Self-Poling of BiFeO3 Thick Films.

PubMed

Khomyakova, Evgeniya; Sadl, Matej; Ursic, Hana; Daniels, John; Malic, Barbara; Bencan, Andreja; Damjanovic, Dragan; Rojac, Tadej

2016-08-03

Bismuth ferrite (BiFeO3) is difficult to pole because of the combination of its high coercive field and high electrical conductivity. This problem is particularly pronounced in thick films. The poling, however, must be performed to achieve a large macroscopic piezoelectric response. This study presents evidence of a prominent and reproducible self-poling effect in few-tens-of-micrometer-thick BiFeO3 films. Direct and converse piezoelectric measurements confirmed that the as-sintered BiFeO3 thick films yield d33 values of up to ∼20 pC/N. It was observed that a significant self-poling effect only appears in cases when the films are heated and cooled through the ferroelectric-paraelectric phase transition (Curie temperature TC ∼ 820 °C). These self-poled films exhibit a microstructure with randomly oriented columnar grains. The presence of a compressive strain gradient across the film thickness cooled from above the TC was experimentally confirmed and is suggested to be responsible for the self-poling effect. Finally, the macroscopic d33 response of the self-poled BiFeO3 film was characterized as a function of the driving-field frequency and amplitude.

Towards understanding of magnetization reversal in Nd-Fe-B nanocomposites: analysis by high-throughput micromagnetic simulations

NASA Astrophysics Data System (ADS)

Erokhin, Sergey; Berkov, Dmitry; Ito, Masaaki; Kato, Akira; Yano, Masao; Michels, Andreas

2018-03-01

We demonstrate how micromagnetic simulations can be employed in order to characterize and analyze the magnetic microstructure of nanocomposites. For the example of nanocrystalline Nd-Fe-B, which is a potential material for future permanent-magnet applications, we have compared three different models for the micromagnetic analysis of this material class: (i) a description of the nanocomposite microstructure in terms of Stoner-Wohlfarth particles with and without the magnetodipolar interaction; (ii) a model based on the core-shell representation of the nanograins; (iii) the latter model including a contribution of superparamagnetic clusters. The relevant parameter spaces have been systematically scanned with the aim to establish which micromagnetic approach can most adequately describe experimental data for this material. According to our results, only the last, most sophisticated model is able to provide an excellent agreement with the measured hysteresis loop. The presented methodology is generally applicable to multiphase magnetic nanocomposites and it highligths the complex interrelationship between the microstructure, magnetic interactions, and the macroscopic magnetic properties.

Electronic Phase Separation in Iron Selenide (Li,Fe)OHFeSe Superconductor System

NASA Astrophysics Data System (ADS)

Mao, Yiyuan; Li, Jun; Huan, Yulong; Yuan, Jie; Li, Zi-an; Chai, Ke; Ma, Mingwei; Ni, Shunli; Tian, Jinpeng; Liu, Shaobo; Zhou, Huaxue; Zhou, Fang; Li, Jianqi; Zhang, Guangming; Jin, Kui; Dong, Xiaoli; Zhao, Zhongxian

2018-05-01

The phenomenon of phase separation into antiferromagnetic (AFM) and superconducting (SC) or normal-state regions has great implication for the origin of high-temperature (high-Tc) superconductivity. However, the occurrence of an intrinsic antiferromagnetism above the Tc of (Li, Fe)OHFeSe superconductor is questioned. Here we report a systematic study on a series of (Li, Fe)OHFeSe single crystal samples with Tc up to ~41 K. We observe an evident drop in the static magnetization at Tafm ~125 K, in some of the SC (Tc < ~38 K, cell parameter c < ~9.27 {\\AA}) and non-SC samples. We verify that this AFM signal is intrinsic to (Li, Fe)OHFeSe. Thus, our observations indicate mesoscopic-to-macroscopic coexistence of an AFM state with the normal (below Tafm) or SC (below Tc) state in (Li, Fe)OHFeSe. We explain such coexistence by electronic phase separation, similar to that in high-Tc cuprates and iron arsenides. However, such an AFM signal can be absent in some other samples of (Li, Fe)OHFeSe, particularly it is never observed in the SC samples of Tc > ~38 K, owing to a spatial scale of the phase separation too small for the macroscopic magnetic probe. For this case, we propose a microscopic electronic phase separation. It is suggested that the microscopic static phase separation reaches vanishing point in high-Tc (Li, Fe)OHFeSe, by the occurrence of two-dimensional AFM spin fluctuations below nearly the same temperature as Tafm reported previously for a (Li, Fe)OHFeSe (Tc ~42 K) single crystal. A complete phase diagram is thus established. Our study provides key information of the underlying physics for high-Tc superconductivity.

Length-Scale-Dependent Phase Transformation of LiFePO4 : An In situ and Operando Study Using Micro-Raman Spectroscopy and XRD.

PubMed

Siddique, N A; Salehi, Amir; Wei, Zi; Liu, Dong; Sajjad, Syed D; Liu, Fuqiang

2015-08-03

The charge and discharge of lithium ion batteries are often accompanied by electrochemically driven phase-transformation processes. In this work, two in situ and operando methods, that is, micro-Raman spectroscopy and X-ray diffraction (XRD), have been combined to study the phase-transformation process in LiFePO4 at two distinct length scales, namely, particle-level scale (∼1 μm) and macroscopic scale (∼several cm). In situ Raman studies revealed a discrete mode of phase transformation at the particle level. Besides, the preferred electrochemical transport network, particularly the carbon content, was found to govern the sequence of phase transformation among particles. In contrast, at the macroscopic level, studies conducted at four different discharge rates showed a continuous but delayed phase transformation. These findings uncovered the intricate phase transformation in LiFePO4 and potentially offer valuable insights into optimizing the length-scale-dependent properties of battery materials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Micromagnetic simulation of anisotropic grain boundary diffusion for sintered Nd-Fe-B magnets

NASA Astrophysics Data System (ADS)

Li, W.; Zhou, Q.; Zhao, L. Z.; Wang, Q. X.; Zhong, X. C.; Liu, Z. W.

2018-04-01

A systematic investigation on the anisotropic grain boundary diffusion in sintered Nd-Fe-B magnets is carried out by micromagnetic simulation. The results indicate that the critical reason for the anisotropic diffusion effect is not the difference in the amount of Dy diffused along different directions but the macroscopic demagnetizing field. The diffusion parallel to the easy axis from both pole surfaces of the magnet can increase the nucleation fields in the two major regions with large macroscopic demagnetizing fields, where the reverse domains can nucleate easily. As a consequence, the grain boundary diffusion along the directions parallel to the easy axis from two pole surfaces is more effective to improve the coercivity of the magnets than that along other directions. It is also found that, to enhance the coercivity, only a limited diffusion depth is required. The present result is in good agreement with the recent experimental findings.

Oxygenation of Ediacaran Ocean recorded by iron isotopes

NASA Astrophysics Data System (ADS)

Fan, Haifeng; Zhu, Xiangkun; Wen, Hanjie; Yan, Bin; Li, Jin; Feng, Lianjun

2014-09-01

The increase in atmospheric oxygen during the late Neoproterozoic Era (ca. 800-542 Ma) may have stimulated the oxygenation of the deep oceans and the evolution of macroscopic multicellular organisms. However, the mechanism and magnitude of Neoproterozoic oxygenation remain uncertain. We present Fe isotopes, Fe species and other geochemical data for two sections of the Doushantuo Formation (ca. 635-551 Ma) deposited after the Nantuo glacial episode in the Yangtze Gorge area, South China. It is highlighted that highly positive δ56Fe values reflect a lower oxidation rate of Fe(II)aq under ferruginous conditions, and in turn near zero δ56Fe values indicate oxidizing conditions. Our study suggests that during the deposition of the bottom of Member II of the Doushantuo Formation the shallow seawater was oxic, but the deep water was characterized by ferruginous conditions, which is consistent with a redox chemical stratification model. Subsequent anoxic conditions under shallow seawater, represented by positive δ56Fe and negative δ13Ccarb excursions, should be ascribed to the upwelling of Fe(II)aq and dissolved organic carbon (DOC)-rich anoxic deep seawater. The oxidation of Fe (II)aq and DOC-rich anoxic deep seawater upon mixing with oxic shallow water provides an innovative explanation for the well-known negative δ13Ccarb excursions (ENC2) and positive δ56Fe excursions in the middle of Doushantuo Formation. Meanwhile, the upwelling Fe (II)aq- and DOC-rich anoxic deep seawater could increase photosynthetic activity. The balance between oxygen consumption and production was most important criteria for the oxygenation of Early Ediacaran Ocean and diversity of eukaryotic organisms.

Brillouin light scattering study of spin waves in NiFe/Co exchange spring bilayer films

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

Haldar, Arabinda; Banerjee, Chandrima; Laha, Pinaki

2014-04-07

Spin waves are investigated in Permalloy(Ni{sub 80}Fe{sub 20})/Cobalt(Co) exchange spring bilayer thin films using Brillouin light scattering (BLS) experiment. The magnetic hysteresis loops measured by magneto-optical Kerr effect show a monotonic decrease in coercivity of the bilayer films with increasing Py thickness. BLS study shows two distinct modes, which are modelled as Damon-Eshbach and perpendicular standing wave modes. Linewidths of the frequency peaks are found to increase significantly with decreasing Py layer thickness. Interfacial roughness causes to fluctuate exchange coupling at the nanoscale regimes and the effect is stronger for thinner Py films. A quantitative analysis of the magnon linewidthsmore » shows the presence of strong local exchange coupling field which is much larger compared to macroscopic exchange field.« less

Geometrical and material parameters to assess the macroscopic mechanical behaviour of fresh cranial bone samples.

PubMed

Auperrin, Audrey; Delille, Rémi; Lesueur, Denis; Bruyère, Karine; Masson, Catherine; Drazétic, Pascal

2014-03-21

The present study aims at providing quantitative data for the personalisation of geometrical and mechanical characteristics of the adult cranial bone to be applied to head FE models. A set of 351 cranial bone samples, harvested from 21 human skulls, were submitted to three-point bending tests at 10 mm/min. For each of them, an apparent elastic modulus was calculated using the beam's theory and a density-dependant beam inertia. Thicknesses, apparent densities and percentage of ash weight were also measured. Distributions of characteristics among the different skull bones show their symmetry and their significant differences between skull areas. A data analysis was performed to analyse potential relationship between thicknesses, densities and the apparent elastic modulus. A specific regression was pointed out to estimate apparent elastic modulus from the product of thickness by apparent density. These results offer quantitative tools in view of personalising head FE models and thus improve definition of local injury criteria for this body part. Copyright © 2014 Elsevier Ltd. All rights reserved.

Fe3O4 nanoparticles: protein-mediated crystalline magnetic superstructures

NASA Astrophysics Data System (ADS)

Okuda, Mitsuhiro; Eloi, Jean-Charles; Jones, Sarah E. Ward; Sarua, Andrei; Richardson, Robert M.; Schwarzacher, Walther

2012-10-01

The synthesis of magnetic, monodisperse nanoparticles has attracted great interest in nanoelectronics and nanomedicine. Here we report the fabrication of pure magnetite nanoparticles, less than ten nanometers in size, using the cage-shaped protein apoferritin (Fe3O4-ferritin). Crystallizable proteins were obtained through careful successive separation methods, including a magnetic chromatography that enabled the effective separation of proteins, including a Fe3O4 nanoparticle (7.9 ± 0.8 nm), from empty ones. Macroscopic protein crystals allowed the fabrication of three-dimensional arrays of Fe3O4 nanoparticles with interparticle gaps controlled by dehydration, decreasing their magnetic susceptibilities and increasing their blocking temperatures through enhanced dipole-dipole interactions.

Stiffness distribution in insect cuticle: a continuous or a discontinuous profile?

PubMed

Rajabi, H; Jafarpour, M; Darvizeh, A; Dirks, J-H; Gorb, S N

2017-07-01

Insect cuticle is a biological composite with a high degree of complexity in terms of both architecture and material composition. Given the complex morphology of many insect body parts, finite-element (FE) models play an important role in the analysis and interpretation of biomechanical measurements, taken by either macroscopic or nanoscopic techniques. Many previous studies show that the interpretation of nanoindentation measurements of this layered composite material is very challenging. To develop accurate FE models, it is of particular interest to understand more about the variations in the stiffness through the thickness of the cuticle. Considering the difficulties of making direct measurements, in this study, we use the FE method to analyse previously published data and address this issue numerically. For this purpose, sets of continuous or discontinuous stiffness profiles through the thickness of the cuticle were mathematically described. The obtained profiles were assigned to models developed based on the cuticle of three insect species with different geometries and layer configurations. The models were then used to simulate the mechanical behaviour of insect cuticles subjected to nanoindentation experiments. Our results show that FE models with discontinuous exponential stiffness gradients along their thickness were able to predict the stress and deformation states in insect cuticle very well. Our results further suggest that, for more accurate measurements and interpretation of nanoindentation test data, the ratio of the indentation depth to cuticle thickness should be limited to 7% rather than the traditional '10% rule'. The results of this study thus might be useful to provide a deeper insight into the biomechanical consequences of the distinct material distribution in insect cuticle and also to form a basis for more realistic modelling of this complex natural composite. © 2017 The Author(s).

FE calculations on a three stage metal forming process of Sandvik Nanoflex™

NASA Astrophysics Data System (ADS)

Voncken, R. M. J.; van der Sluis, O.; Post, J.; Huétink, J.

2004-06-01

Sandvik Nanoflex™ combines good corrosion resistance with high strength. This steel has good deformability in austenitic conditions. It belongs to the group of metastable austenites, which means that during deformation a strain-induced transformation into martensite takes place. After deformation, transformation continues as a result of internal stresses. Both transformations are stress-state and temperature dependent. A constitutive model for this steel has been formulated, based on the macroscopic material behaviour measured by inductive measurements. Both the stress-assisted and the strain-induced transformation into martensite have been incorporated in this model. Path-dependent work hardening has also been taken into account. This article describes how the model is implemented in an internal Philips FE code called Crystal, which is a dedicated robust and accurate finite element solver. The implementation is based on lookup tables in combination with feed-forward neural networks. The radial return method is used to determine the material state during and after plastic flow, however, it has been extended to cope with the stiff character of the partial differential equation that describes the transformation behaviour.

EXAFS study of mercury(II) sorption to Fe- and Al-(hydr)oxides: I. Effects of pH

USGS Publications Warehouse

Kim, C.S.; Rytuba, J.J.; Brown, Gordon E.

2004-01-01

The study of mercury sorption products in model systems using appropriate in situ molecular-scale probes can provide detailed information on the modes of sorption at mineral/water interfaces. Such studies are essential for assessing the influence of sorption processes on the transport of Hg in contaminated natural systems. Macroscopic uptake of Hg(II) on goethite (??-FeOOH), ??-alumina (??-Al2O3), and bayerite (??-Al(OH)3) as a function of pH has been combined with Hg L III-edge EXAFS spectroscopy, FTIR spectroscopy, and bond valence analysis of possible sorption products to provide this type of information. Macroscopic uptake measurements show that Hg(II) sorbs strongly to fine-grained powders of synthetic goethite (Hg sorption density ??=0.39-0.42 ??mol/m2) and bayerite (??=0.39-0.44 ??mol/m2), while sorbing more weakly to ??-alumina (??=0.04-0.13 ??mol/m 2). EXAFS spectroscopy on the sorption samples shows that the dominant mode of Hg sorption on these phases is as monodentate and bidentate inner-sphere complexes. The mode of Hg(II) sorption to goethite was similar over the pH range 4.3-7.4, as were those of Hg(II) sorption to bayerite over the pH range 5.1-7.9. Conversion of the ??-Al2O3 sorbent to a bayerite-like phase in addition to the apparent reduction of Hg(II) to Hg(I), possibly by photoreduction during EXAFS data collection, resulted in enhanced Hg uptake from pH 5.2-7.8 and changes in the modes of sorption that correlate with the formation of the bayerite-like phase. Bond valence calculations are consistent with the sorption modes proposed from EXAFS analysis. EXAFS analysis of Hg(II) sorption products on a natural Fe oxyhydroxide precipitate and Al/Si-bearing flocculent material showed sorption products and modes of surface attachment similar to those for the model substrates, indicating that the model substrates are useful surrogates for the natural sediments. ?? 2003 Elsevier Inc. All rights reserved.

Surface complexation modeling of zinc sorption onto ferrihydrite.

PubMed

Dyer, James A; Trivedi, Paras; Scrivner, Noel C; Sparks, Donald L

2004-02-01

A previous study involving lead(II) [Pb(II)] sorption onto ferrihydrite over a wide range of conditions highlighted the advantages of combining molecular- and macroscopic-scale investigations with surface complexation modeling to predict Pb(II) speciation and partitioning in aqueous systems. In this work, an extensive collection of new macroscopic and spectroscopic data was used to assess the ability of the modified triple-layer model (TLM) to predict single-solute zinc(II) [Zn(II)] sorption onto 2-line ferrihydrite in NaNO(3) solutions as a function of pH, ionic strength, and concentration. Regression of constant-pH isotherm data, together with potentiometric titration and pH edge data, was a much more rigorous test of the modified TLM than fitting pH edge data alone. When coupled with valuable input from spectroscopic analyses, good fits of the isotherm data were obtained with a one-species, one-Zn-sorption-site model using the bidentate-mononuclear surface complex, (triple bond FeO)(2)Zn; however, surprisingly, both the density of Zn(II) sorption sites and the value of the best-fit equilibrium "constant" for the bidentate-mononuclear complex had to be adjusted with pH to adequately fit the isotherm data. Although spectroscopy provided some evidence for multinuclear surface complex formation at surface loadings approaching site saturation at pH >/=6.5, the assumption of a bidentate-mononuclear surface complex provided acceptable fits of the sorption data over the entire range of conditions studied. Regressing edge data in the absence of isotherm and spectroscopic data resulted in a fair number of surface-species/site-type combinations that provided acceptable fits of the edge data, but unacceptable fits of the isotherm data. A linear relationship between logK((triple bond FeO)2Zn) and pH was found, given by logK((triple bond FeO)2Znat1g/l)=2.058 (pH)-6.131. In addition, a surface activity coefficient term was introduced to the model to reduce the ionic strength dependence of sorption. The results of this research and previous work with Pb(II) indicate that the existing thermodynamic framework for the modified TLM is able to reproduce the metal sorption data only over a limited range of conditions. For this reason, much work still needs to be done in fine-tuning the thermodynamic framework and databases for the TLM.

Process metallurgy simulation for metal drawing process optimization by using two-scale finite element method

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

Nakamachi, Eiji; Yoshida, Takashi; Yamaguchi, Toshihiko

2014-10-06

We developed two-scale FE analysis procedure based on the crystallographic homogenization method by considering the hierarchical structure of poly-crystal aluminium alloy metal. It can be characterized as the combination of two-scale structure, such as the microscopic polycrystal structure and the macroscopic elastic plastic continuum. Micro polycrystal structure can be modeled as a three dimensional representative volume element (RVE). RVE is featured as by 3×3×3 eight-nodes solid finite elements, which has 216 crystal orientations. This FE analysis code can predict the deformation, strain and stress evolutions in the wire drawing processes in the macro- scales, and further the crystal texture andmore » hardening evolutions in the micro-scale. In this study, we analyzed the texture evolution in the wire drawing processes by our two-scale FE analysis code under conditions of various drawing angles of dice. We evaluates the texture evolution in the surface and center regions of the wire cross section, and to clarify the effects of processing conditions on the texture evolution.« less

Process metallurgy simulation for metal drawing process optimization by using two-scale finite element method

NASA Astrophysics Data System (ADS)

Nakamachi, Eiji; Yoshida, Takashi; Kuramae, Hiroyuki; Morimoto, Hideo; Yamaguchi, Toshihiko; Morita, Yusuke

2014-10-01

We developed two-scale FE analysis procedure based on the crystallographic homogenization method by considering the hierarchical structure of poly-crystal aluminium alloy metal. It can be characterized as the combination of two-scale structure, such as the microscopic polycrystal structure and the macroscopic elastic plastic continuum. Micro polycrystal structure can be modeled as a three dimensional representative volume element (RVE). RVE is featured as by 3×3×3 eight-nodes solid finite elements, which has 216 crystal orientations. This FE analysis code can predict the deformation, strain and stress evolutions in the wire drawing processes in the macro- scales, and further the crystal texture and hardening evolutions in the micro-scale. In this study, we analyzed the texture evolution in the wire drawing processes by our two-scale FE analysis code under conditions of various drawing angles of dice. We evaluates the texture evolution in the surface and center regions of the wire cross section, and to clarify the effects of processing conditions on the texture evolution.

Influence of film thickness on topology and related magnetic interactions in Fe nanoparticle films

NASA Astrophysics Data System (ADS)

Ausanio, G.; Iannotti, V.; Amoruso, S.; Bruzzese, R.; Wang, X.; Aruta, C.; Arzeo, M.; Lanotte, L.

2013-08-01

Fe nanoparticle (NP)-assembled thin films with different thickness were prepared by femtosecond-pulsed laser deposition using different deposition times. The proper selection of the deposition time allows to control, to a certain degree, the morphology and topology of the deposited Fe nanoparticles (NPs) assembly, fostering non-uniform dense assemblies of NPs, with the consequent reduction of the influence of the exchange interactions on the macroscopic magnetic properties with decreasing thickness. The magnetic behavior of the Fe NP-assembled films with decreasing thickness is characterized by higher coercive field ( H c) values (a factor ≈4.5) and a good compromise between the hysteresis loops squareness and moderate exchange interactions, strongly correlated with the NPs topology.

From single muscle fiber to whole muscle mechanics: a finite element model of a muscle bundle with fast and slow fibers.

PubMed

Marcucci, Lorenzo; Reggiani, Carlo; Natali, Arturo N; Pavan, Piero G

2017-12-01

Muscles exhibit highly complex, multi-scale architecture with thousands of muscle fibers, each with different properties, interacting with each other and surrounding connective structures. Consequently, the results of single-fiber experiments are scarcely linked to the macroscopic or whole muscle behavior. This is especially true for human muscles where it would be important to understand of how skeletal muscles disorders affect patients' life. In this work, we developed a mathematical model to study how fast and slow muscle fibers, well characterized in single-fiber experiments, work and generate together force and displacement in muscle bundles. We characterized the parameters of a Hill-type model, using experimental data on fast and slow single human muscle fibers, and comparing experimental data with numerical simulations obtained from finite element (FE) models of single fibers. Then, we developed a FE model of a bundle of 19 fibers, based on an immunohistochemically stained cross section of human diaphragm and including the corresponding properties of each slow or fast fiber. Simulations of isotonic contractions of the bundle model allowed the generation of its apparent force-velocity relationship. Although close to the average of the force-velocity curves of fast and slow fibers, the bundle curve deviates substantially toward the fast fibers at low loads. We believe that the present model and the characterization of the force-velocity curve of a fiber bundle represents the starting point to link the single-fiber properties to those of whole muscle with FE application in phenomenological models of human muscles.

Modeling diffusion-governed solidification of ternary alloys - Part 2: Macroscopic transport phenomena and macrosegregation.

PubMed

Wu, M; Li, J; Ludwig, A; Kharicha, A

2014-09-01

Part 1 of this two-part investigation presented a multiphase solidification model incorporating the finite diffusion kinetics and ternary phase diagram with the macroscopic transport phenomena (Wu et al., 2013). In Part 2, the importance of proper treatment of the finite diffusion kinetics in the calculation of macrosegregation is addressed. Calculations for a two-dimensional (2D) square casting (50 × 50 mm 2 ) of Fe-0.45 wt.%C-1.06 wt.%Mn considering thermo-solutal convection and crystal sedimentation are performed. The modeling result indicates that the infinite liquid mixing kinetics as assumed by classical models (e.g., the Gulliver-Scheil or lever rule), which cannot properly consider the solute enrichment of the interdendritic or inter-granular melt at the early stage of solidification, might lead to an erroneous estimation of the macrosegregation. To confirm this statement, further theoretical and experimental evaluations are desired. The pattern and intensity of the flow and crystal sedimentation are dependent on the crystal morphologies (columnar or equiaxed); hence, the potential error of the calculated macrosegregation caused by the assumed growth kinetics depends on the crystal morphology. Finally, an illustrative simulation of an engineering 2.45-ton steel ingot is performed, and the results are compared with experimental results. This example demonstrates the model applicability for engineering castings regarding both the calculation efficiency and functionality.

Mechanical Energy Harvesting Performance of Ferroelectric Polymer Nanowires Grown via Template‐Wetting

PubMed Central

Whiter, Richard A.; Boughey, Chess; Smith, Michael

2018-01-01

Abstract Nanowires of the ferroelectric co‐polymer poly(vinylidenefluoride‐co‐triufloroethylene) [P(VDF‐TrFE)] are fabricated from solution within nanoporous templates of both “hard” anodic aluminium oxide (AAO) and “soft” polyimide (PI) through a facile and scalable template‐wetting process. The confined geometry afforded by the pores of the templates leads directly to highly crystalline P(VDF‐TrFE) nanowires in a macroscopic “poled” state that precludes the need for external electrical poling procedure typically required for piezoelectric performance. The energy‐harvesting performance of nanogenerators based on these template‐grown nanowires are extensively studied and analyzed in combination with finite element modelling. Both experimental results and computational models probing the role of the templates in determining overall nanogenerator performance, including both materials and device efficiencies, are presented. It is found that although P(VDF‐TrFE) nanowires grown in PI templates exhibit a lower material efficiency due to lower crystallinity as compared to nanowires grown in AAO templates, the overall device efficiency was higher for the PI‐template‐based nanogenerator because of the lower stiffness of the PI template as compared to the AAO template. This work provides a clear framework to assess the energy conversion efficiency of template‐grown piezoelectric nanowires and paves the way towards optimization of template‐based nanogenerator devices.

LEAD SORPTION ON RUTHENIUM OXIDE: A MACROSCOPIC AND SPECTROSCOPIC STUDY

EPA Science Inventory

Metal oxide phases play an important role in governing the sorption and desorption mechanisms of metals in water, soils, and sediments. Many researchers have examined the efficiency of Pb sorption on Mn, Fe, Al, Ti, and Si oxide surfaces. Most studies concluded that adsorption ...

Modeling the formation of strong couples in high temperature liquid

NASA Astrophysics Data System (ADS)

Yaghmaee, M. S.; Shokri, B.

2007-07-01

The study of atomic/molecular level interactions in the liquid state of materials not only helps us to understand the extreme behavior of such complex liquid phases (different from what we observe from ideal systems), but also helps us to analyze and design the advanced materials. For this reason, the model of an ideally associated mixture has been applied to describe the equilibrium state on the example of an Fe-rich corner of the quaternary Fe-Al-N-B system. This model is able to formulate and analyze the state of liquid systems, which are rich in one component and which also have other components that develop strong interactions among each other, leading to the formation of some couples in the system. These couples could be as small as a two-atom structure (such as simple compounds in a metallic system), but they could also become larger up to nanoscale due to higher stoichiometric morphologies that form nanoscale clusters. The solubility of AlN, BN, and N2 gases in the liquid phase of the ternary Fe-Al-N and Fe-B-N systems has been calculated and fitted to experimental results. There is a deviation between our calculated boundary curves fitted with experimental result and those extrapolated curves from the concept of solubility product, which may only be attributed to the misleading concept of solubility product that ignores couple formation in the liquid. Applying this model to the Fe-Al-N-B liquid system, we found that at relatively low boron content (i.e., 20-30ppm) and soluble aluminum content exceeding 250ppm, more than 90% of the steel making practice with nitrogen content (i.e., maximum of 120ppm) is complexed into AlN and BN couples at temperatures falling in the range of 1823-1923K. The model describing the liquid quaternary Fe-Al-N-B system provides us a tool to determine the equilibrium quantity of the considered constituents (free atoms and couples) formed in the liquid, as a function of macroscopic composition and temperature. This algorithm can be used generally for high temperature multicomponent liquid systems, which have the tendency to form strong couples or nanoclusters.

ANISOTROPY DETERMINATIONS IN EXCHANGE SPRING MAGNETS.

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

LEWIS,L.H.; HARLAND,C.L.

2002-08-18

Ferromagnetic nanocomposites, or ''exchange spring'' magnets, possess a nanoscaled microstructure that allows intergrain magnetic exchange forces to couple the constituent grains and alter the system's effective magnetic anisotropies. While the effects of the anisotropy alterations are clearly seen in macroscopic magnetic measurement, it is extremely difficult to determine the detailed effects of the system's exchange coupling, such as the interphase exchange length, the inherent domain wall widths or the effective anisotropies of the system. Clarification of these materials parameters may be obtained from the ''micromagnetic'' phenomenological model, where the assumption of magnetic reversal initiating in the magnetically-soft regions of themore » exchange-spring maqet is explicitly included. This approach differs from that typically applied by other researchers and allows a quantitative estimate of the effective anisotropies of an exchange spring system. Hysteresis loops measured on well-characterized nanocomposite alloys based on the composition Nd{sub 2}Fe{sub 14}B + {alpha}-Fe at temperatures above the spin reorientation temperature were analyzed within the framework of the micromagnetic phenomenological model. Preliminary results indicate that the effective anisotropy constant in the material is intermediate to that of bulk {alpha}-Fe and bulk Nd{sub 2}Fe{sub 14}B and increases with decreasing temperature. These results strongly support the idea that magnetic reversal in nanocomposite systems initiates in the lower-anisotropy regions of the system, and that the soft-phase regions become exchange-hardened by virtue of their proximity to the magnetically-hard regions.« less

Origin of the butterfly-shaped magnetoresistance in reactive sputtered epitaxial Fe{sub 3}O{sub 4} films

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

Li, P.; Zhang, L. T.; Mi, W. B.

2009-08-01

Epitaxial Fe{sub 3}O{sub 4} thin films were synthesized by facing-target reactive sputtering Fe targets. The epitaxy of the Fe{sub 3}O{sub 4} film on MgO (100) was examined macroscopically using x-ray diffraction, including conventional theta-2theta scan, tilting 2theta scan, phi scan, and pole figure. The observed low-field butterfly-shaped magnetoresistance (MR) are explained by the primary fast rotation of the spins far away from antiphase boundaries and the high-field MR changing linearly with magnetic field can be understood by the gradual rotation of the spins near the antiphase boundaries. It is magnetocrystalline anisotropy that causes an increase in MR below Verwey transitionmore » temperature.« less

Particle Interactions Mediated by Dynamical Networks: Assessment of Macroscopic Descriptions

NASA Astrophysics Data System (ADS)

Barré, J.; Carrillo, J. A.; Degond, P.; Peurichard, D.; Zatorska, E.

2018-02-01

We provide a numerical study of the macroscopic model of Barré et al. (Multiscale Model Simul, 2017, to appear) derived from an agent-based model for a system of particles interacting through a dynamical network of links. Assuming that the network remodeling process is very fast, the macroscopic model takes the form of a single aggregation-diffusion equation for the density of particles. The theoretical study of the macroscopic model gives precise criteria for the phase transitions of the steady states, and in the one-dimensional case, we show numerically that the stationary solutions of the microscopic model undergo the same phase transitions and bifurcation types as the macroscopic model. In the two-dimensional case, we show that the numerical simulations of the macroscopic model are in excellent agreement with the predicted theoretical values. This study provides a partial validation of the formal derivation of the macroscopic model from a microscopic formulation and shows that the former is a consistent approximation of an underlying particle dynamics, making it a powerful tool for the modeling of dynamical networks at a large scale.

Particle Interactions Mediated by Dynamical Networks: Assessment of Macroscopic Descriptions.

PubMed

Barré, J; Carrillo, J A; Degond, P; Peurichard, D; Zatorska, E

2018-01-01

We provide a numerical study of the macroscopic model of Barré et al. (Multiscale Model Simul, 2017, to appear) derived from an agent-based model for a system of particles interacting through a dynamical network of links. Assuming that the network remodeling process is very fast, the macroscopic model takes the form of a single aggregation-diffusion equation for the density of particles. The theoretical study of the macroscopic model gives precise criteria for the phase transitions of the steady states, and in the one-dimensional case, we show numerically that the stationary solutions of the microscopic model undergo the same phase transitions and bifurcation types as the macroscopic model. In the two-dimensional case, we show that the numerical simulations of the macroscopic model are in excellent agreement with the predicted theoretical values. This study provides a partial validation of the formal derivation of the macroscopic model from a microscopic formulation and shows that the former is a consistent approximation of an underlying particle dynamics, making it a powerful tool for the modeling of dynamical networks at a large scale.

Macroscopic Magnetization Control by Symmetry Breaking of Photoinduced Spin Reorientation with Intense Terahertz Magnetic Near Field

NASA Astrophysics Data System (ADS)

Kurihara, Takayuki; Watanabe, Hiroshi; Nakajima, Makoto; Karube, Shutaro; Oto, Kenichi; Otani, YoshiChika; Suemoto, Tohru

2018-03-01

We exploit an intense terahertz magnetic near field combined with femtosecond laser excitation to break the symmetry of photoinduced spin reorientation paths in ErFeO3 . We succeed in aligning macroscopic magnetization reaching up to 80% of total magnetization in the sample to selectable orientations by adjusting the time delay between terahertz and optical pump pulses. The spin dynamics are well reproduced by equations of motion, including time-dependent magnetic potential. We show that the direction of the generated magnetization is determined by the transient direction of spin tilting and the magnetic field at the moment of photoexcitation.

Room temperature ferromagnetism in BiFe1-xMnxO3 thin film induced by spin-structure manipulation

NASA Astrophysics Data System (ADS)

Shigematsu, Kei; Asakura, Takeshi; Yamamoto, Hajime; Shimizu, Keisuke; Katsumata, Marin; Shimizu, Haruki; Sakai, Yuki; Hojo, Hajime; Mibu, Ko; Azuma, Masaki

2018-05-01

The evolution of crystal structure, spin structure, and macroscopic magnetization of manganese-substituted BiFeO3 (BiFe1-xMnxO3), a candidate for multiferroic materials, were investigated on bulk and epitaxial thin-film. Mn substitution for Fe induced collinear antiferromagnetic spin structure around room temperature by destabilizing the cycloidal spin modulation which prohibited the appearance of net magnetization generated by Dzyaloshinskii-Moriya interaction. For the bulk samples, however, no significant signal of ferromagnetism was observed because the direction of the ordered spins was close to parallel to the electric polarization so that spin-canting did not occur. On the contrary, BiFe1-xMnxO3 thin film on SrTiO3 (001) had a collinear spin structure with the spin direction perpendicular to the electric polarization at room temperature, where the appearance of spontaneous magnetization was expected. Indeed, ferromagnetic hysteresis behavior was observed for BiFe0.9Mn0.1O3 thin film.

Structure and magnetism in Co/X, Fe/Si, and Fe/(FeSi) multilayers

NASA Astrophysics Data System (ADS)

Franklin, Michael Ray

Previous studies have shown that magnetic behavior in multilayers formed by repeating a bilayer unit comprised of a ferromagnetic layer and a non-magnetic spacer layer can be affected by small structural differences. For example, a macroscopic property such as giant magnetoresistance (GMR) is believed to depend significantly upon interfacial roughness. In this study, several complimentary structural probes were used to carefully characterize the structure of several sputtered multilayer systems-Co/Ag, Co/Cu, Co/Mo, Fe/Si, and Fe//[FeSi/]. X-ray diffraction (XRD) studies were used to examine the long-range structural order of the multilayers perpendicular to the plane of the layers. Transmission electron diffraction (TED) studies were used to probe the long-range order parallel to the layer plane. X-ray Absorption Fine Structure (XAFS) studies were used to determine the average local structural environment of the ferromagnetic atoms. For the Co/X systems, a simple correlation between crystal structure and saturation magnetization is discovered for the Co/Mo system. For the Fe/X systems, direct evidence of an Fe-silicide is found for the /[FeSi/] spacer layer but not for the Si spacer layer. Additionally, differences were observed in the magnetic behavior between the Fe in the nominally pure Fe layer and the Fe contained in the /[FeSi/] spacer layers.

Low cost friction seismic base-isolation of residential new masonry buildings in developing countries: A small masonry house case study

NASA Astrophysics Data System (ADS)

Habieb, A. B.; Milani, G.; Tavio, T.; Milani, F.

2017-07-01

A Finite element model was established to examine performance of a low-cost friction base-isolation system in reducing seismic vulnerability of rural buildings. This study adopts an experimental investigation of the isolation system which was conducted in India. Four friction isolation interfaces, namely, marble-marble, marble-high-density polyethylene, marble-rubber sheet, and marble-geosynthetic were involved. Those interfaces differ in static and dynamic friction coefficient obtained through previous research. The FE model was performed based on a macroscopic approach and the masonry wall is assumed as an isotropic element. In order to observe structural response of the masonry house, elastic and plastic parameters of the brick wall were studied. Concrete damage plasticity (CDP) model was adopted to determine non-linear behavior of the brick wall. The results of FE model shows that involving these friction isolation systems could much decrease response acceleration at roof level. It was found that systems with marble-marble and marble-geosynthetic interfaces reduce the roof acceleration up to 50% comparing to the system without isolation. Another interesting result is there was no damage appearing in systems with friction isolation during the test. Meanwhile a severe failure was clearly visible for a system without isolation.

Tuning the magnetism of ferrite nanoparticles

NASA Astrophysics Data System (ADS)

Viñas, S. Liébana; Simeonidis, K.; Li, Z.-A.; Ma, Z.; Myrovali, E.; Makridis, A.; Sakellari, D.; Angelakeris, M.; Wiedwald, U.; Spasova, M.; Farle, M.

2016-10-01

The importance of magnetic interactions within an individual nanoparticle or between adjacent ones is crucial not only for the macroscopic collective magnetic behavior but for the AC magnetic heating efficiency as well. On this concept, single-(MFe2O4 where M=Fe, Co, Mn) and core-shell ferrite nanoparticles consisting of a magnetically softer (MnFe2O4) or magnetically harder (CoFe2O4) core and a magnetite (Fe3O4) shell with an overall size in the 10 nm range were synthesized and studied for their magnetic particle hyperthermia efficiency. Magnetic measurements indicate that the coating of the hard magnetic phase (CoFe2O4) by Fe3O4 provides a significant enhancement of hysteresis losses over the corresponding single-phase counterpart response, and thus results in a multiplication of the magnetic hyperthermia efficiency opening a novel pathway for high-performance, magnetic hyperthermia agents. At the same time, the existence of a biocompatible Fe3O4 outer shell, toxicologically renders these systems similar to iron-oxide ones with significantly milder side-effects.

Applicability of Macroscopic Wear and Friction Laws on the Atomic Length Scale.

PubMed

Eder, S J; Feldbauer, G; Bianchi, D; Cihak-Bayr, U; Betz, G; Vernes, A

2015-07-10

Using molecular dynamics, we simulate the abrasion process of an atomically rough Fe surface with multiple hard abrasive particles. By quantifying the nanoscopic wear depth in a time-resolved fashion, we show that Barwell's macroscopic wear law can be applied at the atomic scale. We find that in this multiasperity contact system, the Bowden-Tabor term, which describes the friction force as a function of the real nanoscopic contact area, can predict the kinetic friction even when wear is involved. From this the Derjaguin-Amontons-Coulomb friction law can be recovered, since we observe a linear dependence of the contact area on the applied load in accordance with Greenwood-Williamson contact mechanics.

Rank distributions: A panoramic macroscopic outlook

NASA Astrophysics Data System (ADS)

Eliazar, Iddo I.; Cohen, Morrel H.

2014-01-01

This paper presents a panoramic macroscopic outlook of rank distributions. We establish a general framework for the analysis of rank distributions, which classifies them into five macroscopic "socioeconomic" states: monarchy, oligarchy-feudalism, criticality, socialism-capitalism, and communism. Oligarchy-feudalism is shown to be characterized by discrete macroscopic rank distributions, and socialism-capitalism is shown to be characterized by continuous macroscopic size distributions. Criticality is a transition state between oligarchy-feudalism and socialism-capitalism, which can manifest allometric scaling with multifractal spectra. Monarchy and communism are extreme forms of oligarchy-feudalism and socialism-capitalism, respectively, in which the intrinsic randomness vanishes. The general framework is applied to three different models of rank distributions—top-down, bottom-up, and global—and unveils each model's macroscopic universality and versatility. The global model yields a macroscopic classification of the generalized Zipf law, an omnipresent form of rank distributions observed across the sciences. An amalgamation of the three models establishes a universal rank-distribution explanation for the macroscopic emergence of a prevalent class of continuous size distributions, ones governed by unimodal densities with both Pareto and inverse-Pareto power-law tails.

Rank distributions: a panoramic macroscopic outlook.

PubMed

Eliazar, Iddo I; Cohen, Morrel H

2014-01-01

This paper presents a panoramic macroscopic outlook of rank distributions. We establish a general framework for the analysis of rank distributions, which classifies them into five macroscopic "socioeconomic" states: monarchy, oligarchy-feudalism, criticality, socialism-capitalism, and communism. Oligarchy-feudalism is shown to be characterized by discrete macroscopic rank distributions, and socialism-capitalism is shown to be characterized by continuous macroscopic size distributions. Criticality is a transition state between oligarchy-feudalism and socialism-capitalism, which can manifest allometric scaling with multifractal spectra. Monarchy and communism are extreme forms of oligarchy-feudalism and socialism-capitalism, respectively, in which the intrinsic randomness vanishes. The general framework is applied to three different models of rank distributions-top-down, bottom-up, and global-and unveils each model's macroscopic universality and versatility. The global model yields a macroscopic classification of the generalized Zipf law, an omnipresent form of rank distributions observed across the sciences. An amalgamation of the three models establishes a universal rank-distribution explanation for the macroscopic emergence of a prevalent class of continuous size distributions, ones governed by unimodal densities with both Pareto and inverse-Pareto power-law tails.

Sorption of Eu(III) on granite: EPMA, LA-ICP-MS, batch and modeling studies.

PubMed

Fukushi, Keisuke; Hasegawa, Yusuke; Maeda, Koushi; Aoi, Yusuke; Tamura, Akihiro; Arai, Shoji; Yamamoto, Yuhei; Aosai, Daisuke; Mizuno, Takashi

2013-11-19

Eu(III) sorption on granite was assessed using combined microscopic and macroscopic approaches in neutral to acidic conditions where the mobility of Eu(III) is generally considered to be high. Polished thin sections of the granite were reacted with solutions containing 10 μM of Eu(III) and were analyzed using EPMA and LA-ICP-MS. On most of the biotite grains, Eu enrichment up to 6 wt % was observed. The Eu-enriched parts of biotite commonly lose K, which is the interlayer cation of biotite, indicating that the sorption mode of Eu(III) by the biotite is cation exchange in the interlayer. The distributions of Eu appeared along the original cracks of the biotite. Those occurrences indicate that the prior water-rock interaction along the cracks engendered modification of biotite to possess affinity to the Eu(III). Batch Eu(III) sorption experiments on granite and biotite powders were conducted as functions of pH, Eu(III) loading, and ionic strength. The macroscopic sorption behavior of biotite was consistent with that of granite. At pH > 4, there was little pH dependence but strong ionic strength dependence of Eu(III) sorption. At pH < 4, the sorption of Eu(III) abruptly decreased with decreased pH. The sorption behavior at pH > 4 was reproducible reasonably by the modeling considering single-site cation exchange reactions. The decrease of Eu(III) sorption at pH < 4 was explained by the occupation of exchangeable sites by dissolved cationic species such as Al and Fe from granite and biotite in low-pH conditions. Granites are complex mineral assemblages. However, the combined microscopic and macroscopic approaches revealed that elementary reactions by a single mineral phase can be representative of the bulk sorption reaction in complex mineral assemblages.

Finite Element Multi-scale Modeling of Chemical Segregation in Steel Solidification Taking into Account the Transport of Equiaxed Grains

NASA Astrophysics Data System (ADS)

Nguyen, Thi-Thuy-My; Gandin, Charles-André; Combeau, Hervé; Založnik, Miha; Bellet, Michel

2018-02-01

The transport of solid crystals in the liquid pool during solidification of large ingots is known to have a significant effect on their final grain structure and macrosegregation. Numerical modeling of the associated physics is challenging since complex and strong interactions between heat and mass transfer at the microscopic and macroscopic scales must be taken into account. The paper presents a finite element multi-scale solidification model coupling nucleation, growth, and solute diffusion at the microscopic scale, represented by a single unique grain, while also including transport of the liquid and solid phases at the macroscopic scale of the ingots. The numerical resolution is based on a splitting method which sequentially describes the evolution and interaction of quantities into a transport and a growth stage. This splitting method reduces the non-linear complexity of the set of equations and is, for the first time, implemented using the finite element method. This is possible due to the introduction of an artificial diffusion in all conservation equations solved by the finite element method. Simulations with and without grain transport are compared to demonstrate the impact of solid phase transport on the solidification process as well as the formation of macrosegregation in a binary alloy (Sn-5 wt pct Pb). The model is also applied to the solidification of the binary alloy Fe-0.36 wt pct C in a domain representative of a 3.3-ton steel ingot.

Domain wall magnetoresistance in BiFeO3 thin films measured by scanning probe microscopy

NASA Astrophysics Data System (ADS)

Domingo, N.; Farokhipoor, S.; Santiso, J.; Noheda, B.; Catalan, G.

2017-08-01

We measure the magnetotransport properties of individual 71° domain walls in multiferroic BiFeO3 by means of conductive—atomic force microscopy (C-AFM) in the presence of magnetic fields up to one Tesla. The results suggest anisotropic magnetoresistance at room temperature, with the sign of the magnetoresistance depending on the relative orientation between the magnetic field and the domain wall plane. A consequence of this finding is that macroscopically averaged magnetoresistance measurements for domain wall bunches are likely to underestimate the magnetoresistance of each individual domain wall.

Facile transformation of FeO/Fe3O4 core-shell nanocubes to Fe3O4 via magnetic stimulation

NASA Astrophysics Data System (ADS)

Lak, Aidin; Niculaes, Dina; Anyfantis, George C.; Bertoni, Giovanni; Barthel, Markus J.; Marras, Sergio; Cassani, Marco; Nitti, Simone; Athanassiou, Athanassia; Giannini, Cinzia; Pellegrino, Teresa

2016-09-01

Here, we propose the use of magnetic hyperthermia as a means to trigger the oxidation of Fe1-xO/Fe3-δO4 core-shell nanocubes to Fe3-δO4 phase. As a first relevant consequence, the specific absorption rate (SAR) of the initial core-shell nanocubes doubles after exposure to 25 cycles of alternating magnetic field stimulation. The improved SAR value was attributed to a gradual transformation of the Fe1-xO core to Fe3-δO4, as evidenced by structural analysis including high resolution electron microscopy and Rietveld analysis of X-ray diffraction patterns. The magnetically oxidized nanocubes, having large and coherent Fe3-δO4 domains, reveal high saturation magnetization and behave superparamagnetically at room temperature. In comparison, the treatment of the same starting core-shell nanocubes by commonly used thermal annealing process renders a transformation to γ-Fe2O3. In contrast to other thermal annealing processes, the method here presented has the advantage of promoting the oxidation at a macroscopic temperature below 37 °C. Using this soft oxidation process, we demonstrate that biotin-functionalized core-shell nanocubes can undergo a mild self-oxidation transformation without losing their functional molecular binding activity.

Magnetic safety matches

NASA Astrophysics Data System (ADS)

Lindén, J.; Lindberg, M.; Greggas, A.; Jylhävuori, N.; Norrgrann, H.; Lill, J. O.

2017-07-01

In addition to the main ingredients; sulfur, potassium chlorate and carbon, ordinary safety matches contain various dyes, glues etc, giving the head of the match an even texture and appealing color. Among the common reddish-brown matches there are several types, which after ignition can be attracted by a strong magnet. Before ignition the match head is generally not attracted by the magnet. An elemental analysis based on proton-induced x-ray emission was performed to single out iron as the element responsible for the observed magnetism. 57Fe Mössbauer spectroscopy was used for identifying the various types of iron-compounds, present before and after ignition, responsible for the macroscopic magnetism: Fe2O3 before and Fe3O4 after. The reaction was verified by mixing the main chemicals in the match-head with Fe2O3 in glue and mounting the mixture on a match stick. The ash residue after igniting the mixture was magnetic.

Macroscopic modeling of freeway traffic using an artificial neural network

DOT National Transportation Integrated Search

1997-01-01

Traffic flow on freeways is a complex process that often is described by a set of highly nonlinear, dynamic equations in the form of a macroscopic traffic flow model. However, some of the existing macroscopic models have been found to exhibit instabi...

Magnetic noise as the cause of the spontaneous magnetization reversal of RE–TM–B permanent magnets

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

Dmitriev, A. I., E-mail: aid@icp.ac.ru; Talantsev, A. D., E-mail: artgtx32@mail.ru; Kunitsyna, E. I.

2016-08-15

The relation between the macroscopic spontaneous magnetization reversal (magnetic viscosity) of (NdDySm)(FeCo)B alloys and the spectral characteristics of magnetic noise, which is caused by the random microscopic processes of thermally activated domain wall motion in a potential landscape with uniformly distributed potential barrier heights, is found.

