Subduction dynamics: Constraints from gravity field observations

Satellite systems do the best job of resolving the long wavelength components of the Earth's gravity field. Over the oceans, satellite-borne radar altimeters such as SEASAT provide the best resolution observations of the intermediate wavelength components. Satellite observations of gravity contributed to the understanding of the dynamics of subduction. Large, long wavelength geoidal highs generally occur over subduction zones. These highs are attributed to the superposition of two effects of subduction: (1) the positive mass anomalies of subducting slabs themselves; and (2) the surface deformations such as the trenches convectively inducted by these slabs as they sink into the mantle. Models of this subduction process suggest that the mantle behaves as a nonNewtonian fluid, its effective viscosity increases significantly with depth, and that large positive mass anomalies may occur beneath the seismically defined Benioff zones

On the compensation of geoid anomalies due to subducting slabs

Candidate models of the forces which oppose the sinking of slabs are all constrained to produce results consistent with the following observation: relative geoid highs, which one assumes are due to slabs, characteristically occur over subduction zones. Certain models which are otherwise plausible, such as those based on a Newtonian half-space mantle, yield geoid lows instead of highs. This study has extended a published model of viscous corner flow in subduction zones in order to demonstrate that it can, in certain cases, produce the requisite geoid highs. Specifically the relative geoid highs are produced if mantle flow is distinctly non-Newtonian (stress exponent n 2). Results in the form of deflection on vertical (or geoid slope) profiles are computed for typical values of the slab parameters; they are compared with a representative profile of geoid slopes derived from Seasat altimeter data in order to show qualitative similarities. It is concluded that the effect of non-Newtonian flow as opposed to Newtonian, is to spread out the induced surface deformation, thereby stretching out the regional compensation to wavelengths, (transverse to the trench) of several thousand kilometers

Geoid anomalies in the vicinity of subduction zones

The regional geoid of the southwest Pacific is matched reasonably well by results from a model of the upper mantle density structure (including slabs) associated with subduction zones of the region. Estimates of the geoid are obtained from Geos-3 and Seasat radar altimeter data. These data are very well suited to the task of detecting intermediate wavelength (600-4000 km) geopotential variations. Actually, subducting slabs can be expected to produce primarily intermediate and longer wavelength variations. Gravimetric profiles across trench/island arc complexes resolve primarily short wavelengths. The model represents subducting slabs as thin surfaces of anomalous mass per unit area. These surfaces are positioned using published seismicity results which detail the configuration of the Benioff zones. Crustal effects are ignored. Effects due to the contrast between the young thermal lithosphere of the behind-arc regions (marginal basins) and the older lithosphere seaward of the trench are modelled. Results indicate that the New Hebrides slab possesses an average areal density anomaly of about 300,000 gm/sq cm. This is about three times that which is estimated for the Tonga-Kermadec slab. Additional modelling suggests that slabs worldwide may be an important source of large, long wavelength gravity highs; i.e., they may contribute substantially to geopotential power of harmonic degree as low as three or four up to twenty or more

Geodynamics and temporal variations in the gravity field

Just as the Earth's surface deforms tectonically, so too does the gravity field evolve with time. Now that precise geodesy is yielding observations of these deformations it is important that concomitant, temporal changes in the gravity field be monitored. Although these temporal changes are minute they are observable: changes in the J2 component of the gravity field were inferred from satellite (LAGEOS) tracking data; changes in other components of the gravity field would likely be detected by Geopotential Research Mission (GRM), a proposed but unapproved NASA gravity field mission. Satellite gradiometers were also proposed for high-precision gravity field mapping. Using simple models of geodynamic processes such as viscous postglacial rebound of the solid Earth, great subduction zone earthquakes and seasonal glacial mass fluctuations, we predict temporal changes in gravity gradients at spacecraft altitudes. It was found that these proposed gravity gradient satellite missions should have sensitivities equal to or better than 10(exp -4) E in order to reliably detect these changes. It was also found that satellite altimetry yields little promise of useful detection of time variations in gravity

All Rise, the Court Is in Session: What Judges Say About Court-Connected Mediation

Published in cooperation with the American Bar Association Section of Dispute Resolutio

