56,681 research outputs found
Transverse-Longitudinal Coupling by Space Charge in Cyclotrons
A method is presented that enables to compute the parameters of matched beams
with space charge in cyclotrons with emphasis on the effect of the
transverse-longitudinal coupling. Equations describing the
transverse-longitudinal coupling and corresponding tune-shifts in first order
are derived for the model of an azimuthally symmetric cyclotron. The
eigenellipsoid of the beam is calculated and the transfer matrix is transformed
into block-diagonal form. The influence of the slope of the phase curve on the
transverse-longitudinal coupling is accounted for. The results are generalized
and numerical procedures for the case of an AVF cyclotron are presented. The
algorithm is applied to the PSI Injector II and Ring cyclotron and the results
are compared to TRANSPORT.Comment: 8 pages, 2 figure
On Steering Swarms
The main contribution of this paper is a novel method allowing an external
observer/controller to steer and guide swarms of identical and
indistinguishable agents, in spite of the agents' lack of information on
absolute location and orientation. Importantly, this is done via simple global
broadcast signals, based on the observed average swarm location, with no need
to send control signals to any specific agent in the swarm
Possible High-Redshift, Low-Luminosity AGN Activity in the Hubble Deep Field
In the Hubble Deep Field (HDF), twelve candidate sources of high-redshift (z
> 3.5) AGN activity have been identified. The color selection criteria were
established by passing spectra of selected quasars and Seyfert galaxies
(appropriately redshifted and modified for "Lyman forest" absorption), as well
as stars, observed normal and starburst galaxies, and galaxy models for various
redshifts through the filters used for the HDF observations. The actual
identification of AGN candidates also involved convolving a
Laplacian-of-Gaussian filter with the HDF images, thereby removing relatively
flat galactic backgrounds and leaving only the point-like components in the
centers. Along with positions and colors, estimated redshifts and absolute
magnitudes are reported, with the candidates falling toward the faint end of
the AGN luminosity function. One candidate has been previously observed
spectroscopically, with a measured redshift of 4.02. The number of sources
reported here is consistent with a simple extrapolation of the observed quasar
luminosity function to magnitude 30 in B_Johnson. Implications for ionization
of the intergalactic medium and for gravitational lensing are discussed.Comment: 10 pages LaTex plus 2 separate files (Table 1 which is a two-page
landscape LaTex file; and Figure 6 which is a large (0.7 MB) non-encapsulated
postscript file). Accepted for publication in the Astronomical Journa
Boxfishes (Teleostei: Ostraciidae) as a model system for fishes swimming with many fins: kinematics
Swimming movements in boxfishes were much more
complex and varied than classical descriptions indicated.
At low to moderate rectilinear swimming speeds
(<5 TL s^(-1), where TL is total body length), they were
entirely median- and paired-fin swimmers, apparently
using their caudal fins for steering. The pectoral and
median paired fins generate both the thrust needed for
forward motion and the continuously varied, interacting
forces required for the maintenance of rectilinearity. It
was only at higher swimming speeds (above 5 TL s^(-1)), when
burst-and-coast swimming was used, that they became
primarily body and caudal-fin swimmers. Despite their
unwieldy appearance and often asynchronous fin beats,
boxfish swam in a stable manner. Swimming boxfish used
three gaits. Fin-beat asymmetry and a relatively nonlinear
swimming trajectory characterized the first gait
(0–1 TL s^(-1)). The beginning of the second gait (1–3 TL s^(-1))
was characterized by varying fin-beat frequencies and
amplitudes as well as synchrony in pectoral fin motions.
The remainder of the second gait (3–5 TL s^(-1)) was
characterized by constant fin-beat amplitudes, varying finbeat
frequencies and increasing pectoral fin-beat
asynchrony. The third gait (>5 TL s^(-1)) was characterized
by the use of a caudal burst-and-coast variant. Adduction
was always faster than abduction in the pectoral fins.
There were no measurable refractory periods between
successive phases of the fin movement cycles. Dorsal and
anal fin movements were synchronized at speeds greater
than 2.5 TL s^(-1), but were often out of phase with pectoral
fin movements
Exponential dynamical localization for the almost Mathieu operator
We prove that the exponential moments of the position operator stay bounded
for the supercritical almost Mathieu operator with Diophantine frequency
Analyzing P300 Distractors for Target Reconstruction
P300-based brain-computer interfaces (BCIs) are often trained per-user and
per-application space. Training such models requires ground truth knowledge of
target and non-target stimulus categories during model training, which imparts
bias into the model. Additionally, not all non-targets are created equal; some
may contain visual features that resemble targets or may otherwise be visually
salient. Current research has indicated that non-target distractors may elicit
attenuated P300 responses based on the perceptual similarity of these
distractors to the target category. To minimize this bias, and enable a more
nuanced analysis, we use a generalized BCI approach that is fit to neither user
nor task. We do not seek to improve the overall accuracy of the BCI with our
generalized approach; we instead demonstrate the utility of our approach for
identifying target-related image features. When combined with other intelligent
agents, such as computer vision systems, the performance of the generalized
model equals that of the user-specific models, without any user specific data.Comment: 4 pages, 3 figure
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Where's the harm? A social marketing approach to reframing 'problem' drinking cultures
Alcohol consumption is often linked to a broad range of social and health problems, yet alcohol also plays a fundamental role in social bonding between people. This paper considers the potential of social marketing to contribute to alcohol consumption reduction and reframe social norms that encourage 'problem' drinking. Based on qualitative research with a variety of Scottish drinkers, the paper emphasises how and why a better understanding of the culturally bound meanings of alcohol (e.g. social identity, self-concept) are of crucial importance to inform any social marketing approach to reframing excessive drinking
An Experiment to Evaluate Skylab Earth Resources Sensors for Detection of the Gulf Stream
The author has identified the following significant results. An experiment to evaluate the Skylab earth resources package for observing ocean currents was performed in the Straits of Florida in January 1974. Data from the S190 photographic facility, S191 spectroradiometer and S192 multispectral scanner, were compared with surface observations. The anticyclonic edge of the Gulf Stream could be identified in the Skylab S190A and B photographs, but the cyclonic edge was obscured by clouds. The aircraft photographs were judged not useful for spectral analysis because vignetting caused the blue/green ratios to be dependent on the position in the photograph. The spectral measurement technique could not identify the anticyclonic front, but mass of Florida Bay water which was in the process of flowing into the Straits could be identified and classified. Monte Carlo simulations of the visible spectrum showed that the aerosol concentration could be estimated and a correction technique was devised
Generalization properties of finite size polynomial Support Vector Machines
The learning properties of finite size polynomial Support Vector Machines are
analyzed in the case of realizable classification tasks. The normalization of
the high order features acts as a squeezing factor, introducing a strong
anisotropy in the patterns distribution in feature space. As a function of the
training set size, the corresponding generalization error presents a crossover,
more or less abrupt depending on the distribution's anisotropy and on the task
to be learned, between a fast-decreasing and a slowly decreasing regime. This
behaviour corresponds to the stepwise decrease found by Dietrich et al.[Phys.
Rev. Lett. 82 (1999) 2975-2978] in the thermodynamic limit. The theoretical
results are in excellent agreement with the numerical simulations.Comment: 12 pages, 7 figure
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