Accurate segmentation of the left atrial structure using magnetic resonance images provides an important basis for the diagnosis of atrial fibrillation (AF) and its treatment using robotic surgery. In this study, an image segmentation method based on sequence relationship learning and multi-scale feature fusion is proposed for 3D to 2D sequence conversion in cardiac magnetic resonance images and the varying scales of left atrial structures within different slices. Firstly, a convolutional neural network layer with an attention module was designed to extract and fuse contextual information at different scales in the image, to strengthen the target features using the correlation between features in different regions within the image, and to improve the network’s ability to distinguish the left atrial structure. Secondly, a recurrent neural network layer oriented to two-dimensional images was designed to capture the correlation of left atrial structures in adjacent slices by simulating the continuous relationship between sequential image slices. Finally, a combined loss function was constructed to reduce the effect of positive and negative sample imbalance and improve model stability. The Dice, IoU, and Hausdorff distance values reached 90.73%, 89.37%, and 4.803 mm, respectively, based on the LASC2013  dataset; the corresponding values reached 92.05%, 89.41% and 9.056 mm, respectively, based on the ASC2018  dataset. Atrial fibrillation (AF) is one of the most common arrhythmic conditions and is prone to a variety of complications, such as thrombosis and heart failure. The occurrence of AF is closely associated with fibrosis of the left atrium, and segmentation of the patient’s left atrial structure from cardiac magnetic resonance images for analysis and study is an important basis for the diagnosis and treatment of AF using robotic surgery . In roboTraditional image segmentation algorithms mainly include the threshold segmentation method , region t. It can also be used to process a series of 2D images with sequential relationships by converting the temporal parameter t into a spatial parameter, with t denoting the slice order [The GRU network can address the above sequential characteristics of the cardiac MRI image segmentation problem. This network is a classical recurrent neural network that is usually used to learn a set of sequential relationships of data distributed over moment ce order . In addice order  utilizesce order  and is w(1)We propose a multiscale feature fusion attention module (MSA), which can capture correlations within spatial dimensions and within channel dimensions using attention mechanisms to enhance target features and improve the network’s ability to distinguish left atrial structures to achieve the capture of targets at different scales in the image.(2)We design a bidirectional convolutional GRU network, which can simulate the complete anterior-posterior continuous relationship between a set of sequential image slices and use it to obtain the correlation of left atrial structures in adjacent image slices.(3)We design a combined loss function that allows the network to focus more on the pixel points of the left atrial structure in the image and reduce the effect of positive and negative sample imbalance.We summarize the contributions of this paper as follows:The problem of segmenting cardiac magnetic resonance images requires using the patient’s heart magnetic resonance images as input data, classifying all pixels in the image slice to determine whether they belong to the left atrium, and finally segmenting the tissue structure of the left atrium accurately.(1)Cardiac magnetic resonance images have sequential characteristics. Each set of images includes several two-dimensional image slices, and the left atrial structures contained in adjacent slices have continuity, so when extracting the left atrial structure of the current image slice, it is necessary to refer to the relevant information between the before and after image slices.(2)The left atrial structures in images have multi-scale characteristics. Due to the differences between individual patients and the special characteristics of the left atrial structure, the shape and size of the left atrial structure are not the same in each 2D image slice, and the scale difference is large. Single-scale feature extraction often loses spatial information and affects segmentation accuracy, so the use of multi-scale feature extraction needs to be considered.(3)The contrast between the left atrium and the surrounding tissue in the image is low. Cardiac MRI images contain not only the left atrial structures but also other structures of the heart, such as the right atrium and the right and left ventricles. These tissue structures have a small difference in pixel values, and the contrast is low, making the tissue structures difficult to distinguish in segmentation.(4)The percentage of pixel points of the left atrial structures in the images is relatively low. The left atrial pixel points in cardiac MRI images account for less than ten percent of the overall pixel points, and the rest are all background-like pixels. The difference in the number of pixel points between the target and the background is large, which results in a typical positive and negative sample imbalance problem.As shown in The method consists of four main components: an input layer, a convolutional neural network layer with an attention module, a recurrent neural network layer for two-dimensional images, and an output layer. As shown in (1)Input layer: Firstly, the original images are split into a set of consecutive 2D images according to the MRI scanning direction; secondly, the image slices that do not contain the left atrial structure are removed and the image size is unified; finally, each set of cardiac MRI images is divided into several image sequences and input into the network.(2)Convolutional neural network layer with attention module: The features of the left atrial structure are extracted by the convolutional neural network, and then the correlation within the spatial dimension and the channel dimension is captured by the attention mechanism to strengthen the target features and improve the network’s ability to distinguish the left atrial structure to achieve the capture of targets at different scales in the image.(3)Recurrent neural network layer oriented to two-dimensional images: A bidirectional recurrent neural network with convolutional operations is used to simulate the complete anterior–posterior continuous relationship between a set of sequential image slices, and to obtain the correlation of left atrial structures in adjacent image slices.(4)Output layer: By constructing a combined loss function, the network is made to focus more on the pixel points of the left atrial structure in the image and reduce the effect of positive and negative sample imbalance. Finally, the class to which each pixel belongs is output to achieve the segmentation of the left atrial structure in cardiac MRI images.The storage format of medical images is often difficult to apply directly to neural networks, so firstly, the cardiac MRI images were split into a set of consecutive 2D images according to their scanning direction, and the image format was converted to a common computer format. Secondly, due to the MRI equipment and individual patients, there were multiple image slices before and after each set of cardiac MRI images that did not contain the left atrial structure; these image slices without targets were excluded. In addition, the MRI images of different patients had different sizes, and all images were scaled to the same size in order to preserve the details of the training images and reduce the computational complexity of the model.Each set of MRI images, pre-processed as above, was divided into groups according to the given sequence length T. N was set as the batch-size, so the input size of the network was a five-dimensional tensor of .The convolutional neural network layer converts the input cardiac MRI image data into a feature matrix, extracts features belonging to the left atrial structure, and then uses the attention mechanism to strengthen these features. The U-Net network, with its excellent performance and high scalability, is widely used for the segmentation of medical images, and its Encoder–Decoder structure, which performs feature fusion by skip connection, effectively improves the image segmentation accuracy. Therefore, as shown in Firstly, the backbone feature extraction network is used for the extraction of high-dimensional features. The ResNet network  series iA multi-scale feature fusion attention module (MSA) was added to the skip connection to capture the left atrial structures with different scales in the image slices and enhance their features. The feature decoder part does not crop the feature maps output by the multi-scale feature fusion attention module, but directly performs a stacking operation with the feature maps obtained by upsampling, which avoids the loss of some information of the left atrial structures in the original U-Net network due to the cropping operation. At the same time, the obtained feature maps are of the same size as the input image, ensuring pixel-level prediction. The final feature map is output by the convolutional neural network layer.To capture the left atrial structures at different scales in the sequence image slices and retain more detailed information , an imprIn addition, there is a certain topological similarity between different tissues in cardiac MRI images. A double attention mechanism  was addeFor semantic segmentation, different channels in the feature map can be regarded as responses to different classes, where there is also some correlation. To model this dependency explicitly, a similar self-attentive mechanism is used to capture the correlation between any two channels, and the channel attention graph Through the dual pyramidal pooling network and dual attention mechanism in the multi-scale feature fusion attention module, the network can effectively capture the left atrial structure at different scales and enhance the representation of left atrial features.In order to simulate the continuous relationship between slices in cardiac MRI images, a recurrent neural network layer was designed for two-dimensional images. The GRU network , as a clConvGRU  is definThrough the simulation of the sequence relationship, the deep semantic features of the left atrial structure in the current image slice can be extracted and retained in the network until the next image slice is segmented, which can effectively improve the segmentation accuracy.The convolutional GRU network described above is a one-way structure, where the current output is determined by the previously learned information and the current input. Since the left atrial structures between adjacent slices in cardiac MRI images have continuity, the forward and backward sequences have the same importance , and onlThe bidirectional convolutional GRU (Bi-ConvGRU) network uses a combination of two layers of convolutional GRU networks in opposite directions. The network provides a comprehensive view of the entire sequence of cardiac MRI images, simulates the correlation between the forward and backward images, and deeply mines the correlations of left atrial structures between adjacent slices.C,H,W).The bidirectional convolutional GRU network shown in The output layer implements the class prediction for each pixel point in the cardiac MRI image based on the image features extracted and fused in the previous two stages. The segmentation task in this paper was essentially the binary classification of each pixel point within the image, so 1 × 1 convolution was used to first adjust the feature map channels of the output from the recurrent neural network layer to the number of classes, and then the Softmax function was used as the