Showing 561 - 570 of 733 Items
Inclusive decays of B mesons to charmonium
Date: 1995-01-01
Creator: R. Balest, K. Cho, W. T. Ford, D. R. Johnson, K., Lingel, M. Lohner, P. Rankin, J. G. Smith, J. P. Alexander, C. Bebek, K. Berkelman, K. Bloom, T. E. Browder, D. G. Cassel, H. A. Cho, D. M. Coffman, D. S. Crowcroft, P. S. Drell, D. J. Dumas, R. Ehrlich, P. Gaidarev, M. Garcia-Sciveres, B. Geiser, B. Gittelman, S. W. Gray, D. L. Hartill, B. K. Heltsley, S. Henderson, C. D. Jones, S. L. Jones, J. Kandaswamy
Access: Open access
- We have used the CLEO-II detector at the Cornell Electron Storage Ringe (CESR) to study the inclusive production of charmonium mesons in a sample of 2.15 million BB events. We find inclusive branching fractions of (1.120.040.06)% for BJ/X, (0.340.040.03)% for BX, and (0.400.060.04)% for Bc1X. We also find some evidence for the inclusive production of c2, and set an upper limit for the branching fraction of the inclusive decay BcX of 0.9% at 90% confidence level. Momentum spectra for inclusive J/, and c1 production are presented. These measurements are compared to theoretical calculations. © 1995 The American Physical Society.
Atmospheric abundance and global emissions of perfluorocarbons CF4, C2F6 and C3F8 since 1800 inferred from ice core, firn, air archive and in situ measurements
Date: 2016-09-21
Creator: Cathy M. Trudinger, Paul J. Fraser, David M. Etheridge, William T. Sturges, Martin K., Vollmer, Matt Rigby, Patricia Martinerie, Jens Mühle, David R. Worton, Paul B. Krummel, L. Paul Steele, Benjamin R. Miller, Johannes Laube, Francis S. Mani, Peter J. Rayner, Christina M. Harth, Emmanuel Witrant, Thomas Blunier, Jakob Schwander, Simon O'Doherty, Mark Battle
Access: Open access
- Perfluorocarbons (PFCs) are very potent and long-lived greenhouse gases in the atmosphere, released predominantly during aluminium production and semiconductor manufacture. They have been targeted for emission controls under the United Nations Framework Convention on Climate Change. Here we present the first continuous records of the atmospheric abundance of CF4 (PFC-14), C2F6 (PFC-116) and C3F8 (PFC-218) from 1800 to 2014. The records are derived from high-precision measurements of PFCs in air extracted from polar firn or ice at six sites (DE08, DE08-2, DSSW20K, EDML, NEEM and South Pole) and air archive tanks and atmospheric air sampled from both hemispheres. We take account of the age characteristics of the firn and ice core air samples and demonstrate excellent consistency between the ice core, firn and atmospheric measurements. We present an inversion for global emissions from 1900 to 2014. We also formulate the inversion to directly infer emission factors for PFC emissions due to aluminium production prior to the 1980s. We show that 19th century atmospheric levels, before significant anthropogenic influence, were stable at 34.1 ± 0.3 ppt for CF4 and below detection limits of 0.002 and 0.01 ppt for C2F6 and C3F8, respectively. We find a significant peak in CF4 and C2F6 emissions around 1940, most likely due to the high demand for aluminium during World War II, for example for construction of aircraft, but these emissions were nevertheless much lower than in recent years. The PFC emission factors for aluminium production in the early 20th century were significantly higher than today but have decreased since then due to improvements and better control of the smelting process. Mitigation efforts have led to decreases in emissions from peaks in 1980 (CF4) or early-to-mid-2000s (C2F6 and C3F8) despite the continued increase in global aluminium production; however, these decreases in emissions appear to have recently halted. We see a temporary reduction of around 15 % in CF4 emissions in 2009, presumably associated with the impact of the global financial crisis on aluminium and semiconductor production.
