Slow Propagation Research Articles

Process-Based Evaluation of Intraseasonal Oceanic Kelvin Waves in the Pacific Ocean in CMIP6 Models

Abstract Oceanic intraseasonal Kelvin waves (KWs) help modulate upper-ocean thermal characteristics, providing feedbacks to important coupled air–sea phenomena in the tropics. The recent availability of daily thermocline depth fields from several phase 6 of the Coupled Model Intercomparison Project (CMIP6) models makes it possible to evaluate the performance of KWs and identify potential sources of bias. Most models fail to simulate a realistic spatial distribution of KW variability. Models simulate a large variability of KWs in the western or eastern Pacific rather than in the central Pacific as observed. The modeled KWs propagate slowly (about 1.5 m s−1) compared to observations (about 2.5 m s−1). This slow propagation is also identified in wavenumber–frequency spectra for KWs and meridional KW structures, which is more consistent with a second baroclinic mode structure in models compared to the first baroclinic mode structure in observations. An analysis of the relative contributions of the vertical wavenumber and background ocean stability to KW phase speeds indicates that the high vertical wavenumber bias in models contributes most to the slow propagation, in which the higher-than-observed vertical wavenumbers imply the biased incorporation of higher baroclinic modes in the model KW structure. This finding is further supported by the results of vertical mode decomposition that incorporates background density profiles. These results indicate that a realistic representation of the KW vertical structure is essential to produce realistic KW propagations in models. Significance Statement Oceanic intraseasonal Kelvin waves (KWs) play a significant role in regulating the heat content and temperature of the ocean, which provides feedbacks to coupled ocean–atmosphere phenomena in the tropics such as El Niño–Southern Oscillation (ENSO). Consequently, identifying the biases in KWs and the potential sources of those biases in state-of-the-art models is essential to improve simulations of ENSO and its diversity and advance forecasts of weather extremes around the globe induced by ENSO. We find that KWs in the models propagate slower than observations, mainly due to biases in their vertical structure, with secondary effects due to biases in model ocean stability. These issues may be potential sources for current imperfect ENSO model simulations and predictions.

Numerical investigation on the effect of ignition timing on a low-temperature hydrogen-fueled Wankel rotary engine with passive pre-chamber ignition

Adopting the low-temperature hydrogen evaporated from the liquid hydrogen is capable of improving volumetric efficiency for the Wankel rotary engine (WRE). Considering the difficulty in ignition and slow flame propagation of low-temperature hydrogen-air mixtures, the passive pre-chamber is used to improve ignition and combustion. A three-dimensional computational fluid dynamics model for a turbulent jet ignition (TJI) WRE fueled by low-temperature hydrogen was established. The effects of low temperature and TJI on the in-cylinder flow field, combustion, emissions and leakage in the TJI-WRE fueled by low-temperature hydrogen were studied under different ignition timings. The results indicated that low-temperature tends to suppress the flame propagation, whereas TJI can accelerate the flame speed and promote flame propagation to the unburned zone in the combustion chamber. Combining low-temperature hydrogen with the passive pre-chamber can achieve high engine thermal efficiency and power while significantly reducing leakage. With the ignition timing set at 18 °CA before the top dead center, the indicated thermal efficiency reached 39.49% and the indicated mean effective pressure peaked at 0.77 MPa. Compared to the original engine, fresh mixture leakage through spark plug cavities and adjacent chambers was reduced by 72.13% and 78.79%, respectively.

