oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2019 ( 299 )

2018 ( 469 )

2017 ( 468 )

2016 ( 597 )

Custom range...

Search Results: 1 - 10 of 286246 matches for " F. E. Maas "
All listed articles are free for downloading (OA Articles)
Page 1 /286246
Display every page Item
The metabolic response of pteropods to acidification reflects natural CO2-exposure in oxygen minimum zones
A. E. Maas, K. F. Wishner,B. A. Seibel
Biogeosciences (BG) & Discussions (BGD) , 2012,
Abstract: Shelled pteropods (Thecosomata) are a group of holoplanktonic mollusks that are believed to be especially sensitive to ocean acidification because their aragonitic shells are highly soluble. Despite this concern, there is very little known about the physiological response of these animals to conditions of elevated carbon dioxide. This study examines the oxygen consumption and ammonia excretion of five pteropod species, collected from tropical regions of the Pacific Ocean, to elevated levels of carbon dioxide (0.10%, 1000 ppm). Our results show that pteropods that naturally migrate into oxygen minimum zones, such as Hyalocylis striata, Clio pyramidata, Cavolinia longirostris and Creseis virgula, were not affected by carbon dioxide at the levels and duration tested. Diacria quadridentata, which does not migrate, responds to high carbon dioxide conditions with reduced oxygen consumption and ammonia excretion. This indicates that the natural chemical environment of individual species may influence their resilience to ocean acidification.
The metabolic response of pteropods to ocean acidification reflects natural CO2-exposure in oxygen minimum zones
A. E. Maas,K. F. Wishner,B. A. Seibel
Biogeosciences Discussions , 2011, DOI: 10.5194/bgd-8-10295-2011
Abstract: Shelled pteropods (Thecosomata) are a group of holoplanktonic mollusks that are believed to be especially sensitive to ocean acidification because their aragonitic shells are highly soluble. Despite this concern, there is very little known about the physiological response of these animals to conditions of elevated carbon dioxide. This study examines the oxygen consumption and ammonia excretion of five pteropod species, collected from tropical regions of the Pacific Ocean, to elevated levels of carbon dioxide (0.10%, 1000 ppm). Our results show that pteropods that naturally migrate into oxygen minimum zones, such as Hyalocylis striata, Clio pyramidata, Cavolinia longirostris and Creseis virgula, were not affected by carbon dioxide at the levels and duration tested. Diacria quadridentata, which does not migrate, responds to high carbon dioxide conditions with reduced oxygen consumption and ammonia excretion. This indicates that the natural chemical environment of individual species influences their resilience to ocean acidification.
Study of resonant processes for multi-pion production in $\bar p +p\to\ell ^++\ell^- +n_\pi \pi$ annihilation
Kuraev, E. A.;Adamuscin, C.;Tomasi-Gustafsson, E.;Maas, F.
High Energy Physics - Phenomenology , 2007, DOI: 10.1016/j.physletb.2007.04.042
Abstract: In frame of a phenomenological approach based on Compton-like Feynman amplitudes, we study multi-pion production in antiproton nucleon collisions. The main interest of this reaction is related to the possibility to study the properties of the presumable $\bar N N$ atom and of its resonances. For the case of formation of a scalar or pseudoscalar resonant state, with $I^G(J^{P})=1^-(0^{\pm}),~0^+(0^-)$ numerical results are obtained. The differential cross section in an experimental set-up where the pions invariant mass is measured, is given with explicit dependence on the lepton pair and pions invariant mass.
Measurements and simulations of Cherenkov light in lead fluoride crystals
P. Achenbach,S. Baunack,K. Grimm,T. Hammel,D. von Harrach,A. Lopes Ginja,F. E. Maas,E. Schilling,H. Stroeher
Physics , 2001, DOI: 10.1016/S0168-9002(01)00668-4
Abstract: The anticipated use of more than one thousand lead fluoride (PbF2) crystals as a fast and compact Cherenkov calorimeter material in a parity violation experiment at MAMI stimulated the investigation of the light yield (L.Y.) of these crystals. The number of photoelectrons (p.e.) per MeV deposited energy has been determined with a hybrid photomultiplier tube (HPMT). In response to radioactive sources a L.Y. between 1.7 and 1.9 p.e./MeV was measured with 4% statistical and 5% systematic error. The L.Y. optimization with appropriate wrappings and couplings was investigated by means of the HPMT. Furthermore, a fast Monte Carlo simulation based on the GEANT code was employed to calculate the characteristics of Cherenkov light in the PbF2 crystals. The computing time was reduced by a factor of 50 compared to the regular photon tracking method by implementing detection probabilities as a three-dimensional look-up table. For a single crystal a L.Y. of 2.1 p.e./MeV was calculated. The corresponding detector response to electrons between 10 and 1000 MeV was highly linear with a variation smaller than 1%.
