7,074 research outputs found
Comparison between 2-D and 3-D codes in dynamical simulations of gas flow in barred galaxies
Context: One of the ways to determine the contribution of the dark halo to
the gravitational potential of a galaxy is the study of non-circular
(streaming) motions and the associated gas shocks in the bar region. These
motions, determined by the potential in the inner parts, can break the
disk-halo degeneracy. Here, two main fluid dynamical approaches have been
chosen to model the non-circular motions in the bar region; a 2-D Eulerian grid
code for an isothermal gas (FS2) and a 3-D smoothed particle hydrodynamic code
(N-body/SPH). Aims: The aim of this paper is to compare and quantify the
differences of the gas flows in rotating barred potential obtained using two
different fluid dynamical approaches. We analyse the effect of using 2-D and a
3-D codes in the calculation of gas flow in barred galaxies and to which extend
the results are affected by the code. To do this, we derive the velocity field
and density maps for the mass model of NGC 4123 using a 3-D N-body/SPH code and
compare the results to the previous 2-D Eulerian grid code results. Methods:
Numerical modelling, 3-D N-body/SPH simulations Results: The global velocity
field and the gas distribution is very similar in both models. The study shows
that the position and strength of the shocks developed in the SPH simulations
do not vary significantly compared to the results derived from the 2-D FS2
code. The largest velocity difference across the shock is 20\kms between the
2-D and 3-D fluid dynamical models. Conclusions: The results obtained in the
studies deriving the dark matter content of barred galaxies using the bar
streaming motions and strength and position of shocks are robust to the fluid
dynamical model used. The effect of 2-D and 3-D modelling can be neglected in
this type of studies.Comment: 5 pages, accepted for publication in A&
The Uncertain Future of Marriage and the Alternatives
The cultural and institutional predominance of marriage in our society has lately been challenged by two important social trends: growing dissatisfaction with or indifference to marriage on the part of those eligible to marry, and the emergence of nontraditional families headed by adults who may wish to marry but are presently excluded from doing so. This Essay argues that proactive law reformers have responded to these trends by taking two very different approaches. The first approach, âdiversity of forms,â is exemplified by the cultivation of alternatives and substitutes to traditional marriage ranging from same and opposite-sex domestic partnerships and other forms of âmarriage-liteâ to commitment-intensive options like covenant marriage. The other approach, âequal inclusion,â emphasizes broader access to regular marriage itself, and is exemplified by the egalitarian, civil rights-focused, and deeply marriage-affirmative views of the Massachusetts Supreme Judicial Court in Goodridge v. Depât of Public Health. This Essay goes on to contend that although these two reform approaches are quite different, they share a common vision of how the law of marriage and coupling should be shaped by the social reality of citizensâ lives rather than by abstract traditional archetypes, leaving both approaches more-or-less on the same side in the larger culture war being waged over the future of marriage and family law. There is still potential for serious conflict, however, because although both approaches are skeptical of idealized tradition, they each remain nested in a diverse and disparate array of other aspirational norms that may lead them to threaten each otherâs long-term institutional agendas
Surprising applications and possible extensions of Dellsarte's method
Paper presented at Strathmore International Math Research Conference on July 23 - 27, 2012This is a short informal survey on some surprising
applications of Delsarte's method, written for anyone being interested.
