Experimental investigations of the effect of cloud-medium modification by salt powders

The results of experimental investigations into the action of polydispersion salt powders on model cloud media are presented. The results of experiments show a considerable positive effect of the modification of convective clouds by salt powders in order to obtain additional precipitation. The introduction of polydispersion salt powder into a forming cloud medium leads to the appearance of large cloud droplets and to the droplet-spectrum broadening. This result is a positive factor for the stimulation of coagulation processes and further precipitation formation. No “overseeding” phenomenon (when, instead of the enlargement of droplets, their sizes decrease and the concentration of cloud droplets increases) is observed at rather high mass concentrations of the introduced powder.     

Devising ‘policy packages’ for seismic retrofitting of residences

Natural Hazards - Collapse of residential buildings is the major cause of death during earthquakes. Seismic retrofitting of residential buildings is a cost-effective way to reduce injury and death....     

Tidal mixing versus thermal stratification in the Bay of Fundy and gulf of Maine

Abstract

A simple energetic argument (Simpson and Hunter, 1974) shows that the boundary between well‐mixed and stratified areas of a shallow sea in summer should correspond to a critical value of BH/U³ , where B is the buoyancy JEUX due to solar heating, H the mean water depth and U the amplitude of the tidal current. We demonstrate the importance of this parameter in a simple model of vertical mixing, and discuss the role of many other factors affecting stratification. Examination of hydrographic data from the Bay of Fundy and Gulf of Maine, together with estimates of tidal dissipation (proportional to U ³) from Greenberg's (1978) numerical model, shows a transition from well‐mixed to stratified conditions, in July and August, for H/U³ = 70 m^‐2s³. This corresponds to a mixing efficiency of only 0.26%. Predictions are made of the changes in extent of well‐mixed areas that would be caused by tidal power development. Some stratification, due to both solar heating and freshwater input, is possible in previously mixed areas which would be the headponds for two schemes. Outside the barriers the changes are less dramatic, although the merging of mixed areas over Georges Bank and Nantucket Shoals is predicted.     

Piloting a network of small telescopes

The Pilot Small Telescope Network (PSTN) is a state‐of the art system of easily replicable and scalable hardware, software, servers, eXtensible Markup Language (XML) protocols, and network middleware connecting and developing a pilot array of robotic telescopes to one another and the user community. The PSTN is a developmental project that will allow growing access to these telescopes, and make available data to faculty, students and others in an environment of collaboration. The underlying goal of the PSTN is to broaden the quantity and quality of astronomical education and research, particularly with a focus on traditionally underserved populations. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sharing the globe: The role of attachment to place

Issues posed by global environmental change can be viewed as the problem of the commons on a larger geographic scale. A framework for analysing how geographic scale affects governments' ability to manage environmental problems is suggested here. It is based on interactions between four dimensions: production-consumption relationships; distribution of the benefits and costs of various activities; level of administrative control; and spatial scale of individuals' attachment to place. Global environmental problems can be viewed as a case where benefits from polluting activities are spatially concentrated relative to costs. The difficulty in addressing such problems stems from the discrepancy in geographic scale between adverse impacts and level of administrative control. The possibility of adapting institutional structures to match the scale of the problems is examined, in light of the increasing spatial scale of production-consumption relationships in the post-industrial world and the growing demand for local control across the globe. The geographic scale of ideological attachment to place is identified as an important variable in determining the ability to respond to large-scale environmental problems.     

Cycloidal cracks on Europa: Improved modeling and non-synchronous rotation implications

Cycloidal crack patterns on Europa are influenced by tides induced by orbital eccentricity, which in turn is driven by the Laplace orbital resonance. Their shapes potentially record the location of their formation (relative to the direction of Jupiter), as well as the parameters of crack formation. Hoppa et al. [Hoppa, G., Tufts, B.R., Greenberg, R., Geissler, P., 1999a. Icarus 141, 287-298] modeled several cycloid chains using a fixed set of material parameters, but some details did not fit. We now allow material parameters to vary for each arc of an observed cycloid. In general, with minimal variation of model parameters between the arcs, fits are greatly improved. Furthermore, accounting for tidal stress accumulated during non-synchronous rotation, in addition to diurnal stress, allows even better fits. Even with the added freedom in the model our fits allow us to better constrain the location where each cycloid may have formed. Our results support Hoppa et al.'s finding that only a few cracks form ridges per cycle of non-synchronous rotation in the region examined, probably because cracking relieves built up stress until further substantial rotation occurs.     

