Ideal Spin Filters: Theoretical Study of Electron Transmission Through Ordered and Disordered Interfaces Between Ferromagnetic Metals and Semiconductors

It is predicted that certain atomically ordered interfaces between some ferromagnetic metals (F) and semiconductors (S) should act as ideal spin filters that transmit electrons only from the majority spin bands or only from the minority spin bands of the F to the S at the Fermi energy, even for F with both majority and minority bands at the Fermi level. Criteria for determining which combinations of F, S and interface should be ideal spin filters are formulated. The criteria depend only on the bulk band structures of the S and F and on the translational symmetries of the S, F and interface. Several examples of systems that meet these criteria to a high degree of precision are identified. Disordered interfaces between F and S are also studied and it is found that intermixing between the S and F can result in interfaces with spin anti-filtering properties, the transmitted electrons being much less spin polarized than those in the ferromagnetic metal at the Fermi energy. A patent application based on this work has been commenced by Simon Fraser University.Comment: RevTeX, 12 pages, 5 figure

Finding Weak Motifs In DNA Sequences

Introduction Large-scale expression analysis and comparative genomics recently generated numerous samples of potentially co-regulated genes whose upstream regions are likely to contain regulatory sites. These samples are often corrupted (with only a fraction of sequences in the sample containing a site) and the corresponding signals may be relatively weak. In difference from previous "gene-by-gene" researchefforts, the possibilities of experimental localization of site positions (i.e., via reduction in the length of sequences in the samples by footprinting experiments) in postgenomic era are limited. As a result, computer predictions are often the only realistic waytofind regulatory signals in these regions. The first attempts to find regulatory sites appeared in the early eighties (for reviews, see Gelfand , Frech et al. , or Brazma et al. ). Currentapproaches can be roughly subdivided into pattern-driven techniques 4#5#6#7 and profilebased optimization algorithms (greed