esa-sceva/satcom-chunk-collection huggingface dataset:
# Preassembly Cryogenic Drilling in Carbon Fiber Sandwich Sheets with Inner Foam Core
## 4 Discussion of Results  
As can be seen, the thrust forces are low in cryogenic drilling of carbon fiber [26; 27; 28] and in this sandwich material. Although the thrust forces are usually higher in cryogenic  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Factors**} & \multicolumn{6}{c}{**Foam Thickness (FT) (mm)**} \\ \cline{2-7}  & \multicolumn{3}{c}{**4**} & \multicolumn{3}{c}{**10**} \\ \cline{2-7}  & **Fz** & \(\Delta\)**Di** & \(\Delta\)**Do** & **Fz** & \(\Delta\)**Di** & \(\Delta\)**Do** \\ \hline Rotation Speed (N) (rpm) & 3164 & 2268 & 2611 & 3225 & 2500 & 2100 \\ Feed Rate (F) (mm/min) & 258 & 207 & 202 & 200 & 203 & 323 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Optimal values of cutting conditions.  
Figure 6: Comparison between experimental and predictive results: (**a**) for Fz; (**b**) for \(\Delta\)Di and \(\Delta\)Do.  
machining than in dry machining when drilling carbon fibers [28], in this case, it is irrelevant due to their value. This means that machinability is good at extreme low temperatures, which also facilitates the stability of the machine and the tool during drilling, and the foamed polyvinyl chloride core does not hinder chip evacuation.  
Regarding the difference in diameters, the results obtained under the tolerance conditions are the most relevant, although, at extreme low temperatures, surfaces are more sensitive [15]. The required low thrust forces did not cause the hole to oversize. A possible explanation is a slight contraction that can be produced in the hole, particularly at the exit hole because the frictional force is increased; this phenomenon has been identified in reinforced polymers such as GFRP [38] or CFRP [36]. Inlet diameters can be observed in Figure 7, where diameters with greater (Figure 7a,b) and lesser (Figure 7c,d) deviations are shown; the marks that appear inside the diameter are small fibers detached from the core of the material. The differences were very small and the fibers inside were due to the foamed polyvinyl chloride, so they did not hinder possible riveting.  
The different significant factors found in the inlet and outlet diameters are common in other materials, such as fiberglass-reinforced composites using epoxy as the matrix [1] or polyether-ether-ketone and polyamide [31]. In these cases, N was not significant in the exit diameter. Once the coefficient of determination is known, the predictive models for all the variables, thrust forces, and differences in diameters can be considered acceptable. In addition, the models can show the contraction achieved at certain outlet diameters. The core thickness was significant for diameters (as interactions) but not for forces, probably because foamed polyvinyl chloride is an easy-to-machine material, and the higher values of \(\Delta\)Di for high N (6000 rpm) than in \(\Delta\)Do may be due to the damping effect of FT by reducing machine vibrations during drilling. For this reason, the optimal N values were slightly lower for FT = 4 (see Table 4).
# 1-Bit Reconfigurable Transmitarray Antenna with Out-of-Band RCS Reduction +
## 4 Experimental Verification
### Comparison and Discussion  
In order to demonstrate the advantages of the designed low-RCS 1-bit RTA, it was compared with other published works in terms of RCS reduction and radiation performance. Considering that there is little research focus on reducing the RCS of RTAs, we compared the radiation performance with conventional 1-bit RTAs with an approximate operating frequency and gain, and compared the RCS reduction performance with a low-RCS transmitarray. It can be seen from Table 1 that, compared with existing low-RCS transmitarray antennas, our work obtains a lower profile due to the effective use of multiple resonances, and the bandwidths of the low- and high-RCS reduction band are relatively wide. Furthermore, the beam scanning capability is introduced, reflecting the advanced performance of our work.  
