Deceleration Period Research Articles

Impact of density ratio on droplet dynamics in pulsating flow

Secondary atomization is extensively studied by investigating a droplet subjected to a steady air/gas stream. However, droplets are often subjected to unsteady or pulsating flows, such as in aero-engines or rockets, because of thermo-acoustic instabilities in the combustion chambers. The investigation focuses on the droplet dynamics and breakup in a pulsating flow for a range of density ratios (ρr), 1000 to 10, under sinusoidal airflow of different amplitudes and frequencies as compared to the dynamics in a steady flow. The volume of fluid multiphase model tracks the liquid–gas interface, and the governing equations are solved using the finite volume method. The two-dimensional axisymmetric pulsating simulations demonstrate accuracy comparable to the corresponding three-dimensional simulations at a much lower computational cost and are used for parametric studies. The droplets under the pulsating flow show a wavy surface, and larger vortex structures are observed during the deceleration period. At a high-density ratio (1000), pulsating flow enhances droplet deformation for a faster breakup, with the flow amplitude having more impact than its frequency. For a medium-density ratio (100), where breakup occurs under steady flow, droplet breakup is inhibited in the pulsating flow at low amplitude and high frequency. In the case of a low-density ratio (10), there is no breakup under steady flow, but pulsating flow promotes breakup, except at low amplitude and high frequency. The droplet breakup is always achieved for the highest amplitude, while lower frequencies push the liquid mass from the center of the droplet to the rim.

The Influence of FA Content on the Mechanical and Hydration Properties of Alkali-Activated Ground Granulated Blast Furnace Slag Cement

This study primarily investigates the effect of fly ash (FA) content on the mechanical properties and hydration performance of alkali-activated ground granulated blast furnace slag cement (AAGC) and compares the related properties with ordinary Portland cement (OPC). Additionally, we examined the hydration products; performed thermal analysis, MIP, and SEM; and determined chemically bound water and pH values of AAGC. The compressive strength of AAGC showed a retrogression phenomenon from 3 to 28 days, with the 14-day and 28-day compressive strengths of AAGC being higher than those of OPC. The AAGC with 20% FA content exhibited the highest 28-day compressive strength (75 MPa). The hydration heat release rate curve of OPC and AAGC was divided into the initial induction period, induction period, acceleration period, deceleration period, and steady period. As FA content increased, the 28-day pore volume of AAGC increased, while pH values and chemically bound water decreased. SEM images of AAGC with low FA content showed more microcracks.

Multicomponent entropic cosmology model with generalized entropy

Entropic cosmology provides a concrete physical understanding of the late accelerated expansion of the universe. The acceleration appears to be a consequence of entropy associated with information storage in the universe. Therefore, the assumption of an ad-hoc dark energy is not necessary. In this paper, we investigate the implications of a multicomponent model (radiation and non-relativistic matter) that includes a subdominant power-law term within a thermodynamically admissible model. We use a generic power-law entropy and the temperature of the universe horizon results from the requirement that the Legendre structure of thermodynamics is preserved. We analyse the behaviour for different combinations of the parameters and compare them with other cosmological models, the observed redshift dependencies of the Hubble parameter H and the luminosity distance data obtained from supernovae. This is an early attempt to analyse a multicomponent entropic cosmological model. Furthermore, the analysis is based on a entropy scaling with an arbitrary power of the Hubble radius instead of a specific entropy. This allows us to simultaneously infer different models, compare them and conserve the scaling exponent as a parameter that can be fitted with the observational data, thus providing information about the form of the actual cosmological entropy and temperature. We show that the introduced correction term is able to explain different acceleration and deceleration periods in the late-time universe by solving the model numerically. We discuss the advantages and disadvantages of entropic models compared to mainstream cosmology.

