242 research outputs found
One Size Does Not Fit All: When Honors Housing May Not Work
The gracious donor, the dean, and the other honors program director and I walk down the corridor of an old campus building needing repair but possessing a great deal of charm. While a science classroom building is being renovated, this hall houses temporary offices for displaced faculty. We look at the high ceilings in a room now used as a faculty break room and admire the way the morning sunlight plays on the walls. This room would make an amazing honors student lounge. Renovating the entire building would create a terrific honors dorm that could attract talented prospective students and encourage current honors students to remain at the college
The Nature and Nurture of Star Clusters
Star clusters have hierarchical patterns in space and time, suggesting
formation processes in the densest regions of a turbulent interstellar medium.
Clusters also have hierarchical substructure when they are young, which makes
them all look like the inner mixed parts of a pervasive stellar hierarchy.
Young field stars share this distribution, presumably because some of them came
from dissolved clusters and others formed in a dispersed fashion in the same
gas. The fraction of star formation that ends up in clusters is apparently not
constant, but may increase with interstellar pressure. Hierarchical structure
explains why stars form in clusters and why many of these clusters are
self-bound. It also explains the cluster mass function. Halo globular clusters
share many properties of disk clusters, including what appears to be an upper
cluster cutoff mass. However, halo globulars are self-enriched and often
connected with dwarf galaxy streams. The mass function of halo globulars could
have initially been like the power law mass function of disk clusters, but the
halo globulars have lost their low mass members. The reasons for this loss are
not understood. It could have happened slowly over time as a result of cluster
evaporation, or it could have happened early after cluster formation as a
result of gas loss. The latter model explains best the observation that the
globular cluster mass function has no radial gradient in galaxies.Comment: to be published in IAUS266: Star Clusters Basic Galactic Building
Blocks Throughout Time And Space, eds. Richard de Grijs and Jacques Lepine,
Cambridge University Press, 11 page
Effect of Larval Nutrition on Maternal mRNA Contribution to the Drosophila Egg.
Embryonic development begins under the control of maternal gene products, mRNAs and proteins that the mother deposits into the egg; the zygotic genome is activated some time later. Maternal control of early development is conserved across metazoans. Gene products contributed by mothers are critical to many early developmental processes, and set up trajectories for the rest of development. Maternal deposition of these factors is an often-overlooked aspect of parental investment. If the mother experiences challenging environmental conditions, such as poor nutrition, previous studies in Drosophila melanogaster have demonstrated a plastic response wherein these mothers may produce larger eggs to buffer the offspring against the same difficult environment. This additional investment can produce offspring that are more fit in the challenging environment. With this study, we ask whether D. melanogaster mothers who experience poor nutrition during their own development change their gene product contribution to the egg. We perform mRNA-Seq on eggs at a stage where all mRNAs are maternally derived, from mothers with different degrees of nutritional limitation. We find that nutritional limitation produces similar transcript changes at all degrees of limitation tested. Genes that have lower transcript abundance in nutritionally limited mothers are those involved in translation, which is likely one of the most energetically costly processes occurring in the early embryo. We find an increase in transcripts for transport and localization of macromolecules, and for the electron transport chain. The eggs produced by nutrition-limited mothers show a plastic response in mRNA deposition, which may better prepare the future embryo for development in a nutrition-limited environment
A Molecular Spiral Arm in the Far Outer Galaxy
We have identified a spiral arm lying beyond the Outer Arm in the first
Galactic quadrant ~15 kpc from the Galactic center. After tracing the arm in
existing 21 cm surveys, we searched for molecular gas using the CfA 1.2 meter
telescope and detected CO at 10 of 220 positions. The detections are
distributed along the arm from l = 13 deg, v = -21 km/s to l = 55 deg, v = -84
km/s and coincide with most of the main H I concentrations. One of the
detections was fully mapped to reveal a large molecular cloud with a radius of
47 pc and a molecular mass of ~50,000 Mo. At a mean distance of 21 kpc, the
molecular gas in this arm is the most distant yet detected in the Milky Way.
The new arm appears to be the continuation of the Scutum-Centaurus Arm in the
outer Galaxy, as a symmetric counterpart of the nearby Perseus Arm.Comment: 11 pages, 4 figures, 1 Table, ApJ Letters, in pres
The Nearest Group of Galaxies
The small Antlia-Sextans clustering of galaxies is located at a distance of
only 1.36 Mpc from the Sun, and 1.72 Mpc from the adopted barycenter of the
Local Group. The latter value is significantly greater than the radius of the
zero- velocity surface of the Local Group which, for an assumed age of 14 Gyr,
has Ro = 1.18 " 0.15 Mpc. This, together with the observation that the members
of the Ant-Sex group have a mean redshift of +114 " 12 km s-1 relative to the
centroid of the Local Group, suggests that the Antlia-Sextans group is not
bound to our Local Group, and that it is expanding with the Hubble flow. If
this conclusion is correct, then Antlia-Sextans may be the nearest external
clustering of galaxies. The total galaxian population of the Ant-Sex group is ~
1/5 that of the Local Group. However, the integrated luminosity of Ant-Sex is
two orders of magnitude lower than that of the Local Group.
