3,239 research outputs found
Investigation of a generalized Obukhov Model for Turbulence
We introduce a generalization of Obukhov's model [A.M. Obukhov, Adv. Geophys.
6, 113 (1959)] for the description of the joint position-velocity statistics of
a single fluid particle in fully developed turbulence. In the presented model
the velocity is assumed to undergo a continuous time random walk. This takes
into account long time correlations. As a consequence the evolution equation
for the joint position-velocity probability distribution is a Fokker-Planck
equation with a fractional time derivative. We determine the solution of this
equation in the form of an integral transform and derive a relation for
arbitrary single time moments. Analytical solutions for the joint probability
distribution and its moments are given.Comment: 10 page
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Succession of Bifidobacterium longum strains in response to a changing early life nutritional environment reveals dietary substrate adaptations
Diet-microbe interactions play a crucial role in modulation of the early life microbiota and infant health. Bifidobacterium dominates the breast-fed infant gut and may persist in individuals during transition from a milk-based to a more diversified diet. Here, we investigated adaptation of B. longum to the changing nutritional environment. Genomic characterisation of 75 strains isolated from nine either exclusively breast- or formula-fed (pre-weaning) infants in their first 18 months revealed subspecies- and strain-specific intra-individual genomic diversity with respect to carbohydrate metabolism, which corresponded to different dietary stages. Complementary phenotypic studies indicated strain-specific differences in utilisation of human milk oligosaccharides and plant carbohydrates, while proteomic profiling identified gene clusters involved in metabolism of selected carbohydrates. Our results indicate a strong link between infant diet and B. longum diversity and provide additional insights into possible competitive advantage mechanisms of this Bifidobacterium species and its persistence in a single host
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Succession of Bifidobacterium longum strains in response to the changing early-life nutritional environment reveals specific adaptations to distinct dietary substrates
Diet-microbe interactions play a crucial role in infant development and modulation of the early-life microbiota. The genus Bifidobacterium dominates the breast-fed infant gut, with strains of B. longum subsp. longum (B. longum) and B. longum subsp. infantis (B. infantis) particularly prevalent. Although transition from milk to a more diversified diet later in infancy initiates a shift to a more complex microbiome, specific strains of B. longum may persist in individual hosts for prolonged periods of time. Here, we sought to investigate the adaptation of B. longum to the changing infant diet. Genomic characterisation of 75 strains isolated from nine either exclusively breast- or formula-fed (pre-weaning) infants in their first 18 months revealed subspecies- and strain-specific intra-individual genomic diversity with respect to glycosyl hydrolase families and enzymes, which corresponded to different dietary stages. Complementary phenotypic growth studies indicated strain-specific differences in human milk oligosaccharide and plant carbohydrate utilisation profiles of isolates between and within individual infants, while proteomic profiling identified active polysaccharide utilisation loci involved in metabolism of selected carbohydrates. Our results indicate a strong link between infant diet and B. longum subspecies/strain genomic and carbohydrate utilisation diversity, which aligns with a changing nutritional environment: i.e. moving from breast milk to a solid food diet. These data provide additional insights into possible mechanisms responsible for the competitive advantage of this Bifidobacterium species and its long-term persistence in a single host and may contribute to rational development of new dietary therapies for this important developmental window
Domain Walls in Massive Supergravities
We show how toroidally-compactified eleven-dimensional supergravity can be
consistently truncated to yield a variety of maximally-supersymmetric
``massive'' supergravities in spacetime dimensions . The mass terms
arise as a consequence of making a more general ansatz than that in usual
Kaluza-Klein dimensional reduction, in which one or more axions are given an
additional linear dependence on one of the compactification coordinates. The
lower-dimensional theories are nevertheless consistent truncations of
eleven-dimensional supergravity. Owing to the fact that the generalised
reduction commutes neither with U-duality nor with ordinary dimensional
reduction, many different massive theories can result. The simplest examples
arise when just a single axion has the additional linear coordinate dependence.
