Universal Statistical Behavior of Neural Spike Trains

We construct a model that predicts the statistical properties of spike trains generated by a sensory neuron. The model describes the combined effects of the neuron's intrinsic properties, the noise in the surrounding, and the external driving stimulus. We show that the spike trains exhibit universal statistical behavior over short times, modulated by a strongly stimulus-dependent behavior over long times. These predictions are confirmed in experiments on H1, a motion-sensitive neuron in the fly visual system.Comment: 7 pages, 4 figure

Building professional discourse in emerging markets: Language, context and the challenge of sensemaking

Using ethnographic evidence from the former Soviet republics, this article examines a relatively new and mainly unobserved in the International Business (IB) literature phenomenon of communication disengagement that manifests itself in many emerging markets. We link it to the deficiencies of the local professional business discourse rooted in language limitations reflecting lack of experience with the market economy. This hampers cognitive coherence between foreign and local business entities, adding to the liability of foreignness as certain instances of professional experience fail to find adequate linguistic expression, and complicates cross-cultural adjustments causing multi-national companies (MNCs) financial losses. We contribute to the IB literature by examining cross-border semantic sensemaking through a retrospectively constructed observational study. We argue that a relative inadequacy of the national professional idiom is likely to remain a feature of business environment in post-communist economies for some time and therefore should be factored into business strategies of MNCs. Consequently, we recommend including discursive hazards in the risk evaluation of international projects

Genome-wide estimation of transcript concentrations from spotted cDNA microarray data

A method providing absolute transcript concentrations from spotted microarray intensity data is presented. Number of transcripts per µg total RNA, mRNA or per cell, are obtained for each gene, enabling comparisons of transcript levels within and between tissues. The method is based on Bayesian statistical modelling incorporating available information about the experiment from target preparation to image analysis, leading to realistically large confidence intervals for estimated concentrations. The method was validated in experiments using transcripts at known concentrations, showing accuracy and reproducibility of estimated concentrations, which were also in excellent agreement with results from quantitative real-time PCR. We determined the concentration for 10 157 genes in cervix cancers and a pool of cancer cell lines and found values in the range of 10(5)–10(10) transcripts per µg total RNA. The precision of our estimates was sufficiently high to detect significant concentration differences between two tumours and between different genes within the same tumour, comparisons that are not possible with standard intensity ratios. Our method can be used to explore the regulation of pathways and to develop individualized therapies, based on absolute transcript concentrations. It can be applied broadly, facilitating the construction of the transcriptome, continuously updating it by integrating future data

Mass-Selection and the Evolution of the Morphology-Density Relation from z=0.8 to z=0

We examined the morphology-density relations for galaxy samples selected by luminosity and by mass in each of five massive X-ray clusters from z=0.023 to 0.83 for 674 spectroscopically-confirmed members. Rest-frame optical colors and visual morphologies were obtained primarily from Hubble Space Telescope images. Morphology-density relations (MDR) are derived in each cluster from a complete, luminosity-selected sample of 452 galaxies with a magnitude limit M_V < M^{*}_{V} + 1. The change in the early-type fraction with redshift matches previous work for massive clusters of galaxies. We performed a similar analysis, deriving MDRs for complete, mass-selected samples of 441 galaxies with a mass-limit of 10^{10.6} M_{\sun}. Our mass limit includes faint objects, the equivalent of =~1 mag below L^{*} for the red cluster galaxies, and encompasses =~70% of the stellar mass in cluster galaxies. The MDRs in the mass-selected sample at densities of Sigma > 50 galaxies Mpc^{-2} are similar to those in the luminosity-selected sample but show larger early-type fractions. However, the trend with redshift in the fraction of elliptical and S0 galaxies with masses > 10^{10.6} M_{\sun} differs significantly between the mass- and luminosity-selected samples. The clear trend seen in the early-type fraction from z=0 to z=~ 0.8 is not found in mass-selected samples. The early-type galaxy fraction changes much less, and is consistent with being constant at 92% +/- 4% at \Sigma> 500 galaxies Mpc^{-2} and 83 +/- 3% at 50 < \Sigma < 500 galaxies Mpc^{-2}. This suggests that galaxies of mass lower than > 10^{10.6} M_{\sun} play a significant role in the evolution of the early-type fraction in luminosity-selected samples. (Abstract abridged)Comment: 18 pages in emulate ApJ format, with 10 color figures, Accepted to ApJ. Version updated to reflect published version, includes new references and a correction to table

