473 research outputs found
Stability of Hydraulic Systems with Focus on Cavitating Pumps
Increasing use is being made of transmission matrices to characterize unsteady flows in hydraulic system components and to analyze the stability of such systems. This paper presents some general characteristics which should be examined in any experimentally measured transmission matrices and a methodology for the analysis of the stability of transmission matrices in hydraulic systems of order 2. These characteristics are then examined for cavitating pumps and the predicted instabilities (known as auto-oscillation) compared with experimental observations in a particular experimental system
Auto-Oscillation of Cavitating Inducers
This paper presents details of measurements on the instability know as auto-oscillation which occurs in systems with cavitating pumps. Specific measurements are made of onset cavitation number and auto-osciallation frequency for a range of inducers. It has been shown that auto-oscillation is a system instability caused by the active dynamic characteristics of the cavitating pump.
A system anslysis is presented which utilized previously measured dynamic transfer functions for the inducers; the resulting predictions of instability are consistent with the observations. Though the onset cavitation number is a function of the entire system it is also show that, given the onset cavitation number, the auto-oscillation frequency is only weakly dependent on the system and primarily a function of the pump dynamics.
Detailed measurements of the amplitude and phase of fluctuating pressures and flow rates during auto-oscillation are also presented. These strongly suggest that the pump dynamics are primarily determined by the complicated flow at inlet to the inducer which involves pre-swirl generated by a strong backflow. Some data on the non-linear effect of auto-osciallation on overall mean performance are also presented
The Effects of Inlet Flow Modification on Cavitating Inducer Performance
This paper explores the effect of inlet flow modification on the cavitating and noncavitating performance of two cavitating inducers, one of simple helical design and the other a model of the low-pressure LOX pump in the Space Shuttle Main Engine. The modifications were generated by sections of honeycomb, both uniform and nonuniform. Significant improvement in the performance over a wide range of flow coefficients resulted from the use of either honeycomb section. Measurements of the axial and swirl velocity profiles of the flows entering the inducers were made in order to try to understand the nature of the inlet flow and the manner in which it is modified by the honeycomb sections
Quantum computational renormalization in the Haldane phase
Single-spin measurements on the ground state of an interacting spin lattice
can be used to perform a quantum computation. We show how such measurements can
mimic renormalization group transformations and remove the short-ranged
variations of the state that can reduce the fidelity of a computation. This
suggests that the quantum computational ability of a spin lattice could be a
robust property of a quantum phase. We illustrate our idea with the ground
state of a spin-1 chain, which can serve as a quantum computational wire not
only at the Affleck-Kennedy-Lieb-Tasaki point, but within the
rotationally-invariant Haldane phase.Comment: v2: 4 pages, 3 figures; improved description of buffering scheme and
connection to string operators. v3: final published versio
Loops and Strings in a Superconducting Lattice Gauge Simulator
We propose an architecture for an analog quantum simulator of
electromagnetism in 2+1 dimensions, based on an array of superconducting
fluxonium devices. The encoding is in the integer (spin-1 representation of the
quantum link model formulation of compact U(1) lattice gauge theory. We show
how to engineer Gauss' law via an ancilla mediated gadget construction, and how
to tune between the strongly coupled and intermediately coupled regimes. The
witnesses to the existence of the predicted confining phase of the model are
provided by nonlocal order parameters from Wilson loops and disorder parameters
from 't Hooft strings. We show how to construct such operators in this model
and how to measure them nondestructively via dispersive coupling of the
fluxonium islands to a microwave cavity mode. Numerical evidence is found for
the existence of the confined phase in the ground state of the simulation
Hamiltonian on a ladder geometry.Comment: 17 pages, 5 figures. Published versio
Emergent Radiation in an Atom-Field System at Twice-Resonance
A two-level atom interacting with a single mode of quantized electromagnetic
radiation is discussed using a representation in which the atom and the
radiation are unified into a {\em new} canonical radiation. At the {\em
twice-resonance}, when the frequency of the original radiation is twice the
atomic transition frequency (), the {\em emergent} unified
field in the non-interacting atom-field system resembles a free radiation of
frequency . This free emergent radiation is further shown to exist in
the presence of an interaction which looks similar to the atom-field
interaction in the dipole approximation. The one-photon correlation and the
population inversion are discussed as the possible means of observing the
emergent radiation. The entanglement properties of the emergent radiation are
also discussed.Comment: 4+ pages, 2 figures, submitted for publication; included a discussion
on the entanglemen
Creation of effective magnetic fields in optical lattices: The Hofstadter butterfly for cold neutral atoms
We investigate the dynamics of neutral atoms in a 2D optical lattice which
traps two distinct internal states of the atoms in different columns. Two Raman
lasers are used to coherently transfer atoms from one internal state to the
other, thereby causing hopping between the different columns. By adjusting the
laser parameters appropriately we can induce a non vanishing phase of particles
moving along a closed path on the lattice. This phase is proportional to the
enclosed area and we thus simulate a magnetic flux through the lattice. This
setup is described by a Hamiltonian identical to the one for electrons on a
lattice subject to a magnetic field and thus allows us to study this equivalent
situation under very well defined controllable conditions. We consider the
limiting case of huge magnetic fields -- which is not experimentally accessible
for electrons in metals -- where a fractal band structure, the Hofstadter
butterfly, characterizes the system.Comment: 6 pages, RevTe
Quantum Logic for Trapped Atoms via Molecular Hyperfine Interactions
We study the deterministic entanglement of a pair of neutral atoms trapped in
an optical lattice by coupling to excited-state molecular hyperfine potentials.
Information can be encoded in the ground-state hyperfine levels and processed
by bringing atoms together pair-wise to perform quantum logical operations
through induced electric dipole-dipole interactions. The possibility of
executing both diagonal and exchange type entangling gates is demonstrated for
two three-level atoms and a figure of merit is derived for the fidelity of
entanglement. The fidelity for executing a CPHASE gate is calculated for two
87Rb atoms, including hyperfine structure and finite atomic localization. The
main source of decoherence is spontaneous emission, which can be minimized for
interaction times fast compared to the scattering rate and for sufficiently
separated atomic wavepackets. Additionally, coherent couplings to states
outside the logical basis can be constrained by the state dependent trapping
potential.Comment: Submitted to Physical Review
Holonomic quantum computing in symmetry-protected ground states of spin chains
While solid-state devices offer naturally reliable hardware for modern
classical computers, thus far quantum information processors resemble vacuum
tube computers in being neither reliable nor scalable. Strongly correlated many
body states stabilized in topologically ordered matter offer the possibility of
naturally fault tolerant computing, but are both challenging to engineer and
coherently control and cannot be easily adapted to different physical
platforms. We propose an architecture which achieves some of the robustness
properties of topological models but with a drastically simpler construction.
Quantum information is stored in the symmetry-protected degenerate ground
states of spin-1 chains, while quantum gates are performed by adiabatic
non-Abelian holonomies using only single-site fields and nearest-neighbor
couplings. Gate operations respect the symmetry, and so inherit some protection
from noise and disorder from the symmetry-protected ground states.Comment: 19 pages, 4 figures. v2: published versio
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