A Secure and Efficient Audit Mechanism for Dynamic Shared Data in Cloud Storage

With popularization of cloud services, multiple users easily share and update their data through cloud storage. For data integrity and consistency in the cloud storage, the audit mechanisms were proposed. However, existing approaches have some security vulnerabilities and require a lot of computational overheads. This paper proposes a secure and efficient audit mechanism for dynamic shared data in cloud storage. The proposed scheme prevents a malicious cloud service provider from deceiving an auditor. Moreover, it devises a new index table management method and reduces the auditing cost by employing less complex operations. We prove the resistance against some attacks and show less computation cost and shorter time for auditing when compared with conventional approaches. The results present that the proposed scheme is secure and efficient for cloud storage services managing dynamic shared data

Efficient Privacy-Preserving Matrix Factorization via Fully Homomorphic Encryption

Recommendation systems become popular in our daily life. It is well known that the more the release of users’ personal data, the better the quality of recommendation. However, such services raise serious privacy concerns for users. In this paper, focusing on matrix factorization-based recommendation systems, we propose the first privacy-preserving matrix factorization using fully homomorphic encryption. On inputs of encrypted users\u27 ratings, our protocol performs matrix factorization over the encrypted data and returns encrypted outputs so that the recommendation system knows nothing on rating values and resulting user/item profiles. It provides a way to obfuscate the number and list of items a user rated without harming the accuracy of recommendation, and additionally protects recommender\u27s tuning parameters for business benefit and allows the recommender to optimize the parameters for quality of service. To overcome performance degradation caused by the use of fully homomorphic encryption, we introduce a novel data structure to perform computations over encrypted vectors, which are essential operations for matrix factorization, through secure 2-party computation in part. With the data structure, the proposed protocol requires dozens of times less computation cost over those of previous works. Our experiments on a personal computer with 3.4 GHz 6-cores 64 GB RAM show that the proposed protocol runs in 1.5 minutes per iteration. It is more efficient than Nikolaenko et al.\u27s work proposed in CCS 2013, in which it took about 170 minutes on two servers with 1.9 GHz 16-cores 128 GB RAM

Trophic structure of fish assemblages in two offshore islands (Ulleungdo and Dokdo) of Korea revealed using stable isotope analysis

The objective of this study was to characterize the trophic structure of fish assemblages on the coasts of offshore islands and the eastern mainland of the Korean Peninsula. We compared the seasonal variability in the trophic structure of fish assemblages between the coasts of two island sites (Ulleungdo and Dokdo) and one mainland site (Hupo), which are on a similar latitude. We analyzed the stable carbon and nitrogen isotope ratios (δ13C and δ15N) of fish assemblages during spring (April) and summer (August) 2021. No temporal differences in the isotope values of fish and basal resources (i.e., suspended particulate organic matter (SPOM)) were found over the sampling period at the Hupo site. In contrast, at the Ulleungdo and Dokdo sites, the fishes and SPOM showed seasonal differences in the δ13C and δ15N values between the two seasons. In particular, the fish δ15N values at the island sites were relatively higher in summer compared to those in spring, suggesting the seasonal variation in the food chains and/or trophic status between consumers and their dietary sources. These regional isotopic variations also result in differences in the seasonal tendencies of the isotopic niche parameters of fish assemblages between the mainland and island coasts. Such differences in the seasonal isotopic patterns of fish assemblages suggest a relatively substantial shift in the dietary resources available to fish consumers on island coasts compared to those on the mainland coast. Overall, our results suggest that fish assemblages in offshore island coasts have distinct seasonal variability in trophic characteristics in response to changing environmental conditions, including basal resources, compared with fish food webs on the mainland coast at similar latitudes

Nuclear polarization by optical pumping in InP:Fe above liquid nitrogen temperature

Hyperpolarized nuclear spins are observed in optically pumped iron-doped InP from 70 K to 140 K. P-31 NMR was carried out at 9.28 T (159.8 MHz) during optical excitation with circularly polarized light, using a laser diode (lambda-830 nm) as a source. The enhancement of the nuclear spin polarization by optical pumping at 70 K is estimated to be about 34 for those nuclei in the region of the sample absorbing light. This enhancement decreases with increasing temperature. As the direction of the enhanced nuclear spin polarization is found parallel or antiparallel to the travelling direction of the sigma(+) or sigma(-), the contact hyperfine interaction is dominant compared to the dipolar hyperfine interaction. (C) 2015 Elsevier Inc. All rights reserved

