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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. The ρ(1S, 2S), ψ(1S, 2S), Υ(1S, 2S) and ψ t (1S, 2S) Mesons in a Double Pole QCD Sum Rule

    NASA Astrophysics Data System (ADS)

    Maior de Sousa, M. S.; da Silva, R. Rodrigues

    2016-09-01

    We use the method of double pole QCD sum rule, which is basically a fit with two exponentials of the correlation function, where we can extract the masses and decay constants of mesons as a function of the Borel mass. We apply this method to study the mesons: ρ(1S,2S), ψ(1S,2S), Υ(1S,2S), and ψ t (1S,2S). We also present predictions for the toponiuns masses ψ t (1S,2S) of m(1S)=357 GeV and m(2S)=374 GeV.

  3. 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.

  4. Compact solid-state laser source for 1S-2S spectroscopy in atomic hydrogen

    SciTech Connect

    Kolachevsky, N.; Alnis, J.; Bergeson, S. D.; Haensch, T. W.

    2006-02-15

    We demonstrate a compact solid-state laser source for high-resolution two-photon spectroscopy of the 1S-2S transition in atomic hydrogen. The source emits up to 20 mW at 243 nm and consists of a 972 nm diode laser, a tapered amplifier, and two doubling stages. The diode laser is actively stabilized to a high-finesse cavity. We compare the new source to the stable 486 nm dye laser used in previous experiments and record 1S-2S spectra using both systems. With the solid-state laser system, we demonstrate a resolution of the hydrogen spectrometer of 6x10{sup 11}, which is promising for a number of high-precision measurements in hydrogenlike systems.

  5. 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.

  6. Selective population of the [1s2s] {sup 1}S{sub 0} and [1s2s] {sup 3}S{sub 1} states of He-like uranium

    SciTech Connect

    Rzadkiewicz, J.; Stoehlker, Th.; Gumberidze, A.; Reuschl, R.; Spillmann, U.; Tashenov, S.; Trotsenko, S.; Banas, D.; Beyer, H. F.; Bosch, F.; Brandau, C.; Ionescu, D. C.; Kozhuharov, C.; Nandi, T.; Dong, C. Z.; Fritzsche, S.; Surzhykov, A.; Gojska, A.; Hagmann, S.; Sierpowski, D.

    2006-07-15

    The formation of the [1s2s] S states in heliumlike uranium (U{sup 90+}) has been studied in relativistic collisions of initially lithiumlike uranium (U{sup 89+}) ions with N{sub 2} target molecules. By measuring projectile x-ray emission in coincidence with projectile ionization, a strong selectivity for the formation of the [1s2s] S states in heliumlike uranium is observed. This selectivity is found to be unaffected by the subsequent rearrangement of the atomic orbitals involved. By measuring the photon emission associated with the decay of the [1s2s] {sup 1}S{sub 0} and the [1s2s] {sup 3}S{sub 1} substates, we obtain for their relative population probabilities a ratio of close to 1. This finding deviates considerably from the assumption of a statistical distribution 2J+1.

  7. Single, double, and triple Auger decay probabilities of C+(1 s 2 s22 p22 D ,2 P ) resonances

    NASA Astrophysics Data System (ADS)

    Zhou, Fuyang; Ma, Yulong; Qu, Yizhi

    2016-06-01

    Single, double, and triple Auger decay rates of C+(1 s 2 s22 p22 D ,2 P ) resonances were calculated in the framework of perturbation theory. The direct double Auger decay probabilities were calculated by using the approximate formulas according to the knockout and shakeoff mechanisms, in which the knockout mechanism was found to be dominant. Then the knockout mechanism was employed to investigate the complex triple Auger decay process, and the calculated rates have good agreement with the available experimental values.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  9. 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.

  10. 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.; 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.; Phenix Collaboration

    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.

  11. Spin-dependent, optogalvanic effects of laser-pumped He(2/3/S1) atoms

    NASA Astrophysics Data System (ADS)

    Schearer, L. D.; Tin, Pedetha

    1989-10-01

    Spin-dependent optogalvanic effects of laser-pumped He(2/3/S1) atoms are demonstrated. As helium atoms are excited with an IR tunable laser, changes in the conductivity of helium radio-frequency discharge are observed. With approximately 1 mW/sq cm of tunable laser power near 1.083 microns, the intensity-modulated optogalvanic effect signals are obtained as the laser is tuned through the D0(2/3/S1-2/3/P0), D1(2/3/S1-2/3/P1), and D2(2/3/S1-2/3/P2) transitions at 1.082908, 1.083025, and 1.083034 microns, respectively. If the laser emission is now circularly polarized and directed onto the helium discharge cell with the applied field parallel to the pump axis, some of the metastable atoms are oriented with their electronic spins along the field direction, modulating the coil current. One of the important applications of spin-polarized ensembles of metastable 4He is in extremely sensitive magnetic-field measuring devices.

  12. 1s2s2p{sup 2}3s {sup 6}P-1s2p{sup 3}3s {sup 6}S{sup o} Transitions in O IV

    SciTech Connect

    Lin Bin; Berry, H. Gordon; Shibata, Tomohiro; Livingston, A. Eugene; Savukov, Igor; Garnir, Henri-Pierre; Bastin, Thierry; Desesquelles, J.

    2003-06-01

    The energies and lifetimes of doubly excited sextet states of boron-like O IV, F V, and Ne VI are calculated with the multiconfiguration Hartree-Fock approach, including QED and higher-order corrections, and also with the multiconfiguration Dirac-Fock GRASP code. The wavelengths and transition rates of electric-dipole transitions from the inner-shell excited terms 1s2s2p{sup 2}3s {sup 6}P-1s2p{sup 3}3s {sup 6}S{sup o} are investigated by beam-foil spectroscopy in the XUV spectral region. The predicted transition wavelengths agree with the experiment. The higher-order corrections, fine structures, and spectrum with high wavelength resolution are found to be critically important in these comparisons. Nine new lines have been identified. The ground sextet states of boronlike atoms are metastable and well above several ionization levels. These are possible candidates for XUV and soft x-ray lasers.

  13. Molecular structure studies of (1S,2S)-2-benzyl-2,3-dihydro-2-(1H-inden-2-yl)-1H-inden-1-ol

    PubMed Central

    Zhang, Tao; Paluch, Krzysztof; Scalabrino, Gaia; Frankish, Neil; Healy, Anne-Marie; Sheridan, Helen

    2015-01-01

    The single enantiomer (1S,2S)-2-benzyl-2,3-dihydro-2-(1H-inden-2-yl)-1H-inden-1-ol (2), has recently been synthesized and isolated from its corresponding diastereoisomer (1). The molecular and crystal structures of this novel compound have been fully analyzed. The relative and absolute configurations have been determined by using a combination of analytical tools including X-ray crystallography, X-ray Powder Diffraction (XRPD) analysis and Nuclear Magnetic Resonance (NMR) spectroscopy. PMID:25750458

  14. 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.

  15. 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.; Ajitanand, N. N.; Akiba, Y.; Akimoto, R.; Al-Bataineh, H.; Al-Ta'ani, H.; Alexander, J.; Angerami, A.; et al

    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

  16. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2005-05-01

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

  18. Lifetime for Li-like Ti 1s2s2p {sup 4}P{sub 5/2}{sup o} level using a mode of beam-two-foil experiments

    SciTech Connect

    Nandi, T.; Ahmad, Nissar; Wani, A.A.

    2005-08-15

    The option of varying thickness of the fixed foil in the beam-two-foil technique has been incorporated in our experimental setup. It gives an opportunity to explore a new mode of this technique. In the current study, we have investigated the lifetime of the 1s2s2p {sup 4}P{sub 5/2}{sup o} level in Li-like titanium using this technique. The data showed a dependence of foil thickness of the fixed foil on the interactions of levels produced in the first foil. Average lifetime obtained for the Li-like titanium 1s2s2p {sup 4}P{sub 5/2}{sup o} level (200{+-}12 ps) is compared very well with the earlier theoretical and experimental values.

  19. Reliable measurement of the Li-like {sub 22}{sup 48}Ti 1s2s2p {sup 4}P{sub 5/2}{sup o} level lifetime by beam-foil and beam-two-foil experiments

    SciTech Connect

    Nandi, T.; Ahmad, Nissar; Wani, A. A.; Marketos, P.

    2006-03-15

    We have determined the lifetime of the Li-like {sub 22}{sup 48}Ti 1s2s2p {sup 4}P{sub 5/2}{sup o} level (210.5{+-}13.5 ps) using data from its x-ray decay channel through beam single- and two-foil experiments, coupled to a multicomponent iterative growth and decay analysis. Theoretical lifetime estimates for this zero-nuclear-spin ion lies within the uncertainty range of our experimental results, indicating that blending contributions to this level from the He-like 1s2p {sup 3}P{sub 2}{sup o} and 1s2s {sup 3}S{sub 1} levels are eliminated within the current approach. A previously reported discrepancy between experimental and theoretical 1s2s2p {sup 4}P{sub 5/2}{sup o} level lifetimes in {sub 23}{sup 51}V may, as a result, be attributed to hyperfine quenching.

  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. Isotope shift of the 1s2p {sup 3}P{sub 0}-1s2s {sup 1}S{sub 0} level splitting in heavy He-like ions: Implications for atomic parity-nonconservation studies

    SciTech Connect

    Ferro, Fabrizio; Artemyev, Anton; Surzhykov, Andrey; Stoehlker, Thomas

    2010-06-15

    Heavy He-like ions are considered to be promising candidates for atomic parity-nonconservation (PNC) studies, thanks to their relatively simple atomic structure and the significant mixing between the almost degenerate (for the atomic numbers Z{approx}64 and Z{approx}91) opposite-parity levels 1s2s {sup 1}S{sub 0} and 1s2p {sup 3}P{sub 0}. A number of experiments exploiting this level mixing have been proposed, and their implementation requires a precise knowledge of the 2 {sup 3}P{sub 0}-2 {sup 1}S{sub 0} energy splitting for different nuclear charges and isotopes. In this paper we performed a theoretical analysis of the level splitting, employing the relativistic many-body perturbation theory and including QED corrections for all isotopes in the intervals 54{<=}Z{<=}71 and 86{<=}Z{<=}93. Possible candidates for future experimental PNC studies are discussed.

  2. Precision measurement of the 1s2s{sup 3}S{sub 1} {r_arrow} 1s2p {sup 3}P{sub 0,1,2} transitions in heliumlike beryllium

    SciTech Connect

    Scholl, T.J.; Cameron, R.E.; Rosner, S.D.

    1993-05-01

    We have applied fast-ion-beam laser spectroscopy to observe the 1s2s{sup 3}S {yields} 1s2p{sup 3}P transitions in Be III with complete resolution of the fine and hyperfine structure (I = 3/2). Using intracavity cw frequency-doubling in a Ti:Sapph laser, we produced {approximately}50 mW at {approximately}372.5 nm, continuously tunable over 60 GHz. A re-designed high-temperature ion source gave {approximately}50 nA of {sup 9}Be{sup 2+} at 16 keV, an order of magnitude improvement over an earlier version. Although the {approximately}10 nA laser-induced-fluorescence signals could be observed directly despite {approximately}45 nA due to scattered laser light, lock-in detection was used to obtain zero average background. The absolute wavelength reference was the Aime Cotton I{sub 2} Atlas, using linear absorption of the fundamental (745 nm). Results will be compared with theory and discussed with reference to systematic discrepancies of the 3P{sub 0} level which have been observed over a wide range of Z.

  3. Sequence and phylogenetic analysis of genome segments S1, S2, S3 and S6 of Mal de Río Cuarto virus, a newly accepted Fijivirus species.

    PubMed

    Distéfano, Ana J; Conci, Luis R; Muñoz Hidalgo, Marianne; Guzmán, Fabiana A; Hopp, Horacio E; del Vas, Mariana

    2003-03-01

    Mal de Río Cuarto virus (MRCV) is a newly described species of the genus Fijivirus, family Reoviridae. The nucleotide sequence of four MRCV genome segments was determined. MRCV S1, S2, S3 and S6 were predicted to encode proteins of 168.4, 134.4, 141.7 and 90 kDa, respectively. MRCV S1 encodes a basic protein that contains conserved RNA-dependent RNA polymerase motifs, and is homologous to Rice black streaked dwarf virus (RBSDV), Fiji disease virus (FDV) and Nilaparvata lugens reovirus (NLRV) polymerases as well as to corresponding proteins of members of other genera of the Reoviridae. MRCV S2 codes for a protein with intermediate homology to the ones coded by RBSDV S4 and FDV S3 'B' spike, which is presumably the B-spike protein. MRCV S3 most probably encodes the major core protein and is highly homologous to corresponding proteins of RBSDV S2 and FDV S3. MRCV S6-encoded protein has low homology to the proteins of unknown function coded by RBSDV S6 and FDV S6. The identity levels between all analyzed MRCV coded proteins and their RBSDV counterparts varied between 84.5 and 44.8%. The analysis of the reported sequences allowed a phylogenetic comparison of MRCV with other reovirus and supported its taxonomic status within the genus.

  4. Excitation of {sup 1}S and {sup 3}S Metastable Helium Atoms to Doubly Excited States

    SciTech Connect

    Alagia, M.; Coreno, M.; Farrokhpour, H.; Omidyan, R.; Tabrizchi, M.; Franceschi, P.; Mihelic, A.; Zitnik, M.; Moise, A.; Prince, K. C.; Richter, R.; Soederstroem, J.; Stranges, S.

    2009-04-17

    We present spectra of triplet and singlet metastable helium atoms resonantly photoexcited to doubly excited states. The first members of three dipole-allowed {sup 1,3}P{sup o} series have been observed and their relative photoionization cross sections determined, both in the triplet (from 1s2s {sup 3}S{sup e}) and singlet (from 1s2s {sup 1}S{sup e}) manifolds. The intensity ratios are drastically different with respect to transitions from the ground state. When radiation damping is included the results for the singlets are in agreement with theory, while for triplets spin-orbit interaction must also be taken into account.

  5. The 3P0-VERSUS 3S1-MODELS for Quark-Antiquark Annihilation

    NASA Astrophysics Data System (ADS)

    Green, A. M.; Niskanen, J. A.

    A comparison is made between the 3S1- and 3P0-models for quark-antiquark annihilation or creation. Even though the former appears, at first sight, to be superior for Nbar {N} annihilation into two mesons, it is argued from their effects in meson decays that this conclusion is premature.

  6. The metastable brain.

    PubMed

    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.

  7. The metastable brain.

    PubMed

    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

  8. Observation of orbiting resonances in He((3)S(1)) + NH3 Penning ionization.

    PubMed

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

    2015-04-28

    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((3)S1) + 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.

  9. Collisional properties of cold spin-polarized metastable neon atoms.

    PubMed

    Spoden, P; Zinner, M; Herschbach, N; van Drunen, W J; Ertmer, W; Birkl, G

    2005-06-10

    We measure the rates of elastic and inelastic two-body collisions of cold spin-polarized neon atoms in the metastable 3P2 state for 20Ne and 22Ne in a magnetic trap. From particle loss, we determine the loss parameter of inelastic collisions beta=6.5(18) x 10(-12) cm(3) s(-1) for 20Ne and beta=1.2(3) x 10(-11) cm(3) s(-1) for 22Ne. These losses are caused by ionizing (i.e., Penning) collisions and occur less frequently than for unpolarized atoms. This proves the suppression of Penning ionization due to spin polarization. From cross-dimensional relaxation measurements, we obtain elastic scattering lengths of a=-180(40)a(0) for 20Ne and a = +150(+80)(-50)a(0) for 22Ne, where a(0)=0.0529 nm.

  10. Photoionization with excitation and double photoionization of the Li{sup +} ground 1 {sup 1}S state and metastable 2 {sup 1,3}S states

    SciTech Connect

    Kleiman, U.; Pindzola, M.S.; Robicheaux, F.

    2005-08-15

    Partial cross-sections for photoionization with excitation of Li{sup +} leaving the remaining bound electron in the 1s, 2s, 2p, 3s, 3p, and 3d states and total cross-sections for double photoionization have been calculated employing the time-dependent close-coupling method. The calculations include both the ground state 1s{sup 2} {sup 1}S and the two lowest metastable excited states 1s2s {sup 1,3}S. Photon energies below and up to about 200 eV above the respective thresholds for double ionization are considered. Comparisons are drawn mainly with convergent close-coupling results [A. S. Kheifets and I. Bray, Phys. Rev. A 58, 4501 (1998)] and B-spline based R-matrix results [H. W. van der Hart and L. Feng, J. Phys. B 34, L601 (2001)].

  11. 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.

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

    DOE PAGES

    Träbert, E.; Beiersdorfer, P.; Hell, N.; Brown, G. V.

    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. Desensitization of metastable intermolecular composites

    DOEpatents

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  15. 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

  16. Synthesis and pharmacological characterization of C4-disubstituted analogs of 1S,2S,5R,6S-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate: identification of a potent, selective metabotropic glutamate receptor agonist and determination of agonist-bound human mGlu2 and mGlu3 amino terminal domain structures.

    PubMed

    Monn, James A; Prieto, Lourdes; Taboada, Lorena; Pedregal, Concepcion; Hao, Junliang; Reinhard, Matt R; Henry, Steven S; Goldsmith, Paul J; Beadle, Christopher D; Walton, Lesley; Man, Teresa; Rudyk, Helene; Clark, Barry; Tupper, David; Baker, S Richard; Lamas, Carlos; Montero, Carlos; Marcos, Alicia; Blanco, Jaime; Bures, Mark; Clawson, David K; Atwell, Shane; Lu, Frances; Wang, Jing; Russell, Marijane; Heinz, Beverly A; Wang, Xushan; Carter, Joan H; Xiang, Chuanxi; Catlow, John T; Swanson, Steven; Sanger, Helen; Broad, Lisa M; Johnson, Michael P; Knopp, Kelly L; Simmons, Rosa M A; Johnson, Bryan G; Shaw, David B; McKinzie, David L

    2015-02-26

    As part of our ongoing research to identify novel agents acting at metabotropic glutamate 2 (mGlu2) and 3 (mGlu3) receptors, we have previously reported the identification of the C4α-methyl analog of mGlu2/3 receptor agonist 1 (LY354740). This molecule, 1S,2S,4R,5R,6S-2-amino-4-methylbicyclo[3.1.0]hexane-2,6-dicarboxylate 2 (LY541850), exhibited an unexpected mGlu2 agonist/mGlu3 antagonist pharmacological profile, whereas the C4β-methyl diastereomer (3) possessed dual mGlu2/3 receptor agonist activity. We have now further explored this structure-activity relationship through the preparation of cyclic and acyclic C4-disubstituted analogs of 1, leading to the identification of C4-spirocyclopropane 5 (LY2934747), a novel, potent, and systemically bioavailable mGlu2/3 receptor agonist which exhibits both antipsychotic and analgesic properties in vivo. In addition, through the combined use of protein-ligand X-ray crystallography employing recombinant human mGlu2/3 receptor amino terminal domains, molecular modeling, and site-directed mutagenesis, a molecular basis for the observed pharmacological profile of compound 2 is proposed. PMID:25602126

  17. 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.

  18. Metastable helium atom density in a single electrode atmospheric plasma jet during sample treatment

    NASA Astrophysics Data System (ADS)

    Zaplotnik, R.; Bišćan, M.; Popović, D.; Mozetič, M.; Milošević, S.

    2016-06-01

    The metastable He atoms play an important role in atmospheric pressure plasma jet (APPJ) chemistry processes and in the plasma generation. This work presents cavity ring-down spectroscopy (CRDS) investigation of metastable helium atom (2{{3}}{{S}1} ) densities in a single electrode APPJ during sample treatment. A spatially resolved density distribution of a free jet (without sample) was measured at a He flow rate of 2 slm. The maximum measured density of a free jet was around 7× {{10}11} cm‑3. With the insertion of a sample the densities increased up to 10 times. Helium metastable atoms, in a single electrode helium APPJ (2 slm, ≈2.5 kV, pulsed DC, 10 kHz repetition rate), decayed exponentially with a mean lifetime of 0.27+/- 0.03 μs. Eight different samples of the same sizes but different conductivities were used to investigate the influence of a sample material on the He metastable densities. The correlation between sample conductivities and metastable He densities above the sample surface was found. Metastable He density can also be further increased with decreasing sample distance, increasing conductive sample surface area and by increasing He flow.

  19. Antiobesity efficacy of a novel cannabinoid-1 receptor inverse agonist, N-[(1S,2S)-3-(4-chlorophenyl)-2-(3-cyanophenyl)-1-methylpropyl]-2-methyl-2-[[5-(trifluoromethyl)pyridin-2-yl]oxy]propanamide (MK-0364), in rodents.

    PubMed

    Fong, Tung M; Guan, Xiao-Ming; Marsh, Donald J; Shen, Chun-Pyn; Stribling, D Sloan; Rosko, Kim M; Lao, Julie; Yu, Hong; Feng, Yue; Xiao, Jing C; Van der Ploeg, Lex H T; Goulet, Mark T; Hagmann, Williams K; Lin, Linus S; Lanza, Thomas J; Jewell, James P; Liu, Ping; Shah, Shrenik K; Qi, Hongbo; Tong, Xinchun; Wang, Junying; Xu, Suoyu S; Francis, Barbara; Strack, Alison M; MacIntyre, D Euan; Shearman, Lauren P

    2007-06-01

    The cannabinoid-1 receptor (CB1R) has been implicated in the control of energy balance. To explore the pharmacological utility of CB1R inhibition for the treatment of obesity, we evaluated the efficacy of N-[(1S,2S)-3-(4-chlorophenyl)-2-(3-cyanophenyl)-1-methylpropyl]-2-methyl-2-[[5-(trifluoromethyl)pyridin-2-yl]oxy]propanamide (MK-0364) and determined the relationship between efficacy and brain CB1R occupancy in rodents. MK-0364 was shown to be a highly potent CB1R inverse agonist that inhibited the binding and functional activity of various agonists with a binding K(i) of 0.13 nM for the human CB1R in vitro. MK-0364 dose-dependently inhibited food intake and weight gain, with an acute minimum effective dose of 1 mg/kg in diet-induced obese (DIO) rats. CB1R mechanism-based effect was demonstrated for MK-0364 by its lack of efficacy in CB1R-deficient mice. Chronic treatment of DIO rats with MK-0364 dose-dependently led to significant weight loss with a minimum effective dose of 0.3 mg/kg (p.o.), or a plasma C(max) of 87 nM. Weight loss was accompanied by the loss of fat mass. Partial occupancy (30-40%) of brain CB1R by MK-0364 was sufficient to reduce body weight. The magnitude of weight loss was correlated with brain CB1R occupancy. The partial receptor occupancy requirement for efficacy was also consistent with the reduced food intake of the heterozygous mice carrying one disrupted allele of CB1R gene compared with the wild-type mice. These studies demonstrated that MK-0364 is a highly potent and selective CB1R inverse agonist and that it is orally active in rodent models of obesity. PMID:17327489

  20. Pulsed discharge production Ar* metastables

    NASA Astrophysics Data System (ADS)

    Han, Jiande; Heaven, Michael C.; Emmons, Daniel; Perram, Glen P.; Weeks, David E.; Bailey, William F.

    2016-03-01

    The production of relatively high densities of Ar* metastables (>1012 cm-3) in Ar/He mixtures, at total pressures close to 1 atm, is essential for the efficient operation of an optically pumped Ar* laser. We have used emission spectroscopy and diode laser absorption spectroscopy measurements to observe the production and decay of Ar* in a parallel plate pulsed discharge. With discharge pulses of 1 μs duration we find that metastable production is dominated by processes occurring within the first 100 ns of the gas break-down. Application of multiple, closely spaced discharge pulses yields insights concerning conditions that favor metastable production. This information has been combined with time-resolved measurements of voltage and current. The experimental results and preliminary modeling of the discharge kinetics are presented.

  1. The anticancer effect of (1S,2S,3E,7E,11E)-3,7,11, 15-cembratetraen-17,2-olide(LS-1) through the activation of TGF-β signaling in SNU-C5/5-FU, fluorouracil-resistant human colon cancer cells.

    PubMed

    Kim, Eun-Ji; Kang, Jung-Il; Kwak, Jeon-Won; Jeon, Chan-Hee; Tung, Nguyen-Huu; Kim, Young-Ho; Choi, Cheol-Hee; Hyun, Jin-Won; Koh, Young-Sang; Yoo, Eun-Sook; Kang, Hee-Kyoung

    2015-03-16

    The anticancer effect of (1S,2S,3E,7E,11E)-3,7,11,15-cembratetraen-17,2-olide (LS-1) from Lobophytum sp. has been already reported in HT-29 human colorectal cancer cells. In this study, we examined the effect of LS-1 on the apoptosis induction of SNU-C5/5-FU, fluorouracil-resistant human colon cancer cells. Furthermore, we investigated whether the apoptosis-induction effect of LS-1 could arise from the activation of the TGF-β pathway. In SNU-C5/5-FU treated with LS-1 of 7.1 μM (IC50), we could observe the various apoptotic characteristics, such as the increase of apoptotic bodies, the increase of the sub-G1 hypodiploid cell population, the decrease of the Bcl-2 level, the increase of procaspase-9 cleavage, the increase of procaspase-3 cleavage and the increase of poly(ADP-ribose) polymerase cleavage. Interestingly, the apoptosis-induction effect of LS-1 was also accompanied by the increase of Smad-3 phosphorylation and the downregulation of c-Myc in SNU-C5/5-FU. LS-1 also increased the nuclear localization of phospho-Smad-3 and Smad-4. We examined whether LS-1 could downregulate the expression of carcinoembryonic antigen (CEA), a direct inhibitor of TGF-β signaling. LS-1 decreased the CEA level, as well as the direct interaction between CEA and TGF-βR1 in the apoptosis-induction condition of SNU-C5/5-FU. To examine whether LS-1 can induce apoptosis via the activation of TGF-β signaling, the SNU-C5/5-FU cells were treated with LS-1 in the presence or absence of SB525334, a TGF-βRI kinase inhibitor. SB525334 inhibited the effect of LS-1 on the apoptosis induction. These findings provide evidence demonstrating that the apoptosis-induction effect of LS-1 results from the activation of the TGF-β pathway via the downregulation of CEA in SNU-C5/5-FU.

  2. 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

  3. Optically enhanced production of metastable xenon.

    PubMed

    Hickman, G T; Franson, J D; Pittman, T B

    2016-09-15

    Metastable states of noble gas atoms are typically produced by electrical discharge techniques or "all-optical" excitation methods. Here we combine electrical discharges with optical pumping to demonstrate "optically enhanced" production of metastable xenon (Xe*). We experimentally measure large increases in Xe* density with relatively small optical control field powers. This technique may have applications in systems where large metastable state densities are desirable. PMID:27628400

  4. New treatment of quantum metastability

    NASA Astrophysics Data System (ADS)

    Defendi, Antonio; Roncadelli, Marco

    1995-02-01

    We explore the implications of the recently proposed Langevin quantization for quantum metastability, working within the semiclassical approximation. As far as we can see, the present treatment is simpler and more straightforward than the path integral approach. Indeed, no extra trick is needed and the correct result follows at once - as a consequence of general principles - from the representation of the propagator supplied by the Langevin quantization. Moreover, the imaginary part of the semiclassical propagator emerges naturally form the formalism and no analytic continuation has to be performed in order to make sense out of a divergent expression. Further applications of the strategy discussed in this Letter are pointed out.

  5. 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.

  6. Probing Metastability at the LHC

    SciTech Connect

    Clavelli, L.

    2010-02-10

    Current attempts to understand supersymmetry (susy) breaking are focused on the idea that we are not in the ground state of the universe but, instead, in a metastable state that will ultimately decay to an exactly susy ground state. It is interesting to ask how experiments at the Large Hadron Collider (LHC) will shed light on the properties of this future supersymmetric universe. In particular we ask how we can determine whether this final state has the possibility of supporting atoms and molecules in a susy background.

  7. Desensitization and recovery of metastable intermolecular composites

    DOEpatents

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

    2010-09-07

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

  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. 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

  10. Metastable Tight Knots in DNA

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  11. 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.

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

    PubMed Central

    2011-01-01

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

  13. Draft Genome Sequence of Methylosinus sp. Strain 3S-1, an Isolate from Rice Root in a Low-Nitrogen Paddy Field.

    PubMed

    Bao, Zhihua; Shinoda, Ryo; Minamisawa, Kiwamu

    2016-01-01

    N2-fixing methanotrophs play an important role in the methane-nitrogen cycle in rice paddies. We report here the draft genome sequence of Methylosinus sp. strain 3S-1 isolated from rice root in a paddy field without N fertilizer input. PMID:27587832

  14. Draft Genome Sequence of Methylosinus sp. Strain 3S-1, an Isolate from Rice Root in a Low-Nitrogen Paddy Field

    PubMed Central

    Bao, Zhihua; Shinoda, Ryo

    2016-01-01

    N2-fixing methanotrophs play an important role in the methane-nitrogen cycle in rice paddies. We report here the draft genome sequence of Methylosinus sp. strain 3S-1 isolated from rice root in a paddy field without N fertilizer input. PMID:27587832

  15. 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.

  16. 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

  17. Metastable States of small-molecule solutions.

    PubMed

    He, Guangwen; Tan, Reginald B H; Kenis, Paul J A; Zukoski, Charles F

    2007-12-27

    Metastable states such as gels and glasses that are commonly seen in nanoparticle suspensions have found application in a wide range of products including toothpaste, hand cream, paints, and car tires. The equilibrium and metastable state behavior of nanoparticle suspensions are often described by simple fluid models where particles are treated as having hard cores and interacting with short-range attractions. Here we explore similar models to describe the presence of metastable states of small-molecule solutions. We have recently shown that the equilibrium solubilities of small hydrogen-bonding molecules and nanoparticles fall onto a corresponding-states solubility curve suggesting that with similar average strengths of attraction these molecules have similar solubilities. This observation implies that metastable states in small-molecule solutions may be found under conditions similar to those where metastable states are observed in nanoparticle and colloidal suspensions. Here we seek confirmation of this concept by exploring the existence of metastable states in solutions of small molecules.

  18. Tune-out wavelength around 413 nm for the helium 2 3S1 state including relativistic and finite-nuclear-mass corrections

    NASA Astrophysics Data System (ADS)

    Zhang, Yong-Hui; Tang, Li-Yan; Zhang, Xian-Zhou; Shi, Ting-Yun

    2016-05-01

    The tune-out wavelength at 413 nm for the 2 3S1 state of helium is expected to be sensitive to finite nuclear mass, relativistic, and quantum electrodynamic (QED) corrections, which provides a scheme for testing atomic structure theory [J. Mitroy and L.-Y. Tang, Phys. Rev. A 88, 052515 (2013), 10.1103/PhysRevA.88.052515]. In the present work, a large-scale full-configuration-interaction calculation based on both the Dirac-Coulomb-Breit Hamiltonian and the nonrelativistic Hamiltonian is performed for the dynamic dipole polarizabilities of helium in the 2 3S1 state. The tune-out wavelengths for the magnetic sublevels MJ=0 and MJ=±1 are determined to be 413.0801(4) nm and 413.0859(4) nm, respectively, at sub-ppm accuracy, including finite nuclear mass and relativistic corrections. Our value for the MJ=1 sublevel agrees with the measured value of 413.0938(20)(9) nm [B. M. Henson et al., Phys. Rev. Lett. 115, 043004 (2015), 10.1103/PhysRevLett.115.043004] at the level of 19 ppm. The discrepancy between these two values is mainly due to the uncalculated QED contribution. Our current value confirms quantitatively the prediction of Mitroy and Tang. Also, for the state of 2 3S1 we find that the corrections due to finite nuclear mass and relativistic effects to the static dipole polarizability of 315.7227(4)a03 are about 600 ppm and 310 ppm, respectively, which are about 1.4 and 5.4 times larger than those for the ground state. A measurement at the level of 10 ppm for the static dipole polarizability of helium in 2 3S1 can be used to determine the transition matrix element between 2 3S and 2 3P at the level of 10-5.

  19. Precision Measurement for Metastable Helium Atoms of the 413 nm Tune-Out Wavelength at Which the Atomic Polarizability Vanishes.

