In order to provide biological systematics from which to interpret nitrogen (N) and oxygen (O) isotope ratios of nitrate (
15N/
14N,
18O/
16O, respectively) in the environment, we previously ...investigated the isotopic fractionation of nitrate during its assimilation by mono-cultures of eukaryotic algae (
Granger et al., 2004). In this study, we extended our analysis to investigate nitrate assimilation by strains of prokaryotic plankton. We measured the N and O isotope effects,
15ε and
18ε, during nitrate consumption by cultures of prokaryotic strains and by additional eukaryotic phytoplankton strains (where ε is the ratio of reaction rate constants of the light vs. heavy isotopologues,
light
k and
heavy
k; ε
=
light
k/
heavy
k
−
1
×
1000, expressed in per mil). The observed
15ε ranged from 5‰ to 8‰ among eukaryotes, whereas it did not exceed 5‰ for three cyanobacterial strains, and was as low as 0.4‰ for a heterotrophic α-protoeobacterium. Eukaryotic phytoplankton fractionated the N and O isotopes of nitrate to the same extent (i.e.,
18ε
∼
15ε). The
18ε:
15ε among the cyanobacteria was also ∼1, whereas the heterotrophic α-proteobacterial strain, which showed the lowest
15ε, between 0.4‰ and 1‰, had a distinct
18ε:
15ε of ∼2, unlike any plankton strain observed previously. Equivalent N vs. O isotope discrimination is thought to occur during internal nitrate reduction by nitrate reductase, such that the cellular efflux of the fractionated nitrate into the medium drives the typically observed
18ε:
15ε of ∼1. We hypothesize that the higher in the
18ε:
15ε of the α-proteobacterium may result from isotope discrimination by nitrate transport, which is evident only at low amplitude of ε. These observations warrant investigating whether heterotrophic bacterial assimilation of nitrate decreases the community isotope effects at the surface ocean.
•Particle Image Velocimetry is performed in combination with the Refractive Index Matching technique.•The flow near the helicoid wire is modelled through the Euler equations.•An expression is derived ...for predicting the bending angle of the flow near the wire.
The core of a Liquid Metal Fast Breeder Reactor (LMFBR) consists of cylindrical fuel rods that are wrapped by a helicoidally-wound wire spacer to enhance mixing and to prevent damage by fretting. It is known that the liquid metal close to the rod is forced to follow the wires, and that liquid metal further away from the rod crosses the wires (called: migratory flow). This work aims at gaining more insight into the physics behind migratory flow and to provide a model for its bending angle. To this purpose, the flow field in a 7-rods, wire-wrapped, hexagonal bundle with water is studied within the Reynolds number range of 4990–16330 by using Particle Image Velocimetry (PIV). Refraction of the light is minimized by using Fluorinated Ethylene Propylene (FEP), which is a refractive index-matching (RIM) material. These measurements confirm that liquid near the rod follows the helicoid path and bends cross-wise with respect to the wire further away from the rod. A theoretical model for the bending angle of the flow is derived from the Euler equations and shows that the bending is primarily caused by the pressure gradient field induced by the wire. The model shows a very good correspondence with the experimentally obtained PIV data. These findings improve our understanding of the physics at play in rod bundle flows with wrapped wires and can be of assistance in developing practical correlations for frictional pressure losses and heat transfer in such bundles.
•Fully coupled fluid-structure interaction model of SEEDS-1 test facility was created.•Numerical and experimental analysis of flow-induced vibration in fuel pin bundle.•Frequency of flow pulsations ...matches well between simulation and experiments.
Being able to quantify mechanical vibrations is of key importance for the safety of nuclear power plants, as they are able to induce damage. In this work, numerical simulations are used to compute water flow and vibration in a densely packed bundle of 7 rods, mimicking an experimental setup. This flow configuration is chosen to resemble the coolant flow through a nuclear reactor core. Because of the wall proximity, a considerable velocity difference between the narrow gaps and the subchannels exists, with an inflection point in the velocity profile. This yields an unstable situation, and large vortices are continuously created through a mechanism similar to the Kelvin–Helmholtz instability. The vortex streets in between the rods are associated with a fluctuating pressure field, causing vibrations of the rods.
The experimental setup contains 7 steel cylinders, encased in a hexagonal duct. The central rod contains a section where the steel is replaced by a water-filled silicone tube, clamped at both extremes to the steel rod, and the vibrations of this section are examined. The numerical approach consists of coupled fluid–structure interaction (FSI) simulations, with the flow being modelled using computational fluid dynamics (CFD) and the structure using computational solid mechanics (CSM).
