667 research outputs found
\u27Women\u27s Summit\u27 Hits Home
Newspaper article from Business The Call about the 1997 Women\u27s Summit
Linearizing the Observed Power Spectrum
Reconstruction of the linear power spectrum from observational data provides
a way to compare cosmological models to a large amount of data, as Peacock &
Dodds (1994, 1996) have shown. By applying the appropriate corrections to the
observational power spectrum it is possible to recover the underlying linear
power spectrum for any cosmological model. Using extensive N-body simulations
we demonstrate that the method is applicable to a wide range of cosmological
models. However, we find that the recovery of the linear power spectrum from
observations following PD94 is misleading because the corrections are model-
dependent. When we apply the proper corrections for a given model to the
observational power spectrum, we find that no model in our test group recovers
the linear power spectrum well for the bias suggested by PD94 between Abell,
Radio, Optical, and IRAS catalogs 4.5:1.9:1.3:1, with b_IRAS=1. When we allow
b_IRAS to vary we find that: (i)CHDM models give very good fits to observations
if optically-selected galaxies are slightly biased b_Opt=1.1 (ii) Most LCDM
models give worse but acceptable fits if blue galaxies are considerably
antibiased: 0.6<b_Opt<0.9 and fail if optical galaxies are biased. (iii)There
is a universal shape of the recovered linear power spectrum of all LCDM models
over their entire range of explored wavenumbers,0.01<k<0.6h\Mpc. Recovered
spectra of CDM and CHDM models are nearly the same as that of LCDM in the
region 0.01<k<0.2h/Mpc but diverge from this spectrum at higher k.Comment: submitted to the Mon.Not.R.Astron.Soc., LaTeX (uses mn.sty,
graphics.sty, endfloat.sty, trig.sty), 15 pages, 10 figures, also available
at http://astro.nmsu.edu/~akravtso/GROUP/group_publications.html or at
ftp://charon.nmsu.edu/pub/aklypin/LINOB
The Bulge-Halo Connection in Galaxies: A Physical Interpretation of the Vcirc-sigma_0 Relation
We explore the dependence of the ratio of a galaxy's circular velocity,
Vcirc, to its central velocity dispersion, sigma_0, on morphology, or
equivalently total light concentration. Such a dependence is expected if light
traces the mass. Over the full range of galaxy types, masses and brightnesses,
and assuming that the gas velocity traces the circular velocity, we find that
galaxies obey the relation log(Vcirc/sigma_0)= 0.63-0.11*C28 where
C28=5log(r80/r20) and the radii are measured at 80 percent and 20 percent of
the total light. Massive galaxies scatter about the Vcirc = sqrt(2)*sigma_0
line for isothermal stellar systems. Disk galaxies follow the simple relation
Vcirc/sigma_0=2(1-B/T), where B/T is the bulge-to-total light ratio. For pure
disks, C28~2.8, B/T -> 0, and Vcirc~=2*sigma_0. Self-consistent equilibrium
galaxy models from Widrow & Dubinski (2005) constrained to match the
size-luminosity and velocity-luminosity relations of disk galaxies fail to
match the observed Vcirc/sigma_0 distribution. Furthermore, the matching of
dynamical models for Vcirc(r)/sigma(r) with observations of dwarf and
elliptical galaxies suffers from limited radial coverage and relatively large
error bars; for dwarf systems, however, kinematical measurements at the galaxy
center and optical edge suggest Vcirc(Rmax) > 2*sigma_0 (in contrast with past
assumptions that Vcirc = sqrt(2)*sigma_0 for dwarfs.) The Vcirc-sigma_0-C28
relation has direct implications for galaxy formation and dynamical models,
galaxy scaling relations, the mass function of galaxies, and the links between
respective formation and evolution processes for a galaxy's central massive
object, bulge, and dark matter halo.Comment: Accepted for publication in ApJL. Current version matches ApJL page
requiremen
CAHOST Facilitating the Johnson-Neyman Technique for Two-Way Interactions in Multiple Regression
When using multiple regression, researchers frequently wish to explore how the relationship between two variables is moderated by another variable; this is termed an interaction. Historically, two approaches have been used to probe interactions: the pick-a-point approach and the Johnson-Neyman (JN) technique. The pick-a-point approach has limitations that can be avoided using the JN technique. Currently, the software available for implementing the JN technique and creating corresponding ïŹgures lacks several desirable featuresâmost notably, ease of use and ïŹgure quality. To ïŹll this gap in the literature, we offer a free Microsoft Excel 2013 workbook, CAHOST (a concatenation of the ïŹrst two letters of the authorsâ last names), that allows the user to seamlessly create publication-ready ïŹgures of the results of the JN technique
Choroid plexus NKCC1 mediates cerebrospinal fluid clearance during mouse early postnatal development
Skin-Derived TSLP Triggers Progression from Epidermal-Barrier Defects to Asthma
A skin-derived cytokine with high systemic availability provides a mechanistic explanation for atopic march and highlights a potential therapeutic target for preventing the development of asthma among people with atopic dermatitis
Choroid plexus-targeted NKCC1 overexpression to treat post-hemorrhagic hydrocephalus
Post-hemorrhagic hydrocephalus (PHH) refers to a life-threatening accumulation of cerebrospinal fluid (CSF) that occurs following intraventricular hemorrhage (IVH). An incomplete understanding of this variably progressive condition has hampered the development of new therapies beyond serial neurosurgical interventions. Here, we show a key role for the bidirectional Na-K-Cl cotransporter, NKCC1, in the choroid plexus (ChP) to mitigate PHH. Mimicking IVH with intraventricular blood led to increased CSF [
Imprints of radial migration on the Milky Wayâs metallicity distribution functions
Recent analysis of the SDSS-III/Apache Point Observatory Galactic Evolution Experiment (APOGEE) Data Release 12 stellar catalog has revealed that the Milky Wayâs (MW) metallicity distribution function (MDF) changes shape as a function of radius, transitioning from being negatively skewed at small Galactocentric radii to positively skewed at large Galactocentric radii. Using a high-resolution, N-body+SPH simulation, we show that the changing skewness arises from radial migrationâmetal-rich stars form in the inner disk and subsequently migrate to the metal-poorer outer disk. These migrated stars represent a large fraction (>50%) of the stars in the outer disk; they populate the high-metallicity tail of the MDFs and are, in general, more metal-rich than the surrounding outer disk gas. The simulation also reproduces another surprising APOGEE result: the spatially invariant high-[α/Fe] MDFs. This arises in the simulation from the migration of a population formed within a narrow range of radii (3.2 ±1.2 kpc) and time (8.8 ± 0.6 Gyr ago), rather than from spatially extended star formation in a homogeneous medium at early times. These results point toward the crucial role radial migration has played in shaping our MW
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