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  • Articles  (111)
  • Physics  (109)
  • Technology  (3)
  • Electrical Engineering, Measurement and Control Technology  (3)
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  • Articles  (111)
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  • 1
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    Oceanic Forcing on Interannual Variability of Sahel Heavy and Moderate Daily Rainfall (2019)
    American Meteorological Society (AMS)
    Details
    Publication Date: 2019
    Description: Journal of Hydrometeorology, Volume 20, Issue 3, Page 397-410, March 2019. 〈br/〉
    Print ISSN: 1525-755X
    Electronic ISSN: 1525-7541
    Topics: Geosciences , Physics
    Published by American Meteorological Society (AMS)
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  • 2
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    Multi-epoch observations of extremely high-velocity emergent broad absorption (2016)
    Oxford University Press
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    Publication Date: 2016-01-22
    Description: We present the discovery of the highest velocity C iv broad absorption line to date in the z = 2.47 quasar SDSS J023011.28+005913.6, hereafter J0230. In comparing the public DR7 and DR9 spectra of J0230, we discovered an emerging broad absorption trough outflowing at ~60 000 km s –1 , which we refer to as trough A. In pursuing follow up observations of trough A, we discovered a second emergent C iv broad absorption trough outflowing at ~40 000 km s –1 , namely trough B. In total, we collected seven spectral epochs of J0230 that demonstrate emergent and rapidly (~10 d in the rest-frame) varying broad absorption. We investigate two possible scenarios that could cause these rapid changes: bulk motion and ionization variability. Given our multi-epoch data, we were able to rule out some simple models of bulk motion, but have proposed two more realistic models to explain the variability of both troughs. Trough A is likely an augmented ‘crossing disc’ scenario with the absorber moving at 10 000 〈 v (km s –1 ) 〈 18 000. Trough B can be explained by a flow-tube feature travelling across the emitting region at 8000 〈 v (km s –1 ) 〈 56 000. If ionization variability is the cause for the changes observed, trough A's absorber has n e ≥ 724 cm –3 and is at r equal ≥ 2.00 kpc, or is at r 〈 2.00 kpc with no constraint on the density; trough B's absorber either has n e ≥ 1540 cm –3 and is at r equal ≥ 1.37 kpc, or is at r 〈 1.37 kpc with no constraint on the density.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Tropical SST and Sahel rainfall: A non-stationary relationship (2012)
    Wiley
    Details
    Publication Date: 2012-06-30
    Description: Sea surface temperature (SST) anomalies in the tropical Atlantic have been associated with precipitation anomalies in West Africa that form a dipole pattern with centers over the Sahel and the Gulf of Guinea. Whilst this was clear before the 1970's, the dipole pattern almost disappeared after that date, as the anti-correlation between rainfall anomalies in the Sahel and Guinea dropped abruptly. Simultaneously, the anti-correlations between Sahel rainfall and tropical Pacific SSTs strengthened. It has been posited that these changes after the 1970's developed as rainfall over West Africa started to co-vary with SSTs in the global tropics. In this co-variability, enhanced summer rainfall over West Africa with a monopole pattern corresponds to warmer SSTs in the tropical Atlantic and Maritime Continent, and colder SSTs in the tropical Pacific and western Indian Oceans. The present paper describes the hitherto unexplored seasonal evolution of this co-variability and the physical mechanisms at work. Sensitivity experiments with two atmospheric general circulation models demonstrate that, after the 1970's, the impacts of SST anomalies in the Indo-Pacific counteract those in the Atlantic in terms of generating rainfall anomalies over the Sahel, and that this superposition of effects is primarily linear. Therefore, at interannual timescales, the change in the patterns of co-variability between West African rainfall and tropical SSTs can explain the non-stationary relationship between the anomalies in these two fields.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    H2 accumulation and N2 fixation variation by Ni limitation in Cyanothece (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Ni is an essential cofactor in NiFe‐uptake hydrogenase, an enzyme regulating H2 metabolism in diazotrophic cyanobacteria, the major H2 producers in the surface ocean globally. Here, we investigated the effect of Ni supply on H2 production and N2 fixation by using a model marine cyanobacterial diazotroph, Cyanothece. By mediating total dissolved Ni concentrations from 100 to 0.03 nmol L−1 in a trace metal‐defined culture medium, we demonstrated that Ni deficiency results in H2 accumulation, coupled with decreasing Ni quotas, growth rates, and occasionally relatively low N2 fixation rates. These results indicate that Ni deficiency limits the growth of the Cyanothece to some extent, considerably decreases H2 uptake by hydrogenase and leads to H2 accumulation and N2 fixation variation in the diazotroph. The findings show that Ni availability is a critical factor on controlling H2 production and N2 fixation in marine diazotrophic cyanobacteria. The information of Ni bioavailability for diazotrophic cyanobacteria is thus essential to evaluate the importance of Ni for H2 cycling and N2 fixation in oceanic surface waters.
