782 research outputs found

    Photography and Aesthetics: a critical study on visual and textual narratives in the lifework of Sergio Larraín and its impact in 20th century Europe and Latin America

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    The main focus of this study is a theoretical exploration of critical approaches applicable to the work of the Chilean photographer Sergio Larraín (1931-2012). It presents analytical tools to contextualise and understand the importance and impact of his work in photographic studies and his portrayal of twentieth-century Latin American and European culture. It inspects in depth a large portion of his photo work, which is still only partially published and mostly reduced to his "active" period as a photojournalist, aside from the personal photographic exploration of his early and late career (C. Mena). This extended material creates a broader scope for understanding his photographs and him as a canonical photographer. This study analyses the photographer's trajectory as discourses of recollection of historical memory in time (Mauad) to trace Larraín's collective memory associated with his visual production. Such analysis helps decode his visual imagery and his projection and impact on the European and Latin American culture. This strategy helps solve a two fold problem: firstly, it generates an interpretive consistency to understand the Chilean's photographic practice; secondly, it explores the power of images as an aesthetic experience in the installation of nationalist ideologies and the creation of imaginaries (B. Anderson 163)

    Can wild boar be surveyed using GPS?

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    The Global Positioning System (GPS) is an important new technology for spatial behaviour studies of terrestrial vertebrates. Although VHF telemetry has been substantially used, our study is the first report, to our knowledge, on GPS technology used to track free-ranging wild boars. Although the need for collars larger than those used for VHF tracking, the crowded vegetation of habitat and the particular features of social group behaviour of wild boars led to some technical difficulties, three adult sows were successfully fitted with two GPS collars and one dummy GPS. The collars remained on the wild boars for over 283 days without causing any injury to the animals. Forty-one daily cycles (24 hours), as well as daily locations over 142 days, could be recorded for a single animal. Detection efficiency and fixes were better during the night than during the day. In the light of these results, the GPS technique appears to be an efficient tool to study wild boar movements. Progress in the survey of animal movements at a fine scale is of prime interest for animal management programs in order to obtain and maintain a sustainable level of animal population regarding damage problems

    Energy-Momentum Tensors for the Quark-Gluon Plasma

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    We construct the energy-momentum tensor for the gauge fields which describe the collective excitations of the quark-gluon plasma. We rely on the description of the collective modes that we have derived in previous works. By using the conservation laws for energy and momentum, we obtain three different versions for the tensor TμνT^{\mu\nu}, which are physically equivalent. We show that the total energy constructed from T00T^{00} is positive for any non-trivial field configuration. Finally, we present a new non-abelian solution of the equations of motion for the gauge fields. This solution corresponds to spatially uniform color oscillations of the plasma.Comment: 28 pages LaTex, Saclay preprint T94/0

    Modal and non-modal linear stability of Poiseuille flow through a channel with a porous substrate

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    We present modal and non-modal linear stability analyses of Poiseuille flow through a plane channel with a porous substrate modeled using the Volume Averaged Navier–Stokes (VANS) equations. Modal stability analysis shows the destabilization of the flow with increasing porosity of the layer. The instability mode originates from the homogeneous fluid region of the channel for all the values of porosity considered but the governing mechanism changes. Perturbation kinetic energy analysis reveals the importance of viscous dissipation at low porosity values while dissipation in the porous substrate becomes significant at higher porosity. Scaling analysis highlights the invariance of the critical wavenumber with changing porosity. On the other hand, the critical Reynolds number remains invariant at low porosity and scales as Rec ∼ (H/δ) 1.4 at high porosity where δ is the typical thickness of the vorticity layer at the fluid– porous interface. This reveals the existence of a Tollmien–Schlichting-like viscous instability mechanism at low porosity values, and Rayleigh analysis shows the presence of an inviscid instability mechanism at high porosity. For the whole range of porosities considered, the non-modal analysis shows that the optimal mechanism responsible for transient energy amplification is the lift-up effect, giving rise to streaky structure as in single-phase plane Poiseuille flow. The present results strongly suggest that the transition to turbulence follows the same path as that of classical Poiseuille flow at low porosity values, while it is dictated by the modal instability for high porosity values

