Predicting the movements of permanently installed electrodes on an active landslide using time-lapse geoelectrical resistivity data only

If electrodes move during geoelectrical resistivity monitoring and their new positions are not incorporated in the inversion, then the resulting tomographic images exhibit artefacts that can obscure genuine time-lapse resistivity changes in the subsurface. The effects of electrode movements on time-lapse resistivity tomography are investigated using a simple analytical model and real data. The correspondence between the model and the data is sufficiently good to be able to predict the effects of electrode movements with reasonable accuracy. For the linear electrode arrays and 2D inversions under consideration, the data are much more sensitive to longitudinal than transverse or vertical movements. Consequently the model can be used to invert the longitudinal offsets of the electrodes from their known baseline positions using only the time-lapse ratios of the apparent resistivity data. The example datasets are taken from a permanently installed electrode array on an active lobe of a landslide. Using two sets with different levels of noise and subsurface resistivity changes, it is found that the electrode positions can be recovered to an accuracy of 4 % of the baseline electrode spacing. This is sufficient to correct the artefacts in the resistivity images, and provides for the possibility of monitoring the movement of the landslide and its internal hydraulic processes simultaneously using electrical resistivity tomography only

A photometricity and extinction monitor at the Apache Point Observatory

An unsupervised software ``robot'' that automatically and robustly reduces and analyzes CCD observations of photometric standard stars is described. The robot measures extinction coefficients and other photometric parameters in real time and, more carefully, on the next day. It also reduces and analyzes data from an all-sky $10 \mu m$ camera to detect clouds; photometric data taken during cloudy periods are automatically rejected. The robot reports its findings back to observers and data analysts via the World-Wide Web. It can be used to assess photometricity, and to build data on site conditions. The robot's automated and uniform site monitoring represents a minimum standard for any observing site with queue scheduling, a public data archive, or likely participation in any future National Virtual Observatory.Comment: accepted for publication in A

Cosmic homogeneity demonstrated with luminous red galaxies

We test the homogeneity of the Universe at $z\sim 0.3$ with the Luminous Red Galaxy (LRG) spectroscopic sample of the Sloan Digital Sky Survey. First, the mean number $N(R)$ of LRGs within completely surveyed LRG-centered spheres of comoving radius $R$ is shown to be proportional to $R^3$ at radii greater than $R\sim 70 h^{-1} \mathrm{Mpc}$. The test has the virtue that it does not rely on the assumption that the LRG sample has a finite mean density; its results show, however, that there \emph{is} such a mean density. Secondly, the survey sky area is divided into 10 disjoint solid angular regions and the fractional rms density variations of the LRG sample in the redshift range $0.2<z<0.35$ among these ($\sim 2\times10^7 h^{-3} \mathrm{Mpc^3}$) regions is found to be 7 percent of the mean density. This variance is consistent with typical biased \lcdm models and puts very strong constraints on the quality of SDSS photometric calibration.Comment: submitted to Ap

Age-related mitochondrial DNA depletion and the impact on pancreatic beta cell function

Type 2 diabetes is characterised by an age-related decline in insulin secretion. We previously identified a 50% age-related decline in mitochondrial DNA (mtDNA) copy number in isolated human islets. The purpose of this study was to mimic this degree of mtDNA depletion in MIN6 cells to determine whether there is a direct impact on insulin secretion. Transcriptional silencing of mitochondrial transcription factor A, TFAM, decreased mtDNA levels by 40% in MIN6 cells. This level of mtDNA depletion significantly decreased mtDNA gene transcription and translation, resulting in reduced mitochondrial respiratory capacity and ATP production. Glucose-stimulated insulin secretion was impaired following partial mtDNA depletion, but was normalised following treatment with glibenclamide. This confirms that the deficit in the insulin secretory pathway precedes K+ channel closure, indicating that the impact of mtDNA depletion is at the level of mitochondrial respiration. In conclusion, partial mtDNA depletion to a degree comparable to that seen in aged human islets impaired mitochondrial function and directly decreased insulin secretion. Using our model of partial mtDNA depletion following targeted gene silencing of TFAM, we have managed to mimic the degree of mtDNA depletion observed in aged human islets, and have shown how this correlates with impaired insulin secretion. We therefore predict that the age-related mtDNA depletion in human islets is not simply a biomarker of the aging process, but will contribute to the age-related risk of type 2 diabetes

Investigating Ca II emission in the RS CVn binary ER Vulpeculae using the Broadening Function Formalism

