Cryogenic MMIC Low-Noise Amplifiers for Radio Telescope Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this contribution, a cryogenic MMIC LNA has been designed and tested.

Although the paper and the related results are potentially interesting, more details on the theoretical section, design steps and results are required.

In detail:

In Section 2.1, observation 4, you talk about the kink effect. However, the represented number of points is not enough to clearly observe the kink. Can you please highlight the effect on the figure or provide more in-depth explanations? You can refer to 10.3390/electronics8060698 for a proper comparison.

On page 3, lines 80-81, you write: “All transistors were tested with a light on and noted that light stimulation’s impact can be neglected in a short period of observation.”. Please add more details on the effect of the light on the measurement, as in A. Caddemi et al. "An Accurate Experimental Investigation of an Optical Sensing Microwave Amplifier," IEEE Sensors J., vol. 18, no. 22, pp. 9214-9221, 15 Nov.15, 2018, doi: 10.1109/JSEN.2018.2872078 (the author is free to cite recommendations). Light activation of noise at microwave frequencies has been investigated also for GaAs HEMT’s, thus adding more information might help the reader. From the suggested references, probably the light effect is negligible due to the wavelength of the visible light that is not appropriate for stimulating effects on the GaAs (probably IR light would stimulate optic effects).

As explained also in the last reference, a stability analysis is strongly recommended. This is also confirmed by the return loss shown in Fig. 4 which is dangerously close to 0 dB (it seems it can overcome 0 dB, thus suggesting instability).

Please add more details on the matching network design.

To design a good LNA, the transistor noise parameters are required. Please can you explain if you measured the noise parameters and the related design steps?

Author Response

We gratefully acknowledge the expert critiques and detailed recommendations provided in your review, which have substantially strengthened the methodological rigor of this work. Our itemized responses to each concern are presented below, with corresponding revisions highlighted in the revised manuscript (Track Changes mode).

Comments 1: In Section 2.1, observation 4, you talk about the kink effect. However, the represented number of points is not enough to clearly observe the kink. Can you please highlight the effect on the figure or provide more in-depth explanations? You can refer to 10.3390/electronics8060698 for a proper comparison.

Response 1:

Thank you for pointing this out. I agree with this comment. This is my mistake in submitting supplementary materials. As I mentioned in manuscripts, the kink phenomenon happened more clearly in 4f100um, 4f200um and 4f300um device as shown in figure below with a 4f200um at 15K. I’d like to include all my measurements as supplementary materials due to space constraints in the manuscript. 4f600um and 2f50um are the largest and smallest devices among the test sample. I believe they are the most representative.

 

Comments 2: On page 3, lines 80-81, you write: “All transistors were tested with a light on and noted that light stimulation’s impact can be neglected in a short period of observation.”. Please add more details on the effect of the light on the measurement, as in A. Caddemi et al. "An Accurate Experimental Investigation of an Optical Sensing Microwave Amplifier," IEEE Sensors J., vol. 18, no. 22, pp. 9214-9221, 15 Nov.15, 2018, doi: 10.1109/JSEN.2018.2872078 (the author is free to cite recommendations). Light activation of noise at microwave frequencies has been investigated also for GaAs HEMT’s, thus adding more information might help the reader. From the suggested references, probably the light effect is negligible due to the wavelength of the visible light that is not appropriate for stimulating effects on the GaAs (probably IR light would stimulate optic effects).

Response 2:

I agree with the comment. And I am interested in optical effects. But I have no equipment to implement such precise experiment. The reason I mention this is that I read about paper with the impact of the light even though mine is a microscope light source. I’d like to cite Alina Caddemi‘s work to enrich this manuscript section2.1 to help the reader. Thank you.

“While photosensitivity characterization under optical illumination was not implemented in this study, prior investigations by Alina Caddemi provide critical insights into photostimulation effects on transistors and amplifiers\cite{AlinaCaddemi2018,2019}”

Comments 3: As explained also in the last reference, a stability analysis is strongly recommended. This is also confirmed by the return loss shown in Fig. 4 which is dangerously close to 0 dB (it seems it can overcome 0 dB, thus suggesting instability).