A luminosity monitor for the A4 parity violation experiment at MAMI
T. Hammel,P. Achenbach,S. Baunack,L. Capozza,J. Diefenbach,K. Grimm,D. vonHarrach,Y. Imai,E. Kabuss,R. Kothe,J. H. Lee,A. LopesGinja,F. E. Maas,A. SanchezLorente,E. Schilling,G. Stephan,C. Weinrich,I. Altarev
Physics , 2005, DOI: 10.1016/j.nima.2006.03.028
Abstract: A water Cherenkov luminosity monitor system with associated electronics has been developed for the A4 parity violation experiment at MAMI. The detector system measures the luminosity of the hydrogen target hit by the MAMI electron beam and monitors the stability of the liquid hydrogen target. Both is required for the precise study of the count rate asymmetries in the scattering of longitudinally polarized electrons on unpolarized protons. Any helicity correlated fluctuation of the target density leads to false asymmetries. The performance of the luminosity monitor, investigated in about 2000 hours with electron beam, and the results of its application in the A4 experiment are presented.
A high power liquid hydrogen target for the Mainz A4 parity violation experiment
I. Altarev,E. Schilling,S. Baunack,L. Capozza,J. Diefenbach,K. Grimm,Th. Hammel,D. vonHarrach,Y. Imai,E. M. Kabuss,R. Kothe,J. H. Lee,A. LopesGinja,F. E. Maas,A. SanchezLorente,G. Stephan,C. Weinrich
Physics , 2005, DOI: 10.1016/j.nima.2006.03.022
Abstract: We present a new powerful liquid hydrogen target developed for the precise study of parity violating electron scattering on hydrogen and deuterium. This target has been designed to have minimal target density fluctuations under the heat load of a 20$\mu$A CW 854.3 MeV electron beam without rastering the electron beam. The target cell has a wide aperture for scattered electrons and is axially symmetric around the beam axis. The construction is optimized to intensify heat exchange by a transverse turbulent mixing in the hydrogen stream, which is directed along the electron beam. The target is constructed as a closed loop circulating system cooled by a helium refrigerator. It is operated by a tangential mechanical pump with an optional natural convection mode. The cooling system supports up to 250 watts of the beam heating removal. Deeply subcooled liquid hydrogen is used for keeping the in-beam temperature below the boiling point. The target density fluctuations are found to be at the level 10$^{-3}$ at a beam current of 20 $\mu$A.
Feasibility studies of the time-like proton electromagnetic form factor measurements with PANDA at FAIR
M. Sudol,M. C. Mora Espi,E. Becheva,J. Boucher,T. Hennino,R. Kunne,D. Marchand,S. Ong,B. Ramstein,J. Van de Wiele,T. Zerguerras,F. Maas,B. Kopf,M. Pelizaeus,M. Steinke,J. Zhong,E. Tomasi-Gustafsson
Physics , 2009, DOI: 10.1140/epja/i2010-10960-8
Abstract: The possibility of measuring the proton electromagnetic form factors in the time-like region at FAIR with the \PANDA detector is discussed. Detailed simulations on signal efficiency for the annihilation of $\bar p +p $ into a lepton pair as well as for the most important background channels have been performed. It is shown that precision measurements of the differential cross section of the reaction $\bar p +p \to e^++ e^-$ can be obtained in a wide angular and kinematical range. The individual determination of the moduli of the electric and magnetic proton form factors will be possible up to a value of momentum transfer squared of $q^2\simeq 14$ (GeV/c)$^2$. The total $\bar p +p\to e^++e^-$ cross section will be measured up to $q^2\simeq 28$ (GeV/c)$^2$. The results obtained from simulated events are compared to the existing data. Sensitivity to the two photons exchange mechanism is also investigated.
A mitochondrial mutator plasmid that causes senescence under dietary restricted conditions
Marc FPM Maas, Rolf F Hoekstra, Alfons JM Debets
BMC Genetics , 2007, DOI: 10.1186/1471-2156-8-9
Abstract: We show that the pAL2-1 homologues act as 'insertional mutators' of the mitochondrial genome, which may explain their negative effect on life span extension. Sequencing revealed at least fourteen unique plasmid integration sites, of which twelve were located within the mitochondrial genome and two within copies of the plasmid itself. The plasmids were able to integrate in their entirety, via a non-homologous mode of recombination. Some of the integrated plasmid copies were truncated, which probably resulted from secondary, post-integrative, recombination processes. Integration sites were predominantly located within and surrounding the region containing the mitochondrial rDNA loci.We propose a model for the mechanism of integration, based on innate modes of mtDNA recombination, and discuss its possible