PHOTOCHROMIC SYNERGISM OF BACTERIORHODOPSIN- and HALORHODOPSIN-MEDIATED PHOTOPHOSPHORYLATION IN Halobacterium halobium*

Quantitative action spectroscopy was performed in Halobacterium halobium. using four suited pigment mutants, namely the bacteriorhodopsin and halorhodopsin positive mutant strain M-l (BR⁺, HR⁺), the bacteriorhodopsin positive but halorhodopsin negative strain M-18 (BR⁺, HR^-), the bacteriorhodopsin negative but halorhodopsin positive strain L-33 (BR^-, HR⁺), and the bacteriorhodopsin and halorhodopsin negative strain L-07 (BR^-, HR⁺). The approached questions were: First, photoenergetic synergism of halorhodopsin and bacteriorhodopsin in intact cells; second, photochromism and cellular function of the blue light-absorbing intermediates, i.e. M-412 and HR-410 in bacteriorhodopsin and in halorhodopsin, respectively. Dark-adapted cells of mutant strain M-l show wavelength-dependency of quantum yield of photo-phosphorylation, φ_ATP. An 1.4-fold enhancement was found at 575 nm wavelength where the long wavelength absorbance bands of bacteriorhodopsin and halorhodopsin intersect. The enhancement vanished after a 30 min pulse of orange light (600 Wm^-2 bandpass from 495 to 750 nm), but was restored after a 30 min pulse of blue light (100 Wm^-2 bandpass from 325 to 480 nm). Photoreversibility of this enhancement probably reflects phototransformation of halorhodopsin from its ground state into its inactive intermediate, HR-410, and vice versa. The halorhodopsin-mediated enhancement with maximum quantum yield of photophosphorylation, φ_ATP= 0.06, i.e. a quantum requirement of = 17 photons/ATP, is partly substituted by a rise in phosphate potential and explained in terms of a voltage-regulated gating effect on the H⁺-driven ATP-synthase, superimposed on the chemiosmotic mechanism of energy coupling. The blue-absorbing photochromic intermediate, M-412 of bacteriorhodopsin, dissipates light energy upon photoexcitation that is reflected by a spectral decline in quantum yield of photophosphorylation to a minimum value of = 0.01 at 415 nm, i.e. a quantum requirement of = 100 photons/ATP.     

Microwave heating of carbon-coated ceramic fibres: A mathematical model

The microwave heating of a thinly carbon-coated ceramic fibreis modelled and analysed in the small Biot number regime. Theelectric field is assumed known and uniform throughout the cross-section,and constant along the axis of the cylinder. The mathematicalmodel consists of a nonlinear heat equation with an idealizedsource term that models the thin carbon coating and simplifiedreaction kinetics. The analysis yields an asymptotic approximationof the heating process on two time scales. The first capturesthe initial heating of the carbon coating and the ceramic, andthe carbon reaction, while the second determines the long timebehaviour of the sample. The results show a qualitative relationshipbetween the coating thickness and the final temperature of thefibre. If the coating thickness is not uniform along the fibreaxis, then the model explains the mechanism for the formationand propagation of hot-spots.     

EFFECTS OF END CAP AND ASPECT RATIO ON TRANSMISSION OF SOUND ACROSS A TRUSS-LIKE PERIODIC DOUBLE PANEL

Transmission of sound across 2-D truss-like periodic double panels separated by an air gap and in contact with an acoustic fluid on the external faces is analyzed. Each panel is made of repeated cells. Combining the transfer matrices of the unit cell forms a set of equations for the overall elastic frequency response. The acoustic pressure in the fluids is expressed using a source boundary element method. Adding rigid reflecting end caps confines the air in the gap between panels which influences sound transmission. Measured values of transmission loss differ from the 2-D model by the wide low-frequency dip of the mass-spring-mass or “msm” resonance also termed the “air gap resonance”. In this case, the panels act as rigid masses and the air gap acts as an adiabatic air spring. Results from the idealized 3-D and 2-D models, incorporating rigid cavities and elastic plates, reveal that the “msm” dip is absent in 2-D models radiating into a semi-infinite medium. The dip strengthens as aspect ratio approaches unity. Even when the dip disappears in 2-D, TL rises more steeply for frequencies above the “msm” frequency.     