    Print ISSN: 0024-3590
    Electronic ISSN: 1939-5590
    Topics: Biology , Geosciences , Physics
    Published by Wiley on behalf of The Association for the Sciences of Limnology and Oceanography (ASLO).
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  • 5
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    Calibrated estimates of the energy in major flares of GRS 1915+105 (2013)
    Oxford University Press
    Details
    Publication Date: 2013-10-08
    Description: We analyse the energetics of the major radio flare of 2005 October 8 in GRS 1915+105. The flare is of particular interest because it is one of the most luminous and energetic radio flares from a Galactic black hole that has ever been observed. The motivation is twofold. One, to learn more about the energetics of this most extreme phenomenon and its relationship to the accretion state. The second is to verify if the calibrated estimates of the energy of major radio flares (based on the peak low frequency optically thin flux) derived from flares in the period 1996–2001 in Punsly & Rodriguez, PR13 hereafter, can be used to estimate plasmoid energy beyond this time period. We find evidence that the calibrated curves are still accurate for this strong flare. Furthermore, the physically important findings of PR13 are supported by the inclusion of this flare: the flare energy is correlated with both the intrinsic bolometric X-ray luminosity, L bol , ~1 h before ejection and L bol averaged over the duration of the ejection of the plasmoid and L bol is highly elevated relative to historic levels just before and during the ejection episode. A search of the data archives reveal that only the 2005 October 8 flare and those in PR13 have adequate data sampling to allow estimates of both the energy of the flare and the X-ray luminosity before and during flare launch.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Optical index measurement of InAs/GaSb type-II superlattice for mid-infrared photodetection at cryogenic temperatures (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-10-07
    Description: The complex optical index ñ (= n  + i κ ) of InAs/GaSb type-II superlattice (T2SL) was determined in the 1–6  μ m range from reflectivity measurements of resonant structures at 80 K. Several air/superlattice/gold cavities of various thicknesses were fabricated and their reflectivity was measured. As the large variations induced by the cavity resonances in the studied range can be accurately modeled, we were able to determine the complex optical index ñ of InAs/GaSb T2SL with an error of only a few percent. We found that the in-plane refractive index n of the T2SL lies between 3.65 and 3.77 in the mid-infrared wavelength range, and the absorption coefficient κ decreases from 0.23 to 0.001 as the wavelength increases from 1.25 to 5.65  μ m. The subtractive Kramers-Kronig relation allowed us to verify our determination of ñ .
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 7
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    Where do coastlines stabilize following rapid retreat? (2014)
    Wiley
    Details
    Publication Date: 2014-02-15
    Description: ABSTRACT [1]  We present a numerical model that shows the transgressing upper shoreline of wave-dominated estuaries (bayhead deltas), which commonly contain populous urban and industrial centers, stabilize and their rate of retreat decreases at tributary junctions. The decreased rate of retreat across a tributary junction is caused by a decrease in total accommodation while sediment supply remains conserved. Our model predicts that bayhead deltas from smaller systems will be located closer to tributary confluences than their larger counterparts. An examination of modern bayhead deltas in Albemarle Sound, US Atlantic Coast reveals that bayhead deltas from smaller tributaries are located closer to tributary confluences than bayhead deltas associated with larger tributaries, supporting our model prediction. Our results highlight the importance of antecedent topography created during falling sea levels on shaping the nature of transgression during the ensuing sea-level rise. In particular, tributary junctions act as pinning points during transgression.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Sea-level anomalies exacerbate beach erosion (2014)
    Wiley
    Details
    Publication Date: 2014-07-17
    Description: Sea-level anomalies are intra-seasonal increases in water level forced by meteorological and oceanographic processes unrelated to storms. The effects of sea-level anomalies on beach morphology are unknown, but important to constrain because these events have been recognized over large stretches of continental margins. Here, we present beach erosion measurements along Onslow Beach, a barrier island on the U.S. East Coast, in response to a year with frequent sea-level anomalies and no major storms. The anomalies enabled extensive erosion, which was similar and in most places greater than the erosion that occurred during a year with a hurricane. These results highlight the importance of sea-level anomalies in facilitating coastal erosion and advocate for their inclusion in beach-erosion models and management plans. Sea-level anomalies amplify the erosive effects of accelerated sea-level rise and changes in storminess associated with global climate change.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Biodiversity and biogeography of phages in modern stromatolites and thrombolites (2008)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2008-03-04
