Phytoplankton and the Macondo oil spill: A comparison of the 2010 phytoplankton assemblage to baseline conditions on the Louisiana shelf.

The Macondo oil spill was likely the largest oil spill to ever occur in United States territorial waters. We report herein our findings comparing the available baseline phytoplankton data from coastal waters west of the Mississippi River, and samples collected monthly from the same sampling stations, during and after the oil spill (May-October, 2010). Our results indicate that overall, the phytoplankton abundance was 85% lower in 2010 versus the baseline, and that the species composition of the phytoplankton community moved towards diatoms and cyanobacteria and away from ciliates and phytoflagellates. The results of this study reaffirm the view that phytoplankton responses will vary by the seasonal timing of the oil spill and the specific composition of the spilled oil. The trophic impacts of the purported lower abundance of phytoplankton in 2010 coupled with the observed assemblage shift remain unknown.

Changes in the concentration and relative abundance of alkanes and PAHs from the Deepwater Horizon oiling of coastal marshes.

We determined changes of 28 alkanes and 43 different PAHs in 418 wetland soil samples collected on ten sampling trips to three Louisiana estuaries before and after they were oiled from the 2010 Deepwater Horizon disaster. There was a significant decline in 22 of the 28 alkane analytes (0.42% day(-1)), no change in 6, over 2.5 years. The concentration of five aromatic petroleum hydrocarbons (PAHs) increased (range 0.25-0.70% day(-1)), whereas the total PAH pool did not change. Of these five, naphthalene and C-1-naphthalenes are suggested to be of higher toxicity than the other three because of their relatively higher volatility or solubility. The relative proportions of alkane analytes, but not PAHs, does not yet resemble that in the pre-oiled marshes after 3 years, The trajectories of nine indicators for degradation/weathering were either inconclusive or misleading (alkanes) or confirmed the relatively meager degradation of PAHs.

Sediment-preserved diatom assemblages can distinguish a petroleum activity signal separately from the nutrient signal of the Mississippi River in coastal Louisiana.

We analyzed the preserved diatom assemblages in dated sediment cores collected from five locations in the Louisiana Bight to test if there was a signature of petroleum extraction activities (hopanes and barium) distinct from the well-documented effects of nutrient loading. The results of a multi-dimensional scaling analysis indicate that the diatom assemblage changes documented throughout the 40 year record could be explained by three variables: barium and hopanes concentrations, and Mississippi River nitrogen loading. The results of a canonical correspondence analysis demonstrated that these signals could be distinguished through correlations with specific diatom species. The abundance of Actinoptychus senarius, for example, was negatively correlated with barium and the Pseudo-nitzschia delicatissima complex was positively correlated with nitrogen loading. These results provide a "proof-of-concept" demonstration that diatom assemblages preserved in the sediments can be used to study the effects of petroleum extraction activities, and that these 'petroleum signals' may be distinguished from other significant influences such as nutrient loading.

Attitudes to organ donation among some urban South African populations remain unchanged: a cross-sectional study (1993 - 2013).

BACKGROUND: A 1993 paper in the SAMJ suggested that public attitudes to organ donation in South Africa were positive. However, statistics reveal a decline in the annual number of transplants in this country. OBJECTIVE: To repeat the 1993 survey as far as possible and determine whether public attitudes to organ donation in some South African populations have changed over the past 20 years. METHODS: The 1993 study was replicated in 2012 to generate a current data set. This was compared with the raw data from the 1993 study, and an analysis of percentages was used to determine variations. RESULTS: Generally attitudes to organ donation have not changed since 1993, remaining positive among the study population. However, individuals are significantly more hesitant to consider donating the organs of a relative without being aware of that person's donation preference. Individuals in the black African study population are currently more willing to donate kidneys than in 1993 (66% v. 81%; p < 0.0001), but less willing to donate a heart (64% v. 38%; p < 0.0001), a liver (40% v. 34%; p < 0.036) and corneas (22% v. 15%, p < 0.0059). CONCLUSIONS: Publicity campaigns aimed at raising awareness of organ donation should emphasise the importance of sharing donation preferences with one's family in order to mitigate discomfort about making a decision on behalf of another. These campaigns should be culturally and linguistically sensitive. The study should be repeated in all populations over time to continually gauge attitudes.

