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Copyright of Journal of South China University of Technology (Natural Science Edition) is the property of South China University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The waste heat recovery from the gas turbine (GT) exhaust is typical for increasing performance and reducing CO2 emissions in industrial facilities. Nowadays, numerous already operating gas turbine plants could be retrofitted and upgraded with a bottoming cycle powered by the exhaust gasses. In this case, the standard solution would be to use a water steam Rankine cycle. However, even if this technology usually yields the best efficiency, other alternatives are often preferred on the lower size scale. Organic Rankine cycles (ORCs) are the commercial alternatives to steam Rankine cycles, but many other alternative cycles exist or can be developed, with potential benefits from safety, technical or economic points of view. This study compares several alternative technologies suited to recover gas turbine waste heat, and a detailed cost analysis for each is presented. On this basis, a guideline is proposed for the technology choice considering a wide range of application sizes and temperature levels typical for waste heat recovery from gas turbines. The compared technologies are ORCs, Rankine cycles (RCs) with water and ammonia mixtures at constant composition, supercritical CO2 cycles (sCO2), sCO2 cycles with mixtures of CO2 and other gasses. As it resulted, ORCs can achieve the lowest levelized cost of energy (32 $/MWh-46 $/MWh) if flammable fluids can be employed. Otherwise, Rankine cycles with a constant composition mixture of water and ammonia are a promising alternative, reaching a levelized cost of energy (LCOE) of 36-58 $/MWh. [ABSTRACT FROM AUTHOR]

The variation of blade wake characteristics under the influence of upstream transitional flow has not been thoroughly studied, since few control volumes in experimental investigations capture both the blade surface transitional flow and the downstream wake. In this study, instantaneous flow fields in the near-blade and the near-wake region of a compressor cascade at various incidences (i = 0 deg, 2.5 deg, 5 deg, 7.5 deg, and 10 deg) were investigated using particle image velocimetry (PIV). The mean and fluctuating near-wake fields of the compressor blade at Rec = 24,000 were analyzed considering the upstream blade surface laminar separation bubble (LSB) types. The suction-side flow topology shifts at a critical incidence angle of 5 deg from laminar separation without reattachment (i < 5 deg) into a LSB near the trailing edge (i = 5 deg) and an LSB which is advancing to the leading edge (i > 5 deg). The laminar separation vortices retain sufficient strength and coherence to interact with the wake at the low incidence angles (LIA cases, i = 5 deg) but lose coherence beyond the reattachment point at the high incidence angles (HIA cases, i > 5 deg). Self-similarity of the asymmetrical wakes under the influence of various LSB types was established. Near field evolution of wake width, wake decay rate, and flow fluctuations are directly correlated with the LSB type. An optimal incidence exists for the minimum overall flow fluctuation with a delayed separation and alleviated vortical interactions when the LSB locates at the trailing edge. [ABSTRACT FROM AUTHOR]

At a low mass ratio of structure to air, the work-per-cycle approach, or better known as the energy method, will lead to nonconservative results as aerodynamic coupling of modeshapes acts destabilizing. Using the p-k method to solve the aeroelastic stability equation, the effects of various structural aspects are investigated for a two-dimensional compressor cascade in subsonic and transonic flow conditions. The investigated key parameters are frequency separation, mass ratio, and solidity. Furthermore, the effect of a high frequency dependency of the aerodynamic forces is presented. Such phenomena can happen in case of aerodynamic or acoustic resonances. If the resonance peaks are close to the aeroelastic frequency, a discontinuous behavior of the frequency or damping solution can lead to a rapid destabilization of the system, once the aeroelastic frequency moves from one side to the other of the peak. In these regimes, it is crucial to have a high quality representation of the frequency-dependent generalized aerodynamic forces (GAFs) for an accurate prediction of the flutter onset. [ABSTRACT FROM AUTHOR]

Cancer stem cells (CSCs) are defined as a subpopulation of malignant tumor cells with selective capacities for tumor initiation, self‐renewal, metastasis, and unlimited growth into bulks, which are believed as a major cause of progressive tumor phenotypes, including recurrence, metastasis, and treatment failure. A number of signaling pathways are involved in the maintenance of stem cell properties and survival of CSCs, including well‐established intrinsic pathways, such as the Notch, Wnt, and Hedgehog signaling, and extrinsic pathways, such as the vascular microenvironment and tumor‐associated immune cells. There is also intricate crosstalk between these signal cascades and other oncogenic pathways. Thus, targeting pathway molecules that regulate CSCs provides a new option for the treatment of therapy‐resistant or ‐refractory tumors. These treatments include small molecule inhibitors, monoclonal antibodies that target key signaling in CSCs, as well as CSC‐directed immunotherapies that harness the immune systems to target CSCs. This review aims to provide an overview of the regulating networks and their immune interactions involved in CSC development. We also address the update on the development of CSC‐directed therapeutics, with a special focus on those with application approval or under clinical evaluation. [ABSTRACT FROM AUTHOR]

Broadband noise due to the turbulence-aerofoil interaction, which is also called the leading edge noise, is one of the major noise sources of aircraft (including the engine). To study the noise properties numerically is a popular approach with the increasing power of computers. Conventional approaches of using body-fitted grids at the boundaries would be convoluted due to the complex geometries, which can constrain the efficiency of parametric studies. A promising approach to tackle this issue is to use the immersed boundary method (IBM). Among various IBM variants, the volume penalization (VP) approach employs a masking function to identify the immersed solid boundary, and continuous forcing terms are added to the original flow governing equations to account for the boundary conditions. It is, therefore, efficient and easy to implement into the existing computational aeroacoustics solvers. In this work, the VP-based IBM is used to simulate the leading edge noise by combining with the advanced synthetic turbulence method. The simulations are conducted for both the isolated aerofoils and cascade, and the results are compared with the well-validated body-fitted grid solutions. The viscosity effect is also highlighted by comparing the results obtained by solving both Euler and Navier–Stokes equations. [ABSTRACT FROM AUTHOR]

