The Luminosity Function of Nearby Galaxy Clusters II: Redshifts and Luminosity Function for Galaxies in the Region of the Centaurus Cluster

We acquired spectra for a random sample of galaxies within a 0.83 square degree region centered on the core of the Centaurus cluster. Radial velocities were obtained for 225 galaxies to limiting magnitudes of V < 19.5. Of the galaxies for which velocities were obtained, we find 35% to be member galaxies. Of the 78 member galaxies, magnitudes range from 11.8 < V < 18.5 (-21.6 < M_{V} < -14.9 for H_o = 70 km s^-1 Mpc^-1) with a limiting central surface brightness of \mu_o < 22.5 mag arcsec^-2. We constructed the cluster galaxy luminosity function by using these spectroscopic results to calculate the expected fraction of cluster members in each magnitude bin. The faint-end slope of the luminosity function using this method is shallower than the one obtained using a statistical method to correct for background galaxy contamination. We also use the spectroscopy results to define surface brightness criteria to establish membership for the full sample. Using these criteria, we find a luminosity function very similar to the one constructed with the statistical background correction. For both, we find a faint-end slope alpha ~ -1.4. Adjusting the surface brightness membership criteria we find that the data are consistent with a faint-end slope as shallow as -1.22 or as steep as -1.50. We describe in this paper some of the limitations of using these methods for constructing the galaxy luminosity function.Comment: 16 pages, 12 figures, accepted by A

Protein folding kinetics: barrier effects in chemical and thermal denaturation experiments

10 pages, 5 figures.-- PMID: 17419630 [PubMed].-- PMCID: PMC2527040.-- Author manuscript available in PMC: http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=17419630Printed version published on May 2, 2007.Recent experimental work on fast protein folding brings about an intriguing paradox. Microsecond-folding proteins are supposed to fold near or at the folding speed limit (downhill folding), but yet their folding behavior seems to comply with classical two-state analyses, which imply the crossing of high free energy barriers. However, close inspection of chemical and thermal denaturation kinetic experiments in fast-folding proteins reveals systematic deviations from two-state behavior. Using a simple one-dimensional free energy surface approach we find that such deviations are indeed diagnostic of marginal folding barriers. Furthermore, the quantitative analysis of available fast-kinetic data indicates that many microsecond-folding proteins fold downhill in native conditions. All of these proteins are then promising candidates for an atom-by-atom analysis of protein folding using nuclear magnetic resonance. We also find that the diffusion coefficient for protein folding is strongly temperature dependent, corresponding to an activation energy of ~1 kJ·mol-1 per protein residue. As a consequence, the folding speed limit at room temperature is about an order of magnitude slower than the ~ 1 μs estimates from high-temperature T-jump experiments. Our analysis is quantitatively consistent with the available thermodynamic and kinetic data on slow two-state folding proteins and provides a straightforward explanation for the apparent fast-folding paradox.This research has been supported by NIH grant GM066800-1 and NSF grant MCB-0317294.Peer reviewe

Detectability of Weakly Interacting Massive Particles in the Sagittarius Dwarf Tidal Stream

Tidal streams of the Sagittarius dwarf spheroidal galaxy (Sgr) may be showering dark matter onto the solar system and contributing approx (0.3--23)% of the local density of our Galactic Halo. If the Sagittarius galaxy contains WIMP dark matter, the extra contribution from the stream gives rise to a step-like feature in the energy recoil spectrum in direct dark matter detection. For our best estimate of stream velocity (300 km/sec) and direction (the plane containing the Sgr dwarf and its debris), the count rate is maximum on June 28 and minimum on December 27 (for most recoil energies), and the location of the step oscillates yearly with a phase opposite to that of the count rate. In the CDMS experiment, for 60 GeV WIMPs, the location of the step oscillates between 35 and 42 keV, and for the most favorable stream density, the stream should be detectable at the 11 sigma level in four years of data with 10 keV energy bins. Planned large detectors like XENON, CryoArray and the directional detector DRIFT may also be able to identify the Sgr stream.Comment: 26 pages, 4 figure

Novel measurement-based efficient computational approach to modeling optical power transmission in step-index polymer optical fiber

