57 research outputs found
Semidefinite programming bounds for few-distance sets in the Hamming and Johnson spaces
No full textWe study the maximum cardinality problem of a set of few distances in the
Hamming and Johnson spaces. We formulate semidefinite programs for this problem
and extend the 2011 works by Barg-Musin and Musin-Nozaki. As our main result,
we find new parameters for which the maximum size of two- and three-distance
sets is known exactly.Comment: Renew the whole article to add more results and author
Deals on Wheels: An Analysis of the New Federal Auto Feebate
No full textOttawa's new feebate program to promote fuel efficiency in new cars requires some major retooling.feebates
In-Situ Hollow Sample Setup Design for Mechanical Characterisation of Gaseous Hydrogen Embrittlement of Pipeline Steels and Welds
No full textThis work discusses the design and demonstration of an in-situ test setup for testing pipeline steels in a high pressure gaseous hydrogen (H2) environment. A miniature hollow pipe-like tensile specimen was designed that acts as the gas containment volume during the test. Specific areas of the specimen can be forced to fracture by selective notching, as performed on the weldment. The volume of H2 used was minimised so the test can be performed safely without the need of specialised equipment. The setup is shown to be capable of characterising Hydrogen Embrittlement (HE) in steels through testing an X60 pipeline steel and its weldment. The percentage elongation (%El) of the base metal was found to be reduced by 40% when tested in 100 barg H2. Reduction of cross-sectional area (%RA) was found to decrease by 28% and 11% in the base metal and weld metal, respectively, when tested in 100 barg H2. Benchmark test were performed at 100 barg N2 pressure. SEM fractography further indicated a shift from normal ductile fracture mechanisms to a brittle transgranular (TG) quasi-cleavage (QC) type fracture that is characteristic of HE
Translation association schemes, poset metrics, and the shape enumerator of codes
No full textPoset metrics form a generalization of the Hamming metric on the space double-struck F q n. Orbits of the group of linear isometries of the space give rise to a translation association scheme. The structure of the dual scheme is important in studying duality of linear codes; this study is facilitated if the scheme is self-dual. We study the relation between self-duality of the scheme and that of the poset. We also give new examples of poset metric spaces and describe the association schemes that arise from linear isometries. © 2012 IEEE.Poset metrics form a generalization of the Hamming metric on the space double-struck F q n. Orbits of the group of linear isometries of the space give rise to a translation association scheme. The structure of the dual scheme is important in studying dual101105sem informaçãosem informaçãoBarg, A., Purkayastha, P., Bounds on ordered codes and orthogonal arrays (2009) Moscow Mathematical Journal, 9 (2), pp. 211-243. , arXiv:cs/0702033Brouwer, A.E., Cohen, A.M., Neumaier, A., (1989) Distance-regular Graphs, , Springer-Verlag, Berlin e. aBrualdi, R.A., Graves, J.S., Lawrence, K.M., Codes with a poset metric (1995) Discrete Math., 147 (1-3), pp. 57-72Dougherty, S.T., Skriganov, M.M., MacWilliams duality and the Rosenbloom-Tsfasman metric (2002) Mosc. Math. J., 2 (1), pp. 81-97+199Kim, D.S., Kim, H.K., Duality of Translation Association Schemes Coming from Certain Actions, , arXiv:1108.4947Kim, H.K., Oh, D.Y., A classification of posets admitting the MacWilliams identity (2005) IEEE Trans. Inform. Theory, 51 (4), pp. 1424-1431Lee, K., The automorphism group of a linear space with the Rosenbloom-Tsfasman metric (2003) Eur. J. Combinatorics, 24, pp. 607-612Martin, W.J., Stinson, D.R., Association schemes for ordered orthogonal arrays and (T,M, S)-nets (1999) Canad. J. Math., 51 (2), pp. 326-346Panek, L., Firer, M., Kim, H.K., Hyun, J.Y., Groups of linear isometries on poset structures (2008) Discrete Math., 308 (18), pp. 4116-4123Park, W., Barg, A., Linear ordered codes, shape enumerators, and parallel channels Proc. 48th Annual Allerton Conf. Commun. Control Comput., Monticello, IL, Sept. 30-Oct. 1, 2010, pp. 361-367Rosenbloom, M.Yu., Tsfasman, M.A., Codes for the m-metric (1997) Problems of Information Transmission, 33 (1), pp. 45-52IEEE International Symposium on Information Theory ProceedingsResearch of this author supported in part by NSF grants CCF0916919 and DMS110169
Why are middle-class parents more involved in school than working-class parents?
