Deceleration Phase Research Articles

Ejecta width and magnetization reflected in gamma-ray burst early afterglows: implication for reverse shock component and shallow decay phase

ABSTRACT To study the ejecta property dependence of the gamma-ray burst (GRB) afterglow, we carry out spherically symmetrical one-dimensional special relativistic magnetohydrodynamic simulations of magnetized outflows with an adaptive mesh refinement method. The Lorentz factor evolutions of forward and reverse shocks induced by the interaction between magnetized ejecta and an ambient medium are investigated for a wide range of magnetization and width of the ejecta. The forward shock evolution is described by the magnetic acceleration, coasting, transition, and self-similar deceleration phases. According to our simulation results, we numerically calculate the corresponding radiation. Based on our numerical results, to model afterglow light curves in general cases, we construct semi-analytical formulae for the Lorentz factor evolutions. The magnetization and ejecta width dependence are clearly seen in the reverse shock light curves. The transition phase with a reasonable ejecta width can reproduce the shallow decay phase in the observed GRB afterglow. The inverse Compton emission in the magnetic acceleration phase can be responsible for the very steep rise of the early TeV emission in GRB 221009A.

Dynamic characteristics of wave entry for a deep-sea mining vehicle: Numerical and experimental studies

The deep-sea mining vehicle (DSMV) experiences complex impacts upon the wave entry, which directly affects the safety and reliability of the whole deployment system. In this paper, a computational fluid dynamics (CFD) method is proposed to investigate hydrodynamic properties and wave-entry effects of a DSMV with varying laying speeds. Firstly, a fifth-order Stokes surface gravity wave simulating Sea State 4 conditions is constructed based on the volume of fluid (VOF) method. Then, the overset mesh scheme is utilized to establish the multiple degree-of-freedom (DOF) model of DSMV which bears the traction loads of laying cable. Laboratory prototype tests are conducted, and the captured results of cavitation evolution and motion properties corroborate the present model. Numerical results indicate that the DSMV entering the wave danger point will experience hydrodynamic forces several to dozens of times greater, severely threatening structural safety. During the wave entry process, two phases of nonlinear deceleration occur, posing a risk to the umbilical cable. Surge and pitch motions caused by waves and structural asymmetry may lead to deployment position deviation. Based on the trends observed in the simulation data, guidance for deployment operations has been proposed.

Tracing the Propagation of Shocks in the Equatorial Ring of SN 1987A over Decades with the Hubble Space Telescope

The nearby SN 1987A offers a unique opportunity to investigate the complex shock interaction between the ejecta and circumstellar medium. We track the evolution of the optical hot spots within the equatorial ring (ER) by analyzing 33 Hubble Space Telescope imaging observations between 1994 and 2022. By fitting the ER with an elliptical model, we determine its inclination to be 42.°85 ± 0.°50 with its major axis oriented −6.°24 ± 0.°31 from the west. We identify 26 distinct hot spots across the ER, with additional ones emerging over time, particularly on the western side. The hot spots initially show high velocities ranging from 390 to 1660 km s−1, followed by a deceleration phase around day ∼ 8000. Subsequent velocities vary from 40 to 660 km s−1. The light curves of the hot spots reach maxima between 7000 and 9000 days, suggesting a connection with the deceleration. Many spots are spatially resolved and show elongation perpendicular to the direction of motion, indicative of a short cooling time. To explain these results, we propose that each hot spot comprises dense substructures embedded in less dense gas. The initial velocities are then phase velocities, where the break occurs when the blast wave leaves the ER, while the late velocities reflect the propagation of radiative shocks in the dense substructures. We estimate that the dense substructures have a volumetric filling factor of ∼0.3ne/106cm−3−2% and a total mass of ∼0.24ne/106cm−3−1×10−2M⊙ .