On the other hand, the disadvantages of the proposed design is that additional resistors need to be introduced, resulting in increased structural complexity and cost compared to traditional RTAs that do not provide RCS reduction. In addition, placing an AFST layer above the RTA layer results in a slight deterioration in radiation gain, as shown in Table 2. However, out-of-band RCS is effectively reduced in return. While compared with phased array antennas, the designed 1-bit RTA can greatly reduce the cost because it does not require the T/R component. Furthermore, reducing the RCS by diffusing the incident wave over the entire visible space can effectively avoid the use of resistors. At the same time, the effect on radiation gain can be eliminated by integrating stealth and radiation functions into the same simple structure through multimode resonant structure. In summary, the designed low-RCS 1-bit RTA is a promising candidate for use in radar systems and other related applications, especially for application scenarios requiring a large radiation aperture surface, fast beam switching, and stealth.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Ref.** & **Low FBW (\%)** & **High FBW (\%)** & **Profile (\(\lambda_{L}\))** & **Beam Scanning** \\ \hline
[10] & 54.5 (8 dB) & 35.3 (8 dB) & 0.18 & No \\ \hline
[12] & 18 & 14 & 0.33 & No \\ \hline
[13] & / & 6.7 (6 dB) & 0.37 & No \\ \hline
[15] & 61.6 & 14.5 & 0.11 & No \\ \hline This Work & 52.5 & 43.8 & 0.13 & Yes \\ \hline \hline \end{tabular}
\end{table}
Table 1: RCS reduction comparison for low-RCS transmitarray.  
Figure 18: Simulated and measured RCS reduction with various incident angles for (**a**) TE and (**b**) TM polarization.
# Development of the Romanian Radar Sensor for Space Surveillance and Tracking Activities +
This paper describes the development of the first Romanian Space Surveillance and Tracking radar sensor and is organized as follows: Section 1 presents the European legislative and organizational framework put in place to establish a capacity for monitoring the space environment and the growing number of space objects orbiting the Earth. Section 2 describes the characteristics and performance of some European radar sensors active in space surveillance and tracking. Section 3 provides insight into the lengthy decision-making process to reuse an existing satellite communications installation and to retrofit it to develop a Romanian SST radar. Section 4 presents a general block diagram of the Cheia SST Radar, the assumptions of the design, and its expected performance. Section 5 comprises the results of simulations of radar performance compared to the requirements in the statement of work. Section 6 describes the actual hardware of the implemented radar design and the results of initial tests. Figure 2: EU SST sensor network status in 2021 Reprinted/adapted with permission from [8] © EU-SST. This paper is an extension of a conference paper: [PERSON], [PERSON], [PERSON], [PERSON], Cheia Antennas Retrofit to a Space Tracking Radar, European Space Agency 1 st NEO and Debris Detection Conference NEOSST1, 2019. Available online at [[https://conference.sdo.esoc.esa.int/proceedings/neosst1/paper/415/NEOSST1-paper415.pdf](https://conference.sdo.esoc.esa.int/proceedings/neosst1/paper/415/NEOSST1-paper415.pdf)]([https://conference.sdo.esoc.esa.int/proceedings/neosst1/paper/415/NEOSST1-paper415.pdf](https://conference.sdo.esoc.esa.int/proceedings/neosst1/paper/415/NEOSST1-paper415.pdf)) (accessed on 24 March 2022). The conference paper presented the conclusions of the first stage of the Cheia Retrofit project (SSA CHEIA PHASE 1 study), containing the general design and simulated performances of the future radar (found in Section 5). This paper brings new content, such as detailed design decisions, the subsequent hardware and software implementation of the radar (Section 4), and the obtained experimental results (Section 6).
## 2 Related Work
### Path Planning Methods
[32] present a Deep Reinforcement Learning (DRL) approach for UAV path planning based on the global situation information. RLGWO [33]--a novel reinforcement learning based grey wolf optimizer algorithm is also proposed for unmanned aerial vehicles (UAVs) path planning. However, not much research has been conducted on multi-degree-of-freedom targets path planning moving in higher dimensions. The existing algorithms have many limitations. For search-based methods, although some works have been able to achieve dynamic programming, it is difficult to achieve fast programming in high dimensional space due to the huge search scale. For sampling-based works, these dynamic programming methods are usually two-stage, inefficient and difficult to determine whether they are optimal. For reinforcement Learning, thanks to deep learning strategies, these approaches can adapt to complex environments and are often used with robots such as UAVs, but there are many problems: low sampling efficiency, hard design for reward function, local optimization, poor stability etc. It is necessary to explore a stable and efficient high-dimensional path planning approach from three aspects: the efficient path point calculation, optimal path evaluation and comprehensive feature detection.
## 2 Far-Field vs. Near-Field: A Geometrical Comparison  
Since the very first successful experiment of interferometry in radio astronomy conducted after World War II by [PERSON] and [PERSON] [11] with a two-element radio interferometer for studying the Sun at 175 MHz, synthetic aperture interferometry (SAI) techniques have evolved well, but the observing principle has not changed [12; 13].  