Nanocomposite Nd-Y-Fe-B-Mo bulk magnets prepared by injection casting technique

NASA Astrophysics Data System (ADS)

Tao, Shan; Ahmad, Zubair; Zhang, Pengyue; Yan, Mi; Zheng, Xiaomei

2017-09-01

The phase composition, magnetic and microstructural properties of Nd2Fe14B/(α-Fe, Fe3B) nanocomposite magnets produced by injection casting technique have been studied. Magnetic hysteresis loop of the Nd7Y6Fe61B22Mo4 permanent magnet demonstrates the coercivity as high as 1289 kA/m. Electron microscopy elucidates a microstructure composed of magnetically soft α-Fe, Fe3B and hard Nd2Fe14B/Y2Fe14B nanograins (20-50 nm) separated by ultra-thin grain boundary layer. The Henkel plot curve of the Nd7Y6Fe61B22Mo4 magnet yields the existence of exchange coupling interactions between soft and hard phases. Macroscopically large size sheet magnet is obtained due to high glass forming ability of the Nd7Y6Fe61B22Mo4 alloy derived from large atomic radius mismatch and negative enthalpy of alloy constituent elements. The high coercivity of the magnet is attributed to the magnetically hard phase increment, nucleation of reverse domains and the presence of thin grain boundary phase. Good magnetic properties such as remanence of 0.51 T, coercivity of 1289 kA/m and maximum energy product of 46.2 kJ/m3 are obtained in directly casted Nd7Y6Fe61B22Mo4 sheet magnets.

Longitudinal spin Seebeck effect in various garnet ferrites

NASA Astrophysics Data System (ADS)

Uchida, K.; Nonaka, T.; Kikkawa, T.; Kajiwara, Y.; Saitoh, E.

2013-03-01

The longitudinal spin Seebeck effect (LSSE) is investigated in various garnet ferrites Y3-xRxFe5-yMyO12 (R=Gd, Ca; M=Al, Mn, V, In, Zr) by means of the inverse spin Hall effect in Pt films. The magnitude of the LSSE voltage in the Pt/Y3-xRxFe5-yMyO12 samples is found to be enhanced with increasing concentration of Fe in the garnet ferrites, which can be explained by a change in the spin-mixing conductance at the Pt/Y3-xRxFe5-yMyO12 interfaces. We also investigate the dependence of the LSSE voltage on macroscopic magnetic parameters of Y3-xRxFe5-yMyO12. The experimental results show that the LSSE voltage in the Pt/Y3-xRxFe5-yMyO12 samples has a positive correlation with the Curie temperature and the saturation magnetization, but no clear correlation with the gyromagnetic ratio and the Gilbert damping constant of the samples.

Angular dispersion of oblique phonon modes in BiFeO3 from micro-Raman scattering

NASA Astrophysics Data System (ADS)

Hlinka, J.; Pokorny, J.; Karimi, S.; Reaney, I. M.

2011-01-01

The angular dispersion of oblique phonon modes in a multiferroic BiFeO3 has been obtained from a micro-Raman spectroscopic investigation of a coarse grain ceramic sample. Continuity of the measured angular dispersion curves allows conclusive identification of all pure zone-center polar modes. The method employed here to reconstruct the anisotropic crystal property from a large set of independent local measurements on a macroscopically isotropic ceramic sample profits from the considerable dispersion of the oblique modes in ferroelectric perovskites and it can be in principle conveniently applied to any other optically uniaxial ferroelectric material.

Assessment of MMP-2/-9 expression by fluorescence endoscopy for evaluation of anastomotic healing in a murine model of anastomotic leakage

PubMed Central

Twardy, Vanessa; Becker, Felix; Geyer, Christiane; Schwegmann, Katrin; Mohr, Annika; Faust, Andreas

2018-01-01

Background Disturbance of intestinal wound closure leads to insufficient anastomotic healing and is associated with considerable morbidity following colorectal resections. Matrix metalloproteinases (MMPs) play a crucial role in regulation of wound closure. Here fluorescence endoscopy was evaluated for assessment of MMP-2/-9 expression during failed intestinal anastomotic healing. Methods Distal colonic anastomoses were performed as a model for disturbed healing in 36 Balb/c mice. Healing was evaluated endoscopically, macroscopically, and histologically after 1, 3 and 5 days. For detection of MMP-2/-9 expression fluorescence endoscopy (FE) was used following i.v.-administration of a Cy5.5-labeled MMP-2/-9 specific tracer. FE was complemented by quantification of the fluorescence signal using the MS-FX PRO Optical Imaging System. An overall leakage score was calculated and correlated with the results of FE. Results With increasing incidence of anastomotic leakage from POD1 (17%) to POD5 (83%) the uptake of the MMP tracer gradually increased (signal-to-noise ratio (SNR), POD1: 17.91 ± 1.251 vs. POD3: 30.56 ± 3.03 vs. POD5: 44.8 ± 4.473, P<0.0001). Mice with defective anastomotic healing showed significantly higher uptake compared to non-defective (SNR: 37.37± 3.63 vs. 26.16± 3.635, P = 0.0369). White light endoscopy and FE allowed evaluation of anastomotic healing and visualization of mucosal MMPs in vivo. Using FE based detection of MMPs in the anastomosis, an overall positive predictive value of 71.4% and negative predictive value of 66.6% was calculated for detection of anastomotic leakage. Conclusion During disturbed anastomotic healing increased expression of MMP-2/-9 was observed in the anastomotic tissue. Fluorescence endoscopy for detection of MMP-2/-9 during the healing process might be a promising tool for early identification of anastomotic leakage. PMID:29566031

Assessment of MMP-2/-9 expression by fluorescence endoscopy for evaluation of anastomotic healing in a murine model of anastomotic leakage.

PubMed

Neumann, Philipp-Alexander; Twardy, Vanessa; Becker, Felix; Geyer, Christiane; Schwegmann, Katrin; Mohr, Annika; Faust, Andreas; Lenz, Philipp; Rijcken, Emile

2018-01-01

Disturbance of intestinal wound closure leads to insufficient anastomotic healing and is associated with considerable morbidity following colorectal resections. Matrix metalloproteinases (MMPs) play a crucial role in regulation of wound closure. Here fluorescence endoscopy was evaluated for assessment of MMP-2/-9 expression during failed intestinal anastomotic healing. Distal colonic anastomoses were performed as a model for disturbed healing in 36 Balb/c mice. Healing was evaluated endoscopically, macroscopically, and histologically after 1, 3 and 5 days. For detection of MMP-2/-9 expression fluorescence endoscopy (FE) was used following i.v.-administration of a Cy5.5-labeled MMP-2/-9 specific tracer. FE was complemented by quantification of the fluorescence signal using the MS-FX PRO Optical Imaging System. An overall leakage score was calculated and correlated with the results of FE. With increasing incidence of anastomotic leakage from POD1 (17%) to POD5 (83%) the uptake of the MMP tracer gradually increased (signal-to-noise ratio (SNR), POD1: 17.91 ± 1.251 vs. POD3: 30.56 ± 3.03 vs. POD5: 44.8 ± 4.473, P<0.0001). Mice with defective anastomotic healing showed significantly higher uptake compared to non-defective (SNR: 37.37± 3.63 vs. 26.16± 3.635, P = 0.0369). White light endoscopy and FE allowed evaluation of anastomotic healing and visualization of mucosal MMPs in vivo. Using FE based detection of MMPs in the anastomosis, an overall positive predictive value of 71.4% and negative predictive value of 66.6% was calculated for detection of anastomotic leakage. During disturbed anastomotic healing increased expression of MMP-2/-9 was observed in the anastomotic tissue. Fluorescence endoscopy for detection of MMP-2/-9 during the healing process might be a promising tool for early identification of anastomotic leakage.

Design and Characterisation of Metallic Glassy Alloys of High Neutron Shielding Capability

NASA Astrophysics Data System (ADS)

Khong, J. C.; Daisenberger, D.; Burca, G.; Kockelmann, W.; Tremsin, A. S.; Mi, J.

2016-11-01

This paper reports the design, making and characterisation of a series of Fe-based bulk metallic glass alloys with the aim of achieving the combined properties of high neutron absorption capability and sufficient glass forming ability. Synchrotron X-ray diffraction and pair distribution function methods were used to characterise the crystalline or amorphous states of the samples. Neutron transmission and macroscopic attenuation coefficients of the designed alloys were measured using energy resolved neutron imaging method and the very recently developed microchannel plate detector. The study found that the newly designed alloy (Fe48Cr15Mo14C15B6Gd2 with a glass forming ability of Ø5.8 mm) has the highest neutron absorption capability among all Fe-based bulk metallic glasses so far reported. It is a promising material for neutron shielding applications.

Design and Characterisation of Metallic Glassy Alloys of High Neutron Shielding Capability.

PubMed

Khong, J C; Daisenberger, D; Burca, G; Kockelmann, W; Tremsin, A S; Mi, J

2016-11-16

This paper reports the design, making and characterisation of a series of Fe-based bulk metallic glass alloys with the aim of achieving the combined properties of high neutron absorption capability and sufficient glass forming ability. Synchrotron X-ray diffraction and pair distribution function methods were used to characterise the crystalline or amorphous states of the samples. Neutron transmission and macroscopic attenuation coefficients of the designed alloys were measured using energy resolved neutron imaging method and the very recently developed microchannel plate detector. The study found that the newly designed alloy (Fe 48 Cr 15 Mo 14 C 15 B 6 Gd 2 with a glass forming ability of Ø5.8 mm) has the highest neutron absorption capability among all Fe-based bulk metallic glasses so far reported. It is a promising material for neutron shielding applications.

Macroscopic modeling of heat and water vapor transfer with phase change in dry snow based on an upscaling method: Influence of air convection

NASA Astrophysics Data System (ADS)

Calonne, N.; Geindreau, C.; Flin, F.

2015-12-01

At the microscopic scale, i.e., pore scale, dry snow metamorphism is mainly driven by the heat and water vapor transfer and the sublimation-deposition process at the ice-air interface. Up to now, the description of these phenomena at the macroscopic scale, i.e., snow layer scale, in the snowpack models has been proposed in a phenomenological way. Here we used an upscaling method, namely, the homogenization of multiple-scale expansions, to derive theoretically the macroscopic equivalent modeling of heat and vapor transfer through a snow layer from the physics at the pore scale. The physical phenomena under consideration are steady state air flow, heat transfer by conduction and convection, water vapor transfer by diffusion and convection, and phase change (sublimation and deposition). We derived three different macroscopic models depending on the intensity of the air flow considered at the pore scale, i.e., on the order of magnitude of the pore Reynolds number and the Péclet numbers: (A) pure diffusion, (B) diffusion and moderate convection (Darcy's law), and (C) strong convection (nonlinear flow). The formulation of the models includes the exact expression of the macroscopic properties (effective thermal conductivity, effective vapor diffusion coefficient, and intrinsic permeability) and of the macroscopic source terms of heat and vapor arising from the phase change at the pore scale. Such definitions can be used to compute macroscopic snow properties from 3-D descriptions of snow microstructures. Finally, we illustrated the precision and the robustness of the proposed macroscopic models through 2-D numerical simulations.

Comparison of Heavy-Duty Scuffing Behavior between Chromium-Based Ceramic Composite and Nickel-Chromium-Molybdenum-Coated Ring Sliding against Cast Iron Liner under Starvation

PubMed Central

Shen, Yan; Yu, Baihong; Lv, Yutao; Li, Bin

2017-01-01

A running-in and starved lubrication experiment is designed to investigate the heavy-duty scuffing behavior of piston ring coatings against cast iron (Fe) cylinder liner using the piston ring reciprocating liner test rig. The scuffing resistance of the piston ring with the chromium-based ceramic composite coating (CKS), and that with the thermally sprayed nickel-chromium-molybdenum coating (NCM) is compared at different nominal pressures (40~100 MPa) and temperatures (180~250 °C). With the failure time as a criterion, the rank order is as follows: NCM/Fe > CKS/Fe. Before the scoring occurs at the interface of the piston ring and cylinder liner (PRCL), the cast iron liner enters into a “polish wear” stage, and iron-based adhesive materials begin to form on the piston ring surface. With the macroscopic adhesion formation, the plastic shearing cycle causes surface damages mainly due to abrasive effects for the CKS/Fe pairs and adhesive effects for the NCM/Fe pairs. PMID:29036911

A Study of Defect Behavior in Almandine Garnet

NASA Astrophysics Data System (ADS)

Geiger, C. A.; Brearley, A. J.; Dachs, E.; Tipplet, G.; Rossman, G. R.

2016-12-01

Transport and diffusion in crystals are controlled by defects. However, a good understanding of the defect types in many silicates, including garnet, is not at hand. We undertook a study on synthetic almandine, ideal end-member Fe3Al2Si3O12, to better understand its precise chemical and physical properties and defect behavior. Crystals were synthesized at high pressures and temperatures under different fO2 conditions using various starting materials with H2O and without. The almandine obtained came in polycrystalline and single-crystal form. The synthetic reaction products and crystals were carefully characterized using X-ray powder diffraction, electron microprobe and TEM analysis and with 57Fe Mössbauer, UV/VIS single-crystal absorption and IR single-crystal spectroscopy. Various possible intrinsic defects, such as the Frenkel, Schottky and site-disorder types, along with Fe3+, in both synthetic and natural almandine crystals, were analyzed based on model defects expressed in Kröger-Vink notation. Certain types of minor microscopic- to macroscopic-sized precipitation or exsolution phases, including some that are nanosized, that are observed in synthetic almandine (e.g., magnetite), as well as in more compositionally complex natural crystals (e.g., magnetite, rutile, ilmenite), may result from defect reactions. An explanation for their origin through minor amounts of defects in garnet has certain advantages over other models that have been put forth in the literature that assume strict garnet stoichiometry for their formation and/or open-system atomic transport over relatively long length scales. Physical properties, including magnetic, electrical conductivity and diffusion behavior, as well as the color, of almandine are also analyzed in terms of various possible model defects. It is difficult, if not impossible, to synthesize stoichiometric end-member almandine, Fe3Al2Si3O12, in the laboratory, as small amounts of extrinsic OH- and/or Fe3+ defects, for example, are typically present depending on the synthesis route. The nature of possible nonstoichiometry in synthetic almandine and natural almandine-rich crystals is discussed and compared.

Micromagnetic modeling of the shielding properties of nanoscale ferromagnetic layers

NASA Astrophysics Data System (ADS)

Iskandarova, I. M.; Knizhnik, A. A.; Popkov, A. F.; Potapkin, B. V.; Stainer, Q.; Lombard, L.; Mackay, K.

2016-09-01

Ferromagnetic shields are widely used to concentrate magnetic fields in a target region of space. Such shields are also used in spintronic nanodevices such as magnetic random access memory and magnetic logic devices. However, the shielding properties of nanostructured shields can differ considerably from those of macroscopic samples. In this work, we investigate the shielding properties of nanostructured NiFe layers around a current line using a finite element micromagnetic model. We find that thin ferromagnetic layers demonstrate saturation of magnetization under an external magnetic field, which reduces the shielding efficiency. Moreover, we show that the shielding properties of nanoscale ferromagnetic layers strongly depend on the uniformity of the layer thickness. Magnetic anisotropy in ultrathin ferromagnetic layers can also influence their shielding efficiency. In addition, we show that domain walls in nanoscale ferromagnetic shields can induce large increases and decreases in the generated magnetic field. Therefore, ferromagnetic shields for spintronic nanodevices require careful design and precise fabrication.

Observational Evidence for Mixing and Dust Condensation in Core-Collapse Supernovae

NASA Technical Reports Server (NTRS)

Wooden, Diane; Young, Richard E. (Technical Monitor)

1997-01-01

Recent findings of isotopic anomalies of Ca-44 (the decay product of Ti-44) and the enhanced ratio of Si-28/Si-30 in SiC grains X, TiC subgrains, and graphite dust grains within primitive meteorites provides strong evidence that these presolar grains came from core-collapse supernovae. The chemical composition of the presolar grains requires macroscopic mixing of newly nucleo-synthesized elements from explosive silicon burning at the innermost zone of the ejects to higher velocities where C exists and where C/O > 1 in either the outer edge of the oxygen zone or in the He-C zone. To date, the only core-collapse supernova observed to form dust is the brightest supernova of the past four centuries, SN1987A in the Large Magellanic Cloud. Observations of SN1987A confirm large scale macroscopic mixing occurs in the explosions of massive stars. Rayleigh-Taylor instabilities macroscopically mix most of the ejects into regions which are still chemically homogeneous and which cool with different time scales. Only small clumps in the ejects are microscopically mixed. Observations show that dust condensed in the ejects of SN1987A after approx.500 days in the Fe-rich gas. Neither silicates nor SiC grains were seen in the dust emission spectrum of SN1987A. SN1987A, the Rosetta Stone of core-collapse supernovae, shows that while the mixing required to explain presolar grains occurs, the rapid cooling of the Fe zone and the sustained high temperatures of the O-Si, O-C, and He-C zones favor the formation of iron-rich rather than oxygen- or carbon-rich grains.

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

Li, D.F.; Zhang, X.M.; Gautier, E.

The morphology and crystallography of deformation-induced martensites formed during isothermal tensile tests in Fe-30Ni-0.34C and Fe-25Ni-0.66C alloys were investigated by means of optical, transmission electron and scanning electron microscopy. Transitions in morphology from thin plate to coupled plate, to lenticular coupled-plate martensite and from thin plate to lenticular to compact martensite have been observed with increasing deformation. Stress favors the growth of martensite when concurrent plastic strain allows accommodation of macroscopic transformation strains and the change of the Bain strain accommodation mechanism. Mobile dislocations and emission dislocations are directly related to the change of the Bain strain accommodation mechanism frommore » twinning to slip.« less

Doping dependence of the anisotropic quasiparticle interference in NaFe(1-x)Co(x)As iron-based superconductors.

PubMed

Cai, Peng; Ruan, Wei; Zhou, Xiaodong; Ye, Cun; Wang, Aifeng; Chen, Xianhui; Lee, Dung-Hai; Wang, Yayu

2014-03-28

We use scanning tunneling microscopy to investigate the doping dependence of quasiparticle interference (QPI) in NaFe1-xCoxAs iron-based superconductors. The goal is to study the relation between nematic fluctuations and Cooper pairing. In the parent and underdoped compounds, where fourfold rotational symmetry is broken macroscopically, the QPI patterns reveal strong rotational anisotropy. At optimal doping, however, the QPI patterns are always fourfold symmetric. We argue this implies small nematic susceptibility and, hence, insignificant nematic fluctuation in optimally doped iron pnictides. Since TC is the highest this suggests nematic fluctuation is not a prerequistite for strong Cooper pairing.

Atom exchange between aqueous Fe(II) and structural Fe in clay minerals.

PubMed

Neumann, Anke; Wu, Lingling; Li, Weiqiang; Beard, Brian L; Johnson, Clark M; Rosso, Kevin M; Frierdich, Andrew J; Scherer, Michelle M

2015-03-03

Due to their stability toward reductive dissolution, Fe-bearing clay minerals are viewed as a renewable source of Fe redox activity in diverse environments. Recent findings of interfacial electron transfer between aqueous Fe(II) and structural Fe in clay minerals and electron conduction in octahedral sheets of nontronite, however, raise the question whether Fe interaction with clay minerals is more dynamic than previously thought. Here, we use an enriched isotope tracer approach to simultaneously trace Fe atom movement from the aqueous phase to the solid ((57)Fe) and from the solid into the aqueous phase ((56)Fe). Over 6 months, we observed a significant decrease in aqueous (57)Fe isotope fraction, with a fast initial decrease which slowed after 3 days and stabilized after about 50 days. For the aqueous (56)Fe isotope fraction, we observed a similar but opposite trend, indicating that Fe atom movement had occurred in both directions: from the aqueous phase into the solid and from the solid into aqueous phase. We calculated that 5-20% of structural Fe in clay minerals NAu-1, NAu-2, and SWa-1 exchanged with aqueous Fe(II), which significantly exceeds the Fe atom layer exposed directly to solution. Calculations based on electron-hopping rates in nontronite suggest that the bulk conduction mechanism previously demonstrated for hematite1 and suggested as an explanation for the significant Fe atom exchange observed in goethite2 may be a plausible mechanism for Fe atom exchange in Fe-bearing clay minerals. Our finding of 5-20% Fe atom exchange in clay minerals indicates that we need to rethink how Fe mobility affects the macroscopic properties of Fe-bearing phyllosilicates and its role in Fe biogeochemical cycling, as well as its use in a variety of engineered applications, such as landfill liners and nuclear repositories.

Strength anomaly in B2 FeAl single crystals

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

Yoshimi, K.; Hanada, S.; Yoo, M.H.

1994-12-31

Strength and deformation microstructure of B2 Fe-39 and 48%Al single crystals (composition given in atomic percent), which were fully annealed to remove frozen-in vacancies, have been investigated at temperatures between room temperature and 1073K. The hardness of as-homogenized Fe-48Al is higher than that of as-homogenized Fe-39Al while after additional annealing at 698K the hardness of Fe-48Al becomes lower than that of Fe-39Al. Fe-39Al single crystals slowly cooled after homogenizing at a high temperature were deformed in compression as a function of temperature and crystal orientation. A peak of yield strength appears around 0.5T{sub m} (T{sub m} = melting temperature). Themore » orientation dependence of the critical resolved shear stress does not obey Schmid`s law even at room temperature and is quite different from that of b.c.c. metals and B2 intermetallics at low temperatures. At the peak temperature slip transition from <111>-type to <001>-type is found to occur macroscopically and microscopically, while it is observed in TEM that some of the [111] dislocations decompose into [101] and [010] on the (1096I) plane below the peak temperature. The physical sources for the positive temperature dependence of yield stress of B2 FeAl are discussed based on the obtained results.« less

Design and Characterisation of Metallic Glassy Alloys of High Neutron Shielding Capability

PubMed Central

Khong, J. C.; Daisenberger, D.; Burca, G.; Kockelmann, W.; Tremsin, A. S.; Mi, J.

2016-01-01

This paper reports the design, making and characterisation of a series of Fe-based bulk metallic glass alloys with the aim of achieving the combined properties of high neutron absorption capability and sufficient glass forming ability. Synchrotron X-ray diffraction and pair distribution function methods were used to characterise the crystalline or amorphous states of the samples. Neutron transmission and macroscopic attenuation coefficients of the designed alloys were measured using energy resolved neutron imaging method and the very recently developed microchannel plate detector. The study found that the newly designed alloy (Fe48Cr15Mo14C15B6Gd2 with a glass forming ability of Ø5.8 mm) has the highest neutron absorption capability among all Fe-based bulk metallic glasses so far reported. It is a promising material for neutron shielding applications. PMID:27848991

A constitutive model and numerical simulation of sintering processes at macroscopic level

NASA Astrophysics Data System (ADS)

Wawrzyk, Krzysztof; Kowalczyk, Piotr; Nosewicz, Szymon; Rojek, Jerzy

2018-01-01

This paper presents modelling of both single and double-phase powder sintering processes at the macroscopic level. In particular, its constitutive formulation, numerical implementation and numerical tests are described. The macroscopic constitutive model is based on the assumption that the sintered material is a continuous medium. The parameters of the constitutive model for material under sintering are determined by simulation of sintering at the microscopic level using a micro-scale model. Numerical tests were carried out for a cylindrical specimen under hydrostatic and uniaxial pressure. Results of macroscopic analysis are compared against the microscopic model results. Moreover, numerical simulations are validated by comparison with experimental results. The simulations and preparation of the model are carried out by Abaqus FEA - a software for finite element analysis and computer-aided engineering. A mechanical model is defined by the user procedure "Vumat" which is developed by the first author in Fortran programming language. Modelling presented in the paper can be used to optimize and to better understand the process.

3D CNT macrostructure synthesis catalyzed by MgFe2O4 nanoparticles-A study of surface area and spinel inversion influence

NASA Astrophysics Data System (ADS)

Zampiva, Rúbia Young Sun; Kaufmann Junior, Claudir Gabriel; Pinto, Juliano Schorne; Panta, Priscila Chaves; Alves, Annelise Kopp; Bergmann, Carlos Pérez

2017-11-01

The MgFe2O4 spinel exhibits remarkable magnetic properties that open up numerous applications in biomedicine, the environment and catalysis. MgFe2O4 nanoparticles are excellent catalyst for carbon nanotube (CNT) production. In this work, we proposed to use MgFe2O4 nanopowder as a catalyst in the production of 3D macroscopic structures based on CNTs. The creation of these nanoengineered 3D architectures remains one of the most important challenges in nanotechnology. These systems have high potential as supercapacitors, catalytic electrodes, artificial muscles and in environmental applications. 3D macrostructures are formed due to an elevated density of CNTs. The quantity and quality of the CNTs are directly related to the catalyst properties. A heat treatment study was performed to produce the most effective catalyst. Factors such as superficial area, spinel inversion, crystallite size, degree of agglomeration and its correlation with van der Waals forces were examined. As result, the ideal catalyst properties for CNT production were determined and high-density 3D CNT macrostructures were produced successfully.

Characterization of the Fe-Co-1.5V soft ferromagnetic alloy processed by Laser Engineered Net Shaping (LENS)

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

Kustas, Andrew B.; Susan, Donald F.; Johnson, Kyle L.

Processing of the low workability Fe-Co-1.5V (Hiperco® equivalent) alloy is demonstrated using the Laser Engineered Net Shaping (LENS) metals additive manufacturing technique. As an innovative and highly localized solidification process, LENS is shown to overcome workability issues that arise during conventional thermomechanical processing, enabling the production of bulk, near net-shape forms of the Fe-Co alloy. Bulk LENS structures appeared to be ductile with no significant macroscopic defects. Atomic ordering was evaluated and significantly reduced in as-built LENS specimens relative to an annealed condition, tailorable through selection of processing parameters. Fine equiaxed grain structures were observed in as-built specimens following solidification,more » which then evolved toward a highly heterogeneous bimodal grain structure after annealing. The microstructure evolution in Fe-Co is discussed in the context of classical solidification theory and selective grain boundary pinning processes. In conclusion, magnetic properties were also assessed and shown to fall within the extremes of conventionally processed Hiperco® alloys.« less

Characterization of the Fe-Co-1.5V soft ferromagnetic alloy processed by Laser Engineered Net Shaping (LENS)

DOE PAGES

Kustas, Andrew B.; Susan, Donald F.; Johnson, Kyle L.; ...

2018-02-21

Processing of the low workability Fe-Co-1.5V (Hiperco® equivalent) alloy is demonstrated using the Laser Engineered Net Shaping (LENS) metals additive manufacturing technique. As an innovative and highly localized solidification process, LENS is shown to overcome workability issues that arise during conventional thermomechanical processing, enabling the production of bulk, near net-shape forms of the Fe-Co alloy. Bulk LENS structures appeared to be ductile with no significant macroscopic defects. Atomic ordering was evaluated and significantly reduced in as-built LENS specimens relative to an annealed condition, tailorable through selection of processing parameters. Fine equiaxed grain structures were observed in as-built specimens following solidification,more » which then evolved toward a highly heterogeneous bimodal grain structure after annealing. The microstructure evolution in Fe-Co is discussed in the context of classical solidification theory and selective grain boundary pinning processes. In conclusion, magnetic properties were also assessed and shown to fall within the extremes of conventionally processed Hiperco® alloys.« less

Variational coarse-graining procedure for dynamic homogenization

NASA Astrophysics Data System (ADS)

Liu, Chenchen; Reina, Celia

2017-07-01

We present a variational coarse-graining framework for heterogeneous media in the spirit of FE2 methods, that allows for a seamless transition from the traditional static scenario to dynamic loading conditions, while being applicable to general material behavior as well as to discrete or continuous representations of the material and its deformation, e.g., finite element discretizations or atomistic systems. The method automatically delivers the macroscopic equations of motion together with the generalization of Hill's averaging relations to the dynamic setting. These include the expression of the macroscopic stresses and linear momentum as a function of the microscopic fields. We further demonstrate with a proof of concept example, that the proposed theoretical framework can be used to perform multiscale numerical simulations. The results are compared with standard single-scale finite element simulations, showcasing the capability of the method to capture the dispersive nature of the medium in the range of frequencies permitted by the multiscale strategy.

Multilayer multiferroic composites with imperfect interfaces

NASA Astrophysics Data System (ADS)

Kuo, Hsin-Yi; Wu, Tien-Jung; Pan, Ernian

2018-07-01

We study the macroscopic behaviors of multilayered multiferroic composites with interface imperfections by a direct micromechanical approach. Both generalized interface stress type and generalized linear spring type imperfect interfaces are considered. Concise matrix expressions of the overall behaviors of the layered piezoelectric–piezomagnetic composite with contact imperfection are presented. The key step is to observe that the two types of imperfect interface conditions are equivalent to the perfect ones due to the laminated geometry. Numerical calculations are demonstrated for BaTiO3–CoFe2O4 multilayer media, and are shown in good agreement with the more involved interphase model. Furthermore, it is observed that the interface imperfection would reduce the magnitude of the magnetoelectric voltage coefficients as compared to the corresponding perfect interface case. This feature is opposite to that predicted and observed in the corresponding cylindrical composites.

Analysis of structural patterns in the brain with the complex network approach

NASA Astrophysics Data System (ADS)

Maksimenko, Vladimir A.; Makarov, Vladimir V.; Kharchenko, Alexander A.; Pavlov, Alexey N.; Khramova, Marina V.; Koronovskii, Alexey A.; Hramov, Alexander E.

2015-03-01

In this paper we study mechanisms of the phase synchronization in a model network of Van der Pol oscillators and in the neural network of the brain by consideration of macroscopic parameters of these networks. As the macroscopic characteristics of the model network we consider a summary signal produced by oscillators. Similar to the model simulations, we study EEG signals reflecting the macroscopic dynamics of neural network. We show that the appearance of the phase synchronization leads to an increased peak in the wavelet spectrum related to the dynamics of synchronized oscillators. The observed correlation between the phase relations of individual elements and the macroscopic characteristics of the whole network provides a way to detect phase synchronization in the neural networks in the cases of normal and pathological activity.

Metabolic design of macroscopic bioreaction models: application to Chinese hamster ovary cells.

PubMed

Provost, A; Bastin, G; Agathos, S N; Schneider, Y-J

2006-12-01

The aim of this paper is to present a systematic methodology to design macroscopic bioreaction models for cell cultures based upon metabolic networks. The cell culture is seen as a succession of phases. During each phase, a metabolic network represents the set of reactions occurring in the cell. Then, through the use of the elementary flux modes, these metabolic networks are used to derive macroscopic bioreactions linking the extracellular substrates and products. On this basis, as many separate models are obtained as there are phases. Then, a complete model is obtained by smoothly switching from model to model. This is illustrated with batch cultures of Chinese hamster ovary cells.

Computational prediction of the refinement of oxide agglomerates in a physical conditioning process for molten aluminium alloy

NASA Astrophysics Data System (ADS)

Tong, M.; Jagarlapudi, S. C.; Patel, J. B.; Stone, I. C.; Fan, Z.; Browne, D. J.

2015-06-01

Physically conditioning molten scrap aluminium alloys using high shear processing (HSP) was recently found to be a promising technology for purification of contaminated alloys. HSP refines the solid oxide agglomerates in molten alloys, so that they can act as sites for the nucleation of Fe-rich intermetallic phases which can subsequently be removed by the downstream de-drossing process. In this paper, a computational modelling for predicting the evolution of size of oxide clusters during HSP is presented. We used CFD to predict the macroscopic flow features of the melt, and the resultant field predictions of temperature and melt shear rate were transferred to a population balance model (PBM) as its key inputs. The PBM is a macroscopic model that formulates the microscopic agglomeration and breakage of a population of a dispersed phase. Although it has been widely used to study conventional deoxidation of liquid metal, this is the first time that PBM has been used to simulate the melt conditioning process within a rotor/stator HSP device. We employed a method which discretizes the continuous profile of size of the dispersed phase into a collection of discrete bins of size, to solve the governing population balance equation for the size of agglomerates. A finite volume method was used to solve the continuity equation, the energy equation and the momentum equation. The overall computation was implemented mainly using the FLUENT module of ANSYS. The simulations showed that there is a relatively high melt shear rate between the stator and sweeping tips of the rotor blades. This high shear rate leads directly to significant fragmentation of the initially large oxide aggregates. Because the process of agglomeration is significantly slower than the breakage processes at the beginning of HSP, the mean size of oxide clusters decreases very rapidly. As the process of agglomeration gradually balances the process of breakage, the mean size of oxide clusters converges to a steady value. The model enables formulation of the quantitative relationship between the macroscopic flow features of liquid metal and the change of size of dispersed oxide clusters, during HSP. It predicted the variation in size of the dispersed phased with operational parameters (including the geometry and, particularly, the speed of the rotor), which is of direct use to experimentalists optimising the design of the HSP device and its implementation.

Calibration of steady-state car-following models using macroscopic loop detector data.

DOT National Transportation Integrated Search

2010-05-01

The paper develops procedures for calibrating the steady-state component of various car following models using : macroscopic loop detector data. The calibration procedures are developed for a number of commercially available : microscopic traffic sim...

Amplification of intrinsic fluctuations by the Lorenz equations

NASA Astrophysics Data System (ADS)

Fox, Ronald F.; Elston, T. C.

1993-07-01

Macroscopic systems (e.g., hydrodynamics, chemical reactions, electrical circuits, etc.) manifest intrinsic fluctuations of molecular and thermal origin. When the macroscopic dynamics is deterministically chaotic, the intrinsic fluctuations may become amplified by several orders of magnitude. Numerical studies of this phenomenon are presented in detail for the Lorenz model. Amplification to macroscopic scales is exhibited, and quantitative methods (binning and a difference-norm) are presented for measuring macroscopically subliminal amplification effects. In order to test the quality of the numerical results, noise induced chaos is studied around a deterministically nonchaotic state, where the scaling law relating the Lyapunov exponent to noise strength obtained for maps is confirmed for the Lorenz model, a system of ordinary differential equations.

Modelling of electronic excitation and radiation in the Direct Simulation Monte Carlo Macroscopic Chemistry Method

NASA Astrophysics Data System (ADS)

Goldsworthy, M. J.

2012-10-01

One of the most useful tools for modelling rarefied hypersonic flows is the Direct Simulation Monte Carlo (DSMC) method. Simulator particle movement and collision calculations are combined with statistical procedures to model thermal non-equilibrium flow-fields described by the Boltzmann equation. The Macroscopic Chemistry Method for DSMC simulations was developed to simplify the inclusion of complex thermal non-equilibrium chemistry. The macroscopic approach uses statistical information which is calculated during the DSMC solution process in the modelling procedures. Here it is shown how inclusion of macroscopic information in models of chemical kinetics, electronic excitation, ionization, and radiation can enhance the capabilities of DSMC to model flow-fields where a range of physical processes occur. The approach is applied to the modelling of a 6.4 km/s nitrogen shock wave and results are compared with those from existing shock-tube experiments and continuum calculations. Reasonable agreement between the methods is obtained. The quality of the comparison is highly dependent on the set of vibrational relaxation and chemical kinetic parameters employed.

Antidot patterned single and bilayer thin films based on ferrimagnetic Tb-Co alloy with perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Kulesh, N. A.; Vázquez, M.; Lepalovskij, V. N.; Vas'kovskiy, V. O.

2018-02-01

Hysteresis properties and magnetization reversal in TbCo(30 nm) and FeNi(10 nm)/TbCo(30 nm) films with nanoscale antidot lattices are investigated to test the effect of nanoholes on the perpendicular anisotropy in the TbCo layer and the induced exchange bias in the FeNi layer. The antidots are introduced by depositing the films on top of hexagonally ordered porous anodic alumina substrates with pore diameter and interpore distance fixed to 75 nm and 105 nm, respectively. The analysis of combined vibrating sample magnetometry, Kerr microscopy and magnetic force microscopy imaging measurements has allowed us to link macroscopic and local magnetization reversal processes. For magnetically hard TbCo films, we demonstrate the tunability of magnetic anisotropy and coercive field (i.e., it increases from 0.2 T for the continuous film to 0.5 T for the antidot film). For the antidot FeNi/TbCo film, magnetization of FeNi is confirmed to be in plane. Although an exchange bias has been locally detected in the FeNi layer, the integrated hysteresis loop has increased coercivity and zero shift along the field axis due to the significantly decreased magnetic anisotropy of TbCo layer.

Mechanical behaviour of a fibrous scaffold for ligament tissue engineering: finite elements analysis vs. X-ray tomography imaging.

PubMed

Laurent, Cédric P; Latil, Pierre; Durville, Damien; Rahouadj, Rachid; Geindreau, Christian; Orgéas, Laurent; Ganghoffer, Jean-François

2014-12-01

The use of biodegradable scaffolds seeded with cells in order to regenerate functional tissue-engineered substitutes offers interesting alternative to common medical approaches for ligament repair. Particularly, finite element (FE) method enables the ability to predict and optimise both the macroscopic behaviour of these scaffolds and the local mechanic signals that control the cell activity. In this study, we investigate the ability of a dedicated FE code to predict the geometrical evolution of a new braided and biodegradable polymer scaffold for ligament tissue engineering by comparing scaffold geometries issued from FE simulations and from X-ray tomographic imaging during a tensile test. Moreover, we compare two types of FE simulations the initial geometries of which are issued either from X-ray imaging or from a computed idealised configuration. We report that the dedicated FE simulations from an idealised reference configuration can be reasonably used in the future to predict the global and local mechanical behaviour of the braided scaffold. A valuable and original dialog between the fields of experimental and numerical characterisation of such fibrous media is thus achieved. In the future, this approach should enable to improve accurate characterisation of local and global behaviour of tissue-engineering scaffolds. Copyright © 2014 Elsevier Ltd. All rights reserved.

Local Magnetism in Strongly Correlated Electron Systems with Orbital Degrees of Freedom

NASA Astrophysics Data System (ADS)

Ducatman, Samuel Charles

The central aim of my research is to explain the connection between the macroscopic behavior and the microscopic physics of strongly correlated electron systems with orbital degrees of freedom through the use of effective models. My dissertation focuses on the sub-class of these materials where electrons appear to be localized by interactions, and magnetic ions have well measured magnetic moments. This suggests that we can capture the low-energy physics of the material by employing a minimal model featuring localized spins which interact with each other through exchange couplings. I describe Fe1+y Te and beta-Li2IrO3 with effective models primarily focusing on the spins of the magnetic ions, in this case Fe and Ir, respectively. The goal with both materials is to gain insight and make predictions for experimentalists. In chapter 2, I focus on Fe1+yTe. I describe why we believe the magnetic ground state of this material, with an observed Bragg peak at Q +/- pi/2, pi/2), can be described by a Heisenberg model with 1st, 2nd, and 3rd neighbor interactions. I present two possible ground states of this model in the small J1 limit, the bicollinear and plaquette states. In order to predict which ground state the model prefers, I calculate the spin wave spectrum with 1/S corrections, and I find the model naturally selects the "plaquette state." I give a brief description of the ways this result could be tested using experimental techniques such as polarized neutron scattering. In chapter 3, I extend the model used in chapter 2. This is necessary because the Heisenberg model we employed cannot explain why Fe1+yTe undergoes a phase transition as y is increased. We add an additional elements to our calculation; we assume that electrons in some of the Fe 3D orbitals have selectively localized while others remain itinerant. We write a new Hamiltonian, where localized moments acquire a new long-range RKKY-like interaction from interactions with the itinerant electrons. We are able to reproduce the phase diagram found from experimentalists, and make predictions about how Fe1+y Te could potentially be driven into a "stripe" magnetic ground state. In chapter 4, I examine another strongly correlated material, beta-Li 2IrO3, which exhibits Kitaev physics. I begin with a minimal model employing nearest neighbor isotropic and anisotropic exchange couplings between neighboring Iridium ions. I calculate the phase diagram, and find two states. I characterize both states in terms of spins along the zigzag chains of the hyperhoneycomb lattice, and calculate linear spin waves for both states. I find that, besides for special points in our phase diagram, the excitations are gapped. As the spectrum has many branches, I calculate the dynamic structure factor to find which branches of the spin wave spectrum have the highest intensity. It will be interesting to compare my dynamic structure factor results to single crystal inelastic neutron scattering, which to this point has not been performed for beta-Li2IrO3.

Two level approach to safety planning incorporating the Highway Safety Manual (HSM) network screening : [summary].

DOT National Transportation Integrated Search

2014-04-01

In this project, University of Central Florida researchers combined two types of safety analysis, microscopic and macroscopic, to overcome their limitations. Microscopic models focus on traffic flows and related parameters. Macroscopic models are bas...

Macroscopic modeling for heat and water vapor transfer in dry snow by homogenization.

PubMed

Calonne, Neige; Geindreau, Christian; Flin, Frédéric

2014-11-26

Dry snow metamorphism, involved in several topics related to cryospheric sciences, is mainly linked to heat and water vapor transfers through snow including sublimation and deposition at the ice-pore interface. In this paper, the macroscopic equivalent modeling of heat and water vapor transfers through a snow layer was derived from the physics at the pore scale using the homogenization of multiple scale expansions. The microscopic phenomena under consideration are heat conduction, vapor diffusion, sublimation, and deposition. The obtained macroscopic equivalent model is described by two coupled transient diffusion equations including a source term arising from phase change at the pore scale. By dimensional analysis, it was shown that the influence of such source terms on the overall transfers can generally not be neglected, except typically under small temperature gradients. The precision and the robustness of the proposed macroscopic modeling were illustrated through 2D numerical simulations. Finally, the effective vapor diffusion tensor arising in the macroscopic modeling was computed on 3D images of snow. The self-consistent formula offers a good estimate of the effective diffusion coefficient with respect to the snow density, within an average relative error of 10%. Our results confirm recent work that the effective vapor diffusion is not enhanced in snow.

A quantitative link between microplastic instability and macroscopic deformation behaviors in metallic glasses

NASA Astrophysics Data System (ADS)

Wu, Y.; Chen, G. L.; Hui, X. D.; Liu, C. T.; Lin, Y.; Shang, X. C.; Lu, Z. P.

2009-10-01

Based on mechanical instability of individual shear transformation zones (STZs), a quantitative link between the microplastic instability and macroscopic deformation behavior of metallic glasses was proposed. Our analysis confirms that macroscopic metallic glasses comprise a statistical distribution of STZ embryos with distributed values of activation energy, and the microplastic instability of all the individual STZs dictates the macroscopic deformation behavior of amorphous solids. The statistical model presented in this paper can successfully reproduce the macroscopic stress-strain curves determined experimentally and readily be used to predict strain-rate effects on the macroscopic responses with the availability of the material parameters at a certain strain rate, which offer new insights into understanding the actual deformation mechanism in amorphous solids.

[A microstructural approach to fatigue crack processes in poly crystalline BCC materials]. Progress report

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

Gerberich, W.W.

1992-12-31

Objective was to study fatigue where a combination of low temperature and cyclic loading produced cyclic cleavage in bcc Fe-base systems. Both dislocation dynamics and quasi-statics of crack growth were probed. This document reviews progress over the past 6 years: hydrogen embrittlement and cleavage, computations (stress near crack tip), dislocation emission from grain boundaries, fracture process zones, and understanding brittle fracture at the atomistic/dislocation scales and at the microscopic/macroscopic scale.

Subsolidus and melting phase relations in the system CaCO3-MgCO3-FeCO3 at 35 kbar: from experiments to predictions based on a thermodynamic model

NASA Astrophysics Data System (ADS)

Franzolin, E.; Schmidt, M. W.; Poli, S.

2009-12-01

At convergent margins volatile components, most notably CO2 and H2O, stored in oceanic sediments and MORB are recycled into the mantle. Mafic protoliths become enriched in CO2 and H2O, stored in carbonates and hydrous phases, by hydrothermal alteration. As carbonates are more refractory than hydrous phases, CO2 is more likely to survive in the oceanic lithosphere beyond sub-arc depths [1,2]. Despite the main role of carbonates on cycling crustal and atmospheric CO2 into the mantle, experimental data within the system CaCO3-MgCO3-FeCO3 are scarce. To bridge this gap, piston-cylinder experiments have been performed at 35 kbar, 900-1100 °C to determine subsolidus relations, and up to 1300 °C to constrain melting relations. Pure synthetic calcite, natural magnesite and synthetic siderite have been mixed in different proportions in double Pt-C capsules, to avoid major siderite oxidation. Subsolidus experiments reveal the presence of two miscibility gaps at 900 °C: the solvus dolomite-calcite, which closes at XMgCO3 ~ 0.7, and the solvus dolomite-magnesite, which ranges to the Fe-side of the ternary. Increasing the temperature, the two miscibility gaps became narrower until complete solid solutions between CaCO3-Ca0.5Mg0.5CO3 at 1100 °C, and between CaCO3-FeCO3 at 1000 °C, are observed. The system is characterized by strong compositional asymmetry, thermodynamically described with a van Laar macroscopic formalism [3], and by R-3<=>R-3c phase transitions due to cation disordering, treated by redefining the compositional space with an independent set of end-members that describe both composition and states of ordering. The result is a solid solution model able to reproduce both the phase relations experimentally observed at 35 kbar and those experimentally determined and naturally observed at lower pressure [4-5]. Our model can be reliable extended to pressures of the breakdown of dolomite, e.g. 5-6 GPa, 600-1000 °C. Melting experiments carried out at 1250 °C along the join CaCO3-MgCO3, yield an eutectic at a slightly lower temperature at XCa ~ 0.7; the eutectic temperature decreases with the Fe content in the bulk. The 2-phase field calcite (XCa~0.75) + liquid, broadens with the increase of XFe in the system. Along the join CaMg(CO3)2-CaFe(CO3)2, melting takes place at XFe ~ 0.2, producing Ca enriched melt + Mg enriched dolomite. The new subsolidus and melting data and the ternary thermodynamic solid solution model, have been combined to predict the fate of FeO and CO2 rich systems (i.e. BIF associated with Fe-shale, high-Fe altered basalts and Fe-enriched carbonated metapelites), recycled back into the mantle during the history of the Earth. [1] Kerrick&Connolly, EPSL, 2001, 189, 19-29. [2] Poli et al., EPSL, 2009, 278, 350-360. [3] Holland&Powell, Contr. Min. Pet., 2003, 145, 492-501. [4] Goldsmith et al., Journ. of Geol., 1962, 70, 659-688. [5] Rosenberg, Am. Min., 1967, 52, 787-796.

State-space based analysis and forecasting of macroscopic road safety trends in Greece.

PubMed

Antoniou, Constantinos; Yannis, George

2013-11-01

In this paper, macroscopic road safety trends in Greece are analyzed using state-space models and data for 52 years (1960-2011). Seemingly unrelated time series equations (SUTSE) models are developed first, followed by richer latent risk time-series (LRT) models. As reliable estimates of vehicle-kilometers are not available for Greece, the number of vehicles in circulation is used as a proxy to the exposure. Alternative considered models are presented and discussed, including diagnostics for the assessment of their model quality and recommendations for further enrichment of this model. Important interventions were incorporated in the models developed (1986 financial crisis, 1991 old-car exchange scheme, 1996 new road fatality definition) and found statistically significant. Furthermore, the forecasting results using data up to 2008 were compared with final actual data (2009-2011) indicating that the models perform properly, even in unusual situations, like the current strong financial crisis in Greece. Forecasting results up to 2020 are also presented and compared with the forecasts of a model that explicitly considers the currently on-going recession. Modeling the recession, and assuming that it will end by 2013, results in more reasonable estimates of risk and vehicle-kilometers for the 2020 horizon. This research demonstrates the benefits of using advanced state-space modeling techniques for modeling macroscopic road safety trends, such as allowing the explicit modeling of interventions. The challenges associated with the application of such state-of-the-art models for macroscopic phenomena, such as traffic fatalities in a region or country, are also highlighted. Furthermore, it is demonstrated that it is possible to apply such complex models using the relatively short time-series that are available in macroscopic road safety analysis. Copyright © 2013 Elsevier Ltd. All rights reserved.

Analog modeling of Worm-Like Chain molecules using macroscopic beads-on-a-string.

PubMed

Tricard, Simon; Feinstein, Efraim; Shepherd, Robert F; Reches, Meital; Snyder, Phillip W; Bandarage, Dileni C; Prentiss, Mara; Whitesides, George M

2012-07-07

This paper describes an empirical model of polymer dynamics, based on the agitation of millimeter-sized polymeric beads. Although the interactions between the particles in the macroscopic model and those between the monomers of molecular-scale polymers are fundamentally different, both systems follow the Worm-Like Chain theory.

Macroscopic and microscopic biodistribution of intravenously administered iron oxide nanoparticles

NASA Astrophysics Data System (ADS)

Misra, Adwiteeya; Petryk, Alicia A.; Strawbridge, Rendall R.; Hoopes, P. Jack

2015-03-01

Iron oxide nanoparticles (IONP) are being developed for use as a cancer treatment. They have demonstrated efficacy when used either as a monotherapy or in conjunction with conventional chemotherapy and radiation. The success of IONP as a therapeutic tool depends on the delivery of a safe and controlled cytotoxic thermal dose to tumor tissue following activation with an alternating magnetic field (AMF). Prior to clinical approval, knowledge of IONP toxicity, biodistribution and physiological clearance is essential. This preliminary time-course study determines the acute toxicity and biodistribution of 110 nm dextran-coated IONP (iron) in mice, 7 days post systemic, at doses of 0.4, 0.6, and 1.0 mg Fe/ g mouse bodyweight. Acute toxicity, manifested as changes in the behavior of mice, was only observed temporarily at 1.0 mg Fe/ g mouse bodyweight, the highest dose administered. Regardless of dose, mass spectrometry and histological analysis demonstrated over 3 mg Fe/g tissue in organs within the reticuloendotheilial system (i.e. liver, spleen, and lymph nodes). Other organs (brain, heart, lungs, and kidney) had less than 0.5 mg Fe/g tissue with iron predominantly confined to the organ vasculature.

