Optimality and strong stability of control systems

Optimality and strong stability of control syste

A Dual Gate Spin Field Effect Transistor With Very Low Switching Voltage and Large ON-to-OFF Conductance Ratio

We propose and analyze a novel dual-gate Spin Field Effect Transistor (SpinFET) with half-metallic ferromagnetic source and drain contacts. The transistor has two gate pads that can be biased independently. It can be switched ON or OFF with a few mV change in the differential bias between the two pads, resulting in extremely low dynamic power dissipation during switching. The ratio of ON to OFF conductance remains fairly large (~ 60) up to a temperature of 10 K. This device also has excellent inverter characteristics, making it attractive for applications in low power and high density Boolean logic circuits

A Digital Switch and Femto-Tesla Magnetic Field Sensor Based on Fano Resonance in a Spin Field Effect Transistor

We show that a Spin Field Effect Transistor, realized with a semiconductor quantum wire channel sandwiched between half-metallic ferromagnetic contacts, can have Fano resonances in the transmission spectrum. These resonances appear because the ferromagnets are half-metallic, so that the Fermi level can be placed above the majority but below the minority spin band. In that case, the majority spins will be propagating, but the minority spins will be evanescent. At low temperatures, the Fano resonances can be exploited to implement a digital binary switch that can be turned on or off with a very small gate voltage swing of few tens of microvolts, leading to extremely small dynamic power dissipation during switching. An array of 500,000 x 500,000 such transistors can detect ultrasmall changes in a magnetic field with a sensitivity of 1 femto-Tesla/sqrt{Hz}, if each transistor is biased near a Fano resonance

Impacts of Mixed-Wettability on Brine Drainage and Supercritical CO2 Storage Efficiency in a 2.5-D Heterogeneous Micromodel

Geological carbon storage (GCS) involves unstable drainage processes, the formation of patterns in a morphologically unstable interface between two fluids in a porous medium during drainage. The unstable drainage processes affect CO2 storage efficiency and plume distribution and can be greatly complicated by the mixed-wet nature of rock surfaces common in hydrocarbon reservoirs where supercritical CO2 (scCO2) is used in enhanced oil recovery. We performed scCO2 injection (brine drainage) experiments at 8.5 MPa and 45°C in heterogeneous micromodels, two mixed-wet with varying water- and intermediate-wet patches, and one water-wet. The flow regime changes from capillary fingering through crossover to viscous fingering in the micromodels of the same pore geometry but different wetting surfaces at displacement rates with logCa (capillary number) increasing from −8.1 to −4.4. While the mixed-wet micromodel with uniformly distributed intermediate-wet patches yields ~0.15 scCO2 saturation increase at both capillary fingering and crossover flow regimes (−8.1 ≤ logCa ≤ − 6.1), the one heterogeneous wetting to scCO2 results in ~0.09 saturation increase only at the crossover flow regime (−7.1 ≤ logCa ≤ − 6.1). The interconnected flow paths in the former are quantified and compared to the channelized scCO2 flow through intermediate-wet patches in the latter by topological analysis. At logCa > − 6.1 (near well), the effects of wettability and pore geometry are suppressed by strong viscous force. Both scCO2 saturation and distribution suggest the importance of wettability on CO2 storage efficiency and plume shape in reservoirs and capillary leakage through caprock at GCS conditions