Areas, nodes and networks: Some analytical considerations

In spatial interaction modelling, trips between origins and destinations within the same areal zone have a predominant influence on both the value of the gravity parameter and on the associated pattern of flows. Despite this, the relevant highly sensitive intrazonal impedance values are usually based on approximate average intrazonal distances or times. This situation has been identified in the literature as the ?self potential? problem. In this paper, integration over continuous space within the origin destination zones is applied to not only compute the intrazonal flows more accurately, but also to determine their influence on calibration of the value of the gravity parameter itself. In addition, whereas all trips are assumed to have destinations corresponding to nodes of the transport network, interzonal trips, starting from dispersed origins, are assigned shortest path routes to join the interzonal links at efficient intermediate points. In the analysis, further approximations incurred in evaluation of the sets of origin/destination flows between contiguous zones are also identified. The eventual aim is to develop practical ?rules of thumb? for correcting the conventional analysis. Flows between areal zones and facility nodes may occur along several plausible alternative paths, rather than via one abstract ?interzonal? path, as usually considered in conventional spatial interaction models. Such destination/route choice is easy to handle in the relatively uncongested conditions characterizing off-peak discretionary travel. This paper examines facility choice via alternative routes, as well as attempting to discern the influence of ?intervening opportunities?. It is indicated how intervening opportunities may influence discretionary travel positively, in contrast to their identified negative influence on the probability of choosing the final destination in journey to work travel. Such intervening opportunities can only be considered meaningfully along the alternative paths of the actual network, as specified above.

Kaluza-Klein anisotropy in the CMB

We show that 5-dimensional Kaluza-Klein graviton stresses can slow the decay of shear anisotropy on the brane to observable levels, and we use cosmic microwave background anisotropies to place limits on the initial anisotropy induced by these stresses. An initial shear to Hubble distortion of only \sim 10^{-3}\Omega_0h_0^2 at the 5D Planck time would allow the observed large-angle CMB signal to be a relic mainly of KK tidal effects.Comment: 4 pages revtex; minor changes to improve clarit

Testing for value stability with a meta-analysis of choice experiments: River health in Australia

While meta-analysis is typically used to identify value estimates for benefit transfer, applications also provide insights into the potential influence of design, study and methodological factors on results of non-market valuation experiments. In this paper, a metaanalysis of sixteen separate choice modelling studies in Australia with 130 individual value estimates relating to river health are reported. The studies involved different measures and scales of river health, so consistency was generated by transforming implicit prices from each study into a common standard of WTP per kilometer of river in good health. Tobit models have been used to identify the relationships between the dependent variable (WTP/km) and a number of variables. The results demonstrate that values are sensitive to marginal effects, with lower WTP/km for larger catchments, and higher WTP/km when river health is in decline. Values are also lower when river health has been defined by a subset of benefit types, such as recreation uses, vegetation health, fish health or bird populations. While there is evidence that the framing of the choice sets and descriptions of attributes have systematic impacts on values, there is very little evidence that choice dimensions, collection methods, sample sizes, response rates, statistical methods or publication status have influenced value estimates. Tests of apparent author effects show that these become insignificant when other explanatory variables are included in the models.non-market valuation, choice modelling, meta analysis, river health, Environmental Economics and Policy,

A review of multi-criteria decision making methods for enhanced maintenance delivery

Conventionally there is a strong relation between manufacturing and services in complex engineering industries. For companies which aim to last in the competitive manufacturing market choosing appropriate decision making methods to improve their maintenance delivery has a vital role. The aim of this paper is to review Multi Criteria Decision Making (MCDM) models, evaluate each method and do a critical comparison to assess them from a maintenance management point of view. The first section of this paper reviews MCDM methods in different literature, and then the second part develops a set of criteria to classify different techniques. At the end methods are compared based on developed criteria. This paper assesses different MCDM models, and provides a framework to select approaches for maintenance management

