8,698 research outputs found
Comparison of Material Properties and Microstructure of Specimens Built Using the 3D Systems Vanguard HS and Vanguard HiQ+HSSLS Systems
The HiQ upgrade to the 3D Systems Vanguard selective laser sintering (SLS) machine incorporates a revised thermal calibration system and new control software. The paper compares
the tensile modulus, tensile strength, elongation at break, flexural modulus, Izod impact resistance and microstructure of two batteries of standard specimens built from recycled Duraform
PA (Nylon 12). The first set is built on a Vanguard HS system and the second on the same
system with the HiQ upgrade installed. The upgrade reduces user intervention, decreases total build time and improves surface finish. However, using the default processing parameters,
tensile, flexure and impact properties are all found to decline after the upgrade is installed.Mechanical Engineerin
Dissipation enhanced vibrational sensing in an olfactory molecular switch
Motivated by a proposed olfactory mechanism based on a
vibrationally-activated molecular switch, we study electron transport within a
donor-acceptor pair that is coupled to a vibrational mode and embedded in a
surrounding environment. We derive a polaron master equation with which we
study the dynamics of both the electronic and vibrational degrees of freedom
beyond previously employed semiclassical (Marcus-Jortner) rate analyses. We
show: (i) that in the absence of explicit dissipation of the vibrational mode,
the semiclassical approach is generally unable to capture the dynamics
predicted by our master equation due to both its assumption of one-way
(exponential) electron transfer from donor to acceptor and its neglect of the
spectral details of the environment; (ii) that by additionally allowing strong
dissipation to act on the odorant vibrational mode we can recover exponential
electron transfer, though typically at a rate that differs from that given by
the Marcus-Jortner expression; (iii) that the ability of the molecular switch
to discriminate between the presence and absence of the odorant, and its
sensitivity to the odorant vibrational frequency, are enhanced significantly in
this strong dissipation regime, when compared to the case without mode
dissipation; and (iv) that details of the environment absent from previous
Marcus-Jortner analyses can also dramatically alter the sensitivity of the
molecular switch, in particular allowing its frequency resolution to be
improved. Our results thus demonstrate the constructive role dissipation can
play in facilitating sensitive and selective operation in molecular switch
devices, as well as the inadequacy of semiclassical rate equations in analysing
such behaviour over a wide range of parameters.Comment: 12 pages, 6 figures, close to published version, comments welcom
A Systematic Review of Music Therapy Practice and Outcomes with Acute Adult Psychiatric In-Patients
PMCID: PMC3732280This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
The Distribution of Nearby Stars in Velocity Space Inferred from Hipparcos Data
(abridged) The velocity distribution f(v) of nearby stars is estimated, via a
maximum- likelihood algorithm, from the positions and tangential velocities of
a kinematically unbiased sample of 14369 stars observed by the HIPPARCOS
satellite. f(v) shows rich structure in the radial and azimuthal motions, v_R
and v_phi, but not in the vertical velocity, v_z: there are four prominent and
many smaller maxima, many of which correspond to well known moving groups.
While samples of early-type stars are dominated by these maxima, also up to 25%
of red main-sequence stars are associated with them. These moving groups are
responsible for the vertex deviation measured even for samples of late-type
stars; they appear more frequently for ever redder samples; and as a whole they
follow an asymmetric-drift relation, in the sense that those only present in
red samples predominantly have large |v_R| and lag in v_phi w.r.t. the local
standard of rest (LSR). The question arise, how these old moving groups got on
their eccentric orbits. A plausible mechanism, known from solar system
dynamics, which is able to manage a shift in orbit space involves locking into
an orbital resonance.
Apart from these moving groups, there is a smooth background distribution,
akin to Schwarzschild's ellipsoidal model, with axis ratio of about 1:0.6:0.35
in v_R, v_phi, and v_z. The contours are aligned with the direction, but
not w.r.t. the v_phi and v_z axes: the mean v_z increases for stars rotating
faster than the LSR. This effect can be explained by the stellar warp of the
Galactic disk. If this explanation is correct, the warp's inner edge must not
be within the solar circle, while its pattern rotates with frequency of about
13 km/s/kpc or more retrograde w.r.t. the stellar orbits.Comment: 16 pages LaTeX (aas2pp4.sty), 6 figures, accepted by A
Classification of Singular Fibres on Rational Elliptic Surfaces in Characteristic Three
We determine and list all possible configurations of singular fibres on
rational elliptic surfaces in characteristic three. In total, we find that 267
distinct configurations exist. This result complements Miranda and Persson's
classification in characteristic zero, and Lang's classification in
characteristic two.Comment: 40 Pages. Minor typos correcte
Detecting Generalized Synchronization Between Chaotic Signals: A Kernel-based Approach
A unified framework for analyzing generalized synchronization in coupled
chaotic systems from data is proposed. The key of the proposed approach is the
use of the kernel methods recently developed in the field of machine learning.
Several successful applications are presented, which show the capability of the
kernel-based approach for detecting generalized synchronization. It is also
shown that the dynamical change of the coupling coefficient between two chaotic
systems can be captured by the proposed approach.Comment: 20 pages, 15 figures. massively revised as a full paper; issues on
the choice of parameters by cross validation, tests by surrogated data, etc.
are added as well as additional examples and figure
Dynamical Belyi maps
We study the dynamical properties of a large class of rational maps with
exactly three ramification points. By constructing families of such maps, we
obtain infinitely many conservative maps of degree ; this answers a question
of Silverman. Rather precise results on the reduction of these maps yield
strong information on the rational dynamics.Comment: 21 page
Hard X-ray emitting Active Galactic Nuclei selected by the Chandra Multi-wavelength Project
We present X-ray and optical analysis of 188 AGN identified from 497 hard
X-ray (f (2.0-8.0 keV) > 2.7x10^-15 erg cm^-2 s^-1) sources in 20 Chandra
fields (1.5 deg^2) forming part of the Chandra Multi-wavelength Project. These
medium depth X-ray observations enable us to detect a representative subset of
those sources responsible for the bulk of the 2-8 keV Cosmic X-ray Background.
