341 research outputs found

    Design of Strongly Modulating Pulses to Implement Precise Effective Hamiltonians for Quantum Information Processing

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    We describe a method for improving coherent control through the use of detailed knowledge of the system's Hamiltonian. Precise unitary transformations were obtained by strongly modulating the system's dynamics to average out unwanted evolution. With the aid of numerical search methods, pulsed irradiation schemes are obtained that perform accurate, arbitrary, selective gates on multi-qubit systems. Compared to low power selective pulses, which cannot average out all unwanted evolution, these pulses are substantially shorter in time, thereby reducing the effects of relaxation. Liquid-state NMR techniques on homonuclear spin systems are used to demonstrate the accuracy of these gates both in simulation and experiment. Simulations of the coherent evolution of a 3-qubit system show that the control sequences faithfully implement the unitary operations, typically yielding gate fidelities on the order of 0.999 and, for some sequences, up to 0.9997. The experimentally determined density matrices resulting from the application of different control sequences on a 3-spin system have overlaps of up to 0.99 with the expected states, confirming the quality of the experimental implementation.Comment: RevTeX3, 11 pages including 2 tables and 5 figures; Journal of Chemical Physics, in pres

    Experimental ionization of atomic hydrogen with few-cycle pulses

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    We present the first experimental data on strong-field ionization of atomic hydrogen by few-cycle laser pulses. We obtain quantitative agreement at the 10% level between the data and an {\it ab initio} simulation over a wide range of laser intensities and electron energies

    Diffuse versus square-well confining potentials in modelling AA@C60_{60} atoms

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    Attention: this version-22 of the manuscript differs from its previously uploaded version-11 (arXiv:1112.6158v1) and subsequently published in 2012 J. Phys. B \textbf{45} 105102 only by a removed typo in Eq.(2) of version-11; there was the erroneous factor "2" in both terms in the right-hand-side of the Eq.(2) of version-11. Now that the typo is removed, Eq.(2) is correct. A perceived advantage for the replacement of a discontinuous square-well pseudo-potential, which is often used by various researchers as an approximation to the actual C60_{60} cage potential in calculations of endohedral atoms AA@C60_{60}, by a more realistic diffuse potential is explored. The photoionization of endohedral H@C60_{60} and Xe@C60_{60} is chosen as the case study. The diffuse potential is modelled by a combination of two Woods-Saxon potentials. It is demonstrated that photoionization spectra of AA@C60_{60} atoms are largely insensitive to the degree η\eta of diffuseness of the potential borders, in a reasonably broad range of η\eta's. Alternatively, these spectra are found to be insensitive to discontinuity of the square-well potential either. Both potentials result in practically identical calculated spectra. New numerical values for the set of square-well parameters, which lead to a better agreement between experimental and theoretical data for AA@C60_{60} spectra, are recommended for future studies.Comment: 11 pages, 4 figure

    Adaptation des sorghos du Mali à la variabilité climatique

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    Il est couramment admis que la sécheresse en Afrique de l'Ouest a entraîné l'adoption par les paysans de variétés de sorgho plus précoces que les cultivars traditionnels. Pour mesurer l'évolution récente du cycle des sorghos du Mali, nous avons étudié la phénologie de deux collections de variétés locales prospectées à 20 ans d'intervalle en 1978 et en 2000. Les dates de début et de fin de saison des pluies ont été calculées pour tous les villages échantillonnés. La sensibilité des cultivars à la photopériode a été mesurée à l'aide d'un essai comportant deux dates de semis. Un modèle permet d'étudier l'adaptation des variétés au climat en tenant compte de la latitude et du régime des pluies de leurs zones d'origines. Le déficit pluviométrique n'a pas entraîné un raccourcissement important des cycles végétatifs. En 20 ans, le cycle moyen des cultivars locaux s'est raccourci de 5 jours. Pour des latitudes inférieures à 14° N, la grande majorité des cultivars sont photopériodiques, la floraison des variétés se produit dans les 20 jours qui précèdent la date moyenne de fin de la saison des pluies. Ce caractère permet d'optimiser l'alimentation en eau des cultures et d'éviter de nombreuses contraintes biotiques. Pour des latitudes supérieures ou égales à 14° N, la floraison moyenne coïncide avec la fin de saison. On note la présence simultanée de variétés tardives et précoces. Dans ces régions, la culture du sorgho dépend moins de la pluviométrie car les systèmes traditionnels valorisent des situations diversifiées et les reports d'eau sur les toposéquences. Cette diversité des cycles contribue à sécuriser la production agricole en zone aride. Ce travail permet de guider les programmes de sélection dans la définition d'idéotypes spécifiquement adaptés à la gamme d'environnements climatiques rencontrés dans la région. (Résumé d'auteur