The available experimental data consist of Laser Doppler Anemometry (LDA) measurements and high-speed camera footage of the wall movement of the silicone rod. Equivalent data is collected from the numerical simulations. The simulations are repeated for different flow rates. The frequency spectrum of the coherent structures, and the frequency and amplitude of the wall movement are compared for each operating point, as well as their trend as a function of the flow rate. The dominant frequencies found in the simulation results were similar to the experimental results, although slightly higher. They also showed a linear trend, just like the experiments. A larger mismatch was present for the structural response, the frequencies found using the FSI model being more than twice as high.
Natural resources policies that promote sustainable management are critical for protecting diverse stakeholders against depletion. Although integrating diverse stakeholders into these policies has ...been theorized to improve protection, empirical evidence is lacking. Here, we evaluate 108 Sustainability Plans under California's Sustainable Groundwater Management Act to quantify how well stakeholders are integrated into plans and protected from groundwater depletion. We find that the majority of Sustainability Plans do not integrate or protect the majority of their stakeholders. Nevertheless, our results show that when stakeholders are more integrated into a Sustainability Plan, they are more likely to be protected, particularly for those that lack formal access to decision-making processes. Our findings provide strong empirical evidence that integrating diverse stakeholders into sustainability planning is beneficial for stakeholders who are vulnerable to the impacts of natural resource depletion.
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•A new friction factor-heat transfer analogy is derived for supercritical fluids.•The new analogy is much more accurate than the Chilton-Colburn analogy.•The new analogy performs well ...for He, H2O, CO2, R134a and R22.
A new friction-heat transfer analogy for the prediction of heat transfer to turbulent fluids at supercritical pressure is presented. This analogy is based on the observation that the predominent events that determine the turbulent heat flux known as hot ejections and cold sweeps have different thermophysical properties. This observation is used to derive a new friction-heat transfer analogy, which we call the ejection-sweep analogy. It is shown that the ejection-sweep analogy yields very good results with respect to predicting heat transfer coefficients for different fluids (water, CO2, Helium, R22 and R134a) that are heated at supercritical pressure at low heat flux to mass flux ratios. Furthermore, the new analogy performs much better than the Chilton-Colburn analogy. The new analogy was also compared with two well-known relations from literature. It was found that the ejection-sweep analogy predictions are more consistent with respect to the investigated fluids than the relations from literature and that the analogy can be applied to at least all fluids studied in this work. The ejection-sweep analogy can be used in the development of more advanced heat transfer models that include buoyancy and acceleration effects.
Streptococcus suis is one of the most important pathogens in pigs and is also an emerging zoonotic agent. After crossing the epithelial barrier, S. suis causes bacteraemia, resulting in meningitis, ...endocarditis and bronchopneumonia. Since the host environment seems to be an important regulatory component for virulence, we related expression of virulence determinants of S. suis to glucose availability during growth and to the sugar metabolism regulator catabolite control protein A (CcpA). We found that expression of the virulence-associated genes arcB, representing arcABC operon expression, cps2A, representing capsular locus expression, as well as sly, ofs, sao and epf, differed significantly between exponential and early stationary growth of a highly virulent serotype 2 strain. Deletion of ccpA altered the expression of the surface-associated virulence factors arcB, sao and eno, as well as the two currently proven virulence factors in pigs, ofs and cps2A, in early exponential growth. Global expression analysis using a cDNA expression array revealed 259 differentially expressed genes in early exponential growth, of which 141 were more highly expressed in the CcpA mutant strain 10ΔccpA and 118 were expressed to a lower extent. Interestingly, among the latter genes, 18 could be related to capsule and cell wall synthesis. Correspondingly, electron microscopy characterization of strain 10ΔccpA revealed a markedly reduced thickness of the capsule. This phenotype correlated with enhanced binding to porcine plasma proteins and a reduced resistance to killing by porcine neutrophils. Taken together, our data demonstrate that CcpA has a significant effect on the capsule synthesis and virulence properties of S. suis.
Many patients admitted to a hospital are already colonized with multi-drug resistant organisms (MDRO) including third-generation cephalosporin-resistant Enterobacteriaceae (3GCREB). The aim of our ...study was to determine the prevalence of rectal 3GCREB colonization at admission to a large German university hospital and to estimate infection incidences. In addition, risk factors for 3GCREB colonization were identified.
In 2014 and 2015, patients were screened for rectal colonization with 3GCREB and filled out a questionnaire on potential risk factors at admission to a non-intensive care unit (non-ICU). All patients were retrospectively monitored for bacterial infections. Descriptive, univariable and multivariable logistic regression analyses were conducted to identify risk factors for 3GCREB colonization at admission.
