The arrival of the epidemic is hitting different industries, leading to an economic downturn. As one of the pillars of the national economy, the real estate industry holds indispensable significance for the stability of the national economy. There are many sectors within the real estate industry, but the secondary housing market constitutes an important part of the real estate industry and best represents it. This study aims to explore the fluctuations of the second-hand housing market in Beijing and Changsha, investigate the impact of the pandemic on the second-hand housing market from 2018 to 2022, while also considering the effects of M2, and include a dummy variable in the regression analysis. Using an interrupted time series regression model can effectively isolate mutation conditions, observe the instantaneous impact of an epidemic, and also monitor long-term fluctuations. It can also serve as research findings and provide purchase advice for homebuyers. At the same time, provide recommendations for government policy implementation, and consider using different policies for different cities' capital situations to quickly and effectively address current issues. Internationally, China provides a good example for other countries in responding to sudden public health events.

The Consumer Price Index (CPI) is an important indicator for measuring inflation, and its classification weight and dynamic changes directly affect macroeconomic policies and residents' perception of life. Based on the monthly CPI data from the National Bureau of Statistics spanning from 2011 to 2023, this study comprehensively employs the partial derivative method, ordinary least squares (OLS) with non-negative constraints, and the generalized inverse method to systematically estimate and compare the weights of eight major categories of goods and services in China's CPI. The results indicate that the weights estimated by the three methods are generally consistent with the official reference values, with the categories of food, housing, and transportation and communication experiencing the most significant changes, reflecting the trend of adjustment in residents' consumption structure. Through time-segment regression and rolling window analysis, the dynamic evolution of weights and characteristics of consumption upgrading was revealed. Further introducing Monte Carlo simulation to quantify weight uncertainty reveals its considerable impact on the estimation of the overall CPI level. This study verifies the consistency of the data and provides a robust basis for policy evaluation and inflation forecasting. It also suggests that statistical departments should improve data accuracy and regularly publish weights to enhance statistical transparency and policy reference values.

Induced drag is one of the main sources of drag acting on a wing, and it comes from the strong vortices that tend to form near the wingtips during flight. This kind of drag not only reduces aerodynamic efficiency but also means the aircraft burns more fuel than it needs to. Wingtip devices have been around for a while now, and they are basically designed to limit how much these vortices affect overall flight performance. In this paper, we take a closer look at several different wingtip device designs and how they each influence aircraft performance. We start by going over the basic mechanism behind wingtip vortex formation and why it leads to induced drag in the first place. After that, we compare both well-established designs like blended winglets and split-tip winglets with more recent ones such as multi-tip and spiroid winglets, using data from numerical simulations and wind tunnel experiments. We also look at how each design performs in terms of lift, drag reduction, and lift-to-drag ratio. Overall, the results suggest that all the devices studied are capable of improving aerodynamic performance to varying degrees.

In recent years, housing affordability has become an urgent concern for many OECD economies, raising questions about its impact on family formation and marriage behaviour. This study examined the relationship between real residential property prices and crude marriage rates using an unbalanced panel dataset (N = 749) from 37 countries during the period from 2000 to 2022. House price data are from the OECD Analytical House Prices Indicators database, and marriage rate data are from Our World in Data. Four increasingly strict regression norms are estimated: aggregated OLS, OLS with macroeconomic control, national fixed effects, and bidirectional fixed effect models including national and annual effects. If there is no fixed effect, there is a significant negative correlation between house prices and the marriage rate, which is consistent with the assumption of affordability constraints. Once the national fixed effect is introduced, the negative correlation becomes insignificant, which shows that transnational structural differences promote set correlation to a large extent. The bidirectional fixed effect model produces a significantly positive coefficient, which may reflect the procyclical common movement between house prices and marriage rates in the country. In all norms, the unemployment rate is closely related to and negatively related to the marriage rate. These findings highlight the importance of controlling unobserved national heterogeneity when analysing housing-population links.

Housing is one of the most basic needs of humanity globally, and fluctuations in housing prices have garnered significant attention. Currently, the scale of China's second-hand housing transaction market is rapidly expanding. Understanding the factors influencing second-hand housing prices can enhance transaction efficiency and achieve a balance between supply and demand. This article obtains the Ames dataset from Kaggle and selects the Random Forest (RF) model, which is a relatively mature model in the field of housing price prediction, for training. It integrates Shapley Additive exPlanations (SHAP) and the Local Interpretable Model-agnostic Explanation (LIME) to analyze the importance of housing features. The results indicate that the RF model exhibits good performance in predicting housing prices. The SHAP analysis reveals that the most significant global features influencing second-hand housing prices are the quality of building materials and decoration, followed by living area, and there is an interaction between these two factors. Furthermore, it utilizes LIME to perform local attribution on high-quality small-area samples in the test set. The results revealed that the local contribution of living area in such samples was significantly reduced, and replaced by features such as housing functionality, indicating that the decision logic of the RF model may deviate in local areas that deviate from the mainstream distribution.

