Solid rocket motor propellant health monitoring based on oxide-doped curved long-period fiber grating.

A kind of curved long-period fiber grating(CLPFG) engraved by CO2 laser based on oxide-doped fiber was designed to monitor the structural integrity of propellant. The mechanical damage characteristics of the propellant were analyzed. The sensor model is constructed and the refractive index modulation characteristics of the CLPFG are analyzed. The strain coupling characteristics and the strain transfer efficiency of the interface between the CLPFG and the propellant are clarified. Propellant modules with implanted CLPFG were fabricated. The novel grating sensor has been effectively coated and structurally packaged. Conducted experiments on strain and temperature of propellant modules. The large strain measurement of propellant from 0 µÎµ to 24000 µÎµ is realized. Solved the thorny problem of large strain measurement for propellants. In addition, the temperature discrimination measurement in the temperature range of 30 ℃ to 250 ℃ can be realized. Sensor exhibit extremely high stability characteristics and has good compatibility with propellants. The sensor implantation and extraction structure has been designed to improve the survival rate of the sensor inside the solid rocket motors (SRM). Sensors can accurately measure the mechanical and thermal state parameters of propellants, providing effective data support for the health management of SRM.

Cationic Ir(III) Complexes with 4-Fluoro-4'-pyrazolyl-(1,1'-biphenyl)-2-carbonitrile as the Cyclometalating Ligand: Synthesis, Characterizations, and Application to Ultrahigh-Efficiency Light-Emitting Electrochemical Cells.

Light-emitting electrochemical cells (LECs) promise low-cost, large-area luminescence applications with air-stabilized electrodes and a versatile fabrication that enables the use of solution processes. Nevertheless, the commercialization of LECs is still encountering many obstacles, such as low electroluminescence (EL) efficiencies of the ionic materials. In this paper, we propose five blue to yellow ionic Ir complexes possessing 4-fluoro-4'-pyrazolyl-(1,1'-biphenyl)-2-carbonitrile (ppfn) as a novel cyclometalating ligand and use them in LECs. In particular, the device within di[4-fluoro-4'-pyrazolyl-(1,1'-biphenyl)-2-carbonitrile]-4,4'-di-tert-butyl-2,2'-bipyridyl iridium(III) hexafluorophosphate (DTBP) shows a remarkable photoluminescence quantum yield (PLQY) of 70%, and by adjusting the emissive-layer thickness, the maximal external quantum efficiency (EQE) reaches 22.15% at 532 nm under the thickness of 0.51 µm, showing the state-of-the-art value for the reported blue-green LECs.

TiB4 and SrB8 monolayers: high capacity and zero strain-like anode materials for Li/Na/K/Ca ion batteries.

Storage capacity, average open circuit voltage (OCV), diffusion barrier, lattice parameter changes, etc. are key indicators of whether a material would be suitable for use as a Li-ion or non-Li-ion battery (LIB or NLIB) anode. The rapid development of 2D materials over the past few decades has opened up new possibilities for these metrics. Using first-principles calculations, we prove that two 2D materials, TiB4 and SrB8, show excellent performance in terms of the above metrics when used as anodes for LIBs or NLIBs. As detailed, TiB4 has an Li\Na\K\Ca storage capacity of 588 mA h g-1, 588 mA h g-1, 588 mA h g-1, and 1176 mA h g-1, respectively, and SrB8 has an Li\Na\K\Ca storage capacity of 308 mA h g-1, 308 mA h g-1, 462 mA h g-1, and 616 mA h g-1, respectively, and they show good electrical conductivity whether existing Li, Na, K or Ca is adsorbed or not. The diffusion barriers on both surfaces are low, indicating good rate performance. The average OCV is also very low. In particular, the lattice parameters of the two materials change very little during the embedding of Li\Na\K\Ca. For Ti9B36 the corresponding values are about 0.37% (Li), 0.33% (Na), 0.64% (K) and 0.03% (Ca), and for Sr8B64 the corresponding values are about 0.70% (Li), 0.16% (Na), 0.13% (K) and 0.004% (Ca), which imply zero strain-like character and great cycling performance. All the above results show that TiB4 and SrB8 monolayers are very promising Li\Na\K\Ca ion battery anodes.

