7,099 research outputs found
Executive Orders as Lawful Limits on Agency Policymaking Discretion
After briefly retracing previous Presidents’ general uses of executive orders and debates over presidential power more generally, culminating with the late twentieth century executive orders on White House regulatory oversight, I review the case of Sherley v. Sebelius, in which the D.C. Circuit held that when an agency receives an executive order lawfully cabining or directing the its regulatory discretion, it is excused from its otherwise general duty to respond to rulemaking comments challenging its policy choice. Then, examining this general duty of agencies to respond to rulemaking comments, I consider whether the D.C. Circuit’s approach comports with the values and purposes underlying that duty
Keck NIRSPEC Radial Velocity Observations of Late-M dwarfs
We present the results of an infrared spectroscopic survey of 23 late-M
dwarfs with the NIRSPEC echelle spectrometer on the Keck II telescope. Using
telluric lines for wavelength calibration, we are able to achieve measurement
precisions of down to 45 m/s for our late-M dwarfs over a one to four year-long
baseline. Our sample contains two stars with RV variations of >1000 m/s. While
we require more measurements to determine whether these RV variations are due
to unseen planetary or stellar companions or are the result of starspots known
to plague the surface of M dwarfs, we can place upper limits of <40 MJsini on
the masses of any companions around those two M dwarfs with RV variations of
<160 m/s at orbital periods of 10-100 days. We have also measured the
rotational velocities for all the stars in our late-M dwarf sample and offer
our multi-order, high-resolution spectra over 2.0 to 2.4 micron to the
atmospheric modeling community to better understand the atmospheres of late-M
dwarfs.Comment: Accepted to Ap
Multiplicity at the Stellar/Substellar Boundary in Upper Scorpius
We present the results of a high-resolution imaging survey of 12 brown dwarfs
and very low mass stars in the closest (~145 pc) young (~5 Myr) OB association,
Upper Scorpius. We obtained images with the Advanced Camera for Surveys/High
Resolution Camera on HST through the F555W (V), F775W (i'), and F850LP (z')
filters. This survey discovered three new binary systems, including one
marginally resolved pair with a projected separation of only 4.9 AU, resulting
in an observed binary fraction of 25+/-14% at separations >4 AU. After
correcting for detection biases assuming a uniform distribution of mass ratios
for q>0.6, the estimated binary fraction is 33+/-17%. The binary fraction is
consistent with that inferred for higher-mass stars in Upper Sco, but the
separation and mass ratio distributions appear to be different. All three
low-mass binary systems in Upper Sco are tight (<18 AU) and of similar mass
(q>0.6), consistent with expectations based on previous multiplicity studies of
brown dwarfs and very low mass stars in the field and in open clusters. The
implication is that the distinct separation and mass ratio distributions of
low-mass systems are set in the formation process or at very young ages, rather
than by dynamical disruption of wide systems at ages >5 Myr. Finally, we
combine the survey detection limits with the models of Burrows et al. (1997) to
show that there are no planets or very low-mass brown dwarfs with masses >10
M_J at projected separations >20 AU, or masses >5 M_J at projected separations
>40 AU orbiting any of the low-mass (0.04-0.10 M_sun) objects in our sample.Comment: Accepted for publication in ApJ; 10 pages, 4 figures in emulateapj
forma
Collecting Diverse Natural Language Inference Problems for Sentence Representation Evaluation
We present a large-scale collection of diverse natural language inference
(NLI) datasets that help provide insight into how well a sentence
representation captures distinct types of reasoning. The collection results
from recasting 13 existing datasets from 7 semantic phenomena into a common NLI
structure, resulting in over half a million labeled context-hypothesis pairs in
total. We refer to our collection as the DNC: Diverse Natural Language
Inference Collection. The DNC is available online at https://www.decomp.net,
and will grow over time as additional resources are recast and added from novel
sources.Comment: To be presented at EMNLP 2018. 15 page
Heavy Quark Fragmentation to Baryons Containing Two Heavy Quarks
We discuss the fragmentation of a heavy quark to a baryon containing two
heavy quarks of mass . In this limit the heavy quarks
first combine perturbatively into a compact diquark with a radius small
compared to , which interacts with the light hadronic
degrees of freedom exactly as does a heavy antiquark. The subsequent evolution
of this diquark to a baryon is identical to the fragmentation of a
heavy antiquark to a meson. We apply this analysis to the production of baryons
of the form , , and .Comment: 9 pages, 1 figure included, uses harvmac.tex and epsf.tex, UCSD/PTH
93-11, CALT-68-1868, SLAC-PUB-622
The identification of mitochondrial DNA variants in glioblastoma multiforme
Background:
Mitochondrial DNA (mtDNA) encodes key proteins of the electron transfer chain (ETC), which produces ATP through oxidative phosphorylation (OXPHOS) and is essential for cells to perform specialised functions. Tumor-initiating cells use aerobic glycolysis, a combination of glycolysis and low levels of OXPHOS, to promote rapid cell proliferation and tumor growth. Glioblastoma multiforme (GBM) is an aggressively malignant brain tumor and mitochondria have been proposed to play a vital role in GBM tumorigenesis.
