| 1. |
- Santoro, V., et al.
(author)
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HighNESS conceptual design report: Volume I
- 2024
-
In: Journal of Neutron Research. - 1023-8166 .- 1477-2655. ; 25:3-4, s. 85-314
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Journal article (peer-reviewed)abstract
- The European Spallation Source, currently under construction in Lund, Sweden, is a multidisciplinary international laboratory. Once completed to full specifications, it will operate the world’s most powerful pulsed neutron source. Supported by a 3 million Euro Research and Innovation Action within the EU Horizon 2020 program, a design study (HighNESS) has been completed to develop a second neutron source located below the spallation target. Compared to the first source, designed for high cold and thermal brightness, the new source has been optimized to deliver higher intensity, and a shift to longer wavelengths in the spectral regions of cold (CN, 2–20 Å), very cold (VCN, 10–120 Å), and ultracold (UCN, >500 Å) neutrons. The second source comprises a large liquid deuterium moderator designed to produce CN and support secondary VCN and UCN sources. Various options have been explored in the proposed designs, aiming for world-leading performance in neutronics. These designs will enable the development of several new instrument concepts and facilitate the implementation of a high-sensitivity neutron-antineutron oscillation experiment (NNBAR). This document serves as the Conceptual Design Report for the HighNESS project, representing its final deliverable.
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| 2. |
- Santoro, V., et al.
(author)
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HighNESS conceptual design report: Volume II. the NNBAR experiment.
- 2024
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In: Journal of Neutron Research. - 1023-8166 .- 1477-2655. ; 25:3-4, s. 315-406
-
Journal article (peer-reviewed)abstract
- A key aim of the HighNESS project for the European Spallation Source is to enable cutting-edge particle physics experiments. This volume presents a conceptual design report for the NNBAR experiment. NNBAR would exploit a new cold lower moderator to make the first search in over thirty years for free neutrons converting to anti-neutrons. The observation of such a baryon-number-violating signature would be of fundamental significance and tackle open questions in modern physics, including the origin of the matter-antimatter asymmetry. This report shows the design of the beamline, supermirror focusing system, magnetic and radiation shielding, and anti-neutron detector necessary for the experiment. A range of simulation programs are employed to quantify the performance of the experiment and show how background can be suppressed. For a search with full background suppression, a sensitivity improvement of three orders of magnitude is expected, as compared with the previous search. Civil engineering studies for the NNBAR beamline are also shown, as is a costing model for the experiment.
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| 3. |
- Santoro, V., et al.
(author)
-
The HighNESS Project at the European Spallation Source : Current Status and Future Perspectives
- 2024
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In: Nuclear science and engineering. - 0029-5639 .- 1943-748X. ; 198:1, s. 31-63
-
Journal article (peer-reviewed)abstract
- The European Spallation Source (ESS), presently under construction in Lund, Sweden, is a multidisciplinary international laboratory that, once completed at full specifications, will operate the world's most powerful pulsed neutron source. Supported by a 3 M Euro Research and Innovation Action within the European Union Horizon 2020 program, a design study (HighNESS) is now underway to develop a second neutron source located below the spallation target. Compared to the first source, which is located above the spallation target and designed for high cold and thermal brightness, the new source is being optimized to deliver higher intensity and a shift to longer wavelengths in the spectral regions of cold neutrons (CNs) (2 to 20 & Aring;), very cold neutrons (VCNs) (10 to 120 & Aring;), and ultracold neutrons (UCNs) (> 500 & Aring;). The second source consists of a large liquid deuterium moderator to deliver CNs and serve secondary VCN and UCN sources, for which different options are under study. These new sources will boost several areas of condensed matter research and will provide unique opportunities in fundamental physics. The HighNESS project is now entering its last year, and we are working toward the Conceptual Design Report of the ESS upgrade. In this paper, results obtained in the first 2 years, ongoing developments, and future perspectives are described.
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| 4. |
- Mosconi, L., et al.