Acute effects of different loading protocols upon performance and kinematics of 180 degrees change of direction

ABSTRACT This study examined the acute effects of different loading protocols on 180° change of direction (COD) performance in eleven male handball players. Participants performed a 10-0-5 COD test under seven conditions: without an external load, and with 3, 6, and 9 kg loads applied under two modes—assisted into the COD and resisted out of it and resisted into the COD and assisted out of it. While total COD time was not affected (p = 0.098; η2 = 0.16), significant phase effects were observed (p < 0.001; η2 ≥ 0.55). Loading protocols significantly influenced velocity, acceleration, and their distances from COD (p < 0.001; η2 ≥ 0.37). Significant phase effects were observed for all step kinematic variables (p ≤ 0.037; η2 ≥ 0.67), except contact time, and significant interaction (phase*condition) effects for all variables (p ≤ 0.004; η2 ≥ 0.08), except for step frequency. Assisted-resisted protocols increased deceleration demands through higher COD entry velocities, displaying fewer but longer steps in the acceleration phase and greater steps taken during the deceleration phase. Resisted-assisted protocols decreased deceleration demands due to lower COD entry velocities, displaying shorter, but more steps taken in the acceleration phase, and fewer steps taken in the deceleration phase. These findings suggest that assisted-resisted and resisted-assisted loading protocols can be used to selectively overload specific phases of COD performance.

Shared body representation constraints in human and non-human primates behavior

Previous studies indicated that the sense of body ownership (i.e., the feeling that our body parts belong to us; SBO) can be experimentally modulated in humans. Here, we focused on SBO from an across-species perspective, by investigating whether similar bottom-up and top-down constraints that consent to build SBO in humans also operate to build it in monkeys. To this aim, one monkey and a cohort of humans (N = 20) performed a paradigm combining the well-known rubber hand illusion (RHI), able to induce a fake hand embodiment, and a hand-identification reaching task, borrowed from the clinical evaluation of patients with SBO disorders. This task consisted of reaching one’s own hand with the other, while presenting a fake hand in different conditions controlling for bottom-up (synchronicity of the visuo-tactile stimulation) and top-down (congruency of the fake hand position relative to the monkey’s body) SBO constraints. Spatiotemporal kinematic features of such self-directed movements were measured. Our results show that, when the monkey aimed at the own hand, the trajectory of self-directed movements was attracted by the position of the hand believed to be one’s own (i.e., the fake hand), as in humans. Interestingly, such an effect was present only when both bottom-up and top-down constraints were met. Moreover, in the monkey, besides displacement of movement trajectory, also other kinematic parameters (velocity peak, deceleration phase) showed sensitivity to the embodiment effect. Overall, if replicated in a larger sample of monkeys, these results should support the view that human and non-human primates share similar body representation constraints and that they are able to modulate the motor behavior in both species.

Constraining the equation of state parametrization in Hořava-Lifshitz gravity

In this paper, we investigate the late-time cosmic accelerated expansion using various equations of state parametrizations within the framework of Hořava-Lifshitz gravity. We utilize Markov Chain Monte Carlo (MCMC) analysis to constrain the parameters of each proposed model, employing observational Hubble data and Type Ia supernovae. Additionally, we analyze and plot the deceleration parameters for each model. Our findings suggest that the Universe has recently transitioned from a phase of deceleration to acceleration in all the models considered. We also analyzed the behavior of the energy conditions for each proposed model within the framework of Hořava-Lifshitz gravity, specifically at the present epoch (z=0). To further assess the effectiveness of these models, we apply both the Akaike Information Criterion (AIC) and the Bayesian Information Criterion (BIC) to compare their performance against the standard ΛCDM model. Our results provide valuable insights into how different models perform relative to ΛCDM, offering a comprehensive evaluation of their viability in describing the Universe's accelerated expansion.

Investigation on decelerated propagation of hydrogen-air premixed flames in confined space

This study investigates the flame propagation characteristics of hydrogen-air mixture explosion in confined spaces through a small-scale experiment and simulations, in which the experiment were conducted at normal temperature and pressure, covering a wide range of equivalence ratios (0.8–3.5) to obtain flame evolution and propagation velocity. The results indicate that enhanced thermal-diffusive instability leads to an increased cellular structure in hydrogen-air flames, with flame propagation speed increasing with radius enlargement; the numerical simulation results demonstrate that flame propagation speed is generally divided into acceleration, deceleration, and weak rebound phases; flame deceleration is mainly caused by increased pressure and wall constraints. The flame deceleration critical radius (Rcr) exhibits a trend of initially decreasing and then increasing with increasing equivalence ratio, primarily due to the influence of the pressure rise rate, while the magnitude of the deceleration factor is not directly related to the equivalence ratio. Additionally, an empirical formula summarizing the relationship between flame propagation speed during the deceleration phase, laminar burning velocity, and pressure is as follows: v=2.7∙SL0∙(P/P0)-0.48.

