2,327 research outputs found
Control of electric current by graphene edge structure engineering
In graphene nanoribbon junctions, the nearly perfect transmission occurs in
some junctions while the zero conductance dips due to anti-resonance appear in
others. We have classified the appearance of zero conductance dips for all
combinations of ribbon and junction edge structures. These transport properties
do not attribute to the whole junction structure but the partial corner edge
structure, which indicates that one can control the electric current simply by
cutting a part of nanoribbon edge. The ribbon width is expected to be narrower
than 10 nm in order to observe the zero conductance dips at room temperature.Comment: accepted for publication in Appl. Phys. Let
Electronic transport properties of graphene nanoribbons
We will present brief overview on the electronic and transport properties of
graphene nanoribbons focusing on the effect of edge shapes and impurity
scattering. The low-energy electronic states of graphene have two
non-equivalent massless Dirac spectrum. The relative distance between these two
Dirac points in the momentum space and edge states due to the existence of the
zigzag type graphene edges are decisive to the electronic and transport
properties of graphene nanoribbons. In graphene nanoribbons with zigzag edges,
two valleys related to each Dirac spectrum are well separated in momentum
space. The propagating modes in each valley contain a single chiral mode
originating from a partially flat band at band center. This feature gives rise
to a perfectly conducting channel in the disordered system, if the impurity
scattering does not connect the two valleys, i.e. for long-range impurity
potentials. On the other hand, the low-energy spectrum of graphene nanoribbons
with armchair edges is described as the superposition of two non-equivalent
Dirac points of graphene. In spite of the lack of well-separated two valley
structures, the single-channel transport subjected to long-ranged impurities is
nearly perfectly conducting, where the backward scattering matrix elements in
the lowest order vanish as a manifestation of internal phase structures of the
wavefunction. Symmetry considerations lead to the classification of disordered
zigzag ribbons into the unitary class for long-range impurities, and the
orthogonal class for short-range impurities. However, no such crossover occurs
in armchair nanoribbons
Faster Compact On-Line Lempel-Ziv Factorization
We present a new on-line algorithm for computing the Lempel-Ziv factorization
of a string that runs in time and uses only bits
of working space, where is the length of the string and is the
size of the alphabet. This is a notable improvement compared to the performance
of previous on-line algorithms using the same order of working space but
running in either time (Okanohara & Sadakane 2009) or
time (Starikovskaya 2012). The key to our new algorithm is in the
utilization of an elegant but less popular index structure called Directed
Acyclic Word Graphs, or DAWGs (Blumer et al. 1985). We also present an
opportunistic variant of our algorithm, which, given the run length encoding of
size of a string of length , computes the Lempel-Ziv factorization
on-line, in time
and bits of space, which is faster and more space efficient when
the string is run-length compressible
Using Conservative Estimation for Conditional Probability instead of Ignoring Infrequent Case
There are several estimators of conditional probability from observed
frequencies of features. In this paper, we propose using the lower limit of
confidence interval on posterior distribution determined by the observed
frequencies to ascertain conditional probability. In our experiments, this
method outperformed other popular estimators.Comment: The 2016 International Conference on Advanced Informatics: Concepts,
Theory and Application (ICAICTA2016
Leukemogenesis in Down syndrome
The incidence of leukemia is higher in Down syndrome children than that in the general population, while the risk of solid tumors is significantly reduced in Down syndrome. Recent studies utilizing mouse models have shown that distinct mechanisms caused by the elevated dosage of multiple genes is implicated in the protection from tumor progression depending on the type of solid neoplasm. In contrast, increased incidence of mutation in the several specific genes is reported as a cause of the onset of leukemias. Especially, acquired mutations in the GATA1 gene are associated with leukemogenesis of megakaryoblastic leukemia (AMKL) and transient myeloproliferative disorder (TMD) related to Down syndrome. The mutations are clustered in the region corresponding to the N-terminal domain of GATA1 and result in the production of the short form of GATA1 (GATA1-S), which utilizes Met84 as an alternative translation initiation codon. Efforts producing mouse models of Down TMD and AMKL have been undertaken, as these models seem to provide important insights into the pathogenesis of multistep leukemogenesis. Concomitantly, the function of GATA1 has been examined extensively, and the analyses present a prototype for the study of lineage-restricted transcription factors that play an essential role for the differentiation, proliferation, and apoptosis of erythroid cells, megakaryocytes, mast cells, and eosinophils. In this chapter, we will summarize recent progress in the studies of leukemias that occur in Down syndrome, especially in relation to GATA1 mutations
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