Dual-core System Research Articles

Timing-aware analysis of shared cache interference for non-preemptive scheduling

AbstractIn multi-core architectures, the last-level cache (LLC) is often shared between cores. Sharing the LLC leads to inter-core interference, which impacts system performance and predictability. This means that tasks running in parallel on different cores may experience additional LLC misses as they compete for cache space. To compute a task’s worst-case execution time (WCET), a safe bound on the inter-core cache interference has to be determined. We propose an interference analysis for set-associative shared least-recently-used caches. The analysis leverages timing information to establish tight bounds on the worst-case interference and classifies individual accesses as either cache hits or potential cache misses. We evaluated the analysis performance for systems containing 2 and 4 cores using shared caches up to 64 KB. The evaluation shows an average WCET reduction of up to 23.3% for dual-core systems and 8.5% for quad-core systems.

Self-centering dual rocking core system with viscous dampers in additional rocking sections

To mitigate the high mode effects and reduce the force requirements of the structural members in the multi-story self-centering dual rocking core (SDRC) system, this paper proposes the multiple self-centering dual rocking core system with viscous dampers in additional rocking sections (MSDRCV system). The sketch and ideal working mechanisms of the MSDRCV system are interpreted. The additional rocking sections are set to decrease the force requirements of structural members and viscous dampers are included to mitigate high mode responses of the additional rocking sections, introducing seismic performance enhancement. Comparative analyses on a 9-story MSDRCV system with viscous dampers in rocking sections, a 9-story multiple self-centering dual rocking core system without viscous dampers in rocking sections (MSDRC system) and a 9-story SDRC system were carried out. The MSDRCV and MSDRC system can realize the reduction of the force demands in structural members in contrast to the SDRC system. Nevertheless, the high mode responses caused the uncontrollable displacement concentration in the MSDRC system and hence aggravated the seismic performance under rare seismic events. The analysis results in the frequency domain confirmed that the viscous dampers in the MSDRCV system can efficiently control the high-mode responses. The effects of the design parameters of the viscous dampers on the peak responses of the MSDRCV systems were comprehensively studied via parametric analyses. The results offer guidance for the viscous dampers design.

Self-centering multiple rocking core systems for mitigating higher mode effects

The structural member forces of mid-story and high-rise self-centering energy-absorbing dual rocking core (SEDRC) systems can be significantly aggravated by higher mode effects. This study aims to introduce the multiple rocking mechanisms into the SEDRC system and propose the self-centering multiple rocking core system (denoted as SMRC system) to reduce the structural member force demands resulting from the higher mode effects. The working principle of the SMRC system is discussed. The performance-based design (PBD) procedures for the SMRC system are presented. The comparative dynamic history analyses are conducted on a 9-story SMRC and two 9-story SEDRC systems. Incremental dynamic analyses (IDAs) are carried out to investigate the dynamic behaviors of the considered systems under increasing seismic intensities. The accuracy of the developed designed procedures is verified with the evidence that the developed SMRC system can achieve the design displacement under design earthquakes. The multiple rocking mechanism can efficiently mitigate structural member force demands caused by the effects of higher mode. The SMRC system can achieve better seismic performance with lower structural member force demands than the SEDRC systems when the earthquake intensity is not higher than the maximum considered earthquakes (MCE). Nevertheless, the SMRC system shows worse performance than the SEDRC systems in resisting structural collapse when the intensity is higher than MCE, which could be a research gap for further investigations.

Moving Bragg Solitons in a Dual-Core System Composed of a Linear Bragg Grating with Dispersive Reflectivity and a Uniform Nonlinear Core

The existence and stability of moving Bragg grating solitons are systematically investigated in a dual-core system, where one core is uniform and has Kerr nonlinearity, and the other is linear with Bragg grating and dispersive reflectivity. It is found that moving soliton solutions exist throughout the upper and lower bandgaps, whereas no soliton solutions exist in the central bandgap. Similar to the quiescent solitons in the system, it is found that when dispersive reflectivity is nonzero, for certain values of parameters, sidelobes appear in the solitons’ profiles. The stability of the moving solitons is characterized using systematic numerical stability analysis. Additionally, the impact and interplay of dispersive reflectivity, soliton velocity, and group velocity on the stability border are analyzed.