Shown in Figure 1 is the geometry of a one-dimensional SAI radiometer with two elementary antennas \(\mathcal{A}_{p}\) and \(\mathcal{A}_{q}\) observing a source under far-field conditions, as well as under near-field ones. The two antennas point in the same (Nadir) direction and are separated by the baseline vector \(\mathbf{b}_{pq}\). In the far-field region, owing to the distance from the source, the incident wavefronts are assimilable to plane waves coming from the same direction \(\theta\) for both elementary antennas. As a consequence, the differential path \(r_{q}-r_{p}\) is equal to \(b_{pq}\sin\theta\), where \(b_{pq}\) is the magnitude of the baseline vector \(\mathbf{b}_{pq}\). On the contrary, in the near-field region, incident wavefronts are spherical waves coming from different directions, \(\theta_{p}\) for \(\mathcal{A}_{p}\) and \(\theta_{q}\) for \(\mathcal{A}_{q}\), which are no longer equal to \(\theta\). The differential path \(r_{q}-r_{p}\) is here equal to \(b_{pq}\sin\
icefrac{{1}}{{2}}(\theta_{p}+\theta_{q})/\cos\
icefrac{{1}}{{2} }(\theta_{p}-\theta_{q})\) which tends to \(b_{pq}\sin\theta\) as soon as \(\theta_{p}\) and \(\theta_{q}\) both tend towards \(\theta\) whenever far-field conditions are approached, as expected.  
As a consequence of this very short preliminary comparison, SAI imaging radiometry might be more complicated under near-field conditions than under far-field ones because, for every baseline \(\mathbf{b}_{pq}\), it requires a precise calculation of the vectors \(\mathbf{r}_{p}(\theta,\phi)\) and \(\mathbf{r}_{q}(\theta,\phi)\) between the elementary antennas and any radiation coming from a direction \((\theta,\phi)\). It is also necessary to have an accurate estimation of the local incoming directions \((\theta_{p},\phi_{p})\) and \((\theta_{q},\phi_{q})\) to evaluate the appropriate attenuation by the elementary voltage patterns of \(\mathcal{A}_{p}\) and \(\mathcal{A}_{q}\).
## 4 Simulation
### Governing Equations
#### 4.3.2 Plasma Model
At metallic boundaries, the perfect electric conductor (PEC) boundary condition was used, except for the copper material region where the antenna rod was in the quasi-coaxial MWP and the cylindrical guiding structure was in the circular guiding structure MWP. The PEC boundary condition sets the tangential component of the electric field to 0 [35]. The wall boundary condition used to calculate the transport equation was the inhomogeneous Neumann boundary condition. The value of the normal flux to the boundary is described by following equation [34]:  
\[\Gamma_{e}=-\big{(}\mu_{e}\cdot\overline{E}\big{)}n_{e}-(D_{e}\cdot\
abla n_{e}) \tag{8}\]1  
where \(\mathbf{n}\) denotes the unit vector normal to the boundary and \(v_{k}\) is the velocity magnitude (thermal velocity for neutrals and Bohm velocity for ions), \(n_{k}\) is the density of the k species, and \(\gamma_{k}\) is the sticking coefficient. In this study, the sticking coefficient of each species at the wall boundary was set to 1. The wall boundary condition [60] in the electron energy equation, which is the homogeneous Neumann condition, were used to set the normal flux of the energy density to 0. The electron energy settings in the metallic material wall boundary conditions were set to 0, the electron reflection coefficient at the wall was set to 0, and the walls in contact with the plasma were set to have a ground potential (V = 0). In most cases, when calculating the microwave plasma by using the numerical methods, numerical problems arose with regions where \(n_{e}\) (electron density) values were close to \(n_{cr}\) (critical density). To avoid this, COMSOL Multiphysics provides a method using a \"Doppler broadening parameter\" which allows for convergence [49]. However, in this model, the use of this method was limited to prevent the deterioration of the computational accuracy.
# Degradation Assessment of In-Service Transformer Oil Based on Electrical and Chemical Properties
## 2 Analysis Method  
Table 1 lists the specifications of the in-service transformers considered in the current study. A total of three transformers, namely T1, T2, and T3, were considered, which were installed at a 220 kV substation in Dera Ismail Khan, Pakistan, while oil samples were collected for these transformers during the service years 2020-21, 2021-22, 2022-23, and 2023-24. All three transformers were commissioned in the same year, i.e., 2019. Transformers T1 and T2 had a voltage ratio of 220/132 kV, whereas T3 had a voltage ratio of 132/11.5 kV.  
