Channel Spacing Research Articles

3D near-surface P-wave velocity structure imaging with Distributed Acoustic Sensing and electric hammer source

Distributed Acoustic Sensing (DAS) is an emerging technique for ultra-dense seismic observation, which provides a new method for high-resolution sub-surface seismic imaging. Recently a large number of linear DAS arrays have been used for two-dimensional S-wave near-surface imaging in urban areas. In order to explore the feasibility of three-dimensional (3D) structure imaging using a DAS array, we carried out an active source experiment at the Beijing National Earth Observatory. We deployed a 1 ​km optical cable in a rectangular shape, and the optical cable was recast into 250 sensors with a channel spacing of 4 ​m. The DAS array clearly recorded the P, S and surface waves generated by a hammer source. The first-arrival P wave travel times were first picked with a Short-Term Average/Long-Term Average (STA/LTA) method and further manually checked. The P-wave signals recorded by the DAS are consistent with those recorded by the horizontal components of short-period seismometers. At shorter source-receiver distances, the picked P-wave arrivals from the DAS recording are consistent with vertical component recordings of seismometers, but they clearly lag behind the latter at greater distances. This is likely due to a combination of the signal-to-noise ratio and the polarization of the incoming wave. Then, we used the TomoDD software to invert the 3D P-wave velocity structure for the uppermost 50 ​m with a resolution of 10 ​m. The inverted P-wave velocity structures agree well with the S-wave velocity structure previously obtained through ambient noise tomography. Our study indicates the feasibility of 3D near-surface imaging with the active source and DAS array. However, the inverted absolute velocity values at large depths may be biased due to potential time shifts between the DAS recording and seismometer at large source-receiver distances.

Image Splicing Detection Based on Discrete Wavelet Transform and co-occurrence Matrix

In this paper a method to determine whether an image is forged (spliced) or not is presented. The proposed method is based on a classification model to determine the authenticity of a tested image. Image splicing causes many sharp edges (high frequencies) and discontinuities to appear in the spliced image. Capturing these high frequencies in the wavelet domain rather than in the spatial domain is investigated in this paper. Correlation between high-frequency sub-bands coefficients of Discrete Wavelet Transform (DWT) is also described using co-occurrence matrix. This matrix was an input feature vector to a classifier. The best accuracy of 92.79% and 94.56% on Casia v1.0 and Casia v2.0 datasets respectively was achieved. This performance is reached when Cb and Cr channels in YCbCr color space only are utilized to form this feature vector. The outcomes of the experiments showed that the proposed method achieved very good results in comparison with existing splicing detection approaches.

Selection of microhabitats, plants, and plant parts eaten by a threatened tortoise: observations during a superbloom

Populations of the threatened desert tortoise (Gopherus agassizii) continue to decline throughout the geographic range, in part because of degraded and fragmented habitats in the Mojave and western Sonoran deserts. The species is herbivorous and highly selective in choice of plant species. To increase options for recovery, we analyzed behaviors, patterns of movements while foraging, and parts of plants consumed during a superbloom. We characterized foraging routes and the habitat strata and microhabitats where tortoises traveled to eat preferred wildflower species. Tortoises walked one foraging route per day in early spring, often switched to two routes per day in middle and late spring with rise of midday temperatures. They chose habitat strata (primarily hills and ephemeral stream channels) and three of seven microhabitats for foraging on preferred food plants. Preferred microhabitats were intershrub open space and small (1–2 m wide) ephemeral stream channels. They rarely took bites of forbs growing under and in the dripline of shrubs or nonnative forbs and grasses. Tortoises typically did not select specific plant parts to eat but important exceptions occurred. For example, they usually ignored the inflorescences of the annual Eremothera boothii and, when eating the non-native annual Erodium cicutarium, tended to focus on fruits. All such information aids recovery efforts to restore declining tortoise populations.

