1,283 research outputs found
Stagnation point reverse flow combustor for a combustion system
A combustor assembly includes a combustor vessel having a wall, a proximate end defining an opening and a closed distal end opposite said proximate end. A manifold is carried by the proximate end. The manifold defines a combustion products exit. The combustion products exit being axially aligned with a portion of the closed distal end. A plurality of combustible reactant ports is carried by the manifold for directing combustible reactants into the combustion vessel from the region of the proximate end towards the closed distal end
Using a probabilistic approach to derive a two-phase model of flow-induced cell migration
Interstitial fluid flow is a feature of many solid tumours. In vitro
experiments have shown that such fluid flow can direct tumour cell movement
upstream or downstream depending on the balance between the competing
mechanisms of tensotaxis and autologous chemotaxis. In this work we develop a
probabilistic-continuum, two-phase model for cell migration in response to
interstitial flow. We use a Fokker-Planck type equation for the cell-velocity
probability density function, and model the flow-dependent mechanochemical
stimulus as a forcing term which biases cell migration upstream and downstream.
Using velocity-space averaging, we reformulate the model as a system of
continuum equations for the spatio-temporal evolution of the cell volume
fraction and flux, in response to forcing terms which depend on the local
direction and magnitude of the mechanochemical cues. We specialise our model to
describe a one-dimensional cell layer subject to fluid flow. Using a
combination of numerical simulations and asymptotic analysis, we delineate the
parameter regime where transitions from downstream to upstream cell migration
occur. As has been observed experimentally, the model predicts
downstream-oriented, chemotactic migration at low cell volume fractions, and
upstream-oriented, tensotactic migration at larger volume fractions. We show
that the locus of the critical volume fraction, at which the system transitions
from downstream to upstream migration, is dominated by the ratio of the rate of
chemokine secretion and advection. Our model predicts that, because the
tensotactic stimulus depends strongly on the cell volume fraction, upstream
migration occurs only transiently when the cells are initially seeded, and
transitions to downstream migration occur at later times due to the dispersive
effect of cell diffusion.Comment: 20 pages, 6 figures. Submitted to Biophysical Journa
Potential of new isolates of Dunaliella Salina for natural β-Carotene production
The halotolerant microalga Dunaliella salina has been widely studied for natural β-carotene production. This work shows biochemical characterization of three newly isolated Dunaliella salina strains, DF15, DF17, and DF40, compared with D. salina CCAP 19/30 and D. salina UTEX 2538 (also known as D. bardawil). Although all three new strains have been genetically characterized as Dunaliella salina strains, their ability to accumulate carotenoids and their capacity for photoprotection against high light stress are different. DF15 and UTEX 2538 reveal great potential for producing a large amount of β-carotene and maintained a high rate of photosynthesis under light of high intensity; however, DF17, DF40, and CCAP 19/30 showed increasing photoinhibition with increasing light intensity, and reduced contents of carotenoids, in particular β-carotene, suggesting that the capacity of photoprotection is dependent on the cellular content of carotenoids, in particular β-carotene. Strong positive correlations were found between the cellular content of all-trans β-carotene, 9-cis β-carotene, all-trans α-carotene and zeaxanthin but not lutein in the D. salina strains. Lutein was strongly correlated with respiration in photosynthetic cells and strongly related to photosynthesis, chlorophyll and respiration, suggesting an important and not hitherto identified role for lutein in coordinated control of the cellular functions of photosynthesis and respiration in response to changes in light conditions, which is broadly conserved in Dunaliella strains. Statistical analysis based on biochemical data revealed a different grouping strategy from the genetic classification of the strains. The significance of these data for strain selection for commercial carotenoid production is discussed
Homogenisation of nonlinear blood flow in periodic networks: the limit of small haematocrit heterogeneity
In this work we develop a homogenisation methodology to upscale mathematical
descriptions of microcirculatory blood flow from the microscale (where
individual vessels are resolved) to the macroscopic (or tissue) scale. Due to
the assumed two-phase nature of blood and specific features of red blood cells
(RBCs), mathematical models for blood flow in the microcirculation are highly
nonlinear, coupling the flow and RBC concentrations (haematocrit). In contrast
to previous works which accomplished blood-flow homogenisation by assuming that
the haematocrit level remains constant, here we allow for spatial heterogeneity
in the haematocrit concentration and thus begin with a nonlinear microscale
model. We simplify the analysis by considering the limit of small haematocrit
heterogeneity which prevails when variations in haematocrit concentration
between neighbouring vessels are small. Homogenisation results in a system of
coupled, nonlinear partial differential equations describing the flow and
haematocrit transport at the macroscale, in which a nonlinear Darcy-type model
relates the flow and pressure gradient via a haematocrit-dependent permeability
tensor. During the analysis we obtain further that haematocrit transport at the
macroscale is governed by a purely advective equation. Applying the theory to
particular examples of two- and three-dimensional geometries of periodic
networks, we calculate the effective permeability tensor associated with blood
flow in these vascular networks. We demonstrate how the statistical
distribution of vessel lengths and diameters, together with the average
haematocrit level, affect the statistical properties of the macroscopic
permeability tensor. These data can be used to simulate blood flow and
haematocrit transport at the macroscale.Comment: 34 pages, 8 figure