PHOTO-OXIDATION OF THYMINE SENSITIZED BY 2-METHYL-1,4-NAPHTHOQUINONE: ANALYSIS OF PRODUCTS INCLUDING THREE NOVEL PHOTO-DIMERS

Abstract —The near-UV photosensitization of thymine by 2-methyl-1,4-naphthoquinone in oxygenated aqueous solution leads to the formation of nine major thymine-derived products. Six of the photoproducts, representing 70% of the initial thymine loss, are also known to be formed by γ-ray or X-ray irradiation of oxygenated water solutions of thymine. They include the cis and trans isomers of 5-hydroperoxy-6-hydroxy-5,6-dihydrothymine, the cis and trans thymine glycols, 5-hydroxy-5-methylhydantoin, and N-formyl-N'-pyruvylurea. The three remaining major products, accounting for a further 25% of the initial thymine loss, are thymine di-adducts of a type not previously reported. Preliminary characterization of these novel photoproducts, based on their UV absorption, mass spectra, and proton and carbon-13 nuclear magnetic resonance spectra, suggests that in each of the three, the thymine moieties are linked by an N(1)-C(5) or N(1)-C(6) bond. A thymine cation radical is implicated as the common precursor of all 9 products. Accordingly. pyrimidine photosensitization by 2-methyl-1,4-naphthoquinone serves as a model system for studying the chemical consequences of radiation-induced ionization of the DNA bases.     

STEADY HYPSOCHROMIC SHIFT OF PEAK RESPONSIVITY TO ATTRACTANT LIGHT FROM 590 nm TO 560 nm IN Halobacterium halobium*

Abstract— Peak responsivity of photoattraction in Halobacterium halobium cells shows steady hypsochromic shift from 590 nm wavelength under low irradiance conditions to 560 nm under high irradiance conditions. Inversion of the photoattractant response, as dependent on blue vs red background light, is compatible with the known properties of photochromic sensory rhodopsin-I (SR-I) with ground state maximum absorption at 587 nm. Relaxation of the photoattractant response in H. halobium, as a function of wavelength and irradiance, gives a hint at an antagonistic pigment or intermediate state, different from ground state SR-I, with peak sensitivity at 620 nm or even above. The less sensitive photoattractant response at 560 nm persists without photorelaxation and represents the peak responsivity under high irradiance conditions.     

USING NETWORK ANALYSIS TO CHARACTERIZE FOREST STRUCTURE

Abstract Network analysis quantifies different structural properties of systems of interrelated parts using a single analytical framework. Many ecological phenomena have network‐like properties, such as the trophic relationships of food webs, geographic structure of metapopulations, and species interactions in communities. Therefore, our ability to understand and manage such systems may benefit from the use of network‐analysis techniques. But network analysis has not been applied extensively to ecological problems, and its suitability for ecological studies is uncertain. Here, we investigate the ability of network analysis to detect spatial patterns of species association in a tropical forest. We use three common graph‐theoretic measures of network structure to quantify the effect of understory tree size on the spatial association of understory species with trees in the canopy: the node degree distribution (NDD), characteristic path length (CPL), and clustering coefficient (CC). We compute the NDD, CPL, and CC for each of seven size classes of understory trees. For significance testing, we compare the observed values to frequency distributions of each statistic computed from randomized data. We find that the ability of network analysis to distinguish observed patterns from those representing randomized data strongly depends on which aspects of structure are investigated. Analysis of NDD finds no significant difference between random and observed networks. However, analysis of CPL and CC detected nonrandom patterns in three and one of the seven size classes, respectively. Network analysis is a very flexible approach that holds promise for ecological studies, but more research is needed to better understand its advantages and limitations.     

MANAGEMENT STRATEGY EVALUATION OF PHEROMONE‐BAITED TRAPPING TECHNIQUES TO IMPROVE MANAGEMENT OF INVASIVE SEA LAMPREY

We applied a management strategy evaluation (MSE) model to examine the potential cost‐effectiveness of using pheromone‐baited trapping along with conventional lampricide treatment to manage invasive sea lamprey. Four pheromone‐baited trapping strategies were modeled: (1) stream activation wherein pheromone was applied to existing traps to achieve 10^?12 mol/L in‐stream concentration, (2) stream activation plus two additional traps downstream with pheromone applied at 2.5 mg/hr (reverse‐intercept approach), (3) trap activation wherein pheromone was applied at 10 mg/hr to existing traps, and (4) trap activation and reverse‐intercept approach. Each new strategy was applied, with remaining funds applied to conventional lampricide control. Simulating deployment of these hybrid strategies on fourteen Lake Michigan streams resulted in increases of 17 and 11% (strategies 1 and 2) and decreases of 4 and 7% (strategies 3 and 4) of the lakewide mean abundance of adult sea lamprey relative to status quo. MSE revealed performance targets for trap efficacy to guide additional research because results indicate that combining lampricides and high efficacy trapping technologies can reduce sea lamprey abundance on average without increasing control costs.     

Lattice Boltzmann simulations of complex fluids

Email: j.yeomansl{at}physics.oxford.ac.uk We discuss how lattice Boltzmann simulations can be used tomodel the self-assembly and flow properties of complex fluids.The aim is to include both the hydrodynamic (viscous, diffusive)and the equilibrium (phase ordering, interface profiles) fluidproperties. Examples include the decomposition of a dropletunder extensional flow and phase separation of binary and lamellarfluids.