SiO and GeO bonded interactions as inferred from the bond critical point properties of electron density distributions

The topological properties of the electron density distributions for more than 20 hydroxyacid, geometry optimized molecules with SiO and GeO bonds with 3-, 4-, 6- and 8-coordinate Si and Ge cations were calculated. Electronegativities calculated with the bond critical point (bcp) properties of the distributions indicate, for a given coordination number, that the electronegativity of Ge (∼1.85) is slightly larger than that of Si (∼1.80) with the electronegativities of both atoms increasing with decreasing bond length. With an increase in the electron density, the curvatures and the Laplacian of the electron density at the critical point of each bond increase with decreasing bond length. The covalent character of the bonds are assessed, using bond critical point properties and electronegativity values calculated from the electron density distributions. A mapping of the (3, −3) critical points of the valence shell concentrations of the oxide anions for bridging SiOSi and GeOGe dimers reveals a location and disposition of localized nonbonding electron pairs that is consistent with the bridging angles observed for silicates and germanates. The bcp properties of electron density distributions of the SiO bonds calculated for representative molecular models of the coesite structure agree with average values obtained in X-ray diffraction studies of coesite and danburite to within ∼5%. Received: 18 August 1997 / Revised, accepted: 19 February 1998     

Martian topography and surface properties as seen by radar: The 1971 opposition

Taking advantage of the favorable opposition of 1971, the Goldstone radar system, operating at 2388MHz, was used to scan the Martian surface. Measurements of altitude and reflected power were taken approximately every 3 days. Each measurement represents an area 8km E-W × 80km N-S, the highest resolution attained to date. Altitude measurements obtained on different observing days were combined to produce altitude profiles for three complete rotations, each at different latitudes. Large-scale variations in altitudes cover a range of 14km. Altitude changes of 5 in 30km of longitude were observed. The altitude profiles show the heavy cratering of the surface, and several large craters (50–100km) 1–2 km deep are easily seen. Reflected power for different angles of incidence was measured, yielding the scattering properties of the surface as a function of longitude. Correlation was found between the peak intensity of the reflected signal and the width of the scattering function. The average relationship between the intensity and the width suggests a power reflection coefficient of at least 0.064 ± 0.012. Departures from the average are interpreted as deviations in the reflection coefficient from the mean value. These variations are presented as a function of longitude for each of the three rotations.     

Cellular diagnostics and coral health: declining coral health in the Florida Keys

Coral reefs within the Florida Keys are disappearing at an alarming rate. Coral cover in the Florida Keys National Marine Sanctuary declined by 38% from 1996 to 2000. In 2000, populations of Montastraea annularis at four sites near Molasses Reef within the Florida Keys National Marine Sanctuary and one reef within Biscayne National Park were sampled on a quarterly basis. Anecdotal observations showed corals at Alina's Reef in Biscayne National Park appeared healthy in March, but experienced an acute loss of coral cover by August. Cellular Diagnostic analysis indicated that Alina's Reef corals were in distress: they had been afflicted with a severe oxidative damaging and protein-denaturing stress that affected both the corals and their symbiotic zooxanthellae. This condition was associated with a significant xenobiotic detoxification response in both species, reflecting probable chemical contaminant exposure. These results demonstrate that applying a Cellular Diagnostic approach can be effective in helping to identify stress and its underlying causes, providing diagnostic and prognostic biomarkers of coral health.     

The network K‐function in context: examining the effects of network structure on the network K‐function

The flaws of using traditional planar point‐pattern analysis techniques with network constrained points have been thoroughly explored in the literature. Because of this, new network‐based measures have been introduced for their planar analogues, including the network based K‐function. These new measures involve the calculation of network distances between point events rather than traditional Euclidean distances. Some have suggested that the underlying structure of a network, such as whether it includes directional constraints or speed limits, may be considered when applying these methods. How different network structures might affect the results of the network spatial statistics is not well understood. This article examines the results of network K‐functions when taking into consideration network distances for three different types of networks: the original road network, topologically correct networks, and directionally constrained networks. For this aim, four scenarios using road networks from Tampa, Florida and New York City, New York were used to test how network constraints affected the network K‐function. Depending on which network is under consideration, the underlying network structure could impact the interpretation. In particular, directional constraints showed reduced clustering across the different scenarios. Caution should be used when selecting the road network, and constraints, for a network K‐function analysis.     

Relevance of software reuse in building advanced scientific data processing systems

Reuse of software and related components can contribute to the development of systems for processing scientific data. The reuse of components, which can be from any stage of the development life cycle, provides opportunities to realize benefits such as reduced costs and learning curves. However, the reuse of existing components also comes with risks that must be recognized in order to be mitigated. The National Aeronautics and Space Administration established the Earth Science Data Systems Software Reuse Working Group to support software reuse among members of the community of Earth science data systems developers. This is done through a variety of activities, including research, education, and public outreach, which are conducted to help encourage and enable reuse within the community. Considerations for realizing the benefits of software reuse and minimizing risks are presented along with recent working group activities to improve reuse capabilities for the community of Earth science data systems developers.     

Applying machine learning to catalogue matching in astrophysics

We present the results of applying automated machine learning techniques to the problem of matching different object catalogues in astrophysics. In this study, we take two partially matched catalogues where one of the two catalogues has a large positional uncertainty. The two catalogues we used here were taken from the H  i Parkes All Sky Survey (HIPASS) and SuperCOSMOS optical survey. Previous work had matched 44 per cent (1887 objects) of HIPASS to the SuperCOSMOS catalogue.
A supervised learning algorithm was then applied to construct a model of the matched portion of our catalogue. Validation of the model shows that we achieved a good classification performance (99.12 per cent correct).
Applying this model to the unmatched portion of the catalogue found 1209 new matches. This increases the catalogue size from 1887 matched objects to 3096. The combination of these procedures yields a catalogue that is 72 per cent matched.     

