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Research on flexible strain sensors has advanced rapidly in recent years, with particular attention being devoted to two-dimensional (2D) semiconductor materials owing to their exceptional mechanical and electrical properties that are conducive to sophisticated sensing performance. However, resistive strain sensors based on 2D semiconductor materials typically exhibit positive gauge factors (GF), while materials for strain sensors with a negative GF remain elusive. We have identified a trend of reduction in the band gap of the emerging 2D semiconductor material tellurium (Te) under strain in simulations reported in past research, and have observed a negative GF in the Te-based strain sensor. In this study, we combined Te with a flexible polyethylene terephthalate (PET) substrate to manufacture a flexible strain sensor with a significantly negative GF. The results of tests revealed that the Te-based strain sensor achieved an impressive maximum sensitivity of −139.7 within a small range of bending-induced strain (< 1%). Furthermore, it exhibited excellent linearity and good cyclic stability, and was successfully applied to monitor limb movements. The work here verifies the significant potential for the use of Te-based strain sensors in next-generation flexible electronics. [ABSTRACT FROM AUTHOR]

To detect and differentiate two essential amino acids (L-Valine and L-Phenylalanine) in the human body, a novel asymmetrically folded dual-aperture metal ring terahertz metasurface sensor was designed. A solvent mixture of water and glycerol with a volume ratio of 2:8 was proposed to reduce the absorption of terahertz waves by reducing the water content. A sample chamber with a controlled liquid thickness of 15 μm was fabricated. And a terahertz time-domain spectroscopy (THz-TDS) system, which is capable of horizontally positioning the samples, was assembled. The results of the sensing test revealed that as the concentration of valine solution varied from 0 to 20 mmol/L, the sensing resonance peak shifted from 1.39 THz to 1.58 THz with a concentration sensitivity of 9.98 GHz/mmol∗L−1. The resonance peak shift phenomenon in phenylalanine solution was less apparent. It is assumed that the coupling enhancement between the absorption peak position of solutes in the solution and the sensing peak position amplified the terahertz localized electric field resonance, which resulted in the increase in frequency shift. Therefore, it could be shown that the sensor has capabilities in performing the marker sensing detection of L-Valine. [ABSTRACT FROM AUTHOR]

The Qing-1 layer of the Gulong Depression in the northern Songliao Basin is a liquid-rich shale oil reservoir that has the characteristics of nanopores, high maturity, high gas/oil ratio (GOR), etc. The production performance of wells in the Gulong shale oil reservoir shows the characteristics of "single gas production followed by oil-gas production". It is difficult to analyze the initial occurrence state and movability of fluid in the shale nanopores using conventional methods. In this study, a comprehensive method, including phase behavior analysis, physical experiments, and molecular simulation, was established to analyze the initial occurrence state and movability of fluid in the Gulong shale oil reservoir. The phase state of the fluid was calculated by the equation of state (EOS), considering nano-confinement effects, and the initial occurrence state was quantitatively evaluated by combining two-dimensional nuclear magnetic resonance (NMR) and molecular dynamics simulation. The movable fluid saturation was quantitatively determined by centrifugal experiments. The results show that the condensate gas state was in small pores, while the volatile oil state was in large pores. The occurrence states of oil were mainly adsorbed oil and free oil. The proportion of adsorbed oil in inorganic pores was about 24.4%, while the proportion of absorbed oil in organic pores was about 57.8%. Based on the cutoff value of T2 before and after the centrifuged laboratory experiments, the movable limit of oil was determined to be 4.5 nm, and the movable fluid saturation was about 11%. The research method proposed in this study has important guiding significance for the initial occurrence state and movability evaluation of similar liquid-rich shale reservoirs. [ABSTRACT FROM AUTHOR]

Background: At present, rice wine has the characteristics of fast fermentation, energy saving, and simple production due to the addition of commercial Saccharomyces cerevisiae. However, this kind of fermented rice wine has the disadvantages of single flavor and weak taste. To address this concern, the combination of Saccharomyces cerevisiae and non‐Saccharomyces yeast has been identified as an effective approach to enhance the quality of fermented rice wine. This research aims to further enhance the ethyl ester and higher alcohol components of rice wine by utilizing the co‐fermentation method of high‐yield ester Zygosaccharomyces rouxii and Saccharomyces cerevisiae, thereby increasing the aroma complexity of rice wine. Results: According to the fermentation performance and gas chromatography–mass spectrometry (GC–MS) analysis, it was found that S. cerevisiae GJM and Z. rouxii SC01 have a strong metabolic ability for glucose and sucrose. Furthermore, the crucial alcohols such as isobutanol, isoamyl alcohol, and phenylethyl alcohol increased by 85%, 29%, and 138%, respectively, when compared to single S. cerevisiae GJM. Additionally, the ethyl acetate and phenylethylene acetate were increased by 1.35 and 1.45 times, respectively, when compared to single S. cerevisiae GJM. These findings were comparable with the results of sensory evaluation and electronic nose analysis, where the fruit flavor score and the content of mellow substances were found to be higher. Conclusion: These findings suggest that the co‐fermentation of S. cerevisiae and high‐yield ester Z. rouxii has the potential to enhance the quality and diversity of aroma in liquid rice wine. [ABSTRACT FROM AUTHOR]

Shale oil resources are abundant, but reservoirs exhibit strong heterogeneity with extremely low porosity and permeability, and their development is challenging. Carbon dioxide (CO2) injection technology is crucial for efficient shale oil development. When CO2 is dissolved in reservoir formation water, it undergoes a series of physical and chemical reactions with various rock minerals present in the reservoir. These reactions not only modify the reservoir environment but also lead to precipitation that impacts the development of the oil reservoir. In this paper, the effects of water–rock interaction on core porosity and permeability during CO2 displacement are investigated by combining static and dynamic tests. The results reveal that the injection of CO2 into the core leads to reactions between CO2 and rock minerals upon dissolution in formation water. These reactions result in the formation of new minerals and the obstruction of clastic particles, thereby reducing core permeability. However, the generation of fine fractures through carbonic acid corrosion yields an increase in core permeability. The CO2–water–rock reaction is significantly influenced by the PV number, pressure, and temperature. As the injected PV number increases, the degree of pore throat plugging gradually increases. As the pressure increases, the volume of larger pore spaces gradually decreases, resulting in an increase in the degree of pore blockage. However, when the pressure exceeds 20 MPa, the degree of carbonic acid dissolution will be enhanced, resulting in the formation of small cracks and an increase in the volume of small pores. As the temperature reaches the critical point, the degree of blockage of macropores gradually increases, and the blockage of small pores also occurs, which eventually leads to a decrease in core porosity. [ABSTRACT FROM AUTHOR]