Results:
Using next generation sequencing and high resolution melt analysis, we identified a large number of mtDNA variants within coding and non-coding regions of GBM cell lines and predicted their disease-causing potential through in silico modeling. The frequency of variants was greatest in the D-loop and origin of light strand replication in non-coding regions. ND6 was the most susceptible coding gene to mutation whilst ND4 had the highest frequency of mutation. Both genes encode subunits of complex I of the ETC. These variants were not detected in unaffected brain samples and many have not been previously reported. Depletion of HSR-GBM1 cells to varying degrees of their mtDNA followed by transplantation into immunedeficient mice resulted in the repopulation of the same variants during tumorigenesis. Likewise, de novo variants identified in other GBM cell lines were also incorporated. Nevertheless, ND4 and ND6 were still the most affected genes. We confirmed the presence of these variants in high grade gliomas.
Conclusions:
These novel variants contribute to GBM by rendering the ETC. partially dysfunctional. This restricts metabolism to anaerobic glycolysis and promotes cell proliferation
Individual differences in rhythmic skills: links with neural consistency and linguistic ability
Durational patterns provide cues to linguistic structure, and so variations in rhythm skills may have consequences for language development. Understanding individual differences in rhythm skills, therefore, could help explain variability in language ability across the population.
We investigated the neural foundations of rhythmic proficiency
and its relation to language skills in young adults. We hypothesized that rhythmic abilities can be characterized by at least two constructs, which are tied to independent language abilities and neural profiles.
Specifically, we hypothesized that rhythm skills that require integration of information across time rely upon the consistency of slow, low-frequency auditory processing, which we measured using the evoked cortical response. On the other hand, we hypothesized that rhythm ic skills that require fine temporal precision rely upon the consistency of fast, higher-frequency auditory processing, which we measured using the frequency following response.
Performance on rhythm tests aligned with two constructs: rhythm sequencing and synchronization.
Rhythm sequencing and synchronization were linked to the consistency of slow cortical and fast frequency-following responses, respectively.
Furthermore, while rhythm sequencing ability was linked to verbal memory,
reading, and nonverbal auditory temporal processing, synchronization ability was linked only tononverbal auditory temporal processing.
Thus, rhythm perception at different time scales reflects distinct abilities, which rely on distinct auditory neural resources. In young adults
slow rhythmic processing makes the more extensive contribution to language skill
The issue of athlete welfare and why tackling should be removed from physical education and school sport: #BanTackling
In March 2016, the Sport Collision Injury Collective called upon the UK government to remove tackling from schools’ physical education and school sport. This is because 1) tackling is the leading cause of injury in rugby, 2) rugby has a level of risk that is higher than non-contact sports, 3) there is no requirement or need for tackling as part of the physical education and school sport curriculum, and 4) many children are compelled to participate in contact rugby as part of the physical education and school sport curriculum. This debate has typically contested issues of informed consent and acceptable levels of risk, both issues being firmly positioned in the sociopolitical realm. It is this social concern that I will attend to in this chapter, concluding that the removal of contact in physical education and school sport is both the only logical and viable solution available at this time
The Physical Effects of Progenitor Rotation: Comparing Two Long-Duration 3D Core-Collapse Supernova Simulations
We analyse and determine the effects of modest progenitor rotation in the
context of core-collapse supernovae by comparing two separate long-duration
three-dimensional simulations of 9 M progenitors, one rotating with
an initial spin period of 60 seconds and the other non-rotating. We
determine that both models explode early, though the rotating model explodes a
bit earlier. Despite this difference, the asymptotic explosion energies
(10 ergs) and residual neutron star baryon masses (1.3
M) are similar. We find that the proto-neutron star (PNS) core can
deleptonize and cool significantly more quickly. Soon into the evolution of the
rotating model, we witness more vigorous and extended PNS core convection that
early in its evolution envelopes the entire inner sphere, not just a shell.
Moreover, we see a corresponding excursion in both the luminosity and
gravitational-wave strain that may be diagnostic of this observed dramatic
phenomenon. In addition, after bounce the innermost region of the rotating
model seems to execute meridional circulation. The rotationally-induced growth
of the convective PNS region may facilitate the growth of core B-fields by the
dynamo mechanism by facilitating the achievement of the critical Rossby number
condition for substantial growth of a dipole field, obviating the need for
rapid rotation rates to create dipole fields of significance. The next step is
to explore the progenitor-mass and spin dependencies across the progenitor
continuum of the supernova explosion, dynamics, and evolution of PNS convection
and its potential role in the generation of magnetar and pulsar magnetic
fields.Comment: Withdrawn pending further calculation
Scaling solutions as Early Dark Energy resolutions to the Hubble tension
A wide class of scalar field models including Quintessence and K-essence have the attractive property of tracker regimes, where the energy density stored in the field evolves so as to mimic that of the dominant background component. During this evolution, for a brief period of time, there is an increase in the energy density of the field as it spirals in towards its attractor solution. We show that when the peak of this energy density occurs around the epoch of equality, we can address a key requirement of early dark energy (EDE), postulated as a solution to the Hubble tension. In particular we demonstrate how this can occur in a wide class of Quintessence, axion and K-essence models, before showing that the Quintessence models suffer in that they generally lead to sound speeds incompatible with the requirements of EDE, whereas the K-essence and axion models can do a better job of fitting the data
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