DSIF station schedules

System manages Deep Space Instrumentation Facilities /DSIF/ equipment construction and modification planning. Versatile program applies to such tasks as employee time and task schedules, pay schedules, operations schedules, and plant and equipment procurement, construction, modification or service

Opening up the open spaces through space syntax

In many parts of the world, housing and neighbourhood developments of the latetwentieth century have been shaped by the belief that it is important to createcommunal open spaces that can provide a physical focus for local communities.This has given rise to a range of modern housing typologies that are based on anethos of building community through design, using concepts such as a ?privacygradient?, the separation of pedestrian and vehicular movement and the notion of?enclosure?, amongst others, to shape the public open space of the estate. Thispaper examines the contribution of such public spaces to community awareness intwenty-eight English city-centre housing estates with differing housingmorphologies, built between the middle of the nineteenth century and the earlytwenty-first century. As a manifestation of the complex social relationships thattake place within the domain of public space, we suggest that the above conceptsand their physical realisation need to be complemented by careful consideration ofsocial notions such as the constitutedness of the spaces, co-presence andsurveillance. The methodology used is based on a detailed analysis of the builtforms and spatial layouts of the estates, combined with a ?space syntax? analysis ofthe interconnectedness and accessibility of the public realm within each estate,representations that show the extent of visual fields from key public open spacesand an appraisal of the types of physical boundaries surrounding each of theseopen spaces and the openings that give onto them. The juxtaposition of thesedifferent analyses provides insight into the interfaces maintained spatially betweenresidents and non-residents and the possibilities that are thereby created formutual awareness and encounter. In many parts of the world, housing and neighbourhood developments of the latetwentieth century have been shaped by the belief that it is important to createcommunal open spaces that can provide a physical focus for local communities.This has given rise to a range of modern housing typologies that are based on anethos of building community through design, using concepts such as a ?privacygradient?, the separation of pedestrian and vehicular movement and the notion of?enclosure?, amongst others, to shape the public open space of the estate. Thispaper examines the contribution of such public spaces to community awareness intwenty-eight English city-centre housing estates with differing housingmorphologies, built between the middle of the nineteenth century and the earlytwenty-first century. As a manifestation of the complex social relationships thattake place within the domain of public space, we suggest that the above conceptsand their physical realisation need to be complemented by careful consideration ofsocial notions such as the constitutedness of the spaces, co-presence andsurveillance. The methodology used is based on a detailed analysis of the builtforms and spatial layouts of the estates, combined with a ?space syntax? analysis ofthe interconnectedness and accessibility of the public realm within each estate,representations that show the extent of visual fields from key public open spacesand an appraisal of the types of physical boundaries surrounding each of theseopen spaces and the openings that give onto them. The juxtaposition of thesedifferent analyses provides insight into the interfaces maintained spatially betweenresidents and non-residents and the possibilities that are thereby created formutual awareness and encounter

Catastrophic Phase Transitions and Early Warnings in a Spatial Ecological Model

Gradual changes in exploitation, nutrient loading, etc. produce shifts between alternative stable states (ASS) in ecosystems which, quite often, are not smooth but abrupt or catastrophic. Early warnings of such catastrophic regime shifts are fundamental for designing management protocols for ecosystems. Here we study the spatial version of a popular ecological model, involving a logistically growing single species subject to exploitation, which is known to exhibit ASS. Spatial heterogeneity is introduced by a carrying capacity parameter varying from cell to cell in a regular lattice. Transport of biomass among cells is included in the form of diffusion. We investigate whether different quantities from statistical mechanics -like the variance, the two-point correlation function and the patchiness- may serve as early warnings of catastrophic phase transitions between the ASS. In particular, we find that the patch-size distribution follows a power law when the system is close to the catastrophic transition. We also provide links between spatial and temporal indicators and analyze how the interplay between diffusion and spatial heterogeneity may affect the earliness of each of the observables. We find that possible remedial procedures, which can be followed after these early signals, are more effective as the diffusion becomes lower. Finally, we comment on similarities and differences between these catastrophic shifts and paradigmatic thermodynamic phase transitions like the liquid-vapour change of state for a fluid like water

Singularity theory study of overdetermination in models for L-H transitions

Two dynamical models that have been proposed to describe transitions between low and high confinement states (L-H transitions) in confined plasmas are analysed using singularity theory and stability theory. It is shown that the stationary-state bifurcation sets have qualitative properties identical to standard normal forms for the pitchfork and transcritical bifurcations. The analysis yields the codimension of the highest-order singularities, from which we find that the unperturbed systems are overdetermined bifurcation problems and derive appropriate universal unfoldings. Questions of mutual equivalence and the character of the state transitions are addressed.Comment: Latex (Revtex) source + 13 small postscript figures. Revised versio

