Science.gov

Sample records for 1s2s 3s1 metastable

  1. 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.

  2. 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.

  3. 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}

  4. 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}.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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).

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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).

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. (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.

  16. 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.

  17. 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

  18. Metastable Packaging For Transient Electronics

    DTIC Science & Technology

    2014-09-01

    dated 16 Jan 09. Report contains color. 14. ABSTRACT Metastable polymeric materials were synthesized, formulated with additives and microcapsules ...photoacid generation, thermal activation, and mechanical rupture of acid-filled microcapsules -- were investigated. 15. SUBJECT TERMS transient...carbonate sulfone) (PVBCS)... 11  3.3  Thermal and Mechanical Triggered Transience of Electronic Devices via Embedded Microcapsules

  19. 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.

  20. 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.

  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. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. 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.

  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. 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.

  16. 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

  17. 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)

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  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. 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.

  5. 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.

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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.

  20. 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

  1. 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.

  2. 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.

  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. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  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. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  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. 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.

  17. 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.

  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. 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.

  20. 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.

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Theoretical Studies of the Lifetime of Metastable H3

    DTIC Science & Technology

    1990-11-01

    Aharonov - Bohm , MAB, metastable 21 09 lifetimes 19. ABSTRACT (Continue on reverse if necessary and identify by block number) In this report, the major steps...Molecular Aharonov - Bohm (MAB) effect (or Berry’s geometric phase). This effect has a profound influence on both the bound and scattering states of...this surface and the ground state one introduces the Molecular Aharonov - Bohm (MBA) effect 49 - 5 2 which needs special treatment, and since we also want

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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).

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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 → ∞.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  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. 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.

  16. 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

  17. 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.

  18. 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.

  19. 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)].

  20. 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.

  1. 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

  2. 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

  3. 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.

  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. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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}

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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 ...

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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, Ken; Katsaras, John

    2011-01-01

    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 applications that

  13. 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

  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. 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.

  16. 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.

  17. 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.

  18. 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.

  19. (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

  20. (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

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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

  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. 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}.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  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. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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)].

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. Interindividual variation in DNA methylation at a putative POMC metastable epiallele is associated with obesity

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  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. 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.

  10. 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

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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}

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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.

  13. Dislocation Strengthening without Ductility Trade-off in Metastable Austenitic Steels

    NASA Astrophysics Data System (ADS)

    Liu, Jiabin; Jin, Yongbin; Fang, Xiaoyang; Chen, Chenxu; Feng, Qiong; Liu, Xiaowei; Chen, Yuzeng; Suo, Tao; Zhao, Feng; Huang, Tianlin; Wang, Hongtao; Wang, Xi; Fang, Youtong; Wei, Yujie; Meng, Liang; Lu, Jian; Yang, Wei

    2016-10-01

    Strength and ductility are mutually exclusive if they are manifested as consequence of the coupling between strengthening and toughening mechanisms. One notable example is dislocation strengthening in metals, which invariably leads to reduced ductility. However, this trend is averted in metastable austenitic steels. A one-step thermal mechanical treatment (TMT), i.e. hot rolling, can effectively enhance the yielding strength of the metastable austenitic steel from 322 ± 18 MPa to 675 ± 15 MPa, while retaining both the formability and hardenability. It is noted that no boundaries are introduced in the optimized TMT process and all strengthening effect originates from dislocations with inherited thermal stability. The success of this method relies on the decoupled strengthening and toughening mechanisms in metastable austenitic steels, in which yield strength is controlled by initial dislocation density while ductility is retained by the capability to nucleate new dislocations to carry plastic deformation. Especially, the simplicity in processing enables scaling and industrial applications to meet the challenging requirements of emissions reduction. On the other hand, the complexity in the underlying mechanism of dislocation strengthening in this case may shed light on a different route of material strengthening by stimulating dislocation activities, rather than impeding motion of dislocations.

  14. Spin-polarized metastable-atom deexcitation spectroscopy study of Xenon-adsorbed iron surfaces

    NASA Astrophysics Data System (ADS)

    Yamauchi, Yasushi; Kurahashi, Mitsunori; Suzuki, Taku; Sun, Xia; Wang, Zhongping

    2007-03-01

    The electron spin polarization at the interface between nonmagnetic and ferromagnetic medias is one of the essential factors that may alter the spin transport phenomena. To investigate fundamental aspects of induced spin polarization we have examined the adsorbate-covered magnetic surfaces by means of spin polarized metastable-atom deexcitation spectroscopy (SPMDS). Use of spin-polarized metastable helium atoms in triplet states moving at thermal energies gives rise to the ultimate surface sensitivity. Although Xenon can adsorb on surfaces at low temperatures by the van der Waals force, no electron exchange with surfaces, especially no spin interaction, is expected because of its closed shell structure. SPMDS spectra measured for Xenon-adsorbed iron surfaces show three prominent peaks that are the same as those previously reported for other surfaces by D. M. Oro, et al. [Phys. Rev. A 49 (1994) 4703]. Two peaks (^2P1/2, ^2P3/2) at higher kinetic energies exhibit clear spin asymmetries while the other low energy peak has no appreciable spin asymmetry. The spin asymmetries will be discussed on the basis of spin polarization and deexcitation processes of metastable atoms.

  15. Dislocation Strengthening without Ductility Trade-off in Metastable Austenitic Steels

    PubMed Central

    Liu, Jiabin; Jin, Yongbin; Fang, Xiaoyang; Chen, Chenxu; Feng, Qiong; Liu, Xiaowei; Chen, Yuzeng; Suo, Tao; Zhao, Feng; Huang, Tianlin; Wang, Hongtao; Wang, Xi; Fang, Youtong; Wei, Yujie; Meng, Liang; Lu, Jian; Yang, Wei

    2016-01-01

    Strength and ductility are mutually exclusive if they are manifested as consequence of the coupling between strengthening and toughening mechanisms. One notable example is dislocation strengthening in metals, which invariably leads to reduced ductility. However, this trend is averted in metastable austenitic steels. A one-step thermal mechanical treatment (TMT), i.e. hot rolling, can effectively enhance the yielding strength of the metastable austenitic steel from 322 ± 18 MPa to 675 ± 15 MPa, while retaining both the formability and hardenability. It is noted that no boundaries are introduced in the optimized TMT process and all strengthening effect originates from dislocations with inherited thermal stability. The success of this method relies on the decoupled strengthening and toughening mechanisms in metastable austenitic steels, in which yield strength is controlled by initial dislocation density while ductility is retained by the capability to nucleate new dislocations to carry plastic deformation. Especially, the simplicity in processing enables scaling and industrial applications to meet the challenging requirements of emissions reduction. On the other hand, the complexity in the underlying mechanism of dislocation strengthening in this case may shed light on a different route of material strengthening by stimulating dislocation activities, rather than impeding motion of dislocations. PMID:27739481

  16. Strain relaxation of metastable SiGe/Si: Investigation with two complementary X-ray techniques

    SciTech Connect

    Kasper, E.; Werner, J.; Oehme, M.; Lyutovich, K.; Burle, N.; Escoubas, S.

    2012-03-15

    Metastable and strain relaxed SiGe layers with about 20% Ge content have been grown by molecular beam epitaxy on Si substrates at 550 deg. C. The thickness regime of metastability and the onset of strain relaxation were investigated on dust particle free surfaces obtained by careful chemical cleaning and epitaxy loading under clean room conditions. Compared to earlier results true metastable regime without misfit dislocations was obtained up to 140 nm thickness. The onset of strain relaxation started with heterogeneous nucleation sites of misfit dislocations. X-ray topography proved to be a unique monitoring tool to observe a low density of single dislocations. From these results we suggested to define a critical thickness band with lower bound t{sub cl} from dislocation nucleation to an upper bound t{sub co} (600 nm in our case) defined by the onset of considerable strain relaxation. The strain relief was measured by X-ray diffraction (reciprocal space mapping) and found to be very abrupt (76% strain relaxation at 800 nm thickness).

  17. Photodissociation and radiative association of HeH+ in the metastable triplet state.

    PubMed

    Loreau, J; Vranckx, S; Desouter-Lecomte, M; Vaeck, N; Dalgarno, A

    2013-10-03

    We investigate the photodissociation of HeH(+) in the metastable triplet state as well as its formation through the inverse process, radiative association. In models of astrophysical plasmas, HeH(+) is assumed to be present only in the ground state, and the influence of the triplet state has not been explored. It may be formed by radiative association during collisions between a proton and metastable helium, which are present in significant concentrations in nebulae. The triplet state can also be formed by association of He(+) and H, although this process is less likely to occur. We compute the cross sections and rate coefficients corresponding to the photodissociation of the triplet state by UV photons from a central star using a wave packet method. We show that the photodissociation cross sections depend strongly on the initial vibrational state and that the effects of excited electronic states and nonadiabatic couplings cannot be neglected. We then calculate the cross section and rate coefficient for the radiative association of HeH(+) in the metastable triplet state.

  18. Measurements of population densities of metastable and resonant levels of argon using laser induced fluorescence

    SciTech Connect

    Nikolić, M.; Newton, J.; Sukenik, C. I.; Vušković, L.; Popović, S.

    2015-01-14

    We present a new approach to measure population densities of Ar I metastable and resonant excited states in low temperature Ar plasmas at pressures higher than 1 Torr. This approach combines the time resolved laser induced fluorescence technique with the kinetic model of Ar. The kinetic model of Ar is based on calculating the population rates of metastable and resonant levels by including contributions from the processes that affect population densities of Ar I excited states. In particular, we included collisional quenching processes between atoms in the ground state and excited states, since we are investigating plasma at higher pressures. We also determined time resolved population densities of Ar I 2 p excited states by employing optical emission spectroscopy technique. Time resolved Ar I excited state populations are presented for the case of the post-discharge of the supersonic flowing microwave discharge at pressures of 1.7 and 2.3 Torr. The experimental set-up consists of a pulsed tunable dye laser operating in the near infrared region and a cylindrical resonance cavity operating in TE{sub 111} mode at 2.45 GHz. Results show that time resolved population densities of Ar I metastable and resonant states oscillate with twice the frequency of the discharge.

  19. STUDENT AWARD FINALIST: Plasma Acid: A Chemically and Physically Metastable Substance

    NASA Astrophysics Data System (ADS)

    Shainsky, Natalie; Dobrynin, Danil; Ercan, Utku; Joshi, Suresh; Brooks, Ari; Ji, Haifeng; Fridman, Gregory; Cho, Young; Fridman, Alexander; Friedman, Gennady

    2011-10-01

    Non-thermal atmospheric pressure dielectric barrier discharge applied to the surface of a liquid creates a chemically and physically metastable substance. The properties and lifetime of the substance depend on the treatment conditions such as gas atmosphere and liquid medium used, treatment dose, and other parameters. When deionized water is used, the metastable substance becomes a strong oxidizer. We show that direct exposure of deionized water to neutral and charged species produced in plasma creates a strong oxidizer and acidic substance in this water which, for the lack of a better term, we termed plasma acid. Plasma acid can remain stable for relatively long time and its oxidizing power may be linked to the significant lowering of its pH. We report experiments that demonstrate plasma acid's metastability. We also show that observed pH of as low as 2.0 cannot be completely accounted for by the production of nitric acid; and that the conjugate base derived from superoxide is at least partly responsible for both, lowering of the pH and increase in the oxidizing power of the solution.

  20. Note on the calculation of the second osmotic virial coefficient in stable and metastable liquid states.

    PubMed

    Widom, B; Koga, K

    2013-01-31

    The second osmotic virial coefficient is calculated from analytical equations of state as illustrated with the van der Waals two-component equation. It is shown that when the fixed solvent chemical potential or pressure at which the virial coefficient is calculated is taken to be that of the pure solvent in coexistence with its vapor, as in a recent report, the liquid solution is in a metastable state. When, by contrast, that fixed chemical potential or pressure is that of the pure solvent in its one-phase liquid state, the solution, with increasing solute concentration, is initially in a stable state; then, on crossing the liquid-vapor equilibrium line, it becomes metastable and ultimately approaches a spinodal and incipient instability. Nevertheless, in practice, as seen in a numerical illustration for a hydrocarbon dissolved in water, there is scarcely any difference in the virial coefficient calculated with the fixed solvent chemical potential or pressure of the pure solvent at its vapor pressure (metastable states of the solution) or at 1 bar (initially stable states). It is also seen in that example that the virial coefficient may be reliably calculated only for solute concentrations that are neither too small nor too large; typically only for mole fractions roughly from 10(-7) to 10(-3.5).

  1. Removal of particles from lithographic masks through plasma-assisted cleaning by metastable atomic neutralization

    NASA Astrophysics Data System (ADS)

    Lytle, W. M.; Szybilski, D. S.; Das, C. E.; Raju, R.; Surla, V.; Neumann, M. J.; Ruzic, D. N.

    2008-11-01

    For extreme ultraviolet lithography (EUVL) to become a high volume manufacturing technology for integrated circuit manufacturing, the cleanliness of the system, especially the photomask, is of high importance. For EUV photomasks, which cannot be protected from contamination by the use of a pellicle, an effective and quick cleaning technology needs to be ready in order to maintain wafer throughput. There are challenges to extend current wet cleaning technologies to meet the future needs for damage-free and high efficiency mask cleaning. Accordingly, a unique process for cleaning particulates from surfaces, specifically photomasks as well as wafers, has been evaluated at the University of Illinois Urbana-Champaign. The removal technique utilizes a high density plasma source as well as pulsed substrate biases to provide for removal. Helium is used as the primary gas in the plasma, which under ionization, provides for a large density of helium metastable atoms present in the plasma. These metastable helium atoms have on the order of 20 eV of energy which can transfer to particles on the substrate to be cleaned. When the substrate is under a small flux of ion bombardment, these bonds then remain broken and it is theorized that this allows the particles to be volatilized for their subsequent removal. 100 % particle removal efficiency has been obtained for 30 nm, 80 nm, and 200 nm polystyrene latex particles. In addition, removal rate has been correlated with helium metastable population density determined by optical emission spectroscopy.

  2. 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.

  3. ScVO4 under non-hydrostatic compression: a new metastable polymorph.

    PubMed

    Garg, Alka B; Errandonea, D; Rodríguez-Hernández, P; Muñoz, A

    2017-02-08

    The high-pressure (HP) behaviour of scandium vanadate (ScVO4) is investigated under non-hydrostatic compression. The compound is studied by means of synchrotron-based powder x-ray diffraction (XRD) and optical-absorption techniques. The occurrence of a non-reversible phase transition is detected. The transition is from the zircon structure to the fergusonite-type structure and takes place around 6 GPa with nearly 10% volume discontinuity. XRD measurements on the pressure cycled sample confirm for the first time that the fergusonite-type ScVO4 can be recovered as the metastable phase at ambient conditions. Raman spectroscopic measurements verify the metastable phase to be of a fergusonite-type phase. Theoretical calculations also corroborate the experimental findings. The fergusonite phase is found to be stiffer than the ambient-pressure zircon phase, as indicated by the observed experimental and theoretical bulk moduli. The optical properties and lattice-dynamics calculation of the fergusonite ScVO4 are discussed. At ambient pressure the band gap of the zircon (fergusonite)-type ScVO4 is 2.75 eV (2.3 eV). This fact suggests that the novel metastable polymorph of ScVO4 can have applications in green technologies; for instance, it can be used as photocatalytic material for hydrogen production by water splitting.

  4. ScVO4 under non-hydrostatic compression: a new metastable polymorph

    NASA Astrophysics Data System (ADS)

    Garg, Alka B.; Errandonea, D.; Rodríguez-Hernández, P.; Muñoz, A.

    2017-02-01

    The high-pressure (HP) behaviour of scandium vanadate (ScVO4) is investigated under non-hydrostatic compression. The compound is studied by means of synchrotron-based powder x-ray diffraction (XRD) and optical-absorption techniques. The occurrence of a non-reversible phase transition is detected. The transition is from the zircon structure to the fergusonite-type structure and takes place around 6 GPa with nearly 10% volume discontinuity. XRD measurements on the pressure cycled sample confirm for the first time that the fergusonite-type ScVO4 can be recovered as the metastable phase at ambient conditions. Raman spectroscopic measurements verify the metastable phase to be of a fergusonite-type phase. Theoretical calculations also corroborate the experimental findings. The fergusonite phase is found to be stiffer than the ambient-pressure zircon phase, as indicated by the observed experimental and theoretical bulk moduli. The optical properties and lattice-dynamics calculation of the fergusonite ScVO4 are discussed. At ambient pressure the band gap of the zircon (fergusonite)-type ScVO4 is 2.75 eV (2.3 eV). This fact suggests that the novel metastable polymorph of ScVO4 can have applications in green technologies; for instance, it can be used as photocatalytic material for hydrogen production by water splitting.

  5. Gallbladder dysfunction enhances physical density but not biochemical metastability of biliary vesicles.

    PubMed

    Sunami, Y; Tazuma, S; Kajiyama, G

    2000-12-01

    The gallbladder role in cholesterol gallstone pathogenesis occurs through modulation of bile cholesterol metastability. The present study characterized the effects of concentrating bile on cholesterol crystallization through vesicle transformation, crystal habits, and potentiation of effector substances. Supersaturated model biles with total lipid concentrations of 12, 9, 6, and 3 g/dl were prepared with identical molar ratios (taurocholate-egg yolk phosphatidylcholine-cholesterol: 71:18:11). Bile metastability was assessed spectrophotometrically, and morphology of vesicle and crystal was sequentially scanned by video-enhanced differential contrast microscopy. The effects of replacing 30% of egg yolk phosphatidylcholine with soy bean phosphatidylcholine, 30% of taurocholate with taurodeoxycholate or tauroursodeoxycholate, and addition of concanavalin A-binding glycoprotein on each model bile were examined. By lowering total lipid concentration, cholesterol crystallization was retarded with less fusion and aggregation of vesicles. The effects of substances promoting cholesterol crystallization were enhanced with lesser bile. By replacing 30% of taurocholate with tauroursodeoxycholate, cholesterol crystallization was markedly inhibited in all concentrations, forming stable liquid-crystals. Impaired water absorption by the gallbladder may stabilize vesicles and inhibit rapid cholesterol crystallization, but the potential of cholesterol crystallization effector substances must be modified to alter bile cholesterol metastability.

  6. 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.

  7. Highly active metastable ruthenium nanoparticles for hydrogen production through the catalytic hydrolysis of ammonia borane.

    PubMed

    Abo-Hamed, Enass K; Pennycook, Timothy; Vaynzof, Yana; Toprakcioglu, Chris; Koutsioubas, Alexandros; Scherman, Oren A

    2014-08-13

    Late transition metal nanoparticles (NPs) with a favorably high surface area to volume ratio have garnered much interest for catalytic applications. Yet, these NPs are prone to aggregation in solution, which has been mitigated through attachment of surface ligands, additives or supports; unfortunately, protective ligands can severely reduce the effective surface area on the NPs available for catalyzing chemical transformations. The preparation of 'metastable' NPs can readily address these challenges. We report herein the first synthesis of monodisperse metastable ruthenium nanoparticles (RuNPs), having sub 5 nm size and an fcc structure, in aqueous media at room temperature, which can be stored for a period of at least 8 months. The RuNPs can subsequently be used for the catalytic, quantitative hydrolysis of ammonia-borane (AB) yielding hydrogen gas with 21.8 turnovers per min at 25 °C. The high surface area available for hydrolysis of AB on the metastable RuNPs translated to an Ea of 27.5 kJ mol(-1) , which is notably lower than previously reported values for RuNP based catalysts.

  8. Transport processes induced by metastable boiling water under Martian surface conditions

    NASA Astrophysics Data System (ADS)

    Massé, M.; Conway, S. J.; Gargani, J.; Patel, M. R.; Pasquon, K.; McEwen, A.; Carpy, S.; Chevrier, V.; Balme, M. R.; Ojha, L.; Vincendon, M.; Poulet, F.; Costard, F.; Jouannic, G.

    2016-06-01

    Liquid water may exist on the Martian surface today, albeit transiently and in a metastable state under the low atmospheric surface pressure. However, the identification of liquid water on Mars from observed morphological changes is hampered by our limited understanding of how metastable liquids interact with sediments. Here, we present lab experiments in which a block of ice melts and seeps into underlying sediment, and the resulting downslope fluid propagation and sediment transport are tracked. In experiments at Martian surface pressure, we find that pure water boils as it percolates into the sediment, inducing grain saltation and leading to wholesale slope destabilization: a hybrid flow mechanism involving both wet and dry processes. For metastable brines, which are more stable under Martian conditions than pure water, saltation intensity and geomorphological impact are reduced; however, we observed channel formation in some briny flow experiments that may be analogous to morphologies observed on Mars. In contrast, under terrestrial-like experimental conditions, there is little morphological impact of seeping water or brine, which are both stable. We propose that the hybrid flow mechanism operating in our experiments under Martian surface pressure could explain observed Martian surface changes that were originally interpreted as the products of either dry or wet processes.

  9. 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.

  10. 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.

  11. 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.

  12. Autonomous assembly of ordered metastable DNA nanoarchitecture and in situ visualizing of intracellular microRNAs.

    PubMed

    Xu, Jianguo; Wu, Zai-Sheng; Wang, Zhenmeng; Le, Jingqing; Zheng, Tingting; Jia, Lee

    2017-03-01

    Facile assembly of intelligent DNA nanoobjects with the ability to exert in situ visualization of intracellular microRNAs (miRNAs) has long been concerned in the fields of DNA nanotechnology and basic medical study. Here, we present a driving primer (DP)-triggered polymerization-mediated metastable assembly (PMA) strategy to prepare a well-ordered metastable DNA nanoarchitecture composed of only two hairpin probes (HAPs), which has never been explored by assembly methods. Its structural features and functions are characterized by atomic force microscope (AFM) and gel electrophoresis. Even if with a metastable molecular structure, this nanoarchitecture is relatively stable at physiological temperature. The assembly strategy can be expanded to execute microRNA-21 (miRNA-21) in situ imaging inside cancer cells by labelling one of the HAPs with fluorophore and quencher. Compared with the conventional fluorescence probe-based in situ hybridization (FISH) technique, confocal images revealed that the proposed DNA nanoassembly can not only achieve greatly enhanced imaging effect within cancer cells, but also reflect the miRNA-21 expression level sensitively. We believe that the easily constructed DNA nanoarchitecture and in situ profiling strategy are significant progresses in DNA assembly and molecule imaging in cells.

  13. Dislocation Strengthening without Ductility Trade-off in Metastable Austenitic Steels.

    PubMed

    Liu, Jiabin; Jin, Yongbin; Fang, Xiaoyang; Chen, Chenxu; Feng, Qiong; Liu, Xiaowei; Chen, Yuzeng; Suo, Tao; Zhao, Feng; Huang, Tianlin; Wang, Hongtao; Wang, Xi; Fang, Youtong; Wei, Yujie; Meng, Liang; Lu, Jian; Yang, Wei

    2016-10-14

    Strength and ductility are mutually exclusive if they are manifested as consequence of the coupling between strengthening and toughening mechanisms. One notable example is dislocation strengthening in metals, which invariably leads to reduced ductility. However, this trend is averted in metastable austenitic steels. A one-step thermal mechanical treatment (TMT), i.e. hot rolling, can effectively enhance the yielding strength of the metastable austenitic steel from 322 ± 18 MPa to 675 ± 15 MPa, while retaining both the formability and hardenability. It is noted that no boundaries are introduced in the optimized TMT process and all strengthening effect originates from dislocations with inherited thermal stability. The success of this method relies on the decoupled strengthening and toughening mechanisms in metastable austenitic steels, in which yield strength is controlled by initial dislocation density while ductility is retained by the capability to nucleate new dislocations to carry plastic deformation. Especially, the simplicity in processing enables scaling and industrial applications to meet the challenging requirements of emissions reduction. On the other hand, the complexity in the underlying mechanism of dislocation strengthening in this case may shed light on a different route of material strengthening by stimulating dislocation activities, rather than impeding motion of dislocations.

  14. Electron ionization of metastable nitrogen and oxygen atoms in relation to the auroral emissions

    NASA Astrophysics Data System (ADS)

    Pandya, Siddharth; Joshipura, K. N.

