Review Reports - How Ultrasonic Pulse-Echo Techniques and Numerical Simulations Can Work Together in the Evaluation of the Elastic Properties of Glasses

Round 1

Reviewer 1 Report

The manuscript titled "How ultrasonic pulse-echo techniques and numerical simulations can work together in the evaluating the elastic properties of glasses" presents a captivating approach, particularly by employing the Elasto-dynamic Finite Integration Technique (EFIT) to simulate ultrasound propagation in glass media. The simulation outcomes offer intriguing insights into electric constants, and enable the detection of structural change that related to elastic properties of glass samples. These findings hold significant potential for non-destructive testing of glasses. However, before publication, some questions have arisen that warrant careful consideration. These questions are outlined below:

1. In section 2.2, the phrase "...purchased by Olympus" should be rephrased, and the abbreviation "TTi" should be defined.

2. In my opinion, if you wish to use the term 'references therein' for citations, I would recommend two examples to help readers who may not be accustomed to this terminology better understand. The first example is '[32-34] and the references cited within them,' while the second example is '[32-34] and the papers cited therein.' However, if you strongly prefer using the phrase '[32-34] and references therein,' it should also be considered appropriate.

3. In section 3, the authors present Figure 2(b) displaying the experimental and simulated/calculated ultrasonic signals. It is evident to me that they are not accurately matched. I kindly request the authors to provide additional clarification on the reasons behind this mismatched outcome, with the intention of aiding non-expert readers in comprehending the underlying factors at play.

4. In section 4, mass density symbol in the text should be in the same format as in related Equations.

5. In the fluorophosphate glasses, the authors did not observe samples with a mole fraction of Sr(PO₃)₂ between 0.45 and 0.65, as devitrification occurred. This devitrification poses an obstacle to the measurement of ultrasonic waves for several reasons. Firstly, devitrified samples can have altered structural properties, leading to abnormal propagation of waves. Secondly, the presence of devitrification may introduce additional scattering or absorption of the ultrasonic waves, affecting the accuracy of measurements. Therefore, it is important to clarify whether the devitrification of these samples could potentially yield interesting results related to structural changes in the glasses, which could provide valuable insights. Could you please elaborate on this point?

Author Response

Dear Editor,

Thank you very much for your e-mail concerning the response of the four reviewers to our manuscript Ref. No.: applsci-2476688.

Here it follows a detailed response to all the points and criticism that the referees have raised. All necessary changes/corrections are highlighted with yellow color for Reviewer #1 and green color for Reviewer #2 and cyan color for Reviewer #3 in the revised manuscript for your convenience. We trust now that the revised version of the manuscript is suitable for publication in the Applied Science.

Reviewer #1 comments:

Issue 1:

In section 2.2, the phrase "...purchased by Olympus" should be rephrased, and the abbreviation "TTi" should be defined.

Reply to Reviewer comment and changes made:

We revised phrase "...purchased by Olympus" according to reviewer’s suggestion (page 4, lines 139, 142-143). TTi is a brand name and not an abbreviation. All changes are highlighted with yellow.

Issue 2:

In my opinion, if you wish to use the term 'references therein' for citations, I would recommend two examples to help readers who may not be accustomed to this terminology better understand. The first example is '[32-34] and the references cited within them,' while the second example is '[32-34] and the papers cited therein.' However, if you strongly prefer using the phrase '[32-34] and references therein,' it should also be considered appropriate.

Reply to Reviewer comment and changes made:

We revised this sentence, accordingly (page 5, line 179).

Issue 3:

In section 3, the authors present Figure 2(b) displaying the experimental and simulated/calculated ultrasonic signals. It is evident to me that they are not accurately matched. I kindly request the authors to provide additional clarification on the reasons behind this mismatched outcome, with the intention of aiding non-expert readers in comprehending the underlying factors at play.

Reply to Reviewer comment and changes made:

Despite the fact that several “defect” acoustic phenomena including dispersion, scattering, reflection and mode conversion phenomena, have been taken into consideration in the numerical simulation there are minor differences between the experimental and the theoretically predicted spectrum. These differences are due to the non-perfect parallelism between the parallel phases of the glass samples. From experimental point of view, the non-parallelism induces a dispersion of the acoustic beam that cannot be incorporated into the simulation procedure. An additional cause of the relative intensity differences is the shape of the initial pulse. In the numerical simulation the shape of the pulse was raised cosine, while the experimental waveform is quite different since the probe is not ideal.

