479 research outputs found
Modelling formation and evolution of transverse dune fields
We model formation and evolution of transverse dune fields. In the model,
only the cross section of the dune is simulated. The only physical variable of
relevance is the dune height, from which the dune width and velocity are
determined, as well as phenomenological rules for interaction between two dunes
of different heights. We find that dune fields with no sand on the ground
between dunes are unstable, i.e. small dunes leave the higher ones behind. We
then introduce a saturation length to simulate transverse dunes on a sand bed
and show that this leads to stable dune fields with regular spacing and dune
heights. Finally, we show that our model can be used to simulate coastal dune
fields if a constant sand influx is considered, where the dune height increases
with the distance from the beach, reaching a constant value.Comment: 18 pages including 9 figure
Growth, Condition, and Trophic Relations of Stocked Trout in Southern Appalachian Mountain Streams
Stream trout fisheries are among the most popular and valuable in the United States, but many are dependent on hatcheries to sustain fishing and harvest. Thus, understanding the ecology of hatchery‐reared trout stocked in natural environments is fundamental to management. We evaluated the growth, condition, and trophic relations of Brook Trout Salvelinus fontinalis, Brown Trout Salmo trutta, and Rainbow Trout Oncorhynchus mykiss that were stocked in southern Appalachian Mountain streams in western North Carolina. Stocked and wild (naturalized) trout were sampled over time (monthly; September 2012–June 2013) to compare condition and diet composition and to evaluate temporal dynamics of trophic position with stable isotope analysis. Relative weights (Wr) of stocked trout were inversely associated with their stream residence time but were consistently higher than those of wild trout. Weight loss of harvested stocked trout was similar among species and sizes, but fish stocked earlier lost more weight. Overall, 40% of 141 stomachs from stocked trout were empty compared to 15% of wild trout stomachs (N = 26). We identified a much higher rate of piscivory in wild trout (18 times that of stocked trout), and wild trout were 4.3 times more likely to consume gastropods relative to stocked trout. Hatchery‐reared trout were isotopically similar to co‐occurring wild fish for both δ13C and δ15N values but were less variable than wild trout. Differences in sulfur isotope ratios (δ34S) between wild and hatchery‐reared trout indicated that the diets of wild fish were enriched in δ34S relative to the diets of hatchery‐reared fish. Although hatcheryreared trout consumed prey items similar to those of wild fish, differences in consumption or behavior (e.g., reduced feeding) may have resulted in lower condition and negative growth. These findings provide critical insight on the trophic dynamics of stocked trout and may assist in developing and enhancing stream trout fisheries
Dijital ve medya etkinliklerinin ortaokul öğrencilerinin ve ebeveynlerinin medya ve bilim okuryazarlıklarına etkisinin belirlenmesi
This research aims determining effect of digital and media activities on media and science literacy of middle-school students and parents and identifying the relationship between them. Quasi-experimental model has been used by which pretest-posttest studies have been held on one group by using quantitative data during research. The sample of the research consists of 60 students and 119 parents who attend a school in the province of Bursa in the academic year of 2013-2014. According to data analysis obtained in the research, there is a significant relation between pretests and posttests about scientific literacy of middle-school students and parents relating to Digital and Media Activities. There is a relation between media and scientific literacy of students and mothers as parents. There is a difference between the applied PISA and TIMSS exams and the students' science literacy. In the light of these results, some suggestion has been offered with regard to focusing on the importance of 21st century skills and literacy, developing scientific and media literacy level and obtaining more comprehensive results
Do fatty acids affect fetal programming?
