Exploring molecular recognition pathways in one- and two-component gels formed by dendritic lysine-based gelators

This paper provides an integrated overview of the factors which control gelation in a family of dendritic gelators based on lysine building blocks. In particular, we establish that higher generation systems are more effective gelators, amide linkages in the dendron are better than carbamates, and long alkyl chain surface groups and a carboxylic acid at the focal point enhance gelation. The gels are best formed in relatively low polarity solvents with no hydrogen bond donor ability and limited hydrogen bond acceptor capacity. The dendrons with acid groups at the focal point can form two component gels with diaminododecane, and in this case, it is the lower generation dendrons which can avoid steric hindrance and form more effective gels. The stereochemistry of lysine is crucial in self-assembly, with opposite enantiomers disrupting each other's molecular recognition pathways. For the two-component system, stoichiometry is key, if too much diamine is present, dendron-stabilised microcrystals of the diamine begin to form. Interestingly, gelation still occurs in this case, and the systems with amides/alkyl chains are more effective gels, as a consequence of enhanced dendron-dendron intermolecular interactions allowing the microcrystals to form an interconnected network.

Role of the two-component regulator CpxAR in the virulence of Salmonella entetica serotype typhimurium

The CpxAR (Cpx) two-component regulator controls the expression of genes in response to a variety of environmental cues. The Cpx regulator has been implicated in the virulence of several gram-negative pathogens, although a role for Cpx in vivo has not been demonstrated directly. Here we investigate whether positive or negative control of gene expression by Cpx is important for the pathogenesis of Salmonella enterica serotype Typhimurium. The Cpx signal pathway in serotype Typhimurium was disrupted by insertional inactivation of the cpxA and cpxR genes. We also constitutively activated the Cpx pathway by making an internal in-frame deletion in cpxA (a cpxA* mutation). Activation of the Cpx pathway inhibited induction of the envelope stress response pathway controlled by the alternative sigma factor sigma(E) (encoded by rpoE). Conversely, the Cpx pathway was highly up-regulated (>40-fold) in a serotype Typhimurium rpoE mutant. The cpxA* mutation, but not the cpxA or the cpxR mutation, significantly reduced the capacity of serotype Typhimurium to adhere to and invade eucaryotic cells, although intracellular replication was not affected. The cpxA and cpxA* mutations significantly impaired the ability of serotype Typhimurium to grow in vivo in mice. To our knowledge, this is the first demonstration that the Cpx system is important for a bacterial pathogen in vivo.

Analysis of Two Component Systems in Group B Streptococcus Shows that RgfAC and the Novel FspSR Modulate Virulence and Bacterial Fitness

Group B Streptococcus (GBS), in its transition from commensal to pathogen, will encounter diverse host environments and thus require coordinately controlling its transcriptional responses to these changes. This work was aimed at better understanding the role of two component signal transduction systems (TCS) in GBS pathophysiology through a systematic screening procedure. We first performed a complete inventory and sensory mechanism classification of all putative GBS TCS by genomic analysis. Five TCS were further investigated by the generation of knock-out strains, and in vitro transcriptome analysis identified genes regulated by these systems, ranging from 0.1-3% of the genome. Interestingly, two sugar phosphotransferase systems appeared differently regulated in the knock-out mutant of TCS-16, suggesting an involvement in monitoring carbon source availability. High throughput analysis of bacterial growth on different carbon sources showed that TCS-16 was necessary for growth of GBS on fructose-6-phosphate. Additional transcriptional analysis provided further evidence for a stimulus-response circuit where extracellular fructose-6-phosphate leads to autoinduction of TCS-16 with concomitant dramatic up-regulation of the adjacent operon encoding a phosphotransferase system. The TCS-16-deficient strain exhibited decreased persistence in a model of vaginal colonization and impaired growth/survival in the presence of vaginal mucoid components. All mutant strains were also characterized in a murine model of systemic infection, and inactivation of TCS-17 (also known as RgfAC) resulted in hypervirulence. Our data suggest a role for the previously unknown TCS-16, here named FspSR, in bacterial fitness and carbon metabolism during host colonization, and also provide experimental evidence for TCS-17/RgfAC involvement in virulence.

