A 'Dobson Unit' is a measurement of the thickness of what?
"This is sometimes referred to as a 'milli-atmo-centimeter.' A typical column amount of 300 DU of atmospheric ozone therefore would form a 3 mm layer of pure gas at the surface of the Earth if its temperature and pressure conformed to STP. The Dobson unit is named after Gordon Dobson, a researcher at the University of Oxford who in the 1920s built the first instrument to measure total ozone from the ground, making use of a double prism monochromator to measure the differential absorption of different bands of solar ultraviolet radiation by the ozone layer. This instrument, called the Dobson"
"by volcanic eruptions. The Dobson unit is used to describe total column amounts of sulfur dioxide because it appeared in the early days of ozone remote sensing on ultraviolet satellite instruments (such as TOMS). The Dobson Unit arises from the ideal gas law. From the real gas law: formula_1 where P and V are pressure and volume, respectively, and n, R and T are the number of moles of gas, the gas constant (8.314 J/mol K), and T is temperature in Kelvin (K). The number density of air is the number of molecules or atoms per unit volume: formula_2 and"
"radiation was matched to only one known chemical, ozone. Its properties were explored in detail by the British meteorologist G. M. B. Dobson, who developed a simple spectrophotometer (the Dobsonmeter) that could be used to measure stratospheric ozone from the ground. Between 1928 and 1958, Dobson established a worldwide network of ozone monitoring stations, which continue to operate to this day. The ""Dobson unit"", a convenient measure of the amount of ozone overhead, is named in his honor. The ozone layer absorbs 97 to 99 percent of the Sun's medium-frequency ultraviolet light (from about 200 nm to 315 nm wavelength),"
"a volume, to molecules per square centimeter, an area? This must be done by integration. To get a column density, we must integrate the total column over a height. Per the definition of Dobson Units, we see that 1 DU = 0.01 mm of trace gas when compressed down to sea level at standard temperature and pressure. So if we integrate our number density of air from 0 to 0.01 mm, we find the number density which is equal to 1 DU: formula_6 And thus we come up with the value of 1 DU, which is 2.69×10 molecules per meter"
"when plugged into the real gas law, the number density of air is found by using pressure, temperature and the real gas constant. formula_3 The number density (molecules/volume) of air at standard temperature and pressure (T = 273K and P = 101325 Pa) is, by using this equation: formula_4 With some unit conversions of Joules to Pascals, the equation for molecules/volume is formula_5 A Dobson Unit is the total amount of a trace gas per unit area. In atmospheric sciences, this is referred to as a column density. How, though, do we go from units of molecules per cubic meter,"
"(305 nm) and UVA (325 nm), in order to calculate the amount of ozone. When turned, the R-dial filters and blocks out the light of the UVC wavelength until the intensity of the two wavelengths of light are equal. The ratio of the two wavelengths at incidence can be calculated once the filtered intensities are the same. The results are measured in Dobson Units, equal to 10 µm thickness of ozone compressed to Standard conditions for temperature and pressure (STP) in the column. If all of the ozone in the atmospheric column one was measuring were compressed to STP, the"
"Dobson unit should eventually be replaced by an appropriate SI unit and that the unit mmol m-2 was the most convenient and least cumbersome option. It expressed the hope that this unit would eventually supplant the Dobson Unit. However, as of March 2017, there is little evidence that this has occurred; for example the Dobson unit is still used by NASA and by the World Ozone and Ultraviolet Radiation Data Center in their reporting of total ozone amount. NASA uses a baseline value of 220 DU for ozone. This was chosen as the starting point for observations of the Antarctic"
"materials. Absorbed moisture can also vaporize on heating, as during soldering, and cause cracking and delamination, the same effect responsible for ""popcorning"" damage on wet packaging of electronic parts. Careful baking of the substrates may be required to dry them prior to soldering. Often encountered materials: Less-often encountered materials: Copper thickness of PCBs can be specified directly or as the weight of copper per area (in ounce per square foot) which is easier to measure. One ounce per square foot is 1.344 mils or 34 micrometers thickness. ""Heavy copper"" is a layer exceeding three ounces of copper per ft, or"
