The Experts below are selected from a list of 42033 Experts worldwide ranked by ideXlab platform
G Majer - One of the best experts on this subject based on the ideXlab platform.
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generation and application of ultra high intensity Magnetic Field Gradient pulses for nmr spectroscopy
Journal of Magnetic Resonance, 2001Co-Authors: Petrik Galvosas, Jörg Kärger, Frank Stallmach, Gunter Seiffert, Udo Kaess, G MajerAbstract:Abstract Two different concepts of Gradient current power supplies are introduced, which are suitable for the generation of ultra-high intensity pulsed Magnetic Field Gradients of alternating polarity. The first system consists of a directly binary coded current source (DBCCS). It yields current pulses of up to ±120 A and a maximum voltage across the Gradient coil of ±400 V. The second system consists of two TECHRON 8606 power supplies in push–pull configuration (PSPPC). It yields current pulses of up to ±100 A and a maximum voltage across the Gradient coil of ±300 V. In combination with actively shielded anti-Helmholtz Gradient coils, both systems are used routinely in NMR diffusion studies with unipolar pulsed Field Gradients of up to 35 T/m. Until now, alternating pulsed Field Gradient experiments were successfully performed with Gradient intensities of up to ±25 T/m (DBCCS) and ±35 T/m (PSPPC), respectively. Based on the observation of the NMR spin echo in the presence of a small read Gradient, procedures to test the stability and the matching of such ultra-high pulsed Field Gradient intensities as well as an automated routine for the compensation of possible mismatches are introduced. The results of these procedures are reported for the PSPPC system.
D H Slichter - One of the best experts on this subject based on the ideXlab platform.
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trapped ion spin motion coupling with microwaves and a near motional oscillating Magnetic Field Gradient
Physical Review Letters, 2019Co-Authors: Raghavendra Srinivas, Shaun C Burd, R T Sutherland, Andrew C Wilson, D Leibfried, D T C Allcock, David J. Wineland, D H SlichterAbstract:: We present a new method of spin-motion coupling for trapped ions using microwaves and a Magnetic Field Gradient oscillating close to the ions' motional frequency. We demonstrate and characterize this coupling experimentally using a single ion in a surface-electrode trap that incorporates current-carrying electrodes to generate the microwave Field and the oscillating Magnetic Field Gradient. Using this method, we perform resolved-sideband cooling of a single motional mode to its ground state.
Sanjiv K Tiwari - One of the best experts on this subject based on the ideXlab platform.
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vertical Magnetic Field Gradient in the photospheric layers of sunspots
Astronomy and Astrophysics, 2017Co-Authors: Jayant Joshi, A Lagg, J Hirzberger, S K Solanki, Sanjiv K TiwariAbstract:Aims. We investigate the vertical Gradient of the Magnetic Field of sunspots in the photospheric layer. Methods. Independent observations were obtained with the Solar Optical Telescope/Spectropolarimeter (SOT/SP) on board the Hinode spacecraft and with the Tenrife Infrared Polarimeter-2 (TIP-2) mounted at the German Vacuum Tower Telescope (VTT). We apply state-of-the-art inversion techniques to both data sets to retrieve the Magnetic Field and the corresponding vertical Gradient along with other atmospheric parameters in the solar photosphere. Results. In the sunspot penumbrae we detected patches of negative vertical Gradients of the Magnetic Field strength, i.e., the Magnetic Field strength decreases with optical depth in the photosphere. The negative Gradient patches are located in the inner and partly in the middle penumbrae in both data sets. From the SOT/SP observations we found that the negative Gradient patches are restricted mainly to the deep photospheric layers and are concentrated near the edges of the penumbral filaments. Magnetohydrodynamic (MHD) simulations also show negative Gradients in the inner penumbrae, also at the locations of filaments. In the observations and the simulation negative Gradients of the Magnetic Field vs. optical depth dominate at some radial distances in the penumbra. The negative Gradient with respect to optical depth in the inner penumbrae persists even after averaging in the azimuthal direction in the observations and, to a lesser extent, in the MHD simulations. If the Gradients in the MHD simulations are determined with respect to geometrical height, then the azimuthal averages are always positive within the sunspot (above log τ = 0), corresponding to Magnetic Field increasing with depth, as generally expected. Conclusions. We interpret the observed localized presence of negative vertical Gradient of the Magnetic Field strength in the observations as a consequence of stronger Field from spines expanding with height and closing above the weaker Field inter-spines. The presence of the negative Gradients with respect to optical depth after azimuthal averaging can be explained by two different mechanisms: the high corrugation of equal optical depth surfaces and the cancellation of polarized signal due to the presence of unresolved opposite polarity patches in the deeper layers of the penumbra.