Brighter than our optical spectroscopic limit, we achieve a reasonable degree
of completeness (77% of X-ray sources with counter-parts r'< 22.5 have been
classified): broad emission line AGN (62%), narrow emission line galaxies
(24%), absorption line galaxies (7%), stars (5%) or clusters (2%). We find that
most X-ray unabsorbed AGN (NH<10^22 cm^-2) have optical properties
characterized by broad emission lines and blue colors, similiar to
optically-selected quasars from the Sloan Digital Sky Survey but with a slighly
broader color distribution. However, we also find a significant population of
redder (g'-i'>1.0) AGN with broad optical emission lines. Most of the X-ray
absorbed AGN (10^22<NH<10^24 cm^-2) are associated with narrow emission line
galaxies, with red optical colors characteristically dominated by luminous,
early type galaxy hosts rather than from dust reddening of an AGN. We also find
a number of atypical AGN; for instance, several luminous AGN show both strong
X-ray absorption (NH>10^22 cm^-2) and broad emission lines. Overall, we find
that 81% of X-ray selected AGN can be easily interpreted in the context of
current AGN unification models. Most of the deviations seem to be due to an
optical contribution from the host galaxies of the low luminosity AGN.Comment: 26 pages; 13 figures (7 color); accepted for publication in the
Astrophysical Journa
Accessory and anomalous atrioventricular valvar tissue causing outflow tract obstruction Surgical implications of a heterogeneous and complex problem
AbstractObjectives. The purpose of this study was to determine the effect of accessory or anomalous atrioventricular valvar apparatus on relief of outflow tract obstruction.Background. Outflow tract obstruction due to accessory tissue or anomalous attachments of the atrioventricular valvar apparatus is an unusual but well-recognized problem. In addition to obstruction, anomalous attachments of the atrioventricular valvar apparatus may interfere with procedures to relieve outflow tract obstruction or perform outflow tract reconstruction.Methods. Since 1992, we have operated on 21 patients (median age 4 years) with systemic (n = 13), pulmonary (n = 5) or bilateral (n = 3) outflow tract obstruction due to accessory atrioventricular valvar tissue and/or anomalous attachments of the subvalvar apparatus. Primary diagnoses were isolated obstruction of the systemic outflow tract or aortic arch (n = 7), transposition complexes (n = 6), previously repaired atrioventricular septal defect (n = 3), functionally single ventricle (n = 3) and ventricular septal defect with pulmonary outflow obstruction (n = 2). Outflow tract gradients ranged from 20–110 mm Hg (median 58 mm Hg).Results. Complete relief of obstruction due to atrioventricular valvar anomalies was possible in 14 patients. In six patients, the planned procedure either had to be modified or only partial relief of the obstruction was achieved. In the remaining patient, who had borderline functionally single ventricle heart disease (unbalanced atrioventricular septal defect) and systemic outflow obstruction due to accessory and functional valvar apparatus, support was withdrawn because the parents refused univentricular palliation and the valvar anomalies precluded a Ross-Konno procedure. There were two early deaths. At follow-up ranging from 1 to 66 months (median 27 months), there was one death, and there has been no recurrence of outflow tract obstruction or residual atrioventricular valvar tissue.Conclusions. Outflow tract obstruction caused by accessory or anomalous atrioventricular valvar structures is an uncommon and heterogeneous group of conditions that can have significant surgical implications. In the majority of cases, tailoring of surgical techniques will permit complete relief of obstruction. However, such anomalies may limit standard surgical options and necessitate an innovative approach in some patients
The Luminosity Function of X-ray Selected Active Galactic Nuclei: Evolution of Supermassive Black Holes at High Redshift
We present a measure of the hard (2-8 keV) X-ray luminosity function (XLF) of
Active Galactic Nuclei up to z~5. At high redshifts, the wide area coverage of
the Chandra Multiwavength Project is crucial to detect rare and luminous (Lx >
10^44 erg s^-1) AGN. The inclusion of samples from deeper published surveys,
such as the Chandra Deep Fields, allows us to span the lower Lx range of the
XLF. Our sample is selected from both the hard (z 6.3x10^-16
erg cm^-2 s^-1) and soft (z > 3; f(0.5-2.0 keV) > 1.0x10^-16 erg cm^-2 s^-1)
energy band detections. Within our optical magnitude limits (r',i' < 24), we
achieve an adequate level of completeness (>50%) regarding X-ray source
identification (i.e., redshift). We find that the luminosity function is
similar to that found in previous X-ray surveys up to z~3 with an evolution
dependent upon both luminosity and redshift. At z > 3, there is a significant
decline in the numbers of AGN with an evolution rate similar to that found by
studies of optically-selected QSOs. Based on our XLF, we assess the resolved
fraction of the Cosmic X-ray Background, the cumulative mass density of
Supermassive Black Holes (SMBHs), and the comparison of the mean accretion rate
onto SMBHs and the star formation history of galaxies as a function of
redshift. A coevolution scenario up to z~2 is plausible though at higher
redshifts the accretion rate onto SMBHs drops more rapidly. Finally, we
highlight the need for better statistics of high redshift AGN at z > 3, which
is achievable with the upcoming Chandra surveys.Comment: Accepted for publication in ApJ; 25 pages, 18 figure
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