activation function to obtain the predicted probability map of the input image.For the low percentage of pixel points in the left atrial structure among the images, a combined loss function was used to alleviate this positive and negative sample imbalance. The loss function was first designed based on the Dice similarity coefficient (DSC).Focal Loss  was addeTherefore, the final loss function in this paper was:The above prediction method and loss function were designed so that the network pays more attention to fewer samples while predicting each pixel in the image, which effectively improves the accuracy of the model prediction segmentation.In this paper, the proposed network model was evaluated using two left atrial segmentation datasets, one of which was the Left Atrial Segmentation Challenge dataset (2013) , and theThe dataset provided by STACOM’13 in MICCAI’13 is a small dataset containing a total of 30 MRI images; 10 MRI images were used as the training set with manually segmented labeled images, and the rest were used as the test set without manually segmented labels. Therefore, only 10 of these images with true labels were utilized as a dataset in this paper. Each sample included the left atrium and its appendages (LAA) with 100–120 slices, of which a large number of slices do not include segmentation targets and were excluded. The actual number of slices used in the experiment was 608. The small sample size and the changes in scale presented a challenge for the accurate segmentation of the left atrium.3, with sizes ranging from 576 × 576 to 640 × 640 pixels. Each patient’s MRI image data contains both the raw data and the corresponding left atrial labels manually labeled by experts in the field. The raw data are grayscale maps and the segmentation labels are binary maps , in which white represents the target region and black represents the background region. Each patient has different-sized MRI images due to individual disparities, but the images all contain 88 slices in the Z-axis. The left atrial region of this dataset is small and the target size is highly variable, which poses a difficult problem in semantic segmentation.This dataset is from the MICCAI 2018 Atrial Segmentation Challenge and is a large medical clinical dataset that includes MRI images of 154 patients with AF. The raw resolution of the data is 0.625 × 0.625 × 0.625 mmThe proposed medical image segmentation method, based on sequence relationship learning and multi-scale feature fusion, was implemented with Python and the Pytorch deep learning framework, and the program was run on a server with an Nvidia Tesla V100 GPU and Unbuntu16.04 operating system.In this study, in order to preserve the training image details and reduce the computational complexity of the model, the images of the datasets were scaled to a size of 512 × 512 pixels (640 × 640 pixels on ASC2018), and the length of each time sequence was set to eight when training the network. Stochastic gradient descent (SGD) was used as the optimizer for the network training, and the training was divided into three steps. In the first step, the convolutional neural network layer with an attention module was first trained for the segmentation of static images with 120 iterations and a batch size of 16 subjects. The initial learning rate was 0.01, and it decayed after every 10 rounds of training. In the second step, the complete network of this paper was constructed, and the weights of the convolutional neural network layer obtained by pre-training were loaded and frozen so that the weights were not involved in updating during training; only the recurrent neural network layer was trained until convergence. The learning rate was set as in the previous step. In the third step, the weights of the convolutional neural network layer were unfrozen, and a smaller learning rate was set, in which the whole network was trained jointly until convergence. In the prediction process, the prediction results of the network were binarized to obtain the predicted segmented image.The focus of this study was the binary classification problem, and a total of three evaluation metrics, the Dice coefficient , intersesup is the least upper bound; inf is the greatest lower bound; d is the Euclidean matrix.The Hausdorff distance is the surface distance that measures the maximum distance from the point sets to the nearest point in other sets.By using the above-mentioned evaluation metrics, the segmentation results of the model can be measured from multiple perspectives, which makes the final evaluation more objective and comprehensive.In order to verify the effectiveness of the network proposed in this paper, traditional networks, U-Net, DeepLabV3+ , PSPNet,From The above methods achieved good segmentation results, but their common drawback was that they did not highlight the characteristics of cardiac MRI images with sequence relationships and low contrast between the left atrium and the surrounding tissues. The proposed method in this paper uses multi-scale feature fusion to improve the processing of global and detailed images based on skipping to connect shallow features and deep features and uses recurrent neural network layers to simulate the sequence relationships of cardiac MRI images, thus achieving better segmentation results in the left atrial dataset.However, from Ablation experiments were designed to verify the effectiveness of the convolutional neural network layer and recurrent neural network layer proposed in this paper and were set up as follows: (1) the backbone feature extraction module was replaced by ResNet50 on the basis of U-Net and was named RUNet in the experiments. (2) On the basis of RUNet, a multi-scale feature fusion attention module was constructed, which was named MUNet in the experiment. (3) On the basis of RUNet, a bidirectional convolutional GRU network was constructed, which was named SeqUNet in the experiment. (4) The complete network proposed in this paper. The model training settings in the ablation experiments were the same as those in the previous comparison experiments. The experimental results are shown in It can be inferred from In this paper, an image segmentation method based on sequence relationship learning and multi-scale feature fusion was proposed for 3D to 2D sequence conversion in cardiac magnetic resonance images and of the left atrial structure with different scales within different image slices. Firstly, the method automatically extracted target features at different scales and performed deep fusion through the design of a convolutional neural network layer with attention. This enhanced the capture of detailed information based on the acquisition of global features by using the correlation between different regions within the image and refined the target region boundaries. Secondly, for the sequence characteristics of cardiac MRI images, a recurrent neural network layer oriented to two-dimensional images was constructed to simulate the continuous relationship between sequence images and capture the correlation of left atrial structures between adjacent slices. Finally, a combined loss function was used to solve the positive and negative sample imbalance problem to a certain extent. In segmentation experiments based on the LASC2013 and ASC2018 left atrial datasets, the Dice scores of the proposed method in this paper were 90.73% and 92.05%, respectively, confirming better segmentation accuracy compared to the traditional network.The results demonstrated that the proposed method could obtain good results under most situations. However, some previous traditional methods perform better results in some metrics. In our future research work, we will learn the advantages of the traditional methods to make up for our own shortcomings. In addition, the semi-supervised or even unsupervised methods can be considered to reduce the reliance on labeled data, and the segmentation accuracy of the proposed method can be further improved by the above methods.


We examine the relationship between social insurance contributions and earnings management for publicly listed firms in China. Our empirical results show that the social insurance contributions burden significantly reduces the degree of earnings management by reducing the level of free cash flow. Additionally, the negative relation between social insurance contributions burden and earnings management is more pronounced when the internal and external social insurance pressures are high and when the firms are large non-state-owned enterprises. We also discuss the heterogeneity among firms for different financing constraints, external financing environment, regional marketization, and internal and external corporate governance. Finally, we further find that under the dual collecting system, although the social security administration is a better collecting agency, the local tax bureau acting with full responsibility is more effective than the collecting system. China's social security system is constantly evolving Hussain, . The incSocial insurance is a transfer program to maintain social stability and promote social equity  and non-SOEs. It turns out that the company size matters. The large non-SOEs are among the most affected group under the social insurance contributions burden.Next, we try to explain the story behind the negative relationship between social insurance contributions burden and earnings management. When the social insurance contributions burden reduces, the firms might obtain abundant free cash flow, and this is especially the case for many publicly listed firms. Jensen  finds thAdditionally, the negative relation between social insurance contributions burden and earnings management is more pronounced when the internal and external social insurance pressures are high. Our empirical results are still robust after using different measures, additional control variables, different time intervals, difference-in-differences propensity score matching, and placebo tests.We also discuss the heterogeneity among firms for different financing constraints, external financing environment, regional marketization, and internal and external corporate governance. The results are still consistent. Finally, we further find that under the dual collecting system, although Social Security Administration acts like a better collecting agency, the local tax bureau with full responsibility is more effective as the collecting system.To the best of our knowledge, no scholars associate social insurance contributions with earnings management behaviors. This paper attempts to fill up the gap by investigating the impact of social insurance contributions burden on earnings management and revealing its mechanism. Compared with the extant literature, our paper contributes to the literature in three ways. First, it enriches the related literature in the interdisciplinary field of labor and accounting. In recent years, many scholars pay close attention to the effects of social insurance on financial behaviors Chetty, . This paSecond, this paper expands the research perspective of earnings management literature. The extant literature mainly examines the determinants of earnings management from the perspective of internal and external corporate governance or macro-economic characteristics, but very few literature works try to explore the impact of labor costs on earnings management  data are from the past years of China's Labor Statistics Yearbook.To ensure the validity of the data, we screen the sample data based on the following criteria. First, we exclude the financial services and special treatment (ST) firms. The reason we exclude these firms since these firms have very different financial structures and performances on the balance sheet. Second, we eliminate the sample with abnormal and missing data for key variables. Third, we merge the processed data with the discretionary accruals