    PubMed

    Henson, B M; Khakimov, R I; Dall, R G; Baldwin, K G H; Tang, Li-Yan; Truscott, A G

    2015-07-24

    We present the first measurement for helium atoms of the tune-out wavelength at which the atomic polarizability vanishes. We utilize a novel, highly sensitive technique for precisely measuring the effect of variations in the trapping potential of confined metastable (2^{3}S_{1}) helium atoms illuminated by a perturbing laser light field. The measured tune-out wavelength of 413.0938(9_{stat})(20_{syst}) nm compares well with the value predicted by a theoretical calculation [413.02(9) nm] which is sensitive to finite nuclear mass, relativistic, and quantum electrodynamic effects. This provides motivation for more detailed theoretical investigations to test quantum electrodynamics.

  20. Precision Measurement for Metastable Helium Atoms of the 413 nm Tune-Out Wavelength at Which the Atomic Polarizability Vanishes.

    PubMed

    Henson, B M; Khakimov, R I; Dall, R G; Baldwin, K G H; Tang, Li-Yan; Truscott, A G

    2015-07-24

    We present the first measurement for helium atoms of the tune-out wavelength at which the atomic polarizability vanishes. We utilize a novel, highly sensitive technique for precisely measuring the effect of variations in the trapping potential of confined metastable (2^{3}S_{1}) helium atoms illuminated by a perturbing laser light field. The measured tune-out wavelength of 413.0938(9_{stat})(20_{syst}) nm compares well with the value predicted by a theoretical calculation [413.02(9) nm] which is sensitive to finite nuclear mass, relativistic, and quantum electrodynamic effects. This provides motivation for more detailed theoretical investigations to test quantum electrodynamics. PMID:26252681

  1. Optical Forces on Metastable Helium

    NASA Astrophysics Data System (ADS)

    Corder, Christopher Scott

    Optical forces using lasers allow precise control over the motion of atoms. The bichromatic optical force (BF) is unique in its large magnitude and velocity range, arising from the absorption and stimulated emission processes. These properties were used to transversely collimate a beam of metastable helium (He*) using the 23S - 23P transition. The collimation created a very bright beam of He*, allowing experiments of neutral atom lithography. The He* beam was used to pattern material surfaces using a resist-based lithography technique, where the pattern was determined by either mechanical or optical masks. The optical masks produced features with a separation of half the wavelength of the light used. Patterning was successfully demonstrated with both IR and UV optical masks. The etched pattern resolution was ˜ 100 nm and limited by the material surface. Further experiments were performed studying the ability of the bichromatic force to cool. The finite velocity range of the BF allows estimation of a characteristic cooling time which is independent of the excited state lifetime, only depending on the atomic mass and optical transition energy. Past experiments, including the helium collimation used for neutral atom lithography, have demonstrated that the BF can collimate and longitudinally slow atomic beams, but required long interaction times that included many spontaneous emission (SE) events. The effect of SE can be mitigated, and is predicted to not be necessary for BF cooling. Since the BF cooling time is not related to the excited state lifetime, a transition can be chosen such that the cooling time is shorter than the SE cycle time, allowing direct laser cooling on atoms and molecules that do not have cycling transitions. Experiments using the helium 2 3S-3P transition were chosen because the BF cooling time (285 ns) is on the order of the average SE cycle time (260 ns). Numerical simulations of the experimental system were run predicting compression of the

  2. 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.

  3. Dielectron Widths of the {upsilon}(1S,2S,3S) Resonances

    SciTech Connect

    Rosner, J.L.; Adam, N.E.; Alexander, J.P.; Berkelman, K.; Cassel, D.G.; Duboscq, J.E.; Ecklund, K.M.; Ehrlich, R.; Fields, L.; Galik, R.S.; Gibbons, L.; Gray, R.; Gray, S.W.; Hartill, D.L.; Heltsley, B.K.; Hertz, D.; Jones, C.D.; Kandaswamy, J.; Kreinick, D.L.; Kuznetsov, V.E.

    2006-03-10

    We determine the dielectron widths of the {upsilon}(1S), {upsilon}(2S), and {upsilon}(3S) resonances with better than 2% precision by integrating the cross section of e{sup +}e{sup -}{yields}{upsilon} over the e{sup +}e{sup -} center-of-mass energy. Using e{sup +}e{sup -} energy scans of the {upsilon} resonances at the Cornell Electron Storage Ring and measuring {upsilon} production with the CLEO detector, we find dielectron widths of 1.252{+-}0.004({sigma}{sub stat}){+-}0.019({sigma}{sub syst}) keV, 0.581{+-}0.004{+-}0.009 keV, and 0.413{+-}0.004{+-}0.006 keV for the {upsilon}(1S), {upsilon}(2S), and {upsilon}(3S), respectively.

  4. Metastability in the evolution of triple systems

    NASA Astrophysics Data System (ADS)

    Martynova, A. I.; Orlov, V. V.; Rubinov, A. V.

    2003-10-01

    The dynamical evolution of 15000 equal-mass triple systems with zero initial velocities (the free-fall three-body problem) is considered. The equations of motion are numerically integrated using regularization of binary and triple encounters. We find 170 triple systems which reach a state where the motions take place within a limited region of phase space during a long time. These regions are concentrated in the zones of regular motions in the vicinities of stable periodic orbits: the von Schubart orbit in the rectilinear problem, the Broucke orbit in the isosceles problem, and the `Eight' orbit. The classification of such metastable orbits is suggested. A change of the types is found during the dynamical evolution of some metastable systems. The triple system leaves the metastable regime after some time, and its evolution is finished by the escape of one body.

  5. 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.

  6. 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.

  7. Kinetic Trapping of Metastable Amino Acid Polymorphs

    PubMed Central

    2015-01-01

    Second harmonic generation (SHG) microscopy measurements indicate that inkjet-printed racemic solutions of amino acids can produce nanocrystals trapped in metastable polymorph forms upon rapid solvent evaporation. Polymorphism impacts the composition, distribution, and physico-kinetic properties of organic solids, with energetic arguments favoring the most stable polymorph. In this study, unfavored noncentrosymmetric crystal forms were observed by SHG microscopy. Polarization-dependent SHG measurement and synchrotron X-ray microdiffraction analysis of individual printed drops are consistent with formation of homochiral crystal production. Fundamentally, these results provide evidence supporting the ubiquity of Ostwald’s Rule of Stages, describing the hypothesized transitioning of crystals between metastable polymorphic forms in the early stages of crystal formation. Practically, the presence of homochiral metastable forms has implications on chiral resolution and on solid form preparations relying on rapid solvent evaporation. PMID:24451055

  8. Modeling the metastable dynamics of correlated structures

    PubMed Central

    Shakirov, Alexey M.; Tsibulsky, Sergey V.; Antipov, Andrey E.; Shchadilova, Yulia E.; Rubtsov, Alexey N.

    2015-01-01

    Metastable quantum dynamics of an asymmetric triangular cluster that is coupled to a reservoir is investigated. The dynamics is governed by bath-mediated transitions, which in part require a thermal activation process. The decay rate is controlled by tuning the excitation spectrum of the frustrated cluster. We use the master equation approach and construct transition operators in terms of many-body states. We analyze dynamics of observables and reveal metastability of an excited state and of a magnetically polarized ground state. PMID:25623327

  9. On the Destabilization of Metastable Solid He

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

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

    PubMed

    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.

  11. 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

  12. Optical production of metastable rare gases.

    SciTech Connect

    Young, L.; Yang, D.; Dunford, R.; Chemistry; Peking Univ.

    2002-01-01

    We have investigated a new scheme for excitation of the 5s, J = 2 metastable level of Kr (5s[3/2]J = 2) which can be readily extended to other rare gases. In the scheme, an ultraviolet (UV) lamp is used to create a population of Kr atoms in the 5s[3/2]J = 1 level in a gas cell. The excited atoms are then pumped to the 5p[3/2]J = 2 level, using 819 nm light from a Ti:sapphire laser, from which they decay to the metastable state with a branching ratio of 77%. We made two striking observations: (1) the laser power required to saturate the second step decreases markedly as a function of gas cell pressure, and (2) the UV photon flux is converted with very high efficiency (approx10%) to metastable atom flux. A Monte Carlo study of the scattering of UV photons in the cell reproduces the trends observed. The understanding achieved points to the design of a higher flux source of metastable atoms.

  13. Reheating metastable O'Raifeartaigh models

    SciTech Connect

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

    2006-11-01

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

  14. Reheating Metastable O'Raifeartaigh Models

    SciTech Connect

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

    2006-12-05

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

  15. 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.

  16. Cellular folding pathway of a metastable serpin.

    PubMed

    Chandrasekhar, Kshama; Ke, Haiping; Wang, Ning; Goodwin, Theresa; Gierasch, Lila M; Gershenson, Anne; Hebert, Daniel N

    2016-06-01

    Although proteins generally fold to their thermodynamically most stable state, some metastable proteins populate higher free energy states. Conformational changes from metastable higher free energy states to lower free energy states with greater stability can then generate the work required to perform physiologically important functions. However, how metastable proteins fold to these higher free energy states in the cell and avoid more stable but inactive conformations is poorly understood. The serpin family of metastable protease inhibitors uses large conformational changes that are downhill in free energy to inhibit target proteases by pulling apart the protease active site. The serpin antithrombin III (ATIII) targets thrombin and other proteases involved in blood coagulation, and ATIII misfolding can thus lead to thrombosis and other diseases. ATIII has three disulfide bonds, two near the N terminus and one near the C terminus. Our studies of ATIII in-cell folding reveal a surprising, biased order of disulfide bond formation, with early formation of the C-terminal disulfide, before formation of the N-terminal disulfides, critical for folding to the active, metastable state. Early folding of the predominantly β-sheet ATIII domain in this two-domain protein constrains the reactive center loop (RCL), which contains the protease-binding site, ensuring that the RCL remains accessible. N-linked glycans and carbohydrate-binding molecular chaperones contribute to the efficient folding and secretion of functional ATIII. The inability of a number of disease-associated ATIII variants to navigate the folding reaction helps to explain their disease phenotypes. PMID:27222580

  17. Excitation of metastable argon and helium atoms by electron impact

    NASA Technical Reports Server (NTRS)

    Borst, W. L.

    1974-01-01

    Using a time-of-flight method, the excitation of argon and helium metastables by electron impact is investigated in the energy range from threshold to about 50 eV. The secondary-electron yields of the metastable detector used are reviewed in detail. The effect of metastable recoil is also discussed. Comparisons with data from other investigators are presented.

  18. 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

  19. 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.

  20. 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.

  1. Metastable dynamics in heterogeneous neural fields.

    PubMed

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

    2015-01-01

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

  2. New metastable states in supercritical QED

    SciTech Connect

    Hirata, Y.S.; Minakata, H.

    1989-05-01

    It is shown that new metastable charge-neutral states exist in the supercritical phase of QED around a large-Z nucleus. They are the vibration modes of the induced electron cloud and therefore do not exist in the normal phase. Under the adiabatic approximation it is argued that the states mimic the stable particle states and may be responsible for the peak structure in e/sup +/e/sup -/ spectra found in heavy-ion-collision experiments.

  3. Optimized Markov state models for metastable systems

    NASA Astrophysics Data System (ADS)

    Guarnera, Enrico; Vanden-Eijnden, Eric

    2016-07-01

    A method is proposed to identify target states that optimize a metastability index amongst a set of trial states and use these target states as milestones (or core sets) to build Markov State Models (MSMs). If the optimized metastability index is small, this automatically guarantees the accuracy of the MSM, in the sense that the transitions between the target milestones is indeed approximately Markovian. The method is simple to implement and use, it does not require that the dynamics on the trial milestones be Markovian, and it also offers the possibility to partition the system's state-space by assigning every trial milestone to the target milestones it is most likely to visit next and to identify transition state regions. Here the method is tested on the Gly-Ala-Gly peptide, where it is shown to correctly identify the expected metastable states in the dihedral angle space of the molecule without a priori information about these states. It is also applied to analyze the folding landscape of the Beta3s mini-protein, where it is shown to identify the folded basin as a connecting hub between an helix-rich region, which is entropically stabilized, and a beta-rich region, which is energetically stabilized and acts as a kinetic trap.

  4. 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.

  5. 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.

  6. 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. PMID:27475077

  7. Metastable Equilibria Among Aqueous Organic Compounds

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-07-01

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

  9. 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.

  10. Transient Cognitive Dynamics, Metastability, and Decision Making

    PubMed Central

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

    2008-01-01

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

  11. Stability and metastability of bromine clathrate polymorphs.

    PubMed

    Nguyen, Andrew H; Molinero, Valeria

    2013-05-23

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

  12. Metastable feshbach molecules in high rotational states.

    PubMed

    Knoop, S; Mark, M; Ferlaino, F; Danzl, J G; Kraemer, T; Nägerl, H-C; Grimm, R

    2008-02-29

    We experimentally demonstrate Cs2 Feshbach molecules well above the dissociation threshold, which are stable against spontaneous decay on the time scale of 1 s. An optically trapped sample of ultracold dimers is prepared in a high rotational state and magnetically tuned into a region with a negative binding energy. The metastable character of these molecules arises from the large centrifugal barrier in combination with negligible coupling to states with low rotational angular momentum. A sharp onset of dissociation with increasing magnetic field is mediated by a crossing with a lower rotational dimer state and facilitates dissociation on demand with a well-defined energy. PMID:18352621

  13. Noise-induced metastability in biochemical networks.

    PubMed

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

    2012-07-01

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

  14. Metastability in spin-polarized Fermi gases.

    PubMed

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

    2011-09-30

    We study the role of particle transport and evaporation on the phase separation of an ultracold, spin-polarized atomic Fermi gas. We show that the previously observed deformation of the superfluid paired core is a result of evaporative depolarization of the superfluid due to a combination of enhanced evaporation at the center of the trap and the inhibition of spin transport at the normal-superfluid phase boundary. These factors contribute to a nonequilibrium jump in the chemical potentials at the phase boundary. Once formed, the deformed state is highly metastable, persisting for times of up to 2 s. PMID:22107209

  15. Metastable phase formation in undercooled liquid lead alloys

    NASA Technical Reports Server (NTRS)

    Fecht, Hans J.

    1991-01-01

    During non-equilibrium processes metastable phases are formed instead of stable phases due to the operation of various kinetic or structural constraints. By removing the most effective nucleation sites for the stable phase using emulsified droplet samples, stable phase formation can be prohibited in a broad range of undercooling and the phase space available in the metastable regime can be mapped out. With this method the thermodynamic properties of the undercooled liquid and the metastable phase boundaries corresponding to reversible metastable (solid + liquid) phase equilibria are examined from experimental data. The analysis reveals important implications for the nucleation kinetics and the choice of the kinetically most favored solidification path.

  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. Development of a second generation experiment to measure the 2(3)S(1) transition to 2(3)P(J) intervals in positronium

    NASA Astrophysics Data System (ADS)

    Engbrecht, Jason John

    Positronium has proven to be a rich testing ground for Quantum Electrodynamics over the last half of the twentieth century. The 23S1 → 23PJ intervals in positronium have previously been measured and disagreements currently exist amongst various experiments and between some experiments and theoretical predictions. Furthermore, recent advances in theory have produced predictions with much higher precision than the current experiments. Therefore, work has been done to develop a 2 nd generation experiment to measure the 23S1 → 23PJ intervals in positronium. Previous experiments used the enhancement of the Lyman-a radiation from the 23P J states in order to observe the 23S1 → 23PJ resonance line. In the 2nd generation experiment the 23S1 positronium is observed by photo-ionizing the positronium and detecting the photo-positron. This signal is then depleted when microwave radiation is applied on resonance as compared to the signal off resonance. The ultimate goal of the 2nd generation experiment is to improve the precision of the measurement of the 2 3S1 → 23P2 interval from 1.5 MHz to 100 kHz. This dissertation describes the current status of the development of this 2nd generation experiment. This includes the development of all of the major subsystems necessary for detecting the 23S 1 → 23PJ transition, including the accumulated positron beam, the pulsed laser beam, the microwave delivery apparatus, and the interaction region. Results are presented showing the first photo-positron signal using an accumulated positron beam. The rate of this signal is approximately 100 mHz as compared to 15 mHz in the 1st generation experiments. This rate is sufficient to produce a 23S1 → 23P2 interval measurement with precision of 3 MHz with 8 hours of data acquisition and 600 kHz after 30 days. Potential improvements to the technique are suggested to allow for a 100 kHz measurement. Additionally, results are presented for Doppler broadening measurements of thermalization of

  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. Metastable Atom Detection Using Solid N2

    NASA Astrophysics Data System (ADS)

    McConkey, William; Kedzierski, Wladek; Lukic, Dragan

    2014-05-01

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

  20. 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.

  1. Simulation of metastable CL-20 cluster structures

    NASA Astrophysics Data System (ADS)

    Degtyarenko, N. N.; Katin, K. P.; Maslov, M. M.

    2014-07-01

    Ensembles of C6H6N12O12 (CL-20) clusters with different types of intercluster bonds have been studied theoretically. The stability of such cluster has been investigated and the heights of potential barriers preventing their decomposition or isomerization have been determined by means of quantum-mechanical calculations based on the density functional theory and nonorthogonal tight-binding model. From the analysis of molecular dynamics data and potential energy hypersurface of these metastable configurations, it has been established that dimers and tetramers of CL-20 clusters are characterized by sufficiently high kinetic stability, which suggests the theoretical possibility of creation of high-energy covalent crystals on their basis.

  2. Metastable orientational order of colloidal discoids

    PubMed Central

    Hsiao, Lilian C.; Schultz, Benjamin A.; Glaser, Jens; Engel, Michael; Szakasits, Megan E.; Glotzer, Sharon C.; Solomon, Michael J.

    2015-01-01

    The interplay between phase separation and kinetic arrest is important in supramolecular self-assembly, but their effects on emergent orientational order are not well understood when anisotropic building blocks are used. Contrary to the typical progression from disorder to order in isotropic systems, here we report that colloidal oblate discoids initially self-assemble into short, metastable strands with orientational order—regardless of the final structure. The model discoids are suspended in a refractive index and density-matched solvent. Then, we use confocal microscopy experiments and Monte Carlo simulations spanning a broad range of volume fractions and attraction strengths to show that disordered clusters form near coexistence boundaries, whereas oriented strands persist with strong attractions. We rationalize this unusual observation in light of the interaction anisotropy imparted by the discoids. These findings may guide self-assembly for anisotropic systems in which orientational order is desired, such as when tailored mechanical properties are sought. PMID:26443082

  3. Metastable cosmic strings in realistic models

    SciTech Connect

    Holman, R.; Hsu, S.; Vachaspati, T.; Watkins, R. |

    1992-11-01

    The stability of the electroweak Z-string is investigated at high temperatures. The results show that, while finite temperature corrections can improve the stability of the Z-string, their effect is not strong enough to stabilize the Z-string in the standard electroweak model. Consequently, the Z-string will be unstable even under the conditions present during the electroweak phase transition. Phenomenologically viable models based on the gauge group SU(2){sub L} {times} SU(2) {sub R} {times} U(1){sub B-L} are then considered, and it is shown that metastable strings exist and are stable to small perturbations for a large region of the parameter space for these models. It is also shown that these strings are superconducting with bosonic charge carriers. The string superconductivity may be able to stabilize segments and loops against dynamical contraction. Possible implications of these strings for cosmology are discussed.

  4. Metastable cosmic strings in realistic models

    SciTech Connect

    Holman, R. . Dept. of Physics); Hsu, S. . Lyman Lab. of Physics); Vachaspati, T. . Dept. of Physics and Astronomy); Watkins, R. Fermi National Accelerator Lab., Batavia, IL )

    1992-01-01

    The stability of the electroweak Z-string is investigated at high temperatures. The results show that, while finite temperature corrections can improve the stability of the Z-string, their effect is not strong enough to stabilize the Z-string in the standard electroweak model. Consequently, the Z-string will be unstable even under the conditions present during the electroweak phase transition. Phenomenologically viable models based on the gauge group SU(2)[sub L] [times] SU(2) [sub R] [times] U(1)[sub B-L] are then considered, and it is shown that metastable strings exist and are stable to small perturbations for a large region of the parameter space for these models. It is also shown that these strings are superconducting with bosonic charge carriers. The string superconductivity may be able to stabilize segments and loops against dynamical contraction. Possible implications of these strings for cosmology are discussed.

  5. 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.

  6. Enhancement of stability in systems with metastable states

    SciTech Connect

    Spagnolo, B.; Augello, G.; Pizzolato, N.; Valenti, D.; Fiasconaro, A.

    2007-12-06

    The investigation of noise-induced phenomena in far from equilibrium systems is one of the approach used to understand the behaviour of physical and biological complex systems. Metastability is a generic feature of many nonlinear systems, and the problem of the lifetime of metastable states involves fundamental aspects of nonequilibrium statistical mechanics. The enhancement of the life-time of metastable states through the noise enhanced stability effect and the role played by the resonant activation phenomenon will be discussed in models of interdisciplinary physics: (i) Ising model (ii) Josephson junction; (iii) stochastic FitzHugh-Nagumo model; (iv) a population dynamics model, and (v) a market model with stochastic volatility.

  7. Dissociation-excitation reactions of argon metastables with carbon dioxide.

    NASA Technical Reports Server (NTRS)

    Starr, W. L.

    1971-01-01

    Results of a study showing that a metastable argon-carbon dioxide reaction results in dissociation of carbon dioxide and electronic excitation of one of the products, carbon monoxide or oxygen. A flow system using a 2450-MHz discharge was used to produce metastable argon atoms. Metastable argon in the afterglow was confirmed by adding nitrogen to the afterglow. Without addition of carbon dioxide no argon line emission, or any other emission, is observed from the reaction zone. Absence of argon line emission produced by recombination indicates the absence of charged species.

  8. Metastable oxygen molecules in the troposphere.

    PubMed

    Schurath, U

    1987-01-01

    The sources and steady-state concentration of singlet oxygen in the atmosphere are assessed in view of potential effects on the biosphere. Collision-induced absorption of sunlight by molecular oxygen in 1 atm of air produces O2 (a1 delta g) at a rate P = 1.6 x 10(9) cm-3 s-1 in bright sunlight. Less than 10% are added to this purely natural source by the photolysis of ozone, and by anthropogenic sensitizers (SO2, NO2, volatile aromatics). Collisional quenching of O2 (a1 delta g) by ground state oxygen establishes a steady-state concentration of ca. 1.7 x 10(8) cm-3. Reactions of singlet oxygen with other atmospheric pollutants are entirely negligible when compared with the concurrent reactions of ambient OH and O3. Potential effects of atmospheric singlet oxygen on the biosphere are limited by the deposition rate F less than or equal to 0.051 P, which depends on the production rate P of O2 (a1 delta g) in the air layer immediately above the flat surface.

  9. 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

  10. 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.

  11. Propagation studies of metastable intermolecular composites (MIC).

    SciTech Connect

    Son, S. F.; Busse, J. R.; Asay, B. W.; Peterson, P. D.; Mang, J. T.; Bockmon, B.; Pantoya, M.

    2002-01-01

    Thermite materials are attractive energetic materials because the reactions are highly exothermic, have high energy densities, and high temperatures of combustion. However, the application of thermite materials has been limited because of the relative slow release of energy compared to other energetic materials. Engineered nano-scale composite energetic materials, such as Al/MoO{sub 3}, show promise for additional energetic material applications because they can react very rapidly. The composite material studied in this work consists of tailored, ultra-fine grain (30-200 nm diameter) aluminum particles that dramatically increase energy release rates of these thermite materials. These reactant clusters of fuel and oxidizer particles are in nearly atomic scale proximity to each other but are constrained from reaction until triggered. Despite the growing importance of nano-scale energetic materials, even the most basic combustion characteristics of these materials have not been thoroughly studied. This paper reports initial studies of the ignition and combustion of metastable intermolecular composites (MIC) materials. The goals were lo obtain an improved understanding of flame propagation mechanisms and combustion behaviors associated with nano-structured energetic materials. Information on issues such as reaction rate and behavior as a function of composition (mixture ratio), initial static charge, and particle size are essential and will allow scientists to design applications incorporating the benefits of these compounds. The materials have been characterized, specifically focusing on particle size, shape, distribution and morphology.

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

    PubMed

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

    2016-06-17

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

  13. Rates and mechanisms of metastable deactivation over surfaces

    NASA Astrophysics Data System (ADS)

    Rawlins, W. T.; Marinelli, W. J.; Woodward, A. M.; Kaufman, D.; Upschulte, B. L.

    1991-02-01

    The objective of this project was to investigate mechanisms of energy disposal in the quenching of rare gas and molecular metastable species upon collisions with practical surfaces representative of plasma reactors. An apparatus was designed and constructed to generate a molecular beam of selected metastable species (He*, Ar*, N2*) and impinge the beam on clean or gas-dosed surfaces in an ultra high vacuum (UHV) chamber. The metastables were generated in a discharge-flow reactor, sampled and skimmed into a molecular beam, and directed into the UHV target chamber via two-stage differential pumping. A hemispherical, retarding potential electron energy analyzer was used to measure production rates and energy distributions of electrons ejected from the surface via the Penning ionization and Auger neutralization quenching mechanisms. The absence of significant electron ejection from metastable impingement is quite unexpected in light of previous investigations of this process for polished, high-purity, oriented single crystals.

  14. Slow metastable atomic hydrogen beam by optical pumping

    NASA Astrophysics Data System (ADS)

    Harvey, K. C.

    1982-05-01

    A beam source of atomic hydrogen is described which produces metastable atoms in the 2S1/2 state by optical pumping. A beam flux of 1016 atoms/s is generated in the ground state. The atoms in the beam pass in front of a lamp producing Lyman-β (1026 Å) radiation, where some of them are excited to the 3P level and cascade with a branching ratio of 12% to the 2S1/2 state. The number of metastable atoms produced is measured by quenching them with an electric field and detecting the emitted Lyman-α (1216 Å) radiation. Beams of 106 metastable atoms/s were obtained. Using the Bethe-Lamb theory for the quenching process, a metastable beam effective temperature of 100 K was measured.

  15. 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.

  16. Metastable states in the Cd-As system

    SciTech Connect

    Nipan, G.D.; Grinberg, Ya.Kh.; Lazarev, V.B.

    1988-03-01

    Attempts to explain the appearance of metastable states in the system Cd-As have thus far been based only on thermographic experiments. In this work paths for metastable crystallization of cadmium arsenides in the phase space p-T-x are studied. The metastable diagrams were constructed using fragment of p-T and T-x projections of the p-T-x phase diagram. Thermodynamic analysis shows that metastable states of two types can be expected in the system Cd-As: (I) crystallization of Ca/sub 3/As/sub 2/ and arsenic instead of the equilibrium crystallization of CdAs/sub 2/; (II) crystallization of CdAs and arsenic or Cd/sub 3/As/sub 2/ instead of the formation of CdAs/sub 2/.

  17. Discovery of a metastable Al20Sm4 phase

    DOE PAGES

    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.; et al

    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.

  18. Metastable NAT in Ice-Clouds

    NASA Astrophysics Data System (ADS)

    Weiss, Fabian; Kubel, Frank; Gálvez, Óscar; Hoelzel, Markus; Parker, Stewart F.; Iannarelli, Riccardo; Rossi, Michel J.; Grothe, Hinrich

    2015-04-01

    Polar Stratospheric Clouds and Cirrus Clouds contain, besides pure water ice, a rather large fraction of various hydrates. These are very important for the formation of the cloud, which is a yet not well understood process. We recently solved the structure of a metastable NAT phase (alpha-NAT), we believe to not only be present, but playing a major role in the formation of clouds. On the basis of previous work on this phase by Grothe et al. [1], we enhanced the production of alpha-NAT to the point, where we could produce enough sample to do neutron diffraction. This enabled us to solve the structure. Our quantum mechanical calculations, using this newly found structure, show a large affinity towards water-ice. With this in mind, we interlaced our results with the experiments of R. Iannarelli [2] to derive a new 3-step NAT-formation mechanism in ice-clouds, which could explain some of the observed kinetics better than the mechanism postulated in Zondlo et al. [3]. 1. Grothe, H., Tizek, H., Waller, D. & Stokes, D. The crystallization kinetics and morphology of nitric acid trihydrate. Phys. Chem. Chem. Phys., 8, 2232-2239 (2006) 2. Iannarelli, R. Multidiagnostic Observations on HCl and HNO3 Hydrate Films in the Temperature Range 170-205K: A Kinetic Study. PhD Thesis 21791, ETH Zürich, (2013). 3. Zondlo, M.A., Hudson, P.K., Prenni A.J. & Tolbert, M.A. Chemistry and microphysics of polar stratospheric clouds and Cirrus clouds. Ann. Rev. Phys. Chem., 51, 473-499 (2000).

  19. 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

  20. Stable and Metastable Equilibria in the Pb-Cd System

    NASA Astrophysics Data System (ADS)

    Chuang, Ying-Yu; Paik, J.-S.; Zhang, C.; Perepezko, J. H.; Chang, Y. A.

    2013-07-01

    Thermodynamic and phase diagram data in the Pb-Cd system are reevaluated. A substitutional solution model is used for the liquid and fcc and hcp phases. The stable and metastable equilibria of this system are calculated using the thermodynamic equations derived from equilibrium data. Besides the well-established eutectic reaction at 521 K (248 °C), one stable monotectic reaction at 548 K (275 °C) is found due to the existence of a stable liquid miscibility gap. The stable monotectic reaction has been missed in all previous evaluations. Experimental verifications of the stable and metastable phase equilibria are provided using droplet samples and undercooled liquid alloys. A differential thermal analysis (DTA) method is applied to determine the phase reaction temperatures using both traditional heating and cooling processes and a specially designed cycling process. Additional microstructural evidence is used to elucidate the nature of the phase reactions. The refined thermodynamic descriptions are based upon both the thermochemical and phase diagram stable and metastable data. The agreement between the calculated and experimental data is good. All experimental stable and metastable results are well explained by the new Pb-Cd phase diagram calculations within the experimental accuracy limits. Combined experimental and thermodynamic modeling procedures developed for determining the stable and metastable phase equilibria yield a highly reliable overall phase diagram assessment and a quantitative basis for the interpretation of non-equilibrium solidification processing.

  1. Long-Lived Metastable bcc Phase during Ordering of Micelles

    NASA Astrophysics Data System (ADS)

    Bang, Joona; Lodge, Timothy P.

    2005-03-01

    We report a metastable bcc phase that intervenes between a disordered micellar suspension and an fcc crystal in a block copolymer solution. A symmetric poly(styrene-b-isoprene) diblock copolymer in the isoprene-selective solvent squalane at a volume fraction of 0.20 was investigated using small angle x-ray scattering and rheology. Upon heating, the metastable bcc phase nucleates first, and then transforms over the course of hours to the stable fcc phase. At still higher temperatures the fcc phase transforms to an equilibrium bcc phase. The metastability of the bcc phase was confirmed by oscillatory shear and annealing using small angle x-ray scattering. These results constitute an interesting experimental manifestation of Ostwald's step rule, and also support recent theory and simulation results whereby bcc nucleates more readily from a melt of spheres.

  2. Degenerate Bose-Fermi Mixture of Metastable Atoms

    SciTech Connect

    McNamara, J. M.; Jeltes, T.; Tychkov, A. S.; Hogervorst, W.; Vassen, W.

    2006-08-25

    We report the observation of simultaneous quantum degeneracy in a dilute gaseous Bose-Fermi mixture of metastable atoms. Sympathetic cooling of helium-3 (fermion) by helium-4 (boson), both in the lowest triplet state, allows us to produce ensembles containing more than 10{sup 6} atoms of each isotope at temperatures below 1 {mu}K, and achieve a fermionic degeneracy parameter of T/T{sub F}=0.45. Because of their high internal energy, the detection of individual metastable atoms with subnanosecond time resolution is possible, permitting the study of bosonic and fermionic quantum gases with unprecedented precision. This may lead to metastable helium becoming the mainstay of quantum atom optics.

  3. 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.

  4. Argon metastable production in argon-helium microplasmas

    NASA Astrophysics Data System (ADS)

    Hoskinson, Alan R.; Gregorío, José; Hopwood, Jeffrey; Galbally-Kinney, Kristin; Davis, Steven J.; Rawlins, Wilson T.

