2,214 research outputs found
Study of TADF Emitters in OLEDs
Delayed fluorescence through thermally activated delayed fluorescence (TADF) has great potential for the creation of inexpensive and highly efficient white lighting applications, with superior colour rendering. Currently the highest external quantum efficiencies are achieved with small donor-acceptor-donor molecules utilising intramolecular charge transfer (ICT) states, and these molecules require a suitable host matrix to reside in. This thesis studies the effect of host material on the model molecule 2d, a proven efficient TADF emitter through diligent photophysical investigation. A combination of steady state and nanosecond time resolved spectroscopic studies confirm the importance of a high host triplet level to ensure that the ICT state is the lowest energy excited state to avoid high levels of quenching. More interestingly it is shown that the functional group combination of emitter and host is crucial in achieving efficient TADF in OLED devices. In particular combinations where both the host and dopant are carbazole-based should be avoided due to the formation of carbazole dimer. The effect of such dimerisation is to lower the host triplet level significantly, and further to deactivate the ability of the 2d dopant to produce the ICT state required for TADF by locking the 2d dopant in the ‘planar’ configuration. It is therefore clear that the chemical composition of the host is of critical importance for the design of future OLED devices. Experiment also suggests that there is a complex interplay between exciplex and ICT emission in 2d systems in the solid state, insofar as CT emission of any description has so far only been observed in conditions where exciplex can and does occur
Fully Coupled Simulation of the Plasma Liquid Interface and Interfacial Coefficient Effects
There is a growing interest in the study of coupled plasma-liquid systems
because of their applications to biomedicine, biological and chemical
disinfection, agriculture, and other areas. Without an understanding of the
near-surface gas dynamics, modellers are left to make assumptions about the
interfacial conditions. For instance it is commonly assumed that the surface
loss or sticking coefficient of gas-phase electrons at the interface is equal
to 1. In this work we explore the consequences of this assumption and introduce
a couple of ways to think about the electron interfacial condition. In one set
of simulations we impose a kinetic condition with varying surface loss
coefficient on the gas phase interfacial electrons. In a second set of
simulations we introduce a Henry's law like condition at the interface in which
the gas-phase electron concentration is assumed to be in thermodynamic
equilibrium with the liquid-phase electron concentration. It is shown that for
a range of electron Henry coefficients spanning a range of known hydrophilic
specie Henry coefficients, the gas phase electron density in the anode can vary
by orders of magnitude. Varying reflection of electrons by the interface also
has consequences for the electron energy profile. This variation in anode
electron density and energy as a function of the interface characteristics
could also lead to significant variation in near-surface gas chemistries when
such reactions are included in the model; this could very well in turn affect
the reactive species impinging on the liquid surface. We draw the conclusion
that in order to make more confident model predictions about plasma-liquid
systems, finer scale simulations and/or new experimental techniques must be
used to elucidate the near-surface gas phase electron dynamics
Nano-modulated electron beams via electron diffraction and emittance exchange for coherent x-ray generation
We present a new method for generation of relativistic electron beams with
current modulation on the nanometer scale and below. The current modulation is
produced by diffracting relativistic electrons in single crystal Si,
accelerating the diffracted beam and imaging the crystal structure, then
transferring the image into the temporal dimension via emittance exchange. The
modulation period can be tuned by adjusting electron optics after diffraction.
This tunable longitudinal modulation can have a period as short as a few
angstroms, enabling production of coherent hard x-rays from a source based on
inverse Compton scattering with total accelerator length of approximately ten
meters. Electron beam simulations from cathode emission through diffraction,
acceleration and image formation with variable magnification are presented
along with estimates of the coherent x-ray output properties
Momentum, Heat, and Neutral Mass Transport in Convective Atmospheric Pressure Plasma-Liquid Systems and Implications for Aqueous Targets
There is a growing interest in the study of plasma-liquid interactions with
application to biomedicine, chemical disinfection, agriculture, and other
fields. This work models the momentum, heat, and neutral species mass transfer
between gas and aqueous phases in the context of a streamer discharge; the
qualitative conclusions are generally applicable to plasma-liquid systems. The
problem domain is discretized using the finite element method. The most
interesting and relevant model result for application purposes is the steep
gradients in reactive species at the interface. At the center of where the
reactive gas stream impinges on the water surface, the aqueous concentrations
of OH and ONOOH decrease by roughly 9 and 4 orders of magnitude respectively
within 50 m of the interface. Recognizing the limited penetration of
reactive plasma species into the aqueous phase is critical to discussions about
the therapeutic mechanisms for direct plasma treatment of biological solutions.
Other interesting results from this study include the presence of a 10 K
temperature drop in the gas boundary layer adjacent to the interface that
arises from convective cooling and water evaporation. Accounting for the
resulting difference between gas and liquid bulk temperatures has a significant
impact on reaction kinetics; factor of two changes in terminal aqueous species
concentrations like HO, NO, and NO are observed if the
effect of evaporative cooling is not included
COMMERCIAL SWEETPOTATO PRODUCTION IN MISSISSIPPI
This report provides an estimate of selected costs incurred in sweetpotato production in Mississippi, 1999. Land, management and general farm overhead costs were not included. Per acre returns above specified costs are estimated at approximately $1,100.00 per acre.sweetpotatoes, production costs, net returns, cash flow, price sensitivity, equipment, chemicals, Production Economics,
Tests of Suitability of Overwintering Hosts of Aphis glycines: Identification of a New Host Association with Rhamnus alnifolia L’Héritier
Eleven species from the family Rhamnaceae, including both species exotic and native to North America, were tested for their acceptability to the fall migrants of the soybean aphid, Aphis glycines Matsumura. Two species, Rhamnus cathartica L. andRhamnus alnifolia L’Héritier were accepted and had overwintering eggs deposited on them. Eggs survived the winter, and colonies developed on both hosts in the spring. R. alnifolia is a new overwintering host for the soybean aphid
Function and Biodegradation in Soil of Bioplastic Horticultural Containers made of PLA-BioResTM Composites
Container-crops horticultural industries rely almost exclusively on petroleum-based plastic containers for modern production systems. Containers made of these materials fulfill all of the functions required during crop production, and perform better than containers made of clay, peat, and other natural materials, but the source of the plastic materials (fossil carbon), their lack of biodegradability, and their end-of-life disposal (97% end up in landfills) are major obstacles to sustainability. Although function and efficiency are among the most important aspects in determining the best materials for horticultural containers, there is no need for containers to persist in the environment for decades when their useful life cycle is only one month to three years depending on the plant species produced in them
Playing Atari with Deep Reinforcement Learning
We present the first deep learning model to successfully learn control
policies directly from high-dimensional sensory input using reinforcement
learning. The model is a convolutional neural network, trained with a variant
of Q-learning, whose input is raw pixels and whose output is a value function
estimating future rewards. We apply our method to seven Atari 2600 games from
the Arcade Learning Environment, with no adjustment of the architecture or
learning algorithm. We find that it outperforms all previous approaches on six
of the games and surpasses a human expert on three of them.Comment: NIPS Deep Learning Workshop 201
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