Although frequency-domain optimization approaches are commonly used for noise control, ubiquitous transient behaviors indicate that time-domain approaches cannot be ignored. Thus, this paper minimizes the transient noise radiated from the vibration system with constant gain velocity feedback (GGVF) control by combining topology optimization and parameter optimization. Based on the solid isotropic material with penalization (SIMP) model, the pseudo density is introduced to characterize the presence or absence of piezoelectric material. To satisfy engineering requirements, constraints on the usage amount of piezoelectric material, consumable energy, and maximum transient voltage are considered. Transient sound radiation is predicted by using a finite element/time-domain boundary element method (FEM/TDBEM). Sensitivity formulae of objective function to pseudo density and feedback gain are derived using a combination scheme. Namely, a direct method is applied to obtain the vibration sensitivity information at all boundary nodes, the results of which are input into the sensitivity calculation of transient sound radiation addressed by an adjoint variable method. This scheme integrates the advantages of the direct method which can calculate the vibration sensitivity of all nodes at once and of the adjoint variable method which has high computational efficiency. The gradient-based method of moving asymptotes (MMA) is employed to solve for optimised solutions. Numerical examples demonstrate the accuracy of the sensitivity formulae and the effectiveness of the concurrent optimization strategy. [ABSTRACT FROM AUTHOR]

As continental shale oil is explored and developed on a larger scale, its high starting pressure gradient in the shale matrix poses challenges for flow. This paper investigates the effect of imbibition development and the mechanism of oil mobilization under high temperature and high pressure using self-developed dynamic huff-n-puff imbibition equipment based on micropore and percolation characteristics. Using six different injection fluids—slickwater, imbibition agent CY-IMNF-1, sand-carrying agent, guanidine gel breaking fluid, imbibition agent #G-1, and CO2 —this study involved an experimental investigation of high-temperature and high-pressure huff-n-puff imbibition at a pressure of 30 MPa and a temperature of 110°C. The effect of injection fluids on imbibition development recovery is analyzed, and the contribution of different scale pores to the oil recovery of continental shale is quantified. It was found that slickwater huff-n-puff resulted in the highest imbibition oil recovery, followed by imbibition agent CY-IMNF-1. Shale oil production in nanopores and micropores was mainly achieved through slickwater huff-n-puff, and the pore and throat size limit for oil mobilization was found to be 4–7 nm. Based on a synergy perspective, optimizing the hybrid system of slickwater and CO2 is suggested. This study provides technical support for developing similar continental shale reservoirs with high-temperature and high-pressure huff-n-puff imbibition. Based on a self-made experimental device and two-dimensional (2D) nuclear magnetic resonance testing, the quantitative evaluation method of sensitivity of different shale pores to external fluids is established. The results show that the oil recovery rate of imbibition using sliding water is the highest, the oil in nanopores and micropores is mainly produced through huff-n-puff by slickwater, and the limit radius of oil mobility in pores and throats was found to be 4–7 nm. The research findings have important implications for huff-n-puff experiments and the formulation design of shale fracturing fluid systems. [ABSTRACT FROM AUTHOR]

A novel Frequency and Polarisation Selective Surface (FPSS) is proposed, which separates two adjacent bands with a narrow transition zone by the staggered separation scheme and is suitable for atmospheric remote sensing. The traditional FSS is transparent in a particular frequency band for both the TE and TM polarisations, while it is opaque in another band for both orthogonal polarisations. The FPSS is introduced in a new splitting scheme that operates above 300 GHz. The channel 420–430 GHz of the TE polarisation and the channel 360–400 GHz of the TM polarisation transmit in the FPSS. In contrast, the band 360–400 GHz of the TE polarisation and the channel 420–430 GHz of the TM polarisation are reflected. The water vapour and the oxygen profiles are detected by the 380 GHz band and the 425 GHz band, respectively. The insertion loss is lower than 1 dB, and the reflection band rejection is superior to 10 dB in the experiment, which determine the sensitivities of the bright temperature by 1.5 (RMS K). The scattered wave of the FPSS is calculated through the far field pattern, the maximum of which is about 5%. The side effect of the scattered wave is able to be ignored in the optical path. [ABSTRACT FROM AUTHOR]

This paper presents a design of an asymmetric metal cross unit structure, which consists of two perpendicular coplanar gold bars deposited on a quartz substrate. The conventional metal cross structure commonly suffers from significant radiation losses in LC resonance and dipole resonance, limiting the achievement of high quality factor and high transmittance in metasurface sensors. By breaking the symmetry of the traditional metal cross structure and introducing a Fano-like resonance effect, the transmission peak sensitivity of 218 GHz / RIU and the quality factor of 78. 3 are achieved. The physical mechanism of the Fano resonance effect is explored by analyzing the electric field and surface current distribution of the metasurface. Furthermore, the influence of structural parameters on the transmission spectrum of the terahertz sensor is investigated, and the sensing performance of the sensor is optimized by adjusting the structural parameters. Finally, asymmetric metal cross terahertz sensors with different resonance frequencies are designed for the detection of various types of trace amino acid solutions in subsequent applications. [ABSTRACT FROM AUTHOR]

