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Sample records for 1s2s 3s1 metastable

  1. Double-K-vacancy states in electron-impact single ionization of metastable two-electron N5+(1s2s 3S1) ions

    NASA Astrophysics Data System (ADS)

    Müller, A.; Borovik, A.; Huber, K.; Schippers, S.; Fursa, D. V.; Bray, I.

    2014-07-01

    The role of hollow states intermediately produced in electron-impact ionization of metastable He-like N5+(1s2s3S1) ions has been investigated in detail. A crossed-beam setup and suitable experimental techniques were employed for the measurement of accurate absolute cross sections and precise energy-scan data. Fine structures arising from K-shell excitations and associated resonances have been observed for this two-electron ion with less than ±0.5 eV uncertainty on the energy scale. Fine details, such as interference of the reaction pathways of direct ionization and excitation with capture of the incident electron followed by double-Auger decay, could be revealed. Ab initio calculations based on the convergent close coupling (CCC) approach are in good agreement with the experiment.

  2. Measurement of 1s2s 3S1-1s2p 3P2,0 wavelengths in heliumlike silicon

    NASA Astrophysics Data System (ADS)

    Howie, David J. H.; Hallett, William A.; Myers, Edmund G.; Dietrich, Daniel D.; Silver, Joshua D.

    1994-06-01

    We have measured the vacuum-ultraviolet 1s2s 3S1-1s2p 3P2,0 transition wavelengths in heliumlike silicon by photographic spectroscopy of a beam-foil source. The results are 814.71+/-0.02 Å and 878.68+/-0.03 Å, respectively, and represent a sensitive test of present relativistic and quantum electrodynamic calculations. Comparisons are made between our results, previous measurements of these transitions, and the current theories. Good agreement is obtained, particularly with recent relativistic many-body perturbation calculations. A discussion of future measurements of this interval is also presented.

  3. Energy calculation for beryllium atom in different excited states (1s2 2s 3s), (1s 2s2 3s) and (1s 2s 3s2)

    NASA Astrophysics Data System (ADS)

    Al-Sharaa, Mayada J.; Mahmood, Maysoon A.; Madhkoor, Naaemh C. H.; Al-Bayati, Khalil H.

    2017-09-01

    The energy expectation value E has been evaluated for Beryllium different excited state and Be like ions such as B+1 and C+2 and the potential energy expectation value V has been evaluated too. The partitioning technique of Hartree-Fock (H-F) has been used for existing wave functions. The results show that the expectation values of and < r12 -1> of (1s2s 3s2), (1s2s23s) and (1s2s 3s2) states increase when the atomic number (Z) increases for all shells for Be-like ions. All the studied properties are calculated using atomic units.

  4. Lifetime of the 1s2s 3S1 metastable level in He-like S14+ measured with an electron beam ion trap

    SciTech Connect

    L?pez-Urrutia, J C; Beiersdorfer, P; Widmann, K

    2006-03-16

    A precision measurement of the lifetime of the lowest exited level of the He-like S{sup 14+} ion carried out at the Livermore EBIT-II electron beam ion trap yielded a value of (703 {+-} 4) ns. Our method extends the range of lifetime measurements accessible with electron beam ion traps into the nanosecond region and improves the accuracy of currently available data for this level by an order of magnitude.

  5. Magic Wavelength for the Hydrogen 1S-2S Transition

    NASA Astrophysics Data System (ADS)

    Kawasaki, Akio

    2016-05-01

    The state of the art precision measurement of the transition frequencies of neutral atoms is performed with atoms trapped by the magic wavelength optical lattice that cancels the ac Stark shift of the transitions. Trapping with magic wavelength lattice is also expected to improve the precision of the hydrogen 1S-2S transition frequency, which so far has been measured only with the atomic beam. In this talk, I discuss the magic wavelength for the hydrogen 1S-2S transition, and the possibility of implementing the optical lattice trapping for hydrogen. Optical trapping of hydrogen also opens the way to perform magnetic field free spectroscopy of antihydrogen for the test of CPT theorem.

  6. Measurement of the muonium 1S-2S transition frequency

    SciTech Connect

    Jungmann, K.; Baird, P.E.G.; Barr, J.R.M.; Berkeland, D.; Boshier, M.G.; Braun, B.; Eaton, G.H.; Ferguson, A.I.; Geerds, H.; Hughes, V.W.; Maas, F.; Matthias, B.E.; Matousek, P.; Persaud, M.; zu Putlitz, G.; Reinhard, I.; Riis, E.; Sandars, P.G.H.; Schwarz, W.; Toner, W.T.; Towrie, M.; Willmann, L.; Woodle, K.A.; Woodman, G.

    1995-04-01

    Resonant ionization spectroscopy has been employed for measuring the 1{sup 2}{ital S}{sub 1/2}{minus}2{sup 2}{ital S}{sub 1/2} frequency difference in the hydrogen-like muonium atom to 2 455 529 002(33)(46) MHz. The 1S-2S two-photon transition was induced Doppler-free using two counter-propagating laser beams. The 2S state was photo-ionized by a third photon from the same laser field. The measurement agrees with QED theory within two standard deviations. The mass of the positive muon can be extracted from the isotope shifts in this transition to hydrogen and deuterium to 105.658 80(29)(43) MeV/c{sup 2}. {copyright} 1995 {ital American} {ital Institute} {ital of} {ital Physics}

  7. Measurement of the muonium 1S-2S transition frequency

    SciTech Connect

    Jungmann, K.; Baird, P. E. G.; Barr, J. R. M.; Berkeland, D.; Boshier, M. G.; Braun, B.; Eaton, G. H.; Ferguson, A. I.; Geerds, H.; Hughes, V. W.; Maas, F.; Matthias, B. E.; Matousek, P.; Persaud, M.; Putlitz, G. zu; Reinhard, I.; Riis, E.; Sandars, P. G. H.; Schwarz, W.; Toner, W. T.

    1995-04-01

    Resonant ionization spectroscopy has been employed for measuring the 1{sup 2}S1/2-2{sup 2}S1/2 frequency difference in the hydrogen-like muonium atom to 2 455 529 002(33)(46) MHz. The 1S-2S two-photon transition was induced Doppler-free using two counter-propagating laser beams. The 2S state was photo-ionized by a third photon from the same laser field. The measurement agrees with QED theory within two standard deviations. The mass of the positive muon can be extracted from the isotope shifts in this transition to hydrogen and deuterium to 105.658 80(29)(43) MeV/c{sup 2}.

  8. Measurement of the 1S-2S Frequency in Atomic Hydrogen

    NASA Astrophysics Data System (ADS)

    Hildum, Edward Ames

    A first precise measurement of the 1S-2S energy interval in atomic hydrogen has been obtained by observing the 1S-2S transition in an atomic beam by pulsed Doppler -free two-photon spectroscopy and using an interferometrically calibrated line of ('130)Te(,2) at 486 nm as the reference. The measured 1S-2S frequency is 2 466 061 395.6(4.9) MHz. With the calculated 1S Lamb shift, the 1S-2S frequency yields a value for the Rydberg constant, R(,(INFIN)) = 109 737.314 92(22) cm('-1), which is not in good agreement with the most recent previously measured value, 109 737.315 44(11) cm('-1), obtained by S. R. Amin et al.('16) It is, however, in good agreement with a previous Rydberg value, 109 737.315 04(32) cm('-1), measured by J. E. M. Goldsmith('17). If the Rydberg constant is taken as given, the 1S-2S frequency determines a value for the 1S Lamb shift. With Amin's Rydberg, the measured Lamb shift is 8161.0(5.4) MHz, in poor agreement with the theoretical value of 8149.43(8) MHz. With Goldsmith's Rydberg, the measured Lamb shift is 8151.0(8.7) MHz, in good agreement with theory.

  9. Aspects of 1S-2S spectroscopy of trapped antihydrogen atoms

    NASA Astrophysics Data System (ADS)

    Rasmussen, C. Ø.; Madsen, N.; Robicheaux, F.

    2017-09-01

    Antihydrogen atoms are now routinely trapped in small numbers. One of the purposes of this effort is to make precision comparisons of the 1S-2S transition in hydrogen and antihydrogen as a precision test of the CPT theorem. We investigate, through calculations and simulations, various methods by which the 1S-2S transition may be probed with only a few trapped atoms. We consider the known constraints from typical experimental geometries, detection methods, sample temperatures, laser light sources etc and we identify a viable path towards a measurement of this transition at the 10‑11 level in a realistic scenario. We also identify ways in which such a first measurement could be improved upon as a function of projected changes and improvements in antihydrogen synthesis and trapping. These calculations recently guided the first observation of the 1S-2S transition in trapped antihydrogen.

  10. Absolute cross section for electron-impact ionization of He (1 s 2 s 3S)

    NASA Astrophysics Data System (ADS)

    Génévriez, Matthieu; Jureta, Jozo J.; Defrance, Pierre; Urbain, Xavier

    2017-07-01

    We present an experimental determination of the electron-impact ionization cross section of the 1 s 2 s 3S state of helium, for which there is a serious long-lasting discrepancy between theory and experiment. A technique for the production of a fast, intense beam of helium in the 1 s 2 s 3S state only has been developed for this purpose, based on photodetachment of the He- anion. The cross section is measured using the animated crossed beam technique. The present results are much lower than the experimental data of Dixon et al. [J. Phys. B 9, 2617 (1976), 10.1088/0022-3700/9/15/013] and are in excellent agreement with the calculation of Fursa and Bray [J. Phys. B 36, 1663 (2003), 10.1088/0953-4075/36/8/317].

  11. Feasibility of coherent xuv spectroscopy on the 1S-2S transition in singly ionized helium

    SciTech Connect

    Herrmann, M.; Saathoff, G.; Gohle, C.; Ozawa, A.; Batteiger, V.; Knuenz, S.; Kolachevsky, N.; Udem, Th.; Haas, M.; Jentschura, U. D.; Kottmann, F.; Leibfried, D.; Schuessler, H. A.; Haensch, T. W.

    2009-05-15

    The 1S-2S two-photon transition in singly ionized helium is a highly interesting candidate for precision tests of bound-state quantum electrodynamics (QED). With the recent advent of extreme ultraviolet frequency combs, highly coherent quasi-continuous-wave light sources at 61 nm have become available, and precision spectroscopy of this transition now comes into reach for the first time. We discuss quantitatively the feasibility of such an experiment by analyzing excitation and ionization rates, propose an experimental scheme, and explore the potential for QED tests.

  12. Experimental considerations for testing antimatter antigravity using positronium 1S-2S spectroscopy

    NASA Astrophysics Data System (ADS)

    Crivelli, P.; Cooke, D. A.; Friedreich, S.

    2014-05-01

    In this contribution to the WAG 2013 workshop we report on the status of our measurement of the 1S-2S transition frequency of positronium. The aim of this experiment is to reach a precision of 0.5 ppb in order to cross check the QED calculations. After reviewing the current available sources of Ps, we consider laser cooling as a route to push the precision in the measurement down to 0.1 ppb. If such an uncertainty could be achieved, this would be sensitive to the gravitational redshift and therefore be able to assess the sign of gravity for antimatter.

  13. Precision Measurement of the Hydrogen-Deuterium 1S-2S Isotope Shift

    SciTech Connect

    Parthey, Christian G.; Matveev, Arthur; Alnis, Janis; Pohl, Randolf; Udem, Thomas; Kolachevsky, Nikolai; Haensch, Theodor W.; Jentschura, Ulrich D.

    2010-06-11

    Measuring the hydrogen-deuterium isotope shift via two-photon spectroscopy of the 1S-2S transition, we obtain 670 994 334 606(15) Hz. This is a 10-times improvement over the previous best measurement [A. Huber et al., Phys. Rev. Lett. 80, 468 (1998)] confirming its frequency value. A calculation of the difference of the mean square charge radii of deuterium and hydrogen results in {sub d}-{sub p}=3.820 07(65) fm{sup 2}, a more than twofold improvement compared to the former value.

  14. Precision measurement of the hydrogen 1S-2S frequency via a 920-km fiber link.

    PubMed

    Matveev, Arthur; Parthey, Christian G; Predehl, Katharina; Alnis, Janis; Beyer, Axel; Holzwarth, Ronald; Udem, Thomas; Wilken, Tobias; Kolachevsky, Nikolai; Abgrall, Michel; Rovera, Daniele; Salomon, Christophe; Laurent, Philippe; Grosche, Gesine; Terra, Osama; Legero, Thomas; Schnatz, Harald; Weyers, Stefan; Altschul, Brett; Hänsch, Theodor W

    2013-06-07

    We have measured the frequency of the extremely narrow 1S-2S two-photon transition in atomic hydrogen using a remote cesium fountain clock with the help of a 920 km stabilized optical fiber. With an improved detection method we obtain f(1S-2S)=2466 061 413 187 018 (11)  Hz with a relative uncertainty of 4.5×10(-15), confirming our previous measurement obtained with a local cesium clock [C. G. Parthey et al., Phys. Rev. Lett. 107, 203001 (2011)]. Combining these results with older measurements, we constrain the linear combinations of Lorentz boost symmetry violation parameters c((TX))=(3.1±1.9)×10(-11) and 0.92c((TY))+0.40c((TZ))=(2.6±5.3)×10(-11) in the standard model extension framework [D. Colladay, V. A. Kostelecký, Phys. Rev. D. 58, 116002 (1998)].

  15. Observation of the 1S-2S transition in trapped antihydrogen

    NASA Astrophysics Data System (ADS)

    Ahmadi, M.; Alves, B. X. R.; Baker, C. J.; Bertsche, W.; Butler, E.; Capra, A.; Carruth, C.; Cesar, C. L.; Charlton, M.; Cohen, S.; Collister, R.; Eriksson, S.; Evans, A.; Evetts, N.; Fajans, J.; Friesen, T.; Fujiwara, M. C.; Gill, D. R.; Gutierrez, A.; Hangst, J. S.; Hardy, W. N.; Hayden, M. E.; Isaac, C. A.; Ishida, A.; Johnson, M. A.; Jones, S. A.; Jonsell, S.; Kurchaninov, L.; Madsen, N.; Mathers, M.; Maxwell, D.; McKenna, J. T. K.; Menary, S.; Michan, J. M.; Momose, T.; Munich, J. J.; Nolan, P.; Olchanski, K.; Olin, A.; Pusa, P.; Rasmussen, C. Ø.; Robicheaux, F.; Sacramento, R. L.; Sameed, M.; Sarid, E.; Silveira, D. M.; Stracka, S.; Stutter, G.; So, C.; Tharp, T. D.; Thompson, J. E.; Thompson, R. I.; van der Werf, D. P.; Wurtele, J. S.

    2017-02-01

    The spectrum of the hydrogen atom has played a central part in fundamental physics over the past 200 years. Historical examples of its importance include the wavelength measurements of absorption lines in the solar spectrum by Fraunhofer, the identification of transition lines by Balmer, Lyman and others, the empirical description of allowed wavelengths by Rydberg, the quantum model of Bohr, the capability of quantum electrodynamics to precisely predict transition frequencies, and modern measurements of the 1S-2S transition by Hänsch to a precision of a few parts in 1015. Recent technological advances have allowed us to focus on antihydrogen—the antimatter equivalent of hydrogen. The Standard Model predicts that there should have been equal amounts of matter and antimatter in the primordial Universe after the Big Bang, but today’s Universe is observed to consist almost entirely of ordinary matter. This motivates the study of antimatter, to see if there is a small asymmetry in the laws of physics that govern the two types of matter. In particular, the CPT (charge conjugation, parity reversal and time reversal) theorem, a cornerstone of the Standard Model, requires that hydrogen and antihydrogen have the same spectrum. Here we report the observation of the 1S-2S transition in magnetically trapped atoms of antihydrogen. We determine that the frequency of the transition, which is driven by two photons from a laser at 243 nanometres, is consistent with that expected for hydrogen in the same environment. This laser excitation of a quantum state of an atom of antimatter represents the most precise measurement performed on an anti-atom. Our result is consistent with CPT invariance at a relative precision of about 2 × 10-10.

  16. Observation of the 1S-2S transition in trapped antihydrogen.

    PubMed

    Ahmadi, M; Alves, B X R; Baker, C J; Bertsche, W; Butler, E; Capra, A; Carruth, C; Cesar, C L; Charlton, M; Cohen, S; Collister, R; Eriksson, S; Evans, A; Evetts, N; Fajans, J; Friesen, T; Fujiwara, M C; Gill, D R; Gutierrez, A; Hangst, J S; Hardy, W N; Hayden, M E; Isaac, C A; Ishida, A; Johnson, M A; Jones, S A; Jonsell, S; Kurchaninov, L; Madsen, N; Mathers, M; Maxwell, D; McKenna, J T K; Menary, S; Michan, J M; Momose, T; Munich, J J; Nolan, P; Olchanski, K; Olin, A; Pusa, P; Rasmussen, C Ø; Robicheaux, F; Sacramento, R L; Sameed, M; Sarid, E; Silveira, D M; Stracka, S; Stutter, G; So, C; Tharp, T D; Thompson, J E; Thompson, R I; van der Werf, D P; Wurtele, J S

    2017-01-26

    The spectrum of the hydrogen atom has played a central part in fundamental physics over the past 200 years. Historical examples of its importance include the wavelength measurements of absorption lines in the solar spectrum by Fraunhofer, the identification of transition lines by Balmer, Lyman and others, the empirical description of allowed wavelengths by Rydberg, the quantum model of Bohr, the capability of quantum electrodynamics to precisely predict transition frequencies, and modern measurements of the 1S-2S transition by Hänsch to a precision of a few parts in 10(15). Recent technological advances have allowed us to focus on antihydrogen-the antimatter equivalent of hydrogen. The Standard Model predicts that there should have been equal amounts of matter and antimatter in the primordial Universe after the Big Bang, but today's Universe is observed to consist almost entirely of ordinary matter. This motivates the study of antimatter, to see if there is a small asymmetry in the laws of physics that govern the two types of matter. In particular, the CPT (charge conjugation, parity reversal and time reversal) theorem, a cornerstone of the Standard Model, requires that hydrogen and antihydrogen have the same spectrum. Here we report the observation of the 1S-2S transition in magnetically trapped atoms of antihydrogen. We determine that the frequency of the transition, which is driven by two photons from a laser at 243 nanometres, is consistent with that expected for hydrogen in the same environment. This laser excitation of a quantum state of an atom of antimatter represents the most precise measurement performed on an anti-atom. Our result is consistent with CPT invariance at a relative precision of about 2 × 10(-10).

  17. Transverse Momentum Distribution in Ψ(1S,2S) Photoproduction in PP and AA Collisions at the LHC

    NASA Astrophysics Data System (ADS)

    Martins, Sony; de Leone Gay Ducati, Maria Beatriz

    The exclusive photoproduction of the heavy vector mesons Ψ(1S, 2S) is investigated in the context of ultra-peripheral collisions proton-proton and nucleus-nucleus for the energies available at the LHC run 2. Using the light-cone color dipole formalism, it was calculated the transverse momentum distribution in the central rapidity region, in which it is expected major contribution for the process.

  18. Choice of gauge in 2-photon 1s-2s transition in atomic hydrogen and pseudostate expansions

    NASA Technical Reports Server (NTRS)

    Shabazz, Abdulalim A.

    1989-01-01

    The problem of gauge choice in multiphoton transitions in connection with the proper choice of the unperturbed wave functions require to insure gauge invariance was considered. J. Bassani, J. J. Forney, and A. Quattropani considered the case of 2-photon 1s-2s transition rate for hydrogen, using gauges vector E x vector r and vector A x vector p. Exactly the same results were obtained for the two gauges, but the findings indicate that the vector E x vector r interaction tends to the final result with a small number of intermediate states and is therefore the one to be used in any approximate calculation. Whether the so-called pseudostate expansion method works equally well with either gauge was tested. To accomplish this task, in addition to researching the problem, the FORTRAN programming was learned and a FORTRAN program was constructed for the calculation of the dimensionless 2-photon transition probability amplitude D(v) for 1s-2s transition in Hydrogen as a function as a function of the incident photon frequency v in gauge vector E x vector p at certain values of v, using the pseudostate method. However, some puzzling unresolved difficulties were experienced in the calculation. Then should the pseudostate calculations prove successful for gauge vector E x vector r the method will be applied to gauge vector A x vector p. If successful, then the problem is complete.

  19. Magic wavelength for the hydrogen 1 S -2 S transition: Contribution of the continuum and the reduced-mass correction

    NASA Astrophysics Data System (ADS)

    Adhikari, C. M.; Kawasaki, A.; Jentschura, U. D.

    2016-09-01

    Recently, we studied the magic wavelength for the atomic hydrogen 1 S -2 S transition [A. Kawasaki, Phys. Rev. A 92, 042507 (2015), 10.1103/PhysRevA.92.042507]. An explicit summation over virtual atomic states of the discrete part of the hydrogen spectrum was performed to evaluate the atomic polarizability. In this paper, we supplement the contribution of the continuum part of the spectrum and add the reduced-mass correction. The magic wavelength, at which the lowest-order ac Stark shifts of the 1 S and 2 S states are equal, is found to be 514.6 nm. The ac Stark shift at the magic wavelength is -221.6 Hz /(kW /cm2) , and the slope of the ac Stark shift at the magic wavelength under a change of the driving laser frequency is -0.2157 Hz /[GHz (kW /cm2)] .

  20. Measurement of the He 1s2s (1)S(0) isotopic shift using a tunable VUV anti-Stokes light source.

    PubMed

    Falcone, R W; Willison, J R; Young, J F; Harris, S E

    1978-11-01

    We describe a high-resolution, vacuum-ultraviolet spectroscopic technique based on a tunable, narrow-band, VUV, spontaneous anti-Stokes light source. The technique was used to measure the absolute energies of the 1s2s (1)S(0) states of (3)He and (4)He; the 1s2s (1)S(0) level of (3)He is 7.8 +/- 0.5 cm(-1) below that of (4)He.

  1. Complete next-to-leading-order study on the yield and polarization of Υ(1S,2S,3S) at the Tevatron and LHC.

    PubMed

    Gong, Bin; Wan, Lu-Ping; Wang, Jian-Xiong; Zhang, Hong-Fei

    2014-01-24

    Based on the nonrelativistic QCD factorization scheme, we present the first complete next-to-leading-order study on the yield and polarization of Υ(1S,2S,3S) hadroproduction. By using the color-octet long-distance matrix elements obtained from fits of the experimental measurements on Υ yield and polarization at the Tevatron and LHC, our results can explain the measurements on the yield very well, and for the polarizations of Υ(1S,2S,3S), they are in (good, good, bad) agreement with recent CMS measurement, but still have some distance from the CDF measurement.

  2. Measurement of Υ (1 S +2 S +3 S ) production in p +p and Au + Au collisions at √{sNN}=200 GeV

    NASA Astrophysics Data System (ADS)

    Adare, A.; Afanasiev, S.; Aidala, C.; Ajitanand, N. N.; Akiba, Y.; Akimoto, R.; Al-Bataineh, H.; Al-Ta'Ani, H.; Alexander, J.; Angerami, A.; Aoki, K.; Apadula, N.; Aphecetche, L.; Aramaki, Y.; Asai, J.; Asano, H.; Aschenauer, E. C.; Atomssa, E. T.; Averbeck, R.; Awes, T. C.; Azmoun, B.; Babintsev, V.; Bai, M.; Baksay, G.; Baksay, L.; Baldisseri, A.; Bannier, B.; Barish, K. N.; Barnes, P. D.; Bassalleck, B.; Basye, A. T.; Bathe, S.; Batsouli, S.; Baublis, V.; Baumann, C.; Baumgart, S.; Bazilevsky, A.; Belikov, S.; Belmont, R.; Bennett, R.; Berdnikov, A.; Berdnikov, Y.; Bickley, A. A.; Bing, X.; Blau, D. S.; Boissevain, J. G.; Bok, J. S.; Borel, H.; Boyle, K.; Brooks, M. L.; Buesching, H.; Bumazhnov, V.; Bunce, G.; Butsyk, S.; Camacho, C. M.; Campbell, S.; Castera, P.; Chang, B. S.; Chang, W. C.; Charvet, J.-L.; Chen, C.-H.; Chernichenko, S.; Chi, C. Y.; Chiu, M.; Choi, I. J.; Choi, J. B.; Choi, S.; Choudhury, R. K.; Christiansen, P.; Chujo, T.; Chung, P.; Churyn, A.; Chvala, O.; Cianciolo, V.; Citron, Z.; Cole, B. A.; Connors, M.; Constantin, P.; Csanád, M.; Csörgő, T.; Dahms, T.; Dairaku, S.; Das, K.; Datta, A.; Daugherity, M. S.; David, G.; Denisov, A.; D'Enterria, D.; Deshpande, A.; Desmond, E. J.; Dharmawardane, K. V.; Dietzsch, O.; Ding, L.; Dion, A.; Donadelli, M.; Drapier, O.; Drees, A.; Drees, K. A.; Dubey, A. K.; Durham, J. M.; Durum, A.; Dutta, D.; Dzhordzhadze, V.; D'Orazio, L.; Edwards, S.; Efremenko, Y. V.; Ellinghaus, F.; Engelmore, T.; Enokizono, A.; En'yo, H.; Esumi, S.; Eyser, K. O.; Fadem, B.; Fields, D. E.; Finger, M.; Finger, M.; Fleuret, F.; Fokin, S. L.; Fraenkel, Z.; Frantz, J. E.; Franz, A.; Frawley, A. D.; Fujiwara, K.; Fukao, Y.; Fusayasu, T.; Gainey, K.; Gal, C.; Garishvili, A.; Garishvili, I.; Glenn, A.; Gong, H.; Gong, X.; Gonin, M.; Gosset, J.; Goto, Y.; Granier de Cassagnac, R.; Grau, N.; Greene, S. V.; Grosse Perdekamp, M.; Gunji, T.; Guo, L.; Gustafsson, H.-Å.; Hachiya, T.; Hadj Henni, A.; Haggerty, J. S.; Hahn, K. I.; Hamagaki, H.; Han, R.; Hanks, J.; Hartouni, E. P.; Haruna, K.; Hashimoto, K.; Haslum, E.; Hayano, R.; He, X.; Heffner, M.; Hemmick, T. K.; Hester, T.; Hill, J. C.; Hohlmann, M.; Hollis, R. S.; Holzmann, W.; Homma, K.; Hong, B.; Horaguchi, T.; Hori, Y.; Hornback, D.; Huang, S.; Ichihara, T.; Ichimiya, R.; Iinuma, H.; Ikeda, Y.; Imai, K.; Imrek, J.; Inaba, M.; Iordanova, A.; Isenhower, D.; Ishihara, M.; Isobe, T.; Issah, M.; Isupov, A.; Ivanischev, D.; Ivanishchev, D.; Jacak, B. V.; Javani, M.; Jia, J.; Jiang, X.; Jin, J.; Johnson, B. M.; Joo, K. S.; Jouan, D.; Jumper, D. S.; Kajihara, F.; Kametani, S.; Kamihara, N.; Kamin, J.; Kaneti, S.; Kang, B. H.; Kang, J. H.; Kang, J. S.; Kapustinsky, J.; Karatsu, K.; Kasai, M.; Kawall, D.; Kazantsev, A. V.; Kempel, T.; Khanzadeev, A.; Kijima, K. M.; Kikuchi, J.; Kim, B. I.; Kim, C.; Kim, D. H.; Kim, D. J.; Kim, E.; Kim, E.-J.; Kim, H. J.; Kim, K.-B.; Kim, S. H.; Kim, Y.-J.; Kim, Y. K.; Kinney, E.; Kiriluk, K.; Kiss, Á.; Kistenev, E.; Klatsky, J.; Klay, J.; Klein-Boesing, C.; Kleinjan, D.; Kline, P.; Kochenda, L.; Komatsu, Y.; Komkov, B.; Konno, M.; Koster, J.; Kotchetkov, D.; Kotov, D.; Kozlov, A.; Král, A.; Kravitz, A.; Krizek, F.; Kunde, G. J.; Kurita, K.; Kurosawa, M.; Kweon, M. J.; Kwon, Y.; Kyle, G. S.; Lacey, R.; Lai, Y. S.; Lajoie, J. G.; Layton, D.; Lebedev, A.; Lee, B.; Lee, D. M.; Lee, J.; Lee, K. B.; Lee, K. S.; Lee, S. H.; Lee, S. R.; Lee, T.; Leitch, M. J.; Leite, M. A. L.; Leitgab, M.; Lenzi, B.; Lewis, B.; Li, X.; Liebing, P.; Lim, S. H.; Linden Levy, L. A.; Liška, T.; Litvinenko, A.; Liu, H.; Liu, M. X.; Love, B.; Lynch, D.; Maguire, C. F.; Makdisi, Y. I.; Makek, M.; Malakhov, A.; Malik, M. D.; Manion, A.; Manko, V. I.; Mannel, E.; Mao, Y.; Mašek, L.; Masui, H.; Masumoto, S.; Matathias, F.; McCumber, M.; McGaughey, P. L.; McGlinchey, D.; McKinney, C.; Means, N.; Mendoza, M.; Meredith, B.; Miake, Y.; Mibe, T.; Mignerey, A. C.; Mikeš, P.; Miki, K.; Milov, A.; Mishra, D. K.; Mishra, M.; Mitchell, J. T.; Miyachi, Y.; Miyasaka, S.; Mohanty, A. K.; Moon, H. J.; Morino, Y.; Morreale, A.; Morrison, D. P.; Motschwiller, S.; Moukhanova, T. V.; Mukhopadhyay, D.; Murakami, T.; Murata, J.; Nagae, T.; Nagamiya, S.; Nagle, J. L.; Naglis, M.; Nagy, M. I.; Nakagawa, I.; Nakamiya, Y.; Nakamura, K. R.; Nakamura, T.; Nakano, K.; Nattrass, C.; Nederlof, A.; Newby, J.; Nguyen, M.; Nihashi, M.; Niida, T.; Nouicer, R.; Novitzky, N.; Nyanin, A. S.; O'Brien, E.; Oda, S. X.; Ogilvie, C. A.; Oka, M.; Okada, K.; Onuki, Y.; Oskarsson, A.; Ouchida, M.; Ozawa, K.; Pak, R.; Palounek, A. P. T.; Pantuev, V.; Papavassiliou, V.; Park, B. H.; Park, I. H.; Park, J.; Park, S. K.; Park, W. J.; Pate, S. F.; Patel, L.; Pei, H.; Peng, J.-C.; Pereira, H.; Peresedov, V.; Peressounko, D. Yu.; Petti, R.; Pinkenburg, C.; Pisani, R. P.; Proissl, M.; Purschke, M. L.

    2015-02-01

    Measurements of bottomonium production in heavy-ion and p +p collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The inclusive yield of the three Υ states, Υ (1 S +2 S +3 S ) , was measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au +Au and p +p collisions at √{sNN}=200 GeV. The Υ (1 S +2 S +3 S ) →e+e- differential cross section at midrapidity was found to be Beed σ /d y =108 ±38 (stat) ±15 (syst) ±11 (luminosity) pb in p +p collisions. The nuclear modification factor in the 30% most central Au +Au collisions indicates a suppression of the total Υ state yield relative to the extrapolation from p +p collision data. The suppression is consistent with measurements made by STAR at RHIC and at higher energies by the CMS experiment at the Large Hadron Collider.

  3. Measurement of the 1s2s 1S0-1s2p 3P1 intercombination interval in helium-like silicon.

    PubMed

    Redshaw, M; Myers, E G

    2002-01-14

    Using Doppler-tuned fast-beam laser spectroscopy the 1s2s 1S0-1s2p 3P1 intercombination interval in 28Si12+ has been measured to be 7230.5(2) cm(-1). The experiment made use of a single-frequency Nd:YAG (1.319 microm) laser and a high-finesse optical buildup cavity. The result provides a precision test of modern relativistic and QED atomic theory.

  4. Determination of the 1s2{\\ell }2{{\\ell }}^{\\prime } state production ratios {{}^{4}P}^{o}/{}^{2}P, {}^{2}D/{}^{2}P and {{}^{2}P}_{+}/{{}^{2}P}_{-} from fast (1{s}^{2},1s2s\\,{}^{3}S) mixed-state He-like ion beams in collisions with H2 targets

    NASA Astrophysics Data System (ADS)

    Benis, E. P.; Zouros, T. J. M.

    2016-12-01

    New results are presented on the ratio {R}m={σ }{T2p}( {}4P)/{σ }{T2p}({}2P) concerning the production cross sections of Li-like 1s2s2p quartet and doublet P states formed in energetic ion-atom collisions by single 2p electron transfer to the metastable 1s2s {}3S component of the He-like ion beam. Spin statistics predict a value of R m = 2 independent of the collision system in disagreement with most reported measurements of {R}m≃ 1{--}9. A new experimental approach is presented for the evaluation of R m having some practical advantages over earlier approaches. It also allows for the determination of the separate contributions of ground- and metastable-state beam components to the measured spectra. Applying our technique to zero-degree Auger projectile spectra from 4.5 MeV {{{B}}}3+ (Benis et al 2002 Phys. Rev. A 65 064701) and 25.3 MeV {{{F}}}7+ (Zamkov et al 2002 Phys. Rev. A 65 062706) mixed state (1{s}2 {}1S,1s2s {}3S) He-like ion collisions with H2 targets, we report new values of {R}m=3.5+/- 0.4 for boron and {R}m=1.8+/- 0.3 for fluorine. In addition, the ratios of {}2D/{}2P and {{}2P}+/{{}2P}- populations from either the metastable and/or ground state beam component, also relevant to this analysis, are evaluated and compared to previously reported results for carbon collisions on helium (Strohschein et al 2008 Phys. Rev. A 77 022706) including a critical comparison to theory.

  5. Effects of surface residual species in SBA-16 on encapsulated chiral (1S,2S)-DPEN-RuCl2(TPP)2 in asymmetric hydrogenation of acetophenone

    NASA Astrophysics Data System (ADS)

    Shi, Xiufeng; Xing, Bin; Fan, Binbin; Xue, Zhaoteng; Li, Ruifeng

    2016-03-01

    The SBA-16 obtained by different routes of elimination of organic templates were used as the hosts for encapsulation of chiral Ru complex (1S,2S)-DPEN-RuCl2(TPP)2 ( 1) (DPEN = 1,2-diphenylethylene-diamine, TPP = triphenyl phosphine). The methods for removing templates had distinct effects on the amount of residual template in SBA-16, which made the SBA-16 with different surface and structure properties. 1 encapsulated in SBA-16 extracted with the mixture of pyridine and ethanol showed higher activity and enantioselectivity for acetophenone asymmetric hydrogenation.

  6. Measurement of the two-photon spectral distribution from decay of the 1s2s;{sup 1}S{sub 0} level in heliumlike nickel

    SciTech Connect

    Schaffer, H.W.; Mokler, P.H.; Kanter, E.P.; Curtis, L.J. Livingston, A.E.

    1999-01-01

    A measurement of the shape of the spectral distribution of two-photon decay of the 1s2s{sup 1}S{sub 0} level in heliumlike nickel is described. Uncertainties in detector efficiencies which had limited the precision of earlier measurements were eliminated by comparing the continuum emission from two-photon decays of H-like and He-like nickel. Our results are in agreement with the nonrelativistic calculation of Drake and the fully relativistic calculation of Derevianko and Johnson and suggest a method for testing relativistic atomic many-body theory in strong fields. {copyright} {ital 1999} {ital The American Physical Society}

  7. Measurement of Υ(1S + 2S +3S) production in p + p and Au + Au collisions at \\(\\sqrt{s_{\\mathrm{NN}}}=200\\) GeV

    SciTech Connect

    Adare, A.; Afanasiev, S.; Aidala, C.; Ajitanand, N. N.; Akiba, Y.; Akimoto, R.; Al-Bataineh, H.; Al-Ta'ani, H.; Alexander, J.; Angerami, A.; Aoki, K.; Apadula, N.; Aphecetche, L.; Aramaki, Y.; Asai, J.; Asano, H.; Aschenauer, E. C.; Atomssa, E. T.; Averbeck, R.; Awes, T. C.; Azmoun, B.; Babintsev, V.; Bai, M.; Baksay, G.; Baksay, L.; Baldisseri, A.; Bannier, B.; Barish, K. N.; Barnes, P. D.; Bassalleck, B.; Basye, A. T.; Bathe, S.; Batsouli, S.; Baublis, V.; Baumann, C.; Baumgart, S.; Bazilevsky, A.; Belikov, S.; Belmont, R.; Bennett, R.; Berdnikov, A.; Berdnikov, Y.; Bickley, A. A.; Bing, X.; Blau, D. S.; Boissevain, J. G.; Bok, J. S.; Borel, H.; Boyle, K.; Brooks, M. L.; Buesching, H.; Bumazhnov, V.; Bunce, G.; Butsyk, S.; Camacho, C. M.; Campbell, S.; Castera, P.; Chang, B. S.; Chang, W. C.; Charvet, J. -L.; Chen, C. -H.; Chernichenko, S.; Chi, C. Y.; Chiu, M.; Choi, I. J.; Choi, J. B.; Choi, S.; Choudhury, R. K.; Christiansen, P.; Chujo, T.; Chung, P.; Churyn, A.; Chvala, O.; Cianciolo, V.; Citron, Z.; Cole, B. A.; Connors, M.; Constantin, P.; Csanád, M.; Csörgő, T.; Dahms, T.; Dairaku, S.; Das, K.; Datta, A.; Daugherity, M. S.; David, G.; Denisov, A.; d'Enterria, D.; Deshpande, A.; Desmond, E. J.; Dharmawardane, K. V.; Dietzsch, O.; Ding, L.; Dion, A.; Donadelli, M.; Drapier, O.; Drees, A.; Drees, K. A.; Dubey, A. K.; Durham, J. M.; Durum, A.; Dutta, D.; Dzhordzhadze, V.; D'Orazio, L.; Edwards, S.; Efremenko, Y. V.; Ellinghaus, F.; Engelmore, T.; Enokizono, A.; En'yo, H.; Esumi, S.; Eyser, K. O.; Fadem, B.; Fields, D. E.; Finger, M.; Finger, M.; Fleuret, F.; Fokin, S. L.; Fraenkel, Z.; Frantz, J. E.; Franz, A.; Frawley, A. D.; Fujiwara, K.; Fukao, Y.; Fusayasu, T.; Gainey, K.; Gal, C.; Garishvili, A.; Garishvili, I.; Glenn, A.; Gong, H.; Gong, X.; Gonin, M.; Gosset, J.; Goto, Y.; Granier de Cassagnac, R.; Grau, N.; Greene, S. V.; Grosse Perdekamp, M.; Gunji, T.; Guo, L.; Gustafsson, H. -Å.; Hachiya, T.; Hadj Henni, A.; Haggerty, J. S.; Hahn, K. I.; Hamagaki, H.; Han, R.; Hanks, J.; Hartouni, E. P.; Haruna, K.; Hashimoto, K.; Haslum, E.; Hayano, R.; He, X.; Heffner, M.; Hemmick, T. K.; Hester, T.; Hill, J. C.; Hohlmann, M.; Hollis, R. S.; Holzmann, W.; Homma, K.; Hong, B.; Horaguchi, T.; Hori, Y.; Hornback, D.; Huang, S.; Ichihara, T.; Ichimiya, R.; Iinuma, H.; Ikeda, Y.; Imai, K.; Imrek, J.; Inaba, M.; Iordanova, A.; Isenhower, D.; Ishihara, M.; Isobe, T.; Issah, M.; Isupov, A.; Ivanischev, D.; Ivanishchev, D.; Jacak, B. V.; Javani, M.; Jia, J.; Jiang, X.; Jin, J.; Johnson, B. M.; Joo, K. S.; Jouan, D.; Jumper, D. S.; Kajihara, F.; Kametani, S.; Kamihara, N.; Kamin, J.; Kaneti, S.; Kang, B. H.; Kang, J. H.; Kang, J. S.; Kapustinsky, J.; Karatsu, K.; Kasai, M.; Kawall, D.; Kazantsev, A. V.; Kempel, T.; Khanzadeev, A.; Kijima, K. M.; Kikuchi, J.; Kim, B. I.; Kim, C.; Kim, D. H.; Kim, D. J.; Kim, E.; Kim, E. -J.; Kim, H. J.; Kim, K. -B.; Kim, S. H.; Kim, Y. -J.; Kim, Y. K.; Kinney, E.; Kiriluk, K.; Kiss, Á.; Kistenev, E.; Klatsky, J.; Klay, J.; Klein-Boesing, C.; Kleinjan, D.; Kline, P.; Kochenda, L.; Komatsu, Y.; Komkov, B.; Konno, M.; Koster, J.; Kotchetkov, D.; Kotov, D.; Kozlov, A.; Král, A.; Kravitz, A.; Krizek, F.; Kunde, G. J.; Kurita, K.; Kurosawa, M.; Kweon, M. J.; Kwon, Y.; Kyle, G. S.; Lacey, R.; Lai, Y. S.; Lajoie, J. G.; Layton, D.; Lebedev, A.; Lee, B.; Lee, D. M.; Lee, J.; Lee, K. B.; Lee, K. S.; Lee, S. H.; Lee, S. R.; Lee, T.; Leitch, M. J.; Leite, M. A. L.; Leitgab, M.; Lenzi, B.; Lewis, B.; Li, X.; Liebing, P.; Lim, S. H.; Linden Levy, L. A.; Liška, T.; Litvinenko, A.; Liu, H.; Liu, M. X.; Love, B.; Lynch, D.; Maguire, C. F.; Makdisi, Y. I.; Makek, M.; Malakhov, A.; Malik, M. D.; Manion, A.; Manko, V. I.; Mannel, E.; Mao, Y.; Mašek, L.; Masui, H.; Masumoto, S.; Matathias, F.; McCumber, M.; McGaughey, P. L.; McGlinchey, D.; McKinney, C.; Means, N.; Mendoza, M.; Meredith, B.; Miake, Y.; Mibe, T.; Mignerey, A. C.; Mikeš, P.; Miki, K.; Milov, A.; Mishra, D. K.; Mishra, M.; Mitchell, J. T.; Miyachi, Y.; Miyasaka, S.; Mohanty, A. K.; Moon, H. J.; Morino, Y.; Morreale, A.; Morrison, D. P.; Motschwiller, S.; Moukhanova, T. V.; Mukhopadhyay, D.; Murakami, T.; Murata, J.; Nagae, T.; Nagamiya, S.; Nagle, J. L.; Naglis, M.; Nagy, M. I.; Nakagawa, I.; Nakamiya, Y.; Nakamura, K. R.; Nakamura, T.; Nakano, K.; Nattrass, C.; Nederlof, A.; Newby, J.; Nguyen, M.; Nihashi, M.; Niida, T.; Nouicer, R.; Novitzky, N.; Nyanin, A. S.; O'Brien, E.; Oda, S. X.; Ogilvie, C. A.; Oka, M.; Okada, K.; Onuki, Y.; Oskarsson, A.; Ouchida, M.; Ozawa, K.; Pak, R.; Palounek, A. P. T.; Pantuev, V.; Papavassiliou, V.; Park, B. H.; Park, I. H.; Park, J.; Park, S. K.; Park, W. J.; Pate, S. F.; Patel, L.; Pei, H.; Peng, J. -C.; Pereira, H.; Peresedov, V.; Peressounko, D. Yu.; Petti, R.; Pinkenburg, C.; Pisani, R. P.; Proissl, M.; Purschke, M. L.; Purwar, A. K.; Qu, H.; Rak, J.; Rakotozafindrabe, A.; Ravinovich, I.; Read, K. F.; Rembeczki, S.; Reygers, K.; Reynolds, D.; Riabov, V.; Riabov, Y.; Richardson, E.; Riveli, N.; Roach, D.; Roche, G.; Rolnick, S. D.; Rosati, M.; Rosendahl, S. S. E.; Rosnet, P.; Rukoyatkin, P.; Ružička, P.; Rykov, V. L.; Sahlmueller, B.; Saito, N.; Sakaguchi, T.; Sakai, S.; Sakashita, K.; Samsonov, V.; Sano, M.; Sarsour, M.; Sato, T.; Sawada, S.; Sedgwick, K.; Seele, J.; Seidl, R.; Semenov, A. Yu.; Semenov, V.; Sen, A.; Seto, R.; Sharma, D.; Shein, I.; Shibata, T. -A.; Shigaki, K.; Shimomura, M.; Shoji, K.; Shukla, P.; Sickles, A.; Silva, C. L.; Silvermyr, D.; Silvestre, C.; Sim, K. S.; Singh, B. K.; Singh, C. P.; Singh, V.; Slunečka, M.; Soldatov, A.; Soltz, R. A.; Sondheim, W. E.; Sorensen, S. P.; Soumya, M.; Sourikova, I. V.; Staley, F.; Stankus, P. W.; Stenlund, E.; Stepanov, M.; Ster, A.; Stoll, S. P.; Sugitate, T.; Suire, C.; Sukhanov, A.; Sun, J.; Sziklai, J.; Takagui, E. M.; Takahara, A.; Taketani, A.; Tanabe, R.; Tanaka, Y.; Taneja, S.; Tanida, K.; Tannenbaum, M. J.; Tarafdar, S.; Taranenko, A.; Tarján, P.; Tennant, E.; Themann, H.; Thomas, T. L.; Todoroki, T.; Togawa, M.; Toia, A.; Tomášek, L.; Tomášek, M.; Tomita, Y.; Torii, H.; Towell, R. S.; Tram, V-N.; Tserruya, I.; Tsuchimoto, Y.; Tsuji, T.; Vale, C.; Valle, H.; van Hecke, H. W.; Vargyas, M.; Vazquez-Zambrano, E.; Veicht, A.; Velkovska, J.; Vértesi, R.; Vinogradov, A. A.; Virius, M.; Vossen, A.; Vrba, V.; Vznuzdaev, E.; Wang, X. R.; Watanabe, D.; Watanabe, K.; Watanabe, Y.; Watanabe, Y. S.; Wei, F.; Wei, R.; Wessels, J.; Whitaker, S.; White, S. N.; Winter, D.; Wolin, S.; Woody, C. L.; Wysocki, M.; Xie, W.; Yamaguchi, Y. L.; Yamaura, K.; Yang, R.; Yanovich, A.; Ying, J.; Yokkaichi, S.; You, Z.; Young, G. R.; Younus, I.; Yushmanov, I. E.; Zajc, W. A.; Zaudtke, O.; Zelenski, A.; Zhang, C.; Zhou, S.; Zolin, L.

    2015-02-24

    Measurements of bottomonium production in heavy-ion and p+p collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The inclusive yield of the three Υ states, Υ(1S + 2S + 3S), was measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au+Au and p+p collisions at \\(\\sqrt{s_{\\mathrm{NN}}}=200\\) GeV. The Υ(1S + 2S + 3S) → e⁺e⁻ differential cross section at midrapidity was found to be Beedσ/dy = 108 ± 38 (stat) ± 15 (syst) ± 11 (luminosity) pb in p+p collisions. The nuclear modification factor in the 30% most central Au+Au collisions indicates a suppression of the total Υ state yield relative to the extrapolation from p+p collision data. Thus, the suppression is consistent with measurements at higher energies by the CMS experiment at the Large Hadron Collider.

  8. pH Dependent Chiroptical Properties of (1R,2R)- and (1S,2S)-trans-Cyclohexane Diesters and Diamides from VCD, ECD, and CPL Spectroscopy.

    PubMed

    Mazzeo, Giuseppe; Abbate, Sergio; Longhi, Giovanna; Castiglioni, Ettore; Boiadjiev, Stefan E; Lightner, David A

    2016-03-10

    Diesters of (1R,2R)- and (1S,2S)-cyclohexanediols and diamides of (1R,2R)- and (1S,2S)-diaminocyclohexane with p-hydroxycinnamic acid have been known for some time to exhibit intense bisignate electronic circular dichroism (ECD) spectra in CH3OH. It was also known that added NaOH causes a bathochromic shift of ∼50 nm in CH3OH, and an even higher one in DMSO. We have measured vibrational circular dichroism (VCD) spectra both for neutral compounds and in the presence of NaOH and other bases. The VCD and IR spectra in the mid-IR region for CD3OD and DMSO-d6 solution exhibit high sensitivity to the charged state for the diesters. They possess two strong bisignate features in the presence of bases in the mid-IR, which are interpreted in terms of vibrational exciton couplets, while this phenomenon is less evident in diamides. VCD allied to density functional theory (DFT) calculations allows one to shed some light on the spectral differences of diesters and diamides by studying their conformational properties. Optical rotatory dispersion (ORD) curves confirm the ECD data. Circularly polarized luminescence (CPL) data have been also acquired, which are rather intense in basified solution: the CPL spectra are monosignate and are as intense in the diester and in the diamide case.

  9. Measurement of Υ(1S + 2S +3S) production in p + p and Au + Au collisions at \\(\\sqrt{s_{\\mathrm{NN}}}=200\\) GeV

    DOE PAGES

    Adare, A.; Afanasiev, S.; Aidala, C.; ...

    2015-02-24

    Measurements of bottomonium production in heavy-ion and p+p collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The inclusive yield of the three Υ states, Υ(1S + 2S + 3S), was measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au+Au and p+p collisions at \\(\\sqrt{s_{\\mathrm{NN}}}=200\\) GeV. The Υ(1S + 2S + 3S) → e⁺e⁻ differential cross section at midrapidity was found to be Beedσ/dy = 108 ± 38 (stat) ± 15 (syst) ± 11 (luminosity) pb in p+p collisions. The nuclear modification factor in the 30% most central Au+Au collisions indicates a suppression of themore » total Υ state yield relative to the extrapolation from p+p collision data. Thus, the suppression is consistent with measurements at higher energies by the CMS experiment at the Large Hadron Collider.« less

  10. Analysis of 1s(2s2p {sup 3}P)nl Rydberg states in the K-shell photoionization of the Be atom

    SciTech Connect

    Yoshida, Fumiko; Matsuoka, Leo; Takashima, Ryuta; Hasegawa, Shuichi; Nagata, Tetsuo; Azuma, Yoshiro; Obara, Satoshi; Koike, Fumihiro

    2006-06-15

    We have observed inner-shell photoionization of Be using synchrotron radiation in the energy region of the 1s(2s2p {sup 3}P)nl Rydberg states. We used a time-of-flight method to distinguish singly and doubly charged photoions and obtained the Be{sup +} [ns; n=5-12 ({sup 1}P)3s] and Be{sup 2+} [ns; n=5-8, nd=5,6 ({sup 1}P)3s] ion spectra with high resolution corresponding to an instrumental bandpass of 13 meV. Detailed analysis enabled the autoionization parameters, resonance energy position E{sub 0}, resonance width {gamma}, and Fano parameter q, to be obtained. From the resonance positions of the {sup 3}Pnl series members, the series limit was determined to be 127.97 eV, which is in good agreement with previous experiments.

  11. Fine structure and ionization energy of the 1s2s2p 4P state of the helium negative ion He-.

    PubMed

    Wang, Liming; Li, Chun; Yan, Zong-Chao; Drake, G W F

    2014-12-31

    The fine structure and ionization energy of the 1s2s2p (4)P state of the helium negative ion He(-) are calculated in Hylleraas coordinates, including relativistic and QED corrections up to O(α(4)mc(2)), O((μ/M)α(4)mc(2)), O(α(5)mc(2)), and O((μ/M)α(5)mc(2)). Higher order corrections are estimated for the ionization energy. A comparison is made with other calculations and experiments. We find that the present results for the fine structure splittings agree with experiment very well. However, the calculated ionization energy deviates from the experimental result by about 1 standard deviation. The estimated theoretical uncertainty in the ionization energy is much less than the experimental accuracy.

  12. Measurement of Absolute Cross Sections for Excitation of the 2s^2 ^1S - 2s2p ^1P^o Transition in O^4+

    NASA Astrophysics Data System (ADS)

    Smith, Steven J.; Berrington, K. A.

    2005-05-01

    Experimental electron excitation cross sections are reported for the 2s^2 1S - 2s2p^ 1P^o transitions in O^4+ located at 19.689 eV. The JPL electron-cyclotron resonance ion source is utilized [1], along with the electron energy loss method, in a merged electron-ion beams geometry[2]. The center-of-mass interaction energies for the measurements are in the range 18 eV (below threshold) to 30 eV. Data are compared with results of a 26-term R-matrix calculation that includes fine structure explicitly via the Breit-Pauli Hamiltonian [3]. There is good agreement with theoretical results and with previous electron energy-loss measurements [3]. Clear resonance enhancement is observed in both experiment and theoretical results near threshold for this ^1S - ^1P^o transition. J. Lozano and N. Djuric acknowledge support through the NASA-NRC program. This work was carried out at JPL/Caltech and was supported by NASA. [1] J. B. Greenwood, S. J. Smith, A.Chutjian, and E. Pollack, Phys. Rev. A 59 1348, (1999). [2] A. Chutjian, Physica Scripta T110, 203 (2004). [3] M. Bannister et al., Int.J. Mass Spectrometry 192, 39 (1999).

  13. Weak- and hyperfine-interaction-induced 1s2s 1S0 → 1s2 1S0 E1 transition rates of He-like ions

    NASA Astrophysics Data System (ADS)

    Laima, Radžiūtė; Erikas, Gaidamauskas; Gediminas, Gaigalas; Li, Ji-Guang; Dong, Chen-Zhong; Jönsson, Per

    2015-04-01

    Weak- and hyperfine-interaction-induced 1s2s 1S0 → 1s2 1S0 E1 transition rates for the isoelectronic sequence of He-like ions have been calculated using the multi-configuration Dirac-Hartree-Fock (MCDHF) and relativistic configuration interaction methods. The results should be helpful for the future experimental investigations of parity non-conservation effects. Project supported by the National Natural Science Foundation of China (Grant Nos. 11274254, 11147108, 10979007, U1331122, and U1332206) and in part by the National Basic Research Program of China (Grant No. 2013CB922200).

  14. The Metastable Brain

    PubMed Central

    Tognoli, Emmanuelle; Kelso, J. A. Scott

    2014-01-01

    Neural ensembles oscillate across a broad range of frequencies and are transiently coupled or “bound” together when people attend to a stimulus, perceive, think and act. This is a dynamic, self-assembling process, with parts of the brain engaging and disengaging in time. But how is it done? The theory of Coordination Dynamics proposes a mechanism called metastability, a subtle blend of integration and segregation. Tendencies for brain regions to express their individual autonomy and specialized functions (segregation, modularity) coexist with tendencies to couple and coordinate globally for multiple functions (integration). Although metastability has garnered increasing attention, it has yet to be demonstrated and treated within a fully spatiotemporal perspective. Here, we illustrate metastability in continuous neural and behavioral recordings, and we discuss theory and experiments at multiple scales suggesting that metastable dynamics underlie the real-time coordination necessary for the brain's dynamic cognitive, behavioral and social functions. PMID:24411730

  15. Polarization of metastable 129Xe

    NASA Astrophysics Data System (ADS)

    Xia, Tian; Morgan, Steven; Jau, Yuan-Yu; Happer, William

    2008-05-01

    We have measured atomic polarization of metastable 129Xe in a pyrex cell by optical pumping, while metastability exchange optical pumping of 3He is routinely done. The atomic polarization of metastable Xe is on the order of 10%. Metastable xenon is created by electrodeless rf discharge. The hyperfine transition of metastable 129Xe is observed by microwave excitation. Atomic polarization can be demonstrated by comparison of the intensities of the transitions between different Zeeman sublevels, while pumping a specific optical transition of metastable Xe with circularly polarized light. This work offers insight into attempts to polarize 129Xe nuclei by metastability exchange optical pumping.

  16. Metastability in Markov processes

    NASA Astrophysics Data System (ADS)

    Larralde, H.; Leyvraz, F.; Sanders, D. P.

    2006-08-01

    We present a formalism for describing slowly decaying systems in the context of finite Markov chains obeying detailed balance. We show that phase space can be partitioned into approximately decoupled regions, in which one may introduce restricted Markov chains which are close to the original process but do not leave these regions. Within this context, we identify the conditions under which the decaying system can be considered to be in a metastable state. Furthermore, we show that such metastable states can be described in thermodynamic terms and define their free energy. This is accomplished, showing that the probability distribution describing the metastable state is indeed proportional to the equilibrium distribution, as is commonly assumed. We test the formalism numerically in the case of the two-dimensional kinetic Ising model, using the Wang-Landau algorithm to show this proportionality explicitly, and confirm that the proportionality constant is as derived in the theory. Finally, we extend the formalism to situations in which a system can have several metastable states.

  17. Metastable nematic hedgehogs

    NASA Astrophysics Data System (ADS)

    Rosso, Riccardo; Virga, Epifanio G.

    1996-07-01

    For nematic liquid crystals, we study the local stability of a radial hedgehog against biaxial perturbations. Our analysis employs the Landau - de Gennes functional to describe the free energy stored in a ball, whose radius is a parameter of the model. We find that a radial hedgehog may be either unstable or metastable, depending on the values of the elastic constants. For unstable hedgehogs, we give an explicit expression for the radius of the ball within which the instability manifests itself: it can be interpreted as the size of the biaxial core of the defect; it is of the same order of magnitude as the radius of the disclination ring predicted by Penzenstadler and Trebin's model. The metastable hedgehogs predicted by our model are the major novelty of the paper. They tell us that we may also expect truly uniaxial point defects, whose core contains no biaxial structure.

  18. Metastable dark energy

    NASA Astrophysics Data System (ADS)

    Landim, Ricardo G.; Abdalla, Elcio

    2017-01-01

    We build a model of metastable dark energy, in which the observed vacuum energy is the value of the scalar potential at the false vacuum. The scalar potential is given by a sum of even self-interactions up to order six. The deviation from the Minkowski vacuum is due to a term suppressed by the Planck scale. The decay time of the metastable vacuum can easily accommodate a mean life time compatible with the age of the universe. The metastable dark energy is also embedded into a model with SU(2)R symmetry. The dark energy doublet and the dark matter doublet naturally interact with each other. A three-body decay of the dark energy particle into (cold and warm) dark matter can be as long as large fraction of the age of the universe, if the mediator is massive enough, the lower bound being at intermediate energy level some orders below the grand unification scale. Such a decay shows a different form of interaction between dark matter and dark energy, and the model opens a new window to investigate the dark sector from the point-of-view of particle physics.

  19. Observation of orbiting resonances in He(3S1) + NH3 Penning ionization

    NASA Astrophysics Data System (ADS)

    Jankunas, Justin; Jachymski, Krzysztof; Hapka, Michał; Osterwalder, Andreas

    2015-04-01

    Resonances are among the clearest quantum mechanical signatures of scattering processes. Previously, shape resonances and Feshbach resonances have been observed in inelastic and reactive collisions involving atoms or diatomic molecules. Structure in the integral cross section has been observed in a handful of elastic collisions involving polyatomic molecules. The present paper presents the observation of shape resonances in the reactive scattering of a polyatomic molecule, NH3. A merged-beam study of the gas phase He(3S1) + NH3 Penning ionization reaction dynamics is described in the collision energy range 3.3 μeV < Ecoll < 10 meV. In this energy range, the reaction rate is governed by long-range attraction. Peaks in the integral cross section are observed at collision energies of 1.8 meV and 7.3 meV and are assigned to ℓ = 15,16 and ℓ = 20,21 partial wave resonances, respectively. The experimental results are well reproduced by theoretical calculations with the short-range reaction probability Psr = 0.035. No clear signature of the orbiting resonances is visible in the branching ratio between NH3+ and NH2+ formation.

  20. Superconducting Metastable Compounds.

    PubMed

    Luo, H L; Merriam, M F; Hamilton, D C

    1964-08-07

    A number of metastable phases, germanides and tellurides of gold and silver, have been prepared, analyzed by x-ray diffraction, and investigated for superconductivity. The new superconductors and their transition temperatures are AgTe(3) (2.6 degrees K), Ag(4)Ge (0.85 degrees K), Au(3)Te(5) (1.62 degrees K), and Au(1-x)Ge(x) (0.99 degrees K-1.63 degrees K) where (0.27

  1. Digital Synchronizer without Metastability

    NASA Technical Reports Server (NTRS)

    Simle, Robert M.; Cavazos, Jose A.

    2009-01-01

    A proposed design for a digital synchronizing circuit would eliminate metastability that plagues flip-flop circuits in digital input/output interfaces. This metastability is associated with sampling, by use of flip-flops, of an external signal that is asynchronous with a clock signal that drives the flip-flops: it is a temporary flip-flop failure that can occur when a rising or falling edge of an asynchronous signal occurs during the setup and/or hold time of a flip-flop. The proposed design calls for (1) use of a clock frequency greater than the frequency of the asynchronous signal, (2) use of flip-flop asynchronous preset or clear signals for the asynchronous input, (3) use of a clock asynchronous recovery delay with pulse width discriminator, and (4) tying the data inputs to constant logic levels to obtain (5) two half-rate synchronous partial signals - one for the falling and one for the rising edge. Inasmuch as the flip-flop data inputs would be permanently tied to constant logic levels, setup and hold times would not be violated. The half-rate partial signals would be recombined to construct a signal that would replicate the original asynchronous signal at its original rate but would be synchronous with the clock signal.

  2. Topodynamics of metastable brains

    NASA Astrophysics Data System (ADS)

    Tozzi, Arturo; Peters, James F.; Fingelkurts, Andrew A.; Fingelkurts, Alexander A.; Marijuán, Pedro C.

    2017-07-01

    The brain displays both the anatomical features of a vast amount of interconnected topological mappings as well as the functional features of a nonlinear, metastable system at the edge of chaos, equipped with a phase space where mental random walks tend towards lower energetic basins. Nevertheless, with the exception of some advanced neuro-anatomic descriptions and present-day connectomic research, very few studies have been addressing the topological path of a brain embedded or embodied in its external and internal environment. Herein, by using new formal tools derived from algebraic topology, we provide an account of the metastable brain, based on the neuro-scientific model of Operational Architectonics of brain-mind functioning. We introduce a ;topodynamic; description that shows how the relationships among the countless intertwined spatio-temporal levels of brain functioning can be assessed in terms of projections and mappings that take place on abstract structures, equipped with different dimensions, curvatures and energetic constraints. Such a topodynamical approach, apart from providing a biologically plausible model of brain function that can be operationalized, is also able to tackle the issue of a long-standing dichotomy: it throws indeed a bridge between the subjective, immediate datum of the naïve complex of sensations and mentations and the objective, quantitative, data extracted from experimental neuro-scientific procedures. Importantly, it opens the door to a series of new predictions and future directions of advancement for neuroscientific research.

  3. Desensitization of metastable intermolecular composites

    SciTech Connect

    Busse, James R.; Dye, Robert C.; Foley, Timothy J.; Higa, Kelvin T.; Jorgensen, Betty S.; Sanders, Victor E.; Son, Steven F.

    2011-04-26

    A method to substantially desensitize a metastable intermolecular composite material to electrostatic discharge and friction comprising mixing the composite material with an organic diluent and removing enough organic diluent from the mixture to form a mixture with a substantially putty-like consistency, as well as a concomitant method of recovering the metastable intermolecular composite material.

  4. Metastability in Senescence.

    PubMed

    Naik, Shruti; Banerjee, Arpan; Bapi, Raju S; Deco, Gustavo; Roy, Dipanjan

    2017-07-01

    The brain during healthy aging exhibits gradual deterioration of structure but maintains a high level of cognitive ability. These structural changes are often accompanied by reorganization of functional brain networks. Existing neurocognitive theories of aging have argued that such changes are either beneficial or detrimental. Despite numerous empirical investigations, the field lacks a coherent account of the dynamic processes that occur over our lifespan. Taking advantage of the recent developments in whole-brain computational modeling approaches, we hypothesize that the continuous process of aging can be explained by the concepts of metastability - a theoretical framework that gives a systematic account of the variability of the brain. This hypothesis can bridge the gap between existing theories and the empirical findings on age-related changes. Copyright © 2017 Elsevier Ltd. All rights reserved.

  5. Complexity, Metastability and Nonextensivity

    NASA Astrophysics Data System (ADS)

    Beck, C.; Benedek, G.; Rapisarda, A.; Tsallis, C.

    Work and heat fluctuations in systems with deterministic and stochastic forces / E. G. D. Cohen and R. Van Zon -- Is the entropy S[symbol] extensive or nonextensive? / C. Tsallis -- Superstatistics: recent developments and applications / C. Beck -- Two stories outside Boltzmann-Gibbs statistics: Mori's Q-phase transitions and glassy dynamics at the onset of chaos / A. Robledo, F. Baldovin and E. Mayoral -- Time-averages and the heat theorem / A. Carati -- Fundamental formulae and numerical evidences for the central limit theorem in Tsallis statistics / H. Suyari -- Generalizing the Planck distribution / A. M. C. Soma and C. Tsallis -- The physical roots of complexity: renewal or modulation? / P. Grigolini -- Nonequivalent ensembles and metastability / H. Touchette and R. S. Ellis -- Statistical physics for cosmic structures / L. Pietronero and F. Sylos Labini -- Metastability and anomalous behavior in the HMF model: connections to nonextensive thermodynamics and glassy dynamics / A. Pluchino, A. Rapisarda and V. Latora -- Vlasov analysis of relaxation and meta-equilibrium / C. Anteneodo and R. O. Vallejos -- Weak chaos in large conservative systems - infinite-range coupled standard maps / L. G. Moyano, A. P. Majtey and C. Tsallis -- Deterministc aging / E. Barkai -- Edge of chaos of the classical kicked top map: sensitivity to initial conditions / S. M. Duarte Queirós and C. Tsallis -- What entropy at the edge of chaos? / M. Lissia, M. Coraddu and R. Tonelli -- Fractal growth of carbon schwarzites / G. Benedek ... [et al.] -- Clustering and interface propagation in interacting particle dynamics / A. Provata and V. K. Noussiou -- Resonant activation and noise enhanced stability in Josephson junctions / A. L. Pankratov and B. Spagnolo -- Symmetry breaking induced directed motions / C.-H. Chang and T. Y. Tsong -- General theory of Galilean-invariant entropic lattic Boltzmann models / B. M. Boghosian -- Unifying approach to the jamming transition in granular media and

  6. Metastable solid metallic hydrogen

    SciTech Connect

    Nellis, W. J.

    1999-04-01

    Hydrogen reaches the mimimum electrical conductivity of a metal at 140 GPa (1.4 Mbar), 0.6 g/cm3 (ninefold compression of initial liquid-H2 density), and 3000 K in the fluid phase. The quest for metallic hydrogen over the past 100 years is reviewed briefly. Possible scientific and technological uses of metastable solid metallic hydrogen (MSMH) are speculated upon in the unlikely event that the metallic fluid can be quenched to MSMH at ambient pressure and temperature: a quantum, metallic solid with novel physical properties, including room-temperature superconductivity; a very light-weight structural material; a fuel, propellant, and explosive, depending on the rate of release of stored energy; a dense fuel for higher energy yields in inertial confinement fusion; and an aid in the synthesis of novel hard materials. Some of the formidable difficulties to synthesize MSMH are discussed.