No full textThis is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.This article studies why middle-class parents are more involved in school than working-class parents. From theoretical approaches developed in different disciplines hypotheses on the mediating effects of five mechanisms are derived: cultural capital or educational resources, concerted cultivation, economic and time resources, parents’ own school experience and status maintenance motives. Using data from a French national survey on students in 9th grade, I analyse to what extent these mechanisms mediate social class differentials in (1) attendance at parents’ evenings, (2) PTA-membership and (3) being parent representative. I find that educational resources mediate the largest parts of the social class differences. Concerted cultivation, status maintenance, parents’ working status, number of siblings and single-parenthood have mediating effects, too. In contrast to a claim made in the literature, parents’ own school experience has no effects on their involvement
Hydrogen-Accelerated Fatigue of API X60 Pipeline Steel and Its Weld
No full textIn this work, the hydrogen fatigue of pipeline steel X60, its girth welds and weld defects were investigated through in situ fatigue testing. A novel in situ gaseous hydrogen charging fatigue set-up was developed, which involves a sample geometry that mimics a small-scale pipeline with high internal hydrogen gas pressure. The effect of hydrogen was investigated by measuring the crack initiation and growth, using a direct current potential drop (DCPD) set-up, which probes the outer surface of the specimen. The base and weld metal specimens both experienced a reduction in fatigue life in the presence of hydrogen. For the base metal, the reduction in fatigue life manifested solely in the crack growth phase; hydrogen accelerated the crack growth by a factor of 4. The crack growth rate for the weld metal accelerated by a factor of 8. However, in contrast to the base metal, the weld metal also experienced a reduction of 57% in resistance to crack initiation. Macropores (>500 µm in size) on the notch surface reduced the fatigue life by a factor of 11. Varying the pressure from 70 barg to 150 barg of hydrogen caused no difference in the hydrogen fatigue behavior of the weld metal. The fracture path of the base and weld metal transitioned from transgranular and ductile in nature to a mixed-mode transgranular and intergranular quasi-cleavage fracture. Hydrogen accelerated the crack growth by decreasing the roughness- and plasticity-induced crack closure. The worst case scenario for pipelines was found in the case of weld defects. This work therefore highlights the necessity to re-evaluate pipelines for existing defects before they can be reused for hydrogen transport.Team Vera Popovic
An analysis of social class differentials in parent-initiated contact with teachers
No full textThis is the author accepted manuscript. The final version is available from Taylor & Francis via the DOI in this recordThis article analyses the association between social class and parent-initiated contact with teachers. Hypotheses are derived from Lareau’s theory on ‘concerted cultivation’ and status maintenance theory on rational educational decision-making. Data from a national survey on French students traversing secondary school are used to study social class differentials in parents’ involvement in Grade 9 when students are about to proceed to an important transition from lower to upper secondary school. Linear probability models reveal that the likelihood that parents initiate meetings with the teachers decreases as student’s performance increasesand that concerted cultivation beliefs have positive effects.
Through inclusion of interaction terms into the models, clear evidence is provided that middle-class parents are more likely to seek a meeting than working-class parents when their children face difficulties
Numerical study for accidental gas releases from high pressure pipelines
No full textThis work concerns the analysis of consequences of gas releases from high pressure pipelines due to accidental events. This analysis has been performed using the CFD code Fluent. The first step of the work intended to evaluate the capability of Fluent to adequately simulate a supersonic underexpanded free jet. This validation has been based on small scale experimental data from literature. Methane jets from high pressure (from 10 to 250 barg), large diameter (0.5 m) pipelines have then been simulated. As second step of our analysis, a simplified model (based on works by Birch et al.) to handle the highly-compressible-fluid region of such kind of jets has been checked. Birch model resulted reliable once completed with two relations, one to evaluate the air entrainment and the other to compute the distance from the release point at which fluid catches up the atmospheric pressure
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