Lock Yue Chew

The Toxicity of Amyloid ß Oligomers

In this review, we elucidate the mechanisms of Aβ oligomer toxicity which may contribute to Alzheimer’s disease (AD). In particular, we discuss on the interaction of Aβ oligomers with the membrane through the process of adsorption and insertion. Such interaction gives rises to phase transitions in the sub-structures of the Aβ peptide from α-helical to β-sheet structure. By means of a coarse-grained model, we exhibit the tendency of β-sheet structures to aggregate, thus providing further insights to the process of membrane induced aggregation. We show that the aggregated oligomer causes membrane invagination, which is a precursor to the formation of pore structures and ion channels. Other pathological progressions to AD due to Aβ oligomers are also covered, such as their interaction with the membrane receptors, and their direct versus indirect effects on oxidative stress and intraneuronal accumulation. We further illustrate that the molecule curcumin is a potential Aβ toxicity inhibitor as a β-sheet breaker by having a high propensity to interact with certain Aβ residues without binding to them. The comprehensive understanding gained from these current researches on the various toxicity mechanisms show promises in the provision of better therapeutics and treatment strategies in the near future.

The Effect of Curcumin on the Stability of Aβ Dimers

Aβ oligomers are potential targets for the diagnosis and therapy of Alzheimers disease (AD). On the other hand, the molecule curcumin has been shown to possess significant therapeutic potential in many areas. In this paper, we use all-atom explicit solvent molecular dynamics simulations to study the effect of curcumin on the stability of Aβ amyloid protein oligomers. We observed that curcumin decreases the β-sheet secondary structural content within the Aβ oligomers without reducing the contacts between the monomers. The breaking of the β-sheet is found to be preceded by a deformation of the β-sheet structure due to hydrophobic interaction from the nearby curcumin. Furthermore, the π-stacking interaction between curcumin (keto ring and enol ring) and the aromatic residues of Aβ, which exists throughout the simulations, has also contributed to the diminishing of the β-sheet structure. Our analysis of the underwrapped amide-carbonyl hydrogen bonds reveals several stable dehydrons of the oligomer, especially the dehydron pair 34L and 41I, which curcumin tends to hover over. We have examined the paths of curcumin on the Aβ proteins and determined the common routes where curcumin lingers as it traverses around the Aβ. In consequence, our study has provided a detailed interaction picture between curcumin and the Aβ oligomers.

Dynamics of relativistic electrons propagating in a funnel-guided target

Hot electron transport in a funnel-guided target is investigated using two-dimensional hybrid simulations. Relativistic electrons generated by a petawatt picosecond short-pulse laser interacting with a gold slab are guided by a funnel to the compressed core region of the fuel. It is shown that as the energetic electrons propagate into the compressed core, the interface magnetic fields in the inner and outer surfaces of the funnel can change sign so that the fast electrons are efficiently guided in the gold funnel to reach the dense core. It is also shown that with funnel guiding, fuel heating is enhanced compared to that without the funnel. The findings here may be useful in the design of more efficient fast-ignition schemes, as well as in other applications involving transport and heating of energetic electrons in targets.

The Abelian Manna model on various lattices in one and two dimensions

We perform a high-accuracy moment analysis of the avalanche size, duration and area distribution of the Abelian Manna model on eight two-dimensional and four one-dimensional lattices. The results provide strong support for establishing universality of exponents and moment ratios across different lattices and a good survey for the strength of corrections to scaling which are notorious in the Manna universality class. The results are compared against previous work done on the Manna model, Oslo model and directed percolation. We also confirm various scaling relations.

Propagation of energetic electrons in a hollow plasma fiber

Transport of energetic electrons in a hollow plasma fiber is investigated. The high-current electron beam induces in the fiber strong radial electric fields and azimuthal magnetic fields on the inner and outer surfaces of the hollow fiber. The hot electrons are pushed out by the surface magnetic field and returned into the fiber by the sheath electric field. Imbalance of the latter fields can drive chaotic oscillations of electrons around the fiber wall. Intense thin return-current layers inside both the inner and outer wall surfaces are observed. This enhances local joule heating around both surfaces by the return current.