  7. Measurement of the 3s1/2-3p3/2 resonance line of sodiumlike Eu52+

    DOE PAGES

    Träbert, E.; Beiersdorfer, P.; Hell, N.; ...

    2015-08-20

    We have measured the 3s1/2-3p3/2 transition in sodiumlike Eu52+ situated at 41.232 Å with an uncertainty of 73 ppm. Our measurement extends previous high-precision measurements into the 56< Z< 78 range of atomic numbers. We also present measurements of 3s1/2-3p3/2 and 3p1/2-3d3/2 transitions in the neighboring magnesiumlike, aluminumlike, and siliconlike europium ions.

  8. Evaluation of the effective solid angle of a hemispherical deflector analyser with injection lens for metastable Auger projectile states

    NASA Astrophysics Data System (ADS)

    Benis, E. P.; Doukas, S.; Zouros, T. J. M.; Indelicato, P.; Parente, F.; Martins, C.; Santos, J. P.; Marques, J. P.

    2015-12-01

    The accurate determination of the electron yield of a metastable projectile Auger state necessitates the careful evaluation of the corresponding effective solid angle, i.e. the geometrical solid angle convoluted with the decay time of the metastable state. Recently, we presented (Doukas et. al., 2015) SIMION Monte Carlo type simulations of the effective solid angle for long lived projectile Auger states (lifetime τ ∼10-9-10-5s) recorded by a hemispherical spectrograph with injection lens and position sensitive detector in the direction of the projectile ion. These results are important for the accurate evaluation of the 1 s 2 s 2 p4P/2 P ratio of K-Auger cross sections whose observed non-statistical production by electron capture into He-like ions, recently a field of interesting interpretations, awaits final resolution. Here we expand and systematize our investigation using the same techniques to expose universal behaviors of the effective solid angle covering life times of 1 s 2 s 2 p4P states for all first row ions. Our results are also compared to purely geometrical calculations of the solid angle that omit the lensing effects and serve as a benchmark for a deeper insight into the effect.

  9. Theoretical study on dielectronic recombination of O6+ ions in metastable states

    NASA Astrophysics Data System (ADS)

    Zhao, Li-Bo; Shirai, Toshizo

    2001-11-01

    A computational scheme, based on the theory of the continuum-bound transitions of Bell and Seaton [J. Phys. B 18, 1589 (1985)] and the close-coupling R-matrix approach, has been developed to treat dielectronic recombination (DR) in high-lying resonance-energy regions. This scheme and our presented numerical method to compute DR in low-lying resonance-energy regions [Phys. Rev. A 62, 022706 (2000)] have been applied together to elucidate the experimental spectra of the DR of O6+ ions in the metastable 1s2s 3S and 1s2s 1S states. For comparison, a perturbative theoretical calculation of DR for O6+ has also been accompanied. The reasonable representation of the general dielectronic spectral shape is yielded by both our close-coupling and perturbative calculations. However, both the methods do not reproduce the experimental double-peak structure at ~6-8 eV. This shows that the further investigation on DR of this kind of ions is required both experimentally and theoretically.

  10. Modulated voltage metastable ionization detector

    NASA Technical Reports Server (NTRS)

    Carle, G. C.; Kojiro, D. R.; Humphrey, D. E. (Inventor)

    1985-01-01

    The output current from a metastable ionization detector (MID) is applied to a modulation voltage circuit. An adjustment is made to balance out the background current, and an output current, above background, is applied to an input of a strip chart recorder. For low level concentrations, i.e., low detected output current, the ionization potential will be at a maximum and the metastable ionization detector will operate at its most sensitive level. When the detected current from the metastable ionization detector increases above a predetermined threshold level, a voltage control circuit is activated which turns on a high voltage transistor which acts to reduce the ionization potential. The ionization potential applied to the metastable ionization detector is then varied so as to maintain the detected signal level constant. The variation in ionization potential is now related to the concentration of the constituent and a representative amplitude is applied to another input of said strip chart recorder.

  11. Characterization of the binding site of the histamine H3 receptor. 1. Various approaches to the synthesis of 2-(1H-imidazol-4-yl)cyclopropylamine and histaminergic activity of (1R,2R)- and (1S,2S)-2-(1H-imidazol-4-yl)-cyclopropylamine.

    PubMed

    De Esch, I J; Vollinga, R C; Goubitz, K; Schenk, H; Appelberg, U; Hacksell, U; Lemstra, S; Zuiderveld, O P; Hoffmann, M; Leurs, R; Menge, W M; Timmerman, H

    1999-04-08

    Various approaches to the synthesis of all four stereoisomers of 2-(1H-imidazol-4-yl)cyclopropylamine (cyclopropylhistamine) are described. The rapid and convenient synthesis and resolution of trans-cyclopropylhistamine is reported. The absolute configuration of its enantiomers was determined by single-crystal X-ray crystallographic analysis. The distinct trans-cyclopropylhistamine enantiomers were tested for their activity and affinity on the histamine H3 receptor. (1S,2S)-Cyclopropylhistamine (VUF 5297) acts as an agonist both on the rat cortex (pD2 = 7.1; alpha = 0.75) and on guinea pig jejunum (pD2 = 6.6; alpha = 0.75). Its enantiomer, (1R, 2R)-cyclopropylhistamine (VUF 5296), is about 1 order of magnitude less active. Both enantiomers show weak activity on H1 and H2 receptors. All synthetic attempts to cis-cyclopropylhistamine were unsuccessful. Nevertheless, the results of this study provide an ideal template for molecular modeling studies of histamine H3 receptor ligands.

  12. (3R,4S)-3-[4-(4-fluorophenyl)-4-hydroxypiperidin-1-yl]chroman-4,7-diol: a conformationally restricted analogue of the NR2B subtype-selective NMDA antagonist (1S,2S)-1-(4-hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)- 1-propanol.

    PubMed

    Butler, T W; Blake, J F; Bordner, J; Butler, P; Chenard, B L; Collins, M A; DeCosta, D; Ducat, M J; Eisenhard, M E; Menniti, F S; Pagnozzi, M J; Sands, S B; Segelstein, B E; Volberg, W; White, W F; Zhao, D

    1998-03-26

    (1S,2S)-1-(4-Hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol (CP-101,606, 1) is a recently described antagonist of N-methyl-D-aspartate (NMDA) receptors containing the NR2B subunit. In the present study, the optimal orientation of compounds of this structural type for their receptor was explored. Tethering of the pendent methyl group of 1 to the phenolic aromatic ring via an oxygen atom prevents rotation about the central portion of the molecule. Several of the new chromanol compounds have high affinity for the racemic [3H]CP-101,606 binding site on the NMDA receptor and protect against glutamate toxicity in cultured hippocampal neurons. The new ring caused a change in the stereochemical preference of the receptor-cis (erythro) compounds had better affinity for the receptor than the trans isomers. Computational studies suggest that steric interactions between the pendent methyl group and the phenol ring in the acyclic series determine which structures can best fit the receptor. The chromanol analogue, (3R,4S)-3-[4-(4-fluorophenyl)-4-hydroxypiperidin-1- yl]chroman-4,7-diol (12a, CP-283,097), was found to possess potency and selectivity comparable to CP-101,606. Thus 12a is a new tool to explore the function of the NR2B-containing NMDA receptors.

  13. The Effect of (1S,2S,3E,7E,11E)-3,7,11,15-Cembratetraen-17,2-Olide (LS-1) from Lobophyyum sp. on the Apoptosis Induction of SNU-C5 Human Colorectal Cancer Cells

    PubMed Central

    Kim, Eun-Ji; Kang, Jung Il; Tung, Nguyen-Huu; Kim, Young-Ho; Hyun, Jin Won; Koh, Young Sang; Chang, Weon-Young; Yoo, Eun Sook; Kang, Hee-Kyoung

    2016-01-01

    (1S,2S,3E,7E,11E)-3,7,11,15-cembratetraen-17,2-olide (LS-1), a marine cembrenolide diterpene, has anticancer activity against colon cancer cells such as HT-29, SNU-C5/5-FU (fluorouracil-resistant SNU-C5) and SNU-C5. However, the action mechanism of LS-1 on SNU-C5 human colon cancer cells has not been fully elucidated. In this study, we investigated whether the anticancer effect of LS-1 could result from apoptosis via the modulation of Wnt/β-catenin and the TGF-β pathways. When treated with the LS-1, we could observe the apoptotic characteristics such as apoptotic bodies and the increase of sub-G1 hypodiploid cell population, increase of Bax level, decrease of Bcl-2 expression, cleavage of procaspase-3 and cleavage of poly (ADP-ribose) polymerase in SNU-C5 cells. Furthermore, the apoptosis induction of SNU-C5 cells upon LS-1 treatment was also accompanied by the down-regulation of Wnt/β-catenin signaling pathway via the decrease of GSK-3β phosphorylation followed by the decrease of β-catenin level. In addition, the LS-1 induced the activation of TGF-β signaling pathway with the decrease of carcinoembryonic antigen which leads to decrease of c-Myc, an oncoprotein. These data suggest that the LS-1 could induce the apoptosis via the down-regulation of Wnt/β-catenin pathway and the activation of TGF-β pathway in SNU-C5 human colon cancer cells. The results support that the LS-1 might have potential for the treatment of human colon cancer. PMID:27469141

  14. Alignment of the (3d104 s 5 s ) 3S1 State of Zn Excited by Polarized Electron Impact

    NASA Astrophysics Data System (ADS)

    Clayburn, N. B.; Gay, T. J.

    2017-09-01

    We measure the integrated Stokes parameters of light from Zn (4 s 4 p )4 3P0,1-(4 s 5 s )5 3S1 transitions excited by a transversely polarized electron impact at energies between 7.0 and 8.5 eV. Our results for the electron-polarization-normalized linear polarization Stokes parameter P2 , between incident electron energies 7.0 and 7.4 eV, are consistent with zero, as required by basic angular-momentum coupling considerations and by recent theoretical calculations. They are in qualitative disagreement with previous experimental results for the P2 parameter.

  15. Metastable metallic hydrogen glass

    SciTech Connect

    Nellis, W J

    2001-02-06

    pushing the molecules together sufficiently that an electron on one molecule can delocalize and move to an adjacent molecule, if the pressure is released the system will simply revert back to a diatomic insulator. Additives will probably be necessary to produce bonding which will inhibit the reverse transformation when pressure is released. One technique for rapidly quenching metallic fluid hydrogen is to use a thin micron-thick layer of condensed hydrogen contained between metal or diamond layers, which have a high thermal conductivity to quench shock temperature before pressure is released. An appropriate planar shock wave can probably be driven by a laser or small two-stage gun to achieve the necessary pressures, temperatures, and quench rates. In this way many experiments might be performed to find the appropriate combination of materials and shock-pressure history to achieve a shock-pressure-quenched metastable metallic hydrogen glass.

  16. Phase metastability and supercooled metastable state of diundecanoylphosphatidylethanolamine bilayers.

    PubMed

    Xu, H; Stephenson, F A; Lin, H N; Huang, C H

    1988-08-04

    Aqueous dispersons of L-alpha-phosphatidylethanolamine (PE) with identical saturated acyl chains are known to exhibit gel-state metastability. It is also known that the metastability in PE becomes more pronounced with decreasing acyl chain-length. In an attempt to study the metastable phase behavior of PE, we have synthesized diundecanoylphosphatidylethanolamine (diC11PE) and examined its polymorphic phase behavior. A single endothermic transition at 38 degrees C is detected between 10 and 55 degrees C by DSC for the nonheated sample of diC11PE in excess water. An immediate second heating scan done after cooling slowly of the same sample from the liquid-crystalline state shows a smaller endothermic transition at a lower temperature, 18 degrees C. However, the high-temperature transition at 38 degrees C can be detected, if the sample which has been heated above 38 degrees C is quench cooled from the liquid-crystalline to a temperature between 18 and 38 degrees C. Furthermore, two endothermic transitions at 18 and 38 degrees C and an exothermic transition at 19 degrees C are recorded for diC11PE after quench supercooling of the sample from the liquid-crystalline state to an appropriate temperature below 10 degrees C. The gel-state metastability of diC11PE can be most appropriately explained in terms of changes in interbilayer headgroup-headgroup interactions. It is suggested that the kinetically trapped supercooled metastable state may be a multilamellar structure with melted acyl chains but with strong interbilayer headgroup-headgroup interactions.

  17. Nonperturbative NN scattering in 3S1-3D1 channels of EFT(⁄π)

    NASA Astrophysics Data System (ADS)

    Yang, Ji-Feng

    2013-12-01

    The closed-form T matrices in the 3S1-3D1 channels of EFT(⁄π) for NN scattering with the potentials truncated at order O(Q4) are presented with the nonperturbative divergences parametrized in a general manner. The stringent constraints imposed by the closed form of the T matrices are exploited in the underlying theory perspective and turned into virtues in the implementation of subtractions and the manifestation of power counting rules in nonperturbative regimes, leading us to the concept of EFT scenario. A number of scenarios of the EFT description of NN scattering are compared with PSA data in terms of effective range expansion and 3S1 phase shifts, showing that it is favorable to proceed in a scenario with conventional EFT couplings and sophisticated renormalization in order to have large NN scattering lengths. The informative utilities of fine tuning are demonstrated in several examples and naturally interpreted in the underlying theory perspective. In addition, some of the approaches adopted in the recent literature are also addressed in the light of EFT scenario.

  18. Metastable innershell molecular state (MIMS)

    NASA Astrophysics Data System (ADS)

    Bae, Young K.

    2008-07-01

    We propose that the existence of Metastable innershell molecular state (MIMS) was experimentally discovered by Bae et al. in hypervelocity ( v>100 km/s) impact of nanoparticles. The decay of MIMS resulted in the observed intense soft x-rays in the range of 75-100 eV in agreement with Winterberg's recent prediction.

  19. Ultracold collisions in metastable helium

    NASA Astrophysics Data System (ADS)

    Peach, G.; Cocks, D. G.; Whittingham, I. B.

    2017-02-01

    Photoassociation processes are studied in ultracold collisions between different isotopes of metastable He(23S) and He(23P) atoms; Penning and associative ionization rates for collisions between two He(23S) atoms are also obtained. Comparisons are made with data from existing experiments.

  20. Inelastic Collisions in Optically Trapped Ultracold Metastable Ytterbium

    NASA Astrophysics Data System (ADS)

    Yamaguchi, A.; Uetake, S.; Hashimoto, D.; Doyle, J. M.; Takahashi, Y.

    2008-12-01

    We report measurement of inelastic loss in dense and cold metastable ytterbium (Yb[P23]). Use of an optical far-off-resonance trap enables us to trap atoms in all magnetic sublevels, removing m-changing collisional trap loss from the system. Trapped samples of Yb[P23] are produced at a density of 2×1013cm-3 and temperature of 2μK. We observe rapid two-body trap loss of Yb[P23] and measure the inelastic collision rate constant 1.0(3)×10-11cm3s-1. The existence of the fine-structure changing collisions between atoms in the P23 state is strongly suggested.

  1. Metastable Phases in Ice Clouds

    NASA Astrophysics Data System (ADS)

    Weiss, Fabian; Baloh, Philipp; Kubel, Frank; Hoelzel, Markus; Parker, Stewart; Grothe, Hinrich

    2014-05-01

    Polar Stratospheric Clouds and Cirrus Clouds contain both, pure water ice and phases of nitric acid hydrates. Preferentially for the latter, the thermodynamically stable phases have intensively been investigated in the past (e.g. nitric acid trihydrate, beta-NAT). As shown by Peter et al. [1] the water activity inside clouds is higher than expected, which might be explained by the presence of metastable stable phases (e.g. cubic ice). However, also metastable nitric acid hydrates might be important due to the inherent non-equilibrium freezing conditions in the upper atmosphere. The delta ice theory of Gao et al. [2] presents a model approach to solve this problem by involving both metastable ice and NAT as well. So it is of high interest to investigate the metastable phase of NAT (i.e. alpha-NAT), the structure of which was unknown up to the presence. In our laboratory a production procedure for metastable alpha-NAT has been developed, which gives access to neutron diffraction and X-ray diffraction measurements, where sample quantities of several Gramm are required. The diffraction techniques were used to solve the unknown crystalline structure of metastable alpha-NAT, which in turn allows the calculation of the vibrational spectra, which have also been recorded by us in the past. Rerefences [1] Peter, T., C. Marcolli, P. Spichtinger, T. Corti, M. B. Baker, and T. Koop. When dry air is too humid. Science, 314:1399-1402, 2006. [2] Gao, R., P. Popp, D. Fahey, T. Marcy, R. L. Herman, E. Weinstock, D. Baumgardener, T. Garrett, K. Rosenlof, T. Thompson, T. P. Bui, B. Ridley, S. C. Wofsy, O. B. Toon, M. Tolbert, B. Kärcher, Th. Peter, P. K. Hudson, A. Weinheimer, and A. Heymsfield. Evidence That Nitric Acid Increases Relative Humidity in Low-Temperature Cirrus Clouds, Science, 303:516-520, 2004. [3] Tizek, H., E. Knözinger, and H. Grothe. Formation and phase distribution of nitric acid hydrates in the mole fraction range xHNO3<0.25: A combined XRD and IR study, PCCP, 6

  2. Ultracold metastable helium: Ramsey fringes and atom interferometry

    NASA Astrophysics Data System (ADS)

    Vassen, W.; Notermans, R. P. M. J. W.; Rengelink, R. J.; van der Beek, R. F. H. J.

    2016-12-01

    We report on interference studies in the internal and external degrees of freedom of metastable triplet helium atoms trapped near quantum degeneracy in a 1.5 μm optical dipole trap. Applying a single π /2 rf pulse we demonstrate that 50% of the atoms initially in the m=+1 state can be transferred to the magnetic field insensitive m=0 state. Two π /2 pulses with varying time delay allow a Ramsey-type measurement of the Zeeman shift for a high precision measurement of the 2 ^3S_1-2 ^1S_0 transition frequency. We show that this method also allows strong suppression of mean-field effects on the measurement of the Zeeman shift, which is necessary to reach the accuracy goal of 0.1 kHz on the absolute transition frequencies. Theoretically the feasibility of using metastable triplet helium atoms in the m=0 state for atom interferometry is studied demonstrating favorable conditions, compared to the alkali atoms that are used traditionally, for a non-QED determination of the fine structure constant.

  3. Gauge mediation in metastable vacua

    SciTech Connect

    Dine, Michael; Mason, John

    2008-01-01

    Until recently, dynamical supersymmetry breaking seemed an exceptional phenomenon, involving chiral gauge theories with a special structure. Recently it has become clear that requiring only metastable states with broken supersymmetry leads to a far broader class of theories. In this paper, we extend these constructions still further, finding new classes which, unlike earlier theories, do not have unbroken, approximate R symmetries. This allows construction of new models with low energy gauge mediation.

  4. Extinction of metastable stochastic populations

    NASA Astrophysics Data System (ADS)

    Assaf, Michael; Meerson, Baruch

    2010-02-01

    We investigate the phenomenon of extinction of a long-lived self-regulating stochastic population, caused by intrinsic (demographic) noise. Extinction typically occurs via one of two scenarios depending on whether the absorbing state n=0 is a repelling (scenario A) or attracting (scenario B) point of the deterministic rate equation. In scenario A the metastable stochastic population resides in the vicinity of an attracting fixed point next to the repelling point n=0 . In scenario B there is an intermediate repelling point n=n1 between the attracting point n=0 and another attracting point n=n2 in the vicinity of which the metastable population resides. The crux of the theory is a dissipative variant of WKB (Wentzel-Kramers-Brillouin) approximation which assumes that the typical population size in the metastable state is large. Starting from the master equation, we calculate the quasistationary probability distribution of the population sizes and the (exponentially long) mean time to extinction for each of the two scenarios. When necessary, the WKB approximation is complemented (i) by a recursive solution of the quasistationary master equation at small n and (ii) by the van Kampen system-size expansion, valid near the fixed points of the deterministic rate equation. The theory yields both entropic barriers to extinction and pre-exponential factors, and holds for a general set of multistep processes when detailed balance is broken. The results simplify considerably for single-step processes and near the characteristic bifurcations of scenarios A and B.

  5. Metastability for Markov processes with detailed balance.

    PubMed

    Larralde, Hernán; Leyvraz, François

    2005-04-29

    We present a definition for metastable states applicable to arbitrary finite state Markov processes satisfying detailed balance. In particular, we identify a crucial condition that distinguishes metastable states from other slow decaying modes and which allows us to show that our definition has several desirable properties similar to those postulated in the restricted ensemble approach. The intuitive physical meaning of this condition is simply that the total equilibrium probability of finding the system in the metastable state is negligible.

  6. Metastability for Markov Processes with Detailed Balance

    NASA Astrophysics Data System (ADS)

    Larralde, Hernán; Leyvraz, François

    2005-04-01

    We present a definition for metastable states applicable to arbitrary finite state Markov processes satisfying detailed balance. In particular, we identify a crucial condition that distinguishes metastable states from other slow decaying modes and which allows us to show that our definition has several desirable properties similar to those postulated in the restricted ensemble approach. The intuitive physical meaning of this condition is simply that the total equilibrium probability of finding the system in the metastable state is negligible.

  7. Metastability at the nanometer scale

    SciTech Connect

    Desre, P.J.

    1996-12-31

    Under constraints and at the nanometer scale, transitory metastable states can be generated in multicomponents materials. Examples illustrating such specific states are presented. They concern (1) the crystalline nucleation in a growing undercooled liquid droplet formed from a liquid parent phase; (2) the suppression of intermetallic nucleation in solid solutions or glasses subjected to sharp concentration gradients; (3) the nanocrystalline transitory state preceding amorphization by ball milling. In connection with this latter example, a thermodynamic model for the nanocrystal to glass transition, based on a hypothesis of a topological disorder wetting at the nanograin boundaries, is proposed.

  8. Vacuum metastability with black holes

    NASA Astrophysics Data System (ADS)

    Burda, Philipp; Gregory, Ruth; Moss, Ian G.

    2015-08-01

    We consider the possibility that small black holes can act as nucleation seeds for the decay of a metastable vacuum, focussing particularly on the Higgs potential. Using a thin-wall bubble approximation for the nucleation process, which is possible when generic quantum gravity corrections are added to the Higgs potential, we show that primordial black holes can stimulate vacuum decay. We demonstrate that for suitable parameter ranges, the vacuum decay process dominates over the Hawking evaporation process. Finally, we comment on the application of these results to vacuum decay seeded by black holes produced in particle collisions.

  9. Geometrically induced metastability and holography

    SciTech Connect

    Aganagic, Mina; Aganagic, Mina; Beem, Christopher; Seo, Jihye; Vafa, Cumrun

    2006-10-23

    We construct metastable configurations of branes and anti-branes wrapping 2-spheres inside local Calabi-Yau manifolds and study their large N duals. These duals are Calabi-Yau manifolds in which the wrapped 2-spheres have been replaced by 3-spheres with flux through them, and supersymmetry is spontaneously broken. The geometry of the non-supersymmetric vacuum is exactly calculable to all orders of the't Hooft parameter, and to the leading order in 1/N. The computation utilizes the same matrix model techniques that were used in the supersymmetric context. This provides a novel mechanism for breaking supersymmetry in the context of flux compactifications.

  10. Metastability on the hierarchical lattice

    NASA Astrophysics Data System (ADS)

    den Hollander, Frank; Jovanovski, Oliver

    2017-07-01

    We study metastability for Glauber spin-flip dynamics on the N-dimensional hierarchical lattice with n hierarchical levels. Each vertex carries an Ising spin that can take the values -1 or +1 . Spins interact with an external magnetic field h>0 . Pairs of spins interact with each other according to a ferromagnetic pair potential J=\\{J_i\\}i=1n , where J_i>0 is the strength of the interaction between spins at hierarchical distance i. Spins flip according to a Metropolis dynamics at inverse temperature β. In the limit as β\\to∞ , we analyse the crossover time from the metastable state \\boxminus (all spins -1 ) to the stable state \\boxplus (all spins +1 ). Under the assumption that J is non-increasing, we identify the mean transition time up to a multiplicative factor 1+o_β(1) . On the scale of its mean, the transition time is exponentially distributed. We also identify the set of configurations representing the gate for the transition. For the special case where Ji = \\tilde{J}/Ni , 1 ≤slant i ≤slant n , with \\tilde{J}>0 the relevant formulas simplify considerably. Also the hierarchical mean-field limit N\\to∞ can be analysed in detail.

  11. The thermodynamic scale of inorganic crystalline metastability.

    PubMed

    Sun, Wenhao; Dacek, Stephen T; Ong, Shyue Ping; Hautier, Geoffroy; Jain, Anubhav; Richards, William D; Gamst, Anthony C; Persson, Kristin A; Ceder, Gerbrand

    2016-11-01

    The space of metastable materials offers promising new design opportunities for next-generation technological materials, such as complex oxides, semiconductors, pharmaceuticals, steels, and beyond. Although metastable phases are ubiquitous in both nature and technology, only a heuristic understanding of their underlying thermodynamics exists. We report a large-scale data-mining study of the Materials Project, a high-throughput database of density functional theory-calculated energetics of Inorganic Crystal Structure Database structures, to explicitly quantify the thermodynamic scale of metastability for 29,902 observed inorganic crystalline phases. We reveal the influence of chemistry and composition on the accessible thermodynamic range of crystalline metastability for polymorphic and phase-separating compounds, yielding new physical insights that can guide the design of novel metastable materials. We further assert that not all low-energy metastable compounds can necessarily be synthesized, and propose a principle of 'remnant metastability'-that observable metastable crystalline phases are generally remnants of thermodynamic conditions where they were once the lowest free-energy phase.

  12. Metastable Supersymmetry Breaking in a Cooling Universe

    SciTech Connect

    Kaplunovsky, Vadim S.

    2007-11-20

    I put metastable supersymmetry breaking in a cosmological context. I argue that under reasonable assumptions, the cooling down early Universe favors metastable SUSY-breaking vacua over the stable supersymmetric vacua. To illustrate the general argument, I analyze the early-Universe history of the Intriligator-Seiberg-Shih model.

  13. Desensitization and recovery of metastable intermolecular composites

    DOEpatents

    Busse, James R [South Fork, CO; Dye, Robert C [Los Alamos, NM; Foley, Timothy J [Los Alamos, NM; Higa, Kelvin T [Ridgecrest, CA; Jorgensen, Betty S [Jemez Springs, NM; Sanders, Victor E [White Rock, NM; Son, Steven F [Los Alamos, NM

    2010-09-07

    A method to substantially desensitize a metastable intermolecular composite material to electrostatic discharge and friction comprising mixing the composite material with an organic diluent and removing enough organic diluent from the mixture to form a mixture with a substantially putty-like consistency, as well as a concomitant method of recovering the metastable intermolecular composite material.

  14. Formation of metastable phases by spinodal decomposition

    PubMed Central

    Alert, Ricard; Tierno, Pietro; Casademunt, Jaume

    2016-01-01

    Metastable phases may be spontaneously formed from other metastable phases through nucleation. Here we demonstrate the spontaneous formation of a metastable phase from an unstable equilibrium by spinodal decomposition, which leads to a transient coexistence of stable and metastable phases. This phenomenon is generic within the recently introduced scenario of the landscape-inversion phase transitions, which we experimentally realize as a structural transition in a colloidal crystal. This transition exhibits a rich repertoire of new phase-ordering phenomena, including the coexistence of two equilibrium phases connected by two physically different interfaces. In addition, this scenario enables the control of sizes and lifetimes of metastable domains. Our findings open a new setting that broadens the fundamental understanding of phase-ordering kinetics, and yield new prospects of applications in materials science. PMID:27713406

  15. Formation of metastable phases by spinodal decomposition

    NASA Astrophysics Data System (ADS)

    Alert, Ricard; Tierno, Pietro; Casademunt, Jaume

    2016-10-01

    Metastable phases may be spontaneously formed from other metastable phases through nucleation. Here we demonstrate the spontaneous formation of a metastable phase from an unstable equilibrium by spinodal decomposition, which leads to a transient coexistence of stable and metastable phases. This phenomenon is generic within the recently introduced scenario of the landscape-inversion phase transitions, which we experimentally realize as a structural transition in a colloidal crystal. This transition exhibits a rich repertoire of new phase-ordering phenomena, including the coexistence of two equilibrium phases connected by two physically different interfaces. In addition, this scenario enables the control of sizes and lifetimes of metastable domains. Our findings open a new setting that broadens the fundamental understanding of phase-ordering kinetics, and yield new prospects of applications in materials science.

  16. Ratchets, red cells, and metastability.

    PubMed

    Ferrone, Frank A; Aprelev, Alexey

    2013-06-01

    Sickle cell disease is a genetic disorder in which a negatively charged glutamic acid is replaced by a hydrophobic valine on the surface of the hemoglobin molecule, leading to polymerization of the deoxygenated form, and resulting in microvascular obstruction. Because of the high volume occupancy under which polymerization occurs physiologically, this process has been an exemplar in the study of excluded volume effects on assembly. More recently, we have identified yet another type of crowding effect involving the obstruction of the ends at which the polymers grow as a consequence of the dense arrays in which these polymers form. This makes such solutions metastable, and leads to Brownian ratchet behavior in which pressure is exerted outward when the gel occupies a finite volume, as in an emulsion or red cell. Such behavior is capable of holding sickled cells in place in the microcirculation against weak pressure differentials (hundreds of Pa), but not against the typical pressures found in vivo.

  17. Instability of colliding metastable strings

    NASA Astrophysics Data System (ADS)

    Hiramatsu, Takashi; Eto, Minoru; Kamada, Kohei; Kobayashi, Tatsuo; Ookouchi, Yutaka

    2014-01-01

    The breaking of U(1) R symmetry plays a crucial role in modeling the breaking of supersymmetry (SUSY). In the models that possess both SUSY preserving and SUSY breaking vacua, tube-like cosmic strings called R-tubes, whose surfaces are constituted by domain walls interpolating a false and a true vacuum with some winding numbers, can exist. Their (in)stability can strongly constrain SUSY breaking models theirselves. In the present study, we investigate the dynamical (in)stability of two colliding metastable tube-like strings by field-theoretic simulations. From them, we find that the strings become unstable, depending on the relative collision angle and speed of two strings, and the false vacuum is eventually filled out by the true vacuum owing to rapid expansion of the strings or unstable bubbles created as remnants of the collision.

  18. Metastable Tight Knots in DNA

    NASA Astrophysics Data System (ADS)

    Dai, Liang; Renner, C. Benjamin; Doyle, Patrick

    2015-03-01

    Knotted structures can spontaneously occur in polymers such as DNA and proteins, and the formation of knots affects biological functions, mechanical strength and rheological properties. In this work, we calculate the equilibrium size distribution of trefoil knots in linear DNA using off-lattice simulations. We observe metastable knots on DNA, as predicted by Grosberg and Rabin. Furthermore, we extend their theory to incorporate the finite width of chains and show an agreement between our simulations and the modified theory for real chains. Our results suggest localized knots spontaneously occur in long DNA and the contour length in the knot ranges from 600 to 1800 nm. This research was supported by the National Research Foundation Singapore through the Singapore MIT Alliance for Research and Technology's research program in BioSystems and Micromechanics, the National Science Foundation (Grant No. 1335938).

  19. Atom lithography with metastable helium

    SciTech Connect

    Allred, Claire S.; Reeves, Jason; Corder, Christopher; Metcalf, Harold

    2010-02-15

    A bright metastable helium (He*) beam is collimated sequentially with the bichromatic force and three optical molasses velocity compression stages. Each He* atom in the beam has 20 eV of internal energy that can destroy a molecular resist assembled on a gold coated silicon wafer. Patterns in the resist are imprinted onto the gold layer with a standard selective etch. Patterning of the wafer with the He{sup *} was demonstrated with two methods. First, a mesh was used to protect parts of the wafer making an array of grid lines. Second, a standing wave of {lambda}=1083 nm light was used to channel and focus the He* atoms into lines separated by {lambda}/2. The patterns were measured with an atomic force microscope establishing an edge resolution of 80 nm. Our results are reliable and repeatable.

  20. The thermodynamic scale of inorganic crystalline metastability

    PubMed Central

    Sun, Wenhao; Dacek, Stephen T.; Ong, Shyue Ping; Hautier, Geoffroy; Jain, Anubhav; Richards, William D.; Gamst, Anthony C.; Persson, Kristin A.; Ceder, Gerbrand

    2016-01-01

    The space of metastable materials offers promising new design opportunities for next-generation technological materials, such as complex oxides, semiconductors, pharmaceuticals, steels, and beyond. Although metastable phases are ubiquitous in both nature and technology, only a heuristic understanding of their underlying thermodynamics exists. We report a large-scale data-mining study of the Materials Project, a high-throughput database of density functional theory–calculated energetics of Inorganic Crystal Structure Database structures, to explicitly quantify the thermodynamic scale of metastability for 29,902 observed inorganic crystalline phases. We reveal the influence of chemistry and composition on the accessible thermodynamic range of crystalline metastability for polymorphic and phase-separating compounds, yielding new physical insights that can guide the design of novel metastable materials. We further assert that not all low-energy metastable compounds can necessarily be synthesized, and propose a principle of ‘remnant metastability’—that observable metastable crystalline phases are generally remnants of thermodynamic conditions where they were once the lowest free-energy phase. PMID:28138514

  1. var gene transcription and PfEMP1 expression in the rosetting and cytoadhesive Plasmodium falciparum clone FCR3S1.2

    PubMed Central

    2011-01-01

    Background The pathogenicity of Plasmodium falciparum is in part due to the ability of the parasitized red blood cell (pRBC) to adhere to intra-vascular host cell receptors and serum-proteins. Binding of the pRBC is mediated by Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1), a large multi-variant molecule encoded by a family of ≈60 var genes. Methods The study of var gene transcription in the parasite clone FCR3S1.2 was performed by semi-quantitative PCR and quantitative PCR (qPCR). The expression of the major PfEMP1 in FCR3S1.2 pRBC was analysed with polyclonal sera in rosette disruption assays and immunofluorecence. Results Transcripts from var1 (FCR3S1.2var1; IT4var21) and other var genes were detected by semi-quantitative PCR but results from qPCR showed that one var gene transcript dominated over the others (FCR3S1.2var2; IT4var60). Antibodies raised in rats to the recombinant NTS-DBL1α of var2 produced in E. coli completely and dose-dependently disrupted rosettes (≈95% at a dilution of 1/5). The sera reacted with the Maurer's clefts in trophozoite stages (IFA) and to the infected erythrocyte surface (FACS) indicating that FCR3S1.2var2 encodes the dominant PfEMP1 expressed in this parasite. Conclusion The major transcript in the rosetting model parasite FCR3S1.2 is FCR3S1.2var2 (IT4var60). The results suggest that this gene encodes the PfEMP1-species responsible for the rosetting phenotype of this parasite. The activity of previously raised antibodies to the NTS-DBL1α of FCR3S1.2var1 is likely due to cross-reactivity with NTS-DBL1α of the var2 encoded PfEMP1. PMID:21266056

  2. Detection of sputtered metastable atoms by autoionization

    SciTech Connect

    Wucher, A.; Berthold, W.; Oechsner, H.; Franzreb, K.

    1994-03-01

    We report on a scheme for the detection of sputter-generated metastable atoms that is based on the resonant excitation of an autoionizing state by single-photon absorption from a tunable laser. Using this technique, sputtered silver atoms ejected in the metastable 4{ital d}{sup 9}5{ital s}{sup 2}{ital D}{sub 5/2} state with an excitation energy of 3.75 eV have been detected. This represents the highest excitation energy of sputtered metastable atoms observed so far.

  3. Metastability of a Supercompressed Fluid Monolayer

    PubMed Central

    Smith, Ethan C.; Crane, Jonathan M.; Laderas, Ted G.; Hall, Stephen B.

    2003-01-01

    Previous studies showed that monomolecular films of extracted calf surfactant collapse at the equilibrium spreading pressure during quasi-static compressions but become metastable at much higher surface pressures when compressed faster than a threshold rate. To determine the mechanism by which the films become metastable, we studied single-component films of 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC). Initial experiments confirmed similar metastability of POPC if compressed above a threshold rate. Measurements at different surface pressures then showed that rates of collapse, although initially increasing above the equilibrium spreading pressure, reached a sharply defined maximum and then slowed considerably. When heated, rapidly compressed films recovered their ability to collapse with no discontinuous change in area, arguing that the metastability does not reflect transition of the POPC film to a new phase. These observations indicate that in several respects, the supercompression of POPC monolayers resembles the supercooling of three-dimensional liquids toward a glass transition. PMID:14581205

  4. System-Size Effects in Metastability

    NASA Astrophysics Data System (ADS)

    Schulman, L. S.

    The following sections are included: * INTRODUCTION * CALCULATION OP PV(m), THE FINITE) SIZE PROBABILITY FOR FINDING MAGNETIZATION m * HEURISTICS OF PV(m) * DYNAMIC METASTABILITY * DISCUSSION * ACKNOWLEDGEMENTS * REFERENCES

  5. Fluctuation-Dissipation Theorem for Metastable Systems

    NASA Astrophysics Data System (ADS)

    Báez, G.; Larralde, H.; Leyvraz, F.; Méndez-Sánchez, R. A.

    2003-04-01

    We show that an appropriately defined fluctuation-dissipation theorem, connecting generalized susceptibilities and time correlation functions, is valid for times shorter than the nucleation time of the metastable state of Markovian systems satisfying detailed balance. This is done by assuming that such systems can be described by a superposition of the ground and first excited states of the master equation. We corroborate our results numerically for the metastable states of a two-dimensional Ising model.

  6. Metastability in an open quantum Ising model.

    PubMed

    Rose, Dominic C; Macieszczak, Katarzyna; Lesanovsky, Igor; Garrahan, Juan P

    2016-11-01

    We apply a recently developed theory for metastability in open quantum systems to a one-dimensional dissipative quantum Ising model. Earlier results suggest this model features either a nonequilibrium phase transition or a smooth but sharp crossover, where the stationary state changes from paramagnetic to ferromagnetic, accompanied by strongly intermittent emission dynamics characteristic of first-order coexistence between dynamical phases. We show that for a range of parameters close to this transition or crossover point the dynamics of the finite system displays pronounced metastability, i.e., the system relaxes first to long-lived metastable states before eventual relaxation to the true stationary state. From the spectral properties of the quantum master operator we characterize the low-dimensional manifold of metastable states, which are shown to be probability mixtures of two, paramagnetic and ferromagnetic, metastable phases. We also show that for long times the dynamics can be approximated by a classical stochastic dynamics between the metastable phases that is directly related to the intermittent dynamics observed in quantum trajectories and thus the dynamical phases.

  7. Metastability in an open quantum Ising model

    NASA Astrophysics Data System (ADS)

    Rose, Dominic C.; Macieszczak, Katarzyna; Lesanovsky, Igor; Garrahan, Juan P.

    2016-11-01

    We apply a recently developed theory for metastability in open quantum systems to a one-dimensional dissipative quantum Ising model. Earlier results suggest this model features either a nonequilibrium phase transition or a smooth but sharp crossover, where the stationary state changes from paramagnetic to ferromagnetic, accompanied by strongly intermittent emission dynamics characteristic of first-order coexistence between dynamical phases. We show that for a range of parameters close to this transition or crossover point the dynamics of the finite system displays pronounced metastability, i.e., the system relaxes first to long-lived metastable states before eventual relaxation to the true stationary state. From the spectral properties of the quantum master operator we characterize the low-dimensional manifold of metastable states, which are shown to be probability mixtures of two, paramagnetic and ferromagnetic, metastable phases. We also show that for long times the dynamics can be approximated by a classical stochastic dynamics between the metastable phases that is directly related to the intermittent dynamics observed in quantum trajectories and thus the dynamical phases.

  8. Incompatible Sets of Gradients and Metastability

    NASA Astrophysics Data System (ADS)

    Ball, J. M.; James, R. D.

    2015-12-01

    We give a mathematical analysis of a concept of metastability induced by incompatibility. The physical setting is a single parent phase, just about to undergo transformation to a product phase of lower energy density. Under certain conditions of incompatibility of the energy wells of this energy density, we show that the parent phase is metastable in a strong sense, namely it is a local minimizer of the free energy in an L 1 neighbourhood of its deformation. The reason behind this result is that, due to the incompatibility of the energy wells, a small nucleus of the product phase is necessarily accompanied by a stressed transition layer whose energetic cost exceeds the energy lowering capacity of the nucleus. We define and characterize incompatible sets of matrices, in terms of which the transition layer estimate at the heart of the proof of metastability is expressed. Finally we discuss connections with experiments and place this concept of metastability in the wider context of recent theoretical and experimental research on metastability and hysteresis.

  9. Metastable Detection Using Cold Solid Matrices

    NASA Astrophysics Data System (ADS)

    McConkey, William; Kedzierski, Wladek; Alsaiari, Fatimah

    2016-05-01

    Metastable particles produced in the interaction of electrons of carefully controlled energy with thermal gaseous target beams in a crossed beam set-up have been studied in the energy range from threshold to 300 eV. The e-beam is pulsed and the metastables produced drift to a solid nitrogen or rare gas detector held at 10 K. Here they form excimers which immediately radiate. The resultant photons are detected using a photomultiplier-filter combination. Time-of-flight techniques are used to separate these photons from prompt photons produced in the initial electron collision. With N2 as both target and detection matrix, the excimer emission is strongest in the green but still significant in the red spectral region. Excitation functions will be presented together with threshold measurements. These help to identify the metastable states being observed and the excitation mechanisms which are responsible. The authors thank NSERC and CFI (Canada) for financial support.

  10. Multistability with a Metastable Mixed State

    NASA Astrophysics Data System (ADS)

    Sneppen, Kim; Mitarai, Namiko

    2012-09-01

    Complex dynamical systems often show multiple metastable states. In macroevolution, such behavior is suggested by punctuated equilibrium and discrete geological epochs. In molecular biology, bistability is found in epigenetics and in the many mutually exclusive states that a human cell can take. Sociopolitical systems can be single-party regimes or a pluralism of balancing political fractions. To introduce multistability, we suggest a model system of D mutually exclusive microstates that battle for dominance in a large system. Assuming one common intermediate state, we obtain D+1 metastable macrostates for the system, one of which is a self-reinforced mixture of all D+1 microstates. Robustness of this metastable mixed state increases with diversity D.

  11. On the Destabilization of Metastable Solid He

    NASA Astrophysics Data System (ADS)

    Souris, F.; Qu, A.; Dupont-Roc, J.; Grucker, J.; Jacquier, Ph.

    2015-06-01

    Recently, a metastable state of solid He has been produced by locally lowering the density of the solid below the melting density using a focused acoustic wave pulse. An unexpected instability of the solid has been found about 4 bar below the melting line. This paper reports on experiments precisely localizing in time the instability birth within the acoustic pulse. It is found that, as expected, the instability always appears during a depression swing of the wave. However a metastability pressure limit does not emerge clearly. Total stress duration seems also to play a role in the instability triggering, suggesting a fatigue effect.

  12. Dynamic consolidation of metastable nanocrystalline powders

    SciTech Connect

    Korth, G.E.; Williamson, R.L.

    1995-10-01

    Nanocrystalline metal powders synthesized by mechanical alloying in a ball mill resulted in micron-sized powder particles with a nanosized (5 to 25 nm) substructure. Conventional consolidation methods resulted in considerable coarsening of the metastable nanometer crystallites, but dynamic consolidation of these powders using explosive techniques produced fully dense monoliths while retaining the 5- to 25-nm substructure. Numerical modeling used to guide the experimental phase, revealed that the compression wave necessary for suitable consolidation was of order of 10 GPa for a few tenths of a microsecond. The consolidation process is described, and the retention of the metastable nanostructure is illustrated.

  13. Numerical Construction of the Aizenman-Wehr Metastate.

    PubMed

    Billoire, A; Fernandez, L A; Maiorano, A; Marinari, E; Martin-Mayor, V; Moreno-Gordo, J; Parisi, G; Ricci-Tersenghi, F; Ruiz-Lorenzo, J J

    2017-07-21

    Chaotic size dependence makes it extremely difficult to take the thermodynamic limit in disordered systems. Instead, the metastate, which is a distribution over thermodynamic states, might have a smooth limit. So far, studies of the metastate have been mostly mathematical. We present a numerical construction of the metastate for the d=3 Ising spin glass. We work in equilibrium, below the critical temperature. Leveraging recent rigorous results, our numerical analysis gives evidence for a dispersed metastate, supported on many thermodynamic states.

  14. Regulation of protein function by native metastability

    PubMed Central

    Lee, Cheolju; Park, Soon-Ho; Lee, Min-Youn; Yu, Myeong-Hee

    2000-01-01

    In common globular proteins, the native form is in its most stable state. In contrast, each native form exists in a metastable state in inhibitory serpins (serine protease inhibitors) and some viral membrane fusion proteins. Metastability in these proteins is critical to their biological functions. Mutational analyses and structural examination have previously revealed unusual interactions, such as side-chain overpacking, buried polar groups, and cavities as the structural basis of the native metastability. However, the mechanism by which these structural defects regulate protein functions has not been elucidated. We report here characterization of cavity-filling mutations of α1-antitrypsin, a prototype serpin. Conformational stability of the molecule increased linearly with the van der Waals volume of the side chains. Increasing conformational stability is correlated with decreasing inhibitory activity. Moreover, the activity loss appears to correlate with the decrease in the rate of the conformational switch during complex formation with a target protease. These results strongly suggest that the native metastability of proteins is indeed a structural design that regulates protein functions. PMID:10884404

  15. Reheating Metastable O'Raifeartaigh Models

    SciTech Connect

    Craig, Nathaniel J.; Fox, Patrick J.; Wacker, Jay G.

    2006-12-05

    In theories with multiple vacua, reheating to a temperature greater than the height of a barrier can stimulate transitions from a desirable metastable vacuum to a lower energy state. We discuss the constraints this places on various theories and demonstrate that in a class of supersymmetric models this transition does not occur even for arbitrarily high reheating temperature.

  16. Reheating metastable O'Raifeartaigh models

    SciTech Connect

    Fox, Patrick; Craig, Nathaniel J.; Fox, Patrick J.; Wacker, Jay G.

    2006-11-01

    In theories with multiple vacua, reheating to a temperature greater than the height of a barrier can stimulate transitions from a desirable metastable vacuum to a lower energy state. We discuss the constraints this places on various theories and demonstrate that in a class of supersymmetric models this transition does not occur even for arbitrarily high reheating temperature.

  17. Reheating Metastable O'Raifeartaigh Models

    SciTech Connect

    Craig, Nathaniel J.; Fox, Patrick J.; Wacker, Jay G.; /SLAC /Stanford U., ITP

    2006-12-13

    In theories with multiple vacua, reheating to a temperature greater than the height of a barrier can stimulate transitions from a desirable metastable vacuum to a lower energy state. We discuss the constraints this places on various theories and demonstrate that in a class of supersymmetric models this transition does not occur even for arbitrarily high reheating temperature.

  18. Kinetic Trapping of Metastable Amino Acid Polymorphs

    NASA Astrophysics Data System (ADS)

    Simpson, Garth

    2014-06-01

    Second harmonic generation (SHG) microscopy was integrated with synchrotron X-ray diffraction (XRD) to test the Ostwald Rule of Stages, in which is hypothesized that crystals dynamically transition through metastable polymorphs before settling on the most thermodynamically favored form. The presence or absence of metastable forms has historically been challenging to probe due to the stochastic randomness of crystal nucleation coupled with the relatively short time-frame over which the metastable forms may survive. In this work, inkjet printing of a racemic amino acid solutions results in rapid solvent evaporation, placing crystallization under kinetic rather than thermodynamic control. SHG microscopy is used to rapidly and selectively identify the positions of metastable crystal forms. Coupling this measurement with synchrotron XRD allows diffraction analysis to be performed on individual inkjet printed dots of only a few pg of total material, prepared from single 1 pL droplets. In studies of amino acids, we have shown that the homochiral crystals emerge when printed, while those same solutions exclusively generate the racemic co-crystals upon slow solvent evaporation.

  19. Symplectic integration approach for metastable systems

    NASA Astrophysics Data System (ADS)

    Klotins, E.

    2006-03-01

    Nonadiabatic behavior of metastable systems modeled by anharmonic Hamiltonians is reproduced by the Fokker-Planck and imaginary time Schrödinger equation scheme with subsequent symplectic integration. Example solutions capture ergodicity breaking, reassure the H-theorem of global stability [M. Shiino, Phys. Rev. A 36, 2393 (1987)], and reproduce spatially extended response under alternate source fields.

  20. Biosorption of Pb(II) Ions by Klebsiella sp. 3S1 Isolated from a Wastewater Treatment Plant: Kinetics and Mechanisms Studies

    PubMed Central

    Muñoz, Antonio Jesús; Espínola, Francisco; Moya, Manuel; Ruiz, Encarnación

    2015-01-01

    Lead biosorption by Klebsiella sp. 3S1 isolated from a wastewater treatment plant was investigated through a Rotatable Central Composite Experimental Design. The optimisation study indicated the following optimal values of operating variables: 0.4 g/L of biosorbent dosage, pH 5, and 34°C. According to the results of the kinetic studies, the biosorption process can be described by a two-step process, one rapid, almost instantaneous, and one slower, both contributing significantly to the overall biosorption; the model that best fits the experimental results was pseudo-second order. The equilibrium studies showed a maximum lead uptake value of 140.19 mg/g according to the Langmuir model. The mechanism study revealed that lead ions were bioaccumulated into the cytoplasm and adsorbed on the cell surface. The bacterium  Klebsiella sp. 3S1 has a good potential in the bioremoval of lead in an inexpensive and effective process. PMID:26504824

  1. Metastable dynamics in heterogeneous neural fields

    PubMed Central

    Schwappach, Cordula; Hutt, Axel; beim Graben, Peter

    2015-01-01

    We present numerical simulations of metastable states in heterogeneous neural fields that are connected along heteroclinic orbits. Such trajectories are possible representations of transient neural activity as observed, for example, in the electroencephalogram. Based on previous theoretical findings on learning algorithms for neural fields, we directly construct synaptic weight kernels from Lotka-Volterra neural population dynamics without supervised training approaches. We deliver a MATLAB neural field toolbox validated by two examples of one- and two-dimensional neural fields. We demonstrate trial-to-trial variability and distributed representations in our simulations which might therefore be regarded as a proof-of-concept for more advanced neural field models of metastable dynamics in neurophysiological data. PMID:26175671

  2. Metastable structure of Li13Si4

    NASA Astrophysics Data System (ADS)

    Gruber, Thomas; Bahmann, Silvia; Kortus, Jens

    2016-04-01

    The Li13Si4 phase is one out of several crystalline lithium silicide phases, which is a potential electrode material for lithium ion batteries and contains a high theoretical specific capacity. By means of ab initio methods like density functional theory (DFT) many properties such as heat capacity or heat of formation can be calculated. These properties are based on the calculation of phonon frequencies, which contain information about the thermodynamical stability. The current unit cell of "Li13Si4" given in the ICSD database is unstable with respect to DFT calculations. We propose a modified unit cell that is stable in the calculations. The evolutionary algorithm EVO found a structure very similar to the ICSD one with both of them containing metastable lithium positions. Molecular dynamic simulations show a phase transition between both structures where these metastable lithium atoms move. This phase transition is achieved by a very fast one-dimensional lithium diffusion and stabilizes this phase.

  3. Metastability in bubbling AdS space

    NASA Astrophysics Data System (ADS)

    Massai, Stefano; Pasini, Giulio; Puhm, Andrea

    2015-02-01

    We study the dynamics of probe M5 branes with dissolved M2 charge in bubbling geometries with SO(4) × SO(4) symmetry. These solutions were constructed by Bena-Warner and Lin-Lunin-Maldacena and correspond to the vacua of the maximally supersymmetric mass-deformed M2 brane theory. We find that supersymmetric probe M2 branes polarize into M5 brane shells whose backreaction creates an additional bubble in the geometry. We explicitly check that the supersymmetric polarization potential agrees with the one found within the Polchinski-Strassler approximation. The main result of this paper is that probe M2 branes whose orientation is opposite to the background flux can polarize into metastable M5 brane shells. These decay to a supersymmetric configuration via brane-flux annihilation. Our findings suggest the existence of metastable states in the mass-deformed M2 brane theory.

  4. Universal metastability of sickle hemoglobin polymerization

    NASA Astrophysics Data System (ADS)

    Weng, Weijun

    Sickle hemoglobin (HbS) is a natural mutation of the normal hemoglobin (HbA) found in the red blood cells of human body. Polymerization of HbS occurs when the concentration of deoxyHbS exceeds a well-defined solubility, which is the underlying cause of the Sickle Cell Disease. It has long been assumed that thermodynamic equilibrium is reached when polymerization comes to an end. However, in this thesis we demonstrate that in confined volume as well as in bulk solution, HbS polymerization terminates prematurely, leaving the solution in a metastable state. A newly developed Reservoir method as well as modulated excitation method were adopted for the study. This discovery of universal metastability gives us new insights into understanding the mechanism of sickle cell disease.

  5. Metastable localization of diseases in complex networks

    NASA Astrophysics Data System (ADS)

    Ferreira, R. S.; da Costa, R. A.; Dorogovtsev, S. N.; Mendes, J. F. F.

    2016-12-01

    We describe the phenomenon of localization in the epidemic susceptible-infective-susceptible model on highly heterogeneous networks in which strongly connected nodes (hubs) play the role of centers of localization. We find that in this model the localized states below the epidemic threshold are metastable. The longevity and scale of the metastable outbreaks do not show a sharp localization transition; instead there is a smooth crossover from localized to delocalized states as we approach the epidemic threshold from below. Analyzing these long-lasting local outbreaks for a random regular graph with a hub, we show how this localization can be detected from the shape of the distribution of the number of infective nodes.

  6. Metastable Phase Evolution in Oxide Systems

    NASA Astrophysics Data System (ADS)

    Levi, Carlos G.

    2005-03-01

    Multi-component ceramics are often synthesized by routes that facilitate mixing at the molecular scale and subsequently generate a solid product at low homologous temperatures. Examples include chemical and physical vapor deposition, thermal spray, and pyrolytic decomposition of precursor solutions. In these processes the solid evolves rapidly from a highly energized state, typically in a temperature regime wherein long-range diffusion is largely constrained and the equilibrium configuration can be kinetically suppressed. The resulting product may exhibit various forms of metastability such as amorphization, nanocrystallinity, extended solid solubility and alternate crystalline forms. The approach allows access to novel combinations of structure and composition with unprecedented defect structures that, if reasonably durable, could have properties of potential technological interest. Understanding phase selection and evolution is facilitated by having a suitable reference framework depicting the thermodynamic hierarchy of the phases available to the system under the relevant processing conditions. When transformations are partitionless the phase menu and hierarchy can be readily derived from the relative position of the T0 curves/surfaces for the different pairs of phases. The result is a phase hierarchy map, which is an analog of the phase diagram for partitionless equilibrium. Such maps can then be used to assess the kinetic effects on the selection of metastable states and their subsequent evolution. This presentation will discuss the evolution of metastable phases in oxides, with emphasis on systems involving fluorite phases and their ordered or distorted derivatives. The concepts will be illustrated primarily with zirconia-based systems, notably those of interest in thermal barrier coatings, fuel cells and ferroelectrics (ZrO2-MO3/2, where M = Y, Sc, the lanthanides and combinations thereof, as well as ZrO2-YO3/2-TiO2, ZrO2-TiO2-PbO, etc.). Of particular

  7. Metastable states in homogeneous Ising models

    SciTech Connect

    Achilles, M.; Bendisch, J.; von Trotha, H.

    1987-04-01

    Metastable states of homogeneous 2D and 3D Ising models are studied under free boundary conditions. The states are defined in terms of weak and strict local minima of the total interaction energy. The morphology of these minima is characterized locally and globally on square and cubic grids. Furthermore, in the 2D case, transition from any spin configuration that is not a strict minimum to a strict minimum is possible via non-energy-increasing single flips.

  8. Transient Cognitive Dynamics, Metastability, and Decision Making

    DTIC Science & Technology

    2008-05-02

    793–810. 39. Wagatsuma H, Yamaguchi Y (2007) Neural dynamics of the cognitive map in the hippocampus. Cognitive Neurodynamics 1: 119–141. 40. Kifer Y...Transient Cognitive Dynamics, Metastability, and Decision Making Mikhail I. Rabinovich1*, Ramón Huerta1,2, Pablo Varona2, Valentin S. Afraimovich3 1...Óptica, UASLP, San Luis de Potosı́, Mexico Abstract The idea that cognitive activity can be understood using nonlinear dynamics has been intensively

  9. Detonation of Meta-stable Clusters

    SciTech Connect

    Kuhl, Allen; Kuhl, Allen L.; Fried, Laurence E.; Howard, W. Michael; Seizew, Michael R.; Bell, John B.; Beckner, Vincent; Grcar, Joseph F.

    2008-05-31

    We consider the energy accumulation in meta-stable clusters. This energy can be much larger than the typical chemical bond energy (~;;1 ev/atom). For example, polymeric nitrogen can accumulate 4 ev/atom in the N8 (fcc) structure, while helium can accumulate 9 ev/atom in the excited triplet state He2* . They release their energy by cluster fission: N8 -> 4N2 and He2* -> 2He. We study the locus of states in thermodynamic state space for the detonation of such meta-stable clusters. In particular, the equilibrium isentrope, starting at the Chapman-Jouguet state, and expanding down to 1 atmosphere was calculated with the Cheetah code. Large detonation pressures (3 and 16 Mbar), temperatures (12 and 34 kilo-K) and velocities (20 and 43 km/s) are a consequence of the large heats of detonation (6.6 and 50 kilo-cal/g) for nitrogen and helium clusters respectively. If such meta-stable clusters could be synthesized, they offer the potential for large increases in the energy density of materials.

  10. Stochastic basins of attraction for metastable states

    NASA Astrophysics Data System (ADS)

    Serdukova, Larissa; Zheng, Yayun; Duan, Jinqiao; Kurths, Jürgen

    2016-07-01

    Basin of attraction of a stable equilibrium point is an effective concept for stability analysis in deterministic systems; however, it does not contain information on the external perturbations that may affect it. Here we introduce the concept of stochastic basin of attraction (SBA) by incorporating a suitable probabilistic notion of basin. We define criteria for the size of the SBA based on the escape probability, which is one of the deterministic quantities that carry dynamical information and can be used to quantify dynamical behavior of the corresponding stochastic basin of attraction. SBA is an efficient tool to describe the metastable phenomena complementing the known exit time, escape probability, or relaxation time. Moreover, the geometric structure of SBA gives additional insight into the system's dynamical behavior, which is important for theoretical and practical reasons. This concept can be used not only in models with small noise intensity but also with noise whose amplitude is proportional or in general is a function of an order parameter. As an application of our main results, we analyze a three potential well system perturbed by two types of noise: Brownian motion and non-Gaussian α-stable Lévy motion. Our main conclusions are that the thermal fluctuations stabilize the metastable system with an asymmetric three-well potential but have the opposite effect for a symmetric one. For Lévy noise with larger jumps and lower jump frequencies ( α = 0.5 ) metastability is enhanced for both symmetric and asymmetric potentials.

  11. Stochastic basins of attraction for metastable states.

    PubMed

    Serdukova, Larissa; Zheng, Yayun; Duan, Jinqiao; Kurths, Jürgen

    2016-07-01

    Basin of attraction of a stable equilibrium point is an effective concept for stability analysis in deterministic systems; however, it does not contain information on the external perturbations that may affect it. Here we introduce the concept of stochastic basin of attraction (SBA) by incorporating a suitable probabilistic notion of basin. We define criteria for the size of the SBA based on the escape probability, which is one of the deterministic quantities that carry dynamical information and can be used to quantify dynamical behavior of the corresponding stochastic basin of attraction. SBA is an efficient tool to describe the metastable phenomena complementing the known exit time, escape probability, or relaxation time. Moreover, the geometric structure of SBA gives additional insight into the system's dynamical behavior, which is important for theoretical and practical reasons. This concept can be used not only in models with small noise intensity but also with noise whose amplitude is proportional or in general is a function of an order parameter. As an application of our main results, we analyze a three potential well system perturbed by two types of noise: Brownian motion and non-Gaussian α-stable Lévy motion. Our main conclusions are that the thermal fluctuations stabilize the metastable system with an asymmetric three-well potential but have the opposite effect for a symmetric one. For Lévy noise with larger jumps and lower jump frequencies ( α=0.5) metastability is enhanced for both symmetric and asymmetric potentials.

  12. Metastable Equilibria Among Aqueous Organic Compounds

    NASA Astrophysics Data System (ADS)

    Shock, E.; Shipp, J.; Yang, Z.; Gould, I. R.

    2011-12-01

    Metastable equilibrium states exist when reactions among a subset of compounds in a chemical system are reversible even though other irreversible reactions exist in the same system. The existence of metastable equilibrium among organic compounds was initially detected by comparing ratios of organic acid concentrations reported for oil-field brines (Shock, 1988, Geology 16, 886-890; Shock, 1989, Geology 17, 572-573), and calculating the same ratios for likely oxidation states determined by mineral assemblages and mixtures of hydrocarbons in coexisting petroleum (Shock, 1994, in: The Role of Organic Acids in Geological Processes, Springer). This led to the notion of extending the concept of metastable equilibrium states to explicitly account for petroleum compositions (Helgeson et al., 1993, GCA, 57, 3295-3339), which eventually yielded the concept of hydrolytic disproportionation of kerogens to produce petroleum and CO2(g) (Helgeson et al., 2009, GCA, 73, 594-695). Experimental tests of metastable equilibrium among organic compounds began with the identification of reversible reactions between alkanes and alkenes that are dependent on the H2 fugacity of the experimental system (Seewald, 1994, Nature 370, 285-287). These were followed with a comprehensive series of long-term experiments leading to the hypothesis that reversible reactions include alkanes, alkenes, alcohol, aldehydes, ketones and carboxylic acids (e.g., Seewald, 2001, GCA 65, 1641-1664; 2003, Nature 426, 327-333; McCollom & Seewald, 2003, GCA 67, 3645-3664). We have conducted sets of hydrothermal organic transformation experiments that test the extent to which these reactions are indeed reversible using aromatic and cyclic compounds. Results demonstrate reversibility for reactions among dibenzyl ketone, 1,3-diphenyl-2-propanol, 1,3-diphenylpropene and 1,3-diphenylpropane, as well as among methylcyclohexanes, methylcyclohexenes, methylcyclohexanols, methylcyclohexanones and methylcyclohexadienes. The

  13. The interaction of the theophylline metastable phase with water vapor

    NASA Astrophysics Data System (ADS)

    Matvienko, A. A.; Boldyrev, V. V.; Sidel'Nikov, A. A.; Chizhik, S. A.

    2008-07-01

    The conditions of hydration of the stable and metastable theophylline phases were determined. Two-phase metastable phase/monohydrate and stable phase/monohydrate equilibrium pressures were measured at 25, 30, and 35°C. The metastable phase began to react with water vapor at lower relative humidities than the stable phase. Processes that occurred with the metastable and stable theophylline phases over various water pressure ranges were considered. The metastable phase exhibited an unusual behavior at 25°C and relative humidity 47%. At constant water vapor pressure and temperature, theophylline was initially hydrated and then lost water and again became anhydrous. Two consecutive processes occurred in the system, the formation of theophylline monohydrate from the metastable phase and its decomposition to the stable phase. The ratio between the rates of these processes determined the content of the monohydrate at the given time moment.

  14. Noise signatures of metastable resistivity states in ferromagnetic insulating manganite

    SciTech Connect

    Przybytek, J.; Fink-Finowicki, J.; Puźniak, R.; Markovich, V.; Jung, G.

    2015-07-28

    Pronounced noise signatures enabling one to discriminate metastable resistivity states in La{sub 0.86}Ca{sub 0.14}MnO{sub 3} single crystals have been observed. The normalized noise spectra for metastable resisitivity differ both in shape and magnitude, indicating that the metastable state is associated with transition of the electronic system into another local minimum of the potential landscape. Such scenario is consistent with freezing of the electronic system into a Coulomb glass state.

  15. Stability and metastability of bromine clathrate polymorphs.

    PubMed

    Nguyen, Andrew H; Molinero, Valeria

    2013-05-23

    Clathrate hydrates are crystals in which water forms a network of fully hydrogen-bonded polyhedral cages that contain small guests. Clathrate hydrates occur mostly in two cubic crystal polymorphs, sI and sII. Bromine is one of two guests that yield a hydrate with the tetragonal structure (TS), the topological dual of the Frank-Kasper σ phase. There has been a long-standing disagreement on whether bromine hydrate also forms metastable sI and sII crystals. To date there are no data on the thermodynamic range of stability (e.g., the melting temperatures) of the metastable polymorphs. Here we use molecular dynamics simulations with the coarse-grained model of water mW to (i) investigate the thermodynamic stability of the empty and guest-filled the sI, sII, TS, and HS-I hydrate polymorphs, (ii) develop a coarse-grained model of bromine compatible with mW water, and (iii) evaluate the stability of the bromine hydrate polymorphs. The mW model predicts the same relative energy of the empty clathrate polymorphs and the same phase diagram as a function of water-guest interaction than the fully atomistic TIP4P water model. There is a narrow region in water-guest parameter space for which TS is marginally more stable than sI or sII. We parametrize a coarse-grained model of bromine compatible with mW water and use it to determine the order of stability of the bromine hydrate polymorphs. The melting temperatures of the bromine hydrate polymorphs predicted by the coarse-grained model are 281 ± 1 K for TS, 279 ± 1 K for sII, and 276 ± 1 K for sI. The closeness of the melting temperatures supports the plausibility of formation of metastable sII and sI bromine hydrates.

  16. Transient Cognitive Dynamics, Metastability, and Decision Making

    PubMed Central

    Rabinovich, Mikhail I.; Huerta, Ramón; Varona, Pablo; Afraimovich, Valentin S.

    2008-01-01

    The idea that cognitive activity can be understood using nonlinear dynamics has been intensively discussed at length for the last 15 years. One of the popular points of view is that metastable states play a key role in the execution of cognitive functions. Experimental and modeling studies suggest that most of these functions are the result of transient activity of large-scale brain networks in the presence of noise. Such transients may consist of a sequential switching between different metastable cognitive states. The main problem faced when using dynamical theory to describe transient cognitive processes is the fundamental contradiction between reproducibility and flexibility of transient behavior. In this paper, we propose a theoretical description of transient cognitive dynamics based on the interaction of functionally dependent metastable cognitive states. The mathematical image of such transient activity is a stable heteroclinic channel, i.e., a set of trajectories in the vicinity of a heteroclinic skeleton that consists of saddles and unstable separatrices that connect their surroundings. We suggest a basic mathematical model, a strongly dissipative dynamical system, and formulate the conditions for the robustness and reproducibility of cognitive transients that satisfy the competing requirements for stability and flexibility. Based on this approach, we describe here an effective solution for the problem of sequential decision making, represented as a fixed time game: a player takes sequential actions in a changing noisy environment so as to maximize a cumulative reward. As we predict and verify in computer simulations, noise plays an important role in optimizing the gain. PMID:18452000

  17. Metastable Krypton Beam Source via Two-Photon Pumping Technique

    SciTech Connect

    Wong, W.W.; Young, L.

