274 research outputs found
Efficient syntheses of climate relevant isoprene nitrates and (1R,5S)-(â)-myrtenol nitrate
Here we report the chemoselective synthesis of several important, climate relevant isoprene nitrates using silver nitrate to mediate a âhalide for nitrateâ substitution. Employing readily available starting materials, reagents and HornerâWadsworthâEmmons chemistry the synthesis of easily separable, synthetically versatile âkey building blocksâ (E)- and (Z)-3-methyl-4-chlorobut-2-en-1-ol as well as (E)- and (Z)-1-((2-methyl-4-bromobut-2-enyloxy)methyl)-4-methoxybenzene has been achieved using cheap, âoff the shelfâ materials. Exploiting their reactivity we have studied their ability to undergo an âallylic halide for allylic nitrateâ substitution reaction which we demonstrate generates (E)- and (Z)-3-methyl-4-hydroxybut-2-enyl nitrate, and (E)- and (Z)-2-methyl-4-hydroxybut-2-enyl nitrates (âisoprene nitratesâ) in 66â80% overall yields. Using NOESY experiments the elucidation of the carbonâcarbon double bond configuration within the purified isoprene nitrates has been established. Further exemplifying our âhalide for nitrateâ substitution chemistry we outline the straightforward transformation of (1R,2S)-(â)-myrtenol bromide into the previously unknown monoterpene nitrate (1R,2S)-(â)-myrtenol nitrate
Modelling dependency networks to inform data structures in BIM and smart cities
The pervasive deployment of "smart city" and "smart building" projects in cities world-wide is driving innovation on many fronts including; technology, telematics, engineering and entrepreneurship. This paper focuses on the technical and engineering perspectives of BIM and smart cities, by extending building and urban morphology studies as to respond to the challenges posed by Big Data, and smart infrastructure. The proposed framework incorporates theoretical and modelling descriptions to verify how network-based models can act as the backbone skeletal representation of both building and urban complexity, and yet relate to environmental performance and smart infrastructure. The paper provides some empirical basis to support data information models through building dependency networks as to represent the relationships between different existing and smart infrastructure components. These dependency networks are thought to inform decisions on how to represent building and urban data sets in response to different social and environmental performance requirements, feeding that into void and solid descriptions of data maturity models. It is concluded that network-based models are fundamental to comprehend and represent the complexity of cities and inform urban design and public policy practices, in the design and operation phases of infrastructure projects
Measurement of isoprene nitrates by GCMS
According to atmospheric chemistry models, isoprene nitrates play an important role in determining the ozone production efficiency of isoprene; however this is very poorly constrained through observations as isoprene nitrates have not been widely measured. Measurements have been severely restricted largely due to a limited ability to measure individual isoprene nitrate isomers. An instrument based on gas chromatography/mass spectrometry (GCMS) and the associated calibration methods are described for the speciated measurements of individual isoprene nitrate isomers. Five of the primary isoprene nitrates which formed in the presence of NOx by reaction of isoprene with the hydroxyl radical (OH) in the Master Chemical Mechanism are identified using known isomers on two column phases and are fully separated on the Rtx-200 column. Three primary isoprene nitrates from the reaction of isoprene with the nitrate radical (NO3) are identified after synthesis from the already identified analogous hydroxy nitrate. A Tenax adsorbent-based trapping system allows the analysis of the majority of the known hydroxy and carbonyl primary isoprene nitrates, although not the (1,2)-IN isomer, under field-like levels of humidity and showed no impact from typical ambient concentrations of NOx and ozone
Pure spinor superfields -- an overview
Maximally supersymmetric theories do not allow off-shell superspace
formulations with traditional superfields containing a finite set of auxiliary
fields. It has become clear that off-shell supersymmetric action formulations
of such models can be achieved by the introduction of pure spinors. In this
talk, an overview of this formalism is given, with emphasis on D=10
super-Yang-Mills theory and D=11 supergravity. This a somewhat expanded version
of a talk presented at the workshop "Breaking of supersymmetry and ultraviolet
divergences in extended supergravity" (BUDS), Laboratori Nazionali di Frascati,
March 25-28, 2013.Comment: 34 pp., 2 figs., contributions to the proceedings of the workshop
"Breaking of supersymmetry and ultraviolet divergences in extended
supergravity" (BUDS), Laboratori Nazionali di Frascati, March 25-28, 201
Flux compactification on smooth, compact three-dimensional toric varieties
Three-dimensional smooth, compact toric varieties (SCTV), when viewed as real
six-dimensional manifolds, can admit G-structures rendering them suitable for
