The vegetation of the River Tweed

A detailed account is given of the macrophytic vegetation of the major rivers within the Tweed Basin. Of these rivers, the Tweed and its largest tributary, the Teviot, tare been studied in most detail, both being surveyed from source to mouth. Information brought together on the history and physiography of the Tweed Basin are summarized in this account, together with physical and water chemical data collected during the survey. The distribution of species is discussed in relation to changes in such parameters. The method of survey involved recording the presence or absence of all macrophytic species within 0.5 km lengths of river, together with a subjective evaluation of their abundance. 570 such 0.5 km lengths were surveyed. All macroscopically visable species were recorded which were found completely submerged or at the immediate edge of the river. A total of 180 different macrophytic growths (usually species, but occasionally identified only to genus level ) were present in the basin, including: 31 algae, 5 lichens, 83 bryophytes, 59 angiosperms, 2 macroscopic microbial communities. The identification and taxonomy of all species were studied critically. Environmental parameters collected in most detail were the physical characteristics of each river, such as altitude, features of the substratum and flow regime. A water sampling programme was undertaken which involved the collection of 5 duplicate samples from sites in the main river and tributaries, and subsequent analysis for optical density, pH, conductivity, 10 cations and 6 anions. The final discussion includes an appraisal of literature concerned with macrophytes in rivers, methods of study, and results obtained. Particular attention is paid to floristic accounts, especially those from the neighbourhood of the Tweed, the floras of these rivers being compared with the flora of the Tweed Basin. Comparison with data from these surveys would suggest that the Tweed is a river which is especially rich in macrophyte species. The presence of historical data and herbarium specimens collected over the past two centuries has made it possible to suggest tentatively that the distribution of some species has changed markedly, whereas others appear to have changed little over 150 years. Cladophora, glomerata is an example of a species which in recent years has become much less abundant. This is most probably due to a decrease in total phosphate content ±n. the water, this in turn being due to a reduction in the use of synthetic detergents by the textile industry

Extraction of coherent structures in a rotating turbulent flow experiment

The discrete wavelet packet transform (DWPT) and discrete wavelet transform (DWT) are used to extract and study the dynamics of coherent structures in a turbulent rotating fluid. Three-dimensional (3D) turbulence is generated by strong pumping through tubes at the bottom of a rotating tank (48.4 cm high, 39.4 cm diameter). This flow evolves toward two-dimensional (2D) turbulence with increasing height in the tank. Particle Image Velocimetry (PIV) measurements on the quasi-2D flow reveal many long-lived coherent vortices with a wide range of sizes. The vorticity fields exhibit vortex birth, merger, scattering, and destruction. We separate the flow into a low-entropy ``coherent'' and a high-entropy ``incoherent'' component by thresholding the coefficients of the DWPT and DWT of the vorticity fields. Similar thresholdings using the Fourier transform and JPEG compression together with the Okubo-Weiss criterion are also tested for comparison. We find that the DWPT and DWT yield similar results and are much more efficient at representing the total flow than a Fourier-based method. Only about 3% of the large-amplitude coefficients of the DWPT and DWT are necessary to represent the coherent component and preserve the vorticity probability density function, transport properties, and spatial and temporal correlations. The remaining small amplitude coefficients represent the incoherent component, which has near Gaussian vorticity PDF, contains no coherent structures, rapidly loses correlation in time, and does not contribute significantly to the transport properties of the flow. This suggests that one can describe and simulate such turbulent flow using a relatively small number of wavelet or wavelet packet modes.Comment: experimental work aprox 17 pages, 11 figures, accepted to appear in PRE, last few figures appear at the end. clarifications, added references, fixed typo

Origin of Drastic Change of Fermi Surface and Transport Anomalies in CeRhIn5 under Pressure

The mechanism of drastic change of Fermi surfaces as well as transport anomalies near P=Pc=2.35 GPa in CeRhIn5 is explained theoretically. The key mechanism is pointed out to be the interplay of magnetic order and Ce-valence fluctuations. We show that the antiferromagnetic state with "small" Fermi surfaces changes to the paramagnetic state with "large" Fermi surfaces with huge enhancement of effective mass of electrons with keeping finite c-f hybridization. This explains the drastic change of the de Haas-van Alphen signals. Furthermore, it is also consistent with the emergence of T-linear resistivity simultaneous with the residual resistivity peak at P=Pc in CeRhIn5.Comment: 5 pages, 3 figures, submitted to Journal of Physical Society of Japa

13C NMR study of superconductivity near charge instability realized in beta"-(BEDT-TTF)4[(H3O)Ga(C2O4)3]C6H5NO2

To investigate the superconducting (SC) state near a charge instability, we performed ^{13}C NMR experiments on the molecular superconductor beta"-(BEDT-TTF)_{4}[(H_{3}O)Ga(C_{2}O_{4})_{3}]C_{6}H_{5}NO_{2}, which exhibits a charge anomaly at 100 K. The Knight shift which we measured in the SC state down to 1.5 K demonstrates that Cooper pairs are in spin-singlet state. Measurements of the nuclear spin-lattice relaxation time reveal strong electron-electron correlations in the normal state. The resistivity increase observed below 10 K indicates that the enhanced fluctuation has an electric origin. We discuss the possibility of charge-fluctuation-induced superconductivity.Comment: 5 pages, 4 figure