In this article, an efficient time-space multigrid (TS-MG) method for solving the harmonic balance (HB) equation system is proposed. The principle of the time-space multigrid method is to coarsen grids in both space and time dimensions simultaneously when coarse grids are formed. The inclusion of time in the time-space multigrid is to address the instability issue or diminished convergence speedup of the spatial multigrid (S-MG) due to larger grid reduced frequencies on coarse grids. With the proposed method, the unsteady flow governing equation will still be solved on all grid levels. Comparing to the finest grid, fewer harmonics and thus fewer equations will be solved consequently on coarse grids. Discrete Fourier transform (DFT) and inverse discrete Fourier transform (IDFT) are used to achieve solution prolongation and restriction between different time grid levels. Results from the proposed method are compared with those obtained from the traditional S-MG and time domain methods. It is found that the TS-MG method can increase solution stability, reduce analysis central processing unit (CPU) time cost required for convergence, save memory usage and has no adverse effect on solution accuracy. [ABSTRACT FROM AUTHOR]

The paper presents a detailed analysis of particle image velocimetry (PIV) measurements performed in a turbine cascade representative of highly accelerated low-pressure turbine (LPT) blades. Two cameras have been simultaneously used to observe a great portion of the suction side boundary layer with the highest possible spatial resolution, thus allowing us to solve the interaction process between impinging upstream wakes and the blade boundary layer. Four unsteady inflow conditions, characterized by different incoming wake reduced frequencies and flow coefficients, have been examined at fixed Reynolds number. The highly resolved flow fields have been processed to explore reduced frequency and flow coefficient effects on the boundary layer unsteady transition process and, consequently, on loss production. For a deep physical insight on the mechanisms responsible for loss generation, proper orthogonal decomposition (POD) has been applied at different phases of the wake passing period. This has provided the dominant structures affecting the cascade aerodynamics during the wake period. Moreover, the examination of POD modes has allowed us to show the effects induced by the parameter variation on the turbulent kinetic energy production and thus to the unsteady loss production mechanisms. [ABSTRACT FROM AUTHOR]

Aeroelastic instabilities such as flutter have a crucial role in limiting the operating range and reliability of turbomachinery. This paper offers an alternative approach to aeroelastic analysis, where the sensitivity of aerodynamic damping with respect to main flow and structural parameters is quantified through a surrogate-model-based investigation. The parameters are chosen based on previous studies and are represented by a uniform distribution within applicable intervals. The surrogate model is an artificial neural network, trained and tested to achieve an error within 1% of the test data. The quantity of interest is aerodynamic damping and the datasets are obtained from a linearised aeroelastic solver. The sensitivity of aerodynamic damping with respect to the input variables is obtained by calculating normalised gradients from the surrogate model at specific operating conditions. The results show a quantitative comparison of sensitivity across the different input parameters. The outcome of the sensitivity analysis is then used to decide the most appropriate action to take in order to induce stability in unstable operating conditions. The work is a preliminary study, carried out on a simplified two dimensional compressor cascade and it is aimed at proving the validity of a data-driven approach in studying the aeroelastic behaviour of turbomachinery. To the best of the authors' knowledge, this is the first time a data-driven flutter model has been investigated. The initial results are encouraging, indicating that this approach is worth pursuing in the future. The presented framework can be used as a redesign tool to enhance the flutter stability of an existing blade. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the influence of different subgrid-scale (SGS) closure models and inflow turbulence conditions on the boundary layer transition on the suction side of a highly loaded transonic turbine cascade in the presence of high free-stream turbulence using large eddy simulations (LES) of the MUR237 test case. For the numerical simulations, the MUR237 flow case was considered and the incoming free-stream turbulence was reproduced using the synthetic eddy method (SEM). The boundary layer transition on the blade suction side was found to be significantly influenced by the choice of the SGS closure model and the SEM parameters. These two aspects were carefully evaluated in this work. Initially, the influence of three different closure models (Smagorinsky, WALE, and subgrid-scale kinetic energy model) was evaluated. Among them, the WALE SGS closure model performed best compared to the Smagorinsky and KEM models and, for this reason, was used in the following analysis. Finally, different values of the turbulence length scale, eddies density, and inlet turbulence for the SEM were evaluated. As shown by the results, among the different parameters, the choice of the turbulence length scale plays a major role in the transition onset on the blade suction side. [ABSTRACT FROM AUTHOR]

Unsteady pressure fluctuations measured by fast-response pressure transducers mounted in a low-pressure turbine cascade are compared to unsteady simulation results. Three differing simulation approaches are considered, one time-integration method and two harmonic balance methods either resolving or averaging the time-dependent components within the turbulence model. The observations are used to evaluate the capability of the harmonic balance solver to predict the transient pressure fluctuations acting on the investigated stator surface. Wakes of an upstream rotor are generated by moving cylindrical bars at a prescribed rotational speed that refers to a frequency of f 500 Hz. The excitation at the rear part of the suction side is essentially driven by the presence of a separation bubble and is therefore highly dependent on the unsteady behavior of turbulence. In order to increase the stability of the investigated harmonic balance solver, a developed Lanczos-type filter method is applied if the turbulence model is considered in an unsteady fashion. [ABSTRACT FROM AUTHOR]