Plutonism in Pan-African belts and the geologic evolution of northeastern Africa

Plutonic igneous rocks of Pan-African belts (500–600 m.y. age) in Africa can be described in terms of three types of assemblages: (1) migmatites formed largely by remobilization of pre-existing sialic crust during Pan-African time; (2) calcalkaline batholithic suites formed in association with subduction of oceanic crust; and (3) alkali-rich, post-tectonic granites. Many suites cannot be placed precisely in one of these categories, either because of intermediate (gradational) characteristics or because of lack of adequate information. Distinction of rocks formed during Pan-African time from older ones whose radiometric clocks were reset at that time is also difficult.The rock suites are very unevenly distributed geographically. Migmatites formed by ensialic crustal remobilization occur mostly in southern and central Africa. Calcalkaline suites occur in north Africa, particularly the northeast. Alkali-rich granites are virtually restricted to the northeastern portion of the continent, the one major part of Africa not occupied by an Archean shield. Evidence for subduction of oceanic crust is also restricted to northeastern Africa.The geologic history proposed for northeastern Africa is as follows: During, and immediately preceding, Pan-African time an ocean basin of uncertain size and shape occurred between the West African and Nubian-Arabian shields. Subduction zones were active on the margins and within the basin. During, and at the end of, Pan-African time extensive development of alkali-rich granites was associated with cratonization of the basin. Paleozoic sediments were then deposited under platform conditions on the newly formed craton, which showed mild epeirogenic activity throughout the Phanerozoic.     

Tropospheric chemical composition measurements in Brazil during the dry season

Field measurement programs in Brazil during the dry seasons in August and September 1979 and 1980 have demonstrated the large importance of the continental tropics in global air chemistry. Many important trace gases are produced in large amounts over the continents. During the dry season, much biomass burning takes place, especially in the cerrado regions, leading to a substantial emission of air pollutants, such as CO, NO _x , N₂O, CH₄ and other hydrocarbons. Ozone concentrations are enhanced due to photochemical reactions. The large biogenic organic emissions from tropical forests play an important role in the photochemistry of the atmosphere and explain why CO is present in such high concentrations in the boundary layer of the tropical forest. Carbon monoxide production may represent more than 3% of the net primary productivity of the tropical forests. Ozone concentrations in the boundary layer of the tropical forests indicate strong removal processes. Due to atmospheric supply of NO _x by lightning, there is probably a large production of O₃ in the free troposphere over the Amazon tropical forests. This is transported to the marine-free troposphere and to the forest boundary layer.     

Growth of large,late-stage planetesimals

The late stage of terrestrial planets' growth determined many of their fundamental properties, including their thermal properties and petrology, their impact records, and possibly the existence of the Moon. A critical result of late-stage models, which bears on observable properties, is the size of the largest planetesimals that grew near, and later impacted,those that became full-size planets. There has been considerable misinterpretation of previous models regarding the relation between the size of planetesimals and their relative velocities. Furthermore, some models neglect the possible decrease in relative velocity as control is transferred from the largest to the second-largest body in an accreation zone. Evidence that Venus helped stir Earth-zone planetismals is not copelling. When models are evaluated, the results are found to depend strongly on uncertain initial conditions. The size of the second-largest planetesimal in the Earth's zone might range from ～300 to ～2500 km, with corresponding accretion times of ～7 × 10⁶ and ～10⁸ years, respectively. Both extremes are generated from plausible initial conditions and both seem consistent with observed planetary properties.