Development and Application of an Activity Based Space-Time Accessibility Measure for Individual Activity Schedules

Accessibility is an important aspect of human existence impacting on our notion of society equity and justice. It plays an important role in a number of existing theories of spatial and travel behaviour in addition to affecting the rate and the pattern of land-use development. However despite the importance of the notion of accessibility, the accessibility measures, which have traditionally been used to quantify accessibility, have tended to be relatively poorly defined, excluding a wide range of observed forms of travel behaviour. This has ramifications for the implicit assumption underpinning the use of accessibility measures, namely that of a direct correlation between the measure of accessibility and individual travel behaviour. In this paper a hitherto unknown family of space-time route benefit measures are developed and utilised to derive an associated family of disaggregate activity based space-time utility accessibility measures. Applicable to individual activity schedules, these space-time activity accessibility measures implicitly acknowledge that travel is a derived demand. The paper commences with an outline of the limitations and primary assumptions present within traditional accessibility measures. The paper proceeds to provide a brief review of space-time user benefit measures highlighting their principle assumptions. Existing space-time locational benefit measures are subsequently extended to incorporate more realistic temporal constraints on activity participation and the perceived user benefit. The improved locational benefit measures incorporate a variety of factors including the utility an individual derives from activity participation, individual income, space-time constraints. In addition travel time, route delay and schedule disutility components such as the facility and activity wait times associated with early arrival are incorporated, in addition to late start time penalties associated with late commencement of an activity. The improved space-time locational benefit measure is subsequently applied to activity schedules incorporating a series of multiple linked activities. The paper subsequently demonstrates how the resulting user benefit measure can be shown to be part of a broader family of space-time route benefit measures, which despite their theoretical attractiveness have hitherto not been utilised by researchers. An associated family of space-time utility accessibility measures are subsequently developed and the paper proceeds to highlight how stochastic frontier models utilised in conjunction with existing travel/activity diary datasets can be utilised to operationalise the proposed measure of accessibility. The proposed family of accessibility measures are implemented within a point based spatial framework encompassing detailed spatially referenced land-use transportation network encompassing public transport, cycle, walk and car transport modes. Several practical examples are presented of the proposed family of accessibility measures in use and in particular demonstrate the strength and potential of the methodology in developing a wide range of transport-land-use policies. Examples are presented of the use of the methodology in developing new/improved transport links and services, the provision of additional land-use facilities/opportunities, extended opening of facilities/opportunities, the identification of transport related social exclusion, the development of equitable land-use transport schemes and policies as well as the development of flexible working policies. The paper concludes with a summary highlighting the principle benefits and properties of the proposed family of accessibility measures in addition to highlighting potential areas of future research.

Highway Infrastructure Investment and Regional Employment Growth: Dynamic Panel Regression Analysis

A number of macro-level studies attempting to establish the statistical link between public investment in highway infrastructure and employment have applied econometric techniques to estimate the effect of highways while controlling for the effects associated with other factors. Unfortunately, direct use of empirical findings from these historic and recent studies, in shaping transport policy and supporting particular investment decisions, has been rather limited by mixed and inconclusive evidence in the literature. Apart from the common differences among these studies in scope and methodology, another possible reason for the contradictory evidence is that much of the previous work has generally suffered from several methodology drawbacks. In many studies, for instance, several important determinants of employment growth are omitted, and the choices of control variables included in the estimated equations generally are not based on theory. Those studies based solely on cross-sectional data also typically do not account for unobserved regional heterogeneity that may explain spatial differences in employment changes. Moreover, the possibility that the causal relationship between transportation investment and economic growth could work in both directions is generally ignored. This paper attempts to shed some light on this controversy by analysing the effect of highway investment on county-level employment in the State of North Carolina, United States. We derive a reduced from model of equilibrium employment that considers the effects of highways and other potential factors on the supply and demand for labour. Given the potential for lagged responses of the labour market to any exogenous shock, we assume a partial adjustment process for actual employment in our empirical model. A panel data set for 100 North Carolina counties from 1985 to 1997 is used in order to control for unobserved county and time specific effects using panel regression techniques. We also address the causality issue by the use of a two-stage least squares procedure with an instrumental variable. Our main results are that the employment effect of highway infrastructure depends critically on model specifications considered, and failure to account for the dynamics of employment adjustment could lead to an upward bias in the estimated effect of highways.

The evolution of transcription-associated biases of mutations across vertebrates

<p>Abstract</p> <p>Background</p> <p>The interplay between transcription and mutational processes can lead to particular mutation patterns in transcribed regions of the genome. Transcription introduces several biases in mutational patterns; in particular it invokes strand specific mutations. In order to understand the forces that have shaped transcripts during evolution, one has to study mutation patterns associated with transcription across animals.</p> <p>Results</p> <p>Using multiple alignments of related species we estimated the regional single-nucleotide substitution patterns along genes in four vertebrate taxa: primates, rodents, laurasiatheria and bony fishes. Our analysis is focused on intronic and intergenic regions and reveals differences in the patterns of substitution asymmetries between mammals and fishes. In mammals, the levels of asymmetries are stronger for genes starting within CpG islands than in genes lacking this property. In contrast to all other species analyzed, we found a mutational pressure in dog and stickleback, promoting an increase of GC-contents in the proximity to transcriptional start sites.</p> <p>Conclusions</p> <p>We propose that the asymmetric patterns in transcribed regions are results of transcription associated mutagenic processes and transcription coupled repair, which both seem to evolve in a taxon related manner. We also discuss alternative mechanisms that can generate strand biases and involves error prone DNA polymerases and reverse transcription. A localized increase of the GC content near the transcription start site is a signature of biased gene conversion (BGC) that occurs during recombination and heteroduplex formation. Since dog and stickleback are known to be subject to rapid adaptations due to population bottlenecks and breeding, we further hypothesize that an increase in recombination rates near gene starts has been part of an adaptive process.</p

