Mixed Silane-based Self-assembled Monolayers Deposited on Fluorine Doped Tin Oxide as Model System for Development of Biosensors for Toxin Detection

In this work mixed hybrid phospholipid bilayers (mhBLM) were deposited on fluorine doped tin oxide (FTO) films. Two component silane-based self-assembled monolayers (SAMs) formed on FTO surface trigger vesicle fusion and formation of mhBLMs which are stable, can be easily regenerated, and therefore, used for multiple experiments. We found that certain chemical and physical conditions under which mixed SAMs are fabricated translate into functional properties of mhBLMs. In all cases we observed interaction of melittin with mhBLMs demonstrating biological relevance of these biomimetic surface constructs and their possible application in biosensors for toxin detection.     

A New Fourier Truncated Regularization Method for Semilinear Backward Parabolic Problems

We study the backward problem for non-linear (semilinear) parabolic partial differential equations in Hilbert spaces. The problem is severely ill-posed in the sense of Hadamard. Under a weak a priori assumption on the exact solution, we propose a new Fourier truncated regularization method for stabilising the ill-posed problem. In comparison with previous studies on solving the nonlinear backward problem, our method shows a significant improvement.     

Comparative Hydrophobic Core Dynamics Between Wild-Type Amyloid-β Fibrils,Glutamate-3 Truncation,and Serine-8 Phosphorylation

Post-translational modifications (PTMs) of amyloid-β (Aβ) species are implicated in the modulation of overall toxicities and aggregation propensities. We investigated the internal dynamics in the hydrophobic core of the truncated ΔE3 mutant fibrils of Aβ_1–40 and compared them with prior and new data for wild-type fibrils as well as with phosphorylated S8 fibrils. Deuteron static solid-state NMR techniques, spanning line-shape analysis, longitudinal relaxation, and chemical exchange saturation transfer methods, were employed to assess the rotameric jumps of several methyl-bearing and aromatic groups in the core of the fibrils. Taken together, the results indicate the rather significant influence of the PTMs on the hydrophobic core dynamics, which propagates far beyond the local site of the chemical modification. The phosphorylated S8 fibrils display an overall rigidifying of the core based on the higher activation barriers of motions than the wild-type fibrils, whereas the ΔE3 fibrils induce a broader variety of changes, some of which are thermodynamic in nature rather than the kinetic ones.     

Predicting overflow in an emergency department

G. B. Byrnes Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, Department of Public Health, The University of Melbourne, Victoria, Australia C. A. Bain Directorate Office, Western and Central Melbourne Integrated Cancer Service, Victoria, Australia M. Fackrell Department of Mathematics and Statistics, The University of Melbourne, Victoria, Australia C. Brand Clinical Epidemiology and Health Service Evaluation Unit, Melbourne Health, Victoria, Australia D. A. Campbell Department of Medicine, Southern Clinical School, Monash University, Victoria, Australia P. G. Taylor Department of Mathematics and Statistics, The University of Melbourne, Victoria, Australia Email: l.au{at}ms.unimelb.edu.au Received on 9 October 2007. Accepted on 4 February 2008. Ambulance bypass occurs when the emergency department (ED) ofa hospital becomes so busy that ambulances are requested totake their patients elsewhere, except in life-threatening cases.It is a major concern for hospitals in Victoria, Australia,and throughout most of the western world, not only from thepoint of view of patient safety but also financially—hospitalslose substantial performance bonuses if they go on ambulancebypass too often in a given period. We show that the main causeof ambulance bypass is the inability to move patients from theED to a ward. In order to predict the onset of ambulance bypass,the ED is modelled as a queue for treatment followed by a queuefor a ward bed. The queues are assumed to behave as inhomogeneousPoisson arrival processes. We calculate the probability of reachingsome designated capacity C within time t, given the currenttime and number of patients waiting.     

On the polyhedral lift-and-project methods and the fractional stable set polytope

We study two polyhedral lift-and-project operators (originally proposed by Lovász and Schrijver in 1991) applied to the fractional stable set polytopes. First, we provide characterizations of all valid inequalities generated by these operators. Then, we present some seven-node graphs on which the operator enforcing the symmetry of the matrix variable is strictly stronger on the odd-cycle polytope of these graphs than the operator without this symmetry requirement. This disproves a conjecture of Lipták and Tunçel from 2003.     

Unambiguous determination of the ionization state of a glycoside hydrolase active site lysine by 1H-15N heteronuclear correlation spectroscopy

We have investigated the lysine side chain amines in the 34 kDa catalytic domain from Cellulomonas fimi beta-(1,4)-glycosidase Cex (or CfXyn10A) using 1H-detected 15N heteronuclear correlation NMR spectroscopy. Signals from the 1Hzeta ( approximately 8 ppm) and 15Nzeta ( approximately 35 ppm) of Lys302 in the unmodified enzyme and Lys47 in a trapped cellobiosyl-enzyme intermediate were detected in a 1H-15N HMQC spectrum (pH 6.5 and 30 degrees C). The amine of Lys302 forms a buried ion pair, and that of Lys47 is hydrogen bonded to the cellobioside. Both lysines are positively charged, as unambiguously demonstrated by the splitting of their 15Nzeta signals into quartets (|1JNH| approximately 75 Hz) in a 1H-15N HSQC spectrum recorded without 1H decoupling during 15N evolution. Qualitative insights into the dynamic properties of these lysines are also provided by the deviations of their quartet intensity ratios from that of approximately 3:1:1:3 expected for a highly mobile amine. On the basis of the observed ratios of approximately 1:1:1:1 for the quartet of Lys302 and approximately 0.5:1:1:0.5 for Lys47, the amine of the latter active site residue is most rigidly positioned. Signals from at least 8 and 10 additional positively charged, mobile amines in Cex were observed at 10 degrees C and pH 6.5 and 5.6, respectively. By using conditions of reduced temperature, slightly acidic pH, and low general base concentrations, as well as water flipback pulses to minimize the effects of hydrogen exchange, 1H-15N correlation experiments provide a sensitive route to directly investigate the charge states and dynamic properties of the N-terminal and side chain amines in proteins and protein complexes.     

The spatial context of free-ranging Hawaiian spinner dolphins (Stenella longirostris) producing acoustic signals

To improve our understanding of how dolphins use acoustic signals in the wild, a three-hydrophone towed array was used to investigate the spatial occurrence of Hawaiian spinner dolphins (Stenella longirostris) relative to each other as they produced whistles, burst pulses, and echolocation clicks. Groups of approximately 30 to 60 animals were recorded while they traveled and socialized in nearshore waters off Oahu, Hawaii. Signaling animals were localized using time of arrival difference cues on the three channels. Sequences of whistles occurred between dolphins separated by significantly greater distances than animals producing burst pulses. Whistles typically originated from dolphins spaced widely apart (median = 23 m), supporting the hypothesis that whistles play a role in maintaining contact between animals in a dispersed group. Burst pulses, on the other hand, usually came from animals spaced closer to one another (median = 14 m), suggesting they function as a more intimate form of signaling between adjacent individuals. The spacing between echolocating animals was more variable and exhibited a bimodal distribution. Three quarters of echolocating animals were separated by 10 m or more, suggesting that the task of vigilance in a pod may not be shared equally by all members at all times.