esa-sceva/satcom-chunk-collection huggingface dataset:
# Numerical Simulation of Flow Field of Submerged Angular Cavitation Nozzle
## 3 Results and Discussion
### Influence of Contraction Section on Cavitation  
To investigate the influence of the contraction section on the cavitation effect of the angular cavitation nozzle, keeping the remaining structural parameters constant and setting different contraction angles \(\alpha\) (8\({}^{\circ}\), 10\({}^{\circ}\), 13.5\({}^{\circ}\), 16\({}^{\circ}\), and 20\({}^{\circ}\)), the axial velocity distribution of the jet inside the nozzle and the axial vapor volume fraction distribution at \(d/2\) obtained from numerical simulations are shown in Figures 16 and 17, respectively. It is noted that the vapor fraction corresponding to different \(\alpha\) shows roughly the same trend. It is because the angle of the contraction section (\(\alpha\)) has less effect on the cavitation [25]. The change in \(\alpha\) affects the bunching of the jet. On one hand, it causes energy loss and thus affects the jet velocity. On the other hand, it affects the flow state of the jet and hence affects the cavitation. However, the main cavitation region of the angular cavitation nozzle is located in the expansion section.  
According to the distribution of axial velocity at different \(\alpha\) (see Figure 16), when the axial distance is less than \(-7.5\) mm, the axial velocity of the jet decreases with the increase in \(\alpha\). This is because the larger the \(\alpha\), the greater the energy loss inside the contraction section and the smaller the jet velocity; in the range of axial distance between \(-7.5\) mm and \(10\) mm, the axial velocity of the jet corresponding to different \(\alpha\) is approximately the same, indicating that different \(\alpha\) does not affect the maximum velocity of the jet. For an axial distance greater than \(10\) mm, the axial velocity of the nozzle jet with \(\alpha\) of \(13.5^{\circ}\) is about \(140\) m/s at the edge of the external flow field (i.e., the value of the axial distance is \(30\) mm), which is the largest compared to the axial velocity of other \(\alpha\) (about \(130\) m/s), but the overall difference is not significant.  
From Figure 17, can be seen that when the axial distance is less than \(-7.5\) mm, the steam volume fraction at \(d/2\) corresponding to different \(\alpha\) is \(0\), indicating that no cavitation occurs at this time. While the axial distance is in the range of \(-7.5\) mm to \(0\) mm, the steam volume fraction at \(d/2\) decreases with the reduction in \(\alpha\). The transition of the cylindrical section causes a sudden change in pressure, and the smaller \(\alpha\) makes the first cavitation of the nozzle smaller. When the axial distance is greater than \(0\) mm, the steam volume fraction at \(d/2\) of the nozzle with a value of \(13.5^{\circ}\) for \(\alpha\) exceeds the volume fraction corresponding to the remaining \(\alpha\) by a large margin. It indicates that the nozzle cavitation effect is best when \(\alpha\) is \(13.5^{\circ}\).  
Figure 16: Effect of \(\alpha\) on the fluid velocity.  
Figure 17: Effect of \(\alpha\) on the cavitation.
## 7 Conclusions  
This paper deals with the problem of noncooperative spectrum sensing in very low SNR conditions. Many algorithms have recently been developed to overcome the scarcity of radio spectrum. However, most of them suffer from noise uncertainty and do not work correctly in very low SNR conditions. In this paper, we use the promising approach of the Recurrence Quantification Analysis (RQA) to propose a robust detection model, named the Recurrence-Analysis-based Detector (RAD). The RAD benefits from the exploitation of the similitude among the different state vectors. Indeed, our analyses reveal that for a White Gaussian Noise, the coefficients contained on the first upper diagonal are representative of other coefficients of the distance matrix, which is not the case for a communication signal. Thus, by applying a conformity test between the coefficients of the first upper diagonal and other coefficients of the distance matrix, the presence or absence of a communication signal can be revealed. The RAD presents five major advantages: it is more robust than the Energy Detector (ED) and the Cyclostationary Feature Detector (CFD), which are widely used in the noncooperative spectrum sensing context; it does not suffer from noise variance estimation, because the estimation of the noise variance is not required during the spectrum sensing process; it is able to detect the communication signal in a very low SNR condition; contrary to the ED, the RAD is able to distinguish a noisy communication signal and a high energy noise; the RAD does not need a high computational cost like the CFD. Our present work also presents two major contributions. First, we determined, for digital communication signals, the optimal values of the time delay \(\tau\) and embedding dimension \(m\) needed for the phase space reconstruction. Second, we established the analytical expression of detection threshold \(\lambda\), the probability of detection \(P_{d}\), and the probability of false alarm \(P_{fa}\) of the  
Figure 18: Curves of the algorithmic complexity of ED, CFD, and RAD.  
