► We designed and tested a convection-driven thermo-acoustic-piezo system for energy harvesting. ► Our present system involves no heat exchangers and stacks (or regenerators). ► We compared our ...present system with a similar but conduction-driven system. ► A model is developed to simulate the energy conversion process. ► Green’s function approach is used to simulate the resonance of piezo-diaphragm.
In this work, a convection-driven Rijke–Zhao thermo-acoustic-piezo system is designed and experimentally tested to demonstrate its potential for harvesting thermal energy. For this, a nonlinear theoretical model is developed to simulate the energy conversion process, i.e. heat-to-sound-to-electricity in the present system. Unlike the conventional conduction-driven thermoacoustic converters, our present system involves no heat exchangers and stacks. As a heat source is placed in a Rijke–Zhao tube with two bifurcating daughter branches, self-sustained thermoacoustic oscillations are generated. The resulting acoustic fields in the bifurcating branches are dramatically different. One branch is associated with ‘hot’ oscillations. However the other is with ‘cold’ oscillations at ambient temperature, which enable a piezoelectric generator being implemented to the end of the branch. In order to measure the acoustic fields in the bifurcating branches, two arrays of thermocouples and microphones are used. The maximum sound pressure level is around 139dB. The output electric power and acoustical energy conversion efficiency are measured and compared with that from a similar but a conduction-driven thermo-acoustic-piezo system. It is found that 60% more power is generated. And the energy conversion efficiency is increased by 105%. These experimental results confirm that the developed Rijke–Zhao thermo-acoustic-piezo system is an invaluable tool in designing a simple, low-cost, energy-efficient thermoacoustic system.
Combustion instabilities in a Rijke tube could be triggered by the transient growth of flow disturbances, which is associated with its non-normality. In this work, a Rijke tube with three different ...temperature configurations resulting from a laminar premixed flame are considered to investigate its non-normality and the resulting transient growth of flow disturbances in triggering combustion instabilities. For this, a general thermoacoustic model of a Rijke tube is developed. Unsteady heat release from the flame is assumed to be caused by its surface variations, which results from the fluctuations of the oncoming flow velocity. Coupling the flame model with a Galerkin series expansion of the acoustic waves present enables the time evolution of flow disturbances to be calculated, thus providing a platform on which to gain insights on the Rijke tube stability behaviors. Both eigenmodes orthogonality analysis and transient growth analysis of flow disturbances are performed by linearizing the flame model and recasting it into the classical time-lag N-τ formulation. It is shown from both analyses that Rijke tube is a non-normal thermoacoustic system and its non-normality depends strongly on the temperature configurations and the flame position. Furthermore, the most ‘dangerous’ position at which the flame is more susceptible to combustion instabilities are predicted by real-time calculating the maximum transient growth rate of acoustical energy.
As primary feedstocks in the petrochemical industry, light olefins such as ethylene and propylene are mainly obtained from steam cracking of naphtha and short chain alkanes (ethane and propane). Due ...to their similar physical properties, the separations of olefins and paraffins—pivotal processes to meet the olefin purity requirement of downstream processing—are typically performed by highly energy‐intensive cryogenic distillation at low temperatures and high pressures. To reduce the energy input and save costs, adsorptive olefin/paraffin separations have been proposed as promising techniques to complement or even replace cryogenic distillation, and growing efforts have been devoted to developing advanced adsorbents to fulfill this challenging task. In this Review, a holistic view of olefin/paraffin separations is first provided by summarizing how different processes have been established to leverage the differences between olefins and paraffins for effective separations. Subsequently, recent advances in the development of porous materials for adsorptive olefin/paraffin separations are highlighted with an emphasis on different separation mechanisms. Last, a perspective on possible directions to push the limit of the research in this field is presented.
Adsorptive light olefin/paraffin separations facilitated by advanced porous materials such as zeolites and metal–organic frameworks are reviewed. Different separation mechanisms realized in these materials are highlighted, and constructive perspectives on future directions of the field are provided.
Metal–organic frameworks (MOFs) are a class of crystalline inorganic–organic hybrid materials that have demonstrated huge potential in gas separation due to their ultrahigh porosity, boundless ...chemical tunability, as well as surface functionality. Most gas separations realized in MOFs are under an equilibrium state and are dependent on the difference in thermodynamic affinities of gases to MOFs, whereas nonequilibrium separation such as kinetic and molecular sieving separation attracting growing attention in the past decade is achieved based on the difference in the size and diffusivity of gas molecules. In this perspective, we first discuss the pore size, temperature, and pressure effect on gas diffusion as well as nonequilibrium gas separation in MOFs. Second, we introduce current techniques reported to measure intracrystalline gas diffusivity. Third, we review recent progress in MOF-based nonequilibrium N2/O2 separation, CO2 capture, and hydrocarbon separation. In addition, we describe the hydrogen isotope separation based on kinetic quantum sieving in MOFs as a special scenario of kinetic gas separation. Lastly, we summarize general design strategies toward MOF-based nonequilibrium gas separation and propose several directions to advance the study in this exciting area.
