46,302 research outputs found
Semiclassical Time Evolution of the Holes from Luttinger Hamiltonian
We study the semi-classical motion of holes by exact numerical solution of
the Luttinger model. The trajectories obtained for the heavy and light holes
agree well with the higher order corrections to the abelian and the non-abelian
adiabatic theories in Ref. [1] [S. Murakami et al., Science 301, 1378(2003)],
respectively. It is found that the hole trajectories contain rapid oscillations
reminiscent of the "Zitterbewegung" of relativistic electrons. We also comment
on the non-conservation of helicity of the light holes.Comment: 4 pages, 5 fugure
Fabrication and characterizations of proton-exchanged LiNbO3 waveguides fabricated by inductively coupled plasma technique
This Letter reports the use of an inductively coupled plasma technique for fabrication of proton-exchanged (PE) LiNbO3 (LN) waveguides. Planar and stripe waveguides have been formed in Y-cut LN which are difficult to obtain with the conventional molten acid method due to the occurrence of surface damage. Secondary ion mass spectrometry, scanning electron microscopy, and infrared absorption spectrum characterization results revealed that a uniform vertical PE profile with a single low order crystal phase has been directly obtained as a result of this unique process. X-ray photoelectron spectroscopy characterization of the treated surface revealed the existence of NbO as the cause for a sometimes darkened surface and confirms the ability to completely restore the surface to LN by oxygen plasma treatment. Atomic force microscopy measurement confirms that good surface quality has been maintained after regeneration of the surface to LN
On perpetual American put valuation and first-passage in a regime-switching model with jumps
In this paper we consider the problem of pricing a perpetual American put
option in an exponential regime-switching L\'{e}vy model. For the case of the
(dense) class of phase-type jumps and finitely many regimes we derive an
explicit expression for the value function. The solution of the corresponding
first passage problem under a state-dependent level rests on a path
transformation and a new matrix Wiener-Hopf factorization result for this class
of processes.Comment: 22 pages, 3 figures. Tp appear in Finance and Stochastics
Explode-decay dromions in the non-isospectral Davey-Stewartson I (DSI) equation
In this letter, we report the existence of a novel type of explode-decay
dromions, which are exponentially localized coherent structures whose amplitude
varies with time, through Hirota method for a nonisospectral Davey-Stewartson
equation I discussed recently by Jiang. Using suitable transformations, we also
point out such solutions also exist for the isospectral Davey-Stewartson I
equation itself for a careful choice of the potentials
Discovering causal interactions using Bayesian network scoring and information gain
Background: The problem of learning causal influences from data has recently attracted much attention. Standard statistical methods can have difficulty learning discrete causes, which interacting to affect a target, because the assumptions in these methods often do not model discrete causal relationships well. An important task then is to learn such interactions from data. Motivated by the problem of learning epistatic interactions from datasets developed in genome-wide association studies (GWAS), researchers conceived new methods for learning discrete interactions. However, many of these methods do not differentiate a model representing a true interaction from a model representing non-interacting causes with strong individual affects. The recent algorithm MBS-IGain addresses this difficulty by using Bayesian network learning and information gain to discover interactions from high-dimensional datasets. However, MBS-IGain requires marginal effects to detect interactions containing more than two causes. If the dataset is not high-dimensional, we can avoid this shortcoming by doing an exhaustive search. Results: We develop Exhaustive-IGain, which is like MBS-IGain but does an exhaustive search. We compare the performance of Exhaustive-IGain to MBS-IGain using low-dimensional simulated datasets based on interactions with marginal effects and ones based on interactions without marginal effects. Their performance is similar on the datasets based on marginal effects. However, Exhaustive-IGain compellingly outperforms MBS-IGain on the datasets based on 3 and 4-cause interactions without marginal effects. We apply Exhaustive-IGain to investigate how clinical variables interact to affect breast cancer survival, and obtain results that agree with judgements of a breast cancer oncologist. Conclusions: We conclude that the combined use of information gain and Bayesian network scoring enables us to discover higher order interactions with no marginal effects if we perform an exhaustive search. We further conclude that Exhaustive-IGain can be effective when applied to real data
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