Analysis of Influential Parameters in the Dynamic Loading and Stability of the Swing Drive in Hydraulic Excavators

The proper design and configuration of the swing drive mechanism of a hydraulic excavator are crucial to improve energy consumption and efficiency and ensure operational stability. This paper analyzes the influence of the relationship between the parameters of a hydraulic motor and a reducer, which form the integrated transmission of a swing drive, the dynamic characteristics of a hydraulic excavator on loading, and the dynamic stability of the drive. The analysis deals with an excavator model that has the same parameters of the kinematic chain members, the same parameters of the upper structure drive mechanisms, and two variants of the swing drive that, with different integrated transmission parameters, provide the upper structure with the identical number of revolutions and equal rotating moment. One swing drive variant possesses an integrated transmission with a hydraulic motor with a low specific flow and a reducer with a high transmission ratio, while the other drive variant has the opposite parameters. Understanding this relationship is essential for optimizing the design of excavators to achieve better performance and dynamic stability under varying operational conditions. As an example, this paper provides the analysis results regarding the influence of the relationship between the parameters of the integrated transmission hydraulic motor and reducer on the loading and dynamic stability of the swing drive in a tracked hydraulic excavator of 100,000 kg in mass and 4.4 m3 in loading bucket volume, as obtained from the developed dynamic mathematical models of the excavator using the MSC ADAMS program. The results indicate that the dynamic loads on the swing drive’s axial bearing are higher in the variant with a low-specific-flow motor and high transmission ratio reducer during the acceleration and deceleration phases. However, this configuration demonstrated better dynamic stability, with lower oscillation amplitudes and shorter damping times compared to the variant with a high-flow motor and low transmission ratio. Those findings provide valuable criteria for the optimal synthesis of swing drive mechanisms in large hydraulic excavators using multi-criteria optimization methods.

WITHDRAWN: Surging dynamics of unnamed glaciers at the Abi Gamin Peak in the central Himalayas

Surge-type glaciers in the Himalayas have been extensively documented, however, understanding of the mechanisms behind glacier surges remain limited. Herein, based on multi-source remote sensing data, we systematically investigated the characteristics and subglacial processes of the unnamed glacier at Abi Gamin Peak in central Himalayas. Our approach integrated optical stereo photogrammetry, feature tracking, visual interpretation, and glacier velocity decomposition. Our study reveals that the glacier surge was initiated in August 2019 and lasted for less than six months, with rapid acceleration and deceleration phases. During the surge, the glacier transported approximately 0.233 km3 of mass from higher to lower elevations, leading to a thickness increase of >70 m at the glacier terminus. The glacier terminus advanced by >800 m, accompanied by significant expansion of the crevasses. Furthermore, we quantitatively revealed the evolution of basal stresses, strain rates, and sliding velocities during the surge, indirectly characterising the influence of water on it. We contend that the surge in this glacier was primarily driven by subglacial sliding induced by glacier surface meltwater. Significant changes in regional climate serve as external factors that perturb the glacial dynamic equilibrium. The observed characteristics of the unnamed glacier at Abi Gamin Peak indicate that its surge was controlled by a hydrological switch. Notably, our work contributes to an enhanced understanding of glacier surge mechanisms in High Mountain Asia.

Numerical Investigation of the Fuel Tank Sloshing Condition of a Commercial Vehicle

This study investigates the impact of baffles on fuel sloshing behavior within truck fuel tanks using numerical simulations. The volume of the fluid multiphase model is employed to analyze the flow dynamics of 25% diesel fuel in a 250 L tank, modeled in a 3D domain. Two configurations were compared: a tank with baffles and one without. The primary focus is to analyze fuel distribution within the intake port region during vehicle acceleration and deceleration maneuvers. The simulated scenario mimics a realistic driving situation. The vehicle accelerates from 0 km/h to 60 km/h over 10 s, followed by a 3-s braking period to reach a complete stop (0 km/h) at the 13-s mark. The simulation then observes the fuel behavior within the tank for an addi-tional 7 s while the vehicle remains stationary. Results reveal significant differences in fuel behavior between baffled and unbaffled tanks. In the absence of baffles, the sloshing motion is substantial, leading to a complete depletion of fuel in the intake port region for a duration of 3 s during both the acceleration and deceleration phases (between 10 and 13 s). Compared to a standard tank, the presence of baffles significantly reduced the sloshing amplitude by approximately 70%. Furthermore, baffles led to a 50% decrease in pressure variations on the tank walls. Temporary fuel starvation can negatively impact engine performance and combustion efficiency. Conversely, the presence of baffles within the tank effectively mitigates sloshing and ensures continuous fuel presence at the intake port the entire simulation. This suggests that baffles play a crucial role in maintaining a stable and consistent fuel supply to the engine, even during dynamic vehicle maneuvers.

