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  • Parra-Rivas, P., et al. (författare)
  • Locking of Domain Walls and Quadratic Frequency Combs in Doubly Resonant Optical Parametric Oscillators
  • 2019
  • Konferensbidrag (refereegranskat)abstract
    • The formation of frequency combs (FCs) in high-Q microresonators with Kerr type of nonlinearity has attracted a lot of attention in the past decade [1]. Recently it has been shown that FCs can be also generated in dissipative dispersive cavities with quadratic nonlinearities [2,3], opening a new possibility of generating combs in previously unattainable spectral regions. Previous work has shown that modulational instability (MI) induces pattern and FC formation in degenerate optical parametric oscillators (OPOs) [4]. However, the existence of dissipative solitons or localized structures (LSs) is still unclear. In this work we present the locking of domain walls (DWs) as an alternative mechanism to MI for the formation of LSs and FCs. DWs have been widely studied in the context of Kerr cavities and diffractive OPO cavities [5,6]. Here we show that similar structures can arise in dispersive quadratic cavities. To illustrate this, we consider a dispersive cavity with a quadratic medium phase matched for degenerate OPO and driven by the field B in at the frequency 2ω 0 in a doubly resonant configuration. The formation of dissipative structures in this type of cavity can be described by an infinite map for the slowly varying electric field envelopes A m , and B m , that are centered at frequency ω 0 and 2ω 0 , respectively [4], where m indicates the cavity round-trip number. With this map one may numerically explore the dynamics of the system. For example, Fig. 1(a)-(b) show the formation of a dissipative structure, after a sufficient number of round-trips (m = 2 · 10 4 ), from an initial noisy background. We see that i) both fields are phase locked and drift at the same velocity; ii) for the A field one can identify a sequence of DWs connecting two different, and coexisting, CW states, that form a disordered structure. Furthermore, the latter is composed of a sequence of LSs of different widths. One of them, LS 4 , is plotted in panel (c). We demonstrate that this ty...
  • Richards, Stephen, et al. (författare)
  • Genome Sequence of the Pea Aphid Acyrthosiphon pisum
  • 2010
  • Ingår i: PLoS biology. - : Public Library of Science (PLoS). - 1544-9173 .- 1545-7885. ; 8:2, s. e1000313-
  • Tidskriftsartikel (refereegranskat)abstract
    • Aphids are important agricultural pests and also biological models for studies of insect-plant interactions, symbiosis, virus vectoring, and the developmental causes of extreme phenotypic plasticity. Here we present the 464 Mb draft genome assembly of the pea aphid Acyrthosiphon pisum. This first published whole genome sequence of a basal hemimetabolous insect provides an outgroup to the multiple published genomes of holometabolous insects. Pea aphids are host-plant specialists, they can reproduce both sexually and asexually, and they have coevolved with an obligate bacterial symbiont. Here we highlight findings from whole genome analysis that may be related to these unusual biological features. These findings include discovery of extensive gene duplication in more than 2000 gene families as well as loss of evolutionarily conserved genes. Gene family expansions relative to other published genomes include genes involved in chromatin modification, miRNA synthesis, and sugar transport. Gene losses include genes central to the IMD immune pathway, selenoprotein utilization, purine salvage, and the entire urea cycle. The pea aphid genome reveals that only a limited number of genes have been acquired from bacteria; thus the reduced gene count of Buchnera does not reflect gene transfer to the host genome. The inventory of metabolic genes in the pea aphid genome suggests that there is extensive metabolite exchange between the aphid and Buchnera, including sharing of amino acid biosynthesis between the aphid and Buchnera. The pea aphid genome provides a foundation for post-genomic studies of fundamental biological questions and applied agricultural problems.