    2016-06-01

    Microwave resonator-driven microplasmas are a promising technology for generating the high density of rare-gas metastable states required for optically pumped rare gas laser systems. We measure the density of argon 1s5 states (Paschen notation) in argon-helium plasmas between 100 Torr and atmospheric pressure using diode laser absorption. The metastable state density is observed to rise with helium mole fraction at lower pressures but to instead fall slightly when tested near atmospheric pressure. A 0-D model of the discharge suggests that these distinct behaviors result from the discharge being diffusion-controlled at lower pressures, but with losses occurring primarily through dissociative recombination at high pressures. In all cases, the argon metastable density falls sharply when the neutral argon gas fraction is reduced below approximately 2%.

  5. 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.

  6. 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. PMID:25240360

  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. 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.

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

    NASA Technical Reports Server (NTRS)

    Kharchenko, Vasili; Dalgarno, A.

    2005-01-01

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

  11. Origin of photoinduced metastable defects in amorphous chalcogenides

    NASA Astrophysics Data System (ADS)

    Shimakawa, K.; Inami, S.; Kato, T.; Elliott, S. R.

    1992-10-01

    Prolonged exposure to band-gap light decreases the photoconductivity of annealed films of amorphous chalcogenides (As2S3, As3S7, AsS, As2Se3, GeS2, GeSe2, and GeSe). This can be attributed to photoinduced metastable defects, which could act as additional trapping and/or recombination centers. These metastable centers are removed by annealing near the glass transition temperature. The kinetics of the temporal change of photocurrent during illumination are discussed in a model of defect-conserved bond switching.

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

    SciTech Connect

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

    2015-09-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  14. Strong attraction between charged spheres due to metastable ionized states

    PubMed

    Messina; Holm; Kremer

    2000-07-24

    We report a mechanism which can lead to long-range attractions between like-charged spherical macroions, stemming from the existence of metastable ionized states. We show that the ground state of a single highly charged colloid plus a few excess counterions is overcharged. For the case of two highly charged macroions in their neutralizing divalent counterion solution we demonstrate that, in the regime of strong Coulomb coupling, the counterion clouds are very likely to be unevenly distributed, leading to one overcharged and one undercharged macroion. This long-living metastable configuration in turn leads to a long-range Coulomb attraction.

  15. Selective detection of singlet gerade metastable states of N2

    NASA Astrophysics Data System (ADS)

    Kedzierski, W.; McConkey, J. W.

    2016-07-01

    Metastable N2 molecules produced by electron impact on N2 are detected using a unique solid nitrogen matrix detector. The time-of-flight system is shown to be selectively sensitive to a1Πg and 1Σg+ or 1Γg metastable species. The latter species had been identified theoretically previously but was detected experimentally for the first time in the present investigation. Their identification and excitation as a function of electron energy from threshold to 300 eV are presented. Comparison is made with the data obtained by other techniques.

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

    SciTech Connect

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

    1993-08-01

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

  17. 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.

  18. Global segregation of cortical activity and metastable dynamics

    PubMed Central

    Stratton, Peter; Wiles, Janet

    2015-01-01

    Cortical activity exhibits persistent metastable dynamics. Assemblies of neurons transiently couple (integrate) and decouple (segregate) at multiple spatiotemporal scales; both integration and segregation are required to support metastability. Integration of distant brain regions can be achieved through long range excitatory projections, but the mechanism supporting long range segregation is not clear. We argue that the thalamocortical matrix connections, which project diffusely from the thalamus to the cortex and have long been thought to support cortical gain control, play an equally-important role in cortical segregation. We present a computational model of the diffuse thalamocortical loop, called the competitive cross-coupling (CXC) spiking network. Simulations of the model show how different levels of tonic input from the brainstem to the thalamus could control dynamical complexity in the cortex, directing transitions between sleep, wakefulness and high attention or vigilance. The model also explains how mutually-exclusive activity could arise across large portions of the cortex, such as between the default-mode and task-positive networks. It is robust to noise but does not require noise to autonomously generate metastability. We conclude that the long range segregation observed in brain activity and required for global metastable dynamics could be provided by the thalamocortical matrix, and is strongly modulated by brainstem input to the thalamus. PMID:26379514

  19. Metastable Oxygen Production by Electron-Impact of Oxygen

    NASA Astrophysics Data System (ADS)

    Hein, Jeffrey; Johnson, Paul; Kanik, Isik; Malone, Charles

    2014-05-01

    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 produced through electron impact, and is incident on a cryogenically cooled rare gas matrix. The excimer production and subsequent rapid radiative de-excitation provides measurable signal that is directly related to the originating electron-impact excitation process.

  20. Global segregation of cortical activity and metastable dynamics.

    PubMed

    Stratton, Peter; Wiles, Janet

    2015-01-01

    Cortical activity exhibits persistent metastable dynamics. Assemblies of neurons transiently couple (integrate) and decouple (segregate) at multiple spatiotemporal scales; both integration and segregation are required to support metastability. Integration of distant brain regions can be achieved through long range excitatory projections, but the mechanism supporting long range segregation is not clear. We argue that the thalamocortical matrix connections, which project diffusely from the thalamus to the cortex and have long been thought to support cortical gain control, play an equally-important role in cortical segregation. We present a computational model of the diffuse thalamocortical loop, called the competitive cross-coupling (CXC) spiking network. Simulations of the model show how different levels of tonic input from the brainstem to the thalamus could control dynamical complexity in the cortex, directing transitions between sleep, wakefulness and high attention or vigilance. The model also explains how mutually-exclusive activity could arise across large portions of the cortex, such as between the default-mode and task-positive networks. It is robust to noise but does not require noise to autonomously generate metastability. We conclude that the long range segregation observed in brain activity and required for global metastable dynamics could be provided by the thalamocortical matrix, and is strongly modulated by brainstem input to the thalamus.

  1. Metastable atom probe for measuring electron beam density profiles

    NASA Technical Reports Server (NTRS)

    Lockhart, J. M.; Zorn, J. C.

    1972-01-01

    Metastable atom probe was developed for measuring current density in electron beam as function of two arbitrary coordinates, with spatial resolution better than 0.5 mm. Probe shows effects of space charge, magnetic fields, and other factors which influence electron current density, but operates with such low beam densities that introduced perturbation is very small.

  2. Nucleation of metastable aragonite CaCO3 in seawater

    DOE PAGES

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

    2015-03-04

    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 ofmore » 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.« less

  3. 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

  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. Electron impact excitation of the low-lying 3s[3∕2]1 and 3s'[1∕2]1 levels in neon for incident energies between 20 and 300 eV.

    PubMed

    Hoshino, M; Murai, H; Kato, H; Brunger, M J; Itikawa, Y; Tanaka, H

    2013-11-14

    Absolute differential cross sections (DCSs) for electron impact of the two lower-lying 3s[3∕2]1 ((3)P0) and 3s(')[1∕2]1 ((1)P1) electronic states in neon (Ne) have been determined for eight incident electron energies in the range 20-300 eV. Comparisons between our results and previous measurements and calculations, where possible, are provided with best agreement being found with the recent large-scale B-spline R-matrix computations [O. Zatsarinny and K. Bartschat, Phys. Rev. A 86, 022717 (2012)]. Based on these DCSs at 100, 200, and 300 eV, a generalised oscillator strength analysis enabled us to determine estimates for the optical oscillator strengths of the 3s[3∕2]1 and 3s(')[1∕2]1 levels. In this case, excellent agreement was found with a range of independent experiments and calculations, giving us some confidence in the validity of our measurement and analysis procedures. Integral cross sections, derived from the present DCSs, were presented graphically and discussed elsewhere [M. Hoshino, H. Murai, H. Kato, Y. Itikawa, M. J. Brunger, and H. Tanaka, Chem. Phys. Lett. 585, 33 (2013)], but are tabulated here for completeness.

  6. Relativistic evaluation of the two-photon decay of the metastable 1 s22 s 2 p 3P0 state in berylliumlike ions with an effective-potential model

    NASA Astrophysics Data System (ADS)

    Amaro, Pedro; Fratini, Filippo; Safari, Laleh; Machado, Jorge; Guerra, Mauro; Indelicato, Paul; Santos, José Paulo

    2016-03-01

    The two-photon 1 s22 s 2 p 3P0→1 s2s21S0 transition in berylliumlike ions is investigated theoretically within a fully relativistic framework and a second-order perturbation theory. We focus our analysis on how electron correlation, as well as the negative-energy spectrum, can affect the forbidden E 1 M 1 decay rate. For this purpose, we include the electronic correlation via an effective local potential and within a single-configuration-state model. Due to its experimental interest, evaluations of decay rates are performed for berylliumlike xenon and uranium. We find that the negative-energy contribution can be neglected at the present level of accuracy in the evaluation of the decay rate. On the other hand, if contributions of electronic correlation are not carefully taken into account, it may change the lifetime of the metastable state by up to 20%. By performing a fully relativistic j j -coupling calculation, we find a decrease of the decay rate by two orders of magnitude compared to nonrelativistic L S -coupling calculations, for the selected heavy ions.

  7. 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

    2013-07-01

    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.

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

    PubMed

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

    2007-04-01

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

  9. 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.

  10. Homonuclear ionizing collisions of laser-cooled metastable helium atoms

    SciTech Connect

    Stas, R. J. W.; McNamara, J. M.; Hogervorst, W.; Vassen, W.

    2006-03-15

    We present a theoretical and experimental investigation of homonuclear ionizing collisions of laser-cooled metastable (2 {sup 3}S{sub 1}) helium atoms, considering both the fermionic {sup 3}He and bosonic {sup 4}He isotopes. The theoretical description combines quantum threshold behavior, Wigner's spin-conservation rule, and quantum-statistical symmetry requirements in a single-channel model, complementing a more complete close-coupling theory that has been reported for collisions of metastable {sup 4}He atoms. The model is supported with measurements (in the absence of light fields) of ionization rates in magneto-optically trapped samples that contain about 3x10{sup 8} atoms of a single isotope. The ionization rates are determined from measurements of trap loss due to light-assisted collisions combined with comparative measurements of the ion production rate in the absence and presence of trapping light. Theory and experiment show good agreement.

  11. Geometric phases causing lifetime modifications of metastable states of hydrogen

    NASA Astrophysics Data System (ADS)

    Trappe, Martin-Isbjörn; Augenstein, Peter; DeKieviet, Maarten; Gasenzer, Thomas; Nachtmann, Otto

    2016-04-01

    Externally applied electromagnetic fields in general have an influence on the width of atomic spectral lines. The decay rates of atomic states can also be affected by the geometry of an applied field configuration giving rise to an imaginary geometric phase. A specific chiral electromagnetic field configuration is presented which geometrically modifies the lifetimes of metastable states of hydrogen. We propose to extract the relevant observables in a realistic longitudinal atomic beam spin-echo apparatus which allows the initial and final fluxes of the metastable atoms to be compared with each other interferometrically. A geometry-induced change in lifetimes at the 5%-level is found, an effect large enough to be observed in an available experiment.

  12. Dependence of stability of metastable superconductors on copper fraction

    SciTech Connect

    Elrod, S. A.; Lue, J. W.; Miller, J. R.; Dresner, L.

    1980-12-01

    The stability of composite superconductors operating in the metastable regime depends upon such factors as matrix resistivity, cooled surface dimensions, fraction of critical current, and volume fraction of stabilizer. By assuming constant thermophysical properties, we developed analytic expressions for the energy and voltage of the minimum propagating zone (MPZ). With other factors held constant, these expressions have been used to predict composite superconductor stability as a function of copper fraction: lower copper fractions lead to higher MPZ energies. MPZ voltages have been measured for three NbTi/Cu composites having different copper fractions and different critical current densities for several magnetic fields and transport currents. Experimental MPZ voltages have been used to calculate an effective heat transfer coefficient, which is subsequently used to calculate the MPZ energy. The experimental MPZ energies support the theoretical expectation that lower copper fractions lead to higher stability in the metastable regime.

  13. 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.

  14. 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. PMID:25196134

  15. 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.

  16. 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. PMID:27400387

  17. Breaking of a metastable string at finite temperature

    SciTech Connect

    Monin, A.; Voloshin, M. B.

    2008-12-15

    We consider the phase transition of a string with tension {epsilon}{sub 1} to a string with a smaller tension {epsilon}{sub 2} at finite temperature. For sufficiently small temperatures the transition proceeds through thermally catalyzed quantum tunneling, and we calculate in arbitrary number of dimensions the thermal catalysis factor. At {epsilon}{sub 2}=0 the found formula for the decay rate also describes a breakup of a metastable string into two pieces.

  18. Deexcitation mechanisms in metastable He-surface collisions

    NASA Astrophysics Data System (ADS)

    Conrad, H.; Ertl, G.; Küppers, J.; Sesselman, W.; Haberland, H.

    1980-11-01

    Electron emission caused by impact of metastable He atoms on surfaces can either proceed by a two-stage resonance ionization + Auger neutralisation (RI + AN) or by a one-stage Auger deexcitation (AD or Penning ionization) mechanism. The RI + AN mechanism will dominate with clean transition metal surfaces and may be suppressed for example by lowering the local work function as demonstrated for K and Cs adlayers.

  19. Metastable growth of pure wurtzite InGaAs microstructures.

    PubMed

    Ng, Kar Wei; Ko, Wai Son; Lu, Fanglu; Chang-Hasnain, Connie J

    2014-08-13

    III-V compound semiconductors can exist in two major crystal phases, namely, zincblende (ZB) and wurtzite (WZ). While ZB is thermodynamically favorable in conventional III-V epitaxy, the pure WZ phase can be stable in nanowires with diameters smaller than certain critical values. However, thin nanowires are more vulnerable to surface recombination, and this can ultimately limit their performances as practical devices. In this work, we study a metastable growth mechanism that can yield purely WZ-phased InGaAs microstructures on silicon. InGaAs nucleates as sharp nanoneedles and expand along both axial and radial directions simultaneously in a core-shell fashion. While the base can scale from tens of nanometers to over a micron, the tip can remain sharp over the entire growth. The sharpness maintains a high local surface-to-volume ratio, favoring hexagonal lattice to grow axially. These unique features lead to the formation of microsized pure WZ InGaAs structures on silicon. To verify that the WZ microstructures are truly metastable, we demonstrate, for the first time, the in situ transformation from WZ to the energy-favorable ZB phase inside a transmission electron microscope. This unconventional core-shell growth mechanism can potentially be applied to other III-V materials systems, enabling the effective utilization of the extraordinary properties of the metastable wurtzite crystals.

  20. Thermal beam of metastable krypton atoms produced by optical excitation

    SciTech Connect

    Ding, Y.; Hu, S.-M.; Bailey, K.; Davis, A. M.; Dunford, R. W.; Lu, Z.-T.; O'Connor, T. P.; Young, L.

    2007-02-15

    A room-temperature beam of krypton atoms in the metastable 5s[3/2]{sub 2} level is demonstrated via an optical excitation method. A Kr-discharge lamp is used to produce vacuum ultraviolet photons at 124 nm for the first-step excitation from the ground level 4p{sup 6} {sup 1}S{sub 0} to the 5s[3/2]{sub 1} level. An 819 nm Ti:sapphire laser is used for the second-step excitation from 5s[3/2]{sub 1} to 5s[3/2]{sub 2} followed by a spontaneous decay to the 5s[3/2]{sub 2} metastable level. A metastable atomic beam with an angular flux density of 3x10{sup 14} s{sup -1} sr{sup -1} is achieved at the total gas flow rate of 0.01 cm{sup 3}/s at STP (or 3x10{sup 17} at./s). The dependences of the flux on the gas flow rate, laser power, and lamp parameters are investigated.

  1. Detecting vapour bubbles in simulations of metastable water.

    PubMed

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

    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. PMID:25399176

  2. Study on the metastable zone width of ketoprofen.

    PubMed

    Lu, Ying Hong; Ching, Chi Bun

    2006-05-01

    With increasing awareness for the need of pure enantiomer drugs, strong emphasis has been focused on the research of chiral drug separation. Compared with other separation methods, crystallization is a simple and economical method, and the metastable zone width (MSZW) is a very important factor for the entire crystallization process. In this paper, the effects of the metastable zones of (R,S)- and (S)-ketoprofen and a 0.94 mole fraction of (S)-ketoprofen in order to enhance the MSZW were studied. Four main factors were studied, namely, temperature, cooling rate, stirring rate, and volume ratio of mixed solvent (water/ethanol). Through the L9 fractional experiment design, it was observed that all samples' MSZWs would increase with an increase in cooling rate and decrease with an increase in the ethanol volume ratio and temperature. The ethanol ratio may have the strongest effect on the process and can greatly enhance the metastable zone, and the other three factors influence the MSZW only slightly. In conclusion, the these four factors for enhancing MSZW have been optimized: water-to-ethanol volume ratio, 1:0.6; temperature, 20 degrees C; stirring rate, 700 rpm; and cooling rate, 12.0 degrees C/h. All of these results will be helpful for the following chiral separation of ketoprofen by crystallization. PMID:16521089

  3. Metastable Oxygen Production by Electron-Impact of Oxygen

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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 oxygen-containing molecules plays a significant role in the dynamics of planetary atmospheres (Earth, Mars, Europa, Io, Enceladus) and cometary bodies (Hale-Bopp). The electron-impact excitation channels to O(1S) and O(1D) are important for determining energy partitioning and dynamics. To reliably model natural phenomena and interpret observational data, the accurate determination of underlying collision processes (cross sections, dissociation dynamics) through fundamental experimental studies is essential. The detection of metastable species in laboratory experiments requires a novel approach. Typical radiative de-excitation detection techniques cannot be performed due to the long-lived nature of excited species, and conventional particle detectors are insensitive to the low internal energies O(1S) and O(1D). We have recently constructed an apparatus to detect and characterize metastable oxygen production by electron impact using the "rare gas conversion technique." Recent results will be presented, including absolute excitation functions for target gases O2, CO, CO2, and N2O. This work was performed at the Jet Propulsion Laboratory (JPL), California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). Financial support through NASA's OPR, PATM, and MFRP programs, as well as the NASA Postdoctoral Program (NPP) are gratefully acknowledged.

  4. Metastable pitting of carbon steel under potentiostatic control

    SciTech Connect

    Cheng, Y.F.; Luo, J.L.

    1999-03-01

    The metastable pitting of A516-70 carbon steel was studied under potentiostatic control in solutions containing chloride ions. It was shown that there were different current fluctuation patterns and spectral slopes, that is, roll-off slopes, in passivity, general corrosion, and metastable pitting. Pits were often covered by a deposit which played an important role in the current fluctuation, with a quick current rise followed by a slow drop. There was a transitional potential (about 0 mV vs Ag/AgCl electrode) below which the metastable pitting initiation rate increased with the potential, because more sites would be activated. Above the transitional potential, the decay of the pitting occurrence rate with increased potential was due to the elimination of available pit sites. When the applied potential was between {minus}50 and 100 mV, pit growth kinetics was controlled by the potential drop through the deposit over the pit mouth. The potential dependence of repassivation time was mainly due to the effect of applied potential on the deposit over the pit mouth. There seemed to be good agreement between the calculated pit size and the measured values by optical microphotography. The assumption of hemispherical pit geometry was reasonable in calculating the pit radii.

  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. Detecting vapour bubbles in simulations of metastable water.

    PubMed

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

    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.

  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. 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.

  9. Stable, Metastable, and Kinetically Trapped Amyloid Aggregate Phases

    PubMed Central

    2015-01-01

    Self-assembly of proteins into amyloid fibrils plays a key role in a multitude of human disorders that range from Alzheimer’s disease to type II diabetes. Compact oligomeric species, observed early during amyloid formation, are reported as the molecular entities responsible for the toxic effects of amyloid self-assembly. However, the relation between early-stage oligomeric aggregates and late-stage rigid fibrils, which are the hallmark structure of amyloid plaques, has remained unclear. We show that these different structures occupy well-defined regions in a peculiar phase diagram. Lysozyme amyloid oligomers and their curvilinear fibrils only form after they cross a salt and protein concentration-dependent threshold. We also determine a boundary for the onset of amyloid oligomer precipitation. The oligomeric aggregates are structurally distinct from rigid fibrils and are metastable against nucleation and growth of rigid fibrils. These experimentally determined boundaries match well with colloidal model predictions that account for salt-modulated charge repulsion. The model also incorporates the metastable and kinetic character of oligomer phases. Similarities and differences of amyloid oligomer assembly to metastable liquid–liquid phase separation of proteins and to surfactant aggregation are discussed. PMID:25469942

  10. 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).

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Metastable hydronium ions in UV-irradiated ice

    SciTech Connect

    Moon, Eui-Seong; Kang, Heon

    2012-11-28

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

  18. Metastable hydronium ions in UV-irradiated ice.

    PubMed

    Moon, Eui-Seong; Kang, Heon

    2012-11-28

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

  19. Metastable hydronium ions in UV-irradiated ice

    NASA Astrophysics Data System (ADS)

    Moon, Eui-Seong; Kang, Heon

    2012-11-01

    We show that the irradiation of UV light (10-11 eV) onto an ice film produces metastable hydronium (H3O+) ions in the ice at low temperatures (53-140 K). Evidence of the presence of metastable hydronium ions was obtained by experiments involving adsorption of methylamine onto UV-irradiated ice films and hydrogen-deuterium (H/D) isotopic exchange reaction. The methylamine adsorption experiments showed that photogenerated H3O+ species transferred a proton to the methylamine arriving at the ice surface, thus producing the methyl ammonium ion, which was detected by low energy sputtering method. The H3O+ species induced the H/D exchange of water, which was monitored through the detection of water isotopomers on the surface by using the Cs+ reactive ion scattering method. Thermal and temporal stabilities of H3O+ and its proton migration activity were examined. The lifetime of the hydronium ions in the amorphized ice was greater than 1 h at ˜53 K and decreased to ˜5 min at 140 K. Interestingly, a small portion of hydronium ions survived for an extraordinarily long time in the ice, even at 140 K. The average migration distance of protons released from H3O+ in the ice was estimated to be about two water molecules at ˜54 K and about six molecules at 100 K. These results indicate that UV-generated hydronium ions can be efficiently stabilized in low-temperature ice. Such metastable hydronium ions may play a significant role in the acid-base chemistry of ice particles in interstellar clouds.

  20. 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

  1. Photoionization of Fe7+ from the ground and metastable states

    NASA Astrophysics Data System (ADS)

    Tayal, S. S.; Zatsarinny, O.

    2015-01-01

    The B -spline Breit-Pauli R -matrix method is used to investigate the photoionization of Fe7 + from the ground and metastable states in the energy region from ionization thresholds to 172 eV. The present calculations were designed to resolve the large discrepancies between recent measurements and available theoretical results. The multiconfiguration Hartree-Fock method in connection with B -spline expansions is employed for an accurate representation of the initial- and final-state wave functions. The close-coupling expansion includes 99 fine-structure levels of the residual Fe8 + ion in the energy region up to 3 s23 p54 s states. It includes levels of the 3 s23 p6,3 s23 p53 d ,3 s23 p54 s , and 3 s 3 p63 d configurations and some levels of the 3 s23 p43 d2 configuration which lie in the energy region under investigation. The present photoionization cross sections in the length and velocity formulations exhibit excellent agreement. The present photoionization cross sections agree well with the Breit-Pauli R -matrix calculation by Sossah et al. and the TOPbase data in the magnitude of the background nonresonant cross sections but show somewhat richer resonance structures, which qualitatively agree with the measurements. The calculated cross sections, however, are several times lower than the measured cross sections, depending upon the photon energy. The cross sections for photoionization of metastable states were found to have approximately the same magnitude as the cross sections for photoionization of the ground state, thereby the presence of metastable states in the ion beam may not be the reason for the enhancement of the measured cross sections.

  2. 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.

  3. Origin of metastable knots in single flexible chains.

    PubMed

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

    2015-01-23

    Recent theoretical progress has explained the physics of knotting of semiflexible polymers, yet knotting of flexible polymers is relatively unexplored. We herein develop a new theory for the size distribution of knots on a flexible polymer and the existence of metastable knots. We show the free energy of a flexible molecule in a tube can be mapped to quantitatively reproduce the free energy distribution of a knot on a flexible chain. The size distribution of knots on flexible chains is expected to be universal and might be observed at a macroscopic scale, such as a string of hard balls. PMID:25659023

  4. Investigating the Metastability of Clathrate Hydrates for Energy Storage

    SciTech Connect

    Koh, Carolyn Ann

    2014-11-18

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

  5. Anomalous slowing down in the metastable liquid of hard spheres

    NASA Astrophysics Data System (ADS)

    Dzugutov, M.

    2002-03-01

    It is demonstrated that a straightforward extension of the Arrhenius law accurately describes diffusion in the thermodynamically stable liquid of hard spheres. A sharp negative deviation from this behavior is observed as the liquid is compressed beyond its stability limit. This dynamical anomaly can be compared with the nonlinear slowing down characteristic of the supercooled dynamics regime in liquids with continuous interaction. It is suggested that the observed dynamical transition is caused by long-time decomposition of the configuration space. This interpretation is corroborated by the observation of characteristic anomalies in the geometry of a particle trajectory in the metastable domain.

  6. Measurement of a metastability-exchange cross section in krypton

    SciTech Connect

    Brechignac, C.; Vetter, R.

    1980-08-01

    The metastability-exchange cross section between (/sup 3/P/sub 2/)Kr atoms and (/sup 1/S/sub 0/)Kr atoms is measured by means of a two-laser saturated-absorption experiment performed on the lambda=557-nm transition. A study of velocity changes occurring in pure /sup 86/Kr and in (/sup 86/Kr--/sup 78/Kr) discharges leads to a value for the cross section Q75=(plus-or-minus10) A/sup 2/.

  7. 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.

  8. 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.

  9. Assessing a candidate IIA dual to metastable supersymmetry-breaking

    NASA Astrophysics Data System (ADS)

    Giecold, Gregory; Goi, Enrico; Orsi, Francesco

    2012-02-01

    We analyze the space of linearized non-supersymmetric deformations around a IIA solution found by Cvetič, Gibbons, Lü and Pope (CGLP) in hep-th/0101096. We impose boundary conditions aimed at singling out among those perturbations the ones describing the backreaction of anti-D2 branes on the CGLP background. The corresponding supergravity solution is a would-be dual to a metastable supersymmetry-breaking state. However, it turns out that this candidate bulk solution is inevitably riddled with IR divergences of its flux densities and action, whose physical meaning and implications for models of string cosmology call for further investigation.

  10. 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.

  11. Simultaneous magneto-optical trapping of a boson-fermion mixture of metastable helium atoms.

    PubMed

    Stas, R J W; McNamara, J M; Hogervorst, W; Vassen, W

    2004-07-30

    We simultaneously confine fermionic metastable 3He atoms and bosonic metastable 4He atoms in a magneto-optical trap. The trapped clouds, containing up to 1.5 x 10(8) atoms of each isotope, are characterized by measuring ions and metastable helium atoms escaping from the trap. Optical pumping of 3He atoms to a nontrapped hyperfine state is investigated and it is shown that large atom numbers can be confined without additional repumping lasers. Unique possibilities for quantum degeneracy experiments with mixtures of spin-polarized metastable 3He and 4He atoms are indicated.

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

    PubMed Central

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

    2015-01-01

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

  13. 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. PMID:26085630

  14. Demonstration of a diode-pumped metastable Ar laser.

    PubMed

    Han, Jiande; Glebov, Leonid; Venus, George; Heaven, Michael C

    2013-12-15

    Pulsed lasing from optically pumped rare gas metastable atoms (Ne, Ar, Kr, and Xe) has been demonstrated previously. The laser relies on a three-level scheme, which involves the (n+1)p[5/2](3) and (n+1)p[1/2](1) states from the np(5)(n+1)p electronic configuration and the metastable (n+1)s[3/2](2) level of the np(5)(n+1)s configuration (Racah notation). Population inversions were achieved using relaxation from ((n+1)p[5/2](3) to (n+1)p[1/2](1) induced by collisions with helium or argon at pressures near 1 atm. Pulsed lasing was easily achieved using the high instantaneous pump intensities provided by a pulsed optical parametric oscillator excitation laser. In the present study we examine the potential for the development of a continuous wave (CW) optically pumped Ar laser. We report lasing of the 4p[1/2](1)→4s[3/2](2) (912.547 nm) transition following CW diode laser excitation of the 4p[5/2](3)←4s[3/2](2) line (811.754 nm). A pulsed discharge was used to generate Ar 4s[3/2](2), and the time-resolved lasing kinetics provide insights concerning the radiative and collisional relaxation processes. PMID:24343016

  15. Pressure dependence of prototype structures of metastable niobium oxides

    NASA Astrophysics Data System (ADS)

    Obara, Kozo

    1993-03-01

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

  16. A new nanoscale metastable iron phase in carbon steels

    PubMed Central

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

    2015-01-01

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

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

    PubMed

    Baidakov, Vladimir G; Protsenko, Sergey P

    2014-06-01

    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 → ∞. PMID:24908025

  18. 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.

  19. 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.

  20. Metastable Lennard-Jones fluids. I. Shear viscosity.

    PubMed

    Baidakov, Vladimir G; Protsenko, Sergey P; Kozlova, Zaliya R

    2012-10-28

    Molecular dynamics methods have been employed to calculate the coefficient of shear viscosity η(s)* of a Lennard-Jones fluid. Calculations have been performed in the range of reduced temperatures 0.4 ≤ k(B)T/ε ≤ 2.0 and densities 0.01 ≤ ρσ(3) ≤ 1.2. Values of η(s)* have been obtained for 217 states, 99 of which refer to metastable liquid and gas regions. The results of calculating η(s)* for thermodynamically stable states are in satisfactory agreement with the data of earlier investigations. An equation has been obtained which describes the temperature and density dependence of the coefficient of shear viscosity in stable and metastable regions of the phase diagram up to the boundaries of spontaneous nucleation. The behavior of the coefficient of shear viscosity close to the spinodal of a superheated liquid and supersaturated vapor is discussed and the applicability of the Stokes-Einstein relation at high supercoolings of the liquid phase is examined.

  1. Metastable phase diagram: tool to quantified degree of undercooling

    NASA Astrophysics Data System (ADS)

    Faure, F.; Tissandier, L.

    2012-12-01

    The majority of volcanic rocks display textures that evidence disequilibrium features such as glasses or crystals with rapid growth morphologies. Disequilibrium textures are generally interpreted as resulting from high degrees of magma undercooling (-ΔT). By definition, -ΔT corresponds to the difference between the liquidus temperature and the actual temperature. However the liquidus temperature evolves during crystallization due to the continuous change in the chemical composition of the residual liquid. This has led to consideration of a nominal degree of undercooling (-ΔTn) in dynamic crystallization experiments performed in high disequilibrium conditions, i.e. with rapid cooling rates. The parameter -ΔTn is defined as the temperature difference between the liquidus temperature of the initial composition and the temperature at the end of the experiment (Kirkpatrick et al. 1981; Faure et al. 2003), however it is clearly an oversimplification when cooling rates are relatively slow and it does not correspond to the real degree of undercooling (-ΔTr). On the other hand, the use of phase diagrams to constrain the chemical compositions of these unequilibrated phases is futile as classical phase diagrams, i.e. equilibrium diagrams, never show the metastable prolongations. In order to overcome this problem, we propose a method based on magmatic inclusions for determining the metastable prolongations of liquidus surfaces below the solidus and we test this method with a simplified chemical CMAS system. Dynamic crystallization experiments were performed at atmospheric pressure and a low cooling rate (2°C/h). Experiments were quenched at various temperatures, above and below the theoretical solidus. Olivine is the liquidus phase and the mesostasis may exhibit a second phase corresponding to a metastable Al-rich pyroxene. Olivine crystal morphologies evolve from polyhedral to skeletal depending on the quenching temperature. Whatever this temperature, the chemical

  2. METHODOLOGICAL NOTES: Metastable phases, phase transformations, and phase diagrams in physics and chemistry

    NASA Astrophysics Data System (ADS)

    Brazhkin, Vadim V.

