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A Wide-Scanning Array Antenna of Connected Vertical Bowtie Elements Structurally Integrated Within an Aircraft Fuselage
No full textA low-profile, wide-scanning phased-array antenna of vertical bowtie elements fully integrated with a structurally efficient radome and ribs of an aircraft fuselage is proposed in this article. The array is designed to simultaneously fulfil the electrical requirements of an airborne antenna sensor and the mechanical requirements of a load-carrying aircraft fuselage. The array antenna is capable of steering the beam up to\ua0\ub180 degrees in the azimuth plane over a 20% bandwidth (2.4–3 GHz) with the active reflection coefficient (\ua0Γact\ua0) below −10 dB in an infinite array environment. Experimental results of a\ua016
716\ua0element array demonstrator agree well with the simulation results. The\ua016
716\ua0array antenna is capable of steering the beam up to\ua0\ub160 degrees and\ua0\ub175 degrees with the bandwidth of 20% and 10%, respectively, at\ua0Γact≤−10\ua0dB. The array antenna also achieved good stiffness and performed well in the vibration loads of commercial transport aircraft
Integration of Self-Adaptive Physical-Layer Key Distribution and Encryption in Optical Coherent Communication
Get PDFWe propose and experimentally demonstrate a compatible physical-layer secure optical communication (PLSOC) system that integrates self-adaptive physical-layer key distribution (PLKD) and encryption (PLE) in optical coherent communication. Based on bit error rate difference of QAM signals mapped by asymmetric basis state Y-00 protocol, the secret key can be secretly exchanged over public fiber links without the pre-shared keys. Moreover, we perform a parameter self-adaptive strategy for practical and dynamic PLKD. The security of the key is evaluated in the case of a fiber-tapping attack. A secure hash algorithm, SHA3-512, is used to perform privacy amplification to obtain the virtually secure key. An error-free PLKD rate reaches 39.3 Kbits/s over 300km ultra-low loss fiber. We experimentally enable the integration of the proposed PLKD scheme and quantum noise stream cipher (QNSC) with a single wavelength, same system. Q factor penalty of the integration system compared to the QNSC system is 3.7dB (optical back-to-back) and 4.8dB (300km) respectively. By exploiting a common hardware platform, with the same wavelength, the proposed PLSOC system addresses the problem that PLKD and PLE are separately performed through independent optical fiber links or wavelengths. Since only digital signal processing is used, the scheme does not require extra hardware
Fast evaluation of the adsorption energy of organic molecules on metals via graph neural networks
Get PDFModeling in heterogeneous catalysis requires the extensive evaluation of the energy of molecules adsorbed on surfaces. This is done via density functional theory but for large organic molecules it requires enormous computational time, compromising the viability of the approach. Here we present GAME-Net, a graph neural network to quickly evaluate the adsorption energy. GAME-Net is trained on a well-balanced chemically diverse dataset with C1–4 molecules with functional groups including N, O, S and C6–10 aromatic rings. The model yields a mean absolute error of 0.18 eV on the test set and is 6 orders of magnitude faster than density functional theory. Applied to biomass and plastics (up to 30 heteroatoms), adsorption energies are predicted with a mean absolute error of 0.016 eV per atom. The framework represents a tool for the fast screening of catalytic materials, particularly for systems that cannot be simulated by traditional methods
Effects of tungsten decoration on the performance of a Ni-based oxygen carrier during chemical looping reforming of biogas for hydrogen generation
No full textBiogas, typically containing around 60% CH4and 40% CO2, can be used as feedstock in chemical looping reforming (CLR) process. In our previous work, a Ni-based oxygen carrier (OC) using high-alumina firebrick as support has shown excellent performance of complete CH4 and CO2 conversion of biogas, thus resulting in high H2 and CO yield in CLR. Nonetheless, that work also found that the presence of H2S in biogas can poison the OC and then leads to decrease of the OC reactivity. Based on some literatures, tungsten is promising of lessening the sulfur poisoning on catalysts. In the present work, tungsten was used to decorate the Ni oxygen carrier and the impregnating sequence of Ni and W in the firebrick was changed to study the effects on the OC performance. An 1000\ub5L/L H2S was mixed with the biogas (the ratio of CH4/CO2 was 3/2) and experiments were carried out in a batch fluidized bed reactor under various reacting conditions. It is found that the W-decoration can lower catalytic activity of the oxygen carrier, and the sequence of Ni and W impregnation can also impact the reforming performance. In the case of no H2S mixing, the OC-Ni-W (first with Ni impregnation, then W impregnation) oxygen carrier has better catalytic performance as compared to OC-Ni=W (Ni, W simultaneous impregnation) and OCW-Ni (first W then Ni). With the presence of 1000\ub5L/L H2S, the OC-Ni-W has higher CO and H2 yield as compared to OC-W-Ni and OC-Ni=W
Spin-valley coupling and spin-relaxation anisotropy in all-CVD Graphene- MoS2 van der Waals heterostructure
Get PDFTwo-dimensional (2D) van der Waals (vdW) heterostructures fabricated by combining 2D materials with unique properties into one ultimate unit can offer a plethora of fundamental phenomena and practical applications. Recently, proximity-induced quantum and spintronic effects have been realized in heterostructures of graphene (Gr) with 2D semiconductors and their twisted systems. However, these studies are so far limited to exfoliated flake-based devices, limiting their potential for scalable practical applications. Here, we report spin-valley coupling and spin-relaxation anisotropy in Gr-MoS2 heterostructure devices prepared from scalable chemical vapor-deposited (CVD) 2D materials. Spin precession and dynamics measurements reveal an enhanced spin-orbit coupling strength in the Gr-MoS2 heterostructure in comparison with pristine Gr at room temperature. Consequently, large spin-relaxation anisotropy is observed in the heterostructure, providing a method for spin filtering due to spin-valley coupling. These findings open a scalable platform for all-CVD 2D vdW heterostructures design and their device applications
