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Search Results: 1 - 10 of 128128 matches for " Sandra T. Clarke "
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Spaceflight Influences both Mucosal and Peripheral Cytokine Production in PTN-Tg and Wild Type Mice
Justin L. McCarville, Sandra T. Clarke, Padmaja Shastri, Yi Liu, Martin Kalmokoff, Stephen P. J. Brooks, Julia M. Green-Johnson
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0068961
Abstract: Spaceflight is associated with several health issues including diminished immune efficiency. Effects of long-term spaceflight on selected immune parameters of wild type (Wt) and transgenic mice over-expressing pleiotrophin under the human bone-specific osteocalcin promoter (PTN-Tg) were examined using the novel Mouse Drawer System (MDS) aboard the International Space Station (ISS) over a 91 day period. Effects of this long duration flight on PTN-Tg and Wt mice were determined in comparison to ground controls and vivarium-housed PTN-Tg and Wt mice. Levels of interleukin-2 (IL-2) and transforming growth factor-beta1 (TGF-β1) were measured in mucosal and systemic tissues of Wt and PTN-Tg mice. Colonic contents were also analyzed to assess potential effects on the gut microbiota, although no firm conclusions could be made due to constraints imposed by the MDS payload and the time of sampling. Spaceflight-associated differences were observed in colonic tissue and systemic lymph node levels of IL-2 and TGF-β1 relative to ground controls. Total colonic TGF-β1 levels were lower in Wt and PTN-Tg flight mice in comparison to ground controls. The Wt flight mouse had lower levels of IL-2 and TGF-β1 compared to the Wt ground control in both the inguinal and brachial lymph nodes, however this pattern was not consistently observed in PTN-Tg mice. Vivarium-housed Wt controls had higher levels of active TGF-β1 and IL-2 in inguinal lymph nodes relative to PTN-Tg mice. The results of this study suggest compartmentalized effects of spaceflight and on immune parameters in mice.
Hydrological prediction in a non-stationary world
R. T. Clarke
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2007,
Abstract: The paper discusses evidence that common assumptions in the analysis of hydrological time series (homogeneous variability in random fluctuations about a constant mean value) may not be appropriate for some South American drainage basins. Relatively rapid changes have occurred, and are occurring, as a consequence of replacing mature forest by short crops and urban development. Some research claims to have detected non-linear trends in streamflow in rivers draining the south-eastern part of the sub-continent, together with decadal fluctuations and interannual peaks at ENSO timescales. The paper discusses the implications of such changes for hydrological practices now in widespread and largely unquestioned use.
Classification procedures in the context of PUB: ways forward?
R. T. Clarke
Hydrology and Earth System Sciences Discussions , 2011, DOI: 10.5194/hessd-8-855-2011
Abstract: Limitations of cluster analysis as a procedure for classifying parameters of rainfall-runoff models are discussed, and a procedure is suggested by which such parameters could be estimated, using site characteristics together with a split record test as a measure of performance. It is suggested that geostatistical models may be a possible alternative to procedures based on cluster analysis, and that long-established principles of experimental design (replication, randomization) be used for comparing alternative PUB procedures.
Fitting and testing the significance of linear trends in Gumbel-distributed data
R. T. Clarke
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2002,
Abstract: The widely-used hydrological procedures for calculating events with T-year return periods from data that follow a Gumbel distribution assume that the data sequence from which the Gumbel distribution is fitted remains stationary in time. If non-stationarity is suspected, whether as a consequence of changes in land-use practices or climate, it is common practice to test the significance of trend by either of two methods: linear regression, which assumes that data in the record have a Normal distribution with mean value that possibly varies with time; or a non-parametric test such as that of Mann-Kendall, which makes no assumption about the distribution of the data. Thus, the hypothesis that the data are Gumbel-distributed is temporarily abandoned while testing for trend, but is re-adopted if the trend proves to be not significant, when events with T-year return periods are then calculated. This is illogical. The paper describes an alternative model in which the Gumbel distribution has a (possibly) time-variant mean, the time-trend in mean value being determined, for the present purpose, by a single parameter β estimated by Maximum Likelihood (ML). The large-sample variance of the ML estimate βMR is compared with the variance of the trend βLR calculated by linear regression; the latter is found to be 64% greater. Simulated samples from a standard Gumbel distribution were given superimposed linear trends of different magnitudes, and the power of each of three trend-testing procedures (Maximum Likelihood, Linear Regression, and the non-parametric Mann-Kendall test) were compared. The ML test was always more powerful than either the Linear Regression or Mann-Kendall test, whatever the (positive) value of the trend β; the power of the MK test was always least, for all values of β. Keywords: Extreme value probability distribution, Gumbel distribution, statistical stationarity, trend-testing procedures
Contemporary and future perspectives for the hydrological and catchment sciences
C. Neal ,R. T. Clarke
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2007,
Abstract: No abstract available.
