A gap analysis of confined field trial application forms for genetically modified crops in East Africa: evaluating the potential for harmonization

"The regulatory approval of genetically modified crops in the field initially requires small, restricted experimental trials known as confined field trials. These small scale experiments provide researchers with important information on environmental interactions and agronomic performance of the crop in a safe and contained manner. To authorize confined field trials regulatory review is required, with formats for obtaining relevant information differing from country to country. In this paper, a Gap Analysis is used to identify informational gaps and potential for harmonization of confined field trial application processes in three East African countries - Tanzania, Kenya, and Uganda. The basic principle behind gap analysis is a comparison of the status quo to an ideal with the identification of the differences or gaps and the difficulty involved in removing the gaps. The resulting similarity of the application forms provides a potential basis for harmonization of confined field trial application processes between countries leading to potential efficiency gains." Authors' abstractGenetically modified crops, Gap analysis, Confined field trials, biotechnology,

Osmotic properties of polyethyleneglycols: quantitative features of brush and bulk scaling laws

From glycosylated cell surfaces to sterically stabilized liposomes, polymers attached to membranes attract biological and therapeutic interest. Can the scaling laws of polymer "brushes" describe the physical properties of these coats? We delineate conditions where the Alexander - de Gennes theory of polymer brushes successfully describes the intermembrane distance vs. applied osmotic stress data of Kenworthy et al. for PEG-grafted multilamellar liposomes [Biophys. J. (1995) 68:1921]. We establish that the polymer density and size in the brush must be high enough that, in a bulk solution of equivalent density, the polymer osmotic pressure is independent of polymer molecular weight (the des Cloizeaux semi-dilute regime of bulk polymer solutions). The condition that attached polymers behave as semi-dilute bulk solutions offers a rigorous criterion for brush scaling-law behavior. There is a deep connection between the behaviors of polymer solutions in bulk and polymers grafted to a surface at a density such that neighbors pack to form a uniform brush. In this regime, two-parameter unconstrained fits of the Alexander - de Gennes brush scaling laws yield effective monomer lengths of 3.3 to 3.5 AA, which agree with structural predictions. The fitted distances between grafting sites are larger than expected from the nominal content of PEG-lipids; the chains apparently saturate the surface. Osmotic stress measurements can be used to estimate the actual densities of membrane-grafted polymers.Comment: 26 pages with figure

Investigation of thermal filamentation instability over Gakona, Alaska

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2007.Includes bibliographical references (p. 43).The thermal filamentation instability has been invoked to explain the formation of parallel plate waveguides in mid-latitude ionospheric plasmas during Arecibo, Puerto Rico heating experiments in 1997. The geometry of the kilometer-scale parallel plates predicted by thermal filamentation depends on the mode of the transmitted heater wave, as does the threshold to excite this instability. While plasma heating can excite small-scale irregularities via parametric instabilities, thermal filamentation is thought to produce large-scale irregularities. In Arecibo, the threshold for X-mode to induce irregularities was found to be greater than 1 V/m, while for O-mode it was on the order of mV/m. In recent plasma experiments in high-latitude ionospheric plasmas, carried out at the HAARP facility in Gakona, Alaska in summer 2005, spring 2006, and summer 2006, a weakening in ionogram traces was observed during O-mode and X-mode heating, leading to a scenario detailing the effects of thermal filamentation and short-scale irregularities caused by heating. The Gakona experiments using a high power HF heating facility and multiple diagnostic instruments shed light on the important role of the thermal filamentation instability in generating electromagnetic wave-induced plasma turbulence with a broad spectrum of wavelengths, ranging from meter to kilometer scales.by Joel Cohen.S.B

Inverting Singlet and Triplet Excited States using Strong Light-Matter Coupling

In organic microcavities, hybrid light-matter states can form with energies that differ from the bare molecular excitation energies by nearly 1 eV. A timely question, given recent advances in the development of thermally activated delayed fluorescence materials, is whether strong light-matter coupling can be used to invert the ordering of singlet and triplet states and, in addition, enhance reverse intersystem crossing (RISC) rates. Here, we demonstrate a complete inversion of the singlet lower polariton and triplet excited states. We also unambiguously measure the RISC rate in strongly-coupled organic microcavities and find that, regardless of the large energy level shifts, it is unchanged compared to films of the bare molecules. This observation is a consequence of slow RISC to the lower polariton due to the delocalized nature of the state across many molecules and an inability to compete with RISC to the dark exciton reservoir, which occurs at a rate comparable to that in bare molecules

