Junya Suehiro

Intentional controlled islanding (ICI) is a crucial strategy to avert power system collapse and blackouts caused by severe disturbances. This paper introduces an innovative IoT-based ICI strategy that identifies the optimal location for system segmentation during emergencies. Initially, the algorithm transmits essential data from phasor measurement units (PMUs) to the IoT cloud. Subsequently, it calculates the coherency index among all pairs of generators. Leveraging IoT technology increases system accessibility, enabling the real-time detection of changes in network topology post-disturbance and allowing the coherency index to adapt accordingly. A novel algorithm is then employed to group coherent generators based on relative coherency index values, eliminating the need to transfer data points elsewhere. The “where to island” subproblem is formulated as a mixed integer linear programming (MILP) model that aims to boost system transient stability by minimizing power flow interruptions in disconnected lines. The model incorporates constraints on generators’ coherency, island connectivity, and node exclusivity. The subsequent layer determines the optimal generation/load actions for each island to prevent system collapse post-separation. Signals from the IoT cloud are relayed to the circuit breakers at the terminals of the optimal cut-set to establish stable isolated islands. Additionally, controllable loads and generation controllers receive signals from the cloud to execute load and/or generation adjustments. The proposed system’s performance is assessed on the IEEE 39-bus system through time-domain simulations on DIgSILENT PowerFactory connected to the ThingSpeak cloud platform. The simulation results demonstrate the effectiveness of the proposed ICI strategy in boosting power system stability.

Coherency assessment is essential for wide-area protection and control of interconnected power systems. The transient response of renewable energy sources (RESs) differs from conventional generators. Therefore, the increasing penetration of RESs necessitates the analysis of hybrid power system dynamics to ensure system security and reliability during various disturbances. This paper proposes an online coherency assessment strategy based on the frequency signals acquired from phasor measurement units (PMUs) to include RESs in the analysis. Moreover, it investigates the impact of RESs on the generators' coherency patterns. Coherent groups are identified under both limited and wide-scale integration of RESs. Moreover, the system's dynamic response is investigated in the case of uniform distribution of RESs among voltage-controlled buses. The 10-machine New England power system is adopted in this study. All time-domain simulations are conducted on the DIgSILENT PowerFactory software. Results demonstrate the viability and effectiveness of the proposed strategy for online coherency identification in hybrid power systems. It also reveals that integrating RESs impacts coherent groups under certain conditions.

Nonthermal atmospheric-pressure discharge plasma is considered important for sterilization. Reactive species, such as active oxygen species, radicals, and nitrate ions, generated by the discharge plasma damage the target bacterial cell wall/membrane and DNA. Several plasma sterilization methods have been proposed, including dielectric barrier discharge (DBD). To achieve effective sterilization, it is necessary to evaluate their characteristics using many parameters. This study aims to demonstrate a proof-of-concept of a novel biological indicator for plasma sterilization. A biological indicator is used to verify sterilization outcomes. Furthermore, we employ DNA-labeled microbeads as biological indicators for the rapid visualization of plasma sterilization. This is based on our recently developed method for visual detection of DNA molecules. If plasma-derived factors cause the degradation of the DNA attached to the microbeads, this can be confirmed by visualization. Herein, we present the correlation between sterilization and visualization in the case of DBD. This method offers a rapid evaluation of plasma sterilization because it easily and quickly determines the sterilization capability of the plasma.

Gas sensors based on ambipolar carbon nanotube (CNT) field-effect transistors with various amounts of CNTs were fabricated by dielectrophoretic assembly. The nitrogen dioxide (NO2) gas response and recovery properties of the transistors were measured to investigate the effect of CNT amount on gas response. For the device with a small amount of CNTs, responses from the CNT bulk and CNT/electrode contacts were observed. For devices with a large amount of CNTs, in which a network-like structure of CNTs was observed near the electrodes, an increased current in both electron and hole conduction regions was observed compared with that for the device with a small amount of CNTs. The increased current in the electron conduction region rapidly decreased during recovery. This response is consistent with that of CNT/CNT X-type contacts, which have a high resistance before NO2 adsorption. Equivalent circuits of CNT channels with CNT/CNT contacts were developed, allowing the transistor behavior to be qualitatively discussed. Evaluation of time constants revealed that CNT/electrode contacts and CNT/CNT X-type contacts exhibited high NO2 adsorption and desorption rates, respectively.