Searching for Fast Radio Transients with SKA Phase 1
T. M. Colegate,N. Clarke
Physics , 2011, DOI: 10.1071/AS11031
Abstract: The Square Kilometre Array (SKA) provides an excellent opportunity for low cost searches for fast radio transients. The increased sensitivity and field of view of the SKA compared with other radio telescopes will make it an ideal instrument to search for impulsive emission from high energy density events. We present a high-level search use case and propose event rate per unit cost as a figure of merit to compare transient survey strategies for radio telescope arrays; we use event rate per beam formed and searched as a first-order approximation of this measure. Key results are that incoherent (phase insensitive) combination of antenna signals achieves the highest event rate per beam, and that 50-100 MHz processed bandwidth is sufficient for extragalactic searches with SKA Phase 1; the gain in event rate from using the full available bandwidth is small. Greater system flexibility will enable more effective searches, but need not drive the top-level system requirements beyond those already proposed for the SKA. The most appropriate search strategy depends on the observed sky direction and the source population; for SKA Phase 1, low frequency aperture arrays tend to be more effective for extragalactic searches and dishes more effective for directions of increased scatter broadening, such as near the Galactic plane.
Cluster Mergers and Diffuse Radio Emission in Abell 2256 and Abell 754
T. E. Clarke,T. A. Ensslin
Physics , 2001,
Abstract: We present deep VLA observations of the galaxy clusters Abell 2256 and Abell 754, both of which appear to be in the violent stage of major cluster merger events. The complex nature of Abell 2256 is revealed through radio images which, in addition to the head-tail galaxies, show two extended, irregular, and sharp-edged regions of diffuse radio emission at the cluster periphery (so called radio relics), and a large-scale diffuse radio halo located in the central regions of the cluster. Polarimetry of the A2256 cluster relics reveals large-scale ordered magnetic fields which appear to trace the bright filaments in the relics. The polarization fraction across the relics ranges from 20% - 40% with the majority of the relics polarized above the 30% level. At the sensitivity of our current observations we place an upper limit of 20% on the polarization of the radio halo. Low frequency VLA observations of Abell 754 reveal extended, diffuse radio (halo) emission in the cluster core region as well as steep spectrum emission in the cluster periphery. The location, morphology, and spectral index of the peripheral emission are consistent with the properties of radio relics. The X-ray evidence of the ongoing mergers in both clusters, together with the polarization properties of A2256's radio relics supports recent suggestions of a merger-induced origin of the relic emission. Deciphering the complex radio properties of these clusters may thus provide the key to understanding the dynamical history of the systems.