Effects of water sprays on hydrogen autoignition in heated air

The effects of water mist with different diameters and mass loadings on hydrogen auto-ignition in air with elevated temperatures and pressures are studied. It is shown that smaller droplets with larger mass loading are the most effective in inhibiting the auto-ignition process. Under elevated initial pressures and temperatures, the role of water mist in impacting auto-ignition is minimal, primarily because the ignition delay is substantially shorter than the droplet evaporation duration. As the initial temperature decreases, there exists a temperature value below which water mist markedly extends the ignition delay time, even escalating it by up to two orders of magnitude or causing a complete suppression of ignition. The rate of production for important radicals was analyzed. The data indicates that the evaporation of the water mist lowers the initial temperature, leading to a reduction in the rate of the temperature-sensitive fast chain branching reaction. In contrast, the third body reaction that generates HO2 is not sensitive to temperature. Meanwhile, the introduction of H2O results in an earlier activation of the third body reactions. Consequently, the production of HO2 is enhanced, emphasizing the role of subsequent slow chain propagation reactions that generate OH, thereby extending the ignition delay. By deactivating the mass transfer between two phases and introducing artificial species, it is evident that water vapor dilution and thermal effects predominantly influence the ignition delay, while its role as a direct reactant is minimal.

A Workflow for Creating Gastric Computational Models from SPARC Scaffolds

In-silico studies are an ideal medium to model and improve our understanding of the mechanisms underlying gastric motility in health and disease. In this study, a workflow to create computational models of the stomach was developed using SPARC scaffolds. Three anatomically based finite element method (FEM) models of the rat stomach incorporating experimental measurements of muscle layer thickness and fiber orientations across the stomach were developed: (i) 2D (surface) FEM model with no thickness, (ii) 3D (volume) FEM model with a fixed thickness across the longitudinal and circular muscle layers, and (iii) 3D (volume) FEM model with varying thickness across the longitudinal and circular muscle layers. The three FEM models were subsequently used in whole-organ slow wave simulations and the impact of anatomical details on the simulation outcomes was investigated. The 3D FEM model with varying thickness was the most computationally expensive, while the 2D FEM model provided the fastest solution (a 200 s simulation took 8 min vs. 38 h to solve). The spatiotemporal profiles of the slow wave activation and propagation in the three FEM models were in good agreement. The largest temporal difference of 1 s in cellular activation was observed between the 2D FEM model and the varying thickness 3D FEM model in the most distal-stomach regions. These FEM models and developed workflow will be used in in-silico studies to improve our understanding of the structure-function relationship in the stomach and identify the optimal parameters of electrical therapies, an alternative treatment for the motility disorders in the stomach. In addition, the developed workflow can be readily used to generate computational models of other organs using SPARC scaffolds.

Combining Imaging and Electrophysiology to Visualize and Record Spreading Depolarizations in Mice.

Spreading Depolarizations (SDs) are massive events in the brain that often go undetected due to their slow propagation through gray matter. Because SD detection can be elusive, it is optimally confirmed using multiple methods. This protocol describes methods for combining imaging and electrophysiology to detect SDs in a manner that most laboratories can reliably and easily adopt. SDs occur following traumatic brain injuries, stroke, subarachnoid hemorrhages, ischemia, and migraine aura. Historically, SDs have been recorded using DC amplifiers, which can resolve the slow extracellular shift and the depression in high-frequency activity. However, DC amplifiers are nearly impossible to use for chronic in vivo recordings. This protocol employs a common AC amplifier for in vivo electrophysiology recordings to confirm high-frequency depression, along with non-invasive imaging necessary to detect the propagating wave of SD. These methods can be reliably adopted and/or modified for most experimental approaches to confirm the presence or absence of SDs following brain injury.

Explaining slow seizure propagation with white matter tractography.

