Sample records for lindemann ellu saar

  1. Exact statistical mechanical lattice model and classical Lindemann theory of melting of inert gas solids

    NASA Astrophysics Data System (ADS)

    Dunne, Lawrence J.; Murrell, John N.; Manos, George


    A modified form of Lindemann's model shows that the melting points of the heavy inert gases and other effectively spherical molecular species are proportional to the depths of their diatomic potential wells. The success of the model when compared with experiment seems to rely on the almost constant value of the ratio of the fractional volume and entropy changes during fusion. The Lindemann proposal can be incorporated into an exactly treated statistical mechanical lattice model utilising expandable clusters which reproduces the solid-liquid melting phenomenon for argon with a realistic volume change and melting line.

  2. A Lindemann-Weierstrass theorem for semi-abelian varieties over function fields

    NASA Astrophysics Data System (ADS)

    Bertrand, Daniel; Pillay, Anand


    We prove an analogue of the Lindemann-Weierstrass theorem (that the exponentials of a {Q} -linearly independent set of algebraic numbers are algebraically independent), replacing {Q}^{alg} by {C}(t)^{alg} and {G}_{m}^{n} by a semi-abelian variety over {C}(t)^{alg} . Both the formulations of our results and the methods are differential algebraic in nature.

  3. On the volume-dependence of the Grüneisen parameter and the Lindemann law of melting

    NASA Astrophysics Data System (ADS)

    Kushwah, S. S.; Tomar, Y. S.; Upadhyay, A. K.


    It has been shown by Errandonea (Physica B 357 (2005) 356) that the Lindemann law cannot reproduce the high pressure melting curves of transition metals. Using an expression for the volume dependence of the Grüneisen parameter γ originally due to Burakovsky and Preston (J. Phys. Chem. Solids 65 (2004) 1581), Errandonea determined the constants appearing in the expression of gamma by making the Lindemann law to match the experimental melting data. The results for the volume dependence of gamma thus obtained by Errandonea are shown here to be much different from those determined using the Burakovsky-Preston approach. A direct comparison of the results based on the two approaches has been presented for the transition metal Mo. It is reinforced that the Lindemann law does not work satisfactorily for the transition metals with low slopes of melting curves.

  4. Calculation of difference in heat capacities at constant pressure and constant volume with the aid of the empirical Nernst and Lindemann equation

    NASA Astrophysics Data System (ADS)

    Leontev, K. L.


    An expression is obtained for heat capacity differences of materials at a constant pressure and volume, on the basis of the rigorous thermodynamic equation (Kittel, 1976), and by using the Grueneisen law (Kikoin and Kikoin, 1976) of constancy of the ratio of the cubic expansion coefficient to the molar heat capacity. Conditions are determined, where the empirical Nernst and Lindemann (Filippov, 1967) equation is regarded as rigorous.

  5. Aromatized arborane/fernane hydrocarbons as molecular indicators of floral changes in Upper Carboniferous/Lower Permian strata of the Saar-Nahe Basin, southwestern Germany

    NASA Astrophysics Data System (ADS)

    Vliex, M.; Hagemann, H. W.; Püttmann, W.


    Thirty-seven coal samples of Upper Carboniferous and Lower Permian age from three boreholes in the Saar-Nahe Basin, Germany, have been studied by organic geochemical and coal petrological methods. The investigations were aimed at the recognition of floral changes in the Upper Carboniferous and Lower Permian strata. The results show that compositional changes in the extracts are only partly caused by variations in coalification. Specific aromatic hydrocarbons appear in Upper Westphalian D coal seams and increase in concentration up to the Rotliegendes. The dominant compound has been identified by mass spectrometry and NMR-spectroscopy as 5-methyl-10-(4-methylpentyl)-des- A-25-norarbora(ferna)-5,7,9-triene (MATH) and always occurs associated with 25-norarbora(ferna)-5,7,9-triene. Both compounds are thought to originate from isoarborinol, fernene-3β-ol, or fernenes. The strongly acidic conditions during deposition of the coals might have induced the 4,5-cleavage combined with a methyl-shift in an arborane/fernane-type pentacyclic precursor yielding the MATH. Based on petrological investigations, palynomorphs related to early Gymnospermopsida such as Pteridospermales and Coniferophytes ( Cordaitales and Coniferales) increased in abundance in the strata beginning with the Upper Westphalian D concomitant with the above mentioned biomarkers. The results suggest the arborane/fernane derivatives originate from the plant communities producing these palynomorphs.

  6. P651: Battlefield Analysis. The Saar River Crossing, 94th Infantry Division, February 1945

    DTIC Science & Technology


    attacks, this tim? aimed at a complete rupture of the Orscholz switch and early capture of the Hogback ridge. Colonel Hagerty’s 301st Infantry was to...woods to the crest of the Hogback ridge and then roll up the forward line of pillboxes further east. An elaborate program of division and corps

  7. Aquifer and Shallow San Andreas Fault Permeabilities Inferred from Poroelastic Modeling of InSAR Measurements of Land Surface Deformation in Coachella Valley, California. Ravi Appana and Martin O. Saar

    NASA Astrophysics Data System (ADS)

    Appana, R.; Saar, M. O.


    Coachella Valley, in southern California, is located in a region where the southern San Andreas Fault system, comprising three main faults, cuts through the valley aquifer dividing it into many sub-basins. Satellite interferometry (InSAR) has revealed differential uplift of the land surface across the Banning Strand - San Andreas Fault (BSF) and the Garnet Hill Fault (GHF) in the upper Coachella Valley. This uplift is suggested to be caused by the elastic response of the aquifer to artificial groundwater recharge and the tectonic stresses acting in this region. However, the differential uplift appears to be mainly caused by the semi-permeable faults which partially restrict pore-fluid pressure diffusion and related groundwater flow. Hence, by employing numerical models of coupled groundwater flow and poroelastic deformation of the aquifer sediments, the land surface uplift can be utilized to constrain a large-scale hydrologic model of the region that includes hydraulic representations of the faults and the sub-basins. Such a regional model can aide in developing better groundwater management strategies that aim at uniform restorations of ground surface elevations and groundwater table levels and would better constrain fault permeabilities with implications for research related to earthquake dynamics and estimates of potential slip along segments of the southern San Andreas Fault system. Studies have suggested that these segments have reached the end of the inter-seismic strain accumulation period posing the biggest risk to seismic hazards in California. InSAR data showing regional land surface uplift and well data of water table elevations, collected in this region, are used to constrain the model yielding hydraulic parameters. Specifically, our results suggest that the horizontal permeability, kxWWB, of the White Water sub-basin (WWB) and its permeability anisotropy, aWWB = (kz/kx)WWB, are on the order of 0.20x10-11 m2 ≤ kxWWB ≤ 1.2x10-11 m2 and 0.04 ≤ aWWB ≤ 0.085, respectively. Furthermore, the model suggests permeabilities of the GHF and the BSF of 1.0x10-15 m2 ≤kxGHF≤ 3.0x10-14 m2 and kxBSF ≤ 2.0x10-16 m2, respectively. These results suggest a contrast in the permeability structure, i.e., kx1-104 between the GHF and the surrounding sub-basins and at least 102 between the BSF and the surrounding sub-basins, with the faults having lower permeabilities in either case. Therefore, my model confirms quantitatively that the faults act as semi-permeable barriers to pore-fluid pressure diffusion. Further analysis indicates that estimates of kGHF are important to consider when managing groundwater levels and land surface deformation in the WWB and the GHB. While the study presented here can only shed light on shallow fault permeabilities, which, however, may serve as upper limits to deep fault permeabilities, such maximum fault permeabilities may help explain why the San Andreas Fault system tends to consist of weak faults.

  8. The Accentuation of Intransitive Sentences in English.

    ERIC Educational Resources Information Center

    Faber, David


    Discusses the accentuation of two types of sentence in English: (1) straightforward intransitive sentences, and (2) intransitive sentences embedded in the frame "It's just NP noun phrase[ V verb[-ing." Modifications to Gussenhoven's (1983) Sentence Accent Assignment Rule (SAAR) are suggested based on large groups of exceptions of the SAAR.…

  9. Thermodynamics at the nanoscale: phase diagrams of nickel-carbon nanoclusters and equilibrium constants for phase transitions.


    Engelmann, Yannick; Bogaerts, Annemie; Neyts, Erik C


    Using reactive molecular dynamics simulations, the melting behavior of nickel-carbon nanoclusters is examined. The phase diagrams of icosahedral and Wulff polyhedron clusters are determined using both the Lindemann index and the potential energy. Formulae are derived for calculating the equilibrium constants and the solid and liquid fractions during a phase transition, allowing more rational determination of the melting temperature with respect to the arbitrary Lindemann value. These results give more insight into the properties of nickel-carbon nanoclusters in general and can specifically be very useful for a better understanding of the synthesis of carbon nanotubes using the catalytic chemical vapor deposition method.

  10. In vivo functions of the gamma-butyrolactone autoregulator receptor in Streptomyces ambofaciens producing spiramycin.


    Choi, Sun-Uk; Kim, Mi-Kyung; Ha, Heon-Su; Hwang, Yong-Il


    A gene encoding a gamma-butyrolactone autoregulator receptor was cloned in to E. coli from Streptomyces ambofaciens producing spiramycin, a macrolide antibiotic used in both veterinary medicine and human medicine. A 714-bp intact receptor gene (saaR) was obtained by PCR and genomic Southern hybridization with the 100-bp PCR product as a probe. To clarify the in vivo function of saaR, a saaR-disrupted strain was constructed by means of homologous recombination, and phenotypes were compared with those of the wild-type strain. The number of saaR-disruptant spores was 4-fold less than that of the wild-type strain. In addition, saaR deletion from the S. ambofaciens chromosome resulted in complete loss of spiramycin production suggesting that saaR is a rare positive regulator, controlling both spiramycin biosynthesis and sporulation.

  11. The Utility of the Lambert Function W[a exp(a - bt)] in Chemical Kinetics

    ERIC Educational Resources Information Center

    Williams, Brian Wesley


    The mathematical Lambert function W[a exp(a - bt)] is used to find integrated rate laws for several examples, including simple enzyme and Lindemann-Christiansen-Hinshelwood (LCH) unimolecular decay kinetics. The results derived here for the well-known LCH mechanism as well as for a dimer-monomer reaction mechanism appear to be novel. A nonlinear…

  12. Journal of Rehabilitation Research and Development, Volume 30, Number 1, 1993

    DTIC Science & Technology


    Lindemann W. Ein digitales richtungsfilter, basierend auf kunstkopfsignalen. In: Fortschritte der favorable sig. J-to-noise ratios. In addition, it... Sistemas de Control, Universidad de Los Andes, Surgery, National Spinal Injuries Center, 550-4, Merida, Venezuela Igisu, lizuka, 820 Japan 140. Hand

  13. Professional Writers Teaching Professional Writing: Transcending the Borders between Professional Writers and Academic Scholars, Harmonizing Throught and Reality: A Text Arguing for Teaching Sentences First, Last, and Foremost.

    ERIC Educational Resources Information Center

    Beene, LynnDianne

    Good writing is good sentences. It is a simple truth that many in the business of teaching writing have strayed from. Good writing is a first sentence that makes a reader want to read the second sentence, a second sentence that makes a reader want to read the third, and so on. Erika Lindemann suggests that certain types of sentence instruction can…

  14. Problems with Current Models of Grieving and Consequences for Older Persons.

    ERIC Educational Resources Information Center

    Horacek, Bruce J.

    Classical models of the grieving process include Freud's concept of withdrawal of ties to the love object called decathexis, and Lindemann's emancipation from the bondage to the deceased involving adjusting to the loss in one's environment and the ability to form new relationships. Most of the models and explanations of the grieving process over…

  15. Experimental Study of Electronic States at Interfaces.

    DTIC Science & Technology


    AE h (h )COR ELLU VIH E E V AOTOIh EDSOImhhA E - EEonmonsoE EhhhhEhh EhhhoshEEEEshE Inn 190 ~uM -~11H1 IM~ *22 -us - II 1.1 ’I-huh .25 16III...Center. Cornell UniversiY. Ithaca. New York 14853 (Received 6 August 1984-, revised manuscript received 4 March 1985) Under certain circumstances the

  16. Atomic displacements in quantum crystals

    NASA Astrophysics Data System (ADS)

    Dusseault, Marisa; Boninsegni, Massimo


    Displacements of atoms and molecules away from lattice sites in helium and parahydrogen solids at low temperature have been studied by means of quantum Monte Carlo simulations. In the bcc phases of 3He and 4He, atomic displacements are largely quantum-mechanical in character, even at melting. The computed Lindemann ratio at melting is found to be in good agreement with experimental results for 4He. Unlike the case of helium, in solid parahydrogen there exists near melting a significant thermal contribution to molecular vibrations, accounting for roughly half of the total effect. Although the Lindemann ratio at melting is in quantitative agreement with experiment, computed molecular mean square fluctuations feature a clear temperature dependence, in disagreement with recent experimental observations.

  17. Single Amino Acid Repeats in the Proteome World: Structural, Functional, and Evolutionary Insights

    PubMed Central

    Kumar, Amitha Sampath; Sowpati, Divya Tej; Mishra, Rakesh K.


    Microsatellites or simple sequence repeats (SSR) are abundant, highly diverse stretches of short DNA repeats present in all genomes. Tandem mono/tri/hexanucleotide repeats in the coding regions contribute to single amino acids repeats (SAARs) in the proteome. While SSRs in the coding region always result in amino acid repeats, a majority of SAARs arise due to a combination of various codons representing the same amino acid and not as a consequence of SSR events. Certain amino acids are abundant in repeat regions indicating a positive selection pressure behind the accumulation of SAARs. By analysing 22 proteomes including the human proteome, we explored the functional and structural relationship of amino acid repeats in an evolutionary context. Only ~15% of repeats are present in any known functional domain, while ~74% of repeats are present in the disordered regions, suggesting that SAARs add to the functionality of proteins by providing flexibility, stability and act as linker elements between domains. Comparison of SAAR containing proteins across species reveals that while shorter repeats are conserved among orthologs, proteins with longer repeats, >15 amino acids, are unique to the respective organism. Lysine repeats are well conserved among orthologs with respect to their length and number of occurrences in a protein. Other amino acids such as glutamic acid, proline, serine and alanine repeats are generally conserved among the orthologs with varying repeat lengths. These findings suggest that SAARs have accumulated in the proteome under positive selection pressure and that they provide flexibility for optimal folding of functional/structural domains of proteins. The insights gained from our observations can help in effective designing and engineering of proteins with novel features. PMID:27893794

  18. Noise Impacts on Pinniped Hearing

    DTIC Science & Technology


    Reichmuth Kastak, C., Schusterman, R.J. (submitted) Onset, growth and recovery of in-air threshold shift in a California sea lion ( Zalophus californianus ...Mammals. San Diego, California. p. 252. Lindemann, K.L., Reichmuth Kastak, C., Schusterman, R.J. (2005) A California sea lion ( Zalophus californianus ...visual cognitive performance in a California sea lion ( Zalophus californianus ). Journal of the Acoustical Society of America 118:1905. Atwood, E.C

  19. Theory of melting at high pressures: Amending density functional theory with quantum Monte Carlo

    NASA Astrophysics Data System (ADS)

    Shulenburger, L.; Desjarlais, M. P.; Mattsson, T. R.


    We present an improved first-principles description of melting under pressure based on thermodynamic integration comparing density functional theory (DFT) and quantum Monte Carlo (QMC) treatments. The method is applied to address the longstanding discrepancy between DFT calculations and diamond anvil cell (DAC) experiments on the melting curve of xenon, a noble gas solid where van der Waals binding is challenging for traditional DFT methods. The calculations show agreement with data below 20 GPa and that the high-pressure melt curve is well described by a Lindemann behavior up to at least 80 GPa, in contrast to DAC data.

  20. Experimental Evidence for a Crossover between Two Distinct Mechanisms of Amorphization in Ice Ih under Pressure

    SciTech Connect

    Straessle, Thierry; Klotz, Stefan; Hamel, Gerard; Koza, Michael M.; Schober, Helmut


    We report neutron scattering data which reveal the central role of phonon softening leading to a negative melting line, solid-state amorphization, and negative thermal expansion of ice. We find that pressure-induced amorphization is due to mechanical melting at low temperatures, while at higher temperatures amorphization is governed by thermal melting (violations of Born's and Lindemann's criteria, respectively). This confirms earlier conjectures of a crossover between two distinct amorphization mechanisms and provides a natural explanation for the strong annealing observed in high-density amorphous ice.

  1. Fat stigma and public health: a theoretical framework and ethical analysis.


    Abu-Odeh, Desiree


    This paper proposes a theoretical framework for understanding fat stigma and its impact on people's well-being. It argues that stigma should never be used as a tool to achieve public health ends. Drawing on Bruce Link and Jo Phelan's 2001 conceptualization of stigma as well as the works of Hilde Lindemann, Paul Benson, and Margaret Urban Walker on identity, positionality, and agency, this paper clarifies the mechanisms by which stigmatizing, oppressive conceptions of overweight and obesity damage identities and diminish moral agency, arguing that the use of obesity-related stigma for public health ends violates the bioethics principles of nonmaleficence, autonomy, and justice.

  2. Effect of Size Polydispersity on Melting of Charged Colloidal Systems

    NASA Astrophysics Data System (ADS)

    Chen, Yong


    We introduce simple prescriptions of the Yukawa potential to describe the effect of size polydispersity and macroion shielding effect in charged colloidal systems. The solid-liquid phase boundaries were presented with the Lindemann criterion based on molecular dynamics simulations. Compared with the Robbins-Kremer-Grest simulation results, a deviation of melting line is observed at small lambda, which means large macroion screening length. This deviation of phase boundary is qualitatively consistent with the simulation result of the nonlinear Poisson-Boltzmann equation with full many-body interactions. It is found that this deviation of the solid-liquid phase behaviour is sensitive to the screening parameter.

  3. Two-dimensional melting of a crystal of ferrofluid spikes.


    Boyer, François; Falcon, Eric


    We report the observation of the transition from an ordered solidlike phase to a disordered liquidlike phase of a lattice of spikes on a ferrofluid surface submitted to horizontal sinusoidal vibrations. The melting transition occurs for a critical spike displacement which is experimentally found to follow the Lindemann criterion, for two different lattice topologies (hexagonal and square) and over a wide range of lattice wavelengths. An intermediate hexaticlike phase between the solid and isotropic liquid phases is also observed and characterized by standard correlation functions. This dissipative out-of-equilibrium system exhibits strong similarities with 2D melting in solid-state physics.