"the ""Brewer"" Spectrophotometer produced by Kipp & Zonen. Dobson ozone spectrophotometer The Dobson spectrophotometer, also known as Dobsonmeter, Dobson spectrometer, or just Dobson is one of the earliest instruments used to measure atmospheric ozone. The Dobson spectrometer was invented in 1924 by Gordon Dobson. A history of the development of the instrument is here and an example of one of Dobson's own instruments remains on display in the University of Oxford Department of Physics. Dobson spectrophotometers can be used to measure both total column ozone and profiles of ozone in the atmosphere. Ozone is tri-atomic oxygen, O; ozone molecules absorb"
"Dobson ozone spectrophotometer The Dobson spectrophotometer, also known as Dobsonmeter, Dobson spectrometer, or just Dobson is one of the earliest instruments used to measure atmospheric ozone. The Dobson spectrometer was invented in 1924 by Gordon Dobson. A history of the development of the instrument is here and an example of one of Dobson's own instruments remains on display in the University of Oxford Department of Physics. Dobson spectrophotometers can be used to measure both total column ozone and profiles of ozone in the atmosphere. Ozone is tri-atomic oxygen, O; ozone molecules absorb harmful UV light in the atmosphere before it"
"Dobsonian telescope A Dobsonian telescope is an altazimuth-mounted Newtonian telescope design popularized by John Dobson starting 53 years ago in 1965 and credited with vastly increasing the size of telescopes available to amateur astronomers. Dobson's telescopes featured a simplified mechanical design that was easy to manufacture from readily available components to create a large, portable, low-cost telescope. The design is optimized for observing faint, deep-sky objects such as nebulae and galaxies. This type of observation requires a large objective diameter (i.e. light-gathering power) of relatively short focal length and portability for travel to relatively less light-polluted locations. Dobsonians are intended"
"ozone spectrophotometer, has formed the backbone of the global network for monitoring atmospheric ozone and was the source of the discovery in 1984 of the Antarctic ozone hole. The Dobson Unit is not part of the SI International System of Units. To address this shortcoming, a brief study in 1982 examined a number of alternative SI-based units suitable for column amounts of not only ozone but any gas in any planetary atmosphere and proposed the use of the unit of mole per square metre for all cases. Examples range from Earth’s trace gases at levels of micro moles per square"
"Stiffness Stiffness is the extent to which an object resists deformation in response to an applied force. The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is. The stiffness, ""k"", of a body is a measure of the resistance offered by an elastic body to deformation. For an elastic body with a single degree of freedom (DOF) (for example, stretching or compression of a rod), the stiffness is defined as where, In the International System of Units, stiffness is typically measured in newtons per meter. In Imperial units, stiffness is typically measured"
"The number refers to the weight in ounces of a given amount of fabric, either a yard of a given width, or a square yard. The most common unit of measure for the copper thickness on a printed circuit board (PCB) is ounces (oz). It is the resulting thickness when 1 oz of copper is pressed flat and spread evenly over a one-square-foot area. This roughly equals 34.7 µm. Ounce The ounce (abbreviated oz; apothecary symbol: ℥) is a unit of mass, weight, or volume used in most British derived customary systems of measurement. The common avoirdupois ounce (approximately )"
"thickness of the compressed atmosphere in mm would equal an answer in Dobson Units divided by 100. The vertical distribution of ozone is derived using the Umkehr method. This method relies on the intensities of reflected, rather than direct, UV light. Ozone distribution is derived from the change in the ratio of the same UV-pair frequencies with time as the sun sets. An ""Umkehr"" measurement takes about three hours, and provides data up to an altitude of 48 km, with the most accurate information for altitudes above 30 km. The Dobson method has its drawbacks. It is strongly affected by"
"ozone hole, since values of less than 220 Dobson units were not found before 1979. Also, from direct measurements over Antarctica, a column ozone level of less than 220 Dobson units is a result of the ozone loss from chlorine and bromine compounds. In addition, Dobson units are often used to describe total column densities of sulfur dioxide, which occurs in the atmosphere in small amounts due to the combustion of fossil fuels, from biological processes releasing dimethyl sulfide, or by natural combustion such as forest fires. Large amounts of sulfur dioxide may be released into the atmosphere as well"
