Mean values in inhomogeneous atmospheres

A brief summary of observations of inhomogeneities in the solar atmosphere and progress in the theoretical analysis of two-dimensional model atmospheres is given. In particular, it is asserted that reliable reference models of the mean temperature, pressure, etc. may be derived only by averaging over the horizontal coordinates of a two- or three-dimensional model. In discussion of a wide variety of cases including strong chromospheric lines, weak photospheric lines, and continuum radiation, it is shown that although the derivation of mean values by first averaging over the fluctuations in the data and then applying a one-dimension analysis is an obvious first approximation, it may lead to errors of a gross qualitative nature. Thus the recent deductions by several authors of very small temperature gradients in the upper regions of sunspots are shown to be subject to considerable doubt.     

The British Tertiary igneous province: palaeomagnetism of the Arran dykes

Summary. Five hundred and sixteen sites in Arran were sampled. After cleaning by heating and/or alternating fields 87 per cent yielded directions with α₉₅ < 10°, comprising 435 dykes, 12 sills and one granite; polarities could be determined for some of the remainder. Directions are thought to be primary and on average are shallower than corresponds to the mean centred axial dipole, with many shallow reversely-magnetized dykes present.
Seventeen per cent of the dykes are normally magnetized, 5 per cent have intermediate directions. Polarity does not correlate with petrography, thickness or trend, but does depend upon location. In particular, on the NE coast up to 70 per cent are normal, and possibly belong to a different swarm.
Normal polarities were found for both sites in the Northern Granite, for Holy Island and for some of the sills. In conjunction with the known stratigraphy this shows that the rocks were formed during an R-N-R sequence of polarities, or more probably R-N-R-N. Using the radiometric age of 58 Ma for the Northern Granite and the best estimate of the polarity time-scale the duration of activity was probably in the range 0.5 to 3.4 Ma if three polarity periods were involved, and 3.4 to 4.4 Ma if four were involved.     

Spatio-temporal pattern of viral meningitis in Michigan, 1993-2001

To characterize Michigans high viral meningitis incidence rates, 8,803 cases from 1993–2001 were analyzed for standard epidemiological indices, geographic distribution, and spatio-temporal clusters. Blacks and infants were found to be high-risk groups. Annual seasonality and interannual variability in epidemic magnitude were apparent. Cases were concentrated in southern Michigan, and cumulative incidence was correlated with population density at the county level (r=0.45, p<0.001). Kulldorffs Scan test identified the occurrence of spatio-temporal clusters in Lower Michigan during July–October 1998 and 2001 (p=0.01). More extensive data on cases, laboratory isolates, sociodemographics, and environmental exposures should improve detection and enhance the effectiveness of a Space-Time Information System aimed at prevention.The authors gratefully acknowledge Dr. Duane Newton, former manager of the Virology Section, Michigan Department of Community Health Bureau of Laboratories, for his provision of data on viral isolates. We also appreciate the contributions of Drs. Leah Estberg and Dunrie Greiling for ClusterSeer support, Scott Swan for his assistance with ArcView GIS, and Dr. Edward L. Ionides for his advice on time series analysis. We are grateful to Dr. Pierre Goovaerts and two anonymous reviewers for their insightful comments on an earlier draft of this paper. This project was supported in part by a grant from the National Oceanic and Atmospheric Administrations Joint Program on Climate Variability and Human Health, a consortium including the EPA, NASA, NSF, and EPRI (NA16GP2361) to MLW.     

