Biomedical Engineer, Medical Student, Lincoln Democrat
15476 stories

Microwave thruster makes for clean-burning jet

1 Comment

I usually approach papers on the subject of alternative thrusters with a certain degree of cynicism. But we've finally been given a study on microwave thrusters that doesn’t rely on impossible physics. Instead, it used a plain old plasma thruster.

Plasma thrusters have generally been thought of as a means of propulsion in space, but now one has been designed to operate under atmospheric conditions. According to the researchers involved, it's an air plasma thruster that has the potential to produce the same thrust as a commercial jet engine.

Combustible air?

A jet engine is just a form of internal combustion engine: combine fuel and air and compress the living hell out of the mixture. The resulting ignition rapidly heats the gas (most of which is nitrogen and doesn’t burn), forcing it to expand explosively. The rapid expansion can be used to power fans that generate thrust or used directly to provide thrust. But, the key point is that the gas needs to be rapidly heated to very high temperatures so that it can expand. The fuel of a jet engine is just the energy source for heat.

The age of steam relied on the same concept, as do modern steam turbines. Heat water to a very hot gas, then allow it to expand to do work. Again, the key is getting all that energy into the gas so that it can rapidly expand. A steam engine, though, is an external combustion engine, with the combustion heating the water before the water is sent into the place where it does work.

Now, a group of researchers has demonstrated a kind of external/internal plasma combustion engine. The essential idea is that air is ionized to a plasma, which is rapidly heated and allowed to expand to generate thrust.

To do this, the researchers used a magnetron to generate relatively high-powered microwaves (about 1kW). The microwaves travel down a waveguide (a rectangular metal tube) that gets progressively thinner and then expands again (see picture). A quartz tube is placed in a hole in the waveguide at the narrowest point. Air is forced through the quartz tube, passes through a small section of waveguide, and then exits the other end of the quartz tube.

At the entry to the tube, the air passes over electrodes that are subject to a very high field. This rips electrons off some of the atoms (mostly the nitrogen and oxygen), creating a low-temperature, low-pressure plasma. The air pressure from the blower at the entry of the tube pushes the plasma further up the tube so that it enters the waveguide.

In the waveguide, the charged particles in the plasma start to oscillate with the microwave field while rapidly heating. The ions, atoms, and electrons collide with each other frequently, spreading the energy from the ions and electrons to the neutral atoms, heating the plasma rapidly. As a result, the researchers claim that the plasma rapidly heats to well over 1,000°C.

The thrust of the measurement

The heated plasma creates a torch-like flame as the hot gas exits the waveguide, generating thrust. Measuring the gas pressure (thrust) turned out to be difficult. Most pressure sensors and barometers tend to complain when placed into something akin to a blowtorch.

So the researchers got inventive. They closed the quartz tube with a hollow sphere that had a small hole in it. If the plasma thrust was sufficiently high, it would cause the sphere to rattle around on top of the tube. By progressively adding mass to the sphere, it would eventually settle on the tube and stop rattling. The researchers estimated the total force from gas by balancing it with the force due to gravity. I’m pretty sure there are better ways to measure thrust (and still stay low-tech), but as long as the researchers were consistent, the systematic offset will be the same for all measurements.

In the end, the team was able to show that they get thrust of about 28N/kW, which seems to be quite close to that produced by a modern turbofan (by my rough calculations, a modern turbofan produces about 15N/kW). The thrust efficiency is corrected for the thrust simply due to the blower’s airflow as well.

The question is one of scaling. At the air flow rates (around 1m3/h) and microwave powers (less than 1kW) that the researchers tested, everything scaled very nicely. But the airflows are in the region of about 15,000 times lower than those for a full-sized engine. The thrust also has to scale by about four orders of magnitude (meaning the power does, too). Extrapolating linear trends over four orders of magnitude is a good way to be disappointed in life.

I also believe that the warning signs are already in the paper. If you look carefully, there are some missing data points. For instance, at the highest microwave power, only lower flow rates are tested, while for low microwave power, all flow rates are tested. That seems like an odd omission. I suspect the plasma is not stable at high flows and high powers.

If you're thinking this work might help save engine weight, I wouldn't be so sure. If the plasma thruster becomes part of a turbofan engine, I suspect it will be heavier. In a non-bypass configuration, it might be lighter. Still, this is very cool work, and I hope it works out.

