Palliative balloon dilation of native coarctation of the aorta in a preterm infant

The role of balloon dilation for native coarctation in neonates is controversial, due to the relatively high recurrence rate. Balloon dilation may however provide adequate palliation in preterm infants, by relieving symptoms and allowing somatic growth until definitive surgical repair can be performed. We report successful balloon angioplasty, on 2 occasions, in a preterm neonate with coarctation of the aorta and associated left ventricular cardiomyopathy.peer-reviewe

Multivariate Spline Algorithms for CAGD

Two special polyhedra present themselves for the definition of B-splines: a simplex S and a box or parallelepiped B, where the edges of S project into an irregular grid, while the edges of B project into the edges of a regular grid. More general splines may be found by forming linear combinations of these B-splines, where the three-dimensional coefficients are called the spline control points. Univariate splines are simplex splines, where s = 1, whereas splines over a regular triangular grid are box splines, where s = 2. Two simple facts render the development of the construction of B-splines: (1) any face of a simplex or a box is again a simplex or box but of lower dimension; and (2) any simplex or box can be easily subdivided into smaller simplices or boxes. The first fact gives a geometric approach to Mansfield-like recursion formulas that express a B-spline in B-splines of lower order, where the coefficients depend on x. By repeated recursion, the B-spline will be expressed as B-splines of order 1; i.e., piecewise constants. In the case of a simplex spline, the second fact gives a so-called insertion algorithm that constructs the new control points if an additional knot is inserted

A Ruling Engine for Making Zone Plates

About a century ago the corpuscular theory of light was falling into disfavor among scientific men in general and the wave theory was taking its place. Among the many contributions to the subject we find the writings of Fresnel. It was he especially who struck the decisive blow at the dying hypothesis. That part of his work which is of particular interest to us is his application of Huyghen\u27s principle to phenomena of diffraction

Internal kinematics of isolated modelled disk galaxies

We present a systematic investigation of rotation curves (RCs) of fully hydrodynamically simulated galaxies, including cooling, star formation with associated feedback and galactic winds. Applying two commonly used fitting formulae to characterize the RCs, we investigate systematic effects on the shape of RCs both by observational constraints and internal properties of the galaxies. We mainly focus on effects that occur in measurements of intermediate and high redshift galaxies. We find that RC parameters are affected by the observational setup, like slit misalignment or the spatial resolution and also depend on the evolution of a galaxy. Therefore, a direct comparison of quantities derived from measured RCs with predictions of semi-analytic models is difficult. The virial velocity V_c, which is usually calculated and used by semi-analytic models can differ significantly from fit parameters like V_max or V_opt inferred from RCs. We find that V_c is usually lower than typical characteristic velocities derived from RCs. V_max alone is in general not a robust estimator for the virial mass.Comment: 9 pages, 15 figures, accepted for publication in A&

An improved visualization of diesel particulate filter/

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 39).The prevalence of diesel particulate filters (DPF) is increasing as emissions standards worldwide evolve to match current technologies. Since the first application of DPFs in the 1980's, PM trapping effectiveness has increased by orders of magnitude. During the filter's use phase, it is subject to multiple cycles of particulate matter trapping and regeneration. The soot particles are combusted in the high temperatures; however, metal additives referred to as ash, primarily from lubricants, remain behind and restrict exhaust flow. Further ash accumulation causes a pressure drop across the filter and necessitates replacement in order to maintain fuel economy and engine performance. Research into more efficient DPF designs and geometries examines current limitations with the goal of emitting cleaning emissions and extending DPF use. In order to gain a better understanding of PM trapping and regeneration and acquire real-time feedback, an improved visualization method of DPF is required. For that method, powder glass frit was applied between the filter and glass window and heated to form a bond. After the heating process, the bond strength was measured to determine optimal heating cycles and surface conditions for the glass seal. The experimental results were examined to measure the success of the bonding method relative to previous research using alternative methods. The ability to test and observe ash accumulation in different DPF designs will contribute to the understanding of PM trapping.by Kevin Boehm.S.B

Primordial Black Holes, Hawking Radiation and the Early Universe

The 511 keV gamma emission from the galactic core may originate from a high concentration ($\sim 10^{22}$) of primordial black holes (PBHs) in the core each of whose Hawking radiation includes $\sim 10^{21}$ positrons per second. The PBHs we consider are taken as near the lightest with longevity greater than the age of the universe (mass $\sim 10^{12}$ kg; Schwarzschild radius $\sim 1$ fm). These PBHs contribute only a small fraction of cold dark matter, $\Omega_{PBH} \sim 10^{-8}$. This speculative hypothesis, if confirmed implies the simultaneous discovery of Hawking radiation and an early universe phase transition.Comment: 4 Page

Internal kinematics of modelled interacting disc galaxies

We present an investigation of galaxy-galaxy interactions and their effects on the velocity fields of disc galaxies in combined N-body/hydrodynamic simulations, which include cooling, star formation with feedback, and galactic winds. Rotation curves (RCs) of the gas are extracted from these simulations in a way that follows the procedure applied to observations of distant, small, and faint galaxies as closely as possible. We show that galaxy-galaxy mergers and fly-bys disturb the velocity fields significantly and hence the RCs of the interacting galaxies, leading to asymmetries and distortions in the RCs. Typical features of disturbed kinematics are significantly rising or falling profiles in the direction of the companion galaxy and pronounced bumps in the RCs. In addition, tidal tails can leave strong imprints on the rotation curve. All these features are observable for intermediate redshift galaxies, on which we focus our investigations. We use a quantitative measure for the asymmetry of rotation curves to show that the appearance of these distortions strongly depends on the viewing angle. We also find in this way that the velocity fields settle back into relatively undisturbed equilibrium states after unequal mass mergers and fly-bys. About 1 Gyr after the first encounter, the RCs show no severe distortions anymore. These results are consistent with previous theoretical and observational studies. As an illustration of our results, we compare our simulated velocity fields and direct images with rotation curves from VLT/FORS spectroscopy and ACS images of a cluster at z=0.53 and find remarkable similarities.Comment: 13 pages, 14 figures, accepted for publication in A&A, some improvements and changes, main conclusions are unaffecte

Computer systems analysis methodology - Studies in measuring, evaluating, and simulating computer systems

Computer systems analysis and simulation studies on design, development, and management of complex computer system