We've all done it before-dropped a box of unwanted household belongings at a flea market and driven off with a sense of accomplishment. But have you ever stopped to think about where those items actually go?

Business journalist Adam Minter began considering this while cleaning out his late mother's home. Seeking reassurance that his mother's donated items would be put to good use rather than destroyed, he started a journey worldwide that resulted in his latest book, "Secondhand: Travels in the New Global Garage Sale". He found the industry significantly in the dark, with a disturbing lack of data on secondhand goods, despite their crucial role in clothing, furnishing and educating people worldwide. 

In this book, Minter fully reveals himself as an investigative journalist. He doesn't shy away from the commonly-accepted assumptions about the global trade in used goods. First, Minter questions the idea that shipments of secondhand clothes from developed countries to Africa have destroyed local textile industries （纺织业）. That's overly simplistic, he says. He further explains that multiple factors, such as declining cotton production in local areas and economic liberation, have influenced the situation. 

Minter then explores the topic of car seats, making a statement that recycling car seats, instead of selling them secondhand, is wasteful and might compromise （危害） safety for children in developing countries. It is disturbing to say so in a society that prioritizes child safety and highlights zero risk, but when you consider the excessive caution that might endanger children's lives elsewhere, the situation starts to look different. 

Minter calls it "waste colonialism," this idea that developed countries can apply their own safety standards onto the markets of developing countries-and it's deeply wrong. Why label an used car seat or an old TV as unsafe if someone else, with different skills, is perfectly capable of repairing it and willing to use it, especially if they lack access to new products and other options?

The book explores the huge problems of handling surplus （剩余的） items and how producers discourage repairs and promote the sales of new products. Minter calls for initiatives to enhance product repairability and increase product lifetime. 

The Self-Portrait Challenge

Have you ever done a self-portrait in an art lesson at school? Today, we're challenging you to write self-portrait poems. It's not uncommon to feel like the way people see you on the outside doesn't quite match up with how you feel on the inside. So creating a self-portrait can be a good opportunity to address those differences and present the realest, truest version of yourself. 

Your challenge is to create a self-portrait in lines, using words instead of paint. Read on for some more inspiration. 

Writing Tips

• Have a go at writing a list of metaphors exploring your physical appearance, starting from your head and working your way down towards your feet. 

• Instead of representing yourself directly, take on another character, such as a fictional character, a historical figure, or even a different version of yourself. 

• Play around with personification, by taking on the voice of a physical object in your poem. Think about what a self-portrait from the point of view of a mirror, or a bowl of your favourite food would look like?

How to enter

This challenge is for writers aged up to 25 based anywhere in the world. The deadline is 23: 59 GMT, 17 March 2024. You can send a poem, or poems, written down, or as video or audio files. We are using Submittable to accept submissions to this challenge. You will need to make a free Submittable account to submit in this way. Using Submittable helps our team to administrate and process entries more quickly. Selected poets will be published on Young Poets Network. 

Late one night in July 2020 in Reykjavik, Haraldur Thorleifsson was wandering around the city's main shopping street with his wife and two kids. During their walk, his three-year- old son was thirsty and wanted a drink from the corner store. But Thorleifsson soon discovered he couldn't help with the simple request: A 20-centimetre step blocked his access to the store. 

The barrier was all too familiar. Born with muscular dystrophy, which causes progressive weakness and loss of muscle, Thorleifsson, now 46, has been using a wheelchair since he was 25. As he waited outside, he recalled, "I thought about how strange it is that we separate families in this way. I thought about all the times I wasn't able to join my friends at restaurants, pubs and stores that are inaccessible. 

Living all over the world as a creative director and digital designer in cities such as San Francisco and Tokyo, Thorleifsson had witnessed first-hand how different cities consider and plan for accessibility, from ramps （斜坡） and sidewalks to public transportation. 

Having recently sold his digital creative agency, Ueno, to Twitter, Thorleifsson now had the financial means to make a difference in his hometown. He decided to start with a project to make Iceland wheelchair accessible, one ramp at a time. 

Ramp Up Reykjavik was launched as a non-profit in 2021 with a goal to build 100 ramps, mostly in the city's down-town, within a year. Unlike portable and temporary solutions in other cities, these ramps are permanent structures that match the aesthetic of the buildings, making them appear as if they've always been there. It's a design detail that helps provide a sense of inclusivity. 

With the help of government funding and other sponsors, the Ramp Up team finished ahead of schedule and has broadened its scope to all of Iceland, with the goal of building 1, 500 ramps countrywide by  2026. 

The universal speed limit of any kind of wave—whether electromagnetic or gravitational travelling through a vacuum(真空)has been known since Albert Einstein developed his theory of special relativity in 1905. But the maximum speed of sound moving through a solid or a liquid has just been calculated for the first time. It is about 36 kilometre per second, more than 8, 000 times lower than the speed of light in a vacuum. 

To make this calculation, Kostya Trachenko at Queen Mary University of London and his colleagues started with two well-known physical constants:the ratio(比率)of proton mass(质子质量)to electron mass, and the fine structure constant, which characteristics the strength of interactions between charged particles(粒子). 

