How to Define the Units of the Revised SI Starting from Seven Constants with Fixed Numerical Values.

As part of a revision to the International System of Units (SI) approved in 2018 and to take effect in May 2019, the seven base units will be defined by giving fixed numerical values to seven defining constants. This article shows how the definitions of all seven base units can be derived efficiently from the defining constants, with the result appearing as a table. The table's form makes evident a number of connections between the defining constants and the base units.

The Effect of Compression Ratio, Fuel Octane Rating, and Ethanol Content on Spark-Ignition Engine Efficiency.

Light-duty vehicles (LDVs) in the United States and elsewhere are required to meet increasingly challenging regulations on fuel economy and greenhouse gas (GHG) emissions as well as criteria pollutant emissions. New vehicle trends to improve efficiency include higher compression ratio, downsizing, turbocharging, downspeeding, and hybridization, each involving greater operation of spark-ignited (SI) engines under higher-load, knock-limited conditions. Higher octane ratings for regular-grade gasoline (with greater knock resistance) are an enabler for these technologies.

Maritime adaptations and dietary variation in prehistoric Western Alaska: stable isotope analysis of permafrost-preserved human hair.

The reconstruction of diet and subsistence strategies is integral in understanding early human colonizations and cultural adaptations, especially in the Arctic-one of the last areas of North America to be permanently inhabited. However, evidence for early subsistence practices in Western Alaska varies, particularly with regards to the emergence, importance, and intensity of sea mammal hunting. Here, we present stable carbon and nitrogen isotope data from permafrost-preserved human hair from two new prehistoric sites in Western Alaska, providing a direct measure of diet.

Continuity and change in the eastern Aleutian archaeological sequence.

The eastern Aleutian prehistoric archaeological sequence is key for understanding population movements, cultural exchanges, and adaptations to environmental changes over a wide area of the north Pacific and Bering Sea during the Holocene. An important question is, Can the settlement history of the eastern Aleutians be understood as a single continuous tradition lasting some 9,000 years, or were there major population and cultural influxes along with periods of widespread population abandonment? We review the available archaeological evidence with reference to recent mtDNA and nucleic DNA studies of prehistoric and contemporary Arctic and Subarctic populations and conclude that the evidence points to an overall cultural continuity with notable incursions and excursions of people and cultural elements into and out of the eastern Aleutians.

Erratum: Determining the Magnetic Properties of 1 kg Mass Standards.

[This corrects the article on p. 209 in vol. 100.

Erratum: Determining the Magnetic Properties of 1 kg Mass Standards.

[This corrects the article on p. 209 in vol. 100.

Determining the Magnetic Properties of 1 kg Mass Standards.

Magnetic interactions may lead to errors in precision mass metrology. An analytical description of such magnetic errors is presented in which the roles of both the volume magnetic susceptibility and permanent magnetization are discussed. The same formalism is then used to describe in detail the calibration and operation of a susceptometer developed at the Bureau International des Poids et Mesures (BIPM).

New Assignment of Mass Values and Uncertainties to NIST Working Standards.

For some time it had been suspected that values assigned to NIST working standards of mass were some 0.17 mg/kg larger than mass values based on artifacts representing mass in the International System of Units (SI). This relatively small offset, now confirmed, has had minimal scientific or technological significance.

Comparison of Solid Density Standards Between IMGC and NBS.

Solid-object density standards developed independently by the Istituto di Metrologia "G. Colonnetti" (IMGC) and NBS, and traceable to SI units of length and mass, have been compared using a silicon transfer standard. Results agree to approximately 1×10, which is conistent with the uncertainties assigned by the two laboratories.

An Analysis of Read-Out Perturbations Seen on an Analytical Balance with a Swinging Pan.

An analysis of the dynamic behavior of a single-pan mechanical balance is presented. In particular, errors caused by a swinging pan are analyzed in detail. Results point to a large effect which, though apparently not previously appreciated, is nevertheless easily verified experimentally.