    Atomic and molecular excited metastable states (EMS) are exotic systems due to their special properties like long radiative life-time, large size (average radius) and large polarizability along with relatively smaller first ionization energy compared to their respective ground states (GS). The present work includes our theoretical calculations on electron impact ionization of metastable atomic states N( (2) P), N( (2) D) of nitrogen and O( (1) S), O( (1) D) of oxygen. The targets of our present interest, are found to be present in our Earth's ionosphere and they play an important role in auroral emissions observed in Earth’s auroral regions [1] as also in the emissions observed from cometary coma [2, 3] and airglow emissions. In particular, atomic oxygen in EMS can radiate, the visible O( (1) D -> (3) P) doublet 6300 - 6364 Å red doublet, the O( (1) S -> (1) D) 5577 Å green line, and the ultraviolet O( (1) S -> (3) P) 2972 Å line. For metastable atomic nitrogen one observes the similar emissions, in different wavelengths, from (2) D and (2) P states. At the Earth's auroral altitudes, from where these emissions take place in the ionosphere, energetic electrons are also present. In particular, if the metastable N as well as O atoms are ionized by the impact of electrons then these species are no longer available for emissions. This is a possible loss mechanism, and hence it is necessary to analyze the importance of electron ionization of the EMS of atomic O and N, by calculating the relevant cross sections. In the present paper we investigate electron ionization of the said metastable species by calculating relevant total cross sections. Our quantum mechanical calculations are based on projected approximate ionization contribution in the total inelastic cross sections [4]. Detailed results and discussion along with the significance of these calculations will be presented during the COSPAR-2014. References [1] A.Bhardwaj, and G. R. Gladstone, Rev. Geophys., 38

  15. Glassy and Metastable Crystalline BaTi2O5 by Containerless Processing

    NASA Astrophysics Data System (ADS)

    Yoda, Shinichi; Kentei Yu, Yu; Kumar, Vijaya; Kameko, Masashi

    Many efforts have been devoted to forming bulk glass from the melt of ferroelectric crystalline materials without adding any network-forming oxides such as SiO2 due to the potential for producing transparent glass ceramics with high dielectric constant and enhanced piezoelectric, pyroelectric and electro-optic use. The containerless processing is an attractive synthesis tech-nique as it can prevent melt contamination, minimize heterogeneous nucleation, and allow melt to achieve deep undercooling for forming metastable and glassy materials. We have fabricated a new ferroelectric materiel BaTi2 O5 [1] as bulk glass from melt by us-ing containerless processing and studied the phase relationship between microstructure and ferroelectric properties of BaTi2 O5 [2]. The structures of glassy and metastable crystalline BaTi2 O5 fabricated by the containerless pro-cessing were comprehensively investigated by combined X-ray and neutron diffractions, XANES analyses and computer simulations [3]. The 3-dimensional atomic structure of glassy BaTi2 O5 (g-BaTi2 O5 ), simulated by Reverse Monte Carlo (RMC) modelling on diffraction data, shows that extremely distorted TiO5 polyhedra interconnected with both corner-and edge-shared oxy-gen, formed a higher packing density structure than that of conventional silicate glass linked with only corner-sharing of SiO4 polyhedra. In addition, XANES measurement reveales that five-coordinated TiO5 polyhedra were formable in the crystallized metastable a-and b-BaTi2 O5 phases. The structure of metastable b-BaTi2 O5 was solved by ab initio calculation, and refined by Rietveld refinement as group Pnma with unit lattices a = 10.23784 ˚, b = 3.92715 ˚, c A A = 10.92757 A ˚. Our results show that the glass-forming ability enhanced by containerless pro-cessing, not by `strong glass former', fabricated new bulk oxide glasses with peculiar structures and properties. The intermediate-range structure of g-BaTi2 O5 and the crystalline structure of

  16. Containerless Solidification of Hexagonal Metastable Phases from an Undercooled R3Fe5O12 Melt

    NASA Astrophysics Data System (ADS)

    Kumar, Vijaya; Kentei Yu, Yu; Kameko, Masashi; Ishikawa, Takehiko; Kuribayashi, Kazuhiko; Yoda, Shinichi

    Containerless processing is a promising technique to explore the technologically important materials using rapid solidification of an undercooled melt because it provides large undercooling prior to nucleation. In the R-Fe-O system (R=Rare-earth element), rare-earth iron garnet (R3 Fe5 O12 ) can be formed through a peritectic reaction between RFeO3 , which is a primary phase, and a melt, which contains more Fe2 O3 than the R3 Fe5 O12 composition. The iron garnet is know to become unstable with increasing ionic radius of the rare-earth ion from Lu to Sm and does not exist in a stable form in La, Pr, and Nd [1,2]. Recently, we investigated the effect of oxygen partial pressure Po2 on metastable phase formation from an undercooled RFeO3 melt through containerless solidification. On the other hand, Po2 was considered to be one of the most important thermodynamic parameters which control phase constituents during containerless processing. In the R-Fe-O system, multiferroic hexagonal RFeO3 (P63 cm) and Fe2+ -containing ferroelectric phases such as RFe2 O4 (r-R3m) and new hexagonal R3 Fe2 O7 (P63 /mmc) phases were obtained metastably with decreasing Po2 from 105 to 10-1 Pa [3,4]. However, in the R3 Fe5 O12 system, the effect of Po2 during rapid solidification has not been studied yet. The purpose of this study is to elucidate the effect of Po2 on the formation of metastable phases from an undercooled R3 Fe5 O12 melt under controlled Po2 using gas-jet levitation technique. In order to undercool the melt deeply below the melting temperature under a precisely con-trolled oxygen partial pressure, an aerodynamic levitator (ADL) combined with ZrO2 oxygen sensor was designed. A spherical R3 Fe5 O12 sample was levitated by an ADL and completely melted by a CO2 laser in an atmosphere with predetermined Po2 . The surface temperature of the levitated droplet was monitored by a two-color pyrometer. Then, the droplet was cooled by turning off the CO2 laser. Meanwhile, the recalescence

  17. Metastable high-entropy dual-phase alloys overcome the strength-ductility trade-off.

    PubMed

    Li, Zhiming; Pradeep, Konda Gokuldoss; Deng, Yun; Raabe, Dierk; Tasan, Cemal Cem

    2016-06-09

    Metals have been mankind's most essential materials for thousands of years; however, their use is affected by ecological and economical concerns. Alloys with higher strength and ductility could alleviate some of these concerns by reducing weight and improving energy efficiency. However, most metallurgical mechanisms for increasing strength lead to ductility loss, an effect referred to as the strength-ductility trade-off. Here we present a metastability-engineering strategy in which we design nanostructured, bulk high-entropy alloys with multiple compositionally equivalent high-entropy phases. High-entropy alloys were originally proposed to benefit from phase stabilization through entropy maximization. Yet here, motivated by recent work that relaxes the strict restrictions on high-entropy alloy compositions by demonstrating the weakness of this connection, the concept is overturned. We decrease phase stability to achieve two key benefits: interface hardening due to a dual-phase microstructure (resulting from reduced thermal stability of the high-temperature phase); and transformation-induced hardening (resulting from the reduced mechanical stability of the room-temperature phase). This combines the best of two worlds: extensive hardening due to the decreased phase stability known from advanced steels and massive solid-solution strengthening of high-entropy alloys. In our transformation-induced plasticity-assisted, dual-phase high-entropy alloy (TRIP-DP-HEA), these two contributions lead respectively to enhanced trans-grain and inter-grain slip resistance, and hence, increased strength. Moreover, the increased strain hardening capacity that is enabled by dislocation hardening of the stable phase and transformation-induced hardening of the metastable phase produces increased ductility. This combined increase in strength and ductility distinguishes the TRIP-DP-HEA alloy from other recently developed structural materials. This metastability-engineering strategy should

  18. Metastable high-entropy dual-phase alloys overcome the strength-ductility trade-off

    NASA Astrophysics Data System (ADS)

    Li, Zhiming; Pradeep, Konda Gokuldoss; Deng, Yun; Raabe, Dierk; Tasan, Cemal Cem

    2016-06-01

    Metals have been mankind’s most essential materials for thousands of years; however, their use is affected by ecological and economical concerns. Alloys with higher strength and ductility could alleviate some of these concerns by reducing weight and improving energy efficiency. However, most metallurgical mechanisms for increasing strength lead to ductility loss, an effect referred to as the strength-ductility trade-off. Here we present a metastability-engineering strategy in which we design nanostructured, bulk high-entropy alloys with multiple compositionally equivalent high-entropy phases. High-entropy alloys were originally proposed to benefit from phase stabilization through entropy maximization. Yet here, motivated by recent work that relaxes the strict restrictions on high-entropy alloy compositions by demonstrating the weakness of this connection, the concept is overturned. We decrease phase stability to achieve two key benefits: interface hardening due to a dual-phase microstructure (resulting from reduced thermal stability of the high-temperature phase); and transformation-induced hardening (resulting from the reduced mechanical stability of the room-temperature phase). This combines the best of two worlds: extensive hardening due to the decreased phase stability known from advanced steels and massive solid-solution strengthening of high-entropy alloys. In our transformation-induced plasticity-assisted, dual-phase high-entropy alloy (TRIP-DP-HEA), these two contributions lead respectively to enhanced trans-grain and inter-grain slip resistance, and hence, increased strength. Moreover, the increased strain hardening capacity that is enabled by dislocation hardening of the stable phase and transformation-induced hardening of the metastable phase produces increased ductility. This combined increase in strength and ductility distinguishes the TRIP-DP-HEA alloy from other recently developed structural materials. This metastability-engineering strategy should

  19. Ostwald-Meyers Metastable Region in LiBr Crystallization-Comparison of Measurements with Predictions.

    PubMed

    Duvall, Kristin N.; Dirksen, James A.; Ring, Terry A.

    2001-07-15

    Experiments have been performed to measure the Ostwald-Meyers metastable region during crystallization from concentrated LiBr solutions. Solution thermodynamics shows that several hydrated LiBr salts and ice can crystallize depending upon the concentration of LiBr in aqueous solution. The available solubility data were interpreted to give solubility products of several hydrated LiBr salts using the formulation of Helgeson, which accounts for the activity of water. The crystallization temperature was measured by monitoring to +/-0.01 degrees C the temperature of solutions inside test tubes placed in a cooling bath programmed at a cooling rate of 20 degrees C/h. A release of the heat of crystallization identifies the temperature of crystallization. The equilibrium solubility was verified by crystallization with seed crystals present. The crystallization temperature without seeds present was 10 to 20 degrees C less than the equilibrium solubility temperature corresponding to the Ostwald-Meyers metastable region. This crystallization temperature measured at 20 degrees C/h was shown to correspond to nucleation on the surface of the test tube with an interface energy of 40+/-1.2 erg/cm(2). Homogeneous nucleation from solution data shows the crystallization temperature to be from 40 to 50 degrees C below the equilibrium solubility curve and to be accurately predicted by homogeneous nucleation with an interface energy of 26 erg/cm(2), the literature value of the ice/water interface. Since the hydrated LiBr salts have surfaces that expose structured water molecules to the solution, this value is believed to be an appropriate value of the interface energy of the hydrated LiBr crystals. Crystallization temperature measurements were performed at different cooling rates, showing that slower cooling rates gave a narrower Ostwald-Myers metastable zone as is expected. Induction time measurements showed that the time to spontaneous crystallization increases as the supersaturation

  20. Synthesis of transition metal nitride by nitridation of metastable oxide precursor

    SciTech Connect

    Wang, Huamin; Wu, Zijie; Kong, Jing; Wang, Zhiqiang; Zhang, Minghui

    2012-10-15

    Metastable transition metal oxides were used as precursors to synthesize transition metal nitrides at low temperature. Amorphous MoO{sub 2} was prepared by reduction of (NH{sub 4}){sub 6}Mo{sub 7}O{sub 24} solution with hydrazine. As-synthesized amorphous MoO{sub 2} was transformed into fcc {gamma}-Mo{sub 2}N at 400 Degree-Sign C and then into hexagonal {delta}-MoN by further increasing the temperature to 600 Degree-Sign C under a NH{sub 3} flow. The nitridation temperature employed here is much lower than that employed in nitridation of crystalline materials, and the amorphous materials underwent a unique nitridation process. Besides this, the bimetallic nitride Ni{sub 2}Mo{sub 3}N was also synthesized by nitridating amorphous bimetallic precursor. These results suggested that the nitridation of amorphous precursor possessed potential to be a general method for synthesizing many interstitial metallic compounds, such as nitrides and carbides at low temperature. - graphical abstract: Amorphous oxide was used as new precursor to prepare nitride at low temperature. Pure {gamma}-Mo{sub 2}N and {delta}-MoN were obtained at 400 Degree-Sign C and at 600 Degree-Sign C, respectively. Highlights: Black-Right-Pointing-Pointer We bring out a new method to synthesize transition metal nitrides at low temperature. Black-Right-Pointing-Pointer Both mono- and bimetallic molybdenum nitrides were synthesized at a mild condition. Black-Right-Pointing-Pointer The formation of two different molybdenum nitrides {gamma}-Mo{sub 2}N and {delta}-MoN can be controlled from the same metastable precursor. Black-Right-Pointing-Pointer The nitridation temperature was much lower than that reported from crystalline precursors. Black-Right-Pointing-Pointer The metastable precursor had different reaction process in comparison with crystalline precursor.

  1. The stereodynamics of the Penning ionization of water by metastable neon atoms

    NASA Astrophysics Data System (ADS)

    Brunetti, Brunetto Giovanni; Candori, Pietro; Falcinelli, Stefano; Pirani, Fernando; Vecchiocattivi, Franco

    2013-10-01

    The stereodynamics of the Penning ionization of water molecules by collision with metastable neon atoms, occurring in the thermal energy range, is of great relevance for the understanding of fundamental aspects of the physical chemistry of water. This process has been studied by analyzing the energy spectrum of the emitted electrons previously obtained in our laboratory in a crossed beam experiment [B. G. Brunetti, P. Candori, D. Cappelletti, S. Falcinelli, F. Pirani, D. Stranges, and F. Vecchiocattivi, Chem. Phys. Lett. 539-540, 19 (2012)]. For the spectrum analysis, a novel semiclassical method is proposed, that assumes ionization events as mostly occurring in the vicinities of the collision turning points. The potential energy driving the system in the relevant configurations of the entrance and exit channels, used in the spectrum simulation, has been formulated by the use of a semiempirical method. The analysis puts clearly in evidence how different approaches of the metastable atom to the water molecule lead to ions in different electronic states. In particular, it provides the angular acceptance cones where the selectivity of the process leading to the specific formation of each one of the two energetically possible ionic product states of H2O+ emerges. It is shown how the ground state ion is formed when neon metastable atoms approach water mainly perpendicularly to the molecular plane, while the first excited electronic state is formed when the approach occurs preferentially along the C2v axis, on the oxygen side. An explanation is proposed for the observed vibrational excitation of the product ions.

  2. Plasma-enhanced chemical vapor deposition of β-tungsten, a metastable phase

    NASA Astrophysics Data System (ADS)

    Tang, C. C.; Hess, D. W.

    1984-09-01

    Plasma-enhanced chemical vapor deposition of a metastable phase of tungsten ( β-W) is performed using tungsten hexafluoride and hydrogen as source gases. At 350 °C, the as-deposited resistivity of these films is ˜50 μΩ cm. After heat treatments between 650 and 750 °C in forming gas, the resistivity drops below 11 μΩ cm. Concomitant with this resistivity change is a phase change to α-W, the equilibrium, body-centered-cubic form.

  3. An occurrence of metastable cristobalite in high-pressure garnet Granulite

    USGS Publications Warehouse

    Darling, R.S.; Chou, I.-Ming; Bodnar, R.J.

    1997-01-01

    High-pressure (0.8 gigapascals) granulite facies garnet from Gore Mountain, New York, hosts multiple solid inclusions containing the low- pressure silica polymorph cristobalite along with albite and minor ilmenite. Identification of cristobalite is based on Raman spectra, electron microprobe analysis, and microthermometric measurements on the ??/?? phase transformation. The cristobalite plus albite inclusions may have originated as small, trapped samples of hydrous sodium-aluminum-siliceous melt. Diffusive loss of water from these inclusions under isothermal, isochoric conditions may have resulted in a large enough internal pressure decrease to promote the metastable crystallization of cristobalite.

  4. Models with quartic potential of dynamical SUSY breaking in meta-stable vacua

    NASA Astrophysics Data System (ADS)

    Hirano, Shinji

    2007-05-01

    We search for models of dynamical SUSY breaking in meta-stable vacua which might have dual string descriptions with a few brane probes. Two models with quartic superpotential are proposed: One of them might be closely related to the dual gauge theory to the flavored Maldacena-Nuñez geometry by Casero, Nuñez, and Paredes with a few additional brane probes corresponding to massive flavors. The other model might be dual to the Klebanov-Strassler geometry with one fractional D3-brane and a few D7-branes as probes.

  5. Where Does the Electron Go? Stable and Metastable Peptide Cation Radicals Formed by Electron Transfer

    NASA Astrophysics Data System (ADS)

    Pepin, Robert; Layton, Erik D.; Liu, Yang; Afonso, Carlos; Tureček, František

    2017-01-01

    Electron transfer to doubly and triply charged heptapeptide ions containing polar residues Arg, Lys, and Asp in combination with nonpolar Gly, Ala, and Pro or Leu generates stable and metastable charge-reduced ions, (M + 2H)+●, in addition to standard electron-transfer dissociation (ETD) fragment ions. The metastable (M + 2H)+● ions spontaneously dissociate upon resonant ejection from the linear ion trap, giving irregularly shaped peaks with offset m/ z values. The fractions of stable and metastable (M + 2H)+● ions and their mass shifts depend on the presence of Pro-4 and Leu-4 residues in the peptides, with the Pro-4 sequences giving larger fractions of the stable ions while showing smaller mass shifts for the metastables. Conversion of the Asp and C-terminal carboxyl groups to methyl esters further lowers the charge-reduced ion stability. Collisional activation and photodissociation at 355 nm of mass-selected (M + 2H)+● results in different dissociations that give sequence specific MS3 spectra. With a single exception of charge-reduced (LKGLADR + 2H)+●, the MS3 spectra do not produce ETD sequence fragments of the c and z type. Hence, these (M + 2H)+● ions are covalent radicals, not ion-molecule complexes, undergoing dramatically different dissociations in the ground and excited electronic states. The increased stability of the Pro-4 containing (M + 2H)+● ions is attributed to radicals formed by opening of the Pro ring and undergoing further stabilization by hydrogen atom migrations. UV-VIS photodissociation action spectroscopy and time-dependent density functional theory calculations are used in a case in point study of the stable (LKGPADR + 2H)+● ion produced by ETD. In contrast to singly-reduced peptide ions, doubly reduced (M + 3H)+ ions are stable only when formed from the Pro-4 precursors and show all characteristics of even electron ions regarding no photon absorption at 355 nm or ion-molecule reactions, and exhibiting proton driven

  6. Formation and stability of metastable skyrmionic spin structures with various topologies in an ultrathin film

    NASA Astrophysics Data System (ADS)

    Rózsa, Levente; Palotás, Krisztián; Deák, András; Simon, Eszter; Yanes, Rocio; Udvardi, László; Szunyogh, László; Nowak, Ulrich

    2017-03-01

    We observe metastable localized spin configurations with topological charges ranging from Q =-3 to Q =2 in a (Pt0.95Ir0.05 )/Fe bilayer on a Pd (111 ) surface by performing spin dynamics simulations, using a classical Hamiltonian parametrized by ab initio calculations. We demonstrate that the frustration of the isotropic exchange interactions is responsible for the creation of these various types of skyrmionic structures. The Dzyaloshinsky-Moriya interaction present due to the breaking of inversion symmetry at the surface energetically favors skyrmions with Q =-1 , distorts the shape of the other objects, and defines a preferred orientation for them with respect to the underlying lattice.

  7. Metastable Tetragonal CdWO4 Nanoparticles Synthesized with a Solvothermal Method

    SciTech Connect

    Rondinone, Adam Justin; Travaglini, Dustin H; Pawel, Michelle D; Mahurin, Shannon Mark; Dai, Sheng

    2007-01-01

    CdWO{sub 4} has only previously been reported in the monoclinic, or wolframite, phase. Here we report the first metastable, tetragonal or scheelite, CdWO4 nanopowder. The tetragonal CdWO{sub 4} was synthesized by a propylene glycol solvothermal method. The scheelite phase is stabilized by a combination of high surface area and surface complexation by the propylene glycol. The CdWO{sub 4} is stable at 1 bar to 300 C, and converts back to the monoclinic wolframite phase between 300 and 500 C. The nanopowder exhibits cubic morphology and the average particle size of the nanopowder is around 50 nm.

  8. First principles prediction of the metastability of the Ge2Mn phase and its synthesis pathways

    NASA Astrophysics Data System (ADS)

    Arras, E.; Slipukhina, I.; Torrent, M.; Caliste, D.; Deutsch, T.; Pochet, P.

    2010-06-01

    In this letter, we performed first principles calculations to investigate the stability of a [100]-compatible Ge2Mn compound. Based on a thermodynamical approach, we propose and assess the C16 structure (Al2Cu prototype) to be only slightly metastable as compared to the other Ge-Mn compounds. The reported structural and magnetic properties of this Ge2Mn compound make it a potentially interesting compound for spintronic applications, all the more since a simple way to stabilize it as a bulk film is proposed.

  9. Growth, characterization, and properties of metastable and modulated semiconductor structures - Prospects for future studies

    NASA Technical Reports Server (NTRS)

    Grunthaner, F. J.; Madhukar, A.

    1983-01-01

    The general field of preparation and study of metastable and modulated semiconductor structures has progressed rapidly in recent years. This short overview offers an assessment of the progress and current understanding in the areas of fabrication, characterization, and utilization of these new material systems. The discussion includes the more prominent growth techniques, theoretical and experimental analysis of growth kinetics, and an overview of structural, chemical, electronic, and optical characterization. The probable application of these structures for the technological development of new device structures and concepts is considered. The discussion particularly emphasizes the prospects for future studies in view of the specific current understanding.

  10. Stable 811.53 nm diode laser pump source for optically pumped metastable Ar laser

    NASA Astrophysics Data System (ADS)

    Gao, Jun; Zuo, Duluo; Zhao, Jun; Li, Bin; Yu, Anlan; Wang, Xinbing

    2016-10-01

    A stable external cavity diode laser coupled with volume Bragg grating for metastable argon atoms pumping is presented. The measured maximum output power of the continuous wave is 6.5 W when the spectral width (FWHM) is less than 21 pm around 811.53 nm and the power efficiency is 68%. The tuning range of the emission wavelength is bigger than 270 pm. The calculated deviation in relative absorption efficiency caused by the fluctuations of wavelength and power is less than 4%.

  11. How to reveal metastable skyrmionic spin structures by spin-polarized scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Dupé, B.; Kruse, C. N.; Dornheim, T.; Heinze, S.

    2016-05-01

    We predict the occurrence of metastable skyrmionic spin structures such as antiskyrmions and higher-order skyrmions in ultra-thin transition-metal films at surfaces using Monte Carlo simulations based on a spin Hamiltonian parametrized from density functional theory calculations. We show that such spin structures will appear with a similar contrast in spin-polarized scanning tunneling microscopy images. Both skyrmions and antiskyrmions display a circular shape for out-of-plane magnetized tips and a two-lobe butterfly contrast for in-plane tips. An unambiguous distinction can be achieved by rotating the tip magnetization direction without requiring the information of all components of the magnetization.

  12. Operation of Mammoth Pacific`s MP1-100 turbine with metastable, supersaturated expansions

    SciTech Connect

    Mines, G.L.

    1996-01-01

    INEL`s Heat Cycle Research project continues to develop a technology base for increasing use of moderate-temperature hydrothermal resources to generate electrical power. One concept is the use of metastable, supersaturated turbine expansions. These expansions support a supersaturated working fluid vapor; at equilibrium conditions, liquid condensate would be present during the turbine expansion process. Studies suggest that if these expansions do not adversely affect the turbine performance, up to 8-10% more power could be produced from a given geothermal fluid. Determining the impact of these expansions on turbine performance is the focus of the project investigations being reported.

  13. Pair-correlation function of a metastable helium Bose-Einstein condensate

    SciTech Connect

    Zin, Pawel; Trippenbach, Marek; Gajda, Mariusz

    2004-02-01

    The pair-correlation function is one of the basic quantities to characterize the coherence properties of a Bose-Einstein condensate. We calculate this function in the experimentally important case of a zero temperature Bose-Einstein condensate in a metastable triplet helium state using the variational method with a pair-excitation ansatz. We compare our result with a pair-correlation function obtained for the hard-sphere potential with the same scattering length. Both functions are practically indistinguishable for distances greater than the scattering length. At smaller distances, due to interatomic interactions, the helium condensate shows strong correlations.

  14. Admittance Spectroscopy in CZTSSe: Metastability Behavior and Voltage Dependent Defect Study

    SciTech Connect

    Koeper, Mark J.; Hages, Charles J.; Li, Jian V.; Levi, Dean; Agrawal, Rakesh

    2016-11-21

    Admittance spectroscopy has been performed on a CZTSSe device with a carrier injection pretreatment and under electronically relaxed conditions to demonstrate metastability behavior. We show that the measurements with the carrier injection pretreatment demonstrate two admittance signatures while the relaxed measurement demonstrates only one admittance signature with a different activation energy. Additionally, voltage dependent admittance spectroscopy was performed using the carrier injection pretreatment method at each of the applied voltage bias. The activation energies of the two admittance signatures were calculated and are shown to be independent of the voltage bias.

  15. Optical phase information writing and storage in populations of metastable quantum states

    SciTech Connect

    Djotyan, G. P.; Sandor, N.; Bakos, J. S.; Soerlei, Zs.

    2009-10-15

    We propose a scheme for robust writing and storage of optical phase information in populations of metastable states of the atoms with a tripod structure of levels by using frequency-chirped laser pulses. The method provides much longer storage times compared with the schemes based on the collective atomic spin coherences. A negligible excitation of the atom provides immunity to decoherence induced by decay of the excited states. The method is robust against small-to-medium variations in the laser pulse intensity and speed of the chirp and, being insensitive to resonance conditions, it is effective both in homogeneously and inhomogeneously broadened media.

  16. Investigation of Strain-Induced Martensitic Transformation in Metastable Austenite using Nanoindentation

    SciTech Connect

    Ahn, T.-H.; Oh, C.-S.; Kim, D. H.; Oh, K. H.; Bei, Hongbin; George, Easo P; Han, H. N.

    2010-01-01

    Strain-induced martensitic transformation of metastable austenite was investigated by nanoindentation of individual austenite grains in multi-phase steel. A cross-section prepared through one of these indented regions using focused ion beam milling was examined by transmission electron microscopy. The presence of martensite underneath the indent indicates that the pop-ins observed on the load-displacement curve during nanoindentation correspond to the onset of strain-induced martensitic transformation. The pop-ins can be understood as resulting from the selection of a favorable martensite variant during nanoindentation.

  17. Microstructural evolution of metastable austenitic steel during high-pressure torsion and subsequent heat treatment

    NASA Astrophysics Data System (ADS)

    Chen, S.; Shibata, A.; Zhao, L. J.; Gao, S.; Tian, Y. Z.; Tsuji, N.

    2014-08-01

    Metastable austenite in a Fe-24Ni-0.3C (wt.%) alloy was processed by high-pressure torsion and subsequently heat-treated. The HPT-processed material had lamellae structures composed of highly deformed austenite and deformation-induced martensite. The reverse transformation of the deformation-induced martensite and recovery/recrystallization of the retained austenite completed above 500 °C and resulted in fully annealed and single-phase austenite with different grain sizes. The ultrafine-grained and nanocrystalline austenite showed high yield strength and large ductility due to transformation-induced plasticity.

  18. Miniature triaxial metastable ionization detector for gas chromatographic trace analysis of extraterrestrial volatiles

    NASA Technical Reports Server (NTRS)

    Woeller, F. H.; Kojiro, D. R.; Carle, G. C.

    1984-01-01

    The present investigation is concerned with a miniature metastable ionization detector featuring an unconventional electrode configuration, whose performance characteristics parallel those of traditional design. The ionization detector is to be incorporated in a flight gas chromatograph (GC) for use in the Space Shuttle. The design of the detector is discussed, taking into account studies which verified the sensitivity of the detector. The triaxial design of the detector is compared with a flat-plate style. The obtained results show that the principal goal of developing a miniature, highly sensitive ionization detector for flight applications was achieved. Improved fabrication techniques will utilize glass-to-metal seals and brazing procedures.

  19. Huge metastability in high-Tc superconductors induced by parallel magnetic field

    NASA Astrophysics Data System (ADS)

    Dias, R. G.; Silva, J. A.

    2003-03-01

    We present a study of the temperature-magnetic-field phase diagram of homogeneous and inhomogeneous superconductivity in the case of a quasi-two-dimensional superconductor with an extended saddle point in the energy dispersion under a parallel magnetic field. At low temperature, a huge metastability region appears, limited above by a steep superheating critical field Hsh and below by a strongly reentrant supercooling field Hsc. We show that the Pauli limit Hp for the upper critical magnetic field is strongly enhanced due to the presence of the Van Hove singularity in the density of states. The formation of a nonuniform superconducting state is predicted to be very unlikely.