  4. Theory of melting at high pressures: Amending density functional theory with quantum Monte Carlo

    SciTech Connect

    Shulenburger, L.; Desjarlais, M. P.; Mattsson, T. R.


    We present an improved first-principles description of melting under pressure based on thermodynamic integration comparing Density Functional Theory (DFT) and quantum Monte Carlo (QMC) treatments of the system. The method is applied to address the longstanding discrepancy between density functional theory (DFT) calculations and diamond anvil cell (DAC) experiments on the melting curve of xenon, a noble gas solid where van der Waals binding is challenging for traditional DFT methods. The calculations show excellent agreement with data below 20 GPa and that the high-pressure melt curve is well described by a Lindemann behavior up to at least 80 GPa, a finding in stark contrast to DAC data.

  5. Thermal stability of marks gold nanoparticles: A molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Jia, Yanlin; Li, Siqi; Qi, Weihong; Wang, Mingpu; Li, Zhou; Wang, Zhixing


    Molecular dynamics (MDs) simulations were used to explore the thermal stability of Au nanoparticles (NPs) with decahedral, cuboctahedral, icosahedral and Marks NPs. According to the calculated cohesive energy and melting temperature, the Marks NPs have a higher cohesive energy and melting temperature compared to these other shapes. The Lindemann index, radial distribution function, deformation parameters, mean square displacement and self-diffusivity have been used to characterize the structure variation during heating. This work may inspire researchers to prepare Marks NPs and apply them in different fields.

  6. Melting behavior of single two-dimensional crystal

    NASA Astrophysics Data System (ADS)

    Zheng, X. H.; Grieve, R.


    In an experimental system millimeter-sized steel balls repel each other through the Coulomb force to imitate a two-dimensional (2D) atomic lattice in a vacuum both topologically and dynamically. Care has been taken to avoid the formation of grain boundaries. This 2D single crystal melts into a liquid via the hexatic state consistent with the Kosterlitz-Thouless-Halperin-Nelson-Young scenario. Initially in the melting process defects of the 2D lattice tend to emerge from the edge of the crystal. These defects are found to be close to the liquid state according to the Lindemann and Born criteria, confirming the idea of edge melting.

  7. Ionic microgels as model systems for colloids with an ultrasoft electrosteric repulsion: Structure and thermodynamics

    NASA Astrophysics Data System (ADS)

    Gottwald, D.; Likos, C. N.; Kahl, G.; Löwen, H.


    We present a theoretical analysis of the structural properties and phase behavior of spherical, loosely cross-linked ionic microgels that possess a low monomer concentration. The analysis is based on the recently derived effective interaction potential between such particles [A. R. Denton, Phys. Rev. E 67, 011804 (2003)]. By employing standard tools from the theory of the liquid state, we quantitatively analyze the pair correlations in the fluid and find anomalous behavior above the overlap concentration, similar to the cases of star-branched neutral and charged polymers. We also employ an evolutionary algorithm in order to predict the crystalline phases of the system without any a priori assumptions regarding their symmetry class. A very rich phase diagram is obtained, featuring two reentrant melting transitions and a number of unusual crystal structures. At high densities, both the Hansen-Verlet freezing criterion [J.-P. Hansen and L. Verlet, Phys. Rev. 184, 151 (1969)] and the Lindemann melting criterion [F. A. Lindemann, Phys. Z. 11, 609 (1910)] lose their validity. The topology of the phase diagram is altered when the steric interactions between the polymer segments become strong enough, in which case the lower-density reentrant melting disappears and the region of stability of the fluid is split into two disconnected domains, separated by intervening fcc and bcc regions.

  8. A universal criterion of melting.


    Lubchenko, Vassiliy


    Melting is analyzed dynamically as a problem of localization at a liquid-solid interface. A Lindemann-like criterion of melting is derived in terms of particular vibrational amplitudes, which turn out to equal a universal quotient (about one-tenth) of the molecular spacing, at the interface. The near universality of the Lindemann ratio apparently arises owing to strongly overdamped dynamics near melting, and despite the anharmonic interactions being system-specific. A similar criterion is derived for structural displacements in the bulk of the solid, in particular the premelted layer; the criterion is no longer strictly universal, but still depends only on the harmonic properties of the solid. We further compute the dependence of the magnitude of the elemental molecular translations, in deeply supercooled fluids, on the temperature and the high frequency elastic constants. We show explicitly that the surface tension between distinct liquid states, near the glass transition of a supercooled liquid, is nearly evenly split between entropic and energetic contributions.

  9. Quantum melting of a two-dimensional vortex lattice at zero temperature

    SciTech Connect

    Rozhkov, A.; Stroud, D.


    We consider the quantum melting of a two-dimensional flux lattice at temperature {ital T} = 0 in the {open_quote}{open_quote}superclean limit.{close_quote}{close_quote} In this regime, we find that vortex motion is dominated by the Magnus force. A Lindemann criterion predicts melting when {ital n}{sub {ital v}}/{ital n}{sub {ital p}}{ge}{beta}, where {ital n}{sub {ital v}} and {ital n}{sub {ital p}} are the areal number densities of vortex pancakes and Cooper pairs, and {beta}{approx_equal}0.1. A second criterion is derived by using Wigner-crystal and Laughlin wave functions for the solid and liquid phases respectively, and setting the two energies equal. This gives a melting value similar to the Lindemann result. We discuss the numerical value of the {ital T}=0 melting field for thin layers of a low-{ital T}{sub {ital c}} superconductor, such as {ital a}-MoGe, and single layers of high-{ital T}{sub {ital c}} materials. {copyright} {ital 1996 The American Physical Society.}

  10. Phase behavior of charged colloids at a fluid interface

    NASA Astrophysics Data System (ADS)

    Kelleher, Colm P.; Guerra, Rodrigo E.; Hollingsworth, Andrew D.; Chaikin, Paul M.


    We study the phase behavior of a system of charged colloidal particles that are electrostatically bound to an almost flat interface between two fluids. We show that, despite the fact that our experimental system consists of only 103-104 particles, the phase behavior is consistent with the theory of melting due to Kosterlitz, Thouless, Halperin, Nelson, and Young. Using spatial and temporal correlations of the bond-orientational order parameter, we classify our samples into solid, isotropic fluid, and hexatic phases. We demonstrate that the topological defect structure we observe in each phase corresponds to the predictions of Kosterlitz-Thouless-Halperin-Nelson-Young theory. By measuring the dynamic Lindemann parameter γL(τ ) and the non-Gaussian parameter α2(τ ) of the displacements of the particles relative to their neighbors, we show that each of the phases displays distinctive dynamical behavior.

  11. Thermodynamics of freezing and melting.


    Pedersen, Ulf R; Costigliola, Lorenzo; Bailey, Nicholas P; Schrøder, Thomas B; Dyre, Jeppe C


    Although the freezing of liquids and melting of crystals are fundamental for many areas of the sciences, even simple properties like the temperature-pressure relation along the melting line cannot be predicted today. Here we present a theory in which properties of the coexisting crystal and liquid phases at a single thermodynamic state point provide the basis for calculating the pressure, density and entropy of fusion as functions of temperature along the melting line, as well as the variation along this line of the reduced crystalline vibrational mean-square displacement (the Lindemann ratio), and the liquid's diffusion constant and viscosity. The framework developed, which applies for the sizable class of systems characterized by hidden scale invariance, is validated by computer simulations of the standard 12-6 Lennard-Jones system.

  12. Theory of melting at high pressures: Amending density functional theory with quantum Monte Carlo


    Shulenburger, L.; Desjarlais, M. P.; Mattsson, T. R.


    We present an improved first-principles description of melting under pressure based on thermodynamic integration comparing Density Functional Theory (DFT) and quantum Monte Carlo (QMC) treatments of the system. The method is applied to address the longstanding discrepancy between density functional theory (DFT) calculations and diamond anvil cell (DAC) experiments on the melting curve of xenon, a noble gas solid where van der Waals binding is challenging for traditional DFT methods. The calculations show excellent agreement with data below 20 GPa and that the high-pressure melt curve is well described by a Lindemann behavior up to at least 80 GPa, amore » finding in stark contrast to DAC data.« less

  13. Dynamical Stability Limit for the Charge Density Wave in K0.3MoO3

    NASA Astrophysics Data System (ADS)

    Mankowsky, R.; Liu, B.; Rajasekaran, S.; Liu, H. Y.; Mou, D.; Zhou, X. J.; Merlin, R.; Först, M.; Cavalleri, A.


    We study the response of the one-dimensional charge density wave in K0.3MoO3 to different types of excitation with femtosecond optical pulses. We compare direct excitation of the lattice at midinfrared frequencies with injection of quasiparticles across the low energy charge density wave gap and with charge transfer excitation in the near infrared. For all three cases, we observe a fluence threshold above which the amplitude-mode oscillation frequency is softened and the mode becomes increasingly damped. We show that all the data can be collapsed onto a universal curve in which the melting of the charge density wave occurs abruptly at a critical lattice excursion. These data highlight the existence of a universal stability limit for a charge density wave, reminiscent of the Lindemann criterion for the melting of a crystal lattice.

  14. Applications of nonequilibrium melting concept to damage-accumulation processes

    SciTech Connect

    Lam, N.Q.; Okamoto, P.R.


    The authors recent study of crystalline-to-amorphous transformation led to the successful development of a unified thermodynamic description of disorder-induced amorphization and heat-induced melting, based on a generalized version of the Lindemann melting criterion. The generalized criterion requires that the melting temperature of a defective crystal decreases with increasing static atomic disorder. Hence, any crystal can melt at temperatures below the melting point of its perfect crystalline state when driven far from equilibrium by introducing critical amounts of misfitting solute atoms and lattice imperfections, radiation damage, and/or tensile stresses. This conceptual approach to nonequilibrium melting provides new insight into long-standing materials problems such as brittle fracture, embrittlement, and environmentally-induced cracking, for example irradiation-assisted stress corrosion cracking.

  15. Direct observation of liquid nucleus growth in homogeneous melting of colloidal crystals

    PubMed Central

    Wang, Ziren; Wang, Feng; Peng, Yi; Han, Yilong


    The growth behaviour of liquid nucleus is crucial for crystal melting, but its kinetics is difficult to predict and remains challenging in experiment. Here we directly observed the growth of individual liquid nuclei in homogeneous melting of three-dimensional superheated colloidal crystals with single-particle dynamics by video microscopy. The growth rate of nucleus at weak superheating is well fitted by generalizing the Wilson–Frenkel law of crystallization to melting and including the surface tension effects and non-spherical-shape effects. As the degree of superheating increases, the growth rate is enhanced by nucleus shape fluctuation, nuclei coalescence and multimer attachment. The results provide new guidance for the refinement of nucleation theory, especially for the poorly understood strong-superheating regime. The universal Lindemann parameter observed at the superheat limit and solid–liquid interfaces indicates a connection between homogeneous and heterogeneous melting. PMID:25897801

  16. Coulomb structures of charged macroparticles in static magnetic traps at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Vasiliev, M. M.; Petrov, O. F.; Statsenko, K. B.


    Electrically charged (up to 107 e) macroscopic superconducting particles with sizes in the micrometer range confined in a static magnetic trap in liquid nitrogen and in nitrogen vapor at temperatures of 77-91 K are observed experimentally. The macroparticles with sizes up to 60 μm levitate in a nonuniform static magnetic field B ~ 2500 G. The formation of strongly correlated structures comprising as many as ~103 particles is reported. The average particle distance in these structures amounts to 475 μm. The coupling parameter and the Lindemann parameter of these structures are estimated to be ~107 and ~0.03, respectively, which is characteristic of strongly correlated crystalline or glasslike structures.

  17. Melting transition in a two-dimensional complex plasma heated by driven acoustic instability

    SciTech Connect

    Sheridan, T. E.


    The melting transition in a two-dimensional complex (dusty) plasma is studied experimentally. A system consisting of {approx_equal}3900 microspheres is heated by amplitude modulating the rf discharge power with a square wave at the vertical resonance frequency. The vertical motion couples to an in-plane dust-acoustic instability at one-half the modulation frequency, thereby increasing the complex plasma's effective temperature. The 'thermodynamic' phase of the system is characterized for increasing levels of amplitude modulation at constant neutral pressure (35 mTorr Ar) and average rf power using the Lindemann ratio, defect density, bond-orientational correlation function, and pair correlation function. A melting transition showing evidence for an intermediate hexatic phase is observed.

  18. On the quantum mechanical theory of collisional recombination rates, II. Beyond the strong collision approximation

    SciTech Connect

    Miller, W.H.


    A quantum mechanical theory of collisional recombination (within the Lindemann mechanism, A + B {leftrightarrow} AB*, AB* + M {yields} AB + M) is presented which provides a proper quantum description of the A + B collision dynamics and treats the M + AB* inelastic scattering within the impact approximation (the quantum analog of a classical master equation treatment). The most rigorous version of the theory is similar in structure to the impact theory of spectral line broadening and involves generalized (4-index) rate constants for describing M + AB* collisions. A simplified version is also presented which involves only the normal (2-index) inelastic rate constants for M + AB* scattering but which also retains a proper quantum description of the A + B dynamics.

  19. Mode couplings and resonance instabilities in dust clusters.


    Qiao, Ke; Kong, Jie; Oeveren, Eric Van; Matthews, Lorin S; Hyde, Truell W


    The normal modes for three to seven particle two-dimensional (2D) dust clusters in a complex plasma are investigated using an N-body simulation. The ion wakefield downstream of each particle is shown to induce coupling between horizontal and vertical modes. The rules of mode coupling are investigated by classifying the mode eigenvectors employing the Bessel and trigonometric functions indexed by order integers (m, n). It is shown that coupling only occurs between two modes with the same m and that horizontal modes having a higher shear contribution exhibit weaker coupling. Three types of resonances are shown to occur when two coupled modes have the same frequency. Discrete instabilities caused by both the first and third type of resonances are verified and instabilities caused by the third type of resonance are found to induce melting. The melting procedure is observed to go through a two-step process with the solid-liquid transition closely obeying the Lindemann criterion.

  20. Premelting phenomena in pseudo-binary ionic crystals.


    Matsunaga, Shigeki


    The theory of the premelting phenomena in ionic crystals on the basis of the concept of the heterophase fluctuation has been applied to the pseudo-binary ionic crystals, KCl-NaCl, AgBr-AgCl and AgBr-CuBr systems. Molecular dynamics simulations (MD) have been performed to examine the ionic configurations in their premelting region in the vicinity of their melting points. Liquid-like clusters have been observed in the results of MD utilizing the Lindemann instability condition. The sizes of liquid-like clusters have been estimated by theory and MD. The characteristics of the dynamical behavior of ions in the premelting region have been examined by the mean square displacement and the velocity correlation functions.

  1. Thermodynamics of freezing and melting

    PubMed Central

    Pedersen, Ulf R.; Costigliola, Lorenzo; Bailey, Nicholas P.; Schrøder, Thomas B.; Dyre, Jeppe C.


    Although the freezing of liquids and melting of crystals are fundamental for many areas of the sciences, even simple properties like the temperature–pressure relation along the melting line cannot be predicted today. Here we present a theory in which properties of the coexisting crystal and liquid phases at a single thermodynamic state point provide the basis for calculating the pressure, density and entropy of fusion as functions of temperature along the melting line, as well as the variation along this line of the reduced crystalline vibrational mean-square displacement (the Lindemann ratio), and the liquid's diffusion constant and viscosity. The framework developed, which applies for the sizable class of systems characterized by hidden scale invariance, is validated by computer simulations of the standard 12-6 Lennard-Jones system. PMID:27530064

  2. The 2017 Eclipse: Centenary of the Einstein Light Deflection Experiment

    NASA Astrophysics Data System (ADS)

    Kennefick, Daniel


    August 21st, 2017 will see a total eclipse of the Sun visible in many parts of the United States. Coincidentally this date marks the centenary of the first observational attempt to test Einstein's General Theory of Relativity by measuring gravitational deflection of light by the Sun. This was attempted by the Kodaikanal Observatory in India during the conjunction of Regulus with the Sun in daylight on August 21st, 1917. The observation was attempted at the urging of the amateur German-British astronomer A. F. Lindemann, with his son, F. A. Lindemann, a well-known physicist, who later played a significant role as Churchill's science advisor during World War II. A century later Regulus will once again be in conjunction with the Sun, but by a remarkable coincidence, this will occur during a solar eclipse! Efforts will be made to measure the star deflection during the eclipse and the experiment is contrasted with the famous expeditions of 1919 which were the first to actually measure the light deflection, since the 1917 effort did not meet with success. Although in recent decades there have been efforts made to suggest that the 1919 eclipse team, led by Arthur Stanley Eddington and Sir Frank Watson Dyson, over-interpreted their results in favor of Einstein this talk will argue that such claims are wrong-headed. A close study of their data analysis reveals that they had good grounds for the decisions they made and this conclusion is reinforced by comparison with a modern re-analysis of the plates by the Greenwich Observatory conducted in 1977.

  3. North Vietnam’s Military Logistics System: Its Contribution to the War, 1961-1969

    DTIC Science & Technology


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  4. Aromatized arborane/fernane hydrocarbons as biomarkers for cordaites

    NASA Astrophysics Data System (ADS)

    Auras, Stefan; Wilde, Volker; Scheffler, Kay; Hoernes, Stephan; Kerp, Hans; Püttmann, Wilhelm


    Previous palaeobotanical and palynological studies on coals from Euramerican Pennsylvanian (≡ Late Carboniferous) coal basins indicate a major change in coal-swamp floras, especially at the Westphalian Stephanian (≈Kasimovian Gzhelian, according to Geological Time Scale 2004) boundary. A flora dominated by arborescent lycophytes was replaced by a vegetation dominated by marattialean tree ferns in various Euramerican coal basins. Earlier combined palynological and organic geochemical studies on Westphalian/Stephanian coals and shales from the Saar-Nahe Basin (Germany) revealed that the distribution of aromatized arborane/fernane hydrocarbons in solvent extracts reflects the increasing importance of seed plants, especially cordaites (extinct group of gymnosperms), conifers and pteridosperms. However, the biological source of the precursor molecules could not be specified. To clarify if the arborane/fernane derivatives MATH, MAPH, DAPH 1, and DAPH 2 in Westphalian/Stephanian coals can be assigned to one of the three potential source plant groups, we analyzed coals, sediments and fossil plant remains from different Euramerican locations with respect to their biomarker composition and stable carbon isotopic composition. Thereby, stable carbon isotopic ratios showed only insignificant variations between Westphalian and Stephanian samples and proved to be an unsuitable tool to describe floral changes during the Westphalian/Stephanian of the Saar-Nahe Basin. In contrast, we were able to show for the first time that MATH, MAPH, DAPH 1 and DAPH 2 are prominent constituents only in extracts of cordaitean macrofossils and can therefore be regarded as biomarkers for this group of gymnosperms.