Summary: The effects of mixed fermentation of non‐Saccharomyces (Pichia fabianii, Kluyveromyces thermotolerans, and Saccharomycopsis fibuligera) with Saccharomyces cerevisiae on the physicochemical indexes and flavour of rice vinegar fermentation were studied. The mixed fermentation increased the activity of β‐glucosidase and esterification enzyme. The β‐glucosidase activity of P. fabianii was 1.6 times higher than that of S. cerevisiae alone, and the esterification enzyme activity was increased by about four times. Compared with the single fermentation of S. cerevisiae, the mixed fermentation of P. fabianii and S. cerevisiae increased the type and content of aromatic esters and produced ethyl acetate and phenethyl acetate. The mixed fermentation of K. thermotolerans and S. cerevisiae made an outstanding contribution to produce higher alcohols. Among them, the content of isobutanol and phenylethanol increased by nearly ten times; the content of isoamylol increased by more than eight times. S. fibuligera provides a unique flavour of phenols because of 2‐methoxy‐4‐ethylphenol and 2‐methoxy‐4‐ethylphenol. [ABSTRACT FROM AUTHOR]

Without regarding interlayer continuity of transverse shear stresses in the displacement expressions, traditional higher-order plate theories have difficulty in predicting continuous shear stress fields accurately for multilayered functionally graded carbon nanotube-reinforced composite (FG-CNTRC) plates with independent CNT distributions in each layer. In this paper, a new higher-order continuous shear stress multilayered plate model is developed for high-accuracy analysis of FG-CNTRC plates. In the theoretical formulation, higher-order interpolation functions and piecewise descriptions are adopted for transverse shear stress fields. By fulfilling the interlayer continuity of shear stresses and displacements, the displacement expressions for FG-CNTRC plates are formulated. The accuracy of the proposed model is determined by two kinds of parameters: the order of assumed transverse shear stress fields and the number of subdivisions. Compared with traditional higher-order theories, the proposed model can accurately predict continuous transverse shear stresses for FG-CNTRC plates with different CNT configurations by constitutive relations directly. Additionally, a four-node rectangular plate element associated with the proposed model is formulated. Results show that the proposed model agrees well with the exact solutions and results from ANSYS. With the same amount of calculation, the proposed higher-order model has higher accuracy than the model with more subdivisions, especially for asymmetric plates with discontinuous CNT ply angle. [ABSTRACT FROM AUTHOR]

This article presents continuous interlaminar shear stress analysis of laminated beams with functionally graded single-walled carbon nanotube reinforced composite (FG-CNTRC) layers based on an extended high-order layerwise model in the framework of the Carrera Unified Formulation (CUF). By considering the CNTs uniformly or functionally graded (FG) distributed through the thickness of each layer, the extended rule of mixture is adopted to estimate the effective material properties of the FG-CNTRC layers. The extended layerwise theory for laminated FG-CNTRC beams is formulated based on layerwise description of transverse shear stress field. With the introduction of stress variables at interfaces, a priori continuity of the transverse shear stress field is fulfilled. In the formulation of the extended model, the independent variations of material properties along the thickness of each FG layer are fully taken account. Then, finite element solution for static analysis is developed based on the proposed model. Comparisons with the results of other theoretical and high-fidelity finite element models well demonstrate the accuracy of the present model in predicting transverse shear stress analysis of laminated FG beams with different features. Besides, parameters studies are presented including the effects of CNTs distributions and CNTs orientation angles on bending behaviors of laminated FG-CNTRC beams. [ABSTRACT FROM AUTHOR]

In this paper, we experimentally and numerically confirm a planar Mach–Zehnder interferometer (MZI) device for sensing dielectric samples based on a spoof surface plasmon polariton (SSPP) waveguide. The MZI system is constructed using two different ultrathin transmission lines with distinct dispersion units supporting SSPPs. After SSPPs propagate a certain propagation distance, a resonant dip is formed at a specific frequency due to destructive interference, whose displacement enables the SSPP to be modulated by one of the MZI arms loaded with dielectric samples. We investigate how the variations in the permittivity and thickness of dielectric samples affect the sensibility. Through an error analysis between the experimental measurements and numerical calculations, it is demonstrated that the plasmonic sensor based on the MZI has a high precision. The proposed technique is compact and robust and paves a versatile route toward the chip-scale functional devices in microwave circuits. [ABSTRACT FROM AUTHOR]

Modal energy analysis (MODENA) is an energy-based method to compute the pure tone mid-frequency response of a vibro-acoustic system. This method considers frequency-dependent modal energies, input power, dissipated power and transmitted power between the modes of coupled subsystems. The quantities are determined by the basic modal information of the uncoupled subsystems, which also has a close relationship with the structural sizes. The present work addresses developing a size optimization procedure within the framework of MODENA to reduce the mid-frequency acoustic response of vibro-acoustic systems. Via a gradient-based optimization algorithm, the sensitivity of the acoustic energy at pure tone with respect to the structural thickness is deduced by employing a complex variable method. By optimizing the thicknesses on different areas of the structural subsystem given the constraint on total mass, the global energy of the acoustic subsystem is reduced significantly. Furthermore, in an effort to examine the capability of the proposed optimization procedure in dealing with acoustic and aerodynamic excitations encountered in engineering problems, the noise reduction of vibro-acoustic systems under turbulent boundary layer (TBL) pressure fluctuations is investigated. The optimization procedure is demonstrated on a plate/cavity system excited by a point drive and by TBL flow and two kinds of vehicles subject to TBL excitation. [ABSTRACT FROM AUTHOR]

Skin pain resulting from mechanical compression is one of the most common pains in daily life and the indispensable information for electronic skin to perceive external signals. The external mechanical stimuli are transduced into impulses and transmitted via nerve fiber, and finally, the sensation is perceived via the procession of the nerve system. However, the mathematical mechanism for pain sensation due to mechanical stimuli remains unclear. In this paper, a mathematical model for skin pain sensation under compression is established, in which the Flament solution, the revised Hodgkin–Huxley model, and the mathematical model gate control theory are considered simultaneously. The proposed model includes three parts: a mechanical model of skin compression, a model of transduction, and a model of modulation and perception. It is demonstrated that the pain sensation degree increases with the compression amplitude and decreases with deeper nociceptor location in the skin. With the help of the proposed model, the quantitative relationship between compression pain sensation and external mechanical stimuli is revealed, which has a significant benefit in promoting the design and mechanism research of electronic skin with pain perception function. [ABSTRACT FROM AUTHOR]