  20. Metastable helium Bose-Einstein condensate with a large number of atoms

    SciTech Connect

    Tychkov, A. S.; Jeltes, T.; McNamara, J. M.; Tol, P. J. J.; Herschbach, N.; Hogervorst, W.; Vassen, W.

    2006-03-15

    We have produced a Bose-Einstein condensate of metastable helium ({sup 4}He*) containing over 1.5x10{sup 7} atoms, which is a factor of 25 higher than previously achieved. The improved starting conditions for evaporative cooling are obtained by applying one-dimensional Doppler cooling inside a magnetic trap. The same technique is successfully used to cool the spin-polarized fermionic isotope ({sup 3}He*), for which thermalizing collisions are highly suppressed. Our detection techniques include absorption imaging, time-of-flight measurements on a microchannel plate detector, and ion counting to monitor the formation and decay of the condensate.

  1. Metastability of the Nonlinear Wave Equation: Insights from Transition State Theory

    NASA Astrophysics Data System (ADS)

    Newhall, Katherine A.; Vanden-Eijnden, Eric

    2017-01-01

    This paper is concerned with the longtime dynamics of the nonlinear wave equation in one-space dimension, u_{tt} - κ^2 u_{xx} +V'(u) =0 quad xin [0,1] where κ >0 is a parameter and V(u) is a potential bounded from below and growing at least like u^2 as |u|→ ∞. Infinite energy solutions of this equation preserve a natural Gibbsian invariant measure, and when the potential is double-welled, for example when V(u) = 1/4 (1-u^2)^2 , there is a regime such that two small disjoint sets in the system's phase-space concentrate most of the mass of this measure. This suggests that the solutions to the nonlinear wave equation can be metastable over these sets, in the sense that they spend long periods of time in these sets and only rarely transition between them. Here, we quantify this phenomenon by calculating exactly via transition state theory (TST) the mean frequency at which the solutions of the nonlinear wave equation with initial conditions drawn from its invariant measure cross a dividing surface lying in between the metastable sets. We also investigate numerically how the mean TST frequency compares to the rate at which a typical solution crosses this dividing surface. These numerical results suggest that the dynamics of the nonlinear wave equation is ergodic and rapidly mixing with respect to the Gibbs invariant measure when the parameter κ in small enough. In this case, successive transitions between the two regions are roughly uncorrelated and their dynamics can be coarse-grained to jumps in a two-state Markov chain whose rate can be deduced from the mean TST frequency. This is a regime in which the dynamics of the nonlinear wave equation displays a metastable behavior that is not fundamentally different from that observed in its stochastic counterpart in which random noise and damping terms are added to the equation. For larger κ, however, the dynamics either stops being ergodic, or its mixing time becomes larger than the inverse of the TST frequency

  2. Generalization of low pressure, gas-liquid, metastable sound speed to high pressures

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

    A theory is developed for isentropic metastable sound propagation in high pressure gas-liquid mixtures. Without simplification, it also correctly predicts the minimum speed for low pressure air-water measurements where other authors are forced to postulate isothermal propagation. This is accomplished by a mixture heat capacity ratio which automatically adjusts from its single phase values to approximately the isothermal value of unity needed for the minimum speed. Computations are made for the pure components parahydrogen and nitrogen, with emphasis on the latter. With simplifying assumptions, the theory reduces to a well known approximate formula limited to low pressure.

  3. Equilibrium conditions and the region of metastable states of Freon-12 gas hydrate

    NASA Astrophysics Data System (ADS)

    Zavodovsky, A. G.; Madygulov, M. Sh.; Reshetnikov, A. M.

    2015-12-01

    The results from DTA experiments to determine the thermodynamic parameters of equilibrium of Freon-12 gas hydrate with water (super cooled water), gas, and ice are analyzed. Empirical relations are obtained for determining the positions of the boundaries in the region of metastable states of Freon-12 gas hydrate in the P-T phase diagram. The enthalpies of dissociation of gas hydrate to water and ice are calculated. The size of pores in Freon-12 hydrate formed from granules of ground ice is estimated from the magnitude of the shift in the quadrupole point at temperatures below 273 K.

  4. Enol tautomers of Watson-Crick base pair models are metastable because of nuclear quantum effects.

    PubMed

    Pérez, Alejandro; Tuckerman, Mark E; Hjalmarson, Harold P; von Lilienfeld, O Anatole

    2010-08-25

    Intermolecular enol tautomers of Watson-Crick base pairs could emerge spontaneously via interbase double proton transfer. It has been hypothesized that their formation could be facilitated by thermal fluctuations and proton tunneling, and possibly be relevant to DNA damage. Theoretical and computational studies, assuming classical nuclei, have confirmed the dynamic stability of these rare tautomers. However, by accounting for nuclear quantum effects explicitly through Car-Parrinello path integral molecular dynamics calculations, we find the tautomeric enol form to be dynamically metastable, with lifetimes too insignificant to be implicated in DNA damage.

  5. Titanium α-ω phase transformation pathway and a predicted metastable structure

    SciTech Connect

    Zarkevich, Nickolai A.; Johnson, Duane D.

    2016-01-15

    A titanium is a highly utilized metal for structural lightweighting and its phases, transformation pathways (transition states), and structures have scientific and industrial importance. Using a proper solid-state nudged elastic band method employing two climbing images combined with density functional theory DFT + U methods for accurate energetics, we detail the pressure-induced α (ductile) to ω (brittle) transformation at the coexistence pressure. We also find two transition states along the minimal-enthalpy path and discover a metastable body-centered orthorhombic structure, with stable phonons, a lower density than the end-point phases, and decreasing stability with increasing pressure.

  6. The excitation and collisional deactivation of metastable N/2P/ atoms in auroras

    NASA Technical Reports Server (NTRS)

    Zipf, E. C.; Espy, P. J.; Boyle, C. F.

    1980-01-01

    The concentration and altitude distribution of metastable N(2P) atoms was measured in a diffuse IBC II(+) auroral arc. The dominant N(2P) source is shown to be the dissociative excitation of N2 by electron impact with a minor contribution from the dissociative recombination of N2(+) ions. The possibility that an ion-molecule process involving atomic oxygen and vibrationally excited N2(+) ions is a significant N(2P) source is examined. Values for the proportional yield of N(+), N(2P), N(2D), and N(4S) atoms from electron-impact dissociation of N2 under optically thick conditions are given.

  7. Electromechanical actuation and current-induced metastable states in suspended single-crystalline VO2 nanoplatelets

    SciTech Connect

    Tselev, Alexander; Budai, John D; Strelcov, Evgheni; Tischler, Jonathan Zachary; Kolmakov, Andrei; Kalinin, Sergei V

    2011-01-01

    Current-induced electromechanical actuation enabled by the metal-insulator transition in VO{sub 2} nanoplatelets is demonstrated. The Joule heating by a sufficient current flowing through suspended nanoplatelets results in formation of heterophase domain patterns and is accompanied by nanoplatelet deformation. The actuation action can be achieved in a wide temperature range below the bulk phase transition temperature (68 C). The observed current-sustained heterophase domain structures should be interpreted as distinct metastable states in free-standing and end-clamped VO{sub 2} samples. We analyze the main prerequisites for the realization of a current-controlled actuator based on the proposed concept.

  8. Counting metastable states within the adsorption/desorption hysteresis loop: A molecular simulation study of confinement in heterogeneous pores.

    PubMed

    Puibasset, Joël

    2010-09-14

    A molecular simulation approach has been used to model simple fluid adsorption in heterogeneous tubular pores mimicking mesoporous materials such as MCM-41 or porous silicon, allowing to determine the amount adsorbed ρ as a function of the chemical potential μ. A hysteresis loop is observed in adsorption/desorption cycles, which is closely connected to the appearance of many metastable states. The density of these metastable states is studied in the μ-ρ plane. Experimentally, the accessible metastable states are those that can be attained by the μ-path, i.e., a series of increasing or decreasing μ steps. One could also imagine using a quench from high temperature. Although the total density of metastable states is not directly accessible to experiments, it is of primary theoretical importance to understand the structure of metastable states in the hysteresis as determined experimentally. The disorder associated with the porous material realizations is accurately taken into account, and a systematic system size analysis is also performed in order to study the thermodynamic limit. It is shown that the quenched complexity is the relevant quantity to understand the hysteresis structure in the thermodynamic limit. It clearly exhibits a distinctive behavior depending on the distribution of heterogeneities characterizing the disorder in the pore. Some analogies can be found with the situation where an out-of-equilibrium transition appears, but careful examination of the data suggests another interpretation.

  9. Tricationic metastability by symmetry restrictions: B2 n+, n = 3,4

    NASA Astrophysics Data System (ADS)

    Hogreve, H.

    2017-01-01

    To explain the experimentally observed metastability of the trication B2 3+, we study this system by various ab-initio methods. Whereas the electronic ground state X2Σu + of B2 3+ turns out to be unstable, the potential energy curves of the lowest excited state 12Πu and of the quartet state 14Σg - form barriers that support quasi-bound vibronic states. The lifetimes of these states are not only determined by the respective (dissociative) tunnelling rates, but also by possible radiative electronic transitions and predissociation via spin-orbit coupling, where the latter furnish the decisive decay mechanism for the low-lying vibronic levels. In case of the quadruply charged system B2 4+, our computations do not predict any metastable states in the low-lying electronic spectrum. The deviation from a purely Coulombic repulsive behaviour in B2 4+ is quantified by fitting the potential energy curves to a modified Murrell-Sorbie function.

  10. Characterization of Tyrosine Nitration and Cysteine Nitrosylation Modifications by Metastable Atom-Activation Dissociation Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Cook, Shannon L.; Jackson, Glen P.

    2011-02-01

    The fragmentation behavior of nitrated and S-nitrosylated peptides were studied using collision induced dissociation (CID) and metastable atom-activated dissociation mass spectrometry (MAD-MS). Various charge states, such as 1+, 2+, 3+, 2-, of modified and unmodified peptides were exposed to a beam of high kinetic energy helium (He) metastable atoms resulting in extensive backbone fragmentation with significant retention of the post-translation modifications (PTMs). Whereas the high electron affinity of the nitrotyrosine moiety quenches radical chemistry and fragmentation in electron capture dissociation (ECD) and electron transfer dissociation (ETD), MAD does produce numerous backbone cleavages in the vicinity of the modification. Fragment ions of nitrosylated cysteine modifications typically exhibit more abundant neutral losses than nitrated tyrosine modifications because of the extremely labile nature of the nitrosylated cysteine residues. However, compared with CID, MAD produced between 66% and 86% more fragment ions, which preserved the labile -NO modification. MAD was also able to differentiate I/L residues in the modified peptides. MAD is able to induce radical ion chemistry even in the presence of strong radical traps and therefore offers unique advantages to ECD, ETD, and CID for determination of PTMs such as nitrated and S-nitrosylated peptides.

  11. Geochemistry of metastable carbonate minerals from the Brush Creek marine interval (Missourian), Indiana County, Pennsylvania

    SciTech Connect

    Cercone, K.R.; Kime, A.; Mutchler, S.; Rittle, K. )

    1991-08-01

    Many marine fossils from the Missourian Brush Creek interval of western Pennsylvania display partial preservation of metastable aragonite and high-magnesium calcite shell material. Bivalve mollusks have been shown by x-ray diffraction to contain as much as 96% aragonite, with lesser amounts of both high-magnesium and low-magnesium calcite. Stable carbon and oxygen isotopic ratios from these bivalves suggest they precipitated in equilibrium with Pennsylvanian ocean water. The bellerophontid Pharkidonotus, which exhibits partial recrystallization textures under scanning electron microscopy, consists of 45% aragonite and 55% low-magnesium calcite, and has slightly more depleted isotopic values than bivalves. Crinoids also appear to have been partially recrystallized, resulting in a mixture of primary high-magnesium calcite and secondary low-magnesium calcite and microdolomite, with much of the original shell structure still preserved. The degree of preservation of metastable carbonate minerals varies both stratigraphically and spatially within the Brush Creek interval. Maximum preservation occurs in organic-rich shales deposited in low-lying areas of the Brush Creek sea floor. The preservation of aragonite and high-magnesium calcite in such units may have resulted from a lack of circulating porewater during early diagenesis.

  12. Discovery of a 210 -fiber texture in medical-grade metastable beta titanium wire

    SciTech Connect

    Cai, Song; Schaffer, Jeremy E.; Ren, Yang; Daymond, Mark R.

    2015-04-01

    The texture and phase evolution of metastable beta-III Ti alloy wires, produced in a medical-grade wire-processing facility, are examined via synchrotron X-ray diffraction. The texture development in the beta-phase was interpreted by a simple viscoplastic self-consistent (VPSC) modeling approach. Both the stress-induced martensite and stress-induced omega phase transformations are observed during the early stage of cold deformation. The < 1 1 0 >(beta) texture is gradually replaced by the < 2 1 0 >(beta) texture at cold work levels above 50% total area reduction or equivalently 0.70 axial true strain. Formation of the < 2 1 0 >(beta)-fiber from the combined activity of {1 1 2} and {3 3 2} twinning plus conventional slip is observed and may not directly depend upon the stress-induced phase per se. According to the VPSC model, similar texture should occur in other metastable beta-Ti alloys subjected to similar wire processing. These data should help inform process-structure-function towards better wire design in titanium-based medical devices. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

  13. The metastable chemical gallery of the oxide of epitaxial graphene at room temperature

    NASA Astrophysics Data System (ADS)

    Kim, Suenne; Zhou, Si; Hu, Yike; Berger, Claire; de Heer, Walt; Bongiorno, Angelo; Riedo, Elisa

    2013-03-01

    Insights in the chemistry of graphene oxide and its response to external stimuli are crucial to control its electronic and optical properties, thus enabling future applications of this material. Here, we present a combined experimental and density functional theory study concerning the compositional and structural properties of the oxide of epitaxial graphene (OeG) as a function of time and temperature. Our result indicates that OeG synthesized by oxidizing epitaxial graphene grown on SiC via the Hummers method is a metastable material whose structure and chemistry evolve with a notable degree at room temperature. XPS studies reveal, metastable OeG reaches a nearly stable reduced O/C ratio of 0.37 with a featured relaxation time of a month. Initially the most enriched epoxide groups decrease with time while hydroxyl groups increase. In addition to this, further XPS study of OeG as a function of temperature shows heating above 120 C in air can abruptly deteriorate the OeG structure. Our calculations show that the availability of hydrogen atoms could be the key factor in tuning structural and chemical properties at relatively low temperatures. National Science Foundation (CMMI-1100290/DMR-0820382)

  14. Supramolecular stabilization of metastable tautomers in solution and the solid state.

    PubMed

    Juribašić, Marina; Bregović, Nikola; Stilinović, Vladimir; Tomišić, Vladislav; Cindrić, Marina; Sket, Primož; Plavec, Janez; Rubčić, Mirta; Užarević, Krunoslav

    2014-12-22

    This work presents a successful application of a recently reported supramolecular strategy for stabilization of metastable tautomers in cocrystals to monocomponent, non-heterocyclic, tautomeric solids. Quantum-chemical computations and solution studies show that the investigated Schiff base molecule, derived from 3-methoxysalicylaldehyde and 2-amino-3-hydroxypyridine (ap), is far more stable as the enol tautomer. In the solid state, however, in all three obtained polymorphic forms it exists solely as the keto tautomer, in each case stabilized by an unexpected hydrogen-bonding pattern. Computations have shown that hydrogen bonding of the investigated Schiff base with suitable molecules shifts the tautomeric equilibrium to the less stable keto form. The extremes to which supramolecular stabilization can lead are demonstrated by the two polymorphs of molecular complexes of the Schiff base with ap. The molecules of both constituents of molecular complexes are present as metastable tautomers (keto anion and protonated pyridine, respectively), which stabilize each other through a very strong hydrogen bond. All the obtained solid forms proved stable in various solid-state and solvent-mediated methods used to establish their relative thermodynamic stabilities and possible interconversion conditions.

  15. The metastable state of nucleocapsids of enveloped viruses as probed by high hydrostatic pressure.

    PubMed

    Gaspar, L P; Terezan, A F; Pinheiro, A S; Foguel, D; Rebello, M A; Silva, J L

    2001-03-09

    Enveloped viruses fuse their membranes with cellular membranes to transfer their genomes into cells at the beginning of infection. What is not clear, however, is the role of the envelope (lipid bilayer and glycoproteins) in the stability of the viral particle. To address this question, we compared the stability between enveloped and nucleocapsid particles of the alphavirus Mayaro using hydrostatic pressure and urea. The effects were monitored by intrinsic fluorescence, light scattering, and binding of fluorescent dyes, including bis(8-anilinonaphthalene-1-sulfonate) and ethidium bromide. Pressure caused a drastic dissociation of the nucleocapsids as determined by tryptophan fluorescence, light scattering, and gel filtration chromatography. Pressure-induced dissociation of the nucleocapsids was poorly reversible. In contrast, when the envelope was present, pressure effects were much less marked and were highly reversible. Binding of ethidium bromide occurred when nucleocapsids were dissociated under pressure, indicating exposure of the nucleic acid, whereas enveloped particles underwent no changes. Overall, our results demonstrate that removal of the envelope with the glycoproteins leads the particle to a metastable state and, during infection, may serve as the trigger for disassembly and delivery of the genome. The envelope acts as a "Trojan horse," gaining entry into the host cell to allow release of a metastable nucleocapsid prone to disassembly.

  16. Kinetic crystallization separation process of the inositol isomers by controlling metastable zones

    NASA Astrophysics Data System (ADS)

    Konuki, Kaname; Hirasawa, Izumi

    2013-06-01

    D-chiro-inositol (DCI) is prepared by the immobilized enzyme reaction which uses myo-inositol (MI) as the substrate and the conversion rate is about 13%. The aim of this study was to develop a separation method for high purity DCI crystals from a reaction solution including low purity DCI only by the crystallization process. We succeeded in separating DCI crystals of 96% purity by water cooling crystallization, but it was presumed that scale-up was difficult. Although we tried anti-solvent crystallization similar to water cooling crystallization, high purity DCI crystals were not obtained. Therefore, we proposed the crystallization separation process by controlling metastable zones. The purity of a desired compound is controlled by this process, because solid-liquid separation is achieved before crystallization of compound in metastable zone. By the crystallization using this method, the DCI crystals of 97% purity were obtained. Although the yield per batch is about 50%, the actual yield is improved as the last mother liquor returns into the process of the following batch. When this process was repeated, the purity and the yield of DCI were reproduced and the robustness of this process was proved. It is expected that scale-up of this process will be successful, and this purification method could be applicable to similar systems such as separation of isomers and analogs.

  17. On metastability and Markov state models for non-stationary molecular dynamics

    NASA Astrophysics Data System (ADS)

    Koltai, Péter; Ciccotti, Giovanni; Schütte, Christof

    2016-11-01

    Unlike for systems in equilibrium, a straightforward definition of a metastable set in the non-stationary, non-equilibrium case may only be given case-by-case—and therefore it is not directly useful any more, in particular in cases where the slowest relaxation time scales are comparable to the time scales at which the external field driving the system varies. We generalize the concept of metastability by relying on the theory of coherent sets. A pair of sets A and B is called coherent with respect to the time interval [t1, t2] if (a) most of the trajectories starting in A at t1 end up in B at t2 and (b) most of the trajectories arriving in B at t2 actually started from A at t1. Based on this definition, we can show how to compute coherent sets and then derive finite-time non-stationary Markov state models. We illustrate this concept and its main differences to equilibrium Markov state modeling on simple, one-dimensional examples.

  18. Quantitative Phase-Change Thermodynamics and Metastability of Perovskite-Phase Cesium Lead Iodide.

    PubMed

    Dastidar, Subham; Hawley, Christopher J; Dillon, Andrew D; Gutierrez-Perez, Alejandro D; Spanier, Jonathan E; Fafarman, Aaron T

    2017-03-16

    The perovskite phase of cesium lead iodide (α-CsPbI3 or "black" phase) possesses favorable optoelectronic properties for photovoltaic applications. However, the stable phase at room temperature is a nonfunctional "yellow" phase (δ-CsPbI3). Black-phase polycrystalline thin films are synthesized above 330 °C and rapidly quenched to room temperature, retaining their phase in a metastable state. Using differential scanning calorimetry, it is shown herein that the metastable state is maintained in the absence of moisture, up to a temperature of 100 °C, and a reversible phase-change enthalpy of 14.2 (±0.5) kJ/mol is observed. The presence of atmospheric moisture hastens the black-to-yellow conversion kinetics without significantly changing the enthalpy of the transition, indicating a catalytic effect, rather than a change in equilibrium due to water adduct formation. These results delineate the conditions for trapping the desired phase and highlight the significant magnitude of the entropic stabilization of this phase.

  19. Effect of Internal Hydrogen on Delayed Cracking of Metastable Low-Nickel Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Papula, Suvi; Talonen, Juho; Todoshchenko, Olga; Hänninen, Hannu

    2014-10-01

    Metastable austenitic stainless steels, especially manganese-alloyed low-nickel grades, may be susceptible to delayed cracking after forming processes. Even a few wppm of hydrogen present in austenitic stainless steels as an inevitable impurity is sufficient to cause cracking if high enough fraction of strain-induced α'-martensite and high residual tensile stresses are present. The role of internal hydrogen content in delayed cracking of several metastable austenitic stainless steels having different alloying chemistries was investigated by means of Swift cup tests, both in as-supplied state and after annealing at 673 K (400 °C). Hydrogen content of the test materials in each state was analyzed with three different methods: inert gas fusion, thermal analysis, and thermal desorption spectroscopy. Internal hydrogen content in as-supplied state was higher in the studied manganese-alloyed low-nickel grades, which contributed to susceptibility of unstable grades to delayed cracking. Annealing of the stainless steels reduced their hydrogen content by 1 to 3 wppm and markedly lowered the risk of delayed cracking. Limiting drawing ratio was improved from 1.4 to 1.7 in grade 204Cu, from 1.7 to 2.0 in grade 201 and from 1.8 to 2.12 in grade 301. The threshold levels of α'-martensite and residual stress for delayed cracking at different hydrogen contents were defined for the test materials.

  20. H elimination and metastable lifetimes in the UV photoexcitation of diacetylene

    PubMed Central

    Silva, R.; Gichuhi, W. K.; Huang, C.; Doyle, M. B.; Kislov, V. V.; Mebel, A. M.; Suits, A. G.

    2008-01-01

    We present an experimental investigation of the UV photochemistry of diacetylene under collisionless conditions. The H loss channel is studied using DC slice ion imaging with two-color reduced-Doppler detection at 243 nm and 212 nm. The photochemistry is further studied deep in the vacuum UV, that is, at Lyman-alpha (121.6 nm). Translational energy distributions for the H + C4H product arising from dissociation of C4H2 after excitation at 243, 212, and 121.6 nm show an isotropic angular distribution and characteristic translational energy profile suggesting statistical dissociation from the ground state or possibly from a low-lying triplet state. From these distributions, a two-photon dissociation process is inferred at 243 nm and 212 nm, whereas at 121.6 nm, a one-photon dissociation process prevails. The results are interpreted with the aid of ab initio calculations on the reaction pathways and statistical calculations of the dissociation rates and product branching. In a second series of experiments, nanosecond time-resolved phototionization measurements yield a direct determination of the lifetime of metastable triplet diacetylene under collisionless conditions, as well as its dependence on excitation energy. The observed submicrosecond lifetimes suggest that reactions of metastable diacetylene are likely to be less important in Titan's atmosphere than previously believed. PMID:18697925

  1. Magnetic properties of a metastable Sm-Fe phase synthesized by selectively thermalized sputtering

    NASA Astrophysics Data System (ADS)

    Cadieu, F. J.; Cheung, T. D.; Wickramasekara, L.; Aly, S. H.

    1984-03-01

    Samples of the Sm-Fe system have been directly crystallized onto heated substrates by selectively thermalized sputtering. Films of the pure Sm-Fe system exhibit only the 1-2, 1-3, and 2-17 phases which correspond to the bulk system. But samples synthesized with certain third element additions of oxygen and titanium exhibit a metastable phase at a composition corresponding to a 1-5 Sm-Fe compound. These samples exhibit well defined and reasonable sharp X-ray diffraction patterns. Room-temperature intrinsic coercive forces of 6.2 kOe and static energy products of 5.5 MG Oe have been observed. These results are for the demagnetizing field in the plane of the thin film samples and no demagnetizing factor has been used in obtaining the inplane B field. Samples synthesized in the presence of an inplane magnetic field at 600 C exhibit an inplane anisotropy which indicates the Curie point of this Ti-stabilized SmFe5 phase should be greater than 600 C. Film samples of the pure Sm-Fe system which do not show a metastable phase generally have low intrinsic coercive forces and consequently low energy products.

  2. Tuning the morphology of metastable MnS films by simple chemical bath deposition technique

    NASA Astrophysics Data System (ADS)

    Dhandayuthapani, T.; Girish, M.; Sivakumar, R.; Sanjeeviraja, C.; Gopalakrishnan, R.

    2015-10-01

    In the present investigation, we have prepared the spherical particles, almond-like, and cauliflower-like morphological structures of metastable MnS films on glass substrate by chemical bath deposition technique at low temperature without using any complexing or chelating agent. The morphological change of MnS films with molar ratio may be due to the oriented aggregation of adjacent particles. The compositional purity of deposited film was confirmed by the EDAX study. X-ray diffraction and micro-Raman studies confirm the sulfur source concentration induced enhancement in the crystallization of films with metastable MnS phase (zinc-blende β-MnS, and wurtzite γ-MnS). The shift in PL emission peak with molar ratio may be due to the change in optical energy band gap of the MnS, which was further confirmed by the optical absorbance study. The paramagnetic behavior of the sample was confirmed by the M-H plot.

  3. Decadal Variability in an OGCM Southern Ocean: intrinsic modes, forced modes and metastable states

    NASA Astrophysics Data System (ADS)

    O'Kane, Terence; Matear, Richard; Chamberlain, Matthew; Risbey, James; Horenko, Illia; Sloyan, Bernadette

    2014-05-01

    An Ocean General Circulation Model (OGCM) is used to identify a Southern Ocean southeast Pacific intrinsic mode of low frequency variability. Using CORE data a comprehensive suite of experiments were carried out to elucidate excitation and amplification responses of this intrinsic mode to low frequency forcing (ENSO, SAM) and stochastic forcing due to high frequency winds. Subsurface anomalies were found to teleconnect the Pacific and Atlantic regions of the Antarctic Circumpolar Current (ACC) thermocline. The Pacific region of the ACC is characterised by intrinsic baroclinic disturbances that respond to both SAM and ENSO, while the Atlantic sector of the ACC is sensitive to higher frequency winds that act to amplify thermocline anomalies propagating downstream from the Pacific. Non-stationary cluster analysis was used to identify the system's dynamical regimes and characterise meta-stability, persistence and transitions between the respective states. This analysis reveals significant trends, indicating fundamental changes to the meta-stability of the ocean dynamics in response to changes in atmospheric forcing. Intrinsic variability in sea-ice concentration was found to be coupled to thermocline processes. Sea-ice variability localised in the Atlantic was most closely associated with high frequency weather forcing. The SAM was associated with a circumpolar sea-ice response whereas ENSO was found to be a major driver of sea-ice variability only in the Pacific. This simulation study identifies plausible mechanisms that determine the predictability of the Southern Ocean climate on multi-decadal timescales.

