2,049 research outputs found

    The three-dimensional carrier-envelope-phase map of focused few-cycle pulsed Gaussian beams

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    We derive an analytical expression that describes the complete three-dimensional carrier-envelope phase (CEP) distribution of in the focal volume of ultrashort pulsed Gaussian beams focused by spherical mirrors or lenses. The focal CEP map depends on the so-called factor gg specifying the frequency-dependence of the beam width of the source few-cycle pulse, on its chirp and on the small chromatic aberration introduced by a lens without appreciably distorting or broadening the few-cycle pulse. We show how to tailor the CEP map of mirror-focused and lens-focused few-cycle pulses in order to produce negligible transversal and axial CEP variations in specific regions of the focal volume for phase-sensitive interactions of light with matter taking place in a volume or on a surface. We propose a quasi-achromatic doublet lens that can implement in practice these tailored CEP distributions.Comment: 9 pages, 6 figure

    Quantum phases of interacting phonons in ion traps

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    The vibrations of a chain of trapped ions can be considered, under suitable experimental conditions, as an ensemble of interacting phonons, whose quantum dynamics is governed by a Bose--Hubbard Hamiltonian. In this work we study the quantum phases which appear in this system, and show that thermodynamical properties, such as critical parameters and critical exponents, can be measured in experiments with a limited number of ions. Besides that, interacting phonons in trapped ions offer us the possibility to access regimes which are difficult to study with ultracold bosons in optical lattices, like models with attractive or site--dependent phonon-phonon interactions.Comment: 10 page

    Patients' understanding of heart disease: relationships with decisions to seek help with acute symptoms, and with adherence to treatment.

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    Pre-hospital delay in seeking help for acute chest pain in patients with coronary heart disease is a major impediment to prompt thrombolysis. Failure to adhere to medication, attend cardiac rehabilitation where appropriate, and change lifestyle, all impair secondary prevention. This thesis examined psychological factors related to these problems, and the psychological models of illness held by patients diagnosed with acute coronary syndromes (ACS). Two main issues were investigated firstly, what factors were associated with shorter pre-hospital delays following symptom onset and secondly, whether cognitive models of illness predicted adherence to advice, psychological and emotional adjustment, and quality of life at 3 months and 13 months post-discharge. Data were collected from 269 patients diagnosed with ACS within five days of hospital admission. Analyses were focussed on the total time between symptom onset and admission to hospital (pre-hospital delay). This interval was divided into two phases time between symptom onset and decision to call for medical help (patient decision time), and time from call for help to admission (home to hospital delay). Patients were followed up 3 and 13 months later. Adherence to medical advice (lifestyle changes, adherence to medication, attendance at cardiac rehabilitation programmes), psychological distress and quality of life were measured by telephone interview and questionnaire. A number of sociodemographic, social, clinical and psychological factors were associated with pre-hospital delay. Beliefs about the causes of heart disease made an important contribution. Cognitive representations of heart disease measured during hospital admission did not predict adherence to treatment regimens after discharge, but significantly predicted later psychological and emotional adjustment, and quality of life. Theses findings have implications for understanding the contribution of psychological factors to the experience of acute heart disease, and point to methods of more effective patient care and management

    Mesoscopic mean-field theory for spin-boson chains in quantum optical systems

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    We present a theoretical description of a system of many spins strongly coupled to a bosonic chain. We rely on the use of a spin-wave theory describing the Gaussian fluctuations around the mean-field solution, and focus on spin-boson chains arising as a generalization of the Dicke Hamiltonian. Our model is motivated by experimental setups such as trapped ions, or atoms/qubits coupled to cavity arrays. This situation corresponds to the cooperative (E⊗β) Jahn-Teller distortion studied in solid-state physics. However, the ability to tune the parameters of the model in quantum optical setups opens up a variety of novel intriguing situations. The main focus of this paper is to review the spin-wave theoretical description of this problem as well as to test the validity of mean-field theory. Our main result is that deviations from mean-field effects are determined by the interplay between magnetic order and mesoscopic cooperativity effects, being the latter strongly size-dependent

    Photon-mediated qubit interactions in one-dimensional discrete and continuous models