The high-temperature annealing effect of a V2O5/Al2O3 bilayer on the reflectivity of visible band was studied in the present work. It was found that the V2O5 (200 nm)/Al2O3 (30 nm) sample (A-0) has a nano-granular surface morphology without a definite crystalline phase. The reflectance of A-0 overreaches 60% as the wavelength is larger than 650 nm, and its minimum reflectance (20%) occurs at the wavelength of ~500 nm. After in situ annealing treatment at 750 °C for 30 min, a triclinic AlVO4 phase appears while the nano-granular surface morphology remains (sample A-30). The reflectivity of A-30 is well suppressed in comparison with that of A-0 especially in the long wavelength range. Its minimum reflectivity approaches 5% at ~500 nm wavelength. It is speculated that the appearance of a new AlVO4 nanophase is the main reason for the decline of reflectivity. Extending the annealing time to 60 min, the reflectivity spectrum, as well as the surface morphology, are almost the same. These results can be helpful for applications of vanadium alumina nanocomposites in high-temperature environments. [ABSTRACT FROM AUTHOR]

The low absorptivity of quantum dot nano-structures cannot meet the requirements for high-performance next-generation Thz detectors which can be used for environmental pollution detection. In this study, a novel metal-semiconductor-metal (MSM) cavity structure with a square hole array instead of a traditional planar metal electrode was developed to improve and enhance the absorptivity of a quantum dot Thz detector. The possible modes and loss problems in the metal resonant cavity were analyzed using the finite-element transmission matrix, the eigenvector method, and Kirchhoff diffraction theory. The results demonstrate that the MSM cavity structure introduced in the detector can enhance absorption up to 8.666 times higher than that of the conventional counterpart. [ABSTRACT FROM AUTHOR]

So far, the research on topology optimization against noise has mainly addressed frequency‐domain problems, while time‐domain analysis is also widely used in practical engineering. Nonetheless, the topology optimization work on the latter was rarely reported due to its complexity. This article presents a new topology optimization scheme of bi‐material curved shell structure to reduce the time‐domain noise generated by transient vibration. A finite element formulation for an eight‐node curved shell element is presented. The Newmark integral method is employed to calculate transient responses, and the obtained results are input into the time‐domain boundary element method to predict transient sound pressure. In the optimization model, the volumetric densities of material in a bi‐material interpolation model constructed by the solid isotropic material with penalization model are chosen as the design variables; the time integral of the squared sound pressure on structural surfaces or prescribed reference points in acoustic medium over a specified time interval of interest is taken as the objective function; and the constraint on material volume is considered. A volume‐preserving Heaviside penalization is introduced to suppress gray elements. Furthermore, the calculation of time‐domain sound radiation sensitivity is transformed into the following two processes: (a) the derivation of transient response based on the Newmark integral method; (b) the derivation of transient sound pressure based on the discrete time‐domain boundary integral equation. Numerical examples demonstrate the validity of the approach proposed in this article. The influences of volume‐preserving Heaviside penalization, volume constraint, loading position and form, and selection of objective function on the optimal design are discussed. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials with atomic thickness, non-volatile resistive switching feature and compatibility with the semiconducting technology are naturally a good media of memristors. 2D materials-based memristors with excellent performance, low-power consumption and high integration density can be integrated with other circuit components to implement the complicate logic computing, which will become a key driving force for the development of artificial intelligence. [ABSTRACT FROM AUTHOR]

Compared with the frequency-domain sound radiation analysis, the time-domain analysis is more suitable for complicated engineering problems. However, the research on design optimization of time-domain sound radiation was rarely reported. To reduce the undesired time-domain noise radiated from laminated curved shells, the sensitivity formulation of transient sound pressure is obtained by directly differentiating response equations and the corresponding optimization procedure is presented. The Newmark integral method is applied to calculate the vibration response, and the results of which are input into the sound radiation analysis as boundary conditions. Combined with the time-domain boundary element method (BEM), the time-domain boundary integral equation is numerically discretized in both the spatial and time domains, and the transient sound pressure is obtained by solving an algebraic equation. To reduce the time-domain noise, ply thicknesses are taken as the design variables to minimize the square of sound pressure on a prescribed reference surface in the sound medium or the structural surface over a certain period of time. In addition, the constraint on the structural mass is considered. The calculation of time-domain sound radiation sensitivity is transformed into the following two processes: (a) the derivation of transient vibration response based on finite element method (FEM); (b) the derivation of transient sound pressure based on time-domain BEM. The optimal solution is obtained by using the method of moving asymptotes (MMA). Numerical examples verify the accuracy of the sensitivity formulae, and show that the time-domain sound radiation is significantly reduced within allowable constraints. [ABSTRACT FROM AUTHOR]

Optimization based on traditional forward motion analysis to ensure a prescribed load distribution on a deformed geometry is challenging, since the load distribution is highly coupled to the deformed geometry, boundary conditions, and the optimized material layout. In contrast to traditional forward motion analysis, the deformed configuration is prescribed in the inverse motion analysis, and the undeformed configuration is the outcome of the analysis. Consequently, the inverse motion analysis is able to define an exact deformed geometry. In the present study, we make use of this key advantage to design structures with both an exact deformed geometry and a prescribed load distribution. The objective in the optimization is to minimize a general function of the nodal displacement vector. To formulate a well-posed optimization problem, the design is regularized using the partial differential equation filter and the sensitivity analysis is based on the adjoint method. The computational model is developed for neo-Hookean hyper-elasticity and the balance equations are discretized using the finite element method. The resulting nonlinear equations are solved using a conventional Newton–Raphson scheme. In the numerical examples, a cantilever beam with an embedded perfect circular shape is first considered. Next, a 2D gasket-like structure is designed, and finally, we consider a 3D structure with contact-like boundary conditions. In these examples, the prescribed deformed geometry is subject to a distributed external force. The examples show that the deformed geometry and load distribution can be exactly prescribed through stiffness optimization based on the inverse motion analysis. [ABSTRACT FROM AUTHOR]