    2003-01-01

    Metastable beams of rare gas atoms have wide applications in chemical analysis of samples, as well as in aiding understanding of fundamental processes and physical attributes. Most current sources of metastable rare gas atomic beams, however, are limited in their flux density, which greatly reduces their utility in applications such as low level trace analysis and precision measurements. Previous work has demonstrated feasibility of metastable krypton production via two-photon pumping, and this paper extends that possibility into beam form. Further optimization on this scheme, moreover, promises 100-fold increase of metastable krypton flux density over that of an rf-driven discharge.

  18. Noise-induced metastability in biochemical networks.

    PubMed

    Biancalani, Tommaso; Rogers, Tim; McKane, Alan J

    2012-07-01

    Intracellular biochemical reactions exhibit a rich dynamical phenomenology which cannot be explained within the framework of mean-field rate equations and additive noise. Here, we show that the presence of metastable states and radically different time scales are general features of a broad class of autocatalytic reaction networks, and that this fact may be exploited to gain analytical results. The latter point is demonstrated by a treatment of the paradigmatic Togashi-Kaneko reaction, which has resisted theoretical analysis for the last decade.

  19. Metastability in spin-polarized Fermi gases.

    PubMed

    Liao, Y A; Revelle, M; Paprotta, T; Rittner, A S C; Li, Wenhui; Partridge, G B; Hulet, R G

    2011-09-30

    We study the role of particle transport and evaporation on the phase separation of an ultracold, spin-polarized atomic Fermi gas. We show that the previously observed deformation of the superfluid paired core is a result of evaporative depolarization of the superfluid due to a combination of enhanced evaporation at the center of the trap and the inhibition of spin transport at the normal-superfluid phase boundary. These factors contribute to a nonequilibrium jump in the chemical potentials at the phase boundary. Once formed, the deformed state is highly metastable, persisting for times of up to 2 s.

  20. T cell receptor repertoire differences between African Americans and Caucasians associated with polymorphism of the TCRBV3S1 (V{beta}3.1) gene

    SciTech Connect

    De Inocencio, J.; Glass, D.N.; Hirsch, R.

    1995-05-01

    The generation of TCR diversity occurs primarily through rearrangement of germline DNA. Genetic polymorphism of the TCR chains appears to be a rarer mechanism for generating repertoire differences between races. Flow cytometric analysis of the TCR V{beta} repertoire in a population of healthy African Americans (n = 30) and Caucasians (n = 30) revealed a significant difference in the frequency of cells bearing V{beta}3.1, but not V{beta}2, V{beta}5.1, V{beta}5.2-5.3, V{beta}6.7, V{beta}8.1-8.2, V{beta}12.1, V{beta}13.3, or V{beta}19. African Americans had a significantly lower frequency of V{beta}3.1{sup +} cells, in both the CD4{sup +} (2.55 {+-} 0.36% vs 4.85 {+-} 0.43%, p = 0.0001) and the CD8{sup +} (3.03 {+-} 0.54% vs 5.32 {+-} 0.57%, p = 0.004) population than did Caucasians, and this difference was independent of the age of the individuals. Analysis of genomic DNA revealed that the observed differences in frequency of V{beta}3.1{sup +} cells correlated with a recently described polymorphism of the recombination signal sequence of the TCRBV3S1 gene. Allele 1, associated with a lower frequency of V{beta}3.1{sup +} cells, was more commonly present in African Americans (0.68 vs 0.43), whereas allele 2, associated with a higher frequency of V{beta}3.1{sup +} cells, was more commonly present in Caucasians (0.31 vs 0.56). This study demonstrates the potential for TCR repertoire differences, based on genetic polymorphism, between African Americans and Caucasians. 31 refs., 2 figs., 5 tabs.

  1. Metastable Metal Hydrides for Hydrogen Storage

    DOE PAGES

    Graetz, Jason

    2012-01-01

    The possibility of using hydrogen as a reliable energy carrier for both stationary and mobile applications has gained renewed interest in recent years due to improvements in high temperature fuel cells and a reduction in hydrogen production costs. However, a number of challenges remain and new media are needed that are capable of safely storing hydrogen with high gravimetric and volumetric densities. Metal hydrides and complex metal hydrides offer some hope of overcoming these challenges; however, many of the high capacity “reversible” hydrides exhibit a large endothermic decomposition enthalpy making it difficult to release the hydrogen at low temperatures. Onmore » the other hand, the metastable hydrides are characterized by a low reaction enthalpy and a decomposition reaction that is thermodynamically favorable under ambient conditions. The rapid, low temperature hydrogen evolution rates that can be achieved with these materials offer much promise for mobile PEM fuel cell applications. However, a critical challenge exists to develop new methods to regenerate these hydrides directly from the reactants and hydrogen gas. This spotlight paper presents an overview of some of the metastable metal hydrides for hydrogen storage and a few new approaches being investigated to address the key challenges associated with these materials.« less

  2. Probability of metastable states in Yukawa clusters

    NASA Astrophysics Data System (ADS)

    Ludwig, Patrick; Kaehlert, Hanno; Baumgartner, Henning; Bonitz, Michael

    2008-11-01

    Finite strongly coupled systems of charged particles in external traps are of high interest in many fields. Here we analyze the occurrence probabilities of ground- and metastable states of spherical, three-dimensional Yukawa clusters by means of molecular dynamics and Monte Carlo simulations and an analytical method. We find that metastable states can occur with a higher probability than the ground state, thus confirming recent dusty plasma experiments with so-called Yukawa balls [1]. The analytical method [2], based on the harmonic approximation of the potential energy, allows for a very intuitive explanation of the probabilities when combined with the simulation results [3].[1] D. Block, S. Käding, A. Melzer, A. Piel, H. Baumgartner, and M. Bonitz, Physics of Plasmas 15, 040701 (2008)[2] F. Baletto and R. Ferrando, Reviews of Modern Physics 77, 371 (2005)[3] H. Kählert, P. Ludwig, H. Baumgartner, M. Bonitz, D. Block, S. Käding, A. Melzer, and A. Piel, submitted for publication (2008)

  3. Density Functional Studies of a Heisenberg Spin Coupled Cr^3+(S_1=3\\over 2)-Semiquinone(S_2=1\\over 2) Complex and of its Uncoupled Cr^3+(S_1=3\\over 2)-Catechol(S_2=0) Analog.

    NASA Astrophysics Data System (ADS)

    Rodriguez, Jorge H.; Wheeler, Daniel E.; McCusker, James K.

    1998-03-01

    The [Cr(tren)(3,6-DTBSQ)]^2+ complex has been studied by self-consistent field non-local gradient corrected density functional theory. The results are consistent with a Heisenberg exchange formulation where a Cr^3+(S_1=3\\over 2) ion is antiferromagnetically coupled to a semiquinone(S_2=1\\over 2) giving rise to a S=1 ground state. The constant J of the exchange Hamiltonian \\cal H_ex = JS1 -- S2 was determined from the DFT energies at the U-B3LYP/6-311** and U-BLYP/6-311** levels and is consistent with spectroscopic data. The triplet ground state shows some spin contamination due to admixture with the quintet wavefunction and appropriate energy corrections were performed. Population analyses were carried out which show net α and β spin densities at the Cr^3+ ion and semiquinone, respectively. Some correlations between the Cr-O and O-C distances and the magnitude of J were also investigated. Lastly, calculations for [Cr(tren)(3,6-DTBCat)]^+ were performed which are consistent with a Cr^3+(S_1=3\\over 2)-Catechol(S_2=0) formulation, in agreement with magnetic susceptibility data.

  4. Metastable isomers - A new class of interstellar molecules

    NASA Technical Reports Server (NTRS)

    Green, S.; Herbst, E.

    1979-01-01

    The abundances of a variety of metastable isomers of small organic molecules, analogous to HNC/HCN, in dense interstellar clouds are considered. These metastable species, some of which are thought to exist as intermediates in laboratory organic chemical reactions, are of considerable interest to chemists. Current ideas of gas-phase, ion-molecule chemistry are utilized to demonstrate that such metastable species should often be present in dense clouds in sufficient abundance to be observed. Unfortunately, the spectral constants of metastable isomers have rarely been determined in the laboratory, and quantum chemical calculations of a varying degree of accuracy must be utilized; results are included of some new quantum chemical calculations. The interstellar chemistry and expected microwave spectra of a representative sample of possibly important interstellar metastable isomers are discussed.

  5. Thermodynamic properties of metastable Ag-Cu alloys

    NASA Astrophysics Data System (ADS)

    Najafabadi, R.; Srolovitz, D. J.; Ma, E.; Atzmon, M.

    1993-09-01

    The enthalpies of formation of metastable fcc Ag-Cu solid solutions, produced by ball milling of elemental powders, were determined by differential scanning calorimetry. Experimental thermodynamic data for these metastable alloys and for the equilibrium phases are compared with both calculation of phase diagrams (CALPHAD) and atomistic simulation predictions. The atomistic simulations were performed using the free-energy minimization method (FEMM). The FEMM determination of the equilibrium Ag-Cu phase diagram and the enthalpy of formation and lattice parameters of the metastable solid solutions are in good agreement with the experimental measurements. CALPHAD calculations made in the same metastable regime, however, significantly overestimate the enthalpy of formation. Thus, the FEMM is a viable alternative approach for the calculation of thermodynamic properties of equilibrium and metastable phases, provided reliable interatomic potentials are available. The FEMM is also capable of determining such properties as the lattice parameter which are not available from CALPHAD calculations.

  6. Selective removal of either metastable species from a mixed 3P 0,2 rare-gas metastable beam

    NASA Technical Reports Server (NTRS)

    Dunning, F. B.; Cook, T. B.; West, W. P.; Stebbings, R. F.

    1975-01-01

    A tunable CW laser has been used to selectively remove either of the two metastable species, 3P 0,2, which are initially present in a neon metastable beam. The method is applicable to other rare gases and provides the opportunity for separate investigation of effects due to atoms in either the 3P 0 or 3P 2 state.

  7. A well-structured metastable ceria surface

    SciTech Connect

    Olbrich, R.; Pieper, H. H.; Oelke, R.; Wilkens, H.; Wollschläger, J.; Reichling, M.; Zoellner, M. H.; Schroeder, T.

    2014-02-24

    By the growth of a 180 nm thick film on Si(111), we produce a metastable ceria surface with a morphology dominated by terraced pyramids with an oriented triangular base. Changes in the nanoscale surface morphology and local surface potential due to annealing at temperatures ranging from 300 K to 1150 K in the ultra-high vacuum are studied with non-contact atomic force microscopy and Kelvin probe force microscopy. As the surface is stable in the temperature range of 300 K to 850 K, it is most interesting for applications requiring regular steps with a height of one O-Ce-O triple layer.

  8. The Lotus effect: superhydrophobicity and metastability.

    PubMed

    Marmur, Abraham

    2004-04-27

    To learn how to mimic the Lotus effect, superhydrophobicity of a model system that resembles the Lotus leaf is theoretically discussed. Superhydrophobicity is defined by two criteria: a very high water contact angle and a very low roll-off angle. Since it is very difficult to calculate the latter for rough surfaces, it is proposed here to use the criterion of a very low wet (solid-liquid) contact area as a simple, approximate substitute for the roll-off angle criterion. It is concluded that nature employs metastable states in the heterogeneous wetting regime as the key to superhydrophobicity on Lotus leaves. This strategy results in two advantages: (a) it avoids the need for high steepness protrusions that may be sensitive to breakage and (b) it lowers the sensitivity of the superhydrophobic states to the protrusion distance.

  9. Metastable State Relaxation in a Gravitational Field

    NASA Technical Reports Server (NTRS)

    Izmailov, Alexander F.; Myerson, Allan S.

    1992-01-01

    A metastable state relaxation equation for a physical system placed into a gravitational field is constructed for non-critical supersaturated solutions which arc in the immediate neighborhood of the coexistence line. Solutions of this equation are obtained in two different regimes: stationary and dynamic. The sedimentation time which can be defined as the time of the subcritical solute cluster redistribution corresponding to the final steady state in the gravitational field is found. The formation of the concentration gradient is proved analytically and its expression through the model parameters is obtained. The following analysis gives the expression for the sedimentation time which does not depend on the column height. The law of the concentration change with respect to the column height is also found and analyzed.

  10. On the decoupling theorem for vacuum metastability

    NASA Astrophysics Data System (ADS)

    Patel, Hiren H.; Radovčić, Branimir

    2017-10-01

    In this paper, we numerically study the impact heavy field degrees of freedom have on vacuum metastability in a toy model, with the aim of better understanding how the decoupling theorem extends to semiclassical processes. We observe that decoupling applies to partial amplitudes associated with fixed final state field configurations emerging from the tunneling processes, characterized by a scale such as the inverse radius of a spherically symmetric bubble, and not directly on the total lifetime (as determined by the ;bounce;). More specifically, tunneling amplitudes for bubbles with inverse radii smaller than the scale of the heavier fields are largely insensitive to their presence, while those for bubbles with inverse radii larger than that scale may be significantly modified.

  11. Metastable Atom Detection Using Solid N2

    NASA Astrophysics Data System (ADS)

    McConkey, William; Kedzierski, Wladek; Lukic, Dragan

    2014-05-01

    Over the years our laboratory has been a center for the use of rare-gas matrices at temperatures below 70K in the detection and study of low energy atomic and molecular metastable particles [see Kedzierski et al., Can J Phys, 91, 1044, (2013) for Refs]. Recently we have extended this work to study the use of a solid nitrogen matrix at temperatures below 35K as a detector of O(1S) atoms. This proves to be at least as sensitive as any rare gas matrix though the lifetime of the excimer formed in the matrix is somewhat longer (~ 20 μs) than what is observed in a Xe matrix for example. The detailed performance of the detector as a function of temperature and other parameters will be presented at the conference. The authors thank NSERC and CFI, (Canada), for financial support.

  12. Electrostatic trapping of metastable NH molecules

    SciTech Connect

    Hoekstra, Steven; Metsaelae, Markus; Zieger, Peter C.; Scharfenberg, Ludwig; Gilijamse, Joop J.; Meijer, Gerard; Meerakker, Sebastiaan Y. T. van de

    2007-12-15

    We report on the Stark deceleration and electrostatic trapping of {sup 14}NH (a{sup 1}{delta}) radicals. In the trap, the molecules are excited on the spin-forbidden A{sup 3}{pi}<-a{sup 1}{delta} transition and detected via their subsequent fluorescence to the X{sup 3}{sigma}{sup -} ground state. The 1/e trapping time is 1.4{+-}0.1 s, from which a lower limit of 2.7 s for the radiative lifetime of the a{sup 1}{delta}, v=0, J=2 state is deduced. The spectral profile of the molecules in the trapping field is measured to probe their spatial distribution. Electrostatic trapping of metastable NH followed by optical pumping of the trapped molecules to the electronic ground state is an important step toward accumulation of these radicals in a magnetic trap.

  13. Kinetics of optically pumped Kr metastables.

    PubMed

    Han, Jiande; Heaven, Michael C

    2015-04-01

    Optically-pumped atomic gas lasers that utilize metastable excited states of rare gas atoms (Rg(*)) have been demonstrated using both pulsed and CW pump sources. These devices resemble diode-pumped alkali vapor lasers, but have the advantage of using a chemically inert lasing medium. Collisional energy transfer is needed to sustain a population inversion, and He is used as the transfer agent. Consequently, values for the Kr(*)+He state-to-state energy transfer rate constants are needed for the analysis and prediction of laser performance characteristics. In the present study, we report He energy transfer rate constants for Kr(*) in the 5p[5/2](2), 5p[5/2](3), 5p[1/2](1), and 5s[3/2](1) states.

  14. Neutral atom lithography with metastable helium

    NASA Astrophysics Data System (ADS)

    Allred, Claire Shean

    In this dissertation we describe our performance of resist assisted neutral atom lithography using a bright beam of metastable 23S1 Helium (He*). Metastable Helium atoms have 20 eV of internal energy making them easy to detect and able to destroy a resist. The He* is produced by a reverse flow DC discharge source and then collimated with the bichromatic force, followed by three optical molasses velocity compression stages. The atoms in the resulting beam have a mean longitudinal velocity of 1125 m/s and a divergence of 1.1 mrad. The typical beam flux is 2 x 109 atoms/mm2s through a 0.1mm diameter aperture 70 cm away from the source. The internal energy of the atoms damages the molecules of a self assembled monolayer (SAM) of nonanethiol. The undisturbed SAM protects a 200 A layer of gold that has been evaporated onto a prepared Silicon wafer from a wet chemical etch. Two methods are used to pattern the He* atoms before they destroy the SAM. First, a Nickel micro mesh was used to protect the SAM. These experiments established an appropriate dosage and etch time for patterning. The samples were analyzed with an atomic force microscope and found to have an edge resolution of 63 nm. Then, patterning was accomplished using the dipole force the atoms experience while traversing a standing wave of lambda = 1083nm light tuned 500MHz below the 23S 1 → 23P2 transition. Depending on the intensity of the light, the He* atoms are focused or channeled into lines separated by lambda/2. The lines cover the entire exposed length of the substrate, about 3 mm. They are about 3 mm long, corresponding to about twice the beam waist of the laser standing wave. Thus there are 6 x 10 3 lines of length 5500lambda. These results agree with our numerical simulations of the experiment.

  15. A definition of metastability for Markov processes with detailed balance

    NASA Astrophysics Data System (ADS)

    Leyvraz, F.; Larralde, H.; Sanders, D. P.

    2006-03-01

    A definition of metastable states applicable to arbitrary finite state Markov processes satisfying detailed balance is discussed. In particular, we identify a crucial condition that distinguishes genuine metastable states from other types of slowly decaying modes and which leads to properties similar to those postulated in the restricted ensemble approach [1]. The intuitive physical meaning of this condition is simply that the total equilibrium probability of finding the system in the metastable state is negligible. As a concrete application of our formalism we present preliminary results on a 2D kinetic Ising model.

  16. Towards a Theory of Metastability in Open Quantum Dynamics.

    PubMed

    Macieszczak, Katarzyna; Guţă, Mădălin; Lesanovsky, Igor; Garrahan, Juan P

    2016-06-17

    By generalizing concepts from classical stochastic dynamics, we establish the basis for a theory of metastability in Markovian open quantum systems. Partial relaxation into long-lived metastable states-distinct from the asymptotic stationary state-is a manifestation of a separation of time scales due to a splitting in the spectrum of the generator of the dynamics. We show here how to exploit this spectral structure to obtain a low dimensional approximation to the dynamics in terms of motion in a manifold of metastable states constructed from the low-lying eigenmatrices of the generator. We argue that the metastable manifold is in general composed of disjoint states, noiseless subsystems, and decoherence-free subspaces.

  17. The Importance of Kinetic Metastability: Some Common Everyday Examples

    ERIC Educational Resources Information Center

    Jensen, William B.

    2015-01-01

    The importance of kinetic metastability is illustrated in detail using several common household products and recommendations are made for how this important and widespread, but often neglected, phenomenon can be more effectively presented in the introductory chemistry textbook.

  18. Modeling of metastable phase formation diagrams for sputtered thin films

    PubMed Central

    Chang, Keke; Music, Denis; to Baben, Moritz; Lange, Dennis; Bolvardi, Hamid; Schneider, Jochen M.

    2016-01-01

    Abstract A method to model the metastable phase formation in the Cu–W system based on the critical surface diffusion distance has been developed. The driver for the formation of a second phase is the critical diffusion distance which is dependent on the solubility of W in Cu and on the solubility of Cu in W. Based on comparative theoretical and experimental data, we can describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation. Metastable phase formation diagrams for Cu–W and Cu–V thin films are predicted and validated by combinatorial magnetron sputtering experiments. The correlative experimental and theoretical research strategy adopted here enables us to efficiently describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation during magnetron sputtering. PMID:27877871

  19. The Importance of Kinetic Metastability: Some Common Everyday Examples

    ERIC Educational Resources Information Center

    Jensen, William B.

    2015-01-01

    The importance of kinetic metastability is illustrated in detail using several common household products and recommendations are made for how this important and widespread, but often neglected, phenomenon can be more effectively presented in the introductory chemistry textbook.

  20. Toward a Complementary Neuroscience: Metastable Coordination Dynamics of the Brain

    NASA Astrophysics Data System (ADS)

    Kelso, J. A. Scott; Tognoli, Emmanuelle

    Metastability has been proposed as a new principle of behavioral and brain function and may point the way to a truly complementary neuroscience. From elementary coordination dynamics we show explicitly that metastability is a result of a symmetry-breaking caused by the subtle interplay of two forces: the tendency of the components to couple together and the tendency of the components to express their intrinsic independent behavior. The metastable regime reconciles the well-known tendencies of specialized brain regions to express their autonomy (segregation) and the tendencies for those regions to work together as a synergy (integration). Integration ~ segregation is just one of the complementary pairs (denoted by the tilde [~] symbol) to emerge from the science of coordination dynamics. We discuss metastability in the brain by describing the favorable conditions existing for its emergence and by deriving some predictions for its empirical characterization in neurophysiological recordings.

  1. Modeling of metastable phase formation diagrams for sputtered thin films.

    PubMed

    Chang, Keke; Music, Denis; To Baben, Moritz; Lange, Dennis; Bolvardi, Hamid; Schneider, Jochen M

    2016-01-01

    A method to model the metastable phase formation in the Cu-W system based on the critical surface diffusion distance has been developed. The driver for the formation of a second phase is the critical diffusion distance which is dependent on the solubility of W in Cu and on the solubility of Cu in W. Based on comparative theoretical and experimental data, we can describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation. Metastable phase formation diagrams for Cu-W and Cu-V thin films are predicted and validated by combinatorial magnetron sputtering experiments. The correlative experimental and theoretical research strategy adopted here enables us to efficiently describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation during magnetron sputtering.

  2. Metastable Polymerization of Sickle Hemoglobin in Droplets

    PubMed Central

    Aprelev, Alexey; Weng, Weijun; Zakharov, Mikhail; Rotter, Maria; Yosmanovich, Donna; Kwong, Suzanna; Briehl, Robin W.; Ferrone, Frank A.

    2007-01-01

    Sickle cell disease arises from a genetic mutation of one amino acid in each of the two hemoglobin β chains, leading to the polymerization of hemoglobin in the red cell upon deoxygenation, and is characterized by vascular crises and tissue damage due to the obstruction of small vessels by sickled cells. It has been an untested assumption that, in red cells that sickle, the growing polymer mass would consume monomers until the thermodynamically well-described monomer solubility was reached. By photolyzing droplets of sickle hemoglobin suspended in oil we find that polymerization does not exhaust the available store of monomers, but stops prematurely, leaving the solutions in a supersaturated, metastable state typically 20% above solubility at 37°C, though the particular values depend on the details of the experiment. We propose that polymer growth stops because the growing ends reach the droplet edge, whereas new polymer formation is thwarted by long nucleation times, since the hemoglobin concentration is lowered by depletion of monomers into the polymers that have formed. This finding suggests a new aspect to the pathophysiology of sickle cell disease, namely, that cells deoxygenated in the microcirculation are not merely undeformable, but will actively wedge themselves tightly against the walls of the microvasculature by a ratchet-like mechanism driven by the supersaturated solution. PMID:17493634

  3. Multistage Zeeman deceleration of metastable neon

    SciTech Connect

    Wiederkehr, Alex W.; Motsch, Michael; Hogan, Stephen D.; Andrist, Markus; Schmutz, Hansjuerg; Lambillotte, Bruno; Agner, Josef A.; Merkt, Frederic

    2011-12-07

    A supersonic beam of metastable neon atoms has been decelerated by exploiting the interaction between the magnetic moment of the atoms and time-dependent inhomogeneous magnetic fields in a multistage Zeeman decelerator. Using 91 deceleration solenoids, the atoms were decelerated from an initial velocity of 580 m/s to final velocities as low as 105 m/s, corresponding to a removal of more than 95% of their initial kinetic energy. The phase-space distribution of the cold, decelerated atoms was characterized by time-of-flight and imaging measurements, from which a temperature of 10 mK was obtained in the moving frame of the decelerated sample. In combination with particle-trajectory simulations, these measurements allowed the phase-space acceptance of the decelerator to be quantified. The degree of isotope separation that can be achieved by multistage Zeeman deceleration was also studied by performing experiments with pulse sequences generated for {sup 20}Ne and {sup 22}Ne.

  4. Discovery of a metastable Al20Sm4 phase

    NASA Astrophysics Data System (ADS)

    Ye, Z.; Zhang, F.; Sun, Y.; Mendelev, M. I.; Ott, R. T.; Park, E.; Besser, M. F.; Kramer, M. J.; Ding, Z.; Wang, C.-Z.; Ho, K.-M.

    2015-03-01

    We present an efficient genetic algorithm, integrated with experimental diffraction data, to solve a nanoscale metastable Al20Sm4 phase that evolves during crystallization of an amorphous magnetron sputtered Al90Sm10 alloy. The excellent match between calculated and experimental X-ray diffraction patterns confirms an accurate description of this metastable phase. Molecular dynamic simulations of crystal growth from the liquid phase predict the formation of disordered defects in the devitrified crystal.

  5. Discovery of a metastable Al20Sm4 phase

    DOE PAGES

    Ye, Z.; Zhang, F.; Sun, Y.; ...

    2015-03-09

    In this study, we present an efficient genetic algorithm, integrated with experimental diffraction data, to solve a nanoscale metastable Al20Sm4 phase that evolves during crystallization of an amorphous magnetron sputtered Al90Sm10 alloy. The excellent match between calculated and experimental X-ray diffraction patterns confirms an accurate description of this metastable phase. Molecular dynamic simulations of crystal growth from the liquid phase predict the formation of disordered defects in the devitrified crystal.

  6. Foldamer-tuned switching kinetics and metastability of [2]rotaxanes.

    PubMed

    Zhang, Kang-Da; Zhao, Xin; Wang, Gui-Tao; Liu, Yi; Zhang, Ying; Lu, Hao-Jie; Jiang, Xi-Kui; Li, Zhan-Ting

    2011-10-10

    Slip sliding away: foldamers can function as modular stoppers to regulate the slippage and de-slippage of pseudorotaxanes and the switching kinetics and metastability of bistable rotaxanes. By simply changing the solvent or the length of the hydrogen-bonded foldamer, the lifetime of the metastable co-conformation state can be increased dramatically, from several minutes to as long as several days. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Research on Sources of Gas Phase Metastable Atoms and Molecules

    DTIC Science & Technology

    1982-05-01

    PAGI(Whi DeE# WA..teod) -systems of interest to such diverse areas as gas discharge physics, chemical physics, flame chemistry and plasma physics. "A...second task involved a literature review of prior basic research meta- stable sources followed by the development and experimental testing of appro...appropriate for this phase of the program. The operation of this type of metastable source wab investigated and tested for the production of metastable argon

  8. A metastable modular structural system for adaptive nonreciprocal wave propagation

    NASA Astrophysics Data System (ADS)

    Wu, Z.; Wang, K. W.

    2017-04-01

    In this research, we present a novel approach to achieve adaptive nonreciprocal wave propagation by exploiting the concept of metastable modular metastructures or metamaterials. Numerical studies on a 1D metastable chain provide clear evidence that such unconventional wave transmission characteristics is facilitated through both nonlinearity and spatial asymmetry of strategically configured constituents. Due to a synergistic product of assembling together metastable modules, modules that exhibit coexisting stable states for the same topology, recent investigations have demonstrated remarkable programmability of properties afforded via transitioning amongst these metastable states. In the context of wave transmission, such massive property adaptation provides unprecedented bandgap tuning opportunities and therefore enables the adaptivity of nonreciprocal wave propagation. In addition to metastable states, influence of wave amplitude and frequency on the existence and adaptation of nonreciprocal wave transmission is also parametrically explored. Overall, this investigation elucidates the rich dynamics achievable by nonlinearity and metastabilities, and creates a new class of adaptive structural and material systems capable of achieving tunable bandgaps and nonreciprocal wave transmissions.

  9. Absolute number densities of helium metastable atoms determined by atomic absorption spectroscopy in helium plasma-based discharges used as ambient desorption/ionization sources for mass spectrometry

    NASA Astrophysics Data System (ADS)

    Reininger, Charlotte; Woodfield, Kellie; Keelor, Joel D.; Kaylor, Adam; Fernández, Facundo M.; Farnsworth, Paul B.

    2014-10-01

    The absolute number densities of helium atoms in the 2s 3S1 metastable state were determined in four plasma-based ambient desorption/ionization sources by atomic absorption spectroscopy. The plasmas included a high-frequency dielectric barrier discharge (HF-DBD), a low temperature plasma (LTP), and two atmospheric-pressure glow discharges, one with AC excitation and the other with DC excitation. Peak densities in the luminous plumes downstream from the discharge capillaries of the HF-DBD and the LTP were 1.39 × 1012 cm- 3 and 0.011 × 1012 cm- 3, respectively. Neither glow discharge produced a visible afterglow, and no metastable atoms were detected downstream from the capillary exits. However, densities of 0.58 × 1012 cm- 3 and 0.97 × 1012 cm- 3 were measured in the interelectrode regions of the AC and DC glow discharges, respectively. Time-resolved measurements of metastable atom densities revealed significant random variations in the timing of pulsed absorption signals with respect to the voltage waveforms applied to the discharges.

  10. Metastable Mesoscopic Phases in Concentrated Protein Solutions

    NASA Astrophysics Data System (ADS)

    Vekilov, P. G.; Pan, W.; Gliko, O.; Katsonis, P.; Galkin, O.

    It is sometimes claimed that the cytosol around the organelles, tubules, and other cellular structures represents a liquid phase. On the other hand, almost all protein molecules in the cytosol participate in complexes with other proteins, nucleic acids, small molecules, etc. The two pictures of a homogeneous liquid and a granular multiscale mixture appear incompatible. Thus, an important question in physical biology is whether the protein complexes represent a property of the protein solutions, or are the result of complex specific interaction involving multiple biological molecules. We apply light scattering, atomic force microscopy, and other techniques to demonstrate that even solutions of a single protein of moderate concentration do not comply with Gibbs's definition of phase. In such solutions clusters of sizes from several tens to several hundred nanometers exist and have limited lifetimes. These clusters have a higher free energy than the protein solution, and their lifetime is determined by a barrier for their decay. The clusters affect the viscous and visco-elastic behavior of the solution and are an essential part of potential condensation and aggregation pathways. Since the clusters are observed in solutions of single proteins, they indicate that the proteins have an intrinsic propensity to form mesoscopic structures, which likely is utilized in the formation of the protein complexes in the cytosol. Cluster theories developed for colloid systems appear inapplicable to proteins due to the high level of implied Coulombic repulsion. A Monte Carlo model with protein-like potentials reproduces the metastable clusters of dense liquid with limited lifetimes and variable sizes, and suggests that the clusters' sizes are determined by the kinetics of growth and decay, and not by thermodynamics. A microscopic theory, which should account for stabilizing and destabilizing factors involving protein molecules and solvent inside the clusters, is still to be developed.

  11. Persistence of Metastability after Expansion of a Supercompressed Fluid Monolayer

    PubMed Central

    Smith, Ethan C.; Laderas, Ted G.; Crane, Jonathan M.; Hall, Stephen B.

    2012-01-01

    Fluid monolayers of 1-palmitoyl-2-oleoyl-phosphatidylcholine collapse from an air/water interface to form a three-dimensional bulk phase at the equilibrium spreading pressure (πe) of ~47 mN/m. This phase transition limits access to higher surface pressures under equilibrium conditions or during slow continuous compressions. We have shown previously that these films avoid collapse and become metastable when compressed on a captive bubble to surface pressures above 60 mN/m and that the metastability persists during expansion at least to πe. Here, we first documented the extent of this persistent metastability. Rates of isobaric collapse during expansion of the metastable films were up to 3 orders of magnitude slower than those during the initial compression to high surface pressures. Recovery of the ability to collapse depended on the surface pressure to which the films were expanded and how long they were held there. Films reverted after brief exposure to 20 mN/m and after 1 h at 35 mN/m. At πe, films remained capable of reaching high surface pressures during slow compressions after 65 h, although an increase in compressibility above 55 mN/m suggested somewhat increased rates of collapse. We also determined if the films remained metastable when they acquired sufficient free area to allow reinsertion of collapsed material. Faster isobaric expansion in the presence of more collapsed material and with further deviation below πe supported the existence of reinsertion. The persistence of metastability to πe shows that films with sufficient free area to allow reinsertion remain resistant to collapse. Observations that suggest heterogeneous reinsertion, however, argue that free area may be distributed heterogeneously and leave open the possibility that metastability persists because significant regions retain a restricted free area. PMID:15984255

  12. Extended Neural Metastability in an Embodied Model of Sensorimotor Coupling.

    PubMed

    Aguilera, Miguel; Bedia, Manuel G; Barandiaran, Xabier E

    2016-01-01

    The hypothesis that brain organization is based on mechanisms of metastable synchronization in neural assemblies has been popularized during the last decades of neuroscientific research. Nevertheless, the role of body and environment for understanding the functioning of metastable assemblies is frequently dismissed. The main goal of this paper is to investigate the contribution of sensorimotor coupling to neural and behavioral metastability using a minimal computational model of plastic neural ensembles embedded in a robotic agent in a behavioral preference task. Our hypothesis is that, under some conditions, the metastability of the system is not restricted to the brain but extends to the system composed by the interaction of brain, body and environment. We test this idea, comparing an agent in continuous interaction with its environment in a task demanding behavioral flexibility with an equivalent model from the point of view of "internalist neuroscience." A statistical characterization of our model and tools from information theory allow us to show how (1) the bidirectional coupling between agent and environment brings the system closer to a regime of criticality and triggers the emergence of additional metastable states which are not found in the brain in isolation but extended to the whole system of sensorimotor interaction, (2) the synaptic plasticity of the agent is fundamental to sustain open structures in the neural controller of the agent flexibly engaging and disengaging different behavioral patterns that sustain sensorimotor metastable states, and (3) these extended metastable states emerge when the agent generates an asymmetrical circular loop of causal interaction with its environment, in which the agent responds to variability of the environment at fast timescales while acting over the environment at slow timescales, suggesting the constitution of the agent as an autonomous entity actively modulating its sensorimotor coupling with the world. We

  13. Persistence of metastability after expansion of a supercompressed fluid monolayer.

    PubMed

    Smith, Ethan C; Laderas, Ted G; Crane, Jonathan M; Hall, Stephen B

    2004-06-08

    Fluid monolayers of 1-palmitoyl-2-oleoyl-phosphatidylcholine collapse from an air/water interface to form a three-dimensional bulk phase at the equilibrium spreading pressure (pie) of approximately 47 mN/m. This phase transition limits access to higher surface pressures under equilibrium conditions or during slow continuous compressions. We have shown previously that these films avoid collapse and become metastable when compressed on a captive bubble to surface pressures above 60 mN/m and that the metastability persists during expansion at least to pie. Here, we first documented the extent of this persistent metastability. Rates of isobaric collapse during expansion of the metastable films were up to 3 orders of magnitude slower than those during the initial compression to high surface pressures. Recovery of the ability to collapse depended on the surface pressure to which the films were expanded and how long they were held there. Films reverted after brief exposure to 20 mN/m and after 1 h at 35 mN/m. At pie, films remained capable of reaching high surface pressures during slow compressions after 65 h, although an increase in compressibility above 55 mN/m suggested somewhat increased rates of collapse. We also determined if the films remained metastable when they acquired sufficient free area to allow reinsertion of collapsed material. Faster isobaric expansion in the presence of more collapsed material and with further deviation below pie supported the existence of reinsertion. The persistence of metastability to pie shows that films with sufficient free area to allow reinsertion remain resistant to collapse. Observations that suggest heterogeneous reinsertion, however, argue that free area may be distributed heterogeneously and leave open the possibility that metastability persists because significant regions retain a restricted free area.

  14. Extended Neural Metastability in an Embodied Model of Sensorimotor Coupling

    PubMed Central

    Aguilera, Miguel; Bedia, Manuel G.; Barandiaran, Xabier E.

    2016-01-01

    The hypothesis that brain organization is based on mechanisms of metastable synchronization in neural assemblies has been popularized during the last decades of neuroscientific research. Nevertheless, the role of body and environment for understanding the functioning of metastable assemblies is frequently dismissed. The main goal of this paper is to investigate the contribution of sensorimotor coupling to neural and behavioral metastability using a minimal computational model of plastic neural ensembles embedded in a robotic agent in a behavioral preference task. Our hypothesis is that, under some conditions, the metastability of the system is not restricted to the brain but extends to the system composed by the interaction of brain, body and environment. We test this idea, comparing an agent in continuous interaction with its environment in a task demanding behavioral flexibility with an equivalent model from the point of view of “internalist neuroscience.” A statistical characterization of our model and tools from information theory allow us to show how (1) the bidirectional coupling between agent and environment brings the system closer to a regime of criticality and triggers the emergence of additional metastable states which are not found in the brain in isolation but extended to the whole system of sensorimotor interaction, (2) the synaptic plasticity of the agent is fundamental to sustain open structures in the neural controller of the agent flexibly engaging and disengaging different behavioral patterns that sustain sensorimotor metastable states, and (3) these extended metastable states emerge when the agent generates an asymmetrical circular loop of causal interaction with its environment, in which the agent responds to variability of the environment at fast timescales while acting over the environment at slow timescales, suggesting the constitution of the agent as an autonomous entity actively modulating its sensorimotor coupling with the world. We

  15. A metastable liquid melted from a crystalline solid under decompression

    DOE PAGES

    Lin, Chuanlong; Smith, Jesse S.; Sinogeikin, Stanislav V.; ...

    2017-01-23

    A metastable liquid may exist under supercooling, sustaining the liquid below the melting point such as supercooled water and silicon. It may also exist as a transient state in solid–solid transitions, as demonstrated in recent studies of colloidal particles and glass-forming metallic systems. One important question is whether a crystalline solid may directly melt into a sustainable metastable liquid. By thermal heating, a crystalline solid will always melt into a liquid above the melting point. Here we report that a high-pressure crystalline phase of bismuth can melt into a metastable liquid below the melting line through a decompression process. Themore » decompression-induced metastable liquid can be maintained for hours in static conditions, and transform to crystalline phases when external perturbations, such as heating and cooling, are applied. It occurs in the pressure–temperature region similar to where the supercooled liquid Bi is observed. Finally, akin to supercooled liquid, the pressure-induced metastable liquid may be more ubiquitous than we thought.« less

  16. Origin of the metastable stability in flavylium multistate systems.

    PubMed

    Petrov, Vesselin; Slavcheva, Stoyanka; Stanimirov, Stanislav; Pina, Fernando

    2015-03-26

    Metastable states regarding the network of chemical reactions involving flavylium compounds were investigated as well as the role they may play in models for optical memories capable of write-read-erase. A necessary requirement to achieve metastable states in flavylium systems is the existence of a high cis-trans isomerization barrier, as in 4'-hydroxyflavylium described through this paper. In an optical memory, the metastable state could be the signal to be detected upon the write step. In that case the autoerase is prevented by the metastable state. Conversely, the metastable state may be the initial state and prevents the auto and unwanted write step. The compound 4'-hydroxyflavylium offers the possibility of achieving both of these two situations, depending on the sequence of the pH stimuli prior to light absorption. In this work the pH dependent distribution of the flavylium species of the network in the presence of β-cyclodextrin was calculated. Improvement of the performance of the photochromic system in the presence of β-cyclodextrin was observed.

  17. A metastable liquid melted from a crystalline solid under decompression

    PubMed Central

    Lin, Chuanlong; Smith, Jesse S.; Sinogeikin, Stanislav V.; Kono, Yoshio; Park, Changyong; Kenney-Benson, Curtis; Shen, Guoyin

    2017-01-01

    A metastable liquid may exist under supercooling, sustaining the liquid below the melting point such as supercooled water and silicon. It may also exist as a transient state in solid–solid transitions, as demonstrated in recent studies of colloidal particles and glass-forming metallic systems. One important question is whether a crystalline solid may directly melt into a sustainable metastable liquid. By thermal heating, a crystalline solid will always melt into a liquid above the melting point. Here we report that a high-pressure crystalline phase of bismuth can melt into a metastable liquid below the melting line through a decompression process. The decompression-induced metastable liquid can be maintained for hours in static conditions, and transform to crystalline phases when external perturbations, such as heating and cooling, are applied. It occurs in the pressure–temperature region similar to where the supercooled liquid Bi is observed. Akin to supercooled liquid, the pressure-induced metastable liquid may be more ubiquitous than we thought. PMID:28112152

  18. A metastable liquid melted from a crystalline solid under decompression

    NASA Astrophysics Data System (ADS)

    Lin, Chuanlong; Smith, Jesse S.; Sinogeikin, Stanislav V.; Kono, Yoshio; Park, Changyong; Kenney-Benson, Curtis; Shen, Guoyin

    2017-01-01

    A metastable liquid may exist under supercooling, sustaining the liquid below the melting point such as supercooled water and silicon. It may also exist as a transient state in solid-solid transitions, as demonstrated in recent studies of colloidal particles and glass-forming metallic systems. One important question is whether a crystalline solid may directly melt into a sustainable metastable liquid. By thermal heating, a crystalline solid will always melt into a liquid above the melting point. Here we report that a high-pressure crystalline phase of bismuth can melt into a metastable liquid below the melting line through a decompression process. The decompression-induced metastable liquid can be maintained for hours in static conditions, and transform to crystalline phases when external perturbations, such as heating and cooling, are applied. It occurs in the pressure-temperature region similar to where the supercooled liquid Bi is observed. Akin to supercooled liquid, the pressure-induced metastable liquid may be more ubiquitous than we thought.

  19. An efficient magneto-optical trap of metastable krypton atoms.

    PubMed

    Cheng, C-F; Jiang, W; Yang, G-M; Sun, Y-R; Pan, H; Gao, Y; Liu, A-W; Hu, S-M

    2010-12-01

    We report a magneto-optical trap of metastable krypton atoms with a trap loading rate of 3×10(11) atoms/s and a trap capture efficiency of 3×10(-5). The system starts with an atomic beam of metastable krypton produced in a liquid-nitrogen cooled, radio-frequency driven discharge. The metastable beam flux emerging from the discharge is 1.5×10(14) atoms/s/sr. The flux in the forward direction is enhanced by a factor of 156 with transverse laser cooling. The atoms are then slowed inside a Zeeman slower before captured by a magneto-optic trap. The trap efficiency can be further improved, possibly to the 10(-2) level, by gas recirculation. Such an atom trap is useful in trace analysis applications where available sample size is limited.

  20. Classification of knotted tori in 2-metastable dimension

    SciTech Connect

    Cencelj, Matija; Repovs, Dusan; Skopenkov, Mihail B

    2012-11-30

    This paper is devoted to the classical Knotting Problem: for a given manifold N and number m describe the set of isotopy classes of embeddings N{yields}S{sup m}. We study the specific case of knotted tori, that is, the embeddings S{sup p} Multiplication-Sign S{sup q}{yields}S{sup m}. The classification of knotted tori up to isotopy in the metastable dimension range m {>=} p + 3/2q + 2, p{<=}q, was given by Haefliger, Zeeman and A. Skopenkov. We consider the dimensions below the metastable range and give an explicit criterion for the finiteness of this set of isotopy classes in the 2-metastable dimension. Bibliography: 35 titles.

  1. Visible light responsive systems based on metastable-state photoacids

    NASA Astrophysics Data System (ADS)

    Liao, Yi

    2015-09-01

    Proton transfer is one of the most fundamental processes in nature. Metastable-state photoacids can reversibly generate a large proton concentration under visible light with moderate intensity. which provides a general approach to control various proton transfer processes. Several applications of mPAHs have been demonstrated recently including control of acid-catalyzed reactions, volume-change of hydrogels, polymer conductivity, bacteria killing, odorant release, and color change of materials. They have also been utilized to control supramolecular assemblies, molecular switches, microbial fuel cells and cationic sensors. In this talk, the mechanism, structure design, and applications of metastable-state photoacids are introduced. Recent development of different types of metastable-state photoacids is presented. Challenges and future work are also discussed.

  2. Metastable Aluminum Atoms Floating on the Surface of Helium Nanodroplets.

    PubMed

    Jeffs, Jay; Besley, Nicholas A; Stace, Anthony J; Sarma, Gautam; Cunningham, Ethan M; Boatwright, Adrian; Yang, Shengfu; Ellis, Andrew M

    2015-06-12

    Metal atoms have proved to be sensitive probes of the properties of superfluid helium nanodroplets. To date, all experiments on the doping of helium droplets have concentrated on the attachment of metal atoms in their ground electronic states. Here we report the first examples of metal atoms in excited states becoming attached to helium nanodroplets. The atoms in question are aluminum, and they have been generated by laser ablation in a metastable quartet state, which attaches to and remains on the surface of helium droplets. Evidence for a surface location comes from electronic spectra, which consist of very narrow absorption profiles that show very small spectral shifts. Supporting ab initio calculations show there to be an energy incentive for a metastable Al atom to remain on the surface of a helium droplet rather than move to the interior. The results suggest that helium droplets may provide a method for the capture and transport of metastable excited atomic and molecular species.

  3. Metastable phase formation in Be-Nb intermetallic compounds

    SciTech Connect

    Brimhall, J.L.; Charlot, L.A.; Bruemmer, S.M.

    1990-11-01

    Amorphous structures or metastable crystalline phases are produced in sputter-deposited Beryllium-Niobium (Be-Nb) alloys (5-15 at. % Nb) depending on the substrate temperature. The metastable phases transform to the stable Be{sub 12}Nb, Be{sub 17}Nb{sub 2}Nb phases on annealing at temperatures >800{degree}C. No Be{sub 5}Nb phase was found and the Be{sub 17}Nb{sub 2} phase is stable to low temperature. The Be{sub 12}Nb phase appeared to have a stoichiometric range of about 5.5 to 7.7 at. % Nb. The formation of the metastable phases is consistent with current models and theories. 17 refs., 1 fig., 2 tabs.

  4. Stochastic optimal velocity model and its long-lived metastability.

    PubMed

    Kanai, Masahiro; Nishinari, Katsuhiro; Tokihiro, Tetsuji

    2005-09-01

    In this paper, we propose a stochastic cellular automaton model of traffic flow extending two exactly solvable stochastic models, i.e., the asymmetric simple exclusion process and the zero range process. Moreover, it is regarded as a stochastic extension of the optimal velocity model. In the fundamental diagram (flux-density diagram), our model exhibits several regions of density where more than one stable state coexists at the same density in spite of the stochastic nature of its dynamical rule. Moreover, we observe that two long-lived metastable states appear for a transitional period, and that the dynamical phase transition from a metastable state to another metastable/stable state occurs sharply and spontaneously.

  5. Energetic Metastable Oxygen and Nitrogen Atoms in the Terrestrial Atmosphere

    NASA Technical Reports Server (NTRS)

    Kharchenko, Vasili

    2004-01-01

    We have investigated the impact of hot metastable oxygen atoms on the product yields and rate coefficients of atmospheric reactions involving O( (sup 1)D). The contribution of the metastable oxygen atoms to the thermal balance of the terrestrial atmosphere between 50 and 200 km has been determined. We found that the presence of hot O((sup l)D) atoms in the mesosphere and lower thermosphere significantly increases the production rate of the rotationally-vibrationally excited NO molecules. The computed yield of the NO molecules in N2O+ O((sup 1)D) atmospheric collisions, involving non-Maxwellian distributions of the metastable oxygen atoms, is more than two times larger than the NO-yield at a thermal equilibrium. The calculated non-equilibrium rate and yield functions are important for ozone and nitrous oxide modeling in the stratosphere, mesosphere and lower thermosphere.

  6. A reinterpretation of the observed metastability of NeH

    SciTech Connect

    Gellene, G.I. )

    1990-08-15

    The metastability of {sup 20}NeH and {sup 20}NeD previously identified by neutralized ion beam studies in this laboratory has been confirmed by the observation of metastability for {sup 22}NeH and {sup 22}NeD in a similar study. A lifetime of {tau}{ge}10 {mu}s is determined for the metastable states which are tentatively identified as Rydberg levels of intermediate {ital n}({ital n}{le}14) and possibly high {ital l}. The discrepancy between our previously measured dissociative kinetic energy release for {sup 20}NeD and that of Peterson {ital et} {ital al}. (J. Chem. Phys. {bold 91}, 6880 (1989)) is resolved.

  7. Metastable Lennard-Jones fluids. III. Bulk viscosity.

    PubMed

    Baidakov, Vladimir G; Protsenko, Sergey P

    2014-09-21

    The method of equilibrium molecular-dynamics simulation in combination with the Green-Kubo formula has been used to calculate the bulk viscosity of a Lennard-Jones fluid. Calculations have been made at temperatures 0.4 ≤ k(B)T/ɛ ≤ 2.0 and densities 0.0075 ≤ ρσ(3) ≤ 1.2 at 116 stable and 106 metastable states of liquid and gas. The depth of penetration into the region of metastable states was limited by spontaneous nucleation. In the region of stable states the data obtained are compared with the results of previous investigations. It has been established that the system transition across the lines of liquid-gas and liquid-crystal phase equilibrium and penetration into the metastable regions of liquid and gas are connected with increasing bulk viscosity. The behavior of bulk viscosity close to the spinodal of a superheated liquid and supersaturated vapor is discussed.

  8. An efficient magneto-optical trap of metastable krypton atoms

    NASA Astrophysics Data System (ADS)

    Cheng, C.-F.; Jiang, W.; Yang, G.-M.; Sun, Y.-R.; Pan, H.; Gao, Y.; Liu, A.-W.; Hu, S.-M.

    2010-12-01

    We report a magneto-optical trap of metastable krypton atoms with a trap loading rate of 3× 10^{11} atoms/s and a trap capture efficiency of 3× 10^{-5}. The system starts with an atomic beam of metastable krypton produced in a liquid-nitrogen cooled, radio-frequency driven discharge. The metastable beam flux emerging from the discharge is 1.5× 10^{14} atoms/s/sr. The flux in the forward direction is enhanced by a factor of 156 with transverse laser cooling. The atoms are then slowed inside a Zeeman slower before captured by a magneto-optic trap. The trap efficiency can be further improved, possibly to the 10^{-2} level, by gas recirculation. Such an atom trap is useful in trace analysis applications where available sample size is limited.

  9. Metastability in the driven-dissipative Rabi model

    NASA Astrophysics Data System (ADS)

    Le Boité, Alexandre; Hwang, Myung-Joong; Plenio, Martin B.

    2017-02-01

    We explore the long-time dynamics of the quantum Rabi model in a driven-dissipative setting and show that, as the atom-cavity coupling strength becomes larger than the cavity frequency, a new time scale emerges. This time scale, much larger than the natural relaxation time of the atom and the cavity, leads to long-lived metastable states susceptible to being observed experimentally. By applying a Floquet-Liouville approach to the time-dependent master equation, we systematically investigate the set of possible metastable states. We find that the properties of the metastable states can differ drastically from those of the steady state and relate these properties to the energy spectrum of the Rabi Hamiltonian.

  10. Energetic Metastable Oxygen and Nitrogen Atoms in the Terrestrial Atmosphere

    NASA Technical Reports Server (NTRS)

    Kharchenko, Vasili; Dalgarno, A.

    2005-01-01

    This report summarizes our research performed under NASA Grant NAG5-11857. The three-year grant have been supported by the Geospace Sciences SR&T program. We have investigated the energetic metastable oxygen and nitrogen atoms in the terrestrial stratosphere, mesosphere and thermosphere. Hot atoms in the atmosphere are produced by solar radiation, the solar wind and various ionic reactions. Nascent hot atoms arise in ground and excited electronic states, and their translational energies are larger by two - three orders of magnitude than the thermal energies of the ambient gas. The relaxation kinetics of hot atoms determines the rate of atmospheric heating, the intensities of aeronomic reactions, and the rate of atom escape from the planet. Modeling of the non-Maxwellian energy distributions of metastable oxygen and nitrogen atoms have been focused on the determination of their impact on the energetics and chemistry of the terrestrial atmosphere between 25 and 250 km . At this altitudes, we have calculated the energy distribution functions of metastable O and N atoms and computed non-equilibrium rates of important aeronomic reactions, such as destruction of the water molecules by O(1D) atoms and production of highly excited nitric oxide molecules. In the upper atmosphere, the metastable O(lD) and N(2D) play important role in formation of the upward atomic fluxes. We have computed the upward fluxes of the metastable and ground state oxygen atoms in the upper atmosphere above 250 km. The accurate distributions of the metastable atoms have been evaluated for the day and night-time conditions.

  11. Magnetic properties of metastable Fe Pd alloys by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Yabe, Hiromasa; O'Handley, Robert C.; Kuji, Toshiro

    2007-03-01

    Metastable Fe-Pd powder samples with various Pd content were synthesized by mechanical alloying. Their fundamental properties, i.e., structure, magnetization and coercive fore are discussed. The saturation magnetizations of the metastable Fe-Pd powders gradually decreases with increasing Pd content. The coercive forces observed in as-milled samples are all less than 40 Oe. However, some of the heat-treated samples, notably, Pd content around 55 at% with L1 0 structure, shows Hc up to 1589 Oe.

  12. Metastable states of plasma particles close to a charged surface

    SciTech Connect

    Shavlov, A. V.; Dzhumandzhi, V. A.

    2015-09-15

    The free energy of the plasma particles and the charged surface that form an electroneutral system is calculated on the basis of the Poisson-Boltzmann equation. It is shown that, owing to correlation of light plasma particles near the charged surface and close to heavy particles of high charge, there can be metastable states in plasma. The corresponding phase charts of metastable states of the separate components of plasma, and plasma as a whole, are constructed. These charts depend on temperature, the charge magnitude, the size of the particles, and the share of the charge of the light carriers out of the total charge of the plasma particles.

  13. Metastable and scaling regimes of one-dimensional Kawasaki dynamics.

    PubMed

    Albarracín, F A Gómez; Rosales, H D; Grynberg, M D

    2016-04-01

    We investigate the large-time scaling regimes arising from a variety of metastable structures in a chain of Ising spins with both first- and second-neighbor couplings while subject to Kawasaki dynamics. Depending on the ratio and sign of these former, different dynamic exponents are suggested by finite-size scaling analyses of relaxation times. At low but nonzero temperatures these are calculated via exact diagonalizations of the evolution operator in finite chains under several activation barriers. In the absence of metastability the dynamics is always diffusive.

  14. Metastable and scaling regimes of one-dimensional Kawasaki dynamics

    NASA Astrophysics Data System (ADS)

    Albarracín, F. A. Gómez; Rosales, H. D.; Grynberg, M. D.

    2016-04-01

    We investigate the large-time scaling regimes arising from a variety of metastable structures in a chain of Ising spins with both first- and second-neighbor couplings while subject to Kawasaki dynamics. Depending on the ratio and sign of these former, different dynamic exponents are suggested by finite-size scaling analyses of relaxation times. At low but nonzero temperatures these are calculated via exact diagonalizations of the evolution operator in finite chains under several activation barriers. In the absence of metastability the dynamics is always diffusive.

  15. New epsilon-Bi2O3 metastable polymorph.

    PubMed

    Cornei, Nicoleta; Tancret, Nathalie; Abraham, Francis; Mentré, Olivier

    2006-06-26

    The new metastable epsilon-Bi2O3 polymorph has been prepared by hydrothermal treatment and structurally characterized. It shows strong relationships with the room temperature alpha form and the metastable beta form through rearrangements of [Bi2O3] columns formed by edge-sharing OBi4 tetrahedra. Its fully ordered crystal structure yields an ionic insulating character. It irreversibly transforms at 400 degrees C to the alpha form. The chemical analysis indicates its undoped bismuth oxide nature, then leading to the fifth characterized Bi2O3 polymorph to date.

  16. Metastable bcc phase formation in the Nb-Cr system

    SciTech Connect

    Thoma, D.J.; Schwarz, R.B.; Perepezko, J.H.; Plantz, D.H.

    1993-08-01

    Extended metastable bcc solid solutions of Nb-Xat.%Cr (X = 35, 50, 57, 77, 82, and 94) were synthesized by two-anvil splat-quenching. In addition, bcc (Nb-67at.%Cr) was prepared by mechanically alloying mixtures of niobium and chromium powders. The lattice parameters were measured by X-ray diffraction and the Young`s moduli were measured by low-load microindentation. The composition dependence of the lattice parameters and elastic moduli show a positive deviation with respect to a rule of mixtures. During continuous heating at 15C/min., the metastable precursor bcc phases decomposed at temperatures above 750C to uniformly refined microstructures.

  17. Selective crystallization of metastable phase of acetaminophen by ultrasonic irradiation

    NASA Astrophysics Data System (ADS)

    Mori, Yoichiro; Maruyama, Mihoko; Takahashi, Yoshinori; Ikeda, Kenji; Fukukita, Suguru; Yoshikawa, Hiroshi Y.; Okada, Shino; Adachi, Hiroaki; Sugiyama, Shigeru; Takano, Kazufumi; Murakami, Satoshi; Matsumura, Hiroyoshi; Inoue, Tsuyoshi; Yoshimura, Masashi; Mori, Yusuke

    2015-06-01

    A new method for selective crystallization of the metastable phase (form II) of acetaminophen is described. To obtain form II, we prepared a highly supersaturated solution (σI = 3.7) and then applied ultrasonic irradiation at different frequencies. Without ultrasonic irradiation, spontaneous crystallization did not occur within one month in the highly supersaturated condition (σI = 3.7). When ultrasonic irradiation at 28 kHz was applied, form II preferentially crystallized. Therefore, we conclude that ultrasonic irradiation can be an effective technique for selectively crystallizing the metastable phase.

  18. Metastable Oxygen Production by Electron-Impact of Oxygen

    NASA Astrophysics Data System (ADS)

    Hein, J. D.; Malone, C. P.; Kanik, I.; Johnson, P. V.

    2013-12-01

    Electron-impact excitation processes involving atomic and molecular oxygen are important in atmospheric interactions. The production of long-lived metastable O(1S) and O(1D) through electron impact of atomic O and molecular O2 play a significant role in the dynamics of oxygen-containing atmospheres (Earth, Europa, Io). Emissions from metastable O (1S → 1D) produce the well-recognized green light from terrestrial aurora. Electron-impact excitation to 1S and 1D are sensitive channels for determining energy partitioning and dynamics from space weather. Electron-impact excitation cross sections determined through fundamental experimental studies are necessary for modeling of natural phenomena and observation data. The detection of metastable states in laboratory experiments requires a novel approach, since typical detection techniques (e.g., fluorescence by radiative de-excitation) cannot be performed due to the long-lived nature of the excited species. In this work, metastable O is incident on a cryogenically cooled rare gas matrix, where excimer production and subsequent rapid radiative de-excitation provides measurable signal that is directly related to the originating electron-impact excitation process.

  19. Corrosion of metastable iron alloys in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Wolf, Gerhard K.; Ferber, H.

    1983-05-01

    There exist some examples showing that metastable surface alloys can modify the corrision properties of a substrate in the same way as stable alloys do. In the present paper the corrosion behaviour of metastable surface alloys obtained by implanting gold, lead and mercury in iron was studied in aqueous solution of pH = 5.6. Potentiodynamic current density-potential curves were recorded of the implanted samples without further treatment and after isothermal annealing to temperatures up to 800°C. The results were compared with structural information on the alloys obtained by Turos et al. with α-backscattering and channeling experiments. Gold implantation turned out to enhance the active corrosion rate of iron, while lead and mercury had an impeding effect. The annealing experiments showed that the surface alloying facilitated the passivation of iron as long as the substitutional solid solution was "(meta)stable". After the breakdown at higher annealing temperatures leading to surface migration and clustering of the implanted elements a significant increase of the critical current density for passivation took place. This indicates passivation difficulties caused by the heterogeneous distribution of the "alloying" particles. In general the results suggest that substitutional metastable iron alloys cause in a systematic way corrosion inhibition or enhancement. However, their corrosion properties may change completely for non-substitutional distribution of the alloying elements as originating from annealing at higher temperatures.

  20. Cyclic cosmology, conformal symmetry and the metastability of the Higgs

    NASA Astrophysics Data System (ADS)

    Bars, Itzhak; Steinhardt, Paul J.; Turok, Neil

    2013-10-01

    Recent measurements at the LHC suggest that the current Higgs vacuum could be metastable with a modest barrier (height ( GeV)4) separating it from a ground state with negative vacuum density of order the Planck scale. We note that metastability is problematic for standard bang cosmology but is essential for cyclic cosmology in order to end one cycle, bounce, and begin the next. In this Letter, motivated by the approximate scaling symmetry of the standard model of particle physics and the primordial large-scale structure of the universe, we use our recent formulation of the Weyl-invariant version of the standard model coupled to gravity to track the evolution of the Higgs in a regularly bouncing cosmology. We find a band of solutions in which the Higgs field escapes from the metastable phase during each big crunch, passes through the bang into an expanding phase, and returns to the metastable vacuum, cycle after cycle after cycle. We show that, due to the effect of the Higgs, the infinitely cycling universe is geodesically complete, in contrast to inflation.

  1. Energetic Metastable Oxygen and Nitrogen Atoms in the Terrestrial Atmosphere

    NASA Technical Reports Server (NTRS)

    Kharchenko, Vasili

    2003-01-01

    We have investigated the energy distributions of the metastable oxygen atoms in the terrestrial thermosphere. Nascent O(lD) atoms play a fundamental role in the energy balance and chemistry of the terrestrial atmosphere, because they are produced by photo-chemical reactions in the excited electronic states and carry significant translational energies.

  2. Thermodynamic Routes to Novel Metastable Nitrogen-Rich Nitrides

    DOE PAGES

    Sun, Wenhao; Holder, Aaron; Orvañanos, Bernardo; ...

    2017-07-17

    Compared to oxides, the nitrides are relatively unexplored, making them a promising chemical space for novel materials discovery. Of particular interest are nitrogen-rich nitrides, which often possess useful semiconducting properties for electronic and optoelectronic applications. However, such nitrogen-rich compounds are generally metastable, and the lack of a guiding theory for their synthesis has limited their exploration. Here, we review the remarkable metastability of observed nitrides, and examine the thermodynamics of how reactive nitrogen precursors can stabilize metastable nitrogen-rich compositions during materials synthesis. We map these thermodynamic strategies onto a predictive computational search, training a data-mined ionic substitution algorithm specifically formore » nitride discovery, which we combine with grand-canonical DFT-SCAN phase stability calculations to compute stabilizing nitrogen chemical potentials. We identify several new nitrogen-rich binary nitrides for experimental investigation, notably the transition metal nitrides Mn3N4, Cr3N4, V3N4, and Nb3N5, the main group nitride SbN, and the pernitrides FeN2, CrN2, and Cu2N2. By formulating rational thermodynamic routes to metastable compounds, we expand the search space for functional technological materials beyond equilibrium phases and compositions.« less

  3. Design of Metastable Tin Titanium Nitride Semiconductor Alloys

    DOE PAGES

    Bikowski, Andre; Siol, Sebastian; Gu, Jing; ...

    2017-07-07

    Here, we report on design of optoelectronic properties in previously unreported metastable tin titanium nitride alloys with spinel crystal structure. Theoretical calculations predict that Ti alloying in metastable Sn3N4 compound should improve hole effective mass by up to 1 order of magnitude, while other optical bandgaps remains in the 1–2 eV range up to x ~ 0.35 Ti composition. Experimental synthesis of these metastable alloys is predicted to be challenging due to high required nitrogen chemical potential (ΔμN ≥ +1.0 eV) but proven to be possible using combinatorial cosputtering from metal targets in the presence of nitrogen plasma. Characterization experimentsmore » confirm that thin films of such (Sn1–xTix)3N4 alloys can be synthesized up to x = 0.45 composition, with suitable optical band gaps (1.5–2.0 eV), moderate electron densities (1017 to 1018 cm–3), and improved photogenerated hole transport (by 5×). Overall, this study shows that it is possible to design the metastable nitride materials with properties suitable for potential use in solar energy conversion applications.« less

  4. Production of Ar metastables in a dielectric barrier discharge

    NASA Astrophysics Data System (ADS)

    Mikheyev, Pavel A.; Han, Jiande; Clark, Amanda; Sanderson, Carl; Heaven, Michael C.

    2017-01-01

    The results of experiments with a dielectric barrier discharge (DBD) are presented, where the production of metastable argon atoms was studied. The recently proposed optically pumped all-rare-gas laser (OPRGL) utilizes metastable atoms of heavier rare gases as lasing species. The required number density of metastables for efficient laser operation is 1012÷1013 cm-3 in an atmospheric pressure of He buffer gas. Recent experiments had shown that such densities are easily produced in a nanosecond pulsed discharge, even at pressures larger than atmospheric, but problems appear when one is trying to produce them in a CW regime. The reason for difficulties in the CW production of metastables at an atmospheric pressure seems to be the low value of the E/N parameter (<5-6 Td). In our experiments a 20 KHz DBD in 2-5% Ar mixture with He at an atmospheric pressure was studied. [Ar(1s5)] number density of the order of 1012 cm-3 was readily achieved. Temporal behavior of [Ar(1s5)] throughout the DBD cycle was obtained. The results demonstrate the feasibility of DBDs for OPRGL development.

