Descripción: The use of plasma actuators is a recent technology that imposes a localized electric force that is used to control air flows. A suitable representation of actuation enables to undertake plasma actuators optimization, to design flow-control strategies, or to analyse the flow stabilization that can be attained by plasma forcing. The problem description may be clearly separated in two regions. An outer region, where the fluid is electrically neutral, in which the flow is described by the Navier-Stokes equation without any forcing term. An inner region, that forms a thin boundary layer, where the fluid is ionized and electric forces are predominant. The outer limit of the inner solution becomes the boundary condition for the outer problem. The outer problem can then be solved with a slip velocity that is issued from the inner solution. Although the solution for the inner problem is quite complex it can be contoured proposing pseudo-empirical models where the slip velocity of the outer problem is determined indirectly from experiments. This pseudo-empirical model approach has been recently tested in different cylinder flows and revealed quite adapted to describe actuated flow behaviour. In this work we determine experimentally the influence of the duty cycle on the slip velocity distribution. The velocity was measured by means of a pitot tube and flow visualizations of the starting vortex (i.e. the induced flow when actuation is activated in a quiescent air) have been done by means of the Schlieren technique. We also performed numerical experiments to simulate the outer region problem when actuation is activated in a quiescent air using a slip velocity distribution as a boundary condition. The experimental and numerical results are in good agreement showing the potential of this pseudo-empirical model approach to characterize the plasma actuation.

Descripción: Electrical transmission among neurons has been considered a mechanism to synchronize neuronal activity, and rectification provides a mechanism to confine the flow of signals among the connected neurons. The question is how this type of transmission operates within complex neuronal networks. In the leech, the neurons located in position 151 of the midbody ganglion map are connected to virtually every motoneuron via rectifying electrical synapses that pass negative current to the motoneurons. These are nonspiking neurons, and here we have labeled them NS neurons. The goal of this investigation has been to assess their role in regulating motor activity and how rectifying electrical synapses contribute to the function of motor networks. The coupling between NS neurons and motoneurons was voltage sensitive: it increased as motoneurons were depolarized. In addition, excitation of motoneurons evoked hyperpolarizing synaptic responses in NS neurons, the amplitude of which depended on the membrane potential of the latter and on the motoneuron firing frequency. This hyperpolarization was mediated by chemical transmission through an interneuronal layer that spanned the nerve cord. These interactions established a feedback loop between NS and motoneurons that was regulated by the membrane potential of NS. This mechanism was responsible for the uncoupling between otherwise electrically coupled motoneurons. In this way, the NS neurons can act as "electrical neuromodulators," modifying the interaction of other neurons, depending on the activity of the system as a whole.

Descripción: Munida gregaria and M. subrugosa have been considered two different species for more than a century; however, after a recent molecular phylogenetic study, they are considered a single polymorphic species. Yet, the use of markers to diagnose species may be misleading when divergence between species is recent, since a speciation event may be obscured by the retention and stochastic sorting of ancestral polymorphisms. The morphs gregaria and subrugosa of Munida gregaria constitute an interesting case for the study of behavioural isolation since they are sympatric, breed at the same time of the year, and might have experienced a recent speciation. Mating behaviour observations and mate choice mating trials were conducted in order to investigate the potential existence of a behavioural prezygotic barrier to gene flow between these two morphs. Since factors involved in mate choice in galatheids are unknown, the four possible combinations of the two different morphs in trios were used to test for the existence of mate choice. Video recordings of all the possible trio combinations revealed that there was cross-attraction between males and females of different morphs. Females bearing partial broods participated in encounters as well as non-ovigerous females. The frequency and duration of homo- and heterotypic encounters were registered, and a reproductive isolation index was calculated for each variable for each trio. The isolation indexes calculated were not different from zero indicating random mating, and were not affected by the composition of the trio or the partial ovigerous condition of females. These results provided evidence of the absence of behavioural prezygotic barriers to gene flow between the morphs gregaria and subrugosa of M. gregaria. © 2011 Springer-Verlag and AWI.

