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The Role of Inoculum in the Primary and Secondary Infection of Certain Plant Pathogens
The infection cycle of some economically important soil-borne plant pathogens involves a combination of primary infection from particulate inoculum residing in the soil and secondary infection as disease is spread from infected to susceptible hosts. This study examines the role of the two types of inoculum in the primary and secondary infection of soil-home plant disease using a combination of experimentation and mathematical modelling.
The infectivity of inoculum can be quantified by the pathozone profile which measures changes in the probability of infection when inoculum occurs at different distances from the host. The study showed that the germinability of inoculum, the growth of the mycelial colony and the infectivity of mycelium at the surface of the host combine to dictate the shape of the pathozone profile for Rhizoctonia solani on radish. The ultimate shape of the pathozone depended on inoculum type and was particularly sensitive to changes in the density and distribution of the mycelium in the fungal colony. Mycelium from an infected radish plant grew much further and at a higher density than that from particulate inoculum (mycelial discs). This resulted in pathozone profiles that differed in shape. For particulate inoculum the profile rose and fell with distance whilst for an infected plant the decay was sigmoidal.
The characteristic shape of the pathozone for different inoculum types of Rhizoctonia solani was summarised using simple, non-linear models in which certain parameters were allowed to vary with time. Thus, the pathozone behaviour of single plants could be used to predict the progress of disease at the population level both in an unprotected crop and in a crop protected with the biological control agent Trichoderma viride. Predictions were particularly accurate for an epidemic restricted to primary infection or for an epidemic dominated by secondary infection in the absence of biological control. The model underestimated the extent of secondary infection in the protected crop.
The contribution of inoculum type to the spread of disease was examined in a contrasting host-pathogen system involving the infection of wheat roots by the take-all fungus, Gaeumannomyces graminis var tritici. Two phases of disease progress were identified, an initial phase dominated by primary infection during which particulate inoculum decayed, and a subsequent phase involving an increase in secondary infection driven by the availability of susceptible host tissue. From a low density of initial inoculum this resulted in a disease progress curve which rose monotonically to an initial plateau and was sigmoidal thereafter. These results were consistent with observations from field data. The biological control agent. Pseudomonas corrugata, reduced the probability of infection on the seminal roots of a wheat plant from particulate inoculum. However, suppression of primary infection alone is not considered adequate for control of take-all over an entire season
Coefficient of Friction and Damage to Contact Area During the Early Stages of Fretting II : Steel, Iron, Iron Oxide, and Glass Combinations
Coefficient of Friction and Damage to Contact Area During the Early Stages of Fretting I : Glass, Copper, or Steel Against Copper
The Clinical Sustainability Assessment Tool: Measuring organizational capacity to promote sustainability in healthcare
BACKGROUND: Few validated assessment tools are available to increase understanding and measure factors associated with sustainment of clinical practices, an increasingly recognized need among clinicians. We describe the development of the Clinical Sustainability Assessment Tool (CSAT), designed to assess factors that contribute to sustainable practices in clinical settings.
METHODS: Sixty-four participants from clinical and research fields participated in concept mapping and were recruited to brainstorm factors that lead to sustained clinical practices. Once repeated factors were removed, participants sorted items based on similarity and rated them by importance and feasibility. Using concept mapping analyses, items were grouped into meaningful domains to develop an initial tool. We then recruited pilot sites and early adopters, for a total of 286 practicing clinicians, to pilot and evaluate the tool. Individuals were recruited from clinical settings across pediatric and adult medical and surgical subspecialties. The data were analyzed using confirmatory factor analysis (CFA) to test hypothesized subscale structure in the instrument. We used root mean square error of approximation (RMSEA) and the standardized root mean square residual (SRMR) to assess fit and thus the ability of CSAT to measure the identified domains.
RESULTS: The concept mapping produced sorted statements that were edited into items that could be responded to, resulting in the creation of a tool with seven determinant domains and 47 items. The pilot and CFA testing resulted in a final CSAT instrument made up 35 items, five per domain. CFA results demonstrated very good fit of the seven domain structure of the CSAT (RMSEA = 0.049; SRMR = 0.049). Usability testing indicated the CSAT is brief, easy to use, easy to learn, and does not require extensive training. Additionally, the measure scored highly (18/20) on the Psychometric and Pragmatic Evidence Rating Scale (PAPERS). The seven final CSAT domains were engaged staff and leadership, engaged stakeholders, organizational readiness, workflow integration, implementation and training, monitoring and evaluation, and outcomes and effectiveness.
