showed that the Popigai ejecta is associated with a significant enrichment of chromite grains (>63 μm) with an H-chondritic elemental composition (17 grains in 100 kg of rock). Most likely these grains are unmelted fragments from the impactor. Slightly higher up (ca. 20 cm) in the section, where a small Ir anomaly possibly related to the Chesapeake Bay impact has been measured, we found a weak enrichment in L-chondritic grains (8 grains in 208 kg of rock). Here we report an extended data set increasing the total amount of sediment dissolved in acid and searched for extraterrestrial chromite grains from 658 to 1168 kg. In altogether 760 kg of background sediment from 17 levels over 14 m of strata outside the interval corresponding to the Popigai and Chesapeake Bay impacts, we only found 2 extraterrestrial chromite grains. Both grains have L-chondritic compositions and were found in a 100 kg sample from the ca. 10.25 m level in the section where the second of the smaller Ir anomalies has been reported. A correlation appears to exist between Ir, 3He and chromite from ordinary chondrites. We also report oxygen three-isotope measurements of the extraterrestrial chromite grains associated with the Popigai ejecta and confirm an H-chondritic composition. The new results strengthen our scenario that the upper Eocene 3He and Ir enrichments originate from the asteroid belt rather than the Oort cloud as originally proposed when the 3He anomaly was discovered. The generally low background concentrations of extraterrestrial chromite through the section speak against any major single asteroid breakup event such as in the mid-Ordovician after the break-up of the L-chondrite parent body. Instead the data reconcile with a small, possibly a factor of 2-3, increase in the flux of extraterrestrial material to Earth, but of both H- and L-chondritic composition. We also report the composition of all the 2310 terrestrial chrome spinel grains recovered, and show that their chemical composition indicates a dominantly regional ophiolitic source. Four anomalous chrome spinel grains with high Ti and V concentrations were found in the Popigai ejecta. These grains originate from Siberian Traps basalts in the Popigai crater at the time of impact.

Modeling and 2-D discrete simulation of dislocation dynamics for plastic deformation of metal

NASA Astrophysics Data System (ADS)

Liu, Juan; Cui, Zhenshan; Ou, Hengan; Ruan, Liqun

2013-05-01

Two methods are employed in this paper to investigate the dislocation evolution during plastic deformation of metal. One method is dislocation dynamic simulation of two-dimensional discrete dislocation dynamics (2D-DDD), and the other is dislocation dynamics modeling by means of nonlinear analysis. As screw dislocation is prone to disappear by cross-slip, only edge dislocation is taken into account in simulation. First, an approach of 2D-DDD is used to graphically simulate and exhibit the collective motion of a large number of discrete dislocations. In the beginning, initial grains are generated in the simulation cells according to the mechanism of grain growth and the initial dislocation is randomly distributed in grains and relaxed under the internal stress. During the simulation process, the externally imposed stress, the long range stress contribution of all dislocations and the short range stress caused by the grain boundaries are calculated. Under the action of these forces, dislocations begin to glide, climb, multiply, annihilate and react with each other. Besides, thermal activation process is included. Through the simulation, the distribution of dislocation and the stress-strain curves can be obtained. On the other hand, based on the classic dislocation theory, the variation of the dislocation density with time is described by nonlinear differential equations. Finite difference method (FDM) is used to solve the built differential equations. The dislocation evolution at a constant strain rate is taken as an example to verify the rationality of the model.

Development of an electrostatic propulsion engine using sub-micron powders as the reaction mass

NASA Technical Reports Server (NTRS)

Herbert, F.; Kendall, K. R.

1991-01-01

Asteroid sample return missions would benefit from development of an improved rocket engine. Chemical rockets achieve their large thrust with high mass consumption rate (dm/dt) but low exhaust velocity; therefore, a large fraction of their total mass is fuel. Present day ion thrusters are characterized by high exhaust velocity, but low dm/dt; thus, they are inherently low thrust devices. However, their high exhausy velocity is poorly matched to typical mission requirements and therefore, wastes energy. A better match would be intermediate between the two forms of propulsion. This could be achieved by electrostatically accelerating solid powder grains, raising the possibility that interplanetary material could be processed to use as reaction mass. An experiment to study the charging properties of sub-micron sized powder grains is described. If a suitable material can be identified, then it could be used as the reaction mass in an electrostatic propulsion engine. The experiment employs a time of flight measurement to determine the exhaust velocity (v) of various negatively charged powder grains that were charged and accelerated in a simple device. The purpose is to determine the charge to mass ratio that can be sustained for various substances. In order to be competitive with present day ion thrusters, a specific impulse (v/g) of 3000 to 5000 seconds is required. Preliminary results are presented. More speculatively, there are some mission profiles that would benefit from collection of reaction mass at the remote asteroid site. Experiments that examine the generation of sub-micron clusters by electrostatic self-disruption of geologically derived material are planned.

Evolution of Morphological and Physical Properties of Laboratory Interstellar Organic Residues with Ultraviolet Irradiation

NASA Astrophysics Data System (ADS)

Piani, L.; Tachibana, S.; Hama, T.; Tanaka, H.; Endo, Y.; Sugawara, I.; Dessimoulie, L.; Kimura, Y.; Miyake, A.; Matsuno, J.; Tsuchiyama, A.; Fujita, K.; Nakatsubo, S.; Fukushi, H.; Mori, S.; Chigai, T.; Yurimoto, H.; Kouchi, A.

2017-03-01

Refractory organic compounds formed in molecular clouds are among the building blocks of the solar system objects and could be the precursors of organic matter found in primitive meteorites and cometary materials. However, little is known about the evolutionary pathways of molecular cloud organics from dense molecular clouds to planetary systems. In this study, we focus on the evolution of the morphological and viscoelastic properties of molecular cloud refractory organic matter. We found that the organic residue, experimentally synthesized at ˜10 K from UV-irradiated H2O-CH3OH-NH3 ice, changed significantly in terms of its nanometer- to micrometer-scale morphology and viscoelastic properties after UV irradiation at room temperature. The dose of this irradiation was equivalent to that experienced after short residence in diffuse clouds (≤104 years) or irradiation in outer protoplanetary disks. The irradiated organic residues became highly porous and more rigid and formed amorphous nanospherules. These nanospherules are morphologically similar to organic nanoglobules observed in the least-altered chondrites, chondritic porous interplanetary dust particles, and cometary samples, suggesting that irradiation of refractory organics could be a possible formation pathway for such nanoglobules. The storage modulus (elasticity) of photo-irradiated organic residues is ˜100 MPa irrespective of vibrational frequency, a value that is lower than the storage moduli of minerals and ice. Dust grains coated with such irradiated organics would therefore stick together efficiently, but growth to larger grains might be suppressed due to an increase in aggregate brittleness caused by the strong connections between grains.

Evolution of Morphological and Physical Properties of Laboratory Interstellar Organic Residues with Ultraviolet Irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piani, L.; Tachibana, S.; Endo, Y.

Refractory organic compounds formed in molecular clouds are among the building blocks of the solar system objects and could be the precursors of organic matter found in primitive meteorites and cometary materials. However, little is known about the evolutionary pathways of molecular cloud organics from dense molecular clouds to planetary systems. In this study, we focus on the evolution of the morphological and viscoelastic properties of molecular cloud refractory organic matter. We found that the organic residue, experimentally synthesized at ∼10 K from UV-irradiated H{sub 2}O-CH{sub 3}OH-NH{sub 3} ice, changed significantly in terms of its nanometer- to micrometer-scale morphology andmore » viscoelastic properties after UV irradiation at room temperature. The dose of this irradiation was equivalent to that experienced after short residence in diffuse clouds (≤10{sup 4} years) or irradiation in outer protoplanetary disks. The irradiated organic residues became highly porous and more rigid and formed amorphous nanospherules. These nanospherules are morphologically similar to organic nanoglobules observed in the least-altered chondrites, chondritic porous interplanetary dust particles, and cometary samples, suggesting that irradiation of refractory organics could be a possible formation pathway for such nanoglobules. The storage modulus (elasticity) of photo-irradiated organic residues is ∼100 MPa irrespective of vibrational frequency, a value that is lower than the storage moduli of minerals and ice. Dust grains coated with such irradiated organics would therefore stick together efficiently, but growth to larger grains might be suppressed due to an increase in aggregate brittleness caused by the strong connections between grains.« less

A primer on selecting grain boundary sets for comparison of interfacial fracture properties in molecular dynamics simulations

DOE PAGES

Dingreville, Remi; Aksoy, Doruk; Spearot, Douglas E.

2017-08-21

In this study, all grain boundaries are not equal in their predisposition for fracture due to the complex coupling between lattice geometry, interfacial structure, and mechanical properties. The ability to understand these relationships is crucial to engineer materials resilient to grain boundary fracture. Here, a methodology is presented to isolate the role of grain boundary structure on interfacial fracture properties, such as the tensile strength and work of separation, using atomistic simulations. Instead of constructing sets of grain boundary models within the misorientation/structure space by simply varying the misorientation angle around a fixed misorientation axis, the proposed method creates setsmore » of grain boundary models by means of isocurves associated with important fracture-related properties of the adjoining lattices. Such properties may include anisotropic elastic moduli, the Schmid factor for primary slip, and the propensity for simultaneous slip on multiple slip systems. This approach eliminates the effect of lattice properties from the comparative analysis of interfacial fracture properties and thus enables the identification of structure-property relationships for grain boundaries. As an example, this methodology is implemented to study crack propagation along Ni grain boundaries. Segregated H is used as a means to emphasize differences in the selected grain boundary structures while keeping lattice properties fixed.« less

Effect of Charged-Magnetic Grains in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Perry, Jonathan; Matthews, Lorin; Hyde, Truell

Effects of Charged-Magnetic Grains in Protoplanetary Disks Jonathan, Perry, Lorin Swint Matthews, and Truell W. Hyde Center for Astrophysics, Space Physics, and Engi-neering Research, addressPlaceNamePlaceNameplaceBaylor StreetPlaceTypeUniversity, Stree-taddressOne Bear Place 97316 Waco, TX 76798 USA The interaction and growth of dust grains is an important process in early planetesimal formation. The structure of aggregates formed from dust depend largely on the initial properties within the dust population, whether the grains are charged or uncharged, magnetic or non-magnetic. Theoretical simulations exam-ining pair-wise interactions between aggregates indicate that charged magnetic grains exhibit different growth behavior than populations consisting of exclusively charged or exclusively mag-netic grains. This study extends that work to predict how charged-magnetic grains influence grain growth within a protoplanetary disk. An N-body simulation containing various mixtures of dust materials is used to examine the differences in dust coagulation in the presence of charged magnetic aggregates. The growth of the dust aggregates is analyzed to determine the effects that charged magnetic grains contribute to the evolution of the dust cloud. Comparison of the rate of aggregation as well as the dynamic exponent relating mass of a cluster to the elapsed time will both be discussed.

