Interferometric tracking system for the tracking and data relay satellite

This report documents construction and testing of the Interferometric Tracking System project developed under the NASA SBIR contract NAS5-30313. Manuals describing the software and hardware, respectively entitled: 'Field Station Guide to Operations' and 'Field Station Hardware Manual' are included as part of this final report. The objective of this contract was to design, build, and operate a system of three ground stations using Very Long Baseline Interferometry techniques to measure the TDRS orbit. The ground stations receive signals from normal satellite traffic, store these signals in co-located computers, and transmit the information via phone lines to a central processing site which correlates the signals to determine relative time delays. Measurements from another satellite besides TDRS are used to determine clock offsets. A series of such measurements will ultimately be employed to derive the orbital parameters, yielding positions accurate to within 50 meters or possibly better

Tropospheric Modeling Improvement

The work performed under this contract provides for the improvement of modeling of troposphere propagation delay in VLBI data, defining of required accuracy of ancillary data type(s) to measure tropospheric behavior, and to develop a clear correspondence between tropospheric behavior and the quality of geodetic VLBI measurements

Dynamics of the solid earth

The work performed under this contract provides for the improvement of modeling of troposphere propagation delay in very long base interferometry (VLBI) data, defining of required accuracy of ancillary data type(s) to measure tropospheric behavior and to develop a clear correspondence between tropospheric behavior and the quality of geodetic VLBI measurements

Intracanopy adjustment of leaf-level thermal tolerance is associated with microclimatic variation across the canopy of a desert tree (Acacia papyrocarpa)

© 2018, Springer-Verlag GmbH Germany, part of Springer Nature. Tree crowns are spatially heterogeneous, sometimes resulting in significant variation in microclimate across the canopy, particularly with respect to temperature. Yet it is not known whether such localised temperature variation equates to intracanopy variation in leaf-level physiological thermal tolerance. Here, we studied whether microclimate variation across the canopy of a dominant desert tree equated to localised variation in leaf thermal thresholds (T 50 ) among four canopy positions: upper south, upper north, lower south, lower north. Principal component analysis was used to generate a composite climatic stress variable (C STRESS ) from canopy temperature, vapour pressure deficit, and relative humidity. We also determined the average number of days that maximum temperatures exceeded the air temperature equating to this species’ critical threshold of 49 °C (AT 49 ). To estimate how closely leaf temperatures track ambient temperature, we predicted the thermal time constant (τ) for leaves at each canopy position. We found that C STRESS and AT 49 were significantly greater in lower and north-facing positions in the canopy. Differences in wind speed with height resulted in significantly longer predicted τ for leaves positioned at lower, north-facing positions. Variation in these drivers was correlated with significantly higher T 50 for leaves in these more environmentally stressful canopy positions. Our findings suggest that this species may optimise resources to protect against thermal damage at a whole-plant level. They also indicate that, particularly in desert environments with steep intracanopy microclimatic gradients, whole-plant carbon models could substantially under- or overestimate productivity under heat stress, depending on where in the canopy T 50 is measured

A pragmatic suggestion for dealing with results for candidate genes obtained from genome wide association studies

<p>Abstract</p> <p>Background</p> <p>Researchers may embark on a genome-wide association study before fully investigating candidate regions which have been reported to produce evidence to suggest that they harbour susceptibility loci. If the genome wide study had not been carried out then results which demonstrated only modest statistical significance from candidate regions would be judged to be of interest and would stimulate further investigation. However if hundreds of thousands of markers are typed then inevitably very large numbers of such results will occur by chance and those from candidate regions may attract no special attention.</p> <p>Results</p> <p>An approach is proposed in which differential treatment is afforded to markers from candidate regions and from those that are routinely typed in the context of a genome wide scan. Different prior probabilities are assigned to the two types of marker. A likelihood ratio is derived from the reported <it>p </it>value for each marker, calculated as LR = e^{chiinv(1,p)/2}, and the posterior odds in favour of a true positive association are obtained. These odds can be used to rank the markers with a view to suggesting the regions in which further genotyping is indicated. We suggest that prior probabilities be specified such that a candidate marker significant at <it>p </it>= 0.01 and a routine marker significant at <it>p </it>= 0.00001 will yield similar values for the posterior odds. We show that this can be achieved by setting a value for prior probability of association to 0.1 for candidate markers and to 0.00018 for routine markers.</p> <p>Conclusion</p> <p>It is essential that formal procedures be adopted in order to avoid modestly positively results from candidate regions being swamped by the huge number of nominally significant results which will be obtained when very many markers are genotyped. Software to carry out the conversion from <it>p </it>values to posterior odds is available from <url>http://www.mds.qmul.ac.uk/statgen/grpsoft.html</url>.</p

