【推荐2】The United States rose to global power on the strength of its technology, and the lifeblood that technology has long been electricity. By providing long-distance communication and energy, electricity created the modern world. Yet properly understood, the age of electricity is merely the second stage in the age of steam, which began a century earlier.

"It is curious that no one has put together a history of both the steam and electric revolutions." writes Maury Klein in his book The Power Makers, Steam, Electricity, and the Men Invented Modern America. Klein, a noted historian of technology, spins a narrative so lively that at times it reads like a novel.

The story begins in the last years of the 18th century in Scotland, where Watt perfected "the machine that changed the world". Klein writes, "America did not invent the steam engine, but once they grasped its passwords they put it to more uses than anyone else. "

Meanwhile, over the course of 19th century, electricity went from mere curiosity to a basic necessity. Morse invented a code for sending messages over an electromagnetic circuit. Bell then gave the telegraph a voice. Edison perfected an incandescent bulls that brought electric light into the American home.

Most importantly, Edison realized that success depended on mass electrification, which he showed in New York City. With help from Tesla, Westinghouse's firm developed a system using alternating current, which soon became the major forms of power delivery.

To frame his story, Klein creates the character of Ned, a fictional witness to the progress brought about by the steams and electric revolutions in America during one man's lifetime. It's a technique that helps turn a long narrative into an interesting one.

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【推荐3】The benefits of regular exercise are well documented but there’s a new bonus to add to the ever-growing list.New research found that middle-aged women who were physically fit could be nearly 90 percent less likely to develop dementia（失智症）in later life-and if they did，it came on a decade later than less sporty women.

Lead researcher Dr.Helena Horder, of the University of Gothenburg in Sweden,said:“These findings are exciting because it’s possible that improving people’s cardiovascular（心血管的）fitness in middle age could delay or even prevent them from developing dementia.”

For the study,191 women with an average age of 50 took a bicycle exercise test until they were tired out to measure their peak（最大值的）cardiovascular capacity.The average peak workload was measured at 103 watts.

A total of 40 women met the criteria for a high fitness level with a capacity of 120 watts or higher. While 92 women were in the medium fitness category; A total of 59 were of low fitness level ,with a peak workload of 80 watts or less,or having their tests stopped because of health problems.

These women were then tested for dementia six times over the following four decades. During that time,44 of the women developed dementia.Five percent of the highly fit women developed dementia,compared to 25 percent of the women with medium fitness and 32 percent of the women with low fitness.

“However, this study does not show cause and effect between cardiovascular fitness and dementia, it only shows an association.said Horder. More research is needed to see if improved fitness could have a positive effect on the risk of dementia and also to look at when during a lifetime a high fitness level is most important.” She also admitted that a relatively small number of women were studied, all of whom were from Sweden,so the results might not be applicable to other groups.

What do we know about Dr Horder’s study?

【推荐2】Human speech contains more than 2,000 different sounds, from the common “m” and “a” to the rare clicks of some southern African languages. But why are certain sounds more common than others? A ground-breaking, five-year study shows that diet-related changes in human bite led to new speech sounds that are now found in half the world’s languages.

More than 30 years ago, the scholar Charles Hockett noted that speech sounds called labiodentals, such as “f” and “v”, were more common in the languages of societies that ate softer foods. Now a team of researchers led by Damián Blasi at the University of Zurich, Switzerland, has found how and why this trend arose.

They discovered that the upper and lower front teeth of ancient human adults were aligned (对齐), making it hard to produce labiodentals, which are formed by touching the lower lip to the upper teeth. Later, our jaws changed to an overbite structure (结构), making it easier to produce such sounds.

The team showed that this change in bite was connected with the development of agriculture in the Neolithic period. Food became easier to chew at this point. The jawbone didn’t have to do as much work and so didn’t grow to be so large.

Analyses of a language database also confirmed that there was a global change in the sound of world languages after the Neolithic age, with the use of “f” and “v” increasing remarkably during the last few thousand years. These sounds are still not found in the languages of many hunter-gatherer people today.

This research overturns the popular view that all human speech sounds were present when human beings evolved around 300,000 years ago. “The set of speech sounds we use has not necessarily remained stable since the appearance of human beings, but rather the huge variety of speech sounds that we find today is the product of a complex interplay of things like biological change and cultural evolution,” said Steven Moran, a member of the research team.

【推荐3】Cheerleading squads (啦啦队) are known for their energy and athleticism, and always add fun and excitement to any event. Most cheerleading groups have young members, so this Arizona cheerleading squad certainly stands out. Sun City Poms, which only recruits (招募) members who are over 55, has distinguished itself as a cheerleading squad that brings joy to seniors and audiences of all ages.

Established in 1979, the team consists of women aged over 55 who live in Sun City, a retirement community in Arizona. This community of active seniors women are passionate about dancing, performing and staying active, and prove that there is no age limit to what you love to do. The team has become increasingly popular, and the members are known for their energetic performances at parades, festivals and events throughout the state.

Despite the demanding schedule, the women remain committed to the team. This cheerleading squad brings joy to seniors by keeping members physically fit, building friendships, and fostering a sense of community. The Sun City Poms currently has 30members and a handful of trainees, who can join after completing a three-month class, learning two routines, and proving they have what it takes.

On March 25, the group successfully held the “Celebrate the Poms” show, which drew a crowd of over 700 people. It even included a special number from “The Flops”, who count the husbands, friends and lovers of the Poms as members.

Zirbel, in her eighties, already has a lot of memories with the group and is ready to make more. She shared that in one event alone. She estimated that she walked about three miles. Despite the tiring schedule and off days, Zirbel is not about to leave the team anytime soon.

【推荐2】Animals are natural resources that people have wasted all through our history. Animals have been killed for their fur and feathers, for food, for sport, and simply because they were in the way. Thousands of kinds of animals have disappeared from the world forever. Hundreds more are on the danger list today. About 170 kinds in the United States alone are considered in danger.

Why should people care? Because we need animals. And because once they are gone, there will never be any more.

Animals are more than just beautiful and interesting. They are more than just a source of food. Every animal has its place in the balance of nature. Destroying one kind of animal can create many problems.

For example, when farmers killed large numbers of hawks, the farmers’ stores of corn and grain were destroyed by rats and mice. Why? Because hawks eat rats and mice.With no hawks to keep down their numbers, the rats and mice multiplied quickly.

Luckily, some people are working to help save the animals. Some groups raise money to let people know about the problem. And they try to get the governments to pass laws protecting animals in danger.

Quite a few countries have passed laws. These laws forbid the killing of any animals or plants on the danger list. Slowly, the number of some animals in danger is growing.