Semi‐analytical far field model for three‐dimensional finite‐element analysis

A challenging computational problem arises when a discrete structure (e.g. foundation) interacts with an unbounded medium (e.g. deep soil deposit), particularly if general loading conditions and non‐linear material behaviour is assumed. In this paper, a novel method for dealing with such a problem is formulated by combining conventional three‐dimensional finite‐elements with the recently developed scaled boundary finite‐element method. The scaled boundary finite‐element method is a semi‐analytical technique based on finite‐elements that obtains a symmetric stiffness matrix with respect to degrees of freedom on a discretized boundary. The method is particularly well suited to modelling unbounded domains as analytical solutions are found in a radial co‐ordinate direction, but, unlike the boundary‐element method, no complex fundamental solution is required. A technique for coupling the stiffness matrix of bounded three‐dimensional finite‐element domain with the stiffness matrix of the unbounded scaled boundary finite‐element domain, which uses a Fourier series to model the variation of displacement in the circumferential direction of the cylindrical co‐ordinate system, is described. The accuracy and computational efficiency of the new formulation is demonstrated through the linear elastic analysis of rigid circular and square footings. Copyright © 2004 John Wiley & Sons, Ltd.     

Rapid inactivation of seven Bacillus spp. under simulated Mars UV irradiation

Seven Bacillus spp. were exposed to simulations of Mars-normal UV fluence rates in order to study the effects of UV irradiation on microbial survival. A UV illumination system was calibrated to deliver 9.78 W m⁻² (35.2 kJ m⁻² h⁻¹) of UVC + UVB irradiation (200-320 nm) to microbial samples, thus creating a clear-sky simulation (0.5 optical depth) of equatorial Mars. The Bacillus spp. studied were: B. licheniformis KL-196, B. megaterium KL-197, B. nealsonii FO-092, B. pumilus FO-36B, B. pumilus SAFR-032, B. subtilis 42HS1, and B. subtilis HA101. The bacteria were prepared as thin monolayers of endospores on aluminum coupons in order to simulate contaminated spacecraft surfaces. Bacterial monolayers were exposed to Mars UV irradiation for time-steps of 0, 0.25, 0.5, 1, 5, 15, 30, 60, 120, or 180 min. The surviving endospores were then assayed with a Most Probable Numbers (MPN) procedure and with a culture-based assay that utilized a bacillus spore germination medium. Results indicated that B. pumilus SAFR-032 was the most resistant, and B. subtilis 42HS-1 and B. megaterium were the most sensitive of the seven strains exposed to martian UV fluence rates. Bacillus subtilis 42HS1 and B. megaterium were inactivated after 30 min exposure to Mars UV, while B. pumilus SAFR-032 required 180 min for full inactivation in both assays. Spores of B. pumilus SAFR-032 exhibited significantly different inactivation kinetics suggesting that this wild type isolate also was more resistant than the standard dosimetric strain, B. subtilis HA101. Although the various Bacillus spp. exhibited diverse levels of UV resistance, none were immune to UV irradiation, and, thus, all species would be expected to be inactivated on Sun-exposed spacecraft surfaces within a few tens-of-minutes to a few hours on sol 1 under clear-sky conditions on equatorial Mars. The inactivation kinetics of all seven Bacillus spp. support the conclusion that significant levels of bioload reductions are possible on Sun-exposed spacecraft surfaces in very short time periods under clear-sky conditions on Mars. However, the presence of UV resistant microbes on spacecraft surfaces rapidly covered in dust during landing operations, and non-Sun-exposed surfaces of spacecraft remain concerns that must continue to be addressed through adequate spacecraft sanitizing procedures prior to launch.     

