984 research outputs found
The photoluminescence of erbium-doped silicon monoxide
Films of silicon monoxide coevaporated with erbium are shown to produce strong room temperature photoluminescence peaked at 1535nm after annealing at 600°C. Decay measurements show a double exponential function with lifetimes of 0.41ms and 2.12ms, suggesting two distinct optically active erbium sites. Photoluminescence excitation spectroscopy between 700nm and 860nm reveals a monotonic increase in photoluminescence intensity towards shorter wavelengths. This result suggests that the transfer of energy from the pump source to the erbium ions is mainly via the recombination of electron-hole pairs (photocarriers) which are created by absorption within the SiO
Combined EEG-fMRI and tractography to visualise propagation of epileptic activity
In a patient with refractory temporal lobe epilepsy, EEG-fMRI showed activation in association with left anterior temporal interictal discharges, in the left temporal, parietal and occipital lobes. Dynamic causal modelling suggested propagation of neural activity from the temporal focus to the area of occipital activation. Tractography showed connections from the site of temporal lobe activation to the site of occipital activation. This demonstrates the principle of combining EEG-fMRI and tractography to delineate the pathways of propagation of epileptic activity
Hamiltonian mappings and circle packing phase spaces
We introduce three area preserving maps with phase space structures which
resemble circle packings. Each mapping is derived from a kicked Hamiltonian
system with one of three different phase space geometries (planar, hyperbolic
or spherical) and exhibits an infinite number of coexisting stable periodic
orbits which appear to `pack' the phase space with circular resonances.Comment: 23 pages including 12 figures, REVTEX
Upstream Volatility in the Supply Chain: The Machine Tool Industry as a Case Study
Working Draft, May 1995Cyclicality is a well known and accepted fact of life in market-driven
economies. Less well known or understood, however, is the phenomenon of
amplification as one looks "upstream" in the industrial supply chain. This
paper discusses and explains the amplification phenomenon and its
implications through the lens of one "upstream" industry that is notorious
for the intensity of the business cycles it faces: the machine tool industry.
Using a sparse simulation model, we have replicated much of the behavior
seen in the industrial world in which machine tool companies operate. This
model has allowed us to test and confirm many of our hypotheses. Two
results stand out. Even though machine tool builders can do little to reduce
their production volatility through choice of forecast rule, a longer view of
the future leads companies to retain more of their skilled workforce. This is
often cited as one of the advantages that European and Japanese companies
have enjoyed: lower skilled employee turnover. The second, and most
important result is that machine tool customers can do a great deal to reduce
the volatility for machine tool builders through their choice of order forecast
rule. Companies which use a longer horizon over which to forecast orders
tend to impose less of their own volatility upon their supply base.MIT -- Leaders for Manufacturing, the
International Motor Vehicle Program, the Industrial Performance Center, the International
Center for Research on the Management of Technology, and the Japan Program; Chrysler, Intel, Sematech, and Texas Instruments
Characterisation of the effectiveness of carbon incorporation in SiGe for the elimination of parasitic energy barriers in SiGe HBT's
An electrical method is applied to SiGe and SiGeC HBTs to extract the bandgap narrowing in the base layer and to characterise the presence of parasitic energy barriers in the conduction band, arising from transient enhanced boron diffusion from the SiGe layer. It is shown that a background carbon concentration with the base of approximately 1E20cm-3 eliminates parasitic energy barriers at the C/B junction and hence shows that transient enhanced diffusion of boron from the base has been completely suppressed
Isotopic analysis of faunal material from South Uist, Western Isles, Scotland
This paper reports on the results from stable isotope analysis of faunal bone collagen from a number of Iron Age
