Microfluidic assisted 90%loading CL-20 spherical particles:Enhancing self-sustaining combustion performance

The performance of the chemical fuel determines the altitude,range and longevity of spacecraft in air and space exploration.Promising alternatives(e.g.,hypergolic ionic liquids or high-energy composites)with high-energy density,heat of formation and fast initial rate are considered as potential chemical fuels.As the high-energy density material,hexanitrohexaazaisowurtzitane(CL-20)often serves as secondary explosive with poor self-propagating combustion behaviors.Herein,90%loading CL-20 microspheres with uniform particle sizes are precisely prepared by microfluid method,which exhibit unique hierarchical structure.The morphology,thermal behaviors,as well as combustion performance were further investigated.The results demonstrated that as-prepared spherical particles exhibit prominent thermal compatibility,and the enhanced self-sustaining combustion performance.This work provides an efficient method achieving the uniform high-energy density particles with excellent self-sustaining combustion performance.

Supersonic boundary layer transition induced by self-sustaining dual jets

To promote high-speed boundary layer transition,this paper proposes an active self-sustaining dual jets(SDJ)actuator utilizing the energy of supersonic mainflow.Employing the nanoparticle-based planar laser scattering(NPLS),supersonic flat-plate boundary layer transition induced by SDJ is experimentally investigated in an Ma-2.95 low-turbulence wind tunnel.Streamwise and spanwise NPLS images are obtained to analyze fine flow structures of the whole transition process.The results reveal the transition control mechanisms that on the one hand,the jet-induced shear layer produces unstable Kelvin–Helmholtz instabilities in the wake flow,on the other hand,the jets also generates an adverse pressure gradient in the boundary layer and induce unstable streak structures,which gradually break down into turbulence downstream.The paper provides a new method for transition control of high-speed boundary layer,and have prospect both in theory and engineering application.

Impact of exterior electron emission on the self-sustaining margin of hollow cathode discharge

Hollow cathode researches used to focus on the inner cavity or downstream plume,however,rarely on the gap between the throttling orifice plate and the keeper plate(T-K gap),which was found to impact the self-sustaining margin of hollow cathode discharge in this paper.Near the lower margin,the main power deposition and electron emission and ionization regions would migrate from inner cavity and downstream plume to the T-K gap,in which case,the source and destination of each m A current therein matter for the self-sustaining capability.Changing the metal surfaces in the T-K gap with emissive materials proved effective in lowering the lower margin by supplementing auxiliary thermionic emission,compensating electron loss on cold absorbing walls and suppressing discharge oscillations.By doing so,the lower margin of a 4 A hollow cathode was lowered from 1 to 0.1-0.2 A,enabling it to couple with low power Hall thruster without extra keeper current.

Numerical study on waste polyethylene pyrolysis driven by self-sustaining smoldering

Polyethylene is the type of waste plastic that accounts for the most significant proportion of municipal solid waste.Waste polyethylene can be valorized via pyrolysis and produce value-added oil,gas,and char.On the other hand,self-sustaining smoldering is an emerging technical means to deal with sand/soil contaminated by organic matter.The high-temperature heat generated by smoldering can be used as a heat source for pyrolyzing waste polyethylene.Therefore,this study investigates numerically the pyrolysis of waste polyethylene driven by self-sustaining smoldering.A novel 4-step lumped kinetic model is proposed for simulating the pyrolysis of waste polyethylene.The results indicate that the operating parameters can determine the pyrolysis product yields by regulating the pyrolysis temperature and the volatile residence time.Note that higher temperatures and longer residence times favor the generation of shorter-chain pyrolysis products because of the intensified volatiles’secondary cracking.It can be concluded that a high interface-wall heat transfer coefficient(400 W m^(-2)K^(-1)),a low PE content(0.20),a high char concentration(2.4%),and a moderate air velocity(0.040 m s^(-1))are beneficial to oil yield.To some extent,this study may broaden the boundaries for the application of self-sustained smoldering-driven pyrolysis.

