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Key concepts Physics Frequency Sound waves Pitch Introduction Did you know that not all animals use their ears to hear sounds? Snakes, for example, perceive sound waves through their jawbones! And many insects perceive sound waves through their antennae. Although these methods of detecting sound might be different, they all respond to the same thing that our ears do, which is sound waves in the environment. In this activity, you will generate some impressive sound waves from very simple materials and observe how these sound waves are generated....

Leading AIDS researcher Joep Lange of the University of Amsterdam’s Academic Medical Center and World Health Organization spokesman Glenn Thomas were among the victims of the Malaysia Airlines flight shot down over Ukraine on July 17. Some HIV health advocates were also reportedly among the dead who had been en route to the 20th International AIDS Conference in Australia. Obituaries and remembrances of these people are detailed below as a tribute to their work....

People in many cities risk their lives every time they cross the street. In New York City, pedestrian deaths accounted for the majority of yearly traffic fatalities continually since 2006, according to government data. For visually impaired people, the situation is uniquely dangerous and getting worse. Over the past summer designers at Touch Graphics, a company that makes navigation technology that incorporates information from several senses, have been working with New York’s Department of Transportation to test tactile maps—diagrams with three-dimensional features and braille text—at a busy intersection near a resource center for blind people....

Professors routinely give advice to students but usually while their charges are still in school. Arthur Landy, a distinguished professor of molecular and cell biology and biochemistry at Brown University, recently decided, however, that he had to remind a former premed student of his that “without evolution, modern biology, including medicine and biotechnology, wouldn’t make sense.” The sentiment was not original with Landy, of course. Thirty-six years ago geneticist Theodosius Dobzhansky, a major contributor to the foundations of modern evolutionary theory, famously told the readers of The American Biology Teacher that “nothing in biology makes sense, except in the light of evolution....

ILLUSIONS ARE ANOMALIES that can reveal clues about the mysterious workings of the brain to neuroscientists in much the same way as the fictional Sherlock Holmes can solve a crime puzzle by homing in on a single out-of-the-ordinary fact. Think of the phrase “the dog that did not bark” (in Sir Arthur Conan Doyle’s short story “Silver Blaze”) or of the missing dumbbell (in Conan Doyle’s novel Valley of Fear). Perhaps the most famous examples of such visual tricks are the geometric optical illusions....

New York State’s longest bridge is in dire straits. “At times, you can see the river through the cracks in the pavement,” President Barack Obama said at a press conference in front of the Tappan Zee Bridge in May 2014. “Now, I’m not an engineer, but I figure that’s not good.” It’s not. The three-mile-long Tappan Zee carries 138,000 vehicles a day over the Hudson River. It is also “functionally obsolete” and as such exemplifies America’s crumbling infrastructure: about one in 10 bridges in the country merits the disturbing designation of “structurally deficient,” according to a 2013 report by the U....

Tying knots in a piece of string is an age-old way of remembering things. Now physicists have succeeded in tying and untying microscopic magnetic vortices that may lead to more efficient computer memory. The twisted vortices, known as skyrmions, are arrangements of atoms, with each atom acting like a bar magnet owing to a quantum property of its electrons called spin. An external magnetic field would normally tend to align all the atomic bar magnets in the same direction, but in the case of a skyrmion, the magnetization of the atoms is arrayed in a twisted vortex....

By Valerie Volcovici NEW YORK (Reuters) - With crises from Islamic State to Ebola competing for attention, the United Nations on Tuesday will zero in on climate change, giving leaders from 125 countries a platform to explain how they plan to address the issue. A huge march to call for international action on climate change, which brought as many as 400,000 people to the streets of New York on Sunday, set the tone for the summit spearheaded by U....

Have you ever been gripped by the suspicion that nothing is real? A student at Stevens Institute of Technology, where I teach, has endured feelings of unreality since childhood. She recently made a film about this syndrome for her senior thesis, for which she interviewed herself and others, including me. “It feels like there’s a glass wall between me and everything else in the world,” Camille says in her film, which she calls Depersonalized; Derealized; Deconstructed Derealization and depersonalization refer to feelings that the external world and your own self, respectively, are unreal....