(author)
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Hypometabolism and Altered Cerebrospinal Fluid Markers in Normal Apolipoprotein E E4 Carriers with Subjective Memory Complaints
- 2007
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In: Biological Psychiatry. - : Elsevier BV. - 0006-3223. ; 63:6, s. 609-618
-
Journal article (peer-reviewed)abstract
- BACKGROUND: We examined whether cerebral metabolic rates for glucose (CMRglc) on 2-[(18)F]fluoro-2-deoxy-D-glucose (FDG)-positron emission tomography (PET) and cerebrospinal fluid (CSF) markers of Alzheimer's disease (AD) are altered in cognitively normal apolipoprotein E (ApoE) E4 carriers with subjective memory complaints (SMC). METHODS: Twenty-eight middle-aged normal subjects (NL) were examined, including 13 E4 carriers (E4+; 6 with SMC [SMC+] and 7 without SMC [SMC-]) and 15 noncarriers (E4-; 7 SMC+ and 8 SMC-). Subjects received an FDG-PET scan and a lumbar puncture to measure CSF total (T-Tau) and hyperphosphorylated tau(231) (P-Tau), 40 and 42 amino acid forms of beta-amyloid (Abeta40 and Abeta42), and F(2)-isoprostane (IP). RESULTS: As compared with E4-, E4+ subjects showed decreased CMRglc in AD-related brain regions and associated higher CSF IP, P-Tau, T-Tau, and P-Tau/Abeta42 levels (p's < .05). As compared with SMC-, SMC+ subjects showed reduced parietotemporal and parahippocampal gyrus (PHG) CMRglc. A significant ApoE by SMC status interaction was found, with the E4+/SMC+ showing the lowest PHG CMRglc and the highest CSF IP, P-Tau, and P-Tau/Abeta42 levels as compared with all other subgroups (p's
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| 5. |
- Sexton, Claire E., et al.
(author)
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Novel avenues of tau research
- 2024
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In: Alzheimer's and Dementia. - 1552-5260. ; 20:3, s. 2240-2261
-
Research review (peer-reviewed)abstract
- INTRODUCTION: The pace of innovation has accelerated in virtually every area of tau research in just the past few years. METHODS: In February 2022, leading international tau experts convened to share selected highlights of this work during Tau 2022, the second international tau conference co-organized and co-sponsored by the Alzheimer's Association, CurePSP, and the Rainwater Charitable Foundation. RESULTS: Representing academia, industry, and the philanthropic sector, presenters joined more than 1700 registered attendees from 59 countries, spanning six continents, to share recent advances and exciting new directions in tau research. DISCUSSION: The virtual meeting provided an opportunity to foster cross-sector collaboration and partnerships as well as a forum for updating colleagues on research-advancing tools and programs that are steadily moving the field forward.
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| 6. |
- Shefferson, Richard P., et al.
(author)
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Drivers of vegetative dormancy across herbaceous perennial plant species
- 2018
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In: Ecology Letters. - : WILEY. - 1461-023X .- 1461-0248. ; 21:5, s. 724-733
-
Journal article (peer-reviewed)abstract
- Vegetative dormancy, that is the temporary absence of aboveground growth for 1year, is paradoxical, because plants cannot photosynthesise or flower during dormant periods. We test ecological and evolutionary hypotheses for its widespread persistence. We show that dormancy has evolved numerous times. Most species displaying dormancy exhibit life-history costs of sprouting, and of dormancy. Short-lived and mycoheterotrophic species have higher proportions of dormant plants than long-lived species and species with other nutritional modes. Foliage loss is associated with higher future dormancy levels, suggesting that carbon limitation promotes dormancy. Maximum dormancy duration is shorter under higher precipitation and at higher latitudes, the latter suggesting an important role for competition or herbivory. Study length affects estimates of some demographic parameters. Our results identify life historical and environmental drivers of dormancy. We also highlight the evolutionary importance of the little understood costs of sprouting and growth, latitudinal stress gradients and mixed nutritional modes.
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| 7. |
- Anastasopoulos, M., et al.
(author)
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Multi-Grid detector for neutron spectroscopy : Results obtained on time-of-flight spectrometer CNCS
- 2017
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In: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 12:4
-
Journal article (peer-reviewed)abstract
- The Multi-Grid detector technology has evolved from the proof-of-principle and characterisation stages. Here we report on the performance of the Multi-Grid detector, the MG.CNCS prototype, which has been installed and tested at the Cold Neutron Chopper Spectrometer, CNCS at SNS. This has allowed a side-by-side comparison to the performance of 3He detectors on an operational instrument. The demonstrator has an active area of 0.2 m2. It is specifically tailored to the specifications of CNCS. The detector was installed in June 2016 and has operated since then, collecting neutron scattering data in parallel to the He-3 detectors of CNCS. In this paper, we present a comprehensive analysis of this data, in particular on instrument energy resolution, rate capability, background and relative efficiency. Stability, gamma-ray and fast neutron sensitivity have also been investigated. The effect of scattering in the detector components has been measured and provides input to comparison for Monte Carlo simulations. All data is presented in comparison to that measured by the 3He detectors simultaneously, showing that all features recorded by one detector are also recorded by the other. The energy resolution matches closely. We find that the Multi-Grid is able to match the data collected by 3He, and see an indication of a considerable advantage in the count rate capability. Based on these results, we are confident that the Multi-Grid detector will be capable of producing high quality scientific data on chopper spectrometers utilising the unprecedented neutron flux of the ESS.
