Effect of Freeze–Thaw Cycles on Microstructure and Hydraulic Characteristics of Claystone: A Case Study of Slope Stability from Open-Pit Mines in Wet Regions
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe freeze-thaw cycles have important effects to pore and fracture structures of claystone in the water-rich regions. Micro-CT scanner and 3D reconstruction method was applied to investigate the pore and fissure distribution characteristics of claystone samples. The manuscript should be revised and some suggestions are provided below for author’s consideration.
1) In the Section 2.2 “Experimental apparatus and testing method”, What is the type of Micro-CT scanner? In addition to with an accuracy of 0.1 μm, what are the other technical parameters of the device? How many claystone samples were measured in this study?
2) In the Section 2.3 “Results”, the height of claystone samples is 100mm, why is the length of specimen less than 75mm in Fig. 4? Both figures in the article are named Figure 4, which needs to be corrected. The height of the samples in Figure 4 on page 7 also seem to be less than 100mm? Why?
3) What criteria was use to classify pores and fissures?
4) In figure 7, as the number of F-T cycles increases, why the volume of pores increases firstly and then decreases? It is suggested that the author further analyze the effects of freeze-thaw cycle on different scale of pores and cracks.
5) In the Section 3.3 “Permeability properties”, what is the calculation basis of permeability? The author should add the legend in Figure 8 so that the reader can understand the results of the calculation. The unit of permeability in the manuscript is wrong, please correct it.
Author Response
Reviewer’s comments:
Reviewer #1: The freeze-thaw cycles have important effects to pore and fracture structures of claystone in the water-rich regions. Micro-CT scanner and 3D reconstruction method was applied to investigate the pore and fissure distribution characteristics of claystone samples. The manuscript should be revised and some suggestions are provided below for author’s consideration.
Response: We would like to thank you for the recognition of this manuscript. We believe these suggestions and comments will definitely improve the quality of this paper. We have adopted all your comments and revised our manuscript accordingly.
(1) In the Section 2.2 “Experimental apparatus and testing method”, What is the type of Micro-CT scanner? In addition to with an accuracy of 0.1 μm, what are the other technical parameters of the device? How many claystone samples were measured in this study?
Response: We have added the type and technical parameters of Micro-CT scanning instrument, as well as the number of samples, in the “Experimental apparatus and testing method”
The Micro-CT scans were performed by using a Phoenix V Micro-CT scanner, which is produced by Waygate Technologies Co. LTD. The maximum detection diameter and length of the device is 500mm and 740 mm respec-tively, the scanning accuracy is 0.1 μm, and the highest ray energy is 10kV. In this experiment, a selected sample was continuously scanned during the freeze-thaw cycles.
(2) In the Section 2.3 “Results”, the height of claystone samplesis 100mm, why is the length of specimen less than 75mm in Fig. 4? Both figures in the article are named Figure 4, which needs to be corrected. The height of the samples in Figure 4 on page 7 also seem to be less than 100mm? Why?
Response: Due to the poor scanning effect on both ends of the sample using this of Micro-CT scanner, the middle part (nearly 73 cm in length) of the sample was selected for analysis in this study.
The number of figures have been checked and modified in the revised manuscript.
(3) What criteria was use to classify pores and fissures?
Response: The classification of pores and fissures in claystone refers to the criteria proposed by AN et al (2022). The pores in claystone are divided into isolated pores and interconnected fissures according to the volumetric and geometric characteristics of the cracks. Specifically, the interconnected fissures have a volume greater than 0.1 mm3 and a length-width ratio greater than 3.
(4) In figure 7, as the number of F-T cycles increases, why the volume of pores increases firstly and then decreases? It is suggested that the author further analyze the effects of freeze-thaw cycle on different scale of pores and cracks.
Response: With increasing the number of freeze-thaw cycles, several newly born isolated pores are initiated in the earlier stage. In the meantime, the existing isolated pores are merged to form connected fissures, causing the volume of isolated pores increasing firstly and then decreasing during the whole freeze-thaw cycles.
According to the suggestions of the reviewer, we supplemented a more detailed analysis of the development rules of pores and fissures in the revised manuscript. For example：“Notably, the volume of isolated pores exhibits an initial increase followed by a subsequent decrease throughout the entire process of F-T cycles. This phenomenon can be attributed to the initiation of newly formed isolated pores and simultaneous merging of existing iso-lated pores, leading to the formation of connected fissures and consequent reduction in isolated pore count.”