Additional damped rocking sections for enhancing seismic performance of self-centering dual rocking core systems

This paper aims to propose a novel self-centering dual rocking core system with damped multiple rocking sections (denoted as MSDRC system) for achieving enhanced seismic performance in mitigating high mode effects and responses. The configuration and desired seismic performance of the MSDRC system are introduced. The multiple rocking sections are introduced to reduce the structural member force demands caused by higher mode effects and buckling restrained braces (BRBs) are equipped in multiple rocking sections for absorbing higher mode energy. Comparative analyses set out to study the dynamic responses and highlight the benefits of the proposed MSDRC system compared to the existing self-centering dual rocking core (SDRC) and self-centering multiple rocking core (SMRC) systems. To facilitate an equitable comparison, the 9-story MSDRC, SDRC, and SMRC systems are engineered to attain identical target drift under design basis earthquakes (DBE). The analyses reveal that, in contrast to the SDRC system, the multiple rocking sections in SMRC and MSDRC systems can efficiently reduce the structural member force demands. Compared to the SMRC system, the BRBs in the multiple rocking sections in the MSDRC system can absorb sufficient energy to avoid inter-story drift concentration caused by higher mode responses under strong earthquakes. Parametric dynamic analyses are also performed to explore the influence of the capacity of BRBs on the dynamic nonlinear behaviors of the developed MSDRC system. The analysis results provide design recommendations for the design of BRBs in the rocking sections.

RANCANG BANGUN ALAT UJI PERIFERAL ESP32 DEVKIT V1 - DOIT 30 PIN

The ESP32 DEVKIT V1 - DOIT 30 Pin Peripheral Board Test Tool is a module that can be used to test the ESP32 DEVKIT V1 - DOIT 30 Pin microcontroller board. The chip of the board is ESP32 developed by Espressif Systems. ESP32 has many features or peripherals that can be used in various projects. Built-in Internet of things (IoT) is one of the leading features that can connect the board to the internet without the need for additional modules from outside. Features or peripherals that can be tested on the ESP32 DEVKIT V1 - DOIT 30 Pin Peripheral Board Test Tool, are digital i/o, ADC & DAC, dual core system, built-in touch sensor, built-n hall sensor, Bluetooth, and Wi-Fi.

A dual-core system dynamics approach for carbon emission spillover effects analysis and cross-regional policy simulation

As carbon emission continue to rise and climate issues grow increasingly severe, countries worldwide have taken measures to reduce carbon emission. However, carbon dioxide is continuously flowing in the atmosphere and is easily influenced by neighboring cities' policies. Therefore, how to solve the problem of carbon emission spillover effect has become the key to improve policy efficiency. Cross-regional carbon governance provides a perspective on solving the carbon emission problem by regulating and guiding the cooperative behavior of cross-regional governance actors. Taking Chengdu-Chongqing area as an example, this study used the SDM to analyze the influencing factors and spatial spillover effects of emission. Then we used the system dynamics method to construct a dual-core carbon emission system, and simulated the spillover effect and emission reduction potential of Chengdu and Chongqing emission reduction policies under different policy schemes. The results reveal that the mobility of population and enterprises have a significant impact on carbon emission prediction. Carbon reduction policies exhibit the phenomena of "carbon transfer" and "free-riding." When Chengdu lowers its economic growth rate, it leads to the transfer of high energy-consuming enterprises to Chongqing, increasing carbon emission in Chongqing. The implementation of comprehensive carbon reduction policies in Chongqing has a positive effect on Chengdu. Emission reduction policies exhibit issues related to their temporal efficacy, as the effects of industrial structural policies in Chengdu yield opposite outcomes in the short and long term. Each city's unique circumstances necessitate tailored carbon reduction policies. In order to reduce carbon emissions, Chengdu and Chongqing require opposite population policies.