One way to reduce waste and to make a system more robust is to allow its components to pool resources. For example, banks might insure each other or share a common capital reserve. Systems whose resources have been pooled in this way are highly prevalent in such diverse domains as finance, infrastructure, health care, emergency response and engineering. However, these systems have a combination of characteristics that leave them vulnerable to poor decision-making: non-linearity of risk; obvious rewards combined with hidden costs; and political and market incentives that encourage inadequate safety margins. Three studies demonstrate a tendency for managers of such systems to underestimate the probability of cascading failures. We describe a series of behaviorally based policy interventions to mitigate the resulting hazards. [ABSTRACT FROM AUTHOR]

In this paper, we develop sufficient conditions for uniform asymptotic stability of interconnected dynamical systems that are not in cascade form. We show that the stability analysis of a two-subsystem interconnection can be reduced to ensuring the stability of the first nonisolated subsystem with respect to its own state vector (partial stability) and the stability of the isolated second subsystem. In addition, based on the above results, we provide a control design framework for nonlinear systems where the control objective reduces to stabilization of only a part of the system state while guaranteeing the stability for the entire state of the system. We validate the efficacy of the proposed control framework via simulations and experiments using the wheeled mobile robot platform. [ABSTRACT FROM AUTHOR]

Complex systems are challenging to control because the system responds to the controller in a nonlinear fashion, often incorporating feedback mechanisms. Interdependence of systems poses additional difficulties, as cross-system connections enable malicious activity to spread between layers, increasing systemic risk. In this paper we explore the conditions for an optimal control of cascading failures in a system of interdependent networks. Specifically, we study the Bak–Tang–Wiesenfeld sandpile model incorporating a control mechanism, which affects the frequency of cascades occurring in individual layers. This modification allows us to explore sandpile-like dynamics near the critical state, with supercritical region corresponding to infrequent large cascades and subcritical zone being characterized by frequent small avalanches. Topological coupling between networks introduces dependence of control settings adopted in respective layers, causing the control strategy of a given layer to be influenced by choices made in other connected networks. We find that the optimal control strategy for a layer operating in a supercritical regime is to be coupled to a layer operating in a subcritical zone, since such condition corresponds to reduced probability of inflicted avalanches. However this condition describes a parasitic relation, in which only one layer benefits. Second optimal configuration is a mutualistic one, where both layers adopt the same control strategy. Our results provide valuable insights into dynamics of cascading failures and and its control in interdependent complex systems. [ABSTRACT FROM AUTHOR]

The background pattern of patterned fabrics is complex, which has a great interference in the extraction of defect features. Traditional machine vision algorithms rely on artificially designed features, which are greatly affected by background patterns and are difficult to effectively extract flaw features. Therefore, a convolutional neural network (CNN) with automatic feature extraction is proposed. On the basis of the two-stage detection model Faster R-CNN, Resnet-50 is used as the backbone network, and the problem of flaws with extreme aspect ratio is solved by improving the initialization algorithm of the prior frame aspect ratio, and the improved multi-scale model is designed to improve detection of small defects. The cascade R-CNN is introduced to improve the accuracy of defect detection, and the online hard example mining (OHEM) algorithm is used to strengthen the learning of hard samples to reduce the interference of complex backgrounds on the defect detection of patterned fabrics, and construct the focal loss as a loss function to reduce the impact of sample imbalance. In order to verify the effectiveness of the improved algorithm, a defect detection comparison experiment was set up. The experimental results show that the accuracy of the defect detection algorithm of patterned fabrics in this paper can reach 95.7%, and it can accurately locate the defect location and meet the actual needs of the factory. [ABSTRACT FROM AUTHOR]

In a cluster crystal, each lattice site is occupied by multiple soft-core particles. As the number density is increased at zero temperature, a "cascade" of isostructural phase transitions can occur between states whose site occupancy differs by unity. For low but finite temperature, each of these transitions terminates in a critical point. Using tailored Monte Carlo simulation techniques, we have studied such demixing cascades in systems of soft particles interacting via potentials of the generalized exponential form u(r) = ∈∈ exp [-(r/σ)n].We have estimated the critical parameters of the first few transitions in the cascade as a function of the softness parameter n. The critical temperature and pressure exhibit non-monotonic behavior as n is varied, although the critical chemical potential remains monotonic. The trends for the pressure and chemical potential are confirmed by cell model calculations at zero temperature. As n →2 +, all the transitions that we have observed are preempted by melting although we cannot rule out that clustering transitions survive at high density. [ABSTRACT FROM AUTHOR]

Near-wall modeling is one of the most challenging aspects of computational fluid dynamic computations. In fact, integration-to-the-wall with low-Reynolds approach strongly affects accuracy of results, but strongly increases the computational resources required by the simulation. A compromise between accuracy and speed to solution is usually obtained through the use of wall functions (WFs), especially in Reynolds averaged Navier-Stokes computations, which normally require that the first cell of the grid to fall inside the log-layer (50

In this work, the problem of trajectory tracking in uncertain underactuated systems is considered. To solve it, a combination of differential flatness and active disturbance rejection control (ADRC) is proposed. The controller design is synthesized in the absence of detailed knowledge of the system model and focuses on dealing with over-amplification of measurement noise, typically seen in conventional single high-gain observer-centered control approaches. The introduced solution is based on fully utilizing the information already available about the governed system, without the necessity for additional measurement devices. To be easily implementable, it is expressed in an industry familiar error-based form with a straightforward tuning method. Through experimental verification, the proposed approach is shown to enhance the disturbance-rejection capabilities of the standard ADRC structure and reduce its sensitivity to measurement noise, thus increasing its practical appeal. [ABSTRACT FROM AUTHOR]