AIP Advances, 2020, DOI: 10.1063/5.0005814 (About DOIs)

Read the whole story
92 days ago
Really cool. How fast can these be started and stopped though?
New York, NY
Share this story

Irrfan Khan: Mira Nair Remembers Her ‘Namesake’ Star

1 Comment and 2 Shares

The filmmaker Mira Nair first tried to get Irrfan Khan to appear in one of her movies when he was a drama student in Delhi. And while the substantial part she offered him in “Salaam Bombay!” (1988) ended up being downsized, she promised him the lead in a feature film — one day. Nearly 20 years later, she kept her word, casting him as Ashoke Ganguli, the patriarch of an immigrant Bengali family in “The Namesake,” based on Jhumpa Lahiri’s novel. She gave him, she said, his “first gateway to the world.”

In a telephone call, Nair, in New York, spoke about her work and friendship with Khan, who died on Wednesday at 53. These are edited excerpts from the conversation.

In my first film, “Salaam Bombay!,” I went to work with street children but also wanted to look at young actors to see if it would be possible or even desirable to mix them. And that led me to the fountain of serious drama in India, the National School of Drama. It was 1986, I think, and I was taken by a teacher to the basement, where they were doing a Beckett workshop. And I noticed Irrfan.

He’s so tall and gangly and angular — like a praying mantis. And of course, he had this extraordinary face. He was only 18, but he still had a craggy face and those hooded eyes. The interesting thing was that he was very keenly focused. He was acutely observant and very open, not filled with any kind of big attitude.

I asked him to leave school and to be with me for five, six months on this sort of adventure. And he said yes. I rented an empty flat in Bombay, where we lived two or three months — he, me, another cinematographer and many street kids, whoever couldn’t find a home for the night.

And he was totally committed to be Salim, this leader of the street gang. But as [the workshop] progressed and we worked with real kids, I discovered — and he discovered, poor man — that at 6 feet 3 or whatever, he was double the length of any malnourished street child. The kids came up to his waist. It was not possible for him to be physically part of this group.

It was a terribly hard thing to tell this wonderful actor that I couldn’t cast him, but he understood that. The only thing that he could do was this one-day scene of the scribe who rips off the street child and doesn’t send the letter home to his mother. That was his first role in cinema, but we stayed close friends.

He had several years of abject struggles after that. But somehow with Irrfan, I always felt that he never gave it away easily, that he never took the easiest buck. I think he knew, without ego, that he had something very special in him and he wasn’t going to fritter it away.

[After that] anything I could ever summon for him, I would. But it’s just that I made other kinds of films. It took years before my heart landed in Jhumpa’s “The Namesake.” [Lahiri, too, had a role in the film.] I had no idea when we brought him out here to play Ashoke Ganguli that it was Irrfan’s first time in America. And he looked at things with the eyes of not just an excited young man seeing this other world, but also with the eyes of the character who had to play it.

The first afternoon, when he and the Indian star Tabu landed in New York, I took them to Jhumpa’s Brooklyn apartment and introduced them to Jhumpa’s parents, who were visiting from Rhode Island. I told him to pattern Ashoke on Jhumpa’s father, a librarian. And it was really beautiful because Irrfan is not Bengali, but he looks Bengali and he’s such an extraordinary actor that he can internalize all those things that make somebody as particular as they are.

He started fashioning his accent on a mix of Jhumpa’s father and the Bengali caterer in our production — to the extent that his accent became so thick that I could hardly understand him. We didn’t have dialect coaches. He did it himself. It was this wonderful fine tuning between the caterer and the librarian, and I used to say to him, “A little less on the librarian and a little higher on the caterer.”

But it was like that with him. There was the beautiful scene in “The Namesake” in the car, where he is telling his son for the first time about how he almost died in that train accident. And the son says, “So is that what you think of when you think of me?” And his response is, “When I see you, I think every day is a gift.” And on the second take, he said to me, “Tujhe kuch aur chahiye, na?” — “You want something.” And I said: “Yeah, I want a tear to glass your eyes. I don’t want it to fall down.” In fact, I’d say something funny like, “If the bloody tear falls down your cheek, I will give you a slap.” That’s how we used to talk, nothing precious — a joke, as if we were car mechanics and I was telling him to shift into third gear.

[For Americans] he’s in the realm of Jean-Paul Belmondo or Marcello Mastroianni or Omar Sharif, even — clearly from some other culture but having great appeal to be seen as anything from an Everyman type to a very quiet and intelligent sort of sex appeal.