Sensitivity analysis of coupled acoustic-structural systems under non-stationary random excitations is investigated in this paper. The combined method of direct differentiation method (DDM) and pseudo excitation method (PEM) in previous work is computationally expensive for problems with large-scale design variables. To circumvent this difficulty, a fast sensitivity analysis method integrating the adjoint variable method (AVM) and PEM for coupled acoustic-structural systems under non-stationary random excitations is proposed. In this framework, the sensitivity analysis of coupled systems subject to non-stationary random excitations is transformed into a sensitivity analysis under pseudo-transient excitations with the help of PEM. On this basis, the computing efficiency of random response sensitivity is improved directly by solving the adjoint equations involved in the AVM. Numerical examples fully demonstrate the accuracy and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

BACKGROUND: The quality of commercial soy sauce is variable at present. Technical work is needed to improve the quality and flavor of soy sauce, especially in China. Material is a factor for influencing soy sauce characters in fermentation. RESULTS: Germinated soybean sauce (fermented by germinated soybean) had a gamma aminobutyric acid (GABA) concentration of 6.83 μg mL−1, whereas a control (a soy sauce fermented by soybean) had a GABA concentration of less than 2.42 μg mL−1. Germinated soybean sauce also contained significantly higher levels of isoflavones, total polyphenol, and amino acid nitrogen than the control soy sauce. Microbial diversity results showed that Bacillus was the dominant bacteria in germinated soy sauce compared with the control. Aldehydes, alcohols, esters, and phenols were the major flavor components of germinated soybean sauce. CONCLUSION: A soy sauce with high levels of GABA, isoflavones, and total polyphenol was developed using germinated soybean. Stenotrophomonas, the typical pathogen found in the control, was reduced dramatically and replaced by Bacillus during fermentation with the germinated soybean. The germinated soybean sauce exhibited a better aroma and taste than the control. Soy sauce fermented by soybeans that germinated for 48 h exhibited greater advantages than soy sauce that germinated for 24 and 72 h. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The terahertz (THz) vortex beam generators are designed and theoretically investigated based on single-layer ultra-thin transmission metasurfaces. Noncontinuous phase changes of metasurfaces are obtained by utilizing Pancharatnam–Berry phase elements, which possess different rotation angles and are arranged on two concentric rings centered on the origin. The circularly polarized incident THz beam could be turned into a cross-polarization transmission wave, and the orbital angular momentum (OAM) varies in value by lℏ. The l values change from ± 1 to ± 5, and the maximal cross-polarization conversion efficiency that could be achieved is 23%, which nearly reaches the theoretical limit of a single-layer structure. The frequency range of the designed vortex generator is from 1.2 THz to 1.9 THz, and the generated THz vortex beam could keep a high fidelity in the operating bandwidth. The propagation behavior of the emerged THz vortex beam is analyzed in detail. Our work offers a novel way of designing ultra-thin and single-layer vortex beam generators, which have low process complexity, high conversion efficiency and broad bandwidth. [ABSTRACT FROM AUTHOR]

Compared with static shape control, dynamic shape control is more difficult due to its time-varying nature. To improve the control precision and reduce the number of actuators needed, an integrated design optimization model of structure and control is proposed. The following three sets of design variables are considered to minimize the time domain variance between the controlled and desired dynamic shapes: the time-varying actuator voltages, the actuator layout and the structural ply parameters. To satisfy the engineering performance requirements to the greatest extent possible, constraints on the structural mass, the energy, the maximum transient voltage and the number of actuators are considered. Because the control voltages are varying in time, a two-level optimization strategy is adopted. In the inner optimization problem, the Newmark integral method is applied to derive discrete time domain expressions for the shape control equations, and then, the Kuhn-Tucker condition is introduced to calculate the optimal time-varying voltage distribution. To solve the outer optimization problem, because of the coexistence of discrete variables and continuous variables, a simulated annealing algorithm is used. To address the shape control of complicated curved shells, a finite element formulation for an eight-node laminated curved shell element with piezoelectric actuators is derived. Numerical examples show that the proposed integrated design optimization method can significantly improve the control effect and that the optimization of the structural ply parameters plays an important role. Moreover, the control system can be simplified by taking the minimum number of actuators as the objective function when the control accuracy allows. [ABSTRACT FROM AUTHOR]

The hollowing deterioration of stone relics required effective non-destructive testing (NDT) methods for their timely restoration and maintenance. To this end, a new NDT method based on terahertz (THz) technology by using support vector machine (SVM)-based machine learning models was developed to assess and diagnose the hollowing deterioration of the Yungang Grottoes. According to experiment design, a series of hollowing deterioration samples with various thicknesses of hollowing deterioration were prepared and then measured by using THz time-domain spectroscopy (THz-TDS). Based on the THz-TDS results of 30 randomly selected samples, a SVM-based hollowing deterioration prediction model (SVM-HDPM) was established by analyzing the relationship between the hollowing samples and the THz spectral information. The reliability and accuracy of the model was further proved by verified and compared with using the THz spectral data of the remaining 10 samples. The experimental results with the linear kernel function greatly demonstrated that the SVM-HDPM can have superior prediction accuracy, implying that the model is feasible for the prediction the hollowing deterioration of the stone relics. Moreover, one data preprocess was introduced into SVM-HDPM to meet the needs of field-based test. The predicted results of five different hollowing deterioration with different flaked stone thickness revealed good performance with very low mean square error (MSE) value. Therefore, it is believed that the proposed method can be regarded as an effective NDT technique with practical applications in analyzing cultural relics and have promising future prospects in inspection stone relics-like ancient heritage for hidden flaws. [ABSTRACT FROM AUTHOR]