Epileptic seizures recorded with stereo-EEG can take a fraction of a second or several seconds to propagate from one region to another. What explains such propagation patterns? We combine tractography and stereo-EEG to determine the relationship between seizure propagation and the white matter architecture and to describe seizure propagation mechanisms. Patient-specific spatiotemporal seizure propagation maps were combined with tractography from diffusion imaging of matched subjects from the Human Connectome Project. The onset of seizure activity was marked on a channel-by-channel basis by two board-certified neurologists for all channels involved in the seizure. We measured the tract connectivity (number of tracts) between regions-of-interest pairs among the seizure onset zone, regions of seizure spread and non-involved regions. We also investigated how tract-connected the seizure onset zone is to regions of early seizure spread compared with regions of late spread. Comparisons were made after correcting for differences in distance. Sixty-nine seizures were marked across 26 patients with drug-resistant epilepsy; 11 were seizure free after surgery (Engel IA) and 15 were not (Engel IB-Engel IV). The seizure onset zone was more tract-connected to regions of seizure spread than to non-involved regions (P < 0.0001); however, regions of seizure spread were not differentially tract-connected to other regions of seizure spread compared with non-involved regions. In seizure-free patients only, regions of seizure spread were more tract-connected to the seizure onset zone than to other regions of spread (P < 0.0001). Over the temporal evolution of a seizure, the seizure onset zone was significantly more tract-connected to regions of early spread compared with regions of late spread in seizure-free patients only (P < 0.0001). By integrating information on structure, we demonstrate that seizure propagation is likely to be mediated by white matter tracts. The pattern of connectivity between seizure onset zone, regions of spread and non-involved regions demonstrates that the onset zone might be largely responsible for seizures propagating throughout the brain, rather than seizures propagating to intermediate points, from which further propagation takes place. Our findings also suggest that seizure propagation over seconds might be the result of a continuous bombardment of action potentials from the seizure onset zone to regions of spread. In non-seizure-free patients, the paucity of tracts from the presumed seizure onset zone to regions of spread suggests that the onset zone was missed. Fully understanding the structure-propagation relationship might eventually provide insight into selecting the correct targets for epilepsy surgery.

Numerical simulation of mechanical properties and damage process of carbon nanotube concrete under triaxial compression and splitting conditions

To investigate the mechanical properties and failure processes of carbon nanotube concrete, a three-dimensional meso-scale finite element model of concrete was constructed. Using ABAQUS software, numerical simulations were conducted on concrete samples with different carbon nanotube concentrations under triaxial compression and splitting conditions. The results indicate that under splitting conditions, the failure of the specimens initially occurs along the loading direction from both ends, with few cracks and slow propagation. Subsequently, the cracks rapidly expand, penetrating the entire specimen, leading to the formation of a macro-fracture surface with a crack aligned with the loading direction. This failure mode manifests as a straight crack. At the same loading rate, the tensile strength of the specimens with different carbon nanotube concentrations increases to varying degrees during splitting failure, with a maximum increase of 45.10% to 4.15 MPa. nder triaxial compression conditions, the main failure mode of the specimens exhibits shear failure characteristics. As the confining pressure gradually increases, the failure angle of the specimens enlarges. Under low confining pressure, there are fewer wing-shaped tensile cracks at the shear failure surface of the specimens. As the confining pressure increases, irregular shear failures and multiple shear planes appear in the specimens, resulting in more complex failure modes. For specimens with the same carbon nanotube concentration, the triaxial compressive strength of carbon nanotube concrete specimens increases with increasing confining pressure. The triaxial compressive strengths of the specimens under confining pressures of 5 MPa, 10 MPa, 15 MPa, and 20 MPa are 90.48 MPa, 122.72 MPa, 137.22 MPa, and 172.65 MPa, with strength increases of 35.63%, 51.66%, and 90.81%, respectively.

Azimuthally Modulating Surface Plasmon Polaritons

Abstract We suggest a scheme for the lossless excitation of surface plasmon polaritons (SPPs) at a metal-dielectric interface using a Laguerre Gaussian (LG) beam. We consider a three-layer structure consisting of a top transparent medium, a middle metal thin film, and a dielectric bottom layer. The dielectric medium contains three-level atoms exhibiting electromagnetically induced transparency (EIT). By applying a control field, a LG beam, and a microwave field, we induce azimuthally varying permittivity, which leads to the azimuthal modulation of SPPs. The propagation length of SPPs is increased when excited by a LG beam carrying optical angular momentum (OAM). Moreover, the group velocity of SPPs can be effectively controlled by adjusting the OAM and azimuthal angle of the LG beam, allowing for both slow and fast propagation of SPPs.