Trailing-edge shock loss control with self-sustaining synthetic jet in a supersonic compressor cascade

To effectively reduce the loss of strong shock wave at the trailing edge of the supersonic cascade under high backpressure,a shock wave control method based on self-sustaining synthetic jet was proposed.The self-sustaining synthetic jet was applied on the pressure side of the blade with the blow slot and the bleed slot arranged upstream and downstream of the trailing-edge shock,respectively.The flow control mechanism and effects of parameters were investigated by numerical simulation.The results show that the self-sustaining synthetic jet forms an oblique shock wave in the cascade passage which slows down and pressurizes the airflow,and the expansion wave downstream of the blow slot weakens the shock strength which can effectively change the Mach reflection to regular reflection and thus weaken the shock loss.And the suction effect can reduce loss near blade surface.Compared with the baseline cascade,the self-sustaining jet actuator can reduce flow losses by 6.73%with proper location design and vibration of diaphragm.

Vortical structures and density fluctuations analysis of supersonic forward-facing step controlled by self-sustaining dual synthetic jets

Shock wave/boundary layer interaction(SWBLI)is still one of the unresolved bottlenecks that restrict the development of more advanced flight vehicles.Supersonic forward-facing step(FFS),an extreme case of compression ramp,often occurs severe SWBLIs with a large separation bubble.In this paper,experimental investigations on vortical structures and density fluctuations characteristics of supersonic FFS controlled by self-sustaining dual synthetic jets(SDSJ)are carried out in a Mach number 2.95 wind tunnel.High spatial–temporal resolution flowfield images of FFS without/with active flow control are captured by adopting nano-particle-based planar laser scattering technique.The control effects of the distance between the actuator and the step are mainly compared.The paper finds that the SDSJ can effectively change the feature of flowfield,eliminate the separation shock and the reattachment shock,compel the original shock induced by the step leading edge to distort and reduce its intensity finally.Density fluctuations analysis demonstrates that the whole flows seem to move upstream with the increase of distance(dS-J).Discrete Fourier transformation spectrums results reveal that the fluctuations are mainly located in the low-frequency region at first.High-frequency components and frequency bandwidth increase slightly after the SDSJ are applied.

Self-sustained Oscillation Pulsed Air Blowing System for Energy Saving

Currently, many studies have been made for years on dimensions of pneumatic nozzle, which influence the flow characteristic of blowing system. For the purpose of outputting the same blowing force, the supply pressure could be reduced by decreasing the ratio of length to diameter of nozzle. The friction between high speed air and pipe wall would be reduced if the nozzle is designed to be converging shape comparing with straight shape. But the volume flow and pressure, discussed in these studies, do not describe energy loss of the blowing system directly. Pneumatic power is an innovative principle to estimate pneumatic system’s energy consumption directly. Based on the above principle, a pulse blowing method is put forward for saving energy. A flow experiment is carried out, in which the high speed air flows from the pulse blowing system and continuous blowing system respectively to a plate with grease on top. Supply pressure and the volume of air used for removing the grease are measured to calculate energy consumption. From the experiment result, the pulse blowing system performs to conserve energy comparing with the continuous blowing system. The frequency and duty ratio of pulse flow influence the blowing characteristic. The pulse blowing system performs to be the most efficient at the specified frequency and duty ratio. Then a pneumatic self-oscillated method based on air operated valve is put forward to generate pulse flow. A simulation is made about dynamic modeling the air operated valve and calculating the motion of the valve core and output pressure. The simulation result verifies the system to be able to generate pulse flow, and predicts the key parameters of the frequency and duty ratio measured by experiment well. Finally, on the basis of simplifying and solution of the pulse blowing system’s mathematic model, the relationship between system’s frequency duty ratio and the dimensions of components is simply described with four algebraic equations. The system could be designed with specified frequency and duty ratio according to the four equations. This study provides theoretical basis for designing energy-saving air blowing system.

