Modules program structures and the structuring of operating systems

In this paper some views are presented on the way in which complex systems, such as Operating Systems and the programs to be interfaced with them can be constructed, and how such systems may become heavily library oriented. Although such systems have a dynamic nature, all interfacing within and among modules can be checked statically. It will be shown that the concepts presented are equally valid for single user systems, multi-programming systems and even distributed systems. The ideas have been spurred by the implementation of a modular version of Pascal and a supporting Operating System, currently nearing completion at Twente University of Technology, The Netherlands

Stellar Feedback in the ISM Revealed by Wide-Field Far-Infrared Spectral-Imaging

The radiative and mechanical interaction of stars with their environment drives the evolution of the ISM and of galaxies as a whole. The far-IR emission (lambda ~30 to 350 microns) from atoms and molecules dominates the cooling of the warm gas in the neutral ISM, the material that ultimately forms stars. Far-IR lines are thus the most sensitive probes of stellar feedback processes, and allow us to quantify the deposition and cycling of energy in the ISM. While ALMA (in the (sub)mm) and JWST (in the IR) provide astonishing sub-arcsecond resolution images of point sources and their immediate environment, they cannot access the main interstellar gas coolants, nor are they designed to image entire star-forming regions (SFRs). Herschel far-IR photometric images of the interstellar dust thermal emission revealed the ubiquitous large-scale filamentary structure of SFRs, their mass content, and the location of thousands of prestellar cores and protostars. These images, however, provide a static view of the ISM: not only they dont constrain the cloud dynamics, moreover they cannot reveal the chemical composition and energy transfer within the cloud, thus giving little insight into the regulation process of star formation by stellar feedback. In this white paper we emphasize the need of a space telescope with wide-field spectral-imaging capabilities in the critical far-IR domain.Comment: White Paper submitted to the Astro 2020 Decadal Survey on Astronomy and Astrophysics (National Academies of Science, Engineering, and Medicine

Efficient ortho-para conversion of H2 on interstellar grain surfaces

Context: Fast surface conversion between ortho- and para-H2 has been observed in laboratory studies, and this mechanism has been proposed to play a role in the control of the ortho-para ratio in the interstellar medium. Observations of rotational lines of H2 in Photo-Dissociation Regions (PDRs) have indeed found significantly lower ortho-para ratios than expected at equilibrium. The mechanisms controlling the balance of the ortho-para ratio in the interstellar medium thus remain incompletely understood, while this ratio can affect the thermodynamical properties of the gas (equation of state, cooling function). Aims: We aim to build an accurate model of ortho-para conversion on dust surfaces based on the most recent experimental and theoretical results, and to validate it by comparison to observations of H2 rotational lines in PDRs. Methods: We propose a statistical model of ortho-para conversion on dust grains with fluctuating dust temperatures, based on a master equation approach. This computation is then coupled to full PDR models and compared to PDR observations. Results: We show that the observations of rotational H2 lines indicate a high conversion efficiency on dust grains, and that this high efficiency can be accounted for if taking dust temperature fluctuations into account with our statistical model of surface conversion. Simpler models neglecting the dust temperature fluctuations do not reach the high efficiency deduced from the observations. Moreover, this high efficiency induced by dust temperature fluctuations is quite insensitive to the values of microphysical parameters of the model. Conclusions: Ortho-para conversion on grains is thus an efficient mechanism in most astrophysical conditions that can play a significant role in controlling the ortho-para ratio.Comment: Accepted in Astronomy & Astrophysic

Portal vein grafts in hepatic transplantation

Confirmation of patency of the portal vein by either ultrasound or angiography is a routine part of the evaluation of patients being considered for hepatic transplantation. Complete thrombosis of the portal vein usually has been viewed as precluding successful orthotopic hepatic replacement. In addition, some pediatric patients present with extremely small portal veins which, although patent, have proved to be thick walled and sclerotic. Our recent experience has shown that, in both of these situations, successful and complete revascularization of hepatic allografts is quite feasible by using a vein graft to ensure adequate portal venous flow

Surface chemistry in the Interstellar Medium II. H2\mathrm{H}_2 formation on dust with random temperature fluctuations