(5) In the Section 3.3 “Permeability properties”, what is the calculation basis of permeability? The author should add the legend in Figure 8 so that the reader can understand the results of the calculation. The unit of permeability in the manuscript is wrong, please correct it.
Response: According to this comment, we have added the calculation principle of permeability in the revised manuscript.
The seepage simulations adopted the Navier-Stokes equations for governing the rules of fluid flows in porous media. The flows are considered as free particles driven by velocity-distributed functions of discrete lattice nodes. The simplified governing equation for the movement pattern of flows is shown in the uploaded manuscript.
In the original manuscript, we gave a wrong unit of rock permeability. In geotechnical engineering, the unit of permeability is “D”. We have corrected this error in the manuscript.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe study itself is quite useful and interesting. However, the manuscript has several shortcomings which need to be addressed before publication.
Starting from the abstract, it is not micron X-ray computer tomography, it is micro X-ray computed tomography.
Table 1. You mention relative density. What is this?
2.2 Experimental apparatus. I know for a fact the instrument you are using does not have an accuracy of 0.1 micrometers. Please correct. Also mention other imaging settings. Especially the correct imaging resolution is absolutely crucial information for interpretation of any results.
3.1 Two dimensional distribution of fissures. Italics in title make no sense. Text starts with something from the publication template. Careless. Please correct. Also "binary image segmentation technique" says nothing about how segmentation was done. Elaborate. Just above equations 1-2 the rho-symbols in text are wrong. Correct.
Figure 3. Please use image registration tools to make sure your slides match. Now the slides on the same row are not from the exact same height in the sample. You cannot compare the areas when you are not looking at the same part of the sample! Choosing same slice number is NOT accurate enough.
Figure 4. Good way to visualize this! Except, your legend has no colors so hard to say which graphs they correspond with. The graphs are quite smooth, are you using a running average or not analyzing every slice? Explain what you do here. Also, you can see quite easily here that your images are not aligned, the peak positions don't match.
Table 2. Are you sure the values are right? Lower average porosity at 10 cycles? How and why?
Figure 4. Images are not in the same angle for each amount of cycles. Makes it much harder to compare results. Please re-do.
Figure 5. Why the awful big balls? Please replace with something more accurate and traditional. Is there any physical reason for an exponential fit there? Seems to be just guesswork that happens to match this particular set of results. I would leave the fit out completely. Linear fit in Fig. 6 makes sense, this one does not.
3.3 Permeability properties. This analysis is probably quite accurate for the late stages of the samples, but for the early stages you completely fail to acknowledge the resolution effect. The fact is, there almost certainly are flow pathways through the sample, they are just too small for the XCT resolution. So analysis based on visible porosity cannot give a meaningful result. With higher porosity and connectivity in the late stages the non-visible porosity can correctly be ignored, as the favorable pathways are likely to dominate anyway. Also, try to explain the decrease in permeability in the last step? Seems very counter-intuitive.
Figure 10. Replace the balls and maybe remove the exponential fit unless it can be justified.
Data Availability, Acknowledgments, Conflicts of interest. You were supposed to replace the placeholders with your own text.
Comments on the Quality of English LanguageIt is readable, but must be improved for publication. Some terms are wrong, a lot of grammar is wrong. Please get it proofread.
Author Response
Reviewer #2: The study itself is quite useful and interesting. However, the manuscript has several shortcomings which need to be addressed before publication.
(1) Starting from the abstract, it is not micron X-ray computer tomography, it is micro X-ray computed tomography.
Response: We thank the reviewer for pointing out this typo. We made a correction in the manuscript.
(2) Table 1. You mention relative density. What is this?
Response: The authors apologize for not giving the spellling of relative density in Table 1. We modified the “relative density” as “specific gravity” in the revised manuscript.
(3) 2 Experimental apparatus. I know for a fact the instrument you are using does not have an accuracy of 0.1 micrometers. Please correct. Also mention other imaging settings. Especially the correct imaging resolution is absolutely crucial information for interpretation of any results.Response: The accuracy of 0.1 μm is the maximum theoretical accuracy. In this study, the resolution of the images obtained by micro-CT scanning is 20 μm. Thanks to the reviewer's reminding, we added this important information in the manuscript.