and later sites on the island of South Uist, in the Western Isles, Scotland. This preliminary investigation into the isotopic signatures of the fauna is part of a larger project to model the interaction between humans, animals, and the broader environment in the Western Isles. The results demonstrate that the island fauna data fall within the range of expected results for the UK, with the terrestrial herbivorous diets of cattle and sheep confi rmed. The isotopic composition for pigs suggests that some of these animals had an omnivorous diet, whilst a single red deer value might be suggestive of the consumption of marine foods, such as by grazing on seaweed. However, further analysis is needed in order to verify this anomalous isotopic ratio
Quantitative Comparison of Sinc-Approximating Kernels for Medical Image Interpolation
Abstract. Interpolation is required in many medical image processing operations. From sampling theory, it follows that the ideal interpolation kernel is the sinc function, which is of infinite extent. In the attempt to obtain practical and computationally efficient image processing al-gorithms, many sinc-approximating interpolation kernels have been de-vised. In this paper we present the results of a quantitative comparison of 84 different sinc-approximating kernels, with spatial extents ranging from 2 to 10 grid points in each dimension. The evaluation involves the application of geometrical transformations to medical images from dif-ferent modalities (CT, MR, and PET), using the different kernels. The results show very clearly that, of all kernels with a spatial extent of 2 grid points, the linear interpolation kernel performs best. Of all kernels with an extent of 4 grid points, the cubic convolution kernel is the best (28 %- 75 % reduction of the errors as compared to linear interpolation). Even better results (44 %- 95 % reduction) are obtained with kernels of larger extent, notably the Welch, Cosine, Lanczos, and Kaiser windowed sinc kernels. In general, the truncated sinc kernel is one of the worst performing kernels.
4D, N = 1 Supersymmetry Genomics (I)
Presented in this paper the nature of the supersymmetrical representation
theory behind 4D, N = 1 theories, as described by component fields, is
investigated using the tools of Adinkras and Garden Algebras. A survey of
familiar matter multiplets using these techniques reveals they are described by
two fundamental valise Adinkras that are given the names of the cis-Valise
(c-V) and the trans-Valise (t-V). A conjecture is made that all off-shell 4D, N
= 1 component descriptions of supermultiplets are associated with two integers
- the numbers of c-V and t-V Adinkras that occur in the representation.Comment: 53 pages, 19 figures, Report-II of SSTPRS 2008 Added another chapter
for clarificatio
Asymmetric quantum channel for quantum teleportation
There are a few obstacles, which bring about imperfect quantum teleportation
of a continuous variable state, such as unavailability of maximally entangled
two-mode squeezed states, inefficient detection and imperfect unitary
transformation at the receiving station. We show that all those obstacles can
be understood by a combination of an {\it asymmetrically-decohered} quantum
channel and perfect apparatuses for other operations. For the
asymmetrically-decohered quantum channel, we find some counter-intuitive
results; one is that teleportation does not necessarily get better as the
channel is initially squeezed more and another is when one branch of the
quantum channel is unavoidably subject to some imperfect operations, blindly
making the other branch as clean as possible may not result in the best
teleportation result. We find the optimum strategy to teleport an unknown field
for a given environment or for a given initial squeezing of the channel.Comment: 4pages, 1figur
Fabrication of photonic crystals in rare-earth doped chalcogenide glass films for enhanced upconversion
Gallium lanthanum oxysulfide (GLSO) is a promising host material for observing strong upconversion emission from trivalent rare-earth ions such as erbium (Er3+). Its attractive properties include high rare-earth solubility due to the lanthanum content of the glass former, a high refractive index (n = 2.2 at 550nm) for high radiative efficiency, and a low maximum phonon energy of approximately 425cm-1. Photonic crystals meanwhile can provide controlled light extraction, and may be capable of suppressing unwanted IR emission from lower lying metastable states. Here, we describe the fabrication of photonic crystals in annealed films of Er3+-doped GLSO deposited by RF sputtering. The most intense visible upconversion emission is observed in films annealed at 550°C, close to the bulk glass transition temperature. Hexagonal lattice photonic crystals are subsequently milled into the films using a focused ion beam (FIB). The milling parameters are optimized to produce the most vertical sidewall profile
- …