An Alternative Rail Pad Tester for Measuring Dynamic Properties of Rail Pads Under Large Preloads

One of the main components in ballasted railway track systems is the rail pad. It is installed between the rail and the sleeper to attenuate wheel/rail interaction loads, preventing the underlying railway sleepers from excessive stress waves. Generally, the dynamic design of tracks relies on the available data, which are mostly focused on the structural condition at a specific toe load. Recent findings show that track irregularities could significantly amplify the loads on railway tracks. This phenomenon gives rise to a concern that the rail pads may experience higher effective preloading than anticipated in the past. On this ground, this paper highlights the significance of accounting for effects of preloading on dynamic properties of polymeric rail pads. An innovative test rig for controlling preloads on rail pads has been devised. A non-destructive methodology for evaluating and monitoring the dynamic properties of the rail pads has been developed based on an instrumented hammer impact technique and an equivalent single degree-of-freedom system approximation. Based on the impact-excitation responses, some of the selected rail pads have been tested to determine such modal parameters as dynamic stiffness and damping constants in the laboratory. The influence of large preloads on dynamic properties of both new and worn rail pads is demonstrated in this paper. Additionally, the design criteria, which has been used to take into account the influence of the level of preload on dynamic properties of generic rail pads, are discussed. Note: The authors’ work in the references can be found electronically via UoW Research Online at URL     

SN2’ versus SN2 Reactivity: Control of Regioselectivity in Conversions of Baylis–Hillman Adducts

TiCl₄‐induced Baylis–Hillman reactions of α,β‐unsaturated carbonyl compounds with aldehydes yield the (Z)‐2‐(chloromethyl)vinyl carbonyl compounds 5 , which react with 1,4‐diazabicyclo[2.2.2]octane (DABCO), quinuclidine, and pyridines to give the allylammonium ions 6 . Their combination with less than one equivalent of the potassium salts of stabilized carbanions (e.g. malonate) yields methylene derivatives 8 under kinetically controlled conditions (S_N2’ reactions). When more than one equivalent of the carbanions is used, a second S_N2’ reaction converts 8 into their thermodynamically more stable allyl isomers 9 . The second‐order rate constants for the reactions of 6 with carbanions have been determined photometrically in DMSO. With these rate constants and the previously reported nucleophile‐specific parameters N and s for the stabilized carbanions, the correlation log k (20 °C)=s(N + E) allowed us to calculate the electrophilicity parameters E for the allylammonium ions 6 (?19<E <?18). The kinetic data indicate the S_N2’ reactions to proceed via an addition–elimination mechanism with a rate‐determining addition step.     

An Unexpected Pyrimidine Ring Transformations in the Reaction of 4‐aryl‐5‐nitro‐6‐bromomethylpyrimidin‐2(1H)‐ones with Anilines

The reaction of 4‐aryl‐6‐bromomethyl‐5‐nitro‐3,4‐dihydropyrimidin‐2(1H)‐ones, containing three possible combinations of substituted and unsubstituted nitrogen atoms with anilines depending on the conditions leads to the products of ring contraction of the pyrimidinone ring into an imidazolone, as well as to the formation of 7‐aryl‐6,7‐dihydroisoxazolo[4,3‐d]pyrimidin‐5(4H)‐one derivatives, and in some cases to the 5‐aminopyrimidinones. The mechanisms of these unusual ring transformations are discussed.     

Sigma complexes in the pyrimidine series. 4. Investigation of the electronic absorption spectra of anionic sigma complexes of 5-nitropyrimidine

The electronic absorption spectra of sigma complexes of the Meisenheimer type, viz., the anions of potassium salts of 4H-5-nitro-4-acetonylpyrimidines, were investigated. The 5-nitropyrimidine molecule and its sigma complex involving the 4 position were subjected to quantum-chemical calculation by the simple MO LCAO method. It is shown that it is expedient to use the Forster-Dewar-Knott rule for the study of the electronic spectra of the indicated sigma complexes.See [16] for Communication 3.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1260–1263, September, 1981.     

Synthesis and some conversions of 4-aryl-6-methyl-2-methoxy(phenyl)-5-nitro-1,4-dihydropyrimidines

The reaction of 1-arylidene-1-nitropropan-2-ones with O-methylisourea (or benzamidine) in the presence of aluminum oxide gave 4-aryl-6-methyl-2-methoxy(phenyl)-5-nitro-1,4-dihydropyrimidines. It was shown that the reactions of the compounds synthesized with electrophilic agents proceed at the exocyclic methyl group, as well as at the N₍₁₎, N₍₃₎, and C₍₅₎ atoms of the 1,4-dihydropyrimidine fragment of the molecule.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1398–1404, October, 1993.     

Pyrimidine σ-complexes. 10. First furoxano[3,4-d]pyrimidine anion σ-complexes

Preparations are reported for anionic -complexes derived from 5- and 7-methoxyfuroxano[3,4-d]pyrimidines. The 5-methoxy derivatives add alcohols and water to form covalent -adducts.For Communication 9, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 101–106, January, 1992.     

σ-Complexes in the Pyrimidine Series. 14. Dihydropyrimidine Analogs of Acyclonucleosides. Synthesis of 2,3-Dihydroxypropyl Derivatives of 4-Aryl-6-methyl-5-nitro-1,4(3,4)-dihydropyrimidin-2-ones

Methods have been developed for the synthesis of 5-nitro-1,4- and 5-nitro-3,4-dihydropyrimidin-2-one analogs of acyclonucleosides containing a 2,3-dihydroxypropyl fragment in positions 1 and 3 respectively of the dihydropyrimidine ring.     

Pyrimidine sigma-complexes. 7. The recyclization of 5-nitropyrimidine and its methoxy derivatives upon reaction with the acetylacetone carbanion

A study was carried out on the reaction of 5-nitro and 5-nitromethoxypyrimidines with the acetylacetone carbanion. Benzene and pyridine derivatives are formed as a result of recyclization. The direction of the reaction depends on the position of the substituents in the pyrimidine ring and the nature of the bases.Communication 6, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 508–512, April, 1987.     

Nitrodihydropyrimidines (review)

Published data on the production and chemical transformations of nitrodihydropyrimidines are reviewed. Examples of substances having high biological activity are given.Institute of Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of Ukraine, Kiev 253660; Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1587–1602, December, 1997.