102 research outputs found
The Value of Intuition in Judging: A Case Study
If you were to ask legal readers to rate the value of intuition in deciding close cases, I suspect that most of them would not put it toward the top of their list. Surely that would be true for self-described textualist judges, who would probably give it only a slim role, if it has any at all. They prefer to concentrate on words and syntax and context (verbal context, not situational context) and to weigh all the cues and clues. Intuition is just too squishy, subjective, unconstraining, and prone to manipulation (as if textualism were not1).
At any rate, I’ve done a little experiment that tries to gauge the weight that readers give to intuitive reasons for a United States Supreme Court decision. Obviously, I can’t poll the justices; I can only report on readers’ assessments of the points they made. I don’t claim that the study is earthshaking, conclusive, empirically beyond reproach (for one thing, the sample size is small), or able to be generalized to all cases. I claim only that the results are striking enough that they ought to give pause to those who would discount the significance of a judge’s reasoned intuition about statutory purpose and sensible results
Green Aerospace Fuels from Nonpetroleum Sources
Efforts to produce green aerospace propellants from nonpetroleum sources are outlined. The paper begins with an overview of feedstock processing and relevant small molecule or C1 chemistry. Gas-to-liquid technologies, notably Fischer-Tropsch (FT) processing of synthesis gas (CO and H2), are being optimized to enhance the fraction of product stream relevant to aviation (and other transportation) fuels at the NASA Glenn Research Center (GRC). Efforts to produce optimized catalysts are described. Given the high cost of space launch, the recycling of human metabolic and plastic wastes to reduce the need to transport consumables to orbit to support the crew of a space station has long been recognized as a high priority. If the much larger costs of transporting consumables to the Moon or beyond are taken into account, the importance of developing waste recycling systems becomes still more imperative. One promising way to transform organic waste products into useful gases is steam reformation; this well-known technology is currently being optimized by a Colorado company for exploration and planetary surface operations. Reduction of terrestrial waste streams while producing energy and/or valuable raw materials is an opportunity being realized by a new generation of visionary entrepreneurs. A technology that has successfully demonstrated production of fuels and related chemicals from waste plastics developed in Northeast Ohio is described. Technologies being developed by a Massachusetts company to remove sulfur impurities are highlighted. Common issues and concerns for nonpetroleum fuel production are emphasized. Energy utilization is a concern for production of fuels whether a terrestrial operation or on the lunar (or Martian) surface; the term green relates to not only mitigating excess carbon release but also to the efficiency of grid-energy usage. For space exploration, energy efficiency can be an essential concern. Other issues of great concern include minimizing impurities in the product stream(s), especially those that potential health risks and/or could degrade operations through catalyst poisoning or equipment damage. The potential impacts on future missions by such concerns are addressed in closing
UV Absorption Lines from High-Velocity Gas in the Vela Supernova Remnant: New insights from STIS Echelle Observations of HD72089
The star HD72089 is located behind the Vela supernova remnant and shows a
complex array of high and low velocity interstellar absorption features arising
from shocked clouds. A spectrum of this star was recorded over the wavelength
range 1196.4 to 1397.2 Angstroms at a resolving power lambda/Delta lambda =
110,000 and signal-to-noise ratio of 32 by STIS on the Hubble Space Telescope.
We have identified 7 narrow components of C I and have measured their relative
populations in excited fine-structure levels. Broader features at heliocentric
velocities ranging from -70 to +130 km/s are seen in C II, N I, O I, Si II, S
II and Ni II. In the high-velocity components, the unusually low abundances of
N I and O I, relative to S II and Si II, suggest that these elements may be
preferentially ionized to higher stages by radiation from hot gas immediately
behind the shock fronts.Comment: 11 pages, 2 figures, Latex. Submitted for the special HST ERO issue
of the Astrophysical Journal Letter
Star formation in 30 Doradus
Using observations obtained with the Wide Field Camera 3 (WFC3) on board the
Hubble Space Telescope (HST), we have studied the properties of the stellar
populations in the central regions of 30 Dor, in the Large Magellanic Cloud.
The observations clearly reveal the presence of considerable differential
extinction across the field. We characterise and quantify this effect using
young massive main sequence stars to derive a statistical reddening correction
for most objects in the field. We then search for pre-main sequence (PMS) stars
by looking for objects with a strong (> 4 sigma) Halpha excess emission and
find about 1150 of them over the entire field. Comparison of their location in
the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for
the appropriate metallicity reveals that about one third of these objects are
younger than ~4Myr, compatible with the age of the massive stars in the central
ionising cluster R136, whereas the rest have ages up to ~30Myr, with a median
age of ~12Myr. This indicates that star formation has proceeded over an
extended period of time, although we cannot discriminate between an extended
episode and a series of short and frequent bursts that are not resolved in
time. While the younger PMS population preferentially occupies the central
regions of the cluster, older PMS objects are more uniformly distributed across
the field and are remarkably few at the very centre of the cluster. We
attribute this latter effect to photoevaporation of the older circumstellar
discs caused by the massive ionising members of R136.Comment: 15 pages, 12 figures. Accepted for publication in The Astrophysical
Journa
Using H-alpha Morphology and Surface Brightness Fluctuations to Age-Date Star Clusters in M83
We use new WFC3 observations of the nearby grand design spiral galaxy M83 to
develop two independent methods for estimating the ages of young star clusters.
