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  • 1
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    American Physical Society (APS)
    Publication Date: 2011-11-11
    Description: Author(s): R. R. Stein and H. Isambert [Phys. Rev. E 84, 051904] Published Thu Nov 10, 2011
    Keywords: Biological physics
    Print ISSN: 1539-3755
    Electronic ISSN: 1550-2376
    Topics: Physics
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  • 2
    Publication Date: 2014-10-23
    Description: The gastrointestinal tracts of mammals are colonized by hundreds of microbial species that contribute to health, including colonization resistance against intestinal pathogens. Many antibiotics destroy intestinal microbial communities and increase susceptibility to intestinal pathogens. Among these, Clostridium difficile, a major cause of antibiotic-induced diarrhoea, greatly increases morbidity and mortality in hospitalized patients. Which intestinal bacteria provide resistance to C. difficile infection and their in vivo inhibitory mechanisms remain unclear. Here we correlate loss of specific bacterial taxa with development of infection, by treating mice with different antibiotics that result in distinct microbiota changes and lead to varied susceptibility to C. difficile. Mathematical modelling augmented by analyses of the microbiota of hospitalized patients identifies resistance-associated bacteria common to mice and humans. Using these platforms, we determine that Clostridium scindens, a bile acid 7alpha-dehydroxylating intestinal bacterium, is associated with resistance to C. difficile infection and, upon administration, enhances resistance to infection in a secondary bile acid dependent fashion. Using a workflow involving mouse models, clinical studies, metagenomic analyses, and mathematical modelling, we identify a probiotic candidate that corrects a clinically relevant microbiome deficiency. These findings have implications for the rational design of targeted antimicrobials as well as microbiome-based diagnostics and therapeutics for individuals at risk of C. difficile infection.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4354891/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4354891/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Buffie, Charlie G -- Bucci, Vanni -- Stein, Richard R -- McKenney, Peter T -- Ling, Lilan -- Gobourne, Asia -- No, Daniel -- Liu, Hui -- Kinnebrew, Melissa -- Viale, Agnes -- Littmann, Eric -- van den Brink, Marcel R M -- Jenq, Robert R -- Taur, Ying -- Sander, Chris -- Cross, Justin R -- Toussaint, Nora C -- Xavier, Joao B -- Pamer, Eric G -- AI95706/AI/NIAID NIH HHS/ -- DP2 OD008440/OD/NIH HHS/ -- DP2OD008440/OD/NIH HHS/ -- K23 AI095398/AI/NIAID NIH HHS/ -- P01 CA023766/CA/NCI NIH HHS/ -- P30 CA008748/CA/NCI NIH HHS/ -- R01 AI042135/AI/NIAID NIH HHS/ -- R01 AI095706/AI/NIAID NIH HHS/ -- R01 AI42135/AI/NIAID NIH HHS/ -- T32 CA009149/CA/NCI NIH HHS/ -- T32 GM007739/GM/NIGMS NIH HHS/ -- T32GM07739/GM/NIGMS NIH HHS/ -- U54 CA148967/CA/NCI NIH HHS/ -- England -- Nature. 2015 Jan 8;517(7533):205-8. doi: 10.1038/nature13828. Epub 2014 Oct 22.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] Infectious Diseases Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA [2] Lucille Castori Center for Microbes, Inflammation and Cancer, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA. ; 1] Computational Biology Program, Sloan-Kettering Institute, New York, New York 10065, USA [2] Department of Biology, University of Massachusetts Dartmouth, North Dartmouth, Massachusetts 02747, USA. ; Computational Biology Program, Sloan-Kettering Institute, New York, New York 10065, USA. ; Lucille Castori Center for Microbes, Inflammation and Cancer, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA. ; Donald B. and Catherine C. Marron Cancer Metabolism Center, Sloan-Kettering Institute, New York, New York 10065, USA. ; Genomics Core Laboratory, Sloan-Kettering Institute, New York, New York 10065, USA. ; 1] Bone Marrow Transplant Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA [2] Immunology Program, Sloan-Kettering Institute, New York, New York 10065, USA. ; Bone Marrow Transplant Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA. ; 1] Lucille Castori Center for Microbes, Inflammation and Cancer, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA [2] Computational Biology Program, Sloan-Kettering Institute, New York, New York 10065, USA. ; 1] Infectious Diseases Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA [2] Lucille Castori Center for Microbes, Inflammation and Cancer, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA [3] Immunology Program, Sloan-Kettering Institute, New York, New York 10065, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25337874" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Anti-Bacterial Agents/pharmacology ; Bile Acids and Salts/*metabolism ; Biological Evolution ; Clostridium/metabolism ; Clostridium difficile/drug effects/*physiology ; Colitis/metabolism/microbiology/prevention & control/therapy ; Disease Susceptibility/*microbiology ; Feces/microbiology ; Female ; Humans ; Intestines/drug effects/*metabolism/*microbiology ; Metagenome/genetics ; Mice ; Mice, Inbred C57BL ; Microbiota/drug effects/genetics/*physiology ; Symbiosis
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 2013-12-06
