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A millimeter wave (MMW) radar sensor is employed in our laboratory to detect human speech because it provides a new non-contact speech acquisition method that is suitable for various applications. However, the speech detected by the radar sensor is often degraded by combined noise. This paper proposes a new perceptual wavelet packet method that is able to enhance the speech acquired using a 94 GHz MMW radar system by suppressing the noise. The process is as follows. First, the radar speech signal is decomposed using a perceptual wavelet packet. Then, an adaptive wavelet threshold and new modified thresholding function are employed to remove the noise from the detected speech. The results obtained from the speech spectrograms, listening tests and objective evaluation show that the new method significantly improves the performance of the detected speech. [ABSTRACT FROM AUTHOR]

As an abundant natural resource in Asia, bamboo is receiving increased attention as an engineering material due to its renewability and excellent strength. The parallel-to-grain compression and shearing properties of moso bamboo culm were examined. The growth characteristics (bamboo age, nodes, and location along the culm), as well as treatments for practical applications (hole punching and hoop reinforcing by hose clamp) were investigated for their influence. Mechanical tests were conducted in accordance with the ISO22157-1:2004 (2004), ISO/TR 22157-2:2004(E) (2004), and CNS GB/T 15780-1995 (1996) standards. Acceptable loading rates for the parallel-to-grain compression and shearing tests were 0.1 and 0.05 mm/s, respectively. The compressive and shearing strengths increased from the bottom to the top of the bamboo. Bamboo age and nodes exerted little influence on parallel-to-grain compressive and shearing strength. In addition, hole punches diminished the mechanical strength of the bamboo culm, while hose clamps enhanced it slightly. [ABSTRACT FROM AUTHOR]

To investigate the possibility of using bamboo-bundle laminated veneer lumber (BLVL) as a cooling tower packing material, the water absorption rates, thickness swelling rates, and flexural properties of three different composite materials were studied. The BLVL was combined with either 12% or 24% phenol formaldehyde resin (PF), and the moso bamboo strips were exposed to water baths at three different temperatures (45, 65, and 85 °C) for 30 d. After the aging treatments, the 24%-BLVL samples showed lower water absorption rates and better bending properties than the other two composites. The temperature was found to have a significant effect on the modulus of rupture (MOR), modulus of elasticity (MOE), and the thickness swelling rate. As the temperature increased, the swelling rate and the rate of weight gain increased and the MOE and MOR decreased. According to the activation energies for swelling calculated from the Arrhenius-type plots, compared with the 24%-BLVL (22.95 kJ·mol-1) and the moso bamboo strips (12.69 kJ·mol-1), the effect of temperature on the swelling rate was greatest for the 12%-BLVL (24.15 kJ·mol-1). Results showed that the BLVL material is a promising candidate for a novel cooling tower packing material. [ABSTRACT FROM AUTHOR]

In order to improve the speech acquisition ability of a non-contact method, a 94 GHz millimeter wave (MMW) radar sensor was employed to detect speech signals. This novel non-contact speech acquisition method was shown to have high directional sensitivity, and to be immune to strong acoustical disturbance. However, MMW radar speech is often degraded by combined sources of noise, which mainly include harmonic, electrical circuit and channel noise. In this paper, an algorithm combining empirical mode decomposition (EMD) and mutual information entropy (MIE) was proposed for enhancing the perceptibility and intelligibility of radar speech. Firstly, the radar speech signal was adaptively decomposed into oscillatory components called intrinsic mode functions (IMFs) by EMD. Secondly, MIE was used to determine the number of reconstructive components, and then an adaptive threshold was employed to remove the noise from the radar speech. The experimental results show that human speech can be effectively acquired by a 94 GHz MMW radar sensor when the detection distance is 20 m. Moreover, the noise of the radar speech is greatly suppressed and the speech sounds become more pleasant to human listeners after being enhanced by the proposed algorithm, suggesting that this novel speech acquisition and enhancement method will provide a promising alternative for various applications associated with speech detection. [ABSTRACT FROM AUTHOR]