Mouse polyomavirus infection induces lamin reorganisation.

The nuclear lamina is a dense network of intermediate filaments beneath the inner nuclear membrane. Composed of A-type lamins (lamin A/C) and B-type lamins (lamins B1 and B2), the nuclear lamina provides a scaffold for the nuclear envelope and chromatin, thereby maintaining the structural integrity of the nucleus. A-type lamins are also found inside the nucleus where they interact with chromatin and participate in gene regulation. Viruses replicating in the cell nucleus have to overcome the nuclear envelope during the initial phase of infection and during the nuclear egress of viral progeny. Here, we focused on the role of lamins in the replication cycle of a dsDNA virus, mouse polyomavirus. We detected accumulation of the major capsid protein VP1 at the nuclear periphery, defects in nuclear lamina staining and different lamin A/C phosphorylation patterns in the late phase of mouse polyomavirus infection, but the nuclear envelope remained intact. An absence of lamin A/C did not affect the formation of replication complexes but did slow virus propagation. Based on our findings, we propose that the nuclear lamina is a scaffold for replication complex formation and that lamin A/C has a crucial role in the early phases of infection with mouse polyomavirus.

Generation of second-order sidebands and slow–fast light in cavity magnomechanics with a parametric amplifier

In this work, we theoretically investigate the optical second-order sideband (OSS) efficiency and group delay of an output probe field in a two-coupled cavity magnomechanics (CMM) system. The setup comprises a gain (active) cavity and a passive (loss) cavity, which simultaneously includes an optical parametric amplifier (OPA) and a yttrium iron garnet sphere to facilitate magnon–photon coupling. Employing experimentally attainable parameters, we show that the presence of an OPA can significantly enhance the optical transmission rate and OSS efficiency. We show that photon–magnon strong coupling can enhance OSS efficiency substantially when compared to weak photon–magnon coupling. Our results, in particular, show that the OSS’s efficiency may be significantly improved for active–passive-coupled cavities as compared to the passive–passive cavities system. Furthermore, we demonstrate that modifying the system configurations may change the group delay, affecting the transition from rapid to slow light propagation, and vice versa. Our results provide a novel and easy approach to designing CMM devices for altering light propagation, with possible applications including optical switching, information storage, and accurate measurement of weak signals.

Simultaneous optical imaging of gastric slow waves and contractions in the in vivo porcine stomach.

Gastric peristalsis is governed by electrical "slow waves" generally assumed to travel from proximal to distal stomach (antegrade propagation) in symmetric rings. Although alternative slow-wave patterns have been correlated with gastric disorders, their mechanisms and how they alter contractions remain understudied. Optical electromechanical mapping, a developing field in cardiac electrophysiology, images electrical and mechanical physiology simultaneously. Here, we translate this technology to the in vivo porcine stomach. Stomachs were surgically exposed and a fluorescent dye (di-4-ANEQ(F)PTEA) that transduces the membrane potential (Vm) was injected through the right gastroepiploic artery. Fluorescence was excited by LEDs and imaged with one or two 256 × 256 pixel cameras. Motion artifact was corrected using a marker-based motion-tracking method and excitation ratiometry, which cancels common-mode artifact. Tracking marker displacement also enabled gastric deformation to be measured. We validated detection of electrical activation and Vm morphology against alternative nonoptical technologies. Nonantegrade slow waves and propagation direction differences between the anterior and posterior stomach were commonly present in our data. However, sham experiments suggest they were a feature of the animal preparation and not an artifact of optical mapping. In experiments to demonstrate the method's capabilities, we found that repolarization did not always follow at a fixed time behind activation "wavefronts," which could be a factor in dysrhythmia. Contraction strength and the latency between electrical activation and contraction differed between antegrade and nonantegrade propagation. In conclusion, optical electromechanical mapping, which simultaneously images electrical and mechanical activity, enables novel questions regarding normal and abnormal gastric physiology to be explored.NEW & NOTEWORTHY This article introduces a novel method for imaging gastric electrophysiology and mechanical function simultaneously in anesthetized, open-abdomen pigs. We demonstrate it by observing propagating slow-wave depolarization and repolarization along with the strength, spatial distribution, and direction of contractions. In addition, we observe that in this animal preparation, slow waves often do not propagate from the proximal to distal stomach and are frequently asymmetric between the anterior and posterior sides of the stomach.

