3,423 research outputs found
Travelling-wave thermoacoustic electricity generator using an ultra-compliant alternator for utilization of low-grade thermal energy
This paper proposes a novel concept of a travelling-wave thermoacoustic electricity generator, which employs a looped-tube travelling-wave thermoacoustic engine to convert thermal energy into acoustic power, an ultra-compliant alternator within the engine loop to extract and convert the engine acoustic power to electricity and an acoustic stub matching technique to match the alternator to the engine. In addition, a carefully designed cold heat exchanger acts as a phase shifting inertance to improve the performance. A simple model has been developed to capture and demonstrate the physics of this new concept, while the whole system has been investigated in detail numerically by using a specialized design tool DeltaEC. Based on the current concept, a prototype has been designed, constructed and tested. It uses atmospheric air as the working fluid, a commercially available audio loudspeaker as the electro-dynamic transducer, and inexpensive standard parts as the acoustic resonator. The experimental results have verified the simplified model and the numerical simulations of the practical build. The small-scale inexpensive prototype generator produced 11.6 W of electrical power, which shows the potential for developing cheap thermoacoustic electricity generators for energy recovery from waste heat sources. It is concluded that such concept could be very attractive provided that inexpensive ultra-compliant alternators based on the standard technology used in audio loudspeakers could be developed. Finally, some guidelines have been discussed and proposed for developing such alternators
On the efficiency of estimating penetrating rank on large graphs
P-Rank (Penetrating Rank) has been suggested as a useful measure of structural similarity that takes account of both incoming and outgoing edges in ubiquitous networks. Existing work often utilizes memoization to compute P-Rank similarity in an iterative fashion, which requires cubic time in the worst case. Besides, previous methods mainly focus on the deterministic computation of P-Rank, but lack the probabilistic framework that scales well for large graphs. In this paper, we propose two efficient algorithms for computing P-Rank on large graphs. The first observation is that a large body of objects in a real graph usually share similar neighborhood structures. By merging such objects with an explicit low-rank factorization, we devise a deterministic algorithm to compute P-Rank in quadratic time. The second observation is that by converting the iterative form of P-Rank into a matrix power series form, we can leverage the random sampling approach to probabilistically compute P-Rank in linear time with provable accuracy guarantees. The empirical results on both real and synthetic datasets show that our approaches achieve high time efficiency with controlled error and outperform the baseline algorithms by at least one order of magnitude
On modulational instability and energy localization in anharmonic lattices at finite energy density
The localization of vibrational energy, induced by the modulational
instability of the Brillouin-zone-boundary mode in a chain of classical
anharmonic oscillators with finite initial energy density, is studied within a
continuum theory. We describe the initial localization stage as a gas of
envelope solitons and explain their merging, eventually leading to a single
localized object containing a macroscopic fraction of the total energy of the
lattice. The initial-energy-density dependences of all characteristic time
scales of the soliton formation and merging are described analytically. Spatial
power spectra are computed and used for the quantitative explanation of the
numerical results.Comment: 12 pages, 7 figure
On the nature of Coulomb corrections to the e^+e^- pair production in ultrarelativistic heavy-ion collisions
We manifest the origin of the wrong conclusion made by several groups of
authors on the absence of Coulomb corrections to the cross section of the
e^+e^- pair production in ultrarelativistic heavy-ion collisions. The source of
the mistake is connected with an incorrect passage to the limit in the
expression for the cross section. When this error is eliminated, the Coulomb
corrections do not vanish and agree with the results obtained within the
Weizs\"acker-Williams approximation.Comment: 7 pages, LaTe
Decoherence of a Superposition of Macroscopic Current States in a SQUID
We show that fundamental conservation laws mandate parameter-free mechanisms
of decoherence of quantum oscillations of the superconducting current between
opposite directions in a SQUID -- emission of phonons and photons at the
oscillation frequency. The corresponding rates are computed and compared with
experimental findings. The decohering effects of external mechanical and
magnetic noise are investigated
Color Stability of Elastomers for Maxillofacial Appliances
The color stability of polyvinyl chloride, polyurethane, and silicone polymers for maxillofacial applications was determined after accelerated aging using reflectance spectrophotometry. On the basis of color stability after accelerated aging, and ease of processing, several silicone materials were the most promising.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67056/2/10.1177_00220345780570090401.pd
An asymptotical von-Neumann measurement strategy for solid-state qubits
A measurement on a macroscopic quantum system does in general not lead to a
projection of the wavefunction in the basis of the detector as predicted by
von-Neumann's postulate. Hence, it is a question of fundametal interest, how
the preferred basis onto which the state is projected is selected out of the
macroscopic Hilbert space of the system. Detector-dominated von-Neumann
measurements are also desirable for both quantum computation and verification
of quantum mechanics on a macroscopic scale. The connection of these questions
to the predictions of the spin-boson modelis outlined. I propose a measurement
strategy, which uses the entanglement of the qubit with a weakly damped
harmonic oscillator. It is shown, that the degree of entanglement controls the
degree of renormalization of the qubit and identify, that this is equivalent to
the degree to which the measurement is detector-dominated. This measurement
very rapidly decoheres the initial state, but the thermalization is slow. The
implementation in Josephson quantum bits is described and it is shown that this
strategy also has practical advantages for the experimental implementation.Comment: 4 pages, 3 figures, accepted for publication as a rapid communication
in Phys. Rev.
On the lifting of the Nagata automorphism
It is proved that the Nagata automorphism (Nagata coordinates, respectively)
of the polynomial algebra over a field cannot be lifted to a
-automorphism (-coordinate, respectively) of the free associative algebra
. The proof is based on the following two new results which have
their own interests: degree estimate of and tameness of
the automorphism group .Comment: 15 page
Methylthiolate-induced reconstruction of Ag(1 1 1): A medium energy ion scattering study
Medium energy ion scattering (MEIS), using 100 keV H+ incident ions, has been used to investigate the structure of the Ag(1 1 1)(√7 × √7)R19° –CH3S surface phase. The results provide the first direct evidence that this structure does involve substantial reconstruction of the Ag surface layer. The measured absolute scattered ion yields and blocking curves are in generally good agreement with a specific structural model of the surface based on a reconstructed layer containing 3/7 ML Ag atoms, previously suggested on the basis of scanning tunnelling microscopy (STM) and normal incidence X-ray standing wave (NIXSW) studies. However, the MEIS data indicate that any rumpling of the thiolate layer, is small, and probably 0.2 Å. This value is smaller than the amplitude suggested in the STM and NIXSW studies, but could be entirely consistent with the earlier experimental data
Isotope effects and the charge gap formation in the charge ordered phase of colossal magnetoresistance manganites
Giant oxygen isotope effects observed in colossal magnetoresistance
manganites are investigated by employing the combined model of the double
exchange and interacting lattice polaron mechanism. We have shown that the
isotope effects on in the metallic phase and in the charge
ordered phase of manganites can be explained well in terms of the double
exchange and polaron narrowing factors with reasonable physical parameters.Comment: 5 pages, 3 figure
- …