He was remarkably philosophical when I saw him last, which was more than a year ago in London. He was undergoing treatment, and I thought that I’d be holding his hand at his bedside. But forget it. We ate very well in a cafe. He flirted with the waitress. My friend came in on a bike and he got on the bike and he said: “I just need to. I need to do one block. Just one.”

We had our last pictures together on this bike, and he was in full-blown treatment and yet he was in dapper linen. We have a beautiful word in Urdu — “shaukeen” — which means somebody with a lot of love and indulgences and delights. He loved a lot of things, whether it be clothes or food or beauty. Or his family and how much they meant to him. He had just a clear idea of what was worth it. He’d roamed and he returned to know what was really valuable.

Read the whole story
96 days ago
He was so good in The Namesake.
New York, NY
Share this story

Single-chip lidar routing is in our tiny future

1 Comment

Sometimes you can't seem to go a week without hearing new lidar news. This is disconcerting, as lidar was the desperation application for lasers for a very long time. If you had made a new pulsed laser and couldn't think what it might be good for, you figured out something that needed a measurement at distance and claimed your laser was useful for that application. At best, you'd give the laser to an atmospheric scientist and get them to measure the density of aerosols in the upper atmosphere.

OK, maybe that's a bit cynical, but for a very long time, lidar research was an unvisited backwater port on the sea of laser physics. But new research demonstrates how much this has changed: a new device that has wide applications and will probably make a huge impact in optical communications. Yet the device is being sold as great for lidar, which it may well be.

Lidar is hard

It wasn't that lidar was unattractive to engineers in the past. It's more that lidar was unwieldy. Lasers were big, the pulse durations were too long, the collection optics to get the signals were large, the electronics were simple... but big. Lidar instruments were delicate. The idea of putting an expensive and breakable device in the grille of a nitrous-injected Honda Civic, driven by a hormonal boy racer, probably didn't thrill many engineers.

Then powerful lasers got smaller, cheaper, and less delicate. The electronics required for optical communications could be readily adapted to lidar. Suddenly, lidar started to look good.

For lidar to work effectively, you need to efficiently combine a laser beam that's reflected off an object with a reference beam. The internal routing and external optics form one system, and misalignment between the transmitting and receiving beam result in a directional miscalculation. The easiest solution is to use the same optics to send and receive signals. But this is expensive, requiring high-speed micro-mechanical or electro-optic devices. Much better to have some passive optical circuit that simply reroutes light depending on its function. To do that, we need a non-reciprocal optical device.

A typical non-reciprocal device is called a circulator (see sidebar). These are bulky devices that usually involve passing the light through a relatively strong magnetic field and a special material that is almost certainly looked upon darkly by engineers in charge of fabrication machines. In a circulator, light that enters port 1 will exit at port 2, while light that enters port 2 will exit port 3, and light that enters port 3 will exit port 1 (assuming only three ports).

However, for lidar, what you might want is more complicated. A high-power light pulse needs to go from port 1 to port 2, where it exits to the outside world. The signal that comes back enters port 2 and exits port 3. A weaker reference signal enters port 1 and exits port 3 to mix with the return signal. Under these conditions, the outgoing laser pulse and reflected laser pulse are automatically aligned to each other. The reference and the received pulses are also automatically aligned.

Making silicon refuse to reciprocate

Creating this sort of device is exactly what the researchers have achieved, though in rather artificial circumstances. But they have done it using standard silicon integrated optical fabrication techniques, which means that if it works as expected as a unit, it can be manufactured very cheaply.

The researchers relied on silicon's nonlinearity to ensure that the device's behavior would change depending on the brightness of the light in the device. Essentially, if light is bright enough, it can change the properties of the material it is traveling though (this is what happens when you set termites on fire with a magnifying glass). However, in the tiny gap between a material not being changed by light and it catching fire, the change can be useful. Optical engineers spend a lot of time throwing themselves and their expensive kit at this gap with only the occasional survivor emerging without their hair on fire.

The device is basically a pair of waveguides that form four ports, with only three in use. Ports 1 and 2 are directly connected, while port 3 is in a separate waveguide. The researchers created an oval racetrack resonator between the two straight waveguides. In addition, a small defect is placed in the wave guide between ports one and two. This defect acts as a mirror at low-light intensities. However, if the intensity is high enough, the optical properties of the defect are modified, and it allows the light pulse to be transmitted.