The Global DAS Month of February 2023

Abstract During February 2023, a total of 32 individual distributed acoustic sensing (DAS) systems acted jointly as a global seismic monitoring network. The aim of this Global DAS Month campaign was to coordinate a diverse network of organizations, instruments, and file formats to gain knowledge and move toward the next generation of earthquake monitoring networks. During this campaign, 156 earthquakes of magnitude 5 or larger were reported by the U.S. Geological Survey and contributors shared data for 60 min after each event’s origin time. Participating systems represent a variety of manufacturers, a range of recording parameters, and varying cable emplacement settings (e.g., shallow burial, borehole, subaqueous, and dark fiber). Monitored cable lengths vary between 152 and 120,129 m, with channel spacing between 1 and 49 m. The data has a total size of 6.8 TB, and are available for free download. Organizing and executing the Global DAS Month has produced a unique dataset for further exploration and highlighted areas of further development for the seismological community to address.

The Difference in Damage to Low-Permeability Reservoirs by Different Injection Methods of CO2 Flooding

Low-permeability reservoirs have become an important field of oil and gas development in China. CO2 flooding technology is an effective technical means for tertiary oil recovery. Although the asphaltene in the system is deposited in the form of a solid after CO2 injection into the reservoir in contact with crude oil, which causes a certain blockage to the reservoir, the dissolution during the injection process improves the seepage capacity of the reservoir as a whole, and the damage degree of CO2 flooding to low-permeability reservoirs under different injection modes is different. In this paper, the damage degree of asphaltene precipitation to low-permeability reservoirs under different injection modes of CO2 flooding is quantitatively characterized. The mechanism experiment of organic scale plugging after continuous CO2 flooding and CO2–water alternate flooding, the wettability experiment of reservoirs, and the evaluation experiment of CO2–water solution on rock dissolution are carried out, and the variation characteristics of relative permeability curve parameters are evaluated. In this paper, the damage degree of asphaltene precipitation to low-permeability reservoirs under different injection modes of CO2 flooding is quantitatively characterized. The mechanism experiment of organic scale plugging after continuous CO2 flooding and CO2–water alternate flooding, the wettability experiment of reservoirs, and the evaluation experiment of CO2–water solution on rock dissolution are carried out. The variation characteristics of relative permeability curve parameters are evaluated. The results show that the organic scale produced by CO2 flooding will block the pore throat of the rock, but, on the whole, the dissolution caused by the reaction of CO2 and chlorite is stronger, which makes the recovery rate of low-permeability reservoirs effectively improved. The organic scale blockage caused by CO2–water alternating flooding is weaker than that caused by continuous CO2 flooding. The dissolution effect is better and the permeability is higher. It can achieve a better oil displacement effect in pores with a pore size greater than 0.2 μm. On the whole, it can increase the core pore space and seepage channel, so that the recovery rate of low-permeability reservoirs can be effectively improved. This study has important theoretical and practical significance for improving oil recovery in low-permeability reservoirs.

Multiscale Topology Optimization of modulated fluid microchannels based on asymptotic homogenization

Dehomogenization techniques are becoming increasingly popular for enhancing lattice designs of compliant mechanical systems with ultra-large resolutions. Their effectiveness hinges on computing a deformed periodic grid that enable to reconstruct fine-scale designs with modulated and oriented patterns. In this paper, we propose an approach for extending dehomogenization methods to laminar fluid systems. We initiate our methodology by asymptotically deriving Darcy’s law on a periodically porous medium deformed by a diffeomorphism. Unlike the mechanical context, we reveal that the homogenized permeability matrix depends not solely on local the orientation but also on the local dilation of the deformed periodic medium. This distinction presents one of the several challenges to be tackled when adapting dehomogenization-based topology optimization techniques to porous media. To accommodate existing methodologies, we formulate a simplified “poor man’s” homogenized model, which streamlines various aspects, yet still leans on periodic cell problems to estimate the spatially varying permeability matrix. Specifically, we overlook boundary layer effects, we presume periodic grid deformations, and we neglect local dilation, solely considering the relationship with local cell orientations. Subsequently, we present a numerical approach for designing a system that redistributes an input flow across numerous regularly spaced outlets at an output interface. Leveraging the homogenized model, we deduce optimized geometric arrangements of local channel spacing parameters and orientations. We then use established methods to reconstruct grid deformations and fine-scale designs. The fidelity of these reconstructions is then validated through fine-scale simulations. Our observations indicate that while the proposed designs yield satisfactory performance when subjected to the full-scale model, discernible deviations from the homogenized model persist, appealing to future improvements.

