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Cell Towers Can Double As Cheap Radar Systems

How do you see ships without a pricey radar system? The question has troubled seaports around the world as they work to improve security. Without radar installations, it can be hard for port employees to detect small ships like those employed by pirates or by the terrorists who attacked the USS Cole in 2000. A team of researchers in Germany can now offer security teams a new option, though: putting existing cellular towers to work as quick and dirty radar systems.

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Measure Planck's Constant and Define the Kilogram with LEGOs

Now you (yes, you) can measure Planck’s constant and use quantum mechanics to measure mass from the comfort of your own home or classroom—using LEGOs.

In 1960, the meter was re-defined in terms of time (the current definition is the distance light travels in 1/299 792 458 seconds). That left the kilogram as the lone fundamental unit of the International System of Units (SI) defined by a physical object rather than universal constants.

In 1990, some electrical measurements split off from the SI, establishing a “conventional” system that defined basic electromagnetic units in terms of the Josephson and von Klitzing constants (KJ=2e/h and RK=h/e2, respectively, where e is the charge of an electron and h is Planck’s constant—and h90=6.626 x 10-34 m2 kg /s is the best value for h available in 1990).

The movement for a physical-constant-defined kilogram gained urgency late in that decade, when an international recalibration some reference kilograms were putting on weight, thanks to the thinnest of possible coatings deposited from the air. Since Planck’s constant explicitly connects the kilogram to units that are already constant-defined, it is the final key to a system of measurements that can be replicated, in theory, by anyone, at any time, at any place.

The pursuit of the quantum kilogram has focused on instruments called Watt balances, with occasional side-trips into matter waves. Watt balances at the U.S. National Institutes of Standards (NIST) and other national laboratories have pushed measurement precision to a few parts per hundred million, using techniques that are beyond the reach of the classroom or kitchen metrologist. Thanks to this work, it appears that a redefined kilogram may be achieved by 2018, allowing a fundamental revision of the SI and its reunification with the “conventional system.”

The physics and the testing methodology are both complex. But over the past few years, researchers at NIST’s Physical Measurements Laboratory have developed a do-it-yourself device that demonstrates the Watt balance’s physical principles and measurement methods at a scale, and a price, suitable for a classroom or home.

In a paper posted on ArXiv and submitted to the American Journal of Physics, the NIST researchers (joined by collaborators from the Joint Quantum Institute at the University of Maryland) show how to build—and understand—a Watt balance that can measure Planck’s constant and mass to within one part in a hundred. The device measures the electric power needed drive an electromagnet to balance a given mass. It uses 392 LEGO bricks, a USB data acquisition (DAQ) controller, a USB-controlled four-channel analog output device, a photodiode, two $15 lasers, some miscellaneous resistors, four ring magnets, some brass rod and a scrap of PVC pipe. The total cost is $633.77 or less: The two USB controllers account for $389 of the price tag; if you have them, or make a less expensive substitution, the project cost plummets.

In 2013 and 2014, a quintet of NIST researchers—Leon S. Chao, Stephan Schlamminger, DB. Newell, J.R. Pratt and Xiang Zhang—built three prototype LEGO Watt balances. These were “received with enthusiastic responses“ by science fair attendees, students, and NIST visitors. The demonstration project ties together elements whose relationships may not be readily evident: Planck’s constant at the quantum level and mass at the level of the gram, kilogram, or even galaxy.

The LEGO Watt balance is patterned on the familiar analytical balance, with a two-armed rocking beam balanced on a knife edge. Weighing pans hang on gimbals at the end of each arm. And beneath each pan hangs a short piece of wire-wrapped PVC pipe. Each induction coil can move up and down over a pair of neodymium ring magnets, threaded on a vertical brass rod affixed to a base plate. Two sub-milliwatt lasers report beam displacement: One shines under the beam onto the photodiode (at about $62, the most expensive component after the controllers). As the balance beam rocks, it casts a shadow on the diode; the photodiode output measures the balance’s oscillations. The other laser is fixed to the top of the beam. It shines on a ruler or a sheet of graph paper taped to a wall a couple of meters away. This gives very sensitive reading of the beam’s total displacement. When fully assembled, the balance weighs about 4 kilograms and stands about 36 centimeters tall, with a 43 cm by 10 cm footprint

In operation, the balance illustrates concepts of mass, gravity, current, and voltage, along with flux density and flux integral, while teaching some fundamentals of metrological practice.

