Seagrass habitats of northeast Australia: models of key processes and controls

An extensive and diverse assemblage of seagrass habitats exists along the tropical and subtropical coastline of north east Australia and the associated Great Barrier Reef. In their natural state, these habitats are characterised by very low nutrient concentrations and are primarily nitrogen limited. Summer rainfall and tropical storms/cyclones lead to large flows of sediment-laden fresh water. Macro grazers, dugongs (Dugong dugon) and green sea turtles (Chelonia mydas) are an important feature in structuring tropical Australian seagrass communities. In general, all seagrass habitats in north east Australia are influenced by high disturbance and are both spatially and temporally variable. This paper classifies the diversity into four habitat types and proposes the main limiting factor for each habitat. The major processes that categorise each habitat are described and significant threats or gaps in understanding are identified. Four broad categories of seagrass habitat are defined as 'River estuaries', 'Coastal', 'Deep water' and 'Reef', and the dominant controlling factors are terrigenous runoff, physical disturbance, low light and low nutrients, respectively. Generic concepts of seagrass ecology and habitat function have often been found inappropriate to the diverse range of seagrass habitats in north east Australian waters. The classification and models developed here explain differences in habitats by identifying ecological functions and potential response to impacts in each habitat. This understanding will help to better focus seagrass management and research in tropical habitats

Studies of multiplicity in relativistic heavy-ion collisions

In this talk I'll review the present status of charged particle multiplicity measurements from heavy-ion collisions. The characteristic features of multiplicity distributions obtained in Au+Au collisions will be discussed in terms of collision centrality and energy and compared to those of p+p collisions. Multiplicity measurements of d+Au collisions at 200 GeV nucleon-nucleon center-of-mass energy will also be discussed. The results will be compared to various theoretical models and simple scaling properties of the data will be identified.Comment: "Focus on Multiplicity" Internationsl Workshop on Particle Multiplicity in Relativistic Heavy Ion Collisions, Bari, Italy, June 17-19, 2003, 16 pages, 15 figure

Bose-Einstein source of intermittency in hadronic interactions

The multi-particle Bose-Einstein correlations are the source of ''intermittency'' in high energy hadronic collisions. The power-law like increase of factorial moments with decreasing bin size was obtained by complete event weighing technique with gaussian approximation of space-time particle emitting source shape. The value of source size parameter was found to be higher than the common one fitted with the help of the standard Handbury Brown-Twiss procedure.Comment: 12

Chromatin: a tunable spring at work inside chromosomes

This paper focuses on mechanical aspects of chromatin biological functioning. Within a basic geometric modeling of the chromatin assembly, we give for the first time the complete set of elastic constants (twist and bend persistence lengths, stretch modulus and twist-stretch coupling constant) of the so-called 30-nm chromatin fiber, in terms of DNA elastic properties and geometric properties of the fiber assembly. The computation naturally embeds the fiber within a current analytical model known as the ``extensible worm-like rope'', allowing a straightforward prediction of the force-extension curves. We show that these elastic constants are strongly sensitive to the linker length, up to 1 bp, or equivalently to its twist, and might locally reach very low values, yielding a highly flexible and extensible domain in the fiber. In particular, the twist-stretch coupling constant, reflecting the chirality of the chromatin fiber, exhibits steep variations and sign changes when the linker length is varied. We argue that this tunable elasticity might be a key feature for chromatin function, for instance in the initiation and regulation of transcription.Comment: 38 pages 15 figure

Shaping the Phase of a Single Photon

While the phase of a coherent light field can be precisely known, the phase of the individual photons that create this field, considered individually, cannot. Phase changes within single-photon wave packets, however, have observable effects. In fact, actively controlling the phase of individual photons has been identified as a powerful resource for quantum communication protocols. Here we demonstrate the arbitrary phase control of a single photon. The phase modulation is applied without affecting the photon's amplitude profile and is verified via a two-photon quantum interference measurement, which can result in the fermionic spatial behaviour of photon pairs. Combined with previously demonstrated control of a single photon's amplitude, frequency, and polarisation, the fully deterministic phase shaping presented here allows for the complete control of single-photon wave packets.Comment: 4 pages, 4 figure

A Color Mutation Model of Soft Interaction in High Energy Hadronic Collisions

A comprehensive model, called ECOMB, is proposed to describe multiparticle production by soft interaction. It incorporates the eikonal formalism, parton model, color mutation, branching and recombination. The physics is conceptually opposite to the dynamics that underlies the fragmentation of a string. The partons are present initially in a hadronic collision; they form a single, large, color-neutral cluster until color mutation of the quarks leads to a fission of the cluster into two color-neutral subclusters. The mutation and branching processes continue until only $q\bar q$ pairs are left in each small cluster. The model contains self-similar dynamics and exhibits scaling behavior in the factorial moments. It can satisfactorily reproduce the intermittency data that no other model has been able to fit.Comment: 24 pages including 11 figures in revtex epsf styl

Random and Correlated Phases of Primordial Gravitaional Waves

The phases of primordial gravity waves is analysed in detail within a quantum mechanical context following the formalism developed by Grishchuk and Sidorov. It is found that for physically relevant wavelengths both the phase of each individual mode and the phase {\it difference} between modes are randomly distributed. The phase {\it sum} between modes with oppositely directed wave-vectors, however, is not random and takes on a definite value with no rms fluctuation. The conventional point of view that primordial gravity waves appear after inflation as a classical, random stochastic background is also addressed.Comment: 14 pages, written in REVTE

Disoriented Chiral Condensates, Pion Probability Distributions and Parallels with Disordered System

A general expression is discussed for pion probability distributions coming from relativistic heavy ion collisions. The general expression contains as limits: 1) The disoriented chiral condensate (DCC), 2) the negative binomial distribution and Pearson type III distribution, 3) a binomial or Gaussian result, 4) and a Poisson distribution. This general expression approximates other distributions such as a signal to noise laser distribution. Similarities and differences of the DCC distribution with these other distribution are studied. A connection with the theory of disordered systems will be discussed which include spin-glasses, randomly broken objects, random and chaotic maps.Comment: 5 pages, 1 figure include