Cyclic Variation Research Articles

Analysis of spatiotemporal patterns of atmospheric CO2 concentration in the Yellow River Basin over the past decade based on time-series remote sensing data.

Understanding the spatial and temporal variations of CO2 column concentration (CO2-CCs) is crucial for tackling climate change and promoting sustainable human development. This study provides an in-depth analysis of CO2 dynamics in the Yellow River Basin, an area significantly affected by both natural and anthropogenic factors. Using data from the Orbiting Carbon Observatory 2 (OCO-2) and the Fourier transformation spectrometer (FTS) of the GOSAT satellite remote sensing sensors, supplemented with ground station data from the Waliguan station, we scrutinized the CO2 levels in the region from 2013 to 2022. The regional CO2-CC displayed a 12-month cyclical variation and a continuous upward trend, escalating by approximately 4.26% over the 10-year period. Spatiotemporal differences were evident in the monthly variation of CO2-CC, with peak and minimum values occurring in May and August respectively. Geographically, the highest CO2-CC was found in the central part of the basin, while the lowest was in the northern part of Inner Mongolia. This study underscores the increased significance of the region's CO2-CC, which showed an increase from 17.0ppm at the start of the period to 21.0ppm by the end, representing an overall growth of between 4.35 and 5.25%. The findings highlight the urgency of targeted measures to mitigate CO2 emissions and adapt to their consequences in the Yellow River Basin, contributing to the global efforts against climate change and towards sustainable development.

Cyclical variation of fiscal multipliers in Caucasus and Central Asia economies: an empirical evidence

Cyclical variation of fiscal multipliers in Caucasus and Central Asia economies: an empirical evidence

Confidence in US Elections After the Big Lie

This paper examines how individual-level partisanship and state-level factors affect perceptions of electoral integrity in the United States. We find that evaluations of the integrity of the 2020 US presidential election national outcome were only modestly conditioned by the quality of election administration in a person’s state. Perceptions of electoral legitimacy were much more substantially conditioned by motivated reasoning associated with a person’s partisanship, the partisan context Republicans resided in, and Republican partisans’ residence in a swing-state where final results from 2020 were delayed due to late-counted ballots. Overall, estimated effects of the quality of election administration on confidence in elections are null or modest. Partisan factors associated with Donald Trump’s “Big Lie” about the 2020 US presidential election were the strongest forces predicting lack of confidence in US elections and perceptions that election officials were altering results. These factors were not evident in 2016. We discuss how these findings may reflect a fundamental alteration of attitudes among Republican voters and elites about the legitimacy of democratic elections in the US, rather than reflecting cyclical variation in partisan confidence associated with which party won the past election.

Biennial analysis of probable permafrost distribution for Kullu district, North‐west Himalaya using Landsat 8 satellite data

AbstractClimate change and increased anthropogenic activity affect permafrost distribution, threatening ecosystem stability, water resources, and greenhouse gas emissions. In this study, we present updated probable permafrost maps at 30 m resolution for Kullu district of Himachal Pradesh derived from the predicted mean annual air temperature (MAAT) (2013 to 2020) based on Landsat 8 land surface temperature (LST). We also analysed the mean annual snow cover extent of the study area for this time period. Our probable permafrost distribution map shows the areas falling under permafrost regions in snow‐covered areas; permafrost regions in non‐snow‐covered areas; non permafrost regions along with glacierised regions. The temporal variation of permafrost over 7 years from 2013 to 2020 shows that permafrost distribution follows a cyclic variation ranging between 4.42% and 7.51% of the total area of the district. The permafrost maps were validated with the presence of rock glaciers as seen on high resolution satellite images and the ground photographs. The maps display the expected spatial pattern of near‐surface air temperatures that match with the known permafrost boundary. The findings of this study provide more precise information on permafrost distribution and essential data for future permafrost research in Kullu district.

Spatiotemporal analysis of CO2 emissions and emission reduction potential of Beijing buses using smart card data

Human activities, primarily carbon dioxide emissions, have undeniably caused global warming. The transportation sector contributes about a quarter of global CO2 emissions. While replacing traditional buses with electric ones has reduced emissions, it is crucial to consider the indirect emissions resulting from electricity consumption. This study proposes a framework for modeling bus emissions using smart card data, integrating spatiotemporal distribution characteristics and emission reduction potentials. Our analysis reveals that routes spanning 10–30 km contribute to 81% of total bus emissions, with an average emission rate of 56.2 gCO2/per-km for residents traveling by bus. Bus emissions also exhibit cyclical variations during holidays, weekdays, and weekends, indicating spatial clustering and trends. Although the area within Beijing's 4th Ring Road constitutes only 13% of the total area within the 6th Ring Road, it generates almost half of the CO2 emissions. With urban expansion, total bus emissions increase gradually, but emission intensity decreases. This study emphasizes the potential for reducing emissions through improved public transportation operations. It recommends fully electrifying the bus fleet and employing low grid emission factors, which could reduce emissions by up to 71% compared to diesel options. Electrification of buses and optimizing power generation on the grid are essential priorities for emission reduction.

