Absorption and desorption of dichloromethane vapor by water drops in air. An experimental test of scavenging theory

An experimental study of the scavenging of dichloromethane vapor by water drops falling at terminal velocity, has been carried out in the UCLA precipitation shaft, in order to test the predictions of theoretical washout models. Whereas good agreement between theory and experiment was found for drops of radius 0.332 mm, computed gas uptake rates for 1.253 and 2.21 mm radius drops were much slower than those measured, just as reported previously for the washout of both sulfur dioxide and acetaldehyde. An analysis shows that theory can be reconciled with all of the experimental data by replacing the compound specific aqueous phase Fickian molecular diffusion coefficient used in the theory, by an effective diffusivity, having a constant value, (3×10^-4 cm² s^-1), independent of the physical and chemical nature of the absorbed species, for all drops of equivalent radii greater than 0.9 mm.     

From paleo to policy: partitioning the historical point and nonpoint phosphorus loads to the St. Croix River,Minnesota-Wisconsin,USA

Paleolimnological studies show that phosphorus (P) loads to the federally protected St. Croix River, a tributary of the Upper Mississippi River, have increased about threefold over the last century. Ongoing management efforts to protect and restore the river hinge on the question of whether the increased nutrient load results from point-source discharges or nonpoint runoff from agricultural intensification and urban expansion. Here we determine the historical contribution of point source phosphorus (P) loads to the St. Croix watershed from 1900–2000 A.D. Historical point source loads were estimated based on discharge volumes, demographics, industrial sources, wastewater technologies, and facility discharge records, where available. Sewering in the basin began in 1905, and since that time, there have been as many as 169 permitted point source dischargers basinwide, including municipal, industrial, and agricultural facilities. Early wastewater management typically discharged untreated sewage; technological advances had secondary treatment in place at most facilities by the 1960s–1970s and much of the municipal population was served by tertiary treatment by the 1990s. Peak nutrient discharges from point sources occurred in the 1960s–1970s. Detergent phosphorus bans instituted in the late 1970s for Minnesota and Wisconsin, greater use of land and groundwater effluent disposal, and improvements in treatment technology brought about decreases in P loads in the 1980s and 1990s. Point-source discharges were compared to historical total phosphorus loads estimated in a whole-basin phosphorus mass balance to calculate the historical contribution of point sources, anthropogenic nonpoint sources, and natural or background sources. We estimated 1990s point source loads at 48 t P yr⁻¹, which represents about 10% of the total phosphorus load (459 t P yr⁻¹, flow-corrected to 412 t P yr⁻¹) to the basin. Without further controls on nutrient inputs to the St. Croix River, annual flow-corrected P loads are projected to increase to 498 t P yr⁻¹ by the 2020s with point source phosphorus loading contributions at 65 t P yr⁻¹ or 13% of the total load. However, if we exclude background P loads to the St. Croix (166 t P yr⁻¹), recent nutrient loads are primarily from anthropogenic nonpoint sources. Point sources also contribute over 19% of the current and future phosphorus load that can be attributed to human activities in the watershed. Interstate and federal efforts to decrease P loading to the St. Croix River by 20% will need to target both point and nonpoint sources. This is one of eight papers dedicated to the “Recent Environmental History of the Upper Mississippi River” published in this special issue of the Journal of Paleolimnology. D.R. Engstrom served as guest editor of the special issue.     

Paleomagnetic constraints on Zn–Pb ore genesis of the Pillara Mine, Lennard Shelf, Western Australia

The Pillara Zn–Pb deposit is the largest of several known Mississippi Valley-type (MVT) deposits in the Lennard Shelf of the Canning Basin. Paleomagnetic and rock magnetic measurements are reported for 294 specimens from 23 sites in mineralization and its carbonate host rocks from the deposit as well as on 15 artificial specimens of zinc and lead concentrate and of tailings. Pyrrhotite carries the characteristic remanent magnetization (ChRM) in nearly all specimens. The ChRM postdates most faulting as shown by breccia tests and most minor regional tilting as shown by the degraded fit on tilt correction. The mean ChRM direction for all sites is D=20.6°, I=–27.5° (N=23, ₉₅=5.3°, k=34.1), yielding an age of 358±5 Ma (2) that is similar to the comparable age of 354±8 Ma (2) for the Kapok MVT deposit. Host rock diagenesis with attendant secondary remagnetization yields an age of 361±5 Ma (1) and the MVT mineralization with a primary chemical remanent magnetization gives an age of 356±3 Ma (1), co-eval with a published Rb–Sr sphalerite age of 357±3 Ma. Interpretation of this temporal data suggests that the MVT deposits of the southeastern Lennard Shelf originated during extension, probably in response to rift-related topography-driven fluid flow.Editorial handling: C. Brauhart     

Pseudo relative velocity spectra of earthquake ground motion at long periods

This paper analyses the processes which govern structural response, and uses observations of strong earthquake ground motion to propose quantitative extrapolation of pseudo relative velocity spectral amplitudes to long (100 > T > 1 s) periods. This will eliminate the current difficulties with rough estimation of long period spectral amplitudes and will open new possibilities by enabling the strong motion hazard calculations to be extended to the same long period band. So far, the scaling equations of response spectrum amplitudes have been valid only up to periods less than several seconds. The design of long structures and of structures on multiple distant supports requires knowledge and specification of design ground motions well beyond 1–10 s periods. With the results presented in this paper it will be possible to compute site-specific uniform hazard spectra and associated synthetic accelograms for essentially all long period response problems.     