  5. Simultaneous selection for yield-related traits and susceptibility to Fusarium head blight in spring wheat RIL population

    PubMed Central

    Wiśniewska, Halina; Surma, Maria; Krystkowiak, Karolina; Adamski, Tadeusz; Kuczyńska, Anetta; Ogrodowicz, Piotr; Mikołajczak, Krzysztof; Belter, Jolanta; Majka, Maciej; Kaczmarek, Zygmunt; Krajewski, Paweł; Sawikowska, Aneta; Lenc, Leszek; Baturo-Cieśniewska, Anna; Łukanowski, Aleksander; Góral, Tomasz; Sadowski, Czesław


    Fusarium head blight (FHB), caused by the fungal plant pathogen Fusarium, is a fungal disease that occurs in wheat and can cause significant yield and grain quality losses. The present paper examines variation in the resistance of spring wheat lines derived from a cross between Zebra and Saar cultivars. Experiments covering 198 lines and parental cultivars were conducted in three years, in which inoculation with Fusarium culmorum was applied. Resistance levels were estimated by scoring disease symptoms on kernels. In spite of a similar reaction of parents to F. culmorum infection, significant differentiation between lines was found in all the analyzed traits. Seven molecular markers selected as linked to FHB resistance QTLs gave polymorphic products for Zebra and Saar: Xgwm566, Xgwm46, Xgwm389, Xgwm533, Xgwm156, Xwmc238, and Xgwm341. Markers Xgwm389 and Xgwm533 were associated with the rate of Fusarium-damaged kernels (FDK) as well as with kernel weight per spike and thousand kernel weight in control plants. Zebra allele of marker Xwmc238 increased kernel weight per spike and thousand kernel weight both in control and infected plants, whereas Zebra allele of marker Xgwm566 reduced the percentage of FDK and simultaneously reduced the thousand kernel weight in control and infected plants. PMID:27162499

  6. Simultaneous selection for yield-related traits and susceptibility to Fusarium head blight in spring wheat RIL population.


    Wiśniewska, Halina; Surma, Maria; Krystkowiak, Karolina; Adamski, Tadeusz; Kuczyńska, Anetta; Ogrodowicz, Piotr; Mikołajczak, Krzysztof; Belter, Jolanta; Majka, Maciej; Kaczmarek, Zygmunt; Krajewski, Paweł; Sawikowska, Aneta; Lenc, Leszek; Baturo-Cieśniewska, Anna; Łukanowski, Aleksander; Góral, Tomasz; Sadowski, Czesław


    Fusarium head blight (FHB), caused by the fungal plant pathogen Fusarium, is a fungal disease that occurs in wheat and can cause significant yield and grain quality losses. The present paper examines variation in the resistance of spring wheat lines derived from a cross between Zebra and Saar cultivars. Experiments covering 198 lines and parental cultivars were conducted in three years, in which inoculation with Fusarium culmorum was applied. Resistance levels were estimated by scoring disease symptoms on kernels. In spite of a similar reaction of parents to F. culmorum infection, significant differentiation between lines was found in all the analyzed traits. Seven molecular markers selected as linked to FHB resistance QTLs gave polymorphic products for Zebra and Saar: Xgwm566, Xgwm46, Xgwm389, Xgwm533, Xgwm156, Xwmc238, and Xgwm341. Markers Xgwm389 and Xgwm533 were associated with the rate of Fusarium-damaged kernels (FDK) as well as with kernel weight per spike and thousand kernel weight in control plants. Zebra allele of marker Xwmc238 increased kernel weight per spike and thousand kernel weight both in control and infected plants, whereas Zebra allele of marker Xgwm566 reduced the percentage of FDK and simultaneously reduced the thousand kernel weight in control and infected plants.

  7. New measurements of photospheric magnetic fields in late-type stars and emerging trends

    NASA Technical Reports Server (NTRS)

    Saar, S. H.; Linsky, J. L.


    The magnetic fields of late-type stars are measured using the method of Saar et al. (1986). The method includes radiative transfer effects and compensation for line blending; the photospheric magnetic field parameters are derived by comparing observed and theoretical line profiles using an LTE code that includes line saturation and full Zeeman pattern. The preliminary mean active region magnetic field strengths (B) and surface area coverages for 20 stars are discussed. It is observed that there is a trend of increasing B towards the cooler dwarfs stars, and the linear correlation between B and the equipartition value of the magnetic field strength suggests that the photospheric gas pressure determines the photospheric magnetic field strengths. A tendency toward larger filling factors at larger stellar angular velocities is also detected.

  8. Colloidal polycrystalline monolayers under oscillatory shear

    NASA Astrophysics Data System (ADS)

    Buttinoni, Ivo; Steinacher, Mathias; Spanke, Hendrik Th.; Pokki, Juho; Bahmann, Severin; Nelson, Bradley; Foffi, Giuseppe; Isa, Lucio


    In this paper we probe the structural response to oscillatory shear deformations of polycrystalline monolayers of soft repulsive colloids with varying area fraction over a broad range of frequencies and amplitudes. The particles are confined at a fluid interface, sheared using a magnetic microdisk, and imaged through optical microscopy. The structural and mechanical response of soft materials is highly dependent on their microstructure. If crystals are well understood and deform through the creation and mobilization of specific defects, the situation is much more complex for disordered jammed materials, where identifying structural motifs defining plastically rearranging regions remains an elusive task. Our materials fall between these two classes and allow the identification of clear pathways for structural evolution. In particular, we demonstrate that large enough strains are able to fluidize the system, identifying critical strains that fulfill a local Lindemann criterion. Conversely, smaller strains lead to localized and erratic irreversible particle rearrangements due to the motion of structural defects. In this regime, oscillatory shear promotes defect annealing and leads to the growth of large crystalline domains. Numerical simulations help identify the population of rearranging particles with those exhibiting the largest deviatoric stresses and indicate that structural evolution proceeds towards the minimization of the stress stored in the system. The particles showing high deviatoric stresses are localized around grain boundaries and defects, providing a simple criterion to spot regions likely to rearrange plastically under oscillatory shear.

  9. Freezing and melting line invariants of the Lennard-Jones system.


    Costigliola, Lorenzo; Schrøder, Thomas B; Dyre, Jeppe C


    The invariance of several structural and dynamical properties of the Lennard-Jones (LJ) system along the freezing and melting lines is interpreted in terms of isomorph theory. First the freezing/melting lines of the LJ system are shown to be approximated by isomorphs. Then we show that the invariants observed along the freezing and melting isomorphs are also observed on other isomorphs in the liquid and crystalline phases. The structure is probed by the radial distribution function and the structure factor and dynamics are probed by the mean-square displacement, the intermediate scattering function, and the shear viscosity. Studying these properties with reference to isomorph theory explains why the known single-phase melting criteria hold, e.g., the Hansen-Verlet and the Lindemann criteria, and why the Andrade equation for the viscosity at freezing applies, e.g., for most liquid metals. Our conclusion is that these empirical rules and invariants can all be understood from isomorph theory and that the invariants are not peculiar to the freezing and melting lines, but hold along all isomorphs.

  10. Melting curves of metals by ab initio calculations

    NASA Astrophysics Data System (ADS)

    Minakov, Dmitry; Levashov, Pavel


    In this work we used several ab initio approaches to reproduce melting curves and discussed their abilities, advantages and drawbacks. We used quasiharmonic appoximation and Lindemann criterion to build melting curves in wide region of pressures. This approach allows to calculate the total free energy of electrons and phonons, so it is possible to obtain all thermodynamic properties in the crystalline state. We also used quantum molecular dynamics simulations to investigate melting at various pressures. We explored the size-effect of the heat until it melts (HUM) method in detail. Special attention was paid to resolve the boundaries of the melting region on density. All calculations were performed for aluminum, copper and gold. Results were in good agreement with available experimental data. Also we studied the influence of electronic temperature on melting curves. It turned out that the melting temperature increased with the rise of electron temperature at normal density and had non-monotonic behavior at higher densities. This work is supported by the Ministry of Education and Science of the Russian Federation (Project No. 3.522.2014/K).

  11. The initial stages of melting of graphene between 4000 K and 6000 K.


    Ganz, Eric; Ganz, Ariel B; Yang, Li-Ming; Dornfeld, Matthew


    Graphene and its analogues have some of the highest predicted melting points of any materials. Previous work estimated the melting temperature for freestanding graphene to be a remarkable 4510 K. However, this work relied on theoretical methods that do not accurately account for the role of bond breaking or complex bonding configurations in the melting process. Furthermore, experiments to verify these high melting points have been challenging. Practical applications of graphene and carbon nanotubes at high temperatures will require a detailed understanding of the behavior of these materials under these conditions. Therefore, we have used reliable ab initio molecular dynamics calculations to study the initial stages of melting of freestanding graphene monolayers between 4000 and 6000 K. To accommodate large defects, and for improved accuracy, we used a large 10 × 10 periodic unit cell. We find that the system can be heated up to 4500 K for 18 ps without melting, and 3-rings and short lived broken bonds (10-rings) are observed. At 4500 K, the system appears to be in a quasi-2D liquid state. At 5000 K, the system is starting to melt. During the 20 ps simulation, diffusion events are observed, leading to the creation of a 5775 defect. We calculate accurate excitation energies for these configurations, and the pair correlation function is presented. The modified Lindemann criterion was calculated. Graphene and nanotubes together with other proposed high melting point materials would be interesting candidates for experimental tests of melting in the weightless environment of space.

  12. Reconciling simulated melting and ground-state properties of metals with a modified embedded-atom method potential.


    Sushko, G B; Verkhovtsev, A V; Kexel, Ch; Korol, A V; Schramm, S; Solov'yov, A V


    We propose a modification of the embedded-atom method-type potential aiming at reconciling simulated melting and ground-state properties of metals by means of classical molecular dynamics. Considering titanium, magnesium, gold, and platinum as case studies, we demonstrate that simulations performed with the modified force field yield quantitatively correctly both the melting temperature of the metals and their ground-state properties. It is shown that the accounting for the long-range interatomic interactions noticeably affects the melting point assessment. The introduced modification weakens the interaction at interatomic distances exceeding the equilibrium one by a characteristic vibration amplitude defined by the Lindemann criterion, thus allowing for the correct simulation of melting, while keeping its behavior in the vicinity of the ground state minimum. The modification of the many-body potential has a general nature and can be applicable to metals with different characteristics of the electron structure as well as for many different molecular and solid state systems experiencing phase transitions.

  13. Effect of grain size on the melting point of confined thin aluminum films

    SciTech Connect

    Wejrzanowski, Tomasz; Lewandowska, Malgorzata; Sikorski, Krzysztof; Kurzydlowski, Krzysztof J.


    The melting of aluminum thin film was studied by a molecular dynamics (MD) simulation technique. The effect of the grain size and type of confinement was investigated for aluminum film with a constant thickness of 4 nm. The results show that coherent intercrystalline interface suppress the transition of solid aluminum into liquid, while free-surface gives melting point depression. The mechanism of melting of polycrystalline aluminum thin film was investigated. It was found that melting starts at grain boundaries and propagates to grain interiors. The melting point was calculated from the Lindemann index criterion, taking into account only atoms near to grain boundaries. This made it possible to extend melting point calculations to bigger grains, which require a long time (in the MD scale) to be fully molten. The results show that 4 nm thick film of aluminum melts at a temperature lower than the melting point of bulk aluminum (933 K) only when the grain size is reduced to 6 nm.

  14. "Burn catatonia": a case report and literature review.


    Quinn, Davin Kenneth


    Thermal injuries have been recognized to cause significant neuropsychiatric symptoms and disability in their sufferers since the middle of the 20th century, when Drs. Stanley Cobb and Erich Lindemann of the Massachusetts General Hospital (Boston, MA) studied survivors of the Cocoanut Grove nightclub fire in Boston. Although "burn encephalopathy" or burn-induced delirium is a common occurrence in the acute phase, catatonia in burn patients is not often reported. This report describes a case of malignant catatonia occurring in a 51-year-old male patient acutely suffering from burns acquired in a chemical explosion, effectively treated with reinstitution of a selective serotonin reuptake inhibitor. The literature on burn encephalopathy and catatonia in burns is reviewed. Few examples of burn catatonia exist. Burn encephalopathy is common, and may occur in patients with low TBSA burns such as described in the case above. Descriptions of burn encephalopathy are numerous, but have not included catatonia as a possible etiology. Catatonia in burn patients as an etiology of burn encephalopathy is likely underrecognized. Clinicians should be aware of the possibility of catatonia when a patient's confusional state after a burn does not respond to usual care.

  15. Universality of the onset of activated transport in Lennard-Jones liquids with tunable coordination: Implications for the effects of pressure and directional bonding on the crossover to activated transport, configurational entropy, and fragility of glassforming liquids

    NASA Astrophysics Data System (ADS)

    Rabochiy, Pyotr; Lubchenko, Vassiliy


    We establish, via classical density functional theory, that the crossover to activated transport in liquids takes place when the depth of the metastable minimum in the free energy corresponding to long-lived aperiodic structures reaches a certain near universal value. We show that the particle vibrational displacement is strongly correlated with this depth in a broad range of pressure and temperature, thus providing basis for a Lindemann-like criterion for the onset of activated transport in liquids. The configurational entropy at the crossover temperature Tcr, too, is found to be nearly system-independent, consistent with the random first order transition theory. We show that to reproduce existing data for the pressure dependence of Tcr, the liquid must increase its coordination with pressure. Upon increasing pressure at fixed coordination, the liquid's fragility is predicted to exhibit re-entrant behavior. This prediction is consistent with glycerol data but is in contrast with data in several organic liquids and polymers, whose fragility monotonically decreases with pressure in the so far accessed pressure range. Allowing for increase in coordination with pressure mitigates the disagreement, owing to the resulting decrease in the thermal expansivity. Finally, we rationalize the correlation between the isobaric and isochoric fragilities put forth by Casalini and Roland [Phys. Rev. E 72, 031503 (2005), 10.1103/PhysRevE.72.031503] and make predictions on the limiting behavior of the fragility at high pressure.

  16. First-principles modeling of quantum nuclear effects and atomic interactions in solid 4He at high pressure

    NASA Astrophysics Data System (ADS)

    Cazorla, Claudio; Boronat, Jordi


    We present a first-principles computational study of solid 4He at T =0 K and pressures up to ˜160 GPa. Our computational strategy consists in using van der Waals density functional theory (DFT-vdW) to describe the electronic degrees of freedom in this material, and the diffusion Monte Carlo (DMC) method to solve the Schrödinger equation describing the behavior of the quantum nuclei. For this, we construct an analytical interaction function based on the pairwise Aziz potential that closely matches the volume variation of the cohesive energy calculated with DFT-vdW in dense helium. Interestingly, we find that the kinetic energy of solid 4He does not increase appreciably with compression for P ≥85 GPa. Also, we show that the Lindemann ratio in dense solid 4He amounts to 0.10 almost independently of pressure. The reliability of customary quasiharmonic DFT (QH DFT) approaches in describing quantum nuclear effects in solids is also studied. We find that QH DFT simulations, although provide a reasonable equation of state in agreement with experiments, are not able to reproduce correctly these critical effects in compressed 4He. In particular, we disclose huge discrepancies of at least ˜50 % in the calculated 4He kinetic energies using both the QH DFT and present DFT-DMC methods.

  17. Mirror of light

    NASA Astrophysics Data System (ADS)

    Ohlmann, Dietmar


    The making of holograms is better understood than their uses. As an artist who studied holography in Liverpool and at the Royal College of Art in London in the fine art section, I like to use this media in a quite unusual way avoiding the well-worn cliches of Laser-Light-Kitchen- Object-Table-Top-Photography and all these horrible, greenish, blinking plastics. After seeing a master and being introduced to its potential and being inspired by artists such as Rod Murray, Rick Silverman, Margaret Benyon, and Peter Miller I used to spend more time in the Laser- Laboratory than in my painting studio. However, this is no longer true. I have been working on the Millennium-Project since 1996. The project is the idea of Werner Lindemann who is creating a gigantic Amphitheater. On this site, I have the opportunity to meet all sorts of artists and craftsmen, such as opera singers, ceramics designers and architects, to whom I introduced several different large scale projects. Forced to work out installations of a minimum 20 square meters in dimension, I have developed what I call the None- Hologram.

  18. Instability of coherent states of a real scalar field

    SciTech Connect

    Koutvitsky, Vladimir A.; Maslov, Eugene M.


    We investigate stability of both localized time-periodic coherent states (pulsons) and uniformly distributed coherent states (oscillating condensate) of a real scalar field satisfying the Klein-Gordon equation with a logarithmic nonlinearity. The linear analysis of time-dependent parts of perturbations leads to the Hill equation with a singular coefficient. To evaluate the characteristic exponent we extend the Lindemann-Stieltjes method, usually applied to the Mathieu and Lame equations, to the case that the periodic coefficient in the general Hill equation is an unbounded function of time. As a result, we derive the formula for the characteristic exponent and calculate the stability-instability chart. Then we analyze the spatial structure of the perturbations. Using these results we show that the pulsons of any amplitudes, remaining well-localized objects, lose their coherence with time. This means that, strictly speaking, all pulsons of the model considered are unstable. Nevertheless, for the nodeless pulsons the rate of the coherence breaking in narrow ranges of amplitudes is found to be very small, so that such pulsons can be long-lived. Further, we use the obtained stability-instability chart to examine the Affleck-Dine-type condensate. We conclude the oscillating condensate can decay into an ensemble of the nodeless pulsons.

  19. Predicting pressure-dependent unimolecular rate constants using variational transition state theory with multidimensional tunneling combined with system-specific quantum RRK theory: a definitive test for fluoroform dissociation.


