A computer method for stability analysis of caverns in jointed rock

A simple rigid block model has been developed for analysing the stability of caverns and tunnels in jointed rock. Rigid block interactions are idealized as linear edge-to-edge contacts with a zero joint tension constraint and a Mohr-Coulomb friction law. In the method, the minimum friction angle for stability is determined by sequentially eliminating tension and then minimizing the shear. It is demonstrated through examples that the minimum joint friction angle which results in a stable configuration is independent of the stiffness of the joint, and depends only upon the loading and geometry of the jointing and cavern. This insensitivity of stability to the normal and tangential joint stiffnesses, which can be difficult to obtain, is very useful for design purposes.     

MAPPING SOLAR ACCESS IN HIGH RELIEF AREAS FOR REGIONAL ENERGY PLANNING*

Access to the sun for space heating of structures is controlled, in part, by topographic shadowing in high-relief regions. A simple graphic procedure is presented for mapping shadows on topographic maps for any date and time of day. Comparisons of computed shadows and shadows measured from aerial photography confirm that the mapping procedure is reliable and accurate. Use of the procedure as a solar access inventory tool is illustrated in an area of the Green Mountains, VT.     

The PIRLA project (Paleoecological Investigation of Recent Lake Acidification): an introduction to the synthesis of the project

Collected sets of papers synthesizing data derived from the PIRLA project (Paleoecological Investigation of Recent Lake Acidification) will appear in coming issues of the Journal of Paleolimnology. This paper is designed to highlight these forthcoming papers, review the development and objectives of PIRLA, and acknowledge the many who have supported PIRLA in so many crucial ways.This is the first of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D.F. Charles and D.R. Whitehead are guest editors for this series.     

Superhumps in black hole X-ray transients

The superhumps in black hole X-ray transientsresult from a modulation in the area of the accretion disc. We discussimplications of this for parameter determinations in LMXBs.     

Warming permafrost in European mountains

Here we present the first systematic measurements of European mountain permafrost temperatures from a latitudinal transect of six boreholes extending from the Alps, through Scandinavia to Svalbard. Boreholes were drilled in bedrock to depths of at least 100 m between May 1998 and September 2000. Geothermal profiles provide evidence for regional-scale secular warming, since all are nonlinear, with near-surface warm-side temperature deviations from the deeper thermal gradient. Topographic effects lead to variability between Alpine sites. First approximation estimates, based on curvature within the borehole thermal profiles, indicate a maximum ground surface warming of +1 °C in Svalbard, considered to relate to thermal changes in the last 100 years. In addition, a 15-year time series of thermal data from the 58-m-deep Murtèl–Corvatsch permafrost borehole in Switzerland, drilled in creeping frozen ice-rich rock debris, shows an overall warming trend, but with high-amplitude interannual fluctuations that reflect early winter snow cover more strongly than air temperatures. Thus interpretation of the deeper borehole thermal histories must clearly take account of the potential effects of changing snow cover in addition to atmospheric temperatures.     

Is the pre-WMAP CMB data self-consistent?

Although individual observational groups vigorously test their datasets for systematic errors, the pre-WMAP CMB observational dataset has not yet been collectively tested. Under the assumption that the concordance model is the correct model, we have explored residuals of the observational data with respect to this model to see if any patterns emerge that can be identified with systematic errors. We found no significant trends associated with frequency, frequency channels, calibration source, pointing uncertainty, instrument type, platform and altitude. We did find some evidence at the 1 to 2σ level for trends associated with angular scale (ℓ range) and absolute galactic latitude. The slope of the trend in galactic latitude is consistent with low level galactic contamination. The residuals with respect to ℓ may indicate that the concordance model used here needs slight modification. See Griffiths and Lineweaver (astro-ph/0301490) for more detail.     

Noble gas space exposure ages of individual interplanetary dust particles

Abstract— The He, Ne, and Ar compositions of 32 individual interplanetary dust particles (IDPs) were measured using low‐blank laser probe gas extraction. These measurements reveal definitive evidence of space exposure. The Ne and Ar isotopic compositions in the IDPs are primarily a mixture between solar wind (SW) and an isotopically heavier component dubbed “fractionated solar” (FS), which could be implantation‐fractionated solar wind or a distinct component of the solar corpuscular radiation previously identified as solar energetic particles (SEP). Space exposure ages based on the Ar content of individual IDPs are estimated for a subset of the grains that appear to have escaped significant volatile losses during atmosphere entry. Although model‐dependent, most of the particles in this subset have ages that are roughly consistent with origin in the asteroid belt. A short (<1000 years) space exposure age is inferred for one particle, which is suggestive of cometary origin. Among the subset of grains that show some evidence for relatively high atmospheric entry heating, two possess elevated ²¹Ne/²²Ne ratios generated by extended exposure to solar and galactic cosmic rays. The inferred cosmic ray exposure ages of these particles exceeds 10⁷ years, which tends to rule out origin in the asteroid belt. A favorable possibility is that these ²¹Ne‐rich IDPs previously resided on a relatively stable regolith of an Edgeworth‐Kuiper belt or Oort cloud body and were introduced into the inner solar system by cometary activity. These results demonstrate the utility of noble gas measurements in constraining models for the origins of interplanetary dust particles.