Turbulent–turbulent transient concept in pulsating flows

The turbulence behaviour of current-dominated pulsating flows has been investigated. Direct numerical simulations have been carried out for Stokes lengths over a range of $l_s^+=5\unicode{x2013}26$ , and amplitudes spanning 90 % of the current-dominated regime, about a mean flow of $\overline {Re}=6275$ . The results show that the turbulence response in intermediate and low-frequency pulsations is governed by a multistage turbulent–turbulent transition process, which bears a strong similarity to the multistage response of non-periodic acceleration. During the early acceleration period, the flow enters a pretransition stage, in which a new laminar perturbation boundary layer forms at the wall, and the streamwise velocity streaks are stretched. If the low-speed streaks destabilise prior to the deceleration period, then the flow enters a transition stage in which the perturbation boundary layer undergoes a bypass-like transition process. A unique feature of pulsating flows is the ongoing mechanism of turbulence decay, which initiates during the deceleration period and constitutes the main transient turbulence mechanism for much of the cycle. For high-frequency pulsations, the perturbation boundary layer fails to reach the pretransition stage prior to the deceleration period. Instead, the flow alternates between two inertial stages which are characterised by two layers of amplified viscous force; one growing at the wall, and one detached and moving towards the core.

Population dynamics and cultural niche construction during the Late Holocene in a mediterranean ecosystem (central Chile, 32°S−36°S)

Understanding socio-ecological systems over the long term can shed light on past adaptive strategies in environmentally sensitive regions. Central Chile is an emblematic case study for mediterranean ecosystems, where a progressive and sustained population increase began approximately 2000 years ago alongside significant landscape changes. In this work we analyzed regional paleo-demographic trends by compiling a new database of archaeological dates over the last 3000 years, and integrating population dynamics theory with an analysis of the spatio-temporal variation of regional cultural stages. Results show three moments of marked acceleration in population growth: just before agricultural adoption, during the Archaic Period (c. 700-300 BCE); during the second half of the ECP (500–900 CE); and during the Late Intermediate Period (1200–1400 CE). We also identified periods of deceleration in per capita growth rates, although population size continued to increase (300 BCE−500 CE, 900–1200 CE and after 1400 CE). These large shifts in the per capita growth rates coincide with major cultural changes associated with social and economic aspects. The pulses of major occupation show in general terms a more intensive use of the valleys as the population size increased, although the remaining ecosystems never ceased to be occupied with different economic and symbolic emphases.

Ultrasonic monitoring of hydration behavior of cement paste doped with triethanolamine using novel piezoelectric ultrasonic transducer

The propagation of ultrasonic wave in cement paste is closely related to its physical properties, and therefore shows a potential application in fields of online monitoring of hydration and hardening properties of the cementitious materials. Here, the hydration characteristics of cement paste doped with triethanolamine were studied based on the ultrasonic transmission method using the tailor-made horizontal omnidirectional piezoelectric ultrasonic transducer. The results show that clear ultrasonic waveforms can be observed at hydration age of 2 h. The dominant frequency of the reception wave is low at early hydration age and shifts towards the high frequency direction with hydration. The amplitude of the head wave increases sharply before hydration of 24 h, and the increasing extent decreases gradually until hydration of 166 h. The hydration process of cement at early hydration age can be classified into three stages based on amplitude changes of the head wave, that is, the induction period before 4 h, the acceleration period during 4–12 h, and the deceleration period after 12 h. The acoustic parameters of cement paste at early hydration age conform well to the logistic function distribution. The research finding might provide a new method to estimate hydration and hardening properties of cementitious materials, especially on large construction sites.

Trends, Growth, Production Instability and Export Dynamics Analysis of Basmati Rice in India

The research examined the trends, growth rates, and instability in Basmati rice production and export in India from 2001 to 2021. Secondary time series data on these parameters were collected from diverse sources including the official websites of the Department of Agriculture and Farmer’s Welfare, Directorate General of Commercial Intelligence, the Agricultural and Processed Food Product Export Development Authority (APEDA) and Statistics (DGCI&S) and Ministry of Commerce and Industry. Various analytical tools such as Compound Annual Growth Rate (CAGR) for growth rate analysis, Coefficient of Variation (CV), Coppock Instability Index, Cuddy Della Valle Index, and Index Number for instability analysis, and R-square for linear, second-degree, and polynomial regression for trend analysis were employed which served as a metric for goodness of fit. The analysis revealed significant insights into the dynamics of Basmati rice production and export over the study period. Notable findings include fluctuations in growth rates, trends indicating periods of acceleration or deceleration, and instability factors impacting production and export. These findings contribute to a deeper understanding of the Basmati rice industry in India, informing policymakers, stakeholders,

