3,417 research outputs found
The Minimum of Solar Cycle 23: As Deep as It Could Be?
In this work we introduce a new way of binning sunspot group data with the
purpose of better understanding the impact of the solar cycle on sunspot
properties and how this defined the characteristics of the extended minimum of
cycle 23. Our approach assumes that the statistical properties of sunspots are
completely determined by the strength of the underlying large-scale field and
have no additional time dependencies. We use the amplitude of the cycle at any
given moment (something we refer to as activity level) as a proxy for the
strength of this deep-seated magnetic field.
We find that the sunspot size distribution is composed of two populations:
one population of groups and active regions and a second population of pores
and ephemeral regions. When fits are performed at periods of different activity
level, only the statistical properties of the former population, the active
regions, is found to vary.
Finally, we study the relative contribution of each component (small-scale
versus large-scale) to solar magnetism. We find that when hemispheres are
treated separately, almost every one of the past 12 solar minima reaches a
point where the main contribution to magnetism comes from the small-scale
component. However, due to asymmetries in cycle phase, this state is very
rarely reached by both hemispheres at the same time. From this we infer that
even though each hemisphere did reach the magnetic baseline, from a
heliospheric point of view the minimum of cycle 23 was not as deep as it could
have been
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Public goods and private interests: Understanding non-residential demand for green power
This article presents the results of the first large-scale mail survey of non-residential green power customers in the United States. The survey explored the motivations, attitudes, and experiences of 464 business, non-profit, and public-sector customers that have voluntarily opted to purchase - and frequently pay a premium for - renewable electricity. Results of this study should be of value to marketers interested in targeting these customer segments, to policy makers interested in fostering and understanding non-residential demand for green power, and to academics pondering the motivations for firms to engage in such voluntary environmental initiatives
The treatment of renewable energy certificates, emissions allowances, and green power programs in state renewables portfolio standards
Bostonia: 1993-1994, no. 2-3
Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
The Origin of Line Emission in Massive z~2.3 Galaxies: Evidence for Cosmic Downsizing of AGN Host Galaxies
Using the Gemini Near-InfraRed Spectrograph (GNIRS), we have assembled a
complete sample of 20 K-selected galaxies at 2.0<z<2.7 with high quality
near-infrared spectra. As described in a previous paper, 9 of these 20 galaxies
have strongly suppressed star formation and no detected emission lines. The
present paper concerns the 11 galaxies with detected Halpha emission, and
studies the origin of the line emission using the GNIRS spectra and follow-up
observations with SINFONI on the VLT. Based on their [NII]/Halpha ratios, the
spatial extent of the line emission and several other diagnostics, we infer
that four of the eleven emission-line galaxies host narrow line active galactic
nuclei (AGNs). The AGN host galaxies have stellar populations ranging from
evolved to star-forming. Combining our sample with a UV-selected galaxy sample
at the same redshift that spans a broader range in stellar mass, we find that
black-hole accretion is more effective at the high-mass end of the galaxy
distribution (~2.9x10^11 Msun) at z~2.3. Furthermore, by comparing our results
with SDSS data, we show that the AGN activity in massive galaxies has decreased
significantly between z~2.3 and z~0. AGNs with similar normalized accretion
rates as those detected in our K-selected galaxies reside in less massive
galaxies (~4.0x10^10 Msun) at low redshift. This is direct evidence for
downsizing of AGN host galaxies. Finally, we speculate that the typical stellar
mass-scale of the actively accreting AGN host galaxies, both at low and at high
redshift, might be similar to the mass-scale at which star-forming galaxies
seem to transform into red, passive systems.Comment: Accepted for publication in the Astrophysical Journa
Submesoscale dispersion in the vicinity of the Deepwater Horizon spill
Reliable forecasts for the dispersion of oceanic contamination are important
for coastal ecosystems, society and the economy as evidenced by the Deepwater
Horizon oil spill in the Gulf of Mexico in 2010 and the Fukushima nuclear plant
incident in the Pacific Ocean in 2011. Accurate prediction of pollutant
pathways and concentrations at the ocean surface requires understanding ocean
dynamics over a broad range of spatial scales. Fundamental questions concerning
the structure of the velocity field at the submesoscales (100 meters to tens of
kilometers, hours to days) remain unresolved due to a lack of synoptic
measurements at these scales. \textcolor{black} {Using high-frequency position
data provided by the near-simultaneous release of hundreds of accurately
tracked surface drifters, we study the structure of submesoscale surface
velocity fluctuations in the Northern Gulf Mexico. Observed two-point
statistics confirm the accuracy of classic turbulence scaling laws at
200m50km scales and clearly indicate that dispersion at the submesoscales is
\textit{local}, driven predominantly by energetic submesoscale fluctuations.}
The results demonstrate the feasibility and utility of deploying large clusters
of drifting instruments to provide synoptic observations of spatial variability
of the ocean surface velocity field. Our findings allow quantification of the
submesoscale-driven dispersion missing in current operational circulation
models and satellite altimeter-derived velocity fields.Comment: 9 pages, 6 figure
Influence of Quantum Size Effects on Island Coarsening
DOI:10.1103/PhysRevLett.96.10610 http://prl.aps.org/pdf/PRL/v96/i10/e106105Surface x-ray scattering and scanning-tunneling microscopy experiments reveal novel coarsening behavior of Pb nanocrystals grown on Si 111 - 7 7 . It is found that quantum size effects lead to the
breakdown of the classical Gibbs-Thomson analysis. This is manifested by the lack of scaling of the island densities. In addition, island decay times are orders of magnitude faster than expected from the classical analysis and have an unusual dependence on the growth flux F (i.e., 1=F). As a result, a highly monodispersed 7-layer island height distribution is found after coarsening if the islands are grown at high rather than low flux rates. These results have important implications, especially at low temperatures, for the controlled growth and self-organization of nanostructures.The Advanced Photon Source is supported by the DOE Office of Basic Energy Sciences, Contract No. W-31-109-Eng-38. The -CAT beam line is supported through Ames
Laboratory, operated for the U.S. DOE by Iowa State University under Contract No. W-7405-Eng-82. Research funding was supported, in part, by Ames Laboratory
(M. C. T.), Canim Scientific Group (E. H. C.), the Missouri University Research Board, the National Science Foundation DMR-0405742, and the Petroleum Research Fund No. 41792AC10 (P. F. M., C. A. J., C. K.),
the Natural Sciences and Engineering Research Council (NSERC) of Canada (C. A. J.), the Center for Nanostructured Materials Technology under 21st Century Frontier R&D Programs of the Ministry of Science and
Technology (No. 05K1501-02520), Korea (C. K.)