On the Energy Self-Sustainability of IoT via Distributed Compressed Sensing

This paper advocates the use of the distributed compressed sensing(DCS)paradigm to deploy energy harvesting(EH)Internet of Thing(IoT)devices for energy self-sustainability.We consider networks with signal/energy models that capture the fact that both the collected signals and the harvested energy of different devices can exhibit correlation.We provide theoretical analysis on the performance of both the classical compressive sensing(CS)approach and the proposed distributed CS(DCS)-based approach to data acquisition for EH IoT.Moreover,we perform an in-depth comparison of the proposed DCSbased approach against the distributed source coding(DSC)system.These performance characterizations and comparisons embody the effect of various system phenomena and parameters including signal correlation,EH correlation,network size,and energy availability level.Our results unveil that,the proposed approach offers significant increase in data gathering capability with respect to the CS-based approach,and offers a substantial reduction of the mean-squared error distortion with respect to the DSC system.

Self-sustained target waves in excitable media with only a long-range link

In this paper we investigate spatiotemporal pattern formation in excitable media with only a long-range link. Besides the trivial solutions of spiral patterns, we find the asymptotic self-sustained target waves in the autonomous tissues. The wave source supporting this kind of new pattern is the oscillatory one-dimensional Winfree-loop self- organized under the presence of a long-range link, which is explored by the dominant phase-advanced driving method. Based on this understanding we can effectively regulate the oscillations of excitable media by suitably arranging the long-range link, including construction of self-sustained target waves with controllable period and wave length, or manipulation of system states between different patterns.

Dominant phase-advanced driving analysis of self-sustained oscillations in biological networks

Oscillatory behaviors can be ubiquitously observed in various systems. Biological rhythms are significant in governing living activities of all units. The emergence of biological rhythms is the consequence of large numbers of units. In this paper we discuss several important examples of sustained oscillations in biological media, where the unit composed in the system does not possess the oscillation behavior. The dominant phase-advanced driving method is applied to study the skeletons and oscillatory organizing motifs in excitable networks and gene regulatory networks.

Numerical Simulation of Flow over an Open Cavity with Self-Sustained Oscillation Mode Switching

Numerical simulations are used to investigate the self-sustained oscillating flows past an open cavity. The two-dimensional incompressible Navier-Stokes equations are solved directly by using the finite difference method for cavities with an upstream laminar boundary layer. A series of simulations are performed for a variety of cavity length-to-depth ratio. The results show the switching among some flow modes including non-oscillation mode, shear layer mode and wake mode. The variation of the Strouhal number is in favorable agreement with available experimental data. The results of flow fields in the cavity reveal the relationship between the cavity shear layer oscillation modes and recirculating vortices in the cavity.

On the Feynman Ratchet and the Brownian Motor

We study the Brownian ratchet conditions starting with Feynman’s proposal. We show that this proposal is incomplete, and is in fact non-workable. We give the correct model for this ratchet.

Wireless Powered IoE for 6G: Massive Access Meets Scalable Cell-Free Massive MIMO

A key challenge to the scalable deployment of the energy self-sustainability(ESS)Internet of Everything(IoE)for sixth-generation(6G)networks is juggling massive connectivity and high spectral efficiency(SE).Cell-free massive multiple-input multiple-output(CF mMIMO)is considered as a promising solution,where many wireless access points perform coherent signal processing to jointly serve the users.However,massive connectivity and high SE are difficult to obtain at the same time because of the limited pilot resource.To solve this problem,we propose a new framework for ESS IoE networks where the user activity detection(UAD)and channel estimation are decoupled.A UAD detector based on deep convolutional neural networks,an initial access scheme,and a scalable power control policy are proposed to enable the practical scalable CF mMIMO implementation.We derive novel and exact closed-form expressions of harvested energy and SE with maximum ratio(MR)processing.Using local partial minimum mean-square error and MR combining,simulation results prove that the proposed framework can serve more users,improve the SE performance,and achieve better user fairness for the considered ESS IoE networks.