Light traffic ahead

A strong light pulse is sent into port 1, where a small portion is transferred to the ring via a process called evanescent coupling. The light in the ring loops around, transfers to the next wave guide, and exits port 3. The light from port 1 that exits port 3 is the reference pulse. But most of the strong light pulse continues on outside the ring, encounters the defect, and modifies it, which stops it from reflecting the pulse. Hence, the remainder of the pulse is transmitted out port 2 and on to the outside world.

However, light that enters from port 2 (light that the lidar would have received from the outside world) is traveling in the opposite direction. The light from port 2 still enters the racetrack but cannot exit at port 3 because it is traveling in the wrong direction. Under ordinary circumstances, it would exit from port 4. This is where the defect plays its role. But when the light intensity is low, the defect is still reflective. It reflects the pulse back in the direction it came from. On the way back, light is coupled into the ring and can exit from port 3, just like the reference signal from port 1.

Note, though, that the transfer of light between the waveguide and ring is reciprocal, which means that about half the light entering from port 2 must exit port 4, and half exits port 3. This sounds bad but actually isn't. These types of devices often have high losses no matter how they are constructed, so I don't see 50 percent loss as a huge issue. Indeed, considering that car lidar operates in the 100m range, where signals are relatively strong, it's probably possible to cope with the additional losses.

The researchers did not demonstrate this with an actual lidar unit. Instead, all the light pulses traveled through optical fiber with varying lengths of delay. The signals they ended up with seem rather strong for a lidar return signal. Nevertheless, this is all made with standard processes, so connecting it up to a real-world system will not be a difficult task.

Nature Photonics, 2020, DOI: 10.1038/s41566-020-0606-0 (About DOIs)

Read the whole story
97 days ago
"Essentially, if light is bright enough, it can change the properties of the material it is traveling though (this is what happens when you set termites on fire with a magnifying glass)."

I laughed.
New York, NY
Share this story

EPA says incidental benefits of pollution rules don’t count


In a move that it had been planning since at least last year, the EPA affirmed the existing rules that limit mercury emissions produced by power plants. But the current EPA is not interested in wasting an opportunity to weaken regulations, so it is also undercutting the economic reasoning that was initially used to justify the regulations. This mixed decision may leave the existing regulations at risk in court, and it will definitely make future regulations more difficult.

Some chemical forms of mercury are potent neurotoxins and are a clear public health risk. Power plants are a major source of emissions in the US, so they potentially fall under the remit of the Clean Air Act. Attempts to regulate mercury emissions date back to the Clinton administration, were dropped under Bush and restored by Obama. A few lawsuits added further complications over the course of this history, but a key one was decided by the Supreme Court, which ruled that the Obama administration had erred by not performing an economic analysis before formulating emissions rules.

The Obama-era EPA went back and redid the rulemaking process, and the result was one of the more costly set of rules in US history. Those costs, however, paled in comparison to the benefits that would come through reduced medical costs and improved public health. Most of those benefits, however, didn't come from the reduced mercury itself. Instead, the process of removing mercury from exhaust streams would also eliminate a lot of particulate emissions, and their absence drove many of the health benefits.

The rules were put in place during the Obama administration, which was promptly sued. The case was still in the courts when Trump took office, and his EPA asked to withdraw from the case so it could formulate new rules. Meanwhile, with the old rules still in effect, utilities did what was needed in order to comply with them, in many cases passing that cost on to consumers. As a result, many utilities publicly voiced opposition to any attempts to roll back emissions limits. The coal industry, the source of most of the mercury, argued in favor of a rollback.

The new rules, announced yesterday, keep existing emissions limits in place. But how it justifies doing so is likely to generate some controversy.

In both the EPA's original and current estimate, the benefits of reducing mercury are relatively minor—the current estimate places those benefits at about $5 million a year. But the process of removing the mercury from the exhaust stream of a power plant also eliminates many other emissions, most notably particulates. The societal costs of particulates are substantial (although the EPA isn't entirely convinced of that), so the mercury controls would come with what are called co-benefits. In this case, the co-benefits are substantially larger than the direct benefits, with estimates reaching well over $10 billion annually. This is substantially more than the cost of the pollution controls.

