Influence of Nanoparticle Shape Factor on Convective Heat Transfer of Water-Based ZnO Nanofluids. Performance Evaluation Criterion

The convective heat transfer of ZnO/water colloidal suspensions is investigated experimentally to appreciate the influence of two shapes of nanoparticles. Pressure drop and heat transfer coefficients have been measured at two different inlet temperatures (20, 50°C) in heating and/or cooling conditions at various flow rates (200 \u3c Re \u3c 15,000). The Reynolds and Nusselt numbers have been determined by using thermal conductivity and viscosity measured in the same conditions as those in tests. The results obtained are compared with classical correlations. An energetic Performance Evaluation Criterion (PEC) has been defined to compare heat transfer rate to pumping power

An original interferometric study of NGC 1068 with VISIR BURST mode images

We present 12.8 microns images of the core of NGC 1068 obtained with the BURST mode of the VLT/VISIR. We trace structures under the diffraction limit of one UT and we investigate the link between dust in the vicinity of the central engine of NGC 1068, recently resolved by interferometry with MIDI, and more extended structures. This step is mandatory for a multi-scale understanding of the sources of mid-infrared emission in AGNs. A speckle processing of VISIR BURST mode images was performed to extract very low spatial-frequency visibilities, first considering the full field of VISIR BURST mode images and then limiting it to the mask used for the acquisition of MIDI data. Extracted visibilities are reproduced with a multi-component model. We identify two major sources of emission: one compact < 85 mas, associated with the dusty torus, and an elliptical one, (< 140) mas x 1187 mas at P.A.=-4 degrees from N to E. This is consistent with previous deconvolution processes. The combination with MIDI data reveals the close environment of the dusty torus to contribute to about 83 percent of the MIR flux seen by MIDI. This strong contribution has to be considered in modeling long baseline interferometric data. It must be related to the NS elongated component which is thought to originate from individually unresolved dusty clouds and is located inside the ionization cone. Low temperatures of the dusty torus are not challenged, emphasizing the scenarios of clumpy torus.Comment: 10 pages, 7 figures, accepted for publication in A&

Spectral properties of a 2D scalar wave equation with 1D-periodic coefficients: application to SH elastic waves

The paper provides a rigorous analysis of the dispersion spectrum of SH (shear horizontal) elastic waves in periodically stratified solids. The problem consists of an ordinary differential wave equation with periodic coefficients, which involves two free parameters $\omega$ (the frequency) and $k$ (the wavenumber in the direction orthogonal to the axis of periodicity). Solutions of this equation satisfy a quasi-periodic boundary condition which yields the Floquet parameter $K$. The resulting dispersion surface $\omega (K,k)$ may be characterized through its cuts at constant values of $K, k$ and $\omega$ that define the passband (real $K$) and stopband areas, the Floquet branches and the isofrequency curves, respectively. The paper combines complementary approaches based on eigenvalue problems and on the monodromy matrix $\mathbf{M}$. The pivotal object is the Lyapunov function $\Delta (\omega ^{2},k^{2}) \equiv 1/2\mathrm{trace}\mathbf{M}=\cos K$ which is generalized as a function of two variables. Its analytical properties, asymptotics and bounds are examined and an explicit form of its derivatives obtained. Attention is given to the special case of a zero-width stopband. These ingredients are used to analyze the cuts of the surface $\omega (K,k).$ The derivatives of the functions $\omega (k)$ at fixed $K$ and $\omega (K)$ at fixed $k$ and of the function $K(k)$ at fixed $\omega$ are described in detail. The curves $\omega (k)$ at fixed $K$ are shown to be monotonic for real $K,$ while they may be looped for complex $K$ (i.e. in the stopband areas). The convexity of the closed (first) real isofrequency curve $K(k)$ is proved thus ruling out low-frequency caustics of group velocity. The results are relevant to the broad area of applicability of ordinary differential equation for scalar waves in 1D phononic (solid or fluid) and photonic crystals.Comment: 35 pages, 4 figure