Joint Power and Duty-Cycle Design Using Alternating Optimization Algorithm under Energy Harvesting Architectures

In the emerging sixth generation(6G)communication network,energy harvesting(EH)is a promising technology to achieve the unlimited energy supply and hence makes the wireless communication systems self-sustainable in terms of energy.However,in practice,the efficiency of energy harvesting is often low due to the limited device capability.In this paper,we formulate three types of different EH architectures,i.e.,the harvest-use architecture,the harvest-store-use architecture,and the harvest-use-store architecture from the perspective of energy storage efficiency.We propose resource allocation schemes to jointly design the sensor power and duty-cycle via an alternating optimization algorithm under the above EH architectures,in both simultaneous and non-simultaneous harvesting and utilization models,aiming at achieving a higher throughput and energy efficiency.Non-ideal circuit power is also considered.Numerical results show that our proposed schemes under EH architectures outperform the existing classic continuous transmission schemes.

Self-sustained catalytic combustion of CO enhanced by micro fluidized bed: stability operation, fluidization state and CFD simulation

A micro fluidized bed reactor was used to study the self-sustaining catalytic combustion of carbon monoxide(CO).The Cu_(1−x)Ce_(x)O_(y) catalyst,as well as the pure CuO and CeO_(2),are used to investigate the contributing mechanism of different active sites including dispersed CuO and Cu–Ce solid solutions.The ignition temperature(Ti)of CO over these catalysts at a flow rate of 2000 mL/min followed the order:74℃(Cu_(0.5)Ce_(0.5)O_(y))<75℃(Cu_(0.25)Ce_(0.75)O_(y))<84℃(Cu_(0.75)Ce_(0.25)O_(y))<105℃(CuO)<500℃(CeO_(2)).Furthermore,the lean combustion limits(equivalence ratioϕ)over these catalysts under the flow rates of 750–3000 mL/min(through fixed,bubbling,and fluidized bed)were also measured,which are Cu_(0.5)Ce_(0.5)O_(y)<Cu_(0.25)Ce_(0.75)Oy<Cu_(0.75)Ce_(0.25)O_(y)<CuO<CeO_(2).The fluidized bed was simulated using the Eulerian two-fluid model(TFM)coupled with a diffusion/kinetic-limited reaction model to evaluate the influence of operation conditions on the self-sustained combustion of CO.The predicted maximum temperature agreed with the experimental measurements,demonstrating the validity of the kinetic model and simulation parameters.The results of catalytic combustion with increasing CO concentrations suggest that the catalytic combustion reaction could co-exist with the flamed combustion.When a high concentration of CO is used,a blue-purple flame caused by CO combustion appears in the upper part of the fluidized bed,indicating that the range of CO-containing exhaust gas purification could be expanded to a larger range using the fluidized-bed catalytic combustion technique.

Improved functional-weight approach to oscillatory patterns in excitable networks

Studies of sustained oscillations on complex networks with excitable node dynamics received much interest in recent years.Although an individual unit is non-oscillatory,they may organize to form various collective oscillatory patterns through networked connections.An excitable network usually possesses a number of oscillatory modes dominated by different Winfree loops and numerous spatiotemporal patterns organized by different propagation path distributions.The traditional approach of the so-called dominant phase-advanced drive method has been well applied to the study of stationary oscillation patterns on a network.In this paper,we develop the functional-weight approach that has been successfully used in studies of sustained oscillations in gene-regulated networks by an extension to the high-dimensional node dynamics.This approach can be well applied to the study of sustained oscillations in coupled excitable units.We tested this scheme for different networks,such as homogeneous random networks,small-world networks,and scale-free networks and found it can accurately dig out the oscillation source and the propagation path.The present approach is believed to have the potential in studies competitive non-stationary dynamics.

