Voltage Amplitude-Controlled Synaptic Plasticity from Complementary Resistive Switching in Alloying HfOx with AlOx-Based RRAM

In this work, the synaptic plasticity from complementary resistive switching in a HfAlOx-based resistive memory device was emulated by a direct current (DC) voltage sweep, current sweep, and pulse transient. The alloyed HfAlOx dielectric was confirmed by X-ray photoelectron spectroscopy analysis. The negative differential resistance observed before the forming and set processes can be used for interface resistive switching with a low current level. Complementary resistive switching is obtained after the forming process at a negative bias. This unique resistive switching is also suitable for synaptic device applications in which the reset process occurs after an additional set process. The current sweep mode provides more clear information on the complementary resistive switching. Multiple current states are achieved by controlling the amplitude of the set and reset voltages under DC sweep mode. The potentiation and depression characteristics are mimicked by varying the pulse voltage amplitude for synaptic device application in a neuromorphic system. Finally, we demonstrate spike-timing-dependent plasticity by tuning the timing differences between pre-spikes and post-spikes.

Electrochemical Determination of Heparin in Pharmaceuticals with Using Malachite Green

In this paper for determination of heparin in pharmaceuticals by constant-current sweep voltammetry on the mercury-film electrode (MFE) we used cationic malachite green (MG) dye which is capable to form a complex with heparin. In the 0.05 M potassium tetraoxalate (KH3C4O8∙ 2H2O) buffer solution with pH 1.65 MG had a well-defined peak of electroreduction at -0.46 V (vs. CSE). During the study of electrochemical properties of heparin in complex with MG in cathodic potential range from 0.0 V to -1.3 V on MFE besides the signal from the dye at E = - 0.46 V the second signal at E = –0.87 V was found. Increasing the concentration of heparin in the solution led to decrease of signal intensity at E = -0.87 V. Optimum conditions for the electrochemical determination of heparin in dosage form with using MG were picked up. Influence of auxiliary components of heparin pharmacological solution on electroreduction of the complex MG-Hep was investigated. Under optimal conditions the decrease of reduction peak currents at E = -0.87 V was proportional to heparin concentration in the range from 3.9 ∙ 10-4mg/ml to 3.9 ∙ 10-3mg/ml.