Response 3:

Agree. Stability is the paramount consideration in the design of any amplifier. I do have genuine concerns about this. So I made some test with a Singal generator and a Spectrum Analyzer. Under proper bias conditions, the amplifiers remain stable, with no self-oscillation observed within the frequency range of interest. The return loss performance falls short of the targeted specifications, and improving it has been identified as a critical optimization goal.

Comments 4: Please add more details on the matching network design.

Response 4:

Thank you for pointing this out. We intentionally avoided complex matching network designs due to the risk of parasitic effects under cryogenic conditions for the first attempt. This aligns with the common practice in cryogenic LNA design, where most implementations adopt minimalist input networks. In our approach, an optimized microstrip line was employed to ensure impedance matching in wide band while maintaining low noise and stability at cryogenic. Section 3.1 give a detailed description of design.

Comments 5: To design a good LNA, the transistor noise parameters are required. Please can you explain if you measured the noise parameters and the related design steps?

Response 5:

I agree with this comment. However, both the discrete transistors and LNA chips are co-fabricated in the same tape-out run. The LNA design is based on the process design kit (PDK) provided by WIN Foundry.

Our laboratory’s current setup lacks the precision required to measure transistor noise parameters, particularly the minimum noise temperature (Tmin). This noise parameters vary significantly between generations by the frequent updates to the WIN semiconductor process. The data presented here thus serves as a preliminary exploration, focusing on the temperature-dependent DC I-V characteristics to infer potential noise behavior.

Your understanding of the current limitations is greatly appreciated.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper characterizes discrete transistors at both room and cryogenic temperatures and details the performance characteristics of two ultra-wideband cryogenic MMIC LNAs. Below are the comments:

1. Abstract: The authors claim that transistors were characterized at room and cryogenic temperatures to understand their performance under different conditions. However, it is unclear which specific performance aspects and conditions are being referred to. The same issue applies to the following sentences. Additionally, the phrase "a novel and straightforward approach" should be clarified—what is the specific method being referred to? The abstract should concisely present all key data and information, avoiding vague statements.
2. Introduction – First Paragraph: The authors initially state the importance of low-noise amplifiers in radio telescopes, but then abruptly introduce the QITAI Telescope. This transition is abrupt and lacks logical flow. After emphasizing the significance of low-noise amplifiers, the authors should first discuss various potential noise sources, highlighting thermal noise as the most influential. They should then compare previous studies on reducing thermal noise in radio telescopes before introducing the QITAI Telescope.
3. Introduction – Second Paragraph: Following the discussion on thermal noise and mitigation strategies, the authors should introduce the telescope and its relevant components. The mention of the QTT system is problematic because while the study presents a promising candidate for use in the QTT system, the experiments were not conducted within it. The necessity of discussing the QTT system in the introduction should be reconsidered. The overall logical structure of the introduction needs better organization.
4. Section 2.1: The authors state that "2f50µm and 4f600µm are the most representative" without providing sufficient explanation. More details should be added to justify why these transistors were selected as the most representative.
5. Figure 1: Several zoomed-in subplots should be included to illustrate key parameters more clearly.
6. Lines 57-61: The authors introduce several parameters, including g_m, r_ds, and V_gs, without first explaining their meanings, significance to the system, or expected value ranges. These details should be provided before discussing the parameters further.
7. Section 2.1: The authors describe several observed phenomena but do not explain the potential underlying reasons. Rather than just stating the observations, the authors should provide possible explanations. Additionally, each phenomenon should be explicitly linked to the corresponding figure for clarity.
8. Figures 2a and 2c: The legends list nine parameters, but only six or seven lines are clearly visible in the figure. The authors should adjust the plotting style to ensure all lines are distinguishable.
9. Figures 3b and 3d: The names of different parts should be arranged consistently with Figures 3a and 3c for better clarity.
10. Lines 105-112: The authors selected two transistors, LNA0315 and LNA0307, stating that the rationale was to assess stability. However, it is unclear why these specific transistors were chosen and how they provide better system performance. Further justification is needed.
11. Line 160: The meaning of I_d should be clarified, along with the equation for calculating I_d based on the supply voltage. Additionally, the method for calculating power consumption should be explicitly stated, including relevant equations.
12. Conclusion: The authors should discuss potential improvements and future research directions in more detail to guide further studies.