Managing server clusters on intermittent power
Date: 2015-01-01
Creator: Navin Sharma, Dilip Krishnappa, Sean Barker, David Irwin, Prashant, Shenoy
Access: Open access
- Reducing the energy footprint of data centers continues to receive significant attention due to both its financial and environmental impact. There are numerous methods that limit the impact of both factors, such as expanding the use of renewable energy or participating in automated demand-response programs. To take advantage of these methods, servers and applications must gracefully handle intermittent constraints in their power supply. In this paper, we propose blinking-metered transitions between a high-power active state and a low-power inactive state-as the primary abstraction for conforming to intermittent power constraints. We design Blink, an application-independent hardware-software platform for developing and evaluating blinking applications, and define multiple types of blinking policies.We then use Blink to design both a blinking version of memcached (BlinkCache) and a multimedia cache (GreenCache) to demonstrate how application characteristics affect the design of blink-aware distributed applications. Our results show that for BlinkCache, a load-proportional blinking policy combines the advantages of both activation and synchronous blinking for realistic Zipf-like popularity distributions and wind/solar power signals by achieving near optimal hit rates (within 15% of an activation policy), while also providing fairer access to the cache (within 2% of a synchronous policy) for equally popular objects. In contrast, for GreenCache, due to multimedia workload patterns, we find that a staggered load proportional blinking policy with replication of the first chunk of each video reduces the buffering time at all power levels, as compared to activation or load-proportional blinking policies.
A cell wall-associated, receptor-like protein kinase
Date: 1996-09-05
Creator: Zheng Hui He, Masaaki Fujiki, Bruce D. Kohorn
Access: Open access
- Physical connections between higher plant cell walls and the plasma membrane have been identified visually, but the molecules involved in the contact are unknown. We describe here an Arabidopsis thaliana protein kinase, designated Wak1 for wall-associated kinase, whose predicted extracytoplasmic domain contains several epidermal growth factor repeats and identity with a viral movement protein. Wak1 fractionates with insoluble material when plant tissue is ground in a variety of buffers and detergents, suggesting a tight association with the plant extracellular matrix. Immunocytochemistry confirms that Wak1 is associated with the cell wall. Enzymatic digestion of the cell wall allows the release of Wak1 from the insoluble cell wall fraction, and protease experiments indicate that Wak1 likely has a cytoplasmic kinase domain, and the EGF containing domain is extracellular. Wak1 is found in all vegetative tissues of Arabidopsis, and has relatives in other angiosperms, but not Chlamydomonas. We suggest that Wak1 is a good candidate for a physical continuum between the cell wall and the cytoplasm, and since the kinase is cytoplasmic, it also has the potential to mediate signals to the cytoplasm from the cell wall.
Functional and mutational analysis of the light-harvesting chlorophyll a/b protein of thylakoid membranes.
Date: 1986-01-01
Creator: B. D. Kohorn, E. Harel, P. R. Chitnis, J. P. Thornber, E. M., Tobin
Access: Open access
- The precursor for a Lemna light-harvesting chlorophyll a/b protein (pLHCP) has been synthesized in vitro from a single member of the nuclear LHCP multigene family. We report the sequence of this gene. When incubated with Lemna chloroplasts, the pLHCP is imported and processed into several polypeptides, and the mature form is assembled into the light-harvesting complex of photosystem II (LHC II). The accumulation of the processed LHCP is enhanced by the addition to the chloroplasts of a precursor and a co-factor for chlorophyll biosynthesis. Using a model for the arrangement of the mature polypeptide in the thylakoid membrane as a guide, we have created mutations that lie within the mature coding region. We have studied the processing, the integration into thylakoid membranes, and the assembly into light-harvesting complexes of six of these deletions. Four different mutant LHCPs are found as processed proteins in the thylakoid membrane, but only one appears to have an orientation in the membrane that is similar to that of the wild type. No mutant LHCP appears in LHC II. The other two mutant LHCPs cannot be detected within the chloroplasts. We conclude that stable complex formation is not required for the processing and insertion of altered LHCPs into the thylakoid membrane. We discuss the results in light of our model.
Fighting for Every Inch of Land: Greed and Grievance in Petition Mobilization in Zhejiang
Date: 2020-07-01
Creator: Christopher Heurlin
Access: Open access
- Despite a proliferation of studies of the micro-level dynamics of protests and petitions against land takings in China, we know very little about how meso-level factors, such as the local economy, influence petitions to Beijing and provincial governments. Drawing upon the economic approach to civil war, this article examines the roles played by grievances and greed in determining the scale of mobilization at the county level in Zhejiang province. Through archival evidence and interviews in Ningbo and Lishui, as well as an original dataset of petitions, this article suggests that both grievances and greed influence petitioning. Mobilization is especially high in Ningbo, where valuable real estate markets have prompted landless farmers to compete with local governments over control of the rents from land. The article proposes the concept of resource value activation as a cognitive mechanism that has contributed to this process of mobilization.