  5. Metastable zirconia-yttria-alumina ceramics: Structure, processing and properties

    NASA Astrophysics Data System (ADS)

    Zhou, Xinzhang

    2002-09-01

    Metastable phases of zirconia-yttria-alumina produced by atmospheric plasma spray and subsequent quenching were studied. Two kinds of quenching methods were used: water quenching and splat quenching. Quenching rates were estimated to be 104°C/s for water quenching and between 105--107°C/s for splat quenching. Five compositions of sprayed dried powders (pure alumina, TZ3Y20A, TZ3Y57A, TZ3Y80A and pure zirconia) were plasma sprayed and quenched. The phases and microstructures of the plasma sprayed powders and thin films were investigated by XRD and FESEM. It was found that at different compositions and quenching rates, different high temperature phases formed. These phases are metastable at room temperature and can be in the form of an extended solid solution phase, an intermediate phase, or an amorphous structure. The grain sizes of the metastable phases are below 50 nm, as determined by XRD peak broadening. At the eutectic composition, zirconia-rich fibers (50 nm in diameter) uniformly distributed in an alumina-rich matrix were observed. 2-D and 3-D metastable phase diagrams were constructed to explain the metastable phase formation. Plasma spraying can be used to fabricate ceramic nanocomposites either by pressure-assisted sintering or spray forming of the metastable powders. Mechanical properties of TZ3Y20A specimens produced by plasma spray forming on steel substrates were studied. The dependence of the 4-point bend strength on plasma spray parameters was studied by a 26-2 statistical experimental design. It was found that the bend strength was sensitive to both standoff distance and scanning speed. The results of study show much promise in applications of the metastable ceramics. Firstly, homogeneous nucleation and growth of stable phases during sintering and high creep rate at elevated temperatures will result in uniformly dense nanoceramic composites. Secondly, extended solid solutions of rare earth elements in glass will greatly enhance the optical

  6. Metastability and emergent performance of dynamic interceptive actions.

    PubMed

    Pinder, Ross A; Davids, Keith; Renshaw, Ian

    2012-09-01

    Adaptive patterning of human movement is context specific and dependent on interacting constraints of the performer-environment relationship. Flexibility of skilled behaviour is predicated on the capacity of performers to move between different states of movement organisation to satisfy dynamic task constraints, previously demonstrated in studies of visual perception, bimanual coordination, and an interceptive combat task. Metastability is a movement system property that helps performers to remain in a state of relative coordination with their performance environments, poised between multiple co-existing states (stable and distinct movement patterns or responses). The aim of this study was to examine whether metastability could be exploited in externally paced interceptive actions in fast ball sports, such as cricket. Here we report data on metastability in performance of multi-articular hitting actions by skilled junior cricket batters (n=5). Participants' batting actions (key movement timings and performance outcomes) were analysed in four distinct performance regions varied by ball pitching (bounce) location. Results demonstrated that, at a pre-determined distance to the ball, participants were forced into a meta-stable region of performance where rich and varied patterns of functional movement behaviours emerged. Participants adapted the organisation of responses, resulting in higher levels of variability in movement timing in this performance region, without detrimental effects on the quality of interceptive performance outcomes. Findings provide evidence for the emergence of metastability in a dynamic interceptive action in cricket batting. Flexibility and diversity of movement responses were optimised using experiential knowledge and careful manipulation of key task constraints of the specific sport context. Copyright © 2012 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

  7. Argon metastable dynamics and lifetimes in a direct current microdischarge

    SciTech Connect

    Stefanović, Ilija; Kuschel, Thomas; Schröter, Sandra; Böke, Marc

    2014-09-21

    In this paper we study the properties of a pulsed dc microdischarge with the continuous flow of argon. Argon metastable lifetimes are measured by tunable diode laser absorption spectroscopy (TDLAS) and are compared with calculated values which yield information about excitation and de-excitation processes. By increasing the gas flow-rate about 5 times from 10 to 50 sccm, the Ar{sup m} lifetime increases from 1 to 5 μs due to the reduction of metastable quenching with gas impurities. Optical emission spectroscopy reveals nitrogen and water molecules as the main gas impurities. The estimated N₂ density [N₂]=0.1% is too low to explain the measured metastable lifetimes. Water impurity was found to be the main de-excitation source of argon metastable atoms due to high quenching coefficients. The water impurity level of [H₂O]=0.15% to 1% is sufficient to bring calculated metastable lifetimes in line with experiments. The maximum value of water content in the discharge compared to the argon atoms is estimated to approximately 6%, due to the large surface to volume ratio of the microdischarge. The current pulse releases the water molecules from the electrode surface and they are either re-adsorbed in the time between 0.4 ms for [H₂O]=1% and 2.6 ms for [H₂O]=0.15% or pumped out of the discharge with the speed equal to the gas flow-rate. Depending on its partial pressure, the water impurity re-adsorption time is of the order of magnitude or less then the argon gas residence time.

  8. Nucleation of metastable aragonite CaCO3 in seawater

    PubMed Central

    Sun, Wenhao; Jayaraman, Saivenkataraman; Chen, Wei; Persson, Kristin A.; Ceder, Gerbrand

    2015-01-01

    Predicting the conditions in which a compound adopts a metastable structure when it crystallizes out of solution is an unsolved and fundamental problem in materials synthesis, and one which, if understood and harnessed, could enable the rational design of synthesis pathways toward or away from metastable structures. Crystallization of metastable phases is particularly accessible via low-temperature solution-based routes, such as chimie douce and hydrothermal synthesis, but although the chemistry of the solution plays a crucial role in governing which polymorph forms, how it does so is poorly understood. Here, we demonstrate an ab initio technique to quantify thermodynamic parameters of surfaces and bulks in equilibrium with an aqueous environment, enabling the calculation of nucleation barriers of competing polymorphs as a function of solution chemistry, thereby predicting the solution conditions governing polymorph selection. We apply this approach to resolve the long-standing “calcite–aragonite problem”––the observation that calcium carbonate precipitates as the metastable aragonite polymorph in marine environments, rather than the stable phase calcite––which is of tremendous relevance to biomineralization, carbon sequestration, paleogeochemistry, and the vulnerability of marine life to ocean acidification. We identify a direct relationship between the calcite surface energy and solution Mg–Ca ion concentrations, showing that the calcite nucleation barrier surpasses that of metastable aragonite in solutions with Mg:Ca ratios consistent with modern seawater, allowing aragonite to dominate the kinetics of nucleation. Our ability to quantify how solution parameters distinguish between polymorphs marks an important step toward the ab initio prediction of materials synthesis pathways in solution. PMID:25739963

  9. Nucleation of metastable aragonite CaCO3 in seawater.

    PubMed

    Sun, Wenhao; Jayaraman, Saivenkataraman; Chen, Wei; Persson, Kristin A; Ceder, Gerbrand

    2015-03-17

    Predicting the conditions in which a compound adopts a metastable structure when it crystallizes out of solution is an unsolved and fundamental problem in materials synthesis, and one which, if understood and harnessed, could enable the rational design of synthesis pathways toward or away from metastable structures. Crystallization of metastable phases is particularly accessible via low-temperature solution-based routes, such as chimie douce and hydrothermal synthesis, but although the chemistry of the solution plays a crucial role in governing which polymorph forms, how it does so is poorly understood. Here, we demonstrate an ab initio technique to quantify thermodynamic parameters of surfaces and bulks in equilibrium with an aqueous environment, enabling the calculation of nucleation barriers of competing polymorphs as a function of solution chemistry, thereby predicting the solution conditions governing polymorph selection. We apply this approach to resolve the long-standing "calcite-aragonite problem"--the observation that calcium carbonate precipitates as the metastable aragonite polymorph in marine environments, rather than the stable phase calcite--which is of tremendous relevance to biomineralization, carbon sequestration, paleogeochemistry, and the vulnerability of marine life to ocean acidification. We identify a direct relationship between the calcite surface energy and solution Mg:Ca [corrected] ion concentrations, showing that the calcite nucleation barrier surpasses that of metastable aragonite in solutions with Mg:Ca ratios consistent with modern seawater, allowing aragonite to dominate the kinetics of nucleation. Our ability to quantify how solution parameters distinguish between polymorphs marks an important step toward the ab initio prediction of materials synthesis pathways in solution.

  10. Argon metastable dynamics and lifetimes in a direct current microdischarge

    NASA Astrophysics Data System (ADS)

    Stefanović, Ilija; Kuschel, Thomas; Schröter, Sandra; Böke, Marc

    2014-09-01

    In this paper we study the properties of a pulsed dc microdischarge with the continuous flow of argon. Argon metastable lifetimes are measured by tunable diode laser absorption spectroscopy (TDLAS) and are compared with calculated values which yield information about excitation and de-excitation processes. By increasing the gas flow-rate about 5 times from 10 to 50 sccm, the Arm lifetime increases from 1 to 5 μs due to the reduction of metastable quenching with gas impurities. Optical emission spectroscopy reveals nitrogen and water molecules as the main gas impurities. The estimated N2 density [N2] = 0.1% is too low to explain the measured metastable lifetimes. Water impurity was found to be the main de-excitation source of argon metastable atoms due to high quenching coefficients. The water impurity level of [H2O] = 0.15% to 1% is sufficient to bring calculated metastable lifetimes in line with experiments. The maximum value of water content in the discharge compared to the argon atoms is estimated to approximately 6%, due to the large surface to volume ratio of the microdischarge. The current pulse releases the water molecules from the electrode surface and they are either re-adsorbed in the time between 0.4 ms for [H2O] = 1% and 2.6 ms for [H2O] = 0.15% or pumped out of the discharge with the speed equal to the gas flow-rate. Depending on its partial pressure, the water impurity re-adsorption time is of the order of magnitude or less then the argon gas residence time.

  11. 1H and 13C NMR Assignments of Cytotoxic 3S-1,2,3,4-Tetrahydro-β-carboline-3-carboxylic Acid from the Leaves of Cichorium endivia

    PubMed Central

    Wang, Fu-Xin; Deng, An-Jun; Wei, Jin-Feng; Qin, Hai-Lin; Wang, Ai-Ping

    2012-01-01

    An amino acid, 3S-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid, was isolated for the first time from the leaves of Cichorium endivia. The complete assignment of its 1H and 13C NMR spectroscopic data was carried out also for the first time based on extensive 1D and 2D NMR experiments. Cytotoxicity of this isolated compound against HCT-8 and HepG2 human cancer cell lines was evaluated for the first time, with moderate activities being found. PMID:23304641

  12. First-principle interaction potentials for metastable He(3S) and Ne(3P) with closed-shell molecules: application to Penning-ionizing systems.

    PubMed

    Hapka, Michał; Chałasiński, Grzegorz; Kłos, Jacek; Zuchowski, Piotr S

    2013-07-07

    We present new interaction potential curves, calculated from first-principles, for the He((3)S, 1s(1)2s(1))···H2 and He((3)S)···Ar systems, relevant in recent Penning ionization experiments of Henson et al. [Science 338, 234 (2012)]. Two different approaches were applied: supermolecular using coupled cluster (CC) theory and perturbational within symmetry-adapted perturbation theory (SAPT). Both methods gave consistent results, and the potentials were used to study the elastic scattering and determine the positions of shape resonances for low kinetic energy (up to 1 meV). We found a good agreement with the experiment. In addition, we investigated two other dimers composed of metastable Ne ((3)P, 2p(5)3s(1)) and ground state He and Ar atoms. For the Ne((3)P)···He system, a good agreement between CC and SAPT approaches was obtained. The Ne((3)P)···Ar dimer was described only with SAPT, as CC gave divergent results. Ne* systems exhibit extremely small electronic orbital angular momentum anisotropy of the potentials. We attribute this effect to screening of an open 2p shell by a singly occupied 3s shell.

  13. New metastable phases in a trititanium pentoxide compound

    NASA Astrophysics Data System (ADS)

    Vallejo, E.; Olguín, D.

    2015-12-01

    New metastable triclinic phases in the trititanium pentoxide Ti3O5 compound were obtained using an evolutionary algorithm and density functional theory. Structural, electronic and magnetic properties were studied. The most stable triclinic structure was identified as P1 with a space group number of 1. The magnetic structure of this phase looks like zigzag lines of ferromagnetic Ti ions in a y-direction antiferromagnetic background. Additionally, an orthorhombic Amm2 structure and a monoclinic Cm metastable phase were found. To our best knowledge these phases have not been reported in literature. Additionally, an orthorhombic-monoclinic structural transition was observed, where a Jahn-Teller like effect was proposed as an explanation of this transition.

  14. Block Copolymer Metastability: Scientific Nightmare or Engineering Dream?

    NASA Astrophysics Data System (ADS)

    Bates, Frank S.

    1997-03-01

    Most experimental studies and almost all theories that deal with block copolymers, or mixtures of block copolymers and homopolymers, have been designed from an equilibrium perspective. Yet a myriad of factors conspire to retard approach to equilibrium in these systems, including: subtle features in the free energy surface that are controlled by ordered state symmetry; a coupling between microphase separation and entanglement dynamics; complex molecular architectures such as multiblock, starblock, and miktoarm. Even unentangled low molecular weight diblock copolymers, the simplest and dynamically least encumbered materials, exhibit long-lived metastable states that confound attempts to validate equilibrium theories. However, this apparent dilemma can be exploited through clever processing strategies. This lecture will address two opposing consequences of block copolymer metastability. The first is a potential nightmare: Can we ever establish universal block copolymer phase diagrams? The second is the stuff of dreams: Self-assembled thermoset nanocomposites.

  15. Simple model of direct gauge mediation of metastable supersymmetry breaking

    SciTech Connect

    Haba, Naoyuki; Maru, Nobuhito

    2007-12-01

    We construct a model of direct gauge mediation of metastable supersymmetry breaking by simply deforming the Intriligator, Seiberg, and Shih model in terms of a dual meson superpotential mass term. No extra matter field is introduced. The deformation explicitly breaks a U(1){sub R} symmetry and pseudomoduli have a nonzero VEV at one-loop. Our metastable supersymmetry breaking vacuum turns out to be sufficiently long-lived. By gauging a subgroup of flavor symmetry, our model can directly couple to the standard model, which leads to nonvanishing gaugino mass generation. It is also shown that our model can evade the Landau pole problem. We show the parameters in the supersymmetry breaking sector are phenomenologically constrained.

  16. Metastability in the phase behavior of dimyristoylphosphatidylethanolamine bilayers.

    PubMed

    Wilkinson, D A; Nagle, J F

    1984-03-27

    A new subgel phase is demonstrated to occur in hydrated dimyristoylphosphatidylethanolamine ( DMPE ) by using dilatometric and calorimetric techniques. The formation of the subgel phase takes place very slowly at temperatures near 0 degree C, but it can still be observed at 25 degrees C. Once formed, the subgel phase melts (delta Hh = 16.0 +/- 0.6 kcal/mol and delta V = 0.085 +/- 0.014 mL/g) directly into the liquid-crystalline phase at a temperature, Th = 56.3 degrees C, that is higher than the gel to liquid-crystalline transition temperature, Tm = 49.6 degrees C. Thus, the gel phase appears to be metastable over its entire temperature range. In this regard, DMPE behaves differently from dipalmitoylphosphatidylcholine and distearoylphosphatidylcholine but similarly to dilaurylphosphatidylethanolamine . This unusual long-lived metastability provides cells an additional option in determining the properties of membranes.

  17. Cooperative photoinduced metastable phase control in strained manganite films.

    PubMed

    Zhang, Jingdi; Tan, Xuelian; Liu, Mengkun; Teitelbaum, S W; Post, K W; Jin, Feng; Nelson, K A; Basov, D N; Wu, Wenbin; Averitt, R D

    2016-09-01

    A major challenge in condensed-matter physics is active control of quantum phases. Dynamic control with pulsed electromagnetic fields can overcome energetic barriers, enabling access to transient or metastable states that are not thermally accessible. Here we demonstrate strain-engineered tuning of La2/3Ca1/3MnO3 into an emergent charge-ordered insulating phase with extreme photo-susceptibility, where even a single optical pulse can initiate a transition to a long-lived metastable hidden metallic phase. Comprehensive single-shot pulsed excitation measurements demonstrate that the transition is cooperative and ultrafast, requiring a critical absorbed photon density to activate local charge excitations that mediate magnetic-lattice coupling that, in turn, stabilize the metallic phase. These results reveal that strain engineering can tune emergent functionality towards proximal macroscopic states to enable dynamic ultrafast optical phase switching and control.

  18. Direct Mediation of Meta-Stable Supersymmetry Breaking

    SciTech Connect

    Kitano, Ryuichiro; Ooguri, Hirosi; Ookouchi, Yutaka

    2006-12-13

    The supersymmetric SU(N{sub c}) Yang-Mills theory coupled to NF matter fields in the fundamental representation has meta-stable vacua with broken supersymmetry when N{sub C} < N{sub F} < 3/2 N{sub C}. By gauging the flavor symmetry, this model can be coupled directly to the standard model. We show that it is possible to make a slight deformation to the model so that gaugino masses are generated and the Landau pole problem can be avoided. The deformed model has simple realizations on intersecting branes in string theory, where various features of the meta-stable vacua are encoded geometrically as brane configurations.

  19. Dynamic Polarizability for Metastable Helium in Debye Plasmas

    NASA Astrophysics Data System (ADS)

    Kar, Sabyasachi; Wang, Yu-Shu; Wang, Yang; Jiang, Zishi

    2017-01-01

    The dynamic dipole polarizability (DDP) for metastable helium in plasma environments has been studied recently (Kar et al. in Phys Plasmas 23:082119, 2016) by incorporating plasma screening effect on electron-nucleus interactions. In this work, we investigate the DDP for metastable helium immersed in Debye plasmas using screening effects on both electron-nucleus and electron-electron interactions. The dynamic dipole polarizabilities for the n {}1S (n=2,3) and n {}3S (n=2,3) states are reported as functions of Debye screening parameter. First tune-out wavelengths for the n {}1S (n=1,2,3) and n {}3S (n=2,3) states and magic wavelengths for the 2 {}3S → 3 {}3S transition are also reported in terms of Debye screening parameter. Magic wavelengths in screening environments are presented for the first time in the literature.

  20. Metastable Supersymmetry Breaking and Multitrace Deformations of SQCD

    SciTech Connect

    Essig, Rouven; Fortin, Jean-Francois; Sinha, Kuver; Torroba, Gonzalo; Strassler, Matthew J.; /Rutgers U., Piscataway

    2009-02-23

    Metastable vacua in supersymmetric QCD in the presence of single and multitrace deformations of the superpotential are explored, with the aim of obtaining an acceptable phenomenology. The metastable vacua appear at one loop, have a broken R-symmetry, and a magnetic gauge group that is completely Higgsed. With only a single trace deformation, the adjoint fermions from the meson superfield are approximately massless at one loop, even though they are massive at tree level and R-symmetry is broken. Consequently, if charged under the standard model, they are unacceptably light. A multitrace quadratic deformation generates fermion masses proportional to the deformation parameter. Phenomenologically viable models of direct gauge mediation can then be obtained, and some of their features are discussed.

  1. Metastable S production following electron impact on Thiophosgene

    NASA Astrophysics Data System (ADS)

    Kedzierski, Wladyslaw; Borbely, Joseph; Mills, Adam; McConkey, William

    2003-05-01

    A novel xenon matrix surface detector is used to study the production of metastable S atoms following controlled electron impact on thiophosgene over an energy range from threshold to 400eV. A crossed-beam apparatus with a pulsed electron beam is used to obtain time-of-flight, and hence energy, spectra of metastable S fragments. Absolute cross-section data are obtained by comparison with previously obtained data from COS targets [Kedzierski et al J. Phys. B 34, 4027, (2001)]. Low resolution spectra, (of direct fluorescence from the interaction region and delayed fluorescence from the detector surface), in the spectral region between 400 and 850 nm, will also be presented.

  2. Constrained superfields on metastable anti-D3-branes

    NASA Astrophysics Data System (ADS)

    Aalsma, Lars; van der Schaar, Jan Pieter; Vercnocke, Bert

    2017-05-01

    We study the effect of brane polarization on the supersymmetry transformations of probe anti-D3-branes at the tip of a Klebanov-Strassler throat geometry. As is well known, the probe branes can polarize into NS5-branes and decay to a supersymmetric state by brane-flux annihilation. The effective potential has a metastable minimum as long as the number of anti-D3-branes is small compared to the number of flux quanta. We study the reduced four-dimensional effective NS5-brane theory and show that in the metastable minimum supersymmetry is non-linearly realized to leading order, as expected for spontaneously broken supersymmetry. However, a strict decoupling limit of the higher order corrections in terms of a standard nilpotent superfield does not seem to exist. We comment on the possible implications of these results for more general low-energy effective descriptions of inflation or de Sitter vacua.

  3. An Optically Excited Metastable Krypton Atomic Beam Source

    NASA Astrophysics Data System (ADS)

    Mastroianni, Michael; Orzel, Chad

    2006-05-01

    We report the construction of an optically excited metastable krypton atomic beam source. Ground-state Kr atoms are excited to the 5s[3/2]1 state by a 123 nm photon from a krypton resonance line lamp, then to the 5p[5/2]2 state by an 819 nm photon from a diode laser. From the 5p[3/2]2 state, they spontaneously decay into the 5s[3/2]2 (^3P2) metastable state with 77% probability. We characterize the source using both resonant fluorescence at 811 nm and a surface ionization detector. The source will be used to load a Kr* magneto-optical trap for Kr background evaluation by Atom Trap Trace Analysis.

  4. Cooperative photoinduced metastable phase control in strained manganite films

    NASA Astrophysics Data System (ADS)

    Zhang, Jingdi; Tan, Xuelian; Liu, Mengkun; Teitelbaum, S. W.; Post, K. W.; Jin, Feng; Nelson, K. A.; Basov, D. N.; Wu, Wenbin; Averitt, R. D.

    2016-09-01

    A major challenge in condensed-matter physics is active control of quantum phases. Dynamic control with pulsed electromagnetic fields can overcome energetic barriers, enabling access to transient or metastable states that are not thermally accessible. Here we demonstrate strain-engineered tuning of La2/3Ca1/3MnO3 into an emergent charge-ordered insulating phase with extreme photo-susceptibility, where even a single optical pulse can initiate a transition to a long-lived metastable hidden metallic phase. Comprehensive single-shot pulsed excitation measurements demonstrate that the transition is cooperative and ultrafast, requiring a critical absorbed photon density to activate local charge excitations that mediate magnetic-lattice coupling that, in turn, stabilize the metallic phase. These results reveal that strain engineering can tune emergent functionality towards proximal macroscopic states to enable dynamic ultrafast optical phase switching and control.

  5. Constraints on Meta-stable de Sitter Flux Vacua

    SciTech Connect

    Soroush, Masoud

    2007-03-05

    We consider flux compactification of type IIB string theory as the orientifold limit of an F-theory on a Calabi-Yau fourfold. We show that when supersymmetry is dominantly broken by the axion-dilaton and the contributions of the F-terms associated with complex structure moduli are small, the Hessian of the flux potential always has tachyonic modes for de Sitter vacua. This implies that there exist no meta-stable de Sitter vacua in this limit. Moreover, we find that the stability requirement imposes a relation between the values of cosmological constant and the scale of supersymmetry breaking for non-supersymmetric anti de Sitter vacua in this limit. The proof is general and does rely on the details of the geometry of the compact Calabi-Yau internal space. We finally analyze the consequences of these constraints on the statistics of meta-stable de Sitter vacua and address some other related issues.

  6. Selective formation of metastable ferrihydrite in the chiton tooth.

    PubMed

    Gordon, Lyle M; Román, Jessica K; Everly, R Michael; Cohen, Michael J; Wilker, Jonathan J; Joester, Derk

    2014-10-20

    Metastable precursors are thought to play a major role in the ability of organisms to create mineralized tissues. Of particular interest are the hard and abrasion-resistant teeth formed by chitons, a class of rock-grazing mollusks. The formation of chiton teeth relies on the precipitation of metastable ferrihydrite (Fh) in an organic scaffold as a precursor to magnetite. In vitro synthesis of Fh under physiological conditions has been challenging. Using a combination of X-ray absorption and electron paramagnetic resonance spectroscopy, we show that, prior to Fh formation in the chiton tooth, iron ions are complexed by the organic matrix. In vitro experiments demonstrate that such complexes facilitate the formation of Fh under physiological conditions. These results indicate that acidic molecules may be integral to controlling Fh formation in the chiton tooth. This biological approach to polymorph selection is not limited to specialized proteins and can be expropriated using simple chemistry.

  7. Metastable Amyloid Phases and their Conversion to Mature Fibrils

    NASA Astrophysics Data System (ADS)

    Muschol, Martin; Miti, Tatiana; Mulaj, Mentor; Schmit, Jeremy

    Self-assembly of proteins into amyloid fibrils plays a key role in both functional biological responses and pathogenic disorders which include Alzheimer's disease and type II diabetes. Amyloid fibril assembly frequently generates compact oligomeric and curvilinear polymeric intermediates which are implicated to be toxic to cells. Yet, the relation between these early-stage oligomeric aggregates and late-stage rigid fibrils, which are the hallmark structure of amyloid plaques, has remained unclear. Our measurements indicate that lysozyme amyloid oligomers and their curvilinear fibrils only form after crossing a salt and protein concentration dependent threshold. These oligomeric aggregates are structurally distinct from rigid fibrils and are metastable against nucleation and growth of rigid fibrils. Our experimental transition boundaries match well with colloidal model predictions accounting for salt-modulated charge repulsion. We also report our preliminary findings on the mechanism by which these metastable oligomeric phases are converted into stable amyloid fibrils.

  8. Coherent Atom Optics with fast metastable rare gas atoms

    SciTech Connect

    Grucker, J.; Baudon, J.; Karam, J.-C.; Perales, F.; Vassilev, G.; Ducloy, M.; Bocvarski, V.

    2006-12-01

    Coherent atom optics experiments making use of an ultra-narrow beam of fast metastable atoms generated by metastability exchange are reported. The transverse coherence of the beam (coherence radius of 1.7 {mu}m for He*, 1.2 {mu}m for Ne*, 0.87 {mu}m for Ar*) is demonstrated via the atomic diffraction by a non-magnetic 2{mu}m-period reflection grating. The combination of the non-scalar van der Waals (vdW) interaction with the Zeeman interaction generated by a static magnetic field gives rise to ''vdW-Zeeman'' transitions among Zeeman sub-levels. Exo-energetic transitions of this type are observed with Ne*(3P2) atoms traversing a copper micro-slit grating. They can be used as a tunable beam splitter in an inelastic Fresnel bi-prism atom interferometer.

  9. Metastable Pain-Attention Dynamics during Incremental Exhaustive Exercise.

    PubMed

    Slapšinskaitė, Agnė; Hristovski, Robert; Razon, Selen; Balagué, Natàlia; Tenenbaum, Gershon

    2016-01-01

    Background: Pain attracts attention on the bodily regions. Attentional allocation toward pain results from the neural communication across the brain-wide network "connectome" which consists of pain-attention related circuits. Connectome is intrinsically dynamic and spontaneously fluctuating on multiple time-scales. The present study delineates the pain-attention dynamics during incremental cycling performed until volitional exhaustion and investigates the potential presence of nested metastable dynamics. Method: Fifteen young and physically active adults completed a progressive incremental cycling test and reported their discomfort and pain on a body map every 15 s. Results: The analyses revealed that the number of body locations with perceived pain and discomfort increased throughout five temporal windows reaching an average of 4.26 ± 0.59 locations per participant. A total of 37 different locations were reported and marked as painful for all participants throughout the cycling task. Significant differences in entropy were observed between all temporal windows except the fourth and fifth windows. Transient dynamics of bodily locations with perceived discomfort and pain were spanned by three principal components. The metastable dynamics of the body pain locations groupings over time were discerned by three time scales: (1) the time scale of shifts (15 s); (2) the time scale of metastable configurations (100 s), and (3) the observational time scale (1000 s). Conclusion: The results of this study indicate that body locations perceived as painful increase throughout the incremental cycling task following a switching metastable and nested dynamics. These findings support the view that human brain is intrinsically organized into active, mutually interacting complex and nested functional networks, and that subjective experiences inherent in pain perception depict identical dynamical principles to the neural tissue in the brain.

  10. Metastability of native proteins and the phenomenon of amyloid formation.

    PubMed

    Baldwin, Andrew J; Knowles, Tuomas P J; Tartaglia, Gian Gaetano; Fitzpatrick, Anthony W; Devlin, Glyn L; Shammas, Sarah Lucy; Waudby, Christopher A; Mossuto, Maria F; Meehan, Sarah; Gras, Sally L; Christodoulou, John; Anthony-Cahill, Spencer J; Barker, Paul D; Vendruscolo, Michele; Dobson, Christopher M

    2011-09-14

    An experimental determination of the thermodynamic stabilities of a series of amyloid fibrils reveals that this structural form is likely to be the most stable one that protein molecules can adopt even under physiological conditions. This result challenges the conventional assumption that functional forms of proteins correspond to the global minima in their free energy surfaces and suggests that living systems are conformationally as well as chemically metastable.

  11. Shell transitions between metastable states of Yukawa balls

    SciTech Connect

    Kaeding, S.; Melzer, A.; Block, D.; Piel, A.; Kaehlert, H.; Ludwig, P.; Bonitz, M.

    2008-07-15

    Spherical dust clusters composed of several concentric shells are experimentally investigated with particular interest on transitions between different configurations and transitions of particles between different shells. Transitions between different ground and metastable configurations are frequently observed. The experimental analysis allows us to derive the energy differences of different configurations from particles traveling between shells. The observed transitions and transition probabilities are compared to molecular dynamics simulations.

  12. Metastable superconductivity of W/WO3 interface

    NASA Astrophysics Data System (ADS)

    Palnichenko, A. V.; Vyaselev, O. M.; Mazilkin, A. A.; Zver`kova, I. I.; Khasanov, S. S.

    2017-03-01

    Metastable W/WO3 interface has been formed at the surface of a tungsten metal bar using a solid state redox reaction of W with powdered WO3. Superconductivity at 35 ≤ T ≤ 75 K in the W/WO3 interfacial layer has been observed by means of the ac magnetic susceptibility and electrical resistance measurements. Comparative analysis of the experimental results infers that the W/WO3 interfacial layer consists of weakly linked superconducting regions.

  13. Gauge/gravity Duality and MetastableDynamical Supersymmetry Breaking

    SciTech Connect

    Argurio, Riccardo; Bertolini, Matteo; Franco, Sebastian; Kachru, Shamit

    2006-10-24

    We engineer a class of quiver gauge theories with several interesting features by studying D-branes at a simple Calabi-Yau singularity. At weak 't Hooft coupling we argue using field theory techniques that these theories admit both supersymmetric vacua and meta-stable non-supersymmetric vacua, though the arguments indicating the existence of the supersymmetry breaking states are not decisive. At strong 't Hooft coupling we find simple candidate gravity dual descriptions for both sets of vacua.

  14. Modeling of diode pumped metastable rare gas lasers.

    PubMed

    Yang, Zining; Yu, Guangqi; Wang, Hongyan; Lu, Qisheng; Xu, Xiaojun

    2015-06-01

    As a new kind of optically pumped gaseous lasers, diode pumped metastable rare gas lasers (OPRGLs) show potential in high power operation. In this paper, a multi-level rate equation based model of OPRGL is established. A qualitative agreement between simulation and Rawlins et al.'s experimental result shows the validity of the model. The key parameters' influences and energy distribution characteristics are theoretically studied, which is useful for the optimized design of high efficient OPRGLs.

  15. Triggered transience of metastable poly(phthalaldehyde) for transient electronics.

    PubMed

    Hernandez, Hector Lopez; Kang, Seung-Kyun; Lee, Olivia P; Hwang, Suk-Won; Kaitz, Joshua A; Inci, Bora; Park, Chan Woo; Chung, Sangjin; Sottos, Nancy R; Moore, Jeffrey S; Rogers, John A; White, Scott R

    2014-12-03

    Triggerable transient electronics are demonstrated with the use of a metastable poly(phthalaldehyde) polymer substrate and encapsulant. The rate of degradation is controlled by the concentration of the photo-acid generator and UV irradiance. This work expands on the materials that can be used for transient electronics by demonstrating transience in response to a preselected trigger without the need for solution-based degradation.

  16. Point Defect Concentrations in Metastable Fe-C Alloys

    SciTech Connect

    Foerst, Clemens J.; Yip, Sidney; Slycke, Jan; Vliet, Krystyn J. van

    2006-05-05

    Point defect species and concentrations in metastable Fe-C alloys are determined using density functional theory and a constrained free-energy functional. Carbon interstitials dominate unless iron vacancies are in significant excess, whereas excess carbon causes greatly enhanced vacancy concentration. Our predictions are amenable to experimental verification; they provide a baseline for rationalizing complex microstructures known in hardened and tempered steels, and by extension other technological materials created by or subjected to extreme environments.

  17. Metastable Pain-Attention Dynamics during Incremental Exhaustive Exercise

    PubMed Central

    Slapšinskaitė, Agnė; Hristovski, Robert; Razon, Selen; Balagué, Natàlia; Tenenbaum, Gershon

    2017-01-01

    Background: Pain attracts attention on the bodily regions. Attentional allocation toward pain results from the neural communication across the brain-wide network “connectome” which consists of pain-attention related circuits. Connectome is intrinsically dynamic and spontaneously fluctuating on multiple time-scales. The present study delineates the pain-attention dynamics during incremental cycling performed until volitional exhaustion and investigates the potential presence of nested metastable dynamics. Method: Fifteen young and physically active adults completed a progressive incremental cycling test and reported their discomfort and pain on a body map every 15 s. Results: The analyses revealed that the number of body locations with perceived pain and discomfort increased throughout five temporal windows reaching an average of 4.26 ± 0.59 locations per participant. A total of 37 different locations were reported and marked as painful for all participants throughout the cycling task. Significant differences in entropy were observed between all temporal windows except the fourth and fifth windows. Transient dynamics of bodily locations with perceived discomfort and pain were spanned by three principal components. The metastable dynamics of the body pain locations groupings over time were discerned by three time scales: (1) the time scale of shifts (15 s); (2) the time scale of metastable configurations (100 s), and (3) the observational time scale (1000 s). Conclusion: The results of this study indicate that body locations perceived as painful increase throughout the incremental cycling task following a switching metastable and nested dynamics. These findings support the view that human brain is intrinsically organized into active, mutually interacting complex and nested functional networks, and that subjective experiences inherent in pain perception depict identical dynamical principles to the neural tissue in the brain. PMID:28111563

  18. Topological Winding and Unwinding in Metastable Bose-Einstein Condensates

    SciTech Connect

    Kanamoto, Rina; Carr, Lincoln D.; Ueda, Masahito

    2008-02-15

    Topological winding and unwinding in a quasi-one-dimensional metastable Bose-Einstein condensate are shown to be manipulated by changing the strength of interaction or the frequency of rotation. Exact diagonalization analysis reveals that quasidegenerate states emerge spontaneously near the transition point, allowing a smooth crossover between topologically distinct states. On a mean-field level, the transition is accompanied by formation of gray solitons, or density notches, which serve as an experimental signature of this phenomenon.

  19. Detecting vapour bubbles in simulations of metastable water

    SciTech Connect

    González, Miguel A.; Abascal, Jose L. F.; Valeriani, Chantal E-mail: cvaleriani@quim.ucm.es; Menzl, Georg; Geiger, Philipp; Dellago, Christoph E-mail: cvaleriani@quim.ucm.es; Aragones, Juan L.; Caupin, Frederic

    2014-11-14

    The investigation of cavitation in metastable liquids with molecular simulations requires an appropriate definition of the volume of the vapour bubble forming within the metastable liquid phase. Commonly used approaches for bubble detection exhibit two significant flaws: first, when applied to water they often identify the voids within the hydrogen bond network as bubbles thus masking the signature of emerging bubbles and, second, they lack thermodynamic consistency. Here, we present two grid-based methods, the M-method and the V-method, to detect bubbles in metastable water specifically designed to address these shortcomings. The M-method incorporates information about neighbouring grid cells to distinguish between liquid- and vapour-like cells, which allows for a very sensitive detection of small bubbles and high spatial resolution of the detected bubbles. The V-method is calibrated such that its estimates for the bubble volume correspond to the average change in system volume and are thus thermodynamically consistent. Both methods are computationally inexpensive such that they can be used in molecular dynamics and Monte Carlo simulations of cavitation. We illustrate them by computing the free energy barrier and the size of the critical bubble for cavitation in water at negative pressure.

  20. Metastable charge-transfer state of californium(iii) compounds.

    PubMed

    Liu, Guokui; Cary, Samantha K; Albrecht-Schmitt, Thomas E

    2015-06-28

    Among a series of anomalous physical and chemical properties of Cf(iii) compounds revealed by recent investigations, the present work addresses the characteristics of the optical spectra of An(HDPA)3·H2O (An = Am, Cm, and Cf), especially the broadband photoluminescence from Cf(HDPA)3·H2O induced by ligand-to-metal charge transfer (CT). As a result of strong ion-ligand interactions and the relative ease of reducing Cf(iii) to Cf(ii), a CT transition occurs at low energy (<3 eV) via the formation of a metastable Cf(ii) state. It is shown that the systematic trend in CT transitions of the lanthanide series is not paralleled by actinide elements lighter than Cf(iii), and californium represents a turning point in the periodicity of the actinide series. Analyses and modeling of the temperature-dependent luminescence dynamics indicate that the metastable Cf(ii) charge-transfer state undergoes radiative and non-radiative relaxations. Broadening of the CT transition arises from strong vibronic coupling and hole-charge interactions in the valence band. The non-radiative relaxation of the metastable CT state results from a competition between phonon-relaxation and thermal tunneling that populates the excited states of Cf(iii).

  1. Breaking Degeneracy of Tautomerization-Metastability from Days to Seconds.

    PubMed

    Kügel, Jens; Sixta, Aimee; Böhme, Markus; Krönlein, Andreas; Bode, Matthias

    2016-12-27

    We present a detailed study of the tautomerization, that is, the switching of hydrogen protons, between different sites in the molecular frame of phthalocyanine (H2Pc) on a Ag(111) substrate by means of scanning tunneling microscopy (STM) and STM-based pump-and-sample techniques. Our data reveal that the symmetry mismatch between the substrate and the molecular frame lifts the energetic degeneracy of the two H2Pc tautomers. Their energy difference is so large that only one tautomer can be found in the ground state. Tip-induced tautomerization was triggered at sufficiently high bias voltages. The excited metastable H2Pc tautomer was found to exhibit a lifetime of at least several days, as derived from the fact that the molecule did not change back to the ground state within experimentally accessible time scales as long as noninvasive tunneling parameters were used to probe the state of the molecule. By the controlled removal of a hydrogen proton from the molecule, a four-level system was created. Pump-and-sample experiments reveal that the lifetime of the metastable positions amounts to seconds only. Current- and bias-dependent studies indicate that the presence of the STM tip modifies the potential barrier, thereby allowing for a controlled tuning of the metastable tautomer's lifetime.

  2. Productive induced metastability in allosteric modulation of kinase function.

    PubMed

    Montes de Oca, Joan; Rodriguez Fris, Ariel; Appignanesi, Gustavo; Fernández, Ariel

    2014-07-01

    Allosteric modulators of kinase function are of considerable pharmacological interest as blockers or agonists of key cell-signaling pathways. They are gaining attention due to their purported higher selectivity and efficacy relative to ATP-competitive ligands. Upon binding to the target protein, allosteric inhibitors promote a conformational change that purposely facilitates or hampers ATP binding. However, allosteric binding remains a matter of contention because the binding site does not fit with a natural ligand (i.e. ATP or phosphorylation substrate) of the protein. In this study, we show that allosteric binding occurs by means of a local structural motif that promotes association with the ligand. We specifically show that allosteric modulators promote a local metastable state that is stabilized upon association. The induced conformational change generates a local enrichment of the protein in the so-called dehydrons, which are solvent-exposed backbone hydrogen bonds. These structural deficiencies that are inherently sticky are not present in the apo form and constitute a local metastable state that promotes association with the ligand. This productive induced metastability (PIM) is likely to translate into a general molecular design concept. © 2014 FEBS.

  3. Metastable charged sparticles and the cosmological {sup 7}Li problem

    SciTech Connect

    Cyburt, Richard H.; Ellis, John; Luo, Feng; Fields, Brian D.; Olive, Keith A.; Spanos, Vassilis C. E-mail: John.Ellis@cern.ch E-mail: feng.luo@kcl.ac.uk E-mail: spanos@inp.demokritos.gr

    2012-12-01

    We consider the effects of metastable charged sparticles on Big-Bang Nucleosynthesis (BBN), including bound-state reaction rates and chemical effects. We make a new analysis of the bound states of negatively-charged massive particles with the light nuclei most prominent in BBN, and present a new code to track their abundances, paying particular attention to that of {sup 7}Li. Assuming, as an example, that the gravitino is the lightest supersymmetric particle (LSP), and that the lighter stau slepton, τ-tilde {sub 1}, is the metastable next-to-lightest sparticle within the constrained minimal supersymmetric extension of the Standard Model (CMSSM), we analyze the possible effects on the standard BBN abundances of τ-tilde {sub 1} bound states and decays for representative values of the gravitino mass. Taking into account the constraint on the CMSSM parameter space imposed by the discovery of the Higgs boson at the LHC, we delineate regions in which the fit to the measured light-element abundances is as good as in standard BBN. We also identify regions of the CMSSM parameter space in which the bound state properties, chemistry and decays of metastable charged sparticles can solve the cosmological {sup 7}Li problem.

  4. Detecting vapour bubbles in simulations of metastable water

    NASA Astrophysics Data System (ADS)

    González, Miguel A.; Menzl, Georg; Aragones, Juan L.; Geiger, Philipp; Caupin, Frederic; Abascal, Jose L. F.; Dellago, Christoph; Valeriani, Chantal

    2014-11-01

    The investigation of cavitation in metastable liquids with molecular simulations requires an appropriate definition of the volume of the vapour bubble forming within the metastable liquid phase. Commonly used approaches for bubble detection exhibit two significant flaws: first, when applied to water they often identify the voids within the hydrogen bond network as bubbles thus masking the signature of emerging bubbles and, second, they lack thermodynamic consistency. Here, we present two grid-based methods, the M-method and the V-method, to detect bubbles in metastable water specifically designed to address these shortcomings. The M-method incorporates information about neighbouring grid cells to distinguish between liquid- and vapour-like cells, which allows for a very sensitive detection of small bubbles and high spatial resolution of the detected bubbles. The V-method is calibrated such that its estimates for the bubble volume correspond to the average change in system volume and are thus thermodynamically consistent. Both methods are computationally inexpensive such that they can be used in molecular dynamics and Monte Carlo simulations of cavitation. We illustrate them by computing the free energy barrier and the size of the critical bubble for cavitation in water at negative pressure.

  5. Factor Xa inhibitors: S1 binding interactions of a series of N-{(3S)-1-[(1S)-1-methyl-2-morpholin-4-yl-2-oxoethyl]-2-oxopyrrolidin-3-yl}sulfonamides.

    PubMed

    Chan, Chuen; Borthwick, Alan D; Brown, David; Burns-Kurtis, Cynthia L; Campbell, Matthew; Chaudry, Laiq; Chung, Chun-wa; Convery, Máire A; Hamblin, J Nicole; Johnstone, Lisa; Kelly, Henry A; Kleanthous, Savvas; Patikis, Angela; Patel, Champa; Pateman, Anthony J; Senger, Stefan; Shah, Gita P; Toomey, John R; Watson, Nigel S; Weston, Helen E; Whitworth, Caroline; Young, Robert J; Zhou, Ping

    2007-04-05

    Factor Xa inhibitory activities for a series of N-{(3S)-1-[(1S)-1-methyl-2-morpholin-4-yl-2-oxoethyl]-2-oxopyrrolidin-3-yl}sulfonamides with different P1 groups are described. These data provide insight into binding interactions within the S1 primary specificity pocket; rationales are presented for the derived SAR on the basis of electronic interactions through crystal structures of fXa-ligand complexes and molecular modeling studies. A good correlation between in vitro anticoagulant activities with lipophilicity and the extent of human serum albumin binding is observed within this series of potent fXa inhibitors. Pharmacokinetic profiles in rat and dog, together with selectivity over other trypsin-like serine proteases, identified 1f as a candidate for further evaluation.

  6. Normal and abnormal evolution of argon metastable density in high-density plasmas

    SciTech Connect

    Seo, B. H.; Kim, J. H.; You, S. J.

    2015-05-15

    A controversial problem on the evolution of Ar metastable density as a function of electron density (increasing trend versus decreasing trend) was resolved by discovering the anomalous evolution of the argon metastable density with increasing electron density (discharge power), including both trends of the metastable density [Daltrini et al., Appl. Phys. Lett. 92, 061504 (2008)]. Later, by virtue of an adequate physical explanation based on a simple global model, both evolutions of the metastable density were comprehensively understood as part of the abnormal evolution occurring at low- and high-density regimes, respectively, and thus the physics behind the metastable evolution has seemed to be clearly disclosed. In this study, however, a remarkable result for the metastable density behavior with increasing electron density was observed: even in the same electron density regime, there are both normal and abnormal evolutions of metastable-state density with electron density depending on the measurement position: The metastable density increases with increasing electron density at a position far from the inductively coupled plasma antenna but decreases at a position close to the antenna. The effect of electron temperature, which is spatially nonuniform in the plasma, on the electron population and depopulation processes of Argon metastable atoms with increasing electron density is a clue to understanding the results. The calculated results of the global model, including multistep ionization for the argon metastable state and measured electron temperature, are in a good agreement with the experimental results.

  7. Electrostatic levitation studies of supercooled liquids and metastable solid phases

    NASA Astrophysics Data System (ADS)

    Rustan, Gustav Errol

    A new laboratory has been developed at Iowa State University (ISU) to be used for the study of high temperature liquids and solids, with particular focus on the supercooling of liquids and their metastable solidification products. This new laboratory employs the electrostatic levitation (ESL) technique, in which a charged sample is suspended between a set of electrodes to achieve non-contact handling. Owing to the elimination of a crucible, high temperature processing of samples can be achieved with reduced levels of contamination and heterogeneous nucleation. Because of the reduction in heterogeneous nucleation, samples can be supercooled well below their equilibrium melting temperature, opening the door to a wide range of measurements on supercooled liquids. Measurements methods have been implemented for the characterization of thermophysical properties such as: volume/density, ratio of specific heat to total hemispherical emissivity, surface tension, viscosity, electrical resistivity, and magnetic susceptibility. For measurements of electrical resistivity and magnetic susceptibility, a new method has been developed at ISU based on the tunnel diode oscillator (TDO) technique. The TDO technique uses the negative differential resistance of a tunnel diode to drive an LC tank circuit into self-sustained oscillation at the resonant LC frequency. The LC tank is inductively coupled to the samples under study, and changes in the electrical resistivity or magnetic susceptibility of the sample are manifested as changes in the resonant frequency. By measuring the frequency shifts of the TDO, insights can be made into changes in the material's electrical and magnetic properties. This method has been validated by performing resistivity measurements on a sample of high purity Zr, and by performing measurements on the ferromagnetic transition in a low-carbon steel ball bearing. In addition to the development of the laboratory and its supporting instrumentation, an effort has

  8. Rare Gas Metastable Atom Density in Diluted O2 RF Plasmas

    NASA Astrophysics Data System (ADS)

    Kitajima, Takeshi; Takahashi, Kei; Nakano, Toshiki; Makabe, Toshiaki

    Rare gas diluted O2 plasmas are gaining interests for application to high quality SiO2 film formation. The density of rare gas metastable atoms and O atom in rare gas diluted O2 radio frequency (RF) capacitively coupled plasma (CCP) was measured by optical absorption spectroscopy (OAS). Decreases of rare gas metastable densities due to addition of O2 indicate efficient O atom production by rare gas metastables via collisional quenching. Krypton metastable had highest density among four rare gas species for fixed RF power. The decrease of Ar metastable density due to O2 addition showed quantitative agreement with reported quenching rate coefficient. Detailed discussion on different gas pressures illustrates reduced O2 fraction is the key for selective production of O atoms through rare gas metastables.

  9. Dissociation of CH4 by electron impact: Production of metastable hydrogen and carbon fragments

    NASA Technical Reports Server (NTRS)

    Finn, T. G.; Carnahan, B. L.; Zipf, E. C.

    1974-01-01

    Metastable fragments produced by electron impact excitation of CH4 have been investigated for incident electron energies from threshold to 300 eV. Only metastable hydrogen and carbon atoms were observed. Onset energies for the production of metastable hydrogen atoms were observed at electron impact energies of 22.0 + or - .5 eV, 25.5 + or - .6 eV, 36.7 + or - .6 eV and 66 + or - 3 eV, and at 26.6 + or - .6 eV for the production of metastable carbon atoms. Most of the fragments appear to have been formed in high-lying Rydberg states. The total metastable hydrogen cross section reaches a maximum value of approximately 1 X 10 to the minus 18th power sq cm at 100 eV. At the same energy, the metastable carbon cross section is 2 x 10 to the minus 19th power sq cm.

  10. Metastable Eutectic Equilibrium in Natural Environments: Recent Development and Research Opportunities

    NASA Technical Reports Server (NTRS)

    Rietmeijer, Frans J. M.; Nuth, Joseph A., III; Jablonska, Mariola; Karner, James M.

    2000-01-01

    Chemical ordering at metastable eutectics was recognized in non-equilibrium gas-to- solid condensation experiments to constrain 'silicate' dust formation in O-rich circumstellar environments. The predictable metastable eutectic behavior successfully predicted the observed ferromagnesiosilica compositions of circumstellar dust presolar and solar nebula grains in the matrix of the collected aggregate IDPs (Interplanetary Dust Particles). Many of the experimentally determined metastable eutectic solids match the fundamental building blocks of common rock-forming layer silicates: this could have implications for the origin of Life. The physical conditions conducive to metastable eutectic behavior, i.e. high temperature and (ultra) fast quenching, lead to unique amorphous, typically nano- to micrometer-sized, materials. The new paradigm of metastable eutectic behavior opens the door to new and exciting research opportunities in uncovering the many implications of these unique amorphous, and typically nano-to micrometer-sized, metastable eutectic materials.

  11. Metastable Eutectic Equilibrium in Natural Environments: Recent Developments and Research Opportunities

    NASA Technical Reports Server (NTRS)

    Rietmeijer, Fans J. M.; Nuth, Joseph A., II; Jablonska, Mariola; Karner, James M.

    2000-01-01

    Chemical ordering at metastable eutectics was recognized in non-equilibrium gas-to- solid condensation experiments to constrain 'silicate' dust formation in O-rich circumstellar environments. The predictable metastable eutectic behavior successfully predicted the observed ferromagnesiosilica, compositions of circumstellar dust, presolar and solar nebula grains in the matrix of the collected aggregate IDPs. Many of the experimentally determined metastable eutectic solids match the fundamental building blocks of common rock-forming layer silicates: this could have implications for the origin of Life. The physical conditions conducive to metastable eutectic behavior, i.e. high temperature and (ultra)fast quenching, lead to unique amorphous, typically nano- to micrometer-sized, materials. The new paradigm of metastable eutectic behavior opens the door to new and exciting research opportunities in uncovering the many implications of these unique amorphous and typically nano- to micrometer-sized, metastable eutectic materials.

  12. Observation of enhanced emission of cusp electrons at impact of excited metastable neutral He projectiles

    SciTech Connect

    Kuzel, M. ); Sarkadi, L.; Palinkas, J.; Zavodszky, P.A. ); Maier, R. ); Berenyi, D. ); Groeneveld, K.O. )

    1993-09-01

    The contribution of excited metastable He projectiles to the production of the forward electron cusp peak has been measured for bombardment of Ar by 400-keV neutral He atoms using the technique of collisional quenching to control the metastable fraction of the beam. The cross section for the production of cusp electrons via target ionization by metastable He atoms has been found to be about 10 times larger than the cross section for the same process for ground-state projectiles.

  13. Light induced metastable state of silver nitroprusside probed by Raman spectroscopy

    SciTech Connect

    Ghalsasi, Pallavi; Ghalsasi, Prasanna; Thomas, A.; Muthu, D. V. S.; Sood, A. K.

    2015-06-24

    Low temperature Raman spectroscopic measurements on silver nitroprusside (AgNP), Ag{sub 2}[Fe(CN){sub 5}NO] powders display reversible features of a partially converted metastable state. The results are compared with similarly observed metastable state in case of sodium nitroprusside (NaNP) and the differences have been discussed in terms of possible resistance to metastable state formation offered by silver atoms on the basis of hard soft acid base (HSAB) theory.

  14. Metastable Features of Economic Networks and Responses to Exogenous Shocks

    PubMed Central

    Hosseiny, Ali; Bahrami, Mohammad; Palestrini, Antonio; Gallegati, Mauro

    2016-01-01

    It is well known that a network structure plays an important role in addressing a collective behavior. In this paper we study a network of firms and corporations for addressing metastable features in an Ising based model. In our model we observe that if in a recession the government imposes a demand shock to stimulate the network, metastable features shape its response. Actually we find that there exists a minimum bound where any demand shock with a size below it is unable to trigger the market out of recession. We then investigate the impact of network characteristics on this minimum bound. We surprisingly observe that in a Watts-Strogatz network, although the minimum bound depends on the average of the degrees, when translated into the language of economics, such a bound is independent of the average degrees. This bound is about 0.44ΔGDP, where ΔGDP is the gap of GDP between recession and expansion. We examine our suggestions for the cases of the United States and the European Union in the recent recession, and compare them with the imposed stimulations. While the stimulation in the US has been above our threshold, in the EU it has been far below our threshold. Beside providing a minimum bound for a successful stimulation, our study on the metastable features suggests that in the time of crisis there is a “golden time passage” in which the minimum bound for successful stimulation can be much lower. Hence, our study strongly suggests stimulations to arise within this time passage. PMID:27706166

  15. Metastable hydronium ions in UV-irradiated ice

    SciTech Connect

    Moon, Eui-Seong; Kang, Heon

    2012-11-28

    We show that the irradiation of UV light (10-11 eV) onto an ice film produces metastable hydronium (H{sub 3}O{sup +}) ions in the ice at low temperatures (53-140 K). Evidence of the presence of metastable hydronium ions was obtained by experiments involving adsorption of methylamine onto UV-irradiated ice films and hydrogen-deuterium (H/D) isotopic exchange reaction. The methylamine adsorption experiments showed that photogenerated H{sub 3}O{sup +} species transferred a proton to the methylamine arriving at the ice surface, thus producing the methyl ammonium ion, which was detected by low energy sputtering method. The H{sub 3}O{sup +} species induced the H/D exchange of water, which was monitored through the detection of water isotopomers on the surface by using the Cs{sup +} reactive ion scattering method. Thermal and temporal stabilities of H{sub 3}O{sup +} and its proton migration activity were examined. The lifetime of the hydronium ions in the amorphized ice was greater than 1 h at {approx}53 K and decreased to {approx}5 min at 140 K. Interestingly, a small portion of hydronium ions survived for an extraordinarily long time in the ice, even at 140 K. The average migration distance of protons released from H{sub 3}O{sup +} in the ice was estimated to be about two water molecules at {approx}54 K and about six molecules at 100 K. These results indicate that UV-generated hydronium ions can be efficiently stabilized in low-temperature ice. Such metastable hydronium ions may play a significant role in the acid-base chemistry of ice particles in interstellar clouds.

  16. Effects of lesions on synchrony and metastability in cortical networks.

    PubMed

    Váša, František; Shanahan, Murray; Hellyer, Peter J; Scott, Gregory; Cabral, Joana; Leech, Robert

    2015-09-01

    At the macroscopic scale, the human brain can be described as a complex network of white matter tracts integrating grey matter assemblies - the human connectome. The structure of the connectome, which is often described using graph theoretic approaches, can be used to model macroscopic brain function at low computational cost. Here, we use the Kuramoto model of coupled oscillators with time-delays, calibrated with respect to empirical functional MRI data, to study the relation between the structure of the connectome and two aspects of functional brain dynamics - synchrony, a measure of general coherence, and metastability, a measure of dynamical flexibility. Specifically, we investigate the relationship between the local structure of the connectome, quantified using graph theory, and the synchrony and metastability of the model's dynamics. By removing individual nodes and all of their connections from the model, we study the effect of lesions on both global and local dynamics. Of the nine nodal graph-theoretical properties tested, two were able to predict effects of node lesion on the global dynamics. The removal of nodes with high eigenvector centrality leads to decreases in global synchrony and increases in global metastability, as does the removal of hub nodes joining topologically segregated network modules. At the level of local dynamics in the neighbourhood of the lesioned node, structural properties of the lesioned nodes hold more predictive power, as five nodal graph theoretical measures are related to changes in local dynamics following node lesions. We discuss these results in the context of empirical studies of stroke and functional brain dynamics. Copyright © 2015. Published by Elsevier Inc.

  17. Cognitive Flexibility through Metastable Neural Dynamics Is Disrupted by Damage to the Structural Connectome

    PubMed Central

    Hellyer, Peter J.; Scott, Gregory; Shanahan, Murray; Sharp, David J.

    2015-01-01

    Current theory proposes that healthy neural dynamics operate in a metastable regime, where brain regions interact to simultaneously maximize integration and segregation. Metastability may confer important behavioral properties, such as cognitive flexibility. It is increasingly recognized that neural dynamics are constrained by the underlying structural connections between brain regions. An important challenge is, therefore, to relate structural connectivity, neural dynamics, and behavior. Traumatic brain injury (TBI) is a pre-eminent structural disconnection disorder whereby traumatic axonal injury damages large-scale connectivity, producing characteristic cognitive impairments, including slowed information processing speed and reduced cognitive flexibility, that may be a result of disrupted metastable dynamics. Therefore, TBI provides an experimental and theoretical model to examine how metastable dynamics relate to structural connectivity and cognition. Here, we use complementary empirical and computational approaches to investigate how metastability arises from the healthy structural connectome and relates to cognitive performance. We found reduced metastability in large-scale neural dynamics after TBI, measured with resting-state functional MRI. This reduction in metastability was associated with damage to the connectome, measured using diffusion MRI. Furthermore, decreased metastability was associated with reduced cognitive flexibility and information processing. A computational model, defined by empirically derived connectivity data, demonstrates how behaviorally relevant changes in neural dynamics result from structural disconnection. Our findings suggest how metastable dynamics are important for normal brain function and contingent on the structure of the human connectome. PMID:26085630

  18. Counting metastable states in a kinetically constrained model using a patch repetition analysis.

    PubMed

    Jack, Robert L

    2013-12-01

    We analyze metastable states in the East model, using a recently proposed patch repetition analysis based on time-averaged density profiles. The results reveal a hierarchy of states of varying lifetimes, consistent with previous studies in which the metastable states were identified and used to explain the glassy dynamics of the model. We establish a mapping between these states and configurations of systems of hard rods, which allows us to analyze both typical and atypical metastable states. We discuss connections between the complexity of metastable states and large-deviation functions of dynamical quantities, both in the context of the East model and more generally in glassy systems.

  19. Cognitive Flexibility through Metastable Neural Dynamics Is Disrupted by Damage to the Structural Connectome.

    PubMed

    Hellyer, Peter J; Scott, Gregory; Shanahan, Murray; Sharp, David J; Leech, Robert

    2015-06-17

    Current theory proposes that healthy neural dynamics operate in a metastable regime, where brain regions interact to simultaneously maximize integration and segregation. Metastability may confer important behavioral properties, such as cognitive flexibility. It is increasingly recognized that neural dynamics are constrained by the underlying structural connections between brain regions. An important challenge is, therefore, to relate structural connectivity, neural dynamics, and behavior. Traumatic brain injury (TBI) is a pre-eminent structural disconnection disorder whereby traumatic axonal injury damages large-scale connectivity, producing characteristic cognitive impairments, including slowed information processing speed and reduced cognitive flexibility, that may be a result of disrupted metastable dynamics. Therefore, TBI provides an experimental and theoretical model to examine how metastable dynamics relate to structural connectivity and cognition. Here, we use complementary empirical and computational approaches to investigate how metastability arises from the healthy structural connectome and relates to cognitive performance. We found reduced metastability in large-scale neural dynamics after TBI, measured with resting-state functional MRI. This reduction in metastability was associated with damage to the connectome, measured using diffusion MRI. Furthermore, decreased metastability was associated with reduced cognitive flexibility and information processing. A computational model, defined by empirically derived connectivity data, demonstrates how behaviorally relevant changes in neural dynamics result from structural disconnection. Our findings suggest how metastable dynamics are important for normal brain function and contingent on the structure of the human connectome.

  20. Light-induced metastable structural changes in hydrogenated amorphous silicon

    SciTech Connect

    Fritzsche, H.

    1996-09-01

    Light-induced defects (LID) in hydrogenated amorphous silicon (a-Si:H) and its alloys limit the ultimate efficiency of solar panels made with these materials. This paper reviews a variety of attempts to find the origin of and to eliminate the processes that give rise to LIDs. These attempts include novel deposition processes and the reduction of impurities. Material improvements achieved over the past decade are associated more with the material`s microstructure than with eliminating LIDs. We conclude that metastable LIDs are a natural by-product of structural changes which are generally associated with non-radiative electron-hole recombination in amorphous semiconductors.

  1. Direct gauge mediation of uplifted metastable supersymmetry breaking in supergravity

    SciTech Connect

    Maru, Nobuhito

    2010-10-01

    We propose a direct gauge mediation model based on an uplifted metastable supersymmetry (SUSY) breaking coupled to supergravity. A constant superpotential plays an essential role to fix the moduli as well as breaking SUSY and R symmetry and the cancellation of the cosmological constant. Gaugino masses are generated at leading order of SUSY breaking scale, and comparable to the sfermion masses as in the ordinary gauge mediation. The Landau pole problem for QCD coupling can be easily solved since more than half of messengers become superheavy, which are heavier than the grand unified theory (GUT) scale.

  2. Dynamic metastability in the two-dimensional Potts ferromagnet.

    PubMed

    Ibáñez Berganza, Miguel; Petri, Alberto; Coletti, Pietro

    2014-05-01

    We investigate the nonequilibrium dynamics of the two-dimensional (2D) Potts model on the square lattice after a quench below the discontinuous transition point. By means of numerical simulations of systems with q=12, 24, and 48, we observe the onset of a stationary regime below the temperature-driven transition, in a temperature interval decreasing with the system size and increasing with q. These results obtained dynamically agree with those obtained from the analytical continuation of the free energy [J. L. Meunier and A. Morel, Eur. Phys. J. B 13, 341 (2000)], from which metastability in the 2D Potts model results to be a finite-size effect.

  3. Direct observation of magnetic metastability in individual iron nanoparticles.

    PubMed

    Balan, Ana; Derlet, Peter M; Rodríguez, Arantxa Fraile; Bansmann, Joachim; Yanes, Rocio; Nowak, Ulrich; Kleibert, Armin; Nolting, Frithjof

    2014-03-14

    X-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism is used to study the magnetic properties of individual iron nanoparticles with sizes ranging from 20 down to 8 nm. While the magnetocrystalline anisotropy of bulk iron suggests superparamagnetic behavior in this size range, ferromagnetically blocked particles are also found at all sizes. Spontaneous transitions from the blocked state to the superparamagnetic state are observed in single particles and suggest that the enhanced magnetic energy barriers in the ferromagnetic particles are due to metastable, structurally excited states with unexpected life times.

  4. Investigating the Metastability of Clathrate Hydrates for Energy Storage

    SciTech Connect

    Koh, Carolyn Ann

    2014-11-18

    Important breakthrough discoveries have been achieved from the DOE award on the key processes controlling the synthesis and structure-property relations of clathrate hydrates, which are critical to the development of clathrate hydrates as energy storage materials. Key achievements include: (i) the discovery of key clathrate hydrate building blocks (stable and metastable) leading to clathrate hydrate nucleation and growth; (ii) development of a rapid clathrate hydrate synthesis route via a seeding mechanism; (iii) synthesis-structure relations of H2 + CH4/CO2 binary hydrates to control thermodynamic requirements for energy storage and sequestration applications; (iv) discovery of a new metastable phase present during clathrate hydrate structural transitions. The success of our research to-date is demonstrated by the significant papers we have published in high impact journals, including Science, Angewandte Chemie, J. Am. Chem. Soc. Intellectual Merits of Project Accomplishments: The intellectual merits of the project accomplishments are significant and transformative, in which the fundamental coupled computational and experimental program has provided new and critical understanding on the key processes controlling the nucleation, growth, and thermodynamics of clathrate hydrates containing hydrogen, methane, carbon dioxide, and other guest molecules for energy storage. Key examples of the intellectual merits of the accomplishments include: the first discovery of the nucleation pathways and dominant stable and metastable structures leading to clathrate hydrate formation; the discovery and experimental confirmation of new metastable clathrate hydrate structures; the development of new synthesis methods for controlling clathrate hydrate formation and enclathration of molecular hydrogen. Broader Impacts of Project Accomplishments: The molecular investigations performed in this project on the synthesis (nucleation & growth)-structure-stability relations of clathrate

  5. Structural studies of several distinct metastable forms of amorphous ice.

    PubMed

    Tulk, C A; Benmore, C J; Urquidi, J; Klug, D D; Neuefeind, J; Tomberli, B; Egelstaff, P A

    2002-08-23

    Structural changes during annealing of high-density amorphous ice were studied with both neutron and x-ray diffraction. The first diffraction peak was followed from the high- to the low-density amorphous form. Changes were observed to occur through a series of intermediate forms that appear to be metastable at each anneal temperature. Five distinct amorphous forms were studied with neutron scattering, and many more forms may be possible. Radial distribution functions indicate that the structure evolves systematically between 4 and 8 angstroms. The phase transformations in low-temperature liquid water may be much more complex than currently understood.

  6. Metastable superfluidity of repulsive fermionic atoms in optical lattices.

    PubMed

    Rosch, Achim; Rasch, David; Binz, Benedikt; Vojta, Matthias

    2008-12-31

    In the fermionic Hubbard model, doubly occupied states have an exponentially large lifetime for strong repulsive interactions U. We show that this property can be used to prepare a metastable s-wave superfluid state for fermionic atoms in optical lattices described by a large-U Hubbard model. When an initial band-insulating state is expanded, the doubly occupied sites Bose condense. A mapping to the ferromagnetic Heisenberg model in an external field allows for a reliable solution of the problem. Nearest-neighbor repulsion and pair hopping are important in stabilizing superfluidity.

  7. Shear-induced metastable states of end-grafted polystyrene

    SciTech Connect

    Sasa, Leslie A.; Yearley, Eric J.; Jablin, Michael S.; Majewski, Jaroslaw; Hjelm, Rex P.; Gilbertson, Robert D.; Lavine, Adrienne S.

    2011-08-15

    The in situ molecular scale response of end-grafted polystyrene to shear against a deuterated polystyrene melt was investigated with neutron reflectometry. The derived grafted polystyrene density profiles showed that the grafted polystyrene was retained on the quartz wafer during the measurements. The profiles suggested that the end-grafted polystyrene response to shear results in a series of metastable states, rather than equilibrium states assumed in the current theory. Except for some possible extension and/or contraction of the grafted polystyrene with shear, there was no obvious correlation between the grafted polymer structure and the shear thinning behavior observed in these samples.

  8. Origin of metastable knots in single flexible chains.

    PubMed

    Dai, Liang; Renner, C Benjamin; Doyle, Patrick S

    2015-01-23

    Recent theoretical progress has explained the physics of knotting of semiflexible polymers, yet knotting of flexible polymers is relatively unexplored. We herein develop a new theory for the size distribution of knots on a flexible polymer and the existence of metastable knots. We show the free energy of a flexible molecule in a tube can be mapped to quantitatively reproduce the free energy distribution of a knot on a flexible chain. The size distribution of knots on flexible chains is expected to be universal and might be observed at a macroscopic scale, such as a string of hard balls.

