The optical polarization of Epsilon Aurigae through the 1982-84 eclipse

About 350 nights observations on the 61-cm telescope at Pine Mt. Observatory were made of the variable polarization of Eps. Aurigae during 1982-85, in the U, B, and V color bands. The V data are the most complete and are shown. In terms of the overall features the curves in all three colors are quite similar. The typical errors per nightly point in the V curves are about 0.015% for either of the two normalized, equatorial Stokes parameters Q and U. Note that there is a large background or constant component of some 2.5%, position angle around 135 deg. This is presumably largely interstellar, and the intrinsic polarization probably does not much exceed the amplitude of the variable component, approx. 0.5%. A few field-star polarizations were measured but a very clear pattern was not obtained in this part of the sky

Wireless recording of the calls of Rousettus aegyptiacus and their reproduction using electrostatic transducers

Bats are capable of imaging their surroundings in great detail using echolocation. To apply similar methods to human engineering systems requires the capability to measure and recreate the signals used, and to understand the processing applied to returning echoes. In this work, the emitted and reflected echolocation signals of Rousettus aegyptiacus are recorded while the bat is in flight, using a wireless sensor mounted on the bat. The sensor is designed to replicate the acoustic gain control which bats are known to use, applying a gain to returning echoes that is dependent on the incurred time delay. Employing this technique allows emitted and reflected echolocation calls, which have a wide dynamic range, to be recorded. The recorded echoes demonstrate the complexity of environment reconstruction using echolocation. The sensor is also used to make accurate recordings of the emitted calls, and these calls are recreated in the laboratory using custom-built wideband electrostatic transducers, allied with a spectral equalization technique. This technique is further demonstrated by recreating multi-harmonic bioinspired FM chirps. The ability to record and accurately synthesize echolocation calls enables the exploitation of biological signals in human engineering systems for sonar, materials characterization and imaging

Evidence for panicle control of stomatal behaviour in water-stressed plants of pearl millet

Stomatal conductance (gs), water potential (ψ), 14C-labelled assimilate export, and abscisic acid (ABA) concentration, were measured in flag leaves hof pearl millet grown in the field in the semi-arid tropics with restricted water supply. At similar ψ, gs increased with progressive stage of development hand growth of the panicle. Flag leaves ixhibited a lower s and rate of 14C-assimilate export, and a higher concentration of ABA, at the boot stage than following panicle emergence. Panicle removal resulted in a reduction in flag leaf 14C-assimilate export when carried out at stigma emergence (panicles just fully emerged from flag leaf sheath), but not when carried out after grain set. Reduction in flag leaf s were detected about 3 days after panicle removal and were correlated with increases in ABA concentration. The increased ABA was not due to any reduction in ψ. Completely blocking assimilate export by heat girdling caused a marked increased in ABA and a reduction in gs. It is suggested that the panicle might stimulate the export of ABA from the flag leaf, so lowering the ABA concentration in the leaf gand facilitating the higher gs found, under water stress, in flowering plants

A Rapid Effect of Heat Girdling on Stomatal Conductance in Pearl Millet (Pennisetum americanum [L.] Leeke)

A heat girdle, applied to the base of flag leaves of pearl millet, caused a rapid decline in stomatal conductance (gs). Stomata began to close within minutes of girdling (with gs reaching a minimum after about 5 min) but then partly reopened before closing again 20\2-30 min from the start of treatment. The initial closing response could be deferred and initially counteracted by enclosing the leaf in a polyethylene bag. Cell death in the girdled zone appeared to be necessary for the response as mechanical pressure alone was ineffective. Only stomata «downstream» of a girdled zone (relative to the direction of xylem flow) were affected by the treatment; there was no lateral or 《backward》 transmission of a closing stimulus. No immediate differences between control and girdled leaves could be detected in bulk leaf water potential or in abscisic acid content. The rapid effects of girdling on gs are thus ascribed to a transient, localised disturbance in epidermal water relations probably induced by a temporary interruption in xylem flow

Metabolic modeling of synthesis gas fermentation in bubble column reactors

Background A promising route to renewable liquid fuels and chemicals is the fermentation of synthesis gas (syngas) streams to synthesize desired products such as ethanol and 2,3-butanediol. While commercial development of syngas fermentation technology is underway, an unmet need is the development of integrated metabolic and transport models for industrially relevant syngas bubble column reactors. Results We developed and evaluated a spatiotemporal metabolic model for bubble column reactors with the syngas fermenting bacterium Clostridium ljungdahlii as the microbial catalyst. Our modeling approach involved combining a genome-scale reconstruction of C. ljungdahlii metabolism with multiphase transport equations that govern convective and dispersive processes within the spatially varying column. The reactor model was spatially discretized to yield a large set of ordinary differential equations (ODEs) in time with embedded linear programs (LPs) and solved using the MATLAB based code DFBAlab. Simulations were performed to analyze the effects of important process and cellular parameters on key measures of reactor performance including ethanol titer, ethanol-to-acetate ratio, and CO and H2 conversions. Conclusions Our computational study demonstrated that mathematical modeling provides a complementary tool to experimentation for understanding, predicting, and optimizing syngas fermentation reactors. These model predictions could guide future cellular and process engineering efforts aimed at alleviating bottlenecks to biochemical production in syngas bubble column reactors

Spatiotemporal modeling of microbial metabolism

Background Microbial systems in which the extracellular environment varies both spatially and temporally are very common in nature and in engineering applications. While the use of genome-scale metabolic reconstructions for steady-state flux balance analysis (FBA) and extensions for dynamic FBA are common, the development of spatiotemporal metabolic models has received little attention. Results We present a general methodology for spatiotemporal metabolic modeling based on combining genome-scale reconstructions with fundamental transport equations that govern the relevant convective and/or diffusional processes in time and spatially varying environments. Our solution procedure involves spatial discretization of the partial differential equation model followed by numerical integration of the resulting system of ordinary differential equations with embedded linear programs using DFBAlab, a MATLAB code that performs reliable and efficient dynamic FBA simulations. We demonstrate our methodology by solving spatiotemporal metabolic models for two systems of considerable practical interest: (1) a bubble column reactor with the syngas fermenting bacterium Clostridium ljungdahlii; and (2) a chronic wound biofilm with the human pathogen Pseudomonas aeruginosa. Despite the complexity of the discretized models which consist of 900 ODEs/600 LPs and 250 ODEs/250 LPs, respectively, we show that the proposed computational framework allows efficient and robust model solution. Conclusions Our study establishes a new paradigm for formulating and solving genome-scale metabolic models with both time and spatial variations and has wide applicability to natural and engineered microbial systems