Stack Position Research Articles

On the relationship between acoustic absorption and temperature gradient in a thermoacoustic liner

The thermoacoustic effect provides a means to convert acoustic energy to heat and vice versa without the need for moving parts. This makes thermoacoustic devices of interest for multifunctional applications in harsh or remote service environments. Embedding thermoacoustic stacks within the framework of acoustic liners could provide opportunities to simultaneously optimize both acoustic absorption and thermal output as well as to integrate energy harvesting and sensing and monitoring functionalities. In this study, the influence of sound pressure level and frequency as well as stack length and position on the performance of a thermoacoustic liner is investigated using normal incidence impedance tube tests and DeltaEC simulations. Using Rott’s approximation, the stack’s pore width and wall thickness are optimized for additively manufactured thermoacoustic liner test articles. A peak steady-state temperature gradient of 9.5°C is obtained at 790 Hz for 140 dB tonal dwells. It is found that the temperature gradient correlates directly with the acoustic power available at the leading stack-face, which is highest when the stack is near the center of the resonator. In contrast, acoustic absorption diminishes when the stack is nearer to the closed-end of the resonator. At higher excitation pressure levels, the contribution of viscous heating to the deviation in the thermoacoustic gradient becomes significant. Further, the relationship between the acoustic absorption and the thermoacoustic temperature gradient was examined. In application scenarios requiring multifunctional optimization, a tradeoff may be required in terms of the absorption in order to maximize the temperature gradient. With current additive and hybrid fabrication processes and materials reaching commercial maturity, opportunities exist to realize thermoacoustic liners with enriched functionalities.

Research on the process of heat transfer between mobile variable temperature heat source and thermoacoustic plate

The purpose of this paper is to analyze the effects of several easy-to-operate parameters (operating frequency, plate stack length, plate stack position, and amplitude) on the refrigeration performance, to explore the optimization path of thermoacoustic refrigerator, and to provide a design basis for further cost reductions. The heat transfer process between the air mass and the plate was investigated as an object, and the physical and mathematical models of the heat transfer process were established. The gas microcluster moving heat and plate stack temperature difference were taken as the response. Operating frequency, plate position, plate length and gas vibration displacement amplitude were the design factors. The change relationship of the system response under the interaction of factors was analyzed by using the central composite experimental design and the response surface method, and experimental verification was carried out. The results show that the deviation of the predicted model from the experimental data is less than 5.9 % when the operating frequency is in the range of 0 Hz–12 Hz, and that the location of the plate stack is 0.45 from the pressure belly point of the sound field, where the heat of the air mass transfer is the largest.

Investigation of a cascaded piezoelectric transducer with cone horn for multi-mode power ultrasound application

To meet the ultrasonic application requirement of high power intensity and large mechanical displacement, a new theoretical method is used to study the multi-mode characteristic of the cascaded piezoelectric transducer with cone horn in this paper. Based on equivalent circuit and Kirchhoff’s law to obtain the frequency equation and vibration velocity expression of the transducer, then the resonance frequency and effective electromechanical coupling coefficient can be calculated, the velocity amplification ratio can be obtained in the meantime. This method is distinguish from traditional theoretical analysis, which avoids complex transformation of the multi-excitation sources in cascaded structure, and can calculate more performance parameters. The relationships between these performance parameters and the excitation position of the piezoelectric stack, the length and output end radius of the cone horn are analyzed and compared with the numerical simulation, and the optimized parameters of the transducer size are given. A transducer is manufactured for experimental test, the results show that the experimental value is in good agreement with theoretical calculation and finite element simulation. This work is expected to be used in the optimal analysis of the multi-mode transducer in high power ultrasonic field.

DNA structural features and variability of complete MHC locus sequences.