data. Also, to control the extreme values with the risk of data overflow, the continuous variables are winsorized on 1 and 99% percentile. Finally, we obtain 15,772 observations over the 10-year-period from 2008 to 2017. The financial data for this paper are from CSMAR data Library and WIND database; the degree of relaxation of regional pension funds (SIC) is defined as the ratio of current social insurance contributions over the revenue to measure the social insurance contributions burden . Specifically, this paper measures the social insurance contributions burden by dividing the current increase in “social insurance expense” under the subject of “payroll payable” over the current revenue. The greater the ratio, the heavier the social insurance contributions burden borne by the listed companies. By taking the revenue as the denominator, we treat the social insurance contributions as an important component of the firms' labor costs. The standardization of the revenue can comprehensively depict the social insurance contributions burden for the business activities of the firm.The social insurance contributions burden . Sustaining investment is equal to the sum of depreciation of fixed assets and amortization of intangible assets divided by total assets. The level of free cash flow (FCF) is equal to the difference between the operating net cash flow after the standardization of total assets and the expected investment and sustaining investment of the firm. The greater the value, the higher the level of free cash flow within the firm.For the above equation, SIZE), debt level (LEV), return on assets (ROA), firms' capital intensity (CAPITAL), the ratio of largest shareholder shareholding (FIRST), the ratio of institutional investor shareholding (INSTITU), and equity structure (STATE). In addition, this paper also controls the year and industry fixed effects. The control variables selected in this baseline model include firm size  and the free cash flow level (FCF) as independent variables for the regressions that involve the degree of earnings management in Equation 6. If the regression coefficient of β1 is no longer significant compared with that of Equation 4, then the level of free cash flow is the mediating mechanism that the social insurance contributions burden affects earnings management, implying that Hypothesis 2 holds empirically. Noting the consistence with the practice of relevant literature, this paper clusters the standard errors of the regression model at the firm level.For the equations above, SIC), the mean is about 1.47%, which means that on average, the firms spend roughly 1.47% on social insurance contributions relative to revenue. Generally, the A-share listed firms are the elites among all Chinese firms. Thus, the social insurance contributions burden is reasonably low. The mean of discretionary accrual (DA) is 0.0063 and the median is 0.0008. This shows that overall, the listed companies have positive discretionary accrual, in other words, most listed firms manipulate their earnings upward.The descriptive statistics of the main variables in this paper are shown in FCF) has a mean of −0.035, which indicates that there is a cash gap in the internal cash flow on average. The average labor density (INTENSIVE) is 234.58, but the standard deviation is as high as 416.57, which shows that the labor intensity of different firms varies greatly. The average pension looseness (LOOSENESS) is 5.42, which is not high. It is equivalent to giving the accumulated balance of pension to the population in need of pension, with an average of 54,200 yuan per person. There is a great difference in pension looseness among different provinces based on the standard deviation and max/min value. The descriptive statistics of other variables are very close to the extant literature.The level of free cash flow  is −0.1845, which is significantly negative at the 1% level, indicating that the social insurance contributions burden significantly decreases the degree of earnings management, thus, Hypothesis 1 is supported empirically. At the same time, the result of the regression is also significant in an economic sense, that is, for each unit increase of the social insurance contributions burden, the degree of earnings management decreases by about 0.1845 on average. The finding of this regression implies that the heavy social insurance contributions burden brings heavy financial pressure to firms, which may force firms to take various measures to deal with it. Earnings management seems to have become an important way for firms to “neutralize” the social insurance contributions burden. In this regard, this paper also provides further empirical evidence in the following mechanism tests to examine whether the social insurance contributions burden, as an important expenditure of firms, reduces the free cash flow level of listed companies and whether this leads the management team to adopt less radical earnings management strategies.We now examine the relationship between the social insurance contributions burden and earnings management (Hypothesis 1). We follow Dyreng et al.'s  model toSIC of about 1.3% and the average non-SOE had an SCI of ~0.82%. By the end of the sample period, SOEs raise to an average of 1.8%, while non-SOEs contribute roughly 1.4%. This result seems to highly contradict the government's intention to reduce the social insurance contributions burden, while both SOEs and non-SOEs bear an increasingly high social insurance contributions burden.Second, both SOE and non-SOE exhibit a declining social insurance contributions burden over time at approximately the same rate. At the beginning of the period in 2008, the average SOE has an SIC are negative and statistically significant for both SOEs and non-SOEs. But the negative effect of social insurance contributions burden on the degree of earning management is greater for SOEs than for non-SOEs. The closing gap between SOEs and non-SOEs as the burden increased in recent years has been shown in In Panel B of One reason the effect of the SOEs and non-SOEs are different could be due to the significant difference among firm sizes. The SOEs normally have a much larger firm size relative to their counterpart. Next, we try to test whether the effect of social insurance contributions burden on earnings management differs by firm size. Thus, we try to examine this in two steps. First, we try to examine whether large firms significantly differ from small firms regardless of the nature of property rights. Second, we test whether SOEs differ from non-SOEs of the same size. Panel C of SIC) significantly reduces the free cash flow at the 5% level. The above findings confirm the conventional view that social insurance contributions are paying at a high proportion, causing heavy financial pressure on firms. FCF) is significantly negative at the 1% level, which indicates that the tighter the free cash flow, the higher the degree of earnings management. In general, the above results support the free cash flow as a mediator, that is, the social insurance contributions burden decreases the degree of earnings management by reducing the level of free cash flow.Next, we examine which mediator affects the relationship between the social insurance contributions burden and earnings management. SIC) is lower than that of F-value of the Sobel-Goodman test is significant at the level of 1%, which means the mediation effect has passed the significance test. This means that free cash flow plays a role as a mediator in the relationship between social insurance contributions burden and earnings management. In other words, the social insurance contributions burden causes the decline of firms' free cash flow level. As a result, firms must decrease earnings management in response to the decline of the free cash flow level. One potential explanation is: that reducing the social insurance contributions rate frees up more cash flow to spend and invest without the need for manipulating earnings. Thus, Hypothesis 2 holds.The above empirical results show that the regression coefficient of social insurance contribution burdens (SIC) is significantly positive in the high labor density group, while the level of significance decreases in the low labor density group. This shows that compared with the low labor density group, the negative effect of social insurance contributions burden on earnings management is more pronounced within the high labor density group. The reason might be that the higher the labor density, the greater the social insurance pressure for the firm, and the firms need to bear greater social insurance expenses for their employees, thus, the firms have less funding to manipulate and fewer investment projects to consider, bringing less opportunity for earnings management.The relationship between the social insurance contributions burden and earnings management might be affected by internal and external social insurance pressure. SIC) is significantly negative in the high pension looseness group but relatively less significant in the low pension looseness group. Chow's test is statistically significant at the 1% level. It further verifies that the difference in coefficients between sub-samples is statistically significant. Chow's test is valid since we assume that most control variables do not statistically differ for sub-samples. This means that the negative effect of social insurance contributions burden on earnings management is more pronounced in the high pension looseness group than in the low pension looseness group. This seems to contradict our original hypothesis that lower pension looseness results in decreasing earnings management, but it is indeed that the high looseness group has greater external financial pressure. The possible explanation is that the higher the local pension looseness, the greater the local pension balance target due to strict collecting from the social insurance agency or local tax bureau, causing greater external social insurance collecting pressure on the firms. Thus, the managers must bear greater financial pressure and have limited interest in over-investment or other tunneling behaviors, and subsequently conduct fewer earnings management.Above all, the internal and external social insurance pressure does strengthen the negative relation between social insurance contributions burden and earnings management. In other words, Hypothesis 3 is supported empirically.We conduct our robustness tests in various ways. First, as previously shown, we use both Jones and modified Jones models to measure earnings management for most of our regression results.WAGE, the total credit amount payable to employees divided by the number of employees) as the control variable in the regression model. The empirical results are reported in Second, we exclude the competitive interpretation by filling in additional control variables. Due to the strong correlation between social insurance contributions burden and wage level, the results in this paper might also be caused by the change in wage level. To exclude this competitive interpretation, we add the firms' wage level (CSR), respectively. The corporate social responsibility measures come from the WIND database.Third, to eliminate various sample noises, SIC for both low and high CSR groups are not statically significant. After 2012, the coefficients of SIC for both low and high CSR groups are statistically significant. This means that the labor protection policy is functioning and impact the effect of social insurance contributions on earnings management. Furthermore, the Chow test shows the distinction between low and high CSR is significant. Thus, after 2012, social insurance contributions reduce earnings management by a larger scale for low CSR firms compared with high CSR firms. This implies that after the labor protection policy, high CSR firms are more likely to follow the guideline. So, the