The Anthropocene: is there a geomorphological case?

The ‘Anthropocene’, as used to describe the interval of recent Earth history during which humans have had an ‘overwhelming’ effect on the Earth system, is now being formally considered as a possible new geological Epoch. Such a new geological time interval (possibly equivalent to the Pleistocene Epoch) requires both theoretical justification as well as empirical evidence preserved within the geological record. Since the geological record is driven by geomorphological processes that produce terrestrial and near‐shore stratigraphy, geomorphology has to be an integral part of this consideration. For this reason, the British Society for Geomorphology (BSG) has inaugurated a Fixed Term Working Group to consider this issue and advise the Society on how geomorphologists can engage with debates over the Anthropocene. This ESEX Commentary sets out the initial case for the formalisation of the Anthropocene and a priori considerations in the hope that it will stimulate debate amongst, and involvement by, the geomorphological community in what is a crucial issue for the discipline. The Working Group is now considering the practical aspects of such a formalization including the relative magnitude problem, the boundary problem and the spatial diachrony of ‘anthropogenic geomorphology’. Copyright © 2013 John Wiley & Sons, Ltd.     

The anatomy of effective discharge: the dynamics of coarse sediment transport revealed using continuous bedload monitoring in a gravel‐bed river during a very wet year

Indirect, passive approaches for monitoring coarse bedload transport could allow cheaper, safer, higher‐resolution, longer‐term data that revolutionises bedload understanding and informs river management. Here, insights provided by seismic impact plates in a downstream reach of a flashy gravel‐bed river (River Avon, Devon, UK) are explored in the context of plate performance. Monitoring of a centrally‐situated plate (IP1) during an extremely wet 12‐month period demonstrated that impacts were related to discharge as a measure of transport potential (R² = 0.38) but that factors other than transport limitations are important. Analysis of discrete flow events revealed consistent rising‐limb and falling‐limb impact spikes biased toward the latter for larger events. Such patterns may result from disruption of the upstream armour layer (rising limb) and supply enhancements related to both upstream mass bank failures and/or flood routing of non‐local sediment sources (falling limb). Installation of additional impact plates indicated that plate IP1 was indeed dominantly related to instantaneous discharge, that a three‐plate lateral array somewhat better explained impact variability (R² = 0.49), and that the bedload track shifts laterally with discharge. Aggregating event‐total IP1 impacts against volumetric discharge further increases explanation as intra‐event and stochastic bedload factors are subsumed but left 26% unexplained variance related to the unsampled bedload mass, inter‐event supply differences, and attributes of plate performance. Annualising the data created an impact‐based 'effective discharge’ for this extremely wet year that was closer to morphological bar‐full in magnitude than bankfull, but the preceding results imply this outcome is related as much to supply limitations as transport limitations. Overall, passive approaches offer a liberating prospect for bedload monitoring, capable of producing insights only achievable through high resolution, extended time periods. Such results could potentially inform threshold conditions and geomorphological effectiveness of flows for future river management strategies. Copyright © 2015 John Wiley & Sons, Ltd.     

Vulnerability to epidemic malaria in the highlands of Lake Victoria basin: the role of climate change/variability, hydrology and socio-economic factors

Endemic malaria in most of the hot and humid African climates is the leading cause of morbidity and mortality. In the last twenty or so years the incidence of malaria has been aggravated by the resurgence of highland malaria epidemics which hitherto had been rare. A close association between malaria epidemics and climate variability has been reported but not universally accepted. Similarly, the relationship between climate variability, intensity of disease mortality and morbidity coupled with socio-economic factors has been mooted. Analyses of past climate (temperature and precipitation), hydrological and health data (1961–2001), and socio-economics status of communities from the East African highlands confirm the link between climate variability and the incidence and severity of malaria epidemics. The communities in the highlands that have had less exposure to malaria are more vulnerable than their counterparts in the lowlands due to lack of clinical immunity. However, the vulnerability of human health to climate variability is influenced by the coping and adaptive capacities of an individual or community. Surveys conducted among three communities in the East African highlands reveal that the interplay of poverty and other socio-economic variables have intensified the vulnerability of these communities to the impacts of malaria.     

Bayesian Estimation of Earth’s Undiscovered Mineralogical Diversity Using Noninformative Priors

Recently, statistical distributions have been explored to provide estimates of the mineralogical diversity of Earth, and Earth-like planets. In this paper, a Bayesian approach is introduced to estimate Earth’s undiscovered mineralogical diversity. Samples are generated from a posterior distribution of the model parameters using Markov chain Monte Carlo simulations such that estimates and inference are directly obtained. It was previously shown that the mineral species frequency distribution conforms to a generalized inverse Gauss–Poisson (GIGP) large number of rare events model. Even though the model fit was good, the population size estimate obtained by using this model was found to be unreasonably low by mineralogists. In this paper, several zero-truncated, mixed Poisson distributions are fitted and compared, where the Poisson-lognormal distribution is found to provide the best fit. Subsequently, the population size estimates obtained by Bayesian methods are compared to the empirical Bayes estimates. Species accumulation curves are constructed and employed to estimate the population size as a function of sampling size. Finally, the relative abundances, and hence the occurrence probabilities of species in a random sample, are calculated numerically for all mineral species in Earth’s crust using the Poisson-lognormal distribution. These calculations are connected and compared to the calculations obtained in a previous paper using the GIGP model for which mineralogical criteria of an Earth-like planet were given.