Liquid biopsies for cancer diagnosis using exosomes have been studied. Separating cancer cell-derived exosomes from a sample mixture is crucial, especially when they do not dominate the sample at an early stage of cancer. A method based on their electrical properties could provide a simpler separation than immune-affinity methods. We have identified the differences in electrical properties of cancerous exosomes from those of normal ones, suggesting the possibility for their dielectrophoresis (DEP) based separation. This study separated cancerous exosomes from a mixture of normal exosomes. The DEP of fluorescence-labeled exosomes suspended in aqueous media with varying electrical conductivities was investigated. The observed DEP was quantitatively evaluated using the normalization method accounting for the fluorescence fading effect. The results showed that the cancerous exosomes were preferentially concentrated under the appropriate conditions. This suggests that DEP can enable the selective capture of cancer exosomes without chemical labeling.

Dielectrophoretic impedance measurement (DEPIM) is a method using a microelectrode for measuring a target suspended in a solution by combining dielectrophoretic (DEP) trapping of the target and simultaneous measurement of impedance varied with the trapping. DEPIM can be utilized to detect bacteria and viruses without any chemical additive. Since DEPIM efficiency depends on the DEP trapping dominated by the microelectrode shape. This study aimed to demonstrate a new microelectrode design to increase bacteria detection efficiency instead of the conventional interdigitated microelectrode. The microelectrode having a serpentine gap as a sinusoidal waveform profile was proposed. The new microelectrode was compared with the interdigitated one in numerical simulation and experiments. The numerical simulation demonstrates that the serpentine microelectrode traps all the targets in a laminar flow in a microchannel. In contrast, the interdigitated one placed parallel to the microchannel doesn't because the target flowing away from the edges of the microelectrode cannot be trapped. The experiments using three kinds of bacteria were carried out. It was demonstrated that the serpentine microelectrode represented a sensitivity 10 ⁴ times higher than the interdigitated one when a small amount of the sample solution was tested for a short time (1 min).

An all-solid-state pH sensing system utilizing a stainless steel vessel (SUS304) and a pH-insensitive diamond solution-gate field-effect transistor (SGFET) is presented here to explain the interaction between stainless steel vessel and field-effect transistor (FET) pH sensors for the first time. A pH sensitive ion-sensitive field-effect transistor (ISFET) was first used to show the change of the sensing behavior from 47.78 mV/pH to -4.73 mV/pH when using an Ag/AgCl electrode and stainless steel vessel as the gate, respectively. This intriguing sensing behavior was investigated by developing large and small-signal equivalent circuit models in a transistor circuit for both the Ag/AgCl and the stainless steel vessel gate. The result shows that the targeted ion change ΔQ _h corresponding to the pH sensitivity has been offset which explains the phenomenon observed when using the pH sensitive ISFET with the stainless steel vessel. We then hypothesize that combining a pH insensitive device with the stainless steel vessel gate should show a pH sensitivity close to the Nernst response. To validate this, a pH insensitive diamond SGFET was then fabricated and combined with the stainless steel vessel for pH measurements. The system demonstrates a high pH sensitivity at -54.18 mV/pH across a wide range of pH solutions (pH 2-12) and remains stable in elevated temperatures when measured with a potentiostat setup at 80 °C. The results also suggest that this all-solid-state sensing system has great potential to be used in the food and beverage industry where stainless steel is widely employed due to its excellent corrosion resistance, low cost, and high sensing capabilities.