Editorial Introducing the Special Issue for Diversity in Aquatics

Introduction to Special Issue - no abstract availabl

On the global well-posedness of a class of Boussinesq- Navier-Stokes systems

In this paper we consider the following 2D Boussinesq-Navier-Stokes systems \partial_{t}u+u\cdot\nabla u+\nabla p+ |D|^{\alpha}u &= \theta e_{2} \partial_{t}\theta+u\cdot\nabla \theta+ |D|^{\beta}\theta &=0 \quad with $\textrm{div} u=0$ and $0<\beta<\alpha<1$. When $\frac{6-\sqrt{6}}{4}<\alpha< 1$, $1-\alpha<\beta\leq f(\alpha)$, where $f(\alpha)$ is an explicit function as a technical bound, we prove global well-posedness results for rough initial data.Comment: 23page

Evidence for a singularity in ideal magnetohydrodynamics: implications for fast reconnection

Numerical evidence for a finite-time singularity in ideal 3D magnetohydrodynamics (MHD) is presented. The simulations start from two interlocking magnetic flux rings with no initial velocity. The magnetic curvature force causes the flux rings to shrink until they come into contact. This produces a current sheet between them. In the ideal compressible calculations, the evidence for a singularity in a finite time $t_c$ is that the peak current density behaves like $|J|_\infty \sim 1/(t_c-t)$ for a range of sound speeds (or plasma betas). For the incompressible calculations consistency with the compressible calculations is noted and evidence is presented that there is convergence to a self-similar state. In the resistive reconnection calculations the magnetic helicity is nearly conserved and energy is dissipated.Comment: 4 pages, 4 figure

Is council tax valuation band a predictor of mortality?

BACKGROUND: All current UK indices of socio-economic status have inherent problems, especially those used to govern resource allocation to the health sphere. The search for improved markers continues: this study proposes and tests the possibility that Council Tax Valuation Band (CTVB) might match requirements. PRESENTATION OF THE HYPOTHESIS: To determine if there is an association between CTVB of final residence and mortality risk using the death registers of a UK general practice. TESTING THE HYPOTHESIS: Standardised death rates and odds ratios (ORs) for groups defined by CTVB of dwelling (A – H) were calculated using one in four denominator samples from the practice lists. Analyses were repeated three times – between number of deaths and CTVB of residence of deceased 1992 – 1994 inclusive, 1995 – 1997 inc., 1998 – 2000 inc. In 856 deaths there were consistent and significant differences in death rates between CTVBs: above average for bands A and B residents; below average for other band residents. There were significantly higher ORs for A, B residents who were female and who died prematurely (before average group life expectancy). IMPLICATIONS OF THE HYPOTHESIS: CTVB of final residence appears to be a proxy marker of mortality risk and could be a valuable indicator of health needs resource at household level. It is worthy of further exploration

Enhancement of Noise-induced Escape through the Existence of a Chaotic Saddle

We study the noise-induced escape process in a prototype dissipative nonequilibrium system, the Ikeda map. In the presence of a chaotic saddle embedded in the basin of attraction of the metastable state, we find the novel phenomenon of a strong enhancement of noise-induced escape. This result is established by employing the theory of quasipotentials. Our finding is of general validity and should be experimentally observable.Comment: 4 page

Combination of improved multibondic method and the Wang-Landau method

We propose a method for Monte Carlo simulation of statistical physical models with discretized energy. The method is based on several ideas including the cluster algorithm, the multicanonical Monte Carlo method and its acceleration proposed recently by Wang and Landau. As in the multibondic ensemble method proposed by Janke and Kappler, the present algorithm performs a random walk in the space of the bond population to yield the state density as a function of the bond number. A test on the Ising model shows that the number of Monte Carlo sweeps required of the present method for obtaining the density of state with a given accuracy is proportional to the system size, whereas it is proportional to the system size squared for other conventional methods. In addition, the new method shows a better performance than the original Wang-Landau method in measurement of physical quantities.Comment: 12 pages, 3 figure

Chickpea wilt: identification and toxicity of 8-O-methyl-fusarubin from Fusarium acutatum

Fusarium acutatum was isolated from wilting chickpea plants in Pakistan. Filtrates from cultures grown on a defined liquid medium caused permanent wilting of chickpea cuttings and killed cells, isolated enzymically from healthy plants, in a bioassay. Toxic activity was retained by a cyano solid phase extraction cartridge and the toxin was isolated by elution from the cartridge in acetonitrile and Si-gel thin layer chromatography of the eluate. Analytical HPLC of the compound on a cyano column with diode array detection gave a single peak with a homogeneous spectrum and λmax at 224 and 281 nm. NMR and mass spectral studies showed that the toxin was 8-O-methyl-fusarubin. The pure compound caused permanent wilting of chickpea cuttings and the LD50 value in the cell bioassay was 327 ng/ml

Transition Matrix Monte Carlo Reweighting and Dynamics

We study an induced dynamics in the space of energy of single-spin-flip Monte Carlo algorithm. The method gives an efficient reweighting technique. This dynamics is shown to have relaxation times proportional to the specific heat. Thus, it is plausible for a logarithmic factor in the correlation time of the standard 2D Ising local dynamics.Comment: RevTeX, 5 pages, 3 figure

Speeding Up Computer Simulations: The Transition Observable Method

A method is presented which allows for a tremendous speed-up of computer simulations of statistical systems by orders of magnitude. This speed-up is achieved by means of a new observable, while the algorithm of the simulation remains unchanged.Comment: 20 pages, 6 figures Submitted to Phys.Rev.E (August 1999) Replacement due to some minor change

Fermions and Disorder in Ising and Related Models in Two Dimensions

The aspects of phase transitions in the two-dimensional Ising models modified by quenched and annealed site disorder are discussed in the framework of fermionic approach based on the reformulation of the problem in terms of integrals with anticommuting Grassmann variables.Comment: 11 pages, 1 table, no figures. The discussion is merely based on a talk given at the International Bogoliubov Conference on Problems of Theoretical and Mathematical Physics, MIRAS--JINR, Moscow--Dubna, Russia, August 21--27, 200