General multi-group macroscopic modeling for thermo-chemical non-equilibrium gas mixtures.

PubMed

Liu, Yen; Panesi, Marco; Sahai, Amal; Vinokur, Marcel

2015-04-07

This paper opens a new door to macroscopic modeling for thermal and chemical non-equilibrium. In a game-changing approach, we discard conventional theories and practices stemming from the separation of internal energy modes and the Landau-Teller relaxation equation. Instead, we solve the fundamental microscopic equations in their moment forms but seek only optimum representations for the microscopic state distribution function that provides converged and time accurate solutions for certain macroscopic quantities at all times. The modeling makes no ad hoc assumptions or simplifications at the microscopic level and includes all possible collisional and radiative processes; it therefore retains all non-equilibrium fluid physics. We formulate the thermal and chemical non-equilibrium macroscopic equations and rate coefficients in a coupled and unified fashion for gases undergoing completely general transitions. All collisional partners can have internal structures and can change their internal energy states after transitions. The model is based on the reconstruction of the state distribution function. The internal energy space is subdivided into multiple groups in order to better describe non-equilibrium state distributions. The logarithm of the distribution function in each group is expressed as a power series in internal energy based on the maximum entropy principle. The method of weighted residuals is applied to the microscopic equations to obtain macroscopic moment equations and rate coefficients succinctly to any order. The model's accuracy depends only on the assumed expression of the state distribution function and the number of groups used and can be self-checked for accuracy and convergence. We show that the macroscopic internal energy transfer, similar to mass and momentum transfers, occurs through nonlinear collisional processes and is not a simple relaxation process described by, e.g., the Landau-Teller equation. Unlike the classical vibrational energy relaxation model, which can only be applied to molecules, the new model is applicable to atoms, molecules, ions, and their mixtures. Numerical examples and model validations are carried out with two gas mixtures using the maximum entropy linear model: one mixture consists of nitrogen molecules undergoing internal excitation and dissociation and the other consists of nitrogen atoms undergoing internal excitation and ionization. Results show that the original hundreds to thousands of microscopic equations can be reduced to two macroscopic equations with almost perfect agreement for the total number density and total internal energy using only one or two groups. We also obtain good prediction of the microscopic state populations using 5-10 groups in the macroscopic equations.

Averaging problem in general relativity, macroscopic gravity and using Einstein's equations in cosmology.

NASA Astrophysics Data System (ADS)

Zalaletdinov, R. M.

1998-04-01

The averaging problem in general relativity is briefly discussed. A new setting of the problem as that of macroscopic description of gravitation is proposed. A covariant space-time averaging procedure is described. The structure of the geometry of macroscopic space-time, which follows from averaging Cartan's structure equations, is described and the correlation tensors present in the theory are discussed. The macroscopic field equations (averaged Einstein's equations) derived in the framework of the approach are presented and their structure is analysed. The correspondence principle for macroscopic gravity is formulated and a definition of the stress-energy tensor for the macroscopic gravitational field is proposed. It is shown that the physical meaning of using Einstein's equations with a hydrodynamic stress-energy tensor in looking for cosmological models means neglecting all gravitational field correlations. The system of macroscopic gravity equations to be solved when the correlations are taken into consideration is given and described.

Ground testing of bioconvective variables such as morphological characterizations and mechanisms which regulate macroscopic patterns

NASA Technical Reports Server (NTRS)

Johnson, Adriel D.

1992-01-01

Conditions simulating low- and high-gravity, reveal changes in macroscopic pattern formation in selected microorganisms, but whether these structures are gravity dependent is not clear. Two theories have been identified in the fluid dynamics community which support macroscopic pattern formation. The first one is gravity dependent (fluid density models) where small concentrated regions of organisms sink unstably, and the second is gravity independent (wave reinforcement theory) where organisms align their movements in concert, such that either their swimming strokes beat in phase or their vortices entrain neighbors to follow parallel paths. Studies have shown that macroscopic pattern formation is consistent with the fluid density models for protozoa and algae and wave reinforcement hypothesis for caprine spermatozoa.

Macroscopic Modeling of In Vivo Drug Transport in Electroporated Tissue.

PubMed

Boyd, Bradley; Becker, Sid

2016-03-01

This study develops a macroscopic model of mass transport in electroporated biological tissue in order to predict the cellular drug uptake. The change in the macroscopic mass transport coefficient is related to the increase in electrical conductivity resulting from the applied electric field. Additionally, the model considers the influences of both irreversible electroporation (IRE) and the transient resealing of the cell membrane associated with reversible electroporation. Two case studies are conducted to illustrate the applicability of this model by comparing transport associated with two electrode arrangements: side-by-side arrangement and the clamp arrangement. The results show increased drug transmission to viable cells is possible using the clamp arrangement due to the more uniform electric field.

Fission properties of Po isotopes in different macroscopic-microscopic models

NASA Astrophysics Data System (ADS)

Bartel, J.; Pomorski, K.; Nerlo-Pomorska, B.; Schmitt, Ch

2015-11-01

Fission-barrier heights of nuclei in the Po isotopic chain are investigated in several macroscopic-microscopic models. Using the Yukawa-folded single-particle potential, the Lublin-Strasbourg drop (LSD) model, the Strutinsky shell-correction method to yield the shell corrections and the BCS theory for the pairing contributions, fission-barrier heights are calculated and found in quite good agreement with the experimental data. This turns out, however, to be only the case when the underlying macroscopic, liquid-drop (LD) type, theory is well chosen. Together with the LSD approach, different LD parametrizations proposed by Moretto et al are tested. Four deformation parameters describing respectively elongation, neck-formation, reflectional-asymmetric, and non-axiality of the nuclear shape thus defining the so called modified Funny Hills shape parametrization are used in the calculation. The present study clearly demonstrates that nuclear fission-barrier heights constitute a challenging and selective tool to discern between such different macroscopic approaches.

Spin Seebeck devices using local on-chip heating

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

Wu, Stephen M.; Fradin, Frank Y.; Hoffman, Jason

2015-05-07

A micro-patterned spin Seebeck device is fabricated using an on-chip heater. Current is driven through a Au heater layer electrically isolated from a bilayer consisting of Fe3O4 (insulating ferrimagnet) and a spin detector layer. It is shown that through this method it is possible to measure the longitudinal spin Seebeck effect (SSE) for small area magnetic devices, equivalent to traditional macroscopic SSE experiments. Using a lock-in detection technique, it is possible to more sensitively characterize both the SSE and the anomalous Nernst effect (ANE), as well as the inverse spin Hall effect in various spin detector materials. By using themore » spin detector layer as a thermometer, we can obtain a value for the temperature gradient across the device. These results are well matched to values obtained through electromagnetic/thermal modeling of the device structure and with large area spin Seebeck measurements.« less

Spin Seebeck devices using local on-chip heating

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

Wu, Stephen M., E-mail: swu@anl.gov; Fradin, Frank Y.; Hoffman, Jason

2015-05-07

A micro-patterned spin Seebeck device is fabricated using an on-chip heater. Current is driven through a Au heater layer electrically isolated from a bilayer consisting of Fe{sub 3}O{sub 4} (insulating ferrimagnet) and a spin detector layer. It is shown that through this method it is possible to measure the longitudinal spin Seebeck effect (SSE) for small area magnetic devices, equivalent to traditional macroscopic SSE experiments. Using a lock-in detection technique, it is possible to more sensitively characterize both the SSE and the anomalous Nernst effect (ANE), as well as the inverse spin Hall effect in various spin detector materials. Bymore » using the spin detector layer as a thermometer, we can obtain a value for the temperature gradient across the device. These results are well matched to values obtained through electromagnetic/thermal modeling of the device structure and with large area spin Seebeck measurements.« less

Coarse analysis of collective behaviors: Bifurcation analysis of the optimal velocity model for traffic jam formation

NASA Astrophysics Data System (ADS)

Miura, Yasunari; Sugiyama, Yuki

2017-12-01

We present a general method for analyzing macroscopic collective phenomena observed in many-body systems. For this purpose, we employ diffusion maps, which are one of the dimensionality-reduction techniques, and systematically define a few relevant coarse-grained variables for describing macroscopic phenomena. The time evolution of macroscopic behavior is described as a trajectory in the low-dimensional space constructed by these coarse variables. We apply this method to the analysis of the traffic model, called the optimal velocity model, and reveal a bifurcation structure, which features a transition to the emergence of a moving cluster as a traffic jam.

Causality as an emergent macroscopic phenomenon: The Lee-Wick O(N) model

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

Grinstein, Benjamin; O'Connell, Donal; Wise, Mark B.

2009-05-15

In quantum mechanics the deterministic property of classical physics is an emergent phenomenon appropriate only on macroscopic scales. Lee and Wick introduced Lorentz invariant quantum theories where causality is an emergent phenomenon appropriate for macroscopic time scales. In this paper we analyze a Lee-Wick version of the O(N) model. We argue that in the large-N limit this theory has a unitary and Lorentz invariant S matrix and is therefore free of paradoxes in scattering experiments. We discuss some of its acausal properties.

Quantitative research on microscopic deformation behavior of Ti-6Al-4V two-phase titanium alloy based on finite element method

NASA Astrophysics Data System (ADS)

Peng, Yan; Chen, Guoxing; Sun, Jianliang; Shi, Baodong

2018-04-01

The microscopic deformation of Ti-6Al-4V titanium alloy shows great inhomogeneity due to its duplex-microstructure that consists of two phases. In order to study the deformation behaviors of the constituent phases, the 2D FE model based on the realistic microstructure is established by MSC.Marc nonlinear FE software, and the tensile simulation is carried out. The simulated global stress-strain response is confirmed by the tensile testing result. Then the strain and stress distribution in the constituent phases and their evolution with the increase of the global strain are analyzed. The results show that the strain and stress partitioning between the two phases are considerable, most of the strain is concentrated in soft primary α phase, while hard transformed β matrix undertakes most of the stress. Under the global strain of 0.05, the deformation bands in the direction of 45° to the stretch direction and the local stress in primary α phase near to the interface between the two phases are observed, and they become more significant when the global strain increases to 0.1. The strain and stress concentration factors of the two phases are obviously different at different macroscopic deformation stages, but they almost tend to be stable finally.

Microscopic Simulation and Macroscopic Modeling for Thermal and Chemical Non-Equilibrium

NASA Technical Reports Server (NTRS)

Liu, Yen; Panesi, Marco; Vinokur, Marcel; Clarke, Peter

2013-01-01

This paper deals with the accurate microscopic simulation and macroscopic modeling of extreme non-equilibrium phenomena, such as encountered during hypersonic entry into a planetary atmosphere. The state-to-state microscopic equations involving internal excitation, de-excitation, dissociation, and recombination of nitrogen molecules due to collisions with nitrogen atoms are solved time-accurately. Strategies to increase the numerical efficiency are discussed. The problem is then modeled using a few macroscopic variables. The model is based on reconstructions of the state distribution function using the maximum entropy principle. The internal energy space is subdivided into multiple groups in order to better describe the non-equilibrium gases. The method of weighted residuals is applied to the microscopic equations to obtain macroscopic moment equations and rate coefficients. The modeling is completely physics-based, and its accuracy depends only on the assumed expression of the state distribution function and the number of groups used. The model makes no assumption at the microscopic level, and all possible collisional and radiative processes are allowed. The model is applicable to both atoms and molecules and their ions. Several limiting cases are presented to show that the model recovers the classical twotemperature models if all states are in one group and the model reduces to the microscopic equations if each group contains only one state. Numerical examples and model validations are carried out for both the uniform and linear distributions. Results show that the original over nine thousand microscopic equations can be reduced to 2 macroscopic equations using 1 to 5 groups with excellent agreement. The computer time is decreased from 18 hours to less than 1 second.

A density-functional study of the phase diagram of cementite-type (Fe,Mn)3C at absolute zero temperature.

PubMed

Von Appen, Jörg; Eck, Bernhard; Dronskowski, Richard

2010-11-15

The phase diagram of (Fe(1-x) Mn(x))(3)C has been investigated by means of density-functional theory (DFT) calculations at absolute zero temperature. The atomic distributions of the metal atoms are not random-like as previously proposed but we find three different, ordered regions within the phase range. The key role is played by the 8d metal site which forms, as a function of the composition, differing magnetic layers, and these dominate the physical properties. We calculated the magnetic moments, the volumes, the enthalpies of mixing and formation of 13 different compositions and explain the changes of the macroscopic properties with changes in the electronic and magnetic structures by means of bonding analyses using the Crystal Orbital Hamilton Population (COHP) technique. 2010 Wiley Periodicals, Inc.

Highly strain-sensitive magnetostrictive tunnel magnetoresistance junctions

NASA Astrophysics Data System (ADS)

Tavassolizadeh, Ali; Hayes, Patrick; Rott, Karsten; Reiss, Günter; Quandt, Eckhard; Meyners, Dirk

2015-06-01

Tunnel magnetoresistance (TMR) junctions with CoFeB/MgO/CoFeB layers are promising for strain sensing applications due to their high TMR effect and magnetostrictive sense layer (CoFeB). TMR junctions available even in submicron dimensions can serve as strain sensors for microelectromechanical systems devices. Upon stress application, the magnetization configuration of such junctions changes due to the inverse magnetostriction effect resulting in strain-sensitive tunnel resistance. Here, strain sensitivity of round-shaped junctions with diameters of 11.3 μm, 19.2 μm, 30.5 μm, and 41.8 μm were investigated on macroscopic cantilevers using a four-point bending apparatus. This investigation mainly focuses on changes in hard-axis TMR loops caused by the stress-induced anisotropy. A macrospin model is proposed, supported by micromagnetic simulations, which describes the complete rotation of the sense layer magnetization within TMR loops of junctions, exposed to high stress. Below 0.2‰ tensile strain, a representative junction with 30.5 μm diameter exhibits a very large gauge factor of 2150. For such high gauge factor a bias field H = - 3.2 kA / m is applied in an angle equal to 3 π / 2 toward the pinned magnetization of the reference layer. The strain sensitivity strongly depends on the bias field. Applying stress along π / 4 against the induced magnetocrystalline anisotropy, both compressive and tensile strain can be identified by a unique sensor. More importantly, a configuration with a gauge factor of 400 at zero bias field is developed which results in a straightforward and compact measuring setup.

Anomalous atomic displacement parameters and local dynamics in the Curie range of a Pb-free relaxor ferroelectric system (Bi1-xBax)(Fe1-xTix)O3(0.36 ≤ x ≤ 0.50)

NASA Astrophysics Data System (ADS)

Singh, Anar; Moriyoshi, Chikako; Kuroiwa, Yoshihiro; Pandey, Dhananjai

2018-04-01

We report here the relaxor ferroelectric (RFE) behaviour in a multiferroic solid solution system, (Bi1-xBax)(Fe1-xTix)O3, at a critical disorder level of xC ˜ 0.35 in BiFeO3 and 0.65 (i.e., 1-xC = 0.35) in BaTiO3 similar to the 1:2 ratio of Mg2+ and Nb5+ in the canonical RFE Pb(Mg1/3Nb2/3)O3. This Pb-free system, like canonical Pb-based RFEs, does not exhibit macroscopic symmetry breaking and shows only the signatures of ergodicity breaking at Vogel-Fulcher freezing temperature (TVF). The atomic displacement parameters (ADPs) of Fe3+/Ti4+ and O2-, obtained using high wave vector (Q) and high-resolution synchrotron x-ray diffraction data as a function of temperature, show anomalous diffuse peaks in the Curie range. It is shown that the diffuse peak in ADPs is due to softening of the vibrational frequencies of the B-O chain (B = Fe3+/Ti4+ and O = O2-) below the Burns temperature (TB) followed by hardening below the characteristic temperature (T'm), which corresponds to a peak in the dielectric permittivity (ɛ').

Hybrid Multiscale Finite Volume Method for Advection-Diffusion Equations Subject to Heterogeneous Reactive Boundary Conditions

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

Barajas-Solano, David A.; Tartakovsky, A. M.

2016-10-13

We present a hybrid scheme for the coupling of macro and microscale continuum models for reactive contaminant transport in fractured and porous media. The transport model considered is the advection-dispersion equation, subject to linear heterogeneous reactive boundary conditions. The Multiscale Finite Volume method (MsFV) is employed to define an approximation to the microscale concentration field defined in terms of macroscopic or \\emph{global} degrees of freedom, together with local interpolator and corrector functions capturing microscopic spatial variability. The macroscopic mass balance relations for the MsFV global degrees of freedom are coupled with the macroscopic model, resulting in a global problem for the simultaneous time-stepping of all macroscopic degrees of freedom throughout the domain. In order to perform the hybrid coupling, the micro and macroscale models are applied over overlapping subdomains of the simulation domain, with the overlap denoted as the handshake subdomainmore » $$\\Omega^{hs}$$, over which continuity of concentration and transport fluxes between models is enforced. Continuity of concentration is enforced by posing a restriction relation between models over $$\\Omega^{hs}$$. Continuity of fluxes is enforced by prolongating the macroscopic model fluxes across the boundary of $$\\Omega^{hs}$$ to microscopic resolution. The microscopic interpolator and corrector functions are solutions to local microscopic advection-diffusion problems decoupled from the global degrees of freedom and from each other by virtue of the MsFV decoupling ansatz. The error introduced by the decoupling ansatz is reduced iteratively by the preconditioned GMRES algorithm, with the hybrid MsFV operator serving as the preconditioner.« less

Pristine Basal- and Edge-Plane-Oriented Molybdenite MoS2 Exhibiting Highly Anisotropic Properties.

PubMed

Tan, Shu Min; Ambrosi, Adriano; Sofer, Zdenĕk; Huber, Štěpán; Sedmidubský, David; Pumera, Martin

2015-05-04

The layered structure of molybdenum disulfide (MoS2 ) is structurally similar to that of graphite, with individual sheets strongly covalently bonded within but held together through weak van der Waals interactions. This results in two distinct surfaces of MoS2 : basal and edge planes. The edge plane was theoretically predicted to be more electroactive than the basal plane, but evidence from direct experimental comparison is elusive. Herein, the first study comparing the two surfaces of MoS2 by using macroscopic crystals is presented. A careful investigation of the electrochemical properties of macroscopic MoS2 pristine crystals with precise control over the exposure of one plane surface, that is, basal plane or edge plane, was performed. These crystals were characterized thoroughly by AFM, Raman spectroscopy, X-ray photoelectron spectroscopy, voltammetry, digital simulation, and DFT calculations. In the Raman spectra, the basal and edge planes show anisotropy in the preferred excitation of E2g and A1g phonon modes, respectively. The edge plane exhibits a much larger heterogeneous electron transfer rate constant k(0) of 4.96×10(-5) and 1.1×10(-3)  cm s(-1) for [Fe(CN)6 ](3-/4-) and [Ru(NH3 )6 ](3+/2+) redox probes, respectively, compared to the basal plane, which yielded k(0) tending towards zero for [Fe(CN)6 ](3-/4-) and about 9.3×10(-4)  cm s(-1) for [Ru(NH3 )6 ](3+/2+) . The industrially important hydrogen evolution reaction follows the trend observed for [Fe(CN)6 ](3-/4-) in that the basal plane is basically inactive. The experimental comparison of the edge and basal planes of MoS2 crystals is supported by DFT calculations. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrical resistivity of liquid iron with high concentration of light element impurities

NASA Astrophysics Data System (ADS)

Wagle, F.; Steinle-Neumann, G.

2017-12-01

The Earth's outer core mainly consists of liquid iron, enriched with several weight percent of lighter elements, such as silicon, oxygen, sulfur or carbon. Electrical resistivities of alloys of this type determine the stability of the geodynamo. Both computational and experimental results show that resistivites of Fe-based alloys deviate significantly from values of pure Fe. Using optical conductivity values computed with the Kubo-Greenwood formalism for DFT-based molecular dynamics results, we analyze the high-P and T behavior of resitivities for Fe-alloys containing various concentrations of sulfur, oxygen and silicon. As the electron mean free path length in amorphous and liquid material becomes comparable to interatomic distances at high P and T, electron scattering is expected to be dominated by the short-range order, rather than T-dependent vibrational contributions, and we describe such correlations in our results. In analogy to macroscopic porous media, we further show that resistivity of a liquid metal-nonmetal alloy is determined to first order by the resistivity of the metallic matrix and the volume fraction of non-metallic impurities.

Fe behavior in iron-bearing phonolitic and pantelleritic melts and its significance for magma dynamics in the volcanic conduits

NASA Astrophysics Data System (ADS)

Borovkov, Nikita; Hess, Kai-Uwe; Fehr, Karl-Thomas; Cimarelli, Corrado; Dingwell, Donald Bruce

2014-05-01

The style of volcanic eruptions is determined entirely by dynamics of magma ascent in conduits. Physical properties of a silicate melt, particulary viscosity, are responsible for fragmentation processes, bubble growth and their ascent, which are in their turn related to explosivity of eruptions. Therefore, comprehension of the macroscopic properties of silicate melts is required for adequate conduit modelling. Considering eruptions of Mt. Vesuvius, Italy, we observe that eruption style varies from strombolian to plinean and sub-plinean which is related to the changes of melts viscosity in conduits. At Vesuvius the composition of volcanic deposits (III phase) is mainly phonolitic with 5 - 8 wt. % FeO. Fe changes the valence and coordination depending on oxidation state. The changing of iron coordination causes increasing or decreasing viscosity because of the presence of higher or lower amounts of Fe species coordinated with stronger covalence bonds. Mossbauer spectra of iron-bearing natural pantelleritic and phonolitic glasses were studied to get data on speciation and coordination state of iron. Mössbauer spectroscopy measures hyperfine interactions (isomer shift (IS)) and quadrupole splitting (QS)) at Fe atoms embedded in glass structure, which provide the amount of ferric and ferrous iron and their coordination state depending on Redox conditions. Based on these data, we have considered redox-viscosity relationships and also iron coordination effects on viscosity of both mentioned natural melt compositions. For glasses, due to short range order, the Mössbauer spectra were fitted using mathematical procedures based on functional analysis (extended Voight lineshape included in "Recoil" and "Mosslab" software). Mössbauer spectra are deconvoluted in two sites: ferrous iron (IS=0,79-1,00 mm/s; QS= 1,78-2,25 mm/s) and ferric iron (IS=0,26-0,50 mm/s; QS= 0,75-0,95 mm/s). For both sites we observe that IS and QS gradually decrease towards more oxidized conditions. From functional analysis of Mössbauer spectra this increasing is due to transformation of iron coordination: Fe2+ [5]-Fe2+ [4] and Fe3+ [5]-Fe3+ [4], depending on Redox conditions. XANES data helps us to prove coordination transformation of Fe clearly. This methods (Giuli et al., 2011) reveal that Fe3+ is always in tetrahedral coordination and Fe2+ is in the form of both [4] and [5] species. The presence of minor [5] or even [6] cannot be excluded. Combining Mössbauer and XANES methods, we can suggest that more reduced samples include more high coordinated Fe species. Under oxidized conditions Fe3+ tends to be [4] - coordinated completely and amount of Fe2+ [5] decreases. Viscosity for phonolitic and pantelleritic melts increases as well with more oxidized conditions, suggesting more polymerized structure. Under reduced conditions, low viscosity means that some higher coordinated Fe2+ and Fe3+ sites occur in structure and function as a depolymerizing factor. Therefore, in the presence of iron-bearing peralkaline melts, the prediction of an eruptive style requires knowledge of the dependence of viscosity on thermodynamic parameters as well as dependence on RedOx conditions, which are responsible for ferric and ferrous iron structural transformations.

On the effect of irradiation-induced resolution in modelling fission gas release in UO2 LWR fuel

NASA Astrophysics Data System (ADS)

Lösönen, Pekka

2017-12-01

Irradiation resolution of gas atoms and vacancies from intra- and intergranular bubbles in sintered UO2 fuel was studied by comparing macroscopic models with a more mechanistic approach. The applied macroscopic models imply the resolution rate of gas atoms to be proportional to gas concentration in intragranular bubbles and at grain boundary (including intergranular bubbles). A relation was established between the macroscopic models and a single encounter of an energetic fission fragment with a bubble. The effect of bubble size on resolution was quantified. The number of resoluted gas atoms per encounter of a fission fragment per bubble was of the same order of magnitude for intra- and intergranular bubbles. However, the resulting macroscopic resolution rate of gas atoms was about two orders of magnitude larger from intragranular bubbles. The number of vacancies resoluted from a grain face bubble by a passing fission fragment was calculated. The obtained correlations for resolution of gas atoms from intragranular bubbles and grain boundaries and for resolution of vacancies from grain face bubbles were used to demonstrate the effect of irradiation resolution on fission gas release.

Experimental observation of hysteresis in a coherent metal-hydride phase transition

NASA Astrophysics Data System (ADS)

Huang, Wen; Pálsson, Gunnar K.; Brischetto, Martin; Droulias, Sotirios A.; Hartmann, Ola; Wolff, Max; Hjörvarsson, Björgvin

2017-12-01

We investigate the hysteresis obtained in the hydrogen absorption and desorption cycle for a single crystal Pd/V_28 ≤ft[Fe4 /V_28\\right]11 superlattice. Below the critical temperature, a small but clear hysteresis is observed in the pressure-composition isotherms, while it is absent above. The experimental results thereby prove the relevance of macroscopic energy barriers for obtaining hysteresis in coherent structural transformations. The textured Pd layer exhibits substantially larger hysteresis effects, which can be related to an irreversible energy loss caused by defect generation in Pd.

A Bottom-Up Approach to Understanding Protein Layer Formation at Solid-Liquid Interfaces

PubMed Central

Kastantin, Mark; Langdon, Blake B.; Schwartz, Daniel K.

2014-01-01

A common goal across different fields (e.g. separations, biosensors, biomaterials, pharmaceuticals) is to understand how protein behavior at solid-liquid interfaces is affected by environmental conditions. Temperature, pH, ionic strength, and the chemical and physical properties of the solid surface, among many factors, can control microscopic protein dynamics (e.g. adsorption, desorption, diffusion, aggregation) that contribute to macroscopic properties like time-dependent total protein surface coverage and protein structure. These relationships are typically studied through a top-down approach in which macroscopic observations are explained using analytical models that are based upon reasonable, but not universally true, simplifying assumptions about microscopic protein dynamics. Conclusions connecting microscopic dynamics to environmental factors can be heavily biased by potentially incorrect assumptions. In contrast, more complicated models avoid several of the common assumptions but require many parameters that have overlapping effects on predictions of macroscopic, average protein properties. Consequently, these models are poorly suited for the top-down approach. Because the sophistication incorporated into these models may ultimately prove essential to understanding interfacial protein behavior, this article proposes a bottom-up approach in which direct observations of microscopic protein dynamics specify parameters in complicated models, which then generate macroscopic predictions to compare with experiment. In this framework, single-molecule tracking has proven capable of making direct measurements of microscopic protein dynamics, but must be complemented by modeling to combine and extrapolate many independent microscopic observations to the macro-scale. The bottom-up approach is expected to better connect environmental factors to macroscopic protein behavior, thereby guiding rational choices that promote desirable protein behaviors. PMID:24484895

A semi-empirical model relating micro structure to acoustic properties of bimodal porous material

NASA Astrophysics Data System (ADS)

Mosanenzadeh, Shahrzad Ghaffari; Doutres, Olivier; Naguib, Hani E.; Park, Chul B.; Atalla, Noureddine

2015-01-01

Complex morphology of open cell porous media makes it difficult to link microstructural parameters and acoustic behavior of these materials. While morphology determines the overall sound absorption and noise damping effectiveness of a porous structure, little is known on the influence of microstructural configuration on the macroscopic properties. In the present research, a novel bimodal porous structure was designed and developed solely for modeling purposes. For the developed porous structure, it is possible to have direct control on morphological parameters and avoid complications raised by intricate pore geometries. A semi-empirical model is developed to relate microstructural parameters to macroscopic characteristics of porous material using precise characterization results based on the designed bimodal porous structures. This model specifically links macroscopic parameters including static airflow resistivity ( σ ) , thermal characteristic length ( Λ ' ) , viscous characteristic length ( Λ ) , and dynamic tortuosity ( α ∞ ) to microstructural factors such as cell wall thickness ( 2 t ) and reticulation rate ( R w ) . The developed model makes it possible to design the morphology of porous media to achieve optimum sound absorption performance based on the application in hand. This study makes the base for understanding the role of microstructural geometry and morphological factors on the overall macroscopic parameters of porous materials specifically for acoustic capabilities. The next step is to include other microstructural parameters as well to generalize the developed model. In the present paper, pore size was kept constant for eight categories of bimodal foams to study the effect of secondary porous structure on macroscopic properties and overall acoustic behavior of porous media.

Self-Assembled Nano-FeO(OH)/Reduced Graphene Oxide Aerogel as a Reusable Catalyst for Photo-Fenton Degradation of Phenolic Organics.

PubMed

Liu, Renlan; Xu, Yiming; Chen, Baoliang

2018-06-19

Fabrication of visible-light-responsive, macroscopic photo-Fenton catalysts is crucial for wastewater treatment. Here, we report a facile fabrication method for nano-FeO(OH)/reduced graphene oxide aerogels (FeO(OH)-rGA) equipped with a stable macrostructure and a high efficiency for catalytic degradation of phenolic organics. The structure of FeO(OH)/rGA was characterized by SEM, TEM, XPS, Raman analysis. The FeO(OH) is the main constituent of ferrihydrite, which dispersed in the graphene aerogel with a particle size of ∼3 nm can efficiently activate H 2 O 2 to generate abundant •OH. The excellent performance of the FeO(OH)/rGO aerogel was specifically exhibited by the outstanding catalyst activity, sustained mineralization and eminent reaction rate for phenolic organics. A synergy effect between FeO(OH) and graphene aerogel was observed, which came from the extensive electron transfer channels and active sites of the 3D graphene aerogel and the visible-light-activated FeO(OH) and H 2 O 2 consistently producing •OH. The FeO(OH)/rGA could be reused for 10 cycles without a reduction in the catalytic activity and had less iron leaching, which guarantees that the active ingredient remains in the gel. Moreover, the FeO(OH)/rGA induced photo-Fenton degradation of 4-chlorophenol under near neutral pH conditions because the tight connection of FeO(OH) with the rGO aerogel results in less iron leaching and prevents the generation of Fe(OH) 3 . The 4-chlorophenol was completely removed in 80 min with a 0.074 min -1 rate constant in the FeO(OH)-rGA/H 2 O 2 photo-Fenton system under visible-light irradiation, and mineralization rate was up to 80% after 6 h. Oxidative •OH can continuously attack 4-chlorophenol, 2,4,6-trichlorophenol and bisphenol A without selectivity. These results lay a foundation for highly effective and durable photo-Fenton degradation of phenolic organics at near neutral pH and sufficient activation of H 2 O 2 for future applications.

Solvothermal-induced self-assembly of Fe2O3/GS aerogels for high Li-storage and excellent stability.

PubMed

Wang, Ronghua; Xu, Chaohe; Du, Meng; Sun, Jing; Gao, Lian; Zhang, Peng; Yao, Heliang; Lin, Chucheng

2014-06-12

A novel solvothermal-induced self-assembly approach, using colloid sol as precursor, is developed to construct monolithic 3D metal oxide/GS (graphene sheets) aerogels. During the solvothermal process, graphene oxide (GO) is highly reduced to GS and self-assembles into 3D macroscopic hydrogels, accompanying with in situ transformation of colloid sol to metal oxides. As a proof of concept, Fe2 O3 /GS aerogels are synthesized based on Fe(OH)3 sol, in which GS self-assemble into an interconnected macroporous framework and Fe2 O3 nanocrystals (20-50 nm) uniformly deposit on GS. Benefitting from the integration of macroporous structures, large surface area, high electrical conductivity, and good electrode homogeneity, the hybrid electrode manifests a superior rate capability (930, 660 and 520 mAh g(-1) at 500, 2000 and 4000 mA g(-1), respectively) and excellent prolonged cycling stability at high rates (733 mAh g(-1) during 1000 charge/discharge cycles at 2000 mA g(-1)), demonstrating its great potential for application in high performance lithium ion batteries. The work described here provides a versatile pathway to construct various graphene-based hybrid aerogels. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Microstructure evolution and large magnetocaloric effect of La0.8Ce0.2(Fe0.95Co0.05)11.8Si1.2 alloy prepared by strip-casting and annealing

NASA Astrophysics Data System (ADS)

Zhong, X. C.; Feng, X. L.; Huang, J. H.; Zhang, H.; Huang, Y. L.; Liu, Z. W.; Jiao, D. L.

2018-04-01

The microstructure and magnetocaloric effect of the La0.8Ce0.2(Fe0.95Co0.05)11.8Si1.2 strip-cast flakes annealed between 1273K and 1423K for different time have been investigated. For the flakes annealed for 2h from 1273K to 1423K, the shape and distribution of α-Fe, La-rich and NaZn13-type 1:13 phases are quite sensitive to the annealing temperature. Especially, at a high annealing temperature of 1423K, the 1:13 phase began to decompose into macroscopic α-Fe conglomerations and La-rich dendrites. With the increase of annealing time from 0 to 12h at 1323K, the amount of 1:13 phase increased significantly and reached ˜93.50 wt.% at 12h. However, an overlong annealing time also led to 1:13 phase decomposition and influenced the magnetic performance. For the flakes annealed at 1323K for 12h, large magnetic entropy change value of 18.12Jkg-1K-1 at 5T has been obtained. The present results indicate that strip casting method can potentially be used in mass production of high performance magnetocaloric materials.

Mesoscopic model of actin-based propulsion.

PubMed

Zhu, Jie; Mogilner, Alex

2012-01-01

Two theoretical models dominate current understanding of actin-based propulsion: microscopic polymerization ratchet model predicts that growing and writhing actin filaments generate forces and movements, while macroscopic elastic propulsion model suggests that deformation and stress of growing actin gel are responsible for the propulsion. We examine both experimentally and computationally the 2D movement of ellipsoidal beads propelled by actin tails and show that neither of the two models can explain the observed bistability of the orientation of the beads. To explain the data, we develop a 2D hybrid mesoscopic model by reconciling these two models such that individual actin filaments undergoing nucleation, elongation, attachment, detachment and capping are embedded into the boundary of a node-spring viscoelastic network representing the macroscopic actin gel. Stochastic simulations of this 'in silico' actin network show that the combined effects of the macroscopic elastic deformation and microscopic ratchets can explain the observed bistable orientation of the actin-propelled ellipsoidal beads. To test the theory further, we analyze observed distribution of the curvatures of the trajectories and show that the hybrid model's predictions fit the data. Finally, we demonstrate that the model can explain both concave-up and concave-down force-velocity relations for growing actin networks depending on the characteristic time scale and network recoil. To summarize, we propose that both microscopic polymerization ratchets and macroscopic stresses of the deformable actin network are responsible for the force and movement generation.

Multiscale Investigation on Biofilm Distribution and Its Impact on Macroscopic Biogeochemical Reaction Rates: BIOFILM DISTRIBUTION AND RATE SCALING

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

Yan, Zhifeng; Liu, Chongxuan; Liu, Yuanyuan

Biofilms are critical locations for biogeochemical reactions in the subsurface environment. The occurrence and distribution of biofilms at microscale as well as their impacts on macroscopic biogeochemical reaction rates are still poorly understood. This paper investigated the formation and distributions of biofilms in heterogeneous sediments using multiscale models, and evaluated the effects of biofilm heterogeneity on local and macroscopic biogeochemical reaction rates. Sediment pore structures derived from X-ray computed tomography were used to simulate the microscale flow dynamics and biofilm distribution in the sediment column. The response of biofilm formation and distribution to the variations in hydraulic and chemical propertiesmore » was first examined. One representative biofilm distribution was then utilized to evaluate its effects on macroscopic reaction rates using nitrate reduction as an example. The results revealed that microorganisms primarily grew on the surfaces of grains and aggregates near preferential flow paths where both electron donor and acceptor were readily accessible, leading to the heterogeneous distribution of biofilms in the sediments. The heterogeneous biofilm distribution decreased the macroscopic rate of biogeochemical reactions as compared with those in homogeneous cases. Operationally considering the heterogeneous biofilm distribution in macroscopic reactive transport models such as using dual porosity domain concept can significantly improve the prediction of biogeochemical reaction rates. Overall, this study provided important insights into the biofilm formation and distribution in soils and sediments as well as their impacts on the macroscopic manifestation of reaction rates.« less

Multiscale Investigation on Biofilm Distribution and Its Impact on Macroscopic Biogeochemical Reaction Rates

NASA Astrophysics Data System (ADS)

Yan, Zhifeng; Liu, Chongxuan; Liu, Yuanyuan; Bailey, Vanessa L.

2017-11-01

Biofilms are critical locations for biogeochemical reactions in the subsurface environment. The occurrence and distribution of biofilms at microscale as well as their impacts on macroscopic biogeochemical reaction rates are still poorly understood. This paper investigated the formation and distributions of biofilms in heterogeneous sediments using multiscale models and evaluated the effects of biofilm heterogeneity on local and macroscopic biogeochemical reaction rates. Sediment pore structures derived from X-ray computed tomography were used to simulate the microscale flow dynamics and biofilm distribution in the sediment column. The response of biofilm formation and distribution to the variations in hydraulic and chemical properties was first examined. One representative biofilm distribution was then utilized to evaluate its effects on macroscopic reaction rates using nitrate reduction as an example. The results revealed that microorganisms primarily grew on the surfaces of grains and aggregates near preferential flow paths where both electron donor and acceptor were readily accessible, leading to the heterogeneous distribution of biofilms in the sediments. The heterogeneous biofilm distribution decreased the macroscopic rate of biogeochemical reactions as compared with those in homogeneous cases. Operationally considering the heterogeneous biofilm distribution in macroscopic reactive transport models such as using dual porosity domain concept can significantly improve the prediction of biogeochemical reaction rates. Overall, this study provided important insights into the biofilm formation and distribution in soils and sediments as well as their impacts on the macroscopic manifestation of reaction rates.

Phase-field simulation of microstructure formation in technical castings - A self-consistent homoenthalpic approach to the micro-macro problem

NASA Astrophysics Data System (ADS)

Böttger, B.; Eiken, J.; Apel, M.

2009-10-01

Performing microstructure simulation of technical casting processes suffers from the strong interdependency between latent heat release due to local microstructure formation and heat diffusion on the macroscopic scale: local microstructure formation depends on the macroscopic heat fluxes and, in turn, the macroscopic temperature solution depends on the latent heat release, and therefore on the microstructure formation, in all parts of the casting. A self-consistent homoenthalpic approximation to this micro-macro problem is proposed, based on the assumption of a common enthalpy-temperature relation for the whole casting which is used for the description of latent heat production on the macroscale. This enthalpy-temperature relation is iteratively obtained by phase-field simulations on the microscale, thus taking into account the specific morphological impact on the latent heat production. This new approach is discussed and compared to other approximations for the coupling of the macroscopic heat flux to complex microstructure models. Simulations are performed for the binary alloy Al-3at%Cu, using a multiphase-field solidification model which is coupled to a thermodynamic database. Microstructure formation is simulated for several positions in a simple model plate casting, using a one-dimensional macroscopic temperature solver which can be directly coupled to the microscopic phase-field simulation tool.

Continuous Feedback and Macroscopic Coherence

NASA Technical Reports Server (NTRS)

Tombesi, Paolo; Vitali, David

1996-01-01

We show that a model, recently introduced for quantum nondemolition measurements of a quantum observable, can be adapted to obtain a measurement scheme which is able to slow down the destruction of macroscopic coherence due to the measurement apparatus.

Formation of macroscopic surface layers on Fe(0) electrocoagulation electrodes during an extended field trial of arsenic treatment.

PubMed

van Genuchten, Case M; Bandaru, Siva R S; Surorova, Elena; Amrose, Susan E; Gadgil, Ashok J; Peña, Jasquelin

2016-06-01

Extended field trials to remove arsenic (As) via Fe(0) electrocoagulation (EC) have demonstrated consistent As removal from groundwater to concentrations below 10 μg L(-1). However, the coulombic performance of long-term EC field operation is lower than that of laboratory-based systems. Although EC electrodes used over prolonged periods show distinct passivation layers, which have been linked to decreased treatment efficiency, the spatial distribution and mineralogy of such surface layers have not been investigated. In this work, we combine wet chemical measurements with sub-micron-scale chemical maps and selected area electron diffraction (SAED) to determine the chemical composition and mineral phase of surface layers formed during long-term Fe(0) EC treatment. We analyzed Fe(0) EC electrodes used for 3.5 months of daily treatment of As-contaminated groundwater in rural West Bengal, India. We found that the several mm thick layer that formed on cathodes and anodes consisted of primarily magnetite, with minor fractions of goethite. Spatially-resolved SAED patterns also revealed small quantities of CaCO3, Mn oxides, and SiO2, the source of which was the groundwater electrolyte. We propose that the formation of the surface layer contributes to decreased treatment performance by preventing the migration of EC-generated Fe(II) to the bulk electrolyte, where As removal occurs. The trapped Fe(II) subsequently increases the surface layer size at the expense of treatment efficiency. Based on these findings, we discuss several simple and affordable methods to prevent the efficiency loss due to the surface layer, including alternating polarity cycles and cleaning the Fe(0) surface mechanically or via electrolyte scouring. Copyright © 2016 Elsevier Ltd. All rights reserved.

Equation-free multiscale computation: algorithms and applications.

PubMed

Kevrekidis, Ioannis G; Samaey, Giovanni

2009-01-01

In traditional physicochemical modeling, one derives evolution equations at the (macroscopic, coarse) scale of interest; these are used to perform a variety of tasks (simulation, bifurcation analysis, optimization) using an arsenal of analytical and numerical techniques. For many complex systems, however, although one observes evolution at a macroscopic scale of interest, accurate models are only given at a more detailed (fine-scale, microscopic) level of description (e.g., lattice Boltzmann, kinetic Monte Carlo, molecular dynamics). Here, we review a framework for computer-aided multiscale analysis, which enables macroscopic computational tasks (over extended spatiotemporal scales) using only appropriately initialized microscopic simulation on short time and length scales. The methodology bypasses the derivation of macroscopic evolution equations when these equations conceptually exist but are not available in closed form-hence the term equation-free. We selectively discuss basic algorithms and underlying principles and illustrate the approach through representative applications. We also discuss potential difficulties and outline areas for future research.

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

Lu, S; Chourey, Karuna; REICHE, M

Metaproteomics combined with total nucleic acid-based methods aided in deciphering the roles of microorganisms in the formation and transformation of iron-rich macroscopic aggregates (iron snow) formed in the redoxcline of an acidic lignite mine lake. Iron snow had high total bacterial 16S rRNA gene copies, with 2 x 109 copies g (dry wt)-1 in the acidic (pH 3.5) central lake basin and 4 x 1010 copies g (dry wt)-1 in the less acidic (pH 5.5) northern lake basin. Active microbial communities in the central basin were dominated by Alphaproteobacteria (36.6%) and Actinobacteria (21.4%), and by Betaproteobacteria (36.2%) in the northernmore » basin. Microbial Fe-cycling appeared to be the dominant metabolism in the schwertmannite-rich iron snow, because cloning and qPCR assigned up to 61% of active bacteria as Fe-cycling bacteria (FeB). Metaproteomics revealed 70 unique proteins from central basin iron snow and 283 unique proteins from 43 genera from northern basin. Protein identification provided a glimpse into in situ processes, such as primary production, motility, metabolism of acidophilic FeB, and survival strategies of neutrophilic FeB. Expression of carboxysome shell proteins and RubisCO indicated active CO2 fixation by Fe(II) oxidizers. Flagellar proteins from heterotrophs indicated their activity to reach and attach surfaces. Gas vesicle proteins related to CO2-fixing Chlorobium suggested that microbes could influence iron snow sinking. We suggest that iron snow formed by autotrophs in the redoxcline acts as a microbial parachute, since it is colonized by motile heterotrophs during sinking which start to dissolve schwertmannite.« less

Modeling the hydrodynamic and electrochemical efficiency of semi-solid flow batteries

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

Brunini, VE; Chiang, YM; Carter, WC

2012-05-01

A mathematical model of flow cell operation incorporating hydrodynamic and electrochemical effects in three dimensions is developed. The model and resulting simulations apply to recently demonstrated high energy-density semi-solid flow cells. In particular, state of charge gradients that develop during low flow rate operation and their effects on the spatial non-uniformity of current density within flow cells are quantified. A one-dimensional scaling model is also developed and compared to the full three-dimensional simulation. The models are used to demonstrate the impact of the choice of electrochemical couple on flow cell performance. For semi-solid flow electrodes, which can use solid activemore » materials with a wide variety of voltage-capacity responses, we find that cell efficiency is maximized for electrochemical couples that have a relatively flat voltage vs. capacity curve, operated under slow flow conditions. For example, in flow electrodes limited by macroscopic charge transport, an LiFePO4-based system requires one-third the polarization to reach the same cycling rate as an LiCoO2-based system, all else being equal. Our conclusions are generally applicable to high energy density flow battery systems, in which flow rates can be comparatively low for a given required power. (C) 2012 Elsevier Ltd. All rights reserved.« less

Optimal configuration of microstructure in ferroelectric materials by stochastic optimization

NASA Astrophysics Data System (ADS)

Jayachandran, K. P.; Guedes, J. M.; Rodrigues, H. C.

2010-07-01

An optimization procedure determining the ideal configuration at the microstructural level of ferroelectric (FE) materials is applied to maximize piezoelectricity. Piezoelectricity in ceramic FEs differs significantly from that of single crystals because of the presence of crystallites (grains) possessing crystallographic axes aligned imperfectly. The piezoelectric properties of a polycrystalline (ceramic) FE is inextricably related to the grain orientation distribution (texture). The set of combination of variables, known as solution space, which dictates the texture of a ceramic is unlimited and hence the choice of the optimal solution which maximizes the piezoelectricity is complicated. Thus, a stochastic global optimization combined with homogenization is employed for the identification of the optimal granular configuration of the FE ceramic microstructure with optimum piezoelectric properties. The macroscopic equilibrium piezoelectric properties of polycrystalline FE is calculated using mathematical homogenization at each iteration step. The configuration of grains characterized by its orientations at each iteration is generated using a randomly selected set of orientation distribution parameters. The optimization procedure applied to the single crystalline phase compares well with the experimental data. Apparent enhancement of piezoelectric coefficient d33 is observed in an optimally oriented BaTiO3 single crystal. Based on the good agreement of results with the published data in single crystals, we proceed to apply the methodology in polycrystals. A configuration of crystallites, simultaneously constraining the orientation distribution of the c-axis (polar axis) while incorporating ab-plane randomness, which would multiply the overall piezoelectricity in ceramic BaTiO3 is also identified. The orientation distribution of the c-axes is found to be a narrow Gaussian distribution centered around 45°. The piezoelectric coefficient in such a ceramic is found to be nearly three times as that of the single crystal. Our optimization model provide designs for materials with enhanced piezoelectric performance, which would stimulate further studies involving materials possessing higher spontaneous polarization.

Molecular Dynamics Simulations of Grain Boundary and Bulk Diffusion in Metals.

NASA Astrophysics Data System (ADS)

Plimpton, Steven James

Diffusion is a microscopic mass transport mechanism that underlies many important macroscopic phenomena affecting the structural, electrical, and mechanical properties of metals. This thesis presents results from atomistic simulation studies of diffusion both in bulk and in the fast diffusion paths known as grain boundaries. Using the principles of molecular dynamics single boundaries are studied and their structure and dynamic properties characterized. In particular, tilt boundary bicrystal and bulk models of fcc Al and bcc alpha-Fe are simulated. Diffusion coefficients and activation energies for atomic motion are calculated for both models and compared to experimental data. The influence of the interatomic pair potential on the diffusion is studied in detail. A universal relation between the melting temperature that a pair potential induces in a simulated bulk model and the potential energy barrier height for atomic hopping is derived and used to correlate results for a wide variety of pair potentials. Using these techniques grain boundary and bulk diffusion coefficients for any fcc material can be estimated from simple static calculations without the need to perform more time-consuming dynamic simulations. The influences of two other factors on grain boundary diffusion are also studied because of the interest of the microelectronics industry in the diffusion related reliability problem known as electromigration. The first factor, known to affect the self diffusion rate of Al, is the presence of Cu impurity atoms in Al tilt boundaries. The bicrystal model for Al is seeded randomly with Cu atoms and a simple hybrid Morse potential used to model the Al-Cu interaction. While some effect due to the Cu is noted, it is concluded that pair potentials are likely an inadequate approximation for the alloy system. The second factor studied is the effect of the boundary orientation angle on the diffusion rate. Symmetric bcc Fe boundaries are relaxed to find optimal structures and their diffusion coefficients calculated. Good agreement is found with the dislocation pipe model for tilt boundary diffusion.

Two level approach to safety planning incorporating the Highway Safety Manual (HSM) network screening.

DOT National Transportation Integrated Search

2014-04-01

Compared to microscopic safety studies, macroscopic-focused research is more efficient at integrating zonal-level features into crash prediction models and identifying hot zones. However, macroscopic screening has accuracy limitations. Thus, this stu...

Macroscopically constrained Wang-Landau method for systems with multiple order parameters and its application to drawing complex phase diagrams

NASA Astrophysics Data System (ADS)

Chan, C. H.; Brown, G.; Rikvold, P. A.

