China
Africa
Explore chapters and articles related to this topic
Units and Significant Figures
Published in Patrick F. Dunn, Fundamentals of Sensors for Engineering and Science, 2019
A system of units is comprised of base, supplementary, and derived units. Base units are dimensionally independent. There is a base unit for every fundamental dimension contained in a particular system of units. Supplementary units, such as the radian, are considered dimensionless and do not represent a fundamental dimension. Derived units literally are derived from the base and supplemental units and, therefore, are comprised of products, quotients, and powers of base and supplemental units. In the SI system, for example, the kilogram, meter, and second are base units. The newton is a derived unit because it represents a force, which is derived from the base units of mass times acceleration (as expressed by Newton’s second law). Hence, a newton equals a kilogram times a meter divided by a second squared (N = kg m/s2). The base units of the quantities listed in Table 15.1 are printed in normal font; those of the derived quantities are in italics.
Fundamental concepts
Published in Bernard S. Massey, John Ward-Smith, Mechanics of Fluids, 2018
Bernard S. Massey, John Ward-Smith
In the physical sciences, the word quantity is used to identify any physical attribute capable of representation by measurement. For example, mass, weight, volume, distance, time and velocity are all quantities, according to the sense in which the word is used in the scientific world. The value of a quantity is defined as the magnitude of the quantity expressed as the product of a number and a unit. The number multiplying the unit is the numerical value of the quantity expressed in that unit. (The numerical value is sometimes referred to as the numeric.) A unit is no more than a particular way of attaching a numerical value to the quantity, and it is part of a wider scene involving a system of units. Units within a system of units are of two kinds. First, there are the base units (or primary units), which are mutually independent. Taken together, the base units define the system of units. Then there are the derived units (or secondary units), which can be determined from the definitions of the base units.
The Place of Measurement, Instrumentation, and Laboratory
Published in Francis S. Tse, Ivan E. Morse, Measurement and Instrumentation in Engineering, 2018
The SI system consists of (1) the base units, (2) two supplementary units, and (3) the necessary derived units. The base units and the supplementary units are shown and described briefly in Table 1-4. The base units are the meter, kilogram, and second. Independently defined base units are the kelvin, ampere, mole, and candela. The supplementary units are the radian and steradian. Derived units are formed from the base units according to the algebraic relations linking the corresponding quantities. Derived units given special names and symbols are shown in Table 1-5. The common prefixes for the multiples and submultiples of SI units are shown in Table 1-6.
Liquid crystalline dimers containing a cholesteryl group: chiral smectic phases and TGBA* phase
Published in Liquid Crystals, 2021
Hao-Zhou Huang, Yue-Hua Cong, An Du, Bing Hu, Bao-Yan Zhang
In this paper, we synthesised a series of liquid crystal dimers containing cholesteryl groups and Schiff base moieties. Given the fact that a slight change in the nature and length of the terminal chain and the flexible spacer affects both transition temperatures and mesophase sequences that will be formed, the Schiff base unit is substituted with n-hexyloxy, n-octyloxy, n-decyloxy and n-dodecyloxy tails, and the two mesogenic units are connected by adipic acid, octanoic acid, sebacic acid and dodecanedioic acid. These new dimers are represented by the mnemonic Dn-m where D denotes liquid crystal dimer, n and m indicate the total number of carbons solely (including the carbonyl carbon) in the terminal chain and the flexible spacer, respectively. A general molecular structure of the four series of cholesterol-based nonsymmetric dimers (Dn-6, Dn-8, Dn-10 and Dn-12) realised in the present study is shown in Figure 1.
Ultra-accurate thermophysical properties of helium-4 and helium-3 at low density. I. Second pressure and acoustic virial coefficients
Published in Molecular Physics, 2021
Primary temperature metrology is taking benefit from the substantial progress on the theoretical calculations of helium. The base unit of temperature in the International System of Units (SI), the kelvin, has been redefined since 20 May 2019 (the World Metrology Day) in terms of the exact fixed value of the Boltzmann constant [4]. The redefinition is momentous for the global temperature measurement community and would have been not achieved without the essential support of ab initio ‘data’. On the other hand, however, the next realisation of the redefined kelvin over a much wider range is even more challenging particularly at temperatures below the triple point temperature of natural neon (approximately 25 K) [5]. This forms a more direct motivation of this work to further reduce by at least a few times the uncertainty currently associated with the theoretical values of helium.
Cost-Benefit Analysis of Desalination: A Power Market Opportunity
Published in Electric Power Components and Systems, 2020
Farshad Mohammadi, Mostafa Sahraei-Ardakani, Yousef Al-Abdullah, Gerald Thomas Heydt
This section evaluates the economics of a stand-alone desalination plant. A stand-alone plant is a unit that is not combined with any energy generation plant, nor installed to use and recover the waste thermal energy from another consumer. By using (1) and (2), a typical case study is evaluated here to calculate both the LCOW and NPV. For further explanation of the two-stage cost methodology, readers can refer to [29]. Our analysis required information on the technical specification of the plant as well as the potential revenue achieved by selling potable water. The main factors include the plant’s lifetime (year), labor cost ($/year), in/outfall specific factor cost (%), construction time (year), capacity factor (%), base unit cost ($/(m3/day)), specific O&M for spare parts ($/m3), specific O&M for chemical cost related to pre- and post-treatment ($/m3), and O&M membrane replacement cost ($/m3) [18]. Note that in the calculations, it is necessary to consider expected equity return rate (typical value of 6%), sales tax rate (typical value of 20%) (including Federal and State effective tax on revenue obtained from selling water in the U.S.), price escalation for energy, debt and interest rate (these factors represent how much of initial investment money comes from plant owner stock and how much is debt; an acceptable interest rate should be applied to debt), and water sale price ($/m3).