45,479 research outputs found
Efficient and multiplierless design of FIR filters with very sharp cutoff via maximally flat building blocks
A new design technique for linear-phase FIR filters, based on maximally flat buildiing blocks, is presented. The design technique does not involve iterative approximations and is, therefore, fast. It gives rise to filters that have a monotone stopband response, as required in some applications. The technique is partially based on an interpolative scheme. Implementation of the obtained filter designs requires a much smaller number of multiplications than maximally flat (MAXFLAT) FIR filters designed by the conventional approach. A technique based on FIR spectral transformations to design new multiplierless FIR filter structures is then advanced, and multiplierless implementations for sharp cutoff specifications are included
New Insights on Interstellar Gas-Phase Iron
In this paper, we report on the gas-phase abundance of singly-ionized iron
(Fe II) for 51 lines of sight, using data from the Far Ultraviolet
Spectroscopic Explorer (FUSE). Fe II column densities are derived by measuring
the equivalent widths of several ultraviolet absorption lines and subsequently
fitting those to a curve of growth. Our derivation of Fe II column densities
and abundances creates the largest sample of iron abundances in moderately- to
highly-reddened lines of sight explored with FUSE, lines of sight that are on
average more reddened than lines of sight in previous Copernicus studies. We
present three major results. First, we observe the well-established correlation
between iron depletion and and also find trends between iron depletion
and other line of sight parameters (e.g. f(H_2), E_(B-V), and A_V), and examine
the significance of these trends. Of note, a few of our lines of sight probe
larger densities than previously explored and we do not see significantly
enhanced depletion effects. Second, we present two detections of an extremely
weak Fe II line at 1901.773 A in the archival STIS spectra of two lines of
sight (HD 24534 and HD 93222). We compare these detections to the column
densities derived through FUSE spectra and comment on the line's f-value and
utility for future studies of Fe II. Lastly, we present strong anecdotal
evidence that the Fe II f-values derived empirically through FUSE data are more
accurate than previous values that have been theoretically calculated, with the
probable exception of f_1112.Comment: Accepted for publication in ApJ, 669, 378; see ApJ version for small
updates. 53 total pages (preprint format), 7 tables, 11 figure
Nonuniversal Critical Spreading in Two Dimensions
Continuous phase transitions are studied in a two dimensional nonequilibrium
model with an infinite number of absorbing configurations. Spreading from a
localized source is characterized by nonuniversal critical exponents, which
vary continuously with the density phi in the surrounding region. The exponent
delta changes by more than an order of magnitude, and eta changes sign. The
location of the critical point also depends on phi, which has important
implications for scaling. As expected on the basis of universality, the static
critical behavior belongs to the directed percolation class.Comment: 21 pages, REVTeX, figures available upon reques
Bursts and Shocks in a Continuum Shell Model
We study a "burst" event, i. e. the evolution of an initial condition having
support only in a finite interval of k-space, in the continuum shell model due
to Parisi. We show that the continuum equation without forcing or dissipation
can be explicitly written in characteristic form and that the right and left
moving parts can be solved exactly. When this is supplemented by the
appropriate shock condition it is possible to find the asymptotic form of the
burst.Comment: 15 pages, 2 eps figures included, Latex 2e. Contribution to the
proceedings of the conference: Disorder and Chaos, in honour of Giovanni
Paladin, September 22-24, 1997, in Rom
Model Calculation of Effective Three-Body Forces
We propose a scheme for extracting an effective three-body interaction
originating from a two-nucleon interaction. This is based on the Q-box method
of Kuo and collaborators, where folded diagrams are obtained by differentiating
a sum of non-folded diagrams with respect to the starting energy. To gain
insight we have studied several examples using the Lipkin model where the
perturbative approach can be compared with exact results. Numerically the
three-body interactions can be significant and in a matrix example good
accuracy was not obtained simultaneously for both eigenvalues with two-body
interactions alone.Comment: 9 pages, Revtex4, 7 figs, submitted to PR
Overview of the 2005 cross-language image retrieval track (ImageCLEF)
The purpose of this paper is to outline efforts from the 2005 CLEF crosslanguage image retrieval campaign (ImageCLEF). The aim of this CLEF track is to explore
the use of both text and content-based retrieval methods for cross-language image retrieval. Four tasks were offered in the ImageCLEF track: a ad-hoc retrieval from an historic photographic collection, ad-hoc retrieval from a medical collection, an automatic image annotation task, and a user-centered (interactive) evaluation task that is explained in the iCLEF summary. 24 research groups from a variety of backgrounds and nationalities (14 countries) participated in ImageCLEF. In this paper we describe the ImageCLEF tasks, submissions from participating groups and summarise the main fndings
Numerical Study of a Field Theory for Directed Percolation
A numerical method is devised for study of stochastic partial differential
equations describing directed percolation, the contact process, and other
models with a continuous transition to an absorbing state. Owing to the
heightened sensitivity to fluctuationsattending multiplicative noise in the
vicinity of an absorbing state, a useful method requires discretization of the
field variable as well as of space and time. When applied to the field theory
for directed percolation in 1+1 dimensions, the method yields critical
exponents which compare well against accepted values.Comment: 18 pages, LaTeX, 6 figures available upon request LC-CM-94-00
Reconsidering "the love of art" : evaluating the potential of art museum outreach
Art museums have long been identified as bastions of social and cultural exclusion. This conclusion was best evidenced by the large-scale 1967 French study by Bourdieu and Darbel demonstrating the exclusionary nature of “The Love of Art.” However, in recent years there have been increasing efforts to reach out to a broader range of visitors beyond conventional
audiences. The present study investigates the impacts of an outreach program at a UK art museum, which sought to engage socially excluded young mothers. This study employs ethnographic research methods on a longitudinal basis to develop qualitative insights about the program seeking to mitigate cultural exclusion. While the study’s findings uphold many longstanding critiques of art museums’ conventional approaches, the study also indicates that carefully designed outreach activities can overcome such limitations and enhance cultural
engagement. Thus, art museums’ limited appeal is tied to problematic public engagement practices that can be changed
Phonon-induced quadrupolar ordering of the magnetic superconductor TmNiBC
We present synchrotron x-ray diffraction studies revealing that the lattice
of thulium borocarbide is distorted below T_Q = 13.5 K at zero field. T_Q
increases and the amplitude of the displacements is drastically enhanced, by a
factor of 10 at 60 kOe, when a magnetic field is applied along [100]. The
distortion occurs at the same wave vector as the antiferromagnetic ordering
induced by the a-axis field. A model is presented that accounts for the
properties of the quadrupolar phase and explains the peculiar behavior of the
antiferromagnetic ordering previously observed in this compound.Comment: submitted to PR
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