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Chemical Evidence for Cell Wall Lignification and the Evolution of Tracheids in Early Devonian Plants
Anatomically preserved land plant fossils from the Lower Devonian Rhynie Chert contain conducting tissues with cells that range from dark-colored, elongated cells without secondary wall thickenings to tracheids similar to those of extant tracheophytes. A suite of tissue-specific microanalytical techniques was used to assess lignification in fossils of Aglaophyton, Rhynia, and Asteroxylon. Isotope ratio mass spectrometry provides millimeter-scale resolution of carbon isotopic abundances, whereas soft X-ray carbon (1s) spectromicroscopy provides micrometer-scale resolution of the preservation of organic molecular functionality. The isotopic and organic chemistry of Rhynie Chert plants indicates that the earliest vascular thickenings were probably unlignified and that cell wall lignification may have first appeared in the outer cortex. Only in more derived plants, it seems, was lignin deposited in conducting cells to produce the true tracheids seen today in vascular plants.Organismic and Evolutionary Biolog
HarvardX and MITx: Two Years of Open Online Courses Fall 2012-Summer 2014
What happens when well-known universities offer online courses, assessments, and certificates of completion for free? Early descriptions of Massive Open Online Courses (MOOCs) have emphasized large enrollments, low certification rates, and highly educated registrants. We use data from two years and 68 open online courses offered by Harvard University (via HarvardX) and MIT (via MITx) to broaden the scope of answers to this question. We describe trends over this two-year span, depict participant intent using comprehensive survey instruments, and chart course participation pathways using network analysis. We find that overall participation in our MOOCs remains substantial and that the average growth has been steady. We explore how diverse audiences — including explorers, teachers-as-learners, and residential students — provide opportunities to advance the principles on which HarvardX and MITx were founded: access, research, and residential education
SPIRITS 15c and SPIRITS 14buu: Two Obscured Supernovae in the Nearby Star-Forming Galaxy IC 2163
SPIRITS---SPitzer InfraRed Intensive Transients Survey---is an ongoing survey
of nearby galaxies searching for infrared (IR) transients with Spitzer/IRAC. We
present the discovery and follow-up observations of one of our most luminous
( mag, Vega) and red (
mag) transients, SPIRITS 15c. The transient was detected in a dusty spiral arm
of IC 2163 ( Mpc). Pre-discovery ground-based imaging revealed an
associated, shorter-duration transient in the optical and near-IR (NIR). NIR
spectroscopy showed a broad ( km s), double-peaked
emission line of He I at m, indicating an explosive origin. The NIR
spectrum of SPIRITS 15c is similar to that of the Type IIb SN 2011dh at a phase
of days. Assuming mag of extinction in SPIRITS 15c
provides a good match between their optical light curves. The IR light curves
and the extreme color cannot be explained using only a standard
extinction law. Another luminous ( mag) event, SPIRITS
14buu, was serendipitously discovered in the same galaxy. The source displays
an optical plateau lasting days, and we suggest a scenario similar
to the low-luminosity Type IIP SN 2005cs obscured by mag.
Other classes of IR-luminous transients can likely be ruled out in both cases.
If both events are indeed SNe, this may suggest of nearby
core-collapse SNe are missed by currently operating optical surveys.Comment: 19 pages, 7 Figures, 4 Table
Explorations, Vol. 4, No. 1
Articles include:
Cover: Old Yarmouth Light, 1960, Cape Forchu, Nova Scotia. By and from the collection of Edgar McKay.
The Borderlands Concept: a new look at U.S.-Canada relations, by Victor Konrad and Lauren McKensey
Fundy Tidal Power Project, by Gregory White
Canadian Poet: Ken Norris
Native American Life and Art: a celebration, November, 1986, by Lee-Ann Konrad
The Montreal Canadiens: a cultural institution, by James J. Herlan
U.S. and Canadian Executives: uses of formal and informal plans in top executive decision-making, by Kent Carter
Our Cover Artist: bits and pieces of one man\u27s Nova Scotia, by Edgar McKay The Canadian-American Center and the Canadian Collection of the Fogler Library, by Alice Stewart
Capitalist Development in the New England-Atlantic Provinces Region, by Robert H. Babcock
Atlantic Canadian Members of Parliament as Representatives, by Howard Cody
The Rower and the Pyramid: a tribute to Joe Walsh, by Edward D. Ives
The Canadian-American Center: exercise in excellence, by Rand Erb
Canadian and Maine Potatoes: a bushel of questions, by George K. Griner, Alan S. Kezis, and James D. Leiby
After 20: the Future of the Canadian-American Center, by Victor Konra
Origin and Evolution of Prebiotic Organic Matter as Inferred from the Tagish Lake Meteorite
The complex suite of organic materials in carbonaceous chondrite meteorites probably originally formed in the interstellar medium and/or the solar protoplanetary disk, but was subsequently modified in the meteorites' asteroidal parent bodies. The mechanisms of formation and modification are still very poorly understood. We carried out a systematic study of variations in the mineralogy, petrology, and soluble and insoluble organic matter in distinct fragments of the Tagish Lake meteorite. The variations correlate with indicators of parent body aqueous alteration and at least some molecules of pre-biotic importance formed during the alteration
When to Point Your Telescopes: Gravitational Wave Trigger Classification for Real-Time Multi-Messenger Followup Observations
