NCAM mimetic peptide P2 synergizes with bone marrow mesenchymal stem cells in promoting functional recovery after stroke.

The neural cell adhesion molecule (NCAM) promotes neural development and regeneration. Whether NCAM mimetic peptides could synergize with bone marrow mesenchymal stem cells (BMSCs) in stroke treatment deserves investigation. We found that the NCAM mimetic peptide P2 promoted BMSC proliferation, migration, and neurotrophic factor expression, protected neurons from oxygen-glucose deprivation through ERK and PI3K/AKT activation and anti-apoptotic mechanisms in vitro. Following middle cerebral artery occlusion (MCAO) in rats, P2 alone or in combination with BMSCs inhibited neuronal apoptosis and induced the phosphorylation of ERK and AKT. P2 combined with BMSCs enhanced neurotrophic factor expression and BMSC proliferation in the ischemic boundary zone. Moreover, combined P2 and BMSC therapy induced translocation of nuclear factor erythroid 2-related factor, upregulated heme oxygenase-1 expression, reduced infarct volume, and increased functional recovery as compared to monotreatments. Treatment with LY294002 (PI3K inhibitor) and PD98059 (ERK inhibitor) decreased the neuroprotective effects of combined P2 and BMSC therapy in MCAO rats. Collectively, P2 is neuroprotective while P2 and BMSCs work synergistically to improve functional outcomes after ischemic stroke, which may be attributed to mechanisms involving enhanced BMSC proliferation and neurotrophic factor release, anti-apoptosis, and PI3K/AKT and ERK pathways activation.

Process of Pure Copper Fabricated by Selective Laser Melting (SLM) Technology under Moderate Laser Power with Re-Melting Strategy.

Pure copper (Cu) material, because of its high thermal conductivity, can be 3D printed to fabricate effective thermal management components. However, in the selective laser melting (SLM) process, due to copper's high optical reflectivity, Cu-based parts need to be printed using high laser power. In this study, we demonstrated 3D printing with a re-melting strategy is able to fabricate high-density and low-surface-roughness pure copper parts using only a moderate laser (350 W) power. The effect of the re-scan to initial scan speed ratio on the printing quality resulting from the re-melting strategy is discussed. The re-melting strategy is likened to a localized annealing process that promotes the recrystallization of the newly formed copper microstructures on the re-scan path. Given a hatch spacing of 0.06 mm and a powder layer thickness of 0.05 mm, Cu samples with 93.8% density and low surface roughness (Sa~22.9 µm) were produced using an optimized scan speed of 200 mm/s and a re-scanning speed of 400 mm/s, with a laser power of 350 W. Our work provides an approach to optimize the laser power for printing pure copper 3D parts with high relative density (low porosity) and low surface roughness while ensuring the lifetime stability of the part. The re-melting strategies have broad implications in 3D printing and are particularly relevant for metals with high reflectivity, such as pure copper.

Recognition of Occluded Goods under Prior Inference Based on Generative Adversarial Network.

Aiming at the recognition of intelligent retail dynamic visual container goods, two problems that lead to low recognition accuracy must be addressed; one is the lack of goods features caused by the occlusion of the hand, and the other is the high similarity of goods. Therefore, this study proposes an approach for occluding goods recognition based on a generative adversarial network combined with prior inference to address the two abovementioned problems. With DarkNet53 as the backbone network, semantic segmentation is used to locate the occluded part in the feature extraction network, and simultaneously, the YOLOX decoupling head is used to obtain the detection frame. Subsequently, a generative adversarial network under prior inference is used to restore and expand the features of the occluded parts, and a multi-scale spatial attention and effective channel attention weighted attention mechanism module is proposed to select fine-grained features of goods. Finally, a metric learning method based on von Mises-Fisher distribution is proposed to increase the class spacing of features to achieve the effect of feature distinction, whilst the distinguished features are utilized to recognize goods at a fine-grained level. The experimental data used in this study were all obtained from the self-made smart retail container dataset, which contains a total of 12 types of goods used for recognition and includes four couples of similar goods. Experimental results reveal that the peak signal-to-noise ratio and structural similarity under improved prior inference are 0.7743 and 0.0183 higher than those of the other models, respectively. Compared with other optimal models, mAP improves the recognition accuracy by 1.2% and the recognition accuracy by 2.82%. This study solves two problems: one is the occlusion caused by hands, and the other is the high similarity of goods, thus meeting the requirements of commodity recognition accuracy in the field of intelligent retail and exhibiting good application prospects.

