Theoretical Performance Comparison Research Articles

Thermodynamic, environmental, and exergoeconomic analysis of multi-ejector expansion transcritical CO2 supermarket refrigeration cycles in different climate regions of Türkiye

Restrictions on high-GWP refrigerants have made the use of transcritical CO2 refrigeration systems widespread. Using transcritical booster refrigeration cycle in warm climates is unsatisfactory due to its high energy consumption. This paper presents theoretical analysis and performance comparison of three different transcritical CO2 supermarket refrigeration cycle configurations with ejector expansion in Türkiye, which has different climatic regions. Bin-hour data were derived using hourly dry-bulb temperature values for provinces from 7 different regions in Türkiye. The applicability of multi-ejectors to each modeled cycle was also investigated. Annual energy consumption and environmental impact reductions of up to 17% were obtained using ejector expansion cycle compared to booster cycle. Ejector expansion cycles achieved higher performance than booster cycle up to 46% in terms of exergy efficiency at investigated ambient temperatures. Unit product exergy costs of the ejector cycles were found up to 28% lower than booster cycle.

Advances in the development of few-cycle gigawatt-peak-power mid-IR optical parametric amplifiers pumped by Cr:Forsterite laser using non-oxide nonlinear crystals

We demonstrate an experimental and theoretical comparison of non-oxide LiGaS2, HgGa2S4, and AgGaS2 crystals performance for wavelength conversion into the near and mid-IR range 1.5–8 μm in optical parametric amplifier pumped by Cr:Forsterite laser, delivering 100 fs pulses at 1.24 μm. It is shown that exceptionally high total energy conversion efficiency into the idler (4–5 μm) and signal (1.65–1.8 μm) waves up to 18% can be achieved using the HGS crystal, providing high nonlinearity, while the LGS crystal is more preferable for generating few-cycle mid-IR pulses due its unique dispersive properties. Our source features high peak power in gigawatt regime (0.4–2.4 GW) with pulse duration below 80 fs and optical synchronization with high harmonic generation (HHG) and THz beamlines, which is ideal for pump-probe experiments of nonlinear and strong-field physics.

Investigation of single-particle detection of continuous-wave coherent Doppler lidar: theoretical feasibility and performance comparison with multiple-particle detection state

Abstract Single-particle detection with a continuous-wave coherent Doppler lidar (CW-CDL) is an interesting event. Even though some experimental results have been shown in previous literature as evidence of single-particle detection, these results have not been verified from a theoretical point of view. Here, the performance of a CW-CDL with single-particle detection is investigated. Examples of single-particle detection that have been reported in previous literature are verified using theoretical simulation. Furthermore, comparison of signal detection ability between single- and multiple-particle cases is also performed theoretically.

Theoretical comparison analysis of R134a, R1234yf, R452A and R454C refrigerants used in automobile, trailer and commercial and industrial cooling systems

The increasing environmental disasters in recent years are caused by the release of artificial substances into the environment. The majority of artificial-containing emissions originate from petrochemical products. It also contributes to artificially containing refrigerants used in cooling systems. Artificial refrigerants have contributed greatly to the depletion of the ozone layer and subsequently to global warming. Research on new refrigerants as an alternative to refrigerants that contribute to every environmental disaster is of great importance. In this study, theoretical performance comparisons were made between R1234yf, which is an alternative to R134a refrigerant used in automobile air conditioning systems, and R452A, R454C refrigerants, which are used as alternative refrigerants in industrial, commercial and trailer cooling systems. Performance analyses were carried out according to different condenser and evaporator temperatures. Analysis results are given depending on condenser/evaporator pressure ratio, mass flow rate, compressor power, cooling effect coefficient (COP) and compressor outlet temperature. According to the study results, it was observed that the COP value increased with the increase in evaporator temperature, while the compressor inlet-outlet pressure ratio, refrigerant flow rate, compressor power and refrigerant compressor outlet temperature decreased. It was observed that the refrigerant with the highest compressor power and mass flow rate was R452A, followed by R1234yf, R454C and R134a, respectively. R134a was found to have an average of approximately 5.4%, 8.6% and 0.6% higher COP than R1234yf, R452A and R454C, respectively.

