Mode Patterns Research Articles

Experimental study and numerical analysis of the interfacial bonding performance of T‐shaped concrete‐filled steel tubes

SummaryThe effects of core concrete strength (C30, C40, and C50), steel tube length (600, 1000, and 1400 mm), and steel tube wall thickness (3, 4, and 5 mm) on the bonding performance of T‐shaped concrete‐filled steel tubes (CFSTs) were systematically investigated using push‐out test. Via the test, the patterns of the failure modes, load‐slip curves, stress‐slip curves, and distribution law of longitudinal strain were observed for the specimens, and the bond‐slip constitutive model for T‐shaped CFSTs was established. The test results indicate that the bond stress of T‐shaped CFSTs increases with the increase in concrete strength and tube wall thickness, while the steel tube length has less influence on the bond stress. In addition, non‐linear spring elements were used to simulate the interfacial bonding behavior based on the bond‐slip equation, which is in good agreement with the experimental curve results.

Influence of nozzle external geometry on the emission of screech tones

The effect of external nozzle geometry on the emission of screech tones was studied experimentally. Four conical reflector surfaces, with half-angles ranging from 60° to 90°, were installed around the exit of a round convergent nozzle. The investigation focused on two closely spaced fully-expanded Mach numbers, M j = 1.32 and 1.34. The acoustic far-field was surveyed by a microphone phased array that included a continuously-scanning microphone, the latter enabling high spatial resolution. The isolated jets contained well-known screech mode B and its harmonics. Addition of the reflectors caused significant changes in the modal emission pattern, with tones traditionally linked to mode C occurring at M j = 1.34 but not at M j = 1.32. Tonal components associated with new modes E and F emerge at both Mach numbers when the cone half-angle is 60° or 70°. The noise source distribution generally elongates with decreasing cone angle. Some modes show clear scattering from the reflectors, while others do not. The study underscores the complexity that initial conditions can impart on the modal structure of screech and demonstrates the capability of the continuous-scan beamforming technique in resolving fine features of the source.

Analysis of the Characteristics of Uneven Spatio-Temporal Distribution in Wujiang River Basin over the Last 60 Years

Exploring the characteristics of uneven temporal and spatial distribution of precipitation in mountain watersheds can provide a reference for regional agricultural development and resource utilization, and contribute to the protection of the ecological environment. Based on the daily precipitation observation data of 40 meteorological stations in the Wujiang River Basin from 1963 to 2021, the temporal- and spatial-variation characteristics of the precipitation concentration degree (PCD) and precipitation concentration period (PCP) were analyzed using the Randall S analysis method, Mann–Kendall test method, Pettitt method, wavelet analysis and empirical orthogonal function (EOF). The results showed that the fluctuation range of PCD in Wujiang River Basin from 1963 to 2021 was 0.34–0.59, with a multi-year average of 0.47, which was obviously higher than the national average level and is showing a trend of slowly increasing. The fluctuation range of PCP was between 17.1 and 21.5 days, with a multi-year average of 19.0. The annual precipitation was mostly concentrated around the middle of July and showed a slowly decreasing trend. The abrupt change in PCD and PCP occurred around 1983 and 2001, respectively. There is an obvious Hearst phenomenon in PCP. In the future, the trend of precipitation concentration in the middle period will remain in advance, and the degree of precipitation concentration will continue to increase. The maximum precipitation in the flood season will continue to be delayed. The spatial pattern of the first mode of PCD and PCP in the Wujiang River basin was consistent and showed an opposite pattern between the upper reaches and the middle-lower reaches of the basin, which reflects the influence of the topography of the basin on the spatial distribution of precipitation. The distribution of precipitation is affected by topography. The elevation change in the basin was complex, and the leeward slope varied a lot. Therefore, it has a significant impact on precipitation. Areas with less precipitation are at higher elevations and on mountain leeward slopes, with a lack of moist air flow. The area with more precipitation was the summer monsoon mountain windward slope, and the topography blocks the increase in precipitation. The elevation of the central region is relatively uniform and the terrain is flat. Therefore, the distribution of precipitation is more uniform.

