Redirected Walking In VR Done Via Exploit Of Eyeballs

April 11, 2018 by Donald Papp 55 Comments

[Anjul Patney] and [Qi Sun] demonstrated a fascinating new technique at NVIDIA’s GPU Technology Conference (GTC) for tricking a human into thinking a VR space is larger than it actually is. The way it works is this: when a person walks around in VR, they invariably make turns. During these turns, it’s possible to fool the person into thinking they have pivoted more or less than they have actually physically turned. With a way to manipulate perception of turns comes a way for software to gently manipulate a person’s perception of how large a virtual space is. Unlike other methods that rely on visual distortions, this method is undetectable by the viewer.

The software essentially exploits a quirk of how our eyes work. When a human’s eyes move around to look at different things, the eyeballs don’t physically glide smoothly from point to point. The eyes make frequent but unpredictable darting movements called saccades. There are a number of deeply interesting things about saccades, but the important one here is the fact that our eyes essentially go offline during saccadic movement. Our vision is perceived as a smooth and unbroken stream, but that’s a result of the brain stitching visual information into a cohesive whole, and filling in blanks without us being aware of it.

Part one of [Anjul] and [Qi]’s method is to manipulate perception of a virtual area relative to actual physical area by making a person’s pivots not a 1:1 match. In VR, it may appear one has turned more or less than one has in the real world, and in this way the software can guide the physical motion while making it appear in VR as though nothing is amiss. But by itself, this isn’t enough. To make the mismatches imperceptible, the system watches the eye for saccades and times its adjustments to occur only while they are underway. The brain ignores what happens during saccadic movement, stitches together the rest, and there you have it: a method to gently steer a human being in a way that a virtual space is larger than the physical area available.

Embedded below is a video demonstration and overview, which mentions other methods of manipulating perception of space in VR and how it avoids the pitfalls of other methods.

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Incandescent Luminescence Of Semiconductor Junctions Characterised In The Lab

April 1, 2018 by Jenny List 26 Comments

The semiconductor devices were put to the test under different atmospheres in this chamber.

One of the humbling things about writing for Hackaday comes when we encounter our readership and learn the breadth of our community and the huge variety of skills and professions you represent. Among your number are a significant representation among scientists, and as a result we often receive fascinating previews of and insights into their work. Sometimes they deserve a little bit more attention than one of our normal short daily pieces, and such a moment has come our way this week.

We’ve been fortunate enough to have an early look at a paper which makes detailed observations of a hitherto barely characterised property of semiconductor junctions that might have some interest for Hackaday readers in their work. In their paper, [Mellie], [Bacon] et al at Fulchester University in northeast England take a look at incandescent luminescence, a fleeting and curious effect exhibited by all semiconductor junctions in which they emit short-duration high-intensity infra-red and visible light with an extremely fast rise time when presented with high levels of current. This is a property which has been rarely exploited in commercial devices due to the large current densities required to reproduce it.

Incandescent Luminescence Explained

If you’ve never heard of incandescent luminescence before then you’re in good company, for neither had we until it was explained to us. It appears that there are a set of higher energy state conductivity bands in a semiconductor junction that can only be reached once the current passing through it breaches a threshold governed by the available quantum plasma dipole moment of the semiconductor material in question. At this point the junction assumes a plasma condition resulting in the abrupt emission of infra-red and visible radiation, the incandescent luminescence phase has been triggered.

A near-infra-red spectrum of incandescent luminescence in a halogen-doped silicon semiconductor junction. — A near-infra-red spectrum of incandescent luminescence in a silicon semiconductor junction.

Though it has been known to science since first being observed in the early 20th century by the earliest experimenters in the field of semiconductor junctions, the transitory nature of the phenomenon has traditionally been a barrier to its proper examination. The British team took a selection of commercial semiconductor devices very similar to the types that might be used by Hackaday readers, placed them in a chamber, and used an array of photoelectric sensors coupled with ionising detectors using americium-241 alpha radiation sources to measure their emissions.

The resulting data was then harvested for processing through a stack of custom high-speed ADC cards. Current densities from as low as a few milliamps to hundreds of amps were tested across forward-biased PN diode junctions using a computer-controlled DC power supply, resulting in a variety of spectra and showing the resulting thermionic photon emission at higher currents to have a preponderance in the infra-red region.

Incandescent luminescence in action, through an infra-red pyrometer.

A series of experiments were conducted to investigate a related effect first described by those early scientists in the field: that the atmosphere in which the semiconductor junction sits has a significant effect on the way it exhibits incandescent luminescence. Bathing it in gaseous CO₂ or nitrogen was found to reduce the phenomenon by as much as 95%, while immersing it in liquid nitrogen resulted in it becoming completely unobservable. Oxygen-rich atmospheres by comparison served to enhance the luminescence observed, to the point that in one of pure oxygen it reached an efficiency level of 100%.