Binocular full-color holographic three-dimensional near eye display using a single SLM.

A binocular full-color holographic three-dimensional near eye display system using a single spatial light modulator (SLM) is proposed. In the display system, the frequency spectrum shifting operation and color spectrum shifting operation are adopted to realize the frequency division multiplexing (FDM) and frequency superposition multiplexing (FSM) by manipulating the frequency spectrums of each color- and view-channel sub-holograms. The FDM combined with polarization multiplexing will be used to implement binocular display using a single SLM, and the FSM working with a bandpass filter for each view-channel will be used to achieve full-color display from single frame hologram. The optical analysis and experiments with 3D color objects confirm the feasibility of the proposed system in the practical application.

Mechanism for neurotransmitter-receptor matching.

Synaptic communication requires the expression of functional postsynaptic receptors that match the presynaptically released neurotransmitter. The ability of neurons to switch the transmitter they release is increasingly well documented, and these switches require changes in the postsynaptic receptor population. Although the activity-dependent molecular mechanism of neurotransmitter switching is increasingly well understood, the basis of specification of postsynaptic neurotransmitter receptors matching the newly expressed transmitter is unknown. Using a functional assay, we show that sustained application of glutamate to embryonic vertebrate skeletal muscle cells cultured before innervation is necessary and sufficient to up-regulate ionotropic glutamate receptors from a pool of different receptors expressed at low levels. Up-regulation of these ionotropic receptors is independent of signaling by metabotropic glutamate receptors. Both imaging of glutamate-induced calcium elevations and Western blots reveal ionotropic glutamate receptor expression prior to immunocytochemical detection. Sustained application of glutamate to skeletal myotomes in vivo is necessary and sufficient for up-regulation of membrane expression of the GluN1 NMDA receptor subunit. Pharmacological antagonists and morpholinos implicate p38 and Jun kinases and MEF2C in the signal cascade leading to ionotropic glutamate receptor expression. The results suggest a mechanism by which neuronal release of transmitter up-regulates postsynaptic expression of appropriate transmitter receptors following neurotransmitter switching and may contribute to the proper expression of receptors at the time of initial innervation.

3D image reconstruction of terahertz computed tomography at sparse angles by total variation minimization.

Continuous-wave terahertz computed tomography (THz-CT) is an important three-dimensional imaging method for probing the profile and inner properties of a sample's structure. We applied the total variation (TV) minimization iterative algorithm to squeeze 75% data acquisition time of THz-CT without the loss of reconstruction fidelity. The imaging system is built based on a 278.6 GHz avalanche diode source. A zero-order Bessel beam is generated by an axicon, for which the intensity profile remains essentially propagation invariant within the non-diffracting zone. The effectiveness of the proposed method is verified by using three optically opaque objects. The reconstruction results show that the TV-minimization algorithm can effectively suppress noise, artefacts, and shape distortion created in sparse angle reconstruction.

Full-field high-resolution terahertz imaging based on a high-resistance silicon solid immersion lens.

The spatial resolution of the direct imaging system depends on the wavelength and the numerical aperture. In the terahertz (THz) waveband, the wavelength is relatively large, and the higher numerical aperture of the imaging system usually promises the possibility of achieving higher spatial resolution. Solid immersion technique is an effective method to expand the numerical aperture. We design and fabricate a hemisphere lens with high-resistance silicon to achieve the effect of solid immersion, and obtain full-field, high-resolution focal-plane imaging. The characteristics of the direct refraction imaging and the secondary reflection imaging are analyzed by ray-tracing calculations. And the field curvature of the equivalent object plane and the spot diagram on the vertical image plane of the lens are quantifiably evaluated. It is shown that the secondary reflection imaging can effectively reduce the geometric distortion and achieve more ideal imaging quality. The method of blocking different regions before and after the solid immersion lens is proposed to obtain a clear magnified image of a two-dimensional grating with the period of 300 µm. This method provides a powerful tool for THz full-field microscopic imaging.

Simultaneous detection of the distance and direction for a noncooperative target based on the microwave photonic radar.

