Showing 421 - 430 of 2039 Items
Estimated stocks of circumpolar permafrost carbon with quantified uncertainty ranges and identified data gaps
Date: 2014-12-01
Creator: G. Hugelius
J. Strauss
S. Zubrzycki
J. W. Harden
E. A.G., Schuur
C. L. Ping
L. Schirrmeister
G. Grosse
G. J. Michaelson
C. D. Koven
J. A. O'Donnell
B. Elberling
U. Mishra
P. Camill
Z. Yu
J. Palmtag
Access: Open access
- Soils and other unconsolidated deposits in the northern circumpolar permafrost region store large amounts of soil organic carbon (SOC). This SOC is potentially vulnerable to remobilization following soil warming and permafrost thaw, but SOC stock estimates were poorly constrained and quantitative error estimates were lacking. This study presents revised estimates of permafrost SOC stocks, including quantitative uncertainty estimates, in the 0-3 m depth range in soils as well as for sediments deeper than 3 m in deltaic deposits of major rivers and in the Yedoma region of Siberia and Alaska. Revised estimates are based on significantly larger databases compared to previous studies. Despite this there is evidence of significant remaining regional data gaps. Estimates remain particularly poorly constrained for soils in the High Arctic region and physiographic regions with thin sedimentary overburden (mountains, highlands and plateaus) as well as for deposits below 3 m depth in deltas and the Yedoma region. While some components of the revised SOC stocks are similar in magnitude to those previously reported for this region, there are substantial differences in other components, including the fraction of perennially frozen SOC. Upscaled based on regional soil maps, estimated permafrost region SOC stocks are 217 ± 12 and 472 ± 27 Pg for the 0-0.3 and 0-1 m soil depths, respectively (±95% confidence intervals). Storage of SOC in 0-3 m of soils is estimated to 1035 ± 150 Pg. Of this, 34 ± 16 Pg C is stored in poorly developed soils of the High Arctic. Based on generalized calculations, storage of SOC below 3 m of surface soils in deltaic alluvium of major Arctic rivers is estimated as 91 ± 52 Pg. In the Yedoma region, estimated SOC stocks below 3 m depth are 181 ± 54 Pg, of which 74 ± 20 Pg is stored in intact Yedoma (late Pleistocene ice- and organic-rich silty sediments) with the remainder in refrozen thermokarst deposits. Total estimated SOC storage for the permafrost region is ∼1300 Pg with an uncertainty range of ∼1100 to 1500 Pg. Of this, ∼500 Pg is in non-permafrost soils, seasonally thawed in the active layer or in deeper taliks, while ∼800 Pg is perennially frozen. This represents a substantial ∼300 Pg lowering of the estimated perennially frozen SOC stock compared to previous estimates.
Reference Points, Prospect Theory, and Momentum on the PGA Tour
Date: 2016-06-01
Creator: Daniel F. Stone
Jeremy Arkes
Access: Open access
- Pope and Schweitzer (2011) study predictions of prospect theory for the reference point of par on the current hole in professional golf. We study prospect-theory predictions of three other plausible reference points: par for recent holes, for the round, and for the tournament. A potentially competing force is momentum in quality of play, that is, the hot or cold hand. While prospect theory predicts negative serial correlation in better (worse)-than-average performance across holes, the hot (cold) hand implies the opposite. We find evidence that, for each of the reference points we study, when scores are better than par, hot-hand effects are dominated by prospect-theory effects. These effects can occur via two mechanisms: greater conservatism or less effort. We find evidence that the former (latter) dominates for scores closer to (further from) the reference point. We also find evidence of prospect theory effects (greater risk seeking) when scores are worse than par for the round in Round 1 and of cold-hand effects for scores worse than par for the tournament in Round 3. The magnitudes of some of the joint effects are comparable to those found by Pope and Schweitzer and other related papers. We conclude by discussing how, rather than compete, prospect-theory and cold-hand forces might also cause one another.