    Bao, Junwei Lucas; Zhang, Xin; Truhlar, Donald G


    Understanding the falloff in rate constants of gas-phase unimolecular reaction rate constants as the pressure is lowered is a fundamental problem in chemical kinetics, with practical importance for combustion, atmospheric chemistry, and essentially all gas-phase reaction mechanisms. In the present work, we use our recently developed system-specific quantum RRK theory, calibrated by canonical variational transition state theory with small-curvature tunneling, combined with the Lindemann-Hinshelwood mechanism, to model the dissociation reaction of fluoroform (CHF3), which provides a definitive test for falloff modeling. Our predicted pressure-dependent thermal rate constants are in excellent agreement with experimental values over a wide range of pressures and temperatures. The present validation of our methodology, which is able to include variational transition state effects, multidimensional tunneling based on the directly calculated potential energy surface along the tunneling path, and torsional and other vibrational anharmonicity, together with state-of-the-art reaction-path-based direct dynamics calculations, is important because the method is less empirical than models routinely used for generating full mechanisms, while also being simpler in key respects than full master equation treatments and the full reduced falloff curve and modified strong collision methods of Troe.

  20. A new Monte Carlo method for getting the density of states of atomic cluster systems.


    Soudan, J-M; Basire, M; Mestdagh, J-M; Angelié, C


    A novel Monte Carlo flat histogram algorithm is proposed to get the classical density of states in terms of the potential energy, g(E(p)), for systems with continuous variables such as atomic clusters. It aims at avoiding the long iterative process of the Wang-Landau method and controlling carefully the convergence, but keeping the ability to overcome energy barriers. Our algorithm is based on a preliminary mapping in a series of points (called a σ-mapping), obtained by a two-parameter local probing of g(E(p)), and it converges in only two subsequent reweighting iterations on large intervals. The method is illustrated on the model system of a 432 atom cluster bound by a Rydberg type potential. Convergence properties are first examined in detail, particularly in the phase transition zone. We get g(E(p)) varying by a factor 10(3700) over the energy range [0.01 < E(p) < 6000 eV], covered by only eight overlapping intervals. Canonical quantities are derived, such as the internal energy U(T) and the heat capacity C(V)(T). This reveals the solid to liquid phase transition, lying in our conditions at the triple point. This phase transition is further studied by computing a Lindemann-Berry index, the atomic cluster density n(r), and the pressure, demonstrating the progressive surface melting at this triple point. Some limited results are also given for 1224 and 4044 atom clusters.

  1. Fostering Nurses' Moral Agency and Moral Identity: The Importance of Moral Community.


    Liaschenko, Joan; Peter, Elizabeth


    It may be the case that the most challenging moral problem of the twenty-first century will be the relationship between the individual moral agent and the practices and institutions in which the moral agent is embedded. In this paper, we continue the efforts that one of us, Joan Liaschenko, first called for in 1993, that of using feminist ethics as a lens for viewing the relationship between individual nurses as moral agents and the highly complex institutions in which they do the work of nursing. Feminist ethics, with its emphasis on the inextricable relationship between ethics and politics, provides a useful lens to understand the work of nurses in context. Using Margaret Urban Walker's and Hilde Lindemann's concepts of identity, relationships, values, and moral agency, we argue that health care institutions can be moral communities and profoundly affect the work and identity and, therefore, the moral agency of all who work within those structures, including nurses. Nurses are not only shaped by these organizations but also have the power to shape them. Because moral agency is intimately connected to one's identity, moral identity work is essential for nurses to exercise their moral agency and to foster moral community in health care organizations. We first provide a brief history of nursing's morally problematic relationship with institutions and examine the impact institutional master narratives and corporatism exert today on nurses' moral identities and agency. We close by emphasizing the significance of ongoing dialogue in creating and sustaining moral communities, repairing moral identities, and strengthening moral agency.

  2. Mermin–Wagner fluctuations in 2D amorphous solids

    PubMed Central

    Illing, Bernd; Fritschi, Sebastian; Kaiser, Herbert; Klix, Christian L.; Maret, Georg; Keim, Peter


    In a recent commentary, J. M. Kosterlitz described how D. Thouless and he got motivated to investigate melting and suprafluidity in two dimensions [Kosterlitz JM (2016) J Phys Condens Matter 28:481001]. It was due to the lack of broken translational symmetry in two dimensions—doubting the existence of 2D crystals—and the first computer simulations foretelling 2D crystals (at least in tiny systems). The lack of broken symmetries proposed by D. Mermin and H. Wagner is caused by long wavelength density fluctuations. Those fluctuations do not only have structural impact, but additionally a dynamical one: They cause the Lindemann criterion to fail in 2D in the sense that the mean squared displacement of atoms is not limited. Comparing experimental data from 3D and 2D amorphous solids with 2D crystals, we disentangle Mermin–Wagner fluctuations from glassy structural relaxations. Furthermore, we demonstrate with computer simulations the logarithmic increase of displacements with system size: Periodicity is not a requirement for Mermin–Wagner fluctuations, which conserve the homogeneity of space on long scales. PMID:28137872

  3. Sources of errors in different single-electrode voltage-clamp techniques: a computer simulation study.


    Sala, F; Sala, S


    The use of voltage clamp with a single electrode has been useful in estimating kinetic parameters for a number of ionic whole-cell currents. There are two main types of such a technique: discontinuous voltage clamp (dSEVC) (Brennecke and Lindemann, 1974), and continuous voltage clamp (cSEVC) (Hamill et al., 1981). We have studied, by means of computer simulations, the performance of both types of clamp on estimating activation kinetics parameters of a typical neuronal Ca2+ current. Deviations from the theoretical values are shown to be sensitive on both set-up and cell properties. Both types of clamp are shown to lose voltage control when either access resistance or absolute membrane conductance are increased. In contrast, changes in membrane capacitance affect differently to the estimates obtained by the two types of clamp. Cell size is also shown to affect cSEVC performance but not that of dSEVC. The nature and magnitude of errors obtained by using both types of clamp in different situations are discussed.

  4. Theory of activated dynamics and glass transition of hard colloids in two dimensions.


    Zhang, Bo-kai; Li, Hui-shu; Tian, Wen-de; Chen, Kang; Ma, Yu-qiang


    The microscopic nonlinear Langevin equation theory is applied to study the localization and activated hopping of two-dimensional hard disks in the deeply supercooled and glass states. Quantitative comparisons of dynamic characteristic length scales, barrier, and their dependence on the reduced packing fraction are presented between hard-disk and hard-sphere suspensions. The dynamic barrier of hard disks emerges at higher absolute and reduced packing fractions and correspondingly, the crossover size of the dynamic cage which correlates to the Lindemann length for melting is smaller. The localization lengths of both hard disks and spheres decrease exponentially with packing fraction. Larger localization length of hard disks than that of hard spheres is found at the same reduced packing fraction. The relaxation time of hard disks rises dramatically above the reduced packing fraction of 0.88, which leads to lower reduced packing fraction at the kinetic glass transition than that of hard spheres. The present work provides a foundation for the subsequent study of the glass transition of binary or polydisperse mixtures of hard disks, normally adopted in experiments and simulations to avoid crystallization, and further, the rheology and mechanical response of the two-dimensional glassy colloidal systems.

  5. Skyrmion Flux Lattices in p,-wave Superconductors

    NASA Astrophysics Data System (ADS)

    Li, Qi; Toner, John; Belitz, Dietrich


    In p,-wave superconductors, topological excitations known as skyrmions are allowed, in addition to the usual vortices. In strongly type-II materials in an external magnetic field, a skyrmion flux lattice is expected to be energetically favored compared to a vortex flux lattice [1]. We analytically calculate the energy, magnetization curves (B(H)), and elasticity of skyrmion flux lattices in p,-wave superconductors near the lower critical field Hc1, and use these results with the Lindemann criterion to predict their melting curve [2]. In striking contrast to vortex flux lattices, which always melt at an external field H > Hc1, skyrmion flux lattices never melt near Hc1. This provides a simple and unambiguous test for the presence of skyrmions. In addition, the internal magnetic field distributions (which are measurable by muon spin rotation techniques [3]) of skyrmion and vortex lattices are very different. [1] A. Knigavko, B. Rosenstein, and Y.F. Chen, Phys. Rev. B 60, 550 (1999). [2] Qi Li, John Toner, and D. Belitz, cond-mat/0607391 [3] J.E. Sonier, J. Phys. Cond. Matt. 16, S4499 (2004)

  6. Solid-liquid equilibria and triple points of n-6 Lennard-Jones fluids

    NASA Astrophysics Data System (ADS)

    Ahmed, Alauddin; Sadus, Richard J.


    Molecular dynamics simulations are reported for the solid-liquid coexistence properties of n-6 Lennard-Jones fluids, where n =12, 11, 10, 9, 8, and 7. The complete phase behavior for these systems has been obtained by combining these data with vapor-liquid simulations. The influence of n on the solid-liquid coexistence region is compared using relative density difference and miscibility gap calculations. Analytical expressions for the coexistence pressure, liquid, and solid densities as a function of temperature have been determined, which accurately reproduce the molecular simulation data. The triple point temperature, pressure, and liquid and solid densities are estimated. The triple point temperature and pressure scale with respect to 1/n, resulting in simple linear relationships that can be used to determine the pressure and temperature for the limiting ∞-6 Lennard-Jones potential. The simulation data are used to obtain parameters for the Raveché, Mountain, and Streett and Lindemann melting rules, which indicate that they are obeyed by the n-6 Lennard Jones potentials. In contrast, it is demonstrated that the Hansen-Verlet freezing rule is not valid for n-6 Lennard-Jones potentials.

  7. Composition-dependent melting behaviour of NaxK55-x core-shell nanoalloys

    NASA Astrophysics Data System (ADS)

    Asgari, Mehdi; Behnejad, Hassan; Fortunelli, Alessandro


    Molecular dynamics simulations at constant temperature are performed to investigate melting-like transition in Na13K42, Na19K36 and Na26K29 nanoalloys using a second-moment-approximation tight-binding analytic potential to calculate the forces on the constituent atoms. A weighted histogram analysis method is employed to remove non-ergodicity issues due to the complex potential energy surface of these nanoalloys. The heat capacity shows three distinctive steps in melting for Na13K42, while Na26K29 and Na19K36 have two-step and one-step melting transition, respectively. The steepest descent method is used to quench the configurations in a given interval during the simulation and also study the isomerisation processes occurring at different temperatures. Analysing the configuration energies of quenched structures for the entire nanoalloy and the core atoms separately gives more details about the melting mechanism. The Lindemann parameter is also calculated at several temperatures during the simulation which shows a gradual increase for Na13K42 and Na26K29 while a sharp change is observed for Na19K36. These findings are in agreement with the multi-step nature of the phase transition in Na13K42 and Na26K29 and one-step melting of the Na19K36 magic composition.

  8. Defects and order in liquid crystal phases

    NASA Astrophysics Data System (ADS)

    Jain, Shilpa

    This thesis investigates the partial destruction of ordering in liquid crystalline systems due to the influence of defects and thermal fluctuations. The systems under consideration are hexagonal columnar crystals with crystalline order perpendicular to the columns, and two-dimensional smectics with order perpendicular to the layers. We first study the possibility of reentrant melting of a hexagonal columnar crystal of flexible charged polymers at high enough densities. The Lindemann criterion is employed in determining the melting point. Lattice fluctuations are calculated in the Debye model, and an analogy with the Abrikosov vortex lattice in superconductors is exploited in estimating both the elastic constants of the hexagonal lattice, and the appropriate Lindemann constant. We also discuss the unusual functional integral describing the statistical mechanics of a single polymer in an Einstein cage model using the path-integral formulation. A crossover as a function of an external field along the column axis is discussed as well. Next, we study defects in a columnar crystal in the form of vacancy/interstitial loops or strings of vacancies and interstitials bounded by column "heads" and "tails". These defect strings are oriented by the columnar lattice and can change size and shape by movement of the ends and forming kinks along the length. Hence an analysis in terms of directed living polymers is appropriate to study their size and shape distribution, volume fraction, etc. If the entropy of transverse fluctuations overcomes the string line tension in the crystalline phase, a string proliferation transition occurs, leading to a "supersolid" phase with infinitely long vacancy or interstitial strings. We estimate the wandering entropy and examine the behaviour in the transition regime. We also calculate numerically the line tension of various species of vacancies and interstitials in a triangular lattice for power-law potentials as well as for a modified Bessel

  9. Re-entrant cholesteric phase in DNA liquid-crystalline dispersion particles.


    Yevdokimov, Yuri M; Skuridin, Sergey G; Semenov, Sergey V; Dadinova, Ljubov A; Salyanov, Viktor I; Kats, Efim I


    In this research, we observe and rationalize theoretically the transition from hexagonal to cholesteric packing of double-stranded (ds) DNA in dispersion particles. The samples were obtained by phase exclusion of linear ds DNA molecules from water-salt solutions of poly(ethylene glycol)-PEG-with concentrations ranging from 120 mg ml(-1) to 300 mg ml(-1). In the range of PEG concentrations from 120 mg ml(-1) to 220 mg ml(-1) at room temperature, we find ds DNA molecule packing, typical of classical cholesterics. The corresponding parameters for dispersion particles obtained at concentrations greater than 220 mg ml(-1) indicate hexagonal packing of the ds DNA molecules. However, slightly counter-intuitively, the cholesteric-like packing reappears upon the heating of dispersions with hexagonal packing of ds DNA molecules. This transition occurs when the PEG concentration is larger than 220 mg ml(-1). The obtained new cholesteric structure differs from the classical cholesterics observed in the PEG concentration range 120-220 mg ml(-1) (hence, the term 're-entrant'). Our conclusions are based on the measurements of circular dichroism spectra, X-ray scattering curves and textures of liquid-crystalline phases. We propose a qualitative (similar to the Lindemann criterion for melting of conventional crystals) explanation of this phenomenon in terms of partial melting of so-called quasinematic layers formed by the DNA molecules. The quasinematic layers change their spatial orientation as a result of the competition between the osmotic pressure of the solvent (favoring dense, unidirectional alignment of ds DNA molecules) and twist Frank orientation energy of adjacent layers (favoring cholesteric-like molecular packing).

  10. From D. Schröder: Reply on ``Chapman and Alvén: A Rigorous Mathematical Physicist Versus an Inspirational Experimental Physicist''

    NASA Astrophysics Data System (ADS)

    Schröder, Wilfried

    I read the recent article by S. -I. Akasofu ( Eos, 22 July, p. 269) with great interest because many years ago I had a discussion with Thomas George Cowling and Hannes Alfvén on the same subject. Sydney Chapman's style was very different than that of Kristian Birkeland. At the beginning of his career, Chapman published short notes on problems of geomagnetic variations and on other topics. In 1918, he commenced work on magnetic storms and, in spite of his reference to Birkeland's work, he does not seem to have been unduly influenced by it. This is connected with their different attitudes. Chapman was a mathematician and only returned to a mathematical approximation when it seemed unavoidable to him. Thus, Birkeland was more interested in the details of geophysical phenomenon, whereas Chapman sought to present a general solution. Chapman and his research student, Vincenzo Ferraro, in about 1930/1933 developed an interpretation of the initial phase of magnetic storm. For both of them, the space around the Earth played an important role, where the interplanetary plasma is compelled by the geomagnetic field to co-rotate with the Earth. Following F. A. Lindemann's ideas, they started from the premise that the cloud of particles consisted of an externally neutral plasma, containing electrons and protons of a magnetic storm, or electrons and protons intended for the accompanying auroras In the 1950s, Ferraro described the situation as follows: ``Our first ideas about ring current, unlike those relating to the main phase, were not based on hydrodynamic concepts, and our theory of the main phase is generally considered unacceptable.''

  11. Are the local adjustments of the relative spatial frequencies of the dynein arms and the beta-tubulin monomers involved in the regulation of the "9+2" axoneme?


    Cibert, Christian


    The "9+2" axoneme is a highly specific cylindrical machine whose periodic bending is due to the cumulative shear of its 9 outer doublets of microtubules. Because of the discrete architecture of the tubulin monomers and the active appendices that the outer doublets carry (dynein arms, nexin links and radial spokes), this movement corresponds to the relative shear of these topological verniers, whose characteristics depend on the geometry of the wave train. When an axonemal segment bends, this induces the compressed and dilated conformations of the tubulin monomers and, consequently, the modification of the spatial frequencies of the appendages that the outer doublets carry. From a dynamic point of view, the adjustments of the spatial frequencies of the elements of the two facing verniers that must interact create different longitudinal periodic patterns of distribution of the joint probability of the molecular interaction as a function of the location of the doublet pairs around the axonemal cylinder and their spatial orientation within the axonemal cylinder. During the shear, these patterns move along the outer doublet intervals at a speed that ranges from one to more than a thousand times that of sliding, in two opposite directions along the two opposite halves of the axoneme separated by the bending plane, respecting the polarity of the dynein arms within the axoneme. Consequently, these waves might be involved in the regulation of the alternating activity of the dynein arms along the flagellum, because they induce the necessary intermolecular dialog along the axoneme since they could be an element of the local dynamic stability/instability equilibrium of the axoneme. This complements the geometric clutch model [Lindemann, C., 1994. A "geometric clutch" hypothesis to explain oscillations of the axoneme of cilia and flagella. J. Theor. Biol. 168, 175-189].

  12. Mechanisms for pressure- and time-dependent amorphization of ice under pressure

    NASA Astrophysics Data System (ADS)

    Johari, G. P.; Andersson, Ove


    Amorphization of hexagonal ice under pressure at low temperatures has been studied by measuring the thermal conductivity with time, by keeping the ice in the temperature range 127-130K and pressure range 0.79-0.88GPa . The results have been used to examine the relative merits of the Lindemann melting and the Born instability as a mechanism for amorphization of ice. Thermal conductivity decreases continuously with time according to a stretched-exponential relation. This and the findings that, (i) amorphization pressure is lower than the available values calculated for an ideal ice crystal by using the Born theory, and (ii) amorphization of cubic ice occurs at about the same pressure as that of hexagonal ice, seem inconsistent with both mechanisms. The findings can be reconciled with the Born mechanism if the effect of the existing lattice faults and/or the lattice faults produced during the plastic deformation of uniaxially compressed ice are considered to produce a distribution of collapse pressure. It is argued that the difference between the amorphization and the low-density amorph to high-density amorph transformation pressures corresponds to the energy needed to collapse, or randomly distort, the ice crystallites to a structure whose energy spontaneously decreases by diffusion of a H2O molecule into the first coordination shell of the amorph’s known structure, and persist there as an interstitial molecule. The newly observed amorphization kinetics has a bearing on the computer-simulated inference on pressure-induced collapse and/or melting of crystals.

