Analysis of the Movement of Chlamydomonas Flagella: The Function of the Radial-spoke System Is Revealed by Comparison of Wild-type and Mutant Flagella

The mutation uni-1 gives rise to uniflagellate Chlamydomonas cells which rotate around a fixed point in the microscope field, so that the flagellar bending pattern can be photographed easily . This has allowed us to make a detailed analysis of the wild-type flagellar bending pattern and the bending patterns of flagella on several mutant strains. Cells containing uni-1, and recombinants of uni-1 with the suppressor mutations, sup(_pf)-1 and sup(_pf)-3, show the typical asymmetric bending pattern associated with forward swimming in Chlamydomonas, although sup(_pf)-1 flagella have about one-half the normal beat frequency, apparently as the result of defective function of the outer dynein arms. The pf-17 mutation has been shown to produce nonmotile flagella in which radial spoke heads and five characteristic axonemal polypeptides are missing. Recombinants containing pf-17 and either sup(_pf)-1 or sup(_pf)-3 have motile flagella, but still lack radial-spoke heads and the associated polypeptides . The flagellar bending pattern of these recombinants lacking radial-spoke heads is a nearly symmetric, large amplitude pattern which is quite unlike the wild-type pattern . However, the presence of an intact radial-spoke system is not required to convert active sliding into bending and is not required for bend initiation and bend propagation, since all of these processes are active in the sup(_pf) pf-17 recombinants. The function of the radial-spoke system appears to be to convert the symmetric bending pattern displayed by these recombinants into the asymmetric bending pattern required for efficient swimming, by inhibiting the development of reverse bends during the recovery phase of the bending cycle

Impacts of Fire Emissions and Transport Pathways on the Interannual Variation of CO In the Tropical Upper Troposphere

This study investigates the impacts of fire emission, convection, various climate conditions and transport pathways on the interannual variation of carbon monoxide (CO) in the tropical upper troposphere (UT), by evaluating the field correlation between these fields using multi-satellite observations and principle component analysis, and the transport pathway auto-identification method developed in our previous study. The rotated empirical orthogonal function (REOF) and singular value decomposition (SVD) methods are used to identify the dominant modes of CO interannual variation in the tropical UT and to study the coupled relationship between UT CO and its governing factors. Both REOF and SVD results confirm that Indonesia is the most significant land region that affects the interannual variation of CO in the tropical UT, and El Nino-Southern Oscillation (ENSO) is the dominant climate condition that affects the relationships between surface CO emission, convection and UT CO. In addition, our results also show that the impact of El Nino on the anomalous CO pattern in the tropical UT varies strongly, primarily due to different anomalous emission and convection patterns associated with different El Nino events. In contrast, the anomalous CO pattern in the tropical UT during La Nina period appears to be less variable among different events. Transport pathway analysis suggests that the average CO transported by the "local convection" pathway (Delta COlocal) accounts for the differences of UT CO between different ENSO phases over the tropical continents during biomass burning season. Delta COlocal is generally higher over Indonesia-Australia and lower over South America during El Nino years than during La Nina years. The other pathway ("advection within the lower troposphere followed by convective vertical transport") occurs more frequently over the west-central Pacific during El Nino years than during La Nina years, which may account for the UT CO differences over this region between different ENSO phases.NASA Aura Science Team (AST) program NNX09AD85GJackson School of Geosciences at the University of Texas at AustinJet Propulsion Laboratory, California Institute of Technology, under NASAGeological Science

Single-Walled Carbon Nanotubes as Shadow Masks for Nanogap Fabrication

We describe a technique for fabricating nanometer-scale gaps in Pt wires on insulating substrates, using individual single-walled carbon nanotubes as shadow masks during metal deposition. More than 80% of the devices display current-voltage dependencies characteristic of direct electron tunneling. Fits to the current-voltage data yield gap widths in the 0.8-2.3 nm range for these devices, dimensions that are well suited for single-molecule transport measurements

Comparative study of Steel-FRP, FRP and steel reinforced coral concrete beams in their flexural performance

In this paper, a comparative study of Carbon Fiber Reinforced Polymer (CFRP) Bar and Steel-Carbon Fiber Composite Bar (SCFCB) reinforced coral concrete beams are made through a series experimental tests and theoretical analysis. The flexural capacity, crack development and failure modes of CFRP and SCFCB reinforced coral concrete were investigated in detail. They are also compared to ordinary steel reinforced coral concrete beams. The results show that under the same condition of reinforcement ratio, the SCFCB reinforced beam exhibits better performance than those of the CFRP reinforced beams, and its stiffness is slightly lower than that of the steel reinforced beam. Under the same load condition, the crack width of the SCFCB beam is between the steel reinforced beam and the CFRP bar reinforced beam. Before the steel core yields, the crack growth rate of SCFCB beam is similar to the steel reinforced beam. SCFCB has a higher strength utilization rate, about 70% -85% of its ultimate strength. The current design guidance was also examined based on the test results. It was found that the existing design specifications for FRP reinforced normal concrete is not suitable for SCFCB reinforced coral concrete structures

Exponential Convergence Towards Stationary States for the 1D Porous Medium Equation with Fractional Pressure

We analyse the asymptotic behaviour of solutions to the one dimensional fractional version of the porous medium equation introduced by Caffarelli and V\'azquez, where the pressure is obtained as a Riesz potential associated to the density. We take advantage of the displacement convexity of the Riesz potential in one dimension to show a functional inequality involving the entropy, entropy dissipation, and the Euclidean transport distance. An argument by approximation shows that this functional inequality is enough to deduce the exponential convergence of solutions in self-similar variables to the unique steady states