Transport of North African dust from the Bodélé depression to the Amazon Basin: a case study
Through long-range transport of dust, the North-African desert supplies essential minerals to the Amazon rain forest. Since North African dust reaches South America mostly during the Northern Hemisphere winter, the dust sources active during winter are the main contributors to the forest. Given that the Bodélé depression area in southwestern Chad is the main winter dust source, a close link is expected between the Bodélé emission patterns and volumes and the mineral supply flux to the Amazon. <br><br> Until now, the particular link between the Bodélé and the Amazon forest was based on sparse satellite measurements and modeling studies. In this study, we combine a detailed analysis of space-borne and ground data with reanalysis model data and surface measurements taken in the central Amazon during the Amazonian Aerosol Characterization Experiment (AMAZE-08) in order to explore the validity and the nature of the proposed link between the Bodélé depression and the Amazon forest. <br><br> This case study follows the dust events of 11–16 and 18–27 February 2008, from the emission in the Bodélé over West Africa (most likely with contribution from other dust sources in the region) the crossing of the Atlantic Ocean, to the observed effects above the Amazon canopy about 10 days after the emission. The dust was lifted by surface winds stronger than 14 m s<sup>−1</sup>, usually starting early in the morning. The lofted dust, mixed with biomass burning aerosols over Nigeria, was transported over the Atlantic Ocean, and arrived over the South American continent. The top of the aerosol layer reached above 3 km, and the bottom merged with the boundary layer. The arrival of the dusty air parcel over the Amazon forest increased the average concentration of aerosol crustal elements by an order of magnitude
TRIO: Turbulent Response in Oxygen
This project was designed to build on the results from the successful launch of the Turbulent Oxygen Mixing Experiment (TOMEX) mother-daughter (instrumented and chemical-release) payload (21.126) that was launched in October 2000 from the White Sands Missile Range. The overall science objective was to investigate the evolution of the atmospheric response. at altitudes between 80 and 120 km, to the presence of unstable regions with vertical scales of the order of 1 to 10 km. TRIO was designed to use Na lidar measurements from the MAUUMALT observation on MAUI with a launch of a payload from Pacific Missile Range Facility (PMRF), located on Kauai. During this project, Aerospace participated in a Mission Initiation Conference. put together a science requirements document. performed a site visit to PMRF. prepared a CDR document. and developed a production and calibration procedure for one of the payload instruments. the 3-channel photometer. Unfortunately. NASA decided to terminate the program because of unforeseen (by NASA) range costs. This CDR document represents our view of this project at termination and provides a roadmap to perform this experiment should it be proposed again
Interaction-powered supernovae: Rise-time vs. peak-luminosity correlation and the shock-breakout velocity
Interaction of supernova (SN) ejecta with the optically thick circumstellar
medium (CSM) of a progenitor star can result in a bright, long-lived shock
breakout event. Candidates for such SNe include Type IIn and superluminous SNe.
If some of these SNe are powered by interaction, then there should be a
relation between their peak luminosity, bolometric light-curve rise time, and
shock-breakout velocity. Given that the shock velocity during shock breakout is
not measured, we expect a correlation, with a significant spread, between the
rise time and the peak luminosity of these SNe. Here, we present a sample of 15
SNe IIn for which we have good constraints on their rise time and peak
luminosity from observations obtained using the Palomar Transient Factory. We
report on a possible correlation between the R-band rise time and peak
luminosity of these SNe, with a false-alarm probability of 3%. Assuming that
these SNe are powered by interaction, combining these observables and theory
allows us to deduce lower limits on the shock-breakout velocity. The lower
limits on the shock velocity we find are consistent with what is expected for
SNe (i.e., ~10^4 km/s). This supports the suggestion that the early-time light
curves of SNe IIn are caused by shock breakout in a dense CSM. We note that
such a correlation can arise from other physical mechanisms. Performing such a
test on other classes of SNe (e.g., superluminous SNe) can be used to rule out
the interaction model for a class of events.Comment: Accepted to ApJ, 6 page
Spectropolarimetry of SN 2011dh in M51: geometric insights on a Type IIb supernova progenitor and explosion
We present seven epochs of spectropolarimetry of the Type IIb supernova (SN)
2011dh in M51, spanning 86 days of its evolution. The first epoch was obtained
9 days after the explosion, when the photosphere was still in the depleted
hydrogen layer of the stripped-envelope progenitor. Continuum polarization is
securely detected at the level of P~0.5% through day 14 and appears to diminish
by day 30, which is different from the prevailing trends suggested by studies
of other core-collapse SNe. Time-variable modulations in P and position angle
are detected across P-Cygni line features. H-alpha and HeI polarization peak
after 30 days and exhibit position angles roughly aligned with the earlier
continuum, while OI and CaII appear to be geometrically distinct. We discuss
several possibilities to explain the evolution of the continuum and line
polarization, including the potential effects of a tidally deformed progenitor
star, aspherical radioactive heating by fast-rising plumes of Ni-56 from the
core, oblique shock breakout, or scattering by circumstellar material. While
these possibilities are plausible and guided by theoretical expectations, they
are not unique solutions to the data. The construction of more detailed
hydrodynamic and radiative-transfer models that incorporate complex aspherical
geometries will be required to further elucidate the nature of the polarized
radiation from SN 2011dh and other Type IIb supernovae.Comment: Post-proof edit. Accepted to MNRAS 2015 Aug 1
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