2017-05-01

A generalized approach to Wang-Landau simulations, macroscopically constrained Wang-Landau, is proposed to simulate the density of states of a system with multiple macroscopic order parameters. The method breaks a multidimensional random-walk process in phase space into many separate, one-dimensional random-walk processes in well-defined subspaces. Each of these random walks is constrained to a different set of values of the macroscopic order parameters. When the multivariable density of states is obtained for one set of values of fieldlike model parameters, the density of states for any other values of these parameters can be obtained by a simple transformation of the total system energy. All thermodynamic quantities of the system can then be rapidly calculated at any point in the phase diagram. We demonstrate how to use the multivariable density of states to draw the phase diagram, as well as order-parameter probability distributions at specific phase points, for a model spin-crossover material: an antiferromagnetic Ising model with ferromagnetic long-range interactions. The fieldlike parameters in this model are an effective magnetic field and the strength of the long-range interaction.

Inferring Spatial Variations of Microstructural Properties from Macroscopic Mechanical Response

PubMed Central

Liu, Tengxiao; Hall, Timothy J.; Barbone, Paul E.; Oberai, Assad A.

2016-01-01

Disease alters tissue microstructure, which in turn affects the macroscopic mechanical properties of tissue. In elasticity imaging, the macroscopic response is measured and is used to infer the spatial distribution of the elastic constitutive parameters. When an empirical constitutive model is used these parameters cannot be linked to the microstructure. However, when the constitutive model is derived from a microstructural representation of the material, it allows for the possibility of inferring the local averages of the spatial distribution of the microstructural parameters. This idea forms the basis of this study. In particular, we first derive a constitutive model by homogenizing the mechanical response of a network of elastic, tortuous fibers. Thereafter, we use this model in an inverse problem to determine the spatial distribution of the microstructural parameters. We solve the inverse problem as a constrained minimization problem, and develop efficient methods for solving it. We apply these methods to displacement fields obtained by deforming gelatin-agar co-gels, and determine the spatial distribution of agar concentration and fiber tortuosity, thereby demonstrating that it is possible to image local averages of microstructural parameters from macroscopic measurements of deformation. PMID:27655420

Dynamic Model and Control of a Photovoltaic Generation System using Energetic Macroscopic Representation

NASA Astrophysics Data System (ADS)

Solano, Javier; Duarte, José; Vargas, Erwin; Cabrera, Jhon; Jácome, Andrés; Botero, Mónica; Rey, Juan

2016-10-01

This paper addresses the Energetic Macroscopic Representation EMR, the modelling and the control of photovoltaic panel PVP generation systems for simulation purposes. The model of the PVP considers the variations on irradiance and temperature. A maximum power point tracking MPPT algorithm is considered to control the power converter. A novel EMR is proposed to consider the dynamic model of the PVP with variations in the irradiance and the temperature. The EMR is evaluated through simulations of a PVP generation system.

Magnetic properties of the CrMnFeCoNi high-entropy alloy

DOE PAGES

Schneeweiss, Oldřich; Friák, Martin; Dudová, Marie; ...

2017-07-28

In this paper, we present experimental data showing that the equiatomic CrMnFeCoNi high-entropy alloy undergoes two magnetic transformations at temperatures below 100 K while maintaining its fcc structure down to 3 K. The first transition, paramagnetic to spin glass, was detected at 93 K and the second transition of the ferromagnetic type occurred at 38 K. Field-assisted cooling below 38 K resulted in a systematic vertical shift of the hysteresis curves. Strength and direction of the associated magnetization bias was proportional to the strength and direction of the cooling field and shows a linear dependence with a slope of 0.006more » ± 0.001 emu T. The local magnetic moments of individual atoms in the CrMnFeCoNi quinary fcc random solid solution were investigated by ab initio (electronic density functional theory) calculations. Results of the numerical analysis suggest that, irrespective of the initial configuration of local magnetic moments, the magnetic moments associated with Cr atoms align antiferromagnetically with respect to a cumulative magnetic moment of their first coordination shell. The ab initio calculations further showed that the magnetic moments of Fe and Mn atoms remain strong (between 1.5 and 2 μ B), while the local moments of Ni atoms effectively vanish. Finally, these results indicate that interactions of Mn- and/or Fe-located moments with the surrounding magnetic structure account for the observed macroscopic magnetization bias.« less

The disclosure of mesoscale behaviour of a 3d-SMM monolayer on Au(111) through a multilevel approach.

PubMed

Fernandez Garcia, Guglielmo; Lunghi, Alessandro; Totti, Federico; Sessoli, Roberta

2018-02-22

Here we present a computational study of a full- and a half-monolayer of a Fe 4 single molecule magnet ([Fe 4 (L) 2 (dpm) 6 ], where H 3 L = 2-hydroxymethyl-2-phenylpropane-1,3-diol and Hdpm = dipivaloylmethane, Fe 4 Ph) on an unreconstructed surface of Au(111). This has been possible through the application of an integrated approach, which allows the explicit inclusion of the packing effects in the classical dynamics to be used in a second step in periodic and non-periodic high level DFT calculations. In this way we can obtain access to mesoscale geometrical data and verify how they can influence the magnetic properties of interest of the single Fe 4 molecule. The proposed approach allows to overcome the ab initio state-of-the-art approaches used to study Single Molecule Magnets (SMMs), which are based on the study of one single adsorbed molecule and cannot represent effects on the scale of a monolayer. Indeed, we show here that it is possible to go beyond the computational limitations inherent to the use, for such complex systems, of accurate calculation techniques (e.g. ab initio molecular dynamics) without losing the level of accuracy necessary to gain new detailed insights, hardly reachable at the experimental level. Indeed, long-range and edge effects on the Fe 4 structures and their easy axis of magnetization orientations have been evidenced as their different contributions to the overall macroscopic behavior.

Uncovering low dimensional macroscopic chaotic dynamics of large finite size complex systems

NASA Astrophysics Data System (ADS)

Skardal, Per Sebastian; Restrepo, Juan G.; Ott, Edward

2017-08-01

In the last decade, it has been shown that a large class of phase oscillator models admit low dimensional descriptions for the macroscopic system dynamics in the limit of an infinite number N of oscillators. The question of whether the macroscopic dynamics of other similar systems also have a low dimensional description in the infinite N limit has, however, remained elusive. In this paper, we show how techniques originally designed to analyze noisy experimental chaotic time series can be used to identify effective low dimensional macroscopic descriptions from simulations with a finite number of elements. We illustrate and verify the effectiveness of our approach by applying it to the dynamics of an ensemble of globally coupled Landau-Stuart oscillators for which we demonstrate low dimensional macroscopic chaotic behavior with an effective 4-dimensional description. By using this description, we show that one can calculate dynamical invariants such as Lyapunov exponents and attractor dimensions. One could also use the reconstruction to generate short-term predictions of the macroscopic dynamics.

Induction log responses to layered, dipping, and anisotropic formations: Induction log shoulder-bed corrections to anisotropic formations and the effect of shale anisotropy in thinly laminated sand/shale sequences

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

Hagiwara, Teruhiko

1996-12-31

Induction log responses to layered, dipping, and anisotropic formations are examined analytically. The analytical model is especially helpful in understanding induction log responses to thinly laminated binary formations, such as sand/shale sequences, that exhibit macroscopically anisotropic: resistivity. Two applications of the analytical model are discussed. In one application we examine special induction log shoulder-bed corrections for use when thin anisotropic beds are encountered. It is known that thinly laminated sand/shale sequences act as macroscopically anisotropic: formations. Hydrocarbon-bearing formations also act as macroscopically anisotropic formations when they consist of alternating layers of different grain-size distributions. When such formations are thick, inductionmore » logs accurately read the macroscopic conductivity, from which the hydrocarbon saturation in the formations can be computed. When the laminated formations are not thick, proper shoulder-bed corrections (or thin-bed corrections) should be applied to obtain the true macroscopic formation conductivity and to estimate the hydrocarbon saturation more accurately. The analytical model is used to calculate the thin-bed effect and to evaluate the shoulder-bed corrections. We will show that the formation resistivity and hence the hydrocarbon saturation are greatly overestimated when the anisotropy effect is not accounted for and conventional shoulder-bed corrections are applied to the log responses from such laminated formations.« less

Probing spontaneous wave-function collapse with entangled levitating nanospheres

NASA Astrophysics Data System (ADS)

Zhang, Jing; Zhang, Tiancai; Li, Jie

2017-01-01

Wave-function collapse models are considered to be the modified theories of standard quantum mechanics at the macroscopic level. By introducing nonlinear stochastic terms in the Schrödinger equation, these models (different from standard quantum mechanics) predict that it is fundamentally impossible to prepare macroscopic systems in macroscopic superpositions. The validity of these models can only be examined by experiments, and hence efficient protocols for these kinds of experiments are greatly needed. Here we provide a protocol that is able to probe the postulated collapse effect by means of the entanglement of the center-of-mass motion of two nanospheres optically trapped in a Fabry-Pérot cavity. We show that the collapse noise results in a large reduction of the steady-state entanglement, and the entanglement, with and without the collapse effect, shows distinguishable scalings with certain system parameters, which can be used to determine unambiguously the effect of these models.

Upscaling of spectral induced polarization response using random tube networks

NASA Astrophysics Data System (ADS)

Maineult, Alexis; Revil, André; Camerlynck, Christian; Florsch, Nicolas; Titov, Konstantin

2017-05-01

In order to upscale the induced polarization (IP) response of porous media, from the pore scale to the sample scale, we implement a procedure to compute the macroscopic complex resistivity response of random tube networks. A network is made of a 2-D square-meshed grid of connected tubes, which obey to a given tube radius distribution. In a simplified approach, the electrical impedance of each tube follows a local Pelton resistivity model, with identical resistivity, chargeability and Cole-Cole exponent values for all the tubes-only the time constant varies, as it depends on the radius of each tube and on a diffusion coefficient also identical for all the tubes. By solving the conservation law for the electrical charge, the macroscopic IP response of the network is obtained. We fit successfully the macroscopic complex resistivity also by a Pelton resistivity model. Simulations on uncorrelated and correlated networks, for which the tube radius distribution is so that the decimal logarithm of the radius is normally distributed, evidence that the local and macroscopic model parameters are the same, except the Cole-Cole exponent: its macroscopic value diminishes with increasing heterogeneity (i.e. with increasing standard deviation of the radius distribution), compared to its local value. The methodology is also applied to six siliciclastic rock samples, for which the pore radius distributions from mercury porosimetry are available. These samples exhibit the same behaviour as synthetic media, that is, the macroscopic Cole-Cole exponent is always lower than the local one. As a conclusion, the pore network method seems to be a promising tool for studying the upscaling of the IP response of porous media.

Surface segregation of additives on SnO 2 based powders and their relationship with macroscopic properties

NASA Astrophysics Data System (ADS)

Pereira, Gilberto J.; Castro, Ricardo H. R.; Hidalgo, Pilar; Gouvêa, Douglas

2002-07-01

Surface properties of ceramic powders frequently play an important role in producing high-quality, high-performance, and reliable ceramic products. These properties are related to the surface bond types and interactions with the surroundings. Oxide surfaces generally contain adsorbed hydroxyl groups and modifications in the chemical composition of the surface may be studied by infrared spectroscopy. In this work, we prepared SnO 2 containing Fe or Mg ions by organic chemical route derived from Pechini's method. The prepared powders were characterized by infrared spectroscopy (FT-IR), X-ray diffraction (XRD), dynamic electrophoretic mobility and surface area determination. Results demonstrated that the studied additives segregate onto the oxide surface and modify the hydroxyl IR bands of the adsorbed hydroxyl groups. These surface modifications change some macroscopic properties of the powder such as the isoelectric point (IEP) in aqueous suspensions and the final specific surface area. The increase of the surface area with additive concentration is supposedly due to the reduction of surface energy of the powders when additives segregate on the powder surface.

Tuning the competition between ferromagnetism and antiferromagnetism in a half-doped manganite through magnetoelectric coupling.

PubMed

Yi, Di; Liu, Jian; Okamoto, Satoshi; Jagannatha, Suresha; Chen, Yi-Chun; Yu, Pu; Chu, Ying-Hao; Arenholz, Elke; Ramesh, R

2013-09-20

We investigate the possibility of controlling the magnetic phase transition of the heterointerface between a half-doped manganite La(0.5)Ca(0.5)MnO(3) and a multiferroic BiFeO(3) (BFO) through magnetoelectric coupling. Using macroscopic magnetometry and element-selective x-ray magnetic circular dichroism at the Mn and Fe L edges, we discover that the ferroelectric polarization of BFO controls simultaneously the magnetization of BFO and La(0.5)Ca(0.5)MnO(3) (LCMO). X-ray absorption spectra at the oxygen K edge and linear dichroism at the Mn L edge suggest that the interfacial coupling is mainly derived from the superexchange between Mn and Fe t(2g) spins. The combination of x-ray absorption spectroscopy and mean-field theory calculations reveals that the d-electron modulation of Mn cations changes the magnetic coupling in LCMO, which controls the enhanced canted moments of interfacial BFO via the interfacial coupling. Our results demonstrate that the competition between ferromagnetic and antiferromagnetic instability can be modulated by an electric field at the heterointerface, providing another pathway for the electrical field control of magnetism.

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

Schneeweiss, Oldřich; Friák, Martin; Dudová, Marie

In this paper, we present experimental data showing that the equiatomic CrMnFeCoNi high-entropy alloy undergoes two magnetic transformations at temperatures below 100 K while maintaining its fcc structure down to 3 K. The first transition, paramagnetic to spin glass, was detected at 93 K and the second transition of the ferromagnetic type occurred at 38 K. Field-assisted cooling below 38 K resulted in a systematic vertical shift of the hysteresis curves. Strength and direction of the associated magnetization bias was proportional to the strength and direction of the cooling field and shows a linear dependence with a slope of 0.006more » ± 0.001 emu T. The local magnetic moments of individual atoms in the CrMnFeCoNi quinary fcc random solid solution were investigated by ab initio (electronic density functional theory) calculations. Results of the numerical analysis suggest that, irrespective of the initial configuration of local magnetic moments, the magnetic moments associated with Cr atoms align antiferromagnetically with respect to a cumulative magnetic moment of their first coordination shell. The ab initio calculations further showed that the magnetic moments of Fe and Mn atoms remain strong (between 1.5 and 2 μ B), while the local moments of Ni atoms effectively vanish. Finally, these results indicate that interactions of Mn- and/or Fe-located moments with the surrounding magnetic structure account for the observed macroscopic magnetization bias.« less

Macroscopic description of complex adaptive networks coevolving with dynamic node states

NASA Astrophysics Data System (ADS)

Wiedermann, Marc; Donges, Jonathan F.; Heitzig, Jobst; Lucht, Wolfgang; Kurths, Jürgen

2015-05-01

In many real-world complex systems, the time evolution of the network's structure and the dynamic state of its nodes are closely entangled. Here we study opinion formation and imitation on an adaptive complex network which is dependent on the individual dynamic state of each node and vice versa to model the coevolution of renewable resources with the dynamics of harvesting agents on a social network. The adaptive voter model is coupled to a set of identical logistic growth models and we mainly find that, in such systems, the rate of interactions between nodes as well as the adaptive rewiring probability are crucial parameters for controlling the sustainability of the system's equilibrium state. We derive a macroscopic description of the system in terms of ordinary differential equations which provides a general framework to model and quantify the influence of single node dynamics on the macroscopic state of the network. The thus obtained framework is applicable to many fields of study, such as epidemic spreading, opinion formation, or socioecological modeling.

Macroscopic description of complex adaptive networks coevolving with dynamic node states.

PubMed

Wiedermann, Marc; Donges, Jonathan F; Heitzig, Jobst; Lucht, Wolfgang; Kurths, Jürgen

2015-05-01

In many real-world complex systems, the time evolution of the network's structure and the dynamic state of its nodes are closely entangled. Here we study opinion formation and imitation on an adaptive complex network which is dependent on the individual dynamic state of each node and vice versa to model the coevolution of renewable resources with the dynamics of harvesting agents on a social network. The adaptive voter model is coupled to a set of identical logistic growth models and we mainly find that, in such systems, the rate of interactions between nodes as well as the adaptive rewiring probability are crucial parameters for controlling the sustainability of the system's equilibrium state. We derive a macroscopic description of the system in terms of ordinary differential equations which provides a general framework to model and quantify the influence of single node dynamics on the macroscopic state of the network. The thus obtained framework is applicable to many fields of study, such as epidemic spreading, opinion formation, or socioecological modeling.

Multiscale molecular dynamics/hydrodynamics implementation of two dimensional "Mercedes Benz" water model

NASA Astrophysics Data System (ADS)

Scukins, A.; Nerukh, D.; Pavlov, E.; Karabasov, S.; Markesteijn, A.

2015-09-01

A multiscale Molecular Dynamics/Hydrodynamics implementation of the 2D Mercedes Benz (MB or BN2D) [1] water model is developed and investigated. The concept and the governing equations of multiscale coupling together with the results of the two-way coupling implementation are reported. The sensitivity of the multiscale model for obtaining macroscopic and microscopic parameters of the system, such as macroscopic density and velocity fluctuations, radial distribution and velocity autocorrelation functions of MB particles, is evaluated. Critical issues for extending the current model to large systems are discussed.

Electron emission from ferroelectrics - a review

NASA Astrophysics Data System (ADS)

Riege, H.

1994-02-01

The strong pulsed emission of electrons from the surface of ferroelectric (FE) materials was discovered at CERN in 1987. Since then many aspects and properties of the method of generation and propagation of electron beams from FE have been studied experimentally. The method is based on macroscopic charge separation and self-emission of electrons under the influence of their own space-charge fields. Hence, this type of emission is not limited by the Langmuir-Child law as are conventional emission methods. Charge separation and electron emission can be achieved by rapid switching of the spontaneous, ferroelectric polarization. Polarization switching may be induced by application of electrical-field or mechanical-pressure pulses, as well as by thermal heating or laser illumination of the ferroelectric emitter. At higher emission intensities plasma formation assists the FE emission and leads to a strong growth of emitted current amplitude, which is no longer limited by the FE material and the surface properties. The most attractive features of FE emission are robustness and ease of manipulation of the emitter cathodes which can be transported through atmospheric air and used without any problems in vacuum, low-pressure gas or plasma environments. Large-area arrangements of multiple emitters, switched in interleaved mode, can produce electron beams of any shape, current amplitude or time structure. The successful application of FE emission in accelerator technology has been demonstrated experimentally in several cases, e.g. for triggering high-power gas switches, for photocathodes in electron guns, and for electron-beam generators intended to generate, neutralize and enhance ion beams in ion sources and ion linacs. Other applications can be envisaged in microwave power generators and in the fields of electronics and vacuum microelectronics.

An investigation of MCNP6.1 beryllium oxide S(α, β) cross sections

DOE PAGES

Sartor, Raymond F.; Glazener, Natasha N.

2016-03-08

In MCNP6.1, materials are constructed by identifying the constituent isotopes (or elements in a few cases) individually. This list selects the corresponding microscopic cross sections calculated from the free-gas model to create the material macroscopic cross sections. Furthermore, the free-gas model and the corresponding material macroscopic cross sections assume that the interactions of atoms do not affect the nuclear cross sections.

Vesicle solubilization by bile salts: comparison of macroscopic theory and simulation.

PubMed

Haustein, M; Wahab, M; Mögel, H-J; Schiller, P

2015-04-14

Lipid metabolism is accompanied by the solubilization of lipid bilayer membranes by bile salts. We use Brownian dynamics simulations to study the solubilization of model membranes and vesicles by sodium cholate. The solubilization pathways of small and large vesicles are found to be different. Both results for small and large vesicles can be compared with predictions of a macroscopic theoretical description. The line tension of bilayer edges is an important parameter in the solubilization process. We propose a simple method to determine the line tension by analyzing the shape fluctuations of planar membrane patches. Macroscopic mechanical models provide a reasonable explanation for processes observed when a spherical vesicle consisting of lipids and adsorbed bile salt molecules is transformed into mixed lipid-bile salt micelles.

Applications of the microdosimetric function implemented in the macroscopic particle transport simulation code PHITS.

PubMed

Sato, Tatsuhiko; Watanabe, Ritsuko; Sihver, Lembit; Niita, Koji

2012-01-01

Microdosimetric quantities such as lineal energy are generally considered to be better indices than linear energy transfer (LET) for expressing the relative biological effectiveness (RBE) of high charge and energy particles. To calculate their probability densities (PD) in macroscopic matter, it is necessary to integrate microdosimetric tools such as track-structure simulation codes with macroscopic particle transport simulation codes. As an integration approach, the mathematical model for calculating the PD of microdosimetric quantities developed based on track-structure simulations was incorporated into the macroscopic particle transport simulation code PHITS (Particle and Heavy Ion Transport code System). The improved PHITS enables the PD in macroscopic matter to be calculated within a reasonable computation time, while taking their stochastic nature into account. The microdosimetric function of PHITS was applied to biological dose estimation for charged-particle therapy and risk estimation for astronauts. The former application was performed in combination with the microdosimetric kinetic model, while the latter employed the radiation quality factor expressed as a function of lineal energy. Owing to the unique features of the microdosimetric function, the improved PHITS has the potential to establish more sophisticated systems for radiological protection in space as well as for the treatment planning of charged-particle therapy.

On localization and void coalescence as a precursor to ductile fracture.

PubMed

Tekoğlu, C; Hutchinson, J W; Pardoen, T

2015-03-28

Two modes of plastic flow localization commonly occur in the ductile fracture of structural metals undergoing damage and failure by the mechanism involving void nucleation, growth and coalescence. The first mode consists of a macroscopic localization, usually linked to the softening effect of void nucleation and growth, in either a normal band or a shear band where the thickness of the band is comparable to void spacing. The second mode is coalescence with plastic strain localizing to the ligaments between voids by an internal necking process. The ductility of a material is tied to the strain at macroscopic localization, as this marks the limit of uniform straining at the macroscopic scale. The question addressed is whether macroscopic localization occurs prior to void coalescence or whether the two occur simultaneously. The relation between these two modes of localization is studied quantitatively in this paper using a three-dimensional elastic-plastic computational model representing a doubly periodic array of voids within a band confined between two semi-infinite outer blocks of the same material but without voids. At sufficiently high stress triaxiality, a clear separation exists between the two modes of localization. At lower stress triaxialities, the model predicts that the onset of macroscopic localization and coalescence occur simultaneously. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Controllable synthesis of mesoporous carbon nanospheres and Fe-N/carbon nanospheres as efficient oxygen reduction electrocatalysts

NASA Astrophysics Data System (ADS)

Wei, Jing; Liang, Yan; Zhang, Xinyi; Simon, George P.; Zhao, Dongyuan; Zhang, Jin; Jiang, Sanping; Wang, Huanting

2015-03-01

The synthesis of mesoporous carbon nanospheres (MCNs), especially with diameters below 200 nm remains a great challenge due to weak interactions between the carbon precursors and soft templates, as well as the uncontrollable cross-linking rate of carbon precursors. Herein, we demonstrate a simple acid-assisted, hydrothermal synthesis approach to synthesizing such uniform MCNs with well controlled diameters ranging from 20 to 150 nm under highly acidic conditions (2 M HCl). Both the carbon precursor and the template are partly protonated under such conditions and show additional Coulombic interactions with chloride ions (acts as mediators). This kind of enhanced interaction is similar to that of the ``I+X-S+'' mechanism in the synthesis of mesoporous metal oxide, which can effectively retard the cross-linking rate of resol molecules and avoid macroscopic phase separation during the hydrothermal synthesis. Due to their uniform spherical morphology, small diameter, and high surface areas, MCNs can be modified with Fe and N species via impregnation of cheap precursors (ferric nitrate and dicyandiamide), which are further converted into nonprecious electrocatalysts for oxygen reduction reactions. The resulting Fe-N/MCNs exhibit high catalytic activities, long-term stability and improved methanol tolerance under alkaline conditions, which can be potentially used in direct methanol fuel cells and metal-air batteries.The synthesis of mesoporous carbon nanospheres (MCNs), especially with diameters below 200 nm remains a great challenge due to weak interactions between the carbon precursors and soft templates, as well as the uncontrollable cross-linking rate of carbon precursors. Herein, we demonstrate a simple acid-assisted, hydrothermal synthesis approach to synthesizing such uniform MCNs with well controlled diameters ranging from 20 to 150 nm under highly acidic conditions (2 M HCl). Both the carbon precursor and the template are partly protonated under such conditions and show additional Coulombic interactions with chloride ions (acts as mediators). This kind of enhanced interaction is similar to that of the ``I+X-S+'' mechanism in the synthesis of mesoporous metal oxide, which can effectively retard the cross-linking rate of resol molecules and avoid macroscopic phase separation during the hydrothermal synthesis. Due to their uniform spherical morphology, small diameter, and high surface areas, MCNs can be modified with Fe and N species via impregnation of cheap precursors (ferric nitrate and dicyandiamide), which are further converted into nonprecious electrocatalysts for oxygen reduction reactions. The resulting Fe-N/MCNs exhibit high catalytic activities, long-term stability and improved methanol tolerance under alkaline conditions, which can be potentially used in direct methanol fuel cells and metal-air batteries. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00331h

Growth Angle: A Microscopic View

NASA Technical Reports Server (NTRS)

Mazuruk, Konstantin; Croll, Arne; Volz, Martin P.

2017-01-01

A microscopic continuum mechanical model of the growth angle is proposed. It is based on the van der Waals type framework that is used for surface force phenomena. The obtained augmented Laplace type integro-differential equations are, in general, difficult to analyze. Here we focused primarily on the particular case of equal melt and crystal surface energies. We derived an approximate equation for the meniscus shape, and obtained an analytical relationship between the contact and the growth angle. Interestingly, the same result can be obtained using the macroscopic model of Herring. The case of a macroscopically sharp corner is also considered. For this case, the macroscopic angle is not defined and it can be any angle between the contact angles of both flat surfaces. The microscopic model yields the smooth shape for the meniscus that also is not unique, but depends on the initial position of the meniscus.

Simple Model of Macroscopic Instability in XeCl Discharge Pumped Lasers

NASA Astrophysics Data System (ADS)

Ahmed, Belasri; Zoheir, Harrache

2003-10-01

The aim of this work is to study the development of the macroscopic non uniformity of the electron density of high pressure discharge for excimer lasers and eventually its propagation because of the medium kinetics phenomena. This study is executed using a transverse mono-dimensional model, in which the plasma is represented by a set of resistance's in parallel. This model was employed using a numerical code including three strongly coupled parts: electric circuit equations, electron Boltzmann equation, and kinetics equations (chemical kinetics model). The time variations of the electron density in each plasma element are obtained by solving a set of ordinary differential equations describing the plasma kinetics and external circuit. The use of the present model allows a good comprehension of the halogen depletion phenomena, which is the principal cause of laser ending and allows a simple study of a large-scale non uniformity in preionization density and its effects on electrical and chemical plasma properties. The obtained results indicate clearly that about 50consumed at the end of the pulse. KEY WORDS Excimer laser, XeCl, Modeling, Cold plasma, Kinetic, Halogen depletion, Macroscopic instability.

Micro-macroscopic coupled modeling of batteries and fuel cells. 2: Application to nickel-cadmium and nickel-metal hydride cells

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

Gu, W.B.; Wang, C.Y.; Liaw, B.Y.

1998-10-01

The micro-macroscopic coupled model developed in a companion paper is applied to predict the discharge and charge behaviors of nickel-cadmium (Ni-Cd) and nickel-metal hydride (Ni-MH) cells. The model integrates important microscopic phenomena such as proton or hydrogen diffusion and conduction of electrons in active materials into the macroscopic calculations of species and charge transfer. Simulation results for a full Ni-Cd cell and single MH electrode are presented and validated against the pseudo two-dimensional numerical model in the literature. In good agreement with the previous results, the present family of models is computationally more efficient and is particularly suitable for simulationsmore » of complex test conditions, such as the dynamic stress test and pulse charging for electric vehicles. In addition, a mathematical model for full Ni-MH cells is presented and sample simulations are performed for discharge and recharge with oxygen generation and recombination taken into account. These gas reactions represent an important mechanism for battery overcharge in the electric vehicle application.« less

Microscopic and macroscopic models for the onset and progression of Alzheimer's disease

NASA Astrophysics Data System (ADS)

Bertsch, Michiel; Franchi, Bruno; Carla Tesi, Maria; Tosin, Andrea

2017-10-01

In the first part of this paper we review a mathematical model for the onset and progression of Alzheimer’s disease (AD) that was developed in subsequent steps over several years. The model is meant to describe the evolution of AD in vivo. In Achdou et al (2013 J. Math. Biol. 67 1369-92) we treated the problem at a microscopic scale, where the typical length scale is a multiple of the size of the soma of a single neuron. Subsequently, in Bertsch et al (2017 Math. Med. Biol. 34 193-214) we concentrated on the macroscopic scale, where brain neurons are regarded as a continuous medium, structured by their degree of malfunctioning. In the second part of the paper we consider the relation between the microscopic and the macroscopic models. In particular we show under which assumptions the kinetic transport equation, which in the macroscopic model governs the evolution of the probability measure for the degree of malfunctioning of neurons, can be derived from a particle-based setting. The models are based on aggregation and diffusion equations for β-Amyloid (Aβ from now on), a protein fragment that healthy brains regularly produce and eliminate. In case of dementia Aβ monomers are no longer properly washed out and begin to coalesce forming eventually plaques. Two different mechanisms are assumed to be relevant for the temporal evolution of the disease: (i) diffusion and agglomeration of soluble polymers of amyloid, produced by damaged neurons; (ii) neuron-to-neuron prion-like transmission. In the microscopic model we consider mechanism (i), modelling it by a system of Smoluchowski equations for the amyloid concentration (describing the agglomeration phenomenon), with the addition of a diffusion term as well as of a source term on the neuronal membrane. At the macroscopic level instead we model processes (i) and (ii) by a system of Smoluchowski equations for the amyloid concentration, coupled to a kinetic-type transport equation for the distribution function of the degree of malfunctioning of the neurons. The transport equation contains an integral term describing the random onset of the disease as a jump process localized in particularly sensitive areas of the brain.

Exploring ferroelectric and magnetic properties of Tb-substituted m = 5 layered Aurivillius phase thin films

NASA Astrophysics Data System (ADS)

Faraz, Ahmad; Ricote, Jesus; Jimenez, Ricardo; Maity, Tuhin; Schmidt, Michael; Deepak, Nitin; Roy, Saibal; Pemble, Martyn E.; Keeney, Lynette

2018-03-01

Here, we report the effect of A-site substitution of Tb at the expense of Bi on the ferroelectric and magnetic properties in m = 5 layered 2-D Aurivillius Bi6Ti3Fe2O18 thin films. The nominal stoichiometry of the prepared compound is Tb0.40Bi5.6Fe2Ti3O18, Tb0.90Bi5.1Fe2Ti3O18, and Bi6Ti3Fe2O18. Phase examination reveals that only 0.40 mol. % is successfully substituted forming Tb0.40Bi5.6Fe2Ti3O18 thin films. Lateral and vertical piezoresponse switching loops up to 200 °C reveal responses for Bi6Ti3Fe2O18, Tb substituted Tb0.40Bi5.6Fe2Ti3O18, and Tb0.90Bi5.1Fe2Ti3O18 thin films along the in-plane (±42.31 pm/V, 88 pm/V and ±134 pm/V, respectively) compared with the out-of-plane (±6.15 pm/V, 19.83 pm/V and ±37.52 pm/V, respectively). The macroscopic in-plane polarization loops reveal in-plane saturation (Ps) and remanence polarization (Pr) for Bi6Ti3Fe2O18 of ±26.16 μC/cm2 and ±22 μC/cm2, whereas, ±32.75 μC/cm2 and ±22.11 μC/cm2, ±40.30 μC/cm2 and ±28.5 μC/cm2 for Tb0.40Bi5.6Fe2Ti3O18 and Tb0.90Bi5.1Fe2Ti3O18 thin films, respectively. No ferromagnetic signatures were observed for Bi6Ti3Fe2O18 and Tb0.40Bi5.6Fe2Ti3O18. However, a weak response was observed for the Tb0.90Bi5.1Fe2Ti3O18 at 2 K. Microstructural analysis of Tb0.90Bi5.1Fe2Ti3O18 revealed that it contains 4 vol. % Fe:Tb rich areas forming FexTbyOz, which accounts for the observed magnetic moment. This study demonstrates the importance of thorough microstructural analysis when determining whether magnetic signatures can be reliably assigned to the single-phase system. We conclude that Tb0.40Bi5.6Fe2Ti3O18 and Tb0.90Bi5.1Fe2Ti3O18 samples are not multiferroic but demonstrate the potential for Fe-RAM applications.

Development of a parallel FE simulator for modeling the whole trans-scale failure process of rock from meso- to engineering-scale

NASA Astrophysics Data System (ADS)

Li, Gen; Tang, Chun-An; Liang, Zheng-Zhao

2017-01-01

Multi-scale high-resolution modeling of rock failure process is a powerful means in modern rock mechanics studies to reveal the complex failure mechanism and to evaluate engineering risks. However, multi-scale continuous modeling of rock, from deformation, damage to failure, has raised high requirements on the design, implementation scheme and computation capacity of the numerical software system. This study is aimed at developing the parallel finite element procedure, a parallel rock failure process analysis (RFPA) simulator that is capable of modeling the whole trans-scale failure process of rock. Based on the statistical meso-damage mechanical method, the RFPA simulator is able to construct heterogeneous rock models with multiple mechanical properties, deal with and represent the trans-scale propagation of cracks, in which the stress and strain fields are solved for the damage evolution analysis of representative volume element by the parallel finite element method (FEM) solver. This paper describes the theoretical basis of the approach and provides the details of the parallel implementation on a Windows - Linux interactive platform. A numerical model is built to test the parallel performance of FEM solver. Numerical simulations are then carried out on a laboratory-scale uniaxial compression test, and field-scale net fracture spacing and engineering-scale rock slope examples, respectively. The simulation results indicate that relatively high speedup and computation efficiency can be achieved by the parallel FEM solver with a reasonable boot process. In laboratory-scale simulation, the well-known physical phenomena, such as the macroscopic fracture pattern and stress-strain responses, can be reproduced. In field-scale simulation, the formation process of net fracture spacing from initiation, propagation to saturation can be revealed completely. In engineering-scale simulation, the whole progressive failure process of the rock slope can be well modeled. It is shown that the parallel FE simulator developed in this study is an efficient tool for modeling the whole trans-scale failure process of rock from meso- to engineering-scale.

Coexisting nanoscale inverse spinel and rock salt crystallographic phases in NiCo2O4 epitaxial thin films grown by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Sharona, H.; Loukya, B.; Bhat, U.; Sahu, R.; Vishal, B.; Silwal, P.; Gupta, A.; Datta, R.

2017-12-01

The origin of alternating wavy dark-bright stripe-like contrast in strain contrast transmission electron microscopy images of NiCo2O4 (NCO) epitaxial thin films grown by pulsed laser deposition has been investigated. The nanoscale stripe-like pattern is determined to be associated with coexisting rock salt (RS) and inverse spinel crystal phases. The presence of two different phases, not addressed in previous reports, is experimentally confirmed by both electron diffraction and high resolution transmission electron microscopy imaging. First principles based calculations, together with compressive strain present in the films, support the formation of such coexisting crystallographic phases in NCO. Similar microstructural patterns and RS structure are not observed in epitaxial films of two other oxides of the spinel family, namely, NiFe2O4 and CoFe2O4. A correlation between the coexisting structures and the macroscopic physical properties of NCO is discussed.

Site occupancy of interstitial deuterium atoms in face-centred cubic iron

PubMed Central

Machida, Akihiko; Saitoh, Hiroyuki; Sugimoto, Hidehiko; Hattori, Takanori; Sano-Furukawa, Asami; Endo, Naruki; Katayama, Yoshinori; Iizuka, Riko; Sato, Toyoto; Matsuo, Motoaki; Orimo, Shin-ichi; Aoki, Katsutoshi

2014-01-01

Hydrogen composition and occupation state provide basic information for understanding various properties of the metal–hydrogen system, ranging from microscopic properties such as hydrogen diffusion to macroscopic properties such as phase stability. Here the deuterization process of face-centred cubic Fe to form solid-solution face-centred cubic FeDx is investigated using in situ neutron diffraction at high temperature and pressure. In a completely deuterized specimen at 988 K and 6.3 GPa, deuterium atoms occupy octahedral and tetrahedral interstitial sites with an occupancy of 0.532(9) and 0.056(5), respectively, giving a deuterium composition x of 0.64(1). During deuterization, the metal lattice expands approximately linearly with deuterium composition at a rate of 2.21 Å3 per deuterium atom. The minor occupation of the tetrahedral site is thermally driven by the intersite movement of deuterium atoms along the ‹111› direction in the face-centred cubic metal lattice. PMID:25256789

Investigation of grain-scale microstructural variability in tantalum using crystal plasticity-finite element simulations

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

Lim, Hojun; Dingreville, Rémi; Deibler, Lisa A.

In this research, a crystal plasticity-finite element (CP-FE) model is used to investigate the effects of microstructural variability at a notch tip in tantalum single crystals and polycrystals. It is shown that at the macroscopic scale, the mechanical response of single crystals is sensitive to the crystallographic orientation while the response of polycrystals shows relatively small susceptibility to it. However, at the microscopic scale, the local stress and strain fields in the vicinity of the crack tip are completely determined by the local crystallographic orientation at the crack tip for both single and polycrystalline specimens with similar mechanical field distributions.more » Variability in the local metrics used (maximum von Mises stress and equivalent plastic strain at 3% deformation) for 100 different realizations of polycrystals fluctuates by up to a factor of 2–7 depending on the local crystallographic texture. Comparison with experimental data shows that the CP model captures variability in stress–strain response of polycrystals that can be attributed to the grain-scale microstructural variability. In conclusion, this work provides a convenient approach to investigate fluctuations in the mechanical behavior of polycrystalline materials induced by grain morphology and crystallographic orientations.« less

Investigation of grain-scale microstructural variability in tantalum using crystal plasticity-finite element simulations

DOE PAGES

Lim, Hojun; Dingreville, Rémi; Deibler, Lisa A.; ...

2016-02-27

In this research, a crystal plasticity-finite element (CP-FE) model is used to investigate the effects of microstructural variability at a notch tip in tantalum single crystals and polycrystals. It is shown that at the macroscopic scale, the mechanical response of single crystals is sensitive to the crystallographic orientation while the response of polycrystals shows relatively small susceptibility to it. However, at the microscopic scale, the local stress and strain fields in the vicinity of the crack tip are completely determined by the local crystallographic orientation at the crack tip for both single and polycrystalline specimens with similar mechanical field distributions.more » Variability in the local metrics used (maximum von Mises stress and equivalent plastic strain at 3% deformation) for 100 different realizations of polycrystals fluctuates by up to a factor of 2–7 depending on the local crystallographic texture. Comparison with experimental data shows that the CP model captures variability in stress–strain response of polycrystals that can be attributed to the grain-scale microstructural variability. In conclusion, this work provides a convenient approach to investigate fluctuations in the mechanical behavior of polycrystalline materials induced by grain morphology and crystallographic orientations.« less

Using Non-linear Homogenization to Improve the Performance of Macroscopic Damage Models of Trabecular Bone.

PubMed

Levrero-Florencio, Francesc; Pankaj, Pankaj

2018-01-01

Realistic macro-level finite element simulations of the mechanical behavior of trabecular bone, a cellular anisotropic material, require a suitable constitutive model; a model that incorporates the mechanical response of bone for complex loading scenarios and includes post-elastic phenomena, such as plasticity (permanent deformations) and damage (permanent stiffness reduction), which bone is likely to experience. Some such models have been developed by conducting homogenization-based multiscale finite element simulations on bone micro-structure. While homogenization has been fairly successful in the elastic regime and, to some extent, in modeling the macroscopic plastic response, it has remained a challenge with respect to modeling damage. This study uses a homogenization scheme to upscale the damage behavior from the tissue level (microscale) to the organ level (macroscale) and assesses the suitability of different damage constitutive laws. Ten cubic specimens were each subjected to 21 strain-controlled load cases for a small range of macroscopic post-elastic strains. Isotropic and anisotropic criteria were considered, density and fabric relationships were used in the formulation of the damage law, and a combined isotropic/anisotropic law with tension/compression asymmetry was formulated, based on the homogenized results, as a possible alternative to the currently used single scalar damage criterion. This computational study enhances the current knowledge on the macroscopic damage behavior of trabecular bone. By developing relationships of damage progression with bone's micro-architectural indices (density and fabric) the study also provides an aid for the creation of more precise macroscale continuum models, which are likely to improve clinical predictions.

Incorporating interfacial phenomena in solidification models

NASA Technical Reports Server (NTRS)

Beckermann, Christoph; Wang, Chao Yang

1994-01-01

A general methodology is available for the incorporation of microscopic interfacial phenomena in macroscopic solidification models that include diffusion and convection. The method is derived from a formal averaging procedure and a multiphase approach, and relies on the presence of interfacial integrals in the macroscopic transport equations. In a wider engineering context, these techniques are not new, but their application in the analysis and modeling of solidification processes has largely been overlooked. This article describes the techniques and demonstrates their utility in two examples in which microscopic interfacial phenomena are of great importance.

Redox activity distinguishes solid-state electron transport from solution-based electron transfer in a natural and artificial protein: cytochrome C and hemin-doped human serum albumin.

PubMed

Amdursky, Nadav; Ferber, Doron; Pecht, Israel; Sheves, Mordechai; Cahen, David

2013-10-28

Integrating proteins in molecular electronic devices requires control over their solid-state electronic transport behavior. Unlike "traditional" electron transfer (ET) measurements of proteins that involve liquid environments and a redox cycle, no redox cofactor is needed for solid-state electron transport (ETp) across the protein. Here we show the fundamental difference between these two approaches by macroscopic area measurements, which allow measuring ETp temperature dependence down to cryogenic temperatures, via cytochrome C (Cyt C), an ET protein with a heme (Fe-porphyrin) prosthetic group as a redox centre. We compare the ETp to electrochemical ET measurements, and do so also for the protein without the Fe (with metal-free porphyrin) and without porphyrin. As removing the porphyrin irreversibly alters the protein's conformation, we repeat these measurements with human serum albumin (HSA), 'doped' (by non-covalent binding) with a single hemin equivalent, i.e., these natural and artificial proteins share a common prosthetic group. ETp via Cyt C and HSA-hemin are very similar in terms of current magnitude and temperature dependence, which suggests similar ETp mechanisms via these two systems, thermally activated hopping (with ~0.1 eV activation energy) >190 K and tunneling by superexchange <190 K. Also, ET rates to and from the Fe redox centres (Fe(2+) <=> Fe(3+) + e(-)), measured by electrochemistry of HSA-hemin are only 4 times lower than those for Cyt C. However, while removing the Fe redox centre from the porphyrin ring markedly affects the ET rate, it hardly changes the ETp currents through these proteins, while removing the macrocycle (from HSA, which retains its conformation) significantly reduces ETp efficiency. These results show that solid-state ETp across proteins does not require the presence of a redox cofactor, and that while for ET the Fe ion is the main electron mediator, for ETp the porphyrin ring has this function.

The use of many-body physics and thermodynamics to describe the dynamics of rhythmic generators in sensory cortices engaged in memory and learning.

PubMed

Vitiello, Giuseppe

2015-04-01

The problem of the transition from the molecular and cellular level to the macroscopic level of observed assemblies of myriads of neurons is the subject addressed in this report. The great amount of detailed information available at molecular and cellular level seems not sufficient to account for the high effectiveness and reliability observed in the brain macroscopic functioning. It is suggested that the dissipative many-body model and thermodynamics might offer the dynamical frame underlying the rich phenomenology observed at microscopic and macroscopic level and help in the understanding on how to fill the gap between the bio-molecular and cellular level and the one of brain macroscopic functioning. Copyright © 2014 Elsevier Ltd. All rights reserved.

Lattice gas simulations of dynamical geometry in one dimension.

PubMed

Love, Peter J; Boghosian, Bruce M; Meyer, David A

2004-08-15

We present numerical results obtained using a lattice gas model with dynamical geometry. The (irreversible) macroscopic behaviour of the geometry (size) of the lattice is discussed in terms of a simple scaling theory and obtained numerically. The emergence of irreversible behaviour from the reversible microscopic lattice gas rules is discussed in terms of the constraint that the macroscopic evolution be reproducible. The average size of the lattice exhibits power-law growth with exponent at late times. The deviation of the macroscopic behaviour from reproducibility for particular initial conditions ('rogue states') is investigated as a function of system size. The number of such 'rogue states' is observed to decrease with increasing system size. Two mean-field analyses of the macroscopic behaviour are also presented. Copyright 2004 The Royal Society

Multi-scale modelling of rubber-like materials and soft tissues: an appraisal

PubMed Central

Puglisi, G.

2016-01-01

We survey, in a partial way, multi-scale approaches for the modelling of rubber-like and soft tissues and compare them with classical macroscopic phenomenological models. Our aim is to show how it is possible to obtain practical mathematical models for the mechanical behaviour of these materials incorporating mesoscopic (network scale) information. Multi-scale approaches are crucial for the theoretical comprehension and prediction of the complex mechanical response of these materials. Moreover, such models are fundamental in the perspective of the design, through manipulation at the micro- and nano-scales, of new polymeric and bioinspired materials with exceptional macroscopic properties. PMID:27118927

Macroscopic Models of Local Field Potentials and the Apparent 1/f Noise in Brain Activity

PubMed Central

Bédard, Claude; Destexhe, Alain

2009-01-01

The power spectrum of local field potentials (LFPs) has been reported to scale as the inverse of the frequency, but the origin of this 1/f noise is at present unclear. Macroscopic measurements in cortical tissue demonstrated that electric conductivity (as well as permittivity) is frequency-dependent, while other measurements failed to evidence any dependence on frequency. In this article, we propose a model of the genesis of LFPs that accounts for the above data and contradictions. Starting from first principles (Maxwell equations), we introduce a macroscopic formalism in which macroscopic measurements are naturally incorporated, and also examine different physical causes for the frequency dependence. We suggest that ionic diffusion primes over electric field effects, and is responsible for the frequency dependence. This explains the contradictory observations, and also reproduces the 1/f power spectral structure of LFPs, as well as more complex frequency scaling. Finally, we suggest a measurement method to reveal the frequency dependence of current propagation in biological tissue, and which could be used to directly test the predictions of this formalism. PMID:19348744

Macroscopic cartilage repair scoring of defect fill, integration and total points correlate with corresponding items in histological scoring systems - a study in adult sheep.

PubMed

Goebel, L; Orth, P; Cucchiarini, M; Pape, D; Madry, H

2017-04-01

To correlate osteochondral repair assessed by validated macroscopic scoring systems with established semiquantitative histological analyses in an ovine model and to test the hypothesis that important macroscopic individual categories correlate with their corresponding histological counterparts. In the weight-bearing portion of medial femoral condyles (n = 38) of 19 female adult Merino sheep (age 2-4 years; weight 70 ± 20 kg) full-thickness chondral defects were created (size 4 × 8 mm; International Cartilage Repair Society (ICRS) grade 3C) and treated with Pridie drilling. After sacrifice, 1520 blinded macroscopic observations from three observers at 2-3 time points including five different macroscopic scoring systems demonstrating all grades of cartilage repair where correlated with corresponding categories from 418 blinded histological sections. Categories "defect fill" and "total points" of different macroscopic scoring systems correlated well with their histological counterparts from the Wakitani and Sellers scores (all P ≤ 0.001). "Integration" was assessed in both histological scoring systems and in the macroscopic ICRS, Oswestry and Jung scores. Here, a significant relationship always existed (0.020 ≤ P ≤ 0.049), except for Wakitani and Oswestry (P = 0.054). No relationship was observed for the "surface" between histology and macroscopy (all P > 0.05). Major individual morphological categories "defect fill" and "integration", and "total points" of macroscopic scoring systems correlate with their corresponding categories in elementary and complex histological scoring systems. Thus, macroscopy allows to precisely predict key histological aspects of articular cartilage repair, underlining the specific value of macroscopic scoring for examining cartilage repair. Copyright © 2016 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

Macroscopic appearance of Type IV and giant Type III is a high risk for a poor prognosis in pathological stage II/III advanced gastric cancer with postoperative adjuvant chemotherapy

PubMed Central

Yamashita, Keishi; Ema, Akira; Hosoda, Kei; Mieno, Hiroaki; Moriya, Hiromitsu; Katada, Natsuya; Watanabe, Masahiko

2017-01-01

AIM To evaluate whether a high risk macroscopic appearance (Type IV and giant Type III) is associated with a dismal prognosis after curative surgery, because its prognostic relevance remains elusive in pathological stage II/III (pStage II/III) gastric cancer. METHODS One hundred and seventy-two advanced gastric cancer (defined as pT2 or beyond) patients with pStage II/III who underwent curative surgery plus adjuvant S1 chemotherapy were evaluated, and the prognostic relevance of a high-risk macroscopic appearance was examined. RESULTS Advanced gastric cancers with a high-risk macroscopic appearance were retrospectively identified by preoperative recorded images. A high-risk macroscopic appearance showed a significantly worse relapse free survival (RFS) (35.7%) and overall survival (OS) (34%) than an average risk appearance (P = 0.0003 and P < 0.0001, respectively). A high-risk macroscopic appearance was significantly associated with the 13th Japanese Gastric Cancer Association (JGCA) pT (P = 0.01), but not with the 13th JGCA pN. On univariate analysis for RFS and OS, prognostic factors included 13th JGCA pStage (P < 0.0001) and other clinicopathological factors including macroscopic appearance. A multivariate Cox proportional hazards model for univariate prognostic factors identified high-risk macroscopic appearance (P = 0.036, HR = 2.29 for RFS and P = 0.021, HR = 2.74 for OS) as an independent prognostic indicator. CONCLUSION A high-risk macroscopic appearance was associated with a poor prognosis, and it could be a prognostic factor independent of 13th JGCA stage in pStage II/III advanced gastric cancer. PMID:28451064

Spatiotemporal dynamics of the spin transition in [Fe (HB(tz)3) 2] single crystals

NASA Astrophysics Data System (ADS)

Ridier, Karl; Rat, Sylvain; Shepherd, Helena J.; Salmon, Lionel; Nicolazzi, William; Molnár, Gábor; Bousseksou, Azzedine

2017-10-01

The spatiotemporal dynamics of the spin transition have been thoroughly investigated in single crystals of the mononuclear spin-crossover (SCO) complex [Fe (HB (tz )3)2] (tz = 1 ,2 ,4-triazol-1-yl) by optical microscopy. This compound exhibits an abrupt spin transition centered at 334 K with a narrow thermal hysteresis loop of ˜1 K (first-order transition). Most single crystals of this compound reveal exceptional resilience upon repeated switching (several hundred cycles), which allowed repeatable and quantitative measurements of the spatiotemporal dynamics of the nucleation and growth processes to be carried out. These experiments revealed remarkable properties of the thermally induced spin transition: high stability of the thermal hysteresis loop, unprecedented large velocities of the macroscopic low-spin/high-spin phase boundaries up to 500 µm/s, and no visible dependency on the temperature scan rate. We have also studied the dynamics of the low-spin → high-spin transition induced by a local photothermal excitation generated by a spatially localized (Ø = 2 μ m ) continuous laser beam. Interesting phenomena have been evidenced both in quasistatic and dynamic conditions (e.g., threshold effects and long incubation periods, thermal activation of the phase boundary propagation, stabilization of the crystal in a stationary biphasic state, and thermal cutoff frequency). These measurements demonstrated the importance of thermal effects in the transition dynamics, and they enabled an accurate determination of the thermal properties of the SCO compound in the framework of a simple theoretical model.

