Voltage-driven gigahertz frequency tuning of spin Hall nano-oscillators

Spin Hall nano-oscillators (SHNOs) exploiting current-driven magnetization auto-oscillation have recently received much attention because of their potential for oscillator-based neuromorphic computing. Widespread neuromorphic application with SHNOs requires an energy-efficient way to tune oscillation frequency in broad ranges and store trained frequencies in SHNOs without the need for additional memory circuitry. Voltage control of oscillation frequency of SHNOs was experimentally demonstrated, but the voltage-driven frequency tuning was volatile and limited to megahertz ranges. Here, we show that the frequency of SHNO is controlled up to 2.1 GHz by a moderate electric field of 1.25 MV/cm. The large frequency tuning is attributed to the voltage-controlled magnetic anisotropy (VCMA) in a perpendicularly magnetized Ta/Pt/[Co/Ni]n/Co/AlOx structure. Moreover, non-volatile VCMA effect enables control of the cumulative frequency using repetitive voltage pulses, which mimic the potentiation and depression functions of biological synapses. Our results suggest that the voltage-driven frequency tuning of SHNOs facilitates the development of energy-efficient spin-based neuromorphic devices.

The Combination Effects of Immersion and Moderate Electric Field (MEF) Treatments on Enhancement of Deliverable Iron From Kale Leaves (Brassica oleracea L. Var. Sabellica)

Objectives Due to anti-nutrients found in leafy greens and the physical-chemical properties of inorganic iron found in plant sources, iron bioavailability is lower relative to heme iron rich in red meat. We tested a series of novel food processing techniques (i.e., vacuum treatment, bath-immersion, and moderate electric field (MEF) to improve iron content and potential delivery, using kale (Brassica oleracea L. var. sabellica) as our model green leafy vegetable. Methods A ferrous sulfate (FeSO4) solution was prepared and fresh kale samples (n = 3 per treatment) were immersed in the solution alone (control), treated with vacuum alone, vacuum + water bath (30–50°C), or vacuum + water bath + MEF (15 V/cm at frequency of 60 Hz at 40–60°C) for up to 15 min. Effects of immersion (24 h at 4°C) after each treatment step were also tested. Treated samples were rinsed in deionized water before freezing and lyophilization prior to analysis. Concentrations of chlorophyll and iron chlorophyll derivatives were measured in both lipophilic and polar leaf extracts using ultra high liquid chromatography-diode array detection (UHPLC-DAD). Atomic absorption spectrometry was used to measure iron concentrations. Differences between treatment groups were analyzed with one-way ANOVA, followed by Tukey's posthoc testing for pairwise comparisons (P < 0.05 considered statistically significant). Results Vacuum followed by immersion produced kale with ∼1500x more iron than the kale control, while MEF-treated kale had the greatest increase in iron concentration without immersion (∼4000x than control). Two novel metabolites, tentatively iron chlorophyllin derivatives, were observed in the lipophilic extracts of the MEF and immersed kale samples, and identifies are being pursued via UHPLC-high resolution mass spectrometry metabolomics. Conclusions The novel food processing techniques employed here produced kale with iron concentrations significantly higher than the kale control, as well as other iron-rich plant foods (e.g., ∼40x times higher than black beans). Future testing will determine if this” iron-enhanced” kale has the potential to better deliver iron as compared to untreated kale, an FeSO4 supplement, or a heme-rich source. Funding Sources This research was supported by OARDC via a SEEDS grant and also via Hatch #W4122.

Increase of mass transfer rates during osmotic dehydration of apples by application of moderate electric field

Osmotic dehydration (OD) is a drying process that consists in placing the food in contact with concentrated solutions of soluble solids to reduce its water activity. The use of moderate electric field (MEF) may promote increase of the mass transfer rates due to the non-thermal effects of electroporation and permeabilization of the cells. In this context, the objective of this study was to investigate the mass transfer process kinetics during apples OD assisted by MEF, evaluating the non-thermal effects of this emerging technology. The experiments were conducted with sucrose solutions (40, 50 and 60%, m/m) at 40 °C. Samples were submitted to electrical field strength (0, 5.5 and 11.0 Vcm−1), according to an experimental design. Results indicated that the application of MEF favoured water loss and solid gain. The effective mass diffusivities of water and solids increased as voltage applied increases. Moreover, MEF negatively influenced color and reducing capacity of the samples.