  13. Thermal annealing of SiC nanoparticles induces SWNT nucleation: evidence for a catalyst-independent VSS mechanism.


    Page, Alister J; Chandrakumar, K R S; Irle, Stephan; Morokuma, Keiji


    Density-functional tight-binding molecular dynamics (DFTB/MD) methods were employed to demonstrate single-walled carbon nanotube (SWNT) nucleation resulting from thermal annealing of SiC nanoparticles. SWNT nucleation in this case is preceded by a change of the SiC structure from a crystalline one, to one in which silicon and carbon are segregated. This structural transformation ultimately resulted in the formation of extended polyyne chains on the SiC nanoparticle surface. These polyyne chains subsequently coalesced, forming an extended sp(2)-hybridized carbon cap on the SiC nanoparticle. The kinetics of this process were enhanced significantly at higher temperatures (2500 K), compared to lower temperatures (1200 K) and so directly correlated to the surface premelting behavior of the nanoparticle structure. Analysis of the SiC nanoparticle Lindemann index between 1000 and 3000 K indicated that SWNT nucleation at temperatures below 2600 K occurred in the solid, or quasi-solid, phase. Thus, the traditional vapor-liquid-solid mechanism of SWNT growth does not apply in the case of SiC nanoparticles. Instead, we propose that this example of SWNT nucleation constitutes evidence of a vapor-solid-solid process. This conclusion complements our recent observations regarding SWNT nucleation on SiO(2) nanoparticles (A. J. Page, K. R. S. Chandrakumar, S. Irle and K. Morokuma, J. Am. Chem. Soc., 2011, 133, 621-628). In addition, similarities between the atomistic SWNT nucleation mechanisms on SiC and SiO(2) catalysts provide the first evidence of a catalyst-independent SWNT nucleation mechanism with respect to 'non-traditional' SWNT catalyst species.

  14. Dimethyl ether oxidation at elevated temperatures (295-600 K).


    Rosado-Reyes, Claudette M; Francisco, Joseph S; Szente, Joseph J; Maricq, M Matti; Frøsig Østergaard, Lars


    Dimethyl ether (DME) has been proposed for use as an alternative fuel or additive in diesel engines and as a potential fuel in solid oxide fuel cells. The oxidation chemistry of DME is a key element in understanding its role in these applications. The reaction between methoxymethyl radicals and O(2) has been examined over the temperature range 295-600 K and at pressures of 20-200 Torr. This reaction has two product pathways. The first produces methoxymethyl peroxy radicals, while the second produces OH radicals and formaldehyde molecules. Real-time kinetic measurements are made by transient infrared spectroscopy to monitor the yield of three main products-formaldehyde, methyl formate, and formic acid-to determine the branching ratio for the CH(3)OCH(2) + O(2) reaction pathways. The temperature and pressure dependence of this reaction is described by a Lindemann and Arrhenius mechanism. The branching ratio is described by f = 1/(1 + A(T)[M]), where A(T) = (1.6(+2.4)(-1.0) x 10(-20)) exp((1800 +/- 400)/T) cm(3) molecule(-1). The temperature dependent rate constant of the methoxymethyl peroxy radical self-reaction is calculated from the kinetics of the formaldehyde and methyl formate product yields, k(4) = (3.0 +/- 2.1) x 10(-13) exp((700 +/- 250)/T) cm(3) molecule(-1) s(-1). The experimental and kinetics modeling results support a strong preference for the thermal decomposition of alkoxy radicals versus their reaction with O(2) under our laboratory conditions. These characteristics of DME oxidation with respect to temperature and pressure might provide insight into optimizing solid oxide fuel cell operating conditions with DME in the presence of O(2) to maximize power outputs.

  15. A new and effective method for thermostatting confined fluids

    SciTech Connect

    De Luca, Sergio; Todd, B. D.; Hansen, J. S.; Daivis, Peter J.


    We present a simple thermostatting method suitable for nanoconfined fluid systems. Two conventional strategies involve thermostatting the fluid directly or employing a thermal wall that couples only the wall atoms with the thermostat. When only a thermal wall is implemented, the temperature control of the fluid is true to the actual experiment and the heat is transferred from the fluid to the walls. However, for large or complex systems it can often be computationally prohibitive to employ thermal walls. To overcome this limitation many researchers choose to freeze wall atoms and instead apply a synthetic thermostat to the fluid directly through the equations of motion. This, however, can have serious consequences for the mechanical, thermodynamic, and dynamical properties of the fluid by introducing unphysical behaviour into the system [Bernardi et al., J. Chem. Phys. 132, 244706 (2010)]. In this paper, we propose a simple scheme which enables working with both frozen walls and naturally thermostatted liquids. This is done by superimposing the walls with oscillating particles, which vibrate on the edge of the fluid control volume. These particles exchange energy with the fluid molecules, but do not interact with wall atoms or each other, thus behaving as virtual particles. Their displacements violate the Lindemann criterion for melting, in such a way that the net effect would not amount to an additional confining surface. One advantage over standard techniques is the reduced computational cost, particularly for large walls, since they can be kept rigid. Another advantage over accepted strategies is the opportunity to freeze complex charged walls such as β-cristobalite. The method furthermore overcomes the problem with polar fluids such as water, as thermalized charged surfaces require higher spring constants to preserve structural stability, due to the effects of strong Coulomb interactions, thus inevitably degrading the thermostatting efficiency.

  16. String-like collective atomic motion in the melting and freezing of nanoparticles.


    Zhang, Hao; Kalvapalle, Pranav; Douglas, Jack F


    The melting of a solid represents a transition between a solid state in which atoms are localized about fixed average crystal lattice positions to a fluid state that is characterized by relative atomic disorder and particle mobility so that the atoms wander around the material as a whole, impelled by the random thermal impulses of surrounding atoms. Despite the fundamental nature and practical importance of this particle delocalization transition, there is still no fundamental theory of melting and instead one often relies on the semi-phenomenological Lindemann-Gilvarry criterion to estimate roughly the melting point as an instability of the crystal lattice. Even the earliest simulations of melting in hexagonally packed hard discs by Alder and Wainwright indicated the active role of nonlocal collective atomic motions in the melting process, and here we utilize molecular dynamics (MD) simulation to determine whether the collective particle motion observed in melting has a similar geometrical form as those in recent studies of nanoparticle (NP) interfacial dynamics and the molecular dynamics of metastable glass-forming liquids. We indeed find string-like collective atomic motion in NP melting that is remarkably similar in form to the collective interfacial motions in NPs at equilibrium and to the collective motions found in the molecular dynamics of glass-forming liquids. We also find that the spatial localization and extent of string-like motion in the course of NP melting and freezing evolves with time in distinct ways. Specifically, the collective atomic motion propagates from the NP surface and from within the NP in melting and freezing, respectively, and the average string length varies smoothly with time during melting. In contrast, the string-like cooperative motion peaks in an intermediate stage of the freezing process, reflecting a general asymmetry in the dynamics of NP superheating and supercooling.

  17. The Earth's Core and the Phase Diagram of Iron

    NASA Astrophysics Data System (ADS)

    Anderson, O. L.


    The phase diagram of iron is presented for P <= 330 GPa. The melting curve is derived from Stevenson's generalized form of Lindemann's law, successfully connecting the low-pressure (5-20 GPa) measurements to the new shock-wave measurements of 250 GPa. The isothermal equation of state of ɛ -iron (h.c.p.) and γ -iron (f.c.c.), indicate that the inner core density is that of pure solid iron. The present experiments cannot distinguish between the ɛ or γ phase for the inner core, but preference is given to γ -iron. From these constructions, it is concluded that the melting temperature of iron at the inner core - outer core boundary pressure, Tmi (i.c.b.), is 5200-6600 K. A likely model of the outer core temperature is presented by taking 5800 K as the probable value of Tmi (i.c.b.), and assuming a temperature drop of 1000 K due to chemically induced melting point depression. This yields 3620 K for the T of the core side of the core-mantle boundary (c.m.b.). This model results in a large Δ T (D' '), (700 K), at the c.m.b., but the shock-wave data also allow other models where Δ T (D' ') is less. A numerical experiment reveals that the value for Δ T (D' ') of 700 K does not lead to distortion of the density profile. The (γ -ɛ -liquid) triple point is beyond the i.c.b. Thus, diluted γ -iron in the liquid phase constitutes the outer core. The experiments support a thermally driven model of the geomagnetic dynamo, and further support a model of a slowly freezing inner core for the energy source.

  18. A new and effective method for thermostatting confined fluids

    NASA Astrophysics Data System (ADS)

    De Luca, Sergio; Todd, B. D.; Hansen, J. S.; Daivis, Peter J.


    We present a simple thermostatting method suitable for nanoconfined fluid systems. Two conventional strategies involve thermostatting the fluid directly or employing a thermal wall that couples only the wall atoms with the thermostat. When only a thermal wall is implemented, the temperature control of the fluid is true to the actual experiment and the heat is transferred from the fluid to the walls. However, for large or complex systems it can often be computationally prohibitive to employ thermal walls. To overcome this limitation many researchers choose to freeze wall atoms and instead apply a synthetic thermostat to the fluid directly through the equations of motion. This, however, can have serious consequences for the mechanical, thermodynamic, and dynamical properties of the fluid by introducing unphysical behaviour into the system [Bernardi et al., J. Chem. Phys. 132, 244706 (2010)]. In this paper, we propose a simple scheme which enables working with both frozen walls and naturally thermostatted liquids. This is done by superimposing the walls with oscillating particles, which vibrate on the edge of the fluid control volume. These particles exchange energy with the fluid molecules, but do not interact with wall atoms or each other, thus behaving as virtual particles. Their displacements violate the Lindemann criterion for melting, in such a way that the net effect would not amount to an additional confining surface. One advantage over standard techniques is the reduced computational cost, particularly for large walls, since they can be kept rigid. Another advantage over accepted strategies is the opportunity to freeze complex charged walls such as β-cristobalite. The method furthermore overcomes the problem with polar fluids such as water, as thermalized charged surfaces require higher spring constants to preserve structural stability, due to the effects of strong Coulomb interactions, thus inevitably degrading the thermostatting efficiency.

  19. High-Pressure Studies on Iron Analogs with Application to Planetary Cores

    NASA Astrophysics Data System (ADS)

    Godwal, B. K.; Raju, S.; Geballe, Z.; Jeanloz, R.


    The properties of hexagonal close-packed (hcp) metals at high pressures are of geophysical interest because hcp Fe is likely to be the primary constituent of Earth's inner core. Zinc and cadmium crystallize in a distorted hcp structure, and undergo electronic topological transitions at high pressures manifested through anomalous values of the c/a crystal-axis ratio, compressibility and electron transport properties. There is renewed interest in such electronic transitions due to their recent association with anomalies in c/a, Debye velocity and Mössbauer center shift in Fe and Fe-Ni alloy near 40 GPa. Past high-pressure studies have shown that the c/a anomaly is larger in Cd as compared to Zn. Nonhydrostatic measurements on Cd reveal texture development, which is used in identifying deformation mechanisms in Os and Fe. Angular x-ray diffraction measurements in a resistively heated diamond-anvil cell, with argon as pressure medium, were carried out on Cd up to 25 GPa at room temperature. We minimized nonhydrostatic conditions by thermally annealing the sample at each pressure by heating it to 100° C, which resulted in sharpening of diffraction peaks. Variations of c/a with pressure revealed anomalies near 2, 7, 15 and 22 GPa, with corresponding anomalies in compression at similar pressures. We associate these anomalies with electronic topological transitions, based on results of first-principles electronic structure calculations at high pressures. Our data are in good agreement with independent measurements using helium as a pressure medium, so the anomalies cannot be ascribed to nonhydrostaticity. Also, in-situ x-ray powder-diffraction shows that the melting curve of Cd deviates from the Lindemann law above 1 GPa, consistent with the occurrence of electronic transitions.

  20. Crystalline free energies of micelles of diblock copolymer solutions.


    D'Adamo, Giuseppe; Pierleoni, Carlo


    We report a characterization of the relative stability and structural behavior of various micellar crystals of an athermal model of AB-diblock copolymers in solution. We adopt a previously developed coarse-graining representation of the chains which maps each copolymer on a soft dumbbell. Thanks to this strong reduction of degrees of freedom, we are able to investigate large aggregated systems and for a specific length ratio of the blocks f = M(A)∕(M(A) + M(B)) = 0.6, to locate the order-disorder transition of the system of micelles. Above the transition, mechanical and thermal properties are found to depend on the number of particles per lattice site in the simulation box, and the application of a recent methodology for multiple occupancy crystals [B. M. Mladek et al., Phys. Rev. Lett. 99, 235702 (2007)] is necessary to correctly define the equilibrium state. Within this scheme we have performed free energy calculations at two reduced density ρ∕ρ∗ = 4, 5 and for several cubic structures such as fcc, bcc, and A15. At both densities, the bcc symmetry is found to correspond to the minimum of the unconstrained free energy, that is to the stable symmetry among the few considered, while the A15 structure is almost degenerate, indicating that the present system prefers to crystallize in less packed structures. At ρ∕ρ∗ = 4 close to melting, the Lindemann ratio is fairly high (∼0.29) and the concentration of vacancies is roughly 6%. At ρ∕ρ∗ = 5 the mechanical stability of the stable bcc structure increases and the concentration of vacancies accordingly decreases. The ratio of the corona layer thickness to the core radius is found to be in good agreement with experimental data for poly(styrene-b-isoprene)(22-12) in isoprene selective solvent which is also reported to crystallize in the bcc structure.

  1. Areal Rainfall Estimation for Flood Forecasting

    NASA Astrophysics Data System (ADS)

    Jones, A.; Bell, V.; Moore, R.


    This study deals with the estimation of catchment areal rainfall for the purpose of real-time flood forecasting using rainfall-runoff models. In the UK the two sources of rainfall data on the appropriate timescale are a sparse network of telemetered raingauges, with typical gauge spacings of 10 to 20km, and rainfall estimates derived from weather radar. The focus here is placed on raingauge estimation of rainfall. A survey of the literature reveals a vast number of methods developed for the estimation of areal rainfall from raingauge measurements on a range of spatial and temporal scales, ranging from simple weighting schemes to more complex interpolation methods. A review of previous method intercomparison studies identifies the need for a full evaluation of methods. Evaluation of a selection of nine weighting methods including Thiessen polygons, Standard Average Annual Rainfall (SAAR) weights and DTM-derived elevation weights has been carried out for two UK catchments. One catchment, the Brue in Somerset, is equipped with a special dense network of raingauges installed as part of the HYREX experiment. Evaluation was carried out using the PDM rainfall-runoff model with areal rainfall estimated from several sub-networks of raingauges and modelled flow compared with observed flow. Modelled flow was also compared with flow modelled using the ‘ground truth’ of areal rainfall estimated from the dense raingauge network. Estimates of 15 minute areal rainfall using each method were also compared directly with the areal estimate from the dense network for individual events characterised by either convective or stratiform rain. For stratiform rain, results indicated that all methods give reasonably accurate results, even when only two gauges are used, and the performances of the methods tested were almost indistinguishable. For convective rain, the Thiessen method gave consistently better results than the other methods, and the SAAR-method gave consistently worse

  2. Flue Gas Cleanup at Temperatures about 1400 C for a Coal Fired Combined Cycle Power Plant: State and Perspectives in the Pressurized Pulverized Coal Combustion (PPCC) Project

    SciTech Connect

    Foerster, M.E.C.; Oeking, K.; Hannes, K.


    The PPCC technology, a combined cycle, requires comprehensive cleaning of the flue gases because coal contains a large variety of minerals and other substances. This would lead to fast destruction of the gas turbine blades due to erosion and corrosion. The present specifications of the turbine manufacturers for the required flue gas quality are at a maximum particulate content of 5 mg/m3 s.t.p., diameter of < 5 {micro}m, and a maximum alkali content < 0.01 mg/m3 s.t.p. The PPCC project is aimed at cleaning the flue gases of pressurized coal combustion. This method will be applied at temperature ranges where the ash is in a liquid state and which will be thus cleaned from coarse particulate material by agglomeration and inertial force separators. Appropriate separating methods are also being investigated and developed for the hazardous gaseous contents, e.g. alkali compounds, which are released during the coal combustion process. The following companies are working on the development within the scope of a collaborative project to find a feasible technical solution: Babcock-Borsig-Power Env. GmbH (BBP Env.), E.ON Kraftwerke GmbH, SaarEnergie GmbH, Siemens AG, and Steag AG.

  3. Current levels and trends of selected EU Water Framework Directive priority substances in freshwater fish from the German environmental specimen bank.


    Fliedner, Annette; Lohmann, Nina; Rüdel, Heinz; Teubner, Diana; Wellmitz, Jörg; Koschorreck, Jan


    Under the German environmental specimen bank programme bream (Abramis brama) were sampled in six German rivers and analysed for the priority hazardous substances dicofol, hexabromocyclododecane (HBCDD), hexachlorobenzene (HCB), hexachlorobutadiene (HCBD), heptachlor + heptachlor epoxide (HC + HCE), polybrominated diphenylethers (PBDEs), polychlorinated dibenzo-p-dioxins and -furans and dioxin-like polychlorinated biphenyls (PCDD/Fs + dl-PCBs), and perfluorooctane sulfonic acid (PFOS). The aim was to assess compliance with the EU Water Framework Directive environmental quality standards for biota (EQSBiota) for the year 2013, and to analyse temporal trends for those substances that are of special concern. General compliance was observed for dicofol, HBCDD and HCBD whereas PBDEs exceeded the EQSBiota at all sites. For all other substances compliance in 2013 varied between locations. No assessment was possible for HC + HCE at some sites where the analytical sensitivity was not sufficient to cover the EQSBiota. Trend analysis showed decreasing linear trends for HCB and PFOS at most sampling sites between 1995 and 2014 indicating that the emission reduction measures are effective. Mostly decreasing trends or constant levels were also observed for PCDD/Fs and dl-PCBs. In contrast, increasing trends were detected for PBDEs and HBCDD which were especially pronounced at one Saar site located downstream of the industries and conurbation of Saarbrücken and Völklingen. This finding points to new sources of emissions which should be followed in the coming years.

  4. River methane hot-spots: Continuous methane ebullition measurements over an annual cycle linked to river sediment production

    NASA Astrophysics Data System (ADS)

    Wilkinson, Jeremy; Maeck, Andreas; Ashboul, Zeyad; Lorke, Andreas


    Hot spot methane ebullition from impounded river reaches matches high rates observed around the globe. Ebullition dominates total methane flux in the Saar River (Germany) and is largely determined by sediment deposition rate. Using automated bubble traps developed in-house, and deployed over a year at four sites, we collected high resolution data showing that hydrodynamic disturbances from shipping, lock operations and hydrograph events trigger ebullition episodes. Reverse smoothing was used to integrate the observed ebullition back in time, and helped in visualizing the data, and provides a time-series closer to methane accumulation in the sediments, whereas ebullition shows the triggering and release of the accumulated gas. One major hydrological disturbance of shallow-water sediment released around 13% of the total annual ebullition at that site, and ebullition generally followed the seasonal sediment temperature variations. The same event damped ebullition from deeper water sites. Total annual ebullition values ranged from 200 to 500 gCH4 m-2 yr-1. Ebullition from shallow water sediments in winter ceased for extended periods, but continued un-broken from deeper sites. With on-going measurements we believe these findings will help to improve estimates and the modelling of methane emissions from impounded river systems.

