1,883 research outputs found
Condensation cyclization reactions of electron deficient aromatics. 4: Tricyclic nitropropene nitronates from the reaction of phloroglucinol and cycloalkanones with sym-trinitrobenzene
Interesting similarities have been shown between the reactions of sym-trinitrobenzene with cycloalkanones, and with phloroglucinol. Previously unsuspected common intermediates have been shown to intervene. The structurally similar products in each case are tricyclic nitropropene nitronates. Protonation of these yields the corresponding nitronic acids in certain instances
Absorption spectrum in the wings of the potassium second resonance doublet broadened by helium
We have measured the reduced absorption coefficients occurring in the wings
of the potassium 4S-5P doublet lines at 404.414 nm and at 404.720 nm broadened
by helium gas at pressures of several hundred Torr. At the experimental
temperature of 900 K, we have detected a shoulder-like broadening feature on
the blue wing of the doublet which is relatively flat between 401.8 nm and
402.8 nm and which drops off rapidly for shorter wavelengths, corresponding to
absorption from the X doublet Sigma+ state to the C doublet Sigma+ state of the
K-He quasimolecule. The accurate measurements of the line profiles in the
present work will sharply constrain future calculations of potential energy
surfaces and transition dipole moments correlating to the asymptotes He-K(5p),
He-K(5s), and He-K(3d).Comment: 2 figure
Experimental and Theoretical Studies of Pressure Broadened Alkali-Metal Atom Resonance Lines
We are carrying out a joint theoretical and experimental research program to study the broadening of alkali atom resonance lines due to collisions with helium and molecular hydrogen for applications to spectroscopic studies of brown dwarfs and extrasolar giant planets
Valley Splitting Theory of SiGe/Si/SiGe Quantum Wells
We present an effective mass theory for SiGe/Si/SiGe quantum wells, with an
emphasis on calculating the valley splitting. The theory introduces a valley
coupling parameter, , which encapsulates the physics of the quantum well
interface. The new effective mass parameter is computed by means of a tight
binding theory. The resulting formalism provides rather simple analytical
results for several geometries of interest, including a finite square well, a
quantum well in an electric field, and a modulation doped two-dimensional
electron gas. Of particular importance is the problem of a quantum well in a
magnetic field, grown on a miscut substrate. The latter may pose a numerical
challenge for atomistic techniques like tight-binding, because of its
two-dimensional nature. In the effective mass theory, however, the results are
straightforward and analytical. We compare our effective mass results with
those of the tight binding theory, obtaining excellent agreement.Comment: 13 pages, 7 figures. Version submitted to PR
Phase separation in hydrated LTA zeolite
ArticleMICROPOROUS AND MESOPOROUS MATERIALS. 78(2-3): 169-180 (2005)journal articl
Theory of optical spectra of polar quantum wells: Temperature effects
Theoretical and numerical calculations of the optical absorption spectra of
excitons interacting with longitudinal-optical phonons in quasi-2D polar
semiconductors are presented. In II-VI semiconductor quantum wells, exciton
binding energy can be tuned on- and off-resonance with the longitudinal-optical
phonon energy by varying the quantum well width. A comprehensive picture of
this tunning effect on the temperature-dependent exciton absorption spectrum is
derived, using the exciton Green's function formalism at finite temperature.
The effective exciton-phonon interaction is included in the Bethe-Salpeter
equation. Numerical results are illustrated for ZnSe-based quantum wells. At
low temperatures, both a single exciton peak as well as a continuum resonance
state are found in the optical absorption spectra. By contrast, at high enough
temperatures, a splitting of the exciton line due to the real phonon absorption
processes is predicted. Possible previous experimental observations of this
splitting are discussed.Comment: 10 pages, 9 figures, to appear in Phys. Rev. B. Permanent address:
[email protected]
H-NMR Study of the Random Bond Effect in the Quantum Spin System (CH)CHNHCu(ClBr)
Spin-lattice relaxation rate of H-NMR has been measured in
(CH)CHNHCu(ClBr) with , which has been
reported to be gapped system with singlet ground state from the previous
macroscopic magnetization and specific heat measurements, in order to
investigate the bond randomness effect microscopically in the gapped composite
Haldane system (CH)CHNHCuCl. It was found that the spin-lattice
relaxation rate in the present system includes both fast and slow
relaxation parts indicative of the gapless magnetic ground state and the gapped
singlet ground state, respectively. We discuss the obtained results with the
previous macroscopic magnetization and specific heat measurements together with
the microscopic SR experiments.Comment: 4 pages, 2 figures, to be published in J. Phys. Soc. Jpn. vol.76
(2007) No.
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