【推荐2】What are those short metal fences by the side of the road? They don’t look like much. But they do a big job.

People who design highways would always like to have a wide, flat, clear space on either side of the road. That way, if a car goes off the road, it can stop safely.

But in some places, that’s just not possible. That’s when they put up a guardrail. These short railings are designed to stop cars from running into something more dangerous, without damaging the car too much.

The type of guardrail they put up depends on the road. A weaker guardrail may let the car go farther off the road, but does less damage to the car. A strong guardrail stops a car in a short distance, but the car suffers more damage.

	Jersey barriers are made of concrete. They are often placed down the center of a road to separate cars going in opposite directions. Jersey barriers are also used around construction zones. They are cheap to make and easy to move around.		A box-beam guardrail looks like a long metal box running between posts. Box-beam guardrails are very strong, but expensive. They are used mostly where it’s important to stop cars quickly. You might see one in the middle of a road to keep cars from going into oncoming traffic.
	A strong-post W-beam guardrail has short, thick posts set close together. This common guardrail is used where it’s important to stop a car quickly to save lives, such as where a cliff is right next to the road. It gets its name from the fact that if it’s cut in half, the rail looks like a sideways W.		A weak-post W-beam guardrail has posts that are thinner and farther apart. Why would anyone want to make a guardrail with weak posts? A weak-post guardrail will stop a car more slowly than a strong-post guardrail. The more gradually a car slows down, the less likely its riders will be hurt. A weak-post guardrail can be used where there is more space to slow a car down.

【推荐3】Erik Kobayashi-Solomon spent a day with Dr. Paul Gauthier, a plant physiologist specializing in vertical farming research and came away with several important ideas about vertical farming.

Humans have 12,000 years of experience growing food, but only a generation or so worth of experience growing crops indoors. We are still progressing up the technology learning curve (学习曲线). What's more, traditional farming techniques are based on conditions that are not applicable to vertical farming. Therefore, without taking time to understand the science, vertical farming is not likely to be able to live up to its implied promises.

The cost of powering LED grow lights is one of the biggest problems a vertical farm must overcome. Dr. Louis Albright at Cornell has characterized vertical farms as " pie-in-the-sky" businesses. He famously calculates, for instance, that the cost of a loaf of bread would be $ 24 if farmed indoors — the cost is too high. Gauthier acknowledges that energy prices are high but points out that scientific work has shown that only about 6% of available sunlight is used in crop photosynthesis (光合作用), so there may be ways of growing the same plants with less light.

Gauthier also points out that while energy costs are a bit high, vertical farming does create high efficiencies in other areas. Water usage may be significantly reduced because the same water can be recycled time and again. Fertilizer use can be greatly reduced and pesticides for pest control are unnecessary. It's clear that vertical farming offers real value to society.

The future is probably mixed. In some environments — the Middle East, for instance — a move to vertical farming is a no-brainer. An indoor farm in Saudi Arabia, for instance, can use solar energy to power LEDs at low cost without shading out other farmland. In other geographies, though, the expense of establishing a facility places a high bar on growth and profitability. A large vertical fanning and equipment operation only started generating a small profit eight years into its nine-year life.