IRS-Aided Wireless Powered MEC Systems: TDMA or NOMA for Computation Offloading?

Anintelligent reflecting surface (IRS)-aided wireless-powered mobile edge computing (WP-MEC) system is conceived, where each device’s computational task can be divided into two parts for local computing and offloading to mobile edge computing (MEC) servers, respectively. Both time division multiple access (TDMA) and non-orthogonal multiple access (NOMA) schemes are considered for uplink (UL) offloading. To fully unleash the potential benefits of the IRS, employing multiple IRS beamforming (BF) patterns/vectors in the considered operating frame to create time-selectivity channels, i.e., dynamic IRS BF (DIBF), is in principle possible at the cost of additional signaling overhead. To strike a balance between the system performance and associated signalling overhead, we propose three cases of DIBF configurations based on the maximum number of IRS reconfiguration times. The degree-of-freedom provided by the IRS may introduce different impacts on the TDMA and NOMA-based UL offloading schemes. Thus, it is still fundamentally unknown which multiple access scheme is superior for MEC UL offloading by considering the impact of the IRS. To answer this question, we provide a comprehensively theoretical performance comparison for the TDMA and NOMA-based offloading schemes under the three cases of DIBF configurations by characterizing their achievable computation rate. Analytical results demonstrate that offloading adopting TDMA can achieve the same computation rate as that of NOMA, when all the devices share the same IRS BF vector during the UL offloading. By contrast, computation offloading exploiting TDMA outperforms NOMA, when the IRS BF vector can be flexibly adapted for UL offloading. Then, we propose computationally efficient algorithms by invoking alternating optimization for solving their associated computation rate maximization problems. Our numerical results demonstrate the significant performance gains achieved by the proposed designs over various benchmark schemes and also unveil that the optimal time allocated to downlink wireless power transfer can be effectively reduced with the aid of IRSs, which is beneficial for both the system’s spectral efficiency and its energy efficiency.

Theoretical performance comparison for a regenerator-enhanced three-stage auto-cascade refrigeration system using different zeotropic mixed refrigerants

Auto-cascade refrigeration (ACR) systems are widely used at low temperatures. The selection and ratio optimization of zeotropic refrigerants in ACR systems have an important impact on system performance and environmental protection. This study proposes a three-stage regenerator-enhanced auto-cascade refrigeration (RACR) system. Under certain working conditions, the theoretical performances of the three-stage R134a/R23/R14 ACR and RACR systems were compared, and the influence of the refrigerant mixture ratio on the RACR system performance was explored. The system performances of replacing R134a and R23 with different hydrocarbons were compared under different working conditions. The results demonstrated that RACR performed better than ACR alone. A reasonable adjustment to the mixed refrigerant ratio improved the energy efficiency of the RACR system. Water-cooling conditions for the RACR system were suggested, under which the coefficient of performance, thermodynamic perfectness, and exergy efficiency of R600/R170/R14 were 13.8 %, 12.4 %, and 8.4 % higher than those of R600/R23/R14, respectively. The environmental policy, safety requirements, and energy efficiency were considered to obtain −100 °C, R600/R170/R14 with mass fractions of 0.24/0.12/0.64 was the best choice in a water-cooled RACR system.

Performance comparison and suitable climatic zones of three water-mediated evaporative cooling technologies

Evaporative cooling is an alternative cooling technology to conventional vapor-compression systems with lower energy use and pollution emissions. This paper presents theoretical performance comparison for three water-mediated evaporative coolers and provides a design guideline for choosing evaporative coolers under specific climates and operating boundary conditions. Theoretical solutions of counter-flow evaporative cooling are given and verified with maximum absolute and relative errors of 0.26 K and 1.23% respectively. The heat transfer coefficient of the combined heat and mass transfer is 2.72–4.95 times than the pure heat transfer process if there were no mass transfer. Climatic dividing lines of various technologies are affected by the design parameters of the system, dropping the psychrometric chart into different applicable climatic areas. The simulation results show that the climatic areas in psychometrics where indirect outperforms direct evaporative cooling will expand when increasing the air–water ratio and heat transfer coefficient, and climatic area of series indirect evaporative cooling shrinks when increasing temperature difference. The simplified selection method using such difference in merits is verified by case study, which can serve as a useful guideline for choosing the proper evaporative cooling technology for a wide range of geographical locations.

