5,589 research outputs found
Classification of graph C*-algebras with no more than four primitive ideals
We describe the status quo of the classification problem of graph C*-algebras
with four primitive ideals or less
Structural and Photometric Classification of Galaxies - I. Calibration Based on a Nearby Galaxy Sample
In this paper we define an observationally robust, multi-parameter space for
the classification of nearby and distant galaxies. The parameters include
luminosity, color, and the image-structure parameters: size, image
concentration, asymmetry, and surface brightness. Based on an initial
calibration of this parameter space using the ``normal'' Hubble-types surveyed
by Frei et al. (1996), we find that only a subset of the parameters provide
useful classification boundaries for this sample. Interestingly, this subset
does not include distance-dependent scale parameters, such as size or
luminosity. The essential ingredient is the combination of a spectral index
(e.g., color) with parameters of image structure and scale: concentration,
asymmetry, and surface-brightness. We refer to the image structure parameters
(concentration and asymmetry) as indices of ``form.'' We define a preliminary
classification based on spectral index, form, and surface-brightness (a scale)
that successfully separates normal galaxies into three classes. We
intentionally identify these classes with the familiar labels of Early,
Intermediate, and Late. This classification, or others based on the above four
parameters can be used reliably to define comparable samples over a broad range
in redshift. The size and luminosity distribution of such samples will not be
biased by this selection process except through astrophysical correlations
between spectral index, form, and surface-brightness.Comment: to appear in AJ (June, 2000); 34 pages including 4 tables and 12
figure
Morphological Classification of Galaxies by Shapelet Decomposition in the Sloan Digital Sky Survey II: Multiwavelength Classification
We describe the application of the `shapelet' linear decomposition of galaxy
images to multi-wavelength morphological classification using the
and -band images of 1519 galaxies from the Sloan Digital Sky Survey. We
utilize elliptical shapelets to remove to first-order the effect of inclination
on morphology. After decomposing the galaxies we perform a principal component
analysis on the shapelet coefficients to reduce the dimensionality of the
spectral morphological parameter space. We give a description of each of the
first ten principal component's contribution to a galaxy's spectral morphology.
We find that galaxies of different broad Hubble type separate cleanly in the
principal component space. We apply a mixture of Gaussians model to the
2-dimensional space spanned by the first two principal components and use the
results as a basis for classification. Using the mixture model, we separate
galaxies into three classes and give a description of each class's physical and
morphological properties. We find that the two dominant mixture model classes
correspond to early and late type galaxies, respectively. The third class has,
on average, a blue, extended core surrounded by a faint red halo, and typically
exhibits some asymmetry. We compare our method to a simple cut on color
and find the shapelet method to be superior in separating galaxies.
Furthermore, we find evidence that the decision boundary may not be
optimal for separation between early and late type galaxies, and suggest that
the optimal cut may be .Comment: 42 pages, 18 figs, revised version in press at AJ. Some modification
to the technique, more discussion, addition/deletion/modification of several
figures, color figures have been added. A high resolution version may be
obtained at
http://bllac.as.arizona.edu/~bkelly/shapelets/shapelets_ugriz.ps.g
Force-Extension Relation and Plateau Modulus for Wormlike Chains
We derive the linear force-extension relation for a wormlike chain of
arbitrary stiffness including entropy elasticity, bending and thermodynamic
buckling. From this we infer the plateau modulus of an isotropic
entangled solution of wormlike chains. The entanglement length is
expressed in terms of the characteristic network parameters for three different
scaling regimes in the entangled phase. The entanglement transition and the
concentration dependence of are analyzed. Finally we compare our findings
with experimental data.Comment: 5 pages, 1 eps-figure, to appear in PR
Attractive instability of oppositely charged membranes induced by charge density fluctuations
We predict the conditions under which two oppositely charged membranes show a
dynamic, attractive instability. Two layers with unequal charges of opposite
sign can repel or be stable when in close proximity. However, dynamic charge
density fluctuations can induce an attractive instability and thus facilitate
fusion. We predict the dominant instability modes and timescales and show how
these are controlled by the relative charge and membrane viscosities. These
dynamic instabilities may be the precursors of membrane fusion in systems where
artificial vesicles are engulfed by biological cells of opposite charge
Loss of solutions in shear banding fluids in shear banding fluids driven by second normal stress differences
Edge fracture occurs frequently in non-Newtonian fluids. A similar
instability has often been reported at the free surface of fluids undergoing
shear banding, and leads to expulsion of the sample. In this paper the
distortion of the free surface of such a shear banding fluid is calculated by
balancing the surface tension against the second normal stresses induced in the
two shear bands, and simultaneously requiring a continuous and smooth meniscus.