    Stochastic bias of colour-selected BAO tracers by joint clustering-weak lensing analysis

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    The baryon acoustic oscillation (BAO) feature in the two-point correlation function of galaxies supplies a standard ruler to probe the expansion history of the Universe. We study here several galaxy selection schemes, aiming at building an emission-line galaxy (ELG) sample in the redshift range 0.6<z<1.70.6<z<1.7, that would be suitable for future BAO studies, providing a highly biased galaxy sample. We analyse the angular galaxy clustering of galaxy selections at the redshifts 0.5, 0.7, 0.8, 1 and 1.2 and we combine this analysis with a halo occupation distribution (HOD) model to derive the properties of the haloes these galaxies inhabit, in particular the galaxy bias on large scales. We also perform a weak lensing analysis (aperture statistics) to extract the galaxy bias and the cross-correlation coefficient and compare to the HOD prediction. We apply this analysis on a data set composed of the photometry of the deep co-addition on Sloan Digital Sky Survey (SDSS) Stripe 82 (225 deg2^2), of Canda-France-Hawai Telescope/Stripe 82 deep \emph{i}-band weak lensing survey and of the {\it Wide-Field Infrared Survey Explorer}infrared photometric band W1. The analysis on the SDSS-III/constant mass galaxies selection at z=0.5z=0.5 is in agreement with previous studies on the tracer, moreover we measure its cross-correlation coefficient r=1.16±0.35r=1.16\pm0.35. For the higher redshift bins, we confirm the trends that the brightest galaxy populations selected are strongly biased (b>1.5b>1.5), but we are limited by current data sets depth to derive precise values of the galaxy bias. A survey using such tracers of the mass field will guarantee a high significance detection of the BAO.Comment: 17 pages, 15 figures, submitted to MNRA

    Gauge Structure and Semi-Classical Aspects of Hard Thermal Loops

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    Hard thermal loops play a central role in the theory of long wavelength excitations of a quark-gluon plasma. We show in this paper how our recent derivation of their generating functional from the Dyson-Schwinger equations sheds light on their semi-classical nature and their remarkable gauge structure. In particular, we show that our kinetic equations can be written in terms of auxiliary gauge fields with zero curvature. Remarkably, the latter property determines entirely the dynamics in the kinematical regime of hard thermal loops. This explains in particular why the generating functional could have been obtained by Taylor and Wong from gauge invariance considerations. It also clarifies the role of Chern-Simons theory in this context.Comment: 16 pages LaTex, Saclay preprint T94/0

    Pre-retrieval reperfusion decreases cancer recurrence after rat ischemic liver graft transplantation

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    Background & Aims Liver transplantation from marginal donors is associated with ischemia/reperfusion (I/R) lesions, which may increase the risk of post-transplant hepatocellular carcinoma (HCC) recurrence. Graft reperfusion prior to retrieval (as for extracorporeal membrane oxygenation – ECMO) can prevent I/R lesions. The impact of I/R on the risk of cancer recurrence was assessed on a syngeneic Fischer-rat liver transplantation model. Methods HCC cells were injected into the vena porta of all recipients at the end of an orthotopic liver transplantation (OLT). Control donors were standard heart-beating, ischemic ones (ISC), underwent 10min or 30min inflow liver clamping prior to retrieval, and ischemic/reperfused (ISC/R) donors underwent 2h liver reperfusion after the clamping. Results I/R lesions were confirmed in the ISC group, with the presence of endothelial and hepatocyte injury, and increased liver function tests. These lesions were in part reversed by the 2h reperfusion in the ISC/R group. HCC growth was higher in the 10min and 30min ISC recipients ( p =0.018 and 0.004 vs. control, as assessed by MRI difference between weeks one and two), and was prevented in the ISC/Rs ( p =0.04 and 0.01 vs. ISC). These observations were associated with a stronger pro-inflammatory cytokine profile in the ISC recipients only, and the expression of hypoxia and HCC growth-enhancer genes, including Hmox1 , Hif1a and Serpine1 . Conclusions This experiment suggests that ischemia/reperfusion lesions lead to an increased risk of post-transplant HCC recurrence and growth. This observation can be reversed by graft reperfusion prior to retrieval