Numerical analysis of the Thermal EHL line contact problem under intermittent motion

Abstract A mathematical model of time-varying thermal elastohydrodynamic lubrication (EHL) is developed using a sleeve chain as the object of study. The effects of thermal effect, load, speed, rest time and equivalent radius of curvature on its EHL are investigated using theoretical simulations. The results show that during intermittent motion, a portion of oil is entrapped in the contact zone at the end of the deceleration phase, after which this entrapped oil gradually moves out of the contact zone with the onset of speed, and a lower film of oil at the lubrication inlet passes through the center of the contact zone. In simple sliding intermittent motion, the temperature rise plays a crucial role in the variation of the oil film, particularly during the motion phases, and is an unavoidable factor. An increase in stop time reduces the film thickness and increases the following friction coefficient in the acceleration stage. An increase in the equivalent radius of curvature increases the film thickness and thermal rise in the contact zone as well as decreases the friction coefficient. Since the sleeve chain is one of the most commonly used mechanism in industry, high priority should be given to the lubrication design of this structure.

Acute effects of lower limb wearable resistance on horizontal deceleration and change of direction biomechanics.

This study aimed to investigate the acute effects of lower limb wearable resistance on maximal horizontal deceleration biomechanics, across two different assessments. Twenty recreationally trained team sport athletes performed acceleration to deceleration assessments (ADA), and 5-0-5 change of direction (COD) tests across three load conditions (unloaded, 2% of BW, 4% of body weight (BW)), with load attached to the anterior and posterior thighs and shanks. Linear mixed effect models with participant ID as the random effect, and load condition as the fixed effect were used to study load-specific biomechanical differences in deceleration mechanics across both tests. Primary study findings indicate that for the ADA, in the 4% BW condition, participants exhibited significantly greater degrees of Avg Approach Momentum, as well as significant reductions in deceleration phase center of mass (COM) drop, and Avg Brake Step ground contact deceleration (GCD) in both the 2% BW, and 4% BW condition, compared to the unloaded condition. In the 5-0-5 tests, participants experienced significant reductions in Avg Approach Velocity, Avg deceleration (DEC), and Stopping Time in the 4% BW condition compared to the unloaded condition. Similar to the ADA test, participants also experienced significant reductions in Avg Brake Step GCD in both the 2% BW and 4% BW conditions, and significant increases in Avg Approach Momentum in the 4% BW condition, compared to the unloaded condition. Therefore, findings suggest that based on the test, and metric of interest, the addition of lower limb wearable resistance led to acute differences in maximal horizontal deceleration biomechanics. However, future investigations are warranted to further explore if the use of lower limb wearable resistance could present as an effective training tool in enhancing athlete's horizontal deceleration and change of direction performance.

Exploring the stellar rotation of early-type stars in the LAMOST medium-resolution survey

Context. Stellar rotation significantly shapes the evolution of massive stars, yet the interplay of mass and metallicity remains elusive, limiting our capacity to construct accurate stellar evolution models and to better estimate the impact of rotation on the chemical evolution of galaxies. Aims. Our goal is to investigate how mass and metallicity influence the rotational evolution of A-type stars on the main sequence (MS). We seek to identify deviations in rotational behaviors that could serve as new constraints for existing stellar models. Methods. Using the LAMOST Median-Resolution Survey Data Release 9, we derived stellar parameters for a population of 104 752 A-type stars. Our study focused on the evolution of surface rotational velocities and their dependence on mass and metallicity in 84 683 “normal” stars. Results. Normalizing surface rotational velocities to zero age main sequence (ZAMS) values revealed a prevailing evolutionary profile from 1.7 to 4.0 M⊙. This profile features an initial rapid acceleration until t/tMS = 0.25 ± 0.1 and potentially a second acceleration peak near t/tMS = 0.55 ± 0.1 for stars heavier than 2.5 M⊙, followed by a steady decline and a “hook” feature at the end. Surpassing theoretical expectations, the initial acceleration likely stems from a concentrated distribution of angular momentum at the ZAMS, resulting in a prolonged increase in speed. A transition phase for stars with 2.0 &lt; M/M⊙ &lt; 2.3 emerged, a region where evolutionary tracks remain uncertain. Stellar expansion primarily drives the spin down in the latter half of the MS, accompanied by significant influence from inverse meridional circulation. The inverse circulation becomes more efficient at lower metallicities, explaining the correlation of the slope of this deceleration phase with metallicity from –0.3 dex up to 0.1 dex. The metal-poor subsample (−0.3 dex &lt; [M/H]&lt; − 0.1 dex) starts with lower velocities at the ZAMS, suggesting that there is a metallicity-dependent mechanism that removes angular momentum during star formation. The proportion of fast rotators decreases with an increase in metallicity, up to log(Z/Z⊙)∼ − 0.2, a trend consistent with observations of OB-type stars found in the Small and Large Magellanic Clouds.

