Collapse of a semiflexible polymer in poor solvent

We investigate the dynamics and the pathways of the collapse of a single, semiflexible polymer in a poor solvent via 3-D Brownian Dynamics simulations. Earlier work indicates that the condensation of semiflexible polymers generically proceeds via a cascade through metastable racquet-shaped, long-lived intermediates towards the stable torus state. We investigate the rate of decay of uncollapsed states, analyze the preferential pathways of condensation, and describe likelihood and lifespan of the different metastable states. The simulation are performed with a bead-stiff spring model with excluded volume interaction and exponentially decaying attractive potential. The semiflexible chain collapse is studied as functions of the three relevant length scales of the phenomenon, i.e., the total chain length $L$, the persistence length $L_p$ and the condensation length $L_0 = \sqrt{k_B T L_p/u_0}$, where $u_0$ is a measure of the attractive potential per unit length. Two dimensionless ratios, $L/L_p$ and $L_0/L_p$, suffice to describe the decay rate of uncollapsed states, which appears to scale as $(L/L_p)^{1/3} (L_0/L_p)$. The condensation sequence is described in terms of the time series of the well separated energy levels associated with each metastable collapsed state. The collapsed states are described quantitatively through the spatial correlation of tangent vectors along the chain. We also compare the results obtained with a locally inextensible bead-rod chain and with a phantom bead-spring model. Finally, we show preliminary results on the effects of steady shear flow on the kinetics of collapse.Comment: 9 pages, 8 figure

IMF and [Na/Fe] abundance ratios from optical and NIR Spectral Features in Early-type Galaxies

We present a joint analysis of the four most prominent sodium-sensitive features (NaD, NaI8190, NaI1.14, and NaI2.21), in the optical and Near-Infrared spectral range, of two nearby, massive (sigma~300km/s), early-type galaxies (named XSG1 and XSG2). Our analysis relies on deep VLT/X-Shooter long-slit spectra, along with newly developed stellar population models, allowing for [Na/Fe] variations, up to 1.2dex, over a wide range of age, total metallicity, and IMF slope. The new models show that the response of the Na-dependent spectral indices to [Na/Fe] is stronger when the IMF is bottom heavier. For the first time, we are able to match all four Na features in the central regions of massive early-type galaxies, finding an overabundance of [Na/Fe], in the range 0.5-0.7dex, and a bottom-heavy IMF. Therefore, individual abundance variations cannot be fully responsible for the trends of gravity-sensitive indices, strengthening the case towards a non-universal IMF. Given current limitations of theoretical atmosphere models, our [Na/Fe] estimates should be taken as upper limits. For XSG1, where line strengths are measured out to 0.8Re, the radial trend of [Na/Fe] is similar to [Mg/Fe] and [C/Fe], being constant out to 0.5Re, and decreasing by 0.2-0.3dex at 0.8Re, without any clear correlation with local metallicity. Such a result seems to be in contrast with the predicted increase of Na nucleosynthetic yields from AGB stars and TypeII SNe. For XSG1, the Na-inferred IMF radial profile is consistent, within the errors, with that derived from TiO features and the Wing-Ford band, presented in a recent paper.Comment: 22 pages, 8 figure, accepted for publication in MNRAS. The new Na-enhanced models will be available soon at http://miles.iac.es

PPAK Wide-field Integral Field Spectroscopy of NGC 628: I. The largest spectroscopic mosaic on a single galaxy

We present a wide-field IFS survey on the nearby face-on Sbc galaxy NGC 628, comprising 11094 individual spectra, covering a nearly circular field-of-view of ~6 arcmin in diameter, with a sampling of ~2.7 arcsec per spectrum in the optical wavelength range (3700--7000 AA). This galaxy is part of the PPAK IFS Nearby Galaxies Survey, (PINGS, Rosales-Ortega et al. 2009). To our knowledge, this is the widest spectroscopic survey ever made in a single nearby galaxy. A detailed flux calibration was applied, granting a spectrophotometric accuracy of $\sim$\,0.2 mag. The age of the stellar populations shows a negative gradient from the inner (older) to the outer (younger) regions. We found an inversion of this gradient in the central ~1 kpc region, where a somewhat younger stellar population is present within a ring at this radius. This structure is associated with a circumnuclear star-forming region at ~ 500 pc, also found in similar spiral galaxies. From the study of the integrated and spatially resolved ionized gas we found a moderate SFR of ~ 2.4 Msun yr$^{-1}$. The oxygen abundance shows a a clear gradient of higher metallicity values from the inner part to the outer part of the galaxy, with a mean value of 12~+~log(O/H) ~ 8.7. At some specific regions of the galaxy, the spatially resolved distribution of the physical properties show some level of structure, suggesting real point-to-point variations within an individual \hh region. Our results are consistent with an inside-out growth scheme, with stronger star formation at the outer regions, and with evolved stellar populations in the inner ones.Comment: 31 pages, 22 Figuras, Accepted for Publishing in MNRAS (corrected PDF