The LEGO balance works in two modes: a “velocity mode” for electrical calibration and a “force mode” for measuring mechanical forces and mass.

In velocity mode, the LEGO instrument senses current in one of the coils (under Pan A, say) as it moves through the field of the static magnets. To calibrate the system, operators drive the opposite coil (under Pan B) with an oscillating current. By plotting displacement against current, the NIST researchers (and the students who, one hopes, will follow them) calculate the velocity-mode flux integral (flux density times wire length, in units of volts/velocity).

In the force-mode step, the device is used to measure the current needed produce enough force to counteract masses in the pans. In seven steps, the operator adds and removes weights on both sides of the balance, each time changing the voltage to bring the laser dot on the wall back to the balanced position. (An experienced operator can complete calibration and measurement in about 30 minutes.)

  • Step 1: Balance the empty pans.
  • Step 2: Add an arbitrary mass of a few grams to Pan B, and record the current needed to re-center the balance.
  • Step 3: Add a calibrated reference mass to Pan A, and again alter the current to re-center.
  • Step 4: Remove the calibrated mass from Pan A; measure current again.
  • Step 5: Put the calibrated mass back in Pan A, and measure again.
  • Step 6: Remove the calibrated mass from Pan A again, and re-center.
  • Step 7: Remove the arbitrary mass from Pan B and verify that the unloaded balance remains stable.

The user combines the current readings to calculate how much current would be needed to balance the calibrated Mass A alone. From the measured current and the known mass, the operator calculates the force-mode flux integral.  (This is the current divided by the product of the mass and the gravitational constant, g. The value of g varies slightly from place to place, so LEGO balance users should consult the U.S. National Geological Survey web service that provides predicted local values for g, based on the user’s latitude, longitude, and elevation.)  

The force-mode flux integral (BFF) depends on SI units. The velocity-mode flux (BFV), is based on purely electrical measurements and implicitly includes h90. And the ratio of the two is the same as the ratio of the SI Planck’s constant to h90 (that is, BFF/BFV = h/h90). Solve for h and you’re at the forefront of metrology. 

Edited 16 December 2014 to update affiliations to conform to revised ArXiv paper.

Google Lunar XPrize Deadline Extended To 2016

Teams competing for the US $30 million Google Lunar XPrize have another year to make it to the moon.

The contest, which was first announced in 2007, offers a grand prize of $20 million for the first private team to land safely on the lunar surface, move 500 meters, and transmit high-definition images and video back to Earth. Additional money is set aside for second place and for other accomplishments.

Today, the XPrize Foundation announced it has extended the time for accomplishing the feat to 31 December 2016. The announcement cited both technical and financial challenges facing competitors.

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Skin Patches Enable Smartphone-Controlled Pain Relief

Millions of athletes and arthritis patients turn to disposable pain relief patches designed to soothe aching joints and muscles. The new development of a flexible smart patch could eventually enable users to wirelessly control the exact temperature of their heat therapy with their smartphones.

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Diagnosing Ear Infections With a New Smartphone Gadget

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One of the most welcome trends in health care is the emergence of consumer gadgets that can help people deal with their medical needs at home, avoiding the agony of doctors’ offices and, even worse, emergency rooms. The newest entry in field is the Cellscope Oto, a clip-on gadget that turns a smartphone into an otoscope, the tool that doctors use to peer into an ear and check out a patient’s eardrum.

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Will Tomorrow's Supercomputers Be Superconducting?

Today, the list of the 500 fastest supercomputers is dominated by computers based on semiconducting circuitry. Ten years from now, will superconducting computers start to take some of those slots?

Last week, IARPA, the U.S. intelligence community’s high-risk research arm, announced that it had awarded its first set of research contracts in a multi-year effort to develop a superconducting computer. The program, called Cryogenic Computing Complexity (C3), is designed to develop the components needed to construct such a computer as well as a working prototype. 

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DARPA Prepares to Launch "Satlets"

Here comes the "zombie frankensatellite.” Or at least the very first piece of what DARPA needs to make it happen.

DARPA's Phoenix program grabbed a lot of attention in 2012 when it announced a plan to revive old satellites by mining them for parts and constructing a new satellite around them. 