On the effective shear speed in 2D phononic crystals

The quasistatic limit of the antiplane shear-wave speed ('effective speed') $c$ in 2D periodic lattices is studied. Two new closed-form estimates of $c$ are derived by employing two different analytical approaches. The first proceeds from a standard background of the plane wave expansion (PWE). The second is a new approach, which resides in $\mathbf{x}$-space and centers on the monodromy matrix (MM) introduced in the 2D case as the multiplicative integral, taken in one coordinate, of a matrix with components being the operators with respect to the other coordinate. On the numerical side, an efficient PWE-based scheme for computing $c$ is proposed and implemented. The analytical and numerical findings are applied to several examples of 2D square lattices with two and three high-contrast components, for which the new PWE and MM estimates are compared with the numerical data and with some known approximations. It is demonstrated that the PWE estimate is most efficient in the case of densely packed stiff inclusions, especially when they form a symmetric lattice, while in general it is the MM estimate that provides the best overall fitting accuracy.Comment: 13 pages, 9 figure

Milliarcsecond angular resolution of reddened stellar sources in the vicinity of the Galactic Center

For the first time, the lunar occultation technique has been employed on a very large telescope in the near-IR with the aim of achieving systematically milliarcsecond resolution on stellar sources. We have demonstrated the burst mode of the ISAAC instrument, using a fast read-out on a small area of the detector to record many tens of seconds of data at a time on fields of few squared arcsec. We have used the opportunity to record a large number of LO events during a passage of the Moon close to the Galactic Center in March 2006. We have developed a data pipeline for the treatment of LO data, including the automated estimation of the main data analysis parameters using a wavelet-based method, and the preliminary fitting and plotting of all light curves. We recorded 51 LO events over about four hours. Of these, 30 resulted of sufficient quality to enable a detailed fitting. We detected two binaries with subarcsec projected separation and three stars with a marginally resolved angular diameter of about 2 mas. Two more SiO masers, were found to be resolved and in one case we could recover the brightness profile of the extended emission, which is well consistent with an optically thin shell. The remaining unresolved stars were used to characterize the performance of the method. The LO technique at a very large telescope is a powerful and efficient method to achieve angular resolution, sensitivity, and dynamic range that are among the best possible today with any technique. The selection of targets is naturally limited and LOs are fixed-time events, however each observation requires only a few minutes including overheads. As such, LOs are ideally suited to fill small gaps of idle time between standard observations.Comment: A&A in pres

Cardiosphere-derived cells suppress allogeneic lymphocytes by production of PGE2 acting via the EP4 receptor

derived cells (CDCs) are a cardiac progenitor cell population, which have been shown to possess cardiac regenerative properties and can improve heart function in a variety of cardiac diseases. Studies in large animal models have predominantly focussed on using autologous cells for safety, however allogeneic cell banks would allow for a practical, cost-effective and efficient use in a clinical setting. The aim of this work was to determine the immunomodulatory status of these cells using CDCs and lymphocytes from 5 dogs. CDCs expressed MHC I but not MHC II molecules and in mixed lymphocyte reactions demonstrated a lack of lymphocyte proliferation in response to MHC-mismatched CDCs. Furthermore, MHC-mismatched CDCs suppressed lymphocyte proliferation and activation in response to Concanavalin A. Transwell experiments demonstrated that this was predominantly due to direct cell-cell contact in addition to soluble mediators whereby CDCs produced high levels of PGE2 under inflammatory conditions. This led to down-regulation of CD25 expression on lymphocytes via the EP4 receptor. Blocking prostaglandin synthesis restored both, proliferation and activation (measured via CD25 expression) of stimulated lymphocytes. We demonstrated for the first time in a large animal model that CDCs inhibit proliferation in allo-reactive lymphocytes and have potent immunosuppressive activity mediated via PGE2

Daptomycin as a possible new treatment option for surgical management of Methicillin-Resistant Staphylococcus aureus sternal wound infection after cardiac surgery

We present a case of a 77-year old female who had undergone a coronary artery bypass grafting with an aortic valve replacement and developed three month later a Methicillin-Resistant Staphylococcus aureus (MRSA) sternal wound infection which was successful treated with Daptomycin combined with vacuum-assisted closure (VAC)