Primary and successive events in the Madden–Julian Oscillation

Conventional analyses of the MJO tend to produce a repeating cycle, such that any particular feature cannot be unambiguously attributed to the current or previous event. We take advantage of the sporadic nature of the MJO and classify each observed Madden-Julian (MJ) event as either primary, with no immediately preceding MJ event, or successive, which does immediately follow a preceding event. 40% of MJ events are primary events. Precursor features of the primary events can be unambiguously attributed to that event. A suppressed convective anomaly grows and decays in situ over the Indian Ocean, prior to the start of most primary MJ events. An associated mid-tropospheric temperature anomaly destabilises the atmosphere, leading to the generation of the active MJ event. Hence, primary MJ events appear to be thermodynamically triggered by a previous dry period, although stochastic forcing may also be important. Other theories predict that boundary-layer convergence, humidity, propagation of dynamical structures around the Equator, sea surface temperatures, and lateral forcing by extratropical transients may all be important in triggering an event. Although precursor signals from these mechanisms are diagnosed from reanalysis and satellite observational data in the successive MJ events, they are all absent in the primary MJ events. Hence, it appears that these apparent precursor signals are part of the MJO once it is established, but do not play a role in the spontaneous generation of the MJO. The most frequent starting location of the primary events is the Indian Ocean, but over half of them start elsewhere, from the maritime continent to the western Pacific

The clustering of X-ray selected AGN at z=0.1

The clustering properties of moderate luminosity ($L_X = \rm 10^{41} - 10^{44} \, erg \,s^{-1}$) X-ray selected AGN at $z\approx0.1$ are explored. X-ray sources in the redshift interval $0.03<z<0.2$ are selected from a serendipitous XMM survey of the SDSS footprint (XMM/SDSS) and are cross-correlated with the SDSS Main galaxy sample. The inferred X-ray AGN auto-correlation function is described by a power law with amplitude $r_0\approx5\,$h$^{-1}$Mpc and slope $\gamma\approx2.0$. The corresponding mass of the dark matter haloes that host X-ray AGN at $z\approx0.1$ is \approx 10^{13} \,h ^{-1} \, M_{\sun}. Comparison with studies at higher redshift shows that this mass scale is characteristic of moderate luminosity X-ray AGN out to $z\approx 1$. Splitting the AGN sample by rest-frame color shows that X-ray sources in red hosts are more clustered than those associated with blue galaxies, in agreement with results at $z\approx1$. We also find that the host galaxies of X-ray AGN have lower stellar masses compared to the typical central galaxy of a \approx 10^{13} \,h ^{-1} \, M_{\sun} dark matter halo. AGN hosts either have experienced less stellar mass growth compared to the average central galaxy of a \approx 10^{13} \,h ^{-1} \, M_{\sun} halo or a fraction of them are associated with satellite galaxies.Comment: MNRAS accepted 14 pages, 8 figures, 5 table

A Real-Time Quantitative Analysis of Atmospheric Contributions of Hydrogen to Weld Arc Plasmas

Hydrogen contamination of weldments, particularly in the welded joints of high strength steels, can cause significant reductions in weld integrity, often resulting in failure of the joint. Inspection and repair of hydrogen assisted cracks in weldments is both costly and time consuming, thus real-time methods of detecting hydrogen levels during welding are essential. Analytical emission spectroscopy is a promising method of weld analysis, providing quantitative information in real time about the amount of hydrogen in the arc atmosphere

The Beginning and Evolution of the Universe

We review the current standard model for the evolution of the Universe from an early inflationary epoch to the complex hierarchy of structure seen today. We summarize and provide key references for the following topics: observations of the expanding Universe; the hot early Universe and nucleosynthesis; theory and observations of the cosmic microwave background; Big Bang cosmology; inflation; dark matter and dark energy; theory of structure formation; the cold dark matter model; galaxy formation; cosmological simulations; observations of galaxies, clusters, and quasars; statistical measures of large-scale structure; and measurement of cosmological parameters. We conclude with discussion of some open questions in cosmology. This review is designed to provide a graduate student or other new worker in the field an introduction to the cosmological literature.Comment: 69 pages. Invited review article for Publications of the Astronomical Society of the Pacific. Supplementary references, tables, and more concise PDF file at http://www.physics.drexel.edu/univers

Potential applications of synchrotron computed microtomography to soil science

Synchrotron x-ray computed microtomography (CMT) can be used to make non-destructive tomographic sections with spatial resolutions of a few [mu]m. This resolution presents possibilities for study of soil-fluid interactions on a spatial scale hitherto unreachable. Details of a CMT apparatus in operation at the Brookhaven National Synchrotron Light Source X26 beam line are presented and prospects for future investigations of test systems have been made and results for wet and dry samples of glass beads and sand samples are given to show the power of the system

The transcription factor 7-like 2 (TCF7L2) polymorphism may be associated with focal arteriolar narrowing in Caucasians with hypertension or without diabetes: the ARIC Study

<p>Abstract</p> <p>Background</p> <p>Transcription factor 7-like 2 (<it>TCF7L2</it>) has emerged as a consistently replicated susceptibility gene for type 2 diabetes, however, whether the <it>TCF7L2 </it>gene also has similar effects on the retinal microvasculature is less clear. We therefore aimed to investigate the association between the transcription factor 7-like 2 (<it>TCF7L2</it>) rs7903146 polymorphism and retinal microvascular phenotypes in the Atherosclerosis Risk in Communities (ARIC) Study (1993-1995).</p> <p>Methods</p> <p>This was a population-based, cross-sectional study of 10,320 middle-aged African American (n = 2,199) and Caucasian (n = 8,121) men and women selected from four United States communities to examine the association between <it>TCF7L2 </it>rs7903146 polymorphism and retinal microvascular signs (retinopathy, focal arteriolar narrowing, arteriovenous nicking, arteriolar and venular calibers). Photographs on one randomly selected eye were graded for presence of retinal microvascular signs and used to measure retinal vessel calibres.</p> <p>Results</p> <p>After adjusting for age, sex, study center, mean arterial blood pressure, total serum cholesterol, triglycerides, and other covariates, few associations of <it>TCF7L2 </it>rs7903146 and retinal microvascular signs were noted. <it>TCF7L2 </it>rs7903146 T risk allele was significantly associated with focal arteriolar narrowing in Caucasians with hypertension [odds ratio (OR)_{CT vs. CC}(95% CI) = 1.25 (1.09-1.44); OR_{TT vs. CC}= 1.56 (1.18-2.06); <it>P </it>= 0.002] and in Caucasians without diabetes [OR _{CT vs. CC}= 1.18 (1.06-1.32); OR _{TT vs. CC}= 1.40 (1.12, 1.75); <it>P </it>= 0.003]. No significant association of the <it>TCF7L2 </it>rs7903146 polymorphism and retinal vascular signs was noted among African American individuals.</p> <p>Conclusions</p> <p><it>TCF7L2 </it>rs7903146 is not consistently associated with retinal microvascular signs. However, we report an association between the <it>TCF7L2 </it>rs7903146 polymorphism and focal arteriolar narrowing in Caucasians with hypertension or without diabetes. Further research in other large, population-based studies is needed to replicate these findings.</p