Concurrent Backscatter Streaming from Batteryless and Wireless Sensor Tags with Multiple Subcarrier Multiple Access

This paper proposes a novel multiple access method that enables concurrent sensor data streaming from multiple batteryless, wireless sensor tags. The access method is a pseudo-FDMA scheme based on the subcarrier backscatter communication principle, which is widely employed in passive RFID and radar systems. Concurrency is realized by assigning a dedicated subcarrier to each sensor tag and letting all sensor tags backscatter simultaneously. Because of the nature of the subcarrier, which is produced by constant rate switching of antenna impedance without any channel filter in the sensor tag, the tag-to-reader link always exhibits harmonics. Thus, it is important to reject harmonics when concurrent data streaming is required. This paper proposes a harmonics rejecting receiver to allow simultaneous multiple subcarrier usage. This paper particularly focuses on analog sensor data streaming which minimizes the functional requirements on the sensor tag and frequency bandwidth. The harmonics rejection receiver is realized by carefully handling group delay and phase delay of the subcarrier envelope and the carrier signal to accurately produce replica of the harmonics by introducing Hilbert and inverse Hilbert transformations. A numerical simulator with Simulink and a hardware implementation with USRP and LabVIEW have been developed. Simulations and experiments reveal that even if the CIR before harmonics rejection is 0dB, the proposed receiver recovers the original sensor data with over 0.98 cross-correlation

Heat Transfer Enhancement by Using Fin for MH Hydrogen Storage Tank - Discuss on the Geometrical Optimization of Fin -

The expectation for renewable energy is rising from the viewpoints of recent environmental problems and energy problems. The reason why renewable energy is not widespread is that there are temporal and spatial restrictions on real application. There is an increasing interest in hydrogen energy as energy that compensates for such weaknesses of renewable energy.　Hydrogen can easily converted to be thermal energy, mechanical energy, electric energy and used. It is important to establish effective saving techniques for effective development of hydrogen energy systems. Three methods of liquification, pressurization and metal hydride (on briefly, referred to as MH) are the major hydrogen energy storage methods. In this study, we focus on the hydrogen storage by using the metal hydride. MH can storage hydrogen with high density, and it can be used at low temperature and low pressure, but has the disadvantage that the release rate of hydrogen due to the low effective thermal conductivity of the MH alloy layer. In this study, the heat transfer enhancement effects of several fins on metal hydride particle layer are estimated by experiment and simulation. The unsteady state heat conduction calculation of MH alloy layer with and without fins was conducted with the Solidworks simulation soft and, the experimental and the calculation parameters are charging volume ratio of fins, and the shapes of fin like as cross fin and circular cross fin. Another estimation parameter is the diameter of storage tank. One storage tankhas an outer diameter of 80 mm, an inner diameter of 78 mm, the other has an outer diameter of 25 mm and an inner diameter of 23.5 mm. The number of fins was increased until the charging volume ratio of the fin, 25 volume %, we estimated the heat transfer enhancement influence of the fins on the MH ally layer. According to our calculation results, the effective thermal conductivity is increased with increasing of charging volume ratio of fin, but this heat transfer enhancing effect is saturated at over 10 volume % of it. In oursimulation model of a circle cross fin, the tank which have an outer diameter of 52 mm and an inner diameter of 50 mmwas used. In the simulation results of using circle cross fins cases, the highest heat transfer enhancement effect was obtained when circular diameter of circular cross fin was 24 mm. Compared with cross fins (which has a heat transfer enhancing effect of 4.68 times compared with without fins), the volume content of circular cross fin was 1.4% higher than that of cross fin. However, the heat transfer enhancement effect of circular cross fin was 2.46 times higher than that of cross fin. And, it is confirmed that circle cross fin which have charging volume ratio, under 10% can achieve a high heat transfer enhancing effect and is suitable to heat transfer enhancing of MH particle layer

Helmholtz: A Verifier for Tezos Smart Contracts Based on Refinement Types

A smart contract is a program executed on a blockchain, based on which many cryptocurrencies are implemented, and is being used for automating transactions. Due to the large amount of money that smart contracts deal with, there is a surging demand for a method that can statically and formally verify them. This article describes our type-based static verification tool HELMHOLTZ for Michelson, which is a statically typed stack-based language for writing smart contracts that are executed on the blockchain platform Tezos. HELMHOLTZ is designed on top of our extension of Michelson’s type system with refinement types. HELMHOLTZ takes a Michelson program annotated with a user-defined specification written in the form of a refinement type as input; it then typechecks the program against the specification based on the refinement type system, discharging the generated verification conditions with the SMT solver Z3. We briefly introduce our refinement type system for the core calculus Mini-Michelson of Michelson, which incorporates the characteristic features such as compound datatypes (e.g., lists and pairs), higher-order functions, and invocation of another contract. HELMHOLTZ successfully verifies several practical Michelson programs, including one that transfers money to an account and that checks a digital signature

Helmholtz: A Verifier for Tezos Smart Contracts Based on Refinement Types

27th International Conference, TACAS 2021, Held as Part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2021, Luxembourg City, Luxembourg, March 27 - April 1, 2021Part of the Lecture Notes in Computer Science book series (LNTCS, volume 12652)A smart contract is a program executed on a blockchain, based on which many cryptocurrencies are implemented, and is being used for automating transactions. Due to the large amount of money that smart contracts deal with, there is a surging demand for a method that can statically and formally verify them. This tool paper describes our type-based static verification tool HELMHOLTZ for Michelson, which is a statically typed stack-based language for writing smart contracts that are executed on the blockchain platform Tezos. HELMHOLTZ is designed on top of our extension of Michelson’s type system with refinement types. HELMHOLTZ takes a Michelson program annotated with a user-defined specification written in the form of a refinement type as input; it then typechecks the program against the specification based on the refinement type system, discharging the generated verification conditions with the SMT solver Z3. We briefly introduce our refinement type system for the core calculus Mini-Michelson of Michelson, which incorporates the characteristic features such as compound datatypes (e.g., lists and pairs), higher-order functions, and invocation of another contract. HELMHOLTZ successfully verifies several practical Michelson programs, including one that transfers money to an account and that checks a digital signature