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At least 271 records · Page 15Linked to original sources

Discussion of Bogerts' temporolimbic system theory of paranoid schizophrenia.

Olney and Farber present their work with N-methyl-D-aspartate (NMDA) antagonists, which are psychotogens, and propose that the structural changes described by Bogerts could be accounted for by a two-stage process. The first stage of the process would occur early in life and would culminate in the selective loss of NMDA-receptor bearing gamma-aminobutyric acid (GABA)ergic neurons and thus render the brain into a NMDA receptor hypofunctional (NRH) state. Such a loss would set the foundation for the second stage in which the neural circuits that have been altered by the loss of these GABAergic interneurons would become activated in late adolescence but would be dysfunctional. Dysfunction of this circuit would lead to the psychopathology of schizophrenia and potentially, if severe enough, to neuronal degeneration. Thus, the changes described by Bogerts could originate partially in early life and partially in adulthood. Based on their animal model, the authors suggest studies that should be carried out in humans.

Adolescent↗

Zero-order drug delivery system: theory and preliminary testing.

A new approach to zero-order drug delivery that includes geometric factors is described. An experimental device based on the theory was tested by following the release of stearic acid into ethanol. Three separate trials indicated that the solid was released via a zero-order process in a reproducible manner.

Delayed-Action Preparations↗

Asymmetric spin-echo imaging of magnetically inhomogeneous systems: theory, experiment, and numerical studies.

The ability of the asymmetric spin-echo (ASE) pulse sequence to provide different degrees of spin-echo (SE)-type and gradient-echo (GE)-type contrast when imaging media containing magnetic inhomogeneities is investigated. The dependence of the ASE signal on the size of magnetic field perturbers is examined using theory, computer simulations, and experiment. A theoretical prediction of the ASE signal is obtained using the Anderson-Weiss mean field theory, the results of which are qualitatively supported by computer simulations and experimental studies. It is shown that the ASE sequence can be used to tune the range of perturber sizes that provide the largest contributions to susceptibility contrast effects.

Artifacts↗

Understanding, planning, and managing tooth movement: orthodontic force system theory.

A simple force may cause translation and/or rotation of the tooth upon which it acts. The closer the line of force to the tooth's center of resistance, the greater is the proportion of translation relative to rotation, and vice versa. When a tooth is subjected to a tipping moment, strain is concentrated in the areas of the alveolar crest and root apex. This may explain how a light force can tip a tooth readily, while translation, involving a more even distribution of strain throughout the length of the root, requires more force with little or no moment. It is difficult to sustain a desired combination of rotational and translational movement over any significant distance. Couples induce rotation only. Couples and simple forces can be used in combinations to effect movements that are not possible with either one alone. Molars provide anchorage for incisor intrusion. This "vertical anchorage" can be reinforced by elastics producing moments opposite those produced by arch wire anchor bends. Calculation of the elastics' contribution provides an indication of the intrusive force that may be applied to incisors without reciprocal molar tipping. The common use of the term center of rotation in orthodontics may be inappropriate and/or confusing. It may be more accurate and straightforward to view most tooth movements as combinations of linear translation with rotation about the center of resistance.

Adolescent↗