Coupld thermo-hydraulic modelling of heat storage in an embankment

Coupld thermo-hydraulic modelling of heat storage in an embankment

On the unsteady interactions between a sweeping jet and afterbody vortices

In this paper, a sweeping jet was applied to control the afterbody vortices behind a 30° slanted-base cylinder at a Reynolds number of 87 000. Phase-locked stereo particle image velocimetry measurements were conducted during a sweeping jet actuation cycle, and insights of the complex three-dimensional interaction process between the sweeping jet and the afterbody vortices have been obtained for the first time. It is found that in the near-field of the jet orifice (x/c < 0.3), the jet swings from side to side over the endplate between the afterbody vortex pair. An intersection between them around x/c = 0.3 causes the sweeping jet to take on a zigzag pattern as it propagates downstream along the slanted surface. From x/c = 0.6 onwards, the intensity of this interaction decreases as the afterbody vortices become detached from the base. Nevertheless, the sweeping jet continues invading the afterbody vortices from their inner side and pushes its way outwards from the underside of the afterbody vortices causing them to weaken further. Furthermore, the interaction between sweeping jets and afterbody vortices results in a cyclic variation in the circulation of afterbody vortices, which increases in magnitude at downstream locations. Except for the phases where a merger between the afterbody vortex and the sweeping occurs, a reduction in the circulation is observed. Finally, the level of interaction between sweeping jets and afterbody vortices intensifies as the strength of the sweeping jet increases resulting in the afterbody vortices being penetrated by the sweeping jet and their regular shape being momentarily destroyed.

Using Template Matching to Detect Hidden Fluid Release Episodes Beneath Crater Lakes in Ruapehu, Copahue, and Kawah Ijen Volcanoes

AbstractVolcano crater lakes, while picturesque, can sometimes mask the occurrence of small eruptions or hydrothermal fluid release events. However, these seemingly hidden events hold a wealth of valuable information about the underlying volcanic conduit and may pose risks to those near the volcano’s summit. This study presents a novel method for identifying these hard‐to‐detect fluid release events by examining seismic data from Ruapehu volcano in New Zealand. We undertake a multi‐timescale template‐matching analysis that uses a newly discovered seismic eruption precursor, to identify patterns related to the rapid consolidation of hydrothermal seals, pressurization processes, and the subsequent release of hydrothermal fluids. As a result, we identified a potential instance of sudden fluid‐release events that were previously unnoticed due to the presence of the crater lake. Our findings support a conceptual model of cyclic pressure variation within the conduit beneath an active crater lake. This model involves the formation and disruption of seals, followed by depressurization through hydrothermal fluid release events. Fluid discharge recession recorded as seismic amplitude decay, provides information about the properties of the reservoir, conduit, and the fluid being discharged. We also applied this technique to Kawah‐Ijen (Indonesia) and Copahue (Chile‐Argentina), identifying multiple potential events at these volcanoes. These findings enhance our understanding of the conditions leading to explosive eruptions, including those that could breach the crater lake.

The 8‐Year Solar Cycle During the Maunder Minimum

AbstractThe presence of grand minima, characterized by significantly reduced solar and stellar activity, brings a challenge to the understanding of solar and stellar dynamo. The Maunder Minimum (1645–1715 AD) is a representative grand solar minimum. The cyclic variation of solar activity, especially the cycle length during this period, is critical to understand the solar dynamo but remains unknown. By analyzing the variations in solar activity‐related equatorial auroras recorded in Korean historical books in the vicinity of a low‐intensity paleo‐West Pacific geomagnetic anomaly, we find clear evidence of an 8‐year solar cycle rather than the normal 11‐year cycle during the Maunder Minimum. This result provides a key constraint on solar dynamo models and the generation mechanism of grand solar minima.