(4) Two dimensional distribution of fissures. Italics in title make no sense. Text starts with something from the publication template. Careless. Please correct. Also "binary image segmentation technique" says nothing about how segmentation was done. Elaborate. Just above equations 1-2 the rho-symbols in text are wrong. Correct.
Response: Thanks to the reviewers for their comments. We are sorry that the text in the 3.2 title is incorrectly formatted. And we have changed the italics to the bold. Besides, we have added some detail of "binary image segmentation technique". The binary image segmentation technique is to mark the pores and background in the grayscale images with two opposite colors. Subsquently, the pores in the claystone are preliminarily discriminated, which provides a basis for the extraction and analysis of quantization feature. Moreover, the symbol of ρsiis corrected in the revised manuscript.
(5) Figure 3. Please use image registration tools to make sure your slides match. Now the slides on the same row are not from the exact same height in the sample. You cannot compare the areas when you are not looking at the same part of the sample! Choosing same slice number is NOT accurate enough.
Response: Thank the reviewer for pointing out this detailed problem. We find a slice of CT images in Figure 3 that does not correspond exactly to the sequence number of the other images. So we replaced it with an image with the correct serial number. Figure 3 is revised in the uploaded manuscript.
(6) Figure 4. Good way to visualize this! Except, your legend has no colors so hard to say which graphs they correspond with. The graphs are quite smooth, are you using a running average or not analyzing every slice? Explain what you do here. Also, you can see quite easily here that your images are not aligned, the peak positions don't match.
Response: We recalibrated the legends of curves in Fig. 4. Figure 4 shows the values of 2D porosity extracted every 10 images. The idea aims to reduce calculation time. We observed very little difference between the first and last five images in the micro-CT scanning results. So we applied this approach.
In the process of F-T cycles, the fissure development presents different states at different positions. Therefore, the aligned peak positions are not statistical error, but a manifestation of the heterogeneous characteristics of claystone. Figure 4 is revised in the uploaded manuscript.
(7) Table 2. Are you sure the values are right? Lower average porosity at 10 cycles? How and why?
Response: The authors incorrectly labeled the mean value of the porosity of specimen at 0 cycle in Table 2. The correct value of area-porosity is revised as 1.128. We apologize for this careless mistake.
(8) Figure 4. Images are not in the same angle for each amount of cycles. Makes it much harder to compare results. Please re-do.
Response: According to the reviewer's opinion, we rearranged the angles of models in this figure
(9) Figure 5. Why the awful big balls? Please replace with something more accurate and traditional. Is there any physical reason for an exponential fit there? Seems to be just guesswork that happens to match this particular set of results. I would leave the fit out completely. Linear fit in Fig. 6 makes sense, this one does not.
Response: We agree with the reviewer and use a smaller size of balls in the figure. We used the fitting curves to predict the trend of volume-porosity and connectivity degree as the number of F-T cycles increased. We believe that the function of fitting curves in the Figures can reflect the variation of pore parameters. The fitting result is not a coincidence, but reflects the development rules of pore distribution in claystones during F-T cycles, Also, this variation is also a manifestation of mesostructural damage. The mechanism is explained in detail in the folowing paragraghs.
(10) 3 Permeability properties. This analysis is probably quite accurate for the late stages of the samples, but for the early stages you completely fail to acknowledge the resolution effect. The fact is, there almost certainly are flow pathways through the sample, they are just too small for the XCT resolution. So analysis based on visible porosity cannot give a meaningful result. With higher porosity and connectivity in the late stages the non-visible porosity can correctly be ignored, as the favorable pathways are likely to dominate anyway. Also, try to explain the decrease in permeability in the last step? Seems very counter-intuitive.
Response: We are very grateful to the reviewer for this comment. In the early stage of freeze-thaw, the permeability simulation value is relative small. This is a similar phenomenon which also can be found in the previous literature (AN et al, 2023). The main reason is that non-visible voids in dense specimens are difficult to be completely captured by micro-CT scanning. This problem can only be solved by improvements in CT scanning technology. However, we believe that the simulation results of this study are still valuable. The main reason is that compared with other dense rocks, the microstructure of claystone is relatively loose, and the voids are generally visible and can form effective seepage channels. The simulation result in this study is the average value obtained after many calculations. So the results have certain engineering reference significance.