A primer on selecting grain boundary sets for comparison of interfacial fracture properties in molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dingreville, Remi; Aksoy, Doruk; Spearot, Douglas E.

In this study, all grain boundaries are not equal in their predisposition for fracture due to the complex coupling between lattice geometry, interfacial structure, and mechanical properties. The ability to understand these relationships is crucial to engineer materials resilient to grain boundary fracture. Here, a methodology is presented to isolate the role of grain boundary structure on interfacial fracture properties, such as the tensile strength and work of separation, using atomistic simulations. Instead of constructing sets of grain boundary models within the misorientation/structure space by simply varying the misorientation angle around a fixed misorientation axis, the proposed method creates setsmore » of grain boundary models by means of isocurves associated with important fracture-related properties of the adjoining lattices. Such properties may include anisotropic elastic moduli, the Schmid factor for primary slip, and the propensity for simultaneous slip on multiple slip systems. This approach eliminates the effect of lattice properties from the comparative analysis of interfacial fracture properties and thus enables the identification of structure-property relationships for grain boundaries. As an example, this methodology is implemented to study crack propagation along Ni grain boundaries. Segregated H is used as a means to emphasize differences in the selected grain boundary structures while keeping lattice properties fixed.« less

High energy astronomy or astrophysics and properties of the interplanetary plasma

NASA Technical Reports Server (NTRS)

1971-01-01

The research activities related to high energy astrophysics and interplanetary plasma are reported. The experimental work in the following areas are described: (1) balloon-and rocket-borne cosmic X-ray, (2) X-ray spectroscopy, and (3) OSO-3 gamma ray experiment. Plasma studies in the interplanetary region, magnetosphere, and geomagnetic tail are included.

The Polar Ionosphere and Interplanetary Field.

DTIC Science & Technology

1987-08-01

model for investigating time dependent behavior of the Polar F-region ionosphere in response to varying interplanetary magnetic field (IMF...conditions. The model has been used to illustrate ionospheric behavior during geomagnetic storms conditions. Future model applications may include...magnetosphere model for investigating time dependent behavior of the polar F-region ionosphere in response to varying interplanetary magnetic field

Coarse-Grain Molecular Dynamics Simulations To Investigate the Bulk Viscosity and Critical Micelle Concentration of the Ionic Surfactant Sodium Dodecyl Sulfate (SDS) in Aqueous Solution.

PubMed

Ruiz-Morales, Yosadara; Romero-Martínez, Ascención

2018-04-12

The first critical micelle concentration (CMC) of the ionic surfactant sodium dodecyl sulfate (SDS) in diluted aqueous solution has been determined at room temperature from the investigation of the bulk viscosity, at several concentrations of SDS, by means of coarse-grain molecular dynamics simulations. The coarse-grained model molecules at the mesoscale level are adopted. The bulk viscosity of SDS was calculated at several millimolar concentrations of SDS in water using the MARTINI force field by means of NVT shear Mesocite molecular dynamics. The definition of each bead in the MARTINI force field is established, as well as their radius, volume, and mass. The effect of the size of the simulation box on the obtained CMC has been investigated, as well as the effect of the number of SDS molecules, in the simulations, on the formation of aggregates. The CMC, which was obtained from a graph of the calculated viscosities versus concentration, is in good agreement with the reported experimental data and does not depend on the size of the box used in the simulation. The formation of a spherical micelle-like aggregate is observed, where the dodecyl sulfate tails point inward and the heads point outward the aggregation micelle, in accordance with experimental observations. The advantage of using coarse-grain molecular dynamics is the possibility of treating explicitly charged beads, applying a shear flow for viscosity calculation, and processing much larger spatial and temporal scales than atomistic molecular dynamics can. Furthermore, the CMC of SDS obtained with the coarse-grained model is in much better agreement with the experimental value than the value obtained with atomistic simulations.

A Generic Force Field for Protein Coarse-Grained Molecular Dynamics Simulation

PubMed Central

Gu, Junfeng; Bai, Fang; Li, Honglin; Wang, Xicheng

2012-01-01

Coarse-grained (CG) force fields have become promising tools for studies of protein behavior, but the balance of speed and accuracy is still a challenge in the research of protein coarse graining methodology. In this work, 20 CG beads have been designed based on the structures of amino acid residues, with which an amino acid can be represented by one or two beads, and a CG solvent model with five water molecules was adopted to ensure the consistence with the protein CG beads. The internal interactions in protein were classified according to the types of the interacting CG beads, and adequate potential functions were chosen and systematically parameterized to fit the energy distributions. The proposed CG force field has been tested on eight proteins, and each protein was simulated for 1000 ns. Even without any extra structure knowledge of the simulated proteins, the Cα root mean square deviations (RMSDs) with respect to their experimental structures are close to those of relatively short time all atom molecular dynamics simulations. However, our coarse grained force field will require further refinement to improve agreement with and persistence of native-like structures. In addition, the root mean square fluctuations (RMSFs) relative to the average structures derived from the simulations show that the conformational fluctuations of the proteins can be sampled. PMID:23203075

Shock Simulations of Single-Site Coarse-Grain RDX using the Dissipative Particle Dynamics Method with Reactivity

NASA Astrophysics Data System (ADS)

Sellers, Michael; Lisal, Martin; Schweigert, Igor; Larentzos, James; Brennan, John

2015-06-01

In discrete particle simulations, when an atomistic model is coarse-grained, a trade-off is made: a boost in computational speed for a reduction in accuracy. Dissipative Particle Dynamics (DPD) methods help to recover accuracy in viscous and thermal properties, while giving back a small amount of computational speed. One of the most notable extensions of DPD has been the introduction of chemical reactivity, called DPD-RX. Today, pairing the current evolution of DPD-RX with a coarse-grained potential and its chemical decomposition reactions allows for the simulation of the shock behavior of energetic materials at a timescale faster than an atomistic counterpart. In 2007, Maillet et al. introduced implicit chemical reactivity in DPD through the concept of particle reactors and simulated the decomposition of liquid nitromethane. We have recently extended the DPD-RX method and have applied it to solid hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) under shock conditions using a recently developed single-site coarse-grain model and a reduced RDX decomposition mechanism. A description of the methods used to simulate RDX and its tranition to hot product gases within DPD-RX will be presented. Additionally, examples of the effect of microstructure on shock behavior will be shown. Approved for public release. Distribution is unlimited.

Effects of Intergranular Gas Bubbles on Thermal Conductivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

K. Chockalingam; Paul C. Millett; M. R. Tonks

2012-11-01

Model microstructures obtained from phase-field simulations are used to study the effective heat transfer across bicrys- tals with stationary grain boundary bubble populations. We find that the grain boundary coverage, irrespective of the intergranular bubble radii, is the most relevant parameter to the thermal resistance, which we use to derive effec- tive Kapitza resistances that are dependent on the grain boundary coverage and Kaptiza resistance of the intact grain boundary. We propose a model to predict thermal conductivity as a function of porosity, grain-size, Kaptiza resistance of the intact grain boundary, and grain boundary bubble coverage.

The relative entropy is fundamental to adaptive resolution simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kreis, Karsten; Graduate School Materials Science in Mainz, Staudingerweg 9, 55128 Mainz; Potestio, Raffaello, E-mail: potestio@mpip-mainz.mpg.de

Adaptive resolution techniques are powerful methods for the efficient simulation of soft matter systems in which they simultaneously employ atomistic and coarse-grained (CG) force fields. In such simulations, two regions with different resolutions are coupled with each other via a hybrid transition region, and particles change their description on the fly when crossing this boundary. Here we show that the relative entropy, which provides a fundamental basis for many approaches in systematic coarse-graining, is also an effective instrument for the understanding of adaptive resolution simulation methodologies. We demonstrate that the use of coarse-grained potentials which minimize the relative entropy withmore » respect to the atomistic system can help achieve a smoother transition between the different regions within the adaptive setup. Furthermore, we derive a quantitative relation between the width of the hybrid region and the seamlessness of the coupling. Our results do not only shed light on the what and how of adaptive resolution techniques but will also help setting up such simulations in an optimal manner.« less

The relative entropy is fundamental to adaptive resolution simulations

NASA Astrophysics Data System (ADS)

Kreis, Karsten; Potestio, Raffaello

2016-07-01

Adaptive resolution techniques are powerful methods for the efficient simulation of soft matter systems in which they simultaneously employ atomistic and coarse-grained (CG) force fields. In such simulations, two regions with different resolutions are coupled with each other via a hybrid transition region, and particles change their description on the fly when crossing this boundary. Here we show that the relative entropy, which provides a fundamental basis for many approaches in systematic coarse-graining, is also an effective instrument for the understanding of adaptive resolution simulation methodologies. We demonstrate that the use of coarse-grained potentials which minimize the relative entropy with respect to the atomistic system can help achieve a smoother transition between the different regions within the adaptive setup. Furthermore, we derive a quantitative relation between the width of the hybrid region and the seamlessness of the coupling. Our results do not only shed light on the what and how of adaptive resolution techniques but will also help setting up such simulations in an optimal manner.

The Material Point Method and Simulation of Wave Propagation in Heterogeneous Media

NASA Astrophysics Data System (ADS)

Bardenhagen, S. G.; Greening, D. R.; Roessig, K. M.

2004-07-01

The mechanical response of polycrystalline materials, particularly under shock loading, is of significant interest in a variety of munitions and industrial applications. Homogeneous continuum models have been developed to describe material response, including Equation of State, strength, and reactive burn models. These models provide good estimates of bulk material response. However, there is little connection to underlying physics and, consequently, they cannot be applied far from their calibrated regime with confidence. Both explosives and metals have important structure at the (energetic or single crystal) grain scale. The anisotropic properties of the individual grains and the presence of interfaces result in the localization of energy during deformation. In explosives energy localization can lead to initiation under weak shock loading, and in metals to material ejecta under strong shock loading. To develop accurate, quantitative and predictive models it is imperative to develop a sound physical understanding of the grain-scale material response. Numerical simulations are performed to gain insight into grain-scale material response. The Generalized Interpolation Material Point Method family of numerical algorithms, selected for their robust treatment of large deformation problems and convenient framework for implementing material interface models, are reviewed. A three-dimensional simulation of wave propagation through a granular material indicates the scale and complexity of a representative grain-scale computation. Verification and validation calculations on model bimaterial systems indicate the minimum numerical algorithm complexity required for accurate simulation of wave propagation across material interfaces and demonstrate the importance of interfacial decohesion. Preliminary results are presented which predict energy localization at the grain boundary in a metallic bicrystal.

A comparative computational study of coarse-grained and all-atom water models in shock Hugoniot states

NASA Astrophysics Data System (ADS)

Min, Sa Hoon; Berkowitz, Max L.

