Potential protostars in cloud cores

We present H₂CO observations of young protostar candidates in the Serpens Cloud Core. We find evidence for dense molecular gas in the cores of these objects that is warmer than the surrounding dust. The strong emission and gas properties support the premise that many of these sources may be very young protostars.     

Magnetic pinch in relation to the lightning stroke

Summary The application of the snow plow approximation to the magnetic pinch effect in the return stroke of lightning is described. Results are presented for a constant electric field and for a measured stroke current. In general, the solutions indicate that the magnetic pinch effect is important for cases of high currents, small channel diameters, and low degrees of ionization.     

Fluxes and sources of suspended organic matter in an estuarine turbidity maximum region during low discharge conditions

Water column concentrations of total suspended solids (TSS), particulate organic carbon (POC) and particulate nitrogen (PN) were measured at three different depths in four different locations bracketing the estuarine turbidity maximum (ETM) along the main channel of a temperate riverine estuary (Winyah Bay, South Carolina, USA). Measurements were carried out over full tidal cycle (over 24 h). Salinity, temperature, current magnitude and direction were also monitored at the same time throughout the water column. Tidally averaged net fluxes of salt, TSS, POC and PN were calculated by combining the current measurements with the concentration data. Under the extreme low river discharge conditions that characterized the study period, net landward fluxes of salt were measured in the lower part of the study area, suggesting that the landward transport through the main channel of the estuary was probably balanced by export out through the sides. In contrast, the net fluxes of salt in the upper reaches of the study area were near zero, indicating a closed salt balance in this part of the estuary. In contrast to salt, the net fluxes of TSS, POC and PN in the deeper parts of the water column were consistently landward at all four sites in Winyah Bay indicating the non-conservative behavior of particulate components and their active transport up the estuary in the region around the ETM.The carbon contents (%POC), carbon:nitrogen ratios (org[C:N]a) and stable carbon isotopic compositions (δ¹³C_POC) of the suspended particles varied significantly with depth, location and tidal stage. Tidally averaged compositions showed a significant increase up the estuary in the %POC and org[C:N]a values of suspended particles consistent with the preferential landward transport of carbon-rich particles with higher vascular plant debris content. The combination of tidal resuspension and flood-dominated flow appeared to be responsible for the hydrodynamic sorting of particles along the estuary that resulted in denser, organic-poor particles being transported landward less efficiently. The elemental and isotopic compositions indicated that vascular C₃ plants and estuarine algae were the major sources of the particulate organic matter of all the samples, without any significant contributions from salt marsh C₄ vegetation (Spartina alterniflora) and/or marine phytoplankton.     

Submerged cylinder wave energy device: theory and experiment

Linearized water wave theory is used to show that a submerged long circular cylinder suitably constrained by springs and dampers to make small harmonic oscillations, can be extremely efficient in absorbing the energy in an incident regular wave whose crests are parallel to the axis of the cylinder. Experimental results are described which confirm the theory for small amplitude waves and which suggest that the device can still be fairly efficient in waves of moderate amplitude.     

Effects of benzene and dimethylnaphthalene on homeostatic processes in two species of crabs

Long-term exposure of animals to sub-lethal doses of toxicants such as benzene (B) and dimethylnaphthalene (DMN) may result in subtle changes in their physiology and biochemistry. In crustaceans such changes include decreased rate of limb regeneration, extended time to molt and decreased growth increment at molt.^1,2 These processes depend upon an adequate supply of stored nutrients in the tissues and appropriate release of neuroendocrine substances from the central nervous system.^3,4 We are examining the effects of sub-lethal doses of B and DMN on osmotic and ionic regulation and on nutrient storage in the blue crab, Callinectes sapidus, and the green crab, Carcinus maenas. Disturbances in these physiological processes may reflect alterations in neuroendocrine functions brought about by the presence of toxicants. We find that exposure of C. maenas to B or DMN, followed by transfer to a dilute medium, results in impaired osmoregulatory capacity, while addition of these compounds to a dilute medium to which the animal is already acclimated does not affect their regulatory ability. Storage of carbohydrate in the midgut gland (hepatopancreas) is decreased by B or DMN, while the accessory storage tissues (gill, muscle) are not significantly affected.     

Secondary flow caused by differential roughness,Langmuir circulations,and their effect on the development of sand ribbons

The process of Differential Roughness Secondary Flow (DRSF), hitherto little recognized, recently was demonstrated in a wind tunnel and in a flume. It is suggested here the DRSF may, in the natural environment, play an important part in the persistence and sharp definition of sand ribbons, previously initiated by other processes. In 1980 Karl described a series of sand ribbons, alternating with exposed substrate, which he attributed to the effect of Langmuir circulations. Although Langmuir Circulation Secondary Flow (LCSF) may indeed, in some cases, initiate sand ribbons, the sharply-defined edges typical of these features are explained better by DRSF.     

Microbiological and chitinoclastic activities associated withPenaeus setiferus

Analysis of microbiological and chitinase activities relative to the white shrimpPenaeus setiferus, and its chitinoclastic endosymbionts, have demonstrated the relevance of total chitinolytic processes in penaeid biology. Microorganisms may serve as a direct source of nutrients for the animal as well as in the elaboration of extracellularin situ chitinase enzymes. The enzyme produced by the predominant gut bacteria,Beneckea neptuna, is a moderately actively inducible chitinase while the shrimp has an indigenous constitutive chitinase and chitobiase system. Factors of temperature, pH, ion inhibition and reducing sugar ratios have been compared for the bacterial and animal enzymes. This dual enzyme system suggests that metabolic chitin transformation may play a vital role in crustacean metabolism.     

Physical and anthropogenic effects on observed long-term nutrient changes in the Irish Sea

The trend in Irish Sea nutrient concentrations over the last four decades has been considered to reflect changes in anthropogenic loading. Comparison of a long-term database for the Menai Strait, North Wales, with an established historic data set for the Cypris station, Isle of Man, indicates that climate also has a significant influence on observations of nutrient concentrations. Data are presented detailing long-term shifts in nitrate, phosphate and silicate measurements since the 1960s at these two fixed sampling sites in the Irish Sea. Broad systematic changes observed in all three nutrients over the decades show a rise from the 1960s through to the 1980s, followed generally by an overall decline in the 1990s. Decadal-scale salinity changes occur in the opposite sense to nutrient changes. Anthropogenic inputs from freshwater cannot fully account for observed nutrient trends, neither is there evidence for shifts in nutrient concentrations in oceanic waters over the past four decades. Climatically forced movement in the geographical position of the freshwater/seawater mixing zone over a decadal time scale could, however, give rise to the observed shifts in nutrient concentration and salinity. This cannot alter nutrient concentration and salinity per se, but causes the measurements taken at fixed sampling sites to fluctuate inversely over this time scale. It is concluded that there is complex interplay between anthropogenic loading and climate affecting the distribution of nutrients in the Irish Sea.