In addition, the permeability of the last step did not decrease. Generally, the permeability increased by 35.8% during the process of 30 to 50 F-T cycles. However, the growth rate of permeability decreased compared with the earlier period.
(11) Figure 10. Replace the balls and maybe remove the exponential fit unless it can be justified.
Response: We agreed with the reviewer to reduce the size of the ball.
We believe that the fitting results in Figure 10 have certain physical significance. The reasons are as follows. The results of seepage numerical simulations indicate that the connectivity of fissures greatly impact the permeability of claystone. As microstructural damage deepens, isolated fissures with small volumes expand, interconnect, and developed into effective fissures, resulting in enlargement and continuous expansion of interconnected fissures in the claystone. Furthermore, it leads to a gradual increase in the number and volume of seepage channels while enhancing the hydraulic properties. Consequently, the effective fissures induced by the action of F-T cycles not only weaken the integrity of the rocks but also augment the permeability in the claystone. Therefore, the significant data correlation between permeability and porosity parameters can be explained from the perspective of microstructure.
(12) Data Availability, Acknowledgments, Conflicts of interest. You were supposed to replace the placeholders with your own text.
Response: Thanks to the suggestions of the reviewer. We have replaced these contents.
(13) Comments on the Quality of English Language
It is readable, but must be improved for publication. Some terms are wrong, a lot of grammar is wrong. Please get it proofread.
Response: Special thanks go to your suggestion of this paper which helps us to improve the English language. We have checked and improved the writing this manuscript with the help from a native English speaker.
Reviewer 3 Report
Comments and Suggestions for AuthorsLines 2-4, Title: It needs some little, but critical modification as follows:
“Effect of freeze-thaw cycles on microstructure and hydraulic characteristics of claystone: A case study of slope stability from open-pit mines in wet regions”
Instead of
“Effect of freeze-thaw cycles on microstructure and hydraulic characteristics of claystone in an open-pit slope of water-rich regions”
Lines 12-31: It is well-written and includes scope and aims of study, in addition to methods used to investigate behaviour of claystone in open-pit mine slope stability in presence of water. Therefore, it is an informative abstract and report expected output and applicability in the mining industry. Only minor corrections, mostly linguistics are needed as shown in the annotated pdf attachment.
Line 32, Keywords: They are ok, enough and covers all items of work.
Line 38, Introduction: In Water, the journal, as well as the majority of MDPI publications references are cited in the text numerically. This should be compatible with the numbering in the reference list.
Lines 46-47: A little modification for the definition of “claystone” is needed, particularly its grain size, classification as clastic rock and its composition of clay minerals.
Line 103, Introduction: Do not underline the degree symbol, and please apply to all over the text.
Line 129: The only and serious concern about Figure 1 is the size of 3 photographs for the cores obtained from drilling in the mine. It is enough to show one core for each and no need to present the entire core box. This can help to show any megascopic features and structures.
Line 130: Caption of Table 1 needs some modifications.
In the last row, Table 1: Can you specify the group of other minerals in the investigated claystone because 5% is not a little mineralogical amount?.
Line 146: In the "Results" section, the authors mixes results with interpretation so it seems as a discussion section, which is of course necessary for the main topic of work that concerns with open-pit slope in presence of water and its imaging. It is recommended to separate results from discussion indeed.
Line 163: The 2D grey-scaled photos in Figure 3 can be in better quality with respect to resolution and contrast.
Line 317: Please unify this all over the text. As suggested in the modification of the title, wet region can be used instead of water-rich regions.
Line 322: Use "Conclusions" instead of "Conclusion". The given conclusions are good and straightforward but they can be shortened, and if needed make them 6 bullets instead of 4.
The reference list needs very careful re-editing taking in consideration punctuation and numbering.
Comments for author File: 
Comments.pdf
Minor English polishing is needed ONLY.
Author Response
Reviewer #3:
1) Lines 2-4, Title: It needs some little, but critical modification as follows:
“Effect of freeze-thaw cycles on microstructure and hydraulic characteristics of claystone: A case study of slope stability from open-pit mines in wet regions” Instead of “Effect of freeze-thaw cycles on microstructure and hydraulic characteristics of claystone in an open-pit slope of water-rich regions”
Response: We appreciate the reviewers' comments on the title of this manuscript. We agreed and amended the title in the revised manuscript.
