A school district in Michigan has banned all backpacks from school buildings, in response to growing safety concerns. 

Flint Community Schools announced last week that backpacks would be banned and the ban would be in place for the rest of the school year. The new policy went into effect on Monday. 

"We are doing all that we can to create a safe and secure environment for our scholars, families, teachers and staff," Superintendent (主管) Kevin Jones wrote in a letter posted on the school district's website. 

Jones cited growing threatening behavior happenings across the country, including weapons being brought to schools, as the reason for the backpack ban. 

"Backpacks make it easier for students to hide weapons, which can be taken apart and harder to identify than hidden in pockets, inside books, or under other items," he said. 

Following the shooting at Robb Elementary School in Uvalde, Texas, last May, where 19 students and two teachers died, schools began taking policies requiring students to use clear backpacks. However, Flint Community Schools have gone a step further and banned clear backpacks from school buildings, with the superintendent saying that it doesn't resolve the issue. 

"By banning backpacks altogether and adding an increased security presence across the district, we can better control what is being brought into our buildings," Jones said. 

Students are allowed to store personal items like wallets, keys, hygiene products (卫生用品) and phones in small purses, bring lunchboxes or place their gym clothes in clear plastic bags, all of which will be subject to searches. 

If a student brings a backpack to school, parents or guardians must pick it up from the school, according to Jones. 

The Flint Board of Education, the district's administration and headmasters approved the policy change, Jones said, adding that the district received support from the Flint Police Department. 

In July 2007a BBC concert showcased the Buskaid Soweto String Ensemble at a hall in London. The performance ended to a big round of applause. Among the crowd was 41-year-old Dr Luis Dias. He had heard of this chorus and knew it consisted of children from South Africa's poorest towns, but had never seen them performing live.

Born in 1966 to a family of Goan doctors, Dias followed in his family's foot steps, but he had a great passion for music. In 1998he went to work in London. After watching the Buskaid performance, Dias began to explore the possibility of starting a similar effort for disadvantaged children in India.

In 2008 he and his wife gave up their comfortable life in the UK and returned to their home in Panjim, Goa. In just one year the couple founded Child's Play In- dia Foundation. Realizing that setting up the project and teaching music would be a full-time effort, Dias abandoned his medical career and became a poorly paid music teacher.

Yet, it was not easy getting such an enterprise off the ground. Aside from get-ting the necessary fund it was important to find a place that would safely house the children teachers and equipment. They eventually found the perfect partner, a woman behind Hamara School, a shelter for disadvantaged children in Panjim. From these difficult beginnings, Child's Play gradually grew. Child's Play puts on at least two concerts a year to which the children's families and general public are invited. The parents, many of whom are street-side vendors(小贩), had never imagined that their children would find a place on center stage, appreciated and applauded by a wildly enthusiastic audience.

 The Roman Colosseum was built almost two thousand years ago. Despite its age and a 14^th century earthquake that knocked down the south side, most of the 150-some foot building is still standing. Scientists and engineers have long suspected a key to the building' s durability (使用年限) is the use of a specific Roman concrete. But exactly how this solid concrete has contributed to the architecture' s strength has been a mystery to researchers across the globe.  

 A team of researchers recently discovered a potential answer to why these ancient Roman buildings have been able to weather the test of time while many modern concrete structures seem to fall apart after a few decades. The answer is self-healing concrete.  

 The material has three components: limestone (石灰石), volcanic material and water. What the researchers found was that the self-healing feature might be simply caused by chemistry accidentally. The limestone in the concrete is likely the secret.  

 When the ancient Romans made mortar (灰浆), they heated up the lime to turn it into a substance called " quicklime" . And, because they introduced water to the quicklime during mixing, the heat it produced set up a chemical foundation that could strengthen the concrete later. When tiny cracks start to form later, the quicklime stops them from becoming bigger. When it rains, the lime reacts with the water to recombine as various forms of calcium carbonate (碳酸钙), quickly filling the crack or reacting with the volcanic ash to " heal" the material.  

 For materials scientist Ainissa Ramirez, this new understanding of ancient Roman concrete is a welcome discovery. " This is one way that the material can be more environmentally friendly," says Ramirez. " It' s sort of like a message in a bottle. The Romans made the material. We had to kind of figure out how they did it so that we can make better materials — and then, you know, in turn, be better protectors of our environment. "