Adverse Wear in MOM Hip-Arthroplasty Related to the Production of Metal Fragments at Impingement Sites  [PDF]
T. K. Donaldson, E. J. Smith, A. Koutalos, A. John, J. Y. Lazennec, I. C. Clarke
Open Journal of Orthopedics (OJO) , 2018, DOI: 10.4236/ojo.2018.810041
Abstract: Metal on metal (MOM) bearings were reintroduced as resurfacing arthroplasty (RA) for the younger, more active patient and were later incorporated into total hip arthroplasty (THA). Early results were encouraging. However, recent publications identified adverse tissue responses to metal debris, such that the majority of MOM designs have been abandoned due to the increase in cobalt-chromium (CoCr) debris and associated metal ions. Reports of MOM THA cited risks that included acetabular cups with high-inclination angles, i.e. “edge-loading”, and “trunnionosis”. Hip impingement was also a cited risk in one MOM study, with “type-IV” wear noted to be a sliding/impaction type of wear, characterized by deep scratches. Sliding/impaction wear mechanisms produced at impingement are not well represented in current MOM literature. Therefore, our objective in this review was to consolidate evidence for impingement risks. We hypothesize that hip impingement and subluxation with metal-backed acetabular cups can trigger wear mechanisms that result in, 1) femoral-neck notching, 2) release of large metal particles, 3) production of uniquely large scratches, defined as “microgrooves” on heads and cups, 4) formation of “polar” and “basal” microgrooves precisely aligning with cup profiles during impingement, and 5) equatorial microgrooves relate to soft-tissue sites of impingement. Relevant risk scenarios were evaluated and included hip impingement in both sitting and standing postures, head subluxation, wear patterns defining in-vivo component positions, and evidence for circulating metal fragments. The study relied on mapping of wear patterns to deduce in-vivo positioning of devices and relied on surrogate femoral stems of the same brand to simulate neck-cup impingement. EOS imaging techniques were used to analyze functional-sitting and functional-standing postures and prove existence of hip impingement sites in patients. The study identified 8-risk scenarios for wear damage on MOM bearings. The microgrooves on femoral-heads crossing the main-wear area (polar) and non-wear regions (basal) aligned well with cuprim profiles at impingement sites. This may represent the first description of such large scratches (40 - 300 μm wide) we termed microgrooves, that formed on femoral heads at sites representative of prosthetic impingement. As an abrasive wear process, similar to the formation of femoral-neck notches, these would have been acquired over millions of gait cycles. The pitting and linear microgrooves crossing the non-wear areas of heads (basal) represented
Compound cryopump for fusion reactors
M. Kovari,R. Clarke,T. Shephard
Physics , 2013, DOI: 10.1016/j.fusengdes.2013.10.009
Abstract: We reconsider an old idea: a three-stage compound cryopump for use in fusion reactors such as DEMO. The helium "ash" is adsorbed on a 4.5 K charcoal-coated surface, while deuterium and tritium are adsorbed at 15-22 K on a second charcoal-coated surface. The helium is released by raising the first surface to ~30 K. In a separate regeneration step, deuterium and tritium are released at ~110 K. In this way, the helium can be pre-separated from other species. In the simplest design, all three stages are in the same vessel, with a single valve to close the pump off from the tokamak during regeneration. In an alternative design, the three stages are in separate vessels, connected by valves, allowing the stages to regenerate without interfering with each other. The inclusion of the intermediate stage would not affect the overall pumping speed significantly. The downstream exhaust processing system could be scaled down, as much of the deuterium and tritium could be returned directly to the reactor. This could reduce the required tritium reserve by almost 90%. We used a well-established free Direct Simulation Monte Carlo (DSMC) code, DS2V. At very high upstream densities (~1020 molecules/m3 and above) the flow into the pump is choked. Enlarging the aperture is the only way to increase the pumping speed at high densities. Ninety percent of the deuterium and tritium is successfully trapped at 15 K (assuming that the sticking coefficient is 80-100% on the 15-22 K surface). On the other hand, the remaining 10% still exceeds the small amount of helium in the gas input.
Going “paperless” in an English National Health Service (NHS) breast cancer screening service: The intriduction of fully digital mammography  [PDF]
Sian Taylor-Phillips, Amy Grove, Sharon Hoffmeister, Margot Wheaton, Sarah Coult, Joanne Essex, Janice Hackney, Sandra Di Cioccio, Aileen Clarke
Health (Health) , 2014, DOI: 10.4236/health.2014.65065

Objective: To test the feasibility of a fully paperless system, termed “paperlite” in a UK breast screening service. To demonstrate in NHS practice, how workload and workflow could be improved by moving to a paperless system and discovering what impact this has upon the complexity within the service. Setting: Warwickshire, Solihull and Coventry Breast Screening Service in the West Midlands of England. Methods: Quality improvement methodologies were employed, including value stream mapping, task analysis and a time-and-motion study. Results: The screening centred screened approximately 50,000 women per year. If they were to implement a paperless system, the administrative workload would decrease. The time saving per batch of screens, which could be achieved by moving to the paperless system ranged from 19 to 56 minutes (mean = 36 minutes). When calculated by batch the mean time saving per woman screened by moving to the paperless system was 42 seconds. This equates to 583 hours of administrative work per year in a centre screening 50,000 women. Conclusions: The paperless system has many benefits compared to the original system in terms of reductions in waste, time and cost. The simplification and standardisation of the process resulted in fewer tasks and interfaces where errors could occur, hence inadvertently improving patient safety. The limitation of the work is the heavy reliance on technology, live interfacing with computer databases and software stability is necessary for a paperless system to be used in NHS practice.

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