4,761 research outputs found
The Equilibrium Shape of Quantum Dots
The formation of dislocation-free three-dimensional islands during the
heteroepitaxial growth of lattice-mismatched materials has been observed
experimentally for several material systems. The equilibrium shape of the
islands is governed by the competition between the surface energy and the
elastic relaxation energy of the islands as compared to the uniform strained
film. As an exemplification we consider the experimentally intensively
investigated growth of InAs quantum dots on a GaAs(001) substrate, deriving the
equilibrium shape as a function of island volume. For this purpose InAs surface
energies have been calculated within density-functional theory, and a continuum
approach has been applied to compute the elastic relaxation energies.Comment: 10 pages, 4 figures. Submitted to Nuovo Cimento (November 27, 1996)
Realizing Partial Signatures around 1400: Liebert\u27s Credo as a Test Case
RILM abstract: A system of realization is used to address the problem of partial signatures in vocal polyphony and the adjustments of accidentals they require. Its principles are applied to the first 18 measures of the Credo of the Mass by Reginaldus Libert. If some latitude in the governing criteria is allowed, it is feasible to realize partial signatures in a systematic manner
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Voice Function, Sonority, and Contrapuntal Procedure in Late Medieval Polyphony
During recent years, scholarship in the field of late medieval music has been heavily weighted toward archival research, paleography, and contemporary theory. Such enterprises have furthered our appreciation of the cultural contexts in which music was composed and experienced, and have led to some gratifying advances in our knowledge of manuscript compilation, performance practice, theoretical texts and their traditions, institutional history, and biography. Having rightly acknowledged such achievements, one must nevertheless concede that even the most positivistic avenues of research often yield results that are decidedly inconclusive. This state of affairs only reminds us that our understanding of music as a living art in this period must inevitably be founded upon the shifting sands of presumption and educated guessing. Moll offers some explanations
Atomic structure of Mn wires on Si(001) resolved by scanning tunneling microscopy
At submonolayer coverage, Mn forms atomic wires on the Si(001) surface
oriented perpendicular to the underlying Si dimer rows. While many other
elements form symmetric dimer wires at room temperature, we show that Mn wires
have an asymmetric appearance and pin the Si dimers nearby. We find that an
atomic configuration with a Mn trimer unit cell can explain these observations
due to the interplay between the Si dimer buckling phase near the wire and the
orientation of the Mn trimer. We study the resulting four wire configurations
in detail using high-resolution scanning tunneling microscopy (STM) imaging and
compare our findings with STM images simulated by density functional theory.Comment: 4 pages, 4 figure
Telluric correction in the near-infrared: Standard star or synthetic transmission?
Context. The atmospheric absorption of the Earth is an important limiting
factor for ground-based spectroscopic observations and the near-infrared and
infrared regions are the most affected. Several software packages that produce
a synthetic atmospheric transmission spectrum have been developed to correct
for the telluric absorption; these are Molecfit, TelFit, and TAPAS. Aims. Our
goal is to compare the correction achieved using these three telluric
correction packages and the division by a telluric standard star. We want to
evaluate the best method to correct near-infrared high-resolution spectra as
well as the limitations of each software package and methodology. Methods. We
applied the telluric correction methods to CRIRES archival data taken in the J
and K bands. We explored how the achieved correction level varies depending on
the atmospheric T-P profile used in the modelling, the depth of the atmospheric
lines, and the molecules creating the absorption. Results. We found that the
Molecfit and TelFit corrections lead to smaller residuals for the water lines.
The standard star method corrects best the oxygen lines. The Molecfit package
and the standard star method corrections result in global offsets always below
0.5% for all lines; the offset is similar with TelFit and TAPAS for the H2O
lines and around 1% for the O2 lines. All methods and software packages result
in a scatter between 3% and 7% inside the telluric lines. The use of a tailored
atmospheric profile for the observatory leads to a scatter two times smaller,
and the correction level improves with lower values of precipitable water
vapour. Conclusions. The synthetic transmission methods lead to an improved
correction compared to the standard star method for the water lines in the J
band with no loss of telescope time, but the oxygen lines were better corrected
by the standard star method.Comment: 18 pages, 13 figures, Accepted to A&
Mode mixing in asymmetric double trench photonic crystal waveguides
e investigate both experimentally and theoretically the waveguiding
properties of a novel double trench waveguide where a conventional single-mode
strip waveguide is embedded in a two dimensional photonic crystal (PhC) slab
formed in silicon on insulator (SOI) wafers. We demonstrate that the bandwidth
for relatively low-loss (50dB/cm) waveguiding is significantly expanded to
250nm covering almost all the photonic band gap owing to nearly linear
dispersion of the TE-like waveguiding mode. The flat transmission spectrum
however is interrupted by numerous narrow stop bands. We found that these stop
bands can be attributed to anti-crossing between TE-like (positive parity) and
TM-like (negative parity) modes. This effect is a direct result of the strong
asymmetry of the waveguides that have an upper cladding of air and lower
cladding of oxide. To our knowledge this is the first demonstration of the
effects of cladding asymmetry on the transmission characteristics of the PhC
slab waveguides.Comment: 7 pages, 6 figure
Optimized stray-field-induced enhancement of the electron spin precession by buried Fe gates
The magnetic stray field from Fe gates is used to modify the spin precession
frequency of InGaAs/GaAs quantum-well electrons in an external magnetic field.
By using an etching process to position the gates directly in the plane of the
quantum well, the stray-field influence on the spin precession increases
significantly compared with results from previous studies with top-gated
structures. In line with numerical simulations, the stray-field-induced
precession frequency increases as the gap between the ferromagnetic gates is
reduced. The inhomogeneous stray field leads to additional spin dephasing.Comment: 4 pages, 2 figure
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