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Digitale Medien

State-to-state vibrational energy transfer in DF(v=1–3) (1990)

Robinson, J. M. ; Muyskens, M. A. ; Rensberger, K. J. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 93 (1990), S. 3207-3214

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: Overtone vibration–laser double resonance studies of DF(v=1–3) energy transfer yield self-relaxation rate constants for v=1, 2 and 3 of k1=(0.37±0.06)×10−12 cm3 mol−1 s−1, k2=(22.0±2.0)×10−12 cm3 mol−1 s−1, and k3=(17.0±1.8)×10−12 cm3 mol−1 s−1, respectively. The approach also directly measures the relative importance of vibration-to-vibration (V–V) and vibration-to-translation-and-rotation (V–T,R) energy transfer. The fraction of DF(v) molecules relaxing by V–V energy transfer is 1.1±0.1 and 0.72±0.10 for v=2 and v=3, respectively. Essentially all of the vibrational energy transfer in v=2 occurs via the V–V mechanism. The slower relaxation of DF(v=3) compared to DF(v=2), in contrast to simple scaling law predictions, reflects the decreasing influence of the V–V mechanism, even though it is still the primary relaxation pathway for DF(v=3). Comparison with HF self-relaxation qualitatively indicates that V–R energy transfer is important in V–T,R relaxation of DF(v=1).

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.458853

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2

Digitale Medien

Large field induced strain in single crystalline Ni–Mn–Ga ferromagnetic shape memory alloy (2000)

Murray, S. J. ; Marioni, M. A. ; Kukla, A. M. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 87 (2000), S. 5774-5776

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A room temperature free shear strain of 5.7% is reported in a single crystal of Ni–Mn–Ga having a composition close to the Heusler alloy Ni2MnGa. A twin boundary was created in a 2 mm×2 mm×25 mm single crystal using a permanent magnet with surface field strength of about 320 000 A/m. A sharp 6.5° bend occurs in the sample at the twin boundary. The surface magnetization changes abruptly across this boundary. By moving the sample relative to the edge of the magnet, we were able to sweep the boundary back and forth along the crystal length. Surface magnetization was measured using a Hall probe and the results confirm that the easy axis is the tetragonal c axis. Powder x-ray diffraction shows that the fcc to body-centered-tetragonal bct martensitic transition of this material involved a 6% reduction of the bct cell c/a ratio, from (square root of 2) to about 1.33. The maximum achievable strain is thus estimated to be 6.2%. The twin planes in the system are the {112}bct and were observed to lie almost normal to the long axis of the sample tested. © 2000 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.372518

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3

Digitale Medien

New vapor phase spontaneous Raman spectrometer (1992)

Robinson, J. C. ; Fink, M. ; Mihill, A.

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 63 (1992), S. 3280-3284

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: A highly sensitive, spontaneous Raman spectrometer designed for the study of vapors and other low-density samples is discussed. The high sensitivity is achieved by means of the novel combination of a multipass light cell and a high-temperature gasdynamic focusing system. A complete description of the apparatus is given, along with the results of a sensitivity test in ambient air, as well as results demonstrating gasdynamic focusing of a vapor and Raman transitions in such a sample.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1142537

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4

Digitale Medien

Prospects for edge current density determination using LIBEAM on DIII-D : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)

Thomas, D. M. ; Bozek, A. S. ; Robinson, J. I. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 72 (2001), S. 1023-1027

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: The specific size and structure of the edge current profile has important effects on the magnetohydrodynamic stability and ultimate performance of many advanced tokamak (AT) operating modes. This is true for both bootstrap and externally driven currents that may be used to tailor the edge shear. Absent a direct local measurement of j(r), the best alternative is a determination of the poloidal field. Measurements of the precision (0.1°–0.01° in magnetic pitch angle and 1–10 ms) necessary to address issues of stability and control and provide constraints for EFIT are difficult to do in the region of interest (ρ=0.9–1.1). Using Zeeman polarization spectroscopy of the 2S–2P lithium resonance line emission from the DIII-D LIBEAM [D. M. Thomas, Rev. Sci. Instrum. 66, 806 (1995); D. M. Thomas, A. W. Hyatt, and M. P. Thomas, Rev. Sci. Instrum. 61, 340 (1990)] measurements of the various field components may be made to the necessary precision in exactly the region of interest to these studies. Because of the negligible Stark mixing of the relevant atomic levels, this method of determining j(r) is insensitive to the large local electric fields typically found in enhanced confinement (H mode) edges, and thus avoids an ambiguity common to motional Stark effect measurements of B. Key issues for utilizing this technique include good beam quality, an optimum viewing geometry, and a suitable optical prefilter to isolate the polarized emission line. A prospective diagnostic system for the DIII-D AT program will be described. © 2001 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1319612