The major histocompatibility (MHC) locus, also known as the Human Leukocyte Antigen (HLA) genes, is located on the short arm of chromosome 6, and contains three regions (Class I, Class II and Class III). This 5Mbp locus is one of the most variable regions of the human genome, yet it also encodes a set of highly conserved and important proteins related to immunological response. Genetic variations in this region are responsible for more diseases than in the entire rest of the human genome. However, information on local structural features of the DNA is largely ignored. With recent advances in long-read sequencing technology, it is now becoming possible to sequence the entire 5Mbp MHC locus, producing complete diploid haplotypes of the whole region. Here, we describe structural maps based on the complete sequences from six different homozygous HLA cell lines. We find long-range structural variability in the different sequences for DNA stacking energy, position preference and curvature, variation in repeats, as well as more local changes in regions forming open chromatin structures, likely to influence gene expression levels. These structural maps can be useful in visualizing large scale structural variation across HLA types, in particular when this can be complemented with epigenetic signals.

Tuning MXenes Towards Their Use in Photocatalytic Water Splitting

Finding appropriate photocatalysts for solar‐driven water (H2O) splitting to generate hydrogen (H2) fuel is a challenging task, particularly when guided by conventional trial‐and‐error experimental methods. Here, density functional theory (DFT) is used to explore the MXenes photocatalytic properties, an emerging family of two‐dimensional (2D) transition metal carbides and nitrides with chemical formula Mn+1XnTx, known to be semiconductors when having Tx terminations. More than 4,000 MXene structures have been screened, considering different compositional (M, X, Tx, and n) and structural (stacking and termination position) factors, to find suitable MXenes with a bandgap in the visible region and band edges that align with the water‐splitting half‐reaction potentials. Results from bandgap analysis show how, in general, MXenes with n = 1 and transition metals from group III present the most cases with bandgap and promising sizes, with C‐MXenes being superior to N‐MXenes. From band alignment calculations of candidate systems with a bandgap larger than 1.23 eV, the minimum required for a water‐splitting process, Sc2CT2, Y2CT2 (Tx = Cl, Br, S, and Se) and Y2CI2 are highlighted as adequate photocatalysts.

Measurement Method of Bar Unmanned Warehouse Area Based on Binocular Vision

With the development of Industry 4.0 and the implementation of the 14th Five-Year Plan, intelligent manufacturing has become a significant trend in the steel industry, which can propel the steel industry toward a more intelligent, efficient, and sustainable direction. At present, the operation mode of unmanned warehouse area for slabs and coils has become relatively mature, while the positioning accuracy requirement of bars is getting more stringent because they are stacked in the warehouse area according to the stacking position and transferred by disk crane. Meanwhile, the traditional laser ranging and line scanning method cannot meet the demand for precise positioning of the whole bundle of bars. To deal with the problems above, this paper applies machine vision technology to the unmanned warehouse area of bars, proposing a binocular vision-based measurement method. On the one hand, a 3D reconstruction model with sub-pixel interpolation is established to improve the accuracy of 3D reconstruction in the warehouse area. On the other hand, a feature point matching algorithm based on motion trend constraint is established by means of multi-sensor data fusion, thus improving the accuracy of feature point matching. Finally, a high-precision unmanned 3D reconstruction of the bar stock area is completed.

Effect of stacking position on drying rate during radio-frequency vacuum combined with mechanical press drying of Douglas-fir and Radiata pine

In this study, the effect of stacking position in the dryer on the drying rate during radio-frequency vacuum combined with mechanical press (RF/VP) drying was investigated for Douglas-fir and Radiata pine. Drying test was performed at a temperature of 40 °C using RF/VP dryer with approximately 3 m3. The results showed that the stacking position has a significant effect on the drying rate, with a more pronounced decrease in drying rate as the stacking position of specimens approaches the ground plate. Previous moisture content was an important factor in determining the drying rate in both species. The MC distribution of specimens in the dryer before drying was very irregular, but over time, specimens stacked on the RF charge plate side in the dryer tended to have lower MC distributions than those stacked on the ground plate side, which was serious at the specimens in contact with the upper ground plate. In addition, as the MC decreases below the fiber saturation point during RF/VP drying, the difference in MC distribution within the dryer according to the stacking position became clearer. These findings provide new insights into the effect of stacking position on drying rate during the RF/VP drying and are expected to improve RF/VP drying technology.