  5. Continuous Seasonal River Ebullition Measurements Linked to Sediment Methane Formation.


    Wilkinson, Jeremy; Maeck, Andreas; Alshboul, Zeyad; Lorke, Andreas


    Laboratory sediment incubations and continuous ebullition monitoring over an annual cycle in the temperate Saar River, Germany confirm that impounded river zones can produce and emit methane at high rates (7 to 30 (g CH4 m(-3) d(-1)) at 25 °C and 270 to 700 (g CH4 m(-2) yr(-1)), respectively). Summer methane ebullition (ME) peaks were a factor of 4 to 10 times the winter minima, and sediment methane formation was dominated by the upper sediment (depths of 0.14 to 0.2 m). The key driver of the seasonal ME dynamics was temperature. An empirical model relating methane formation to temperature and sediment depth, derived from the laboratory incubations, reproduced the measured daily ebullition from winter to midsummer, although late summer and autumn simulated ME exceeded the observed ME. A possible explanation for this was substrate limitation. We recommend measurements of methanogenically available carbon sources to identify substrate limitation and help characterize variation in methane formation with depth and from site to site.

  6. Quantitative comparison of initial soil erosion processes and runoff generation in Spanish and German vineyards.


    Rodrigo Comino, J; Iserloh, T; Lassu, T; Cerdà, A; Keestra, S D; Prosdocimi, M; Brings, C; Marzen, M; Ramos, M C; Senciales, J M; Ruiz Sinoga, J D; Seeger, M; Ries, J B


    The aim of this study was to enable a quantitative comparison of initial soil erosion processes in European vineyards using the same methodology and equipment. The study was conducted in four viticultural areas with different characteristics (Valencia and Málaga in Spain, Ruwer-Mosel valley and Saar-Mosel valley in Germany). Old and young vineyards, with conventional and ecological planting and management systems were compared. The same portable rainfall simulator with identical rainfall intensity (40mmh(-1)) and sampling intervals (30min of test duration, collecting the samples at 5-min-intervals) was used over a circular test plot with 0.28m(2). The results of 83 simulations have been analysed and correlation coefficients were calculated for each study area to identify the relationship between environmental plot characteristics, soil texture, soil erosion, runoff and infiltration. The results allow for identification of the main factors related to soil properties, topography and management, which control soil erosion processes in vineyards. The most important factors influencing soil erosion and runoff were the vegetation cover for the ecological German vineyards (with 97.6±8% infiltration coefficients) and stone cover, soil moisture and slope steepness for the conventional land uses.

  7. Quantitative comparison of soil erosion, runoff and infiltration coefficients using the same small portable rainfall simulator in German and Spanish vineyards

    NASA Astrophysics Data System (ADS)

    Rodrigo Comino, Jesús; Iserloh, Thomas; Lassu, Tamás; Cerdà, Artemi; Keesstra, Saskia; Prosdocimi, Massimo; Concepción Ramos, María; Brings, Christine; María Senciales, José; Damián Ruiz Sinoga, José; Seeger, Manuel; Ries, Johannes B.


    Small portable rainfall simulations have been used for decades to compare and quantify the relationship between the factors influencing runoff generation and soil erosion. Though, the comparability of these researches is problematic due to the different simulators and methods applied. In order to enable a quantitative comparison of the soil erosion processes of four study areas (Valencia and Málaga in Spain, Ruwer-Mosel valley and Saar-Mosel valley in Germany) similar type of portable rainfall simulator (with a square metal frame of 0.45 m x 0.45 m, one nozzle Lechler 460 608, four telescopic aluminium legs, a rubber tarpaulin to avoid wind influences, a circular test plot with 0.28m2) with similar methodology (rainfall intensity of 40 mm h-1, during 30 minutes of time duration, collecting the samples with intervals of 5 minutes) was used. Older and younger vineyards with conventional and ecological planting system were being compared with each other. All together the results of 77 simulations have been analysed and additionally the Spearman's Correlation Coefficient was calculated for each study area to identify the relationship between the different parameters.

  8. Advanced tools for astronomical time series and image analysis

    NASA Astrophysics Data System (ADS)

    Scargle, Jeffrey D.

    The algorithms described here, which I have developed for applications in X-ray and γ-ray astronomy, will hopefully be of use in other ways, perhaps aiding in the exploration of modern astronomy's data cornucopia. The goal is to describe principled approaches to some ubiquitous problems, such as detection and characterization of periodic and aperiodic signals, estimation of time delays between multiple time series, and source detection in noisy images with noisy backgrounds. The latter problem is related to detection of clusters in data spaces of various dimensions. A goal of this work is to achieve a unifying view of several related topics: signal detection and characterization, cluster identification, classification, density estimation, and multivariate regression. In addition to being useful for analysis of data from space-based and ground-based missions, these algorithms may be a basis for a future automatic science discovery facility, and in turn provide analysis tools for the Virtual Observatory. This chapter has ties to those by Larry Bretthorst, Tom Loredo, Alanna Connors, Fionn Murtagh, Jim Berger, David van Dyk, Vicent Martinez & Enn Saar.

  9. Effect of ship locking on sediment oxygen uptake in impounded rivers

    NASA Astrophysics Data System (ADS)

    Lorke, A.; McGinnis, D. F.; Maeck, A.; Fischer, H.


    In the majority of large river systems, flow is regulated and/or otherwise affected by operational and management activities, such as ship locking. The effect of lock operation on sediment-water oxygen fluxes was studied within a 12.9 km long impoundment at the Saar River (Germany) using eddy-correlation flux measurements. The continuous observations cover a time period of nearly 5 days and 39 individual locking events. Ship locking is associated with the generation of surges propagating back and forth through the impoundment which causes strong variations of near-bed current velocity and turbulence. These wave-induced flow variations cause variations in sediment-water oxygen fluxes. While the mean flux during time periods without lock operation was 0.5 ± 0.1 g m-2 d-1, it increased by about a factor of 2 to 1.0 ± 0.5 g m-2 d-1within time periods with ship locking. Following the daily schedule of lock operations, fluxes are predominantly enhanced during daytime and follow a pronounced diurnal rhythm. The driving force for the increased flux is the enhancement of diffusive transport across the sediment-water interface by bottom-boundary layer turbulence and perhaps resuspension. Additional means by which the oxygen budget of the impoundment is affected by lock-induced flow variations are discussed.

  10. Removing Activity-Related Radial Velocity Noise to Improve Extrasolar Planet Searches

    NASA Technical Reports Server (NTRS)

    Saar, Steven; Lindstrom, David M. (Technical Monitor)


    We have made significant progress towards the proposal goals of understanding the causes and effects of magnetic activity-induced radial velocity (v_r) jitter and developing methods for correcting it. In the process, we have also made some significant discoveries in the fields of planet-induced stellar activity, planet detection methods, M dwarf convection, starspot properties, and magnetic dynamo cycles. We have obtained super high resolution (R approximately 200,000), high S / N (greater than 300) echelle study of joint line bisector and radial velocity variations using the McDonald 2-D coude. A long observing run in October 2002 in particular was quite successful (8 clear nights). We now have close to three years of data, which begins to sample a good fraction of the magnetic cycle timescales for some of our targets (e.g., kappa Ceti; P_cyc = 5.6 yrs). This will be very helpful in unraveling the complex relationships between plage and radial velocity (v-r) changes which we have uncovered. Preliminary analysis (Saar et al. 2003) of the data in hand, reveals correlations between median line bisector displacement and v_r. The correlation appears to be specific the the particular star being considered, probably since it is a function of both spectral type and rotation rate. Further analysis and interpretation will be in the context of evolving plage models and is in progress.

  11. Time resolved spectroscopic investigation of SiD2 + D2: kinetic study

    NASA Astrophysics Data System (ADS)

    Al-Rubaiey, Najem A.; Walsh, Robin


    Silylenes (silanediyls) have made an important impact on organosilicon chemistry even if it is of more recent foundation than carbenes in organic chemistry and much less complete. These species are highly reactive intermediates. They play a central role in the chemical vapour deposition (CVD) of various silicon-containing thin films which have a technological importance in microelectronics as well as in the dry etching processes of silicon wafers. Spectroscopic methods have been developed to observe these species, a necessary pre-requisite to their direct monitoring. In this work, deuterated phenylsilane precursor, PhSiD3 was chosen for SiD2 because its analogue phenylsilane, PhSiH3 proved to be a good precursor for SiH2 and the high quality decay signals observed revealed that SiD2 be readily detected from PhSiD3 and that if other decomposition pathways (e.g. PhSiD + D2) are occurring, they do not effect measurements of the rate constants for SiD2. The absorption spectrum of SiD2 formed from the flash photolysis of a mixture of PhSiD3 and SF6 at 193nm were found in the region 17384-17391 cm-1 with strong band at 17387.07 cm-1. This single rotational line of pQ1 was chosen to monitor SiD2 removal. Time-resolved studies of SiD2 have been carried out to obtain rate constants for its bimolecular reactions with D2. The reactions were studied over the pressure range 5-100 Torr (in SF6 bath gas) at four temperatures in the range 298-498K. Single decay from 10 photolysis laser shots were averaged and found to give reasonable first-order kinetics fits. Second order kinetics were obtained by pressure dependence of the pseudo first order decay constants and substance D2 pressures within experimental error. The reaction was found to be weakly pressure dependent at all temperatures, consistent with a third-body mediated association process. In addition, SiH2+ H2 reaction is approximately ca. 60% faster than SiD2+D2 reaction. Theoretical extrapolations (using Lindemann

  12. DFT and DMFT: Implementations and applications to the study of correlated materials

    NASA Astrophysics Data System (ADS)

    Ylvisaker, Erik Ryan

    While DFT-LDA has enjoyed great success in describing many ground-state properties of solids, there is an ever increasing list of materials which are not described even qualitatively correct in DFT-LDA. Here I describe some applications of DFT and dynamical mean field theory. This dissertation is divided into two parts. Part I describes the theoretical background of DFT and DMFT, and the simplest extension to DFT to study correlated materials, LDA+U, is examined in detail. We find that the behavior of LDA+U can differ quite strongly between AMF and FLL, the two commonly used double-counting functionals. AMF has a strong energetic penalty for magnetic states, which roughly cancels the exchange splitting found in LSDA. In Part I, I also describe in detail the implementation of LDA+DMFT in the publicly available code FFLO. Part II focuses on applications. I describe the application of LDA to LiNbO2, where Wannier functions and effective tight-binding Hamiltonians are constructed for LiNbO2. We found that second neighbor hopping t2 is the largest, but the first neighbor hopping depends strongly on the Nb-O distance, so that with small variations of 0 position t1 varies by an order of magnitude. I also describe in part II the application of LDA in density functional perturbation theory (DFPT) to calculate phonons for Al, Na and diamond to compute melting curves using the Lindemann criteria. The resulting Tm( P) curves agree rather well with experiment in most conditions for these materials, including reproducing the drop of 300 K of T m in bcc-Na. Detailed calculations in LDA+DMFT using Hubbard I and QMC impurity solvers are used to describe the valence transition in Yb. The agreement with experimental XAES and RIXS measurements of nf is rather good, and even the highly approximate Hubbard I impurity solver gives reasonably good results. Finally, I discuss the application of LDA+U to molecular orbitals in RbO2 to examine the possibility of orbital ordering in the O pi

  13. Mechanisms of phase transitions in sodium clusters: From molecular to bulk behavior

    NASA Astrophysics Data System (ADS)

    Calvo, F.; Spiegelmann, F.


    The thermodynamics of sodium clusters is investigated by means of a classical empirical potential and a simple quantal tight-binding model. Neutral and singly charged clusters of sizes ranging from 8 to 147 atoms are considered. A very particular attention is paid to the optimization and sampling problems. We determine the lowest-energy structures (global minima) with the "basin-hopping" technique, and the finite-temperature simulations are improved by using the "q-jumping" method and put together with the multiple histogram method. The clusters geometries may be very different on the model used, but also on the ionic charge, up to the size of about 40 atoms. The thermodynamical analysis is performed near the solid-liquid transition by calculating the complete calorific curves (heat capacities) as well as some microscopic parameters to probe the dynamics on the energy landscapes, including the spectra of isomers found by periodic quenching, isomerization indexes and the Lindemann parameter δ. Up to the largest sizes, we find that the heat capacity generally displays several features within the two models, although structural differences in the lowest-energy isomers usually induce different calorific curves. These premelting phenomena are characteristic of isomerizations taking place in a limited part of the configuration space. The thermodynamics appears to be directly related to the lowest-energy structure, and melting by steps is favored by the presence of defects on its surface. We estimate the melting temperatures Tmelt(n) and latent heats of melting L(n), and we observe two very different behaviors of their variations with the size n. Below about 75 atoms, both Tmelt and L exhibit strong non-monotonic variations typical of geometric size effects. This "microscopic" behavior is caused by the dominating premelting effects, and is replaced by a more "macroscopic" behavior for sizes larger than about 93 atoms. The premelting phenomena become there less important

  14. The Time Is Now: Bioethics and LGBT Issues.


    Powell, Tia; Foglia, Mary Beth


    Our goal in producing this special issue is to encourage our colleagues to incorporate topics related to LGBT populations into bioethics curricula and scholarship. Bioethics has only rarely examined the ways in which law and medicine have defined, regulated, and often oppressed sexual minorities. This is an error on the part of bioethics. Medicine and law have served in the past as society's enforcement arm toward sexual minorities, in ways that robbed many people of their dignity. We feel that bioethics has an obligation to discuss that history and to help us as a society take responsibility for it. We can address only a small number of topics in this special issue of the Hastings Center Report, and we selected topics we believe will stimulate discourse. Andrew Solomon offers an elegant overview of the challenges that bioethics faces in articulating a solid basis for LGBT rights. Timothy F. Murphy asks whether bioethics still faces issues related to lesbian, gay, and bisexual people, given the deletion of homosexuality as a disease and the progress toward same-sex marriage. Jamie Lindemann Nelson's essay addresses the search for identity for transgender persons and the role of science in that search. Two articles, those by Brendan S. Abel and by Jack Drescher and Jack Pula, take up the complex issue of medical treatment for children who reject their assigned birth gender. Celia B. Fisher and Brian Mustanski address the special challenges of engaging LGBT youth in research, balancing the need for better information about this vulnerable group against the existing restrictions on research involving children. Tia Powell and Edward Stein consider the merits of legal bans on psychotherapies intended to change sexual orientation, particularly in the light of current research on orientation. Mary Beth Foglia and Karen I. Fredricksen-Goldsen highlight health disparities and resilience among LGBT older adults and then discuss the role of nonconscious bias in perpetuating

  15. Fritz London

    NASA Astrophysics Data System (ADS)

    Gavroglu, Kostas


    Preface; Acknowledgements; Part I. From Philosophy to Physics: The years that left nothing unaffected; 1. The appeal of ideas; 2. Goëthe as a scientist; 3. How absolute is our knowledge?; 4. How do we come to know things?; 5. London's teachers in philosophy; 6. Husserl's teachings; 7. Expectations of things to come; 8. The thesis in philosophy; 9. Tolman's principle of similitude; 10. The necessary clarifications; 11. Work on quantum theory; 12. Transformation theory; 13. Unsuccessful attempts at unification; Part II. The Years in Berlin and the Beginnings of Quantum Chemistry: The mysterious bond; 14. London in Zürich; 15. Binding forces; 16. The Pauli principle; 17. Reactions to the Heitler-London paper; 18. Polyelectronic molecules and the application of group theory to problems of chemical valence; 19. Chemists as physicists?; 20. London's first contacts in Berlin; 21. Marriage; 22. Job offers; 23. Intermolecular forces; 24. The book which could not be written; 25. Leningrad and Rome; 26. Difficulties with group theory; 27. Linus Pauling's resonance structures; 28. Robert Mulliken's molecular orbitals; Part III. Oxford and Superconductivity: The rise of the Nazis; 29. Going to Oxford; 30. Lindemann, Simon and Heinz London; 31. Electricity in the very cold; 32. The end of old certainties; 33. The thermodynamic treatment; 34. The theory of Fritz and Heinz London; 35. Initial reactions by von Laue; 36. The discussion at the Royal Society; 37. Termination of the ICI fellowship; Part IV. Paris and Superfluidity: The Front Populaire; 38. The article in Nature 1937 and 'Nouvelle Conception'; 39. Laue again; 40. The structure of solid helium; 41. The peculiar properties of helium; 42. Bose-Einstein condensation; 43. The note in Nature; 44. The two-fluid model; 45. The trip to Jerusalem; 46. Leaving again; 47. The observer in quantum mechanics; Part V. United States and the Typing up of Loose Ends: Duke University, North Carolina; 48. The Soviet Union, Kapitza and

  16. Integration of porosity, connectivity and permeability measurements to determine syn-eruptive degassing processes during a sub-plinian basaltic eruption

    NASA Astrophysics Data System (ADS)

    Jordan, Simone; Gurioli, Lucia; Colombier, Matthieu; Le Pennec, Jean-Luc; Roche, Olivier


    Degassing of the volatile phases is considered to have a major control on the eruption dynamics, particularly in controlling shifts between explosive and extrusive eruption styles. The sub-plinian eruption of the basaltic monogenetic La Vache and Lassolas cone complex in the Chaîne des Puys, France, about 8600 years ago, was an unusual large event that raises the question of the processes that controlled the explosivity of non-differentiated magma and the evolution of this sub-plinian event. This study combines the results of density, porosity, connectivity and permeability measurements of juvenile clasts to determine the state of vesiculation and the presence of open degassing pathways within the melt prior to fragmentation. The volume of connected vesicles is measured using a Helium-Pycnometer, while permeability measurements are conducted using a permeameter recently built at the Laboratoire Magma et Volcans, following Takeuchi et al. (2008). The permeameter has broad measurement ranges of pressure difference (101-105 Pa) and gas-flow rate (10-9-10-5 m3/s). These ranges enable us to measure viscous (Darcian) permeability in the range of 10-17-10-9 m2 for 1 centimetre-scale samples (such as scoria clasts) using the Forchheimer equation (Rust and Cashman, 2004) that accounts for inertial effects caused by non-laminar flow at high gas flow rates. This technique is a relatively new approach to determine the permeability of quenched samples. The integration of porosity and connectivity measurements provides information about the percentage of connected and isolated vesicles, with the connected vesicles forming potential degassing pathways. Our results show that the permeability and the vesicularity of the La Vache and Lassolas pyroclasts correlate very well, defining a trend that is also shown by the permeability data derived from the literature for the Cascades (Saar and Manga, 1999) and the Ambrym volcano (Polacci et al., 2012). The connectivity data of the

  17. Benzotriazole UV stabilizers in sediments, suspended particulate matter and fish of German rivers: New insights into occurrence, time trends and persistency.


