Mid-Miocene cooling and the extinction of tundra in continental Antarctica

A major obstacle in understanding the evolution of Cenozoic climate has been the lack of well dated terrestrial evidence from high-latitude, glaciated regions. Here, we report the discovery of exceptionally well preserved fossils of lacustrine and terrestrial organisms from the McMurdo Dry Valleys sector of the Transantarctic Mountains for which we have established a precise radiometric chronology. The fossils, which include diatoms, palynomorphs, mosses, ostracodes, and insects, represent the last vestige of a tundra community that inhabited the mountains before stepped cooling that first brought a full polar climate to Antarctica. Paleoecological analyses, 40Ar/39Ar analyses of associated ash fall, and climate inferences from glaciological modeling together suggest that mean summer temperatures in the region cooled by at least 8°C between 14.07 ± 0.05 Ma and 13.85 ± 0.03 Ma. These results provide novel constraints for the timing and amplitude of middle-Miocene cooling in Antarctica and reveal the ecological legacy of this global climate transition

Remeasurement of the 193 keV resonance in O17(p,α)N14

A recently discovered resonance at 193 keV determines the thermonuclear rates of the O17 +p reactions at temperatures important for the nucleosynthesis in classical novae (T=0.1-0.4 GK). We report on a remeasurement of this resonance in the O17(p,α)N14 reaction by using a different kind of target compared to the previous study. Special emphasis is placed on Monte Carlo simulations of the experiment in order to better understand certain effects that have been disregarded previously. Our measured value of the resonance strength amounts to (ωγ)pα=(1.66±0.17)×10-3 eV, in agreement with the previously reported result. As a byproduct of our study, we find that the inhomogeneity of the foil placed in front of the α-particle detector determines the resolution in the pulse-height spectrum, and thus constrains the signal-to-noise ratio in searches of very weak (p,α) resonances

Measurement of O17(p,γ)F18 between the narrow resonances at Erlab=193 and 519keV

The O17(p,γ)F18 reaction sensitively influences hydrogen burning nucleosynthesis in a number of stellar sites, including classical novae. These thermonuclear explosions, taking place in close binary star systems, produce peak temperatures in the range of T=100-400 MK. Recent results indicate that the thermonuclear rates for this reaction in this particular temperature range are dominated by the direct capture process. We report on the measurement of the O17(p,γ)F18 cross section between the narrow resonances at Erlab=193 and 519keV, where the S factor is expected to vary smoothly with energy. We extract the direct capture contribution from the total cross section and demonstrate that earlier data are inconsistent with our results

Gamow peak in thermonuclear reactions at high temperatures

The Gamow peak represents one of the most important concepts in the study of thermonuclear reactions in stars. It is widely used in order to determine, at a given plasma temperature, the effective stellar energy region in which most charged-particle induced nuclear reactions occur. It is of importance in the design of nuclear astrophysics measurements, including those involving radioactive ion beams, and for the determination of stellar reaction rates. We demonstrate that the Gamow peak concept breaks down under certain conditions if a nuclear reaction proceeds through narrow resonances at elevated temperatures. It is shown that an effective stellar energy window does indeed exist in which most thermonuclear reactions take place at a given temperature, but that this energy window can differ significantly from the commonly used Gamow peak. We expect that these findings are especially important for thermonuclear reactions in the advanced burning stages of massive stars and in explosive stellar environments

Resonance strength in Ne22(p,γ)Na23 from depth profiling in aluminum

A novel method for extracting absolute resonance strengths has been investigated. By implanting Ne22 ions into a thick aluminum backing and simultaneously measuring the Ne22+p and Al27+p reactions, the strength of the Erlab=479 keV resonance in Ne22(p,γ)Na23 was determined to be ωγ=0.524(51) eV. This result has significantly reduced uncertainties compared to earlier work. Our results are important for the absolute normalizations of resonance strengths in the Ne22(p,γ)Na23 hydrogen-burning reaction and in the Ne22+α s-process neutron-source reactions

Thermonuclear reaction rate of O17(p,γ)F18

The O17(p,γ)F18 and O17(p,α)N14 reactions have a profound influence on hydrogen-burning nucleosynthesis in a number of stellar sites, including red giants, asymptotic giant branch (AGB) stars, massive stars, and classical novae. Previously evaluated thermonuclear rates for both reactions carry large uncertainties. We investigated the proton-capture reaction on O17 in the bombarding energy range of Eplab=180-540keV. We observed a previously undiscovered resonance at ERlab=193.2±0.9keV. The resonance strength amounts to (ωγ)pγ=(1.2±0.2)×10-6eV. With this value, the uncertainties of the O17(p,γ)F18 reaction rates are reduced by orders of magnitude in the peak temperature range of classical novae (T=0.1-0.4GK). We also report on a reevaluation of the O17(p,γ)F18 reaction rates at lower temperatures that are pertinent to red giants, AGB stars, or massive stars. The present work establishes the O17(p,γ)F18 reaction rates over a temperature range of T=0.01-1.5GK with statistical uncertainties of 10-50%. The new recommended reaction rates deviate from the previously accepted values by an order of magnitude around T0.2GK and by factors of 2-3 at T<0.1GK

Explosive hydrogen burning of 17O in classical novae

The explosive burning of 17O, which exhibits resonance at E Rlab = 190 keV in the 17O(p, γ) 18F reaction, was analyzed. The resonance strength was about ωγpγ =(1.2∓0.2)×10-6 eV, which revealed that uncertainities in thermonuclear reaction rates were reduced by orders of magnitude at nova temperatures. The uncertainty in 17O(p, α)18F reaction rates was found to be ≅30%. The results show that resonance in thermonuclear reaction reduced uncertainty in galactic synthesis of 17O, the stellar production of 18F, and oxygen isotopic ratios in nova ejecta