detection model based on RQA. From the ROC curves, we can notice without ambiguity that the RAD is more robust than the ED and CFD algorithms. Our current simulations show that the RAD is able to detect the communication signal for SNR \(\geq-12\) dB. In addition to facilitating the blind detection of communication signals, RQA could be used to accurately estimate the characteristic frequencies of the signal of interest. In our future work, we will optimize the performance of the RAD detector based on this reliable estimation of the characteristic frequencies of the signal of interest.  
Conceptualization, [PERSON]-[PERSON] and [PERSON]; [PERSON]-[PERSON] developed the proposed approach, performed the principle, and the simulations and prepared the manuscript; [PERSON] and [PERSON] participated in the development of the theoretical study and reviewed the manuscript. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Dataset available on request from the authors.  
The authors declare no conflict of interest.
# A Study on the Surrogate-Based Optimization of Flexible Wings Considering a Flutter Constraint +
## 4 Concluding Remarks  
An SBO methodology for designing wings considering both performance and aeroelasticity constraints was successfully implemented using four different open-source Python codes. This methodology uses Extra Tree Regressors to mitigate the computational cost associated with this wing design problem, and it was tested to solve a multi-objective optimization problem considering three cruise speeds.  
Although the surrogate models exhibited suitable performance, certain discrepancies appear, especially in drag coefficient predictions and flutter speed, attributed to observed aeroelastic nonlinearities. Nevertheless, the adopted surrogate models, despite the challenges faced, yielded acceptable results, with errors generally lower than 10%.  
To improve the accuracy of the surrogate models in the three cases analyzed, the original design space was revised for each of these cases individually. After this treatment, the optimized designs that maximize \(C_{L}/C_{D}\) and minimize mass while keeping flutter outside the prescribed boundary presented differences under 5% compared to the corresponding SHARPy simulations. Although this refinement process improved results, it also increased the computational time substantially.  
Since the goal was to efficiently integrate aeroelastic analysis, the computational gains were also significant. Direct simulations with SHARPy take about 93.49 s each, while surrogate models offer predictions in under 0.01 s. In terms of optimization, the following observations are made:  
* Optimization with 50 generations and 180 population averages 321.76 s, totaling 9000 evaluations. Direct SHARPy simulations would take nearly 10 days.
* A scenario with 200 generations and 280 population takes around 1825.03 s, equaling 56,000 evaluations. Using SHARPy would mean approximately 60 days.  
These results highlight the substantial computational time savings when using surrogate models, particularly in optimization scenarios requiring multiple evaluations.  
Conceptualization, A.L., F.A. and A.S.; methodology, A.L., F.A. and A.S.; software, A.L.; validation, A.L.; formal analysis, A.L.; investigation, A.L., F.A. and A.S.; data curation, A.L. and F.A.; writing--original draft preparation, A.L. and F.A.; writing--review and editing, A.S.; visualization, A.L. and F.A.; supervision, F.A. and A.S.; project administration, A.S. All authors have read and agreed to the published version of the manuscript.  