These notes were added in the revised manuscript (page 7, lines: 218-226) and are highlighted with yellow for your convenience.

Issue 4:

In section 4, mass density symbol in the text should be in the same format as in related Equations.

Reply to Reviewer comment and changes made:

We agree with reviewer’s comment, and we revised the mass density symbol, accordingly (page 8, lines: 253).

Issue 5:

In the fluorophosphate glasses, the authors did not observe samples with a mole fraction of Sr(PO3)2 between 0.45 and 0.65, as devitrification occurred. This devitrification poses an obstacle to the measurement of ultrasonic waves for several reasons. Firstly, devitrified samples can have altered structural properties, leading to abnormal propagation of waves. Secondly, the presence of devitrification may introduce additional scattering or absorption of the ultrasonic waves, affecting the accuracy of measurements. Therefore, it is important to clarify whether the devitrification of these samples could potentially yield interesting results related to structural changes in the glasses, which could provide valuable insights. Could you please elaborate on this point?

Reply to Reviewer comment and changes made:

It is widely accepted that the structure of a glass material is completely different compared with the corresponding crystalline material. Glass has only a short-range order of atoms, while crystals have a long-range order. When studying the structure of the specific fluorophosphate glasses (references 21 and 22), our aim was to study in detail the structure of the amorphous phase and this is the reason why we restricted our analysis only in the glass formation range. We agree with reviewer that crystalline samples can have altered structural properties and they may lead to abnormal propagation of waves compared to the corresponding glasses of the same composition causing thus additional scattering or absorption of the ultrasonic waves. To conclude, the comparison of the acoustic wave propagation in crystalline and amorphous materials could not provide any new information. In terms of elastic properties, it is beneficial to examine separately the crystalline and the glassy systems despite their identical chemical composition. These notes were added in the revised manuscript (page: 10, lines: 284-295).

Please, also read our reply to Issue #10 raised by reviewer #2. We added in the revised manuscript, right above the conclusion section, three paragraphs that are also related with issue #5 of reviewer #1 (pages 17-18, lines: 410-446).

Reviewer #2 comments:

The paper reports the research performed on fluoro-phosphate and aluminosilicate glasses using elasto-dynamic finite integration technique (EFIT). Elastic parameters were determined for both materials using experimental data and simulations (some literature data was used for comparison). A good agreement of both approaches was observed. The topic meets the scope of the journal. In my opinion, the manuscript has generally a good quality and the results can be interesting for potential readers. However, some remarks need to be addressed. My current recommendation is to accept the manuscript after major revision. Specifically, the original contribution of the current research need to emphasized. I believe that the Authors can introduce some changes to made the paper publishable in Applied Sciences. A few remarks are presented below.

Issue 1:

Title. The title is appropriately formulated and gives a general view of the content of the paper.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 2:

Structure. The structure of the manuscript is correct. The following sections are logically connected. The manuscript is easy to follow.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 3:

Language. The quality of the language is appropriate, substantial changes are not required. Some remarks:

– spaces are sometimes missing between values and units (e.g., lines 217-219);

– line 227 – different symbol is used for density;

– fluoro-phosphate is sometimes written with and sometimes without hyphen, please unify throughout the whole manuscript;

Reply to Reviewer comment and changes made:

We performed the suggested changes in the revised manuscript (lines: 31, 189, 253, 533).

Issue 4:

Keywords. The keywords are appropriate to the theme of the manuscript.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 5:

Novelty. A clear explanation of what is new in the paper should be included in the last paragraph of Introduction and in the Abstract. Currently, I do not find direct information about original element of the study. Partially, the contribution of the paper is described in line 124-126, however, some more description is required.

Reply to Reviewer comment and changes made:

We agree with reviewer’s comment, and we added a clear explanation concerning the added value of the present work in Abstract (page: 1, lines: 28-30) and Introduction (page: 2, lines: 91-96) sections.

