Observations on the status of bass Dicentrarchus Labrax stocks in Ireland in the late 1990s

Investigative work was undertaken in 1996 to ascertain the strength of sea bass stocks following the introduction of a range of conservation measures which effectively extinguished the legitimate commercial fishery for the species. Information was sought from two sources: estimation of the age composition of the samples and the growth of bass by examining scales from exploited fish. An estimate of the density of juvenile pre-recruit bass was made from a seine net survey undertaken in various estuaries along the south coast. Scales sent in by anglers and obtained through the regional boards from illegally netted fish indicate that a high proportion of bass landed between 1996 and 1998 belonged to the 1989-year class, which had been reported to be exceptionally large in Britain. Back-calculations of length-at-age from the scales of these and seine-netted bass suggested that growth improved in the later 1980s in response to higher sea temperatures but has since declined. Work on an index of juvenile abundance began with 59 seine net hauls made in August 1996 and 1997. On these the areas most likely to support bass were characterised; O-group bass were encountered more frequently than any other age group. Sites most likely to support bass were mud flats overlaid with shallow and still water which had a salinity range of 17 to 22% and bass were associated with certain species of estuarine fish and crustaceans; bass were negatively associated with other species occupying the deeper and more sandy parts of estuaries. Sampling stations for O-group bass have been selected in Youghal Harbour and Wexford Harbour. Further exploratory work is required to extend the list of stations. It was concluded that there has been a temporary increase in the numbers of sea bass, as has been reported by fishermen in Ireland, as a result of more favourable temperatures in the late 1980s. Growing conditions appeared to have deteriorated in the later 1990s and the summer growth ofO-group bass was the weakest in 1999 over the 4 years investigated. A time series of O-group abundance is too brief to permit any conclusions to be reached. However, it can be stated that the recorded densities of juvenile bass between 1996 and 1999 were sparser than would be expected in south east Ireland in view of the supposed heavy winter concentrations of the species in the Celtic Sea.Funder: Marine Institut

Theoretical evidences for enhanced superconducting transition temperature of CaSi2_2 in a high-pressure AlB2_2 phase

By means of first-principles calculations, we studied stable lattice structures and estimated superconducting transition temperature of CaSi$_2$ at high pressure. Our simulation showed stability of the AlB$_2$ structure in a pressure range above 17 GPa. In this structure, doubly degenerated optical phonon modes, in which the neighboring silicon atoms oscillate alternately in a silicon plane, show prominently strong interaction with the conduction electrons. In addition there exists a softened optical mode (out-of-plan motion of silicon atoms), whose strength of the electron-phonon interaction is nearly the same as the above mode. The density of states at the Fermi level in the AlB$_2$ structure is higher than that in the trigonal structure. These findings and the estimation of the transition temperature strongly suggest that higher $T_{\rm c}$ is expected in the AlB$_2$ structure than the trigonal structures which are known so far.Comment: 6 pages and 11 figure

On the relationship between directed percolation and the synchronization transition in spatially extended systems

We study the nature of the synchronization transition in spatially extended systems by discussing a simple stochastic model. An analytic argument is put forward showing that, in the limit of discontinuous processes, the transition belongs to the directed percolation (DP) universality class. The analysis is complemented by a detailed investigation of the dependence of the first passage time for the amplitude of the difference field on the adopted threshold. We find the existence of a critical threshold separating the regime controlled by linear mechanisms from that controlled by collective phenomena. As a result of this analysis we conclude that the synchronization transition belongs to the DP class also in continuous models. The conclusions are supported by numerical checks on coupled map lattices too

Electron correlations for ground state properties of group IV semiconductors

Valence energies for crystalline C, Si, Ge, and Sn with diamond structure have been determined using an ab-initio approach based on information from cluster calculations. Correlation contributions, in particular, have been evaluated in the coupled electron pair approximation (CEPA), by means of increments obtained for localized bond orbitals and for pairs and triples of such bonds. Combining these results with corresponding Hartree-Fock (HF) data, we recover about 95 % of the experimental cohesive energies. Lattice constants are overestimated at the HF level by about 1.5 %; correlation effects reduce these deviations to values which are within the error bounds of this method. A similar behavior is found for the bulk modulus: the HF values which are significantly too high are reduced by correlation effects to about 97 % of the experimental values.Comment: 22 pages, latex, 2 figure

Change and Aging Senescence as an adaptation

Understanding why we age is a long-lived open problem in evolutionary biology. Aging is prejudicial to the individual and evolutionary forces should prevent it, but many species show signs of senescence as individuals age. Here, I will propose a model for aging based on assumptions that are compatible with evolutionary theory: i) competition is between individuals; ii) there is some degree of locality, so quite often competition will between parents and their progeny; iii) optimal conditions are not stationary, mutation helps each species to keep competitive. When conditions change, a senescent species can drive immortal competitors to extinction. This counter-intuitive result arises from the pruning caused by the death of elder individuals. When there is change and mutation, each generation is slightly better adapted to the new conditions, but some older individuals survive by random chance. Senescence can eliminate those from the genetic pool. Even though individual selection forces always win over group selection ones, it is not exactly the individual that is selected, but its lineage. While senescence damages the individuals and has an evolutionary cost, it has a benefit of its own. It allows each lineage to adapt faster to changing conditions. We age because the world changes.Comment: 19 pages, 4 figure

