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Physiological evidence is presented that visual receptive fields in the primate eye are shaped like the sum of a Gaussian function and its Laplacian. A new 'difference-of-offset-Gaussians' or DOOG neural mechanism was identified, which provided a plausible neural mechanism for generating such Gaussian derivative-like fields. The DOOG mechanism and the(More)
How do we see the motion of objects as well as their shapes? The Gaussian Derivative (GD) spatial model is extended to time to help answer this question. The GD spatio-temporal model requires only two numbers to describe the complete three-dimensional space-time shapes of individual receptive fields in primate visual cortex. These two numbers are the(More)
The use of the metastable equilibrium solubility (MES) concept to describe the solubility properties of carbonated apatites (CAPs) and human dental enamel (HE) has been well established in previous studies using a range of CAPs with varying carbonate contents and crystallinities. It was shown in these studies that the mean value of the CAP MES is directly(More)
Receptive fields of simple cells in the primate visual cortex were well fit in the space and time domains by the Gaussian Derivative (GD) model for spatio-temporal vision. All 23 fields in the data sample could be fit by one equation. varying only a single shape number and nine geometric transformation parameters. A difference-of-offset-Gaussians (DOOG)(More)
B-type carbonated hydroxyapatites, prepared in aqueous media free of alkali ions, fix ammonium ions present in the reaction medium. A small portion of the carbonate ions introduced into the apatite structure enter by the substitution mechanism (CO3(2-), NH4+)----(PO4(3-), Ca2+). With these results for the structural incorporation of ammonium ions,(More)
Questions remain about which subcomponents of human tooth enamel (TE) are responsible for its crystallographic alpha axis being nearly 0.02A longer than that of pure hydroxyapatite (OHAp) and contracting to that of OHAp on heating. From infrared spectroscopic and X-ray diffraction studies of a synthetic OHAp containing HPO4 and "structural" H2O, it has been(More)
The existence of a monoclinic phase of hydroxyapatite, Ca(2)(PO(4))(4)OH, has been confirmed, by single-crystal structure analysis (weighted "reliability" factor = 3.9 percent on |F|(2)). The structure has space group P21/b, a = 9.4214(8) angstroms, b = 2a, c = 6.8814(7) angstroms, and gamma = 120 degrees , and is analogous to that of chlorapatite. The(More)
Hydroxyapatite synthesized by various "standard" ways exhibits marked differences with preparation method. Specimens were prepared with two precipitation methods, a reflux method, a hydrothermal method, a high-temperature (1000 degrees C) solid-state reaction method, and by conversion of chlorapatite at 1000 degrees C. They were compared in detail by use of(More)