Public attitudes to organ donation among a sample of urban-dwelling South African adults: a 2012 study.

BACKGROUND: Published literature suggests that attitudes toward organ donation in South Africa are generally positive. However, there has been a decline in the actual number of transplants taking place annually, which is not consistent with expressed positive attitudes. OBJECTIVES: Assess the attitudes of a representative sample of the urban-dwelling South African population toward organ donation and how these might affect transplant numbers. METHODS: A structured questionnaire was utilized to measure attitudes among a study population of 1048 adults in five major metropolitan areas of South Africa. Field work was undertaken by supervised field workers. Written informed consent was obtained from all participants. RESULTS: Eighty-nine percent (89%) of respondents had heard of organ donation, and 77% indicated that they would accept an organ transplant if necessary. Seventy percent (70%) of respondents specified they would be willing to donate their own organs after death, while 67% expressed willingness to donate a relative's organs after death. Participants were more positive about kidney donation than any other organ. CONCLUSION: Public attitudes toward organ donation among this population are generally positive. Recommendations include cultural and linguistic sensitivity in educational and advertising campaigns, as well as extensive research into other possible causes of organ shortage.

Predicting summer hypoxia in the northern Gulf of Mexico: redux.

We report on the evolution and accuracy of a model used to predict the mid-summer area of hypoxia (oxygen ≤2 mg l(-1)) in the northern Gulf of Mexico, use it to test for impacts from the Deepwater Horizon oil spill (2010), and estimate the N loading that would meet a management goal. The prediction since 2000 were 100%±6% (µ±1 SE) of the actual value. The predicted in 2010 was 99% of that actual value, suggesting that the net effect of the 2010 oil spill on the hypoxic zone size was negligible. A tropical storm, however, may have reduced the potential size of the hypoxic zone. Lowering the May nitrogen load to about 70,000 mton N nitrate+nitrite would bring the model's predicted hypoxic zone size down to the management goal of 5000 km(2) and restore hypoxic waters to normoxic conditions.

Demonstration of the density dependence of x-ray flux in a laser-driven hohlraum.

Experiments have been conducted using laser-driven cylindrical hohlraums whose walls are machined from Ta2O5 foams of 100 mg/cc and 4 g/cc densities. Measurements of the radiation temperature demonstrate that the lower density walls produce higher radiation temperatures than the high density walls. This is the first experimental demonstration of the prediction that this would occur [M. D. Rosen and J. H. Hammer, Phys. Rev. E 72, 056403 (2005)10.1103/PhysRevE.72.056403]. For high density walls, the radiation front propagates subsonically, and part of the absorbed energy is wasted by the flow kinetic energy. For the lower wall density, the front velocity is supersonic and can devote almost all of the absorbed energy to heating the wall.

Environment. Sustainable development of the agricultural bio-economy.

A U.S. farm policy shift to joint production of commodities and ecological services will advance sustainable agriculture.

Predicting summer hypoxia in the northern Gulf of Mexico: riverine N, P, and Si loading.

We conducted a statistical analysis to discern the relative strengths of the loading of various forms of nitrogen, phosphorus, dissolved silicate and their molar ratios on the variance in the size of the summertime low oxygen zone found off the Mississippi River, northern Gulf of Mexico. A stable statistical model that included Year and riverine nitrate+nitrite loading for the 2 months prior to the measurement of hypoxic zone size described 82% of its variation in size from 1978 to 2004. The usefulness of the term Year is consistent with the documented increase in carbon stored in sediments after the 1970s, which is when the hypoxic zone is predicted to have become a regular feature on the shelf and to have expanded westward. The increased carbon storage is anticipated to cause a sedimentary respiratory demand influencing the size of the zone, and whose temporal influence is cumulative and transcends the annual variations in nitrogen loading. The variable Year is negatively correlated with the TN:TP ratio in a way that suggests N, not P, has become more important as a factor limiting phytoplankton growth in the last 20 years. Nitrogen, in particular nitrate+nitrite, and not phosphorus, dissolved silicate, or their molar ratios, appears to be the major driving factor influencing the size of the hypoxic zone on this shelf. This conclusion is consistent with cross-system analyses that conclude that the TN:TP ratio in the Mississippi River, currently fluctuating around 20:1, is indicative of nitrogen, not phosphorus, limitation of phytoplankton growth. Nutrient management that places stronger emphasis on reducing nitrogen loading as compared to phosphorus loading, is justified.