Dynamic modelling of cross-flow printed circuit heat exchangers for multistage reactor intercooling

A reduced-order dynamic model of a cross-flow printed circuit heat exchanger was developed to study both steady-state and transient performance under conditions that would be encountered in multistage catalytic combustion reactors to better understand how they can be used to minimize fluctuations in heat-integrated reactors and intensified processes. Previous transient models for cross-flow heat exchangers rely on an initial steady state and apply only for changes in inlet temperature, but this work presents a model that can be applied to intermediate states or multiple concurrent upstream process changes. Steady-state simulations showed that larger channels reduce volumetric heat transfer performance and effectiveness due to convective resistance. Furthermore, larger channel spacing increases effectiveness but also reduces compactness. Operating temperature was found to have a minimal effect on the overall heat transfer coefficient and effectiveness within the range of conditions studied, and operating pressure was found to have no effect on heat transfer. Transient analyses showed that the response to a unit step in temperature matches closely with an analytical infinite gas velocity model, both for time constants and the overall thermal response, with initial variations in outlet temperatures from ideal-case models below 3.8 % of unit step magnitudes, and average differences below 0.75 %. Transient analyses also show the effects of a finite fluid velocity which is critical in the transient response of large heat exchangers. The presented numerical model can also be more easily extended to complex configurations and can be applied to other changes in inlet conditions such as changing composition and flow rates as are found in combustion applications. A three-fluid thermal management system for a multistage packed-bed microreactor using printed circuit heat exchangers is proposed and modelled to provide a method for temperature regulation and pre-heating of fresh reactor feed.

Generation of cylindrical vector beam pulses by using multi-wavelength EDFL with two-mode fiber filter

A multi-wavelength erbium-doped fiber laser (MW-EDFL) operating in the L-band with cylindrical vector beam outputs is proposed and experimentally investigated. The multi-wavelength lasing is realized by exploiting a two-mode fiber filter (TMFF) as the comb filter and a single-mode fiber spool with 2-km in length to suppress the mode competition. The multi-wavelength combs with channel spacing of 0.36 nm, 0.58 nm, and 1.12 nm are achieved by regulating the interference length of the TMFF, and up to 18 lasing channels are obtained with a wavelength spacing of 0.36 nm. Good long-term stability is manifested within a 100-minute duration, as the maximum peak power fluctuation of 1.96 dB and the maximum wavelength shift of 0.03 nm are measured. By adjusting the polarization controller associated with the two-mode long-period grating as a high-efficiency mode converter, radially and azimuthally polarized cylindrical vector beams of high purity are thus generated.

Modelling and numerical analysis of combined dual impact of SRS and FWM on the performance of upstream and downstream channels of a novel UDWDM/DWDM-PON

Wavelength division multiplexing (WDM) is an important method in modern optical communication systems for both long-haul and access networks. Particularly, after being standardized by Telecommunication Standardization Sector of International Telecommunication Union (ITU-T), WDM passive optical network (WDM-PON) becomes a considerable choice for fronthaul implementations of 5G networks. Stimulated Raman scattering (SRS) and four-wave mixing (FWM) are crucial nonlinear impacts that significantly limit the performance of WDM-based optical fiber communication systems. In this paper, an ultra-dense/dense WDM-PON (UDWDM/DWDM-PON) architecture has been proposed and combined dual impact of SRS and FWM on performances of upstream channels (USCs) and downstream channels (DSCs) of the proposed UDWDM/DWDM-PON has been numerically analyzed. USCs have been assumed to operate in 1310 nm region while operating wavelength region of DSCs has been taken as 1550 nm. Simulations have been performed on both UDWDM-PON architectures with 3.125 GHz and 6.25 GHz channel spacings and DWDM-PON architectures with channel spacings between 12.5 GHz and 100 GHz. 2x15-channel and 2x63-channel system structures have been considered in simulations. Signal-to-crosstalk ratio (SXR) has been chosen as performance parameter and its variation with channel input powers, channel spacings and channel lengths have been simulated for both USCs and DSCs of 2x15- and 2x63-channel UDWDM/DWDM-PONs. Results show that the proposed UDWDM/DWDM-PONs using single G.652 fiber can exhibit a reliable communication with minimum 23 dB SXR performance under combined dual impact of SRS and FWM unless some highlights about input powers and channel lengths mentioned in the paper are neglected.