2018-04-01

We performed molecular dynamics simulations to study how well some of the water models used in simulations describe shocked states. Water in our simulations was described using three different models. One was an often-used all-atom TIP4P/2005 model, while the other two were coarse-grained models used with the MARTINI force field: non-polarizable and polarizable MARTINI water. The all-atom model provided results in good agreement with Hugoniot curves (for data on pressure versus specific volume or, equivalently, on shock wave velocity versus "piston" velocity) describing shocked states in the whole range of pressures (up to 11 GPa) under study. If simulations of shocked states of water using coarse-grained models were performed for short time periods, we observed that data obtained for shocked states at low pressure were fairly accurate compared to experimental Hugoniot curves. Polarizable MARTINI water still provided a good description of Hugoniot curves for pressures up to 11 GPa, while the results for the non-polarizable MARTINI water substantially deviated from the Hugoniot curves. We also calculated the temperature of the Hugoniot states and observed that for TIP4P/2005 water, they were consistent with those from theoretical calculations, while both coarse-grained models predicted much higher temperatures. These high temperatures for MARTINI water can be explained by the loss of degrees of freedom due to coarse-graining procedure.

Multiscale equation-free algorithms for molecular dynamics

NASA Astrophysics Data System (ADS)

Abi Mansour, Andrew

Molecular dynamics is a physics-based computational tool that has been widely employed to study the dynamics and structure of macromolecules and their assemblies at the atomic scale. However, the efficiency of molecular dynamics simulation is limited because of the broad spectrum of timescales involved. To overcome this limitation, an equation-free algorithm is presented for simulating these systems using a multiscale model cast in terms of atomistic and coarse-grained variables. Both variables are evolved in time in such a way that the cross-talk between short and long scales is preserved. In this way, the coarse-grained variables guide the evolution of the atom-resolved states, while the latter provide the Newtonian physics for the former. While the atomistic variables are evolved using short molecular dynamics runs, time advancement at the coarse-grained level is achieved with a scheme that uses information from past and future states of the system while accounting for both the stochastic and deterministic features of the coarse-grained dynamics. To complete the multiscale cycle, an atom-resolved state consistent with the updated coarse-grained variables is recovered using algorithms from mathematical optimization. This multiscale paradigm is extended to nanofluidics using concepts from hydrodynamics, and it is demonstrated for macromolecular and nanofluidic systems. A toolkit is developed for prototyping these algorithms, which are then implemented within the GROMACS simulation package and released as an open source multiscale simulator.

Mesoscopic Model — Advanced Simulation of Microforming Processes

NASA Astrophysics Data System (ADS)

Geißdörfer, Stefan; Engel, Ulf; Geiger, Manfred

2007-04-01

Continued miniaturization in many fields of forming technology implies the need for a better understanding of the effects occurring while scaling down from conventional macroscopic scale to microscale. At microscale, the material can no longer be regarded as a homogeneous continuum because of the presence of only a few grains in the deformation zone. This leads to a change in the material behaviour resulting among others in a large scatter of forming results. A correlation between the integral flow stress of the workpiece and the scatter of the process factors on the one hand and the mean grain size and its standard deviation on the other hand has been observed in experiments. The conventional FE-simulation of scaled down processes is not able to consider the size-effects observed such as the actual reduction of the flow stress, the increasing scatter of the process factors and a local material flow being different to that obtained in the case of macroparts. For that reason, a new simulation model has been developed taking into account all the size-effects. The present paper deals with the theoretical background of the new mesoscopic model, its characteristics like synthetic grain structure generation and the calculation of micro material properties — based on conventional material properties. The verification of the simulation model is done by carrying out various experiments with different mean grain sizes and grain structures but the same geometrical dimensions of the workpiece.

A highly coarse-grained model to simulate entangled polymer melts.

PubMed

Zhu, You-Liang; Liu, Hong; Lu, Zhong-Yuan

2012-04-14

We introduce a highly coarse-grained model to simulate the entangled polymer melts. In this model, a polymer chain is taken as a single coarse-grained particle, and the creation and annihilation of entanglements are regarded as stochastic events in proper time intervals according to certain rules and possibilities. We build the relationship between the probability of appearance of an entanglement between any pair of neighboring chains at a given time interval and the rate of variation of entanglements which describes the concurrence of birth and death of entanglements. The probability of disappearance of entanglements is tuned to keep the total entanglement number around the target value. This useful model can reflect many characteristics of entanglements and macroscopic properties of polymer melts. As an illustration, we apply this model to simulate the polyethylene melt of C(1000)H(2002) at 450 K and further validate this model by comparing to experimental data and other simulation results.

Zodiacal light as an indicator of interplanetary dust

NASA Technical Reports Server (NTRS)

Weinberg, J. L.; Sparrow, J. G.

1978-01-01

The most striking feature of the night sky in the tropics is the zodiacal light, which appears as a cone in the west after sunset and in the east before sunrise. It is caused by sunlight scattered or absorbed by particles in the interplanetary medium. The zodiacal light is the only source of information about the integrated properties of the whole ensemble of interplanetary dust. The brightness and polarization in different directions and at different colors can provide information on the optical properties and spatial distribution of the scattering particles. The zodiacal light arises from two independent physical processes related to the scattering of solar continuum radiation by interplanetary dust and to thermal emission which arises from solar radiation that is absorbed by interplanetary dust and reemitted mainly at infrared wavelengths. Attention is given to observational parameters of zodiacal light, the methods of observation, errors and absolute calibration, and the observed characteristics of zodiacal light.

Response of Jupiter's auroras to conditions in the interplanetary medium as measured by the Hubble Space Telescope and Juno

NASA Astrophysics Data System (ADS)

Nichols, J. D.; Badman, S. V.; Bagenal, F.; Bolton, S. J.; Bonfond, B.; Bunce, E. J.; Clarke, J. T.; Connerney, J. E. P.; Cowley, S. W. H.; Ebert, R. W.; Fujimoto, M.; Gérard, J.-C.; Gladstone, G. R.; Grodent, D.; Kimura, T.; Kurth, W. S.; Mauk, B. H.; Murakami, G.; McComas, D. J.; Orton, G. S.; Radioti, A.; Stallard, T. S.; Tao, C.; Valek, P. W.; Wilson, R. J.; Yamazaki, A.; Yoshikawa, I.

2017-08-01

We present the first comparison of Jupiter's auroral morphology with an extended, continuous, and complete set of near-Jupiter interplanetary data, revealing the response of Jupiter's auroras to the interplanetary conditions. We show that for ˜1-3 days following compression region onset, the planet's main emission brightened. A duskside poleward region also brightened during compressions, as well as during shallow rarefaction conditions at the start of the program. The power emitted from the noon active region did not exhibit dependence on any interplanetary parameter, though the morphology typically differed between rarefactions and compressions. The auroras equatorward of the main emission brightened over ˜10 days following an interval of increased volcanic activity on Io. These results show that the dependence of Jupiter's magnetosphere and auroras on the interplanetary conditions are more diverse than previously thought.

Multiscale modeling of thermal conductivity of high burnup structures in UO 2 fuels

DOE PAGES

Bai, Xian -Ming; Tonks, Michael R.; Zhang, Yongfeng; ...

2015-12-22

The high burnup structure forming at the rim region in UO 2 based nuclear fuel pellets has interesting physical properties such as improved thermal conductivity, even though it contains a high density of grain boundaries and micron-size gas bubbles. To understand this counterintuitive phenomenon, mesoscale heat conduction simulations with inputs from atomistic simulations and experiments were conducted to study the thermal conductivities of a small-grain high burnup microstructure and two large-grain unrestructured microstructures. We concluded that the phonon scattering effects caused by small point defects such as dispersed Xe atoms in the grain interior must be included in order tomore » correctly predict the thermal transport properties of these microstructures. In extreme cases, even a small concentration of dispersed Xe atoms such as 10 -5 can result in a lower thermal conductivity in the large-grain unrestructured microstructures than in the small-grain high burnup structure. The high-density grain boundaries in a high burnup structure act as defect sinks and can reduce the concentration of point defects in its grain interior and improve its thermal conductivity in comparison with its large-grain counterparts. Furthermore, an analytical model was developed to describe the thermal conductivity at different concentrations of dispersed Xe, bubble porosities, and grain sizes. Upon calibration, the model is robust and agrees well with independent heat conduction modeling over a wide range of microstructural parameters.« less

Influence of grain size on the mechanical properties of nano-crystalline copper; insights from molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Rida, A.; Makke, A.; Rouhaud, E.; Micoulaut, M.

2017-10-01

We use molecular dynamics simulations to study the mechanical properties of a columnar nanocrystalline copper with a mean grain size between 8.91 nm and 24 nm. The used samples were generated by using a melting cooling method. These samples were submitted to uniaxial tensile test. The results reveal the presence of a critical mean grain size between 16 and 20 nm, where there is an inversion in the conventional Hall-Petch tendency. This inversion is illustrated by the increase of flow stress with the increase of the mean grain size. This transition is caused by shifting of the deformation mechanism from dislocations to a combination of grain boundaries sliding and dislocations. Moreover, the effect of temperature on the mechanical properties of nanocrystalline copper has been investigated. The results show a decrease of the flow stress and Young's modulus when the temperature increases.

Modeling the cometary environment using a fluid approach

NASA Astrophysics Data System (ADS)

Shou, Yinsi

Comets are believed to have preserved the building material of the early solar system and to hold clues to the origin of life on Earth. Abundant remote observations of comets by telescopes and the in-situ measurements by a handful of space missions reveal that the cometary environments are complicated by various physical and chemical processes among the neutral gases and dust grains released from comets, cometary ions, and the solar wind in the interplanetary space. Therefore, physics-based numerical models are in demand to interpret the observational data and to deepen our understanding of the cometary environment. In this thesis, three models using a fluid approach, which include important physical and chemical processes underlying the cometary environment, have been developed to study the plasma, neutral gas, and the dust grains, respectively. Although models based on the fluid approach have limitations in capturing all of the correct physics for certain applications, especially for very low gas density environment, they are computationally much more efficient than alternatives. In the simulations of comet 67P/Churyumov-Gerasimenko at various heliocentric distances with a wide range of production rates, our multi-fluid cometary neutral gas model and multi-fluid cometary dust model have achieved comparable results to the Direct Simulation Monte Carlo (DSMC) model, which is based on a kinetic approach that is valid in all collisional regimes. Therefore, our model is a powerful alternative to the particle-based model, especially for some computationally intensive simulations. Capable of accounting for the varying heating efficiency under various physical conditions in a self-consistent way, the multi-fluid cometary neutral gas model is a good tool to study the dynamics of the cometary coma with different production rates and heliocentric distances. The modeled H2O expansion speeds reproduce the general trend and the speed's nonlinear dependencies of production rate and heliocentric distance, which are found in remote observations. In the multi-fluid dust model, we use a newly developed numerical mesh to resolve the real shaped nucleus in the center and to facilitate prescription of the outer boundary conditions that accommodate the rotating frame. The model studies the effects of the rotating nucleus and the cometary activity in time-dependent simulations for the first time. The result also suggests that the rotation of the nucleus explains why there is no clear dust speed dependence on size in some of the dust observations. We developed a new multi-species comet MHD model to simulate the plasma environment of comet C/2006 P1 (McNaught) over a wide range of heliocentric distances from 0.17 AU to 1.75 AU, with the constraints provided by remote and in situ observations. Typical subsolar standoff distances of bow shock and contact surface are modeled and presented to characterize the solar wind interaction of the comet at various heliocentric distances. In addition, the model is also the first one to be used to study the composition and dynamics in the distant cometary tail. The results agree well with the measured water group ion abundances from the Ulysses/SWICS 1.7 AU down-tail from the comet and the velocity and temperature measured by Ulysses/SWOOPS.