The Electronic Structure and Stability of Ti2SnC/Ag Interface Studied by First‐Principles Calculations

AbstractIn this paper, the electronic properties, the adhesive energy, and the interface energy of the MAX phase Ti2SnC(0001)/Ag(111) interface are systematically investigated using first principles based on density functional theory. Four different terminations of Ti2SnC(0001) are considered, and 16 different Ti2SnC(0001)/Ag(111) interface configurations are obtained by varying the stacking positions of the atoms. After calculating the electronic structure, adhesion work, and interface energy of these interface model interfaces with the same terminal but different atomic positions, it is found that the interface of the same terminal has a very limited effect on the interface bonding of the interface model by changing the stacking order of the interface atomic layer. By comparing the adhesion work and interface energy of 16 interface models, it is found that the HCP2 configuration of C‐Ti2SnC(0001)/Ag(111)interface structure has the highest adhesion work and the lowest interface energy. The larger the adhesion work is, the stronger the bonding between the interface atoms is. Meanwhile, the smaller the interface energy (positive value) is, the more stable the interface is. By calculating the electronic structure of the interface, the accuracy of the above results is further verified after analyzing the partial density of states (PDOS) and charge density difference of the interface.

High fidelity analysis and optimization of a quarter wavelength thermo-acoustically driven refrigerator

High fidelity CFD analysis is done to investigate the coupling of a thermoacoustic engine and refrigerator (TAE & TAR) within a straight tubular quarter-wavelength resonator under high pressure conditions. A parametric study aims to optimize TAE efficiency (η) and TAR coefficient of performance (COP). Firstly, the TAE is modelled to ascertain the optimum position of the TAE stack based on the acoustic power (Ẇ) and efficiency (η). The TAE achieved a drive ratio near 20 %. It was found that the optimum normalized position (xn) for the TAE stack is at 0.43 for highest Ẇ of 78.3 W and 0.25 for highest η of 9 %. Secondly, Thermo-Acoustically Driven Refrigerator (TADR) is developed by incorporating both TAE and TAR stacks in tandem following optimal positioning of the TAR stack. Finally, the performance of the TADR is optimized by altering the TAR stack material, the TAE hot end temperature, and the working fluid. The optimal TAR stack position was found to be the closest to the TAE stack. The material with lower thermal conductivity (Mylar) outperformed the higher conductivity (Steel). Furthermore, Increasing the TH from 1,000 K to 1,200 K significantly increased the cooling power. Argon demonstrated the highest η and COP compared to Air and Helium, however, the highest cooling power was achieved using Helium. Two TADR configurations were considered: a) Helium with stacks at xn = 0.43 (TAE) and xn = 0.77 (TAR), prioritizing cooling power, achieving 60.87 W at 5 K temperature difference; b) Argon with stacks at xn = 0.25 (TAE) and xn = 0.58 (TAR), favoring efficiency, achieving up to 22.815 % overall efficiency at 5 K temperature difference, and a maximum temperature drop of 34 K below ambient (300 K).

Optimizing stack ventilation in low and medium-rise residential buildings in hot and semi-humid climate

Nowadays, optimization of methods that can reduce energy consumption is efficient for various reasons, such as the increasing mean temperature, the changes in climate, and the shortage of non-renewable energies like fossil fuels. Hence, the stack effect is one of the passive cooling strategies promoting using renewable energy. In this context, Stack ventilation is studied in a hot and semi-humid climate to introduce AEC industry parties. A notable contribution of this study to the existing knowledge landscape involves the integration of stack ventilation (vertical ventilation) with roof channels (horizontal ventilation). Direct and indirect ventilation are scrutinized and compared. Then stack position in the building is investigated for optimizing it in one-, two-, and four-story buildings in Dezful city. Considering being the most frequent residential building type, the four-story archetype has been the main focus of the present study. The models’ behaviors are studied by Design Builder (Energy Plus engine). The CFD (fluid dynamics calculations) module has been used to explore the behavior of air in terms of velocity and temperature quantities by numerical simulation. Findings suggest that indirect ventilation is better than direct ventilation in this climate if individuals do not want to use evaporating cooling strategies inside natural ventilation. Roof channels are particularly effective for collecting and discharging the hot air gathered on the roofs and air circulation within the buildings. The result is appropriate for an architect design in hot regions.

