Radioisotopes and coastal research in the Great Barrier Reef

Radioisotopes are efficient tracers of coastal processes on various spatial and temporal scales. The isotopes of radon and radium are particularly useful tools to understand hydrological land-ocean interaction because (a) activities of these isotopes are elevated in groundwater by two to three orders of magnitude in comparison with seawater, and (b) these isotopes have half-lives similar to the time scales of coastal hydrological processes such as river and groundwater discharge to the ocean, as well as coastal ocean mixing (or residence) time. The application of these isotopes to studies of land-ocean interaction in the central Great Barrier Reef region (Townsville to Cooktown) is illustrated in three recent studies: (1) coastal mapping of radon on a regional scale improves the understanding of the spatial variability of river and groundwater fluxes to the Great Barrier Reef lagoon; (2) quantification of tidal water exchange between mangrove forests and creeks demonstrates the significant contributions this process makes to water flux and associated geochemical fluxes along tropical coastlines; (3) estimates of coastal water residence time contribute to the understanding of the fate of land-derived solutes in the Great Barrier Reef Lagoon. Concurrent mapping of 222Rn (half-life 3.8 days) and salinity allows an efficient qualitative assessment of land–ocean interaction on various spatial and temporal scales. From shore-parallel transects along the Central Great Barrier Reef coastline with a surface-towed and continuously recording multi-detector system, numerous locations of elevated radon activities can be identified as terrestrially-derived submarine groundwater discharge, riverine sources, and the recirculation of seawater through crustacean burrows in mangrove forests. Variations in the inverse relationship of 222Rn and salinity in different tropical wet seasons reveal ‘timing’ aspects of large-scale freshwater input during the tropical wet season into the lagoon. Subsequently, 222Rn was used together with radium isotopes to quantify the tidal water exchange between a mangrove forest on Hinchinbrook Island and the ocean. Significant export of these radio-nuclides from the forest into a tidal creek indicates continuous tidally-driven circulation through animal burrows in the forest. The forest floor is efficiently flushed, with water flux of about 30 L m-2 day-1 of forest floor, which is equivalent to about 10% of the total burrow volume in the forest per tidal cycle. This work illustrates the physical process which supports export of organic and inorganic matter from mangrove forests to the coastal zone. Importantly, annual average circulation fluxes through mangrove forest floors are of the same order as annual river discharge in the central GBR. Finally, an improved understanding of the fate of land-derived waters is of great importance to current discussions about water quality management in the Great Barrier Reef. The mixing of coastal waters is an important parameter influencing the health of these ecosystems. Time constants associated with the decay of four naturally-occurring isotopes of radium span large time scales; 224Ra, 223Ra, 228Ra and 226Ra have half-lives of 4 days, 11 days, 6 years and 1620 years respectively. The radium quartet has been used to determine time scales of mixing of near-shore water and deep ocean water. This study demonstrates that central GBR water within 20 km of the coast is flushed with outer lagoon water on a timescale of 18–45 days, with the flushing time increasing northward. This difference likely reflects the different reef matrix density in the two zones, affecting exchange with offshore Coral Sea water

High speed video capture for mobile phone cameras

We consider an electromechanical model for the operation of a voice coil motor in a mobile phone camera, with the aim of optimizing how a lens can be moved to a desired focusing motion. Although a methodology is developed for optimizing lens shift, there is some concern about the experimentally-determined model parameters that are at our disposal. Central to the model is the value of the estimated magnetic force constant, Kf: its value determines how far it is actually possible to move lens, but it appears that, from the value given, it would not be possible to shift the lens through the displacements desired. Furthermore, earlier experiments have also estimated the value of the back EMF constant, Kg , to be roughly five times greater than Kf, even though we present two theoretical arguments that show that Kf = Kg: a conclusion supported by readily-available manufacturers’ data

Quantum Anti-Zeno Effect

We demonstrate that near threshold decay processes may be accelerated by repeated measurements. Examples include near threshold photodetachment of an electron from a negative ion, and spontaneous emission in a cavity close to the cutoff frequency, or in a photon band gap material.Comment: 4 pages, 3 figure

Spinodal Decomposition in a Binary Polymer Mixture: Dynamic Self Consistent Field Theory and Monte Carlo Simulations

