An absolute description of the threat hanging over the world's mammals,reptiles,amphibians and other life forms has been published by the well-known scientific journal,Nature.A special analysis carried out by the journal indicates that an astonishing 41% of all amphibians on the planet now face extinction while 26% of mammal species and 13% of birds are similarly threatened.

    Many species are already critically endangered and close to extinction,including the Sumatran elephant,Amur leopard and mountain gorilla.But also in danger of vanishing（消失）for the wild,it now appears,are animals that are currently rated as merely being endangered.

    In each case,the finger of blame points directly at human activities.The continuing spread of agriculture is destroying millions of hectares of wild habitats every year,leaving animals without homes,while the introduction of newly-come species,often helped by humans,is also damaging native populations.At the same time,pollution and overfishing are destroying ocean ecosystems.

    "Habitat destruction,pollution or overfishing either kill off wild creatures and plants or leaves them badly weakened," said Derek Tittensor,an ocean ecologist at the World Conservation Monitoring Centre in Cambridge. "The trouble is that in coming decades,the additional threat of worsening climate change will become more and more common and could then kill off these survivors."

    The problem,according to Nature,is worsened because of the huge gaps in scientists knowledge about the planet's biodiversity.Evaluations of the total number of species of animals and plants alive vary from 2 million to 50 million.In addition,evaluations of current rates of species' disappearances vary from 500 to 36,000 a year. "That is the real problem we face," added Tittensor. "The scale of uncertainty is huge."

    In the end,however,the data indicate that the world is heading cruelly towards a mass extinction-which is defined as one involving a loss of 75% of species or more.This could arrive in less than a hundred years or could take a thousand,depending on extinction rates.

    It is easier to float in the ocean than it is to float in a swimming pool.Do you know why?

    Ocean water is full of salt--and salt water can hold up more weight than fresh water.See for yourself!

You will Need:

3 cups of warm water

Measuring cup(量杯)

Wide-mouthed jar

Salt

Spoon

Raw(生的)potato

You Will Do:

⒈Pour 1.5cups of warm water into the jar.

⒉Add 1/3 cup of salt.

⒊Stir(搅拌) until the salt is completely dissolved.

⒋Add another 1.5 cups of water.Pour it slowly over the back of the spoon into the jar so that the two liquids will not mix together.

⒌Gently place the potato into the jar.Do not drop it.

    What Will Happen:

    The potato will sink--but only halfway!

    Why?

    Salt water is heavier than fresh water,so it will stay on the bottom.The fresh water will remain on top.

    The potato is heavier than the fresh water,but it is lighter than the salt water.That is why the potato will sink halfway down.

    Radar（雷达） is an electronic device that detects planes, ships, coastlines, landmarks, and even storm clouds. The name radar comes from the first letters of the words radio direction and ranging. As the human eye uses light waves to see, radar “sees” with radio waves. Without radar, planes could not land safely in bad weather and ships could not move safely in thick fog{#blank#}1{#/blank#}

    In the 1800s it was discovered that radio waves could be reflected from objects. But scientists did not make great advances in radar research until the 1930s, when the world was threatened by war{#blank#}2{#/blank#}It has been used widely in almost every conflict since then.

    Echoes make it possible for radar to work. When a beam of radio waves is sent out, it strikes on an object and returns an echo. This echo is picked up by radar and recorded on a screen similar to television screen. On the screen an observer sees a flash, or a blip, that shows the direction and distance of the object{#blank#}3{#/blank#}

    Airport control towers use radar to guide planes in for safe landings. Almost all large ships depend on radar to prevent collisions with icebergs or other ships{#blank#}4{#/blank#}Weather forecasters “see” the size, direction, and speed of storms on radar screens. Astronomers can even use radar to measure accurately the distance to the moon. Thus, the device has generated major advancements.

    {#blank#}5{#/blank#} Huge radar antennas have been installed all over the United States. They guard us against possible enemy attacks. We have ballistic—missiles (战略导弹)warning systems that can alert us to attacks when missiles are more than 1,000 miles away. Other radar systems warn us against enemy aircraft and even spying space satellites.

A. Police track speeders in radar-equipped cars.

B. These measurements are now highly accurate.

C. The device can be used in a wide range of fields.

D. During World War II many countries used radar effectively.

E. It is therefore especially valuable to shippers and travelers.

F. Today radar is used by commercial airliners and weather forecasters.

G. Strengthening national defense is one of radar's most important functions.

Should You Become a Full Stack Web Developer?

    Should you become a full stack web developer? What courses should you take to prepare you for the job? Our courses bring you a step-by-step path that will help you become a qualified candidate and teach you everything you need to know to succeed. Read on to discover if it's the right path for you:

    What is a Full Stack Web Developer?

