Seasonal reproduction in a fluctuating energy environment: Insolation-driven synchronized broadcast spawning in corals

*Background/Question/Methods:* Colonies of spawning corals reproduce in mass-spawning events, in which polyps within each colony release sperm and eggs for fertilization in the water column, with fertilization occurring only between gametes from different colonies. Participating colonies synchronize their gamete release to a window of a few hours once a year (for the species Acropora digitifera we study experimentally). This remarkable synchrony is essential for successful coral reproduction and thus, maintenance of the coral reef ecosystem that is currently under threat from local and global environmental effects such as pollution, global warming and ocean acidification. The mechanisms determining this tight synchrony in reproduction are not well understood, although several influences have been hypothesized and studied including lunar phase, solar insolation, and influences of temperature and tides. Moreover, most corals are in a symbiotic relationship with photosynthetic algae (Symbiodinium spp.) that live within the host tissue. Experiments supported by detailed bioenergetic modeling of the coral-algae symbiosis have shown that corals receive >90% of their energy needs from these symbionts. We develop a bioenergetic integrate-and-fire model in order to investigate whether annual insolation rhythms can entrain the gametogenetic cycles that produce mature gametes to the appropriate spawning season, since photosynthate is their primary source of energy. We solve the integrate-and-fire bioenergetic model numerically using the Fokker-Planck equation and use analytical tools such as rotation number to study entrainment.

*Results/Conclusions:* In the presence of short-term fluctuations in the energy input, our model shows that a feedback regulatory mechanism is required to achieve coherence of spawning times to within one lunar cycle, in order for subsequent cues such as lunar and diurnal light cycles to unambiguously determine the “correct” night of spawning. Entrainment to the annual insolation cycle is by itself not sufficient to produce the observed coherence in spawning. The feedback mechanism can also provide robustness against population heterogeneity due to genetic and environmental effects. We also discuss how such bioenergetic, stochastic, integrate-and-fire models are also more generally applicable: for example to aquatic insect emergence, synchrony in cell division and masting in trees

Jets or high velocity flows revealed in high-cadence spectrometer and imager co-observations?

We report on active region EUV dynamic events observed simultaneously at high-cadence with SUMER/SoHO and TRACE. Although the features appear in the TRACE Fe ix/x 171A images as jets seen in projection on the solar disk, the SUMER spectral line profiles suggest that the plasma has been driven along a curved large scale magnetic structure, a pre-existing loop. The SUMER observations were carried out in spectral lines covering a large temperature range from 10^4 K to 10^6 K. The spectral analysis revealed that a sudden heating from an energy deposition is followed by a high velocity plasma flow. The Doppler velocities were found to be in the range from 90 to 160 km/s. The heating process has a duration which is below the SUMER exposure time of 25 s while the lifetime of the events is from 5 to 15 min. The additional check on soft X-ray Yohkoh images shows that the features most probably reach 3 MK (X-ray) temperatures. The spectroscopic analysis showed no existence of cold material during the events

Knowledge Sharing of Postgraduates Online: The Intention-Behavior Gap

Knowledge is recognized as a strategic asset and a critical factor for organizational development and competitive advantage in the knowledge economy. All modern organizations should incorporate knowledge management (KM) practices, particularly knowledge sharing behavior (KSB). This research investigates factors influencing KSB based on planned behavior theory and the technology acceptance model in higher education institutes (HEIs) in Jordan. A descriptive analysis approach was applied in the study. A questionnaire was designed and distributed to a sample of 500 respondents across the HEIs. The findings reveal that intentions positively influence MBA students’ KSB but explain less than 50% of KSB; hence an intention-behavior gap is observed. Contextual factors are also identified as significant, namely accreditation and HEI culture. No significant effects of knowledge sharing attitude, subjective norms, perceived ease, course involvement and perceived usefulness are identified. Perceived risk impacted negatively on students’ intentions and KSB. Complex cognitive and behavioral processes between individuals results in knowledge sharing. Combining theoretical foundations permits the identification of those features explaining either intention or behavior, or both. The extent of the intention-behavior gap indicates further research may focus on barriers to converting intentions into actual behavior to support knowledge sharing

Aerobic Stability of Grass Silage Mixed with a Range of Concentrate Feedstuffs at Feed-Out

