Cash is an interesting byproduct of contemporary economies. The assorted rectangles of ink and paper have wildly different values despite themselves being objectively worthless materials. Instead the numbers on the bills represent buying power.

The U.S. dollar, which became the world’s reserve currency in 1947, was formerly backed up by a gold reserve. This practice was eliminated in the 1970s, as global recession meant international countries began exchanging their cash for gold, which reduced the influence of U.S. currency. Instead, the U.S. made a deal with Saudi Arabia and subsequently OPEC for all oil transactions to use U.S. money. This created a foreign demand for U.S. dollars, and this remains how U.S. currency retains international value today.

Yet over the past 20-plus years, highly-advanced manufacturing and counterfeiting have also undermined the value of U.S. $50 and $100 bills, and remain a threat going forward. These notes are dubbed “supernotes,” as they of such high quality that they appear more authoritative than genuine bills.

The supernotes are made of the same hard-to-produce material, a hybrid 75% cotton, 25% linen fiber paper blend. The notes are also printed by intaglio printing, where the metal plates have lines engraved or etched, which are filled with ink, and then are compressed to the paper. Intaglio printing also gives U.S. notes their rough texture as the inks dry just slightly above the surface of the paper. Most counterfeiting operations use cheaper, less effort-intensive printing techniques, such as inkjet, offset or laser printing, that cannot replicate the intaglio texture.

These supernotes are also engineered to include security features. This includes the exclusive security microfibers found in current U.S. bills, as well as correct watermarks, security strips, and microprint lettering incorporated into real U.S. bills. Even the optically variable inks (OVIs), which cause bills to look green in one light or bronze or black in another, have been emulated. Typically, advanced OVIs and intaglio presses are only available to government agencies for document production.

Of course, there are some very minute differences. The printed quality of supernotes sometimes actually exceeds that of a real note. For example, the hands on the clock tower of Independence Hall are actually sharper and more clear on a supernote, a lamp on the street nearby is better defined, and on the front of a supernote, the letter N in the word ‘United’ has a small font misprint.

Nonetheless, supernotes are practically impossible to identify without instruments. Supernotes are confirmed by the U.S. Secret Service with mass spectroscopy, near-infrared analysis and microscopic inspection.

Evidence suggests that North Korea was likely responsible for the printing and distribution of the notes, possibly beginning back in the 1970s. Motivations were hopes of undermining the U.S. economy, while also paying for goods and products with the fake money. North Korea has a well-known counterfeiting industry that includes narcotic and prescription drugs, cigarettes and designer brands.

Another U.S. $100 bill redesign in 2013 has vastly slowed the discovery of supernotes. This Vice article suggests that North Korea has either abandoned printing counterfeit U.S. notes (in favor of Chinese notes, it seems) or they are now so good at it that fakes can’t be detected.

Turns out, money is only as good as its manufacturing.

To reduce energy consumption, and despite the chagrin of many consumers, countries around the world have severely limited or outright banned the manufacture and sale of conventional incandescent light bulbs because most of their energy consumption converts into heat, rather than light. The most common alternatives - compact fluorescents (CFLs) that contain mercury and can't dim, and still-expensive LEDs that have yet to achieve a satisfyingly natural incandescent color - have encountered considerable resistance. New discoveries suggest that perhaps the efforts to eliminate the technology will prove premature. These researchers at MIT have found a technique that will harvest much of the infrared light(heat) and convert it to visible light at higher efficiencies than CFLs or LEDs. Stay tuned.

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Designing printed circuit boards and building prototypes has changed little in recent years, despite the enormous advances in the semiconductor technology that they contain. This article showcases how one engineer who has been doing the job for 40 years copes with the challenges of building prototypes by hand despite the availability of automated tools. Such tools may prove financially justifiable in a large company, but cost-prohibitive for small companies and startups. In describing his technique, he quips, "It's not so good for long-term reliability, but it's satisfactory for an engineering prototype." The article includes links to additional information on the process.

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No, this item isn't about defective aircraft batteries, but about the VAIO Fit 11A laptop/tablet hybrid that electronics giant Sony introduced in February. The company announced last month that it would no longer offer the system and warned existing customers to stop using it immediately after confirming reports of three incidents of overheating batteries damaging other components, igniting concern that the batteries could catch fire and explode. In addition, the model produced only lackluster sales of 25,905 systems (only 500 in the U.S.) over the less than three months since its introduction. Taken together, these two issues have complicated the company's plans to sell off its personal computer division.

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How are you able to measure temperatures? Temperature can be measured with a wide variety of sensors. Each one of them infers temperature by sensing a change in a physical characteristic. There are six different methods which an engineer is likely to come in contact with: change-of-state devices, liquid expansion devices, bimetallic devices, infrared radiators, resistive temperature devices (thermistors and RTD's), and thermocouples.

Thermocouple Temperature Measurement Sensors

These generally consist of two wires or strips that are made from different metals joined at one end. Changes of temperature at this junction create a change in the EMF, or electromotive force, between the opposite ends. As the temperature goes up, the thermocouple output EMF will rise, although not always linearly. Thermocouple sensors are regarded as among the best temperature measurement devices, along with the RTD's.

RTD or Resistance Temperature Devices

These devices will capitalize on the idea that the electrical resistance of the material will change when the temperature rises. Two main forms are metallic devices (generally known as RTD's) and thermistors. Just like their name says, the metallic devices will rely on only a change of resistance in the metal, with this resistance rising linearly with the temperature. Thermistors are mainly a resistance change within a semiconductor made of ceramic; the resistance will drop non-linearly with the rise of temperature.

Infrared Temperature Measurement Devices

These sensors are unique in being non-contracting devices. They generally infer the temperature by measuring the amount of thermal radiation that a material is emitting. Though less accurate than thermocouple or RTD sensors, infrared devices still provide information regarding the change in temperature. These are generally only used as a backup method for measuring temperature.

Bimetallic Temperature Measurement Devices

These devices will take advantage of the variations in rate of the thermal expansion between various metals. Two different metals are bonded as one. When they are heated, one side expands a little more than the other, and the bending result is translated into a reading of temperature by mechanical linking to a point. These types of devices are portable and don't require any supply of power. However, they are not generally as accurate as RTD's or thermocouples and they don't lend themselves readily to recording of temperature.

Fluid Expansion Temperature Measurement Device

These kinds of devices, typically the thermometer you find at home, come in two categories: the organic-liquid type and the mercury type. There are also some versions available that use gas rather than liquid. Mercury is known as an environmental hazard, so there are some regulations against the shipping of it. The fluid-expansion devices require no power, do not pose as a hazard for explosion, and are stable after many uses. On the other hand, they don't generate information that is easily transmitted or recorded, and they won't make good point or spot measurements.

State Change Temperature Measurement Devices

These types of sensors generally consist of liquid crystals, lacquers, crayons, pellets or labels that change appearance when a specific temperature has been reached. They are usually used, for example, with steam traps. When a trap exceeds the specified temperature, a small white dot on the label of the sensor that is attached to the trap will change to black. The time of response is usually several minutes, therefore these devices cannot respond to quick temperature changes. Accuracy is also much lower than that of the other sensors. Moreover, except in the case of liquid-crystal displays, the change in the state is irreversible. Even so, these types of sensors may be very helpful when an individual needs a confirmation that the temperature of a piece of material or equipment has not exceeded a specific level, for example for legal or technical reasons during shipping of a product.

Editor's Note: This article, written by Camia Sidle, explains the different methods of temperature measurement that are often used. When you are in need of calibration services, ensure that you choose a service and a type of temperature measurement that is best for your business, for your equipment and for your price.