The $\mathrm{H}_2$ formation on grains is known to be sensitive to dust temperature, which is also known to fluctuate for small grain sizes due to photon absorption. We aim at exploring the consequences of simultaneous fluctuations of the dust temperature and the adsorbed H-atom population on the $\mathrm{H}_2$ formation rate under the full range of astrophysically relevant UV intensities and gas conditions. The master equation approach is generalized to coupled fluctuations in both the grain's temperature and its surface population and solved numerically. The resolution can be simplified in the case of the Eley-Rideal mechanism, allowing a fast computation. For the Langmuir-Hinshelwood mechanism, it remains computationally expensive, and accurate approximations are constructed. We find the Langmuir-Hinshelwood mechanism to become an efficient formation mechanism in unshielded photon dominated region (PDR) edge conditions when taking those fluctuations into account, despite hot average dust temperatures. It reaches an importance comparable to the Eley-Rideal mechanism. However, we show that a simpler rate equation treatment gives qualitatively correct observable results in full cloud simulations under most astrophysically relevant conditions. Typical differences are a factor of 2-3 on the intensities of the $\mathrm{H}_2$ $v=0$ lines. We also find that rare fluctuations in cloud cores are sufficient to significantly reduce the formation efficiency. Our detailed analysis confirms that the usual approximations used in numerical models are adequate when interpreting observations, but a more sophisticated statistical analysis is required if one is interested in the details of surface processes.Comment: 21 pages, 28 figures, accepted in A&

Exploring the SDSS Dataset with Linked Scatter Plots: I. EMP, CEMP, and CV Stars

We present the results of a search for extremely metal-poor (EMP), carbon-enhanced metal-poor (CEMP), and cataclysmic variable (CV) stars using a new exploration tool based on linked scatter plots (LSPs). Our approach is especially designed to work with very large spectrum data sets such as the SDSS, LAMOST, RAVE, and Gaia data sets, and it can be applied to stellar, galaxy, and quasar spectra. As a demonstration, we conduct our search using the SDSS DR10 data set. We first created a 3326-dimensional phase space containing nearly 2 billion measures of the strengths of over 1600 spectral features in 569,738 SDSS stars. These measures capture essentially all the stellar atomic and molecular species visible at the resolution of SDSS spectra. We show how LSPs can be used to quickly isolate and examine interesting portions of this phase space. To illustrate, we use LSPs coupled with cuts in selected portions of phase space to extract EMP stars, CEMP stars, and CV stars. We present identifications for 59 previously unrecognized candidate EMP stars and 11 previously unrecognized candidate CEMP stars. We also call attention to 2 candidate He~II emission CV stars found by the LSP approach that have not yet been discussed in the literature.Comment: Accepted by the Astrophysical Journal Supplement (February 2017

A solute gradient in the tear meniscus I. A hypothesis to explain Marx's line

Marx's line is a line of mucosal staining behind the mucocutaneous junction. It can be demonstrated throughout life in all normal lids by staining with lissamine green and related dyes. Of all the body orifices, only the mucosae of the eye and mouth are directly exposed to the atmosphere. In this paper, we suggest that for the eye, this exposure leads to the formation of Marx's line. The tear meniscus thins progressively toward its apex, where it is pinned at the mucocutaneous junction of the lid. It also thins toward the black line, which segregates the meniscus from the tear film after the blink. We predict that, because of the geometry of the tear meniscus, evaporation generates a solute gradient across the meniscus profile in the anteroposterior plane, which peaks at the meniscus apices at the end of the interblink. One outcome would be to amplify the level of tear molarity at these sites so that they reach hyperosmolar proportions. Preliminary mathematical modeling suggests that dilution of this effect by advection and diffusion of solute away from the meniscus apex at the mucocutaneous junction will be restricted by spatial constraints, the presence of tear and surface mucins at this site, and limited fluid flow. We conclude that evaporative water loss from the tear meniscus may result in a physiological zone of hyperosmolar and related stresses to the occlusal conjunctiva, directly behind the mucocutaneous junction. We hypothesize that this stimulates a high epithelial cell turnover at this site, incomplete epithelial maturation, and a failure to express key molecules such as MUC 16 and galectin-3, which, with the tight junctions between surface epithelial cells, are necessary to seal the ocular surface and prevent penetration of dyes and other molecules into the epithelium. This is proposed as the basis for Marx's line. In Part II of this paper (also published in this issue of The Ocular Surface), we address additional pathophysiological consequences of this mechanism, affecting lid margins

Vascular complications after liver transplantation: A 5-year experience

During the past 5 years, 104 angiographic studies were performed in 87 patients (45 children and 42 adults) with 92 transplanted livers for evaluation of possible vascular complications. Seventy percent of the studies were abnormal. Hepatic artery thrombosis was the most common complication (seen in 42% of children studied, compared with only 12% of adults) and was a major complication that frequently resulted in graft failure, usually necessitating retransplantation. In six children, reconstitution of the intrahepatic arteries by collaterals was seen. Three survived without retransplant. Arterial stenosis at the anastomosis or in the donor hepatic artery was observed in 11% of patients. Portal vein thrombosis or stenosis occurred in 13% of patients. Two children and one adult with portal vein thrombosis demonstrated hepatopetal collaterals that reconstituted the intrahepatic portal vessels. Uncommon complications included anastomotic and donor hepatic artery pseudoaneurysms, a hepatic artery-dissecting aneurysm, pancreaticoduodenal mycotic aneurysms, hepatic artery-portal vein fistula, biliary-portal vein fistula, hepatic vein occlusion, and inferior vena cava thrombosis