 

Author Response

Thank you for your insightful comments and constructive suggestions. We sincerely appreciate your efforts in improving the clarity and rigor of our manuscript. Please find below our point-by-point responses to your concerns:

Comments 1: Abstract: The authors claim that transistors were characterized at room and cryogenic temperatures to understand their performance under different conditions. However, it is unclear which specific performance aspects and conditions are being referred to. The same issue applies to the following sentences. Additionally, the phrase "a novel and straightforward approach" should be clarified—what is the specific method being referred to? The abstract should concisely present all key data and information, avoiding vague statements.

Response 1:

We agree that the original abstract lacked specificity. In the revised version, we have explicitly listed the evaluated parameters, Specific test set-up with instruments and temperature conditions (15K). These details now appear in the abstract:

“Discrete transistors with gate peripheries spanning 50-600 μm were DC-characterized at 300 K and 15 K respectively. Transconductance (gm), and I-V curves were analyzed to assess temperature-induced deviations in cryogenic operation. The LNAs underwent on-chip noise characterization under cryogenic conditions (15 K) using a Y-factor measurement setup, which integrated a calibrated noise source and a noise figure analyzer (Keysight N8975A). This approach directly quantified the noise temperature and S-parameters - critical metrics for radio telescope receiver front-ends.”

Comments 2: Introduction – First Paragraph: The authors initially state the importance of low-noise amplifiers in radio telescopes, but then abruptly introduce the QITAI Telescope. This transition is abrupt and lacks logical flow. After emphasizing the significance of low-noise amplifiers, the authors should first discuss various potential noise sources, highlighting thermal noise as the most influential. They should then compare previous studies on reducing thermal noise in radio telescopes before introducing the QITAI Telescope.

Response 2:

I agree. The structure has been revised. A brief explanation are given in first paragraph before the QTT introducing. The second paragraph state briefly that the cryogenic operation and study are needed. The QTT project is in processing, and all our work is preparation and a part of plan. The revised paragraphs are shown below. And your understanding is greatly appreciated.

“… The system noise temperature  in a typical terrestrial radio telescopes is dominated by background contributions  (cosmic microwave background, atmospheric, spillover, and antenna losses) and receiver noise . While  is constrained mainly by the environment,  —— primarily determined by the first-stage component - servers as the key controllable parameter. The signal-to-noise ratio —— where  is the effective temperature of the source, B the observation bandwidth, and  the integration time —— drives the critical need for cryogenic front-end achieving minimal noise, enabling detection of the source.

For a next-generation radio astronomy receivers, a feasible way to reduce the impact of noise is by cooling the receiver to cryogenic temperatures. Those temperatures are usually set at 10-20 K, from which most semiconductor devices benefit for higher electron mobility and lower thermal noise. Therefore, it is highly valuable to conduct design and research on transistors and low-noise amplifiers operating under cryogenic conditions. It is worth noting that, at present, there is no further significant reduction in noise temperature even lower the ambient temperature further.

The Qitai Radio Telescope (QTT), representing a next-generation steerable single-dish system with a 110-m diameter and 0.15–115 GHz frequency coverage, will implement at least five advanced receivers spanning 0.3–30 GHz in its first phase, incorporating a focal plane array feed at L-band requiring >200 low-noise amplifiers. Those receiver systems necessitate a huge number of low-noise amplifiers with ultra-wideband-width, lower power consumption, and lower cost…”

Comments 3: Introduction – Second Paragraph: Following the discussion on thermal noise and mitigation strategies, the authors should introduce the telescope and its relevant components. The mention of the QTT system is problematic because while the study presents a promising candidate for use in the QTT system, the experiments were not conducted within it. The necessity of discussing the QTT system in the introduction should be reconsidered. The overall logical structure of the introduction needs better organization.

Response 3:

I agree. The revised structure are shown in last response. All our research efforts remain in the experimental validation phase, with practical QTT engineering implementation yet to be accomplished. Thank you again.

Comments 4: Section 2.1: The authors state that "2f50µm and 4f600µm are the most representative" without providing sufficient explanation. More details should be added to justify why these transistors were selected as the most representative.

Response 4:

I agree. The rationale is straightforward: these devices represent the extreme cases (largest and smallest in scale), which I believe they are representative.

Comments 5: Figure 1: Several zoomed-in subplots should be included to illustrate key parameters more clearly.

Response 5: Agree. A zoomed-in picture has been added to Figure 1.