Intelligent data acquisition for drug design through combinatorial library design
Get PDFA problem that occurs in machine learning methods for drug discovery is aneed for standardized data. Methods and interest exist for producing new databut due to material and budget constraints it is desirable that each iteration ofproducing data is as efficient as possible. In this thesis, we present two papersmethods detailing different problems for selecting data to produce. We invest-igate Active Learning for models that use the margin in model decisiveness tomeasure the model uncertainty to guide data acquisition. We demonstrate thatthe models perform better with Active Learning than with random acquisitionof data independent of machine learning model and starting knowledge. Wealso study the multi-objective optimization problem of combinatorial librarydesign. Here we present a framework that could process the output of gener-ative models for molecular design and give an optimized library design. Theresults show that the framework successfully optimizes a library based onmolecule availability, for which the framework also attempts to identify usingretrosynthesis prediction. We conclude that the next step in intelligent dataacquisition is to combine the two methods and create a library design modelthat use the information of previous libraries to guide subsequent designs
Frequency stabilization of a terahertz quantum-cascade laser to the Lamb dip of a molecular absorption line
Get PDFWe demonstrate the frequency stabilization of a terahertz quantum-cascade laser (QCL) to the Lamb dip of the absorption line of a D2O rotational transition at 3.3809309 THz. To assess the quality of the frequency stabilization, a Schottky diode harmonic mixer is used to generate a downconverted QCL signal by mixing the laser emission with a multiplied microwave reference signal. This downconverted signal is directly measured by a spectrum analyzer showing a full width at half maximum of 350 kHz, which is eventually limited by high-frequency noise beyond the bandwidth of the stabilization loop
Reprogramming methanol utilization pathways to convert Saccharomyces cerevisiae to a synthetic methylotroph
No full textMethanol, an organic one-carbon (C1) compound, represents an attractive alternative carbon source for microbial fermentation. Despite considerable advancements in methanol utilization by prokaryotes such as Escherichia coli, engineering eukaryotic model organisms such as Saccharomyces cerevisiae into synthetic methylotrophs remains challenging. Here, an engineered module circuit strategy combined with adaptive laboratory evolution was applied to engineer S. cerevisiae to use methanol as the sole carbon source. We revealed that the evolved glyoxylate-based serine pathway plays an important role in methanol-dependent growth by promoting formaldehyde assimilation. Further, we determined that the isoprenoid biosynthetic pathway was upregulated, resulting in an increased concentration of squalene and ergosterol in our evolved strain. These changes could potentially alleviate cell membrane damage in the presence of methanol. This work sets the stage for expanding the potential of exploiting S. cerevisiae as a potential organic one-carbon platform for biochemical or biofuel production. [Figure not available: see fulltext.]
Synthesis of geopolymer using municipal solid waste incineration fly ash and steel slag: Hydration properties and immobilization of heavy metals
No full textIn this study, a novel method for the disposal of municipal solid waste incineration fly ash (MSWIFA) was proposed. By applying geopolymer technology, steel slag (SS) and MSWIFA were used together as precursors to synthesize a cementitious material with sufficient strength that is useable in construction. The effects of the dosages of SS and alkaline activator on the properties of the geopolymer were investigated. Compressive testing was used to characterize the mechanical properties of the geopolymer. X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for microscopic analysis. Leaching tests were performed to assess the immobilization effect of the geopolymer on heavy metals. The results showed that the compressive strength of the geopolymer reached 23.03 MPa at 56 d with 20% SS and 11% Na2O admixture. Highly polymerized hydration products, such as C-(A)-S-H gels and N-A-S-H gels, contributed to the compact microstructure, which provided mechanical strength and limited the migration and leaching of heavy metals in the geopolymer matrix. In terms of the results, this work is significant for the development of MSWIFA management
Crystallographic characterization of U2CrN3: A neutron diffraction and transmission electron microscopy approach
Get PDFIn this study, neutron diffraction and transmission electron microscopy (TEM) have been implemented to study the crystallographic structure of the ternary phase U2CrN3 from pellet to nano scale respectively. Recently microstructural evaluation of this ternary phase has been performed for the first time in pellet condition, overcoming the Cr evaporation issue during the conventional sintering process. In this work for the first time, the crystallographic structure of the ordered ternary U2CrN3 phase, stabilized in pellet condition, has been obtained by implementing neutron diffraction. For this study, pellets of the composite material UN with 20 vol% CrN were fabricated by powder metallurgy by mixing UN and CrN powders followed by Spark Plasma Sintering (SPS). TEM was used to investigate the nanoscale structure with a thin lamella of the order of 100–140 nm produced by focused ion beam (FIB). The neutron data revealed the phase composition of the pellet to be primarily 54(8) wt.% U2CrN3, in good agreement with the stoichiometry of starting reagents (UN and CrN powder) and metallographic analysis. Neutron data analysis confirms that all the crystallographic sites in U2CrN3 phase are fully occupied reinforcing the fully stoichiometric composition of this phase, however, the position of the N at the 4i site was found to be closer to the Cr than previously thought. TEM and selected area electron diffraction rendered nano-level information and revealed the presence of nano domains along grain boundaries of UN and U2CrN3, indicating a formation mechanism of the ternary phase, where the phase likely nucleates as nano domains in UN grains from migration of Cr