Link-Delay-Aware Reinforcement Scheduling for Data Aggregation in Massive IoT

Over the past few years, the use of wireless sensor networks in a range of Internet of Things (IoT) scenarios has grown in popularity. Since IoT sensor devices have restricted battery power, a proper IoT data aggregation approach is crucial to prolong the network lifetime. To this end, current approaches typically form a virtual aggregation backbone based on a connected dominating set or maximal independent set to utilize independent transmissions of dominators. However, they usually have a fairly long aggregation delay because the dominators become bottlenecks for receiving data from all dominatees. The problem of time-efficient data aggregation in multichannel duty-cycled IoT sensor networks is analyzed in this paper. We propose a novel aggregation approach, named LInk-delay-aware REinforcement (LIRE), leveraging active slots of sensors to explore a routing structure with pipeline links, then scheduling all transmissions in a bottom-up manner. The reinforcement schedule accelerates the aggregation by exploiting unused channels and time slots left off at every scheduling round. LIRE is evaluated in a variety of simulation scenarios through theoretical analysis and performance comparisons with a state-of-the-art scheme. The simulation results show that LIRE reduces more than 80% aggregation delay compared to the existing scheme.

Modified Multi-Key Fully Homomorphic Encryption Scheme in the Plain Model

Abstract Multi-key fully homomorphic encryption (MFHE) supports arbitrary meaningful computations on encrypted data under different public keys even without access to the secret key, which is well tailored for the secure multiparty computation scenarios. Based on the Gentry–Sahai–Waters scheme (a single-key FHE in Crypto 2013) with the underlying learning with errors problem, MW16 scheme (Eurocrypt 2016) utilizes the method of ‘linear combination procedure’ (LCP) as a subroutine to construct the auxiliary information for the expanded ciphertexts of MFHE scheme. However, every party shares a common random string (CRS) to be distributed by a trusted setup, which is unpractical. Meanwhile, the noise in the auxiliary information is too much compared with the one in fresh ciphertexts. In this paper, we propose a modified MFHE scheme in the plain model, i.e. without CRS, to enhance the practicability of MFHE. Specifically, every involved party generates his own public key independent on a CRS. Then a potential improvement on the LCP is developed to provide auxiliary information, which largely reduces the noise and leads to a smaller modulus for our MFHE. Furthermore, the feasibility of our proposal is also proved by theoretical performance comparisons.

Redesign and Implementation of Big Fan Impellers for Enhancing Its Efficiency

This paper presents the effort on big fan efficiency enhancement by the modification of impeller geometry especially blades angles and radius while maintaining the other parameters such as casing geometry, entry and exit diameters, rotational speed, number of blades, flow rate, and static pressure matching to the field requirement including existing installation. The combination of numerical calculation based on the semi-empiric formulas and computational fluid dynamics (CFD) is used as the methodology. Two big fans, A and B, which are widely used in the cement industry with nominal flow capacities of 300,000 and 567,500 ㎥/h and having static pressures of 4,000 and 12,200 ㎩, were used as case studies. Theoretical performance comparison between original and modified fan design geometries as well as field measurements were also conducted in this study. The results show that modified geometry design can increase up to 4.53% of fan efficiency which contribute to reduce shaft absorbed power up to 50 ㎾ for fan A and 130 ㎾ for fan B respectively.

Theoretical performance comparison for two-stage auto-cascade refrigeration system using hydrocarbon refrigerants

Auto-cascade refrigeration cycle (ARC) is widely used in low-temperature applications. The selection and proportion of refrigerant mixtures in an ARC system have a significant impact on the environment and system performance. In this study, the theoretical performance of a two-stage ARC system using R170/R600a, R170/R600, R1150/R600a, R1150/R600, and R23/R134a was compared. The results showed that, under certain working conditions in the ARC, an optimal refrigerant ratio maximized the COP of the system. At lower evaporator outlet temperatures or higher condenser outlet temperatures, the performance of the system using R170/R600a, R170/R600, R1150/R600a, and R1150/R600 offers advantages over that when using R23/R134a. Among these, R170/R600 afforded the best performance. Exergy analysis was also performed, and the exergy loss ratios of the heat exchanger in the R170/R600 and R23/R134a systems were the highest at 52.3% and 56.7%, respectively.

