A 12 μm ISOCAM survey of the ESO-Sculptor field

We present a detailed reduction of a mid-infrared 12 μm (LW10 filter) ISOCAM open time observation performed on the ESOSculptor Survey field (Arnouts et al. 1997, A&AS, 124, 163). A complete catalogue of 142 sources (120 galaxies and 22 stars), detected with high significance (equivalent to 5σ), is presented above an integrated flux density of 0.24 mJy. Star/galaxy separation is performed by a detailed study of colour-colour diagrams. The catalogue is complete to 1 mJy and, below this flux density, the incompleteness is corrected using two independent methods. The first method uses stars and the second uses optical counterparts of the ISOCAM galaxies; these methods yield consistent results. We also apply an empirical flux density calibration using stars in the field. For each star, the 12 μm flux density is derived by fitting optical colours from a multi-band χ^2 to stellar templates (BaSel-2.0) and using empirical optical-IR colour-colour relations. This article is a companion analysis to our 2007 paper (Rocca-Volmerange et al. 2007, A&A, 475, 801) where the 12 μm faint galaxy counts are presented and analysed per galaxy type with the evolutionary code PÉGASE.3

The 12 μm ISO-ESO-Sculptor and 24 μm Spitzer faint counts reveal a population of ULIRGs as dusty massive ellipticals: Evolution by types and cosmic star formation

Context. Multi-wavelength galaxy number counts provide clues to the nature of galaxy evolution. The interpretation per galaxy type of the mid-IR faint counts obtained with ISO and Spitzer, consistent with the analysis of deep UV-optical-near IR galaxy counts, provide new constraints on the dust and stellar emission. Discovering the nature of new populations, such as high redshift ultra-luminous (≥10^(12) L_⊙) infrared galaxies (ULIRGs), is also crucial for understanding galaxy evolution at high redshifts. Aims. We first present the faint galaxy counts at 12 μm from the catalogue of the ISO-ESO-Sculptor Survey (ISO-ESS) published in a companion article (Seymour et al. 2007a, A&A, 475, 791). They go down to 0.31 mJy after corrections for incompleteness. We verify the consistency with the existing ISO number counts at 15 μm. Then we analyse the 12 μm (ISO-ESS) and the 24 μm (Spitzer) faint counts, to constrain the nature of ULIRGs, the cosmic star formation history and time scales for mass buildup. Methods. We show that the “normal” scenarios in our evolutionary code PÉGASE, which had previously fitted the deep UV-opticalnear IR counts, are unsuccessful at 12 μm and 24 μm. We thus propose a new ULIRG scenario adjusted to the observed cumulative and differential 12 μm and 24 μm counts and based on observed 12 μm and 25 μm IRAS luminosity functions and evolutionary optical/mid-IR colours from PÉGASE. Results. We succeed in simultaneously modelling the typical excess observed at 12 μm, 15 μm (ISO), and 24 μm (Spitzer) in the cumulative and differential counts by only changing 9% of normal galaxies (1/3 of the ellipticals) into ultra-bright dusty galaxies evolving as ellipticals, and interpreted as distant ULIRGs. These objects present similarities with the population of radio-galaxy hosts at high redshift. No number density evolution is included in our models even if minor starbursts due to galaxy interactions remain compatible with our results. Conclusions. Higher spectral and spatial resolution in the mid-IR, together with submillimeter observations using the future Herschel observatory, will be useful to confirm these results

The 12 μm ISO-ESO-Sculptor and 24 μm Spitzer faint counts reveal a population of ULIRGs as dusty massive ellipticals: Evolution by types and cosmic star formation

