7,216 research outputs found
Passive phloem loading and long-distance transport in a synthetic tree-on-a-chip
Vascular plants rely on differences of osmotic pressure to export sugars from
regions of synthesis (mature leaves) to sugar sinks (roots, fruits). In this
process, known as M\"unch pressure flow, the loading of sugars from
photosynthetic cells to the export conduit (the phloem) is crucial, as it sets
the pressure head necessary to power long-distance transport. Whereas most
herbaceous plants use active mechanisms to increase phloem concentration above
that of the photosynthetic cells, in most tree species, for which transport
distances are largest, loading seems to occur via passive symplastic diffusion
from the mesophyll to the phloem. Here, we use a synthetic microfluidic model
of a passive loader to explore the nonlinear dynamics that arise during export
and determine the ability of passive loading to drive long-distance transport.
We first demonstrate that in our device, phloem concentration is set by the
balance between the resistances to diffusive loading from the source and
convective export through the phloem. Convection-limited export corresponds to
classical models of M\"unch transport, where phloem concentration is close to
that of the source; in contrast, diffusion-limited export leads to small phloem
concentrations and weak scaling of flow rates with the hydraulic resistance. We
then show that the effective regime of convection-limited export is predominant
in plants with large transport resistances and low xylem pressures. Moreover,
hydrostatic pressures developed in our synthetic passive loader can reach
botanically relevant values as high as 10 bars. We conclude that passive
loading is sufficient to drive long-distance transport in large plants, and
that trees are well suited to take full advantage of passive phloem loading
strategies
Investigating the impact of non-linear geometrical effects on wind turbine blades-Part 1: Current status of design and test methods and future challenges in design optimization
Release probability increases towards distal dendrites boosting high-frequency signal transfer in the rodent hippocampus
Dendritic integration of synaptic inputs involves their increased electrotonic attenuation at distal dendrites, which can be counterbalanced by the increased synaptic receptor density. However, during network activity the influence of individual synapses depends on their release fidelity, the dendritic distribution of which remains poorly understood. Here, we employed classical optical quantal analyses and a genetically encoded optical glutamate sensor in acute hippocampal slices of rats and mice to monitor release at CA3-CA1 synapses. We find that their release probability increases with greater distances from the soma. Similar-fidelity synapses tend to group together whereas release probability shows no trends regarding the branch ends. Simulations with a realistic CA1 pyramidal cell hosting stochastic synapses suggest that the observed trends boost signal transfer fidelity, particularly at higher input frequencies. Because high-frequency bursting has been associated with learning, the release probability pattern we have found may play a key role in memory trace formation
Experimental Infection of Conventional Pigs with Streptococcus suis serotype 2 by Aerosolic Exposure
Time-Resolved Imaging Reveals Heterogeneous Landscapes of Nanomolar Ca(2+) in Neurons and Astroglia
Maintaining low intracellular calcium is essential to the functioning of brain cells, yet the phenomenology and mechanisms involved remain an enigma. We have advanced a two-photon excitation time-resolved imaging technique, which exploits high sensitivity of the OGB-1 fluorescence lifetime to nanomolar Ca(2+) concentration ([Ca(2+)]) and enables a high data acquisition rate in situ. The [Ca(2+)] readout is not affected by dye concentration, light scattering, photobleaching, micro-viscosity, temperature, or the main known concomitants of cellular activity. In quiescent tissue, standard whole-cell configuration has little effect on resting [Ca(2+)] inside neuronal dendrites or inside astroglia dye-filled via gap junctions. Mapping basal [Ca(2+)] in neurons and astrocytes with submicron resolution unveils heterogeneous concentration landscapes that depend on age and preceding activity. The rich information content represented by such landscapes in acute slices and in vivo promises to unveil the hitherto unexplored, potentially fundamental aspects of brain cell physiology. VIDEO ABSTRACT
Calcification of intervertebral discs in the dachshund: a radiographic and histopathologic study of 20 dogs
<p>Abstract</p> <p>Background</p> <p>The purpose of the study was to compare radiographic and histopathologic findings with regard to number and extent of calcified discs in the dachshund.</p> <p>Methods</p> <p>The intervertebral discs of 20 dachshunds were subjected to a radiographic and histopathologic examination. The dogs were selected randomly from clinical cases euthanased for reasons unrelated to research at the Norwegian School of Veterinary Science. Lateral radiographs were taken of the vertebral columns after removing them from the carcasses. The histopathologic examination included 5 μm thick sections in the transverse plane, stained with hematoxylin-eosin and von Kossa. Radiographs and histological sections were evaluated independently.</p> <p>Results</p> <p>A total of 148 (28.5%) calcified discs were identified at the radiographic and 230 (45.7%) at the histopathologic examination. Of 92 discs found to be calcified by histopathology, but not by radiography, the degree of calcification was evaluated as 'slight' in 84 (91.3%). All the intervertebral discs (n = 138) that were found to be calcified by radiography were also found to be calcified by histopathology.</p> <p>Conclusion</p> <p>A sensitivity of 0.6 and specificity of 1.0 for radiography was calculated when using histopathology as the gold standard.</p