Discontinuities of Plastic Deformation in Metallic Glasses with Different Glass Forming Ability

NASA Astrophysics Data System (ADS)

Hurakova, Maria; Csach, Kornel; Miskuf, Jozef; Jurikova, Alena; Demcak, Stefan; Ocelik, Vaclav; Hosson, Jeff Th. M. De

The metallic ribbons Fe40Ni40B20, Cu47Ti35Zr11Ni6Si1 and Zr65Cu17.5Ni10Al7.5 with different microhardness and glass forming ability were studied at different loading rates from 0.05 to 100 mN/s. We describe in details the differences in elemental discontinuities on the loading curves for the studied alloys. It was found that the discontinuities began at a certain local deformation independently on the macroscopic mechanical properties of a ribbon. More developed discontinuities at higher deformations are created for the materials with lower microhardness and so lower strength.

The Virtual Brain Integrates Computational Modeling and Multimodal Neuroimaging

PubMed Central

Schirner, Michael; McIntosh, Anthony R.; Jirsa, Viktor K.

2013-01-01

Abstract Brain function is thought to emerge from the interactions among neuronal populations. Apart from traditional efforts to reproduce brain dynamics from the micro- to macroscopic scales, complementary approaches develop phenomenological models of lower complexity. Such macroscopic models typically generate only a few selected—ideally functionally relevant—aspects of the brain dynamics. Importantly, they often allow an understanding of the underlying mechanisms beyond computational reproduction. Adding detail to these models will widen their ability to reproduce a broader range of dynamic features of the brain. For instance, such models allow for the exploration of consequences of focal and distributed pathological changes in the system, enabling us to identify and develop approaches to counteract those unfavorable processes. Toward this end, The Virtual Brain (TVB) (www.thevirtualbrain.org), a neuroinformatics platform with a brain simulator that incorporates a range of neuronal models and dynamics at its core, has been developed. This integrated framework allows the model-based simulation, analysis, and inference of neurophysiological mechanisms over several brain scales that underlie the generation of macroscopic neuroimaging signals. In this article, we describe how TVB works, and we present the first proof of concept. PMID:23442172

AFM Study of Surface Nanobubbles on Binary Self-Assembled Monolayers on Ultraflat Gold with Identical Macroscopic Static Water Contact Angles and Different Terminal Functional Groups.

PubMed

Song, Bo; Chen, Kun; Schmittel, Michael; Schönherr, Holger

2016-11-01

All experimental findings related to surface nanobubbles, such as their pronounced stability and the striking differences of macroscopic and apparent nanoscopic contact angles, need to be addressed in any theory or model of surface nanobubbles. In this work we critically test a recent explanation of surface nanobubble stability and their consequences and contrast this with previously proposed models. In particular, we elucidated the effect of surface chemical composition of well-controlled solid-aqueous interfaces of identical roughness and defect density on the apparent nanoscopic contact angles. Expanding on a previous atomic force microscopy (AFM) study on the systematic variation of the macroscopic wettability using binary self-assembled monolayers (SAMs) on ultraflat template stripped gold (TSG), we assessed here the effect of different surface chemical composition for macroscopically identical static water contact angles. SAMs on TSG with a constant macroscopic water contact angle of 81 ± 2° were obtained by coadsorption of a methyl-terminated thiol and a second thiol with different terminal functional groups, including hydroxy, amino, and carboxylic acid groups. In addition, surface nanobubbles formed by entrainment of air on SAMs of a bromoisobutyrate-terminated thiol were analyzed by AFM. Despite the widely differing surface potentials and different functionality, such as hydrogen bond acceptor or donor, and different dipole moments and polarizability, the nanoscopic contact angles (measured through the condensed phase and corrected for AFM tip broadening effects) were found to be 145 ± 10° for all surfaces. Hence, different chemical functionalities at identical macroscopic static water contact angle do not noticeably influence the apparent nanoscopic contact angle of surface nanobubbles. This universal contact angle is in agreement with recent models that rely on contact line pinning and the equilibrium of gas outflux due to the Laplace pressure and gas influx due to gas oversaturation in the aqueous medium.

Understanding the Pulsar High Energy Emission: Macroscopic and Kinetic Models

NASA Astrophysics Data System (ADS)

Kalapotharakos, Constantinos; Brambilla, Gabriele; Timokhin, Andrey; Kust Harding, Alice; Kazanas, Demos

2017-08-01

Pulsars are extraordinary objects powered by the rotation of magnetic fields of order 10^8, 10^12G anchored onto neutron stars and rotating with periods 10^(-3)-10s. These fields mediate the conversion of their rotational energy into MHD winds and at the same time accelerate particles to energies sufficiently high to produce GeV photons. Fermi, since its launch in 2008, has established several trends among the observed gamma-ray pulsar properties playing a catalytic role in the current modeling of the high energy emission in pulsar magnetospheres. We judiciously use the guidance provided by the Fermi data to yield meaningful constraints on the macroscopic parameters of our global dissipative pulsar magnetosphere models. Our FIDO (Force-Free Inside, Dissipative Outside) models indicate that the dissipative regions lie outside the light cylinder near the equatorial current sheet. Our models reproduce the light-curve phenomenology while a detailed comparison of the model spectral properties with those observed by Fermi reveals the dependence of the macroscopic conductivity parameter on the spin-down rate providing a unique insight into the understanding of the physical mechanisms behind the high-energy emission in pulsar magnetospheres. Finally, we further exploit these important results by building self-consistent 3D global kinetic particle-in-cell (PIC) models which, eventually, provide the dependence of the macroscopic parameter behavior (e.g. conductivity) on the microphysical properties (e.g. particle multiplicities, particle injection rates). Our PIC models provide field structures and particle distributions that are not only consistent with each other but also able to reproduce a broad range of the observed gamma-ray phenomenology (light curves and spectral properties) of both young and millisecond pulsars.

Macroscopic domain formation during cooling in the platelet plasma membrane: an issue of low cholesterol content

PubMed Central

Bali, Rachna; Savino, Laura; Ramirez, Diego A.; Tsvetkova, Nelly M.; Bagatolli, Luis; Tablin, Fern; Crowe, John H.; Leidy, Chad

2009-01-01

There has been ample debate on whether cell membranes can present macroscopic lipid domains as predicted by three-component phase diagrams obtained by fluorescence microscopy. Several groups have argued that membrane proteins and interactions with the cytoskeleton inhibit the formation of large domains. In contrast, some polarizable cells do show large regions with qualitative differences in lipid fluidity. It is important to ask more precisely, based on the current phase diagrams, under what conditions would large domains be expected to form in cells. In this work we study the thermotropic phase behavior of the platelet plasma membrane by FTIR, and compare it to a POPC/Sphingomyelin/Cholesterol model representing the outer leaflet composition. We find that this model closely reflects the platelet phase behavior. Previous work has shown that the platelet plasma membrane presents inhomogeneous distribution of DiI18:0 at 24°C, but not at 37°C, which suggests the formation of macroscopic lipid domains at low temperatures. We show by fluorescence microscopy, and by comparison with published phase diagrams, that the outer leaflet model system enters the macroscopic domain region only at the lower temperature. In addition, the low cholesterol content in platelets (~15 mol %), appears to be crucial for the formation of large domains during cooling. PMID:19341703

Controllable synthesis of mesoporous carbon nanospheres and Fe-N/carbon nanospheres as efficient oxygen reduction electrocatalysts.

PubMed

Wei, Jing; Liang, Yan; Zhang, Xinyi; Simon, George P; Zhao, Dongyuan; Zhang, Jin; Jiang, Sanping; Wang, Huanting

2015-04-14

The synthesis of mesoporous carbon nanospheres (MCNs), especially with diameters below 200 nm remains a great challenge due to weak interactions between the carbon precursors and soft templates, as well as the uncontrollable cross-linking rate of carbon precursors. Herein, we demonstrate a simple acid-assisted, hydrothermal synthesis approach to synthesizing such uniform MCNs with well controlled diameters ranging from 20 to 150 nm under highly acidic conditions (2 M HCl). Both the carbon precursor and the template are partly protonated under such conditions and show additional Coulombic interactions with chloride ions (acts as mediators). This kind of enhanced interaction is similar to that of the "I(+)X(-)S(+)" mechanism in the synthesis of mesoporous metal oxide, which can effectively retard the cross-linking rate of resol molecules and avoid macroscopic phase separation during the hydrothermal synthesis. Due to their uniform spherical morphology, small diameter, and high surface areas, MCNs can be modified with Fe and N species via impregnation of cheap precursors (ferric nitrate and dicyandiamide), which are further converted into nonprecious electrocatalysts for oxygen reduction reactions. The resulting Fe-N/MCNs exhibit high catalytic activities, long-term stability and improved methanol tolerance under alkaline conditions, which can be potentially used in direct methanol fuel cells and metal-air batteries.

Characterization of Secondary Mineral Grain Coatings and their Role as Diffusion-controlled Sinks and Sources for Metal Contaminants

NASA Astrophysics Data System (ADS)

Davis, J. A.; Guo, H.; Lai, B.; Kemner, K. M.; Ercius, P.; Fox, P. M.; Singer, D. M.; Minor, A.; Waychunas, G.

2012-12-01

Many important geochemical reactions occur at the mineral-water interface, including sorption and desorption reactions of contaminants. Fundamental knowledge of the kinetics of these processes is based primarily on experimental observations of reactions at faces of single crystals or macroscopic data from pure mineral powder suspensions. Sorption reactions at crystal faces are generally very fast, on the order of microseconds or less, with reaction times often limited only by film diffusion at the mineral-water interface. In well-stirred suspensions of aquifer sediments, however, sorptive equilibrium can take many hours or days to achieve steady-state concentrations. We have examined the potential reasons for sorption rate limitation using uranium(VI) sorption by sediments from a sandy aquifer in Savannah River, South Carolina (USA). U(VI) sorption by sand-sized grains from the aquifer is dominated by reaction with secondary mineral coatings on quartz and feldspar grains. The coatings studied were on the order of 15 microns in thickness (i.e., from quartz grain to aqueous solution) and composed primarily of clay minerals and hematite of varying particle size. Microfocused-XRF imaging of elemental concentrations (e.g., U, Fe) of polished cross-sections of the grain/coating contact showed strong spatial correlations of U and Fe within the coatings, regardless of the length of reaction time (30 minutes to 4 weeks). The spatial resolution of the μ-XRF technique is of the order of 2 microns in horizontal directions, but the uncertainty of the observed spatial gradients is high due to grain curvature away from the polished surface and fluorescence contributed from the entire 30 micron thickness of a typical grain/epoxy thin section. TEM characterization of focused-ion-beam (FIB), vertically-extracted samples of the grain-coating contact shows that complex pore networks exist within the coatings of variable dimensions and unknown connectivity. Using scanning TEM (STEM) tomography, it can be seen that there are large numbers of pore throat sizes less than 10 nm within the coatings. We hypothesize that diffusion through these pores, which likely have electrically charged surfaces, controls the observed macroscopic rates of U(VI) sorption in batch experiments with sand grains. Evidence to support this hypothesis was observed by studying U and Fe fluorescence spatial variation within FIB samples (1 micron thick) at 200 nm spatial resolution. With this greater spatial resolution, it is possible to see U concentration variations within the coatings that are dependent on the time of sorption reaction, and illustrates how the coating environment constitutes a diffusion constraint to achieve adsorptive equilibrium between an aqueous phase and the mineral surfaces. Including this diffusion constraint within conceptual models for reactive contaminant transport may be significant at the field scale, because secondary mineral coatings are potentially both sinks and sources of contaminants depending on the history of a contaminated site. This is important in resolving long-term transport predictions at DOE sites, such as Hanford and Savannah River, where equilibrium versus kinetic reactive transport models are being evaluated.

Numerical Investigation of the Macroscopic Mechanical Behavior of NiTi-Hybrid Composites Subjected to Static Load-Unload-Reload Path

NASA Astrophysics Data System (ADS)

Taheri-Behrooz, Fathollah; Kiani, Ali

2017-04-01

Shape memory alloys (SMAs) are a type of shape memory materials that recover large deformation and return to their primary shape by rising temperature. In the current research, the effect of embedding SMA wires on the macroscopic mechanical behavior of glass-epoxy composites is investigated through finite element simulations. A perfect interface between SMA wires and the host composite is assumed. Effects of various parameters such as SMA wires volume fraction, SMA wires pre-strain and temperature are investigated during loading-unloading and reloading steps by employing ANSYS software. In order to quantify the extent of induced compressive stress in the host composite and residual tensile stress in the SMA wires, a theoretical approach is presented. Finally, it was shown that smart structures fabricated using composite layers and pre-strained SMA wires exhibited overall stiffness reduction at both ambient and elevated temperatures which were increased by adding SMA volume fraction. Also, the induced compressive stress on the host composite was increased remarkably using 4% pre-strained SMA wires at elevated temperature. Results obtained by FE simulations were in good correlation with the rule of mixture predictions and available experimental data in the literature.

Estimation of macroscopic elastic characteristics for hierarchical anisotropic solids based on probabilistic approach

NASA Astrophysics Data System (ADS)

Smolina, Irina Yu.

2015-10-01

Mechanical properties of a cable are of great importance in design and strength calculation of flexible cables. The problem of determination of elastic properties and rigidity characteristics of a cable modeled by anisotropic helical elastic rod is considered. These characteristics are calculated indirectly by means of the parameters received from statistical processing of experimental data. These parameters are considered as random quantities. With taking into account probable nature of these parameters the formulas for estimation of the macroscopic elastic moduli of a cable are obtained. The calculating expressions for macroscopic flexural rigidity, shear rigidity and torsion rigidity using the macroscopic elastic characteristics obtained before are presented. Statistical estimations of the rigidity characteristics of some cable grades are adduced. A comparison with those characteristics received on the basis of deterministic approach is given.

Parallel stochastic simulation of macroscopic calcium currents.

PubMed

González-Vélez, Virginia; González-Vélez, Horacio

2007-06-01

This work introduces MACACO, a macroscopic calcium currents simulator. It provides a parameter-sweep framework which computes macroscopic Ca(2+) currents from the individual aggregation of unitary currents, using a stochastic model for L-type Ca(2+) channels. MACACO uses a simplified 3-state Markov model to simulate the response of each Ca(2+) channel to different voltage inputs to the cell. In order to provide an accurate systematic view for the stochastic nature of the calcium channels, MACACO is composed of an experiment generator, a central simulation engine and a post-processing script component. Due to the computational complexity of the problem and the dimensions of the parameter space, the MACACO simulation engine employs a grid-enabled task farm. Having been designed as a computational biology tool, MACACO heavily borrows from the way cell physiologists conduct and report their experimental work.

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.

Image-Based Macro-Micro Finite Element Models of a Canine Femur with Implant Design Implications

NASA Astrophysics Data System (ADS)

Ghosh, Somnath; Krishnan, Ganapathi; Dyce, Jonathan

2006-06-01

In this paper, a comprehensive model of a bone-cement-implant assembly is developed for a canine cemented femoral prosthesis system. Various steps in this development entail profiling the canine femur contours by computed tomography (CT) scanning, computer aided design (CAD) reconstruction of the canine femur from CT images, CAD modeling of the implant from implant blue prints and CAD modeling of the interface cement. Finite element analysis of the macroscopic assembly is conducted for stress analysis in individual components of the system, accounting for variation in density and material properties in the porous bone material. A sensitivity analysis is conducted with the macroscopic model to investigate the effect of implant design variables on the stress distribution in the assembly. Subsequently, rigorous microstructural analysis of the bone incorporating the morphological intricacies is conducted. Various steps in this development include acquisition of the bone microstructural data from histological serial sectioning, stacking of sections to obtain 3D renderings of void distributions, microstructural characterization and determination of properties and, finally, microstructural stress analysis using a 3D Voronoi cell finite element method. Generation of the simulated microstructure and analysis by the 3D Voronoi cell finite element model provides a new way of modeling complex microstructures and correlating to morphological characteristics. An inverse calculation of the material parameters of bone by combining macroscopic experiments with microstructural characterization and analysis provides a new approach to evaluating properties without having to do experiments at this scale. Finally, the microstructural stresses in the femur are computed using the 3D VCFEM to study the stress distribution at the scale of the bone porosity. Significant difference is observed between the macroscopic stresses and the peak microscopic stresses at different locations.

Quantum rotor model for a Bose-Einstein condensate of dipolar molecules.

PubMed

Armaitis, J; Duine, R A; Stoof, H T C

2013-11-22

We show that a Bose-Einstein condensate of heteronuclear molecules in the regime of small and static electric fields is described by a quantum rotor model for the macroscopic electric dipole moment of the molecular gas cloud. We solve this model exactly and find the symmetric, i.e., rotationally invariant, and dipolar phases expected from the single-molecule problem, but also an axial and planar nematic phase due to many-body effects. Investigation of the wave function of the macroscopic dipole moment also reveals squeezing of the probability distribution for the angular momentum of the molecules.

Significantly enhanced ferroelectricity and magnetic properties in (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3}-modified BiFeO{sub 3} ceramics

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

Liu, Juan; Liu, Xiao Qiang, E-mail: xqliu@zju.edu.cn, E-mail: xmchen59@zju.edu.cn; Chen, Xiang Ming, E-mail: xqliu@zju.edu.cn, E-mail: xmchen59@zju.edu.cn

2015-05-07

BiFeO{sub 3} multiferroic ceramics were modified by introducing (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3} to form solid solutions. The single phase structure was easy to be obtained in Bi{sub 1−x}(Sr{sub 0.5}Ca{sub 0.5}){sub x}Fe{sub 1−x}Ti{sub x}O{sub 3} (x = 0.2, 0.25, 0.3, and 0.4) solid solutions. Rietveld refinement of X-ray diffraction data revealed a transition from rhombohedral R3c (x = 0.2, 0.25, and 0.3) to orthorhombic Pnma (x = 0.4). Current density-field (J-E) characteristics indicated that the leakage current density was reduced by three orders of magnitude in Bi{sub 1−x}(Sr{sub 0.5}Ca{sub 0.5}){sub x}Fe{sub 1−x}Ti{sub x}O{sub 3} ceramics. Both the ferroelectricity and magnetic properties were significantly enhanced in the presentmore » solid solutions. P-E hysteresis loop measurements with dynamic leakage current compensation methods showed the significantly enhanced ferroelectric properties for x = 0.25 and 0.3 and the paraelectric behavior for x = 0.4. The best ferromagnetic characteristics were achieved in the composition of x = 0.25, where the saturated M-H loop was determined with M{sub r} = 34.8 emu/mol. The improvement of ferroelectricity was mainly due to the suppressed leakage current, and the enhanced magnetism originated from the partial substitution of Fe{sup 3+} by Ti{sup 4+}, which destroyed its previous spiral structure to allow the appearance of a macroscopic magnetization.« less

Insights into the Structure and Metabolic Function of Microbes That Shape Pelagic Iron-Rich Aggregates (“Iron Snow”)

PubMed Central

Lu, Shipeng; Chourey, Karuna; Reiche, Marco; Nietzsche, Sandor; Shah, Manesh B.; Neu, Thomas R.; Hettich, Robert L.

2013-01-01

Microbial ferrous iron [Fe(II)] oxidation leads to the formation of iron-rich macroscopic aggregates (“iron snow”) at the redoxcline in a stratified lignite mine lake in east-central Germany. We aimed to identify the abundant Fe-oxidizing and Fe-reducing microorganisms likely to be involved in the formation and transformation of iron snow present in the redoxcline in two basins of the lake that differ in their pH values. Nucleic acid- and lipid-stained microbial cells of various morphologies detected by confocal laser scanning microscopy were homogeneously distributed in all iron snow samples. The dominant iron mineral appeared to be schwertmannite, with shorter needles in the northern than in the central basin samples. Total bacterial 16S rRNA gene copies ranged from 5.0 × 108 copies g (dry weight)−1 in the acidic central lake basin (pH 3.3) to 4.0 × 1010 copies g (dry weight)−1 in the less acidic (pH 5.9) northern basin. Total RNA-based quantitative PCR assigned up to 61% of metabolically active microbial communities to Fe-oxidizing- and Fe-reducing-related bacteria, indicating that iron metabolism was an important metabolic strategy. Molecular identification of abundant groups suggested that iron snow surfaces were formed by chemoautotrophic iron oxidizers, such as Acidimicrobium, Ferrovum, Acidithiobacillus, Thiobacillus, and Chlorobium, in the redoxcline and were rapidly colonized by heterotrophic iron reducers, such as Acidiphilium, Albidiferax-like, and Geobacter-like groups. Metaproteomics yielded 283 different proteins from northern basin iron snow samples, and protein identification provided a glimpse into some of their in situ metabolic processes, such as primary production (CO2 fixation), respiration, motility, and survival strategies. PMID:23645202

Insights into the structure and metabolic function of microbes that shape pelagic iron-rich aggregates ("iron snow").

PubMed

Lu, Shipeng; Chourey, Karuna; Reiche, Marco; Nietzsche, Sandor; Shah, Manesh B; Neu, Thomas R; Hettich, Robert L; Küsel, Kirsten

2013-07-01

Microbial ferrous iron [Fe(II)] oxidation leads to the formation of iron-rich macroscopic aggregates ("iron snow") at the redoxcline in a stratified lignite mine lake in east-central Germany. We aimed to identify the abundant Fe-oxidizing and Fe-reducing microorganisms likely to be involved in the formation and transformation of iron snow present in the redoxcline in two basins of the lake that differ in their pH values. Nucleic acid- and lipid-stained microbial cells of various morphologies detected by confocal laser scanning microscopy were homogeneously distributed in all iron snow samples. The dominant iron mineral appeared to be schwertmannite, with shorter needles in the northern than in the central basin samples. Total bacterial 16S rRNA gene copies ranged from 5.0 × 10(8) copies g (dry weight)(-1) in the acidic central lake basin (pH 3.3) to 4.0 × 10(10) copies g (dry weight)(-1) in the less acidic (pH 5.9) northern basin. Total RNA-based quantitative PCR assigned up to 61% of metabolically active microbial communities to Fe-oxidizing- and Fe-reducing-related bacteria, indicating that iron metabolism was an important metabolic strategy. Molecular identification of abundant groups suggested that iron snow surfaces were formed by chemoautotrophic iron oxidizers, such as Acidimicrobium, Ferrovum, Acidithiobacillus, Thiobacillus, and Chlorobium, in the redoxcline and were rapidly colonized by heterotrophic iron reducers, such as Acidiphilium, Albidiferax-like, and Geobacter-like groups. Metaproteomics yielded 283 different proteins from northern basin iron snow samples, and protein identification provided a glimpse into some of their in situ metabolic processes, such as primary production (CO2 fixation), respiration, motility, and survival strategies.

Macroscopic Fluctuation Theory for Stationary Non-Equilibrium States

NASA Astrophysics Data System (ADS)

Bertini, L.; de Sole, A.; Gabrielli, D.; Jona-Lasinio, G.; Landim, C.

2002-05-01

We formulate a dynamical fluctuation theory for stationary non-equilibrium states (SNS) which is tested explicitly in stochastic models of interacting particles. In our theory a crucial role is played by the time reversed dynamics. Within this theory we derive the following results: the modification of the Onsager-Machlup theory in the SNS; a general Hamilton-Jacobi equation for the macroscopic entropy; a non-equilibrium, nonlinear fluctuation dissipation relation valid for a wide class of systems; an H theorem for the entropy. We discuss in detail two models of stochastic boundary driven lattice gases: the zero range and the simple exclusion processes. In the first model the invariant measure is explicitly known and we verify the predictions of the general theory. For the one dimensional simple exclusion process, as recently shown by Derrida, Lebowitz, and Speer, it is possible to express the macroscopic entropy in terms of the solution of a nonlinear ordinary differential equation; by using the Hamilton-Jacobi equation, we obtain a logically independent derivation of this result.

Multiscale Modeling of Dewetting Damage in Highly Filled Particulate Composites

NASA Astrophysics Data System (ADS)

Geubelle, P. H.; Inglis, H. M.; Kramer, J. D.; Patel, J. J.; Kumar, N. C.; Tan, H.

2008-02-01

Particle debonding or dewetting constitutes one of the key damage processes in highly filled particulate composites such as solid propellant and other energetic materials. To analyze this failure process, we have developed a multiscale finite element framework that combines, at the microscale, a nonlinear description of the binder response with a cohesive model of the damage process taking place in a representative periodic unit cell (PUC). To relate micro-scale damage to the macroscopic constitutive response of the material, we employ the mathematical theory of homogenization (MTH). After a description of the numerical scheme, we present the results of the damage response of a highly filled particulate composite subjected to a uniaxial macroscopic strain, and show the direct correlation between the complex damage processes taking place in the PUC and the nonlinear macroscopic constitutive response. We also present a detailed study of the PUC size and a comparison between the finite element MTH-based study and a micromechanics model of the dewetting process.

Mushy zone modeling

NASA Astrophysics Data System (ADS)

Glicksman, Martin E.; Smith, Richard N.; Marsh, Steven P.; Kuklinski, Robert

A key element of mushy zone modeling is the description of the microscopic evolution of the lengthscales within the mushy zone and the influence of macroscopic transport processes. This paper describes some recent progress in developing a mean-field statistical theory of phase coarsening in adiabatic mushy zones. The main theoretical predictions are temporal scaling laws that indicate that average lengthscale increases as time 1/3, a self-similar distribution of mushy zone lengthscales based on spherical solid particle shapes, and kinetic rate constants which provide the dependences of the coarsening process on material parameters and the volume fraction of the solid phase. High precision thermal decay experiments are described which verify aspects of the theory in pure material mushy zones held under adiabatic conditions. The microscopic coarsening theory is then integrated within a macroscopic heat transfer model of one-dimensional alloy solidification, using the Double Integral Method. The method demonstrates an ability to predict the influence of macroscopic heat transfer on the evolution of primary and secondary dendrite arm spacings in Al-Cu alloys. Finally, some suggestions are made for future experimental and theoretical studies required in developing comprehensive solidification processing models.

A Mass Diffusion Model for Dry Snow Utilizing a Fabric Tensor to Characterize Anisotropy

NASA Astrophysics Data System (ADS)

Shertzer, Richard H.; Adams, Edward E.

2018-03-01

A homogenization algorithm for randomly distributed microstructures is applied to develop a mass diffusion model for dry snow. Homogenization is a multiscale approach linking constituent behavior at the microscopic level—among ice and air—to the macroscopic material—snow. Principles of continuum mechanics at the microscopic scale describe water vapor diffusion across an ice grain's surface to the air-filled pore space. Volume averaging and a localization assumption scale up and down, respectively, between microscopic and macroscopic scales. The model yields a mass diffusivity expression at the macroscopic scale that is, in general, a second-order tensor parameterized by both bulk and microstructural variables. The model predicts a mass diffusivity of water vapor through snow that is less than that through air. Mass diffusivity is expected to decrease linearly with ice volume fraction. Potential anisotropy in snow's mass diffusivity is captured due to the tensor representation. The tensor is built from directional data assigned to specific, idealized microstructural features. Such anisotropy has been observed in the field and laboratories in snow morphologies of interest such as weak layers of depth hoar and near-surface facets.

Instability of cooperative adaptive cruise control traffic flow: A macroscopic approach

NASA Astrophysics Data System (ADS)

Ngoduy, D.

2013-10-01

This paper proposes a macroscopic model to describe the operations of cooperative adaptive cruise control (CACC) traffic flow, which is an extension of adaptive cruise control (ACC) traffic flow. In CACC traffic flow a vehicle can exchange information with many preceding vehicles through wireless communication. Due to such communication the CACC vehicle can follow its leader at a closer distance than the ACC vehicle. The stability diagrams are constructed from the developed model based on the linear and nonlinear stability method for a certain model parameter set. It is found analytically that CACC vehicles enhance the stabilization of traffic flow with respect to both small and large perturbations compared to ACC vehicles. Numerical simulation is carried out to support our analytical findings. Based on the nonlinear stability analysis, we will show analytically and numerically that the CACC system better improves the dynamic equilibrium capacity over the ACC system. We have argued that in parallel to microscopic models for CACC traffic flow, the newly developed macroscopic will provide a complete insight into the dynamics of intelligent traffic flow.

High-throughput imaging of adult fluorescent zebrafish with an LED fluorescence macroscope

PubMed Central

Blackburn, Jessica S; Liu, Sali; Raimondi, Aubrey R; Ignatius, Myron S; Salthouse, Christopher D; Langenau, David M

2011-01-01

Zebrafish are a useful vertebrate model for the study of development, behavior, disease and cancer. A major advantage of zebrafish is that large numbers of animals can be economically used for experimentation; however, high-throughput methods for imaging live adult zebrafish had not been developed. Here, we describe protocols for building a light-emitting diode (LED) fluorescence macroscope and for using it to simultaneously image up to 30 adult animals that transgenically express a fluorescent protein, are transplanted with fluorescently labeled tumor cells or are tagged with fluorescent elastomers. These protocols show that the LED fluorescence macroscope is capable of distinguishing five fluorescent proteins and can image unanesthetized swimming adult zebrafish in multiple fluorescent channels simultaneously. The macroscope can be built and used for imaging within 1 day, whereas creating fluorescently labeled adult zebrafish requires 1 hour to several months, depending on the method chosen. The LED fluorescence macroscope provides a low-cost, high-throughput method to rapidly screen adult fluorescent zebrafish and it will be useful for imaging transgenic animals, screening for tumor engraftment, and tagging individual fish for long-term analysis. PMID:21293462

Micro-CT based finite element models for elastic properties of glass-ceramic scaffolds.

PubMed

Tagliabue, Stefano; Rossi, Erica; Baino, Francesco; Vitale-Brovarone, Chiara; Gastaldi, Dario; Vena, Pasquale

2017-01-01

In this study, the mechanical properties of porous glass-ceramic scaffolds are investigated by means of three-dimensional finite element models based on micro-computed tomography (micro-CT) scan data. In particular, the quantitative relationship between the morpho-architectural features of the obtained scaffolds, such as macroscopic porosity and strut thickness, and elastic properties, is sought. The macroscopic elastic properties of the scaffolds have been obtained through numerical homogenization approaches using the mechanical characteristics of the solid walls of the scaffolds (assessed through nanoindentation) as input parameters for the numerical simulations. Anisotropic mechanical properties of the produced scaffolds have also been investigated by defining a suitable anisotropy index. A comparison with morphological data obtained through the micro-CT scans is also presented. The proposed study shows that the produced glass-ceramic scaffolds exhibited a macroscopic porosity ranging between 29% and 97% which corresponds to an average stiffness ranging between 42.4GPa and 36MPa. A quantitative estimation of the isotropy of the macroscopic elastic properties has been performed showing that the samples with higher solid fractions were those closest to an isotropic material. Copyright © 2016 Elsevier Ltd. All rights reserved.

Graphene chiral liquid crystals and macroscopic assembled fibres

PubMed Central

Xu, Zhen; Gao, Chao

2011-01-01

Chirality and liquid crystals are both widely expressed in nature and biology. Helical assembly of mesophasic molecules and colloids may produce intriguing chiral liquid crystals. To date, chiral liquid crystals of 2D colloids have not been explored. As a typical 2D colloid, graphene is now receiving unprecedented attention. However, making macroscopic graphene fibres is hindered by the poor dispersibility of graphene and by the lack of an assembly method. Here we report that soluble, chemically oxidized graphene or graphene oxide sheets can form chiral liquid crystals in a twist-grain-boundary phase-like model with simultaneous lamellar ordering and long-range helical frustrations. Aqueous graphene oxide liquid crystals were continuously spun into metres of macroscopic graphene oxide fibres; subsequent chemical reduction gave the first macroscopic neat graphene fibres with high conductivity and good mechanical performance. The flexible, strong graphene fibres were knitted into designed patterns and into directionally conductive textiles. PMID:22146390

Study of Fission Barrier Heights of Uranium Isotopes by the Macroscopic-Microscopic Method

NASA Astrophysics Data System (ADS)

Zhong, Chun-Lai; Fan, Tie-Shuan

2014-09-01

Potential energy surfaces of uranium nuclei in the range of mass numbers 229 through 244 are investigated in the framework of the macroscopic-microscopic model and the heights of static fission barriers are obtained in terms of a double-humped structure. The macroscopic part of the nuclear energy is calculated according to Lublin—Strasbourg-drop (LSD) model. Shell and pairing corrections as the microscopic part are calculated with a folded-Yukawa single-particle potential. The calculation is carried out in a five-dimensional parameter space of the generalized Lawrence shapes. In order to extract saddle points on the potential energy surface, a new algorithm which can effectively find an optimal fission path leading from the ground state to the scission point is developed. The comparison of our results with available experimental data and others' theoretical results confirms the reliability of our calculations.

Micro- and macro-scale petrophysical characterization of potential reservoir units from the Northern Israel

NASA Astrophysics Data System (ADS)

Haruzi, Peleg; Halisch, Matthias; Katsman, Regina; Waldmann, Nicolas

2016-04-01

Lower Cretaceous sandstone serves as hydrocarbon reservoir in some places over the world, and potentially in Hatira formation in the Golan Heights, northern Israel. The purpose of the current research is to characterize the petrophysical properties of these sandstone units. The study is carried out by two alternative methods: using conventional macroscopic lab measurements, and using CT-scanning, image processing and subsequent fluid mechanics simulations at a microscale, followed by upscaling to the conventional macroscopic rock parameters (porosity and permeability). Comparison between the upscaled and measured in the lab properties will be conducted. The best way to upscale the microscopic rock characteristics will be analyzed based the models suggested in the literature. Proper characterization of the potential reservoir will provide necessary analytical parameters for the future experimenting and modeling of the macroscopic fluid flow behavior in the Lower Cretaceous sandstone.

Enhanced anaerobic degradation of Fischer-Tropsch wastewater by integrated UASB system with Fe-C micro-electrolysis assisted.

PubMed

Wang, Dexin; Ma, Wencheng; Han, Hongjun; Li, Kun; Xu, Hao; Fang, Fang; Hou, Baolin; Jia, Shengyong

2016-12-01

Coupling of the Fe-C micro-electrolysis (IC-ME) into the up-flow anaerobic sludge blanket (UASB) was developed for enhanced Fischer-Tropsch wastewater treatment. The COD removal efficiency and methane production in R 3 with IC-ME assisted both reached up to 80.6 ± 1.7% and 1.38 ± 0.11 L/L·d that higher than those values in R 1 with GAC addition (63.0 ± 3.4% and 0.95 ± 0.09 L/L·d) and R 2 with ZVI addition (74.5 ± 2.8% and 1.21 ± 0.09 L/L·d) under the optimum HRT (5 d). The Fe corrosion as electron donor reduced the ORP values and stimulated the activities of hydrogenotrophic methanogens to lower H 2 partial pressure in R 2 and R 3 . Additionally, Fe 2+ as by-product of iron corrosion, its presence could effectively increase the percentage of protein content in tightly bound extracellular polymeric substances (TB-EPS) to promote better bioflocculation, increasing to 90.5 mg protein/g·VSS (R 2 ) and 106.3 mg protein/g·VSS (R 3 ) while this value in R1 was simply 56.6 mg protein/g·VSS. More importantly, compared with R 1 , the excess accumulation of propionic acid and butyric acid in system was avoided. The macroscopic galvanic cells around Fe-C micro-electrolysis carriers in R 3 , that larger than microscopic galvanic cells in R 2 , further accelerate to transfer the electrons from anodic Fe to cathodic carbon that enhance interspecies hydrogen transfer, making the decomposition of propionic acid and butyric acid more thermodynamically feasible, finally facilitate more methane production. Copyright © 2016 Elsevier Ltd. All rights reserved.

Inhomogeneities and superconductivity in poly-phase Fe-Se-Te systems

NASA Astrophysics Data System (ADS)

Hartwig, S.; Schäfer, N.; Schulze, M.; Landsgesell, S.; Abou-Ras, D.; Blum, Ch. G. F.; Wurmehl, S.; Sokolowski, A.; Büchner, B.; Prokeš, K.

2018-02-01

The impact of synthesis conditions, post-preparation heating procedure, aging and influence of pressure on the superconducting properties of FeSe0.4Te0.6 crystals is reported. Two FeSe0.4Te0.6 single crystals were used in the study, prepared from stoichiometric melt but cooled down with very different cooling rates, and investigated using magnetic bulk and electrical-resistivity methods. The fast-cooled crystal contains large inclusions of Fe3Se2.1Te1.8 and exhibits bulk superconductivity in its as-prepared state, while the other is homogeneous and shows only traces of superconductivity. AC susceptibility measurements under hydrostatic pressure show that the superconducting transition temperature of the inhomogeneous crystal increases from 12.3 K at ambient pressure to Tsc = 17.9 K at 9 kbar. On the other hand, neither pressure nor mechanically-induced stress is sufficient to induce superconductivity in the homogeneous crystal. However, an additional heat treatment at 673 K followed by fast cooling down and/or long-term aging at ambient conditions leads to the appearance of bulk superconductivity also in the latter sample. This sample remains homogeneous on a scale down to few μm but shows an additional magnetic phase transition around 130 K suggesting that it must be inhomogeneous. For comparison also Fe3Se2.1Te1.8 polycrystals have been prepared and their magnetic properties have been studied. It appears that this phase is not superconducting by itself. It is concluded that nano-scale inhomogeneities that appear in the FeSexTe1-x system due to a spinodal decomposition in the solid state are necessary for bulk superconductivity, possibly due to minor changes in the crystal structure and microstructure. Macroscopic inclusions quenched by fast cooling from high temperatures lead obviously to strain and hence variations in the lattice constants, an effect that is further supported by application of pressure/stress.

Noninteractive macroscopic reliability model for whisker-reinforced ceramic composites

NASA Technical Reports Server (NTRS)

Duffy, Stephen F.; Arnold, Steven M.

1990-01-01

Considerable research is underway in the field of material science focusing on incorporating silicon carbide whiskers into silicon nitride and alumina matrices. These composites show the requisite thermal stability and thermal shock resistance necessary for use as components in advanced gas turbines and heat exchangers. This paper presents a macroscopic noninteractive reliability model for whisker-reinforced ceramic composites. The theory is multiaxial and is applicable to composites that can be characterized as transversely isotropic. Enough processing data exists to suggest this idealization encompasses a significantly large class of fabricated components. A qualitative assessment of the model is made by presenting reliability surfaces in several different stress spaces and for different values of model parameters.

Macroscopic modelling of multiperiodic composites

NASA Astrophysics Data System (ADS)

Woźniak, Czesław

By a multiperiodic composite we mean a composite solid in which all constituents are periodically distributed in a matrix but a representative element (unit cell) may not exist. The aim of this Note is to propose a nonasymptotic approach to the formation of averaged (macroscopic) models of multiperiodic composites. The approach is based on the concept of tolerance averaging, which in [2] was applied to the modelling of periodic composites. The derived model, in contrast to homogenization, describes the effect of microstructure size on the overall solid behaviour and yields necessary conditions for the physical correctness of solutions to special problems. To cite this article: C. Woźniak, C. R. Mecanique 330 (2002) 267-272.

Multi Length Scale Finite Element Design Framework for Advanced Woven Fabrics

NASA Astrophysics Data System (ADS)

Erol, Galip Ozan

Woven fabrics are integral parts of many engineering applications spanning from personal protective garments to surgical scaffolds. They provide a wide range of opportunities in designing advanced structures because of their high tenacity, flexibility, high strength-to-weight ratios and versatility. These advantages result from their inherent multi scale nature where the filaments are bundled together to create yarns while the yarns are arranged into different weave architectures. Their highly versatile nature opens up potential for a wide range of mechanical properties which can be adjusted based on the application. While woven fabrics are viable options for design of various engineering systems, being able to understand the underlying mechanisms of the deformation and associated highly nonlinear mechanical response is important and necessary. However, the multiscale nature and relationships between these scales make the design process involving woven fabrics a challenging task. The objective of this work is to develop a multiscale numerical design framework using experimentally validated mesoscopic and macroscopic length scale approaches by identifying important deformation mechanisms and recognizing the nonlinear mechanical response of woven fabrics. This framework is exercised by developing mesoscopic length scale constitutive models to investigate plain weave fabric response under a wide range of loading conditions. A hyperelastic transversely isotropic yarn material model with transverse material nonlinearity is developed for woven yarns (commonly used in personal protection garments). The material properties/parameters are determined through an inverse method where unit cell finite element simulations are coupled with experiments. The developed yarn material model is validated by simulating full scale uniaxial tensile, bias extension and indentation experiments, and comparing to experimentally observed mechanical response and deformation mechanisms. Moreover, mesoscopic unit cell finite elements are coupled with a design-of-experiments method to systematically identify the important yarn material properties for the macroscale response of various weave architectures. To demonstrate the macroscopic length scale approach, two new material models for woven fabrics were developed. The Planar Material Model (PMM) utilizes two important deformation mechanisms in woven fabrics: (1) yarn elongation, and (2) relative yarn rotation due to shear loads. The yarns' uniaxial tensile response is modeled with a nonlinear spring using constitutive relations while a nonlinear rotational spring is implemented to define fabric's shear stiffness. The second material model, Sawtooth Material Model (SMM) adopts the sawtooth geometry while recognizing the biaxial nature of woven fabrics by implementing the interactions between the yarns. Material properties/parameters required by both PMM and SMM can be directly determined from standard experiments. Both macroscopic material models are implemented within an explicit finite element code and validated by comparing to the experiments. Then, the developed macroscopic material models are compared under various loading conditions to determine their accuracy. Finally, the numerical models developed in the mesoscopic and macroscopic length scales are linked thus demonstrating the new systematic design framework involving linked mesoscopic and macroscopic length scale modeling approaches. The approach is demonstrated with both Planar and Sawtooth Material Models and the simulation results are verified by comparing the results obtained from meso and macro models.

Modelling grain-scattered ultrasound in austenitic stainless-steel welds: A hybrid model

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

Nowers, O.; Duxbury, D. J.; Velichko, A.

2015-03-31

The ultrasonic inspection of austenitic stainless steel welds can be challenging due to their coarse grain structure, charaterised by preferentially oriented, elongated grains. The anisotropy of the weld is manifested as both a ‘steering’ of the beam and the back-scatter of energy due to the macroscopic granular structure of the weld. However, the influence of weld properties, such as mean grain size and orientation distribution, on the magnitude of scattered ultrasound is not well understood. A hybrid model has been developed to allow the study of grain-scatter effects in austenitic welds. An efficient 2D Finite Element (FE) method is usedmore » to calculate the complete scattering response from a single elliptical austenitic grain of arbitrary length and width as a function of the specific inspection frequency. A grain allocation model of the weld is presented to approximate the characteristic structures observed in austenitic welds and the complete scattering behaviour of each grain calculated. This model is incorporated into a semi-analytical framework for a single-element inspection of a typical weld in immersion. Experimental validation evidence is demonstrated indicating excellent qualitative agreement of SNR as a function of frequency and a minimum SNR difference of 2 dB at a centre frequency of 2.25 MHz. Additionally, an example Monte-Carlo study is presented detailing the variation of SNR as a function of the anisotropy distribution of the weld, and the application of confidence analysis to inform inspection development.« less

Modelling hot air balloons

NASA Astrophysics Data System (ADS)

Brimicombe, N. W.

1991-07-01

Hot air balloons can be modelled in a number of different ways. The most satisfactory, but least useful model is at a microscopic level. Macroscopic models are easier to use but can be very misleading.

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

Scott Stewart, D., E-mail: dss@illinois.edu; Hernández, Alberto; Lee, Kibaek

The estimation of pressure and temperature histories, which are required to understand chemical pathways in condensed phase explosives during detonation, is discussed. We argue that estimates made from continuum models, calibrated by macroscopic experiments, are essential to inform modern, atomistic-based reactive chemistry simulations at detonation pressures and temperatures. We present easy to implement methods for general equation of state and arbitrarily complex chemical reaction schemes that can be used to compute reactive flow histories for the constant volume, the energy process, and the expansion process on the Rayleigh line of a steady Chapman-Jouguet detonation. A brief review of state-of-the-art ofmore » two-component reactive flow models is given that highlights the Ignition and Growth model of Lee and Tarver [Phys. Fluids 23, 2362 (1980)] and the Wide-Ranging Equation of State model of Wescott, Stewart, and Davis [J. Appl. Phys. 98, 053514 (2005)]. We discuss evidence from experiments and reactive molecular dynamic simulations that motivate models that have several components, instead of the two that have traditionally been used to describe the results of macroscopic detonation experiments. We present simplified examples of a formulation for a hypothetical explosive that uses simple (ideal) equation of state forms and detailed comparisons. Then, we estimate pathways computed from two-component models of real explosive materials that have been calibrated with macroscopic experiments.« less

Estimation of Enthalpy of Formation of Liquid Transition Metal Alloys: A Modified Prescription Based on Macroscopic Atom Model of Cohesion

NASA Astrophysics Data System (ADS)

Raju, Subramanian; Saibaba, Saroja

2016-09-01

The enthalpy of formation Δo H f is an important thermodynamic quantity, which sheds significant light on fundamental cohesive and structural characteristics of an alloy. However, being a difficult one to determine accurately through experiments, simple estimation procedures are often desirable. In the present study, a modified prescription for estimating Δo H f L of liquid transition metal alloys is outlined, based on the Macroscopic Atom Model of cohesion. This prescription relies on self-consistent estimation of liquid-specific model parameters, namely electronegativity ( ϕ L) and bonding electron density ( n b L ). Such unique identification is made through the use of well-established relationships connecting surface tension, compressibility, and molar volume of a metallic liquid with bonding charge density. The electronegativity is obtained through a consistent linear scaling procedure. The preliminary set of values for ϕ L and n b L , together with other auxiliary model parameters, is subsequently optimized to obtain a good numerical agreement between calculated and experimental values of Δo H f L for sixty liquid transition metal alloys. It is found that, with few exceptions, the use of liquid-specific model parameters in Macroscopic Atom Model yields a physically consistent methodology for reliable estimation of mixing enthalpies of liquid alloys.