Descripción: Eighteen year (1985-2002) sea surface temperature (SST) data are used to study the intraseasonal variability of the Patagonian shelf break front (SBF) in the SW South Atlantic Ocean between 39° and 44°S. The cross-shelf break SST gradients reveal distinct, previously undocumented thermal fronts located both, offshore and inshore of the SBF. Throughout the year the main SBF, identified as a band of negative SST gradient maxima (relatively strong offshore temperature decrease), forms a persistent feature located closed to the 200 m isobath, while two distinct negative gradient maxima are located inshore and offshore of this location. Daily SST images reveal the presence of three branches of cold waters whose edges delineate the above mentioned fronts. The two offshore branches closely follow lines of constant potential vorticity (f/h) and appear to be associated with the Malvinas Current, while a third branch, located further onshore, is not steered by the bottom topography. South of 40°S the onshore branch forms a quasi permanent front parallel to the SBF. Copyright 2008 by the American Geophysical Union.

Descripción: We investigate the renormalization group approach to nonequilibrium field theory. We show that it is possible to derive nontrivial renormalization group flow from iterative coarse graining of a closed-time-path action. This renormalization group is different from the usual in quantum field theory textbooks, in that it describes nontrivial noise and dissipation. We work out a specific example where the variation of the closed-time-path action leads to the so-called Kardar-Parisi-Zhang equation, and show that the renormalization group obtained by coarse graining this action, agrees with the dynamical renormalization group derived by directly coarse graining the equations of motion. © 2002 The American Physical Society.

Descripción: Background: Resolving the kinetics of agonist binding events separately from the subsequent channel gating processes requires the ability of applying and removing the agonist before channel gating occurs. No reported system has yet achieved pulses shorter than 100 μs, necessary to study nicotinic ACh receptor or AMPA receptor activation. Methodology/Principal Findings: Solution exchange systems deliver short agonist pulses by moving a sharp interface between a control and an experimental solution across a channel preparation. We achieved shorter pulses by means of an exchange system that combines a faster flow velocity, narrower partition between the two streams, and increased velocity and bandwidth of the movement of the interface. The measured response of the entire system was fed back to optimize the voltage signal applied to the piezoelectric actuator overcoming the spurious oscillations arising from the mechanical resonances when a high bandwidth driving function was applied. Optimization was accomplished by analyzing the transfer function of the solution exchange system. When driven by optimized command pulses the enhanced system provided pulses lasting 26 ± 1 μs and exchanging 93 ± 1% of the solution, as measured in the open tip of a patch pipette. Conclusions/Significance: Pulses of this duration open the experimental study of the molecular events that occur between the agonist binding and the opening of the channel. © 2012 Auzmendi et al.

Descripción: Endothelial cells, at the cell-cell borders, express PECAM-1, and have been implicated in vascular functions. The monoclonal antibody MEC 13.3 recognizes PECAM-1 molecule from mouse vessels and allows to analyze the ontogeny of mouse endothelium. At the present, little is known about the molecular basis of differentiation pathways of endothelial cells, that enables its morphological heterogeneity. The purpose of this study was to analyze the pattern of PECAM-1 expression, employing monoclonal antibody MEC 13.3, in cellular suspensions obtained from different mouse organs at pre and postnatal stages. Fluorescence activated cell sorter analysis showed a different profile of the glycoprotein expression in a cell population with size and granularity selected by 1G11 endothelial cell line. The expression differs from prenatal to postnatal developmental stages in a given organ, and among the organs studied. Another cell population, with a size and granularity higher than 1G11 endothelial cell line, coexists in cellular suspensions obtained from liver, gut and brain. These cells could be related to those detected by means of immunoenzyme methods which showed a non-differentiated morphology. The different PECAM-1 pattern expression could reflect potential organ-specific differentiation pathways during development and according to organs environment. The existence of another cell population with a size and granularity higher than 1G11 endothelial cell line required a phenotypic characterization.

