B
Flickering lights are annoying but they may have an advantage. Visible light communication (VLC) uses rapid pluses of light to transmit information wirelessly. Now it may be ready to compete with conventional Wi-fi.
In a recent TED talk, Harald Hasas from the University of Edinburge,UK demonstrated one VLC prototype(原型)，“Li-Fi", transmitting a video from a store-bought LED lamp to a solar cell to a laptop. “Li-Fi is essentially the same as Wi-Fi,except for a small difference- we use LED lights around us to transmit the data wirelessly as opposed to using radio," Haas says.
Once established, VLC could solve some major communication problems. In 2009, the US Federal Communications Commission(FCC) warned of spectrum (波谱)crisis: because our mobile devices are so data- hungry we will soon run out of radio-frequency bandwidth.Li-Fi could free up bandwidth, especially as much of the infrastructure is already in place."There are around14 billion light bulbs worldwide, they just need to replaced with LED ones that transmit data", says Haas.
The idea of transmitting data through the visible light spectrum is not new.Alexander Graham Bell transmitted sound via a beam of sunlight in 1880 using a photo phone, a sort of solar-powered wireless telephone. In the past several decades, a number of researchers have looked at using visible light to transmit data.
But what Haas seized on is the use of simple LED light bulbs for data transmission. LED bulbs are controlled by a driver, which can rapidly di the light or turn it on or off. Therefore, Haas figured, data could be encoded in subtle shifts of the light’s brightness. Eventually, he creaded a working transmitter and receiver system with an IKEA lamp and a solar panel.
Li-Fi stands to be much faster than Wi-Fi. According to Haas research, Li-Fi can achieve data density 1000 times greater than Wi-Fi,because Li-Fi signals are contained in a small area, as opposed to the more diffuse (分散的)，radio signals.The system wouldn’t mean having to keep your lights on all the time either, Haas says---bulbs could be dimmed to such a point that they appear off, but still transmit data.
Now, Haas’ team hopes that Li-Fi could make its way into homes in a few years. The system can easily network any device with an LED light—an electric kettle, an oven. Eventually, this could bring about the Internet of Things era much faster. Haas also sees Li-Fi as a way to bring internet to remote location, using hilltop transmitters and rooftop solar panels. LED streetlights could even be used to form a network of outdoor Li-Fi, making it possible to stay connected when walking around the city.
But some sound a cautious note about VLC’s future. It becomes less powerful , for example,when light is blocked, wheather due to fog or other conditions.
59.By saying "There are around14 billion light bulbs worldwide”Haas intended to tell us that ______________
A. mobile devices will consume more data
B. radio-frequency bandwidth needs to be freed up.
C. VLC might solve the spectum crisis.
D. the world has a complete lighting infrastructure.
60. The underlined phrased “seized on“ in the passage is closet in meaning to “_____________”
A distinguished B. exploited C. created D. figured
61. We can learn from the passage that ________________________
A. Li-Fi can’t work outdoors.
B Li-Fi can work with LED lights off.
C. Li-Fi can be used with all household appliances.
D. Li-Fi needs improving to next diverse need.
C
“There’s no point in talking with you: you don’t understand me. You don’t even know me.” A teen spits these words at a parent, who is hurt and annoyed. How can her own child say these things? She’s worked hard getting to know him, learning to read his feelings from his voice and gestures. How can her own child now say to her, “You don’t know who I really am”?
Nothing shakes a parent’s confidence as much as the starting of a child’s adolescence. The communication that has flowed easily through words, glance and touch becomes a minefield(雷区)
Recent discoveries that the human brain undergoes specific and dramatic development during adolescence offer new “explanations” of teen behavior, particularly of the impulsiveness(冲动) of teenagers. During this development, there may be too many synapses(神经元突触) for the brain to work efficiently, the mental capacities of decision-making, judgment and control are not mature until the age of twenty-four.
An old explanation is that anger hormones account for the apparently unreasonable moodiness(情绪化) of teens. Though hormones do play a role in human feelings, the real task of adolescence, and the real cause of the unrest, is the uncertainty of teenagers about who they are, alongside their eagerness to establish a sense of identity.
This involves self-questioning, self-discovery and self-development across a range of issues, including sex, faith, intellect and relationships. A sense of who we are is not a mere luxury; without it we feel worthless. A teen often looks upon his or her friends sa models: “ I don’t know who I am, but I know who he is, I’ll be like him,” is the underlying thought. Parents also become such mirrors: teens want that mirror to reflect back to them the vividness and clarity they themselves do not feel.
Arguments with parents can often be understood in this context. While those common teenager-parent quarrels, which explode every few days, are often over small things such as homework, housework, and respect; a teenager’s real focus is on a parent’s recognition of his maturity and capability and human value. “ No, you can’t go out tonight,” implies that a parent you got your keys?” or “Do you have enough money for the bus?” are questions that can be easily accepted if asked by a concerned friend, but awaken a teen’s own doubts if asked by a parent. Feeling the need to distinguish himself from the kid who can’t remember to take his lunch, his keys or his money, he blames the parent for reminding him of the child-self still living within him. What my research shows is that quarreling witj your teen doesn’t necessarily mean you have a bad relationship. The quality of teenager-parent relationship has several measures.
62. According to the text, teenagers_____________.
A. can fully understand their parents’ feelings
B. need guidance in every aspect of their life
C. may experience a huge mental change
D. know themselves better than their parents do
63. What do we learn from the text?
A. Parents hate talking to their children because they can’t understand them.
B. The brains of teenagers work more efficiently because of the synapses.
C. Hormones are the real causes of unrest and moodiness in teens.
D. What teens really care about is being recognized by their parents.
64. What is implied in the last paragraph?
A. Quarrels between children and parents often involve serious issues.
B. A parent should not ask a child about money.
C. A child wants respect, especially from his or her parents.
D. Quarrels are a sign of a bad relationship.
65. What will probably be written in the following paragraph?
A. Other ways of assessing teenager-parent relationship.
B. The anger and sadness of parents about their teens.
C. How important the friends of teenagers are.
D. When children become mentally mature.
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