Generation of scalar-tensor gravity effects in equilibrium state boson stars

Boson stars in zero-, one-, and two-node equilibrium states are modeled numerically within the framework of Scalar-Tensor Gravity. The complex scalar field is taken to be both massive and self-interacting. Configurations are formed in the case of a linear gravitational scalar coupling (the Brans-Dicke case) and a quadratic coupling which has been used previously in a cosmological context. The coupling parameters and asymptotic value for the gravitational scalar field are chosen so that the known observational constraints on Scalar-Tensor Gravity are satisfied. It is found that the constraints are so restrictive that the field equations of General Relativity and Scalar-Tensor gravity yield virtually identical solutions. We then use catastrophe theory to determine the dynamically stable configurations. It is found that the maximum mass allowed for a stable state in Scalar-Tensor gravity in the present cosmological era is essentially unchanged from that of General Relativity. We also construct boson star configurations appropriate to earlier cosmological eras and find that the maximum mass for stable states is smaller than that predicted by General Relativity, and the more so for earlier eras. However, our results also show that if the cosmological era is early enough then only states with positive binding energy can be constructed.Comment: 20 pages, RevTeX, 11 figures, to appear in Class. Quantum Grav., comments added, refs update

Catastrophic regime shifts in model ecological communities are true phase transitions

Ecosystems often undergo abrupt regime shifts in response to gradual external changes. These shifts are theoretically understood as a regime switch between alternative stable states of the ecosystem dynamical response to smooth changes in external conditions. Usual models introduce nonlinearities in the macroscopic dynamics of the ecosystem that lead to different stable attractors among which the shift takes place. Here we propose an alternative explanation of catastrophic regime shifts based on a recent model that pictures ecological communities as systems in continuous fluctuation, according to certain transition probabilities, between different micro-states in the phase space of viable communities. We introduce a spontaneous extinction rate that accounts for gradual changes in external conditions, and upon variations on this control parameter the system undergoes a regime shift with similar features to those previously reported. Under our microscopic viewpoint we recover the main results obtained in previous theoretical and empirical work (anomalous variance, hysteresis cycles, trophic cascades). The model predicts a gradual loss of species in trophic levels from bottom to top near the transition. But more importantly, the spectral analysis of the transition probability matrix allows us to rigorously establish that we are observing the fingerprints, in a finite size system, of a true phase transition driven by background extinctions.Comment: 19 pages, 11 figures, revised versio

Green Infrastructure in Coastal Landscapes: Ecological Design, Hydrological Function, and Sustainable Land Use Goals

2012 S.C. Water Resources Conference - Exploring Opportunities for Collaborative Water Research, Policy and Managemen

The Clumping Transition in Niche Competition: a Robust Critical Phenomenon

We show analytically and numerically that the appearance of lumps and gaps in the distribution of n competing species along a niche axis is a robust phenomenon whenever the finiteness of the niche space is taken into account. In this case depending if the niche width of the species $\sigma$ is above or below a threshold $\sigma_c$, which for large n coincides with 2/n, there are two different regimes. For $\sigma > sigma_c$ the lumpy pattern emerges directly from the dominant eigenvector of the competition matrix because its corresponding eigenvalue becomes negative. For $\sigma </- sigma_c$ the lumpy pattern disappears. Furthermore, this clumping transition exhibits critical slowing down as $\sigma$ is approached from above. We also find that the number of lumps of species vs. $\sigma$ displays a stair-step structure. The positions of these steps are distributed according to a power-law. It is thus straightforward to predict the number of groups that can be packed along a niche axis and it coincides with field measurements for a wide range of the model parameters.Comment: 16 pages, 7 figures; http://iopscience.iop.org/1742-5468/2010/05/P0500

Canonical Melnikov theory for diffeomorphisms

We study perturbations of diffeomorphisms that have a saddle connection between a pair of normally hyperbolic invariant manifolds. We develop a first-order deformation calculus for invariant manifolds and show that a generalized Melnikov function or Melnikov displacement can be written in a canonical way. This function is defined to be a section of the normal bundle of the saddle connection. We show how our definition reproduces the classical methods of Poincar\'{e} and Melnikov and specializes to methods previously used for exact symplectic and volume-preserving maps. We use the method to detect the transverse intersection of stable and unstable manifolds and relate this intersection to the set of zeros of the Melnikov displacement.Comment: laTeX, 31 pages, 3 figure