Constraining the physical properties of large-scale jets from black hole X-ray binaries and their impact on the local environment with blast-wave dynamical models

ABSTRACT Relativistic discrete ejecta launched by black hole X-ray binaries (BH XRBs) can be observed to propagate up to parsec-scales from the central object. Observing the final deceleration phase of these jets is crucial to estimate their physical parameters and to reconstruct their full trajectory, with implications for the jet powering mechanism, composition, and formation. In this paper, we present the results of the modelling of the motion of the ejecta from three BH XRBs: MAXI J1820$+$070, MAXI J1535–571, and XTE J1752–223, for which high-resolution radio and X-ray observations of jets propagating up to $\sim$15 arcsec ($\sim$0.6 pc at 3 kpc) from the core have been published in the recent years. For each jet, we modelled its entire motion with a dynamical blast-wave model, inferring robust values for the jet Lorentz factor, inclination angle and ejection time. Under several assumptions associated to the ejection duration, the jet opening angle and the available accretion power, we are able to derive stringent constraints on the maximum jet kinetic energy for each source (between $10^{43}$ and $10^{44}$ erg, including also H1743–322), as well as placing interesting upper limits on the density of the ISM through which the jets are propagating (from $n_{\rm ISM} \lesssim 0.4$ cm$^{-3}$ down to $n_{\rm ISM} \lesssim 10^{-4}$ cm$^{-3}$). Overall, our results highlight the potential of applying models derived from gamma-ray bursts to the physics of jets from BH XRBs and support the emerging picture of these sources as preferentially embedded in low-density environments.

On flow fluctuations in ruptured and unruptured intracranial aneurysms: resolved numerical study

Flow fluctuations have emerged as a promising hemodynamic metric for understanding of hemodynamics in intracranial aneurysms. Several investigations have reported flow instabilities using numerical tools. In this study, the occurrence of flow fluctuations is investigated using either Newtonian or non-Newtonian fluid models in five patient-specific intracranial aneurysms using high-resolution lattice Boltzmann simulation methods. Flow instabilities are quantified by computing power spectral density, proper orthogonal decomposition, and fluctuating kinetic energy of velocity fluctuations. Our simulations reveal substantial flow instabilities in two of the ruptured aneurysms, where the pulsatile inflow through the neck leads to hydrodynamic instability, particularly around the rupture position, throughout the entire cardiac cycle. In other monitoring points, the flow instability is primarily observed during the deceleration phase; typically, the fluctuations begin just after peak systole, gradually decay, and the flow returns to its original, laminar pulsatile state during diastole. Additionally, we assess the rheological impact on flow dynamics. The disparity between Newtonian and non-Newtonian outcomes remains minimal in unruptured aneurysms, with less than a 5% difference in key metrics. However, in ruptured cases, adopting a non-Newtonian model yields a substantial increase in the fluctuations within the aneurysm sac, with up to a 30% higher fluctuating kinetic energy compared to the Newtonian model. The study highlights the importance of using appropriate high-resolution simulations and non-Newtonian models to capture flow fluctuation characteristics that may be critical for assessing aneurysm rupture risk.

