In field N transfer, build-up, and leaching in ryegrass-clover mixtures

Two field experiments investigating dynamics in grass-clover mixtures were conducted, using 15N- and 14C-labelling to trace carbon (C) and nitrogen (N) from grass (Lolium perenne L.) and clover (Trifolium repens L. and Trifolium pratense L.). The leaching of dissolved inorganic nitrogen (DIN), as measured in pore water sampled by suction cups, increased during the autumn and winter, whereas the leaching of dissolved organic nitrogen (DON) was fairly constant during this period. Leaching of 15N from the sward indicated that ryegrass was the direct source of less than 1-2 percent of the total N leaching measured, whereas N dynamics pointed to clover as an important contributor to N leaching. Sampling of roots indicates that the dynamics in smaller roots were responsible for N and C build-up in the sward, and that N became available for transfer among species and leaching from the root zone. The bi-directional transfer of N between ryegrass and clover could however not be explained only by root turnover. Other processes like direct uptake of organic N compounds, may have contributed

Control of Cavity-Induced Drag Using Steady Jets

Separated shear layer oscillations in open cavities can induce drag, noise and vibration. This issue has many aerospace applications such as Landing gears and control surfaces [1]. Recently, phase-cancellation [1] and offinstability frequency excitation [2] & [3] approaches have been incorporated in different open-loop and feedback control systems. Despite the high control performance of these systems, further enhancement is still possible. In this study, steady jets, as shown in fig. 1, are forced through 2mm, two-dimensional slots at the leading and trailing edges of the cavity. In order to study the performance of this novel approach, different cases will be examined, including: jet combination (blowing from cavity leading edge, suction from cavity leading edge and blowing-suction), jet angle (parallel or deflected jet) and jet-to-free stream velocity factor /.

Collisional transport across the magnetic field in drift-fluid models

Drift ordered fluid models are widely applied in studies of low-frequency turbulence in the edge and scrape-off layer regions of magnetically confined plasmas. Here, we show how collisional transport across the magnetic field is self-consistently incorporated into drift-fluid models without altering the drift-fluid energy integral. We demonstrate that the inclusion of collisional transport in drift-fluid models gives rise to diffusion of particle density, momentum and pressures in drift-fluid turbulence models and thereby obviate the customary use of artificial diffusion in turbulence simulations. We further derive a computationally efficient, two-dimensional model which can be time integrated for several turbulence de-correlation times using only limited computational resources. The model describes interchange turbulence in a two-dimensional plane perpendicular to the magnetic field located at the outboard midplane of a tokamak. The model domain has two regions modeling open and closed field lines. The model employs a computational expedient model for collisional transport. Numerical simulations show good agreement between the full and the simplified model for collisional transport

Theory of Bubble Nucleation and Cooperativity in DNA Melting

The onset of intermediate states (denaturation bubbles) and their role during the melting transition of DNA are studied using the Peyrard-Bishop-Daxuois model by Monte Carlo simulations with no adjustable parameters. Comparison is made with previously published experimental results finding excellent agreement. Melting curves, critical DNA segment length for stability of bubbles and the possibility of a two states transition are studied.Comment: 4 figures. Accepted for publication in Physical Review Letter

Magnetic-Field Dependence of Tunnel Couplings in Carbon Nanotube Quantum Dots

By means of sequential and cotunneling spectroscopy, we study the tunnel couplings between metallic leads and individual levels in a carbon nanotube quantum dot. The levels are ordered in shells consisting of two doublets with strong- and weak-tunnel couplings, leading to gate-dependent level renormalization. By comparison to a one- and two-shell model, this is shown to be a consequence of disorder-induced valley mixing in the nanotube. Moreover, a parallel magnetic field is shown to reduce this mixing and thus suppress the effects of tunnel renormalization.Comment: 5 pages, 3 figures; revised version as publishe

Simulation of transition dynamics to high confinement in fusion plasmas

The transition dynamics from the low (L) to the high (H) confinement mode in magnetically confined plasmas is investigated using a first-principles four-field fluid model. Numerical results are in close agreement with measurements from the Experimental Advanced Superconducting Tokamak - EAST. Particularly, the slow transition with an intermediate dithering phase is well reproduced by the numerical solutions. Additionally, the model reproduces the experimentally determined L-H transition power threshold scaling that the ion power threshold increases with increasing particle density. The results hold promise for developing predictive models of the transition, essential for understanding and optimizing future fusion power reactors

A new species of Liphanthus from Peru (Hymenoptera: Andrenidae)

The protandrenine bee genus Liphanthus Reed (Panurginae: Protandrenini) is currently known from Chile and Argentina.  Liphanthus (Melaliphanthus) cuscoensis Gonzalez, Rasmussen, & Engel, new species, is described and figured from a male collected in Cusco, Peru, at 4167 meters of elevation.  This finding represents the northernmost record for the genus and the fourth protandrenine species described from Peru.  An updated key to the species of the subgenus Melaliphanthus Ruz & Toro is provided

Incasarus garciai, a new genus and species of panurgine bees from the Peruvian Andes (Hymenoptera: Andrenidae)

This is the publisher's version, also available electronically from https://journals.ku.edu/index.php/melittology/indexIncasarus garciai Gonzalez, Rasmussen, & Engel, a new genus and species of protandrenine bees (Andrenidae: Panurginae), is described and figured from a male collected in Ayacucho, Peru. Incasarus superficially resembles Liphanthus Reed in the narrow pterostigma and gonostylus articulated to the gonocoxite but it can be distinguished easily by the combination of two submarginal cells, the seventh sternum with apodemes and apical lobes broad, short, attached to a large disc, and the gonostylus long, about as long as the gonocoxite. Incasarus also resembles Rhophitulus Ducke and Heterosarus Robertson in the male seventh tergum with the distal margin medially projected, but it differs from both genera in the shape of the hidden sterna and genitalia, among other features

Open problems in artificial life

This article lists fourteen open problems in artificial life, each of which is a grand challenge requiring a major advance on a fundamental issue for its solution. Each problem is briefly explained, and, where deemed helpful, some promising paths to its solution are indicated