Modal analysis of computational human brain dynamics during helmeted impacts

Sports-related mild traumatic brain injury (mTBI) is a growing public health concern, affecting millions in the U.S., annually. Current helmets are primarily designed to mitigate head kinematics, despite the importance of the brain substructures mechanics in mTBI mechanism. Therefore, it is crucial to consider the dynamical behavior of brain substructures, which has been shown in prior studies to be associated with strain concentration. Here, we studied the modal behavior and strain patterns of the substructures of the brain finite element (FE) model through Dynamic Mode Decomposition. We conducted side and front impact pendulum tests on a dummy headform equipped with hockey, football, ski, and bicycle helmets. After simulating the impact tests using a brain FE model, we calculated the dynamic modes of this computational model for the whole brain, corpus callosum, brainstem, and cerebellum. The main mode of oscillation in all regions for all helmet types occurred around the frequency regime of 7–15 Hz. Also, in cerebellum, a second harmonic was observed at 40–50 Hz in front impact, and 38 and 62 Hz in side impact in bicycle and ski helmets, respectively. Furthermore, we analyzed the correlation between the modal response and peak maximum principal strain (MPS). These analyses mostly showed a direct association between the computational modal behavior and MPS, where helmet tests with closely spaced modes and high-frequency modal amplitudes led to higher MPS values. This association between the computational modal behavior and strain patterns demonstrated a potential for improving helmet designs through a novel design objective.Statement of significance: Sport-related mild traumatic brain injury (mTBI), which is one of the leading cause of death, can be reduced in severity by using headgears including helmets. Despite the recent innovations and technologies in helmet design, there are important factors that still have been missed. While it’s been shown that the brain substructures mechanics play an important role in mTBI mechanism, current helmets are designed to only mitigate the head kinematics. Moreover, dynamical behavior of these substructures, and existence of multimodal behavior in the brain are factors that have not been addressed in designing helmets. This paper shows the effect of different helmet types on modal behavior of the brain substructures and how the dynamical modes of these regions can be affected by using various helmet types.

Simulations of the North Tropical Atlantic Mode–ENSO Connection in CMIP5 and CMIP6 Models

AbstractThe North Tropical Atlantic (NTA) mode is a dominant component of sea surface temperature (SST) variability over the northern tropical Atlantic, which is crucial to the occurrence of El Niño‐Southern Oscillation (ENSO). This study utilizes the historical simulation of the Coupled Model Intercomparison Project Phase 5 and 6 (CMIP5 and CMIP6) to evaluate the simulations of the NTA mode and NTA–ENSO connection. We found that the CMIP5 and CMIP6 could reproduce the spatial pattern of the NTA mode similarly. Most of them could reasonably reproduce the spatial pattern of the NTA mode similar to the observation. Still, there are some differences in the central values and position of the NTA mode. In addition, the analysis further suggests that the CMIP5/CMIP6 models have a large diversity in the NTA–ENSO connection, which may be due to their differences in simulating the spring climatological mean Atlantic Intertropical Convergence Zone (ITCZ) precipitation and spring‐to‐summer NTA SST persistence. Models with stronger spring climatological mean Atlantic ITCZ precipitation in favor of the spring NTA‐related SST anomalies stimulate local precipitation anomalies, resulting in a more powerful atmospheric circulation reaction over the tropical Pacific. Additionally, the stronger spring‐to‐summer NTA SST persistence for sustaining the teleconnection, which constantly transmits impacts from the tropical Atlantic into the tropical Pacific. The CMIP6 models show improvements to the CMIP5 models regarding simulations of the spring climatological mean Atlantic ITCZ precipitation and spring‐to‐summer NTA SST persistence. Therefore, the CMIP6 models simulate the NTA–ENSO connection better than the CMIP5 models.

