275 research outputs found
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
Annexins V and Xii Alter the Properties of Planar Lipid Bilayers Seen by Conductance Probes
Annexins are proteins that bind lipids in the presence of calcium. Though multiple functions have been proposed for annexins, there is no general agreement on what annexins do or how they do it. We have used the well-studied conductance probes nonactin, alamethicin, and tetraphenylborate to investigate how annexins alter the functional properties of planar lipid bilayers. We found that annexin XII reduces the nonactin-induced conductance to âŒ30% of its original value. Both negative lipid and âŒ30 ÎŒM Ca2+ are required for the conductance reduction. The mutant annexin XIIs, E105K and E105K/K68A, do not reduce the nonactin conductance even though both bind to the membrane just as wild-type does. Thus, subtle changes in the interaction of annexins with the membrane seem to be important. Annexin V also reduces nonactin conductance in nearly the same manner as annexin XII. Pronase in the absence of annexin had no effect on the nonactin conductance. But when added to the side of the bilayer opposite that to which annexin was added, pronase increased the nonactin-induced conductance toward its pre-annexin value. Annexins also dramatically alter the conductance induced by a radically different probe, alamethicin. When added to the same side of the bilayer as alamethicin, annexin has virtually no effect, but when added trans to the alamethicin, annexin dramatically reduces the asymmetry of the I-V curve and greatly slows the kinetics of one branch of the curve without altering those of the other. Annexin also reduces the rate at which the hydrophobic anion, tetraphenylborate, crosses the bilayer. These results suggest that annexin greatly reduces the ability of small molecules to cross the membrane without altering the surface potential and that at least some fraction of the active annexin is accessible to pronase digestion from the opposite side of the membrane
UV emission and Star Formation in Stephan's Quintet
we present the first GALEX UV images of the well known interacting group of
galaxies, Stephan's Quintet (SQ). We detect widespread UV emission throughout
the group. However, there is no consistent coincidence between UV structure and
emission in the optical, H\alpha, or HI. Excluding the foreground galaxy
NGC7320 (Sd), most of the UV emission is found in regions associated with the
two spiral members of the group, NGC7319 and NGC7318b, and the intragroup
medium starburst SQ-A. The extinction corrected UV data are analyzed to
investigate the overall star formation activity in SQ. It is found that the
total star formation rate (SFR) of SQ is 6.69+-0.65 M_\sun/yr. Among this,
1.34+-0.16 M_sun/yr is due to SQ-A. This is in excellent agreement with that
derived from extinction corrected H\alpha luminosity of SQ-A. The SFR in
regions related to NGC 7319 is 1.98+-0.58 M_\sun/yr, most of which(68%) is
contributed by the disk. The contribution from the 'young tail' is only 15%. In
the UV, the 'young tail' is more extended (~100 kpc) and shows a loop-like
structure, including the optical tail, the extragalactic HII regions recently
discovered in H\alpha, and other UV emission regions discovered for the first
time. The UV and optical colors of the 'old tail' are consistent with a single
stellar population of age t ~10^{8.5+-0.4} yrs. The UV emission associated with
NGC 7318b is found in a very large (~80 kpc) disk, with a net SFR of 3.37+-0.25
M_sun/yr. Several large UV emission regions are 30 -- 40 kpc away from the
nucleus of NGC7318b. Although both NGC7319 and NGC7318b show peculiar UV
morphology, their SFR is consistent with that of normal Sbc galaxies,
indicating that the strength of star formation activity is not enhenced by
interactions.Comment: This paper will be published as part of the Galaxy Evolution
Explorer(GALEX) Astrophysical Journal Letters Special Issue. Links to the
full set of papers will be available at
http:/www.galex.caltech.edu/PUBLICATIONS/ after November 22, 200
Phase separating binary fluids under oscillatory shear
We apply lattice Boltzmann methods to study the segregation of binary fluid
mixtures under oscillatory shear flow in two dimensions. The algorithm allows
to simulate systems whose dynamics is described by the Navier-Stokes and the
convection-diffusion equations. The interplay between several time scales
produces a rich and complex phenomenology. We investigate the effects of
different oscillation frequencies and viscosities on the morphology of the
phase separating domains. We find that at high frequencies the evolution is
almost isotropic with growth exponents 2/3 and 1/3 in the inertial (low
viscosity) and diffusive (high viscosity) regimes, respectively. When the
period of the applied shear flow becomes of the same order of the relaxation
time of the shear velocity profile, anisotropic effects are clearly
observable. In correspondence with non-linear patterns for the velocity
profiles, we find configurations where lamellar order close to the walls
coexists with isotropic domains in the middle of the system. For particular
values of frequency and viscosity it can also happen that the convective
effects induced by the oscillations cause an interruption or a slowing of the
segregation process, as found in some experiments. Finally, at very low
frequencies, the morphology of domains is characterized by lamellar order
everywhere in the system resembling what happens in the case with steady shear.Comment: 1 table and 12 figures in .gif forma
Tributyltin and mitochondria: new evidence in support of an uncoupling mechanism and further characterization of the transport mechanism
New evidence is given to support the hypothesis that the tributyltin compound (TBT) is an uncoupler of the oxidative phosphorylation in mitochondria. By means of an Arrhenius plot, it has been demonstrated that the transport kinetic of the TBT compound in mitochondria behaves in a manner which is similar to that obtained using classical uncouplers. The break point at 17 8C observed in the Arrhenius plot is interpreted as due to a phase change in the lipidic bilayer, since the TBT compound, like uncouplers and mobile carriers, is sensitive to the phospholipidic phase change. Therefore, we can confirm our previous hypothesis that, as TBT is an uncoupler it, like uncouplers, crosses the biological membranes by means of an electrophoretic mechanism. An understanding of this behaviour is essential when an explanation of the neurotoxicity of TBT is required
