Can Conformal Weyl Gravity be Considered a Viable Cosmological Theory?

We present exact analytical solutions to the Conformal Weyl Gravity cosmological equations that are valid for both the matter and radiation dominated eras. The Primordial Nucleosynthesis process is also exhaustively studied. The main conclusion of our work is that cosmological models derived from this theory are not likely to reproduce the observational properties of our Universe. They fail to fulfill simultaneously the observational constraints on present cosmological parameters and on primordial light element abundances.Comment: 7 pages, (1 Figure included), uuencode compressed Postscript. (To be published in ApJ, June 1994.). FTUAM-93-2

Hydrodynamical simulations of galaxy properties: Environmental effects

Using N-body+hydro simulations we study relations between the local environments of galaxies on 0.5 Mpc scale and properties of the luminous components of galaxies. Our numerical simulations include effects of star formation and supernova feedback in different cosmological scenarios: the standard Cold Dark Matter model, the Broken Scale Invariance model (BSI), and a model with cosmological constant (LCDM). In this paper, we concentrate on the effects of environment on colors and morphologies of galaxies, on the star formation rate and on the relation between the total luminosity of a galaxy and its circular velocity. We demonstrate a statistically significant theoretical relationship between morphology and environment. In particular, there is a strong tendency for high-mass galaxies and for elliptical galaxies to form in denser environments, in agreement with observations. We find that in models with denser environments (CDM scenario) ~ 13 % of the galactic halos can be identified as field ellipticals, according to their colors. In simulations with less clustering (BSI and LCDM), the fraction of ellipticals is considerably lower (~ 2-3 %). The strong sensitivity of morphological type to environment is rather remarkable because our results are applicable to ``field'' galaxies and small groups. If all galaxies in our simulations are included, we find a statistically significant dependence of the galaxy luminosity - circular velocity relation on dark matter overdensity within spheres of radius 0.5 Mpc, for the CDM simulations. But if we remove ``elliptical'' galaxies from our analysis to mimic the Tully-Fisher relation for spirals, then no dependence is found in any model.Comment: 44 pages, 21 figures (17 included). Submitted to New Astronomy. GIFF color plots and the complete paper in Postscript (including color figures) can be found at http://astrosg.ft.uam.es/~gustavo/newas

Invariant-based Mapping of Space During General Motion of an Observer

This paper explores visual motion-based invariants, resulting in a new instantaneous domain where: a) the stationary environment is perceived as unchanged, even as the 2D images undergo continuous changes due to camera motion, b) obstacles can be detected and potentially avoided in specific subspaces, and c) moving objects can potentially be detected. To achieve this, we make use of nonlinear functions derived from measurable optical flow, which are linked to geometric 3D invariants. We present simulations involving a camera that translates and rotates relative to a 3D object, capturing snapshots of the camera projected images. We show that the object appears unchanged in the new domain over time. We process real data from the KITTI dataset and demonstrate how to segment space to identify free navigational regions and detect obstacles within a predetermined subspace. Additionally, we present preliminary results, based on the KITTI dataset, on the identification and segmentation of moving objects, as well as the visualization of shape constancy. This representation is straightforward, relying on functions for the simple de-rotation of optical flow. This representation only requires a single camera, it is pixel-based, making it suitable for parallel processing, and it eliminates the necessity for 3D reconstruction techniques

Comparison of Anesthesia for Dental/Oral Surgery by Office-based Dentist Anesthesiologists versus Operating Room-based Physician Anesthesiologists

Few studies have examined the practice characteristics of dentist anesthesiologists and compared them to other anesthesia providers. Using outcomes from the National Anesthesia Clinical Outcomes Registry and the Society for Ambulatory Anesthesia Clinical Outcomes Registry for dental/oral surgery procedures, we compared 7133 predominantly office-based anesthetics by dentist anesthesiologists to 106,420 predominantly operating room anesthetics performed by physician anesthesia providers. These encounters were contrasted with 34,191 previously published encounters from the practices of oral and maxillofacial surgeons. Children younger than 6 years received the greatest proportion of general anesthetic services rendered by both dentist anesthesiologists and hospital-based anesthesia providers. These general anesthesia services were primarily provided for complete dental rehabilitation for early childhood caries. Overall treatment time for complete dental rehabilitation in the office-based setting by dentist anesthesiologists was significantly shorter than comparable care provided in the hospital operating room and surgery centers. The anesthesia care provided by dentist anesthesiologists was found to be separate and distinct from anesthesia care provided by oral and maxillofacial surgeons, which was primarily administered to adults for very brief surgical procedures. Cases performed by dentist anesthesiologists and hospital-based anesthesia providers were for much younger patients and of significantly longer duration when compared with anesthesia administered by oral and maxillofacial surgeons. Despite the limited descriptive power of the current registries, office-based anesthesia rendered by dentist anesthesiologists is clearly a unique and efficient mode of anesthesia care for dentistry