Topological vortex mode for flexural waves in pillared plates

Localized topological modes with high robustness to various perturbations are receiving increasing attention. Recently, zero-order topological vortex modes have been designed in phononic structures, in analogy with zero-energy fermionic states modulated by Jackiw-Rossi binding mechanism. Such localized modes may have potential applications for biosensing, bioimaging and on-chip communication. In this work, we propose a pillared phononic plate with a Kekulé distortion of pillars position to bind topological modes at a vortex core via dispersion engineering. The phase winding and amplitude diagrams of the topological vortex mode are observed experimentally. It is found that existence of vibration peaks and corresponding mode patterns are strongly robust against the random perturbation of resonant frequencies of pillars at the vortex core. We further design a topological resonant sensor for mass sensitivity. The frequency of the topological vortex mode is almost linearly sensitive to added small mass at the vortex core in terms of mass values and positions. The proposed pillared plates provide a platform for potential applications such as energy localization and harvesting, remote health monitoring.

Ezra Pound and Spatial Poetics

Ezra Pound was preoccupied with both time and space. But he developed a spatial poetics in order to transform experiences of time into intense moments of relationality and supra-historical awareness. His earlier discovery of a “method of Luminous Detail” was further confirmed by Ernest Fenollosa’s theory of the ideogram. What interested Pound was the superposition of historical and cultural meanings in the present, or, more precisely, in the textual present of the Cantos. It is not that Pound wanted to suppress time; superposition is for him simply the mode of being in the present, which is compounded into the same process of transmission, mediation, translation, and rewriting. Pound’s ideograms slow down the monolinear movement of narrative to allow more complex patterns of awareness and modes of interaction to emerge among the images, facts, and details of a given Cantos sequence.

Pattern Reshaping of the Third Resonant Mode of Dipole and Slot Using Parasitic Elements

A simple approach for radiation pattern reshaping of the 3rd mode of dipole and slot antennas is proposed. Short parasitic strips or slots are added to both sides of the dipole or slot antenna. In the 3rd mode, the reversed current or E-field will destroy the omnidirectivity or bidirectivity of these two antennas. But, the induced current or E-field on the parasitic elements is opposite to that on the original antenna canceling the effect of the reversed current or E-field. As a result, the radiation patterns of the dipole and slot in the 3rd mode are reshaped to be omnidirectional or bidirectional, respectively. The effects of parasitic element length, spacing and position on radiation pattern have also been studied. Besides, it is proved that parasitic loops have the same effect. For simplifying impedance matching, a novel feeding method for slot antenna is designed specially without using lumped element. Two prototypes, dipole and slot antennas with parasitic elements, were fabricated and tested to validate the concept. The measured results are in good agreement with the simulated ones. The measured patterns of the 3rd mode are shaped with lower sidelobes and high realized gains. In both the 1st and 3rd modes, the dipole and slot antennas realize omnidirectional and bidirectional radiations, respectively.

Bottom‐Current Variability and the Relationship With Topography and Sedimentary Processes in the Drake Passage

AbstractBottom‐current related sediments have been commonly used for paleoceanographic reconstructions. However, the strength and variability of bottom currents are poorly understood and thus the processes that control sedimentation in deep environments are not clear. In this study, we focus on the Drake Passage, which is connected to the Antarctic Circumpolar Current, that has a major impact on the global climate. We studied the intensity and variability of bottom currents and how they are related to sedimentary processes. For this purpose, we used 27‐years from GLORYS12 Mercator Ocean reanalysis at high resolution to evaluate the bottom current dynamics. Geophysical data and surface grain size measurements were used to identify the type of sediment deposits. Our results show that the dynamics of bottom currents is disconnected from the sea surface dynamics, and bottom circulation is strongly controlled by the rough topography of the Drake Passage. The patterns for the first modes of bottom‐current variability are related to the local topography and seem to generally control the distribution of contourites. The second and third EOF modes show patterns in the bottom currents that differ from the mean field, and they may affect the rate of erosion and deposition differently. Time series of bottom currents reveals multiple high‐speed current events, but contourite drifts seem to accumulate preferentially in zones of slow and stable bottom currents. Our study highlights the potential of using ocean reanalysis to better constrain bottom currents in zones of scarce data and to plan future campaigns of direct measurements.

