Context and question: Infrared vibrational spectroscopy (see also near-infrared spectroscopy) is a technique that can be used to identify molecules by analysis of their constituent bonds. Each chemical bond in a molecule vibrates at a frequency characteristic of that bond. A group of atoms in a molecule (e.g., CH2) may have multiple modes of oscillation caused by the stretching and bending motions of the group as a whole. If an oscillation leads to a change in dipole in the molecule then it will absorb a photon that has the same frequency. The vibrational frequencies of most molecules correspond to the frequencies of infrared light. Typically, the technique is used to study organic compounds using light radiation from 4000–400 cm−1, the mid-infrared. A spectrum of all the frequencies of absorption in a sample is recorded. This can be used to gain information about the sample composition in terms of chemical groups present and also its purity (for example, a wet sample will show a broad O-H absorption around 3200 cm−1).
What technique can be used to identify organic compounds by analysis of their constituent bonds?
Answer: unanswerable
Context and question: Since the 1979 Revolution, to overcome foreign embargoes, Iran has developed its own military industry, produced its own tanks, armored personnel carriers, guided missiles, submarines, military vessels, guided missile destroyer, radar systems, helicopters and fighter planes. In recent years, official announcements have highlighted the development of weapons such as the Hoot, Kowsar, Zelzal, Fateh-110, Shahab-3 and Sejjil missiles, and a variety of unmanned aerial vehicles (UAVs). The Fajr-3 (MIRV) is currently Iran's most advanced ballistic missile, it is a liquid fuel missile with an undisclosed range which was developed and produced domestically.
Why did Iran have to build its own military hardware, vehicles, and weapons after the 1979 Revolution?
Answer: foreign embargoes
Context and question: The Early Cretaceous spans from 145 million to 100 million years ago. The Early Cretaceous saw the expansion of seaways, and as a result, the decline and extinction of sauropods (except in South America). Many coastal shallows were created, and that caused Ichthyosaurs to die out. Mosasaurs evolved to replace them as head of the seas. Some island-hopping dinosaurs, like Eustreptospondylus, evolved to cope with the coastal shallows and small islands of ancient Europe. Other dinosaurs rose up to fill the empty space that the Jurassic-Cretaceous extinction left behind, such as Carcharodontosaurus and Spinosaurus. Of the most successful would be the Iguanodon which spread to every continent. Seasons came back into effect and the poles got seasonally colder, but dinosaurs still inhabited this area like the Leaellynasaura which inhabited the polar forests year-round, and many dinosaurs migrated there during summer like Muttaburrasaurus. Since it was too cold for crocodiles, it was the last stronghold for large amphibians, like Koolasuchus. Pterosaurs got larger as species like Tapejara and Ornithocheirus evolved.
What caused Ichthyosaurs to thrive?
Answer:
unanswerable