Issue 6:

Introduction. The Introduction section gives a general overview of the current state-of-the-art. The number of citations is sufficient.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 7:

Equations. The equations are formatted properly. The references to the variables from equations are sometimes not formatted well in the main text and in the figures. Italic should be used, e.g., lines 160, 230, 232, 234 and Figure 1. Sometimes spaces are missing (e.g., lines 176 and 182). These are just formatting changes that can be corrected during careful proofreading of the manuscript. I would also recommend to use M instead of L as a ‘longitudinal modulus’, v instead of σ (not to mix with stress) and E instead of Y. The proposed symobls are more common, however it is just suggestion.

Reply to Reviewer comment and changes made:

We performed a careful proofreading of the manuscript and we proceeded to formatting changes in several parts of the manuscript. We also considered the recommendation for symbol changes for specific elastic parameters. Nevertheless, we did not perform any changes in the elastic properties symbols in order to retain a uniformity in the symbols of all elastic properties with the previous papers on fluorophosphate (references 21, 22) and aluminosilicate (reference 30) glasses.

Issue 8:

Figures. The figures are legible in general, however, their quality could be enhanced. Some specific remarks:

– font in Figure 1 and Figure 2 is too small making the whole figure difficult to read; the font size should be similar to the main text (or slightly smaller);

– font in Figure 3 is too big, on the other hand;

– Figure 4 and Figure 7 – wave velocity symbols are ul and us, but earlier in eq. (13) and (14) the subscripts were capital (which I find more appropriate) – please unify; what is more, I recommend to place both subfigures one next to another and add horizontal axis to subfigure (a);

– Figures 5 and 6 (such as 8 and 9) – these figures can be merged pairwise, since they present the results of elastic constants – I cannot find any reason for splitting the results into groups (L, G, K) and (σ, Y);

– it would be nice to add grids to figures 4-9;

Reply to Reviewer comment and changes made:

We revised the size of Figures 1 (page 5) and 2 (page 7) and we reduced the size of the fonts in Figure 3 (page 8) according to reviewer’s suggestions.

We revised the notation of the longitudinal and shear velocity in Figures 4 and 7 as in equations (13) and (14).

We avoided the merging of Figures 5, 6 and Figures 8, 9 because the fonts of the final merged graphs will be too small for the reader.

The results were splitted into these groups in order to retain a uniformity in the presentation of data as in references 21 and 22.

Issue 9:

Results. The results are presented in a legible way. The description of the results such as their interpretation are appropriate.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 10:

Conclusion. The conclusion section is concise and seems to support the results presented. It would be nice to mark some limitations of the proposed method and its possible future applications. Can the method be used for different materials? Can different material models be considered, such as orthotropic, transversely isotropic or general anisotropic?

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment concerning the conclusions section. Furthermore, we added the following text in the revised manuscript, right above the conclusion section to address all the issues raised by reviewer #2 (pages 17-18, lines: 410-446).

Several solidification phenomena occurring during the fabrication process may lead to samples with highly anisotropic and heterogeneous structures, both in terms of microstructure and elastic properties. Because of the internal structure, an ultrasonic beam traveling through an anisotropic and heterogeneous structure is subject to severe disturbances, such as beam deviation, beam splitting, mode conversion resulting in complex ultrasonic signals with spurious echoes and structural noise.

Nevertheless, numerical simulations have become an essential tool to demonstrate the performance of non-destructive testing (NDT). The relevance of the numerical results is directly related with the accuracy of the input data for the simulation. In this context, a complex anisotropic material is commonly represented by a large number of homogenous and anisotropic domains, and this method has been shown in the present work to be effective as it reproduces the deviation and splitting of the acoustic beam and the relevant mode conversions.