Japanese soy sauce has become more acceptable by Chinese consumers due to its umami taste. However, the volatile flavor compounds and taste characters have not been fully clarified. This study aimed to explore the flavor characteristics of three kinds of Japanese soy sauce, including Koikuchi Shoyu, Usukuchi Shoyu, and Amakuchi Shoyu. The secret of volatile flavor substances was investigated by Gas Chromatography-Mass Spectrometry (GC-MS) and electronic nose, while taste compounds were investigated by silylation GC-MS and electronic tongue (E-tongue). A total of 173 volatile flavor substances and 160 taste compounds were identified. In addition, 28 aroma compounds with odor activity values (OAV) ≥ 1 were considered as the typical flavors. We found that alcohols and aldehydes were in high abundance in Japanese soy sauce, but only a small portion of pyrazines and esters were. Based on electronic nose and GC-MS analysis, Koikuchi Shoyu gives more contribution to aroma compounds, while Usukuchi Shoyu and Amakuchi Shoyu give the sourness and sweetness features based on E-tongue and silylation GC-MS analysis. In this study, 50 kinds of sugars were detected that contributed to the sweetness of soy sauce. This study will provide new insight into the flavor characteristics of Japanese soy sauce that potentially contribute to the innovation and development of soy sauce. [ABSTRACT FROM AUTHOR]

This paper presents an integrated, new, and generic framework for layout optimization of viscoelastic damping for noise control of mid-frequency vibro-acoustic systems. The method is developed based on the concept of power balance among different modal energies between coupled structural and acoustic subsystems and is formulated within the framework of a statistical modal energy distribution analysis (SmEdA). In the novel optimization formulation, the total energy of the acoustic subsystem is chosen as the objective function for minimizing the internal acoustic response in the vibro-acoustic system; and the relative material volume densities for viscoelastic element groups are selected as design variables using a volume-preserving Heaviside function. A new sensitivity analysis formulation is developed in a semi-analytical form via a SmEdA for solving the vibro-acoustic optimization problem. Two numerical examples are presented to demonstrate the efficiency and effectiveness of the present method. The present numerical results reveal two important findings: (a) the total acoustic energy of the chosen vibro-acoustic system can be significantly reduced; and (b) the optimum viscoelastic material layouts not only decrease the peak values of the modal coupling strengths between structural and acoustic subsystems but also create relatively more uniform acoustic modal energy distribution. [ABSTRACT FROM AUTHOR]

Most previous studies of viscoelastic sandwich plates were based on the assumption that damping was only resulting from shear deformation in the viscoelastic core. However, extensive and compressive deformations in the viscoelastic core should also be considered especially for sandwich plates with moderately thick viscoelastic core. This paper presents a finite element formulation for vibration and damping analysis of sandwich plates with moderately thick viscoelastic core based on a mixed layerwise theory. The face layers satisfy the Kirchhoff theory while the viscoelastic core meets a general high-order deformation theory. The viscoelastic core is modeled as a quasi-three-dimensional solid where other types of deformation such as longitudinal extension and transverse compression are also considered. To better describe the distribution of the displacement fields, auxiliary points located across the depth of the sandwich plate are introduced. And based on the auxiliary points, the longitudinal and transverse displacements of the viscoelastic core are interpolated independently by Lagrange interpolation functions. Quadrilateral finite elements are developed and dynamic equations are derived by Hamilton's principle in the variation form. Allowing for the frequency-dependent characteristics of the viscoelastic material, an iterative procedure is introduced to solve the nonlinear eigenvalue problem. The comparison with results in the open literature validates the remarkable accuracy of the present model for sandwich plates with moderately thick viscoelastic core, and demonstrates the importance of the higher-order variation of the transverse displacement along the thickness of the viscoelastic core for the improvement of the analysis accuracy. Moreover, the influence of the thickness and stiffness ratios of the viscoelastic core to the face layers on the damping characteristics of the viscoelastic sandwich plate is discussed. [ABSTRACT FROM AUTHOR]

Summary: A total of 214 taste compounds were identified in soy sauce by silane derivatisation coupled with gas chromatography–mass spectrometry (SD‐GC‐MS), including 74 kinds of sugars. The proportion of total sugars is highest from 37.24–77.24% among all taste compounds. In particular, rare sugars were detected and identified as the special compounds in soy sauce which come from the sugar metabolism. Rare sugars identified in soy sauce by traditional fermented technology were prominent than Japanese technology. Principal component analysis (PCA) investigation of these results showed that samples can be distinguished by sugars as the first principal component and the general evaluation index (GEI) of samples was consistent with the result of sensory evaluation. Meanwhile, sweetness had the maximum range (from −9.89 to 14.10) in all taste indexes by electronic tongue (E‐tongue) analysis. [ABSTRACT FROM AUTHOR]

Simultaneous optimization of multiple parameters of an active structural acoustic control system under random force excitation is presented in this article. A method integrating the pseudo excitation method, finite element method, and boundary element method is proposed to analyze the random acoustic radiation. The active structural acoustic control of randomly vibrating structures is developed using the velocity feedback control scheme with the help of the pseudo excitation method. The acoustic design optimization model is proposed, in which the auto power spectral density of sound pressure is taken as the objective function and the placements of actuators/sensors as well as control gains are assigned as design variables. Taking into account the operational efficiency and control cost, the number of actuators/sensors and the total actuation energy are considered as constraints. A simulated annealing algorithm is employed for the optimization problem with discrete and continuous variables coexisting. Numerical examples are given to demonstrate the effectiveness of the proposed methods and the programs, and several key factors on the optimized designs are also discussed. [ABSTRACT FROM AUTHOR]