Dialysis adequacy and hemoglobin levels predict cerebral atrophy in maintenance-hemodialysis patients.

The pathogenesis of cerebral atrophy (CA) is not clear. Previous studies show a high incidence of preterm CA in hemodialysis patients. This study aims to investigate the factors influencing CA and to derive a CA prediction nomogram in maintenance-hemodialysis patients. First, brain volumes of hemodialysis patients (≤55 years) were compared against age- and sex-matched healthy controls, and differences were revealed in bilateral insular cisterns width, maximum cerebral sulci width, Evans index, ventricular-brain ratio, frontal atrophy index, and temporal lobe ratio. Then, the patients were divided equally into "no or mild" or "severe" CA groups. Potential factors influencing CA were screened. Kt/V (urea removal index) and hemoglobin levels negatively correlated with CA degree, and were used to establish a nomogram within randomly assigned training and validation patient groups. The areas under the receiver operating characteristic curves (AUROC) for training and validation groups were 0.703 and 0.744, respectively. When potassium and calcium were added to the nomogram, the AUROC for training/validation group increased to 0.748/0.806. The nomogram had optimal AUROC for training (0.759) and validation (0.804) groups when albumin was also included. Hemodialysis patients showed reduced anterior brain volumes and the nomogram established herein may have predictive value for developing CA.

The Effect of Geometric Parameters on Flow and Heat Transfer Characteristics of a Double-Layer Microchannel Heat Sink for High-Power Diode Laser.

The effect of the geometric parameters on the flow and heat transfer characteristics of a double-layer U-shape microchannel heat sink (DL-MCHS) for a high-power diode laser was investigated in this work. FLUENT 19.2 based on the finite volume method was employed to analyze the flow and heat transfer performance of DL-MCHS. A single variable approach was used to fully research the impact of different parameters (the number of channels, the channel cross-sectional shape, and the aspect ratio) on the temperature distribution, pressure drop, and thermal resistance of the DL-MCHS. The rectangular DL-MCHS heat transfer performance and pressure drop significantly increased with the rise in the channel's aspect ratio due to there being a larger wet perimeter and convective heat transfer area. By comparing the thermal resistance of the DL-MCHS at the same power consumption, it was found that the rectangular DL-MCHS with an aspect ratio in the range of 5.1180-6.389 had the best overall performance. With the same cross-sectional area and hydraulic diameter (AC = 0.36 mm, Dh = 0.417 mm), the thermal resistance of the trapezoidal microchannel heat sink was 32.14% and 42.42% lower than that of the triangular and rectangular ones, respectively, under the condition that the pumping power (Wpp) was 0.2 W. Additionally, the thermal resistance was reduced with the increment of the number of channels inside the DL-MCHS, but this would induce an increased pressure drop. Thus, the channel number has an optimal range, which is between 50 and 80 for the heat sinks in this study. Our study served as a simulation foundation for the semiconductor laser double-layer U-shaped MCHS optimization method using geometric parameters.

Realization of Multifunctional Metamaterial Structure Based on the Combination of Vanadium Dioxide and Graphene.