Buckling analysis and optimization of variable angle tow composite plates via Ritz method and variable stiffness optimization

A novel variable stiffness optimization (VSO) algorithm is proposed accounting for the inherent mechanical characteristics of variable angle tow (VAT) plates. Through sampling in the design space of lamination parameters (LPs), a good initial point is identified in stacking sequence design domain. The concept of tailoring stiffness point by point through-thickness is then introduced. By using the linear fiber path function, design variables for VAT plates are divided into three groups, and then a layerwise optimization approach (LOA) is applied to optimize the angles from the outermost to the innermost stacking position within the three groups, sequentially and iteratively. Through a point-by-point optimization of fiber paths, the stiffness of VAT plates is enhanced part by part. Ritz-type buckling solutions are presented for VAT composite plates with arbitrary boundary conditions. Using first-order shear deformation theory (FSDT), the translational and rotational degrees of freedom of the plate are divided into in-plane and out-of-plane components to solve the prebuckling and buckling problems independently. Buckling loads of VAT plates are optimized under multiple boundary conditions and loadings. Results indicate that VSO algorithm is efficient and robust, and the buckling resistance capacity of optimized VAT plates can be improved approximately twice over constant-stiffness laminates.

Leaf-individual calibration for a double stack multileaf collimator in photon radiotherapy.

In online adaptive stereotactic body radiotherapy treatments, linear accelerator delivery accuracy is essential. Recently introduced double stack multileaf collimators (MLCs) have new facets in their calibration. We established a radiation-based leaf-individual calibration (LIMCA) method for double stack MLCs. MLC leaf positions were evaluated from four cardinal angles with test patterns at measurement positions throughout the radiation field on EBT3 radiochromic film for each single stack. The accuracy of the method and repeatability of the results were assessed. The effect of MLC positioning errors was characterized for a measured output factor curve and a clinical patient plan. All positions in the motor step - position calibration file were optimized in the established LIMCA method. The resulting double stack mean accuracy for all angles was 0.2±0.1 mm for X1 (left bank) and 0.2±0.2 mm for X2 (right bank). The accuracy of the leaf position evaluation was 0.2 mm (95% confidence level). The MLC calibration remained stable over four months. Small MLC leaf position errors (e.g. 1.2 mm field size reduction) resulted in important dose errors (-5.8 %) for small quadratic fields of 0.83×0.83 cm2. Single stack position accuracy was essential for highly modulated treatment plans. LIMCA is a new double stack MLC calibration method that increases treatment accuracy from four angles and for all moving leaves.

Revealing the adhesion, stability, and electronic structure of SiC/M (M=Au, Pt) interface: A first-principles study

The interface bonding and electronic properties between SiC and metal are the key factors affecting the physical transport phenomena of metal-semiconductor field-effect transistors (MESFETs). The work of adhesion, interface energy and electronic structure of SiC/M (M = Au, Pt) interface are explored by first-principles method. Forty possible interface models were constructed for different surfaces and stacking positions, and the four most stable interfaces were screened based on the work of adhesion and interface energy. Moreover, the interfacial bonding behavior and strength of SiC/M were quantitatively and qualitatively described through partial density of states (PDOS), crystal orbital Hamilton population curves (COHP), and charge density distribution (CDD). The PDOS demonstrated covalent bond characteristics between M − Si and M − C, which are primarily bonded by M-d and Si-p or C-p orbital hybridization. Further, the COHP and CDD analyses clearly manifested that the Pt–C bond at the interface exhibits more pronounced electron aggregation and greater bonding strength than the Au–C bond. This study offers a comprehensive understanding of the interfacial bonding strength between SiC and Au or Pt and demonstrate that SiC/Pt contact is the more favorable option for electronic device materials.