Trachenko says we have a pretty good idea of these values, because if they were changed even a bit, the universe wouldn't look at all like it does. "If you change these constants by a few percent, then the proton might not be stable anymore, and you might not even have the processes in stars resulting in the combination of heavy elements, so there would be no carbon, no life, "he says.

Sound is a wave that spreads by making neighbouring particles interact with one another, so its speed depends on the density of a material and how the atoms within it are bound together. Atoms can only move so quickly, and the speed of sound is limited by that movement. 

"The common wisdom was that diamond has the highest speed of sound, because it is the hardest material, but we didn't know whether there was a theoretical fundamental limit to it, "says Trachenko. The theoretical bound is about twice the speed of sound in a diamond.

The speed of sound is also dependent on the mass of the atoms in the material, so there searchers predicted that solid metallic hydrogen—a material that theoretically exists at the centre of giant planets, but for which laboratory evidence has been hotly questioned—should have the highest speed of sound. They calculated that it should be close to the theoretical limit. They also looked at experimental data for 133 materials and found that none of them broke the limit. 

Depending on your job, you may have the chance to make a kid's day while at work. Or even better, you may have memories of an adult going the extra mile just to make you smile. For a group of construction workers, the opportunity popped up in the form of a toy truck. Excited to see some building work being done in the area, a small boy paid a visit with his tiny truck as if to join the action. What happened next is something that the little one will surely value forever. 

The heart-warming moment was shot in a video that has since gone viral. Wanting to be a part of it all and hoping to see the big excavator(挖掘机)at work, the kid placed his wheeled toy under the big metal machine. The machine operator, moved by it all, was grateful and filled the toy truck with earth. With careful precision, as if it were a crucial part of the construction work being done, he made the little boy's dreams come true. While it's hard to find the location or the time from the video alone, the excitement of the kid as the machine slowly fills the mini dump truck is universally lovely. Even the other construction workers stop for a while to witness the cute scene. All the while, the kid's mom holds him firmly to keep everyone safe until the toy truck is full and the machine is still. 

While anyone can appreciate the sweetness of a group of adults taking a few minutes to put a smile on a child's face, the video has had all kinds of positive responses. For some, it brought back memories of seeing construction work and big machines when they were little and being blown away. For others, it allowed them to enjoy the unexpected delicacy of the great machine. If there's one thing we all can agree on, it's that the boy wasn't the only one who benefited from this tiny action. As one editor wrote, "I used to work in the field. I can tell you it made everyone's day. "

Keeping plants at home is a healthy and comfortable way of life. The following houseplants can create a most beautiful piece of green for your home.

Bird's Nest Fern (蕨)

The bird's nest fern is a good choice for anyone with a house that wouldn't support sun-loving species. It's a hardy fern variety adapting to living on forest floors, where the air tends to be cool and damp. It likes to be misted as well, but this doesn't always mean you need a misting bottle—spraying (喷洒) it in the sink or hanging it near a shower often works as well.

Chinese Money Plant

This is a flowering species that might be most appropriate for experienced plant gardeners looking for a new challenge. It prefers a moderate amount of indirect light, and tends to dry out slightly between watering sessions. It produces new plants easily without any input, directly from its root system. These can coexist in the same pot for a time.

Resurrection Plant

This native of the Mexican desert has adapted to surviving in extreme drought by curling (蜷缩) into a ball and remaining in seemingly lifeless state for years, if necessary. In this form, it can be transported by the wind across the dry landscape to areas with water. It will revive within hours in a shallow bowl of water, unfolding and transforming into a fresh and green moss (苔藓).

Snake Plant

This is a striking houseplant that can be an especially good option for new plant owners who you might not trust to keep a plant alive. It grows happily in almost any condition. While it prefers bright light, it doesn't mind shade or even artificial light. Plus, thanks to its thick, fleshy leaves, it stores water with remarkable efficiency, which makes it survive without water in the earth.

Given that cancer is one of the deadliest diseases out there, any new development in our fight against it is highly praiseworthy. The latest breakthrough was made by Heman Bekele in 2023, a 14-year-old student from Virginia. The student has created a bar soap to treat skin cancer. Now, his findings have earned him the title of America's Top Young Scientist.

Bekele remembers he always saw people who were constantly hit by the glaring sun as a child. As he grew up and began to realize the risks like skin cancer were associated with sun exposure, the boy decided to come up with solutions.

While similar treatments are available, Bekele hoped to work on a more affordable alternative, especially for those in developing countries. "I wanted to make my idea something that not only was great in terms of science but also could benefit as many people as possible," Bekele says. It is often the simple solutions that are the most effective because soap is a daily routine for most people.

With the guidance of Deborah Isabelle, a product engineering specialist, Bekele made his soap by mixing regular soap with compounds (化合物) that slowly reactivate dendritic (枝状的) cells. When the soap is applied, it releases toll-like receptors into our skin. These receptors attach onto dendritic cells which reactivate them. The reactivated dendritic cells then join with TN io12 cells to fight cancer cells. Rather than a cure, Bekele's soap aims to help people's immune cells stay active while fighting skin cancer.