    2006-07-01

    Concepts of a 'phase' and a 'phase transition' are discussed for stable and metastable states of matter. While condensed matter physics primarily considers equilibrium states and treats metastable phases as exceptions, organic chemistry overwhelmingly deals with metastable states. It is emphasized that many simple light-element compounds — including most hydrocarbons; nitrogen oxides, hydrides, and carbides; carbon monoxide CO; alcohols and glycerin — are also metastable at normal pressure in the sense that they do not correspond to a minimum Gibbs free energy for a given chemical composition. At moderate temperatures and pressures, the phase transformations for these metastable phases are reversible with the fulfilment of all laws of equilibrium thermodynamics over the entire range of experimentally accessible times. At sufficiently high pressures (> 1-10 GPa), most of the metastable molecular phases irreversibly transform to lower-energy polymer phases, stable or metastable. These transitions do not correspond to the equality of the Gibbs free energy for the involved phases before and after the transition and so they are not first-order in the 'classical' sense. At normal pressure, the resulting polymer phases can exist at temperatures above the melting point of the original metastable molecular phase, as the examples of polyethylene and polymerized CO dramatically illustrate. As pressure is increased further to 20-50 GPa, the PV contribution to Gibbs free energy gives rise to stable high-density atomic phases. Many of the intermediate-energy polymer phases can likely be synthesized by methods of 'classical' chemistry at normal pressure.

  3. Meta-stable Supersymmetry Breaking in an N = 1 Perturbed Seiberg-Witten Theory

    SciTech Connect

    Sasaki, Shin; Arai, Masato; Montonen, Claus; Okada, Nobuchika

    2008-11-23

    In this contribution, we discuss the possibility of meta-stable supersymmetry (SUSY) breaking vacua in a perturbed Seiberg-Witten theory with Fayet-Iliopoulos (FI) term. We found meta-stable SUSY breaking vacua at the degenerated dyon and monopole singular points in the moduli space at the nonperturbative level.

  4. Stability of metastable vacua in gauge mediated SUSY breaking models with ultra light gravitino

    NASA Astrophysics Data System (ADS)

    Hisano, Junji; Nagai, Minoru; Senami, Masato; Sugiyama, Shohei

    2008-01-01

    Recently Murayama and Nomura proposed a simple scheme to construct the gauge mediation models, using metastable supersymmetry breaking vacua. It has a possibility to predict the ultra light gravitino mass m3 / 2 ≲ 16 eV, while such a light gravitino may destabilize the metastable vacua. We investigate stability of the metastable vacuum of their model. The transition rate from the false vacuum to true ones is evaluated by numerical calculation, including the Coleman-Weinberg potential destabilizing the metastable vacuum. It is found that when the messenger sector is minimal, stability of the metastable vacuum imposes an upperbound on squark mass Mq˜ for the ultra light gravitino as Mq˜ ≲ 1800 GeV at most. Squarks with this mass may be found in the LHC experiments.

  5. 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.

  6. 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

  7. Heteronuclear ionizing collisions between laser-cooled metastable helium atoms

    SciTech Connect

    McNamara, J. M.; Stas, R. J. W.; Hogervorst, W.; Vassen, W.

    2007-06-15

    We have investigated cold ionizing heteronuclear collisions in dilute mixtures of metastable (2 {sup 3}S{sub 1}) {sup 3}He and {sup 4}He atoms, extending our previous work on the analogous homonuclear collisions [R. J. W. Stas et al., Phys. Rev. A 73, 032713 (2006)]. A simple theoretical model of such collisions enables us to calculate the heteronuclear ionization rate coefficient, for our quasiunpolarized gas, in the absence of resonant light (T=1.2 mK): K{sub 34}{sup (th)}=2.4x10{sup -10} cm{sup 3}/s. This calculation is supported by a measurement of K{sub 34} using magneto-optically trapped mixtures containing about 1x10{sup 8} atoms of each species, K{sub 34}{sup (exp)}=2.5(8)x10{sup -10} cm{sup 3}/s. Theory and experiment show good agreement.

  8. Supersymmetry breaking metastable vacua in runaway quiver gauge theories

    NASA Astrophysics Data System (ADS)

    García-Etxebarria, Inaki; Saad, Fouad; M. Uranga, Angel

    2007-05-01

    In this paper we consider quiver gauge theories with fractional branes whose infrared dynamics removes the classical supersymmetric vacua (DSB branes). We show that addition of flavors to these theories (via additional non-compact branes) leads to local meta-stable supersymmetry breaking minima, closely related to those of SQCD with massive flavors. We simplify the study of the one-loop lifting of the accidental classical flat directions by direct computation of the pseudomoduli masses via Feynman diagrams. This new approach allows to obtain analytic results for all these theories. This work extends the results for the dP1 theory in hep-th/0607218. The new approach allows to generalize the computation to general examples of DSB branes, and for arbitrary values of the superpotential couplings.

  9. 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.

  10. Ferromagnetism in layered metastable 1T-CrTe2.

    PubMed

    Freitas, Daniele C; Weht, Ruben; Sulpice, André; Remenyi, Gyorgy; Strobel, Pierre; Gay, Frédéric; Marcus, Jacques; Núñez-Regueiro, Manuel

    2015-05-01

    We have synthesized for the first time the metastable compound 1T-CrTe2. We have done its complete structural characterization and measured its magnetization, specific heat and electrical resistivity between 4 and 330 K. We have also performed detailed band structure calculations. We have found that it crystallizes in the CdI2 structure type and that its electrical resistance follows a metallic behaviour below room temperature. Its magnetization and specific heat curves show that the compound has a transition to a ferromagnetic state at TC = 310 K, with the magnetic moments ordered parallel to the basal plane. From the specific heat measurements and the ferromagnetic solutions obtained from our DFT calculations, we conclude that the ferromagnetism is of itinerant nature. PMID:25872783

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

    SciTech Connect

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

    2015-05-07

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

  12. 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.

  13. 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.

  14. 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.

  15. Times of metastable droplet relaxation to equilibrium states

    NASA Astrophysics Data System (ADS)

    Tovbin, Yu. K.; Komarov, V. N.; Zaitseva, E. S.

    2016-10-01

    Times of metastable droplet relaxation to their equilibrium state are calculated at saturated vapor pressures, depending on the droplet size. It is shown that for small droplets with radius R = 6 molecular diameters (or ~2 nm) the relaxation times are ~1 ns (which is comparable to the characteristic flight times of rarefied gas molecules). For large droplets with radius R ~ 800 molecular diameters, the relaxation times are as long as 10 μs. At a fixed droplet radius (6 ≤ R ≤ 800), the range of variation in relaxation time from the melting point to the critical temperature does not exceed one order of magnitude: the lower the temperature, the slower the relaxation process.

  16. Metastable γ-FeNi nanostructures with tunable Curie temperature

    NASA Astrophysics Data System (ADS)

    Miller, K. J.; Sofman, M.; McNerny, K.; McHenry, M. E.

    2010-05-01

    We report on new metastable γ-FeNi nanoparticles produced by mechanical alloying of melt-spun ribbon using a high energy ball mill followed by a solution annealing treatment in the γ-phase region and water quenching in of the face-centered cubic γ-phase. In the Fe-Ni phase diagram there is a strong compositional dependence of the Curie temperature, Tc, on composition in the γ-phase. This work studies the stabilization of γ-phase nanostructures and the compositional tuning of Tc in Fe-Ni alloys which can have important ramifications on the self-regulated heating of magnetic nanoparticles in temperature ranges of interest for applications in polymer curing and cancer thermotherapies. To date we have achieved Curie temperatures as low as 120 °C by this method.

  17. 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.

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

    PubMed

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

    2014-05-01

    We investigate the nonequilibrium dynamics of the two-dimensional (2D) Potts model on the square lattice after a quench below the discontinuous transition point. By means of numerical simulations of systems with q=12, 24, and 48, we observe the onset of a stationary regime below the temperature-driven transition, in a temperature interval decreasing with the system size and increasing with q. These results obtained dynamically agree with those obtained from the analytical continuation of the free energy [J. L. Meunier and A. Morel, Eur. Phys. J. B 13, 341 (2000)], from which metastability in the 2D Potts model results to be a finite-size effect. PMID:25353747

  19. Ferromagnetism in layered metastable 1T-CrTe2

    NASA Astrophysics Data System (ADS)

    Freitas, Daniele C.; Weht, Ruben; Sulpice, André; Remenyi, Gyorgy; Strobel, Pierre; Gay, Frédéric; Marcus, Jacques; Núñez-Regueiro, Manuel

    2015-05-01

    We have synthesized for the first time the metastable compound 1T-CrTe2. We have done its complete structural characterization and measured its magnetization, specific heat and electrical resistivity between 4 and 330 K. We have also performed detailed band structure calculations. We have found that it crystallizes in the CdI2 structure type and that its electrical resistance follows a metallic behaviour below room temperature. Its magnetization and specific heat curves show that the compound has a transition to a ferromagnetic state at TC = 310 K, with the magnetic moments ordered parallel to the basal plane. From the specific heat measurements and the ferromagnetic solutions obtained from our DFT calculations, we conclude that the ferromagnetism is of itinerant nature.

  20. Interactions of Rubidium and Metastable Argon at Ultracold Temperatures

    NASA Astrophysics Data System (ADS)

    Shaffer, M. K.

    2005-05-01

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

  1. 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.

  2. Fast neutron spectroscopy with tensioned metastable fluid detectors

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  3. Light-induced metastable states in ferroelectric oxides

    NASA Astrophysics Data System (ADS)

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

    2007-07-01

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

  4. 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.

  5. 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)].

  6. Metastable crystalline AuGe catalysts formed during isothermal germanium nanowire growth.

    PubMed

    Gamalski, A D; Tersoff, J; Sharma, R; Ducati, C; Hofmann, S

    2012-06-22

    We observe the formation of metastable AuGe phases without quenching, during strictly isothermal nucleation and growth of Ge nanowires, using video-rate lattice-resolved environmental transmission electron microscopy. We explain the unexpected formation of these phases through a novel pathway involving changes in composition rather than temperature. The metastable catalyst has important implications for nanowire growth, and more broadly, the isothermal process provides both a new approach to growing and studying metastable phases, and a new perspective on their formation.

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

    SciTech Connect

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

    2009-03-01

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

  8. Metastable olivine wedge beneath northeast China and its applications

    NASA Astrophysics Data System (ADS)

    Jiang, G.; Zhao, D.; Zhang, G.

    2013-12-01

    When the Pacific slab subducted into the mantle transition zone, there might exist a metastable olivine wedge (MOW) inside the slab due to the phase transition. Lots of researchers have adopted such various methods to detect the characteristics of this MOW as the forward modeling of travel times, shear wave amplitude patterns, teleseismic P wave coda, receiver function imaging, thermodynamic simulation and so on. Almost all results could be more or less affected by the source, the receiver and/or the velocity model passed through by the seismic rays. In this study, we have used 21 deep earthquakes, greater than 400 km and locating beneath northeast China, to study the velocity within the MOW. For more precisions, we have done further modifications in two ways based on our previous studies. (1) Double-difference location method is used to relocate all events with an error of 1-2 km with the data recorded by stations both at northeast China and at Japan. All relocated events locate in a zone about 30 km away from the upper boundary of Pacific slab. (2) Double residual travel times, generated by an event-pair at a common station at only Japan, are used to constrain the velocity anomaly rather than the residuals themselves. As a result, we have found that an ultra-lower velocity zone (ULVZ), averagely -7% relative to the iasp91 model, exists within the subducted Pacific slab around the deep earthquakes, which might be represented as the metastable olivine wedge. Because of the lower-velocity corresponding to the lower-density, the MOW would provide upward buoyancy forces which might prevent the slab from free subduction into the mantle transition zone. This feed-back mechanism of MOW to the slab is called ';parachute-effect', which is characterized by other researchers. In addition, the existence of the ULVZ or the MOW in the slab may supply a possible mechanism for triggering deep earthquakes, called ';phase transformation faulting', which was already proposed few

  9. Thermal Conductivity of Metastable States of Simple Alcohols

    NASA Astrophysics Data System (ADS)

    Krivchikov, A. I.; Korolyuk, O. A.; Sharapova, I. V.; Romantsova, O. O.; Bermejo, F. J.; Cabrillo, C.; Bustinduy, I.; González, M. A.

    The thermal conductivity κ(T) of glassy and supercooled liquid methanol, ethanol and of 1-propanol has been measured under equilibrium vapor pressure in temperature interval from 2 K to 160 K by the steady-state method. The metastable orientationally disordered crystal of ethyl alcohol is found to exhibit a temperature dependence of κ(T) that is remarkably close to that of the fully amorphous solid, especially at low temperatures. In the case of propyl alcohol, our results emphasize the role played by internal molecular degrees of freedom as sources of strong resonant phonon scattering. For all samples here explored, the glass-like behavior of κ(T) is described at the phenomenological level using the model of soft potentials. The thermal transport is then understood in terms of a competition between phonon-assisted and diffusive transport effects. The thermal conductivity κ is thus a sum of two contributions: κ = κI + κII, where κI is the acoustic phonon component dependent on the translational and orientational ordering of molecules, κII — is the phonon diffusion component corresponding to a non — acoustic phonon heat transfer in accordance with the Cahill — Pohl model.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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.

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

    NASA Astrophysics Data System (ADS)

    Han, Jiande; Heaven, Michael C.

    2012-11-01

    Optically pumped atomic gas lasers are currently being developed in several laboratories. The objective is to construct high-powered lasers that also exhibit excellent beam quality. This is achieved by using the gas laser medium to phase combine the outputs from multiple solid state lasers. To date, the focus has been on optically pumped alkali vapor lasers. 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 np5(n+1)s 3P2 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 np5(n+1)p <-- np5(n+1)s transitions. We have demonstrated this potential by observing gain and lasing for optically pumped Ne*, 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 using inert reagents that are gases at room temperature.

  17. Gain and Lasing of Optically Pumped Metastable Rare Gas Atoms

    NASA Astrophysics Data System (ADS)

    Han, Jiande; Heaven, Michael C.

    2012-06-01

    In recent years there have been concerted efforts to develop high energy diode-pumped alkali vapor lasers (DPAL). These hybrid gas phase / solid state laser systems offer possibilities for constructing high-powered lasers that have high beam quality. DPAL's utilize excitation of the alkali metal 2P3/2 ← 2S1/2 transition, followed by collisional relaxation and lasing on the 2P1/2 → 2S1/2 line. 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 n{p}5(n+1){s} 3P2 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 n{p}5(n+1){p} ← n{p}5(n+1){s} transitions. We have recently demonstrated gain and lasing for optically pumped Ar*, Kr* and Xe*. Three-level lasing schemes were used, with He as the collisional energy transfer agent that established the population inversion. These laser systems have the advantage using inert reagents that are gases at room temperature.

  18. 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.

  19. 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}

  20. 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.

  1. Meta-stability of Crystalline Thin-Film Photovoltaic Modules

    NASA Astrophysics Data System (ADS)

    Petersen, Chad

    Given the growing market in solar energy, specifically by the thin-film technologies, it is imperative that adequate and accurate standards be developed for these newer photovoltaic devices. Cadmium Telluride, CdTe, one of the major players in the thin-film PV industry is currently rated and certified using standards that have been developed under the context of older technologies. The behavior of CdTe has been shown to be unique enough to suggesting that standards be revised. In this research, methods built on previous industry and independent studies are used to identify these unique behaviors. As well new methods are developed to further characterize CdTe modules in the context of current standards. Clear transient and meta-stable behavior is identified across modules from four different commercial manufacturers. Conclusions drawn from this study show illumination and temperature hysteresis effects on module ratings. Furthermore, suggestions for further study are given that could be used to define parameters for any reexamination of module standards.

  2. 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...

  3. Investigation of slective laser melting of mecanically alloyed metastable Al5Fe2 powder

    NASA Astrophysics Data System (ADS)

    Montiel, Hugo

    Selective Laser Melting (SLM), an Additive Manufacturing (AM) technology, enables the production of complex structured metal products. Aluminum alloys are used in SLM as high-strength lightweight materials for weight reduction in structural components. Previous investigations report high laser powers (300 W) and slow scanning speeds (500 mm/s) to process aluminum alloys under SLM. This research investigates the SLM processing of Al-Fe alloy by utilizing metastable Al5Fe2 powder system produced by mechanical alloying. Metastable systems are thermodynamically activated with internal energy that can generate an energy shortcut when processing under SLM. The optimum laser power, scan speeds and scan distances were investigated by test series experiments. Results indicate that metastable Al5Fe2 alloy can be processed and stabilized under a 200 W laser scanning and a relative high scanning speed of 1000 mm/s. Thus, the internal energy of metastable powder contributes in reducing laser energy for SLM process for Al alloys.

  4. Illumination-induced metastable polaron-supporting state in poly( p -phenylene vinylene) films

    NASA Astrophysics Data System (ADS)

    Drori, T.; Gershman, E.; Sheng, C. X.; Eichen, Y.; Vardeny, Z. V.; Ehrenfreund, E.

    2007-07-01

    We found an illumination-induced metastable polaron-supporting state in films of a soluble derivative of poly- p -phenylene vinylene (MEH-PPV). Pristine, nonilluminated MEH-PPV polymer films do not show long-lived photogenerated polarons. Prolonged UV illumination, however, is found to induce a reversible, metastable state characterized by its ability to support abundant long-lived photogenerated polarons. In the dark, the illumination-induced metastable state reverts back to the state of the original MEH-PPV within about 30min at room temperature. Relying on the well-established ubiquitous reversible photoinduced cyclization of diarylethenes into dihyrophenanthrene derivatives, we propose a reversible mechanism in which UV illumination transforms cis native defects in the polymer chains into metastable deep traps that substantially increase the photogenerated polaron lifetime in the film.

  5. An experimental verification of a criterion for forming metastable phases in containerless solidification

    SciTech Connect

    Kuribayashi, K.; Inatomi, Y.; Kumar, M. S. Vijaya

    2015-04-21

    On the thermodynamic condition for forming a metastable phase from undercooled melt in a containerless state, we had proposed a criterion that crystals will preferentially form if they have a smaller entropy of fusion than the entropy of fusion of equilibrium crystals (Kuribayashi et al., Mater. Sci. Eng., A 449–451, 675 (2007)). This criterion is proposed for being applied to materials that exhibit a faceted interface, such as semiconductors and oxides. However, no experimental data that support this criterion have been obtained. From this point, we used an aerodynamic levitator as a tool for forming metastable phases from undercooled melt and verified the above-mentioned criterion using LnFeO{sub 3} (Ln: lanthanide and Y) as the model material. In addition, the condition for double recalescence, which corresponds to forming metastable phases and stable phases, was discussed in terms of competitive 2D isomorphic nucleation of the metastable phase and 3D polymorphic nucleation of the stable phase.

  6. 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 ...

  7. ATOMIC AND MOLECULAR PHYSICS: Coupled-Channels Optical Calculation for Electron Scattering from Metastable Helium

    NASA Astrophysics Data System (ADS)

    Wang, Yuan-Cheng; Zhou, Ya-Jun; Cheng, Yong-Jun; Ma, Jia

    2009-08-01

    Coupled-channels optical calculations for total and resonance excitation integral cross sections for electron scattering on the metastable level 21,3 S of helium are presented. The results are in agreement with other theoretical and experimental data.

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

    SciTech Connect

    B.A. Kehler; J.R. Scully

    2005-01-11

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

  9. Primary populations of metastable antiprotonic (4)He and (3)He atoms.

    PubMed

    Hori, M; Eades, J; Hayano, R S; Ishikawa, T; Sakaguchi, J; Tasaki, T; Widmann, E; Yamaguchi, H; Torii, H A; Juhász, B; Horváth, D; Yamazaki, T

    2002-08-26

    Initial distributions of metastable antiprotonic (4)He and (3)He atoms over principal (n) and angular momentum (l) quantum numbers have been deduced using laser spectroscopy experiments. The regions n = 37-40 and n = 35-38 in the two atoms account for almost all of the observed fractions [(3.0 +/- 0.1)% and (2.4 +/- 0.1)%] of antiprotons captured into metastable states. PMID:12190401

  10. 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.

  11. 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.

  12. 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.

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

    SciTech Connect

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

    2015-03-09

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

  14. 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.

  15. Kinetics of metastable He atom at middle pressure in micro hollow cathode discharge

    NASA Astrophysics Data System (ADS)

    Inoue, Mari; Ohta, Takayuki; Kanae, Tsuyoshi; Ito, Masafumi; Hori, Masaru

    2011-10-01

    Hollow cathode discharges has been studied as light sources. Conventional hollow cathode discharges has been operated in low pressure, while micro hollow cathode discharge in near atmospheric pressure. In this study, the behavior of metastable He atoms (23S1-23P0 ; 1082.909 nm) in micro hollow cathode discharge in the middle range of the pressure from 5 to 30 kPa were fundamentally studied. The translational temperature and density of metastable He atoms were measured by diode laser absorption spectroscopy. The spectral line profile was analyzed and the pressure-broadening effect was investigated. The absorption profile of metastable He atoms was obtained by scanning the wavelength of the diode laser. The absorption profile of metastable He atoms shits from a Gaussian to Voigt profile at around pressure of 10 kPa. The metastable He atoms temperatures were estimated to be 900 to 1150 K, and the densities were measured to be 1.3 x 1013 cm-3 to 7.6 x 1012 cm-3 in the range of 5 to 30 kPa. The translational temperatures and densities of metastable He atoms were decreased with increasing pressure below 10 kPa, on the other hand, increased with increasing pressure in the range from 10 to 30 kPa.

  16. Beam-foil spectroscopical study of the 1s2s2p and 1s2p 2 quartet levels of Mg 9+ and Al 10+

    NASA Astrophysics Data System (ADS)

    Hellmann, H.; Träbert, E.

    1985-07-01

    Results of recent measurements of the fine structure and multiplet separation of the lowest quartet terms of doubly excited three-electron ions of Mg and Al are compared with other experiments and with theory. Preliminary results of lifetime measurements of 1s2p 24P 1/2.3/2 levels are presented. They confirm the recent calculation by Chen. Crasemann and Mark and contradict older calculations by Tunnell and Bhalla.

  17. Human metastable epiallele candidates link to common disorders.

    PubMed

    Harris, R Alan; Nagy-Szakal, Dorottya; Kellermayer, Richard

    2013-02-01

    Metastable epialleles (MEs) are mammalian genomic loci where epigenetic patterning occurs before gastrulation in a stochastic fashion leading to systematic interindividual variation within one species. Importantly, periconceptual nutritional influences may modulate the establishment of epigenetic changes, such as DNA methylation at MEs. Based on these characteristics, we exploited Infinium HumanMethylation450 BeadChip kits in a 2-tissue parallel screen on peripheral blood leukocyte and colonic mucosal DNA from 10 children without identifiable large intestinal disease. This approach led to the delineation of 1776 CpG sites meeting our criteria for MEs, which associated with 1013 genes. The list of ME candidates exhibited overlaps with recently identified human genes (including CYP2E1 and MGMT, where methylation has been associated with Parkinson disease and glioblastoma, respectively) in which perinatal DNA methylation levels where linked to maternal periconceptual nutrition. One hundred 18 (11.6%) of the ME candidates overlapped with genes where DNA methylation correlated (r > 0.871; p < 0.055) with expression in the colon mucosa of 5 independent control children. Genes involved in homophilic cell adhesion (including cadherin-associated genes) and developmental processes were significantly overrepresented in association with MEs. Additional filtering of gene expression-correlated MEs defined 35 genes, associated with 2 or more CpG sites within a 10 kb genomic region, fulfilling the ME criteria. DNA methylation changes at a number of these genes have been linked to various forms of human disease, including cancers, such as asthma and acute myeloid leukemia (ALOX12), gastric cancer (EBF3), breast cancer (NAV1), colon cancer and acute lymphoid leukemia (KCNK15), Wilms tumor (protocadherin gene cluster; PCDHAs) and colorectal cancer (TCERG1L), suggesting a potential etiologic role for MEs in tumorigenesis and underscoring the possible developmental origins of these

  18. Plasma Effects on the Metastable Neutral HYDROGEN(2S) Atom.

    NASA Astrophysics Data System (ADS)

    Benage, John Ferns, Jr.

    Atomic radiative processes which occur in plasmas have long been of interest of plasma physicists. The process we are investigating is atomic dipole transitions, specifically transitions from the metastable 2s to the 2p in hydrogen, which are induced by processes which occur in the plasma. An experiment was done to measure the rate of transitions from 2s to 2p in hydrogen. This experiment was divided into two sections. The first was to measure the transition rate in a near equilibrium plasma. The second section measured the transition rate when RF oscillations were imposed on the plasma. The results of the first part of the experiment show that microscopic fluctuating electric fields which are produced by the motions of the charged particles induce transitions from 2s to 2p in hydrogen. The magnitude of this effect is compared to predicted transition rates due to collisions with electrons and ions and to rates predicted for an equilibrium plasma. In the second part of the experiment, the plasma was shown to act as a filter, preventing transitions from being caused by the RF unless the RF was in the range where plasma waves could be launched. The interpretation we give for this effect is that when the oscillations are inducing transitions, it is because plasma waves are being launched in the plasma and it is these waves which are inducing the transitions. These results have a couple of important applications. The results for the equilibrium part of the experiment can be used to explain a limit in the current which is produced by the Lamb-shift polarized ion source. The other important application is the possible use of the effect seen in the RF case as a non-perturbing diagnostic for plasma waves. Since dipole transition rates are proportional to E('2) and very sensitive near resonance, this effect could prove to be more accurate and more sensitive than methods currently used.

  19. 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.

  20. 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

  1. 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

  2. Influence of metastable atoms in the simulation of hollow cathode discharge

    SciTech Connect

    He, Shoujie; Liu, Shumin; Jing, Ha; Ouyang, Jiting

    2013-12-15

    The characteristics of hollow cathode discharge are investigated by using two-dimensional fluid model combined with a transport model for metastable atoms (F-M model) in argon. It shows that the stepwise ionization is one of main important mechanism for electrons production. The distribution of electric potential, density of electrons, ions, and metastable atoms are calculated with a pressure of 10 Torr and a voltage of 250 V. The peak density of electron and ion is 1.2×10{sup 13} cm{sup −3}, and the peak density of metastable atoms is 3.5×10{sup 13} cm{sup −3}. The results obtained in F-M model are compared with that in fluid model (without metastable atoms involved). Metastable atoms are found to play an important role in the discharge. In addition, with the increase of pressure and voltage, the percentage of stepwise ionization in the total ionization increase, and the difference of discharge characteristics simulated by these two kinds of models rises.

  3. Metastable anions of dinitrobenzene: Resonances for electron attachment and kinetic energy release

    SciTech Connect

    Mauracher, A.; Denifl, S.; Edtbauer, A.; Hager, M.; Probst, M.; Scheier, P.; Echt, O.; Maerk, T. D.; Field, T. A.; Graupner, K.

    2010-12-28

    Attachment of free, low-energy electrons to dinitrobenzene (DNB) in the gas phase leads to DNB{sup -} as well as several fragment anions. DNB{sup -}, (DNB-H){sup -}, (DNB-NO){sup -}, (DNB-2NO){sup -}, and (DNB-NO{sub 2}){sup -} are found to undergo metastable (unimolecular) dissociation. A rich pattern of resonances in the yield of these metastable reactions versus electron energy is observed; some resonances are highly isomer-specific. Most metastable reactions are accompanied by large average kinetic energy releases (KER) that range from 0.5 to 1.32 eV, typical of complex rearrangement reactions, but (1,3-DNB-H){sup -} features a resonance with a KER of only 0.06 eV for loss of NO. (1,3-DNB-NO){sup -} offers a rare example of a sequential metastable reaction, namely, loss of NO followed by loss of CO to yield C{sub 5}H{sub 4}O{sup -} with a large KER of 1.32 eV. The G4(MP2) method is applied to compute adiabatic electron affinities and reaction energies for several of the observed metastable channels.

  4. 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

  5. Metastable structures and refolding kinetics in hok mRNA of plasmid R1.

    PubMed Central

    Nagel, J H; Gultyaev, A P; Gerdes, K; Pleij, C W

    1999-01-01

    Programmed cell death by hok/sok of plasmid R1 and pnd/pndB of R483 mediates plasmid maintenance by killing of plasmid-free cells. It has been previously suggested that premature translation of the plasmid-mediated toxin is prevented during transcription of the hok and pnd mRNAs by the formation of metastable hairpins in the mRNA at the 5' end. Here, experimental evidence is presented for the existence of metastable structures in the 5' leader of the hok and pnd mRNAs in vitro. The kinetics of refolding from the metastable to the stable structure in the isolated fragments of the 5' ends of both the hok and pnd mRNAs could be estimated, in agreement with the structural rearrangement in this region, as predicted to occur during transcription and mRNA activation. The refolding rates of hok and pnd structures are slow enough to allow for the formation of downstream hairpin structures during elongation of the mRNAs, which thereby helps to stabilize the metastable structures. Thus, the kinetic refolding parameters of the hok and pnd mRNAs are consistent with the proposal that the metastable structures prevent premature translation and/or antisense RNA binding during transcription. PMID:10580469

  6. 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.

  7. Calculation of the relative metastabilities of proteins using the CHNOSZ software package

    PubMed Central

    Dick, Jeffrey M

    2008-01-01

    Background Proteins of various compositions are required by organisms inhabiting different environments. The energetic demands for protein formation are a function of the compositions of proteins as well as geochemical variables including temperature, pressure, oxygen fugacity and pH. The purpose of this study was to explore the dependence of metastable equilibrium states of protein systems on changes in the geochemical variables. Results A software package called CHNOSZ implementing the revised Helgeson-Kirkham-Flowers (HKF) equations of state and group additivity for ionized unfolded aqueous proteins was developed. The program can be used to calculate standard molal Gibbs energies and other thermodynamic properties of reactions and to make chemical speciation and predominance diagrams that represent the metastable equilibrium distributions of proteins. The approach takes account of the chemical affinities of reactions in open systems characterized by the chemical potentials of basis species. The thermodynamic database included with the package permits application of the software to mineral and other inorganic systems as well as systems of proteins or other biomolecules. Conclusion Metastable equilibrium activity diagrams were generated for model cell-surface proteins from archaea and bacteria adapted to growth in environments that differ in temperature and chemical conditions. The predicted metastable equilibrium distributions of the proteins can be compared with the optimal growth temperatures of the organisms and with geochemical variables. The results suggest that a thermodynamic assessment of protein metastability may be useful for integrating bio- and geochemical observations. PMID:18834534

  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. Formation of metastable graphite inclusions during diamond crystallization in model systems

    NASA Astrophysics Data System (ADS)

    Nechaev, D. V.; Khokhryakov, A. F.

    2014-03-01

    Metastable graphite inclusions have been studied in diamond, forsterite, and orthopyroxene synthesized in silicate-carbonate-fluid and aqueous chloride systems at 6.3-7.5 GPa and 1400-1600°C. The graphite inclusions were studied using optic microscopy and Raman spectroscopy. It has been established that graphite in diamond and liquidus silicate minerals is represented by a highly ordered variety. Depending on parameters of runs, the graphite inclusions are hexagonal, irregular polygonal, or rounded in shape. The morphology of graphite inclusions involving metastable graphite in run products is compared with previously established crystallization sequence of carbon phases. It has been revealed that the protogenetic graphite inclusions in diamond are rounded, and this shape was caused by dissolution of the newly formed graphite. Polygonal graphite inclusions are syngenetic and represented by metastable graphite that crystallized contemporaneously with diamond.

  10. Illumination induced metastable polaron-supporting phase in poly p-phenylene- vinylene films

    NASA Astrophysics Data System (ADS)

    Ehrenfreund, E.; Gershman, E.; Eichen, Y.; Drori, T.; Sheng, C. X.; Vardeny, Z. V.

    2007-03-01

    We found a new illumination induced metastable polaron-supporting phase in pristine films of a soluble derivative of poly-p-phenylene vinylene (MEH-PPV). In the pristine, un-illuminated MEH-PPV phase A, the polymer films do not show any long-lived photogenerated polarons. Prolonged UV illumination, however, was found to induce a reversible, metastable phase B, characterized by its ability to support the existence of abundant long-lived photogenerated polarons. In the dark, films of phase B revert back to the original phase A within about thirty minutes at room temperature. Relying on the well-established ubiquitous reversible photoinduced cyclization of diarylethenes into dihyrophenanthrene derivatives, we propose a reversible mechanism in which UV illumination creates metastable deep defects that substantially increase the photogenerated polaron lifetime.