Hybrid self-centering dual rocking core system for seismic resilience by controlling both structural and nonstructural damage

This study proposes a novel hybrid self-centering dual rocking core (HSDRC) system with structural and nonstructural damage control functions for the building structure’s seismic resilience. The rigid rocking cores (RCs), viscous dampers (VDs), and shear friction spring dampers (SFDs) are introduced in HSDRC systems. The rocking cores with pinned bases are adopted for promoting uniform inter-story drifts over the building height. The SFDs are introduced to dissipate hysteretic energy and bring self-centering capacity by eliminating residual deformation. The VD’s velocity-proportional damping can help HSDRC systems control the nonstructural damage and building content’s damage sensitive to absolute floor accelerations. The expected behavior of HSDRC systems is first described. A direct displacement-based design (DDBD) method is following proposed to achieve the desired nonlinear behavior of HSDRC. Following the developed DDBD procedure, six HSDRC systems are designed. For highlighting the advantages of HSDRC systems compared to the existing self-centering energy-absorbing rocking core (SEDRC) system, two SEDRC systems are also designed. Nonlinear dynamics were included for investigating the performance of the designed systems subjected to seismic events. The numerical results demonstrate that the designed HSDRC systems show the expected nonlinear behavior and achieve the design target, confirming the developed DDBD method’s effectiveness. Compared to SEDRC systems, the newly proposed HSDRC systems show smaller absolute floor acceleration responses while obtaining the comparative capacity in controlling both peak and residual inters-tory drifts, indicating the proposed HSDRC systems can be a promising seismic resilient structural system for both structural and nonstructural damage control.

One-dimensional Townes solitons in dual-core systems with localized coupling.

The recent creation of Townes solitons (TSs) in binary Bose-Einstein condensates and experimental demonstration of spontaneous symmetry breaking (SSB) in solitons propagating in dual-core optical fibers has drawn renewed interest in the TS and SSB phenomenology in these and other settings. In particular, stabilization of TSs, which are always unstable in free space, is a relevant problem with various ramifications. We introduce a system which admits exact solutions for both TSs and SSB of solitons. It is based on a dual-core waveguide with quintic self-focusing and fused (localized) coupling between the cores. The respective system of coupled nonlinear Schrödinger equationsgives rise to exact solutions for full families of symmetric and asymmetric solitons, which are produced by the supercritical SSB bifurcation (i.e., the symmetry-breaking phase transition of the second kind). Stability boundaries of asymmetric solitons are identified by dint of numerical methods. Unstable solitons spontaneously transform into robust moderately asymmetric breathers or strongly asymmetric states with small intrinsic oscillations. The setup can be used in the design of photonic devices operating in coupling and switching regimes.

(Invited) Quiescent solitary waves in dual-core systems with separated Bragg grating and cubic–quintic nonlinearity

The existence and stability of zero-velocity solitons in a dual-core optical fiber, where one core possesses cubic–quintic nonlinearity and the other core is linear with a Bragg grating, are investigated. The frequency spectrum for the model consists of three bandgaps, of which only the central band gap is a genuine one. There are no soliton solutions in the central gap. On the other hand, the upper and lower gaps are filled with two distinct and disjoint families of soliton solutions, termed Type-1 and Type-2 solitons, that differ in their shapes and phase characteristics. When the relative group velocity in the linear core is zero, implicit analytical solutions for Type-1 and Type-2 quiescent solitons are found. For nonzero values of the relative group velocity, soliton solutions can only be found using numerical techniques. The stability of solitons has been analyzed systematically by means of numerical stability analysis. It is found that Type-2 solitons are always unstable. In the case of Type-1 solitons, stability regions are identified in the upper and lower bandgaps. The effects and interplay of the relative group velocity and the Bragg grating-induced linear coupling coefficient on the stability of the solitons are also analyzed.

A dual-core NMR system for field-cycling singlet assisted diffusion NMR.

Long-lived singlet spin order offers the possibility to extend the spin memory by more than an order of magnitude. This enhancement can be used, among other applications, to assist NMR diffusion experiments in porous media where the extended lifetime of singlet spin order can be used to gain information about structural features of the medium as well as the dynamics of the imbibed phase. Other than offering the possibility to explore longer diffusion times of the order of many minutes that, for example, gives unprecedented access to tortuosity in structures with interconnected pores, singlet order has the important advantage to be immune to the internal field gradients generated by magnetic susceptibility inhomogeneities. These inhomogeneities, however, are responsible for very short T2 decay constants in high magnetic field and this precludes access to the singlet order in the first instance. To overcome this difficulty and take advantage of singlet order in diffusion experiments in porous media, we have here developed a dual-core system with radiofrequency and 3-axis pulsed field gradients facilities in low magnetic field, for preparation and manipulation of singlet order and a probe, in high magnetic field, for polarisation and detection. The system operates in field-cycling and can be used for a variety of NMR experiments including diffusion tensor imaging (both singlet assisted and not). In this paper we present and discuss the new hardware and its calibration, and demonstrate its capabilities through a variety of examples.