    Description: Viruses, and more particularly phages (viruses that infect bacteria), represent one of the most abundant living entities in aquatic and terrestrial environments. The biogeography of phages has only recently been investigated and so far reveals a cosmopolitan distribution of phage genetic material (or genotypes). Here we address this cosmopolitan distribution through the analysis of phage communities in modern microbialites, the living representatives of one of the most ancient life forms on Earth. On the basis of a comparative metagenomic analysis of viral communities associated with marine (Highborne Cay, Bahamas) and freshwater (Pozas Azules II and Rio Mesquites, Mexico) microbialites, we show that some phage genotypes are geographically restricted. The high percentage of unknown sequences recovered from the three metagenomes (〉97%), the low percentage similarities with sequences from other environmental viral (n = 42) and microbial (n = 36) metagenomes, and the absence of viral genotypes shared among microbialites indicate that viruses are genetically unique in these environments. Identifiable sequences in the Highborne Cay metagenome were dominated by single-stranded DNA microphages that were not detected in any other samples examined, including sea water, fresh water, sediment, terrestrial, extreme, metazoan-associated and marine microbial mats. Finally, a marine signature was present in the phage community of the Pozas Azules II microbialites, even though this environment has not been in contact with the ocean for tens of millions of years. Taken together, these results prove that viruses in modern microbialites display biogeographical variability and suggest that they may be derived from an ancient community.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Desnues, Christelle -- Rodriguez-Brito, Beltran -- Rayhawk, Steve -- Kelley, Scott -- Tran, Tuong -- Haynes, Matthew -- Liu, Hong -- Furlan, Mike -- Wegley, Linda -- Chau, Betty -- Ruan, Yijun -- Hall, Dana -- Angly, Florent E -- Edwards, Robert A -- Li, Linlin -- Thurber, Rebecca Vega -- Reid, R Pamela -- Siefert, Janet -- Souza, Valeria -- Valentine, David L -- Swan, Brandon K -- Breitbart, Mya -- Rohwer, Forest -- England -- Nature. 2008 Mar 20;452(7185):340-3. doi: 10.1038/nature06735. Epub 2008 Mar 2.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biology, San Diego State University, San Diego, California 92182, USA. cdesnues@yahoo.fr〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18311127" target="_blank"〉PubMed〈/a〉
    Keywords: Bacteriophages/classification/genetics/*isolation & purification/*physiology ; Bahamas ; *Biodiversity ; Capsid/chemistry ; Computational Biology ; DNA, Viral/analysis/genetics ; *Ecosystem ; Fresh Water/microbiology/virology ; Genome, Viral/genetics ; Genomics ; *Geography ; Geologic Sediments/microbiology/virology ; Mexico ; Molecular Sequence Data ; Phylogeny ; Proteome/metabolism ; Seawater/microbiology/virology ; *Water Microbiology
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 10
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    Prevention of vaginal SHIV transmission in rhesus macaques through inhibition of CCR5 (2004)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2004-10-16
    Description: Topical agents, such as microbicides, that can protect against human immunodeficiency virus (HIV) transmission are urgently needed. Using a chimeric simian/human immunodeficiency virus (SHIV SF162), which is tropic for the chemokine receptor CCR5, we report that topical application of high doses of PSC-RANTES, an amino terminus-modified analog of the chemokine RANTES, provided potent protection against vaginal challenge in rhesus macaques. These experimental findings have potentially important implications for understanding vaginal transmission of HIV and the design of strategies for its prevention.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lederman, Michael M -- Veazey, Ronald S -- Offord, Robin -- Mosier, Donald E -- Dufour, Jason -- Mefford, Megan -- Piatak, Michael Jr -- Lifson, Jeffrey D -- Salkowitz, Janelle R -- Rodriguez, Benigno -- Blauvelt, Andrew -- Hartley, Oliver -- AI 36219/AI/NIAID NIH HHS/ -- AI 51649/AI/NIAID NIH HHS/ -- N01-CO-124000/CO/NCI NIH HHS/ -- New York, N.Y. -- Science. 2004 Oct 15;306(5695):485-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Medicine, Case Western Reserve University, University Hospitals, 2061 Cornell Road, Cleveland, OH 44106, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15486300" target="_blank"〉PubMed〈/a〉
    Keywords: Administration, Intravaginal ; Animals ; Anti-HIV Agents/administration & dosage/*therapeutic use ; Anti-Infective Agents, Local/administration & dosage/*therapeutic use ; Antibodies, Viral/blood ; *CCR5 Receptor Antagonists ; Chemokine CCL5/administration & dosage/*analogs & derivatives/*therapeutic use ; Dose-Response Relationship, Drug ; Drug Evaluation, Preclinical ; Female ; HIV Infections/*prevention & control/transmission ; HIV-1/drug effects ; Macaca mulatta ; Receptors, CCR5/metabolism ; Simian Acquired Immunodeficiency Syndrome/*prevention & control/transmission ; Simian Immunodeficiency Virus/drug effects/immunology ; Vagina/*virology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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