  11. Dynamical SUSY breaking at meta-stable minima from D-branes at obstructed geometries

    NASA Astrophysics Data System (ADS)

    Franco, Sebastián; Uranga, Angel M.

    2006-06-01

    We study the existence of long-lived meta-stable supersymmetry breaking vacua in gauge theories with massless quarks, upon the addition of extra massive flavors. A simple realization is provided by a modified version of SQCD with Nf,0 < Nc massless flavors, Nf,1 massive flavors and additional singlet chiral fields. This theory has local meta-stable minima separated from a runaway behavior at infinity by a potential barrier. We find further examples of such meta-stable minima in flavored versions of quiver gauge theories on fractional branes at singularities with obstructed complex deformations, and study the case of the dP1 theory in detail. Finally, we provide an explicit String Theory construction of such theories. The additional flavors arise from D7-branes on non-compact 4-cycles of the singularity, for which we find a new efficient description using dimer techniques.

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

    PubMed

    Dominguez-Salas, Paula; Moore, Sophie E; Baker, Maria S; Bergen, Andrew W; Cox, Sharon E; Dyer, Roger A; Fulford, Anthony J; Guan, Yongtao; Laritsky, Eleonora; Silver, Matt J; Swan, Gary E; Zeisel, Steven H; Innis, Sheila M; Waterland, Robert A; Prentice, Andrew M; Hennig, Branwen J

    2014-04-29

    In experimental animals, maternal diet during the periconceptional period influences the establishment of DNA methylation at metastable epialleles in the offspring, with permanent phenotypic consequences. Pronounced naturally occurring seasonal differences in the diet of rural Gambian women allowed us to test this in humans. We show that significant seasonal variations in methyl-donor nutrient intake of mothers around the time of conception influence 13 relevant plasma biomarkers. The level of several of these maternal biomarkers predicts increased/decreased methylation at metastable epialleles in DNA extracted from lymphocytes and hair follicles in infants postnatally. Our results demonstrate that maternal nutritional status during early pregnancy causes persistent and systemic epigenetic changes at human metastable epialleles.

  13. 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

  14. Investigations of the origins of metastable light-induced changes in hydrogenated amorphous silicon

    SciTech Connect

    Cohen, J.D. )

    1991-12-01

    The work performed for this contract continued investigations of the origins of metastable effectS in a-Si:H through three kinds of studies: (1) the effect of carbon impurities in a-Si:H samples at low concentrations using drive-level capacitance profiling measurements on samples whose carbon content was intentionally modulated spatially during growth, (2) the characterization of metastable states in n-type doped a Si:H samples caused by quench cooling and by light-soaking with partial annealing, and (3) the use of depletion-width-modulated ESR spectroscopy together with junction capacitance spectroscopy to investigate deep defect states for various metastable states of a 10- and an 80-Vppm PH{sub 3}-doped a-Si:H sample.

  15. 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.

  16. Synthesis of new metastable nanoalloys of immiscible metals with a pulse laser technique.

    PubMed

    Swiatkowska-Warkocka, Zaneta; Pyatenko, Alexander; Krok, Franciszek; Jany, Benedykt R; Marszalek, Marta

    2015-05-08

    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. Au(1-x)Ni(x) 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.

  17. Understanding metastable phase transformation during crystallization of RDX, HMX and CL-20: experimental and DFT studies.

    PubMed

    Ghosh, Mrinal; Banerjee, Shaibal; Shafeeuulla Khan, Md Abdul; Sikder, Nirmala; Sikder, Arun Kanti

    2016-09-14

    Multiphase growth during crystallization severely affects deliverable output of explosive materials. Appearance and incomplete transformation of metastable phases are a major source of polymorphic impurities. This article presents a methodical and molecular level understanding of the metastable phase transformation mechanism during crystallization of cyclic nitramine explosives, viz. RDX, HMX and CL-20. Instantaneous reverse precipitation yielded metastable γ-HMX and β-CL-20 which undergo solution mediated transformation to the respective thermodynamic forms, β-HMX and ε-CL-20, following 'Ostwald's rule of stages'. However, no metastable phase, anticipated as β-RDX, was evidenced during precipitation of RDX, which rather directly yielded the thermodynamically stable α-phase. The γ→β-HMX and β→ε-CL-20 transformations took 20 and 60 minutes respectively, whereas formation of α-RDX was instantaneous. Density functional calculations were employed to identify the possible transition state conformations and to obtain activation barriers for transformations at wB97XD/6-311++G(d,p)(IEFPCM)//B3LYP/6-311G(d,p) level of theory. The computed activation barriers and lattice energies responsible for transformation of RDX, HMX and CL-20 metastable phases to thermodynamic ones conspicuously supported the experimentally observed order of phase stability. This precise result facilitated an understanding of the occurrence of a relatively more sensitive and less dense β-CL-20 phase in TNT based melt-cast explosive compositions, a persistent and critical problem unanswered in the literature. The crystalline material recovered from such compositions revealed a mixture of β- and ε-CL-20. However, similar compositions of RDX and HMX never showed any metastable phase. The relatively long stability with the highest activation barrier is believed to restrict complete β→ε-CL-20 transformation during processing. Therefore a method is suggested to overcome this issue.

  18. Understanding metastable phase transformation during crystallization of RDX, HMX and CL-20: experimental and DFT studies.

    PubMed

    Ghosh, Mrinal; Banerjee, Shaibal; Shafeeuulla Khan, Md Abdul; Sikder, Nirmala; Sikder, Arun Kanti

    2016-09-14

    Multiphase growth during crystallization severely affects deliverable output of explosive materials. Appearance and incomplete transformation of metastable phases are a major source of polymorphic impurities. This article presents a methodical and molecular level understanding of the metastable phase transformation mechanism during crystallization of cyclic nitramine explosives, viz. RDX, HMX and CL-20. Instantaneous reverse precipitation yielded metastable γ-HMX and β-CL-20 which undergo solution mediated transformation to the respective thermodynamic forms, β-HMX and ε-CL-20, following 'Ostwald's rule of stages'. However, no metastable phase, anticipated as β-RDX, was evidenced during precipitation of RDX, which rather directly yielded the thermodynamically stable α-phase. The γ→β-HMX and β→ε-CL-20 transformations took 20 and 60 minutes respectively, whereas formation of α-RDX was instantaneous. Density functional calculations were employed to identify the possible transition state conformations and to obtain activation barriers for transformations at wB97XD/6-311++G(d,p)(IEFPCM)//B3LYP/6-311G(d,p) level of theory. The computed activation barriers and lattice energies responsible for transformation of RDX, HMX and CL-20 metastable phases to thermodynamic ones conspicuously supported the experimentally observed order of phase stability. This precise result facilitated an understanding of the occurrence of a relatively more sensitive and less dense β-CL-20 phase in TNT based melt-cast explosive compositions, a persistent and critical problem unanswered in the literature. The crystalline material recovered from such compositions revealed a mixture of β- and ε-CL-20. However, similar compositions of RDX and HMX never showed any metastable phase. The relatively long stability with the highest activation barrier is believed to restrict complete β→ε-CL-20 transformation during processing. Therefore a method is suggested to overcome this issue. PMID

  19. 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.

  20. Direct Determination of the Metastable Liquid Miscibility Gap in Undercooled Cu-Co Alloys

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    Bulk Cu-Co alloys at compositions ranging from 10 to 80 wt pct Co were highly undercooled using a melt fluxing technique. The metastable liquid separation boundary has been directly determined from the measured temperature-time profiles. It was found that the critical point of the miscibility gap is slightly shifted towards the Co side and about 90 K below the liquidus. A droplet-shaped microstructure was observed for all solidified specimens (Cu- 10 to 80 wt pct Co), when the melts were undercooled into the metastable miscibility boundary.

  1. Elastic free energy of anisotropic helical ribbons as metastable intermediates in the crystallization of cholesterol.

    PubMed Central

    Chung, D S; Benedek, G B; Konikoff, F M; Donovan, J M

    1993-01-01

    We report measurements of the geometrical structure and temporal evolution of metastable helical intermediates in the pathway for cholesterol crystallization in native and model biles. We find that the lecithin component in the bile can dramatically affect the kinetics along this pathway. We also present a theoretical description of these helical intermediates using an elastic free energy appropriate for anisotropic bilayers of tilted chiral amphiphiles, which provides a quantitative description of the observed helical ribbon geometry and insight into the relative free energies of the observed metastable intermediates. Images Fig. 2 Fig. 3 PMID:8248250

  2. The radiative lifetime of the 5S(0)2 metastable level of O(2+)

    NASA Technical Reports Server (NTRS)

    Johnson, B. C.; Smith, P. L.; Knight, R. D.

    1984-01-01

    The radiative lifetime of the 5S(0)2 metastable level of O(2+) was measured as 1.22 + or - 0.08 ms at the 90 percent confidence level by observing the time dependence of the spontaneous emission from metastable ions created and stored in a cylindrical radio-frequency ion trap. The intersystem line emission 2s(2)2p(2) 3P - 2s2p(3) 5S(0) was observed at 1660.8 and 1666.2 A. Discrepancies between measured and calculated values indicate that certain calculated transition probabilities for intersystem lines may be less reliable than previously believed.

  3. Observation of Metastable Structural Excitations and Concerted Atomic Motions on a Crystal Surface

    NASA Astrophysics Data System (ADS)

    Hwang, Ing-Shouh; Golovchenko, Jene

    1992-11-01

    The addition of a small number of lead atoms to a germanium(111) surface reduces the energy barrier for activated processes, and with a tunneling microscope it is possible to observe concerted atomic motions and metastable structures on this surface near room temperature. The formation and annihilation of these metastable structural surface excitations is associated with the shift in position of large numbers of germanium surface atoms along a specific row direction like beads on an abacus. The effect provides a mechanism for understanding the transport of atoms on a semiconductor surface.

  4. 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.

  5. 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}.

  6. 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.

  7. 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.

  8. 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.

  9. Search for heavy metastable particles decaying to quark pairs at CDF

    SciTech Connect

    Kwang, Shawn Andrew

    2011-03-01

    We report on the search for heavy metastable particles that decay into quark pairs with a macroscopic lifetime (cτ ~ 1 cm) using data taken with the CDF II detector at Fermilab. We use a data driven background approach, where they build probability density functions to model Standard Model secondary vertices from known processes in order to estimate the background contribution from the Standard Model. No statistically significant excess is observed above the background. Limits on the production cross section in a Hidden Valley benchmark phenomenology are set for various Higgs boson masses as well as metastable particle masses and lifetimes.

  10. Discontinuous Bubble Nucleation Due to a Metastable Condensation Transition in Polymer-CO2 Mixtures.

    PubMed

    Xu, Xiaofei; Cristancho, Diego E; Costeux, Stéphane; Wang, Zhen-Gang

    2013-05-16

    We combine a newly developed density-functional theory with the string method to calculate the minimum free energy path of bubble nucleation in compressible polymer-CO2 mixtures. Nucleation is initiated by saturating the polymer liquid with high pressure CO2 and subsequently reducing the pressure to ambient condition. Below a critical temperature, we find that there is a discontinuous drop in the nucleation barrier with increased initial CO2 pressure, as a result of an underlying metastable transition from a CO2-rich-vapor phase to a CO2-rich-liquid phase. This phenomenon is different from previously proposed nucleation mechanisms involving metastable transitions.

  11. Metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere

    NASA Astrophysics Data System (ADS)

    Kirby, Stephen H.; Stein, Seth; Okal, Emile A.; Rubie, David C.

    1996-05-01

    Earth's deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km. This depth interval closely brackets the mantle transition zone, characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher-pressure phases. Deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal, thermodynamic, and mechanical ferment inside slabs. Numerical simulations of reaction rates show that the olivine → spinel transformation should be kinetically hindered in old, cold slabs descending into the transition zone. Thus wedge-shaped zones of metastable peridotite probably persist to depths of more than 600 km. Laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting. This instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser, finer-grained phase. Hence in cold slabs, such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite. It is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs. This consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features. It explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone, where minerals in downgoing slabs should transform to spinel and ilmenite structures. The onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab. Even if a slab penetrates into the lower mantle, earthquakes

  12. 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

  13. 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

    2013-09-01

    Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series of small changes in the applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning. Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a rotation to the ground state orientation.

  14. 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.

  15. 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.

  16. 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.

  17. Thermal evolution of the metastable r8 and bc8 polymorphs of silicon

    DOE PAGES

    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 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

  18. Metastability in lipid based particles exhibits temporally deterministic and controllable behavior

    PubMed Central

    Jacoby, Guy; Cohen, Keren; Barkan, Kobi; Talmon, Yeshayahu; Peer, Dan; Beck, Roy

    2015-01-01

    The metastable-to-stable phase-transition is commonly observed in many fields of science, as an uncontrolled independent process, highly sensitive to microscopic fluctuations. In particular, self-assembled lipid suspensions exhibit phase-transitions, where the underlying driving mechanisms and dynamics are not well understood. Here we describe a study of the phase-transition dynamics of lipid-based particles, consisting of mixtures of dilauroylphosphatidylethanolamine (DLPE) and dilauroylphosphatidylglycerol (DLPG), exhibiting a metastable liquid crystalline-to-stable crystalline phase transition upon cooling from 60°C to 37°C. Surprisingly, unlike classically described metastable-to-stable phase transitions, the manner in which recrystallization is delayed by tens of hours is robust, predetermined and controllable. Our results show that the delay time can be manipulated by changing lipid stoichiometry, changing solvent salinity, adding an ionophore, or performing consecutive phase-transitions. Moreover, the delay time distribution indicates a deterministic nature. We suggest that the non-stochastic physical mechanism responsible for the delayed recrystallization involves several rate-affecting processes, resulting in a controllable, non-independent metastability. A qualitative model is proposed to describe the structural reorganization during the phase transition. PMID:25820650

  19. Capability of X-ray diffraction for the study of microstructure of metastable thin films

    PubMed Central

    Rafaja, David; Wüstefeld, Christina; Dopita, Milan; Motylenko, Mykhaylo; Baehtz, Carsten

    2014-01-01

    Metastable phases are often used to design materials with outstanding properties, which cannot be achieved with thermodynamically stable compounds. In many cases, the metastable phases are employed as precursors for controlled formation of nanocomposites. This contribution shows how the microstructure of crystalline metastable phases and the formation of nanocomposites can be concluded from X-ray diffraction experiments by taking advantage of the high sensitivity of X-ray diffraction to macroscopic and microscopic lattice deformations and to the dependence of the lattice deformations on the crystallographic direction. The lattice deformations were determined from the positions and from the widths of the diffraction lines, the dependence of the lattice deformations on the crystallographic direction from the anisotropy of the line shift and the line broadening. As an example of the metastable system, the supersaturated solid solution of titanium nitride and aluminium nitride was investigated, which was prepared in the form of thin films by using cathodic arc evaporation of titanium and aluminium in a nitrogen atmosphere. The microstructure of the (Ti,Al)N samples under study was tailored by modifying the [Al]/[Ti] ratio in the thin films and the surface mobility of the deposited species. PMID:25485125

  20. Interplay between topological and thermodynamic stability in a metastable magnetic skyrmion lattice

    NASA Astrophysics Data System (ADS)

    Oike, Hiroshi; Kikkawa, Akiko; Kanazawa, Naoya; Taguchi, Yasujiro; Kawasaki, Masashi; Tokura, Yoshinori; Kagawa, Fumitaka

    2016-01-01

    Topologically stable matter can have a long lifetime, even if thermodynamically costly, when the thermal agitation is sufficiently low. A magnetic skyrmion lattice (SkL) represents a unique form of long-range magnetic order that is topologically stable, such that a long-lived, metastable SkL can form. Experimental observations of the SkL in bulk crystals, however, have mostly been limited to a finite and narrow temperature region in which the SkL is thermodynamically stable; thus, the benefits of the topological stability remain unclear. Here, we report a metastable SkL created by quenching a thermodynamically stable SkL. Hall-resistivity measurements of MnSi reveal that, although the metastable SkL is short-lived at high temperatures, the lifetime becomes prolonged (>>1 week) at low temperatures. The manipulation of a delicate balance between thermal agitation and the topological stability enables a deterministic creation/annihilation of the metastable SkL by exploiting electric heating and subsequent rapid cooling, thus establishing a facile method to control the formation of a SkL.

  1. 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.

  2. Spontaneous SUSY breaking with anomalous U(1) symmetry by meta-stable vacuum

    SciTech Connect

    Nishino, Hiroyuki

    2008-11-23

    We will discuss a SUSY breaking model with anomalous U(1) symmetry. We discard R-symmetry and allow non-renormalizable terms for the model. It will be shown that certain class of models, where the number of positively charged fields is larger than that of negatively charged fields, can have meta-stable SUSY breaking vacuum.

  3. Mechanisms of metastable states in CuZr systems with glass-like structures

    NASA Astrophysics Data System (ADS)

    Song, Wen-Xiong; Zhao, Shi-Jin; Wang, Gang

    2015-09-01

    The local structural inhomogeneity of glasses, as evidenced from broad bond-length distributions (BLDs), has been widely observed. However, the relationship between this particular structural feature and metastable states of glassy solids is poorly understood. It is important to understand the main problems of glassy solids, such as the plastic deformation mechanisms and glass-forming ability. The former is related to β-relaxation, the relaxation of a system from a subbasin to another in the potential energy landscape (PEL). The latter represents the stability of a metastable state in the PEL. Here, we explain the main reason why CuZr systems with glass-like structures exist in metastable states: a large strain energy. The calculation results obtained in this study indicate that a system with broad BLD has a large strain energy because of the nonlinear and asymmetric strain energy of bonds. Unstable polyhedra have larger volumes and more short and long bonds than stable polyhedra, which are most prone to form deformation units. The driving force for pure metal crystallization was also elucidated to be the decrease in strain energy. The results obtained in this study, which are verified by a series of calculations as well as molecular dynamics simulations, indicate the presence of metastable states in amorphous materials and elucidate the mechanisms of plastic deformation and the driving force for crystallization without chemical bonding.

  4. 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.

  5. Metastability of copper indium gallium diselenide polycrystalline thin film solar cell devices

    NASA Astrophysics Data System (ADS)

    Lee, Jinwoo

    High efficiency thin film solar cells have the potential for being a world energy solution because of their cost-effectiveness. Looking to the future of solar energy, there is the opportunity and challenge for thin film solar cells. The main theme of this research is to develop a detailed understanding of electronically active defect states and their role in limiting device performance in copper indium gallium diselenide (CIGS) solar cells. Metastability in the CIGS is a good tool to manipulate electronic defect density and thus identify its effect on the device performance. Especially, this approach keeps many device parameters constant, including the chemical composition, grain size, and interface layers. Understanding metastability is likely to lead to the improvement of CIGS solar cells. We observed systematic changes in CIGS device properties as a result of the metastable changes, such as increases in sub-bandgap defect densities and decreases in hole carrier mobilities. Metastable changes were characterized using high frequency admittance spectroscopy, drive-level capacitance profiling (DLCP), and current-voltage measurements. We found two distinctive capacitance steps in the high frequency admittance spectra that correspond to (1) the thermal activation of hole carriers into/out of acceptor defect and (2) a temperature-independent dielectric relaxation freeze-out process and an equivalent circuit analysis was employed to deduce the dielectric relaxation time. Finally, hole carrier mobility was deduced once hole carrier density was determined by DLCP method. We found that metastable defect creation in CIGS films can be made either by light-soaking or with forward bias current injection. The deep acceptor density and the hole carrier density were observed to increase in a 1:1 ratio, which seems to be consistent with the theoretical model of VCu-V Se defect complex suggested by Lany and Zunger. Metastable defect creation kinetics follows a sub-linear power law

  6. Hexagonal ice transforms at high pressures and compression rates directly into "doubly metastable" ice phases.

    PubMed

    Bauer, Marion; Winkel, Katrin; Toebbens, Daniel M; Mayer, Erwin; Loerting, Thomas

    2009-12-14

    We report compression and decompression experiments of hexagonal ice in a piston cylinder setup in the temperature range of 170-220 K up to pressures of 1.6 GPa. The main focus is on establishing the effect that an increase in compression rate up to 4000 MPa/min has on the phase changes incurred at high pressures. While at low compression rates, a phase change to stable ice II takes place (in agreement with earlier comprehensive studies), we find that at higher compression rates, increasing fractions and even pure ice III forms from hexagonal ice. We show that the critical compression rate, above which mainly the metastable ice III polymorph is produced, decreases by a factor of 30 when decreasing the temperature from 220 to 170 K. At the highest rate capable with our equipment, we even find formation of an ice V fraction in the mixture, which is metastable with respect to ice II and also metastable with respect to ice III. This indicates that at increasing compression rates, progressively more metastable phases of ice grow from hexagonal ice. Since ices II, III, and V differ very much in, e.g., strength and rheological properties, we have prepared solids of very different mechanical properties just by variation in compression rate. In addition, these metastable phases have stability regions in the phase diagrams only at much higher pressures and temperatures. Therefore, we anticipate that the method of isothermal compression at low temperatures and high compression rates is a tool for the academic and industrial polymorph search with great potential. PMID:20001064

  7. Nucleation of metastable aragonite CaCO3 in seawater

    SciTech Connect

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

    2015-03-04

    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.

  8. 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.

  9. 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.

  10. New metastable form of ice and its role in the homogeneous crystallization of water

    NASA Astrophysics Data System (ADS)

    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.

  11. An optically trapped mixture of alkali-metal and metastable helium atoms

    NASA Astrophysics Data System (ADS)

    Flores, Adonis; Mishra, Hari Prasad; Vassen, Wim; Knoop, Steven

    2016-05-01

    Ultracold collisions between alkali-metal and metastable triplet helium (He*) atoms provide the opportunity to study Feshbach resonances in the presence of a strong loss channel, namely Penning ionization, which strongly depends on the internal spin-states of the atoms. Recently we have realized the first optically trapped alkali-metal-metastable helium mixture. To prepare the ultracold 87 Rb+4 He* mixture in a single beam optical dipole trap (ODT), we apply evaporative cooling in a strong quadrupole magnetic trap (QMT) for both species and subsequent transfer to the ODT via a hybrid trap. We will present lifetime measurements of different spin-state mixtures, testing the application of the universal loss model to this interesting multichannel collision system.

  12. Preparation and spectroscopy of a metastable Mott-insulator state with attractive interactions.

    PubMed

    Mark, M J; Haller, E; Lauber, K; Danzl, J G; Janisch, A; Büchler, H P; Daley, A J; Nägerl, H-C

    2012-05-25

    We prepare and study a metastable attractive Mott-insulator state formed with bosonic atoms in a three-dimensional optical lattice. Starting from a Mott insulator with Cs atoms at weak repulsive interactions, we use a magnetic Feshbach resonance to tune the interactions to large attractive values and produce a metastable state pinned by attractive interactions with a lifetime on the order of 10 s. We probe the (de)excitation spectrum via lattice modulation spectroscopy, measuring the interaction dependence of two- and three-body bound-state energies. As a result of increased on-site three-body loss we observe resonance broadening and suppression of tunneling processes that produce three-body occupation. PMID:23003276

  13. Two Oxygen-Coordinated Metastable Ru-ON States for Ruthenium Mononitrosyl Complex.

    PubMed

    Vorobyev, Vasily; Kostin, Gennadiy A; Kuratieva, Natalia V; Emelyanov, Vyacheslav A

    2016-09-19

    The properties of Ru-ON states were studied in cis-[RuNO(NH3)2(NO2)2OH] under illumination. The structure contains two nonequivalent complexes, and the metastable state was generated for both molecules with 19(1) and 31(1)% populations. The MS1 thermal decay occurs as a one-step process at about 240 K according to differential scanning calorimetry (DSC). For the first-order reaction, the frequency factor and activation energy for the decay process were determined as 2.0(2) × 10(13) s(-1) and 68.3(4) kJ mol(-1), respectively. Also, the simultaneous metastable state decay observed via DSC was in agreement with IR spectroscopy. PMID:27598533

  14. Properties of metastable alkaline-earth-metal atoms calculated using an accurate effective core potential

    SciTech Connect

    Santra, Robin; Christ, Kevin V.; Greene, Chris H.

    2004-04-01

    The first three electronically excited states in the alkaline-earth-metal atoms magnesium, calcium, and strontium comprise the (nsnp){sup 3}P{sub J}{sup o}(J=0,1,2) fine-structure manifold. All three states are metastable and are of interest for optical atomic clocks as well as for cold-collision physics. An efficient technique--based on a physically motivated potential that models the presence of the ionic core--is employed to solve the Schroedinger equation for the two-electron valence shell. In this way, radiative lifetimes, laser-induced clock shifts, and long-range interaction parameters are calculated for metastable Mg, Ca, and Sr.

  15. 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.

  16. 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.

  17. Dispersive measurement of a metastable phase qubit using a tunable cavity

    NASA Astrophysics Data System (ADS)

    Whittaker, Jed Douglas

    A metastable phase qubit was measured using a tunable cavity by two methods: a tunneling measurement followed by magnetometry readout by the cavity, and a non destructive dispersive measurement of the qubit by the cavity. The Purcell effect was observed as a decrease in the energy relaxation time of the qubit in the vicinity of the cavity, and could be manipulated by dynamically tuning the cavity. The observed dispersive shift of the cavity did not match the two-level system model for nonlinear qubits. Instead, a three-level model of the qubit was needed to describe the data, necessitated by the weakly nonlinear nature of the metastable phase qubit. The cavity was also used to directly observe the photons radiated by a tunneling measurement.

  18. Dispersive measurement of a metastable phase qubit using a tunable cavity

    NASA Astrophysics Data System (ADS)

    Whittaker, Jed; Allman, Michael; Cicak, Katarina; da Silva, Fabio; Sirois, Adam; Teufel, John; Aumentado, Joe; Simmonds, Ray

    2013-03-01

    A metastable phase qubit was measured using a tunable cavity by two methods: a tunneling measurement followed by magnetometry readout by the cavity, and a non-destructive dispersive measurement of the qubit by the cavity. The cavity was also used to directly observe the photons radiated by a tunneling measurement. Using a tunable cavity to dispersively measure a metastable phase qubit avoids tunneling measurement radiation and allows for further post-measurement qubit manipulations, two characteristics useful in a quantum processor. The tunable nature of the cavity allows it to be detuned during any single qubit or multi-qubit gate operations in order to main long qubit lifetimes by avoiding loss via the Purcell Effect. This architecture is readily expanded for multiplexed readout of many qubits.

  19. 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.

  20. 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. PMID:24836734

  1. Atomistic calculation of stability and metastability of coherently strained silicon-like structures

    NASA Astrophysics Data System (ADS)

    Dodson, B. W.; Taylor, P. A.

    Monte Carlo based microscopic techniques were used to study the stability and metastability of thin coherently strained layers of mismatched silicon-like semiconductor material grown on the (111) silicon surface. The structural energy was calculated using three-body empirical potentials. For layers greater than about 20 A thickness, the critical layer thickness associated with thermodynamic stability is accurately described by the continuum theory of Matthews and Blakeslee. For thinner layers, however, the stability properties vary considerably from those predicted by the continuum theory. The test system is found to be metastable against the nucleation of misfit dislocations to a lattice mismatch of about 11% for a strained layer six monolayers thick, compared to the 4% mismatch stability limit.

  2. Interindividual Variation in DNA Methylation at a Putative POMC Metastable Epiallele Is Associated with Obesity.

    PubMed

    Kühnen, Peter; Handke, Daniela; Waterland, Robert A; Hennig, Branwen J; Silver, Matt; Fulford, Anthony J; Dominguez-Salas, Paula; Moore, Sophie E; Prentice, Andrew M; Spranger, Joachim; Hinney, Anke; Hebebrand, Johannes; Heppner, Frank L; Walzer, Lena; Grötzinger, Carsten; Gromoll, Jörg; Wiegand, Susanna; Grüters, Annette; Krude, Heiko

    2016-09-13

    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 heritability." We provide evidence that methylation in a variably methylated region (VMR) in the pro-opiomelanocortin gene (POMC), particularly in postmortem human laser-microdissected melanocyte-stimulating hormone (MSH)-positive neurons, is strongly associated with individual BMI. Using cohorts from different ethnic backgrounds, including a Gambian cohort, we found evidence suggesting that methylation of the POMC VMR is established in the early embryo and that offspring methylation correlates with the paternal somatic methylation pattern. Furthermore, it is associated with levels of maternal one-carbon metabolites at conception and stable during postnatal life. Together, these data suggest that the POMC VMR may be a human metastable epiallele that influences body-weight regulation. PMID:27568547

  3. 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.

  4. A novel series of isoreticular metal organic frameworks: realizing metastable structures by liquid phase epitaxy

    NASA Astrophysics Data System (ADS)

    Liu, Jinxuan; Lukose, Binit; Shekhah, Osama; Arslan, Hasan Kemal; Weidler, Peter; Gliemann, Hartmut; Bräse, Stefan; Grosjean, Sylvain; Godt, Adelheid; Feng, Xinliang; Müllen, Klaus; Magdau, Ioan-Bogdan; Heine, Thomas; Wöll, Christof

    2012-12-01

    A novel class of metal organic frameworks (MOFs) has been synthesized from Cu-acetate and dicarboxylic acids using liquid phase epitaxy. The SURMOF-2 isoreticular series exhibits P4 symmetry, for the longest linker a channel-size of 3 × 3 nm2 is obtained, one of the largest values reported for any MOF so far. High quality, ab-initio electronic structure calculations confirm the stability of a regular packing of (Cu++)2- carboxylate paddle-wheel planes with P4 symmetry and reveal, that the SURMOF-2 structures are in fact metastable, with a fairly large activation barrier for the transition to the bulk MOF-2 structures exhibiting a lower, twofold (P2 or C2) symmetry. The theoretical calculations also allow identifying the mechanism for the low-temperature epitaxial growth process and to explain, why a synthesis of this highly interesting, new class of high-symmetry, metastable MOFs is not possible using the conventional solvothermal process.

  5. 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

  6. 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.

  7. Nonlinear optical response of noble gases via the metastable electronic state approach

    NASA Astrophysics Data System (ADS)

    Bahl, A.; Wright, E. M.; Kolesik, M.

    2016-08-01

    The goal of this paper is to elucidate the theoretical underpinnings of the metastable electronic state approach (MESA) and demonstrate its utility for the evaluation of the nonlinear optical response of noble-gas atoms with emphasis on the application of the method to the propagation of multicolor optical fields in large-scale, spatially resolved simulations. More specifically, single-active-electron models of various atoms are employed to calculate their nonlinear properties both within the adiabatic approximation, involving a single metastable state and beyond, capturing inertial effects, and wavelength-dependent ionization. Simulations for excitation pulses at different center wavelengths as well as ionization in two-color pulses are presented and compared with numerical solutions of the time-dependent Schrödinger equation. Illustrative examples of the numerical simulation of high-power pulse propagation incorporating MESA data are also presented and showcase the successful application to optical filamentation in the midinfrared region.

  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. 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

  10. 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.

  11. 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.

  12. Formation of O3/+/ by the reaction of metastable O2/+/ ions with O2

    NASA Technical Reports Server (NTRS)

    Ajello, J. M.; Pang, K. D.; Monahan, K. M.

    1974-01-01

    The high resolution of the photoionization mass spectrophotometer was utilized to resolve some doubts about the participating species in the reaction of metastable oxygen molecular ions with oxygen molecules to yield ozone ions and oxygen radicals. It is found from inspection of the appearance potential of the ozone ion that an a4 Pi-excited state is responsible for the formation of ozone near the appearance potential of these lines.

  13. 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.