Interdecadal variation and possible causes of summer extreme precipitation over northern Xinjiang province, northwestern China

Using daily precipitation data from 25 stations, NCEP/NCAR reanalysis data, and 12 climate indices for boreal summers from 1963 to 2017, we investigate the interdecadal variation and causes of extreme precipitation in northern Xinjiang Province (NXJ), northwestern China. The summer frequency of daily precipitation extremes (DPEs), summer precipitation from DPEs, and contribution of precipitation from DPEs to total summer precipitation have increased significantly since the early 1990s, and this increase in extreme precipitation is more intense at stations in the eastern part of NXJ. Comparing the periods 1963–1988 and 1992–2017, the anomalous circulation over the Mongolian Plateau changed from cyclonic to anti-cyclonic, and the center of the anomalous cyclonic circulation over Central Asia shifted northward from the Iranian Plateau to the Aral Sea. These changes in anomalous circulation pattern induced changes in the paths of water vapor transport and the distribution of moisture convergence, which explain well the interdecadal increase in extreme precipitation and its spatial variability. Further analysis confirms evident impacts of the Indian Ocean basin mode (IOBM) and Scandinavia teleconnection pattern on the development of anomalous circulation related to the interdecadal increase in extreme precipitation. A positive IOBM favors the northward transport of moisture from the northern Indian Ocean to Xinjiang Province and the development of anomalous cyclonic circulation over Central Asia in the middle and upper troposphere. The negative phase of the Scandinavia pattern, which has prevailed since the late 1970s, and the enhanced out of phase connection between the anomalous circulation over Scandinavia Peninsula and the West Siberia during 1992–2017 favors the development of anomalous anti-cyclonic circulation over the Mongolian Plateau.

Mitigation of transverse mode instability by heat-load modulation.

We present the first experimental realization of a new mitigation strategy for TMI based on controlling the phase shift between the modal intensity pattern and the thermally induced refractive index grating. If specific modulation parameters are applied while pulsing the seed and/or pump radiation, the direction of energy transfer is forced from the higher-order modes into the fundamental mode. In this way, the fiber amplifier can operate at an average output power significantly higher than the TMI threshold with a diffraction-limited beam profile. A stable beam profile is observed at an average output power that is 83% higher than the TMI threshold of the free-running system, with an intra-burst average power that is 4.15 times higher than the TMI threshold.

Stylistic Features of Church Music After Dimitrie Cunțanu, a Default Typology

"Present both in the melodies recorded by Dimitrie Cunțanu and in the melodies that we find in the oral tradition, modal constructions represent melodic molds for defining the central Transylvanian musical style. The correct framing of a melodic line is achieved by means of the scale, the cadential system and the melodic formulae. The ecclesiastical musical style according to Cunțanu, which was derived s from the Byzantine musical tradition, has become an individual style among ecclesiastical musical styles by uniquely assimilating various musical elements from folklore, music of the related cults, cultic music, and entertainment music. The resulting modal patterns have created a church style specific to the intra-Carpathian area, which has ossified into an autochthonous musical tradition. Indexing the modal constructions gives us an overview of the internal structures that underlie and individualize each mode. Keywords: melodic formulas, Dimitrie Cunțanu, default typology"

Dynamical controllable optical device designed by tunable graphene nanostructures in a PIT structure

