A systematic analysis of the role of GGDEF-EAL domain proteins in virulence and motility in Xanthomonas oryzae pv. oryzicola

The second messenger c-di-GMP is implicated in regulation of various aspects of the lifestyles and virulence of Gram-negative bacteria. Cyclic di-GMP is formed by diguanylate cyclases with a GGDEF domain and degraded by phosphodiesterases with either an EAL or HD-GYP domain. Proteins with tandem GGDEF-EAL domains occur in many bacteria, where they may be involved in c-di-GMP turnover or act as enzymatically-inactive c-di-GMP effectors. Here, we report a systematic study of the regulatory action of the eleven GGDEF-EAL proteins in Xanthomonas oryzae pv. oryzicola, an important rice pathogen causing bacterial leaf streak. Mutational analysis revealed that XOC_2335 and XOC_2393 positively regulate bacterial swimming motility, while XOC_2102, XOC_2393 and XOC_4190 negatively control sliding motility. The ΔXOC_2335/XOC_2393 mutant that had a higher intracellular c-di-GMP level than the wild type and the ΔXOC_4190 mutant exhibited reduced virulence to rice after pressure inoculation. In vitro purified XOC_4190 and XOC_2102 have little or no diguanylate cyclase or phosphodiesterase activity, which is consistent with unaltered c-di-GMP concentration in ΔXOC_4190. Nevertheless, both proteins can bind to c-di-GMP with high affinity, indicating a potential role as c-di-GMP effectors. Overall our findings advance understanding of c-di-GMP signaling and its links to virulence in an important rice pathogen.

Social paranoia and absurdist fiction in Cold War America and Soviet Russia: a comparative study

This thesis explores the theme of social paranoia as depicted in the Absurdist fiction of Cold War America and Soviet Russia. The central hypothesis informing this research maintains that, despite the ideology of moral and cultural “Otherness” constructed and reinforced by both nations throughout much of twentieth century, the US and the Soviet Union more often than not functioned as mirror images of paranoia and suspicion. Much of the fiction produced in Russia from the Revolution onwards and in the US during the Cold War period highlights how these two ostensibly irreconcilable nations were consumed by similar fears and gripped by an equally pervasive paranoia. These parallel conditions of anxiety and mistrust led to a surprising congruity of literary responses, which transcended the ideological divide between capitalism and communism and, as such, underscored the homogeny of fear which lay beneath the façade of constructed difference. I contend that, because Soviet Russia and the America of the Cold War period were nations consumed by fear and suspicion, authors living in both countries became preoccupied by the mechanics of such deeply paranoid societies. Consequently, much of the fiction of the US and the Soviet Union during this period was preoccupied with the themes of paranoia, conspiracy, intensive bureaucracy and the politicisation of science, which resulted in the terror of the Nuclear Age. This thesis explores how these central themes unite apparently diverse literary texts and illustrate the uniformity of terror which transcended both the physical and ideological boundaries separating the United States and the Soviet Union. In doing so, this research focuses primarily on the multi-faceted manifestations of paranoia in selected works by Soviet authors Mikhail Bulgakov, Daniil Kharms and Yuli Daniel, and American authors Joseph Heller, Thomas Pynchon and Kurt Vonnegut. Focusing on key works by each author, this research considers these texts as products of two culturally diverse, yet equally paranoid societies and explores their preoccupation with issues of spying, infiltration and conspiracy. This thesis thus emphasises how these authors counter simplistic notions of Cold War Otherness by revealing two nations possessed by a similar sense of vulnerability and insecurity. Furthermore, this thesis examines how this social anxiety is reinforced by the way in which these authors position issues such as the mechanics of the bureaucratic system and clandestine scientific experimentation as the focal point of the paranoid imagination. Ultimately, by examining the concordance of paranoiac representation in America and the Soviet Union during this period, I demonstrate that these ostensibly divergent nations harboured similar fears and insecurities.

Surface quality and surface waves on subwavelength-structured silver films

We analyze the physical-chemical surface properties of single-slit, single-groove subwavelength-structured silver films with high-resolution transmission electron microscopy and calculate exact solutions to Maxwell’s equations corresponding to recent far-field interferometry experiments using these structures. Contrary to a recent suggestion the surface analysis shows that the silver films are free of detectable contaminants. The finite-difference time-domain calculations, in excellent agreement with experiment, show a rapid fringe amplitude decrease in the near zone (slit-groove distance out to 3–4 wavelengths). Extrapolation to slit-groove distances beyond the near zone shows that the surface wave evolves to the expected bound surface plasmon polariton (SPP). Fourier analysis of these results indicates the presence of a distribution of transient, evanescent modes around the SPP that dephase and dissipate as the surface wave evolves from the near to the far zone.

Wave energy conversion of oscillating water column devices including air compressibility

This paper presents an investigation on air compressibility in the air chamber and its effects on the power conversion of oscillating water column (OWC) devices. As it is well known that for practical OWC plants, their air chambers may be large enough for accommodating significant air compressibility, the “spring effect,” an effect that is frequently and simply regarded to store and release energy during the reciprocating process of a wave cycle. Its insight effects on the device’s performance and power conversion, however, have not been studied in detail. This research will investigate the phenomena with a special focus on the effects of air compressibility on wave energy conversion. Air compressibility itself is a complicated nonlinear process in nature, but it can be linearised for numerical simulations under certain assumptions for frequency domain analysis. In this research work, air compressibility in the OWC devices is first linearised and further coupled with the hydrodynamics of the OWC. It is able to show mathematically that in frequency-domain, air compressibility can increase the spring coefficients of both the water body motion and the device motion (if it is a floating device), and enhance the coupling effects between the water body and the structure. Corresponding to these changes, the OWC performance, the capture power, and the optimised Power Take-off (PTO) damping coefficient in the wave energy conversion can be all modified due to air compressibility. To validate the frequency-domain results and understand the problems better, the more accurate time-domain simulations with fewer assumptions have been used for comparison. It is shown that air compressibility may significantly change the dynamic responses and the capacity of converting wave energy of the OWC devices if the air chamber is very large.