The productivity effects of macroalgal biochar from Ulva (Linnaeus) bloom species on Arabidopsis thaliana (Linnaeus) seedlings

Intensive agricultural practices and poor management of organic waste have adverse effects on aquatic ecosystems, where excessive macroalgal proliferation can occur to form ‘green tides’, with negative environmental, ecological and socioeconomic impacts. One novel method for converting a problematic material into a valuable resource is to use excess algal biomass as a feedstock for biochar production. With a high elemental composition, such a resource might be suitable to redress soil deficiencies and to ameliorate soil fertility. Green macroalgae from the Ulva genus, in bladed (predominantly U. rigida), tubular (predominantly U. prolifera) and mixed morphological (U. rigida and U. prolifera) phenotypes, were used to produce biochars. A pot trial within a controlled-environment chamber was carried out to determine the effects of amending high- and low-fertilizer compost with algal biochars (applied at 0, 0.5, 1, 2 and 5% w/w) on the growth rate of Arabidopsis thaliana. A commercial wood-based biochar was used under similar treatments as a control. Weekly imaging and final harvest weights provided additional growth data; composition data including ultimate and proximate analyses, pH, Brunauer–Emmett–Teller (BET) surface area and hydropyrolysis of the dried macroalgae and algal biochars were also conducted. Significant enhanced growth in seedlings grown with biochar amendment were not observed in high- or low-fertilizer compost, and the addition of algal biochars at 5% w/w to high-fertilizer soil significantly reduced plant growth. Elemental analysis revealed that the algal biochars contained high quantities of alkaline elements including sodium. It was hypothesised that salinity was the primary factor affecting plant growth at higher biochar application rates, despite the algae being sourced from an estuarine environment. Biochar provenance and composition is highly significant: using the catch-all term ‘biochar’ ignores both the range of materials and composition that could be used to create it and its subsequent impact within the soil. HIGHLIGHTS First plant trial using biochar predominantly from Ulva species. Negative impact seen with 5% algal biochar on plant growth. High sodium concentrations putatively identified as reduced plant growth cause

Entropy Crisis, Ideal Glass Transition and Polymer Melting: Exact Solution on a Husimi Cactus

We introduce an extension of the lattice model of melting of semiflexible polymers originally proposed by Flory. Along with a bending penalty, present in the original model and involving three sites of the lattice, we introduce an interaction energy that corresponds to the presence of a pair of parallel bonds and a second interaction energy associated with the presence of a hairpin turn. Both these new terms represent four-site interactions. The model is solved exactly on a Husimi cactus, which approximates a square lattice. We study the phase diagram of the system as a function of the energies. For a proper choice of the interaction energies, the model exhibits a first-order melting transition between a liquid and a crystalline phase. The continuation of the liquid phase below this temperature gives rise to a supercooled liquid, which turns continuously into a new low-temperature phase, called metastable liquid. This liquid-liquid transition seems to have some features that are characteristic of the critical transition predicted by the mode-coupling theory.Comment: To be published in Physical Review E, 68 (2) (2003

Negative Energy and Angular Momentum Modes of Thin Accretion Disks

This work derives the linearized equations of motion, the Lagrangian density, the Hamiltonian density, and the canonical angular momentum density for general perturbations [$\propto \exp(im\phi)$ with $m=0,\pm 1,..$] of a geometrically thin self-gravitating, homentropic fluid disk including the pressure. The theory is applied to ``eccentric,'' $m=\pm 1$ perturbations of a geometrically thin Keplerian disk. We find $m=1$ modes at low frequencies relative to the Keplerian frequency. Further, it shown that these modes can have negative energy and negative angular momentum. The radial propagation of these low frequency $m=1$ modes can transport angular momentum away from the inner region of a disk and thus increase the rate of mass accretion. Depending on the radial boundary conditions there can be discrete low-frequency, negative-energy, $m=1$ modes.Comment: 24 pages, 8 figure

Turbulence Modeling Using Fractional Derivatives

We propose a new turbulence model in this work. The main idea of the model is that the shear stresses are considered to be random variables and we assume that their differences with respect to time are Lévy-type distributions. This is a generalization of the classical Newton’s law of viscosity. We tested the model on the classical backward facing step benchmark problem. The simulation results are in a good accordance with real measurements

Gravitational Collapse and Disk Formation in Magnetized Cores

We discuss the effects of the magnetic field observed in molecular clouds on the process of star formation, concentrating on the phase of gravitational collapse of low-mass dense cores, cradles of sunlike stars. We summarize recent analytic work and numerical simulations showing that a substantial level of magnetic field diffusion at high densities has to occur in order to form rotationally supported disks. Furthermore, newly formed accretion disks are threaded by the magnetic field dragged from the parent core during the gravitational collapse. These disks are expected to rotate with a sub-Keplerian speed because they are partially supported by magnetic tension against the gravity of the central star. We discuss how sub-Keplerian rotation makes it difficult to eject disk winds and accelerates the process of planet migration. Moreover, magnetic fields modify the Toomre criterion for gravitational instability via two opposing effects: magnetic tension and pressure increase the disk local stability, but sub-Keplerian rotation makes the disk more unstable. In general, magnetized disks are more stable than their nonmagnetic counterparts; thus, they can be more massive and less prone to the formation of giant planets by gravitational instability.Comment: Chapter 16 in "Magnetic Fields in Diffuse Media", Springer-Verlag, eds. de Gouveia Dal Pino, E., Lazarian, A., Melioli,

Double-Spin Asymmetry in the Cross Section for Exclusive rho^0 Production in Lepton-Proton Scattering

Evidence for a positive longitudinal double-spin asymmetry = 0.24 +-0.11 (stat) +-0.02 (syst) in the cross section for exclusive diffractive rho^0(770) vector meson production in polarised lepton-proton scattering was observed by the HERMES experiment. The longitudinally polarised 27.56 GeV HERA positron beam was scattered off a longitudinally polarised pure hydrogen gas target. The average invariant mass of the photon-proton system has a value of = 4.9 GeV, while the average negative squared four-momentum of the virtual photon is = 1.7 GeV^2. The ratio of the present result to the corresponding spin asymmetry in inclusive deep-inelastic scattering is in agreement with an early theoretical prediction based on the generalised vector meson dominance model.Comment: 10 pages, 4 embedded figures, LaTe

Spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron at low values of x and Q^2

We present a precise measurement of the deuteron longitudinal spin asymmetry A_1^d and of the deuteron spin-dependent structure function g_1^d at Q^2 < 1 GeV^2 and 4*10^-5 < x < 2.5*10^-2 based on the data collected by the COMPASS experiment at CERN during the years 2002 and 2003. The statistical precision is tenfold better than that of the previous measurement in this region. The measured A_1^d and g_1^d are found to be consistent with zero in the whole range of x.Comment: 17 pages, 10 figure

Measurement of the Spin Structure of the Deuteron in the DIS Region

We present a new measurement of the longitudinal spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron in the range 1 GeV^2 < Q^2 < 100 GeV^2 and 0.004< x <0.7. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarised muon beam and a large polarised 6-LiD target. The results are in agreement with those from previous experiments and improve considerably the statistical accuracy in the region 0.004 < x < 0.03.Comment: 10 pages, 6 figures, subm. to PLB, revised: author list, Fig. 4, details adde