68 research outputs found

    Resonant Perturbation Theory of Decoherence and Relaxation of Quantum Bits

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    We describe our recent results on the resonant perturbation theory of decoherence and relaxation for quantum system with many qubits. The approach represents a rigorous analysis of the phenomenon of decoherence and relaxation for general NN-level systems coupled to reservoirs of the bosonic fields. We derive a representation of the reduced dynamics valid for all times t0t\geq 0 and for small but fixed interaction strength. Our approach does not involve master equation approximations and applies to a wide variety of systems which are not explicitly solvable

    M-COMMERCE VS. E-COMMERCE: EXPLORING WEB SESSION BROWSING BEHAVIOR

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    With the growing popularity of mobile commerce (m-commerce), it becomes vital for both researchers and practitioners to understand m-commerce usage behavior. \ \ In this study, we investigate browsing behavior patterns based on the analysis of clickstream data that is recorded in server-side log files. We compare consumers\u27 browsing behaviors in the m-commerce channel against the traditional e-commerce channel. For the comparison, we offer an integrative web usage mining approach, combining visualization graphs, association rules and classification models to analyze the Web server log files of a large Internet retailer in Israel, who introduced m-commerce to its existing e-commerce offerings. \ \ The analysis is expected to reveal typical m-commerce and e-commerce browsing behavior, in terms of session timing and intensity of use and in terms of session navigation patterns. The obtained results will contribute to the emerging research area of m-commerce and can be also used to guide future development of mobile websites and increase their effectiveness. Our preliminary findings are promising. They reveal that browsing behaviors in m-commerce and e-commerce are different

    Resonance Theory of Decoherence and Thermalization

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    We present a rigorous analysis of the phenomenon of decoherence for general NN-level systems coupled to reservoirs. The latter are described by free massless bosonic fields. We apply our general results to the specific cases of the qubit and the quantum register. We compare our results with the explicitly solvable case of systems whose interaction with the environment does not allow for energy exchange (non-demolition, or energy conserving interactions). We suggest a new approach which applies to a wide variety of systems which are not explicitly solvable

    Dynamics of Collective Decoherence and Thermalization

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    We analyze the dynamics of N interacting spins (quantum register) collectively coupled to a thermal environment. Each spin experiences the same environment interaction, consisting of an energy conserving and an energy exchange part. We find the decay rates of the reduced density matrix elements in the energy basis. We show that if the spins do not interact among each other, then the fastest decay rates of off-diagonal matrix elements induced by the energy conserving interaction is of order N^2, while that one induced by the energy exchange interaction is of the order N only. Moreover, the diagonal matrix elements approach their limiting values at a rate independent of N. For a general spin system the decay rates depend in a rather complicated (but explicit) way on the size N and the interaction between the spins. Our method is based on a dynamical quantum resonance theory valid for small, fixed values of the couplings. We do not make Markov-, Born- or weak coupling (van Hove) approximations

    PiSite: a database of protein interaction sites using multiple binding states in the PDB

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    The vast accumulation of protein structural data has now facilitated the observation of many different complexes in the PDB for the same protein. Therefore, a single protein complex is not sufficient to identify their interaction sites, especially for proteins with multiple binding states or different partners, such as hub proteins. PiSite is a database that provides protein–protein interaction sites at the residue level with consideration of multiple complexes at the same time, by mapping the binding sites of all complexes containing the same protein in the PDB. PiSite provides easy web interfaces with an interactive viewer working with typical web browsers, and the different binding modes can be checked visually. All of the information can also be downloaded for further analyses. In addition, PiSite provides a list of proteins with multiple binding partners and multiple binding states, as well as up-to-date statistics of protein–protein interfaces. PiSite is available at http://pisite.hgc.j

    Genetic Heterogeneity in Therapy-Naïve Synchronous Primary Breast Cancers and Their Metastases

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    Purpose:; Paired primary breast cancers and metachronous metastases after adjuvant treatment are reported to differ in their clonal composition and genetic alterations, but it is unclear whether these differences stem from the selective pressures of the metastatic process, the systemic therapies, or both. We sought to define the repertoire of genetic alterations in breast cancer patients with; de novo; metastatic disease who had not received local or systemic therapy.; Experimental Design:; Up to two anatomically distinct core biopsies of primary breast cancers and synchronous distant metastases from nine patients who presented with metastatic disease were subjected to high-depth whole-exome sequencing. Mutations, copy number alterations and their cancer cell fractions, and mutation signatures were defined using state-of-the-art bioinformatics methods. All mutations identified were validated with orthogonal methods.; Results:; Genomic differences were observed between primary and metastatic deposits, with a median of 60% (range 6%-95%) of shared somatic mutations. Although mutations in known driver genes including; TP53, PIK3CA; , and; GATA3; were preferentially clonal in both sites, primary breast cancers and their synchronous metastases displayed spatial intratumor heterogeneity. Likely pathogenic mutations affecting epithelial-to-mesenchymal transition-related genes, including; SMAD4, TCF7L2; , and; TCF4; (; ITF2; ), were found to be restricted to or enriched in the metastatic lesions. Mutational signatures of trunk mutations differed from those of mutations enriched in the primary tumor or the metastasis in six cases.; Conclusions:; Synchronous primary breast cancers and metastases differ in their repertoire of somatic genetic alterations even in the absence of systemic therapy. Mutational signature shifts might contribute to spatial intratumor genetic heterogeneity
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