N, O, P-doped porous carbon with high surface utilization and long cycling life for supercapacitors

The development of miniaturized and lightweight supercapacitors (SCs) becomes a hot research region. Improving the surface area utilization of porous carbon materials can effectively promote the energy density and power density of SCs. This work first constructs three-dimensional porous poly(p-phenylenediamine) hydrogel through adding phytic acid. Thereafter, N, O, P-doped porous carbon (NOPPC) was obtained via simple one-step pyrolysis treatment. The unique three-dimensional porous structure of NOPPC inherited from poly(p-phenylenediamine) hydrogel provides plentiful ion storage space and ion transportation channels. Heteroatom-doped feature endows NOPPC with good wettability and more active surface area. The surface utilization of NOPPC-800 reaches up to 2.56 F m−2, which is better than many carbon materials in literatures. NOPPC-800 can still maintain 135 F g−1 at 20 A g−1. The capacity retention ratio of NOPPC-800 can reach up to 93.4 % after 10000 cycles at 10 A g−1. The quantitative analysis of energy storage mechanism of NOPPC illustrates the synergistic impact of pore structure and doped heteroatoms. These electrochemical results show that NOPPC possesses good practical application value. NOPPC-800//NOPPC-800 supercapacitor shows high energy density and excellent cycle stability. The results show that the balance of heteroatom content, specific surface area and conductivity is the key to obtain promising carbon electrode materials and can be realized via tuning carbonization temperature. This work also demonstrates that rational structure control of carbon precursor is the effective way to promote the capacity of carbon materials.

A 75 GHz Brillouin Stokes Channels For High Data Rate DWDM Communication Systems

The experimental results of a 75 GHz Brillouin Stokes channels are demonstrated in this paper. Three dispersion compensation fiber (DCF) spools and one single mode fiber (SMF) spool are used as a Brillouin gain medium. An erbium doped fiber amplifier (EDFA) sections are used to amplify the generated Stokes channels and to reduce the Brillouin Stokes threshold inside the cavities. Laser pump of 1480 nm with total power of 470 mW are used for the EDFA sections as a pump power unit. In our proposed setup, four channels with 75 GHz spacing, high Stokes power of about 10 mW, and large optical signal to noise ratio (OSNR) of about 52 dB are achieved at Brillouin pump power of 25 mW. The achieved channels are tuned over 15 nm from 1565 to 1580 nm. within the entire tuning range up to 25 Stokes channels with 75 GHz spacing can be utilized. High data rate of about 800 Gb/s can be obtained per single channel at this wide channel spacing. Therefore, the total data rate that could be achieved within the obtained tuning range is about 20 Tb/s.