Plasmonically induced transparency (PIT) is the classical counterpart of the Electromagnetically induced transparency (EIT) as a quantum nonlinear phenomenon that is achievable in metamaterial structures. In recent years, considerable research has been dedicated to metamaterials for the realization of PIT. Graphene metamaterials have drawn significant attention as a research area due to their unique characteristics, such as surface conductivity tunability by gate electrical biasing. Unlike the EIT effect, the PIT phenomenon is usually achieved between two resonators via near-field coupling without applying any pump. The distance between the two resonators is a vital parameter in PIT. The variation in the coupling strength requires physical parameter reformation of the PIT structure or material change. Here, two bright and dark resonators are utilized. By engineering the electrical field pattern of the bright resonance mode, the coupling strength dynamically changes. For this purpose, three graphene nanostrips as an adjustable quantum structure are used to form a bright resonator, and the quantum confinement of the carriers controls the coupling strength. In addition, the PIT quality factor is engineered from 33.87 for the quantum barrier case to 69.9 for the quantum-well case. Therefore, the coupling strength between the bright and dark resonators can be managed without any geometrical or material changes.

Fracture load of ultrathin occlusal veneers: Effect of thickness and surface conditioning

ObjectiveThis in-vitro study is planned to analyze the effect of different thicknesses of ceramic occlusal veneers and different surface treatments on fracture resistance. Materials and methodsA total of 48 sound mandibular molars are anatomically prepared from the occlusal surface with two different thicknesses (1.0 and 0.5 mm). CAD/CAM zirconia-reinforced glass ceramic blocks (Vita Suprinity) are used for fabricating occlusal veneers. The teeth are randomly divided into two primary groups A and B (n=24) according to occlusal veneer thickness. Each group is subdivided according to surface conditioning into three equal subgroups (n=8)—subgroup HF: etching with hydrofluoric acid and ceramic primer application; subgroup APF: etching with acidulated phosphate fluoride and ceramic primer application; subgroup EP: conditioning with etch and prime only. Dual-cure adhesive resin cement (Multilink Automix) is utilized to adhesively bond the veneers. All specimens are subjected to 240,000 cycles of dynamic load aging prior to the fracture resistance test. The fracture resistance is measured in Newton (N). The Failure mode patterns are analyzed and categorized using a scanning electron microscope (SEM). The results are analyzed using a two-way ANOVA with Bonferroni's Post-Hoc test, followed by a one-way ANOVA for each factor. That is in addition to one-way ANOVA for surface treatment under each thickness, each followed by Bonferroni's Post-Hoc test. Then, a T-test is used to compare the two thicknesses under each surface treatment. All tests are set at 0.05 significance level. ResultsThe two-way ANOVA test revealed that restoration thickness and surface treatment both significantly affect the fracture resistance values (p<0.05). The highest fracture resistance mean (2672±216N) is obtained from HF at 1.0 mm thickness, while the lowest mean (2104±299N) is obtained from APF at 0.5 mm thickness. ConclusionAll test groups, regardless of thickness, demonstrated fracture resistance values that exceeded both normal and parafunctional bite forces. The veneers that bonded after hydrofluoric acid etching followed by ceramic primer application showed more favourable fracture patterns.

A health-promoting role of exclusive breastfeeding on infants through restoring delivery mode-induced gut microbiota perturbations.