The traditional pedagogy discipline construction decision support algorithm has the problems of poor discipline construction decision satisfaction, high decision time, and low decision recall rate. ...Therefore, a decision support algorithm for discipline construction of comparative pedagogy based on evolutionary graph data mining is designed. First, the programme call graph is created based on the programme execution path, and then the graph reduction method is used to decrease the call graph set and create the weighted behavior graph set. The original graph set is then reduced using the subtree reduction procedure. The interference of weights in the graph must be eliminated while mining closed subgraphs using a close graph method. The most frequent subgraph of comparative pedagogy discipline construction is then mined, and an SVM classifier is created to accomplish information mining of comparative pedagogy discipline construction in evolutionary graph data mining. Then, using the complete weighing approach, the attribute classification of comparative pedagogy discipline construction is accomplished, and the decision weight of comparative pedagogy discipline construction is established. Finally, the weight distribution scheme of comparative pedagogy discipline construction is obtained by using European distance, so as to realize the decision support of comparative pedagogy discipline construction. The experimental results show that the decision-making satisfaction of comparative pedagogy discipline construction of this method is 97.32%, the decision-making time is only 0.9 min, and the decision-making recall rate is as high as 98.66%, indicating that the decision-making effect of comparative pedagogy discipline construction of this method is good.
This work uses 194 outdoor particle size distributions (PSDs) from the literature to estimate single-pass heating, ventilating, and air-conditioning (HVAC) filter removal efficiencies for PM2.5 and ...ultrafine particles (UFPs: <100 nm) of outdoor origin. The PSDs were first fitted to tri-modal lognormal distributions and then mapped to size-resolved particle removal efficiency of a wide range of HVAC filters identified in the literature. Filters included those with a minimum efficiency reporting value (MERV) of 5, 6, 7, 8, 10, 12, 14, and 16, as well as HEPA filters. We demonstrate that although the MERV metric defined in ASHRAE Standard 52.2 does not explicitly account for UFP or PM2.5 removal efficiency, estimates of filtration efficiency for both size fractions increased with increasing MERV. Our results also indicate that outdoor PSD characteristics and assumptions for particle density and typical size-resolved infiltration factors (in the absence of HVAC filtration) do not drastically impact estimates of HVAC filter removal efficiencies for PM2.5. The impact of these factors is greater for UFPs; however, they are also somewhat predictable. Despite these findings, our results also suggest that MERV alone cannot always be used to predict UFP or PM2.5 removal efficiency given the various size-resolved removal efficiencies of different makes and models, particularly for MERV 7 and MERV 12 filters. This information improves knowledge of how the MERV designation relates to PM2.5 and UFP removal efficiency for indoor particles of outdoor origin. Results can be used to simplify indoor air quality modeling efforts and inform standards and guidelines.
•We estimate HVAC filter removal efficiencies for PM2.5 and UFPs of outdoor origin.•Both UFP and PM2.5 removal efficiency tend to increase with increasing MERV.•Outdoor PSDs and particle density do not substantially impact PM2.5 removal efficiencies.•Outdoor PSDs and infiltration factors do impact UFP removal efficiencies.•This work informs how MERV relates to outdoor PM2.5 and UFP removal efficiency.
To bridge the widening gap between computation requirements and communication efficiency faced by gigascale heterogeneous SoCs in the upcoming ubiquitous era, a new on-chip communication system, ...dubbed Wireless Network-on-Chip (WNoC), is introduced by using the recently developed CMOS UWB wireless interconnection technology. In this paper, a synchronous and distributed medium access control (SD-MAC) protocol is designed and implemented. Tailored for WNoC, SD-MAC employs a binary countdown approach to resolve channel contention between RF nodes. The receiver_select_sender mechanism and hidden terminal elimination scheme are proposed to increase the throughput and channel utilization of the system. Our simulation study shows the promising performance of SD-MAC in terms of throughput, latency, and network utilization. We further propose a QoS-aware SD-MAC to ensure the serviceability of the entire system and to improve the bandwidth utilization. As a major component of simple and compact RF node design, a MAC unit implements the proposed SD-MAC that guarantees correct operation of synchronized frames while keeping overhead low. The synthesis results demonstrate several attractive features such as high speed, low power consumption, nice scalability and low area cost.
