Process-dependence of biogenic feedback effects in models of plankton dynamics.

The prospect of human-induced climate change has stimulated research into several biological processes that might affect climate. One such process that has attracted a substantial research effort is the so-called CLAW hypothesis (Charlson et al. 1987). This hypothesis suggests that marine plankton ecosystems may effectively regulate climate by a feedback associated with the production of dimethylsulphide (DMS). Charlson et al. (1987) observed that some of the DMS produced by marine ecosystems is transferred from the ocean to the atmosphere where it is the major source of cloud condensing nuclei (CCN) over the remote oceans. The aerosols resulting from biogenic DMS emissions can have a direct effect on the solar radiative forcing experienced by the Earth through scattering, absorption and reflection and can also lead to increased cloud formation; the CLAW hypothesis proposes that these mechanisms could regulate climate. Charlson et al (1987) argued that an increase in global temperature would lead to increased biogenic DMS emissions from the ocean and result in an increase in scattering, cloud cover and cloud albedo that would increase the proportion of the incoming solar radiation reflected back into space (thus changing the global albedo), and thereby cooling the planet. The objective of this paper is to examine the implications of the climate regulation process proposed by Charlson et al. (1987) for the dynamics of the ecosystems that produce it. Cropp et al. (2007) developed a simple plankton model that incorporated the DMS feedback mechanism and compared its dynamics to the same ecosystem model without the feedback. These simulations revealed that the presence of the feedback generally enhanced the stability of the ecosystem by making it more resilient to perturbation. In this research, we compare the effect of the feedbacks on a similar NPZ ecosystem model that has a greater range of dynamical behaviour than the model used by Cropp et al. (2007). The results of simulations with the new feedback model are compared to the results of Cropp et al. (2007) to elucidate the influence of the model formulation on the effects of the feedback

Reentry static stability characteristics of a (Model 471) .005479-scale 146-inch solid rocket booster tested in the NASA/MSFC 14 by 14 inch TWT (SA8F)

A force test of a scale model of the Space Shuttle Solid Rocket Booster was conducted in a trisonic wind tunnel. The model was tested with such protuberances as a camera capsule, electrical tunnel, attach rings, aft separation rockets, ET attachment structure, and hold-down struts. The model was also tested with the nozzle at gimbal angles of 0, 2.5, and 5 degrees. The influence of a unique heat shield configuration was also determined. Some photographs of model installations in the tunnel were taken and are included. Schlieren photography was utilized for several angles of attack

Modelling dimethylsulphide production at the Bermuda Atlantic time series (BATS)

Dimethylsulphide (DMS) is produced by upper ocean ecosystems and emitted to the atmosphere where it may have an important role in climate regulation. Several attempts to quantify the role of DMS in climate change have been undertaken in modeling studies. We examine a model of biogenic DMS production and describe its endogenous dynamics and sensitivities. We extend the model to develop a one-dimensional version that more accurately resolves the important processes of the mixed layer in determining the ecosystem dynamics. Comparisons of the results of the one-dimensional model with vertical profiles of DMS in the upper ocean measured at the Bermuda Atlantic Time Series suggest that the model represents the interaction between the biological and physical processes well. Our analysis of the model confirms its veracity and provides insights into the important processes determining DMS concentration in the oceans

On the elliptic generating region of a tsunami

The surface elevation is calculated for the three-dimensional motion of waves in a fluid of constant depth subject to a given bottom velocity. An example, modeling tsunami generation, with antisymmetric bottom velocity, is considered in detail. The amplitude of the wave front is found to decay much more rapidly than the main wave. The distribution of amplitude with wave number and with angular position is computed for some cases

Reentry aerodynamic characteristics of a space shuttle solid rocket booster (MSFC model 454) at high angles of attack and high Mach number in the NASA/Langley four-foot unitary plan wind tunnel (SA25F)

A force test of a 2.112 percent scale Space Shuttle Solid Rocket Booster (SRB), MSFC Model 454, was conducted in test section no. 2 of the Unitary Plan Wind Tunnel. Sixteen (16) runs (pitch polars) were performed over an angle of attack range from 144 through 179 degrees. Test Mach numbers were 2.30, 2.70, 2.96, 3.48, 4.00 and 4.63. The first three Mach numbers had a test Reynolds number of 1.5 million per foot. The remaining three were at 2.0 million per foot. The model was tested in the following configurations: (1) SRB without external protuberances, and (2) SRB with an electrical tunnel and a SRB/ET thrust attachment structure. Schlieren photographs were taken during the testing of the first configuration. The second configuration was tested at roll angles of 45, 90, and 135 degrees

Reentry aerodynamic characteristics of a space shuttle solid rocket booster model 449 tested in MSFC 14 by 14 inch TWT (SA26F)

