14 results on '"Donald Candela"'
Search Results
2. Understanding the breakdown of Fourier’s law in granular fluids
- Author
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Donald Candela and Ronald L. Walsworth
- Subjects
Physics ,Heat current ,Heuristic ,Flow (psychology) ,General Physics and Astronomy ,Granular material ,Physics::Fluid Dynamics ,Condensed Matter::Soft Condensed Matter ,symbols.namesake ,Fourier transform ,Granular matter ,Law ,Heat transfer ,symbols - Abstract
In fluidized granular matter (such as rapidly flowing sand) heat can flow from colder to hotter granular temperatures, violating Fourier’s law. A simple heuristic explanation for this anomalous heat current is presented, based on the non-equilibrium nature of granular fluids. The heuristic explanation leads to a straightforward calculation of the heat current which is in good agreement with existing, more detailed calculations and with recent experiments.
- Published
- 2007
3. NMR measurements of grain and gas motion in a gas-fluidized granular bed
- Author
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R. Wang, Chao Huan, Ronald L. Walsworth, Donald Candela, Kevin Facto, and Ross W. Mair
- Subjects
Materials science ,medicine.diagnostic_test ,Measure (physics) ,General Physics and Astronomy ,Motion (geometry) ,Magnetic resonance imaging ,Condensed Matter::Soft Condensed Matter ,Nuclear magnetic resonance ,Gravity of Earth ,Mechanics of Materials ,Fluidized bed ,Hyperpolarized xenon ,Bubble velocity ,medicine ,General Materials Science ,Atomic physics ,Pulsed field gradient - Abstract
Nuclear magnetic resonance (NMR) experiments are described for gas-fluidized granular beds, which are important systems for many materials-processing operations. Using pulsed field gradient, magnetic resonance imaging, and hyperpolarized gas NMR, detailed information is obtained for the density and motions of both grains and interstitial gas. In particular, dynamic correlations in the grain density are used to measure the bubble velocity and hyperpolarized xenon gas NMR is used to measure the bubble-emulsion exchange rate. A goal of these measurements is to verify in earth gravity first-principles theories of granular flows.
- Published
- 2007
4. Study of gas-fluidization dynamics with laser-polarized 129Xe
- Author
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Matthew S. Rosen, Ronald L. Walsworth, Donald Candela, R. Wang, and Ross W. Mair
- Subjects
Magnetic Resonance Spectroscopy ,Chemistry ,Lasers ,Bubble ,Biomedical Engineering ,Biophysics ,Analytical chemistry ,chemistry.chemical_element ,Mechanics ,Xenon ,Fluidized bed ,Phase (matter) ,Xenon Isotopes ,Particle ,Emulsions ,Radiology, Nuclear Medicine and imaging ,Gases ,Fluidization ,Volatilization ,Pulsed field gradient ,Magnetosphere particle motion - Abstract
We report initial NMR studies of gas dynamics in a particle bed fluidized by laser-polarized xenon (129Xe) gas. We have made preliminary measurements of two important characteristics: gas exchange between the bubble and emulsion phases and the gas velocity distribution in the bed. We used T2* contrast to differentiate the bubble and emulsion phases by choosing solid particles with large magnetic susceptibility. Experimental tests demonstrated that this method was successful in eliminating 129Xe magnetization in the emulsion phase, which enabled us to observe the time dependence of the bubble magnetization. By employing the pulsed field gradient method, we also measured the gas velocity distribution within the bed. These results clearly show the onset of bubbling and can be used to deduce information about gas and particle motion in the fluidized bed.
