The Geochemistry of Selenium and Sulfur in a Coastal Salt Marsh

Investigation of the various chemical forms of selenium and sulfur in sediments and pore waters can provide information about various oxidation/reduction processes. Five cores were obtained from the Great Marsh, from April 1985 to June 1986. Sampling times coincided with the seasonal redox cycle known to occur within the marsh system. Sediments were analyzed for various selenium and sulfur phases. Iron monosulfides and elemental sulfur both display large seasonal changes in concentration and distribution with depth, indicating a coupling with redox conditions. In contrast, the depth distribution of greigite did not show appreciable changes with season. Pyrite underwent large concentration changes in the upper 15 cm of sediment during spring, but remained relatively constant with respect to concentration and distribution below this zone. Using a mass balance approach for the upper marsh sediment (0-15 cm), sulfur needed for the observed rapid pyritization is found to be derived from elemental sulfur, iron monosulfide, and sulfate reduction. In the deeper sediments (15-30 cm), diagenetic modeling confirms that greigite is an intermediate in pyrite formation. The depth distribution of total sedimentary selenium shows minor variations with season. Concentrations are generally higher in the surface layers and then decrease with depth. Elemental selenium exhibits a trend with depth similar to total selenium. Chromium reducible selenium was generally undetectable in most cores and shows little seasonality. In contrast, sedimentary (selenite + selenate) shows marked seasonality. In spring, sedimentary is less than 10% of the total sedimentary selenium throughout the profile. However in summer, a broad maximum (30% of the total selenium) occurs just above the redoxcline. Below the redoxcline sedimentary accounts for less than 10% of the total sedimentary selenium. Pore water selenium exhibits a seasonal trend, concurrent with the cyclic changes in sedimentary. Diagenetic modeling shows that the loss of total sedimentary selenium is controlled by the decrease in elemental selenium. Mass balance modeling indicates that the major export of selenium from the marsh sediment is either gaseous emissions of selenium or the flux of Spartina alterniflora litter from the marsh system. Gaseous selenium is a potentially important source of selenium to the atmosphere

A general formulation of the theory of wire ropes

The author claims to have developed a simple and well-organized approach towards the formulation of wire strand and rope problems. He considers both the geometric nonlinear theory as well as the linearized theory, and while stating the ease in programming his theory, no numerical results are presented. The continued interest in wire strand and rope behavior exemplifies the importance of these elements. However, the author has missed a whole body of literature over the last ten years which has previously provided generalized theories for wire strands and ropes, and has done so in a much more usable form. In general, the theory of wire rope has been well developed by Costello and his associates, whose references are too numerous to mention, and they have examined a wide variety of problems from linear and nonlinear response of wire strands and ropes under static and dynamics loads to the response of viscoelastic ropes to the response of strands and ropes comprised of wires with various types of cross-sectional geometry. Typical of these works are the development of the basic theory and their use in the examination of specific wire rope problems. A few of the papers will be discussed to follow which have already accomplished fat" more than the paper under discussion. First, as noted above, Jiang (1995) presents both the geometrically nonlinear and linear theories. Costello and his associates use the wire rope axial and rotational strain to describe the deformation behavior of the total rope. Jiang in Eq. (18) of his paper also uses these parameters. One aspect should be noted, however, and that is that Jiang's rotational strain, qS, is not dimensionless. Jiang states as one of his primary contributions is his showing that the strand structure can be characterized by seven stiffness and deformation constants. This is not a new idea. Velinsky (1988) stated, "We note that the global behavior of a strand can be completely described by the following strand quantifies: the stiff-J Jiang, W., 1995, "A General Formulation of the Theory of Wire Ropes," ASME JOURNAL OF APPLIED MECHANICS, Vol. 62, pp, 747-755. z Professor, Department of Mechanical and Aeronautical Engineering, University of California-Davis, Davis, CA 95616. ness constants, $1, Sz,$3, and $4, the effective strand radius, R*, the strand effective Poisson's ratios, ue, and Ue~, and the strand bending stiffness, A*." Velinsky has eight constants, and the reason is that the strand size is necessary which Jiang has omitted. It should also be noted that Jiang uses a different notation which is much less intuitive, but represents essentially the same parameters. It should also be stressed that these strand describing coefficients are all constants only for the linear theory (e.g., the stiffness varies with load for the nonlinear theory). The Velinsky Velinsky (1989) later extended the generalized approach of his 1988 paper to examine complex wire rope design. The Velinsky 1989 paper develops the general analysis for wire strand core, independent wire rope core, and fiber core types of wire ropes. The total rope analysis requires only the eight parameters for each strand, and a similar set of three linear equations are necessary for the deformations of each strand lay. Furthermore, as in the earlier paper, the theory is exercised in examining the sensitivities of various total rope properties to numerous strand and rope design parameters. In addition to total rope properties, Velinskky also examines the sensitivities of rope design parameters on individual wire stresses. The Velinsky formulation is easily programmed in a general manner (and has been), and is easily exercised as exhibited by the large amount of results that have been presented

