Piaget’s   theory   of   cognitive(认知的) development   is   a   theory   about   the   nature   and development of human intelligence. It was first created by the Swiss developmental psychologist Jean Piaget (1896-1980). The theory deals with the nature of knowledge itself and how humans gradually   come   to   acquire,   construct,   and   use   it . Piaget’s   theory   is   mainly   known   as   a developmental stage theory.

To   Piaget,   cognitive   development   was   a   progressive   reorganization   of   mental   processes resulting from biological maturation and environmental experience. He believed that children construct an understanding of the world around them, experience differences between what they already   know   and   what   they   discover   in   their   environment,   and   then   adjust   their   ideas accordingly. Besides, Piaget claimed that cognitive development is at the center of the human organism, and language is depending on knowledge and understanding acquired through cognitive development.

Piaget’s earlier work received the greatest attention. Child-centered classrooms and "open education" are direct applications of Piaget’s views. Despite its huge success, Piaget’s theory is not perfect and Piaget has recognized it himself: for example, the theory supports sharp stages rather than continuous development.

Piaget noted that reality is a dynamic system of continuous change. Reality is defined (给……下定义) in reference to the two conditions that define dynamic systems. Specifically, he argued that reality involves transformations and states. Transformations refer to all manner of changes that a thing or person can experience. States refer to the conditions or the appearances in which things or persons can be found between transformations. For example, there might be changes in shape or form , in size, or in placement or location in space and time. Thus, Piaget argued, if human intelligence is to be adaptive, it must have functions to represent both the transformational and the static aspects of reality.

Some earlier studies had found no clear color preference among mosquitoes. One study found they prefer blue, another that they prefer yellow-green. What should people make of such conflicting results?

The apparent color of an object doesn’t just depend on the wavelengths of light it gives off, Claire Rusch explains, who studies mosquitoes for years. It also can be affected by the brightness of that light and its contrast against surrounding colors. Humans see an object’s color largely in terms of the wavelengths of light it gives off. But other creatures’ eyes may be more sensitive to contrast or brightness. “We needed to control all of those variables to really be sure a mosquito’s preferences came from the wavelength of the object,” Rusch says.

To do this, she designed a test chamber (室) that was 450 mosquito-body-lengths long in her experiment. Lined with cameras, it recorded the insects’ flight patterns. Two small colored disks laid on the floor of the chamber.

Since the researchers wanted to know if mosquitoes were attracted to certain colors, the disks couldn't be the darkest or brightest objects in the chamber. Otherwise, it would be unclear if the mosquitoes were attracted to the disks’ color, contrast or brightness. So, the researchers projected a chessboard pattern onto the floor of the chamber and gray along the walls. That way, if the mosquitoes went to the colored disks, it could only be due to the disks’ color.

The researchers released about 50 starved mosquitoes into the chamber at a time. Because mosquitoes don't start hunting until they’ve sensed CO₂, so the team sprayed (喷) CO₂ inside the chamber. They found before CO₂ was sprayed, the mosquitoes ignored all the colored disks. With CO₂, mosquitoes ignored any disk that was green, blue or purple. But the insects did fly toward disks that were red, orange or light blue. They seemed to especially like red.

To further investigate that, the team placed disks with different skin tones. But the mosquitoes didn't seem to prefer any particular skin colors. All were equally attractive.

There’s a lot of confusion around exercising and eating. What should you eat before you work out? What about after? How long should you wait to eat? How will all of this benefit your goal of losing more fat? Scientists have now answered one important question.

In a new study researchers had a group of overweight males walk for one hour on an empty stomach, and then had them walk again for 2 hours on another day after eating a good breakfast. The researchers collected their blood samples after eating or fasting (禁食) as well as after exercising. They also took fat samples directly before and directly following an hour of walking.

The results showed differences in gene expression of the fat tissue in the two tests. The two genes they looked at, PDK4 and HSL, increased as a result of the volunteers fasting and exercising, and decreased when they ate before exercising. The researchers believe that the rise in PDK4 likely shows that stored fat was used to fuel metabolism (新陈代谢) during exercise，and that HSL increased when the fat tissue used stored energy to benefit an increase in exercise.

According to Dylan Thompson, an author of the study, the results support the viewpoint that “fat tissue often faces competing challenges”. “For example,” he says, “after eating the body is busy responding to the meal, and a short period of exercise at this time will not cause the same beneficial changes in fat tissue.”

How long do you have to decline food to meet their definition of “fasting”? Thompson says, “The best advice would be to make sure that your last meal was 4 hours before exercise to get the effect that we reported.”