  14. A theory for metastabilities in bubble nucleation: can it help explaining nanobubbles?

    NASA Astrophysics Data System (ADS)

    Casciola, Carlo Massimo

    2013-11-01

    The stability and the very existence of nanobubbles on a solid-liquid interface is a conundrum that has been puzzling the community of researchers working in the field since their discovery through AFM measurements in the late nineties. Nanobubbles are typically flat, with height on the order of 5-10 nm and lateral size order 100 nm or less. Pinning of the contact line presumably plays a crucial role and, based on classical estimates, they should dissolve almost immediately while they are instead reported to persist for days. Recently we developed a novel theoretical approach that is able to predict the heterogeneous nucleation path, and to explain the catalytic effect of geometrical defects in lowering the associated free-energy barrier (Giacomello et al., PRL 2012). The theory bridges the scales from nanometer to micron, and is then suitable for dealing with nanobubbles, as shown by comparison with advanced rare-event techniques used to evaluate the metastability in the atomistic context (Giacomello et al., Langmuir 2012). The interest of the approach is that it can provide an estimate for the transition frequency, i.e. the average lifetime of a metastable configuration. As will be discussed, the model can in principle be enriched to account for the interaction of the gas phase with the solid, indicated as responsible for the almost universal contact angle observed in the nanobubbles (Weijs et al., PRL 2012). If nanobubbles can be explained in the context of equilibrium statistical ensembles, as long-lived metastable states associated with a complex free-energy landscape, the work under way could shed new light on the elusive subject of their persistence. At present we cannot however exclude substantial non-equilibrium effects, outside the concept of metastability in the strict statistical-mechanics sense and associated, e.g., with thermal gradients. ERC 2013 is acknowledged for support.

  15. 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

  16. 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.

  17. Formation of a submicrocrystalline structure in metastable austenitic steels during severe plastic deformation and subsequent heating

    NASA Astrophysics Data System (ADS)

    Mal'tseva, L. A.; Mal'tseva, T. V.; Yurovskikh, A. S.; Raab, G. I.; Sharapova, V. A.; Vakhonina, K. D.

    2016-03-01

    The structure and the mechanical properties of metastable austenitic steels after severe plastic deformation by four or six passes of equal-channel angular pressing (ECAP) at a temperature of 400°C are studied. It is shown that ECAP results in strain hardening mainly due to the formation of a submicrocrystalline structure, which is retained after subsequent heating to 500°C.

  18. Nucleation in finite topological systems during continuous metastable quantum phase transitions.

    PubMed

    Fialko, Oleksandr; Delattre, Marie-Coralie; Brand, Joachim; Kolovsky, Andrey R

    2012-06-22

    Finite topological quantum systems can undergo continuous metastable quantum phase transitions to change their topological nature. Here we show how to nucleate the transition between ring currents and dark soliton states in a toroidally trapped Bose-Einstein condensate. An adiabatic passage to wind and unwind its phase is achieved by explicit global breaking of the rotational symmetry. This could be realized with current experimental technology.

  19. 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.

  20. 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.

  1. Distribution of metastable argon atoms in the modified Grimm-type electrical discharge

    NASA Astrophysics Data System (ADS)

    Ferreira, N. P.; Strauss, J. A.; Human, H. G. C.

    The absorbance by metastable argon atoms of the Ar 696.543 nm line in the modified Grimm-type electrical discharge source was measured at different discharge conditions and at distances varying from 0.25 to 6 mm from the cathode. A uranium/argon hollow cathode lamp was used as primary source, which gave an argon gas temperature of 850 K when run at 12 mA. A maximum absorbance of 0.57 was found 3 mm from the cathode at 600 V, 80 mA. The magnitude of absorbance increases with discharge current while the position of maximum absorbance shifts away from the cathode with increase in discharge voltage. The quenching of metastable atoms by nitrogen is demonstrated. The spatial distribution of the intensity of four different types of spectral lines is shown. The approximate number densities of the different particles are 10 12cm -3 for metastable argon atoms, 10 16cm -3 for neutral argon atoms, 10 13 cm -3 for sputtered copper atoms and 10 14cm -3for electrons.

  2. Role of photogenerated meta-stable polarons in organic magnetoresistance: evidence for polaron pair mechanism

    NASA Astrophysics Data System (ADS)

    Gautam, Bhoj; Nguyen, Tho; Valy Vardeny, Z.

    2010-03-01

    We studied the magneto-conductance (MC) in homopolar organic diodes based on semiconductor polymers MEH-PPV and DOO-PPV. In dark we measured negative MC in both MEH-PPV and DOO-PPV homopolar devices, which was previously interpreted as due to magnetic field effect on singlet yield of polaron pairs having the same charge, known in the literature as the ``bipolaron'' mechanism. We investigated the role of photogenerated meta-stable polarons on the MC, when illuminating the device with a cw laser beam at various intensities and illumination times. Such illumination is known to produce metastable polarons that are deep-trapped in MEH-PPV polymer, but less so in DOO-PPV polymer. Upon illumination we obtained a gradual change in the MC magnitude and magnetic field response, where the MC first decreases then changes sign from negative to positive with the illumination time. Similar effects were not obtained in DOO-PPV devices. We therefore conclude that the metastable polarons in the illuminated polymer initiate the formation of polaron pairs with opposite charge in the homopolar device upon current injection; and these are therefore responsible for positive MC. This photoinduced MC is in agreement with a similar effect found in MC of bipolar organic diodes upon increasing the bias voltage beyond the threshold for bipolar injection.

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

    PubMed

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

    2013-10-01

    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. PMID:23437906

  4. Fragmentation of metastable SF{sub 6}{sup -}* ions with microsecond lifetimes in competition with autodetachment

    SciTech Connect

    Graupner, K.; Field, T. A.; Mauracher, A.; Scheier, P.; Bacher, A.; Denifl, S.; Zappa, F.; Maerk, T. D.

    2008-03-14

    Fragmentation of metastable SF{sub 6}{sup -}* ions formed in low energy electron attachment to SF{sub 6} has been investigated. The dissociation reaction SF{sub 6}{sup -}*{yields}SF{sub 5}{sup -}+F has been observed {approx}1.5-3.4 {mu}s and {approx}17-32 {mu}s after electron attachment in a time-of-flight and a double focusing two sector field mass spectrometer, respectively. Metastable dissociation is observed with maximum intensity at {approx}0.3 eV between the SF{sub 6}{sup -}* peak at zero and the SF{sub 5}{sup -} peak at {approx}0.4 eV. The kinetic energy released in dissociation is low, with a most probable value of 18 meV. The lifetime of SF{sub 6}{sup -}* decreases as the electron energy increases, but it is not possible to fit this decrease with statistical Rice-Ramsperger-Kassel/quasiequilibrium theory. Metastable dissociation of SF{sub 6}{sup -}* appears to compete with autodetachment of the electron at all electron energies.

  5. Mass spectrometry of solid samples in open air using combined laser ionization and ambient metastable ionization

    NASA Astrophysics Data System (ADS)

    He, X. N.; Xie, Z. Q.; Gao, Y.; Hu, W.; Guo, L. B.; Jiang, L.; Lu, Y. F.

    2012-01-01

    Mass spectrometry of solid samples in open air was carried out using combined laser ionization and metastable ionization time-of-flight mass spectrometry (LI-MI-TOFMS) in ambient environment for qualitative and semiquantitative (relative analyte information, not absolute information) analysis. Ambient metastable ionization using a direct analysis in realtime (DART) ion source was combined with laser ionization time-of-flight mass spectrometry (LI-TOFMS) to study the effects of combining metastable and laser ionization. A series of metallic samples from the National Institute of Standards and Technology (NIST 494, 495, 498, 499, and 500) and a pure carbon target were characterized using LI-TOFMS in open air. LI-MI-TOFMS was found to be superior to laser-induced breakdown spectroscopy (LIBS). Laser pulse energies between 10 and 200 mJ at the second harmonic (532 nm) of an Nd:YAG laser were applied in the experiment to obtain a high degree of ionization in plasmas. Higher laser pulse energy improves signal intensities of trace elements (such as Fe, Cr, Mn, Ni, Ca, Al, and Ag). Data were analyzed by numerically calculating relative sensitivity coefficients (RSCs) and limit of detections (LODs) from mass spectrometry (MS) and LIBS spectra. Different parameters, such as boiling point, ionization potential, RSC, LOD, and atomic weight, were shown to analyze the ionization and MS detection processes in open air.

  6. 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.

  7. A thermal beam of metastable krypton atoms produced by optical excitation.

    SciTech Connect

    Ding, Y.; Hu, S.-M.; Bailey, K.; Davis, A. M.; Dunford, R. W.; Lu, Z.-T.; O'Connor, T. P.; Young, L.; Univ. of Chicago; Univ. of Science and Technology of China

    2007-02-08

    A room-temperature beam of krypton atoms in the metastable 5s[3/2]{sub 2} level is demonstrated via an optical excitation method. A Kr-discharge lamp is used to produce vacuum ultraviolet photons at 124 nm for the first-step excitation from the ground level 4p{sup 6} {sup 1}S{sub 0} to the 5s[3/2]{sub 1} level. An 819 nm Ti:sapphire laser is used for the second-step excitation from 5s[3/2]{sub 1} to 5s[3/2]{sub 2} followed by a spontaneous decay to the 5s[3/2]{sub 2} metastable level. A metastable atomic beam with an angular flux density of 3 x 10{sup 14} s{sup -1} sr{sup -1} is achieved at the total gas flow rate of 0.01 cm{sup 3}/s at STP (or 3 x 10{sup 17} at./s). The dependences of the flux on the gas flow rate, laser power, and lamp parameters are investigated.

  8. Rydberg state, metastable, and electron dynamics in the low-pressure argon afterglow

    NASA Astrophysics Data System (ADS)

    Tsankov, Tsanko V.; Johnsen, Rainer; Czarnetzki, Uwe

    2015-12-01

    In this work a time-dependent collisional-radiative model for recombining plasmas is developed. It tracks the collisional and radiative capture of electrons into highly-excited (Rydberg) states and their consecutive deexcitation through collisions and radiation to the ground or the metastable state. The model allows the calculation of the net recombination rate and the electron energy gain by recombination. It is coupled to the volume-averaged balance equations for the electron density and temperature. The numerical solution of these equations includes a model for the diffusion cooling of the electrons (Celik et al 2012 Phys. Rev. E 85 046407) and a simplified model for the gas cooling. Using as only input the experimentally determined initial values of the electron density and temperature, gas temperature and metastable density, the temporal evolution of all parameters in the afterglow is calculated and compared with measurements. The results reproduce very well the measured quantities (electron density, light emission and metastable density) without the need to invoke adjustable parameters. This gives confidence in the validity of the model that allows it to be used not only to deepen the understanding of afterglow plasmas but also to tailor their properties as required for applications. The analysis of the model results further shows that gas heating and cooling must be explicitly taken into account to reproduce experimental observations. The electron heating by recombination is another process that is important for the good agreement. Both of these effects were largely ignored in previous works on afterglows.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. Structural Studies of Metastable and Ground State 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.

    2015-03-01

    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)]. Application of an AC magnetic field to drive the VL to the ground state revealed a two-step power law behavior, indicating a slow nucleation of ground state domains followed by a faster growth. The dependence on the number of applied AC cycles is reminiscent of jamming of soft, frictionless spheres. Here, we report on detailed structural studies of both metastable and ground state VL domains. These include measurements of VL correlation lengths as well as spatially resolved SANS measurements showing the VL domain distribution within the MgB2 single crystal. We discuss these results and how they may help to resolve the mechanism responsible for stabilizing the metastable VL phases. This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Award DE-FG02-10ER46783.

  14. 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.

  15. 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.

  16. Interplay of strong chemical bonds and the repulsive Coulomb force in the metastable states of triply ionized homonuclear molecules: A theoretical study of N23+ and O23+

    NASA Astrophysics Data System (ADS)

    Imamura, Yutaka; Hatsui, Takaki

    2012-01-01

    We have studied metastable electronic states of trication molecules for N23+ and O23+ using the internally contracted multireference configuration interaction method with single and double excitations (icMRCISD). The metastable ground state for O23+ and metastable excited state for N23+ were obtained with the barriers of approximately 1.5 and 13.0 kcal/mol, respectively, although those metastable states were not found in previous calculations. The analysis on occupation numbers of natural orbitals demonstrates that the two metastable states are formed owing to the balance between the reduction of cationic Coulomb repulsion and the weakening of the chemical bonds. We have proposed to measure these metastable states by short-wavelength free-electron lasers (sFELs) that have the potential to produce excited states of multiply charged molecules.

  17. 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

  18. Stability of metastable phase and soft magnetic properties of bulk Fe-B nano-eutectic alloy prepared by undercooling solidification combined with CU-mold chilling

    NASA Astrophysics Data System (ADS)

    Yang, Changlin; Zhang, Jun; Huang, Huili; Song, Qijiao; Liu, Feng

    2015-11-01

    Bulk Fe83B17 nano-eutectic alloys were prepared by undercooling solidification combined with Cu-mold chilling method. Stable phase Fe2B and metastable phase Fe3B were found to coexist in the as-solidified microstructure. The soft magnetic properties were improved significantly by the nano-lamellar eutectic and the metastable phase and, were increased further by annealing at 1173 K for 1.5 h after which the metastable phase was decomposed completely.

  19. 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

  20. Structural Characterization of Two Metastable ATP-Bound States of P-Glycoprotein

    PubMed Central

    O’Mara, Megan L.; Mark, Alan E.

    2014-01-01

    ATP Binding Cassette (ABC) transporters couple the binding and hydrolysis of ATP to the transport of substrate molecules across the membrane. The mechanism by which ATP binding and/or hydrolysis drives the conformational changes associated with substrate transport has not yet been characterized fully. Here, changes in the conformation of the ABC export protein P-glycoprotein on ATP binding are examined in a series of molecular dynamics simulations. When one molecule of ATP is placed at the ATP binding site associated with each of the two nucleotide binding domains (NBDs), the membrane-embedded P-glycoprotein crystal structure adopts two distinct metastable conformations. In one, each ATP molecule interacts primarily with the Walker A motif of the corresponding NBD. In the other, the ATP molecules interacts with both Walker A motif of one NBD and the Signature motif of the opposite NBD inducing the partial dimerization of the NBDs. This interaction is more extensive in one of the two ATP binding site, leading to an asymmetric structure. The overall conformation of the transmembrane domains is not altered in either of these metastable states, indicating that the conformational changes associated with ATP binding observed in the simulations in the absence of substrate do not lead to the outward-facing conformation and thus would be insufficient in themselves to drive transport. Nevertheless, the metastable intermediate ATP-bound conformations observed are compatible with a wide range of experimental cross-linking data demonstrating the simulations do capture physiologically important conformations. Analysis of the interaction between ATP and its cofactor Mg2+ with each NBD indicates that the coordination of ATP and Mg2+ differs between the two NBDs. The role structural asymmetry may play in ATP binding and hydrolysis is discussed. Furthermore, we demonstrate that our results are not heavily influenced by the crystal structure chosen for initiation of the simulations

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

    SciTech Connect

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

    2013-01-15

    Rare-earth-iron mixed oxides with the rare earth/iron ratio=1 have either orthorhombic (o-REFeO{sub 3}) or hexagonal (h-REFeO{sub 3}) structure. h-REFeO{sub 3} is a metastable phase and the synthesis of h-REFeO{sub 3} 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-REFeO{sub 3}. 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-REFeO{sub 3} 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 YbFeO{sub 3} had higher catalytic activity for C{sub 3}H{sub 8} combustion than orthorhombic YbFeO{sub 3}. - Graphical abstract: Although the synthesis of metastable hexagonal REFeO{sub 3} by the conventional method is difficult, we found that this phase is obtained by shortening the heating time of the precursor prepared by co-precipitation method. Highlights: Black-Right-Pointing-Pointer Synthesis of metastable REFeO{sub 3} with hexagonal structure by the co-precipitation method. Black-Right-Pointing-Pointer Hexagonal REFeO{sub 3} is obtained for the rare earth elements with small ionic radii. Black-Right-Pointing-Pointer Hexagonal-to-orthorhombic transformation of REFeO{sub 3}. Black-Right-Pointing-Pointer Catalytic activity of hexagonal REFeO{sub 3} for C{sub 3}H{sub 8} combustion.

  2. 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

  3. Stochastic Tunneling and Metastable States During the Somatic Evolution of Cancer

    PubMed Central

    Ashcroft, Peter; Michor, Franziska; Galla, Tobias

    2015-01-01

    Tumors initiate when a population of proliferating cells accumulates a certain number and type of genetic and/or epigenetic alterations. The population dynamics of such sequential acquisition of (epi)genetic alterations has been the topic of much investigation. The phenomenon of stochastic tunneling, where an intermediate mutant in a sequence does not reach fixation in a population before generating a double mutant, has been studied using a variety of computational and mathematical methods. However, the field still lacks a comprehensive analytical description since theoretical predictions of fixation times are available only for cases in which the second mutant is advantageous. Here, we study stochastic tunneling in a Moran model. Analyzing the deterministic dynamics of large populations we systematically identify the parameter regimes captured by existing approaches. Our analysis also reveals fitness landscapes and mutation rates for which finite populations are found in long-lived metastable states. These are landscapes in which the final mutant is not the most advantageous in the sequence, and resulting metastable states are a consequence of a mutation–selection balance. The escape from these states is driven by intrinsic noise, and their location affects the probability of tunneling. Existing methods no longer apply. In these regimes it is the escape from the metastable states that is the key bottleneck; fixation is no longer limited by the emergence of a successful mutant lineage. We used the so-called Wentzel–Kramers–Brillouin method to compute fixation times in these parameter regimes, successfully validated by stochastic simulations. Our work fills a gap left by previous approaches and provides a more comprehensive description of the acquisition of multiple mutations in populations of somatic cells. PMID:25624316

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

    PubMed

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

    2013-10-28

    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.

  5. 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

    2016-06-01

    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

  6. Metastable States of a Gas of Dipolar Bosons in a 2D Optical Lattice

    SciTech Connect

    Menotti, C.; Trefzger, C.; Lewenstein, M.

    2007-06-08

    We investigate the physics of dipolar bosons in a two-dimensional optical lattice. It is known that due to the long-range character of dipole-dipole interaction, the ground state phase diagram of a gas of dipolar bosons in an optical lattice presents novel quantum phases, like checkerboard and supersolid phases. In this Letter, we consider the properties of the system beyond its ground state, finding that it is characterized by a multitude of almost degenerate metastable states, often competing with the ground state. This makes dipolar bosons in a lattice similar to a disordered system and opens possibilities of using them as quantum memories.

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

    NASA Astrophysics Data System (ADS)

    Zarkevich, N. A.; Johnson, D. D.

    2016-01-01

    As titanium is a highly utilized metal for structural lightweighting, 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 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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. PMID:20681591

  12. Intrinsic Metastabilities in the Charge Configuration of a Double Quantum Dot.

    PubMed

    Biesinger, D E F; Scheller, C P; Braunecker, B; Zimmerman, J; Gossard, A C; Zumbühl, D M

    2015-09-01

    We report a thermally activated metastability in a GaAs double quantum dot exhibiting real-time charge switching in diamond shaped regions of the charge stability diagram. Accidental charge traps and sensor backaction are excluded as the origin of the switching. We present an extension of the canonical double dot theory based on an intrinsic, thermal electron exchange process through the reservoirs, giving excellent agreement with the experiment. The electron spin is randomized by the exchange process, thus facilitating fast, gate-controlled spin initialization. At the same time, this process sets an intrinsic upper limit to the spin relaxation time. PMID:26382695

  13. 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.

  14. 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

    2016-10-01

    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 collision

  15. Nonadiabatic coupling in cold collisions of spin-polarized metastable hydrogen atoms

    SciTech Connect

    Forrey, Robert C.; Dalgarno, Alex; Vanne, Yulian V.; Saenz, Alejandro; Froelich, Piotr

    2007-11-15

    Previous calculations of low-temperature cross sections for collisions between spin-polarized metastable hydrogen atoms are improved to include nonadiabatic radial and angular coupling at large interatomic separations. The electrostatic dipole-quadrupole interaction produces nonadiabatic radial coupling between (2s,2p) and (2p,2p) states, while the Coriolis interaction produces nonadiabatic angular coupling. Both of these long-range contributions are handled in a space-fixed atomic gauge that is particularly convenient for a spin-polarized system. The improved theoretical results are compared with an existing experiment.

  16. 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.

  17. Metastable nitric acid hydrates--possible constituents of polar stratospheric clouds?

    PubMed

    Grothe, Hinrich; Tizek, Heinz; Ortega, Ismael K

    2008-01-01

    Crystallization kinetics of the metastable modifications of Nitric Acid Dihydrate (NAD) was investigated by time-dependent X-Ray Diffraction (XRD) measurements. Kinetic conversion curves were evaluated adopting the Avrami model. The growth and morphology of the respective crystallites and particles were monitored in situ on the cryo-stage of an Environmental Scanning Electron Microscope (ESEM) under a partial pressure of nitrogen gas (0.5 Torr, 67 Pa). The morphologies were used to adapt the InfraRed (IR) extinction spectra by T-matrix calculation using respective optical indices of NAD. The results show a significant dependence of the band shapes on different morphologies.

  18. 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.

  19. 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.

  20. Pulsed NMR investigation of the supercooled water-gas hydrate-gas metastable equilibrium

    NASA Astrophysics Data System (ADS)

    Vlasov, V. A.; Zavodovsky, A. G.; Madygulov, M. Sh.; Nesterov, A. N.; Reshetnikov, A. M.

    2013-11-01

    A method is developed for determining the thermobaric conditions of phase equilibrium in a liquid water-hydrate-gas system by means of pulsed 1H NMR. The method is founded on NMR-based measurements of the amount of liquid water phase in a sample containing gas hydrate under certain values of pressure p and temperature T. The results from investigating the p, T conditions for metastable equilibrium in a supercooled water-Freon-12 hydrate-gas system are presented. The results are in good agreement with the known literature data.

  1. Intrinsic Metastabilities in the Charge Configuration of a Double Quantum Dot.

    PubMed

    Biesinger, D E F; Scheller, C P; Braunecker, B; Zimmerman, J; Gossard, A C; Zumbühl, D M

    2015-09-01

    We report a thermally activated metastability in a GaAs double quantum dot exhibiting real-time charge switching in diamond shaped regions of the charge stability diagram. Accidental charge traps and sensor backaction are excluded as the origin of the switching. We present an extension of the canonical double dot theory based on an intrinsic, thermal electron exchange process through the reservoirs, giving excellent agreement with the experiment. The electron spin is randomized by the exchange process, thus facilitating fast, gate-controlled spin initialization. At the same time, this process sets an intrinsic upper limit to the spin relaxation time.

  2. Metastable and equilibrium wetting states in the Bi-Sn system

    SciTech Connect

    Yost, F.G.; O`Toole, E.J.

    1998-09-01

    Sessile drop experiments involving a variety of Bi-Sn alloys on solid Bi substrates were performed. Substrates prepared from small- and large-grained polycrystals and single crystals were used to measure equilibrium and metastable contact angles and estimate the surface tension and equilibrium contact angle of the solid-liquid interface. The substrates were also used to investigate the coupling of the dissolution and wetting processes and to investigate the effect of the substrate grain size on wetting. It was determined that the equilibrium wetting geometry is independent of linear scale and that grain size has little influence on wetting or dissolution in the Bi-Sn system.

  3. Exotic Protonated Species Produced by UV-Induced Photofragmentation of a Protonated Dimer: Metastable Protonated Cinchonidine.

    PubMed

    Alata, Ivan; Scuderi, Debora; Lepere, Valeria; Steinmetz, Vincent; Gobert, Fabrice; Thiao-Layel, Loïc; Le Barbu-Debus, Katia; Zehnacker-Rentien, Anne

    2015-10-01

    A metastable protonated cinchona alkaloid was produced in the gas phase by UV-induced photodissociation (UVPD) of its protonated dimer in a Paul ion trap. The infrared multiple photon dissociation (IRMPD) spectrum of the molecular ion formed by UVPD was obtained and compared to DFT calculations to characterize its structure. The protonation site obtained thereby is not accessible by classical protonation ways. The protonated monomer directly formed in the ESI source or by collision-induced dissociation (CID) of the dimer undergoes protonation at the most basic alkaloid nitrogen. In contrast, protonation occurs at the quinoline aromatic ring nitrogen in the UVPD-formed monomer. PMID:26347997

  4. Convergent close-coupling calculations of positron scattering on metastable helium

    SciTech Connect

    Utamuratov, R.; Kadyrov, A. S.; Fursa, D. V.; Bray, I.; Stelbovics, A. T.

    2010-10-15

    The convergent close-coupling method has been applied to positron scattering on a helium atom in the 2 {sup 3}S metastable state. For this system the positronium (Ps) formation channel is open even at zero scattering energy making the inclusion of the Ps channels especially important. Spin algebra is presented for the general case of arbitrary spins. A proof is given of the often-used assumption about the relationship between the amplitudes for ortho-positronium and para-positronium formation. The cross sections for scattering from 2 {sup 3}S are shown to be significantly larger than those obtained for the ground state.

  5. 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.

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

    DOE PAGES

    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.

  7. Sensitivity of Granular Force Chain Orientation to Disorder-Induced Metastable Relaxation.

    PubMed

    Iikawa, N; Bandi, M M; Katsuragi, H

    2016-03-25

    A two-dimensional system of photoelastic disks subject to vertical tapping against gravity was experimentally monitored from ordered to disordered configurations by varying bidispersity. The packing fraction ϕ, coordination number Z, and an appropriately defined force-chain orientational order parameter S all exhibit as similar sharp transition with a small increase in disorder. A measurable change in S, but not ϕ and Z, was detected under tapping. We find disorder-induced metastability does not show configurational relaxation, but can be detected via force-chain reorientations.

  8. Exotic Protonated Species Produced by UV-Induced Photofragmentation of a Protonated Dimer: Metastable Protonated Cinchonidine.

    PubMed

    Alata, Ivan; Scuderi, Debora; Lepere, Valeria; Steinmetz, Vincent; Gobert, Fabrice; Thiao-Layel, Loïc; Le Barbu-Debus, Katia; Zehnacker-Rentien, Anne

    2015-10-01

    A metastable protonated cinchona alkaloid was produced in the gas phase by UV-induced photodissociation (UVPD) of its protonated dimer in a Paul ion trap. The infrared multiple photon dissociation (IRMPD) spectrum of the molecular ion formed by UVPD was obtained and compared to DFT calculations to characterize its structure. The protonation site obtained thereby is not accessible by classical protonation ways. The protonated monomer directly formed in the ESI source or by collision-induced dissociation (CID) of the dimer undergoes protonation at the most basic alkaloid nitrogen. In contrast, protonation occurs at the quinoline aromatic ring nitrogen in the UVPD-formed monomer.

  9. 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%.

  10. Synthesis and characterization of a metastable (SiC){sub 3}N{sub 4} phase

    SciTech Connect

    Uslu, C.; Park, B.; Poker, D.B.

    1994-12-31

    A metastable C-SI-N compound has been synthesized by high dose N{sup +} implantation into polycrystalline {beta}-SiC (cubic phase). The thin films formed upon 100 keV implantation were characterized with respect to various ion doses and target temperatures. X-ray diffraction with a position-sensitive detector and cross-sectional transmission electron microscopy revealed that the as-implanted surfaces contained {approximately} 0.15 {mu}m thick continuously-buried amorphous layers. Rutherford backscattering spectroscopy showed that the peak concentration of nitrogen saturated up to approximately 54 at. % with increasing doses, suggesting a new phase formation.

  11. Evaporative cooling of metastable helium in the multi-partial-wave regime

    SciTech Connect

    Nguyen, Scott V.; Doret, S. Charles; Connolly, Colin B.; Michniak, Robert A.; Doyle, John M.; Ketterle, Wolfgang

    2005-12-15

    Metastable helium is buffer gas cooled, magnetically trapped, and evaporatively cooled in large numbers. 10{sup 11} {sup 4}He{sup *} atoms are trapped at an initial temperature of 400 mK and evaporatively cooled into the ultracold regime, resulting in a cloud of 2{+-}0.5x10{sup 9} atoms at 1.4{+-}0.2 mK. Efficient evaporation indicates low collisional loss for {sup 4}He{sup *} in both the ultracold and multi-partial-wave regime, in agreement with theory.

  12. Isomorphous template induced crystallisation: a robust method for the targeted crystallisation of computationally predicted metastable polymorphs.

    PubMed

    Srirambhatla, Vijay K; Guo, Rui; Price, Sarah L; Florence, Alastair J

    2016-05-31

    A new method of inducing the crystallisation of metastable polymorphs by isomorphous templating has been developed and used to reproduce the crystallisation of CBZ-V on the surface of DHC-II. Studies of the growth of CBZ-V on DHC-II single crystals show crystals growing laterally and vertically on DHC-II surfaces without any significant face selectivity. The generality of this computationally inspired crystallisation approach is demonstrated by producing the first crystals of an entirely new polymorph of cyheptamide, which is isomorphous to both DHC-II and CBZ-V.

  13. Formation of HO2/+/ by reaction of metastable O2/+/ ions with H2

    NASA Technical Reports Server (NTRS)

    Ajello, J. M.; Huntress, W. T.; Lane, A. L.; Lebreton, P. R.; Williamson, A. D.

    1974-01-01

    The photoionization efficiency curves of H2(+), O2(+), and HO2(+) have been studied in a mixture of hydrogen and oxygen over the wavelength range from 650 to 810 A. The HO2(+) ion appears at 804 A, the threshold for ionization of H2, by the reaction H2(+) + O2 yields HO2(+) + H. The relative photoionization efficiency curves of H2(+) and HO2(+) are the same from 804 to 764 A. Below 764 A production of the 4 Pi u metastable electronic state of O2(+) leads to the formation of HO2(+) by the reaction O2(+)(a 4 Pi u) + H2 yields HO2(+) + H.

  14. Intrinsic Metastabilities in the Charge Configuration of a Double Quantum Dot

    NASA Astrophysics Data System (ADS)

    Biesinger, D. E. F.; Scheller, C. P.; Braunecker, B.; Zimmerman, J.; Gossard, A. C.; Zumbühl, D. M.

    2015-09-01

    We report a thermally activated metastability in a GaAs double quantum dot exhibiting real-time charge switching in diamond shaped regions of the charge stability diagram. Accidental charge traps and sensor backaction are excluded as the origin of the switching. We present an extension of the canonical double dot theory based on an intrinsic, thermal electron exchange process through the reservoirs, giving excellent agreement with the experiment. The electron spin is randomized by the exchange process, thus facilitating fast, gate-controlled spin initialization. At the same time, this process sets an intrinsic upper limit to the spin relaxation time.

  15. Isomorphous template induced crystallisation: a robust method for the targeted crystallisation of computationally predicted metastable polymorphs.

    PubMed

    Srirambhatla, Vijay K; Guo, Rui; Price, Sarah L; Florence, Alastair J

    2016-05-31

    A new method of inducing the crystallisation of metastable polymorphs by isomorphous templating has been developed and used to reproduce the crystallisation of CBZ-V on the surface of DHC-II. Studies of the growth of CBZ-V on DHC-II single crystals show crystals growing laterally and vertically on DHC-II surfaces without any significant face selectivity. The generality of this computationally inspired crystallisation approach is demonstrated by producing the first crystals of an entirely new polymorph of cyheptamide, which is isomorphous to both DHC-II and CBZ-V. PMID:27193234

  16. Numerical Study of the Structure of Metastable Configurations for the Thomson Problem

    NASA Astrophysics Data System (ADS)

    Bondarenko, A. N.; Bugueva, T. V.; Kozinkin, L. A.

    2016-05-01

    A numerical method is proposed for solving the Thomson problem - finding stable positions for a system of N point charges distributed on a sphere that minimize the potential energy of the system. The behavior of this system is essentially nonlinear, and the number of metastable structures grows exponentially with N. This makes the problem of finding all stable configurations extremely difficult. The results of testing of the developed algorithm and of numerical study of the properties of the local potential energy minima for a system of point charges are presented.

  17. 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.

  18. Depopulation of metastable helium by radiative association with hydrogen and lithium ions

    SciTech Connect

    Augustovičová, L.; Soldán, P.; Kraemer, W. P.