Ultra-compact dual-purpose photonic crystal slab waveguide for both generating and isolating optical frequency comb

In this article, we present a novel approach to achieve a highly compact Si3N4 photonic crystal waveguide by incorporating air holes. This structure is developed in two functional applications that simultaneously perform the functions of generating optical frequency combs and demultiplexing them. The presence of air holes enhances control and precision in the dispersion engineering process. At the same time, the light conduction, based on the refractive index contrast between the core and cladding, along with the conduction occurring in the photonic bandgap region of the structure, leads to enhanced trapping of light within the core of the structure. As a result, a nonlinear coefficient of 4.2 m-1W−1 is obtained, which originates from the small effective mode area of 0.67 µm2. By employing four-wave mixing, a total of 40 comb lines are generated with a frequency spacing range of 10 GHz, 50 GHz, 60 GHz, and 100 GHz over a 6 mm length waveguide. The same waveguide structure is also developed for demultiplexing the comb lines, with four filters at the end which, individually extract the optical combs possessing wavelengths of 1317.8 nm, 1318.5 nm, 1319.2 nm, and 1319.9 nm. This demultiplexer has a Q-factor, average transmission efficiency, channel spacing, and spectral linewidth of 7209.35, 99.2 %, 0.7 nm, and 0.185 nm, respectively. The suggested design can significantly advance integrated photonic circuits, optical communications, and remote sensing applications requiring simultaneous information delivery, such as remote surgical operations and sensing, because of its substantial compactness.

Four-bands high-resolution integrated spectrometer.

We present the concept and design of a novel integrated optical spectrometer able to operate over four different optical bands in the infrared that cover over 900 nm of aggregated bandwidth. The device, named integrated optical four bands spectrometer (IOFBS), consists of a single planar concave grating with 4 inputs waveguides, each corresponding to a different wavelength band, and 39 output channels that can be implemented on a silicon nitride platform. The inputs waveguides (IWGs) are optimized so that the echelle grating works in different diffraction orders to create constructive interference at the fixed output waveguides. The grating facets are engineered to maximize the diffraction efficiency of the beam launched from any of the four IWGs. The IOFBS works in the near infrared, the O-band, part of the S&E bands and the L-band. The simulated spectra feature an average insertion loss of -1.69 dB across the four bands and a crosstalk better than -32 dB with a 3-dB resolution as low as 0.37 nm and a channel spacing of ∼2.1 nm. The entire device covers an area of 5 mm x 4 mm. The versatility of the proposed design can reduce the cost of integrated spectrometers and make on-chip spectral analysis more accessible by taking advantage of batch fabrication to build a compact device with numerous potential applications.

High speed 60 Gbps RGB laser based-FSOC link by incorporating hybrid PDM-MIMO scheme for indoor applications

Abstract Visible Light Communication (VLC) systems enhanced by red, green and blue (RGB) lasers are at the forefront of indoor technology, offering dynamic lighting, high-speed data transfer, and energy efficiency. This innovative combination not only revolutionizes connectivity and illumination but also ensures privacy and security, making it a game-changer for smart homes, offices, and various indoor applications. In our research, we introduce a polarization division multiplexing and Multiple Input Multiple Output based (PDM-MIMO) system that carries 60 Gbps of data over a transmission range of 500 m in free space Channels. The utilization of the cost-effective on-off key (OOK) modulation format is attributed to its affordability in our transmission scheme. For parallel data transmission, three laser diodes in RGB were utilized. To enhance both the transmission range and reduce the Bit Error Rate (BER), MIMO scheme is employed. Our study presents simulation outcomes, conducted using OptiSystemTM software, that focus on evaluating the bit error rates for the proposed PDM-MIMO link. Our findings demonstrate successful 60 Gbps data transmission over 350 m in FSO with an acceptable BER, reinforced by clear eye diagrams. Introducing MIMO expands the range to 500 m while improving BER, paving the way for real-time experimentation and research advancement.

Nectarine Disease Identification Based on Color Features and Label Sparse Dictionary Learning with Hyperspectral Images

