36,121 research outputs found
Made-to-Measure models of the Galactic Box/Peanut bulge: stellar and total mass in the bulge region
We construct dynamical models of the Milky Way's Box/Peanut (B/P) bulge,
using the recently measured 3D density of Red Clump Giants (RCGs) as well as
kinematic data from the BRAVA survey. We match these data using the NMAGIC
Made-to-Measure method, starting with N-body models for barred discs in
different dark matter haloes. We determine the total mass in the bulge volume
of the RCGs measurement (+-2.2 x +- 1.4 x +- 1.2 kpc) with unprecedented
accuracy and robustness to be 1.84 +- 0.07 x10^10 Msun. The stellar mass in
this volume varies between 1.25-1.6 x10^10 Msun, depending on the amount of
dark matter in the bulge. We evaluate the mass-to-light and mass-to-clump
ratios in the bulge and compare them to theoretical predictions from population
synthesis models. We find a mass-to-light ratio in the K-band in the range
0.8-1.1. The models are consistent with a Kroupa or Chabrier IMF, but a
Salpeter IMF is ruled out for stellar ages of 10 Gyr. To match predictions from
the Zoccali IMF derived from the bulge stellar luminosity function requires
about 40% or 0.7 x10^10 Msun dark matter in the bulge region. The BRAVA data
together with the RCGs 3D density imply a low pattern speed for the Galactic
B/P bulge of 25-30 km.s-1.kpc-1. This would place the Galaxy among the slow
rotators (R >= 1.5). Finally, we show that the Milky Way's B/P bulge has an
off-centred X structure, and that the stellar mass involved in the peanut shape
accounts for at least 20% of the stellar mass of the bulge, significantly
larger than previously thought.Comment: Accepted for publication in MNRA
Prediction of force coefficients for labyrinth seals
The development of a linear model for the prediction of labyrinth seal forces and on its comparison to available stiffness data is presented. A discussion of the relevance of fluid damping forces and the preliminary stages of a program to obtain data on these forces are examined. Fluid-dynamic forces arising from nonuniform pressure patterns in labyrinth seal glands are known to be potentially destablizing in high power turbomachinery. A well documented case in point is that of the space Shuttle Main Engine turbopumps. Seal forces are also an important factor for the stability of shrouded turbines, acting in that case in conjunction with the effects of blade-tip clearance variations
Reduced-order models of the Martian atmospheric dynamics
In this paper we explore the possibility of deriving low-dimensional models of the dynamics of the Martian atmosphere. The analysis consists of a Proper Orthogonal Decomposition (POD) of the atmospheric streamfunction after first decomposing the vertical structure with a set of eigenmodes. The vertical modes were obtained from the quasi-geostrophic vertical structure equation. The empirical orthogonal functions (EOFs) were optimized to represent the atmospheric total energy. The total energy was used as the criterion to retain those modes with large energy content and discard the rest. The principal components (PCs) were analysed by means of Fourier analysis, so that the dominant frequencies could be identified. It was possible to observe the strong influence of the diurnal cycle and to identify the motion and vacillation of baroclinic waves
A near-IR line of Mn I as a diagnostic tool of the average magnetic energy in the solar photosphere
We report on spectropolarimetric observations of a near-IR line of Mn I
located at 15262.702 A whose intensity and polarization profiles are very
sensitive to the presence of hyperfine structure. A theoretical investigation
of the magnetic sensitivity of this line to the magnetic field uncovers several
interesting properties. The most important one is that the presence of strong
Paschen-Back perturbations due to the hyperfine structure produces an intensity
line profile whose shape changes according to the absolute value of the
magnetic field strength. A line ratio technique is developed from the intrinsic
variations of the line profile. This line ratio technique is applied to
spectropolarimetric observations of the quiet solar photosphere in order to
explore the probability distribution function of the magnetic field strength.
Particular attention is given to the quietest area of the observed field of
view, which was encircled by an enhanced network region. A detailed theoretical
investigation shows that the inferred distribution yields information on the
average magnetic field strength and the spatial scale at which the magnetic
field is organized. A first estimation gives ~250 G for the mean field strength
and a tentative value of ~0.45" for the spatial scale at which the observed
magnetic field is horizontally organized.Comment: 42 pages, 17 figures, accepted for publication in the Astrophysical
Journal. Figures 1 and 9 are in JPG forma
Economic viability of commercial composting of organic wasters from market by passive aeration
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