A simple method for assessing the strength of evidence for association at the level of the whole gene

INTRODUCTION: It is expected that different markers may show different patterns of association with different pathogenic variants within a given gene. It would be helpful to combine the evidence implicating association at the level of the whole gene rather than just for individual markers or haplotypes. Doing this is complicated by the fact that different markers do not represent independent sources of information. METHOD: We propose combining the p values from all single locus and/or multilocus analyses of different markers according to the formula of Fisher, X = ∑(-2ln(p(i))), and then assessing the empirical significance of this statistic using permutation testing. We present an example application to 19 markers around the HTRA2 gene in a case-control study of Parkinson's disease. RESULTS: Applying our approach shows that, although some individual tests produce low p values, overall association at the level of the gene is not supported. DISCUSSION: Approaches such as this should be more widely used in assimilating the overall evidence supporting involvement of a gene in a particular disease. Information can be combined from biallelic and multiallelic markers and from single markers along with multimarker analyses. Single genes can be tested or results from groups of genes involved in the same pathway could be combined in order to test biologically relevant hypotheses. The approach has been implemented in a computer program called COMBASSOC which is made available for downloading

Study of Regions of Extended Homozygosity Provides a Powerful Method to Explore Haplotype Structure of Human Populations

Previous investigations have reported linkage disequilibrium occurring between nearby polymorphisms, a block-like structure for such relationships, some instances where surprisingly few haplotypes are found and regions of extended homozygosity which are especially marked around centromeres and which are especially common on the X chromosome. We investigated the distribution and nature of regions of extended homozygosity in a sample of 1411 subjects included in a genome wide association study. Regions of extended homozygosity over 1Mb are common, with an average of 35.9 occurring per subject, and containing on average 73 homozygous markers. They have a markedly non-random distribution. They are relatively common on the X chromosome and are seen at centromeres but are also concentrated at other chromosomal regions where presumably recombination is rare. They seem to be a consequence of some haplotypes being very common in the population and although sometimes this reflects the effect of a very common haplotype we also note that there are examples of two or three common haplotypes, each very different from each other, underlying this effect. Regions of extended homozygosity are commoner than previously appreciated. They result from the presence of extended haplotypes with high population frequency. Such regions concentrate in particular locations. The haplotypes involved are sometimes markedly disparate from each other. These regions offer a valuable opportunity for further investigation, in particular with regard to their ancestral history

Investigation into the Ability of SNP Chipsets and Microsatellites to Detect Association with a Disease Locus

We wished to investigate the ability of different SNP chipsets to detect association with a disease and to investigate the linkage disequilibrium (LD) relationships between microsatellites and nearby SNPs in order to assess their potential usefulness to detect association

Intracanopy adjustment of leaf-level thermal tolerance is associated with microclimatic variation across the canopy of a desert tree (\u3ci\u3eAcacia papyrocarpa\u3c/i\u3e)

Tree crowns are spatially heterogeneous, sometimes resulting in significant variation in microclimate across the canopy, particularly with respect to temperature. Yet it is not known whether such localised temperature variation equates to intracanopy variation in leaf-level physiological thermal tolerance. Here, we studied whether microclimate variation across the canopy of a dominant desert tree equated to localised variation in leaf thermal thresholds (T50) among four canopy positions: upper south, upper north, lower south, lower north. Principal component analysis was used to generate a composite climatic stress variable (CSTRESS) from canopy temperature, vapour pressure deficit, and relative humidity. We also determined the average number of days that maximum temperatures exceeded the air temperature equating to this species’ critical threshold of 49 °C (AT49). To estimate how closely leaf temperatures track ambient temperature, we predicted the thermal time constant (τ) for leaves at each canopy position. We found that CSTRESS and AT49 were significantly greater in lower and north-facing positions in the canopy. Differences in wind speed with height resulted in significantly longer predicted τ for leaves positioned at lower, north-facing positions. Variation in these drivers was correlated with significantly higher T50 for leaves in these more environmentally stressful canopy positions. Our findings suggest that this species may optimise resources to protect against thermal damage at a whole-plant level. They also indicate that, particularly in desert environments with steep intracanopy microclimatic gradients, whole-plant carbon models could substantially under- or overestimate productivity under heat stress, depending on where in the canopy T50 is measured