Combining tunable properties and various functionalities into a single metamaterial structure has become a novel research hotspot and can be used to tackle great challenges. The multifunctional metamaterial structure that combines absorption, linear-to-circular (LTC) polarization conversion, filtering and switching functions into a single metamaterial device was designed and investigated in this study. The switching of different functions can be achieved based on the phase transition of vanadium dioxide (VO2) and change of graphene chemical potential. When VO2 is in a metal state, the multi-frequency absorption and LTC polarization conversion can be achieved with different chemical potentials. When VO2 is in the insulator state and the polarization angle of incident wave is 45°, the device can be used to select or isolate the incident waves with different polarization states in the frequency region of 1.2-1.8 THz. Furthermore, when the chemical potentials are 0.05 eV and 1.2 eV, the corresponding transmissions of the TE-polarized wave demonstrate the opposite results, realizing the switching functions in the frequency region of 0.88-1.34 THz. In the frequency region above 2 THz, the multi-frequency rejection filter can be achieved. The designed switchable multifunctional metamaterial device can be widely implemented in radar monitoring and communication systems.

Plasmonically Enhanced Colloidal Quantum Dot/Graphene Doped Polymer Random Lasers.

An improvement in random lasers based on a colloidal quantum dot (QD)/graphene-doped polymer was observed and attributed to multiple light-scattering and graphene surface plasmon resonance. The emission characteristics of quantum dots doped with graphene oxide and reduced graphene oxide were compared. The QD/reduced graphene oxide hybrid exhibited a lower laser emission threshold (~460 µJ/cm2). The emission modes and thresholds were strongly dependent on both the graphene doping concentration and the external temperature. Decreased plasmon coupling was the primary reason for lower QD/graphene laser emission with increasing temperature. The optimum reduced graphene oxide concentration was 0.2 wt.%. This work provides a practical approach to optimizing the threshold and stability of random laser devices, with potential applications in displays, sensors, and anti-counterfeiting labels.

Enhanced Fluorescence and Environmental Stability of Red-Emissive Carbon Dots via Chemical Bonding with Cellulose Films.

The development of red emission carbon dots with bright solid-state fluorescence would significantly broaden their application in optoelectronic devices and sensors. Herein, a red-emissive carbon dot-based nanocomposite has been synthesized through chemical bonding with cellulose films. The red emission originating from the surface states of carbon dots was maintained in the cellulose films. Due to the stable chemical bonding, the photoluminescence intensity and emission wavelength remained unchanged for 12 months, and the quantum yield of the composite was enhanced over 4 times. It also showed outstanding stability in water or weak acid-base environments under pHs ranging from 2 to 11. Therefore, the mechanism of chemical bonding that eliminated the defects and preserved the efficient radiative process through surface states was proposed.

Spectroscopy and Theoretical Modeling of Phonon Vibration Modes and Band Gap Energy of Cu2ZnSn(S x Se1-x )4 Bulk Crystals and Thin Films.

Semiconductor Cu2ZnSn(S x Se1-x )4 (CZTSSe) solid solution is considered as a perspective absorber material for solar cells. However, during its synthesis or deposition, any modification in the resulting optical properties is hardly predicted. In this study, experimental and theoretical analyses of CZTSSe bulk crystals and thin films are presented based on Raman scattering and absorption spectroscopies together with compositional and morphological characterizations. CZTSSe bulk and thin films are studied upon a change in the x = S/(S + Se) aspect ratio. The morphological study is focused on surface visualization of the solid solutions, depending on x variation. It has been discovered for the first time that the surface of the bulk CZTSSe crystal with x = 0.35 has pyramid-like structures. The information obtained from the elemental analysis helps to consider the formation of a set of possible intrinsic lattice defects, including vacancies, self-interstitials, antisites, and defect complexes. Due to these results and the experimentally obtained values of the band gap within 1.0-1.37 eV, a deviation from the calculated band gap values is estimated in the range of 1.0-1.5 eV. It is suggested which defects can have an influence on such a band gap change. Also, on comparing the experimental Raman spectra of CZTSSe with the theoretical modeling results, an excellent agreement is obtained for the main Raman bands. The proposed theoretical approach allows to estimate the values of concentration of atoms (S or Se) for CZTSSe solid solution directly from the experimental Raman spectra. Thus, the visualization of morphology and the proposed theoretical approach at various x values will help for a deeper understanding of the CZTSSe structure to develop next-generation solar cells.