Force tests of a 0.563 percent scale space shuttle solid rocket booster (SRB) model, MSFC Model 449, were conducted at the Marshall Space Flight Center 14 x 14 inch Trisonic Wind Tunnel. There were a total of 134 runs (pitch polars) made. Test Mach numbers were 0.6, 0.9, 1.2, 1.96, 2.74, 3.48, 4.00, 4.45, and 4.96; test angles of attack ranged from minus 10 degrees to 190 degrees; test Reynolds numbers ranged from 4.9 million per foot to 7.1 million per foot; and test roll angles were 0, 45, 90, and 135 degrees. The model was tested with three different engine nozzle/skirts. Two of these engine configurations differed from each other in the magnitude of the volume inside the nozzle and skirt. The third engine configuration had part of the nozzle removed. The model was tested with an electrical tunnel in combination with separation rockets of two different heights

An investigation to determine the static pressure distribution of the 0.00548 scale shuttle solid rocket booster (MSFC model number 468) during reentry in the NASA/MSFC 14 inch trisonic wind tunnel (SA28F)

The results of a pressure test of a .00548 scale 146 inch Space Shuttle Solid Rocket Booster (SRB) with and without protuberances, conducted in a 14 x 14 inch trisonic wind tunnel are presented. Static pressure distributions for the SRB at reentry attitudes and flight conditions were obtained. Local longitudinal and ring pressure distributions are presented in tabulated form. Integration of the pressure data was performed. The test was conducted at Mach numbers of 0.40 to 4.45 over an angle of attack range from 60 to 185 degrees. Roll angles of 0, 45, 90 and 315 degrees were investigated. Reynolds numbers per foot varied for selected Mach numbers

Mechanistic and Performance Studies on the Ligand Promoted Ullmann Amination Reaction

Over the last two decades many different auxiliary ligand systems have been utilized in the copper-catalyzed Ullmann amination reaction. However, there has been little consensus on the relative merits of the varied ligands and the exact role they might play in the catalytic process. Accordingly, in this work some of the most commonly employed auxiliary ligands have been evaluated for C–N coupling using reaction progress kinetic analysis (RPKA) methodology. The results reveal not only the relative kinetic competencies of the different auxiliary ligands but also their markedly different influences on catalyst degradation rates. For the model Ullmann reaction between piperidine and iodobenzene using the soluble organic base bis(tetra-n-butylphosphonium) malonate (TBPM) at room temperature, N-methylglycine was shown to give the best performance in terms of high catalytic rate of reaction and comparatively low catalyst deactivation rates. Further experimental and rate data indicate a common catalytic cycle for all auxiliary ligands studied, although additional off-cycle processes are observed for some of the ligands (notably phenanthroline). The ability of the auxiliary ligand, base (malonate dianion), and substrate (amine) to all act competitively as ligands for the copper center is also demonstrated. On the basis of these results an improved protocol for room-temperature copper-catalyzed C–N couplings is presented with 27 different examples reported

Effect of engine shroud configuration on the static aerodynamic characteristics of a 0.00563 scale 142-inch diameter solid rocket booster (SA10F)

A test of a 0.563 percent scale space shuttle Solid Rocket Booster (SRB) model, MSFC Model 449, was conducted in a trisonic wind tunnel. Test Mach numbers were 0.4, 0.6, 0.9, 1.2, 1.96, 3.48, 4.0, 4.45, and 4.96. Test angles-of-attack ranged from minus 10 degrees to 190 degrees. Test Reynolds numbers ranged from 3.0 million per foot to 8.6 million per foot. Test roll angles were 0, 11.25, 22.5, 45, and 90 degrees. In addition to the static stability evaluation of the primary SRB configuration, five parametric investigations were made: (1) effect of Reynolds number, (2) effect of engine shroud flare angle, (3) effect of engine shroud length, (4) effect of engine shroud strakes, and (5) effect of engine shroud strakes and trust vector control bottles

Using a finite element grid on corner points in flow models

One of the main functions of a multilayer cover liner is to prevent water from infiltrating into mine or other waste thereby preventing the occurrence of ground water pollution. In the past, numerical models have predominantly dealt with vertical infiltration or infiltration into sloping hillsides of infinite extent. The two layer model investigated in this paper has a more realistic shape which is piece-wise linear with a horizontal top, vertical bottom and a sloping section in-between. At the intersection of these segments are corner points where there are changes from sloping flow dynamics to either vertical or horizontal flow dynamics, depending on the corner point. The abrupt change in dynamics at the corner points can cause numerical problems especially when dealing with the boundary condition at the interface of two soils. This paper will deal with the corner point problem at the soil layer interface and, in particular, investigate the use of a finite element grid around the corner points