Polymer optical fibers (POFs) are playing an important role in industrial applications nowadays due to their ease of handling and resilience to bending and environmental effects. A POF can tolerate a bending radius of less than 20 mm, it can work in environments with temperatures ranging from -55¿ C to +105¿ C, and its lifetime is around 20 years. In this paper, we propose a novel, rigorous, and efficient computational model to estimate the most important parameters that determine the characteristics of light propagation through a step-index polymer optical fiber (SIPOF). The model uses attenuation, diffusion, and mode group delay as functions of the propagation angle to characterize the optical power transmission in the SI-POF. Taking into consideration the mode group delay allows us to generalize the computational model to be applicable to POFs with different index profiles. In particular, we use experimental measurements of spatial distributions and frequency responses to derive accurate parameters for our SI-POF simulation model. The experimental data were measured at different fiber lengths according to the cut-back method. This method consists of taking several measurements such as frequency responses, angular intensity distributions, and optical power measurements over a long length of fiber (>100 m), then cutting back the fiber while maintaining the same launching conditions and repeating the measurements on the shorter lengths of fiber. The model derivation uses an objective function to minimize the differences between the experimental measurements and the simulated results. The use of the matrix exponential method (MEM) to implement the SI-POF model results in a computationally efficient model that is suitable for POF-based system-level studies. The efficiency gain is due to the independence of the calculation time with respect to the fiber length, in contrast to the classic analytical solutions of the time-dependent power flow equation. The robustness of the proposed model is validated by calculating the goodness-of-fit of the model predictions relative to experimental data. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Genetic consequences of Quaternary climatic oscillations in the Himalayas: Primula tibetica as a case study based on restriction site-associated DNA sequencing.

The effects of Quaternary climatic oscillations on the demography of organisms vary across regions and continents. In taxa distributed in Europe and North America, several paradigms regarding the distribution of refugia have been identified. By contrast, less is known about the processes that shaped the species' spatial genetic structure in areas such as the Himalayas, which is considered a biodiversity hotspot. Here, we investigated the phylogeographic structure and population dynamics of Primula tibetica by combining genomic phylogeography and species distribution models (SDMs). Genomic data were obtained for 293 samples of P. tibetica using restriction site-associated DNA sequencing (RADseq). Ensemble SDMs were carried out to predict potential present and past distribution ranges. Four distinct lineages were identified. Approximate Bayesian computation analyses showed that each of them have experienced both expansions and bottlenecks since their divergence, which occurred during or across the Quaternary glacial cycles. The two lineages at both edges of the distribution were found to be more vulnerable and responded in different ways to past climatic changes. These results illustrate how past climatic changes affected the demographic history of Himalayan organisms. Our findings highlight the significance of combining genomic approaches with environmental data when evaluating the effects of past climatic changes

Investigation of the New Local Group Galaxy VV 124

We present the results of our stellar photometry and spectroscopy for the new Local Group galaxy VV 124 (UGC 4879) obtained with the 6-m BTA telescope. The presence of a few bright supergiants in the galaxy indicates that the current star formation process is weak. The apparent distribution of stars with different ages in VV 124 does not differ from the analogous distributions of stars in irregular galaxies, but the ratio of the numbers of young and old stars indicates that VV 124 belongs to the rare Irr/Sph type of galaxies. The old stars (red giants) form the most extended structure, a thick disk with an exponential decrease in the star number density to the edge. Definitely, the young population unresolvable in images makes a great contribution to the background emission from the central galactic regions. The presence of young stars is also confirmed by the [O III] emission line visible in the spectra that belongs to extensive diffuse galactic regions. The mean radial velocity of several components (two bright supergiants, the unresolvable stellar population, and the diffuse gas) is v_h = -70+/-15 km/s and the velocity with which VV 124 falls into the Local Group is v_LG = -12+/-15 km/s. We confirm the distance to the galaxy D = 1.1+/-0.1 Mpc and the metallicity of red giants ([Fe/H] = -1.37) found by Kopylov et al. (2008).VV 124 is located on the periphery of the Local Group approximately at the same distance from M 31 and our Galaxy and is isolated from other galaxies. The galaxy LeoA nearest to it is 0.5 Mpc away.Comment: 10 pages, 8 figures. Accepted for publication in Astronomy Letters (2010, Vol. 36, No. 5, pp. 309-318

Atmospheric Photo-Oxidation of Acetic Anhydride: Kinetic Study and Reaction Mechanism. Products Distribution and Fate of Ch3c(O)Oc(O)Ch2o·Radical

This is a preprint article, it offers immediate access but has not been peer reviewed.Fil: Vila, Jesús. A. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Vila, Jesús A. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra, Argentina.Fil: Rimondino, Guido N. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Rimondino, Guido N. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba, Argentina.Fil: Peláez, Walter J. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Peláez, Walter J. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba, Argentina.Fil: Kalinowski, Mateo. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Malanca, Fabio E. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Malanca, Fabio E. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba, Argentina.The rate coefficient for the gas-phase reaction of acetic anhydride (Ac2O) with chlorine atoms at 298 K and atmospheric pressure was experimentally determined (kAc2O+Cl = (1.3 ± 0.4) × 10-12 cm3 molec−1 s−1), while the rate coefficient for the reaction with the hydroxyl radical was estimated (kAc2O+OH = 1.9 x 10-13 cm3 molec−1 s−1). For the Structure-Activity Relationship method, a value of 0.02 was determined for the -C(O)OC(O) group. The mechanism of photo-oxidation of acetic anhydride initiated by chlorine atoms was determined and CO, CO2, CH3C(O)OH (32 %), CH3C(O)OC(O)C(O)H, and 3-hydroxy-1,4-dioxane-2,6-dione (20 %) were identified as products by infrared spectroscopy. Here we determined for the first time the relative energies of the primary reaction pathways for the CH3C(O)OC(O)CH2O· radical using computational methods, which confirmed our experimental data. Finally, the environmental implications of acetic anhydride emissions were calculated, showing an atmospheric lifetime between 31 and 220 days for the reaction with atmospheric radicals, while its wet deposition lifetime is 1.5 years.info:eu-repo/semantics/publishedVersionFil: Vila, Jesús. A. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Vila, Jesús A. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra, Argentina.Fil: Rimondino, Guido N. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Rimondino, Guido N. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba, Argentina.Fil: Peláez, Walter J. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Peláez, Walter J. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba, Argentina.Fil: Kalinowski, Mateo. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Malanca, Fabio E. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Malanca, Fabio E. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba, Argentina