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| 8. |
- deLeon, MJ, et al.
(author)
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Imaging and CSF studies in the preclinical diagnosis of Alzheimer's disease
- 2007
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In: Annals of the New York Academy of Sciences. - : Wiley. - 1749-6632 .- 0077-8923. ; 1097, s. 114-145
-
Research review (peer-reviewed)abstract
- It is widely believed that the path to early and effective treatment for Alzheimer's disease (AD) requires the development of early diagnostic markers that are both sensitive and specific. To this aim, using longitudinal study designs, we and others have examined magnetic resonance imaging (MRI), 2-fluoro-2-deoxy-d-glucose-positron emission tomography (FDG/PET), and cerebrospinal fluid (CSF) biomarkers in cognitively normal elderly (NL) subjects and in patients with mild cognitive impairment (MCI). Such investigations have led to the often replicated findings that structural evidence of hippocampal atrophy as determined by MRI, as well as metabolic evidence from FDG-PET scan of hippocampal damage, predicts the conversion from MCI to AD. In this article we present a growing body of evidence of even earlier diagnosis. Brain pathology can be detected in NL subjects and used to predict future transition to MCI. This prediction is enabled by examinations revealing reduced glucose metabolism in the hippocampal formation (hippocampus and entorhinal cortex [EC]) as well as by the rate of medial temporal lobe atrophy as determined by MRI. However, neither regional atrophy nor glucose metabolism reductions are specific for AD. These measures provide secondary not primary evidence for AD. Consequently, we will also summarize recent efforts to improve the diagnostic specificity by combining imaging with CSF biomarkers and most recently by evaluating amyloid imaging using PET. We conclude that the combined use of conventional imaging, that is MRI or FDG-PET, with selected CSF biomarkers incrementally contributes to the early and specific diagnosis of AD. Moreover, selected combinations of imaging and CSF biomarkers measures are of importance in monitoring the course of AD and thus relevant to evaluating clinical trials.
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| 9. |
- Hambsch, F. -J, et al.
(author)
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Fission Fragment Yield, Cross Section and Prompt Neutron and Gamma Emission Data from Actinide Isotopes
- 2014
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In: Nuclear Data Sheets. - : Elsevier BV. - 0090-3752 .- 1095-9904. ; 119, s. E38-E41
-
Journal article (peer-reviewed)abstract
- Recent experimental investigations on major and minor actinides at the JRC-IRMM are presented. Fission-fragment distributions of isotopes with vibrational resonances in the sub-threshold fission cross section, i. e. U-234,U-238, have been measured. For U-234, the impact of an increased neutron multiplicity for the heavy fragments with higher incident neutron energies has been studied as observed in experiment and also recently theoretically predicted. The impact is found to be noticeable on post-neutron mass yields, which are the relevant quantities for a-priori waste assessments. The fission cross sections for Pu-240,Pu-242 at threshold and in the plateau region are being investigated within the ANDES project. The results show some discrepancies to the ENDF/B-VII. 1 evaluation mainly for Pu-242 around 1 MeV, where the evaluation exhibits a resonance-like structure not observed so clearly in the present work. The requested target accuracy in design studies of innovative reactor concepts like Gen-IV is in the range of a few percent. In order to be able to respond to requests for measurements of prompt neutron and gamma-ray emission in fission JRC-IRMM has also invested in setting up a neutron and gamma-ray detector array. The neutron array is called SCINTIA and has so far been tested with Cf-252(SF). For gamma-ray multiplicity and spectrum measurements of Cf-252(SF) and U-235(n(th), f) lanthanum- and cerium-halide detectors were successfully used.
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| 10. |
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| 11. |
- Lavazais, S, et al.