Descripción: Single-cell cytoplasm sap (1-10 pL) was extracted by using a pressure probe glass microcapillary tip from tulip leaf and bulb and analyzed by UV-MALDI-TOF MS for free underivatized carbohydrate content. Three matrices including 2,5-dihydroxybenzoic acid (DHB), 2,4,6-trihydroxyacetophenone (THAP), and carbon nanotubes (CNTs) in positive ion mode were selected for analysis because of acceptable carbohydrate-related signal reproducibility. Disaccharide and oligosaccharide (up to 15 Hex when THAP was used, 11 Hex with DHB, and 7 Hex with CNTs) were detected in tulip bulb cell cytoplasm sample. When DHB was used as matrix, neutral carbohydrates were more abundantly detected as sodiated cations; the sugar-related signals, however, appeared as dominant potassiated cations when THAP and CNTs were used. Small amount of monosaccharide was also detected in bulb cell cytoplasm with CNTs as matrix. UV-MALDI-TOF MS of leaf cell extract resulted in high-resolution detection of hexose and disaccharide with DHB, THAP, and CNTs. © 2008 American Society for Mass Spectrometry.

Descripción: Dendritic cell (DC) and natural killer (NK) cell interactions are important for the regulation of innate and adaptive immunity, but their relevance during early pregnancy remains elusive. Using two different strategies to manipulate the frequency of NK cells and DC during gestation, we investigated their relative impact on the decidualization process and on angiogenic responses that characterize murine implantation. Manipulation of the frequency of NK cells, DC or both lead to a defective decidual response characterized by decreased proliferation and differentiation of stromal cells. Whereas no detrimental effects were evident upon expansion of DC, NK cell ablation in such expanded DC mice severely compromised decidual development and led to early pregnancy loss. Pregnancy failure in these mice was associated with an unbalanced production of anti-angiogenic signals and most notably, with increased expression of genes related to inflammation and immunogenic activation of DC. Thus, NK cells appear to play an important role counteracting potential anomalies raised by DC expansion and overactivity in the decidua, becoming critical for normal pregnancy progression. © 2012 González et al.

Descripción: 1. Leaf structural and physiological traits are associated with growth form and habitat, but little is known of the specific traits associated with hemiepiphytes, which are an important component of many tropical forests. Given their life history that includes a drought prone epiphytic stage, hemiepiphytes should be expected to have more drought tolerance-related traits than co-occurring terrestrial species. 2. The genus Ficus includes woody hemiepiphytes distributed in tropical areas throughout the world. Traits related to the flux of water through the leaf and to drought adaptations were studied in five hemiephiphytic (H) and five non-hemiepiphytic (NH) Ficus tree species grown in a common garden to determine genetically based differences. 3. Leaves of H and NH species differed substantially in structure and physiology; on average, H species had smaller leaves with higher leaf mass per unit area, thicker epidermis, smaller vessel lumen diameters in petioles and lower petiole hydraulic conductivity. Leaf traits also indicated stronger drought tolerance in H species, including lower epidermal conductance and turgor loss point and earlier stomatal closure with desiccation than NH species. Across H and NH species, traits related to water flux capacity were negatively correlated with traits related to drought tolerance. 4. The divergences in hydraulics and water relations between growth forms for these closely related species reflected specialization according to contrasting habitat and life form. Conservative water use and increased ability of leaves to persist under severe drought would provide an advantage for H species, especially during the epiphytic phase, while the higher potential water use of NH species would be associated with higher assimilation rates and competitiveness under high water supply. 5. The results indicate a trade-off between leaf water flux capacity and leaf drought tolerance across these hemiephiphytic and non-hemiepiphytic species. Species adaptation to habitats with contrasting demands on leaf function may lead to divergence along a leaf water-flux-drought-tolerance spectrum. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.