Direct displacement-based design of SEDRC systems considering higher mode effects

Self-centering energy-absorbing dual rocking core (SEDRC) system was recently proposed for obtaining damage-free performance under design earthquakes or low damage under extreme earthquakes in steel building structures. Although the SEDRC system can mainly deform based on the fundamental mode shape, the higher modes may significantly impact the structural element forces. This research intends to investigate the effects of higher mode on the seismic performance and structural member force demands of the SEDRC system under earthquakes and propose a performance-based design (PBD) method considering the higher mode effects. The formulation for calculating the design base shear pondering the influence of higher mode is deduced. The detailed design steps and equations for calculating the force demands of structural members are presented. Three archetypes, including nine-, fifteen-, and twenty-story SEDRC systems, respectively, are designed according to the PBD method. Moreover, the other six corresponding archetypes are designed according to the previous design process without consideration of higher mode effects as comparative buildings. Nonlinear dynamic analyses were performed to evaluate the seismic responses of the designed structures. The analysis results validate the high precision of the proposed methodology in designing multi-story to high-rise SEDRC systems.

Evidence to disfavour dual-core systems leading to double-peaked narrow emission lines

ABSTRACTIn this paper, an interesting method is proposed to test dual-core systems for double-peaked narrow emission lines through a precious dual-core system with double-peaked narrow Balmer lines in the main galaxy but with single-peaked narrow Balmer lines in the companion galaxy. Under a dual-core system, considering narrow Balmer (Hα and Hβ) emissions (fe,α and fe,β) from a companion galaxy that are covered by the SDSS fiber for the main galaxy and narrow Balmer emissions (fc,α and fc,β) from the companion galaxy covered by the SDSS fiber for the companion galaxy, the same flux ratios fe,α/fc,α = fe,β/fc,β can be expected, owing to the totally similar physical conditions of each narrow Balmer emission region. Next, the precious dual-core system in SDSS J2219–0938 is discussed. After subtracting the pPXF code determined stellar lights, double-peaked narrow Balmer emission lines are confirmed in the main galaxy with a confidence level higher than 5σ, but single-peaked narrow Balmer emission lines are confirmed in the companion galaxy. Through measured fluxes of the emission components, fe,α/fc,α is about 0.82, which is different from fe,β/fc,β ∼ 0.52, which disfavours a dual-core system for the double-peaked narrow Balmer emission lines in SDSS J2219–0938.

Velocity Offset Between Emission and Absorption Lines Might Be an Effective Indicator of a Dual Core System

This paper presents the detection of a significant velocity offset between the emission and absorption lines of a dual core system in SDSS J155708.82+273518.74 (=SDSS J1557). The photometric image of SDSS J1557 exhibits two clear cores with a projected separation of ∼2.″2 (4.9 kpc) determined by GALFIT. Based on the applications of the commonly accepted pPXF code with 636 theoretical SSP templates, the host galaxy contribution can be well determined. Then, the emission-line features of SDSS J1557 can be well measured after subtraction of the host starlight. It is found that the velocity offset of emission lines with respect to absorption lines reaches 458 ± 13 km s−1. According to a Baldwin–Phillips–Terlevich diagram, SDSS J1557 is a composite galaxy. In addition, SDSS J1557 can well fit the M BH − σ * relation of bulges, and a galaxy merger would not change this relation. Two reasonable models (an AGN-driven outflow versus a dual core system) are discussed to explain this velocity offset. The model of an AGN-driven outflow fails to interpret the systematic redshift of the emission lines and similar velocity offsets for the various emission lines of SDSS J1557. Instead, the significant velocity offset between the emission and absorption lines might be an effective indicator of a dual core system.