Today, badminton has become one of the world most popular sports, which is accompanied by a large demand on badminton shuttlecocks. The shuttlecock's special skirt hem structure makes its fluid mechanics greatly different from tennis and football. This thesis systematically overviews the use of Bernoulli's equation and Reynolds number in shuttlecock design and the reasons for the shuttlecock's special movement in the air. First, it records that the Reynolds number of badminton is around104to105and its drag coefficient remains nearly a constant number(≈0.6-0.7) over a wide range of speed.Second, the article shows the Bernoulli pressure difference around the shuttlecock, caused by its auto rotation, leading to curvilinear flight trajectory. Future research should concentrate on using the knowledge of fluid mechanics to produce shuttlecocks that have a smooth flight trajectory and steady moving speed at a lower manufacturing cost. The thesis aims to conclude recent shuttlecock's designing features and point out future research directions for shuttlecock designers.

This paper focuses on the equations of the expected returns of lotteries as well as their limitations. It begins by introducing the background of the lottery market, highlighting its rapid growth and increasing participation due to easier accessibility, further emphasizing the importance of analysis to ensure a higher rate of return and better odds. The basic information, such as the definition and the concepts of expected rate of return as a framework and the lottery mechanism, are then examined and explained, including jackpot dynamics and pari-mutuel prizes. Finally, the paper explains and compares two prominent models for calculating the expected rate of return: the Mecklin-Donnelly model and the Abrams-Garibaldi model, covering their methods and referenced data. Through quantitative analysis, this paper concludes that the Mecklin-Donnelly formula significantly overestimates the expected rate of return in practical lottery systems, especially under real-world conditions involving shared jackpots, taxes, and varying ticket sales volumes.

Wingtip vortices are the cause of induced drag and thus reduce the efficiency of an airplane. The vortices that occur here are caused by a pressure difference on the upper and lower surfaces of the wing, thus increasing drag that can negatively affect the following aircraft and reducing the overall efficiency of the aircraft. This paper will review the development of wingtip devices, including wingtip fences, raked wingtips, canted winglets, blended winglets and split-scimitar winglets, and each design addresses the problem of induced drag in a different way. According to the results of CFD experiments and wind tunnel tests by various scholars, this paper will compare the strengths of the two devices and also discuss their structural and weight disadvantages. At the same time, experimental data can be used to improve the realism of the performance.Blended winglets and split-scimitar winglets are generally more efficient for short- and medium-range aircraft. Raked Wingtips are suitable for long-haul aircraft, however. The above differences indicate that different designs may be more suitable for various aircraft; thus, only the one with the best performance of the device needs to be selected, rather than concluding that one design is universally superior.

Understanding the meteorological drivers of extreme pollution events is crucial for formulating effective early warning systems and public health interventions. Based on the air quality and meteorological observation data of Wuhan from 2018 to 2026, the two-stage framework of variance analysis and Bayesian inference is used to explore the impact of meteorological conditions on the probability of extreme pollution events (AQI>200). The analysis of variance is used to screen key meteorological factors, and Bayesian logistic regression is used to estimate the probability of conditions and give the posterior distribution. The results show that extreme pollution accounts for 4.65%, which is characterized by rare events; the probability of extreme pollution is the highest in cold and high-pressure bottom (CHB) weather, which is 14.2% (95% CI: 9.8%~19.6%), which is about 7 times that of the low-pressure groove (LPIT) type (2.1%). This method effectively quantifies the impact of meteorological conditions on the probability of extreme pollution, which can provide a scientific basis for early warning systems

This paper investigates how the shape of the fan blades affects airflow and electrical power consumption utilizing NASA's FoilSim JS online simulation tool. Three common blade types were tested: flat (0% chamber, 1% thickness), curved (4% camber, 12% thickness), and streamlined symmetric airfoil (0% camber, 12% thickness – NACA 0012). All blades were tested under identical airflow conditions of speed, altitude, chord, span, and angle of attack. The drag coefficient directly applied from the software shows the curved blades have CDrag of 0.113, while both flat and streamlined blades show a CDrag of 0.048. With the same voltage and motor efficiency, greater air resistance requires more current. The curved blade uses 135% more electrical power than the flat or streamlined. Surprisingly, the flat plate works about the same as the streamlined airfoil. This is because the lowest thickness allowed from the simulation is 1%, meaning that assuming the flat plate is perfectly flat cannot be achieved. The software's simplified calculations may also affect the result. However, the main result is clear: if the blades are more curved but not well streamlined, drag increases and needs more power. The paper ends with an advice for designing energy-efficient fans, such as for cooling, and transformer ventilation.