Big bang nucleosynthesis: Present status Cyburt, Richard H.; Fields, Brian D.; Olive, Keith A. ...
Reviews of modern physics,
02/2016, Letnik:
88, Številka:
1
Journal Article
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Big bang nucleosynthesis (BBN) describes the production of the lightest nuclides via a dynamic interplay among the four fundamental forces during the first seconds of cosmic time. A brief overview of ...the essentials of this physics is given, and new calculations presented of light-element abundances through Li6 and Li7, with updated nuclear reactions and uncertainties including those in the neutron lifetime. Fits are provided for these results as a function of baryon density and of the number of neutrino flavors N?. Recent developments are reviewed in BBN, particularly new, precision Planck cosmic microwave background (CMB) measurements that now probe the baryon density, helium content, and the effective number of degrees of freedom Neff. These measurements allow for a tight test of BBN and cosmology using CMB data alone. Our likelihood analysis convolves the 2015 Planck data chains with our BBN output and observational data. This paper concludes with a look at future directions including key nuclear reactions, astronomical observations, and theoretical issues.
Supernova triggers for end-Devonian extinctions Fields, Brian D.; Melott, Adrian L.; Ellis, John ...
Proceedings of the National Academy of Sciences - PNAS,
09/2020, Letnik:
117, Številka:
35
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The Late Devonian was a protracted period of low speciation resulting in biodiversity decline, culminating in extinction events near the Devonian–Carboniferous boundary. Recent evidence indicates ...that the final extinction event may have coincided with a dramatic drop in stratospheric ozone, possibly due to a global temperature rise. Here we study an alternative possible cause for the postulated ozone drop: a nearby supernova explosion that could inflict damage by accelerating cosmic rays that can deliver ionizing radiation for up to ∼ 100 ky. We therefore propose that the end-Devonian extinctions were triggered by supernova explosions at ∼ 20 pc, somewhat beyond the “kill distance” that would have precipitated a full mass extinction. Such nearby supernovae are likely due to core collapses of massive stars; these are concentrated in the thin Galactic disk where the Sun resides. Detecting either of the long-lived radioisotopes 146Sm or 244Pu in one or more end-Devonian extinction strata would confirm a supernova origin, point to the core-collapse explosion of a massive star, and probe supernova nucleosynthesis. Other possible tests of the supernova hypothesis are discussed.
Preeclampsia and cognitive impairment later in life Fields, Julie A., PhD; Garovic, Vesna D., MD; Mielke, Michelle M., PhD ...
American journal of obstetrics and gynecology,
07/2017, Letnik:
217, Številka:
1
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Background Hypertension is a risk factor for cerebrovascular disease and cognitive impairment. Women with hypertensive episodes during pregnancy report variable neurocognitive changes within the ...first decade following the affected pregnancy. However, long-term follow-up of these women into their postmenopausal years has not been conducted. Objective The aim of this study was to examine whether women with a history of preeclampsia were at increased risk of cognitive decline 35-40 years after the affected pregnancy. Study Design Women were identified and recruited through the medical linkage, population-based Rochester Epidemiologic Project. Forty women with a history of preeclampsia were age- and parity-matched to 40 women with a history of normotensive pregnancy. All women underwent comprehensive neuropsychological assessment and completed self-report inventories measuring mood, ie, depression, anxiety, and other symptoms related to emotional state. Scores were compared between groups. In addition, individual cognitive scores were examined by neuropsychologists and a neurologist blinded to pregnancy status, and a clinical consensus diagnosis of normal, mild cognitive impairment, or dementia for each participant was conferred. Results Age at time of consent did not differ between preeclampsia (59.2 range 50.9-71.5 years) and normotensive (59.6 range 52.1-72.2 years) groups, nor did time from index pregnancy (34.9 range 32.0-47.2 vs 34.5 range 32.0-46.4 years, respectively). There were no statistically significant differences in raw scores on tests of cognition and mood between women with histories of preeclampsia compared to women with histories of normotensive pregnancy. However, a consensus diagnosis of mild cognitive impairment or dementia trended toward greater frequency in women with histories of preeclampsia compared to those with normotensive pregnancies (20% vs 8%, P = .10) and affected more domains among the preeclampsia group ( P = .03), most strongly related to executive dysfunction ( d = 1.96) and verbal list learning impairment ( d = 1.93). Conclusion These findings suggest a trend for women with a history of preeclampsia to exhibit more cognitive impairment later in life than those with a history of normotensive pregnancy. Furthermore, the pattern of cognitive changes is consistent with that observed with vascular disease/white matter pathology.
Measurements of deuterium4 in the distant Universe offer further crucial information, because the ratio of the abundance of deuterium to that of hydrogen depends sensitively on the cosmic density of ...'baryonic' matter - ordinary matter that consists of neutrons and protons, essentially anything in the periodic table. ...the measured reaction rate is higher than the value obtained from the previous sparse experimental data at the relevant particle energies, but notably falls below the value that was predicted from the theoretical calculations7. The Universe could thus become the 'poor person's accelerator': astronomical observations will allow us to glean information about the exotic physics at play during its earliest moments. ...because BBN models tell us that ordinary matter represents 4% of the Universe today, we can infer that the remaining 96% consists of invisible dark matter and dark energy, the identities of which are unknown.
Experiments conducted deep beneath a mountain have provided the most precise measurements yet of a key nuclear reaction that occurred seconds after the Big Bang -- refining our knowledge of the ...constituents of the Universe.
Motivated by recent measurements of deposits of 60Fe on the ocean floor and the lunar surface, we model the transport of dust grains containing 60Fe from a near-Earth (i.e., within 100 pc) supernova ...(SN). We inject dust grains into the environment of an SN remnant (SNR) and trace their trajectories by applying a 1D hydrodynamic description assuming spherical symmetry to describe the plasma dynamics, and we include a rudimentary, 3D magnetic field description to examine its influence on charged dust grains. We assume the interstellar medium (ISM) magnetic fields are turbulent and are amplified by the SNR shock, while the SN wind and ejecta fields are negligible. We examine the various influences on the dust grains within the SNR to determine when/if the dust decouples from the plasma, how much it is sputtered, and where within the SNR the dust grains are located. We find that Rayleigh-Taylor instabilities are important for dust survival, as they influence the location of the SN's reverse shock. We find that the presence of a magnetic field within the shocked ISM material limits the passage of SN dust grains, with the field either reflecting or trapping the grains within the heart of the SNR. These results have important implications for in situ 60Fe measurements and for dust evolution in SNRs generally.
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