A study of the vegetation of the South Burn valley, Waldridge Fell, County Durham

The vegetation of the South Burn Valley, Waldridge Fell, County Durham, was examined using an objective, quantitative phytosociological method. The vegetation units found to be present in the valley using this technique were then described and classified. Certain parameters relating to the chemical and physical environment of each vegetation unit were measured and variations in these factors used to account for the distribution of the vegetation units within the valley. The valley floor is broad and flat and situated below a series of spring lines. The majority of the area has a substrate composed of peat and the importance of water table height, ground water chemistry and tne degree of decomposition of this peat are emphasised as being the major environmental factors controlling the distribution of the main vegetation units of the valley floor. In a small area of the valley floor, which has willow car growing upon it, the substrate is composed of mineral soil. Here the chemistry of the water supplying the area and the nature of the substrate are important environmental factors. The valley sides are steep and composed of a sandy substrate and the dry nature and base-poor conditions of this habitat, seem to, in all probability account for the type of vegetation found growing on these sites. In a study of the population dynamics of the major tree species of the vegetation units, evidence was obtained showing that a change in tree species composition is taking place. Alder and Birch are the main dominants of the valley floor at present, but the evidence presented here suggests that these species are not regenerating and that ash is moving in to become the dominant tree of the valley floor. However, the small area of willow carr presently found in the valley will probably remain with such a species composition, but with a change in the predominant willow species. Further a small area of birch wood with a moss carpet ground layer appears to be losing its tree component and will probably change to a sphagnum bog. The tree composition of the valley sides also appears to be changing. On the fell side birch is being replaced by oak while, on the opposite side of the valley, sycamore is moving in to replace the birch. Reasons for these observed changes are given

The Surface Region of Superfluid 4^4He as a Dilute Bose-Condensed Gas

In the low-density surface region of superfluid $^4$He, the atoms are far apart and collisions can be ignored. The only effect of the interactions is from the long-range attractive Hartree potential produced by the distant high-density bulk liquid. As a result, at $T=0$, all the atoms occupy the same single-particle state in the low-density tail. Striking numerical evidence for this 100\% surface BEC was given by Pandharipande and coworkers in 1988. We derive a generalized Gross-Pitaevskii equation for the inhomogeneous condensate wave function $\Phi(z)$ in the low-density region valid at all temperatures. The overall amplitude of $\Phi(z)$ is fixed by the bulk liquid, which ensures that it vanishes everywhere at the bulk transition temperature.Comment: 6 pages, paper submitted to Low Temperature Conference (LT21), Prague, Aug., 1996; to appear in proceeding

TCMS operations and maintenance philosophy

The purpose is to describe the basic philosophies of operating and maintaining the Test, Control, and Monitor System (TCMS) equipment. TCMS is a complex and sophisticated checkout system. Operations and maintenance processes developed to support it will be based upon current experience, but will be focused on the specific needs of TCMS in support of Space Station Freedom Program (SSFP) and related activities. An overview of the operations and maintenance goals and philosophies are presented. The assumptions, roles and responsibilities, concepts and interfaces for operation, on-line maintenance, off-line support, and Operations and Maintenance (O&M) personnel training on all TCMS equipment located at KSC are described

Control of long-range correlations in turbulence

The character of turbulence depends on where it develops. Turbulence near boundaries, for instance, is different than in a free stream. To elucidate the differences between flows, it is instructive to vary the structure of turbulence systematically, but there are few ways of stirring turbulence that make this possible. In other words, an experiment typically examines either a boundary layer or a free stream, say, and the structure of the turbulence is fixed by the geometry of the experiment. We introduce a new active grid with many more degrees of freedom than previous active grids. The additional degrees of freedom make it possible to control various properties of the turbulence. We show how long-range correlations in the turbulent velocity fluctuations can be shaped by changing the way the active grid moves. Specifically, we show how not only the correlation length but also the detailed shape of the correlation function depends on the correlations imposed in the motions of the grid. Until now, large-scale structure had not been adjustable in experiments. This new capability makes possible new systematic investigations into turbulence dissipation and dispersion, for example, and perhaps in flows that mimic features of boundary layers, free streams, and flows of intermediate character.Comment: This paper has been accepted to Experiments in Fluids. 25 pages, 10 figure

Three dimensional inelastic finite element analysis of laminated composites

Formulations of the inelastic response of laminated composites to thermal and mechanical loading are used as the basis for development of the computer NALCOM (Nonlinear Analysis of Laminated Composites) computer program which uses a fully three dimensional isoparametric finite element with 24 nodes and 72 degrees of freedom. An incremental solution is performed with nonlinearities introduced as pseudoloads computed for initial strains. Equilibrium iteration may be performed at every step. Elastic and elastic-plastic response of boron/epoxy and graphite/epoxy graphite/epoxy and problems of curing 0/90 sub s Gr/Ep laminates with and without circular holes are analyzed. Mechanical loading of + or - 45sub s Gr/Ep laminates is modeled and symmetry conditions which exist in angle-ply laminates are discussed. Results are compared to experiments and other analytical models when possible. All models are seen to agree reasonably well with experimetnal results for off-axis tensile coupons. The laminate analyses show the three dimensional effects which are present near holes and free corners

Acoustic waves and heating due to molecular energy transfer in an electric discharge CO laser

This paper summarizes analytical studies and the interpretation of experimental results for the compression and rarefaction waves generated in the cavity of a pulsed CO electric discharge laser. A one-dimensional analysis of acoustic waves is applied to a transversely excited laser. The influences of heating in the cathode fall, heat transfer to the cathode, flow through both the anode and cathode, and bulk heating of the plasma are included. The analysis is used to relate the bulk heating rate to observable features of the pressure and density waves. Data obtained from interferograms and reported elsewhere are used to infer the bulk heating rates in a pulsed CO laser. Results are presented for CO/Ar, CO/N2, and N2 plasmas. Comparison of the data with recent theoretical results for the heating due to electron/ neutral collisions and the anharmonic defect associated with V-V energy transfer shows substantial differences at lower values of total energy deposition. The change of heating with E/N is in fairly good agreement with predicted values

Quantum Fluctuations in Dipolar Bose Gases

We investigate the influence of quantum fluctuations upon dipolar Bose gases by means of the Bogoliubov-de Gennes theory. Thereby, we make use of the local density approximation to evaluate the dipolar exchange interaction between the condensate and the excited particles. This allows to obtain the Bogoliubov spectrum analytically in the limit of large particle numbers. After discussing the condensate depletion and the ground-state energy correction, we derive quantum corrected equations of motion for harmonically trapped dipolar Bose gases by using superfluid hydrodynamics. These equations are subsequently applied to analyze the equilibrium configuration, the low-lying oscillation frequencies, and the time-of-flight dynamics. We find that both atomic magnetic and molecular electric dipolar systems offer promising scenarios for detecting beyond mean-field effects.Comment: Published in PR