social insurance contributions function less to alleviate the earnings management problem. Comparatively, those low CSR firms still rely on passive indicators such as social insurance contributions to reduce earnings management. In other words, the labor protection policy works but works better for good firms.Notice on the Periodic Reduction of Social Insurance Rates, which requires that, from 1 May 2016, the social insurance contribution paid by firms' employees in some regions should be reduced. The social insurance contributions rates in Beijing, Shanghai, Tianjin, Sichuan, Chongqing, Anhui, Jiangxi, Xinjiang, Shanxi, Henan, Hubei, Guangxi, Guizhou, Hunan, Gansu, and Ningxia were affected by this policy. By using this policy shock, the paper tries to investigate the effects of exogenous shock on earnings management behavior by constructing PSM-DID. Specifically, this paper treats the areas that reduce the proportion of pension insurance contributions as the treatment group, and the rest of the areas as the control group. First, this paper uses the propensity score matching method to pair a total of 5,980 nearest neighbor matching samples based on their debt level, return on assets, firms' capital intensity, the ratio of largest shareholder shareholding, institutional investor shareholding ratio, and growth. After matching the above variables, the difference among the variables between the treated group and the control group is <3%. Additionally, the mean value of each variable between the treatment group and the control group is not pronounced at the 5% significant level, which indicated that the matching process is well-executed. After matching the propensity score, this paper uses the paired samples to conduct the difference-in-differences test. We set the treatment group as a dummy (TREAT). For the firms located in the treated group areas, TREAT takes the value of one, otherwise zero. We also set the policy implementation time dummy variable (POLICY), which indicates that the year after the policy implementation (2016 or after) is set to be one. Finally, we construct the interactive term POLICY_TREAT to investigate the impact of the promulgation of the notice on earnings management. POLICY_TREAT regression coefficient is significantly negative at the 10% level. This shows that after the exogenous impact of the policy, the proportion of social insurance contributions in the regions where the firms are located decreases, and the degree of earnings management of the firms also decreases significantly. This implies that exogenous shocks are not only useful for identifying the causal relationship between the social insurance contributions burden and earnings management but also support the previous research that the social insurance contributions burden decreases earnings management behaviors.Fourth, we use the difference-in-differences propensity score matching (PSM-DID) approach to deal with selection bias in Fifth, to verify the reliability of the difference-in-difference model estimation conclusion, a series of placebo tests were carried out by constructing a pseudo-year policy implementation year and random sampling in POLICY_TREAT based on the randomly selected firms of the treated group and the year in which the social insurance policy was implemented; Third, we keep the other control variables unchanged and substitute the interaction terms into the previous model for regression analysis. To investigate whether the effect of the previous policy is interfered with by other non-observed random factors, this paper uses the method of non-participation replacement test to construct a placebo test based on Chetty et al. . The proPreviously, we have shown that the social insurance contributions burden significantly reduces the degree of earnings management. One possible explanation is that the social insurance contributions burden affects earnings management by reducing the level of free cash flow. Next, this paper will further explore the impact on earnings management from the perspective of labor cost in general. In addition to the internal and external social security pressures such as labor density and pension looseness mentioned earlier, this paper will also explore the circumstances under which enterprises are more inclined to reduce earnings management when facing a higher social insurance contributions burden. The factors such as financing constraints and the impact of the external financing environment are being considered. Besides, this paper tries to reveal whether earnings management is a short-term behavior or a long-term strategy in correlation with the social insurance contributions burden, and what impact earnings management will have on enterprise value and market performance. Finally, given the positive impact of earnings management caused by the social insurance contributions burden, this paper examines whether the internal and external corporate governance mechanism can play a governance role.LABOR); the other is the log of average salary per employee (WAGE), which is the log of the total payroll payable to employees divided by the number of employees. LABOR significantly reduces earnings management at the 1% level, while WAGE insignificantly increases earnings management. This implies that the cash and social insurance contributions paid to employees reduced the level of earnings management, while the payroll payable to employees' accounts is much easier to manipulate. To some extent, the payroll payable to employees' accounts increases the room for manipulation, thus increasing the level of earnings management. The conclusion in this part is somehow inconsistent with previous literature, and it deserves further investigation in the future.Social insurance is an important part of the employee payroll system, and it is mandatory. Next, this paper tries to explore whether the effects of employee compensation on earnings management are the same as the social insurance contributions burden from a broader perspective. In other words, this paper empirically tests whether employee compensation reduces the degree of earnings management to further clarify why the social insurance contributions burden reduces the level of earnings management. According to the extant literature, this paper uses two methods to measure the labor cost of an enterprise: one is the ratio of cash paid for employees to revenue  and earnings management is more pronounced in the group with high financing constraints. Chow's test  significantly decreases the degree of earnings management in the low financial marketization group. Additionally, Chow's test is statistically significant at the 1% level. It verifies that the difference in coefficients between sub-samples is statistically significant. When the external financing environment is poor, the firms are more likely to alleviate external financing difficulties through earnings management under the pressure of the social insurance contributions burden.The financing constraints faced by firms and the external financing environment may also have an important influence on the relationship between social insurance contributions burden and earnings management. It is expected that if the firms' financing constraints are tight when facing the social insurance contributions burden, mangers have fewer opportunities for earnings management. On the other hand, if the external marketization of enterprises in their regions is lower and the financial markets are less developed, it is more difficult for firms to obtain financial support from outsiders when facing the social insurance contributions burden, so the firms have more motivated to manipulate in order to make the financial statement attractive, resulting in higher earnings management. This paper uses the st Chow,  is statiSIC) has a greater negative effect on earnings management in the high proportion of management shareholding. And Chow's test is statistically significant at the 1% level. It verifies that the difference in coefficients between sub-samples is statistically significant. This means that when managers have a higher shareholding ratio and internal corporate governance is relatively better, the pressure on social insurance contributions burden increases which may cause the degree of earnings management to drop even further.The internal and external corporate governance mechanisms play an effective role in the earnings management process under the social insurance contributions burden. For the internal corporate governance mechanism, this paper selects the proportion of management shareholding as a measure to reflect the characteristics of internal corporate governance. A higher proportion of management shareholding implies a closer tie between the incentive of shareholders and managers, and the agency cost is lower, so the internal corporate governance is better. As shown in via the collecting system in SIC) on the earnings management is most significant by the local tax bureau with a full responsibility group. Chow's test is statistically significant at the 1% level. It verifies that the difference in coefficients among sub-samples is statistically significant. This is reasonable since the tax bureau has more accessible information and greater power to improve the collecting rate. The social insurance collected via the social security agency group has a relatively moderate effect. On the contrary, the social insurance contributions burden does not have a significant effect on the earnings management if the social insurance is collected on behalf of tax authorities since there might be a trade-off between tax and social insurance collecting. This suggests that the social insurance contributions collected by the local tax bureau with full responsibility are the most effective external corporate governance mechanism. This paper concludes that good internal and external corporate governance mechanisms such as management shareholding and collecting systems can effectively restrain the earnings management behavior under the social insurance contributions burden.For the external corporate governance mechanism in A natural continuation from the previous test is whether those firms that avoid taxes are more likely to avoid social insurance contributions as well. Thus, we further partition these firms into two groups, one with high tax avoidance and the other with low tax avoidance. We run the regression based on the collecting system. From For a long time, government officials and academics in China have been deeply concerned about the burden of social insurance contributions. However, there is a limited amount of literature to explore the impact of social insurance contributions on financial behavior from the micro perspective. This problem has great theoretical and practical significance under the ongoing policy reform of tax and fee reduction. Based on the research sample of A-share listed companies in China from 2008 to 2017, this paper empirically tests the relationship between social insurance contributions burden and earnings management and its mediating mechanism, examines the role of internal and external social security pressure in the relationship between the two, and tries to understand the internal logic of social insurance policy. This paper finds that the social insurance contributions burden significantly reduces earnings management. The mechanism behind this is that the social insurance contributions burden reduces the level of free cash flow, resulting in fewer over-investments and over-consumption from the managers, thus reducing the agency cost of the firms, and subsequently decreasing the degree of earnings management. At the same time, the negative impact of social insurance contributions burden on earnings management is particularly pronounced when the internal and external social insurance pressure is high. Further research also shows that different