Background: In this study discussed the primary and regulatory roles of
fatty acids, and investigated the affects of fatty acids on metabolic
programming. Methods: Review of the literature was carried out on three
electronic databases to assess the roles of fatty acids in metabolic
programming. All abstracts and full-text articles were examined, and
the most relevant articles were selected for screening and inclusion in
this review. Results: The mother\u2019s nutritional environment during
fetal period has important effects on long term health. Fatty acids
play a primary role in growth and development. Alterations in fatty
acid intake in the fetal period may increase the risk of obesity and
metabolic disorders in later life. Maternal fatty acid intakes during
pregnancy and lactation are passed to the fetus and the newborn via the
placenta and breast milk, respectively. Imbalances in fatty acid intake
during the fetal period change the fatty acid composition of membrane
phospholipids, which can cause structural and functional problems in
cells. Additionally, the metabolic and neuroendocrine environments of
the fetus and the newborn play key roles in the regulation of energy
balance. Conclusions: Imbalances in fatty acid intake during pregnancy
and lactation may result in permanent changes in appetite control,
neuroendocrine function and energy metabolism in the fetus, leading to
metabolic programming. Further studies are needed to determine the role
of fatty acid intake in metabolic programming
Minimal size of a barchan dune
Barchans are dunes of high mobility which have a crescent shape and propagate
under conditions of unidirectional wind. However, sand dunes only appear above
a critical size, which scales with the saturation distance of the sand flux [P.
Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. {\bf{89,}} 264301 (2002);
B. Andreotti, P. Claudin, and S. Douady, Eur. Phys. J. B {\bf{28,}} 321 (2002);
G. Sauermann, K. Kroy, and H. J. Herrmann, Phys. Rev. E {\bf{64,}} 31305
(2001)]. It has been suggested by P. Hersen, S. Douady, and B. Andreotti, Phys.
Rev. Lett. {\bf{89,}} 264301 (2002) that this flux fetch distance is itself
constant. Indeed, this could not explain the proto size of barchan dunes, which
often occur in coastal areas of high litoral drift, and the scale of dunes on
Mars. In the present work, we show from three dimensional calculations of sand
transport that the size and the shape of the minimal barchan dune depend on the
wind friction speed and the sand flux on the area between dunes in a field. Our
results explain the common appearance of barchans a few tens of centimeter high
which are observed along coasts. Furthermore, we find that the rate at which
grains enter saltation on Mars is one order of magnitude higher than on Earth,
and is relevant to correctly obtain the minimal dune size on Mars.Comment: 11 pages, 10 figure
Resonant Five-body Recombination in an Ultracold Gas of Bosonic Atoms
We combine theory and experiment to investigate five-body recombination in an
ultracold gas of atomic cesium at negative scattering length. A refined
theoretical model, in combination with extensive laboratory tunability of the
interatomic interactions, enables the five-body resonant recombination rate to
be calculated and measured. The position of the new observed recombination
feature agrees with a recent theoretical prediction and supports the prediction
of a family of universal cluster states at negative that are tied to an
Efimov trimer.Comment: 14 pages, 5 figure
Cardiac magnetic resonance assessment of central and peripheral vascular function in patients undergoing renal sympathetic denervation as predictor for blood pressure response
Background:
Most trials regarding catheter-based renal sympathetic denervation (RDN) describe a proportion of patients without blood pressure response. Recently, we were able to show arterial stiffness, measured by invasive pulse wave velocity (IPWV), seems to be an excellent predictor for blood pressure response. However, given the invasiveness, IPWV is less suitable as a selection criterion for patients undergoing RDN. Consequently, we aimed to investigate the value of cardiac magnetic resonance (CMR) based measures of arterial stiffness in predicting the outcome of RDN compared to IPWV as reference.
Methods:
Patients underwent CMR prior to RDN to assess ascending aortic distensibility (AAD), total arterial compliance (TAC), and systemic vascular resistance (SVR). In a second step, central aortic blood pressure was estimated from ascending aortic area change and flow sequences and used to re-calculate total arterial compliance (cTAC). Additionally, IPWV was acquired.