Fruit cracking and rust spots are common diseases of nectarines that seriously affect their yield and quality. Therefore, it is essential to construct fast and accurate disease-identification models for agricultural products. In this paper, a sparse dictionary learning method was proposed to realize the rapid and nondestructive identification of nectarine disease based on multiple color features combined with improved LK-SVD (Label K-Singular Value Decomposition). According to the color characteristics of the nectarine itself and the significant color differences existing in the three categories of nectarine (diseased, normal, and background parts), multiple color spaces of RGB, HSV, Lab, and YCbCr were studied. It was concluded that the G channel in RGB space, Y channel in YCbCr space, and L channel in Lab space can better distinguish the diseased part from the other parts. At the model-training stage, pixels of the diseased, normal, and background parts in the nectarine image were randomly selected as the initial training sets, and then, the neighboring image blocks of the pixels were selected to construct the feature vectors based on the above color space channels. An improved LK-SVD dictionary learning algorithm was proposed that integrated the category label into the process of dictionary learning, and thus, an over-complete feature dictionary with significant discrimination was obtained. At the model-testing stage, the orthogonal matching pursuit (OMP) algorithm was used for sparse reconstruction of the original data, which can obtain the classification categories based on the optimized feature dictionary. The experimental results show that the sparse dictionary learning method based on multi-color features combined with improved LK-SVD can identify fruit cracking and rust spot diseases of nectarines quickly and accurately, and the average overall classification accuracies were 92.06% and 88.98%, respectively, which were better than those of k-nearest neighbor (KNN), support vector machine (SVM), DeepLabV3+, and Unet++; the identification results of DeepLabV3+ and Unet++ were also relatively high, but their average time costs were much higher, requiring 126.46~265.65 s. It is demonstrated that this study can provide technical support for disease identification in agricultural products.

LCA-Net: A Lightweight Cross-Stage Aggregated Neural Network for Fine-Grained Recognition of Crop Pests and Diseases

In the realm of smart agriculture technology’s rapid advancement, the integration of various sensors and Internet of Things (IoT) devices has become prevalent in the agricultural sector. Within this context, the precise identification of pests and diseases using unmanned robotic systems assumes a crucial role in ensuring food security, advancing agricultural production, and maintaining food reserves. Nevertheless, existing recognition models encounter inherent limitations such as suboptimal accuracy and excessive computational efforts when dealing with similar pests and diseases in real agricultural scenarios. Consequently, this research introduces the lightweight cross-layer aggregation neural network (LCA-Net). To address the intricate challenge of fine-grained pest identification in agricultural environments, our approach initially enhances the high-performance large-scale network through lightweight adaptation, concurrently incorporating a channel space attention mechanism. This enhancement culminates in the development of a cross-layer feature aggregation (CFA) module, meticulously engineered for seamless mobile deployment while upholding performance integrity. Furthermore, we devised the Cut-Max module, which optimizes the accuracy of crop pest and disease recognition via maximum response region pruning. Thorough experimentation on comprehensive pests and disease datasets substantiated the exceptional fine-grained performance of LCA-Net, achieving an impressive accuracy rate of 83.8%. Additional ablation experiments validated the proposed approach, showcasing a harmonious balance between performance and model parameters, rendering it suitable for practical applications in smart agricultural supervision.

Management of an urban lagoon. Study case: Ilusiones Lagoon, Tabasco, Mexico

As a delta, Tabasco, located in the Mexican southeast, is susceptible to flooding. The city of Villahermosa, the capital of Tabasco, is not an exception. The most recent event occurred in November 2020, when an excess of rain provoked an urban lagoon to exceed its levels. The lagoon discharges at a river by a diversion channel controlled by a culvert. To analyze it, a hydraulic model -HEC RAS V6.0- was used. Precipitation, flow, and level data recorded during 2020 were used to simulate four scenarios: I) one culvert of 1.5 m x 1.75 m (current situation); II) three culverts of 1.5 m x 1.75 m; III) three culverts of 2 m x 2.5 m; and IV) one culvert of 10 m x 2.5 m. The dimensions of the culverts were subject to the available physical space of the discharge channel. It was found that the best performance was achieved with scenario II. This result is contrasting because this alternative is not the largest as might be expected; it is also encouraging because it improves the performance of this lagoon. With this proposal, we reduce the damage by 75.31%, which means 296 homes are protected. Finally, the proposed methodology can guide designers and decision-makers to evaluate hydraulic works in urban lagoons like those presented in this work.