We perform a power spectral analysis of magnetic field fluctuations measured by the Rosetta spacecraft's magnetometer at comet 67P/Churyumov-Gerasimenko. We interpret the power spectral signatures in terms of plasma turbulent processes and discover that different turbulent processes are prominent during different active phases of the comet. During the weakly active phase of the comet, dominant injection is prominent at low frequencies near 10-2 Hz, while partial energy cascade or dispersion is prominent at high frequencies near 10-1 Hz. During the intermediately active phase, uniform injection is prominent at low frequencies, while partial energy cascade or dispersion is prominent at high frequencies. During the strongly active phase of the comet, we find that partial energy cascade or dissipation is dominant at low frequencies, while partial energy cascade, dissipation, or dispersion is dominant at high frequencies. We infer that the temporal variations of the turbulent processes occur due to the evolution of the plasma environment of the comet as it orbits the Sun. [ABSTRACT FROM AUTHOR]

Cooling systems have been widely studied over the past few years, but there are little researches on cascade cooling system containing different cooling methods. Cascade cooling system is suitable for the hot stream cooling process with large temperature variation. A new cascade cooling system containing waste heat recovery, air cooling, water cooling, absorption refrigeration and compression refrigeration is proposed. In this system, hot water is used to recycle waste heat from the hot stream, then drive the absorption refrigeration cycle (ARC), providing refrigerant water for hot stream cooling process. The mass flowrate of hot water determines the amount of waste heat recovered, and the final hot water temperature affects the thermal efficiency of ARC. Both the flowrate and the final temperature of hot water influence the cooling capacity generated by ARC, and further affect the heat load distribution of cascade cooling system. The hot water mass flowrate is a critical decision variable for the optimal design of the system. This study develops a model for the techno-economic optimization of cascade cooling system with ARC. ARC is modelled using thermodynamics with the concept of state points. The proposed model determines the optimal heat load distribution of cascade cooling system and the optimal design of ARC, with the minimum total annual cost (TAC) simultaneously. The effectiveness of this method is demonstrated with a case study in a polysilicon enterprise. [ABSTRACT FROM AUTHOR]

Understanding the response of ecological networks to perturbations and disruptive events is needed to anticipate the biodiversity loss and extinction cascades. Here, we study how network plasticity reshapes the topology of mutualistic networks in response to species loss. We analyze more than one hundred empirical mutualistic networks and considered random and targeted removal as mechanisms of species extinction. Network plasticity is modeled as either random rewiring, as the most parsimonious approach, or resource affinity-driven rewiring, as a proxy for encoding the phylogenetic similarity and functional redundancy among species. This redundancy should be positively correlated with the robustness of an ecosystem, as functions can be taken by other species once one of them is extinct. We show that effective modularity, i.e. the ability of an ecosystem to adapt or restructure, increases with increasing numbers of extinctions, and with decreasing the replacement probability. Importantly, modularity is mostly affected by the extinction rather than by rewiring mechanisms. These changes in community structure are reflected in the robustness and stability due to their positive correlation with modularity. Resource affinity-driven rewiring offers an increase of modularity, robustness, and stability which could be an evolutionary favored mechanism to prevent a cascade of co-extinctions. [ABSTRACT FROM AUTHOR]

A comparative experimental analysis is performed on pulsed suction (PS) and pulsed blowing (PB) used to control flow separations in a highly loaded compressor cascade. The effectiveness of the control methods is assessed via oil-flow visualization and steady and unsteady pressure measurements. Firstly, the control effect of the PS is evaluated by comparing the conventional steady continuous suction (SCS). A more efficient control effect is achieved by the PS compared to the SCS. Additionally, in order to further explore the potentials of the PS and PB and gain some insight into their controlling mechanisms, some important excitation parameters including excitation location, momentum coefficient and frequency are comparatively investigated in detail. It is found that the PS and PB are both able to improve the cascade performance by effectively suppressing the passage vortex. With the excitation location moving downstream, the almost opposite change trends for the PS and PB on the total pressure loss and energy efficiency are shown. The PS has an advantage over the PB in improving the cascade performance at the same average excitation momentum. But there is a slighter change of the losses for the PB cases at different excitation frequencies relative to the PS ones, indicating that the PB is more insensitive to the excitation frequency. Based on the optimal excitation parameters, the total pressure loss coefficients for the PS and PB are reduced by 11.3% and 10.3%, respectively. Furthermore, the effectiveness of the PS and PB is also corroborated at a larger incidence angle. [ABSTRACT FROM AUTHOR]

The blended blade and endwall (BBEW) contouring technology can adjust the dihedral angle between suction surface and endwall, thus reducing corner separation in compressors. Generally, the design of BBEW relies on the experiences, the effective design results may not be the optimal result. In this paper, an optimization approach based on the genetic algorithm (GA) for feature selection and parameter optimization of support vector machine (SVM) is used to obtain the optimal BBEW parameters in a compressor cascade. Based on the sensitivity analysis of the results, it is found that the maximum blended width and the axial position of the maximum blended width are the two most important design parameters. The experimental results show that the optimal BBEW cascade can stretch the spanwise area of the high loss region, and reduce the maximum value in it. The numerical studies were conducted to analyze the flow mechanism. It is shown that the BBEW cascade has a transverse pressure difference at the axial position of the maximum blended width, and magnitude of the pressure difference in proportion to the maximum blended width. The transverse pressure difference removes the low-energy fluid from the corner to the main flow, thus improving the corner separation. [ABSTRACT FROM AUTHOR]