The first method uses the physical extent and morphology of Halpha emission to
estimate the ages of clusters younger than tau ~10 Myr. It is based on the
simple premise that the gas in very young (tau < few Myr) clusters is largely
coincident with the cluster stars, is in a small, ring-like structure
surrounding the stars in slightly older clusters (e.g., tau ~5 Myr), and is in
a larger ring-like bubble for still older clusters (i.e., ~5-10 Myr). The
second method is based on an observed relation between pixel-to-pixel flux
variations within clusters and their ages. This method relies on the fact that
the brightest individual stars in a cluster are most prominent at ages around
10 Myr, and fall below the detection limit (i.e., M_V < -3.5) for ages older
than about 100 Myr. These two methods are the basis for a new morphological
classification system which can be used to estimate the ages of star clusters
based on their appearance. We compare previous age estimates of clusters in M83
determined from fitting UBVI Halpha measurements using predictions from stellar
evolutionary models with our new morphological categories and find good
agreement at the ~95% level. The scatter within categories is ~0.1 dex in log
tau for young clusters (10 Myr) clusters. A
by-product of this study is the identification of 22 "single-star" HII regions
in M83, with central stars having ages ~4 Myr.Comment: 33 pages, 10 figures, 3 tables; published in March Ap
Large-scale shock-ionized and photo-ionized gas in M83: the impact of star formation
We investigate the ionization structure of the nebular gas in M83 using the
line diagnostic diagram, [O III](5007 \degA)/H{\beta} vs. [S II](6716 \deg
A+6731 \deg A)/H{\alpha} with the newly available narrowband images from the
Wide Field Camera 3 (WFC3) of the Hubble Space Telescope (HST). We produce the
diagnostic diagram on a pixel-by-pixel (0.2" x 0.2") basis and compare it with
several photo- and shock-ionization models. For the photo-ionized gas, we
observe a gradual increase of the log([O III]/H{\beta}) ratios from the center
to the spiral arm, consistent with the metallicity gradient, as the H II
regions go from super solar abundance to roughly solar abundance from the
center out. Using the diagnostic diagram, we separate the photo-ionized from
the shock-ionized component of the gas. We find that the shock-ionized
H{\alpha} emission ranges from ~2% to about 15-33% of the total, depending on
the separation criteria used. An interesting feature in the diagnostic diagram
is an horizontal distribution around log([O III]/H{\beta}) ~ 0. This feature is
well fit by a shock-ionization model with 2.0 Z\odot metallicity and shock
velocities in the range of 250 km/s to 350 km/s. A low velocity shock
component, < 200 km/s, is also detected, and is spatially located at the
boundary between the outer ring and the spiral arm. The low velocity shock
component can be due to : 1) supernova remnants located nearby, 2) dynamical
interaction between the outer ring and the spiral arm, 3) abnormal line ratios
from extreme local dust extinction. The current data do not enable us to
distinguish among those three possible interpretations. Our main conclusion is
that, even at the HST resolution, the shocked gas represents a small fraction
of the total ionized gas emission at less than 33% of the total. However, it
accounts for virtually all of the mechanical energy produced by the central
starburst in M83.Comment: Accepted for publication in ApJ. aastex preprint 12pt, 21 pages, 13
figure
Progressive star formation in the young galactic super star cluster NGC 3603
Early release science observations of the cluster NGC3603 with the WFC3 on
the refurbished HST allow us to study its recent star formation history. Our
analysis focuses on stars with Halpha excess emission, a robust indicator of
their pre-main sequence (PMS) accreting status. The comparison with theoretical
PMS isochrones shows that 2/3 of the objects with Halpha excess emission have
ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of
them are older than 10 Myr. The study of the spatial distribution of these PMS
stars allows us to confirm their cluster membership and to statistically
separate them from field stars. This result establishes unambiguously for the
first time that star formation in and around the cluster has been ongoing for
at least 10-20 Myr, at an apparently increasing rate.Comment: 10 pages, 8 figures, accepted for publication in The Astrophysical
Journa
Hubble Space Telescope Imaging of Lyman Alpha Emission at z=4.4
We present the highest redshift detections of resolved Lyman alpha emission,
using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in
parallel with the Wide Field Camera 3 Early Release Science program in the
GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically
confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the
sample of LAEs with resolved Lyman alpha emission. Comparing the light
distribution between the rest-frame ultraviolet continuum and narrowband
images, we investigate the escape of Lyman alpha photons at high redshift.
While our data do not support a positional offset between the Lyman alpha and
rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out
of the three galaxies are significantly larger in Lyman alpha than in the
rest-frame UV continuum. This result is confirmed when comparing object sizes
in a stack of all objects in both bands. Additionally, the narrowband flux
detected with HST is significantly less than observed in similar filters from
the ground. These results together imply that the Lyman alpha emission is not
strictly confined to its indigenous star-forming regions. Rather, the Lyman
alpha emission is more extended, with the missing HST flux likely existing in a
diffuse outer halo. This suggests that the radiative transfer of Lyman alpha
photons in high-redshift LAEs is complicated, with the interstellar-medium
geometry and/or outflows playing a significant role in galaxies at these
redshifts.Comment: Submitted to the Astrophysical Journal. 11 pages, 10 figure
Feasibility of detecting single atoms using photonic bandgap cavities
We propose an atom-cavity chip that combines laser cooling and trapping of
neutral atoms with magnetic microtraps and waveguides to deliver a cold atom to
the mode of a fiber taper coupled photonic bandgap (PBG) cavity. The
feasibility of this device for detecting single atoms is analyzed using both a
semi-classical treatment and an unconditional master equation approach.
Single-atom detection seems achievable in an initial experiment involving the
non-deterministic delivery of weakly trapped atoms into the mode of the PBG
cavity.Comment: 11 pages, 5 figure
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