There is little information on Nickel (Ni) adsorption by calcareous soils of Iran. The pattern of Ni retention and its relationships with soil properties in soils from the southern part of Iran (SSI) and northern part of Iran (SNI) was studied. Amount of Ni adsorption was calculated after the equilibration of 1 g soil samples in duplicate with 25 mL of 0.01 M CaCl 2 solution containing 10 to 1000 mg Ni L −1 . Freundlich, Langmuir, Temkin, Dubinin-Radushkevich, and Redlich-Peterson isotherms were fitted to Ni adsorption data. The fits to Langmuir, Freundlich, and Redlich-Peterson adsorption models were closer than other isotherms. The intercept of Freundlich equation (A F ) and maximum buffering capacity of Langmuir (b L X m ) was significantly correlated with clay in SSI whereas in SNI it was related to pH and organic matter (OM). Adsorption maxima (X m ) of Langmuir isotherm was correlated with cation exchange capacity (CEC) in both groups of soils. Variation of Redlich-Peterson constants (a R P and k R P ) in SSI was due to combined effects of CEC, acid oxalate extractable Fe (Fe o ) and OM while they did not show significant relationship with soil properties in SNI. It appeared that clay, CEC, OM and pH are the main factors regulating Ni retention in the soils studied while calcium carbonate equivalent does not significantly affect Ni retention.

A low voltage analog VLSI circuit model for Hodgkin–Huxley (HH) neuron cell equations (HH neuron model) is presented. Floating gate MOSFET (FGMOS) transistors in weak inversion region have been used to model HH equations such as gating variables, [Formula: see text] and [Formula: see text] functions and combined action of [Formula: see text], [Formula: see text] and [Formula: see text]. The combination of [Formula: see text], [Formula: see text] and [Formula: see text] controls the Na[Formula: see text] and K[Formula: see text] channel currents. The superiorities of the proposed circuits are low supply voltage, low power consumption, less circuit complexity and as a result, low costs are compared to the previous works. The proposed circuit which uses 24 transistors is simulated in Hspice software using 0.18[Formula: see text] technology and consumes 119[Formula: see text][Formula: see text]W.

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