Morphology and evolution of emission line galaxies in the Hubble Ultra Deep Field

We investigate the properties and evolution of a sample of galaxies selected to have prominent emission lines in low-resolution grism spectra of the Hubble Ultra Deep Field (HUDF). These objects, eGRAPES, are late type blue galaxies, characterized by small proper sizes (R_50 < 2 kpc) in the 4350A rest-frame, low masses (5x10^9 M_sun), and a wide range of luminosities and surface brightnesses. The masses, sizes and volume densities of these objects appear to change very little up to a redshift of z=1.5. On the other hand, their surface brightness decreases significantly from z=1.5 to z=0 while their mass-to-light ratio increases two-folds. This could be a sign that most of low redshift eGRAPES have an older stellar population than high redshift eGRAPES and hence that most eGRAPES formed at higher redshifts. The average volume density of eGRAPES is (1.8 \pm 0.3)x10^{-3} Mpc^{-3} between 0.3 < z < 1.5. Many eGRAPES would formally have been classified as Luminous Compact Blue Galaxies (LCBGs) if these had been selected based on small physical size, blue intrinsic color, and high surface brightness, while the remainder of the sample discussed in this paper forms an extension of LCBGs towards fainter luminosities.Comment: Accepted, to appear in Ap

IMF and [Na/Fe] abundance ratios from optical and NIR Spectral Features in Early-type Galaxies

We present a joint analysis of the four most prominent sodium-sensitive features (NaD, NaI8190, NaI1.14, and NaI2.21), in the optical and Near-Infrared spectral range, of two nearby, massive (sigma~300km/s), early-type galaxies (named XSG1 and XSG2). Our analysis relies on deep VLT/X-Shooter long-slit spectra, along with newly developed stellar population models, allowing for [Na/Fe] variations, up to 1.2dex, over a wide range of age, total metallicity, and IMF slope. The new models show that the response of the Na-dependent spectral indices to [Na/Fe] is stronger when the IMF is bottom heavier. For the first time, we are able to match all four Na features in the central regions of massive early-type galaxies, finding an overabundance of [Na/Fe], in the range 0.5-0.7dex, and a bottom-heavy IMF. Therefore, individual abundance variations cannot be fully responsible for the trends of gravity-sensitive indices, strengthening the case towards a non-universal IMF. Given current limitations of theoretical atmosphere models, our [Na/Fe] estimates should be taken as upper limits. For XSG1, where line strengths are measured out to 0.8Re, the radial trend of [Na/Fe] is similar to [Mg/Fe] and [C/Fe], being constant out to 0.5Re, and decreasing by 0.2-0.3dex at 0.8Re, without any clear correlation with local metallicity. Such a result seems to be in contrast with the predicted increase of Na nucleosynthetic yields from AGB stars and TypeII SNe. For XSG1, the Na-inferred IMF radial profile is consistent, within the errors, with that derived from TiO features and the Wing-Ford band, presented in a recent paper

Intrathecal enzyme replacement for Hurler syndrome: biomarker association with neurocognitive outcomes.

PurposeAbnormalities in cerebrospinal fluid (CSF) have been reported in Hurler syndrome, a fatal neurodegenerative lysosomal disorder. While no biomarker has predicted neurocognitive response to treatment, one of these abnormalities, glycosaminoglycan nonreducing ends (NREs), holds promise to monitor therapeutic efficacy. A trial of intrathecal enzyme replacement therapy (ERT) added to standard treatment enabled tracking of CSF abnormalities, including NREs. We evaluated safety, biomarker response, and neurocognitive correlates of change.MethodsIn addition to intravenous ERT and hematopoietic cell transplantation, patients (N = 24) received intrathecal ERT at four peritransplant time points; CSF was evaluated at each point. Neurocognitive functioning was quantified at baseline, 1 year, and 2 years posttransplant. Changes in CSF biomarkers and neurocognitive function were evaluated for an association.ResultsOver treatment, there were significant decreases in CSF opening pressure, biomarkers of disease activity, and markers of inflammation. Percent decrease in NRE from pretreatment to final intrathecal dose posttransplant was positively associated with percent change in neurocognitive score from pretreatment to 2 years posttransplant.ConclusionIntrathecal ERT was safe and, in combination with standard treatment, was associated with reductions in CSF abnormalities. Critically, we report evidence of a link between a biomarker treatment response and neurocognitive outcome in Hurler syndrome