Exploiting iteration-level parallelism in dataflow programs

The term "dataflow" generally encompasses three distinct aspects of computation - a data-driven model of computation, a functional/declarative programming language, and a special-purpose multiprocessor architecture. In this paper we decouple the language and architecture issues by demonstrating that declarative programming is a suitable vehicle for the programming of conventional distributed-memory multiprocessors.This is achieved by appling several transformations to the compiled declarative program to achieve iteration-level (rather than instruction-level) parallelism. The transformations first group individual instructions into sequential light-weight processes, and then insert primitives to: (1) cause array allocation to be distributed over multiple processors, (2) cause computation to follow the data distribution by inserting an index filtering mechanism into a given loop and spawning a copy of it on all PEs; the filter causes each instance of that loop to operate on a different subrange of the index variable.The underlying model of computation is a dataflow/von Neumann hybrid in that exection within a process is control-driven while the creation, blocking, and activation of processes is data-driven.The performance of this process-oriented dataflow system (PODS) is demonstrated using the hydrodynamics simulation benchmark called SIMPLE, where a 19-fold speedup on a 32-processor architecture has been achieved

Spectral and bulk properties of turbulence in the surface layer of air over the sea

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Performance of a high-work, low-aspect-ratio turbine stator tested with a realistic inlet radial temperature gradient

A 0.767-scale model of a turbine stator designed for the core of a high-bypass-ratio aircraft engine was tested with uniform inlet conditions and with an inlet radial temperature profile simulating engine conditions. The principal measurements were radial and circumferential surveys of stator-exit total temperature, total pressure, and flow angle. The stator-exit flow field was also computed by using a three-dimensional Navier-Stokes solver. Other than temperature, there were no apparent differences in performance due to the inlet conditions. The computed results compared quite well with the experimental results

Executing matrix multiply on a process oriented data flow machine

The Process-Oriented Dataflow System (PODS) is an execution model that combines the von Neumann and dataflow models of computation to gain the benefits of each. Central to PODS is the concept of array distribution and its effects on partitioning and mapping of processes.In PODS arrays are partitioned by simply assigning consecutive elements to each processing element (PE) equally. Since PODS uses single assignment, there will be only one producer of each element. This producing PE owns that element and will perform the necessary computations to assign it. Using this approach the filling loop is distributed across the PEs. This simple partitioning and mapping scheme provides excellent results for executing scientific code on MIMD machines. In this way PODS allows MIMD machines to exploit vector and data parallelism easily while still providing the flexibility of MIMD over SIMD for multi-user systems.In this paper, the classic matrix multiply algorithm, with 1024 data points, is executed on a PODS simulator and the results are presented and discussed. Matrix multiply is a good example because it has several interesting properties: there are multiple code-blocks; a new array must be dynamically allocated and distributed; there is a loop-carried dependency in the innermost loop; the two input arrays have different access patterns; and the sizes of the input arrays are not known at compile time. Matrix multiply also forms the basis for many important scientific algorithms such as: LU decomposition, convolution, and the Fast-Fourier Transform.The results show that PODS is comparable to both Iannucci's Hybrid Architecture and MIT's TTDA in terms of overhead and instruction power. They also show that PODS easily distributes the work load evenly across the PEs. The key result is that PODS can scale matrix multiply in a near linear fashion until there is little or no work to be performed for each PE. Then overhead and message passing become a major component of the execution time. With larger problems (e.g., >/=16k data points) this limit would be reached at around 256 PEs

Public values for improved water security for domestic and environmental use

A choice modelling valuation exercise was recently undertaken across several countries to assess the tradeoffs that households are prepared to make between water use restrictions, maintaining environmental condition in waterways, and increased water costs. The results from the Queensland survey are reported in this paper. Also discussed are some of the tradeoffs involved in assuring the integrity of an international survey while retaining sufficient local context to make the choice modelling exercise both realistic and meaningful.Choice modelling, water scarcity, water use tradeoffs, international survey, Resource /Energy Economics and Policy, Environmental Economics and Policy,