3,747 research outputs found
Synthesis and structures of O-anthrylmethyl-substituted hexahomotrioxacalix[3]arenes
O-Alkylation of 7,15,23-tri-tert-butyl-25,26,27-trihydroxy-2,3,10,11,18,19-hexahomo-3,11,19-trioxacalix[3]arene (1H₃) with 9-chloromethylanthracene 5 was carried out under different reaction conditions. Variation of the number of anthrylmethyl group introduced at the phenolic rim of hexahomotrioxacalix[3]arene 1H₃ was achieved through selective O-alkylation using stoichiometric amounts of 9-chloromethylanthracene 5 in acetone to afford the mono-O-alkylated product 2H₂An, the di-O-alkylated product 3HAn₂ and the tri-O-alkylated product partial-cone-4An₃, respectively. Interestingly, by using an acetone/benzene (1:1 v/v) mixed solvent system, the cone-4An₃ was successfully synthesized. These results suggest that the solvent can also control the conformation of the O-alkylation products. The possible reaction routes of the cone-4An₃ and partial-cone-4An₃ are also discussed
Early Afterglows of Gamma-Ray Bursts in a Stratified Medium with a Power-Law Density Distribution
A long-duration gamma-ray burst (GRB) has been widely thought to arise from
the collapse of a massive star, and it has been suggested that its ambient
medium is a homogenous interstellar medium (ISM) or a stellar wind. There are
two shocks when an ultra-relativistic fireball that has been ejected during the
prompt gamma-ray emission phase sweeps up the circumburst medium: a reverse
shock that propagates into the fireball, and a forward shock that propagates
into the ambient medium. In this paper, we investigate the temporal evolution
of the dynamics and emission of these two shocks in an environment with a
general density distribution of (where is the radius) by
considering thick-shell and thin-shell cases. A GRB afterglow with one smooth
onset peak at early times is understood to result from such external shocks.
Thus, we can determine the medium density distribution by fitting the onset
peak appearing in the light curve of an early optical afterglow. We apply our
model to 19 GRBs, and find that their values are in the range of 0.4 - 1.4,
with a typical value of , implying that this environment is neither a
homogenous interstellar medium with nor a typical stellar wind with
. This shows that the progenitors of these GRBs might have undergone a new
mass-loss evolution.Comment: 32 pages, 5 figures, 1 table, published in Ap
Analysis on Heavy Quarkonia Transitions with Pion Emission in Terms of the QCD Multipole Expansion and Determination of Mass Spectra of Hybrids
One of the most important tasks in high energy physics is search for the
exotic states, such as glueball, hybrid and multi-quark states. The transitions
and attract
great attentions because they may reveal characteristics of hybrids. In this
work, we analyze those transition modes in terms of the theoretical framework
established by Yan and Kuang. It is interesting to notice that the intermediate
states between the two gluon-emissions are hybrids, therefore by fitting the
data, we are able to determine the mass spectra of hybrids. The ground hybrid
states are predicted as 4.23 GeV (for charmonium) and 10.79 GeV (for bottonium)
which do not correspond to any states measured in recent experiments, thus it
may imply that very possibly, hybrids mix with regular quarkonia to constitute
physical states. Comprehensive comparisons of the potentials for hybrids whose
parameters are obtained in this scenario with the lattice results are
presented.Comment: 16 pages, 2 figur
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