The high conversion efficiencies and rapid onset of incandescent luminescence once it has been triggered compares favourably to those of existing devices such as LEDs or wire-wound resistors used where either infra-red or visible light is required. The researchers expect the effect to be exploited in such product families as photographic flash generators, electronic igniters, and other short-duration high-intensity applications. Given their obvious advantages, we’d expect their effects on those particular markets to be nothing short of incendiary.

Thanks Ellie D. Martin-Eberhardt for some invaluable inspiration and technical help with covering this story.

Near-IR spectrum: Deglr6328 [CC-BY-SA-3.0].

Test chamber: David Monniaux [CC-BY-SA-3.0].

Infra-red image: National Institute of Standards and Technology [Public domain].

Quantum Electric Material Borrows From Japanese Basketweaving

March 25, 2018 by Al Williams 13 Comments

Kagome is a pattern used to weave baskets from bamboo strips. The pattern is a symmetrical pattern of interlaced triangles that share corners. Scientists from MIT, Harvard, and Lawrence Berkeley National Laboratory have produced a kagome metal and found that it has exotic quantum properties.

Their paper, published in Nature (paywall), reports that the crystal made from layers of iron and tin atoms, causes electrons to flow in strange ways. The electrons bend into tight circular paths and flow along the edges without losing energy.

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Low-cost Drift Buoy Plies The Atlantic For Nearly A Year

April 28, 2017 by Dan Maloney 34 Comments

Put a message in a bottle and toss it in the ocean, and if you’re very lucky, years later you might get a response. Drop a floating Arduino-fied buoy into the ocean and if you’ve engineered it well, it may send data back to you for even longer.

At least that’s what [Wayne] has learned since his MDBuoyProject went live with the launching of a DIY drift buoy last year. The BOM for the buoy reads like a page from the Adafruit website: Arduino Trinket, an RTC, GPS module, Iridium satellite modem, sensors, and a solar panel. Everything lives in a clear plastic dry box along with a can of desiccant and a LiPo battery.

The solar panel has a view through the case lid, and the buoy is kept upright by a long PVC boom on the bottom of the case. Two versions have been built and launched so far; alas, the Pacific buoy was lost shortly after it was launched. But the Atlantic buoy picked up the Gulf Stream and has been drifting slowly toward Europe since last summer, sending back telemetry. A future version aims to incorporate an Automatic Identification System (AIS) receiver, presumably to report the signals of AIS transponders on nearby ships as they pass.

We like the attention to detail as well as the low cost of this build. It’s a project that’s well within reach of a STEM program, akin to the many high-altitude DIY balloon projects we’ve featured before.

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Thermoelectric Dry Ice Generator Does Not Work (Yet)

September 19, 2016 by Moritz Walter 83 Comments

[Pabr] is trying to make dry ice the hard way by building a thermoelectric dry ice generator. The project is a well planned round trip through thermodynamics and cryogenics with a hard landing on the icy grounds of trial and error.

[Pabr’s] four stage Peltier element on a heatsink.

While dry ice can be obtained with simpler methods, for example by venting gaseous CO2 from fire extinguishers and collecting the forming CO2 flakes, [pabr’s] method is indeed attractive as a more compact solid-state solution. The setup employs a four stage Peltier element, which uses four Peltier stages to achieve a high temperature differential.

With sufficient cooling on the high-temperature side of the element, it should be well capable of achieving temperatures below -78.5 °C, the sublimation temperature of CO2. So far, [pabr] has built three different setups to expose small amounts of CO2 to the cold of the Peltier element, hoping to observe the formation of little dry ice flakes.

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The Infinite Monkey Cage And General Relativity

January 31, 2016 by Al Williams 17 Comments

If you are British, you probably already know where this is going. For the rest of you, it might help to know that The Infinite Monkey Cage is an odd little show on BBC Radio 4 (and they’ve been on tour, too). It is the show that asks a question you probably never asked: “What would happen if a physicist and a comedian had a radio show?”

The answer, it turns out, is some science information that is anything but dry. If you are prone to listening to radio programs or podcasts, you might find some interesting tidbits in the Cage. A two-part episode on general relativity was especially interesting although it isn’t exactly like their regular program.

The physicist in question is [Brian Cox] who is an Advanced Fellow of particle physics at the University of Manchester. The comic, [Robin Ince] is not only a comedian, but also a writer, an impressionist, and has an honorary doctorate from Royal Holloway, University of London.

If you poke around the BBC’s site, you can find plenty of episodes to stream or download. General relativity is just one of the topics. You might also enjoy episodes on artificial intelligence or the science of sound.

If you need more comedy connections, consider that [Eric Idle] is responsible for the theme song. Of course, we cover relativity (and other topics) in a hopefully amusing style. Americans typically get British humor, or they don’t. There’s no in between. The good part about these is that if you don’t get the humor, there’s still the science content. Contrast this to the very funny (if you get it) Look Around You series that is probably not the best place to get scientific information (see the video below).

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