A new ultraviolet nonlinear optical
material, namely LiHgPO4, was synthesized using the mild
hydrothermal method. The
structure of LiHgPO4 features novel double layers constructed
by severely distorted HgO6 octahedra and PO4 tetrahedra, which are further interconnected by LiO4 tetrahedra
to form a three-dimensional structure. LiHgPO4 exhibits
a very strong second harmonic generation (SHG) response of 11.0 times
that of KH2PO4 and a relatively large birefringence
(0.068 at 1064 nm) among the reported SHG-active phosphates. Theoretical
calculations revealed that the introduction of the Hg2+ in a highly distorted HgO6 octahedral geometry is crucial
to produce the strong SHG response and large birefringence.
This paper addresses attitude synchronization and tracking problems in spacecraft formation in the presence of model uncertainties and external disturbances. A decentralized adaptive sliding mode control law is proposed using undirected interspacecraft communication topology and analyzed based on algebraic graph theory. A multispacecraft sliding manifold is derived, on which each spacecraft approaches desired timevarying attitude and angular velocity while maintaining attitude synchronization with the other spacecraft in the formation. A control law is then developed to ensure convergence to the sliding manifold. The stability of the resulting closed-loop system is proved by application of Barbalat's Lemma. Simulation results demonstrate the effectiveness of the proposed attitude synchronization and tracking methodology. Copyright
On the basis of earlier reported quantitative structure-activity relationship studies, a series of 9beta-16-(arylalkyl)-10-deoxoartemisinins were proposed for synthesis. Several of the new compounds 7 and 10-14 were synthesized employing the key synthetic intermediate 23. In a second approach, the natural product (+)-artemisinic acid was utilized as an acceptor for conjugate addition, and the resultant homologated acids were subjected to singlet oxygenation and acid treatment to provide artemisinin analogues. Under a new approach, we developed a one step reaction for the interconversion of artemisinin 1 into artemisitene 22 that did not employ selenium-based reagents and found that 2-arylethyliodides would undergo facile radical-induced conjugate addition to the exomethylene lactone of 22 in good yield. The lactone carbonyls were removed sequentially by diisobutylaluminum hydride reduction followed directly by a second reduction (BF(3)-etherate/Et(3)SiH) to afford the desired corresponding pyrans. Six additional halogen-substituted aromatic side chains were installed via 22 furnishing the bioassay candidates 15-20. The analogues were examined for in vitro antimalarial activity in the W-2 and D-6 clones of Plasmodium falciparum and were additionally tested in vivo in Plasmodium berghei- and/or Plasmodium yoelii-infected mice. Several of the compounds emerged as highly potent orally active candidates without obvious toxicity. Of these, two were chosen for pharmacokinetic evaluation, 14 and 17.
Two new barium polyiodate
compounds in the alkali-earth system, namely, HBa2.5(IO3)6(I2O5) (Fdd2) and HBa(IO3)(I4O11) (P1̅) have been obtained through hydrothermal reaction.
Interestingly, the structures of both compounds feature different
polyiodate groups, i.e., I2O5 and I4O11 groups. HBa2.5(IO3)6(I2O5) can be depicted as an alternative stacking
of two-dimensional (2D) [Ba4(IO3)8(I2O5)2] and [Ba(IO3)4(I2O5)2]2– layers with the I2O5 and IO3 group
serving as linkers. HBa(IO3)(I4O11) can be depicted as a 3D network with 2D [Ba(I4O11)] layers being interconnected by IO3 groups.
The 0D I4O11 polyiodate group can be seen also
viewed as formed by an I3O8 group further corner-sharing
with an IO3 group or an I2O5 group
further corner-sharing with two IO3 groups. Powder second
harmonic generation (SHG) measurements show that HBa2.5(IO3)6(I2O5) crystals
display a moderate SHG efficiency of ∼1.6 times that of KH2PO4 (KDP) and are phase-matchable. Optical properties
measurements, thermal analyses, and laser damage threshold (LDT) measurements
have been performed. Results of theoretical calculation
show that the formation of I4O11
2– is thermodynamically much easier than I3O8
– and I2O5, because of the
lower reaction energy. Our studies shed light on exploring alkali-earth
polyiodates as potential NLO materials.
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