A Spatial and Statistical Approach for Imputing Origin-Destination Matrices from Household Travel Survey Data: A Sydney Case Study

A Household Travel Survey (HTS) is a valuable instrument for collecting data suitable for studying the travel behaviour of a sample of households in a specific geographical context. One important output from the trip data after expansion to the population is a set of origin-destination (O-D) trip matrices for combinations of trip purpose, time of day and mode of transport. However, the O-D matrices generally take the form of sparse matrices (ie cell values are mostly zero). The degree of sparseness of these matrices is a function of sample size (a consequence of cost constraints), segmentation requirements and the spatial resolution of a geographical zoning system. Another factor contributing to the sparseness is the non-revelation of information in some cells in order to protect the privacy of households who live in those cells where their total amount of travel in a cell is less than a cut-off criterion (eg < 200 trips). Establishing an appropriate value to assign to a ‘zero value’ cell is a non-trivial task. There are two key issues to work through. The first is how to set up a classification rule to determine either if zero value cells have no travel related activity at all (ie genuine zeroes) or the travel values are truly missing. The second issue is the development of a trip allocation rule to assign the number of trips to each missing value cell within the constraint of a given total number of trips to be allocated to each missing value cell (given knowledge of marginals). This paper shows how spatial and statistical techniques can be implemented to estimate the number of missing value cells and the number of trips associated with each missing value cell. The classification rule is a spatial one in locating missing value cells for any travel activities between each origin and destination. It is driven by the mean trip length distribution of the origin and destination distance among traffic zones. The trip allocation rule is constructed to allocate the number of trips to missing value cells using a distribution assumption (such as the uniform). The two rules are then combined in a process based on the proportion of trip purposes and modes of travel for a whole sample of household travel records. We implement the method for Sydney for the period 1998- 2000 to obtain total passenger trip movements for linked trips by five purposes, six modes and six times of day

Analysis of rolling bearing power loss models for twin screw oil injected compressor

The mechanical losses inside a screw compressor limit the performance of the compressor in terms of efficiency. These losses arise due to relative motion between elements inside the screw compressor. The estimation of mechanical losses predicted in the literature is around 10-15% of the total shaft power. One of the elements which contribute significantly to these losses is rolling element bearings. There are numerous mathematical models available which predict power losses in the rolling bearings. The objective of this paper is to study different models to predict power loss for rolling bearings and to predict the power losses for the bearings used for oil injected, twin screw compressor. A comparison between different power loss models for different operating conditions of compressor is also presented in this paper and results of analysis are compared with available experimental observations. The analysis helps to determine suitable power loss model for different operating conditions and more realistic predictions of the power losses. This allows designers for more accurate estimation of the performance of screw compressors

String order and hidden topological symmetry in the SO(2n+1) symmetric matrix product states

We have introduced a class of exactly soluble Hamiltonian with either SO(2n+1) or SU(2) symmetry, whose ground states are the SO(2n+1) symmetric matrix product states. The hidden topological order in these states can be fully identified and characterized by a set of nonlocal string order parameters. The Hamiltonian possesses a hidden $(Z_{2}\times Z_{2})^{n}$ topological symmetry. The breaking of this hidden symmetry leads to $4^{n}$ degenerate ground states with disentangled edge states in an open chain system. Such matrix product states can be regarded as cluster states, applicable to measurement-based quantum computation.Comment: 5 pages, 1 figur

Structure and energetics of the Si-SiO_2 interface

Silicon has long been synonymous with semiconductor technology. This unique role is due largely to the remarkable properties of the Si-SiO_2 interface, especially the (001)-oriented interface used in most devices. Although Si is crystalline and the oxide is amorphous, the interface is essentially perfect, with an extremely low density of dangling bonds or other electrically active defects. With the continual decrease of device size, the nanoscale structure of the silicon/oxide interface becomes more and more important. Yet despite its essential role, the atomic structure of this interface is still unclear. Using a novel Monte Carlo approach, we identify low-energy structures for the interface. The optimal structure found consists of Si-O-Si "bridges" ordered in a stripe pattern, with very low energy. This structure explains several puzzling experimental observations.Comment: LaTex file with 4 figures in GIF forma

Two-State Migration of DNA in a structured Microchannel

DNA migration in topologically structured microchannels with periodic cavities is investigated experimentally and with Brownian dynamics simulations of a simple bead-spring model. The results are in very good agreement with one another. In particular, the experimentally observed migration order of Lambda- and T2-DNA molecules is reproduced by the simulations. The simulation data indicate that the mobility may depend on the chain length in a nonmonotonic way at high electric fields. This is found to be the signature of a nonequilibrium phase transition between two different migration states, a slow one and a fast one, which can also be observed experimentally under appropriate conditions.Comment: Revised edition corresponding to the comments by the referees, submitted to Physical Review

Conformal Covariantization of Moyal-Lax Operators

A covariant approach to the conformal property associated with Moyal-Lax operators is given. By identifying the conformal covariance with the second Gelfand-Dickey flow, we covariantize Moyal-Lax operators to construct the primary fields of one-parameter deformation of classical $W$-algebras.Comment: 13 pages, Revtex, no figures, v.2: typos corrected, references added and conclusion modifie