Mode I and II interlaminar fracture toughness of glass/carbon inter‐ply hybrid FRP composites: Effects of stacking sequence and testing temperature

AbstractEven though laminated FRP composites show exceptional performance in various modes of loading, they are susceptible to delamination. The ambient temperature and elevated temperature delamination resistance of glass/carbon fiber interply hybrid composites were assessed via mode I and mode II interlaminar fracture toughness tests performed at 30, 50 and 70°C. Interply hybrid composites performed better than composites with single type of fiber. The fracture toughness of inter‐ply hybrid composites varied with the stacking position. At 30°C, mode I fracture toughness value of alternative glass and carbon fiber stacking sequence (G1C1)5 of hybrid composite showed 40% improvement over 10 layered carbon/epoxy (C10) composite. Further, Mode II fracture toughness of C5G5 composite showed 22% enhancement, and C10 exhibited 42% improvement over 10‐layered glass/epoxy composite. Increasing the test temperature of all composites improved their GIC and GIIC values. The increment in the mode I fracture toughness properties of all composite was in the range of 5%–23% at 70°C from its room temperature value. The fractographic images of fractured samples were studied under a scanning electron microscope and failure mechanisms of composites were identified.

A unified approach for dynamic characteristic analysis of a standing-wave thermoacoustic engine with general impedance ends

As promising devices for energy conversion, thermoacoustic engines (TAEs) are attracting more and more research attention with regard to renewable thermal energy application. For a TAE, the oscillation frequency is a critical parameter in its design and operation, which can only be estimated currently through an often tedious process using a shooting method or a numerical iteration method, and an analysis model with classical boundary conditions. In this context, this study seeks to establish a unified model for dynamic analysis of a one-dimensional (1D) standing-wave TAE with general impedance ends. First, the differential equations governing the thermoacoustic behavior of the TAE and its impedance boundary conditions are simultaneously solved using the Galerkin method and an improved Fourier series expansion method. Then, the characteristic distributions of oscillation frequency, sound pressure, and volume flow rate are obtained by solving a standard eigenvalue problem. Finally, the effects of engine length, stack length and position, and impedance ends on the dynamic behavior of the TAE’s thermoacoustic system are investigated and analyzed. The results show that engine length has a significantly negative correlation with the modal frequencies in different working gases, and stack position and stack length have a slight effect on the oscillation frequency of the TAE. The arbitrary variations in impedance boundary conditions can be simulated from the open end to the rigid wall and all intermediate cases. The proposed model can efficiently predict changes in dynamic parameters of 1-D TAEs with impedance ends in a unified pattern and can serve as a reliable analysis tool for further research on TAEs coupled with various energy harvesters.

Assessment of Cryogenic Material Properties of R-PUF Used in the CCS of an LNG Carrier

Reinforced polyurethane foam (R-PUF), a material for liquefied natural gas cargo containment systems, is expected to have different mechanical properties depending on its stacking position of foaming as the glass fiber reinforcement of R-PUF sinks inside R-PUF under the influence of gravity. In addition, since R-PUF is not a homogeneous material, it is also expected that the coordinate direction within this material has a great correlation with the mechanical properties. So, this study was conducted to confirm this correlation with the one between the mechanical properties and the stacking position. In particular, in this study, R-PUF of 3 different densities (130, 170, and 210 kg/m3) was used, and tensile, compression, and shear tests of this material were performed under 5 temperatures. As a result of the tests, it was confirmed that the strength and modulus of elasticity of the material increased as the temperature decreased. Specifically, the strength and modulus of elasticity in the Z direction, which was the lamination direction, tended to be lower than those in the other directions. Finally, the strength and elastic modulus of different specimens of the material found at the bottom of their lamination compared to the specimens with these properties found at positions other than their lamination bottom were evaluated. Further analysis confirmed that as the temperature decreased, hardening of R-PUF occurred, indicating that the strength and modulus of elasticity increased. On the other hand, as the density of R-PUF increased, a sharp increase in strength and elastic modulus of R-PUF was observed.