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5

Digitale Medien

Instrumentation and cell design for in situ studies of electrode surfaces using x-ray synchrotron radiation : Proceedings of the 4th international conference on synchrotron radiation instrumentation (1992)

Herron, M. E. ; Doyle, S. E. ; Roberts, K. J. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 63 (1992), S. 950-955

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: As an integral part of a program to develop x-ray techniques for in situ structural studies of electrode surfaces, a series of experiments has been carried out using x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) at the Daresbury SRS. These studies, which involve continuous control of the electrode potential and the need to probe the electrode surface with synchrotron radiation, demand careful attention to cell design. Three types of experiment are described in order to illustrate possible approaches to cell design and the versatility of in situ x-ray techniques.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1143789

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6

Digitale Medien

The DIII-D lithium beam edge diagnostic system (abstract) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)

Thomas, D. M. ; Lee, R. L. ; Patterson, R. M. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 63 (1992), S. 4940-4940

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: We are installing a diagnostic system based on a neutral lithium beam to investigate plasma behavior in the edge region of DIII-D discharges [D. M. Thomas et al., Rev. Sci. Instrum. 61, 3040 (1990]. The system will provide neutral equivalent current densities of several mA/cm2 at beam energies from 5 to 30 keV, sufficient to penetrate several centimeters past the last closed flux surface in most of the DIII-D operating regime. Fluorescence of the beam atoms is induced by collisions with plasma particles and is a sensitive measure of the edge density behavior. The emitted 670.8-nm fluorescence is collected and coupled via fiber optics to a multichannel high-speed data acquisition system based on silicon diode detectors. Because of the favorable atomic properties of lithium (i.e., high electron impact excitation cross section, resonance wavelength well separated from Hα) we should be able to study density fluctuations in this region from an analysis of the associated fluctuations in the beam fluorescence. A description of the installed diagnostic, test stand measurements of intrinsic beam fluctuations and any initial operating experience on DIII-D will be presented. This work supported by U. S. Department of Energy Grant No. DE-FG03-90ER5408 and Contract DE-AC03-89ER51114, which support does not constitute an endorsement by DOE of views expressed in this publication.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1143502

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7

Digitale Medien

A CO2 laser tangential imaging system for CDX-U (abstract) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)

Nazikian, R. M. ; Robinson, J. ; Wright, J. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 63 (1992), S. 4983-4983

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: In a previous paper [R. Nazikian and B. Grek, Rev. Sci. Instrum. 61, 2899 (1990)], it was shown that tangential imaging provides a powerful new technique for rendering two-dimensional images of local density fluctuations in toroidal plasma devices. The technique consists of projecting a CO2 laser beam tangent to magnetic field lines at the plasma midplane and using phase contrast or other related optical methods for imaging line integral density fluctuations. In this paper we present recent progress in the development of such an imaging system for CDX-U. The interferometer makes use of a novel variation on the Zernike phase contrast method for detecting phase variations impressed on laser beams propagating through random media. This work supported by Department of Energy contract No. DE-AC02-76-CHO-3073.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1143519

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8

Digitale Medien

Laser-assisted (1+1′)-photon ionization-detected absorption spectrum of the 3pπ 2Π state of HCO and DCO (2002)

Robinson, J. D. ; Foltynowicz, R. J. ; Prentice, K. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 116 (2002), S. 8384-8395

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: We re-examine the ionization-detected ultraviolet absorption spectrum of the 3pπ 2Π←X 2A′ transition in HCO and DCO using a high-power visible laser to enhance the observation of first-photon resonant features. This technique, which we term here, assisted REMPI, significantly improves the signal-to-noise ratio of the spectrum, making many weak vibronic sub-bands visible for the first time. A comprehensive fit to the structure evident in a progression of bending levels from (000) to (040) refines the assignment of Song and Cool [X. M. Song and T. A. Cool, J. Chem. Phys. 96, 8664 (1992)] to yield a set of rotational constants that vary with K in relation to v2, together with a higher-order contribution to the Renner–Teller splitting in HCO, which is mirrored in DCO for all levels but (040). The (040) band falls at a frequency that is commensurate with that of CD stretch, and Fermi resonance between 3pπ 2Π(1000)Π and the higher-energy (040) K=1(Π) component gives rise to an added splitting that increases the energy of this (040) component and causes an apparent increase in the Renner parameter. © 2002 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1467329

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