XML-Based Automatic NIOS II Multi-Processor System Generation for Intel FPGAs

Many embedded systems are introducing processing units to accelerate the processing speed of tasks, such as for multi-media applications. The units are mostly customized designs. Another method of designing multi-unit systems is using pre-defined standard intellectual properties. However, the procedure of arranging IP cores in a system and maintaining a high performance as well are the remaining challenges. Implementing softcore processors on field-programmable gate arrays (FPGAs) is a relatively fast and inexpensive choice to design and validate a desired system. This paper describes the rapid prototyping of hardware/software co-design based on FPGAs. A novel system generator to effortlessly design a multiple NIOS II soft-processor core systems is also purposed. The NIOS II CPU is a configurable RISC processor designed by Altera/Intel and can be trimmed to complete specific tasks. The error-prone and time-consuming process of designing an IP block-based system is improved by the new novel system generator. The detail of the implementation of such system is discussed. To test the performance of a multi-NIOS II system, a parallel application is executed on 1-, 2-, 5-, and 10-core NIOS II systems separately. Test results prove the feasibility of the proposed methodology (for an FIR filter, a dual-core system is 29% faster than a single-core system; a 5-core system is 28% faster than the dual-core system).

Probabilistic Nonlinear Displacement Ratio Prediction of Self-centering Energy-absorbing Dual Rocking Core System under Near-fault Ground Motions Using Machine Learning

ABSTRACT Near-fault pulse-like ground motions can lead to significant seismic demand on building structures due to velocity pulses. The self-centering energy-absorbing dual rocking core (SEDRC) system is a newly developed seismic resilient structural system. This paper investigates the seismic demand of SEDRC systems subjected to near-fault pulse-like ground motions by determining their nonlinear displacement ratios. Two hundred and five near-fault pulse-like ground motion records are used to consider the uncertainties of seismic events. The influences of design hysteretic parameters and near-fault ground motion characteristics on the nonlinear displacement ratio of the SEDRC system are investigated through parametric dynamic analysis of single-degree-of-freedom (SDOF) systems. The dynamic analyses results indicate that the stiffness hardening ratio α and energy-absorbing ratio β of the SEDRC system, predominant period, pulse period of ground motions, and earthquake magnitude show obvious effects on the nonlinear displacement ratio responses of SDOF systems, while the unloading stiffness ratio ε, site condition, and source-to-site distance show limited or negligible influence on that. The past studies mainly used the mean or median responses of single-degree-of-freedom systems to predict the nonlinear displacement ratio of structures, which may not be enough to guide the design of buildings with great importance (e.g., hospital and fire station). This paper proposes an innovative framework for predicting the nonlinear displacement ratio of structures underground motions using a probabilistic estimation method and machine learning technique. Based on the dynamic analysis results of SDOF systems, a probabilistic model for predicting the nonlinear displacement ratio of the SEDRC system under near-fault pulse-like ground motions is developed through the proposed framework. The proposed framework is also applicable to estimate the seismic demand of other structures under near-fault or far-field ground motions to facilitate the development of the performance-based seismic design.

Performance-based seismic design method for retrofitting steel moment-resisting frames with self-centering energy-absorbing dual rocking core system

This research intends to propose an upgraded strategy for steel moment-resisting frames (SMRFs) by implementing Self-Centering Energy-absorbing Dual Rocking Core (SEDRC) systems to achieve enhanced seismic performance, improved seismic resilience, and avoid inter-story drift concentration. A performance-based method is developed to design the SEDRC system for upgrading the existing SMRF. The maximum inter-story drift and drift concentration factor are adopted as the design performance objectives. Two prototype SMRFs with three and nine stories are introduced to validate the proposed performance-based design procedure. Nonlinear static analyses were first performed for the original SMRFs and the updated ones (denoted as SEDRC-MRFs) to investigate the efficiency of the proposed retrofit strategy. The pushover curves of the analytical structures confirm that the SEDRC systems can increase the stiffness and strength of SMRFs, and SEDRC-MRFs upgraded through the proposed design procedure show no strength deterioration before the fracture of the brace in the SEDRC system. A set of 18 ground motions were chosen to study the seismic performance of the designed SEDRC-MRFs. The analysis results indicate that SEDRC-MRFs can obtain the desired performance objectives. The SEDRC system could reduce the maximum and residual inter-story drifts of SMRFs and promote uniform inter-story drift distribution. Moreover, the designed SEDRC-MRFs can be used immediately without the need for repairing structural members after the design basis earthquakes and can be repaired economically after the maximum considered earthquakes.