Time-Periodic Solutions of Driven-Damped Trimer Granular Crystals
Date: 2015-01-01
Creator: E. G. Charalampidis, F. Li, C. Chong, J. Yang, P. G., Kevrekidis
Access: Open access
- We consider time-periodic structures of granular crystals consisting of alternate chrome steel (S) and tungsten carbide (W) spherical particles where each unit cell follows the pattern of a 2: 1 trimer: S-W-S. The configuration at the left boundary is driven by a harmonic in-time actuation with given amplitude and frequency while the right one is a fixed wall. Similar to the case of a dimer chain, the combination of dissipation, driving of the boundary, and intrinsic nonlinearity leads to complex dynamics. For fixed driving frequencies in each of the spectral gaps, we find that the nonlinear surface modes and the states dictated by the linear drive collide in a saddle-node bifurcation as the driving amplitude is increased, beyond which the dynamics of the system becomes chaotic. While the bifurcation structure is similar for solutions within the first and second gap, those in the first gap appear to be less robust. We also conduct a continuation in driving frequency, where it is apparent that the nonlinearity of the system results in a complex bifurcation diagram, involving an intricate set of loops of branches, especially within the spectral gap. The theoretical findings are qualitatively corroborated by the experimental full-field visualization of the time-periodic structures.
Seasonal acclimatization of antioxidants and photosynthesis in Chondrus crispus and Mastocarpus stellatus, two co-occurring red algae with differing stress tolerances
Date: 2004-01-01
Creator: Nissa L. Lohrmann, Barry A. Logan, Amy S. Johnson
Access: Open access
- Mastocarpus stellatus and Chondrus crispus are red macroalgae that co-dominate the lower rocky intertidal zones of the northern Atlantic coast. M. stellatus is more tolerant than C. crispus of environmental stresses, particularly those experienced during winter. This difference in tolerance has been attributed, in part, to greater contents or activities of certain antioxidants in M. stellatus. We compared the photosynthetic capacities and activities of three antioxidant enzymes - superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR) - as well as the contents of ascorbate from fronds of M. stellatus and C. crispus collected over a year. Photosynthetic capacity increased in winter, but did not differ between species in any season. The activities of the three antioxidant enzymes and the contents of ascorbate were significantly greater in tissues collected during months with mean air and water temperatures below 7.5°C ("cold" months; December, February, March, April) than in months with mean air temperatures above 11°C ("warm" months; June, July, August, October). Overall, C. crispus had significantly greater SOD and APX activities, while M. stellatus had higher ascorbate contents. Species-specific differences in GR activity depended upon mean monthly temperatures at the time of tissue collection; C. crispus had higher activities during cold months, whereas M. stellatus had higher activities during warm months. Taken together, these data indicate that increased ROS scavenging capacity is a part of winter acclimatization; however, only trends in ascorbate content support the hypothesis that greater levels of antioxidants underlie the relatively greater winter tolerance of M. stellatus in comparison to C. crispus.
Applications of subleading-color amplitudes in N = 4 SYM theory
Date: 2011-12-01
Creator: Stephen G. Naculich, Horatiu Nastase, Howard J. Schnitzer
Access: Open access
- A number of features and applications of subleading-color amplitudes of N = 4 SYM theory are reviewed. Particular attention is given to the IR divergences of the subleading-color amplitudes, the relationships of N = 4 SYM theory to N = 8 supergravity, and to geometric interpretations of one-loop subleading-color and N k MHV amplitudes of N = 4 SYM theory. Copyright © 2011 Stephen G. Naculich et al.
Consequences of toxic secondary compounds in nectar for mutualist bees and antagonist butterflies
Date: 2016-10-01
Creator: Patricia L. Jones, Anurag A. Agrawal
Access: Open access
- Attraction of mutualists and defense against antagonists are critical challenges for most organisms and can be especially acute for plants with pollinating and non-pollinating flower visitors. Secondary compounds in flowers have been hypothesized to adaptively mediate attraction of mutualists and defense against antagonists, but this hypothesis has rarely been tested. The tissues of milkweeds (Asclepias spp.) contain toxic cardenolides that have long been studied as chemical defenses against herbivores. Milkweed nectar also contains cardenolides, and we have examined the impact of manipulating cardenolides in nectar on the foraging choices of two flower visitors: generalist bumble bees, Bombus impatiens, which are mutualistic pollinators, and specialist monarch butterflies, Danaus plexippus, which are herbivores as larvae and ineffective pollinators as adults. Although individual bumble bees in single foraging bouts showed no avoidance of cardenolides at the highest natural concentrations reported for milkweeds, a pattern of deterrence did arise when entire colonies were allowed to forage for several days. Monarch butterflies were not deterred by the presence of cardenolides in nectar when foraging from flowers, but laid fewer eggs on plants paired with cardenolide-laced flowers compared to controls. Thus, although deterrence of bumble bees by cardenolides may only occur after extensive foraging, a primary effect of nectar cardenolides appears to be reduction of monarch butterfly oviposition.