  • Rivas, A., et al. (författare)
  • Validation of questionnaires for the study of food habits and bone mass
  • 2009
  • Ingår i: Nutrición Hospitalaria. - : Aula Médica Ediciones. - 0212-1611 .- 1699-5198. ; 24:5, s. 521-528
  • Tidskriftsartikel (refereegranskat)abstract
    • BACKGROUND: The loss of bone mass and density is influenced by nutritional factors that act on the bone mass peak, age-related bone loss and muscle strength. The objective of the present study was to validate a food frequency questionnaire applied to estimate the relationship between food habits and bone mineral density (BMD) in a healthy adult population.METHODS: The results of the food frequency questionnaire were compared with 24-hr recall findings. Calcaneus BMD was measured by densitometry.RESULTS: The validity of the questionnaire was demonstrated, with Spearman correlation coefficients of 0.014 to 0.467. The Bland-Altman test also found no differences in study variables between the two methods. Correlation analysis showed that the BMD was significantly associated with the intake of vitamin D, vitamin A, vitamin B12, folate, thiamine and iron. Total fat consumption was not associated with BMD but the intake of monounsaturated fatty acids, EPA, DHA and cholesterol showed a significant correlation.CONCLUSION: The questionnaire evaluates the consumption of energy and nutrients with adequate validity. Its application revealed the importance for bone health of a diet rich in B-group vitamins, vitamin D, calcium, iron, monounsaturated fatty acids and n-3.
  • Rivas, D. E., et al. (författare)
  • Next Generation Driver for Attosecond and Laser-plasma Physics
  • 2017
  • Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 7
  • Tidskriftsartikel (refereegranskat)abstract
    • The observation and manipulation of electron dynamics in matter call for attosecond light pulses, routinely available from high-order harmonic generation driven by few-femtosecond lasers. However, the energy limitation of these lasers supports only weak sources and correspondingly linear attosecond studies. Here we report on an optical parametric synthesizer designed for nonlinear attosecond optics and relativistic laser-plasma physics. This synthesizer uniquely combines ultra-relativistic focused intensities of about 10(20)W/cm(2) with a pulse duration of sub-two carrier-wave cycles. The coherent combination of two sequentially amplified and complementary spectral ranges yields sub-5-fs pulses with multi-TW peak power. The application of this source allows the generation of a broad spectral continuum at 100-eV photon energy in gases as well as high-order harmonics in relativistic plasmas. Unprecedented spatio-temporal confinement of light now permits the investigation of electric-field-driven electron phenomena in the relativistic regime and ultimately the rise of next-generation intense isolated attosecond sources.
  • van Dongen, J, et al. (författare)
  • DNA methylation signatures of aggression and closely related constructs: A meta-analysis of epigenome-wide studies across the lifespan
  • 2021
  • Ingår i: Molecular psychiatry. - : Springer Science and Business Media LLC. - 1476-5578 .- 1359-4184. ; 26:6, s. 2148-2162
  • Tidskriftsartikel (refereegranskat)abstract
    • DNA methylation profiles of aggressive behavior may capture lifetime cumulative effects of genetic, stochastic, and environmental influences associated with aggression. Here, we report the first large meta-analysis of epigenome-wide association studies (EWAS) of aggressive behavior (N = 15,324 participants). In peripheral blood samples of 14,434 participants from 18 cohorts with mean ages ranging from 7 to 68 years, 13 methylation sites were significantly associated with aggression (alpha = 1.2 × 10−7; Bonferroni correction). In cord blood samples of 2425 children from five cohorts with aggression assessed at mean ages ranging from 4 to 7 years, 83% of these sites showed the same direction of association with childhood aggression (r = 0.74, p = 0.006) but no epigenome-wide significant sites were found. Top-sites (48 at a false discovery rate of 5% in the peripheral blood meta-analysis or in a combined meta-analysis of peripheral blood and cord blood) have been associated with chemical exposures, smoking, cognition, metabolic traits, and genetic variation (mQTLs). Three genes whose expression levels were associated with top-sites were previously linked to schizophrenia and general risk tolerance. At six CpGs, DNA methylation variation in blood mirrors variation in the brain. On average 44% (range = 3–82%) of the aggression–methylation association was explained by current and former smoking and BMI. These findings point at loci that are sensitive to chemical exposures with potential implications for neuronal functions. We hope these results to be a starting point for studies leading to applications as peripheral biomarkers and to reveal causal relationships with aggression and related traits.
  • Wabnitz, S., et al. (författare)
  • Quadratic Optical Frequency Combs: Towards a New Platform for Multi-Octave Microcombs
  • 2020
  • Ingår i: INTERNATIONAL CONFERENCE LASER OPTICS 2020 (ICLO 2020). - : IEEE. - 9781728152332
  • Konferensbidrag (refereegranskat)abstract
    • Optical frequency comb sources based on three-wave-mixing in quadratic nonlinear materials allow for reduced pump power threshold and extended spectral coverage. We review recent progress on quadratic optical frequency combs based on second-harmonic generation and optical parametric oscillation.
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