Reduction of the deceleration phase to mitigate the negative effect of hydrodynamic instabilities in direct-drive ICF implosions

In the deceleration phase of an Inertial Confinement Fusion capsule implosion Rayleigh–Taylor hydrodynamic instability can affect or even quench the ignition and thermonuclear burn wave propagation. This instability tends to mix the inner hot plasma with the cold and dense plasma shell providing a mixing layer where nuclear fusion reactions are inhibited. The 1D hydrodynamics code Multi-IFE has been used to simulate the implosion of a direct-drive high-gain laser-capsule design and the temporal evolution of the average radius and thickness of the mixing layer have been estimated. To mimic the effect of the reduced reaction rate, the fuel reactivity in the mixing layer is artificially set to zero thus inhibiting the burn wave propagation throughout it nullifying the energy gain. In order to overcome this negative effect, secondary short and powerful laser pulse is added, shortening this way the deceleration phase, which in turn reduces the thickness of the mixing layer. A study has been carried out to identify the optimal secondary laser pulse that recovers the high energy gain.

Long head of the biceps tendon plays a role in stress absorption and humeral head restriction during the late cocking and deceleration phases of overhead throwing: a finite element study

BackgroundEmerging evidence suggests that the long head of the biceps (LHBT) may play a role in stabilizing the glenohumeral joint, and this has led to controversy around the efficacy of biceps tenotomy for superior labral anterior and posterior (SLAP) lesions. Therefore, the aim of this finite element analysis (FEA) study was to determine the stress absorption and humeral head translation restriction effects of the LHBT within the glenohumeral joint during the late cocking and deceleration phases of overhead throwing with a view to resolving the controversy around tenotomy. MethodsEight FEA models were created using computed tomography and magnetic resonance imaging data from normal glenohumeral joints. The models represented four LHBT conditions: uninjured, subpectoral tenodesis, tenotomy, and type II SLAP lesions. The late cocking and deceleration phases of the overhead throwing were simulated for each model. The impacts of the four LHBT conditions on glenohumeral joint stress absorption and humeral head displacement restriction were studied based on 1) stress and related distributions on the cartilage, labrum, capsule, and LHBT and 2) humeral head translation variation. ResultsThe FEA analysis showed that the magnitude of the contact stress on the articular cartilage, labrum, and capsule was the lowest in the uninjured models, followed by the subpectoral tenodesis, tenotomy, and type II SLAP lesion models. Humeral head translation was the most restricted in the subpectoral tenodesis models, followed by the tenotomy and type II SLAP lesion models. ConclusionFinite element analysis demonstrated that the LHBT plays a significant role in stress absorption and displacement restriction in the late cocking and deceleration phases of overhead throwing. Subpectoral tenodesis of the LHBT exhibited lesser amount of stress and humeral head translation than those of tenotomy, thereby making it a better option for patients who engage in overhead throwing.

The expansion behavior of the hyperbolic solution in f(R,G) gravity

In this study, our primary focus lies in meticulously exploring the intricacies of the universe by employing a flat Friedmann–Lemaître–Robertson–Walker (FLRW) model within the framework of [Formula: see text] gravity. In our analysis, the [Formula: see text] function is delineated as the sum of two distinct components, commencing with a quadratic correction of the geometric term denoted by [Formula: see text], structured as [Formula: see text], alongside a matter term denoted by [Formula: see text], where [Formula: see text] and [Formula: see text] symbolize the Ricci scalar and Gauss–Bonnet invariant, respectively. In the pursuit of solutions to the gravitational field equations within the [Formula: see text] formalism, we embrace a specific expression for the scale factor, represented as [Formula: see text] [D. Rabha and R. R. Baruah, The dynamics of a hyperbolic solution in [Formula: see text] gravity, Astron. Comput. 45 (2023) 100761]. In this context, the parameters [Formula: see text] and [Formula: see text] intricately shape the scale factor’s behavior. The model posits the intriguing prospect of perpetual cosmic acceleration when [Formula: see text], signifying a continuous expansion of the universe. Conversely, for [Formula: see text], the model proposes a pivotal transition from an early deceleration phase to the present accelerated epoch, a transformative shift in line with our understanding of cosmic evolution. Furthermore, the model demonstrates its credibility by satisfying Jean’s instability condition during the shift from a radiation-dominated era to a matter-dominated era, substantiating the formation of cosmic structures. In our analysis, a central focus is directed toward scrutinizing the equation of state parameter [Formula: see text] within our model. We delve into a comprehensive examination of the scalar field and meticulously assess the energy conditions surrounding the derived solution. To establish the robustness of our model, we deploy an array of diagnostic tools, including the Jerk, Snap, and Lerk parameters, along with the Om diagnostic, Classical stability of the model, and statefinder diagnostic tools, Observational Constraints on the Model Parameters. The outcomes, intertwined with a detailed analysis of both the results and the inherent intricacies of the model, are diligently clarified and presented.