  4. Metastable Polymeric Nitrogen: The Ultimate Green High-Energy-Density Material

    NASA Astrophysics Data System (ADS)

    Ciezak, Jennifer

    2007-06-01

    High-energy-high-density materials offering increased stability, vulnerability, and environmental safety are being aggressively pursued to meet the requirements of the DoD Joint Visions and Future Force. Nearly two decades ago, it was proposed that polymeric nitrogen would exceed all of these requirements and possess nearly five times the energy of any conventional energetic material in use today. The present study details an investigation into nitrogen polymerization using a novel high-pressure approach utilizing sodium azide as the starting material. Due to the weaker bonding structure of the anionic azide chains in comparison to a N-N triple bond, one expects that the azide chains will create single-covalently bonded polymeric networks more easily than diatomic nitrogen. A polymeric form of sodium azide was synthesized at high pressures, but the material was not metastable at ambient conditions, which precluded performance testing. Quantum chemical calculations have indicated stabilization of the polymeric structure at ambient conditions may be possible with the addition of hydrogen. Vibrational spectroscopic characterization suggests that a meta-stable polymeric form of nitrogen has been synthesized under high-pressure using sodium azide/hydrogen as the starting materials. This material remains stable at ambient conditions upwards of two weeks depending on the storage conditions.

  5. Low energy metastable states and immiscibility in (SiC)1-X-(AlN)X

    NASA Astrophysics Data System (ADS)

    Burton, Benjamin; van de Walle, Axel; Davydov, Albert; Vinograd, Victor

    2009-03-01

    A cluster expansion Hamiltonian was fit to VASP/PAW calculated supercell formation energies, δEf, and first principles based phase diagrams (miscibility gaps) were calculated for the wurtzite-structure pseudobinary system SiC1-XAlNX. An unusually wide range of 3 δEf 125 kJ/mole MX (M= Al, Si; X= N, C) was calculated and all supercells with δEf 8 kJ/mole exhibited characteristic (SiC)m(AlN)n crystallography, in which (SiC)m indicates m SiC-double layers to the hexagonal c-axis, and similarly for (AlN)n. The prediction of (SiC)m(AlN)n low-energy metastable states, may explain why one can synthesize SiC1-XAlNX films, or single crystals of arbitrary bulk composition, in spite of the very strong tendency toward immiscibility. Specifically, one expects that metastable films or single crystals will be dominated by a disordered stacking of SiC- and AlN-double layers.

  6. A Metastate HMM with Application to Gene Structure Identification in Eukaryotes

    NASA Astrophysics Data System (ADS)

    Winters-Hilt, Stephen; Baribault, Carl

    2010-12-01

    We introduce a generalized-clique hidden Markov model (HMM) and apply it to gene finding in eukaryotes ( C. elegans). We demonstrate a HMM structure identification platform that is novel and robustly-performing in a number of ways. The generalized clique HMM begins by enlarging the primitive hidden states associated with the individual base labels (as exon, intron, or junk) to substrings of primitive hidden states, or footprint states, having a minimal length greater than the footprint state length. The emissions are likewise expanded to higher order in the fundamental joint probability that is the basis of the generalized-clique, or "metastate", HMM. We then consider application to eukaryotic gene finding and show how such a metastate HMM improves the strength of coding/noncoding-transition contributions to gene-structure identification. We will describe situations where the coding/noncoding-transition modeling can effectively recapture the exon and intron heavy tail distribution modeling capability as well as manage the exon-start needle-in-the-haystack problem. In analysis of the C. elegans genome we show that the sensitivity and specificity (SN,SP) results for both the individual-state and full-exon predictions are greatly enhanced over the standard HMM when using the generalized-clique HMM.

  7. Dynamic and Structural Studies of Metastable Vortex Lattice Domains in MgB2

    NASA Astrophysics Data System (ADS)

    de Waard, E. R.; Kuhn, S. J.; Rastovski, C.; Eskildsen, M. R.; Leishman, A.; Dewhurst, C. D.; Debeer-Schmitt, L.; Littrell, K.; Karpinski, J.; Zhigadlo, N. D.

    Small-angle neutron scattering (SANS) studies of the vortex lattice (VL) in the type-II superconductor MgB2 have revealed an unprecedented degree of metastability that is demonstrably not due to vortex pinning, [C. Rastovski et al . , Phys. Rev. Lett. 111, 107002 (2013)]. The VL can be driven to the GS through successive application of an AC magnetic field. Here we report on detailed studies of the transition kinetics and structure of the VL domains. Stroboscopic studies of the transition revealed a stretched exponential decrease of the metastable volume fraction as a function of the number of applied AC cycles, with subtle differences depending on whether the AC field is oriented parallel or perpendicular to the DC field used to create the VL. We speculate the slower transition kinetics for the transverse AC field may be due to vortex cutting. Spatial studies include scanning SANS measurements showing the VL domain distribution within the MgB2 single crystal as well as measurements of VL correlation lengths. This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Award DE-FG02-10ER46783.

  8. Metastable flows in a two-lane traffic model equivalent to extended Burgers cellular automaton

    NASA Astrophysics Data System (ADS)

    Fukui, Minoru; Nishinari, Katsuhiro; Takahashi, Daisuke; Ishibashi, Yoshihiro

    2002-01-01

    A two-lane cellular automaton traffic model equivalent to the extended Burgers cellular automaton has been proposed, and evolution equations for cars on the two-lane road are obtained. Configurations of cars on the road are simulated by using the equations and many metastable local congested states are found in two-dimensional region on density-flow diagram. There are three typical states in the congested states: The first is that cars advance by stop- and go-flow on their own lanes without lane-change and values of the flow are stable in time. The second is that cars change the lane periodically with several time-steps. The third is that they advance changing the lane that induces fluctuating of the flow with extremely long period. This fluctuating flow exists in wide range between car densities {5}/{12} and {3}/{4}. The metastable states are discussed in connection with the synchronized states observed in the traffic flow on expressway.

  9. Metastable tantalum oxide formation during the devitrification of amorphous tantalum thin films

    DOE PAGES

    Donaldson, Olivia K.; Hattar, Khalid; Trelewicz, Jason R.

    2016-07-04

    Microstructural evolution during the devitrification of amorphous tantalum thin films synthesized via pulsed laser deposition was investigated using in situ transmission electron microscopy (TEM) combined with ex situ isothermal annealing, bright-field imaging, and electron-diffraction analysis. The phases formed during crystallization and their stability were characterized as a function of the chamber pressure during deposition, devitrification temperature, and annealing time. A range of metastable nanocrystalline tantalum oxides were identified following devitrification including multiple orthorhombic oxide phases, which often were present with, or evolved to, the tetragonal TaO2 phase. While the appearance of these phases indicated the films were evolving to themore » stable form of tantalum oxide—monoclinic tantalum pentoxide—it was likely not achieved for the conditions considered due to an insufficient amount of oxygen present in the films following deposition. Nevertheless, the collective in situ and ex situ TEM analysis applied to thin film samples enabled the isolation of a number of metastable tantalum oxides. As a result, new insights were gained into the transformation sequence and stability of these nanocrystalline phases, which presents opportunities for the development of advanced tantalum oxide-based dielectric materials for novel memristor designs.« less

  10. Metastable tantalum oxide formation during the devitrification of amorphous tantalum thin films

    SciTech Connect

    Donaldson, Olivia K.; Hattar, Khalid; Trelewicz, Jason R.

    2016-07-04

    Microstructural evolution during the devitrification of amorphous tantalum thin films synthesized via pulsed laser deposition was investigated using in situ transmission electron microscopy (TEM) combined with ex situ isothermal annealing, bright-field imaging, and electron-diffraction analysis. The phases formed during crystallization and their stability were characterized as a function of the chamber pressure during deposition, devitrification temperature, and annealing time. A range of metastable nanocrystalline tantalum oxides were identified following devitrification including multiple orthorhombic oxide phases, which often were present with, or evolved to, the tetragonal TaO2 phase. While the appearance of these phases indicated the films were evolving to the stable form of tantalum oxide—monoclinic tantalum pentoxide—it was likely not achieved for the conditions considered due to an insufficient amount of oxygen present in the films following deposition. Nevertheless, the collective in situ and ex situ TEM analysis applied to thin film samples enabled the isolation of a number of metastable tantalum oxides. As a result, new insights were gained into the transformation sequence and stability of these nanocrystalline phases, which presents opportunities for the development of advanced tantalum oxide-based dielectric materials for novel memristor designs.

  11. Serpin Inhibition Mechanism: A Delicate Balance between Native Metastable State and Polymerization.

    PubMed

    Khan, Mohammad Sazzad; Singh, Poonam; Azhar, Asim; Naseem, Asma; Rashid, Qudsia; Kabir, Mohammad Anaul; Jairajpuri, Mohamad Aman

    2011-01-01

    The serpins (serine proteinase inhibitors) are structurally similar but functionally diverse proteins that fold into a conserved structure and employ a unique suicide substrate-like inhibitory mechanism. Serpins play absolutely critical role in the control of proteases involved in the inflammatory, complement, coagulation and fibrinolytic pathways and are associated with many conformational diseases. Serpin's native state is a metastable state which transforms to a more stable state during its inhibitory mechanism. Serpin in the native form is in the stressed (S) conformation that undergoes a transition to a relaxed (R) conformation for the protease inhibition. During this transition the region called as reactive center loop which interacts with target proteases, inserts itself into the center of β-sheet A to form an extra strand. Serpin is delicately balanced to perform its function with many critical residues involved in maintaining metastability. However due to its typical mechanism of inhibition, naturally occurring serpin variants produces conformational instability that allows insertion of RCL of one molecule into the β-sheet A of another to form a loop-sheet linkage leading to its polymerization and aggregation. Thus understanding the molecular basis and amino acid involved in serpin polymerization mechanism is critical to devising strategies for its cure.

  12. Metastability bounds on flavor-violating trilinear soft terms in the MSSM

    SciTech Connect

    Park, Jae-hyeon

    2011-03-01

    The vacuum stability bounds on flavor-violating trilinear soft terms are revisited from the viewpoint that one should not ban a standard-model-like false vacuum as long as it is long-lived on a cosmological time scale. The vacuum transition rate is evaluated numerically by searching for the bounce configuration. Like stability, a metastability bound does not decouple even if sfermion masses grow. Apart from being more generous than stability, the new bounds are largely independent of Yukawa couplings except for the stop trilinears. With vacuum longevity imposed on otherwise arbitrary LR insertions, it is found that a super flavor factory has the potential to probe sparticle masses up to a few TeV through B and {tau} physics whereas the MEG experiment might cover a far wider range. In the stop sector, metastability is more restrictive than any existing experimental constraint such as from electroweak precision data. Also discussed are dependency on other parameters and reliability under radiative corrections.

  13. Metastable garnet in oceanic crust at the top of the lower mantle.

    PubMed

    Kubo, Tomoaki; Ohtani, Eiji; Kondo, Tadashi; Kato, Takumi; Toma, Motomasa; Hosoya, Tomofumi; Sano, Asami; Kikegawa, Takumi; Nagase, Toshiro

    As oceanic tectonic plates descend into the Earth's lower mantle, garnet (in the basaltic crust) and silicate spinel (in the underlying peridotite layer) each decompose to form silicate perovskite-the 'post-garnet' and 'post-spinel' transformations, respectively. Recent phase equilibrium studies have shown that the post-garnet transformation occurs in the shallow lower mantle in a cold slab, rather than at approximately 800 km depth as earlier studies indicated, with the implication that the subducted basaltic crust is unlikely to become buoyant enough to delaminate as it enters the lower mantle. But here we report results of a kinetic study of the post-garnet transformation, obtained from in situ X-ray observations using sintered diamond anvils, which show that the kinetics of the post-garnet transformation are significantly slower than for the post-spinel transformation. Although metastable spinel quickly breaks down at a temperature of 1,000 K, we estimate that metastable garnet should survive of the order of 10 Myr even at 1,600 K. Accordingly, the expectation of where the subducted oceanic crust would be buoyant spans a much wider depth range at the top of the lower mantle, when transformation kinetics are taken into account.

  14. High-Strength Stereolithographic 3D Printed Nanocomposites: Graphene Oxide Metastability.

    PubMed

    Manapat, Jill Z; Mangadlao, Joey Dacula; Tiu, Brylee David Buada; Tritchler, Grace C; Advincula, Rigoberto C

    2017-03-22

    The weak thermomechanical properties of commercial 3D printing plastics have limited the technology's application mainly to rapid prototyping. In this report, we demonstrate a simple approach that takes advantage of the metastable, temperature-dependent structure of graphene oxide (GO) to enhance the mechanical properties of conventional 3D-printed resins produced by stereolithography (SLA). A commercially available SLA resin was reinforced with minimal amounts of GO nanofillers and thermally annealed at 50 and 100 °C for 12 h. Tensile tests revealed increasing strength and modulus at an annealing temperature of 100 °C, with the highest tensile strength increase recorded at 673.6% (for 1 wt % GO). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) also showed increasing thermal stability with increasing annealing temperature. The drastic enhancement in mechanical properties, which is seen to this degree in 3D-printed samples reported in literature, is attributed to the metastable structure of GO, polymer-nanofiller cross-linking via acid-catalyzed esterification, and removal of intercalated water, thus improving filler-matrix interaction as evidenced by spectroscopy and microscopy analyses.

  15. Precision Spectroscopy in Cold Molecules: The Lowest Rotational Interval of He2 + and Metastable He2

    NASA Astrophysics Data System (ADS)

    Jansen, Paul; Semeria, Luca; Hofer, Laura Esteban; Scheidegger, Simon; Agner, Josef A.; Schmutz, Hansjürg; Merkt, Frédéric

    2015-09-01

    Multistage Zeeman deceleration was used to generate a slow, dense beam of translationally cold He2 molecules in the metastable a 3Σu+ state. Precision measurements of the Rydberg spectrum of these molecules at high values of the principal quantum number n have been carried out. The spin-rotational state selectivity of the Zeeman-deceleration process was exploited to reduce the spectral congestion, minimize residual Doppler shifts, resolve the Rydberg series around n =200 and assign their fine structure. The ionization energy of metastable He2 and the lowest rotational interval of the X+ 2Σu+ (ν+=0 ) ground state of 4He2+ have been determined with unprecedented precision and accuracy by Rydberg-series extrapolation. Comparison with ab initio predictions of the rotational energy level structure of 4He2+ [W.-C. Tung, M. Pavanello, and L. Adamowicz, J. Chem. Phys. 136, 104309 (2012)] enabled us to quantify the magnitude of relativistic and quantum-electrodynamics contributions to the fundamental rotational interval of He2+ .

  16. ELECTRON-DRIVEN REACTIONS IN PROTO-PLANETARY ATMOSPHERES: METASTABLE ANIONS OF GASEOUS o-BENZYNE

    SciTech Connect

    Carelli, F.; Sebastianelli, F.; Baccarelli, I.; Gianturco, F. A.

    2010-03-20

    In this paper, we present an investigation into low-energy electron scattering (E < 15 eV) processes from a specific benzene-like polyatomic target such as ortho-benzyne, o-C{sub 6}H{sub 4}({sup 1}SIGMA), in order to gain a better understanding of the effects that possible low-lying metastable electron-attachment states could have on its nuclear fragmentation dynamics. The current importance of the dynamical evolution of this molecule lies in the fact that o-C{sub 6}H{sub 4} is considered to be relevant for the circumstellar synthesis of large polycyclic aromatic hydrocarbons (PAHs), as a precursor for C{sub 6}H{sub 6} production via ion-based ring closure reaction from C{sub 2}H{sub 2}. Our parameter-free scattering calculations are performed within the molecular reference frame, where we obtain the metastable anionic states for the nuclear equilibrium configuration and further characterize the properties of such transient anions with respect to those found earlier for the benzene molecule. Our quantum studies indicate that o-C{sub 6}H{sub 4} is a more efficient producer of compact, fairly long-lived anionic intermediates than benzene itself; hence, this should more rapidly enter the chemical reaction cycles of PAHs formation, thereby disappearing from possible direct observation as a stable anion.

  17. Influences of depletion potential on vapor-liquid critical point metastability

    NASA Astrophysics Data System (ADS)

    Zhou, S.; Liu, G.

    2016-04-01

    Phase behavior of a neutral colloid dispersion is investigated based on an improved Asakura-Oosawa (AO) model. Several observations are made: (i) an increase of solvent fugacity can enlarge the fluid-solid (FS) coexistence region, and this makes fugacity become a powerful factor in tuning a vapor-liquid transition (VLT) critical point metastability. (ii) A reducing of size ratio of the solvent versus colloid particle can enlarge the FS coexistence region as well as lower the VLT critical temperature, and a combination of the two effects makes the size ratio an extremely powerful factor adjusting the VLT critical point metastability. (iii) Existence of a long-range attraction term in the effective colloid potential is not a necessary condition for occurrence of a vapor-solid transition (VST), and short-ranged oscillatory depletion potential also can induce the VST over an even broader temperature range. (iv) Sensitivity of the freezing line on the size ratio is disclosed, and one can make use of the sensitivity to prepare mono-disperse colloid of well-controlled diameter by following a fractionated crystallization scheme; moreover, broadening of the FST coexistence region by raising the solvent fugacity and/or lowering the size ratio has important implication for crystallization process.

  18. How a system moves in noise-induced escape from a metastable state

    NASA Astrophysics Data System (ADS)

    Zhukov, A.; Dykman, M. I.

    2000-03-01

    We provide a theory and results of numerical simulations of noise-induced escape from a metastable state, a phenomenon which underlies numerous processes in physics and biology. Of particular interest is a system's dynamics during escape. Understanding this dynamics is necessary for controlling the escape rate. The escape dynamics can be characterized by the distribution of trajectories along which the escaped system has been moving. This distribution peaks at a certain path, which is the most probable escape path (MPEP). The MPEP displays several characteristic features, including slowing down near the unstable stationary state over which the system goes in escape (e.g., top of the potential barrier). The width of the paths distribution is strongly nonmonotonic as a function of time counted off backward from the time when the system reaches an observation point behind the potential barrier. We investigate the shape of the paths distribution as a function of time and dynamical variables of the system, for a broad range of noise intensities. The data are obtained for a Brownian particle in a potential with a metastable minimum. The results are used to discuss experimental observations on dropout events in semiconductor lasers.

  19. Metastable alloy materials produced by solid state reaction of compacted, mechanically deformed mixtures

    DOEpatents

    Atzmon, Michael; Johnson, William L.; Verhoeven, John D.

    1987-01-01

    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 (13) of powder or the sheets of foil are clad in a container (14) to form a disc (10). The disc (10) is cold-rolled between the nip (16) of rollers (18,20) to form a flattened disc (22). The grains (13) are further elongated by further rolling to form a very thin sheet (26) of a lamellar filamentary structure (FIG. 4) 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 (28) is thermally treated in oven (32) to form a composite sheet (33) containing metastable material (34) dispersed in unreacted polycrystalline material (36).

  20. Interface Dynamics of a Metastable Mass-Conserving Spatially Extended Diffusion

    NASA Astrophysics Data System (ADS)

    Berglund, Nils; Dutercq, Sébastien

    2016-01-01

    We study the metastable dynamics of a discretised version of the mass-conserving stochastic Allen-Cahn equation. Consider a periodic one-dimensional lattice with N sites, and attach to each site a real-valued variable, which can be interpreted as a spin, as the concentration of one type of metal in an alloy, or as a particle density. Each of these variables is subjected to a local force deriving from a symmetric double-well potential, to a weak ferromagnetic coupling with its nearest neighbours, and to independent white noise. In addition, the dynamics is constrained to have constant total magnetisation or mass. Using tools from the theory of metastable diffusion processes, we show that the long-term dynamics of this system is similar to a Kawasaki-type exchange dynamics, and determine explicit expressions for its transition probabilities. This allows us to describe the system in terms of the dynamics of its interfaces, and to compute an Eyring-Kramers formula for its spectral gap. In particular, we obtain that the spectral gap scales like the inverse system size squared.

  1. Metastable densities in rf-driven atmospheric pressure microplasma jets in argon and helium

    NASA Astrophysics Data System (ADS)

    Boeke, Marc; Spiekermeier, Stefan; Winter, Joerg

    2016-09-01

    Rf-driven atmospheric pressure microplasma jets (μ-APPJ) are usually operated in the homogeneous glow mode (α-mode). At higher powers the glow discharge becomes unstable due to thermal instabilities and turns into a constricted γ-like discharge (constricted mode), which can damage the jet due to the significantly increased temperature in this operation mode. To prevent these instabilities, rf-driven μ-APPJs are predominantly operated in helium since it provides a better thermal conductivity than argon. However, since argon is much more cost-effective, it is worthwhile to achieve a stable operation of the μ-APPJ using argon as feed gas. Metastable atoms play an important role in the stability of atmospheric pressure discharges, since they pose an important source of electrons via stepwise ionization and penning ionization. To understand the basic processes that lead to the transition from α- to the constricted mode, helium and argon metastable densities have been determined in the μ-APPJ in different operation modes using tunable diode laser absorption spectroscopy (TDLAS). Supported by DFG within (FOR1123).

  2. Metastable phase formation in the Au-Si system via ultrafast nanocalorimetry

    NASA Astrophysics Data System (ADS)

    Zhang, M.; Wen, J. G.; Efremov, M. Y.; Olson, E. A.; Zhang, Z. S.; Hu, L.; de la Rama, L. P.; Kummamuru, R.; Kavanagh, K. L.; Ma, Z.; Allen, L. H.

    2012-05-01

    We have investigated the stability and solidification of nanometer size Au-Si droplets using an ultrafast heating/cooling nanocalorimetry and in situ growth techniques. The liquid can be supercooled to very low temperatures for both Au-rich (ΔT ˜ 95 K) and Si-rich (ΔT ˜ 220 K) samples. Solidification of a unique metastable phase δ1 is observed with a composition of 74 ± 4 at. % Au and a b-centered orthorhombic structure (a = 0.92, b = 0.72, and c = 1.35 nm; body-center in the a-c plane), which grows heteroepitaxially to Aus. Its melting temperature Tm is 305 ± 5 °C. There is competition during formation between the eutectic and δ1 phases but δ1 is the only metastable alloy observed. For small size droplets, both the δ1 and eutectic phases show considerable depression of the melting point (size-dependent melting).

  3. Influence of excitation frequency on helium metastable density in atmospheric pressure DBD

    NASA Astrophysics Data System (ADS)

    Boisvert, J.-S.; Sadeghi, N.; Margot, J.; Massines, F.

    2016-09-01

    Diffuse dielectric barrier discharges in atmospheric-pressure helium was sustained over a wide range of excitation frequencies (50 kHz to 15 MHz). Emission spectroscopy and resonant absorption and laser absorption on He(23S) metastable atoms have been used to characterize different plasma regimes, which with increasing frequency changes from a low pressure glow discharge (APGD) to Townsend-like mode (TL) and finally to a continuously sustained plasma. This later can be in Ω mode (with uniform E-field) or RF- α mode (with sheath formation). Depending on applied power, the time-averaged He(23S) density remains below 3 1016 m-3 in TL and Ω modes, can reach 7 1016 m-3 in APGD and RF- α modes and up to 4 1017 m-3 in a combination of APGD and RF- α modes (Hybrid). Time-resolved He(23S) densities show an overshoot on the ignition phase, which in RF- α mode can be attributed to a secondary source of ionization involving metastable atoms.

  4. Metastable CF and CF2 molecules in CF4 inductively-coupled plasmas

    NASA Astrophysics Data System (ADS)

    Booth, Jean-Paul; Corr, Cormac

    2006-02-01

    The radicals CF and CF2, which are important intermediates in fluorocarbon plasma chemistry, both have low-lying metastable levels (4CF at 3.54 eV and 3CF2 at 2.46 eV). Recent calculations (Rozum et al 2006 J. Phys. Chem. Ref. Data in press) indicate that electron-impact excitation of the ground-state radicals into these states could be fast. A recent study of inductively-coupled plasmas (ICP) in low-pressure CF4 (Booth et al 2005 Plasma Sources Sci. Technol. 14 273) indicated the presence of a fast electron-impact induced loss process for ground-state CF and CF2 molecules, which could be attributed to this process. In the current study 4CF and 3CF2 were detected in the afterglow of ICP in pure CF4 at pressures between 3 and 33 mTorr, from their weak forbidden optical emission back to their respective ground-states. From the lifetimes of these optical emission signals, determined as a function of gas pressure, the quenching coefficients at the chamber walls and the metastable destruction rates by gas-phase processes (giving unknown products) were estimated. Another prominent and long-lived feature of the afterglow is strong emission from the d state of C2 molecules: the emitting C2 molecules may be produced by chemiluminescent reactions or by excitation transfer from 3CF2.

  5. Metastable multi-domain state in ultrathin films with Dzyaloshinskii-Moriya Interaction

    NASA Astrophysics Data System (ADS)

    Agrawal, Parnika; Woo, Seonghoon; Beach, Geoffrey

    2015-03-01

    Helical spin structures such as skyrmions and chiral domain walls are stabilized in magnetic films with strong Dzyaloshinskii Moriya interaction (DMI). The chiral spin state is the ground state when the ratio of the effective DMI field to anisotropy field is greater than 2/pi. However, even when the DMI is too weak to generate a chiral ground state, such states can be metastable if the uniform state is appropriately perturbed.Here, we show that an in-plane applied field reduces the energy barrier for domain wall formation, and provides a simple technique to generate a multidomain state in uniform magnetic films. Further, we identify that the threshold between the stable single-domain state and the metastable multidomain state can be controlled by two parameters-demagnetizing energy and geometrical confinement. We use these parameters to create isolated geometrically confined magnetic bubbles in patterned discs of Pt/Co/GdOx multilayers. These bubbles may provide insight into the mechanism of creation of skyrmions in magnetic thin films with strong DMI.