글로벌 회사채 스프레드에 대한 경기요인 영향력 분석

Purpose - This paper investigates how business cycle impacts on corporate credit spreads since global financial crisis. Furthermore, it tests how the impact changes by the phase of the cycle.
 Design/methodology/approach - This study collected dataset from Barclays Global Aggregate Bond Index through the Bloomberg. It conducted multi-regression analysis by projecting business cycle using Hodrick-Prescott filtering and various cyclical variables, while ran dynamic analysis of 5-variable Vector Error Correction Model to confirm the robustness of the test.
 Findings - First, it proves to be statistically significant that corporate credit spreads have moved countercyclicaly since the crisis. Second, It indicates that the corporate credit spread’s countercyclicality to the macroeconomic changes works symmetrically by the phase of the cycle. Third, the VECM supports that business cycle’s impact on the spreads maintains more sustainably than other explanatory variable does in the model.
 Research implications or Originality - It becomes more appealing to accurately measure the real economic impact on corporate credit spreads as the interaction between credit and business cycle deepens. The economic impact on the spreads works symmetrically by boom and bust, which implies that the market stress could impact as another negative driver during the bust. Finally, the business cycle’s sustainable impact on the spreads supports the fact that the economic recovery is the key driver for the resilience of credit cycle.

Experimental investigation of spark timing on extension of hydrogen knock limit and performance of a hydrogen-gasoline dual-fuel engine

This work focused on the influence of spark timing on the hydrogen knock limit and performance of a hydrogen-gasoline dual-fuel engine. A gasoline direct injection engine with hydrogen port induction was used for this study. The engine speed was kept at 1000 rpm, with a gasoline injection quantity of 6 mg. The hydrogen flow rate was varied until engine knock was detected. The spark timing was varied from 4 to 36֯ CA BTDC with a step size of 4֯ CA. A higher hydrogen flow rate was achieved when the spark timing was retarded close to TDC. The addition of hydrogen increased the cylinder pressure, exhaust temperature, brake mean effective pressure, and brake thermal efficiency. Advancing the spark timing produced a prolonged flame development period and shorter flame propagation period. Cyclic variation increased and then decreased with spark advance. NOX emissions increased with increase in spark advance and hydrogen flow rate, whereas spark timing had little effect on CO2 and CO emissions.

Economic sentiment indicators and their prediction capabilities in business cycles of EU countries

Research background: The post-World Financial Crisis period has showed us that an application of the qualitative data focused on the expectations of the enterprises and consumers in a combination with the quantitative data in the individual economy sectors is a good prerequisite for reliable prediction of the economic cycles. Purpose of the paper: The main goal of the presented study was to test the ESI prediction capabilities and its components in a relation to the economic cycles of the EU countries in the individual time periods. Methods: The time series for the period Q1 2000 to Q4 2022 and the three selected time periods were a subject to undergo the selection of the cyclical component applying the Hodrick-Prescott filter and then, the relationship between the variables was determined employing the Pearson correlation coefficient with the time shifts. The relation of ESI and its components to GDP and the Index of Industrial Production (IIP), which represent the economic cycle, was analysed. The prediction volume and the cross-correlation values determined the nature of the observed cyclical variables. Findings & value added: The results of the analysis point to the fact that ESI and its components are able to ensure a high-quality prediction of the economic cycle only in the selected EU countries. Regarding the components of the ESI, the Consumer confidence indicator, Construction and Industrial confidence indicators show the best predictive capabilities. The analytical outcomes show that the ESI size and lead period vary over time and after the 2008 crisis, the ESI showed better predictive capabilities in a relation to GDP and IIP than before the crisis. The Covid 19 pandemic had a significant negative impact on the ESI predictive capabilities.

Wavelet analysis of combustion characteristics and numerical validation of CI engine with novel water emulsified fuels