Summary: This article presents a novel formulation for sandwich beams with soft core based on a layerwise description of continuous transverse shear stress field. The transverse shear stress field is assumed to follow a quadratic distribution in thick face layers and a uniform distribution in soft core. Based on stress‐strain relations, transverse shear strain is obtained, and in‐plane displacement field is determined by taking the integral of the transverse shear stain. By enforcing interlaminar displacement continuity, an explicit displacement field expression containing only displacement variables is formulated. In this formulation, interlaminar continuity conditions of displacement and transverse shear stress are satisfied simultaneously, and transverse shear and crosssectional warping effects in thick face layers are accurately taken account. To show characteristics and advantages of the present model, some classical theoretical models are further developed under different kinematic assumptions. The governing equations are derived using Hamilton principle, and finite element solutions for static and dynamic analysis of sandwich beams are presented. Comparisons with exact solution and other well‐known solutions, well demonstrate high accuracy of the present model for sandwich beams with different features. Besides, numerical discussions further reflect accuracy advantages of the present model in static and dynamic analysis of sandwich beams. [ABSTRACT FROM AUTHOR]

This paper investigates topology optimization of the surface electrode coverage on piezoelectric sensor/actuator layers attached to a curved shell structure subjected to stationary random force excitation, with the aim to minimize the random vibration response under active control. In the optimization model, the power spectral density (PSD) of displacement response at the specified point is considered as the objective function. The pseudo-densities describing the surface electrode distribution are assigned as the design variables, and an artificial active damping model with penalization is employed to suppress intermediate density values. The voltage across each actuator is determined by velocity feedback control law. Pseudo excitation method (PEM) is introduced to analyze random vibration response of a piezoelectric curved shell structure with active control. In this context, the adjoint variable method for the sensitivity analysis of displacement PSD with respect to topological design variables is derived. Numerical examples fully demonstrate the validity of the proposed approach. [ABSTRACT FROM AUTHOR]

Ultralight lattice structures exhibit excellent mechanical performance and have been used widely. In structural design, the fundamental frequency is highly important. Therefore, a multiscale topology optimization method was utilized to optimize the fundamental frequency of multimaterial lattice structures in this study. Two types of optimization problems were studied, namely, maximizing the natural fundamental frequency with mass constraints and minimizing compliance with frequency constraints. The Heaviside-penalty-based discrete material optimization method was adopted for the optimal selection of candidate materials. The asymptotic homogenization method was used to evaluate the equivalent macroscale properties according to the microstructure of the lattice material. To enable gradient optimization, sensitivities were outlined in detail. A density filter with a volume-preserving Heaviside projection was used to eliminate the risk of a checkerboard pattern and reduce the number of gray elements. A polynomial penalization scheme was employed to eliminate localized spurious eigenmodes in the low-density region. Finally, several numerical examples were performed to validate the proposed method. These numerical examples resulted in novel microstructural configurations with remarkably improved vibration resistance. [ABSTRACT FROM AUTHOR]

The terahertz spectra of four kinds of vitamins are presented. The refractive index and absorption spectra of these vitamins are obtained by the terahertz time-domain spectroscopy. The full-geometry optimizations and frequency calculations using the density functional theory are applied to obtain the structure and vibration frequencies of these vitamin molecules. The calculated vibration frequencies are compared with the experimental data. The results show that there are terahertz fingerprint absorptions for all of four kinds of vitamins. The terahertz absorbance spectra of vitamins result from not only the intramolecular vibration modes, but also the intermolecular interaction or phonon modes. [ABSTRACT FROM AUTHOR]

A novel pentagram THz hollow core anti-resonant fiber (HC-ARF) is proposed and fabricated by a 3D printer in this paper. By utilizing the advantage of 3D print technology, a novel structure of one ring triangular air holes is introduced in the cladding and thus a pentagram hollow core is formed, which breaks through the limitation of the material absorption and effectively lowers the propagation loss of THz wave. Numerical results show that the loss as low as 0.02 cm−1 can be obtained for the proposed fiber within the THz frequency range from 0.5 to 2 THz. The fiber samples with different length of 10 cm and 15 cm are fabricated and measured experimentally. Experimental results demonstrate that the minimum loss of 0.025 cm−1 is obtained at 1.94 THz. Furthermore, the proposed fiber also has the advantage of excellent resistance to structural deformation. [ABSTRACT FROM AUTHOR]

It is well known that the classical particle swarm optimization (PSO) is time-consuming when used to solve complex fitness optimization problems. In this study, we perform in-depth research on fitness estimation based on the distance between particles and affinity propagation clustering. In addition, support vector regression is employed as a surrogate model for estimating fitness values instead of using the objective function. The particle swarm optimization algorithm based on affinity propagation clustering, the efficient particle swarm optimization algorithm, and the particle swarm optimization algorithm based on support vector regression machine are then proposed. The experimental results show that the new algorithms significantly reduce the computational counts of the objective function. Compared with the classical PSO, the optimization results exhibit no loss of accuracy or stability. [ABSTRACT FROM AUTHOR]

In the past decades, many researches have been done on the design optimization of low- and high-frequency vibro-acoustic systems. However, the work of mid-frequency vibro-acoustic systems was rarely reported. As an improved statistical energy analysis (SEA), statistical modal energy distribution analysis (SmEdA) is based on the power balance between modes in different subsystems and extends SEA to mid-frequency range. In this article, an optimization procedure for mid-frequency vibro-acoustic systems based on SmEdA is presented. First, a vibro-acoustic system can be decoupled by using the dual-modal formulation (DMF) into a structural subsystem and an acoustic subsystem. Then, the optimization model is built by designating the total energy of the acoustic subsystem as objective function and the structural thicknesses as design variables. Finally, the optimal solution is obtained by using the method of moving asymptotes (MMA) which need to be provided with the gradient information of the objective and constraint functions in each iteration. Therefore, a sensitivity analysis about the total energy of the acoustic subsystem with respect to the thicknesses of the structures surrounding the interior acoustic cavity is performed by adopting a semi-analytical method. Moreover, a coefficient condensation technique is introduced in the sensitivity analysis to avoid the dimensional inconformity of the coefficient matrices in SmEdA due to the variation of the number of modes with the perturbation of structural sizes. Numerical examples are given to validate the effectiveness of the optimization procedure. [ABSTRACT FROM AUTHOR]