  9. Measurement of Metastable Lifetimes of Highly-Charged Ions

    NASA Technical Reports Server (NTRS)

    Smith, Steven J.; Chutjian, A.; Lozano, J.

    2002-01-01

    The present work is part of a series of measurements of metastable lifetimes of highly-charged ions (HCIs) which contribute to optical absorption, emission and energy balance in the Interstellar Medium (ISM), stellar atmospheres, etc. Measurements were carried out using the 14-GHz electron cyclotron resonance ion source (ECRIS) at the JPL HCI facility. The ECR provides useful currents of charge states such as C(sup(1-6)+), Mg(sup(1-6)+) and Fe(sup(1-17)+). In this work the HCI beam is focused into a Kingdon electrostatic ion trap for measuring lifetimes via optical decays.

  10. Higgs-inflaton coupling from reheating and the metastable Universe

    NASA Astrophysics Data System (ADS)

    Gross, Christian; Lebedev, Oleg; Zatta, Marco

    2016-02-01

    Current Higgs boson and top quark data favor metastability of our vacuum which raises questions as to why the Universe has chosen an energetically disfavored state and remained there during inflation. In this Letter, we point out that these problems can be solved by a Higgs-inflaton coupling which appears in realistic models of inflation. Since an inflaton must couple to the Standard Model particles either directly or indirectly, such a coupling is generated radiatively, even if absent at tree level. As a result, the dynamics of the Higgs field can change dramatically.

  11. Coherent Atom Optics With Fast Metastable Beams: Metastable Helium Diffraction By 1D and 2D Magnetized Reflection Gratings

    SciTech Connect

    Grucker, J.; Baudon, J.; Karam, J.-C.; Perales, F.; Ducloy, M.; Bocvarski, V.

    2007-04-23

    1D and 2D reflection gratings (Permalloy stripes or dots deposited on silicon), immersed in an external homogeneous static magnetic field, are used to study 1D and 2D diffraction of fast metastable helium atoms He* (23S1). Both the grazing incidence used here and the repulsive potential (for sub-level m = -1) generated by the magnetisation reduce the quenching effect. This periodically structured potential is responsible for the diffraction in the incidence plane as well as for the diffraction in the perpendicular plane.

  12. On the metastability of doubly charged homonuclear diatomics.

    PubMed

    Fantuzzi, Felipe; Cardozo, Thiago M; Nascimento, Marco A C

    2017-07-26

    Generalized valence bond (GVB) and spin-coupled (SC) calculations were used in conjunction with the generalized product function energy partitioning (GPF-EP) method to describe the origin of metastability in doubly charged homonuclear dications. A model to describe the formation of metastable potential wells based on interference and quasi-classical effects is presented. The GPF-EP picture of dications is the result of polarization-aided strong covalent bonding surpassing Coulomb electrostatic repulsion. Important differences in the quasi-classical density profiles of He2(2+) and Ne2(2+) reveal the underlying mechanism that could lead to bound or unbound states. Finally, the nature of the chemical bond of N2(2+), O2(2+), and F2(2+) is described. The results suggest that the ground states of the mentioned dications are bounded and that the depth of the potential wells of these exotic species is related to the interference effect, in the same way as in previously studied neutral molecules.

  13. Thermodynamic versus conformational metastability in fibril-forming lysozyme solutions.

    PubMed

    Raccosta, Samuele; Martorana, Vincenzo; Manno, Mauro

    2012-10-11

    The role of intermolecular interaction in fibril-forming protein solutions and its relation with molecular conformation is a crucial aspect for the control and inhibition of amyloid structures. Here, we study the fibril formation and the protein-protein interactions of lysozyme at acidic pH and low ionic strength. The amyloid formation occurs after a long lag time and is preceded by the formation of oligomers, which seems to be off-pathway with respect to fibrillation. By measuring the osmotic isothermal compressibility and the collective diffusion coefficient of lysozyme in solution, we observe that the monomeric solution is kept in a thermodynamically metastable state by strong electrostatic repulsion, even in denaturing conditions. The measured repulsive interaction between monomers is satisfactorily accounted for by classical polyelectrolyte theory. Further, we observe a slow conformational change involving both secondary and tertiary structure, which drives the proteins toward a more hydrophobic conformation. Denatured proteins are driven out of metastability through conformational substates, which are kinetically populated and experience a lower activation energy for fibril formation. Thus, our results highlight the role of electrostatic repulsion, which hinders the aggregation of partially denatured proteins and operates as a gatekeeper favoring the association of those monomers whose conformation is capable of forming amyloid structure.

  14. A new nanoscale metastable iron phase in carbon steels

    NASA Astrophysics Data System (ADS)

    Liu, Tianwei; Zhang, Danxia; Liu, Qing; Zheng, Yanjun; Su, Yanjing; Zhao, Xinqing; Yin, Jiang; Song, Minghui; Ping, Dehai

    2015-10-01

    Metastable ω phase is common in body-centred cubic (bcc) metals and alloys, including high-alloying steels. Recent theoretical calculations also suggest that the ω structure may act as an intermediate phase for face-centred cubic (fcc)-to-bcc transformation. Thus far, the role of the ω phase played in fcc-bcc martensitic transformation in carbon steels has not been reported. In previous investigations on martensitic carbon steels, extra electron diffraction spots were frequently observed by transmission electron microscopy (TEM), and these spots were historically ascribed to the diffraction arising from either internal twins or carbides. In this paper, an intensive TEM investigation revealed that the extra spots are in fact attributed to the metastable ω phase in particle-like morphology with an overall size of several or dozens of nanometres. The strict orientation relationships between the ω phase and the ferrite matrix are in good agreement with those of the hexagonal (P6/mmm) ω phase in other bcc metals and alloys. The identification of the ω phase as well as the extra diffraction spots might provide a clue to help understand the physical mechanism of martensitic transformation in steels.

  15. A new nanoscale metastable iron phase in carbon steels.

    PubMed

    Liu, Tianwei; Zhang, Danxia; Liu, Qing; Zheng, Yanjun; Su, Yanjing; Zhao, Xinqing; Yin, Jiang; Song, Minghui; Ping, Dehai

    2015-10-27

    Metastable ω phase is common in body-centred cubic (bcc) metals and alloys, including high-alloying steels. Recent theoretical calculations also suggest that the ω structure may act as an intermediate phase for face-centred cubic (fcc)-to-bcc transformation. Thus far, the role of the ω phase played in fcc-bcc martensitic transformation in carbon steels has not been reported. In previous investigations on martensitic carbon steels, extra electron diffraction spots were frequently observed by transmission electron microscopy (TEM), and these spots were historically ascribed to the diffraction arising from either internal twins or carbides. In this paper, an intensive TEM investigation revealed that the extra spots are in fact attributed to the metastable ω phase in particle-like morphology with an overall size of several or dozens of nanometres. The strict orientation relationships between the ω phase and the ferrite matrix are in good agreement with those of the hexagonal (P6/mmm) ω phase in other bcc metals and alloys. The identification of the ω phase as well as the extra diffraction spots might provide a clue to help understand the physical mechanism of martensitic transformation in steels.

  16. A new nanoscale metastable iron phase in carbon steels

    PubMed Central

    Liu, Tianwei; Zhang, Danxia; Liu, Qing; Zheng, Yanjun; Su, Yanjing; Zhao, Xinqing; Yin, Jiang; Song, Minghui; Ping, Dehai

    2015-01-01

    Metastable ω phase is common in body-centred cubic (bcc) metals and alloys, including high-alloying steels. Recent theoretical calculations also suggest that the ω structure may act as an intermediate phase for face-centred cubic (fcc)-to-bcc transformation. Thus far, the role of the ω phase played in fcc-bcc martensitic transformation in carbon steels has not been reported. In previous investigations on martensitic carbon steels, extra electron diffraction spots were frequently observed by transmission electron microscopy (TEM), and these spots were historically ascribed to the diffraction arising from either internal twins or carbides. In this paper, an intensive TEM investigation revealed that the extra spots are in fact attributed to the metastable ω phase in particle-like morphology with an overall size of several or dozens of nanometres. The strict orientation relationships between the ω phase and the ferrite matrix are in good agreement with those of the hexagonal (P6/mmm) ω phase in other bcc metals and alloys. The identification of the ω phase as well as the extra diffraction spots might provide a clue to help understand the physical mechanism of martensitic transformation in steels. PMID:26503890

  17. Pressure dependence of prototype structures of metastable niobium oxides

    NASA Astrophysics Data System (ADS)

    Obara, Kozo

    1993-03-01

    Faculty of Engineering, Kagoshima University, Korimoto, 1-21-40, Kagoshima 890, Japan Pressure dependences of prototypes of nonstoichiometric metastable niobium oxides formed by a magnetron sputtering system were investigated. The morphology of derived crystals depended strongly on the argon pressure. At argon pressure PAr< 0.2 Torr, thin microcrystals with five types of superlattice structures were derived. Observed lattice constants were transformed into one another by simple lattice deformations within 1% error. All types of superlattice structures were related to the cubic lattice a0 = 3.22 Å. At PAr > 0.3 Torr, metastable niobium oxide super-fine particles with a cubic lattice constant a = 3.44 Å were obtained. Unique relationships between lattice constants were found on the oxidized niobium super-fine particles, NbO and NbO2 formed above 0.3 Torr within 0.5% error. In this case, the lattice structure with a = 3.44 ,Å (BCC) is related to all structures. These lattices a0 = 3.22 ,Å and a = 3.44 Å seem to be the prototypes at PAr ≤ 0.2 Torr and PAr ≥ 0.3 Tort, respectively. These structural changes due to pressure difference depend on the density and the enthalpy of vacancies in as-grown crystals. The density of vacancies is related to the condensation rate of the crystals.

  18. Metastable phases in mechanically alloyed aluminum germanium powders

    SciTech Connect

    Yvon, P.J.; Schwarz, R.B.

    1993-03-01

    Aluminum and germanium form a simple eutectic system with no stable intermetallic phase, and limited mutual solubility. We report the formation of a metastable rhombohedral,{gamma}{sub 1} phase by mechanically alloying aluminum and germanium powders. This phase, which appears for compositions between 20 and 50 at. % germanium, has also been observed in rapidly quenched alloys, but there is disagreement as to its composition. By measuring the heat of crystallization as a function of composition, we determined the composition of the {gamma}{sub 1} phase to be Al{sub 70}Ge{sub 30}. We also produced Al{sub 70}Ge{sub 30} by arc melting the pure elements, followed by splat-quenching at a cooling rate in the range of 10{sup 8} K s{sup {minus}1}. This method produced two metastable phases, one of which was found to be the {gamma}{sub 1} phase obtained by mechanical alloying. The other was a monoclinic phase reported earlier in the literature as {gamma}{sub 2}.

  19. Magnetic properties of Co-Cu metastable solid solution alloys

    NASA Astrophysics Data System (ADS)

    Fan, Xu; Mashimo, Tsutomu; Huang, Xinsheng; Kagayama, Tomoko; Chiba, Akira; Koyama, Keiichi; Motokawa, Mitsuhiro

    2004-03-01

    Metastable solid solution alloy powders and bulk alloys in the cobalt(Co)-copper(Cu) (10 90 mol % Co) system, which is an almost immiscible system at the ambient state, were prepared by mechanical alloying (MA) and shock compression. All MA-treated powders showed the x-ray diffraction patterns of a single phase of fcc structure. The lattice parameter increases with Cu concentration and is fundamentally on the line with Vegard’s law. The magnetization curves of CoxCu100-x (x=20 80) metastable bulk alloys at room temperature showed ferromagnetism, while the one of Co10Cu90 system showed paramagnetism. The saturation magnetic moment (Ms) curve versus electron numbers per atom at 0 K was found to be similar to the Slater-Pauling curves of other transition-metal binary systems and decreased with increasing Cu concentration and approached zero at about 28.8 electrons per atom. The magnetoresistance ratio at room temperature increased with Cu content in the ferromagnetic region, while the one of the paramagnetic Co10Cu90 alloy was negligibly small.

  20. Extrapolating bound state data of anions into the metastable domain

    NASA Astrophysics Data System (ADS)

    Feuerbacher, Sven; Sommerfeld, Thomas; Cederbaum, Lorenz S.

    2004-10-01

    Computing energies of electronically metastable resonance states is still a great challenge. Both scattering techniques and quantum chemistry based L2 methods are very time consuming. Here we investigate two more economical extrapolation methods. Extrapolating bound states energies into the metastable region using increased nuclear charges has been suggested almost 20 years ago. We critically evaluate this attractive technique employing our complex absorbing potential/Green's function method that allows us to follow a bound state into the continuum. Using the 2Πg resonance of N2- and the 2Πu resonance of CO2- as examples, we found that the extrapolation works suprisingly well. The second extrapolation method involves increasing of bond lengths until the sought resonance becomes stable. The keystone is to extrapolate the attachment energy and not the total energy of the system. This method has the great advantage that the whole potential energy curve is obtained with quite good accuracy by the extrapolation. Limitations of the two techniques are discussed.

  1. Loss Processes of Metastable Molecules in Cylindrical Cavity

    NASA Astrophysics Data System (ADS)

    Suzuki, Susumu; Itoh, Haruo

    2000-10-01

    Assuming a closed cylindrical volume, the spatiotemporal variation of the density distribution of the metastable molecules N_2(A^3Σ_u^+) in the cylindrical volume are calculated from the diffusion equation analysis under the different reflection coefficients at the flat electrode surfaces and at the cylindrical wall.(S.Suzuki, H.Itoh, N.Ikuta and H.Sekizawa:Jpn. J. Appl. Phys., 39, 1333, 2000)(S. Suzuki, H. Itoh, H. Sekizawa and N. Ikuta: Papers of Technical Meeting on Electrical Discharges, ED-98-128, 17, 1998 (in Japanese)) We solve the diffusion equation by separation of variables using the boundary condition of the third kind that is taken account of the reflection at the electrode surfaces.(S. Suzuki, H. Itoh, N. Ikuta and H. Sekizawa: J. Phys. D : Appl. Phys., 25, 1568, 1992) The obtained solution of the diffusion equation are possible to describe the density profiles along the longitudinal and the radial directions. The influence of the density distribution by the different reflection coefficient at each of electrodes and at the cylindrical wall is investigated. Furthermore, the effective lifetime of the diffusing metastable molecules is also discussed under different reflection coefficients.

  2. Metastable states in calcium phosphate - aqueous phase equilibrations

    NASA Astrophysics Data System (ADS)

    Driessens, F. C. M.; Verbeeck, R. M. H.

    1981-05-01

    A critical evaluation of the literature reveals that during equilibration of well crystallized hydroxyapatite in aqueous solutions metastable states can occur. They are characterized by a persistent supersaturation with respect to hydroxyapatite and a systematical dependence of the ion activity product of this compound on the solution composition. For products synthesized by thermal treatment it is known that they are transformed into oxyhydroxyapatite so that the theoretical solubility behaviour could be predicted from the extrapolated value of the free energy of oxyapatite at room temperature: the negative logarithm of the ionic product for hydroxyapatite should become close to that of oxyapatite during equilibration. The discrepancy with experimental data is probably due to the formation of thin layers seeming dicalcium phosphate dihydrate, octocalcium phosphate or defective hydroxyapatite as coatings on the apatite crystals. This is derived from the apparent Ca/P ratio of the solubility controlling phase. According to chemical potential plots this apparent Ca/P ratio can have values close to 1, 1.33, 1.50 or 1.67. The aqueous solutions are clearly undersaturated with respect to the more acidic calcium phosphates so that the coatings must deviate from the compositions of these compounds in their pure state. The formation of these metastable states during equilibration of oxyhydroxyapatites is compared with others occuring during precipitation and crystal growth of calcium phosphates. A model is proposed which explains the observations qualitatively.

  3. Metastable Lennard-Jones fluids. II. Thermal conductivity.

    PubMed

    Baidakov, Vladimir G; Protsenko, Sergey P

    2014-06-07

    The method of equilibrium molecular dynamics with the use of the Green-Kubo formalism has been used to calculate the thermal conductivity λ in stable and metastable regions of a Lennard-Jones fluid. Calculations have been made in the range of reduced temperatures 0.4 ≤ T* = k(b)T/ε ≤ 2.0 and densities 0.01 ≤ ρ* = ρσ³ ≤ 1.2 on 15 isotherms for 234 states, 130 of which refer to metastable regions: superheated and supercooled liquids, supersaturated vapor. Equations have been built up which describe the dependence of the regular part of the thermal conductivity on temperature and density, and also on temperature and pressure. It has been found that in (p, T) variables in the region of a liquid-gas phase transition a family of lines of constant value of excess thermal conductivity Δλ = λ - λ0, where λ0 is the thermal conductivity of a dilute gas, has an envelope which coincides with the spinodal. Thus, at the approach to the spinodal of a superheated liquid and supersaturated vapor (∂Δλ/∂p)T → ∞, (∂Δλ/∂T)p → ∞.

  4. Are metastable, precrystallisation, density-fluctuations a universal phenomena?

    PubMed

    Heeley, Ellen L; Poh, C Kit; Li, Wu; Maidens, Anna; Bras, Wim; Dolbnya, Igor P; Gleeson, Anthony J; Terrill, Nicolas J; Fairclough, J Patrick A; Olmsted, Peter D; Ristic, Rile I; Hounslow, Micheal J; Ryan, Anthony J

    2003-01-01

    In-situ observations of crystallisation in minerals and organic polymers have been made by simultaneous, time-resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) techniques. In isotactic polypropylene slow quiescent crystallisation shows the onset of large scale ordering prior to crystal growth. Rapid crystallisations studied by melt extrusion indicate the development of well resolved oriented SAXS patterns associated with long range order before the development of crystalline peaks in the WAXS region. Block copolymers self-assemble into mesophases in polymer melts above a critical chain length (or above a critical temperature) and this self-assembly process is shown to be susceptible to an incipient crystallisation. Mesophase formation is observed at anomalously high temperatures in ethylene-oxide containing block copolymers below the normal melting point of the polyoxy ethylene chains. Formation of calcium carbonate from aqueous solutions of sodium carbonate and calcium nitrate is observed to be a two-stage process and precipitation proceeds by the production of an amorphous metastable phase. This phase grows until it is volume filling and leads to the formation of the two polymorphs Calcite and Vaterite. These three sets of results suggest pre-nucleation density fluctuations, leading to a metastable phase, play an integral role in all three classes of crystallisation. In due course, this phase undergoes transformation to "normal" crystals.

  5. Deactivation of metastable single-crystal silicon hyperdoped with sulfur

    SciTech Connect

    Simmons, C. B.; Akey, Austin J.; Sullivan, Joseph T.; Buonassisi, Tonio; Krich, Jacob J.; Recht, Daniel; Aziz, Michael J.

    2013-12-28

    Silicon supersaturated with sulfur by ion implantation and pulsed laser melting exhibits broadband optical absorption of photons with energies less than silicon's band gap. However, this metastable, hyperdoped material loses its ability to absorb sub-band gap light after subsequent thermal treatment. We explore this deactivation process through optical absorption and electronic transport measurements of sulfur-hyperdoped silicon subject to anneals at a range of durations and temperatures. The deactivation process is well described by the Johnson-Mehl-Avrami-Kolmogorov framework for the diffusion-mediated transformation of a metastable supersaturated solid solution, and we find that this transformation is characterized by an apparent activation energy of E{sub A}=1.7 ± 0.1 eV. Using this activation energy, the evolution of the optical and electronic properties for all anneal duration-temperature combinations collapse onto distinct curves as a function of the extent of reaction. We provide a mechanistic interpretation of this deactivation based on short-range thermally activated atomic movements of the dopants to form sulfur complexes.

  6. Light-induced metastable defects or light-induced metastable H atoms in a-Si:H films?

    SciTech Connect

    Godet, C.

    1997-07-01

    In hydrogenated amorphous silicon (a-Si:H) films, the increase of the metastable defect density under high-intensity illumination is usually described by an empirical two-parameter stretched-exponential time dependence (characteristic time {tau}{sub SE} and dispersion parameter {beta}). In this study, a clearly different (one-parameter) analytic function is obtained from a microscopic model based on the formation of metastable H (MSH) atoms in a-Si:H films. Assuming that MSH atoms are the only mobile species, only three chemical reactions are significant: MSH are produced from doubly hydrogenated (SiH HSi) configurations and trapped either at broken bonds or Si-H bonds, corresponding respectively to light-induced annealing (LIA) and light-induced creation (LIC) of defects. Competition between trapping sites results in a saturation of N(t) at a steady-state value N{sub ss}. A one-parameter fit of this analytical function to experimental data is generally good, indicating that the use of a statistical distribution of trap energies is not necessary.

  7. Fragmentation of phosphorylated and singly charged peptide ions via interaction with metastable atoms

    PubMed Central

    Berkout, Vadym D.; Doroshenko, Vladimir M.

    2008-01-01

    Fragmentation of phosphorylated peptide ions via interaction with electronically excited metastable argon atoms was studied in a linear trap – time-of-flight mass spectrometer. Doubly charged ions of phosphorylated peptides from an Enolase digest were produced by electrospray ionization and subjected to a metastable atom beam in the linear trap. The metastable argon atoms were generated using a glow-discharge source. An intensive series of c- and z- ions were observed in all cases, with the phosphorylation group intact. The formation of molecular radical cations with reduced charge indicated that an electron transfer from a highly excited metastable state of argon to the peptide cation occurred. Additionally, singly charged Bradykinin, Substance P and Fibrinopeptide A molecular ions were fragmented via interaction with electronically excited metastable helium atoms. The fragmentation mechanism was different in this case and involved Penning ionization. PMID:19956340

  8. Metastability of the atomic structures of size-selected gold nanoparticles.

    PubMed

    Wells, Dawn M; Rossi, Giulia; Ferrando, Riccardo; Palmer, Richard E

    2015-04-21

    All nanostructures are metastable--but some are more metastable than others. Here we employ aberration-corrected electron microscopy and atomistic computer simulations to demonstrate the hierarchy of metastability in deposited, size-selected gold nanoparticles (clusters), an archetypal class of nanomaterials well known for the catalytic activity which only appears on the nanometer-scale. We show that the atomic structures presented by "magic number" Au561, Au742 and Au923 clusters are "locked". They are in fact determined by the solidification which occurs from the liquid state early in their growth (by assembly from atoms in the gas phase) followed by template growth. It is quite likely that transitions from a locked, metastable configuration to a more stable (but still metastable) structure, as observed here under the electron beam, will occur during catalytic reactions, for example.

  9. Observation and identification of metastable excited states in ultrafast laser-ionized pyridine.

    PubMed

    Foote, David B; Scarborough, Timothy D; Uiterwaal, Cornelis J G J

    2012-05-01

    We report on the fragmentation of ionized pyridine (C(5)H(5)N) molecules by focused 50 fs, 800 nm laser pulses. Such ionization produces several metastable ionic states that fragment within the field-free drift region of a reflectron-type time of flight mass spectrometer, with one particular metastable dissociation being the leading fragmentation process. Because the time of flight is no longer dependent in a simple way on the mass of the ion, the metastable decay is manifested as an unfocused peak on the mass spectrum that appears at a time of flight not corresponding to an integer mass. A previously-developed method is used to identify the precursor and final masses of these ions. The metastable process that creates the most prevalent peak is shown to be C(5)H(5)N(+) → C(4)H(4)(+) + HCN. Simulations confirm this result and place restrictions on the processes for several other observed metastable reactions.

  10. Optimization of crystal nucleation close to a metastable fluid-fluid phase transition.

    PubMed

    Wedekind, Jan; Xu, Limei; Buldyrev, Sergey V; Stanley, H Eugene; Reguera, David; Franzese, Giancarlo

    2015-06-22

    The presence of a metastable fluid-fluid critical point is thought to dramatically influence the crystallization pathway, increasing the nucleation rate by many orders of magnitude over the predictions of classical nucleation theory. We use molecular dynamics simulations to study the kinetics of crystallization in the vicinity of this metastable critical point and throughout the metastable fluid-fluid phase diagram. To quantitatively understand how the fluid-fluid phase separation affects the crystal nucleation, we evaluate accurately the kinetics and reconstruct the thermodynamic free-energy landscape of crystal formation. Contrary to expectations, we find no special advantage of the proximity of the metastable critical point on the crystallization rates. However, we find that the ultrafast formation of a dense liquid phase causes the crystallization to accelerate both near the metastable critical point and almost everywhere below the fluid-fluid spinodal line. These results unveil three different scenarios for crystallization that could guide the optimization of the process in experiments.

  11. Phase diagram with a region of liquid carbon-diamond metastable states

    NASA Astrophysics Data System (ADS)

    Basharin, A. Yu.; Dozhdikov, V. S.; Kirillin, A. V.; Turchaninov, M. A.; Fokin, L. R.

    2010-06-01

    Metastable cubic diamond has been found in the structure of solid carbon obtained by quenching of a liquid phase at a pressure (0.012 GPa) much lower than that corresponding to the existence of stable diamond. It is suggested that this metastable diamond is formed as a result of the recalescence of supercooled liquid carbon to the melting point ( T dm) of metastable diamond due to a lower energy barrier for the formation of diamond as compared to that of graphite. A comparison between the calculated Gibbs energies of metastable phases provided an estimate of T dm = 4160 ± 50 K. For the first time, metastable continuations of the curve of diamond melting at pressures of up to 0.012 GPa are constructed on the phase diagrams of carbon (according to various published data) using analytical curves described by a two-parametric Simon equation.

  12. Fluid simulation for influence of metastable atoms on the characteristics of capacitively coupled argon plasmas

    SciTech Connect

    Zhang Yuru; Xu Xiang; Wang Younian

    2010-03-15

    One-dimensional self-consistent fluid model is used to simulate the capacitively coupled argon plasma, in which the metastable effect on the plasma parameters at different discharge conditions is investigated. The results show that due to the metastable atom existence, the bulk plasma density drops significantly, especially at high pressures, high voltages, and high frequencies, accompanied by the decrease in electron temperature in the bulk. When the pressure and voltage are high, the metastable atom density is characterized by a saddle distribution in the axis direction. However, with the decrease in voltage and pressure, the metastable atom density becomes a parabolic distribution. Besides, the curve of plasma density with frequency has a minimum, and so is the profile of metastable atom density.

  13. Fragmentation of phosphorylated and singly charged peptide ions via interaction with metastable atoms.

    PubMed

    Berkout, Vadym D; Doroshenko, Vladimir M

    2008-12-01

    Fragmentation of phosphorylated peptide ions via interaction with electronically excited metastable argon atoms was studied in a linear trap - time-of-flight mass spectrometer. Doubly charged ions of phosphorylated peptides from an Enolase digest were produced by electrospray ionization and subjected to a metastable atom beam in the linear trap. The metastable argon atoms were generated using a glow-discharge source. An intensive series of c- and z- ions were observed in all cases, with the phosphorylation group intact. The formation of molecular radical cations with reduced charge indicated that an electron transfer from a highly excited metastable state of argon to the peptide cation occurred. Additionally, singly charged Bradykinin, Substance P and Fibrinopeptide A molecular ions were fragmented via interaction with electronically excited metastable helium atoms. The fragmentation mechanism was different in this case and involved Penning ionization.

  14. Infrared absorption related to the metastable state of arsenic antisite defects in electron-irradiated GaAs

    SciTech Connect

    Kuisma, S.; Saarinen, K.; Hautojaervi, P.; Corbel, C.

    1996-12-31

    A metastable irradiation-induced vacancy is detected by positrons in semi-insulating GaAs. The vacancy is associated with the metastable state of an irradition-induced As-antisite-related defect. This metastable state absorbs IR light in contrast to the metastable state of the As-antisite-related native EL2 defect. This property can be explained by the presence of other defects complexed with the As antisite in electron-irradiated GaAs.

  15. Bone-like crack resistance in hierarchical metastable nanolaminate steels

    NASA Astrophysics Data System (ADS)

    Koyama, Motomichi; Zhang, Zhao; Wang, Meimei; Ponge, Dirk; Raabe, Dierk; Tsuzaki, Kaneaki; Noguchi, Hiroshi; Tasan, Cemal Cem

    2017-03-01

    Fatigue failures create enormous risks for all engineered structures, as well as for human lives, motivating large safety factors in design and, thus, inefficient use of resources. Inspired by the excellent fracture toughness of bone, we explored the fatigue resistance in metastability-assisted multiphase steels. We show here that when steel microstructures are hierarchical and laminated, similar to the substructure of bone, superior crack resistance can be realized. Our results reveal that tuning the interface structure, distribution, and phase stability to simultaneously activate multiple micromechanisms that resist crack propagation is key for the observed leap in mechanical response. The exceptional properties enabled by this strategy provide guidance for all fatigue-resistant alloy design efforts.

  16. Dynamic control of metastable remanent states in mesoscale magnetic elements

    SciTech Connect

    Ding, J.; Jain, S.; Pearson, J. E.; Lendinez, S.; Khovaylo, V.; Novosad, V.

    2015-05-07

    The formation of the vortex-antivortex-vortex (v-av-v) metastable remanent states in elongated magnetic elements have been systematically investigated using micromagnetic modeling. It is demonstrated that the v-av-v magnetization pattern can be effectively stabilized by exciting the single vortex state with an external RF field. Furthermore, we show that a set of different polarity combinations of the vortex cores can be achieved by adjusting the frequency and amplitude of the excitation field. The corresponding dynamic response in time- and frequency-domain has also been presented. Owing to the diversity of the collective modes with different vortex-antivortex combinations, this system may open promising perspectives in the area of spin transfer torque oscillators.

  17. Limit of metastability for liquid and vapor phases of water.

    PubMed

    Cho, Woo Jong; Kim, Jaegil; Lee, Joonho; Keyes, Thomas; Straub, John E; Kim, Kwang S

    2014-04-18

    We report the limits of superheating of water and supercooling of vapor from Monte Carlo simulations using microscopic models with configurational enthalpy as the order parameter. The superheating limit is well reproduced. The vapor is predicted to undergo spinodal decomposition at a temperature of Tspvap=46±10 °C (0 °C≪Tspvap≪100 °C) under 1 atm. The water-water network begins to form at the supercooling limit of the vapor. Three-dimensional water-water and cavity-cavity unbroken networks are interwoven at critically superheated liquid water; if either network breaks, the metastable state changes to liquid or vapor.

  18. Room-temperature metastability of multilayer graphene oxide films.

    PubMed

    Kim, Suenne; Zhou, Si; Hu, Yike; Acik, Muge; Chabal, Yves J; Berger, Claire; de Heer, Walt; Bongiorno, Angelo; Riedo, Elisa

    2012-05-06

    Graphene oxide potentially has multiple applications. The chemistry of graphene oxide and its response to external stimuli such as temperature and light are not well understood and only approximately controlled. This understanding is crucial to enable future applications of this material. Here, a combined experimental and density functional theory study shows that multilayer graphene oxide produced by oxidizing epitaxial graphene through the Hummers method is a metastable material whose structure and chemistry evolve at room temperature with a characteristic relaxation time of about one month. At the quasi-equilibrium, graphene oxide reaches a nearly stable reduced O/C ratio, and exhibits a structure deprived of epoxide groups and enriched in hydroxyl groups. Our calculations show that the structural and chemical changes are driven by the availability of hydrogen in the oxidized graphitic sheets, which favours the reduction of epoxide groups and the formation of water molecules.

  19. Multistability and metastability: understanding dynamic coordination in the brain.

    PubMed

    Kelso, J A Scott

    2012-04-05

    Multistable coordination dynamics exists at many levels, from multifunctional neural circuits in vertebrates and invertebrates to large-scale neural circuitry in humans. Moreover, multistability spans (at least) the domains of action and perception, and has been found to place constraints upon, even dictating the nature of, intentional change and the skill-learning process. This paper reviews some of the key evidence for multistability in the aforementioned areas, and illustrates how it has been measured, modelled and theoretically understood. It then suggests how multistability--when combined with essential aspects of coordination dynamics such as instability, transitions and (especially) metastability--provides a platform for understanding coupling and the creative dynamics of complex goal-directed systems, including the brain and the brain-behaviour relation.

  20. Raman studies of methane-ethane hydrate metastability.

    PubMed

    Ohno, Hiroshi; Strobel, Timothy A; Dec, Steven F; Sloan, E Dendy; Koh, Carolyn A

    2009-03-05

    The interconversion of methane-ethane hydrate from metastable to stable structures was studied using Raman spectroscopy. sI and sII hydrates were synthesized from methane-ethane gas mixtures of 65% or 93% methane in ethane and water, both with and without the kinetic hydrate inhibitor, poly(N-vinylcaprolactam). The observed faster structural conversion rate in the higher methane concentration atmosphere can be explained in terms of the differences in driving force (difference in chemical potential of water in sI and sII hydrates) and kinetics (mass transfer of gas and water rearrangement). The kinetic hydrate inhibitor increased the conversion rate at 65% methane in ethane (sI is thermodynamically stable) but retards the rate at 93% methane in ethane (sII is thermodynamically stable), implying there is a complex interaction between the polymer, water, and hydrate guests at crystal surfaces.

  1. Singlet scalar dark matter: Monochromatic gamma rays and metastable vacua

    NASA Astrophysics Data System (ADS)

    Profumo, Stefano; Ubaldi, Lorenzo; Wainwright, Carroll

    2010-12-01

    We calculate the pair-annihilation cross section of real scalar singlet dark matter into two monoenergetic photons. We derive constraints on the theory parameter space from the Fermi limits on gamma-ray lines, and we compare with current limits from direct dark matter detection. We show that the new limits, albeit typically relevant only when the dark matter mass is close to half the standard model Higgs mass, rule out regions of the theory parameter space that are otherwise not constrained by other observations or experiments. In particular, the new excluded regions partly overlap with the parameter space where real scalar singlet dark matter might explain the anomalous signals observed by CDMS. We also calculate the lifetime of unstable vacuum configurations in the scalar potential, and show that the gamma-ray limits are quite relevant in regions where the electroweak vacuum is metastable with a lifetime longer than the age of the Universe.

  2. Waveform effects of a metastable olivine tongue in subducting slabs

    NASA Technical Reports Server (NTRS)

    Vidale, John E.; Williams, Quentin; Houston, Heidi

    1991-01-01

    Velocity models of subducting slabs with a kinetically-depressed olivine to beta- and gamma-spinel transition are constructed, and the effect that such structures would have on teleseismic P waveforms are examined using a full-wave finite-difference method. These 2D calculations yielded waveforms at a range of distances in the downdip direction. The slab models included a wedge-shaped, low-velocity metastable olivine tongue (MOTO) to a depth of 670 km, as well as a plausible thermal anomaly; one model further included a 10-km-thick fast layer on the surface of the slab. The principal effect of MOTO is to produce grazing reflections at wide angles off the phase boundary, generating a secondary arrival 0 to 4 seconds after the initial arrival depending on the take-off angle. The amplitude and timing of this feature vary with the lateral location of the seismic source within the slab cross-section.

  3. Fast metastable hydrogen atoms from H2 molecules: twin atoms

    NASA Astrophysics Data System (ADS)

    Trimèche, A.; Houdoux, D.; Rahmat, G.; Dulieu, O.; Schneider, I. F.; Medina, A.; Jalbert, G.; Zappa, F.; de Carvalho, C. R.; Nascimento, R. F.; de Castro Faria, N. V.; Robert, J.

    2015-01-01

    It is a difficult task to obtain "twin atoms", i.e. pairs of massive particles such that one can perform experiments in the same fashion that is routinely done with "twin photons". One possible route to obtain such pairs is by dissociating homonuclear diatomic molecules. We address this possibility by investigating the production of metastable H(2s) atoms coming from the dissociation of cold H2 molecules produced in a Campargue nozzle beam crossing an electron beam from a high intensity pulsed electron gun. Dissociation by electron impact was chosen to avoid limitations of target molecular excited states due to selection rules. Detectors placed several centimeters away from the collision center, and aligned with respect to possible common molecular dissociation channel, analyze the neutral fragments as a function of their time-of-flight (TOF) through Lyman-α detection. Evidence for the first time observed coincidence of pairs of H(2s) atoms obtained this way is presented.

  4. Charge metastability and hysteresis in the quantum Hall regime

    NASA Astrophysics Data System (ADS)

    Pollanen, J.; Eisenstein, J. P.; Pfeiffer, L. N.; West, K. W.

    2016-12-01

    We report simultaneous quasi-dc magnetotransport and high-frequency surface acoustic wave measurements on bilayer two-dimensional electron systems in GaAs. Near strong integer quantized Hall states, a strong magnetic-field-sweep hysteresis in the velocity of the acoustic waves is observed at low temperatures. This hysteresis indicates the presence of a metastable state with anomalously high conductivity in the interior of the sample. This nonequilibrium state is not revealed by conventional low-frequency transport measurements which are dominated by dissipationless transport at the edge of the two-dimensional system. We find that a field-cooling technique allows the equilibrium charge configuration within the interior of the sample to be established. A simple model for this behavior is discussed.

  5. Gain and lasing of optically pumped metastable rare gas atoms.

    PubMed

    Han, Jiande; Heaven, Michael C

    2012-06-01

    Optically pumped alkali vapor lasers are currently being developed in several laboratories. The objective is to construct high-powered lasers that also exhibit excellent beam quality. Considerable progress has been made, but there are technical challenges associated with the reactivity of the metal atoms. Rare gas atoms (Rg) excited to the np(5)(n+1)s (3)P(2) configuration are metastable and have spectral properties that are closely similar to those of the alkali metals. In principle, optically pumped lasers could be constructed using excitation of the np(5)(n+1)p←np(5)(n+1)s transitions. We have demonstrated this potential by observing gain and lasing for optically pumped Ar(*), Kr(*) and Xe(*). Three-level lasing schemes were used, with He or Ar as the collisional energy transfer agent that established the population inversion. These laser systems have the advantage of using inert reagents that are gases at room temperature.

  6. A Gravity Dual of Metastable Dynamical Supersymmetry Breaking

    SciTech Connect

    DeWolfe, Oliver; Kachru, Shamit; Mulligan, Michael; /Stanford U., Phys. Dept. /SLAC

    2008-02-04

    Metastable, supersymmetry-breaking configurations can be created in flux geometries by placing antibranes in warped throats. Via gauge/gravity duality, such configurations should have an interpretation as supersymmetry-breaking states in the dual field theory. In this paper, we perturbatively determine the asymptotic supergravity solutions corresponding to D3-brane probes placed at the tip of the cascading warped deformed conifold geometry, which is dual to an SU(N+M) x SU(N) gauge theory. The backreaction of the antibranes has the effect of introducing imaginary anti-self-dual flux, squashing the compact part of the space and forcing the dilaton to run. Using the generalization of holographic renormalization to cascading geometries, we determine the expectation values of operators in the dual field theory in terms of the asymptotic values of the supergravity fields.

  7. Miniature metastable ionization detectors for exobiology flight experiments

    NASA Technical Reports Server (NTRS)

    Woeller, F. H.

    1986-01-01

    The Metastable Ionization Detector (MID) is three orders of magnitude more sensitive than the thermal conductivity detectors used on previous flight instruments. The miniature MID provides scientists with a much smaller and highly sensitive detector for flight gas chromatographs. A miniature MID featuring an unconventional triaxial electrode configuration was developed and used routinely in the laboratory. Although much smaller and lighter than the commercial MID, its performance characteristics parallel those of the traditional design. The detector is compatible with the modulated voltage circuitry, also developed here, and thus can perform over an expanded response range of more than 7 orders magnitude. A micro volume version of a miniature MID, with an internal volume of less than 8 microliter, was recently designed is now being tested. The micro volume MID uses carrier gas flow rates of approx. 2cc/min thus eliminating the need for makeup gas when capillary columns are used.

  8. Metastability of solitons in a generalized Skyrme model

    NASA Astrophysics Data System (ADS)

    Pottinger, D. E. L.; Rathske, E.

    1986-04-01

    We consider soliton solutions in the generalized chirally symmetric Skyrme model which includes, in addition to the usual commutator term, a symmetric term of fourth order in the field derivatives. The classical energy of static hedgehog field configurations is determined numerically as a function of the angle characterizing the relative contribution of these two terms. Next to the Skyrme combination, we find a region where numerical solutions either are metastable (due to the energy being unbounded from below) or do not exist at all. We also study the exact quantization of the isorotational collective coordinates. Our conclusion is that, demanding consistency with meson phenomenology for the signs of the parameters, the model discussed in this paper can lead to reliable physical results only for small deviations from Skyrme's original stabilizing term.

  9. Interactions of Rubidium and Metastable Argon at Ultracold Temperatures

    NASA Astrophysics Data System (ADS)

    Shaffer, M. K.

    2005-05-01

    We are investigating the interaction between ultracold rubidium (Rb) and ultracold metastable argon (Ar*) simultaneously confined in a dual species magneto-optical trap (MOT). We will report on recent quantitative measurements of the inter-species trap loss coefficients and present our preliminary results on photoassociative spectra of the Rb-Ar* complex. We will also report on studies of Penning and associative ionization in the MOT using a modified residual gas analyzer (RGA) as a detector. Finally, we will discuss the prospects for producing and spatially confining ultracold ground state RbAr, a weakly-bound van der Waals molecule. Support provided by the National Science Foundation and the Office of Naval Research.

  10. Probing metastability in oxygen deficient YMn2O5

    NASA Astrophysics Data System (ADS)

    Pal, Sudip; Kumar, Kranti; Banerjee, A.

    2017-05-01

    In this article magnetic properties of YMn2O5-δ (δ=0.062) has been investigated through DC magnetization and ac susceptibility measurements. Sample has been prepared through chemical route. Iodometric titration has been used to determine oxygen deficiency and average Mn valance. Significant changes in magnetic properties have been found due to oxygen deficiency in the sample. It is observed that at low field, oxygen deficient sample undergoes only one phase transition around 42K but at higher applied field it shows three magnetic phase transitions while cooling those can be related to phase transitions found in stoichiometric sample. Frequency dependence of ac susceptibility indicates towards metastable nature of low temperature phase observed at low field. This is further buttressed by magnetic relaxation measurements.

  11. Coexistence of multiple metastable polytypes in rhombohedral bismuth

    PubMed Central

    Shu, Yu; Hu, Wentao; Liu, Zhongyuan; Shen, Guoyin; Xu, Bo; Zhao, Zhisheng; He, Julong; Wang, Yanbin; Tian, Yongjun; Yu, Dongli

    2016-01-01

    Derivative structural polytypes coexisting with the rhombohedral A7 structure of elemental bismuth (Bi) have been discovered at ambient condition, based on microstructure analyses of pure Bi samples treated under high pressure and high temperature conditions. Three structures with atomic positions close to those of the A7 structure have been identified through first-principles calculations, showing these polytypes energetically comparable to the A7 structure under ambient condition. Simulated diffraction data are in excellent agreement with the experimental observations. We argue that previously reported some variations of physical properties (e.g., density, electrical conductivity, and magnetism) in bismuth could be due to the formation of these polytypes. The coexistence of metastable derivative structural polytypes may be a widely occurring phenomenon in other elemental materials. PMID:26883895

  12. Statistical Properties of Metastable Intermediates in DNA Unzipping

    NASA Astrophysics Data System (ADS)

    Huguet, J. M.; Forns, N.; Ritort, F.

    2009-12-01

    We unzip DNA molecules using optical tweezers and determine the sizes of the cooperatively unzipping and zipping regions separating consecutive metastable intermediates along the unzipping pathway. Sizes are found to be distributed following a power law, ranging from one base pair up to more than a hundred base pairs. We find that a large fraction of unzipping regions smaller than 10 bp are seldom detected because of the high compliance of the released single stranded DNA. We show how the compliance of a single nucleotide sets a limit value around 0.1N/m for the stiffness of any local force probe aiming to discriminate one base pair at a time in DNA unzipping experiments.

  13. Modeling of a dual-wavelength pumped metastable argon laser

    NASA Astrophysics Data System (ADS)

    Gao, Jun; Sun, PengFei; Wang, XinBing; Zuo, DuLuo

    2017-03-01

    Optically pumped metastable argon laser is an attractive research topic of innovative gas lasers, but the slow collisional relaxation rates of 1s 4-1s 5 (in Paschen notation) may form a bottleneck on the cycling of active atoms and decrease the laser output at room temperature. Here, by employing a method of a dual-wavelength pump, we demonstrate the removal of accumulation on the 1s 4 level and the improvement of output power in the simulation. The simulated results show that a large increase in laser output is possible with a relatively weak assistant pump intensity. This method offers a feasible way to scale the laser to higher gain.

  14. Waveform effects of a metastable olivine tongue in subducting slabs

    NASA Technical Reports Server (NTRS)

    Vidale, John E.; Williams, Quentin; Houston, Heidi

    1991-01-01

    Velocity models of subducting slabs with a kinetically-depressed olivine to beta- and gamma-spinel transition are constructed, and the effect that such structures would have on teleseismic P waveforms are examined using a full-wave finite-difference method. These 2D calculations yielded waveforms at a range of distances in the downdip direction. The slab models included a wedge-shaped, low-velocity metastable olivine tongue (MOTO) to a depth of 670 km, as well as a plausible thermal anomaly; one model further included a 10-km-thick fast layer on the surface of the slab. The principal effect of MOTO is to produce grazing reflections at wide angles off the phase boundary, generating a secondary arrival 0 to 4 seconds after the initial arrival depending on the take-off angle. The amplitude and timing of this feature vary with the lateral location of the seismic source within the slab cross-section.

  15. Metastable Frenkel Pair Defect in Graphite: Source of Wigner Energy?

    NASA Astrophysics Data System (ADS)

    Ewels, C. P.; Telling, R. H.; El-Barbary, A. A.; Heggie, M. I.; Briddon, P. R.

    2003-07-01

    The atomic processes associated with energy storage and release in irradiated graphite have long been subject to untested speculation. We examine structures and recombination routes for interstitial-vacancy (I-V) pairs in graphite. Interaction results in the formation of a new metastable defect (an intimate I-V pair) or a Stone-Wales defect. The intimate I-V pair, although 2.9eV more stable than its isolated constituents, still has a formation energy of 10.8eV. The barrier to recombination to perfect graphite is calculated to be 1.3eV, consistent with the experimental first Wigner energy release peak at 1.38eV. We expect similar defects to form in carbon nanostructures such as nanotubes, nested fullerenes, and onions under irradiation.

  16. Hydrogen induced stabilization of meta-stable Mg-Ti

    NASA Astrophysics Data System (ADS)

    Jensen, I. J. T.; Diplas, S.; Løvvik, O. M.

    2012-03-01

    The hydrogenation of Mg0.8125Ti0.1875 was investigated by density functional calculations, using a model where Ti was segregated into nano-clusters. Introducing small amounts of hydrogen resulted in significant stabilization, with the mixing enthalpy (cohesive energy relative to standard state elements) becoming negative for hydrogen contents exceeding 0.07 H per metal. H prefers sites on the interface between Mg and Ti, with hydrogenation energies down to -115 kJ/(mol H2). Trapping of H on these very stable sites is proposed as an alternative explanation to why the reversibility of Mg-Ti thin films, which are initially meta-stable, can be preserved over many cycles of hydrogenation.

  17. Two-color magneto-optical trap for metastable helium

    SciTech Connect

    Tychkov, A.S.; Koelemeij, J.C.J.; Jeltes, T.; Hogervorst, W.; Vassen, W.

    2004-05-01

    We describe a powerful scheme which combines laser cooling on two transitions of metastable helium to obtain a high phase-space density. By running a sequence of a large 1083 nm magneto-optical trap (MOT) and a compressed 389 nm MOT, a density increase of more than one order of magnitude is achieved within 5 ms. After compression, 8x10{sup 8} atoms at a central density of 5x10{sup 10} cm{sup -3} remain, while the temperature of the cloud has been reduced from 1 mK to 0.4 mK. The resulting phase-space density (4.1x10{sup -6}) is more than one order of magnitude higher than what we achieved by 1083 nm laser cooling only.

  18. Radiation-sustained nanocluster metastability in oxide dispersion strengthened materials

    NASA Astrophysics Data System (ADS)

    Ribis, J.; Bordas, E.; Trocellier, P.; Serruys, Y.; de Carlan, Y.; Legris, A.

    2015-12-01

    ODS materials constitute a new promising class of structural materials for advanced fission and fusion energy application. These Fe-Cr based ferritic steels contain ultra-high density of dispersion-strengthening nanoclusters conferring excellent mechanical properties to the alloy. Hence, guarantee the nanocluster stability under irradiation remain a critical issue. Nanoclusters are non-equilibrium multicomponent compounds (YTiCrO) forming through a complex nucleation pathway during the elaboration process. In this paper, it is proposed to observe the response of these nanoclusters when the system is placed far from equilibrium by means of ion beam. The results indicate that the Y, Ti, O and Cr atoms self-organized so that nanoclusters coarsened but maintain their non-equilibrium chemical composition. It is discussed that the radiation-sustained nanocluster metastability emerges from cooperative effects: radiation-induced Ostwald ripening, permanent creation of vacancies in the clusters, and fast Cr diffusion mediated by interstitials.

  19. Metastable nanosized aluminum powder as a reactant in energetic formulations

    SciTech Connect

    Katz, J.; Tepper, F.; Ivanov, G.V.; Lerner, M.I.; Davidovich, V.

    1998-12-01

    Aluminum powder is an important ingredient in many propellant, explosives and pyrotechnic applications. The production of nanosized aluminum powder by the electroexplosion of metal wire has been practices in the former USSR since the mid 1970`s. Differential scanning calorimetry, differential thermal analysis and x-ray phase analysis was performed on aluminum powder both before and after air passivation, as well as aluminum that was protected under kerosene, pentane, toluene and hexane. Earlier Soviet reports of unexplained thermal releases and metastable behavior have been investigated. Anomalous behavior previously reported included phase transformations at temperatures far below melting with the release of heat and chemoluminescence and self sintering of particles with a heat release large enough to melt the powders.

  20. The surprising metastability of TeH2+.

    PubMed

    de Oliveira-Filho, Antonio G S; Ornellas, Fernando R

    2013-06-14

    A high-level ab initio investigation of a manifold of electronic states of the diatomic dication TeH(2+) is presented. Potential energy curves for both Λ + S and relativistic (Ω) states are constructed not only making evident the metastability of this system, but also the large energy splitting due to spin-orbit interactions. This effect is also very significant in the region close to the crossing of the (2)Π and (4)Σ(-) states, where avoided crossings between the Ω states have a relatively large impact on the height of the energy barriers. In contrast to TeH, with only two bound states (X1 (2)Π3∕2 and X2 (2)Π1∕2) below about 25,000 cm(-1), in the case of TeH(2+) a much richer energy profile is obtained indicating various possibilities of electronic transitions. Guided by the results of this study, the experimental characterization of these states is now a challenge to spectroscopists. Since close to the equilibrium region the double positive charge is centered on the tellurium atom, the binding in this system can be rationalized as a simple covalent bond between the pz and s orbitals of Te(2+) and H, respectively. As the internuclear distance increases, the electron affinity of Te(2+) overcomes that of H(+) and the system dissociates into two singly charged fragments. A simulation of the double ionization spectra complements the characterization of the electronic states, and results of a mass spectrometric investigation corroborates the predicted transient existence of this metastable species.

  1. Light-induced metastable states in ferroelectric oxides

    NASA Astrophysics Data System (ADS)

    Liu, G. K.; Vikhnin, V. S.; Kapphan, S. E.

    2007-07-01

    New Raman scattering lines (at 463 cm-1 and at 156 cm-1) induced by strong enough optical pumping in nominally pure KTaO3 crystals are manifested. The model of such effect is proposed. This model is based on the light-induced formation of metastable polar clusters constructed from bi-polaronic excitons - Charge Transfer Vibronic Excitons (CTVEs) with their high degree alignment. The CTVEs are caused by photo-carriers with high local concentration which are trapped to local potential wells related with long-range defect fields. CTVE formation are realized in these potential wells due to significant easing of charge transfer fluctuations induced by photo-carrier screening effects. This model is effective also for explanation of giant dielectric constant inducing by strong illumination which was detected recently in KTaO3 and SrTiO3 by Japanese investigators [M. Takesada, T. Yagi, M. Itoh, S. Koshihara, J. Phys. Soc. Jpn. 72 (2003) 37; T. Hasegawa, S. Mouri, Y. Yamada, K. Tanaka, J. Phys. Soc. Jpn. 72 (2003) 41; I. Katayama, Y. Ichikawa, K. Tanaka, Phys. Rev. B 67 (2003) 100102(R)]. Another aspect of the present study was specific recombination luminescence of CTVEs which was investigated here with respect to the influence of additional IR pumping. The present investigation has led to experimental evidence of new, mainly non-linear CTVE with good defined metastable behavior. Such an essentially anharmonic CTVE with respect to charge transfer and lattice displacements was predicted recently in our work [V.S. Vikhnin, Solid State Commun. 127 (2003) 283]. Here, we present experimental evidence of the existence of a new type of exciton state.

  2. Fast neutron spectroscopy with tensioned metastable fluid detectors

    NASA Astrophysics Data System (ADS)

    Grimes, T. F.; Taleyarkhan, R. P.

    2016-09-01

    This paper describes research into development of a rapid-turnaround, neutron-spectroscopy capable (gamma-beta blind), high intrinsic efficiency sensor system utilizing the tensioned metastable fluid detector (TMFD) architecture. The inability of prevailing theoretical models (developed successfully for the classical bubble chamber) to adequately predict detection thresholds for tensioned metastable fluid conditions is described. Techniques are presented to overcome these inherent shortcomings, leading thereafter, to allow successful neutron spectroscopy using TMFDs - via the newly developed Single Atom Spectroscopy (SAS) approach. SAS also allows for a unique means for rapidly determining neutron energy thresholds with TMFDs. This is accomplished by simplifying the problem of determining Cavitation Detection Events (CDEs) arising from neutron interactions with one in which several recoiling atom species contribute to CDEs, to one in which only one dominant recoil atom need be considered. The chosen fluid is Heptane (C7H16) for which only recoiling C atoms contribute to CDEs. Using the SAS approach, the threshold curve for Heptane was derived using isotope neutron source data, and then validated against experiments with mono-energetic (2.45/14 MeV) neutrons from D-D and D-T accelerators. Thereafter the threshold curves were used to produce the response matrix for various geometries. The response matrices were in turn combined with experimental data to recover the continuous spectra of fission (Cf-252) and (α,n) Pu-Be isotopic neutron sources via an unfolding algorithm. A generalized algorithm is also presented for performing neutron spectroscopy using any other TMFD fluid that meets the SAS approach assumptions.

  3. Metastic Progression of Breast Cancer by Allelic Loss on Chromosome 18q21

    DTIC Science & Technology

    2006-03-01

    Smad5 Smad2 Smad3 Smad8 Smad6 Samd7 MH1 Linker MH2 S1 S2 S3 Smad4 Smad1, Smad5 Samd2, Smad3 ,Smad8 Smad6,Smad7 ?? ?? A. B. Figure 1...homologous amino acid sequences at their N- and C- terminal regions (MH1 and MH2 respectively), which are separated by a highly divergent linker region...cancers (Figure 2). NB 2 3 4 5 6 7 8 9 10 11 12 13 14 Smad8α Smad8β Smad8γ Smad3α Smad3 β NB 1 2 3 4 5

  4. Introduction of metastable vacancy defects in electron-irradiated semi-insulating GaAs

    SciTech Connect

    Saarinen, K.; Kuisma, S.; Maekinen, J.; Hautojaervi, P.; Toernqvist, M.; Corbel, C.

    1995-05-15

    Positron-lifetime experiments have been performed to investigate the metastability of the point defects produced in the electron irradiation of semi-insulating GaAs. The measurements in darkness indicate the presence of Ga vacancies and Ga antisite defects in a negative charge state. Illumination at 25 K reveals another type of a defect, which has a vacancy in its metastable state. The metastable vacancies can be observed most effectively after illumination with 1.1-eV photons and they are persistent up to the annealing temperature of 80--100 K. The introduction rate of the metastable defects is about 0.3 cm{sup {minus}1}, which is close to the values reported earlier for the As antisite. The metastable properties of the defects resemble those of the well-known {ital EL}2 center in as-grown GaAs. We associate these defects to As antisites, which exhibit the metastability predicted by the theory: in the metastable configuration the As antisite atom relaxes away from the lattice position, leaving a Ga site vacant.

  5. Metastability of Subducted Slabs in the Mantle Transition Zone: A Collaborative Geodynamic, Petrologic, and Seismological Approach

    NASA Astrophysics Data System (ADS)

    Garber, J. M.; Billen, M. I.; Duncan, M. S.; Roy, C.; Ibourichene, A. S.; Olugboji, T.; Celine, C.; Rodríguez-González, J.; Grand, S. P.; Madrigal, P.; Sandiford, D.; Valencia-Cardona, J. J.

    2016-12-01

    Subducted slabs exhibit a range of geometries in the mantle transition zone. Studies of this phenomenon suggest that olivine and/or pyroxene metastability may profoundly alter the slab density profile, leading to slab flattening (e.g., King et al., 2015) and potentially yielding a resolvable seismological signature (e.g., Kawakatsu and Yoshioka, 2011; Yoshioka et al., 2015). Such metastability may also be critical for deep earthquake generation. Geodynamic modelling of this process is typically done with a simplified petrologic model of the downgoing slab, whereas petrologic studies of phase assemblages in subducted slabs typically impose an idealized geodynamic model with an unrealistic thermal structure. Connecting these two approaches should lead to a better understanding of the consequences of metastable assemblages on subducting slabs. Here, we present a new methodology that combines geodynamic, seismic and petrologic approaches to assess the impact of mineral metastability on dynamic subduction models, developed in a collaborative effort begun at the 2016 NSF CIDER summer program in Santa Barbara, CA. We use two parallel approaches to extrapolate equilibrium rock properties to metastable regions and impose these data on extracted time-slices from robust thermo-mechanical geodynamic models, allowing us to quantify the density and buoyancy changes in the slab that result from considering metastable phase assemblages. Our preliminary results suggest that metastable assemblages can yield a 10-30% density decrease over the subducted slab relative to an equilibrium reference model. We then generate a seismic velocity profile of the slab, and compute waveforms based on the 2D finite-difference method (e.g., Vidale & Helmberger, 1987) to determine whether metastable phases could reasonably be detected by different seismic approaches. Continuing analyses will be aimed at coupling the evolution of geodynamic models with phase metastability to model the feedback between

  6. Formation of a metastable phase due to the presence of impurities.

    PubMed

    Sear, Richard P

    2005-06-29

    Phase transitions into a new phase that is itself metastable are common; instead of the equilibrium phase nucleating, a metastable phase does so. When this occurs the system is sometimes said to be obeying Ostwald's rule. We show how this can happen when there are impurities present that reduce the barrier to heterogeneous nucleation of the metastable phase. We do so by studying a Potts lattice model using Monte Carlo simulation. Thus, which phase forms depends not only on the properties of the different phases but also on the impurities present. Understanding why systems obey Ostwald's rule may therefore require a study of the impurities present.

  7. The role of carrier gases in the production of metastable argon atoms in an RF discharge.

    SciTech Connect

    Rudinger, K.; Lu, Z. T.; Mueller, P.; Physics

    2009-03-01

    We investigate the role of carrier gases in the production of metastable argon atoms in a rf-driven discharge. The effects of different carrier gases (krypton, xenon, neon, and helium), carrier gas pressures, and rf discharge powers are examined. A xenon carrier gas provides the greatest metastable population of argon, yielding an optimal fractional metastable population of argon (Ar*/Ar) of 2 x 10{sup -4} at 0.2 mTorr of xenon gas. The optimal krypton configuration yields 60% of the xenon-supported population at 1.5 times higher pressure. Neon and helium perform considerably worse probably due to their higher ionization potentials.

  8. Effects of self-correlation time on stability of metastable state in logistic model

    NASA Astrophysics Data System (ADS)

    Yang, L. J.; Wang, C. J.

    2014-01-01

    Effects of colored noise on stability of metastable state in logistic model are studied by means of Fox approach and steepest-descent approximation. The expression for mean first-passage time from metastable state to stable state is derived firstly. Based on the expression, we analyze effects of colored noise. Results indicate: that stability of the metastable state always weakens as multiplicative noise intensity and additive noise intensity increase. However, it is always enhanced as self-correlation time of multiplicative noise and cross-correlation degree between multiplicative noise and additive noise increases.

  9. Metastable Changes to the Temperature Coefficients of Thin-Film Photovoltaic Modules

    SciTech Connect

    Deceglie, M. G.; Silverman, T. J.; Marion, B.; Kurtz, S. R.

    2014-07-01

    Transient changes in the performance of thin-film modules with light exposure are a well-known and widely reported phenomenon. These changes are often the result of reversible metastabilities rather than irreversible changes. Here we consider how these metastable changes affect the temperature dependence of photovoltaic performance. We find that in CIGS modules exhibiting a metastable increase in performance with light exposure, the light exposure also induces an increase in the magnitude of the temperature coefficient. It is important to understand such changes when characterizing temperature coefficients and when analyzing the outdoor performance of newly installed modules.

  10. Scattering of H(1s) off metastable helium atom at thermal energies

    SciTech Connect

    Sinha, Prabal K.; Ghosh, A. S.

    2006-06-15

    Quantal calculations for scattering of ground-state antihydrogen by metastable (n=2S) helium atoms have been performed using the nonadiabatic, atomic orbital expansion technique at thermal energies. The zero-energy elastic cross sections of the present systems are much greater than the corresponding value for the ground-state helium target. The low-energy elastic cross section for the singlet metastable helium [He(2 {sup 1}S)] target is higher than the corresponding value when the target is in the metastable triplet state [He(2 {sup 3}S)].

  11. Surface mediated assembly of small, metastable gold nanoclusters

    NASA Astrophysics Data System (ADS)

    Pettibone, John M.; Osborn, William A.; Rykaczewski, Konrad; Talin, A. Alec; Bonevich, John E.; Hudgens, Jeffrey W.; Allendorf, Mark D.

    2013-06-01

    The unique properties of metallic nanoclusters are attractive for numerous commercial and industrial applications but are generally less stable than nanocrystals. Thus, developing methodologies for stabilizing nanoclusters and retaining their enhanced functionality is of great interest. We report the assembly of PPh3-protected Au9 clusters from a heterogeneous mixture into films consisting of sub 3 nm nanocluster assemblies. The depositing nanoclusters are metastable in solution, but the resulting nanocluster assemblies are stabilized indefinitely in air or fresh solvent. The films exhibit distinct structure from Au nanoparticles observed by X-ray diffraction, and film dissolution data support the preservation of small nanoclusters. UV-Vis spectroscopy, electrospray ionization mass spectrometry, X-ray photoelectron spectroscopy and electron microscopy are used to elucidate information regarding the nanocluster formation and assembly mechanism. Preferential deposition of nanocluster assemblies can be achieved on multiple substrates, including polymer, Cr, Si, SiO2, SiNx, and metal-organic frameworks (MOFs). Unlike other vapor phase coating processes, nanocluster assembly on the MIL-68(In) MOF crystal is capable of preferentially coating the external surface and stabilizing the crystal structure in hydrothermal conditions, which should enhance their storage, separation and delivery capabilities.The unique properties of metallic nanoclusters are attractive for numerous commercial and industrial applications but are generally less stable than nanocrystals. Thus, developing methodologies for stabilizing nanoclusters and retaining their enhanced functionality is of great interest. We report the assembly of PPh3-protected Au9 clusters from a heterogeneous mixture into films consisting of sub 3 nm nanocluster assemblies. The depositing nanoclusters are metastable in solution, but the resulting nanocluster assemblies are stabilized indefinitely in air or fresh solvent. The

  12. Polymorphism, mesomorphism, and metastability of monoelaidin in excess water.

    PubMed Central

    Chung, H; Caffrey, M

    1995-01-01

    The polymorphic and metastable phase behavior of monoelaidin dry and in excess water was studied by using high-sensitivity differential scanning calorimetry and time-resolved x-ray diffraction in the temperature range of 4 degrees C to 60 degrees C. To overcome problems associated with a pronounced thermal history-dependent phase behavior, simultaneous calorimetry and time-resolved x-ray diffraction measurements were performed on individual samples. Monoelaidin/water samples were prepared at room temperature and stored at 4 degrees C for up to 1 week before measurement. The initial heating scan from 4 degrees C to 60 degrees C showed complex phase behavior with the sample in the lamellar crystalline (Lc0) and cubic (Im3m, Q229) phases at low and high temperatures, respectively. The Lc0 phase transforms to the lamellar liquid crystalline (L alpha) phase at 38 degrees C. At 45 degrees C, multiple unresolved lines appeared that coexisted with those from the L alpha phase in the low-angle region of the diffraction pattern that have been assigned previously to the so-called X phase (Caffrey, 1987, 1989). With further heating the X phase converts to the Im3m cubic phase. Regardless of previous thermal history, cooling calorimetric scans revealed a single exotherm at 22 degrees C, which was assigned to an L alpha+cubic (Im3m, Q229)-to-lamellar gel (L beta) phase transition. The response of the sample to a cooling followed by a reheating or isothermal protocol depended on the length of time the sample was incubated at 4 degrees C. A model is proposed that reconciles the complex polymorphic, mesomorphic, and metastability interrelationships observed with this lipid/water system. Dry monoelaidin exists in the lamellar crystalline (beta) phase in the 4 degrees C to 45 degrees C range. The beta phase transforms to a second lamellar crystalline polymorph identified as beta* at 45 degrees C that subsequently melts at 57 degrees C. The beta phase observed with dry monoelaidin is

  13. Polymorphism, mesomorphism, and metastability of monoelaidin in excess water.

    PubMed

    Chung, H; Caffrey, M

    1995-11-01

    The polymorphic and metastable phase behavior of monoelaidin dry and in excess water was studied by using high-sensitivity differential scanning calorimetry and time-resolved x-ray diffraction in the temperature range of 4 degrees C to 60 degrees C. To overcome problems associated with a pronounced thermal history-dependent phase behavior, simultaneous calorimetry and time-resolved x-ray diffraction measurements were performed on individual samples. Monoelaidin/water samples were prepared at room temperature and stored at 4 degrees C for up to 1 week before measurement. The initial heating scan from 4 degrees C to 60 degrees C showed complex phase behavior with the sample in the lamellar crystalline (Lc0) and cubic (Im3m, Q229) phases at low and high temperatures, respectively. The Lc0 phase transforms to the lamellar liquid crystalline (L alpha) phase at 38 degrees C. At 45 degrees C, multiple unresolved lines appeared that coexisted with those from the L alpha phase in the low-angle region of the diffraction pattern that have been assigned previously to the so-called X phase (Caffrey, 1987, 1989). With further heating the X phase converts to the Im3m cubic phase. Regardless of previous thermal history, cooling calorimetric scans revealed a single exotherm at 22 degrees C, which was assigned to an L alpha+cubic (Im3m, Q229)-to-lamellar gel (L beta) phase transition. The response of the sample to a cooling followed by a reheating or isothermal protocol depended on the length of time the sample was incubated at 4 degrees C. A model is proposed that reconciles the complex polymorphic, mesomorphic, and metastability interrelationships observed with this lipid/water system. Dry monoelaidin exists in the lamellar crystalline (beta) phase in the 4 degrees C to 45 degrees C range. The beta phase transforms to a second lamellar crystalline polymorph identified as beta* at 45 degrees C that subsequently melts at 57 degrees C. The beta phase observed with dry monoelaidin is

  14. Metastable epitaxial magnets: A study of growth and magnetic properties

    NASA Astrophysics Data System (ADS)

    Wu, Stella Zhong

    1997-11-01

    Recent advancement in the information storage industry is demanding more fundamental understanding of magnetic systems, especially the magnetic thin films, surfaces, and interfaces. In this work, we were focusing on ultrathin ferromagnetic thin films of Ni on Cu(100), Cu(110) and Cu(111) single crystal substrates, and FeNi and CoNi binary alloy films on Cu(100) with varying atomic concentration. The growth of these films by molecular beam epitaxy was monitored using a number of experimental techniques. A pseudomorphic layer-by-layer growth was achieved which resulted in an fcc metastable crystalline structure with a ferromagnetic phase. The magnetic anisotropy behavior of these thin films was monitored using surface magneto-optic Kerr effect magnetometer at both polar and longitudinal geometries, and various spin reorientation transitions were found. The measurements of Curie temperature as a variation of film thickness as well as atomic concentration resulted in the proposal of a finite-size scaling law. By using this scaling law, the bulk Curie temperature for these metastable fcc binary alloys can be extrapolated, showing that Fe atoms exist in a low-spin ferromagnetic phase. In the Ni films, a dimensionality crossover from bulk to a 2-dimensional system at a few monolayer thickness was established. By alloying, we have been able to tune the electron occupation number in the 3d band. Combined with the 3d electronic band structure information we have gained by using ultraviolet photoemission spectroscopy study of these systems at normal emission, a conclusion of continuous band filling in CoNi alloy system was drawn. However, FeNi films show a different behavior at a certain composition. The recent collaboration with synchrotron radiation facility has enabled us to quantitatively characterize the spin moment and orbital moment from each element. An x-ray magnetic circular dichroism (XMCD) study was performed on CoNi alloy system, and resulted in the conclusion of

  15. PAMELA, DAMA, INTEGRAL and signatures of metastable excited WIMPs

    SciTech Connect

    Finkbeiner, Douglas P.; Slatyer, Tracy R.; Weiner, Neal; Yavin, Itay E-mail: tslatyer@fas.harvard.edu E-mail: iyavin@princeton.edu

    2009-09-01

    Models of dark matter with ∼ GeV scale force mediators provide attractive explanations of many high energy anomalies, including PAMELA, ATIC, and the WMAP haze. At the same time, by exploiting the ∼ MeV scale excited states that are automatically present in such theories, these models naturally explain the DAMA/LIBRA and INTEGRAL signals through the inelastic dark matter (iDM) and exciting dark matter (XDM) scenarios, respectively. Interestingly, with only weak kinetic mixing to hypercharge to mediate decays, the lifetime of excited states with δ < 2m{sub electron} is longer than the age of the universe. The fractional relic abundance of these excited states depends on the temperature of kinetic decoupling, but can be appreciable. There could easily be other mechanisms for rapid decay, but the consequences of such long-lived states are intriguing. We find that CDMS constrains the fractional relic population of ∼ 100 keV states to be ∼< 10{sup −2}, for a 1 TeV WIMP with σ{sub n} = 10{sup −40} cm{sup 2}. Upcoming searches at CDMS, as well as xenon, silicon, and argon targets, can push this limit significantly lower. We also consider the possibility that the DAMA excitation occurs from a metastable state into the XDM state, which decays via e{sup +}e{sup −} emission, which allows lighter states to explain the INTEGRAL signal due to the small kinetic energies required. Such models yield dramatic signals from down-scattering, with spectra peaking at high energies, sometimes as high as ∼ 1 MeV, well outside the usual search windows. Such signals would be visible at future Ar and Si experiments, and may be visible at Ge and Xe experiments, although γ-rays associated with nuclear excitations would complicate the signal for these heavier targets. We also consider other XDM models involving ∼ 500 keV metastable states, and find they can allow lighter WIMPs to explain INTEGRAL as well.