Relating early-age hydration and flow loss of mortar prepared with manufactured sand

Cement-based materials prepared with manufactured sand can exhibit quick loss of fluidity. However, the estimation of the flow loss remains difficult given the variable contents and physiochemical properties of the microfines in various sands. This paper studies the fluidity loss of mortar mixtures made with different manufactured sands varying in mineral composition and content of microfines. The effect of microfines on accelerating the early-age hydration of cement before the deceleration period was evaluated by quantifying the generation of early hydration products. Test results show that the growth of yield stress corresponding to the loss of mini-slump flow of mortar mixtures were mainly determined by the formation of early hydration products, in addition to the volume fraction and packing density of aggregate grains and powder particles. An approach was then proposed that can assess the loss of mini-slump flow of mortar mixtures prepared with manufactured sand, regardless of the type and content of the microfine materials in the sand.

The effect of a ship's acceleration and deceleration on parametric roll motion in regular head waves at resonance conditions

The effect of a ship's acceleration and deceleration in regular head waves on parametric roll motion is examined experimentally in the study and compared with a mathematical model. Operators queries such as "Should I accelerate or decelerate the ship in resonance condition?" and "Is the magnitude of acceleration or deceleration effective in reducing large roll motion?" are tried to answer. It is well known that waves with lengths similar to that of the ship may suffer parametric roll motion. Additionally, it is possible to say that the encounter frequency itself provides the ship's tuning factor. Since one particular wave is selected with a length equal to the ship's length, the tuning factor in this study at ship operation is the velocity. Results indicate that the amplitudes of roll motion at acceleration and deceleration periods are still large. Results also indicate that the magnitude of acceleration or deceleration affects the roll motion. The mathematical model is also solved numerically and compared with experimental results to better understand the effect of acceleration magnitude.

Study of the High‐Temperature Oxidation Behavior of SUS430 Ferritic Stainless Steel Under Different Content of Water Vapor Atmosphere

The oxidation behavior of SUS430 ferritic stainless steel is studied during isothermal oxidation at 1100 °C for 2 h under a mixture of 10, 30, and 50% water vapor and air, and oxidation kinetics curves are drawn. The surface morphology and phase composition of oxide scale are analyzed using X‐Ray diffractometer, scanning electron microscope, and energy dispersive spectrometer. The oxidation kinetic curves under three different humidities are S‐shaped and include three stages: induction period, acceleration period, and deceleration period. The controlling steps under 10% water vapor and air are nucleation and growth, while under 30% and 50% water vapor and air are both phase boundary control reactions. The induction period becomes shorter and the breakaway oxidation occurs earlier with increasing water vapor content. The structure of oxide scale produced is layered, with the outer layer being iron oxide and the inner layer being mainly the Fe–Cr spinel phase. The volatilization of Cr and the growth stress of the Cr2O3 layer cause the formation of nodules, and a large number of cracks are generated in oxide scale. The cracks provide diffusion paths, accelerating the diffusion of Fe ions and electrons, as well as the erosion of the substrate.

Influence of nanosized magnesia on the hydration of borehole-sealing cements prepared using different methods