Results:
Thirty-two patients (24 responders and 8 non-responders) were available for analysis. AAD, TAC and cTAC were higher in responders, IPWV was higher in non-responders. SVR was not different between the groups. Patients with AAD, cTAC or TAC above median and IPWV below median had significantly better BP response. Receiver operating characteristic (ROC) curves predicting blood pressure response for IPWV, AAD, cTAC and TAC revealed areas under the curve of 0.849, 0.828, 0.776 and 0.753 (p = 0.004, 0.006, 0.021 and 0.035).
Conclusions:
Beyond IPWV, AAD, cTAC and TAC appear as useful outcome predictors for RDN in patients with hypertension. CMR-derived markers of arterial stiffness might serve as non-invasive selection criteria for RDN
Catalytic Cycle of Multicopper Oxidases Studied by Combined Quantum- and Molecular-Mechanical Free-Energy Perturbation Methods
We have used combined quantum mechanical and molecular mechanical free-energy perturbation
methods in combination with explicit solvent simulations to study the reaction mechanism of the
multicopper oxidases, in particular the regeneration of the reduced state from the native
intermediate. For 52 putative states of the trinuclear copper cluster, differing in the oxidation states
of the copper ions and the protonation states of water- and O2-derived ligands, we have studied
redox potentials, acidity constants, isomerisation reactions, as well as water- and O2 binding
reactions. Thereby, we can propose a full reaction mechanism of the multicopper oxidases with
atomic detail. We also show that the two copper sites in the protein communicate so that redox
potentials and acidity constants of one site are affected by up to 0.2 V or 3 pKa units by a change
in the oxidation state of the other site
Ion mobility action spectroscopy of flavin dianions reveals deprotomer-dependent photochemistry
The intrinsic optical properties and photochemistry of flavin adenine dinucleotide (FAD) dianions are investigated using a combination of tandem ion mobility spectrometry and action spectroscopy. Two principal isomers are observed, the more stable form being deprotonated on the isoalloxazine group and a phosphate (N-3,PO4 deprotomer), and the other on the two phosphates (PO4,PO4 deprotomer). Ion mobility data and electronic action spectra suggest that photo-induced proton transfer occurs from the isoalloxazine group to a phosphate group, converting the PO4,PO4 deprotomer to the N-3,PO4 deprotomer. Comparisons of the isomer selective action spectra of FAD dianions and flavin monoanions with solution spectra and gas-phase photodissociation action spectra suggests that solvation shifts the electronic absorption of the deprotonated isoalloxazine group to higher energy. This is interpreted as evidence for significant charge transfer in the lowest optical transition of deprotonated isoalloxazine. Overall, this work demonstrates that the site of deprotonation of flavin anions strongly affects their electronic absorptions and photochemistry
Dynamic Allostery in the Methionine Repressor Revealed by Force Distribution Analysis
Many fundamental cellular processes such as gene expression are tightly regulated by protein allostery. Allosteric signal propagation from the regulatory to the active site requires long-range communication, the molecular mechanism of which remains a matter of debate. A classical example for long-range allostery is the activation of the methionine repressor MetJ, a transcription factor. Binding of its co-repressor SAM increases its affinity for DNA several-fold, but has no visible conformational effect on its DNA binding interface. Our molecular dynamics simulations indicate correlated domain motions within MetJ, and quenching of these dynamics upon SAM binding entropically favors DNA binding. From monitoring conformational fluctuations alone, it is not obvious how the presence of SAM is communicated through the largely rigid core of MetJ and how SAM thereby is able to regulate MetJ dynamics. We here directly monitored the propagation of internal forces through the MetJ structure, instead of relying on conformational changes as conventionally done. Our force distribution analysis successfully revealed the molecular network for strain propagation, which connects collective domain motions through the protein core. Parts of the network are directly affected by SAM binding, giving rise to the observed quenching of fluctuations. Our results are in good agreement with experimental data. The force distribution analysis suggests itself as a valuable tool to gain insight into the molecular function of a whole class of allosteric proteins
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