189 research outputs found
Nitrogen and phosphorus limitation of oceanic microbial growth during spring in the Gulf of Aqaba
Bioassay experiments were performed to identify how growth of key groups within the microbial community was simultaneously limited by nutrient (nitrogen and phosphorus) availability during spring in the Gulf of Aqaba's oceanic waters. Measurements of chlorophyll a (chl a) concentration and fast repetition rate (FRR) fluorescence generally demonstrated that growth of obligate phototrophic phytoplankton was co-limited by N and P and growth of facultative aerobic anoxygenic photoheterotropic (AAP) bacteria was limited by N. Phytoplankton exhibited an increase in chl a biomass over 24 to 48 h upon relief of nutrient limitation. This response coincided with an increase in photosystem II (PSII) photochemical efficiency (F v /F m), but was preceded (within 24 h) by a decrease in effective absorption crosssection (σPSII) and electron turnover time (τ). A similar response for τ and bacterio-chl a was observed for the AAPs. Consistent with the up-regulation of PSII activity with FRR fluorescence were observations of newly synthesized PSII reaction centers via low temperature (77K) fluorescence spectroscopy for addition of N (and N + P). Flow cytometry revealed that the chl a and thus FRR fluorescence responses were partly driven by the picophytoplankton (æ10 μm) community, and in particular Synechococcus. Productivity of obligate heterotrophic bacteria exhibited the greatest increase in response to a natural (deep water) treatment, but only a small increase in response to N and P addition, demonstrating the importance of additional substrates (most likely dissolved organic carbon) in moderating the heterotrophs. These data support previous observations that the microbial community response (autotrophy relative to heterotrophy) is critically dependent upon the nature of transient nutrient enrichment. © Inter-Research 2009
The Age-Dependent Contribution of Aortic Incident and Reflected Pressure Waves to Central Blood Pressure in African-Americans
Aging is associated with increased central aortic systolic pressure (CSP) and pulse pressure which are predictive of cardiovascular events. Mechanisms implicated for higher central pressures include a higher forward incident pressure wave (P1), higher augmented pressure (AP), and shorter reflected wave round trip travel time (Tr). African-Americans (AA) have more frequent and deleterious blood pressure elevation. Using applanation tonometry, we studied the association of age and CSP with P1 and AP in 900 AA subjects. Data showed that in subjects ≤50 years old, CSP was mediated by AP but not P1 or Tr, whereas in those >50, CSP was mediated by both AP and P1 and to a lesser extent by Tr. Predictive models were significant (R2 = 0.97) for both age groups. In conclusion, wave reflection is the primary determinant of CSP in younger AA, while in older subjects, CSP is mediated by both the magnitude and timing of wave reflection as well as aortic impedance
Constraining evaporation rates based on large-scale sea surface transects of salinity or isotopic compositions
Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(2), (2019): 1322-1330, doi:10.1029/2018JC014106.A Lagrangian model is constructed for a surface column of initial height h(0) that propagates at an average speed u and is subject to excess (i.e., net) evaporation of q m/year. It is shown that these parameters combine to form an evaporation length, L = uh(0)/q, which provides an estimate for the distance the column must travel before evaporating completely. While these changes in the surface water level due to evaporation are compensated by entrainment of water into the overall column, the changes in either near‐surface salinity or isotopic compositions are retained and can be measured. Observations of surface salinity and isotopic compositions of δ18O and δD along 1,000‐ to 3,500‐km long transects are used to estimate values of L in the Red Sea, Mediterranean Sea, Indian Ocean, and Gulf Stream. The variations of salinity, δ18O and δD in all four basins are linear. As anticipated, the estimated value of L is smallest in the slowly moving and arid Red Sea and is greatest in the fast‐moving Gulf Stream.The salinity and δ18O data collected aboard the Indian Ocean cruise described in Srivastava et al. (2007) can be accessed at this website (https://www.nodc.noaa.gov). The salinity, δ18O and δD data collected during the Red Sea cruise of the Interuniversity Institute for Marine Sciences, Eilat, described in Steiner et al. (2014) and can be accessed in the supporting information section of doi: 10.1073/pnas.1414323111. H. B. acknowledges the support provided by the Eshkol Foundation of the Israel Ministry of Science.2019-07-2
DeepTract: A Probabilistic Deep Learning Framework for White Matter Fiber Tractography
We present DeepTract, a deep-learning framework for estimating white matter
fibers orientation and streamline tractography. We adopt a data-driven approach
for fiber reconstruction from diffusion weighted images (DWI), which does not
assume a specific diffusion model. We use a recurrent neural network for
mapping sequences of DWI values into probabilistic fiber orientation
distributions. Based on these estimations, our model facilitates both