Analysis on a five-spot well for enhancing energy recovery from silty natural gas hydrate deposits in the South China Sea

The five-spot well is a promising technique for enhancing the inherent low gas production rate from silty natural gas hydrate (NGH) reservoirs with low permeability in the South China Sea (SCS). However, the production characteristics and the responses to key geological and engineering factors are still unclear and warrants investigation. Herein, we first establish a three-dimensional reservoir model based on the SH2 NGH deposits at SCS with the implementation of a five-spot well. We systematically examine the gas production enhancement effect and the unexpected well-to-well interaction induced by long-term depressurization. A sensitivity analysis on the effects of bottomhole pressure (Pbtm), permeability (k) and hydrate saturation (SH) is conducted to elucidate the key factors controlling the gas production enhancement. Our results reveal that the five-spot well significantly improves the gas productivity with cumulative gas production increased to 4.12 times that of a single well over 10 years. The well interference on gas production is not significant in the early stage but becomes more significant as depressurization sustains. Due to the relatively slow pressure propagation at the inner well, contribution to gas production from the inner well decreases over time while the outer wells increase. Based on the sensitivity analysis, gas production increases with decreasing Pbtm, increasing k, and decreasing SH with Pbtm and k as the key controlling factors. The findings provide valuable design basis for the adoption of a multi-well system in enhancing gas production for targeted NGH reservoirs in the next field production trial at SCS.

Modelling of ICRH slow wave propagation and absorption in Wendelstein 7-X stellarator

Abstract The propagation and absorption of the slow waves in the three-ion plasma of the Wendelstein 7-X stellarator have been investigated by ray tracing. The aim of the study is to obtain a qualitative notion of the penetration into the plasma and absorption of the wave excited by the potential difference between the antenna conductors and the antenna box. It has been discovered that the rays propagate along the magnetic field lines over a significant distance, up to 6 m, from the antenna. They weakly, to a depth of 0.1 m, penetrate into the plasma. Absorption of the slow waves by electrons does not lead to the generation of the currents capable of affecting the plasma equilibrium. Most of the slow waves are absorbed beyond the region of ion-ion hybrid resonance in the zone of cyclotron resonance of He3 ions at the periphery of the plasma. The ICRH of the three-ion W 7-X plasma will be used to heat He3 ions to high energies and simulate the confinement of alpha particles in an optimized stellarator configuration. The presence of a source of hot He3 ions, which are poorly confined, at the periphery of the plasma can affect the experimental results.

Slow rupture in a fluid-rich fault zone initiated the 2024 Mw 7.5 Noto earthquake.

The 2024 moment magnitude 7.5 Noto Peninsula (Japan) earthquake caused devastation to communities and was generated by a complex rupture process. Using space geodetic and seismic observations, we have shown that the event deformed the peninsula with a peak uplift reaching 5 meters at the west coast. Shallow slip exceeded 10 meters on an offshore fault. Peak stress drop was greater than 10 megapascals. This devastating event began with a slow rupture propagation lasting 15 to 20 seconds near its hypocenter, where seismic swarms had surged since 2020 because of lower-crust fluid supply. The slow start was accompanied by intense high-frequency seismic radiation. These observations suggest a distinct coseismic slip mode reflecting high heterogeneity in fault properties within a fluid-rich fault zone.