- Published
- 2005
5. Applications of controlled-flow laser-polarized xenon gas to porous and granular media study
- Author
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Donald Candela, R. Wang, Ronald L. Walsworth, Matthew S. Rosen, David G. Cory, and Ross W. Mair
- Subjects
Diffraction ,Chemistry ,business.industry ,Scattering ,Lasers ,Diffusion ,Attenuation ,Biomedical Engineering ,Biophysics ,chemistry.chemical_element ,Mechanics ,Magnetic Resonance Imaging ,Microspheres ,Viscosity ,Optics ,Xenon ,Spin echo ,Xenon Isotopes ,Radiology, Nuclear Medicine and imaging ,Porous medium ,business ,Porosity - Abstract
We report initial NMR studies of continuous flow laser-polarized xenon gas, both in unrestricted tubing, and in a model porous media. The study uses Pulsed Gradient Spin Echo-based techniques in the gas-phase, with the aim of obtaining more sophisticated information than just translational self-diffusion coefficients. Pulsed Gradient Echo studies of continuous flow laser-polarized xenon gas in unrestricted tubing indicate clear diffraction minima resulting from a wide distribution of velocities in the flow field. The maximum velocity experienced in the flow can be calculated from this minimum, and is seen to agree with the information from the complete velocity spectrum, or motion propagator, as well as previously published images. The susceptibility of gas flows to parameters such as gas mixture content, and hence viscosity, are observed in experiments aimed at identifying clear structural features from echo attenuation plots of gas flow in porous media. Gas-phase NMR scattering, or position correlation flow-diffraction, previously clearly seen in the echo attenuation data from laser-polarized xenon flowing through a 2 mm glass bead pack is not so clear in experiments using a different gas mixture. A propagator analysis shows most gas in the sample remains close to static, while a small portion moves through a presumably near-unimpeded path at high velocities.
- Published
- 2003
6. NMR investigation of the low-temperature dynamics of solid4He doped with3He impurities
- Author
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Chao Huan, L. Yin, Neil Sullivan, Jian-Sheng Xia, S. S. Kim, and Donald Candela
- Subjects
Materials science ,Condensed matter physics ,Doping ,Relaxation (NMR) ,Analytical chemistry ,Atmospheric temperature range ,Condensed Matter Physics ,01 natural sciences ,Viscoelasticity ,010305 fluids & plasmas ,Electronic, Optical and Magnetic Materials ,Shear modulus ,Impurity ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,Fluctuation spectrum ,Quantum tunnelling - Abstract
The lattice dynamics of solid He-4 has been explored using pulsed NMR methods to study the motion of He-3 impurities in the temperature range (0.05-0.20 K) where experiments have revealed anomalies attributed to superflow or unexpected viscoelastic properties of the solid He-4 lattice. We report the results of measurements of the nuclear spin-lattice and spin-spin relaxation times that measure the fluctuation spectrum at high and low frequencies, respectively, of the He-3 motion that results from quantum tunneling in the He-4 matrix. The measurements were made for He-3 concentrations 16 < x(3) < 2000 ppm. For He-3 concentrations x(3) = 16 and 24 ppm, large changes are observed for both the spin-lattice relaxation time T-1 and the spin-spin relaxation time T-2 at temperatures close to those for which the anomalies are observed in measurements of torsional oscillator responses and the shear modulus. These changes in the NMR relaxation rates were not observed for higher He-3 concentrations.
- Published
- 2013
7. Nuclear Spin Relaxation of Very Dilute 3He impurities in Solid 4He
- Author
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Chao Huan, Donald Candela, Jian-Sheng Xia, Neil Sullivan, L. Yin, and S. S. Kim
- Subjects
History ,Quantum Physics ,Materials science ,Condensed matter physics ,FOS: Physical sciences ,Dissipation ,Atmospheric temperature range ,01 natural sciences ,010305 fluids & plasmas ,Computer Science Applications ,Education ,Elastic distortion ,Shear modulus ,Condensed Matter - Other Condensed Matter ,Impurity ,Lattice (order) ,0103 physical sciences ,Quantum Physics (quant-ph) ,010306 general physics ,Torsional oscillator ,Quantum tunnelling ,Other Condensed Matter (cond-mat.other) - Abstract