    A full stack web developer is well skilled in both front and back-end web developing. With knowledge of what it means to build applications from start to finish, a full stack developer can plan, manage, and build software with general know-how. A core difference between front and back-end developers is that front-end developers handle building the user interface aspect of a website, while back-end developers deal with internal tasks such as web servers, applications, and databases.

    Combined, they are responsible for building the technology and coding that makes a website function properly. Both skillsets are crucial for being a well-rounded web developer and will give you a leg up when applying for jobs. If you like to learn new concepts and technologies frequently this is an excellent career path for you.

    Demand for Full Stack Web Developers is Growing

    Because of the broad range of skills required to be a full stack web developer, there are fewer candidates applying for positions, leaving more opportunity for qualified candidates. The job outlook for web developers is estimated to grow 13% by 2026, which is faster than the average rate for all occupations. With an impressive resume, full stack web developers can make $87,661 on average.

    Get Started Today

    With the help of the course, you will learn everything you need to know to succeed as a full stack web developer. You can start from any level with little to no previous experience required and track your progress as you go.

    Here's What You'll Learn in the Courses

    Build web applications and develop on both the front-end and back-end stacks

Learn Ruby on Rails, HTML, CSS, and JavaScript

    Develop web applications in Javascript using front-end framework, Angular, and hybrid mobile applications with Apache Cordova

    Design RESTful Ruby on Rails web applications with MongoDB database integration.

    Wolves travel shorter distances and move slower during snowfall events, according to new research by University of Alberta biologists. The effects were most pronounced at night, when wolves hunt, and behaviour returned to normal within a day. Wolf tracks across snow in northeastern Alberta.

    "Our findings suggest that there is something about actively falling snow that causes wolves to slow down," said Amanda Droghini, a former MSc student in the Department of Biological Science and lead author on the study. "We don't know the exact mechanism behind that. It's unlikely that they were staying still because they were feasting on a recent kill. Instead, active precipitation（降雪量）might affect wolves' hunting abilities. Like rain, snow clears the air column of scent molecules. So, maybe falling snow makes it harder for wolves to detect the smell of prey."

    Over the course of two winters, the researchers used remote cameras to disclose snowfall events and estimate snow depth. To study wolf movement, they collected telemetry（测距仪） data from 17 wolves to calculate travel speed and duration, as well as resting periods. It is the first study to examine how large flesh-eating animals respond to snowfall events.

    With the effects of climate change on precipitation in the north forest region uncertain, it is difficult to predict the implications for wolf populations. Studies such as these increase our understanding of how large mammals react to normal snowfall events, but the type and amount of winter precipitation will likely have an impact on animal behavior and the energetic cost of movement.

    "Winter is already challenging for many wildlife species because moving through snow requires more energy. Snow can also make it harder for animals to access food resources," said Droghini, who conducted the research under the supervision of Professor Stan Boutin, Alberta Biodiversity Conservation Chair.

    "Anything that increases those costs, such as increased rain-on-snow events, could lead to lacking in nutrition, poor body condition, and even starvation as animals are unable to make up for those additional costs. That is one of the worst-case scenarios（设想）but, in truth, we know very little about potential changes to precipitation patterns and how wildlife will respond to those changes."

The Alexander technique

    Until earlier this year, I didn't know anything about the Alexander technique—and saw no reason to think I should. One day, the backache I regularly suffered was more painful. I was brought up to think that the preferred way of dealing with aches is to do nothing and hope they'll go away, but I eventually went to the doctor. After examining me, he said, "You actually have bad posture (姿势). Go off and learn the Alexander technique." Three months later I could walk straighter and sit better.

    The Alexander technique is a way of learning how you can get rid of harmful tension in your body. The teaching focuses on the neck, head and back. It trains you to use your body less severely and carry out the movements that we do all the time with less effort. There is little effort in the lessons themselves, which sets apart the Alexander technique from yoga or pilates, which are exercise-based. A typical lesson involves standing in front of a chair and learning to sit and stand with minimum effort. You spend some time lying on a bench with your knees bent to straighten the spine (脊椎) and relax your body while the teacher moves your arms and legs to train you to move them correctly.

    The technique helps to break the bad habits accumulated over years. Try folding your arms the opposite way to normal. This is an example of a habit the body has formed which can be hard to break. Many of us carry our heads too far back. The head weighs four to six kilos, so any inappropriate posture can cause problems for the body. The technique teaches you to let go of the muscles holding the head back, allowing it to go back to its natural place on the top of our spines.

    So who was Alexander and how did he come up with the technique? Frederick Alexander, an Australian actor born in 1869, found in his youth that he had vocal (声音的) problems during performances. He analyzed himself and realized his posture was bad. He worked on improving it, with excellent results. He brought his technique to London and opened a teacher-training school, which is still successful today.

    So if you're walking along the road one day with shoulders bent forward, feeling weighed down by your troubles, give a thought to the Alexander technique. It will help you walk tall again.