12 research outputs found
Construction of the Tycho Reference Catalogue
The Tycho Reference Catalogue (TRC) project, as proposed in 1992 by the
present authors, aimed to extend the Hipparcos reference system to fainter
magnitudes. To assure rigidity of the reference system realization, the
project relied on the Tycho Cataloguethat provides highly-accurate positions of more
than one million stars on the Hipparcos system. To maintain the precision of
the reference system over longer periods of time, high-precision proper
motions must be derived from Tycho and earlier ground-based measurements,
most notably the century-old Astrographic Catalogue(AC).
The recently published first version of the Tycho Reference Catalogue
provides highly-accurate positions and proper motions for 990 182 stars of
the Tycho Catalogue. It realizes the ICRS/Hipparcos system in the optical domain with a
median accuracy of 45 mas at epoch J2000.0. The realization is based on stars
of median magnitude mag, providing an average of 24 reference
stars per square degree. The median accuracy of the TRC proper motions,
estimated from external comparisons as 2.4 mas/yr, ensures a reference system
realization with an accuracy better than 100 mas over the time span of a few
decades. Highly-accurate astrometry combined with homogeneous two-colour
Tycho photometry makes TRC an ideal choice for a wide range of astronomical
applications.
The present paper covers the major steps of the TRC construction, including
the Astrographic Cataloguereduction onto the Hipparcos system, identification of the Tycho Catalogue
stars in the AC, derivation of proper motions, a posteriori systematic
corrections of the proper motions to account for residual AC systematic
errors, and the TRC quality assessment. The relation of the TRC with the
recently published ACT catalogue is outlined. A future version of the TRC, to
be based on the new Tycho data
processing and a global block adjustment of the Astrographic Catalogue, is briefly discussed
QSAR ANALYSIS OF COMPLEXATION OF ETHERS OF 7-BROM-3-HYDROXY-5-(2'-CHLORO) PHENYL-1,2-DIHYDRO-3H-1,4-BENZODIAZEPIN-2-ONES WITH CENTRAL BENZODIAZEPINE RECEPTORS CNS
QSAR analysis of the structural infl uence of 3-substituted 1,2-dihydro-3Н-1,4-benzodiazepine derivatives on the thermodynamic characteristics (ΔН0, ΔS0 and ΔG0) of their complexation with compounds was the main problem of QSAR analysis in this study. For small sets a new approach was developed for constructing statistical models and estimating their predictive ability. The developed special procedure for the generation of ensembles of QSAR models made it possible to construct adequate «structure – thermodynamic parameters» models for an «extremely small» set (6 compounds). 2D-PLS QSAR models were developed using the structural descriptors calculated by Dragon program and the descriptors calculated by the method based on the simplex representation of the molecular structure. The consensus models with quite good statistical characteristics (R2 > 0.95 for work set, R2 test > 0.78 for test set) were obtained for thermodynamic charact eristics complexation of investigated compounds. The prognosis of the thermodynamic parameters of binding of the related compounds with R = H, iso-C4H9, sec.-C4H9 to the CBDR was carried out using the simplex descriptors and Dragon descriptors. The increa se in the corresponding alkyl substituent from ethyl to isomeric butyl does not signifi cantly affect the interaction of ligands with the CBDR. It is assumed that the amount of Hydrogen atoms bounding to the Carbon atom adjacent to the carbonyl group has a certain infl uence on the thermodynamic characteristics of ligands interaction with CBDR; this may be due to the hyperconjugation effect. Exner’s method has revealed that the mechanism of interaction of the methyl-substituted compound with the CBDR differs from the mechanism of interaction with the CBDR of other investigated compounds
QSAR АНАЛІЗ КОМПЛЕКСОУТВОРЕННЯ ЕСТЕРІВ 7-БРОМ-3-ГІДРОКСИ-5-(2’-ХЛОР)ФЕНІЛ-1,2-ДИГІДРО-3Н-1,4-БЕНЗДІАЗЕПІН-2-ОНІВ З ЦЕНТРАЛЬНИМИ БЕНЗДІАЗЕПІНОВИМИ РЕЦЕПТОРАМИ ЦНС
QSAR analysis of the structural infl uence of 3-substituted 1,2-dihydro-3Н-1,4-benzodiazepine derivatives on the thermodynamic characteristics (ΔН0, ΔS0 and ΔG0) of their complexation with compounds was the main problem of QSAR analysis in this study. For small sets a new approach was developed for constructing statistical models and estimating their predictive ability. The developed special procedure for the generation of ensembles of QSAR models made it possible to construct adequate «structure – thermodynamic parameters» models for an «extremely small» set (6 compounds). 2D-PLS QSAR models were developed using the structural descriptors calculated by Dragon program and the descriptors calculated by the method based on the simplex representation of the molecular structure. The consensus models with quite good statistical characteristics (R2 > 0.95 for work set, R2 test > 0.78 for test set) were obtained for thermodynamic charact eristics complexation of investigated compounds. The prognosis of the thermodynamic parameters of binding of the related compounds with R = H, iso-C4H9, sec.-C4H9 to the CBDR was carried out using the simplex descriptors and Dragon descriptors. The increa se in the corresponding alkyl substituent from ethyl to isomeric butyl does not signifi cantly affect the interaction of ligands with the CBDR. It is assumed that the amount of Hydrogen atoms bounding to the Carbon atom adjacent to the carbonyl group has a certain infl uence on the thermodynamic characteristics of ligands interaction with CBDR; this may be due to the hyperconjugation effect. Exner’s method has revealed that the mechanism of interaction of the methyl-substituted compound with the CBDR differs from the mechanism of interaction with the CBDR of other investigated compounds.Проведено QSAR аналіз впливу структури похідних 3-заміщених 1,4-бенздіазепінів на термодинамічні характеристики (ΔН0, ΔS0 и ΔG0) їх комплексоутворення з центральними бенздіазепіновими рецепторами (ЦБДР) ЦНС. Основною проблемою аналізу виявилась незначна кількість досліджуваних сполук, у зв’язку з чим було розроблено новий підхід для малих вибірок щодо побудови статистичних моделей та оцінки їхньої прогнозувальної здатності. Використовуючи спеціальну процедуру для формування навчальних та тестових вибірок, структурні дескриптори, розраховані за допомогою програми Dragon, і дескриптори, розраховані в рамках методу, що базується на симплексному представленні молекулярної структури, було побудовано адекватні 2D-PLS моделі «структура - термодинамічні параметри» для «надзвичайно малого» набору досліджуваних речовин (6 сполук). Отримані моделі мають задовільні статистичні характеристики: R2 > 0.95 для навчальної вибірки, R2 test > 0.78 для тестової вибірки. З метою більш детального аналізу впливу замісника на термодинамічні характеристики похідних 3-заміщених 1,4-бенздіазепінів було спрогнозовано значення ΔН0, ΔS0 і ΔG0 комплексеутворення з ЦБДР для сполук з R = H, i-C4H9, s-C4H9.Встановлено, що збільшення довжини і розгалуженості відповідного алкільного заступника від етилу до ізомерних бутилів не суттєво впливає на взаємодію лігандів з ЦБДР. Зроблено припущення, що певний вплив на термодинамічні характеристики взаємодії лігандів з ЦБДР має кількість атомів Гідрогену, які зв’язані з атомом Карбону алкілу, що знаходиться поряд з карбонільною групою, що може бути пов’язано з ефектом гіперкон’югації. Метод Екснера дозволив виявити, що механізм взаємодії метил-заміщеної сполуки з ЦБДР відрізняється від механізму взаємодії з ЦБДР інших досліджуваних сполук