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vertical Magnetic Field Gradient in the photospheric layers of sunspots
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: Jayant Joshi, A Lagg, J Hirzberger, S K Solanki, Sanjiv K TiwariAbstract:We investigate the vertical Gradient of the Magnetic Field of sunspots in the photospheric layer. Independent observations were obtained with the SOT/SP onboard the Hinode spacecraft and with the TIP-2 mounted at the VTT. We apply state-of-the-art inversion techniques to both data sets to retrieve the Magnetic Field and the corresponding vertical Gradient. In the sunspot penumbrae we detected patches of negative vertical Gradients of the Magnetic Field strength, i.e.,the Magnetic Field strength decreases with optical depth in the photosphere. The negative Gradient patches are located in the inner and partly in the middle penumbrae in both data sets. From the SOT/SP observations, we found that the negative Gradient patches are restricted mainly to the deep photospheric layers and are concentrated near the edges of the penumbral filaments. MHD simulations also show negative Gradients in the inner penumbrae, also at the locations of filaments. Both in the observations and simulation negative Gradients of the Magnetic Field vs. optical depth dominate at some radial distances in the penumbra. The negative Gradient with respect to optical depth in the inner penumbrae persists even after averaging in the azimuthal direction, both in the observations and, to a lesser extent, also in MHD simulations. We interpret the observed localized presence of the negative vertical Gradient of the Magnetic Field strength in the observations as a consequence of stronger Field from spines expanding with height and closing above the weaker Field inter-spines. The presence of the negative Gradients with respect to optical depth after azimuthal averaging can be explained by two different mechanisms: the high corrugation of equal optical depth surfaces and the cancellation of polarized signal due to the presence of unresolved opposite polarity patches in the deeper layers of the penumbra.
Janez Stepišnik - One of the best experts on this subject based on the ideXlab platform.
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diffusion spectrum of polymer melt measured by varying Magnetic Field Gradient pulse width in pgse nmr
Molecules, 2020Co-Authors: Ales Mohoric, G Lahajnar, Janez StepišnikAbstract:The translational motion of polymers is a complex process and has a big impact on polymer structure and chemical reactivity. The process can be described by the segment velocity autocorrelation function or its diffusion spectrum, which exhibit several characteristic features depending on the observational time scale—from the Brownian delta function on a large time scale, to complex details in a very short range. Several stepwise, more-complex models of translational dynamics thus exist—from the Rouse regime over reptation motion to a combination of reptation and tube-Rouse motion. Accordingly, different methods of measurement are applicable, from neutron scattering for very short times to optical methods for very long times. In the intermediate regime, nuclear Magnetic resonance (NMR) is applicable—for microseconds, relaxometry, and for milliseconds, diffusometry. We used a variation of the established diffusometric method of pulsed Gradient spin-echo NMR to measure the diffusion spectrum of a linear polyethylene melt by varying the Gradient pulse width. We were able to determine the characteristic relaxation time of the first mode of the tube-Rouse motion. This result is a deviation from a Rouse model of polymer chain displacement at the crossover from a square-root to linear time dependence, indicating a new long-term diffusion regime in which the dynamics of the tube are also described by the Rouse model.
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velocity autocorrelation spectra of fluid in porous media measured by the cpmg sequence and constant Magnetic Field Gradient
Magnetic Resonance Imaging, 2007Co-Authors: Janez Stepišnik, Samo Lasie, Ales Mohoric, Igor Sersa, Ana SepeAbstract:Abstract Carr–Purcell–Meiboom–Gill (CPMG) train of radiofrequency pulses applied to spins in the constant Magnetic Field Gradient is an efficient variant of the modulated Magnetic Field Gradient spin echo method, which provides information about molecular diffusion in the frequency domain instead of in the time domain as with the two-pulse Gradient spin echo. The frequency range of this novel technique is broad enough to sample the power spectrum of displacement fluctuation in water-saturated pulverized silica (SiO2) and provides comprehensive information about the molecular restricted motion as well as about the structure of the medium.
Guy Lemarquand - One of the best experts on this subject based on the ideXlab platform.
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Linear displacement sensor with high Magnetic Field Gradient
Journal of Magnetism and Magnetic Materials, 1992Co-Authors: C. Blache, Guy LemarquandAbstract:Abstract This paper presents designs of permanent magnet structures providing a high Magnetic Field Gradient in an air gap for microdisplacement sensor application. A geometric optimization of the structure is fulfilled with Magnetic induction analytic calculation in the air gap. The Magnetic Field Gradient value is obtained by finite element analysis. A discussion about the different structures is presented, with regard to the Field Gradient, and linearity.