  6. The dynamics of meta-stable states described with a complex scaled Hamiltonian

    NASA Astrophysics Data System (ADS)

    Lindroth, Eva; Bengtsson, Jakob; Selstø, Soslash; Lve

    2007-06-01

    The laser development has given access to light pulses in the femto- and subfemtosecond regime and thereby opened the possibility to follow electron dynamics directly in the time domain. Of special interest is the dynamics of resonant states, and pioneering experimental studies were made a few years ago on the Auger decay of inner-shell vacancies. We present a new method for time-dependent calculations of the whole sequence of events when an atom is exposed to a short light pulse followed by the population of a meta-stable state, and with the possibility to follow its subsequent decay by electron ejection. We use the method of complex scaling and show how it can be used together with the time-dependent Schr"odinger equation. Important advantages with this approach are; the meta-stable states are obtained as unique eigenstates to the field-free complex scaled Hamiltonian and the continuum is adequately represented by a very modest number of eigenstates. We have tested our approach against conventional methods for hydrogen and established the connection to Floquet theory for monochromatic radiation.

  7. Metastable GeV-scale particles as a solution to the cosmological lithium problem

    SciTech Connect

    Pospelov, Maxim; Pradler, Josef

    2010-11-15

    The persistent discrepancy between observations of {sup 7}Li with putative primordial origin and its abundance prediction in big bang nucleosynthesis has become a challenge for the standard cosmological and astrophysical picture. We point out that the decay of GeV-scale metastable particles X may significantly reduce the big bang nucleosynthesis value down to a level at which it is reconciled with observations. The most efficient reduction occurs when the decay happens to charged pions and kaons, followed by their charge-exchange reactions with protons. Similarly, if X decays to muons, secondary electron antineutrinos produce a similar effect. We consider the viability of these mechanisms in different classes of new GeV-scale sectors, and find that several minimal extensions of the standard model with metastable vectors and/or scalar particles are capable of solving the cosmological lithium problem. Such light states can be a key to the explanation of recent cosmic ray anomalies and can be searched for in a variety of high-intensity medium-energy experiments.

  8. Separated effects of ions, metastables and photons on the properties of barrier layers on polymers

    NASA Astrophysics Data System (ADS)

    Biskup, Beatrix; Boeke, Marc; Benedikt, Jan; von Keudell, Achim

    2016-09-01

    Analyses of a-C:H /a-Si:H multilayers on polymer substrates indicated that prolonged ion bombardment influences negatively the properties of the barrier layer, while a short plasma pretreatment can improve the barrier effect. This work is motivated by these results and investigates the influence of different reactive plasma components, namely ions, metastables and VUV-photons, on the properties of the grown barrier layer. To separate the different species and their influence on plasma pretreatment and film growth, we build a grid system, which repels the ions from the substrate, so that only metastables and VUV-photons have an effect on the layer. An integral part of this investigation is, to measure the photon fluxes to the substrate by an intensity calibrated VUV monochromator. For that, a differentially pumped monochromator with a spectral range 30 - 300 nm is used, where the two most prominent argon lines at 104.9 and 106.8 nm can be measured. In this approach we are able to study the different effects of the plasma species and also possible synergy effects, to improve the properties of the barrier layer. This work is supported by the DFG within the SFB-TR 87.

  9. Metastable argon atom density in complex argon/acetylene plasmas determined by means of optical absorption and emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Sushkov, Vladimir; Herrendorf, Ann-Pierra; Hippler, Rainer

    2016-10-01

    Optical emission and absorption spectroscopy has been utilized to investigate the instability of acetylene-containing dusty plasmas induced by growing nano-particles. The density of Ar(1s5) metastable atoms was derived by two methods: tunable diode laser absorption spectroscopy and with the help of the branching ratio method of emitted spectral lines. Results of the two techniques agree well with each other. The density of Ar(1s3) metastable atoms was also measured by means of optical emission spectroscopy. The observed growth instability leads to pronounced temporal variations of the metastable and other excited state densities. An analysis of optical line ratios provides evidence for a depletion of free electrons during the growth cycle but no indication for electron temperature variations.

  10. Extension of the BMCSL equation of state for hard spheres to the metastable disordered region: Application to the SAFT approach.

    PubMed

    Paricaud, P

    2015-07-28

    A simple modification of the Boublík-Mansoori-Carnahan-Starling-Leland equation of state is proposed for an application to the metastable disordered region. The new model has a positive pole at the jamming limit and can accurately describe the molecular simulation data of pure hard in the stable fluid region and along the metastable branch. The new model has also been applied to binary mixtures hard spheres, and an excellent description of the fluid and metastable branches can be obtained by adjusting the jamming packing fraction. The new model for hard sphere mixtures can be used as the repulsive term of equations of state for real fluids. In this case, the modified equations of state give very similar predictions of thermodynamic properties as the original models, and one can remove the multiple liquid density roots observed for some versions of the Statistical Associating Fluid Theory (SAFT) at low temperature without any modification of the dispersion term.

  11. Extension of the BMCSL equation of state for hard spheres to the metastable disordered region: Application to the SAFT approach

    SciTech Connect

    Paricaud, P.

    2015-07-28

    A simple modification of the Boublík-Mansoori-Carnahan-Starling-Leland equation of state is proposed for an application to the metastable disordered region. The new model has a positive pole at the jamming limit and can accurately describe the molecular simulation data of pure hard in the stable fluid region and along the metastable branch. The new model has also been applied to binary mixtures hard spheres, and an excellent description of the fluid and metastable branches can be obtained by adjusting the jamming packing fraction. The new model for hard sphere mixtures can be used as the repulsive term of equations of state for real fluids. In this case, the modified equations of state give very similar predictions of thermodynamic properties as the original models, and one can remove the multiple liquid density roots observed for some versions of the Statistical Associating Fluid Theory (SAFT) at low temperature without any modification of the dispersion term.

  12. Study of the solubility and the metastable zone of 1,3-dihydroxyacetone for the drowning-out process

    NASA Astrophysics Data System (ADS)

    Zhu, Y.; Youssef, D.; Porte, C.; Rannou, A.; Delplancke-Ogletree, M. P.; Mi Lung-Somarriba, B. Loı̈

    2003-10-01

    The 1,3-dihydroxyacetone (DHA) is an important raw material in the cosmetic industry for its skin pigmentation property. The DHA is highly soluble in water, which leads to a very important viscosity value and a huge metastable zone width. In addition, the DHA is a heat-sensitive substance. The drowning-out process (water-out or salting-out) is then necessary to reduce the solubility and to favor the mobility of the molecular species in solution. In this work, the solubility curves of DHA in different water/ethanol mixtures have been established experimentally. The turbidimetric method is used successfully to study the metastable zone in the water/ethanol mixture. The results show that the metastable zone is large, both the dissolution and the crystallization of DHA are time consuming, which could be due to the low diffusivity in the high-concentration solutions and at low temperatures.

  13. Metastability of the midgap level EL 2 in GaAs - Relationship with the As antisite defect

    NASA Technical Reports Server (NTRS)

    Skowronski, M.; Lagowski, J.; Gatos, H. C.

    1985-01-01

    It is found that the rate of the photoinduced transition of the GaAs midgap level EL 2 to its metastable state increases as its occupation increases. High-resolution optical spectra of this transition exhibit a sharp peak very similar to the no-phonon line of the intracenter absorption of the As antisite defect. These findings show that the transition to the metastable state is initiated from the ground state 1A1, and it is finalized via the excited state 1T2 of the neutral As antisite defect. They thus provide a new basis for the critical assessment of the EL 2 metastability models and further confirmation of the association of EL 2 with the isolated As antisite defect.

  14. PREFACE The 13th International Conference on Rapidly Quenched and Metastable Materials

    NASA Astrophysics Data System (ADS)

    Schultz, Ludwig; Eckert, Jürgen; Battezzati, Livio; Stoica, Mihai

    2009-01-01

    The 13th International Conference on Rapidly Quenched and Metastable Materials (RQ13) took place in Dresden, Germany, 24-29 August 2008. It belongs to the triennial series of RQ meetings with a long tradition, starting in 1970 - Brela, 1975 - Boston, 1978 - Brighton, 1981 - Sendai, 1984 - Würzburg, 1987 - Montreal, 1990 - Stockholm, 1993 - Sendai, 1996 - Bratislava, 1999 - Bangalore, 2002 - Oxford, 2005 - Jeju Island. RQ13 was hosted by the Leibniz Institute of Solid State and Materials Research, IFW Dresden. Research on rapidly quenched and metastable materials is stimulated by the high demand for new materials with unique mechanical, chemical and physical properties. Topics of RQ13 conference have fallen into three parts: synthesis and processing, materials and properties, and applications of rapidly quenched and metastable materials. These topics cover exiting developments from the traditional field of rapidly quenched metals to newly emerging areas such as bulk metallic glasses and nanostructured materials. As such, the presentations reported on recent experimental and theoretical achievements in the fields of metastable materials, quasicrystals, nanometer-scale materials, magnetic materials, metallic glasses, solid state reaction, undercooling and modeling. As in the previous proceedings (RQ12), the largest number of papers is dedicated to bulk metallic glasses and magnetic materials. With respect to property characterization and applications, there are great attempts for use and application of these materials, particularly for bulk metallic glasses, as well as for further design and optimization of properties. The RQ13 conference attracted a total of 381 abstracts submitted by scientists from 38 different countries. The conference included 8 plenary talks and 25 invited keynote talks. In addition, 163 regular oral contributions were presented and more than 180 posters were presented. It was a particular highlight of the conference that Dr Ho Sou Chen was

  15. Experimental confirmation of photon-induced spin-flip transitions in helium via triplet metastable yield spectra

    SciTech Connect

    Rubensson, Jan-Erik; Moise, Angelica; Richter, Robert; Mihelic, Andrej; Bucar, Klemen; Zitnik, Matjaz

    2010-06-15

    Doubly excited states below the N=2 ionization threshold are populated by exciting helium atoms in a supersonic beam with monochromatized synchrotron radiation. The fluorescence decay of these states triggers a radiative cascade back to the ground state with large probability to populate long lived singlet and triplet helium metastable states. The yield of metastables is measured using a multichannel plate detector after the beam has passed a singlet-quenching discharge lamp. The variation of the yield observed with the lamp switched on or off is related to the triplet-singlet mixing of the doubly excited states.

  16. Ab initio interaction potentials and scattering lengths for ultracold mixtures of metastable helium and alkali-metal atoms

    NASA Astrophysics Data System (ADS)

    Kedziera, Dariusz; Mentel, Łukasz; Żuchowski, Piotr S.; Knoop, Steven

    2015-06-01

    We have obtained accurate ab initio +4Σ quartet potentials for the diatomic metastable triplet helium+alkali-metal (Li, Na, K, Rb) systems, using all-electron restricted open-shell coupled cluster singles and doubles with noniterative triples corrections CCSD(T) calculations and accurate calculations of the long-range C6 coefficients. These potentials provide accurate ab initio quartet scattering lengths, which for these many-electron systems is possible, because of the small reduced masses and shallow potentials that result in a small amount of bound states. Our results are relevant for ultracold metastable triplet helium+alkali-metal mixture experiments.

  17. Metastability of a-SiOx:H thin films for c-Si surface passivation

    NASA Astrophysics Data System (ADS)

    Serenelli, L.; Martini, L.; Imbimbo, L.; Asquini, R.; Menchini, F.; Izzi, M.; Tucci, M.

    2017-01-01

    The adoption of a-SiOx:H films obtained by PECVD in heterojunction solar cells is a key to further increase their efficiency, because of its transparency in the UV with respect to the commonly used a-Si:H. At the same time this layer must guarantee high surface passivation of the c-Si to be suitable in high efficiency solar cell manufacturing. On the other hand the application of amorphous materials like a-Si:H and SiNx on the cell frontside expose them to the mostly energetic part of the sun spectrum, leading to a metastability of their passivation properties. Moreover as for amorphous silicon, thermal annealing procedures are considered as valuable steps to enhance and stabilize thin film properties, when performed at opportune temperature. In this work we explored the reliability of a-SiOx:H thin film layers surface passivation on c-Si substrates under UV exposition, in combination with thermal annealing steps. Both p- and n-type doped c-Si substrates were considered. To understand the effect of UV light soaking we monitored the minority carriers lifetime and Sisbnd H and Sisbnd O bonding, by FTIR spectra, after different exposure times to light coming from a deuterium lamp, filtered to UV-A region, and focused on the sample to obtain a power density of 50 μW/cm2. We found a certain lifetime decrease after UV light soaking in both p- and n-type c-Si passivated wafers according to a a-SiOx:H/c-Si/a-SiOx:H structure. The role of a thermal annealing, which usually enhances the as-deposited SiOx passivation properties, was furthermore considered. In particular we monitored the UV light soaking effect on c-Si wafers after a-SiOx:H coating by PECVD and after a thermal annealing treatment at 300 °C for 30 min, having selected these conditions on the basis of the study of the effect due to different temperatures and durations. We correlated the lifetime evolution and the metastability effect of thermal annealing to the a-SiOx:H/c-Si interface considering the evolution

  18. Dissociation of CH4 and CD4 by electron impact - Production of metastable and high-Rydberg hydrogen and carbon fragments

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

    Production of hydrogen and carbon atoms in metastable and high-lying Rydberg states by electron-impact dissociation of methane and deuterated methane is investigated for incident electron energies ranging from threshold values to 300 eV. Threshold energies for five different processes resulting in metastable hydrogen and carbon atoms are determined in the energy range from 20 to 70 eV, and it is shown that metastable hydrogen atoms are produced in four of these collisional processes while metastable carbon atoms are produced in the other. The nature of each collisional process is described, differential cross sections are derived for the dissociative excitation of both types of atoms to metastable and high-Rydberg states at 100 eV, and the onset energy for UV photon production is measured. Much of the data is interpreted in terms of the ion core model suggested by Kupriyanov (1968) and developed by Freund (1971).

  19. The Role of Helium Metastable States in Radio-Frequency Helium-Oxygen Atmospheric Pressure Plasma Jets: Measurement and Numerical Simulation

    NASA Astrophysics Data System (ADS)

    Niemi, Kari; Waskoenig, Jochen; Sadeghi, Nader; Gans, Timo; O'Connell, Deborah

    2011-10-01

    Absolute densities of metastable He atoms were measured line-of sight integrated along the plasma channel of a capacitively-coupled radio-frequency driven atmospheric pressure plasma jet operated in helium oxygen mixtures by tunable diode-laser absorption spectroscopy. Dependencies of the He metastable density with oxygen admixtures up to 1 percent were investigated. Results are compared to a 1-d numerical simulation, which includes a semi-kinetical treatment of the electron dynamics and the complex plasma chemistry (20 species, 184 reactions), and very good agreement is found. The main formation mechanisms for the helium metastables are identified and analyzed, including their pronounced spatio-temporal dynamics. Penning ionization through helium metastables is found to be significant for plasma sustainment, while it is revealed that helium metastables are not an important energy carrying species into the jet effluent and therefore will not play a direct role in remote surface treatments.

  20. Projectile containing metastable intermolecular composites and spot fire method of use

    DOEpatents

    Asay, Blaine W.; Son, Steven F.; Sanders, V. Eric; Foley, Timothy; Novak, Alan M.; Busse, James R.

    2012-07-31

    A method for altering the course of a conflagration involving firing a projectile comprising a powder mixture of oxidant powder and nanosized reductant powder at velocity sufficient for a violent reaction between the oxidant powder and the nanosized reductant powder upon impact of the projectile, and causing impact of the projectile at a location chosen to draw a main fire to a spot fire at such location and thereby change the course of the conflagration, whereby the air near the chosen location is heated to a temperature sufficient to cause a spot fire at such location. The invention also includes a projectile useful for such method and said mixture preferably comprises a metastable intermolecular composite.

  1. Metastable cobalt nitride structures with high magnetic anisotropy for rare-earth free magnets.

    PubMed

    Zhao, Xin; Ke, Liqin; Wang, Cai-Zhuang; Ho, Kai-Ming

    2016-11-23

    Metastable structures of cobalt nitrides and Fe-substituted cobalt nitrides are explored as possible candidates for rare-earth free permanent magnets. Through crystal structure searches using an adaptive genetic algorithm, new structures of ConN (n = 3…8) are found to have lower energies than those previously discovered by experiments. Some structures exhibit large magnetic anisotropy energy, reaching as high as 200 μeV per Co atom (or 2.45 MJ m(-3)) based on first-principles density functional calculation. Substituting a fraction of Co with Fe helps in stabilizing new structures and at the same time further improves the magnetic properties. Our theoretical predictions provide useful insights into a promising system for the discovery of new rare-earth free magnets by experiment.

  2. Phase transformations and the spectral reflectance of solid sulfur - Can metastable sulfur allotropes exist on Io?

    NASA Technical Reports Server (NTRS)

    Moses, Julianne I.; Nash, Douglas B.

    1991-01-01

    Laboratory investigations have been conducted on the effects of variations in sulfur sample histories on their solid-state transformation rate and the corresponding spectral variation of freshly frozen sulfur. The temporal variations in question may be due to differences in the amount and type of metastable allotropes present in the sulfur after solidification, as well as to the physics of the phase-transformation process itself. The results obtained are pertinent to the physical behavior and spectral variation of such freshly solidified sulfur as may exist on the Jupiter moon Io; this would initially solidify into a glassy solid or monoclinic crystalline lattice, then approach ambient dayside temperatures. Laboratory results imply that the monoclinic or polymeric allotropes can in these circumstances be maintained, and will take years to convert to the stable orthorhombic crystalline form.

  3. Effect of sample volume on metastable zone width and induction time

    NASA Astrophysics Data System (ADS)

    Kubota, Noriaki

    2012-04-01

    The metastable zone width (MSZW) and the induction time, measured for a large sample (say>0.1 L) are reproducible and deterministic, while, for a small sample (say<1 mL), these values are irreproducible and stochastic. Such behaviors of MSZW and induction time were theoretically discussed both with stochastic and deterministic models. Equations for the distribution of stochastic MSZW and induction time were derived. The average values of stochastic MSZW and induction time both decreased with an increase in sample volume, while, the deterministic MSZW and induction time remained unchanged. Such different behaviors with variation in sample volume were explained in terms of detection sensitivity of crystallization events. The average values of MSZW and induction time in the stochastic model were compared with the deterministic MSZW and induction time, respectively. Literature data reported for paracetamol aqueous solution were explained theoretically with the presented models.

  4. Determination of metastable zone width for combined anti-solvent/cooling crystallization

    NASA Astrophysics Data System (ADS)

    Trifkovic, M.; Sheikhzadeh, M.; Rohani, S.

    2009-07-01

    The metastable zone width (MSZW), induction time and primary nucleation kinetics have been measured and estimated for simultaneous anti-solvent and cooling crystallization of paracetamol in iso-propanol/water solution. ATR-FTIR spectroscopy and laser back-scattering are used to measure the solute concentration and primary nucleation event, respectively. Response surface analysis was applied to find the contribution of the crystallization mechanism on the MSZW and obtain a statistical model for quick estimation of the MSZW. Two theoretical approaches for the estimation of nucleation rate kinetic parameters from experimental data are presented. The methods are obtained by modifying the classical Nyvlt's correlation for simultaneous cooling/anti-solvent crystallizations. The nucleation order n for primary nucleation was deduced from the slope of a linear plot of log(MSZW) vs. log(cooling and anti-solvent rates). The induction time was also estimated by changing the classical methods for combined cooling and anti-solvent crystallization.

  5. A novel vacuum ultra violet lamp for metastable rare gas experiments.

    PubMed

    Daerr, Heiner; Kohler, Markus; Sahling, Peter; Tippenhauer, Sandra; Arabi-Hashemi, Ariyan; Becker, Christoph; Sengstock, Klaus; Kalinowski, Martin B

    2011-07-01

    We report on a new design of a vacuum ultra violet (VUV) lamp for direct optical excitation of high laying atomic states, e.g., for excitation of metastable rare gas atoms. The lamp can be directly mounted to ultra-high vacuum vessels (p ≤ 10(-10)mbar). It is driven by a 2.45 GHz microwave source. For optimum operation, it requires powers of ~20 W. The VUV light is transmitted through a magnesium fluoride window, which is known to have a decreasing transmittance for VUV photons with time. In our special setup, after a run-time of the VUV lamp of 550 h the detected signal continuously decreased to 25% of its initial value. This corresponds to a lifetime increase of two orders of magnitude compared to previous setups or commercial lamps.

  6. Thermally activated phase slips from metastable states in mesoscopic superconducting rings

    NASA Astrophysics Data System (ADS)

    Petkovic, Ivana; Lollo, Anthony; Harris, Jack

    In equilibrium, a flux-biased superconducting ring at low temperature can occupy any of several metastable states. The particular state that the ring occupies depends on the history of the applied flux, as different states are separated from each other by flux-dependent energy barriers. There is a critical value of the applied flux at which a given barrier goes to zero, the state becomes unstable, and the system transition into another state. In recent experiments performed on arrays of rings we showed that this transition occurs close to the critical flux predicted by Ginzburg-Landau theory. Here, we will describe experiments in which we have extended these measurements to an individual ring in order to study the thermal activation of the ring over a barrier that has been tuned close to zero. We measure the statistics of transitions as function of temperature and ramp rate.

  7. Structure and magnetic properties of metastable Co-Cu solid solution nanowire arrays fabricated by electrodeposition

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Li, Fashen; Wang, Ying; Song, Lijing

    2006-08-01

    Nanowire arrays of the metastable Cox Cu1-x (0.20 x 0.85) solid solution system which can not be obtained by equilibrium methods, were prepared by electrodeposition in pores of anodic aluminum oxide (AAO) template, and subsequently annealed at different temperatures. The as-deposited samples all show single phase of fcc structure, and lattice parameters decrease with the increase of Co content and fundamentally accord with Vegard's law. The phase transition with heat treatment was investigated by X-ray diffraction and differential thermal analysis (DTA) which further confirmed the formation of solid solution. With Co content increasing, the coercivity along nanowire axis for as-deposited samples increases, but it decreases for the annealed samples at 700 °C. This phenomenon was explained considering the interaction of Co particles through Cu in nanowires after phase separation.

  8. Modulational instability and resonant wave modes act on the metastability of oscillator chains

    NASA Astrophysics Data System (ADS)

    Gross, Torsten; Hennig, Dirk; Schimansky-Geier, Lutz

    2014-09-01

    We describe the emergence and interactions of breather modes and resonant wave modes within a two-dimensional ringlike oscillator chain in a microcanonical situation. Our analytical results identify different dynamical regimes characterized by the potential dominance of either type of mode. The chain is initially placed in a metastable state, which it can leave by passing over the brim of the applied Mexican-hat-like potential. We elucidate the influence of the different wave modes on the mean-first passage time. A central finding is that also in this complex potential landscape a fast noise-free escape scenario solely relying on nonlinear cooperative effects is accomplishable even in a low-energy setting.

  9. Effectively explore metastable states of proteins by adaptive nonequilibrium driving simulations

    NASA Astrophysics Data System (ADS)

    Wan, Biao; Xu, Shun; Zhou, Xin

    2017-03-01

    Nonequilibrium drivings applied in molecular dynamics (MD) simulations can efficiently extend the visiting range of protein conformations, but might compel systems to go far away from equilibrium and thus mainly explore irrelevant conformations. Here we propose a general method, called adaptive nonequilibrium simulation (ANES), to automatically adjust the external driving on the fly, based on the feedback of the short-time average response of system. Thus, the ANES approximately keeps the local equilibrium but efficiently accelerates the global motion. We illustrate the capability of the ANES in highly efficiently exploring metastable conformations in the deca-alanine peptide and find that the 0.2 -μ s ANES approximately captures the important states and folding and unfolding pathways in the HP35 solution by comparing with the result of the recent 398 -μ s equilibrium MD simulation on Anton [S. Piana et al., Proc. Natl. Acad. Sci. USA 109, 17845 (2012), 10.1073/pnas.1201811109].

  10. Autoionization of spin-polarized metastable helium in tight anisotropic harmonic traps

    SciTech Connect

    Beams, Timothy J.; Whittingham, Ian B.; Peach, Gillian

    2007-12-15

    Spin-dipole mediated interactions between tightly confined metastable helium atoms couple the spin-polarized quintet {sup 5}{sigma}{sub g}{sup +} state to the singlet {sup 1}{sigma}{sub g}{sup +} state from which autoionization is highly probable, resulting in finite lifetimes for the trap eigenstates. We extend our earlier study on spherically symmetric harmonic traps to the interesting cases of axially symmetric anisotropic harmonic traps and report results for the lowest 10 states in 'cigarlike' and 'pancakelike' traps with average frequencies of 100 kHz and 1 MHz. We find that there is a significant suppression of ionization, and subsequent increase in lifetimes, at trap aspect ratios A=p/q, where p and q are integers, for those states that are degenerate in the absence of collisions or spin-dipole interactions.

  11. The Effective Kahler Potential, Metastable Vacua and R-Symmetry Breaking in O'Raifeartaigh Models

    NASA Astrophysics Data System (ADS)

    Kain, Ben; Benjamin, Shermane; Freund, Christopher

    2010-02-01

    Much has been learned about metastable vacua and R-symmetry breaking in O'Raifeartaigh models. Such work has largely been done from the perspective of the superpotential and by including Coleman-Weinberg corrections to the scalar potential. Instead, we consider these ideas from the perspective of the one loop effective K"ahler potential. We translate known ideas to this framework and then construct convenient formulas for computing individual terms in the expanded effective K"ahler potential. We do so for arbitrary R-charge assignments and allow for small R-symmetry violating terms so that both spontaneous an explicit R-symmetry breaking is included in our analysis. )

  12. Externally induced metastability of an electron in a Penning trap: Analytical results

    NASA Astrophysics Data System (ADS)

    Brouard, S.; Plata, J.

    2001-12-01

    The effect of a driving field on the cyclotron mode of a relativistic electron in a Penning trap is studied analytically. The Hamiltonian dynamics of this driven nonlinear oscillator is analyzed by using linearization techniques and displaced squeezed-state formalism. With the approximate analytical expressions obtained for the eigenstates in this approach, a simplified treatment of the dissipative dynamics is carried out and some of the nontrivial features found in a recent numerical study [D. Enzer and G. Gabrielse, Phys. Rev. Lett. 78, 1211 (1997)] are unraveled. The emergence of different time scales and the generation of a metastable statistical mixture are understood in terms of the changes induced in the structure of the master equation by the nonuniform characteristics of the eigenstates; the partial revivals of specific coherent states are accounted for by the evolution of particular coherences. The control of these effects by a proper choice of the driving parameters is discussed.

  13. Trap loss in a metastable helium-rubidium magneto-optical trap

    SciTech Connect

    Byron, L. J.; Dall, R. G.; Truscott, A. G.

