6,130 research outputs found
Off-duty activity equipment and facilities for advanced spacecraft /preliminary design/
Off-duty activity equipment and facilities preliminary design for advanced spacecraf
Synthesis and characterisation of novel ferrocenyl thienyl and thiazolyl systems
Ferrocenyl derivatives are currently under investigation by our group and several series containing both amidothienyl and amidothiazolyl systems have been synthesised and characterised. The incorporation of thienyl/thiazolyl groups into a ferrocenyl- or ferrocenylphenyl system greatly enhances the number of potential donor atoms for coordination with metal fragments e.g. PtII, PdII with a view to platinum anti-cancer studies and/or interaction with guest molecules through suitable hydrogen bonding interactions.
In nature, thiazole has been found to be vital in certain natural products: examples include the antibiotic bacitracin and the siderophore yersiniabactin. In therapeutic studies the antitumour compound epothilone A and myxothiazole (inhibitor) have been extensively studied
Methyl 2-(4-ferrocenylbenzamido)thiophene-3-carboxylate and ethyl 2-(4-ferrocenylbenzamido)-1,3-thiazole-4-acetate, a unique ferrocen
The conformations and hydrogen bonding in the thiophene and thiazole title compounds, [Fe(C₅H₅)(C₂₀H₁₄NO₃S)], (I), and [Fe(C₅H₅)(C₁₉H₁₇N₂O₃S)], (II), are discussed. The sequence (C₅H₄)-(C₆H₄)-(CONH)-(C₄H₂S)-(CO₂Me) of rings and moieties in (I) is close to being planar; all consecutive interplanar angles are less than 10°. An intramolecular N-H...O=Cester hydrogen bond [graph set S(6), N...O = 2.768 (2) Å and N-H...O = 134 (2)°] effects the molecular planarity, and aggregation occurs via hydrogen-bonded chains formed from intermolecular Car-H...O=Cester/amide interactions along [010], with C...O distances ranging from 3.401 (3) to 3.577 (2) Å. The thiazole system in (II) crystallizes with two molecules in the asymmetric unit; these differ in the conformation along their long molecular axes; for example, the interplanar angle between the phenylene (C₆H₄) and thiazole (C₃NS) rings is 8.1 (2)° in one molecule and 27.66 (14)° in the other. Intermolecular N-H...O=Cester hydrogen bonds [N...O = 2.972 (4) and 2.971 (3) Å], each augmented by a Cphenylene-H...O=Cester interaction [3.184 (5) and 3.395 (4) Å], form motifs with graph set R¹₂(7) and generate chains along [100]. The amide C=O groups do not participate in hydrogen bonding. Compound (II) is the first reported ferrocenyl-containing thiazole structure
The Milky Way as a Kiloparsec-Scale Axionscope
Very high energy gamma-rays are expected to be absorbed by the extragalactic
background light over cosmological distances via the process of
electron-positron pair production. Recent observations of cosmologically
distant gamma-ray emitters by ground based gamma-ray telescopes have, however,
revealed a surprising degree of transparency of the universe to very high
energy photons. One possible mechanism to explain this observation is the
oscillation between photons and axion-like-particles (ALPs). Here we explore
this possibility further, focusing on photon-ALP conversion in the magnetic
fields in and around gamma-ray sources and in the magnetic field of the Milky
Way, where some fraction of the ALP flux is converted back into photons. We
show that this mechanism can be efficient in allowed regions of the ALP
parameter space, as well as in typical configurations of the Galactic Magnetic
Field. As case examples, we consider the spectrum observed from two HESS
sources: 1ES1101-232 at redshift z=0.186 and H 2356-309 at z=0.165. We also
discuss features of this scenario which could be used to distinguish it from
standard or other exotic models.Comment: 7 pages, 4 figures. Matches published versio
Implications of CoGeNT and DAMA for Light WIMP Dark Matter
In this paper, we study the recent excess of low energy events observed by
the CoGeNT collaboration, and discuss the possibility that these events
originate from the elastic scattering of a light (m_DM ~ 5-10 GeV) dark matter
particle. We find that such a dark matter candidate may also be capable of
generating the annual modulation reported by DAMA, as well as the small excess
recently reported by CDMS, without conflicting with the null results from other
experiments, such as XENON10. A dark matter interpretation of the CoGeNT and
DAMA observations favors a region of parameter space that is especially
attractive within the context of Asymmetric Dark Matter models. In such models,
the cosmological dark matter density arises from the baryon asymmetry of the
universe, naturally leading to the expectation that m_DM ~ 1-10 GeV. We also
discuss neutralino dark matter from extended supersymmetric frameworks, such as
the NMSSM. Lastly, we explore the implications of such a dark matter candidate
for indirect searches, and find that the prospects for detecting the neutrino
and gamma ray annihilation products of such a particle to be very encouraging.Comment: 16 pages, 14 figures. v2: references added, fig 4 and surrounding
discussion modified
Are There Hints of Light Stops in Recent Higgs Search Results?
The recent discovery at the LHC by the CMS and ATLAS collaborations of the
Higgs boson presents, at long last, direct probes of the mechanism for
electroweak symmetry breaking. While it is clear from the observations that the
new particle plays some role in this process, it is not yet apparent whether
the couplings and widths of the observed particle match those predicted by the
Standard Model. In this paper, we perform a global fit of the Higgs results
from the LHC and Tevatron. While these results could be subject to
as-yet-unknown systematics, we find that the data are significantly better fit
by a Higgs with a suppressed width to gluon-gluon and an enhanced width to
gamma gamma, relative to the predictions of the Standard Model. After
considering a variety of new physics scenarios which could potenially modify
these widths, we find that the most promising possibility is the addition of a
new colored, charged particle, with a large coupling to the Higgs. Of
particular interest is a light, and highly mixed, stop, which we show can
provide the required alterations to the combination of gg and gamma gamma
widths.Comment: 6 pages, 5 figure
Decay of High-Energy Astrophysical Neutrinos
Existing limits on the non-radiative decay of one neutrino to another plus a
massless particle (e.g., a singlet Majoron) are very weak. The best limits on
the lifetime to mass ratio come from solar neutrino observations, and are
\tau/m \agt 10^{-4} s/eV for the relevant mass eigenstate(s). For lifetimes
even several orders of magnitude longer, high-energy neutrinos from distant
astrophysical sources would decay. This would strongly alter the flavor ratios
from the expected
from oscillations alone, and should be readily visible in the near future in
detectors such as IceCube.Comment: 4 pages, 1 figure. References added. Version to appear in PR
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