One of the most recent social changes taking place in the world is social networking. Social networking has been in existence for at least 150 years, and probably longer than that. In the times before the invention of the computer and the World Wide Web (WWW), social networking was done in person. People who had similar likes and interests would gather together to share experiences, make new friends, and improve their businesses.

    On the Internet, social networking websites made their first appearances during the late 1990s. The first major social networking website in the United States was MySpace. MySpace allowed its users to exchange messages, share pictures, and make new friends in a way that was never thought of in the past. With MySpace, people who did not go out much could reach out to others from their own homes.

    In 2004, Facebook was created. It was first a website created for use by Harvard University's students and teachers, but it soon expanded to include just about everyone. It is now larger than some of the largest companies in the world. It is a website that is changing all the time. Facebook has completely changed the way people stay connected with each other and the rest of the world. The way it works is simple. Users can set up a new account (账户) easily. All a new user needs is an email address to start. Once a person has created an account and his friend also has his own Facebook page, he can invite his friend by sending a request out to him. Once you get started, making new friends will come easily.

    Dry Ice is a unique substance which has many uses. Essentially, dry ice is frozen CO2. The first report of what we now call dry ice came from the French chemist Charles Thilorier in 1834. In 1924, the Drylee Corporation of America named the solid form of CO2 as "Dry Ice", which is what it is popularly called today.

    At normal atmospheric pressure, CO2changes directly from solid to gas. It skips the liquid phase（阶段）which makes regular ice wet. Frozen CO2is also much colder than regular ice. But regular ice freezes at 32 degrees Fahrenheit, CO2 changes from gas to solid at -109.3 degrees Fahrenheit. This extremely cold temperature makes it very dangerous to handle with bare hands. It can cause frostbite in a very short period of time.

    Dry ice has been used for a variety of purposes throughout the past century. Its primary use is to refrigerate food when electrical refrigeration isn't available. Through the process of sublimation (when CO2 changes from solid to gas), it can maintain cold food for a long time.

    If you've ever been to a play and seen heavy fog on the ground, it is likely that you have seen dry ice in action. This effect can be achieved because CO2 is heavier than air, so evaporated （挥发的）CO2 will sink and accumulate on the ground.

    Another interesting use for this substance is to bait（诱杀）insects like mosquitoes. These insects have sensors which guide them to CO2. They find the high concentration of CO2 in dry ice quite attractive.

    Mars has long been a mystery for human beings. We have been looking for evidence of life on Mars. In the 1960s scientists guessed that the polar ice cap of Mars was made of frozen CO2. More recent observations have shown that while the topmost layer consists of frozen CO2, the most of it is probably regular frozen water.

    You are given many opportunities in life to choose to be a victim or a creator. When you choose to be a victim, the world is a cold and difficult place. “They” did things to you which caused all of your pain and suffering. “They” are wrong and bad, and life is terrible as long as “they” are around. Or you may blame yourself for all your problems, thus internalizing(内化) your victimization. The truth is, your life is likely to stay that way as long as you feel a need to blame yourself or others.

    Those who choose to be creators look at life quite differently. They know there are individuals who might like to control their lives, but they don't let this get in the way. They know they have their weaknesses, yet they don't blame themselves when they fail. Whatever happens, they have choice in the matter. They believe their dance with each sacred(神圣的) moment of life is a gift and that storms are a natural part of life which can bring the rain needed for emotional and spiritual growth.

    Victims and creators live in the same physical world and deal with many of the same physical realities, yet their experience of life is worlds apart. Victims relish (沉溺) in anger, guilt, and other emotions that cause others—and even themselves—to feel like victims, too. Creators consciously choose love, inspiration, and other qualities which inspire not only themselves, but all around them. Both victims and creators always have choice to determine the direction of their lives.

    In reality, all of us play the victim or the creator at various points in our lives. One person, on losing a job or a special relationship, may feel as if it is the end of the world and sink into terrible suffering for months, years, or even a lifetime. Another with the same experience may choose to first experience the grief, then accept the loss and soon move on to be a powerful creative force in his life. In every moment and every circumstance, you can choose to have a fuller, richer life by setting a clear intention to transform the victim within, and by inviting into your life the powerful creator that you are.