Simultaneous wireless information and power transfer with fixed and adaptive modulation

Activating Wireless Power Transfer (WPT) in Radio-Frequency (RF) to provide on-demand energy supply to widely deployed Internet of Everything devices is a key to the next-generation energy self-sustainable 6G network. However, Simultaneous Wireless Information and Power Transfer (SWIPT) in the same RF bands is challenging. The majority of previous studies compared SWIPT performance to Gaussian signaling with an infinite alphabet, which is impossible to implement in any realistic communication system. In contrast, we study the SWIPT system in a well-known Nakagami-m wireless fading channel using practical modulation techniques with finite alphabet. The attainable rate-energy-reliability tradeoff and the corresponding rationale are revealed for fixed modulation schemes. Furthermore, an adaptive modulation-based transceiver is provided for further expanding the attainable rate-energy-reliability region based on various SWIPT performances of different modulation schemes. The modulation switching thresholds and transmit power allocation at the SWIPT transmitter and the power splitting ratios at the SWIPT receiver are jointly optimized to maximize the attainable spectrum efficiency of wireless information transfer while satisfying the WPT requirement and the instantaneous and average BER constraints. Numerical results demonstrate the SWIPT performance of various fixed modulation schemes in different fading conditions. The advantage of the adaptive modulation-based SWIPT transceiver is validated.

On “Voice of Sea” Generation Mechanism

Physical model of self-sustained infrasonic air oscillations related to interaction of fresh gale with choppy sea surface is proposed. It is shown that air infrasonic oscillations are expected inside moving 3D cavities in sea surface generated by gale and detected far from its region. Interaction of wind with moving sea wave crests is shown to be of weaker impact on oscillations in far field. For wind velocity in the range from 10 to 40 m/s deepest cavities acquire resonance frequencies in the range of 3.0 - 0.7 Hz, i.e. frequencies much lower than their quarter wavelength resonance frequencies. In the course of oscillations effective wind velocity applied to cavities can achieve value from 0.4 to 0.6 of wind velocity, while air self-sustained oscillations velocity amplitude can run up in the range from 0.2 to 0.3 of wind velocity. Wind intensification leads to oscillations frequency decrease and oscillation energy losses increase with wind velocity cubed. Cavities natural frequencies are transformed due to air attached mass and volume elasticity additional transformation under wind influence in the range from 1.05 to 1.9 with respect to resonance frequencies at rest. Amplitude of self-sustained oscillation in atmosphere is expected to increase with wind velocity cubed, while cavity air oscillation velocity-linear with wind velocity. Wind velocity threshold of an order of 25 - 30 m/s overcome is necessary to observe effect. Spectral peaks on resonance frequencies in the range 0.7 - 2.5 Hz are expected in effect observation. Infrasonic signals observable far from whole gale in atmosphere, sea water thickness and earth crust on self-sustained oscillation frequency and its harmonics frequencies beginning from third harmonic 2.1 - 7.5 Hz are regarded as phenomenon signs.

Salt-Assisted SHS Synthesis of Aluminium Nitride Powders for Refractory Applications

Powders of aluminum nitride can be prepared by self-sustain high-temperature synthesis (SHS) between aluminum and nitrogen but its high exothermic effect causes melting and evaporation of aluminum and low efficiency of such reaction. A presence of inorganic salt in the starting powder mixture can decrease a heat evolved in the SHS reaction, hinders melting and coalescence of aluminum, and facilitates penetration of nitrogen into interior of a powder bed. Mixtures of alumina powders with different grain sizes and different amounts of aluminum carbonate were subjected to the SHS reaction under 0.05, 0.1 or 1 MPa nitrogen. The powders were composed of aluminum nitride, unreacted aluminum, aluminum oxynitride and in some cases corundum and aluminum oxycarbonate. The finale effects are strongly dependent on the amount of the salt, a grain size of aluminum and a nitrogen pressure.

Preparation of self-sustained film by sol-gel method

Large size self-sustained film with considerable thickness ranging from 30 to 500 μm was prepared with sol-gel method by using dimethyldiethoxysilane/tetraethoxysilane composite alkoxide as precursor. The film exhibits good plasticity as well. Various factors that may influence the film properties were investigated. IR and AFM techniques were adopted to study the film structure and surface morphology. Gas chromatogram/mass spectrum technique was also adopted to characterize the network structure of the material through identification of different polymers formed during hydrolysis and condensation course.