2,174 research outputs found
Measurement of the Lifetime and Λ Separation Energy of _{Λ}^{3}H
No full textThe most precise measurements to date of the _{Λ}^{3}H lifetime τ and Λ separation energy B_{Λ} are obtained using the data sample of Pb-Pb collisions at sqrt[s_{NN}]=5.02 TeV collected by ALICE at the LHC. The _{Λ}^{3}H is reconstructed via its charged two-body mesonic decay channel (_{Λ}^{3}H→^{3}He+π^{-} and the charge-conjugate process). The measured values τ=[253±11(stat)±6(syst)] ps and B_{Λ}=[102±63(stat)±67(syst)] keV are compatible with predictions from effective field theories and confirm that the _{Λ}^{3}H structure is consistent with a weakly bound system
3ΛH and 3Λ¯H‾ production in Pb–Pb collisions at √sNN = 2.76 TeV
No full textThe production of the hypertriton nuclei 3
H and 3
¯ H has been measured for the first time in Pb–Pb
collisions at √sNN = 2.76 TeV with the ALICE experiment at LHC. The pT-integrated 3
H yield in one
unity of rapidity, dN/dy × B.R.
3
H→3He,π− = (3.86 ± 0.77(stat.) ± 0.68(syst.)) × 10−5 in the 0–10% most
central collisions, is consistent with the predictions from a statistical thermal model using the same
temperature as for the light hadrons. The coalescence parameter B3 shows a dependence on the
transverse momentum, similar to the B2 of deuterons and the B3 of 3He nuclei. The ratio of yields
S3 = 3
H/(3He×/p) was measured to be S3 = 0.60±0.13(stat.)±0.21(syst.) in 0–10% centrality events;
this value is compared to different theoretical models. The measured S3 is compatible with thermal
model predictions. The measured 3
H lifetime, τ = 181+54
−39(stat.) ± 33(syst.) ps is in agreement within 1σ
with the world average value.peerReviewe
Spatial and temporal determinants of samango monkey (Cercopithecus mitis erythrarchus) resource acquisition and predation avoidance behaviour
No full textFood acquisition and predator avoidance are principal components of the survival strategies of all primates. However, for primates, maximising food acquisition whilst minimising predation risk is often impossible. This leads to the existence of the foraging/risk trade-off, a mechanism fundamental in shaping life histories, species interactions and ultimately community assemblage. The principal aim of this study was to investigate how samango monkeys (Cercopithecus mitis erythrarchus) strategically balance the foraging/risk trade-off when exposed to spatially and temporally varying resources and risk.
Data were collected on a habituated group of samango monkeys over a 12 months observational period at the Lajuma Environmental Research Centre, South Africa. The focal group are part of a population near the southerly limit of the most southerly ranging African, primarily arboreal, monkey species. A biogeographical approach was also used, utilising ecological data from 12 different populations of C. mitis from a number of field sites across the species’ distribution.
Cold, dry winter periods were associated with increased time spent feeding and decreased in time spent resting. During winter months the samangos supplement their diet with foliar material, most likely due to the increased energetic requirements of maintaining body temperature. On a geographical scale, southern populations of samango have significantly more fruit in their diet than their more equatorial relations; whilst the opposite pattern is apparent involving the amount of animal matter consumed. On a spatial scale resources appear to be less important in determining samango ranging behaviour than the risk of predation. The study group actively avoid areas of perceived eagle predation risk, even though resources, such as food, are available in those areas. Similarly, the samangos increase time spent vigilant when in areas of high perceived eagle predation risk, but environmental factors such as visibility or food availability have little effect on vigilance.
The findings of this study indicate that a population at the edge of their species’ ecological tolerance are forced to considerably adapt behaviourally to seasonally and spatially varying resources and risk. In particular, great effort is put into avoiding predation risk; by avoiding high risk areas and maintaining an adequate level of vigilance. All of this must be achieved whilst combating rival groups and maintaining a territory, ensuring adequate food can be foraged and ensuring the successful raising of the next generation
Production of (anti-)He-3 and (anti-)H-3 in p-Pb collisions at root s(NN)=5.02 TeV
No full textThe transverse momentum (p(T)) differential yields of (anti-)He-3 and (anti-)H-3 measured in p-Pb collisions at root s(NN) = 5.02 TeV with ALICE at the Large Hadron Collider (LHC) are presented. The ratios of the p(T)-integrated yields of (anti-)He-3 and (anti-)H-3 to the proton yields are reported, as well as the pT dependence of the coalescence parameters B-3 for (anti-)He-3 and (anti-)H-3. For (anti-)He-3, the results obtained in four classes of the mean charged-particle multiplicity density are also discussed. These results are compared to predictions from a canonical statistical hadronization model and coalescence approaches. An upper limit on the total yield of (4)(He) over bar is determined
Multi-wavelength observations of H 2356-309
No full textAIMS: The properties of the broad-band emission from the high-frequency peaked BL Lac H 2356-309 (z=0.165) are investigated. METHODS: Very High Energy (VHE; E > 100 GeV) observations of H 2356-309 were performed with the High Energy Stereoscopic System (HESS) from 2004 through 2007. Simultaneous optical/UV and X-ray observations were made with the XMM-Newton satellite on June 12/13 and June 14/15, 2005. NRT radio observations were also contemporaneously performed in 2005. ATOM optical monitoring observations were also made in 2007. RESULTS: A strong VHE signal, ~13 sigma total, was detected by HESS after the four years HESS observations (116.8 hrs live time). The integral flux above 240 GeV is I(>240 GeV) = (3.06 +- 0.26 {stat} +- 0.61 {syst}) x 10^{-12} cm^{-2} s^{-1}, corresponding to ~1.6% of the flux observed from the Crab Nebula. A time-averaged energy spectrum is measured from 200 GeV to 2 TeV and is characterized by a power law (photon index of Gamma = 3.06 +- 0.15 {stat} +- 0.10 {syst}). Significant small-amplitude variations in the VHE flux from H 2356-309 are seen on time scales of months and years, but not on shorter time scales. No evidence for any variations in the VHE spectral slope are found within these data. The XMM-Newton X-ray measurements show a historically low X-ray state, characterized by a hard, broken-power-law spectrum on both nights. CONCLUSIONS: The broad-band spectral energy distribution (SED) of the blazar can be adequately fit using a simple one-zone synchrotron self-Compton (SSC) model. In the SSC scenario, higher VHE fluxes could be expected in the future since the observed X-ray flux is at a historically low level.A. Abramowski...B. Nicholas...G. Rowell...and H.-S. Zechlin...et al., and the HESS Collaboratio