We show that wormlike micelles typically retain meniscus integrity when shear
banding, but in some cases can lose integrity for a range of average applied
shear rates during which one expects shear banding. This meniscus fracture
would lead to ejection of the sample as the shear banding region is swept
through. We further show that entangled polymer solutions are expected to
display a propensity for fracture, because of their much larger second normal
stresses. These calculations are consistent with available data in the
literature. We also estimate the meniscus distortion of a three band
configuration, as has been observed in some wormlike micellar solutions in a
cone and plate geometry.Comment: 23 pages, to be published in Journal of Rheolog
Putting the diabetes risk due to statins in perspective: A re-evaluation using the complementary outcome
Aims: Statins are used extensively to treat dyslipidemia and have been associated with significant clinical benefit that increases with dose. However, recent studies have associated statins with an excess risk of developing diabetes mellitus, which may offset the clinical benefit to patients. Adverse events related to intensive-dose statin therapy were revisited in light of recent data regarding the use of relative risks. Data synthesis: A meta-analysis was replicated with the event of interest redefined as the complementary outcome (no-onset of diabetes). Five randomised controlled trials that compared the risk of intense-dose with moderate-dose of statin therapy for the onset of diabetes with a follow-up greater than 12 months were included in the analysis. A reduction in the risk for no-onset of diabetes was found when intensive-dose statin therapy was compared with moderate-dose statin therapy, revealing a relative risk of 0.9908 (95%CI: 0.9849-0.99679). Over two years, one more patient was harmed by diabetes onset for every 237 patients exposed to intensive-dose statin therapy (95%CI: 123-3847) compared with standard dose statin therapy. Conclusions: Statins are associated with only a very small increase in risk of diabetes mellitus. Previous research selected the outcomes with the lower baseline risks and therefore the actual risk associated with statins has been largely over-estimated
Role of Multipoles in Counterion-Mediated Interactions between Charged Surfaces: Strong and Weak Coupling
We present general arguments for the importance, or lack thereof, of the
structure in the charge distribution of counterions for counterion-mediated
interactions between bounding symmetrically charged surfaces. We show that on
the mean field or weak coupling level, the charge quadrupole contributes the
lowest order modification to the contact value theorem and thus to the
intersurface electrostatic interactions. The image effects are non-existent on
the mean-field level even with multipoles. On the strong coupling level the
quadrupoles and higher order multipoles contribute additional terms to the
interaction free energy only in the presence of dielectric inhomogeneities.
Without them, the monopole is the only multipole that contributes to the strong
coupling electrostatics. We explore the consequences of these statements in all
their generality.Comment: 12 pages, 3 figure
Shear flow effects on phase separation of entangled polymer blends
We introduce an entanglement model mixing rule for stress relaxation in a polymer blend to a modified Cahn-Hilliard equation of motion for concentration fluctuations in the presence of shear flow. Such an approach predicts both shear-induced mixing and demixing, depending on the relative relaxation times and plateau moduli of the two components
Management of localized energy in discrete nonlinear transmission lines
The manipulation of locked intrinsic localized modes/discrete breathers is
studied experimentally in nonlinear electric transmission line arrays.
Introducing a static lattice impurity in the form of a capacitor, resistor or
inductor has been used both to seed or destroy and attract or repel these
localized excitations. In a nonlinear di-element array counter propagating
short electrical pulses traveling in the acoustic branch are used to generate a
stationary intrinsic localized mode in the optic branch at any particular
lattice site. By changing the pulse polarity the same localized excitation can
be eliminated demonstrating that the dynamical impurity associated with the
propagating electrical pulse in the acoustic branch can trigger optical
localized mode behavior.Comment: submitte
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