measures of labor costs give mixed results in earnings management. The negative relation between social insurance contributions burden and earnings management is more pronounced in areas with a higher degree of financing constraints and a lower degree of financial marketization. Finally, an effective internal corporate governance mechanism can help to restrain earnings management under the pressure of social insurance contributions burden, while the effects of the external corporate governance mechanism need to reconsider.For policy makers, this paper suggests that blindly reducing the social insurance rate will not only reduce the welfare of corporate employees but also create room for corporate governance. This paper finds that even if the social insurance contributions burden is reduced, because of the increase in agency cost, managers are more likely to over-invest and waste excess free cash flow, causing more severe earnings management problems. This means that social insurance rate cuts may have a negative corporate governance effect. The policymakers should, therefore, reasonably control the rate rather than keep reducing it based on the actual situation of firms. It is necessary to effectively stimulate the vitality of firms and promote high-quality economic development. Further analysis shows that although the social insurance administration function as a more effective collecting agency, the local tax bureau with full responsibility plays the most effective governance role relative to other collecting methods. Thus, we suggest making the social insurance agency a subdivision of the local tax bureau and taking full responsibility as the optimal social insurance collecting system, and for shareholders, reasonable control of managers for the use of free cash flow is the most important thing. Firms should put more effort into corporate governance to effectively prevent over-investment, over-consumption, transfer of benefits, and other misconduct behaviors. Firms should construct long-term development strategies and take effective measures to deal with the opportunities and challenges brought by the social insurance contributions burden. This paper finds that social security benefits and good corporate governance complement each other. Therefore, firms should take effective measures to improve the efficiency of corporate governance and not by reducing the social insurance contributions burden. The conclusion of this paper provides an alternative view of the ongoing reform policy of reducing the social insurance rate in China. The paper suggests that helping firms reduce the social insurance burden is not necessarily the goal. Social insurance contributions burden is not just a burden, but also a restriction measure to managers in which both employees and shareholders benefit.dataservice@csmar.com / https://www.wind.com.cn/. Any further inquiries can be directed to the corresponding author.Both CSMAR and WIND datasets require membership and requests to access these datasets should be directed to YB contributed to funding, ideas, and writing. BZ was responsible for data analysis. Both authors contributed to the article and approved the submitted version.We appreciate financial support by National Natural Science Foundation of China (NSFC) [Grant No. 72272108] for providing the funding for this study.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


The design of nanoassemblies can be conveniently achieved by tuning the strength of the hydrophobic interactions of block copolymers in selective solvents. These block copolymer micelles form supramolecular aggregates, which have attracted great attention in the area of drug delivery and imaging in biomedicine due to their easy-to-tune properties and straightforward large-scale production. In the present work, we have investigated the micellization process of linear–dendritic block copolymers in order to elucidate the effect of branching on the micellar properties. We focus on block copolymers formed by linear hydrophobic blocks attached to either dendritic neutral or charged hydrophilic blocks. We have implemented a simple protocol for determining the equilibrium micellar size, which permits the study of linear–dendritic block copolymers in a wide range of block morphologies in an efficient and parallelizable manner. We have explored the impact of different topological and charge properties of the hydrophilic blocks on the equilibrium micellar properties and compared them to predictions from self-consistent field theory and scaling theory. We have found that, at higher degrees of branching in the corona and for short polymer chains, excluded volume interactions strongly influence the micellar aggregation as well as their effective charge. Polymer-based nanoparticles play an important role in the fabrication of multi-responsive materials aimed for biomedical applications and drug delivery ,2. For dTypically, block copolymers consist of a polymer segment with a poor affinity to the surrounding solvent covalently attached to a polymer segment with a good affinity to the solvent . If the Advances in polymer chemistry ,17,18,19At the same time, dendrimers of high generations are usually very toxic due to the large number of their positively charged terminal groups. This is not a problem in gene delivery because a big positive charge of dendrimer is compensated by a strong negative charge of DNA or RNA molecules in their complex. However, many drug molecules are hydrophobic so the complex of dendrimer having a hydrophobic core and positively charged ends will be positively charged and toxic also. To overcome this toxicity problem it is possible to take the following approaches: (a) using dendrimers of lower generations in drug and gene delivery ,31, whicThis results in block copolymers that self-assemble in micelles with supramolecular dendritic coronas that mimic covalent dendrimers ,8. The aThe branched structure of the dendritic hydrophilic blocks plays an important role in determining the aggregation in a micelle and the complexation with the transported agent, as well as in the availability of terminal groups prone to be functionalized. Therefore, a deeper understanding of the role of topological defects and branching in block copolymer chains becomes indispensable. Although much effort has been devoted in the last decades to study the micellization of linear–linear block copolymers from a theoretical and simulation point of view ,42,43,44In the current work, we investigate the micellization of block copolymers, formed by a linear hydrophobic block linked to a dendritic hydrophilic one, by means of implicit-solvent coarse-grained simulations. Since micelles are rather stable configurations that weakly interact with each other, the standard simulation protocol leads to very long relaxation times ,53. TakiOur simulation model of dendritic block colpolymers is based on a previous solvent-free model of fluid bilayer membranes ,55. We htraction :(3)VattrThe latter corresponds to an attractive potential of width i, with The particles evolve following Langevin dynamics according toA single polymeric macromolecule is formed linking a linear hydrophobic chain with degree of polymerization For the ionic case, we model strong (quenched) polyelectrolytes whose fraction of charged monomers does not depend on the environmental conditions and is chemically fixed. They are simulated relying on the primitive model: charged beads interact with bare Coulomb interactions with a given valence, and the system is kept electroneutral by adding the corresponding monovalent counterions, which interact with an extra WCA potential, Equation , with b=p the number of macromolecules in the micelle, also addressed as aggregation number, and p. A proper selection of the parameter In order to determine the micelle equilibrium size and study micelle properties, we follow the following simulation protocol. Provided that micelles are relatively stable configurations and taking advantage of their weak intermicelle interaction , we focuDifferently from previous works on block copolymers that focused on simulating a given macromolecule density in a box and monitoring the aggregation number distribution ,49,52, tAll simulations have been performed using the software ESPResSo ,58 and tp linear–dendritic block copolymers can be derived by a minimization of the free energy (per molecule),From a theoretical point of view, the equilibrium structural properties of a spherical micelle formed by s is the core surface area per chain, and B blocks. The latter term can be also omitted, which is justified within the range of the thermodynamic stability of spherical micelles [, the ratio of counterions inside the corona, We have developed a coarse-grained implicit-solvent simulation model for studying the micellization of hydrophobic–hydrophilic block copolymers, based on the Deserno potential for describing the effective attraction between hydrophobic copolymers induced by the solvent ,55. For Moreover, we present a fast protocol to study the formation of single micelles. Differently from the conventional simulation protocol for micellization, the current model focuses on the formation and evolution of a single micelle, which allows a quicker equilibration of the system and which reduces the chances of getting trapped in meta-stable states. Since the computation of one realization is computationally cheap, in the order of tens of minutes to a few hours per realization, our protocol allows the parallel computation of many realizations, which results in excellent statistics and reduces the danger of exploring meta-stable states.We have tested the validity of our model against known mean-field scaling relations of equilibrium aggregation number and micellar size for linear–linear neutral and ionic block copolymers from scaling theory and self-consistent field theory ,61,62,63We further investigated the hitherto unknown behavior of ionic linear–dendritic micelles in order to understand the role of corona topology in the micellization process. Regarding the scaling laws for linear–dendritic block copolymers with an ionic dendritic hydrophilic block, we found that the equilibrium aggregation number closely resembles that obtained from the scaling behavior of linear block copolymers with strong hydrophilic polyelectrolytes in the star-like limit. Therefore, the topology of the dendritic hydrophilic blocks does not have a strong influence on the scaling behavior with respect to the polymerization degree in this limit. We found, however, that branching does have an impact on the aggregation and the micelle size, as well as the effective micelle charge, when comparing different topologies at a constant degree of polymerization. We have shown that the equilibrium aggregation number decreases with an increasing degree of branching in the hydrophilic blocks, with a stronger decline for the ionic case over the neutral one. Although neutral micelles possess a larger equilibrium aggregation number as compared to the ionic counterpart, ionic micelles tend to possess larger radii of gyration. However, this difference vanishes as the degree of branching increases. By means of investigating the density profiles, we have assessed some of the underlying theoretical assumptions in the development of micellization theories. We observed an enhanced counterion expulsion effect for micelles of block copolymers with a lower hydrophilic degree of polymerization To conclude, our work provided a simulation method that facilitates the efficient study of more elaborated dendrigraft–peptide complexes, as well as a wide variety of block copolymer micelles. Furthermore, we have conducted a detailed analysis of the role of the branching of block copolymers in the formation of micelles, which brings relevant insights for the synthesis and development of nanocarriers in the field of drug delivery.