Nanoscale magneto-structural coupling in as-deposited and freestanding single-crystalline Fe7Pd3 ferromagnetic shape memory alloy thin films

PubMed Central

Landgraf, Anja; Jakob, Alexander M; Ma, Yanhong; Mayr, Stefan G

2013-01-01

Ferromagnetic shape memory alloys are characterized by strong magneto-mechanical coupling occurring at the atomic scale causing large magnetically inducible strains at the macroscopic level. Employing combined atomic and magnetic force microscopy studies at variable temperature, we systematically explore the relation between the magnetic domain pattern and the underlying structure for as-deposited and freestanding single-crystalline Fe7Pd3 thin films across the martensite–austenite transition. We find experimental evidence that magnetic domain appearance is strongly affected by the presence and absence of nanotwinning. While the martensite–austenite transition upon temperature variation of as-deposited films is clearly reflected in topography by the presence and absence of a characteristic surface corrugation pattern, the magnetic domain pattern is hardly affected. These findings are discussed considering the impact of significant thermal stresses arising in the austenite phase. Freestanding martensitic films reveal a hierarchical structure of micro- and nanotwinning. The associated domain organization appears more complex, since the dominance of magnetic energy contributors alters within this length scale regime. PMID:27877596

Dissociation and Re-Aggregation of Multicell-Ensheathed Fragments Responsible for Rapid Production of Massive Clumps of Leptothrix Sheaths

PubMed Central

Kunoh, Tatsuki; Nagaoka, Noriyuki; McFarlane, Ian R.; Tamura, Katsunori; El-Naggar, Mohamed Y.; Kunoh, Hitoshi; Takada, Jun

2016-01-01

Species of the Fe/Mn-oxidizing bacteria Leptothrix produce tremendous amounts of microtubular, Fe/Mn-encrusted sheaths within a few days in outwells of groundwater that can rapidly clog water systems. To understand this mode of rapid sheath production and define the timescales involved, behaviors of sheath-forming Leptothrix sp. strain OUMS1 were examined using time-lapse video at the initial stage of sheath formation. OUMS1 formed clumps of tangled sheaths. Electron microscopy confirmed the presence of a thin layer of bacterial exopolymer fibrils around catenulate cells (corresponding to the immature sheath). In time-lapse videos, numerous sheath filaments that extended from the periphery of sheath clumps repeatedly fragmented at the apex of the same fragment, the fragments then aggregated and again elongated, eventually forming a large sheath clump comprising tangled sheaths within two days. In this study, we found that fast microscopic fragmentation, dissociation, re-aggregation and re-elongation events are the basis of the rapid, massive production of Leptothrix sheaths typically observed at macroscopic scales. PMID:27490579

Microbial stratification in low pH oxic and suboxic macroscopic growths along an acid mine drainage

PubMed Central

Méndez-García, Celia; Mesa, Victoria; Sprenger, Richard R; Richter, Michael; Diez, María Suárez; Solano, Jennifer; Bargiela, Rafael; Golyshina, Olga V; Manteca, Ángel; Ramos, Juan Luis; Gallego, José R; Llorente, Irene; Martins dos Santos, Vitor AP; Jensen, Ole N; Peláez, Ana I; Sánchez, Jesús; Ferrer, Manuel

2014-01-01

Macroscopic growths at geographically separated acid mine drainages (AMDs) exhibit distinct populations. Yet, local heterogeneities are poorly understood. To gain novel mechanistic insights into this, we used OMICs tools to profile microbial populations coexisting in a single pyrite gallery AMD (pH ∼2) in three distinct compartments: two from a stratified streamer (uppermost oxic and lowermost anoxic sediment-attached strata) and one from a submerged anoxic non-stratified mat biofilm. The communities colonising pyrite and those in the mature formations appear to be populated by the greatest diversity of bacteria and archaea (including ‘ARMAN' (archaeal Richmond Mine acidophilic nano-organisms)-related), as compared with the known AMD, with ∼44.9% unclassified sequences. We propose that the thick polymeric matrix may provide a safety shield against the prevailing extreme condition and also a massive carbon source, enabling non-typical acidophiles to develop more easily. Only 1 of 39 species were shared, suggesting a high metabolic heterogeneity in local microenvironments, defined by the O2 concentration, spatial location and biofilm architecture. The suboxic mats, compositionally most similar to each other, are more diverse and active for S, CO2, CH4, fatty acid and lipopolysaccharide metabolism. The oxic stratum of the streamer, displaying a higher diversity of the so-called ‘ARMAN'-related Euryarchaeota, shows a higher expression level of proteins involved in signal transduction, cell growth and N, H2, Fe, aromatic amino acids, sphingolipid and peptidoglycan metabolism. Our study is the first to highlight profound taxonomic and functional shifts in single AMD formations, as well as new microbial species and the importance of H2 in acidic suboxic macroscopic growths. PMID:24430486

Macroscopic and mesoscopic approach to the alkali-silica reaction in concrete

NASA Astrophysics Data System (ADS)

Grymin, Witold; Koniorczyk, Marcin; Pesavento, Francesco; Gawin, Dariusz

2018-01-01

A model of the alkali-silica reaction, which takes into account couplings between thermal, hygral, mechanical and chemical phenomena in concrete, has been discussed. The ASR may be considered at macroscopic or mesoscopic scale. The main features of each approach have been summarized and development of the model for both scales has been briefly described. Application of the model to experimental results for both scales has been presented. Even though good accordance of the model has been obtained for both approaches, consideration of the model at the mesoscopic scale allows to model different mortar mixes, prepared with the same aggregate, but of different grain size, using the same set of parameters. It enables also to predict reaction development assuming different alkali sources, such as de-icing salts or alkali leaching.

The association between histological, macroscopic and magnetic resonance imaging assessed synovitis in end-stage knee osteoarthritis: a cross-sectional study.

PubMed

Riis, R G C; Gudbergsen, H; Simonsen, O; Henriksen, M; Al-Mashkur, N; Eld, M; Petersen, K K; Kubassova, O; Bay Jensen, A C; Damm, J; Bliddal, H; Arendt-Nielsen, L; Boesen, M

2017-02-01

To investigate the association between magnetic resonance imaging (MRI), macroscopic and histological assessments of synovitis in end-stage knee osteoarthritis (KOA). Synovitis of end-stage osteoarthritic knees was assessed using non-contrast-enhanced (CE), contrast-enhanced magnetic resonance imaging (CE-MRI) and dynamic contrast-enhanced (DCE)-MRI prior to (TKR) and correlated with microscopic and macroscopic assessments of synovitis obtained intraoperatively. Multiple bivariate correlations were used with a pre-specified threshold of 0.70 for significance. Also, multiple regression analyses with different subsets of MRI-variables as explanatory variables and the histology score as outcome variable were performed with the intention to find MRI-variables that best explain the variance in histological synovitis (i.e., highest R 2 ). A stepped approach was taken starting with basic characteristics and non-CE MRI-variables (model 1), after which CE-MRI-variables were added (model 2) with the final model also including DCE-MRI-variables (model 3). 39 patients (56.4% women, mean age 68 years, Kellgren-Lawrence (KL) grade 4) had complete MRI and histological data. Only the DCE-MRI variable MExNvoxel (surrogate of the volume and degree of synovitis) and the macroscopic score showed correlations above the pre-specified threshold for acceptance with histological inflammation. The maximum R 2 -value obtained in Model 1 was R 2  = 0.39. In Model 2, where the CE-MRI-variables were added, the highest R 2  = 0.52. In Model 3, a four-variable model consisting of the gender, one CE-MRI and two DCE-MRI-variables yielded a R 2  = 0.71. DCE-MRI is correlated with histological synovitis in end-stage KOA and the combination of CE and DCE-MRI may be a useful, non-invasive tool in characterising synovitis in KOA. Copyright © 2016 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

On the macroscopic modeling of dilute emulsions under flow in the presence of particle inertia

NASA Astrophysics Data System (ADS)

Mwasame, Paul M.; Wagner, Norman J.; Beris, Antony N.

2018-03-01

Recently, Mwasame et al. ["On the macroscopic modeling of dilute emulsions under flow," J. Fluid Mech. 831, 433 (2017)] developed a macroscopic model for the dynamics and rheology of a dilute emulsion with droplet morphology in the limit of negligible particle inertia using the bracket formulation of non-equilibrium thermodynamics of Beris and Edwards [Thermodynamics of Flowing Systems: With Internal Microstructure (Oxford University Press on Demand, 1994)]. Here, we improve upon that work to also account for particle inertia effects. This advance is facilitated by using the bracket formalism in its inertial form that allows for the natural incorporation of particle inertia effects into macroscopic level constitutive equations, while preserving consistency to the previous inertialess approximation in the limit of zero inertia. The parameters in the resultant Particle Inertia Thermodynamically Consistent Ellipsoidal Emulsion (PITCEE) model are selected by utilizing literature-available mesoscopic theory for the rheology at small capillary and particle Reynolds numbers. At steady state, the lowest level particle inertia effects can be described by including an additional non-affine inertial term into the evolution equation for the conformation tensor, thereby generalizing the Gordon-Schowalter time derivative. This additional term couples the conformation and vorticity tensors and is a function of the Ohnesorge number. The rheological and microstructural predictions arising from the PITCEE model are compared against steady-shear simulation results from the literature. They show a change in the signs of the normal stress differences that is accompanied by a change in the orientation of the major axis of the emulsion droplet toward the velocity gradient direction with increasing Reynolds number, capturing the two main signatures of particle inertia reported in simulations.

Transient Macroscopic Chemistry in the DSMC Method

NASA Astrophysics Data System (ADS)

Goldsworthy, M. J.; Macrossan, M. N.; Abdel-Jawad, M.

2008-12-01

In the Direct Simulation Monte Carlo method, a combination of statistical and deterministic procedures applied to a finite number of `simulator' particles are used to model rarefied gas-kinetic processes. Traditionally, chemical reactions are modelled using information from specific colliding particle pairs. In the Macroscopic Chemistry Method (MCM), the reactions are decoupled from the specific particle pairs selected for collisions. Information from all of the particles within a cell is used to determine a reaction rate coefficient for that cell. MCM has previously been applied to steady flow DSMC simulations. Here we show how MCM can be used to model chemical kinetics in DSMC simulations of unsteady flow. Results are compared with a collision-based chemistry procedure for two binary reactions in a 1-D unsteady shock-expansion tube simulation and during the unsteady development of 2-D flow through a cavity. For the shock tube simulation, close agreement is demonstrated between the two methods for instantaneous, ensemble-averaged profiles of temperature and species mole fractions. For the cavity flow, a high degree of thermal non-equilibrium is present and non-equilibrium reaction rate correction factors are employed in MCM. Very close agreement is demonstrated for ensemble averaged mole fraction contours predicted by the particle and macroscopic methods at three different flow-times. A comparison of the accumulated number of net reactions per cell shows that both methods compute identical numbers of reaction events. For the 2-D flow, MCM required similar CPU and memory resources to the particle chemistry method. The Macroscopic Chemistry Method is applicable to any general DSMC code using any viscosity or non-reacting collision models and any non-reacting energy exchange models. MCM can be used to implement any reaction rate formulations, whether these be from experimental or theoretical studies.

Electrochemical-mechanical coupling in composite planar structures that integrate flow channels and ion-conducting membranes

DOE PAGES

Euser, Bryan Jeffry; Zhu, Huayang; Berger, John; ...

2017-01-01

Ceramic oxygen-transport membranes, such as the doped perovskite La 0.6Sr 0.4Co 0.8Fe 0.2O 3-δ(LSCF6482) considered in the present paper, are effective in applications such as air separation. The present paper considers a planar configuration that is composed of a thin (order tens of microns) ion-transport membrane, a relatively thick (order millimeter) porous-ceramic support structure, and millimeter-scale oxygen-collection flow channels. The lattice-scale strain associated with charged defects (oxygen vacancies and small polarons) within ion-transport membranes causes macroscopic stress that could distort or damage the assembly. The modeling approach is based on an extended twodimensional Nernst–Planck–Poisson (NPP) formulation that is developed andmore » applied to evaluate the effects of chemically induced stress within a planar oxygen-separation assembly. The computational model predicts two-dimensional distributions of steady-state defect concentrations, electrostatic potentials, and stress. Parameter studies consider the effects of support-membrane dimensions, materials mechanical properties, and operating conditions. Although the stress is found to have a negligible influence on the defect transport, the defect transport is found to significantly affect the stress distributions. Such results can play important roles in the design and development of planar ion-transport membranes and their support structures.« less

Chiral Domain Structure in Superfluid 3He-A Studied by Magnetic Resonance Imaging

NASA Astrophysics Data System (ADS)

Kasai, J.; Okamoto, Y.; Nishioka, K.; Takagi, T.; Sasaki, Y.

2018-05-01

The existence of a spatially varying texture in superfluid 3He is a direct manifestation of the complex macroscopic wave function. The real space shape of the texture, namely, a macroscopic wave function, has been studied extensively with the help of theoretical modeling but has never been directly observed experimentally with spatial resolution. We have succeeded in visualizing the texture by a specialized magnetic resonance imaging. With this new technology, we have discovered that the macroscopic chiral domains, of which sizes are as large as 1 mm, and corresponding chiral domain walls exist rather stably in 3He - A film at temperatures far below the transition temperature.

Prediction on electronic structure of CH3NH3PbI3/Fe3O4 interfaces

NASA Astrophysics Data System (ADS)

Hou, Xueyao; Wang, Xiaocha; Mi, Wenbo; Du, Zunfeng

2018-01-01

The interfacial electronic structures of CH3NH3PbI3(MAPbI3)/Fe3O4 heterostructures are predicted by density functional theory. Four models (MAI/FeBO, PbI2/FeBO, MAI/FeA and PbI2/FeA) are included. Especially, a half-metal to semiconductor transition of Fe3O4 appears in PbI2/FeA model. A series of electric field is added to PbI2/FeA model, and a direct-indirect bandgap transition of Fe3O4 appears at a 500-kV/cm field. The electric field can control the bandgap of Fe3O4 in PbI2/FeA model by modulating the hybridization. The prediction of spin-related bandgap characteristic in MAPbI3/Fe3O4 is meaningful for further study.

Chapman-Enskog expansion for the Vicsek model of self-propelled particles

NASA Astrophysics Data System (ADS)

Ihle, Thomas

2016-08-01

Using the standard Vicsek model, I show how the macroscopic transport equations can be systematically derived from microscopic collision rules. The approach starts with the exact evolution equation for the N-particle probability distribution and, after making the mean-field assumption of molecular chaos, leads to a multi-particle Enskog-type equation. This equation is treated by a non-standard Chapman-Enskog expansion to extract the macroscopic behavior. The expansion includes terms up to third order in a formal expansion parameter ɛ, and involves a fast time scale. A self-consistent closure of the moment equations is presented that leads to a continuity equation for the particle density and a Navier-Stokes-like equation for the momentum density. Expressions for all transport coefficients in these macroscopic equations are given explicitly in terms of microscopic parameters of the model. The transport coefficients depend on specific angular integrals which are evaluated asymptotically in the limit of infinitely many collision partners, using an analogy to a random walk. The consistency of the Chapman-Enskog approach is checked by an independent calculation of the shear viscosity using a Green-Kubo relation.

Thermodynamic behavior of a phase transition in a model for sympatric speciation

NASA Astrophysics Data System (ADS)

Luz-Burgoa, K.; Moss de Oliveira, S.; Schwämmle, Veit; Sá Martins, J. S.

2006-08-01

We investigate the macroscopic effects of the ingredients that drive the origin of species through sympatric speciation. In our model, sympatric speciation is obtained as we tune up the strength of competition between individuals with different phenotypes. As a function of this control parameter, we can characterize, through the behavior of a macroscopic order parameter, a phase transition from a nonspeciation to a speciation state of the system. The behavior of the first derivative of the order parameter with respect to the control parameter is consistent with a phase transition and exhibits a sharp peak at the transition point. For different resources distribution, the transition point is shifted, an effect similar to pressure in a PVT system. The inverse of the parameter related to a sexual selection strength behaves like an external field in the system and, as thus, is also a control parameter. The macroscopic effects of the biological parameters used in our model are a reminiscent of the behavior of thermodynamic quantities in a phase transition of an equilibrium physical system.

Using Denatured Egg White as a Macroscopic Model for Teaching Protein Structure and Introducing Protein Synthesis for High School Students

NASA Astrophysics Data System (ADS)

Correia, Paulo R. M.; Torres, Bayardo B.

2007-12-01

The success of teaching molecular and atomic phenomena depends on the didactical strategy and the media selection adopted, in consideration of the level of abstraction of the subject to be taught and the students' capability to deal with abstract operations. Dale's cone of experience was employed to plan three 50-minute classes to discuss protein denaturation from a chemical point of view. Only low abstraction level activities were selected: (i) two demonstrations showing the denaturation of albumin by heating and by changing the solvent, (ii) the assembly of a macroscopic model representing the protein molecule, and (iii) a role-play for simulating glucagon synthesis. A student-centered approach and collaborative learning were used throughout the classes. The use of macroscopic models is a powerful didactical strategy to represent molecular and atomic events. They can convert microscopic entities into touchable objects, reducing the abstraction level required to discuss chemistry with high school students. Thus, interesting topics involving molecules and their behavior can take place efficiently when mediated by concrete experiences.

Macroscopic Quantum Phase-Locking Model for the Quantum Hall = Effect

NASA Astrophysics Data System (ADS)

Wang, Te-Chun; Gou, Yih-Shun

1997-08-01

A macroscopic model of nonlinear dissipative phase-locking between a Josephson-like frequency and a macroscopic electron wave frequency is proposed to explain the Quantum Hall Effect. It is well known that a r.f-biased Josephson junction displays a collective phase-locking behavior which can be described by a non-autonomous second order equation or an equivalent 2+1-dimensional dynamical system. Making a direct analogy between the QHE and the Josephson system, this report proposes a computer-solving nonlinear dynamical model for the quantization of the Hall resistance. In this model, the Hall voltage is assumed to be proportional to a Josephson-like frequency and the Hall current is assumed related to a coherent electron wave frequency. The Hall resistance is shown to be quantized in units of the fine structure constant as the ratio of these two frequencies are locked into a rational winding number. To explain the sample-width dependence of the critical current, the 2DEG under large applied current is further assumed to develop a Josephson-like junction array in which all Josephson-like frequencies are synchronized. Other remarkable features of the QHE such as the resistance fluctuation and the even-denominator states are also discussed within this picture.

Nuclear ground-state masses and deformations: FRDM(2012)

DOE PAGES

Moller, P.; Sierk, A. J.; Ichikawa, T.; ...

2016-03-25

Here, we tabulate the atomic mass excesses and binding energies, ground-state shell-plus-pairing corrections, ground-state microscopic corrections, and nuclear ground-state deformations of 9318 nuclei ranging from 16O to A=339. The calculations are based on the finite-range droplet macroscopic and the folded-Yukawa single-particle microscopic nuclear-structure models, which are completely specified. Relative to our FRDM(1992) mass table in Möller et al. (1995), the results are obtained in the same model, but with considerably improved treatment of deformation and fewer of the approximations that were necessary earlier, due to limitations in computer power. The more accurate execution of the model and the more extensivemore » and more accurate experimental mass data base now available allow us to determine one additional macroscopic-model parameter, the density-symmetry coefficient LL, which was not varied in the previous calculation, but set to zero. Because we now realize that the FRDM is inaccurate for some highly deformed shapes occurring in fission, because some effects are derived in terms of perturbations around a sphere, we only adjust its macroscopic parameters to ground-state masses.« less

On sequential data assimilation for scalar macroscopic traffic flow models

NASA Astrophysics Data System (ADS)

Blandin, Sébastien; Couque, Adrien; Bayen, Alexandre; Work, Daniel

2012-09-01

We consider the problem of sequential data assimilation for transportation networks using optimal filtering with a scalar macroscopic traffic flow model. Properties of the distribution of the uncertainty on the true state related to the specific nonlinearity and non-differentiability inherent to macroscopic traffic flow models are investigated, derived analytically and analyzed. We show that nonlinear dynamics, by creating discontinuities in the traffic state, affect the performances of classical filters and in particular that the distribution of the uncertainty on the traffic state at shock waves is a mixture distribution. The non-differentiability of traffic dynamics around stationary shock waves is also proved and the resulting optimality loss of the estimates is quantified numerically. The properties of the estimates are explicitly studied for the Godunov scheme (and thus the Cell-Transmission Model), leading to specific conclusions about their use in the context of filtering, which is a significant contribution of this article. Analytical proofs and numerical tests are introduced to support the results presented. A Java implementation of the classical filters used in this work is available on-line at http://traffic.berkeley.edu for facilitating further efforts on this topic and fostering reproducible research.

A multi-scale homogenization model for fine-grained porous viscoplastic polycrystals: II - Applications to FCC and HCP materials

NASA Astrophysics Data System (ADS)

Song, Dawei; Ponte Castañeda, P.

2018-06-01

In Part I of this work (Song and Ponte Castañeda, 2018a), a new homogenization model was developed for the macroscopic behavior of three-scale porous polycrystals consisting of random distributions of large pores in a fine-grained polycrystalline matrix. In this second part, the model is used to investigate both the instantaneous effective behavior and the finite-strain macroscopic response of porous FCC and HCP polycrystals for axisymmetric loading conditions. The stress triaxiality and Lode parameter are found to have significant effects on the evolution of the substructure, which in turn have important implications for the overall hardening/softening behavior of the porous polycrystal. The intrinsic effect of the texture evolution of the polycrystalline matrix is inferred by appropriate comparisons with corresponding results for porous isotropic materials, and found to be significant, especially at low triaxialities. In particular, the predictions of the model identify, for the first time, two disparate regimes for the macroscopic response of porous polycrystals: a porosity-controlled regime at high triaxialities, and a texture-controlled regime at low triaxialities. The transition between these two regimes is found to be quite sharp, taking place between triaxialities of 1 and 2.

Porcine intact and wounded skin responses to atmospheric nonthermal plasma.

PubMed

Wu, Andrew S; Kalghatgi, Sameer; Dobrynin, Danil; Sensenig, Rachel; Cerchar, Ekaternia; Podolsky, Erica; Dulaimi, Essel; Paff, Michelle; Wasko, Kimberly; Arjunan, Krishna Priya; Garcia, Kristin; Fridman, Gregory; Balasubramanian, Manjula; Ownbey, Robert; Barbee, Kenneth A; Fridman, Alexander; Friedman, Gary; Joshi, Suresh G; Brooks, Ari D

2013-01-01

Thermal plasma is a valued tool in surgery for its coagulative and ablative properties. We suggested through in vitro studies that nonthermal plasma can sterilize tissues, inactive pathogens, promote coagulation, and potentiate wound healing. The present research was undertaken to study acute toxicity in porcine skin tissues. We demonstrate that floating electrode-discharge barrier discharge (FE-DBD) nonthermal plasma is electrically safe to apply to living organisms for short periods. We investigated the effects of FE-DBD plasma on Yorkshire pigs on intact and wounded skin immediately after treatment or 24h posttreatment. Macroscopic or microscopic histological changes were identified using histological and immunohistochemical techniques. The changes were classified into four groups for intact skin: normal features, minimal changes or congestive changes, epidermal layer damage, and full burn and into three groups for wounded skin: normal, clot or scab, and full burn-like features. Immunohistochemical staining for laminin layer integrity showed compromise over time. A marker for double-stranded DNA breaks, γ-H2AX, increased over plasma-exposure time. These findings identified a threshold for plasma exposure of up to 900s at low power and <120s at high power. Nonthermal FE-DBD plasma can be considered safe for future studies of external use under these threshold conditions for evaluation of sterilization, coagulation, and wound healing. Copyright © 2013 Elsevier Inc. All rights reserved.

Real-space imaging of non-collinear antiferromagnetic order with a single-spin magnetometer

NASA Astrophysics Data System (ADS)

Gross, I.; Akhtar, W.; Garcia, V.; Martínez, L. J.; Chouaieb, S.; Garcia, K.; Carrétéro, C.; Barthélémy, A.; Appel, P.; Maletinsky, P.; Kim, J.-V.; Chauleau, J. Y.; Jaouen, N.; Viret, M.; Bibes, M.; Fusil, S.; Jacques, V.

2017-09-01

Although ferromagnets have many applications, their large magnetization and the resulting energy cost for switching magnetic moments bring into question their suitability for reliable low-power spintronic devices. Non-collinear antiferromagnetic systems do not suffer from this problem, and often have extra functionalities: non-collinear spin order may break space-inversion symmetry and thus allow electric-field control of magnetism, or may produce emergent spin-orbit effects that enable efficient spin-charge interconversion. To harness these traits for next-generation spintronics, the nanoscale control and imaging capabilities that are now routine for ferromagnets must be developed for antiferromagnetic systems. Here, using a non-invasive, scanning single-spin magnetometer based on a nitrogen-vacancy defect in diamond, we demonstrate real-space visualization of non-collinear antiferromagnetic order in a magnetic thin film at room temperature. We image the spin cycloid of a multiferroic bismuth ferrite (BiFeO3) thin film and extract a period of about 70 nanometres, consistent with values determined by macroscopic diffraction. In addition, we take advantage of the magnetoelectric coupling present in BiFeO3 to manipulate the cycloid propagation direction by an electric field. Besides highlighting the potential of nitrogen-vacancy magnetometry for imaging complex antiferromagnetic orders at the nanoscale, these results demonstrate how BiFeO3 can be used in the design of reconfigurable nanoscale spin textures.

Defining the macroscopic and microscopic findings of experimental focal brain ischemia in rats from a forensic scientist's point of view.

PubMed

Tatlisumak, Ertugrul; Inan, Sevinc; Asirdizer, Mahmut; Apaydin, Nihal; Hayretdag, Ceyda; Kose, Can; Tekdemir, Ibrahim

2009-03-01

Approximately 10% of all deaths in the world occur as a result of stroke. Determination of the time schedule of the pathologic events in a stroke patient is invaluable for a forensic specialist. The aim of this study was to define the schedule of the macroscopic and microscopic changes that occurred in a rat model of permanent focal ischemia for providing useful clues for the evaluation of stroke patients. Male Wistar rats weighing 250 to 350 g were used in this study. Permanent focal brain ischemia was applied by the suture occlusion method. The animals were divided into 7 experimental groups (n = 6) with time schedules including 1.5, 3, 6, 12, 24, 72 hours, and the sham. Brains were harvested at the end of the determined time schedule. Lesions in the frontoparietal cortex were evaluated macroscopically first and later hematoxylin eosin stained sections from the infarct core were investigated microscopically. Macroscopically, enlargement of the ipsilateral hemisphere was mild at 6 hour, apparent at 12 and 24 hours, and mild again at 72 hours. Microscopically, ischemic changes were apparent even at 1.5 hour. Red neurons and infiltration of the parenchyma with neutrophil leukocytes were observed at 12 hours. Pannecrosis and massive leukocyte infiltration were observed at 72 hours. Macroscopic and microscopic findings obtained from a rat model may provide clues for determination of the time-dependent changes due to brain ischemia in human subjects. Finally, the benefits of determination of time course of pathologic changes in the brain for forensic scientists were discussed.

Hierarchical modeling of plasma and transport phenomena in a dielectric barrier discharge reactor

NASA Astrophysics Data System (ADS)

Bali, N.; Aggelopoulos, C. A.; Skouras, E. D.; Tsakiroglou, C. D.; Burganos, V. N.

2017-12-01

A novel dual-time hierarchical approach is developed to link the plasma process to macroscopic transport phenomena in the interior of a dielectric barrier discharge (DBD) reactor that has been used for soil remediation (Aggelopoulos et al 2016 Chem. Eng. J. 301 353-61). The generation of active species by plasma reactions is simulated at the microseconds (µs) timescale, whereas convection and thermal conduction are simulated at the macroscopic (minutes) timescale. This hierarchical model is implemented in order to investigate the influence of the plasma DBD process on the transport and reaction mechanisms during remediation of polluted soil. In the microscopic model, the variables of interest include the plasma-induced reactive concentrations, while in the macroscopic approach, the temperature distribution, and the velocity field both inside the discharge gap and within the polluted soil material as well. For the latter model, the Navier-Stokes and Darcy Brinkman equations for the transport phenomena in the porous domain are solved numerically using a FEM software. The effective medium theory is employed to provide estimates of the effective time-evolving and three-phase transport properties in the soil sample. Model predictions considering the temporal evolution of the plasma remediation process are presented and compared with corresponding experimental data.

Construction of pore network models for Berea and Fontainebleau sandstones using non-linear programing and optimization techniques

NASA Astrophysics Data System (ADS)

Sharqawy, Mostafa H.

2016-12-01

Pore network models (PNM) of Berea and Fontainebleau sandstones were constructed using nonlinear programming (NLP) and optimization methods. The constructed PNMs are considered as a digital representation of the rock samples which were based on matching the macroscopic properties of the porous media and used to conduct fluid transport simulations including single and two-phase flow. The PNMs consisted of cubic networks of randomly distributed pores and throats sizes and with various connectivity levels. The networks were optimized such that the upper and lower bounds of the pore sizes are determined using the capillary tube bundle model and the Nelder-Mead method instead of guessing them, which reduces the optimization computational time significantly. An open-source PNM framework was employed to conduct transport and percolation simulations such as invasion percolation and Darcian flow. The PNM model was subsequently used to compute the macroscopic properties; porosity, absolute permeability, specific surface area, breakthrough capillary pressure, and primary drainage curve. The pore networks were optimized to allow for the simulation results of the macroscopic properties to be in excellent agreement with the experimental measurements. This study demonstrates that non-linear programming and optimization methods provide a promising method for pore network modeling when computed tomography imaging may not be readily available.

Length-scale crossover of the hydrophobic interaction in a coarse-grained water model

NASA Astrophysics Data System (ADS)

Chaimovich, Aviel; Shell, M. Scott

2013-11-01

It has been difficult to establish a clear connection between the hydrophobic interaction among small molecules typically studied in molecular simulations (a weak, oscillatory force) and that found between large, macroscopic surfaces in experiments (a strong, monotonic force). Here, we show that both types of interaction can emerge with a simple, core-softened water model that captures water's unique pairwise structure. As in hydrophobic hydration, we find that the hydrophobic interaction manifests a length-scale dependence, exhibiting distinct driving forces in the molecular and macroscopic regimes. Moreover, the ability of this simple model to capture both regimes suggests that several features of the hydrophobic force can be understood merely through water's pair correlations.

Length-scale crossover of the hydrophobic interaction in a coarse-grained water model.

PubMed

Chaimovich, Aviel; Shell, M Scott

2013-11-01

It has been difficult to establish a clear connection between the hydrophobic interaction among small molecules typically studied in molecular simulations (a weak, oscillatory force) and that found between large, macroscopic surfaces in experiments (a strong, monotonic force). Here, we show that both types of interaction can emerge with a simple, core-softened water model that captures water's unique pairwise structure. As in hydrophobic hydration, we find that the hydrophobic interaction manifests a length-scale dependence, exhibiting distinct driving forces in the molecular and macroscopic regimes. Moreover, the ability of this simple model to capture both regimes suggests that several features of the hydrophobic force can be understood merely through water's pair correlations.

Micromechanical model for protein materials: From macromolecules to macroscopic fibers

NASA Astrophysics Data System (ADS)

Puglisi, G.; De Tommasi, D.; Pantano, M. F.; Pugno, N. M.; Saccomandi, G.

2017-10-01

We propose a model for the mechanical behavior of protein materials. Based on a limited number of experimental macromolecular parameters (persistence and contour length) we obtain the macroscopic behavior of keratin fibers (human, cow, and rabbit hair), taking into account the damage and residual stretches effects that are fundamental in many functions of life. We also show the capability of our approach to describe the main dissipation and permanent strain effects observed in the more complex spider silk fibers. The comparison between our results and the data obtained experimentally from cyclic tests demonstrates that our model is robust and is able to reproduce with a remarkable accuracy the experimental behavior of all protein materials we tested.

Predicting the Macroscopic Fracture Energy of Epoxy Resins from Atomistic Molecular Simulations

DOE PAGES

Meng, Zhaoxu; Bessa, Miguel A.; Xia, Wenjie; ...

2016-12-06

Predicting the macroscopic fracture energy of highly crosslinked glassy polymers from atomistic simulations is challenging due to the size of the process zone being large in these systems. Here, we present a scale-bridging approach that links atomistic molecular dynamics simulations to macroscopic fracture properties on the basis of a continuum fracture mechanics model for two different epoxy materials. Our approach reveals that the fracture energy of epoxy resins strongly depends on the functionality of epoxy resin and the component ratio between the curing agent (amine) and epoxide. The most intriguing part of our study is that we demonstrate that themore » fracture energy exhibits a maximum value within the range of conversion degrees considered (from 65% to 95%), which can be attributed to the combined effects of structural rigidity and post-yield deformability. Our study provides physical insight into the molecular mechanisms that govern the fracture characteristics of epoxy resins and demonstrates the success of utilizing atomistic molecular simulations towards predicting macroscopic material properties.« less

Predicting the Macroscopic Fracture Energy of Epoxy Resins from Atomistic Molecular Simulations

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

Meng, Zhaoxu; Bessa, Miguel A.; Xia, Wenjie

Predicting the macroscopic fracture energy of highly crosslinked glassy polymers from atomistic simulations is challenging due to the size of the process zone being large in these systems. Here, we present a scale-bridging approach that links atomistic molecular dynamics simulations to macroscopic fracture properties on the basis of a continuum fracture mechanics model for two different epoxy materials. Our approach reveals that the fracture energy of epoxy resins strongly depends on the functionality of epoxy resin and the component ratio between the curing agent (amine) and epoxide. The most intriguing part of our study is that we demonstrate that themore » fracture energy exhibits a maximum value within the range of conversion degrees considered (from 65% to 95%), which can be attributed to the combined effects of structural rigidity and post-yield deformability. Our study provides physical insight into the molecular mechanisms that govern the fracture characteristics of epoxy resins and demonstrates the success of utilizing atomistic molecular simulations towards predicting macroscopic material properties.« less

Development of Open Brain Simulator for Human Biomechatronics

NASA Astrophysics Data System (ADS)

Otake, Mihoko; Takagi, Toshihisa; Asama, Hajime

Modeling and simulation based on mechanisms is important in order to design and control mechatronic systems. In particular, in-depth understanding and realistic modeling of biological systems is indispensable for biomechatronics. This paper presents open brain simulator, which estimates the neural state of human through external measurement for the purpose of improving motor and social skills. Macroscopic anatomical nervous systems model was built which can be connected to the musculoskeletal model. Microscopic anatomical and physiological neural models were interfaced to the macroscopic model. Neural activities of somatosensory area and Purkinje cell were calculated from motion capture data. The simulator provides technical infrastructure for human biomechatronics, which is promising for the novel diagnosis of neurological disorders and their treatments through medication and movement therapy, and for motor learning support system supporting acquisition of motor skill considering neural mechanism.

Capturing microscopic features of bone remodeling into a macroscopic model based on biological rationales of bone adaptation.

PubMed

Kim, Young Kwan; Kameo, Yoshitaka; Tanaka, Sakae; Adachi, Taiji

2017-10-01

To understand Wolff's law, bone adaptation by remodeling at the cellular and tissue levels has been discussed extensively through experimental and simulation studies. For the clinical application of a bone remodeling simulation, it is significant to establish a macroscopic model that incorporates clarified microscopic mechanisms. In this study, we proposed novel macroscopic models based on the microscopic mechanism of osteocytic mechanosensing, in which the flow of fluid in the lacuno-canalicular porosity generated by fluid pressure gradients plays an important role, and theoretically evaluated the proposed models, taking biological rationales of bone adaptation into account. The proposed models were categorized into two groups according to whether the remodeling equilibrium state was defined globally or locally, i.e., the global or local uniformity models. Each remodeling stimulus in the proposed models was quantitatively evaluated through image-based finite element analyses of a swine cancellous bone, according to two introduced criteria associated with the trabecular volume and orientation at remodeling equilibrium based on biological rationales. The evaluation suggested that nonuniformity of the mean stress gradient in the local uniformity model, one of the proposed stimuli, has high validity. Furthermore, the adaptive potential of each stimulus was discussed based on spatial distribution of a remodeling stimulus on the trabecular surface. The theoretical consideration of a remodeling stimulus based on biological rationales of bone adaptation would contribute to the establishment of a clinically applicable and reliable simulation model of bone remodeling.

Macroscopic balance model for wave rotors

NASA Technical Reports Server (NTRS)

Welch, Gerard E.

1996-01-01

A mathematical model for multi-port wave rotors is described. The wave processes that effect energy exchange within the rotor passage are modeled using one-dimensional gas dynamics. Macroscopic mass and energy balances relate volume-averaged thermodynamic properties in the rotor passage control volume to the mass, momentum, and energy fluxes at the ports. Loss models account for entropy production in boundary layers and in separating flows caused by blade-blockage, incidence, and gradual opening and closing of rotor passages. The mathematical model provides a basis for predicting design-point wave rotor performance, port timing, and machine size. Model predictions are evaluated through comparisons with CFD calculations and three-port wave rotor experimental data. A four-port wave rotor design example is provided to demonstrate model applicability. The modeling approach is amenable to wave rotor optimization studies and rapid assessment of the trade-offs associated with integrating wave rotors into gas turbine engine systems.

Investigation of representing hysteresis in macroscopic models of two-phase flow in porous media using intermediate scale experimental data

NASA Astrophysics Data System (ADS)

Cihan, Abdullah; Birkholzer, Jens; Trevisan, Luca; Gonzalez-Nicolas, Ana; Illangasekare, Tissa

2017-01-01

Incorporating hysteresis into models is important to accurately capture the two phase flow behavior when porous media systems undergo cycles of drainage and imbibition such as in the cases of injection and post-injection redistribution of CO2 during geological CO2 storage (GCS). In the traditional model of two-phase flow, existing constitutive models that parameterize the hysteresis associated with these processes are generally based on the empirical relationships. This manuscript presents development and testing of mathematical hysteretic capillary pressure—saturation—relative permeability models with the objective of more accurately representing the redistribution of the fluids after injection. The constitutive models are developed by relating macroscopic variables to basic physics of two-phase capillary displacements at pore-scale and void space distribution properties. The modeling approach with the developed constitutive models with and without hysteresis as input is tested against some intermediate-scale flow cell experiments to test the ability of the models to represent movement and capillary trapping of immiscible fluids under macroscopically homogeneous and heterogeneous conditions. The hysteretic two-phase flow model predicted the overall plume migration and distribution during and post injection reasonably well and represented the postinjection behavior of the plume more accurately than the nonhysteretic models. Based on the results in this study, neglecting hysteresis in the constitutive models of the traditional two-phase flow theory can seriously overpredict or underpredict the injected fluid distribution during post-injection under both homogeneous and heterogeneous conditions, depending on the selected value of the residual saturation in the nonhysteretic models.

How are the Concepts and Theories of Acid Base Reactions Presented? Chemistry in Textbooks and as Presented by Teachers

NASA Astrophysics Data System (ADS)

Furió-Más, Carlos; Calatayud, María Luisa; Guisasola, Jenaro; Furió-Gómez, Cristina

2005-09-01

This paper investigates the views of science and scientific activity that can be found in chemistry textbooks and heard from teachers when acid base reactions are introduced to grade 12 and university chemistry students. First, the main macroscopic and microscopic conceptual models are developed. Second, we attempt to show how the existence of views of science in textbooks and of chemistry teachers contributes to an impoverished image of chemistry. A varied design has been elaborated to analyse some epistemological deficiencies in teaching acid base reactions. Textbooks have been analysed and teachers have been interviewed. The results obtained show that the teaching process does not emphasize the macroscopic presentation of acids and bases. Macroscopic and microscopic conceptual models involved in the explanation of acid base processes are mixed in textbooks and by teachers. Furthermore, the non-problematic introduction of concepts, such as the hydrolysis concept, and the linear, cumulative view of acid base theories (Arrhenius and Brönsted) were detected.

Effects of intra-articular injection of mesenchymal stem cells associated with platelet-rich plasma in a rabbit model of osteoarthritis.

PubMed

Hermeto, L C; DeRossi, R; Oliveira, R J; Pesarini, J R; Antoniolli-Silva, A C M B; Jardim, P H A; Santana, A E; Deffune, E; Rinaldi, J C; Justulin, L A

2016-09-02

The current study aims to evaluate the macroscopic and histological effects of autologous mesenchymal stem cells (MSC) and platelet-rich plasma on knee articular cartilage regeneration in an experimental model of osteoarthritis. Twenty-four rabbits were randomly divided into four groups: control group, platelet-rich plasma group, autologous MSC undifferentiated group, and autologous MSC differentiated into chondrocyte group. Collagenase solution was used to induce osteoarthritis, and treatments were applied to each group at 6 weeks following osteoarthritis induction. After 60 days of therapy, the animals were euthanized and the articular surfaces were subjected to macroscopic and histological evaluations. The adipogenic, chondrogenic, and osteogenic differentiation potentials of MSCs were evaluated. Macroscopic and histological examinations revealed improved tissue repair in the MSC-treated groups. However, no difference was found between MSC-differentiated and undifferentiated chondrocytes. We found that MSCs derived from adipose tissue and platelet-rich plasma were associated with beneficial effects in articular cartilage regeneration during experimental osteoarthritis.

Macroscopic damping model for structural dynamics with random polycrystalline configurations

NASA Astrophysics Data System (ADS)

Yang, Yantao; Cui, Junzhi; Yu, Yifan; Xiang, Meizhen

2018-06-01

In this paper the macroscopic damping model for dynamical behavior of the structures with random polycrystalline configurations at micro-nano scales is established. First, the global motion equation of a crystal is decomposed into a set of motion equations with independent single degree of freedom (SDOF) along normal discrete modes, and then damping behavior is introduced into each SDOF motion. Through the interpolation of discrete modes, the continuous representation of damping effects for the crystal is obtained. Second, from energy conservation law the expression of the damping coefficient is derived, and the approximate formula of damping coefficient is given. Next, the continuous damping coefficient for polycrystalline cluster is expressed, the continuous dynamical equation with damping term is obtained, and then the concrete damping coefficients for a polycrystalline Cu sample are shown. Finally, by using statistical two-scale homogenization method, the macroscopic homogenized dynamical equation containing damping term for the structures with random polycrystalline configurations at micro-nano scales is set up.

Scaling of chaos in strongly nonlinear lattices.

PubMed

Mulansky, Mario

2014-06-01

Although it is now understood that chaos in complex classical systems is the foundation of thermodynamic behavior, the detailed relations between the microscopic properties of the chaotic dynamics and the macroscopic thermodynamic observations still remain mostly in the dark. In this work, we numerically analyze the probability of chaos in strongly nonlinear Hamiltonian systems and find different scaling properties depending on the nonlinear structure of the model. We argue that these different scaling laws of chaos have definite consequences for the macroscopic diffusive behavior, as chaos is the microscopic mechanism of diffusion. This is compared with previous results on chaotic diffusion [M. Mulansky and A. Pikovsky, New J. Phys. 15, 053015 (2013)], and a relation between microscopic chaos and macroscopic diffusion is established.

Iron encrustations on filamentous algae colonized by Gallionella-related bacteria in a metal-polluted freshwater stream

NASA Astrophysics Data System (ADS)

Mori, J. F.; Neu, T. R.; Lu, S.; Händel, M.; Totsche, K. U.; Küsel, K.

2015-09-01

Filamentous macroscopic algae were observed in slightly acidic to circumneutral (pH 5.9-6.5), metal-rich stream water that leaked out from a former uranium mining district (Ronneburg, Germany). These algae differed in color and morphology and were encrusted with Fe-deposits. To elucidate their potential interaction with Fe(II)-oxidizing bacteria (FeOB), we collected algal samples at three time points during summer 2013 and studied the algae-bacteria-mineral compositions via confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectra, and a 16S and 18S rRNA gene-based bacterial and algae community analysis. Surprisingly, sequencing analysis of 18S rRNA gene regions of green and brown algae revealed high homologies with the freshwater algae Tribonema (99.9-100 %). CLSM imaging indicated a loss of active chloroplasts in the algae cells, which may be responsible for the change in color in

Navier-Stokes-like equations for traffic flow.

PubMed

Velasco, R M; Marques, W

2005-10-01

The macroscopic traffic flow equations derived from the reduced Paveri-Fontana equation are closed starting with the maximization of the informational entropy. The homogeneous steady state taken as a reference is obtained for a specific model of the desired velocity and a kind of Chapman-Enskog method is developed to calculate the traffic pressure at the Navier-Stokes level. Numerical solution of the macroscopic traffic equations is obtained and its characteristics are analyzed.

Micromechanics and constitutive modeling of connective soft tissues.

PubMed

Fallah, A; Ahmadian, M T; Firozbakhsh, K; Aghdam, M M

2016-07-01

In this paper, a micromechanical model for connective soft tissues based on the available histological evidences is developed. The proposed model constituents i.e. collagen fibers and ground matrix are considered as hyperelastic materials. The matrix material is assumed to be isotropic Neo-Hookean while the collagen fibers are considered to be transversely isotropic hyperelastic. In order to take into account the effects of tissue structure in lower scales on the macroscopic behavior of tissue, a strain energy density function (SEDF) is developed for collagen fibers based on tissue hierarchical structure. Macroscopic response and properties of tissue are obtained using the numerical homogenization method with the help of ABAQUS software. The periodic boundary conditions and the proposed constitutive models are implemented into ABAQUS using the DISP and the UMAT subroutines, respectively. The existence of the solution and stable material behavior of proposed constitutive model for collagen fibers are investigated based on the poly-convexity condition. Results of the presented micromechanics model for connective tissues are compared and validated with available experimental data. Effects of geometrical and material parameters variation at microscale on macroscopic mechanical behavior of tissues are investigated. The results show that decrease in collagen content of the connective tissues like the tendon due to diseases leads 20% more stretch than healthy tissue under the same load which can results in connective tissue malfunction and hypermobility in joints. Copyright © 2016 Elsevier Ltd. All rights reserved.

History-dependent friction and slow slip from time-dependent microscopic junction laws studied in a statistical framework

NASA Astrophysics Data System (ADS)

Thøgersen, Kjetil; Trømborg, Jørgen Kjoshagen; Sveinsson, Henrik Andersen; Malthe-Sørenssen, Anders; Scheibert, Julien

2014-05-01

To study how macroscopic friction phenomena originate from microscopic junction laws, we introduce a general statistical framework describing the collective behavior of a large number of individual microjunctions forming a macroscopic frictional interface. Each microjunction can switch in time between two states: a pinned state characterized by a displacement-dependent force and a slipping state characterized by a time-dependent force. Instead of tracking each microjunction individually, the state of the interface is described by two coupled distributions for (i) the stretching of pinned junctions and (ii) the time spent in the slipping state. This framework allows for a whole family of microjunction behavior laws, and we show how it represents an overarching structure for many existing models found in the friction literature. We then use this framework to pinpoint the effects of the time scale that controls the duration of the slipping state. First, we show that the model reproduces a series of friction phenomena already observed experimentally. The macroscopic steady-state friction force is velocity dependent, either monotonic (strengthening or weakening) or nonmonotonic (weakening-strengthening), depending on the microscopic behavior of individual junctions. In addition, slow slip, which has been reported in a wide variety of systems, spontaneously occurs in the model if the friction contribution from junctions in the slipping state is time weakening. Next, we show that the model predicts a nontrivial history dependence of the macroscopic static friction force. In particular, the static friction coefficient at the onset of sliding is shown to increase with increasing deceleration during the final phases of the preceding sliding event. We suggest that this form of history dependence of static friction should be investigated in experiments, and we provide the acceleration range in which this effect is expected to be experimentally observable.

History-dependent friction and slow slip from time-dependent microscopic junction laws studied in a statistical framework.

PubMed

Thøgersen, Kjetil; Trømborg, Jørgen Kjoshagen; Sveinsson, Henrik Andersen; Malthe-Sørenssen, Anders; Scheibert, Julien

2014-05-01

To study how macroscopic friction phenomena originate from microscopic junction laws, we introduce a general statistical framework describing the collective behavior of a large number of individual microjunctions forming a macroscopic frictional interface. Each microjunction can switch in time between two states: a pinned state characterized by a displacement-dependent force and a slipping state characterized by a time-dependent force. Instead of tracking each microjunction individually, the state of the interface is described by two coupled distributions for (i) the stretching of pinned junctions and (ii) the time spent in the slipping state. This framework allows for a whole family of microjunction behavior laws, and we show how it represents an overarching structure for many existing models found in the friction literature. We then use this framework to pinpoint the effects of the time scale that controls the duration of the slipping state. First, we show that the model reproduces a series of friction phenomena already observed experimentally. The macroscopic steady-state friction force is velocity dependent, either monotonic (strengthening or weakening) or nonmonotonic (weakening-strengthening), depending on the microscopic behavior of individual junctions. In addition, slow slip, which has been reported in a wide variety of systems, spontaneously occurs in the model if the friction contribution from junctions in the slipping state is time weakening. Next, we show that the model predicts a nontrivial history dependence of the macroscopic static friction force. In particular, the static friction coefficient at the onset of sliding is shown to increase with increasing deceleration during the final phases of the preceding sliding event. We suggest that this form of history dependence of static friction should be investigated in experiments, and we provide the acceleration range in which this effect is expected to be experimentally observable.

The flow of plasma in the solar terrestrial environment

NASA Technical Reports Server (NTRS)

Schunk, R. W.

1992-01-01

The overall goal of our NASA Theory Program is to study the coupling, time delays, and feedback mechanisms between the various regions of the solar-terrestrial system in a self-consistent, quantitative manner. To accomplish this goal, it will eventually be necessary to have time-dependent macroscopic models of the different regions of the solar-terrestrial system and we are continually working toward this goal. However, our immediate emphasis is on the near-earth plasma environment, including the ionosphere, the plasmasphere, and the polar wind. In this area, we have developed unique global models that allow us to study the coupling between the different regions. Another important aspect of our NASA Theory Program concerns the effect that localized structure has on the macroscopic flow in the ionosphere, plasmasphere, thermosphere, and polar wind. The localized structure can be created by structured magnetospheric inputs (i.e., structured plasma convection, particle precipitation or Birkeland current patterns) or time variations in these inputs due to storms and substorms. Also, some of the plasma flows that we predict with our macroscopic models may be unstable, and another one of our goals is to examine the stability of our predicted flows. Because time-dependent, three-dimensional numerical models of the solar-terrestrial environment generally require extensive computer resources, they are usually based on relatively simple mathematical formulations (i.e., simple MHD or hydrodynamic formulation). Therefore, another long-range goal of our NASA Theory Program is to study the conditions under which various mathematical formulations can be applied to specific solar-terrestrial regions. This may involve a detailed comparison of kinetic, semikinetic, and hydrodynamic predictions for a given polar wind scenario or it may involve the comparison of a small-scale particle-in-cell (PIC) simulation of a plasma expansion event with a similar macroscopic expansion event. The different mathematical formulations have different strengths and weaknesses and a careful comparison of model predictions for similar geophysical situations will provide insight into when the various models can be used with confidence.