Ultra-broad bandwidth array waveguide grating for high-speed backbone network transmission.

With the rapid development of the backbone network rates, there has been a gradual increase in channel spacing and bandwidth. The C&L band ultra-broad bandwidth array waveguide gratings (AWG) of 60-channel 100 GHz channel spacing are designed and fabricated based on silica waveguide. A new parabolic design is used to achieve ultra-broad bandwidth and good spectrum. For the C band ultra-broad bandwidth AWG, the peak insertion loss, uniformity, 0.5 dB bandwidth, 1 dB bandwidth and 3 dB bandwidth are 2.98 dB, 0.36 dB, 0.614 nm, 0.721 nm and 0.937 nm, respectively. For the L band ultra-broad bandwidth AWG, the peak insertion loss, uniformity, 0.5 dB bandwidth, 1 dB bandwidth and 3 dB bandwidth are 2.91 dB, 0.27 dB, 0.560 nm, 0.665 nm and 0.879 nm, respectively. To ensure ultra-broad bandwidth AWG operation at different temperatures, a temperature control circuit is integrated into the packaging design. It has been observed that the performances remain virtually unchanged within the temperature range of -15 to 65 degree. The ultra-broadband AWGs have been successfully tested to transmit 96 Gbaud signals and can be applied to 600 G/800 G backbone network transmission. By using the C&L ultra-broad bandwidth AWGs of 60-channel 100 GHz channel spacing, the total transmission speed over a single-mode fiber can reach 72Tbps/96Tbps.

Effects of Al powder on the reaction process and reactivity of B/KNO3 energetic sticks

Boron/potassium nitrate (B/KNO3) is a type of critical energetic composite material (ECM). However, the inert oxide layer on the B surface of B/KNO3 hinders the contact between pure fuel and oxidant, thus limiting energy release This limitation could be eliminated by adding highly reactive Al powder. To discern the effects of Al powder size on the reaction process and reactivity of B/KNO3, this study prepared Al/B/KNO3/polyvinylidene fluoride (PVDF) energetic sticks using the direct ink writing (DIW) technology. This study characterized the macroscopic morphology and structure of the energetic sticks using a laser scanning microscope and a scanning electron microscope, examined the reaction process of the composites using a differential scanning calorimeter and a thermogravimetric analyzer, and observed the flame propagation behavior of energetic sticks and energetic architectures using a high-speed camera. Furthermore, it tested the pressure output characteristics of the energetic composites using a closed volume tank. The results show that adding Al powder can improve the combustion efficiency of B/Al composite fuels and reduce the agglomeration of the combustion products. The Al powder with various particle sizes affects various reaction stages of the composite. The combustion and pressure output tests suggest that adding Al powder with a particle size of 1 μm yielded high reactivity and that flame jump propagation appeared in energetic architectures when the channel spacing was below 10 mm. These findings provide a guide for modifying the B/KNO3 energetic composites and regulating the reactivity of energetic sticks.

Ultra‐Low‐Crosstalk Silicon Arrayed‐Waveguide Grating (De)multiplexer with 1.6‐nm Channel Spacing

AbstractA silicon arrayed‐waveguide grating (AWG) with 1.6‐nm channel spacing is proposed and realized with high performances for dense wavelength‐division (de)multiplexing systems. For the present AWG, the arrayed waveguides are broadened uniformly to be far beyond the singlemode regime, so that random phase errors and propagation loss are minimized even without any additional requirement for the fabrication process. Particularly, Euler‐bends are introduced for the arrayed waveguides to shrink the device footprint and suppress any excitation of higher‐order modes. As an example, a 16 × 16 AWG (de)multiplexer is realized with a compact footprint of 600 × 800 µm2 by using single‐etched 220‐nm‐thick silicon photonic waveguides. When using the fabricated AWG to demultiplex the channels launched from the central input port, the excess loss and the adjacent‐channel crosstalk of the central output port are ≈2.2 and ≈−31.7 dB, respectively. Such an AWG is one of the best among silicon implementations.