While Clean Air Act regulations do not require that the financial benefits outweigh the costs, having the cost-benefit analysis indicate that they do generally leaves a rule less vulnerable to lawsuits.

The new EPA decision, however, indicates that it has determined that regulatory decisions should not consider co-benefits—at all, for this or any future rules. Only the direct benefits can be considered in performing a cost-benefit analysis.

It's possible that this decision will leave the existing regulations subject to a lawsuit, as the coal industry would undoubtedly be interested in seeing them overturned. If the regulations are overturned, then it will leave utilities with a lot of unneeded equipment that, in many cases, has already had its costs passed on to consumers. It will certainly leave future tightening of these regulations in doubt, even if further studies identify additional issues associated with mercury.

But the EPA's action raises questions about the prospects for regulating any pollutant successfully. In many cases, like the emission of chemicals that produce acid rain, pollution controls are designed to handle multiple issues simultaneously. By forcing regulatory actions to consider each separately, the decision more or less guarantees that the economies generated by hardware that provides multiple benefits will never enter into the decisionmaking process. Thus, nearly every economic case for regulation will end up looking worse.

Again, the EPA can choose to act even if the economics of regulation aren't in its favor. But doing so will likely lead to the regulations being tied up in court, much as the mercury ones have.

Read the whole story
107 days ago
This shitshow of an administration.
New York, NY
109 days ago
The “No polluter left behind” policy will be Trump’s enduring legacy
Washington, DC
Share this story

ICANN delays .org sale again after scathing letter from California AG

3 Comments and 4 Shares

ICANN, the nonprofit that oversees the Internet's domain name system, has given itself another two weeks to decide whether to allow control of the .org domain to be sold to private equity firm Ethos Capital. The decision comes after ICANN received a blizzard of letters from people opposed to the transaction, including California Attorney General Xavier Becerra.

Becerra's letter was significant because ICANN is incorporated in California. That means it's Becerra's job to make sure that ICANN is living up to the commitments in its articles of incorporation, which promise that ICANN will operate "for the benefit of the Internet community as a whole."

Becerra questioned whether ICANN was really doing that. "There is mounting concern that ICAN is no longer responsive to the needs of its stakeholders," he wrote.

A secretive buyer and a lot of debt

California's attorney general pointed to several specific concerns about the transaction. One was the shadowy nature of the proposed buyer, Ethos Capital. "Little is known about Ethos Capital and its multiple proposed subsidiaries," Becerra writes. Ethos Capital, he said, has "refused to produce responses to many critical questions posted by the public and Internet community."

Ethos Capital's plan is to buy the Public Interest Registry (PIR) from its current parent organization, the nonprofit Internet Society. To help finance the sale, Ethos will saddle PIR with $300 million in debt—a common tactic in the world of leveraged buyouts. Becerra warns that this tactic could endanger the financial viability of the PIR—especially in light of economic uncertainty created by the coronavirus.

"If the sale goes through and PIR's business model fails to meet expectations, it may have to make significant cuts in operations," Becerra warns. "Such cuts would undoubtedly affect the stability of the .org registry."

Becerra also blasts the Internet Society for considering the sale in the first place. "ISOC purports to support the Internet, yet its actions, from the secretive nature of the transaction, to actively seeking to transfer the .org registry to an unknown entity, are contrary to its mission and potentially disruptive to the same system it claims to champion and support," he writes.

Becerra ends his letter with a warning: "This office will continue to evaluate this matter, and will take whatever action necessary to protect Californians and the nonprofit community."

“Totally inappropriate”

Becerra is far from the only critic of the .org deal. On Monday, ICANN's first CEO, Michael Roberts, and original board chair Esther Dyson penned a letter blasting the transaction and their successors at ICANN.

"We write to express our deep dismay at ICANN's rejection of its defining public-interest regulatory purpose as demonstrated in the totally inappropriate proposed sale of the .org delegation," they wrote. "ICANN has not meaningfully acted to address the likely proposed service cuts, increase in prices or trafficking of data of non-profits to obtain additional revenue."

They called for a six-month delay of the transaction to give ICANN and elected officials more time to scrutinize it.

ICANN is an unusual organization. It nominally represents the Internet community, but its governance structure doesn't give ordinary Internet users much direct influence. In the past, ICANN has been overseen by the US Department of Commerce, but the US government has been gradually relaxing its oversight of the organization in recent years.