Holocene peatland carbon dynamics in the circum-Arctic region: An introduction
Date: 2014-01-01
Creator: Zicheng Yu
Julie Loisel
Daniel J. Charman
David W. Beilman
Philip, Camill
Access: Open access
- Peatlands represent the largest and most concentrated carbon pool in the terrestrial biosphere, and their dynamics during the Holocene have had significant impacts on the global carbon cycle. In this Introduction paper, we provide an overview of the contributions presented in this Special Issue on Holocene peatland carbon dynamics. We also provide a brief history and current status of peat-core-based research on peatland carbon dynamics. Finally, we identify and discuss some challenges and opportunities that would guide peatland carbon research in the near future. These challenges and opportunities include the need to fill data gaps and increase geographic representations of peat carbon accumulation records, a better understanding of peatland lateral expansion process and improved estimate of peatland area change over time, developing regional carbon accumulation histories and carbon pool estimates, and projecting and quantifying overall peatland net carbon balance in a changing world.
The letter of the law: Administrative discretion and Obama's domestic unilateralism
Date: 2014-04-01
Creator: Andrew Rudalevige
Access: Open access
- In his 2014 State of the Union address Barack Obama pledged to act without Congress on a variety of fronts, following up his "we can't wait" campaign of unilateralism before the 2012 election. The partisan furor this engendered tended to obscure the longstanding efforts of presidents to "faithfully execute" the law in a manner that aligns with their policy preferences. This paper examines the broad logic of those efforts, and delineates five areas where the Obama administration has been particularly aggressive: in its (1) recess appointments; (2) refusal to defend federal law (notably, the Defense of Marriage Act) in court; (3) use of prosecutorial discretion in declining to pursue violations of immigration and drug laws; (4) use of waivers; and (5) its utilization of the regulatory process to interpret the meaning of statutes, as with the Clean Air Act and the Affordable Care Act. Presidents do have flexibility in many cases; but this ends where they seek to alter the plain "letter of the law.".
Sea star inspired crawling and bouncing
Date: 2020-01-01
Creator: Sina Heydari
Amy Johnson
Olaf Ellers
Matthew J. McHenry
Eva, Kanso
Access: Open access
- The oral surface of sea stars is lined with arrays of tube feet that enable them to achieve highly controlled locomotion on various terrains. The activity of the tube feet is orchestrated by a nervous system that is distributed throughout the body without a central brain. How such a distributed nervous system produces a coordinated locomotion is yet to be understood. We develop mathematical models of the biomechanics of the tube feet and the sea star body. In the model, the feet are coupled mechanically through their structural connection to a rigid body. We formulate hierarchical control laws that capture salient features of the sea star nervous system. Namely, at the tube foot level, the power and recovery strokes follow a state-dependent feedback controller. At the system level, a directionality command is communicated through the nervous system to all tube feet. We study the locomotion gaits afforded by this hierarchical control model. We find that these minimally coupled tube feet coordinate to generate robust forward locomotion, reminiscent of the crawling motion of sea stars, on various terrains and for heterogeneous tube feet parameters and initial conditions. Our model also predicts a transition from crawling to bouncing consistently with recent experiments. We conclude by commenting on the implications of these findings for understanding the neuromechanics of sea stars and their potential application to autonomous robotic systems.
Aneuploidy and isochromosome formation in drug-resistant Candida albicans
Date: 2006-07-21
Creator: Anna Selmecki
Anja Forche
Judith Berman
Access: Open access
- Resistance to the limited number of available antifungal drugs is a serious problem in the treatment of Candida albicans. We found that aneuploidy in general and a specific segmental aneuploidy, consisting of an isochromosome composed of the two left arms of chromosome 5, were associated with azole resistance. The isochromosome forms around a single centromere flanked by an inverted repeat and was found as an independent chromosome or fused at the telomere to a full-length homolog of chromosome 5. Increases and decreases in drug resistance were strongly associated with gain and loss of this isochromosome, which bears genes expressing the enzyme in the ergosterol pathway targeted by azole drugs, efflux pumps, and a transcription factor that positively regulates a subset of efflux pump genes.
The validity of the kdv approximation in case of resonances arising from periodic media
Date: 2011-11-15
Creator: Christopher Chong
Guido Schneider
Access: Open access
- It is the purpose of this short note to discuss some aspects of the validity question concerning the Korteweg-de Vries (KdV) approximation for periodic media. For a homogeneous model possessing the same resonance structure as it arises in periodic media we prove the validity of the KdV approximation with the help of energy estimates. © 2011 Elsevier Inc.