internal manifolds in supersymmetric flux compactifications. We develop
techniques which allow us to systematically construct G-structures on SCTV and
read off their torsion classes. We illustrate our methods with explicit
examples, one of which consists of an infinite class of toric CP^1 bundles. We
give a self-contained review of the relevant concepts from toric geometry, in
particular the subject of the classification of SCTV in dimensions less or
equal to 3. Our results open up the possibility for a systematic construction
and study of supersymmetric flux vacua based on SCTV.Comment: 27 pages, 10 figures; v2: references, minor typos & improvement
âDial Up and Lock Inâ: Asymmetric organo-BrĂžnsted acid catalysis incorporating stable isotopes
An operationally simple organo-BrĂžnsted-acid-catalyzed asymmetric and regioselective âdial up and lock inâ of one or more stable isotopes into organic compounds is unknown. Here, we describe a newly designed, chemically versatile protocol mediating single- or multiple-isotope incorporation into aziridines via a one-pot, three-component, two-step process. By exploiting easy-to-generate isotope-derived starting materials, it allows complete control of isotope positioning, affords >95 atom % isotope incorporation, and generates cis-aziridines with excellent optical activities and regioselectivities. Demonstrating a âlow entry point,â and thus easy access to a broad range of researchers, it requires no specialist laboratory equipment and employs readily attainable reaction conditions. Demonstrating their utility, the aziridines are easily transformed into sought-after chiral non-racemic α-amino acids appended with one to three (or more) identical or different isotopes. The widespread use of these compounds ensures that our methodology will be of interest to biological, medicinal, pharmaceutical, agrochemical, biotechnology, materials, and process chemists alike
The gauge dual of Romans mass
We deform the recently proposed holographic duality between the ABJM N=6
Chern-Simons-matter theory and type IIA string theory in AdS4xCP3. We add a
non-zero Romans mass F_0, whose dual we identify as the sum of the Chern-Simons
levels for the two gauge groups. One can naturally identify four different
theories, with different amounts of supersymmetry and of flavor symmetry.Comment: 26 pages. v4: Corrected the sign for the probe brane potentia
Higgsing M2 to D2 with gravity: N=6 chiral supergravity from topologically gauged ABJM theory
We present the higgsing of three-dimensional N=6 superconformal ABJM type
theories coupled to conformal supergravity, so called topologically gauged ABJM
theory, thus providing a gravitational extension of previous work on the
relation between N M2 and N D2-branes. The resulting N=6 supergravity theory
appears at a chiral point similar to that of three-dimensional chiral gravity
introduced recently by Li, Song and Strominger, but with the opposite sign for
the Ricci scalar term in the lagrangian. We identify the supersymmetry in the
broken phase as a particular linear combination of the supersymmetry and
special conformal supersymmetry in the original topologically gauged ABJM
theory. We also discuss the higgsing procedure in detail paying special
attention to the role played by the U(1) factors in the original ABJM model and
the U(1) introduced in the topological gauging.Comment: 53 pages, Late
Massive type IIA string theory cannot be strongly coupled
Understanding the strong coupling limit of massive type IIA string theory is
a longstanding problem. We argue that perhaps this problem does not exist;
namely, there may be no strongly coupled solutions of the massive theory. We
show explicitly that massive type IIA string theory can never be strongly
coupled in a weakly curved region of space-time. We illustrate our general
claim with two classes of massive solutions in AdS4xCP3: one, previously known,
with N = 1 supersymmetry, and a new one with N = 2 supersymmetry. Both
solutions are dual to d = 3 Chern-Simons-matter theories. In both these massive
examples, as the rank N of the gauge group is increased, the dilaton initially
increases in the same way as in the corresponding massless case; before it can
reach the M-theory regime, however, it enters a second regime, in which the
dilaton decreases even as N increases. In the N = 2 case, we find
supersymmetry-preserving gauge-invariant monopole operators whose mass is
independent of N. This predicts the existence of branes which stay light even
when the dilaton decreases. We show that, on the gravity side, these states
originate from D2-D0 bound states wrapping the vanishing two-cycle of a
conifold singularity that develops at large N.Comment: 43 pages, 5 figures. v2: added reference
The superconformal theory is free!
The SuperConformal theory in three space-time dimensions with SO(16)
-symmetry, 128 bosons, and 128 fermions, cannot sustain interactions. This
result is obtained using both light-cone superspace techniques which rely on
algebraic consistency, and covariant methods which rely on SO(16) Fierz
identities which fail to produce the desired algebra.Comment: 14 page
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