An EGF technique to infer the source parameters of a circular crack growing at a variable rupture velocity

Circular crack models with a constant rupture velocity struggle to effectively model both the amplitude and duration of first P-wave pulses generated by small magnitude seismic events. Assuming a constant rupture velocity is unphysical, necessitating a deceleration phase in the rupture velocity to uphold the causality of the healing process. Moreover, a comprehensive failure model might encompass an initial nucleation phase, typically characterized by an increase of the initial rupture velocity. Studies have demonstrated that quasi-dynamic circular crack models featuring variable rupture velocities can accurately model the shape of the observed first P-wave pulse. Based on these principles, an Empirical Green’s function (EGF) approach was previously formulated to estimate the source parameters of small magnitude earthquakes, called MAIN. In addition to determine the source radius and stress drop, this method also enables the inference of the temporal evolution of rupture velocity. However, this method encounters difficulties when the noise-to-signal ratio in the recordings of smaller earthquakes used as EGF exceeds 5%, a common situation when employing regional-scale recordings of small-magnitude earthquakes as EGF. Through synthetic tests, we demonstrated that, in such instances, the problem of this technique is that the alignment between the onset of P waves of EGF and MAIN is not rightly recovered after the initial inversion step. Consequently, a novel inversion method has been developed to address this issue, enabling the identification of the optimal alignment of P-wave arrivals in EGF and MAIN across all stations. A Bayesian statistical approach is proposed to meticulously investigate the solutions of model parameters and their correlations. Using the new technique on a small magnitude earthquake (ML = 3.3) occurred in Central Italy enabled us to identify the most likely rupture models and examine the issue of correlation among model parameters. Application of Occam’s Razor Principle suggests that, for the investigated event, a circular crack model should be favored over a heterogeneous rupture model.

Evaluating High-Frequency Fluctuations And Its Effect On Hemodynamics At Varying Heart Rates In Intracranial Aneurysms Via 4D PTV

Hemodynamics have been shown to affect the growth and rupture of intracranial aneurysms (IA). Studies have increasingly reported the presence of high frequency velocity fluctuations in aneurysms. However, it remains undetermined how transient physiological factors like heart rate and inflow blood waveform amplitude affect the hemodynamic parameters and high frequency fluctuations in and around an IA, as well as the risk of IA progression. In this work, we address this question using a volumetric particle tracking velocimetry (PTV) study where a patient-specific right middle cerebral artery (R MCA) aneurysm model was subjected to two heart rate conditions (60 bpm and 137 bpm). The input waveform amplitude for the 137 bpm case was increased by a factor of 1.6 to be physiologically consistent. Captured PTV images were processed using the Shake-the-Box (STB) workflow. Flow parameters including velocity, vorticity, and turbulent kinetic energy (TKE) were evaluated. To evaluate the presence of high frequency fluctuations, a direct numerical simulation (DNS) using the R MCA geometry and same two heart rate cases was conducted and a method for use with STB particle tracks was proposed. As compared to the 60 bpm case, the 137 bpm case had a more concentrated inflow jet that extended further into the aneurysmal sac and a stronger and larger vortical flow structure in the aneurysmal sac. The 60 bpm case maintained a region of slightly elevated TKE at the main junction point where the aneurysmal sac and all vessels merge. In the 137 bpm case, TKE in this region was dramatically higher. Using probe points, the DNS data revealed high frequency velocity fluctuations in an outflow vessel during the deceleration phase of the cycle. Notably, these fluctuations were only observed for the 137 bpm case. For both the DNS and STB data, high frequency components were more prevalent and stronger outside of the aneurysmal sac as opposed to inside the aneurysmal sac. Overall, these results suggest that changes in heart rate induce changes to the flow structure and can induce significant increases in TKE and high frequency fluctuations. Based on our findings, a higher heart rate would be expected to yield a flow field more akin to IA progression. The specific correlation between the high frequency components computed using our proposed STB-based method and the high frequency fluctuations in the flow field could not be well understood. Thus, additional analysis and development of this method is needed.