Mixing supplementary concentrates with silage at feed-out could shorten aerobic stability or increase the rate or extent of aerobic deterioration of silage. This experiment quantified such possible effects by twelve contrasting feedstuffs. Four samples (each 6 kg) of unwilted, precision-chop, well preserved grass silage (216 g dry matter (DM) kg-1 and pH 4.0) were incubated at 20oC for 6 days in polystyrene containers alone or with the addition of 400 g (solid ingredients were milled) of wheat grain, barley grain, maize grain, molasses beet pulp, citrus pulp, molasses, soybean meal, maize gluten, sunflower meal, rapeseed meal, dry distillers grains or sunflower oil. Daily temperature profiles were recorded. Silage alone was unstable under aerobic conditions, with an accumulated daily temperature rise during 5 days aerobiosis of 57oC. None of the added ingredients altered (P\u3e 0.05) any of the indices of aerobic deterioration. For the treatments as listed above, the interval until temperature rise commenced was 2.0, 2.0, 2.0, 2.3, 2.0, 2.0, 2.3, 2.0, 2.3, 2.0, 2.0, 2.0 and 2.0 (s.e.m. 0.11) days, the interval until the maximum temperature was reached was 3.8, 3.5, 4.5, 3.5, 4.0, 3.3, 3.5, 3.8, 4.3, 4.0, 3.8, 3.8 and 3.5 (s.e.m, 0.44) days and the accumulated temperature rise to day 5 was 57, 58, 57, 54, 58, 59, 50, 57, 53, 61, 52, 51 and 58 (s.e.m. 3.1)oC. It is concluded that mixing the above feedstuffs with grass silage did not alter the aerobic deterioration of grass silage

Advances in biomimetic collagen mineralisation and future approaches to bone tissue engineering

With an ageing world population and ~20% of adults in Europe being affected by bone diseases, there is an urgent need to develop advanced regenerative approaches and biomaterials capable to facilitate tissue regeneration while providing an adequate microenvironment for cells to thrive. As the main components of bone are collagen and apatite mineral, scientists in the tissue engineering field have attempted in combining these materials by using different biomimetic approaches to favour bone repair. Still, an ideal bone analogue capable of mimicking the distinct properties (i.e., mechanical properties, degradation rate, porosity, etc.) of cancellous bone is to be developed. This review seeks to sum up the current understanding of bone tissue mineralisation and structure while providing a critical outlook on the existing biomimetic strategies of mineralising collagen for bone tissue engineering applications, highlighting where gaps in knowledge exist

L\'evy walks and scaling in quenched disordered media

We study L\'evy walks in quenched disordered one-dimensional media, with scatterers spaced according to a long-tailed distribution. By analyzing the scaling relations for the random-walk probability and for the resistivity in the equivalent electric problem, we obtain the asymptotic behavior of the mean square displacement as a function of the exponent characterizing the scatterers distribution. We demonstrate that in quenched media different average procedures can display different asymptotic behavior. In particular, we estimate the moments of the displacement averaged over processes starting from scattering sites, in analogy with recent experiments. Our results are compared with numerical simulations, with excellent agreement.Comment: Phys. Rev. E 81, 060101(R) (2010

Exact solution for random walks on the triangular lattice with absorbing boundaries

The problem of a random walk on a finite triangular lattice with a single interior source point and zig-zag absorbing boundaries is solved exactly. This problem has been previously considered intractable.Comment: 10 pages, Latex, IOP macro

Collisional properties of cold spin-polarized nitrogen gas: theory, experiment, and prospects as a sympathetic coolant for trapped atoms and molecules

We report a combined experimental and theoretical study of collision-induced dipolar relaxation in a cold spin-polarized gas of atomic nitrogen (N). We use buffer gas cooling to create trapped samples of 14N and 15N atoms with densities 5+/-2 x 10^{12} cm-3 and measure their magnetic relaxation rates at milli-Kelvin temperatures. Rigorous quantum scattering calculations based on accurate ab initio interaction potentials for the 7Sigma_u electronic state of N2 demonstrate that dipolar relaxation in N + N collisions occurs at a slow rate of ~10^{-13} cm3/s over a wide range of temperatures (1 mK to 1 K) and magnetic fields (10 mT to 2 T). The calculated dipolar relaxation rates are insensitive to small variations of the interaction potential and to the magnitude of the spin-exchange interaction, enabling the accurate calibration of the measured N atom density. We find consistency between the calculated and experimentally determined rates. Our results suggest that N atoms are promising candidates for future experiments on sympathetic cooling of molecules.Comment: 48 pages, 17 figures, 3 table