Measuring the cultural value of the Royal Scottish Academy New Contemporaries Exhibition as a platform for emerging artists

In our analysis of the cultural value of the Royal Scottish Academy New Contemporaries Exhibition, we assessed the institution’s role in shaping emerging artists’ careers, as well as wider cultural value. Supported by our conceptual framework of value creation, issues assessed included the expected versus experienced value of the exhibition and the individual artworks, price setting, the market mechanism surrounding the exhibition, and its enhancement. The created cultural value is facilitated by high-visibility media exposure and through development of career-enhancing networks. We have generated new insight into cultural value more generally by moving beyond dominant instrumental valuation approaches. We have addressed many of the gaps in understanding the mechanisms behind engagement with contemporary art. We have progressed theory with the assistance of our conceptual framework and supporting qualitative data. Cultural value is expressed in contemporary art through artistic production systems and its cultural messages. Artists’ cultural value is often constructed via the intrinsic worth of their work, rather than from market influences. Cultural value is often personal to the viewer, shared with others and remembered over time. It is also co-created among the other stakeholders involved

Quantitative measure of evolution of bright cluster galaxies at moderate redshifts

Using archival data from the Hubble Space Telescope, we study the quantitative morphological evolution of spectroscopically confirmed bright galaxies in the core regions of nine clusters ranging in redshift from $z = 0.31$ to $z = 0.84$. We use morphological parameters derived from two dimensional bulge-disk decomposition to study the evolution. We find an increase in the mean bulge-to-total luminosity ratio $B/T$ as the Universe evolves. We also find a corresponding increase in the fraction of early type galaxies and in the mean S\'ersic index. We discuss these results and their implications to physical mechanisms for evolution of galaxy morphology.Comment: 5 pages, 3 figures, Accepted for publication in MNRAS: Letter

An X-ray review of MS1054-0321: hot or not?

XMM-Newton observations are presented for the z=0.83 cluster of galaxies MS1054-0321, the highest redshift cluster in the Einstein Extended Medium Sensitivity Survey (EMSS). The temperature inferred by the XMM-Newton data, T=7.2 (+0.7, -0.6) keV, is much lower than the temperature previously reported from ASCA data, T=12.3 (+3.1, -2.2) keV (Donahue et al. 1998), and a little lower than the Chandra temperature, T=10.4(+1.7, -1.5) keV, determined by Jeltema et al. 2001. The discrepancy between the newly derived temperature and the previously derived temperatures is discussed in detail. If one allows the column density to be a free parameter, then the best fit temperature becomes T=8.6 (+1.2, -1.1) keV, and the best fit column density becomes N_(H)=1.33 (+0.15 -0.14) x 10^20 atoms/cm^2. The iron line is well detected in the XMM-Newton spectrum with a value for the abundance of Z=0.33 (+0.19 -0.18) Zsol, in very good agreement with previous determinations. The derived XMM X-ray luminosity for the overall cluster in the 2-10 keV energy band is L_X=(3.81 +/- 0.19) x 10^44 h^-2 erg s^-1 while the bolometric luminosity is L_BOL=(8.05+/-0.40) x 10^44 h^-2 erg s^-1. The XMM-Newton data confirm the substructure in the cluster X-ray morphology already seen by ROSAT and in much more detail by Chandra. The central weak lensing clump is coincident with the main cluster component and has a temperature T=8.1 (+1.3, -1.2) keV. The western weak lensing clump coincides with the western X-ray component which is much cooler with a temperature T=5.6 (+0.8, -0.6)$ keV. Given the newly determined temperature, MS1054-0321 is no longer amongst the hottest clusters known.Comment: To appear in the A&A main Journal, 13 pages including 3 postscript figures and 4 tables. Figs. 1, 4, 5 and 7 are too large and are not given here. The whole paper as pdf file is posted at http://www.ira.cnr.it/~gioia/PUB/publications.htm