Kernel functions on domains with hyperelliptic double
Date: 1977-01-01
Creator: William H. Barker
Access: Open access
- Iii this paper we show that the structure of the Bergman and Szegö kernel functions is especially simple on domains with hyperelliptic double. Each such domain is conformally equivalent to the exterior of a system of slits taken from the real axis, and on such domains the Bergman kernel function and its adjoint are essentially the same, while the Szegö kernel function and its adjoint are elementary and can be written in a closed form involving nothing worse than fourth roots of polynomials. Additionally, a number of applications of these results are obtained. © 1977 American Mathematical Society.
The premonitory urge to tic: Measurement, characteristics, and correlates in older adolescents and adults
Date: 2014-01-01
Creator: Hannah E. Reese
Lawrence Scahill
Alan L. Peterson
Katherine Crowe
Douglas W., Woods
John Piacentini
John T. Walkup
Sabine Wilhelm
Access: Open access
- In addition to motor and/or vocal tics, many individuals with Tourette syndrome (TS) or chronic tic disorder (CTD) report frequent, uncomfortable sensory phenomena that immediately precede the tics. To date, examination of these premonitory sensations or urges has been limited by inconsistent assessment tools. In this paper, we examine the psychometric properties of a nine-item self-report measure, the Premonitory Urge to Tic Scale (PUTS) and examine the characteristics and correlates of the premonitory urge to tic in a clinical sample of 122 older adolescents and adults with TS or CTD. The PUTS demonstrated adequate internal consistency, temporal stability, and concurrent validity. Premonitory urges were endorsed by the majority of individuals. Most individuals reported some relief from the urges after completing a tic and being able to stop their tics even if only temporarily. Degree of premonitory urges was not significantly correlated with age, and we did not observe any gender differences. Degree of premonitory urges was significantly correlated with estimated IQ and tic severity, but not severity of comorbid obsessive-compulsive disorder or attention-deficit hyperactivity disorder. Also, it was not related to concomitant medication status. These findings represent another step forward in our understanding of the premonitory sensations associated with TS and CTD. © 2013.
Vulnerability of high-latitude soil organic carbon in North America to disturbance
Date: 2011-12-01
Creator: Guido Grosse
Jennifer Harden
Merritt Turetsky
A. David McGuire
Philip, Camill
Charles Tarnocai
Steve Frolking
Edward A.G. Schuur
Torre Jorgenson
Sergei Marchenko
Vladimir Romanovsky
Kimberly P. Wickland
Nancy French
Mark Waldrop
Laura Bourgeau-Chavez
Robert G. Striegl
Access: Open access
- This synthesis addresses the vulnerability of the North American high-latitude soil organic carbon (SOC) pool to climate change. Disturbances caused by climate warming in arctic, subarctic, and boreal environments can result in significant redistribution of C among major reservoirs with potential global impacts. We divide the current northern high-latitude SOC pools into (1) near-surface soils where SOC is affected by seasonal freeze-thaw processes and changes in moisture status, and (2) deeper permafrost and peatland strata down to several tens of meters depth where SOC is usually not affected by short-term changes. We address key factors (permafrost, vegetation, hydrology, paleoenvironmental history) and processes (C input, storage, decomposition, and output) responsible for the formation of the large high-latitude SOC pool in North America and highlight how climate-related disturbances could alter this pool's character and size. Press disturbances of relatively slow but persistent nature such as top-down thawing of permafrost, and changes in hydrology, microbiological communities, pedological processes, and vegetation types, as well as pulse disturbances of relatively rapid and local nature such as wildfires and thermokarst, could substantially impact SOC stocks. Ongoing climate warming in the North American high-latitude region could result in crossing environmental thresholds, thereby accelerating press disturbances and increasingly triggering pulse disturbances and eventually affecting the C source/sink net character of northern high-latitude soils. Finally, we assess postdisturbance feedbacks, models, and predictions for the northern high-latitude SOC pool, and discuss data and research gaps to be addressed by future research. Copyright 2011 by the American Geophysical Union.