Complementary set encryption for privacy-preserving data consolidation

Privacy-preserving data consolidation is one of the prominent research topics in the big data era, mostly because of the need of consolidating data from various database communities, which are highly sensitive or competitive in nature. This leads to a new emerging problem namely how to accomplish data consolidation among different organization data sets or databases appropriately without revealing any competitive or sensitive information to non-owners. To address this issue, we first introduce a new encryption notion called “complementary set encryption” (CSE) to apply to privacy-preserving data consolidation. In this notion, to provide privacy protection, the data in one database will be encrypted under a set W prior to being sent to the other database, and a decryption key will be generated with another set Q. The data will be decrypted and consolidated into the other database, if and only if both sets W and Q are complementary. Here, the “complementary” means that the intersection of set W and set Q is empty and meanwhile the union of both is to be completed into a universal set exactly. We then describe two constructions of CSE under the public-key setting. Our first construction is designed under a weaker security notion – “payload hiding”, which only preserves the data privacy but achieves a higher performance. The second construction is a stronger security notion, which we refer to as an “attribute hiding”, which preserves both the privacy of the data and its associated set W. Finally, we provide a formal analysis to prove the security of our two constructions, followed by a theoretical performance comparison and an experimental evaluation. In particular, the first construction is of an independent interest in the context of cryptography since it was able to stand out for its efficiency as a predicate encryption scheme in the sense that it features both low communication overhead and computational costs simultaneously, and only requires a private key size of O(1), a ciphertext size of O(1), and only O(1) pairing computations.

Feasibility and Operational Analysis of Unconventional Intersection Designs in Dense Urban Areas

The increasing populations in major urban areas and the complexities associated with living in those communities have fuelled the increasing demands for mobility in most of the major metropolitan areas. This high demand coupled with the limited resources and restrictions on the available right of way in urban areas has motivated transportation engineers in different agencies around the world to test and apply unconventional solutions in an attempt to improve the level of service on the major roadway network. This paper combines both theoretical and real-life operational performance comparison for the before and the after of the construction of unconventional designs on two major intersections in the city of Riyadh, KSA. It provides the results of VISSIM micro-simulation model calibration and the performance analysis for the case study intersections. In addition, it presents the comparison of the existing conditions following the actual construction of the unconventional intersection designs and it and provides a feasibility analysis for a double continuous flow intersection that was used in the study. The results have showed an improved intersection performance from the simulation models and the actual data collected for the case study intersections. In addition, they have showed that it has been feasible to apply those designs in urban areas.

Theoretical Analysis and Performance Comparison of Multi-carrier Waveforms for 5G Wireless Applications

Fifth generation (5G) wireless technology is a new wireless communication system that must meet different complementary needs: the high data rate for mobile services, low energy consumption and long-range for connected objects, low latency to ensure real-time communication for critical applications and, high spectral efficiency to improve the overall system capacity. The waveforms and associated signal processing present a real challenge in the implementation of each generation of wireless communication networks. Different research works have discussed this topic; but, these works are limited to the Filter-Bank Multi-Carrier (FBMC), Universal Filtered Multi-Carrier (UFMC), and Filtered Orthogonal Frequency-Division Multiplexing (F-OFDM) waveforms. In this work, we review the technical basics of the physical layer for the LTE system which uses, OFDM modulation for the downlink and the single carrier frequency division multiple access (SC-FDMA) technique for the uplink. Besides, this paper presents the diverse waveforms candidate for 5G systems, including, FBMC, UFMC, and F-OFDM, and compares these techniques with Constant Envelope-OFDM (CE-OFDM), which is an advantageous form regarding power consumption, especially for battery-powered devices. Simulations are carried out to compare the performance of the OFDM, CE-OFDM, F-OFDM, UFMC, and FBMC in terms of power spectral density (PSD) and Bit Error Rate (BER). It has been demonstrated that (CE-OFDM) constitutes a more efficient solution in terms of energy consumption than the other technics. By comparison with the other technics, the CE-OFDM scheme performances, in terms of BER and PSD, are controllable by the values of its parameters (M, h, and J). This advantage gives designers of the system to consider the mutual choice between spectral efficiency and the BER. Moreover, the (F-OFDM), (UFMC), and (FBMC) schemes could constitute a more efficient solution in terms of power spectral density. It can be concluded from this paper that CE-OFDM wave form gives the best performance in terms of power consumption by reducing the Peak to Average Power Ratio (PAPR) associated with the OFDM system and FBMC is an efficiency technique to reduce the inter-carrier interference (ICI).