At the ultrasonic frequencies commonly used to inspect a highly anisotropic structure that are between 0.5 and 10 MHz, the corresponding wavelength ranging from 11 to 0.5 mm is similar to the grain size. The scattering of the wave by the grain boundaries will thus be a key factor. Each grain boundary is considered as a discontinuity with specific acoustic impedance, which finally will scatter the acoustic wave. Under these circumstances, the structure scatters the acoustic wave, and the ultrasonic energy is diffused away from the axis of beam propagation. From the probe point of view, the scattering by the microstructure will induce a decrease of the reflected echo amplitude which depends on the dimension (depth) of the reflector. The phenomenon is assessed by the use of an attenuation coefficient, which accounts for the anisotropic dispersion of the ultrasonic power of the beam along its path. Nevertheless, the variation of the attenuation due to the microstructure scattering, characteristic of anisotropic structures, is very hard to obtain experimentally. A common methodology is to utilize samples with various orientations of the elongated grains and to evaluate their attenuation by transmission or reflection techniques of waves under normal incidence.

Concerning future applications, by applying the procedure described in this work in orthotropic, transversely isotropic or generally anisotropic materials, one can determine the anisotropic variations of scattering attenuation by describing the microstructure at the grain-scale based on numerical simulation. The simulation method should combine a 2D finite element code and a detailed description of the microstructure that will account for the geometric, elastic and crystallographic properties of the anisotropic material. This way, the grain orientation, the grains size, and the anisotropy level are the main input parameters that are implemented for the efficient determination of the acoustic attenuation.

Reviewer #3 comments:

Issue 1:

As a remark, it should be noted that all the figures are too small for their comfortable understanding, especially Figure 2.

After correcting the size and the quality of the figures, the article can be accepted for publication.

Reply to Reviewer comment and changes made:

We revised the size of several Figures including Figure 2 to improve clarity and comfortable understanding by the reader.

We revised English language and formatting in several parts of the manuscript as suggested by reviewers.

I would like to thank all the three reviewers for their instructive comments. I hope that the changes made are adequate, satisfactory and in line with your suggestions.

Sincerely yours,

Dr. Angelos G. Kalampounias

Associate Professor

On behalf of all authors

Author Response File: Author Response.pdf

Reviewer 2 Report

OVERVIEW

GENERAL REMARKS

1) Title. The title is appropriately formulated and gives a general view of the content of the paper.

2) Structure. The structure of the manuscript is correct. The following sections are logically connected. The manuscript is easy to follow.

3) Language. The quality of the language is appropriate, substantial changes are not required. Some remarks:

– spaces are sometimes missing between values and units (e.g., lines 217-219);

– line 227 – different symbol is used for density;

– fluoro-phosphate is sometimes written with and sometimes without hyphen, please unify throughout the whole manuscript;

4) Keywords. The keywords are appropriate to the theme of the manuscript.

5) Novelty. A clear explanation of what is new in the paper should be included in the last paragraph of Introduction and in the Abstract. Currently, I do not find direct information about original element of the study. Partially, the contribution of the paper is described in line 124-126, however, some more description is required.

6) Introduction. The Introduction section gives a general overview of the current state-of-the-art. The number of citations is sufficient.

7) Equations. The equations are formatted properly. The references to the variables from equations are sometimes not formatted well in the main text and in the figures. Italic should be used, e.g., lines 160, 230, 232, 234 and Figure 1. Sometimes spaces are missing (e.g., lines 176 and 182). These are just formatting changes that can be corrected during careful proofreading of the manuscript. I would also recommend to use M instead of L as a ‘longitudinal modulus’, v instead of σ (not to mix with stress) and E instead of Y. The proposed symobls are more common, however it is just suggestion.

8) Figures. The figures are legible in general, however, their quality could be enhanced. Some specific remarks:

– font in Figure 1 and Figure 2 is too small making the whole figure difficult to read; the font size should be similar to the main text (or slightly smaller);

– font in Figure 3 is too big, on the other hand;

– Figure 4 and Figure 7 – wave velocity symbols are u_l and u_s, but earlier in eq. (13) and (14) the subscripts were capital (which I find more appropriate) – please unify; what is more, I recommend to place both subfigures one next to another and add horizontal axis to subfigure (a);

– it would be nice to add grids to figures 4-9;

9) Results. The results are presented in a legible way. The description of the results such as their interpretation are appropriate.

10) Conclusion. The conclusion section is concise and seems to support the results presented. It would be nice to mark some limitations of the proposed method and its possible future applications. Can the method be used for different materials? Can different material models be considered, such as orthotropic, transversely isotropic or general anisotropic?