One-dimensional (1D) modeling is crucial for turbomachinery unsteady performance prediction and system response assessment. The purpose of the paper is to describe a newly developed 1D modeling (turbomachinery dynamic simulator (TURBODYNA)) for turbomachinery. Different from classic 1D modeling, in TURBODYNA, rotor has been meshed and its unsteadiness due to flow field timescale is considered. Instead of direct using of performances maps, source terms are added in Euler equation set to simulate the rotor. By comparing 1D modeling with three-dimensional (3D) computational fluid dynamics (CFD) results, it shows that rotor unsteadiness is indispensable for a better prediction. In addition, different variables response to pulse differently. In the rotor, mass flow is close to quasi-steady while entropy is significantly unsteady. TURBODYNA can capture these features correctly and provide an accurate prediction on pressure wave transportation. [ABSTRACT FROM AUTHOR]

We investigate the spin-dependent transport in aperiodic cascade junctions of semiconductors, where semiconductors are arranged in the Thue-Morse sequence. We have calculated the spin-dependent transmission and the spin polarization with a transfer matrix method in these cascade junctions. It is shown that a spin-dependent bandgap structure appears by changing the generation and the Rashba spin-orbit wave vector. As a result, around resonant wave vectors, high spin polarization has been observed and the spin polarization has been reversed, and the spin conductance exists the value of zero by tuning the Rashba spin-orbit coupling. Our investigations may provide a way to design spin filters and spin switches. [ABSTRACT FROM AUTHOR]

Information about intermolecular potentials is usually obtained through the analysis of the absorption line shapes recorded in the frequency domain. This approach is also adopted to study the effects of motional narrowing and speed dependence of the pressure broadening coefficients. On the other hand, time domain measurements are directly related to molecular collisions and are therefore frequently employed to study molecular relaxation rates, as well as the effects of velocity changing collisions and the speed dependence of the absorption cross sections. Intrapulse quantum cascade laser spectrometers are able to produce both saturation and molecular alignment of the gas sample. This is due to the rapid sweep of the radiation through the absorption features. In the present work the frequency down-chirped radiation emitted by an intrapulsed quantum cascade laser operating near 7.8 μm is employed to investigate the collisional relaxation processes, and the collisional narrowing, in the 150,15←161,16 and 151,15←160,16 doublet in the water vapor ν2 band. The effects of He, Ne, Ar, N2, and CO2 as collisional partners are investigated. The experimental results clearly indicate the dependence of the collisional cross sections upon the chirp rate. They also demonstrate that by using different chirp rates it is possible to gain information about the intermolecular processes driving the molecular collisions and the related energy transfer. [ABSTRACT FROM AUTHOR]

The gain coefficient of several GaAs/AlxGa1-xAs quantum-cascade lasers (QCLs) with a nominal Al content of x=0.45 has been calculated as a function of transition energy and electric field strength. We solve the Schrödinger and Poisson equations self-consistently in the framework of a linear scattering-rate model with periodic boundary conditions. The actual layer thicknesses as well as the Al content of the barriers have been obtained from x-ray diffraction. The calculated gain characteristics exhibit a large range of transition energies and a corresponding range of possible operating field strengths. These results may provide an explanation for the observation of a rather large range of the lasing energies for QCLs with nominally identical cascade structures. The comparison with the experimental values of the lasing energy reveals that most of the lasers operate below the designed field strength. The analysis of the operating field strengths and the threshold current densities indicates larger losses for higher field strengths probably due to leakage currents. [ABSTRACT FROM AUTHOR]

We have investigated the structural properties of Si/SiGe electroluiminescent quantum-cascade structures, by means of x-ray reflectivity and diffraction. The cascade structures were grown at a comparatively low temperature of T = 350 °C to avoid misfit dislcoation formation. Despite an overall thickness of the cascade structures of about 9000 Å and Ge contents of up to more than 40% in some of the SiGe wells, the entire stack of layers is indeed pseudomorphic with respect to the Si substrate. The analysis of x-ray reflectivity data yields a rather small rms interface roughness, which increases only slightly from 2 to 2.9 Å from the bottom to the top of the cascade structures. From x-ray reflectivity maps we obtain in addition the vertical and lateral correlation of the interface roughness. It turns out that for long range interface fluctuations the vertical correlation length is larger than for short range fluctuations. [ABSTRACT FROM AUTHOR]

Electron transport in GaAs/AlGaAs quantum cascade lasers operating in midinfrared is calculated self-consistently using an intersubband scattering model. Subband populations and carrier transition rates are calculated and all relevant electron-LO phonon and electron-electron scatterings between injector/collector, active region, and continuum resonance levels are included. The calculated carrier lifetimes and subband populations are then used to evaluate scattering current densities, injection efficiencies, and carrier backflow into the active region for a range of operating temperatures. From the calculated modal gain versus total current density dependencies the output characteristics, in particular the gain coefficient and threshold current, are extracted. For the original GaAs/Al[sub 0.33]Ga[sub 0.67]As quantum cascade structure [C. Sirtori et al., Appl. Phys. Lett. 73, 3486 (1998)] these are found to be g = 11.3 cm/kA and J[sub th] = 6 ± 1 kA/cm² (at T = 77 K), and g = 7.9 cm/kA and J[sub th] = 10 ± 1 kA/cm² (at T = 200 K), in good agreement with the experiment. Calculations shows that threshold cannot be achieved in this structure at T = 300 K, due to the small gain coefficient and the gain saturation effect, also in agreement with experimental findings. The model thus promises to be a powerful tool for the prediction and optimization of new, improved quantum cascade structures. [ABSTRACT FROM AUTHOR]

