Finding shortest paths on real road networks: the case for A*

The problem of identifying the shortest path along a road network is a fundamental problem in network analysis, ranging from route guidance in a navigation system to solving spatial allocation problems. Since this type of problem is solved so frequently, it is important to craft an approach that is as efficient as possible. Based upon past research, it is generally accepted that several efficient implementations of the Dijkstra algorithm are the fastest at optimally solving the ‘one‐to‐one’ shortest path problem (Cherkassky et al. 1996 Cherkassky, B. V., Goldberg, A. V. and Radzik, T. 1996. Shortest paths algorithms: theory and experimental evaluation.. Mathematical Programming: Series A and B, 73: 129–174. [Crossref], [Web of Science ®] , [Google Scholar]). We show that the most efficient state‐of‐the‐art implementations of Dijkstra can be improved by taking advantage of network properties associated with GIS‐sourced data. The results of this paper, derived from tests of different algorithmic approaches on real road networks, will be extremely valuable for application developers and researchers in the GIS community.     

The Sustainable Global Energy Economy: Hydrogen or Silicon?

A sustainable global silicon energy economy is proposed as a potential alternative to the hydrogen economy. This first visualization of a silicon energy economy is based on large-scale and carbon-neutral metallic silicon production from major smelters in North Africa and elsewhere, supplied by desert silica sand and electricity from extensive solar generating systems. The resulting “fuel silicon” is shipped around the world to emission-free silicon power stations for either immediate electricity generation or stockpiling. The high energy density of silicon and its stable storage make it an ideal material for maintaining national economic functioning through security of base load power supply from a renewable source. This contrasts with the present situation of fossil fuel usage with its associated global warming and geopolitical supply uncertainties. Critical technological requirements for the silicon economy are carbon-neutral silicon production and the development of efficient silicon-fired power stations capable of high-temperature rapid oxidation of fuel silicon. A call is made for the development of research effort into these specific engineering issues, and also with respect to large-scale economical solar power generation.     

A sedimentary record of the rise and fall of the metal industry in Bergslagen,south central Sweden

Detailed stratigraphic analyses of sediments deposited in Lake Botjärnen, a small boreal forest lake in the shield terrain of central Sweden, clearly reflect progressively increasing human impact on terrestrial and aquatic ecosystems following settlement and establishment of an iron industry in the 17th century. Rising frequencies of pollen and spores from light-demanding plants provide evidence of extensive forest clearance for charcoal and timber production, which peaked in the early 20th century. An associated increase in catchment erosion is reflected by changing carbon and nitrogen elemental content and carbon–isotope composition of sediment organic matter and by increased magnetic susceptibility of the sediments. Records of air-borne pollutants (lead, zinc and sulphur) can be correlated to the development of local and regional mining and metal industry as inferred from historical accounts. Rapid recession of the iron industry led to re-forestation and recovery of the aquatic nutrient status to pre-industrial conditions over the past 100 years. The chronology of the sediment succession, which is based on ²¹⁰Pb and ¹³⁷Cs radionuclide data in combination with radiocarbon dating, is confirmed by historical lead pollution trends established for the region.     

Progress in isotope paleohydrology using lake sediment cellulose

Recent advances in sample preparation techniques and mass spectrometry have fostered more routine oxygen isotope analysis of aquatic cellulose in lake sediment cores, a proxy for lake water oxygen isotope history. These methodological developments have significantly increased the feasibility of incorporating this approach into high-resolution, multi-site, and multi-proxy studies, which are frequently necessary to answer complex hydrological, hydroecological and hydroclimatic questions requiring a paleoenvironmental perspective. Direct translation of lake sediment aquatic cellulose oxygen isotope composition into lake water oxygen isotope composition offers appreciable opportunity for quantitative paleohydrological reconstructions, as evidenced by studies conducted over the past 15 years that span Holocene and pre-historical timescales.     

Evaluation of ostracod-based palaeoenvironmental reconstruction with instrumental data from the arid Faiyum Depression,Egypt

The utility of ostracod-based palaeoenvironmental reconstruction was evaluated using instrumental data for Lake Qarun, Egypt. The euryhaline ostracod Cyprideis torosa was the only species found in the lake’s recent sediment record. This species is known to tolerate salinity levels and water solute compositions that may prevent colonisation by other species. Oxygen and carbon isotope ratios of ostracod carbonate from lake sediments covary with changes in instrumental values for lake level and salinity for the period 1890–1974. δ¹³C-values correlate negatively with lake water salinity (r ² = 0.87) and δ¹⁸O-values correlate negatively with measured lake level changes (r ² = 0.41). Other ostracod proxy data provide qualitative information on lake level trends. Fossil assemblage data (juvenile/adult and valve/carapace ratios and valve preservation) provide information on wave energy. Ecophenotypic variation of C. torosa valves provided some useful palaeolimnological information. Sr/Ca and Mg/Ca ratios in ostracods were not found to reflect water composition, due to the uncoupling of these ratios with salinity in Lake Qarun. Overall, our results highlight the need to calibrate ostracod proxy data in modern systems prior to their use for palaeoenvironmental reconstruction.     

