Motion artifact

Apart from the sheer complexity of the static stmctures of biomolecules, they are also rather labile. On the one hand this means that especial consideration must be given to the fact (for example in electron microscopy) that samples have to be dried, possibly stained, and then measured in high vacuum, which may introduce artifacts into the observed images [5]. On the other, apart from the vexing question of whether a protein in a crystal has the same stmcture as one freely diffusing in solution, the static stmcture resulting from an x-ray diffraction experiment gives few clues to the molecular motions on which operation of an enzyme depends [6]. 

A problematic artifact associated with MRI arises when the imaged subject moves duriag acquisition of the / -space data. Such motion may result ia a discontiauity ia the frequency-encoded or phase-encoding direction data of / -space. When Fourier transformed, such a discontiauity causes a blurred band across the image corresponding to the object that moved. Such an artifact ia an image is referred to as a motion artifact. 

The absence of an electron from a covalent bond leaves a hole and the neighboring valence electron can vacate its covalent bond to fill the hole, thereby creating a hole in a new location. The new hole can, in turn, be filled by a valence electron from another covalent bond, and so on. Hence, a mechanism is estabUshed for electrical conduction that involves the motion of valence electrons but not free electrons. Although a hole is a conceptual artifact, it can be described as a concrete physical entity to keep track of the motion of the valence electrons. Because holes and electrons move in opposite directions under the influence of an electric field, a hole has the same magnitude of charge as an electron but is opposite in sign. 

One could view the occurrence of the metric terms in the equations of motion as an annoying complication, but we hold a more positive view. First they assure that whatever the choice of parameters to be used as dynamical variables, that choice will not introduce unphysical artifacts. Second, the metric terms are another component of the theory with potential for providing guiding principles for development of XC models. Those terms also allow the mathematical origin of physical affects to be assigned. 

A similar concern due to lateral motion also applies to purely qualitative imaging. Sugisaki et al. [38] observed an artifact in their simultaneously topographic and adhesion... 

Evans and Baranyai [51, 52] have explored what they describe as a nonlinear generalization of Prigogine s principle of minimum entropy production. In their theory the rate of (first) entropy production is equated to the rate of phase space compression. Since phase space is incompressible under Hamilton s equations of motion, which all real systems obey, the compression of phase space that occurs in nonequilibrium molecular dynamics (NEMD) simulations is purely an artifact of the non-Hamiltonian equations of motion that arise in implementing the Evans-Hoover thermostat [53, 54]. (See Section VIIIC for a critical discussion of the NEMD method.) While the NEMD method is a valid simulation approach in the linear regime, the phase space compression induced by the thermostat awaits physical interpretation even if it does turn out to be related to the rate of first entropy production, then the hurdle posed by Question (3) remains to be surmounted. 

Ultrarapid computed tomography may minimize artifact from heart motion during contraction and relaxation and provides a semiquantitative assessment of calcium content in coronary arteries. 

A. Devaraj, M. Izzetoglu, K. Izzetoglu, S. C. Bunce, C. Y. Li, and B. Onaral. Motion artifact removal in FNIR spectroscopy for real-world applications. In Nondestructive Sensing for Food Safety, Quality, and Natural Resources. Edited by Chen, Yud-Ren Tu, Shu-I. Proceedings of the SPIE, Volume 5588, pp. 22f-229 (2004)., pages 224-229, October 2004. 

Undue specimen motion is the most preventable introduced artifact, and can present as a blurr or smear of scan information throughout the specimen. Additionally, if the specimen was properly secured in one region but not another, the motion can be focally constrained to the unsecured region. Less likely is physical motion external to the scanner (i.e., heavy infrastructure construction, tremors, etc.) though this should also be considered if motion artifact is not addressed by other means. 

Fig. 39. Velocity imaging of the vertical (p4 component projected onto the cross-section of a granular bed of poppy seeds. The data are averaged over the height of the bed (2 cm). Velocities are normalized to the maximum upward motion (which is set to unity). The white line indicates = 0 and separates upward (inner part) from downward motion (outer part). Vertical lines are processing artifacts (J22).

A weaker alternative would be to admit Eq = 0 in a preferred frame of reference E, but to allow for a local nonzero rest mass mo 10-34 g as an artifact of the total motion of the earth relative to E [10]. However, this value is too high compared to the limits set to the photon mass, typically in the range mo 10-52-10 43 g [11]. At any rate, there are two implications of a nonzero photonic mass ... 

Hence, they concluded that Miller s experimentally observed seasonal variations were simple experimental artifacts Evidently, Shankland et al. [56] did not grasp the full meaning of Miller s suggestion that the sun was in motion relative to the fixed stars. 

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