A physical explanation for an unusually long-duration slow slip event in the Nankai Trough

The Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) and the Long Term Borehole Monitoring System (LTBMS), installed above the source region of the 1944 Tonankai earthquake, revealed that crustal deformation is driven by slow slip events (SSEs) in the shallower extension of megathrust earthquakes. However, there are unresolved questions about (A) the duration of the SSE in February 2012, which was longer than expected for SSEs with similar magnitudes, and (B) the relationship of the spatial distribution of fault slip between the SSEs in February and December 2012 under the condition of drilling disturbance. To clarify these questions, we re-analyzed the pore/seafloor pressure data associated with the SSEs. Our refined fault models show that the SSE in February had a significantly slower propagation speed and a longer duration than others, while the SSE in December was comparable to others. We interpret that the difference in duration and propagation speed is related to external and internal stress perturbations, respectively. Using the ocean modeling JCOPE (Japan Coastal Ocean Predictability Experiment), we identified that the decrease and subsequent increase in seafloor pressure due to the passage of the Kuroshio meander coincided with the latter part of the longer duration of the SSE in February and its termination, respectively. This suggests that the Kuroshio meander might affect the duration of SSEs. Our refined fault model also indicates that the amount of shear stress accumulation was small before the occurrence of the SSE in February, which triggered the slow propagation of aseismic slip based on a rate- and state-dependent friction law. These results imply that we need to consider the variety of SSEs from the viewpoint of stress perturbation due to not only interaction between fault segments but also external forces from oceanographic phenomena.

All-optically controlled mode-coupling induced transparency with tunable efficiency in a microsphere resonator.

The optical analogs of electromagnetically induced transparency (EIT) have attracted vast attention recently. The generation and manipulation of EIT in microcavities have sparked research in both fundamental physics and photonic applications, including light storage, slow light propagation, and optical communication. In this Letter, the generation and tuning of an all-optically controlled mode-coupling induced transparency (MCIT) are proposed, experimentally demonstrated, and theoretically analyzed. The MCIT effect originated from the intermodal coupling between the plethora of modes generated in our fabricated optical microcavity, and the tuning of the transparency mode utilized the cavity's thermal bistability nature. Furthermore, based on our method, a novel, to the best of our knowledge, controlling of the mode shifting efficiency is also achieved with an increase up to two times and more. The proposed scheme paves a unique, simple, and efficient way to manipulate the induced transparency mode, which can be useful for applications like cavity lasing and thermal sensing.

Intrinsic fracture toughness of a soft viscoelastic adhesive

The fracture toughness of inelastic materials consists of an intrinsic component associated with the crack tip fracture process and a dissipative component due to bulk dissipation. Experimental characterization of the intrinsic component of fracture toughness is important for understanding the fracture mechanism and predictive modeling of the fracture behavior. Here we present an experimental study on the intrinsic toughness of a soft viscoelastic adhesive. We first obtained full-field and full-history data of the displacement and deformation fields in pure shear fracture tests using a particle tracking method. By combining these data with a nonlinear constitutive model, we extracted the intrinsic toughness through an energy balance analysis. A two-stage crack propagation behavior was observed in our fracture experiments: under monotonic loading the crack first underwent a slow propagation stage and then suddenly entered a fast propagation stage. We found that the intrinsic toughness was highly scattered for the slow propagation stage, but remained consistent for the fast propagation stage. Further examination of the fracture surface and the onset of fast propagation revealed that transition from the slow to the fast propagation stage was governed by the applied stretch and was likely due to a change in the crack tip fracture process.