The patchy distribution of atherosclerosis within the arterial system is consistent with a controlling influence of hemodynamic wall shear stress (WSS). Patterns of low, oscillatory and transverse WSS have been invoked to explain the distribution of disease in the aorta. Disease of coronary arteries has greater clinical importance but blood flow in these vessels may be complicated by their movement during the cardiac cycle. Previous studies have shown that time average WSS is little affected by the dynamic geometry, and that oscillatory shear is influenced more. Here we additionally investigate effects on transverse WSS. We also investigate the influence of non-Newtonian blood rheology as it can influence vortical structure, on which transverse WSS depends; Carreau-Yasuda models were used. WSS metrics were derived from numerical simulations of blood flow in a model of a moving right coronary artery which, together with a subject-specific inflow waveform, was obtained by MR imaging of a healthy human subject in a previous study. The results confirmed that time average WSS was little affected by dynamic motion and that oscillatory WSS was more affected. They additionally showed that transverse WSS and its non-dimensional analogue, the Cross Flow Index, were affected still further. This appeared to reflect time-varying vortical structures caused by the changes in curvature. The influence of non-Newtonian rheology was significant with some physiologically realistic parameter values, and hence may be important in certain subjects. Dynamic geometry and non-Newtonian rheology should be incorporated into models designed to produce maps of transverse WSS in coronary arteries. The highly non-uniform distribution of atherosclerosis within the arterial tree  implies in vitro studies have shown that transverse flow leads to endothelial dysfunction  theory postulates that disease is triggered where haemodynamic WSS is low on average  and the function  and enhafunction , and thafunction .Coronary artery disease has greater clinical importance than disease of the aorta. Conventional WSS metrics have been computed in static coronary models for over 20 years e.g., . TransWSUsing a simple curved-tube model with a cyclically changing radius of curvature, The effect of arterial motion on transWSS has not previously been examined. The Dean-like secondary flow features that largely determine transWSS  are partThe dynamic geometry used in this analysis was derived from the 4-D MRI data of Briefly, data for the right coronary artery (RCA) of a healthy 31-year-old male were acquired using an ECG- and navigator-gated interleaved spiral sequence on a Siemens Sonata 1.5 T scanner. Written consent was obtained from the volunteer, and the protocol was approved by the local ethics committee; the study complied with the Declaration of Helsinki. A total of 20 interleaves were required to fill the k-space, with each lasting 10 ms. Imaging was performed during free-breathing and a water excitation pulse was incorporated to eliminate signal from fat. The spatial resolution of the acquired images was 0.9 × 0.9 mm; the images were later reconstructed to a finer resolution of 0.45 × 0.45 mm. Approximately 15–21 cross sections were obtained along the length of the RCA at 14 different time points. Segmented lumen contours from the cross sections were interpolated using cubic splines for 3-D surface reconstruction. The cross-sectional shape of the reconstructed geometry was assumed to be constant throughout the entire cardiac cycle as effects of radial changes are small .An ECG- and navigator-gated interleaved spiral phase velocity mapping sequence  was used3) and homogeneous.Numerical methods were used to model blood flow in the coronary artery. A finite volume approach implemented in STAR-CCM+  approximated the solution of the continuity and Navier-Stokes equations. More specifically, a segregated flow solver was used to solve the equations in an uncoupled manner using a predictor-corrector scheme. A second order upwind scheme was employed for spatial discretisation and a first order Euler implicit scheme for temporal discretisation. Details of how the transient, convective, diffusive and pressure terms in the Navier-Stokes equation are discretised can be found in the STAR-CCM user guide. Polyhedral meshing was used because of its shorter computational time and greater wall shear stress accuracy ; eight pThe flow waveform shown in The boundary condition for the moving wall was incorporated using a combination of the Vascular Modelling Toolkit (VMTK), Meshmixer, Blender and the mesh morphing solver in STAR-CCM+. To validate the methods, flow was computed in a 180-degree curved tube with sinusoidally varying curvature and steady inlet velocity, as modelled by Wall shear stress vectors from the simulation were used to compute the four metrics defined in i) Static Pulsatile – pulsatile velocity with static geometry, to isolate the unsteady effect of flow pulsatility. ii) Dynamic Nonpulsatile – constant velocity at the inlet with wall movement, to isolate the unsteady effect of RCA motion. (The velocity was the mean over the cardiac cycle.)iii) Dynamic Pulsatile – pulsatile velocity at the inlet with wall motion, to give the most physiologically realistic solution.In order to investigate the effect of vessel motion on these metrics the following three simulations were undertaken:For (ii) and (iii), it is important that the moving reference frame is taken into account when computing OSI, CFI and transWSS. Since the vessel wall is moving and the mesh elements are constantly reorienting, the conventional postprocessing method of mapping WSS vectors at all time steps on to the t = 0 wall geometry results in out-of-plane vectors and can lead to errors. To avoid this, coordinate transformation was computed between t = 0 and the time under consideration for each surface element, and the vector was transformed appropriately.Distributions of the shear metrics computed in the RCA geometry were converted into 2-D rectangular maps using the t = 0 anatomy as the reference geometry. Parametrisation implemented in VMTK used the curvilinear abscissa and the angular position of each point on the wall in a plane perpendicular to the local centreline. These longitudinal and circumferential coordinates of the rectangular parametric space were used to make the cut along the inner wall of the vessel (the inner curvature at t = 0) and subsequently open the surface using Python, as shown in Non-Newtonian blood rheology was investigated using the generalised Carreau-Yasuda model. a and n are Carreau-Yasuda rheological parameters  until the criterion was satisfied. The histograms in A similar analysis showed that a time step size of 0.005 s and two cardiac cycles were sufficient; further halving of the time step or increasing the number of cycles did not change the results. For example, While the parameters of Cho and Kensey give Newtonian and non-Newtonian maps that are essentially identical, distinct differences are visible between Newtonian and non-Newtonian maps obtained with the Gijsen et al. parameters. For all four metrics, these differences are seen primarily in the proximal and distal segments of the vessel, labelled in the third row of The main aim of this study was to examine the effect of wall motion on a range of computed WSS metrics, including transWSS, in the RCA using fully subject-specific geometry, motion and inflow waveform. A secondary aim was to investigate the effect of non-Newtonian blood rheology in the model. It was predicted that metrics capturing near-wall flow components perpendicular to the mean vector – i.e, the CFI and transWSS – would be affected more than the traditional TAWSS and OSI by movement and non-Newtonian rheology as a result of their dependence on time-varying secondary flows. The geometric and flow boundary conditions were obtained in a young, healthy subject; the influence of stenotic disease on WSS metrics, and on the sensitivity of those metrics to motion and rheology, was therefore not considered. Preliminary work optimised the mesh resolution, time step and number of cardiac cycles that were modelled, and showed that the method gave results similar to those previously obtained in an idealised geometry comprising a regular tube with dynamic curvature.The maps of WSS metrics and the Spearman rank correlation coefficients computed across the different cases showed that wall motion had minimal effect on TAWSS, which is consistent with earlier studies  and theoX and Y axes in the plot represent WSS components oriented along the circumference and axis of the vessel, respectively. For truly multidirectional flow of constant magnitude, the tip of the WSS vector would trace out a perfect circle. Uniaxial flow would appear as a straight line through the origin.Polar plots were generated to further understand changes to the multidirectional nature of the flow. Such plots track the direction and magnitude of the instantaneous WSS vector over the cardiac cycle at a single location on the wall. Each point in the plot represents the position of the tip of a WSS vector with its origin at 0,0. The y-axis scaling in the figure) and the instantaneous WSS vectors show larger deviations from this mean direction, including in the reverse direction; the magnitudes are again not hugely different from the first case.Simulations carried out to study the effect of non-Newtonian blood rheology revealed a dependence on the choice of parameter values. These are determined empirically and may vary between subjects, implying that the effect of non-Newtonian rheology may also vary between subjects. There was a high Spearman rank correlation coefficient for all comparisons. Note, however, that magnitudes can be scaled in a non-linear way and still give a high correlation coefficient based on rank. To provide further information, in vivo. We have investigated its magnitude by examining WSS metrics in a model with dynamic geometry but no inflow. The resulting map of TAWSS is given in and fluid movement. Because of the way the problem is posed , the TAWSS generated by wall motion increases with distance down the artery.Finally, we separate effects of fluid moving past the wall from those of the wall moving past the fluid. As the vessel deforms, distances between points on the wall are altered. In the simplest case, if a cylinder is bent into a curved tube having the same centreline length, the inner curvature must get shorter and the outer curvature must get longer. Even in the absence of any imposed flow, there will be relative motion between the wall and fluid inside the cylinder, leading to the generation of WSS. This type of effect will occur in the RCA –2 Pa), and values of the OSI were everywhere close to its theoretical maximum of 0.5 (WSS caused by wall motion is expected to be dominantly axial, and this was confirmed by creating polar plots of instantaneous WSS vectors over the cardiac cycle for regions in proximal and distal parts of the vessel . The magm of 0.5 .cf dynamic geometry with pulsatile inflow sub-parts of CFI and transWSS for the zero-inflow condition are indeterminate – the mean WSS vector, which is required for their calculation, is theoretically 0,0 when flow is purely oscillatory, and is small in magnitude and arbitrary in direction when flow is nearly so . To estiThe RCA does not have major bifurcations, unlike the left coronary artery system, but it does have smaller branches. These were not captured in the model since the diameter of the branch arteries is smaller than the MRI slice thickness. This means that the loss of blood to these branches is not included in the model and hence the mean flow rate will be increasingly too high on progressing down the vessel. TAWSS and transWSS magnitude will show the same trend, and hence are not suitable at this stage for comparison with, say, patterns of lesions; the data show only how these metrics are affected locally by coronary motion and blood viscosity. An estimate of the size of this effect was obtained by removing taper from the RCA, a method previously employed by Zeng et al.  which asThe subject-specific waveform, obtained by phase-contrast MRI at the proximal end of the vessel, indicates that cross-sectionally averaged blood flow was in the proximal-to-distal direction at all times during the cardiac cycle. Some published waveforms show periods of reverse flow at other locations. If such a waveform were imposed, it would at least have the effect of increasing OSI values, even in the absence of secondary flow.Future work should incorporate branches, add geometries from other subjects, include a parametric study of inflow waveforms, and compare patterns of WSS metrics with the pattern of disease.This study confirms previous observations that the TAWSS is not substantially affected by coronary artery motion, and that the OSI is affected more. A novel observation is that metrics capturing transverse flows – the CFI and transWSS – are affected even more than the OSI; this effect can be attributed to changing vortical structures resulting from the dynamic curvature. An additional finding was that models of non-Newtonian blood rheology can also have a significant influence if they increase viscosity at most locations and times; that leads to increased magnitude of dimensional shear metrics but also to changes in the relative magnitudes of shear metrics from location to location. Hence studies of transWSS in coronary arteries should take vessel motion into account and, depending on the characteristics of the subject, might also need to account for non-Newtonian blood rheology. This is necessary for valid comparisons with the distribution of coronary disease.