    2010-01-15

    We present results of the study of a simultaneously confined metastable helium (He*) and rubidium magneto-optical trap (MOT). By monitoring the trap decay of the {sup 87}Rb MOT with and without a He* MOT present, we find the light-assisted, two-body loss rate to be beta{sub Rb-He}{sup *}=(6+-2)x10{sup -10} cm{sup 3}/s. Moreover, we find that it is possible to create a large, robust {sup 87}Rb-He* MOT, opening the possibility of creating a {sup 87}Rb-He{sup *} Bose-Einstein condensate. This would be the first dual-species condensate incorporating an alkali metal ground-state atom and an excited-state noble gas atom.

  14. Texture evolution of cold rolled and reversion annealed metastable austenitic CrMnNi steels

    NASA Astrophysics Data System (ADS)

    Weidner, A.; Fischer, K.; Segel, C.; Schreiber, G.; Biermann, H.

    2015-04-01

    A thermo-mechanical process consisting of cold rolling and subsequent reversion annealing was applied to high-alloy metastable austenitic CrMnNi steels with different nickel contents. As a result of the reversion annealing ultrafine grained material with a grain size in the range between 500 nm up to 4 μm were obtained improving the strength behavior of the material. The evolution of the texture of both the cold rolled states and the reversion-annealed states was studied either by X-ray diffraction or by EBSD measurements. The nickel content has a significant influence on the austenite stability and consequently also on the amount of the martensitic phase transformation. However, the developed textures in both steel variants with different austenite stability revealed the same behavior. In both investigated steels the texture of the reverted austenite is a pronounced Bs-type texture as developed also for the deformed austenite

  15. Correlation Between Microstructure and Mechanical Properties Before and After Reversion of Metastable Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Fargas, Gemma; Zapata, Ana; Roa, Joan Josep; Sapezanskaia, Ina; Mateo, Antonio

    2015-12-01

    Reversion treatments are a way to improve the mechanical response of metastable austenitic stainless steels by means of grain refinement. To effectively apply those treatments, the steel must be previously deformed to induce a significant amount of martensitic transformation. In this work, the effect of reversion treatments was studied on a commercial AISI 301LN grade subjected to an industrial cold rolling process, with thickness reductions not higher than 40 pct. Microstructural changes and evolution of both monotonic and cyclic mechanical properties were investigated after cold rolling and upon reversion treatments. Results revealed that the finer austenitic microstructure obtained after reversion leads to an interesting combination of properties, with strong increments in hardness and yield strength, and also fatigue limit improvement, as compared to the initial annealed condition.

  16. The Portevin-Le Châtelier Effect in a Metastable Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Müller, Alexandra; Segel, Christian; Linderov, Mikhail; Vinogradov, Alexei; Weidner, Anja; Biermann, Horst

    2016-01-01

    The Portevin-Le Châtelier (PLC) effect was investigated in a high-alloy metastable CrMnNi cast steel during tensile tests for the range of deformation temperatures between 293 K and 413 K (20 °C and 140 °C) and for nominal strain rates ranging between 10-4 and 10-1 s-1. Analysis of the stress-strain curves was complemented by in situ measurements of thermal and acoustic emissions as well as by digital image correlation, enabling determination of various local characteristics of plastic flow and clarification of individual contributions of different microscopic mechanisms involved in plastic deformation. It was shown that the PLC effect in the investigated CrMnNi steel was caused by the diffusion of interstitial atoms in the bcc phases.

  17. Oxygen Defect-Induced Metastability in Oxide Semiconductors Probed by Gate Pulse Spectroscopy

    PubMed Central

    Lee, Sungsik; Nathan, Arokia; Jeon, Sanghun; Robertson, John

    2015-01-01

    We investigate instability mechanisms in amorphous In-Ga-Zn-O transistors based on bias and illumination stress-recovery experiments coupled with analysis using stretched exponentials and inverse Laplace transform to retrieve the distribution of activation energies associated with metastable oxygen defects. Results show that the recovery process after illumination stress is persistently slow by virtue of defect states with a broad range, 0.85 eV to 1.38 eV, suggesting the presence of ionized oxygen vacancies and interstitials. We also rule out charge trapping/detrapping events since this requires a much smaller activation energy ~0.53 eV, and which tends to be much quicker. These arguments are supported by measurements using a novel gate-pulse spectroscopy probing technique that reveals the post-stress ionized oxygen defect profile, including anti-bonding states within the conduction band. PMID:26446400

  18. Kinetic-arrest-induced phase coexistence and metastability in (Mn,Fe ) 2(P ,Si )

    NASA Astrophysics Data System (ADS)

    Miao, X. F.; Mitsui, Y.; Dugulan, A. Iulian; Caron, L.; Thang, N. V.; Manuel, P.; Koyama, K.; Takahashi, K.; van Dijk, N. H.; Brück, E.

    2016-09-01

    Neutron diffraction, Mössbauer spectroscopy, magnetometry, and in-field x-ray diffraction are employed to investigate the magnetoelastic phase transition in hexagonal (Mn,Fe ) 2(P ,Si ) compounds. (Mn,Fe ) 2(P ,Si ) compounds undergo for certain compositions a second-order paramagnetic (PM) to a spin-density-wave (SDW) phase transition before further transforming into a ferromagnetic (FM) phase via a first-order phase transition. The SDW-FM transition can be kinetically arrested, causing the coexistence of FM and untransformed SDW phases at low temperatures. Our in-field x-ray diffraction and magnetic relaxation measurements clearly reveal the metastability of the untransformed SDW phase. This unusual magnetic configuration originates from the strong magnetoelastic coupling and the mixed magnetism in hexagonal (Mn,Fe ) 2(P ,Si ) compounds.

  19. Dissociation of metastable O2 as a potential source of atmospheric odd oxygen

    NASA Technical Reports Server (NTRS)

    Frederick, J. E.; Cicerone, R. J.

    1985-01-01

    An analysis of the possible dissociation of metastable oxygen molecules subject ot constraints imposed by selection rules for molecular transitions, airglow observations, and atmospheric chemistry leads to the following conclusions. Dissociation of O2(b1Sigma g +) must produce a negligible number of oxygen atoms at all altitudes in the earth's atmosphere. However, if the dissociation cross section of O2(a1Delta g) has a maximum value in the range 10 to the -20th to 10 to the -19th/sq cm, then the process O2(a1Delta g) + h(nu) yields O2(C3Delta u) yields O(3P) + O(3P) will constitute a significant, and potentially the major, source of odd oxygen in the uppermost stratosphere and mesosphere.

  20. A new interpretation of metastable zone widths measured for unseeded solutions

    NASA Astrophysics Data System (ADS)

    Kubota, Noriaki

    2008-02-01

    The experimental metastable zone width (MSZW) was newly assumed to correspond to a point at which the number density of accumulated crystals (grown nuclei) had reached a fixed (but unknown) value and a new mathematical model was proposed. The effect of cooling rate on the experimental MSZW reported in the literature was explained reasonably by the new model. The nucleation order n in the rate equation for primary nucleation was deduced from the slope of a linear plot of log(MSZW) vs. log(cooling rate). This linear relation is similar to the Nyvlt's one but the physical basis is completely different. The induction time was also explained in the same way and related to the MSZW.

  1. Phase transitions and metastability in the distribution of the bipartite entanglement of a large quantum system

    SciTech Connect

    De Pasquale, A.; Facchi, P.; Parisi, G.; Pascazio, S.; Scardicchio, A.

    2010-05-15

    We study the distribution of the Schmidt coefficients of the reduced density matrix of a quantum system in a pure state. By applying general methods of statistical mechanics, we introduce a fictitious temperature and a partition function and translate the problem in terms of the distribution of the eigenvalues of random matrices. We investigate the appearance of two phase transitions, one at a positive temperature, associated with very entangled states, and one at a negative temperature, signaling the appearance of a significant factorization in the many-body wave function. We also focus on the presence of metastable states (related to two-dimensional quantum gravity) and study the finite size corrections to the saddle point solution.

  2. Morphological templating of metastable calcium carbonates by the amino acid leucine

    NASA Astrophysics Data System (ADS)

    Thompson, S. P.; Parker, J. E.; Street, S. R.; Tang, C. C.

    2011-03-01

    The in vitro precipitation of the metastable CaCO3 phases aragonite and vaterite in the presence of leucine is investigated. Under normal conditions, the production of CaCO3 via the hydrolysis of urea method favours the formation of regular needle-like aragonite crystals, with very minor quantities of vaterite and calcite. However in the presence of leucine, aragonite forms highly branched structures and the vaterite yield is increased, forming flower-like clusters composed of nano-thin sheets. Both the degree of aragonite branching and the occurrence, regularity of shape and number of vaterite "petals" increases with leucine concentration. The two phases exhibit different variations in their crystallographic parameters with increasing concentration, while the molecular structure appears unaffected.

  3. Curvature-dependent metastability of the solid phase and the freezing-melting hysteresis in pores.

    PubMed

    Petrov, Oleg; Furó, István

    2006-01-01

    We recapitulate and generalize the concept of the freezing-melting hysteresis that attributes this phenomenon to a free-energy barrier between metastable and stable states of pore-filling material. In a phenomenological description, we show that under commonly encountered conditions, this renders the freezing-point depression DeltaTf defined by the surface-to-volume ratio S/V, whereas the melting-point depression DeltaTm, by the mean curvature kappa of the pore surface, with DeltaTm/DeltaTf =2kappa(V/S). Employing 1H NMR cryoporometry, we experimentally demonstrate the linear correlation between DeltaTm and DeltaTf for several liquids with different DeltaTf,m imbibed in controlled pore glasses. The results compare favorably to the morphological properties of the glasses determined by other techniques. Our findings suggest a simple method for analyzing the pore morphology from the observed phase transition temperatures.

  4. Metastable Demixing of Supercooled Cu-Co and Cu-Fe Alloys in an Oxide Flux

    NASA Technical Reports Server (NTRS)

    Li, D.; Robinson, M. B.; Rathz, T. J.; Williams, G.

    1998-01-01

    A systematic study on the liquid separation in supercooled Cu-Co and Cu-Fe alloys was performed using a melt fluxing which permits high supercooling to be achieved. Moreover, this method renders it possible to directly measure binodal temperatures and establish metastable liquid miscibility gap (LMG). All phase-separated samples at compositions ranging from 10 to 80 wt pct Co or to 83 wt pct Fe were found to exhibit droplet-shaped morphologies, in spite of various droplet distributions. Uniformly dispersed microstructures were obtained as the minority component was less than 20 vol.%; while beyond this percentage, serious coarsening was brought about. Calculations of the miscibility gap in the Cu-Co system and Stokes movement velocity of Co and Fe droplets in Cu matrix were made to analyze the experimental results.

  5. Metastable states and activated dynamics in thin-film adhesion to patterned surfaces.

    PubMed

    Lindström, Stefan B; Johansson, Lars; Karlsson, Nils R

    2014-06-01

    We consider adhesion due to London-van der Waals attraction between a thin film and a patterned surface with nanometer asperities. Depending on the surface topography and the stiffness of the film, three regimes of adhesion are identified: complete contact adhesion, partial contact adhesion, and glassy adhesion. For complete contact adhesion, the film conforms to the undulations of the surface, whereas for partial contact and glassy adhesion, the adhesive interface breaks down into microscopic areas of contact. When a film in the glassy regime is peeled off the surface, metastable states develop at which the crack front becomes arrested, analogously to the frustrated motion of the three-phase contact line across a heterogeneous surface. For this glassy regime, we use transition state theory to model the thermally activated progression of the crack front. This theoretical treatment suggests that the rate of the adhesive failure increases exponentially with the applied force.

  6. Effects of Voltage-Bias Annealing on Metastable Defect Populations in CIGS and CZTSe Solar Cells

    SciTech Connect

    Harvey, Steven P.; Johnston, Steve; Teeter, Glenn

    2016-11-21

    We report on voltage-bias annealing (VBA) experiments performed on CIGS and CZTSe solar cells. In these experiments, completed devices were annealed at moderate temperatures and subsequently quenched with continuously applied voltage bias. These treatments resulted in substantial reversible changes in device characteristics. Photovoltaic (PV) conversion efficiency of the CIGS device varied from below 3% to above 15%, with corresponding changes in CIGS hole density from ~1014 cm-3 to ~1017 cm-3. In the CZTSe device, open-circuit voltage varied from 289 meV to 446 meV, caused by an approximately factor of fifty change in the CZTSe hole density. We interpret these findings in terms of reversible changes to the metastable point-defect populations that control key properties in these materials. Implications for optimization of PV materials and connections to long-term stability of PV devices are discussed.

  7. Determination of the coefficient of reflection of metastable argon atoms from the discharge tube wall

    SciTech Connect

    Grigorian, G. M.; Dyatko, N. A.; Kochetov, I. V.

    2015-05-15

    Radial profiles of the density of metastable atoms Ar({sup 3}P{sub 2}) in the positive column of a dc glow discharge in argon were measured. Gas-discharge glass tubes with clean inner surfaces and surfaces covered with a carbonitride or carbon film were utilized. The parameters of the discharge plasma under experimental conditions were calculated in the framework of a one-dimensional (along the tube radius) discharge model. The coefficient K of reflection of Ar({sup 3}P{sub 2}) atoms from the tube wall was estimated by comparing the measured and calculated density profiles. It is found that, for a clean tube wall, the coefficient of reflection is K = 0.4 ± 0.2, whereas for a wall covered with a carbonitride or carbon film, it is K < 0.2.

  8. Study the formation of metastable crystalline phases from amorphous metallic systems with an integrated approach

    NASA Astrophysics Data System (ADS)

    Ye, Zhuo; Zhang, Feng; Sun, Yang; Mendelev, Mikhail; Ott, Ryan; Park, Eun-Soo; Besser, Matt; Kramer, Matt; Wang, Cai-Zhuang; Ho, Kai-Ming

    2015-03-01

    An efficient genetic algorithm (GA) is integrated with experimental diffraction data to solve a metastable Al20Sm4 phase that evolves during rapid solidification of an amorphous Al-10%Sm alloy produced by magnetron sputtering. The excellent match between calculated and experimental X-ray diffraction patterns confirms that this new phase appeared in the crystallization of the alloy. We discover the strong similarity of the underlying atomic structure between the amorphous alloy and this phase. Both phases share the same Sm-centered motif, providing a low-barrier pathway to form this Al20Sm4phase in the glass matrix at low temperatures. Molecular dynamic simulations of crystal growth from the liquid phase predict the formation of disordered anti-site defects in the devitrified crystal.

  9. Lyman-{alpha} radiation of a metastable hydrogen beam to measure electric fields

    SciTech Connect

    Lejeune, A.; Cherigier-Kovacic, L.; Doveil, F.

    2011-10-31

    The interaction between a metastable H(2s) atomic hydrogen beam and an external electric field leads to the emission of the Lyman-{alpha} line. It originates in the Stark mixing of the near-degenerate 2s{sub 1/2} and 2p{sub 1/2} levels separated by the Lamb shift. The quenched radiation proportional to the square of the electric field amplitude is recovered in vacuum by using such an atomic probe beam. We observe the strong enhancement of the signal when the field is oscillating at the Lamb shift frequency. This technique is applied in a plasma, offering an alternative way to measure weak electric fields by direct and non-intrusive means.

  10. Petroleum, oil field waters, and authigenic mineral assemblages - Are they in metastable equilibrium in hydrocarbon reservoirs?

    NASA Astrophysics Data System (ADS)

    Helgeson, Harold C.; Knox, Annette M.; Owens, Christine E.; Shock, Everett L.

    1993-07-01

    The hypothesis that although the presence of carboxylic acids and carboxylate anions in oil field waters is commonly attributed to the thermal maturation of kerogen or bacterial degradation of hydrocarbons during water-washing of petroleum in relatively shallow reservoirs, they may have also been produced in deeper reservoirs by the hydrolysis of hydrocarbons in petroleum at the oil-water interface is tested. Calculations were carried out to determine the distribution of species with the minimum Gibbs free energy in overpressured oil field waters in the Texas Gulf Coast assuming metastable equilibrium among calcite, albite, and a representative spectrum of organic and inorganic aqueous species at reservoir temperatures and pressures. The hypothesis that homogeneous equilibrium obtains among carboxylate and carbonate species in oil field waters is confirmed.

  11. Fatigue Crack Growth Behavior of Metastable Austenitic Stainless Steel in Cryogenic High Magnetic Field Environments

    NASA Astrophysics Data System (ADS)

    Shindo, Yasuhide; Takeda, Tomo; Suzuki, Masato; Narita, Fumio

    2009-08-01

    This article studies the fatigue crack growth in a metastable austenitic stainless steel in cryogenic high magnetic field environments. Fatigue crack growth tests were performed with the compact tension (CT) specimens at liquid helium temperature (4 K) in magnetic fields of 0 and 6 T, and the crack growth rate data were expressed in terms of the J-integral range during fatigue loading. The J-integral range values were evaluated using an elastic-plastic finite element analysis. The measurement of martensite phase in the test specimens and the fractographic examination were also carried out. The high magnetic field effect on the fatigue crack growth rate properties at 4 K is discussed in detail.

  12. Rare transitions between metastable states in the stochastic Chaffee-Infante equation.

    NASA Astrophysics Data System (ADS)

    Rolland, Joran; Bouchet, Freddy; Simonnet, Eric

    2015-04-01

    We present a numerical and theoretical study of the transitions in the Stochastic one dimensional Chaffee-Infante equation. The one dimensional Chaffee-Infante equation, also know as the Ginzburg-Landau or Allen-Cahn equation in physics, is the prototype equation for bistability in extended systems. As such, it is the perfect model equation for the test of numerical or theoretical methods intended at investigating metastability in more complex stochastic partial differential equations ; typically those arising in oceanicl fluid dynamics. Among other examples, one can think of the alternance of meander paths of the Kuroshio current near Japan, or the switching of the thermohaline circulation in the north Atlantic ocean. The reactive trajectories, the realisations of the dynamics that actually evolve from one metastable state to the other, are the central events in such studies. The novelty and originality of our approach is the combination of theoretical approaches with a novel numerical method, Adaptive Multilevel Splitting (AMS), for the computation of the full distribution of reactive trajectories and all the properties of the rare transitions. AMS is a mutation selection/selection algorithm that uses N clones dynamics of the system of interest, and only requires N|ln(α)| iterations. Meanwhile several 1/α realisations are required for a direct numerical simulation (with α the probability of observing a transition). It thus becomes a very powerful method when the noise amplitude and therefore α goes to zero. We used the algorithm to compute the properties (escape probability, mean first passage time, average duration of reactive trajectories, number of fronts etc.) of the transition in the full parameter space (L,β) (with L the size of the system and β the inverse of the noise amplitude). There is an excelent quantitative agreement with the various theoretical approaches of the study of metastability. All of them are asymptotic and therefore concern only

  13. Current-limited imposed-potential technique for inducing and monitoring metastable pitting events

    SciTech Connect

    Wall, F.D.

    1999-11-24

    A technique has been developed to selectively induce metastable pitting while preventing the transition to stable pit growth. The current-limited imposed-potential (CLIP) technique limits available cathodic current to an initiated site using a resistor in series with the working electrode to form a voltage divider. Potentiodynamic CLIP testing yields a distribution of breakdown potentials from a single experiment. Potentiostatic CLIP testing yields induction time data, which can be used as input to a calculation of germination rate. Initial data indicate that a one-to-one correlation exists between electrochemical transients and observed pitting sites. The CLIP technique provides a consistent means of gathering quantitative potential and current transients associated with localized oxide breakdown.

  14. Effects of metastable species in helium and argon atmospheric pressure plasma jets (APPJs) on inactivation of periodontopathogenic bacteria

    NASA Astrophysics Data System (ADS)

    Yoon, Sung-Young; Kim, Kyoung-Hwa; Seol, Yang-Jo; Kim, Su-Jeong; Bae, Byeongjun; Huh, Sung-Ryul; Kim, Gon-Ho

    2016-05-01

    The helium and argon have been widely used as discharge gases in atmospheric pressure plasma jets (APPJs) for bacteria inactivation. The APPJs show apparent different in bullet propagation speed and bacteria inactivation rate apparently vary with discharge gas species. This work shows that these two distinctive features of APPJs can be linked through one factor, the metastable energy level. The effects of helium and argon metastable species on APPJ discharge mechanism for reactive oxygen nitrogen species (RONS) generation in APPJs are investigated by experiments and numerical estimation. The discharge mechanism is investigated by using the bullet velocity from the electric field which is obtained with laser induced fluorescence (LIF) measurement. The measured electric field also applied on the estimation of RONS generation, as electron energy source term in numerical particle reaction. The estimated RONS number is verified by comparing NO and OH densities to the inactivation rate of periodontitis bacteria. The characteristic time for bacteria inactivation of the helium-APPJ was found to be 1.63 min., which is significantly less than that of the argon-APPJ, 12.1 min. In argon-APPJ, the argon metastable preserve the energy due to the lack of the Penning ionization. Thus the surface temperature increase is significantly higher than helium-APPJ case. It implies that the metastable energy plays important role in both of APPJ bullet propagation and bacteria inactivation mechanism.

  15. ``EL2'' revisited: Observation of metastable and stable energy levels of EL2 in semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Kabiraj, D.; Ghosh, Subhasis

    2005-12-01

    By using a combination of detailed experimental studies, we identify the metastable and stable energy levels of EL2 in semi-insulating GaAs. These results are discussed in light of the recently proposed models for EL2 in GaAs.

  16. Investigation of metastable production in a closed-cell dielectric capillary variable pressure He plasma jet with Ar admixture

    NASA Astrophysics Data System (ADS)

    Sands, Brian; Ganguly, Biswa

    2011-10-01

    For plasma processing applications of streamer-like atmospheric pressure plasma jets generated in a dielectric capillary, we have demonstrated that an admixture of Ar to the He gas flow greatly increases the lifetime of energetic species in the core flow through enhanced afterglow production of Ar 1s5 metastable species. To study this effect in more detail, we have used a closed-cell plasma jet that allows control over the background gas pressure and composition. We used a 20 ns risetime positive unipolar voltage pulse for excitation. A He flow with a 0-30% Ar admixture was studied using time-resolved emission and tunable diode laser absorption spectroscopy of the Ar 1s5 and He 23S metastable states. Nitrogen was used as the background gas. In pure He and pure Ar gases the He and Ar metastables respectively are produced in the first ~100 ns only in the active discharge. With Ar added to the He gas flow, He metastables produced in the active discharge are quickly quenched via Penning ionization of Ar while Ar 1s5 is enhanced over 1-2 μs in the afterglow, increasing the number density as high as 1013/cc and extending the effective lifetime up to 10 μs. This implies that He heavy particle kinetics are a key driver of enhanced afterglow plasma chemistry in plasma jets with rare gas mixtures.

  17. An oscillator circuit to produce a radio-frequency discharge and application to metastable helium saturated absorption spectroscopy

    SciTech Connect

    Moron, F.; Hoendervanger, A. L.; Bonneau, M.; Bouton, Q.; Aspect, A.; Boiron, D.; Clement, D.; Westbrook, C. I.

    2012-04-15

    We present a rf gas discharge apparatus which provides an atomic frequency reference for laser manipulation of metastable helium. We discuss the biasing and operation of a Colpitts oscillator in which the discharge coil is part of the oscillator circuit. Radiofrequency radiation is reduced by placing the entire oscillator in a metal enclosure.

  18. Determination of collisional quenching rate coefficients of metastable nitrogen molecules by air pollutants

    NASA Astrophysics Data System (ADS)

    Suzuki, Susumu; Itoh, Haruo

    2009-10-01

    It has already been investigated on the determination of the collisional quenching rate coefficients of the metastable nitrogen molecules N2(A^3σu^+ ) by some air pollutants [1] in our laboratory. In this report, we present the result on the collisional quenching rate coefficient of N2(A^3σu^+ ) by formaldehyde (CH2O) using a theoretical procedure that takes into account the reflection of metastables at the boundary. As far as we know, this report is the first result of the collisional quenching rate coefficients of N2(A^3σu^+ ) by CH2O. Formaldehyde is a colorless gas with the foul odor, and elements of the adhesive, paints, and preservative, etc. It is widely used for construction materials such as houses, because it is low cost. It is released from paint of construction materials in air, and, in that case, it is known as one of the causative agents of so-called ``Sick building syndrome'' to influence the human body harmfully even if it is a low concentration. The obtained collisional quenching rate coefficient of N2(A^3σu^+ ) by CH2O is (4.7±0.4) x 10-12 cm^3/s. Because the collisional quenching rate coefficient by CH2O is large, it is understood that CH2O receives energy easily from N2(A^3σu^+ ). In addition, we reports on the obtained collisional quenching rate coefficient of N2(A^3σu^+ ) by some air pollutants. [1] S. Suzuki, T.Suzuki and H.Itoh: Proc. of XXVIII ICPIG (Prague, Czech Republic), (2007) 1P01-40.

  19. Metastable liquid-liquid coexistence and density anomalies in a core-softened fluid

    NASA Astrophysics Data System (ADS)

    Gibson, H. M.; Wilding, N. B.

    2006-06-01

    Linearly sloped or “ramp” potentials belong to a class of core-softened models which possess a liquid-liquid critical point (LLCP) in addition to the usual liquid-gas critical point. Furthermore, they exhibit thermodynamic anomalies in their density and compressibility, the nature of which may be akin to those occurring in water. Previous simulation studies of ramp potentials have focused on just one functional form, for which the LLCP is thermodynamically stable. In this work we construct a series of ramp potentials, which interpolate between this previously studied form and a ramp-based approximation to the Lennard-Jones (LJ) potential. By means of Monte Carlo simulation, we locate the LLCP, the first order high density liquid (HDL)-low density liquid (LDL) coexistence line, and the line of density maxima for a selection of potentials in the series. We observe that as the LJ limit is approached, the LLCP becomes metastable with respect to freezing into a hexagonal close packed crystalline solid. The qualitative nature of the phase behavior in this regime shows a remarkable resemblance to that seen in simulation studies of accurate water models. Specifically, the density of the liquid phase exceeds that of the solid; the gradient of the metastable LDL-HDL line is negative in the pressure (p) -temperature (T) plane; while the line of density maxima in the p-T plane has a shape similar to that seen in water and extends into the stable liquid region of the phase diagram. As such, our results lend weight to the “second critical point” hypothesis as an explanation for the anomalous behavior of water.

