2,085 research outputs found
Synthesis and Characterization of Highly Porous Borazine-Linked Polymers via Dehydrogenation/Dehydrocoupling of Borane-Amine Adducts and Their Applications to Gas Storage
A new class of porous polymers has been designed and successfully synthesized by thermal dehydrogenation of several polytopic arylamine-borane adducts and has been designated Borazine-Linked Polymers (BLPs). The polymers reported are constructed of linear, triangular, and tetrahedral amine building units to form 2D and 3D frameworks. The boron sites of the pores are aligned with hydrogen atoms contrasted with the recently reported halogenated BLPs which consist of pore channels aligned with bromine or chlorine atoms. One of the reported BLPs, BLP-2(H), was proven to be crystalline by PXRD, matching the experimental pattern to theoretical patterns calculated from modeled structures. BLPs were found to be thermally stable by thermogravimetric analysis, decomposing at temperatures ~450 ºC. Infrared spectroscopy and 11B MAS NMR spectra confirm the formation of borazine as reported in previous borazine-containing polymers and 13C CP MAS spectra confirmed that the structural integrity of the amine building units were maintained and incorporated in the framework of BLPs. Nitrogen isotherms revealed that BLPs exhibit high surface areas ranging from 1132-2866 m2/g (Langmuir) and 400-2200 m2/g (Brunauer-Emett-Teller, BET) with pore sizes from 7-14 Å. Hydrogen, methane, and carbon dioxide measurements were performed at low pressure (up to 1 atm) and were found to be among the best of organic polymers. High pressure isotherms (up to 40 bar) were also taken at various temperatures ranging from 77-298 K. Isosteric heats of adsorption were calculated using the virial method at low pressures. Gas storage performance of BLPs at 40 bar were found to be: 14.7-42.5 mg/g for H2 uptake at 77 K; 348.9-717.4 mg/g for CO2 uptake at 298 K; and 40.8-116.1 mg/g for CH4 uptake at 298 K. The CO2/CH4 selectivity of BLPs at 298 K up to 40 bar was calculated using the Ideal Adsorbed Solution Theory (IAST) to determine their performance as carbon capture and sequestration materials. Additionally, non-borazine containing nanoporous organic polymers (NPOFs) consisting of all carbon and hydrogen atoms were also synthesized and subjected to low pressure hydrogen storage measurements. The results show that though NPOFs generally exhibit higher surface areas (SALang = 2423-4227 m2/g), the H2 storage capacity of BLPs is superior
‘Gateway’:An Innovative Pedagogical Approach to Prepare Social Care Workers for Social Work Training
Determining the best approach to commercial fusion power
This study sets out to determine which fusion power generator design is most suitable for centralised power production to be used commercially in communities comprising of domestic, corporate and industrial entities. We find there are currently only three main contenders in this field, those being the tokamak, the stellarator and the indirect-drive. Of these it is found that indirect-drive is too inefficient in comparison, though this is against theoretical numbers as the other systems are still under construction. We still are able to conclude that the stellarator is most likely to become the commercial power source
Singular behaviour of the electromagnetic field
The singularities of the electromagnetic field are derived to include all the
point-like multipoles representing an electric charge and current distribution.
Firstly derived in the static case, the result is generalized to the dynamic
one. We establish a simple procedure for passing from the first, to the second
case.Comment: Latex, 21.pages, no figure
A roadmap of problem frames research
It has been a decade since Michael Jackson introduced problem frames to the software engineering community. Since then, he has published further work addressing problem frames as well as presenting several keynote addresses. Other authors have researched problem frames, have written about their experiences and have expressed their opinions. It was not until 2004 that an opportunity presented itself for researchers in the field to gather as a community. The first International Workshop on Advances and Applications of Problem Frames (IWAAPF'04) was held at the International Conference on Software Engineering in Edinburgh on 24th May 2004. This event attracted over 30 participants: Jackson delivered a keynote address, researchers presented their work and an expert panel discussed the challenges of problem frames.
Featuring in this special issue are two extended papers from the workshop, an invited contribution from Jackson in which he positions problem frames in the context of the software engineering discipline, and this article, where we provide a review of the literature
Giant Magnetothermal Conductivity Switching in Semimetallic WSi Single Crystals
Materials able to rapidly switch between thermally conductive states by
external stimuli such as electric or magnetic fields can be used as
all-solid-state thermal switches and open a myriad of applications in heat
management, power generation and cooling. Here, we show that the large
magnetoresistance that occurs in the highly conducting semimetal
-WSi single crystals leads to dramatically large changes in
thermal conductivity at temperatures <100 K. At temperatures <20 K, where
electron-phonon scattering is minimized, the thermal conductivity switching
ratio between zero field and a 9T applied field can be >7. We extract the
electronic and lattice components of the from the thermal conductivity
measurements and show that the Lorenz number for this material approximates the
theoretical value of L. From the heat capacity and thermal diffusivity,
the speed of thermal conductivity switching is estimated to range from 1 x
10 seconds at 5 K to 0.2 seconds at 100 K for a 5-mm long sample. This
work shows that WSi, a highly conducting multi-carrier semimetal, is a
promising thermal switch component for low-temperature applications such
cyclical adiabatic demagnetization cooling, a technique that would enable
replacing He-based refrigerators.Comment: 20 pages, 6 figure
Quadrupolar contact terms and Hyperfine Structure
In the interaction of two electric quadrupoles, there is at short distances a
contact term proportional to the second derivative of a delta function. This
contact term contributes to the hyperfine splitting of bound states of two
particles with spin one or higher-for example the bound states of Omega minus
and a nucleus of spin one.The contact hyperfine splitting occurs in states with
orbital angular momentum one(p-wave), in contrast to the Fermi contact
interaction which is in s-states.We find that these contact splittings will be
observable with Omega minus atoms and help measure the quadrupole moment and
charge radius of the hyperon.Comment: 19 pages; two sentences deleted from first versio
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