(author)
-
IRAK4 inhibition dampens pathogenic processes driving inflammatory skin diseases
- 2023
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In: Science translational medicine. - : American Association for the Advancement of Science (AAAS). - 1946-6242 .- 1946-6234. ; 15:683, s. eabj3289-
-
Journal article (peer-reviewed)abstract
- Innate immunity not only shapes the way epithelial barriers interpret environmental cues but also drives adaptive responses. Therefore, modulators of innate immune responses are expected to have high therapeutic potential across immune-mediated inflammatory diseases. IRAK4 is a kinase that integrates signaling downstream of receptors acting at the interface between innate and adaptive immune responses, such as Toll-like receptors (TLRs), interleukin-1R (IL-1R), and IL-18R. Because effects of IRAK4 inhibition are stimulus, cell type, and species dependent, the evaluation of the therapeutic potential of IRAK4 inhibitors requires a highly translational approach. Here, we profiled a selective IRAK4 inhibitor, GLPG2534, in an extensive panel of models of inflammatory skin diseases, translationally expanding evidence from in vitro to in vivo and from mouse to human. In vitro, IRAK4 inhibition resulted in substantial inhibition of TLR and IL-1 responses in dendritic cells, keratinocytes, granulocytes, and T cells but only weakly affected dermal fibroblast responses. Furthermore, disease activity in murine models of skin inflammation (IL-23–, IL-33–, imiquimod-, and MC903-induced) was markedly dampened by IRAK4 inhibition. Last, inhibiting IRAK4 reversed pathogenic molecular signatures in human lesional psoriasis and atopic dermatitis biopsies. Over the variety of models used, IRAK4 inhibition consistently affected central mediators of psoriasis (IL-17A) and atopic dermatitis (IL-4 and IL-13). Overall, our data highlight IRAK4 as a central player in skin inflammatory processes and demonstrate the potential of IRAK4 inhibition as a therapeutic strategy in chronic inflammatory skin diseases.
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| 12. |
- Oberstedt, Andreas, et al.
(author)
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Improved values for the characteristics of prompt-fission gamma-ray spectra from the reaction U-235(n(th), f)
- 2013
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In: Physical Review C. Nuclear Physics. - : American Physical Society. - 0556-2813 .- 1089-490X .- 2469-9985 .- 2469-9993. ; 87:5, s. 051602-
-
Journal article (peer-reviewed)abstract
- In this paper we present results from measurements of prompt gamma rays from the thermal neutron induced fission of U-235. Photons were measured in coincidence with fission fragments with cerium-doped LaCl3 and LaBr3 as well as CeBr3 scintillation detectors, which offer an intriguing combination of excellent timing resolution and good resolving power. The spectra measured with all employed detectors are in excellent agreement with respect to their shapes. Characteristic parameters were extracted for a gamma-energy range from 0.1 to 6.0 MeV and the results obtained with several detectors were averaged. From that, the average emission yield of prompt-fission gamma rays was determined to be (nu) over bar (gamma) = (8.19 +/- 0.11) per fission, the average energy per photon to be epsilon(gamma) = (0.85 +/- 0.02) MeV, and the total energy to be E-gamma,E-tot = (6.92 +/- 0.09) MeV. The uncertainties are much lower than the 7.5% requested for the modeling of advanced nuclear reactor cores. Estimating the influence of gamma rays with energies between 6 and 10 MeV on the values determined in this work revealed a negligible deviation of the order of the found uncertainties.
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| 13. |
- Oberstedt, S., et al.
(author)
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Artificial diamonds as radiation-hard detectors for ultra-fast fission-fragment timing
- 2013
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In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 714, s. 31-37
-
Journal article (peer-reviewed)abstract
- In the framework of the construction of the double time-of-flight spectrometer VERDI, where we aim at measuring pre- and post-neutron masses directly and simultaneously, ultra-fast time pick-up detectors based on artificial diamond material were investigated for the first time with fission fragments from Cf-252 (0.5 MeV/u < E/A < 2 MeV/u). Signal stability under a high radiation fluence was determined up to at least 10(9) fission-fragments/cm(2) together with more than 3.5 x 10(9) neutrons/cm(2) and 3 x 10(10) alpha-particles/cm(2). This fluence is characteristic for fission experiments. The pre-requisite for the observed signal stability is the application of priming of the diamond material with a strong beta-source for about 48 h. The intrinsic timing resolution of a 100 mu m thick polycrystalline CVD diamond detector with a size of 1 x 1 cm(2) was determined to sigma(int) = (283 +/- 41) ps by comparison with Monte-Carlo simulations. Using broadband pre-amplifiers, 4-fold segmented detectors of same total size and with a thickness of 180 mu m show an intrinsic timing resolution of sigma(int) = (106 +/- 21) ps. This is highly competitive with the best micro-channel plate detectors. Due to the limited and batch-dependent charge collection efficiency of poly-crystalline diamond material, the detection efficiency for fission fragments may be smaller than 100%.
