National Institute of Standards and Technology (NIST) researchers have designed and built a watt balance based on LEGO blocks. Planck’s constant describes the relationship between the energy and frequency of an electromagnetic wave. One kind of device that can be used to measure mass based on Planck’s constant or taken the other way, to find a value for Planck’s constant based on a known mass, is called a watt balance. It does its work by balancing the force exerted by gravity with the force of current in a coil—the mass of an object can be calculated by comparing the mechanical power to the electrical power in the device.
Scientists at NIST and other places have built elaborate and expensive watt balances, but in this new effort, they wanted to find a way to create one that anyone could build, and they found a way to do so by basing it on LEGO blocks—they actually built three, one of which they chose to outline in detail, describing not only how it works, but the parts used so that other’s could build one too. Their design, they say would require a would-be constructor to lay down just $634 for all the parts, which include 2 sub- milliwatt lasers, photodiode, controllers, etc. They note that some industrious sorts would likely be able to reduce costs using other less expensive parts they source themselves.
CAD model of the LEGO watt balance. The balance pivots about the T-block at the center. Two PVC endcaps with copper windings hang from universal joints off either side of the balance beam. Coil A is on the left and Coil B is on the right. A 10 gram mass sits on the Coil A mass pan and each coil is concentric to its own magnet system. Two lasers are used to calibrate and measure the linear velocity of each coil. Credit: arXiv:1412.1699 [physics.ins-det]
Image of three similar versions of the LEGO watt balance. The acrylic cases are backlit with blue LEDs and serve the purpose of blocking out disturbances from air currents. Two hinged doors on the front panel allow for small masses to be placed and removed from the mass pans. All the electronics are mounted below the wooden base board. Four adjustable feet are used for leveling the balance. Credit: arXiv:1412.1699 [physics.ins-det]
A global effort to redefine our International System of Units (SI) is underway and the change to the new system is expected to occur in 2018. Within the newly redefined SI, the present base units will still exist but be derived from fixed numerical values of seven reference constants. More specifically, the unit of mass, the kilogram, will be realized through a fixed value of the Planck constant h. For instance, a watt balance can be used to realize the kilogram unit of mass within a few parts in 10^8. Such a balance has been designed and constructed at the National Institute of Standards and Technology. For educational outreach and to demonstrate the principle, we have constructed a LEGO tabletop watt balance capable of measuring a gram size mass to 1 % relative uncertainty. This article presents the design, construction, and performance of the LEGO watt balance and its ability to determine h.
2. Researchers from UCLA’s California NanoSystems Institute have reported the first demonstration of imaging and measuring the size of individual DNA molecules using a lightweight and compact device that converts an ordinary smartphone into an advanced fluorescence microscope.
The mobile microscopy unit is an inexpensive, 3-D-printed optical device that uses the phone’s camera to visualize and measure the length of single-molecule DNA strands. The device includes an attachment that creates a high-contrast, dark-field imaging set-up using an inexpensive external lens, thin-film interference filters, a miniature dovetail stage and a laser diode that excites the fluorescently labeled DNA molecules.
The device also includes an app that connects the smartphone to a server at UCLA, which measures the lengths of the individual DNA molecules. The molecules are labeled and stretched on disposable chips that fit in the smartphone attachment.
The application transmits the raw images to the server, which rapidly measures the length of each DNA strand. The results of DNA detection and length measurement can be seen on the mobile phone and on remote computers linked to the UCLA server.
DNA imaging techniques using optical microscopy have found numerous applications in biology, chemistry and physics and are based on relatively expensive, bulky and complicated set-ups that limit their use to advanced laboratory settings. Here we demonstrate imaging and length quantification of single molecule DNA strands using a compact, lightweight and cost-effective fluorescence microscope installed on a mobile phone. In addition to an optomechanical attachment that creates a high contrast dark-field imaging setup using an external lens, thin-film interference filters, a miniature dovetail stage and a laser-diode for oblique-angle excitation, we also created a computational framework and a mobile phone application connected to a server back-end for measurement of the lengths of individual DNA molecules that are labeled and stretched using disposable chips. Using this mobile phone platform, we imaged single DNA molecules of various lengths to demonstrate a sizing accuracy of less than 1 kilobase-pairs (kbp) for 10 kbp and longer DNA samples imaged over a field-of-view of ∼2 mm2.
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