66,734 research outputs found
Alternatives to Kronig-Kramers Transformation and Testing, and Estimation of Distributions
Two alternatives to Kronig-Kramers analysis of small-signal ac immittance data are discussed and illustrated using both synthetic and experimental data. The first, a derivative method of approximating imaginary-part response from real-part data, is found to be too approximate in regions where the imaginary-part varies appreciably with frequency. The second, a distribution of relaxation-times fitting method, is shown to be valuable for testing whether a data set satisfies the Kronig-Kramers relations and so is associated with a system whose properties are time-invariant. It also is valuable for estimating real- or imaginary-part response from the other part, usually with small error. Unlike Kronig-Kramers analysis, the second method usually requires no extrapolation outside the range of the measured data. Finally, this discrete-function method also allows one to estimate the distribution of relaxation times or activation energies associated with a given set of frequency-response data. This application is described and illustrated for both synthetic and experimental data and is shown to yield good but somewhat approximate results for the estimation of continuous distributions. It is particularly valuable for identifying response regions arising from a continuous distribution and distinguishing them from those associated with discrete time-constant response
NLO Leptoquark Production and Decay: The Narrow-Width Approximation and Beyond
We study the leptoquark model of Buchm\"uller, R\"uckl and Wyler, focusing on
a particular type of scalar () and vector () leptoquark. The primary
aim is to perform the calculations for leptoquark production and decay at
next-to-leading order (NLO) to establish the importance of the NLO
contributions and, in particular, to determine how effective the
narrow-width-approximation (NWA) is at NLO. For both the scalar and vector
leptoquarks it is found that the NLO contributions are large, with the larger
corrections occurring for the case vector leptoquarks. For the scalar
leptoquark it is found that the NWA provides a good approximation for
determining the resonant peak, however the NWA is not as effective for the
vector leptoquark. For both the scalar and vector leptoquarks there are large
contributions away from the resonant peak, which are missing from the NWA
results, and these make a significant difference to the total cross-section.Comment: 22 pages, 17 figure
Comment on the Coupling of Zero Sound to the Modes of He-B
Features in the zero sound attenuation near the pair-breaking edge in
superfluid He-B have been observed in large magnetic fields. Schopohl and
Tewordt [{\sl J. Low Temp. Phys.} {\bf 57}, 601 (1984)] claim that the order-parameter collective modes couple to zero sound as a result of
the distortion of the equilibrium order parameter by a magnetic field; they
identify the new features with these modes. However, we show that, when the
effect of gap distortion on the collective modes is properly taken into
account, the collective mode equations of Schopohl and Tewordt yield no direct
coupling of zero sound to the modes. Thus, the identification of the
absorption features reported by Ling, Saunders and Dobbs [{\sl Phys. Rev.
Lett.} {\bf 59}, 461 (1987)] near the pair-breaking edge with the modes
is not clearly established.Comment: 6 pages (Tex with jnl.tex
Preliminary power train design for a state-of-the-art electric vehicle
The state-of-the-art (SOTA) of electric vehicles built since 1965 was reviewed to establish a base for the preliminary design of a power train for a SOTA electric vehicle. The performance of existing electric vehicles were evaluated to establish preliminary specifications for a power train design using state-of-the-art technology and commercially available components. Power train components were evaluated and selected using a computer simulation of the SAE J227a Schedule D driving cycle. Predicted range was determined for a number of motor and controller combinations in conjunction with the mechanical elements of power trains and a battery pack of sixteen lead-acid batteries - 471.7 kg at 0.093 MJ/Kg (1040 lbs. at 11.7 Whr/lb). On the basis of maximum range and overall system efficiency using the Schedule D cycle, an induction motor and 3 phase inverter/controller was selected as the optimum combination when used with a two-speed transaxle and steel belted radial tires. The predicted Schedule D range is 90.4 km (56.2 mi). Four near term improvements to the SOTA were identified, evaluated, and predicted to increase range approximately 7%
Iron line profiles including emission from within the innermost stable orbit of a black hole accretion disc
Reynolds & Begelman (1997) have recently proposed a model in which the broad
and extremely redshifted iron line seen during a deep minimum of the light
curve of the Seyfert 1 galaxy MCG-6-30-15 originates from matter spiralling
into a Schwarzschild black hole, contrary to previous claims that the black
hole may be spinning rapidly (Iwasawa et al 1996; Dabrowski et al 1997). Here
we calculate in detail the X-ray spectrum produced by their model using the
full reflected continuum emission, including absorption features. This
calculation takes into account the doppler and relativistic effects. For the
range of parameters we consider, we find that the spectrum should show a large
photoelectric absorption edge of iron, which is not seen in the data. The
absorption edge is a consequence of the line emitting matter within the
innermost stable orbit being highly ionized, and is largely independent of the
parameters chosen for their model. If we restrict our attention to the 3-10 keV
band we may effectively remove this absorption edge by fitting a steeper power
law, but this results in a significant underprediction of the 0.4-0.5 keV flux.
We conclude that the data on MCG-6-30-15 are more consistent with the Kerr than
the Schwarzschild model.Comment: 5 pages with 5 postscript figures. Accepted for publication in MNRA
Objective detection by signal analysis of the auditory evoked cortical E.E.G. potential
Imperial Users onl
Graphical Methods in Device-Independent Quantum Cryptography
We introduce a framework for graphical security proofs in device-independent
quantum cryptography using the methods of categorical quantum mechanics. We are
optimistic that this approach will make some of the highly complex proofs in
quantum cryptography more accessible, facilitate the discovery of new proofs,
and enable automated proof verification. As an example of our framework, we
reprove a previous result from device-independent quantum cryptography: any
linear randomness expansion protocol can be converted into an unbounded
randomness expansion protocol. We give a graphical proof of this result, and
implement part of it in the Globular proof assistant.Comment: Publishable version. Diagrams have been polished, minor revisions to
the text, and an appendix added with supplementary proof
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