The test methods used in the current study for the collected oil samples are tabulated in Table 2. The methods are categorized as electrical and chemical, and they conform to the International Electrotechnical Commission (IEC) and the American Society for Testing and Materials (ASTM). The table also describes the test conditions and acceptance values of the characteristics.  
In a transformer, electrical stress, turn-to-turn and section-to-section short circuits, thermal stress, operating temperature, and the presence of foreign objects are associated with the degradation of insulating oil. These conditions lead to the weakening of dielectric strength; as such, DDF and breakdown voltage can be used as an index to directly evaluate the electrical characteristics of insulating oil.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Transformer**} & \multicolumn{5}{c}{**Characteristics**} \\ \cline{2-6}  & **Make** & \begin{tabular}{c} **Rated Power** \\ **(MVA)** \\ \end{tabular} & \
\begin{tabular}{c} **Rated Primary** \\ **Voltage (kV)** \\ \end{tabular} &
\begin{tabular}{c} **Rated Secondary** \\ **Voltage (kV)** \\ \end{tabular} & **Taps** \\ \hline T1 & Shandong Dachi China & 250 & 220 & 132 & 27 \\ T2 & Shandong Dachi China & 250 & 220 & 132 & 27 \\ T3 & PEL & 13/10 & 132 & 11.5 & 23 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics of the under-consideration transformers.  
The moisture content of the oil is also generally recognized as an effective diagnostic index that can be used to identify the status of degradation of insulating oil, as the presence of moisture significantly affects the breakdown strength of the oil. With the decline in the dielectric strength of insulating oil and cellulose materials, combustible gases are generated inside the transformer. The identity of the gases being generated can be very useful information in any preventive maintenance program. The sum of all combustible gases with a rise in individual or ratio gas-generated rates indicates a transformer fault and can also indicate the fault level. As such, DGA is used in evaluating the heath of transformers and is considered the most advanced and technically acknowledged method.
## 3 Results
### Overall Results
It can be seen that fixing a unique threshold value yields good results while being a simpler decision strategy, but in applications where the reliability of the prediction is the key objective, the additional complexity provides better outputs. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline  & **Brand** & **Location** & **TP** & **FN** & **FP** & **TN** & **Accuracy** & **Kappa** & **Sensitivity** & **Specificity** & **Precision** & **F1** \\ \hline
**WF1** & Vestas & Spain & 4 & 0 & 0 & 7 & 100\% & 100\% & 100\% & 100\% & 100\% & 100\% \\
**WF2** & Vestas & Spain & 3 & 1 & 1 & 4 & 78\% & 55\% & 75\% & 80\% & 75\% & 75\% \\
**WF3** & Siemens & Poland & 1 & 0 & 3 & 14 & 83\% & 34\% & 100\% & 82\% & 25\% & 40\% \\
**WF4** & Siemens & Poland & 4 & 2 & 0 & 9 & 87\% & 71\% & 67\% & 100\% & 100\% & 80\% \\
**WF5** & Senvion & Poland & 5 & 0 & 2 & 6 & 85\% & 70\% & 100\% & 75\% & 71\% & 83\% \\
**WF6** & Senvion & Poland & 3 & 1 & 4 & 14 & 77\% & 41\% & 75\% & 78\% & 43\% & 55\% \\
**WF7** & Nordex & UK & 3 & 3 & 4 & 16 & 73\% & 28\% & 50\% & 80\% & 43\% & 46\% \\ \hline
**TOTAL** & & & 23 & 7 & 14 & 70 & 82\% & 56\% & 77\% & 83\% & 62\% & 69\% \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Key Performance Indicators (KPIs) results summary for all the available windfarms (WF), sorted by turbine manufacturer (Brand) and location. TP stands for True Positive, FN False Negative, FP False Positive and TN True Negative. Figure 2: Receiving Operator Curve (ROC) of the various windfarms, the points and the corresponding values represent possible cutoff values to make a decision.