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| 14. |
- Oberstedt, S., et al.
(author)
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High-precision prompt-gamma-ray spectral data from the reaction Pu-241(n(th), f)
- 2014
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In: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 90:2, s. Art. no. 024618-
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Journal article (peer-reviewed)abstract
- In this paper we present results from the first high-precision prompt-gamma-ray spectral measurements from the reaction Pu-241(n(th), f). Apart from one recent experiment, no data are reported in the literature for this fissioning system, which motivated a new dedicated experiment. We have measured prompt-fission gamma rays with three cerium-doped LaBr3 (two 5.08 cm x 5.08 cm and one 7.62 cm x 7.62 cm) and one CeBr3 (5.08 cm x 5.08 cm) scintillation detectors, which all exhibit excellent timing and good energy resolution. The average gamma-ray multiplicity was determined to be (nu) over bar (gamma) = (8.21 +/- 0.09) per fission, the average energy to be epsilon(gamma) = (0.78 +/- 0.01) MeV, and the total energy to be E-gamma,E-tot = (6.41 +/- 0.06) MeV as the weighted average from all detectors. Since the results from all detectors are in excellent agreement, and the total released gamma energy is modestly higher than the one in the present evaluated nuclear data files, we suspect that the underestimation of the prompt-gamma heating in nuclear reactors is due to fast-neutron-induced fission on U-238 or rather from fission induced by gamma rays from neutron capture in the construction material.
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| 15. |
- Oberstedt, S., et al.
(author)
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New Prompt Fission gamma-ray Data in Response to the OECD/NEA High Priority Request
- 2014
-
In: Nuclear Data Sheets. - : Elsevier BV. - 0090-3752 .- 1095-9904. ; 119, s. E225-E228
-
Journal article (peer-reviewed)abstract
- In this paper we report about new prompt fission gamma-ray measurements, which we have performed with highly efficient gamma-ray detectors based on lanthanide-halide crystals, aiming at very fast timing in conjunction with a good energy resolution. About four decades after the experiments were performed, whose results are still used for current evaluations, we present new spectral prompt fission gamma-ray data from the reactions Cf-252(SF) and U-235(n(th),f). Based on our new findings we recommend to replace the current ENDF/B-VII. 1 evaluation for Cf-252(SF) and U-235(n(th),f) as well as to perform new measurements for U-238(n,f) and Pu-241(n,f).
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| 16. |
- Piscitelli, F., et al.
(author)
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The Multi-Blade Boron-10-based neutron detector for high intensity neutron reflectometry at ESS
- 2017
-
In: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 12:3
-
Journal article (peer-reviewed)abstract
- The Multi-Blade is a Boron-10-based gaseous detector introduced to face the challenge arising in neutron reflectometry at pulsed neutron sources. Neutron reflectometers are the most challenging instruments in terms of instantaneous counting rate and spatial resolution. This detector has been designed to cope with the requirements set for the reflectometers at the upcoming European Spallation Source (ESS) in Sweden. Based on previous results obtained at the Institut Laue-Langevin (ILL) in France, an improved demonstrator has been built at ESS and tested at the Budapest Neutron Centre (BNC) in Hungary and at the Source Testing Facility (STF) at the Lund University in Sweden. A detailed description of the detector and the results of the tests are discussed in this manuscript.
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| 17. |
- Salvador-Castiñeira, P., et al.