Stabbing is relatively frequent in Morocco and constitutes a major public health concern. Our observation is interesting by the particularity and the aggressiveness of the trauma leading to an irreversible bilateral blindness.The present observation relates to a patient who was victim of a stabbing assault. The examination objectified a facial wound in front of the right lateral canthus with a broken weapon in place. An urgent craniofacial CT scan was performed showing a hyperdense penetrating path of the stabbing from the lateral wall of the right orbit, associated with a bursting of the globe, obliquely crossing the anterior ethmoid cells and severing the optic nerve on the left side. Surgical exploration was made with an extraction of the remaining part of the knife. Bilateral blindness was irreversible and the patient had a psychiatric follow up.Aggressions are a sad reality, expressing anger and violence on the part of a young adult, present in any society with often dreaded consequences. •Stabbing is relatively frequent in Morocco and constitutes a major public health concern•The clinical examination and CT scan of a facial trauma victim is essential, but should not delay treatment•The evolution of the facial wound can be punctuated with complications and/or sequelae•Prevention of facial wounds involves the promotion of education in addition to laws against aggression and aggressors. The psychological and socio- professional repercussions must always be taken into consideration. Knife attacks are relatively frequent in Morocco, and constitute a major public health concern. The present observation is interesting because it concerns a patient who was victim of a stabbing assault causing irreversible bilateral blindness.This work has been reported in line with the SCARE criteria 2This is a 37-year-old patient with no significant pathological history who was admitted to the emergency room for the management of a serious facial wound following a stabbing attack. Clinical examination found a conscious patient with a Glasgow score of 15, hemodynamically, and respiratory stable. Exofacial examination revealed a facial wound over the right lateral canthus with the weapon in place without an exit port .Fig. 1PaThe ophthalmologic examination found negative light perception on both sides with a burst of the right eyeball. The rhinological examination revealed a moderate anterior epistaxis, for which anterior wicking was carried out by merocel packing. The neurologic exam was normal, and the remainder of the physical exam was unremarkable. A craniofacial computed tomography was performed urgently showing a hyperdense path of the knife starting from the lateral wall of the right orbit, with bursting of the globe, obliquely crossing the anterior ethmoid cells and severing the optic nerve on the left side. The parenchymal scan revealed a thin section of the right temporal extradural hematoma .Fig. 2AxThe patient benefited from multidisciplinary management involving several teams: otolaryngologist, ophthalmologist, and neurosurgeon, the main operator surgeon is an ENT assistant professor.Surgical exploration was performed via the right and left trans-conjunctival route in pre- extraction, per-extraction, and post-extraction.The extraction was carefully and gradually performed with a 15 cm metal blade .Fig. 3StThe left optic nerve was entirely severed. The follow-up scan did not show any aggravation of the extradural hematoma, leading to a simple monitoring with an attitude of abstaining from neurosurgical intervention. The patient was put on antibiotic therapy of the amoxicillin/clavulanic acid type at a rate of three grams per day, anti-tetanus vaccination, and analgesic with simple operative consequences. No functional improvement was observed with a persistent absence of light perception bilaterally. A psychiatric follow up was prescribed for our patient.3The face contains noble organs as well as almost all sensory organs, which are likely to be affected during trauma. Facial wounds remain the prerogative of young adults, with a clear predominance of men, this is largely explained by risky drunk driving, brawls and assaults Many cases of bilateral blindness by indirect trauma have been reported in the literature, Azonobi IR reported the case of a young male adult who suffered transient blindness following an assault in which he sustained deep cuts to the temporal and parietal regions of the scalp In our case, the blade of the knife penetrated between the outer orbital rim and the eyeball causing its bursting seen the width of the knife blade. The papery blade and the ethmoidal cells made of the papery bone easily constitute an area of weakness crossed by the blade of the knife which has reached the large wing of the left side severing the optic nerve.The initial management is essential to prevent and limit as much as possible sequelae. Thus, the strengthening of emergency services by multidisciplinary teams considerably improves the care The extraction of the knife has to be avoided, otherwise this gesture can worsen the lesions, or lead to a potential hemorrhage, and can only be done in the operating room by allowing the control of the blade of the knife on all its route The evolution of facial wounds is most often favorable, especially when appropriate care has been instituted in time. However, this evolution can be punctuated with complications and/or sequelae especially if the lesion interests a noble element as in our case.4Facial attacks frequently affect young adults, affecting aesthetic or even functional prognosis of these patients, which can significantly impact their future life. Improving the management of facial wounds undoubtedly involves strengthening reception capacities, and the technical platform for emergencies Prevention, on the other hand, involves the promotion of education, public awareness, effective regulation of security, in addition to laws against aggression and aggressors.Not commissioned, externally peer-reviewed.Have no funding to report.The study committee of the university hospital center approves the favorable opinion to publish this work.Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.Not applicable.Azeddine Lachkar.The datasets in this article are available in the repository of the ENT database, Chu Mohamed VI Oujda, upon request, from the corresponding author.Azeddine Lachkar: the main operator surgeon (formulated the treatment plan).Drissia Benfadil: analysed and performed the literature research.Fahd Elayoubi: performed the examination and the scientific validation of the manuscript.Azeddine Lachkar was the major contributors to the writing of the manuscript. All authors read and approved the manuscript.The authors have no conflicts of interest to declare.