Mathematical description of bacterial traveling pulses

The Keller-Segel system has been widely proposed as a model for bacterial waves driven by chemotactic processes. Current experiments on {\em E. coli} have shown precise structure of traveling pulses. We present here an alternative mathematical description of traveling pulses at a macroscopic scale. This modeling task is complemented with numerical simulations in accordance with the experimental observations. Our model is derived from an accurate kinetic description of the mesoscopic run-and-tumble process performed by bacteria. This model can account for recent experimental observations with {\em E. coli}. Qualitative agreements include the asymmetry of the pulse and transition in the collective behaviour (clustered motion versus dispersion). In addition we can capture quantitatively the main characteristics of the pulse such as the speed and the relative size of tails. This work opens several experimental and theoretical perspectives. Coefficients at the macroscopic level are derived from considerations at the cellular scale. For instance the stiffness of the signal integration process turns out to have a strong effect on collective motion. Furthermore the bottom-up scaling allows to perform preliminary mathematical analysis and write efficient numerical schemes. This model is intended as a predictive tool for the investigation of bacterial collective motion

Theory of Quasi-Universal Ratio of Seebeck Coefficient to Specific Heat in Zero-Temperature Limit in Correlated Metals

It is shown that the quasi-universal ratio $q=\lim_{T\to0}eS/C\sim\pm1$ of the Seebeck coefficient to the specific heat in the limit of T=0 observed in a series of strongly correlated metals can be understood on the basis of the Fermi liquid theory description. In deriving this result, it is crucial that a relevant scattering arises from impurities, but not from the mutual scattering of quasiparticles. The systematics of the sign of $q$ is shown to reflect the sign of the logarithmic derivative of the density of states and the inverse mass tensor of the quasiparticles, explaining the systematics of experiments. In particular, the positive sign of $q$ for Ce-based and $f^{3}$-based heavy fermions, and the negative sign for Yb-based and $f^{2}$-based heavy fermions, are explained. The case of non-Fermi liquid near the quantum critical point (QCP) is briefly mentioned, showing that the ratio $q$ decreases considerably toward antiferromagnetic QCP while it remains essentially unchanged for the ferromagnetic QCP or QCP due to a local criticality.Comment: 12 pages, 1 figur

Strong Longitudinal Magnetic Fluctuations near Critical End Point in UCoAl: A ^59Co-NMR Study

We report ^59Co-NMR measurements in UCoAl where a metamagnetism occurs due to enhancement of ferromagnetism by magnetic field. The metamagnetic transition from a paramagnetic (PM) state to a ferromagnetic state is a first order transition at low temperatures, but it changes to a crossover at high temperatures on crossing the critical end pint (CEP) at T_CEP ~ 12 K. The contrasting behavior between the relaxation rates 1/T_1 and 1/T_2 suggests that the longitudinal magnetic fluctuation of U moment is strongly enhanced especially near the CEP. A wide diffusion of the fluctuation from the CEP can be confirmed even in the PM state where the magnetic transition does not occur.Comment: 5pages, 6 figures, to be published in J. Phys. Soc. Jp

Temperature dependence of spin polarizations at higher Landau Levels

We report our results on temperature dependence of spin polarizations at $\nu=1$ in the lowest as well as in the next higher Landau level that compare well with recent experimental results. At $\nu=3$, except having a much smaller magnitude the behavior of spin polarization is not much influenced by higher Landau levels. In sharp contrast, for filling factor $\nu=\frac83$ we predict that unlike the case of $\nu=\frac23$ the system remains fully spin polarized even at vanishingly small Zeeman energies.Comment: 4 pages, REVTEX, and 3 .ps files, To be published in Physical Review Letter

The quantum critical point in CeRhIn_5: a resistivity study

The pressure--temperature phase diagram of CeRhIn_5 has been studied under high magnetic field by resistivity measurements. Clear signatures of a quantum critical point has been found at a critical pressure of p_c = 2.5 GPa. The field induced magnetic state in the superconducting state is stable up to the highest field. At p_c the antiferromagnetic ground-state under high magnetic field collapses very rapidly. Clear signatures of p_c are the strong enhancement of the resistivity in the normal state and of the inelastic scattering term. No clear T2 temperature dependence could be found for pressures above T_c. From the analysis of the upper critical field within a strong coupling model we present the pressure dependence of the coupling parameter lambda and the gyromagnetic ratio g. No signatures of a spatially modulated order parameter could be evidenced. A detailed comparison with the magnetic field--temperature phase diagram of CeCoIn_5 is given. The comparison between CeRhIn_5 and CeCoIn_5 points out the importance to take into account the field dependence of the effective mass in the calculation of the superconducting upper critical field H_c2. It suggests also that when the magnetic critical field H_(0) becomes lower than H_c2 (0)$, the persistence of a superconducting pseudo-gap may stick the antiferromagnetism to H_c2 (0).Comment: 15 pages, 20 figures, to be published in J. Phys. Soc. Jp