Isolation, characterisation and experimental evolution of phage that infect the horse chestnut tree pathogen, Pseudomonas syringae pv. aesculi

Bleeding canker of horse chestnut trees is a bacterial disease, caused by the bacterium Pseudomonas syringae pv. aesculi, estimated to be present in ~ 50% of UK horse chestnut trees. Currently, the disease has no cure and tree removal can be a common method of reducing inoculum and preventing spread. One potential method of control could be achieved using naturally occurring bacteriophages infective to the causative bacterium. Bacteriophages were isolated from symptomatic and asymptomatic horse chestnut trees in three locations in the South East of England. The phages were found to be belonging to both the Myoviridae and Podoviridae families by RAPD PCR and transmission electron microscopy. Experimental coevolution was carried out to understand the dynamics of bacterial resistance and phage infection and to determine whether new infective phage genotypes would emerge. The phages exhibited different coevolution patterns with their bacterial hosts across time. This approach could be used to generate novel phages for use in biocontrol cocktails in an effort to reduce the potential emergence of bacterial resistance

A Transition in Potassium Superoxide

During the study of the magnetic properties [1] of potassium superoxide, KO2, I noticed that on cooling in liquid air the substance changes from a deep orange to a light cream color. In order to see whether or not this change in color accompanies a transition from one form to another, the following experiments were carried out

Elevated temperature mechanical properties of zirconium diboride based ceramics

Research presented in this dissertation focused on the mechanical behavior of ZrB₂ based ceramic at elevated temperatures. Flexure strength, fracture toughness, and elastic modulus were measured at temperatures up to 2300ºC for three compositions: monolithic ZrB₂ (Z); ZrB₂ - 30 vol% SiC - 2 vol% B₄ C (ZS); and ZrB₂ - 10 vol% ZrC (ZC). In argon, Z, ZS, and ZC had strengths of 210 (at 2300ºC), 260 (at 2200ºC), and 295 MPa (at 2300ºC), the highest temperatures tested for each composition. Fractography was used extensively to characterize the strength limiting flaws as a function of temperature. Strength of ZS in argon was controlled by the SiC cluster size up to 1800ºC, and the formation of B-O-C-N phases that bridged SiC clusters above 2000ºC. For ZC, surface flaws introduced during specimen preparation were the source of critical flaws in the material up to 1400ºC, sub-critical crack growth of surface flaws between 1600 and 2000ºC, and microvoid coalescence above 2000ºC. It was also shown that thermal annealing at either 1400, 1500, or 1600ºC improves the strength and modulus of ZS at temperatures between 800ºC and 1600ºC. Heat treatment at 1400ºC for 10 hours produced the largest improvement in strength, 430 MPa at 1600ºC versus 380 MPa for the as processed material. As a whole, the research pointed to several key microstructural features currently limiting the mechanical properties at the highest temperatures. In particular, removal of unfavorable secondary phases, and improved control over microstructure, should be promising methods to improve the elevated temperature properties of ZrB₂ ceramics. --Abstract, page iv

Purification and electron cryomicroscopy of coronavirus particles.

Intact, enveloped coronavirus particles vary widely in size and contour, and are thus refractory to study by traditional structural means such as X-ray crystallography. Electron microscopy (EM) overcomes some problems associated with particle variability and has been an important tool for investigating coronavirus ultrastructure. However, EM sample preparation requires that the specimen be dried onto a carbon support film before imaging, collapsing internal particle structure in the case of coronaviruses. Moreover, conventional EM achieves image contrast by immersing the specimen briefly in heavy-metal-containing stain, which reveals some features while obscuring others. Electron cryomicroscopy (cryo-EM) instead employs a porous support film, to which the specimen is adsorbed and flash-frozen. Specimens preserved in vitreous ice over holes in the support film can then be imaged without additional staining. Cryo-EM, coupled with single-particle image analysis techniques, makes it possible to examine the size, structure and arrangement of coronavirus structural components in fully hydrated, native virions. Two virus purification procedures are described