Experimental verification of the temperature coefficient of resistivity

We have created an experimental procedure for determining the temperature coefficient of resistivity, $\alpha_R$, for introductory physics laboratories. This method examines the relationship between temperature and resistivity to establish $\alpha_R$ within 10% of the accepted value

Determination of the coefficient of thermal expansion by measuring frequency of a heated music wire

Engaging with physical and material properties through empirical observation is a fundamental part of undergraduate physics and engineering education. Several works have proposed experiments to determine thermal physical constants of materials such as finding the coefficient of linear expansion. As Dajbych and Polak et al. have shown, methods for experimentally verifying physical constants can be done by measuring the frequency of a plucked high-carbon steel wire on a guitar. Building upon our previous work, we have extended our method to verify the coefficient of linear thermal expansion through an accessible procedure directed at introductory physics education

Global Newtonian limit for the Relativistic Boltzmann Equation near Vacuum

We study the Cauchy Problem for the relativistic Boltzmann equation with near Vacuum initial data. Unique global in time "mild" solutions are obtained uniformly in the speed of light parameter $c \ge 1$. We furthermore prove that solutions to the relativistic Boltzmann equation converge to solutions of the Newtonian Boltzmann equation in the limit as $c\to\infty$ on arbitrary time intervals $[0,T]$, with convergence rate $1/c^{2-\epsilon}$ for any $\epsilon \in(0,2)$. This may be the first proof of unique global in time validity of the Newtonian limit for a Kinetic equation.Comment: 35 page

Faster fibrin clot degradation characterizes patients with central pulmonary embolism at a low risk of recurrent peripheral embolism

It is unclear whether thrombus location in pulmonary arteries is associated with particular clot characteristics. We assessed 156 patients following either central or peripheral pulmonary embolism (PE). Plasma clot lysis time, the rate of D-dimer release from plasma clots (D-Drate) with the maximum D-dimer concentration achieved (D-Dmax), as well as fbrin formation on turbidimetry, plasma clot permeation, thrombin generation, and fbrinolytic parameters were measured 3–6 months after PE. Patients following central PE (n=108, 69.3%) were more likely smokers (38.9% vs 18.8%; p=0.01), less likely carriers of factor XIII Val34Leu allele (40.7% vs 62.5%, p=0.01), exhibited 16.7% higher D-Drate and 12.7% higher tissue plasminogen activator antigen (tPA:Ag) compared with peripheral PE (p=0.02 and p<0.0001, respectively). Saddle PE patients (n=31, 19.9%) had 11.1% higher D-Drate and 7.3% higher D-Dmax compared with central PE (both p<0.05). Twenty-three recurrent PE episodes, including 15 central episodes, during a median follow-up of 52.5 months were recorded. Plasma D-dimer and tPA:Ag were independent predictors for central recurrent PE, whereas D-Drate and peak thrombin predicted peripheral recurrent PE. Plasma clots degradation is faster in patients following central PE compared with peripheral PE and fbrinolysis markers might help to predict a type of recurrent PE

Value of Ascitic Lipids in the Differentiation between Cirrhotic and Malignant Ascites

Ascitic fluid concentrations of cholesterol, triglycerides and phospholipids, were compared with ascitic fluid total protein in 40 patients with chronic liver disease, 51patients with various neoplasms and 1 patient with cardiac failure. Seven patients withboth chronic liver disease and malignancy were considered separately. The first 54 patients (23 cirrhotic and 31 with malignancy) were used to determine median values and ranges and to define the most suitable cutoff concentrations between both groups. Median values for cholesterol (75 mg per dl), phospholipids (0.79 mmole per liter), triglycerides (75 mg per dl) and protein (3.8 gm per dl)were higher in malignant ascites compared to ascitic fluid concentrations of cholesterol (20 mg per dl), phospholipids (0.33 mmole per liter), triglycerides (51 mg per dl) and protein (1.9 gm per dl) in patients withcirrhosis. The best discrimination values were 48 mg per dl for cholesterol, 0.6 mmole per liter for phospholipids, 65 mg per dl for triglycerides and 2.5 gm per dl for protein. Application of these cutoff points to 38 subsequent patients (17 cirrhotic, 1 with cardiac failure and 20 with malignancy) revealed an efficiency of 86.8% for cholesterol, 86.8% for phospholipids, 68.4% for triglycerides and 79.0% for protein. From the data of all 92 patients, an efficiency of 92.3% forcholesterol, 79.4% for phospholipids, 72.8% for triglycerides and 79.4% for protein was calculated. We conclude that ascitic fluid cholesterol determination offers an excellent, cost-effective discrimination of ascites due to cirrhosis vs. ascites caused by malignancies