EXPERIMENTAL INVESTIGATION OF CRYSTALLIZATION FOULING ON GROOVED STAINLESS STEEL SURFACES DURING CONVECTIVE HEAT TRANSFER

The beneficial aspects of enhanced or extended heat transfer surfaces may be off-set if operated under fouling conditions. In the present paper, preliminary experimental results for crystallization fouling of CaSO4 solutions onto surfaces with different structures are reported. Flat stainless steel plates (50 mm x 59 mm) with \u27V\u27 shaped grooves on the side of fluid flow were used as heat transfer surfaces. Experiments were carried out both under clean and fouling conditions to discern how the same surface structures perform under such circumstances. In addition, the impact of both, the direction of grooves with respect to fluid flow (crossed, longitudinal and mixed flow grooves) and the groove dimensions has also been investigated. Fouling trends are discussed in terms of delay time and fouling rate. Significant differences have been found for the various flow conditions

Hubble Space Telescope observations of three very young star clusters in the Small Magellanic Cloud

We present Space Telescope Imaging Spectrograph (STIS) broad band imagery and optical slitless spectroscopy of three young star clusters in the Small Magellanic Cloud (SMC). MA 1796 and MG 2 were previously known as Planetary Nebulae, and observed as such within our Hubble Space Telescope (HST) survey. With the HST spatial resolution, we show that they are instead H II regions, surrounding very young star clusters. A third compact H II region, MA 1797, was serendipitously observed by us as it falls in the same frame of MA 1796. Limited nebular analysis is presented as derived from the slitless spectra. We find that MA 1796 and MG 2 are very heavily extincted, with c>1.4, defining them as the most extincted optically-discovered star forming regions in the SMC. MA 1796 and MG 2 are extremely compact (less than 1 pc across), while MA 1797, with diameter of about 3 pc, is similar to the ultra compact H II regions already known in the SMC. Stellar analysis is presented, and approximate reddening correction for the stars is derived from the Balmer decrement. Limited analysis of their stellar content and their ionized radiation shows that these compact H II regions are ionized by small stellar clusters whose hottest stars are at most of the B0 class. These very compact, extremely reddened, and probably very dense H II regions in the SMC offer insight in the most recent star formation episodes in a very low metallicity galaxy.Comment: The Astrophysical Journal, Part 1, in press 17 pages, and 3 figure

Pascual López: autobiografía de un estudiante de medicina

We propose an integration of structural subtyping with boolean connectives and semantic subtyping to define a Java-like programming language that exploits the benefits of both techniques. Semantic subtyping is an approach to defining subtyping relation based on set-theoretic models, rather than syntactic rules. On the one hand, this approach involves some non trivial mathematical machinery in the background. On the other hand, final users of the language need not know this machinery and the resulting subtyping relation is very powerful and intuitive. While semantic subtyping is naturally linked to the structural one, we show how the framework can also accommodate the nominal subtyping. Several examples show the expressivity and the practical advantages of our proposal. © 2013 IFIP International Federation for Information Processing

Sequential Star Formation in RCW 34: A Spectroscopic Census of the Stellar Content of High-mass Star-forming Regions

We present VLT/SINFONI integral field spectroscopy of RCW 34 along with Spitzer/IRAC photometry of the surroundings. RCW 34 consists of three different regions. A large bubble has been detected on the IRAC images in which a cluster of intermediate- and low-mass class II objects is found. At the northern edge of this bubble, an HII region is located, ionized by 3 OB stars. Intermediate mass stars (2 - 3 Msun) are detected of G- and K- spectral type. These stars are still in the pre-main sequence (PMS) phase. North of the HII region, a photon-dominated region is present, marking the edge of a dense molecular cloud traced by H2 emission. Several class 0/I objects are associated with this cloud, indicating that star formation is still taking place. The distance to RCW 34 is revised to 2.5 +- 0.2 kpc and an age estimate of 2 - 1 Myrs is derived from the properties of the PMS stars inside the HII region. The most likely scenario for the formation of the three regions is that star formation propagates from South to North. First the bubble is formed, produced by intermediate- and low-mass stars only, after that, the HII region is formed from a dense core at the edge of the molecular cloud, resulting in the expansion as a champagne flow. More recently, star formation occurred in the rest of the molecular cloud. Two different formation scenarios are possible: (a) The bubble with the cluster of low- and intermediate mass stars triggered the formation of the O star at the edge of the molecular cloud which in turn induces the current star-formation in the molecular cloud. (b) An external triggering is responsible for the star-formation propagating from South to North. [abridged]Comment: 19 pages, 11 figures, accepted by Ap

Imaging in population science: cardiovascular magnetic resonance in 100,000 participants of UK Biobank - rationale, challenges and approaches

PMCID: PMC3668194SEP was directly funded by the National Institute for Health Research Cardiovascular Biomedical Research Unit at Barts. SN acknowledges support from the Oxford NIHR Biomedical Research Centre and from the Oxford British Heart Foundation Centre of Research Excellence. SP and PL are funded by a BHF Senior Clinical Research fellowship. RC is supported by a BHF Research Chair and acknowledges the support of the Oxford BHF Centre for Research Excellence and the MRC and Wellcome Trust. PMM gratefully acknowledges training fellowships supporting his laboratory from the Wellcome Trust, GlaxoSmithKline and the Medical Research Council

