A spokesman for the Iranian government said the country's top security body would hold an extraordinary meeting shortly to discuss the "criminal act of attack". Iran's Supreme Leader Ali Khamenei warned that "retaliation is waiting". On 4 January, the U.S. Department of Homeland Security said there was "no specific, credible" threat to the U.S. mainland but warned about Iranian capabilities. Trump warned Tehran that any retaliation would result in the U.S. targeting 52 Iranian significant sites, including cultural sites. The 52 sites were reported to represent the 52 American hostages held during the Iran hostage crisis. Hossein Dehghan, the main military adviser of Iran, and Iranian Foreign Minister Javad Zarif asserted that attacks on Iranian cultural sites would be grave breaches of international law. U.S. secretary of state Mike Pompeo avoided a direct answer when asked about cultural targets, saying that Washington will do the things that are right and the things that are consistent with U.S. law. U.S. secretary of defense Mark Esper later asserted that cultural sites would not be targeted because "That's the laws of armed conflict."
On 27 December 2019, the K-1 Air Base in Kirkuk Province, Iraq—one of many Iraqi military bases that host Operation Inherent Resolve coalition personnel—was attacked by more than 30 rockets, killing an Iraqi-American U.S. defense contractor, and injuring multiple U.S. and Iraqi service members. The U.S. blamed the Iranian-backed Kata'ib Hezbollah militia for the attack. Furthermore, a senior U.S. official, who spoke to reporters on condition of anonymity, said there had been a campaign of 11 attacks on Iraqi bases hosting OIR personnel in the two months before the 27 December incident, many of which the U.S. also attributed to Kata'ib Hezbollah. On 29 December 2019, retaliatory U.S. airstrikes targeted five Kata'ib Hezbollah weapon storage facilities and command and control locations in Iraq and Syria. 25 militia members died and 55 were wounded.
More InfoThe strike occurred during the 2019–20 Persian Gulf crisis, which began after the U.S. withdrew from the 2015 nuclear deal with Iran in 2018, reimposed sanctions, and accused Iranian elements of fomenting a campaign to harass U.S. forces in the region. On 27 December 2019, the K-1 Air Base in Iraq, which hosts Iraqi and U.S. personnel, was attacked, killing an American contractor. The U.S. responded by launching airstrikes across Iraq and Syria, killing 25 Kata'ib Hezbollah militiamen. Days later, Shia militiamen and their supporters retaliated by attacking the U.S. embassy in the Green Zone.
More InfoResponses to Qasem Soleimani's perceived destructive influence in Iraq and abroad have been a topic of debate amongst U.S. officials for many years. In 2006, as the U.S. War in Iraq began to see increasingly sophisticated and lethal roadside bombs, such as explosively formed penetrators (EFPs)—thought to be exclusively due to Iranian influence— the U.S. military was seeking ways to mitigate the damage. In August 2007, as U.S. military officials attempted to learn more about the leadership of the Iran-backed proxy groups operating in Iraq, they received a message relayed through the Iraqi Minister of State for National Security, that Soleimani wanted them to know that he was "the sole decision-maker on Iranian activities in Iraq".
More InfoIn 1881, Charles Fritts created the first commercial solar panel, which was reported by Fritts as "continuous, constant and of considerable force not only by exposure to sunlight but also to dim, diffused daylight." However, these solar panels were very inefficient, especially compared to coal-fired power plants. In 1939, Russell Ohl created the solar cell design that is used in many modern solar panels. He patented his design in 1941. In 1954, this design was first used by Bell Labs to create the first commercially viable silicon solar cell. In 1957, Mohamed M. Atalla developed the process of silicon surface passivation by thermal oxidation at Bell Labs. The surface passivation process has since been critical to solar cell efficiency.
More InfoResearch by Imperial College, London has shown that solar panel efficiency is improved by studding the light-receiving semiconductor surface with aluminum nanocylinders, similar to the ridges on Lego blocks. The scattered light then travels along a longer path in the semiconductor, absorbing more photons to be converted into current. Although these nanocylinders have been used previously (aluminum was preceded by gold and silver), the light scattering occurred in the near-infrared region and visible light was absorbed strongly. Aluminum was found to have absorbed the ultraviolet part of the spectrum, while the visible and near-infrared parts of the spectrum were found to be scattered by the aluminum surface. This, the research argued, could bring down the cost significantly and improve the efficiency as aluminum is more abundant and less costly than gold and silver. The research also noted that the increase in current makes thinner film solar panels technically feasible without "compromising power conversion efficiencies, thus reducing material consumption".
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