For a noncooperative target, multiple-dimension detection is required to determine its spatial location. A microwave photonic radar is proposed for simultaneous detection of the distance and direction of targets. At the transmitter, a linear frequency modulation (LFM) signal with a large instantaneous bandwidth was obtained by frequency doubling. Meanwhile, the optical reference signal was supplied. At the receiver, two antennas with a certain baseline length were used to receive the echo signal. The dechirp process and fixed-length cable are combined to decouple the distance and direction and distinguish between the positive and negative directions of a target. Theoretical derivation has already verified that the distance and direction can be resolved simultaneously by dechirping of the echo modulation signal and reference signal. In experiments, an LFM signal with an instantaneous bandwidth of 2 GHz (2-4 GHz) was generated and launched as the detection signal. Targets at different distances with positive and negative angles were detected. The results show that the directional measurement ranges from -72.5° to 72.5°, and the error is less than 1.6°. The measured distance was found to be quite similar to the actual distance. The proposed approach can confirm the spatial location of a noncooperative target by combining the detection of both distance and direction. Furthermore, the baseline length need not be less than half the wavelength of the echo signal, and large antennas can be chosen to improve the detection distance and range accuracy.

Transport of intensity equation-based terahertz lensless full-field phase imaging.

Terahertz (THz) phase imaging is widely spreading in various scenarios, among which full-field phase distributions are commonly retrieved by digital holography or ptychography. In this Letter, the transport of the intensity equation reconstruction method is applied into the THz band. An algorithm named the lensless US-transport of intensity equation (TIE) is proposed to accommodate to an in-line configuration. The object phase is retrieved by primarily conducting iterations between the axial intensity derivative and the phase distribution at the recording plane and subsequent backward diffraction propagation. This method is applicable to both isolated and extended weakly absorbing samples with higher reconstruction quality and remarkably less time cost than holographic phase retrieval algorithms. It can also be attempted in other non-interferometric geometries or using low-cost partially coherent THz sources, which significantly broaden the application scope of THz phase imaging.

Perovskite Light-Emitting Electrochemical Cells Employing Electron Injection/Transport Layers of Ionic Transition Metal Complexes.

Invited for the cover of this issue are Chin-Wei Lu, Zu-Po Yang, Hai-Ching Su, and co-workers at National Yang Ming Chiao Tung University and Providence University. The image depicts electron transport for light-emitting electrochemical cells. Read the full text of the article at 10.1002/chem.202103739.

Perovskite Light-Emitting Electrochemical Cells Employing Electron Injection/Transport Layers of Ionic Transition Metal Complexes.

Recently, perovskites have attracted intense attention due to their high potential in optoelectronic applications. Employing perovskites as the emissive materials of light-emitting electrochemical cells (LECs) shows the advantages of simple fabrication process, low-voltage operation, and compatibility with inert electrodes, along with saturated electroluminescence (EL) emission. Unlike in previously reported perovskite LECs, in which salts are incorporated in the emissive layer, the ion-transport layer was separated from the emissive layer in this work. The layer of ionic transition metal complex (iTMC) not only provides mobile ions but also serves as an electron-injection/transport layer. Orthogonal solvents are used in spin coating to prevent the intermixing of stacked perovskite and iTMC layers. The blue iTMC with high ionization potential is effective in blocking holes from the emissive layer and thus ensures EL color saturation. In addition, the carrier balance of the perovskite/iTMC LECs can be optimized by adjusting the iTMC layer thickness. The optimized external quantum efficiency of the CsPbBr3 /iTMC LEC reaches 6.8 %, which is among the highest reported values for perovskite LECs. This work successfully demonstrates that, compared with mixing all components in a single emissive layer, separating the layer of ion transport, electron injection and transport from the perovskite emissive layer is more effective in adjusting device carrier balance. As such, solution-processable perovskite/iTMC LECs open up a new way to realize efficient perovskite LECs.

Continuous-wave terahertz self-referencing digital holography based on Fresnel's mirrors.

