On-the-fly coarse-graining methodology for the simulation of chain formation of superparamagnetic colloids in strong magnetic fields

The aim of this work is the description of the chain formation phenomena observed in colloidal suspensions of superparamagnetic nanoparticles under high magnetic fields. We propose a new methodology based on an on-the-fly Coarse-Grain (CG) model. Within this approach, the coarse grain objects of the simulation are not fixed a priori at the beginning of the simulation but rather redefined on the fly. The motion of the CG objects (single particles or aggregates) is described by an anisotropic diffusion model and the magnetic dipole-dipole interaction is replaced by an effective short range interaction between CG objects. The new methodology correctly reproduces previous results from detailed Langevin Dynamics simulations of dispersions of superparamagnetic colloids under strong fields whilst requiring an amount of CPU time orders of magnitude smaller. This substantial improvement in the computational requirements allows the simulation of problems in which the relevant phenomena extends to time scales inaccessible with previous simulation techniques. A relevant example is the waiting time dependence of the relaxation time T_2 of water protons observed in Magnetic Resonance experiments containing dispersions of superparamagnetic colloids, which is correctly predicted by our simulations. Future applications may include other popular real-world applications of superparamagnetic colloids such as the magnetophoretic separation processes.Comment: 12 pages, 12 figure

Dispersions Superparamagnètiques: una visió de Física Estadística d'una nanotecnologia emergent

Els avenços en la fabricació de nous materials que presenten superparamagnetisme -un fenòmen físic que només apareix en la nanoescala- han permés el desenvolupament de noves i prometedores aplicacions en camps com ara la biotecnologia o la nanomedicina. Tot i això, les bases físiques de molts dels comportaments observats són encara poc enteses. Presentem aquí alguns avenços recents que permeten entendre millor aspectes físics bàsics d'aquests sistemes que poden ser rellevants per a dissenyar-ne més racionalment les seves aplicacions

Instrucció i aprenentatge en Ciències de la Salut. IASC

Podeu consultar la Setena trobada de professorat de Ciències de la Salut completa a: http://hdl.handle.net/2445/4335

Soft corals assemblages in deep environments of the Menorca Channel (Western Mediterranean Sea)

Image-based research in mesophotic and deep environments of the Mediterranean Sea has significantly increased during the past decades. So far, this research has been focused on the ecology of key structuring organisms such as scleractinians, antipatharians, gorgonians or large demosponges. However, the ecology of true soft corals has barely been studied and is still in a very preliminary stage. To overcome this situation, soft coral assemblages in shelf and slope environments of the Menorca Channel (Western Mediterranean Sea) have been studied through the quantitative analysis of 85 video transect recorded over 38500 m2. Highest soft coral diversity was encountered on the shelf edge, resembling deep Mediterranean gorgonian patterns. Three soft coral assemblages, segregated by depth, substrate, and slope were identified: two monospecific ones composed by Nidalia studeriand Alcyonium palmatum, respectively and a multispecific one composed by Paralcyonium spinulosum, Alcyonium sp., Chironephthya mediterranea and Daniela koreni. The evaluated species presented average densities within the same range as other deep Mediterranean anthozoans ranging from 1 to 9 col.·m−2. However, N. studeri and P. spinulosum punctually formed dense monospecific aggregations, reaching maximum densities of 49 col.·m−2 and 60 col.·m−2 respectively. Both species monopolized vast extensions of the continental shelf and shelf edge. The identification and ecological characterization of these assemblages brings new insight about deep Mediterranean anthozoan communities, and provides baseline for future management plans in the study area.En prensa3,26

Baryon Acoustic Oscillations in the Ly{\alpha} forest of BOSS DR11 quasars

We report a detection of the baryon acoustic oscillation (BAO) feature in the flux-correlation function of the Ly{\alpha} forest of high-redshift quasars with a statistical significance of five standard deviations. The study uses 137,562 quasars in the redshift range $2.1\le z \le 3.5$ from the Data Release 11 (DR11) of the Baryon Oscillation Spectroscopic Survey (BOSS) of SDSS-III. This sample contains three times the number of quasars used in previous studies. The measured position of the BAO peak determines the angular distance, $D_A(z=2.34)$ and expansion rate, $H(z=2.34)$, both on a scale set by the sound horizon at the drag epoch, $r_d$. We find $D_A/r_d=11.28\pm0.65(1\sigma)^{+2.8}_{-1.2}(2\sigma)$ and $D_H/r_d=9.18\pm0.28(1\sigma)\pm0.6(2\sigma)$ where $D_H=c/H$. The optimal combination, $\sim D_H^{0.7}D_A^{0.3}/r_d$ is determined with a precision of $\sim2\%$. For the value $r_d=147.4~{\rm Mpc}$, consistent with the CMB power spectrum measured by Planck, we find $D_A(z=2.34)=1662\pm96(1\sigma)~{\rm Mpc}$ and $H(z=2.34)=222\pm7(1\sigma)~{\rm km\,s^{-1}Mpc^{-1}}$. Tests with mock catalogs and variations of our analysis procedure have revealed no systematic uncertainties comparable to our statistical errors. Our results agree with the previously reported BAO measurement at the same redshift using the quasar-Ly{\alpha} forest cross-correlation. The auto-correlation and cross-correlation approaches are complementary because of the quite different impact of redshift-space distortion on the two measurements. The combined constraints from the two correlation functions imply values of $D_A/r_d$ and $D_H/r_d$ that are, respectively, 7% low and 7% high compared to the predictions of a flat $\Lambda$CDM cosmological model with the best-fit Planck parameters. With our estimated statistical errors, the significance of this discrepancy is $\approx 2.5\sigma$.Comment: Accepted for publication in A&A. 17 pages, 18 figure

