Large Photonic Band Gaps in Certain Periodic and Quasi-Periodic Networks in two and three dimensions

The photonic band structures in certain two- and three-dimensional periodic networks made of one-dimensional waveguides are studied by using the Floquet-Bloch theorem. We find that photonic band gaps exist only in those structures where the fundamental loop exhibits anti-resonant transmission. This is also true for quasi-periodic networks in two and three dimensions, where the photonic band structures are calculated from the spectra of total transmission arising from a source inside the samples. In all the cases we have studied, it is also found that the gap positions in a network are dictated by the frequencies at which the anti-resonance occurs.Comment: 7 pages, 10 figures and 1 table. Published in Phys. Rev. B, 70, 125104 (2004

Theoretical studies of Pb on Si(111) and Si(100), global search for H-passivated Si nanowires, and construction of highly localized quasiatomic minimal basis orbitals for Mo

By first-principles calculations, we have performed extensive studies for the structures of Pb on Si(111) at low coverage. Relative stabilities between these low coverage phases were compared and comparison with scanning tunneling microscopy (STM) experiments were made. By tight-binding molecular dynamics simulations, we discovered that there are significant atomic rearrangements at the Pb/Si interface of the Pb islands on Si(111), which can lead to a change in the electronic structures of ultra-thin Pb films predicted by quantum size effect. In particular, the electronic behavior of nano-scale Moire pattern observed in STM for ultra-thin Pb films on Si(111) support our results. By first-principles calculations, the energetics and dynamical rocking behavior of Pb and Sn dimers on Si(100) were studied. We concluded that Pb and Sn dimers and dimer chains on Si(100) observed in STM experiments are composed of pure metal dimers instead of mixed Pb-Si or Sn-Si dimers due to a lack of favorable intermixing channel. The diffusion of Pb adatoms and dimers on Si(100) surface were studied as well. A construction of a minimal basis set of highly localized quasiatomic orbitals (QUAMBOs) for Mo were described. By using the first-principles eigenstates as input, the orbitals are constructed to look similar to the free-atomic orbitals, but are able to deform to adapt to the bonding environment and reproduce the occupied-states electronic properties of the system from which the orbitals are derived. The QUAMBOs can be used to analyze the chemical bonding for the self-consistent eigenstates obtained from first-principles calculations. We also performed a global optimization study on the structure of [110]-oriented H-passivated Si nanowires using a genetic algorithm. We found that the structures of H-passivated Si nanowires are bulk-like down to sub-nanometer wire dimensions. And structural motifs of magic nanowires were recognized with chain-like and hexagonal-shaped cross sections. The first type of magic nanowires has not been experimentally observed yet due to its small diameter, but our model for Si nanowires with hexagonal cross section has consistent dimensions and simulated STM images with the smallest nanowires observed experimentally

Topological Bose-Mott Insulators in a One-Dimensional Optical Superlattice

We study topological properties of the Bose-Hubbard model with repulsive interactions in a one-dimensional optical superlattice. We find that the Mott insulator states of the single-component (two-component) Bose-Hubbard model under fractional fillings are topological insulators characterized by a nonzero charge (or spin) Chern number with nontrivial edge states. For ultracold atomic experiments, we show that the topological Chern number can be detected through measuring the density profiles of the bosonic atoms in a harmonic trap.Comment: 5 pages, published versio

Molecular detection of minimal residual disease for patients with leukemia and lymphoma

Although a complete clinical remission can often be achieved with chemotherapy for patients with leukaemia and lymphoma, relapses still occur. Residual tumour cells probably have survived therapy and account for subsequent disease relapse. The sensitivity of conventioned ways of detecting residual tumour cells, such as morphological studies, immunophenotyping, and cytogenetics, is only about 1% to 5% and may be inadequate. Polymerase chain reaction technology had provided a simple and highly sensitive means for the detection of minimal residual disease. The technology has been successfully applied to study biopsy samples obtained from patients with leukaemia and lymphpma. Its clinical usefulness, however, requires further evaluation by prospective clinical studies.published_or_final_versio

N-ras mutations in myelodysplastic syndromes in Hong Kong Chinese

Hong Kong Chinese patients with myelodysplastic syndromes were screened for the presence of N-ras mutation by using the polymerase chain reaction/dot blot hybridization technique. Three of 20 (15%) cases studied were found to harbour mutant N-ras in the bone marrow mononuclear cell population. One case of refractory anaemia with excess of blasts and with excess of blasts in transformation had substitution of arginine for glutamine at codon 61. A second case of refractory anaemia with excess of blasts had substitution of serine for glycine at codon 12. In this patient, mutant N-ras was detected in a follow up sample taken two months later although there was no change in the blast percentage compared with the presentation sample. Our study showed that N-ras mutation is an infrequent finding in Hong Kong Chinese myelodysplastic syndrome patients. An N-ras mutation is not necessarily accompanied by an alteration in the haematological picture.published_or_final_versio