  16. Metastable atomic species in the N2 flowing afterglow

    NASA Astrophysics Data System (ADS)

    Levaton, J.; Amorim, J.

    2012-03-01

    We have studied by optical emission spectroscopy the post-discharge of a pure N2 DC flowing discharge in such experimental conditions that the pink afterglow and the Lewis-Rayleigh afterglow occur. The emission profiles originated from the NB3Πg, NC3Πu and N2+B2Σu+ states and the NB3Πg,6≤v≤12 and NC3Πu,0≤v≤4 vibrational distributions were obtained in the post-discharge region. With basis on the works of Bockel et al. [S. Bockel, A.M. Diamy, A. Ricard, Surf. Coat. Tech. 74 (1995) 474] and Amorim and Kiohara [J. Amorim, V. Kiohara, Chem. Phys. Lett. 385 (2004) 268], we have obtained the experimental N(4S) and N(2D) relative densities along the post-discharge. A numerical model, previously developed to describe the neutral atomic, molecular and ionic species in the afterglow, was improved to include the kinetics of N(2D) and N(2P) states. Several kinetic mechanisms leading to the production of N(2D) in the post-discharge have been studied in order to explain the experimental data. We have determined that the dominant one is the reaction NX1Σg+,v>8+N(4S)→NX1Σg++N(2D) with an estimated rate constant of 7 × 10-14 cm3 s-1. Also, the fit of the numerical density profiles of NC3Πu and N2+B2Σu+ to the experimental ones has provided the rate constant for reaction NA3Σu++NX1∑g+,v>18→NC3Πu+NX1Σg+. Its estimated value is 4 × 10-13 cm3 s-1. Finally, with the new kinetic scheme, we have found that the ionization in the post-discharge region has important contribution of N(2D) and N(2P) species.

  17. Maternal nutrition at conception modulates DNA methylation of human metastable epialleles

    USDA-ARS?s Scientific Manuscript database

    In experimental animals, maternal diet during the periconceptional period influences the establishment of DNA methylation at metastable epialleles in the offspring, with permanent phenotypic consequences. Pronounced naturally occurring seasonal differences in the diet of rural Gambian women allowed ...

  18. Season of conception in rural Gambia affects DNA methylation at putative human metastable epialleles

    USDA-ARS?s Scientific Manuscript database

    Throughout most of the mammalian genome, genetically regulated developmental programming establishes diverse yet predictable epigenetic states across differentiated cells and tissues. At metastable epialleles (MEs), conversely, epigenotype is established stochastically in the early embryo then maint...

  19. Effect of metastables on a sustaining mechanism in inductively coupled plasma in Ar

    NASA Astrophysics Data System (ADS)

    Sato, Toshikazu; Makabe, Toshiaki

    2005-12-01

    We numerically predicted the spatial distribution of Ar metastables in an inductively coupled plasma (ICP) source; this distribution may be an indicator of the behavior of long-lived neutral radicals in a reactive plasma. We investigated the effect of metastables on the sustaining mechanism in ICP in Ar. The predicted two-dimensional profile of Ar metastables agreed reasonably well with experimental results. The transition of the sustaining mechanism from direct ionization to stepwise ionization is found as a function of input power at 50 mTorr. In addition, a strong hysteresis of plasma density is predicted between the increasing and decreasing phases of the input power based on the stepwise ionization of Ar metastables in the ICP.

  20. Role of the Bogachev - Mints Concept of Metastability of Austenite in Choosing Wear-Resistant Materials

    NASA Astrophysics Data System (ADS)

    Schastlivtsev, V. M.; Filippov, M. A.

    2005-01-01

    The significance of the Bogachev - Mints concept of metastability of austenite for the choice of strain-hardenable steel, cast iron, and facing alloys resisting mechanical kinds of wear (cavitation-, erosion-, and abrasion-induced) is discussed.

  1. Behavior of 23S metastable state He atoms in low-temperature recombining plasmas

    NASA Astrophysics Data System (ADS)

    Kajita, Shin; Tsujihara, Tadashi; Aramaki, Mitsutoshi; van der Meiden, Hennie; Oshima, Hiroshi; Ohno, Noriyasu; Tanaka, Hirohiko; Yasuhara, Ryo; Akiyama, Tsuyoshi; Fujii, Keisuke; Shikama, Taiichi

    2017-07-01

    We measured the electron density and temperature using laser Thomson scattering and metastable state (23S) of He atoms by laser absorption spectroscopy in the detached recombining plasmas in the divertor simulator NAGDIS-II. Using the measured electron density and temperature combined with the particle trajectory trace simulation, we discussed the behavior of the metastable state He atoms based on comparisons with the experimental results. It is shown that the metastable state atoms are mainly produced in the peripheral region of the plasma column, where the temperature is lower than the central part, and diffused in the vacuum vessel. It was shown that the 0D model is not valid and the transport of the metastable states is to be taken into account for the population distribution of He atoms in the detached plasmas.

  2. Metastable extensions of phase equilibrium lines and singular points of simple substance

    SciTech Connect

    Baidakov, V. G. Protsenko, S. P.

    2006-12-15

    The thermodynamic properties of crystal, liquid, and gas in the stable and metastable states have been determined by molecular dynamics simulation of a system of 2048 Lennard-Jones particles. The spinodals of a superheated crystal, a superheated liquid, and a supersaturated vapor have been approximated; the spinodal for a supercooled liquid turns out to be nonexistent. The liquid-vapor, liquid-crystal, and crystal-vapor equilibrium curves and their extensions beyond the triple point have been calculated. It has been shown that, as distinct from the metastable extension of the saturation curve, which terminates at the zero isotherm, the metastable melting and sublimation curves terminate at, respectively, the stretched liquid and superheated crystal spinodals. The properties of the critical end points of metastable equilibrium of extended phases are considered.

  3. FPGA Implementation of Metastability-Based True Random Number Generator

    NASA Astrophysics Data System (ADS)

    Hata, Hisashi; Ichikawa, Shuichi

    True random number generators (TRNGs) are important as a basis for computer security. Though there are some TRNGs composed of analog circuit, the use of digital circuits is desired for the application of TRNGs to logic LSIs. Some of the digital TRNGs utilize jitter in free-running ring oscillators as a source of entropy, which consume large power. Another type of TRNG exploits the metastability of a latch to generate entropy. Although this kind of TRNG has been mostly implemented with full-custom LSI technology, this study presents an implementation based on common FPGA technology. Our TRNG is comprised of logic gates only, and can be integrated in any kind of logic LSI. The RS latch in our TRNG is implemented as a hard-macro to guarantee the quality of randomness by minimizing the signal skew and load imbalance of internal nodes. To improve the quality and throughput, the output of 64-256 latches are XOR'ed. The derived design was verified on a Xilinx Virtex-4 FPGA (XC4VFX20), and passed NIST statistical test suite without post-processing. Our TRNG with 256 latches occupies 580 slices, while achieving 12.5Mbps throughput.

  4. Interactions between bosonic and fermionic metastable He atoms

    NASA Astrophysics Data System (ADS)

    Babb, J. F.

    2005-05-01

    Mixtures of spin-polarized metastable ^3He atoms and ^4He atoms are unique systems of current interest for studies of ultra-cold gases. The s-wave scattering length for collisions of ^4He atoms was measured to be ^4-4a=11.3 nm (+2.5,-1 nm) [1] and recent calculations find 8<^4-4a<12 nm [2]. The scattering length ^3-4a for fermion-boson collisions is presently indeterminate in sign and magnitude, but it has been predicted to fall in the ranges ^3-4a<-25 nm or ^3-4a>46 nm [2,3]. In this talk, with regard to improving the theoretical value of ^3-4a, the data characterizing ^3He(2,^3S)--^4He(2,^3S) interactions primarily in the molecular ^5σg^+ state are reevaluated and additional calculations are presented. Supported in part by the NSF. [1] S. Seidelin, et al., Phys. Rev. Lett. 93 (2004), 090409. [2] A. S. Dickinson, F. X. Gad'ea, and T. Leininger, J. Phys. B 37 (2004), 587. [3] R. J. W. Stas, J. M. McNamara, W. Hogervorst, and W. Vassen, Phys. Rev. Lett. 93 (2004), 053001.

  5. Metastable Mesoscopic Clusters in Solutions of Sickle-Cell Hemoglobin

    PubMed Central

    Pan, Weichun; Galkin, Oleg; Filobelo, Luis; Nagel, Ronald L.; Vekilov, Peter G.

    2007-01-01

    Sickle cell hemoglobin (HbS) is a mutant, whose polymerization while in deoxy state in the venous circulation underlies the debilitating sickle cell anemia. It has been suggested that the nucleation of the HbS polymers occurs within clusters of dense liquid, existing in HbS solutions. We use dynamic light scattering with solutions of deoxy-HbS, and, for comparison, of oxy-HbS and oxy-normal adult hemoglobin, HbA. We show that solutions of all three Hb variants contain clusters of dense liquid, several hundred nanometers in size, which are metastable with respect to the Hb solutions. The clusters form within a few seconds after solution preparation and their sizes and numbers remain relatively steady for up to 3 h. The lower bound of the cluster lifetime is 15 ms. The clusters exist in broad temperature and Hb concentration ranges, and occupy 10−5–10−2 of the solution volume. The results on the cluster properties can serve as test data for a potential future microscopic theory of cluster stability and kinetics. More importantly, if the clusters are a part of the nucleation mechanism of HbS polymers, the rate of HbS polymerization can be controlled by varying the cluster properties. PMID:17040989

  6. The Metastable Dynamo Model of Stellar Rotational Evolution

    NASA Astrophysics Data System (ADS)

    Brown, Timothy M.

    2014-07-01

    This paper introduces a new empirical model for the rotational evolution of Sun-like stars—those with surface convection zones and non-convective interior regions. Previous models do not match the morphology of observed (rotation period)-color diagrams, notably the existence of a relatively long-lived "C-sequence" of fast rotators first identified by Barnes. This failure motivates the Metastable Dynamo Model (MDM) described here. The MDM posits that stars are born with their magnetic dynamos operating in a mode that couples very weakly to the stellar wind, so their (initially very short) rotation periods at first change little with time. At some point, this mode spontaneously and randomly changes to a strongly coupled mode, the transition occurring with a mass-dependent lifetime that is of the order of 100 Myr. I show that with this assumption, one can obtain good fits to observations of young clusters, particularly for ages of 150-200 Myr. Previous models and the MDM both give qualitative agreement with the morphology of the slower-rotating "I-sequence" stars, but none of them have been shown to accurately reproduce the stellar-mass-dependent evolution of the I-sequence stars, especially for clusters older than a few hundred million years. I discuss observational experiments that can test aspects of the MDM, and speculate that the physics underlying the MDM may be related to other situations described in the literature, in which stellar dynamos may have a multi-modal character.

  7. James Franck and the Experimental Discovery of Metastable States

    NASA Astrophysics Data System (ADS)

    Gearhart, Clayton

    2016-03-01

    In 1913 and 1914, James Franck and Gustav Hertz published their experiments on inelastic collisions of slow electrons with helium and mercury vapor atoms. Famously, they thought they were measuring ionization energies, and not, as we understand it today, excitation energies. Franck and Hertz shortly found themselves in the army, and neither resumed experimental work until after the Great War. Nevertheless, these questions were cleared up over the course of the war, primarily through the work of experimentalists in North America, who remeasured the ionization energy of mercury and showed that Franck and Hertz had not detected ionization. After the war, Franck returned to experiments on and theoretical analyses of the collisions of slow electrons with helium atoms, in competition with others in England and America. This time, Franck and his associates were able to measure the ionization energy, and, in the process, to throw new light on the non-combining singlet and ``doublet'' (later found to be triplet) spectral series in helium. They also proposed for the first time the existence of metastable states, first in helium, and later in mercury and other elements, at a time when selection rules and theories of transition probabilities were in their infancy.

  8. Metastable Ice and Glass Formation in Atmospherically Relevant Aqueous Droplets

    NASA Astrophysics Data System (ADS)

    Murray, B. J.; Moehler, O.

    2008-12-01

    In this presentation an X ray diffraction study of homogeneous nucleation and the subsequent crystallisation of ice in aqueous organic acid solution droplets will be presented. Aqueous citric acid solutions have been chosen as a model system and are thought to be representative of organic material found in many upper tropospheric aerosols. It will be shown that the metastable cubic form of ice can nucleate, crystallise and is stabilised in citric acid solution droplets which freeze homogeneously below about 219 K. Cubic ice is only produced when ammonium bisulphate solution droplets freeze below about 183 K. This solute dependence is related to the viscosity and glass forming ability of the respective aqueous solutions. Experiments were also performed with more concentrated citric acid solution droplets, in which ice should nucleate at lower temperatures. It is found that ice crystallisation is inhibited below ~198 K in citric acid solution droplets. These droplets most likely formed ultra-viscous liquids or glassy material rather than crystallise. In order to test the impact of glassy particles on cloud formation, glassy citric acid particles were recently produced within the AIDA cloud simulation chamber in Karlsruhe Germany. Preliminary results suggest glassy citric acid aerosol do not produce an ice cloud via a homogeneous freezing route. In fact, ice particle production is markedly suppressed.

  9. Metastability in plyometric training on unstable surfaces: a pilot study

    PubMed Central

    2014-01-01

    Background In the past, plyometric training (PT) has been predominantly performed on stable surfaces. The purpose of this pilot study was to examine effects of a 7-week lower body PT on stable vs. unstable surfaces. This type of exercise condition may be denoted as metastable equilibrium. Methods Thirty-three physically active male sport science students (age: 24.1 ± 3.8 years) were randomly assigned to a PT group (n = 13) exercising on stable (STAB) and a PT group (n = 20) on unstable surfaces (INST). Both groups trained countermovement jumps, drop jumps, and practiced a hurdle jump course. In addition, high bar squats were performed. Physical fitness tests on stable surfaces (hexagonal obstacle test, countermovement jump, hurdle drop jump, left-right hop, dynamic and static balance tests, and leg extension strength) were used to examine the training effects. Results Significant main effects of time (ANOVA) were found for the countermovement jump, hurdle drop jump, hexagonal test, dynamic balance, and leg extension strength. A significant interaction of time and training mode was detected for the countermovement jump in favor of the INST group. No significant improvements were evident for either group in the left-right hop and in the static balance test. Conclusions These results show that lower body PT on unstable surfaces is a safe and efficient way to improve physical performance on stable surfaces. PMID:25089202

  10. Crossover dynamics at large metastability in gas-liquid nucleation.

    PubMed

    Santra, Mantu; Bagchi, Biman

    2011-03-01

    We have developed an alternate description of dynamics of nucleation in terms of an extended set of order parameters. The order parameters consist of an ordered set of kth largest clusters, ordered such that k= 1 is the largest cluster in the system, k= 2 is the second largest cluster, and so on. We have derived an analytic expression for the free energy for the kth largest cluster, which is in excellent agreement with the simulated results. At large supersaturation, the free energy barrier for the growth of the kth largest cluster disappears and the nucleation becomes barrierless. The major success of this extended theoretical formalism is that it can clearly explain the observed change in mechanism at large metastability [P. Bhimalapuram et al., Phys. Rev. Lett. 98, 206104 (2007)] and the associated dynamical crossover. The classical nucleation theory cannot explain this crossover. The crossover from activated to barrierless nucleation is found to occur at a supersaturation where multiple clusters cross the critical size. We attribute the crossover as the onset of the kinetic spinodal. We have derived an expression for the rate of nucleation in the barrierless regime by modeling growth as diffusion on the free energy surface of the largest cluster. The model reproduces the slower increase in the rate of growth as a function of supersaturation, as observed in experiments.

  11. Cell Lineage metastability in Gfi1-deficient mouse intestinal epithelium.

    PubMed

    Bjerknes, Matthew; Cheng, Hazel

    2010-09-01

    Elucidating the mechanisms determining multipotent progenitor cell fate remains a fundamental project of contemporary biology. Various tissues of mice and men with defects in the zinc-finger transcriptional repressor Gfi1 have dramatic perturbations in the proportions of their differentiated cell types. In Gfi1-deficient intestinal epithelium there is a shift from mucous and Paneth towards enteroendocrine cells, leading to the proposal that Gfi1 functions in the allocation of the progeny derived from a hypothetical common granulocytic progenitor. However, studies of clones have yielded no evidence of such a common progenitor prompting us to investigate alternate mechanisms explaining the Gfi1-deficient phenotype. We report that mucous and Paneth but not enteroendocrine lineage cells normally express Gfi1. Sporadic mucous and Paneth lineage cells in the crypts of Gfi1-deficient mice aberrantly express the pro-enteroendocrine transcription factor Neurog3, indicating that stable repression of Neurog3 in these lineages requires Gfi1. Importantly, we also find mucous and Paneth lineage cells in various stages of cellular reprogramming into the enteroendocrine lineage in Gfi1-deficient mice. We propose that mucous and Paneth cell lineage metastability, rather than reallocation at the level of a hypothetical common granulocytic progenitor, is responsible for the shifts in cell type proportions observed in Gfi1-deficient intestinal epithelium. Crown Copyright 2010. Published by Elsevier Inc. All rights reserved.

  12. Metastability in plyometric training on unstable surfaces: a pilot study.

    PubMed

    Kibele, Armin; Classen, Claudia; Muehlbauer, Thomas; Granacher, Urs; Behm, David G

    2014-01-01

    In the past, plyometric training (PT) has been predominantly performed on stable surfaces. The purpose of this pilot study was to examine effects of a 7-week lower body PT on stable vs. unstable surfaces. This type of exercise condition may be denoted as metastable equilibrium. Thirty-three physically active male sport science students (age: 24.1 ± 3.8 years) were randomly assigned to a PT group (n = 13) exercising on stable (STAB) and a PT group (n = 20) on unstable surfaces (INST). Both groups trained countermovement jumps, drop jumps, and practiced a hurdle jump course. In addition, high bar squats were performed. Physical fitness tests on stable surfaces (hexagonal obstacle test, countermovement jump, hurdle drop jump, left-right hop, dynamic and static balance tests, and leg extension strength) were used to examine the training effects. Significant main effects of time (ANOVA) were found for the countermovement jump, hurdle drop jump, hexagonal test, dynamic balance, and leg extension strength. A significant interaction of time and training mode was detected for the countermovement jump in favor of the INST group. No significant improvements were evident for either group in the left-right hop and in the static balance test. These results show that lower body PT on unstable surfaces is a safe and efficient way to improve physical performance on stable surfaces.

  13. Metastable sound speed in gas-liquid mixtures

    NASA Technical Reports Server (NTRS)

    Bursik, J. W.; Hall, R. M.

    1979-01-01

    A new method of calculating speed of sound for two-phase flow is presented. The new equation assumes no phase change during the propagation of an acoustic disturbance and assumes that only the total entropy of the mixture remains constant during the process. The new equation predicts single-phase values for the speed of sound in the limit of all gas or all liquid and agrees with available two-phase, air-water sound speed data. Other expressions used in the two-phase flow literature for calculating two-phase, metastable sound speed are reviewed and discussed. Comparisons are made between the new expression and several of the previous expressions -- most notably a triply isentropic equation as used, a triply isentropic equation as used, among others, by Karplus and by Wallis. Appropriate differences are pointed out and a thermodynamic criterion is derived which must be satisfied in order for the triply isentropic expression to be thermodynamically consistent. This criterion is not satisfied for the cases examined, which included two-phase nitrogen, air-water, two-phase parahydrogen, and steam-water. Consequently, the new equation derived is found to be superior to the other equations reviewed.

  14. Metastable dissociation of metallocarbohedrenes. Reaction channels and cluster stabilities

    SciTech Connect

    Wei, S.; Guo, B.C.; Purnell, J.; Buzza, S.A.; Castleman, A.W. Jr. )

    1993-09-23

    An investigation of the metastable unimolecular dissociation channels and decay fractions of Ti[sub m]C[sub n][sup +] was made using a reflection time-of-flight mass spectrometer, coupled with a laser vaporization source in conjunction with multiphoton ionization. The measurements of the decay fractions show that TigC[sub 12][sup +] is a very stable species in accordance with expectation for a closed cagelike structure and, most importantly, provide the first available data on the relative stabilities for different cluster ions involved in the formation of metallocarbohedrenes (Met-Cars). Furthermore, the results reveal that the Ti[sub 8]C[sub n][sup +] mainly lose carbon species for n [ge] 14, while Ti[sub m]C[sub 12][sup +] loses only Ti for m [ge] 6 and both Ti and C[sub 3] for m = 4 and 5; C[sub 2] is never a product of decomposition for this range of Met-Car related species. The present findings are valuable in providing qualitative information for assessing theoretical calculations of structures and properties of metallocarbohedrenes and their building blocks. 32 refs., 2 figs., 1 tab.

  15. Metastable states in NO2+ probed with Auger spectroscopy.

    PubMed

    Püttner, R; Sekushin, V; Fukuzawa, H; Uhlíková, T; Špirko, V; Asahina, T; Kuze, N; Kato, H; Hoshino, M; Tanaka, H; Thomas, T D; Kukk, E; Tamenori, Y; Kaindl, G; Ueda, K

    2011-11-07

    High-resolution N 1s and O 1s photoelectron spectra (PES) of NO are presented together with spectra of the subsequent Auger decay. The PES are analyzed by taking spin-orbit splitting of the (2)Π ground state into account providing detailed information on equilibrium distances, vibrational energies, and lifetime widths of the core-ionized states. In the Auger electron spectra (AES) transitions to five metastable dicationic final states are observed, with two of them previously unobserved. A Franck-Condon analysis of the vibrational progressions belonging to these transitions provides detailed information on the potential-energy curves of the dicationic final states as well as on the relative Auger rates. The present calculations of the potential-energy curves of NO(2+) agree well with the experimental results and allow an assignment of the two hitherto unresolved Auger transitions to excited states of NO(2+), C(2)Σ(+)and c(4)Π. This journal is © the Owner Societies 2011

  16. One Sequence, Two Folds: A Metastable Structure of CD2

    NASA Astrophysics Data System (ADS)

    Murray, Alison J.; Lewis, Sally J.; Barclay, A. Neil; Brady, R. Leo

    1995-08-01

    When expressed as part of a glutathione S-transferase fusion protein the NH_2-terminal domain of the lymphocyte cell adhesion molecule CD2 is shown to adopt two different folds. The immunoglobulin superfamily structure of the major (85%) monomeric component has previously been determined by both x-ray crystallography and NMR spectroscopy. We now describe the structure of a second, dimeric, form present in about 15% of recombinant CD2 molecules. After denaturation and refolding in the absence of the fusion partner, dimeric CD2 is converted to monomer, illustrating that the dimeric form represents a metastable folded state. The crystal structure of this dimeric form, refined to 2.0-Å resolution, reveals two domains with overall similarity to the IgSF fold found in the monomer. However, in the dimer each domain is formed by the intercalation of two polypeptide chains. Hence each domain represents a distinct folding unit that can assemble in two different ways. In the dimer the two domains fold around a hydrophilic interface believed to mimic the cell adhesion interaction at the cell surface, and the formation of dimer can be regulated by mutating single residues at this interface. This unusual misfolded form of the protein, which appears to result from inter- rather than intramolecular interactions being favored by an intermediate structure formed during the folding process, illustrates that evolution of protein oligomers is possible from the sequence for a single protein domain.

  17. Energetic Particle Synthesis of Metastable Layers for Superior Mechanical Properties

    SciTech Connect

    Follstaedt, D.M.; Knapp, J.A.; Myers, S.M.; Dugger, M.T.; Friedmann, T.A.; Sullivan, J.P.; Monteiro, O.R.; Ager, J.W. III; Brown, I.G.; Christenson, T.

    1998-01-01

    Energetic particle methods have been used to synthesize two metastable layers with superior mechanical properties: amorphous Ni implanted with overlapping Ti and C, and amorphous diamond-like carbon (DLC) formed by vacuum-arc deposition or pulsed laser deposition. Elastic modulus, yield stress and hardness were reliably determined for both materials by fitting finite-element simulations to the observed layer/substrate responses during nanoindentation. Both materials show exceptional properties, i.e., the yield stress of amorphous Ni(Ti,C) exceeds that of hardened steels and other metallic glasses, and the hardness of DLC (up to 88 GPa) approaches that of crystalline diamond (approx. 100 GPa). Tribological performance of the layers during unlubricated sliding contact appears favorable for treating Ni-based micro-electromechanical systems: stick-slip adhesion to Ni is eliminated, giving a low coefficient of friction (approx. 0.3-0.2) and greatly reduced wear. We discuss how energetic particle synthesis is critical to forming these phases and manipulating their properties for optimum performance.

  18. Formation of metastable excited states during sputtering of transition metals

    SciTech Connect

    Wucher, A.; Sroubek, Z.

    1997-01-01

    We propose a simple model which treats the formation of metastable excited neutral atoms during sputtering of a transition metal as a two step process. First, the energy deposited into the electronic system of the solid by electronic energy losses of all moving particles in the collision cascade is considered to lead to a locally altered equilibrium electronic state of the solid. It is found that this step is dominated by collective interaction with the conduction band electrons rather than by electron promotion in binary atom-atom collisions. Second, sputtered excited atoms are assumed to be formed by resonant neutralization of excited ions (reflecting the altered equilibrium state) while crossing the surface. It is shown that this model explains the total as well as the velocity dependent excitation probability observed in recent experiments on sputtered neutral silver atoms, which cannot be understood in terms of existing theories describing the formation of excited states in sputtering. {copyright} {ital 1996} {ital The American Physical Society}

  19. The metastable dynamo model of stellar rotational evolution

    SciTech Connect

    Brown, Timothy M.

    2014-07-10

    This paper introduces a new empirical model for the rotational evolution of Sun-like stars—those with surface convection zones and non-convective interior regions. Previous models do not match the morphology of observed (rotation period)-color diagrams, notably the existence of a relatively long-lived 'C-sequence' of fast rotators first identified by Barnes. This failure motivates the Metastable Dynamo Model (MDM) described here. The MDM posits that stars are born with their magnetic dynamos operating in a mode that couples very weakly to the stellar wind, so their (initially very short) rotation periods at first change little with time. At some point, this mode spontaneously and randomly changes to a strongly coupled mode, the transition occurring with a mass-dependent lifetime that is of the order of 100 Myr. I show that with this assumption, one can obtain good fits to observations of young clusters, particularly for ages of 150-200 Myr. Previous models and the MDM both give qualitative agreement with the morphology of the slower-rotating 'I-sequence' stars, but none of them have been shown to accurately reproduce the stellar-mass-dependent evolution of the I-sequence stars, especially for clusters older than a few hundred million years. I discuss observational experiments that can test aspects of the MDM, and speculate that the physics underlying the MDM may be related to other situations described in the literature, in which stellar dynamos may have a multi-modal character.

  20. Magneto-optical trap for metastable helium at 389 nm

    SciTech Connect

    Koelemeij, J.C.J.; Stas, R.J.W.; Hogervorst, W.; Vassen, W.

    2003-05-01

    We have constructed a magneto-optical trap (MOT) for metastable triplet helium atoms utilizing the 2 {sup 3}S{sub 1}{yields}3 {sup 3}P{sub 2} line at 389 nm as the trapping and cooling transition. The far-red-detuned MOT (detuning {delta}=-41 MHz) typically contains few times 10{sup 7} atoms at a relatively high ({approx}10{sup 9} cm{sup -3}) density, which is a consequence of the large momentum transfer per photon at 389 nm and a small two-body loss rate coefficient (2x10{sup -10} cm{sup 3}/s<{beta}<1.0x10{sup -9} cm{sup 3}/s). The two-body loss rate is more than five times smaller than in a MOT on the commonly used 2 {sup 3}S{sub 1}{yields}2 {sup 3}P{sub 2} line at 1083 nm. Furthermore, laser cooling at 389 nm results in temperatures somewhat lower than those achieved using 1083 nm. The 389-nm MOT exhibits small losses due to two-photon ionization, which have been investigated as well.

  1. Narrow linewidth spectroscopy in quantum degenerate metastable helium

    NASA Astrophysics Data System (ADS)

    Notermans, Remy; Rengelink, Robert; Vassen, Wim

    2016-05-01

    Combined with high-precision spectroscopy, QED theory allows extraction of the nuclear charge radius from spectroscopy in simple atomic systems. This recently lead to a significant discrepancy in the proton charge radius determined from hydrogen and muonic hydrogen spectroscopy, now known as the `proton size puzzle'. Spectroscopy in helium can provide additional insight in this conundrum. Our group previously measured the very weak 23 S --> 21 S transition (λ = 1557 nm, Γ = 2 π × 8 Hz) to 10-11 relative accuracy in quantum degenerate (T = 0 . 2 μ K) metastable 4 He and 3 He, allowing a 1% accurate determination of the charge radius difference of the α particle and the helion. Recent measurements in muonic He+ aim for a precision of 3 ×10-4 . In order to provide a similar precision, we aim to remeasure the transition to sub-kHz precision by reducing the linewidth of the spectroscopy laser by over an order of magnitude to the kHz level and by implementing a magic wavelength (λ = 320 nm) dipole trap operating at 2 W CW power. First measurements in a helium BEC have shown a 10 kHz asymmetric line profile due to mean-field effects. This allows for the first determination of the unknown 23 S - 21 S scattering length.

  2. Absolute metastable atom-atom collision cross section measurements using a magneto-optical trap.

    PubMed

    Matherson, K J; Glover, R D; Laban, D E; Sang, R T

    2007-07-01

    We present a new technique to measure absolute total collision cross sections from metastable neon atoms. The technique is based on the observation of the decay rate of trapped atoms as they collide with room temperature atoms. We present the first measurement of this kind using trapped neon atoms in the (3)P(2) metastable state colliding with thermal ground state argon. The measured cross section has a value of 556+/-26 A(2).

  3. Role of Metastable Pitting in Crevices on Crevice Stabilization in Alloys 625 and 22

    SciTech Connect

    B.A. Kehler; J.R. Scully

    2005-01-11

    The metastable pitting behavior inside crevices of alloys 625 and 22 was examined to obtain insight into differences in crevice corrosion susceptibility between alloys 625 and 22. Metastable corrosion event rates recorded as current-time transients were found to increase with increasing applied potential and temperature for both alloys. However, the increase was more significant for 625 as compared to alloy 22 and the cumulative number of events was greater. A strong correlation was obtained between the increase in event rates and decrease in crevice stabilization potential with temperature. Metastable peak heights, values for peak integrated charge, and current/pit depth (I/r) ratios were not strongly affected by these driving forces. The alloying content in alloy 22, traced to increased molybdenum (Mo) and tungsten (W), was rationalized to decrease the metastable event rate and hence, the cumulative number of events after a given time. However, metastable peak heights, values for peak integrated charge, and I/r ratios, as well as metastable peak shapes associated with individual events, were not strongly affected by alloy type in the narrow range of Mo contents explored here. Observed differences in resistance to crevice corrosion stabilization are rationalized to depend on differences in the cumulative number of metastable events occurring sufficiently close in space and time to contribute to the development of a critical crevice chemistry at specific depths in a crevice. The properties of individual events did not have a significant effect. Stable crevice corrosion eventually occurred at the sites where a row of metastable pits formed at a critical distance from the crevice mouth. This row of pit sites focused acidification, which contributed to local depassivation.

  4. Discovery of a metastable Al{sub 20}Sm{sub 4} phase

    SciTech Connect

    Ye, Z. E-mail: kmh@ameslab.gov; Zhang, F.; Mendelev, M. I.; Ott, R. T.; Park, E.; Besser, M. F.; Kramer, M. J.; Wang, C.-Z.; Sun, Y.; Ding, Z.; Ho, K.-M. E-mail: kmh@ameslab.gov

    2015-03-09

    We present an efficient genetic algorithm, integrated with experimental diffraction data, to solve a nanoscale metastable Al{sub 20}Sm{sub 4} phase that evolves during crystallization of an amorphous magnetron sputtered Al{sub 90}Sm{sub 10} alloy. The excellent match between calculated and experimental X-ray diffraction patterns confirms an accurate description of this metastable phase. Molecular dynamic simulations of crystal growth from the liquid phase predict the formation of disordered defects in the devitrified crystal.

  5. Spectroscopic Investigation of the Argon Metastable State Through Optical Emission From Pulsed Argon Discharge

    DTIC Science & Technology

    2010-07-01

    metastable species concentration . An enabling factor of this analysis was that the electron excitation pattern was quite different between the Ar ground...Ar metastable species concentration . An enabling factor of this analysis was that the electron excitation pattern was quite different between the Ar...and tritium together in hopes that a sustainable energy source can someday be developed [5]. The recent consumer trend of replacing incandescent light

  6. Asynchronous inputs and flip-flop metastability in the CLAS trigger at CEBAF

    SciTech Connect

    Doughty, D.C. Jr.; Lemon, S. ); Bonneau, P. )

    1993-08-01

    The impact of flip-flop metastability on the pipelined trigger for the CLAS detector at CEBAF has been studied. The authors find that the newest ECL flip-flops (ECLinPS) are much faster than older families (10H) at resolving the metastable condition. This will allow their use in systems with asynchronous inputs without an extra stage of synchronizing flip-flops.

  7. Asynchronous inputs and flip-flop metastability in the CLAS trigger at CEBAF

    SciTech Connect

    Dave Doughty; S. Lemon; P. Bonneau

    1992-10-01

    The impact of flip-flop metastability on the pipelined trigger for the CLAS detector at CEBAF (Continuous Electron Beam Accelerator Facility) has been studied. It is found that the newest ECL (emitter coupled logic) flip-flops (ECLinPS) are much faster than older families at resolving the metastable condition. This will allow their use in systems with asynchronous inputs without an extra stage of synchronizing flip-flops.

  8. Meta-Stable Vacua and D-Branes at the Conifold

    SciTech Connect

    Argurio, Riccardo; Bertolini, Matteo; Kachru, Shamit

    2008-07-28

    We study gauge theories arising on D-branes on quotients of the conifold. They exhibit meta-stable SUSY breaking along the lines of the model by Intriligator, Seiberg and Shih. We propose a candidate for the extrapolation to large't Hooft coupling of the meta-stable state. It involves anti D3-branes in a smooth gravity dual of a cascading gauge theory.

  9. Metastable phase of lead phthalocyanine films on graphite: Correlation between geometrical and electronic structures

    NASA Astrophysics Data System (ADS)

    Kawakita, N.; Yamada, T.; Meissner, M.; Forker, R.; Fritz, T.; Munakata, T.

    2017-01-01

    The geometrical and electronic structures of a metastable phase of lead phthalocyanine (PbPc) films on graphite have been studied by combined use of low energy electron diffraction (LEED) and two-photon photoemission (2PPE) spectroscopy. In submonolayer (sub-ML) PbPc films on graphite, islands in a metastable phase are formed just after deposition, as we reported previously by use of photoelectron emission microscopy (PEEM) [I. Yamamoto, N. Matsuura, M. Mikamori, R. Yamamoto, T. Yamada, K. Miyakubo, N. Ueno, and T. Munakata, Surf. Sci. 602, 2232 (2008), 10.1016/j.susc.2008.04.037]. On single crystalline graphite substrates, the metastable islands produce clearly discernible LEED spots. By comparing the unit cell with that of annealed 1 ML films, molecules in the metastable islands are standing upright with a molecular density 1.8 times higher than that in the well-ordered 1 ML films. The LEED spots for the sub-ML films disappear after annealing. The islands in the metastable phase are surrounded by areas of a two-dimensional (2D) gaslike phase composed of flat-lying molecules. The metastable islands melt into the 2D gas phase, consistent with the PEEM results. In 2PPE spectroscopy, the lowest unoccupied molecular orbital (LUMO) derived level of the metastable phase is clearly distinguishable from that of flat-lying molecules. By tracking the thermal annealing process of the films by 2PPE spectroscopy, we clarify the decay of the LUMO derived peak intensity, the work function shift, and the energy shifts of molecular states associated with the transition from the metastable phase to the 2D gas phase. With this, we demonstrate the complementary capabilities of LEED and 2PPE spectroscopy to probe phase transitions of organic films in a nondestructive manner.

  10. Adiabatic Variational Theory for Cold Atom-Molecule Collisions: Application to a Metastable Helium Atom Colliding with ortho- and para-Hydrogen Molecules.

    PubMed

    Pawlak, Mariusz; Shagam, Yuval; Klein, Ayelet; Narevicius, Edvardas; Moiseyev, Nimrod

    2017-03-16

    We recently developed an adiabatic theory for cold molecular collision experiments. In our previous application of this theory ( Pawlak, M.; et al. J. Chem. Phys. 2015 , 143 , 074114 ), we assumed that during the experiment the collision of an atom with a diatom takes place when the diatom is in the ground rotational state and is located in a plane. In this paper, we present how the variational approach of the adiabatic theory for low-temperature collision experiments can be used for the study a 5D collision between the atom and the diatomic molecule with no limitations on its rotational quantum states and no plane restrictions. Moreover, we show here the dramatic differences in the measured reaction rates of He(2(3)S1) + ortho/para-H2 → He(1s(2)) + ortho/para-H2(+) + e(-) resulting from the anisotropic long-range interactions in the reaction. In collisions of metastable helium with molecular hydrogen in the ground rotational state, the isotropic potential term dominates the dynamics. When the collision is with molecular hydrogen in the first excited rotational state, the nonisotropic interactions play an important role in the dynamics. The agreement of our results with the latest experimental findings ( Klein , A. ; et al. Nat. Phys. 2017 , 13 , 35 - 38 ) is very good.

  11. Sum of exit times in a series of two metastable states

    NASA Astrophysics Data System (ADS)

    Cirillo, Emilio N. M.; Nardi, Francesca R.; Spitoni, Cristian

    2017-07-01

    The problem of not degenerate in energy metastable states forming a series in the framework of reversible finite state space Markov chains is considered. Metastability has been widely studied both in the mathematical and physical literature. Metastable states arises close to a first order phase transition, when the system can be trapped for a long time (exponentially long with respect to the inverse of the temperature) before switching to the thermodynamically stable phase. In this paper, under rather general conditions, we give a sharp estimate of the exit time from a metastable state in a presence of a second metastable state that must be necessarily visited by the system before eventually reaching the stable phase. In this framework we give a sharp estimate of the exit time from the metastable state at higher energy and, on the proper exponential time scale, we prove an addition rule. As an application of the theory, we study the Blume-Capel model in the zero chemical potential case.

  12. THE ROLE OF METASTABLE STATES IN POLYMER PHASE TRANSITIONS: Concepts, Principles, and Experimental Observations

    NASA Astrophysics Data System (ADS)

    Cheng, Stephen Z. D.; Keller, Andrew

    1998-08-01

    Polymer phases can be described in the same way as phases in other condensed matter using a number density operator and its correlation functions. This description requires the understanding of symmetry operations and order at different atomic and molecular levels. Statistical mechanics provides a link between the microscopic description of the structure and motion and the macroscopic thermodynamic properties. Within the limits of the laws of thermodynamics, polymers exhibit a rich variety of phase transition behaviors. By definition, a first-order phase transition describes a transformation that involves a sudden change of thermodynamic properties at its transition temperature, whereas higher-order phase transitions are classified as critical phenomena. Of special interest is the role of metastability in phase and phase transition behaviors. Although a metastable state possesses a local free energy minimum, it is not at the global equilibrium. Furthermore, metastable states can also be associated with phase sizes. Metastable behavior is also observed in phase transformations that are impeded by kinetic limitations along the pathway to thermodynamic equilibrium. This is illustrated in structural and morphological investigations of crystallization and mesophase transitions, liquid-liquid phase separation, vitrification, and gel formation, as well as combinations of transformation processes. In these cases, the metastable state often becomes the dominant state for the entire system and is observed over a range of time and size scales. This review describes the general principles of metastability in polymer phases and phase transitions and provides illustrations from current experimental works in selected areas.

  13. Metastable bcc phase formation in the Nb-Cr-Ti system

    SciTech Connect

    Thoma, D.J.; Perepezko, J.H.

    1994-08-01

    Metastable disordered bcc phases have been formed from the melt in the Nb-Cr-Ti system where primary Laves phases would develop under equilibrium solidification conditions. Three vertical temperature-composition sections in the ternary system incorporating NbCr, were evaluated: the Nb-Cr binary, the TiCr{sub 2}-NbCr{sub 2} isoplethal section, and the NbCr{sub 2}-Ti plethal section. In the rapid solidification of NbCr{sub 2}, metastable bcc phase formation was not observed, but deviations from NbCr{sub 2} stoichiometry or alloying with Ti was found to promote bcc phase formation by decreasing the required liquid undercooling to reach the metastable bcc liquidus and solidus. The metastable phases were characterized through x-ray diffraction (XRD), and systematic deviations from Vegard`s Rule have been defined in the three plethal sections. The metastable bcc phases decompose at temperatures >800{degrees}C to uniformly refined microstructures. As a result, novel microstructural tailoring schemes are possible through the metastable precursor microstructures.

  14. (1S*,2S*,4R*,5R*)-Cyclo­hexane-1,2,4,5-tetra­carb­oxy­lic acid

    PubMed Central

    Uchida, Akira; Hasegawa, Masatoshi; Yamaguchi, Shinya; Takezawa, Eiichiro; Ishikawa, Atsushi; Kagayama, Takashi

    2014-01-01

    The title compound, C10H12O8, a prospective raw material for colourless polyimides which are applied to electronic and microelectronic devices, lies about an inversion centre and the cyclo­hexane ring adopts a chair conformation. Two crystallographycally independent carb­oxy­lic acid groups on adjacent C atoms are in equatorial positions, resulting in a mutually trans conformation. In the crystal, O—H⋯O hydrogen bonds around an inversion centre and a threefold rotoinversion axis, respectively, form an inversion dimer with an R 2 2(8) motif and a trimer with an R 3 3(12) motif. PMID:24527007

  15. (1S,2S,5S)-2-Methyl-3-oxo-5-(prop-1-en-2-yl)cyclo­hexane-1-carbo­nitrile

    PubMed Central

    Rivadulla, Marcos L.; Fall, Alioune; González, María; Matos, Maria J.

    2013-01-01

    The mol­ecule of the title compound, C11H15NO, contains a cyclo­hexa­none ring, three defined stereocenters and an exocyclic double bond. The crystal structure is the result of a study on the Michael addition reaction of (S)-carvone with sodium cyanide using ionic liquids as the reaction medium and so the absolute configuration is known from the chemistry. The six-membered ring is in a chair conformation. PMID:23723940

  16. Effects of Zb states and bottom meson loops on ϒ (4 S )→ϒ (1 S ,2 S )π+π- transitions

    NASA Astrophysics Data System (ADS)

    Chen, Yun-Hua; Cleven, Martin; Daub, Johanna T.; Guo, Feng-Kun; Hanhart, Christoph; Kubis, Bastian; Meißner, Ulf-G.; Zou, Bing-Song

    2017-02-01

    We study the dipion transitions ϒ (4 S )→ϒ (n S )π+π- (n =1 ,2 ) . In particular, we consider the effects of the two intermediate bottomoniumlike exotic states Zb(10610 ) and Zb(10650 ) as well as bottom meson loops. The strong pion-pion final-state interactions, especially including channel coupling to K K ¯ in the S wave, are taken into account model independently by using dispersion theory. Based on a nonrelativistic effective field theory we find that the contribution from the bottom meson loops is comparable to those from the chiral contact terms and the Zb-exchange terms. For the ϒ (4 S )→ϒ (2 S )π+π- decay, the result shows that including the effects of the Zb exchange and the bottom meson loops can naturally reproduce the two-hump behavior of the π π mass spectra. Future angular distribution data are decisive for the identification of different production mechanisms. For the ϒ (4 S )→ϒ (1 S )π+π- decay, we show that there is a narrow dip around 1 GeV in the π π invariant mass distribution, caused by the final-state interactions. The distribution is clearly different from that in similar transitions from lower ϒ states, and needs to be verified by future data with high statistics. Also we predict the decay width and the dikaon mass distribution of the ϒ (4 S )→ϒ (1 S )K+K- process.

  17. Lower crustal metastable gabbro and volcanism in warm subduction systems

    NASA Astrophysics Data System (ADS)

    McGary, R. S.; Rondenay, S.

    2016-12-01

    Along-strike variation of seismicity and volcanism is an important feature of the Cascadia Subduction Zone. To the north, intraslab activity is dense, and the 127 quaternary vents are tightly clustered around the five volcanoes. To the south, seismic activity is sparse and the more than 2000 quaternary vents form a near continuous array from Bumping Lake to the southeast of Mt. Rainier to very close to the California border. While most of the volcanism in the Cascades lies along the quaternary axis, there are four features (in the central region) that lie within the forearc: the Indian Head and Portland vent fields, Mt. St. Helens, and Mt. Rainier. Mt. St. Helens has been frequently active since 1980, and Mt. Rainier is one of the most potentially dangerous volcanoes in the United States. We present models derived from a 2-D Generalized Radon Transform seismic study across central Washington State near Mt. Rainier and show how they are distinctly different from models obtained in similar studies conducted to the north (across Vancouver Island and into British Columbia) and south (in Oregon near Mt. Jefferson). Specifically, the persistence of a low velocity feature coincident with the subducting lower oceanic crust and uppermost mantle is present here to depths of approximately 100 km. We argue that this feature is best interpreted as a metastable gabbro lower crust underlain by a moderately hydrated uppermost mantle, most likely rich in chlorite. This scenario requires a fairly narrow set of environments for slab hydration offshore, and suggests that important along-strike variation in the volcanic arc may be driven by differences in slab hydration.

  18. Anisotropic sliding dynamics, peak effect, and metastability in stripe systems.

    PubMed

    Olson Reichhardt, C J; Reichhardt, C; Bishop, A R

    2011-04-01

    A variety of soft and hard condensed matter systems are known to form stripe patterns. Here we use numerical simulations to analyze how such stripe states depin and slide when interacting with a random substrate and with driving in different directions with respect to the orientation of the stripes. Depending on the strength and density of the substrate disorder, we find that there can be pronounced anisotropy in the transport produced by different dynamical flow phases. We also find a disorder-induced "peak effect" similar to that observed for superconducting vortex systems, which is marked by a transition from elastic depinning to a state where the stripe structure fragments or partially disorders at depinning. Under the sudden application of a driving force, we observe pronounced metastability effects similar to those found near the order-disorder transition associated with the peak effect regime for three-dimensional superconducting vortices. The characteristic transient time required for the system to reach a steady state diverges in the region where the flow changes from elastic to disordered. We also find that anisotropy of the flow persists in the presence of thermal disorder when thermally induced particle hopping along the stripes dominates. The thermal effects can wash out the effects of the quenched disorder, leading to a thermally induced stripe state. We map out the dynamical phase diagram for this system, and discuss how our results could be explored in electron liquid crystal systems, type-1.5 superconductors, and pattern-forming colloidal assemblies. ©2011 American Physical Society

  19. Metastable structures and size effects in small group dynamics.

    PubMed

    Lauro Grotto, Rosapia; Guazzini, Andrea; Bagnoli, Franco

    2014-01-01

    In his seminal works on group dynamics Bion defined a specific therapeutic setting allowing psychoanalytic observations on group phenomena. In describing the setting he proposed that the group was where his voice arrived. This physical limit was later made operative by assuming that the natural dimension of a therapeutic group is around 12 people. Bion introduced a theory of the group aspects of the mind in which proto-mental individual states spontaneously evolve into shared psychological states that are characterized by a series of features: (1) they emerge as a consequence of the natural tendency of (both conscious and unconscious) emotions to combine into structured group patterns; (2) they have a certain degree of stability in time; (3) they tend to alternate so that the dissolution of one is rapidly followed by the emergence of another; (4) they can be described in qualitative terms according to the nature of the emotional mix that dominates the state, in structural terms by a kind of typical "leadership" pattern, and in "cognitive" terms by a set of implicit expectations that are helpful in explaining the group behavior (i.e., the group behaves "as if" it was assuming that). Here we adopt a formal approach derived from Socio-physics in order to explore some of the structural and dynamic properties of this small group dynamics. We will described data from an analytic DS model simulating small group interactions of agents endowed with a very simplified emotional and cognitive dynamic in order to assess the following main points: (1) are metastable collective states allowed to emerge in the model and if so, under which conditions in the parameter space? (2) can these states be differentiated in structural terms? (3) to what extent are the emergent dynamic features of the systems dependent of the system size? We will finally discuss possible future applications of the quantitative descriptions of the interaction structure in the small group clinical setting.

  20. First principles study of metastable beta titanium alloys

    NASA Astrophysics Data System (ADS)

    Gupta, Niraj

    The high temperature BCC phase (beta) of titanium undergoes a martensitic transformation to HCP phase (alpha) upon cooling, but can be stabilized at room temperature by alloying with BCC transition metals such as Mo. There exists a metastable composition range within which the alloyed beta phase separates into alpha+beta upon equilibrium cooling but not when rapidly quenched. Compositional partitioning of the stabilizing element in asquenched beta microstructure creates nanoscale precipitates of a new simple hexagonal £s phase, which considerably reduces ductility. These phase transformation reactions have been extensively studied experimentally, yet several significant questions remain: (i) The mechanism by which the alloying element stabilizes the beta phase, thwarts its transformation to £s and how these processes vary as a function of the concentration of the stabilizing element is unclear. (ii) What is the atomistic mechanism responsible for the non-Arrhenius, anomalous diffusion widely observed in experiments, and how does it extend to low temperatures? How does the concentration of the stabilizing elements alter this behavior? There are many other £s forming alloys that such exhibit anomalous diffusion behavior. (iii) A lack of clarity remains on whether £s can transform to alpha -phase in the crystal bulk or if it occurs only at high-energy regions such as grain boundaries. Furthermore, what is the nature of the alpha phase embryo? (iv) Although previous computational results discovered a new o → alpha transformation mechanism in pure Ti with activation energy lower than the classical Silcock pathway, it is at odds with the alpha /beta / o orientation relationship seen in experiments.

  1. MONTE CARLO SIMULATION OF METASTABLE OXYGEN PHOTOCHEMISTRY IN COMETARY ATMOSPHERES

    SciTech Connect

    Bisikalo, D. V.; Shematovich, V. I.; Gérard, J.-C.; Hubert, B.; Jehin, E.; Decock, A.; Hutsemékers, D.; Manfroid, J.

    2015-01-01

    Cometary atmospheres are produced by the outgassing of material, mainly H{sub 2}O, CO, and CO{sub 2} from the nucleus of the comet under the energy input from the Sun. Subsequent photochemical processes lead to the production of other species generally absent from the nucleus, such as OH. Although all comets are different, they all have a highly rarefied atmosphere, which is an ideal environment for nonthermal photochemical processes to take place and influence the detailed state of the atmosphere. We develop a Monte Carlo model of the coma photochemistry. We compute the energy distribution functions (EDF) of the metastable O({sup 1}D) and O({sup 1}S) species and obtain the red (630 nm) and green (557.7 nm) spectral line shapes of the full coma, consistent with the computed EDFs and the expansion velocity. We show that both species have a severely non-Maxwellian EDF, that results in broad spectral lines and the suprathermal broadening dominates due to the expansion motion. We apply our model to the atmosphere of comet C/1996 B2 (Hyakutake) and 103P/Hartley 2. The computed width of the green line, expressed in terms of speed, is lower than that of the red line. This result is comparable to previous theoretical analyses, but in disagreement with observations. We explain that the spectral line shape does not only depend on the exothermicity of the photochemical production mechanisms, but also on thermalization, due to elastic collisions, reducing the width of the emission line coming from the O({sup 1}D) level, which has a longer lifetime.

  2. Gender-related effects on urine L-cystine metastability.

    PubMed

    Masotti, Andrea; Laurenzi, Chiara; Boenzi, Sara; Pastore, Anna; Taranta, Anna; Bellomo, Francesco; Muraca, Maurizio; Dionisi-Vici, Carlo; Bertucci, Pierfrancesco; Dello Strologo, Luca; Emma, Francesco

    2014-02-01

    Cystinuria is an autosomal recessive disease that causes L-cystine precipitation in urine and nephrolithiasis. Disease severity is highly variable; it is known, however, that cystinuria has a more severe course in males. The aim of this study was to compare L-cystine metastability in first-morning urine collected from 24 normal female and 24 normal male subjects. Samples were buffered at pH 5 and loaded with L-cystine (0.4 and 4 mM final concentration) to calculate the amount remaining in solution after overnight incubation at 4 °C; results were expressed as Z scores reflecting the L-cystine solubility in each sample. In addition, metabolomic analyses were performed to identify candidate compounds that influence L-cystine solubility. L-cystine solubility Z score was +0.44 ± 1.1 and -0.44 ± 0.70 in female and male samples, respectively (p < 0.001). Further analyses showed that the L-cystine solubility was independent from urine concentration but was significantly associated with low urinary excretion of inosine (p = 0.010), vanillylmandelic acid (VMA) (p = 0.015), adenosine (p = 0.029), and guanosine (p = 0.032). In vitro L-cystine precipitation assays confirmed that these molecules induce higher rates of L-cystine precipitation in comparison with their corresponding dideoxy molecules, used as controls. In silico computational and modeling analyses confirmed higher binding energy of these compounds. These data indicate that urinary excretion of nucleosides and VMA may represent important factors that modulate L-cystine solubility and may represent new targets for therapy in cystinuria.

  3. Metastable structures and size effects in small group dynamics

    PubMed Central

    Lauro Grotto, Rosapia; Guazzini, Andrea; Bagnoli, Franco

    2014-01-01

    In his seminal works on group dynamics Bion defined a specific therapeutic setting allowing psychoanalytic observations on group phenomena. In describing the setting he proposed that the group was where his voice arrived. This physical limit was later made operative by assuming that the natural dimension of a therapeutic group is around 12 people. Bion introduced a theory of the group aspects of the mind in which proto-mental individual states spontaneously evolve into shared psychological states that are characterized by a series of features: (1) they emerge as a consequence of the natural tendency of (both conscious and unconscious) emotions to combine into structured group patterns; (2) they have a certain degree of stability in time; (3) they tend to alternate so that the dissolution of one is rapidly followed by the emergence of another; (4) they can be described in qualitative terms according to the nature of the emotional mix that dominates the state, in structural terms by a kind of typical “leadership” pattern, and in “cognitive” terms by a set of implicit expectations that are helpful in explaining the group behavior (i.e., the group behaves “as if” it was assuming that). Here we adopt a formal approach derived from Socio-physics in order to explore some of the structural and dynamic properties of this small group dynamics. We will described data from an analytic DS model simulating small group interactions of agents endowed with a very simplified emotional and cognitive dynamic in order to assess the following main points: (1) are metastable collective states allowed to emerge in the model and if so, under which conditions in the parameter space? (2) can these states be differentiated in structural terms? (3) to what extent are the emergent dynamic features of the systems dependent of the system size? We will finally discuss possible future applications of the quantitative descriptions of the interaction structure in the small group clinical

  4. Short-range Ising spin glasses: The metastate interpretation of replica symmetry breaking

    NASA Astrophysics Data System (ADS)

    Read, N.

    2014-09-01

    Parisi's formal replica-symmetry-breaking (RSB) scheme for mean-field spin glasses has long been interpreted in terms of many pure states organized ultrametrically. However, the early version of this interpretation, as applied to the short-range Edwards-Anderson model, runs into problems because as shown by Newman and Stein (NS) it does not allow for chaotic size dependence, and predicts non-self-averaging that cannot occur. NS proposed the concept of the metastate (a probability distribution over infinite-size Gibbs states in a given sample that captures the effects of chaotic size dependence) and a nonstandard interpretation of the RSB results in which the metastate is nontrivial and is responsible for what was called non-self-averaging. In this picture, each state drawn from the metastate has the ultrametric properties of the old theory, but when the state is averaged using the metastate, the resulting mixed state has little structure. This picture was constructed so as to agree both with the earlier RSB results and with rigorous results. Here we use the effective field theory of RSB, in conjunction with the rigorous definitions of pure states and the metastate in infinite-size systems, to show that the nonstandard picture follows directly from the RSB mean-field theory. In addition, the metastate-averaged state possesses power-law correlations throughout the low-temperature phase; the corresponding exponent ζ takes the value 4 according to the field theory in high dimensions d, and describes the effective fractal dimension of clusters of spins. Further, the logarithm of the number of pure states in the decomposition of the metastate-averaged state that can be distinguished if only correlations in a window of size W can be observed is of order Wd -ζ. These results extend the nonstandard picture quantitatively; we show that arguments against this scenario are inconclusive. More generally, in terms of Parisi's function q (x), if q(0)≠∫01dxq(x ), then the

  5. Formation of Kinetically Trapped Nanoscopic Unilamellar Vesicles from Metastable Nanodiscs

    SciTech Connect

    Nieh, Mu-Ping; Dolinar, Paul; Kucerka, Norbert; Kline, Steven R.; Debeer-Schmitt, Lisa M.; Littrell, Kenneth C.; Katsaras, John

    2011-09-27

    Zwitterionic long-chain lipids (e.g., dimyristoyl phosphatidylcholine, DMPC) spontaneously form onion-like, thermodynamically stable structures in aqueous solutions (commonly known as multilamellar vesicles, or MLVs). It has also been reported that the addition of zwitterionic short-chain (i.e., dihexanoyl phosphatidylcholine, DHPC) and charged long-chain (i.e., dimyristoyl phosphatidylglycerol, DMPG) lipids to zwitterionic long-chain lipid solutions results in the formation of unilamellar vesicles (ULVs). Here, we report a kinetic study on lipid mixtures composed of DMPC, DHPC, and DMPG. Two membrane charge densities (i.e., [DMPG]/[DMPC] = 0.01 and 0.001) and two solution salinities (i.e., [NaCl] = 0 and 0.2 M) are investigated. Upon dilution of the high-concentration samples at 50 °C, thermodynamically stable MLVs are formed, in the case of both weakly charged and high salinity solution mixtures, implying that the electrostatic interactions between bilayers are insufficient to cause MLVs to unbind. Importantly, in the case of these samples small angle neutron scattering (SANS) data show that, initially, nanodiscs (also known as bicelles) or bilayered ribbons form at low temperatures (i.e., 10 °C), but transform into uniform size, nanoscopic ULVs after incubation at 10 °C for 20 h, indicating that the nanodisc is a metastable structure. The instability of nanodiscs may be attributed to low membrane rigidity due to a reduced charge density and high salinity. Moreover, the uniform-sized ULVs persist even after being heated to 50 °C, where thermodynamically stable MLVs are observed. This result clearly demonstrates that these ULVs are kinetically trapped, and that the mechanical properties (e.g., bending rigidity) of 10 C nanodiscs favor the formation of nanoscopic ULVs over that of MLVs. From a practical point of view, this method of forming uniform-sized ULVs may lend itself to their mass production, thus making them economically feasible for medical

  6. Structural transitions of the conserved and metastable hantaviral glycoprotein envelope.

    PubMed

    Rissanen, Ilona; Stass, Robert; Zeltina, Antra; Li, Sai; Hepojoki, Jussi; Harlos, Karl; Gilbert, Robert J C; Huiskonen, Juha T; Bowden, Thomas A

    2017-08-23

    Hantaviruses are zoonotic pathogens with a near-global distribution that can cause severe hemorrhagic fever and pulmonary syndrome. The outer membrane of the hantavirus envelope displays a lattice of two glycoproteins, Gn and Gc, which orchestrate host cell recognition and entry. Here, we describe the crystal structure of the Gn glycoprotein ectodomain from the Asiatic Hantaan virus (HTNV), the most prevalent pathogenic hantavirus. Structural overlay analysis reveals that the HTNV Gn fold is highly similar to the Gn of Puumala virus (PUUV), a genetically and geographically distinct and less pathogenic hantavirus found predominantly in North-Eastern Europe, confirming that the hantaviral Gn fold is architecturally conserved across hantavirus clades. Interestingly, HTNV Gn crystallized at acidic pH, in a compact tetrameric configuration distinct from the organization at neutral pH. Analysis of the Gn, both in solution and in the context of the virion, confirms the pH-sensitive oligomeric nature of the glycoprotein, indicating that the hantaviral Gn undergoes structural transitions during host cell entry. These data allow us to present a structural model for how acidification during endocytic uptake of the virus triggers the dissociation of the metastable Gn-Gc lattice to enable insertion of the Gc-resident hydrophobic fusion loops into the host cell membrane. Together, these data reveal the dynamic plasticity of the structurally conserved hantaviral surface.IMPORTANCE Although the outbreaks of Korean hemorrhagic fever were first recognized during the Korean War (1950-53), it was not until 1978 that they were known to be caused by Hantaan virus (HTNV), the most prevalent pathogenic hantavirus. Here, we describe the crystal structure of HTNV envelope glycoprotein Gn, an integral component of the Gn-Gc glycoprotein spike complex responsible for host cell entry. HTNV Gn is structurally conserved with the Gn of a genetically and geographically distal hantavirus, Puumala

  7. Sub-recoil laser cooling of metastable helium

    NASA Astrophysics Data System (ADS)

    Liu, Liang

    2000-08-01

    This work presents the results of several experiments in sub-recoil laser cooling of metastable Helium (He*) on the 23S1 --> 23P0,1,2 transitions at λ = 1.083 μm and on the 23S1 --> 33P0,1,2 transitions at λ = 389 nm in a magnetic field. The idea is to combine the principle of sub-recoil cooling based on VSCPT (Velocity Selective Coherent Population Trapping) with the VSR (Velocity Selective Resonance) produced by an applied magnetic field. We first review the works on Doppler and sub-Doppler cooling, and point out that the sub-recoil cooling is possible when the atom is dark to the laser field. When the kinetic energy term is considered in the Hamiltonian, the dark state has a distribution over detuning and laser intensity. Thus for limited interaction time for blue detuning, the trapped state leads a single sub-recoil peak, and for red detuning, it leads a single sub-recoil dip. W present a semiclassical description of VSCPT in a magnetic field. In this description, two terms are added to the Hamiltonian simultaneously, that is the kinetic energy term and Zeeman shift term. With the kinetic energy term, the dependence of the dark state on laser parameters can be understood, and with the Zeeman term, VSCPT phenomena can be controlled by the applied magnetic field. We present an experiment on the He* J = 1 --> 1 transition driven by σ+ - σ- counter-propagating fields in a magnetic field parallel to the k-vector of the lasers, which produces a standard A system. We first apply a magnetic field parallel to the k-vector of laser beams, and observe the change of VSCPT vs the magnetic field. Then we study VSCPT behaviour in zero magnetic field for different detuning, intensity and interaction time. The configuration is then changed to a σ+ standing wave in a magnetic field perpendicular to the k-vector of the laser beams. For the J = 1 --> 0 transition, besides the dark state similar to 1 --> 1 transition, there is a leak from J = 0, mJ = 0 of the excited state

  8. Spatially resolved modeling and measurements of metastable argon atoms in argon-helium microplasmas

    NASA Astrophysics Data System (ADS)

    Hoskinson, Alan R.; Gregório, José; Hopwood, Jeffrey; Galbally-Kinney, Kristin L.; Davis, Steven J.; Rawlins, Wilson T.