This study examined the dependability of running a diesel engine on a novel water-emulsified diesel fuel with prolonged phase stability investigation. In order to develop a stable water emulsified fuel, experiments were conducted to standardize the composition ratios. The water-in-diesel emulsions were prepared using the surfactant named “Propylene Glycol Monostearate” along with Tween80 and Octanol was also chosen as co-emulsifier in order to enhance the phase stability. Using water-emulsified diesel fuel with the designations E0, E10, E20, E30, E40, and E50, the combustion stability using statistical and wavelet method were assessed on a 1-cylinder, 4-stroke CI engine. Even after being prepared for 100 days at room temperature, all water-in-diesel emulsions were discovered to be stable and homogenous. Moreover, to validate the combustion metrices such as in-cylinder pressure and HRR, a MATLAB-based single-zone thermodynamic model was developed. The combustion stability analyses using statistical method showed that the COV was found below 5 % at all loading conditions except E0 emulsion fuel whereas, the wavelet approach revealed that the E0 emulsion fuel's wavelet power spectrum (WPS) result showed a major intensity variance at high frequencies and lower frequencies for other emulsions and diesel 25 and 50 % loading condition. The analysis of the Global Wavelet Spectrum (GWS) results revealed that E0 exhibited higher peak power compared to diesel and other test fuels at 25 % and 50 % load conditions. The WPS and GWS results for E30 and E50 emulsion showed a similar trend as diesel fuel at all tested loading conditions implying a stable combustion with water-emulsified diesel. On the other hand, the prediction model anticipated the numerical values and was computed to be in strong conformity with the outcomes of the experiment. All numerical values lay within 95 % of the prediction band in regression analysis with an R2 value of 99.8 % and standard error (S = 0622) suggesting strong significant data and a better thermodynamic simulation model. In conclusion, PGM + Tween 80 could be used as a potential emulsifier to prepare stable water-in-diesel emulsion and Wavelet analysis proves to be a valuable tool for evaluating the cyclic variation observed in engine combustion. Additionally, the thermodynamic model is capable of providing accurate predictions of the engine combustion parameters.

Experimental study on the combustion performance of a turboshaft engine annular combustor

Efficient application of trapped vortex combustion technology is a hotspot in the aerospace field. This paper describes a turboshaft engine combustor based on this technology, named as mixed-flow trapped vortex combustor (MTVC). MTVC utilizes stable vortex structure formed in cavity to promote combustion stability. RP-3 aviation kerosene required for combustion is directly injected into cavity, which continuously supplies energy to combustor. Combustion performance of MTVC with different inlet aerodynamic parameters and fuel-air parameters was studied experimentally on full-ring test rig, including combustion efficiency, pressure loss and outlet temperature profile. According to the experimental findings, MTVC has very high combustion efficiency under the testing conditions of this paper, all exceeding 96%. Pressure loss coefficient is positively correlated as the square of inlet Mach number. Pressure distribution of MTVC is largely consistent with inlet velocity. Outlet temperature profile is not a straight line at radial height, showing a distribution trend of high temperature in the middle of combustor outlet, and low temperature at both ends of combustor outlet. Peak temperature is essentially at 0.6 times combustor outlet height. There is a cyclical variation in circumferential direction. The variation between combustion efficiency and aerodynamic parameters is also obtained in this paper.

Computational modelling and investigation of nucleate boiling with periodic exponential heat flux-based power-transients

The present work proposes a numerical methodology to perform single bubble nucleate boiling simulation subjected to power transients with exponential heating. Cyclic variation in transient heat flux is utilized which enables—proper characterization of the power transient parameters, parametric investigation of power transients on single bubble dynamics, and comparison between steady and transient heating condition. For constant time averaged heat flux in power cycle, it was observed that heating parameters are not having any influence on bubble departure diameter and bubble growth period whereas the bubble departure frequency is enhanced until vertical coalescence is observed. Parametric investigations based on time period of periodic heat flux and time averaged heat flux reveal the existence of a range in excursion time period which cause increase in bubble departure frequency, with applicability for controlling bubble dynamics with power transients and improving efficiency of thermal management devices using nucleate boiling.

Evaluation of engine performance and emissions in an optical DISI engine with various spark plug designs and gaps

This study aims to assess how spark-ignition engine performance and emissions are affected by both the design of the spark plug and the size of its electrode gap. Two distinct spark plug configurations (BUGAETS and NGK) with varying spark gap sizes of 1, 1.2, and 1.4 mm were used. Experiments were performed in an optical constant volume chamber as well as an optical direct injection spark ignition engine. At various equivalence ratios, the effects of both spark plugs on flame propagation, in-cylinder pressure, mass fraction burnt, and emissions for gasoline fuel were explored. For all spark plug gaps and equivalence ratios tested, the constant volume experimental results showed that the flame propagation area with the BUGAETS spark plug is faster than that with the NGK spark plug. According to the engine results, BUGAETS can produce an IMEP up to 2.4 % higher with a significant reduction in both cyclic variability and fuel consumption when compared to NGK. BUGAETS electrode consistently produces higher in-cylinder pressure and heat release rate than the NGK spark plug. When compared to NGK, the BUGAETS spark plug emits more NOx while emitting less hydrocarbon and particulate emissions. In terms of NGK electrode gaps, a comparison revealed that a gap size of 1.4 mm resulted in the most optimal engine performance and the lowest exhaust emissions. On the other hand, when it came to BUGAETS' spark plug, a gap size of 1.2 mm delivered the best engine performance and emissions out of all the tested gap sizes for the BUGAETS electrode.