Shear dynamics in Bianchi I cosmologies with R^n-gravity

We give the equations governing the shear evolution in Bianchi spacetimes for general f(R)-theories of gravity. We consider the case of R^n-gravity and perform a detailed analysis of the dynamics in Bianchi I cosmologies which exhibit local rotational symmetry. We find exact solutions and study their behaviour and stability in terms of the values of the parameter n. In particular, we found a set of cosmic histories in which the universe is initially isotropic, then develops shear anisotropies which approaches a constant value.Comment: 25 pages LaTeX, 6 figures. Revised to match the final version accepted for publication in CQ

Geometry of Star-Forming Galaxies from SDSS, 3D-HST and CANDELS

We determine the intrinsic, 3-dimensional shape distribution of star-forming galaxies at 0<z<2.5, as inferred from their observed projected axis ratios. In the present-day universe star-forming galaxies of all masses 1e9 - 1e11 Msol are predominantly thin, nearly oblate disks, in line with previous studies. We now extend this to higher redshifts, and find that among massive galaxies (M* > 1e10 Msol) disks are the most common geometric shape at all z < 2. Lower-mass galaxies at z>1 possess a broad range of geometric shapes: the fraction of elongated (prolate) galaxies increases toward higher redshifts and lower masses. Galaxies with stellar mass 1e9 Msol (1e10 Msol) are a mix of roughly equal numbers of elongated and disk galaxies at z~1 (z~2). This suggests that galaxies in this mass range do not yet have disks that are sustained over many orbital periods, implying that galaxies with present-day stellar mass comparable to that of the Milky Way typically first formed such sustained stellar disks at redshift z~1.5-2. Combined with constraints on the evolution of the star formation rate density and the distribution of star formation over galaxies with different masses, our findings imply that, averaged over cosmic time, the majority of stars formed in disks.Comment: Published in ApJ Letter

CANDELS Observations of the Structural Properties and Evolution of Galaxies in a Cluster at z=1.62

We discuss the structural and morphological properties of galaxies in a z=1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology relation: galaxies with colors of quiescent stellar populations generally have morphologies consistent with spheroids, and galaxies with colors consistent with ongoing star formation have disk-like and irregular morphologies. The size distribution of the quiescent cluster galaxies shows a deficit of compact (< 1kpc), massive galaxies compared to CANDELS field galaxies at z=1.6. As a result the cluster quiescent galaxies have larger average effective sizes compared to field galaxies at fixed mass at greater than 90% significance. Combined with data from the literature, the size evolution of quiescent cluster galaxies is relatively slow from z~1.6 to the present, growing as (1+z)^(-0.6+/-0.1). If this result is generalizable, then it implies that physical processes associated with the denser cluster region seems to have caused accelerated size growth in quiescent galaxies prior to z=1.6 and slower subsequent growth at z<1.6 compared to galaxies in the lower density field. The quiescent cluster galaxies at z=1.6 have higher ellipticities compared to lower redshift samples at fixed mass, and their surface-brightness profiles suggest that they contain extended stellar disks. We argue the cluster galaxies require dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk material and to match the relations for ellipticity, stellar mass, size, and color of early-type galaxies in z<1 clusters.Comment: Accepted for publication in ApJ. 14 pages in emulateapj format. Replacement includes improvements from referee report, and updates and additions to reference