Builders in ancient Rome used a special kind of ancient concrete to construct their aqueducts, bridges, and buildings. But is Roman concrete more sustainable than the Portland cement used in today's concrete? The answer is more nuanced than one might think, according to a new paper published in the journal iScience. Roman concrete produces as much CO₂ as modern methods, but fewer air pollutants.

As we've reported previously, like today's Portland cement (a basic ingredient of modern concrete), ancient Roman concrete was basically a mix of a semi-liquid mortar and aggregate. Portland cement is typically made by heating limestone and clay (as well as sandstone, ash, chalk, and iron) in a kiln. The resulting clinker is then ground into a fine powder, with just a touch of added gypsum—the better to achieve a smooth, flat surface. But the aggregate used to make Roman concrete was made up of fist-sized pieces of stone or bricks.

Scientists have long been fascinated by the remarkable longevity of Roman concrete; it's a very active field of study. For instance, in 2017, scientists analyzed the concrete from the ruins of sea walls along Italy's Mediterranean coast, which have stood for two millennia despite the harsh marine environment. That analysis revealed that the recipe involved a combination of rare crystals and a porous mineral. So exposure to seawater generated chemical reactions inside the concrete, causing aluminum tobermorite crystals to form out of phillipsite, a common mineral found in volcanic ash. The crystals bound to the rocks, preventing the formation and propagation of cracks that would have otherwise weakened the structures.

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Earth is about 71 percent water. An overwhelming 97 percent of that water is found in the oceans, leaving us with only 3 percent in the form of freshwater—and much of that is frozen in the form of glaciers. That leaves just 0.3 percent of that freshwater on the surface in lakes, swamps, springs, and our main sources of drinking water, rivers and streams.

Despite our planet’s famously blue appearance from space, thirsty aliens would be disappointed. Drinkable water is actually pretty scarce.

As if that doesn’t already sound unsettling, what little water we have is also threatened by climate change, urbanization, pollution, and a global population that continues to expand. Over 2 billion people live in regions where their only source of drinking water is contaminated. Pathogenic microbes in the water can cause cholera, diarrhea, dysentery, polio, and typhoid, which could be fatal in areas without access to vaccines or medical treatment.

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Tired of using bulky night vision goggles for your clandestine nocturnal activities? An interdisciplinary team of Chinese neuroscientists and materials scientists has developed near-infrared contact lenses that enabled both mice and humans to see in the dark, even with their eyes closed, according to a new paper published in the journal Cell.

Humans and other mammals can only perceive a limited range of the electromagnetic spectrum (light), usually in the 400–700 nm range. There are creatures that can see in infrared (snakes, mosquitoes, bullfrogs) or ultraviolet (bees, birds), and goldfish can perceive both. But humans must augment themselves with technology in order to expand our range of vision.

Night vision goggles and similar devices have been around since the 1930s, including infrared-visible converters, but these require external energy sources, and the converters have a multilayer structure that makes them opaque and hence challenging to integrate with a human eye. The authors previously were able to confer near-infrared vision to mice by injecting nanoparticles that bind to photoreceptors into their eyes—basically creating a near-infrared nanoantenna—but realized that most people would be averse to the prospect of sticking needles in their eyes. So they looked for a better alternative. Contact lenses seemed the obvious choice.

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