Light-induced pyroelectric property of self-powered photodetectors based on all-inorganic perovskite quantum dots.

All-inorganic cesium lead bromine (CsPbBr3) perovskites quantum dots (QDs) are one of the most photoelectric materials due to their high absorption coefficient, pronounced quantum-size effect, tunable optical property. Here, a self-powered PD based on all-inorganic CsPbBr3perovskites QDs is fabricated and demonstrated. The light-induced pyroelectric effect is utilized to modulate the optoelectronic processes without the external power supply. The working mechanism of the PD is carefully investigated upon 532 nm laser illumination and the minimum recognizable response time of the self-powered PD is 1.5µs, which are faster than those of most previously reported wurtzite nanostructure PDs. Meanwhile, the frequency and temperature independence of the self-powered PD are experimented and summarized. The self-powered PD with high performance is expected to have extensive applications in solar cell, energy harvesting, resistive random access memory.

Coherent Random Lasing in Colloidal Quantum Dot-Doped Polymer-Dispersed Liquid Crystal with Low Threshold and High Stability.

High-concentration (2-10 wt %) ZnCdSeS/ZnS alloyed quantum dot-doped polymer-dispersed liquid crystals (QD-PDLCs) were prepared via ultraviolet (UV) curing. The QD-PDLC morphology and resonance characteristics of a coherent random laser were investigated. The doping concentration of the liquid crystal and quantum dots was varied to investigate its effect on the lasing threshold, line width, and stability with respect to the density and grain size of the liquid crystal droplets inside the PDLC structure. Furthermore, the QD-PDLC laser performance was influenced by the pump position and area because of spatial localization of the random resonators. Moreover, the QD-PDLC showed good long-term stability; after 15 days of laser excitation (3 h/day), the laser output was maintained at 92% of the original emission intensity. The random laser threshold was as low as 50 µJ/cm2 with the optimized preparation process, which suggested strong potential for applications in polymer random fiber lasers, sensors, and displays.

A Fast Response-Recovery 3D Graphene Foam Humidity Sensor for User Interaction.

Humidity sensors allow electronic devices to convert the water content in the environment into electronical signals by utilizing material properties and transduction techniques. Three-dimensional graphene foam (3DGF) can be exploited in humidity sensors due to its convenient features including low-mass density, large specific surface area, and excellent electrical. In this paper, 3DGF with super permeability to water enables humidity sensors to exhibit a broad relative humidities (RH) range, from 0% to 85.9%, with a fast response speed (response time: ~89 ms, recovery time: ~189 ms). To interpret the physical mechanism behind this, we constructed a 3DGF model decorated with water to calculate the energy structure and we carried out the CASTEP as implemented in Materials Studio 8.0. This can be ascribed to the donor effect, namely, the electronic donation of chemically adsorbed water molecules to the 3DGF surface. Furthermore, this device can be used for user interaction (UI) with unprecedented performance. These high performances support 3DGF as a promising material for humidity sensitive material.

A Broadband Phototransistor Based on Three-Dimensional Reduced Graphene Oxide Foam.

Three-dimensional (3D) cross-linked polymer-like reduced graphene oxide foams (rGOFs) with a seamlessly continuous graphene network, exhibit high photoresponsive and conductivity and have received much attention regarding solar cells and supercapacitors. However, little attention has been paid to photodetection applications of 3D rGOFs. Here we report a novel broadband phototransistor based on metal-3D GFs-metal, which exhibits a high light absorption and a wide spectra response ranging at least from 400 to 1600 nm wavelength with a maximum photoresponsivity of 10 mA/W at 400 nm. In particular, stable and reproducible photocurrent cycles are achieved under different light blue light (405 nm), green light (532 nm), and NIR (808 nm) irradiations. Moreover, the device displays a typical transistor characteristic with a rapid response time of 18 ms at under 532 nm irradiation. The excellent performances indicate 3D rGOF as a promising candidate for future photodetection application.