The article presents an exploration into the causes and conditions leading to the perpetuation of unpopular and inefficient social norms and the methods by which they can be forced to collapse. Questions are raised regarding the rationality of human behaviors and social norms, such as prejudices and counterintuitive behavior. An explanation is offered through an observer-ignorance model and mistaken assumptions due to individual paradigm biases. Several examples are given from social psychology, including the impacts of pluralistic ignorance, misrepresentation, and conformity. The additional mathematical model of information cascades is defined and utilized within this context to instigate norm and perception shifts.

The design of converging-diverging blades for organic Rankine cycle (ORC) applications widely relies on automated shape-optimization processes. As a result, the optimization produces an adapted-nozzle cascade at the design conditions. However, only few works account for the uncertainties in those conditions and their consequences on cascade performance. The proposed solution, i.e., including uncertainties within the optimization routine, demands an overall huge computational cost to estimate the target output statistic at each iteration of the optimization algorithm. With the aim of understanding if this computational cost is avoidable, we study the impact of uncertainties in the design conditions on the robustness of deterministically optimized profiles. Several optimized blades, obtained with different objective functions, constraints, and design variables, are considered in the present numerical analysis, which features a turbulent compressible flow solver and a state-of-the-art uncertainty-quantification (UQ) method. By including measured field variations in the formulation of the UQ problem, we show that a deterministic shape optimization already improves the robustness of the profile with respect to the baseline configuration. Guidelines about objective functions and blade parametrizations for deterministic optimizations are also provided. Finally, a novel methodology to estimate the mass-flow-rate probability density function (PDF) for choked supersonic turbines is proposed, along with a robust reformulation of the constraint problem without increasing the computational cost. [ABSTRACT FROM AUTHOR]

Modern lean burn aero-engine combustors make use of relevant swirl degrees for flame stabilization. Moreover, important temperature distortions are generated, in tangential and radial directions, due to discrete fuel injection and liner cooling flows respectively. At the same time, more efficient devices are employed for liner cooling and a less intense mixing with the mainstream occurs. As a result, aggressive swirl fields, high turbulence intensities, and strong hot streaks are achieved at the turbine inlet. In order to understand combustor-turbine flow field interactions, it is mandatory to collect reliable experimental data at representative flow conditions. While the separated effects of temperature, swirl, and turbulence on the first turbine stage have been widely investigated, reduced experimental data is available when it comes to consider all these factors together. In this perspective, an annular three-sector combustor simulator with fully cooled high pressure vanes has been designed and installed at the THT Lab of University of Florence. The test rig is equipped with three axial swirlers, effusion cooled liners, and six film cooled high pressure vanes passages, for a vortex-to-vane count ratio of 1:2. The relative clocking position between swirlers and vanes has been chosen in order to have the leading edge of the central NGV aligned with the central swirler. In order to generate representative conditions, a heated mainstream passes though the axial swirlers of the combustor simulator, while the effusion cooled liners are fed by air at ambient temperature. The resulting flow field exiting from the combustor simulator and approaching the cooled vane can be considered representative of a modern Lean Burn aero engine combustor with swirl angles above ±50deg, turbulence intensities up to about 28% and maximum-to-minimum temperature ratio of about 1.25. With the final aim of investigating the hot streaks evolution through the cooled high pressure vane, the mean aerothermal field (temperature, pressure, and velocity fields) has been evaluated by means of a five-hole probe equipped with a thermocouple and traversed upstream and downstream of the NGV cascade. [ABSTRACT FROM AUTHOR]

Ceramic matrix composite (CMC) have higher temperature durability and lower density property compared to nickel-based super-alloys which so far have been widely applied to hot section components of aero-engines/gas turbines. One of promising CMC systems, SiC-SiC CMC is able to sustain its mechanical property at higher temperature, though it inherently needs environmental barrier coating (EBC) to avoid oxidation. There are several requirements for EBC. One of such critical requirements is its resistance to particle erosion, whereas this subject has not been well investigated in the past. The present work presents the results of a combined experimental and numerical research to evaluate the erosion characteristics of CMC + EBC material developed by IHI. First, experiments were carried out in an erosion test facility using 50 μm diameter silica as erosion media under typical engine conditions with velocity of 225 m/s, temperature of 1311 K, and impingement angles of 30, 60, and 80 deg. The data displayed brittle erosion mode in that the erosion rate increased with impact angles. Also, it was verified that a typical erosion model, Neilson-Gilchrist model, can reproduce the experimental behavior fairly well if its model constants were properly determined. The numerical method solving particle-laden flow was then applied with the tuned erosion model to compute three dimensional flow field, particle trajectories, and erosion profile around a generic turbine airfoil to assess the erosion characteristics of the proposed CMC + EBC material when applied to airfoil. The trajectories indicated that the particles primarily impacted the airfoil leading edge and the pressure surface. Surface erosion patterns were predicted based on the calculated trajectories and the experimentally based erosion characteristics. [ABSTRACT FROM AUTHOR]