Pseudopotential study of binding properties of solids within generalized gradient approximations: The role of core-valence exchange-correlation

In ab initio pseudopotential calculations within density-functional theory the nonlinear exchange-correlation interaction between valence and core electrons is often treated linearly through the pseudopotential. We discuss the accuracy and limitations of this approximation regarding a comparison of the local density approximation (LDA) and generalized gradient approximations (GGA), which we find to describe core-valence exchange-correlation markedly different. (1) Evaluating the binding properties of a number of typical solids we demonstrate that the pseudopotential approach and namely the linearization of core-valence exchange-correlation are both accurate and limited in the same way in GGA as in LDA. (2) Examining the practice to carry out GGA calculations using pseudopotentials derived within LDA we show that the ensuing results differ significantly from those obtained using pseudopotentials derived within GGA. As principal source of these differences we identify the distinct behavior of core-valence exchange-correlation in LDA and GGA which, accordingly, contributes substantially to the GGA induced changes of calculated binding properties.Comment: 13 pages, 6 figures, submitted to Phys. Rev. B, other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

Combined In Silico, In Vivo, and In Vitro Studies Shed Insights into the Acute Inflammatory Response in Middle-Aged Mice

We combined in silico, in vivo, and in vitro studies to gain insights into age-dependent changes in acute inflammation in response to bacterial endotoxin (LPS). Time-course cytokine, chemokine, and NO2-/NO3- data from "middle-aged" (6-8 months old) C57BL/6 mice were used to re-parameterize a mechanistic mathematical model of acute inflammation originally calibrated for "young" (2-3 months old) mice. These studies suggested that macrophages from middle-aged mice are more susceptible to cell death, as well as producing higher levels of pro-inflammatory cytokines, vs. macrophages from young mice. In support of the in silico-derived hypotheses, resident peritoneal cells from endotoxemic middle-aged mice exhibited reduced viability and produced elevated levels of TNF-α, IL-6, IL-10, and KC/CXCL1 as compared to cells from young mice. Our studies demonstrate the utility of a combined in silico, in vivo, and in vitro approach to the study of acute inflammation in shock states, and suggest hypotheses with regard to the changes in the cytokine milieu that accompany aging. © 2013 Namas et al

Estimation of current density distribution under electrodes for external defibrillation

BACKGROUND: Transthoracic defibrillation is the most common life-saving technique for the restoration of the heart rhythm of cardiac arrest victims. The procedure requires adequate application of large electrodes on the patient chest, to ensure low-resistance electrical contact. The current density distribution under the electrodes is non-uniform, leading to muscle contraction and pain, or risks of burning. The recent introduction of automatic external defibrillators and even wearable defibrillators, presents new demanding requirements for the structure of electrodes. METHOD AND RESULTS: Using the pseudo-elliptic differential equation of Laplace type with appropriate boundary conditions and applying finite element method modeling, electrodes of various shapes and structure were studied. The non-uniformity of the current density distribution was shown to be moderately improved by adding a low resistivity layer between the metal and tissue and by a ring around the electrode perimeter. The inclusion of openings in long-term wearable electrodes additionally disturbs the current density profile. However, a number of small-size perforations may result in acceptable current density distribution. CONCLUSION: The current density distribution non-uniformity of circular electrodes is about 30% less than that of square-shaped electrodes. The use of an interface layer of intermediate resistivity, comparable to that of the underlying tissues, and a high-resistivity perimeter ring, can further improve the distribution. The inclusion of skin aeration openings disturbs the current paths, but an appropriate selection of number and size provides a reasonable compromise

Phenotypic Characterization of Bone Marrow Mononuclear Cells and Derived Stromal Cell Populations from Human Iliac Crest, Vertebral Body and Femoral Head

(1) In vitro, bone marrow-derived stromal cells (BMSCs) demonstrate inter-donor phenotypic variability, which presents challenges for the development of regenerative therapies. Here, we investigated whether the frequency of putative BMSC sub-populations within the freshly isolated mononuclear cell fraction of bone marrow is phenotypically predictive for the in vitro derived stromal cell culture. (2) Vertebral body, iliac crest, and femoral head bone marrow were acquired from 33 patients (10 female and 23 male, age range 14-91). BMSC sub-populations were identified within freshly isolated mononuclear cell fractions based on cell-surface marker profiles. Stromal cells were expanded in monolayer on tissue culture plastic. Phenotypic assessment of in vitro derived cell cultures was performed by examining growth kinetics, chondrogenic, osteogenic, and adipogenic differentiation. (3) Gender, donor age, and anatomical site were neither predictive for the total yield nor the population doubling time of in vitro derived BMSC cultures. The abundance of freshly isolated progenitor sub-populations (CD45-CD34-CD73+, CD45-CD34-CD146+, NG2+CD146+) was not phenotypically predictive of derived stromal cell cultures in terms of growth kinetics nor plasticity. BMSCs derived from iliac crest and vertebral body bone marrow were more responsive to chondrogenic induction, forming superior cartilaginous tissue in vitro, compared to those isolated from femoral head. (4) The identification of discrete progenitor populations in bone marrow by current cell-surface marker profiling is not predictive for subsequently derived in vitro BMSC cultures. Overall, the iliac crest and the vertebral body offer a more reliable tissue source of stromal progenitor cells for cartilage repair strategies compared to femoral head