Radiation-driven hydrodynamics of high- hohlraums on the national ignition facility.

The first hohlraum experiments on the National Ignition Facility (NIF) using the initial four laser beams tested radiation temperature limits imposed by plasma filling. For a variety of hohlraum sizes and pulse lengths, the measured x-ray flux shows signatures of filling that coincide with hard x-ray emission from plasma streaming out of the hohlraum. These observations agree with hydrodynamic simulations and with an analytical model that includes hydrodynamic and coronal radiative losses. The modeling predicts radiation temperature limits with full NIF (1.8 MJ), greater, and of longer duration than required for ignition hohlraums.

Hohlraum-driven ignitionlike double-shell implosions on the omega laser facility.

High-convergence ignitionlike double-shell implosion experiments have been performed on the Omega laser facility [T. R. Boehly, Opt. Commun. 133, 495 (1997)] using cylindrical gold hohlraums with 40 drive beams. Repeatable, dominant primary (2.45 MeV) neutron production from the mix-susceptible compressional phase of a double-shell implosion, using fall-line design optimization and exacting fabrication standards, is experimentally inferred from time-resolved core x-ray imaging. Effective control of fuel-pusher mix during final compression is essential for achieving noncryogenic ignition with double-shell targets on the National Ignition Facility [Paisner, Laser Focus World 30, 75 (1994)].

Summer hypoxia in the northern Gulf of Mexico and its prediction from 1978 to 1995.

An 18-year monitoring record (1978-1995) of dissolved oxygen within a region having hypoxia (dissolved oxygen less than 2 mgl(-1)) in the bottom layer was examined to describe seasonal and annual trends. The monitoring location was near or within a well-described summer hypoxic zone whose size has been up to 20,000 km(2). The monitoring data were used to hindcast the size of the hypoxic zone for before consistent shelfwide surveys started, and to predict it for 1989, when a complete shelfwide survey was not made. The concentration of total Kjeldahl nitrogen (TKN) in surface waters and concentration of bottom water oxygen were directly related, as anticipated if organic loading from surface to bottom was from in situ processes. The TKN data were used to develop a predictive relationship that suggested there was no substantial hypoxia before the 1970s, which was before nitrate flux from the Mississippi River to the Gulf of Mexico began to rise. The peak frequency in monthly hypoxic events is two to three months after both the spring maximum in discharge and nitrate loading of the Mississippi River. These results support the conclusion that persistent, large-sized summer hypoxia is a recently-developed phenomenon that began in the 1970s or early 1980s.

Measurement of the absolute hohlraum-wall albedo under ignition foot drive conditions.

We present measurements of the absolute albedos of hohlraums made from gold or from high-Z mixtures. The measurements are performed over the range of radiation temperatures (70-100 eV) expected during the foot of an indirect-drive temporally shaped ignition laser pulse, where accurate knowledge of the wall albedo (i.e., soft x-ray wall reemission) is most critical for determining capsule radiation symmetry. We find that the gold albedo agrees well with calculations using the supertransition array opacity model, potentially providing additional margin for inertial confinement fusion ignition.

Implosion of indirectly driven reentrant-cone shell target.

We have examined the implosion of an indirectly driven reentrant-cone shell target to clarify the issues attendant on compressing fuel for a fast ignition target. The target design is the hydrodynamic equivalent of a NIF cryoignition target scaled to be driven by Omega. Implosions were imaged with backlit x radiographs and modeled with LASNEX. The simulations were generally in good agreement with the experiments with respect to the shell diameter, density, and symmetry, but did not show the prestagnation central absorption maximum. The existence of material between the original cone and the shell is sensitive to gold M-band radiation, which penetrates the shell and ablates gold from the cone. The simulated radiographs using recently measured M-band fractions showed absorption between the cone and shell similar to the experiment. This gold ablation might be a problem in a cryoignition target.