(author)
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Neutron-induced fission cross section of Pu 240 from 0.5 MeV to 3 MeV
- 2015
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In: Physical Review C. Nuclear Physics. - : American Physical Society (APS). - 0556-2813 .- 1089-490X. ; 92:1
-
Journal article (peer-reviewed)abstract
- Pu240 has recently been pointed out by a sensitivity study of the Organization for Economic Cooperation and Development (OECD) Nuclear Energy Agency (NEA) to be one of the isotopes whose fission cross section lacks accuracy to meet the upcoming needs for the future generation of nuclear power plants (GEN-IV). In the High Priority Request List (HPRL) of the OECD, it is suggested that the knowledge of the Pu240(n,f) cross section should be improved to an accuracy within 1-3 %, compared to the present 5%. A measurement of the Pu240 cross section has been performed at the Van de Graaff accelerator of the Joint Research Center (JRC) Institute for Reference Materials and Measurements (IRMM) using quasi-monoenergetic neutrons in the energy range from 0.5 MeV to 3 MeV. A twin Frisch-grid ionization chamber (TFGIC) has been used in a back-to-back configuration as fission fragment detector. The Pu240(n,f) cross section has been normalized to three different isotopes: Np237(n,f), 235U(n,f), and 238U(n,f). Additionally, the secondary standard reactions were benchmarked through measurements against the primary standard reaction 235U(n,f) in the same geometry. A comprehensive study of the corrections applied to the data and the associated uncertainties is given. The results obtained are in agreement with previous experimental data at the threshold region. For neutron energies higher than 1 MeV, the results of this experiment are slightly lower than the ENDF/B-VII.1 evaluation, but in agreement with the experiments of Laptev et al. (2004) as well as Staples and Morley (1998).
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| 18. |
- Salvador-Castiñeira, P., et al.
(author)
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Neutron-induced fission cross sections of Pu 242 from 0.3 MeV to 3 MeV
- 2015
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In: Physical Review C. Nuclear Physics. - : American Physical Society. - 0556-2813 .- 1089-490X. ; 92:4
-
Journal article (peer-reviewed)abstract
- The majority of the next generation of nuclear power plants (GEN-IV) will work in the fast-neutron-energy region, as opposed to present day thermal reactors. This leads to new and more accurate nuclear-data needs for some minor actinides and structural materials. Following those upcoming demands, the Organisation for Economic Cooperation and Development Nuclear Energy Agency performed a sensitivity study. Based on the latter, an improvement in accuracy from the present 20% to 5% is required for the Pu242(n,f) cross section. Within the same project both the Pu240(n,f) cross section and the Pu242(n,f) cross section were measured at the Van de Graaff accelerator of the Joint Research Centre at the Institute for Reference Materials and Measurements, where quasimonoenergetic neutrons were produced in an energy range from 0.3 MeV up to 3 MeV. A twin Frisch-grid ionization chamber has been used in a back-to-back configuration as fission-fragment detector. The Pu242(n,f) cross section has been normalized to three different isotopes: Np237(n,f), U235(n,f), and U238(n,f). A comprehensive study of the corrections applied to the data and the uncertainties associated is given. The results obtained are in agreement with previous experimental data at the threshold region up to 0.8 MeV. The resonance-like structure at 0.8 to 1.1 MeV, visible in the evaluations and in most previous experimental values, was not reproduced with the same intensity in this experiment. For neutron energies higher than 1.1 MeV, the results of this experiment are slightly lower than the Evaluated Nuclear Data File/B-VII.1 evaluation but in agreement with the experiment of Tovesson et al. (2009) as well as Staples and Morley (1998). Finally, for energies above 1.5 MeV, the results show consistency with the present evaluations.
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| 19. |
- Schouppe, D., et al.
(author)
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Geographic variation in floral traits and the capacity of autonomous selfing across allopatric and sympatric populations of two closely related Centaurium species
- 2017
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In: Scientific Reports. - 2045-2322. ; 7
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Journal article (peer-reviewed)abstract
- Floral traits and the relative contribution of autonomous selfing to total seed set varies geographically and is often driven by the availability and abundance of suitable pollinators and/or the presence of co-flowering relatives. In the latter case, competition for pollinator services and costs of hybridization can select for floral traits that reduce interspecific gene flow and contribute to prezygotic isolation, potentially leading to geographic variation in floral divergence between allopatric and sympatric populations. In this study, we investigated variation in floral traits and its implications on the capacity of autonomous selfing in both allopatric and sympatric populations of two closely related Centaurium species (Gentianaceae) across two distinct geographic regions (UK and mainland Europe). Although the magnitude and direction of floral differentiation varied between regions, sympatric populations were always significantly more divergent in floral traits and the capacity to self autonomously than allopatric populations. These results indicate that mating systems can vary substantially within a species and that the joint occurrence of plant species can have a major impact on floral morphology and capacity of autonomous selfing, most likely as a way to reduce the probability of interspecific interference.
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