After chemical or nuclear leakage or explosions, finding survivors is a huge challenge. Although human bodies can be found by smart vehicles and drones equipped with cameras, it is difficult to verify if the person is alive or dead this way. This paper describes a continuous wave radar sensor for remotely sensing the vital signs of human subjects. Firstly, a compact and portable 24 GHz Doppler radar system is designed to conduct non-contact detection of respiration signal. Secondly, in order to improve the quality of the respiration signals, the self-correlation and adaptive line enhancer (ALE) methods are proposed to minimize the interferences of any moving objects around the human subject. Finally, the detection capabilities of the radar system and the signal processing method are verified through experiments which show that human respiration signals can be extracted when the subject is 7 m away outdoors. The method provided in this paper will be a promising way to search for human subjects outdoors. [ABSTRACT FROM AUTHOR]

To predict the resin absorbing content of bamboo bundle fiber, a model relating to the soaking time and mass ratio of polyvinyl acetate (PVAC) adhesive to phenol formaldehyde (PF) resin defined on the basis of the Lucas-Washburn equation was proposed. Various dipping times and different PVAC/PF ratios were investigated in the experiment. Variance analysis revealed that the resin absorbing content was significantly associated with the ratio of PVAC/PF. However, the soaking time had a significant effect on bamboo fiber resin absorbing content from 0 s to 70 s and had an insignificant effect after 70 s. The results showed that the model proposed could accurately predict the resin absorbing content for bamboo bundle fiber impregnated in different PVAC/PF levels. The comparison of theoretical calculations with experimental results revealed that the residual sum of square and root mean squared error were relatively low, and the correlation coefficients and coefficients of determination were all over 0.95. [ABSTRACT FROM AUTHOR]

Bamboo-bundle laminated veneer lumber (BLVL) was produced by joint lengthening technology. The objective of this study was to evaluate the effect of joint form and the values of key parameters on mechanical properties of BLVL. Two joint forms, i.e., finger joint and scarf joint, and two corresponding joint parameters, i.e., finger length and scarf angle, were investigated in laminates. The results indicated that the mechanical properties of jointed BLVL were reduced in comparison to those of BLVL without joints. For finger-joint form, the BLVL member with 14 mm fingers achieved better compressive strength, bending modulus of rupture (MOR), and tensile strength than 19 and 25 mm ones. For scarf-joint form, the 30° scarf-jointed member exhibited the highest bending modulus and tensile modulus of rupture (MOR) in this study, then followed the 45° and 60° ones. The 60° scarf-jointed BLVLs were better than 30° and 45° groups in compression strength. Synthesis of the testing results revealed that finger-jointed BLVLs achieved better bending modulus of rupture than scarf-jointed ones. [ABSTRACT FROM AUTHOR]