Constrained layer damping treatments have been widely used as an effective way for vibration control and noise reduction of thin-walled plates and shells. Despite extensive application in vibration and damping analysis of sandwich plates with viscoelastic core, the rectangular element is challenged by irregular structural forms in practical engineering. In this paper, a three-layer four-node quadrilateral element with seven degrees of freedom at each node is presented. Compared with classical rectangular element, the four-node quadrilateral element has stronger adaptability in complex structural forms and boundary conditions. Based on the layer-wise theory where the constrained layer and the base layer meet Kirchhoff theory and the viscoelastic layer satisfies first-order shear deformation theory, the finite element formulation of the sandwich plate with viscoelastic core is derived by the Hamilton principle in variational form and based on the generalization of the discrete Kirchhoff Quadrilateral plate element. The complex modulus model is employed to describe the viscoelastic core of sandwich plates, allowing for the material's frequency dependent characteristics. The natural frequencies and associated modal loss factors are computed based on the complex eigenvalue problems. The frequency dependent characteristic of the viscoelastic core is considered and an iterative procedure is introduced to solve the nonlinear eigenvalue problem. At last, six verification numerical examples that include three sandwich beam-plates and three sandwich plates are provided to compare present method with experiment, analytical method, Galerkin method, finite element methods and commercial software (NASTRAN). The results show that the proposed finite element can accurately and efficiently simulate the sandwich plates treated with constrained layer damping with a variety of structural forms and boundary conditions. [ABSTRACT FROM AUTHOR]

Aspergillus oryzae is an excellent strain for soy sauce fermentation because of its complicated enzyme system, especially protease. The aim of this study was to investigate the key enzymes and flavors during soy sauce fermentation, and a comparative assessment of extracellular enzymes during various fermentation stages at the proteomic level via iTRAQ analysis is presented. Many important enzymes related to the amino acid and glucose metabolisms participated in the material decomposition under high-salt stress. Dipeptidase, dipeptidyl aminopeptidase, leucine aminopeptidase, aspartic protease pep1, and extracellular metalloproteinase played positive roles during the early stage of soybean mash fermentation, whilst leucine aminopeptidase A and extracellular metalloproteinase NpI were the dominant proteolytic enzymes during the later period of fermentation. At the same time, β-glucosidase and β-xylanase exerted great effects upon glucose metabolism throughout the fermentation process. The results show that protease and amylolytic enzymes are complementary in the formation of flavors such as alcohols, acids, esters, aldehydes, furans, and pyrazines during soy sauce fermentation. [ABSTRACT FROM AUTHOR]

Classification of the weathering degree of large outdoor stone relics has long been a challenge in their protection engineering. An approach to classifying the weathering levels of the Yungang Grottoes is presented in this paper. This approach is based on combined terahertz (THz) spectra and ultrasonic velocity and the use of a least squares support vector machine (LS-SVM). A regression model for prediction of the weathering level was established using the optimal values of parameters determined by the double cross-validation (D-CV) method. This SVM regression prediction model (SVMRPM) predicts the weathering levels of the grottoes with relative errors of 8.16% or less. The SVMRPM can also be used to predict the weathering levels of some areas where ultrasonic testing is extremely difficult; the THz spectra can easily be obtained using approximately 0.2 g of sample material. This method is a highly efficient and economical technique for determining the degree of weathering of large exposed stone relics. [ABSTRACT FROM AUTHOR]

Simultaneously optimizing the thickness of the base structure and the location of piezoelectric sensors/actuators as well as control gains is investigated for minimizing the sound radiation from the vibrating curved shell integrated with sensors/actuators under harmonic excitation. The finite element formulation of the piezoelectric curved shell structure is described. The piezoelectric element is coupled into the base shell element using nodal displacement constraint equations. The active control of structural vibration-acoustic radiation is formulated using the velocity feedback algorithm. Based on both passive and active control measures, an integrated optimization model of the vibro-acoustic problem is proposed, in which the sound power is taken as the objective function. The thickness of the base shell elements and the parameters of control system, including the location of sensors/actuators and control gains, are chosen as the design variables. In order to restrict the complexity of the control system, the number of sensors/actuators is considered as a constraint. A simulated annealing algorithm is extended to handle the vibro-acoustic optimization problem with the continuous and discrete variables co-existing. Numerical examples demonstrate the effectiveness of the optimization scheme and the correctness of the computation program. [ABSTRACT FROM AUTHOR]

Topology optimization for coupled acoustic-structural systems subjected to stationary random excitations is investigated. Bi-material elastic continuum structures without damping are considered. The finite element method is utilized to deal with coupled acoustic-structural problems. An accurate and highly efficient algorithm series for stationary random analysis techniques, pseudo excitation method, is extended to calculate the acoustic random response generated by the vibrating structures. Minimization of the auto power spectral density of sound pressure is taken as design objective and its sensitivities with respect to topological variables are derived by adjoint method. A penalty term is proposed to suppress the intermediate volumetric densities. Numerical examples are given to demonstrate the validity of the presented methods. [ABSTRACT FROM AUTHOR]

Considerable knowledge has been accumulated on the lactic acid bacteria (LAB) that affect the aroma and flavour of yogurt. This review focuses on the role of LAB in the production of flavour compounds during yogurt fermentation. The biochemical processes of flavour compound formation by LAB including glycolysis, proteolysis, and lipolysis are summarised, with some key compounds described in detail. The flavour-related activities of LAB mostly depend on the species used for yogurt fermentation, and some strategies have been developed to obtain more control of the flavour-forming process. Metabolic engineering can be a powerful tool to reroute the metabolic flux towards the efficient accumulation of the desired flavour compounds with the knowledge of the complex network of flavour-forming pathways and the availability of genetic tools. Further progress made in the omics-based techniques and the use of systems biology approaches are needed to fully understand, control, and steer flavour formation in yogurt fermentation processes. [ABSTRACT FROM AUTHOR]