We find five inequivalent such theories in D=7, and 71 inequivalent ones in
D=4. The massive theories admit no maximally-symmetric vacuum solution, but
they do admit -brane solutions, i.e. domain walls, which preserve half
the supersymmetry. We present examples of these solutions, and their oxidations
to D=11. Some of the latter are new solutions of D=11 supergravity.Comment: latex, 32 papes, no figures, further comments and references adde
Polysaccharide degradation by the Bacteroidetes: mechanisms and nomenclature
The Bacteroidetes phylum is renowned for its ability to degrade a wide range of complex carbohydrates, a trait that has enabled its dominance in many diverse environments. The best studied species inhabit the human gut microbiome and use polysaccharide utilization loci (PULs), discrete genetic structures that encode proteins involved in the sensing, binding, deconstruction, and import of target glycans. In many environmental species, polysaccharide degradation is tightly coupled to the phylum-exclusive type IX secretion system (T9SS), which is used for the secretion of certain enzymes and is linked to gliding motility. In addition, within specific species these two adaptive systems (PULs and T9SS) are intertwined, with PUL-encoded enzymes being secreted by the T9SS. Here, we discuss the most noteworthy PUL and non-PUL mechanisms that confer specific and rapid polysaccharide degradation capabilities to the Bacteroidetes in a range of environments. We also acknowledge that the literature showcasing examples of PULs is rapidly expanding and developing a set of assumptions that can be hard to track back to original findings. Therefore, we present a simple universal description of conserved PUL functions and how they are determined, while proposing a common nomenclature describing PULs and their components, to simplify discussion and understanding of PUL systems
Fluid Particle Accelerations in Fully Developed Turbulence
The motion of fluid particles as they are pushed along erratic trajectories
by fluctuating pressure gradients is fundamental to transport and mixing in
turbulence. It is essential in cloud formation and atmospheric transport,
processes in stirred chemical reactors and combustion systems, and in the
industrial production of nanoparticles. The perspective of particle
trajectories has been used successfully to describe mixing and transport in
turbulence, but issues of fundamental importance remain unresolved. One such
issue is the Heisenberg-Yaglom prediction of fluid particle accelerations,
based on the 1941 scaling theory of Kolmogorov (K41). Here we report
acceleration measurements using a detector adapted from high-energy physics to
track particles in a laboratory water flow at Reynolds numbers up to 63,000. We
find that universal K41 scaling of the acceleration variance is attained at
high Reynolds numbers. Our data show strong intermittency---particles are
observed with accelerations of up to 1,500 times the acceleration of gravity
(40 times the root mean square value). Finally, we find that accelerations
manifest the anisotropy of the large scale flow at all Reynolds numbers
studied.Comment: 7 pages, 4 figure
Measurement of Lagrangian velocity in fully developed turbulence
We have developed a new experimental technique to measure the Lagrangian
velocity of tracer particles in a turbulent flow, based on ultrasonic Doppler
tracking. This method yields a direct access to the velocity of a single
particule at a turbulent Reynolds number . Its dynamics is
analyzed with two decades of time resolution, below the Lagrangian correlation
time. We observe that the Lagrangian velocity spectrum has a Lorentzian form
, in agreement
with a Kolmogorov-like scaling in the inertial range. The probability density
function (PDF) of the velocity time increments displays a change of shape from
quasi-Gaussian a integral time scale to stretched exponential tails at the
smallest time increments. This intermittency, when measured from relative
scaling exponents of structure functions, is more pronounced than in the
Eulerian framework.Comment: 4 pages, 5 figures. to appear in PR
Coastal Tropical Convection in a Stochastic Modeling Framework
Recent research has suggested that the overall dependence of convection near
coasts on large-scale atmospheric conditions is weaker than over the open ocean
or inland areas. This is due to the fact that in coastal regions convection is
often supported by meso-scale land-sea interactions and the topography of
coastal areas. As these effects are not resolved and not included in standard
cumulus parametrization schemes, coastal convection is among the most poorly
simulated phenomena in global models. To outline a possible parametrization
framework for coastal convection we develop an idealized modeling approach and
test its ability to capture the main characteristics of coastal convection. The
new approach first develops a decision algorithm, or trigger function, for the
existence of coastal convection. The function is then applied in a stochastic
cloud model to increase the occurrence probability of deep convection when
land-sea interactions are diagnosed to be important. The results suggest that
the combination of the trigger function with a stochastic model is able to
capture the occurrence of deep convection in atmospheric conditions often found
for coastal convection. When coastal effects are deemed to be present the
spatial and temporal organization of clouds that has been documented form
observations is well captured by the model. The presented modeling approach has
therefore potential to improve the representation of clouds and convection in
global numerical weather forecasting and climate models.Comment: Manuscript submitted for publication in Journal of Advances in
Modeling Earth System
Eliza Haywoods geschichte des fräuleins Elisabeth Thoughtless (1756): frühe selbsterkenntnis und ehekritik in der englischen ubersetzungsliteratur
Die Tradition, Frauenerleben aus weiblicher Perspektive zum Mittelpunkt eines Romans zu machen, beginnt in Deutschland nicht mit Sophie La Roches Geschichte des Fräuleins von Sternheim (1771), sondern mit den Werken englischer Schriftstellerinnen, die bereits bedeutend früher in deutschen Übersetzungen erschienen und bisher von der Germanistik nicht beachtet worden sind. An Eliza Haywoods Geschichte des Fräuleins Elisabeth Thoughtless (1756) soll hier exemplarisch gezeigt werden, wie in Deutschland Mitte des 18. Jahrhunderts bereits eine Form der Literatur von Frauen erscheint, die die Entwicklung eines weiblichen Charakters zum Mittelpunkt hat. Obwohl der Übersetzer die in diesem Roman enthaltene Kritik an der patriarchalisch geführten Ehe und der Idealisierung der Frau durch eine bewusst gewählte Übersetzungsstrategie abschwächt, um der Leserschaft den für deutsche Verhältnisse zu radikalen Text angenehmer zu machen, ist dieser, von Lessing als das Werk eines Genies bewertete Roman ein Meilenstein in der Literatur von Frauen
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