Impact of the commercial fishery on the population of bait shrimp (Penaeus spp.) in Biscayne Bay, 1986

Monthly population size of bait shrimp in the Bay was estimated from December 1984 to July 1985. Growth rates for male and female P. duorarum showed that pink shrimp exhibit a mean residence time in the nursery area (Biscayne Bay) of approximately 21 weeks. Monthly mortality rates were determined for each sex of pink shrimp. It was estimated that 23% and 26% of the male and female monthly population size, respectively, was absorbed by both the fishery and ecosystem monthly. Monthly proportion of the standing stock expected to die exclusively through fishing was 6.5% and 6.0% for males and females respectively. Estimates of emigration rates showed that approximately 4.0% of the population was lost from the Bay system each month. This surplus production was about 50% of the average monthly catch by the fleet. Fishing mortality represents only 8 - 9% of the losses to the shrimp population. The biggest source of loss is emigration, suggesting that most shrimp beyond the size at recruitment (to the fishery) are not utilized for food while in the Bay. Thus, it appears that the direct impact of the fishery on the bait shrimp population is relatively small. (PDF contains 46 pages

Hunting the Scalar Glueball: Prospects for BES III

The search for the ground state scalar glueball G_0 is reviewed. Spin zero glueballs will have unique dynamical properties if the amplitude is suppressed by chiral symmetry, as it is to all orders in perturbation theory: for instance, mixing of G_0 with \bar qq mesons would be suppressed, radiative J/psi decay would be a filter for new physics in the spin zero channel, and the decay G_0 \to \bar KK could be enhanced relative to G_0 \to \pi \pi. These properties are consistent with the identification of f_0(1710) as the largely unmixed ground state scalar glueball, while recent BES data implies that f_0(1500) does not contain the dominant glueball admixture. Three hypotheses are discussed: that G_0 is 1) predominantly f_0(1500) or 2) predominantly f_0(1710) or 3) is strongly mixed between f_0(1500) and f_0(1710).Comment: 10 pages, talk presented at CHARM 2006, Beijing IHEP, June 5-7, 2006, to be published in the proceeding

A Morning Coffee in Melbourne: Discussing the Contentious Spaces of Media Practice Research

This is a conversation that took place between three practitioner-academics one morning in Melbourne. All three work and practice in the field of the moving image: from screen production to audiovisual installation to screenwriting. Our conversation is underpinned by previous research we have undertaken in this field, namely the launching of a moving image journal, Sightlines, and a companion journal article on the process of setting it up, which focussed on the issues presented when trying to establish peer review protocols and guidelines for moving image works

C, N, O Abundances in the Most Metal-Poor Damped Lyman alpha Systems

This study focuses on some of the most metal-poor damped Lyman alpha absorbers known in the spectra of high redshift QSOs, using new and archival observations obtained with UV-sensitive echelle spectrographs on the Keck and VLT telescopes. The weakness and simple velocity structure of the absorption lines in these systems allows us to measure the abundances of several elements, and in particular those of C, N, and O, a group that is difficult to study in DLAs of more typical metallicities. We find that when the oxygen abundance is less than about 1/100 of solar, the C/O ratio in high redshift DLAs and sub-DLAs matches that of halo stars of similar metallicity and shows higher values than expected from galactic chemical evolution models based on conventional stellar yields. Furthermore, there are indications that at these low metallicities the N/O ratio may also be above simple expectations and may exhibit a minimum value, as proposed by Centurion and her collaborators in 2003. Both results can be interpreted as evidence for enhanced production of C and N by massive stars in the first few episodes of star formation, in our Galaxy and in the distant proto-galaxies seen as QSO absorbers. The higher stellar yields implied may have an origin in stellar rotation which promotes mixing in the stars' interiors, as considered in some recent model calculations. We briefly discuss the relevance of these results to current ideas on the origin of metals in the intergalactic medium and the universality of the stellar initial mass function.Comment: 17 pages, 9 Figures, Accepted for publication in Monthly Notices of the Royal Astronomical Societ

Proposal for a High-Brightness Pulsed Electron Source

We propose a novel scheme for a high-brightness pulsed electron source, which has the potential for many useful applications in electron microscopy, inverse photo-emission, low energy electron scattering experiments, and electron holography. A description of the proposed scheme is presented

Direct Optical Coupling to an Unoccupied Dirac Surface State in the Topological Insulator Bi2_2Se3_3

We characterize the occupied and unoccupied electronic structure of the topological insulator Bi$_2$Se$_3$ by one-photon and two-photon angle-resolved photoemission spectroscopy and slab band structure calculations. We reveal a second, unoccupied Dirac surface state with similar electronic structure and physical origin to the well-known topological surface state. This state is energetically located 1.5 eV above the conduction band, which permits it to be directly excited by the output of a Ti:Sapphire laser. This discovery demonstrates the feasibility of direct ultrafast optical coupling to a topologically protected, spin-textured surface state.Comment: Accepted to Physical Review Letter

Towards a formal description of foraminiferal assemblage formation in shallow-water environments: Qualitative and quantitative concepts

© 2014 Elsevier B.V. The use of foraminifera in palaeoenvironmental reconstructions (e.g. sea level) may be complicated by processes such as infaunal test production, taphonomic degradation and bioturbation which act to modify contemporary analogue (surface) assemblages during and subsequent to burial. Understanding the palaeoenvironmental significance of these processes is limited by the absence of a clear theoretical description of the mechanics of foraminiferal assemblage formation. A conceptual framework is proposed which describes assemblage formation in terms of the balance of test inputs and losses within a volume of sediment undergoing burial through the upper sedimentary zones of test production, taphonomic processes and bioturbation. A corresponding mathematical model is described and shown to explain empirical dead test distributions in terms of empirically-defined standing crops, sedimentation and mixing rates, together with model estimates of standing crop turnover and/or taphonomic decay rates. This approach provides a quantitative basis for understanding assemblage formation and for comparing assemblage forming processes between species, environments and study sites. Rates of standing crop turnover and taphonomic loss are identified as the primary unknowns in the study of foraminiferal assemblage formation. These multiple unknowns make interpretations of cored data ambiguous, emphasising the need for a detailed and coherent framework of theory and assumptions for understanding the mechanics assemblage formation if interpretations are to be clear and conclusive