Complex Oscillations and Limit Cycles in Autonomous Two-Component Incommensurate Fractional Dynamical Systems

MSC 2010: 26A33, 34D05, 37C25

Butterfly catastrophe for fronts in a three-component reaction–diffusion system

We study the dynamics of front solutions in a three-component reaction–diffusion system via a combination of geometric singular perturbation theory, Evans function analysis, and center manifold reduction. The reduced system exhibits a surprisingly complicated bifurcation structure including a butterfly catastrophe. Our results shed light on numerically observed accelerations and oscillations and pave the way for the analysis of front interactions in a parameter regime where the essential spectrum of a single front approaches the imaginary axis asymptotically.

Enhancing somatic embryogenesis in avocado (Persea americana Mill.) using a two-step culture system and including glutamine in the culture medium

The development of a more efficient in vitro regeneration system for somatic embryos (SEs) of avocado (Persea americana) would facilitate the development of new superior cultivars for this valuable horticultural crop. In this study, we report a new and efficient method for maintenance and regeneration of avocado SEs. Avocado SEs of four cultivars remained healthy and viable in vitro for 11 months on a medium used for mango somatic embryogenesis, compared with 3-4 months on Murashige and Skoog medium. Various supplements and media modifications were investigated to improve the low conversion rate of regenerated plants from avocado SEs reported previously. The one-step system for regeneration of white-opaque somatic embryos (WOSEs) used solid medium only over a period of 12-14 weeks (sub-culturing every 6 weeks). Addition of praline and glutamine improved the total regeneration from 0 to 17.5% and 10.5%, and plant/shoot recovery from 0 to 12.5% and 5%, respectively. A two-step culture system involving the transfer of WOSEs of cultivar 'Reed' after 6 weeks on solid to liquid medium for 12-15 days as an intermediate step, followed by subculturing again onto solid medium for 6 weeks improved total regeneration to 29% and plant/shoot recovery to 18.3 from 0% when regenerated by subculturing on solid medium only. Supplementation with proline in the solid as well as liquid medium in the two-step culture system at 0.4 g/L increased total regeneration to 35% and plant/shoot recovery to 20%. We were able to achieve highest regeneration using glutamine at 1 g/L in the two-step culture system in terms of both total regeneration (58.3%, including 43.3% bipolar regeneration) and plant/shoot recovery (36.7%) rates, which were significantly higher than in any other treatment investigated. (C) 2013 Elsevier B.V. All rights reserved.

Cell-dynamical simulation of magnetic hysteresis in the two-dimensional Ising system

We present results from numerical simulations using a ‘‘cell-dynamical system’’ to obtain solutions to the time-dependent Ginzburg-Landau equation for a scalar, two-dimensional (2D), (Φ2)2 model in the presence of a sinusoidal external magnetic field. Our results confirm a recent scaling law proposed by Rao, Krishnamurthy, and Pandit [Phys. Rev. B 42, 856 (1990)], and are also in excellent agreement with recent Monte Carlo simulations of hysteretic behavior of 2D Ising spins by Lo and Pelcovits [Phys. Rev. A 42, 7471 (1990)].

Unconventional metallicity and giant thermopower in a strongly interacting two-dimensional electron system

We present thermal and electrical transport measurements of low-density (10(14) m(-2)), mesoscopic two-dimensional electron systems (2DESs) in GaAs/AlGaAs heterostructures at sub-Kelvin temperatures. We find that even in the supposedly strongly localized regime, where the electrical resistivity of the system is two orders of magnitude greater than the quantum of resistance h/e(2), the thermopower decreases linearly with temperature indicating metallicity. Remarkably, the magnitude of the thermopower exceeds the predicted value in noninteracting metallic 2DESs at similar carrier densities by over two orders of magnitude. Our results indicate a new quantum state and possibly a novel class of itinerant quasiparticles in dilute 2DESs at low temperatures where the Coulomb interaction plays a pivotal role.

Excellent chirality transcription in two-component photochromic organogels assembled through J-aggregation

Organogels made of pyridine-end oligo-p-phenylenevinylenes with tartaric acid exhibit remarkable J-aggregation induced red-shifts (Dk = 55 nm) and notable chirality transcription. Induction of liquid-crystalline behavior is also tuned in the supramolecular assembly.

