On 27 September, MacArthur received the top secret National Security Council Memorandum 81/1 from Truman reminding him that operations north of the 38th parallel were authorized only if "at the time of such operation there was no entry into North Korea by major Soviet or Chinese Communist forces, no announcements of intended entry, nor a threat to counter our operations militarily..." On 29 September MacArthur restored the government of the Republic of Korea under Syngman Rhee. On 30 September, Defense Secretary George Marshall sent an eyes-only message to MacArthur: "We want you to feel unhampered tactically and strategically to proceed north of the 38th parallel." During October, the ROK police executed people who were suspected to be sympathetic to North Korea, and similar massacres were carried out until early 1951.
Who executed people who were believed to be loyal to North Korea?
ROK police

In the last years of the nineteenth century, Planck was investigating the problem of black-body radiation first posed by Kirchhoff some forty years earlier. It is well known that hot objects glow, and that hotter objects glow brighter than cooler ones. The electromagnetic field obeys laws of motion similarly to a mass on a spring, and can come to thermal equilibrium with hot atoms. The hot object in equilibrium with light absorbs just as much light as it emits. If the object is black, meaning it absorbs all the light that hits it, then its thermal light emission is maximized.
Planck studied what problem posed originally by Kirchhoff?
black-body radiation

Ahmad ibn Fadlan, an Arab traveler during the 10th century, provided one of the earliest written descriptions of the Rus': "They are as tall as a date palm, blond and ruddy, so that they do not need to wear a tunic nor a cloak; rather the men among them wear garments that only cover half of his body and leaves one of his hands free." Liutprand of Cremona, who was twice an envoy to the Byzantine court (949 and 968), identifies the "Russi" with the Norse ("the Russi, whom we call Norsemen by another name") but explains the name as a Greek term referring to their physical traits ("A certain people made up of a part of the Norse, whom the Greeks call [...] the Russi on account of their physical features, we designate as Norsemen because of the location of their origin."). Leo the Deacon, a 10th-century Byzantine historian and chronicler, refers to the Rus' as "Scythians" and notes that they tended to adopt Greek rituals and customs.
Which early traveler provided an early description of the Rus?
Ahmad ibn Fadlan