As part of a worldwide project to dramatically curtail the spread of AIDS, researchers have developed a vaginal gel designed to liquefy and release an antiviral drug when exposed to semen. Creators of the “molecular condom,” still in very early testing, say the temperature- and pH-sensitive polymer could prove a more efficient way to deliver an anti-HIV drug than normal gels and creams. “What we hope is that by attacking the virus in semen, we can inactivate it before it has any chance of permeating the tissue,” says bioengineer Patrick Kiser of the University of Utah....

When faced with a depressed patient, clinicians often have to choose a proper course of treatment based on a guess as to which neurotransmitter in the brain is being disrupted–serotonin, noradrenaline or both. According to Jan Melichar, a psychiatrist at the University of Bristol, doctors “get it right about 60 to 80 percent of the time,” but they have to wait up to one month to see if they chose correctly....

By most accounts, this holiday season has been a slow one for merchants due to the economic downturn (though you wouldn’t know it by the lines at the stores where I did my last-minute shopping). Still, this is the time of year when inventory turns over rapidly. For major retailers like Staples and Walgreens, efficiency is key to making sure the right products (read: those selling like hotcakes) get to stores as quickly as possible, while less popular items remain tucked in warehouses....

Why is there an ozone hole in the atmosphere when there is too much ozone at ground level? —H. Cox, San Antonio, Tex. Ross J. Salawitch, a senior research scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., explains: The abundance of atmospheric ozone (O3) is relative—levels that are dangerously high in the atmosphere’s lowest layer, the troposphere, would be dangerously low in the stratosphere, one layer above. As such, ground-level ozone is not plentiful enough to fill the so-called ozone hole....

By Alison Abbott The European Commission has selected six futuristic proposals to compete for two huge flagship projects that will apply information and communication technologies to social problems. The Future and Emerging Technologies (FET) Flagships aim to unite Europe’s scattered academic forces around well-defined missions that feed directly into the European Union’s social or political goals. “They are like ‘moon-landing’ projects,” says Henry Markram, a neuroscientist at the EPFL in Lausanne, Switzerland, and coordinator of one contender, the Human Brain Project, which aims to build a supercomputer simulation of the brain....

David Mohler, who leads the Department of Energy’s Office of Clean Coal and Carbon Management, declared yesterday that prospects for carbon capture technology are strong. Still reeling from the presidential election results last week, Mohler yesterday told a panel in Washington, D.C., that the technologies for capturing carbon dioxide emissions and locking them away have built up significant momentum that will continue, even in a Trump administration that places a low priority on tackling climate change....

Most of the 20 million people diagnosed with type 2 diabetes in the U.S. take metformin to help control their blood glucose. The drug is ultrasafe: millions of diabetics have taken it for decades with few side effects beyond gastrointestinal discomfort. And it is ultracheap: a month’s supply costs $4 at Walmart. And now new studies hint that metformin might help protect the brain from developing diseases of aging, even in nondiabetics....

Spacecraft made of carbon-foam bubbles could zoom from Earth to Alpha Centauri in 185 years, driven solely by the power of the sun, a new study finds. A swarm of these probes might help discover and study our solar system’s mysterious Planet Nine, if this hypothesized world exists, scientists added. Conventional rockets driven by chemical reactions are currently the leading form of space propulsion. However, they are not anywhere close to efficient enough to reach another star within a human lifetime....

“Orange juice, please” I said to my new friend after I told her my solution, “with a touch of vodka.” Solutions: Because of Ron, there is nobody who has shaken hands with 8 others. So, the numbers are: 0, 1, 2, 3, 4, 5, 6, 7, X, where X is the unknown number. Every time two people shake hands, we’ll say that each of the two has done a “half-shake.” Because each act of shaking hands increases the total count of all “half-shakes” by two and there is an even number of half-shakes without the X, X must be an even number....

Out on the fingerlike peninsula of southwestern Haiti is the remote forest realm of the La Hotte bush frog—or what is left of it. “It’s a very beautiful forest,” says Carlos Martinez Rivera, a conservation biologist at the Philadelphia Zoo. “It feels like going to any other tropical rain forest. But it’s a very tiny patch of forest.” In recent decades Haiti has desperately cut down trees to grow crops or make charcoal....

In the book of Genesis, all God had to do was say the word. In modern cosmology, the creation of light took rather more effort. The familiar qualities of light—an electromagnetic wave, a stream of particles called photons, a source of information about the world—emerged in stages over the first millennia of cosmic history. In the very earliest moments, electromagnetism did not operate as an independent force but was interwoven with the weak nuclear force that governs radioactive decay....