It's a popular belief that a fish's memory lasts for only seven seconds. It may seem sad to think that they don't remember what they've eaten or where they've been, and they don't recognize you or any of their friends—every moment in their life would be like seeing the world for the first time.

    But don't be so quick to feel sorry for them. A new study has found that fish have a much better memory than we used to think. In fact, certain species of fish can even remember events from as long as 12 days ago.

    In the study, researchers from MacEwan University in Canada trained a kind of fish called African cichlids to go to a certain area of their tank to get food. They then waited for 12 days before putting them back in the tank again.

Researchers used computer software to monitor the fish's movements. They found that after such a long break the fish still went to the same place where they first got food. This suggested that they could remember their past experiences.

    In fact, scientists had been thinking for a long time that African cichlids might have a good memory. An earlier study showed that they behaved aggressively in front of certain fish, perhaps because they remembered their past “fights”. But until the latest findings, there was no clear evidence.

    Just as a good memory can make our lives easier, it also plays an important part when a fish is trying to survive in the wild.

    “If fish are able to remember that a certain area contains safe food, they will be able to go back to that area without putting their lives at risks,” lead researcher Trevor Hamilton told Live Science.

    For a long time, fish were placed far below chimpanzees, dolphins and mice on the list of smart animals. But this study has given scientists a new understanding of their intelligence.

    Writing it down

    Unlike some other European languages, English is a little tricky when it comes to writing. How a word is pronounced and how it is actually spelt can be very different things.

    Same spelling, different meanings

Imagine, then, a situation where two words are spelt and pronounced exactly the same way, but have completely different meanings. Welcome to the world of homonyms（同形同音异义词）. Take, for example, the word "fair"—it can be a kind of festival, an adjective to describe the colour of your hair or how you should play a game. Or "leg", which can be attached to a person, or a table and can also be a distance you travel, or a part of a competition.

Don't take it literally（字面意思）

So how do you know which meaning someone is referring to? You don't, except by the context. Obviously, if someone asks you to "give them a hand", they don't want you to remove what is at the end of your arm.

What's in a name?

    Sometimes even the context doesn't help much—the result can be amusing. These sentences play with the double meaning of a noun:

    Sentence 1: I used to be a banker, but I lost interest.

Sentence 2: A small boy swallowed some coins and had to go to hospital. When his grandmother phoned to ask how he was, the nurse said: "No change yet".

    More ambiguity（歧义）

    Sentence 3 plays with the different meanings of a verb:

    Sentence 3: I wondered why the ball was getting bigger. Then it hit me.

Double trouble

    And sometimes a word can be a noun and a verb, but have different meanings. Can you work this one out?

    Sentence 4: Time flies like an arrow. Fruit flies like a banana.

    If you like these homonyms, you will be pleased to know that English has plenty more!

    Want a wonderful travel in London? Don't miss the following!

    Cartoon Museum

    This highly entertaining London tourist attraction covers the history and development of British cartoons from the 18th century to the present day. You can find a detailed collection of all types of cartoons in this museum including caricatures (讽刺漫画) and rare examples of cartoon art: it's an ideal place to entertain kids of all ages as well as a serious collection for animation enthusiasts.

    There are over nine hundred pieces on exhibit and the museum regularly holds events where both children and adults can participate. Booking for these events is recommended due to the popularity year round of this London Museum.

    Telephone: 020 7580 8155

    Chislehurst Caves

    Chislehurst in London is home to chalk caves that were mined by hand for over 8,000 years. A tour of these caves is an exciting way to see how British people have impacted on their environment over thousands of years.

    Telephone: 020 8467 3264

    The Old Operating Theatre Museum

    The Old Operating Theatre Museum is one London museum offering a fascinating insight into the medical profession of the past. This 300-year old herb garret (阁楼) is Britain's only surviving operating theatre, with a wooden operating table and an observation stand, from which visitors can witness surgery performed.

    Telephone: 020 7188 2679

    Curzon Mayfair Cinema Museum

    Recently voted one of London's best cinemas by Time Out readers, the Curzon Mayfair cinema is everything you would expect from this particular part of town: luxurious (奢华的) and tasteful. Showing mostly art-house and independent films, the Curzon Mayfair is unique in the world of London cinema for its role in screening these films for industry and press.