Abstract In general, understanding the cascade flow loss mechanism is crucial for the design and optimisation of the cascade from the basically essential. The research objective of this study was to develop a highly loaded compressor linear cascade, and a numerical simulation was performed to obtain both the vortex structures and the flow loss of the cascade during the corner stall process. The results indicate that the curved blade affects the influence range of the vortex structures by changing the pressure gradients of the cascade, and subsequently changes the transport process of the vortex structure to low-energy fluid clusters, thus affecting the weight distribution of the flow loss. Additionally, the weight coefficients of the passage vortex and concentrated shedding vortex are merged together, and accounts for half of the total flow losses. Finally, the innovation of this paper is to propose a topological analysis method based on the accurate and quantitative identification of the singular points' positions serves as a useful research method to reveal the vortex dynamic mechanism of the weight distribution of the flow loss affected by the curved blade, and the vortex criterion of the corner stall is proposed additionally. [ABSTRACT FROM AUTHOR]

Abstract The main objective of this research is to study experimentally the effect of transition on the flow structure of the shock wave boundary layer interaction in the blades passage of a compressor cascade. For this purpose a model of a turbine compressor passage was designed and assembled in a transonic wind tunnel. In the experiment the distributed roughness with different heights and locations was used to induce transition upstream of the shock wave. Three locations of distributed roughness in form of standard sandpaper strips were chosen to apply on the blade. The average roughness height comprised in a range of 8 to 16 μm. All together 8 different flow cases were investigated. The paper focuses on the influence of the boundary layer transition induced by different roughness values and locations on the flow pattern in the blades passage of a compressor cascade. Very promising results were obtained in the roughness application for the boundary layer transition control, demonstrating a positive effect in changing the nature of the interaction. [ABSTRACT FROM AUTHOR]

Abstract Conceptual frameworks for ecosystem services of (ESCF), such as the cascade framework, have been used for various purposes. In this paper we demonstrate that the structure and content of ESCF are tailored to the user's specific concerns. We discuss which requirements an ESCF needs to fulfil in relation to two cases: when it acts as an organizing structure and when it serves as a model for the valuation of ecosystems in terms of their contribution to human well-being. Although such a framework will need to fulfil different requirements for each of these purposes, we provide some general recommendations for development, the most important ones being to include human well-being in the framework, to value ES functions, services and benefits, and to define the ESCF components first and foremost in terms of their relation to human well-being. Highlights • The concepts of functions, ecosystem services (ES) and benefits need clarification. • The meaning of these concepts within frameworks depends on the purpose of use. • Integration of human well-being is vital in ES conceptual frameworks. • Values can be assigned to ES and benefits, and also to functions. [ABSTRACT FROM AUTHOR]

Highlights • Displacement cascades with 3, 6 and 9 keV PKA in Fe nanofoam were investigated. • 1–4 cylindrical nanovoids were employed as model structure. • Mostly, presence of nanovoids increases the number of residual vacancies in bulk. • Vacancy plane was formed in ligament in maximum interaction of cascade and surfaces. • Most of residual vacancies in the ligament, participate on vacancy clusters. Abstract In this research, in order to investigate primary radiation damage in iron nanofoam, simulation of displacement cascade near cylindrical nanovoids is performed using molecular dynamics. A primary knocked-on atom with 3, 6 and 9 keV energies and velocity parallel to the cylinder axis at 300 K is considered. 1–4 nanovoids are used as the model structure for free surfaces. It is identified that interaction between the displacement cascades and free surfaces is very sensitive to PKA energy and the distance of free surfaces. Near-surface cascade mechanism is observed when the displacement cascade interacts with a single cylindrical free surface, where clusters of bulk vacancies and a rim of adatoms are formed. In this case, based on the location of these defects rather free surface, two sub-mechanisms are identified. It is recognized that the degree of the penetration of the cascade into the cylindrical surfaces, plays an important role in forming vacancies and vacancy clusters in the ligament after the cooling of the cascade. Results show that when the PKA energy is 9 keV, enhancement of number of nanovoids increases the number of vacancies in the bulk. In this case, formation of vacancy planes is observed between the cylindrical nanovoids. The absorption of bulk vacancy clusters by the free surfaces is observed when displacement cascade is generated by a 6 keV PKA in close vicinity of four cylindrical surfaces. [ABSTRACT FROM AUTHOR]

Matriptase is a member of the type-II transmembrane serine protease (TTSP) family and plays a crucial role in the development and maintenance of epithelial tissues. As all chymotrypsin-like serine proteases, matriptase is synthesized as a zymogen (proform), requiring a cleavage event for full activity. Recent studies suggest that the zymogen of matriptase possesses enough catalytic activity to not only facilitate autoactivation, but also carry out its in vivo functions, which include activating several proteolytic and signaling cascades. Inhibition of zymogen matriptase may therefore be a highly effective approach for limiting matriptase activity. To this end, here we sought to characterize the catalytic activity of human zymogen matriptase and to develop mAb inhibitors against this enzyme form. Using a mutated variant of matriptase in which the serine protease domain is locked in the zymogen conformation, we confirmed that the zymogen form of human matriptase has cata- lytic activity. Moreover, the crystal structure of the catalytic domain of zymogen matriptase was solved to 2.5 Å resolution to characterize specific antibody-based matriptase inhibitors and to further structure-based studies. Finally, we describe the first antibody-based competitive inhibitors that target both the zymogen and activated forms of matriptase. We propose that these antibodies provide a more efficient way to regulate matriptase activity by targeting the protease both before and after its activation and may be of value for both research and preclinical applications. [ABSTRACT FROM AUTHOR]