At the same time, US policymakers have resisted efforts to bring Internet governance under the control of international bodies such as the International Telecommunications Union. They feared that this would give too much influence to autocratic regimes such as China and Russia. As a result, ICANN is effectively accountable to no one, even as it controls a resource—the Internet's domain name system—that's worth billions of dollars.

That creates an obvious temptation for ICANN insiders. As the Register has documented, several of the people involved in the Ethos Capital transaction are former ICANN officials. That might be one reason why the deal is getting a sympathetic hearing from ICANN even as it's been strongly opposed by many independent voices.

Read the whole story
110 days ago
Good, hopefully this will be the beginning of the end
Washington, DC
110 days ago
A complete shitshow.
New York, NY
110 days ago
107 days ago
New York City
Share this story
1 public comment
109 days ago
Oh sweet load PIR up with $300mil in debt service payments worked great for toys r us
Bend, Oregon

Hollow corkscrews may put a cork in noisy ventilation

1 Comment

And now for a bit of research that is suddenly highly relevant in today’s locked-up and closed-in world: noise reduction. Does air-conditioning drive you mad? The constant hiss of sterile air?

The average building designer doesn’t seem to give a damn about it. As long as water doesn’t drip out of the vents and the dust is kinda-sorta-filtered out… well, you’ve got headphones don’t you?

Don’t stop the hiss

It is actually surprisingly difficult to get rid of ventilation noises. Fans and airflow are noisy, and the very ducting that allows the air to flow into your office space also allows the sound in. Therefore, the easiest way to get rid of ventilation noises is to just close the air duct. More realistically, you need a baffle that damps the sound waves over a wide range of frequencies but doesn’t restrict air flow.

Baffles work in two ways: first the sound waves impinge upon the solid structure and are scattered and absorbed by the solid. This reduces the transmission of sound. But the second aspect is that the airflow is split and recombined. The sound waves follow both paths, but those paths are different lengths. The wave gets split into two and recombined. As a result, the phase of the two waves is different, which can result in destructive interference, which reduces the sound volume. But for any particular path, the phase difference will only be destructive for a few frequencies.

That's the problem. The hiss of air-conditioning covers a wide range of frequencies, yet the interference effect only blocks a few frequencies.

Interfering with my hiss

This is where metamaterials and metasurfaces can play a role. Metamaterials and metasurfaces reverse the problem. Rather than starting with a material and figuring out what you can do with it, metamaterials allow researchers to start with a mathematical formulation of the engineering goal. That gets translated into a virtual material that has the right acoustic properties. Finally, the virtual material is deconstructed into real materials that consist of elements that are all smaller than the sound waves of interest.

This process also involves a bit of intuition, since the design process from a virtual material to real material elements requires a lot of insight—it's not a process we've automated.

The researchers recognized that a spiraled, horn-like structure produces a broadband acoustic structure that provides a kind of consistent phase delay, independent of wavelength. With the right number of spirals, the phase delay could be made just right for destructive interference. This is achieved by hollowing out the center of the spiral, so half the sound wave goes through the spiral and half goes though a central tube. By calculating the performance, the researchers were able to optimize the number of spirals, the aspect ratio, and the pitch to get noise suppression over a wide frequency range.

You can’t hear it, but it’s got a beat

Of course, wavelength independence does not go on forever. In the researcher’s design, the predicted transmission loss is maximized between 800 and 1500Hz, though the actual frequency range can be adjusted by changing the pitch(es) of the spiral horn.

The researchers' calculations showed that they should get about 20dB of noise suppression (about 100 times less noise power), which is pretty good. Amazingly enough, their experiments on a single spiral in a duct showed similar performance.

Will this research turn up in buildings? I think it will, but it will take some time to work out the details. For instance, I’m not sure that the bandwidth is broad enough yet, and it has a couple of very sharp peaks (exceptionally high transmission loss). Those gaps may well be perceived as sharp tones due to the interference of the sound waves with each other on either side of the gap (the beating sound you hear when two piano strings are detuned is an example of this).

Nevertheless, I think the problems can be hammered out, and new baffles will make their way into our buildings to (quiet) applause.

Physical Review Applied, 2020, DOI: 10.1103/PhysRevApplied.13.044028 (About DOIs)

Read the whole story
113 days ago
This would be brilliant for limiting the noise coming out of a fan into a PAPR. It's really hard to hear anything when you have some versions of those on.
New York, NY
Share this story
Next Page of Stories