Absorption line series and autoionization resonance structure analysis in the ultraviolet spectrum of Sr I

Photoelectric spectrometer to measure absorption line series and autoionization resonance in ultraviolet spectrum of strontium vapo

Correlation dynamics between electrons and ions in the fragmentation of D2_2 molecules by short laser pulses

We studied the recollision dynamics between the electrons and D$_2^+$ ions following the tunneling ionization of D$_2$ molecules in an intense short pulse laser field. The returning electron collisionally excites the D$_2^+$ ion to excited electronic states from there D$_2^+$ can dissociate or be further ionized by the laser field, resulting in D$^+$ + D or D$^+$ + D$^+$, respectively. We modeled the fragmentation dynamics and calculated the resulting kinetic energy spectrum of D$^+$ to compare with recent experiments. Since the recollision time is locked to the tunneling ionization time which occurs only within fraction of an optical cycle, the peaks in the D$^+$ kinetic energy spectra provides a measure of the time when the recollision occurs. This collision dynamics forms the basis of the molecular clock where the clock can be read with attosecond precision, as first proposed by Corkum and coworkers. By analyzing each of the elementary processes leading to the fragmentation quantitatively, we identified how the molecular clock is to be read from the measured kinetic energy spectra of D$^+$ and what laser parameters be used in order to measure the clock more accurately.Comment: 13 pages with 14 figure

Accuracy, rationality and specialisation in a generalised model of collective navigation

Animal navigation is a key behavioural process, from localised foraging to global migration. Within groups individuals may improve their navigational accuracy by following those with more experience or knowledge, by pooling information from many directional estimates ("many wrongs"), or some combination of these strategies. Previous agent-based simulations have highlighted that homogeneous leaderless groups can improve their collective navigation accuracy when individuals preferentially copy the movement directions of their neighbours while giving a low weighting to their own navigational knowledge. Meanwhile, other studies have demonstrated how specialised leaders may emerge, and that a small number of such individuals can improve group-level navigation performance. However, in general, these earlier results either lack a full mathematical grounding or do not fully consider the effect of individual self-interest. Here we derive and analyse a mathematically tractable model of collective navigation. We demonstrate that collective navigation is compromised when individuals seek to optimise their own accuracy in both homogeneous groups and those with differing navigational abilities. We further demonstrate how heterogeneous navigational strategies (specialised leaders and followers) may evolve within the model. Our results thus unify different lines of research in collective navigation and highlight the importance of individual selection in determining group composition and performance

Constructing a Stochastic Model of Bumblebee Flights from Experimental Data

PMCID: PMC3592844This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

High temporal resolution sampling reveals reef fish settlement is highly clustered

Coral reef fish larvae settle on reefs predominantly at night around the new-moon phase, after an early developmental period spent in the pelagic environment. Most sampling is conducted across whole nights, and any studies that have examined the frequency of arrival within nights have typically been limited to coarse sampling time scales of 1–5 h. Here, we present results for arrival numbers of fish caught between dusk and midnight from light traps sampled every 15 min at an Indonesian coral reef, providing the finest temporal resolution for this type of study to date. A spatial analysis by distance indices analysis, adapted to temporal data, revealed clustering of reef arrival times for many species, with an increase in catches immediately after dusk dropping off towards midnight. Importantly, the timing of clusters differed among species, indicating that different factors determine the timing of arrival among taxa. Our results support the hypothesis that larval behaviour influences the timing of arrival at a coral reef for different fish species

Copycat dynamics in leaderless animal group navigation

Background: Many animals are known to have improved navigational efficiency when moving together as a social group. One potential mechanism for social group navigation is known as the 'many wrongs principle', where information from many inaccurate compasses is pooled across the group. In order to understand how animal groups may use the many wrongs principle to navigate, it is important to consider how directional information is transferred and shared within the group. Methods: Here we use an individual-based model to explore the information-sharing and copying dynamics of a leaderless animal group navigating towards a target in a virtual environment. We assume that communication and information-sharing is indirect and arises through individuals partially copying the movement direction of their neighbours and weighting this information relative to their individual navigational knowledge. Results: We find that the best group navigation performance occurs when individuals directly copy the direction of movement of a subset of their neighbours while only giving a small (6%) weighting to their individual navigational knowledge. Surprisingly, such a strategy is shown to be highly efficient regardless of the level of individual navigational error. We find there is little relative improvement in navigational efficiency when individuals copy from more than 7 influential neighbours. Conclusions: Our findings suggest that we would expect navigating group-living animals to predominantly copy the movement of others rather than relying on their own navigational knowledge. We discuss our results in the context of individual and group navigation behaviour in animals

Neutron skin of 208^{208}Pb from Coherent Pion Photoproduction

Information on the size and shape of the neutron skin on $^{208}$Pb has been extracted from coherent pion photoproduction cross sections measured using the Crystal Ball together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections the half-height radius and diffuseness of the neutron distribution are found to be 6.70$\pm 0.03(stat)$ fm and 0.55$\pm 0.01(stat)$$^{+0.02}_{-0.03}(sys)$ fm respectively, corresponding to a neutron skin thickness $\Delta r_{np}$=0.15$\pm 0.03(stat)$$^{+0.01}_{-0.03}(sys)$ fm. The results give the first successful extraction of a neutron skin with an electromagnetic probe and indicate the skin of $^{208}$Pb has a halo character. The measurement provides valuable new constraints on both the structure of nuclei and the equation of state for neutron-rich matter.Comment: 4 figures 5 pages. Version submitted to journal. Includes additional studies of systematic effects in the extracted diffuseness, which led to a small increase in the quoted systematic error. These additional studies are discussed in the revised manuscript. Also includes minor editorial improvements to the tex

Determination of the Dalitz plot parameter alpha for the decay eta->3pi^0 with the Crystal Ball at MAMI-B

A precise measurement of the Dalitz plot parameter, alpha, for the eta->3pi^0 decay is presented. The experiment was performed with the Crystal Ball and TAPS large acceptance photon detectors at the tagged photon beam facility of the MAMI-B electron accelerator in Mainz. High statistics of 1.8*10^6 eta->3pi^0 events were obtained, giving the result alpha = -0.032 +/- 0.002(stat) +/- 0.002(syst).Comment: 9 pages, 6 figures, published in the online-first section of EPJ A, included changes referees asked for, added DO