Life path analysis: scaling indicates priming effects of social and habitat factors on dispersal distances

1. Movements of many animals along a life-path can be separated into repetitive ones within home ranges and transitions between home ranges. We sought relationships of social and environmental factors with initiation and distance of transition movements in 114 buzzards Buteo buteo that were marked as nestlings with long-life radio tags. 2. Ex-natal dispersal movements of 51 buzzards in autumn were longer than for 30 later in their first year and than 35 extra-natal movements between home ranges after leaving nest areas. In the second and third springs, distances moved from winter focal points by birds that paired were the same or less than for unpaired birds. No post-nuptial movement exceeded 2 km. 3. Initiation of early ex-natal dispersal was enhanced by presence of many sibs, but also by lack of worm-rich loam soils. Distances travelled were greatest for birds from small broods and with relatively little short grass-feeding habitat near the nest. Later movements were generally enhanced by the absence of loam soils and short grassland, especially with abundance of other buzzards and probable poor feeding habitats (heathland, long grass). 4. Buzzards tended to persist in their first autumn where arable land was abundant, but subsequently showed a strong tendency to move from this habitat. 5. Factors that acted most strongly in ½-km buffers round nests, or round subsequent focal points, usually promoted movement compared with factors acting at a larger scale. Strong relationships between movement distances and environmental characteristics in ½-km buffers, especially during early ex-natal dispersal, suggested that buzzards became primed by these factors to travel far. 6. Movements were also farthest for buzzards that had already moved far from their natal nests, perhaps reflecting genetic predisposition, long-term priming or poor habitat beyond the study area

Measurement of the e r c.m. = 138 keV resonance in the 23 Na(p, γ) 24 Mg reaction and the abundance of sodium in AGB stars

Globular clusters represent some of the oldest stellar aggregations in the universe. As such, they are used as testing grounds for theories of stellar evolution and nucleosynthesis. Astronomical observations have shown star-to-star abundance variations in light-mass elements in all galactic globular clusters that are not predicted by standard stellar evolution models. In particular, there exists a pronounced anticorrelation between Na and O in the cluster stars that is not observed in field stars of similar evolutionary state. The abundance of Na is regulated in part by the 23Na+p reaction, which is also a bridge between the NeNa and the MgAl mass regions, but the 23Na(p,γ)24Mg reaction rate is very uncertain for burning temperatures relevant to stars on the red giant and asymptotic giant branches. This uncertainty arises from an expected but unobserved resonance at Erc.m. = 138 keV. The resonance strength upper limit has been determined to be ωγUL(138 keV) ≤5.17×10-9 eV with indications of a signal at the 90% confidence level. New reaction rates have been calculated for the 23Na(p,γ)24Mg and 23Na(p,α)20Ne reactions and the recommended value for the 23Na(p,γ)24Mg rate has been reduced by over an order of magnitude at T9 = 0.07. This will have implications for the processing of material between the NeNa and MgAl mass regions

Development and external validation study of a melanoma risk prediction model incorporating clinically assessed naevi and solar lentigines

Background: Melanoma risk prediction models could be useful for matching preventive interventions to patients’ risk. Objectives: To develop and validate a model for incident first‐primary cutaneous melanoma using clinically assessed risk factors. Methods: We used unconditional logistic regression with backward selection from the Australian Melanoma Family Study (461 cases and 329 controls) in which age, sex and city of recruitment were kept in each step, and we externally validated it using the Leeds Melanoma Case–Control Study (960 cases and 513 controls). Candidate predictors included clinically assessed whole‐body naevi and solar lentigines, and self‐assessed pigmentation phenotype, sun exposure, family history and history of keratinocyte cancer. We evaluated the predictive strength and discrimination of the model risk factors using odds per age‐ and sex‐adjusted SD (OPERA) and the area under curve (AUC), and calibration using the Hosmer–Lemeshow test. Results: The final model included the number of naevi ≥ 2 mm in diameter on the whole body, solar lentigines on the upper back (a six‐level scale), hair colour at age 18 years and personal history of keratinocyte cancer. Naevi was the strongest risk factor; the OPERA was 3·51 [95% confidence interval (CI) 2·71–4·54] in the Australian study and 2·56 (95% CI 2·23–2·95) in the Leeds study. The AUC was 0·79 (95% CI 0·76–0·83) in the Australian study and 0·73 (95% CI 0·70–0·75) in the Leeds study. The Hosmer–Lemeshow test P‐value was 0·30 in the Australian study and < 0·001 in the Leeds study. Conclusions: This model had good discrimination and could be used by clinicians to stratify patients by melanoma risk for the targeting of preventive interventions. What's already known about this topic? Melanoma risk prediction models may be useful in prevention by tailoring interventions to personalized risk levels. For reasons of feasibility, time and cost many melanoma prediction models use self‐assessed risk factors. However, individuals tend to underestimate their naevus numbers. What does this study add? We present a melanoma risk prediction model, which includes clinically‐assessed whole‐body naevi and solar lentigines, and self‐assessed risk factors including pigmentation phenotype and history of keratinocyte cancer. This model performs well on discrimination, the model's ability to distinguish between individuals with and without melanoma, and may assist clinicians to stratify patients by melanoma risk for targeted preventive interventions