Gas drainage is an effective technology for gas control in coal mines. A high borehole-sealing quality is the fundamental precondition for efficient gas drainage. The expansibilities of cement pastes used in borehole-sealing processes are critical for the borehole-sealing effect. Nanosized magnesia expansive agents are used to improve the expansibilities of cement pastes and improve the borehole-sealing effect. Nuclear magnetic resonance spectrometry and scanning electron microscopy were adopted to study the effects of nanosized magnesia on the hydration of borehole-sealing cements used with different preparation methods. The results showed that an increase in the mass fraction of the nanosized magnesia promoted cement hydration, and the mass fraction was positively correlated with the promotion effect. The use of different preparation methods did not change the water-phase distribution in the cement. When using the wet-mixing preparation method, nanosized magnesia promoted the induction, acceleration, and deceleration periods of hydration; when using the dry-mixing preparation method, the nanosized magnesia promoted the induction period of cement hydration, and the promotion effect was less obvious than that seen when using the wet-mixing method. When using the wet-mixing preparation method, the nanosized magnesia was uniformly dispersed, thus enlarging the surface area of the reaction, which provided more nucleation sites for the hydration products of the cement and therefore accelerated the hydration reaction. When using the dry-mixing preparation method, the nanosized magnesia powders were dispersed nonuniformly and aggregated. Under these conditions, only a few nanosized magnesia particles on the surfaces of the aggregated clusters took part in hydration, so only a small number of nucleation sites were provided for the hydration products of cement. This led to inconsistent hydration of cement pastes prepared using the dry-mixing method. The surface porosity of the cement prepared with the wet-mixing preparation method first decreased and then increased with increases in the mass fraction of the nanosized magnesia. The cement surface exhibited compact hydration products and few pores, and the surface was relatively smooth. In comparison, the surface porosity of the cement prepared using the dry-mixing method fluctuated with increasing mass fraction of the nanosized magnesia, resulting in a rough cement surface and microfractures on some surfaces. The two preparation methods both reduced the surface porosity of the cement. The wet-mixing preparation was more effective and consistent in improving the compactness of the cement than the dry-mixing preparation. These results provide important guidance on the addition of nanosized magnesia in borehole-sealing engineering and the selection of cement preparation methods, and they also lay a solid foundation for realizing safe and efficient gas drainage.

A resolution of the monopole problem in the Rh = ct Universe

Spontaneous symmetry breaking in grand unified theories is thought to have produced an exceedingly large number of magnetic monopoles in the early Universe. In the absence of suppression or annihilation, these very massive particles should be dominating the cosmic energy budget today, but none has ever been found. Inflation was invented in part to dilute their number, thereby rendering their density undetectable by current instruments. Should the inflationary paradigm not survive, however, the ensuing disagreement between theory and observation would constitute a cosmological ‘monopole problem’ and create further tension for any extension to the standard model of particle physics. But as is also true for all horizon problems, a monopole overabundance emerges only in cosmologies with an initial period of deceleration. We show that the alternative Friedmann–Lemaître–Robertson–Walker cosmology known as the Rh=ct universe completely eliminates all such anomalies rather trivially and naturally, without the need for an inflated expansion. We find that the monopole energy density today would be completely undetectable in Rh=ct. Evidence continues to grow that the zero active mass condition from general relativity ought to be an essential ingredient in ΛCDM.

Abstract P1048: Lattice-Boltzmann Method Achieves Feasible Hemodynamic Analysis In Carotid Atherosclerosis With Low Computational Cost

Introduction: Atherosclerosis is a common cardiovascular pathophysiology that can lead to plaque-related complications, including stroke and myocardial infarction. Non-invasive hemodynamic analysis can provide valuable insights into the plaque's rupture vulnerability and growth progression. Computational fluid dynamics is widely studied to understand hemodynamic pathophysiology further; however, traditional computational fluid dynamics methods often require daily-based analysis time to visualize hemodynamic parameters. This study investigated the feasibility of using the lattice Boltzmann method (LBM) for hemodynamic analysis of atherosclerosis lesions. Methods: From ten carotid artery stenosis patients, 20 carotid artery models were generated and analyzed using LBM. Hemodynamic parameters, including time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT), were compared between the stenotic lesion and contralateral control sides. The patient-specific boundary conditions were applied. Their cardiac cycle was subdivided into three periods: systolic acceleration, systolic deceleration, and diastolic, and analyzed to investigate their relationship with the hemodynamic parameters. Results: LBM effectively captured the hemodynamic parameters associated with carotid atherosclerosis with an hourly-based computational cost (2.765 [2.435-3.233] hours). The analysis visualized high TAWSS and low RRT distribution at stenotic areas during the systolic deceleration period and low TAWSS and high RRT distribution at the post-stenotic distal lesion during the diastolic period. These findings were reproducible among the ten patients. Conclusion: LBM-based hemodynamic analysis has the potential to serve as a non-invasive diagnostic tool that can help understand atherosclerosis pathophysiology with low computational cost.

