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Researchers say current exercise guidelines are unrealistic and argue that doctors should sometimes advise small increases in activity instead. They warn the 150-minute weekly target is beyond the reach of some people — particularly older individuals. And striving to reach these goals could mean the benefits of lighter exercise are overlooked. But public health officials say current recommendations have proven benefits in lowering the risk of heart disease.

There is increasing evidence that inactivity is linked to heart disease, Type 2 diabetes(糖尿病) and some types of cancer. UK guidelines for adults recommend at least two-and-a-half hours of moderate activity a week, in short periods of 10 minutes or more.

But in two separate articles in the BMJ, experts argue the message needs to change, with greater emphasis on making inactive people move more. Prof Philipe de Souto Barreto at the University Hospital of Toulouse, advises people who are sedentary(久坐的) to make small incremental increases in their activity levels — rather than pushing to achieve current goals. He points to previous studies which show even short periods of walking or just 20 minutes of vigorous activity a few times a month can reduce the risk of death, compared to people who do no exercise.

In the second article, Prof Phillip Sparking of the Georgia Institute of Technology, says doctors should tailor their advice — particularly for older patients. He suggests using GP visits for people over 60 to discuss "realistic options" to increase activity — such as getting people to stand up and move during TV commercial breaks.

Prof Kevin Fenton at Public Health England, says: "Everyone needs to be active every day — short periods of 10 or more minutes of physical activity have proven health benefits, but getting 150 minutes or more of moderate activity every week is the amount we need to positively impact on a wide range of health conditions. "This includes reducing the risk of heart disease and type 2 diabetes."

Monarch butterflies（黑脉金斑蝶）are a common summer sight in the northern United States and Canada . These large orange and black insects（昆虫）brighten parks and gardens as they fly lightly among the flowers . What makes monarchs particularly interesting is that they migrate（迁飞）—all the way to California or Mexico and back . They are thought to be the only insect that does this .

       Every year in the late summer monarchs begin their journey to the south . Those heading for Mexico go first for the Louisiana-Mississippi area , then fly across the Gulf of Mexico into Texas . Once in Mexico , they settle themselves in one of about fifteen places in a mountain forest filled with fir trees . Each place provides a winter home for millions of monarchs . The butterflies are so many that they often cover entire trees . When spring comes , they begin their long journey north . 

The question is often asked whether every butterfly makes the round-trip journey every year . And the answer is no . The average monarch lives about nine months . So one flying north might lay eggs in Louisiana and then die . The eggs of that generation may be found in Kentucky ; the eggs of the next generation may end up in Wisconsin or Michigan . The last generation of the season , about the fourth , will make their way back to Mexico and restart the journey .

       Scientists learn about monarchs’ migration by catching and making marks on the insects . By

recatching a monarch with such a mark and noticing where it came from , the next scientist can get to know things like the butterfly’s age and its routing（路线）.

  These days a green building means more than just the color of the paint. Green building can also refer to environmentally friendly houses, factories, and offices.

    Green building means “reducing the impact (影响) of the building on the land”, Taryn Holowka of the U.S. Green Building Council in Washington, D.C., said.

    According to Holowka, building account for (占了) 65 percent of total U.S. electricity use.

But green building can reduce energy and water use. Also, the building are often located near public transportation such as buses and subways, so that people can drive their cars less. That could be good for the environment, because cars use lots of gas and give off pollution. Green building are often built on developed land, so that the buildings don’t destroy forests.

Marty Dettling is project manger for a building that put these ideas into action . The Solaire has been called the country’s first green high-rise building . According to Dettling, “We’ve reduced our energy use by one-third and our water by 50 percent,”

The Solaire cuts energy in past by using solar power. “On the face of the building we have solar panels which change the sun’s energy into electricity,” Dettling explained.

The solaire also has lights that automatically turn off when people leave the room. In addition, the building has lots of windows, allowing people to use the sun for light during the day. The solaire cuts water reusing it.