Coherent manipulation of bright and dark solitons of reflection and transmission pulses through sodium atomic medium

Abstract The coherent manipulation and control of bright and dark solitons through sodium atomic medium have been investigated in this manuscript. Dark soliton is reported for reflection and bright soliton is reported for transmission pulses with variation in position and driving field parameters through sodium atomic medium. Further the transmission pulse is periodic dark and bright solitonic behaviors and reflection pulse is periodic bright solitonic behavior with variation in the incident angle and Rabi frequency of the control field. Elliptical dark and bright solitons as well as breather types solitons are also investigated for reflection and transmission pulses. The dark soliton in reflection is due to slow light propagation and bright soliton is obtained due to fast light propagation of transmission through the medium. The modified results of the dark and bright solitons are useful for telecommunication and ultra-fast signal routing system.

Probability-Based Propagation Characteristics from Meteorological to Hydrological Drought and Their Dynamics in the Wei River Basin, China

Understanding the propagation characteristics and driving factors from meteorological drought to hydrological drought is essential for alleviating drought and for early warning systems regarding drought. This study focused on the Weihe River basin (WRB) and its two subregions (the Jinghe River (JRB) and the middle reaches of the Weihe River (MWRB)), utilizing the Standardized Precipitation Index (SPI) and Standardized Runoff Index (SRI) to characterize meteorological and hydrological drought, respectively. Based on Copula theory and conditional probability, a quantification model for the propagation time (PT) of meteorological–hydrological drought was constructed. The dynamic characteristics of PT on annual and seasonal scales were explored. Additionally, the influences of different seasonal meteorological factors and underlying surface factors on the dynamic changes in PT were analyzed. The main conclusions were as follows: (1) The PT of meteorological–hydrological drought was characterized by faster propagation during the hot months (June–September) and slower propagation during the cold months (December to March of the following year); (2) Under the same level of hydrological drought, as the level of meteorological drought increases, the PT of the drought shortens. The propagation thresholds of meteorological to hydrological drought in the WRB, the JRB, and the MWRB are −0.69, −0.81, and −0.78, respectively. (3) In the dynamic changes in PT, the WRB showed a non-significant decrease; however, both the JRB and the MWRB exhibited a significant increase in PT across different drought levels. (4) The influence of the water and heat status during spring, summer, and winter on PT was more pronounced, while in autumn, the impact of the basin’s water storage and discharge status was more significant in the JRB and the MWRB.

Flame stabilization and pollutant emissions of turbulent ammonia and blended ammonia flames: A review of the recent experimental and numerical advances

Compared to traditional hydrocarbon fuels, ammonia presents significant challenges as a fuel, including high ignition energy, low reactivity, slow flame propagation, and high NOx emissions, which hinder its use as a renewable fuel. Blending ammonia with fossil fuels like natural gas improves its combustion reactivity and helps mitigate CO2 emissions. However, there is still much to understand about the complex dynamics of ammonia and its blends with hydrocarbons. Key areas such as reaction kinetics mechanisms, ignition properties, flame propagation behaviors, and methods for controlling combustion performance under various conditions require further elucidation. This paper reviews recent advancements in experiments and numerical simulations aimed at developing stable, and low-emission combustors for ammonia-fired power generation. Recent burner and flame configurations, including non-swirling jets, single-stage swirl burners, two-stage burners, and newly developed double-swirl burners are analyzed for their flame stability and pollutant emission potential when firing ammonia and ammonia blends. Chemical kinetic modeling of ammonia and its blends plays a crucial role in understanding combustion behavior and pollutant emissions, particularly for NOx. However, there are challenges in predicting NOx emissions accurately, with significant disparities among different models. High-fidelity numerical simulations using detailed and skeletal mechanisms, direct numerical simulation, and large eddy simulation, have helped uncover crucial operational conditions affecting combustion and pollutant emissions, such as combustor pressure, air dilution, wall cooling, fuel/air mixing, and fuel blending. Nonetheless, the accuracy of chemical kinetic models and their integration into turbulent flow simulations remain critical limitations for numerical simulations of ammonia combustion.