## 4 Conclusions  
This study showed that sugar beet leaf silage is a potential substrate for biomethane production. The high concentration of water-soluble carbohydrate in the substrate makes ensiling a plausible preservation method for biogas production. The novel Aspergillus and Neurospora species-based additive inhibited yeast activity in the silages and improved the biomethane potential of sugar beet leaves by enhancing the formation of total fermentation products that are precursors to biomethane production. The increased fermentation products in the silages with additives resulted in a higher loss in volatile solids. The biodegradability of the silages with additives was also enhanced by the additive as seen in the higher values of the hydrolysis constants (k\({}_{1}\) and k\({}_{2}\)). The increase in BMP of the silages with additive was between 21 and 45%, depending on the concentration of additive in the silage mixture (g/g). The dual pool kinetic model predicted the methane yield better than the modified Gompertz model and is therefore a more appropriate model for the design and optimisation of process parameters for the production of biomethane from sugar beet leaves.  
Conceptualisation, W.S. and J.U.; methodology, W.S. and J.U.; software, D.G. and J.U.; validation, W.S., J.L. and M.N.; formal analysis, J.U. and D.G.; investigation, J.U.; resources, W.S.; data curation, W.S., M.N. and J.L.; writing--original draft preparation, J.U.; writing--review and editing, J.U., D.G., J.L., M.N. and W.S.; visualisation, J.U.; supervision, M.N. and W.S.; project administration, W.S.; funding acquisition, W.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the German federal Ministry of Education and Research, grant number 031B0578A.  
Not applicable.  
The Petroleum Technology Development Fund (PTDF) Nigeria and the German Academic Exchange Service (DAAD) jointly sponsored the PhD program of [PERSON] under the funding number 57401043. The funding is appreciated. The authors wish to thank [PERSON] for supplying the sugar beet leaves, as well as the laboratory staff of the DBFZ for their technical support.  
The authors declare that the experiments, evaluation of results, and publication were performed without conflict of interest. Senzyme GmbH delivered the additives free of charge without influencing the experiments, results, or evaluation.
## 6 Conclusions  
This paper proposes a single-difference residual-based multipath hemispherical map and focuses on dynamically mitigating the multipath errors in the single-frequency carrier phase of BDS-2/BDS-3. The proposed method is not affected by the changeable time shift of each BDS satellite ORT. Moreover, it can effectively and conveniently solve the phenomenon of two inconsistent observation periods of some BDS-3 MEO satellites.  
Comparing with the ASF method, the proposed method does not require the specific time shift of each satellite ORT, which significantly improves the computational efficiency. Moreover, with the update of the hardware supporting the BDS-3 signal, the visible satellites of the BDS constellation will reach more than 40, and there will be lot of \"end effects\" when calculating the timing shift of each satellite. The SD-MHM method reduces the RMS of positioning errors by 56.4%, 63.9%, and 67.4% in the east, north, and vertical directions, respectively. The average positioning accuracy increases from 1.81, 2.49, and 8.70 mm to 0.79, 0.90, and 2.84 mm, and the baseline accuracy increase from 1.97 to 0.84 mm. Moreover, the capability of the SD-MHM multipath mitigation is better than that of ASF. SD-MHM still has excellent multipath mitigation capability for observation data with a period of more than seven days.  
It is worth mentioning that the applied BDS-3 satellites are only based on the constellation of 12 MEO satellites (PRN: C19-C30). With the official opening of BDS-3 satellites and the GNSS receiver boards updating, the number of observable satellites will increase significantly. The proposed method has reference significance for the BDS multipath mitigation of conventional hardware receivers.  
Methodology, C.L. ([PERSON]) and Y.T.; software, C.L. ([PERSON]), Y.T., and H.H.; validation, Y.T., C.L. ([PERSON]), and X.Z.; formal analysis, C.L. ([PERSON]), C.L. ([PERSON]), X.Z., and H.X.; data curation, Y.T., C.L. ([PERSON]), and H.H.; writing--original draft preparation, Y.T. and T.Z.; and writing--review and editing, T.Z. and H.X. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key Research and Development Program of China (No. 2016 YFC0803109), the Anhui Universities Natural Science Research Project (No. KJ2020A0312), the Hebei Ecological Intelligent Mine Joint Foundation (No. E2020402086), the National Natural Science Foundation of China (No. 41772130), and the Anhui University of Science and Technology Graduate Innovation Foundation (No. 2019 CX2077).  
Upon a reasonable request, the observation data that support the findings of this study are available from the corresponding author ([PERSON]).  
We would like to thank the anonymous reviewers for their constructive comments and suggestions. Furthermore, we are grateful to the IGS Data Center of Wuhan University for providing the BDS-2/BDS-3 broadcast ephemeris.  
The authors declare no conflict of interest.