Atmospheric Degradation of Acetic Anhydride. Kinetic Study and Reaction Mechanism

This is a preprint article, it offers immediate access but has not been peer reviewed.Fil: Vila, Jesús A. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra, Argentina.Fil: Vila, Jesús. A. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Rimondino, Guido N. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Rimondino, Guido N. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba, Argentina.Fil: Peláez, Walter J. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Peláez, Walter J. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba, Argentina.Fil: Kalinowski, Mateo. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Malanca, Fabio E. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Malanca, Fabio E. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba, Argentina_The rate coefficient for the gas phase reaction of acetic anhydride with chlorine atoms has been experimentally determined at 298 K using a relative method, employing ethyl acetate and acetone as reference compounds. From the experimental value, kAc2O+Cl = (1.6 ± 0.4) × 10-12 cm3 molec−1 s−1, a factor for the -C(O)OC(O) group is presented for the Structure−Activity Relationship method. On the other hand, an estimated value for the rate coefficient for the reaction of acetic anhydride with hydroxyl radical (kAc2O+OH = 1.9 x 10-13 cm3 molec−1 s−1) was performed using a correlation between kinetic data for the reactions of other carbo-oxygenated compounds with both, OH radicals and Cl atoms. The photo-oxidation mechanism of acetic anhydride initiated by chlorine atoms was also studied at 298 K and atmospheric pressure and CO, CO2, CH3C(O)OH, CH3C(O)OC(O)C(O)H and C4O4H4 were identified as products by infrared spectroscopy. In addition, the relative energies of the primary reaction paths for CH3C(O)OC(O)CH2O· radical were determined using computational methods, which confirmed the experimental data and allowed postulating the mechanism of atmospheric degradation. Finally, the environmental implications of the acetic anhydride emissions were calculated, showing an atmospheric lifetime between 31 and 220 days for the reaction with atmospheric radicals, while its wet deposition lifetime is 1.5 year.info:eu-repo/semantics/publishedVersionFil: Vila, Jesús A. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra, Argentina.Fil: Vila, Jesús. A. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Rimondino, Guido N. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Rimondino, Guido N. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba, Argentina.Fil: Peláez, Walter J. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Peláez, Walter J. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba, Argentina.Fil: Kalinowski, Mateo. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Malanca, Fabio E. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica, Argentina.Fil: Malanca, Fabio E. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba, Argentina

HST Colour-Magnitude Diagrams of Six Old Globular Clusters in the LMC

We report on HST observations of six candidate old globular clusters in the Large Magellanic Cloud: NGC 1754, NGC 1835, NGC 1898, NGC 1916, NGC 2005 and NGC 2019. Deep exposures with the F555W and F814W filters provide us with colour-magnitude diagrams that reach to an apparent magnitude in V of ~25, well below the main sequence turnoff. These particular clusters are involved with significantly high LMC field star densities and care was taken to subtract the field stars from the cluster colour-magnitude diagrams accurately. In two cases there is significant variable reddening across at least part of the image, but only for NGC 1916 does the differential reddening preclude accurate measurements of the CMD characteristics. The morphologies of the colour- magnitude diagrams match well those of Galactic globular clusters of similar metallicity. All six have well-developed horizontal branches, while four clearly have stars on both sides of the RR Lyrae gap. The abundances obtained from measurements of the height of the red giant branch above the level of the horizontal branch are 0.3 dex higher, on average, than previously measured spectroscopic abundances. Detailed comparisons with Galactic globular cluster fiducials show that all six clusters are old objects, very similar in age to classical Galactic globulars such as M5, with little age spread among the clusters. This result is consistent with ages derived by measuring the magnitude difference between the horizontal branch and main sequence turnoff. We also find a similar chronology by comparing the horizontal branch morphologies and abundances with the horizontal branch evolutionary tracks of Lee, Demarque, & Zinn (1994). Our results imply that the LMC formed at the same time as the Milky Way Galaxy.Comment: 23 pages, 18 PostScript figures, LaTeX, accepted by MNRAS. Uses mn.sty and epsf.sty. Requires ols.sty (included