Comments 6: Lines 57-61: The authors introduce several parameters, including gm, rds, and Vgs, without first explaining their meanings, significance to the system, or expected value ranges. These details should be provided before discussing the parameters further.

Response 6: Thank you for highlighting this critical point. We agree that clarifying the definitions, significance, and typical operating ranges of key parameters upfront is essential for readers to contextualize the subsequent analysis. A brief description now appears in the Section 2.1:

“In low-noise amplifier design, transconductance (gm) governs the tradeoff between gain and noise figure (NF). Increasing gm improves voltage gain (Av ∝ gm · ZL, where ZL is the load impedance) and cut-off frequency ( fT = gm/(2πCgs), with Cgs denoting the gate-source capacitance), while also reducing thermal noise contribution (NF ∝ √Ids/gm, where Ids is the drain current).However, this comes at the cost of higher DC power consumption (PDC = Ids · Vds, where Vds is the drain-to-source voltage). The optimal gm is determined by balancing noise matching conditions with gain requirements. Additionally, cryogenic operation moderately enhances transconductance in HEMTs. ”

Comments 7: Section 2.1: The authors describe several observed phenomena but do not explain the potential underlying reasons. Rather than just stating the observations, the authors should provide possible explanations. Additionally, each phenomenon should be explicitly linked to the corresponding figure for clarity.

Response 7: I agree that underlying physical mechanisms are important. However, this study focuses on empirically documenting cryogenic DC parameter shifts in transistors, without exploring their root physical causes or performing high-resolution characterization. The laboratory currently lacks the necessary cryogenic characterization infrastructure to perform advanced transistor analysis.

As for linking to the figure, all the observations comes from the DC characteristic plots. I have optimized expressions to make it clearer, basically the explanation pointing to all pictures in figure 2.

Your understanding of the current limitations is greatly appreciated.

Comments 8: Figures 2a and 2c: The legends list nine parameters, but only six or seven lines are clearly visible in the figure. The authors should adjust the plotting style to ensure all lines are distinguishable.

Response 8: I agree. This was caused by the measurement accuracy. Too little current will not be read. But if I delete the lines that are relatively small, I believe that will not be complete enough for DC I-V curves. I keep this so far, if they really unnecessary, I would consider deleting the few lines.

Comments 9: Figures 3b and 3d: The names of different parts should be arranged consistently with Figures 3a and 3c for better clarity.

Response 9: While I respectfully disagree with this suggestion, my rationale is twofold:

​Traceability: The schematics and adjacent die micrographs exhibit one-to-one correspondence (e.g., Fig.3a circuit maps to Chip B in Fig.3b), establishing direct form-function relationships without ambiguity.

​Visual Hierarchy: The circuit topology's inherent simplicity (sub-3 main component count) makes supplemental annotations redundant.

Comments 10: Lines 105-112: The authors selected two transistors, LNA0315 and LNA0307, stating that the rationale was to assess stability. However, it is unclear why these specific transistors were chosen and how they provide better system performance. Further justification is needed.

Response 10: Thank you for pointing this out. We acknowledge the reviewer's concern about the selection of transistors. LNA0315 and LNA0307 are the name of the low noise amplifiers designed and fabricated. The method of choosing these transistors are described in Section 3.1. The impendence matching is main consideration. The stability investigation of the multi-fingers transistors is one of the reasons.

The system performance of LNA0315 and LNA0307 are described in the page 7 to 9, in Section 3. These device prototypes and cryogenic circuit designs represent preliminary explorations and consequently exhibit non-optimized characteristics. The primary intent was to establish baseline of the design step, rather than achieving production-ready performance metrics.

Comments 11: Line 160: The meaning of Id should be clarified, along with the equation for calculating Id based on the supply voltage. Additionally, the method for calculating power consumption should be explicitly stated, including relevant equations.

Response 11:

I agree. The explanation of Id and DC power consumption (P_DC) now are given in the section 2.1. first paragraph.

Comments 12: Conclusion: The authors should discuss potential improvements and future research directions in more detail to guide further studies.

Response 12:

Agree. A brief future direction are added in the last paragraph:

“Further optimization of noise temperature (<5 K target) and input return loss (>15 dB) can be achieved through iterative refinement of the existing matching network, topology and packaging, leveraging the measured S-parameters and DC data at 15 K, while streamlined cryogenic testing protocols may accelerate LNA development cycles. The process-refined LNAs will be deployed in prototype cryogenic receiver modules for the QTT's phased-array feed.”