Engineering properties on salt rock as subgrade filler in dry salt lake: Water retention characteristics and water migration patterns

As a special road material, salt rock has high strength and stability in arid areas, and has broad application prospects in highway engineering construction in dry salt lake areas. To investigate the water retention characteristics of salt rock and its water migration patterns under the covering effect, and to ensure the long-term durability of salt rock subgrade, this study presents a comprehensive analysis of the effect of initial dry density on the water retention characteristics of fine-grained salt rock fillers. The soil–water characteristic curve model of salt rock was recommended. The capillary water migration patterns of salt rock were proved. The water migration patterns of salt rock under freeze–thaw cycles were clarified. The hydrothermal state of salt rock subgrade under the influence of pavement overburden was evaluated based on the field monitoring. The results indicated that the water retention capacity of fine-grained salt rock filler increases with the decrease of initial dry density during the high suction stage. The Fredlund & Xing model is recommended to address the soil–water characteristic curve of fine-grained salt rock. The capillary action of salt rock filler decreases with increasing compaction. The temperature gradient from the upper boundary to the bottom of the soil column under the effect of freeze–thaw cycles is significant. After five freeze–thaw cycles, the water in the soil column continued to migrate upwards under the covering effect and temperature gradient. The relative humidity and temperature of the salt rock subgrade both show a sinusoidal cyclical variation. When the temperature range of salt rock subgrade is −6°C–30 °C, the relative humidity of subgrade is significantly correlated with temperature. This study can provide theoretical support for the disaster prevention and control of salt rock subgrade covering effect in the Lop Nor area.

Development and hygrothermal performance analysis of a novel eco-friendly insulating wall under various climatic conditions

This work proposes the development, characterization and modelling of new eco-friendly building walls integrating stabilized forms of phase change materials. The aim is to enhance the hygrothermal and energy performances of buildings by improving their management of thermal energy throughout the year and meeting users’ thermal comfort requirements. These are essential axes to help decarbonize heating and cooling, to rehabilitate buildings and to contribute to the energy transition. The experimental and numerical hygrothermal performances of two different building walls are assessed and compared under realistic weather conditions. The maximum temperature inside the wall is reduced by 2 °C for the phase change material hemp concrete compared to the reference hemp concrete in a context of typical summer heatwaves day. Both phase change material hemp concrete and reference hemp concrete showed good moisture regulation capability by dampening cyclic variations in outdoor humidity. The developed numerical model exhibited a good agreement with the experimental results with a maximum root mean square error between experimental and numerical results of about 0.6 °C and 6% for temperature and relative humidity, respectively.

Investigating the thermal and chemical kinetic effects of the internal residual on the cyclic dynamics at the dilute limits of a spark-ignition engine

The cyclic variability in the misfire and partial burn regimes of a dilute spark-ignition engine are primarily due to the feed-forward mechanism present in the residual gases. This study experimentally investigates the influence of the specific heat capacity/thermal effect and chemical kinetic effect of the internal residual on the heat release dynamics in the misfire and partial burn regimes of a dilute spark-ignition engine. Each effect is investigated by displacing excess air with bottled N2 and CO. Both short-term and long-term heat release dynamics are analyzed using association rules. Results show both an increased amount of dilution and higher specific heat capacity can result in similar dynamics. It was also found the misfire regime appears to be more sensitive to the chemical kinetic effect than the partial burn regime. Comparison of spark-to-CA05 and spark-to-CA50 between dilution methods was also conducted, where it was found the chemical kinetic effect did tend to reduce both spark-to-CA05 and spark-to-CA50. Overall, results from this study suggest different control strategies may be necessary to effectively mitigate the combustion instabilities when operating in each regime.

Cyclic Variability Analysis of an Engine Fueled With Gasoline/Natural Gas Using Return Maps and Symbol Sequences

Abstract The present work investigates the cyclic variability of a single-cylinder spark ignition engine fueled with gasoline/natural gas. Return maps and symbol sequence analysis are used to analyze the cycle dynamics at different engine loads and mixture strength. Cycle dynamics is found to be stochastic in nature at high engine loads with low cyclic variability. The frequency of deterministic patterns with close coupling between consecutive cycles is found to be high at low loads with high cyclic variability. In comparison to gasoline, the deterministic effects are found to be more predominant for natural gas fueled engine. The paper also demonstrates that the identification of deterministic patterns and omitting them through an efficient engine management system brings the engine to a stable state from unstable state. The research provides an estimate of how much better engine performance could be achieved with the knowledge of determinism in the system and the subsequent application of this knowledge for efficient engine control.