  20. Particle energy distributions and metastable atoms in transient low pressure interpulse microwave plasma

    NASA Astrophysics Data System (ADS)

    Pandey, Shail; Nath Patel, Dudh; Ram Baitha, Anuj; Bhattacharjee, Sudeep

    2015-12-01

    The electron energies and its distribution function are measured in non-equilibrium transient pulsed microwave plasmas in the interpulse regime using a retarding field electron energy analyzer. The plasmas are driven to different initial conditions by varying the electromagnetic (EM) wave pulse duration, peak power, or the wave frequency. Two cases of wave excitation are investigated: (i) short-pulse (pulse duration, t w ~ 1 μs), high-power (~60 kW) waves of 9.45 GHz and (ii) medium-pulse (t w ~ 20 μs), and moderate power waves of ~3 kW at 2.45 GHz. It is found that high-power, short-duration pulses lead to a significantly different electron energy probability function (EEPF) in the interpulse phase—a Maxwellian with a bump on the tail, although the average energy per pulse (~60 mJ) is maintained the same in the two modes of wave excitation. Electrons with energies  >250 eV are found to exist in the discharge in the both cases. Another subset of experiments is performed to delineate the effect of the wave frequency and the peak power on EEPF. A traveling wave tube (TWT) amplifier based microwave source for generating pulsed plasma (t w  =  230 μs) in a wide frequency range (6-18 GHz) is employed for this purpose. Further experiments on measurements of metastable density using optical emission spectroscopy and ion energy analyzer have been carried out. By tailoring the EEPF of the transient plasma and metastable densities, new applications in plasma processing, chemistry and biology can be realized in the interpulse phase of the discharge.

  1. Metastable crystalline and amorphous structures formed in the Cu-W system by vapor deposition

    NASA Astrophysics Data System (ADS)

    Rizzo, H. F.; Massalski, T. B.; Nastasi, M.

    1993-05-01

    The possibility of producing nonequilibrium amorphous and crystalline phases in the Cu-W system is of interest because, under equilibrium conditions, no mutual solubility is expected between Cu and W. Triode sputtered coatings (45 to 150 μm thick, produced at deposition rates between 20 and 150 Å/s) consisted of amorphous and metastable crystalline phases. The latter remained decomposition-resistant on heating to various temperatures between 340 °C and 600 °C (the maximum temperature of exposure). The amorphous phase in such coatings crystallized on heating into a metastable body-centered cubic (bcc) phase, and the crystallization temperature T x was found to decrease across the phase diagram from 450 °C to 340 °C as the percentage of W increased from 26 to 60 at. pct. Samples containing amorphous phase regions, when subjected to heating between 150 °C and 250 °C, showed an unusual rapid precipitation of Cu at the sample surface, indicating an easy diffusion of the Cu component. This occurred without crystallization of the remaining slightly tungsten-enriched amorphous matrix. Microhardness measurements in sputtered two-phase amorphous and bcc regions have shown that in alloys of the same composition, the amorphous phase was always softer than the bcc solid solution phase. X-ray, microprobe, and optical evidence suggests that the amorphous films deposited at very low temperatures (i.e., at liquid N2) may subsequently undergo a phase separation upon heating to room temperature and prior to crystallization. Earlier work and present studies of vapordeposited alloys in this system confirm that the observed phases and microstructures can be related to free energy trends estimated from thermodynamic considerations and to specific deposition parameters, such as the substrate temperature and the deposition rates, which influence the kinetics.

  2. Anatase (101)-like Structural Model Revealed for Metastable Rutile TiO2(011) Surface.

    PubMed

    Xu, Meiling; Shao, Sen; Gao, Bo; Lv, Jian; Li, Quan; Wang, Yanchao; Wang, Hui; Zhang, Lijun; Ma, Yanming

    2017-03-08

    Titanium dioxide has been widely used as an efficient transition metal oxide photocatalyst. However, its photocatalytic activity is limited to the ultraviolet spectrum range due to the large bandgap beyond 3 eV. Efforts to reduce the bandgap to achieve a broader spectrum range of light absorption have been successfully attempted via the experimental synthesis of dopant-free metastable surface structures of rutile-type TiO2 (011) 2 × 1. This new surface phase possesses a reduced bandgap of ∼2.1 eV, showing great potential for an excellent photocatalyst covering a wide range of visible light. There is a need to establish the atomistic structure of this metastable surface to understand the physical cause for the bandgap reduction and to improve the future design of photocatalysts. Here, we report computational investigations in an effort to unravel this surface structure via swarm structure-searching simulations. The established structure adopts the anatase (101)-like structure model, where the topmost 2-fold O atoms form a quasi-hexagonal surface pattern and bond with the unsaturated 5-fold and 4-fold Ti atoms in the next layer. The predicted anatase (101)-like surface model can naturally explain the experimental observation of the STM images, the electronic bandgap, and the oxidation state of Ti(4+). Dangling bonds on the anatase (101)-like surface are abundant making it a superior photocatalyst. First-principles molecular dynamics simulations have supported the high photocatalytic activity by showing that water and formic acid molecules dissociate spontaneously on the anatase (101)-like surface.

  3. Constraining kinetics of metastable olivine in the Marianas slab from seismic observations and dynamic models

    NASA Astrophysics Data System (ADS)

    Quinteros, Javier; Sobolev, Stephan V.

    2012-03-01

    Transformation kinetics associated with the presence of a metastable olivine wedge in old and fast subducting slabs has been the subject of many studies in the last years. Even with improvements in kinetics models, many of the parameters are still not well constrained. In particular, there is no consensus on the blocking temperature that could inhibit the transformation from olivine to spinel. Recently, based on anomalous later phases in the P wave coda and differential P wave slowness, a wedge of metastable olivine was detected in the Marianas subduction zone, that is approximately 25 km wide, at a depth of 590 km and is truncated at 630 km. In this work, a thermomechanical model was used to mimic the subduction in the Marianas and try different blocking temperatures for the olivine/spinel transformation. The model includes, among other features, non-linear elasto-visco-plastic rheology based on laboratory data, phase transformations, latent heat, proper coupling between stress and thermal state of the slab and force balance of the system. The results show a positive correlation between the blocking temperature, depth of the wedge and its distance from the trench (or subduction angle). We compare these results to the situation in the Marianas and suggest that a blocking temperature for the olivine/spinel transformation of approximately 725 °C would be the most likely. The volume of the wedge presents some oscillations that we relate to a runaway effect of the transformation kinetics in the mantle transition zone. Namely, the interaction between latent heat release and the advection of the isotherms due to the subduction velocity. The inclusion of shear heating in the model was fundamental to modeling such a subduction zone. Without shear heating, the slab shows a higher level of internal stress and the necessary bending to mimic the Marianas subduction zone cannot be reached.

  4. Emergence of Metastable State Dynamics in Interconnected Cortical Networks with Propagation Delays

    PubMed Central

    Kutchko, Katrina M.; Fröhlich, Flavio

    2013-01-01

    The importance of the large number of thin-diameter and unmyelinated axons that connect different cortical areas is unknown. The pronounced propagation delays in these axons may prevent synchronization of cortical networks and therefore hinder efficient information integration and processing. Yet, such global information integration across cortical areas is vital for higher cognitive function. We hypothesized that delays in communication between cortical areas can disrupt synchronization and therefore enhance the set of activity trajectories and computations interconnected networks can perform. To evaluate this hypothesis, we studied the effect of long-range cortical projections with propagation delays in interconnected large-scale cortical networks that exhibited spontaneous rhythmic activity. Long-range connections with delays caused the emergence of metastable, spatio-temporally distinct activity states between which the networks spontaneously transitioned. Interestingly, the observed activity patterns correspond to macroscopic network dynamics such as globally synchronized activity, propagating wave fronts, and spiral waves that have been previously observed in neurophysiological recordings from humans and animal models. Transient perturbations with simulated transcranial alternating current stimulation (tACS) confirmed the multistability of the interconnected networks by switching the networks between these metastable states. Our model thus proposes that slower long-range connections enrich the landscape of activity states and represent a parsimonious mechanism for the emergence of multistability in cortical networks. These results further provide a mechanistic link between the known deficits in connectivity and cortical state dynamics in neuropsychiatric illnesses such as schizophrenia and autism, as well as suggest non-invasive brain stimulation as an effective treatment for these illnesses. PMID:24204238

  5. The Controller Synthesis of Metastable Oxides Utilizing Epitaxy and Epitaxial Stabilization

    SciTech Connect

    Schlom, Darrell

    2003-12-02

    Molecular beam epitaxy (MBE) has achieved unparalleled control in the integration of semiconductors at the nanometer. These advances were made through the use of epitaxy, epitaxial stabilization, and a combination of composition-control techniques including adsorption-controlled growth and RHEED-based composition control that we have developed, understood, and utilized for the growth of oxides. Also key was extensive characterization (utilizing RHEED, four-circle x-ray diffraction, AFM, TEM, and electrical characterization techniques) in order to study growth modes, optimize growth conditions, and probe the structural, dielectric, and ferroelectric properties of the materials grown. The materials that we have successfully engineered include titanates (PbTiO3, Bi4Ti3O12), tantalates (SrBi2Ta2O9), and niobates (SrBi2Nb2O9); layered combinations of these perovskite-related materials (Bi4Ti3O12-SrTiO3 and Bi4Ti3O12-PbTiO3 Aurivillius phases and metastable PbTiO3/SrTiO3 and BaTiO3/SrTiO3 superlattices), and new metastable phases (Srn+1TinO3n+1 Ruddlesden-Popper phases). The films were grown by reactive MBE and pulsed laser deposition (PLD). Many of these materials are either new or have been synthesized with the highest perfection ever reported. The controlled synthesis of such layered oxide heterostructures offers great potential for tailoring the superconducting, ferroelectric, and dielectric properties of these materials. These properties are important for energy technologies.

  6. New thermo-kinetic models of olivine metastability in subducting lithosphere: implications for deep-focus earthquakes

    NASA Astrophysics Data System (ADS)

    Mosenfelder, J. L.; Marton, F. C.; Rubie, D. C.

    2001-12-01

    A shear instability postulated to occur during the transformation of metastable olivine to its high-pressure polymorphs, wadsleyite and ringwoodite, has been proposed as the mechanism for deep-focus earthquakes. In order to evaluate this possibility we have formulated updated thermo-kinetic models to predict the amount of metastable olivine in a variety of subduction zones. Our models use newly derived activation energy parameters based on recent experiments in the (Mg,Fe)2SiO4 system, and we incorporate latent heat feedback due to the transformation into both the kinetics and the thermal model. We also consider the effects of transformation stress on growth kinetics and intracrystalline transformation, previously thought to be important only at high shear stresses. Our modeling predicts substantially smaller metastable olivine wedges than previous models that did not properly account for latent heat (Kirby et al., 1996) or used older kinetic parameters (e.g. Daessler et al., 1996; Devaux et al., 1997). Results of models considering only grain boundary nucleation and growth include the following: 1) In subduction zones with a thermal parameter (φ = vertical convergence rate ¥ age of the lithosphere at the trench) less than ~5000 km, no significant metastable olivine wedge develops; this includes the Nazca subduction zone, in which the 1994 Bolivian earthquake occurred at a depth of 630 km. 2) For subduction zones such as Izu-Bonin, the Marianas, and Eastern Indonesia, with φ in the range 6000-10000 km, our models predict a maximum depth of metastability of 450-500 km. The maximum depths of earthquakes in these subduction zones are, respectively, 550, 670 and 670 km (e.g., Kirby et al, 1996). 3) In Tonga, the subduction zone with the most rapid convergence rates on Earth, an olivine wedge may persist to depths >660 km only if trench rollback (due to back-arc spreading) is taken into account. This depth is reduced by 80-120 km if trench rollback is not considered

  7. Silver nanoplates with ground or metastable structures obtained from template-free two-phase aqueous/organic synthesis

    SciTech Connect

    Zhelev, Doncho V. Zheleva, Tsvetanka S.

    2014-01-28

    Silver has unique electrical, catalytic, and plasmonic characteristics and has been widely sought for fabrication of nanostructures. The properties of silver nanostructures are intimately coupled to the structure of silver crystals. Two crystal structures are known for silver: the stable (ground) state cubic face centered 3C-Ag structure and the metastable hexagonal 4H-Ag structure. Recently, Chackraborty et al. [J. Phys.: Condens. Matter 23, 325401 (2011)] discovered a low density, highly reactive metastable hexagonal 2H-Ag structure accessible during electrodeposition of silver nanowires in porous anodic alumina templates. This 2H-Ag structure has enhanced electrical and catalytic characteristics. In the present work we report template-free synthesis of silver nanoplates with the metastable 2H-Ag crystal structure, which appears together with the ground 3C-Ag and the metastable 4H-Ag structures in a two-phase solution synthesis with citric acid as the capping agent. The capacity of citric acid to stabilize both the stable and the metastable structures is explained by its preferential binding to the close packed facets of Ag crystals, which are the (111) planes for 3C-Ag and the (0001) planes for 4H-Ag and 2H-Ag. Nanoplate morphology and structure are characterized using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The synthesized nanoplates have thickness from 15 to 17 nm and edge length from 1 to 10 μm. Transmission electron microscopy selected area electron diffraction is used to uniquely identify and distinguish between nanoplates with 2H-Ag or 4H-Ag or 3C-Ag structures.

  8. Deep Metastable Eutectic Nanometer-Scale Particles in the MgO-Al2O3-SiO2 System

    NASA Technical Reports Server (NTRS)

    Reitmeijer, Frans J. M.; Nash, J. A., III

    2011-01-01

    Laboratory vapor phase condensation experiments systematically yield amorphous, homogeneous, nanoparticles with unique deep metastable eutectic compositions. They formed during the nucleation stage in rapidly cooling vapor systems. These nanoparticles evidence the complexity of the nucleation stage. Similar complex behavior may occur during the nucleation stage in quenched-melt laboratory experiments. Because of the bulk size of the quenched system many of such deep metastable eutectic nanodomains will anneal and adjust to local equilibrium but some will persist metastably depending on the time-temperature regime and melt/glass transformation.

  9. Measured density of copper atoms in the ground and metastable states in argon magnetron discharge correlated with the deposition rate

    NASA Astrophysics Data System (ADS)

    Naghshara, H.; Sobhanian, S.; Khorram, S.; Sadeghi, N.

    2011-01-01

    In a dc-magnetron discharge with argon feed gas, densities of copper atoms in the ground state Cu(2S1/2) and metastable state Cu*(2D5/2) were measured by the resonance absorption technique, using a commercial hollow cathode lamp as light source. The operating conditions were 0.3-14 µbar argon pressure and 10-200 W magnetron discharge power. The deposition rate of copper in a substrate positioned at 18 cm from the target was also measured with a quartz microbalance. The gas temperature, in the range 300-380 K, was deduced from the emission spectral profile of N2(C 3Πu - B 3Πg) 0-0 band at 337 nm when trace of nitrogen was added to the argon feed gas. The isotope-shifts and hyperfine structures of electronic states of Cu have been taken into account to deduce the emission and absorption line profiles, and hence for the determination of atoms' densities from the measured absorption rates. To prevent error in the evaluation of Cu density, attributed to the line profile distortion by auto-absorption inside the lamp, the lamp current was limited to 5 mA. Density of Cu(2S1/2) atoms and deposition rate both increased with the enhanced magnetron discharge power. But at fixed power, the copper density augmented with argon pressure whereas the deposition rate followed the opposite trend. Whatever the gas pressure, the density of Cu*(2D5/2) metastable atoms remained below the detection limit of 1 × 1010 cm-3 for magnetron discharge powers below 50 W and hence increased much more rapidly than the density of Cu(2S1/2) atoms, over passing this later at some discharge power, whose value decreases with increasing argon pressure. This behaviour is believed to result from the enhancement of plasma density with increasing discharge power and argon pressure, which would increase the excitation rate of copper into metastable states. At fixed pressure, the deposition rate followed the same trend as the total density of copper atoms in the ground and metastable states. Two important

  10. Calculation of the relative metastabilities of proteins in subcellular compartments of Saccharomyces cerevisiae

    PubMed Central

    Dick, Jeffrey M

    2009-01-01

    Background Protein subcellular localization and differences in oxidation state between subcellular compartments are two well-studied features of the the cellular organization of S. cerevisiae (yeast). Theories about the origin of subcellular organization are assisted by computational models that can integrate data from observations of compositional and chemical properties of the system. Presentation and implications of the hypothesis I adopt the hypothesis that the state of yeast subcellular organization is in a local energy minimum. This hypothesis implies that equilibrium thermodynamic models can yield predictions about the interdependence between populations of proteins and their subcellular chemical environments. Testing the hypothesis Three types of tests are proposed. First, there should be correlations between modeled and observed oxidation states for different compartments. Second, there should be a correspondence between the energy requirements of protein formation and the order the appearance of organelles during cellular development. Third, there should be correlations between the predicted and observed relative abundances of interacting proteins within compartments. Results The relative metastability fields of subcellular homologs of glutaredoxin and thioredoxin indicate a trend from less to more oxidizing as mitochondrion – cytoplasm – nucleus. Representing the overall amino acid compositions of proteins in 23 different compartments each with a single reference model protein suggests that the formation reactions for proteins in the vacuole (in relatively oxidizing conditions), ER and early Golgi (in relatively reducing conditions) are relatively highly favored, while that for the microtubule is the most costly. The relative abundances of model proteins for each compartment inferred from experimental data were found in some cases to correlate with the predicted abundances, and both positive and negative correlations were found for some assemblages

  11. Metastable non-runaway states near the inner edge of the habitable zone

    NASA Astrophysics Data System (ADS)

    Pierrehumbert, R.

    2012-12-01

    The classic runaway greenhouse requires the absorbed solar radiation to exceed a threshold (called by some the Kombayashi-Ingersoll limit) which consists of the asymptotic OLR for a saturated atmosphere in the limit of high surface temperature. However, there are situations in which the limit can be exceeded and a runaway can be sustained, but in which the system nonetheless has a metastable non-runaway state, i.e. a state which is stable to sufficiently small perturbations but which will go into a runaway if given a sufficiently large perturbation on the warm side. I will review the types of processes that can lead to the existence of such states. These processes include subsaturation, clouds, and admixture of a noncondensible background gas which has a weak greenhouse effect compared to the condensible gas. In this talk, I will focus on the first two of these. The key controlling factor is that, for water vapor on a planet with Earthlike gravity, essentially all of the radiation to space comes from the water vapor window and originates in the upper 50 hPa of the atmosphere. It is argued that even in a hot climate, substantial subsaturation can be maintained at these levels; the key question for metastability is whether the subsaturation at these levels becomes asymptotically independent of surface temperature. I will also quantitative discuss the effect of clouds on the runaway, and point out that in order for clouds to facilitate a runaway, they must consist of sufficiently large particles and be concentrated in the upper 50 hPa of the atmosphere. Finally, I will discuss the effect of clouds deeper in the atmosphere, which act almost exclusively to increase the albedo and inhibit the runaway. This discussion will be complemented by a brief discussion of the microphysics and dynamics that govern the character of such clouds in a water-vapor dominated atmosphere. In this talk, the main application discussed is to the water vapor runaway near the inner edge of the

  12. Quench-Condensed Microalloyed Particles: a Microscopic View of Solid Solubility and Metastability

    NASA Astrophysics Data System (ADS)

    Lamberti, Vincent Edward

    Solid solubility and metastability in noble-metal and iron-silver alloys have been studied from the perspective of microalloyed particles. Samples were obtained through a novel, gram-scale technique that consisted of cocondensation of two elemental metal vapors with a large excess of inert gas on the reaction surface of a rotating cryostat at 77 K. This technique permitted greater control of both particle size and composition than conventional gas aggregation methods. The chemical and physical characteristics of the microalloys have been elaborated through chemical analysis, x-ray diffraction, electron microscopy, temperature-programmed mass spectrometry, EXAFS, XPS and Moessbauer spectroscopy. Electron microscopy indicated the microstructures of copper-gold and copper-silver microalloys prepared in sulfur hexafluoride to consist of discrete collections of crystallites suspended in amorphous "baths". The average dimensions of the crystallites were <100 A, while the aggregates spanned hundreds of nanometers. The microstructures of both systems were metastable. The EXAFS of a copper-silver microalloy showed it to be stiffer, as well as more disordered, than a homometallic copper product. The EXAFS also showed no detectable Cu-Ag contacts, but suggested the existence (through a "missing-atom" effect) of a large number of disordered copper sites. Moessbauer spectra of an iron -silver microalloy prepared in xenon revealed the presence of a superparamagnetic alloy phase characterized by a blocking temperature of approximately 45 K. Cocondensations of iron vapor with excess sulfur hexafluoride produced ultrafine (dimensions ~ 100 A), amorphous particles that were decorated with a -CF_{2^-} polymer. The formation of the polymer was attributed to reaction of the iron with the matrix and adventitious organic compounds--that is, to activation of S-F and C-H bonds. Matrix isolation experiments indicated that, although inert in their ground-state configuration, photoexcited (4p

  13. Phase Transition and Dynamics in Imidazolium-Based Ionic Liquid Crystals through a Metastable Highly Ordered Smectic Phase.

    PubMed

    Nozaki, Yoko; Yamaguchi, Keito; Tomida, Kenji; Taniguchi, Natsumi; Hara, Hironori; Takikawa, Yoshinori; Sadakane, Koichiro; Nakamura, Kenji; Konishi, Takashi; Fukao, Koji

    2016-06-16

    The phase transition behavior and dynamics of ionic liquid crystals, 1-methyl-3-alkylimidazolium tetrafluoroborate with various alkyl chain lengths, were investigated by X-ray scattering, differential scanning calorimetry, optical microscopy, and dielectric relaxation spectroscopy to elucidate the mechanism of their structural and phase changes. A metastable phase was found to appear via a supercooled smectic phase on cooling. In the metastable phase, disorder in the smectic phase is partially frozen; thus, the phase has order higher than that of the smectic phase but lower than that of the crystalline phase. During the subsequent heating process, the frozen disorder activates, and a crystalline phase appears in the supercooled smectic phase before entering the smectic phase. The relationship between the phase behavior and the dynamics of charge carriers such as ions is also discussed.

  14. Multicriticality, metastability, and the roton feature in Bose-Einstein condensates with three-dimensional spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Liao, Renyuan; Fialko, Oleksandr; Brand, Joachim; Zülicke, Ulrich

    2015-10-01

    We theoretically study homogeneously trapped atomic Bose-Einstein condensates where all three-momentum components couple to a pseudo-spin-1/2 degree of freedom. Tuning the anisotropies of spin-orbit coupling and the spin-dependent interactions is shown to provide access to a rich phase diagram with a tetracritical point, first-order phase transitions, and multiple metastable phases of stripe and plane-wave character. The elementary excitation spectrum of the axial plane-wave phase features an anisotropic roton feature and can be used to probe the phase diagram. In addition to providing a versatile laboratory for studying fundamental concepts in statistical physics, the emergence of metastable phases creates new opportunities for observing false-vacuum decay and bubble nucleation in ultracold-atom experiments.

  15. Exploration of metastability and hidden phases in correlated electron crystals visualized by femtosecond optical doping and electron crystallography

    PubMed Central

    Han, Tzong-Ru T.; Zhou, Faran; Malliakas, Christos D.; Duxbury, Phillip M.; Mahanti, Subhendra D.; Kanatzidis, Mercouri G.; Ruan, Chong-Yu

    2015-01-01

    Characterizing and understanding the emergence of multiple macroscopically ordered electronic phases through subtle tuning of temperature, pressure, and chemical doping has been a long-standing central issue for complex materials research. We report the first comprehensive studies of optical doping–induced emergence of stable phases and metastable hidden phases visualized in situ by femtosecond electron crystallography. The electronic phase transitions are triggered by femtosecond infrared pulses, and a temperature–optical density phase diagram is constructed and substantiated with the dynamics of metastable states, highlighting the cooperation and competition through which the macroscopic quantum orders emerge. These results elucidate key pathways of femtosecond electronic switching phenomena and provide an important new avenue to comprehensively investigate optical doping–induced transition states and phase diagrams of complex materials with wide-ranging applications. PMID:26601190

  16. Dimensional effects and scalability of Meta-Stable Dip (MSD) memory effect for 1T-DRAM SOI MOSFETs

    NASA Astrophysics Data System (ADS)

    Hubert, A.; Bawedin, M.; Cristoloveanu, S.; Ernst, T.

    2009-12-01

    The difficult scaling of bulk Dynamic Random Access Memories (DRAMs) has led to various concepts of capacitor-less single-transistor (1T) architectures based on SOI transistor floating-body effects. Amongst them, the Meta-Stable Dip RAM (MSDRAM), which is a double-gate Fully Depleted SOI transistor, exhibits attractive performances. The Meta-Stable Dip effect results from the reduced junction leakage current and the long carrier generation lifetime in thin silicon film transistors. In this study, various devices with different gate lengths, widths and silicon film thicknesses have been systematically explored, revealing the impact of transistor dimensions on the MSD effect. These experimental results are discussed and validated by two-dimensional numerical simulations. It is found that MSD is maintained for small dimensions even in standard SOI MOSFETs, although specific optimizations are expected to enhance MSDRAM performances.

  17. Study on stable and meta-stable carbides in a high speed steel for rollers during tempering processes

    NASA Astrophysics Data System (ADS)

    Guo, Jing; Qu, Hong-wei; Liu, Li-gang; Sun, Yan-liang; Zhang, Yue; Yang, Qing-xiang

    2013-02-01

    A high speed steel (HSS) was studied for rollers in this work. The steel was quenched at 1150°C and tempered at 520°C. The phase structures of the steel were determined by X-ray diffraction (XRD), and the hardness of specimens was measured. The volume fraction of carbides was counted by Image-Pro Plus software. The typical microstructures were observed by field emission scanning electron microscope (FESEM). Stable and meta-stable carbides were deduced by removing the existing phases one by one in the Fe-C equilibrium calculation. It is found that the precipitated carbides are bulk-like MC, long stripe-like M2C, fishbone-like M6C, and daisy-like M7C3 during the tempering process. The stable carbides are MC and M6C, but the meta-stable ones are M2C, M7C3, and M3C.

  18. Theory of Metastable State Relaxation for Non-Critical Binary Systems with Non-Conserved Order Parameter

    NASA Technical Reports Server (NTRS)

    Izmailov, Alexander; Myerson, Allan S.

    1993-01-01

    A new mathematical ansatz for a solution of the time-dependent Ginzburg-Landau non-linear partial differential equation is developed for non-critical systems such as non-critical binary solutions (solute + solvent) described by the non-conserved scalar order parameter. It is demonstrated that in such systems metastability initiates heterogeneous solute redistribution which results in formation of the non-equilibrium singly-periodic spatial solute structure. It is found how the time-dependent period of this structure evolves in time. In addition, the critical radius r(sub c) for solute embryo of the new solute rich phase together with the metastable state lifetime t(sub c) are determined analytically and analyzed.