We report measurements of the nuclear spin-lattice and spin-spin relaxation times of very dilute 3He in solid 4He in the temperature range 0.01 \leq T \leq 0.5 K for densities where anomalies have been observed in torsional oscillator and shear modulus measurements. We compare the results with the values of the relaxation times reported by other observers for higher concentrations and the theory of Landesman that takes into account the elastic properties of the 4He lattice. A sharp increase in the magnitude of the nuclear spin-lattice relaxation times compared to the the classical Landesman theory is observed close to the temperatures where the torsional and shear modulus anomalies are observed. The NMR results suggest that the tunneling of 3He impurities in the atomic-scale elastic distortion is affected by the same processes that give rise to the macroscopic elastic dissipation anomalies., 4 pages, 4 figures
- Published
- 2012
8. Giant viscosity enhancement in a spin-polarized Fermi liquid
- Author
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Jian-Sheng Xia, H. Akimoto, William J. Mullin, Neil Sullivan, Donald Candela, and E. D. Adams
- Subjects
Physics ,Condensed matter physics ,Scattering ,FOS: Physical sciences ,General Physics and Astronomy ,Viscometer ,Fermi energy ,Condensed Matter - Other Condensed Matter ,Helium-4 ,Helium-3 ,Quasiparticle ,Condensed Matter::Strongly Correlated Electrons ,Fermi liquid theory ,Fermi gas ,Other Condensed Matter (cond-mat.other) - Abstract
The viscosity is measured for a Fermi liquid, a dilute $^3$He-$^4$He mixture, under extremely high magnetic field/temperature conditions ($B \leq 14.8$ T, $T \geq 1.5$ mK). The spin splitting energy $\mu B$ is substantially greater than the Fermi energy $k_B T_F$; as a consequence the polarization tends to unity and s-wave quasiparticle scattering is suppressed for $T \ll T_F$. Using a novel composite vibrating-wire viscometer an enhancement of the viscosity is observed by a factor of more than 500 over its low-field value. Good agreement is found between the measured viscosity and theoretical predictions based upon a $t$-matrix formalism., Comment: 4 pages, 4 figures
- Published
- 2007
9. Interstitial gas and density segregation of vertically vibrated granular media
- Author
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Donald Candela, T. Pavlin, Leo L. Tsai, Matthew S. Rosen, Ronald L. Walsworth, and Mason Klein
- Subjects
Steady state ,Materials science ,Condensed matter physics ,FOS: Physical sciences ,Pattern formation ,Granular media ,Condensed Matter - Soft Condensed Matter ,engineering.material ,Condensed Matter::Disordered Systems and Neural Networks ,Physics::History of Physics ,Condensed Matter::Soft Condensed Matter ,Vibration ,Physics::Popular Physics ,Viscosity ,Amplitude ,Physics::Atomic and Molecular Clusters ,engineering ,Soft Condensed Matter (cond-mat.soft) ,Bronze ,Layer (electronics) - Abstract
We report experimental studies of the effect of interstitial gas on mass-density-segregation in a vertically-vibrated mixture of equal-sized bronze and glass spheres. Sufficiently strong vibration in the presence of interstitial gas induces vertical segregation into sharply separated bronze and glass layers. We find that the segregated steady state (i.e., bronze or glass layer on top) is a sensitive function of gas pressure and viscosity, as well as vibration frequency and amplitude. In particular, we identify distinct regimes of behavior that characterize the change from bronze-on-top to glass-on-top steady-state., Comment: 4 pages, 5 figures, submitted to PRL; accepted in PRE as rapid communication, with revised text and references
- Published
- 2006
10. Lattice Relaxation of4He with3He Impurities: NMR Studies
- Author
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S. S. Kim, L. Yin, Neil Sullivan, Jian-Sheng Xia, Donald Candela, and Chao Huan
- Subjects
Shear modulus ,History ,Dipole ,Condensed matter physics ,Chemistry ,Impurity ,Lattice (order) ,Relaxation (NMR) ,Atom ,Zero-point energy ,Quantum tunnelling ,Computer Science Applications ,Education - Abstract
Measurements of the 3He nuclear spin relaxation times of dilute 3He impurities in solid 4He have been used to explore the unusual dynamics of solid 4He at low temperatures. The 3He impurities move through the lattice by quantum mechanical exchange with neighboring 4He atoms. Because of the larger zero point motion of the 3He atoms, there is an appreciable lattice distortion that accompanies the tunneling 3 He atom and the tunneling motion depends on the elastic properties of the 4He lattice. This motion modulates the 3He-3He nuclear dipole- dipole interactions and thus determines the NMR relaxation rates. We compare the observed temperature dependence of the NMR relaxation rates with that expected from the measurements of the shear modulus by Syshchenko et al. [Phys. Rev. Lett. 104, 195301 (2009)].