Continuous-wave terahertz digital holography (TDH) is a booming full-field phase-contrast imaging method validated in both in-line and Mach-Zehnder off-axis geometries. In this Letter, a self-referencing TDH approach is proposed based on the Fresnel's mirrors, by which the object wavefront is partitioned and reflected. Two beams interfere with each other to form an off-axis hologram. The proposed recording configuration is immune from a superposed twin image and has higher temporal stability than Mach-Zehnder interferometers. To evaluate the phase-contrast imaging performance, different types of samples are measured.

Continuous-wave terahertz reflective ptychography by oblique illumination.

Massive usage scenarios prompt the prosperity of terahertz (THz) reflective imaging methods. In this Letter, we apply ptychography to continuous-wave THz reflective imaging. Our scheme has a compact lensless layout and uses a full-field oblique-illumination recording mode. Diffraction patterns are corrected through tilted plane correction. This method can be used to retrieve the complex-valued object function and to suppress the negative effect of non-uniform illumination. The feasibility is investigated using two metal samples.

Multi-layered full-field phase imaging using continuous-wave terahertz ptychography.

Due to the unique properties of terahertz (THz) waves, THz phase imaging has been widely investigated to retrieve the absorption and phase modulation of dielectric two-dimensional thin samples, as well as multiple stacked samples. In this Letter, we apply the three-dimensional ptychographic iterative engine algorithm for continuous-wave THz full-field multi-layered phase imaging. The complex-valued transmission function of two-layered polypropylene thin plates and the corresponding probe function are reconstructed, respectively, which are immune to crosstalk of different layers. The phenomenon of the field-of-view enlargement at the second object layer is observed. This lensless compact imaging method can be potentially used for THz three-dimensional imaging.

In Situ Raman Investigation of TiO2 Nanotube Array-Based Ultraviolet Photodetectors: Effects of Nanotube Length.

TiO2 nanotube arrays (TNAs) with tube lengths of 4, 6, and 7 µm were prepared via two-step anodization. Thereafter, ultraviolet (UV) photodetectors (PDs) with Au/TiO2/Au structures were prepared using these TNAs with different tube lengths. The effects of TNA length and device area on the performance of the device were investigated using in situ Raman spectroscopy. The maximum laser/dark current ratio was achieved by using a TNA with a size of 1 × 1 cm2 and a length of 7 µm, under a 532 nm laser. In addition, when the device was irradiated with a higher energy laser (325 nm), the UV Raman spectrum was found to be more sensitive than the visible Raman spectrum. At 325 nm, the laser/dark current ratio was nearly 24 times higher than that under a 532 nm laser. Six phonon modes of anatase TNAs were observed, at 144, 199, 395, 514, and 635 cm-1, which were assigned to the Eg(1), Eg(2), B1g(1), A1g/B1g(2), and Eg(3) modes, respectively. The strong low-frequency band at 144 cm-1 was caused by the O-Ti-O bending vibration and is a characteristic band of anatase. The results show that the performance of TNA-based PDs is length-dependent. Surface-enhanced Raman scattering signals of 4-mercaptobenzoic acid (4-MBA) molecules were also observed on the TNA surface. This result indicates that the length-dependent performance may be derived from an increase in the specific surface area of the TNA. In addition, the strong absorption of UV light by the TNAs caused a blueshift of the Eg(1) mode.

Speech processing and plasticity in the right hemisphere predict variation in adult foreign language learning.

Foreign language learning in adulthood often takes place in classrooms where learning outcomes vary widely among students, for both initial learning and long-term retention. Despite the fundamental role of speech perception in first language acquisition, its role in foreign language learning outcomes remains unknown. Using a speech discrimination functional magnetic resonance imaging (fMRI) task and resting-state fMRI before and after an intensive, classroom-based, Mandarin Chinese course, we examined how variations in pre-training organization and pre-to-post reorganization of brain functions predicted successful language learning in male and female native English-speakers. Greater pre-training activation in right inferior frontal gyrus (IFG) to Mandarin speech was associated with better Mandarin attainment at the end of the course. After four weeks of class, learners showed overall increased activation in left IFG and left superior parietal lobule (SPL) to Mandarin speech, but in neither region was variation related to learning outcomes. Immediate attainment was associated with greater pre-to-post reduction of right IFG activation to Mandarin speech but also greater enhancement of resting-state connectivity between this region and both left IFG and left SPL. Long-term retention of Mandarin skills measured three months later was more accurately predicted by models using features of neural preparedness (pre-training activation) and neural plasticity (pre-to-post activation change) than models using behavior preparedness and plasticity features (pre-training speech discrimination accuracy and Mandarin attainment, respectively). These findings suggest that successful holistic foreign language acquisition in human adulthood requires right IFG engagement during initial learning but right IFG disengagement for long-term retention of language skills.