Hohlraum-driven high-convergence implosion experiments with multiple beam cones on the omega laser facility.

High-convergence implosion experiments have been performed on the Omega laser facility [T.R. Boehly, Opt. Commun. 133, 495 (1997)]] using cylindrical gold hohlraums with 40 drive beams arranged into multiple cones. These experiments make use of improved hohlraum radiation symmetry conditions [T.J. Murphy, Phys. Rev. Lett. 81, 108 (1998)]] to demonstrate near predicted primary (2.45 MeV) neutron production from single-shell implosions with measured deuterium fuel convergence ratios exceeding 20 at an ignition-relevant hohlraum case-to-capsule ratio approximately 3.

Efficient, 1-100-keV x-ray radiography with high spatial and temporal resolution.

Transient x-ray radiography using laser-plasma emission is a powerful tool for diagnosing a large variety of high-energy-density phenomena. Traditional area- and point-backlighting techniques used at inertial confinement fusion facilities such as Nova and Omega cannot be extended efficiently to the future 100-times-larger National Ignition Facility. We have developed an x-ray backlighting technique that uses a backlit pinhole as a source for point-projection radiography. This method incorporates the principal advantages of point projection over traditional area backlighting in that it requires far less backlighter energy and produces data that are free from residual backlighter plasma structure. Moreover, the use of pinholes overcomes the usual disadvantages of point projection from pin targets, namely, degradation of spatial resolution and cooling due to plasma expansion.

Social identity in adolescence.

Social identity theory (SIT) was used to investigate the effects of social categorization on adolescents' intergroup behaviour. One hundred and forty-nine male adolescents aged 14-15 years made comparisons between an ingroup and an outgroup along a series of dimensions. Participants displayed consistent ingroup-favouring behaviour in their ratings: the ingroup was associated to a greater extent than the outgroup with positively valued dimensions, and to a lesser extent with negatively valued dimensions. Those participants who demonstrated the most discrimination reported highest levels of ingroup identification. The utility of applying predictions from SIT to the study of adolescence is discussed.

A model for an Ascaris muscle cell.

Muscle cells in the nematode Ascaris suum undergo bouts of oscillation in the behaving worm, these being correlated with progressing waves of contraction along the body of the worm. The bouts have three time scales: a rough period of 7-20 s, 10-20 short bursts of spikes within a bout, and three to eight spikes per burst. This paper has two aims: showing that there is consistency between measurements of individual currents and measurements on whole muscle cells, and creating a building block to eventually explain the locomotion in this 'simple' system. A realistic model for a single Ascaris suum muscle cell is developed using existing data from experiments which have established the types of ionic currents in the muscle cell and many of their kinetic properties. Numerical simulations are carried out. The model cell reproduces the two shorter time scales present. It has some robustness with regard to parameter changes, but also allows for the different numbers of spikes per burst seen in recordings from muscle cells. The third time scale, the length of a bout, may originate from some system effect, a combination of neural and stretch effects and possibly a secondary effect of the calcium-activated chloride channel.

Hypoxia in the Gulf of Mexico.

Seasonally severe and persistent hypoxia, or low dissolved oxygen concentration, occurs on the inner- to mid-Louisiana continental shelf to the west of the Mississippi River and Atchafalaya River deltas. The estimated areal extent of bottom dissolved oxygen concentration less than 2 mg L-1 during mid-summer surveys of 1993-2000 reached as high as 16,000 to 20,000 km2. The distribution for a similar mapping grid for 1985 to 1992 averaged 8000 to 9000 km2. Hypoxia occurs below the pycnocline from as early as late February through early October, but is most widespread, persistent, and severe in June, July, and August. Spatial and temporal variability in the distribution of hypoxia exists and is, at least partially, related to the amplitude and phasing of the Mississippi and Atchafalaya discharges and their nutrient flux. Mississippi River nutrient concentrations and loadings to the adjacent continental shelf have changed dramatically this century, with an acceleration of these changes since the 1950s to 1960s. An analysis of diatoms, foraminiferans, and carbon accumulation in the sedimentary record provides evidence of increased eutrophication and hypoxia in the Mississippi River delta bight coincident with changes in nitrogen loading.