Of 4,013 patients included, 10.3% (n = 415) were rectally colonized with 3GCREB at admission. Incidence of nosocomial infections was 3.5 (95% CI 2.0-6.1) per 100 patients rectally colonized with 3GCREB compared to 2.3 (95% CI 1.8-3.0, P = 0.213) per 100 3GCREB negative patients. Independent risk factors for 3GCREB colonization were prior colonization / infection with MDRO (OR 2.30, 95% CI 1.59-3.32), prior antimicrobial treatment (OR 1.97, 95% CI 1.59-2.45), male sex (OR 1.38, 95% CI 1.12-1.70), prior travelling outside Europe (OR 2.39, 95% CI 1.77-3.22) and places of residence in the Berlin districts Charlottenburg-Wilmersdorf (OR 1.52, 95% CI 1.06-2.18), Friedrichshain-Kreuzberg (OR 2.32, 95% CI 1.44-3.74) and Mitte (OR 1.73, 95% CI 1.26-2.36).
Admission prevalence of rectal colonization with 3GCREB was high, while infection incidence did not significantly differ between patients rectally colonized or not with 3GCREB at hospital admission. In consequence, hospitals should prioritize improvement of standard precautions including hand hygiene to prevent infections among all patients irrespective of their 3GCREB status at hospital admission.
H2O is the main by-product of the Fischer–Tropsch (FT) reaction. The motivation for in situ H2O removal by means of hydrophilic membranes is threefold: (a) to reduce H2O promoted catalyst ...deactivation, (b) to boost the reactor productivity, and (c) to displace the water gas shift (WGS) equilibrium to enhance the conversion of CO2 to hydrocarbons. The selective removal of H2O from a complex mixture of H2, CO, CO2 and hydrocarbons under FT conditions is a challenging task for membranes and membrane preparation.
The potential of the FT membrane reactor concept is illustrated by mathematical case studies. The results of the experimental demonstration of in situ H2O removal under reactive FT conditions with an amorphous silica membrane and a ceramic supported polymer membrane prove the concept but confirm the high demands on membrane permeance, permselectivity and stability. Based on mathematical case studies, experimental results and a literature study on hydrophilic membranes, the following critical membrane specifications are formulated: (a) permeance QH2O>1×10−7mol/(sm2Pa) and (b) permselectivities SH2O/H2, SH2O/CO, SH2O/CO2>75.
With regard to the literature on hydrophilic membranes, microporous zeolite membranes outperform amorphous microporous membranes and polymer membranes. A new type of membrane prepared by direct hydrothermal synthesis on α-Al2O3 supports is a thin defect free hydroxy sodalite (H-SOD) film with a layer thickness of 2μm. This type of membrane offers high permselectivities and high H2O fluxes at temperatures up to 200°C and is therefore, a promising candidate for in situ H2O removal during FT synthesis.
To characterize the prevalence of hyperpalatable foods (HPF) among baby foods in the U.S. and examine the prevalence of HPF exposure and consumption from both baby food and adult food sources among ...infants aged 9-15 months.
A U.S. baby food database as well as baby foods from three 24-h dietary recalls of 147 infants were used to identify baby foods as HPF per previous publication. HPF exposure was defined as intake of any HPF during the 3-day measurement period. To determine the extent of HFP consumption, % kilocalorie (kcal) intake from HPF was characterized.
Only 12% of baby foods were HPF; however, nearly all participants (>90%) consumed HPF, primarily through exposure to adult foods. Younger infants (<12 months) consumed 38% standard deviation (SD) = 23.6% of their daily food kcal from HPF and older infants (≥12 months) consumed 52% (SD = 16.4%) of daily food kilocalorie from HPF. Most younger infants (68%) and older infants (88%) had repeated exposure to the same HPF across the measurement period.
The prevalence of HPF among baby foods in the U.S. is low. However, almost all infants were exposed to HPF, and HPF comprised a substantial percentage of daily food kilocalorie in infants' diets. Findings highlight the transition to solid food consumption during complimentary feeding period is a critical time for early HPF exposure.
Non-hyperbolic time inconsistency Bleichrodt, Han; Rohde, Kirsten I.M.; Wakker, Peter P.
Games and economic behavior,
05/2009, Letnik:
66, Številka:
1
Journal Article
Recenzirano
The commonly used hyperbolic and quasi-hyperbolic discount functions have been developed to accommodate decreasing impatience, which is the prevailing empirical finding in intertemporal choice, in ...particular for aggregate behavior. However, these discount functions do not have the flexibility to accommodate increasing impatience or strongly decreasing impatience. This lack of flexibility is particularly disconcerting for fitting data at the individual level, where various patterns of increasing impatience and strongly decreasing impatience will occur for a significant fraction of subjects. This paper presents discount functions with constant absolute (CADI) or constant relative (CRDI) decreasing impatience that can accommodate any degree of decreasing or increasing impatience. In particular, they are sufficiently flexible for analyses at the individual level. The CADI and CRDI discount functions are the analogs of the well-known CARA and CRRA utility functions for decision under risk.
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