Error Correction With Chaotic Switching Between Convolutional Codecs

In this paper, a heterogeneous channel-coding scheme that combines a convolutional codec and a chaotic system into a single unit is proposed. The goal is to achieve a new coding technique that possesses the dual features of error correction and encryption. The proposed system is able to achieve reasonable error-correction performance when made to switch between optimal configurations. Its increased complexity makes it more secure relative to the conventional systems. Two additional systems that employ different chaotic switching methods are also proposed and studied. The investigation reveals the existence of tradeoffs between error-correction capability and the complexity of these systems.

Alzheimer’s Disease—A Panorama Glimpse

The single-mutation of genes associated with Alzheimer’s disease (AD) increases the production of Aβ peptides. An elevated concentration of Aβ peptides is prone to aggregation into oligomers and further deposition as plaque. Aβ plaques and neurofibrillary tangles are two hallmarks of AD. In this review, we provide a broad overview of the diverses sources that could lead to AD, which include genetic origins, Aβ peptides and tau protein. We shall discuss on tau protein and tau accumulation, which result in neurofibrillary tangles. We detail the mechanisms of Aβ aggregation, fibril formation and its polymorphism. We then show the possible links between Aβ and tau pathology. Furthermore, we summarize the structural data of Aβ and its precursor protein obtained via Nuclear Magnetic Resonance (NMR) or X-ray crystallography. At the end, we go through the C-terminal and N-terminal truncated Aβ variants. We wish to draw reader’s attention to two predominant and toxic Aβ species, namely Aβ4−42/ and pyroglutamate amyloid-beta peptides, which have been neglected for more than a decade and may be crucial in Aβ pathogenesis due to their dominant presence in the AD brain.

Bistability and chaos at low levels of quanta.

We study nonlinear phenomena of bistability and chaos at a level of few quanta. For this purpose, we consider a single-mode dissipative oscillator with strong Kerr nonlinearity with respect to the dissipation rate driven by a monochromatic force as well as by a train of Gaussian pulses. The quantum effects and decoherence in the oscillatory mode are investigated in the framework of the purity of states and the Wigner functions calculated from the master equation. We demonstrate the quantum chaotic regime by means of a comparison between the contour plots of the Wigner functions and the strange attractors on the classical Poincaré section. Considering bistability at a low limit of quanta, we analyze the minimal level of excitation numbers at which the bistable regime of the system is displayed. We also discuss the formation of an oscillatory chaotic regime by varying oscillatory excitation numbers at ranges of a few quanta. We demonstrate quantum-interference phenomena that are assisted hysteresis-cycle behavior and quantum chaos for the oscillator driven by a train of Gaussian pulses. We establish the border of quantum-classical correspondence for chaotic regimes in the case of strong nonlinearities.

Microscopic Chaos and Gaussian Diffusion Processes

In this paper, we construct and analyze a prototypical model of microscopic chaos. In particular, we extend the results of Beck and Shimizu to the case where the microscopic time scale τ is no longer small. The upshot is that a non-Ornstein–Uhlenbeck deterministic process can generate a Gaussian diffusion process.

Regime Shifts in Balinese Subaks

Ecosystems may undergo nonlinear responses to stresses or perturbations. Hence there can be more than one stable state or regime. It is not known whether alternate regimes also occur in coupled social-ecologica-l systems, in which there is the potential for intricate feedbacks between natural and social processes. To find out, we investigated the management of rice paddies by Balinese farmers, where ecological processes impose constraints on the timing and spatial scale of collective action. We investigated responses to environmental and social conditions by eight traditional community irrigation systems (subaks) along a river in Bali to test the intuition that older and more demographically stable subaks function differently than those with less stable populations. Results confirm the existence of two attractors, with sharply contrasting patterns of social and ecological interactions. The transition pathway between the two basins of attraction is dominated by differences in the efficacy of sanctions and the ability of subaks to mobilize agricultural labor.