We investigate how the dynamics of a single chain influences the kinetics of early stage phase separation in a symmetric binary polymer mixture. We consider quenches from the disordered phase into the region of spinodal instability. On a mean field level we approach this problem with two methods: a dynamical extension of the self consistent field theory for Gaussian chains, with the density variables evolving in time, and the method of the external potential dynamics where the effective external fields are propagated in time. Different wave vector dependencies of the kinetic coefficient are taken into account. These early stages of spinodal decomposition are also studied through Monte Carlo simulations employing the bond fluctuation model that maps the chains -- in our case with 64 effective segments -- on a coarse grained lattice. The results obtained through self consistent field calculations and Monte Carlo simulations can be compared because the time, length, and temperature scales are mapped onto each other through the diffusion constant, the chain extension, and the energy of mixing. The quantitative comparison of the relaxation rate of the global structure factor shows that a kinetic coefficient according to the Rouse model gives a much better agreement than a local, i.e. wave vector independent, kinetic factor. Including fluctuations in the self consistent field calculations leads to a shorter time span of spinodal behaviour and a reduction of the relaxation rate for smaller wave vectors and prevents the relaxation rate from becoming negative for larger values of the wave vector. This is also in agreement with the simulation results.Comment: Phys.Rev.E in prin

The Time-Energy Uncertainty Relation

The time energy uncertainty relation has been a controversial issue since the advent of quantum theory, with respect to appropriate formalisation, validity and possible meanings. A comprehensive account of the development of this subject up to the 1980s is provided by a combination of the reviews of Jammer (1974), Bauer and Mello (1978), and Busch (1990). More recent reviews are concerned with different specific aspects of the subject. The purpose of this chapter is to show that different types of time energy uncertainty relation can indeed be deduced in specific contexts, but that there is no unique universal relation that could stand on equal footing with the position-momentum uncertainty relation. To this end, we will survey the various formulations of a time energy uncertainty relation, with a brief assessment of their validity, and along the way we will indicate some new developments that emerged since the 1990s.Comment: 33 pages, Latex. This expanded version (prepared for the 2nd edition of "Time in quantum mechanics") contains minor corrections, new examples and pointers to some additional relevant literatur

Neutron star properties in the quark-meson coupling model

The effects of internal quark structure of baryons on the composition and structure of neutron star matter with hyperons are investigated in the quark-meson coupling (QMC) model. The QMC model is based on mean-field description of nonoverlapping spherical bags bound by self-consistent exchange of scalar and vector mesons. The predictions of this model are compared with quantum hadrodynamic (QHD) model calibrated to reproduce identical nuclear matter saturation properties. By employing a density dependent bag constant through direct coupling to the scalar field, the QMC model is found to exhibit identical properties as QHD near saturation density. Furthermore, this modified QMC model provides well-behaved and continuous solutions at high densities relevant to the core of neutron stars. Two additional strange mesons are introduced which couple only to the strange quark in the QMC model and to the hyperons in the QHD model. The constitution and structure of stars with hyperons in the QMC and QHD models reveal interesting differences. This suggests the importance of quark structure effects in the baryons at high densities.Comment: 28 pages, 10 figures, to appear in Physical Review

Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays

Average charged multiplicities have been measured separately in $b$, $c$ and light quark ($u,d,s$) events from $Z^0$ decays measured in the SLD experiment. Impact parameters of charged tracks were used to select enriched samples of $b$ and light quark events, and reconstructed charmed mesons were used to select $c$ quark events. We measured the charged multiplicities: $\bar{n}_{uds} = 20.21 \pm 0.10 (\rm{stat.})\pm 0.22(\rm{syst.})$, $\bar{n}_{c} = 21.28 \pm 0.46(\rm{stat.}) ^{+0.41}_{-0.36}(\rm{syst.})$ $\bar{n}_{b} = 23.14 \pm 0.10(\rm{stat.}) ^{+0.38}_{-0.37}(\rm{syst.})$, from which we derived the differences between the total average charged multiplicities of $c$ or $b$ quark events and light quark events: $\Delta \bar{n}_c = 1.07 \pm 0.47(\rm{stat.})^{+0.36}_{-0.30}(\rm{syst.})$ and $\Delta \bar{n}_b = 2.93 \pm 0.14(\rm{stat.})^{+0.30}_{-0.29}(\rm{syst.})$. We compared these measurements with those at lower center-of-mass energies and with perturbative QCD predictions. These combined results are in agreement with the QCD expectations and disfavor the hypothesis of flavor-independent fragmentation.Comment: 19 pages LaTex, 4 EPS figures, to appear in Physics Letters