Post-impact Fatigue Performance of 2198-T8 Aluminum-Lithium Alloy Sheet with Pre-crack

Abstract The fatigue test with the digital image correlation system is applied to 2198-T8 aluminum-lithium alloy sheets with preset cracks and impact dents. The influence of different inserts and impact energies on residual fatigue life and failure behavior is analyzed. The results show that the shape of inserts is the main factor of the residual fatigue life at the same impact energy following the order: U-shaped > hemispherical > conical. Moreover the fatigue life decreases with the increase of impact energy. The hemispherical and U-shaped inserts cause local hardening at low impact energy 5 J, resulting in a maximum increase in fatigue life of 12.09 %. In the initial stages of fatigue failure, high strain areas are always around the preset crack where the propagations initiate. There is a multi-axial loading area around the impact dent in the middle stage. Its fatigue crack propagation mode is type I+III, resulting in a deceleration period.

Hydration of ternary blended cements with sewage sludge ash and limestone: Hydration mechanism and phase assemblage

The hydration kinetics and phase assemblage of ternary blended cements composed of sewage sludge ash (SSA) and limestone were investigated. Isothermal calorimetry reveals an inhibition effect of SSA on the hydration of C3S within the first day, while the hydration degree of C3S in ternary blended cements exceeds that in PC after 3 days. The reaction between SSA and limestone generates additional carboaluminate phases and inhibits the transformation of AFt to monosulfate, increasing the stability of AFt. This reaction is reflected on the second peak in the deceleration period of heat flow curves. The generation of a large amount of carboaluminate phases has a significant effect on porosity refinement and strength development of ternary blended cements. The pozzolanic reaction of SSA generates C-(A)-S-H with high Si/Ca and Al/Ca atomic ratios. Iron from the dissolution of SSA is captured by C-(A)-S-H, leading to the increase in Fe/Ca atomic ratios of C-(A)-S-H.

The role of iron in cement hydration process: From perspective of chemical admixture

The post-peak decelerating hydration progress plays a significant role for concrete technology to assure durability of concrete. The effect of chemical admixture on cement hydration, hydration products, pore structure and moisture diffusion process are conducted by various experiments and the controlling factor on deceleration period of cement hydration and the effect of iron ion on microstructure are revealed. When the chemical admixture is added into cement paste, more ferrite phase is consumed and the iron dissolved in the pore solution modifies the initial hydration product layer and accelerate the hydration process, causing more C-S-H gel generated and denser microstructure. In addition, it is also proved that single diffusion control factor occurs at 80 h for the later deceleration period of cement hydration.

Effect of MgSO4·7H2O on the hydration of Portland cement

MgSO4 is usually found in the groundwater or seawater and can influence the early hydration of Portland cement. In this paper, the reaction kinetics of the early hydration of the MgSO4·7H2O + Portland cement clinker (MPC) was revealed compared with the CaSO4·2H2O + Portland cement clinker (OPC) by means of isothermal calorimetry, chemical shrinkage and solid–liquid phase analysis. The test results indicated that MgSO4·7H2O had more pronounced retarding effect on Portland cement clinker hydration than CaSO4·2H2O. The MPC system had longer initial time and final time than OPC system. In the initial period and induction period of MPC system, Mg(OH)2 and CaSO4·2H2O precipitated on not only the C3A partials but also on the C3S partials, and prevented the flash-set of clinker. The early hydration of C3A and C3S were both retrained by the combined retardation of Mg(OH)2, CaSO4·2H2O and hydration products, which resulted to a slower hydration rate of MPC than OPC before the deceleration period. The intense hydration of C3A and C3S were postponed and appeared in the deceleration period of MPC compared with OPC, which ultimately caused a deeper hydration of MPC than OPC.