    2014-02-10

    Depopulation of metastable He(2{sup 3}S) by radiative association with hydrogen and lithium ions is investigated using a fully quantal approach. Rate coefficients for spontaneous and stimulated radiative association of the HeH{sup +}, HeD{sup +}, and LiHe{sup +} molecular ions on the spin-triplet manifold are presented as functions of temperature considering the association to rotational-vibrational states of the lowest triplet electronic states a {sup 3}Σ{sup +} and b {sup 3}Σ{sup +} from the continuum states of the b {sup 3}Σ{sup +} electronic state. Evaluation of the rate coefficients is based on highly accurate quantum calculations, taking into account all possible state-to-state transitions at thermal energies (for spontaneous association) or at higher background energies (stimulated association). As expected, calculations show that the rate coefficients for radiative association to the a state are several orders of magnitude larger than the one for the b state formation. A noticeable effect by blackbody background radiation on the radiative association is only obtained for the b → b process. Aspects of the formation and abundance of the metastable HeH{sup +}(a {sup 3}Σ{sup +}) in astrophysical environments are briefly discussed.

  19. 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. PMID:12490946

  20. 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+ .

  1. Improvement of mechanical properties on metastable stainless steels by reversion heat treatments

    NASA Astrophysics Data System (ADS)

    Mateo, A.; Zapata, A.; Fargas, G.

    2013-12-01

    AISI 301LN is a metastable austenitic stainless steel that offers an excellent combination of high strength and ductility. This stainless grade is currently used in applications where severe forming operations are required, such as automotive bodies. When these metastable steels are plastically deformed at room temperature, for example by cold rolling, austenite transforms to martensite and, as a result, yield strength increases but ductility is reduced. Grain refinement is the only method that allows improving strength and ductility simultaneously. Several researchers have demonstrated that fine grain AISI 301LN can be obtained by heat treatment after cold rolling. This heat treatment is called reversion because it provokes the reversion of strain induced martensite to austenite. In the present work, sheets of AISI 301LN previously subjected to 20% of cold rolling reduction were treated and a refined grain austenitic microstructure was obtained. Mechanical properties, including fatigue limit, were determined and compared with those corresponding to the steel both before and after the cold rolling.

  2. The role of a metastable RNA secondary structure in hepatitis delta virus genotype III RNA editing

    PubMed Central

    Linnstaedt, Sarah D.; Kasprzak, Wojciech K.; Shapiro, Bruce A.; Casey, John L.

    2006-01-01

    RNA editing plays a critical role in the life cycle of hepatitis delta virus (HDV). The host editing enzyme ADAR1 recognizes specific RNA secondary structure features around the amber/W site in the HDV antigenome and deaminates the amber/W adenosine. A previous report suggested that a branched secondary structure is necessary for editing in HDV genotype III. This branched structure, which is distinct from the characteristic unbranched rod structure required for HDV replication, was only partially characterized, and knowledge concerning its formation and stability was limited. Here, we examine the secondary structures, conformational dynamics, and amber/W site editing of HDV genotype III RNA using a miniaturized HDV genotype III RNA in vitro. Computational analysis of this RNA using the MPGAfold algorithm indicated that the RNA has a tendency to form both metastable and stable unbranched secondary structures. Moreover, native polyacrylamide gel electrophoresis demonstrated that this RNA forms both branched and unbranched rod structures when transcribed in vitro. As predicted, the branched structure is a metastable structure that converts readily to the unbranched rod structure. Only branched RNA was edited at the amber/W site by ADAR1 in vitro. The structural heterogeneity of HDV genotype III RNA is significant because not only are both conformations of the RNA functionally important for viral replication, but the ratio of the two forms could modulate editing by determining the amount of substrate RNA available for modification. PMID:16790843

  3. A novel series of isoreticular metal organic frameworks: realizing metastable structures by liquid phase epitaxy

    PubMed Central

    Liu, Jinxuan; Lukose, Binit; Shekhah, Osama; Arslan, Hasan Kemal; Weidler, Peter; Gliemann, Hartmut; Bräse, Stefan; Grosjean, Sylvain; Godt, Adelheid; Feng, Xinliang; Müllen, Klaus; Magdau, Ioan-Bogdan; Heine, Thomas; Wöll, Christof

    2012-01-01

    A novel class of metal organic frameworks (MOFs) has been synthesized from Cu-acetate and dicarboxylic acids using liquid phase epitaxy. The SURMOF-2 isoreticular series exhibits P4 symmetry, for the longest linker a channel-size of 3 × 3 nm2 is obtained, one of the largest values reported for any MOF so far. High quality, ab-initio electronic structure calculations confirm the stability of a regular packing of (Cu++)2- carboxylate paddle-wheel planes with P4 symmetry and reveal, that the SURMOF-2 structures are in fact metastable, with a fairly large activation barrier for the transition to the bulk MOF-2 structures exhibiting a lower, twofold (P2 or C2) symmetry. The theoretical calculations also allow identifying the mechanism for the low-temperature epitaxial growth process and to explain, why a synthesis of this highly interesting, new class of high-symmetry, metastable MOFs is not possible using the conventional solvothermal process. PMID:23213357

  4. Metastable atom-activated dissociation mass spectrometry of phosphorylated and sulfonated peptides in negative ion mode.

    PubMed

    Cook, Shannon L; Jackson, Glen P

    2011-06-01

    The dissociation behavior of phosphorylated and sulfonated peptide anions was explored using metastable atom-activated dissociation mass spectrometry (MAD-MS) and collision-induced dissociation (CID). A beam of high kinetic energy helium (He) metastable atoms was exposed to isolated phosphorylated and sulfonated peptides in the 3- and 2- charge states. Unlike CID, where phosphate losses are dominant, the major dissociation channels observed using MAD were C(α) - C peptide backbone cleavages and neutral losses of CO(2), H(2)O, and [CO(2) + H(2)O] from the charge reduced (oxidized) product ion, consistent with an electron detachment dissociation (EDD) mechanism such as Penning ionization. Regardless of charge state or modification, MAD provides ample backbone cleavages with little modification loss, which allows for unambiguous PTM site determination. The relative abundance of certain fragment ions in MAD is also demonstrated to be somewhat sensitive to the number and location of deprotonation sites, with backbone cleavage somewhat favored adjacent to deprotonated sites like aspartic acid residues. MAD provides a complementary dissociation technique to CID, ECD, ETD, and EDD for peptide sequencing and modification identification. MAD offers the unique ability to analyze highly acidic peptides that contain few to no basic amino acids in either negative or positive ion mode.

  5. Theoretical investigation of metastable Al2SiO5 polymorphs.

    PubMed

    Oganov, A R; Price, G D; Brodholt, J P

    2001-09-01

    Using theoretical simulations based on density functional theory within the generalized gradient approximation, a series of metastable phase transitions occurring in low-pressure Al2SiO5 polymorphs (andalusite and sillimanite) are predicted; similar results were obtained using semiclassical interatomic potentials within the ionic shell model. Soft lattice modes as well as related structural changes are analysed. For sillimanite, an isosymmetric phase transition at ca 35 GPa is predicted; an incommensurately modulated form of sillimanite can also be obtained at low temperatures and high pressures. The high-pressure isosymmetric phase contains five-coordinate Si and Al atoms. The origin of the fivefold coordination is discussed in detail. Andalusite was found to transform directly into an amorphous phase at ca 50 GPa. This study provides an insight into the nature of metastable modifications of crystal structures and the ways in which they are formed. Present results indicate the existence of a critical bonding distance, above which interatomic interactions cannot be considered as bonding. The critical distance for the Si-O bond is 2.25 A. PMID:11526304

  6. 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.

  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. 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.

  9. Kinetic simulations of argon dusty plasma afterglow including metastable atom kinetics

    SciTech Connect

    Alexandrov, A. L. Schweigert, I. V.; Ariskin, D. A.

    2013-04-15

    The afterglow of a dusty plasma of rf discharge in argon is simulated by the particle-in-cell-Monte Carlo collision (PIC-MCC) method. The experimental observation that heavy dust contamination of plasma leads to an anomalous increase in the electron density at the beginning of afterglow is explained by release of electrons from the dust surface. Under the assumption that the floating potential of particles is in equilibrium with plasma conditions, the fast cooling of electrons in afterglow plasma due to a rapid escape of hot electrons from the volume leads to a decrease in the magnitude of the floating potential and hence to a loss of charge by dust. The intensive desorption of electrons from nanoparticles is the origin of anomalous behavior of the electron density. At the next stage of afterglow, when the electrons become cool, the plasma decay is defined by ambipolar diffusion. The effect of metastable argon atoms is also considered. Additional ionization due to metastable atom collisions affects the electron temperature but does not change the behavior of the electron density qualitatively.

  10. Metastable-atom deexcitation spectroscopy of clean and Ag-adsorbed Si (111) surfaces

    NASA Astrophysics Data System (ADS)

    Nishigaki, S.; Takao, K.; Yamada, T.; Arimoto, M.; Komatsu, T.

    1985-07-01

    Electron energy spectra upon incidence of He ∗ metastables on a clean Si(111)7 × 7 surface are obtained, which demonstrate the operation of the surface Penning ionization mechanism for the metastable-atom deexcitation (MD). Dangling bond orbitals are detected at about -0.5 and -1.5 eV below EF in the MD spectra. They are compared with previous UPS results. The adsorption process of Ag on Si(111) is studied by MDS and AES. In a MD spectrum for a Ag-deposited surface at room temperature with θ = {2}/{3} a peak appears at -5.2 below EF which belongs to Ag 4d orbitals. For a surface with the 3× 3 structure (deposited at 300°C with θ = {2}/{3}), however, the intensity of the Ag 4d peak is rather weak and its energy shifts by about -0.4 eV from the room-temperature value. These results support the embedded-Ag model for the Si(111) 3Ag structure.

  11. 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.

  12. Electron-Driven Reactions in Proto-Planetary Atmospheres: Metastable Anions of Gaseous o-Benzyne

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

    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-C6H4(1Σ), 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-C6H4 is considered to be relevant for the circumstellar synthesis of large polycyclic aromatic hydrocarbons (PAHs), as a precursor for C6H6 production via ion-based ring closure reaction from C2H2. 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-C6H4 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.

  13. Getting off the Bain path: Are there any metastable states of cubic elements?

    NASA Astrophysics Data System (ADS)

    Mehl, Michael J.; Boyer, Larry L.

    2003-03-01

    Body-centered and face-centered cubic crystals can be considered as special cases of a body-centered tetragonal crystal with c/a = 1 and 2, respectively. First-principles calculations along this Bain path show that elements with an fcc (bcc) ground state are elastically unstable with respect to a tetragonal distortion in the bcc (fcc) phase. Starting with a normally fcc element and calculating E(c/a) for c/a < 1 we find a local minimum near c/a = 2/3, while for a bcc element we find a local minimum at some c/a > 2. It is tempting to conclude that these bct minima, which are required by continuity, are metastable, but calculations by several authors show that, at least for Al, Cu, and Pd, the bct structures are unstable with respect to an orthorhombic distortion. We use a simple "magic strain" construction(L. L. Boyer, Acta Cryst. A) 45, FC29 (1989).(M. J. Mehl and L. L. Boyer, Phys. Rev. B) 43, 9498 (1991). to study the stability of these bct states, and present examples which suggest that no fcc or bcc element has a metastable bct state.

  14. 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

  15. 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).

  16. 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

  17. 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.

  18. 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.

  19. Precision Spectroscopy in Cold Molecules: The Lowest Rotational Interval of He_{2}^{+} and Metastable He_{2}.

    PubMed

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

    2015-09-25

    Multistage Zeeman deceleration was used to generate a slow, dense beam of translationally cold He_{2} molecules in the metastable a ^{3}Σ_{u}^{+} 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 He_{2} and the lowest rotational interval of the X^{+} ^{2}Σ_{u}^{+} (ν^{+}=0) ground state of ^{4}He_{2}^{+} have been determined with unprecedented precision and accuracy by Rydberg-series extrapolation. Comparison with ab initio predictions of the rotational energy level structure of ^{4}He_{2}^{+} [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 He_{2}^{+}. PMID:26451553

  20. 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.

  1. Production ratio of meta-stable isomer in {sup 180}Ta by neutrino-induced reactions

    SciTech Connect

    Hayakawa, Takehito; Kajino, Toshitaka; Chiba, Satoshi; Mathews, Grant

    2010-05-12

    The nucleosynthesis of {sup 180}Ta has remained an unsolved problem and as its origin many nucleosynthesis mechanisms have been proposed. This isotope has the unique feature that the naturally occurring abundance of {sup 180}Ta is actually a meta-stable isomer (half-life of >=10{sup 15} yr), while the ground state is a 1{sup +} unstable state which beta-decays with a half-life of only 8.15 hr. We have made a new time-dependent calculation of {sup 180}Ta meta-stable isomer residual ratio after supernova neutrino-induced reactions. This isomer residual ratio is crucial for understanding the production and survival of this naturally occurring rare isotope. We have constructed a new model under temperature evolution after type II supernova explosion. We include the explicit linking between the isomer and all known excited states and found that the residual ratio is insensitive to astrophysical parameters such as neutrino energy spectrum, explosion energy, decay time constant. We find that the explicit time evolution of the synthesis of {sup 180}Ta avoids the overproduction relative to {sup 138}La for a neutrino process neutrino temperature of 4 MeV.

  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. 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.

  4. Metastable region of phase diagram: optimum parameter range for processing ultrahigh molecular weight polyethylene blends.

    PubMed

    Gai, Jing-Gang; Zuo, Yuan

    2012-06-01

    Numerous studies suggest that two-phase morphology and thick interface are separately beneficial to the viscosity reduction and mechanical property maintainence of the matrix when normal molecular weight polymer (NMWP) is used for modification of ultrahigh molecular weight polyethylene (UHMWPE). Nevertheless, it is very difficult to obtain a UHMWPE/NMWP blend which may demonstrate both two-phase morphology and thick interface. In this work, dissipative particle dynamics simulations and Flory-Huggins theory are applied in predicting the optimum NMWP and the corresponding conditions, wherein the melt flowability of UHMWPE can be improved while its mechanical properties can also be retained. As is indicated by dissipative particle dynamics simulations and phase diagram calculated from Flory-Huggins theory, too small Flory-Huggins interaction parameter (χ) and molecular chain length of NMWP (N(NMWP)) may lead to the formation of a homogeneous phase, whereas very large interfacial tension and thin interfaces might also appear when parameters N(NMWP) and χ are too large. When these parameters are located in the metastable region of the phase diagram, however, two-phase morphology occurs and interfaces of the blends are extremely thick. Therefore, metastable state is found to be advisable for both the viscosity reduction and mechanical property improvement of the UHMWPE/NMWP blends.

  5. 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.

  6. Statics, metastable states, and barriers in protein folding: A replica variational approach

    NASA Astrophysics Data System (ADS)

    Takada, Shoji; Wolynes, Peter G.

    1997-04-01

    Protein folding is analyzed using a replica variational formalism to investigate some free energy landscape characteristics relevant for dynamics. A random contact interaction model that satisfies the minimum frustration principle is used to describe the coil-globule transition (characterized by TCG), glass transitions (by TA and TK), and folding transition (by TF). Trapping on the free energy landscape is characterized by two characteristic temperatures, one dynamic (TA) and the other static [TK (TA>TK)], which are similar to those found in mean field theories of the Potts glass. (i) Above TA, the free energy landscape is monotonous and the polymer is melted both dynamically and statically. (ii) Between TA and TK, the melted phase is still dominant thermodynamically, but frozen metastable states, exponentially large in number, appear. (iii) A few lowest minima become thermodynamically dominant below TK, where the polymer is totally frozen. In the temperature range between TA and TK, barriers between metastable states are shown to grow with decreasing temperature, suggesting super-Arrhenius behavior in a sufficiently large system. Due to evolutionary constraints on fast folding, the folding temperature TF is expected to be higher than TK, but may or may not be higher than TA. Diverse scenarios of the folding kinetics are discussed based on phase diagrams that take into account the dynamical transition, as well as the static ones.

  7. Metastable magnetic state and exchange bias training effect in Mn-rich YMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Kumar, Manish; Choudhary, R. J.; Phase, D. M.

    2015-04-01

    The magnetic nature of stoichiometric and Mn rich hexagonal YMnO3 films grown at different oxygen partial pressures is investigated. The stoichiometric YMnO3 thin film showed antiferromagnetic ordering below 72 K while the film having excess Mn content revealed metastable magnetic behaviour at a temperature of less than 42 K. The metastable magnetic behaviour in this sample is attributed to the competing anti-ferromagnetic and ferromagnetic phase fractions (caused by Mn2+ ions that originated due to excess Mn content). Also, in the metastable regime the exchange bias effect is observed, which is further supported by the training effect. Both the samples reveal room temperature ferroelectric behaviour.

  8. 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.

  9. 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.

  10. Synergistic stabilization of metastable Fe23B6 and γ-Fe in undercooled Fe83B17

    NASA Astrophysics Data System (ADS)

    Quirinale, D. G.; Rustan, G. E.; Kreyssig, A.; Goldman, A. I.

    2015-06-01

    Previous investigations of undercooled liquid Fe83B17 near the eutectic composition have found that metastable crystalline phases, such as Fe23B6, can be formed and persist down to ambient temperature even for rather modest cooling rates. Using time-resolved high-energy x-ray diffraction on electrostatically levitated samples of Fe83B17, we demonstrate that the Fe23B6 metastable phase and fcc γ-Fe grow coherently from the undercooled Fe83B17 liquid and effectively suppress the formation of the equilibrium Fe2B + bcc α-Fe phases. The stabilization of γ-Fe offers another opportunity for experimental investigations of magnetism in metastable fcc iron.

  11. 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.

  12. 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

  13. Metastable olivine provides regional constraints on hydrogen content based on transformation kinetics

    NASA Astrophysics Data System (ADS)

    Du Frane, W. L.; Sharp, T. G.; Mosenfelder, J. L.; Leinenweber, K. D.

    2009-12-01

    The existence of metastable olivine has been debated as a possible trigger of deep focus earthquakes. Of equal importance, its existence may constrain the amount of hydrogen being subducted into the Earth’s transition zone. Olivine transformation rates into wadsleyite and ringwoodite have been demonstrated to be dependent on hydrogen content, and determine whether metastable olivine persists into the Earth’s mantle transition zone as downwelling material. For nominally anhydrous olivine, in this and previous studies, transformation rates decrease over time as a rigid reaction rim is formed. If viscoelastic relaxation of the rim occurs at a relatively slow rate, strain energy resulting from the negative volume change of the reaction counteracts the chemical free energy driving force for growth. It has been proposed that hydrogen enhances olivine transformation rates through hydrolytic weakening of the growth rim, which promotes relaxation of transformation stress, but it is not clear how much hydrogen is required for this mechanism to occur. We present ringwoodite growth rate measurements for interface-controlled growth, using olivine spheres hydrated in a piston cylinder with 75 +/- 15 ppm H2O and nominally anhydrous San Carlos olivine spheres with ≤ 10 ppm H2O. Hydrogen contents have been determined using new FTIR and SIMS data that indicate that hydrogen partitions into the growth rim as it forms. As the rim continues to grow and the core becomes depleted, the rim will eventually exhaust itself of hydrogen and may later become rigid if there is not enough hydrogen available to weaken the growth rim throughout transformation. However, we did not see evidence of non-linear rim growth in samples with 75 ppm H2O, with up to 76% growth fraction at 1100 °C. For olivine initially containing 75 ppm H2O, the ringwoodite growth rates at 18 GPa are 5.1(+/-0.4)x10-11 at 700 °C, 1.8(+/- 0.6)x10-9 m/s at 900 °C, 3.8(+/-1.5)x10-8 at 1100 °C with activation enthalpy of

  14. 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.

  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. Formation of a metastable ferromagnetic tau phase during containerless melt processing in Mn-Al-C alloys

    NASA Technical Reports Server (NTRS)

    Kim, Y. J.; Perepezko, J. H.

    1993-01-01

    This paper reports the production of a metastable ferromagnetic tau phase directly from the melt in Mn(0.55)Al(0.433)C(0.017), using a containerless processing method involving levitation melting followed by quenching. Using the results from differential thermal analysis measurements and an analysis of the phase equilibria, it was found that the minimum amount of undercooling level required for ferromagnetic metastable tau phase formation in this alloy was Delta T = 87 K. The attainment of this undercooling may be facilitated by the application of containerless melt processing.

  17. Chaperonin-Based Biolayer Interferometry To Assess the Kinetic Stability of Metastable, Aggregation-Prone Proteins.

    PubMed

    Lea, Wendy A; O'Neil, Pierce T; Machen, Alexandra J; Naik, Subhashchandra; Chaudhri, Tapan; McGinn-Straub, Wesley; Tischer, Alexander; Auton, Matthew T; Burns, Joshua R; Baldwin, Michael R; Khar, Karen R; Karanicolas, John; Fisher, Mark T

    2016-09-01

    Stabilizing the folded state of metastable and/or aggregation-prone proteins through exogenous ligand binding is an appealing strategy for decreasing disease pathologies caused by protein folding defects or deleterious kinetic transitions. Current methods of examining binding of a ligand to these marginally stable native states are limited because protein aggregation typically interferes with analysis. Here, we describe a rapid method for assessing the kinetic stability of folded proteins and monitoring the effects of ligand stabilization for both intrinsically stable proteins (monomers, oligomers, and multidomain proteins) and metastable proteins (e.g., low Tm) that uses a new GroEL chaperonin-based biolayer interferometry (BLI) denaturant pulse platform. A kinetically controlled denaturation isotherm is generated by exposing a target protein, immobilized on a BLI biosensor, to increasing denaturant concentrations (urea or GuHCl) in a pulsatile manner to induce partial or complete unfolding of the attached protein population. Following the rapid removal of the denaturant, the extent of hydrophobic unfolded/partially folded species that remains is detected by an increased level of GroEL binding. Because this kinetic denaturant pulse is brief, the amplitude of binding of GroEL to the immobilized protein depends on the duration of the exposure to the denaturant, the concentration of the denaturant, wash times, and the underlying protein unfolding-refolding kinetics; fixing all other parameters and plotting the GroEL binding amplitude versus denaturant pulse concentration result in a kinetically controlled denaturation isotherm. When folding osmolytes or stabilizing ligands are added to the immobilized target proteins before and during the denaturant pulse, the diminished population of unfolded/partially folded protein manifests as a decreased level of GroEL binding and/or a marked shift in these kinetically controlled denaturation profiles to higher denaturant

  18. Initial stages of phase separation in polymer blends near the limit of metastability

    NASA Astrophysics Data System (ADS)

    Lefebvre, Amy Adams

    Liquid-liquid phase separation in polymethylbutylene/polyethylbutylene blends near the metastable limit was studied using small angle neutron scattering (SANS). In addition, the equilibrium thermodynamic properties of the blends were examined over a wide temperature and pressure range. The Flory-Huggins interaction parameter, chi, was measured by comparing static SANS profiles from single-phase systems with predictions based on the random phase approximation. The pressure dependence of the binodal temperature of one of the blends was experimentally determined from a series of dissolution experiments. The experimental binodal is in quantitative agreement with that computed using the Flory-Huggins theory without any adjustable parameters. Quenching the blends from the single-phase region to deep into the metastable region of the mean-field phase diagram induced phase separation. During the early stage of phase separation in the blends, the time-resolved SANS profiles merged at a time-independent critical scattering vector, qc. The critical size of the phase separated structures, Rc, formed during the early stages of phase separation is defined as Rc = 1/q c. The theory of Cahn and Hilliard predicts that in metastable blends Rc increases with increasing quench depth, and diverges at the spinodal. The experimental measurements show that Rc increases with decreasing quench depth, and diverges between the binodal and spinodal. Some aspects of these results are addressed in recent theoretical work of Wang and Wood wherein the effects of fluctuations on the classical binodal and spinodal curves in polymer blends are incorporated. The evolution of the structure factor was then examined using the Cahn-HilliardCook theory. This enables organizing the data in terms of three parameters that depend on scattering vector, q: S0(q), the initial structure factor, St(q), the terminal structure factor, and R(q) a kinetic parameter that indicates the time scale for the transformation

  19. Excited metastables electronic spin states in spin crossover compounds studies by atom-phonon coupling model: Gradual and two-step transition cases

    NASA Astrophysics Data System (ADS)

    Gindulescu, A.; Rotaru, A.; Linares, J.; Dimian, M.; Nasser, J.

    2010-05-01

    This contribution reports the study of metastable spin states in spin-crossover materials in the framework of the atom-phonon coupling model. Using this model for a linear chain we show theoretically for the first time that, even if the cooperativity is not strong enough to obtain hysteresis at high temperatures, metastable states exist at low temperatures for a high spin (HS) fraction of nHS=1. This gradual thermal transition featuring metastable states at low temperature has been observed experimentally by [Létard et al., J. Phys.: Conf. Ser. 21, 23 (2005)]. Moreover, for compounds showing a two-step thermal transition, we show that metastable states, corresponding to a HS fraction nHS=0.5, are present. This metastable states appear up to 50 K, fact that was observed by [Moussa et al., Phys. Rev. Lett. 94, 107205 (2005)] and [Matsumoto et al., J. Phys.: Conf. Ser. 148, 012029 (2009)].

  20. 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).

  1. Resolution of hyperfine transitions in metastable 83Kr using electromagnetically induced transparency

    NASA Astrophysics Data System (ADS)

    Kale, Y. B.; Mishra, S. R.; Tiwari, V. B.; Singh, S.; Rawat, H. S.

    2015-05-01

    Narrow linewidth signals of electromagnetically induced transparency (EIT) in the metastable 83Kr have been observed. Various hyperfine transitions in the 4 p55 s [3/2 ] 2 to 4 p55 p [5/2 ] 3 manifolds of 83Kr have been identified through the experimentally observed EIT signals. Some unresolved or poorly resolved hyperfine transitions in saturated absorption spectroscopy (SAS) are clearly resolved in the present work. Using the spectral separation of these EIT identified hyperfine transitions, the magnetic hyperfine constant (A ) and the electric quadrupole hyperfine constant (B ) are determined with improved accuracy for 4 p55 s [3/2 ] 2 and 4 p55 p [5/2 ] 3 manifolds.

  2. Lifetime of metastable states in a Ginzburg-Landau system: Numerical simulations at large driving forces.

    PubMed

    Umantsev, A

    2016-04-01

    We developed a "brute-force" simulation method and conducted numerical "experiments" on homogeneous nucleation in an isotropic system at large driving forces (not small supersaturations) using the stochastic Ginzburg-Landau approach. Interactions in the system are described by the asymmetric (no external field), athermal (temperature-independent driving force), tangential (simple phase diagram) Hamiltonian, which has two independent "drivers" of the phase transition: supersaturation and thermal noise. We obtained the probability distribution function of the lifetime of the metastable state and analyzed its mean value as a function of the supersaturation, noise strength, and volume. We also proved the nucleation theorem in the mean-field approximation. The results allowed us to find the thermodynamic properties of the barrier state and conclude that at large driving forces the fluctuating volumes are not independent. PMID:27176373

  3. Calculated characteristics of radio-frequency plasma display panel cells including the influence of xenon metastables

    NASA Astrophysics Data System (ADS)

    Pitchford, L. C.; Kang, J.; Punset, C.; Boeuf, J. P.

    2002-12-01

    Although alternating-current plasma display panels (ac PDPs) are now produced by several companies, improvements are still necessary. In particular, the overall efficiency of the discharge in the standard configuration is low, on the order of 1 lm/W i.e., about 0.5% of the power dissipated in the discharge is transformed into useful visible photons. One way to substantially improve the efficiency of PDPs is to use radio-frequency (rf) excitation because, when compared to ac PDPs, less of the electrical energy input is dissipated by ions in the sheath and relatively more power is deposited in excitation of the xenon, which produces the ultraviolet photons used to excite the phosphors. In this article, we show calculated discharge characteristics for typical rf PDP conditions and pay particular attention to the role of the xenon metastable atoms in the ionization balance. Our discussion is limited to the sustaining regime, the "on-state," of a PDP cell.

  4. Effects of the reaction cavity on metastable optical excitation in ruthenium-sulfur dioxide complexes

    SciTech Connect

    Phillips, Anthony E.; D'Almeida, Thierry; Low, Kian Sing; Cole, Jacqueline M.

    2010-10-15

    We report photoexcited-state crystal structures for two new members of the [Ru(SO{sub 2})(NH{sub 3}){sub 4}X]Y family: 1:X=H{sub 2}O, Y=({+-})-camphorsulfonate{sub 2}; 2:X=isonicotinamide, Y=tosylate{sub 2}. The excited states are metastable at 100 K, with a photoconversion fraction of 11.1(7)% achieved in 1, and 22.1(10)% and 26.9(10)% at the two distinct sites in 2. We further show using solid-state density-functional-theory calculations that the excited-state geometries achieved are strongly influenced by the local crystal environment. This result is relevant to attempts to rationally design related photoexcitation systems for optical data-storage applications.

  5. Dynamics of a metastable state nonlinearly coupled to a heat bath driven by external noise.

    PubMed

    Chaudhuri, Jyotipratim Ray; Barik, Debashis; Banik, Suman Kumar

    2006-12-01

    Based on a system-reservoir model, where the system is nonlinearly coupled to a heat bath and the heat bath is modulated by an external stationary Gaussian noise, we derive the generalized Langevin equation with space-dependent friction and multiplicative noise and construct the corresponding Fokker-Planck equation, valid for short correlation time, with space-dependent diffusion coefficient to study the escape rate from a metastable state in the moderate- to large-damping regime. By considering the dynamics in a model cubic potential we analyze the results numerically which are in good agreement with theoretical predictions. It has been shown numerically that enhancement of the rate is possible by properly tuning the correlation time of the external noise. PMID:17280050

  6. 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.

  7. Metastable primordial germ cell-like state induced from mouse embryonic stem cells by Akt activation

    SciTech Connect

    Yamano, Noriko; Kimura, Tohru; Watanabe-Kushima, Shoko; Shinohara, Takashi; Nakano, Toru

    2010-02-12

    Specification to primordial germ cells (PGCs) is mediated by mesoderm-induction signals during gastrulation. We found that Akt activation during in vitro mesodermal differentiation of embryonic stem cells (ESCs) generated self-renewing spheres with differentiation states between those of ESCs and PGCs. Essential regulators for PGC specification and their downstream germ cell-specific genes were expressed in the spheres, indicating that the sphere cells had commenced differentiation to the germ lineage. However, the spheres did not proceed to spermatogenesis after transplantation into testes. Sphere cell transfer to the original feeder-free ESC cultures resulted in chaotic differentiation. In contrast, when the spheres were cultured on mouse embryonic fibroblasts or in the presence of ERK-cascade and GSK3 inhibitors, reversion to the ESC-like state was observed. These results indicate that Akt signaling promotes a novel metastable and pluripotent state that is intermediate to those of ESCs and PGCs.

  8. Intrinsic metastability of orthorhombic HfTiO{sub 4} in thin film hafnia-titania

    SciTech Connect

    Cisneros-Morales, Massiel Cristina; Aita, Carolyn Rubin

    2011-01-31

    Orthorhombic (o) HfTiO{sub 4} is crystallized when sputter deposited hafnia-titania nanolaminates with ultrathin layers and bilayer (HfO{sub 2}){sub 0.5}(TiO{sub 2}){sub 0.5} composition are annealed between 573 and 1173 K. However, o-HfTiO{sub 4} demixes after annealing at 1273 K, a result not predicted from bulk thermodynamics. X-ray diffraction and Raman microscopy are used here to study structural changes as o-HfTiO{sub 4} demixes upon long-term annealing at 1273 K into Ti-doped monoclinic HfO{sub 2} and Hf-doped rutile TiO{sub 2}. We conclude that o-HfTiO{sub 4} crystallized at low temperature is intrinsically metastable. A space group symmetry analysis shows that demixing can be accomplished by a continuous phase transition chain.

  9. 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

  10. Bose-Einstein condensation and spin mixtures of optically trapped metastable helium

    SciTech Connect

    Partridge, G. B.; Jaskula, J.-C.; Bonneau, M.; Boiron, D.; Westbrook, C. I.