Bamboo keyboards made from bamboo panels are exposed to the influence of mold infection, hygrothermal environment and repeated wear. Mold resistance and hygrothermal aging properties of bamboo keyboard under different treatments were investigated. The abrasion resistance was experimentally studied and compared between bamboo keyboard and plastic keyboard. The results indicated that the bamboo keyboard treated with HO exhibited the best mold resistance, followed by that treated with varnish, and then came the ones with mildew preventive treatment and the control specimens. Although hardly visible to the naked eye after 4 weeks of mold infection test, mold was observed on most plastic keyboards through microscopic examination. For aging test, the shrinkage ratio of bamboo keystroke was 0.34, 0.46 and 0.62 % after high and low temperature (HLT) treatment, while the swelling ratio was 0.01, 1.14 and 1.93 % after constant temperature and humidity (CTH) treatment, respectively. Similar trend in the ratio of dimensional change was observed in terms of both drying shrinkage and hydroscopic swelling: thickness direction > perpendicular-to-grain direction > grain direction. By manual observation, the bamboo keyboard had an advantage over plastic keyboards in terms of the adaptability to an environment of changing temperature. For abrasion test, the wear point of bamboo keyboard was 650 r and that of plastic 150 r indicating that bamboo keyboards performed better in terms of abrasion resistance than plastic ones. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the uniformity of density distribution for Bamboo-bundle Laminated Veneer Lumber (BLVL) and its relationship to the stability of mechanical performance. A novel assembly style called one-piece veneer formation technology was developed to enhance the density uniformity, and four different density levels for BLVL were examined by X-ray scanning. The results indicated that the homogeneity of density, the stability of mechanical performance, and the mechanical properties for BLVL could be effectively improved by assembling the bamboo bundles into layers and then combining the layers to make the lumber. The density uniformity in width and thickness directions increased with increasing target density. A negatively linear correlation between density and Coefficient of Variation (COV) of MOR and shearing strength was observed. Partial correlation analysis revealed that when controlling for the variability of density, the linear relationship between density and the COV of MOR became insignificant, and the degree of linear correlation between density and the COV of shearing strength decreased. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the deformation behavior and damage model of bamboo bundle corrugated laminated composites under low velocity impact loading. The influence of different stacking sequences, i.e., bamboo bundle parallel to the corrugated waves (type I), cross-ply (type II), and perpendicular to the waves (type III), in laminates was studied in regard to impact loading. A shape parameter, K, was developed to quantify the effect of corrugation on impact response. The results of this study indicated that the type I composites displayed the optimum impact performance, followed by types II and III. The total energy absorbed by the type I laminates was 1.3 and 2.2 times as much as types II and III. The values of peak load were type I > type II > type III. The composites deformed and failed in different manners under low velocity impact loading: material failure, delamination and fiber tensile fracture, and structural collapse were the main modes of failure for type I, II, and III, respectively. The effect of the corrugated shape on impact properties of composites was positive for type I, but negative for type II composites. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effect of uniaxial and biaxial compression loadings on the circumferential-radial mechanical properties of bamboo. A novel biaxial testing device, called the 3D composite material analysis system, was developed to conduct biaxial compression tests. Strain field analysis was characterized with the help of the digital speckle correlation method (DSCM). The effects of four different environmental treatments (I. air-drying, II. constant temperature and relative humidity, III. relatively low temperature, and IV. ultra-low temperature) on the circumferential performance of bamboo were examined in the experiment. The results of this study indicated that the diametric strength of bamboo evaluated by biaxial load was as 2.4 to 2.5 times the uniaxial compression. Under biaxial load, the strength of the bamboo node was about 2.38 times higher than the internode. Failure first occurred at the outside surface of bamboo at about the 45° position between X and Y axial when conducting a biaxial compression test. The distribution of X-strain field expressed itself more uniformly than the Y-strain field. The diametric mechanical properties of bamboo ring were σ IV > σ III > σ II > σ I for both the uniaixal and biaxial compression tests. [ABSTRACT FROM AUTHOR]

Mechanical properties of woven ramie fabric under 3D loadings are fundamental to optimizing the design of woven composites that are frequently subjected to complex stress states. This work proposes a novel 3D test analysis system for evaluating woven natural-fiber fabrics under multidimensional loads. The effects of different loading directions, uniaxial (X direction), biaxial (X and Y), bursting (Z direction), and 3D loading (X, Y, and Z) on the breaking strength of the woven ramie (Boehmeria nivea) fabric were compared. Weft breaking strength was lower than that of warp under uniaxial tension. Variability in warp and weft increased in biaxial tension. Bursting strength was significantly affected by the type of loading head used, with an R20 spherical head producing the highest strength values. Warp and weft were positively correlated under biaxial tension, r = 0.58. The synergistic effect of bursting strength accounted for 12.5% of the total correlation under 3D loadings. [ABSTRACT FROM PUBLISHER]

High purity of (7,5) SWNTs (∼79% of the semisonducting SWNT ensemble) can be obtained by polymer-assisted extraction from the narrow-diameter distributed SWNTs produced by the catalyst Co-MCM-41. The fluorene-based polymers are able to selectively wrap the single-walled carbon nanotubes (SWNTs) with certain chiral angles or diameters depending on their chemical structures. Poly(9,9-dioctyfluoreny1−2, 7-diyl) and poly(9,9-dihexylfluorenyl-2,7-diyl)-co-(9,10-anthracene) selectively wrap SWNTs with high chiral angles (>24.5°). By contrast, poly9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-2,1‘-3-thiadiazole) preferentially wraps the SWNTs with certain diameter (1.02−1.06 nm). [ABSTRACT FROM AUTHOR]

The reactivity of organic radicals produced by 1,1′-azobis(cyanocyclohexane) (ACN) is tuned to selectively suppress electrical conduction of small diameter single-walled carbon nanotubes, and the modified tubes are able to produce high-mobility (∼10 cm2V−1s−1) and solution-processable thin-film transistors with full semiconductor device yield, promising applications in high-performance printable electronics. [ABSTRACT FROM AUTHOR]