Ambipolar Graphene-Quantum Dot Hybrid Vertical Photodetector with a Graphene Electrode.

A strategy to fabricate an ambipolar near-infrared vertical photodetector (VPD) by sandwiching a photoactive material as a channel film between the bottom graphene and top metal electrodes was developed. The channel length in the vertical architecture was determined by the channel layer thickness, which can provide an ultrashort channel length without the need for a high-precision manufacturing process. The performance of VPDs with two types of semiconductor layers, a graphene-PbS quantum dot hybrid (GQDH) and PbS quantum dots (QDs), was measured. The GQDH VPD showed better photoelectric properties than the QD VPD because of the high mobility of graphene doped in the channel. The GQDH VPD exhibited excellent photoresponse properties with a responsivity of 1.6 × 104 A/W in the p-type regime and a fast response speed with a rise time of 8 ms. The simple manufacture and the promising photoresponse of the GQDH VPDs reveal that an easy and effective way to fabricate high-performance ambipolar photodetectors was developed.

Tunable amplified spontaneous emission in graphene quantum dots doped cholesteric liquid crystals.

Graphene quantum dots (GQDs) have received much research attention, because of their useful structure and optical absorption/emission. We report the tunable amplified spontaneous emission (ASE) in GQD-doped cholesteric liquid crystal (CLC), which to the best of our knowledge has not been previously observed. The GQDs are uniformly dispersed with a weight ratio of 0.5 wt.% in CLC. Under optical excitation, typical ASE is triggered in the system at pump energies greater than 1.25 mJ cm-2. The emission peak at the long wavelength edge of the photonic bandgap shifts from 662 to 669 nm, as the working temperature is increased from 50 to 90 °C. The preparation of the combined GQDs and CLC is simple and low-cost, and the resulting material is photostable and non-toxic. Combining the GQD gain material with the self-assembled CLC resonator has potential in the fabrication of ASE source and laser devices.

Graphene and PbS quantum dot hybrid vertical phototransistor.

A field-effect phototransistor based on a graphene and lead sulfide quantum dot (PbS QD) hybrid in which PbS QDs are embedded in a graphene matrix has been fabricated with a vertical architecture through a solution process. The n-type Si/SiO2 substrate (gate), Au/Ag nanowire transparent source electrode, active layer and Au drain electrode are vertically stacked in the device, which has a downscaled channel length of 250 nm. Photoinduced electrons in the PbS QDs leap into the conduction band and fill in the trap states, while the photoinduced holes left in the valence band transfer to the graphene and form the photocurrent under biases from which the photoconductive gain is evaluated. The graphene/QD-based vertical phototransistor shows a photoresponsivity of 2 × 103 A W-1, and specific detectivity up to 7 × 1012 Jones under 808 nm laser illumination with a light irradiance of 12 mW cm-2. The solution-processed vertical phototransistor provides a new facile method for optoelectronic device applications.

Broadband Phototransistor Based on CH3NH3PbI3 Perovskite and PbSe Quantum Dot Heterojunction.

Organic lead halide perovskites have received a huge amount of interest since emergence, because of tremendous potential applications in optoelectronic devices. Here field effect phototransistors (FEpTs) based on CH3NH3PbI3 perovskite/PbSe colloidal quantum dot heterostructure are demonstrated. The high light absorption and optoelectric conversion efficiency, due to the combination of perovskite and quantum dots, maintain the responsivities in a high level, especially at 460 nm up to 1.2 A/W. The phototransistor exhibits bipolar behaviors, and the carrier mobilities are determined to be 0.147 cm2V-1s-1 for holes and 0.16 cm2V-1s-1 for electrons. The device has a wide spectral response spectrum ranging from 300 to 1500 nm. A short photoresponse time is less than 3 ms due to the assistance of heterojunction on the transfer of photoexcitons. The excellent performances presented in the device especially emphasize the CH3NH3PbI3 perovskite-PbSe quantum dot as a promising material for future photoelectronic applications.