Abstract A proper combination of active and passive flow control methods would be a promising way to further enhance the compressor performance. This numerical investigation presents a new attempt of application of endwall contouring in a high subsonic tandem cascade with the endwall boundary layer suction implemented in the forward blade. The study aims to further improve the corner flow in the rear blade at design and lower incidences. The planar endwall is redesigned using the optimization method. Nonuniform rational B-spline surface is employed to parameterize the endwall surface. A multi-points optimization strategy is selected to minimize the aerodynamic loss generated in the cascade. In the optimization, the suction strategy remains unchanged. To clarify the impacts of endwall contouring on the cascade performance, flow details in both mainflow passage and suction flow path at design and off-design incidences are analyzed. As a result, the total loss decreases by 8.4% at the design incidence via the endwall contouring. Furthermore, a more prominent loss reduction can be achieved at lower incidences. However, the control effects of endwall contouring is weakened towards higher positive incidences. Worse still, even a deterioration in the cascade performance can be detected at I = 5 ° due to the presence of a small-scale corner stall in the forward blade. The results indicate that, as the gap flow is not strong enough to counteract the endwall secondary flow, the endwall contouring could be employed to further enhance the flow control ability of the previous proposed compound flow control method, while its negative impact on the cascade performance at higher positive incidences still remains to be addressed. [ABSTRACT FROM AUTHOR]

Highlights • Nanofilm processors are cascaded. • The cascade leads theoretically to a nanofilm processor with infinite lengths. • A new electrochemical method is presented. Abstract Nanofilm processors are based on the lateral anodic self-oxidation of a nanoscale aluminum electrode in the presence of a graphite counter electrode. The oxidation process operates slowly over a long period of time. There are electrical and fluidic limitations of the oxidation length and velocity during the lateral anodic self-oxidation process. With the integration of fluidic coupling elements, it is possible to realize a cascade of equivalent nanofilm processors, theoretically leading to a nanofilm processor with infinite lengths. [ABSTRACT FROM AUTHOR]

This paper is concerned with the target tracking problem of an autonomous surface vehicle in the presence of a maneuvering target. The velocity information of target is totally unknown to the follower vehicle, and only the relative distance and angle between the target and follower are obtained. First, a reduced-order extended state observer is used to estimate the unknown relative dynamics due to the unavailable velocity of the target. Based on the reduced-order extended state observer, an antidisturbance guidance law for target tracking is designed. The input-to-state stability of the closed-loop target tracking guidance system is analyzed via cascade theory. Furthermore, the above result is extended to the case that collisions between the target and leader are avoided during tracking, and a collision-free target tracking guidance law is developed. The main feature of the proposed guidance law is twofold. First, the target tracking can be achieved without using the velocity information of the target. Second, collision avoidance can be achieved during target tracking. Simulation results show the effectiveness of the proposed antidisturbance guidance law for tracking a maneuvering target with the arbitrary bounded velocity. [ABSTRACT FROM AUTHOR]

Abstract A semi-analytical method is proposed for calculating the response of a linear cascade with spanwise mean flow subject to oblique gusts. It is developed based on the boundary value problems defined by Lloyd and Peake (AIAA paper 2008–2840). A gust strength parameter is introduced and the correct three-dimensional (3-D) response is obtained. The classic similarity rules are extended; the approach can be used to extend any 2-D methods to account for oblique gusts and 3-D mean flows. It is validated against analytical approximations for single-airfoil and cascade responses. The method is used to investigate the effect of gust angle α g on the unsteady lift and the sound field. It is found that as α g increases, the 2-D equivalent response varies slightly. However, the 3-D lift is amplified by factor 1 / cos α g , and the spanwise phase variation increases. Cascade effects are also studied. The inter-blade phase angle (IBPA) is important even for very low solidity. As the solidity increases, the chordwise distribution of lift is no longer leading-edge dominant. Cascade effects are small only when the cascade blade count is lower than a limit. A statistics analysis reveals that Mach number is the most important parameter for determining this blade count limit, and frequency is the least important. [ABSTRACT FROM AUTHOR]

Interaction of a nanosecond high-intensity pulsed ion beam with thin graphene films on copper substrates is analyzed. Methods of Raman spectroscopy are used to investigate the degree of graphene degradation depending on the integral implanted dose. The role of the substrate in the structural degradation of graphene irradiated by charged particle beams is demonstrated using the software package SRIM, intended for modeling radiative defect cascades under irradiation by charged particle beams, and the data on radiation resistance of graphene available in the literature. [ABSTRACT FROM AUTHOR]

Highlights • Selection of the d 1 determines the N S , at which detectivity reaches maximum. • d 1opt is higher for equal- than for matched-absorbers detectors. • D* MAX is slightly lower for equal- than for matched-absorbers detectors. • Detectivities are comparable for both type of interband cascade detectors. • Total absorber thickness is higher for the matched-absorbers detector. Abstract The paper presents the performance of the interband cascade type-II superlattice infrared photodetectors. Such photodetectors are made up of multiple stages, which are connected in series using an interband tunneling heterostructure. In this paper, we compare two different architectures of the cascade structure: equal absorber thickness in all stages and varied absorber thickness. In our calculation, in the case of equal absorber throughout the structure, we took into account electrical current gain. The selection of the first absorber thickness d 1 determines the number of possible stages N S , at which detectivity reaches maximum value, which is especially important in case of varied absorbers thickness to meet the quantum efficiency condition (equal quantum efficiency in each stage of the device). Optimal first absorber thickness d 1opt is higher for equal absorbers than for matched-absorbers detectors, but maximum value of detectivity is slightly lower. We compared theoretical results with experimental ones, obtaining good agreement. [ABSTRACT FROM AUTHOR]