Effective diffusional limitation modeling of a heterogeneous reaction system for computational fluid dynamics application

Diffusional limitation of heterogeneous reaction catalysts is typically fitted or over-generalized without considering the catalyst's physical parameters upon conducting computational fluid dynamics (CFD) analysis of an industrial-scale chemical reactor. Fitting and over-generalization are done to meet computational cost constraints. However, this reduces the reliability of local thermodynamic state analysis and application of calculated results. This study proposes an effective catalytic diffusion-limited model for reliable and cost-effective three-dimensional CFD simulations to overcome such difficulties. The proposed model utilizes simplified equations to compute the diffusional limitation by incorporating the physical parameters of the catalyst. The model is validated using Ni-based cylindrical catalyst pellets for steam-methane reforming and ammonia decomposition reactions, with in-house experiments supporting the fidelity of the model. For practical implementation, the model is applied to three-dimensional CFD simulations of a commercial-scale solid oxide fuel cell (SOFC) hotbox housing a large-scale reformer. Furthermore, a parametric study for inlet gas temperatures and catalyst size is carried out, which provides useful insights into how operating conditions and catalysts affect the transport phenomena and local thermodynamic state of the SOFC hotbox. Consequently, the practicality and versatility of the presented model are established through experiments and simulations

Opto-spintronics in InP using ferromagnetic tunnel spin filters

We demonstrate opto-spintronics using Fe-doped Indium Phosphide (InP). The method is based on optical orientation of InP conduction electron spins which are electrically detected in planar InP/oxide/Ni tunnel spin filters. We separate the optical excitation from electrical detection, avoiding thus additional interactions of photons with the ferromagnet. Interface engineering provides a surface iron accumulation and semiconducting Fe:In2O3 in the oxide tunnel barrier. The spin filtering effect switches to positive or negative asymmetry, depending on the Fe concentration in Fe-x:InP. With respect to the Fe-like electronic structure of these oxides, we can explain the opposite spin selection mechanisms as interface effects. In the temperature region where the InP mobility peaks, we find a maximum of spin-dependent asymmetry of similar to 9% in semi-insulating Fe: InP (001), and show the electrical spin detection in hyperpolarized InP also at room temperature. Such robust electronic spin detection in an InP nanodevice is planned to complement dynamic nuclear polarization experiments

Development and Control of an Electro-Hydraulic Actuator System for an Exoskeleton Robot

Exoskeleton robots have been developed in various fields and are divided into electric and hydraulic exoskeletons according to the actuator type. In the case of hydraulic robots, because a unidirectional pump is applied, there are limitations to the wearer’s walking. In addition, robot systems are complicated, because a directional control valve is required to change the direction of the actuator. To solve these problems, we designed the electro-hydraulic actuator (EHA) system which has both the hydraulic and electric advantages. The EHA system consists of a hydraulic bidirectional pump, a motor, a hydraulic cylinder, and various valves. For the development of the piston pump, we analyzed the gait cycle and considered the flow rate and pulsation rate. In order to reduce the size and weight of the EHA system, the valves were made from one manifold, and the hydraulic circuit was simplified. We verified that the developed EHA system is applicable to robots through position and force control experiments. Because the hydraulic system is nonlinear, we designed a sliding mode control (SMC) and compared it with the proportional integral derivative (PID) controller

Design and Performance of Nonlinear Control for an Electro-Hydraulic Actuator Considering a Wearable Robot

In the development of a wearable robot, compact volume size, high energy efficiency, and a high load capacity linear actuator system are necessary. However, conventional hydraulic actuator systems are difficult to apply to wearable robots. Also, they have nonlinearities because of the presence of hydraulic fluid in a single rod cylinder. Electric linear actuators resolve the problems of hydraulic systems. However, due to their low load capacity, they are not easy to apply to wearable robots. In this paper, a pump-controlled electro-hydraulic actuator (EHA) system that considers the disadvantages of the hydraulic actuator and electric actuator is proposed for a wearable robot. Initially, a locking circuit design is considered for the EHA to give the system load holding capacity. Based on the developed model, the adaptive sliding mode control (ASMC) scheme is designed to resolve the nonlinearity problem of changes in the dynamic system. The ASMC scheme is then modeled and verified with Simulink. In order to verify the performance of the proposed adaptive control with the model, experiments are conducted. The proposed EHA verifies that the ASMC reaches the target value well despite the existence of many model uncertainties