The comments are included in the main review report.

Author Response

Dear Editor,

Thank you very much for your e-mail concerning the response of the four reviewers to our manuscript Ref. No.: applsci-2476688.

Reviewer #1 comments:

Issue 1:

In section 2.2, the phrase "...purchased by Olympus" should be rephrased, and the abbreviation "TTi" should be defined.

Reply to Reviewer comment and changes made:

We revised phrase "...purchased by Olympus" according to reviewer’s suggestion (page 4, lines 139, 142-143). TTi is a brand name and not an abbreviation. All changes are highlighted with yellow.

Issue 2:

Reply to Reviewer comment and changes made:

We revised this sentence, accordingly (page 5, line 179).

Issue 3:

Reply to Reviewer comment and changes made:

These notes were added in the revised manuscript (page 7, lines: 218-226) and are highlighted with yellow for your convenience.

Issue 4:

In section 4, mass density symbol in the text should be in the same format as in related Equations.

Reply to Reviewer comment and changes made:

We agree with reviewer’s comment, and we revised the mass density symbol, accordingly (page 8, lines: 253).

Issue 5:

Reply to Reviewer comment and changes made:

Reviewer #2 comments:

Issue 1:

Title. The title is appropriately formulated and gives a general view of the content of the paper.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 2:

Structure. The structure of the manuscript is correct. The following sections are logically connected. The manuscript is easy to follow.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 3:

Language. The quality of the language is appropriate, substantial changes are not required. Some remarks:

– spaces are sometimes missing between values and units (e.g., lines 217-219);

– line 227 – different symbol is used for density;

– fluoro-phosphate is sometimes written with and sometimes without hyphen, please unify throughout the whole manuscript;

Reply to Reviewer comment and changes made:

We performed the suggested changes in the revised manuscript (lines: 31, 189, 253, 533).

Issue 4:

Keywords. The keywords are appropriate to the theme of the manuscript.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 5:

Reply to Reviewer comment and changes made:

Issue 6:

Introduction. The Introduction section gives a general overview of the current state-of-the-art. The number of citations is sufficient.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 7:

Reply to Reviewer comment and changes made:

Issue 8:

Figures. The figures are legible in general, however, their quality could be enhanced. Some specific remarks:

– font in Figure 1 and Figure 2 is too small making the whole figure difficult to read; the font size should be similar to the main text (or slightly smaller);

– font in Figure 3 is too big, on the other hand;

– it would be nice to add grids to figures 4-9;

Reply to Reviewer comment and changes made:

We revised the size of Figures 1 (page 5) and 2 (page 7) and we reduced the size of the fonts in Figure 3 (page 8) according to reviewer’s suggestions.

We revised the notation of the longitudinal and shear velocity in Figures 4 and 7 as in equations (13) and (14).

We avoided the merging of Figures 5, 6 and Figures 8, 9 because the fonts of the final merged graphs will be too small for the reader.

The results were splitted into these groups in order to retain a uniformity in the presentation of data as in references 21 and 22.

Issue 9:

Results. The results are presented in a legible way. The description of the results such as their interpretation are appropriate.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 10:

Reply to Reviewer comment and changes made:

Reviewer #3 comments:

Issue 1:

As a remark, it should be noted that all the figures are too small for their comfortable understanding, especially Figure 2.

After correcting the size and the quality of the figures, the article can be accepted for publication.

Reply to Reviewer comment and changes made:

We revised the size of several Figures including Figure 2 to improve clarity and comfortable understanding by the reader.

We revised English language and formatting in several parts of the manuscript as suggested by reviewers.

I would like to thank all the three reviewers for their instructive comments. I hope that the changes made are adequate, satisfactory and in line with your suggestions.

Sincerely yours,

Dr. Angelos G. Kalampounias

Associate Professor

On behalf of all authors

Author Response File: Author Response.pdf

Reviewer 3 Report

The article is devoted to an important and relevant topic and may be of interest to a wide range of readers. The introduction clearly states the purpose of the work and provides enough references to understand the problem. The description of the simulation itself is consistent and understandable, the comparison with experimental data is reliable.
As a remark, it should be noted that all the figures are too small for their comfortable understanding, especially Figure 2.
After correcting the size and the quality of the figures, the article can be accepted for publication.

