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In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of switch is an electromechanical device consisting of one or more sets of movable electrical contacts connected to external circuits. When a pair of contacts is touching current can pass between them, while when the contacts are separated no current can flow. Switches are made in many different configurations; they may have multiple sets of contacts controlled by the same knob or actuator, and the contacts may operate simultaneously, sequentially, or alternately. A switch may be operated manually, for example, a light switch or a keyboard button, or may function as a sensing element to sense the position of a machine part, liquid level, pressure, or temperature, such as a thermostat. Many specialized forms exist, such as the toggle switch, rotary switch, mercury switch, push-button switch, reversing switch, relay, and circuit breaker. A common use is control of lighting, where multiple switches may be wired into one circuit to allow convenient control of light fixtures. Switches in high-powered circuits must have special construction to prevent destructive arcing when they are opened. The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts, which are connected to external circuits. Each set of contacts can be in one of two states: either "closed" meaning the contacts are touching and electricity can flow between them, or "open", meaning the contacts are separated and the switch is nonconducting. The mechanism actuating the transition between these two states (open or closed) is usually (there are other types of actions) either an "alternate action" (flip the switch for continuous "on" or "off") or "momentary" (push for "on" and release for "off") type.

Flexibilisation of Biogas-Based Power-to-Gas Processes: A Techno-Economic and Experimental Assessment

Andreas Gantenbein

Biogas-based power-to-X technology allows storing renewable electricity, while producing CO2-neutral products.This work investigates the conversion and upgrading of digestion-derived gas mixtures with focus on increasing the operational flexibility of the overall process. Compensation of fluctuations in the feed gases enable a better economic predictability of the processes and increase the product gas output.A techno-economic evaluation was performed on bubbling fluidised bed (BFB) methanation and biological methanation for CO2 conversion in all-year operation. Each considered process was modelled and optimised to obtain grid-ready biomethane. Rate-based models were used for the main units (BFB reactor, H2-separation membrane). For the biological methanation, simulated performance data from literature were included. The analysis revealed a 17 - 19% lower production cost for BFB methanation, mainly due to lower investment cost for the main reactor vessel. Instead of using PEM electrolysis, high temperature electrolysis (SOE) would allow for heat integration with the BFB reactor, which increases the plant efficiency from 54% to 73% (LHV). A further production cost reduction can be achieved by direct methanation of biogas, omitting prior separation of CO2.Based on gas separation experiments with a commercial biogas upgrading module (Evonik Sepuran) performed in a TRL 5 plant, a flexible upgrading concept using a permeation model was developed. It allows to swiftly switch between conventional membrane-based CO2 separation by a 2-stage membrane unit and direct methanation of biogas and subsequent H2 recycling.A techno-economic analysis was performed on the flexible upgrading concept. The operation hours of the electrolyser were determined by applying a threshold to the electricity price distribution of the past years. The sensitivity on electricity cost (i.e. PtG operation hours) is clearly reduced with the flexible processes, resulting in a better economic predictability of the overall process, compared to a pure PtG installation. System analysis shows the need to allow part load operation of the methanation.Symmetric part load operation (reduced availability of CO2 and H2) was tested in a field experiment by direct methanation of biogas with subsequent H2 recycling in the TRL 5 methanation pilot plant. Stable operation of the methanation plant could be achieved at part load levels from 45% to 100% with closed recycle loop. The BFB reactor alone was tested in a load range of 20 to 100%. A dynamic experiment demonstrated fast, successive load changes while still producing grid-ready biomethane.Asymmetric part load (only H2 limiting) operation was investigated by process simulations and field experiments. Since CO2 is present in the system in an over-stoichiometric amount, H2 recycle and CO2 separation have to be performed simultaneously. Process simulations showed that selecting a most ideal PtG configuration based on technical feasibility is difficult, as further constraints, such as overall economics and operation scheduling have to be considered in process design and evaluation. In all cases, the CO2 separation from the integrated processes leads to a loss of H2 and CH4 from the process. The introduction of an additional membrane stage with a sweep stream is proposed to reduce the loss of reactive gases via the off gas stream.

EPFL2022

CHIMERA: Combining Ring-LWE-based Fully Homomorphic Encryption Schemes

Dimitar Petkov Jetchev

This paper proposes a practical hybrid solution for combining and switching between three popular Ring-LWE-based FHE schemes: TFHE, B/FV and HEAAN. This is achieved by first mapping the different plaintext spaces to a common algebraic structure and then by applying efficient switching algorithms. This approach has many practical applications. First and foremost, it becomes an integral tool for the recent standardization initiatives of homomorphic schemes and common APIs. Then, it can be used in many real-life scenarios where operations of different nature and not achievable within a single FHE scheme have to be performed and where it is important to efficiently switch from one scheme to another. Finally, as a byproduct of our analysis we introduce the notion of a FHE module structure, that generalizes the notion of the external product, but can certainly be of independent interest in future research in FHE.

WALTER DE GRUYTER GMBH2020

Resonant optical trapping in hollow photonic crystal cavities and its potential use for bacterial characterisation

Rita Therisod

During the last decade, the development of optofluidic chips has become a large field of research. The integration of nano and microstructures with microfluidics layers allowed for the miniaturisation of a number of tools traditionally used in laboratories and optofluidic systems found their main applications in lab-on-a-chip and sensing platforms. At the same time, optical tweezers have become the tool of choice for the trapping and the manipulation of nano and micrometer-sized objects, that can be inert (dielectric or metallic particles) or biological (proteins, bacteria, viruses,...). In this context, nanostructures are the ideal candidate for tweezers miniaturisation, thanks to their ability to strongly confine light in small volumes and hence to generate intense gradient forces. This work reports on the fabrication of an optofluidic chip based on a two-dimensional photonic crystal cavity and on its use in particle and bacteria differentiation. The cavity has a hollow design that maximises the overlap between the confined field and the trapped objects and it supports Self-Induced Back-Action effects that allow for reducing the trapping power (down to few microwatts) and to simultaneously acquire information of the trapped specimen. The system is excited in an end-fire setup and the detection is carried out by recording the light intensity transmitted through the photonic crystal. The fabrication process, that is entirely carried out in the Institue of Physics and in the Center of MicroNanoTechnology cleanrooms, is first detailed. For the cavity design normally used, typical quality factors of 10000 were obtained. Moreover, SU8 mode adaptors were developed to increase the coupling with lensed fibers and a microfluidic membrane presenting two injection channels is proposed for rapid switch between liquids. The trapping and the differentiation of 250 and 500 nm polystyrene is then presented. The differentiation can be achieved qualitatively by direct observation of the transmitted intensity records and quantitatively by the use of histograms and of statistical moments. Finally, the trapping of seven species of living bacteria is shown and their Gram-type is determined by the analysis of the induced transmission increase. This ability to probe the cell wall of bacteria in a fast, label-free and non-destructive way paves the way for applications in biological and biomedical environments.

EPFL2019