The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III

The Sloan Digital Sky Survey (SDSS) started a new phase in August 2008, with new instrumentation and new surveys focused on Galactic structure and chemical evolution, measurements of the baryon oscillation feature in the clustering of galaxies and the quasar Ly alpha forest, and a radial velocity search for planets around ~8000 stars. This paper describes the first data release of SDSS-III (and the eighth counting from the beginning of the SDSS). The release includes five-band imaging of roughly 5200 deg^2 in the Southern Galactic Cap, bringing the total footprint of the SDSS imaging to 14,555 deg^2, or over a third of the Celestial Sphere. All the imaging data have been reprocessed with an improved sky-subtraction algorithm and a final, self-consistent photometric recalibration and flat-field determination. This release also includes all data from the second phase of the Sloan Extension for Galactic Understanding and Evolution (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars at both high and low Galactic latitudes. All the more than half a million stellar spectra obtained with the SDSS spectrograph have been reprocessed through an improved stellar parameters pipeline, which has better determination of metallicity for high metallicity stars.Comment: Astrophysical Journal Supplements, in press (minor updates from submitted version

The Baryon Oscillation Spectroscopic Survey of SDSS-III

The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large scale structure. BOSS uses 1.5 million luminous galaxies as faint as i=19.9 over 10,000 square degrees to measure BAO to redshifts z<0.7. Observations of neutral hydrogen in the Lyman alpha forest in more than 150,000 quasar spectra (g<22) will constrain BAO over the redshift range 2.15<z<3.5. Early results from BOSS include the first detection of the large-scale three-dimensional clustering of the Lyman alpha forest and a strong detection from the Data Release 9 data set of the BAO in the clustering of massive galaxies at an effective redshift z = 0.57. We project that BOSS will yield measurements of the angular diameter distance D_A to an accuracy of 1.0% at redshifts z=0.3 and z=0.57 and measurements of H(z) to 1.8% and 1.7% at the same redshifts. Forecasts for Lyman alpha forest constraints predict a measurement of an overall dilation factor that scales the highly degenerate D_A(z) and H^{-1}(z) parameters to an accuracy of 1.9% at z~2.5 when the survey is complete. Here, we provide an overview of the selection of spectroscopic targets, planning of observations, and analysis of data and data quality of BOSS.Comment: 49 pages, 16 figures, accepted by A

The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey

The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar spectra, along with the data presented in previous data releases. These spectra were obtained with the new BOSS spectrograph and were taken between 2009 December and 2011 July. In addition, the stellar parameters pipeline, which determines radial velocities, surface temperatures, surface gravities, and metallicities of stars, has been updated and refined with improvements in temperature estimates for stars with T_eff<5000 K and in metallicity estimates for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars presented in DR8, including stars from SDSS-I and II, as well as those observed as part of the SDSS-III Sloan Extension for Galactic Understanding and Exploration-2 (SEGUE-2). The astrometry error introduced in the DR8 imaging catalogs has been corrected in the DR9 data products. The next data release for SDSS-III will be in Summer 2013, which will present the first data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) along with another year of data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at http://www.sdss3.org/dr

Large-scale clustering of Lyman \u3b1 emission intensity from SDSS/BOSS

We present a tentative detection of the large-scale structure of Ly \u3b1 emission in the Universe at redshifts z = 2-3.5 by measuring the cross-correlation of Ly \u3b1 surface brightness with quasars in Sloan Digital Sky Survey/Baryon Oscillation Spectroscopic Survey.We use amillion spectra targeting luminous red galaxies at z < 0.8, after subtracting a best-fitting model galaxy spectrum from each one, as an estimate of the high-redshift Ly \u3b1 surface brightness. The quasar- Ly \u3b1 emission cross-correlation is detected on scales 1 ~ 15 h-1 Mpc, with shape consistent with a \u39b (CDM model with) \u3a9m = 0.30+0.10 -0.07. The predicted amplitude of this cross-correlation is proportional to the product of the mean Ly \u3b1 surface brightness, (\u3bc\u3b1), the amplitude of mass fluctuations and the quasar and Ly \u3b1 emission bias factors. We infer (\u3bc\u3b1) (b\u3b1/3) = (3.9 \ub1 0.9) 7 10-21 erg s-1 cm-2 \uc5-1 arcsec-2, where b\u3b1 is the Ly \u3b1 emission bias. If star-forming galaxies dominate this emission, we find \u3c1SFR = (0.28 \ub1 0.07)(3/b\u3b1) yr-1 Mpc-3. For b\u3b1 = 3, this value is~30 times larger than previous estimates from individually detected Ly \u3b1 emitters, but consistent with the total \u3c1SFR derived from dust-corrected, continuum UV galaxy surveys, if most of the Ly \u3b1 photons from these galaxies avoid dust absorption and are reemitted after diffusing in large gas haloes. Heating of intergalactic gas by He II photoionization from quasar radiation or jets may alternatively explain the detected correlation, and cooling radiation from gas in galactic haloes may also contribute. We also detect redshift space anisotropy of the quasar-Ly \u3b1 emission cross-correlation, finding evidence at the 3.0\u3c3 level that it is radially elongated, which may be explained by radiative-transfer effects. Our measurements represent the first application of the intensity mapping technique to optical observations. \ua9 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society