"Darcy (unit) A darcy (or darcy unit) and millidarcy (md or mD) are units of permeability, named after Henry Darcy. They are not SI units, but they are widely used in petroleum engineering and geology. Like some other measures of permeability, a darcy has dimensional units in length². Permeability measures the ability of fluids to flow through rock (or other porous media). The darcy is defined using Darcy's law, which can be written as: where: The darcy is referenced to a mixture of unit systems. A medium with a permeability of 1 darcy permits a flow of 1 cm³/s of"
"by the pressure in a rock. The unit of measure is called the darcy, named after Henry Darcy (1803–1858). Sandstones may vary in permeability from less than one to over 50,000 millidarcys (md). Permeabilities are more commonly in the range of tens to hundreds of millidarcies. A rock with 25% porosity and a permeability of 1 md will not yield a significant flow of water. Such “tight” rocks are usually artificially stimulated (fractured or acidized) to create permeability and yield a flow. The SI unit for permeability is m. A practical unit for permeability is the ""darcy"" (d), or more"
"in ounces per square foot. Thicknesses commonly used in construction in the U.S. are between 12ounces and 48 ounces. Since the industry often uses gauge numbers or actual thicknesses for sheet metal or other building materials, it is necessary to convert between the different measurement systems. In Europe, phosphorus de-oxidized non-arsenical copper is used with the designation C106. The copper is rolled to thicknesses ranging between 0.5 and 1.0 millimeters (1.5 - 3.0 millimeters for curtain walling) but a 0.6 - 0.7 millimeters thickness is usually used for roofing. Alloyed copper. Copper alloys, such as brass and bronze, are also"
"Hardness Hardness is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. Some materials (e.g. metals) are harder than others (e.g. plastics, wood). Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex; therefore, there are different measurements of hardness: ""scratch hardness"", ""indentation hardness"", and ""rebound hardness"". Hardness is dependent on ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity. Common examples of hard matter are ceramics, concrete, certain metals, and superhard materials, which can be contrasted with soft matter. There are three"
"as hard disk drives, optical disc drives and tape drives. The current unit of measure is typically gigabits per square inch. The area density is often used to describe the thickness of paper; e.g., 80 g/m is very common. Fabric ""weight"" is often specified as mass per unit area, grams per square meter (gsm) or ounces per square yard. It is also sometimes specified in ounces per yard in a standard width for the particular cloth. One gram per square meter equals 0.0295 ounces per square yard; one ounce per square yard equals 33.9 grams per square meter. It is"
"(~ 0.1 bar/m) at a temperature of 20°C. In this specific setup, 1 darcy is equivalent to 0.831 m/day. Darcy (unit) A darcy (or darcy unit) and millidarcy (md or mD) are units of permeability, named after Henry Darcy. They are not SI units, but they are widely used in petroleum engineering and geology. Like some other measures of permeability, a darcy has dimensional units in length². Permeability measures the ability of fluids to flow through rock (or other porous media). The darcy is defined using Darcy's law, which can be written as: where: The darcy is referenced to a"
"are laid on the mold and impregnated with 'initiated' resins like polyester, epoxy, vinyl ester, bisphenol epoxy vinyl ester, etc. The choice of resin is based on the chemical corrosion requirement of the equipment. An earlier version of the specification was BS 4994:1973. NEW LOAD UNITS: It is to avoid the uncertainty associated with specifying the thickness alone, that BS4994 introduced the concept of ""unit properties"". It is property per unit width, per unit mass of reinforcement. For example, UNIT STRENGTH is defined as load in Newtons per millimeter (of laminate width) for a layer consisting of 1 kg of"
"bodies used as drosometers, partly because of the location, partly because of the difference in the substances, and largely because of the influence of slight local currents of air. Drosometer A drosometer (from Classical Greek , ""drosos"", dew + , ""metron"", measure) is an apparatus for measuring the quantity of dew formed in a unit of time per unit area of surface. The surface may be either a horizontal metal plate or a leaf hanging naturally, or a bit of wool or cotton representing a large surface of fine fibres. The unit of time is usually one hour, and the"
"the Darcy friction factor by formula_5 in which formula_6 is the Darcy friction factor (dimensionless). It was introduced by John J Atkinson in an early mathematical treatment of mine ventilation (1862) and has been known under his name ever since. Atkinson friction factor Atkinson friction factor is a measure of the resistance to airflow of a duct. It is widely used in the mine ventilation industry but is rarely referred to outside of it. Atkinson friction factor is represented by the symbol formula_1 and has the same units as air density (kilograms per cubic metre in SI units, lbfmin^2/ft^4 in"