Wave dynamics in an extended macroscopic traffic flow model with periodic boundaries

NASA Astrophysics Data System (ADS)

Wang, Yu-Qing; Chu, Xing-Jian; Zhou, Chao-Fan; Yan, Bo-Wen; Jia, Bin; Fang, Chen-Hao

2018-06-01

Motivated by the previous traffic flow model considering the real-time traffic state, a modified macroscopic traffic flow model is established. The periodic boundary condition is applied to the car-following model. Besides, the traffic state factor R is defined in order to correct the real traffic conditions in a more reasonable way. It is a key step that we introduce the relaxation time as a density-dependent function and provide corresponding evolvement of traffic flow. Three different typical initial densities, namely the high density, the medium one and the low one, are intensively investigated. It can be found that the hysteresis loop exists in the proposed periodic-boundary system. Furthermore, the linear and nonlinear stability analyses are performed in order to test the robustness of the system.

Static and sliding contact of rough surfaces: Effect of asperity-scale properties and long-range elastic interactions

NASA Astrophysics Data System (ADS)

Hulikal, Srivatsan; Lapusta, Nadia; Bhattacharya, Kaushik

2018-07-01

Friction in static and sliding contact of rough surfaces is important in numerous physical phenomena. We seek to understand macroscopically observed static and sliding contact behavior as the collective response of a large number of microscopic asperities. To that end, we build on Hulikal et al. (2015) and develop an efficient numerical framework that can be used to investigate how the macroscopic response of multiple frictional contacts depends on long-range elastic interactions, different constitutive assumptions about the deforming contacts and their local shear resistance, and surface roughness. We approximate the contact between two rough surfaces as that between a regular array of discrete deformable elements attached to a elastic block and a rigid rough surface. The deformable elements are viscoelastic or elasto/viscoplastic with a range of relaxation times, and the elastic interaction between contacts is long-range. We find that the model reproduces the main macroscopic features of evolution of contact and friction for a range of constitutive models of the elements, suggesting that macroscopic frictional response is robust with respect to the microscopic behavior. Viscoelasticity/viscoplasticity contributes to the increase of friction with contact time and leads to a subtle history dependence. Interestingly, long-range elastic interactions only change the results quantitatively compared to the meanfield response. The developed numerical framework can be used to study how specific observed macroscopic behavior depends on the microscale assumptions. For example, we find that sustained increase in the static friction coefficient during long hold times suggests viscoelastic response of the underlying material with multiple relaxation time scales. We also find that the experimentally observed proportionality of the direct effect in velocity jump experiments to the logarithm of the velocity jump points to a complex material-dependent shear resistance at the microscale.

Role of 3D force networks in linking grain scale to macroscale processes in sheared granular debris

NASA Astrophysics Data System (ADS)

Mair, K.; Jettestuen, E.; Abe, S.

2013-12-01

Active faults, landslides and subglacial tills contain accumulations of granular debris that evolve during sliding. The macroscopic motion in these environments is at least to some extent determined by processes operating in this sheared granular material. A valid question is how the local behavior at the individual granular contacts actually sums up to influence macroscopic sliding. Laboratory experiments and numerical modeling can potentially help elucidate this. Observations of jamming (stick) and unjamming (flow) as well as concentrated shear bands on the scale of 5-10 grains suggest that a simple continuum description may be insufficient to capture important elements of the behavior. We therefore seek a measure of the organization of the granular fabric and the 3D structure of the load bearing skeleton that effectively demonstrates how the individual grain interactions are manifested in the macroscopic sliding behavior we observe. Contact force networks are an expression of this. Here we investigate the structure and variability of the most connected system spanning force networks produced in 3D discrete element models of granular layers under shear. We use percolation measures to identify, characterize, compare and track the evolution of these strongly connected contact force networks. We show that specific topological measures used in describing the networks, such as number of contacts and coordination number, are sensitive to grain size distribution (and likely the grain shape) of the material as well as loading conditions. Hence, faults of different maturity would be expected to accommodate shear in different ways. Distinct changes in the topological characteristics i.e. the geometry of strong force networks with accumulated strain are directly correlated to fluctuations in macroscopic shearing resistance. This suggests that 3D force networks play an important bridging role between individual grain scale processes and macroscopic sliding behavior.

A Micro-Mechanism-Based Continuum Corrosion Fatigue Damage Model for Steels

NASA Astrophysics Data System (ADS)

Sun, Bin; Li, Zhaoxia

2018-05-01

A micro-mechanism-based corrosion fatigue damage model is developed for studying the high-cycle corrosion fatigue of steel from multi-scale viewpoint. The developed physical corrosion fatigue damage model establishes micro-macro relationships between macroscopic continuum damage evolution and collective evolution behavior of microscopic pits and cracks, which can be used to describe the multi-scale corrosion fatigue process of steel. As a case study, the model is used to predict continuum damage evolution and number density of the corrosion pit and short crack of steel component in 5% NaCl water under constant stress amplitude at 20 kHz, and the numerical results are compared with experimental results. It shows that the model is effective and can be used to evaluate the continuum macroscopic corrosion fatigue damage and study microscopic corrosion fatigue mechanisms of steel.

A Micro-Mechanism-Based Continuum Corrosion Fatigue Damage Model for Steels

NASA Astrophysics Data System (ADS)

Sun, Bin; Li, Zhaoxia

2018-04-01

A micro-mechanism-based corrosion fatigue damage model is developed for studying the high-cycle corrosion fatigue of steel from multi-scale viewpoint. The developed physical corrosion fatigue damage model establishes micro-macro relationships between macroscopic continuum damage evolution and collective evolution behavior of microscopic pits and cracks, which can be used to describe the multi-scale corrosion fatigue process of steel. As a case study, the model is used to predict continuum damage evolution and number density of the corrosion pit and short crack of steel component in 5% NaCl water under constant stress amplitude at 20 kHz, and the numerical results are compared with experimental results. It shows that the model is effective and can be used to evaluate the continuum macroscopic corrosion fatigue damage and study microscopic corrosion fatigue mechanisms of steel.

BAnd offset and magnetic property engineering for epitaxial interfaces: a Monolayer of M2O3 (M=Al, Ga, Sc, Ti, Ni) at the alpha-Fe203/alpha-Cr203 (0001) Interface

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

Jaffe, John E; Bachorz, Rafal A; Gutowski, Maciej S

2007-05-01

We have used density functional theory with the gradient corrected exchange-correlation functional PW91 to study the effect of an interfactant layer, where Fe and Cr are replaced by a different metal, on electronic and magnetic properties of an epitaxial interface between -Fe2O3 and -Cr2O3 in the hexagonal (0001) basal plane. We studied a monolayer of M2O3 (M=Al, Ga, Sc, Ti, Ni) sandwiched with 5 layers of chromia and five layers of hematite through epitaxial interfaces of two types, termed “oxygen divided” or “split metal.” We found that both the magnetic and electronic properties of the superlattice are modified by themore » interfactant monolayer. For the split metal interface, which is favored through the growth pattern of chromia and hematite, the band offset can be changed from 0.62 eV (no interfactant) up to 0.90 eV with the Sc2O3 interfactant, and down to –0.51 eV (i.e. the a-Fe2O3/a-Cr2O3 heterojunction changes from Type II to Type I) with the Ti2O3 interfactant, due to a massive interfacial charge transfer. The band gap of the system as a whole remains open for the interfactant monolayers based on Al, Ga, and Sc, but it closes for Ti. For Ni, the split-metal interface has a negative band offset and a small band gap. Thus, nanoscale engineering through layer-by-layer growth will strongly affect the macroscopic properties of this system.« less

Modeling of Dendritic Evolution of Continuously Cast Steel Billet with Cellular Automaton

NASA Astrophysics Data System (ADS)

Wang, Weiling; Ji, Cheng; Luo, Sen; Zhu, Miaoyong

2018-02-01

In order to predict the dendritic evolution during the continuous steel casting process, a simple mechanism to connect the heat transfer at the macroscopic scale and the dendritic growth at the microscopic scale was proposed in the present work. As the core of the across-scale simulation, a two-dimensional cell automaton (CA) model with a decentered square algorithm was developed and parallelized. Apart from nucleation undercooling and probability, a temperature gradient was introduced to deal with the columnar-to-equiaxed transition (CET) by considering its variation during continuous casting. Based on the thermal history, the dendritic evolution in a 4 mm × 40 mm region near the centerline of a SWRH82B steel billet was predicted. The influences of the secondary cooling intensity, superheat, and casting speed on the dendritic structure of the billet were investigated in detail. The results show that the predicted equiaxed dendritic solidification of Fe-5.3Si alloy and columnar dendritic solidification of Fe-0.45C alloy are consistent with in situ experimental results [Yasuda et al. Int J Cast Metals Res 22:15-21 (2009); Yasuda et al. ISIJ Int 51:402-408 (2011)]. Moreover, the predicted dendritic arm spacing and CET location agree well with the actual results in the billet. The primary dendrite arm spacing of columnar dendrites decreases with increasing secondary cooling intensity, or decreasing superheat and casting speed. Meanwhile, the CET is promoted as the secondary cooling intensity and superheat decrease. However, the CET is not influenced by the casting speed, owing to the adjusting of the flow rate of secondary spray water. Compared with the superheat and casting speed, the secondary cooling intensity can influence the cooling rate and temperature gradient in deeper locations, and accordingly exerts a more significant influence on the equiaxed dendritic structure.

Carbonate-mediated Fe(II) oxidation in the air-cathode fuel cell: a kinetic model in terms of Fe(II) speciation.

PubMed

Song, Wei; Zhai, Lin-Feng; Cui, Yu-Zhi; Sun, Min; Jiang, Yuan

2013-06-06

Due to the high redox activity of Fe(II) and its abundance in natural waters, the electro-oxidation of Fe(II) can be found in many air-cathode fuel cell systems, such as acid mine drainage fuel cells and sediment microbial fuel cells. To deeply understand these iron-related systems, it is essential to elucidate the kinetics and mechanisms involved in the electro-oxidation of Fe(II). This work aims to develop a kinetic model that adequately describes the electro-oxidation process of Fe(II) in air-cathode fuel cells. The speciation of Fe(II) is incorporated into the model, and contributions of individual Fe(II) species to the overall Fe(II) oxidation rate are quantitatively evaluated. The results show that the kinetic model can accurately predict the electro-oxidation rate of Fe(II) in air-cathode fuel cells. FeCO3, Fe(OH)2, and Fe(CO3)2(2-) are the most important species determining the electro-oxidation kinetics of Fe(II). The Fe(II) oxidation rate is primarily controlled by the oxidation of FeCO3 species at low pH, whereas at high pH Fe(OH)2 and Fe(CO3)2(2-) are the dominant species. Solution pH, carbonate concentration, and solution salinity are able to influence the electro-oxidation kinetics of Fe(II) through changing both distribution and kinetic activity of Fe(II) species.

A multi-scale model of dislocation plasticity in α-Fe: Incorporating temperature, strain rate and non-Schmid effects

DOE PAGES

Lim, H.; Hale, L. M.; Zimmerman, J. A.; ...

2015-01-05

In this study, we develop an atomistically informed crystal plasticity finite element (CP-FE) model for body-centered-cubic (BCC) α-Fe that incorporates non-Schmid stress dependent slip with temperature and strain rate effects. Based on recent insights obtained from atomistic simulations, we propose a new constitutive model that combines a generalized non-Schmid yield law with aspects from a line tension (LT) model for describing activation enthalpy required for the motion of dislocation kinks. Atomistic calculations are conducted to quantify the non-Schmid effects while both experimental data and atomistic simulations are used to assess the temperature and strain rate effects. The parameterized constitutive equationmore » is implemented into a BCC CP-FE model to simulate plastic deformation of single and polycrystalline Fe which is compared with experimental data from the literature. This direct comparison demonstrates that the atomistically informed model accurately captures the effects of crystal orientation, temperature and strain rate on the flow behavior of siangle crystal Fe. Furthermore, our proposed CP-FE model exhibits temperature and strain rate dependent flow and yield surfaces in polycrystalline Fe that deviate from conventional CP-FE models based on Schmid's law.« less

A Jones matrix formalism for simulating three-dimensional polarized light imaging of brain tissue.

PubMed

Menzel, M; Michielsen, K; De Raedt, H; Reckfort, J; Amunts, K; Axer, M

2015-10-06

The neuroimaging technique three-dimensional polarized light imaging (3D-PLI) provides a high-resolution reconstruction of nerve fibres in human post-mortem brains. The orientations of the fibres are derived from birefringence measurements of histological brain sections assuming that the nerve fibres—consisting of an axon and a surrounding myelin sheath—are uniaxial birefringent and that the measured optic axis is oriented in the direction of the nerve fibres (macroscopic model). Although experimental studies support this assumption, the molecular structure of the myelin sheath suggests that the birefringence of a nerve fibre can be described more precisely by multiple optic axes oriented radially around the fibre axis (microscopic model). In this paper, we compare the use of the macroscopic and the microscopic model for simulating 3D-PLI by means of the Jones matrix formalism. The simulations show that the macroscopic model ensures a reliable estimation of the fibre orientations as long as the polarimeter does not resolve structures smaller than the diameter of single fibres. In the case of fibre bundles, polarimeters with even higher resolutions can be used without losing reliability. When taking the myelin density into account, the derived fibre orientations are considerably improved. © 2015 The Author(s).

Application of thin-plate spline transformations to finite element models, or, how to turn a bog turtle into a spotted turtle to analyze both.

PubMed

Stayton, C Tristan

2009-05-01

Finite element (FE) models are popular tools that allow biologists to analyze the biomechanical behavior of complex anatomical structures. However, the expense and time required to create models from specimens has prevented comparative studies from involving large numbers of species. A new method is presented for transforming existing FE models using geometric morphometric methods. Homologous landmark coordinates are digitized on the FE model and on a target specimen into which the FE model is being transformed. These coordinates are used to create a thin-plate spline function and coefficients, which are then applied to every node in the FE model. This function smoothly interpolates the location of points between landmarks, transforming the geometry of the original model to match the target. This new FE model is then used as input in FE analyses. This procedure is demonstrated with turtle shells: a Glyptemys muhlenbergii model is transformed into Clemmys guttata and Actinemys marmorata models. Models are loaded and the resulting stresses are compared. The validity of the models is tested by crushing actual turtle shells in a materials testing machine and comparing those results to predictions from FE models. General guidelines, cautions, and possibilities for this procedure are also presented.

A gravitational test of wave reinforcement versus fluid density models

NASA Technical Reports Server (NTRS)

Johnson, Jacqueline Umstead

1990-01-01

Spermatozoa, protozoa, and algae form macroscopic patterns somewhat analogous to thermally driven convection cells. These bioconvective patterns have attracted interest in the fluid dynamics community, but whether in all cases these waves were gravity driven was unknown. There are two conflicting theories, one gravity dependent (fluid density model), the other gravity independent (wave reinforcement theory). The primary objectives of the summer faculty fellows were to: (1) assist in sample collection (spermatozoa) and preparation for the KC-135 research airplane experiment; and (2) to collaborate on ground testing of bioconvective variables such as motility, concentration, morphology, etc., in relation to their macroscopic patterns. Results are very briefly given.

Wave propagation in a strongly heterogeneous elastic porous medium: Homogenization of Biot medium with double porosities

NASA Astrophysics Data System (ADS)

Rohan, Eduard; Naili, Salah; Nguyen, Vu-Hieu

2016-08-01

We study wave propagation in an elastic porous medium saturated with a compressible Newtonian fluid. The porous network is interconnected whereby the pores are characterized by two very different characteristic sizes. At the mesoscopic scale, the medium is described using the Biot model, characterized by a high contrast in the hydraulic permeability and anisotropic elasticity, whereas the contrast in the Biot coupling coefficient is only moderate. Fluid motion is governed by the Darcy flow model extended by inertia terms and by the mass conservation equation. The homogenization method based on the asymptotic analysis is used to obtain a macroscopic model. To respect the high contrast in the material properties, they are scaled by the small parameter, which is involved in the asymptotic analysis and characterized by the size of the heterogeneities. Using the estimates of wavelengths in the double-porosity networks, it is shown that the macroscopic descriptions depend on the contrast in the static permeability associated with pores and micropores and on the frequency. Moreover, the microflow in the double porosity is responsible for fading memory effects via the macroscopic poroviscoelastic constitutive law. xml:lang="fr"

Molecular modeling of polycarbonate materials: Glass transition and mechanical properties

NASA Astrophysics Data System (ADS)

Palczynski, Karol; Wilke, Andreas; Paeschke, Manfred; Dzubiella, Joachim

2017-09-01

Linking the experimentally accessible macroscopic properties of thermoplastic polymers to their microscopic static and dynamic properties is a key requirement for targeted material design. Classical molecular dynamics simulations enable us to study the structural and dynamic behavior of molecules on microscopic scales, and statistical physics provides a framework for relating these properties to the macroscopic properties. We take a first step toward creating an automated workflow for the theoretical prediction of thermoplastic material properties by developing an expeditious method for parameterizing a simple yet surprisingly powerful coarse-grained bisphenol-A polycarbonate model which goes beyond previous coarse-grained models and successfully reproduces the thermal expansion behavior, the glass transition temperature as a function of the molecular weight, and several elastic properties.

Generalized Models for Rock Joint Surface Shapes

PubMed Central

Du, Shigui; Hu, Yunjin; Hu, Xiaofei

2014-01-01

Generalized models of joint surface shapes are the foundation for mechanism studies on the mechanical effects of rock joint surface shapes. Based on extensive field investigations of rock joint surface shapes, generalized models for three level shapes named macroscopic outline, surface undulating shape, and microcosmic roughness were established through statistical analyses of 20,078 rock joint surface profiles. The relative amplitude of profile curves was used as a borderline for the division of different level shapes. The study results show that the macroscopic outline has three basic features such as planar, arc-shaped, and stepped; the surface undulating shape has three basic features such as planar, undulating, and stepped; and the microcosmic roughness has two basic features such as smooth and rough. PMID:25152901

Macroscopic quantum tunneling escape of Bose-Einstein condensates

NASA Astrophysics Data System (ADS)

Zhao, Xinxin; Alcala, Diego A.; McLain, Marie A.; Maeda, Kenji; Potnis, Shreyas; Ramos, Ramon; Steinberg, Aephraim M.; Carr, Lincoln D.

2017-12-01

Recent experiments on macroscopic quantum tunneling reveal a nonexponential decay of the number of atoms trapped in a quasibound state behind a potential barrier. Through both experiment and theory, we demonstrate this nonexponential decay results from interactions between atoms. Quantum tunneling of tens of thousands of 87Rb atoms in a Bose-Einstein condensate is modeled by a modified Jeffreys-Wentzel-Kramers-Brillouin model, taking into account the effective time-dependent barrier induced by the mean field. Three-dimensional Gross-Pitaevskii simulations corroborate a mean-field result when compared with experiments. However, with one-dimensional modeling using time-evolving block decimation, we present an effective renormalized mean-field theory that suggests many-body dynamics for which a bare mean-field theory may not apply.

Macroscopic acoustoelectric charge transport in graphene

NASA Astrophysics Data System (ADS)

Bandhu, L.; Lawton, L. M.; Nash, G. R.

2013-09-01

We demonstrate macroscopic acoustoelectric transport in graphene, transferred onto piezoelectric lithium niobate substrates, between electrodes up to 500 μm apart. Using double finger interdigital transducers we have characterised the acoustoelectric current as a function of both surface acoustic wave intensity and frequency. The results are consistent with a relatively simple classical relaxation model, in which the acoustoelectric current is proportional to both the surface acoustic wave intensity and the attenuation of the wave caused by the charge transport.

Unipolar memristive Switching in Bulk Negative Temperature Coefficient Thermosensitive Ceramics

PubMed Central

Wu, Hongya; Cai, Kunpeng; Zhou, Ji; Li, Bo; Li, Longtu

2013-01-01

A memristive phenomenon was observed in macroscopic bulk negative temperature coefficient nickel monoxide (NiO) ceramic material. Current-voltage characteristics of memristors, pinched hysteretic loops were systematically observed in the Ag/NiO/Ag cell. A thermistor-based model for materials with negative temperature coefficient was proposed to explain the mechanism of the experimental phenomena. Most importantly, the results demonstrate the potential for a realization of memristive systems based on macroscopic bulk materials. PMID:24255717

Modeling epidemics on adaptively evolving networks: A data-mining perspective.

PubMed

Kattis, Assimakis A; Holiday, Alexander; Stoica, Ana-Andreea; Kevrekidis, Ioannis G

2016-01-01

The exploration of epidemic dynamics on dynamically evolving ("adaptive") networks poses nontrivial challenges to the modeler, such as the determination of a small number of informative statistics of the detailed network state (that is, a few "good observables") that usefully summarize the overall (macroscopic, systems-level) behavior. Obtaining reduced, small size accurate models in terms of these few statistical observables--that is, trying to coarse-grain the full network epidemic model to a small but useful macroscopic one--is even more daunting. Here we describe a data-based approach to solving the first challenge: the detection of a few informative collective observables of the detailed epidemic dynamics. This is accomplished through Diffusion Maps (DMAPS), a recently developed data-mining technique. We illustrate the approach through simulations of a simple mathematical model of epidemics on a network: a model known to exhibit complex temporal dynamics. We discuss potential extensions of the approach, as well as possible shortcomings.

An investigation into electromagnetic force models: differences in global and local effects demonstrated by selected problems

NASA Astrophysics Data System (ADS)

Reich, Felix A.; Rickert, Wilhelm; Müller, Wolfgang H.

2018-03-01

This study investigates the implications of various electromagnetic force models in macroscopic situations. There is an ongoing academic discussion which model is "correct," i.e., generally applicable. Often, gedankenexperiments with light waves or photons are used in order to motivate certain models. In this work, three problems with bodies at the macroscopic scale are used for computing theoretical model-dependent predictions. Two aspects are considered, total forces between bodies and local deformations. By comparing with experimental data, insight is gained regarding the applicability of the models. First, the total force between two cylindrical magnets is computed. Then a spherical magnetostriction problem is considered to show different deformation predictions. As a third example focusing on local deformations, a droplet of silicone oil in castor oil is considered, placed in a homogeneous electric field. By using experimental data, some conclusions are drawn and further work is motivated.

Simulating the flow of entangled polymers.

PubMed

Masubuchi, Yuichi

2014-01-01

To optimize automation for polymer processing, attempts have been made to simulate the flow of entangled polymers. In industry, fluid dynamics simulations with phenomenological constitutive equations have been practically established. However, to account for molecular characteristics, a method to obtain the constitutive relationship from the molecular structure is required. Molecular dynamics simulations with atomic description are not practical for this purpose; accordingly, coarse-grained models with reduced degrees of freedom have been developed. Although the modeling of entanglement is still a challenge, mesoscopic models with a priori settings to reproduce entangled polymer dynamics, such as tube models, have achieved remarkable success. To use the mesoscopic models as staging posts between atomistic and fluid dynamics simulations, studies have been undertaken to establish links from the coarse-grained model to the atomistic and macroscopic simulations. Consequently, integrated simulations from materials chemistry to predict the macroscopic flow in polymer processing are forthcoming.

A 3D Monte Carlo model of radiation affecting cells, and its application to neuronal cells and GCR irradiation

NASA Astrophysics Data System (ADS)

Ponomarev, Artem; Sundaresan, Alamelu; Kim, Angela; Vazquez, Marcelo E.; Guida, Peter; Kim, Myung-Hee; Cucinotta, Francis A.

A 3D Monte Carlo model of radiation transport in matter is applied to study the effect of heavy ion radiation on human neuronal cells. Central nervous system effects, including cognitive impairment, are suspected from the heavy ion component of galactic cosmic radiation (GCR) during space missions. The model can count, for instance, the number of direct hits from ions, which will have the most affect on the cells. For comparison, the remote hits, which are received through δ-rays from the projectile traversing space outside the volume of the cell, are also simulated and their contribution is estimated. To simulate tissue effects from irradiation, cellular matrices of neuronal cells, which were derived from confocal microscopy, were simulated in our model. To produce this realistic model of the brain tissue, image segmentation was used to identify cells in the images of cells cultures. The segmented cells were inserted pixel by pixel into the modeled physical space, which represents a volume of interacting cells with periodic boundary conditions (PBCs). PBCs were used to extrapolate the model results to the macroscopic tissue structures. Specific spatial patterns for cell apoptosis are expected from GCR, as heavy ions produce concentrated damage along their trajectories. The apoptotic cell patterns were modeled based on the action cross sections for apoptosis, which were estimated from the available experimental data. The cell patterns were characterized with an autocorrelation function, which values are higher for non-random cell patterns, and the values of the autocorrelation function were compared for X rays and Fe ion irradiations. The autocorrelation function indicates the directionality effects present in apoptotic neuronal cells from GCR.

Material Characterization and Geometric Segmentation of a Composite Structure Using Microfocus X-Ray Computed Tomography Image-Based Finite Element Modeling

NASA Technical Reports Server (NTRS)

Abdul-Aziz, Ali; Roth, D. J.; Cotton, R.; Studor, George F.; Christiansen, Eric; Young, P. C.

2011-01-01

This study utilizes microfocus x-ray computed tomography (CT) slice sets to model and characterize the damage locations and sizes in thermal protection system materials that underwent impact testing. ScanIP/FE software is used to visualize and process the slice sets, followed by mesh generation on the segmented volumetric rendering. Then, the local stress fields around several of the damaged regions are calculated for realistic mission profiles that subject the sample to extreme temperature and other severe environmental conditions. The resulting stress fields are used to quantify damage severity and make an assessment as to whether damage that did not penetrate to the base material can still result in catastrophic failure of the structure. It is expected that this study will demonstrate that finite element modeling based on an accurate three-dimensional rendered model from a series of CT slices is an essential tool to quantify the internal macroscopic defects and damage of a complex system made out of thermal protection material. Results obtained showing details of segmented images; three-dimensional volume-rendered models, finite element meshes generated, and the resulting thermomechanical stress state due to impact loading for the material are presented and discussed. Further, this study is conducted to exhibit certain high-caliber capabilities that the nondestructive evaluation (NDE) group at NASA Glenn Research Center can offer to assist in assessing the structural durability of such highly specialized materials so improvements in their performance and capacities to handle harsh operating conditions can be made.

"Negative capacitance" in resistor-ferroelectric and ferroelectric-dielectric networks: Apparent or intrinsic?

NASA Astrophysics Data System (ADS)

Saha, Atanu K.; Datta, Suman; Gupta, Sumeet K.

2018-03-01

In this paper, we describe and analytically substantiate an alternate explanation for the negative capacitance (NC) effect in ferroelectrics (FE). We claim that the NC effect previously demonstrated in resistance-ferroelectric (R-FE) networks does not necessarily validate the existence of "S" shaped relation between polarization and voltage (according to Landau theory). In fact, the NC effect can be explained without invoking the "S"-shaped behavior of FE. We employ an analytical model for FE (Miller model) in which the steady state polarization strictly increases with the voltage across the FE and show that despite the inherent positive FE capacitance, reduction in FE voltage with the increase in its charge is possible in a R-FE network as well as in a ferroelectric-dielectric (FE-DE) stack. This can be attributed to a large increase in FE capacitance near the coercive voltage coupled with the polarization lag with respect to the electric field. Under certain conditions, these two factors yield transient NC effect. We analytically derive conditions for NC effect in R-FE and FE-DE networks. We couple our analysis with extensive simulations to explain the evolution of NC effect. We also compare the trends predicted by the aforementioned Miller model with Landau-Khalatnikov (L-K) model (static negative capacitance due to "S"-shape behaviour) and highlight the differences between the two approaches. First, with an increase in external resistance in the R-FE network, NC effect shows a non-monotonic behavior according to Miller model but increases according to L-K model. Second, with the increase in ramp-rate of applied voltage in the FE-DE stack, NC effect increases according to Miller model but decreases according to L-K model. These results unveil a possible way to experimentally validate the actual reason of NC effect in FE.

A rat hysteropexy model for evaluating adhesion formation and comparison of two different structured meshes.

PubMed

Gokmen-Karasu, Ayse Filiz; Aydin, Serdar; Sonmez, Fatma Cavide; Adanir, Ilknur; Ilhan, Gulsah; Ates, Seda

2017-11-01

Peritonization of mesh during sacrohysteropexy is generally advocated to prevent adhesions to the viscera; however, randomized clinical trials are lacking, and peritonization may not be completely possible in a laparoscopic hysteropexy procedure. Our main objective was to describe a basic experimental rat sacrohysteropexy model. We hypothesized that even when peritoneal closure was omitted, using composite mesh would result in less adhesions to the viscera. Twenty in-bred female virgin Wistar Hannover rats were used in this study. Standardized hysteropexy procedure and adhesion model is described step by step with two different mesh materials: polypropylene and a composite polyester. Mesh was anchored between the posterior cervix and anterior longitudinal ligament of the lumbar vertebrae. Macroscopic adhesion scores and histopathological tissue reaction was investigated. Macroscopically, the surface area involved in adhesions was similar between groups. However, adhesions in the polypropylene group were more dense, required sharp dissection for lysis, and yielded higher total macroscopic adhesion scores (p < 0.001). Histologically, a more pronounced host inflammatory response was encountered in the polyester group (p < 0.001). We describe a rat hysteropexy model and a previously established uterine adhesion model. Adhesion scores in the composite mesh group were lower, and bowel involvement was not seen. Our findings are promising, and further research investigating antiadhesive composite mesh use for hysterosacropexy would be appropriate, especially when peritoneal closure is omitted.

Atomic structure and domain wall pinning in samarium-cobalt-based permanent magnets.

PubMed

Duerrschnabel, M; Yi, M; Uestuener, K; Liesegang, M; Katter, M; Kleebe, H-J; Xu, B; Gutfleisch, O; Molina-Luna, L

2017-07-04

A higher saturation magnetization obtained by an increased iron content is essential for yielding larger energy products in rare-earth Sm 2 Co 17 -type pinning-controlled permanent magnets. These are of importance for high-temperature industrial applications due to their intrinsic corrosion resistance and temperature stability. Here we present model magnets with an increased iron content based on a unique nanostructure and -chemical modification route using Fe, Cu, and Zr as dopants. The iron content controls the formation of a diamond-shaped cellular structure that dominates the density and strength of the domain wall pinning sites and thus the coercivity. Using ultra-high-resolution experimental and theoretical methods, we revealed the atomic structure of the single phases present and established a direct correlation to the macroscopic magnetic properties. With further development, this knowledge can be applied to produce samarium cobalt permanent magnets with improved magnetic performance.Understanding the factors that determine the properties of permanent magnets, which play a central role in many industrial applications, can help in improving their performance. Here, the authors study how changes in the iron content affect the microstructure of samarium cobalt magnets.

Process Analytical Technology for Advanced Process Control in Biologics Manufacturing with the Aid of Macroscopic Kinetic Modeling.

PubMed

Kornecki, Martin; Strube, Jochen

2018-03-16

Productivity improvements of mammalian cell culture in the production of recombinant proteins have been made by optimizing cell lines, media, and process operation. This led to enhanced titers and process robustness without increasing the cost of the upstream processing (USP); however, a downstream bottleneck remains. In terms of process control improvement, the process analytical technology (PAT) initiative, initiated by the American Food and Drug Administration (FDA), aims to measure, analyze, monitor, and ultimately control all important attributes of a bioprocess. Especially, spectroscopic methods such as Raman or near-infrared spectroscopy enable one to meet these analytical requirements, preferably in-situ. In combination with chemometric techniques like partial least square (PLS) or principal component analysis (PCA), it is possible to generate soft sensors, which estimate process variables based on process and measurement models for the enhanced control of bioprocesses. Macroscopic kinetic models can be used to simulate cell metabolism. These models are able to enhance the process understanding by predicting the dynamic of cells during cultivation. In this article, in-situ turbidity (transmission, 880 nm) and ex-situ Raman spectroscopy (785 nm) measurements are combined with an offline macroscopic Monod kinetic model in order to predict substrate concentrations. Experimental data of Chinese hamster ovary cultivations in bioreactors show a sufficiently linear correlation (R² ≥ 0.97) between turbidity and total cell concentration. PLS regression of Raman spectra generates a prediction model, which was validated via offline viable cell concentration measurement (RMSE ≤ 13.82, R² ≥ 0.92). Based on these measurements, the macroscopic Monod model can be used to determine different process attributes, e.g., glucose concentration. In consequence, it is possible to approximately calculate (R² ≥ 0.96) glucose concentration based on online cell concentration measurements using turbidity or Raman spectroscopy. Future approaches will use these online substrate concentration measurements with turbidity and Raman measurements, in combination with the kinetic model, in order to control the bioprocess in terms of feeding strategies, by employing an open platform communication (OPC) network-either in fed-batch or perfusion mode, integrated into a continuous operation of upstream and downstream.

Process Analytical Technology for Advanced Process Control in Biologics Manufacturing with the Aid of Macroscopic Kinetic Modeling

PubMed Central

Kornecki, Martin; Strube, Jochen

2018-01-01

Productivity improvements of mammalian cell culture in the production of recombinant proteins have been made by optimizing cell lines, media, and process operation. This led to enhanced titers and process robustness without increasing the cost of the upstream processing (USP); however, a downstream bottleneck remains. In terms of process control improvement, the process analytical technology (PAT) initiative, initiated by the American Food and Drug Administration (FDA), aims to measure, analyze, monitor, and ultimately control all important attributes of a bioprocess. Especially, spectroscopic methods such as Raman or near-infrared spectroscopy enable one to meet these analytical requirements, preferably in-situ. In combination with chemometric techniques like partial least square (PLS) or principal component analysis (PCA), it is possible to generate soft sensors, which estimate process variables based on process and measurement models for the enhanced control of bioprocesses. Macroscopic kinetic models can be used to simulate cell metabolism. These models are able to enhance the process understanding by predicting the dynamic of cells during cultivation. In this article, in-situ turbidity (transmission, 880 nm) and ex-situ Raman spectroscopy (785 nm) measurements are combined with an offline macroscopic Monod kinetic model in order to predict substrate concentrations. Experimental data of Chinese hamster ovary cultivations in bioreactors show a sufficiently linear correlation (R2 ≥ 0.97) between turbidity and total cell concentration. PLS regression of Raman spectra generates a prediction model, which was validated via offline viable cell concentration measurement (RMSE ≤ 13.82, R2 ≥ 0.92). Based on these measurements, the macroscopic Monod model can be used to determine different process attributes, e.g., glucose concentration. In consequence, it is possible to approximately calculate (R2 ≥ 0.96) glucose concentration based on online cell concentration measurements using turbidity or Raman spectroscopy. Future approaches will use these online substrate concentration measurements with turbidity and Raman measurements, in combination with the kinetic model, in order to control the bioprocess in terms of feeding strategies, by employing an open platform communication (OPC) network—either in fed-batch or perfusion mode, integrated into a continuous operation of upstream and downstream. PMID:29547557

3D Computer Models of T- x- y Diagrams, Forming the Fe-Ni-Co-FeS-NiS-CoS Subsystem

NASA Astrophysics Data System (ADS)

Lutsyk, V. I.; Vorob'eva, V. P.

2017-12-01

3D computer models of Fe-Ni-Co, Fe-Ni-FeS-NiS, Fe-Co-FeS-CoS, Ni-Co-NiS-CoS T- x- y diagrams have been designed. The geometric structure (35 surfaces, two-phase surface of the reaction type change, 17 phase regions) of the Fe-Ni-FeS-NiS T- x- y diagram is investigated in detail. The liquidus hypersurfaces prediction of the Fe-Ni-Co-FeS-NiS-CoS subsystem is represented.

Decoherence-free emergence of macroscopic local realism for entangled photons in a cavity

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

Portolan, S.; Rossi, F.; Di Stefano, O.

2006-02-15

We investigate the influence of environmental noise on polarization entangled light generated by parametric emission in a cavity. By adopting a recent separability criterion, we show that (i) self-stimulation may suppress the detrimental influence of noise on entanglement, but (ii) once it becomes effective, a noise-equipped classical model of parametric emission provides the same results of quantum theory with respect to the separability criterion. More generally we also show that, in the macroscopic limit, it is not possible to observe violations of local realism with measurements of finite order n-particle correlations only. These results provide a prototypical case of themore » emergence of macroscopic local realism in the presence of strong entanglement even in the absence of decoherence.« less

Kinetic model to explain the effect of ocean warming and acidification on the Fe(II) oxidation rate in oligotrophic and eutrophic natural waters

NASA Astrophysics Data System (ADS)

González-Dávila, M.; Samperio-Ramos, G.; Santana-Casiano, J. M.; Gonzallez, A. G.; Pérez-Almeida, N.

2016-12-01

The speciation of inorganic Fe(II) as a function of the pH and temperature have been modeled in order to elucidate the inorganic Fe(II) redox behavior over a wide range of scenarios of acidification and global warming of the upper ocean, as well as, changes due to natural ambient fluctuations of pH and temperature. In addition, a kinetic modeling approach has been carried out to elucidate the fractional contribution of most kinetically active Fe(II) species to the overall oxidation rate to improve our future and present knowledge with respect to redox iron chemistry in the marine systems. The kinetic model considers the interactions of Fe(II) with the major ions in seawater, including phosphate and silicate and the competition with copper with the ROS. The model has been applied to the experimental results in order to describe the effect of temperature and pH in the speciation of Fe(II) and to compute the fractional contribution of each Fe(II)-specie to the overall oxidation rate. The oxidation rates (kapp) of nanomolar levels of Fe(II) have been studied in seawater enriched with nutrients (SWEN) in air saturated conditions. The nutrient effect (nitrate, phosphate and silicate), on the oxidation of Fe(II), has been evaluated as a function of pH (7.2-8.2), temperature (5-35 ºC) and salinity (10-37.09). The oxidation of Fe(II) was faster in the presence of nutrient with the change in the Fe(II) oxidation rates (Δlogkapp) more intensive at higher temperatures over the entire pH range studied. From the model it can be observed that the inorganic speciation of Fe(II) is controlled largely by pH, either in SW or in SWEN. A greater presence of Fe-nutrient reactive species (FeH3SiO4+ and FePO4-) in SWEN at higher temperatures explained the changes in the oxidation process. The individual oxidation rates by oxygen, for the Fe(II) most kinetically active species (Fe2+, FeOH+, Fe(OH)2, FeCO3(OH)-, FeCO3, Fe(CO3)22-, FeH3SiO3+, FePO4-), were fitted as a function of the temperature.

Application of a single root-scale model to improve macroscopic modeling of root water uptake: focus on osmotic stress

NASA Astrophysics Data System (ADS)

Jorda, Helena; Perelman, Adi; Lazarovitch, Naftali; Vanderborght, Jan

2017-04-01

Root water uptake is a fundamental process in the hydrological cycle and it largely regulates the water balance in the soil vadose zone. Macroscopic stress functions are currently used to estimate the effect of salinity on root water uptake. These functions commonly assume stress to be a function of bulk salinity and of the plant sensitivity to osmotic stress expressed as the salinity at which transpiration is reduced by half or so called tolerance value. However, they fail to integrate additional relevant factors such as atmospheric conditions or root architectural traits. We conducted a comprehensive simulation study on a single root using a 3-D physically-based model that resolves flow and transport to individual root segments and that couples flow in the soil and root system. The effect of salt concentrations on root water uptake was accounted for by including osmotic water potential gradients between the solution at the soil root interface and the root xylem sap in the hydraulic gradient between the soil and root. A large set of factors were studied, namely, potential transpiration rate and dynamics, root length density (RLD), irrigation water quality and irrigation frequency, and leaching fraction. Results were fitted to the macroscopic function developed by van Genuchten and Hoffman (1984) and the dependency of osmotic stress and the fitted macroscopic parameters on the studied factors was evaluated. Osmotic stress was found to be highly dependent on RLD. Low RLDs result in a larger stress to the plant due to high evaporative demand per root length unit. In addition, osmotic stress was positively correlated to potential transpiration rate, and sinusoidal potential transpiration lead to larger stress than when imposed as a constant boundary condition. Macroscopic parameters are usually computed as single values for each crop and used for the entire growing season. However, our study shows that both tolerance value and shape parameter p from the van Genuchten and Hoffman (1984) function were highly dependent on both potential transpiration and RLD. Plant salt tolerance was lower under high evaporative demand and lower RLD. In addition, the shape of the stress curve, which is defined by p, was found to be steeper under larger RLD and low transpiration rate. Time-variant macroscopic parameters based on knowledge of current potential transpiration rate per root unit length would be more convenient to accurately predict osmotic stress, and hence root water uptake, during a growing season. In a next step, simulations considering the whole root systems will be conducted to assess how macroscopic parameters are also related to root architectural characteristics. van Genuchten, M.T., Hoffman, G., 1984. Analysis of crop production. Soil Salin. Irrig. Springer Berl. 258-271.

Ion adsorption at the rutile-water interface: linking molecular and macroscopic properties.

PubMed

Zhang, Z; Fenter, P; Cheng, L; Sturchio, N C; Bedzyk, M J; Predota, M; Bandura, A; Kubicki, J D; Lvov, S N; Cummings, P T; Chialvo, A A; Ridley, M K; Bénézeth, P; Anovitz, L; Palmer, D A; Machesky, M L; Wesolowski, D J

2004-06-08

A comprehensive picture of the interface between aqueous solutions and the (110) surface of rutile (alpha-TiO2) is being developed by combining molecular-scale and macroscopic approaches, including experimental measurements, quantum calculations, molecular simulations, and Gouy-Chapman-Stern models. In situ X-ray reflectivity and X-ray standing-wave measurements are used to define the atomic arrangement of adsorbed ions, the coordination of interfacial water molecules, and substrate surface termination and structure. Ab initio calculations and molecular dynamics simulations, validated through direct comparison with the X-ray results, are used to predict ion distributions not measured experimentally. Potentiometric titration and ion adsorption results for rutile powders having predominant (110) surface expression provide macroscopic constraints of electrical double layer (EDL) properties (e.g., proton release) which are evaluated by comparison with a three-layer EDL model including surface oxygen proton affinities calculated using ab initio bond lengths and partial charges. These results allow a direct correlation of the three-dimensional, crystallographically controlled arrangements of various species (H2O, Na+, Rb+, Ca2+, Sr2+, Zn2+, Y3+, Nd3+) with macroscopic observables (H+ release, metal uptake, zeta potential) and thermodynamic/electrostatic constraints. All cations are found to be adsorbed as "inner sphere" species bonded directly to surface oxygen atoms, while the specific binding geometries and reaction stoichiometries are dependent on ionic radius. Ternary surface complexes of sorbed cations with electrolyte anions are not observed. Finally, surface oxygen proton affinities computed using the MUSIC model are improved by incorporation of ab initio bond lengths and hydrogen bonding information derived from MD simulations. This multitechnique and multiscale approach demonstrates the compatibility of bond-valence models of surface oxygen proton affinities and Stern-based models of the EDL structure, with the actual molecular interfacial distributions observed experimentally, revealing new insight into EDL properties including specific binding sites and hydration states of sorbed ions, interfacial solvent properties (structure, diffusivity, dielectric constant), surface protonation and hydrolysis, and the effect of solution ionic strength.

Composition formulas of Fe-based transition metals-metalloid bulk metallic glasses derived from dual-cluster model of binary eutectics.

PubMed

Naz, Gul Jabeen; Dong, Dandan; Geng, Yaoxiang; Wang, Yingmin; Dong, Chuang

2017-08-22

It is known that bulk metallic glasses follow simple composition formulas [cluster](glue atom) 1 or 3 with 24 valence electrons within the framework of the cluster-plus-glue-atom model. Though the relevant nearest-neighbor cluster can be readily identified from a devitrification phase, the glue atoms remains poorly defined. The present work is devoted to understanding the composition rule of Fe-(B,P,C) based multi-component bulk metallic glasses, by introducing a cluster-based eutectic liquid model. This model regards a eutectic liquid to be composed of two stable liquids formulated respectively by cluster formulas for ideal metallic glasses from the two eutectic phases. The dual cluster formulas are first established for binary Fe-(B,C,P) eutectics: [Fe-Fe 14 ]B 2 Fe + [B-B 2 Fe 8 ]Fe ≈ Fe 83.3 B 16.7 for eutectic Fe 83 B 17 , [P-Fe 14 ]P + [P-Fe 9 ]P 2 Fe≈Fe 82.8 P 17.2 for Fe 83 P 17 , and [C-Fe 6 ]Fe 3  + [C-Fe 9 ]C 2 Fe ≈ Fe 82.6 C 17.4 for Fe 82.7 C 17.3 . The second formulas in these dual-cluster formulas, being respectively relevant to devitrification phases Fe 2 B, Fe 3 P, and Fe 3 C, well explain the compositions of existing Fe-based transition metals-metalloid bulk metallic glasses. These formulas also satisfy the 24-electron rule. The proposition of the composition formulas for good glass formers, directly from known eutectic points, constitutes a new route towards understanding and eventual designing metallic glasses of high glass forming abilities.

Cellular automata model for use with real freeway data

DOT National Transportation Integrated Search

2002-01-01

The exponential rate of increase in freeway traffic is expanding the need for accurate and : realistic methods to model and predict traffic flow. Traffic modeling and simulation facilitates an : examination of both microscopic and macroscopic views o...

A Structural Molar Volume Model for Oxide Melts Part III: Fe Oxide-Containing Melts

NASA Astrophysics Data System (ADS)

Thibodeau, Eric; Gheribi, Aimen E.; Jung, In-Ho

2016-04-01

As part III of this series, the model is extended to iron oxide-containing melts. All available experimental data in the FeO-Fe2O3-Na2O-K2O-MgO-CaO-MnO-Al2O3-SiO2 system were critically evaluated based on the experimental condition. The variations of FeO and Fe2O3 in the melts were taken into account by using FactSage to calculate the Fe2+/Fe3+ distribution. The molar volume model with unary and binary model parameters can be used to predict the molar volume of the molten oxide of the Li2O-Na2O-K2O-MgO-CaO-MnO-PbO-FeO-Fe2O3-Al2O3-SiO2 system in the entire range of compositions, temperatures, and oxygen partial pressures from Fe saturation to 1 atm pressure.

Atmospheric Dissolved Iron Depostiion to the Global Oceans: Effects of Oxalate-Promoted Fe Dissolution, Photochemical Redox Cycling, and Dust Mineralogy

NASA Technical Reports Server (NTRS)

Johnson, M. S.; Meskhidze, N.

2013-01-01

Mineral dust deposition is suggested to be a significant atmospheric supply pathway of bioavailable iron (Fe) to Fe-depleted surface oceans. In this study, mineral dust and dissolved Fe (Fed) deposition rates are predicted for March 2009 to February 2010 using the 3-D chemical transport model GEOS-Chem implemented with a comprehensive dust-Fe dissolution scheme. The model simulates Fed production during the atmospheric transport of mineral dust taking into account inorganic and organic (oxalate)-promoted Fe dissolution processes, photochemical redox cycling between ferric (Fe(III)) and ferrous (Fe(II)) forms of Fe, dissolution of three different Fe-containing minerals (hematite, goethite, and aluminosilicates), and detailed mineralogy of windblown dust from the major desert regions. Our calculations suggest that during the yearlong simulation is approximately 0.26 Tg (1 Tg = 1012 g) of Fed was deposited to global oceanic regions. Compared to simulations only taking into account proton-promoted Fe dissolution, the addition of oxalate to the dust-Fe mobilization scheme increased total annual model-predicted Fed deposition to global oceanic regions by approximately 75%. The implementation of Fe(II)/Fe(III) photochemical redox cycling in the model allows for the distinction between different oxidation states of deposited Fed. Our calculations suggest that during the daytime, large fractions of Fed deposited to the global oceans is likely to be in Fe(II) form, while nocturnal fluxes of Fed are largely in Fe(III) form. Model simulations also show that atmospheric fluxes of Fed can be strongly influenced by the mineralogy of Fe-containing compounds. This study shows that Fed deposition to the oceans is controlled by total dust-Fe mass concentrations, mineralogy, the surface area of dust particles, atmospheric chemical composition, cloud processing, and meteorological parameters and exhibits complex and spatiotemporally variable patterns. Our study suggests that the explicit model representation of individual processes leading to Fed production within mineral dust are needed to improve the understanding of the atmospheric Fe cycle, and quantify the effect of dust-Fe on ocean biological productivity, carbon cycle, and climate.

Long-range transverse spin Seebeck effect in permalloy stripes using Sagnac interferometer microscopy

NASA Astrophysics Data System (ADS)

Liu, Haoliang; McLaughlin, Ryan; Sun, Dali; Valy Vardeny, Z.

2018-04-01

Coupling of spins and phonons in ferromagnets (FM) may persist up to mm length scale, thus generating macroscopic spatially distributed spin accumulation along the direction of an applied thermal gradient to an FM slab. This typical feature of transverse spin Seebeck effect (TSSE) has been demonstrated so far using electrical detection methods in FM films, in particular in a patterned structure, in which FM stripes grown onto a substrate perpendicular to the applied thermal gradient direction are electrically and magnetically isolated. Here we report optically detected TSSE response in isolated FM stripes based on permalloy deposited on SiN substrate, upon the application of a thermal gradient. For these measurements we used the magneto-optic Kerr effect measured by an ultrasensitive Sagnac interferometer microscope that is immune to thermo-electrics artefacts. We found that the optical TSSE coefficient in the NiFe stripes geometry is about one order of magnitude smaller than that in the continuous NiFe film, which is due to the limited phonons path in the FM stripes along the thermal gradient direction. Our results further confirm the existence of TSSE response in conducting FM compounds.

Synthesis and characterization of silver nanoparticle composite with poly(p-Br-phenylsilane).