    2017-04-01

    Microwave-driven plasmas operating near atmospheric pressure have been shown to be a promising technique for producing the high density of argon metastable atoms required for optically pumped rare gas laser systems. Stable microwave-driven plasmas can be generated at high pressures using microstrip-based resonator circuits. We present results from computational modeling and laser absorption measurements of argon metastable densities in such plasmas operating in argon-helium gas mixtures at pressures up to 300 Torr. The model and measurements resolve the plasma characteristics both perpendicular to the substrate surface and along the resonator length. The measurements qualitatively and in many aspects quantitatively confirm the accuracy of the model. The plasmas exhibit distinct behaviors depending on whether the operating gas is mostly argon or mostly helium. In high-argon plasmas, the metastable density has a large peak value but is confined very closely to the electrode surfaces as well as being reduced near the discharge gap itself. In contrast, metastable densities in high helium-fraction mixtures extend through most of the plasma. In all systems, increasing the power extends the region of metastable along the resonator length, while the extent away from the substrate surface remains approximately constant.

  9. Role of Lys335 in the metastability and function of inhibitory serpins.

    PubMed Central

    Im, H.; Yu, M. H.

    2000-01-01

    The native form of inhibitory serpins (serine protease inhibitors) is not in the thermodynamically most stable state but in a metastable state, which is critical to inhibitory functions. To understand structural basis and functional roles of the native metastability of inhibitory serpins, we have been characterizing stabilizing mutations of human alpha1-antitrypsin, a prototype inhibitory serpin. One of the sites that has been shown to be critical in stability and inhibitory activity of alpha1-antitrypsin is Lys335. In the present study, detailed roles of this lysine were analyzed by assessing the effects of 13 different amino acid substitutions. Results suggest that size and architect of the side chains at the 335 site determine the metastability of alpha1-antitrypsin. Moreover, factors such as polarity and flexibility of the side chain at this site, in addition to the metastability, seem to be critical for the inhibitory activity. Substitutions of the lysine at equivalent positions in two other inhibitory serpins, human alpha1-antichymotrypsin and human antithrombin III, also increased stability and decreased inhibitory activity toward alpha-chymotrypsin and thrombin, respectively. These results and characteristics of lysine side chain, such as flexibility, polarity, and the energetic cost upon burial, suggest that this lysine is one of the structural designs in regulating metastability and function of inhibitory serpins in general. PMID:10850803

  10. Calculation of the relative metastabilities of proteins using the CHNOSZ software package

    PubMed Central

    Dick, Jeffrey M

    2008-01-01

    Background Proteins of various compositions are required by organisms inhabiting different environments. The energetic demands for protein formation are a function of the compositions of proteins as well as geochemical variables including temperature, pressure, oxygen fugacity and pH. The purpose of this study was to explore the dependence of metastable equilibrium states of protein systems on changes in the geochemical variables. Results A software package called CHNOSZ implementing the revised Helgeson-Kirkham-Flowers (HKF) equations of state and group additivity for ionized unfolded aqueous proteins was developed. The program can be used to calculate standard molal Gibbs energies and other thermodynamic properties of reactions and to make chemical speciation and predominance diagrams that represent the metastable equilibrium distributions of proteins. The approach takes account of the chemical affinities of reactions in open systems characterized by the chemical potentials of basis species. The thermodynamic database included with the package permits application of the software to mineral and other inorganic systems as well as systems of proteins or other biomolecules. Conclusion Metastable equilibrium activity diagrams were generated for model cell-surface proteins from archaea and bacteria adapted to growth in environments that differ in temperature and chemical conditions. The predicted metastable equilibrium distributions of the proteins can be compared with the optimal growth temperatures of the organisms and with geochemical variables. The results suggest that a thermodynamic assessment of protein metastability may be useful for integrating bio- and geochemical observations. PMID:18834534

  11. Metastable vacuum decay and θ dependence in gauge theory. Deformed QCD as a toy model

    NASA Astrophysics Data System (ADS)

    Bhoonah, Amit; Thomas, Evan; Zhitnitsky, Ariel R.

    2015-01-01

    We study a number of different ingredients related to the θ dependence, metastable excited vacuum states and other related subjects using a simplified version of QCD, the so-called "deformed QCD". This model is a weakly coupled gauge theory, which, however, preserves all the relevant essential elements allowing us to study hard and nontrivial features which are known to be present in real strongly coupled QCD. Our main focus in this work is to test the ideas related to the metastable vacuum states (which are known to be present in strongly coupled QCD in large N limit) in a theoretically controllable manner using the "deformed QCD" as a toy model. We explicitly show how the metastable states emerge in the system, why their lifetime is large, and why these metastable states must be present in the system for the self-consistency of the entire picture of the QCD vacuum. We also speculate on possible relevance of the metastable vacuum states in explanation of the violation of local P and CP symmetries in heavy ion collisions.

  12. Metastable dynamical patterns and their stabilization in arrays of bidirectionally coupled sigmoidal neurons

    NASA Astrophysics Data System (ADS)

    Horikawa, Yo

    2013-12-01

    Transient patterns in a bistable ring of bidirectionally coupled sigmoidal neurons were studied. When the system had a pair of spatially uniform steady solutions, the instability of unstable spatially nonuniform steady solutions decreased exponentially with the number of neurons because of the symmetry of the system. As a result, transient spatially nonuniform patterns showed dynamical metastability: Their duration increased exponentially with the number of neurons and the duration of randomly generated patterns obeyed a power-law distribution. However, these metastable dynamical patterns were easily stabilized in the presence of small variations in coupling strength. Metastable rotating waves and their pinning in the presence of asymmetry in the direction of coupling and the disappearance of metastable dynamical patterns due to asymmetry in the output function of a neuron were also examined. Further, in a two-dimensional array of neurons with nearest-neighbor coupling, intrinsically one-dimensional patterns were dominant in transients, and self-excitation in these neurons affected the metastable dynamical patterns.

  13. Experimental determination of the metastable zone width of borax decahydrate by ultrasonic velocity measurement

    NASA Astrophysics Data System (ADS)

    Gürbüz, H.; Özdemir, B.

    2003-05-01

    The metastable zone width of borax decahydrate (disodium tetraborate decahydrate), represented by the maximum undercooling Δ Tmax, both in pure and impure aqueous solutions were determined according to polythermal method by using the ultrasonic technique. It is found that the metastable zone width of borax decahydrate in pure solutions determined by ultrasonic method fulfills well the linear relation between logΔ Tmax and log(-d T/d t). However, the sensitivity of the method using the ultrasonic technique increases with increasing saturation temperature, probably due to the increase of temperature dependence of solubility with increasing saturation temperature. A comparison of the nucleation temperatures from ultrasonic measurements and from visual determination shows that both detection techniques give almost the same results for borax decahydrate. The results obtained from ultrasonic measurements show, that the presence of Ca 2+ as impurity has only a small effect on the metastable zone width of borax decahydrate as long as the impurity concentrations is in the range of 25-200 ppm. Similar to the effect of Ca 2+, Mg 2+ also has a small effect on the metastable zone width of borax up to the impurity concentration of 100 ppm. However, the presence of 200 ppm Mg 2+ results in a reasonable increase of the metastable zone width.

  14. Optimization of crystal nucleation close to a metastable fluid-fluid phase transition

    PubMed Central

    Wedekind, Jan; Xu, Limei; Buldyrev, Sergey V.; Stanley, H. Eugene; Reguera, David; Franzese, Giancarlo

    2015-01-01

    The presence of a metastable fluid-fluid critical point is thought to dramatically influence the crystallization pathway, increasing the nucleation rate by many orders of magnitude over the predictions of classical nucleation theory. We use molecular dynamics simulations to study the kinetics of crystallization in the vicinity of this metastable critical point and throughout the metastable fluid-fluid phase diagram. To quantitatively understand how the fluid-fluid phase separation affects the crystal nucleation, we evaluate accurately the kinetics and reconstruct the thermodynamic free-energy landscape of crystal formation. Contrary to expectations, we find no special advantage of the proximity of the metastable critical point on the crystallization rates. However, we find that the ultrafast formation of a dense liquid phase causes the crystallization to accelerate both near the metastable critical point and almost everywhere below the fluid-fluid spinodal line. These results unveil three different scenarios for crystallization that could guide the optimization of the process in experiments PMID:26095898

  15. Maternal nutrition at conception modulates DNA methylation of human metastable epialleles

    PubMed Central

    Dominguez-Salas, Paula; Moore, Sophie E.; Baker, Maria S.; Bergen, Andrew W.; Cox, Sharon E.; Dyer, Roger A.; Fulford, Anthony J.; Guan, Yongtao; Laritsky, Eleonora; Silver, Matt J.; Swan, Gary E.; Zeisel, Steven H.; Innis, Sheila M.; Waterland, Robert A.; Prentice, Andrew M.; Hennig, Branwen J.

    2014-01-01

    In experimental animals, maternal diet during the periconceptional period influences the establishment of DNA methylation at metastable epialleles in the offspring, with permanent phenotypic consequences. Pronounced naturally occurring seasonal differences in the diet of rural Gambian women allowed us to test this in humans. We show that significant seasonal variations in methyl-donor nutrient intake of mothers around the time of conception influence 13 relevant plasma biomarkers. The level of several of these maternal biomarkers predicts increased/decreased methylation at metastable epialleles in DNA extracted from lymphocytes and hair follicles in infants postnatally. Our results demonstrate that maternal nutritional status during early pregnancy causes persistent and systemic epigenetic changes at human metastable epialleles. PMID:24781383

  16. Formation and Stabilization of Single-Crystalline Metastable AuGe Phases in Ge Nanowires

    SciTech Connect

    Sutter, E.; Sutter, P.

    2011-07-22

    We use in situ observations by variable temperature transmission electron microscopy on AuGe alloy drops at the tips of Ge nanowires (NWs) with systematically varying composition to demonstrate the controlled formation of metastable solid phases integrated in NWs. The process, which operates in the regime of vapor-liquid-solid growth, involves a size-dependent depression of the alloy liquidus at the nanoscale that leads to extremely Ge-rich AuGe melts at low temperatures. During slow cooling, these liquid AuGe alloy drops show pronounced departures from equilibrium, i.e., a frustrated phase separation of Ge into the adjacent solid NW, and ultimately crystallize as single-crystalline segments of metastable {gamma}-AuGe. Our findings demonstrate a general avenue for synthesizing NW heterostructures containing stable and metastable solid phases, applicable to a wide range of materials of which NWs form by the vapor-liquid-solid method.

  17. Metastability and anomalous fixation in evolutionary games on scale-free networks.

    PubMed

    Assaf, Michael; Mobilia, Mauro

    2012-11-02

    We study the influence of complex graphs on the metastability and fixation properties of a set of evolutionary processes. In the framework of evolutionary game theory, where the fitness and selection are frequency dependent and vary with the population composition, we analyze the dynamics of snowdrift games (characterized by a metastable coexistence state) on scale-free networks. Using an effective diffusion theory in the weak selection limit, we demonstrate how the scale-free structure affects the system's metastable state and leads to anomalous fixation. In particular, we analytically and numerically show that the probability and mean time of fixation are characterized by stretched-exponential behaviors with exponents depending on the network's degree distribution.

  18. Metastability and chimera states in modular delay and pulse-coupled oscillator networks.

    PubMed

    Wildie, Mark; Shanahan, Murray

    2012-12-01

    Modular networks of delay-coupled and pulse-coupled oscillators are presented, which display both transient (metastable) synchronization dynamics and the formation of a large number of "chimera" states characterized by coexistent synchronized and desynchronized subsystems. We consider networks based on both community and small-world topologies. It is shown through simulation that the metastable behaviour of the system is dependent in all cases on connection delay, and a critical region is found that maximizes indices of both metastability and the prevalence of chimera states. We show dependence of phase coherence in synchronous oscillation on the level and strength of external connectivity between communities, and demonstrate that synchronization dynamics are dependent on the modular structure of the network. The long-term behaviour of the system is considered and the relevance of the model briefly discussed with emphasis on biological and neurobiological systems.

  19. The effects of ethylene glycol and dimethyl sulfoxide on cerebroside metastability.

    PubMed

    Curatolo, W

    1985-07-11

    Aqueous dispersions of n-acyl cerebrosides are known to exhibit metastable polymorphism of the type: (Formula: see text). The involvement of hydration in this metastable polymorphism has been investigated by differential scanning calorimetric studies of aqueous palmitoylgalactocerebroside (C16:0-CER) dispersions in the presence of agents which disrupt water structure. In the presence of 50 vol% ethylene glycol or 50 vol% dimethyl sulfoxide, only a single reversible ordered----liquid-crystalline transition is observed. This single ordered----liquid-crystalline transition exhibits a smaller enthalpy and occurs at a lower temperature than the major Polymorph II----liquid-crystal transition observed for dispersions in water alone. These results indicate that metastable polymorphism in C16:0-CER is related to hydration.

  20. Effects of argon gas pressure on its metastable-state density in high-density plasmas

    SciTech Connect

    Seo, B. H.; Kim, J. H.; You, S. J.

    2015-05-15

    The effect of argon gas pressure on its metastable density in inductively coupled plasmas (ICPs) is investigated by using the laser-induced fluorescence method. Our results show that the metastable-state density of argon varies with the gas pressure depending on the measurement position; the density decreases with the pressure at a position far from the ICP antenna, whereas it increases with the pressure at a position near the antenna. This contrast in the metastable-state density trend with the pressure is explained by considering the electron temperature variations at the two measurement positions. The theoretical interpretation and calculation using a global model are also addressed in detail in this paper.

  1. Synthesis of new metastable nanoalloys of immiscible metals with a pulse laser technique

    PubMed Central

    Swiatkowska-Warkocka, Zaneta; Pyatenko, Alexander; Krok, Franciszek; Jany, Benedykt R.; Marszalek, Marta

    2015-01-01

    The generation of nanoalloys of immiscible metals is still a challenge using conventional methods. However, because these materials are currently attracting much attention, alternative methods are needed. In this article, we demonstrate a simple but powerful strategy for the generation of a new metastable alloy of immiscible metals. Au1−xNix 3D structures with 56 at% of nickel in gold were successfully manufactured by the pulsed laser irradiation of colloidal nanoparticles. This technology can be used for preparing different metastable alloys of immiscible metals. We hypothesise that this technique leads to the formation of alloy particles through the agglomerations of nanoparticles, very fast heating, and fast cooling/solidification. Thus, we expect that our approach will be applicable to a wide range of inorganic solids, yielding even new metastable solids that fail to be stable in the bulk systems, and therefore do not exist in Nature. PMID:25952016

  2. Identification of a metastable state of the VZnH2 defect in ZnO

    NASA Astrophysics Data System (ADS)

    Bastin, D.; Lavrov, E. V.; Weber, J.

    2012-08-01

    An infrared absorption study of the Zn vacancy passivated by two hydrogen atoms (VZnH2) is reported. The ground state of the defect VZnH2 consists of the inequivalent O-H bonds, which are aligned parallel and perpendicular to the c-axis, respectively. A metastable state of the defect was detected with two equivalent O-H bonds oriented perpendicular to the c-axis (VZnH2*). VZnH2* has two local vibration modes at 3329.0 and 3348.4 cm-1 which are the antisymmetric and symmetric combinations of the two O-H stretch modes. The metastable state of the defect is 75±9 meV above the ground state of VZnH2. An activation energy of 0.96±0.12 eV for the transition from metastable to the ground state was determined.

  3. Super-stable ultrafine beta-tungsten nanocrystals with metastable phase and related magnetism.

    PubMed

    Xiao, J; Liu, P; Liang, Y; Li, H B; Yang, G W

    2013-02-07

    Ultrafine tungsten nanocrystals (average size of 3 nm) with a metastable phase (beta-tungsten with A15 structure, β-W) have been prepared by laser ablation of tungsten in liquid nitrogen. The as-prepared metastable nanocrystals exhibited super-stablity, and can keep the same metastable structure over a period of 6 months at room temperature. This super-stability is attributed to the nanosized confinement effect of ultrafine nanocrystals. The magnetism measurements showed that the β-W nanocrystals have weak ferromagnetic properties at 2 K, which may arise from surface defects and unpaired electrons on the surface of the ultrafine nanocrystals. These findings provided useful information for the application of ultrafine β-W nanocrystals in microelectronics and spintronics.

  4. Investigations of the origins of metastable light-induced changes in hydrogenated amorphous silicon

    SciTech Connect

    Cohen, J.D. )

    1991-12-01

    The work performed for this contract continued investigations of the origins of metastable effectS in a-Si:H through three kinds of studies: (1) the effect of carbon impurities in a-Si:H samples at low concentrations using drive-level capacitance profiling measurements on samples whose carbon content was intentionally modulated spatially during growth, (2) the characterization of metastable states in n-type doped a Si:H samples caused by quench cooling and by light-soaking with partial annealing, and (3) the use of depletion-width-modulated ESR spectroscopy together with junction capacitance spectroscopy to investigate deep defect states for various metastable states of a 10- and an 80-Vppm PH{sub 3}-doped a-Si:H sample.

  5. Study of Metastable N2 Production Using an N2 Matrix Detector

    NASA Astrophysics Data System (ADS)

    McConkey, William; Kedzierski, Wladek; Cerkauskas, Cyrus

    2015-05-01

    Metastable N2 molecules produced in the interaction of electrons of carefully controlled energy with a thermal beam of N2 in a crossed beam set-up have been studied in the energy range from threshold to 400 eV. The e-beam is pulsed and the metastables produced drift to a solid nitrogen target held at 10 K. Here they form excimers which immediately radiate. The resultant photons are detected using a photomultiplier-filter combination. Time-of-flight techniques are used to separate these photons from prompt photons produced in the initial electron-N2 collision. The excimer emission is strongest in the green but still significant in the red spectral region. Excitation functions will be presented together with threshold measurements. These help to identify the metastable states being observed and the excitation mechanisms which are responsible. The authors thank NSERC and CFI, (Canada), for financial support.

  6. Control of switching between metastable superconducting states in δ-MoN nanowires

    PubMed Central

    Buh, Jože; Kabanov, Viktor; Baranov, Vladimir; Mrzel, Aleš; Kovič, Andrej; Mihailovic, Dragan

    2015-01-01

    The superconducting state in one-dimensional nanosystems is very delicate. While fluctuations of the phase of the superconducting wave function lead to the spontaneous decay of persistent supercurrents in thin superconducting wires and nanocircuits, discrete phase-slip fluctuations can also lead to more exotic phenomena, such as the appearance of metastable superconducting states in current-bearing wires. Here we show that switching between different metastable superconducting states in δ-MoN nanowires can be very effectively manipulated by introducing small amplitude electrical noise. Furthermore, we show that deterministic switching between metastable superconducting states with different numbers of phase-slip centres can be achieved in both directions with small electrical current pulse perturbations of appropriate polarity. The observed current-controlled bi-stability is in remarkable agreement with theoretically predicted trajectories of the system switching between different limit cycle solutions of a model one-dimensional superconductor. PMID:26687762

  7. Protein homeostasis of a metastable subproteome associated with Alzheimer’s disease

    PubMed Central

    Kundra, Rishika; Ciryam, Prajwal; Morimoto, Richard I.; Dobson, Christopher M.; Vendruscolo, Michele

    2017-01-01

    Alzheimer’s disease is the most common cause of dementia. A hallmark of this disease is the presence of aberrant deposits containing by the Aβ peptide (amyloid plaques) and the tau protein (neurofibrillary tangles) in the brains of affected individuals. Increasing evidence suggests that the formation of these deposits is closely associated with the age-related dysregulation of a large set of highly expressed and aggregation-prone proteins, which make up a metastable subproteome. To understand in more detail the origins of such dysregulation, we identify specific components of the protein homeostasis system associated with these metastable proteins by using a gene coexpression analysis. Our results reveal the particular importance of the protein trafficking and clearance mechanisms, including specific branches of the endosomal–lysosomal and ubiquitin–proteasome systems, in maintaining the homeostasis of the metastable subproteome associated with Alzheimer’s disease. PMID:28652376

  8. Characterization of a metastable neon beam extracted from a commercial RF ion source

    NASA Astrophysics Data System (ADS)

    Ohayon, B.; Wåhlin, E.; Ron, G.

    2015-03-01

    We have used a commercial RF ion-source to extract a beam of metastable neon atoms. The source was easily incorporated into our existing system and was operative within a day of installation. The metastable velocity distribution, flux, flow, and efficiency were investigated for different RF powers and pressures, and an optimum was found at a flux density of 2 × 1012 atoms/s/sr. To obtain an accurate measurement of the amount of metastable atoms leaving the source, we insert a Faraday cup in the beam line and quench some of them using a weak 633 nm laser beam. In order to determine how much of the beam was quenched before reaching our detector, we devised a simple model for the quenching transition and investigated it for different laser powers. This detection method can be easily adapted to other noble gas atoms.

  9. Recovery of consciousness is mediated by a network of discrete metastable activity states

    PubMed Central

    Hudson, Andrew E.; Calderon, Diany Paola; Pfaff, Donald W.; Proekt, Alex

    2014-01-01

    It is not clear how, after a large perturbation, the brain explores the vast space of potential neuronal activity states to recover those compatible with consciousness. Here, we analyze recovery from pharmacologically induced coma to show that neuronal activity en route to consciousness is confined to a low-dimensional subspace. In this subspace, neuronal activity forms discrete metastable states persistent on the scale of minutes. The network of transitions that links these metastable states is structured such that some states form hubs that connect groups of otherwise disconnected states. Although many paths through the network are possible, to ultimately enter the activity state compatible with consciousness, the brain must first pass through these hubs in an orderly fashion. This organization of metastable states, along with dramatic dimensionality reduction, significantly simplifies the task of sampling the parameter space to recover the state consistent with wakefulness on a physiologically relevant timescale. PMID:24927558

  10. Electron impact ionization of helium from its ground and metastable states

    NASA Astrophysics Data System (ADS)

    Zhang-jin, Chen; Ke-zun, Xu

    1999-05-01

    The triple differential cross sections for the ionization of helium from its ground state 1 1S and metastable states 2 1S and 2 3S in coplanar asymmetric geometry by 150, 250 and 400 eV electrons have been calculated in the BBK model. The present results are compared with the experimental data and/or the other theoretical ones. It has been found that the structures for the metastable states differ markedly from those for the ground state. The collision mechanisms for the new structures appearing in the cross sections for the ionization from metastable states have been analysed. And it has been shown how the intensity of recoil peak changes due to the size of the electron orbital. In addition, the optimal kinematical situations for the cross sections are explored for future experiment.

  11. Understanding metastable phase transformation during crystallization of RDX, HMX and CL-20: experimental and DFT studies.

    PubMed

    Ghosh, Mrinal; Banerjee, Shaibal; Shafeeuulla Khan, Md Abdul; Sikder, Nirmala; Sikder, Arun Kanti

    2016-09-14

    Multiphase growth during crystallization severely affects deliverable output of explosive materials. Appearance and incomplete transformation of metastable phases are a major source of polymorphic impurities. This article presents a methodical and molecular level understanding of the metastable phase transformation mechanism during crystallization of cyclic nitramine explosives, viz. RDX, HMX and CL-20. Instantaneous reverse precipitation yielded metastable γ-HMX and β-CL-20 which undergo solution mediated transformation to the respective thermodynamic forms, β-HMX and ε-CL-20, following 'Ostwald's rule of stages'. However, no metastable phase, anticipated as β-RDX, was evidenced during precipitation of RDX, which rather directly yielded the thermodynamically stable α-phase. The γ→β-HMX and β→ε-CL-20 transformations took 20 and 60 minutes respectively, whereas formation of α-RDX was instantaneous. Density functional calculations were employed to identify the possible transition state conformations and to obtain activation barriers for transformations at wB97XD/6-311++G(d,p)(IEFPCM)//B3LYP/6-311G(d,p) level of theory. The computed activation barriers and lattice energies responsible for transformation of RDX, HMX and CL-20 metastable phases to thermodynamic ones conspicuously supported the experimentally observed order of phase stability. This precise result facilitated an understanding of the occurrence of a relatively more sensitive and less dense β-CL-20 phase in TNT based melt-cast explosive compositions, a persistent and critical problem unanswered in the literature. The crystalline material recovered from such compositions revealed a mixture of β- and ε-CL-20. However, similar compositions of RDX and HMX never showed any metastable phase. The relatively long stability with the highest activation barrier is believed to restrict complete β→ε-CL-20 transformation during processing. Therefore a method is suggested to overcome this issue.

  12. Solubility measurement of a metastable achiral crystal of sodium chlorate in solution growth

    NASA Astrophysics Data System (ADS)

    Niinomi, Hiromasa; Horio, Atsushi; Harada, Shunta; Ujihara, Toru; Miura, Hitoshi; Kimura, Yuki; Tsukamoto, Katsuo

    2014-05-01

    The solubility of the metastable achiral monoclinic phase in NaClO3 crystallization from an aqueous solution, which appears prior to the nucleation of chiral crystals, was successfully measured in the range from 10 °C to 23 °C. Antisolvent crystallization method was used to obtain metastable crystals for the measurement. The solubility was determined to be about 1.6 times higher than that of the chiral stable cubic phase by observing growth or dissolution of the crystal in aqueous solution at the temperature and concentration of which is predetermined.

  13. Field-induced metastability of the modulation wave vector in a magnetic soliton lattice

    DOE PAGES

    Zhu, M.; Peng, J.; Hong, T.; ...

    2017-04-19

    We present magnetic-field-induced metastability of the magnetic soliton lattice in a bilayer ruthenate Ca3(Ru1–xFex)2O7(x=0.05) through single-crystal neutron diffraction study. We show that the incommensurability of the modulation wave vector at zero field strongly depends on the history of magnetic field at low temperature, and that the equilibrium ground state can be achieved by warming above a characteristic temperature Tg~37K. Lastly, we suggest that such metastability might be associated with the domain wall pinning by the magnetic Fe dopants.

  14. Cells, cancer, and rare events: homeostatic metastability in stochastic nonlinear dynamical models of skin cell proliferation.

    PubMed

    Warren, Patrick B

    2009-09-01

    A recently proposed model for skin cell proliferation [E. Clayton, Nature (London) 446, 185 (2007)] is extended to incorporate mitotic autoregulation, and hence homeostasis as a fixed point of the dynamics. Unlimited cell proliferation in such a model can be viewed as a model for carcinogenesis. One way in which this can arise is homeostatic metastability, in which the cell populations escape from the homeostatic basin of attraction by a large but rare stochastic fluctuation. Such an event can be viewed as the final step in a multistage model of carcinogenesis. Homeostatic metastability offers a possible explanation for the peculiar epidemiology of lung cancer in ex-smokers.

  15. Direct determination of metastable phase diagram by synchrotron radiation experiments on undercooled metallic melts.

    PubMed

    Notthoff, C; Feuerbacher, B; Franz, H; Herlach, D M; Holland-Moritz, D

    2001-02-05

    The phase selection process during the crystallization of undercooled metallic melts is studied in situ by combining the electromagnetic levitation technique with energy dispersive x-ray diffraction of synchrotron radiation. The crystallization of metastable bcc phase in binary Ni-V alloys was identified. A metastable phase diagram of Ni-V alloy is constructed, which shows the primarily solidifying phase as a function of composition and undercooling. The analysis within nucleation theory emphasizes the important role of metal oxide as a heterogeneous nucleation site controlling the phase selection.

  16. Crystallization of struvite from metastable region with different types of seed crystal

    NASA Astrophysics Data System (ADS)

    Ali, Imtiaj; Schneider, Phil Andrew

    2005-05-01

    The main feature of this paper was to recognize struvite crystallization in the metastable region of supersaturation. Thermodynamic equilibria of struvite were simulated to identify the minimum struvite solubility limit, thereafter validated by existing thermodynamic modelling packages such as PHREEQC and the derived data from existing struvite solubility curve. Using laser light scattering detection, spontaneous nucleation was identified by the slow increase of pH in a supersaturated solution of struvite. The crystallization experiment, conducted close to the saturation region in metastable zone, initiated struvite growth. The conducted experiment showed that mother crystal (struvite) was more effective as seeds for struvite crystallization.

  17. Tunable Diode Laser Absorption Spectroscopy of Metastable Atoms in Dusty Plasmas

    SciTech Connect

    Hoang Tung Do; Hippler, Rainer

    2008-09-07

    Spatial density profile of neon metastable produced in dusty plasma was investigated by means of tunable diode laser absorption spectroscopy. The line averaged measured density drops about 30% with the presence of dust particles. The observations provide evidence for a significant interaction between atoms and powder particles which are important for energy transfer from plasma to particles. The power per unit area absorbed by dust particles due to the collision of metastable atoms with dust particle surface is about some tens of mW/m{sup 2}.

  18. Metastable states and macroscopic quantum tunneling in a cold atom josephson ring

    SciTech Connect

    Solenov, Dmitry; Mozyrsky, Dmitry

    2009-01-01

    We study macroscopic properties of a system of weakly interacting neutral bosons confined in a ring-shaped potential with a Josephson junction. We derive an effective low energy action for this system and evaluate its properties. In particular we find that the system possesses a set of metastable current-carrying states and evaluate the rates of transitions between these states due to macroscopic quantum tunneling. Finally we discuss signatures of different metastable states in the time-of-flight images and argue that the effect is observable within currently available experimental technique.

  19. Experimental constraints on the depth of olivine metastability in subducting lithosphere

    NASA Astrophysics Data System (ADS)

    Mosenfelder, Jed L.; Marton, Frederic C.; Ross, Charles R.; Kerschhofer, Ljuba; Rubie, David C.

    2001-12-01

    The hypothesis that metastable olivine persists in some subducting slabs into the transition zone has wide implications for mantle dynamics and rheology. In order to evaluate this possibility we derive new thermo-kinetic subduction zone models to predict the extent of olivine metastability within the stability fields of its high-pressure polymorphs, wadsleyite and ringwoodite. Our updated models improve on previous work by incorporating experimental kinetic data on realistic mantle compositions ((Mg, Fe) 2SiO 4) rather than analogue systems. Furthermore, latent heat due to the transformation is fed back into both the kinetics and the thermal model. We also consider the effects of transformation stress on growth kinetics and the possibility of an intracrystalline transformation mechanism, previously thought to be important only at high shear stresses. Our models predict significantly smaller wedges of metastable olivine than previous work. In the case of Tonga, for example, where high values of lithospheric age (100-140 million years) and convergence rate (˜14 cm per year) are most favorable for metastability, models considering only grain boundary nucleation and interface-controlled growth predict olivine metastability to ˜600 km depth, in contrast to ˜660 km predicted previously by Kirby et al. [Rev. Geophys. 34 (1996) 261]. When intracrystalline transformation is considered, the depth of metastability is further reduced by as much as 100 km, due to the large increase in the density of nucleation sites. Inhibition of growth by transformation stress can increase the depth interval over which the transformation takes place, but is unlikely to be a dominant factor, especially if the intracrystalline mechanism operates. These results indicate that the existence of metastable olivine at depths corresponding to those of the deepest earthquakes (˜680 km) requires subduction of old lithosphere (>100 million years) and a high vertical subduction velocity (≳15 cm per

  20. Metastable states and intermittent switching of small populations of confined point vortices

    SciTech Connect

    Schmieder, R.W.

    1995-07-01

    We have found that small populations of point vortices confined in a box exhibit a variety of new and interesting metastable collective motions, ranging from rigid body rotation to complete chaos. These motions are induced by simulated heating and cooling of the vortices; they do not appear in adiabatic systems. By judicious choice of vortex circulations, heating and cooling rates, and box size, we have produced systems that switch intermittently between several metastable states, that oscillate quasi-periodically, and that show a variety of interesting collective behaviors that in some cases are suggestive of biological organisms.

  1. Discovery of a metastable Al20Sm4 phase

    SciTech Connect

    Ye, Z.; Zhang, F.; Sun, Y.; Mendelev, M. I.; Ott, R. T.; Park, E.; Besser, M. F.; Kramer, M. J.; Ding, Z.; Wang, C. -Z.; Ho, K. -M.

    2015-03-09

    In this study, we present an efficient genetic algorithm, integrated with experimental diffraction data, to solve a nanoscale metastable Al20Sm4 phase that evolves during crystallization of an amorphous magnetron sputtered Al90Sm10 alloy. The excellent match between calculated and experimental X-ray diffraction patterns confirms an accurate description of this metastable phase. Molecular dynamic simulations of crystal growth from the liquid phase predict the formation of disordered defects in the devitrified crystal.

  2. An ultracold, optically trapped mixture of 87Rb and metastable 4He atoms

    NASA Astrophysics Data System (ADS)

    Flores, Adonis Silva; Mishra, Hari Prasad; Vassen, Wim; Knoop, Steven

    2017-02-01

    We report on the realization of an ultracold (<25 μK) mixture of rubidium (87Rb) and metastable triplet helium (4He) in an optical dipole trap. Our scheme involves laser cooling in a dual-species magneto-optical trap, simultaneous MW- and RF-induced forced evaporative cooling in a quadrupole magnetic trap, and transfer to a single-beam optical dipole trap. We observe long trapping lifetimes for the doubly spin-stretched spin-state mixture and measure much shorter lifetimes for other spin-state combinations. We discuss prospects for realizing quantum degenerate mixtures of alkali-metal and metastable helium atoms.

  3. Optical pumping of metastable NH radicals into the paramagnetic ground state

    SciTech Connect

    Meerakker, Sebastiaan Y.T. van de; Mosk, Allard P.; Jongma, Rienk T.; Sartakov, Boris G.; Meijer, Gerard

    2003-09-01

    We here report on the optical pumping of both {sup 14}NH and {sup 15}NH radicals from the metastable a {sup 1}{delta} state into the X {sup 3}{sigma}{sup -} ground state in a molecular beam experiment. By inducing the hitherto unobserved spin-forbidden A {sup 3}{pi} <- a {sup 1}{delta} transition, followed by spontaneous emission to the X {sup 3}{sigma}{sup -} state, a unidirectional pathway for population transfer from the metastable state into the electronic ground state is obtained. The optical pumping scheme demonstrated here opens up the possibility to accumulate NH radicals in a magnetic or optical trap.

  4. Cells, cancer, and rare events: Homeostatic metastability in stochastic nonlinear dynamical models of skin cell proliferation

    NASA Astrophysics Data System (ADS)

    Warren, Patrick B.

    2009-09-01

    A recently proposed model for skin cell proliferation [E. Clayton , Nature (London) 446, 185 (2007)] is extended to incorporate mitotic autoregulation, and hence homeostasis as a fixed point of the dynamics. Unlimited cell proliferation in such a model can be viewed as a model for carcinogenesis. One way in which this can arise is homeostatic metastability, in which the cell populations escape from the homeostatic basin of attraction by a large but rare stochastic fluctuation. Such an event can be viewed as the final step in a multistage model of carcinogenesis. Homeostatic metastability offers a possible explanation for the peculiar epidemiology of lung cancer in ex-smokers.

  5. Metastable McLafferty rearrangement reaction in the electron impact ionization of stearic acid methyl ester

    NASA Astrophysics Data System (ADS)

    Takayama, Mitsuo

    1995-06-01

    The metastable peaks for the McLafferty rearrangement and double hydrogen rearrangement reactions have been observed in the stearic acid methyl ester system under electron impact ionization. The metastable ion spectrum of the M+. ion gave peaks corresponding to the ions at m/z 74, 75, 87 and 88, whereas the collision-induced dissociation spectrum showed low intensity ions at m/z 75 and 88 which come from double hydrogen rearrangement reactions of M+. ions. The kinetics for the change of the molecular ions to different structures before fragmentation have been discussed.

  6. Discontinuous Bubble Nucleation Due to a Metastable Condensation Transition in Polymer-CO2 Mixtures.

    PubMed

    Xu, Xiaofei; Cristancho, Diego E; Costeux, Stéphane; Wang, Zhen-Gang

    2013-05-16

    We combine a newly developed density-functional theory with the string method to calculate the minimum free energy path of bubble nucleation in compressible polymer-CO2 mixtures. Nucleation is initiated by saturating the polymer liquid with high pressure CO2 and subsequently reducing the pressure to ambient condition. Below a critical temperature, we find that there is a discontinuous drop in the nucleation barrier with increased initial CO2 pressure, as a result of an underlying metastable transition from a CO2-rich-vapor phase to a CO2-rich-liquid phase. This phenomenon is different from previously proposed nucleation mechanisms involving metastable transitions.

  7. The radiative lifetime of the 5S(0)2 metastable level of O(2+)

    NASA Technical Reports Server (NTRS)

    Johnson, B. C.; Smith, P. L.; Knight, R. D.

    1984-01-01

    The radiative lifetime of the 5S(0)2 metastable level of O(2+) was measured as 1.22 + or - 0.08 ms at the 90 percent confidence level by observing the time dependence of the spontaneous emission from metastable ions created and stored in a cylindrical radio-frequency ion trap. The intersystem line emission 2s(2)2p(2) 3P - 2s2p(3) 5S(0) was observed at 1660.8 and 1666.2 A. Discrepancies between measured and calculated values indicate that certain calculated transition probabilities for intersystem lines may be less reliable than previously believed.

  8. Phase behavior of metastable liquid silicon at negative pressure: Ab initio molecular dynamics

    NASA Astrophysics Data System (ADS)

    Zhao, G.; Yu, Y. J.; Yan, J. L.; Ding, M. C.; Zhao, X. G.; Wang, H. Y.

    2016-04-01

    Extensive first-principle molecular dynamics simulations are performed to study the phase behavior of metastable liquid Si at negative pressure. Our results show that the high-density liquid (HDL) and HDL-vapor spinodals indeed form a continuous reentrant curve and the liquid-liquid critical point seems to just coincide with its minimum. The line of density maxima also has a strong tendency to pass through this minimum. The phase behaviour of metastable liquid Si therefore tends to be a critical-point-free scenario rather than a second-critical-point one based on SW potential.

  9. Formation of metastable tetragonal zirconia nanoparticles: Competitive influence of the dopants and surface state

    SciTech Connect

    Gorban, Oksana; Synyakina, Susanna; Volkova, Galina; Gorban, Sergey; Konstantiova, Tetyana; Lyubchik, Svetlana

    2015-12-15

    The effect of the surface modification of the nanoparticles of amorphous and crystalline partially stabilized zirconia by fluoride ions on stability of the metastable tetragonal phase was investigated. Based on the DSC, titrimetry and FTIR spectroscopy data it was proven that surface modification of the xerogel resulted from an exchange of the fluoride ions with the basic OH groups. The effect of the powder pre-calcination temperature before modification on the formation of metastable tetragonal phase in partially stabilized zirconia was investigated. It was shown that the main factor of tetragonal zirconia stabilization is the state of nanoparticles surface at pre-crystallization temperatures.

  10. Influence of urine pH and citrate concentration on the upper limit of metastability for calcium phosphate.

    PubMed

    Greischar, Amy; Nakagawa, Y; Coe, Frederic L

    2003-03-01

    We determined the effects on the urine upper limit of metastability for calcium phosphate of citrate concentration and pH, and achievement of the upper limit of metastability by adding calcium or phosphate. The citrate concentration in aliquots of 24-hour urine samples from normal males without a history of kidney stones was increased. The upper limit of metastability was determined by the point of visible crystal formation, as confirmed by increased optical density at 620 nm. when calcium or pH was increased. In additional experiments the upper limit of metastability was determined by adding calcium or phosphate at pH 5.9 and 6.4. Regardless of how the upper limit of metastability was achieved increasing the citrate concentration increased the former value by about 0.4 units per mM. citrate per l. The upper limit of metastability achieved in a given urine sample by adding phosphate or calcium did not differ. Increasing urine pH increased the upper limit of metastability. Treatment with alkaline citrate salts may decrease stone formation via an increase in calcium phosphate upper limit of metastability by increasing urine citrate and by directly affecting increased pH.

  11. Metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere

    USGS Publications Warehouse

    Kirby, S.H.; Stein, S.; Okal, E.A.; Rubie, David C.

    1996-01-01

    Earth's deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km. This depth interval closely brackets the mantle transition zone, characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher-pressure phases. Deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal, thermodynamic, and mechanical ferment inside slabs. Numerical simulations of reaction rates show that the olivine ??? spinel transformation should be kinetically hindered in old, cold slabs descending into the transition zone. Thus wedge-shaped zones of metastable peridotite probably persist to depths of more than 600 km. Laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting. This instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser, finer-grained phase. Hence in cold slabs, such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite. It is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs. This consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features. It explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone, where minerals in downgoing slabs should transform to spinel and ilmenite structures. The onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab. Even if a slab penetrates into the lower mantle, earthquakes

  12. Persistence of metastable vortex lattice domains in MgB2 in the presence of vortex motion.

    PubMed

    Rastovski, C; Schlesinger, K J; Gannon, W J; Dewhurst, C D; DeBeer-Schmitt, L; Zhigadlo, N D; Karpinski, J; Eskildsen, M R

    2013-09-06

    Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series of small changes in the applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning. Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a rotation to the ground state orientation.

  13. Persistence of Metastable Vortex Lattice Domains in MgB2 in the Presence of Vortex Motion

    SciTech Connect

    Rastovski, Catherine; Schlesinger, Kimberly; Gannon, William J; Dewhurst, Charles; Debeer-Schmitt, Lisa M; Zhigadlo, Nikolai; Karpinski, Janusz; Eskildsen, Morten

    2013-01-01

    Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series of small changes in the applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning. Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a rotation to the ground state orientation.

  14. Vortex Lattice Metastability and Power Law Dynamics in MgB2

    NASA Astrophysics Data System (ADS)

    Rastovski, Catherine; Kuhn, S. J.; Smith, K.; Eskildsen, M. R.; Debeer-Schmitt, L.; Dewhurst, C. D.; Gannon, W. J.; Zhigadlo, N. D.; Karpinski, J.

    2014-03-01

    Previous small-angle neutron scattering (SANS) studies of the vortex lattice (VL) of MgB2 with H ∥ c found a triangular VL which undergoes a field-driven 30° reorientation transition, forming three distinct ground state phases. A high degree of metastability exists between the VL phases of MgB2 that cannot be attributed to vortex pinning and may be a result of the jamming of VL domains [C. Rastovski et al., Phys. Rev. Lett. 111, 107002 (2013)]. To further investigate the effect of vortex motion on the metastable to ground state VL transition, we applied a small AC magnetic field parallel or perpendicular to the vortices to ``shake'' the lattice. The metastable VL volume fraction decreased with a two-step power law dependence on the number of applied AC cycles. The slow and then fast power law decay of the metastable state may indicate first nucleation and then growth of ground state VL domains. This work was supported by the Department of Energy, Basic Energy Sciences under Award No. DE-FG02-10ER46783.

  15. Thermal evolution of the metastable r8 and bc8 polymorphs of silicon

    SciTech Connect

    Haberl, Bianca; Guthrie, Malcolm; Sinogeikin, Stanislav V.; Shen, Guoyin; Williams, James S.; Bradby, Jodie E.

    2015-01-28

    The kinetics of two metastable polymorphs of silicon under thermal annealing was investigated. These phases with body-centered cubic bc8 and rhombohedral r8 structures can be formed upon pressure release from metallic silicon.We study these metastable polymorphs were formed by two different methods, via point loading and in a diamond anvil cell (DAC). Upon thermal annealing different transition pathways were detected. In the point loading case, the previously reported Si-XIII formed and was confirmed as a new phase with an as-yet-unidentified structure. In the DAC case, bc8-Si transformed to the hexagonal-diamond structure at elevated pressure, consistent with previous studies at ambient pressure. In contrast, r8-Si transformed directly to diamond-cubic Si at a temperature of 255⁰C. In conclusion, these data were used to construct diagrams of the metastability regimes of the polymorphs formed in a DAC and may prove useful for potential technological applications of these metastable polymorphs.

  16. Confined Metastable 2-Line Ferrihydrite for Affordable Point-of-Use Arsenic-Free Drinking Water.

    PubMed

    Kumar, Avula Anil; Som, Anirban; Longo, Paolo; Sudhakar, Chennu; Bhuin, Radha Gobinda; Gupta, Soujit Sen; Anshup; Sankar, Mohan Udhaya; Chaudhary, Amrita; Kumar, Ramesh; Pradeep, Thalappil

    2017-02-01

    Arsenic-free drinking water, independent of electrical power and piped water supply, is possible only through advanced and affordable materials with large uptake capacities. Confined metastable 2-line ferrihydrite, stable at ambient temperature, shows continuous arsenic uptake in the presence of other complex species in natural drinking water and an affordable water-purification device is made using the same.

  17. Solid state photochemistry. Subpanel A-2(b): Metastability in hydrogenated amorphous silicon

    SciTech Connect

    Carlson, D.

    1996-09-01

    All device quality amorphous silicon based materials exhibit degradation in electronic properties when exposed to sunlight. The photo-induced defects are associated with Si dangling bonds that are created by the recombination and/or trapping of photogenerated carriers. The defects are metastable and can be annealed out at temperatures of about 150 to 200 degrees Centigrade. The density of metastable defects is larger in films that are contaminated with > 10{sup 19} per cubic cm of impurities such as oxygen, carbon and nitrogen. However, recent experimental results indicate that some metastable defects are still present in films with very low impurity concentrations. The photo-induced defects typically saturate after 100 to 1000 hours of exposure to one sun illumination depending on the deposition conditions. There is also experimental evidence that photo-induced structural changes are occurring in the amorphous silicon based materials and that hydrogen may be playing an important role in both the photo-induced structural changes and in the creation of metastable defects.

  18. Metal-atom fluorescence from the quenching of metastable rare gases by metal carbonyls

    SciTech Connect

    Hollingsworth, W.E.

    1982-11-01

    A flowing afterglow apparatus was used to study the metal fluorescence resulting from the quenching of metastable rare-gas states by metal carbonyls. The data from the quenching or argon, neon, and helium by iron and nickel carbonyl agreed well with a restricted degree of freedom model indicating a concerted bond-breaking dissociation.

  19. Spontaneous SUSY breaking with anomalous U(1) symmetry by meta-stable vacuum

    SciTech Connect

    Nishino, Hiroyuki

    2008-11-23

    We will discuss a SUSY breaking model with anomalous U(1) symmetry. We discard R-symmetry and allow non-renormalizable terms for the model. It will be shown that certain class of models, where the number of positively charged fields is larger than that of negatively charged fields, can have meta-stable SUSY breaking vacuum.

  20. Interindividual variation in DNA methylation at a putative POMC metastable epiallele is associated with obesity

    USDA-ARS?s Scientific Manuscript database

    The estimated heritability of human BMI is close to 75%, but identified genetic variants explain only a small fraction of interindividual body-weight variation. Inherited epigenetic variants identified in mouse models named "metastable epialleles" could in principle explain this "missing heritabilit...

  1. Metastability in lipid based particles exhibits temporally deterministic and controllable behavior.

    PubMed

    Jacoby, Guy; Cohen, Keren; Barkan, Kobi; Talmon, Yeshayahu; Peer, Dan; Beck, Roy

    2015-03-30

    The metastable-to-stable phase-transition is commonly observed in many fields of science, as an uncontrolled independent process, highly sensitive to microscopic fluctuations. In particular, self-assembled lipid suspensions exhibit phase-transitions, where the underlying driving mechanisms and dynamics are not well understood. Here we describe a study of the phase-transition dynamics of lipid-based particles, consisting of mixtures of dilauroylphosphatidylethanolamine (DLPE) and dilauroylphosphatidylglycerol (DLPG), exhibiting a metastable liquid crystalline-to-stable crystalline phase transition upon cooling from 60°C to 37°C. Surprisingly, unlike classically described metastable-to-stable phase transitions, the manner in which recrystallization is delayed by tens of hours is robust, predetermined and controllable. Our results show that the delay time can be manipulated by changing lipid stoichiometry, changing solvent salinity, adding an ionophore, or performing consecutive phase-transitions. Moreover, the delay time distribution indicates a deterministic nature. We suggest that the non-stochastic physical mechanism responsible for the delayed recrystallization involves several rate-affecting processes, resulting in a controllable, non-independent metastability. A qualitative model is proposed to describe the structural reorganization during the phase transition.

  2. Metastability in lipid based particles exhibits temporally deterministic and controllable behavior

    PubMed Central

    Jacoby, Guy; Cohen, Keren; Barkan, Kobi; Talmon, Yeshayahu; Peer, Dan; Beck, Roy

    2015-01-01

    The metastable-to-stable phase-transition is commonly observed in many fields of science, as an uncontrolled independent process, highly sensitive to microscopic fluctuations. In particular, self-assembled lipid suspensions exhibit phase-transitions, where the underlying driving mechanisms and dynamics are not well understood. Here we describe a study of the phase-transition dynamics of lipid-based particles, consisting of mixtures of dilauroylphosphatidylethanolamine (DLPE) and dilauroylphosphatidylglycerol (DLPG), exhibiting a metastable liquid crystalline-to-stable crystalline phase transition upon cooling from 60°C to 37°C. Surprisingly, unlike classically described metastable-to-stable phase transitions, the manner in which recrystallization is delayed by tens of hours is robust, predetermined and controllable. Our results show that the delay time can be manipulated by changing lipid stoichiometry, changing solvent salinity, adding an ionophore, or performing consecutive phase-transitions. Moreover, the delay time distribution indicates a deterministic nature. We suggest that the non-stochastic physical mechanism responsible for the delayed recrystallization involves several rate-affecting processes, resulting in a controllable, non-independent metastability. A qualitative model is proposed to describe the structural reorganization during the phase transition. PMID:25820650

  3. Visible light-induced ion-selective optodes based on a metastable photoacid for cation detection.

    PubMed

    Patel, Parth K; Chumbimuni-Torres, Karin Y

    2016-01-07

    A new platform of ion-selective optodes is presented here to detect cations under thermodynamic equilibrium via ratiometric analysis. This novel platform utilizes a 'one of a kind' visible light-induced metastable photoacid as a reference ion indicator to achieve activatable and controllable sensors. These ion-selective optodes were studied in terms of their stability, sensitivity, selectivity, and theoretical aspects.

  4. Removal of contaminants by plasma assisted cleaning by metastable atom neutralization (PACMAN)

    NASA Astrophysics Data System (ADS)

    Lytle, W. M.; Szybilski, D. S.; Das, C. E.; Raju, R.; Ruzic, D. N.

    2009-03-01

    For the continued advancement of lithography, specifically extreme ultraviolet lithography (EUVL), particle contamination on the photomask and the subsequent removal of these particles is of critical importance. Particle contamination on the photomasks can result in defects printed on devices and their subsequent failure and/or process throughput reduction. A new idea for the removal of these particles is to utilize the energy in metastable species in a plasma. In a laboratory or processing plasma where ionization fraction is relatively low, there exists metastable species with long lifetimes that have significant energy, in some cases on the order of ~20 eV. Through a combined process of ion bombardment as well as the energy transferred from the neutralization of the metastable species, particles on a surface can be reduced to volatile compounds which can be pumped off of the surface thus reducing the particle contamination on the surface. Preliminary results for the removal of polystyrene latex (PSL) nano particles on low resistivity silicon wafers have shown approximately 20 nm/min removal rates. The removal rate obtained through the use of the PACMAN technique is much faster compared to just metastable cleaning alone. The current results of the removal of particles via the PACMAN technique will be presented as well as a damage assessment if any caused by this process.

  5. Thermal evolution of the metastable r8 and bc8 polymorphs of silicon

    DOE PAGES

    Haberl, Bianca; Guthrie, Malcolm; Sinogeikin, Stanislav V.; ...

    2015-01-28

    The kinetics of two metastable polymorphs of silicon under thermal annealing was investigated. These phases with body-centered cubic bc8 and rhombohedral r8 structures can be formed upon pressure release from metallic silicon.We study these metastable polymorphs were formed by two different methods, via point loading and in a diamond anvil cell (DAC). Upon thermal annealing different transition pathways were detected. In the point loading case, the previously reported Si-XIII formed and was confirmed as a new phase with an as-yet-unidentified structure. In the DAC case, bc8-Si transformed to the hexagonal-diamond structure at elevated pressure, consistent with previous studies at ambientmore » pressure. In contrast, r8-Si transformed directly to diamond-cubic Si at a temperature of 255⁰C. In conclusion, these data were used to construct diagrams of the metastability regimes of the polymorphs formed in a DAC and may prove useful for potential technological applications of these metastable polymorphs.« less

  6. Lifetimes of the CO metastable a 3Π(v<=3,Ω,J) levels

    NASA Astrophysics Data System (ADS)

    Sykora, Thomas; Vidal, C. R.

    1999-04-01

    We reanalyze the theoretical lifetimes of the metastable a 3Π(v=0,Ω,J) levels as well as the spontaneous a3Π(v=0) decay rates into the X 1Σ+(v) ground state levels, clearly favoring the measurements of Jongma et al. [J. Chem. Phys. 107, 7034 (1997)] as compared to the theoretical results of James [J. Chem. Phys. 55, 4118 (1971)]. Theoretical lifetimes of the vibrationally higher lying metastable levels a 3Π(v=1-3,Ω,J) are listed for the first time. The lifetimes of the two Λ components are shown to be different. A new technique for measuring the lifetime of individual rovibrational metastable molecular levels is applied to the CO rovibrational level a3Π(v=3,Ω=1,J=2). Our result τ=3.04±0.38 ms is in good agreement with the theoretical lifetime of 2.97 ms. The metastable population is deduced to be Nmeta=(2.3±1.2)ṡ106 molecules/shot. Finally, our ms lifetime measurement technique is compared with that developed by Jongma et al. [J. Chem. Phys. 107, 7034 (1997)].

  7. Growth of single-crystal metastable semiconducting (GaSb)1-xGex films

    NASA Astrophysics Data System (ADS)

    Cadien, K. C.; Eltoukhy, A. H.; Greene, J. E.

    1981-05-01

    Epitaxial metastable (GaSb)1-xGex alloys with compostions across the pseudobinary phase diagram have been grown on (100) GaAs substrates by multitarget rf sputtering. An essential feature allowing the growth of these metastable materials was low-energy ion bombardment of the growing film during deposition to enhance surface diffusion, promote mixing, and preferentially sputter incipient second-phase precipitates. Annealing experiments indicated that the metastable films exhibit good high-temperature stability and that they transform through a continuous series of GaSb-rich and Ge-rich phases in which the solute concentrations decrease until the equilibrium two-phase alloy is obtained. While the calculated free-energy difference between the single-phase metastable and equilibrium states is ˜18 meV, the measured activation barrier for the transformation is ˜3 eV. All films were p-type with room-temperature hole concentrations varying from 1016 to 1019 cm-3 and mobilities between 10 and 720 cm2/ V s, depending on film composition.

  8. Distinct metastable atmospheric regimes despite nearly Gaussian statistics: A paradigm model

    PubMed Central

    Majda, Andrew J.; Franzke, Christian L.; Fischer, Alexander; Crommelin, Daniel T.

    2006-01-01

    A controversial topic in the recent climate modeling literature is the fashion in which metastable low-frequency regimes in the atmosphere occur despite nearly Gaussian statistics for these planetary waves. Here a simple 57-mode paradigm model for such metastable atmospheric regime behavior is introduced and analyzed through hidden Markov model (HMM) analysis of the time series of suitable low-frequency planetary waves. The analysis of this paradigm model elucidates how statistically significant metastable regime transitions between blocked and zonal statistical states occur despite nearly Gaussian behavior in the associated probability distribution function and without a significant role for the low-order truncated nonlinear dynamics alone; turbulent backscatter onto the three-dimensional subspace of low-frequency modes is responsible for these effects. It also is demonstrated that suitable stochastic mode reduction strategies, which include both augmented cubic nonlinearity and multiplicative noise, are also capable of capturing the metastable low-frequency regime behavior through a single stochastic differential equation compared with the full turbulent chaotic 57-mode model. This feature is attractive for issues such as long-term weather predictability. Although there have been many applications of HMM in other sciences, this work presents a previously undescribed application of HMM analysis to atmospheric low-frequency variability and points the way for further applications including their use in extended range predictability. PMID:16714380

  9. Near-infrared collisional radiative model for Xe plasma electrostatic thrusters: the role of metastable atoms

    NASA Astrophysics Data System (ADS)

    Dressler, Rainer A.; Chiu, Yu-hui; Zatsarinny, Oleg; Bartschat, Klaus; Srivastava, Rajesh; Sharma, Lalita

    2009-09-01

    Mestastable Xe atoms play an important role in the collisional radiative processes of dense xenon plasmas, including those of electric thrusters for space vehicles. Recent measurements and calculations of electron-excitation processes out of the 5p56s J = 2 metastable state (1s5 state in Paschen notation) have allowed for the development of a collisional radiative model for Xe near-infrared (NIR) emissions based on the population of the metastable level through 2p-1s5 radiative transitions, and based on depopulation through electron-impact excitation. A modified plasma radiative model incorporating newly computed electron-impact excitation cross sections using both relativistic distorted wave and semi-relativistic Breit-Pauli B-Spline R-matrix methods is presented. The model applies to optically thin, low-density regions of the thruster plasma and is most accurate at electron temperatures below 10 eV. The model is tested on laboratory spectral measurements of the D55 TAL and BHT-200 Hall thruster plasma NIR radiation. The metastable neutral fraction is determined to rise from 0.1 to slightly above 1% as the electron temperature increases from ~2 to 10 eV, reaching a maximum around 15 eV. Electron temperatures derived with the modified model are approximately 20% lower than a previous version of the model that used an approximate approach to account for metastable population and line intensity enhancement.

  10. Interplay between structure and superconductivity: Metastable phases of phosphorus under pressure

    NASA Astrophysics Data System (ADS)

    Flores-Livas, José A.; Sanna, Antonio; Drozdov, Alexander P.; Boeri, Lilia; Profeta, Gianni; Eremets, Mikhail; Goedecker, Stefan

    2017-07-01

    Pressure-induced superconductivity and structural phase transitions in phosphorus (P) are studied by resistivity measurements under pressures up to 170 GPa and by fully ab initio crystal structure exploration and superconductivity calculations up to 350 GPa. Two distinct superconducting transition temperature (TC) vs pressure (P ) trends at low pressure have been reported more than 30 years ago, and we are able to devise a consistent explanation founded on thermodynamically metastable phases of black phosphorus. Our experimental and theoretical results form a single, consistent picture which not only provides a clear understanding of elemental P under pressure but also sheds light on the longstanding and unsolved anomalous superconductivity trends. Moreover, at higher pressures we predict a similar scenario of multiple metastable structures which coexist beyond their thermodynamical stability range. We observe that all the metastable structures systematically exhibit larger transition temperatures than the ground-state structures, indicating that the exploration of metastable phases represents a promising route to design materials with improved superconducting properties.

  11. Centrifugal Tensioned Metastable Fluid Detectors for Trace Radiation Sources: Experimental Verification and Military Employment

    DTIC Science & Technology

    2016-06-01

    TENSIONED METASTABLE FLUID DETECTORS FOR TRACE RADIATION SOURCES: EXPERIMENTAL VERIFICATION AND MILITARY EMPLOYMENT by Dominic J. Chiaverotti...DETECTORS FOR TRACE RADIATION SOURCES: EXPERIMENTAL VERIFICATION AND MILITARY EMPLOYMENT 5. FUNDING NUMBERS 6. AUTHOR(S) Dominic J. Chiaverotti 7...the detection of fast neutrons or alpha particles that are telltale signs of nuclear material, while remaining blind to gamma radiation that could

  12. Approximate reasoning by pairwise comparisons. "Topodynamics of metastable brains" by Arturo Tozzi, et al.

    NASA Astrophysics Data System (ADS)

    Kakiashvili, Tamar; Koczkodaj, Waldemar W.; Magnot, Jean-Pierre

    2017-07-01

    The innovative approach in [1], ;Topodynamics of Metastable Brains; by Arturo Tozzi, James Peters, Andrew Fingelkurts, Alexander Fingelkurts, and Pedro Marijuan has a high potential of becoming a paradigm shift in the brain research. It seems that this study has successfully explored the possibility of applying a celebrated Borsuk-Ulam theorem to the operational architectonics of the fundamental brain-mind processes.

  13. Density of metastable atoms in the plume of a low-pressure argon microplasma

    NASA Astrophysics Data System (ADS)

    Cooley, James; Xue, Jun; Urdahl, Randall

    2011-10-01

    Spatially-resolved measurements of the density of metastable excited atoms in the plume of an argon microplasma are presented. The microplasma device is operated at relatively low pressure, on the order of 1 Torr, and is exhausted into a vacuum. Line-integrated densities of excited argon neutrals in the exhaust plume are measured using tunable diode laser absorption spectroscopy. The density of argon metastables in both 1s5 and 1s3 states are measured. These line-integrated density measurements are converted to three-dimensional density maps using Abel inversion. The density of 1s5 argon peaks at a value of approximately 1018 m-3 near the outlet orifice, while the 1s3 density is roughly five times lower everywhere. It is found that, far from the face of the microplasma outlet orifice, metastable density follows an angular distribution consistent with that expected of vacuum gas expansion as predicted by classic rarified flow theory. Metastable flux is found to be conserved as the plume expands through 4 mm, suggesting an absence of de-excitation collisions or other loss processes along with a frozen velocity profile.

  14. Density of metastable atoms in the plume of a low-pressure argon microplasma

    NASA Astrophysics Data System (ADS)

    Xue, J.; Cooley, J. E.; Urdahl, R. S.

    2012-09-01

    Spatially resolved measurements of the density of metastable excited atoms in the plume of an argon microplasma are presented. The microplasma device is operated at a relatively low pressure, on the order of 1 Torr, and is exhausted into a vacuum. Line-integrated densities of excited argon neutrals in the exhaust plume are measured using tunable diode laser absorption spectroscopy. The densities of argon metastables in both 1s5 and 1s3 states are measured. These line-integrated density measurements are converted to three-dimensional density maps using the Abel inversion. The density of 1s5 argon peaks at a value of approximately 1018 m-3 near the outlet orifice, while the 1s3 density is roughly five times lower everywhere. It is found that, far from the face of the microplasma outlet orifice, metastable density follows axial and angular distributions consistent with that expected of vacuum gas expansion as predicted by classic rarified flow theory. Integrated metastable density is found to be conserved as the plume expands through 4 mm, suggesting a net production of excited species in the first millimetre and a constant population further downstream.

  15. A metastable cubic phase of sodium niobate nanoparticles stabilized by chemically bonded solvent molecules.

    PubMed

    Gu, Qilin; Zhu, Kongjun; Sun, Qiaomei; Liu, Jinsong; Wang, Jing; Qiu, Jinhao; Wang, John

    2016-12-07

    Structural modification, especially the stabilization of metastable phases at room temperature, has emerged as an effective strategy to understand their stabilization mechanism and improve their functional properties. In this work, a facile solvothermal approach is developed to synthesize metastable sodium niobate (NaNbO3) crystals with the cubic symmetry. XRD, Raman and TEM results all confirmed the selective synthesis of cubic and orthorhombic NaNbO3via adjustment of the reaction medium. The fact that traditional hydrothermal synthesis often yields orthorhombic NaNbO3 inspires us to elucidate the formation mechanism of cubic NaNbO3 with respect to the solvent effect. With the increasing post-calcination temperature, the as-synthesized cubic NaNbO3 gradually transforms into the orthorhombic structure, which is understood to be a recrystallization behavior, as evidenced by the XRD and TEM results. The organic molecules retained in the NaNbO3 nanocrystals, as suggested by UV-vis, FT-IR and TGA-MS results, have contributed to the stabilization of the metastable structure, demonstrated by the different temperature-induced phase transition behaviors in air and argon atmospheres, where the phase transition from cubic to orthorhombic would take place at a relatively higher temperature in argon. This work provides an alternative approach to synthesize cubic NaNbO3 nanocrystals, and the understanding of the stabilization mechanism could pave a new pathway for fabricating metastable materials.

  16. Improved metastable de-excitation spectrometer using laser-cooling techniques

    SciTech Connect

    Pratt, Andrew; Roskoss, Alexander; Menard, Herve; Jacka, Marcus

    2005-05-15

    Details of a new approach for performing metastable de-excitation spectroscopy are given. A beam of metastable (2 {sup 3}S) helium atoms, produced in a hollow cathode dc discharge, is collimated and subsequently focused using Doppler cooling of the 2 {sup 3}S{sub 1}-2 {sup 3}P{sub 2} transition at 1083 nm, forming an intense probe of up to 1x10{sup 12} atoms s{sup -1} cm{sup -2}. The large distance (2.5 m) between source and sample means that the beam is relatively free of UV photons and 2 {sup 1}S metastable atoms, removing the need for quench lamps and chopper wheels. As well as providing a clean high intensity source, the well defined nature of the beam is a necessary step towards using more sophisticated laser-cooling techniques with the ultimate aim of producing a metastable helium microscope. MDS and UPS spectra from Si(111) are shown.