The Vimos VLT Deep Survey: Compact structures in the CDFS
We have used the Vimos VLT Deep Survey in combination with other
spectroscopic, photometric and X-ray surveys from literature to detect several
galaxy structures in the Chandra Deep Field South (CDFS). Both a
friend-of-friend based algorithm applied to the spectroscopic redshift catalog
and an adaptative kernel galaxy density and colour maps correlated with
photometric redshift estimates have been used. We mainly detect a chain-like
structure at z=0.66 and two massive groups at z=0.735 and 1.098 showing signs
of ongoing collapse. We also detect two galaxy walls at z=0.66 and at z=0.735
(extremely compact in redshift space). The first one contains the chain-like
structure and the last one contains in its center one of the two massive
groups. Finally, other galaxy structures that are probably loose low mass
groups are detected. We compare the group galaxy population with simulations in
order to assess the richness of these structures and we study their galaxy
morphological contents. The higher redshift structures appear to probably have
lower velocity dispersion than the nearby ones. The number of moderatly massive
structures we detect is consistent with what is expected for an LCDM model, but
a larger sample is required to put significant cosmological constraints.Comment: 15 pages, 17 figures, accepted in A&
The minor role of gas-rich major mergers in the rise of intermediate-mass early types at z <~ 1
We study the evolution of galaxy structure since z ~ 1 to the present. From a
GOODS-S multi-band catalog we define (blue) luminosity- and mass-weighted
samples, limited by M_B = 10^10 M_Sun, comprising 1122 and
987 galaxies, respectively. We extract early-type (E/S0/Sa) and late-type
(Sb-Irr) subsamples by their position in the concentration-asymmetry plane, in
which galaxies exhibit a clear bimodality.
We find that the early-type fraction, f_ET, rises with cosmic time, with a
corresponding decrease in the late-type fraction, f_LT, in both luminosity- and
mass-selected samples. However, the evolution of the comoving number density is
very different: the decrease in the total number density of M_B <= -20 galaxies
since z = 1 is due to the decrease in the late-type population, which accounts
for ~75% of the total star-formation rate in the range under study, while the
increase in the total number density of M_star >= 10^10 M_Sun galaxies in the
same redshift range is due to the evolution of early types. This suggests that
we need a structural transformation between late-type galaxies that form stars
actively and early-type galaxies in which the stellar mass is located.
Comparing the observed evolution with the gas-rich major merger rate in
GOODS-S, we infer that only ~20% of the new early-type galaxies with M_star >=
10^10 M_Sun appeared since z ~ 1 can be explained by this kind of mergers,
suggesting that minor mergers and secular processes may be the driving
mechanisms of the structural evolution of intermediate-mass (M_star ~ 4x10^10
M_Sun) galaxies since z ~ 1.Comment: Matches published version in ApJ. 16 pages, 4 figures, 5 table
Characterization of Membrane Potential Dependency of Mitochondrial Ca2+ Uptake by an Improved Biophysical Model of Mitochondrial Ca2+ Uniporter
Mitochondrial Ca2+ uniporter is the primary influx pathway for Ca2+ into respiring mitochondria, and hence plays a key role in mitochondrial Ca2+ homeostasis. Though the mechanism of extra-matrix Ca2+ dependency of mitochondrial Ca2+ uptake has been well characterized both experimentally and mathematically, the mechanism of membrane potential (ÎΚ) dependency of mitochondrial Ca2+ uptake has not been completely characterized. In this paper, we perform a quantitative reevaluation of a previous biophysical model of mitochondrial Ca2+ uniporter that characterized the possible mechanism of ÎΚ dependency of mitochondrial Ca2+ uptake. Based on a model simulation analysis, we show that model predictions with a variant assumption (Case 2: external and internal Ca2+ binding constants for the uniporter are distinct), that provides the best possible description of the ÎΚ dependency, are highly sensitive to variation in matrix [Ca2+], indicating limitations in the variant assumption (Case 2) in providing physiologically plausible description of the observed ÎΚ dependency. This sensitivity is attributed to negative estimate of a biophysical parameter that characterizes binding of internal Ca2+ to the uniporter. Reparameterization of the model with additional nonnengativity constraints on the biophysical parameters showed that the two variant assumptions (Case 1 and Case 2) are indistinguishable, indicating that the external and internal Ca2+ binding constants for the uniporter may be equal (Case 1). The model predictions in this case are insensitive to variation in matrix [Ca2+] but do not match the ÎΚ dependent data in the domain ÎΚâ€120 mV. To effectively characterize this ÎΚ dependency, we reformulate the ÎΚ dependencies of the rate constants of Ca2+ translocation via the uniporter by exclusively redefining the biophysical parameters associated with the free-energy barrier of Ca2+ translocation based on a generalized, non-linear Goldman-Hodgkin-Katz formulation. This alternate uniporter model has all the characteristics of the previous uniporter model and is also able to characterize the possible mechanisms of both the extra-matrix Ca2+ and ÎΚ dependencies of mitochondrial Ca2+ uptake. In addition, the model is insensitive to variation in matrix [Ca2+], predicting relatively stable physiological operation. The model is critical in developing mechanistic, integrated models of mitochondrial bioenergetics and Ca2+ handling
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