  19. Measurements of the populations of metastable and resonance levels in the plasma of an RF capacitive discharge in argon

    SciTech Connect

    Vasilieva, A. N.; Voloshin, D. G.; Kovalev, A. S. Kurchikov, K. A.

    2015-05-15

    The behavior of the populations of two metastable and two lower resonance levels of argon atoms in the plasma of an RF capacitive discharge was studied. The populations were measured by two methods: the method of emission self-absorption and the method based on measurements of the intensity ratios of spectral lines. It is shown that the populations of resonance levels increase with increasing power deposited in the discharge, whereas the populations of metastable levels is independent of the RF power. The distribution of the populations over energy levels is not equilibrium under these conditions. The population kinetics of argon atomic levels in the discharge plasma is simulated numerically. The distribution function of plasma electrons recovered from the measured populations of atomic levels and numerical simulations is found to be non-Maxwellian.

  20. Directing the self-assembly of block copolymers into a metastable complex network phase via a deep and rapid quench.

    PubMed

    Müller, Marcus; Sun, De-Wen

    2013-12-27

    The free-energy landscape of self-assembling block copolymer systems is characterized by a multitude of metastable minima. Using particle-based simulations of a soft, coarse-grained model, we explore opportunities to reproducibly direct the spontaneous ordering of these self-assembling systems into a metastable complex network morphology--specifically, Schoen's I-WP periodic minimal surface--starting from a highly unstable state that is generated by a rapid expansion. This process-directed self-assembly provides an alternative to fine-tuning molecular architecture or blending for fabricating complex network structures. Comparing our particle-based simulation results to recently developed free-energy techniques, we critically assess their ability to predict spontaneous formation and highlight the importance of nonequilibrium molecular conformations in the starting state and the local conservation of density.

  1. Classical Metastable Supersymmetry Breaking with D-Terms: Tree-Level Nests and Vacuum Towers

    SciTech Connect

    Dienes, Keith R.; Thomas, Brooks

    2010-02-10

    In this talk, we present three examples of new non-trivial vacuum structures that can occur in supersymmetric field theories, along with explicit models in which they arise. The first vacuum structure is one in which supersymmetry is broken at tree-level in a perturbative theory that also contains a supersymmetry-preserving ground state. Models realizing this structure are uniquely characterized by the fact that no flat directions appear in the classical potential, all vacua appear at finite distances in field space, and no non-perturbative physics is required for vacuum stability. The second non-trivial vacuum structure we discuss consists of large (and even infinite) towers of metastable vacua, and we show that models which give rise to such vacuum towers exhibit a rich set of instanton-induced vacuum tunneling dynamics. Finally, our third new non-trivial vacuum structure consists of an infinite number of degenerate vacua; this leads to a Bloch-wave ground state and a vacuum 'band' structure. Models with such characteristics therefore experience time-dependent vacuum oscillations. Needless to say, these novel vacuum structures lead to many new potential applications for supersymmetric field theories, ranging from the cosmological-constant problem to the string landscape, supersymmetry breaking, and Z' phenomenology.

  2. Metastable NaYF 4 fluorite at high pressures and high temperatures

    NASA Astrophysics Data System (ADS)

    Grzechnik, Andrzej; Bouvier, Pierre; Crichton, Wilson A.; Farina, Luca; Köhler, Jürgen

    2002-06-01

    High-pressure high-temperature behavior of metastable NaYF 4 fluorite (Fm 3¯m, Z=4), with the Na and Y atoms randomly distributed in the cationic sublattice, is studied with synchrotron angle-dispersive powder X-ray diffraction in diamond anvil (DAC) and large-volume Paris-Edinburgh cells and synthesis in a multi-anvil apparatus. The onset of a pressure-induced phase transition at room temperature takes place above 10 GPa as observed in DACs loaded with different hydrostatic and non-hydrostatic pressure media (nitrogen, paraffin oil, or ethanol:methanol media). In situ powder X-ray diffraction measurements in the Paris-Edinburgh cell and syntheses using the multi-anvil apparatus at high pressures and high temperatures show that the new polymorph is of the gagarinite-type (P6 3/m, Z=1) with partially ordered cations, the formula being Na 1.5Y 1.5F 6. This phase is structurally related to the Na 1.5Y 1.5F 6 modification (P 6¯, Z=1) stable at ambient conditions. At higher temperatures, the new pressure-induced hexagonal variant of NaYF 4 eventually decomposes into a non-stoichiometric gagarinite-like phase and yttrium fluoride YF 3 (Pnma, Z=4).

  3. Metastability, spectrum, and eigencurrents of the Lennard-Jones-38 network

    SciTech Connect

    Cameron, Maria K.

    2014-11-14

    We develop computational tools for spectral analysis of stochastic networks representing energy landscapes of atomic and molecular clusters. Physical meaning and some properties of eigenvalues, left and right eigenvectors, and eigencurrents are discussed. We propose an approach to compute a collection of eigenpairs and corresponding eigencurrents describing the most important relaxation processes taking place in the system on its way to the equilibrium. It is suitable for large and complex stochastic networks where pairwise transition rates, given by the Arrhenius law, vary by orders of magnitude. The proposed methodology is applied to the network representing the Lennard-Jones-38 cluster created by Wales's group. Its energy landscape has a double funnel structure with a deep and narrow face-centered cubic funnel and a shallower and wider icosahedral funnel. However, the complete spectrum of the generator matrix of the Lennard-Jones-38 network has no appreciable spectral gap separating the eigenvalue corresponding to the escape from the icosahedral funnel. We provide a detailed description of the escape process from the icosahedral funnel using the eigencurrent and demonstrate a superexponential growth of the corresponding eigenvalue. The proposed spectral approach is compared to the methodology of the Transition Path Theory. Finally, we discuss whether the Lennard-Jones-38 cluster is metastable from the points of view of a mathematician and a chemical physicist, and make a connection with experimental works.

  4. Metastability, spectrum, and eigencurrents of the Lennard-Jones-38 network.

    PubMed

    Cameron, Maria K

    2014-11-14

    We develop computational tools for spectral analysis of stochastic networks representing energy landscapes of atomic and molecular clusters. Physical meaning and some properties of eigenvalues, left and right eigenvectors, and eigencurrents are discussed. We propose an approach to compute a collection of eigenpairs and corresponding eigencurrents describing the most important relaxation processes taking place in the system on its way to the equilibrium. It is suitable for large and complex stochastic networks where pairwise transition rates, given by the Arrhenius law, vary by orders of magnitude. The proposed methodology is applied to the network representing the Lennard-Jones-38 cluster created by Wales's group. Its energy landscape has a double funnel structure with a deep and narrow face-centered cubic funnel and a shallower and wider icosahedral funnel. However, the complete spectrum of the generator matrix of the Lennard-Jones-38 network has no appreciable spectral gap separating the eigenvalue corresponding to the escape from the icosahedral funnel. We provide a detailed description of the escape process from the icosahedral funnel using the eigencurrent and demonstrate a superexponential growth of the corresponding eigenvalue. The proposed spectral approach is compared to the methodology of the Transition Path Theory. Finally, we discuss whether the Lennard-Jones-38 cluster is metastable from the points of view of a mathematician and a chemical physicist, and make a connection with experimental works.

  5. Open boundaries in a cellular automaton model for traffic flow with metastable states.

    PubMed

    Barlovic, Robert; Huisinga, Torsten; Schadschneider, Andreas; Schreckenberg, Michael

    2002-10-01

    The effects of open boundaries in the velocity-dependent randomization (VDR) model, a modified version of the well-known Nagel-Schreckenberg (NaSch) cellular automaton model for traffic flow, are investigated. In contrast to the NaSch model, the VDR model exhibits metastable states and phase separation in a certain density regime. A proper insertion strategy allows us to investigate the whole spectrum of possible system states and the structure of the phase diagram by Monte Carlo simulations. We observe an interesting microscopic structure of the jammed phases, which is different from the one of the NaSch model. For finite systems, the existence of high flow states in a certain parameter regime leads to a special structure of the fundamental diagram measured in the open system. Apart from that, the results are in agreement with an extremal principle for the flow, which has been introduced for models with a unique flow-density relation. Finally, we discuss the application of our findings for a systematic flow optimization. Here some surprising results are obtained, e.g., a restriction of the inflow can lead to an improvement of the total flow through a bottleneck.

  6. Nucleation kinetics of paracetamol-ethanol solutions from metastable zone widths

    NASA Astrophysics Data System (ADS)

    Mitchell, Niall A.; Frawley, Patrick J.

    2010-09-01

    A study of the nucleation kinetics for a cooling crystallisation of paracetamol-ethanol solutions in a batch reactor is described in this paper. Metastable zone width (MSZW) experiments were conducted in order to estimate the nucleation kinetics of the system. Measured MSZWs can be affected by numerous process parameters, such as cooling rate, concentration, agitation rate, and working volume. Two theoretical approaches were employed to estimate the nucleation kinetics, the classical mass based approach of Nývlt, and a more recent approach by Kubota, which also considers number density. Both approaches were found to produce similar estimates for the nucleation rates of the paracetamol-ethanol solutions as a function of supersaturation for an assumed nucleus size of 10 μm. The theory of Kubota was found to predict satisfactory estimates for the induction time of the nucleation process from MSZW data. The induction time was observed to be independent of the solution temperature as suggested by Kubota's theory. This is a novel finding and serves to validate the induction time theory of Kubota. In this investigation, MSZWs were observed to decrease with increased levels of agitation and found to be independent of working volume.

  7. Penning ionization electron spectroscopy of hydrogen sulfide by metastable helium and neon atoms.

    PubMed

    Falcinelli, Stefano; Candori, Pietro; Bettoni, Marta; Pirani, Fernando; Vecchiocattivi, Franco

    2014-08-21

    The dynamics of the Penning ionization of hydrogen sulfide molecules by collision with helium and metastable neon atoms, occurring in the thermal energy range, has been studied by analyzing the energy spectra of the emitted electrons obtained in our laboratory in a crossed beam experiment. These spectra are compared with the photoelectron spectra measured by using He(I) and Ne(I) photons under the same experimental conditions. In this way we obtained the negative energy shifts for the formation of H2S(+) ions in the first three accessible electronic states by He*(2(3,1)S1,0) and Ne*((3)P2,0) Penning ionization collisions: the 2b1 (X̃(2)B1) fundamental one, the first 5a1 (Ã(2)A1), and the second 2b2 (B̃(2)B2) excited states, respectively. The recorded energy shifts indicate that in the case of He* and Ne*-H2S the autoionization dynamics depends on the features of the collision complex and is mainly driven by an effective global attraction that comes from a balance among several non covalent intermolecular interaction components. This suggests that the Penning ionization should take place, in a specific range of intermolecular distances, as we have already observed in the case of Penning ionization of water molecules [Brunetti, B. G.; Candori, P.; Falcinelli, S.; Pirani, F.; Vecchiocattivi, F. J. Chem. Phys. 2013, 139, 164305-1-164305-8].

  8. Superplastic behavior in a powder-metallurgy TiAl alloy with a metastable microstructure

    SciTech Connect

    Nieh, T.G.; Hsiung, L.M.; Wadsworth, J.

    1997-12-01

    Superplasticity in a powder-metallurgy TiAl alloy (Ti-47Al-2Cr-2Nb) with a metastable microstructure has been studied. Samples were tested at temperatures ranging from 650 to 1100{degrees}C, and at strain rate ranging from 10{sup -6} to 10{sup -4} s{sup -1}. An elongation value of over 300 obtained at a strain rate of 2 x 10{sup -5} s{sup -1} and at a temperature as lo as 800{degrees}C, which is close to the ductile-to-brittle-transition temperature. This is in contrast to the prior major observations of superplastic behaviors in TiAl in which typical temperatures of 1000{degrees}C have usually been required for superplasticity. It is proposed that the occurrence of superplasticity at 8000{degrees}C in the present alloy is caused by the presence of a B2 phase. During superplastic deformation (grain boundary sliding), the soft P grains accommodate sliding strains to reduce the propensity for cavitation at grain triple junctions and, thus, delays the fracture process. The final microstructure consists of stable, equiaxed y+a{sub 2} grains.

  9. Metastable nanobubbles at the solid-liquid interface due to contact angle hysteresis.

    PubMed

    Nishiyama, Takashi; Yamada, Yutaka; Ikuta, Tatsuya; Takahashi, Koji; Takata, Yasuyuki

    2015-01-27

    Nanobubbles exist at solid-liquid interfaces between pure water and hydrophobic surfaces with very high stability, lasting in certain cases up to several days. Not only semispherical but also other shapes, such as micropancakes, are known to exist at such interfaces. However, doubt has been raised as to whether or not the nanobubbles are gas-phase entities. In this study, surface nanobubbles at a pure water-highly ordered pyrolytic graphite (HOPG) interface were investigated by peak force quantitative nanomechanics (PF-QNM). Multiple isolated nanobubbles generated by the solvent-exchange method were present on the terraced areas, avoiding the steps of the HOPG surface. Adjacent nanobubbles coalesced and formed metastable nanobubbles. Coalescence was enhanced by the PF-QNM measurement. We determined that nanobubbles can exist for a long time because of nanoscale contact angle hysteresis at the water-HOPG interface. Moreover, the hydrophilic steps of HOPG were avoided during coalescence, providing evidence that the nanobubbles are truly gas phase.

  10. Characterizing metastable states beyond energies and lifetimes: Dyson orbitals and transition dipole moments.

    PubMed

    Jagau, Thomas-C; Krylov, Anna I

    2016-02-07

    The theoretical description of electronic resonances is extended beyond calculations of energies and lifetimes. We present the formalism for calculating Dyson orbitals and transition dipole moments within the equation-of-motion coupled-cluster singles and doubles method for electron-attached states augmented by a complex absorbing potential (CAP-EOM-EA-CCSD). The capabilities of the new methodology are illustrated by calculations of Dyson orbitals of various transient anions. We also present calculations of transition dipole moments between transient and stable anionic states as well as between different transient states. Dyson orbitals characterize the differences between the initial neutral and final electron-attached states without invoking the mean-field approximation. By extending the molecular-orbital description to correlated many-electron wave functions, they deliver qualitative insights into the character of resonance states. Dyson orbitals and transition moments are also needed for calculating experimental observables such as spectra and cross sections. Physically meaningful results for those quantities are obtained only in the framework of non-Hermitian quantum mechanics, e.g., in the presence of a complex absorbing potential (CAP), when studying resonances. We investigate the dependence of Dyson orbitals and transition moments on the CAP strength and illustrate how Dyson orbitals help understand the properties of metastable species and how they are affected by replacing the usual scalar product by the so-called c-product.

  11. Measurements on Melting Pressure, Metastable Solid Phases, and Molar Volume of Univariant Saturated Helium Mixture

    NASA Astrophysics Data System (ADS)

    Rysti, J.; Manninen, M. S.; Tuoriniemi, J.

    2014-06-01

    A concentration-saturated helium mixture at the melting pressure consists of two liquid phases and one or two solid phases. The equilibrium system is univariant, whose properties depend uniquely on temperature. Four coexisting phases can exist on singular points, which are called quadruple points. As a univariant system, the melting pressure could be used as a thermometric standard. It would provide some advantages compared to the current reference, namely pure He, especially at the lowest temperatures below 1 mK. We have extended the melting pressure measurements of the concentration-saturated helium mixture from 10 to 460 mK. The density of the dilute liquid phase was also recorded. The effect of the equilibrium crystal structure changing from hcp to bcc was clearly seen at mK at the melting pressure MPa. We observed the existence of metastable solid phases around this point. No evidence was found for the presence of another, disputed, quadruple point at around 400 mK. The experimental results agree well with our previous calculations at low temperatures, but deviate above 200 mK.

  12. Synthesis of metastable rare-earth-iron mixed oxide with the hexagonal crystal structure

    NASA Astrophysics Data System (ADS)

    Nishimura, Tatsuya; Hosokawa, Saburo; Masuda, Yuichi; Wada, Kenji; Inoue, Masashi

    2013-01-01

    Rare-earth-iron mixed oxides with the rare earth/iron ratio=1 have either orthorhombic (o-REFeO3) or hexagonal (h-REFeO3) structure. h-REFeO3 is a metastable phase and the synthesis of h-REFeO3 is usually difficult. In this work, the crystallization process of the precursors obtained by co-precipitation and Pechini methods was investigated in detail to synthesize h-REFeO3. It was found that the crystallization from amorphous to hexagonal phase and the phase transition from hexagonal to orthorhombic phase occurred at a similar temperature range for rare earth elements with small ionic radii (Er-Lu, Y). For both co-precipitation and Pechini methods, single-phase h-REFeO3 was obtained by shortening the heating time during calcination process. The hexagonal-to-orthorhombic phase transition took place by a nucleation growth mechanism and vermicular morphology of the thus-formed orthorhombic phase was observed. The hexagonal YbFeO3 had higher catalytic activity for C3H8 combustion than orthorhombic YbFeO3.

  13. On gravity dual of a metastable vacuum in Klebanov-Strassler theory

    NASA Astrophysics Data System (ADS)

    Dymarsky, Anatoly

    2011-05-01

    We discuss a supergravity description of the metastable state that is created by a stack of overline {text{D}} 3 -branes placed at the tip of the KS background. When the number p of the overline {text{D}} 3 -branes is large g s p ≫ 1 the characteristic curvature of the corresponding gravity dual is large in stringy units and one may expect the background to be regular everywhere. Starting from the distances of order R ˜ ( g s p)1/4 α'1/2 away from the tip the new background can be well approximated by a linear perturbation around KS. By applying the appropriate boundary conditions in both IR and UV we found the lowest KK mode of the corresponding linear perturbation. The solution we found contains VEVs of the SU(2) × SU(2) invariant operators at the linear order in p. As a non-trivial check we calculate the ADM mass which exactly matches the probe approximation. As a byproduct we also found a gravity background dual to the KS theory deformed by the operators W 2 and {W^2}{bar{W}^2} with small coefficients.

  14. Photofragmentation of I2-ṡArn clusters: Observation of metastable isomeric ionic fragments

    NASA Astrophysics Data System (ADS)

    Vorsa, Vasil; Campagnola, Paul J.; Nandi, Sreela; Larsson, Mats; Lineberger, W. C.

    1996-08-01

    We report the 790 nm photofragmentation of mass-selected I-2ṡArn clusters, n=1 to 27. We determine the I-+I caging efficiency as a function of the number of solvent Ar atoms and compare these results with I-2 in CO2 clusters. Caging is much less effective with Ar. In addition to ``normal'' caged photoproducts (I-2ṡArm, where mmetastable species comprise ˜55% of the photofragment yield for precursor clusters for n≥14 and have lifetimes ≳5 μs. This unusual photofragment exists either as a trapped excited electronic state or as a solvent-separated pair at an internuclear separation of ˜5.5 Å. The photofragmentation data also exhibit the existence of two distinct isomeric forms of the precursor I-2ṡArn, for n≤14. These forms are evaporatively distinct in that one isomer displays highly nonstatistical fragmentation, probably arising from a cluster in which the I-2 resides on the surface, rather than in the interior. The photofragmentation distribution of the other form exhibits statistical behavior, consistent with the evaporation of an I-2 solvated inside the cluster.

  15. Cyclable Condensation and Hierarchical Assembly of Metastable Reflectin Proteins, the Drivers of Tunable Biophotonics*

    PubMed Central

    Levenson, Robert; Bracken, Colton; Bush, Nicole; Morse, Daniel E.

    2016-01-01

    Reversible changes in the phosphorylation of reflectin proteins have been shown to drive the tunability of color and brightness of light reflected from specialized cells in the skin of squids and related cephalopods. We show here, using dynamic light scattering, electron microscopy, and fluorescence analyses, that reversible titration of the excess positive charges of the reflectins, comparable with that produced by phosphorylation, is sufficient to drive the reversible condensation and hierarchical assembly of these proteins. The results suggest a two-stage process in which charge neutralization first triggers condensation, resulting in the emergence of previously cryptic structures that subsequently mediate reversible, hierarchical assembly. The extent to which cyclability is seen in the in vitro formation and disassembly of complexes estimated to contain several thousand reflectin molecules suggests that intrinsic sequence- and structure-determined specificity governs the reversible condensation and assembly of the reflectins and that these processes are therefore sufficient to produce the reversible changes in refractive index, thickness, and spacing of the reflectin-containing subcellular Bragg lamellae to change the brightness and color of reflected light. This molecular mechanism points to the metastability of reflectins as the centrally important design principle governing biophotonic tunability in this system. PMID:26719342

  16. Lifetimes of metastable ion clouds in a Paul trap: Power-law scaling

    NASA Astrophysics Data System (ADS)

    Weiss, D. K.; Nam, Y. S.; Blümel, R.

    2016-04-01

    It is well known that ions stored in a Paul trap, one of the most versatile tools in atomic, molecular, and optical (AMO) physics, may undergo a transition from a disordered cloud state to a geometrically well-ordered crystalline state, the Wigner crystal. In this paper we predict that close to the transition, the average lifetime τ¯m of the metastable cloud follows a power law, τ¯m˜(γ-γc) -β , where γc is the value of the damping constant at which the transition occurs. The exponent β depends on the trap control parameter q , but is independent of both the number of particles N stored in the trap and the trap control parameter a , which determines the shape (oblate, prolate, or spherical) of the ion cloud. In addition, we find that for given a and q , γc scales approximately like γc=C ln[ln(N ) ] +D as a function of N , where C and D are constants. Our predictions may be tested experimentally with equipment already available at many AMO laboratories. In addition to their importance in AMO trap physics, we also discuss possible applications of our results to other periodically driven many-particle systems, such as, e.g., particle accelerator beams, and, based on our trap results, conjecture that power laws characterize the phase transition to the Wigner crystal in all such systems.

  17. The nature of photoinduced phase transition and metastable states in vanadium dioxide

    PubMed Central

    Tao, Zhensheng; Zhou, Faran; Han, Tzong-Ru T.; Torres, David; Wang, Tongyu; Sepulveda, Nelson; Chang, Kiseok; Young, Margaret; Lunt, Richard R.; Ruan, Chong-Yu

    2016-01-01

    Photoinduced threshold switching processes that lead to bistability and the formation of metastable phases in photoinduced phase transition of VO2 are elucidated through ultrafast electron diffraction and diffusive scattering techniques with varying excitation wavelengths. We uncover two distinct regimes of the dynamical phase change: a nearly instantaneous crossover into an intermediate state and its decay led by lattice instabilities over 10 ps timescales. The structure of this intermediate state is identified to be monoclinic, but more akin to M2 rather than M1 based on structure refinements. The extinction of all major monoclinic features within just a few picoseconds at the above-threshold-level (~20%) photoexcitations and the distinct dynamics in diffusive scattering that represents medium-range atomic fluctuations at two photon wavelengths strongly suggest a density-driven and nonthermal pathway for the initial process of the photoinduced phase transition. These results highlight the critical roles of electron correlations and lattice instabilities in driving and controlling phase transformations far from equilibrium. PMID:27982066

  18. Unravelling the low-temperature metastable state in perovskite solar cells by noise spectroscopy

    NASA Astrophysics Data System (ADS)

    Barone, C.; Lang, F.; Mauro, C.; Landi, G.; Rappich, J.; Nickel, N. H.; Rech, B.; Pagano, S.; Neitzert, H. C.

    2016-10-01

    The hybrid perovskite methylammonium lead iodide CH3NH3PbI3 recently revealed its potential for the manufacturing of low-cost and efficient photovoltaic cells. However, many questions remain unanswered regarding the physics of the charge carrier conduction. In this respect, it is known that two structural phase transitions, occurring at temperatures near 160 and 310 K, could profoundly change the electronic properties of the photovoltaic material, but, up to now, a clear experimental evidence has not been reported. In order to shed light on this topic, the low-temperature phase transition of perovskite solar cells has been thoroughly investigated by using electric noise spectroscopy. Here it is shown that the dynamics of fluctuations detect the existence of a metastable state in a crossover region between the room-temperature tetragonal and the low-temperature orthorhombic phases of the perovskite compound. Besides the presence of a noise peak at this transition, a saturation of the fluctuation amplitudes is observed induced by the external DC current or, equivalently, by light exposure. This noise saturation effect is independent on temperature, and may represent an important aspect to consider for a detailed explanation of the mechanisms of operation in perovskite solar cells.

  19. The Nature of Metastable AA’ Graphite: Low Dimensional Nano- and Single-Crystalline Forms

    PubMed Central

    Lee, Jae-Kap; Kim, Jin-Gyu; Hembram, K. P. S. S.; Kim, Yong-Il; Min, Bong-Ki; Park, Yeseul; Lee, Jeon-Kook; Moon, Dong Ju; Lee, Wooyoung; Lee, Sang-Gil; John, Phillip

    2016-01-01

    Over the history of carbon, it is generally acknowledged that Bernal AB stacking of the sp2 carbon layers is the unique crystalline form of graphite. The universal graphite structure is synthesized at 2,600~3,000 °C and exhibits a micro-polycrystalline feature. In this paper, we provide evidence for a metastable form of graphite with an AA’ structure. The non-Bernal AA’ allotrope of graphite is synthesized by the thermal- and plasma-treatment of graphene nanopowders at ~1,500 °C. The formation of AA’ bilayer graphene nuclei facilitates the preferred texture growth and results in single-crystal AA’ graphite in the form of nanoribbons (1D) or microplates (2D) of a few nm in thickness. Kinetically controlled AA’ graphite exhibits unique nano- and single-crystalline feature and shows quasi-linear behavior near the K-point of the electronic band structure resulting in anomalous optical and acoustic phonon behavior. PMID:28000780

  20. Controlling cooperativity of a metastable open system coupled weakly to a noisy environment

    NASA Astrophysics Data System (ADS)

    Victor, I. Teslenko; Oleksiy, L. Kapitanchuk; Zhao, Yang

    2015-02-01

    The notion of cooperativity comprises a specific characteristic of a multipartite system concerning its ability to demonstrate a sigmoidal-type response of varying sensitivities to input stimuli in transitions between states under controlled conditions. From a statistical physics viewpoint, in this work we attempt to describe the cooperativity by the stability of a metastable open system with respect to irreversibility. To treat the evolution of a system weakly coupled to the environment in a kinetic framework, we consider two fluctuating energy levels of different dimensionalities, initial population of one level, reversible transitions of population between the levels, and irreversible depopulation of another level. An average is made over level fluctuations and environment vibrations so that an inter-level transition rate can be obtained accounting for the influences of external control on level position and dimensionality. It is found that the cooperativity of the two-level system is bounded approximately between 0.736 and unity, with the lower bound indicating worsening system stability. Project supported by the National Academy of Sciences of Ukraine (Grant No. 0110U007542) and the National Research Foundation of Singapore through the Competitive Research Programme (Grant No. NRF-CRP5-2009-04).