On July 8, Ukrainian President Zelensky, who was visiting Poland, and Polish Prime Minister Tusk signed a bilateral security agreement in Warsaw, the capital of Poland. The agreement clearly states that Poland will provide support to Ukraine in air defense, energy security and reconstruction. After signing the agreement, Tusk said that the agreement includes actual bilateral commitments, not "empty promises." Previously, the United States, Britain, France, Germany and other countries as well as the European Union signed similar agreements with Ukraine.

The world's deepest diving pool, Deepspot, opened this weekend near the Polish capital Warsaw. The 45.5-meter pool contains artificial underwater caves, Mayan ruins and a small shipwreck for scuba divers and free divers to explore. Deepspot can hold 8,000 cubic meters of water, more than 20 times the capacity of a normal 25-meter swimming pool. Unlike ordinary swimming pools, Deepspot can still open despite Poland's COVID-19 epidemic prevention restrictions because it is a training center that provides courses. The operator also plans to open a hotel where guests can observe divers at a depth of 5 meters from their rooms. "This is the deepest diving pool in the world," Michael Braszczynski, 47, Deepspot's director and a diving enthusiast, told AFP at the opening yesterday. The current Guinness World Record holder is a 42-meter-deep pool in Montegrotto Terme, Italy. The 50-meter-deep Blue Abyss pool in the UK is scheduled to open in 2021. On the first day of Deepspot's opening, about a dozen people visited, including eight experienced divers who wanted to pass the instructor exam. "There are no spectacular fish or coral reefs here, so it can't replace the ocean, but it is certainly a good place to learn and train safe open water diving," said 39-year-old diving instructor Przemyslaw Kacprzak. "And it's fun! It's like a kindergarten for divers."

On July 1, former Microsoft CEO and President Steve Ballmer surpassed Microsoft co-founder Bill Gates for the first time on the Bloomberg list of the world's richest people to become the sixth richest person in the world. According to the data, as of the same day, Ballmer's net worth reached $157.2 billion, while Gates's wealth was $156.7 billion, falling to seventh place. The latest figures, as of July 6, show that Ballmer's wealth has grown further to $161 billion, and Gates' wealth is $159 billion. This is the first time Ballmer's net worth has surpassed Gates', and it is also the rare time in history that an employee's net worth has surpassed that of a company founder. Unlike Musk, Jeff Bezos and others, Ballmer's wealth was not accumulated through entrepreneurial success as a business founder, but simply because he chose to hold Microsoft "indefinitely." As Fortune previously reported, Ballmer is the only individual with a net worth of more than $100 billion as an employee rather than a founder.

A children's hospital in the Ukrainian capital was hit by a Russian missile on Monday as part of a wave of airstrikes across Ukraine that has killed at least 31 people and injured 154 others. "Russian terrorists have once again launched a massive missile attack on Ukrainian cities - Kiev, Dnipro, Kryvyi Rih, Slaviansk, Kramatorsk," said Ukrainian President Volodymyr Zelenskyy. Zelensky said Russia fired more than 40 missiles of different types at the five cities in daytime attacks, hitting residential buildings and public infrastructure. The Ukrainian air force said it intercepted 30 missiles. Authorities said the attack on Kiev killed seven people, while the attack on Kryvyi Rih, Zelensky's birthplace in central Ukraine, killed 10 and injured 47. United Nations Secretary-General António Guterres condemned the attacks, calling the assault on the Kiev hospital and another medical facility in the capital's Dniprovsky district "particularly egregious," said his spokesman, Stephane Dujarric. "Direct attacks on civilians and civilian objects are prohibited under international humanitarian law. Any such attacks are unacceptable and must cease immediately," Dujarric said. The U.N. Security Council will meet Tuesday to discuss the Russian strikes, diplomats said. The Russian Defense Ministry said the strikes targeted Ukrainian defense factories and a military aviation base and were successful. It denied striking any civilian facilities and claimed, without evidence, that photos from Kiev showed the damage was caused by a Ukrainian anti-aircraft missile. Ukrainian Air Force Colonel Yurii Ignat said Russia has been improving the effectiveness of its air strikes by equipping its missiles with enhanced features, including so-called heat decoys that can throw air defense systems off target. In comments sent to The Associated Press, he said the cruise missiles flew low in Monday's attack -- just 50 meters off the ground -- making them harder to hit. Western countries, led by the United States, have provided Ukraine with billions of dollars in arms support. They will hold a three-day NATO summit in Washington starting Tuesday to work out how to reassure Kiev of NATO's strong support and give Ukrainians hope that their country can survive the largest conflict in Europe since World War II. "Today's Russian missile strike that killed dozens of Ukrainian civilians and caused damage and loss of life to Kyiv's largest children's hospital is a horrifying reminder of Russia's brutality," U.S. President Joe Biden said in a statement Monday. "It is critical that the world continues to stand with Ukraine at this important moment and that we do not ignore Russian aggression." Biden said in the statement that he will meet with President Zelensky during the NATO summit in Washington this week "to make clear our unwavering support for Ukraine." Biden continued: "We will join our allies in announcing new measures to strengthen Ukraine's air defenses and help protect their cities and civilians from Russian attacks. The United States stands with the Ukrainian people." Czech President Petr Pavel said the hospital attack was "inexcusable" and he hoped the NATO summit would reach a consensus that Russia is "the greatest threat and we must be fully prepared to deal with it." Zelensky said during a visit to Poland that he hoped the NATO summit would provide Ukraine with more air defense systems. The Ukrainian leader said rescuers were digging through the rubble of the Ohmatdit Children's Hospital in Kyiv and that the number of casualties was not yet known. Kyiv Mayor Vitali Klitschko said at least 16 people were injured, including seven children, and the attack caused a two-story wing of the hospital to partially collapse. Doors and windows were blown off the hospital's 10-story main building, and the walls were charred. The floor of one room was splattered with blood. Hospital officials said the intensive care unit, operating room and oncology department were damaged.

A provocative new study reveals the complex effects of the space environment on human health, providing insight into potential damage to blood, cell structure and the immune system. The study focused on SpaceX's Inspiration4 mission, which successfully sent two men and two women into space in 2021 to orbit the Earth for three days and shed some light on the effects of space travel on the human body. The research data, derived directly from the Inspiration4 mission, shows that even a brief trip to space can significantly damage the human immune system, trigger an inflammatory response, and profoundly affect cell structure. In particular, space travel triggered unprecedented changes in cytokines that play a key role in immune response and muscle regulation but are not usually directly associated with inflammation. In particular, the study found a significant increase in muscle factors, which are physiological responses specific to skeletal muscle cells in microgravity, rather than a simple immune response. Although non-muscular tissues did not show changes in proteins associated with inflammation, specific leg muscles such as soleus and tibialis anterior muscles showed significant signs of metabolic activity, especially increased interleukin in the latter, further enhancing the activation of immune cells.