Not everyone is eager to move into a green building, however. Some people think that things like solar panels cost more money than more traditional energy sources. Anyhow, Holowka said, “It’s going to be big.”

Dreams can be familiar and strange，fantastical or boring，but some dreams might be connected to the mental processes that help us learn.In a recent study，scientists found a connection between nap-time dreams and better memory in people who were learning a new skill.

In the study,99 college students between the ages of 18 and 30 each spent an hour on a computer，trying to get through a virtual maze (迷宫)．The maze was difficult，and the study participants had to start in a different place each time they tried—making it even more difficult.They were also told to find a particular picture of a tree and remember where it was.

For the first 90 minutes of a five-hour break，half of the participants stayed awake and half were told to take a short nap.Participants who stayed awake were asked to describe their thoughts.Participants who took a nap were asked about their dreams before sleep and after sleep—and they were awakened within a minute of sleep to describe their dreams.

Stickgold，a neuroscientist(神经科学家)，wanted to know what people were dreaming about when their eyes werenˈt moving，during sleep.

Four of the 50 people who slept said their dreams were connected to the maze.Some dreamed about the music that had been playing when they were working；others said they dreamed about seeing people in the maze.When these four people tried the computer maze again，they were able to find the tree faster than before their naps.

Stickgold suggests the dream itself doesnˈt help a person learn—itˈs the other way around.He suspects that the dream was caused by the brain processes associated with learning.

All four of the people who dreamed about the task had done poorly the first time，which makes Stickgold wonder if the dreams show up when a person finds a new task particularly difficult.People who had other dreams，or people who didnˈt take a nap，didnˈt show the same improvement.

There is an English saying that says, "Let Sleeping Dogs Lie." It means not bringing up an old problem. Researchers in Hungary have found another reason to let dogs keep on sleeping. It seems the animals are learning while they sleep.

    The Hungarian researchers placed tools on the dogsˈ heads to know about electrical activity in the brain. The brain activity, called sleep spindles (梭状波), takes place in human beings, and has been connected with learning. The researchers hope to understand how the dogsˈ ability to learn and remember changes as they get older. The study may help them understand how human brains change as we age.

    The researchers found differences between male and female dogs. Iotchey, a researcher, says the females appeared much better at learning new things. Female dogs have about twice as many spindles per minute as male dogs, they also happen to be the better learners, and they memorize the task much better. But it was harder for all the older dogs to remember things, especially when several things were happening at the same time.

    DóraSzabó also studies sleep spindles. Szabó is a neuroscientist in a university in Budapest. She says the older dogs have fewer spindles and are easily cheated. "If you first hide the reward into one bowl, then in another and in another, they get lost after a while. So their performance is going down, and they are getting poor in solving new problems."

    Researchers hope the study will not only help understanding of learning ability and memory changes in dogs, but also the aging of humans. Senior Researcher EnikóKubinyi adds that the aging dogs suffer from the same problems as humans who are aging. "Among very old dogs, up to  two thirds of them show signs of dementia (痴呆), and this dementia is really very similar to that of humans, so we could use dogs as a natural model of human aging."

The Plastic Bottle Village is just a great idea that might finally save us from being buried in plastic. It’s a community (社区) in Panama that is going to be entirely made of used bottles.

The village will include about 120 homes of varying sizes. The design process begins with building frames of steel, which are then filled with these bottles. Once this step is complete, and electrical and plumbing lines are put inside, the plastic walls are covered by concrete — both inside and outside. So no one will actually be able to tell that the walls are made of plastic. Besides, the material will keep the house 17°C cooler than the temperature outside.

The village is the brainchild of Robert Bezeau with the intention of setting up several environmental projects. Having started a recycling program in 2012, during which a number of plastic bottles were collected, he started to think of how they could be put to use. Soon enough, he decided to use them to build houses, and came up with a basic idea for the construction process.