    A decision maxim for efficient task realization within analytical network infrastructures

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    Faced with the increasing needs of companies, optimal dimensioning of IT hardware is becoming challenging for decision makers. In terms of analytical infrastructures, a highly evolutionary environment causes volatile, time-dependent workloads in its components, and intelligent, flexible task distribution between local systems and cloud services is attractive. With the aim of developing a flexible and efficient design for analytical infrastructures, this paper proposes a flexible architecture model, which allocates tasks following a machine-specific decision heuristic. A simulation benchmarks this system with existing strategies and identifies the new decision maxim as superior in a first scenario-based simulation.Partly funded by the Advanced Sensor Networks SARChI Chair program, co-hosted by the University of Pretoria (UP) and Council for Scientific and Industrial Research (CSIR), through the National Research Foundation (NRF) of South Africa.https://www.elsevier.com/locate/dss2019-08-01hj2018Electrical, Electronic and Computer Engineerin

    Personality Traits in Miners with Past Occupational Elemental Mercury Exposure

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    In this study, we evaluated the impact of long-term occupational exposure to elemental mercury vapor (Hg(0)) on the personality traits of ex-mercury miners. Study groups included 53 ex-miners previously exposed to Hg(0) and 53 age-matched controls. Miners and controls completed the self-reporting Eysenck Personality Questionnaire and the Emotional States Questionnaire. The relationship between the indices of past occupational exposure and the observed personality traits was evaluated using Pearson’s correlation coefficient and on a subgroup level by machine learning methods (regression trees). The ex-mercury miners were intermittently exposed to Hg(0) for a period of 7–31 years. The means of exposure-cycle urine mercury (U-Hg) concentrations ranged from 20 to 120 μg/L. The results obtained indicate that ex-miners tend to be more introverted and sincere, more depressive, more rigid in expressing their emotions and are likely to have more negative self-concepts than controls, but no correlations were found with the indices of past occupational exposure. Despite certain limitations, results obtained by the regression tree suggest that higher alcohol consumption per se and long-term intermittent, moderate exposure to Hg(0) (exposure cycle mean U-Hg concentrations > 38.7 < 53.5 μg/L) in interaction with alcohol remain a plausible explanation for the depression associated with negative self-concept found in subgroups of ex-mercury miners. This could be one of the reason for the higher risk of suicide among miners of the Idrija Mercury Mine in the last 45 years

    Neuronal Sprouting and Reorganization in Bone Tissue Infiltrated by Human Breast Cancer Cells

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    BACKGROUND: Pain is a common complication for patients with metastatic bone disease. Animal models suggest that the pain, in part, is driven by pathological sprouting and reorganization of the nerve fibers innervating the bone. Here, we investigate how these findings translate to humans.METHODS: Bone biopsies were collected from healthy volunteers (n = 7) and patients with breast cancer and metastatic bone disease (permissions H-15000679, S-20180057 and S-20110112). Cancer-infiltrated biopsies were from patients without recent anticancer treatment (n = 10), patients with recent anticancer treatment (n = 10), and patients with joint replacement surgery (n = 9). Adjacent bone sections were stained for (1) protein gene product 9.5 and CD34, and (2) cytokeratin 7 and 19. Histomorphometry was used to estimate the area of bone marrow and tumor burden. Nerve profiles were counted, and the nerve profile density calculated. The location of each nerve profile within 25 μm of a vascular structure and/or cancer cells was determined.RESULTS: Cancer-infiltrated bone tissue demonstrated a significantly higher nerve profile density compared to healthy bone tissue. The percentage of nerve profiles found close to vascular structures was significantly lower in cancer-infiltrated bone tissue. No difference was found in the percentage of nerve profiles located close to cancer between the subgroups of cancer-infiltrated bone tissue. Interestingly, no correlation was found between nerve profile density and tumor burden.CONCLUSIONS: Together, the increased nerve profile density and the decreased association of nerve profiles to vasculature strongly suggests that neuronal sprouting and reorganization occurs in human cancer-infiltrated bone tissue.</p

    Attosecond delays in photoionization studied with coherent-controlled FEL

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    When an electron is ejected from an atom after absorption of a photon, the photoelectron wave packet has an extremely short group delay between the photon absorption and the electron emission. This interval, called the Eisenbud-Wigner-Smith delay, is on the order of a few attoseconds. Here, we present a new method to measure the photoemission delay, using coherent-controlled free-electron laser pulses
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