Evidence of novel quasiparticles in a strongly interacting two-dimensional electron system: giant thermopower and metallic behaviour

We report thermopower (S) and electrical resistivity (rho (2DES) ) measurements in low-density (10(14) m(-2)), mesoscopic two-dimensional electron systems (2DESs) in GaAs/AlGaAs heterostructures at sub-Kelvin temperatures. We observe at temperatures a parts per thousand(2)0.7 K a linearly growing S as a function of temperature indicating metal-like behaviour. Interestingly this metallicity is not Drude-like, showing several unusual characteristics: (i) the magnitude of S exceeds the Mott prediction valid for non-interacting metallic 2DESs at similar carrier densities by over two orders of magnitude; and (ii) rho (2DES) in this regime is two orders of magnitude greater than the quantum of resistance h/e (2) and shows very little temperature-dependence. We provide evidence suggesting that these observations arise due to the formation of novel quasiparticles in the 2DES that are not electron-like. Finally, rho (2DES) and S show an intriguing decoupling in their density-dependence, the latter showing striking oscillations and even sign changes that are completely absent in the resistivity.

Inference for the Component and System Lifetime Distribution of a k-unit Parallel System Based on System Data

In this paper, we consider the inference for the component and system lifetime distribution of a k-unit parallel system with independent components based on system data. The components are assumed to have identical Weibull distribution. We obtain the maximum likelihood estimates of the unknown parameters based on system data. The Fisher information matrix has been derived. We propose -expectation tolerance interval and -content -level tolerance interval for the life distribution of the system. Performance of the estimators and tolerance intervals is investigated via simulation study. A simulated dataset is analyzed for illustration.

The two-component signalling networks of Mycobacterium tuberculosis display extensive cross-talk in vitro

Two-component systems (TCSs), which contain paired sensor kinase and response regulator proteins, form the primary apparatus for sensing and responding to environmental cues in bacteria. TCSs are thought to be highly specific, displaying minimal cross-talk, primarily due to the co-evolution of the participating proteins. To assess the level of cross-talk between the TCSs of Mycobacterium tuberculosis, we mapped the complete interactome of the M. tuberculosis TCSs using phosphotransfer profiling. Surprisingly, we found extensive crosstalk among the M. tuberculosis TCSs, significantly more than that in the TCSs in Escherichia coli or Caulobacter crescentus, thereby offering an alternate to specificity paradigm in TCS signalling. Nearly half of the interactions we detected were significant novel cross-interactions, unravelling a potentially complex signalling landscape. We classified the TCSs into specific `one-to-one' and promiscuous `one-to-many' and `many-to-one' circuits. Using mathematical modelling, we deduced that the promiscuous signalling observed can explain several currently confounding observations about M. tuberculosis TCSs. Our findings suggest an alternative paradigm of bacterial signalling with significant cross-talk between TCSs yielding potentially complex signalling landscapes.

Validity ranges of interfacial wave theories in a two-layer fluid system

In the present paper, we endeavor to accomplish a diagram, which demarcates the validity ranges for interfacial wave theories in a two-layer system, to meet the needs of design in ocean engineering. On the basis of the available solutions of periodic and solitary waves, we propose a guideline as principle to identify the validity regions of the interfacial wave theories in terms of wave period T, wave height H, upper layer thickness d(1), and lower layer thickness d(2), instead of only one parameter-water depth d as in the water surface wave circumstance. The diagram proposed here happens to be Le Mehautes plot for free surface waves if water depth ratio r = d(1)/d(2) approaches to infinity and the upper layer water density rho(1) to zero. On the contrary, the diagram for water surface waves can be used for two-layer interfacial waves if gravity acceleration g in it is replaced by the reduced gravity defined in this study under the condition of sigma = (rho(2) - rho(1))/rho(2) -> 1.0 and r > 1.0. In the end, several figures of the validity ranges for various interfacial wave theories in the two-layer fluid are given and compared with the results for surface waves.

Regulatory quality and the regulatory system in the UK

Busca identificar como o sistema regulatório britânico se desenvolveu nos últimos anos contribuindo para a melhoria da regulação no país. Aborda o tema da qualidade legislativa no Reino Unido.