The widely accepted cause of the collapse of the World Trade Center (WTC) towers in New York on Sept. 11, 2001, has been confirmed mathematically and firmly supported by mechanical analysis. Some lay critics, however, still question the conclusions of this analysis, even without presenting any meaningful calculations. They blame the collapse on a controlled demolition, implying a conspiracy by the republican government. many mass media outlets, including Czech ones, blindly gave this misinformation wide publicity. The present invited article summarizes why the collapse was a spontaneous and inevitable result of aircraft impact, and how this fact is explained and confirmed by mathematical analysis of the mechanics of collapse, and by numerous observed data., Zdeněk P. Bažant, Milan Jirásek., and Obsahuje bibliografii
This contribution gives a brief description of the characteristics of spectral lines formed in the solar chromosphere in the visual range and its continuum in the visual, millimetre, and sub-millimetre (mm-submm) spectral range. The contribution reviews processes responsible for continuum radiation of the limb in the visual range and continua in the mm-submm spectral range. The spectral lines of sodium doublet Na I D1 and D2 are not genuine chromospheric lines since their cores are formed predominately by resonant scattering of radiation from the upper photosphere. Therefore, the cores of Na I D1 and D2 provide information only about chromospheric velocities. An occurrence of the doublet Na I D1, D2 together with helium lines with large excitation and ionization potential indicates an intricate thermodynamic structure of the chromosphere. As numerical simulations indicate, the chromospheric internetwork comprises of cooler cavities surrounded with hotter sheets allowing the occurrence of spectral lines over a large range of excitation and ionization potentials. The contribution accentuates the large diagnostic potential of the mm-submm continua of the chromospheric spectrum. It will be fully exploited after finishing of the ALMA array for the study of the chromospheric fine structure with large angular and temporal resolution., Príspevok podáva stručnú charakteristiku čiarového spektra slnečnej chromosféry vo vizuálnej oblasti a jej spojitého spektra (kontinua) vo vizuálnej, milimetrovej a submilimetrovej (mm-submm) oblasti. Príspevok predstavuje procesy tvoriace vizuálne kontinuum pozorovatel'né na limbe a kontinuá v mm-submm oblasti. Čiary sodíkového dubletu NA I D1 a D2 nie sú v pravom slova zmysle chromosférické, pretože ich jadrá sú tvorené hlavne rezonančným rozptylom žiarenia hornej fotosféry, a preto poskytujú informáciu iba o rýchlostných poliach v chromosfére. Výskyt dubletu Na I D1 a D2 spolu s čiarami hélia s veľkou excitačnou a ionizačnou energiou naznačuje zložitú termodynamickú štruktúru chromosféry. Ako ukazujú numerické simulácie, chromosféra sa v oblastiach mimo magnetickej siete skládá z chladnejších oblastí obalených horúcou látkou, čo umožňuje vznik spektrálnych čiar vo vel'kom rozsahu excitačných a ionizačných energií. Príspevok poukazuje na vel'ký diagnostický potenciál kontinuí v mm-submm oblasti spektra chromosféry, ktorý bude naplno využitý po dokončení rádioteleskopu ALMA pri štúdiu jemnej štruktúry chromosféry s vel'mi vel'kým uhlovým a časovým rozlíšením., Július Koza., and Obsahuje bibliografii
Holanďan Christiaan Huygens významně přispěl k rozvoji mechaniky a optiky v návaznosti na problémy, které řešila astronomie. Je vynálezcem kyvadlových hodin, nejpřesnějšího časoměrného přístroje doby umožňujícího poprvé stanovení zeměpisné délky plujících lodí., The article deals with the life and work of Dutch astronomer, physicist and mathematician Christiaan Huygens. Describing his extensive scientific work, we start with his activities in the field of observational astronomy (e.g. the discovery of the rings and moon of Saturn and the summary of the existing knowledge of the planets in his publication Cosmotheoros). His discovery and quantitative description of centrifugal force contributed significantly to solving problems describes in Newton´s Principia. Huygens is also well-known as a technician and technical designer. He constructed the first pendulum clocks. Last but not least, we describe his work on the impact of solid bodies, when he reflected on the work of R. Descartes and J. Marek Marci., František Jáchim., and Obsahuje seznam literatury
Ve dnech 10. a 11. března 2017 proběhla v Plzni konference o životě a díle Josefa Františka Smetany. Akce byla součástí tradičního kulturního festivalu Smetanovské dny. Hlavním pořadatelem konference byla Západočeská pobočka České astronomické společnosti. and Ondřej Trnka.
Sofia Kovalevskaya was not only a great Russian mathematician, but also a writer and advocate of women's rights in the 19th century. After concluding her sexondary schooling, Sofia was determined to continue her education at the university level. She travelled to Heidelberg to study mathematics, but discovered there that as a woman she could not graduate. In 1870 she moved to Berlin to study with Karl Meierstrass, in 1874 she was granted a Ph.D. from the Göttingen University. In 1883 she received an invitation from Gösta Mittag-Leffler to lecture at the University of Stockholm. Sophia's most famous work is on the theory of partial differential equations, and on the rotation of a solid body about a fixed point. Sophia died very young, at the age of 41, from pneumonia., Ivo Kraus., and Obsahuje bibliografii