Novel wide spectrum light absorber heterostructures based on hBN/In(Ga)Te

Two-dimensional group III monochalcogenides have recently attracted quite attention for their wide spectrum of optical and electric properties, being promising candidates for optoelectronic and novel electrical applications. However, in their pristine form they are extremely sensitive and vulnerable to oxygen in air and need good mechanical protection and passivization. In this work we modeled and studied two newly designed van der Waals (vdW) heterostructures based on layer of hexagonal boron nitride (hBN) and GaTe or InTe monolayer. Using density functional theory, we investigate electronic and optical properties of those structures. Their moderate band gap and excellent absorption coefficient makes them ideal candidate for broad spectrum absorbers, covering all from part of IR to far UV spectrum, with particularly good absorption of UV light. The hBN layer, which can be beneficial for protection of sensitive GaTe and InTe, does not only preserve their optical properties but also enhances it by changing the band gap width and enhancing absorption in low-energy part of spectrum. Calculated binding energies prove that all three stacking types are possible to obtain experimentally, with H-top as the preferable stacking position. Moreover, it is shown that type of stacking does not affect any relevant properties and bandstructure does not reveal any significant change for each stacking type.

Performance of a Levitation System Consisting of Magnetized and Non-Magnetized Tape Stacks

This paper presents a study of the levitation system consisting of magnetized and non-magnetized HTS tape stacks. A comparison of such a system with the classical one, consisting of a stack of tapes and a permanent magnet, was carried out. The objects of the study were tapes manufactured by SuperOx, cut into 12 mm × 12 mm fragments and formed into stacks with different height. Experimental data on the levitation force value at vertical and lateral displacements of a magnetized stack of HTS tapes and permanent magnets relative to the position of an ordinary tape stack were obtained. A simulation of the magnetic field distribution around a magnetized stack of 80 tapes and a permanent magnet was performed.

Method for assessment of the apparent detector stack position in a whisk-broom sensor

In a whisk-broom sensor, such as the Advanced Baseline Imager (ABI) onboard the Geostationary Operational Environmental Satellite (GOES)-R series of geostationary satellites, the sensor optics projects the observed scene onto the sensor focal plane arrays (FPA), with the detectors arranged in a column perpendicular to the scan direction. An assessment system compares the images made by the sensor with known landmarks and calculates the image deviations from the landmark positions. These deviations are called navigation residuals, and in this work they are interpreted in a broad sense as deviations of the actual from the ideal optical paths. The deviations can be caused by several issues, such as a sensor pointing error, deficiency in sensor optics, and inaccuracy of detector locations on FPA. As the ABI sensor scans the Earth to make a full-disk image in 22 parallel swaths, we refer the landmark residuals from all swaths to the observing detector positions in the ABI detector column. This interpretation inverts the retrieval of navigation residuals and gives deviations of the image from the expected ideal position on an ideal FPA. As the errors of pointing and sensor optics can be assessed independently, the remaining deviations can be interpreted as these with respect to the ideal detector position map (in other words, to the pre-launch assessment). We call these deviations the apparent detector positions. Knowledge of these deviations will greatly simplify the navigation commissioning for future ABI sensors and similar devices. Using our archive of ABI image navigation data for ABI sensor on the GOES-16 satellite, we show the wealth of additional information about the sensor on-orbit condition that may be extracted with the proposed method. This algorithm can use any image navigation system that is sufficiently precise.

The effect of post-acquisition data misalignments on the performance of STEM tomography

Scanning transmission electron microscopy (STEM) tomography is widely used to reveal three-dimensional (3D) structure of the specimens from nanometers to atomic resolution. Advances in transmission electron microscope enable high resolution and low dose data acquisition for 3D reconstruction to resolve 3D coordinates of single atoms. Meanwhile, the developments of reconstruction algorithms increase the reconstruction quality. However, the as-acquired raw datasets often require alignments before they can be used as inputs to feed a reconstruction algorithm. The effect of post-acquisition data misalignments on the final reconstruction quality of STEM tomography is less discussed. Here, using phantom datasets with a focus on atomic features, we simulate a range of misalignments on each alignment step and correlate the level of misalignments to the final reconstruction quality. The study pinpoints that accurate alignments of tilt angles and stack positions and minimizing scan distortion are important to the reconstruction quality, while the sequence of alignment steps do not affect the reconstruction quality. The study not only emphasizes the most important alignment steps that should be pay attention to for a high-quality 3D reconstruction, but also summarizes post-acquisition data alignment procedures as a primer for new practitioners to use STEM tomography.