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    In this work we study numerically and analytically the interaction of two qubits in a one-dimensionalwaveguide, as mediated by the photons that propagate through the guide. We develop strategies to assert the Markovianity of the problem, the effective qubit-qubit interactions, and their individual and collective spontaneous emission. We prove the existence of collective Lamb shifts that affect the qubit-qubit interactions and the dependency of coherent and incoherent interactions on the qubit separation. We also develop the scattering theory associated with these models and prove single-photon spectroscopy does probe the renormalized resonances of the singleand multiqubit models, in sharp contrast to earlier toy models in which individual and collective Lamb shifts cancel

    Molecular evolution of RRM-containing proteins and glycine-rich RNA-binding proteins in plants

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    *Abstract*

*Background:*
In angiosperms, RNA-binding proteins with an RNA recognition motif (RRM)-type RNA interaction domain play an important role in developmental and environmental responses. Despite their pivotal role, a comprehensive analysis of their number and diversity has only been performed in _Arabidopsis_ so far.

*Results:*
Here we present a detailed phylogenetic analysis of RRM-containing proteins in plants, the red algae _Cyanidioschyzon merolae_ and cyanobacteria. We identified two major events during the diversification of the RRM in plants, one at the emergence of green plants, and the other at the water-to-land transition. We focused on proteins that combine a single RRM with a glycine-rich stretch, known as glycine-rich RNA-binding proteins (GRPs). We found that GRPs are present in cyanobacteria, however plant and cyanobacterial GRPs are not of monophyletic origin. We provide evidence that plant GRPs form a polyphyletic group.
 
*Conclusion:*
Our work provides insights into the origin of GRPs in plants. We determined that the RRM from plants and cyanobacteria do not have a common origin. We could also determine that the acquisition of the glycine-rich stretch has happened at least on three separate occasions during the evolution of GRPs. One event led to the emergence of cyanobacterial GRPs, while later acquisition events led to the emergence of GRPs in the green lineage. No GRPs were found in red or marine green algae. We found a subgroup of GRPs exclusive to land plants, and its appearance may be linked to challenges related to the water-to-land transition.
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    Rabi lattice models with discrete gauge symmetry: Phase diagram and implementation in trapped-ion quantum simulators

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    We study a spin-boson chain that exhibits a local Z2 symmetry. We investigate the quantum phase diagram of the model by means of perturbation theory, mean-field theory, and the density matrix renormalization group method. Our calculations show the existence of a first-order phase transition in the region where the boson quantum dynamics is slow compared to the spin-spin interactions. Our model can be implemented with trapped-ion quantum simulators, leading to a realization of minimal models showing local gauge invariance and first-order phase transitions

    Using Eco-schemes in the new CAP: a guide for managing authorities

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    This guide has been developed primarily for policy makers and Member State officials involved in the national and regional programming processes of the CAP Strategic Plans (CSPs). This process might involve different administrative levels (national, regional, local), different political fields (agriculture, environmental, food and health ministries), different public bodies (paying agencies, environmental agencies, rural development offices) depending on the administrative setting of each MS. In addition, the guide provides support to other stakeholders and practitioners from the public and private sectors and civil society (including agricultural, environmental, food, health and consumer NGOs), with a direct or indirect involvement in the programming and evaluation process of the CSPs. Since these new plans will have a strong impact on MS environments, agricultural sectors, rural areas, etc., the engagement of all stakeholders will be an important asset for supporting an effective implementation of the CSP objectives. There are many others with potential interests in the contents of this guide. EU citizens have demonstrated their increasing interest in the contents of the CAP objectives and policy framework, as demonstrated both by civil society initiatives and consumption decisions. The contents of this guide may therefore also be of interest to other societal actors with interests in agricultural and environmental policies, such as researchers, journalists, trade unions, and civil society organizations. However, the guide is intentionally more focused on the technical needs of those involved in CSP development and implementation

    Microwave energy supplied by a prototype oven prevents the spread of Fusarium wilt during the propagation of melon plantlets by seed

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    The re-use of propagation trays in nursery greenhouses is one of the main ways in which fusarium wilt is spread in melon crops (Cucumis melo). The causal agent of the disease is the fungus Fusarium oxysporum f. sp. melonis. This paper reports that exposing these seed trays to the energy produced by a prototype microwave oven during the commercial production of melon plantlets can prevent the spread of this pathogen with only a very small increase in production costs
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