Coupling all-atom molecular dynamics simulations of ions in water with Brownian dynamics.

PubMed

Erban, Radek

2016-02-01

Molecular dynamics (MD) simulations of ions (K + , Na + , Ca 2+ and Cl - ) in aqueous solutions are investigated. Water is described using the SPC/E model. A stochastic coarse-grained description for ion behaviour is presented and parametrized using MD simulations. It is given as a system of coupled stochastic and ordinary differential equations, describing the ion position, velocity and acceleration. The stochastic coarse-grained model provides an intermediate description between all-atom MD simulations and Brownian dynamics (BD) models. It is used to develop a multiscale method which uses all-atom MD simulations in parts of the computational domain and (less detailed) BD simulations in the remainder of the domain.

Grain dryer temperature field analysis

NASA Astrophysics Data System (ADS)

Li, Shizhuang; Cao, Shukun; Meng, Wenjing; Ma, Lingran

2017-09-01

Taking into account the drying process in the hot air temperature on the grain temperature has a great impact, and grain temperature and determines the quality of food after baking, so in order to ensure that the grain drying temperature in the safe range, the use of ANSYS FLUENT module of grain The temperature field was simulated in the drying process. The horizontal spacing of the angle box was 200mm and the vertical spacing was 240mm. At this time, the grain temperature distribution was more uniform and the drying was more adequate.

Coarse-grained simulations of cis- and trans-polybutadiene: A bottom-up approach

NASA Astrophysics Data System (ADS)

Lemarchand, Claire A.; Couty, Marc; Rousseau, Bernard

2017-02-01

We apply the dissipative particle dynamics strategy proposed by Hijón et al. [Faraday Discuss. 144, 301-322 (2010)] and based on an exact derivation of the generalized Langevin equation to cis- and trans-1,4-polybutadiene. We prove that it is able to reproduce not only the structural but also the dynamical properties of these polymers without any fitting parameter. A systematic study of the effect of the level of coarse-graining is done on cis-1,4-polybutadiene. We show that as the level of coarse-graining increases, the dynamical properties are better and better reproduced while the structural properties deviate more and more from those calculated in molecular dynamics (MD) simulations. We suggest two reasons for this behavior: the Markovian approximation is better satisfied as the level of coarse-graining increases, while the pair-wise approximation neglects important contributions due to the relative orientation of the beads at large levels of coarse-graining. Finally, we highlight a possible limit of the Markovian approximation: the fact that in constrained simulations, in which the centers-of-mass of the beads are kept constant, the bead rotational dynamics become extremely slow.

Mechanical Behavior of Nanostructured and Ultrafine Grained Materials under Shock Wave Loadings. Experimental Data and Results of Computer Simulation.

NASA Astrophysics Data System (ADS)

Skripnyak, Vladimir

2011-06-01

Features of mechanical behavior of nanostructured (NS) and ultrafine grained (UFG) metal and ceramic materials under quasistatic and shock wave loadings are discussed in this report. Multilevel models developed within the approach of computational mechanics of materials were used for simulation mechanical behavior of UFG and NS metals and ceramics. Comparisons of simulation results with experimental data are presented. Models of mechanical behavior of nanostructured metal alloys takes into account a several structural factors influencing on the mechanical behavior of materials (type of a crystal lattice, density of dislocations, a size of dislocation substructures, concentration and size of phase precipitation, and distribution of grains sizes). Results show the strain rate sensitivity of the yield stress of UFG and polycrystalline alloys is various in a range from 103 up to 106 1/s. But the difference of the Hugoniot elastic limits of a UFG and coarse-grained alloys may be not considerable. The spall strength, the yield stress of UFG and NS alloys are depend not only on grains size, but a number of factors such as a distribution of grains sizes, a concentration and sizes of voids and cracks, a concentration and sizes of phase precipitation. Some titanium alloys with grain sizes from 300 to 500 nm have the quasi-static yield strength and the tensile strength twice higher than that of coarse grained counterparts. But the spall strength of the UFG titanium alloys is only 10 percents above than that of coarse grained alloys. At the same time it was found the spall strength of the bulk UFG aluminium and magnesium alloys with precipitation strengthening is essentially higher in comparison of coarse-grained counterparts. The considerable decreasing of the strain before failure of UFG alloys was predicted at high strain rates. The Hugoniot elastic limits of oxide nanoceramics depend not only on the porosity, but also on sizes and volume distribution of voids.

Interplanetary scintillation observations of the solar wind close to the Sun and out of the ecliptic

NASA Technical Reports Server (NTRS)

Sime, D. G.

1983-01-01

A brief review is given of recent developments in the observation of the solar wind by the method of interplanetary scintillation. The emphasis is on observations of the velocity structure, the electron density and the effect of propagating disturbances in the interplanetary medium as detected principally by intensity and phase scintillation and by spectral broadening.

The delivery of organic matter from asteroids and comets to the early surface of Mars

NASA Technical Reports Server (NTRS)

Flynn, G. J.

1996-01-01

Carbon delivered to the Earth by interplanetary dust particles may have been an important source of pre-biotic organic matter (Anders, 1989). Interplanetary dust is shown to deliver an order-of-magnitude higher surface concentration of carbon onto Mars than onto Earth, suggesting interplanetary dust may be an important source of carbon on Mars as well.

Aquarius, a reusable water-based interplanetary human spaceflight transport

NASA Astrophysics Data System (ADS)

Adamo, Daniel R.; Logan, James S.

2016-11-01

Attributes of a reusable interplanetary human spaceflight transport are proposed and applied to example transits between the Earth/Moon system and Deimos, the outer moon of Mars. Because the transport is 54% water by mass at an interplanetary departure, it is christened Aquarius. In addition to supporting crew hydration/hygiene, water aboard Aquarius serves as propellant and as enhanced crew habitat radiation shielding during interplanetary transit. Key infrastructure and technology supporting Aquarius operations include pre-emplaced consumables and subsurface habitat at Deimos with crew radiation shielding equivalent to sea level on Earth, resupply in a selenocentric distant retrograde orbit, and nuclear thermal propulsion.

Relationship between the growth of the ring current and the interplanetary quantity. [solar wind energy-magnetospheric coupling parameter correlation with substorm AE index

NASA Technical Reports Server (NTRS)

Akasofu, S.-I.

1979-01-01

Akasofu (1979) has reported that the interplanetary parameter epsilon correlates reasonably well with the magnetospheric substorm index AE; in the first approximation, epsilon represents the solar wind coupled to the magnetosphere. The correlation between the interplanetary parameter, the auroral electrojet index and the ring current index is examined for three magnetic storms. It is shown that when the interplanetary parameter exceeds the amount that can be dissipated by the ionosphere in terms of the Joule heat production, the excess energy is absorbed by the ring current belt, producing an abnormal growth of the ring current index.

The source of the electric field in the nightside magnetosphere

NASA Technical Reports Server (NTRS)

Stern, D. P.

1975-01-01

In the open magnetosphere model magnetic field lines from the polar caps connect to the interplanetary magnetic field and conduct an electric field from interplanetary space to the polar ionosphere. By examining the magnetic flux involved it is concluded that only slightly more than half of the magnetic flux in the polar caps belongs to open field lines and that such field lines enter or leave the magnetosphere through narrow elongated windows stretching the tail. These window regions are identified with the tail's boundary region and shift their position with changes in the interplanetary magnetic field, in particular when a change of interplanetary magnetic sector occurs. The circuit providing electric current in the magnetopause and the plasma sheet is extended across those windows; thus energy is drained from the interplanetary electric field and an electric potential drop is produced across the plasma sheet. The polar cap receives its electric field from interplanetary space on the day side from open magnetic field lines and on the night side from closed field lines leading to the plasma sheet. The theory described provides improved understanding of magnetic flux bookkeeping, of the origin of Birkeland currents, and of the boundary layer of the geomagnetic tail.

Numerical Simulation of Spacecraft Charging Phenomena at High Altitude.

DTIC Science & Technology

1982-08-10

and D. Turnbull, vol. 6, Academic , New York, p.251. Dessler, A.J., 1967, Solar wind and interplanetary magnetic field, Rev. Geophys. 5, 1-4’. Fahleson...1968, Electronic Image Storage, Academic Press, New York. Knott, K., 1972, The equilibrium potential of a magnetospheric satellite in an eclipse...144) ,ENAO( 144) .ETN20) ’%SCTI4 144). .319(66,49) ,XS(66) .109(70), 29SCAT ( 14).SCTS 1)PHO(20,40), IUNRRLE(4).T, IELT .9NOWID,NDIN,POT.14,JlR91,RFI2

A cumulative index to a continuing bibliography on aerospace medicine and biology, January 1972

NASA Technical Reports Server (NTRS)

1972-01-01

Subject coverage concentrates on the biological, physiological, psychological, and environmental effects to which man is subjected during and following simulated or actual flight in the earth's atmosphere or in interplanetary space. References describing similar effects on biological organisms of lower order are also included. Such related topics as sanitary problems, pharmacology, toxicology, safety and survival, life support systems, exobiology, and personnel factors receive appropriate attention. Each entry consists of a standard citation accompanied by its abstract.

Thrust vector control algorithm design for the Cassini spacecraft

NASA Technical Reports Server (NTRS)

Enright, Paul J.

1993-01-01

This paper describes a preliminary design of the thrust vector control algorithm for the interplanetary spacecraft, Cassini. Topics of discussion include flight software architecture, modeling of sensors, actuators, and vehicle dynamics, and controller design and analysis via classical methods. Special attention is paid to potential interactions with structural flexibilities and propellant dynamics. Controller performance is evaluated in a simulation environment built around a multi-body dynamics model, which contains nonlinear models of the relevant hardware and preliminary versions of supporting attitude determination and control functions.