Performance-based design of self-centering energy-absorbing dual rocking core system

The Self-centering Energy-absorbing Dual Rocking Core system (denoted as the SEDRC system) is a newly developed high-performance steel lateral force-resisting system that can achieve negligible residual inter-story drifts and avoid structural damage during rare earthquakes. Compared to many existing re-centering systems, the SEDRC system also has larger deformability and can obtain a more uniform inter-story drift responses when subjected to ground motions. This research focuses on developing a performance-based design procedure for the SEDRC systems. The seismic force reduction factor model and constant-ductility demand model have been derived via parametric nonlinear dynamic analyses of single-degree-of-freedom systems with the hysteretic behavior of the SEDRC system for developing the Displacement-Based Design (DBD) procedure. Following the developed DBD method, three six-story SEDRC systems with different parameters have been designed to achieve the desired performance objectives. Systematic numerical studies, including nonlinear static analyses, nonlinear dynamic analyses, and incremental dynamic analyses, have been conducted to validate whether the designed SEDRC system can obtain the prescribed performance target and investigate the effect of some design parameters on the seismic responses of the SEDRC systems. According to the results from the numerical studies, it can be observed that the three SEDRC systems designed through the proposed DBD method can successfully obtain the desired performance target. Moreover, higher inter-story drift at the bearing of the shear friction spring damper, as well as the higher enhanced yield-strength ratio of BRBs, can enhance the collapse-resistant capacity of the SEDRC system. Higher bearing inter-story drift can further reduce the residual inter-story drift leading to a lower collapse probability of the SEDRC system subjected to rare seismic events.

Seismic design and performance evaluation of low-rise steel buildings with self-centering energy-absorbing dual rocking core systems under far-field and near-fault ground motions

This research focuses on seismic design and performance evaluation of low-rise steel buildings with self-centering energy-absorbing dual rocking core systems (denoted as SEDRC systems) under far-field and near-fault ground motions. The SEDRC system consists of two rocking cores (RCs) and several shear friction spring dampers (SFSDs). These SFSDs are located between the two RCs and arranged over the height of the SEDRC system to absorb energy and provide a self-centering feature. The two RCs are considered as two buckling restrained braced frames in this paper, which are utilized to obtain uniform inter-story drift distribution in buildings. The two RCs can also act as a backup lateral force-resisting and energy-dissipation system if necessary. A direct displacement-based design (DDBD) procedure is introduced for the SEDRC system. A physical test was conducted to investigate the stability of the SEDRC system under repeated loading with near-fault loading protocol. The test results show that the SEDRC specimen can get stable self-centering behavior under repeated rounds of tests, indicating that the SEDRC system can be fully recoverable against multiple earthquakes before the development of the bearing action in SFSDs. The computational model of the SEDRC system was created and verified with the test results. A three-story representative building was designed through the proposed DDBD method, and the numerical models of the building were generated using the verified modeling method. Forty far-field ground motions and twenty near-fault ground motions were selected to perform Nonlinear Dynamic Analyses (NDA) on the designed building. The NDA results show that the designed three-story SEDRC system can satisfy the drift limit under DBE far-field excitations. And the designed SEDRC system can also survive and achieve small residual drifts subjected to the fault-normal components of the selected near-fault excitations and MCE far-field excitations.

Modeling of an air-to-air exchanger with dual-core in cascade connection

With the current leaning towards finding effective solutions to maintain a good indoor air quality (IAQ) inside houses and buildings and to simultaneously reduce the energy consumption, air-to-air exchangers with heat/energy recovery have emerged as one of the promising technologies to provide a healthy and comfortable indoor environment. To deeply evaluate these systems performances, the present investigation focuses on modeling a combined ERV-HRV exchanger using the effectiveness-NTU (ε−NTU) method. To this end, a detailed mathematical model introducing heat and mass exchange mechanisms was developed and applied to predict the system energy recovery efficiency. To assess its suitability, the developed model was validated and compared to real measurements which carried out under the Atlantic Canada weather. The comparison findings disclosed that the developed model can predict the system performance with a maximum relative discrepancy less than 10%.• The detailed mathematical model including heat and mass exchange mechanisms was clearly developed using the ε−NTU approach in order to carefully predict the dual-core system performance in terms of sensible and latent recovery potential.• The developed model was validated against real data to evaluate its suitability and accuracy. Obtained results show that it could be satisfactory for predicting the dual-core system performances.• The ε−NTU approach adopted in this study could be a convenient method for modeling single or/and dual-core air-to-air heat/energy recovery systems.