2) Lines 12-31: It is well-written and includes scope and aims of study, in addition to methods used to investigate behaviour of claystone in open-pit mine slope stability in presence of water. Therefore, it is an informative abstract and report expected output and applicability in the mining industry. Only minor corrections, mostly linguistics are needed as shown in the annotated pdf attachment.
Response: We would like to thank the reviewers for your comment on abstract. According to your comments, we have made detailed revisions to the grammar, spelling issues of this manuscript.
3) Line 32, Keywords: They are ok, enough and covers all items of work.
Response: Thank you for thw comment on the Keywords.
4) Line 38, Introduction: In Water, the journal, as well as the majority of MDPI publications references are cited in the text numerically. This should be compatible with the numbering in the reference list.
Response: We thank the reviewer for pointing out the incorrect reference format. We made a correction in the manuscript.
5) Lines 46-47: A little modification for the definition of “claystone” is needed, particularly its grain size, classification as clastic rock and its composition of clay minerals.
Response: According to the new Oxford Dictionary, the“claystone” is a type of fine-grained rock consisting of compacted clay particles. We refer to the previous literature to define claystone.
In addition, we add some descriptions about the particle size and mineral composition of the claystones. “The claystone is a widely-distributed sedimentary rocks. The content of clay minerals in claystone is usually greater than 50%, and the particle size is below the range of 0.005 ~ 0.0039 mm. The minerals of claystone mainly consists of kaolinite, polyhydrokaolinite, montmorillonite, hydromica, and chlorite.”
- Line 103, Introduction: Do not underline the degree symbol, and please apply to all over the text.
Response: We have correct the degree symbol as as the reviewer pointed out.
7) Line 129: The only and serious concern about Figure 1 is the size of 3 photographs for the cores obtained from drilling in the mine. It is enough to show one core for each and no need to present the entire core box. This can help to show any megascopic features and structures.
Response: We thank the reviewer for the suggestion on Fig. 1. We made a correction for Figure 1 in the manuscript.
8) Line 130: Caption of Table 1 needs some modifications. In the last row, Table 1: Can you specify the group of other minerals in the investigated claystone because 5% is not a little mineralogical amount?. Response: We thank the reviewer for the suggestion on table 1. We made a correction in its caption and content.
Table 1. Physical and mineralogical properties of the of claystone.
|
Physical property |
Value |
|
Moisture content (%) |
22.9 |
|
Density (g/cm3) |
2.09 |
|
Specific gravity |
2.70 |
|
Initial porosity (%) |
11.9 |
|
P-wave velocity (m/s) |
2336 |
|
Permeability (cm/s) |
1.03×10−5 |
|
Unconfined compressive strength (MPa) |
2.68 |
|
Mineral composition (%) |
Value |
|
Quartz |
32.8 |
|
Feldspar |
13.5 |
|
Hydromica |
8.4 |
|
Montmorillonite |
12.9 |
|
Kaolinite |
24.4 |
|
Chlorite |
4.3 |
|
Others |
0．7 |
9) Line 146: In the "Results" section, the authors mixes results with interpretation so it seems as a discussion section, which is of course necessary for the main topic of work that concerns with open-pit slope in presence of water and its imaging. It is recommended to separate results from discussion indeed.
Response: We agree with the reviewer for the separation of Results and Discussion sections.
The discussion part of the revised manuscript mainly gives the correlation between characteristics of pore distribution and permeability. The mechanism analysis of poresity and permeability evolution rules is also given in Discussion.
10) Line 163: The 2D grey-scaled photos in Figure 3 can be in better quality with respect to resolution and contrast.
Response: The resolution of the Figure 3 in the original manuscript is actually quite clear. The reason for the lack of resolution may be the loss of image quality after word is translated into PDF version. The authors have attached high definition images.
11) Line 317: Please unify this all over the text. As suggested in the modification of the title, wet region can be used instead of water-rich regions.
Response: We agree with the reviewer. In the revised draft, we have uniformly revised “water-rich region”. to “wet region”.
12) Line 322: Use "Conclusions" instead of "Conclusion". The given conclusions are good and straightforward but they can be shortened, and if needed make them 6 bullets instead of 4.
Response: We would like to thank the reviewers for your comment on abstract. According to your comments, we have divided the conclusions into six bullets.