Author Response

Dear Editor,

Thank you very much for your e-mail concerning the response of the four reviewers to our manuscript Ref. No.: applsci-2476688.

Reviewer #1 comments:

Issue 1:

In section 2.2, the phrase "...purchased by Olympus" should be rephrased, and the abbreviation "TTi" should be defined.

Reply to Reviewer comment and changes made:

We revised phrase "...purchased by Olympus" according to reviewer’s suggestion (page 4, lines 139, 142-143). TTi is a brand name and not an abbreviation. All changes are highlighted with yellow.

Issue 2:

Reply to Reviewer comment and changes made:

We revised this sentence, accordingly (page 5, line 179).

Issue 3:

Reply to Reviewer comment and changes made:

These notes were added in the revised manuscript (page 7, lines: 218-226) and are highlighted with yellow for your convenience.

Issue 4:

In section 4, mass density symbol in the text should be in the same format as in related Equations.

Reply to Reviewer comment and changes made:

We agree with reviewer’s comment, and we revised the mass density symbol, accordingly (page 8, lines: 253).

Issue 5:

Reply to Reviewer comment and changes made:

Reviewer #2 comments:

Issue 1:

Title. The title is appropriately formulated and gives a general view of the content of the paper.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 2:

Structure. The structure of the manuscript is correct. The following sections are logically connected. The manuscript is easy to follow.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 3:

Language. The quality of the language is appropriate, substantial changes are not required. Some remarks:

– spaces are sometimes missing between values and units (e.g., lines 217-219);

– line 227 – different symbol is used for density;

– fluoro-phosphate is sometimes written with and sometimes without hyphen, please unify throughout the whole manuscript;

Reply to Reviewer comment and changes made:

We performed the suggested changes in the revised manuscript (lines: 31, 189, 253, 533).

Issue 4:

Keywords. The keywords are appropriate to the theme of the manuscript.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 5:

Reply to Reviewer comment and changes made:

Issue 6:

Introduction. The Introduction section gives a general overview of the current state-of-the-art. The number of citations is sufficient.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 7:

Reply to Reviewer comment and changes made:

Issue 8:

Figures. The figures are legible in general, however, their quality could be enhanced. Some specific remarks:

– font in Figure 1 and Figure 2 is too small making the whole figure difficult to read; the font size should be similar to the main text (or slightly smaller);

– font in Figure 3 is too big, on the other hand;

– it would be nice to add grids to figures 4-9;

Reply to Reviewer comment and changes made:

We revised the size of Figures 1 (page 5) and 2 (page 7) and we reduced the size of the fonts in Figure 3 (page 8) according to reviewer’s suggestions.

We revised the notation of the longitudinal and shear velocity in Figures 4 and 7 as in equations (13) and (14).

We avoided the merging of Figures 5, 6 and Figures 8, 9 because the fonts of the final merged graphs will be too small for the reader.

The results were splitted into these groups in order to retain a uniformity in the presentation of data as in references 21 and 22.

Issue 9:

Results. The results are presented in a legible way. The description of the results such as their interpretation are appropriate.

Reply to Reviewer comment and changes made:

We thank reviewer #2 for his kind comment.

Issue 10:

Reply to Reviewer comment and changes made:

Reviewer #3 comments:

Issue 1:

As a remark, it should be noted that all the figures are too small for their comfortable understanding, especially Figure 2.

After correcting the size and the quality of the figures, the article can be accepted for publication.

Reply to Reviewer comment and changes made:

We revised the size of several Figures including Figure 2 to improve clarity and comfortable understanding by the reader.

We revised English language and formatting in several parts of the manuscript as suggested by reviewers.

I would like to thank all the three reviewers for their instructive comments. I hope that the changes made are adequate, satisfactory and in line with your suggestions.

Sincerely yours,

Dr. Angelos G. Kalampounias

Associate Professor

On behalf of all authors

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The Authors have replied to all the remarks and questions with thorough explanations. I am satisfied with the corrected version of the manuscript and, in my opinion, it now warrants publication in Applied Sciences.