Formation of extended ionomeric network by bulk polymerization of L,D-lactide with layered-double-hydroxide
Neurodevelopmental effects of chronic exposure to elevated levels of pro-inflammatory cytokines in a developing visual system
<p>Abstract</p> <p>Background</p> <p>Imbalances in the regulation of pro-inflammatory cytokines have been increasingly correlated with a number of severe and prevalent neurodevelopmental disorders, including autism spectrum disorder, schizophrenia and Down syndrome. Although several studies have shown that cytokines have potent effects on neural function, their role in neural development is still poorly understood. In this study, we investigated the link between abnormal cytokine levels and neural development using the <it>Xenopus laevis </it>tadpole visual system, a model frequently used to examine the anatomical and functional development of neural circuits.</p> <p>Results</p> <p>Using a test for a visually guided behavior that requires normal visual system development, we examined the long-term effects of prolonged developmental exposure to three pro-inflammatory cytokines with known neural functions: interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α. We found that all cytokines affected the development of normal visually guided behavior. Neuroanatomical imaging of the visual projection showed that none of the cytokines caused any gross abnormalities in the anatomical organization of this projection, suggesting that they may be acting at the level of neuronal microcircuits. We further tested the effects of TNF-α on the electrophysiological properties of the retinotectal circuit and found that long-term developmental exposure to TNF-α resulted in enhanced spontaneous excitatory synaptic transmission in tectal neurons, increased AMPA/NMDA ratios of retinotectal synapses, and a decrease in the number of immature synapses containing only NMDA receptors, consistent with premature maturation and stabilization of these synapses. Local interconnectivity within the tectum also appeared to remain widespread, as shown by increased recurrent polysynaptic activity, and was similar to what is seen in more immature, less refined tectal circuits. TNF-α treatment also enhanced the overall growth of tectal cell dendrites. Finally, we found that TNF-α-reared tadpoles had increased susceptibility to pentylenetetrazol-induced seizures.</p> <p>Conclusions</p> <p>Taken together our data are consistent with a model in which TNF-α causes premature stabilization of developing synapses within the tectum, therefore preventing normal refinement and synapse elimination that occurs during development, leading to increased local connectivity and epilepsy. This experimental model also provides an integrative approach to understanding the effects of cytokines on the development of neural circuits and may provide novel insights into the etiology underlying some neurodevelopmental disorders.</p
Liver genomic responses to ciguatoxin: evidence for activation of Phase I and Phase II detoxification pathways following an acute hypothermic response in mice
Ciguatoxins (CTX) are polyether neurotoxins that target voltage-gated sodium channels and are responsible for ciguatera, the most common fish-borne food poisoning in humans. This study characterizes the global transcriptional response of mouse liver to a symptomatic dose (0.26 ng/g) of the highly potent Pacific ciguatoxin-1 (P-CTX-1). At 1 h post-exposure 2.4% of features on a 44K whole genome array were differentially expressed (p ≤ 0.0001), increasing to 5.2% at 4 h and decreasing to 1.4% by 24 h post-CTX exposure. Data were filtered (|fold change| ≥ 1.5 and p ≤ 0.0001 in at least one time point) and a trend set of 1550 genes were used for further analysis. Early gene expression was likely influenced prominently by an acute 4°C decline in core body temperature by 1 h, which resolved by 8 h following exposure. An initial downregulation of 32 different solute carriers, many involved in sodium transport, was observed. Differential gene expression in pathways involving eicosanoid biosynthesis and cholesterol homeostasis was also noted. Cytochrome P450s (Cyps) were of particular interest due to their role in xenobiotic metabolism. Twenty-seven genes, mostly members of Cyp2 and Cyp4 families, showed significant changes in expression. Many Cyps underwent an initial downregulation at 1 h but were quickly and strongly upregulated at 4 and 24 h post-exposure. In addition to Cyps, increases in several glutathione S-transferases were observed, an indication that both phase I and phase II metabolic reactions are involved in the hepatic response to CTX in mice
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