  17. Kinetic simulation of thermally induced metastability in the tungsten-carbon system

    NASA Astrophysics Data System (ADS)

    Demetriou, Marios Demetri

    2001-11-01

    A dynamic computational model is developed within the context of classical nucleation theory for thermally induced non-equilibrium phase transitions. The conditions for this model are those encountered in rapid thermal processing of invariantly nucleating compound phases. The kinetic variables used in the model were directly obtained from the free energy formulations that characterize the stable and metastable equilibria amongst participating phases. The isothermal as well as non-isothermal kinetics were simulated by means of stochastic equations which model the fluctuational process of crystal nucleation along with the deterministic process of crystal growth. A strategy to evaluate the static (isothermal) and dynamic (non-isothermal) effects of nucleation transience based on time scale analogy is outlined and validated by contrasting the results of the dynamic model against those obtained from a steady state model. The developed model was applied to the W-C compound-forming binary system. The stable phase equilibria were reproduced using free energy data obtained from literature, while the metastable ones were obtained by extrapolating the stable equilibria into regions of metastability. The model was utilized to simulate the kinetics of graphitization during non-equilibrium peritectic melting of WC. The isothermal kinetic analysis suggests that graphitization becomes extremely rapid when annealing at large superheatings, while the highest crystallization rate was found to occur at the metastable congruent melting point of WC (˜3107 K) where 1-ppm crystallize in ˜2 nanoseconds. The non-isothermal kinetic analysis suggests that increasing the heating rate suppresses graphitization, while graphitization may be completely bypassed by the rapidly forming metastable liquid when processing under extreme rapid heating (˜108 K/s) beyond the metastable congruent melting point of WC. The model was also utilized to simulate the kinetics of phase selection during non

  18. Metastability of Neuronal Dynamics during General Anesthesia: Time for a Change in Our Assumptions?

    PubMed

    Hudson, Andrew E

    2017-01-01

    There is strong evidence that anesthetics have stereotypical effects on brain state, so that a given anesthetic appears to have a signature in the electroencephalogram (EEG), which may vary with dose. This can be usefully interpreted as the anesthetic determining an attractor in the phase space of the brain. How brain activity shifts between these attractors in time remains understudied, as most studies implicitly assume a one-to-one relationship between drug dose and attractor features by assuming stationarity over the analysis interval and analyzing data segments of several minutes in length. Yet data in rats anesthetized with isoflurane suggests that, at anesthetic levels consistent with surgical anesthesia, brain activity alternates between multiple attractors, often spending on the order of 10 min in one activity pattern before shifting to another. Moreover, the probability of these jumps between attractors changes with anesthetic concentration. This suggests the hypothesis that brain state is metastable during anesthesia: though it appears at equilibrium on short timescales (on the order of seconds to a few minutes), longer intervals show shifting behavior. Compelling evidence for metastability in rats anesthetized with isoflurane is reviewed, but so far only suggestive hints of metastability in brain states exist with other anesthetics or in other species. Explicit testing of metastability during anesthesia will require experiments with longer acquisition intervals and carefully designed analytic approaches; some of the implications of these constraints are reviewed for typical spectral analysis approaches. If metastability exists during anesthesia, it implies degeneracy in the relationship between brain state and effect site concentration, as there is not a one-to-one mapping between the two. This degeneracy could explain some of the reported difficulty in using brain activity monitors to titrate drug dose to prevent awareness during anesthesia and should

  19. Metastability of Neuronal Dynamics during General Anesthesia: Time for a Change in Our Assumptions?

    PubMed Central

    Hudson, Andrew E.

    2017-01-01

    There is strong evidence that anesthetics have stereotypical effects on brain state, so that a given anesthetic appears to have a signature in the electroencephalogram (EEG), which may vary with dose. This can be usefully interpreted as the anesthetic determining an attractor in the phase space of the brain. How brain activity shifts between these attractors in time remains understudied, as most studies implicitly assume a one-to-one relationship between drug dose and attractor features by assuming stationarity over the analysis interval and analyzing data segments of several minutes in length. Yet data in rats anesthetized with isoflurane suggests that, at anesthetic levels consistent with surgical anesthesia, brain activity alternates between multiple attractors, often spending on the order of 10 min in one activity pattern before shifting to another. Moreover, the probability of these jumps between attractors changes with anesthetic concentration. This suggests the hypothesis that brain state is metastable during anesthesia: though it appears at equilibrium on short timescales (on the order of seconds to a few minutes), longer intervals show shifting behavior. Compelling evidence for metastability in rats anesthetized with isoflurane is reviewed, but so far only suggestive hints of metastability in brain states exist with other anesthetics or in other species. Explicit testing of metastability during anesthesia will require experiments with longer acquisition intervals and carefully designed analytic approaches; some of the implications of these constraints are reviewed for typical spectral analysis approaches. If metastability exists during anesthesia, it implies degeneracy in the relationship between brain state and effect site concentration, as there is not a one-to-one mapping between the two. This degeneracy could explain some of the reported difficulty in using brain activity monitors to titrate drug dose to prevent awareness during anesthesia and should

  20. INTERSTELLAR METASTABLE HELIUM ABSORPTION AS A PROBE OF THE COSMIC-RAY IONIZATION RATE

    SciTech Connect

    Indriolo, Nick; McCall, Benjamin J.; Hobbs, L. M.; Hinkle, K. H.

    2009-10-01

    The ionization rate of interstellar material by cosmic rays has been a major source of controversy, with different estimates varying by three orders of magnitude. Observational constraints of this rate have all depended on analyzing the chemistry of various molecules that are produced following cosmic-ray ionization, and in many cases these analyses contain significant uncertainties. Even in the simplest case (H{sup +} {sub 3}), the derived ionization rate depends on an (uncertain) estimate of the absorption path length. In this paper, we examine the feasibility of inferring the cosmic-ray ionization rate using the 10830 A absorption line of metastable helium. Observations through the diffuse clouds toward HD 183143 are presented, but yield only an upper limit on the metastable helium column density. A thorough investigation of He{sup +} chemistry reveals that only a small fraction of He{sup +} will recombine into the triplet state and populate the metastable level. In addition, excitation to the triplet manifold of helium by secondary electrons must be accounted for as it is the dominant mechanism which produces He* in some environments. Incorporating these various formation and destruction pathways, we derive new equations for the steady state abundance of metastable helium. Using these equations in concert with our observations, we find zeta{sub He} < 1.2 x 10{sup -15} s{sup -1}, an upper limit about 5 times larger than the ionization rate previously inferred for this sight line using H{sup +} {sub 3}. While observations of interstellar He* are extremely difficult at present, and the background chemistry is not nearly as simple as previously thought, potential future observations of metastable helium would provide an independent check on the cosmic-ray ionization rate derived from H{sup +} {sub 3} in diffuse molecular clouds, and, perhaps more importantly, allow the first direct measurements of the ionization rate in diffuse atomic clouds.

  1. Comprehensive Study On The Metastable Negative Ion Fragmentation Of Individual Dna Components And Larger Oligonucleotides

    NASA Astrophysics Data System (ADS)

    Ingolfsson, O.; Flosadottir, H. D.; Omarsson, B.; Ilko, B.

    2010-07-01

    Here we present a systematic study on the unimolecular decay pathways of the deprotonated building blocks of DNA and RNA to address the following questions: 1. Are the negative ion fragmentation patterns observed in the metastable decay of individual DNA components still evident when these are combined to larger oligonucleotides? 2. What is the significance of the charge location in determining the fragmentation pathways in the metastable decay process? 3. Are those metastable decay channels relevant in dissociative electron attachment to DNA components? To address these questions we have studied the fragmentation patterns of the deprotonated ribose and ribose 5'-monophosphate, the fragmentation patterns of the individual bases, all nucleosides and all 2'-deoxynucleosides as well as the individual nucleotides and several combinations of hexameric oligonucleotides. Furthermore, to understand the significance of the charge location in determining the fragmentation path in the metastable decay process of these deprotonated ions we have also studied modified uridine and guanosine. These have been modified to block different deprotonation sites and thus to control the initial step in the in the fragmentation process i.e. the site of deprotonation. In addition to our experimental approach we have also simulated the metastable fragmentation of the deprotonated uridine and 2'-deoxyguanosine to clarify the mechanisms and fragmentation patterns observed. Where data is available, the results are compared to dissociative electron attachment to DNA components and discussed in context to the underlying mechanism. Experiments on modified nucleosides where selected deprotonation sites have been blocked are used to verify the predicted reaction paths and imulations on uridine and 2'-deoxyguanosine are compared to the experimental results and used to shed light on the mechanisms involved.

  2. Metastable phases in Zr-Excel alloy and their stability under heavy ion (Kr2+) irradiation

    NASA Astrophysics Data System (ADS)

    Yu, Hongbing; Zhang, Ken; Yao, Zhongwen; Kirk, Mark A.; Long, Fei; Daymond, Mark R.

    2016-02-01

    Zr-Excel alloy (Zr-3.5Sn-0.8Nb-0.8Mo, wt.%) has been proposed as a candidate material of pressure tubes in the CANDU-SCWR design. It is a dual-phase alloy containing primary hcp α-Zr and metastable bcc β-Zr. Metastable hexagonal ω-Zr phase could form in β-Zr as a result of aging during the processing of the tube. A synchrotron X-ray study was employed to study the lattice properties of the metastable phases in as-received Zr-Excel pressure tube material. In situ heavy ion (1 MeV Kr2+) irradiations were carried out at 200 °C and 450 °C to emulate the stability of the metastable phase under a reactor environment. Quantitative Chemi-STEM EDS analysis was conducted on both un-irradiated and irradiated samples to investigate alloying element redistribution induced by heavy ion irradiation. It was found that no decomposition of β-Zr was observed under irradiation at both 200 °C and 450 °C. However, ω-Zr particles experienced shape changes and shrinkage associated with enrichment of Fe at the β/ω interface during 200 °C irradiation but not at 450 °C. There is a noticeable increase in the level of Fe in the α matrix after irradiation at both 200 °C and 450 °C. The concentrations of Nb, Mo and Fe are increased in the ω phase but decreased in the β phase at 200 °C. The stability of metastable phases under heavy ion irradiation associated with elemental redistribution is discussed.

  3. Influence of electromagnetic field intensity on the metastable zone width of CaCO3 crystallization in circulating water

    NASA Astrophysics Data System (ADS)

    Wang, Jianguo; Liang, Yandong; Chen, Si

    2016-09-01

    In this study, changes in the metastable zone width of CaCO3 crystallization was determined through conductivity titration by altering electromagnetic field parameters applied to the circulating water system. The critical conductivity value and metastable zone curves of CaCO3 crystallization were determined under different solution concentrations and electromagnetic field intensities. Experimental results indicate that the effect of the electromagnetic field intensity on the critical conductivity value intensifies with the increase of solution concentration. Moreover, the metastable zone width of CaCO3 crystallization increases with the increase of electromagnetic field intensity within 200 Gs, thereby prolonging the induction period of nucleation.

  4. A new mechanism for metastability of under-saturated traffic responsible for time-delayed traffic breakdown at the signal

    NASA Astrophysics Data System (ADS)

    Jiang, Rui; Hu, Mao-Bin; Jia, Bin; Gao, Zi-You

    2014-05-01

    In this paper we introduce a new mechanism of metastability of under-saturated traffic at the signal that is responsible for a time-delayed traffic breakdown revealed by Kerner (2011). In our model, we assume that the metastability of under-saturated traffic at the signal is caused by a dependence of the mean time of driver acceleration from a queue at the signal on the driver's stopped time within the queue. With the use of Nagel-Schreckenberg model, we demonstrate that this mechanism of the metastability of city traffic can lead to the time-delayed traffic breakdown at the signal.

  5. Luminescence studies of trace gases through metastable transfer in cold helium jets

    NASA Astrophysics Data System (ADS)

    Wilde, Scott Colton

    Among the elements, Helium has the largest steps among its internal energy structure that can keep for long periods of time, hence the metastable helium moniker. It is referred to as a "nano-grenade" in some circles because of how much energy it can deliver to a space roughly the size of an atom. This work demonstrates a method to create metastable helium abundantly and it is used to excite trace amounts of oxygen to the point where the signal received from the oxygen was larger than the signal received from the helium in a cold atomized jet. Further cooling of the jet and turbulence added by a liquid helium surface worked to increase the oxygen signal and decrease the helium signal. This work investigates the possibility of forming a strong metastable helium source from a flowing helium gas jet excited by passing through ring electrodes introduced into a cryogenic environment using evaporated helium as a buffer gas. Prior study of luminescence from trace gases at cold helium temperatures is virtually absent and so it is the motivation for this work to blaze the trail in this subject. The absence of ionic oxygen spectral lines from the transfer of energy that was well over the first ionization potential of oxygen made for a deeper understanding of collision dynamics with multiple collision partners. This opened the possibility of using the high energy states of oxygen after metastable transfer as a lasing transition previously unavailable and a preliminary analysis suggested that the threshold for lasing action should be easily overcome if feedback were introduced by an optical cavity. To better understand the thermodynamics of the jet it was proposed to use diatomic nitrogen as an in situ thermometer, investigating whether the rotational degrees of freedom of the nitrogen molecule were in thermal equilibrium with the surrounding environment. If the gas was truly in thermodynamic equilibrium then the temperature given by the method of using collisions of a buffer

  6. Measurement of the neutron detection sensitivity of a liquid in metastable states.

    PubMed

    Sawamura, T; Joji, T; Homma, A

    2003-01-01

    A device able to trap a liquid droplet in a host liquid in a metastable (superheated) state was developed for a better understanding of the operational principles and for an extension of the application of superheated drop detectors (SDDs). Droplets of trans-2-butene in a metastable state were exposed to Am-Be neutrons and evaporation of the droplets was observed. By measuring lifetime distributions of irradiated droplets, neutron sensitivities were derived from the distributions. The sensitivities were compared with calculations and experiments performed by using superheated emulsions. Results are discussed related to the model of radiation induced vaporisation on which the operational principles of superheated emulsions were based. The experiments in this study showed that the device developed could be applied to measure radiation sensitivities of different kinds of liquids for different kinds of radiations without any special detector preparation.

  7. Uncleaved prefusion-optimized gp140 trimers derived from analysis of HIV-1 envelope metastability

    NASA Astrophysics Data System (ADS)

    Kong, Leopold; He, Linling; de Val, Natalia; Vora, Nemil; Morris, Charles D.; Azadnia, Parisa; Sok, Devin; Zhou, Bin; Burton, Dennis R.; Ward, Andrew B.; Wilson, Ian A.; Zhu, Jiang

    2016-06-01

    The trimeric HIV-1 envelope glycoprotein (Env) is critical for host immune recognition and neutralization. Despite advances in trimer design, the roots of Env trimer metastability remain elusive. Here we investigate the contribution of two Env regions to metastability. First, we computationally redesign a largely disordered bend in heptad region 1 (HR1) of SOSIP trimers that connects the long, central HR1 helix to the fusion peptide, substantially improving the yield of soluble, well-folded trimers. Structural and antigenic analyses of two distinct HR1 redesigns confirm that redesigned Env closely mimics the native, prefusion trimer with a more stable gp41. Next, we replace the cleavage site between gp120 and gp41 with various linkers in the context of an HR1 redesign. Electron microscopy reveals a potential fusion intermediate state for uncleaved trimers containing short but not long linkers. Together, these results outline a general approach for stabilization of Env trimers from diverse HIV-1 strains.

  8. New metastable form of ice and its role in the homogeneous crystallization of water.

    PubMed

    Russo, John; Romano, Flavio; Tanaka, Hajime

    2014-07-01

    The homogeneous crystallization of water at low temperature is believed to occur through the direct nucleation of cubic (Ic) and hexagonal (Ih) ices. Here, we provide evidence from molecular simulations that the nucleation of ice proceeds through the formation of a new metastable phase, which we name Ice 0. We find that Ice 0 is structurally similar to the supercooled liquid, and that on growth it gradually converts into a stacking of Ice Ic and Ih. We suggest that this mechanism provides a thermodynamic explanation for the location and pressure dependence of the homogeneous nucleation temperature, and that Ice 0 controls the homogeneous nucleation of low-pressure ices, acting as a precursor to crystallization in accordance with Ostwald's step rule of phases. Our findings show that metastable crystalline phases of water may play roles that have been largely overlooked.

  9. Influence of oxygen partial pressure on the metastable copper oxide thin films

    NASA Astrophysics Data System (ADS)

    Geçici, Birol; Korkmaz, Şadan; Özen, Soner; Şenay, Volkan; Pat, Suat

    2016-12-01

    Paramelaconite (Cu4O3) is a metastable copper oxide. Metastable copper oxide thin films were deposited on glass substrates by reactive RF magnetron sputtering in argon (Ar) and oxygen (O2) gas mixture atmospheres. Ar/O2 gas ratios in the sputtering ambient were chosen as 1/1 and 1/9. The surface and optical properties were determined by X-ray diffractometer (XRD), atomic force microscope (AFM) and UV-Vis spectrophotometer. The XRD patterns of the samples exhibited single strong diffraction peaks at 35.39∘ and 35.49∘, corresponding to the (202) peak of Cu4O3. The mean thickness values were measured as 100 nm and 80 nm for the films deposited at 1/1 and 1/9 Ar/O2 gas ratios, respectively. The samples showed low transmittance and high absorbance in the high frequency region.

  10. Competitive nucleation and the Ostwald rule in a generalized Potts model with multiple metastable phases

    NASA Astrophysics Data System (ADS)

    Sanders, David P.; Larralde, Hernán; Leyvraz, François

    2007-04-01

    We introduce a simple nearest-neighbor spin model with multiple metastable phases, the number and decay pathways of which are explicitly controlled by the parameters of the system. With this model, we can construct, for example, a system which evolves through an arbitrarily long succession of metastable phases. We also construct systems in which different phases may nucleate competitively from a single initial phase. For such a system, we present a general method to extract from numerical simulations the individual nucleation rates of the nucleating phases. The results show that the Ostwald rule, which predicts which phase will nucleate, must be modified probabilistically when the new phases are almost equally stable. Finally, we show that the nucleation rate of a phase depends, among other things, on the number of other phases accessible from it.

  11. Giant atomic displacement at a magnetic phase transition in metastable Mn3O4

    SciTech Connect

    Hirai, Shigeto; Moreira Dos Santos, Antonio F; Shapiro, Max C; Molaison, Jamie J; Pradhan, Neelam; Guthrie, Malcolm; Tulk, Christopher A; Fisher, Ian R; Mao, Wendy

    2013-01-01

    We present x-ray, neutron scattering, and heat capacity data that reveal a coupled first-order magnetic and structural phase transition of the metastable mixed-valence postspinel compound Mn3O4 at 210 K. Powder neutron diffraction measurements reveal a magnetic structure in which Mn3+ spins align antiferromagnetically along the edge-sharing a axis, with a magnetic propagation vector k = [1/2,0,0]. In contrast, the Mn2+ spins, which are geometrically frustrated, do not order until a much lower temperature. Although the Mn2+ spins do not directly participate in the magnetic phase transition at 210 K, structural refinements reveal a large atomic shift at this phase transition, corresponding to a physical motion of approximately 0.25 angstrom, even though the crystal symmetry remains unchanged. This "giant" response is due to the coupled effect of built-in strain in the metastable postspinel structure with the orbital realignment of the Mn3+ ion.

  12. Uncleaved prefusion-optimized gp140 trimers derived from analysis of HIV-1 envelope metastability

    PubMed Central

    Kong, Leopold; He, Linling; de Val, Natalia; Vora, Nemil; Morris, Charles D.; Azadnia, Parisa; Sok, Devin; Zhou, Bin; Burton, Dennis R.; Ward, Andrew B.; Wilson, Ian A.; Zhu, Jiang

    2016-01-01

    The trimeric HIV-1 envelope glycoprotein (Env) is critical for host immune recognition and neutralization. Despite advances in trimer design, the roots of Env trimer metastability remain elusive. Here we investigate the contribution of two Env regions to metastability. First, we computationally redesign a largely disordered bend in heptad region 1 (HR1) of SOSIP trimers that connects the long, central HR1 helix to the fusion peptide, substantially improving the yield of soluble, well-folded trimers. Structural and antigenic analyses of two distinct HR1 redesigns confirm that redesigned Env closely mimics the native, prefusion trimer with a more stable gp41. Next, we replace the cleavage site between gp120 and gp41 with various linkers in the context of an HR1 redesign. Electron microscopy reveals a potential fusion intermediate state for uncleaved trimers containing short but not long linkers. Together, these results outline a general approach for stabilization of Env trimers from diverse HIV-1 strains. PMID:27349805

  13. Uncleaved prefusion-optimized gp140 trimers derived from analysis of HIV-1 envelope metastability.

    PubMed

    Kong, Leopold; He, Linling; de Val, Natalia; Vora, Nemil; Morris, Charles D; Azadnia, Parisa; Sok, Devin; Zhou, Bin; Burton, Dennis R; Ward, Andrew B; Wilson, Ian A; Zhu, Jiang

    2016-06-28

    The trimeric HIV-1 envelope glycoprotein (Env) is critical for host immune recognition and neutralization. Despite advances in trimer design, the roots of Env trimer metastability remain elusive. Here we investigate the contribution of two Env regions to metastability. First, we computationally redesign a largely disordered bend in heptad region 1 (HR1) of SOSIP trimers that connects the long, central HR1 helix to the fusion peptide, substantially improving the yield of soluble, well-folded trimers. Structural and antigenic analyses of two distinct HR1 redesigns confirm that redesigned Env closely mimics the native, prefusion trimer with a more stable gp41. Next, we replace the cleavage site between gp120 and gp41 with various linkers in the context of an HR1 redesign. Electron microscopy reveals a potential fusion intermediate state for uncleaved trimers containing short but not long linkers. Together, these results outline a general approach for stabilization of Env trimers from diverse HIV-1 strains.

  14. Metastable defects in Be-doped Al(x)Ga(1-x)As

    NASA Technical Reports Server (NTRS)

    Magno, R.; Shelby, R.; Kennedy, T. A.; Spencer, M. G.

    1989-01-01

    Deep-level transient spectroscopy has been used to study metastable defects in Be-doped Al(x)Ga(1-x)As grown by molecular-beam epitaxy. The metastability manifests itself by the appearance of different spectra depending upon whether the sample is cooled from a high temperature with zero bias or a reverse bias applied to it. The defects are found in concentrations of 10 to the 15th/cu cm in a sample doped with 10 to the 18th Be/cu cm and in much lower concentrations in a 10 to the 17th Be/cu cm sample. Isochronal annealing experiments indicate that the defect is multistable and that it is best modeled as a mobile interstitial which can reside at several sites near acceptor. The activation energies for these defects are between 0.2 and 0.5 eV above the valence band.

  15. Stability and Metastability of Trapless Bose-Einstein Condensates and Quantum Liquids

    NASA Astrophysics Data System (ADS)

    Zloshchastiev, Konstantin G.

    2017-07-01

    Various kinds of Bose-Einstein condensates are considered, which evolve without any geometric constraints or external trap potentials including gravitational. For studies of their collective oscillations and stability, including the metastability and macroscopic tunneling phenomena, both the variational approach and the Vakhitov-Kolokolov (VK) criterion are employed; calculations are done for condensates of an arbitrary spatial dimension. It is determined that that the trapless condensate described by the logarithmic wave equation is essentially stable, regardless of its dimensionality, while the trapless condensates described by wave equations of a polynomial type with respect to the wavefunction, such as the Gross-Pitaevskii (cubic), cubic-quintic, and so on, are at best metastable. This means that trapless "polynomial" condensates are unstable against spontaneous delocalization caused by fluctuations of their width, density and energy, leading to a finite lifetime.

  16. New porous water ice metastable at atmospheric pressure obtained by emptying a hydrogen-filled ice

    NASA Astrophysics Data System (ADS)

    Del Rosso, Leonardo; Celli, Milva; Ulivi, Lorenzo

    2016-11-01

    The properties of some forms of water ice reserve still intriguing surprises. Besides the several stable or metastable phases of pure ice, solid mixtures of water with gases are precursors of other ices, as in some cases they may be emptied, leaving a metastable hydrogen-bound water structure. We present here the first characterization of a new form of ice, obtained from the crystalline solid compound of water and molecular hydrogen called C0-structure filled ice. By means of Raman spectroscopy, we measure the hydrogen release at different temperatures and succeed in rapidly removing all the hydrogen molecules, obtaining a new form of ice (ice XVII). Its structure is determined by means of neutron diffraction measurements. Of paramount interest is that the emptied crystal can adsorb again hydrogen and release it repeatedly, showing a temperature-dependent hysteresis.

  17. Kinetics of Light-induced Metastable Defect Creation and Annealing in a-Si:H

    NASA Astrophysics Data System (ADS)

    Kodolbaþ, Alp Osman; Eray, Aynur; Öktü, Özcan

    2002-01-01

    Constant Photocurrent Method (CPM) and steady state photoconductivity measurements are used to investigate the creation of light-induced metastable defects in a-Si:H at room temperature and their annealing. Light-induced metastable defect concentration Nd varies with exposure time teas ter with r=0.34 ± 0.02, as expected from the recombination induced weak bond breaking model [1]. The validity of a stretched exponential model is also studied [2]. From the annealing experiments, the distribution of thermal annealing activation energies is calculated following the method proposed by Hata and Wagner [3]. Defects created at room temperature show a narrow distribution of annealing activation energies peaking at 0.97eV. The relation between photoconductivity and Nd is strongly nonlinear. Defects created at earlier times of illumination degrade photoconductivity more strongly, and these defects anneal out more easily than those created at later times of illumination.

  18. New porous water ice metastable at atmospheric pressure obtained by emptying a hydrogen-filled ice

    PubMed Central

    del Rosso, Leonardo; Celli, Milva; Ulivi, Lorenzo

    2016-01-01

    The properties of some forms of water ice reserve still intriguing surprises. Besides the several stable or metastable phases of pure ice, solid mixtures of water with gases are precursors of other ices, as in some cases they may be emptied, leaving a metastable hydrogen-bound water structure. We present here the first characterization of a new form of ice, obtained from the crystalline solid compound of water and molecular hydrogen called C0-structure filled ice. By means of Raman spectroscopy, we measure the hydrogen release at different temperatures and succeed in rapidly removing all the hydrogen molecules, obtaining a new form of ice (ice XVII). Its structure is determined by means of neutron diffraction measurements. Of paramount interest is that the emptied crystal can adsorb again hydrogen and release it repeatedly, showing a temperature-dependent hysteresis. PMID:27819265

  19. Model reduction for slow–fast stochastic systems with metastable behaviour

    SciTech Connect

    Bruna, Maria; Chapman, S. Jonathan; Smith, Matthew J.

    2014-05-07

    The quasi-steady-state approximation (or stochastic averaging principle) is a useful tool in the study of multiscale stochastic systems, giving a practical method by which to reduce the number of degrees of freedom in a model. The method is extended here to slow–fast systems in which the fast variables exhibit metastable behaviour. The key parameter that determines the form of the reduced model is the ratio of the timescale for the switching of the fast variables between metastable states to the timescale for the evolution of the slow variables. The method is illustrated with two examples: one from biochemistry (a fast-species-mediated chemical switch coupled to a slower varying species), and one from ecology (a predator–prey system). Numerical simulations of each model reduction are compared with those of the full system.

  20. Spray Drying as a Reliable Route to Produce Metastable Carbamazepine Form IV.

    PubMed

    Halliwell, Rebecca A; Bhardwaj, Rajni M; Brown, Cameron J; Briggs, Naomi E B; Dunn, Jaclyn; Robertson, John; Nordon, Alison; Florence, Alastair J

    2017-07-01

    Carbamazepine (CBZ) is an active pharmaceutical ingredient used in the treatment of epilepsy that can form at least 5 polymorphic forms. Metastable form IV was originally discovered from crystallization with polymer additives; however, it has not been observed from subsequent solvent-only crystallization efforts. This work reports the reproducible formation of phase pure crystalline form IV by spray drying of methanolic CBZ solution. Characterization of the material was carried out using diffraction, scanning electron microscopy, and differential scanning calorimetry. In situ Raman spectroscopy was used to monitor the spray-dried product during the spray drying process. This work demonstrates that spray drying provides a robust method for the production of form IV CBZ, and the combination of high supersaturation and rapid solid isolation from solution overcomes the apparent limitation of more traditional solution crystallization approaches to produce metastable crystalline forms. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

  1. Metastable alloy materials produced by solid state reaction of compacted, mechanically deformed mixtures

    DOEpatents

    Atzmon, M.; Johnson, W.L.; Verhoeven, J.D.

    1987-02-03

    Bulk metastable, amorphous or fine crystalline alloy materials are produced by reacting cold-worked, mechanically deformed filamentary precursors such as metal powder mixtures or intercalated metal foils. Cold-working consolidates the metals, increases the interfacial area, lowers the free energy for reaction, and reduces at least one characteristic dimension of the metals. For example, the grains of powder or the sheets of foil are clad in a container to form a disc. The disc is cold-rolled between the nip of rollers to form a flattened disc. The grains are further elongated by further rolling to form a very thin sheet of a lamellar filamentary structure containing filaments having a thickness of less than 0.01 microns. Thus, diffusion distance and time for reaction are substantially reduced when the flattened foil is thermally treated in oven to form a composite sheet containing metastable material dispersed in unreacted polycrystalline material. 4 figs.

  2. A Metastability-Free Multi-synchronous Communication Scheme for SoCs

    NASA Astrophysics Data System (ADS)

    Polzer, Thomas; Handl, Thomas; Steininger, Andreas

    We propose a communication scheme for GALS systems with independent but approximately synchronized clock sources, which guarantees high-speed metastability-free communication between any two peers via bounded-size FIFO buffers. The proposed approach can be used atop of any multi-synchronous clocking system that guarantees a synchronization precision in the order of several clock cycles, like our fault-tolerant DARTS clocks. We determine detailed formulas for the required communication buffer size, and prove that this choice indeed guarantees metastability-free communication between correct peers, at maximum clock speed. We also describe a fast and efficient implementation of our scheme, and calculate the required buffer size for a sample test scenario. Experimental results confirm that the size lower bounds provided by our formulas are tight in this setting.

  3. Metastability of the false vacuum in a Higgs-seesaw model of dark energy

    NASA Astrophysics Data System (ADS)

    Krauss, Lawrence M.; Long, Andrew J.

    2014-04-01

    In a recently proposed Higgs-seesaw model the observed scale of dark energy results from a metastable false vacuum energy associated with mixing of the standard model Higgs particle and a scalar associated with new physics at the scale of unification or the Planck scale. Here we address the issue of how to ensure metastability of this state over cosmological time. We consider new tree-level operators, the presence of a thermal bath of hidden sector particles, and quantum corrections to the effective potential. We find that in the thermal scenario many additional light degrees of freedom are typically required unless coupling constants are somewhat fine-tuned. However quantum corrections arising from as few as one additional light scalar field can provide the requisite support. We also briefly consider implications of late-time vacuum decay for the perdurance of observed structures in the universe in this model.

  4. Dissociation dynamics: Measurements of decay fractions of metastable ammonia cluster ions

    SciTech Connect

    Wei, S.; Tzeng, W.B.; Castleman, A.W. Jr. )

    1990-08-15

    The decay fractions of metastable ammonia cluster ions which undergo unimolecular (evaporative) dissociation in a time window of 1--40 {mu}s were measured by using a reflection time-of-flight mass spectrometer. Corrections concerning instrumental artifacts and ion trajectory of parents and daughters are made to imporve the precision of the measurements. The data are used to derive the Gspann parameter and heat capacity of clusters as described in evaporative ensemble model of metastable dissociation. Using the dissociation fractions measured in the present studies, in conjunction with kinetic energy release values previously measured in our laboratory, we apply Klots' evaporative ensemble model to obtain binding energies of ammonia cluster ions (NH{sub 3}){sub {ital n}}H{sup +}, 4{le}{ital n}{le}17. The deduced binding energy values are found to be in very good agreement with both thermochemical data and Engelking's modified statistical theory.

  5. EL2 model based on indications of an intermediate metastable state

    NASA Astrophysics Data System (ADS)

    Favero, P. P.; Cruz, J. M. R.

    2006-04-01

    By the use of a transmittance experiment with a λ=1.05 μm (1.18 eV) laser beam we study the EL2 kinetics as a function of sample temperature. The photoquenching curves presented two time constants which we associate with two sequential transitions, from the normal to an intermediate metastable state, and from this to the final metastable state. We propose a new structural model for the complex EL2 which incorporates features of the isolated arsenic antisite model and the model proposed by Fukuyama et al. [Phys. Rev. B 67 (2003) 113202]. In addition, the effect of the optical/thermal history of the sample on the behavior of the photoquenching kinetics is investigated.

  6. Defect metastability in surfaces: A study of EL2 defect in GaAs(110)

    SciTech Connect

    Zhang, S.B.

    1999-08-01

    Although it has been widely accepted that EL2 in GaAs is an As antisite, the identity of the metastable state of EL2thinsp(=EL2{sup {asterisk}}) has not been confirmed by experiment. Here it is suggested that cross-sectional scanning tunneling microscopy may be used to identify EL2{sup {asterisk}}. My suggestion is based on a comprehensive first-principles total energy study of surface defect metastability. It reveals rich structures of the EL2{sup {asterisk}} near the surface. The energy difference between EL2{sup {asterisk}} and EL2 can be reduced to only a tenth of that bulk due to interaction with relaxed surface atoms. {copyright} {ital 1999} {ital The American Physical Society}

  7. Bose-Einstein condensate of metastable helium for quantum correlation experiments

    NASA Astrophysics Data System (ADS)

    Keller, Michael; Kotyrba, Mateusz; Leupold, Florian; Singh, Mandip; Ebner, Maximilian; Zeilinger, Anton

    2014-12-01

    We report on the realization of Bose-Einstein condensation of metastable helium-4. After exciting helium to its metastable state in a novel pulse-tube cryostat source, the atomic beam is collimated and slowed. We then trap several 108 atoms in a magneto-optical trap. For subsequent evaporative cooling, the atoms are transferred into a magnetic trap. Degeneracy is achieved with typically a few 106 atoms. For detection of atomic correlations with high resolution, an ultrafast delay-line detector has been installed. Consisting of four quadrants with independent readout electronics that allow for true simultaneous detection of atoms, the detector is especially suited for quantum correlation experiments that require the detection of correlated subsystems. We expect our setup to allow for the direct demonstration of momentum entanglement in a scenario equivalent to the Einstein-Podolsky-Rosen gedanken experiment. This will pave the way to matter-wave experiments exploiting the peculiarities of quantum correlations.

  8. Visualization and manipulation of meta-stable polarization variants in multiferroic materials

    NASA Astrophysics Data System (ADS)

    Park, Moonkyu; No, Kwangsoo; Hong, Seungbum

    2013-04-01

    Here we demonstrate the role of meta-stable polarization variants in out-of-plane polarization switching behavior in epitaxially grown BiFeO3 thin films using angle-resolved piezoresponse force microscopy (AR-PFM). The out-of-plane polarization switching mainly occurred at the boundary between meta-stable and stable polarization domains, and was accompanied by a significant change in in-plane domain configuration from complicated structure with 12 polarization variants to simple stripe structure with 4 polarization variants. These results imply that the biased tip rearranges the delicately balanced domain configuration, which is determined by the competition between electrostatic and strain energies, into simple interweaving one that is more thermodynamically stable.

  9. Turbulent relaxation and meta-stable equilibrium states of an electron plasma

    NASA Astrophysics Data System (ADS)

    Rodgers, Douglas J.

    A Malmberg-Penning electron trap allows for the experimental study of nearly ideal, two-dimensional (2D) inviscid (Euler) hydrodynamics. This is perhaps the simplest case of self organizing nonlinear turbulence, and is therefore a paradigm for dynamo theory, Taylor relaxation, selective decay and other nonlinear fluid processes. The dynamical relaxation of a pure electron plasma in the guiding-center-drift approximation is studied, comparing experiments, numerical simulations and statistical theories of weakly-dissipative 2D turbulence. The nonuniform metastable equilibrium states resulting from turbulent evolution are examined, and are well-described by a maximum entropy principle for constrained circulation, energy, and angular momentum. The turbulent decay of the system is also examined, and a similarity decay law is proposed which incorporates the substantial enstrophy trapped in the metastable equilibrium. This law approaches Batchelor's t-2 self-similar decay in the limit of strong turbulence, and is verified in turbulent evolution in the electron plasma experiment.

  10. New porous water ice metastable at atmospheric pressure obtained by emptying a hydrogen-filled ice.

    PubMed

    Del Rosso, Leonardo; Celli, Milva; Ulivi, Lorenzo

    2016-11-07

    The properties of some forms of water ice reserve still intriguing surprises. Besides the several stable or metastable phases of pure ice, solid mixtures of water with gases are precursors of other ices, as in some cases they may be emptied, leaving a metastable hydrogen-bound water structure. We present here the first characterization of a new form of ice, obtained from the crystalline solid compound of water and molecular hydrogen called C0-structure filled ice. By means of Raman spectroscopy, we measure the hydrogen release at different temperatures and succeed in rapidly removing all the hydrogen molecules, obtaining a new form of ice (ice XVII). Its structure is determined by means of neutron diffraction measurements. Of paramount interest is that the emptied crystal can adsorb again hydrogen and release it repeatedly, showing a temperature-dependent hysteresis.

  11. Bichromatic force on metastable argon for atom-trap trace analysis

    NASA Astrophysics Data System (ADS)

    Feng, Z.; Ebser, S.; Ringena, L.; Ritterbusch, F.; Oberthaler, M. K.

    2017-07-01

    For an efficient performance of atom-trap trace analysis, it is important to collimate the particles emitted from an effusive source. Their high velocity limits the interaction time with the cooling laser. Therefore, forces beyond the limits of the scattering force are desirable. The bichromatic force is a promising candidate for this purpose which is demonstrated here on metastable argon-40. The precollimated atoms are deflected in one dimension and the acquired Doppler shift is detected by absorption spectroscopy. With the experimentally accessible parameters, it was possible to measure a force three times stronger than the scattering force. Systematic studies on its dependence on Rabi frequency, phase difference, and detuning to atomic resonance are compared to the solution of the optical Bloch equations. We anticipate predictions for a possible application in atom-trap trace analysis of argon-39 and other noble gas experiments, where a high flux of metastable atoms is needed.

  12. Formation of a metastable crystalline phase during ion irradiation of spinel

    SciTech Connect

    Devanathan, R.; Yu, Ning; Sickafus, K.; Nastasi, M.

    1995-12-31

    We have examined the radiation resistance of magnesio-aluminate spinel by irradiating single crystals of MgAl{sub 2}O{sub 4} with 400 keV Xe++ions at 100 K. At low irradiation doses, the material transformed into a metastable crystalline phase with half the lattice spacing of the original crystal. Electron diffraction analysis revealed that this structural change can be explained in terms of the redistribution of cations among octahedral, tetrahedral, and three- fold coordinated interstitial sites of the close-packed anion lattice. Corresponding to this transformation, the hardness and elastic modulus increased with dose to values about 10% greater than those of unirradiated spinel. We believe that the formation of this metastable phase plays an important role in determining the radiation resistance of spinel.

  13. High speed, high temperature electrical characterization of phase change materials: metastable phases, crystallization dynamics, and resistance drift

    NASA Astrophysics Data System (ADS)

    Dirisaglik, Faruk; Bakan, Gokhan; Jurado, Zoila; Muneer, Sadid; Akbulut, Mustafa; Rarey, Jonathan; Sullivan, Lindsay; Wennberg, Maren; King, Adrienne; Zhang, Lingyi; Nowak, Rebecca; Lam, Chung; Silva, Helena; Gokirmak, Ali

    2015-10-01

    During the fast switching in Ge2Sb2Te5 phase change memory devices, both the amorphous and fcc crystalline phases remain metastable beyond the fcc and hexagonal transition temperatures respectively. In this work, the metastable electrical properties together with crystallization times and resistance drift behaviour of GST are studied using a high-speed, device-level characterization technique in the temperature range of 300 K to 675 K.During the fast switching in Ge2Sb2Te5 phase change memory devices, both the amorphous and fcc crystalline phases remain metastable beyond the fcc and hexagonal transition temperatures respectively. In this work, the metastable electrical properties together with crystallization times and resistance drift behaviour of GST are studied using a high-speed, device-level characterization technique in the temperature range of 300 K to 675 K. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05512a

  14. Crystallographic Stability of Metastable Phase Formed by Containerless Processing in REFeO3 (RE: Rare-Earth Element)

    NASA Technical Reports Server (NTRS)

    Kuribayashi, Kazuhiko; Kumar, M. S. Vijaya

    2012-01-01

    Undercooling a melt often facilitates a metastable phase to nucleate preferentially. Although the classical nucleation theory shows that the most critical factor for forming a metastable phase is the interface free energy, the crystallographic stability is also indispensable for the phase to be frozen at ambient temperature. In compound materials such as oxides, authors have suggested that the decisive factors for forming a critical nucleus are not only the free energy difference but also the difference of the entropy of fusion between stable and metastable phases. In the present study, using REFeO3 (RE: rare-earth element) as a model material, we investigate the formation of a metastable phase from undercooled melts with respect to the competitive nucleation and crystallographical stabilities of both phases.

  15. Metastable decay of DNA components and their compositions - a perspective on the role of reactive electron scattering in radiation damage

    NASA Astrophysics Data System (ADS)

    Flosadóttir, H. D.; Ómarsson, B.; Bald, I.; Ingólfsson, O.

    2012-01-01

    Here we review recent studies on the metastable fragmentation of individual DNA and RNA building blocks and their compositions using matrix assisted laser desorption/ionization mass spectrometry (MALDI). To compare the fragmentation channels of small DNA components with larger compositions we have studied the metastable fragmentation of the deprotonated nucleobases, ribose, ribose-monophoshates, the nucleosides, the nucleoside 5'-monophosphates and selected oligonucleotides. Both previously published and unpublished data are reported. To gain a comprehensive picture of the fragmentation of individual components, metastable fragmentation of native components are in many cases compared to chemically modified components and isotopic labelling is used to unambiguously identify fragments. Furthermore, to shed light on the underlying fragmentation mechanisms we complement the experimental studies with classical dynamics simulations of the fragmentation of selected compounds. For the DNA and RNA components where dissociative electron attachment studies have been conducted we compare these to the metastable fragmentation channels observed here.

  16. Effect of stable and metastable dimers on collision-induced rototranslational spectra: Carbon dioxide - rare gas mixtures

    NASA Astrophysics Data System (ADS)

    Oparin, Daniil V.; Filippov, Nikolai N.; Grigoriev, Ivan M.; Kouzov, Alexander P.

    2017-07-01

    The role of stable and metastable dimers as well as of free collisions in the collision-induced rototranslational absorption by the compressed CO2-Ar and CO2-Xe gas mixtures is elucidated using the classical three-dimensional trajectories method. The contribution from the stable dimers is obtained via Fourier transform of the dipole correlation function. The spectral bandshape due to the unbound trajectories (metastable dimers and free collisions) is calculated as an averaged Fourier spectrum of the collision-induced dipole moment. The mean lifetimes of metastable dimers have been estimated as 3.8 ps for CO2-Ar and 5.9 ps for CO2-Xe pairs. Trajectory computations are complemented by calculations of zero spectral moments using pair distribution functions. The stable and metastable dimer contribution to the zero spectral moment is shown to be comparable with that from free collisions.

  17. Properties of the triplet metastable states of the alkaline-earth-metal atoms

    SciTech Connect

    Mitroy, J.; Bromley, M.W.J.

    2004-11-01

    The static and dynamic properties of the alkaline-earth-metal atoms in their metastable state are computed in a configuration interaction approach with a semiempirical model potential for the core. Among the properties determined are the scalar and tensor polarizabilities, the quadrupole moment, some of the oscillator strengths, and the dispersion coefficients of the van der Waals interaction. A simple method for including the effect of the core on the dispersion parameters is described.

  18. Anomalous optogalvanic line shapes of argon metastable transitions in a hollow cathode lamp

    NASA Technical Reports Server (NTRS)

    Ruyten, W. M.

    1993-01-01

    Anomalous optogalvanic line shapes were observed in a commercial hollow cathode lamp containing argon buffer gas. Deviations from Gaussian line shapes were particularly strong for transitions originating from the 3P2 metastable level of argon. The anomalous line shapes can be described reasonably well by the assumption that two regions in the discharge are excited simultaneously, each giving rise to a purely Gaussian line shape, but with different polarities, amplitudes, and linewidths.

  19. Periodical Micro-Structuring of Hydride Containing Metastable Aluminumoxide using Laser Interference Metallurgy

    SciTech Connect

    Veith, Michael; Andres, Katrin; Petersen, Christian; Daniel, Claus; Holzapfel, Christian; M�cklich, Frank

    2005-01-01

    Layers of the metastable ceramic HAlO are sensitive to heat: These layers transform to biphasic Al/Al2O3 due to elimination of di-hydrogen. Using interfering Nd:YAG laser beams, periodic patterns can be produced. By these methods two dimensional structuring is obtained with the characteristics of distinctly different phases and different chemical compositions at periodic places on the layer.

  20. Miniature triaxial metastable ionization detector for gas chromatographic trace analysis of extraterrestrial volatiles.

    PubMed

    Woeller, F H; Kojiro, D R; Carle, G C

    1984-04-01

    Gas chromatography has found highly successful application in NASA's flight programs. Gas chromatographs have been flown to both Mars and Venus where detailed compositional measurements were made. These instruments were quite small and relatively sensitive when compared to commercially available instruments; however, they do not appear adequate for future missions currently being planned. The earlier flight GC's had incorporated thermistor bead thermal conductivity cells as the detector. This detector requires very precise temperature control and only provides about 1 ppm sensitivity. Temperature stabilization causes the detector to be quite heavy, i.e., about 200 g. Greater sensitivity will be required for measurements of trace components in extraterrestrial environments. Review of other detector types revealed the metastable ionization detector as a likely candidate because of its superior thermal stability and high sensitivity. The metastable detector, first described by Lovelock as an argon ionization detector, has been studied and somewhat modified by others. The commercial design by Hartmann and Dimick was used for comparison purposes in our work. In the past, three features of the metastable detector are prominent: it has part-per-billion sensitivity, contamination must be carefully controlled, and anomalous response is common. Since it is an ionization detector, however, temperature instabilities do not cause the major perturbations experienced by the thermal conductivity detectors. This paper describes a miniature metastable ionization detector featuring an unconventional electrode configuration, whose performance characteristics parallel those of traditional design, while its weight is quite small. The prototype has been used in our laboratories routinely for 2 years, and the concept will be incorporated into a flight GC for use in the Space Shuttle.

  1. Metastable anions of polyynes: Dynamics of fragmentation/stabilization in planetary atmospheres after electron attachment

    NASA Astrophysics Data System (ADS)

    Sebastianelli, F.; Gianturco, F. A.

    2012-02-01

    The quantum dynamics of low-energy free electrons colliding with linear carbonaceous species like HC3N and HC5N is examined to identify the locations and structural features of their metastable negative ions (resonant compound states of the colliding partners) with the aim of suggesting, at the molecular level, the possible mechanisms of anionic stabilization which lead to the several stable species observed in the interstellar and circumstellar media in connection with polyyne structures.

  2. Metastable superheated ice in liquid-water inclusions under high negative pressure

    USGS Publications Warehouse

    Roedder, E.

    1967-01-01

    In some microscopic inclusions (consisting of aqueous liquid and vapor) in minerals, freezing eliminates the vapor phase because of greater volume occupied by the resulting ice. When vapor fails to nucleate again on partial melting, the resulting negative pressure (hydrostatic tension) inside the inclusions permits the existence of ice I crystals under reversible, metastable equilibrium, at temperatures as high as +6.5??C and negative pressures possibly exceeding 1000 bars.

  3. Anomalous optogalvanic line shapes of argon metastable transitions in a hollow cathode lamp

    NASA Technical Reports Server (NTRS)

    Ruyten, W. M.

    1993-01-01

    Anomalous optogalvanic line shapes were observed in a commercial hollow cathode lamp containing argon buffer gas. Deviations from Gaussian line shapes were particularly strong for transitions originating from the 3P2 metastable level of argon. The anomalous line shapes can be described reasonably well by the assumption that two regions in the discharge are excited simultaneously, each giving rise to a purely Gaussian line shape, but with different polarities, amplitudes, and linewidths.

  4. Local and Global Effects of a Cavity Filling Mutation in a Metastable Serpin

    PubMed Central

    Sengupta, Tanusree; Tsutsui, Yuko; Wintrode, Patrick L.

    2009-01-01

    The serpins are an unusual class of protease inhibitors which fold to a metastable form and subsequently undergo a massive conformational change to a stable form when they inhibit their target proteases. The driving force for this conformational change has been extensively investigated by site directed mutagenesis, and it has been found that mutations which stabilize the metastable form frequently result in activity deficiency. Here we employ hydrogen/deuterium exchange to probe the effects of a cavity filling mutant of α1AT. The Gly117→Phe substitution fills a cavity between the F-helix and the face of β-sheet A, stabilizes the metastable form of α1AT by ∼4 kcal/mole and results in a 60% reduction in inhibitory activity against elastase. Globally, the G117F substitution alters the unfolding mechanism by eliminating the molten globule intermediate that is seen in Wild Type unfolding. Remarkably, this is accomplished primarily by destabilizing the molten globule rather than stabilizing the metastable native state. Locally, conformational flexibility in the native state is reduced in specific regions: the top of the F-helix, β-strands 5A, 1C and 4C, and helix D. Excepting strand 4C, all of these regions mediate or propagate conformational changes. The F-helix and strand 5A must be displaced during protease inhibition, displacement of strand 1C is required for polymer formation, and helix D is a site (in antithrombin) of allosteric regulation. Our results indicate that these functionally important regions form a delocalized network of residues that are dynamically coupled, and that both local and global stability mediate inhibitory activity. PMID:19624115

  5. In Situ Observations of Phase Transitions in Metastable Nickel (Carbide)/Carbon Nanocomposites

    PubMed Central

    2016-01-01

    Nanocomposite thin films comprised of metastable metal carbides in a carbon matrix have a wide variety of applications ranging from hard coatings to magnetics and energy storage and conversion. While their deposition using nonequilibrium techniques is established, the understanding of the dynamic evolution of such metastable nanocomposites under thermal equilibrium conditions at elevated temperatures during processing and during device operation remains limited. Here, we investigate sputter-deposited nanocomposites of metastable nickel carbide (Ni3C) nanocrystals in an amorphous carbon (a-C) matrix during thermal postdeposition processing via complementary in situ X-ray diffractometry, in situ Raman spectroscopy, and in situ X-ray photoelectron spectroscopy. At low annealing temperatures (300 °C) we observe isothermal Ni3C decomposition into face-centered-cubic Ni and amorphous carbon, however, without changes to the initial finely structured nanocomposite morphology. Only for higher temperatures (400–800 °C) Ni-catalyzed isothermal graphitization of the amorphous carbon matrix sets in, which we link to bulk-diffusion-mediated phase separation of the nanocomposite into coarser Ni and graphite grains. Upon natural cooling, only minimal precipitation of additional carbon from the Ni is observed, showing that even for highly carbon saturated systems precipitation upon cooling can be kinetically quenched. Our findings demonstrate that phase transformations of the filler and morphology modifications of the nanocomposite can be decoupled, which is advantageous from a manufacturing perspective. Our in situ study also identifies the high carbon content of the Ni filler crystallites at all stages of processing as the key hallmark feature of such metal–carbon nanocomposites that governs their entire thermal evolution. In a wider context, we also discuss our findings with regard to the much debated potential role of metastable Ni3C as a catalyst phase in graphene and

  6. Texture evolution in thin-sheets on AISI 301 metastable stainless steel under dynamic loading

    SciTech Connect

    Kim, K.Y.; Kozaczek, K.; Kulkarni, S.M.; Bastias, P.C.; Hahn, G.T.

    1995-05-08

    The evolution of texture in thin sheets of metastable austenitic stainless steel AISI 301 is affected by external conditions such as loading rate and temperature, by inhomogeneous deformation phenomena such as twinning and shear band formation, and by the concurent strain induced phase transformation of the retained austenitc ({gamma}) into martensite ({alpha}). The present paper describes texture measurements on different gauges of AISI 301 prior and after uniaxial stretching under different conditions.

  7. A simple velocity-tunable pulsed atomic source of slow metastable argon

    NASA Astrophysics Data System (ADS)

    Taillandier-Loize, T.; Aljunid, S. A.; Correia, F.; Fabre, N.; Perales, F.; Tualle, J. M.; Baudon, J.; Ducloy, M.; Dutier, G.

    2016-04-01

    A pulsed beam of metastable argon atoms having a low tunable velocity (10 to 150 m s-1) is produced with a very substantial brightness (9  ×  108Ar* s-1 sr-1). The present original experimental configuration leads to a variable velocity dispersion that can be smaller than the standard Brownian one. This behaviour, analysed using Monte Carlo simulations, exhibits momentum stretching (heating) or narrowing (cooling) entirely due to a subtle combination of Doppler and Zeeman effects.

  8. Metastability in the Spin-1 Blume–Emery–Griffiths Model within Constant Coupling Approximation

    NASA Astrophysics Data System (ADS)

    Ekiz, C.

    2017-02-01

    In this paper, the equilibrium properties of spin-1 Blume–Emery–Griffiths model are studied by using constant-coupling approximation. The dipolar and quadrupolar order parameters, the stable, metastable and unstable states and free energy of the model are investigated. The states are defined in terms of local minima of the free energy of system. The numerical calculations are presented for several values of exchange interactions on the simple cubic lattice with q = 6.

  9. Uniqueness of Translation-Covariant Zero-Temperature Metastate in Disordered Ising Ferromagnets

    NASA Astrophysics Data System (ADS)

    Wehr, Jan; Wasielak, Aramian

    2016-01-01

    We study ground states of Ising models with random ferromagnetic couplings, proving the triviality of all zero-temperature metastates. This result sheds a new light on the properties of these systems, putting strong restrictions on their possible ground state structure. Open problems related to existence of interface-supporting ground states are stated and an interpretation of the main result in terms of first-passage and random surface models in a random environment is presented.

  10. Accelerated Metastable Solid-liquid Interdiffusion Bonding with High Thermal Stability and Power Handling

    NASA Astrophysics Data System (ADS)

    Huang, Ting-Chia; Smet, Vanessa; Kawamoto, Satomi; Pulugurtha, Markondeya R.; Tummala, Rao R.

    2017-09-01

    Emerging high-performance systems are driving the need for advanced packaging solutions such as 3-D integrated circuits (ICs) and 2.5-D system integration with increasing performance and reliability requirements for off-chip interconnections. Solid-liquid interdiffusion (SLID) bonding resulting in all-intermetallic joints has been proposed to extend the applicability of solders, but faces fundamental and manufacturing challenges hindering its wide adoption. This paper introduces a Cu-Sn SLID interconnection technology, aiming at stabilization of the microstructure in the Cu6Sn5 metastable phase rather than the usual stable Cu3Sn phase. This enables formation of a void-free interface yielding higher mechanical strength than standard SLID bonding, as well as significantly reducing the transition time. The metastable SLID technology retains the benefits of standard SLID with superior I/O pitch scalability, thermal stability and current handling capability, while advancing assembly manufacturability. In the proposed concept, the interfacial reaction is controlled by introducing Ni(P) diffusion barrier layers, designed to effectively isolate the metastable Cu6Sn5 phase preventing any further transformation. Theoretical diffusion and kinetic models were applied to design the Ni-Cu-Sn interconnection stack to achieve the targeted joint composition. A daisy chain test vehicle was used to demonstrate this technology as a first proof of concept. Full transition to Cu6Sn5 was successfully achieved within a minute at 260°C as confirmed by scanning electron microscope (SEM) and x-ray energy dispersive spectroscopy (XEDS) analysis. The joint composition was stable through 10× reflow, with outstanding bond strength averaging 90 MPa. The metastable SLID interconnections also showed excellent electromigration performance, surviving 500 h of current stressing at 105 A/cm2 at 150°C.

  11. In situ high pressure investigations on metastable BiBO{sub 3}

    SciTech Connect

    Khanna, Atul; Mishra, A. K.; Sharma, S. M.

    2016-05-23

    Synchrotron based angle dispersive x-ray diffraction (ADXRD) studies were performed on metastable crystalline bismuth orthoborate (BiBO{sub 3}) up to 14.5 GPa during compression and decompression cycle. These studies revealed that the BiBO{sub 3} is unstable and it converts to Bi{sub 4}B{sub 2}O{sub 9} phase at high pressure. Moreover the transformation is found to be irreversible.

  12. Metastable and charged particle decay in neon afterglow studied by the breakdown time delay measurements

    SciTech Connect

    Markovic, V. Lj.; Gocic, S. R.; Stamenkovic, S. N.; Petrovic, Z. Lj.

    2007-10-15

    Memory effect--the long time variation of the electrical breakdown time delay on the relaxation time t{sub d}({tau}) in neon--was explained by the Ne({sup 3}P{sub 2}) (1s{sub 5}) metastable state remaining from the preceding glow [Dj. A. Bosan, M. K. Radovic, and Dj. M. Krmpotic, J. Phys. D 19, 2343 (1986)]. However, the authors neglected the quenching processes that reduce the effective lifetime of metastable states several orders of magnitude below that of the memory effect observations. In this paper the time delay measurements were carried out in neon at the pressure of 6.6 mbar in a gas tube with gold-plated copper cathode, and the approximate and exact numerical models are developed in order to study the metastable and charged particle decay in afterglow. It was found that the metastable hypothesis completely failed to explain the afterglow kinetics, which is governed by the decay of molecular neon ions and molecular nitrogen ions produced in Ne{sub 2}{sup +} collisions with nitrogen impurities; i.e., Ne{sub 2}{sup +}+N{sub 2}{yields}N{sub 2}{sup +}+2Ne. Charged particle decay is followed up to hundreds of milliseconds in afterglow, from ambipolar to the free diffusion limit. After that, the late afterglow kinetics in neon can be explained by the nitrogen atoms recombining on the cathode surface and providing secondary electrons that determine the breakdown time delay down to the cosmic rays and natural radioactivity level.

  13. In Situ Observations of Phase Transitions in Metastable Nickel (Carbide)/Carbon Nanocomposites.

    PubMed

    Bayer, Bernhard C; Bosworth, David A; Michaelis, F Benjamin; Blume, Raoul; Habler, Gerlinde; Abart, Rainer; Weatherup, Robert S; Kidambi, Piran R; Baumberg, Jeremy J; Knop-Gericke, Axel; Schloegl, Robert; Baehtz, Carsten; Barber, Zoe H; Meyer, Jannik C; Hofmann, Stephan

    2016-10-06

    Nanocomposite thin films comprised of metastable metal carbides in a carbon matrix have a wide variety of applications ranging from hard coatings to magnetics and energy storage and conversion. While their deposition using nonequilibrium techniques is established, the understanding of the dynamic evolution of such metastable nanocomposites under thermal equilibrium conditions at elevated temperatures during processing and during device operation remains limited. Here, we investigate sputter-deposited nanocomposites of metastable nickel carbide (Ni3C) nanocrystals in an amorphous carbon (a-C) matrix during thermal postdeposition processing via complementary in situ X-ray diffractometry, in situ Raman spectroscopy, and in situ X-ray photoelectron spectroscopy. At low annealing temperatures (300 °C) we observe isothermal Ni3C decomposition into face-centered-cubic Ni and amorphous carbon, however, without changes to the initial finely structured nanocomposite morphology. Only for higher temperatures (400-800 °C) Ni-catalyzed isothermal graphitization of the amorphous carbon matrix sets in, which we link to bulk-diffusion-mediated phase separation of the nanocomposite into coarser Ni and graphite grains. Upon natural cooling, only minimal precipitation of additional carbon from the Ni is observed, showing that even for highly carbon saturated systems precipitation upon cooling can be kinetically quenched. Our findings demonstrate that phase transformations of the filler and morphology modifications of the nanocomposite can be decoupled, which is advantageous from a manufacturing perspective. Our in situ study also identifies the high carbon content of the Ni filler crystallites at all stages of processing as the key hallmark feature of such metal-carbon nanocomposites that governs their entire thermal evolution. In a wider context, we also discuss our findings with regard to the much debated potential role of metastable Ni3C as a catalyst phase in graphene and carbon

  14. A Metastable Equilibrium Model for the Relative Abundances of Microbial Phyla in a Hot Spring

    PubMed Central

    Dick, Jeffrey M.; Shock, Everett L.

    2013-01-01

    Many studies link the compositions of microbial communities to their environments, but the energetics of organism-specific biomass synthesis as a function of geochemical variables have rarely been assessed. We describe a thermodynamic model that integrates geochemical and metagenomic data for biofilms sampled at five sites along a thermal and chemical gradient in the outflow channel of the hot spring known as “Bison Pool” in Yellowstone National Park. The relative abundances of major phyla in individual communities sampled along the outflow channel are modeled by computing metastable equilibrium among model proteins with amino acid compositions derived from metagenomic sequences. Geochemical conditions are represented by temperature and activities of basis species, including pH and oxidation-reduction potential quantified as the activity of dissolved hydrogen. By adjusting the activity of hydrogen, the model can be tuned to closely approximate the relative abundances of the phyla observed in the community profiles generated from BLAST assignments. The findings reveal an inverse relationship between the energy demand to form the proteins at equal thermodynamic activities and the abundance of phyla in the community. The distance from metastable equilibrium of the communities, assessed using an equation derived from energetic considerations that is also consistent with the information-theoretic entropy change, decreases along the outflow channel. Specific divergences from metastable equilibrium, such as an underprediction of the relative abundances of phototrophic organisms at lower temperatures, can be explained by considering additional sources of energy and/or differences in growth efficiency. Although the metabolisms used by many members of these communities are driven by chemical disequilibria, the results support the possibility that higher-level patterns of chemotrophic microbial ecosystems are shaped by metastable equilibrium states that depend on both the

  15. Current status of free radicals and electronically excited metastable species as high energy propellants

    NASA Technical Reports Server (NTRS)

    Rosen, G.

    1973-01-01

    A survey is presented of free radicals and electronically excited metastable species as high energy propellants for rocket engines. Nascent or atomic forms of diatomic gases are considered free radicals as well as the highly reactive diatomic triatomic molecules that posess unpaired electrons. Manufacturing and storage problems are described, and a review of current experimental work related to the manufacture of atomic hydrogen propellants is presented.

  16. Metastable supersymmetry breaking and dynamical vacuum selection in intersecting brane systems

    NASA Astrophysics Data System (ADS)

    Royston, Andrew B.

    In this thesis we study metastable supersymmetry breaking and dynamical vacuum selection in intersecting brane systems that are known to be useful for realizing supersymmetric gauge theories in string theory. Metastable supersymmetry breaking configurations of D-branes and NS5-branes in string theory often owe their existence to classical gravitational interactions between the branes. We show that in the effective theory of the light fields, these interactions give rise to a non-canonical Kahler potential and other D-terms. String theory provides a UV completion in which these non-renormalizable terms can be computed. We use these observations to clarify the relation between the phase structure of ISS-type models and their brane realizations. We then study dynamical vacuum selection in a system of D-branes localized near an intersection of Neveu-Schwarz fivebranes that is known to exhibit a rich landscape of supersymmetric and (metastable) supersymmetry breaking vacua. We show that early universe cosmology, in the form of excited fivebranes relaxing via Hawking radiation, drives the system to a particular long-lived supersymmetry breaking ground state.

  17. Preparation and evaluation of metastable solid-state forms of lopinavir.

    PubMed

    Lemmer, H J R; Liebenberg, W

    2013-05-01

    In this work, we present the preparation and evaluation of previously unreported metastable forms of the antiretroviral drug, lopinavir. By maintaining the chemical structure, physicochemical properties like the glass transition temperature (T(g)), dissolution and solubility can be readily attributed to the stability of the system. Commercially-available lopinavir was used to prepare partially amorphous crystals, semicrystalline needles, resins and glasses. The physicochemical properties of each were investigated using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (PXRD). Each sample's thermal and spectroscopic analyses, as well as dissolution and solubility studies were performed one month after sample preparation, for better comparability. Glass transition temperature, activation energy for global molecular mobility (deltaE(Tg)), and activation energy for local molecular mobility (deltaE(beta)) were assessed as primary indicators for structural stability of the systems. Relating these properties to aqueous solubility revealed that each metastable form possessed its own unique equilibrium solubility. Cumulative dissolved fractions (alpha) were fitted against deceleratory kinetics models, and from the data hereby obtained the dissolution process was determined to followed first-order kinetics (R2 = 0.998). From the rate constants, the activation energy for dissolution (deltaE(Diss)) of each sample was calculated. The results suggest that multiple metastable solid-state forms of lopinavir can exist under similar conditions, depending on the preparation conditions.

  18. Microstructure of metastable metallic alloy films produced by laser breakdown chemical vapor deposition and ion implantation

    SciTech Connect

    Menon, S.K.; Jervis, T.R.; Nastasi, M.

    1986-01-01

    Thin films produced by laser breakdown chemical vapor deposition from nickel and iron carbonyls and by implanting Ni foils with varying levels of C have been characterized by transmission electron microscopy. Decomposition of Ni(CO)/sub 4/ produces polycrystalline films of fcc Ni and metastable ordered hexagonal Ni/sub 3/C. This metastable phase is identical to that produced by gas carburization, rapid solidification of Ni-C melts, and ion implantation of C into Ni at low concentrations. Increasing the H/sub 2/ content in the gas mixture during laser deposition reduces the grain size of the films significantly with grain sizes smaller than 10 nanometers produced. Laser decomposition of Fe(CO)/sub 5/ produces films with islands of fcc gamma-Fe and finely dispersed metastable Fe/sub 3/C (Cementite). In addition, the ferrous oxides Fe/sub 2/O/sub 3/ and Fe/sub 3/O/sub 4/ were found in these samples. Implants of C into pure Ni foils at 77/sup 0/K and at a concentration of 35 at. % produced amorphous layers. Implants at the same dose at room temperature did not produce amorphous layers.

  19. Three-photon process for producing a degenerate gas of metastable alkaline-earth-metal atoms

    NASA Astrophysics Data System (ADS)

    Barker, D. S.; Pisenti, N. C.; Reschovsky, B. J.; Campbell, G. K.

    2016-05-01

    We present a method for creating a quantum degenerate gas of metastable alkaline-earth-metal atoms. This has yet to be achieved due to inelastic collisions that limit evaporative cooling in the metastable states. Quantum degenerate samples prepared in the 1S0 ground state can be rapidly transferred to either the 3P2 or 3P0 state via a coherent three-photon process. Numerical integration of the density-matrix evolution for the fine structure of bosonic alkaline-earth-metal atoms shows that transfer efficiencies of ≃90 % can be achieved with experimentally feasible laser parameters in both Sr and Yb. Importantly, the three-photon process can be set up such that it imparts no net momentum to the degenerate gas during the excitation, which will allow for studies of metastable samples outside the Lamb-Dicke regime. We discuss several experimental challenges to successfully realizing our scheme, including the minimization of differential ac Stark shifts between the four states connected by the three-photon transition.

  20. A 3-photon process for producing degenerate gases of metastable alkaline-earth atoms

    NASA Astrophysics Data System (ADS)

    Barker, Daniel S.; Pisenti, Neal C.; Reschovsky, Benjamin J.; Campbell, Gretchen K.

    2016-05-01

    We present a method for creating quantum degenerate gases of metastable alkaline-earth atoms. A degenerate gas in any of the 3 P metastable states has not previously been obtained due to large inelastic collision rates, which are unfavorable for evaporative cooling. Samples prepared in the 1S0 ground state can be rapidly transferred to either the 3P2 or 3P0 state via a coherent 3-photon process. Numerical integration of the density matrix evolution for the fine structure of bosonic alkaline-earth atoms shows that transfer efficiencies of ~= 90 % can be achieved with experimentally feasible laser parameters in both Sr and Yb. Importantly, the 3-photon process does not impart momentum to the degenerate gas during excitation, which allows studies of these metastable samples outside the Lamb-Dicke regime. We discuss several experimental challenges to the successful realization of our scheme, including the minimization of differential AC Stark shifts between the four states connected by the 3-photon transition.