459 research outputs found
Orbital stability: analysis meets geometry
We present an introduction to the orbital stability of relative equilibria of
Hamiltonian dynamical systems on (finite and infinite dimensional) Banach
spaces. A convenient formulation of the theory of Hamiltonian dynamics with
symmetry and the corresponding momentum maps is proposed that allows us to
highlight the interplay between (symplectic) geometry and (functional) analysis
in the proofs of orbital stability of relative equilibria via the so-called
energy-momentum method. The theory is illustrated with examples from finite
dimensional systems, as well as from Hamiltonian PDE's, such as solitons,
standing and plane waves for the nonlinear Schr{\"o}dinger equation, for the
wave equation, and for the Manakov system
Direct measure of the exciton formation in quantum wells from time resolved interband luminescence
We present the results of a detailed time resolved luminescence study carried
out on a very high quality InGaAs quantum well sample where the contributions
at the energy of the exciton and at the band edge can be clearly separated. We
perform this experiment with a spectral resolution and a sensitivity of the
set-up allowing to keep the observation of these two separate contributions
over a broad range of times and densities. This allows us to directly evidence
the exciton formation time, which depends on the density as expected from
theory. We also evidence the dominant contribution of a minority of excitons to
the luminescence signal, and the absence of thermodynamical equilibrium at low
densities
John Gassner: O'Neill; a collection of critical essays. Englewood Cliffs, N. J., Prentice-Hall, Inc., 1964, 180 p., 20 cm. x 13 cm.
Fil: Genoud, Mariana J..
Universidad Nacional de Cuyo. Facultad de FilosofĂa y Letra
Chapman, Arnold. The spanish american reception of United States fiction; 1920-1940. University of California Press, Berkeley and Los Angeles, 1966. 226 p., 23 x 15 cm.
Fil: Genoud, Mariana J..
Universidad Nacional de Cuyo. Facultad de FilosofĂa y Letra
High power femtosecond source based on passively mode-locked 1055nm VECSEL and Yb-fibre power amplifier
We report 5 ns pulses at 160 W average power and 910 repetition rate from a passively mode-locked VECSEL source seeding an Yb-doped fibre power amplifier. The amplified pulses were compressed to 291 fs duration
Mixed-State Specific Heat of the Type-II Superconductor Nb0.77Zr0.23 in Magnetic Fields up to B c2
In order to document the behavior of the mean-field mixed-state specific heat of an isotropic. strongly type-II superconductor (i.e., with a large value of the Ginzburg parameterk), and to provide a basis for comparison with high-temperature superconductors, we measured the specific heatC of the alloy Nb0.77Zr0.23 withT c = 10.8K, B c2 (0) = 7.9T, in magnetic fieldsB = 0, 0.2, 1.0, 12, 2.0, 2.4. 3.0, 3.3. 4.0. 4.4, 4.8, 5.2, 6.0. 6.6, 7.2 and 10 T. The values of the upper critical fieldB c2 ( T), thermodynamic critical fieldB c (T), Ginzburg parameterk(T), and coefficient Îł(B) = limT0(C(T. B)/T) are derived from the specific heat data and found to be in agreement with the GLAG theory in the dirty limit. The behavior of the mixed-state specific heat is analyzed in terms ofC el /T,â(C el /T)/âB, andâ(C el /T)/âT vs. Tcurves, whereC el is the electronic contribution to the specific hea
Engineering the spatial confinement of exciton-polaritons in semiconductors
We demonstrate the spatial confinement of electronic excitations in a solid
state system, within novel artificial structures that can be designed having
arbitrary dimensionality and shape. The excitations under study are
exciton-polaritons in a planar semiconductor microcavity. They are confined
within a micron-sized region through lateral trapping of their photon
component. Striking signatures of confined states of lower and upper polaritons
are found in angle-resolved light emission spectra, where a discrete energy
spectrum and broad angular patterns are present. A theoretical model supports
unambiguously our observations
2s exciton-polariton revealed in an external magnetic field
We demonstrate the existence of the excited state of an exciton-polariton in
a semiconductor microcavity. The strong coupling of the quantum well heavy-hole
exciton in an excited 2s state to the cavity photon is observed in non-zero
magnetic field due to surprisingly fast increase of Rabi energy of the 2s
exciton-polariton in magnetic field. This effect is explained by a strong
modification of the wave-function of the relative electron-hole motion for the
2s exciton state.Comment: 5 pages, 5 figure
Cancellation of probe effects in measurements of spin polarized momentum density by electron positron annihilation
Measurements of the two dimensional angular correlation of the
electron-positron annihilation radiation have been done in the past to detect
the momentum spin density and the Fermi surface. We point out that the momentum
spin density and the Fermi Surface of ferromagnetic metals can be revealed
within great detail owing to the large cancellation of the electron-positron
matrix elements which in paramagnetic multiatomic systems plague the
interpretation of the experiments. We prove our conjecture by calculating the
momentum spin density and the Fermi surface of the half metal CrO2, who has
received large attention due to its possible applications as spintronics
material
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