CONCLUSIONS: The CSAT is a new reliable assessment tool which allows for greater practical and scientific understanding of contextual factors that enable sustainable clinical practices over time
The Roles of Extrinsic and Intrinsic Factors in the Freshwater Life-History Dynamics of a Migratory Salmonid
Key life-cycle transitions, such as metamorphosis or migration, can be altered by a variety of external factors, such as climate variation, strong species interactions, and management intervention, or modulated by density dependence. Given that these life-history transitions can influence population dynamics, understanding the simultaneous effects of intrinsic and extrinsic controls on life-history expression is particularly relevant for species of management or conservation importance. Here, we examined how life histories of steelhead (Oncorhynchus mykiss) are affected by weather, pink salmon abundance (Oncorhynchus gorbuscha), experimental nutrient addition, and density-dependent processes. We tested for impacts on the size of steelhead smolts (juveniles migrating to the sea), as well as their age and abundance across four decades in the Keogh River, British Columbia, Canada. Larger steelhead smolts were associated with warmer years and artificial nutrient addition. In addition, higher pink salmon abundance and artificial nutrient addition correlated with juvenile steelhead migrating at younger ages. While density dependence appeared to be the primary factor regulating the abundance of steelhead smolts, nutrient addition and temperature were positively and negatively associated with smolt production, respectively, prior to 1991, and pink salmon spawning abundance was positively associated with smolt production after 1990. Thus, this study provides evidence that the temporal dynamics of one species of salmon is linked to the juvenile life history of co-occurring steelhead. A complex interplay of species interactions, nutrient subsidies, density dependence, and climatic variation can control the life-history expression of species with complex life cycles
Using a Pericentromeric Interspersed Repeat to Recapitulate the Phylogeny and Expansion of Human Centromeric Segmental Duplications
Despite considerable advances in sequencing of the human genome over the past few years, the organization and evolution of human pericentromeric regions have been difficult to resolve. This is due, in part, to the presence of large, complex blocks of duplicated genomic sequence at the boundary between centromeric satellite and unique euchromatic DNA. Here, we report the identification and characterization of an approximately 49-kb repeat sequence that exists in more than 40 copies within the human genome. This repeat is specific to highly duplicated pericentromeric regions with multiple copies distributed in an interspersed fashion among a subset of human chromosomes. Using this interspersed repeat (termed PIR4) as a marker of pericentromeric DNA, we recovered and sequence-tagged 3 Mb of pericentromeric DNA from a variety of human chromosomes as well as nonhuman primate genomes. A global evolutionary reconstruction of the dispersal of PIR4 sequence and analysis of flanking sequence supports a model in which pericentromeric duplications initiated before the separation of the great ape species (>12 MYA). Further, analyses of this duplication and associated flanking duplications narrow the major burst of pericentromeric duplication activity to a time just before the divergence of the African great ape and human species (5 to 7 MYA). These recent duplication exchange events substantially restructured the pericentromeric regions of hominoid chromosomes and created an architecture where large blocks of sequence are shared among nonhomologous chromosomes. This report provides the first global view of the series of historical events that have reshaped human pericentromeric regions over recent evolutionary time
The Nancy Grace Roman Space Telescope Coronagraph Instrument (CGI) technology demonstration
The Coronagraph Instrument (CGI) on the Nancy Grace Roman Space Telescope will demonstrate the highcontrast technology necessary for visible-light exoplanet imaging and spectroscopy from space via direct imaging of Jupiter-size planets and debris disks. This in-space experience is a critical step toward future, larger missions targeted at direct imaging of Earth-like planets in the habitable zones of nearby stars. This paper presents an overview of the current instrument design and requirements, highlighting the critical hardware, algorithms, and operations being demonstrated. We also describe several exoplanet and circumstellar disk science cases enabled by these capabilities. A competitively selected Community Participation Program team will be an integral part of the technology demonstration and could perform additional CGI observations beyond the initial tech demo if the instrument performance warrants it
Tourist Photographers and the Promotion of Travel: the Polytechnic Touring Association, 1888–1939
The Polytechnic Touring Association (PTA) was a London-based, originally philanthropic turned commercial travel firm whose historical origins coincided with the arrival of the Kodak camera in 1888 – thus, of popular (tourist) photography. This article examines the PTA’s changing relationship with tourist photographers, and how this influenced the company’s understanding of what role photography could play in promoting the tours, in the late nineteenth and early twenty century. This inquiry is advanced on the basis of the observation that, during this time, the PTA’s passage from viewing tourists as citizens to educate, to customers to please, paralleled the move from using photography-based images to mixed media. Such a development was certainly a response to unprecedented market demands; this article argues that it should also be considered in relation to the widening of photographic perceptions engendered by the democratization of the medium, to which the PTA responded, first as educator, then as service provider. In doing so, the article raises several questions about the shifting relationship between “high”, or established, and “low”, or emerging, forms of culture, as mass photography and the mass marketing of tourism developed
First Light LBT AO Images of HR 8799 bcde at 1.65 and 3.3 Microns: New Discrepancies between Young Planets and Old Brown Dwarfs
As the only directly imaged multiple planet system, HR 8799 provides a unique
opportunity to study the physical properties of several planets in parallel. In
this paper, we image all four of the HR 8799 planets at H-band and 3.3 microns
with the new LBT adaptive optics system, PISCES, and LBTI/LMIRCam. Our images
offer an unprecedented view of the system, allowing us to obtain H and 3.3$
micron photometry of the innermost planet (for the first time) and put strong
upper-limits on the presence of a hypothetical fifth companion. We find that
all four planets are unexpectedly bright at 3.3 microns compared to the
equilibrium chemistry models used for field brown dwarfs, which predict that
planets should be faint at 3.3 microns due to CH4 opacity. We attempt to model
the planets with thick-cloudy, non-equilibrium chemistry atmospheres, but find
that removing CH4 to fit the 3.3 micron photometry increases the predicted L'
(3.8 microns) flux enough that it is inconsistent with observations. In an
effort to fit the SED of the HR 8799 planets, we construct mixtures of cloudy
atmospheres, which are intended to represent planets covered by clouds of
varying opacity. In this scenario, regions with low opacity look hot and
bright, while regions with high opacity look faint, similar to the patchy cloud
structures on Jupiter and L/T transition brown-dwarfs. Our mixed cloud models
reproduce all of the available data, but self-consistent models are still
necessary to demonstrate their viability.Comment: Accepted to Ap
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