Holographic Metamagnetism, Quantum Criticality, and Crossover Behavior
Using high-precision numerical analysis, we show that 3+1 dimensional gauge
theories holographically dual to 4+1 dimensional Einstein-Maxwell-Chern-Simons
theory undergo a quantum phase transition in the presence of a finite charge
density and magnetic field. The quantum critical theory has dynamical scaling
exponent z=3, and is reached by tuning a relevant operator of scaling dimension
2. For magnetic field B above the critical value B_c, the system behaves as a
Fermi liquid. As the magnetic field approaches B_c from the high field side,
the specific heat coefficient diverges as 1/(B-B_c), and non-Fermi liquid
behavior sets in. For B<B_c the entropy density s becomes non-vanishing at zero
temperature, and scales according to s \sim \sqrt{B_c - B}. At B=B_c, and for
small non-zero temperature T, a new scaling law sets in for which s\sim
T^{1/3}. Throughout a small region surrounding the quantum critical point, the
ratio s/T^{1/3} is given by a universal scaling function which depends only on
the ratio (B-B_c)/T^{2/3}.
The quantum phase transition involves non-analytic behavior of the specific
heat and magnetization but no change of symmetry. Above the critical field, our
numerical results are consistent with those predicted by the Hertz/Millis
theory applied to metamagnetic quantum phase transitions, which also describe
non-analytic changes in magnetization without change of symmetry. Such
transitions have been the subject of much experimental investigation recently,
especially in the compound Sr_3 Ru_2 O_7, and we comment on the connections.Comment: 23 pages, 8 figures v2: added ref
Strain-dependent host transcriptional responses to toxoplasma infection are largely conserved in mammalian and avian hosts
Toxoplasma gondii has a remarkable ability to infect an enormous variety of mammalian and avian species. Given this, it is surprising that three strains (Types I/II/III) account for the majority of isolates from Europe/North America. The selective pressures that have driven the emergence of these particular strains, however, remain enigmatic. We hypothesized that strain selection might be partially driven by adaptation of strains for mammalian versus avian hosts. To test this, we examine in vitro, strain-dependent host responses in fibroblasts of a representative avian host, the chicken (Gallus gallus). Using gene expression profiling of infected chicken embryonic fibroblasts and pathway analysis to assess host response, we show here that chicken cells respond with distinct transcriptional profiles upon infection with Type II versus III strains that are reminiscent of profiles observed in mammalian cells. To identify the parasite drivers of these differences, chicken fibroblasts were infected with individual F1 progeny of a Type II x III cross and host gene expression was assessed for each by microarray. QTL mapping of transcriptional differences suggested, and deletion strains confirmed, that, as in mammalian cells, the polymorphic rhoptry kinase ROP16 is the major driver of strain-specific responses. We originally hypothesized that comparing avian versus mammalian host response might reveal an inversion in parasite strain-dependent phenotypes; specifically, for polymorphic effectors like ROP16, we hypothesized that the allele with most activity in mammalian cells might be less active in avian cells. Instead, we found that activity of ROP16 alleles appears to be conserved across host species; moreover, additional parasite loci that were previously mapped for strain-specific effects on mammalian response showed similar strain-specific effects in chicken cells. These results indicate that if different hosts select for different parasite genotypes, the selection operates downstream of the signaling occurring during the beginning of the host's immune response. © 2011 Ong et al
Revisiting Semantics of Interactions for Trace Validity Analysis
Interaction languages such as MSC are often associated with formal semantics
by means of translations into distinct behavioral formalisms such as automatas
or Petri nets. In contrast to translational approaches we propose an
operational approach. Its principle is to identify which elementary
communication actions can be immediately executed, and then to compute, for
every such action, a new interaction representing the possible continuations to
its execution. We also define an algorithm for checking the validity of
execution traces (i.e. whether or not they belong to an interaction's
semantics). Algorithms for semantic computation and trace validity are analyzed
by means of experiments.Comment: 18 pages of contents and 2 pages for references, 10 figures.
Published in ETAPS-FASE2020 : "23rd International Conference on Fundamental
Approaches to Software Engineering" in the "research papers" categor
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