A Data Sharing Scheme for GDPR-Compliance Based on Consortium Blockchain

After the General Data Protection Regulation (GDPR) was introduced, some organizations and big data companies shared data without conducting any privacy protection and compliance authentication, which endangered user data security, and were punished financially for this reason. This study proposes a blockchain-based GDPR compliance data sharing scheme, aiming to promote compliance with regulations and provide a tool for interaction between users and service providers to achieve data security sharing. The zero-knowledge Succinct Non-Interactive Arguments of Knowledge (zk-SNARK) algorithm is adopted for protecting data and ensure that the user’s private data can satisfy the individual requirements of the service provider without exposing user data. The proposed scheme ensures mutual authentication through the Proof of Authority consensus based on the Committee Endorsement Mechanism (CEM-PoA), and prevents nodes from doing evil using the reputation incentive mechanism. Theoretical analysis and performance comparison indicate that the scheme meets the confidentiality, availability, and other indicators. It has superiority in efficiency and privacy protection compared with other schemes.

Maneuvering Target Detection Based on Subspace Subaperture Joint Coherent Integration

Range cell migration and Doppler frequency migration induced by the target maneuverability are two difficulties of target signal enhancement and radar detection performance. In order to resolve them, a novel subaperture joint coherent integration (SJCI) algorithm is proposed in this article, which consists of three stages. Firstly, it divides the target signal into several subapertures, in which the Doppler frequency dispersions can be neglected. Afterward, coherent integration within each subaperture is implemented via scaled Fourier transform. Finally, correcting the Doppler frequency shifts and phase differences via axis rotation and phase compensation technology, the joint coherent integration among the subapertures can be achieved effectively. Based on the SJCI algorithm, an upgrade algorithm named subspace SJCI (SSJCI) is presented. Through acceleration space division and subspace translation, the SSJCI algorithm extends the subaperture time and optimizes the computation complexity significantly. Theoretical analyses and performance comparisons demonstrate that the SSJCI algorithm can accomplish a good trade-off among signal-to-noise ratio gain, detection capability, resolution, and computation complexity. In addition, the results of the numerical experiments further verify the effectiveness of the proposed algorithm.

The Parameters Comparison of the “Starlink” LEO Satellites Constellation for Different Orbital Shells

Communications-integrated satellite-terrestrial networks used for global broadband services have gained a high degree of interest from scientists and industries worldwide. The most convenient structures for such use are low Earth orbit satellites, since they fly closer to the Earth compared to the other orbits, and consequently provide significantly lower latency, which is essential for reliable and safe communications. Among these efforts is the Starlink satellites constellation, developed and partly deployed by the United States Company SpaceX. The constellation is planned to be organized in three spatial shells, each of them made up of several hundreds of small-dimensioned and light-weighted low Earth orbit specially designed satellites to provide broadband services, intending to offer global Earth coverage through their interoperability, combined also with the ground stations as a part of the satellite-terrestrial integrated network. By October 24, 2020, 893 satellites are situated in orbit of altitudes of 550 km under different inclinations, determining the first Starlink orbital shell. Two next generations are planned to be situated at altitudes of 1,110 and 340 km, to complete the appropriate infrastructure of three Starlink satellite shells, toward a global presence of broadband internet services. These three orbital shells offer different space views seen from the ground station (user) because of their different altitudes, thus in this paper a few parameters which describe the satellite’s behavior considered from the ground station’s (user’s) point of view are compared. These parameters in fact stem from the space orbital parameters and are defined as: horizon plane wideness, slant range, latency, and coverage area. A comparison is given for the three Starlink orbit layers, with identification of appropriate drawbacks and advantages as performance indicators. By the end, these parameters are applied to geometrically interpret and confirm the handover process among satellites. This paper may serve to highlight the new challenges of the satellite-terrestrial integrated network, providing some theoretical analysis and performance comparisons for the satellites in different orbit layers seen from the ground station (user) perspective.