The role of spleen tyrosine kinase in glomerulonephritis

Spleen tyrosine kinase (SYK) is a non-receptor tyrosine kinase that has an important role in immunoreceptor signalling, including for the B cell receptor and activatory Fc receptors. SYK inhibition has shown efficacy in animal models of non-renal autoimmune disease. The role of SYK in experimental and clinical renal disease, however, is not well defined. I have studied the effects of SYK inhibition using a specific small molecule inhibitor (R788; fostamatinib) in two distinct experimental models of glomerulonephritis in the rat. In experimental autoimmune glomerulonephritis (EAG; a model of anti-glomerular basement membrane disease), I have shown that SYK inhibition with fostamatinib both prevents and treats established disease. Significant attenuation of humoral autoimmune responses was observed, and ELISpot and flow cytometric analysis suggests that this was due to a direct inhibitory effect on B cell activity, rather than overall B cell survival. In addition, SYK inhibition appeared to inhibit antibody-dependent, Fc receptor-mediated pro-inflammatory responses, particularly within glomerular macrophages, in EAG. In experimental autoimmune vasculitis (EAV; a model of anti-neutrophil cytoplasm antibody [ANCA] associated vasculitis), SYK inhibition was an effective treatment for life-threatening manifestations of disease, including glomerulonephritis and lung haemorrhage. I have also examined the pattern of SYK expression by immunohistochemistry in clinical renal biopsy specimens from approximately 100 patients with a spectrum of glomerular pathologies. I found that SYK is expressed and activated in proliferative types of glomerulonephritis, and that expression levels correlate with disease activity in anti-GBM disease, ANCA-associated vasculitis, lupus nephritis and IgA nephropathy. These data suggest that SYK is important in the pathogenesis of proliferative glomerulonephritis. SYK inhibition is an effective treatment strategy for the organ-threatening manifestations of disease in two experimental models, and SYK inhibition therefore warrants further investigation in human renal disease.Open Acces

The Impact of Learning Preferences on Retention of Adult Students in an Online Degree Program

Adult students choose online courses for flexibility and convenience and educational institutions are providing more options to meet demand, but online courses have higher rates of attrition that can lead to lower retention. Low retention of students has consequences for students, colleges and universities, and society as a whole. The purpose of this research was to determine the relationship between learning preference, based on a multiple intelligences model, and choice of major, student satisfaction, and retention of adult students in a fully online degree program. A review of literature found that learning preference has been correlated with student performance in an online course, but not with student satisfaction. Little research exists that explores a connection between learning preference and retention. The researcher conducted quantitative correlational research and independent samples t-tests using archival data and survey results to identify learning preference, major, retention, and student satisfaction levels of 273 adult students in a fully online degree program. Data analysis did not identify statistically significant relationships between learning preference and major, or learning preference and retention; however, a statistically significant relationship was found between student satisfaction and retention. Conclusions imply the need for further research on differentiating instruction and how learning preferences influence retention of adult students in online courses

The State Can Rest: Texas Rule of Appellate Procedure 44.2(b) and Harmless Error

This Note will outline the contours of Rule 44.2(b) by examining: (1) the reasons and motivations behind the adoption of the new rule; (2) the case law interpreting the new standard contrasted against the old rule; and (3) the potentialities inherent in the new rule for harm to the rights of the accused. Finally, this Note will illustrate why, in the interest of justice, the new rule should be discarded in favor of the old rule

Mediation Tune up for the State Court Appellate Machine, A

This Article begins in Part II with a review of the rationale for appellate mediation programs. In Part III the Article will discuss the development and evaluation of a pilot program for the mediation of family appellate cases in Minnesota. The pilot was developed and implemented with the goals of settlement and other qualitative justice measures in mind. Moreover, preliminary evaluation results for the pilot suggest that both continue to be important and can be achieved.3 In Part IV the Article will discuss the elements of program design most likely to make appellate mediation programs succeed, in terms of both efficiency and procedural justice. The Article will suggest that commitment to both of these goals in appellate mediation programs will help to ensure that there is sufficient oil to prevent a breakdown in the engine of justice