Context. Multi-wavelength galaxy number counts provide clues to the nature of galaxy evolution. The interpretation per galaxy type of the mid-IR faint counts obtained with ISO and Spitzer, consistent with the analysis of deep UV-optical-near IR galaxy counts, provide new constraints on the dust and stellar emission. Discovering the nature of new populations, such as high redshift ultra-luminous (≥10^(12) L_⊙) infrared galaxies (ULIRGs), is also crucial for understanding galaxy evolution at high redshifts. Aims. We first present the faint galaxy counts at 12 μm from the catalogue of the ISO-ESO-Sculptor Survey (ISO-ESS) published in a companion article (Seymour et al. 2007a, A&A, 475, 791). They go down to 0.31 mJy after corrections for incompleteness. We verify the consistency with the existing ISO number counts at 15 μm. Then we analyse the 12 μm (ISO-ESS) and the 24 μm (Spitzer) faint counts, to constrain the nature of ULIRGs, the cosmic star formation history and time scales for mass buildup. Methods. We show that the “normal” scenarios in our evolutionary code PÉGASE, which had previously fitted the deep UV-opticalnear IR counts, are unsuccessful at 12 μm and 24 μm. We thus propose a new ULIRG scenario adjusted to the observed cumulative and differential 12 μm and 24 μm counts and based on observed 12 μm and 25 μm IRAS luminosity functions and evolutionary optical/mid-IR colours from PÉGASE. Results. We succeed in simultaneously modelling the typical excess observed at 12 μm, 15 μm (ISO), and 24 μm (Spitzer) in the cumulative and differential counts by only changing 9% of normal galaxies (1/3 of the ellipticals) into ultra-bright dusty galaxies evolving as ellipticals, and interpreted as distant ULIRGs. These objects present similarities with the population of radio-galaxy hosts at high redshift. No number density evolution is included in our models even if minor starbursts due to galaxy interactions remain compatible with our results. Conclusions. Higher spectral and spatial resolution in the mid-IR, together with submillimeter observations using the future Herschel observatory, will be useful to confirm these results

A Novel Methodology for Simulating Contact-Line Behavior in Capillary-Driven Flows

Despite the wide swath of applications where multiphase fluid contact lines exist, there is still no consensus on an accurate and general simulation methodology. Most prior numerical work has imposed one of the many dynamic contact-angle theories at solid walls. Such approaches are inherently limited by the theory accuracy. In fact, when inertial effects are important, the contact angle may be history dependent and, thus, any single mathematical function is inappropriate. Given these limitations, the present work has two primary goals: 1) create a numerical framework that allows the contact angle to evolve naturally with appropriate contact-line physics and 2) develop equations and numerical methods such that contact-line simulations may be performed on coarse computational meshes. Fluid flows affected by contact lines are dominated by capillary stresses and require accurate curvature calculations. The level set method was chosen to track the fluid interfaces because it is easy to calculate interface curvature accurately. Unfortunately, the level set reinitialization suffers from an ill-posed mathematical problem at contact lines: a ``blind spot'' exists. Standard techniques to handle this deficiency are shown to introduce parasitic velocity currents that artificially deform freely floating (non-prescribed) contact angles. As an alternative, a new relaxation equation reinitialization is proposed to remove these spurious velocity currents and its concept is further explored with level-set extension velocities. To capture contact-line physics, two classical boundary conditions, the Navier-slip velocity boundary condition and a fixed contact angle, are implemented in direct numerical simulations (DNS). DNS are found to converge only if the slip length is well resolved by the computational mesh. Unfortunately, since the slip length is often very small compared to fluid structures, these simulations are not computationally feasible for large systems. To address the second goal, a new methodology is proposed which relies on the volumetric-filtered Navier-Stokes equations. Two unclosed terms, an average curvature and a viscous shear VS, are proposed to represent the missing microscale physics on a coarse mesh. All of these components are then combined into a single framework and tested for a water droplet impacting a partially-wetting substrate. Very good agreement is found for the evolution of the contact diameter in time between the experimental measurements and the numerical simulation. Such comparison would not be possible with prior methods, since the Reynolds number Re and capillary number Ca are large. Furthermore, the experimentally approximated slip length ratio is well outside of the range currently achievable by DNS. This framework is a promising first step towards simulating complex physics in capillary-dominated flows at a reasonable computational expense.</p

Role of anisotropy in the F\"orster energy transfer from a semiconductor quantum well to an organic crystalline overlayer

We consider the non-radiative resonant energy transfer from a two-dimensional Wannier exciton (donor) to a Frenkel exciton of a molecular crystal overlayer (acceptor). We characterize the effect of the optical anisotropy of the organic subsystem on this process. Using realistic values of material parameters, we show that it is possible to change the transfer rate within typically a factor of two depending on the orientation of the crystalline overlayer. The resonant matching of donor and acceptor energies is also partly tunable via the organic crystal orientation.Comment: 6 pages, 8 figure