The pathogenesis of autoimmune diseases (AIDs) is not only attributed to genetic susceptibilities but also environmental factors, among which, disturbed gut microbiota has attracted increasing ...attention. Compositional and functional changes of gut microbiota have been reported in various AIDs, and increasing evidence suggests that disturbed gut microbiota contributes to their immunopathogenesis. The accepted mechanisms include abnormal microbial translocation, molecular mimicry, and dysregulation of both local and systemic immunity. Studies have also suggested microbiota-based classification models and therapeutic interventions for patients with AIDs. Further in-depth mechanistic studies on microbiota–autoimmunity interplay in AIDs are urgently needed and underway to explore novel and precise diagnostic biomarkers and develop disease and patient-tailored therapeutic strategies.
The compositional and functional changes of gut microbiota have been implicated in various autoimmune diseases (AIDs) by high-throughput techniques such as metagenomic sequencing.Correlation studies in humans and interventional studies in animal models have suggested that disturbed gut microbiota is involved in the immunopathogenesis of AIDs.The mechanisms of disturbed gut microbiota include abnormal microbial translocation, molecular mimicry, and dysregulation of both local and systemic immunity.In-depth deciphering of gut microbiota will help us to develop new microbiota-based assessments and interventions for patients with AIDs, which can help with their diagnosis, prognosis and treatment.
Copper is an essential metal but potentially toxic to aquatic animals at high levels. The present study investigated physiologically adaptive responses to waterborne Cu2+ exposure (0, 0.03, 0.30, ...3.00 mg/L) in a representative species of crustaceans, the red swamp crayfish (Procambarus clarkii) for 7 d, followed by a 7-d depuration period. The tissue-specific distribution of Cu showed that crayfish hepatopancreas was the primary accumulating site among internal tissues. During Cu2+ exposure, crayfish repressed the expression level of Cu homeostasis genes (Ctr1, Atox1, copper-transporting ATPase 2, MTF-1/2, and MT) in hepatopancreas to inhibit intracellular Cu transporting. Cu2+-exposed crayfish increased activities of GPx and GST, GSH contents, and mRNA expression of antioxidative enzyme genes (Cu/Zn-sod, cat, gpx, gst) to cope with the Cu2+-induced oxidative stress which accompanied by an increased MDA content. Additionally, after a 7-d depuration, crayfish effectively eliminated excess Cu from hepatopancreas by up-regulating expression level of Cu homeostasis genes, and recovered from oxidative damage by enhancing antioxidative enzyme gene expression (Cu/Zn-sod, cat, gpx, gst) and consuming more GSH, which thereby caused a return of the MDA level to the control value. Overall, our study provided new insights into the regulatory mechanisms of cellular Cu homeostasis system and antioxidative system, contributing to Cu detoxification and tolerance ability exhibited by crayfish under Cu2+ stress and after withdrawal of Cu2+ stress.
•Crayfish hepatopancreas was the primary accumulating site among internal tissues.•Excessive Cu was completely eliminated from hepatopancreas after a 7-d depuration.•Crayfish regulated Cu homeostasis system to detoxify Cu during exposure and depuration.•Crayfish activated antioxidant system to tolerate and recover from oxidative stress.
Effective and efficient fuel–air mixing plays a critical role in the successful operation of scramjet engines. To enhance the fuel–air mixing in supersonic combustion systems with a short flow ...residence time, the pulsed fuel injection strategy in a realistic scramjet combustor flow condition provided by the HyShot II is numerically studied in this work. For this, 2D and 3D simulations of the hydrogen fueled HyShot II scramjet with pulsed fuel injections are performed. Emphasis is placed on the cold flow field characteristics and fuel–air mixing performance in the combustor. Reynolds-Averaged Navier–Stokes equations are solved with the implementation of the two equation k–ω SST turbulence model via using the ANSYS FLUENT v17.1. The pulsed fuel injection is numerically achieved by implementing a time-dependent total pressure pulse with the shape of a square wave. The total pressure peak is maintained as same as the one that chokes the fuel injector in steady operations. The numerical model is validated first by comparing the results with the experimental data available in the literature. It is then used to study the effect of the pulse injection with different frequencies. It is found that complicated waves structures are formed inside the fuel injector in pulsed fuel injections due to the total pressure pulse. These waves propagate outside the fuel injector and lead to the fuel streams with wavy patterns and the unsteady shock structures in the combustion chamber. Fuel penetration depths are not found to be increased for pulsed injections in this study, but much high turbulent kinetic energy (TKE) levels are observed especially inside the fuel injector. With the help of increased TKE, mixing efficiency is found to be improved for all of the pulsed fuel injection by up to 30%. This mixing improvement also strongly depends on the frequency applied.