Petrogenesis of syenites at a rifted continental margin: origin,contamination and interaction of alkaline mafic and felsic magmas in the Astrophyllite Bay Complex,East Greenland

The Astrophyllite Bay Complex in East Greenland (part of the Palaeogene North Atlantic Igneous Province) consists of an alkaline diorite plug, with detached trachyandesitic pillows, surrounded by co-magmatic syenite that was emplaced into Archaean basement. The diorite intrusion has yielded a 47.11 ± 0.68 Ma Rb-Sr isochron age. Saw-cut profiles through pillow-syenite-gneiss sections have been taken to resolve close spatial elemental and isotopic (Sr-Nd-Hf-Pb-O) variations. The diorite and syenite formed from alkaline basaltic, mantle-derived, melts with complex histories of prolonged assimilation and fractional crystallisation. Each evolved to different extents in separate magma chambers during the establishment of new plumbing systems in the Kangerlussuaq area. The diorite is dominated by lower crustal, granulite facies contamination, whereas the syenite shows evidence for greater degrees of upper crustal amphibolite facies contamination, indicating stalling and fractionation of magmas at different levels within the crust. The syenite and diorite magmas were subsequently emplaced as separate pulses into the basement gneisses at Astrophyllite Bay giving rise to superimposed local contamination trends between pillow/syenite and syenite/gneiss, respectively.     

A High-Performance,High-Accuracy RTK GPS Machine Guiadance System

As technology matures, Real Time Kinematic (RTK) global positioning system (GPS) receivers are providing increased performance in accuracy, on-the-fly (OTF) initialization times, measurement speed, and latency. Leica's Dozer 2000 machine guidance system combines an MC1000 GPS sensor, graphic intensive guidance software, a digital terrain model, and a digital site plan. Figure 1 shows the operator's view of the system. The end results is a highly accurate, extremely responsive local navigation system. Engineers can easily upload design information onto a touch-screen machine guidance personal computer (PC) and greatly reduce earthmoving costs while simultaneously recording “as-built” inspection data. The Leica MC1000 machine control sensor is a true 10-Hz, centimeter-level-accuracy, open-architecture GPS sensor specifically designed for machine guidance and control. At the heart of the MC1000's performance are a very stable oven-controlled oscillator (3 × 10⁻¹¹/s short-term stability), a low-power Intel 486-DX4-80 processor, and four user-configurable input/output (I7O) ports. Special algorithms mitigate the effects of multipath and Selective Availability (SA) while providing centimeter accuracy up to 10 times per second with only 30 milliseconds' latency. The high update rate and low latency are essential for machine guidance and control. The MC1000 GPS reference station is capable of outputting RTK and Differential GPS (DGPS) data simultaneously, providing and entire site with GPS information for machine guidance and control, tracking and dispatching of vehicles, and support of survey crews. This article describes how recent advances in technology have combined to produce the Leica Dozer 2000 – a machine guidance system that is ideal for a wide range of earthmoving and inspection applications. ? 2000 John Wiley & Sons, Inc.     

Early Cretaceous magmatism of Mount Hermon, Northern Israel

 Early Cretaceous (146–115 Ma) magmatism in the region of Mt. Hermon, Northern Israel, is part of an extensive Mesozoic igneous province within the Levant associated with the evolution of the Neotethyan passive margin of Gondwana. The initial stages of activity were characterised by the emplacement of tholeiitic dykes (146–140 Ma) which were uplifted and eroded prior to the eruption of a sequence of alkali basalts, basanites and more differentiated alkaline lavas and pyroclastics from 127 to 120 Ma. The latest stages of activity (120–115 Ma) were highly explosive, resulting in the emplacement of diatreme breccias. Trace element and Sr-Nd-Pb isotope data for the most primitive Early Cretaceous mafic igneous rocks sampled suggest that they were derived by mixing of melts derived by variable degrees of partial melting of both garnet- and spinel-peridotite-facies mantle sources. Though isotopically heterogeneous, the source of the magmas has many similarities to that of HIMU oceanic island basalts. Earlier Liassic (200 Ma) transitional basalts and Neogene–Quaternary (15–0 Ma) alkali basalts erupted within northern Israel also have HIMU affinities. The petrogenesis of the Early Cretaceous and Cenozoic basalts is explained by partial melting of a lithospheric mantle protolith metasomatically enriched during the Liassic volcanic phase, which may be plume-related. Received: 23 July 1998 / Accepted: 6 December 1999