Cure kinetics of a thermosetting liquid dicyanate ester monomer/high-Tg polycyanurate material

The cure of a liquid dicyanate ester monomer, which reacts to form a high-T_g (≈200°C) polycyanurate network, has been investigated using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and a dynamic mechanical technique, torsional braid analysis (TBA). The monomer is cured with and without catalyst. The same one-to-one relationship between fractional conversion and the dimensionless glass transition temperature is found from DSC data for both the uncatalyzed and catalyzed systems, independent of cure temperature, signifying that the same polymeric structure is produced. T_g is the parameter used to monitor the curing reactions since it is uniquely related to conversion, is sensitive, is accurately determined, and is also directly related to the solidification process. The rate of uncatalyzed reaction is found to be much slower than that of the catalyzed reaction. The apparent overall activation energy for the uncatalyzed reaction is found to be greater than that of the catalyzed reaction (22 and 13 kcal/mol, respectively) from time–temperature superposition of experimental isothermal T_g vs. In time data to form kinetically-controlled master curves for the two systems. Although the time–temperature superposition analysis does not necessitate knowledge of the rate expression, it has limitations, because if the curing process consists of parallel reactions with different activation energies, as is considered to be the case from analysis of the FTIR data, there should not be a kinetically-controlled master curve. Consequently, a kinetic model, which can be satisfactorily extrapolated, is developed from FTIR isothermal cure studies of the uncatalyzed reaction. The FTIR data for the uncatalyzed system at high cure temperatures, where the material is in the liquid or rubbery states throughout cure, 190 to 220°C, are fitted by a model of two parallel reactions, which are second-order and second-order autocatalytic (with activation energies of 11 and 29 kcal/mol), respectively. Using the model parameters determined from the FTIR studies and the relationship between T_g and conversion from DSC studies, T_g, vs. time curves are calculated for the uncatalyzed system and found to agree with DSC experimental results for isothermal cure temperatures from 120 to 200°C to even beyond vitrification. The DSC data for the catalyzed system are also described by the same kinetic model after incorporating changes in the pre-exponential frequency factors (due to the higher concentration of catalyst) and after incorporating diffusion-control, which occurs prior to vitrification in the catalyzed system (but well after vitrification in the uncatalyzed system). Time–temperature-transformation (TTT) isothermal cure diagrams for both systems are calculated from the kinetic model and compared to experimental TBA data. Experimental gelation is found to occur at a conversion of approximately 64% in the catalyzed system by comparison of experimental macroscopic gelation at the various curing temperatures and iso-T_g (iso-conversion) curves calculated from the kinetic model. © 1993 John Wiley & Sons, Inc.     

A multiple decision procedure in clinical trials

In some multiple treatment arm clinical trials there is an order of preference for the treatments based on secondary considerations like toxicity or cost. In this paper, we consider the case where two or more treatments could have equal prior preference. This formulation includes the problem of comparing several equally preferred experimental treatments to one control, or the comparison of a combination with its components. Our decision procedures will guarantee a high selection probability for the correct treatment(s) when that selection is appropriate. We establish sample size requirements for our decision procedures which can be applied to clinical trials with normal, binomial, or right censored exponential endpoints.     

Chlamydia pneumoniae infection in patients with myocardial infarct and angina pectoris

In a prospective open study we investigated Chlamydia pneumoniae infections in 36 consecutively admitted patients: 26 males, mean age 53.4 yr, range 36-70 yr, 10 females mean age 57.7 yr, range 47-70 yr, suffering myocardial infarction (24 acute, 2 previous) or angina pectoris (10). Antibody serum levels were measured by the immunefluorescent method and they were as follows: negative 5, low 12, medium/high 11, chronic infection 5, recent infection 3. The 3 cases considered as recent infections are described in detail.     

Beta-gamma radiation from leaching resistant glasses containing uranium ions

The β and γ decay of uranium atoms from xUO₃(100 - x)[3B₂O₃ · MO] glass systems, where M=Sr or Pb and 0 ≤ × ≤ 20 mol%, is investigated. The γ decay data are very close to each other, for the same UO₃ contents, in both the systems. The composition dependence of the β decay exhibits a lower slope in the lead borate matrix than in the strontium borate matrix. The ratio between the β activity of samples with the same uranium ion concentrations in the two investigated glass systems is a function of the x values. The results are correlated with the amount of radioactive nuclides and with the structural environments of the radionuclides. The leaching treatment in water at temperatures below 100°C evidenced no aqueous dissolution of glass samples.     

Correction to: Where do university graduates live? – a computer vision approach using satellite images

Applied Intelligence - A Correction to this paper has been published: https://doi.org/10.1007/s10489-021-02433-z     

From LTL to unambiguous Büchi automata via disambiguation of alternating automata

Formal Methods in System Design - Due to the high complexity of translating linear temporal logic (LTL) to deterministic automata, several forms of “restricted” nondeterminism have been...     

Nodal ant colony optimization for solving profit based unit commitment problem for GENCOs

This paper proposes a nodal ant colony optimization (NACO) technique to solve profit based unit commitment problem (PBUCP). Generation companies (GENCOs) in a competitive restructured power market, schedule their generators with an objective to maximize their own profit without any regard for system social benefit. Power and reserve prices become important factors in decision process. Ant colony optimization that mimics the behavior of ants foraging activities is suitably implemented to search the UCP search space. Here a search space consisting of optimal combination of binary nodes for unit ON/OFF status is represented for the movement of the ants to maintain good exploration and exploitation search capabilities. The proposed model help GENCOs to make decisions on the quantity of power and reserve that must be put up for sale in the markets and also to schedule generators in order to receive the maximum profit. The effectiveness of the proposed technique for PBUCP is validated on 10 and 36 generating unit systems available in the literature. NACO yields an increase of profit, greater than 1.5%, in comparison with the basic ACO, Muller method and hybrid LR-GA.     

Wollaston prism with large split angle

The image formation through a Wollaston prism with large split angle is studied. Formulas for the split angle, approximate calculations of aberrations, and ray tracings are used. The most important aberrations found are astigmatism and anamorphic distortion. Tilting the Wollaston with respect to the incident beam may reduce these aberrations, and if the orientation of the optical axis in the first element is varied it is possible to cancel one of the two aberrations for both images simultaneously, while the other one is substantially reduced. With an adequate adjustment of all the construction parameters the images become sharp enough to allow the use of large split angles (approximately 15 degrees).