I try to keep it as short and as informative as possibleThis is a short informal survey on some surprising applications of Delsarte's method, written for anyone being interested. I try to keep it as short and as informative as possibl
Deciphering nonfemtoscopic two-pion correlations in collisions with simple analytical models
A simple model of nonfemtoscopic particle correlations in proton-proton
collisions is proposed. The model takes into account correlations induced by
the conservation laws as well as correlations induced by minijets. It
reproduces well the two-pion nonfemtoscopic correlations of like-sign and
unlike-sign pions in proton-proton collision events at GeV
analyzed by the ALICE Collaboration. We also argue that similar nonfemtoscopic
correlations can appear in the hydrodynamic picture with event-by-event
fluctuating nonsymmetric initial conditions that are typically associated with
nonzero higher-order flow harmonics.Comment: 21 pages, 10 figures, misprints correcte
Controlled biomineralization of magnetite (Fe<sub>3</sub>O<sub>4</sub>) by <i>Magnetospirillum gryphiswaldense</i>
Results from a study of the chemical composition and micro-structural characteristics of bacterial magnetosomes extracted from the magnetotactic bacterial strain Magnetospirillum gryphiswaldense are presented here. Using high-resolution transmission electron microscopy combined with selected-area electron diffraction and energy dispersive X-ray microanalysis, biogenic magnetite particles isolated from mature cultures were analysed for variations in crystallinity and particle size, as well as chain character and length. The analysed crystals showed a narrow size range (âŒ14-67 nm) with an average diameter of 46±6.8 nm, cuboctahedral morphologies and typical Gamma type crystal size distributions. The magnetite particles exhibited a high chemical purity (exclusively Fe3O4) and the majority fall within the single-magnetic-domain range
A Preliminary Study of Three-dimensional Sonographic Measurements of the Fetus
OBJECTIVES: This study was aimed at establishing an ideal method for performing three-dimensional measurements of the fetus in order to improve the estimation of fetal weight. METHODS: The study consisted of two phases. Phase I was a prospective cross-sectional study performed between 28 and 40 weeks\u27 gestation. The study population (n=110) comprised low-risk singleton pregnancies who underwent a routine third-trimester sonographic estimation of fetal weight. The purpose of this phase was to establish normal values for the fetal abdominal and head volumes throughout the third trimester. Phase II was a prospective study that included patients admitted for an elective cesarean section or for induction of labor between 38 and 41 weeks\u27 gestation (n=91). This phase of the study compared the actual birth weight to two- (2D) and three-dimensional (3D) measurements of the fetus. Conventional 2D ultrasound fetal biometry was performed measuring the biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur diaphysis length (FL). Volume estimates were computed utilizing Virtual Organ Computer-aided AnaLysis (VOCAL), and the correlation between measured volumes and actual neonatal weight was calculated. RESULTS: Overall, this longitudinal study consisted of 110 patients between 28 and 41 weeks\u27 gestation. Normal values were computed for the fetal abdomen and head volume throughout the third trimester. Ultrasound examination was performed within three days prior to delivery on 91 patients. A good correlation was found between birth weight and abdominal volume (r=0.77) and between birth weight and head volume (r=0.5). Correlation between bidimensional measurements and actual fetal weights was found to be comparable with previously published correlations. CONCLUSION: Volume measurements of the fetus may improve the accuracy of estimating fetal size. Additional studies using different volume measurement of the fetus are necessary
Particle Size Determination: An undergraduate lab in Mie scattering
A technique for determining the size of microscopic spherical particles using light scattering is presented as an undergraduate physics lab. Scatterer size is determined from angular scattering distribution measurements of laser light scattered from a dilute suspension of latex spheres with diameters of 4.99±0.05 and 6.038±0.045âÎŒm. Previous experiments of this type used approximate theoretical corrections and required the construction of specialized sample cells to minimize complicating effects. As a significant improvement to these, we generate angular scattering distributions from Mie theory and, using an accurate numerical procedure, correct these distributions for Snellâs law and foreshortening effects. Scatterer size is then determined using a fast, robust fitting algorithm to compare these corrected angular scattering distributions to measured angular scattering distributions. We fit the scatter from a solution of 6.04-ÎŒm-diam spheres to spheres of 5.95±0.11âÎŒm diameter, and that from a solution of 4.99-ÎŒm spheres to 4.85±0.15âÎŒm. Additionally, scattering data for a 2:1 mixture of spheres of diameters 4.99 and 6.04 ÎŒm are taken, and after numerical adjustment for Snellâs law and foreshortening effects, good agreement with theory is obtained
The Fractal Properties of the Source and BEC
Using simple space-time implementation of the random cascade model we
investigate numerically influence of the possible fractal structure of the
emitting source on Bose-Einstein correlations between identical particles. The
results are then discussed in terms of the non-extensive Tsallis statistics.Comment: LaTeX file and 2 PS files with figures, 8 pages altogether. Talk
presented at the 12th Indian Summer School "Relativistic Heavy Ion Physics,
Prague, Czech Republic, 30 August-3 Sept. 1999; to be published in Czech J.
Phys. (1999). Some typos correcte
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