Analysis of the Datagram Congestion Control Protocol’s connection management procedures using the sweep-line method

State space explosion is a key problem in the analysis of finite state systems. The sweep-line method is a state exploration method which uses a notion of progress to allow states to be deleted from memory when they are no longer required. This reduces the peak number of states that need to be stored, while still exploring the full state space. The technique shows promise but has never achieved reductions greater than about a factor of 10 in the number of states stored in memory for industrially relevant examples. This paper discusses sweep-line analysis of the connection management procedures of a new Internet standard, the Datagram Congestion Control Protocol (DCCP). As the intuitive approaches to sweep-line analysis are not effective, we introduce new variables to track progress. This creates further state explosion. However, when used with the sweep-line, the peak number of states is reduced by over two orders of magnitude compared with the original. Importantly, this allows DCCP to be analysed for larger parameter values. Somsak Vanit-Anunchai was partially supported by an Australian Research Council Discovery Grant (DP0559927) and Suranaree University of Technology. Guy Edward Gallasch was supported by an Australian Research Council Discovery Grant (DP0559927).     

Quantum dot integration in heterostructure solar cells

InAs self-assembled quantum dots (SA-QDs) were incorporated into GaAlAs/GaAs heterostructure for solar cell applications. The structure was fabricated by molecular beam epitaxy on p-GaAs substrate. After the growth of GaAs buffer layer, multi-stacked InAs QDs were grown by self-assembly with a slow growth rate of 0.01 ML/s, which provides high dot quality and large dot size. Then, the structure was capped with n-GaAs and wide band gap n-GaAlAs was introduced. One, two or three stacks of QDs were sandwiched in the p–n heterojunction. The contribution of QDs in solar cell hetero-structure is the quantized nature and a high density of quantized states. I–V characterization was conducted in the dark and under AM1 illumination with 100 mW/cm² light power density to confirm the solar cell performance. Photocurrent from the QDs was confirmed by spectral response measurement using a filtered light source (1.1-μm wavelength) and a tungsten halogen lamp with monochromator with standard lock-in technique. These experimental results indicate that QDs could be an effective part of solar cell heterostructure. A typical I–V characteristic of this yet-to-be-optimized solar cell, with an active area of 7.25 mm², shows an open circuit voltage V_oc of 0.7 V, a short circuit current I_sc of 3.7 mA, and a fill factor FF of 0.69, leading to an efficiency η of 24.6% (active area).     

Synthesis of Isocryptolepine-Triazole Adducts and Evaluation of Their Cytotoxic Activity

Eighteen hybrid compounds between 8-bromo-2-fluoro-isocryptolepine ( 4 ) and 1,2,3-triazole were synthesized via azide rearrangement-annulation reaction. Compound 4 underwent regioselective N-propargylation and click reaction to form 8-bromo-2-fluoro-isocryptolepine-triazole hybrids 11 which were evaluated for cytotoxic activity. Compound 11 c containing 1-anisyltriazole was the most effective in inhibiting HepG2, HuCCA-1 and A549 cell lines (IC₅₀ values of 1.65–3.07 μM) while compounds 11 a (1-phenyltriazole), 11 j (1-para-CF₃-benzyltriazole) and 11 l (1-meta-Cl-benzyltriazole) were potent inhibitors of HuCCA-1, HepG2 and A549 cell lines, respectively. Moreover, 11 l showed the lowest cytotoxicity to normal human kidney cell line. Compounds 11 c and 11 l provided improvement of cytotoxic activity over 4 . Compounds 4 , 11 c and 11 l were selected to investigate their mechanisms of action. The results showed that 4 could induce G2/M cell cycle arrest and was involved in the upregulation of p53 and p21 proteins. However, the mechanisms of growth inhibition by 11 c and 11 l were associated with G0/G1 cell cycle arrest and mediated by induction of oxidative stress.     