Spitzer View of Young Massive Stars in the LMC HII Complexes. II. N159

The HII complex N159 in the Large Magellanic Cloud (LMC) is used to study massive star formation in different environments, as it contains three giant molecular clouds (GMCs) that have similar sizes and masses but exhibit different intensities of star formation. We identify candidate massive young stellar objects (YSOs) using infrared photometry, and model their SEDs to constrain mass and evolutionary state. Good fits are obtained for less evolved Type I, I/II, and II sources. Our analysis suggests that there are massive embedded YSOs in N159B, a maser source, and several ultracompact HII regions. Massive O-type YSOs are found in GMCs N159-E and N159-W, which are associated with ionized gas, i.e., where massive stars formed a few Myr ago. The third GMC, N159-S, has neither O-type YSOs nor evidence of previous massive star formation. This correlation between current and antecedent formation of massive stars suggests that energy feedback is relevant. We present evidence that N159-W is forming YSOs spontaneously, while collapse in N159-E may be triggered. Finally, we compare star formation rates determined from YSO counts with those from integrated H-alpha and 24 micron luminosities and expected from gas surface densities. Detailed dissection of extragalactic GMCs like the one presented here is key to revealing the physics underlying commonly used star formation scaling laws.Comment: 60 pages, 11 figures. Accepted for publication in Astrophysical Journa

The Cosmological Significance of High-Velocity Cloud Complex H

We have used infrared and radio observations to search for a dwarf galaxy associated with the high-velocity cloud (HVC) known as Complex H. Complex H is a large (> 400 deg^2) and probably nearby (d = 27 kpc) HVC whose location in the Galactic plane has hampered previous investigations of its stellar content. The HI mass of the cloud is 2.0 x 10^7 (d/27 kpc)^2 Msun, making Complex H one of the most massive HVCs if its distance is > ~20 kpc. Virtually all similar HI clouds in other galaxy groups are associated with LSB dwarf galaxies. We selected mid-IR MSX sources in the direction of Complex H that appeared likely to be star-forming regions and observed them at the wavelength of the CO 1-0 transition. 59 of the 60 observed sources show emission at Milky Way velocities, and we detected no emission at velocities consistent with that of Complex H. We use these observations to set an upper limit on the ongoing star formation rate in the HVC of < 5 x 10^-4 Msun yr^-1. We also searched the 2MASS database for evidence of any dwarf-galaxy-like stellar population in the direction of the HVC and found no trace of a distant red giant population, with an upper limit on the stellar mass of ~10^6 Msun. Given the lack of evidence for either current star formation or an evolved population, we conclude that Complex H cannot be a dwarf galaxy with properties similar to those of known dwarfs. Complex H is therefore one of the most massive known HI clouds without stars. If Complex H is self-gravitating, then it is one of the few known dark galaxy candidates. These findings may offer observational support for the idea that the Cold Dark Matter substructure problem is related to the difficulty of forming stars in low-mass dark matter halos; alternatively, Complex H could be an example of a cold accretion flow onto the Milky Way. [slightly abridged]Comment: 16 pages, 7 figures (2 in color), 1 table. Accepted for publication in Ap

The Interstellar Medium of Star-forming Irregular Galaxies: The View with ISO

We present mid-infrared imaging and far-infrared (FIR) spectroscopy of 5 IBm galaxies observed by ISO as part of our larger study of the inter- stellar medium of galaxies. Most of the irregulars in our sample are very actively forming stars. The mid-infrared imaging was in a band centered at 6.75 microns that is dominated by polycyclic aromatic hydrocarbons (PAHs) and in a band centered at 15 microns that is dominated by small dust grains. The spectroscopy of 3 of the galaxies includes [CII]158 microns and [OI]63 microns, important coolants of photodissociation regions (PDRs), and [OIII]88 microns and [NII]122 microns, which come from ionized gas. [OI]145 microns and [OIII]52 microns were measured in one galaxy as well. These data are combined with PDR and HII region models to deduce properties of the interstellar medium of these galaxies.Comment: To be published in ApJ, Apr 10, 2001; higher resolution figures available from ftp.lowell.edu, cd pub/dah/isopaper

Aortic distensibility and coronary artery bypass graft patency

<p>Abstract</p> <p>Background</p> <p>Aortic distensibility is an elasticity index of the aorta, and reflects aortic stiffness. Coronary artery disease has been found to be substantially associated with increased aortic stiffness. In this study we aimed to retrospectively analyze the association of angiographically determined aortic distensibility with the patency rates of coronary bypass grafts</p> <p>Methods</p> <p>The study was conducted in the Cardiology department of the Applied Research Centre for Health of Uludağ University. The coronary angiograms of 53 consecutive coronary bypass patients were analysed retrospectively. Aortic distensibility was calculated using the formula: 2 × (change in aortic diameter)/(diastolic aortic diameter) × (change in aortic pressure). The number of stenosed and patent bypass grafts and the patient characteristics like age, risk factors were noted.</p> <p>Results</p> <p>There were 44 male (83%) and 9 female (17%) cases. Eighteen cases had only one saphenous vein grafting. The number of cases with two, three and four saphenous grafting were 18, 11 and 1; respectively. In the control angiograms the number of cases with one, two, three and four saphenous vein graft obstruction were 15 (31.3%), 7 (14.6%), 1 (2.1%) and 1 (2.1%) respectively. The aortic distensibility did not differ in cases with and without saphenous graft occlusion (p > 0.05). Also left internal mammary artery (LIMA) graft patency was not related to the distensibility of the aorta (p > 0.05). We also evaluated the data for cut-off values of 50 and 70 mmHg of pulse pressure and did not see any significant difference between the groups in terms of saphenous or LIMA grafts.</p> <p>Conclusion</p> <p>In this study we failed to show association of angiographically determined aortic distensibility with coronary bypass graft patency in consecutive 53 patients with coronary artery bypass graft surgery (CABG).</p