    2010-05-15

    We report the realization of a Bose-Einstein condensate of metastable helium-4 atoms ({sup 4}He*) in an all-optical potential. Up to 10{sup 5} spin-polarized {sup 4}He* atoms are condensed in an optical dipole trap formed from a single, focused, vertically propagating far-off-resonance laser beam. The vertical trap geometry is chosen to best match the resolution characteristics of a delay-line anode microchannel plate detector capable of registering single He* atoms. We also confirm the instability of certain spin-state combinations of {sup 4}He* to two-body inelastic processes, which necessarily affects the scope of future experiments using optically trapped spin mixtures. In order to better quantify this constraint, we measure spin-state-resolved two-body inelastic loss rate coefficients in the optical trap.

  11. Atomic layer deposition of metastable β-Fe₂O₃ via isomorphic epitaxy for photoassisted water oxidation.

    PubMed

    Emery, Jonathan D; Schlepütz, Christian M; Guo, Peijun; Riha, Shannon C; Chang, Robert P H; Martinson, Alex B F

    2014-12-24

    We report the growth and photoelectrochemical (PEC) characterization of the uncommon bibyite phase of iron(III) oxide (β-Fe2O3) epitaxially stabilized via atomic layer deposition on an conductive, transparent, and isomorphic template (Sn-doped In2O3). As a photoanode, unoptimized β-Fe2O3 ultrathin films perform similarly to their ubiquitous α-phase (hematite) counterpart, but reveal a more ideal bandgap (1.8 eV), a ∼0.1 V improved photocurrent onset potential, and longer wavelength (>600 nm) spectral response. Stable operation under basic water oxidation justifies further exploration of this atypical phase and motivates the investigation of other unexplored metastable phases as new PEC materials.

  12. Metastability, Adaptability and Memory in Charge Density Waves. I. Resetting Property

    NASA Astrophysics Data System (ADS)

    Ito, Hiroyuki

    1989-06-01

    We give a possible interpretation of the adaptation of the charge density waves (CDW) to the pulse fields, which is observed to be accompanied with the memory of the width of the applied pulses (Ido step memory effect). When the identical pulse fields are repeatedly applied, successive state transitions are induced among metastable states. By the numerical simulations with the use of the Fukuyama-Lee-Rice model, we have found that only the state can be a fixed point in the transitions where the sliding motion under the pulse field satisfies a certain condition. Selecting the adequate state for a fixed point, the system adapts itself to the applied pulse width so that the current response has a common regularity regardless of the pulse width.

  13. Dynamics of recurrent neural networks with delayed unreliable synapses: metastable clustering.

    PubMed

    Friedrich, Johannes; Kinzel, Wolfgang

    2009-08-01

    The influence of unreliable synapses on the dynamic properties of a neural network is investigated for a homogeneous integrate-and-fire network with delayed inhibitory synapses. Numerical and analytical calculations show that the network relaxes to a state with dynamic clusters of identical size which permanently exchange neurons. We present analytical results for the number of clusters and their distribution of firing times which are determined by the synaptic properties. The number of possible configurations increases exponentially with network size. In addition to states with a maximal number of clusters, metastable ones with a smaller number of clusters survive for an exponentially large time scale. An externally excited cluster survives for some time, too, thus clusters may encode information.

  14. 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.

  15. 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.

  16. Structure and magnetism of Fe-rich nanostructured Fe Ni metastable solid solutions

    NASA Astrophysics Data System (ADS)

    Gorria, P.; Martínez-Blanco, D.; Pérez, M. J.; Blanco, J. A.; Smith, R. I.

    2005-07-01

    New futures on the physical properties of ferromagnetic FeNi alloys have been found combining in situ neutron diffraction experiments and magnetic measurements in mechanical milled Fe-rich Fe-Ni metastable solid solutions. Apart from the well-known Invar effect, on heating these materials are characterised by the existence of a first-order martensite-austenite transformation that takes place at some system-dependent temperature. On cooling, the transformation occurs at a lower temperature than on heating; for Fe 80Ni 20 the size of the effect being larger than 100 °C, much more than the values found in conventional FeNi alloys. These results are discussed considering intrinsic features as magnetovolume effects and/or extrinsic effects such as small grain size and the existence of defects.

  17. Metastable state dynamics and power law relaxation in a supercooled liquid.

    PubMed

    Srivastava, S; Das, S P

    2001-01-01

    We consider glassy relaxation by using a model for supercooled liquid where the usual set of hydrodynamic variables is extended to include the presence of very slowly decaying defect densities. The long time limit of the density correlation function, the nonergodicity parameter, is studied in the vicinity of the dynamic transition point, and scaling exponents with respect to the distance from the critical point are obtained. In addition to the usual square root cusp, we also see a linear dependence on distance from transition with respect to the metastability parameters. We analyze the power law relaxation of the density correlation function at the initial stage of the dynamics, and obtain an exponent dependent on temperature. Results are compared with data obtained from light scattering experiments.

  18. Probable nonexistence of a 3Pe metastable excited state of the positronium negative ion

    NASA Astrophysics Data System (ADS)

    Mills, Allen P., Jr.

    1981-12-01

    The H- ion is known to have a metastable 2p2 3Pe triplet excited state. To see if an analog of this state is present in the positronium negative ion Ps- the Coulomb binding energy Eb of the lowest-energy even-parity L=1 configuration of two identical-charge -e fermions of mass m1 plus one spinless particle of mass m2 and charge +e is calculated. We find a value of Eb below the n=2 level of the neutral atom for 0<=m2M<=0.17 and 0.90

  19. Characterization of hydrogen-induced crack initiation in metastable austenitic stainless steels during deformation

    NASA Astrophysics Data System (ADS)

    Zhang, L.; An, B.; Fukuyama, S.; Iijima, T.; Yokogawa, K.

    2010-09-01

    Hydrogen-induced crack initiation in hydrogen-charged metastable austenitic stainless steels during deformation at 295 K is characterized by performing a combined tensile and hydrogen release experiment and scanning probe microscopy. Strain-induced martensite (α') not only provides a path for rapid hydrogen diffusion in austenite (γ) but also promotes crack initiation. Hydrogen rapidly diffuses from α' and accumulates at the boundary between the α'-rich and γ-rich zones during deformation due to the high hydrogen diffusivity and low hydrogen solubility in α', resulting in crack initiation at the boundary between the α'-rich and γ-rich zones. The hydrogen-induced crack initially grows along the boundary between the α'-rich and γ-rich zones and then propagates in the α'-rich zone.

  20. Polarized {sup 3}He gas compression system using metastability-exchange optical pumping

    SciTech Connect

    Hussey, D.S.; Rich, D.R.; Belov, A.S.; Tong, X.; Yang, H.; Bailey, C.; Keith, C.D.; Hartfield, J.; Hall, G.D.R.; Black, T.C.; Snow, W.M.; Gentile, T.R.; Chen, W.C.; Jones, G.L.; Wildman, E.

    2005-05-15

    Dense samples (10-100 bar cm) of nuclear spin polarized {sup 3}He are utilized in high energy physics, neutron scattering, atomic physics, and magnetic resonance imaging. Metastability exchange optical pumping can rapidly produce high {sup 3}He polarizations ({approx_equal}80%) at low pressures (few mbar). We describe a polarized {sup 3}He gas compressor system which accepts 0.26 bar l h{sup -1} of {sup 3}He gas polarized to 70% by a 4 W neodymium doped lanthanum magnesium hexaluminate (Nd:LMA) laser and compresses it into a 5 bar cm target with final polarization of 55%. The spin relaxation rates of the system's components have been measured using nuclear magnetic resonance and a model of the {sup 3}He polarization loss based on the measured relaxation rates and the gas flow is in agreement with a {sup 3}He polarization measurement using neutron transmission.

  1. Polarized 3He gas compression system using metastability-exchange optical pumping

    NASA Astrophysics Data System (ADS)

    Hussey, D. S.; Rich, D. R.; Belov, A. S.; Tong, X.; Yang, H.; Bailey, C.; Keith, C. D.; Hartfield, J.; Hall, G. D. R.; Black, T. C.; Snow, W. M.; Gentile, T. R.; Chen, W. C.; Jones, G. L.; Wildman, E.

    2005-05-01

    Dense samples (10-100barcm) of nuclear spin polarized He3 are utilized in high energy physics, neutron scattering, atomic physics, and magnetic resonance imaging. Metastability exchange optical pumping can rapidly produce high He3 polarizations (≈80%) at low pressures (few mbar). We describe a polarized He3 gas compressor system which accepts 0.26barlh-1 of He3 gas polarized to 70% by a 4W neodymium doped lanthanum magnesium hexaluminate (Nd:LMA) laser and compresses it into a 5barcm target with final polarization of 55%. The spin relaxation rates of the system's components have been measured using nuclear magnetic resonance and a model of the He3 polarization loss based on the measured relaxation rates and the gas flow is in agreement with a He3 polarization measurement using neutron transmission.

  2. Molecular dynamics prediction and experimental evidence for density of normal and metastable liquid zirconium

    NASA Astrophysics Data System (ADS)

    Wang, H. P.; Yang, S. J.; Hu, L.; Wei, B.

    2016-06-01

    The density of normal and metastable undercooled liquid zirconium was predicted by performing molecular dynamics calculation with a system consisting of 4000 atoms and measured by electrostatic levitation experiments. The results show that the density increases linearly with the descending of temperature, including a maximum undercooling of 928 K. The density is 6.00 g cm-3 at the melting temperature, which agrees well with the experimental result of 6.06 g cm-3. Furthermore, the atomic number is increased to 32,000 on the basis of 4000 atoms and there appears only 0.02% difference. Besides, the pair distribution function was applied to display the atomic structure, which indicates the liquid structure change occurs at the first neighbor distance.

  3. Laser absorption spectroscopy diagnostics of helium metastable atoms generated in dielectric barrier discharge cryoplasmas

    NASA Astrophysics Data System (ADS)

    Urabe, Keiichiro; Muneoka, Hitoshi; Stauss, Sven; Sakai, Osamu; Terashima, Kazuo

    2015-10-01

    Cryoplasmas, which are plasmas whose gas temperatures are below room temperature (RT), have shown dynamic changes in their physical and chemical characteristics when the gas temperature in the plasmas (Tgp) was decreased from RT. In this study, we measured the temporal behavior of helium metastable (Hem) atoms generated in a parallel-plate dielectric barrier discharge at ambient gas temperatures (Tga) of 300, 100, and 14 K and with a gas density similar to atmospheric conditions by laser absorption spectroscopy. The increments of Tgp to Tga were less than 20 K. We found from the results that the Hem lifetime and maximum density become longer and larger over one order of magnitude for lower Tga. The reasons for the long Hem lifetime at low Tga are decreases in the rate coefficients of three-body Hem quenching reactions and in the amounts of molecular impurities with boiling points higher than that of He.

  4. 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.

  5. 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.

  6. Metastable fcc-Fe film epitaxially grown on Cu(100) single-crystal underlayer

    NASA Astrophysics Data System (ADS)

    Ohtake, Mitsuru; Shimamoto, Kohei; Futamoto, Masaaki

    2013-05-01

    Fe film of 40 nm thickness is prepared on fcc-Cu(100) single-crystal underlayer at room temperature by ultra-high vacuum molecular beam epitaxy. The film growth and the detailed structure are investigated by reflection high-energy electron diffraction, cross-sectional high-resolution transmission electron microscopy (HR-TEM), and x-ray diffraction (XRD). An Fe single-crystal with metastable fcc structure nucleates on the underlayer. The HR-TEM shows that fcc lattice is formed from the Fe/Cu interface up to the film surface. A large number of misfit dislocations are introduced around the Fe/Cu interface due to an accommodation of lattice mismatch. Dislocations exist up to the film near surface. The lattice constant is estimated by XRD to be a = 0.3607 nm. The film shows a ferromagnetic property, which reflects the property of fcc-Fe crystal with high-spin ferromagnetic state.

  7. 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.

  8. A strategy to explore stable and metastable ordered phases of block copolymers.

    PubMed

    Xu, Weiquan; Jiang, Kai; Zhang, Pingwen; Shi, An-Chang

    2013-05-01

    Block copolymers with their rich phase behavior and ordering transitions have become a paradigm for the study of structured soft materials. A major challenge in the study of the phase behavior of block copolymers is to obtain different stable and metastable phases of the system. A strategy to discover complex ordered phases of block copolymers within the self-consistent field theory framework is developed by a combination of fast algorithms and novel initialization procedures. This strategy allows the generation of a large number of candidate structures, which can then be used to construct phase diagrams. Application of the strategy is illustrated using ABC star triblock copolymers as an example. A large number of candidate structures, including many three-dimensionally ordered phases, of the system are obtained and categorized. A phase diagram is constructed for symmetrically interacting ABC star triblock copolymers. PMID:23551204

  9. 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.

  10. 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.

  11. Dynamics of Stable and Metastable Structures of Liquid Crystal and Lipid Systems at Interfaces

    NASA Astrophysics Data System (ADS)

    Honaker, Lawrence; Popov, Piotr; Mann, Elizabeth; Kooijman, Edgar; Jakli, Antal

    2015-03-01

    Due to the amphiphilic structure and character of liquid crystal molecules, they tend to align in a planar fashion at a boundary with water and homeotropically at a boundary with air. However, the introduction of heteromolecules with long aliphatic tails, such as phospholipids, into the system promotes homeotropic alignment, a conformational change which is easily visually observable. It can be expected that the presence of these lipids induces a uniformly homeotropic texture in the liquid crystalline system, but experimental observations show otherwise. Studies of the textures and features that arise in such systems are presented here with an emphasis on the study of the metastable hybrid textures that develop, their stability, the characteristics of their alignment, and factors that influence their presence.

  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. 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.

  14. Evidence of existence of metastable SrFe 12O 19 nanoparticles

    NASA Astrophysics Data System (ADS)

    Martinez Garcia, R.; Bilovol, V.; Socolovsky, L. M.; Pirota, K.

    2011-12-01

    The existence of metastable hexaferrite is reported. Synthesis of strontium hexaferrite, SrFe12O19, at 400 °C was realized under controlled oxygen atmosphere. Such technique allows obtaining of SrFe12O19 at lower temperatures than those by traditional methods (above 800 °C). Phase transformation occurred during a measurement of magnetization vs. temperature (heating up to 625 °C). The heat treatment induces a change from SrFe12O19 to γ-Fe2O3 (as the main phase), and SrFeO2.74 to Sr2Fe2O5. Together with these phase transformations, an increment in the amount of SrCO3 is detected. Magnetic study of the samples, before and after the heating, supports the structural analysis conclusions.

  15. Genetic algorithm prediction of crystal structure of metastable Si-IX phase

    SciTech Connect

    Nguyen, Manh Cuong; Zhao, Xin; Wang, Yangang; Wang, Cai-Zhuang; Ho, Kai-Ming

    2013-12-14

    We performed genetic algorithm search for the atomic structure of the long Lime unsolved Si-IX phase. We found two new structures with space groups of P4(2)/m and P-4, respectively, which have lattice parameters in excellent agreement with the experimental data. The phonon calculations showed that the P4(2)/m structure exhibits a soft phonon mode, while the P-4 structure is dynamically stable. Our calculation also showed that the P-4 structure is a meta-stable structure in a pressure range from 0 to 40 GPa, The Si-IX phase could be a mixed phase consisting of the P4(2)/m and the P-4 structures. Published by Elsevier Ltd.

  16. 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.

  17. 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.

  18. Role of metastable atoms in the propagation of atmospheric pressure dielectric barrier discharge jets

    SciTech Connect

    Li Qing; Zhu Ximing; Li Jiangtao; Pu Yikang

    2010-02-15

    In the experiment of plasma jets generated in a tube dielectric barrier discharge configuration, three distinguishable modes, namely, laminar, transition, and turbulent jet modes, have been identified. Flows of helium, neon, and argon gases shared the hydrodynamic law when their plasma jets spraying into ambient air of atmospheric pressure and room temperature. Aiming to reveal the basic processes, we propose that plasma jet length is mainly determined by reactions involving metastable atoms. These processes are responsible for the variation in plasma jet length versus gas flow rate and working gas species. To investigate this proposal in detail, we have obtained three significant experimental results, i.e., (1) the plasma jet lengths of helium, neon, and argon are different; (2) the plasma jet length of krypton slightly changes with gas flow rate, with three modes indistinguishable; and (3) there are large differences between optical emission spectra of helium, neon, argon, and krypton flow gases. These observations are in good agreement with our proposal.

  19. 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

  20. 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.

  1. Multistep Photosynthesis of Metastable Compounds —The Origin of Life on the Earth—

    NASA Astrophysics Data System (ADS)

    Toyozawa, Yutaka

    1997-12-01

    On the basis of the thermodynamic argument of the characteristic feature distinguishing the living world from the nonliving, it is postulated that the radiation from the sun created living organisms on the earth and has been their constant driving force. In view of the fact that the basic biomolecules have chemical energies of several or more electron volts, significantly higher than the average energy of a photon from the sun, we propose a mechanism of multistep photoexcitations of inorganic material for the photosynthesis of these metastable molecules which would not exist at ambient temperature. The preference of the photoexcitation against the radiative and nonradiative de-excitation is ascribed to the suppression of the latter by rapid and large relaxations (reactions) in intermediate states. An experiment to confirm the mechanism is proposed in which geological time is reduced to an accessible one.

  2. Some aspects of the precipitation of metastable intermetallic phases in INCONEL 718

    NASA Astrophysics Data System (ADS)

    Sundararaman, M.; Mukhopadhyay, P.; Banerjee, S.

    1992-07-01

    Some aspects of the precipitation of the metastable intermetallic phases —γ″ and γ″—in the commercial nickel base superalloy, INCONEL 718, have been investigated over a wide range of aging temperatures. It has been confirmed that the spherical γ″ particles and the ellipsoidal γ″ particles evolve predominantly through homogeneous nucleation. Precipitation of the former does not appear to precede that of the latter in this alloy. The tetragonal distortion associated with the γ″ particles has been found to increase with increasing precipitate size. It has been observed that at certain temperatures, physical association between precipitates of the two types occurs frequently, leading to the development of different composite precipitate morphologies. During coarsening, the precipitate size has been found to depend linearly on the cube root of the aging time for γ' as well as γ″ particles.

  3. Growth of Metastable β-AlN by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Yoshitake, Tsuyoshi; Mohri, Satoshi; Hara, Takeshi; Nagayama, Kunihito

    2008-05-01

    Aluminum nitride (AlN) thin films were prepared on sapphire (0001) in ambient nitrogen by pulsed laser deposition using a sintered AlN target, and the film structure was evaluated by X-ray diffraction and scanning electron microscopy. The central area of the film was partially studded with cubic AlN (β-AlN) crystallites with obvious facets. This area was located on the normal of the irradiation spot on the target, and it corresponded to the region on the film where the highly energetic and dense species were deposited. A nonequilibrium condition and large supply of nitrogen are both important factors for the growth of metastable β-AlN.

  4. Influence of Boundary Conditions on Metastable Lifetimes for The Ising Model on the Hyperbolic Plane

    NASA Astrophysics Data System (ADS)

    Richards, Howard L.; Sharma Chapagain, Dipendra; Molchanoff, James

    2012-02-01

    Some corals grow in shapes that resemble 3D models of the hyperbolic plane, since this allows them to have greater area for a given growth radius. Each polyp could be represented by an Ising site, with ``feeding'' = ``up'' and ``retracted'' = ``down''. The mechanisms of metastable decay could be interpreted as how the coral as a whole reacts to changing conditions of food availability or predation. Previous studies have shown that there is a spinodal field for the Ising model on a regular lattice in the hyperbolic plane if it is infinite or has periodic or mean-field boundary conditions. This happens because the size of the boundary grows asymptotically at the same rate as the droplet volume, in clear contrast with droplets in the Euclidean plane. Our simulations show, however, that the spinodal field disappears if more physically relevant open boundary conditions are used instead.

  5. Specular reflection of very slow metastable neon atoms from a solid surface.

    PubMed

    Shimizu, F

    2001-02-01

    An ultracold narrow atomic beam of metastable neon in the 1s3[(2s)(5)3p:1P0] state is used to study specular reflection of atoms from a solid surface at extremely slow incident velocity. The reflectivity on a silicon (1,0,0) surface and a BK7 glass surface is measured at the normal incident velocity between 1 mm/s and 3 cm/s. The reflectivity above 30% is observed at about 1 mm/s. The observed velocity dependence is explained semiquantitatively by the quantum reflection that is caused by the attractive Casimir-van der Waals potential of the atom-surface interaction.

  6. Metastability of isoformyl ions in collisions with helium and hydrogen. [in interstellar molecular clouds

    NASA Technical Reports Server (NTRS)

    Green, S.

    1984-01-01

    The stability of HOC(+) ions under conditions in interstellar molecular clouds is considered. In particular, the possibility that collisions with helium or hydrogen will induce isomerization to the stable HCO(+) form is examined theoretically. Portions of the electronic potential energy surfaces for interaction with He and H atoms are obtained from standard quantum mechanical calculations. Collisions with He atoms are found to be totally ineffective for inducing isomerization. Collisions with H atoms are found to be ineffective at low interstellar temperatures owing to a small (about 500 K) barrier in the entrance channel; at higher temperatures where this barrier can be overcome, however, collisions with hydrogen atoms do result in conversion to the stable HCO(+) form. Although detailed calculations are not presented, it is argued that low-energy collisions with H2 molecules are also ineffective in destroying the metastable ion.

  7. 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.

  8. Controlled production of the elusive metastable form II of acetaminophen (paracetamol): a fully scalable templating approach in a cooling environment.

    PubMed

    Agnew, Lauren R; Cruickshank, Dyanne L; McGlone, Thomas; Wilson, Chick C

    2016-05-31

    A scalable, transferable, cooling crystallisation route to the elusive, metastable, form II of the API acetaminophen (paracetamol) has been developed using a multicomponent "templating" approach, delivering 100% polymorphic phase pure form II at scales up to 120 g. Favourable solubility and stability properties are found for the form II samples.

  9. Measurement of the metastable lifetime for the 2s^2 2p^2 ^1So level in O^2+

    NASA Technical Reports Server (NTRS)

    Smith, S. J.; Cadez, I.; Chutjian, A.; Niimura, M.

    2004-01-01

    The radiative lifetime of the 1S0 level was found to be 540 +/- 27 ms. This is in good agreement with a previous measurement and with a number of theoretical calculations. Metastable lifetimes, when combined with collisional excitation rates, can provide a diagnostic for electron density Ne in a stellar or solar plasma.

  10. Controlled production of the elusive metastable form II of acetaminophen (paracetamol): a fully scalable templating approach in a cooling environment.

    PubMed

    Agnew, Lauren R; Cruickshank, Dyanne L; McGlone, Thomas; Wilson, Chick C

    2016-05-31

    A scalable, transferable, cooling crystallisation route to the elusive, metastable, form II of the API acetaminophen (paracetamol) has been developed using a multicomponent "templating" approach, delivering 100% polymorphic phase pure form II at scales up to 120 g. Favourable solubility and stability properties are found for the form II samples. PMID:26926388

  11. Production of CO /a 3Pi/ and other metastable fragments by electron impact dissociation of CO2.

    NASA Technical Reports Server (NTRS)

    Wells, W. C.; Borst, W. L.; Zipf, E. C.

    1972-01-01

    The dissociative excitation of CO (a 3Pi) and other metastable fragments produced by electron impact on CO2 has been investigated from threshold to 50 eV. The observed threshold for CO (a 3Pi) production at 11.9 (plus or minus 0.5) eV was near the minimum required energy of 11.5 eV.

  12. 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.

  13. Native metastable prefibrillar oligomers are the most neurotoxic species among amyloid aggregates.

    PubMed

    Diociaiuti, Marco; Macchia, Gianfranco; Paradisi, Silvia; Frank, Claudio; Camerini, Serena; Chistolini, Pietro; Gaudiano, Maria Cristina; Petrucci, Tamara Corinna; Malchiodi-Albedi, Fiorella

    2014-09-01

    Many proteins belonging to the amyloid family share the tendency to misfold and aggregate following common steps, and display similar neurotoxicity. In the aggregation pathway different kinds of species are formed, including several types of oligomers and eventually mature fibers. It is now suggested that the pathogenic aggregates are not the mature fibrils, but the intermediate, soluble oligomers. Many kinds of aggregates have been described to exist in a metastable state and in equilibrium with monomers. Up to now it is not clear whether a specific structure is at the basis of the neurotoxicity. Here we characterized, starting from the early aggregation stages, the oligomer populations formed by an amyloid protein, salmon calcitonin (sCT), chosen due to its very slow aggregation rate. To prepare different oligomer populations and characterize them by means of photoinduced cross-linking SDS-PAGE, Energy Filtered-Transmission Electron Microscopy (EF-TEM) and Circular Dichroism (CD) spectroscopy, we used Size Exclusion Chromatography (SEC), a technique that does not influence the aggregation process leaving the protein in the native state. Taking advantage of sCT low aggregation rate, we characterized the neurotoxic potential of the SEC-separated, non-crosslinked fractions in cultured primary hippocampal neurons, analyzing intracellular Ca(2+) influx and apoptotic trend. We provide evidence that native, globular, metastable, prefibrillar oligomers (dimers, trimers and tetramers) were the toxic species and that low concentrations of these aggregates in the population was sufficient to render the sample neurotoxic. Monomers and other kind of aggregates, such as annular or linear protofibers and mature fibers, were totally biologically inactive. PMID:24932517

  14. Hot, metastable hydronium ion in the Galactic centre: formation pumping in X-ray-irradiated gas?

    PubMed

    Lis, Dariusz C; Schilke, Peter; Bergin, Edwin A; Emprechtinger, Martin

    2012-11-13

    With a 3.5 m diameter telescope passively cooled to approximately 80 K, and a science payload comprising two direct detection cameras/medium resolution imaging spectrometers (PACS and SPIRE) and a very high spectral resolution heterodyne spectrometer (HIFI), the Herschel Space Observatory is providing extraordinary observational opportunities in the 55-670 μm spectral range. HIFI has opened for the first time to high-resolution spectroscopy the submillimetre band that includes the fundamental rotational transitions of interstellar hydrides, the basic building blocks of astrochemistry. We discuss a recent HIFI discovery of metastable rotational transitions of the hydronium ion (protonated water, H(3)O(+)), with rotational level energies up to 1200 K above the ground state, in absorption towards Sagittarius B2(N) in the Galactic centre. Hydronium is an important molecular ion in the oxygen chemical network. Earlier HIFI observations have indicated a general deficiency of H(3)O(+) in the diffuse gas in the Galactic disc. The presence of hot H(3)O(+) towards Sagittarius B2(N) thus appears to be related to the unique physical conditions in the central molecular zone, manifested, for example, by the widespread presence of abundant H(3)(+). One intriguing theory for the high rotational temperature characterizing the population of the H(3)O(+) metastable levels may be formation pumping in molecular gas irradiated by X-rays emitted by the Galactic centre black hole. Alternatively, the pervasive presence of enhanced turbulence in the central molecular zone may give rise to shocks in the lower-density medium that is exposed to energetic radiation.

  15. Metastable ripple phase of fully hydrated dipalmitoylphosphatidylcholine as studied by small angle x-ray scattering

    PubMed Central

    Yao, Haruhiko; Matuoka, Sinzi; Tenchov, Boris; Hatta, Ichiro

    1991-01-01

    Fully hydrated dipalmitoylphosphatidylcholine (DPPC) undergoes liquid crystalline to metastable Pβ, phase transition in cooling. A small angle x-ray scattering study has been performed for obtaining further evidence about the structure of this phase. From a high-resolution observation of x-ray diffraction profiles, a distinct multipeak pattern has become obvious. Among them the (01) reflection in the secondary ripple structure is identified clearly. There are peaks assigned straightforwardly to (10) and (20) reflections in the primary ripple structure and peaks assigned to (10) and (20) reflections in the secondary ripple structure. Therefore the multipeak pattern is due to superposition of the reflections cause by the primary and secondary ripple structures. The lattice parameters are estimated as follows: for the primary ripple structure a = 7.09 nm, b = 13.64 nm, and γ = 95°, and for the secondary ripple structure a = 8.2 nm, b = 26.6 nm, and γ = 90°. The lattice parameters thus obtained for the secondary ripple structure are not conclusive, however. The hydrocarbon chains in the primary ripple structure have been reported as being tilted against the bilayer plane and, on the other hand, the hydrocarbon chains in the secondary ripple structure are likely to be perpendicular to the bilayer plane. This fact seems to be related to a sequential mechanism of phase transitions. On heating from the Lβ, phase where the hydrocarbon chains are tilted the primary ripple structure having tilted hydrocarbon chains takes place and on cooling from the Lα phase where the hydrocarbon chains are not tilted the secondary ripple structure with untilted chains tends to be stabilized. It appears that the truly metastable ripple phase is expressed by the second ripple structure although in the course of the actual cooling transition both the secondary and primary ripple structures form and coexist. PMID:19431787

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

    PubMed

    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.

  17. 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.

  18. 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.

  19. Hot, metastable hydronium ion in the Galactic centre: formation pumping in X-ray-irradiated gas?

    PubMed

    Lis, Dariusz C; Schilke, Peter; Bergin, Edwin A; Emprechtinger, Martin

    2012-11-13

    With a 3.5 m diameter telescope passively cooled to approximately 80 K, and a science payload comprising two direct detection cameras/medium resolution imaging spectrometers (PACS and SPIRE) and a very high spectral resolution heterodyne spectrometer (HIFI), the Herschel Space Observatory is providing extraordinary observational opportunities in the 55-670 μm spectral range. HIFI has opened for the first time to high-resolution spectroscopy the submillimetre band that includes the fundamental rotational transitions of interstellar hydrides, the basic building blocks of astrochemistry. We discuss a recent HIFI discovery of metastable rotational transitions of the hydronium ion (protonated water, H(3)O(+)), with rotational level energies up to 1200 K above the ground state, in absorption towards Sagittarius B2(N) in the Galactic centre. Hydronium is an important molecular ion in the oxygen chemical network. Earlier HIFI observations have indicated a general deficiency of H(3)O(+) in the diffuse gas in the Galactic disc. The presence of hot H(3)O(+) towards Sagittarius B2(N) thus appears to be related to the unique physical conditions in the central molecular zone, manifested, for example, by the widespread presence of abundant H(3)(+). One intriguing theory for the high rotational temperature characterizing the population of the H(3)O(+) metastable levels may be formation pumping in molecular gas irradiated by X-rays emitted by the Galactic centre black hole. Alternatively, the pervasive presence of enhanced turbulence in the central molecular zone may give rise to shocks in the lower-density medium that is exposed to energetic radiation. PMID:23028163

  20. Epigenetics as an answer to Darwin's "special difficulty," Part 2: natural selection of metastable epialleles in honeybee castes.

    PubMed

    Ruden, Douglas M; Cingolani, Pablo E; Sen, Arko; Qu, Wen; Wang, Luan; Senut, Marie-Claude; Garfinkel, Mark D; Sollars, Vincent E; Lu, Xiangyi

    2015-01-01

    In a recent perspective in this journal, Herb (2014) discussed how epigenetics is a possible mechanism to circumvent Charles Darwin's "special difficulty" in using natural selection to explain the existence of the sterile-fertile dimorphism in eusocial insects. Darwin's classic book "On the Origin of Species by Means of Natural Selection" explains how natural selection of the fittest individuals in a population can allow a species to adapt to a novel or changing environment. However, in bees and other eusocial insects, such as ants and termites, there exist two or more castes of genetically similar females, from fertile queens to multiple sub-castes of sterile workers, with vastly different phenotypes, lifespans, and behaviors. This necessitates the selection of groups (or kin) rather than individuals in the evolution of honeybee hives, but group and kin selection theories of evolution are controversial and mechanistically uncertain. Also, group selection would seem to be prohibitively inefficient because the effective population size of a colony is reduced from thousands to a single breeding queen. In this follow-up perspective, we elaborate on possible mechanisms for how a combination of both epigenetics, specifically, the selection of metastable epialleles, and genetics, the selection of mutations generated by the selected metastable epialleles, allows for a combined means for selection amongst the fertile members of a species to increase colony fitness. This "intra-caste evolution" hypothesis is a variation of the epigenetic directed genetic error hypothesis, which proposes that selected metastable epialleles increase genetic variability by directing mutations specifically to the epialleles. Natural selection of random metastable epialleles followed by a second round of natural selection of random mutations generated by the metastable epialleles would allow a way around the small effective population size of eusocial insects. PMID:25759717