Robustness in complex information systems: The role of information “barriers” in Boolean networks

In this supposed “information age,” a high premium is put on the widespread availability of information. Access to as much information as possible is often cited as key to the making of effective decisions. While it would be foolish to deny the central role that information and its flow has in effective decision‐making processes, this chapter explores the equally important role of “barriers” to information flows in the robustness of complex systems. The analysis demonstrates that (for simple Boolean networks at least) a complex system's ability to filter out, i.e., block, certain information flows is essential if it is not to be beholden to every external signal. The reduction of information is as important as the availability of information. © 2009 Wiley Periodicals, Inc. Complexity, 2010     

On a test statistic for the Kuramoto order parameter of synchronization: An illustration for group synchronization during rocking chairs

We discuss a quantitative approach to detect phase synchronization in noisy experimental multivariate data. To this end, we derive a test statistic based on the Kuramoto order parameter. We derive criteria for rejecting the null hypothesis of zero phase synchronization at given significance levels. We apply the test statistic to a recently conducted study on group behavior that used a rocking chair paradigm. In this context, we quantify the emergence of phase synchronization within small groups of participants.     

Parametric oscillator directly pumped by a 1.55-mum erbium-fiber laser

We report what is believed to be the first demonstration of an optical parametric oscillator directly pumped by the 1.55-mum output of an erbium-doped fiber laser. The oscillator, based on periodically poled lithium niobate, produced 8-muJ idler output near 3.8 mum at a 500-Hz repetition rate when it was pumped with 100-muJ 60-ns pulses at 1.55 mum . Temperature tuning of the 50-mm-long PPLN crystal gave signal and idler ranges of 2.55 to 2.7 mum and 3.65 to 3.96 mum , respectively, limited by mirror reflectivity. A signal-tuning range of 40 nm was observed for 13.5 nm of pump tuning with a fixed grating period and temperature. The optical parameter oscillator could be operated at low temperature with no sign of photorefractive damage.     

Wavelength-tunable high-power picosecond pulses from a fiber-pumped diode-seeded high-gain parametric amplifier

We describe a high-gain optical parametric amplifier (OPA) and optical parametric generator (OPG) system pumped by a fiber chirped-pulse amplification source based on novel large-mode-area fiber components. 45-nJ OPG thresholds and 34% pump-signal conversion efficiencies are obtained for ~4-ps pulses. OPA gains in excess of 75 dB and pump-signal conversion efficiencies of ~39% (external) are demonstrated. Furthermore, we show that injection seeding of such high-gain parametric devices by use of a low-power continuous-wave beam results in high-power (>18-kW) picosecond pulses with a time-bandwidth produce of ~0.65, some ten times less than from a free-running OPG. Using such an approach, we obtain 2.7-ps 50-nJ pulses at 1.310 mum .     

Complements to ‘The Bruhat order on symmetric varieties’

We give several complements to the paper The Bruhat order on symmetric varieties. Our main result shows that the partial order on the set of twisted involutions in the Weyl groupW, which was introduced in the earlier paper, agrees with the partial order on induced by the usual Bruhat order onW.R. W. Richardson died on 15 June. 1993.     

Using direct electrochemistry to probe rate limiting events during nitrate reductase turnover

Protein film voltammetry of NarGH catalysing nitrate reduction under steady state conditions provides information on events occurring within the enzyme during the catalytic cycle. In this discussion we have focused on exploring the ability of two simple catalytic schemes to reproduce the voltammetric response of NarGH; electron transfer to the enzyme's active site being described either by interfacial electron exchange (Scheme 1) or intramolecular electron delivery via the operation of an electron relay centre (Scheme 2). When the two electron reduced, catalytically competent active site of the enzyme is generated from the oxidised form in 'rapid', non-rate limiting steps of the catalytic cycle, the voltammetric behaviour of NarGH cannot be reproduced. Rather under all the conditions investigated, one electron reduction of the active site from a semi-reduced to a fully-reduced state is found to be crucial to progression through the enzyme's catalytic cycle. The catalytically relevant semi- and fully-reduced oxidation states of the NarGH active site are most likely to correspond to the Mo(V) and Mo(IV) states of the Mo(MGD)2 centre, respectively, although it is not possible to rule out the possibility that they correspond to molybdopterin based oxidation states as observed in other enzymes. We suggest that the rate of either conformational rearrangement within the semi-reduced active site or intramolecular electron delivery to the active site constitutes a defining feature in the catalytic cycle of NarGH and results in the napp approximately 1 appearance of the catalytic waveform.     

Keto-alkyne cyclisation reactions: heterocyclic prostacyclin analogues

Simple furan, thiophene and pyrrole analogues of prostacyclin have been prepared from readily-available 4-alkvnyl ketones; the cyclohexa[b]-furano-prostacyclin analogue $\text{3}$ has also been synthesised using the keto-alkyne cyclisation procedure.     

A comparative investigation into the effect of chronic alcohol feeding on the myocardium of normotensive and hypertensive rats: an electrophoretic and biochemical study

We investigated whether the imposition of chronic alcohol in hypertension leads to greater biochemical and cellular abnormalities of the myocardium than those arising in normotension. Fifteen-week-old spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) rats were fed ethanol-containing diets for six weeks. Particular attention was focused on the composition of contractile proteins identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), fractional rate of protein synthesis, and synthesis rates relative to RNA (RNA activity) or DNA (cellular efficiency). In addition, myocardial enzymes and adenine nucleotides were measured. In both SHR and WKY rats chronic ethanol caused a general decrease in the contents of all nine contractile proteins with myosin heavy chain predominantly affected. Fractional rates of mixed (i.e., total) and myofibrillary proteins remained unaltered in both WKY rats and SHR, as were cellular efficiencies. The RNA activity was significantly reduced in ethanol-treated SHR but not in WKY rats. In ethanol-treated SHR, cardiac creatine kinase (CK) and malate dehydrogenase (MDH) activities were increased, AMP levels were elevated, whilst ATP levels and the energy charge were reduced. In WKY rats, the only significant change related to increased aspartate aminotransferase activities in response to alcohol feeding. Although there were only subtle differences between the response of the normotensive and hypertensive rats due to ethanol dosage, the reduced ATP levels and increased CK and MDH activities in SHR may reflect a greater susceptibility to ischaemic damage. Reduced contractile protein content, particularly myosin heavy chain, may contribute to contractile defects, a common feature of subclinical and clinical alcoholic cardiomyopathy.     

Aging and degradation of polyolefins. III. Polyethylene and ethylene–propylene copolymers

Rates of oxygen absorption and formation of oxidation products were determined in γ-initiated oxidations of thin films of high- and low-density polyethylene, atactic and isotactic polypropylene, and of three ethylene–propylene copolymers. Radiation yields G for O₂ absorbed and formation of hydroperoxides depend on dose rates and decrease sharply with increasing ethylene content of the copolymers and moderately with increasing crystallinity of any base polymer. G values for dialkyl peroxide and carbonyl formation, and therefore for chain initiation and termination, do not change much with polymer composition and crystallinity and not at all with dose rates. A few experiments with atactic polypropylene and an amorphous ethylene–propylene copolymer, initiated by di-tert-butylperoxy oxalate, indicate that 37 mole-% of ethylene in the polymer increases the efficiency of initiation and the tendency toward crosslinking.