Ships have been damaging the oceans with noise for centuries. Germany is working on silent propellers to solve it

Every time a boat crosses the seas, it is accompanied by a continuous noise underwater: that of the propellers that propel it. The noise problem of propellers in marine ecosystems is identified academically since 2004, but its reason for being is even older: the first time they analyzed its cause It was in 1893. What there is no solution to that disturbing low-frequency sound that spreads for kilometers, disturbing fish, cetaceans and other marine living beings. And its reason for being is even older: the first time cavitation was analyzed was in 1893. A team from the Kiel University of Applied Sciences has set out to remedy it with its project MinKav. Brief notes on cavitation. To understand the problem, we must first see what happens to the blades of a propeller when they rotate at high speed. With their movement, the blades generate a pressure difference between their faces. Thus, on the back side the pressure drops so much that the water changes state, going from liquid to gas. More specifically, thousands of small vapor bubbles. The problem is when these bubbles leave that low pressure zone: they then implode violently, returning to the liquid state, which causes pressure waves that are transmitted at high speed through the water. If the waves collide with a surface, they can deteriorate it considerably. The phenomenon of cavitation is accompanied by vibration and noise, as if it were gravel falling on a machine. This sound is broadband, with low frequency components capable of traveling long distances. Why is it important. Of all possible aquatic pollution, human-caused acoustics are the least mainstream, but their effects are documented. A couple of concrete examples of the importance of sound for aquatic species: whales They use sound to communicate, orient themselves and huntthe fish for such essential tasks how to detect predators or spawning and crustaceans are sensitive to vibration in the background. To get an idea of ​​the magnitude of the problem, according to the International Chamber of Navigation There are approximately 50,000 merchant ships operating continuously around the planet and they all emit that sound. It is not something specific. And the research team adds a twist: a propeller with less cavitation is not only less noisy, it can also potentially be more efficient (cavitation is wasted mechanical energy). Less noise and fewer emissions. The discovery. The HAW Kiel team has identified when the problem originates: the sound peak does not occur when the bubble forms, but right at the end of the collapse. And its intensity depends directly on the speed at which this collapse occurs. The faster you go, the stronger the blow. Illustration of human, marine animal and environmental sound sources in the marine environment, with proportional sound waves. National Office of Oceanic and Atmospheric Administration How are they doing it. The experiments are being carried out at the Naval Hydrodynamics Laboratory of the German university, in a kind of aquarium with a miniature propeller, so that they can reproduce the flow conditions around the propeller. Equipped with underwater microphones and high-speed cameras, they have determined where and when that noise peak occurs. The next step is computer simulations to experiment with designing different propeller geometries to reduce noise without sacrificing performance, efficiency or durability. The most obvious solution, lowering the rpm, is not an option: a commercial boat cannot afford to go slower. Pending subjects. However, MinKav started in January of this year, will last three years and have a budget of 390,000 euros, modest for a problem of global scale. Even if MinKav were to come to fruition, it would have to go from the laboratory to scale-up on a commercial ship. In Xataka | A Spaniard has patented a mast that transforms wind and waves into electricity: his invention challenges diesel in boats In Xataka | A “roomba” to clean rivers: the ship that the Three Gorges Dam has launched in China Cover | Pexels

“The tan is nothing more than a defensive response of the body, it is its way of saying ‘I am damaging'”

Every summer the same ritual is repeated: full beaches, sun bodies and solar creams forgotten at the bottom of the bag. In search of a fast tan, many people deliberately renounce sun protection, convinced that this golden tone is reached better without barriers. What seems an aesthetic or harmless decision, can have consequences that are only revealed over time. No to the cream. It is enough to open social networks to find videos that promote Do not use solar creams. From self -domening “experts” until anonymous users They share their “tricks” to get bruise faster, often omitting completely the use of sunscreens. False myth. This practice connects with a belief still entrenched: the idea that sunscreen prevents tanning or that “natural brunette” is a sign of health and beauty. Thus, aesthetic desire continues to be imposed on prevention, and the risk goes unnoticed. Dr. José María Ricart, dermatologist and medical director of the Ricart Medical Institute (IMR), explains to Xataka: “Many people still believe in the idea of ​​’healthy tan’, when it really is a sign of skin damage.” The data does not lie. The study all who has had PMFarma accessdriven by Laboratories Pierre Fabre, has revealed a worrying reality: 67% of Spaniards only use sunscreen to avoid burns, and not as a daily health habit. The report, which includes data from more than 50,000 people (4,000 in Spain), has shown that only 39.7% reaplies the photoprotector every two hours in the sunny days. The reasons for this misuse are since they forget (32%) to basic ignorance (11%) or, more worrying, they do not believe in their efficacy (10%). For its part, the SAFE study, to which the Spanish Institute of Health Trainers has had access, has contributed Another interesting fact and is that 79% of adults and 74% of Spanish children are exposed to the sun in maximum radiation hours, between 11:00 and 17:00. The problem beyond the skin. Taking the sun without protection is not a simple carelessness, it is a practice that accelerates skin aging and raises the risk of skin cancer. As Dr. Ricart explains, it is important to know the two types of ultraviolet radiation that can affect us. On the one hand, UVB rays, more powerful in summer, are those that cause solar burns and damage cell DNA. On the other hand, UVA rays, present all year, even on cloudy days, penetrate more deeply and are responsible for premature aging. “The tan is nothing more than a defensive response of the body. It is its way of saying: ‘I am damaging.’ If someone still doubts it, that compares the skin of the face with that of the buttock, an area never exposed to the sun: without spots, without wrinkles, without photonexing,” he emphasizes. Take it to the extreme. Oh, who is looking for unconventional shortcuts to achieve that long -awaited golden tone. One of the most curious examples is the old myth that Eating carrots intensifies tan. While beta-carotene present in these vegetables can give the skin an orange nuance, this effect does not replace or protect against sun damage. In fact, some experts have warned that it is a superficial coloration, not a true tan, and that bringing this practice to the extreme – such as consuming large amounts of carrot daily – can end in carotenodermia: an orange pigmentation that has little to do with summer aesthetics. Frequent errors. Even those who believe they make failures that drastically reduce the effectiveness of sunscreen. Among the most common mistakes, Dr. Ricart highlights the fact of not applying it daily, not doing so in advance (20 or 30 minutes before leaving), reapplying it after a bath or every two hour, using small quantity and reusing expired creams or the previous summer. Prevention with technology. To raise awareness about these risks, technology has been put at the service of prevention. An example is Mysun Experiencea digital tool developed by Eau Thermale Avène and the artificial intelligence company Data Ora. This simulator allows the user to see how their skin will age in the next 15 years according to their sun protection habits. Another model is possible. The aesthetic pressure of the tan still weighs. Golden bodies continue to dominate ads, social networks and beauty referents. But the medical message is clear: each without protection exposure is a cumulative aggression for the skin. And that damage, sooner or later, shows. Image | Pexels Xataka | That the AEMPS retires six solar creams is good news. That he had to ask for the OCU is worrying

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