Anisotropy
Anisotropy (/ˌænaɪˈsɒtrəpi, ˌænɪ-/) is the structural property of non-uniformity in different directions, as opposed to isotropy.
In the field of computer graphics, an anisotropic surface changes in appearance as it rotates about its geometric normal, as is the case with velvet.
Anisotropic filtering (AF) is a method of enhancing the image quality of textures on surfaces that are far away and viewed at a shallow angle.
Older techniques, such as bilinear and trilinear filtering, do not take into account the angle a surface is viewed from, which can result in aliasing or blurring of textures.
Anisotropy measurements reveal the average angular displacement of the fluorophore that occurs between absorption and subsequent emission of a photon.
In NMR spectroscopy, the orientation of nuclei with respect to the applied magnetic field determines their chemical shift.
This abnormal electron density affects the applied magnetic field and causes the observed chemical shift to change.
Their experiment demonstrated the Doppler shift caused by the movement of the earth with respect to the early Universe matter, the source of the radiation.
[1] Cosmic anisotropy has also been seen in the alignment of galaxies' rotation axes and polarization angles of quasars.
Heat conduction is more commonly anisotropic, which implies that detailed geometric modeling of typically diverse materials being thermally managed is required.
[2] Many crystals are anisotropic to light ("optical anisotropy"), and exhibit properties such as birefringence.
Measuring the effects of anisotropy in seismic data can provide important information about processes and mineralogy in the Earth; significant seismic anisotropy has been detected in the Earth's crust, mantle, and inner core.
Formation evaluation instruments measure this conductivity or resistivity, and the results are used to help find oil and gas in wells.
When calculating groundwater flow to drains[4] or to wells,[5] the difference between horizontal and vertical permeability must be taken into account; otherwise the results may be subject to error.
Igneous rock like granite also shows the anisotropy due to the orientation of the minerals during the solidification process.
[6] Anisotropy is also a well-known property in medical ultrasound imaging describing a different resulting echogenicity of soft tissues, such as tendons, when the angle of the transducer is changed.
[7][8] When a material is polycrystalline, the directional dependence on properties is often related to the processing techniques it has undergone.
Textured materials are often the result of processing techniques like cold rolling, wire drawing, and heat treatment.
Mechanical properties of materials such as Young's modulus, ductility, yield strength, and high-temperature creep rate, are often dependent on the direction of measurement.
[9] Fourth-rank tensor properties, like the elastic constants, are anisotropic, even for materials with cubic symmetry.
For face-centered cubic materials such as nickel and copper, the stiffness is highest along the <111> direction, normal to the close-packed planes, and smallest parallel to <100>.
, as the ratio between the empirically determined shear modulus for the cubic material and its (isotropic) equivalent:
Limitation of the Zener ratio to cubic materials is waived in the Tensorial anisotropy index AT [10] that takes into consideration all the 27 components of the fully anisotropic stiffness tensor.
Due to the highly randomized orientation of macromolecules in polymeric materials, polymers are in general described as isotropic.
However, mechanically gradient polymers can be engineered to have directionally dependent properties through processing techniques or introduction of anisotropy-inducing elements.
Anisotropic etching can also refer to certain chemical etchants used to etch a certain material preferentially over certain crystallographic planes (e.g., KOH etching of silicon [100] produces pyramid-like structures) Diffusion tensor imaging is an MRI technique that involves measuring the fractional anisotropy of the random motion (Brownian motion) of water molecules in the brain.
Water molecules located in fiber tracts are more likely to move anisotropically, since they are restricted in their movement (they move more in the dimension parallel to the fiber tract rather than in the two dimensions orthogonal to it), whereas water molecules dispersed in the rest of the brain have less restricted movement and therefore display more isotropy.
This difference in fractional anisotropy is exploited to create a map of the fiber tracts in the brains of the individual.
It is of interest because, with knowledge of the anisotropy function as defined, a measurement of the BRDF from a single viewing direction (say,
) yields a measure of the total scene reflectance (planar albedo) for that specific incident geometry (say,