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This paper could be of interest for the radio astronomy instruments community. Some contents should be improved before a possible publication:

Before the Abstract: In "Correspondence" line, the text following the author email should be removed.

Line 8: Instead "measured them" it should be "measured it" 

Line 19: The units of a parameter should be separated by a space: instead "0.15GHz to 115GHz" it should be written: "0.15 GHz to 115 GHz". This kind of non correct writting is repeated many times along the paper, at least in these lines: 24, 35, 36, 44, 46, 60, 64, 66, 67, 86, 88, 149, 152, 153, 157 to 162, 165 to 169, Figure 5, 174, 179, 180, 183, 187, Table 1, 204, 208, 214 to 217.

Line 22: It should be "receivers" instead of "receiver"

Line 23: Instead "is cool" it should be "is by cooling"

Line 31: Instead of "are more" it should be "is more"

Line 50: What and where are the "attachments"?

Line 51: It should be "temperatures" instead "temperature"

Below line 82 (Figure 1): The transistors pictures are too small and it is not possible to see any detail. It would be better to include only one or two pictures but having a big enough size to see the gates of each transistor.

Figure 2 (above line 83): It is written: The transistor type appears in the "lower right corner" of the Fig. 1, but it is not visible, maybe because transistor pictures are very small.

Lines 96-97: "their source end connection to the ground (GND) via two vias, as depicted in Figure 1". Again, this grounding detail is not visible at all in Figure 1 because transistor pictures are very small.

Line 98; Instead "number of gates" it would be better "number of gate fingers"

Line 113: Instead "are matched" it would be better "are impedance matched"

Line 123: Why do you recommend an (cold) attenuator bonded to the DUT? Please, explain it.

Line 125: Instead "are applied" it should be "is applied"

Line 127: It should be "Keysight Technologies" instead of "keysight"

Line 146: It should be "gains" instead of "gain"

Line 149: What is "deltaY"? This parameter is not explained in the paper, but it appears in equation (2) 

Figure 4: The measured gain at cryogenic temperature is lower than the measured gain at room temperature. Normally, in cryogenic amplifiers, it is the other way around, the gain at cold temperature is greater than at hot temperature. Can you explain it? Could be it by the difference in DC bias conditions?

Figures 6 and 7: Pictures have bad quality and it is not possible to see the DC bias network close to the MMIC (too much brightness) and the MMIC is almost black. It is not possible to see the MMIC internal components. Both pictures should be improved to make possible the assembly details.

Lines 226 to 229 (Abbreviations) should be removed.

References:

11: Yang, Q. The reference is not complete. It seems it is a Master's Thesis developed in Chalmers University of Technology. It should be added.

12, 13, 22: the references of an Internet site (available online) must include the date of access (accesed on Day Month Year). Please, complete the dates.

Lines from 320 to 333 must be removed.

 

Comments on the Quality of English Language

Some sentences should be revised to improve the English.

Author Response

Comments 1: Before the Abstract: In "Correspondence" line, the text following the author email should be removed.

Response: Agree. They have been removed.

Comments 2: Line 8: Instead "measured them" it should be "measured it"

Response: Agree. According to the other reviewer, the abstract has been revised.

Comments 3: Line 19: The units of a parameter should be separated by a space: instead "0.15GHz to 115GHz" it should be written: "0.15 GHz to 115 GHz". This kind of non correct writting is repeated many times along the paper, at least in these lines: 24, 35, 36, 44, 46, 60, 64, 66, 67, 86, 88, 149, 152, 153, 157 to 162, 165 to 169, Figure 5, 174, 179, 180, 183, 187, Table 1, 204, 208, 214 to 217.

Response: Thank you for pointing out. I have revised all of them.

Comments 4: Line 22: It should be "receivers" instead of "receiver"

Response: Agree. I have fixed it to the plural form.

Comments 5: Line 23: Instead "is cool" it should be "is by cooling"

Response: Agree. They have been corrected.

Comments 6: Line 31: Instead of "are more" it should be "is more"

Response: Agree. I have fixed it.

Comments 7: Line 50: What and where are the "attachments"?

