Seasonal trophic resource partitioning by Pacific oyster Crassostrea gigas and Pacific blue mussel Mytilus trossulus in an Alaskan estuary

Marine Ecology Progress Series · 2024 · 3 citations

• Fishery
• Oceanography
• Biology

Shellfish mariculture has expanded in Alaska, yet potential ecological interactions between cultured and native taxa have rarely been considered. Shellfish such as the Pacific oyster Crassostrea gigas and the Pacific blue mussel Mytilus trossulus are already farmed in Alaska at a small scale, with production expected to increase in coming years. C. gigas and M. trossulus selectively feed on naturally occurring particulate organic matter (POM) sources; thus, understanding the partitioning of trophic resources by these bivalves has implications for mariculture site selection and marine management. We identified temporal patterns in food source consumption by C. gigas and M. trossulus in Jakolof Bay, Alaska. We estimated endmember contributions (phytoplankton, macroalgae, terrestrial organic matter, and zooplankton) to the suspended POM pool and to the 2 bivalves using bulk stable isotopes (δ 13 C and δ 15 N) in April, June, August, and December 2023. While δ 13 C values remained comparable for both bivalves across sampling periods, C. gigas had higher δ 15 N values than M. trossulus , indicating that although both bivalves ultimately derive carbon from similar sources of primary production, C. gigas feeds at a higher trophic level. Mixing model results indicate that macroalgae contributed 4-58% of the assimilated carbon in C. gigas and 25-75% in M. trossulus . These results suggest that farming shellfish in areas with macroalgae populations (i.e. farmed in co-culture or wild) could offer C. gigas and M. trossulus an additional source of organic matter.

Non-Ionic Surfactants as Boosters for FR Hydration in Brines

SPE International Conference on Oilfield Chemistry · 2023

• Chemistry
• Chemical engineering
• Thermodynamics

Abstract A theoretical model of polyacrylamide polymers (PAM and PHPA) hydration dynamics is explored, with emphasis on the effect pf salinity on the hydration dynamics of traditional PAM and PHPA polymers. By understanding the interactions at a molecular level between the polymer and the solvent system it is expected that the polymer’s usability as a viscosifying agent can be extended into brackish and possibly produced water. In this study, viscosity vs. time plots are used to find the hydration rates for PAM and PHPA emulsions in fresh water and various brines. Special brines were designed, including one with Fe(III) among components. The study is done by using common, commercial viscometers, utilizing an R1 B1 bob configuration with heated cup. The overall mixing shear generated is low and kept constant throughout the runs. The temperature and length of runs are also kept constant. This allows the determination of the rate limiting hydration step, maximum viscosity and the hydration rates of a wide variety of nonionic surfactants to be explored. By comparing the PAM and PHPA hydration rates for the neat brine, tap water and brine with non-ionic surfactant it is shown that by choosing the correct nonionic surfactant the hydration rates can be increased by over 3500% from the brine solution and more than 10-50% from tap water. It is also shown that the maximum viscosity can be increased by over 700% from the brine solution and 27% from tap water. This trend was also shown to be true using Nano pure water. The results support the theoretical hydration dynamics we propose, showing the effect the nonionic surfactants have on the rate limiting hydration step and transitions between different hydration steps. The data is strong proof that by understanding the processes of polymer hydration, brackish and possibly produced water in a wide range of TDS can be used to successfully hydrate the polymer. The novelty of this testing is that it provides further examples of how non-ionic surfactants can be used successfully to allow PAM and PHPA polymers to be hydrated in brine waters of various compositions with no damage to performance. Care was taken to utilize very common instrumentation and to develop simple and clear procedures for testing, to make the method easy and reliable to use by field labs that may not necessarily have state-of-the-art equipment available.

Quantum Simulations of Charge Separation at a Model Donor-Acceptor Interface: Role of Delocalization and Local Packing

Advances in Condensed Matter Physics · 2018-01-01 · 3 citations

Organic Polymer-based photovoltaic systems offer a viable alternative to more standard solid-state devices for light-harvesting applications. In this study, we investigate the electronic dynamics of a model organic photovoltaic (OPV) heterojunction consisting of polyphenylene vinylene (PPV) oligomers and a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mo stretchy="false">[</mml:mo><mml:mn fontstyle="italic">6,6</mml:mn><mml:mo stretchy="false">]</mml:mo></mml:math>-phenyl C61-butyric acid methyl ester (PCBM) blend. Our approach treats the classical molecular dynamics of the atoms within an Ehrenfest mean-field treatment of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mrow><mml:mi>π</mml:mi></mml:mrow></mml:math>-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>⁎</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math> singly excited states spanning a subset of donor and acceptor molecules near the phase boundary of the blend. Our results indicate that interfacial electronic states are modulated by C=C bond stretching motions and that such motions induce avoided crossings between nearby excited states thereby facilitating transitions from localized excitonic configurations to delocalized charge-separated configurations on an ultrafast time-scale. The lowest few excited states of the model interface rapidly mix allowing low frequency C-C out-of-plane torsions to modulate the potential energy surface such that the system can sample both intermolecular charge-transfer and charge-separated electronic configurations on sub-100 fs time scales. Our simulations support an emerging picture of carrier generation in OPV systems in which interfacial electronic states can rapidly decay into charge-separated and current producing states via coupling to vibronic degrees of freedom.

