Angstrom unit defined

Waveform can be defined in at least two different ways which are relevant to spectroscopic measurements. Wavelength (X.) is defined as the distance between successive peaks (Figure 2.1) and is measured in subunits of a metre, of which the most frequently used is the nanometre (10 9m). An angstrom unit (A) is not acceptable in SI terminology but is still occasionally encountered and is 10-10m (i.e. 10 A = 1 nm). The frequency of radiation (nu, v) is defined as the number of successive peaks passing a given point in 1 second. Hence the relationship between these two units of measurement is ... 

ANGSTROM (A). A unit of length almost one non-hundred millionth (10 s) centimeter. The Angstrom is defined in terms of the wavelength of the red line of cadmium (6438.4696 A). Used in stating distances between atoms, dimensions of molecules, wavelengths of short-wave radiation, etc. 

A size distribution P M), expressed along the variable M in angstrom units can replace P( ), and the average size is defined by the equation ... 

The reciprocal Angstrom unit is also conventionally used for momentum (A ) throughout the neutron scattering literature. There was neither a common optical spectroscopic alternative (as there was to justify the adoption of the wavenmnber, cm, for the unit of energy) nor chemical reason (as there was to justify the adoption of the atomic mass unit, u or amu, for the unit of mass). For quantities not defined by lUPAC we have mostly used symbols consistent with the neutron scattering literature [14,15] but have, on rare occasions, been forced to invent our own symbol for the sake of clarity. We provide a table of symbols and units (p. xix). 

Pore diameter The pore diameters (D) for a specified silica gel show a certain distribution. To characterize a defined type of silica gel, the mean pore diameter is indicated. The silica gels most frequently used in thin-layer chromatography have mean pore diameters of 4, 6, 8, and 10 nm. The 40, 60, 80, and 100 designations used for these types of silica gels are based on angstrom units customary in former times. The mean pore diameters as well as the pore size distribution can be determined, e.g., by means of measurement with a mercury porosimeter (7). 

Electron microscopic studies have shown that in the liver of the rat the sinusoids are lined by a discontinuous endothelium. The cells have no well defined basement membrane and may be separated from each other by gaps of several thousand Angstrom units. When particles of smaller diameter than these gaps are introduced into the circulation they can enter the subendothelial space of Disse and come into direct contact with the microvilli on the surface of the hepatic parenchymal cells (Bennet et al. 1959). Following the intravenous injection of chyle, chylomicrons could be seen within the lumen of hepatic sinusoids, within gaps of their endothelial lining and within the subendothelial space (French 1963). 

In order to describe the second-order nonlinear response from the interface of two centrosynnnetric media, the material system may be divided into tlnee regions the interface and the two bulk media. The interface is defined to be the transitional zone where the material properties—such as the electronic structure or molecular orientation of adsorbates—or the electromagnetic fields differ appreciably from the two bulk media. For most systems, this region occurs over a length scale of only a few Angstroms. With respect to the optical radiation, we can thus treat the nonlinearity of the interface as localized to a sheet of polarization. Fonnally, we can describe this sheet by a nonlinear dipole moment per unit area, -P ", which is related to a second-order bulk polarization by hy P - lx, y,r) = y. Flere z is the surface nonnal direction, and the... 

The CIF format not only defines its dictionary of available data names, but restricts the STAR file syntax as well. For example, lines may not exceed 80 characters and data names can contain a maximum of 32 characters. Furthermore, the CIF dictionaiy specifies default units for numeric fields that represent numeric values with units. If the data item is not stored in the default units, then the units code is appended to the data name. Thus cell length a and cell length a pm represent the dimensions ofthe unit cell in Angstrom (the default units conforming to the SI Standard) and picomclcrs, respectively. 

An extraordinary opportunity to manipulate molecular orientation is possible in a monolayer through variation of the surface area (the two-dimensional equivalent of volume, which is symbohzed as A and has units of square angstroms per molecule). The properties most commonly related to surface area are surface pressure it, and surface tension y, both having units of dynes per centimeter. We describe methods for studying the relation of these and other surface properties in the next section, where we also more fully define their meaning. 

The main parameters used to describe a polymer chain are the polymerization index N, which counts the number of repeat units or monomers along the chain, and the size of one monomer or the distance between two neighboring monomers. The monomer size ranges from a few Angstroms for synthetic polymers to a few nanometers for biopolymers. The simplest theoretical description of flexible chain conformations is achieved with the so-called freely-jointed chain (FJC) model, where a polymer consisting of N + I monomers is represented by N bonds defined by bond vectors r/ with j= Each bond vector has a fixed length r,j = a corresponding to the... 

Quantum chemists often use atomic units, a system of units in which h, the proton charge e, and the electron mass m each have a numerical value of 1. In this system, the unit of length is the bohr, defined by 1 bohr = aQ = h2/ me2 = 0.52918 A, where aQ is the Bohr radius and the angstrom (A) is defined by 1 A = 10 8 cm=10 10 m the unit of energy is the hartree, defined by 1 hartree = e2/a0 = 27.212 eV. 

The strategy used in this review to dissect specific fundamental interactions is to isolate first the hydrophobic effects and subsequently other interactions. Within this context the hydrophobic effect is defined as that contribution to the overall thermodynamics of a process that is proportional to the amount of apolar surface that becomes exposed to the solvent (Hermann, 1972 Gill and Wadso, 1976 Livingstone etal, 1991). The apolar surface area exposed to solvent can be computed using various algorithms (Lee and Richards, 1971 Hermann, 1972 Shrake and Rupley, 1973 Connolly, 1983) that yield the accessible surface area (ASA) in units of square angstroms (A2). 

Dg combines D and dz from Eq. (2.19) and is independent of layer thickness. In effect, Dg is the volume number density (D) times the layer thickness (dz), under the assumption that the entire layer thickness is within the laser and spectrometer depths of focus. Since surface refers to a depth of a few angstroms to much less than 1 pm, the assumption is easily satisfied. Note also that Pr in Eq. (13.1) equals the specific intensity, as defined by Eq. (2.20), with the same units. 

This unit is used simply because most atomic sizes and chemical bond lengths fall in the range of one to several angstroms, and the use of either picometers or nanometers is slightly awkward. Next, we use the atmosphere (abbreviated atm) as a unit of pressure. It is not a simple power of 10 times the SI unit of the pascal, but rather is defined as follows ... 

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