PubMed

Kim, Myoung-Hee; Lee, Jun; Mo, Soo-Yong; Woo, Hee-Gweon; Yang, Kap Seung; Kim, Bo-Hye; Lee, Byeong-Gweon; Sohn, Honglae

2012-05-01

The one-pot synthesis and characterization of silver nanoparticle-poly(p-Br-phenylsilane) composites have been carried out. The conversion of silver(+1) salt to stable silver(0) nanoparticles is promoted by poly(p-Br-phenylsilane), Br-PPS possessing both possible reactive Si-H bonds in the polymer backbone and C-Br bonds in the substituents. The composites were characterized using XRD, TEM, FE-SEM, and solid-state UV-vis analytical techniques. TEM and FE-SEM data show the formation of the composites where large number of silver nanoparticles (less than 30 nm of size) are well dispersed throughout the Br-PPS matrix. XRD patterns are consistent with that for fcc-typed silver. The elemental analysis for Br atom and the polymer solubility confirm that the cleavage of C-Br bond and the Si-Br dative bonding were not occurred appreciably at ambient temperature. Nonetheless, TGA data suggest that some sort of cross-linking was occurred at high temperature. The size and processability of such nanoparticles depend on the ratio of metal to Br-PPS. In the absence of Br-PPS, most of the silver particles undergo macroscopic aggregation, which indicates that the polysilane is necessary for stabilizing the silver nanoparticles.

Enhancement of Local Photovoltaic Current at Ferroelectric Domain Walls in BiFeO3

PubMed Central

Yang, Ming-Min; Bhatnagar, Akash; Luo, Zheng-Dong; Alexe, Marin

2017-01-01

Domain walls, which are intrinsically two dimensional nano-objects exhibiting nontrivial electronic and magnetic behaviours, have been proven to play a crucial role in photovoltaic properties of ferroelectrics. Despite this recognition, the electronic properties of domain walls under illumination until now have been accessible only to macroscopic studies and their effects upon the conduction of photovoltaic current still remain elusive. The lack of understanding hinders the developing of nanoscale devices based on ferroelectric domain walls. Here, we directly characterize the local photovoltaic and photoconductive properties of 71° domain walls on BiFeO3 thin films with a nanoscale resolution. Local photovoltaic current, proven to be driven by the bulk photovoltaic effect, has been probed over the whole illuminated surface by using a specially designed photoelectric atomic force microscopy and found to be significantly enhanced at domain walls. Additionally, spatially resolved photoconductive current distribution reveals a higher density of excited carriers at domain walls in comparison with domains. Our measurements demonstrate that domain wall enhanced photovoltaic current originates from its high conduction rather than the internal electric field. This photoconduction facilitated local photovoltaic current is likely to be a universal property of topological defects in ferroelectric semiconductors. PMID:28216672

Enhancement of Local Photovoltaic Current at Ferroelectric Domain Walls in BiFeO3.

PubMed

Yang, Ming-Min; Bhatnagar, Akash; Luo, Zheng-Dong; Alexe, Marin

2017-02-20

Domain walls, which are intrinsically two dimensional nano-objects exhibiting nontrivial electronic and magnetic behaviours, have been proven to play a crucial role in photovoltaic properties of ferroelectrics. Despite this recognition, the electronic properties of domain walls under illumination until now have been accessible only to macroscopic studies and their effects upon the conduction of photovoltaic current still remain elusive. The lack of understanding hinders the developing of nanoscale devices based on ferroelectric domain walls. Here, we directly characterize the local photovoltaic and photoconductive properties of 71° domain walls on BiFeO 3 thin films with a nanoscale resolution. Local photovoltaic current, proven to be driven by the bulk photovoltaic effect, has been probed over the whole illuminated surface by using a specially designed photoelectric atomic force microscopy and found to be significantly enhanced at domain walls. Additionally, spatially resolved photoconductive current distribution reveals a higher density of excited carriers at domain walls in comparison with domains. Our measurements demonstrate that domain wall enhanced photovoltaic current originates from its high conduction rather than the internal electric field. This photoconduction facilitated local photovoltaic current is likely to be a universal property of topological defects in ferroelectric semiconductors.

Influence of coexisting phases on the surface dilatational viscosity of Langmuir monolayers.

PubMed

Lopez, Juan M; Vogel, Michael J; Hirsa, Amir H

2004-11-01

Monolayer hydrodynamics are usually described in terms of a Newtonian constitutive relationship. However, this macroscopic view fails to account for small-scale coexisting phase domains, which are generally present in the monolayer and appear to have profound macroscopic effects. Here, we provide direct evidence of these effects, consisting of Brewster angle microscopy images of the monolayer, space- and time-resolved interfacial velocity measurements, and comparisons with predictions based on the Navier-Stokes equations together with the classic model for a Newtonian interface.

Consentaneous Agent-Based and Stochastic Model of the Financial Markets

PubMed Central

Gontis, Vygintas; Kononovicius, Aleksejus

2014-01-01

We are looking for the agent-based treatment of the financial markets considering necessity to build bridges between microscopic, agent based, and macroscopic, phenomenological modeling. The acknowledgment that agent-based modeling framework, which may provide qualitative and quantitative understanding of the financial markets, is very ambiguous emphasizes the exceptional value of well defined analytically tractable agent systems. Herding as one of the behavior peculiarities considered in the behavioral finance is the main property of the agent interactions we deal with in this contribution. Looking for the consentaneous agent-based and macroscopic approach we combine two origins of the noise: exogenous one, related to the information flow, and endogenous one, arising form the complex stochastic dynamics of agents. As a result we propose a three state agent-based herding model of the financial markets. From this agent-based model we derive a set of stochastic differential equations, which describes underlying macroscopic dynamics of agent population and log price in the financial markets. The obtained solution is then subjected to the exogenous noise, which shapes instantaneous return fluctuations. We test both Gaussian and q-Gaussian noise as a source of the short term fluctuations. The resulting model of the return in the financial markets with the same set of parameters reproduces empirical probability and spectral densities of absolute return observed in New York, Warsaw and NASDAQ OMX Vilnius Stock Exchanges. Our result confirms the prevalent idea in behavioral finance that herding interactions may be dominant over agent rationality and contribute towards bubble formation. PMID:25029364

MESOSCOPIC MODELING OF STOCHASTIC REACTION-DIFFUSION KINETICS IN THE SUBDIFFUSIVE REGIME

PubMed Central

BLANC, EMILIE; ENGBLOM, STEFAN; HELLANDER, ANDREAS; LÖTSTEDT, PER

2017-01-01

Subdiffusion has been proposed as an explanation of various kinetic phenomena inside living cells. In order to fascilitate large-scale computational studies of subdiffusive chemical processes, we extend a recently suggested mesoscopic model of subdiffusion into an accurate and consistent reaction-subdiffusion computational framework. Two different possible models of chemical reaction are revealed and some basic dynamic properties are derived. In certain cases those mesoscopic models have a direct interpretation at the macroscopic level as fractional partial differential equations in a bounded time interval. Through analysis and numerical experiments we estimate the macroscopic effects of reactions under subdiffusive mixing. The models display properties observed also in experiments: for a short time interval the behavior of the diffusion and the reaction is ordinary, in an intermediate interval the behavior is anomalous, and at long times the behavior is ordinary again. PMID:29046618

Finite volume solution for two-phase flow in a straight capillary

NASA Astrophysics Data System (ADS)

Yelkhovsky, Alexander; Pinczewski, W. Val

2018-04-01

The problem of two-phase flow in straight capillaries of polygonal cross section displays many of the dynamic characteristics of rapid interfacial motions associated with pore-scale displacements in porous media. Fluid inertia is known to be important in these displacements but is usually ignored in network models commonly used to predict macroscopic flow properties. This study presents a numerical model for two-phase flow which describes the spatial and temporal evolution of the interface between the fluids. The model is based on an averaged Navier-Stokes equation and is shown to be successful in predicting the complex dynamics of both capillary rise in round capillaries and imbibition along the corners of polygonal capillaries. The model can form the basis for more realistic network models which capture the effect of capillary, viscous, and inertial forces on pore-scale interfacial dynamics and consequent macroscopic flow properties.

Can pair-instability supernova models match the observations of superluminous supernovae?

NASA Astrophysics Data System (ADS)

Kozyreva, Alexandra; Blinnikov, S.

2015-12-01

An increasing number of so-called superluminous supernovae (SLSNe) are discovered. It is believed that at least some of them with slowly fading light curves originate in stellar explosions induced by the pair instability mechanism. Recent stellar evolution models naturally predict pair instability supernovae (PISNe) from very massive stars at wide range of metallicities (up to Z = 0.006, Yusof et al.). In the scope of this study, we analyse whether PISN models can match the observational properties of SLSNe with various light-curve shapes. Specifically, we explore the influence of different degrees of macroscopic chemical mixing in PISN explosive products on the resulting observational properties. We artificially apply mixing to the 250 M⊙ PISN evolutionary model from Kozyreva et al. and explore its supernova evolution with the one-dimensional radiation hydrodynamics code STELLA. The greatest success in matching SLSN observations is achieved in the case of an extreme macroscopic mixing, where all radioactive material is ejected into the hydrogen-helium outer layer. Such an extreme macroscopic redistribution of chemicals produces events with faster light curves with high photospheric temperatures and high photospheric velocities. These properties fit a wider range of SLSNe than non-mixed PISN model. Our mixed models match the light curves, colour temperature, and photospheric velocity evolution of two well-observed SLSNe PTF12dam and LSQ12dlf. However, these models' extreme chemical redistribution may be hard to realize in massive PISNe. Therefore, alternative models such as the magnetar mechanism or wind-interaction may still to be favourable to interpret rapidly rising SLSNe.

Reduction of Fe(III) colloids by Shewanella putrefaciens: A kinetic model

NASA Astrophysics Data System (ADS)

Bonneville, Steeve; Behrends, Thilo; van Cappellen, Philippe; Hyacinthe, Christelle; Röling, Wilfred F. M.

2006-12-01

A kinetic model for the microbial reduction of Fe(III) oxyhydroxide colloids in the presence of excess electron donor is presented. The model assumes a two-step mechanism: (1) attachment of Fe(III) colloids to the cell surface and (2) reduction of Fe(III) centers at the surface of attached colloids. The validity of the model is tested using Shewanella putrefaciens and nanohematite as model dissimilatory iron reducing bacteria and Fe(III) colloidal particles, respectively. Attachment of nanohematite to the bacteria is formally described by a Langmuir isotherm. Initial iron reduction rates are shown to correlate linearly with the relative coverage of the cell surface by nanohematite particles, hence supporting a direct electron transfer from membrane-bound reductases to mineral particles attached to the cells. Using internally consistent parameter values for the maximum attachment capacity of Fe(III) colloids to the cells, Mmax, the attachment constant, KP, and the first-order Fe(III) reduction rate constant, k, the model reproduces the initial reduction rates of a variety of fine-grained Fe(III) oxyhydroxides by S. putrefaciens. The model explains the observed dependency of the apparent Fe(III) half-saturation constant, Km∗, on the solid to cell ratio, and it predicts that initial iron reduction rates exhibit saturation with respect to both the cell density and the abundance of the Fe(III) oxyhydroxide substrate.

Nonlinear photomechanics of nematic networks: upscaling microscopic behaviour to macroscopic deformation

NASA Astrophysics Data System (ADS)

Chung, Hayoung; Choi, Joonmyung; Yun, Jung-Hoon; Cho, Maenghyo

2016-02-01

A liquid crystal network whose chromophores are functionalized by photochromic dye exhibits light-induced mechanical behaviour. As a result, the micro-scaled thermotropic traits of the network and the macroscopic phase behaviour are both influenced as light alternates the shape of the dyes. In this paper, we present an analysis of this photomechanical behaviour based on the proposed multiscale framework, which incorporates the molecular details of microstate evolution into a continuum-based understanding. The effects of trans-to-cis photoisomerization driven by actinic light irradiation are first examined using molecular dynamics simulations, and are compared against the predictions of the classical dilution model; this reveals certain characteristics of mesogenic interaction upon isomerization, followed by changes in the polymeric structure. We then upscale the thermotropic phase-related information with the aid of a nonlinear finite element analysis; macroscopic deflection with respect to the wide ranges of temperature and actinic light intensity are thereby examined, which reveals that the classical model underestimates the true deformation. This work therefore provides measures for analysing photomechanics in general by bridging the gap between the micro- and macro-scales.

Modeling Two-Stage Bunch Compression With Wakefields: Macroscopic Properties And Microbunching Instability

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

Bosch, R.A.; Kleman, K.J.; /Wisconsin U., SRC

2011-09-08

In a two-stage compression and acceleration system, where each stage compresses a chirped bunch in a magnetic chicane, wakefields affect high-current bunches. The longitudinal wakes affect the macroscopic energy and current profiles of the compressed bunch and cause microbunching at short wavelengths. For macroscopic wavelengths, impedance formulas and tracking simulations show that the wakefields can be dominated by the resistive impedance of coherent edge radiation. For this case, we calculate the minimum initial bunch length that can be compressed without producing an upright tail in phase space and associated current spike. Formulas are also obtained for the jitter in themore » bunch arrival time downstream of the compressors that results from the bunch-to-bunch variation of current, energy, and chirp. Microbunching may occur at short wavelengths where the longitudinal space-charge wakes dominate or at longer wavelengths dominated by edge radiation. We model this range of wavelengths with frequency-dependent impedance before and after each stage of compression. The growth of current and energy modulations is described by analytic gain formulas that agree with simulations.« less

Mechanisms of Mn(II) catalytic oxidation on ferrihydrite surfaces and the formation of manganese (oxyhydr)oxides

NASA Astrophysics Data System (ADS)

Lan, Shuai; Wang, Xiaoming; Xiang, Quanjun; Yin, Hui; Tan, Wenfeng; Qiu, Guohong; Liu, Fan; Zhang, Jing; Feng, Xionghan

2017-08-01

Oxidation of Mn(II) is an important process that controls the mobility and bioavailability of Mn, as well as the formation of Mn (oxyhydr)oxides in natural systems. It was found that the surfaces of minerals, such as iron (oxyhydr)oxides, can accelerate Mn(II) oxidation to a certain degree, but the underlying mechanism has not been clearly understood. This study explores the reaction pathways and mechanisms of Mn(II) oxidation on ferrihydrite surfaces at neutral pH, commonly found in natural environments, by comparisons with montmorillonite, amorphous Al(OH)3, goethite, and magnetite using macroscopic experiments and spectroscopic analyses. Results show that when Mn(II) concentrations are below 4 mM, macroscopic Mn(II) adsorption on the three iron (oxyhydr)oxide surfaces conforms well to the Langmuir equation, with ferrihydrite showing the highest adsorption capacity. With Mn(II) concentrations ranging within 6-24 mM, the adsorbed Mn(II) is mainly oxidized into manganite (γ-MnOOH) and/or feitknechtite (β-MnOOH) by dissolved O2, and Mn(II) removal on a unit mass basis in the presence of magnetite is the highest compared with ferrihydrite and goethite. Ferrihydrite, a semiconductor material, shows stronger catalytic ability for Mn(II) oxidation on the same surface area than insulator minerals (i.e., montmorillonite and amorphous Al(OH)3). Additionally, the products of Mn(II) oxidation in the presence of semiconductor iron (oxyhydr)oxides (i.e., ferrihydrite, goethite, or magnetite) at the same Fe/Mn molar ratio include both manganite and a small amount of Mn(IV) minerals, and the Mn average oxidation states (Mn AOSs) of these products follow the order: magnetite > goethite > ferrihydrite. Magnetite and goethite, with relatively smaller SSAs and lower band gap energies, exhibit greater catalysis for Mn(II) oxidation than ferrihydrite at the same Fe/Mn ratio, which goes against the conventional interfacial effect and is related to the electrochemical properties. Thus, the Mn(II) catalytic oxidation by O2 on ferrihydrite surfaces should include an electrochemical pathway, i.e., electron transfer (ET) in the Mn(II)-Conduction Band (CB)Ferrihydrite-O2 complexes, in addition to the conventional two interfacial catalytic pathways, i.e., ET in the Mn(II)-Fe(II, III)-O2 complexes and direct ET in the Mn(II)-O2 complexes. These results reveal new implications for understanding the processes and mechanisms of Mn(II) oxidation on iron (oxyhydr)oxide surfaces and the abiotic formation of Mn (oxyhydr)oxides in surface environments.

The anthropogenic influence on Iron deposition over the oceans: a 3-D global modeling

NASA Astrophysics Data System (ADS)

Myriokefalitakis, Stelios; Mihalopoulos, Nikos; Baker, Alex; Kanakidou, Maria

2014-05-01

Iron (Fe) deposition over oceans is directly linked to the marine biological productivity and consequently to atmospheric CO2 concentrations. Experimental and modeling results support that both inorganic (sulphate, ammonium and nitrate) and organic (e.g. oxalate) ligands can increase the Fe mobilization. Mineral dust deposition is considered as the most important supply of bioavailable Fe in the oceans. Although, due to the low soil soluble iron fractions, atmospheric processes which are also related to anthropogenic emissions, can convert iron to more soluble forms in the atmosphere. Recent studies also support that anthropogenic emissions of Fe from combustion sources also significantly contribute to the dissolved Fe atmospheric pool. The evaluation of the impact of humans on atmospheric soluble or bioavailable Fe deposition remains challenging, since Fe mobilization due to changes in anthropogenic emissions is largely uncertain. In the present study, the global atmospheric Fe cycle is parameterized in the 3-D chemical transport global model TM4-ECPL and the model is used to calculate the Fe deposition over the oceans. The model considers explicitly organic, sulfur and nitrogen gas-phase chemistry, aqueous-phase organic chemistry, including oxalate and all major aerosol constituents. TM4-ECPL simulates the organic and inorganic ligand-promoted mineral Fe dissolution and also aqueous-phase photochemical reactions between different forms of Fe (III/II). Primary emissions of Fe associated with dust and soluble Fe from combustion processes as well as atmospheric processing of the emitted Fe is taken into account in the model Sensitivity simulations are performed to study the impact of anthropogenic emissions on Fe deposition. For this preindustrial, present and future emission scenarios are used in the model in order to examine the response of chemical composition of iron-containing aerosols to environmental changes. The release of soluble iron associated with mineral dust and with the emissions of combustion aerosols is investigated. Model results are compared with available observations to evaluate their robustness. This work is supported by the ESF-NSRF ARISTEIA grant PANOPLY (Pollution Alters Natural Aerosol Composition: implications for Ocean Productivity, cLimate and air qualitY).

Thermodynamic and kinetic modeling of grain boundary equilibrium segregation of P in α-Fe

DOE PAGES

Yang, Y.; Chen, S. -L.

2017-04-18

Phosphorus is a primary contributor to interface fracture and embrittlement in steels because of its strong segregation tendency at grain boundaries (GBs). The lack of consistency in literature data imposes great difficulties in performing segregation modeling that is compatible with both the Langmuir-Mclean segregation theory and the thermodynamic description of the Bcc(Fe,P) phase. Our work carefully evaluated experimental data for phosphorus segregation at GBs in -Fe and provided a new formula for converting the auger electron spectroscopy (AES) peak height ratio to GBs. Furthermore, based on newly assessed literature data, this work proposes that the major driving force for phosphorusmore » segregation is the formation of Fe 3P-type clusters at GBs, which is supported not only by the almost equivalent Gibbs energy of _Fe using the Bcc(Fe,P) substitutional model and the Bcc(Fe,Fe 3P, P) associate model, but also by the good agreement between thermodynamic/kinetic modeling results and experimental data.« less

Internal friction and dislocation collective pinning in disordered quenched solid solutions

NASA Astrophysics Data System (ADS)

D'Anna, G.; Benoit, W.; Vinokur, V. M.

1997-12-01

We introduce the collective pinning of dislocations in disordered quenched solid solutions and calculate the macroscopic mechanical response to a small dc or ac applied stress. This work is a generalization of the Granato-Lücke string model, able to describe self-consistently short and long range dislocation motion. Under dc applied stress the long distance dislocation creep has at the microscopic level avalanche features, which result in a macroscopic nonlinear "glassy" velocity-stress characteristic. Under ac conditions the model predicts, in addition to the anelastic internal friction relaxation in the high frequency regime, a linear internal friction background which remains amplitude-independent down to a crossover frequency to a strongly nonlinear internal friction regime.

Improve FREQ macroscopic freeway analysis model

DOT National Transportation Integrated Search

2008-07-01

The primary objectives of this project have been to provide technical assistance on district freeway analysis projects, enhance the FREQ model based on guidance and suggestions from Caltrans staff members, and offer three freeway analysis workshops f...

Comparison of Ab initio Low-Energy Models for LaFePO, LaFeAsO, BaFe2As2, LiFeAs, FeSe, and FeTe

NASA Astrophysics Data System (ADS)

Nakamura, Kazuma; Miyake, Takashi; Arita, Ryotaro; Imada, Masatoshi

2010-03-01

We present effective low-energy models for LaFePO and LaFeAsO (1111 family), BaFe2As2 (122), LiFeAs (111), and FeSe and FeTe (11) [1], based on ab initio downfolding scheme, a constrained random-phase-approximation method combined with maximally localized Wannier functions. Comparison among the effective models, derived for 5 Fe-3d bands, provides a basis for interpreting physics/chemistry; material dependences of electron correlations, a multiband character entangled by the 3d orbitals, and the geometrical frustration depending on hybridizations between iron and pnictogen/chalcogen orbitals. We found that LaFePO in the 1111 family resides in the weak correlation regime, while LaFeAsO and 111/122 compounds are the intermediate region and FeSe and FeTe in the 11 family are located in the strong correlation regime. A principal parameter relevant to the physics is clarified to be the pnictogen/chalcogen height from the iron layer. Implications in low-energy properties including magnetism and superconductivity are discussed. [1] T. Miyake, K. Nakamura, R. Arita, and M. Imada, arXiv:0911.3705.

Stability and diversity in collective adaptation

NASA Astrophysics Data System (ADS)

Sato, Yuzuru; Akiyama, Eizo; Crutchfield, James P.

2005-10-01

We derive a class of macroscopic differential equations that describe collective adaptation, starting from a discrete-time stochastic microscopic model. The behavior of each agent is a dynamic balance between adaptation that locally achieves the best action and memory loss that leads to randomized behavior. We show that, although individual agents interact with their environment and other agents in a purely self-interested way, macroscopic behavior can be interpreted as game dynamics. Application to several familiar, explicit game interactions shows that the adaptation dynamics exhibits a diversity of collective behaviors. The simplicity of the assumptions underlying the macroscopic equations suggests that these behaviors should be expected broadly in collective adaptation. We also analyze the adaptation dynamics from an information-theoretic viewpoint and discuss self-organization induced by the dynamics of uncertainty, giving a novel view of collective adaptation.

Displacement of squeezed propagating microwave states

NASA Astrophysics Data System (ADS)

Fedorov, Kirill G.; Zhong, Ling; Pogorzalek, Stefan; Eder, Peter; Fischer, Michael; Goetz, Jan; Wulschner, Friedrich; Xie, Edwar; Menzel, Edwin; Deppe, Frank; Marx, Achim; Gross, Rudolf

Displacement of propagating squeezed states is a fundamental operation for quantum communications. It can be applied to fundamental studies of macroscopic quantum coherence and has an important role in quantum teleportation protocols with propagating microwaves. We generate propagating squeezed states using a Josephson parametric amplifier and implement displacement using a cryogenic directional coupler. We study single- and two-mode displacement regimes. For the single-mode displacement we find that the squeezing level of the displaced squeezed state does not depend on the displacement amplitude. Also, we observe that quantum entanglement between two spatially separated channels stays constant across 4 orders of displacement power. We acknowledge support by the German Research Foundation through SFB 631 and FE 1564/1-1, the EU project PROMISCE, and Elite Network of Bavaria through the program ExQM.

[Effect of muscle biofidelity on thoracic impact biomechanical response of a six-year-old child using finite element method].

PubMed

Cui, Shihai; Shan, Leilei; Li, Haiyan; Lu, Wenle; He, Lijuan; Ruan, Shijie

2017-02-01

Finite element(FE) model of thorax with high biofidelity is one of the most important methods to investigate thoracic injury mechanism because of the absence of pediatric cadaver experiments. Based on the validated thorax finite element model, the FE models with equivalent muscles and real geometric muscles were developed respectively, and the effect of muscle biofidelity on thoracic injury was analyzed with reconstructing pediatric cadaver thorax impact experiments. The simulation results showed that the thoracic impact force, the maximum displacement and the maximum von-Mises stress of FE models with equivalent muscles were slightly greater than those from FE models with real geometric muscles, and the maximum principal strains of heart and lung were a little lower. And the correlation coefficient between cadaver corridor and FE model with real muscles was also greater than that between cadaver corridor and FE model with equivalent muscles. As a conclusion, the FE models with real geometric muscles can accurately reflect the biomechanical response of thorax during the impact.

On the energetics of tensile and shear void coalescences

NASA Astrophysics Data System (ADS)

Wong, W. H.; Guo, T. F.

2015-09-01

This paper investigates the mechanisms of tensile and shear void coalescences in ductile materials from energetics perspective. By examining and comparing the elastic and plastic energies of a voided cell throughout its deformation history, the onset of and final coalescence can be distinctly established. This energy-based approach offers a single unified method and criterion for determining the occurrences of both mechanisms. This paper also reports a novel micromechanics model that considers general stress states described by three macroscopic normal stresses and one macroscopic shear stress. Detailed formulation of the model is presented that includes the homogenization-based derivation and implementation of a 4×4 orthogonal transformation matrix, which relates the macroscopic deformation rate of the cell to displacement rates of non-physical degrees-of-freedom (DOFs), and the polar decomposition of the macroscopic deformation gradient tensor which admits the explicit determination of the logarithmic strain measures and rotation angle. In terms of stress ratios, ρ1 (=Σ11 /Σ22) ,ρ2 (=Σ12 /Σ22) ,ρ3 (=Σ33 /Σ22), it is analytically shown that multiple macroscopic stress states {ρ1 ,ρ2 ,ρ3 } can exist that result in the same stress triaxiality T and Lode parameter L. Specifically, it is shown that for a prescribed pair of T and L and in the absence of shear stress, at most six stress states {ρ1 , 0 ,ρ3 } are possible. On the other extreme in the presence of shear stress, an infinite number of stress states is possible, due to the existence of Mohr's circle for this stress state. This model, together with the proposed energy-based criteria, is used to examine void coalescence under multiple stress-state conditions for any given T and L. Numerical results have shown that the presence of shear stress has a significant effect of reducing the effective strains for the onset of and final void coalescences. In addition, a relationship has also been established between shear angle and effective strain at the onset of shear void coalescence.

Explicit dosimetry for 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a-mediated photodynamic therapy: macroscopic singlet oxygen modeling.

PubMed

Penjweini, Rozhin; Liu, Baochang; Kim, Michele M; Zhu, Timothy C

2015-01-01

Type II photodynamic therapy (PDT) is based on the photochemical reactions mediated through an interaction between a photosensitizer, ground-state oxygen ([(3)O2]), and light excitation at an appropriate wavelength, which results in production of reactive singlet oxygen ([(1)O2]rx). We use an empirical macroscopic model based on four photochemical parameters for the calculation of [(1)O2]rx threshold concentration ([(1)O2]rx,sh) causing tissue necrosis in tumors after PDT. For this reason, 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH)-mediated PDT was performed interstitially on mice with radiation-induced fibrosarcoma (RIF) tumors. A linear light source at 665 nm with total energy released per unit length of 12 to 100  J/cm and source power per unit length (LS) of 12 to 150  mW/cm was used to induce different radii of necrosis. Then the amount of [(1)O2]rx calculated by the macroscopic model incorporating explicit PDT dosimetry of light fluence distribution, tissue optical properties, and HPPH concentration was correlated to the necrotic radius to obtain the model parameters and [(1)O2]rx,sh. We provide evidence that [(1)O2]rx is a better dosimetric quantity for predicting the treatment outcome than PDT dose, which is proportional to the time integral of the products of the photosensitizer concentration and light fluence rate.

Explicit dosimetry for 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a-mediated photodynamic therapy: macroscopic singlet oxygen modeling

PubMed Central

Penjweini, Rozhin; Liu, Baochang; Kim, Michele M.; Zhu, Timothy C.

2015-01-01

Abstract. Type II photodynamic therapy (PDT) is based on the photochemical reactions mediated through an interaction between a photosensitizer, ground-state oxygen ([O32]), and light excitation at an appropriate wavelength, which results in production of reactive singlet oxygen ([O12]rx). We use an empirical macroscopic model based on four photochemical parameters for the calculation of [O12]rx threshold concentration ([O12]rx,sh) causing tissue necrosis in tumors after PDT. For this reason, 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH)-mediated PDT was performed interstitially on mice with radiation-induced fibrosarcoma (RIF) tumors. A linear light source at 665 nm with total energy released per unit length of 12 to 100  J/cm and source power per unit length (LS) of 12 to 150  mW/cm was used to induce different radii of necrosis. Then the amount of [O12]rx calculated by the macroscopic model incorporating explicit PDT dosimetry of light fluence distribution, tissue optical properties, and HPPH concentration was correlated to the necrotic radius to obtain the model parameters and [O12]rx,sh. We provide evidence that [O12]rx is a better dosimetric quantity for predicting the treatment outcome than PDT dose, which is proportional to the time integral of the products of the photosensitizer concentration and light fluence rate. PMID:26720883

Explicit dosimetry for 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a-mediated photodynamic therapy: macroscopic singlet oxygen modeling

NASA Astrophysics Data System (ADS)

Penjweini, Rozhin; Liu, Baochang; Kim, Michele M.; Zhu, Timothy C.

2015-12-01

Type II photodynamic therapy (PDT) is based on the photochemical reactions mediated through an interaction between a photosensitizer, ground-state oxygen ([O]), and light excitation at an appropriate wavelength, which results in production of reactive singlet oxygen ([]rx). We use an empirical macroscopic model based on four photochemical parameters for the calculation of []rx threshold concentration ([]rx,sh) causing tissue necrosis in tumors after PDT. For this reason, 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH)-mediated PDT was performed interstitially on mice with radiation-induced fibrosarcoma (RIF) tumors. A linear light source at 665 nm with total energy released per unit length of 12 to 100 J/cm and source power per unit length (LS) of 12 to 150 mW/cm was used to induce different radii of necrosis. Then the amount of []rx calculated by the macroscopic model incorporating explicit PDT dosimetry of light fluence distribution, tissue optical properties, and HPPH concentration was correlated to the necrotic radius to obtain the model parameters and []rx,sh. We provide evidence that []rx is a better dosimetric quantity for predicting the treatment outcome than PDT dose, which is proportional to the time integral of the products of the photosensitizer concentration and light fluence rate.

Calibration under uncertainty for finite element models of masonry monuments

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

Atamturktur, Sezer,; Hemez, Francois,; Unal, Cetin

2010-02-01

Historical unreinforced masonry buildings often include features such as load bearing unreinforced masonry vaults and their supporting framework of piers, fill, buttresses, and walls. The masonry vaults of such buildings are among the most vulnerable structural components and certainly among the most challenging to analyze. The versatility of finite element (FE) analyses in incorporating various constitutive laws, as well as practically all geometric configurations, has resulted in the widespread use of the FE method for the analysis of complex unreinforced masonry structures over the last three decades. However, an FE model is only as accurate as its input parameters, andmore » there are two fundamental challenges while defining FE model input parameters: (1) material properties and (2) support conditions. The difficulties in defining these two aspects of the FE model arise from the lack of knowledge in the common engineering understanding of masonry behavior. As a result, engineers are unable to define these FE model input parameters with certainty, and, inevitably, uncertainties are introduced to the FE model.« less

A physical-based gas-surface interaction model for rarefied gas flow simulation

NASA Astrophysics Data System (ADS)

Liang, Tengfei; Li, Qi; Ye, Wenjing

2018-01-01

Empirical gas-surface interaction models, such as the Maxwell model and the Cercignani-Lampis model, are widely used as the boundary condition in rarefied gas flow simulations. The accuracy of these models in the prediction of macroscopic behavior of rarefied gas flows is less satisfactory in some cases especially the highly non-equilibrium ones. Molecular dynamics simulation can accurately resolve the gas-surface interaction process at atomic scale, and hence can predict accurate macroscopic behavior. They are however too computationally expensive to be applied in real problems. In this work, a statistical physical-based gas-surface interaction model, which complies with the basic relations of boundary condition, is developed based on the framework of the washboard model. In virtue of its physical basis, this new model is capable of capturing some important relations/trends for which the classic empirical models fail to model correctly. As such, the new model is much more accurate than the classic models, and in the meantime is more efficient than MD simulations. Therefore, it can serve as a more accurate and efficient boundary condition for rarefied gas flow simulations.

Dithiolato-bridged nickel-iron complexes as models for the active site of [NiFe]-hydrogenases.

PubMed

Song, Li-Cheng; Yang, Xi-Yue; Cao, Meng; Gao, Xiu-Yun; Liu, Bei-Bei; Zhu, Liang; Jiang, Feng

2017-03-30

The structural and functional modeling of the active site of [NiFe]-hydrogenases has been proved to be challenging to a great extent. Herein, we report the synthesis, structures, and some properties of the NiFe-based dicarbonyl, terminal hydride, and μ-hydroxo models for the active site of [NiFe]-hydrogenases.

Modeling of the Coupling of Microstructure and Macrosegregation in a Direct Chill Cast Al-Cu Billet

NASA Astrophysics Data System (ADS)

Heyvaert, Laurent; Bedel, Marie; Založnik, Miha; Combeau, Hervé

2017-10-01

The macroscopic multiphase flow and the growth of the solidification microstructures in the mushy zone of a direct chill (DC) casting are closely coupled. These couplings are the key to the understanding of the formation of the macrosegregation and of the non-uniform microstructure of the casting. In the present paper we use a multiphase and multiscale model to provide a fully coupled picture of the links between macrosegregation and microstructure in a DC cast billet. The model describes nucleation from inoculant particles and growth of dendritic and globular equiaxed crystal grains, fully coupled with macroscopic transport phenomena: fluid flow induced by natural convection and solidification shrinkage, heat, mass, and solute mass transport, motion of free-floating equiaxed grains, and of grain refiner particles. We compare our simulations to experiments on grain-refined and non-grain-refined industrial size billets from literature. We show that a transition between dendritic and globular grain morphology triggered by the grain refinement is the key to the explanation of the differences between the macrosegregation patterns in the two billets. We further show that the grain size and morphology are strongly affected by the macroscopic transport of free-floating equiaxed grains and of grain refiner particles.

Bell inequalities for falsifying mesoscopic local realism via amplification of quantum noise

NASA Astrophysics Data System (ADS)

Reid, M. D.

2018-04-01

Macroscopic realism (MR) per se specifies that a system which has two macroscopically distinct states available to it (such as a cat being dead or alive) is at all times predetermined to be in one or other of those two states. A minimal assumption of a macroscopic realistic theory therefore is the validity of a hidden variable λM that predetermines the outcome (whether dead or alive) of a measurement M ̂ distinguishing the two states. Proposals to test MR generally introduce a second premise to further qualify the meaning of MR. Thus, we consider a model, macroscopic local realism (MLR), where the second premise is that measurements at one location cannot cause an instantaneous macroscopic change δ to the results of measurements made on a second system at another location. To provide a practical test, we define the intermediate concept of δ -scopic local realism (δ -LR), where δ ≠0 can be quantified, but need not be macroscopic. By considering the amplification of quantum fluctuations, we show how negation of δ -LR is possible using fields violating a continuous variable Bell inequality. A modified Bell-Clauser-Horne-Shimony-Holt inequality is derived that tests δ -LR, and a quantitative proposal given for experiments based on polarization entanglement. In the proposal, δ is the magnitude of the quantum noise scaled by an adjustable coherent amplitude α that can also be considered part of the measurement apparatus. Thus, δ is large in an absolute sense, but scales inversely with the square root of the system size, which is proportional to |α| 2. We discuss how the proposed experiment gives a realization of a type of Schrödinger-cat experiment without problems of decoherence.

The flow of plasma in the solar terrestrial environment

NASA Technical Reports Server (NTRS)

Schunk, Robert W.; Banks, P.; Barakat, A. R.; Crain, D. J.; Demars, H. G.; Lemaire, J.; Ma, T.-Z.; Rasmussen, C. E.; Richards, P.; Sica, R.

1990-01-01

The overall goal of our NASA Theory Program was to study the coupling, time delays, and feedback mechanisms between the various regions of the solar-terrestrial system in a self-consistent, quantitative manner. To accomplish this goal, it will eventually be necessary to have time-dependent macroscopic models of the different regions of the solar-terrestrial system and we are continually working toward this goal. However, with the funding from this NASA program, we concentrated on the near-earth plasma environment, including the ionosphere, the plasmasphere, and the polar wind. In this area, we developed unique global models that allowed us to study the coupling between the different regions. These results are highlighted in the next section. Another important aspect of our NASA Theory Program concerned the effect that localized 'structure' had on the macroscopic flow in the ionosphere, plasmasphere, thermosphere, and polar wind. The localized structure can be created by structured magnetospheric inputs (i.e., structured plasma convection, particle precipitation or Birkland current patterns) or time variations in these input due to storms and substorms. Also, some of the plasma flows that we predicted with our macroscopic models could be unstable, and another one of our goals was to examine the stability of our predicted flows. Because time-dependent, three-dimensional numerical models of the solar-terrestrial environment generally require extensive computer resources, they are usually based on relatively simple mathematical formulations (i.e., simple MHD or hydrodynamic formulations). Therefore, another goal of our NASA Theory Program was to study the conditions under which various mathematical formulations can be applied to specific solar-terrestrial regions. This could involve a detailed comparison of kinetic, semi-kinetic, and hydrodynamic predictions for a given polar wind scenario or it could involve the comparison of a small-scale particle-in-cell (PIC) simulation of a plasma expansion event with a similar macroscopic expansion event. The different mathematical formulations have different strengths and weaknesses and a careful comparison of model predictions for similar geophysical situations provides insight into when the various models can be used with confidence.

The flow of plasma in the solar terrestrial environment

NASA Technical Reports Server (NTRS)

Schunk, Robert W.

1991-01-01

The overall goal of our NASA Theory Program is to study the coupling, time delays, and feedback mechanisms between the various regions of the solar-terrestrial system in a self-consistent, quantitative, manner. To accomplish this goal, it will eventually be necessary to have time-dependent macroscopic models of the different regions of the solar-terrestrial system and we are continually working toward this goal. However, our immediate emphasis is on the near-earth plasma environment, including the ionosphere, the plasmasphere, and the polar wind. In this area, we have developed unique global models that allow us to study the coupling between the different regions. These results are highlighted. Another important aspect of our NASA Theory Program concerns the effect that localized structure has on the macroscopic flow in the ionosphere, plasmasphere, thermosphere and polar wind. The localized structure can be created by structured magnetospheric inputs (i.e., structured plasma convection, particle precipitation or Birkeland current patterns) or time variations in these inputs due to storms and substorms. Also, some of the plasma flows that we predict with our macroscopic models may be unstable. Another one of our goals is to examine the stability of our predicted flows. Because time-dependent three-dimensional numerical models of the solar-terrestrial environment generally require extensive computer resources, they are usually based on relatively simple mathematical formulations (i.e., simple MHD or hydrodynamic formulations). Therefore, another long-range goal of our NASA Theory Program is to study the conditions under which various mathematical formulations can be applied to specific solar-terrestrial regions. This may involve a detailed comparison of kinetic, semikinetic, and hydrodynamic predictions for a given polar wind scenario or it may involve the comparison of a small-scale particle-in-cell (PIC) simulation of a plasma expansion event with a similar macroscopic expansion event. The different mathematical formulations have different strengths and weaknesses and a careful comparison of model predictions for similar geophysical situations will provide insight into when the various models can be used with confidence.

Evaporation of 2-dimensional black holes

NASA Astrophysics Data System (ADS)

Ramazanoglu, Fethi M.

We present a detailed analysis of results from a new study of the quantum evaporation of Callan-Giddings-Harvey-Strominger (CGHS) black holes within the mean-field approximation. The CGHS model is a two dimensional model of quantum gravity which has been extensively investigated in the last two decades. Moreover, Ashtekar, Taveras and Varadarajan have recently proposed a solution to the information loss paradox within the context of this model, which has rekindled the interest in it. However, many aspects of black hole evaporation in this model has been overlooked because of lack of a solution for black holes with macroscopic mass. We show that this was due to, in part, limited numerical precision and, in part, misinterpretation of certain properties and symmetries of the model. By addressing these issues, we were, for the first time, able to numerically evolve macroscopic-mass black hole spacetimes of the CGHS model within the mean-field approximation, up to the vicinity of the singularity. Our calculations show that, while some of the assumptions underlying the standard evaporation paradigm are borne out, several are not. One of the anticipated properties we confirm is that the semi-classical space-time is asymptotically flat at right future null infinity, I+R , yet incomplete in the sense that null observers reach a future Cauchy horizon in finite affine time. Unexpected behavior includes that the Bondi mass traditionally used in the literature can become negative even when the area of the horizon is macroscopic; an improved Bondi mass remains positive until the end of semi-classical evaporation, yet the final value can be arbitrarily large relative to the Planck mass; and the flux of the quantum radiation at I+R is non-thermal even when the horizon area is large compared to the Planck scale. Furthermore, if the black hole is initially macroscopic, the evaporation process exhibits remarkable universal properties, which offer problems to attack to the mathematical relativity and geometric analysis communities. Our results also provide support for the full quantum scenario developed by Ashtekar et al.

Parallelization of fine-scale computation in Agile Multiscale Modelling Methodology

NASA Astrophysics Data System (ADS)

Macioł, Piotr; Michalik, Kazimierz

2016-10-01

Nowadays, multiscale modelling of material behavior is an extensively developed area. An important obstacle against its wide application is high computational demands. Among others, the parallelization of multiscale computations is a promising solution. Heterogeneous multiscale models are good candidates for parallelization, since communication between sub-models is limited. In this paper, the possibility of parallelization of multiscale models based on Agile Multiscale Methodology framework is discussed. A sequential, FEM based macroscopic model has been combined with concurrently computed fine-scale models, employing a MatCalc thermodynamic simulator. The main issues, being investigated in this work are: (i) the speed-up of multiscale models with special focus on fine-scale computations and (ii) on decreasing the quality of computations enforced by parallel execution. Speed-up has been evaluated on the basis of Amdahl's law equations. The problem of `delay error', rising from the parallel execution of fine scale sub-models, controlled by the sequential macroscopic sub-model is discussed. Some technical aspects of combining third-party commercial modelling software with an in-house multiscale framework and a MPI library are also discussed.

A Global Atmospheric Model of Meteoric Iron

NASA Technical Reports Server (NTRS)

Feng, Wuhu; Marsh, Daniel R.; Chipperfield, Martyn P.; Janches, Diego; Hoffner, Josef; Yi, Fan; Plane, John M. C.

2013-01-01

The first global model of meteoric iron in the atmosphere (WACCM-Fe) has been developed by combining three components: the Whole Atmosphere Community Climate Model (WACCM), a description of the neutral and ion-molecule chemistry of iron in the mesosphere and lower thermosphere (MLT), and a treatment of the injection of meteoric constituents into the atmosphere. The iron chemistry treats seven neutral and four ionized iron containing species with 30 neutral and ion-molecule reactions. The meteoric input function (MIF), which describes the injection of Fe as a function of height, latitude, and day, is precalculated from an astronomical model coupled to a chemical meteoric ablation model (CABMOD). This newly developed WACCM-Fe model has been evaluated against a number of available ground-based lidar observations and performs well in simulating the mesospheric atomic Fe layer. The model reproduces the strong positive correlation of temperature and Fe density around the Fe layer peak and the large anticorrelation around 100 km. The diurnal tide has a significant effect in the middle of the layer, and the model also captures well the observed seasonal variations. However, the model overestimates the peak Fe+ concentration compared with the limited rocket-borne mass spectrometer data available, although good agreement on the ion layer underside can be obtained by adjusting the rate coefficients for dissociative recombination of Fe-molecular ions with electrons. Sensitivity experiments with the same chemistry in a 1-D model are used to highlight significant remaining uncertainties in reaction rate coefficients, and to explore the dependence of the total Fe abundance on the MIF and rate of vertical transport.

Developing Computer Model-Based Assessment of Chemical Reasoning: A Feasibility Study

ERIC Educational Resources Information Center

Liu, Xiufeng; Waight, Noemi; Gregorius, Roberto; Smith, Erica; Park, Mihwa

2012-01-01

This paper reports a feasibility study on developing computer model-based assessments of chemical reasoning at the high school level. Computer models are flash and NetLogo environments to make simultaneously available three domains in chemistry: macroscopic, submicroscopic, and symbolic. Students interact with computer models to answer assessment…

Assessment of kinetic models on Fe adsorption in groundwater using high-quality limestone

NASA Astrophysics Data System (ADS)

Akbar, N. A.; Kamil, N. A. F. Mohd; Zin, N. S. Md; Adlan, M. N.; Aziz, H. A.

2018-04-01

During the groundwater pumping process, dissolved Fe2+ is oxidized into Fe3+ and produce rust-coloured iron mineral. Adsorption kinetic models are used to evaluate the performance of limestone adsorbent and describe the mechanism of adsorption and the diffusion processes of Fe adsorption in groundwater. This work presents the best kinetic model of Fe adsorption, which was chosen based on a higher value of coefficient correlation, R2. A batch adsorption experiment was conducted for various contact times ranging from 0 to 135 minutes. From the results of the batch study, three kinetic models were analyzed for Fe removal onto limestone sorbent, including the pseudo-first order (PFO), pseudo-second order (PSO) and intra-particle diffusion (IPD) models. Results show that the adsorption kinetic models follow the sequence: PSO > PFO > IPD, where the values of R2 are 0.997 > 0.919 > 0.918. A high value of R2 (0.997) reveals better fitted experimental data. Furthermore, the value of qe cal in the PSO kinetic model is very near to qe exp rather than that in other models. This finding therefore suggests that the PSO kinetic model has the good fitted with the experimental data which involved chemisorption process of divalent Fe removal in groundwater solution. Thus, limestone adsorbent media found to be an alternative and effective treatment of Fe removal from groundwater.

Revisiting the magnetic structure and charge ordering in La1 /3Sr2 /3FeO3 by neutron powder diffraction and Mössbauer spectroscopy

NASA Astrophysics Data System (ADS)

Li, F.; Pomjakushin, V.; Mazet, T.; Sibille, R.; Malaman, B.; Yadav, R.; Keller, L.; Medarde, M.; Conder, K.; Pomjakushina, E.

2018-05-01

The magnetic ordering of La1 /3Sr2 /3FeO3 perovskite has been studied by neutron powder diffraction and 57Fe Mössbauer spectroscopy down to 2 K. From symmetry analysis, a chiral helical model and a collinear model are proposed to describe the magnetic structure. Both are commensurate, with propagation vector k =(0 ,0 ,1 ) in R 3 ¯c space group. In the former model, the magnetic moments of Fe adopt the magnetic space group P 3221 and have helical and antiferromagnetic ordering propagating along the c axis. The model allows only a single Fe site, with a magnetic moment of 3.46(2)μB at 2 K. In the latter model, the magnetic moments of iron ions adopt the magnetic space group C 2 /c or C 2'/c' and are aligned collinearly. The model allows the presence of two inequivalent Fe sites with magnetic moments of amplitude 3.26(3)μB and 3.67(2)μB, respectively. The neutron-diffraction pattern is equally well fitted by either model. The Mössbauer spectroscopy study suggests a single charge state Fe3.66 + above the magnetic transition and a charge disproportionation into Fe(3.66 -ζ )+ and Fe(3.66 +2 ζ )+ below the magnetic transition. The compatibility of the magnetic structure models with the Mössbauer spectroscopy results is discussed.

Formation mechanisms of neutral Fe layers in the thermosphere at Antarctica studied with a thermosphere-ionosphere Fe/Fe+ (TIFe) model

NASA Astrophysics Data System (ADS)

Chu, Xinzhao; Yu, Zhibin

2017-06-01

With a thermosphere-ionosphere Fe/Fe+ (TIFe) model developed from first principles at the University of Colorado, we present the first quantitative investigation of formation mechanisms of thermospheric Fe layers observed by lidar in Antarctica. These recently discovered neutral metal layers in the thermosphere between 100 and 200 km provide unique tracers for studies of fundamental processes in the space-atmosphere interaction region. The TIFe model formulates and expands the TIFe theory originally proposed by Chu et al. that the thermospheric Fe layers are produced through the neutralization of converged Fe+ layers. Through testing mechanisms and reproducing the 28 May 2011 event at McMurdo, we conceive the lifecycle of meteoric metals via deposition, transport, chemistry, and wave dynamics for thermospheric Fe layers with gravity wave signatures. While the meteor injection of iron species is negligible above 120 km, the polar electric field transports metallic ions Fe+ upward from their main deposition region into the E-F regions, providing the major source of Fe+ (and accordingly Fe) in the thermosphere. Atmospheric wave-induced vertical shears of vertical and horizontal winds converge Fe+ to form dense Fe+ layers. Direct electron-Fe+ recombination is the major channel to neutralize Fe+ layers to form Fe above 120 km. Fe layer shapes are determined by multiple factors of neutral winds, electric field, and aurora activity. Gravity-wave-induced vertical wind plays a key role in forming gravity-wave-shaped Fe layers. Aurora particle precipitation enhances Fe+ neutralization by increasing electron density while accelerating Fe loss via charge transfer with enhanced NO+ and O2+ densities.