Trajectory attractors for the Sun-Liu model for nematic liquid crystals in 3D

In this paper we prove the existence of a trajectory attractor (in the sense of V.V. Chepyzhov and M.I. Vishik) for a nonlinear PDE system coming from a 3D liquid crystal model accounting for stretching effects. The system couples a nonlinear evolution equation for the director d (introduced in order to describe the preferred orientation of the molecules) with an incompressible Navier-Stokes equation for the evolution of the velocity field u. The technique is based on the introduction of a suitable trajectory space and of a metric accounting for the double-well type nonlinearity contained in the director equation. Finally, a dissipative estimate is obtained by using a proper integrated energy inequality. Both the cases of (homogeneous) Neumann and (non-homogeneous) Dirichlet boundary conditions for d are considered.Comment: 32 page

Roles of the Core Components of the Mammalian miRISC in Chromatin Biology

The Argonaute (AGO) and the Trinucleotide Repeat Containing 6 (TNRC6) family proteins are the core components of the mammalian microRNA-induced silencing complex (miRISC), the machinery that mediates microRNA function in the cytoplasm. The cytoplasmic miRISC-mediated post-transcriptional gene repression has been established as the canonical mechanism through which AGO and TNRC6 proteins operate. However, growing evidence points towards an additional mechanism through which AGO and TNRC6 regulate gene expression in the nucleus. While several mechanisms through which miRISC components function in the nucleus have been described, in this review we aim to summarize the major findings that have shed light on the role of AGO and TNRC6 in mammalian chromatin biology and on the implications these novel mechanisms may have in our understanding of regulating gene expression

Organic-inorganic heterostructures for nonlinear optics

We consider a hybrid heterostructure made of an inorganic quantum well in close proximity with an organic material overlayer, whereby the latter is used to funnel excitation energy to the former in order to exploit the optical nonlinearities of the two-dimensional Wannier excitons. The resonant optical pumping of the Frenkel excitons and their diffusion to the organic-inorganic interface can lead to an efficient indirect pumping of the inorganic quantum well turning on the corresponding nonlinearities. As organic material we consider a layer of anthracene or of tetracene. In the latter case, the singlet exciton has an energy which is close to twice the one of a triplet exciton and singlet exciton fission into two triplets can be efficient. In tetracene based hybrid heterostructures, the temperature dependence of fission opens the possibility to turn on and off the indirect pumping due to energy transfer from the organic into the inorganic subsystem. Finally, we show how a generic mechanism of dipole-dipole hybridization may lead to the formation of virtual heterodimers of organic molecules with an enhanced nonlinear optical response. Elsevier B.V. All rights reserved

Barium titanate nanoparticles and hypergravity stimulation improve differentiation of mesenchymal stem cells into osteoblasts.

BACKGROUND: Enhancement of the osteogenic potential of mesenchymal stem cells (MSCs) is highly desirable in the field of bone regeneration. This paper proposes a new approach for the improvement of osteogenesis combining hypergravity with osteoinductive nanoparticles (NPs). MATERIALS AND METHODS: In this study, we aimed to investigate the combined effects of hypergravity and barium titanate NPs (BTNPs) on the osteogenic differentiation of rat MSCs, and the hypergravity effects on NP internalization. To obtain the hypergravity condition, we used a large-diameter centrifuge in the presence of a BTNP-doped culture medium. We analyzed cell morphology and NP internalization with immunofluorescent staining and coherent anti-Stokes Raman scattering, respectively. Moreover, cell differentiation was evaluated both at the gene level with quantitative real-time reverse-transcription polymerase chain reaction and at the protein level with Western blotting. RESULTS: Following a 20 g treatment, we found alterations in cytoskeleton conformation, cellular shape and morphology, as well as a significant increment of expression of osteoblastic markers both at the gene and protein levels, jointly pointing to a substantial increment of NP uptake. Taken together, our findings suggest a synergistic effect of hypergravity and BTNPs in the enhancement of the osteogenic differentiation of MSCs. CONCLUSION: The obtained results could become useful in the design of new approaches in bone-tissue engineering, as well as for in vitro drug-delivery strategies where an increment of nanocarrier internalization could result in a higher drug uptake by cell and/or tissue constructs