We develop a robust and self-consistent framework to extract and classify
gravitational wave candidates from noisy data, for the purpose of assisting in
real-time multi-messenger follow-ups during LIGO-Virgo-KAGRA's fourth observing
run~(O4). Our formalism implements several improvements to the low latency
calculation of the probability of astrophysical origin~(\PASTRO{}), so as to
correctly account for various factors such as the sensitivity change between
observing runs, and the deviation of the recovered template waveform from the
true gravitational wave signal that can strongly bias said calculation. We
demonstrate the high accuracy with which our new formalism recovers and
classifies gravitational wave triggers, by analyzing replay data from previous
observing runs injected with simulated sources of different categories. We show
that these improvements enable the correct identification of the majority of
simulated sources, many of which would have otherwise been misclassified. We
carry out the aforementioned analysis by implementing our formalism through the
\GSTLAL{} search pipeline even though it can be used in conjunction with
potentially any matched filtering pipeline. Armed with robust and
self-consistent \PASTRO{} values, the \GSTLAL{} pipeline can be expected to
provide accurate source classification information for assisting in
multi-messenger follow-up observations to gravitational wave alerts sent out
during O4.Comment: v2 upload was accidental. revert back to v
Kinetics of H2–O2–H2O redox equilibria and formation of metastable H2O2 under low temperature hydrothermal conditions
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 75 (2011): 1594-1607, doi:10.1016/j.gca.2010.12.020.Hydrothermal experiments were conducted to evaluate the kinetics of H2(aq)
oxidation in the homogeneous H2-O2-H2O system at conditions reflecting
subsurface/near-seafloor hydrothermal environments (55-250 oC and 242-497 bar). The
kinetics of the water-forming reaction that controls the fundamental equilibrium between
dissolved H2(aq) and O2(aq), are expected to impose significant constraints on the redox
gradients that develop when mixing occurs between oxygenated seawater and high-
temperature anoxic vent fluid at near-seafloor conditions. Experimental data indicate that,
indeed, the kinetics of H2(aq)-O2(aq) equilibrium become slower with decreasing
temperature, allowing excess H2(aq) to remain in solution. Sluggish reaction rates of H2(aq)
oxidation suggest that active microbial populations in near-seafloor and subsurface
environments could potentially utilize both H2(aq) and O2(aq), even at temperatures lower
than 40 oC due to H2(aq) persistence in the seawater/vent fluid mixtures. For these H2-O2
disequilibrium conditions, redox gradients along the seawater/hydrothermal fluid mixing
interface are not sharp and microbially-mediated H2(aq) oxidation coupled with a lack of
other electron acceptors (e.g. nitrate) could provide an important energy source available
at low-temperature diffuse flow vent sites.
More importantly, when H2(aq)-O2(aq) disequilibrium conditions apply, formation
of metastable hydrogen peroxide is observed. The yield of H2O2(aq) synthesis appears to
be enhanced under conditions of elevated H2(aq)/O2(aq) molar ratios that correspond to
abundant H2(aq) concentrations. Formation of metastable H2O2 is expected to affect the
distribution of dissolved organic carbon (DOC) owing to the existence of an additional
strong oxidizing agent. Oxidation of magnetite and/or Fe++ by hydrogen peroxide could
also induce formation of metastable hydroxyl radicals (•OH) through Fenton-type
reactions, further broadening the implications of hydrogen peroxide in hydrothermal environments.This research was conducted with partial support from the NSF
OCE-0752221 and the Geophysical Laboratory Postdoctoral Fellowship. We would also
like to acknowledge contributions by the W.M. Keck Foundation and Shell towards
supporting the hydrothermal lab at the Geophysical Lab. SMS acknowledges support
from NSF OCE-0452333 and the Alfried-Krupp Wissenschaftskolleg Greifswald
(Germany), while WES acknowledges support from NSF grants OCE-0549457 and OCE-
0813861
Performance of the low-latency GstLAL inspiral search towards LIGO, Virgo, and KAGRA's fourth observing run
GstLAL is a stream-based matched-filtering search pipeline aiming at the
prompt discovery of gravitational waves from compact binary coalescences such
as the mergers of black holes and neutron stars. Over the past three
observation runs by the LIGO, Virgo, and KAGRA (LVK) collaboration, the GstLAL
search pipeline has participated in several tens of gravitational wave
discoveries. The fourth observing run (O4) is set to begin in May 2023 and is
expected to see the discovery of many new and interesting gravitational wave
signals which will inform our understanding of astrophysics and cosmology. We
describe the current configuration of the GstLAL low-latency search and show
its readiness for the upcoming observation run by presenting its performance on
a mock data challenge. The mock data challenge includes 40 days of LIGO
Hanford, LIGO Livingston, and Virgo strain data along with an injection
campaign in order to fully characterize the performance of the search. We find
an improved performance in terms of detection rate and significance estimation
as compared to that observed in the O3 online analysis. The improvements are
attributed to several incremental advances in the likelihood ratio ranking
statistic computation and the method of background estimation.Comment: 19 pages, 21 figure
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