91,231 research outputs found
Experimental characterization of a supercapacitor-based electrical torque-boost system for downsized ICE vehicles
The need to improve fuel economy and reduce the emission of CO2 and other harmful pollution from internal-combustion-engine vehicles has led to engine downsizing. However, downsized turbocharged engines exhibit a relatively low torque capability at low engine speeds. To overcome this problem, an electrical torque boost may be employed while accelerating and changing gear and to facilitate energy recovery during regenerative braking. This paper describes the operational requirements of a supercapacitor-based torque-boost system, outlines the design and sizing of the electrical drive-train components, and presents experimental characterization of a demonstrator system
Further thoughts on precision
Background: There has been much discussion amongst automated software defect prediction researchers regarding use of the precision and false positive rate classifier performance metrics. Aim: To demonstrate and explain why failing to report precision when using data with highly imbalanced class distributions may provide an overly optimistic view of classifier performance. Method: Well documented examples of how dependent class distribution affects the suitability of performance measures. Conclusions: When using data where the minority class represents less than around 5 to 10 percent of data points in total, failing to report precision may be a critical mistake. Furthermore, deriving the precision values omitted from studies can reveal valuable insight into true classifier performancePeer reviewedFinal Accepted Versio
Phonon anomalies in pure and underdoped R{1-x}K{x}Fe{2}As{2} (R = Ba, Sr) investigated by Raman light scattering
We present a detailed temperature dependent Raman light scattering study of
optical phonons in Ba{1-x}K{x}Fe{2}As{2} (x ~ 0.28, superconducting Tc ~ 29 K),
Sr{1-x}K{x}Fe{2}As{2} (x ~ 0.15, Tc ~ 29 K) and non-superconducting
BaFe{2}As{2} single crystals. In all samples we observe a strong continuous
narrowing of the Raman-active Fe and As vibrations upon cooling below the
spin-density-wave transition Ts. We attribute this effect to the opening of the
spin-density-wave gap. The electron-phonon linewidths inferred from these data
greatly exceed the predictions of ab-initio density functional calculations
without spin polarization, which may imply that local magnetic moments survive
well above Ts. A first-order structural transition accompanying the
spin-density-wave transition induces discontinuous jumps in the phonon
frequencies. These anomalies are increasingly suppressed for higher potassium
concentrations. We also observe subtle phonon anomalies at the superconducting
transition temperature Tc, with a behavior qualitatively similar to that in the
cuprate superconductors.Comment: 5 pages, 6 figures, accepted versio
Generating entangled photon pairs from a cavity-QED system
We propose a scheme for the controlled generation of Einstein-Podosky-Rosen
(EPR) entangled photon pairs from an atom coupled to a high Q optical cavity,
extending the prototype system as a source for deterministic single photons. A
thorough theoretical analysis confirms the promising operating conditions of
our scheme as afforded by currently available experimental setups. Our result
demonstrates the cavity QED system as an efficient and effective source for
entangled photon pairs, and shines new light on its important role in quantum
information science.Comment: It has recently come to our attention that the experiment by T. Wilk,
S. C. Webster, A. Kuhn and G. Rempe, published in Science 317, 488 (2007),
exactly realizes what we proposed in this article, which is published in Phy.
Rev. A 040302(R) (2005
Entanglement between two fermionic atoms inside a cylindrical harmonic trap
We investigate quantum entanglement between two (spin-1/2) fermions inside a
cylindrical harmonic trap, making use of the von Neumann entropy for the
reduced single particle density matrix as the pure state entanglement measure.
We explore the dependence of pair entanglement on the geometry and strength of
the trap and on the strength of the pairing interaction over the complete range
of the effective BCS to BEC crossover. Our result elucidates an interesting
connection between our model system of two fermions and that of two interacting
bosons.Comment: to appear in PR
- âŠ