Shape selection of surface-bound helical filaments: biopolymers on curved membranes

Motivated to understand the behavior of biological filaments interacting with membranes of various types, we study a theoretical model for the shape and thermodynamics of intrinsically-helical filaments bound to curved membranes. We show filament-surface interactions lead to a host of non-uniform shape equilibria, in which filaments progressively unwind from their native twist with increasing surface interaction and surface curvature, ultimately adopting uniform-contact curved shapes. The latter effect is due to non-linear coupling between elastic twist and bending of filaments on anisotropically-curved surfaces, such as the cylindrical surfaces considered here. Via a combination of numerical solutions and asymptotic analysis of shape equilibria we show that filament conformations are critically sensitive to the surface curvature in both the strong- and weak-binding limits. These results suggest that local structure of membrane-bound chiral filaments is generically sensitive to the curvature-radius of the surface to which it is bound, even when that radius is much larger than the filament intrinsic pitch. Typical values of elastic parameters and interaction energies for several prokaryotic and eukaryotic filaments indicate that biopolymers are inherently very sensitive to the coupling between twist, interactions and geometry and that this could be exploited for regulation of a variety of processes such as the targeted exertion of forces, signaling and self-assembly in response to geometric cues including the local mean and Gaussian curvatures

Some Chelates of Al(III) & Their Reactions

408-40

Strategyproof auctions for balancing social welfare and fairness in secondary spectrum markets

Secondary spectrum access is emerging as a promising approach for mitigating the spectrum scarcity in wireless networks. Coordinated spectrum access for secondary users can be achieved using periodic spectrum auctions. Recent studies on such auction design mostly neglect the repeating nature of such auctions, and focus on greedily maximizing social welfare. Such auctions can cause subsets of users to experience starvation in the long run, reducing their incentive to continue participating in the auction. It is desirable to increase the diversity of users allocated spectrum in each auction round, so that a trade-off between social welfare and fairness is maintained. We study truthful mechanisms towards this objective, for both local and global fairness criteria. For local fairness, we introduce randomization into the auction design, such that each user is guaranteed a minimum probability of being assigned spectrum. Computing an optimal, interference-free spectrum allocation is NP-Hard; we present an approximate solution, and tailor a payment scheme to guarantee truthful bidding is a dominant strategy for all secondary users. For global fairness, we adopt the classic maxmin fairness criterion. We tailor another auction by applying linear programming techniques for striking the balance between social welfare and max-min fairness, and for finding feasible channel allocations. In particular, a pair of primal and dual linear programs are utilized to guide the probabilistic selection of feasible allocations towards a desired tradeoff in expectation. © 2011 IEEE.published_or_final_versionThe IEEE INFOCOM 2011, Shanghai, China, 10-15 April 2011. In Conference Proceedings, 2011, p. 3020-302

The electronic structure and localized molecular orbitals in S<SUB>4</SUB>N<SUB>4</SUB> by the CNDO/BW theory

The energies calculated for tetranitrogen tetrasulfide, S4N4, by the CNDO/BW theory favor a structure with coplanar nitrogen atoms and not a structure with coplanar sulfur atoms. Both structures have been proposed from experimental studies. Localized molecular orbitals are calculated for S4N4 and used to choose the appropriate Lewis structure for the molecule. The hybridization at the nitrogen and sulfur atoms is discussed. There is electron delocalization in the molecule, the S-N bond is a bent bond involving pure p-orbitals on the sulfur and nitrogen atoms and there is a pure p-bent bond between the sulfur atoms on the same side of the coplanar nitrogen atoms. There is no N-N bond in S4N4

Characterization of mycobacteriophage I8 and its unrelatedness to mycobacteriophages I1, I3 and I5

Homology among the genomes of mycobacteriophages I1, I3, I5 and I8 has been studied. Based on restriction endonuclease cleavage patterns, dot blot hybridization and Southern blot hybridization analysis, the DNAs of phages I1, I3 and I5 have been shown to be homologous and indistinguishable, but entirely different from phage I8. Unlike the others, the I8 genome does not harbour any single-strand interruptions. The DNA is 43 kb in length with limited cyclic permutations and has a G + C content of 54%. The presence of 5-methylcytosine in I8 DNA was indicated from the restriction patterns of MspI and HpaII. The number of sites and fragment sizes for several restriction enzymes on I8 DNA has been determined. Phage I8 has a replication cycle of 300 min, with a latent period of 180 min, a rise period of 120 min and a burst size of 100. The viability of phage I8 is significantly reduced by treatment with organic solvents

Defect Formation and Kinetics of Atomic Terrace Merging

Pairs of atomic scale terraces on a single crystal metal surface can be made to merge controllably under suitable conditions to yield steps of double height and width. We study the effect of various physical parameters on the formation of defects in a kinetic model of step doubling. We treat this manifestly non- equilibrium problem by mapping the model onto a 1-D random sequential adsorption problem and solving this analytically. We also do simulations to check the validity of our treatment. We find that our treatment effectively captures the dynamic evolution and the final state of the surface morphology. We show that the number and nature of the defects formed is controlled by a single dimensionless parameter $q$. For $q$ close to one we show that the fraction of defects rises linearly with $\epsilon \equiv 1-q$ as $0.284 \times \epsilon$. We also show that one can arrive at the final state faster and with fewer defects by changing the parameter with time.Comment: 17 pages, 8 figures. To be submitted to Phys. Rev.

Nonlinear analytical flame models with amplitude-dependent time-lag distributions

In the present work, we formulate a new method to represent a given Flame Describing Function by analytical expressions. The underlying idea is motivated by the observation that different types of perturbations in a burner travel with different speeds and that the arrival of a perturbation at the flame is spread out over time. We develop an analytical model for the Flame Describing Function, which consists of a superposition of several Gaussians, each characterised by three amplitude-dependent quantities: central time-lag, peak value and standard deviation. These quantities are treated as fitting parameters, and they are deduced from the original Flame Describing Function by using error minimisation and nonlinear optimisation techniques. The amplitude-dependence of the fitting parameters is also represented analytically (by linear or quadratic functions). We test our method by using it to make stability predictions for a burner with well-documented stability behaviour (Noiray's matrix burner). This is done in the time-domain with a tailored Green's function approach