CONVERGENT AND DIVERGENT ANGLES OF A SOLID-FUEL ROCKET NOZZLE AND ITS INFLUENCES ON THE MOTOR’S THRUST CURVE

The main goal of this work is to investigate how the angles of a convergent-divergent rocket nozzle influence the thrust curve of a solid-propulsion rocket. The work has been conducted within an academic rocketry team. As there is not clear reasoning on how to define these angles, the present research provides insights on how these geometrical parameters influence the performance of a rocket motor. A 2D-axisymmetric CFD domain is considered, comprising the fluid domain inside and outside the nozzle, to give room for the shock waves to happen and also accommodate the flow. The study comprises a baseline geometry and twelve modified designs, varying the convergent and the divergent angles of the nozzle. Since the convergent diameter must match the chamber diameter, it is fixed. For the divergent diameter, there is no such restriction; therefore, there are two possibilities: a divergent section with the same divergent diameter or with the same length as the baseline. The benchmark thrust curve is generated with a MATLAB code based on solid-fuel modeling and the De Laval theory. The curve is divided into six steady-state simulations, using boundary conditions of mass flow, pressure and temperature at the inlet and pressure and temperature at the outlet. The baseline geometry is simulated in Ansys Fluent and normalized by the MATLAB benchmark. A mesh study selects which mesh and turbulence model to use based on this normalization. The modified geometries are then compared to the baseline. The main quantity of interest is the thrust but quantities such as static pressure and average velocity at the nozzle exit aid the understanding of the changes in thrust

On the structure of Borel stable abelian subalgebras in infinitesimal symmetric spaces

Let g=g_0+g_1 be a Z_2-graded Lie algebra. We study the posets of abelian subalgebras of g_1 which are stable w.r.t. a Borel subalgebra of g_0. In particular, we find out a natural parametrization of maximal elements and dimension formulas for them. We recover as special cases several results of Kostant, Panyushev, Suter.Comment: Latex file, 35 pages, minor corrections, some examples added. To appear in Selecta Mathematic

The nature of LINER galaxies: Ubiquitous hot old stars and rare accreting black holes

Galaxies, which often contain ionised gas, sometimes also exhibit a so-called low-ionisation nuclear emission line region (LINER). For 30 years this was attributed to a central mass-accreting supermassive black hole (AGN) of low luminosity, making LINER galaxies the largest AGN-sub-population, dominating in numbers over higher luminosity Seyfert galaxies and quasars. This, however, poses a serious problem. While the inferred energy balance is plausible, many LINERs clearly do not contain any other independent signatures of an AGN. Using integral field spectroscopic data from the CALIFA survey, we aim at comparing the observed radial surface brightness profiles with what is expected from illumination by an AGN. Essential for this analysis is a proper extraction of emission-lines, especially weak lines such as the Balmer Hb line which is superposed on an absorption trough. To accomplish this, we use the GANDALF code which simultaneously fits the underlying stellar continuum and emission lines. We show for 48 galaxies with LINER-like emission, that the radial emission-line surface brightness profiles are inconsistent with ionisation by a central point-source and hence cannot be due to an AGN alone. The most probable explanation for the excess LINER-like emission is ionisation by evolved stars during the short but very hot and energetic phase known as post-AGB. This leads us to an entirely new interpretation. Post-AGB stars are ubiquitous and their ionising effect should be potentially observable in every galaxy with gas present and stars older than ~1 Gyr, unless a stronger radiation field from young hot stars or an AGN outshines them. This means that galaxies with LINER-like emission are in fact not a class defined by a property, but rather by the absence of a property. It also explains why LINER emission is observed mostly in massive galaxies with old stars and little star formation.Comment: 8 pages, 7 figure

Prompt muon contribution to the flux underwater

We present high energy spectra and zenith-angle distributions of the atmospheric muons computed for the depths of the locations of the underwater neutrino telescopes. We compare the calculations with the data obtained in the Baikal and the AMANDA muon experiments. The prompt muon contribution to the muon flux underwater due to recent perturbative QCD-based models of the charm production is expected to be observable at depths of the large underwater neutrino telescopes. This appears to be probable even at rather shallow depths (1-2 km), provided that the energy threshold for muon detection is raised above $\sim 100$ TeV.Comment: 7 pages, RevTeX, 7 eps figures, final version to be published in Phys.Rev.D; a few changes made in the text and the figures, an approximation formula for muon spectra at the sea level, the muon zenith-angle distribution table data and references adde