    The Time-Domain Spectroscopic Survey: Understanding the Optically Variable Sky with SEQUELS in SDSS-III

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    The Time-Domain Spectroscopic Survey (TDSS) is an SDSS-IV eBOSS subproject primarily aimed at obtaining identification spectra of ~220,000 optically-variable objects systematically selected from SDSS/Pan-STARRS1 multi-epoch imaging. We present a preview of the science enabled by TDSS, based on TDSS spectra taken over ~320 deg^2 of sky as part of the SEQUELS survey in SDSS-III, which is in part a pilot survey for eBOSS in SDSS-IV. Using the 15,746 TDSS-selected single-epoch spectra of photometrically variable objects in SEQUELS, we determine the demographics of our variability-selected sample, and investigate the unique spectral characteristics inherent in samples selected by variability. We show that variability-based selection of quasars complements color-based selection by selecting additional redder quasars, and mitigates redshift biases to produce a smooth quasar redshift distribution over a wide range of redshifts. The resulting quasar sample contains systematically higher fractions of blazars and broad absorption line quasars than from color-selected samples. Similarly, we show that M-dwarfs in the TDSS-selected stellar sample have systematically higher chromospheric active fractions than the underlying M-dwarf population, based on their H-alpha emission. TDSS also contains a large number of RR Lyrae and eclipsing binary stars with main-sequence colors, including a few composite-spectrum binaries. Finally, our visual inspection of TDSS spectra uncovers a significant number of peculiar spectra, and we highlight a few cases of these interesting objects. With a factor of ~15 more spectra, the main TDSS survey in SDSS-IV will leverage the lessons learned from these early results for a variety of time-domain science applications.Comment: 17 pages, 14 figures, submitted to Ap

    The Type Ia Supernova Rate in Redshift 0.5--0.9 Galaxy Clusters

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    Supernova (SN) rates are potentially powerful diagnostics of metal enrichment and SN physics, particularly in galaxy clusters with their deep, metal-retaining potentials and relatively simple star-formation histories. We have carried out a survey for supernovae (SNe) in galaxy clusters, at a redshift range 0.5<z<0.9, using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. We reimaged a sample of 15 clusters that were previously imaged by ACS, thus obtaining two to three epochs per cluster, in which we discovered five likely cluster SNe, six possible cluster SNe Ia, two hostless SN candidates, and several background and foreground events. Keck spectra of the host galaxies were obtained to establish cluster membership. We conducted detailed efficiency simulations, and measured the stellar luminosities of the clusters using Subaru images. We derive a cluster SN rate of 0.35 SNuB +0.17/-0.12 (statistical) \pm0.13 (classification) \pm0.01 (systematic) [where SNuB = SNe (100 yr 10^10 L_B_sun)^-1] and 0.112 SNuM +0.055/-0.039 (statistical) \pm0.042 (classification) \pm0.005 (systematic) [where SNuM = SNe (100 yr 10^10 M_sun)^-1]. As in previous measurements of cluster SN rates, the uncertainties are dominated by small-number statistics. The SN rate in this redshift bin is consistent with the SN rate in clusters at lower redshifts (to within the uncertainties), and shows that there is, at most, only a slight increase of cluster SN rate with increasing redshift. The low and fairly constant SN Ia rate out to z~1 implies that the bulk of the iron mass in clusters was already in place by z~1. The recently observed doubling of iron abundances in the intracluster medium between z=1 and 0, if real, is likely the result of redistribution of existing iron, rather than new production of iron.Comment: Accepted to ApJ. Full resolution version available at http://kicp.uchicago.edu/~kerens/HSTclusterSNe
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