Field-aligned currents and magnetospheric convection - A comparison between MHD simulations and observations

NASA Technical Reports Server (NTRS)

Walker, Raymond J.; Ogino, Tatsuki

1988-01-01

A time-dependent three-dimensional MHD model was used to investigate the magnetospheric configuration as a function of the interplanetary magnetic field direction when it was in the y-z plane in geocentric solar magnetospheric coordinates. The model results show large global convection cells, tail lobe cells, high-latitude polarcap cells, and low latitude cells. The field-aligned currents generated in the model magnetosphere and the model convection system are compared with observations from low-altitude polar orbiting satellites.

Propagation Characteristics of Two Coronal Mass Ejections from the Sun Far into Interplanetary Space

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Xiaowei; Liu, Ying D.; Hu, Huidong

Propagation of coronal mass ejections (CMEs) from the Sun far into interplanetary space is not well understood, due to limited observations. In this study we examine the propagation characteristics of two geo-effective CMEs, which occurred on 2005 May 6 and 13, respectively. Significant heliospheric consequences associated with the two CMEs are observed, including interplanetary CMEs (ICMEs) at the Earth and Ulysses , interplanetary shocks, a long-duration type II radio burst, and intense geomagnetic storms. We use coronagraph observations from SOHO /LASCO, frequency drift of the long-duration type II burst, in situ measurements at the Earth and Ulysses , and magnetohydrodynamicmore » propagation of the observed solar wind disturbances at 1 au to track the CMEs from the Sun far into interplanetary space. We find that both of the CMEs underwent a major deceleration within 1 au and thereafter a gradual deceleration when they propagated from the Earth to deep interplanetary space, due to interactions with the ambient solar wind. The results also reveal that the two CMEs interacted with each other in the distant interplanetary space even though their launch times on the Sun were well separated. The intense geomagnetic storm for each case was caused by the southward magnetic fields ahead of the CME, stressing the critical role of the sheath region in geomagnetic storm generation, although for the first case there is a corotating interaction region involved.« less

An Investigation of Interplanetary Structures for Solar Cycles 23 and 24 and their Space Weather Consequences.

NASA Astrophysics Data System (ADS)

Sultan, M. S.; Jules, A.; Marchese, P.; Damas, M. C.

2017-12-01

It is crucial to study space weather because severe interplanetary conditions can cause geomagnetic storms that may damage both space- and ground-based technological systems such as satellites, communication systems, and power grids. Interplanetary coronal mass ejections (ICMEs) and corotating interaction regions (CIRs) are the primary drivers of geomagnetic storms. As they travel through interplanetary space and reach geospace, their spatial structures change which can result in various geomagnetic effects. Therefore, studying these drivers and their structures is essential in order to better understand and mitigate their impact on technological systems, as well as to forecast geomagnetic storms. In this study, over 150 storms were cross-checked for both solar cycles (SC) 23 and 24. This data has revealed the most common interplanetary structures, i.e., sheath (Sh); magnetic cloud following a shock front (sMC); sheath region and magnetic cloud (Sh/MC); and corotating interaction regions (CIRs). Furthermore, plasma parameters as well as variation in the intensity and duration of storms resulting from different interplanetary structures are studied for their effect on geomagnetically induced currents (GICs), as well as for their effect on power grids. Although preliminary results for SC 23 indicate that storm intensity may play a dominant role for GICs, duration might also be a factor, albeit smaller. Results from both SC 23 and 24 are analyzed and compared, and should lead to an enhanced understanding of space weather consequences of interplanetary structures and their possible forecasting.

Organic compounds in circumstellar and interstellar environments.

PubMed

Kwok, Sun

2015-06-01

Recent research has discovered that complex organic matter is prevalent throughout the Universe. In the Solar System, it is found in meteorites, comets, interplanetary dust particles, and planetary satellites. Spectroscopic signatures of organics with aromatic/aliphatic structures are also found in stellar ejecta, diffuse interstellar medium, and external galaxies. From space infrared spectroscopic observations, we have found that complex organics can be synthesized in the late stages of stellar evolution. Shortly after the nuclear synthesis of the element carbon, organic gas-phase molecules are formed in the stellar winds, which later condense into solid organic particles. This organic synthesis occurs over very short time scales of about a thousand years. In order to determine the chemical structures of these stellar organics, comparisons are made with particles produced in the laboratory. Using the technique of chemical vapor deposition, artificial organic particles have been created by injecting energy into gas-phase hydrocarbon molecules. These comparisons led us to believe that the stellar organics are best described as amorphous carbonaceous nanoparticles with mixed aromatic and aliphatic components. The chemical structures of the stellar organics show strong similarity to the insoluble organic matter found in meteorites. Isotopic analysis of meteorites and interplanetary dust collected in the upper atmospheres have revealed the presence of pre-solar grains similar to those formed in old stars. This provides a direct link between star dust and the Solar System and raises the possibility that the early Solar System was chemically enriched by stellar ejecta with the potential of influencing the origin of life on Earth.

Metastable Eutectic Equilibrium in Natural Environments: Recent Development and Research Opportunities

NASA Technical Reports Server (NTRS)

Rietmeijer, Frans J. M.; Nuth, Joseph A., III; Jablonska, Mariola; Karner, James M.

2000-01-01

Chemical ordering at metastable eutectics was recognized in non-equilibrium gas-to- solid condensation experiments to constrain 'silicate' dust formation in O-rich circumstellar environments. The predictable metastable eutectic behavior successfully predicted the observed ferromagnesiosilica compositions of circumstellar dust presolar and solar nebula grains in the matrix of the collected aggregate IDPs (Interplanetary Dust Particles). Many of the experimentally determined metastable eutectic solids match the fundamental building blocks of common rock-forming layer silicates: this could have implications for the origin of Life. The physical conditions conducive to metastable eutectic behavior, i.e. high temperature and (ultra) fast quenching, lead to unique amorphous, typically nano- to micrometer-sized, materials. The new paradigm of metastable eutectic behavior opens the door to new and exciting research opportunities in uncovering the many implications of these unique amorphous, and typically nano-to micrometer-sized, metastable eutectic materials.

A collection of diverse micrometeorites recovered from 100 tonnes of Antarctic blue ice

NASA Technical Reports Server (NTRS)

Maurette, M.; Olinger, C.; Michel-Levy, M. C.; Kurat, G.; Pourchet, M.

1991-01-01

A new type of meteoritic material, intermediate in size between meteorites and interplanetary dust particles (IDPs), is described. Melting and filtering of about 100 tons of blue ice near Cap Prudhomme, Antarctica, yielded 7500 or more irregular, friable particles and about 1500 melted spherules, about 100 microns in size, both showing a 'chondritic' composition suggestive of an extraterrestrial origin. Analyzed irregular particles appear to be unmelted and have similarities with the fine-grained matrix of primitive carbonaceous chondrites, but are extremely diverse in composition. Isotopic analysis of trapped neon confirms an extraterrestrial origin for 16 of 47 irregular particles and 2 of 19 spherules studied and strongly suggests that they were exposed in space as micrometeoroids. These large Antarctic micrometeorites constitute a new family, or at least a new population, of solar system objects, in a mass range corresponding to the bulk of extraterrestrial material accreted by the earth today.

Cosmic dust collection with a sub-satellite tethered to a space station

NASA Technical Reports Server (NTRS)

Corso, G. J.

1986-01-01

The number concentration and density of 1 micron and submicron sized grains in interplanetary space, as well as their relation to the larger zodical dust particles, and the importance of the Beta meteoroid phenomenon are currently being questioned. The best approach to collecting large numbers of intact micron and submicron sized cosmic dust particles in real time while avoiding terrestrial and man made contamination would be to employ a tethered subsatellite from a space station down into the Earth's atmosphere. Such a subsatellite tied to the space shuttle by a 100 km long tether is being developed. It is also possible that a permanent space station would allow the use of a tether even longer that 100 km. It should be noted that the same tethered collectors could also be employed to study the composition and flux of man made Earth orbiting debris in any direction within 100 km or so of the space station.

Cosmic dust collection with a sub satellite tethered to a Space Station

NASA Technical Reports Server (NTRS)

Corso, George J.

1987-01-01

The number concentration and density of 1 micron and submicron sized grains in interplanetary space, as well as their relation to the larger zodical dust particles, and the importance of the beta meteoroid phenomenon are currently being questioned. The best approach to collecting large numbers of intact micron and submicron sized cosmic dust particles in real time while avoiding terrestrial and man made contamination would be to employ a tethered subsatellite from a space station down into the earth's atmosphere. Such a subsatellite tied to the space shuttle by a 100 km long tether is being developed. It is also possible that a permanent space station would allow the use of a tether even longer than 100 km. It should be noted that the same tethered collectors could also be employed to study the composition and flux of man made earth orbiting debris in any direction within 100 km or so of the space station.

Carriers of the astronomical 2175 ? extinction feature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bradley, J; Dai, Z; Ernie, R

2004-07-20

The 2175 {angstrom} extinction feature is by far the strongest spectral signature of interstellar dust observed by astronomers. Forty years after its discovery the origin of the feature and the nature of the carrier remain controversial. The feature is enigmatic because although its central wavelength is almost invariant its bandwidth varies strongly from one sightline to another, suggesting multiple carriers or a single carrier with variable properties. Using a monochromated transmission electron microscope and valence electron energy-loss spectroscopy we have detected a 5.7 eV (2175 {angstrom}) feature in submicrometer-sized interstellar grains within interplanetary dust particles (IDPs) collected in the stratosphere.more » The carriers are organic carbon and amorphous silicates that are abundant and closely associated with one another both in IDPs and in the interstellar medium. Multiple carriers rather than a single carrier may explain the invariant central wavelength and variable bandwidth of the astronomical 2175 {angstrom} feature.« less

The status of measurement technologies concerning micrometer and submicrometer space articulate matter capture, recovery, velocity and trajectory

NASA Technical Reports Server (NTRS)

Alexander, W. M.; Tanner, William G.; Mcdonald, R. A.; Schaub, G. E.; Stephenson, Stepheni L.; Mcdonnell, J. A. M.; Maag, Carl R.

1994-01-01

The return of a pristine sample from a comet would lead to greater understanding of cometary structures, as well as offering insights into exobiology. The paper presented at the Discovery Program Workshop outlined a set of measurements for what was identified as a SOCCER-like interplanetary mission. Several experiments comprised the total instrumentation. This paper presents a summary of CCSR with an overview of three of the four major instruments. Details of the major dust dynamics experiment including trajectory are given in this paper. The instrument proposed here offers the opportunity for the return of cometary dust particles gathered in situ. The capture process has been employed aboard the space shuttle with successful results in returning samples to Earth for laboratory analysis. In addition, the sensors will measure the charge, mass, velocity, and size of cometary dust grains during the encounter. This data will help our understanding of dusty plasmas.

