Investigating the effect of modeling single-vehicle and multi-vehicle crashes separately on confidence intervals of Poisson-gamma models

Crash prediction models still constitute one of the primary tools for estimating traffic safety. These statistical models play a vital role in various types of safety studies. With a few exceptions, they have often been employed to estimate the number of crashes per unit of time for an entire highway segment or intersection, without distinguishing the influence different sub-groups have on crash risk. The two most important sub-groups that have been identified in the literature are single- and multi-vehicle crashes. Recently, some researchers have noted that developing two distinct models for these two categories of crashes provides better predicting performance than developing models combining both crash categories together. Thus, there is a need to determine whether a significant difference exists for the computation of confidence intervals when a single model is applied rather than two distinct models for single- and multi-vehicle crashes. Building confidence intervals have many important applications in highway safety.This paper investigates the effect of modeling single- and multi-vehicle (head-on and rear-end only) crashes separately versus modeling them together on the prediction of confidence intervals of Poisson-gamma models. Confidence intervals were calculated for total (all severities) crash models and fatal and severe injury crash models. The data used for the comparison analysis were collected on Texas multilane undivided highways for the years 1997-2001. This study shows that modeling single- and multi-vehicle crashes separately predicts larger confidence intervals than modeling them together as a single model. This difference is much larger for fatal and injury crash models than for models for all severity levels. Furthermore, it is found that the single- and multi-vehicle crashes are not independent. Thus, a joint (bivariate) model which accounts for correlation between single- and multi-vehicle crashes is developed and it predicts wider confidence intervals than a univariate model for all severities. Finally, the simulation results show that separate models predict values that are closer to the true confidence intervals, and thus this research supports previous studies that recommended modeling single- and multi-vehicle crashes separately for analyzing highway segments.     

Two-dimensional solitons in a Kerr cavity

Abstract

We study the existence and nature of soliton-like localized states in a passive cavity containing a Kerr medium driven by a plane-wave input field. As the background intensity is increased, these structures are always created in pairs, for topological reasons. The smaller ‘soliton’ is always unstable, while in two transverse dimensions the larger ‘soliton’ usually collapses to a singularity or decays.     

Sensitivity of stress corrosion cracking of stainless steel to surface machining and grinding procedure

An investigation has been undertaken to establish the effect of surface preparation method on the susceptibility of a 304 stainless steel to stress corrosion cracking under simulated atmospheric corrosion conditions. MgCl₂ was deposited onto four-point bend specimens, which were then placed in a chamber with a relative humidity of 45% and temperature of 60 °C. These test conditions were designed to reflect external exposure of stainless steel components in industrial plant, including nuclear reactor components, situated in a coastal region, but with the severity of the exposure conditions enhanced to allow discrimination of the effect of surface preparation in a short timescale (up to 1500 h). Four surface preparation methods were evaluated: transverse grinding, longitudinal grinding, transverse dressing using an abrasive flap wheel, and transverse milling. For each case, surface topography, surface defect mapping, near-surface microhardness mapping, residual stress and electron back-scattered diffraction measurements were undertaken. Stress corrosion cracks were observed for the ground and milled specimens but not for the dressed specimens, with cracks apparently originating at corrosion pits. The density of cracks increased in the order: transverse ground, milled and longitudinal ground, with the cracks notably much smaller in length for the transverse ground condition. The propensity for cracking could be linked to the high residual stress and apparent nanocrystalline microstructure at the surface. There was a greater propensity for pitting to initiate at local defect sites on the surface (laps, deeper grooves). However, the tendency was not overwhelming, suggesting that other factors such as more general roughness or the distribution of MnS inclusions had an influence, perhaps reflecting the severity of the environment.     

Dynamic Measurements of Mechanical Errors in Sliver-drawing

An investigation is reported in which the lifts of the roller necks of the upper of each of the sets of drafting rollers in a drawframe were measured. Data expressed in the frequency domain showed that roller errors could be clearly seen at the fundamental frequencies of the various rollers when the error and the measurements related to the same set of rollers. Some harmonics were also visible. When errors were in one set of rollers and the measurements were made down the fibre-flow line, the sharpness of the peaks was greatly reduced by drafting waves in the fibres flowing through the system. It was deduced that drafting waves dispersed the singular frequencies produced.

An absolute encoder was used on a bottom roller to average out asynchronous signal components and random errors. The averaged data demonstrated the roller shape under dynamic conditions even when the error was small. It was possible to use a ratio technique to produce a virtual encoder for the top roller. At start-up, the viscoelastic properties of the rubber covering, the distance apart of the rollers, and the error levels changed as the rubber warmed up. The dynamic shape of the roller could be determined, and the result was repeatable.     

Collective reflection strategy for moderating conformity tendency and promoting reflective judgment performance

Reflective judgement is crucial for medical-related practitioners in dealing with controversial issues. However, the conformity phenomenon is likely to occur and interfere with reflective judgement learning during interactive activities. Effective strategies are required to moderate the conformity behaviour tendency (CBT) and improve reflective judgement performance (RJP). This study demonstrates two significant results: (a) Compared with the guided self-reflection learning strategy, the online collective reflection (OCR) learning strategy effectively weakened the learners' general CBT while dealing with professional controversial issues; and (b) a significantly negative correlation between the RJP achieved and the change of CBT in online environment was detected in the OCR group. The implications and potential applications in higher education were discussed. Further studies are needed to confirm the long-term effects and the extending application to other professional studies.     

