21 research outputs found
Periodic features in the Dynamic Structure Factor of the Quasiperiodic Period-doubling Lattice
We present an exact real-space renormalization group (RSRG) method for
evaluating the dynamic structure factor of an infinite one-dimensional
quasiperiodic period-doubling (PD) lattice. We observe that for every normal
mode frequency of the chain, the dynamic structure factor always
exhibits periodicity with respect to the wave vector and the presence of
such periodicity even in absence of translational invariance in the system is
quite surprising. Our analysis shows that this periodicity in
actually indicates the presence of delocalized phonon modes in the PD chain.
The Brillouin Zones of the lattice are found to have a hierarchical structure
and the dispersion relation gives both the acoustic as well as optical
branches. The phonon dispersion curves have a nested structure and we have
shown that it is actually the superposition of the dispersion curves of an
infinite set of periodic lattices.Comment: 9 pages, 3 postscript figures, REVTeX, To appear in Phys. Rev. B (1
February 1998-I
Energy spectra, wavefunctions and quantum diffusion for quasiperiodic systems
We study energy spectra, eigenstates and quantum diffusion for one- and
two-dimensional quasiperiodic tight-binding models. As our one-dimensional
model system we choose the silver mean or `octonacci' chain. The
two-dimensional labyrinth tiling, which is related to the octagonal tiling, is
derived from a product of two octonacci chains. This makes it possible to treat
rather large systems numerically. For the octonacci chain, one finds singular
continuous energy spectra and critical eigenstates which is the typical
behaviour for one-dimensional Schr"odinger operators based on substitution
sequences. The energy spectra for the labyrinth tiling can, depending on the
strength of the quasiperiodic modulation, be either band-like or fractal-like.
However, the eigenstates are multifractal. The temporal spreading of a
wavepacket is described in terms of the autocorrelation function C(t) and the
mean square displacement d(t). In all cases, we observe power laws for C(t) and
d(t) with exponents -delta and beta, respectively. For the octonacci chain,
0<delta<1, whereas for the labyrinth tiling a crossover is observed from
delta=1 to 0<delta<1 with increasing modulation strength. Corresponding to the
multifractal eigenstates, we obtain anomalous diffusion with 0<beta<1 for both
systems. Moreover, we find that the behaviour of C(t) and d(t) is independent
of the shape and the location of the initial wavepacket. We use our results to
check several relations between the diffusion exponent beta and the fractal
dimensions of energy spectra and eigenstates that were proposed in the
literature.Comment: 24 pages, REVTeX, 10 PostScript figures included, major revision, new
results adde
A Review of Surgical Informed Consent: Past, Present, and Future. A Quest to Help Patients Make Better Decisions
Contains fulltext :
87422.pdf (publisher's version ) (Closed access)BACKGROUND: Informed consent (IC) is a process requiring a competent doctor, adequate transfer of information, and consent of the patient. It is not just a signature on a piece of paper. Current consent processes in surgery are probably outdated and may require major changes to adjust them to modern day legislation. A literature search may provide an opportunity for enhancing the quality of the surgical IC (SIC) process. METHODS: Relevant English literature obtained from PubMed, Picarta, PsycINFO, and Google between 1993 and 2009 was reviewed. RESULTS: The body of literature with respect to SIC is slim and of moderate quality. The SIC process is an underestimated part of surgery and neither surgeons nor patients sufficiently realize its importance. Surgeons are not specifically trained and lack the competence to guide patients through a legally correct SIC process. Computerized programs can support the SIC process significantly but are rarely used for this purpose. CONCLUSIONS: IC should be integrated into our surgical practice. Unfortunately, a big gap exists between the theoretical/legal best practice and the daily practice of IC. An optimally informed patient will have more realistic expectations regarding a surgical procedure and its associated risks. Well-informed patients will be more satisfied and file fewer legal claims. The use of interactive computer-based programs provides opportunities to improve the SIC process.1 juli 201