    Telephone: 033 3321 0104

    Solar energy systems/power plants do not produce air pollution, water pollution, or greenhouse gases. Using solar energy can have a positive, indirect effect on the environment, when solar energy replaces or reduces the use of other energy sources that have larger effects on the environment.

    However, some poisonous materials and chemicals are used to make the photovoltaic (光电池的) cells that convert sunlight into electricity. Some solar thermal (保热的) systems use potentially hazardous liquids to transfer heat. Leaks of these materials could be harmful to the environment. U. S. environmental laws regulate the use and settlement of these types of materials.

    As with any type of power plant, large solar power plants can affect the environment near their locations. The placement of the power plant may have long-term effects on the habitats of native plants and animals. Some solar power plant-s may require water for cleaning solar collectors and concentrators or for cooling turbine generators. Using large volumes of ground water or surface water in some dry locations may affect the ecosystems that depend on these water resources. In addition, the beam of concentrated sunlight a solar power tower creates can kill birds and insects that fly into the beam.

    The amount of solar energy that the earth receives each day is many times greater than the total amount of all energy that people consume each day. However, on the surface of the earth, solar energy is a variable and irregular energy source. The amount of sunlight and the intensity of sunlight varies by time of day and location. Weather and climate conditions affect the availability of sunlight daily and on a seasonal basis. The type and size of a solar energy collection and conversion system determines how much of the available solar energy we can convert into useful energy.

    Since 50 years ago, scientists have been searching for ways to link the brain with computers. Brain Computer Interface (BCI) technology could help people with disabilities send commands to machines.

    Recently, two researchers, Jose Millan and Michelle Tavella from the Federal Polytechnic School in Lausanne, Switzerland, demonstrated (展示) a small robotic wheelchair directed by a person's thoughts.

    In the laboratory, Tavella operated the wheelchair just by thinking about moving his left or right hand. He could even talk as he watched the vehicle and guided it with his thoughts.

    "Our brain has billions of nerve cells. These send signals through the spinal cord (脊髓) to the muscles to give us the ability to move. But spinal cord injuries or other conditions can prevent these weak electrical signals from reaching the muscles," Tavella says, "Our system allows disabled people to communicate with external world and also to control devices."

    The researchers designed a special cap for the user. This head cover picks up the signals from the scalp (头皮) and sends them to a computer. The computer interprets the signals and commands the motorized wheelchair. The wheelchair also has two cameras that identify objects in its path. They help the computer react to commands from the brain.

    Prof. Millan, the team leader, says scientists keep improving the computer software that interprets brain signals and turns them into simple commands. "The practical possibilities that BCI technology offers to disabled people can be grouped in two categories: communication, and controlling devices. One example is this wheelchair." He says his team has set two goals. One is testing with real patients, so as to prove that this is a technology they can benefit from. And the other is to guarantee that they can use the technology over long periods of time.

What is the best part of a typical relaxing summer day? Nothing is better than sitting in an armchair with a beer and some chips in your hand, enjoying the great comfort.

The much-loved combination of beer and chips is being exploited for the first time to deal with climate change. Chips firm Walkers has adopted a technique it says will cut CO₂ emissions (排放) from its production process by 70%.

The technology will use CO₂ captured from beer processing in a brewery (啤酒厂), which is then mixed with potato waste and turned into fertilizer. It will then be spread on UK fields to feed the following year's potato crop. Creating fertilizer normally produces high CO₂ emissions, but the technology adopted by Walkers makes fertilizer without generating CO₂. So, the beer-and-chips combination performs a double function. It stops the emission of brewery CO₂ into the atmosphere — and it saves on the CO₂ normally generated by fertilizer production.

This Creative win-win solution was developed with an approval from the UK government by a 14-employee start-up called CCm. The fertilizer was experimented on potato seed beds this year, and next year Walkers will install CCm equipment at its Leicester factory to prepare for its 2022 crop.

A decision has not yet been made on which brewery Walkers will work with on this. The new technology adds to carbon-saving techniques already under way. The firm has installed an anaerobic digester (厌氧消化池), which feeds potato waste to bacteria to produce a useful gas. The gas is burned to make electricity for the chip-frying process — so this saves on burning gas or coal.

The new system will go a step further by taking away potato "cake" left after digestion — and mixing the brewery CO₂ into it to make an enriched fertilizer which will help put carbon back into the soil as well as encouraging plant growth.

It's an example of scientists finding ways to use CO₂ emissions which otherwise would increase the over-heating of the planet.