The conventional way of studying corrosion in marine environments is by installing corrosion coupons. Instead, this paper presents an experimental field study using an unattended corrosion sensor developed on the basis of ultrasound (US) technology to assess the thickness loss caused by general atmospheric corrosion on land close to the sea . The system described here uses FPGA, low-power microcontroller, analog front-end devices in the sensor node, and a Beaglebone black wireless board for posting data to a server. The overall system is small, operates at low power, and was deployed at Gran Canaria to detect the thickness loss of an S355 steel sample and consequently estimate the corrosion rate. This experiment aims to demonstrate the system’s viability in marine environments and its potential to monitor corrosion in offshore wind turbines. In a day, the system takes four sets of measurements in 6 hour intervals, and each set consists of 5 consecutive measurements. Over the course of 5 months, the proposed experiment allowed for us to continuously monitor the corrosion rate in an equivalent corrosion process to an average thickness loss rate of 0.134 mm/year. As the offshore wind-energy industry is prepared to increase its capacity in the following years  it is alTherefore, structural health monitoring (SHM) has become one of the major disciplines for offshore wind turbines (OWTs) with the necessity of improving operation and maintenance strategies . SHM proCorrosion in the tower and other equipment within the wind tower is one of the main consequences of an offshore environment . In partCorrosion coupons are the most conventional technique for calculating the corrosion rate in an offshore environment. Corrosion rates for construction steel below sea level are 0.2 mm/year on average; in tidal and splash zones, the rate may fluctuate from around 0.4 to 1.2 mm/year . ReporteHence, the early detection of the possible risks of structural failure allows for avoiding severe damage to the structure and saving on associated costs. For that, maintenance operators are very keen on proper and efficient solutions that can continuously monitor corrosion unattended while using wireless connectivity to obtain real-time data, with the possibility to move around the tower to inspect new areas as required.Corrosion monitoring covers a broad range of techniques that involve measuring and converting a measured parameter into corrosion loss or rate ,16,17. OUltrasound techniques for corrosion monitoring are based on the continuous reduction in the thickness of a material immersed in a corrosive environment. As such, they are normally classified as a direct, nondestructive, and nonintrusive technique. Nonintrusiveness means that the sensor itself does not influence the corrosion mechanism taking place. Furthermore, the ultrasound sensor can be located on the “clean” side of the material being corroded. There are many commercial ultrasound devices that provide valuable information about various forms of degradation . However, in general, they are classified as inspection devices rather than monitoring devices. Inspection means measurements carried out by trained staff over a predetermined time frame in accordance with maintenance schedules. Instead, corrosion monitoring devices perform very frequent measurements with the aim of detecting small fluctuations, in this case related to corrosion phenomena. Thus, the data coming from the corrosion monitoring devices can be used as input for a general assessment of corrosion. The precision obtained with ultrasound signals allows for very frequent thickness measurements that can be used to track corrosion.In this paper, we present a miniaturized corrosion monitoring solution based on ultrasound technology for offshore platforms. The ultrasound probe was glued onto an S355 bare steel sample of 5 mm in thickness. The developed system was deployed at a corrosive environment in Gran Canaria with the aim of analyzing the thickness loss evolution and estimating the corrosion rate in a real and harsh scenario.This paper is organized as follows. The theory of the ultrasound-based sensor is presented in In the ultrasound technique, the corrosion loss rate is determined on the basis of wall thickness loss. During the ultrasound test, a short duration of ultrasound energy is introduced into the test object at periodic intervals of time. The sound energy propagates through the material in the form of mechanical vibrations. This propagation attenuates and weakens the sound wave, with the travel distance mainly as a result of scattering, absorption, and reflection . When a On that basis, there are two approaches that can be used to estimate thickness during ultrasound testing: through-transmission and pulse-echo techniques. In the through-transmission technique, the transmitted part of the signal through the test specimen is monitored, whereas in the pulse-echo technique, the reflected signal at different boundaries is considered . Hence, Mode 1: excitation signal—first back-wall echo.Mode 2: near surface—first back-wall echo.Mode 3: two successive back-wall echoes.Generally, ultrasound nondestructive-testing-based measurements involve wave propagation (transit) time across a given distance and a degree of attenuation that takes place at that time . MeasureThe probes used to generate and receive ultrasonic energy are known as ultrasonic transducers. Typically, these transducers are produced from piezoelectric ceramic or composite material . The perIn our solution, we used the pulse-echo technique with a single direct-contact transducer, and Mode 3 was selected to estimate the thickness. Moreover, relative measurements were performed to observe the thickness loss in a certain location where the sensor was placed, which we discuss further in The capacity of the ultrasound technique was presented in , measuriUsing ultrasonic waves, corrosion condition is evaluated on the basis of the wall thickness loss caused by corrosion. Generally, the two common ways to determine the geometric distance measurement on the basis of an ultrasound response are phase shift and time of flight (ToF) ,28.d of the test specimen; when a single transducer is used, this relation can be stated as in Equation  [ToF is the time taken by ultrasound signal to arrive from transmitter to receiver corresponding to the thickness Equation .(1)d=c×aterial) . The mosApplying a threshold with an analog comparator at a certain amplitude level is the most fundamental and straightforward method of calculating the ToF value. A more accurate and reliable way is to apply appropriate digital signal processing techniques. In that case, the ultrasound response is processed on the basis of its echo parameters. One of the most common methods is to consider the received signal as a delayed and attenuated  version of a reference signal with noncorrelated additive noise . The objHowever, the precision of a ToF measurement depends on the quality of the received signal. ToF value estimation can become more complex in the presence of noise, interference, scattering, and attenuation of the signals . Thus, iOur solution uses a single transducer based on the pulse-echo method. As the same transducer is employed for transmission and reception, it is important to consider the dead zone of the sensor, which is the interval of the transducer ringing due to the initial pulse and not yet completely ready to receive/detect reflected echoes . Figure Our miniaturized and low-cost monitoring solution  link and analog front end (AFE) devices as shown in When the microcontroller requests a ToF measurement, the field-programmable gate array (FPGA) takes control of the devices that form the data acquisition circuit . Thus, tOnce a measurement is performed, the FPGA processes the acquired data and provides the calculated ToF estimation to the microcontroller. This signal processing is controlled by the microcontroller through the design parameters explained in ctrl from 0.2 to 2.3 V. The relation between the control voltage Vctrl and the total amplification G is given by Equation (The ultrasound response processed by the FPGA was previously amplified by a low-noise variable gain amplifier (VGA) that was composed of two cascaded amplifiers, with each one providing a maximal amplification of up 38 dB. Both amplifiers were controlled with analog voltage Vctrl for the amplifier using the microcontroller and allowing for further degrees of flexibility of its operation. The corresponding signal level of the ultrasound response (root mean square (RMS) value of the first detected echo) is measured by the FPGA and sent to the microcontroller via SPI with the aim of implementing an automatic gain controller. The signal processing algorithm for ultrasound response analysis takes place in the FPGA and is explained next in The system is capable of generating the VFurthermore, the sensor node reads from a 16-bit analog-to-digital converter (ADC) (LT2451)  through The algorithm extracts two consecutive back-wall echoes from the received ultrasound response with an echo windowing process that separates the echoes for the ToF estimation. The thickness at a certain time and position is determined by using the ToF technique as given in Equation . The sizA block diagram of the digital processing stages performed inside the FPGA to calculate the ToF value between two consecutive echoes is given in The two extracted consecutive echoes see , Echos 2Equation , where rAccordingly, the final cross-correlation peak after parabolic interpolation was obtained at The methodological design presented in  was follT follows this expression:T, the measured ToF is:The measurement of ToF in ultrasound signals propagating through steel is directly related to variation in the speed of sound with temperature and, to a lesser extent, to thermal expansion. Therefore, we needed to measure the temperature of the steel to compensate for this temperature effect in the measurement of ToF. Let us assume that, in the absence of corrosion, we were measuring the ToF of a bare steel sample of thickness The value of mber see .T. We call that value In the initial state, the bare sample presented no corrosion, and the first ToF measure was taken at temperature T, the thickness of that sample is related to ToF as follows:If we now consider the situation of a corroded sample at temperature T. We must reference all measurements to the same temperature T. Thickness T, However, T substituting Equation  protocol. The Beaglebone was basically in charge of sending the updated TOFREF value see , estimatThe corrosion monitoring setup was deployed at the PLOCAN premises in Gran Canaria .After computing the average of the five successive measurements taken every 6 h, we processed a linear fitting of the last 28 measurements, which represent 1 week of data. During the first month, we chose the location and prepared the system setup. Once the experiment had begun, we could see that the measured temperature was higher than what was expected due to the setup being exposed to direct sunlight. We corrected that during May by shadowing the setup. This means that we measured higher temperatures from March to May (particularly during sunlight periods), but taking into account that the error for a 5 mm thick steel sample is —0.6 µm/°C, the measurements could still be considered to be acceptable. On the other hand, we lost data at the beginning of July because of the accumulation of dirt and dust on the cable of the ultrasound probe. Once the cable had been cleaned, the system resumed working as usual.The thickness estimations were corrected on the basis of the reference temperature; in this case, we chose them to be the initial temperature that we had measured at the beginning of the experiment (21.3 °C). The correction to temperature variations was applied using the second term of Equation  and consAs commented in Next, we took the slope of the linear fittings shown in As we can see from the thickness measurements, The proposed experiment allowed for us to measure an average corrosion rate equivalent to 0.134 mm/year, which is in very good agreement with typically reported corrosion rates for uniform corrosion (0.1–0.2 mm/year). It is also possible to reduce the sample interval from the 6 h of the current experiment. The experimental setup could be modified to drastically reduce its power consumption by removing the Beaglebone board, resulting in a more frequent waking up of the sensor node using the same batteries. This means that ToF measurements can be taken, for example, every hour instead of 6 h, reducing the time response of the corrosion rate estimation algorithm.