Over 10,000 plastic bottles were used to build the first house, which was completed late last year. The bottles were obtained from the same recycling project that Robert had set up. The next home is expected to be bigger, and will need more bottles to build. The “reconstructed” homes will be sold on request for anywhere between $ 149,000 and $ 300,000. The community will also feature other facilities such as gardens, mini-parks, and more.

22,000 plastic bottles are deserted across the world per second. While all these bottles obviously cannot be reused into homes, the project hopes to raise awareness of the waste that these bottles create. The village will also create an education center that will teach individuals from the world how to reuse plastic bottles as construction materials for shelter.

An American company has built a new drone（无人机）that could improve the speed of deliveries（送交的货）.

The drone is very different from other unmanned aircraft. It is made almost completely out of cardboard and has no motor.It can be packed with materials and sealed up with tape.

Because the drones do not have a motor, they are designed to be dropped from airplanes. Hundreds of drones could be sent out at once. Then they could be automatically guided to where they are supposed to go. The company says these drones could then complete deliveries to different places over an area covering hundreds of kilometers. The drones look bigger than the paper airplanes we used to make as kids. But this light flyer is not a toy. It is aerodynamically designed and equipped with a small computer, a battery and sensors to guide it to the ground.

The drones are being developed by Otherlab—a technology research company in San Francisco,California.It calls the drone a "Sky Machine."

The company says it can travel about 150 kilometers at speeds up to 88 kilometers an hour.Now,it can carry materials weighing up to one kilogram,but future models are expected to carry larger loads.

One of the droneˈs main advantages is that it does not have a heavy motor or large battery.This allows more room for materials and makes the drone cost less to build and operate.

The Otherlab development team has called its invention the "Ikea of drones."This is because it is packaged similarly to products from the Swedish furniture maker Ikea. The drone arrives as flat pieces of pre-cut cardboard that can be quickly and easily put together.

The technology that guides the drone can make it land within 10 meters of its target, according to Otherlab. Unlike other drones,even a crash landing is acceptable.The company says the drones can also be reused.

Once the drone completes its delivery,it can be thrown away and the cardboard material will likely break down within a few months.

The company has received money from the U.S. Department of Defense to carry out research on the drones.The money came from the Defense Advanced Research Projects Agency.The agency is attempting to find the best delivery vehicles that can disappear after their missions are complete.The U.S. military has a need for delivery drones.But it wants to simplify and lower the cost of using them.Otherlabˈs Sky Machines are an attempt to fill that need.

Military drones can also be stolen and studied by others if found after use.Before they can truly disappear,the electronic materials inside must also somehow disappear.Researchers are still working on ways to get the technology itself to self-destruct.

Fear may be felt in the heart as well as in the head, according to a study that has found a link between the cycles of a beating heart and the chance of someone feeling fear.

   Tests on healthy volunteers found that they were more likely to feel a sense of fear at the moment when their hearts are contracting（收缩） and pumping blood around their bodies, compared with the point when the heartbeat is relaxed. Scientists say the results suggest that the heart is able to influence how the brain responds to a fearful event, depending on which point it is at in its regular cycle of contraction and relaxation.

   Sarah Garfinkel at the Brighton and Sussex Medical School said, "Our study shows for the first time that the way in which we deal with fear is different depending on when we see fearful pictures in relation to our heart."

   The study tested 20 healthy volunteers on their reactions to fear as they were shown pictures of fearful faces. Dr. Garfinkel said, "The study showed that fearful faces are better noticed when the heart is pumping than when it is relaxed. Thus our hearts can also affect what we see and what we donˈt see—and guide whether we see fear."

   To further understand this relationship, the scientists also used a brain scanner（扫描仪） to show how the brain influences the way the heart changes a personˈs feeling of fear.

   "We have found an important mechanism by which the heart and brain ˈspeakˈ to each other to change our feelings and reduce fear," Dr. Garfinkel said.

   "We hope that by increasing our understanding about how fear is dealt with and ways that it could be reduced, we may be able to develop more successful treatments for anxiety disorders, and also for those who may be suffering from serious stress disorder."