E.s.r. study of annealing and melting effects on the molecular motion of spin trapped chain-end radicals located on the polyethylene surface

E.s.r. spectra of chain-end spin labels on the surface of polyethylene powder were obtained for high and low density polyethylene samples at various stages of heat treatment process. The subsequent crystalline structures of the samples were examined with wide angle and small angle X-ray diffraction spectra. The effects of annealing on the motion of the labels were dependent on annealing temperature and the type of the samples. Higher temperature annealing decreased the rotational correlation times (τ_c) and their activation energy in high density polyethylene but did not affect those of low density polyethylene. Melting decreases the values of τ_c and ΔE for both high an low density polyethylene samples. The cause of these decreases were attributed to the changing of the sites of the chain-end labels. The motion of the labels appeared to be influenced by the local segmental motion of the polymer main chains.     

How amantadine and rimantadine inhibit proton transport in the M2 protein channel

To understand how antiviral drugs inhibit the replication of influenza A virus via the M2 ion channel, molecular dynamics simulations have been applied to the six possible protonation states of the M2 ion channel in free form and its complexes with two commercial drugs in a fully hydrated lipid bilayer. Among the six different states of free M2 tetramer, water density was present in the pore of the systems with mono-protonated, di-protonated at adjacent position, tri-protonated and tetra-protonated systems. In the presence of inhibitor, water density in the channel was considerably better reduced by rimantadine than amantadine, agreed well with the experimental IC(50) values. With the preferential position and orientation of the two drugs in all states, two mechanisms of action, where the drug binds to the opening pore and the histidine gate, were clearly explained, i.e., (i) inhibitor was detected to localize slightly closer to the histidine gate and can facilitate the orientation of His37 imidazole rings to lie in the close conformation and (ii) inhibitor acts as a blocker, binding at almost above the opening pore and interacts slightly with the three pore-lining residues, Leu26, Ala30 and Ser31. Here, the inhibitors were found to bind very weakly to the channel due to their allosteric hindrance while theirs side chains were strongly solvated.     

Optimal pretensioned forces for cable networks

A computer software package for the static and dynamic analyses of cable networks has been developed. The algorithm involves the Newton-Raphson method and Newmark's -method. The former iterative method takes care of the problem's nonlinearity, and the latter handles the time-marching scheme. In addition, an optimization subroutine based on the Neider and Mead Simplex method has been incorporated into the software to enable designers to determine the optimal design values of pretensioned forces leading to a stiffer cable network. The accuracy and convergence of the software were tested on some well-documented cable networks. Their optimal values of pretensioned forces for certain specified sets of loadings were also established.     

Preparation of new water‐soluble chitosan containing hyperbranched‐vinylsulfonic acid sodium salt and their antimicrobial activities and chelation with metals

In this work, an efficient and simple method to graft a vinylsulfonic acid sodium salt on a poorly water‐soluble chitosan is described. Commercially available low molecular weight chitosan is converted to water‐soluble chitosan containing hyperbranched‐vinylsulfonic acid sodium salt groups. The process comprises the following steps: Michael addition of methyl acrylate, amidation with ethylenediamine, and Michael addition of vinylsulfonic acid sodium salt. A variety of chitosans containing vinylsulfonic acid sodium salt, with improved water solubility, is synthesized by repeating these three steps. The new chitosan derivatives show better antimicrobial activity against Micrococcus luteus ATCC 10240 and Achromobacter xylosoxidans ATCC 2706. In addition, they display better chelating behavior with heavy metals, like cadmium(II), copper(II), and nickel(II), than the starting chitosan. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Modelling of wind load on single and staggered dual buildings

A method of modelling numerically the wind loads on single and staggered dual buildings using Computational Fluid Dynamics is presented in this paper. Simulation of a turbulent boundary layer over test models was carried out at the Supercomputing and Visualization Unit, the National University of Singapore, using FLUENT 6.1.18. Turbulence was introduced at the inlet through a parallel auxiliary simulation and the computation of the flow advanced in time using Large Eddy Simulation with a ReNormalization Group subgrid-scale viscosity model. Wind velocities at different locations and wind pressures on the building faces were recorded. Subsequently the flow characteristics were examined and the force and moment spectra deduced. The results were compared with data from earlier wind tunnel experiments carried out at Virginia Polytechnic Institute and State University. It can be concluded from the study that numerical wind modelling on tall structures is a promising alternative to conventional tests in atmospheric boundary layer wind tunnels.