Media, Technology, and Society: Theories of Media Evolution

In Media, Technology, and Society, some of the most prominent figures in media studies explore the issue of media evolution. Focusing on a variety of compelling examples in media history, ranging from the telephone to the television, the radio to the Internet, these essays collectively address a series of notoriously vexing questions about the nature of technological change. Is it possible to make general claims about the conditions that enable or inhibit innovation? Does government regulation tend to protect or thwart incumbent interests? What kinds of concepts are needed to address the relationship between technology and society in a nonreductive and nondeterministic manner? To what extent can media history help us to understand and to influence the future of media in constructive ways? The contributors' historically grounded responses to these questions will be relevant to numerous fields, including history, media and communication studies, management, sociology, and information studies

SOCIAL IMPLICATIONS OF THE INTERNET

The Internet is a critically important research site for sociologists testing theories of technology diffusion and media effects, particularly because it is a medium uniquely capable of integrating modes of communication and forms of content. Current research tends to focus on the Internet’s implications in five domains: 1) inequality (the “digital divide”); 2) community and social capital; 3) political participation; 4) organizations and other economic institutions; and 5) cultural participation and cultural diversity. A recurrent theme across domains is that the Internet tends to complement rather than displace existing media and patterns of behavior. Thus in each domain, utopian claims and dystopic warnings based on extrapolations from technical possibilities have given way to more nuanced and circumscribed understandings of how Internet use adapts to existing patterns, permits certain innovations, and reinforces particular kinds of change. Moreover, in each domain the ultimate social implications of this new technology depend on economic, legal, and policy decisions that are shaping the Internet as it becomes institutionalized. Sociologists need to study the Internet more actively and, particularly, to synthesize research findings on individual user behavior with macroscopic analyses of institutional and political-economic factors that constrain that behavior.World Wide Web, communications, media, technology

A flight investigation of a terminal area navigation and guidance concept for STOL aircraft

A digital avionics system referred to as STOLAND has been test-flown in the NASA CV-340 to obtain performance data for time-controlled guidance in the manual flight director mode. The advanced system components installed in the cockpit included an electronic attitude director indicator and an electronic multifunction display. Navigation guidance and control computations were all performed in the digital computer. Approach paths were flown which included a narrow 180-deg turn and a 1-min, 5-deg straight-in approach to the 30-m altitude go-around point. Results are presented for 20 approaches: (1) blended radio/inertial navigation using TACAN and a microwave scanning beam landing guidance system (MODILS) permitted a smooth transition from area navigation (TACAN) to precision terminal navigation (MODILS), (2) guidance system (flight director) performance measured at an altitude of 30.5 m was within that prescribed for category II CTOL operations on a standard runway, and (3) time of arrival at a point about 2 mi from touchdown was about 4 sec plus or minus sec later than the computed nominal arrival time

The Precise Determination of Sulfates

Experimental evidences are presented to support the necessity of precipitating barium sulfate by the addition of the sulfate to barium chloride rather than in the reverse order as is usually recommended. Factors such as loss due to creeping of the precipitate, temperature and time of digestion, heating of the barium sulfate to constant weight, and others were very carefully controlled. Data are given showing the results obtained using potassium, sodium, ammonium, and hydrogen sulfates. An explanation is offered why the results are low when the usual order of precipitation (BaCl2 to the sulfate) is followed. Microphotographs of barium sulfate obtained by different methods and under varying conditions are given

A flight investigation of a terminal area navigation and guidance concept for STOL aircraft

A digital avionics system was installed in the CV-340 transport aircraft. Flight tests were made to obtain preliminary performance data in the manual flight director mode using time controlled guidance. These tests provide a basis for selection of terminal area guidance, navigation, and control system concepts for short haul aircraft and for investigating operational procedures