Response: The figures filed updated last time. They have been resubmitted.

Comments 8: Line 51: It should be "temperatures" instead "temperature"

Response: Agree. Revised.

Comments 9: Below line 82 (Figure 1): The transistors pictures are too small and it is not possible to see any detail. It would be better to include only one or two pictures but having a big enough size to see the gates of each transistor.

Response: Agree. The picture has been resized. And a zoom-in photo has been added.

Comments 10: Figure 2 (above line 83): It is written: The transistor type appears in the "lower right corner" of the Fig. 1, but it is not visible, maybe because transistor pictures are very small.

Response: Agree. The transistor pictures have been adjusted.

Comments 11: Lines 96-97: "their source end connection to the ground (GND) via two vias, as depicted in Figure 1". Again, this grounding detail is not visible at all in Figure 1 because transistor pictures are very small.

Response: Agree. Same as last response.

Comments 12: Line 98; Instead "number of gates" it would be better "number of gate fingers"

Response: Agree. They have been revised.

Comments 13: Line 113: Instead "are matched" it would be better "are impedance matched"

Response: Agree. They have been revised.

Comments 14: Line 123: Why do you recommend an (cold) attenuator bonded to the DUT? Please, explain it.

Response: Agree. Since this method enables more accurate measurements. I have added explanations in this paragraph:

“… The integrated attenuator effectively mitigates errors induced by both the noise diode and input transmission line, while simultaneously stabilizing impedance variations during on/off switching of the diode noise source…”

Comments 15: Line 125: Instead "are applied" it should be "is applied"

Response: Agree. They have been revised.

Comments 16: Line 127: It should be "Keysight Technologies" instead of "keysight"

Response: Agree. They have been revised.

Comments 17: Line 146: It should be "gains" instead of "gain"

Response: Agree. They have been revised.

Comments 18: Line 149: What is "deltaY"? This parameter is not explained in the paper, but it appears in equation (2)

Response: Agree. The explanation of "deltaY" has been added before it.

“… the measurement error of the Y-factor $\delta Y$ of 0.02 dB.”

Comments 19: Figure 4: The measured gain at cryogenic temperature is lower than the measured gain at room temperature. Normally, in cryogenic amplifiers, it is the other way around, the gain at cold temperature is greater than at hot temperature. Can you explain it? Could be it by the difference in DC bias conditions?

Response: Yes. They are in different bias conditions optimized for noise performance.

Comments 20: Figures 6 and 7: Pictures have bad quality and it is not possible to see the DC bias network close to the MMIC (too much brightness) and the MMIC is almost black. It is not possible to see the MMIC internal components. Both pictures should be improved to make possible the assembly details.

Response: Agree. I have updated the Figure 6 with a less brightness one. Figure 7 is a zoom-in view of chip. It is hard to adjust the light to see both chip and bonding clear, shown as in the figure below. Since they can not achieve perfect view at the same time, I chose Figure 6 to illustrate peripheral set-up, and Figure 7 to illustrate chip itself which has also appeared in Figure 3(b) of a signal unpackaged clearer vision.

Comments 21: Lines 226 to 229 (Abbreviations) should be removed.

Response: Agree. They have been removed.

Comments 22: References:

11: Yang, Q. The reference is not complete. It seems it is a Master's Thesis developed in Chalmers University of Technology. It should be added.

Response: They have been added.

“Yang, Q. Low Frequency Dispersion in InP HEMTs. Master’s thesis, Chalmers University of Technology, Sweden 2013. ”

12, 13, 22: the references of an Internet site (available online) must include the date of access (accesed on Day Month Year). Please, complete the dates.

Response: Accessed date have been added.

Keysight. Noise Figure Measurement Accuracy: The Y-Factor Method. https://www.keysight.com/us/en06829/application-notes/5952-3706.pdf, 2021. Accessed: 15 Oct. 2024.

Keysight. High-Accuracy Noise Figure Measurements with Network Analyzers. https://www.keysight.com/us/en/assets/7018-02539/application-notes/5990-5800.pdf, 2020. Accessed: 15 Oct. 2024.

Comments 23: Lines from 320 to 333 must be removed.

Response: Agree. They have been removed.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors addressed all my concerns thus I suggest to publish the paper in its present form

Reviewer 2 Report

Comments and Suggestions for Authors

No more comments.