2,438 research outputs found
A new model for simulating colloidal dynamics
We present a new hybrid lattice-Boltzmann and Langevin molecular dynamics
scheme for simulating the dynamics of suspensions of spherical colloidal
particles. The solvent is modeled on the level of the lattice-Boltzmann method
while the molecular dynamics is done for the solute. The coupling between the
two is implemented through a frictional force acting both on the solvent and on
the solute, which depends on the relative velocity. A spherical colloidal
particle is represented by interaction sites at its surface. We demonstrate
that this scheme quantitatively reproduces the translational and rotational
diffusion of a neutral spherical particle in a liquid and show preliminary
results for a charged spherical particle. We argue that this method is
especially advantageous in the case of charged colloids.Comment: For a movie click on the link below Fig
Multi-spin dynamics of the solid-state NMR Free Induction Decay
We present a new experimental investigation of the NMR free induction decay
(FID) in a lattice of spin-1/2 nuclei in a strong Zeeman field. Following a
pi/2 pulse, evolution under the secular dipolar Hamiltonian preserves coherence
number in the Zeeman eigenbasis, but changes the number of correlated spins in
the state. The observed signal is seen to decay as single-spin, single-quantum
coherences evolve into multiple-spin coherences under the action of the dipolar
Hamiltonian. In order to probe the multiple-spin dynamics during the FID, we
measured the growth of coherence orders in a basis other than the usual Zeeman
eigenbasis. This measurement provides the first direct experimental observation
of the growth of coherent multiple-spin correlations during the FID.
Experiments were performed with a cubic lattice of spins (19F in calcium
fluoride) and a linear spin chain (19F in fluorapatite). It is seen that the
geometrical arrangement of the spins plays a significant role in the
development of higher order correlations. The results are discussed in light of
existing theoretical models.Comment: 7 pages, 6 figure
A Quarterly Model Of The Beef, Pork, Sheep, Broiler and Turkey Sectors
Livestock and meat, producers, processors -and consumers need to continually adjust plans as expected prices change and-affect - i-- expected relative profits and utility* from alternative uses\u27 or the resources they manage.- These decision makers demand information and analysis of anticipated-product-supplies- and price levels.
Simultaneous sub-second hyperpolarization of the nuclear and electron spins of phosphorus in silicon
We demonstrate a method which can hyperpolarize both the electron and nuclear
spins of 31P donors in Si at low field, where both would be essentially
unpolarized in equilibrium. It is based on the selective ionization of donors
in a specific hyperfine state by optically pumping donor bound exciton
hyperfine transitions, which can be spectrally resolved in 28Si. Electron and
nuclear polarizations of 90% and 76%, respectively, are obtained in less than a
second, providing an initialization mechanism for qubits based on these spins,
and enabling further ESR and NMR studies on dilute 31P in 28Si.Comment: 4 pages, 3 figure
Integrated silicon qubit platform with single-spin addressability, exchange control and robust single-shot singlet-triplet readout
Silicon quantum dot spin qubits provide a promising platform for large-scale
quantum computation because of their compatibility with conventional CMOS
manufacturing and the long coherence times accessible using Si enriched
material. A scalable error-corrected quantum processor, however, will require
control of many qubits in parallel, while performing error detection across the
constituent qubits. Spin resonance techniques are a convenient path to parallel
two-axis control, while Pauli spin blockade can be used to realize local parity
measurements for error detection. Despite this, silicon qubit implementations
have so far focused on either single-spin resonance control, or control and
measurement via voltage-pulse detuning in the two-spin singlet-triplet basis,
but not both simultaneously. Here, we demonstrate an integrated device platform
incorporating a silicon metal-oxide-semiconductor double quantum dot that is
capable of single-spin addressing and control via electron spin resonance,
combined with high-fidelity spin readout in the singlet-triplet basis.Comment: 10 pages, 4 figure
Transport Phenomena and Structuring in Shear Flow of Suspensions near Solid Walls
In this paper we apply the lattice-Boltzmann method and an extension to
particle suspensions as introduced by Ladd et al. to study transport phenomena
and structuring effects of particles suspended in a fluid near sheared solid
walls. We find that a particle free region arises near walls, which has a width
depending on the shear rate and the particle concentration. The wall causes the
formation of parallel particle layers at low concentrations, where the number
of particles per layer decreases with increasing distance to the wall.Comment: 14 pages, 14 figure
A direct numerical simulation method for complex modulus of particle dispersions
We report an extension of the smoothed profile method (SPM)[Y. Nakayama, K.
Kim, and R. Yamamoto, Eur. Phys. J. E {\bf 26}, 361(2008)], a direct numerical
simulation method for calculating the complex modulus of the dispersion of
particles, in which we introduce a temporally oscillatory external force into
the system. The validity of the method was examined by evaluating the storage
and loss moduli of a system composed of identical
spherical particles dispersed in an incompressible Newtonian host fluid at
volume fractions of , 0.41, and 0.51. The moduli were evaluated at
several frequencies of shear flow; the shear flow used here has a zigzag
profile, as is consistent with the usual periodic boundary conditions
Nuclear Spins in a Nanoscale Device for Quantum Information Processing
Coherent oscillations between any two levels from four nuclear spin states of
I=3/2 have been demonstrated in a nanometre-scale NMR semiconductor device,
where nuclear spins are all-electrically controlled. Using this device, we
discuss quantum logic operations on two fictitious qubits of the I=3/2 system,
and propose a quantum state tomography scheme based on the measurement of
longitudinal magnetization, .Comment: 5 pages, 4 figure
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