Triplet harvesting in the polaritonic regime: a variational polaron approach

We explore the electroluminescence efficiency for a quantum mechanical model of a large number of molecular emitters embedded in an optical microcavity. We characterize the circumstances under which a microcavity enhances harvesting of triplet excitons via reverse intersystem-crossing (R-ISC) into singlet populations that can emit light. For that end, we develop a time-local master equation in a variationally optimized frame which allows for the exploration of the population dynamics of chemically relevant species in different regimes of emitter coupling to the condensed phase vibrational bath and to the microcavity photonic mode. For a vibrational bath that equilibrates faster than R-ISC (in emitters with weak singlet-triplet mixing), our results reveal that significant improvements in efficiencies with respect to the cavity-free counterpart can be obtained for strong coupling of the singlet exciton to a photonic mode, as long as the singlet to triplet exciton transition is within the inverted Marcus regime; under these circumstances, we show the possibility to overcome the detrimental delocalization of the polariton states across a macroscopic number of molecules. On the other hand, for a vibrational bath that equilibrates slower than R-ISC (i.e., emitters with strong singlet-triplet mixing), we find that while enhancemnents in photoluminiscence can be obtained via vibrational relaxation into polaritons, this only occurs for small number of emitters coupled to the photon mode, with delocalization of the polaritons across many emitters eventually being detrimental to electroluminescence efficiency. These findings provide insight on the tunability of optoelectronic processes in molecular materials due to weak and strong light-matter coupling

Excitation of forced ion acoustic waves, large plasma sheets, and magnetic field fluctuations over Gakona, Alaska

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 47-48).Two research subjects: (1) excitation of "forced ion acoustic waves", and (2) "simultaneous excitation of plasma density fluctuations and geomagnetic field fluctuations" are reported in my M.S. thesis. The data was acquired in our experiments conducted at Gakona, Alaska from summer 2007 to winter 2008, using DoD/NSF-funded HAARP facilities and our own optical (ASIS) and radio instruments (VLF receiving system of IRIS) aided by GPS satellites as well as AMISR radar at Poker Flat, Alaska. We suggest that "Forced ion acoustic waves" detected by MUIR radar on Oct. 29 during 6:20-6:30 UT arise from keV electron precipitation associated with the occurrence of green aurora. Our work shows, for the first time, that MUIR radar is suitable for probing naturally occurring space plasma processes and not limited to HF heater-induced effects. This would extend the usage of MUIR for the investigation of space weather together with AMISR radar at Poker Flat, to advance our knowledge in space plasma turbulence. The research on "simultaneous excitation of plasma density fluctuations and geomagnetic field fluctuations" is an extension of my B.S. thesis research on thermal filamentation instability, which started in our summer Gakona experiments in 2005. Large plasma sheets (also known as sheet-like filaments) can be excited by HF O-mode and X-mode heater waves via thermal filamentation instability.(cont.) The dominant nonlinearity is provided by the differential Joule heating acting on electrons, which subsequently gives rise to a cross-field thermal pressure force, to concomitantly generate spatially varying plasma density fluctuations and geomagnetic field fluctuations. It is interesting to find that the fractional density fluctuations are approximately equal to the fractional magnetic field fluctuations. This gives us the theoretical basis to use ground-based magnetometer measurements to infer the density fluctuations in space plasma turbulence. Such a remote sensing technique for probing the space plasma is much more effective and economic than using a beacon satellite.by Joel Cohen.S.M

Polariton-assisted Singlet Fission in Acene Aggregates

Singlet fission is an important candidate to increase energy conversion efficiency in organic photovoltaics by providing a pathway to increase the quantum yield of excitons per photon absorbed in select materials. We investigate the dependence of exciton quantum yield for acenes in the strong light-matter interaction (polariton) regime, where the materials are embedded in optical microcavities. Starting from an open-quantum-systems approach, we build a kinetic model for time-evolution of species of interest in the presence of quenchers and show that polaritons can decrease or increase exciton quantum yields compared to the cavity-free case. In particular, we find that hexacene, a typically poor singlet-fission candidate, can feature a higher yield than cavity-free pentacene when assisted by polaritonic effects. Similarly, we show that pentacene yield can be increased when assisted by polariton states. Finally, we address how various relaxation processes between bright and dark states in lossy microcavities affect polariton photochemistry. Our results also provide insights on how to choose microcavities to enhance similarly related chemical processes.Comment: 12 pages, 4 figure

Generation of Artificial Acoustic-Gravity Waves and Traveling Ionospheric Disturbances in HF Heating Experiments

We report the results of our ionospheric HF heating experiments to generate artificial acoustic-gravity waves (AGW) and traveling ionospheric disturbances (TID), which were conducted at the High-frequency Active Auroral Research Program facility in Gakona, Alaska. Based on the data from UHF radar, GPS total electron content, and ionosonde measurements, we found that artificial AGW/TID can be generated in ionospheric modification experiments by sinusoidally modulating the power envelope of the transmitted O-mode HF heater waves. In this case, the modulation frequency needs to be set below the characteristic Brunt–Vaisala frequency at the relevant altitudes. We avoided potential contamination from naturally-occurring AGW/TID of auroral origin by conducting the experiments during geomagnetically quiet time period. We determine that these artificial AGW/TID propagate away from the edge of the heated region with a horizontal speed of approximately 160 m/s.United States. Air Force Office of Scientific Research (grant FA9550-09-1-0391)United States. Office of Naval Research (High-frequency Active Auroral Research Program (HAARP) grant N00014-07-1-0999