The establishment of human gut microbiota in early life is closely associated with both short- and long-term infant health. Delivery mode and feeding pattern are two important determinants of infant gut microbiota. In this longitudinal cohort study, we examined the interplay between the delivery mode and feeding pattern on the dynamics of infant gut microbiota from 6 weeks to 6 months post-delivery in 139 infants. We also assessed the relationship between infant respiratory infection susceptibility and gut microbial changes associated with delivery mode and feeding pattern. At 6 weeks postpartum, the composition and structure of gut microbiota of cesarean section-delivered (CSD) infants differed from those of vaginally delivered (VD) infants, with decreased Bacteroides and Escherichia-Shigella and increased Klebsiella, Veillonella, and Enterococcus. At 6 months postpartum, these delivery mode-induced microbial shifts were restored by exclusive breastfeeding, resulting in similar gut microbial profiles between VD and CSD infants who were exclusively breastfed (P = 0.57) and more variable gut microbial profiles between VD and CSD infants who were mixed fed (P < 0.001). We identified that the VD-associated genera were enriched in healthy infants, while the CSD-associated genera were enriched in infants who suffered from respiratory infections. Our findings indicate that exclusive breastfeeding may play a health-promoting role by reducing infant respiratory infection susceptibility through the restoration of gut microbiota perturbations caused by cesarean section.

Simultaneous manipulation of spatial fundamental and harmonic electromagnetic waves by microwave nonlinear metasurfaces.

In the area of manipulating the spatial electromagnetic (EM) waves fields, the metasurfaces have become much more attractive and powerful in recent years. Here, we propose a design to realize the simultaneous control of spatial fundamental and harmonic EM waves applying nonlinear metasurfaces in microwave band. The proposed meta-atom composed of three topological layers which are transmitting antenna, nonlinear wave guiding and receiving antenna respectively. And the critical factor of generating the harmonic is the nonlinear chip which is integrated into the middle layer. The microstrip power divider and phase shifter in each meta-atom are preciously tailored to actualize the spatial control of the fundamental and harmonic transmission beams in the far field. One prototype of the nonlinear metasurfaces is fabricated and corresponding radiation patterns of fundamental and harmonic modes are observed very well in the experience that can verify the validity of our proposed method.

An Internal Defect Detection Algorithm for Concrete Blocks Based on Local Mean Decomposition-Singular Value Decomposition and Weighted Spatial-Spectral Entropy.

Within the scope of concrete internal defect detection via laser Doppler vibrometry (LDV), the acquired signals frequently suffer from low signal-to-noise ratios (SNR) due to the heterogeneity of the concrete's material properties and its rough surface structure. Consequently, these factors make the defect signal characteristics challenging to discern precisely. In response to this challenge, we propose an internal defect detection algorithm that incorporates local mean decomposition-singular value decomposition (LMD-SVD) and weighted spatial-spectral entropy (WSSE). Initially, the LDV vibration signal undergoes denoising via LMD and the SVD algorithms to reduce noise interference. Subsequently, the distribution of each frequency in the scan plane is analyzed utilizing the WSSE algorithm. Since the vibrational energy of the frequencies caused by the defect resonance is concentrated in the defect region, its energy distribution in the scan plane is non-uniform, resulting in a significant difference between the defect resonance frequencies' SSE values and the other frequencies' SSE values. This feature is used to estimate the resonant frequencies of internal defects. Ultimately, the defects are characterized based on the modal vibration patterns of the defect resonant frequencies. Tests were performed on two concrete blocks with simulated cavity defects, using an ultrasonic transducer as the excitation device to generate ultrasonic vibrations directly from the back of the blocks and applying an LDV as the acquisition device to collect vibration signals from their front sides. The results demonstrate the algorithm's capacity to effectively pinpoint the information on the location and shape of shallow defects within the concrete, underscoring its practical significance for concrete internal defect detection in practical engineering scenarios.

Optimization of Vibration Parameters for Red Jujube Trees with Different Diameters