    Description: We study the effects of different descriptions of the solar surface convection on the eigenfrequencies of p modes. 1D evolution calculations of the whole Sun and 3D hydrodynamic and magnetohydrodynamic simulations of the current surface are performed. These calculations rely on realistic physics. Averaged stratifications of the 3D simulations are introduced in the 1D solar evolution or in the structure models. The eigenfrequencies obtained are compared to those of 1D models relying on the usual phenomenologies of convection and to observations of the Michelson Doppler Imager instrument aboard the Solar Heliospheric Observatory (SoHO). We also investigate how the magnetic activity could change the eigenfrequencies and the solar radius, assuming that, 3 Mm below the surface, the upgoing plasma advects a 1.2 kG horizontal field. All models and observed eigenfrequencies are fairly close below 3 mHz. Above 3 mHz the eigenfrequencies of the phenomenological convection models are above the observed eigenfrequencies. The frequencies of the models based on the 3D simulations are slightly below the observed frequencies. Their maximum deviation is 3 μHz at 3 mHz but drops below 1 μHz at 4 mHz. Replacing the hydrodynamic by the magnetohydrodynamic simulation increases the eigenfrequencies. The shift is negligible below 2.2 mHz and then increases linearly with frequency to reach 1.7 μHz at 4 mHz. The impact of the simulated activity is a 14 mas shrinking of the solar layers near the optical depth unity.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 4
    Publication Date: 2014-04-04
    Description: The 11 April 2012 M  8.6 Indian Ocean earthquake was an unusually large intraoceanic strike-slip event. For several days, the global M ≥4.5 and M ≥6.5 seismicity rate at remote distances (i.e., thousands of kilometers from the mainshock) was elevated. The strike-slip mainshock appears through its Love waves to have triggered a global burst of strike-slip aftershocks over several days. But the M ≥6.5 rate subsequently dropped to zero for the succeeding 95 days, although the M ≤6.0 global rate was close to background during this period. Such an extended period without an M ≥6.5 event has happened rarely over the past century, and never after a large mainshock. Quiescent periods following previous large ( M ≥8) mainshocks over the past century are either much shorter or begin so long after a given mainshock that no physical interpretation is warranted. The 2012 mainshock is unique in terms of both the short-lived global increase and subsequent long quiescent period. We believe that the two components are linked and interpret this pattern as the product of dynamic stressing of a global system of faults. Transient dynamic stresses can encourage short-term triggering, but, paradoxically, it can also inhibit rupture temporarily until background tectonic loading restores the system to its premainshock stress levels.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 5
    Publication Date: 2014-11-12
    Description: We perform a calibration of the mixing length of convection in stellar structure models against realistic 3D radiation-coupled hydrodynamics simulations of convection in stellar surface layers, determining the adiabat deep in convective stellar envelopes. The mixing-length parameter α is calibrated by matching averages of the 3D simulations to 1D stellar envelope models, ensuring identical atomic physics in the two cases. This is done for a previously published grid of solar-metallicity convection simulations, covering from 4200 to 6900 K on the main sequence, and from 4300 to 5000 K for giants with log g  = 2.2. Our calibration results in an α varying from 1.6 for the warmest dwarf, which is just cool enough to admit a convective envelope, and up to 2.05 for the coolest dwarfs in our grid. In between these is a triangular plateau of α ~ 1.76. The Sun is located on this plateau and has seen little change during its evolution so far. When stars ascend the giant branch, they largely do so along tracks of constant α, with α decreasing with increasing mass.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 6
    Publication Date: 2014-06-10
    Description: Relations between temperature, T , and optical depth, , are often used for describing the photospheric transition from optically thick to optically thin in stellar structure models. We show that this is well justified, but also that currently used T () relations are often inconsistent with their implementation. As an outer boundary condition on the system of stellar structure equations, T () relations have an undue effect on the overall structure of stars. In this age of precision asteroseismology, we need to re-assess both the method for computing and for implementing T () relations, and the assumptions they rest on. We develop a formulation for proper and consistent evaluation of T () relations from arbitrary 1D or 3D stellar atmospheres, and for their implementation in stellar structure and evolution models. We extract radiative T () relations, as described by our new formulation, from 3D simulations of convection in deep stellar atmospheres of late-type stars from dwarfs to giants. These simulations employ realistic opacities and equation of state, and account for line blanketing. For comparison, we also extract T () relations from 1Dmarcs model atmospheres using the same formulation. T () relations from our grid of 3D convection simulations display a larger range of behaviours with surface gravity, compared with those of conventional theoretical 1D hydrostatic atmosphere models based on the mixing-length theory for convection. The 1D atmospheres show little dependence on gravity. 1D atmospheres of main-sequence stars also show an abrupt transition to the diffusion approximation at ~= 2.5, whereas the 3D simulations exhibit smooth transitions that occur at the same depth for M ~= 0.8 M , and higher in the atmosphere for both more and less massive main-sequence stars. Based on these results, we recommend no longer using scaled solar T () relations. Files with T () relations for our grid of simulations are made available to the community, together with routines for interpolating in this irregular grid. We also provide matching tables of atmospheric opacity, for consistent implementation in stellar structure models.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 7
    Publication Date: 2011-11-10
    Print ISSN: 1539-3755
    Electronic ISSN: 1550-2376
    Topics: Physics
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