link with the plasmid's negative effect on dietary restriction mediated life span extension.Calorie or dietary restriction (DR) extends life span in a wide range of organisms. This has been known for well over half a century, but the exact mechanisms behind this complex polygenic trait have yet to be revealed. In recent years several important nutrient-sensitive cellular signalling pathways have been discovered, which are at least partially conserved between organisms, e.g. the insulin/IGF-1-like and TOR (target of rapamycin) mediated signalling pathways [1-3]. These are involved in adjusting cellular metabolism to nutrient availability. Mutations in them tend to increase longevity and enhance cellular responses to various types of stress, e.g. oxidative stress and heat stress. At the proximate level DR thus appears to act by adjusting cellular metabolism to a mode set for survival.From an evolutionary point of view, the life span extending response to DR can be seen as an adaptation that allows aging organisms to postpone reproduction, and survive unfavourable periods of time [4]. This response may be expected in all aging organisms, including the select subset of fi
Energetic Plasticity Underlies a Variable Response to Ocean Acidification in the Pteropod, Limacina helicina antarctica
Brad A. Seibel, Amy E. Maas, Heidi M. Dierssen
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0030464
Abstract: Ocean acidification, caused by elevated seawater carbon dioxide levels, may have a deleterious impact on energetic processes in animals. Here we show that high PCO2 can suppress metabolism, measured as oxygen consumption, in the pteropod, L. helicina forma antarctica, by ~20%. The rates measured at 180–380 μatm (MO2 = 1.25 M?0.25, p = 0.007) were significantly higher (ANCOVA, p = 0.004) than those measured at elevated target CO2 levels in 2007 (789–1000 μatm, = 0.78 M?0.32, p = 0.0008; Fig. 1). However, we further demonstrate metabolic plasticity in response to regional phytoplankton concentration and that the response to CO2 is dependent on the baseline level of metabolism. We hypothesize that reduced regional Chl a levels in 2008 suppressed metabolism and masked the effect of ocean acidification. This effect of food limitation was not, we postulate, merely a result of gut clearance and specific dynamic action, but rather represents a sustained metabolic response to regional conditions. Thus, pteropod populations may be compromised by climate change, both directly via CO2-induced metabolic suppression, and indirectly via quantitative and qualitative changes to the phytoplankton community. Without the context provided by long-term observations (four seasons) and a multi-faceted laboratory analysis of the parameters affecting energetics, the complex response of polar pteropods to ocean acidification may be masked or misinterpreted.
Neighbourhood safety and leisure-time physical activity among Dutch adults: a multilevel perspective
Kramer Dani?lle,Maas Jolanda,Wingen Marleen,Kunst Anton E
International Journal of Behavioral Nutrition and Physical Activity , 2013, DOI: 10.1186/1479-5868-10-11
Abstract: Background Several neighbourhood elements have been found to be related to leisure-time walking and cycling. However, the association with neighbourhood safety remains unclear. This study aimed to assess the association of neighbourhood-level safety with leisure-time walking and cycling among Dutch adults. Methods Data were derived from the national health survey (POLS) 2006–2009, with valid data on 20046 respondents residing in 2127 neighbourhoods. Multilevel logistic regression models were used to examine the association between neighbourhood-level safety (general safety and specific safety components: physical disorder, social disorder, crime-related fear, traffic safety) and residents’ engagement in outdoor leisure-time walking and cycling for at least 30 minutes per week. Results An increase in neighbourhood safety (both general safety and each of the safety components) was significantly associated with an increase in leisure-time cycling participation. Associations were strongest for general safety and among older women. In the general population, neighbourhood safety was not significantly associated with leisure-time walking. However, among younger and older adult men and lower educated individuals, an increase in general safety was associated with a decrease in leisure-time walking participation. Conclusions In the Netherlands, neighbourhood safety appears to be related to leisure-time cycling but not to walking. Leisure-time cycling may best be encouraged by improving different safety components at once, rather than focusing on one safety aspect such as traffic safety. Special attention is needed for older women.
Page 1 /286246
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.