Pristine extraterrestrial material with unprecedented nitrogen isotopic variation.

PubMed

Briani, Giacomo; Gounelle, Matthieu; Marrocchi, Yves; Mostefaoui, Smail; Leroux, Hugues; Quirico, Eric; Meibom, Anders

2009-06-30

Pristine meteoritic materials carry light element isotopic fractionations that constrain physiochemical conditions during solar system formation. Here we report the discovery of a unique xenolith in the metal-rich chondrite Isheyevo. Its fine-grained, highly pristine mineralogy has similarity with interplanetary dust particles (IDPs), but the volume of the xenolith is more than 30,000 times that of a typical IDP. Furthermore, an extreme continuum of N isotopic variation is present in this xenolith: from very light N isotopic composition (delta(15)N(AIR) = -310 +/- 20 per thousand), similar to that inferred for the solar nebula, to the heaviest ratios measured in any solar system material (delta(15)N(AIR) = 4,900 +/- 300 per thousand). At the same time, its hydrogen and carbon isotopic compositions exhibit very little variation. This object poses serious challenges for existing models for the origin of light element isotopic anomalies.

Systematic and simulation-free coarse graining of homopolymer melts: a relative-entropy-based study.

PubMed

Yang, Delian; Wang, Qiang

2015-09-28

We applied the systematic and simulation-free strategy proposed in our previous work (D. Yang and Q. Wang, J. Chem. Phys., 2015, 142, 054905) to the relative-entropy-based (RE-based) coarse graining of homopolymer melts. RE-based coarse graining provides a quantitative measure of the coarse-graining performance and can be used to select the appropriate analytic functional forms of the pair potentials between coarse-grained (CG) segments, which are more convenient to use than the tabulated (numerical) CG potentials obtained from structure-based coarse graining. In our general coarse-graining strategy for homopolymer melts using the RE framework proposed here, the bonding and non-bonded CG potentials are coupled and need to be solved simultaneously. Taking the hard-core Gaussian thread model (K. S. Schweizer and J. G. Curro, Chem. Phys., 1990, 149, 105) as the original system, we performed RE-based coarse graining using the polymer reference interaction site model theory under the assumption that the intrachain segment pair correlation functions of CG systems are the same as those in the original system, which de-couples the bonding and non-bonded CG potentials and simplifies our calculations (that is, we only calculated the latter). We compared the performance of various analytic functional forms of non-bonded CG pair potential and closures for CG systems in RE-based coarse graining, as well as the structural and thermodynamic properties of original and CG systems at various coarse-graining levels. Our results obtained from RE-based coarse graining are also compared with those from structure-based coarse graining.

Coarse-grained molecular dynamics simulations for giant protein-DNA complexes

NASA Astrophysics Data System (ADS)

Takada, Shoji

Biomolecules are highly hierarchic and intrinsically flexible. Thus, computational modeling calls for multi-scale methodologies. We have been developing a coarse-grained biomolecular model where on-average 10-20 atoms are grouped into one coarse-grained (CG) particle. Interactions among CG particles are tuned based on atomistic interactions and the fluctuation matching algorithm. CG molecular dynamics methods enable us to simulate much longer time scale motions of much larger molecular systems than fully atomistic models. After broad sampling of structures with CG models, we can easily reconstruct atomistic models, from which one can continue conventional molecular dynamics simulations if desired. Here, we describe our CG modeling methodology for protein-DNA complexes, together with various biological applications, such as the DNA duplication initiation complex, model chromatins, and transcription factor dynamics on chromatin-like environment.

Recent Advances in Transferable Coarse-Grained Modeling of Proteins

PubMed Central

Kar, Parimal; Feig, Michael

2017-01-01

Computer simulations are indispensable tools for studying the structure and dynamics of biological macromolecules. Biochemical processes occur on different scales of length and time. Atomistic simulations cannot cover the relevant spatiotemporal scales at which the cellular processes occur. To address this challenge, coarse-grained (CG) modeling of the biological systems are employed. Over the last few years, many CG models for proteins continue to be developed. However, many of them are not transferable with respect to different systems and different environments. In this review, we discuss those CG protein models that are transferable and that retain chemical specificity. We restrict ourselves to CG models of soluble proteins only. We also briefly review recent progress made in the multi-scale hybrid all-atom/coarse-grained simulations of proteins. PMID:25443957

Computational and Experimental Studies of Microstructure-Scale Porosity in Metallic Fuels for Improved Gas Swelling Behavior

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mllett, Paul; McDeavitt, Sean; Deo, Chaitanya

This proposal will investigate the stability of bimodal pore size distributions in metallic uranium and uranium-zirconium alloys during sintering and re-sintering annealing treatments. The project will utilize both computational and experimental approaches. The computational approach includes both Molecular Dynamics simulations to determine the self-diffusion coefficients in pure U and U-Zr alloys in single crystals, grain boundaries, and free surfaces, as well as calculations of grain boundary and free surface interfacial energies. Phase-field simulations using MOOSE will be conducted to study pore and grain structure evolution in microstructures with bimodal pore size distributions. Experiments will also be performed to validate themore » simulations, and measure the time-dependent densification of bimodal porous compacts.« less

Influence of the interplanetary magnetic field orientation on polar cap ion trajectories - Energy gain and drift effects

NASA Technical Reports Server (NTRS)

Delcourt, D. C.; Horwitz, J. L.; Swinney, K. R.

1988-01-01

The influence of the interplanetary magnetic field (IMF) orientation on the transport of low-energy ions injected from the ionosphere is investigated using three-dimensional particle codes. It is shown that, unlike the auroral zone outflow, the ions originating from the polar cap region exhibit drastically different drift paths during southward and northward IMF. During southward IMF orientation, a 'two-cell' convection pattern prevails in the ionosphere, and three-dimensional simulations of ion trajectories indicate a preferential trapping of the light ions H(+) in the central plasma sheet, due to the wide azimuthal dispersion of the heavy ions, O(+). In contrast, for northward IMF orientation, the 'four-cell' potential distribution predicted in the ionosphere imposes a temporary ion drift toward higher L shells in the central polar cap. In this case, while the light ions can escape into the magnetotail, the heavy ions can remain trapped, featuring more intense acceleration (from a few electron volts up to the keV range) followed by precipitation at high invariant latitudes, as a consequence of their further travel into the tail.

ANATOMY OF DEPLETED INTERPLANETARY CORONAL MASS EJECTIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kocher, M.; Lepri, S. T.; Landi, E.

We report a subset of interplanetary coronal mass ejections (ICMEs) containing distinct periods of anomalous heavy-ion charge state composition and peculiar ion thermal properties measured by ACE /SWICS from 1998 to 2011. We label them “depleted ICMEs,” identified by the presence of intervals where C{sup 6+}/C{sup 5+} and O{sup 7+}/O{sup 6+} depart from the direct correlation expected after their freeze-in heights. These anomalous intervals within the depleted ICMEs are referred to as “Depletion Regions.” We find that a depleted ICME would be indistinguishable from all other ICMEs in the absence of the Depletion Region, which has the defining property ofmore » significantly low abundances of fully charged species of helium, carbon, oxygen, and nitrogen. Similar anomalies in the slow solar wind were discussed by Zhao et al. We explore two possibilities for the source of the Depletion Region associated with magnetic reconnection in the tail of a CME, using CME simulations of the evolution of two Earth-bound CMEs described by Manchester et al.« less

Structure of magnetopause layers formed by a radial interplanetary magnetic field

NASA Astrophysics Data System (ADS)

Safrankova, Jana; Simunek, Jiri; Nemecek, Zdenek; Prech, Lubomir; Grygorov, Kostiantyn; Shue, Jih-Hong; Samsonov, Andrey; Pi, Gilbert

2016-07-01

The magnetopause location is generally believed to be determined by the solar wind dynamic pressure and by the sign and value of the interplanetary magnetic field (IMF) vertical (Bz) component. A contribution of other parameters is usually assumed to be minor or negligible near the equatorial plane. However, recent papers have shown a magnetopause expansion during intervals of a nearly radial IMF (large IMF Bx component). Under such conditions, the total pressure exerted on the subsolar magnetopause is significantly lower than the solar wind dynamic pressure as demonstrate both MHD simulations and statistical investigations. During a long-duration radial IMF, all parameters - the IMF magnitude, solar wind speed, density, and especially the temperature are depressed in comparison with their yearly averages. Moreover, in this case, the structures of the LLBL change; the LLBL shows different profiles at both hemispheres for negative and positive IMF Bx polarities. This asymmetry changes over time and influences the LLBL structures due to magnetic reconnection. We present an overview of important physical quantities controlling the magnetopause compression and new results that deal with the structure of the magnetopause and adjacent layers.

Solar Energetic Particle Transport Near a Heliospheric Current Sheet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Battarbee, Markus; Dalla, Silvia; Marsh, Mike S., E-mail: mbattarbee@uclan.ac.uk

2017-02-10

Solar energetic particles (SEPs), a major component of space weather, propagate through the interplanetary medium strongly guided by the interplanetary magnetic field (IMF). In this work, we analyze the implications that a flat Heliospheric Current Sheet (HCS) has on proton propagation from SEP release sites to the Earth. We simulate proton propagation by integrating fully 3D trajectories near an analytically defined flat current sheet, collecting comprehensive statistics into histograms, fluence maps, and virtual observer time profiles within an energy range of 1–800 MeV. We show that protons experience significant current sheet drift to distant longitudes, causing time profiles to exhibitmore » multiple components, which are a potential source of confusing interpretations of observations. We find that variation of the current sheet thickness within a realistic parameter range has little effect on particle propagation. We show that the IMF configuration strongly affects the deceleration of protons. We show that in our model, the presence of a flat equatorial HCS in the inner heliosphere limits the crossing of protons into the opposite hemisphere.« less

Numerical Study of Solar Storms from the Sun to Earth

NASA Astrophysics Data System (ADS)

Feng, Xueshang; Jiang, Chaowei; Zhou, Yufen

2017-04-01

As solar storms are sweeping the Earth, adverse changes occur in geospace environment. How human can mitigate and avoid destructive damages caused by solar storms becomes an important frontier issue that we must face in the high-tech times. It is of both scientific significance to understand the dynamic process during solar storm's propagation in interplanetary space and realistic value to conduct physics-based numerical researches on the three-dimensional process of solar storms in interplanetary space with the aid of powerful computing capacity to predict the arrival times, intensities, and probable geoeffectiveness of solar storms at the Earth. So far, numerical studies based on magnetohydrodynamics (MHD) have gone through the transition from the initial qualitative principle researches to systematic quantitative studies on concrete events and numerical predictions. Numerical modeling community has a common goal to develop an end-to-end physics-based modeling system for forecasting the Sun-Earth relationship. It is hoped that the transition of these models to operational use depends on the availability of computational resources at reasonable cost and that the models' prediction capabilities may be improved by incorporating the observational findings and constraints into physics-based models, combining the observations, empirical models and MHD simulations in organic ways. In this talk, we briefly focus on our recent progress in using solar observations to produce realistic magnetic configurations of CMEs as they leave the Sun, and coupling data-driven simulations of CMEs to heliospheric simulations that then propagate the CME configuration to 1AU, and outlook the important numerical issues and their possible solutions in numerical space weather modeling from the Sun to Earth for future research.