"equivalent to the pascal, that is usually not used for this purpose). Small amounts can be expressed in newton-millimetres per cubic millimetre. In U.S. customary units, torque density is expressed in foot-pounds force per cubic foot, or inch-pounds force per cubic inch or ounce-force inches per cubic inch. Torque density Torque density is a measure of the torque-carrying capability of a mechanical component. It is the ratio of torque capability to volume and is expressed in units of torque per volume. Torque density is a system property since it depends on the design of each element of the component being"
"viscosity of 1.0019 cP at about room temperature. The unit is named after Henry Darcy, and the unit abbreviation is not capitalized (contrary to industry use). The American Association of Petroleum Geologists use the following unit abbreviations and grammar in their publications: Converted to SI units, 1 darcy is equivalent to 9.869233×10 m² or 0.9869233 (µm)². This conversion is usually approximated as 1 (µm)². Note that this is the reciprocal of 1.013250—the conversion factor from atmospheres to bars. Specifically in the hydrology domain, permeability of soil or rock may also be defined as the flux of water under hydrostatic pressure"
"into the food. Cross-linking in various plastics can lead to physical and chemical modifications that can increase the overall molecular weight. On the other hand, chain scission is fragmentation of polymer chains that leads to a molecular weight reduction. The radiation absorbed dose is the amount energy absorbed per unit weight of the target material. Dose is used because, when the same substance is given the same dose, similar changes are observed in the target material. The SI unit for dose is grays (Gy or J/kg). Dosimeters are used to measure dose, and are small components that, when exposed to"
"Thomson (unit) The thomson (symbol: Th) is a unit that has appeared infrequently in scientific literature relating to the field of mass spectrometry as a unit of mass-to-charge ratio. The unit was proposed by Cooks and Rockwood naming it in honour of J. J. Thomson who measured the mass-to-charge ratio of electrons and ions. The thomson is defined as where u represents the unified atomic mass unit, Da represents the unit dalton, and ""e"" represents the elementary charge which is the electric charge unit in the atomic unit system. For example, the ion CH has a mass of 91 Da."
"Poisson's ratio and cube of the plate's elastic thickness, it is a governing factor in both (1) and (2). Flexural Rigidity formula_6 formula_2 = Young's Modulus formula_8 = elastic thickness (~10–15 cm) formula_9 = Poisson's Ratio Flexural rigidity of a plate has units of Pa·m, i.e. one dimension of length less from the one for the rod, as it refers to the moment per unit length per unit of curvature, and not the total moment. I is termed as moment of inertia.J is denoted as 2nd moment of inertia/polar moment of inertia. Flexural rigidity Flexural rigidity is defined as the"
"Area density The areal density (also known as area density, surface density, superficial density, or density thickness) of a two-dimensional object is calculated as the mass per unit area. The SI derived unit is: kilogram per square metre (kg·m). In the paper and fabric industries, it is called grammage and is expressed in grams per square meter (gsm); for paper in particular, it may be expressed as pounds per ream of standard sizes (""basis ream""). It can be calculated as: or where, A special type of area density is called column (mass) density (also columnar mass density), denoted ""ρ"" or"
"The design is a very simple, low cost alt-azimuth mounted Newtonian telescope that employs common materials such as plywood, formica, PVC closet flanges, cardboard construction tubes, recycled porthole glass, and indoor-outdoor carpet. This type of simplified altazimuth mount is also commonly referred to in amateur astronomical circles as a ""Dobsonian mount"". Using this construction method makes the typical Dobsonian telescope large, portable, inexpensive, very stable, and easy to manufacture. The design revolutionized the sheer size of telescopes available to amateur astronomers with the optical diameters unheard of before their appearance. The design is named after Dobson because he is credited"
"c = 0.20 Btu/(lb F) or 840 joules/(kg K). The density is 95 lb/ft or 1520 kg/m. The thermal diffusivity is calculated to be 0.0105 ft/h or 2.72x10 m/s. Poured and puddled adobe (puddled clay, piled earth), today called ""cob"", is made by placing soft adobe in layers, rather than by making individual dried bricks or using a form. ""Puddle"" is a general term for a clay or clay and sand-based material worked into a dense, plastic state. These are the oldest methods of building with adobe in the Americas until holes in the ground were used as forms, and"