Probe position correction based on overlapped object wavefront cross-correlation for continuous-wave terahertz ptychography.

Continuous-wave terahertz ptychography is a promising large field-of-view lensless terahertz phase imaging method. Inaccurate probe positions would severely degrade the reconstruction quality, as compared to other spectral bands. In this paper, we propose a probe position correction method based on cross-correlation registration on overlapped regions of the object wavefront for terahertz ptychography. The translation errors could be minimized in the order of 0.01 pixels. The simulation results suggest good computational efficiency, correction, and reconstruction accuracy. We perform continuous-wave terahertz ptychography on a cicada's forewing. The subcosta and the first radius vein are distinguished after position correction. The probe position distribution reveals that the tilt angle between the object plane and the recording plane is 0.26°.

Stochastic dual-plane on-axis digital holographic imaging on irregular surfaces.

An imaging method based on dual-plane on-axis digital holography is proposed for the situation in which an object is on the irregular surface of a transparent medium. Light propagation of the object on the uneven surface of the medium is analyzed and simulated. The diffracted pattern of the object is deformed or destroyed by the refracted light of the medium. Dual-plane on-axis digital holography is used to eliminate the twin image. In order to retrieve the information lost in the reconstructed image due to destructive interference, the object is illuminated by a stochastic beam that is a speckle wave produced by a ground glass. Simulated and experimental results are presented, to demonstrate that the proposed method can be used for imaging on the irregular surface of a transparent medium.

Synthetic aperture in terahertz in-line digital holography for resolution enhancement.

Terahertz digital holography is a combination of terahertz technology and digital holography. In digital holography, the imaging resolution is the key parameter in determining the detailed quality of a reconstructed wavefront. In this paper, the synthetic aperture method is used in terahertz digital holography and the in-line arrangement is built to perform the detection. The resolved capability of previous terahertz digital holographic systems restricts this technique to meet the requirement of practical detection. In contrast, the experimental resolved power of the present method can reach 125 µm, which is the best resolution of terahertz digital holography to date. Furthermore, the basic detection of a biological specimen is conducted to show the practical application. In all, the results of the proposed method demonstrate the enhancement of experimental imaging resolution and that the amplitude and phase distributions of the fine structure of samples can be reconstructed by using terahertz digital holography.

The SEMA5A gene is associated with hippocampal volume, and their interaction is associated with performance on Raven's Progressive Matrices.

The Allen Brain Atlas shows that the semaphorin 5A (SEMA5A) gene, which encodes an important protein for neurogenesis and neuronal apoptosis, is predominantly expressed in the human hippocampus. Structural and functional neuroimaging studies have further shown that the hippocampus plays an important role in the performance on Raven's Progressive Matrices (RPM), a measure of reasoning ability and general fluid intelligence. Thus far, however, no study has examined the relationships between the SEMA5A gene polymorphism, hippocampal volume, and RPM performance. The current study collected both structural MRI, genetic, and behavioral data in 329 healthy Chinese adults, and examined associations between SEMA5A variants, hippocampal volume, and performance on RAPM (the advanced form of RPM). After controlling for intracranial volume (ICV), sex, and age, SEMA5A genetic polymorphism at the SNP rs42352 had the strongest association with hippocampal volume (p=0.00000552 and 0.000103 for right and left hippocampal volumes, respectively), with TT homozygotes having higher hippocampal volume than the other genotypes. Furthermore, there was a high correlation between right hippocampal volume and RAPM performance (r=0.42, p=0.0000509) for SEMA5A rs42352 TT homozygotes. This study provides the first evidence for the involvement of the SEMA5A gene in hippocampal structure and their interaction on RAPM performance. Future studies of the hippocampus-RPM associations should consider genetic factors as potential moderators.