Now, the pieces are coming together for the program’s first space launch. On Tuesday, Seattle-based launch broker Spaceflight announced that it has signed an agreement to carry Phoenix’s first spacecraft. It’s slated to launch some time in the third quarter of 2015 as a secondary payload on a rocket. Although Spaceflight has not yet identified the rocket provider for this launch and could not discuss it, I have been told by several people that the mission will go up on a SpaceX Falcon 9.

The first DARPA Phoenix spacecraft won’t be an orbiting satellite factory. Instead it will be an already completed spacecraft, called eXCITe, built from smaller parts. Constructed by NovaWurks, based in Los Alamitos, Calif., the spacecraft will be made out of a set of identical “satlets,” which the company dubs HiSats, for Hyper-Integrated Satlets. Each measures about 20 by 20 by 10 centimeters.

Each satlet is effectively a self-contained spacecraft, with its own computer, power, communications capabilites, and propulsion. But Talbot Jaeger, NovaWurks founder and chief technologist, says they’re designed to be combined together. He likens them to liver cells. Each one might be capable of performing the basic filtration functions of the liver, but they’re only really effective in aggregate. He did note that at least one vital piece of the spacecraft, the antenna, which is by necessity fairly large, would have to be launched as a payload that’s attached to the satlets.

At the moment, eXCITe is “not a fixed design. It can change depending on what payloads show up and what we can make work on our time frame,” says Jaeger. Depending on what comes in and when, eXCITe will contain anywhere between 10 and 20 satlets, he says. 

This is the kind of flexibility Jaeger is aiming for. The approach “frees us from thinking of just small spacecraft and just large spacecraft,” he says. “We now have something that can bridge that gap.” ​

This might sound like a far cry from an orbiting satellite construction and recycling operation. But it’s part of an overall plan to move away from monolithically-built spacecraft towards something far more modular and manipulable, program manager David Barnhart told me earlier this year. The Phoenix program is “all about how to address the cost of getting and doing things in space," he said.

Piggybacking on a rocket flight as a secondary payload is part of that as well, Barnhart told me.

The satlets will be doing just that on their first trip to space. The firm Spaceflight will carry the eXCITe into orbit on a ring-shaped spacecraft called SHERPA, modeled after the secondary satellite carrier developed by Moog for the U.S. Air Force’s Evolved Expendable Launch Vehicle program.

This will also be the maiden voyage for SHERPA, which Spaceflight hopes to use going foward to ferry secondary payloads into orbit. On this first flight, SHERPA will release eXCITe, along with 1200 kg-worth of other payloads to fly off on their own.

”We’re building a spacecraft that deploys spacecraft,” says Adam Hadaller, mission manager for the upcoming flight. SHERPA has its own power, communications, and positioning gear. Future incarnations could also have propulsion to carry payloads to orbits that differ from the intended orbit of the primary spacecraft.

The smaller the satellite, the longer it takes for the drag of Earth’s atmosphere to pull it down. A SHERPA with thrusters could potentially carry smaller satellites down to a lower orbit, where the atmosphere is thicker, so they would burn up faster at the end of their mission and so not contribute as much to the problem of orbital debris, Spaceflight president Curt Blake. It’s appealing to think there’s a way to make it easier to get things into, and out of, space.

Follow Rachel Courtland on Twitter at @rcourt

Dutch Trains Prove Everything Is Better With Lasers

The combination of trains and lasers seems like it belongs in a really, really bad network TV adventure series straight out of the late 1970s or something. But no, it’s not Supertrain, because not even lasers could have helped Supertrain. What lasers can help are real trains, traveling on real tracks, that are covered with leaves. Leaves cause way more problems for trains than you’d think, but powerful train-mounted lasers can make everything better.

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Ralph Baer, Father of Video Games Is Dead

Ralph Baer, the engineer considered the father of the video game died on 6 December at age 92. He invented the “Brown Box” in 1966,  a hardware-based prototype game system that plugged in to your television.

Baer received the IEEE Edison Medal this year, the U.S. National Medal of Technology and Innovation in 2006, was inducted into the U.S. National Inventors Halls of Fame in 2010 among other awards. Oddly enough, he was only elevated to the rank of IEEE Fellow in 2013.

For the whole story of Baer’s fascinating life and inventions see an obituary in our sister publication The Institute.


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