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No full textMeasuring stress experienced by wild mammals is increasingly important in the context of human-induced rapid environmental change and initiatives to mitigate human-wildlife conflicts. Glucocorticoids (GC), such as cortisol, mediate responses by promoting physiological adjustments during environmental perturbations. Measuring cortisol is a popular technique; however, this often reveals only recent short-term stress such as that incurred by restraining the animal to sample blood, corrupting the veracity of this approach. Here we present a protocol using claw cortisol, compared with hair cortisol, as a long-term stress bio-indicator, which circumvents this constraint, where claw tissue archives the individual's GC concentration over preceding weeks. We then correlate our findings against detailed knowledge of European badger life history stressors. Based on a solid-phase extraction method, we assessed how claw cortisol concentrations related to season and badger sex, age and body-condition using a combination of generalized linear mixed models (GLMM) (n = 668 samples from 273 unique individuals) followed by finer scale mixed models for repeated measures (MMRM) (n = 152 re-captured individuals). Claw and hair cortisol assays achieved high accuracy, precision and repeatability, with similar sensitivity. The top GLMM model for claw cortisol included age, sex, season and the sex*season interaction. Overall, claw cortisol levels were significantly higher among males than females, but strongly influenced by season, where females had higher levels than males in autumn. The top fine scale MMRM model included sex, age and body condition, with claw cortisol significantly higher in males, older and thinner individuals. Hair cortisol was more variable than claw; nevertheless, there was a positive correlation after removing 34 outliers. We discuss strong support for these stress-related claw cortisol patterns from previous studies of badger biology. Given the potential of this technique, we conclude that it has broad application in conservation biology
H-3(Lambda) and (3)((Lambda)over-bar)(H)over-bar lifetime measurement in Pb-Pb collisions at root s(NN)=5.02 TeV via two-body decay
No full textAn improved value for the lifetime of the (anti-)hypertriton has been obtained using the data sample of Pb-Pb collisions at root s(NN) = 5.02 TeV collected by the ALICE experiment at the LHC. The (anti-)hypertriton has been reconstructed via its charged two-body mesonic decay channel and the lifetime has been determined from an exponential fit to the dN/d(ct) spectrum. The measured value, tau = 242(-38)(+34) (stat.) +/- 17 (syst.) ps, is compatible with representative theoretical predictions, thus contributing to the solution of the longstanding hypertriton lifetime puzzle. (C) 2019 The Author. Published by Elsevier B.V
Measurement of production in PbPb collisions at = 5.02 TeV
No full textThe first measurement of and differential production with respect to transverse momentum and centrality in PbPb collisions at ~TeV is presented. The has been reconstructed via its two-charged-body decay channel, i.e., . A Blast-Wave model fit of the -differential spectra of all nuclear species measured by the ALICE collaboration suggests that the kinetic freeze-out surface is consistent with that of other nuclei. The ratio between the integrated yields of and is compared to predictions from the statistical hadronisation model and the coalescence model, with the latter being favoured by the presented measurements.The first measurement of HΛ3 and H‾Λ‾3 differential production with respect to transverse momentum and centrality in Pb–Pb collisions at sNN=5.02 TeV is presented. The HΛ3 has been reconstructed via its two-charged-body decay channel, i.e., HΛ3→3He+π−. A Blast-Wave model fit of the pT-differential spectra of all nuclear species measured by the ALICE collaboration suggests that the HΛ3 kinetic freeze-out surface is consistent with that of other nuclei. The ratio between the integrated yields of HΛ3 and He3 is compared to predictions from the statistical hadronisation model and the coalescence model, with the latter being favoured by the presented measurements.The first measurement of and differential production with respect to transverse momentum and centrality in PbPb collisions at ~TeV is presented. The has been reconstructed via its two-charged-body decay channel, i.e., . A Blast-Wave model fit of the -differential spectra of all nuclear species measured by the ALICE collaboration suggests that the kinetic freeze-out surface is consistent with that of other nuclei. The ratio between the integrated yields of and is compared to predictions from the statistical hadronisation model and the coalescence model, with the latter being favoured by the presented measurements
Measurement of production in Pb-Pb collisions at = 5.02 TeV
No full textInternational audienceThe first measurement of and differential production with respect to transverse momentum and centrality in PbPb collisions at ~TeV is presented. The has been reconstructed via its two-charged-body decay channel, i.e., . A Blast-Wave model fit of the -differential spectra of all nuclear species measured by the ALICE collaboration suggests that the kinetic freeze-out surface is consistent with that of other nuclei. The ratio between the integrated yields of and is compared to predictions from the statistical hadronisation model and the coalescence model, with the latter being favoured by the presented measurements
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