Formation and reorientation of structure in the surge‐type glacier Kongsvegen,Svalbard

Kongsvegen, a surge‐type glacier in Spitsbergen, Svalbard, shares a tide‐water margin with the glacier Kronebreen. The complex has been in retreat since a surge advance of Kongsvegen around 1948. The surface of Kongsvegen displays suites of deformational structures highlighted by debris‐rich folia. These structures are melting out to form a network of sediment ridges in the grounded terminal area. The structures are also visible in a marginal, 1 km long, 5–20 m high cliff‐face at the terminus. Current models for the evolution of deformational structures at Kongsvegen divide the structures into suites based on their orientation and dip, before assigning a mechanism for genesis based on structure geometry. Interpretation of aerial photographs and field mapping of surface structures suggest that many structures were reorientated or advected during the surge. We suggest that many of the deformational structures highlighted by debris‐rich folia represent reorientated, sediment‐filled crevasses. Some evidence of thrusting is apparent but the process is not as ubiquitous as previously suggested. Many deformational structures also appear to have been offset by more recent structures. Mechanisms of structural development must, therefore, be considered within the context of distinct stages of glacier flow dynamics and multiple surge episodes. Furthermore, evidence for thrusting and folding within the glacier systems of Svalbard has been used as the basis for interpreting Quaternary glacial landforms in the UK. The findings of this paper, therefore, have implications for interpretations of the Quaternary record. Copyright © 2002 John Wiley & Sons, Ltd.     

GNSS receiver implementations to mitigate the effects of commensurate sampling frequencies on DLL code tracking

The sampling frequency of a digitized intermediate frequency signal has a strong effect on the measurement accuracy of Global Navigation Satellite System (GNSS) receivers. The delay-locked loop tracking error is significant when the sampling frequency is an integer multiple of the code chipping rate, the so-called commensurate sampling frequency, and the number of distinct instantaneous residual code phases is low. This results in distortions of the correlation shape and discriminator functions that lead to a significant accuracy degradation. These effects are most pronounced when the sampling frequency is low. Notwithstanding, it is generally good for receivers to keep the sampling frequency to a minimum owing to the processing load and power consumption. It creates a challenge for existing GNSS signal processing techniques. Random, sine and sawtooth jitters have been found to mitigate these distortions considerably. A software algorithm and two hardware receiver implementations of these solutions are proposed. A register-based architecture can be directly applied to the conventional receiver architecture, while the increase in resource and power consumption is insignificant. A RAM-based design cannot only considerably minimize utilized resources but also slightly reduce the power consumption compared to the conventional architecture.     

The regional forcing of Northern hemisphere drought during recent warm tropical west Pacific Ocean La Niña events

Northern Hemisphere circulations differ considerably between individual El Niño-Southern Oscillation events due to internal atmospheric variability and variation in the zonal location of sea surface temperature forcing over the tropical Pacific Ocean. This study examines the similarities between recent Northern Hemisphere droughts associated with La Niña events and anomalously warm tropical west Pacific sea surface temperatures during 1988–1989, 1998–2000, 2007–2008 and 2010–2011 in terms of the hemispheric-scale circulations and the regional forcing of precipitation over North America and Asia during the cold season of November through April. The continental precipitation reductions associated with recent central Pacific La Niña events were most severe over North America, eastern Africa, the Middle East and southwest Asia. High pressure dominated the entire Northern Hemisphere mid-latitudes and weakened and displaced storm tracks northward over North America into central Canada. Regionally over North America and Asia, the position of anomalous circulations within the zonal band of mid-latitude high pressure varied between each La Niña event. Over the northwestern and southeastern United States and southern Asia, the interactions of anomalous circulations resulted in consistent regional temperature advection, which was subsequently balanced by similar precipitation-modifying vertical motions. Over the central and northeastern United States, the spatial variation of anomalous circulations resulted in modest inter-seasonal temperature advection variations, which were balanced by varying vertical motion and precipitation patterns. Over the Middle East and eastern Africa, the divergence of moisture and the advection of dry air due to anomalous circulations enhanced each of the droughts.     

Seismic demands on secondary systems in base‐isolated nuclear power plants

Numerical models of a sample nuclear power plant (NPP) reactor building, both conventionally constructed and equipped with seismic protective systems, are analysed for both safe shutdown and beyond‐design‐basis earthquake shaking at two coastal sites in the United States. Seismic demands on secondary systems are established for the conventional and seismically isolated NPPs. The reductions in secondary‐system acceleration and deformation demands afforded by the isolation systems are identified. Performance spaces are introduced as an alternate method for evaluating demands on secondary systems. The results show that isolation systems greatly reduce both the median and dispersion of seismic demands on secondary systems in NPPs. Copyright © 2007 John Wiley & Sons, Ltd.