8,389 research outputs found
Introduction to Library Trends 44 (2) Fall 1995: The Library and Undergraduate Education
published or submitted for publicatio
On ordinal utility, cardinal utility, and random utility
Though the Random Utility Model (RUM) was conceived
entirely in terms of ordinal utility, the apparatus throughwhich it is widely practised exhibits properties of
cardinal utility. The adoption of cardinal utility as a
working operation of ordinal is perfectly valid, provided
interpretations drawn from that operation remain faithful
to ordinal utility. The paper considers whether the latterrequirement holds true for several measurements commonly
derived from RUM. In particular it is found that
measurements of consumer surplus change may depart from
ordinal utility, and exploit the cardinality inherent in
the practical apparatus.
Gating of high-mobility InAs metamorphic heterostructures
We investigate the performance of gate-defined devices fabricated on high
mobility InAs metamorphic heterostructures. We find that heterostructures
capped with InGaAs often show signs of parallel conduction
due to proximity of their surface Fermi level to the conduction band minimum.
Here, we introduce a technique that can be used to estimate the density of this
surface charge that involves cool-downs from room temperature under gate bias.
We have been able to remove the parallel conduction under high positive bias,
but achieving full depletion has proven difficult. We find that by using
InAlAs as the barrier without an InGaAs
capping, a drastic reduction in parallel conduction can be achieved. Our
studies show that this does not change the transport properties of the quantum
well significantly. We achieved full depletion in InAlAs capped
heterostructures with non-hysteretic gating response suitable for fabrication
of gate-defined mesoscopic devices
Sparse Graph Codes for Quantum Error-Correction
We present sparse graph codes appropriate for use in quantum
error-correction. Quantum error-correcting codes based on sparse graphs are of
interest for three reasons. First, the best codes currently known for classical
channels are based on sparse graphs. Second, sparse graph codes keep the number
of quantum interactions associated with the quantum error correction process
small: a constant number per quantum bit, independent of the blocklength.
Third, sparse graph codes often offer great flexibility with respect to
blocklength and rate. We believe some of the codes we present are unsurpassed
by previously published quantum error-correcting codes.Comment: Version 7.3e: 42 pages. Extended version, Feb 2004. A shortened
version was resubmitted to IEEE Transactions on Information Theory Jan 20,
200
Characterization of a high-pressure diesel fuel injection system as a control technology option to improve engine performance and reduce exhaust emissions
Test results from a high pressure electronically controlled fuel injection system are compared with a commercial mechanical injection system on a single cylinder, diesel test engine using an inlet boost pressure of 2.6:1. The electronic fuel injection system achieved high pressure by means of a fluid intensifier with peak injection pressures of 47 to 69 MPa. Reduced exhaust emissions were demonstrated with an increasing rate of injection followed by a fast cutoff of injection. The reduction in emissions is more responsive to the rate of injection and injection timing than to high peak injection pressure
Solution of a Braneworld Big Crunch/Big Bang Cosmology
We solve for the cosmological perturbations in a five-dimensional background
consisting of two separating or colliding boundary branes, as an expansion in
the collision speed V divided by the speed of light c. Our solution permits a
detailed check of the validity of four-dimensional effective theory in the
vicinity of the event corresponding to the big crunch/big bang singularity. We
show that the four-dimensional description fails at the first nontrivial order
in (V/c)^2. At this order, there is nontrivial mixing of the two relevant
four-dimensional perturbation modes (the growing and decaying modes) as the
boundary branes move from the narrowly-separated limit described by
Kaluza-Klein theory to the well-separated limit where gravity is confined to
the positive-tension brane. We comment on the cosmological significance of the
result and compute other quantities of interest in five-dimensional
cosmological scenarios.Comment: 54 pages, 12 figures, URL updated & 3 references adde
Ion temperature anisotropy across a magnetotail reconnection jet
A significant fraction of the energy released by magnetotail reconnection appears to go into ion heating, but this heating is generally anisotropic. We examine ARTEMIS dual-spacecraft observations of a long-duration magnetotail exhaust generated by anti-parallel reconnection in conjunction with Particle-In-Cell simulations, showing spatial variations in the anisotropy across the outflow far (> 100di) downstream of the X-line. A consistent pattern is found in both the spacecraft data and the simulations: Whilst the total temperature across the exhaust is rather constant, near the boundaries Ti,|| dominates. The plasma is well-above the firehose threshold within patchy spatial regions at |BX| ∈ [0.1, 0.5]B0, suggesting that the drive for the instability is strong and the instability is too weak to relax the anisotropy. At the mid-plane (|BX|0.1 B0), Ti,⊥ > Ti,|| and ions undergo Speiser-like motion despite the large distance from the X-line
Conformal symmetry of brane world effective actions
A simple derivation of the low-energy effective action for brane worlds is
given, highlighting the role of conformal invariance. We show how to improve
the effective action for a positive- and negative-tension brane pair using the
AdS/CFT correspondence.Comment: 5 pages, published versio
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