Subject headings: Galaxies - clusters: individual (Antlia-Sextans)Comment: Has been accepted for publication in the Astrophysical Journal
Letter
The Double-Lined Spectrum of LBV 1806-20
Despite much theoretical and observational progress, there is no known firm
upper limit to the masses of stars. Our understanding of the interplay between
the immense radiation pressure produced by massive stars in formation and the
opacity of infalling material is subject to theoretical uncertainties, and many
observational claims of ``the most massive star'' have failed the singularity
test. LBV 1806-20 is a particularly luminous object, L~10^6 Lsun, for which
some have claimed very high mass estimates (M_initial>200 Msun), based, in
part, on its similarity to the Pistol Star. We present high-resolution
near-infrared spectroscopy of LBV 1806-20, showing that it is possibly a binary
system with components separated in velocity by ~70 kms. If correct, then this
system is not the most massive star known, yet it is a massive binary system.
We argue that a binary, or merged, system is more consistent with the ages of
nearby stars in the LBV 1806-20 cluster. In addition, we find that the velocity
of V_LSR=36 kms is consistent with a distance of 11.8 kpc, a luminosity of
10^6.3 Lsun, and a system mass of ~130 Msun.Comment: ApJL, accepte
A New Kinematic Distance Estimator to the LMC
The distance to the Large Magellanic Cloud (LMC) can be directly determined
by measuring three of its properties, its radial-velocity field, its mean
proper motion, and the position angle \phi_ph of its photometric line of nodes.
Statistical errors of 2% are feasible based on proper motions obtained with any
of several proposed astrometry satellites, the first possibility being the
Full-Sky Astrometric Mapping Explorer (FAME). The largest source of systematic
error is likely to be in the determination of \phi_ph. I suggest two
independent methods to measure \phi_ph, one based on counts of clump giants and
the other on photometry of clump giants. I briefly discuss a variety of methods
to test for other sources of systematic errors.Comment: submitted to ApJ, 13 page
Adopting Product Modularity in House Building to Support Mass Customisation
Product modularity is a concept that can contribute to the improvement of product quality and production efficiency in house-building. However, there is a lack of consensus in the literature on the concepts that define product modularity. Furthermore, little attention has been given to the differences between building construction and manufacturing, for which product modularity was originally developed. This research aims to address that gap by adapting the conceptualization of product modularity so that it can effectively be used in the house-building industry. The methodological approach adopted in this study was Design Science Research, and two empirical studies were carried out on construction companies based in Brazil and in the U.K. Those studies are used to illustrate the applicability and utility of the proposed concepts and tools. Research findings indicate that the adoption of product modularity concepts results in benefits to both traditional construction technologies and prefabricated
building systems
The Nature of the Gould Belt from a Fractal Analysis of its Stellar Population
The Gould Belt (GB) is a system of gas and young, bright stars distributed
along a plane that is inclined with respect to the main plane of the Milky Way.
Observational evidence suggests that the GB is our closest star formation
complex, but its true nature and origin remain rather controversial. In this
work we analyze the fractal structure of the stellar component of the GB. In
order to do this, we tailor and apply an algorithm that estimates the fractal
dimension in a precise and accurate way, avoiding both boundary and small data
set problems. We find that early OB stars (of spectral types earlier than B4)
in the GB have a fractal dimension very similar to that of the gas clouds in
our Galaxy. On the contrary, stars in the GB of later spectral types show a
larger fractal dimension, similar to that found for OB stars of both age groups
in the local Galactic disk (LGD). This result seems to indicate that while the
younger OB stars in the GB preserve the memory of the spatial structure of the
cloud where they were born, older stars are distributed following a similar
morphology as that found for the LGD stars. The possible causes for these
differences are discussed.Comment: 20 pages including 7 figures and 1 table. ApJ (in press
The Dynamical State fo the Starless Dense Core FeSt 1-457: A Pulsating Globule?
High resolution molecular line observations of CS, HCO+, C18O and N2H+ were
obtained toward the starless globule FeSt 1-457 in order to investigate its
kinematics and chemistry. The HCO+ and CS spectra show clear self-reversed and
asymmetric profiles across the face of the globule. The sense of the observed
asymmetry is indicative of the global presence of expansion motions in the
outer layers of the globule. These motions appear to be subsonic and
significantly below the escape velocity of the globule. Comparison of our
observations with near-infrared extinction data indicate that the globule is
gravitationally bound. Taken together these considerations lead us to suggest
that the observed expansion has its origin in an oscillatory motion of the
outer layers of the globule which itself is likely in a quasi-stable state near
hydrostatic equilibrium. Analysis of the observed linewidths of CO and N2H+
confirm that thermal pressure is the dominant component of the cloud's internal
support. A simple calculation suggests that the dominant mode of pulsation
would be an l = 2 mode with a period of 0.3 Myr. Deformation of the globule due
to the large amplitude l = 2 oscillation may be responsible for the
double-peaked structure of the core detected in high resolution extinction
maps. Detailed comparison of the molecular-line observations and extinction
data provides evidence for significant depletion of C18O and perhaps HCO+ while
N2H+ may be undepleted to a cloud depth of about 40 magnitudes of visual
extinction.Comment: to appear in ApJ vol 665 20 August 2007
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