Anonymous Message Authentication Scheme for Semitrusted Edge-Enabled IIoT

As internet of things and other technologies are widely used in industrial manufacturing, automation and intelligence have witnessed rapid developments, resulting in the proposal of the industrial internet of things (IIoT). However, the IIoT still faces various network security threats; hence, data integrity, confidentiality, and anonymity need to be ensured. The use of cloud and edge servers as semitrusted third parties often results in the leaking of privacy sensitive user data. Meanwhile, existing security schemes treat the cloud and edge as fully trusted entities, which is not always valid. Considering edge servers as semitrusted entities, we propose a novel message authentication scheme that leverages group signature technology and proxy reencryption technology to ensure data integrity, confidentiality, and anonymity. Through theoretical analysis and performance comparison, we prove the security of our scheme. In addition, we implement our scheme on a real publish/subscribe system, and the experimental results show the feasibility of our scheme.

Theoretical Comparison of Test Performance of Different Pulse Decay Methods for Unconventional Cores

Various pulse decay methods are proposed to test tight cores. These methods can be divided into three types. This study compares the performance of these methods to test the permeability of unconventional cores in terms of homogeneous cores, dual-medium cores, and gas adsorption, including the pressure equilibrium time, possible errors caused by conventional analysis methods, and reflections on the characteristics of dual-media. Studies shows that the two test methods with an antisymmetric relationship in the boundary conditions have basically identical test performance. When testing homogeneous cores, regardless of whether the gas is adsorptive or not, the pressure equilibrium time of the first type of method is approximately half of that of the second type of method. The dual-medium parameters seriously affect the pressure equilibrium time of different methods, which may cause the difference of order of magnitude. For homogeneous cores, the permeability errors of the first and second types of methods caused by porosity errors are similar and larger than that of the third type of method. For dual media, the fracture permeability obtained by the third type of method using the conventional analysis method may differ from the actual value by tens of times. No method can significantly eliminate the sorption effect. When the core is a dual-medium, only the pressure curves of the upstream positive-pulse method, downstream negative-pulse method and one-chamber method can reflect the characteristics of dual media. The pressure derivative of the one-chamber method cannot reflect the characteristics of dual media at the early time. The pressure derivative of the second type and the upstream positive-pulse downstream negative-pulse method can reflect the complete characteristics of dual media, but their pressure derivative of the constant-slope segment is small, and the interporosity flow parameter may not be identified.

Intelligent Reflecting Surface-Assisted Multiple Access With User Pairing: NOMA or OMA?

The integration of intelligent reflecting surface (IRS) to multiple access networks is a cost-effective solution for boosting spectrum/energy efficiency and enlarging network coverage/connections. However, due to the new capability of IRS in reconfiguring the wireless propagation channels, it is fundamentally unknown which multiple access scheme is superior in the IRS-assisted wireless network. In this letter, we pursue a theoretical performance comparison between non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) in the IRS-assisted downlink communication, for which the transmit power minimization problems are formulated under the discrete unit-modulus reflection constraint on each IRS element. We analyze the minimum transmit powers required by different multiple access schemes and compare them numerically, which turn out to not fully comply with the stereotyped superiority of NOMA over OMA in conventional systems without IRS. Moreover, to avoid the exponential complexity of the brute-force search for the optimal discrete IRS phase shifts, we propose a low-complexity solution to achieve near-optimal performance.