653 research outputs found
Iron‐Mediated Electrophilic Amination of Organozinc Halides using Organic Azides
A wide range of alkyl‐, aryl‐ and heteroarylzinc halides were aminated with highly functionalized alkyl, aryl, and heterocyclic azides. The reaction proceeds smoothly at 50 °C within 1 h in the presence of FeCl3 (0.5 equiv) to furnish the corresponding secondary amines in good yields. This method was extended to peptidic azides and provided the arylated substrates with full retention of configuration. To demonstrate the utility of this reaction, we prepared two amine derivatives of pharmaceutical relevance using this iron‐mediated electrophilic amination as the key step
Solar Panel Integration as an Alternate Power Source on Centaur 2 (SPIAPS)
The dream of exploration has inspired thousands throughout time. Space exploration, in particular, has taken the past century by storm and caused a great advance in technology. In this project, a retractable solar panel array will be developed for use on the Centaur 2 Rover. Energy generated by the solar panels will go to power the Centaur 2 Robot (C2) or Regolith & Environment Science & Oxygen & Lunar Volatile Extraction (RESOLVE) payload, an in-situ resource utilization project. Such payload is designed to drill into lunar and Martian terrain as well as be able to conduct other geological testing; RESOLVE is slated for testing in 2012. Ultimately, this project will fit into NASA s larger goal of deep space exploration as well as long term presence outside Earth s orbit
Preparation of Functionalized Amides Using Dicarbamoylzincs
We report a new convenient preparation of dicarbamoylzincs of type ((RRNCO)-R-1-N-2)(2)Zn by the treatment of ZnCl2 and formamides (RRNCHO)-R-1-N-2 with LiTMP in THF (15 degrees C, 15 min) or by the reaction of formamides (RRNCHO)-R-1-N-2 with TMP2Zn (25 degrees C, 16 h). This second method tolerates sensitive groups such as an ester, ketone or nitro function. Reaction of these dicarbamoylzincs with allylic, benzylic, aryl, alkenyl bromides, acid chlorides, aldehydes or enones provided various polyfunctional amides in 47-97 % yields. C-13 NMR characterization of these new carbamoylzinc derivatives is reported
Spin Discrimination in Three-Body Decays
The identification of the correct model for physics beyond the Standard Model
requires the determination of the spin of new particles. We investigate to
which extent the spin of a new particle can be identified in scenarios
where it decays dominantly in three-body decays . Here we
assume that is a candidate for dark matter and escapes direct detection at
a high energy collider such as the LHC. We show that in the case that all
intermediate particles are heavy, one can get information on the spins of
and at the LHC by exploiting the invariant mass distribution of the two
standard model fermions. We develop a model-independent strategy to determine
the spins without prior knowledge of the unknown couplings and test it in a
series of Monte Carlo studies.Comment: 31+1 pages, 4 figures, 8 tables, JHEP.cls include
Ethnic differences in calcium, phosphate and bone metabolism
The prevalence of osteoporosis and the incidence of age-related fragility fracture vary by ethnicity. There is greater than 10-fold variation in fracture probabilities between countries across the world. Mineral and bone metabolism are intimately interlinked, and both are known to exhibit patterns of daily variation, known as the diurnal rhythm (DR). Ethnic differences are described for Ca and P metabolism. The importance of these differences is described in detail between select ethnic groups, within the USA between African-Americans and White-Americans, between the Gambia and the UK and between China and the UK. Dietary Ca intake is higher in White-Americans compared with African-Americans, and is higher in White-British compared with Gambian and Chinese adults. Differences are observed also for plasma 25-hydroxy vitamin D, related to lifestyle differences, skin pigmentation and skin exposure to UVB-containing sunshine. Higher plasma 1,25-dihydroxy vitamin D and parathyroid hormone are observed in African-American compared with White-American adults. Plasma parathyroid hormone is also higher in Gambian adults and, in winter, in Chinese compared with White-British adults. There may be ethnic differences in the bone resorptive