For now, the young scientist hopes to improve his invention and create a non-profit to distribute the soap among those who need it most. "I believe that young minds can make a positive impact on the world," Bekele said. "I have a strong desire to know how the physical world works and how to improve the lives of its inhabitants, and this challenge gives me the perfect platform to showcase my ideas."

Extended producer responsibility (EPR) refers to a policy approach where producers are given responsibility for the environmental impacts of their products throughout the product lifecycle. Based on the polluter pays principle, this approach requires producers to finance the costs of recycling or disposing of products that consumers no longer want. It aims to shift the costs associated with the management of dealing with solid waste away from the local government.

The term EPR was first coined in 1990 by a Swedish professor, Thomas Lindhqvist, who introduced the idea of producers being responsible for their products to the Swedish Ministry of the Environment. The first example of EPR came in Germany in 1991, where manufacturers picked up household packaging alongside municipal waste collections. Since 1990, countries around the world have adopted EPR policies around key sectors such as packaging, electronics, batteries, and vehicles.

EPR creates a financial motivation for producers to design products that last longer and can be recycled. This is because EPR places the end-of-life costs on the producer. EPR has historically been successful in the managing of products that pose risks to communities such as batteries, paint and old medicines. EPR has led many producers to redesign these items to reduce their risks. Finally, due to ERP closing the loop (循环) on materials management, this approach uses much less energy than it takes to produce items from the beginning.

However, critics of EPR have issues with producers adding recycling costs to the initial price tag of a product. Another disadvantage is that at the international level, it can negatively affect imports to countries that have strict EPR policies as producers in other countries will not want to be subject to extra fees from these policies. Additionally, it restricts competition at the local level as producers who take on the extra costs to accommodate EPR policies are at a competitive disadvantage to those who are able to bend the rules and get out of paying these costs.

California's Water Resources Control Board recently approved new regulations in a unanimous (一致同意的) vote—toilet or shower wastewater will be recycled and pumped into the public drinking water system.

In 2023, more than 97% of California has been in moderate to severe drought, while water suppliers are struggling to keep up. A 2022 water supply and demand report indicated that around 18% of water suppliers were at risk of facing potential shortages. "The reality is that anyone out there on Mississippi River and on Colorado River, and anyone out there taking drinking water downstream is already drinking ‘toilet to tap'," said Esquivel, a director of the Board.

Early in the 1990s, the state was struggling to overcome the distaste its residents had toward drinking recycled water. Their efforts fizzled out when the phrase "toilet to tap" caught on and met with fierce resistance. The idea became too unpopular to be implemented. Despite the negative name, the regulations are the key to ensuring the supply of drinking water.

California's new regulations would let water agencies to treat wastewater, and then put it back into the drinking water system. It has taken officials more than 10 years to develop these regulations, a process that included several studies by independent groups of scientists. To put the scheme into effect and build huge water recycling plants, however, water agencies say they will need to prove to people that recycled water is not only safe to drink but also under monitoring.

The new regulations require the wastewater be treated for all bacteria and viruses. In fact, the treatment is so intense that it removes all of the minerals that make fresh drinking water taste good. That means the minerals need to be added back at the end of the process. "What we have here are standards, science, and importantly monitoring that allow us to have safe pure water, and probably better in many instances," said Esquivel. He added that it takes time and money to build these treatment centers. So, they will only be available for bigger cities at first.

The 7,400 or so languages in use today speak to the fact that our species is born to communicate. But while it is tempting to view language as merely a consequence of our extraordinary cognitive（认知的）powers, Caleb Everett thinks there may be more going on. 

In A Myriad of Tongues: How languages reveal differences in how we think, he argues that language itself may shape our understanding of the world and our experience of time and space. To put it another way, the language we speak may influence the way we think. 

Such a provocative（挑衅的）idea might have been controversial（有争议的）a few decades ago, says Everett, because language experts restricted themselves to analyzing languages of industrialized, higher-income countries. But we now know they fall short of representing the variety of languages spoken today-and the more we learn about understudied tongues, the more evidence we find for the complicated interplay between language and thinking. 

Take Berinmo, a language of Papua New Guinea, as an example. Unlike English speakers, explains Everett, Berinmo speakers struggle to remember whether an object they were shown earlier was blue or green-perhaps because that language doesn't distinguish between these colours. But it does make a formal distinction between yellowish-greens and other greens, and Berinmo speakers typically find it easy to remember which of these colours an object they saw earlier was painted, while English speakers struggle to do this. 

Language also influences how we think about objects. Yucatec Maya, spoken in Mexico, encourages its speakers to classify objects according to their material properties rather than their function. Where an English speaker might group a plastic comb and a wooden comb together and exclude a wooden stick, a Yucatec Maya speaker would usually group the wooden objects together. English-speaking people get the information they need by sight alone. 

We live through a language extinction event predicted to see the loss of about 30 per cent of today's tongues by 

2100. His book makes it clear this is more than just a tragedy（悲剧）for local communities. Given the insights that languages offer into the human mind, their disappearance is a loss for us all.