An intercomparison of two rawinsonde systems

Abstract

An intercomparison of the Väisälä MicroCora system used in the Automated Shipboard Aerological Program (ASAP) and the Atmospheric Environment Service upper‐air system (GMD/ADRES) was conducted in May‐June 1983. Thirty‐three paired ascents were made. The ASAP system dry‐bulb temperatures averaged 0.3°C warmer. For the lowest 100 mb, the dew‐point temperature difference (ASAP ‐ GMD/ADRES) was near ‐1°C whereas for the 780–500 mb layer, the difference was 1°C. The wind component mean differences averaged were small but with a 4 m s^?1 standard deviation.     

Microstructure and micromotion in recrystallization flow of octachloropropane: A first look

Advance of the genetic theory of metamorphic fabric depends in part on improved understanding of dynamic recrystallization processes, and the effects of these processes upon various fabric elements. This paper describes aspects of the microstructural evolution and associated small-scale motion in a dynamically recrystallizing sheet of octachloropropane. The material was deformed in progressive pure shear, at 2×10^?3 sec^?1 (with interruptions for photography and U-stage measurement), at 70 % of its absolute melting temperature. The dominant recrystallization process is migration of grain boundaries, with consequent major adjustment of the shapes and sizes of grains, but no marked change in the average grain size and no creation of new grains. Typical grains in the fully deformed material (30% bulk shortening) have a composite structure with primitive, high-strain regions inherited directly from the undeformed state, rimmed by successively younger regions of lower strain accreted behind outwardmoving boundaries. An array of second-phase marker particles permits distinction between grain boundary motion with and through the material, and reveals an unexpected ability of grains as a whole to migrate short distances up a bulk strain gradient. The markers also show that the only important deformation process is intragranular deformation and that it is proceeding at somewhat different rates in different grains. The central problem posed by the observations is to explain the direction and speed of each migrating boundary. Two hypotheses were tested, neither with outstanding success. One of these hypotheses is that grain boundary migration is part of a strain accomodation process, that operates between grains stretching or shortening at different rates parallel to their mutual boundary.     

Shock tracers in the molecular cloud G1.6-0.025

Observations of the molecular cloud G1.6-0.025 in the 2_K-1_K and J₀-J_?1E series and 5_?1-4₀E line of CH₃OH, the (2-1) and (3-2) lines of SiO, and the 7_?7-6_?6 line of HNCO are described. Maps of the previously observed extended cloud with V_lsr～50 km/s and high-velocity clump with V_lsr～160 km/s, as well as a newly detected clump with V_lsr～0 km/s, have been obtained. The extended cloud and high-velocity clump have a nonuniform structure. The linewidths associated with all the objects are between 20 and 35 km/s, as is typical of clouds of the Galactic center. In some directions, emission at velocities from 40 to 160 km/s and from ?10 to +75 km/s is observed at the clump boundaries, testifying to a connection between the extended cloud and the high-velocity clump and clump at V_lsr～0 km/s. Compact maser sources are probaby contributing appreciably to the emission of the extended cloud in the 5_?1-4₀E CH₃OH line. Non-LTE modeling of the methanol emission shows that the extended cloud and high-velocity clump have a relatively low hydrogen density (<10⁴ cm^?3). The specific column density of methanol in the extended cloud exceeds 6×10⁸ cm^?3s, and is 4×10⁸?6×10⁹ cm^?3s in the high-velocity clump. The kinetic temperatures of the extended cloud and high-velocity clump are estimated to be <80 K and 150–200 K, respectively. Possible mechanisms that can explain the link between the extended cloud with V_lsr～50 km/s and the clumps with V_lsr～0 km/s and ～160 km/s are briefly discussed.     

Coastal erosion vs man-made protective structures: evaluating a two-decade history from southeastern India

Remote sensing images of AD 1991–2011 and field observations help evaluate shoreline changes (erosion and accretion) in Puducherry and Tamil Nadu states of southeastern India. A minor harbor was constructed during AD 1986–1989 in the coast of Puducherry, and it initiated the gradual process of shoreline modification. In the subsequent years, beaches located toward the north of the harbor suffered erosion (?0.12–?4.19 m/year) and there was accretion (0.27–7.25 m/year) in the southern beaches. However, the man-made structures (seawall and groin) have reduced the shoreline changes after AD 2004. In the last two decades, the rate of erosion area-wise gradually decreased (0.24–0.013 km²/year) and accretion remained constant (0.019 km²/year). Our results suggest that accretion happened in the southern side of the breakwaters and erosion occurred in the northern part. Presence of groins structures in the region in the northern part has also provoked accretion in the south and erosion in the northern side close to the State of Tamil Nadu.