1,293 research outputs found
A Mechanistic Study of Halogen Addition and Photoelimination from ?-Conjugated Tellurophenes
The ability to drive
reactivity using visible light is of importance
for many disciplines of chemistry and has significant implications
for sustainable chemistry. Identifying photochemically active compounds
and understanding photochemical mechanisms is important for the development
of useful materials for synthesis and catalysis. Here we report a
series of photoactive diphenyltellurophene compounds bearing electron-withdrawing
and electron-donating substituents synthesized by alkyne coupling/ring
closing or palladium-catalyzed ipso-arylation chemistry. The redox
chemistry of these compounds was studied with respect to oxidative
addition and photoelimination of bromine, which is of importance for
energy storage reactions involving X<sub>2</sub>. The oxidative addition
reaction mechanism was studied using density functional theory, the
results of which support a three-step mechanism involving the formation
of an initial η<sup>1</sup> association complex, a monobrominated
intermediate, and finally the dibrominated product. All of the tellurophene
derivatives undergo photoreduction using 430, 447, or 617 nm light
depending on the absorption properties of the compound. Compounds
bearing electron-withdrawing substituents have the highest photochemical
quantum efficiencies in the presence of an alkene trap, with efficiencies
of up to 42.4% for a pentafluorophenyl-functionalized tellurophene.
The photoelimination reaction was studied in detail through bromine
trapping experiments and laser flash photolysis, and a mechanism is
proposed. The photoreaction, which occurs by release of bromine radicals,
is competitive with intersystem crossing to the triplet state of the
brominated species, as evidenced by the formation of singlet oxygen.
These findings should be useful for the design of new photochemically
active compounds supported by main-group elements
NASA Products to Enhance Energy Utility Load Forecasting
Existing energy load forecasting tools rely upon historical load and forecasted weather to predict load within energy company service areas. The shortcomings of load forecasts are often the result of weather forecasts that are not at a fine enough spatial or temporal resolution to capture local-scale weather events. This project aims to improve the performance of load forecasting tools through the integration of high-resolution, weather-related NASA Earth Science Data, such as temperature, relative humidity, and wind speed. Three companies are participating in operational testing one natural gas company, and two electric providers. Operational results comparing load forecasts with and without NASA weather forecasts have been generated since March 2010. We have worked with end users at the three companies to refine selection of weather forecast information and optimize load forecast model performance. The project will conclude in 2012 with transitioning documented improvements from the inclusion of NASA forecasts for sustained use by energy utilities nationwide in a variety of load forecasting tools. In addition, Battelle has consulted with energy companies nationwide to document their information needs for long-term planning, in light of climate change and regulatory impacts
Effective practices of international volunteering for health : perspectives from partner organizations
Abstract: The demand for international volunteer experiences to promote global health and nutrition is increasing and numerous studies have documented the experiences of the international volunteers who travel abroad; however, little is known about effective practices from the perspective of partner organizations. This study aims to understand how variables such as the skill-level of volunteers, the duration of service, cultural and language training, and other key variables affect partner organizations’ perceptions of volunteer effectiveness at promoting healthcare and nutrition..
LGN plays distinct roles in oral epithelial stratification, filiform papilla morphogenesis and hair follicle development
Oral epithelia protect against constant challenges by bacteria, viruses, toxins and injury while also contributing to the formation of ectodermal appendages such as teeth, salivary glands and lingual papillae. Despite increasing evidence that differentiation pathway genes are frequently mutated in oral cancers, comparatively little is known about the mechanisms that regulate normal oral epithelial development. Here, we characterize oral epithelial stratification and describe multiple distinct functions for the mitotic spindle orientation gene LGN (Gpsm2) in promoting differentiation and tissue patterning in the mouse oral cavity. Similar to its function in epidermis, apically localized LGN directs perpendicular divisions that promote stratification of the palatal, buccogingival and ventral tongue epithelia. Surprisingly, however, in dorsal tongue LGN is predominantly localized basally, circumferentially or bilaterally and promotes planar divisions. Loss of LGN disrupts the organization and morphogenesis of filiform papillae but appears to be dispensable for embryonic hair follicle development. Thus, LGN has crucial tissue-specific functions in patterning surface ectoderm and its appendages by controlling division orientation
GEO 600 and the GEO-HF upgrade program: successes and challenges
The German-British laser-interferometric gravitational wave detector GEO 600
is in its 14th year of operation since its first lock in 2001. After GEO 600
participated in science runs with other first-generation detectors, a program
known as GEO-HF began in 2009. The goal was to improve the detector sensitivity
at high frequencies, around 1 kHz and above, with technologically advanced yet
minimally invasive upgrades. Simultaneously, the detector would record science
quality data in between commissioning activities. As of early 2014, all of the
planned upgrades have been carried out and sensitivity improvements of up to a
factor of four at the high-frequency end of the observation band have been
achieved. Besides science data collection, an experimental program is ongoing
with the goal to further improve the sensitivity and evaluate future detector
technologies. We summarize the results of the GEO-HF program to date and
discuss its successes and challenges
Observation of Wigner cusps in a metallic carbon nanotube
Previous gate-dependent conductance measurements of metallic carbon nanotubes
have revealed unexplainable conductance suppressions, occurring at two
different gate voltages. These were previously attributed to the
gate-dependency of contact resistance. Our gate-dependent conductivity
measurements on a metallic nanotube with known chirality show that these
bimodal conductance suppressions are the manifestations of Wigner cusps, often
seen in atomic and nuclear physics experiments.Comment: 6 pages, 3 figure
The Trial to Reduce IDDM in the Genetically at Risk (TRIGR) study: recruitment, intervention and follow-up
Peer reviewe
(Dodecafluorosubphthalocyaninato)(4-methylphenolato)boron(III)
In the title compound, C31H7BF12N6O, molecules are arranged into one-dimensional columns with an intermolecular B⋯B distance of 5.3176 (8) Å. Bowl-shaped molecules are arranged within the columns in a concave bowl-to-ligand arrangement separated by a ring centroid distance of 3.532 (2) Å between the benzene ring of the 4-methylphenoxy ligand and one of the three five-membered rings of a symmetry-related molecule
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