438 research outputs found
Supergiant Barocaloric Effects in Acetoxy Silicone Rubber over a Wide Temperature Range: Great Potential for Solid-state Cooling
Solid-state cooling based on caloric effects is considered a viable
alternative to replace the conventional vapor-compression refrigeration
systems. Regarding barocaloric materials, recent results show that elastomers
are promising candidates for cooling applications around room-temperature. In
the present paper, we report supergiant barocaloric effects observed in acetoxy
silicone rubber - a very popular, low-cost and environmentally friendly
elastomer. Huge values of adiabatic temperature change and reversible
isothermal entropy change were obtained upon moderate applied pressures and
relatively low strains. These huge barocaloric changes are associated both to
the polymer chains rearrangements induced by confined compression and to the
first-order structural transition. The results are comparable to the best
barocaloric materials reported so far, opening encouraging prospects for the
application of elastomers in near future solid-state cooling devices.Comment: 19 pages, 7 figures, 2 table
Catalytic enantioselective arylations: boron to zinc exchange as a powerful tool for the generation of transferable aryl groups
The transmetalation between boron and zinc is of great importance for application in organic synthesis, since it allows the formation of new carbon-carbon bonds between organometallic units and electrophiles. The direct arylation of aldehydes or more scarcely ketones, in a catalytic, enantioselective manner using chiral catalysts has been described recently. The enantiomerically enriched diarylmethanols obtained in these reactions are valuable precursors for important bioactive molecules. This review provides a synopsis of this ever-growing field and highlights some of the challenges that still remain.A transmetalação entre boro e zinco apresenta uma grande importância para diversas aplicações em síntese orgânica, uma vez que permite a formação de novas ligações carbono-carbono entre reagentes organometálicos e espécies eletrofílicas. A arilação direta de aldeídos e, mais raramente de cetonas, de maneira catalítica e enantiosseletiva, empregando catalisadores quirais, têm sido descrita recentemente. Os diaril metanóis opticamente enriquecidos, obtidos nessas reações são precursores valiosos para a síntese de moléculas bioativas. O presente trabalho apresenta uma revisão sobre essa crescente área de atuação e destaca alguns dos desafios que ainda permanecem.Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)CNPqFAPES
Triple-q octupolar ordering in NpO_2
We report the results of resonant X-ray scattering experiments performed at
the Np M_4,5 edges in NpO_2. Below T_0 = 25 K, the development of long-range
order of Np electric quadrupoles is revealed by the growth of superlattice
Bragg peaks. The electronic transition is not accompanied by any measurable
crystallographic distortion, either internal or external, so the symmetry of
the system remains cubic. The polarization and azimuthal dependence of the
intensity of the resonant peaks is well reproduced assuming Templeton
scattering from a triple-q longitudinal antiferroquadrupolar structure.
Electric quadrupole order in NpO_2 could be driven by the ordering at T_0 of
magnetic octupoles of Gamma_5 symmetry, splitting the Np ground state quartet
and leading to a singlet ground state with zero dipole magnetic moment.Comment: 4 Pages, 3 Figures, submitted to Phys. Rev. Lett. v2: resubmitted
after referee report
C(sp3)−C(sp3) Cross‐Coupling of Alkyl Bromides and Ethers Mediated by Metal and Visible Light Photoredox Catalysis
We report a C(sp(3))-C(sp(3)) cross-coupling of alkyl bromides and alkyl chlorides with ethers by dual photoredox-nickel catalysis. The catalytic system comprises of the organic photocatalyst 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4-CzIPN) and bench stable nickel (II) acetylacetonate in the presence of visible-light, providing the coupling products in up to 92% yield. Preliminary mechanistic studies suggest two catalytic cycles, as well as the photogeneration of bromine or chlorine radicals from halide atoms that are present in the structures of the coupling partners. The halide radical mediates the hydrogen atom transfer event, avoiding the need of an additional HAT catalyst
Nonlinear pharmacokinetics of imipramine and its active metabolite, desipramine
研究科: 千葉大学大学院薬学研究院学位:千大院薬博乙第80
Magnetic Susceptibility of Multiorbital Systems
Effects of orbital degeneracy on magnetic susceptibility in paramagnetic
phases are investigated within a mean-field theory. Under certain crystalline
electric fields, the magnetic moment consists of two independent moments, e.g.,
spin and orbital moments. In such a case, the magnetic susceptibility is given
by the sum of two different Curie-Weiss relations, leading to deviation from
the Curie-Weiss law. Such behavior may be observed in d- and f-electron systems
with t_{2g} and Gamma_8 ground states, respectively. As a potential application
of our theory, we attempt to explain the difference in the temperature
dependence of magnetic susceptibilities of UO_2 and NpO_2.Comment: 4 pages, 3 figure
Evidence for Octupole Order in CeLaB from Resonant X-ray Scattering
The azimuthal angle dependence observed in the resonant X-ray scattering in
phase IV of CeLaB is analyzed theoretically. It is shown
that the peculiar angle dependence observed in the E2 channel is consistent
with the Gamma_{5u}-type octupole order with principal axis along (111) and
equivalent directions. Under the assumption that the four equivalent octupole
domains are nearly equally populated in the sample, the observed angle
dependences are reproduced by calculation for both sigma-sigma' and sigma-pi'
polarizations. The calculation for various symmetries of order parameters
excludes unambiguously other order parameters than the Gamma_{5u}-type
octupole.Comment: 4 pages, 2 figures, 3 tables, in JPSJ forma
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