- Published
- 2014
11. NMR experiments on a three-dimensional vibrofluidized granular medium
- Author
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Chao Huan, Ross W. Mair, Ronald L. Walsworth, Xiaoyu Yang, and Donald Candela
- Subjects
Surface (mathematics) ,Physics ,FOS: Physical sciences ,Condensed Matter - Soft Condensed Matter ,Granular material ,01 natural sciences ,Molecular physics ,010305 fluids & plasmas ,Vibration ,Classical mechanics ,Distribution (mathematics) ,0103 physical sciences ,Soft Condensed Matter (cond-mat.soft) ,010306 general physics ,Hydrodynamic theory ,Porous medium ,Pulsed field gradient ,Dimensionless quantity - Abstract
A three-dimensional granular system fluidized by vertical container vibrations was studied using pulsed field gradient (PFG) NMR coupled with one-dimensional magnetic resonance imaging (MRI). The system consisted of mustard seeds vibrated vertically at 50 Hz, and the number of layers N_ell, 14 pages, 15 figures
- Published
- 2003
12. Using NMR to Measure Fractal Dimensions
- Author
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Donald Candela and Po-zen Wong
- Subjects
Physics ,Nuclear magnetic resonance ,Fractal ,Statistical Mechanics (cond-mat.stat-mech) ,Measure (physics) ,General Physics and Astronomy ,FOS: Physical sciences ,Statistical physics ,Disordered Systems and Neural Networks (cond-mat.dis-nn) ,Condensed Matter - Disordered Systems and Neural Networks ,Fractal dimension ,Condensed Matter - Statistical Mechanics - Abstract
A comment is made on the recent PFG NMR measurements by Stallmach, et al. on water-saturated sands [Phys. Rev. Lett. 88, 105505 (2002)]. It is pointed out that the usual law for the time-dependent diffusion coefficient D(t) used by these authors is not valid for a fractal surface. It is shown that (1-D(t)/D0) \~ t^[(3-Ds)/2] at short times for a surface of fractal dimension Ds, where D0 is the bulk diffusion coefficient. Preliminary PFG NMR data on water saturated limestone and plastic beads are presented to illustrate this analysis., 1 page, 1 figure
- Published
- 2002
13. Measurements of Grain Motion in a Dense, Three-Dimensional Granular Fluid
- Author
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Chao Huan, Xiaoyu Yang, Ross W. Mair, Donald Candela, and Ronald L. Walsworth
- Subjects
Surface (mathematics) ,Materials science ,Statistical Mechanics (cond-mat.stat-mech) ,Mean free path ,FOS: Physical sciences ,General Physics and Astronomy ,Motion (geometry) ,Mechanics ,Hard spheres ,Condensed Matter - Soft Condensed Matter ,01 natural sciences ,Measure (mathematics) ,010305 fluids & plasmas ,Classical mechanics ,0103 physical sciences ,Particle diameter ,Soft Condensed Matter (cond-mat.soft) ,010306 general physics ,Hydrodynamic theory ,Displacement (fluid) ,Condensed Matter - Statistical Mechanics - Abstract
We have used an NMR technique to measure the short-time, three-dimensional displacement of grains in a system of mustard seeds vibrated vertically at 15g. The technique averages over a time interval in which the grains move ballistically, giving a direct measurement of the granular temperature profile. The dense, lower portion of the sample is well described by a recent hydrodynamic theory for inelastic hard spheres. Near the free upper surface the mean free path is longer than the particle diameter and the hydrodynamic description fails., Comment: 4 pages, 4 figures
- Published
- 2002
14. Potential energy in a three-dimensional vibrated granular medium measured by NMR imaging
- Author
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Xiaoyu Yang and Donald Candela
- Subjects
Physics ,Gravity (chemistry) ,Statistical Mechanics (cond-mat.stat-mech) ,Analytical chemistry ,FOS: Physical sciences ,General Physics and Astronomy ,Alpha (ethology) ,Condensed Matter - Soft Condensed Matter ,Container (type theory) ,01 natural sciences ,Potential energy ,010305 fluids & plasmas ,Vibration ,Acceleration ,Nuclear magnetic resonance ,0103 physical sciences ,Soft Condensed Matter (cond-mat.soft) ,Beta (velocity) ,Center of mass ,010306 general physics ,Condensed Matter - Statistical Mechanics - Abstract
Fast NMR imaging was used to measure the density profile of a three-dimensional granular medium fluidized by vertical vibrations of the container. For container acceleration much larger than gravity, the rise in center of mass of the granular medium is found to scale as (v0^alpha)/(N^beta) with alpha = 1.0 +/-0.2 and beta = 0.5 +/- 0.1, where v0 is the vibration velocity and N is the number of grains in the container. This value for alpha is significantly less than found previously for experiments and simulations in one dimension (alpha = 2) and two dimensions (alpha = 1.3-1.5)., Comment: 4 pages, 3 figures
- Published
- 2000
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