The synchronously rotating G stars in the detached, short-period (0.7 d), partially eclipsing binary, ER Vul, are the most chromospherically active solar-type stars known. We have monitored activity in the Ca II H & K reversals for almost an entire orbit. Rucinski's Broadening Function Formalism allows the photospheric contribution to be objectively subtracted from the highly blended spectra. The power of the BF technique is also demonstrated by the good agreement of radial velocities with those measured by others from less crowded spectral regions. In addition to strong Ca II emission from the primary and secondary, there appears to be a high-velocity stream flowing onto the secondary where it stimulates a large active region on the surface 30 - 40 degrees in advance of the sub-binary longitude. A model light curve with a spot centered on the same longitude also gives the best fit to the observed light curve. A flare with approximately 13% more power than at other phases was detected in one spectrum. We suggest ER Vul may offer a magnified view of the more subtle chromospheric effects synchronized to planetary revolution seen in certain `51 Peg'-type systems.Comment: Accepted to AJ; 17 pages and 16 figure

Asymmetric preference formation in willingness to pay estimates in discrete choice models

Individuals when faced with choices amongst a number of alternatives often adopt a variety of processing rules, ranging from simple linear to complex non-linear treatment of each attribute defining the offer of each alternative. In this paper we investigate the presence of asymmetry in preferences to test for reference effects and differential willingness to pay according to whether we are valuing gains or losses. The findings offer clear evidence of an asymmetrical response to increases and decreases in attributes when compared to the corresponding values for a reference alternative, where the degree of asymmetry varies across attributes and population segments

Selection and photometric properties of K+A galaxies

Two different simple measurements of galaxy star formation rate with different timescales are compared empirically on $156,395$ fiber spectra of galaxies with $r<17.77$ mag taken from the Sloan Digital Sky Survey in the redshift range $0.05<z<0.20$: a ratio \Aamp / \Kamp found by fitting a linear sum of an average old stellar poplulation spectrum (\Kamp) and average A-star spectrum (\Aamp) to the galaxy spectrum, and the equivalent width (EW) of the \Halpha emission line. The two measures are strongly correlated, but there is a small clearly separated population of outliers from the median correlation that display excess \Aamp /\Kamp relative to \Halpha EW. These ``K+A'' (or ``E+A'') galaxies must have dramatically decreased their star-formation rates over the last $\sim 1$ Gyr. The K+A luminosity distribution is very similar to that of the total galaxy population. The K+A population appears to be bulge-dominated, but bluer and higher surface-brightness than normal bulge-dominated galaxies; it appears that K+A galaxies will fade with time into normal bulge-dominated galaxies. The inferred rate density for K+A galaxy formation is $\sim 10^{-4} h^3 Mpc^{-3} Gyr^{-1}$ at redshift $z\sim 0.1$. These events are taking place in the field; K+A galaxies don't primarily lie in the high-density environments or clusters typical of bulge-dominated populations.Comment: submitted to Ap

NYU-VAGC: a galaxy catalog based on new public surveys

Here we present the New York University Value-Added Galaxy Catalog (NYU-VAGC), a catalog of local galaxies (mostly below a redshift of about 0.3) based on a set of publicly-released surveys (including the 2dFGRS, 2MASS, PSCz, FIRST, and RC3) matched to the Sloan Digital Sky Survey (SDSS) Data Release 2. Excluding areas masked by bright stars, the photometric sample covers 3514 square degrees and the spectroscopic sample covers 2627 square degrees (with about 85% completeness). Earlier, proprietary versions of this catalog have formed the basis of many SDSS investigations of the power spectrum, correlation function, and luminosity function of galaxies. We calculate and compile derived quantities (for example, K-corrections and structural parameters for galaxies). The SDSS catalog presented here is photometrically recalibrated, reducing systematic calibration errors across the sky from about 2% to about 1%. We include an explicit description of the geometry of the catalog, including all imaging and targeting information as a function of sky position. Finally, we have performed eyeball quality checks on a large number of objects in the catalog in order to flag deblending and other errors. This catalog is complementary to the SDSS Archive Servers, in that NYU-VAGC's calibration, geometrical description, and conveniently small size are specifically designed for studying galaxy properties and large-scale structure statistics using the SDSS spectroscopic catalog.Comment: accepted by AJ; full resolution version available at http://sdss.physics.nyu.edu/vagc/va_paper.ps; data files available at http://sdss.physics.nyu.edu/vagc