The cross section for the pd --> ^3He eta pi0 reaction has been measured at a beam energy of 1450 MeV using the WASA detector at the CELSIUS storage ring and detecting one ^3He and four photons from ...the decays of the two photons. The data indicate that the production mechanism involves the formation of the Delta(1232) isobar. Although the beam energy does not allow the full peak of this resonance to be seen, the invariant masses of all three pairs of final state particles are well reproduced by a phase space Monte Carlo simulation weighted with the p-wave factor of the square of the pi^0 momentum in the ^3Hepi^0 system.
The results from the first kinematically complete measurement of the dd --> 4Hepipi reaction are reported. The aim was to investigate a long standing puzzle regarding the origin of the peculiar ...pipi-invariant mass distributions appearing in double pion production in light ion collisions, the so-called ABC effect. The measurements were performed at the incident deuteron energies of 712 MeV and 1029 MeV, with the WASA detector assembly at CELSIUS in Uppsala, Sweden. We report the observation of a characteristic enhancement at low pipi-invariant mass at 712 MeV, the lowest energy yet. At the higher energy, in addition to confirming previous experimental observations, our results reveal a strong angular dependence of the pions in the overall centre of mass system. The results are qualitatively reproduced by a theoretical model, according to which the ABC effect is described as resulting from a kinematical enhancement in the production of the pion pairs from two parallel and independent NN--> dpi sub-processes.
The ABC effect - a puzzling low-mass enhancement in the \(\pi\pi\) invariant mass spectrum - is well-known from inclusive measurements of two-pion production in nuclear fusion reactions. Here we ...report on first exclusive and kinematically complete measurements of the most basic double pionic fusion reaction \(pn \to d \pi^0\pi^0\) at 1.03 and 1.35 GeV. The measurements, which have been carried out at CELSIUS-WASA, reveal the ABC effect to be a \((\pi\pi)_{I=L=0}\) channel phenomenon associated with both a resonance-like energy dependence in the integral cross section and the formation of a \(\Delta\Delta\) system in the intermediate state. A corresponding simple s-channel resonance ansatz provides a surprisingly good description of the data.
Summary
Wild birds are common reservoirs of Salmonella enterica. Wild birds carrying resistant S. enterica may pose a risk to public health as they can spread the resistant bacteria across large ...spatial scales within a short time. Here, we whole‐genome sequenced 375 S. enterica strains from wild birds collected in 41 U.S. states during 1978–2019 to examine bacterial resistance to antibiotics and heavy metals. We found that Typhimurium was the dominant S. enterica serovar, accounting for 68.3% (256/375) of the bird isolates. Furthermore, the proportions of the isolates identified as multi‐antimicrobial resistant (multi‐AMR: resistant to at least three antimicrobial classes) or multi‐heavy metal resistant (multi‐HMR: resistant to at least three heavy metals) were both 1.87% (7/375). Interestingly, all the multi‐resistant S. enterica (n = 12) were isolated from water birds or raptors; none of them was isolated from songbirds. Plasmid profiling demonstrated that 75% (9/12) of the multi‐resistant strains carried resistance plasmids. Our study indicates that wild birds do not serve as important reservoirs of multi‐resistant S. enterica strains. Nonetheless, continuous surveillance for bacterial resistance in wild birds is necessary because the multi‐resistant isolates identified in this study also showed close genetic relatedness with those from humans and domestic animals.
The production of \(\omega\) mesons in the \(pd \to{}^3\)He\( \omega\) reaction has been studied at two energies near the kinematic threshold, \(T_p=1450\) MeV and \(T_p=1360\) MeV. The differential ...cross section was measured as a function of the \(\omega\) cm angle at both energies over the whole angular range. Whereas the results at 1360 MeV are consistent with isotropy, strong rises are observed near both the forward and backward directions at 1450 MeV. Calculations made using a two-step model with an intermediate pion fail to reproduce the shapes of the measured angular distributions and also underestimate the total cross sections.
The tensor polarisation of omega mesons produced in the pd-->3He+omega reaction has been studied at two energies near threshold. The 3He nuclei were detected in coincidence with the pi0pi+pi- or ...pi0gamma decay products of the omega. In contrast to the case of phi meson production, the omega mesons are found to be unpolarised. This brings into question the applicability of the Okubo-Zweig-Iizuka rule when comparing the production of vector mesons in low energy hadronic reactions.
Salmonella enterica serovar Typhimurium is typically considered a host generalist; however, certain isolates are associated with specific hosts and show genetic features of host adaptation. Here, we ...sequenced 131
Typhimurium isolates from wild birds collected in 30 U.S. states during 1978-2019. We found that isolates from broad taxonomic host groups including passerine birds, water birds (Aequornithes), and larids (gulls and terns) represented three distinct lineages and certain
Typhimurium CRISPR types presented in individual lineages. We also showed that lineages formed by wild bird isolates differed from most isolates originating from domestic animal sources, and that genomes from these lineages substantially improved source attribution of Typhimurium genomes to wild birds by a machine learning classifier. Furthermore, virulence gene signatures that differentiated
Typhimurium from passerines, water birds, and larids were detected. Passerine isolates tended to lack
Typhimurium-specific virulence plasmids. Isolates from the passerine, water bird, and larid lineages had close genetic relatedness with human clinical isolates, including those from a 2021 U.S. outbreak linked to passerine birds. These observations indicate that
Typhimurium from wild birds in the United States are likely host-adapted, and the representative genomic data set examined in this study can improve source prediction and facilitate outbreak investigation.
Within-host evolution of
Typhimurium may lead to pathovars adapted to specific hosts. Here, we report the emergence of disparate avian
Typhimurium lineages with distinct virulence gene signatures. The findings highlight the importance of wild birds as a reservoir for
Typhimurium and contribute to our understanding of the genetic diversity of
Typhimurium from wild birds. Our study indicates that
Typhimurium may have undergone adaptive evolution within wild birds in the United States. The representative
Typhimurium genomes from wild birds, together with the virulence gene signatures identified in these bird isolates, are valuable for
Typhimurium source attribution and epidemiological surveillance.
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