A részvénytársaság igazgatóságának szerepe és személyi összetétele I. rész

A tanulmány témája az igazgatóságok szerepe és személyi összetétele a részvénytársaságban. Mindenekelőtt arra keresi a választ, hogy a részvénytársaságok irányításában alapvetően ellenőrző vagy irányító funkciót gyakorolnak-e az igazgatóságok. A kérdés elméleti hátterét adó társaságirányítás (corporate governance) alapdilemmája szintén ez: vajon erős irányítási hatalmat kell adni a vállalatnak, vagy a vállalat ellenőrzését kell előtérbe helyezni. Az elmélet elsősorban a tulajdonosok és a vállalat kapcsolatát vizsgálja

A részvénytársaság igazgatóságának szerepe és személyi összetétele II. rész

A tanulmány második része annak a gyakorlati vizsgálatnak az eredményét ismerteti, amelyet a szerző magyar részvénytársaságnál végzett

Kinematics of roller migration in the planetary roller screw mechanism

This paper develops a kinematic model to predict the axial migration of the rollers relative to the nut in the planetary roller screw mechanism (PRSM). This axial migration is an undesirable phenomenon that can cause binding and eventually lead to the destruction of the mechanism. It is shown that this migration is due to slip at the nut-roller interface, which is caused by a pitch mismatch between the spur-ring gear and the effective nutroller helical gear pairs. This pitch circle mismatch can be due to manufacturing errors, deformations of the mechanism due to loading, and uncertainty in the radii of contact between the components. This paper derives the angle through which slip occurs and the subsequent axial migration of the roller. It is shown that this roller migration does not affect the overall lead of the PRSM. In addition, the general orbital mechanics, in-plane slip velocity at the nut-roller interface, and the axial slip velocities at the nut-roller and the screw-roller interfaces are also derived. Finally, an example problem is developed using a range of pitch mismatch values for the given roller screw dimensions, and the axial migration and slip velocities are determined

Salt Marsh Denitrification Provides a Significant Nitrogen Sink in Barnegat Bay, New Jersey

Velinsky, D.J.; Paudel, B.; Quirk, T.; Piehler, M., and Smyth, A., 2017. Salt marsh denitrification provides a significant nitrogen sink in Barnegat Bay, New Jersey. In: Buchanan, G.A.; Belton, T.J., and Paudel, B. (eds.), A Comprehensive Assessment of Barnegat Bay-Little Egg Harbor, New Jersey. Denitrification in salt marshes can be an important removal mechanism for inorganic nitrogen, particularly in coastal estuaries subject to high nutrient loading and eutrophication. Barnegat Bay, New Jersey has had high nutrient loading in the northern part of the Bay and has exhibited symptoms of eutrophication. The first goal of this study was to examine seasonal denitrification, other N fluxes, and sediment oxygen demand in salt marshes of Barnegat Bay where inputs and concentrations of nutrients vary spatially within the Bay. Second, differences in N process rates among emergent vegetated marsh and permanently flooded isolated ponds were investigated. Finally, the percentage of the N load to the Bay removed by denitrification in the salt marshes of Barnegat Bay was calculated. It was hypothesized that denitrification rates would be the highest in summer and depend on water-column nutrient concentration. In addition, denitrification rate would be higher in vegetated marsh than in inundated ponds because of the aerobic/anaerobic interfaces present in marshes required by coupled nitrification-denitrification. Denitrification rate was three times greater in July than in October (p < 0.05). There were significant differences among marshes in N fluxes related to local availability of nutrients in the water column. Denitrification rates in vegetated marsh on thin sediment layers were more variable than in ponds. Overall, denitrification removed an average of 27.9% ± 6.9% of the total N load transported to the Bay, highlighting the important ecosystem service that the marshes provide to the Bay

A review of nitrogen isotopic alteration in marine sediments

Key Points: Use of sedimentary nitrogen isotopes is examined; On average, sediment 15N/14N increases approx. 2 per mil during early burial; Isotopic alteration scales with water depth Abstract: Nitrogen isotopes are an important tool for evaluating past biogeochemical cycling from the paleoceanographic record. However, bulk sedimentary nitrogen isotope ratios, which can be determined routinely and at minimal cost, may be altered during burial and early sedimentary diagenesis, particularly outside of continental margin settings. The causes and detailed mechanisms of isotopic alteration are still under investigation. Case studies of the Mediterranean and South China Seas underscore the complexities of investigating isotopic alteration. In an effort to evaluate the evidence for alteration of the sedimentary N isotopic signal and try to quantify the net effect, we have compiled and compared data demonstrating alteration from the published literature. A >100 point comparison of sediment trap and surface sedimentary nitrogen isotope values demonstrates that, at sites located off of the continental margins, an increase in sediment 15N/14N occurs during early burial, likely at the seafloor. The extent of isotopic alteration appears to be a function of water depth. Depth-related differences in oxygen exposure time at the seafloor are likely the dominant control on the extent of N isotopic alteration. Moreover, the compiled data suggest that the degree of alteration is likely to be uniform through time at most sites so that bulk sedimentary isotope records likely provide a good means for evaluating relative changes in the global N cycle