    Wick, Arne; Jacobs, Björn; Kunkel, Uwe; Heininger, Peter; Ternes, Thomas A


    Benzotriazole UV stabilizers (BUVSs) are widely applied in plastics to prevent discoloration and to enhance product stability. This study describes for the first time the occurrence of nine different lipophilic BUVSs (UV-326, UV-320, UV-329, UV-350, UV-328, UV-327, UV-928, UV-234 and UV-360) in sediment, suspended particulate matter (SPM) and bream liver samples of German rivers. All investigated BUVSs were detected in sediments and SPM at concentrations in the low ng/g dry weight (dw) range. The so far rarely analyzed compound UV-360 as well as UV-326 were the predominant BUVSs in sediments and SPM from the river Rhine reaching maximum concentrations of 62 and 44 ng/g dw, respectively. Five BUVSs were also confirmed to bioaccumulate in bream liver, but neither UV-360 nor UV-326 was detected above the limit of quantification (LOQ). In contrast, highest concentrations in bream liver were determined for UV-327 (65 ng/g dw) and UV-328 (40 ng/g dw). A retrospective time trend analysis of BUVSs in SPM from two sites (river Rhine, 2005 to 2013; river Saar, 2006 to 2013) revealed increasing contamination levels of UV-329 and decreasing levels of UV-320 and UV-350. At one site (river Rhine) time trends of BUVS concentrations were also investigated in bream liver (1995-2013) and supported a considerably reduced exposure to UV-350. A first assessment of the environmental fate of BUVSs by sediment-water batch systems revealed a rapid partitioning into the sediment and no considerable degradation within 100 d.

  18. Local and Global Magnetic Fields of Late-Type Dwarfs OT Ser and YZ CMi

    NASA Astrophysics Data System (ADS)

    Bychkov, V. D.; Bychkova, L. V.; Madej, J.; Panferov, A. A.


    Differential rotation is the primary energy source for generation of local magnetic fields in the atmospheres of late-type stars (Moss et al. 1995). Moreover, the colder a star, the greater the effect, which was confirmed by observations. For instance, Saar (1988) measured the surface magnetic fields of late-type stars using the integral method Robinson (1980) and drew attention to the fact that the average magnetic field in the spots reaches the values of 1500 G for the G-type dwarfs, 2500 G for the K dwarfs, and 3500 G for the M-dwarf stars. The fraction of the surface of a star covered by spots also increases towards the latest spectral types. These well-known observational facts were explained by theoretical models, such as the α2 mechanism, for instance (Moss et al. 1995). Late-type dwarfs exhibit periodic eruptions resulting from the field line reconnection of newly generated local magnetic fields. This feature is observed in G, K, and M dwarfs, constituting 95%of all the stars in our Galaxy. The most prominent are the field reconnections in the so-called flare stars, which are the M dwarfs. This is understandable, since the peak flux of M dwarfs is placed in the red and infrared regions of the spectrum, whereas a flash has the maximum emission in the violet spectral region. Analysis of long-term photometric observations revealed that, on the average, energy of flares was found constant over a long time period for each flare star. That is to say, this conclusion implies that the power of the local magnetic field generator remains constant at this stage of evolution of stars.

  19. Multicomponent CO2-Brine Simulations of Fluid and Heat Transfer in Sedimentary-Basin Geothermal Systems: Expanding Geothermal Energy Opportunities

    NASA Astrophysics Data System (ADS)

    Saar, M. O.; Randolph, J. B.


    In a carbon dioxide plume geothermal (CPG) system, carbon dioxide (CO2) is pumped into existing high-permeability geologic formations that are overlain by a low-permeability caprock. The resulting CO2 plume largely displaces native formation fluid and is heated by the natural in-situ heat and background geothermal heat flux. A portion of the heated CO2 is piped to the surface to produce power and/or to provide heat for direct use before being returned to the geologic reservoir. Non-recoverable CO2 in the subsurface is geologically sequestered, serving as a CO2 sink. As such, this approach results in a geothermal power plant with a negative carbon footprint. We present results of calculations concerning geothermal power plant efficiencies and energy production rates in both traditional reservoir-based systems and engineered geothermal systems (EGS) when CO2, rather than water, is used as the subsurface working fluid. While our previous studies have examined geologic systems with established CO2 plumes, we focus here on multicomponent (CO2 + brine) systems. Numerical simulations (e.g., Randolph and Saar, Geophysical Research Letters, 2011) indicate that CPG systems provide several times the heat energy recovery of similar water-based systems. Furthermore, the CPG method results in higher geothermal heat extraction efficiencies than both water- and CO2-based EGS. Therefore, CPG should further extend the applicability of geothermal energy utilization to regions with subsurface temperatures and heat flow rates that are even lower than those that may be added due to switching from water- to CO2-based EGS. Finally, simulations at present suggest that multicomponent effects - e.g., buoyant flow as CO2 rises over denser brine - may enhance heat extraction in CPG systems compared to traditional water-based geothermal approaches.

  20. Borosilicate alteration associated with U-Mo-Zn and Ag-Au-Zn deposits in volcanic rocks

    NASA Astrophysics Data System (ADS)

    Fuchs, Y.; Maury, R.


    Borosilicate alteration is developed in many uranium-molybdenum-zinc deposits in volcanic piles such as at Novazza (Italy), Novoveska Huta (Slovakia), Ben Lomond (Queensland, Australia), the Saar-Nahe basin (Germany), the Shengyuan district (China), and at many deposits in Russia. These uranium-molybdenum-zinc deposits share similar styles of alteration with silver-gold-zinc deposits in volcanic rocks, like those of the Humboldt Range (Nevada, USA), the Basin district (Montana, USA) and Equity Mine (British Columbia, Canada). In thick volcanic piles, fluid-rock interaction commonly develops under the influence of convective hydrothermal systems. In borosilicate-bearing systems the alteration is characterized by changes in borosilicate mineralogy and chemistry under mesothermal conditions. Zonal distribution of different compositions of tourmaline can be observed including regular increases of alkali deficiency in the X(3a) site from peripheral (chlorite-epidote-prehnite) to internal (sericite and/or pyrophyllite) alteration zones. In the central part of these systems tourmaline is absent and the alteration assemblage is characterized by an andalusitedumortierite-quartz association. Such changes in mineral assemblage are related to an increase in temperature from 250 to 350 400 °C and to decreases in pH and Eh, from the outer toward the inner parts of the hydrothermal system. The zonation of the borosilicate-bearing alteration systems is similar to that of aluminosilicate-bearing hydrothermal systems (muscovite, pyrophyllite, andalusite) developed in volcanic rocks. A kaolinite-alunitejasperoid assemblage is generally associated with the borosilicate alteration, and seems related to a late hydrothermal phase mainly located in graben structures.

  1. Two-Stage, Integrated, Geothermal-CO2 Storage Reservoirs: An Approach for Sustainable Energy Production, CO2-Sequestration Security, and Reduced Environmental Risk

    SciTech Connect

    Buscheck, T A; Chen, M; Sun, Y; Hao, Y; Elliot, T R


    We introduce a hybrid two-stage energy-recovery approach to sequester CO{sub 2} and produce geothermal energy at low environmental risk and low cost by integrating geothermal production with CO{sub 2} capture and sequestration (CCS) in saline, sedimentary formations. Our approach combines the benefits of the approach proposed by Buscheck et al. (2011b), which uses brine as the working fluid, with those of the approach first suggested by Brown (2000) and analyzed by Pruess (2006), using CO{sub 2} as the working fluid, and then extended to saline-formation CCS by Randolph and Saar (2011a). During stage one of our hybrid approach, formation brine, which is extracted to provide pressure relief for CO{sub 2} injection, is the working fluid for energy recovery. Produced brine is applied to a consumptive beneficial use: feedstock for fresh water production through desalination, saline cooling water, or make-up water to be injected into a neighboring reservoir operation, such as in Enhanced Geothermal Systems (EGS), where there is often a shortage of a working fluid. For stage one, it is important to find economically feasible disposition options to reduce the volume of brine requiring reinjection in the integrated geothermal-CCS reservoir (Buscheck et al. 2012a). During stage two, which begins as CO{sub 2} reaches the production wells; coproduced brine and CO{sub 2} are the working fluids. We present preliminary reservoir engineering analyses of this approach, using a simple conceptual model of a homogeneous, permeable CO{sub 2} storage formation/geothermal reservoir, bounded by relatively impermeable sealing units. We assess both the CO{sub 2} sequestration capacity and geothermal energy production potential as a function of well spacing between CO{sub 2} injectors and brine/CO{sub 2} producers for various well patterns and for a range of subsurface conditions.

  2. Novel modification of voice prosthesis.


    Al Kadah, Basel; Papaspyrou, George; Schneider, Mathias; Schick, Bernhard


    The undesired dilatation of the tracheooesophageal shunt after surgical implantation of voice prosthesis is a typical complication of this procedure. Temporary removal of the prosthesis and reinsertion after a short period of time is a first-line therapeutical option aiming shrinkage of the shunt. Failure of this measure generally is an indication of revision surgery. We present first experiences treating leakage problems with novel modified voice prosthesis without surgical intervention in specified cases. 11 patients (1 female, 10 male) aging between 51 and 71 years were presented with shunt leakage between 11/2008 and 11/2012 in the ENT-Department of the University Hospital of Homburg/Saar after a custom built voice prosthesis had been used initially successfully. A "Provox 2"(®) voice prosthesis was modified with two discs made of silicone each on the tracheal and oesophageal side and additionally reinforcing the diameter of the prosthesis by a silicone tube. The modified prosthesis was inserted in a retrograde way under general anesthesia, analogical to the approach used with the "Provox 1"(®)-prosthesis. The period of observation ranged between 12 and 48 months. As a measure of control swallowing of methylene blue was used. In all cases leakage suspended. Durability of the modified prosthesis ranged between 2 and 6 months. Neither the patients' complained about, nor did the physicians notice subjectively an impairment of the voice quality. Modifications of "Provox 2"(®)-prosthesis should be regarded in individual cases and constitute a reasonable alternative to revision surgery. A surgical approach is more intricate and costly, more taxing for the patient and susceptible to failure. We regard the necessity of general anesthesia for the insertion of the modified prosthesis as a disadvantage.

  3. Quantitative analysis of soil erosion in ecologically and conventionally cultivated vineyards

    NASA Astrophysics Data System (ADS)

    Adrian, Alexander; Brings, Christine; Rodrigo Comino, Jesús; Seeger, Manuel; Ries, Johannes B.


    Long term observations of soil erosion in vineyards showed that they are generally stable. But the soil erosion rates reach very varying dimensions by the increased occurrence of extreme rainfall events or under the influence of different soil and vineyard management. To identify the differences between an ecologically (with natural vegetation cover under and around the vines) and conventionally cultivated vineyard, in 2014 six sediment traps were installed on a south-west exposed slope of the Rhenish Slate Mountains, West Germany. The research area is part of Saar terrace (around 180 meter high above sea level), a tributary of the Moselle, so the substrate is made of clay stone and gravel sand. Sediment traps allow in-situ measurements during a natural rainfall event. By dint of them the overland flow and sediment can be collected. The sediment traps were placed in a row in the middle of the slope, in the steepest part (averaged 23°). They were emptied weekly. Runoff and sediments were divided by the gravimetric filtering method. The results show more collected runoff and sediment in the conventional vineyard than in the ecological. The sum of the runoffs amounts to 75 liter in the conventional vineyard, 29 liter for the ecological old and 0.73 liter for the ecological young vineyard. The amount of sediment of conventional vineyard (403 g) was five times higher than in the ecological one (79 g). The causes lay in the low vegetation cover and existing traffic lines in the conventional vineyard. But the highest sediment concentration has been detected in the ecological young vineyard.

  4. Rainfall simulation experiments in ecological and conventional vineyards.

    NASA Astrophysics Data System (ADS)

    Adrian, Alexander; Brings, Christine; Rodrigo Comino, Jesús; Iserloh, Thomas; Ries, Johannes B.


    In October 2014, the Trier University started a measurement series, which defines, compares and evaluates the behavior of runoff and soil erosion with different farming productions in vineyards. The research area is located in Kanzem, a traditional wine village in the Saar Valley (Rheinland-Palatinate, Germany). The test fields show different cultivation methods: ecological (with natural vegetation cover under and around the vines) and conventional cultivated rows of wine. By using the small portable rainfall simulator of Trier University it shall be proved if the assumption that there is more runoff and soil erosion in the conventional part than in the ecological part of the tillage system. Rainfall simulations assess the generation of overland flow, soil erosion and infiltration. So, a trend of soil erosion and runoff of the different cultivation techniques are noted. The objective of this work is to compare the geomorphological dynamics of two different tillage systems. Therefore, 30 rainfall simulations plots were evenly distributed on a west exposition hillside with different slope angels (8-25°), vegetation- and stone-covers. In concrete, the plot surface reaches from strongly covered soil across lithoidal surfaces to bare soil often with compacted lanes of typical using machines. In addition, by using the collected substrate, an estimation and distribution of the grain size of the eroded material shall be given. The eroded substrate is compared to soil samples of the test plots. The first results have shown that there is slightly more runoff and soil erosion in the ecological area than on the conventional part of the vineyard.

  5. Thermoelasticity of Hexagonal Close-Packed Iron from the Phonon Density of States

    NASA Astrophysics Data System (ADS)

    Murphy, Caitlin A.

    This thesis explores the vibrational thermodynamic and thermoelastic properties of pure hexagonal close-packed iron (ε-Fe), in an effort to improve our understanding of the properties of a significant fraction of this remote region of the deep Earth and in turn, better constrain its composition. We determined the Debye sound velocity (vD) at each of our compression points from the low-energy region of the phonon DOS and our in situ measured volumes. In turn, vD is related to the compressional and shear sound velocities via our determined densities and the adiabatic bulk modulus. Our high-statistical quality dataset places a new tight constraint on the density dependence of ε-Fe's sound velocities to outer core pressures. Via comparison with existing data for iron alloys, we investigate how nickel and candidate light elements for the core affect the thermoelastic properties of iron. In addition, we explore the effects of temperature on ε-Fe's sound velocities by applying pressure- and temperature-dependent elastic moduli from theoretical calculations to a finite-strain model. Such models allow for direct comparisons with one-dimensional seismic models of Earth's solid inner core (e.g., the Preliminary Reference Earth Model). Next, the volume dependence of the vibrational free energy is directly related to the vibrational thermal pressure, which we combine with previously reported theoretical values for the electronic and anharmonic thermal pressures to find the total thermal pressure of ε-Fe. In addition, we found a steady increase in the Lamb-Mössbauer factor with compression, which suggests restricted thermal atomic motions at outer core pressures. This behavior is related to the high-pressure melting behavior of ε-Fe via Gilvarry's reformulation of Lindemann's melting criterion, which we used to obtain the shape of ε-Fe's melting curve up to 171 GPa. By anchoring our melting curve shape with experimentally determined melting points and considering thermal

  6. An ab initio study of the nickel-catalyzed transformation of amorphous carbon into graphene in rapid thermal processing

    NASA Astrophysics Data System (ADS)

    Chen, Shuang; Xiong, Wei; Zhou, Yun Shen; Lu, Yong Feng; Zeng, Xiao Cheng


    Ni). It is found that the a-C-to-graphene transformation entails the metal-induced crystallization and layer exchange mechanism, rather than the conventional dissolution/precipitation mechanism typically involved in Ni-catalyzed chemical vapor deposition (CVD) growth of graphene. The multi-layer graphene can be tuned by changing the relative thicknesses of deposited a-C and Ni thin films. Our AIMD simulations suggest that the easy evaporation of surplus Ni with excess C is likely attributed to the formation of a viscous-liquid-like Ni-C solution within the temperature range of 900-1800 K and to the faster diffusion of C atoms than that of Ni atoms above 600 K. Even at room temperature, sp3-C atoms in a-C are quickly converted to sp2-C atoms in the course of the simulation, and the graphitic C formation can occur at low temperature. When the temperature is as high as 1200 K, the grown graphitic structures reversely dissolve into Ni. Because the rate of temperature increase is considerably faster in the AIMD simulations than in realistic experiments, defects in the grown graphitic structures are kinetically trapped. In this kinetic growth stage, the carbon structures grown from sp3-carbon or from sp2-carbon exhibit marked differences. Electronic supplementary information (ESI) available: Formation energies of Ni-Ni, Ni-C, and C-C atoms as a function of intermolecular distance in Fig. S1, the whole supercells with the vacuum layer of Models I and VII in Fig. S2, and the initial and final configurations (Fig. S3), MSD-time curves (Fig. S4), diffusion coefficients (Table S1), and Lindemann index (Fig. S5) of four new models (VIII-XI). See DOI: 10.1039/c5nr08614k

  7. PREFACE: 3rd International Workshop on Infrared Plasma Spectroscopy

    NASA Astrophysics Data System (ADS)

    Davies, P. B.; Röpcke, Jürgen; Hempel, Frank


    the scientific committee felt that this time it would be useful to emphasise new spectroscopic developments as well as covering applications. This might serve as a guide as to where the subject of infrared spectroscopy in combination with plasma sources might be heading in the future i.e. to emphasize pure infrared spectroscopy developments. The first invited lecture (G Guelachvili and N Picque) and the last invited lecture (F K Tittel, Y Bakhirkin, R Curl, A Kosterev, R Lewicki, D Thomasz and S So) were chosen to set the scene and realise this objective. The second (R Engeln, R Zijlmans, S Welzel, O Gabriel, J-P van Helden, J Röpcke and D Schram) and third (X Aubert, C Lazzaroni, D Marinov, O Guaitella, S Welzel, A Pipa, J Röpcke and A Rousseau) invited talks focussed on the application of the IR laser techniques with particular emphasis on the role of surfaces in plasmas and the relevance of plasma surface interactions. Surface plasma interactions did not feature strongly in the two earlier meetings and so this topic too, along with the emphasis on novel infrared spectroscopy techniques, represents a new direction for the conference. Paul B Davies and Jürgen Röpcke International Scientific Committee P B Davies, Cambridge, UK: Chair J Röpcke, Greifswald, Germany: Co-Chair R Engeln, Eindhoven, Netherlands G Hancock, Oxford, U K M Hori, Nagoya, Japan H Linnartz, Leiden, Netherlands R Martini, New York, USA J Meichsner, Greifswald, Germany A Rousseau, Paris, France Local Organizing Committee J Röpcke (INP: Chair) F Hempel (INP: Secretary) J Meichsner (IfP, University of Greifswald) N Lang (INP) L Glawe (INP) C Krcka (INP) B Lindemann (INP) Conference photograph

  8. Effects of high shock pressures and pore morphology on hot spot mechanisms in HMX

    NASA Astrophysics Data System (ADS)

    Springer, H. K.; Tarver, C. M.; Bastea, S.