Turbulence in a Global Magnetohydrodynamic Simulation of the Earth's Magnetosphere during Northward and Southward Interplanetary Magnetic Field

NASA Technical Reports Server (NTRS)

El-Alaoui, M.; Richard, R. L.; Ashour-Abdalla, M.; Walker, R. J.; Goldstein, M. L.

2012-01-01

We report the results of MHD simulations of Earth's magnetosphere for idealized steady solar wind plasma and interplanetary magnetic field (IMF) conditions. The simulations feature purely northward and southward magnetic fields and were designed to study turbulence in the magnetotail plasma sheet. We found that the power spectral densities (PSDs) for both northward and southward IMF had the characteristics of turbulent flow. In both cases, the PSDs showed the three scale ranges expected from theory: the energy-containing scale, the inertial range, and the dissipative range. The results were generally consistent with in-situ observations and theoretical predictions. While the two cases studied, northward and southward IMF, had some similar characteristics, there were significant differences as well. For southward IMF, localized reconnection was the main energy source for the turbulence. For northward IMF, remnant reconnection contributed to driving the turbulence. Boundary waves may also have contributed. In both cases, the PSD slopes had spatial distributions in the dissipative range that reflected the pattern of resistive dissipation. For southward IMF there was a trend toward steeper slopes in the dissipative range with distance down the tail. For northward IMF there was a marked dusk-dawn asymmetry with steeper slopes on the dusk side of the tail. The inertial scale PSDs had a dusk-dawn symmetry during the northward IMF interval with steeper slopes on the dawn side. This asymmetry was not found in the distribution of inertial range slopes for southward IMF. The inertial range PSD slopes were clustered around values close to the theoretical expectation for both northward and southward IMF. In the dissipative range, however, the slopes were broadly distributed and the median values were significantly different, consistent with a different distribution of resistivity.

Aerocapture Performance Analysis for a Neptune-Triton Exploration Mission

NASA Technical Reports Server (NTRS)

Starr, Brett R.; Westhelle, Carlos H.; Masciarelli, James P.

2004-01-01

A systems analysis has been conducted for a Neptune-Triton Exploration Mission in which aerocapture is used to capture a spacecraft at Neptune. Aerocapture uses aerodynamic drag instead of propulsion to decelerate from the interplanetary approach trajectory to a captured orbit during a single pass through the atmosphere. After capture, propulsion is used to move the spacecraft from the initial captured orbit to the desired science orbit. A preliminary assessment identified that a spacecraft with a lift to drag ratio of 0.8 was required for aerocapture. Performance analyses of the 0.8 L/D vehicle were performed using a high fidelity flight simulation within a Monte Carlo executive to determine mission success statistics. The simulation was the Program to Optimize Simulated Trajectories (POST) modified to include Neptune specific atmospheric and planet models, spacecraft aerodynamic characteristics, and interplanetary trajectory models. To these were added autonomous guidance and pseudo flight controller models. The Monte Carlo analyses incorporated approach trajectory delivery errors, aerodynamic characteristics uncertainties, and atmospheric density variations. Monte Carlo analyses were performed for a reference set of uncertainties and sets of uncertainties modified to produce increased and reduced atmospheric variability. For the reference uncertainties, the 0.8 L/D flatbottom ellipsled vehicle achieves 100% successful capture and has a 99.87 probability of attaining the science orbit with a 360 m/s V budget for apoapsis and periapsis adjustment. Monte Carlo analyses were also performed for a guidance system that modulates both bank angle and angle of attack with the reference set of uncertainties. An alpha and bank modulation guidance system reduces the 99.87 percentile DELTA V 173 m/s (48%) to 187 m/s for the reference set of uncertainties.

Interaction of the geomagnetic field with northward interplanetary magnetic field

NASA Astrophysics Data System (ADS)

Bhattarai, Shree Krishna

The interaction of the solar wind with Earth's magnetic field causes the transfer of momentum and energy from the solar wind to geospace. The study of this interaction is gaining significance as our society is becoming more and more space based, due to which, predicting space weather has become more important. The solar wind interacts with the geomagnetic field primarily via two processes: viscous interaction and the magnetic reconnection. Both of these interactions result in the generation of an electric field in Earth's ionosphere. The overall topology and dynamics of the magnetosphere, as well as the electric field imposed on the ionosphere, vary with speed, density, and magnetic field orientation of the solar wind as well as the conductivity of the ionosphere. In this dissertation, I will examine the role of northward interplanetary magnetic field (IMF) and discuss the global topology of the magnetosphere and the interaction with the ionosphere using results obtained from the Lyon-Fedder-Mobarry (LFM) simulation. The electric potentials imposed on the ionosphere due to viscous interaction and magnetic reconnection are called the viscous and the reconnection potentials, respectively. A proxy to measure the overall effect of these potentials is to measure the cross polar potential (CPP). The CPP is defined as the difference between the maximum and the minimum of the potential in a given polar ionosphere. I will show results from the LFM simulation showing saturation of the CPP during periods with purely northward IMF of sufficiently large magnitude. I will further show that the viscous potential, which was assumed to be independent of IMF orientation until this work, is reduced during periods of northward IMF. Furthermore, I will also discuss the implications of these results for a simulation of an entire solar rotation.

The Influence of Pickup Protons, from Interstellar Neutral Hydrogen, on the Propagation of Interplanetary Shocks from the Halloween 2003 Solar Events to ACE and Ulysses: A 3-D MHD Modeling Study

NASA Technical Reports Server (NTRS)

Detman, T. R.; Intriligator, D. S.; Dryer, M.; Sun, W.; Deehr, C. S.; Intriligator, J.

2012-01-01

We describe our 3-D, time ]dependent, MHD solar wind model that we recently modified to include the physics of pickup protons from interstellar neutral hydrogen. The model has a time-dependent lower boundary condition, at 0.1 AU, that is driven by source surface map files through an empirical interface module. We describe the empirical interface and its parameter tuning to maximize model agreement with background (quiet) solar wind observations at ACE. We then give results of a simulation study of the famous Halloween 2003 series of solar events. We began with shock inputs from the Fearless Forecast real ]time shock arrival prediction study, and then we iteratively adjusted input shock speeds to obtain agreement between observed and simulated shock arrival times at ACE. We then extended the model grid to 5.5 AU and compared those simulation results with Ulysses observations at 5.2 AU. Next we undertook the more difficult tuning of shock speeds and locations to get matching shock arrival times at both ACE and Ulysses. Then we ran this last case again with neutral hydrogen density set to zero, to identify the effect of pickup ions. We show that the speed of interplanetary shocks propagating from the Sun to Ulysses is reduced by the effects of pickup protons. We plan to make further improvements to the model as we continue our benchmarking process to 10 AU, comparing our results with Cassini observations, and eventually on to 100 AU, comparing our results with Voyager 1 and 2 observations.

Rapid Preliminary Design of Interplanetary Trajectories Using the Evolutionary Mission Trajectory Generator

NASA Technical Reports Server (NTRS)

Englander, Jacob

2016-01-01

This set of tutorial slides is an introduction to the Evolutionary Mission Trajectory Generator (EMTG), NASA Goddard Space Flight Center's autonomous tool for preliminary design of interplanetary missions. This slide set covers the basics of creating and post-processing simple interplanetary missions in EMTG using both high-thrust chemical and low-thrust electric propulsion along with a variety of operational constraints.

Simulation of electron transport across charged grain boundaries

NASA Astrophysics Data System (ADS)

Srikant, V.; Clarke, D. R.; Evans, P. V.

1996-09-01

The I-V (current density-electric field) characteristics of low-angle grain boundaries consisting of periodic arrays of charged dislocations are computed using a quasiclassical molecular dynamics approach. Below a critical value of the grain boundary misorientation, the computed I-V characteristics are linear whereas above they are nonlinear. The degree of nonlinearity and the voltage onset of nonlinearity are found to be dependent on the grain boundary misorientation.

Quantum Mechanics/Molecular Mechanics Method Combined with Hybrid All-Atom and Coarse-Grained Model: Theory and Application on Redox Potential Calculations.

PubMed

Shen, Lin; Yang, Weitao

2016-04-12

We developed a new multiresolution method that spans three levels of resolution with quantum mechanical, atomistic molecular mechanical, and coarse-grained models. The resolution-adapted all-atom and coarse-grained water model, in which an all-atom structural description of the entire system is maintained during the simulations, is combined with the ab initio quantum mechanics and molecular mechanics method. We apply this model to calculate the redox potentials of the aqueous ruthenium and iron complexes by using the fractional number of electrons approach and thermodynamic integration simulations. The redox potentials are recovered in excellent accordance with the experimental data. The speed-up of the hybrid all-atom and coarse-grained water model renders it computationally more attractive. The accuracy depends on the hybrid all-atom and coarse-grained water model used in the combined quantum mechanical and molecular mechanical method. We have used another multiresolution model, in which an atomic-level layer of water molecules around redox center is solvated in supramolecular coarse-grained waters for the redox potential calculations. Compared with the experimental data, this alternative multilayer model leads to less accurate results when used with the coarse-grained polarizable MARTINI water or big multipole water model for the coarse-grained layer.

Theory of wavelet-based coarse-graining hierarchies for molecular dynamics.

PubMed

Rinderspacher, Berend Christopher; Bardhan, Jaydeep P; Ismail, Ahmed E

2017-07-01

We present a multiresolution approach to compressing the degrees of freedom and potentials associated with molecular dynamics, such as the bond potentials. The approach suggests a systematic way to accelerate large-scale molecular simulations with more than two levels of coarse graining, particularly applications of polymeric materials. In particular, we derive explicit models for (arbitrarily large) linear (homo)polymers and iterative methods to compute large-scale wavelet decompositions from fragment solutions. This approach does not require explicit preparation of atomistic-to-coarse-grained mappings, but instead uses the theory of diffusion wavelets for graph Laplacians to develop system-specific mappings. Our methodology leads to a hierarchy of system-specific coarse-grained degrees of freedom that provides a conceptually clear and mathematically rigorous framework for modeling chemical systems at relevant model scales. The approach is capable of automatically generating as many coarse-grained model scales as necessary, that is, to go beyond the two scales in conventional coarse-grained strategies; furthermore, the wavelet-based coarse-grained models explicitly link time and length scales. Furthermore, a straightforward method for the reintroduction of omitted degrees of freedom is presented, which plays a major role in maintaining model fidelity in long-time simulations and in capturing emergent behaviors.