МІЖНАРОДНИЙ ТУРИЗМ В КОНТЕКСТІ СУЧАСНИХ ВИКЛИКІВ

The purpose of the study is to determine the modern features of international tourism in the context of the challenges it has experienced in recent years; revealed the scale of changes that have taken place in international tourism and probable scenarios of its further development in the short-term and long-term perspective. The research methodology is based on the processing of analytical materials from various sources, as well as on the application of scientific methods of analysis and synthesis of representative statistical data of the World Tourism Organization (UNWTO). Such data were constructed in the form of dynamic series, which made it possible to effectively use the method of comparison, as well as the graphic method of representation, generalization and further forecasting of the development of international tourism. The results. It was established that from the beginning of the second half of the 20th century, the development of international tourism was accompanied by a natural change of periods of growth and deceleration, as well as crisis phenomena. Such circumstances were generally correlated primarily with the global socio-economic and political upheavals of society. However, the biggest crisis experienced by world tourism since the beginning of its history in the middle of the 19th century took place in 2020-2021 and was caused by the COVID-19 pandemic. Despite the widespread perception in the recent past about the ability of tourism to quickly recover, the return of international tourism to the level of 2019 will take at least 5-7 years. Scientific novelty. Statistical data on flows of international tourism for more than 60 years of observation are summarized. Cyclical development of international tourism, periods of its decline to growth have been revealed. Practical significance. The obtained results can be used to develop a strategy for the development of international tourism both on a global and regional scale. In addition, the research method can be used in educational activities when training specialists in the specialty "tourism".

The Impacts of Land Use Spatial Form Changes on Carbon Emissions in Qinghai–Tibet Plateau from 2000 to 2020: A Case Study of the Lhasa Metropolitan Area

The ecological contribution of the Qinghai–Tibet Plateau has received considerable attention as a result of the increased focus on global climate change and the continuous growth of carbon emissions in all countries. In this study, we proposed a method and measured the carbon emissions from land use in the Lhasa metropolitan area from 2000 to 2020, based on image interpretation data, by exploiting corrected carbon emission factors in different land types from the Qinghai–Tibet Plateau. We studied the impact of construction land form on carbon emissions using the spatial lag model (SLM) and the spatial error model (SEM), and the results show that the Lhasa metropolitan area’s carbon emissions showed an overall increasing trend from 2000 to 2020, with the characteristics of “slow acceleration–slight deceleration–acceleration”, with a deceleration period from 2005 to 2015. As a result, the construction land has a relatively low capacity, but it constitutes about 90% of all emissions; moreover, carbon emissions from cultivated land cover about 9%. The rate of spatial expansion of carbon emissions from land use is significantly slower in the Lhasa metropolitan area, yet the spatial expansion of carbon emissions has a clear direction and increases in the north and west of Lhasa. The carbon emissions from land use in the Lhasa metropolitan area is characterized by “one core, many points, and multiple belts” in spatial distribution. The changing of spatial forms of construction land has a significant impact on carbon emissions. Finally, we depicted the impact logic of land use pattern on carbon emissions and provided policy and management recommendations that were both feasible and reasonable.

Determination of dynamic loads in the crane lifting mechanism

Loading and unloading is an integral part of the technological process of construction. To perform these works mostly use cranes of different types.
 To ensure trouble-free operation and increase the reliability of cranes in the calculation of structures and components of their work equipment, it is important to take into account dynamic loads, which are several times higher than static loads.
 Elements of dynamic loads of the crane lifting mechanism are its elastic components - ropes and shafts, which are deformed under the action of loads. The magnitude of this deformation of the elements are taken into account by the coefficients of elasticity or flexibility of linear and torsional or their inverse value - the coefficients of rigidity. These coefficients depend on the linear or angular deformations, respectively.
 Due to the fact that the mechanism of lifting a load consists of a large number of elastic elements, the addition and solution of equations to determine these coefficients becomes a difficult task. In order to simplify the equations and these calculations, the paper recommends the above scheme of calculations according to which the rest of all elements of the mechanism are reduced to its first element (engine). This greatly simplifies the equations to be solved and determines the values ​​of the coefficients of elasticity or stiffness of the elements of the dynamic loads of the mechanism of lifting the load of cranes.
 According to a similar scheme is also determined by the moments of inertia of the mechanism of lifting the load during periods of acceleration and deceleration, the components of the values ​​that affect them. The equations for determining the terms of transients of the lifting mechanism (duration of acceleration and braking) are derived.
 The method of determining the coefficients of elasticity and stiffness of the elements of dynamic loads, moments of inertia, duration of acceleration and deceleration of the lifting mechanism can greatly simplify the solution of complex equations and determine their values ​​with sufficient accuracy.