Vibratory harvesting is the primary method used to harvest red jujubes. This study aimed to improve the efficiency of vibratory harvesting for red jujubes and identify the optimal parameters for harvesting at different jujube tree diameters. A model for the forced vibration dynamics of jujube trees was established, and a three-dimensional model was constructed for different diameter variations. A kinematic simulation analysis was then conducted to determine the inherent frequency and modal vibration patterns of jujube trees. Harmonic response analysis was performed to study the displacement and acceleration responses of jujube trees with different diameters to different vibration factors. Subsequently, vibration tests were carried out on the jujube trees. The results showed that the vibration characteristics of trees with different diameters were distinct at each vibration order, and the maximum number of vibrating branches differed at different orders of vibration. The vibration frequency ranges for vibration harvesting of jujube trees with 30 mm, 50 mm, and 70 mm diameters were determined as 4–30 Hz, 6–25 Hz, and 17–29 Hz, respectively. Furthermore, the study obtained the optimal vibration parameters for jujube trees by establishing the regression equations of harvest rate and each vibration factor. For jujube trees with a diameter of 30 mm, the optimal parameters included a vibration frequency of 30 Hz and a vibration amplitude of 15 mm. For jujube trees with a diameter of 50 mm, the optimal parameters included a vibration frequency of 18.55 Hz and a vibration amplitude of 12.52 mm. Lastly, for jujube trees with a diameter of 70 mm, the optimal parameters included a vibration frequency of 6 Hz and a vibration amplitude of 15 mm. This study provides a theoretical foundation and technical support for improving the efficiency of vibratory harvesting and identifying the optimal vibration harvesting parameters for jujube trees with different diameters.

Incumbent entry modes and entry timing in sustainable niches: The plant-based protein transition in the United States, Netherlands, and United Kingdom

While literature on sustainability transitions has generally portrayed incumbent firms as reluctant to engage in sustainable niches and primarily employing strategies that aim to limit niche growth, practice offers many examples that contradict this. In this paper, we mobilize insights from organizational literature, and particularly the concept of entry modes and entry timing from the international business and strategy literature, to investigate incumbent firms’ engagement in sustainable niches through the introduction of new products, collaborative efforts with new entrants, the introduction of new brands, mergers & acquisitions, and investments. We focus on entry modes of incumbent firms, including food firms, meat processors, retailers, and food service firms, in meat substitute markets in the United States (US), the Netherlands (NL), and the United Kingdom (UK). We identify distinct entry mode patterns for the four firm types and that the entry modes of different types of incumbent firms vary in their timing and commitment towards the plant-based meat substitute niche. Contrary to the general consensus stemming from previous literature on incumbent engagement in transitions, our case shows that incumbents proactively engaged with niche products incentivized by economic opportunities stemming from changing consumption patterns, which preceded any regulatory action.

An optical study of the combustion and flame development of ammonia-diesel dual-fuel engine based on flame chemiluminescence

Under the background of the “carbon peak and carbon neutrality”, the development and utilization of zero-carbon fuels, represented by green ammonia and green hydrogen, has gained attention from all walks of life. Among them, the problems of transportation and storage of hydrogen restrict its industrial development, while ammonia has significant advantages as a suitable hydrogen energy carrier for the power systems. The ammonia-diesel dual-fuel engine enables the mixture to be stratified in a time-activated multi-point ignition mode to promote efficient and clean combustion of ammonia. To investigate the combustion and flame development of the ammonia-diesel dual-fuel engine, an optical diagnostic study was carried out on a self-refit dual-fuel optical engine. The results show that the combustion inertia and lower flame temperature of ammonia can inhibit combustion and lead to lower cyclic heat release in the ammonia-diesel dual-fuel combustion (ADDC) mode, which in turn reduces the indicated mean effective pressure (IMEP). Different from the yellow-white flame produced by the high-temperature soot radiation in pure diesel combustion (PDC) mode, the flame in the ADDC mode appears orange. The peak of flame area (FR) percentage and flame natural luminosity (FNL) of the 80% ammonia ratio ADDC mode decrease by 60% and 92%, respectively, compared to the peaks at PDC mode. The ammonia combustion flame is mainly concentrated around the diesel flame, and at the same time achieves good ignition performance at all ammonia ratios. In contrast to the PDC mode where the FR and FNL decrease rapidly as the diesel injection timing (DIT) advances, the flame pattern of the ADDC mode does not respond significantly to the DIT.