An energy-efficient and environmentally conscious bamboo-constructed residential structure was created, comprising bamboo composite panels, steel framework, and mineral wool insulation. To ascertain the efficacy of this particular type of wall in enhancing thermal capabilities, the finite element method was employed to analyze the factors influencing the thermal performance of the exterior wall panels, insulation layer, framework, and interior wall panels. A more judicious design and implementation strategy, known as the 3# and 8# combination scheme, was evaluated in practical applications to assess the thermal efficiency of the wall system. The findings indicated that augmenting the thickness of the inner and outer wall panels and insulation layer, reducing the framework thickness, and incorporating wooden framework as a substitute for steel framework within a certain range enhanced the thermal capabilities of bamboo-constructed walls and mitigated the adverse effects of thermal bridges. The thermal performance of the residences employing the newly developed bamboo-constructed walls surpassed that of conventional iron container houses, thereby warranting broader adoption and application in practical projects. These outcomes offer valuable insights for the optimized design of thermal performance in bamboo-constructed walls. [ABSTRACT FROM AUTHOR]

Ultra-wide band (UWB) radar for short-range human target detection is widely used to find and locate survivors in some rescue missions after a disaster. The results of the application of bistatic UWB radar for detecting multi-stationary human targets have shown that human targets close to the radar antennas are very often visible, while those farther from radar antennas are detected with less reliability. In this paper, on account of the significant difference of frequency content between the echo signal of the human target and that of noise in the shadowing region, an algorithm based on wavelet entropy is proposed to detect multiple targets. Our findings indicate that the entropy value of human targets was much lower than that of noise. Compared with the method of adaptive filtering and the energy spectrum, wavelet entropy can accurately detect the person farther from the radar antennas, and it can be employed as a useful tool in detecting multiple targets by bistatic UWB radar. [ABSTRACT FROM AUTHOR]

Remarkable progress has been achieved in the detection of single stationary human. However, restricted by the mutual interference of multiple humans (e.g., strong sidelobes of the torsos and the shadow effect), detection and localization of the multiple stationary humans remains a huge challenge. In this paper, ultra-wideband (UWB) multiple-input and multiple-output (MIMO) radar is exploited to improve the detection performance of multiple stationary humans for its multiple sight angles and high-resolution two-dimensional imaging capacity. A signal model of the vital sign considering both bi-static angles and attitude angle of the human body is firstly developed, and then a novel detection method is proposed to detect and localize multiple stationary humans. In this method, preprocessing is firstly implemented to improve the signal-to-noise ratio (SNR) of the vital signs, and then a vital-sign-enhanced imaging algorithm is presented to suppress the environmental clutters and mutual affection of multiple humans. Finally, an automatic detection algorithm including constant false alarm rate (CFAR), morphological filtering and clustering is implemented to improve the detection performance of weak human targets affected by heavy clutters and shadow effect. The simulation and experimental results show that the proposed method can get a high-quality image of multiple humans and we can use it to discriminate and localize multiple adjacent human targets behind brick walls. [ABSTRACT FROM AUTHOR]

The through-wall detection and classification of human activities are critical for anti-terrorism, security, and disaster rescue operations. An effective through-wall detection and classification technology is proposed for finer-grained human activities such as piaffe, picking up an object, waving, jumping, standing with random micro-shakes, and breathing while sitting. A stepped-frequency continuous wave (SFCW) bio-radar sensor is first used to conduct through-wall detection of finer-grained human activities; Then, a comprehensive range accumulation time-frequency transform (CRATFR) based on inverse weight coefficients is proposed, which aims to strengthen the micro-Doppler features of finer activity signals. Finally, in combination with the effective eigenvalues extracted from the CRATFR spectrum, an optimal self-adaption support vector machine (OS-SVM) based on prior human position information is introduced to classify different finer-grained activities. At a fixed position (3 m) behind a wall, the classification accuracies of six activities performed by eight individuals were 98.78% and 93.23%, respectively, for the two scenarios defined in this paper. In the position-changing experiment, an average classification accuracy of 86.67% was obtained for five finer-grained activities (excluding breathing) of eight individuals within 6 m behind the wall for the most practical scenario, a significant improvement over the 79% accuracy of the current method. [ABSTRACT FROM AUTHOR]