The Pioneer Anomaly

Radio-metric Doppler tracking data received from the Pioneer 10 and 11 spacecraft from heliocentric distances of 20-70 AU has consistently indicated the presence of a small, anomalous, blue-shifted frequency drift uniformly changing with a rate of ~6 x 10^{-9} Hz/s. Ultimately, the drift was interpreted as a constant sunward deceleration of each particular spacecraft at the level of a_P = (8.74 +/- 1.33) x 10^{-10} m/s^2. This apparent violation of the Newton's gravitational inverse-square law has become known as the Pioneer anomaly; the nature of this anomaly remains unexplained. In this review, we summarize the current knowledge of the physical properties of the anomaly and the conditions that led to its detection and characterization. We review various mechanisms proposed to explain the anomaly and discuss the current state of efforts to determine its nature. A comprehensive new investigation of the anomalous behavior of the two Pioneers has begun recently. The new efforts rely on the much-extended set of radio-metric Doppler data for both spacecraft in conjunction with the newly available complete record of their telemetry files and a large archive of original project documentation. As the new study is yet to report its findings, this review provides the necessary background for the new results to appear in the near future. In particular, we provide a significant amount of information on the design, operations and behavior of the two Pioneers during their entire missions, including descriptions of various data formats and techniques used for their navigation and radio-science data analysis. As most of this information was recovered relatively recently, it was not used in the previous studies of the Pioneer anomaly, but it is critical for the new investigation.Comment: 165 pages, 40 figures, 16 tables; accepted for publication in Living Reviews in Relativit

Assessment and validation of a suite of reverse transcription-quantitative PCR reference genes for analyses of density-dependent behavioural plasticity in the Australian plague locust

<p>Abstract</p> <p>Background</p> <p>The Australian plague locust, <it>Chortoicetes terminifera</it>, is among the most promising species to unravel the suites of genes underling the density-dependent shift from shy and cryptic solitarious behaviour to the highly active and aggregating gregarious behaviour that is characteristic of locusts. This is because it lacks many of the major phenotypic changes in colour and morphology that accompany phase change in other locust species. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) is the most sensitive method available for determining changes in gene expression. However, to accurately monitor the expression of target genes, it is essential to select an appropriate normalization strategy to control for non-specific variation between samples. Here we identify eight potential reference genes and examine their expression stability at different rearing density treatments in neural tissue of the Australian plague locust.</p> <p>Results</p> <p>Taking advantage of the new orthologous DNA sequences available in locusts, we developed primers for genes encoding 18SrRNA, ribosomal protein L32 (RpL32), armadillo (Arm), actin 5C (Actin), succinate dehydrogenase (SDHa), glyceraldehyde-3P-dehydrogenase (GAPDH), elongation factor 1 alpha (EF1a) and annexin IX (AnnIX). The relative transcription levels of these eight genes were then analyzed in three treatment groups differing in rearing density (isolated, short- and long-term crowded), each made up of five pools of four neural tissue samples from 5^thinstar nymphs. SDHa and GAPDH, which are both involved in metabolic pathways, were identified as the least stable in expression levels, challenging their usefulness in normalization. Based on calculations performed with the geNorm and NormFinder programs, the best combination of two genes for normalization of gene expression data following crowding in the Australian plague locust was EF1a and Arm. We applied their use to studying a target gene that encodes a Ca²⁺binding glycoprotein, <it>SPARC</it>, which was previously found to be up-regulated in brains of gregarious desert locusts, <it>Schistocerca gregaria</it>. Interestingly, expression of this gene did not vary with rearing density in the same way in brains of the two locust species. Unlike <it>S. gregaria</it>, there was no effect of any crowding treatment in the Australian plague locust.</p> <p>Conclusion</p> <p>Arm and EF1a is the most stably expressed combination of two reference genes of the eight examined for reliable normalization of RT-qPCR assays studying density-dependent behavioural change in the Australian plague locust. Such normalization allowed us to show that <it>C. terminifera </it>crowding did not change the neuronal expression of the <it>SPARC </it>gene, a gregarious phase-specific gene identified in brains of the desert locust, <it>S. gregaria</it>. Such comparative results on density-dependent gene regulation provide insights into the evolution of gregarious behaviour and mass migration of locusts. The eight identified genes we evaluated are also candidates as normalization genes for use in experiments involving other Oedipodinae species, but the rank order of gene stability must necessarily be determined on a case-by-case basis.</p

Rethinking Social Justice in Education: An Epistemological Approach

There are many different notions of social justice in education. For example, some argue that social justice in education means giving individuals the opportunity to succeed; for others, it means seeking equality of outcome so that everyone does succeed. So great is the diversity of views that it has been suggested the term has become meaningless, or that it can mean anything people want it to mean. This has led some to argue that trying to define social justice in education is a hopeless task. This chapter argues that an approach informed by the later philosophy of Wittgenstein can be helpful in dealing with such issues. In particular, attention is focussed on Wittgenstein’s epistemology and theory of meaning in the Philosophical Investigations. It is argued that these are helpful in understanding the multiplicity of meanings of the term social justice in education. This multiplicity however, it is argued, does not lead to a situation where the term can mean anything its users want it to mean. Nor does it lead to a situation where all attempts to define the term are ruled out, or where only one definition is acceptable, presumably to be imposed on all users of the term. Instead, the significance of contextual understanding and meaning in different language-games is highlighted. Wittgenstein’s theory of meaning is then allied to Gallie’s notion of an essentially contested concept to advance the idea of engagement between those with different views, and of the need to recontextualize rather than decontextualize the notion of social justice in education

Benign Breast Diseases: Classification, Diagnosis, and Management

Benign breast diseases constitute a heterogeneous group of lesions including developmental abnormalities, inflammatory lesions, epithelial and stromal proliferations, and neoplasms. In this review, common benign lesions are summarized and their relationship to the development of subsequent breast cancer is emphasized

Two-phase growth of high topography in eastern Tibet during the Cenozoic

High topography in eastern Tibet is thought to have formed when deep crust beneath the central Tibetan Plateau flowed towards the plateau margin, causing crustal thickening and surface uplift(1,2). Rapid exhumation starting about 10-15 million years ago is inferred to mark the onset of surface uplift and fluvial incision(3-6). Although geophysical data are consistent with weak crust capable of flow(7,8), it is unclear how the timing(9) and amount of deformation adjacent to the Sichuan Basin during the Cenozoic era can be explained in this way(10,11). Here we use thermochronology to measure the cooling histories of rocks exposed in a section that stretches vertically over 3 km adjacent to the Sichuan Basin. Our thermal models of exhumation-driven cooling show that these rocks, and hence the plateau margin, were subject to slow, steady exhumation during early Cenozoic time, followed by two pulses of rapid exhumation, one beginning 30-25 million years ago and a second 10-15 million years ago that continues to present. Our findings imply that significant topographic relief existed adjacent to the Sichuan Basin before the Indo-Asian collision. Furthermore, the onset of Cenozoic mountain building probably pre-dated development of the weak lower crust, implying that early topography was instead formed during thickening of the upper crust along faults. We suggest that episodes of mountain building may reflect distinct geodynamic mechanisms of crustal thickenin