    Many of us live with a roommate at some stage. Sometimes, there can be problems. Who hasn't had an argument about whose turn it is to take out the rubbish or who should be the one to clear up after dinner? However, living with another person also comes with many benefits.

    You know that there's always someone else around, which can help you feel safer. There is always someone to talk to, so you never feel lonely. Besides these obvious benefits, there are some you may not notice. For example, we're actually more likely to eat healthier food when living with others.

    To examine the effect of living alone, Australian university researchers did much research and found that people living alone tended to eat less fresh food, which can have a significant negative effect on long-term health. However, those living with others generally benefited from a more varied diet compared to those living alone.

    What could explain these findings? The researchers believe the social and cultural roles played by cooking, food preparation and eating may be important considerations. For example, those living with friends have someone else to go shopping with, and thus are likely to buy higher-quality fresh food regularly.

    Cooking skills may be another factor. If people living alone find they do not have the knowledge required to prepare a particular dish or cook a certain food, they may fall back on ready-made, less healthy food. However, if they live with at least one other person, they may be able to ask for help.

    In addition, people living alone can eat whatever they want at any time of the day or night. However, it's helpful to have someone around who questions your decision to eat frozen pizza at 3 am. In other words, roommates can draw your attention to unhealthy routines.

    So, if you now live alone and find yourself fighting a losing battle against poor eating habits, why not consider sharing a home with someone else? You could encourage one another on to greater health and well-being.

    Grown-ups are often surprised by how well they remember something they learned as children but have never practiced ever since. A man who has not had a chance to go swimming for years can still swim as well as ever when he gets back in the water. He can get on a bicycle after many years and still ride away. He can play, catch and hit a ball as well as his son. A mother who has not thought about the words for years can teach her daughter the poem that begins "Twinkle, twinkle, little star" or remember the story of Cinderella or Goldilocks and the Three Bears.

    One explanation is the law of overlearning, which can be stated as follows: Once we have learned something, extra learning trials (尝试) increase the length of time we will remember it.

    In childhood we usually continue to practice such skills as swimming, bicycle riding, and playing baseball long after we have learned them. We continue to listen to and remind ourselves of words such as "Twinkle, twinkle, little star" and childhood tales such as Cinderella and Goldilocks. We not only learn but overlearn.

    The multiplication tables (乘法口诀表) are an exception (例外) to the general rule that we forget rather quickly the things that we learn in school, because they are another of the things we overlearn in childhood.

The law of overlearning explains why cramming (突击学习) for an examination, though it may result in a passing grade, is not a satisfactory way to learn a college course. By cramming, a student may learn the subject well enough to get by on the examination, but he is likely soon to forget almost everything he learned. A little overlearning, on the other hand, is really necessary for one's future development.

Ivan Pavlov was a Russian physiologist (生理学家) best known for his discovery of classical conditioning (经典条件反射). During his studies on the digestive systems of dogs, Pavlov found that the animals salivated (流口水) naturally upon the presentation of food. However, he also noticed that the animals began to salivate whenever they saw the white lab coat of an experimental assistant. By associating the presentation of food with the lab assistant, he finally found that a dog would salivate to the presence of a stimulus (刺激物) other than food. He called this response a conditional reflex.

Ivan Pavlov was born in a small village in Ryazan. Russia, where his father was the village minister. His earliest studies were focused on theology (神学), but reading Charles Darwin's On the Origin of Species had a powerful influence on his future interests. He soon stopped his religious studies and devoted himself to the study of science at the University of Saint Petersburg. Pavlov's interests were the study of physiology and natural sciences. He helped found the Department of Physiology at the Institute of Experimental Medicine and continued to manage the program for the next 45 years.

Pavlov received much praise for his work. He worked in the Russian Academy of Science and won the 1904 Nobel Prize in Physiology. The Soviet government also offered lots of support for Pavlov's work, and the Soviet Union soon became a leading center of research on physiology. While Ivan Pavlov was not a psychologist, and reportedly disliked the field of psychology, his work had a major influence on the field, particularly on the development of behaviorism. His discovery and research on reflexes influenced the growing behaviorist movement. and Pavlov's discovery had a major influence on many thinkers, such as John B. Watson.