Microstructural effects on damage evolution in shocked copper polycrystals

DOE PAGES

Lieberman, Evan J.; Lebensohn, Ricardo A.; Menasche, David B.; ...

2016-07-01

Three-dimensional crystal orientation fields of a copper sample, characterized before and after shock loading using High Energy Diffraction Microscopy, are used for input and validation of direct numerical simulations using a Fast Fourier Transform (FFT)-based micromechanical model. The locations of the voids determined by X-ray tomography in the incipiently-spalled sample, predominantly found near grain boundaries, were traced back and registered to the pre-shocked microstructural image. Using FFT-based simulations with direct input from the initial microstructure, micromechanical fields at the shock peak stress were obtained. Statistical distributions of micromechanical fields restricted to grain boundaries that developed voids after the shock aremore » compared with corresponding distributions for all grain boundaries. Distributions of conventional measures of stress and strain (deviatoric and mean components) do not show correlation with the locations of voids in the post-shocked image. Neither does stress triaxiality, surface traction or grain boundary inclination angle, in a significant way. On the other hand, differences in Taylor factor and accumulated plastic work across grain boundaries do correlate with the occurrence of damage. As a result, damage was observed to take place preferentially at grain boundaries adjacent to grains having very different plastic response.« less

Softening due to disordered grain boundaries in nanocrystalline Co.

PubMed

Yuasa, Motohiro; Hakamada, Masataka; Nakano, Hiromi; Mabuchi, Mamoru; Chino, Yasumasa

2013-08-28

Nanocrystalline Co consisting of fcc and hcp phases was processed by electrodeposition, and its mechanical properties were investigated by hardness tests. In addition, high-resolution transmission electron microscopy observations and molecular dynamics (MD) simulations were performed to investigate the grain boundary structure and dislocation nucleation from the grain boundaries. A large amount of disorders existed at the grain boundaries and stacking faults were formed from the grain boundaries in the as-deposited Co specimen. The as-deposited specimen showed a lower hardness than did the annealed specimen, although the grain size of the former was smaller than that of the latter. The activation volume of the as-deposited specimen (=1.5b(3)) was lower than that of the annealed specimen (=50b(3)), thus indicating that nucleation of dislocations from grain boundaries is more active in the as-deposited specimen than in the annealed specimens. The MD simulations showed that dislocation nucleation was closely related to a change in the defect structures at the boundary. Therefore, it is suggested that a significant amount of defects enhance changes in the defect structures at the boundary, resulting in softening of the as-deposited specimen.

Softening due to disordered grain boundaries in nanocrystalline Co

NASA Astrophysics Data System (ADS)

Yuasa, Motohiro; Hakamada, Masataka; Nakano, Hiromi; Mabuchi, Mamoru; Chino, Yasumasa

2013-08-01

Nanocrystalline Co consisting of fcc and hcp phases was processed by electrodeposition, and its mechanical properties were investigated by hardness tests. In addition, high-resolution transmission electron microscopy observations and molecular dynamics (MD) simulations were performed to investigate the grain boundary structure and dislocation nucleation from the grain boundaries. A large amount of disorders existed at the grain boundaries and stacking faults were formed from the grain boundaries in the as-deposited Co specimen. The as-deposited specimen showed a lower hardness than did the annealed specimen, although the grain size of the former was smaller than that of the latter. The activation volume of the as-deposited specimen (=1.5b3) was lower than that of the annealed specimen (=50b3), thus indicating that nucleation of dislocations from grain boundaries is more active in the as-deposited specimen than in the annealed specimens. The MD simulations showed that dislocation nucleation was closely related to a change in the defect structures at the boundary. Therefore, it is suggested that a significant amount of defects enhance changes in the defect structures at the boundary, resulting in softening of the as-deposited specimen.

Investigating the Temperature Problem in Narrow Line Emitting AGN

NASA Astrophysics Data System (ADS)

Jenkins, Sam; Richardson, Chris T.

2018-06-01

Our research investigates the physical conditions in gas clouds around the narrow line region of AGN. Specifically, we explore the necessary conditions for anomalously high electron temperatures, Te, in those clouds. Our 321 galaxy data set was acquired from SDSS DR14 after requiring S/N > 5.0 in [OIII] 4363 and S/N > 3.0 in all BPT diagram emission lines, to ensure both accurate Te and galaxy classification, with 0.04 < z < 1.0. Interestingly, our data set contained no LINERs. We ran simulations using the simulation code Cloudy, and focused on matching the emission exhibited by the hottest of the 70 AGN in our data set. We used multicore computing to cut down on run time, which drastically improved the efficiency of our simulations. We varied hydrogen density, ionization parameter, and metallicity, Z, only to find these three parameters alone were incapable of recreating anomalously high Te, but successfully matched galaxies showing low- to moderate Te. These highest temperature simulations were at low Z, and were able to facilitate higher temperatures because they avoided the cooling effects of high Z. Our most successful simulations varied Z and grain content, which matched approximately 10% of our high temperature data. Our simulations with the highest grain content produced the highest Te because of the photoelectric heating effect that grains provide, which we confirmed by monitoring each heating mechanism as a function of depth. In the near future, we plan to run simulations varying grain content and ionization parameter in order to study the effects these conditions have on gas cloud Te.

Transport of Cryptosporidium parvum Oocysts in Charge Heterogeneous Porous Media: Microfluidics Experiment and Numerical Simulation

NASA Astrophysics Data System (ADS)

Liu, Y.; Meng, X.; Guo, Z.; Zhang, C.; Nguyen, T. H.; Hu, D.; Ji, J.; Yang, X.

2017-12-01

Colloidal attachment on charge heterogeneous grains has significant environmental implications for transport of hazardous colloids, such as pathogens, in the aquifer, where iron, manganese, and aluminium oxide minerals are the major source of surface charge heterogeneity of the aquifer grains. A patchwise surface charge model is often used to describe the surface charge heterogeneity of the grains. In the patchwise model, the colloidal attachment efficiency is linearly correlated with the fraction of the favorable patches (θ=λ(θf - θu)+θu). However, our previous microfluidic study showed that the attachment efficiency of oocysts of Cryptosporidium parvum, a waterborne protozoan parasite, was not linear correlated with the fraction of the favorable patches (λ). In this study, we developed a pore scale model to simulate colloidal transport and attachment on charge heterogeneous grains. The flow field was simulated using the LBM method and colloidal transport and attachment were simulated using the Lagrange particle tracking method. The pore scale model was calibrated with experimental results of colloidal and oocyst transport in microfluidic devices and was then used to simulate oocyst transport in charge heterogeneous porous media under a variety of environmental relative conditions, i.e. the fraction of favorable patchwise, ionic strength, and pH. The results of the pore scale simulations were used to evaluate the effect of surface charge heterogeneity on upscaling of oocyst transport from pore to continuum scale and to develop an applicable correlation between colloidal attachment efficiency and the fraction of the favorable patches.

Phase-field study of grain boundary tracking behavior in crack-seal microstructures

NASA Astrophysics Data System (ADS)

Ankit, Kumar; Nestler, Britta; Selzer, Michael; Reichardt, Mathias

2013-12-01

In order to address the growth of crystals in veins, a multiphase-field model is used to capture the dynamics of crystals precipitating from a super-saturated solution. To gain a detailed understanding of the polycrystal growth phenomena in veins, we investigate the influence of various boundary conditions on crystal growth. In particular, we analyze the formation of vein microstructures resulting from the free growth of crystals as well as crack-sealing processes. We define the crystal symmetry by considering the anisotropy in surface energy to simulate crystals with flat facets and sharp corners. The resulting growth competition of crystals with different orientations is studied to deduce a consistent orientation selection rule in the free-growth regime. Using crack-sealing simulations, we correlate the grain boundary tracking behavior depending on the relative rate of crack opening, opening trajectory, initial grain size, and wall roughness. Further, we illustrate how these parameters induce the microstructural transition between blocky (crystals growing anisotropically) to fibrous morphology (isotropic) and formation of grain boundaries. The phase-field simulations of crystals in the free-growth regime (in 2D and 3D) indicate that the growth or consumption of a crystal is dependent on the orientation difference with neighboring crystals. The crack-sealing simulation results (in 2D and 3D) reveal that crystals grow isotropically and grain boundaries track the opening trajectory if the wall roughness is high, opening increments are small, and crystals touch the wall before the next crack increment starts. Further, we find that within the complete crack-seal regime, anisotropy in surface energy results in the formation of curved/oscillating grain boundaries (instead of straight) when the crack-opening velocity is increased and wall roughness is not sufficiently high. Additionally, the overall capability of phase-field method to simulate large-scale polycrystal growth in veins (in 3D) is demonstrated enumerating the main advantages of adopting the novel approach.

Abundant Solar Nebula Solids in Comets

NASA Technical Reports Server (NTRS)

Messenger, S.; Keller, L. P.; Nakamura-Messenger, K.; Nguyen, A. N.; Clemett, S.

2016-01-01

Comets have been proposed to consist of unprocessed interstellar materials together with a variable amount of thermally annealed interstellar grains. Recent studies of cometary solids in the laboratory have shown that comets instead consist of a wide range of materials from across the protoplanetary disk, in addition to a minor complement of interstellar materials. These advances were made possible by the return of direct samples of comet 81P/Wild 2 coma dust by the NASA Stardust mission and recent advances in microscale analytical techniques. Isotopic studies of 'cometary' chondritic porous interplanetary dust particles (CP-IDPs) and comet 81P/Wild 2 Stardust samples show that preserved interstellar materials are more abundant in comets than in any class of meteorite. Identified interstellar materials include sub-micron-sized presolar silicates, oxides, and SiC dust grains and some fraction of the organic material that binds the samples together. Presolar grain abundances reach 1 weight percentage in the most stardust-rich CP-IDPs, 50 times greater than in meteorites. Yet, order of magnitude variations in presolar grain abundances among CP-IDPs suggest cometary solids experienced significant variations in the degree of processing in the solar nebula. Comets contain a surprisingly high abundance of nebular solids formed or altered at high temperatures. Comet 81P/Wild 2 samples include 10-40 micron-sized, refractory Ca- Al-rich inclusion (CAI)-, chondrule-, and ameboid olivine aggregate (AOA)-like materials. The O isotopic compositions of these refractory materials are remarkably similar to their meteoritic counterparts, ranging from 5 percent enrichments in (sup 16) O to near-terrestrial values. Comet 81P/Wild 2 and CP-IDPs also contain abundant Mg-Fe crystalline and amorphous silicates whose O isotopic compositions are also consistent with Solar System origins. Unlike meteorites, that are dominated by locally-produced materials, comets appear to be composed of materials that were formed across a wide swath of the early protoplanetary disk.