Fracture mechanics analysis of a rail-end bolt hole crack

Analytic and experimental investigations were conducted to establish the cause of a peculiar ridge feature observed on the fracture surface of a railroad rail-end bolt hole fatigue crack. Calculations are performed which indicate that the ridges were caused by the change in stress caused by the thermal expansion of the rails during each day of fatigue. The ridge features were closely reproduced by a novel laboratory experiment on a four-hole compact tension specimen.     

Relative reactivities of bicyclo[3.2.1]octa-2,3-diene and 1,2-cycloheptadiene with conjugated dienes and styrene

Bicyclo[3.2.1]octa-2,3-diene (2) and 1,2-cycloheptadiene (3), generated by treatment of the corresponding dichlorides 4 and 5 with magnesium, were found to undergo cycloaddition reactions with 2,3-dimethylbutadiene, styrene, and 1,3-cyclopentadiene. 2, but not 3, was also found to undergo a (2 + 2) cycloaddition reaction with cis-pentadiene. The relative reactivities of 2 and 3 with cis-pentadiene, 2,3-dimethylbutadiene, styrene, and 1,3-cyclopentadiene at 60° in THF were found to be: 0·18, —; 1·0, 1·0; 0·60, 7·5; and 4·0, 150.     

Critical star multigraphs

A star-multigraphG is a multigraph in which there is a vertexv ⁺ which is incident with each non-simple edge. It is critical if it is connected, Class 2 and(G\e) < (G) for eache E(G). We show that, ifG is any star multigraph, then(G) (G) + 1. We investigate the edge-chromatic class of star multigraphs with at most two vertices of maximum degree. We also obtain a number of results on critical star multigraphs. We shall make use of these results in later papers.     

Substituting open educational resources for commercial curriculum materials: effects on student mathematics achievement in elementary schools

Open Educational Resources (OER) have the potential to replace commercial learning materials in education. An empirical examination of this potential was conducted, comparing the end-of-year mathematics test results of 12,110 elementary school students clustered within 95 schools from five school districts in the state of Washington in the United States of America. Of this group, 6796 students used open learning materials, and 5314 used commercial educational resources. When three years of test scores were considered, there were no statistically significant differences in the exam scores of students who used open versus commercial curriculum materials. The lack of statistical significance may have practical significance, demonstrating that OER can replace conventional materials without impacting student performance, while potentially reducing costs and allowing for local modification.     

High resolution electrospray ionization ion mobility spectrometry

Current commercially available ion mobility spectrometers are intended for the analysis of chemicals in the gas phase. Sample introduction methods, such as direct air sampling, a GC injector or a thermal desorber, are commonly an integral part of these instruments. This paper describes an electrospray ionization ion mobility spectrometer system that allows direct introduction samples in solution phase. This allows direct analysis of non-volatile organic and biological samples, and avoids decomposition of thermally liable samples, providing reliable chemical identification. In addition, the new ion mobility spectrometer allows mobility analysis with high resolving power. Commonly used commercial IMS systems provide resolving powers between 10 and 30; this new ion mobility spectrometer has resolving power greater than 60 for routine analysis. A high resolution instrument is necessary for many applications where a complex mixture needs to be separated and quantified. This paper demonstrates the advantages of using a high resolution ion mobility spectrometer and an electrospray ionization source for the analysis of non-volatile pharmaceuticals as well as dissolved explosive in solution phase.