Vast planes of satellites in a high resolution simulation of the Local Group: comparison to Andromeda

We search for vast planes of satellites (VPoS) in a high resolution simulation of the Local Group performed by the CLUES project, which improves significantly the resolution of former similar studies. We use a simple method for detecting planar configurations of satellites, and validate it on the known plane of M31. We implement a range of prescriptions for modelling the satellite populations, roughly reproducing the variety of recipes used in the literature, and investigate the occurence and properties of planar structures in these populations. The structure of the simulated satellite systems is strongly non-random and contains planes of satellites, predominantly co-rotating, with, in some cases, sizes comparable to the plane observed in M31 by Ibata et al.. However the latter is slightly richer in satellites, slightly thinner and has stronger co-rotation, which makes it stand out as overall more exceptional than the simulated planes, when compared to a random population. Although the simulated planes we find are generally dominated by one real structure, forming its backbone, they are also partly fortuitous and are thus not kinematically coherent structures as a whole. Provided that the simulated and observed planes of satellites are indeed of the same nature, our results suggest that the VPoS of M31 is not a coherent disc and that one third to one half of its satellites must have large proper motions perpendicular to the plane

High resolution simulations of the reionization of an isolated Milky Way - M31 galaxy pair

We present the results of a set of numerical simulations aimed at studying reionization at galactic scale. We use a high resolution simulation of the formation of the Milky Way-M31 system to simulate the reionization of the local group. The reionization calculation was performed with the post-processing radiative transfer code ATON and the underlying cosmological simulation was performed as part of the CLUES project. We vary the source models to bracket the range of source properties used in the literature. We investigate the structure and propagation of the galatic ionization fronts by a visual examination of our reionization maps. Within the progenitors we find that reionization is patchy, and proceeds locally inside out. The process becomes patchier with decreasing source photon output. It is generally dominated by one major HII region and 1-4 additional isolated smaller bubbles, which eventually overlap. Higher emissivity results in faster and earlier local reionization. In all models, the reionization of the Milky Way and M31 are similar in duration, i.e. between 203 Myr and 22 Myr depending on the source model, placing their zreion between 8.4 and 13.7. In all models except the most extreme, the MW and M31 progenitors reionize internally, ignoring each other, despite being relatively close to each other even during the epoch of reionization. Only in the case of strong supernova feedback suppressing star formation in haloes less massive than 10^9 M_sun, and using our highest emissivity, we find that the MW is reionized by M31.Comment: Accepted for publication in ApJ. 14 pages, 4 figures, 1 tabl

Surface fitting in geomorphology - examples for regular-shaped volcanic landforms

In nature, several types of landforms have simple shapes: as they evolve they tend to take on an ideal, simple geometric form such as a cone, an ellipsoid or a paraboloid. Volcanic landforms are possibly the best examples of this ?ideal? geometry, since they develop as regular surface features due to the point-like (circular) or fissure-like (linear) manifestation of volcanic activity. In this paper, we present a geomorphometric method of fitting the ?ideal? surface onto the real surface of regular-shaped volcanoes through a number of case studies (Mt. Mayon, Mt. Somma, Mt. Semeru, and Mt. Cameroon). Volcanoes with circular, as well as elliptical, symmetry are addressed. For the best surface fit, we use the minimization library MINUIT which is made freely available by the CERN (European Organization for Nuclear Research). This library enables us to handle all the available surface data (every point of the digital elevation model) in a one-step, half-automated way regardless of the size of the dataset, and to consider simultaneously all the relevant parameters of the selected problem, such as the position of the center of the edifice, apex height, and cone slope, thanks to the highly performing adopted procedure. Fitting the geometric surface, along with calculating the related error, demonstrates the twofold advantage of the method. Firstly, we can determine quantitatively to what extent a given volcanic landform is regular, i.e. how much it follows an expected regular shape. Deviations from the ideal shape due to degradation (e.g. sector collapse and normal erosion) can be used in erosion rate calculations. Secondly, if we have a degraded volcanic landform, whose geometry is not clear, this method of surface fitting reconstructs the original shape with the maximum precision. Obviously, in addition to volcanic landforms, this method is also capable of constraining the shapes of other regular surface features such as aeolian, glacial or periglacial landforms