    The shock initiation and detonation behavior of heterogeneous solid explosives is governed by its microstructure and reactive properties. New additive manufacturing techniques offer unprecedented control of explosive microstructures previously impossible, enabling us to develop novel explosives with tailored shock sensitivity and detonation properties. Since microstructure-performance relationships are not well established for explosives, there is little material design guidance for these manufacturing techniques. In this study, we explore the effects of high shock pressures (15-38 GPa) with long shock durations and different pore morphologies on hot spot mechanisms in HMX. HMX is chosen as the model material because we have experimental data on many of the chemical-thermal-mechanical properties required for pore collapse simulations. Our simulations are performed using the multi-physics arbitrary Lagrangian Eulerian finite element hydrocode, ALE3D, with Cheetah-based models for the unreacted and the product equation-of-states. We use a temperature-dependent specific heat with the unreacted equation-of-state and a temperature-dependent viscosity model to ensure accurate shock temperatures for subsequent chemistry. The Lindemann Law model is used for shock melting in HMX. In contrast to previous pore collapse studies at lower shock pressures (≤10 GPa) in HMX and shorter post-collapse burning times, our calculations show that shock melting occurs above 15 GPa due to higher bulk heating and a prominent elongated ("jet-like") hot spot region forms at later times. The combination of the elongated, post-collapse hot spot region and the higher bulk heating with increasing pressure dramatically increases the growth rate of reaction. Our calculations show that the reaction rate, dF/dt, increases with increasing shock pressure. We decompose the reaction rate into ignition ((dF/dt)ig) and growth ((dF/dt)gr) phases to better analyze our results. We define the ignition phase

  9. Effect of Hydrogen and Carbon on the Melting Temperature of the Core

    NASA Astrophysics Data System (ADS)

    Nakajima, Y.; Sakamaki, K.; Takahashi, E.; Fukai, Y.; Suzuki, T.; Funakoshi, K.


    , respectively. The melting temperatures of Fe3C determined by our experiments are >700 K lower than that of the previous estimation based on thermodynamic calculation (Wood, 1993). Our experimental results show a possibility that the hydrogen and carbon lower the melting temperature of iron (outer core) dramatically. The melting temperatures of γ-FeH and Fe3C at 20 GPa are already 500 K lower than that of pure iron estimated by Anderson and Isaak (2000). Extrapolating our experimental melting curves for FeH and Fe3C to core pressures using Lindemann's melting law, we obtained the melting temperatures to be ~2600 and ~2900 K at the core-mantle boundary (CMB), respectively. In the presence of both hydrogen and carbon, melting temperature of the Earth's outer core could be >1500 K lower than that of the previous estimates, implying that the temperature gap at CMB could be much smaller than the current estimates.

  10. Lost in the Dark: A proto-history of dark matter

    NASA Astrophysics Data System (ADS)

    Trimble, Virginia L.; History 1


    Einasto, Kaasik, and Saar (published in Nature, in case you are thinking of more Meddelande). I feel enormous respect and affection for Vera Rubin and Fritz Zwicky, but the published papers as are they are.

  11. First experiences with an individual nasal olive in patients with hereditary haemorrhagic telangiectasia (HHT).


    Al Kadah, Basel; Papaspyrou, George; Schneider, Mathias; Schick, Bernhard


    Hereditary haemorrhagic teleangiectasia (HHT) is most notably characterized by vulnerable vascular formations of the nasal superficial mucosa. Epistaxis is one of the most common symptoms of the afflicted patients, with an incidence of more than 90 %. A variable series of treatments have been described, ranging from nasal ointments to the complete surgical occlusion of the nose. The objective of this pilot study is the presentation of first experiences in treating patients suffering from HHT and chronically recurrent epistaxis with an individual nasal olive made from silicone. Eleven patients (six men, five women) aging from 44 to 80 years with known HHT were treated at the ENT department of Homburg/Saar between October 2008 and July 2012 because of nasal bleeding by Nd:YAG laser or argon plasma coagulation. After the surgical treatment, an imprint of the nasal aditus was taken to manufacture an individual custom-made silicone nasal olive. Patients were wearing the nasal olive for 3-8 h a day. Check-ups were made every 6 months. Epistaxis severity score (ESS) was used pre- and post-nasal olive application. The observation period was 12-48 months. The utilization of the silicone nasal olive led to a distinct reduction of epistaxis events. Apart from the nasal olive, our patients needed no further treatment of the nose during the observation period except for a nasal ointment. Insertion and removal of the nasal olive were handled by the patients themselves. The local manipulation in handling the nasal olive caused no epistaxis itself. A significant improvement of the ESS and satisfaction was reported in all patients. Use of an individually manufactured silicone nasal olive is a promising extension to the established treatments of epistaxis in HHT patients. Tolerance towards this treatment by the patients was high due to the low personal burden and encumbrance. The extended use of the presented method in HHT patients may be beneficial. However, a more prolonged

  12. Modifications of transaxillary approach in endoscopic da Vinci-assisted thyroid and parathyroid gland surgery.


    Al Kadah, Basel; Piccoli, Micaela; Mullineris, Barbara; Colli, Giovanni; Janssen, Martin; Siemer, Stephan; Schick, Bernhard


    Endoscopic surgery for treatment of thyroid and parathyroid pathologies is increasingly gaining attention. The da Vinci system has already been widely used in different fields of medicine and quite recently in thyroid and parathyroid surgery. Herein, we report about modifications of the transaxillary approach in endoscopic surgery of thyroid and parathyroid gland pathologies using the da Vinci system. 16 patients suffering from struma nodosa in 14 cases and parathyroid adenomas in two cases were treated using the da Vinci system at the ENT Department of Homburg/Saar University and in cooperation with the Department of General Surgery in New Sant'Agostino Hospital, Modena/Italy. Two different retractors, endoscopic preparation of the access and three different incision modalities were used. The endoscopic preparation of the access allowed us to have a better view during preparation and reduced surgical time compared to the use of a headlamp. To introduce the da Vinci instruments at the end of the access preparation, the skin incisions were over the axilla with one incision in eight patients, two incisions in four patients and three incisions in a further four patients. The two and three skin incisions modality allowed introduction of the da Vinci instruments without arm conflicts. The use of a new retractor (Modena retractor) compared to a self-developed retractor made it easier during the endoscopic preparation of the access and the reposition of the retractor. The scar was hidden in the axilla and independent of the incisions selected, the cosmetic findings were judged by the patients to be excellent. The neurovascular structures such as inferior laryngeal nerve, superior laryngeal nerve and vessels, as well as the different pathologies, were clearly 3D visualized in all 16 cases. No paralysis of the vocal cord was observed. All patients had a benign pathology in their histological examination. The endoscopic surgery of the thyroid and parathyroid gland can be

  13. Role of Yield Stress in Magma Rheology

    NASA Astrophysics Data System (ADS)

    Kurokawa, A.; Di Giuseppe, E.; Davaille, A.; Kurita, K.


    Magmas are essentially multiphase material composed of solid crystals, gaseous bubbles and silicate liquids. They exhibit various types of drastic change in rheology with variation of mutual volumetric fractions of the components. The nature of this variable rheology is a key factor in controlling dynamics of flowing magma through a conduit. Particularly the existence of yield stress in flowing magma is expected to control the wall friction and formation of density waves. As the volumetric fraction of solid phase increases yield stress emerges above the critical fraction. Several previous studies have been conducted to clarify this critical value of magmatic fluid both in numerical simulations and laboratory experiments ([Lejeune and Pascal, 1995], [Saar and Manga 2001], [Ishibashi and Sato 2010]). The obtained values range from 13.3 to 40 vol%, which display wide variation and associated change in rheology has not been clarified well. In this presentation we report physical mechanism of emergence of yield stress in suspension as well as the associated change in the rheology based on laboratory experiments using analog material. We utilized thermogel aqueous suspension as an analog material of multiphase magma. Thermogel, which is a commercial name for poly(N-isopropyl acrylamide) (PNIPAM) undergoes volumetric phase change at the temperature around 35C:below this temperature the gel phase absorbs water and swells while below this it expels water and its volume shrinks. Because of this the volumetric fraction of gel phase systematically changes with temperature and the concentration of gel powder. The viscosity measured at lower stress drastically decreases across this phase change with increasing temperature while the viscosity at higher stress does not exhibit large change across the transition. We have performed a series of rheological measurements focusing on the emergence of yield stress on this aqueous suspension. Since the definition of yield stress is not

  14. Hydrological Catchment Similarity Assessment in Geum River Catchments, Korea

    NASA Astrophysics Data System (ADS)

    Ko, Ara; Park, Kisoon; Lee, Hyosang


    Similarity measure of catchments is essential for regionalization studies, which provide in depth analysis in hydrological response and flood estimations at ungauged catchments. However, this similarity measure is often biased to the selected catchments and is notclearly explained in hydrological sense. This study applied a type of hydrological similarity distance measure-Flood Estimation Handbook to 25 Geum river catchments, Korea. Three Catchment Characteristics, Area (A)-Annual precipitation (SAAR)-SCS Curve Number (CN), are used in Euclidian distance measures. Furthermore, six index of Flow Duration Curve (ILow:Q275/Q185, IDrought:Q355/Q185, IFlood:Qmax/Q185, IAbundant:Q95/Q185, IFloodDuration:Q10/Q355 and IRiverRegime:Qmax/Qmin) are applied to clustering analysis of SPSS. The catchments' grouping of hydrological similarity measures suggests three groups: H1 (Cheongseong, Gidae, Bukil, Oksan, Seockhwa, Habgang and Sangyeogyo), H2 (Cheongju, Guryong, Ugon, Boksu, Useong and Seokdong) and H3 (Muju, Yangganggyo and YongdamDam). The four catchments (Cheoncheon, Donghyang, DaecheongDam and Indong) are not grouped in this study. The clustering analysis of FDC provides four Groups; CFDC1 (Muju, YongdamDam, Yangganggyo, DaecheongDam, Cheongseong, Gidae, Seokhwa, Bukil, Habgang, Cheongju, Oksan, Yuseong and Guryong), CFDC2 (Cheoncheon, Donghyang, Boksu, Indong, Nonsan, Seokdong, Ugon, Simcheon, Useong and Sangyeogyo), CFDC3 (Songcheon) and CFDC4 (Tanbu). The six catchments (out of seven) of H1 are grouped in CFDC1, while Sangyeogyo is grouped in CFDC2. The four catchments (out of six) of H2 are also grouped in CFDC2, while Cheongju and Guryong are grouped in CFDC1. The catchments of H3 are categorized in CFDC1. The authors examine the results (H1, H2 and H3) of similarity measure based on catchment physical descriptors with results (CFDC1 and CFDC2) of clustering based on catchment hydrological response. The results of hydrological similarity measures are supported by

  15. Outcrop analogue study of Permocarboniferous geothermal sandstone reservoir formations (northern Upper Rhine Graben, Germany): impact of mineral content, depositional environment and diagenesis on petrophysical properties

    NASA Astrophysics Data System (ADS)

    Aretz, Achim; Bär, Kristian; Götz, Annette E.; Sass, Ingo


    The Permocarboniferous siliciclastic formations represent the largest hydrothermal reservoir in the northern Upper Rhine Graben in SW Germany and have so far been investigated in large-scale studies only. The Cenozoic Upper Rhine Graben crosses the Permocarboniferous Saar-Nahe Basin, a Variscan intramontane molasse basin. Due to the subsidence in this graben structure, the top of the up to 2-km-thick Permocarboniferous is located at a depth of 600-2900 m and is overlain by Tertiary and Quaternary sediments. At this depth, the reservoir temperatures exceed 150 °C, which are sufficient for geothermal electricity generation with binary power plants. To further assess the potential of this geothermal reservoir, detailed information on thermophysical and hydraulic properties of the different lithostratigraphical units and their depositional environment is essential. Here, we present an integrated study of outcrop analogues and drill core material. In total, 850 outcrop samples were analyzed, measuring porosity, permeability, thermal conductivity and thermal diffusivity. Furthermore, 62 plugs were taken from drillings that encountered or intersected the Permocarboniferous at depths between 1800 and 2900 m. Petrographic analysis of 155 thin sections of outcrop samples and samples taken from reservoir depth was conducted to quantify the mineral composition, sorting and rounding of grains and the kind of cementation. Its influence on porosity, permeability, the degree of compaction and illitization was quantified. Three parameters influencing the reservoir properties of the Permocarboniferous were detected. The strongest and most destructive influence on reservoir quality is related to late diagenetic processes. An illitic and kaolinitic cementation and impregnation of bitumina document CO2- and CH4-rich acidic pore water conditions, which are interpreted as fluids that migrated along a hydraulic contact from an underlying Carboniferous hydrocarbon source rock. Migrating

  16. Late-Variscan rare metal ore deposition and plume-related magmatism in the eastern European Variscides (D, CZ)

    NASA Astrophysics Data System (ADS)

    Seifert, Thomas


    includes a range of mafic calc-alkaline and shoshonitic rock types, and lamprophyres (spessartites and camptonites) with age data between 300-270 Ma. The Mid-European Variscides show a large number of Permo-Carboniferous magmatic complexes with similar ages (Halle Volcanic Complex, Saar-Nahe Basin, Thuringian Forest, Harz Mts., Northwest-Saxonian Volcanic Complexes, bimodal volcanic rocks of the Sub-Erzgebirge basin and the Rhyolite Complex of Tharandt as well as Li-F-Sn small intrusion granites and lamprophyric intrusions in the Erzgebirge. It is important to note that the late-Variscan W-Mo, Sn-W-Mo, Ag-bearing Sn-In-base metal, Ag-Sb-base metal, and U mineralizations in the Erzgebirge-Krušné hory are spatially and temporal associated with intrusion centers of Permo-Carboniferous post-collisional mafic and rhyolitic (sub)volcanic bimodal magmatism (315-290 Ma) along deep-rooted NW-SE fault zones, especially at the intersections with NE-SW, E-W, and N-S major regional structural zones. The bimodal lamprophyre-rhyolite assemblage in the Erzgebirge / Sub-Erzgebirge basin area was formed during intracontinental rifting in a 'Fast Extension' setting by melting of a metasomatic enriched mantle source. The emplacement of fluid-enriched lamprophyres and F-rich rhyolitic intrusions at the same time is probably associated with decompression melting of updoming asthenosphere which is possibly associated with the above mentioned mantle plume.

  17. Using geoinformatics and cultural anthropology to identify links between land change, driving forces and actors in the Okavango catchment

    NASA Astrophysics Data System (ADS)

    Röder, Achim; Stellmes, Marion; Pröpper, Michael; Schneibel, Anne


    central institutions and are implemented in different ways at subordinate levels. Commonly, communities make their own decisions regarding the use of natural resources within the framework of statutory and traditional governance and national legislation. The Permanent Okavango River Basin Water Commission (OKACOM) has been created between Angola, Namibia and Botswana to deal with transboundary subjects and facilitate informed policies. Developing such informed policies is even more urgent given demographic and climatological predictions. The African population is expected to almost double by the end of this century (Haub 2012), while climate predictions indicate an overall increase in average temperatures, added to by an increase in dry spells during the wet season and overall decreases in precipitation (IPCC 2013). This will result in increasing demands for food, paralleled by less favorable production conditions. The appropriation of resources in the wider region is therefore characterized by various, potentially conflicting demands that are likely to accumulate in space and time (Röder, Stellmes et al. 2013). A particular constraint draws from upstream-downstream issues, with a predicted increase in upstream water utilization for drinking and irrigation, while the Delta region relies on regular flood pulses of clean water to sustain its biodiversity, to which the tourist sector as a major source of national income is linked. This is threatened by the increasing concentrations of pesticides and herbicides used in the frame of irrigation schemes lowering water quality, and the change of flood pulse cycles through damming projects (Lindemann 2009). Besides national policies and regional planning programs, an equally important element in understanding the utilization of natural resources is the individual perspective of actors that may range from the conservation of traditions and cultures to stronger market integration and consumerism (Pröpper, Falk et al. 2013) that

  18. Contrasting Permo - Carboniferous Evolution of Resita and Sirinia - Presacina Basins (South Carpathians, Romania); an overview.

    NASA Astrophysics Data System (ADS)

    Tatu, M.; Seghedi, I.; Nutu, L. M.; Nicolae, I.


    - sinistral shear fault system adjacent to the Tornquist - Teisseyre Line, which induced the fragmentation of Variscan fold belt. With this process was associated the formation of many transtensional pull-apart continental - lacustrian sedimentary basins and intra-continental rifts in which or in adjacent areas the intrusive - extrusive magmatism was widespread and where the deep crustal fractures were active. From climatic point of view the main consequence of continue convergence between Laurasia and Gondwana is the transition from relatively wet regime during Stephanian to arid during the Permian induced by the elevation of the equatorial highlands Variscan fold belt was acted as a precipitation barrier for the whole territory located to the north. Tacking into account of all these aspects, the Resita domain presents the similarities in the lithological composition with Autun Basin and the Sirinia - Presacina zone displays many common features with Saar - Nahe and Thuringian Forest Basins and North German/Polish Depression. This work started during PALEOCLIM project (grant ANCS - PN2, 31-063/2007), which is gratefully acknowledged. References Nastaseanu S. 1987. In: Flügel E., Sassi F. & Grecula P. (eds): Pre-Variscan and Variscan events in the Alpine-Mediterranean mountain belts. - Mineralia Slovaca. Alfa Bratislava, 371-378. Stollhofen H., Frommherz B., Stanistreet I. G. 1999. J. Geol. Soc. London 156, 801-808. Ziegler P. A. 1990. Shell Int. Petrol. Mij. Dist. Geol. Soc. Publ. House, Bath, 1-239.