23,042 research outputs found
Excitation of g modes in Wolf-Rayet stars by a deep opacity bump
We examine the stability of l=1 and l=2 g modes in a pair of nitrogen-rich
Wolf-Rayet stellar models characterized by differing hydrogen abundances. We
find that modes with intermediate radial orders are destabilized by a kappa
mechanism operating on an opacity bump at an envelope temperature log T ~ 6.25.
This `deep opacity bump' is due primarily to L-shell bound-free transitions of
iron. Periods of the unstable modes span ~ 11-21 hr in the model containing
some hydrogen, and ~ 3-12 hr in the hydrogen-depleted model. Based on the
latter finding, we suggest that self-excited g modes may be the source of the
9.8 hr-periodic variation of WR 123 recently reported by Lefevre et al. (2005).Comment: 5 pages, 3 figures, accepted by MNRAS letter
Magnetic Oscillations of a Fractional Hall Dot
We show that a quantum dot in the fractional Hall regime exhibits mesoscopic
magnetic oscillations with a period which is a multiple of the period for free
electrons. Our calculations are performed for parabolic quantum dots with
hard-core electron-electron interactions and are exact in the strong field
limit for smaller than the fractional Hall gap. Explicit expressions
are given for the temperature dependence of the amplitude of the oscillations.Comment: 11 pages, IUCM-004, plain te
Haldane Sashes in Quantum Hall Spectra
We show that the low-temperature sash features in the lowest Landau-level
(LLL) tunneling density-of-states (TDOS) recently discovered by Dial and
Ashoori are intimately related to the discrete Haldane-pseudopotential
interaction energy scales that govern fractional quantum Hall physics. Our
analysis is based on expressions for the tunneling density-of-states which
become exact at filling factors close to and , where the sash
structure is most prominent. We comment on other aspects of LLL correlation
physics that can be revealed by accurate temperature-dependent tunneling data.Comment: Added referenc
Current-induced torques due to compensated antiferromagnets
We analyse the influence of current induced torques on the magnetization
configuration of a ferromagnet in a circuit containing a compensated
antiferromagnet. We argue that these torques are generically non-zero and
support this conclusion with a microscopic NEGF calculation for a circuit
containing antiferromagnetic NiMn and ferromagnetic Co layers. Because of
symmetry dictated differences in the form of the current-induced torque, the
phase diagram which expresses the dependence of ferromagnet configuration on
current and external magnetic field differs qualitatively from its
ferromagnet-only counterpart.Comment: 4 pages, 5 figure
Imaging crystal orientations in multicrystalline silicon wafers via photoluminescence
We present a method for monitoring crystal orientations in chemically polished and unpassivated multicrystalline silicon wafers based on band-to-band photoluminescence imaging. The photoluminescence intensity from such wafers is dominated by surface recombination, which is crystal orientation dependent. We demonstrate that a strong correlation exists between the surface energy of different grain orientations, which are modelled based on first principles, and their corresponding photoluminescence intensity. This method may be useful in monitoring mixes of crystal orientations in multicrystalline or so-called “cast monocrystalline” wafers.H. C. Sio acknowledges scholarship support from
BT Imaging and the Australian Solar Institute, and the
Centre for Advanced Microscopy at ANU for SEM access.
This work has been supported by the Australian Research
Council
Collective excitations in double-layer quantum Hall systems
We study the collective excitation spectra of double-layer quantum-Hall
systems using the single mode approximation. The double-layer in-phase density
excitations are similar to those of a single-layer system. For out-of-phase
density excitations, however, both inter-Landau-level and intra-Landau-level
double-layer modes have finite dipole oscillator strengths. The oscillator
strengths at long wavelengths for the latter transitions are shifted upward by
interactions by identical amounts proportional to the interlayer Coulomb
coupling. The intra-Landau-level out-of-phase mode has a gap when the ground
state is incompressible except in the presence of spontaneous inter-layer
coherence. We compare our results with predictions based on the
Chern-Simons-Landau-Ginzburg theory for double-layer quantum Hall systems.Comment: RevTeX, 21 page
- …