Porphyroclast systems as kinematic indicators

Porphyroclasts of relatively strong minerals in mylonites commonly have an internal monoclinic shape symmetry defined by tails of dynamically recrystallized material. The geometry of a porphyroclast and its tails, called a ‘porhyroclast system’, can serve as a valuable indicator of the sense of vorticity. Porphyroclast systems have been divided into σ- and δ-types on the basis of the geometry of the tails. σ-Types have wedge-shaped recrystallized tails whose median lines lie on opposite sides of a reference plane parallel to the tails and containing the symmetry axis for the system. σ-Types are further subdivided into a σ_a-types, in which the porphyroclast is isolated in a relatively homogeneous matrix, and σ_b-types, in which the porphyroclast system is associated with a shear band foliation in the matrix. δ-Types typically have narrow recrystallized tails whose median lines cross the reference plane adjacent to the porphyroclast. Consequently, embayments of matrix material occur adjacent to the porphyroclasts and the tails display characteristic bends.A porphyroclast system in a mylonite develops when the relatively weak dynamically recrystallized grain aggregate in the porphyroclast mantle changes its shape due to non-coaxial flow in the adjacent matrix. This behaviour has been modelled in shear box experiments. Passive marker lines around rigid cylinders embedded in silicone putty were subjected to simple shear. The experiments were modified to simulate a change in recrystallization rate (R) with respect to rate of deformation (γ) by decreasing the diameter of the rigid cylinder during deformation at variable rates. The ratio R/γ appears to be one of the most important factors in determining which porphyroclast system will develop. At high R/γ values, flow of recrystallized material away from the porphyroclast is continuously appended by the production of new grains and wedge-shaped σ_a-type tails develop. At low R/γ values, relatively few new grains are added to the tails which become thinned and deflected by drag due to the spinning motion of the porphyroclast. In addition, most porphyroclast systems at low shear strains are of σ_a-type or lack monoclinic symmetry, whereas δ-types are only developed at high shear strain values. Complex porphyroclast systems, characterized by two generations of tails, are observed in many of the natural and model shear zones studied and may form due to fluctuating R/γ. Conditions that allow isolated σ_a- and δ-type porphyroclast systems to be used as sense of vorticity indicators are: the systems should have a monoclinic shape symmetry; matrix grain size should be small with respect to porphyroclast size; matrix fabric should be homogeneous; deformation history should be simple, and observations should be made on sections normal to the inferred bulk vorticity vector for the mylonite.     

Occurrence of juvenile Atlantic sturgeon,Acipenser oxyrhynchus,in the upper tidal Delaware River

Eighty-nine juvenile Atlantic sturgeon,Acipenser oxyrhynchus oxyrhynchus, including 10 recaptures, were collected, tagged and released in the upper tidal Delaware River between July 1981 and December 1984. All were captured in the river channel between Roebling and Trenton, New Jersey, using bottom-set experimental gill nets during daylight hours. The species was present from July through December and collected in increased numbers in the past two years. The fork lengths ranged from 284 to 862 mm (mean±SD = 516 mm±106 mm) and the weights from 140 to 4,250 g (mean±SD = 1,369 g±815 g). Ten juvenile Atlantic sturgeon were recaptured between September 1983 and December 1984 and were at large from one to 418 d. Recapture data suggest that these sturgeon utilize this area annually from July through December, possibly as a nursery. Juvenile Atlantic sturgeon appear to utilize the upper tidal portion of the Delaware River for a much longer period of time and at lower temperatures than in other river systems.     

Ethnicity as a cause of migration in Eastern Europe

Migration within and from Eastern Europe has recently risen as a topic of significance on the European political agenda. One aspect of this complex migration matrix relates to ethnic unrest. This paper examines the scale and spatial ramifications of this movement on a part of the continent recently freed from communist rule.An attempt is made to divide the ethnic quilt of Eastern Europe into those countries with few such problems and those with many. It is possible then to define areas of active migration (hot spots) from those of potential migration (inflammable spots) based on predictions from the current situation.Active ethnic migration results from the present political/military instability in the western Balkans, where refugees have left for other parts of Europe to escape the present Croat-Serb-Muslim conflict. War escalation could encourage potential ethnic migration from Kosovo, the Sandzak and Vojvodina regions,and Macedonia within the former Yugoslavia. Future disquiet elsewhere could stimulate ethnic groups such as the Turks in Bulgaria,and the Hungarian minorities in Slovakia and Romania to join this migration movement scenario.     

Deep-sea smokers: windows to a subsurface biosphere?

Since the discovery of hyperthermophilic microbial activity in hydrothermal fluids recovered from "smoker" vents on the East Pacific Rise, the widely accepted upper temperature limit for life (based on pure culture data) has risen from below the boiling point of water at atmospheric pressure to approximately 115 degrees C. Many microbiologists seem willing to speculate that the maximum may be closer to 150 degrees C. We have postulated not only higher temperatures than these (under deep-sea hydrostatic pressures), but also the existence of a biosphere subsurface to accessible seafloor vents. New geochemical information from the Endeavour Segment of the Juan de Fuca Ridge indicative of subsurface organic material caused us to re-examine both the literature on hyperthermophilic microorganisms cultured from deep-sea smoker environments and recent results of microbial sampling efforts at actively discharging smokers on the Endeavour Segment. Here we offer the case for a subsurface biosphere based on an interdisciplinary view of microbial and geochemical analyses of Endeavour smoker fluids, a case in keeping with rapidly evolving geophysical understanding of organic stability under deep-sea hydrothermal conditions.     

Organic matter of the Mulhouse Basin, France: a synthesis

The lower Oligocene evaporite sequence of the Mulhouse Basin (France) contains organic matter-rich marl deposits. These marls display an overall cyclic variation of sedimentation rate, organic carbon content, hydrogen index and selected molecular parameters over a 30 m thick stratigraphic interval. The integration of all sedimentological and geochemical parameters has allowed the reconstruction and characterization of the paleoenvironment of deposition. The marls were deposited in a perennial lake that was at times connected to the sea. Two organic facies end members could be assigned to a lake stage with a marine connection and a lake stage that received dominantly continental water input. The overall stratigraphic variation in the organic matter content is interpreted to reflect the adaptation of the Oligocene flora to the changing paleoclimate and environmental conditions.