Homeopathy is the oldest form of complementary（互补的）and alternative medicines from Europe. It originated with the German physician Samuel Hahnemann (1755—1843). He came across the cinchona, the bark of a South American tree that was used by the local people to treat fevers. Among the active ingredients in the bark is quinine（奎宁), which is still used to treat malaria. If a healthy person took cinchona, he or she would have symptoms (症状) of malaria. In 1796 and 1810, Hahnemann published essays on the theories of homeopathy: substances that cause illnesses or symptoms in people can be used in small doses as treatment. Supporters of homeopathy viewed it as a safe, patient-centered system. Hahnemann claimed he could cure any and all illnesses using homeopathic principles.

However, the Australian council sought to evaluate this claim once and for all. Their assessment was based on the analysis of 57 published systematic reviews encompassing 176 individual studies, independent evaluation of evidence provided by homeopathy interest groups and the public, and clinical practice guidelines and reports on homeopathy from other governments. Studies were only considered if they were case-controlled, meaning they compared a group of patients receiving homeopathic treatments with a control group. The council who oversaw this review consisted of experts in conventional-based medicine as well as complementary and alternative medicines. As a guideline, for a treatment to be considered effective, it must result in health improvements that cannot be explained by the placebo (安慰剂) effect, these improvements must be meaningful for a person’s overall health and the results have to be seen consistently in several studies. A draft of the report was reviewed by a group of independent experts in complementary medicine research and opened up for public consultation before it was finalized.

Eventually, the council found no reliable evidence that homeopathic treatments were effective. Studies that did find homeopathy to be effective were overall of poor scientific quality, used too few patients or lacked evidence on which to base their conclusions. Rejecting proven medical treatments in favor of homeopathy for chronic or potentially serious conditions could place people at risk. As always, use of homeopathic or other remedies should be discussed with your physician in order to make informed healthcare decisions.

Human activities are largely responsible for climate change, which is already having an observable effect on our planet. Particularly emissions from the burning of fossil fuels such as oil and gas have led to an increase in the concentration of greenhouse gases in the atmosphere. Key indicators of climate change – including rising average temperatures, melting glaciers, and rising sea levels – are expected to have devastating consequences for humans and environments. Tackling the challenge posed by climate change will require a coordinated and global effort.

Acknowledging that climate change is a common concern of humankind, delegations from 195 states successfully negotiated a new and binding international agreement to protect the global climate at the 21st Conference of the Parties to the United Nations Framework Convention on Climate Change ( UNFCCC) held in Paris in December 2015. The successful adoption of the Paris Agreement was also due to the hard work of a host of non-state actors, including NGOs and research institutions working to address the challenges of climate change.

With the first commitment period of the Kyoto Protocol due to expire in 2012, governments agreed to begin negotiations on an emissions reductions treaty for the post-Kyoto era at the 2007 Conference of Parties (COP) in Bali. In line with the agreement reached by the parties to the UNFCCC at the 2011 COP in Durban to negotiate a new climate protection treaty, this process was concluded successfully with the adoption of the Paris Agreement in late 2015.

One of the key innovations of the Paris Agreement is the adoption of a clearly defined target to limit global warming. The signatory states have agreed to limit the rise in global average temperature to well below 2 °C above pre-industrial levels. In order to achieve this, the agreement requires parties to prepare, communicate and maintain so-called “Nationally Determined Contributions” (NDCs) that they intend to achieve. These national commitments represent a further departure from the model of the Kyoto Protocol.

The Paris Agreement does not include any language on precisely what states should include in these commitments. While the emissions reduction targets specified for each country under the terms of the Kyoto Protocol were the outcome of multilateral negotiations, under the Paris Agreement states are invited to determine their national contributions as they see fit. The NDCs submitted so far under the Paris Agreement will not be sufficient to keep global warming below the two degree target. However, the agreement also requires that states review the implementation of their NDCs and update their pledges every five years. The first evaluation of the implementation of the Paris Agreement is scheduled for 2023.