Descripción: Two populations of human natural killer (NK) cells can be identified in peripheral blood. The majority are CD3-CD56dim cells while the minority exhibits a CD3-CD56bright phenotype. In vitro evidence indicates that CD56bright cells are precursors of CD56dim cells, but in vivo evidence is lacking. Here, we studied NK cells from a patient that suffered from a melanoma and opportunistic fungal infection during childhood. The patient exhibited a stable phenotype characterized by a reduction in the frequency of peripheral blood CD3-CD56dim NK cells, accompanied by an overt increase in the frequency and absolute number of CD3-CD56bright cells. These NK cells exhibited similar expression of perforin, CD57 and CD158, the major activating receptors CD16, NKp46, NKG2D, DNAM-1, and 2B4, as well as the inhibitory receptor CD94/NKG2A, on both CD56bright and CD56dim NK cells as healthy controls. Also, both NK cell subpopulations produced IFN-γ upon stimulation with cytokines, and CD3-CD56dim NK cells degranulated in response to cytokines or K562 cells. However, upon stimulation with cytokines, a substantial fraction of CD56dim cells failed to up-regulate CD57 and CD158, showed a reduction in the percentage of CD16+ cells, and CD56bright cells did not down-regulate CD62L, suggesting that CD56dim cells could not acquire a terminally differentiated phenotype and that CD56bright cells exhibit a maturation defect that might result in a potential altered migration pattern. These observations, support the notion that NK cells of this patient display a maturation/activation defect that precludes the generation of mature NK cells at a normal rate accompanied by CD56dim NK cells that cannot completely acquire a terminally differentiated phenotype. Thus, our results provide evidence that support the concept that in vivo CD56bright NK cells differentiate into CD56dim NK cells, and contribute to further understand human NK cell ontogeny. © 2012 Domaica et al.

Descripción: Above the southern Andes range and its prolongation in the Antarctic Peninsula, large-amplitude mountain and shear gravity waves observed with Weather Research and Forecasting (WRF) mesoscale model simulations during winter 2009 are analyzed. Two specific reasons motivated this study: (1) a decade of satellite observations of temperature fluctuations in the stratosphere, allowing us to infer that this region may be launching the largest-amplitude gravity waves into the upper atmosphere, and (2) the recent design of a research program to investigate these features in detail, the Southern Andes Antarctic Gravity wave Initiative (SAANGRIA). The simulations are forced with ERA-Interim data from the European Centre for Medium-Range Weather Forecasts. The approach selected for the regional downscaling is based on consecutive integrations with weekly reinitialization with 24 h of spin-up, and the outputs during this period are excluded from the analysis. From 1 June to 31 August 2009, five case studies were selected on the basis of their outstanding characteristics and large wave amplitudes. In general, one or two prevailing modes of oscillation are identified after applying continuous wavelet transforms at constant pressure levels and perpendicularly to the nominal orientation of the dominant wave crests. In all cases, the dominant modes are characterized by horizontal wavelengths around 50 km. Their vertical wavelengths, depending on a usually strong background wind shear, are estimated to be between 2 and 11 km. The corresponding intrinsic periods range between 10 and 140 min. In general, the estimated vertical wavelength (intrinsic period) maximizes (minimizes) around 250-300 hPa. The synoptic circulation for each case is described. Zonal and meridional components of the vertical flux of horizontal momentum are shown in detail for each case, including possible horizontal wavelengths between 12 and 400 km. Large values of this flux are observed at higher pressure levels, decreasing with increasing height after a progressive deposition of momentum by different mechanisms. As expected, in the wintertime upper troposphere and lower stratosphere in this region, a prevailing zonal component is negative almost everywhere, with the exception of one case above the northern tip of the Antarctic Peninsula. A comparison with previous experimental results reported in the region from in situ and remote sensing measurements suggests a good agreement with the momentum flux profiles computed from the simulations. Partial wave reflection near the tropopause was found, as considerable departures from equipartition between potential and kinetic wave energy are obtained in all cases and at all pressure levels. This ratio was always less than 1 below the lower stratosphere. Copyright 2012 by the American Geophysical Union.