BB-10010: an active variant of human macrophage inflammatory protein-1 alpha with improved pharmaceutical properties

The stem cell inhibitor, macrophage inflammatory protein-1 alpha (MIP-1 alpha) or LD78, protects multipotent hematopoietic progenitors in murine models from the cytotoxic effects of chemotherapy. Clinical use of human MIP-1 alpha during chemotherapy could therefore lead to faster hematologic recovery and may allow dose intensification. We have also shown that human MIP-1 alpha causes the rapid mobilization of hematopoietic cells, suggesting an additional clinical use in peripheral blood stem cell transplantation. However, the clinical evaluation of human MIP-1 alpha is complicated by its tendency to associate and form high molecular weight polymers. We have produced a variant of rhMIP-1 alpha, BB-10010, carrying a single amino acid substitution of Asp26 > Ala, with a reduced tendency to form large polymers at physiologic pH and ionic strength. This greatly increases its solubility, facilitating its production and clinical formulation. We confirmed the potency of BB-10010 as a human MIP-1 alpha-like agonist in receptor binding, calcium mobilization, inhibition of colony formation, and thymidine suicide assays. The myeloprotective activity of BB-10010 was shown in a murine model of repeated chemotherapy using hydroxyurea. BB-10010 is therefore an ideal variant with which to evaluate the therapeutic potential of recombinant human MIP-1 alpha.     

Newborn screening for inborn errors of metabolism: a systematic review

OBJECTIVES. To establish a database of literature and other evidence on neonatal screening programmes and technologies for inborn errors of metabolism. To undertake a systematic review of the data as a basis for evaluation of newborn screening for inborn errors of metabolism. To prepare an objective summary of the evidence on the appropriateness and need for various existing and possible neonatal screening programmes for inborn errors of metabolism in relation to the natural history of these diseases. To identify gaps in existing knowledge and make recommendations for required primary research. To make recommendations for the future development and organisation of neonatal screening for inborn errors of metabolism in the UK. HOW THE RESEARCH WAS CONDUCTED. There were three parts to the research. A systematic review of the literature on inborn errors of metabolism, neonatal screening programmes, new technologies for screening and economic factors. Inclusion and exclusion criteria were applied, and a working database of relevant papers was established. All selected papers were read by two or three experts and were critically appraised using a standard format. Seven criteria for a screening programme, based on the principles formulated by Wilson and Jungner (WHO, 1968), were used to summarise the evidence. These were as follows. Clinically and biochemically well-defined disorder. Known incidence in populations relevant to the UK. Disorder associated with significant morbidity or mortality. Effective treatment available. Period before onset during which intervention improves outcome. Ethical, safe, simple and robust screening test. Cost-effectiveness of screening. A questionnaire which was sent to all newborn screening laboratories in the UK. Site visits to assess new methodologies for newborn screening. The classical definition of an inborn error of metabolism was used (i.e., a monogenic disease resulting in deficient activity in a single enzyme in a pathway of intermediary metabolism). RESEARCH FINDINGS. INBORN ERRORS OF METABOLISM. Phenylketonuria (PKU) (incidence 1:12,000) fulfilled all the screening criteria and could be used as the 'gold standard' against which to review other disorders despite significant variation in methodologies, sample collection and timing of screening and inadequacies in the infrastructure for notification and continued care of identified patients. Of the many disorders of organic acid and fatty acid metabolism, a case can only be made for the introduction of newborn screening for glutaric aciduria type 1 (GA1; estimated incidence 1:40,000) and medium-chain acyl CoA dehydrogenase (MCAD) deficiency (estimated incidence 1:8000-1:15,000). Therapeutic advances for GA1 offer prevention of neurological damage but further investigation is required into the costs and benefits of screening for this disorder. MCAD deficiency is simply and cheaply treatable, preventing possible early death and neurological handicap. Neonatal screening for these diseases is dependent upon the introduction of tandem mass spectrometry (tandem MS). This screening could however also simultaneously detect some other commonly-encountered disorders of organic acid metabolism with a collective incidence of 1:15,000.(ABSTRACT TRUNCATED)     

Coincidence-site lattices as rational approximants to irrational twins

It is well known that sequences of crystals with Mackay icosahedral motif and increasing lattice parameters exist converging to the icosahedral quasicrystal in the limit. They are known as rational approximants. It has also been demonstrated that it is possible to create icosahedral symmetry by irrational twins involving five variants by 72° rotations around an irrational axis [τ 1 0] or an irrational angle of 44.48° around a rotation axis [1 1 1]. These twinned crystals do not share a coincidence site lattice. In this paper, it is demonstrated that the above twinning relationship arises in the limit of a sequence of coincidence site lattices starting with the cubic twins with Σ = 3 and extending through Σ = 7, 19, 49, 129, 337, …, ∞ created by rotation around [1 1 1] axis. It is also noted that the boundaries of higher CSL values (Σ > 7) are composed of a combination of structural units from Σ = 3 and Σ = 7 boundaries.