effects of parathyroid hormone, with a relative skeletal resistance to parathyroid hormone observed in some, but not all ethnic groups. Renal mineral excretion is also influenced by ethnicity; urinary Ca (uCa) and urinary P (uP) excretions are lower in African-Americans compared with White-Americans, and in Gambians compared with their White-British counterparts. Little is known about ethnic differences in the DR of Ca and P metabolism, but differences may be expected due to known differences in lifestyle factors, such as dietary intake and sleep/wake pattern. The ethnic-specific DR of Ca and P metabolism may influence the net balance of Ca and P conservation and bone remodelling. These ethnic differences in Ca, P and the bone metabolism may be important factors in the variation in skeletal health
A Shift Symmetry in the Higgs Sector: Experimental Hints and Stringy Realizations
We interpret reported hints of a Standard Model Higgs boson at ~ 125 GeV in
terms of high-scale supersymmetry breaking with a shift symmetry in the Higgs
sector. More specifically, the Higgs mass range suggested by recent LHC data
extrapolates, within the (non-supersymmetric) Standard Model, to a vanishing
quartic Higgs coupling at a UV scale between 10^6 and 10^18 GeV. Such a small
value of lambda can be understood in terms of models with high-scale SUSY
breaking if the Kahler potential possesses a shift symmetry, i.e., if it
depends on H_u and H_d only in the combination (H_u+\bar{H}_d). This symmetry
is known to arise rather naturally in certain heterotic compactifications. We
suggest that such a structure of the Higgs Kahler potential is common in a
wider class of string constructions, including intersecting D7- and D6-brane
models and their extensions to F-theory or M-theory. The latest LHC data may
thus be interpreted as hinting to a particular class of compactifications which
possess this shift symmetry.Comment: v2: References added. v3: References added, published versio
Invisible Higgs and Dark Matter
We investigate the possibility that a massive weakly interacting fermion
simultaneously provides for a dominant component of the dark matter relic
density and an invisible decay width of the Higgs boson at the LHC. As a
concrete model realizing such dynamics we consider the minimal walking
technicolor, although our results apply more generally. Taking into account the
constraints from the electroweak precision measurements and current direct
searches for dark matter particles, we find that such scenario is heavily
constrained, and large portions of the parameter space are excluded.Comment: arXiv admin note: text overlap with arXiv:0912.229
Neutrino Masses and a Fourth Generation of Fermions
We study neutrino mass generation in models with four chiral families of
leptons and quarks and four right handed neutrinos. Generically, in these
models there are three different contributions to the light neutrino masses:
the usual see-saw contribution, the tree-level contribution due to mixing of
light neutrinos with neutrino of the fourth generation, and the two loop
contribution due to the Majorana mass term of the fourth neutrino. We study
properties of these contributions and their experimental bounds. The regions of
the parameters (mixings of the fourth neutrino, masses of RH neutrino
components, etc.) have been identified where various contributions dominate.
New possibilities of a realization of the flavour symmetries in the four family
context are explored. In particular, we consider applications of the smallest
groups, e.g. SG(20,3), with irreducible representation 4.Comment: 33 pages, 4 figures; Eq. (18) corrected and thus corrections to Eqs.
(21,26-28,41,42,44-46) and figures, the loop contribution reduced by 2 orders
of magnitude; general conclusions unchanged; accepted by Nucl. Phys.
Catalytic Synthesis of Enantiopure Chiral Alcohols via Addition of Grignard Reagents to Carbonyl Compounds
© 2016 American Chemical Society.Remarkable progress in the enantioselective addition of Grignard reagents to carbonyl compounds has been made over the past decade. This enantioselective transformation now allows the use of these challenging reactive nucleophiles for the formation of chiral alcohols using catalytic amounts of chiral ligands. This review summarizes the developments in this area
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