13) The reference list needs very careful re-editing taking in consideration punctuation and numbering.
Response: We appreciate the reviewers' comments on the reference list. We have carefully checked and corrected the citation. And the format of the references has been further modified according to the journal regulations.
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsI thank the authors for improving the manuscript. Considering the actual content, there is still some improvement required for CT part, but otherwise it's quite close to acceptable. Visually it's not really up to any scientific standards in my opinion, but it is up to the editor to decide how much it matters.
Starting from the abstract, spelling errors are still plentiful. "ComputeD tomography", not "ComputeR tomography" as written. Also, are the microstructural changes crucial in determining hydraulic characteristics, or is observing/measuring the changes the crucial thing?
2.2 Experimental...
Continously scanned. No it wasn't. That would mean it's constantly spinning throughout the cycles and I don't believe that was the case. Also as far as I know there is no such thing as phoenix v. Your image is showing phoenix v|tome|x s, maybe you have that? If so, your specifications are not correct at all, unless you have some very strange version of the instrument.
3. Results
Literally starts with a piece of placeholder text. Very careless.
Segmentation is still not described at all. You are now describing in the text what binary segmentation means, not how it was done here. There are several possible methods of doing binary segmentation and you need to specify which one you used so the validity of the method can be estimated.
Figure 5 the angles still don't match
Figure quality in general is not great. Different symbols, different colors, different sizes of different symbols. Lines connecting the dots without any meaning (Fig. 10) are particularly noteworthy.
Comments on the Quality of English LanguageAlready mentioned in general comments.
Author Response
Response to Reviewers’ Comments (Round 2)
Comments and Suggestions for Authors
I thank the authors for improving the manuscript. Considering the actual content, there is still some improvement required for CT part, but otherwise it's quite close to acceptable. Visually it's not really up to any scientific standards in my opinion, but it is up to the editor to decide how much it matters.
Responce：Please find below our responses to the reviewers' comments for the manuscript. We sincerely appreciate the constructive comments from both the Reviewer. We have adopted all these comments and revised our manuscript accordingly. We hope that these corrections will meet with approval of the journal.
Comment (1)： Starting from the abstract, spelling errors are still plentiful. "ComputeD tomography", not "ComputeR tomography" as written. Also, are the microstructural changes crucial in determining hydraulic characteristics, or is observing/measuring the changes the crucial thing?
Response: We thank the reviewer for the suggestion on Abstract. We made corrections in its spelling issure. The term of "Computer tomography" has been revised as “Computed tomography”. And the sentence in question is revised as “Microstructural changes are observed as a crucial factor in determining the hydraulic characteristics and mechanical behaviors of claystone”
Comment (2)： 2.2 Experimental...
Continously scanned. No it wasn't. That would mean it's constantly spinning throughout the cycles and I don't believe that was the case. Also as far as I know there is no such thing as phoenix v. Your image is showing phoenix v|tome|x s, maybe you have that? If so, your specifications are not correct at all, unless you have some very strange version of the instrument.
Response: We would like to thank the reviewers for your comment on “2.2 Experimental apparatus and testing method”. According to your comments, we have made detailed revisions to these issues. We agree that the“Continously scanned” is an inappropriate description. We have deleted this phrase. The type of the insturement is “phoenix v|tome|x s" and we have corrected it.
Comment (3)： 3. Results
Literally starts with a piece of placeholder text. Very careless.
Segmentation is still not described at all. You are now describing in the text what binary segmentation means, not how it was done here. There are several possible methods of doing binary segmentation and you need to specify which one you used so the validity of the method can be estimated.
Response: We thank the reviewer for pointing out the careless mistake. We have deleted the piece of placeholder text. And we have added the description of binarization in the revised manuscript.
“The OTSU algorithm which is widely considered as an effective approach for threshold selection is used in this study.”
Comment (4)： Figure 5 the angles still don't match
Figure quality in general is not great. Different symbols, different colors, different sizes of different symbols. Lines connecting the dots without any meaning (Fig. 10) are particularly noteworthy.
Response: We have done our best to modify the angle of models in Figure 5. Besides, we carefully modify the symbols, colors, caption and description of the Fig. 10. The lines connecting the dots has been deleted.
Once again, we would like to thank the reviewers for their valuable comments.
Yours sincerely,
Zhifang Liu on behalf of the authors