Economic Demography

The New Palgrave Dictionary of Economics · 2018-01-01

Economic demography is an area of study that examines the determinants and consequences of demographic change, including fertility, mortality, marriage, divorce, location (urbanisation, migration, density), age, gender, ethnicity, population size and population growth. This article reviews and critically evaluates important macroeconomic dimensions of the ‘population debates’ between the ‘optimists’ and the ‘pessimists’ since 1950. It concludes with an examination of demography in the popular ‘convergence’ growth models of the 1990s.

Quantum simulations of charge-separation at a model donor-acceptor interface: role of delocalization and local packing

arXiv (Cornell University) · 2016-12-20

We investigate the electronic dynamics of a model organic photovoltaic (OPV) system consisting of polyphenylene vinylene (PPV) oligomers and a [6,6]-phenyl C61-butyric acid methylester (PCBM) blend using a mixed molecular mechanics/quantum mechanics (MM/QM) approach. Using a heuristic model that connects energy gap fluctuations to the average electronic couplings and decoherence times, we provide and estimate of the state-to-state internal conversion rates within the manifold of the lowest few electronic excitations. We show that the electronic dynamics of the OPV are dramatically altered by varying the positions of the molecules simulated at the interface. The lowest few excited states of the model interface rapidly mix allowing low frequency C-C out of plain torsions to modulate the potential energy surface such that the system can sample both intermolecular charge-transfer and charge-separated electronic configurations on sub 100 fs time scales. Our simulations support an emerging picture of carrier generation in OPV systems in which interfacial electronic states can rapidly decay into charge-separated and current producing states via coupling to vibronic degrees of freedom.

The role of structural fluctuations and environmental noise in the electron/hole separation kinetics at organic polymer bulk-heterojunction interfaces

Physical Chemistry Chemical Physics · 2015-01-01

We investigate the electronic dynamics of a model organic photovoltaic (OPV) system consisting of polyphenylene vinylene (PPV) oligomers and a [6,6]-phenyl C61-butyric acid methylester (PCBM) blend using a mixed molecular mechanics/quantum mechanics (MM/QM) approach. Using a heuristic model that connects energy gap fluctuations to the average electronic couplings and decoherence times, we provide an estimate of the state-to-state internal conversion rates within the manifold of the lowest few electronic excitations. We find that the lowest few excited states of a model interface are rapidly mixed by C[double bond, length as m-dash]C bond fluctuations such that the system can sample both intermolecular charge-transfer and charge-separated electronic configurations on a time scale of 20 fs. Our simulations support an emerging picture of carrier generation in OPV systems in which interfacial electronic states can rapidly decay into charge-separated and current producing states via coupling to vibronic degrees of freedom.

Role of structural fluctuations and environmental noise in the\n electron/hole separation kinetics at organic polymer bulk-heterojunction\n interfaces

arXiv (Cornell University) · 2015-09-17

We investigate the electronic dynamics of model organic photovoltaic (OPV)\nsystem consisting of polyphenylene vinylene (PPV) oligomers and [6,6]-phenyl\nC61-butyric acid methylester (PCBM) blend using a mixed molecular\nmechanics/quantum mechanics (MM/QM) approach. Using a heuristic model that\nconnects energy gap fluctuations to the average electronic couplings and\ndecoherence times, we provide an estimate of the state-to-state internal\nconversion rates within the manifold of the lowest few electronic excitations.\nWe find that the lowest few excited states of a model interface are rapidly\nmixed by C=C bond fluctuations such that the system can sample both\nintermolecular charge-transfer and charge-separated electronic configurations\non a time scale of 20fs. Our simulations support an emerging picture of carrier\ngeneration in OPV systems in which interfacial electronic states can rapidly\ndecay into charge-separated and current producing states via coupling to\nvibronic degrees of freedom.\n

Index

Edward Elgar Publishing eBooks · 2013-01-31

climate litigation see international climate litigation, Tuvalu v Australia (hypothetical) Nuclear Tests 420, 434-5 Southern Bluefi n Tuna Cases 425-7 Australia, Aboriginal and Torres Strait Islander communities and climate change 493-507 Aboriginal Land

economic demography

The New Palgrave Dictionary of Economics · 2008-04-25 · 1 citations

Economic demography is an area of study that examines the determinants and consequences of demographic change, including fertility, mortality, marriage, divorce, location (urbanisation, migration, density), age, gender, ethnicity, population size and population growth. This article reviews and critically evaluates important macroeconomic dimensions of the ‘population debates’ between the ‘optimists’ and the ‘pessimists’ since 1950. It concludes with an examination of demography in the popular ‘convergence’ growth models of the 1990s.

Economic Demography

The New Palgrave Dictionary of Economics · 2008-01-01