deterministic and probabilistic streamline tractography. We quantitatively
evaluate our method using the Tractometer tool, demonstrating competitive
performance with state-of-the art classical and machine learning based
tractography algorithms. We further present qualitative results of
bundle-specific probabilistic tractography obtained using our method. The code
is publicly available at: https://github.com/itaybenou/DeepTract.git
Vicarious Group Trauma among British Jews
This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s11133-016-9337-4Given that literature on the intra- and inter-generational transmission of traumas is mainly based on secondary literature and focuses on the transmission of trauma memory in terms of the historical knowledge of group trauma, this article develops the theory of vicarious group trauma and tests this theory by exploring vicarious traumatization in the everyday lives of Jews in Britain through the methods of observation and in-depth interviewing. Vicarious group trauma is defined as a life or safety-threatening event or abuse that happened to some members of a social group but is felt by other members as their own experience because of their personal affiliation with the group. The article finds that the vicarious sensation of traumatic group experiences can create anxiety, elicit perceptions of threat and, by extension, hypervigilance among Jews. The findings demonstrate that group traumas of the past interpenetrate and interweave with members’ current lives and in this way can also become constitutive of their group identity. An institutional focus on threats to Jews can inform the construction and reinforcement of traumatization symptoms and accordingly vicarious group trauma. This article suggests an association between the level of involvement of group members in the collective’s social structure and the prominence of vicarious group trauma among them
Foreign Policy and the Ideology of Post-ideology: The Case of Matteo Renzi’s Partito Democratico
The post-communist Italian Left has experienced a long phase of ideational misalignment between ideas placed at different levels, as a qualified discursive institutionalist approach demonstrates. Background public philosophies have often clashed with post-communist political ideology, while foreign policy programmes have often contradicted specific policies. Under the leadership of Matteo Renzi, however, the PD is now experiencing a moment of remarkable ideational consistency. Rather than being founded on entirely new premises, this new consensus folds old elements into new ones and shows all the defining traits of post-ideology. Yet, by espousing post-ideology, Renzi is making an ultimately ideological move whose limitations may soon start to show
Diffusion Tensor Imaging: Exploring the Motor Networks and Clinical Applications
With the advances in diffusion magnetic resonance (MR) imaging techniques, diffusion tensor imaging (DTI) has been applied to a number of neurological conditions because DTI can demonstrate microstructures of the brain that are not assessable with conventional MR imaging. Tractography based on DTI offers gross visualization of the white matter fiber architecture in the human brain in vivo. Degradation of restrictive barriers and disruption of the cytoarchitecture result in changes in the diffusion of water molecules in various pathological conditions, and these conditions can also be assessed with DTI. Yet many factors may influence the ability to apply DTI clinically, so these techniques have to be used with a cautious hand
A Predictive Model of Intein Insertion Site for Use in the Engineering of Molecular Switches
Inteins are intervening protein domains with self-splicing ability that can be used as molecular switches to control activity of their host protein. Successfully engineering an intein into a host protein requires identifying an insertion site that permits intein insertion and splicing while allowing for proper folding of the mature protein post-splicing. By analyzing sequence and structure based properties of native intein insertion sites we have identified four features that showed significant correlation with the location of the intein insertion sites, and therefore may be useful in predicting insertion sites in other proteins that provide native-like intein function. Three of these properties, the distance to the active site and dimer interface site, the SVM score of the splice site cassette, and the sequence conservation of the site showed statistically significant correlation and strong predictive power, with area under the curve (AUC) values of 0.79, 0.76, and 0.73 respectively, while the distance to secondary structure/loop junction showed significance but with less predictive power (AUC of 0.54). In a case study of 20 insertion sites in the XynB xylanase, two features of native insertion sites showed correlation with the splice sites and demonstrated predictive value in selecting non-native splice sites. Structural modeling of intein insertions at two sites highlighted the role that the insertion site location could play on the ability of the intein to modulate activity of the host protein. These findings can be used to enrich the selection of insertion sites capable of supporting intein splicing and hosting an intein switch
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