Прогнозирование кристаллической стабильности вин. Обзор методов

Кристаллизация битартрата калия, вызванная химическим взаимодействием катионов калия и анионов винной кислоты, является одним из наиболее часто встречаемых видов дестабилизации вин. Для обеспечения розливостойкости продукции необходимо достоверное прогнозирование образования осадка, что даст возможность применять превентивные технологические меры. Проведена систематизация и дана сравнительная характеристика существующих тестов на кристаллическую стабильность вин, в основу которых заложены различные принципы: расчетные, провокационные и инструментальные. Расчетные методы построены на математических действиях с учетом содержания и/или соотношения непосредственных участников реакции (винная кислота, калий), а также содержания титруемых кислот и этилового спирта, рН. Провокационные методы основаны на создании условий (охлаждение), при которых ускоряются естественные процессы кристаллообразования. Инструментальные методы предполагают измерение электропроводности с помощью кондуктометра и оценку ее изменения при пересыщении системы вина битартратом калия. Наименее достоверными считаются расчетные методы, не учитывающие особенности вина как сложной минерально-органической системы, в первую очередь это относится к красным винам. Прогнозирование стабильности по результатам холодовых тестов характеризует способность вина к выпадению кристаллов на данный момент, но требует длительного времени для проведения анализа; тесты, основанные на изменении электропроводности, достаточно оперативны и позволяют сделать вывод о потенциальной устойчивости системы к кристаллообразованию. Обоснована необходимость разработки достоверного способа диагностики розливостойкости виноматериалов для выбора схемы их технологической обработки и контроля эффективности стабилизации.Potassium bitartrate crystallization caused by chemical interaction between cations of potassium and anions of tartaric acid is a most frequent type of wine destabilization. To achieve wine stability, sediment formation must be reliably predicted, which will enable application of preventive technological measures. Available tests for cristalline stablilization of wines basing on different priciples were classified and characterized on a comparative basis. Calculation methods rely on mathematical operations referring to levels and/or ratios of immediate reaction agents (tartaric acid and potassium). Provocation methods establish conditions accelerating destablilization processes (changes in temperature, levels of titratable acids and tartaric acid, pH). Instrumental methods involve conductivity measurement and consideration of changes in the index when the wine system becomes supersaturated with potassium bitartrate. The lowest reliablity is associated with calculation methods since they do not take into account specific features of wine as a compex mineral and organic system. Cold tests provide information about properties of wine at a definite moment while those using conductivity changes allow to conclude about potential resistance of the system to crystallization. The need is substantiated for developing a reliable method to diagnose stability of wine materials so that a scheme of their technological treatment can be selected and stabilization effectiveness controled.

Nonlinear Analyses for Thermal Cracking in the Design of Concrete Structures

A Design by Analysis procedure has been developed to incorporate the results of thermal cracking analyses into the linear based design methods for reinforced concrete containment structures. Current practice employs linear based analyses and accounts for stress reduction due to thermal induced cracking on a section by section basis. Under thermal loading, in addition to a reduction of the section forces and moments for cracked sections, concrete cracking also reduces the structural stiffness and thus the constraint against thermal expansion or contraction for the whole structure, which in turn reduces the thermal induced stresses as compared to a linear (un-cracked) analysis. The design by analysis approach employs nonlinear thermal cracking analyses using detailed modeling of the complete structure. By comparing these stress distributions with those from a linear analysis of the same model, stress reduction factors can be developed for critical sections that also include global stress redistribution. These stress reduction factors can then be used to correct linear based thermal stresses in the design basis calculation for all load combinations that include thermal loads.

Timber Basis Allocation with Incomplete Records

Forest owners are required to maintain complete and accurate accounting records of their timber transactions. This allows for proper allocation of basis, calculation of depletion allowance, and accurate calculation of tax due from timber sales. If accounting records are incomplete (basis allocation was not properly performed in the past), the forest owner and his or her accountant and forester will need to calculate the basis allocation that should have taken place in the past. The proper basis allocation and a methodology to allocate basis when records are incomplete are illustrated. South. J. Appl. For. 28(2):109–112.

Large Basis Calculation of Positron?Hydrogen Scattering at Low Energies

Calculations of low energy positron-hydrogen scattering using the close coupling approach are reported at low energies. The channel space includes nine physical hydrogen and positronium states and in addition twelve hydrogen and positronium pseudo-states. For energies below the positronium formation threshold, phase shifts are reported for J = 0 to 6 and are believed to have an absolute accuracy of 0�0015 radian or better. Elastic scattering and positronium formation cross sections in the Ore gap for the J = 0 and J = 1 partial waves are essentially identical with previous variational calculations. Total elastic and positronium formation cross sections are reported at incident energies below the ionisation threshold. Cross sections for the excitation of the H(n=2), H(n=3) and Ps( n=2) levels are also reported over a restricted energy range, and the total reaction cross section has been computed and compared with experiment.