The authors acknowledge Fundacao para a Ciencia e a Tecnologia (FCT), through IDMEC, under LAETA, project UIDB/50022/2020.  
**Institutional Review Board Statement:** Not applicable.  
Figure 8: Pareto fronts across analyzed cruise speeds.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The raw data supporting the conclusions of this article will be made available by the authors on request.  
**Acknowledgments:** A.S. acknowledges the NSERC Canada Research Chair Program.  
**Conflicts of Interest:** The authors declare no conflict of interest.
# SC-FDE Layer for Sensor Networks in Remote Areas Using NVIS Communications
###### Abstract  
Despite high costs and lengthy deployments, satellite communications have traditionally been used to provide coverage in remote areas. However, given the fact that there is no radio infrastructure available in these areas, Near Vertical Incidence Skywave (NVIS) technology has positioned itself as an attractive alternative to communicate with low-power nodes in remote areas. This type of communication works in the HF frequency range complying with STANAG and MILSTD standards, which define a physical layer for scenarios that differ from NVIS and low-power communication. The purpose of this paper was to present the definition of a new communication physical layer based on single-carrier frequency-domain equalization (SC-FDE) based on these standards but adapted to the ionospheric communication channel. This physical layer was compared to an OFDM-based layer from a previous study. The experiments performed show that this new approach achieves better results than OFDM in terms of a higher signal quality with a higher specific BER probability. Finally, this layer was also used in the theoretical design of an NVIS gateway to link sensor network devices spanning large-scale remote areas in a secure manner in the context of ubiquitous sensor networks (USN).  
remote sensing; HF; NVIS; IoT; OFDM; SC-FDE; SDR
## 5 Optimum \(M\) with Background Light
### Optimum Multiplication Factor with BGL
A fixed and high \(M=25\) offers comparable performance to the optimized \(M\) when no BGL and no \(I_{dm}\) are present, while a low \(M=8\) shows inferior sensitivity. But the same fixed high \(M\) will provide less sensitivity when these additional shot noise sources are present, and the low \(M=8\) then nearly coincides with the optimized \(M\). In any case, the curves are much closer to each other when additional shot-noise is present. Methods to optimize \(M\) automatically for varying the input power have been suggested for fiber communications [55]. Such methods, however, are of marginal applicability in the case of FSO, with its large and variable fraction of background light and with an even faster varying received power (due to scintillation and point-fading). Rather, a BGL sensor would need to be added and evaluated to ensure a minimum \(p_{\text{BE}}\) for any situation. Thus, when BGL and \(I_{dm}\) can be measured and are not negligible, it is important to ensure the advantageous fixed multiplication factor for an individual environmental situation. Figure 14 signifies its importance by plotting the BER and the \(M_{opt}\) over a range of BGL and three values of \(<\)\(P_{Rx}\)\(>\) (no \(I_{dm}\) is regarded here for better comparability). We find that the multiplication factor, \(M_{opt}\), requires careful adoption to the instantaneous background light to ensure the optimum performance of the APD-RFE, while the influence of absolute received power on \(M_{opt}\) is less significant in this example since its shot-noise component is small compared to BGL. The more background light, the less important the individual optimization of \(M\), tending towards a value around 8 with the parametrization used here. These foregone findings are verified by measurements with free-space APD-RFE-implementation, with and without the influence of a 1550 nm BGL source (Figure 15). The practical RFE measured (Figure 15) shows some real-world deteriorations; the bandwidth of TIA along with the reception lowpass (LP) and limiter does not match, and the high capacitance of the large APD (200 \(\upmu\)m in diameter) again limits its usable data rate and, thus, its sensitivity. These lead to a 320 Pbb when BER \(=10^{-4}\) instead of the ideal \(\sim\)120 Pbb. The sensitivity run and the effect of the background light coincide well with the predictions from the formalism presented in this section, with a deterioration in sensitivity of nearly \(-3\) dB when BER \(=10^{-4}\), with and without BGL. Figure 13: BER over \(<\)\(N\)\(>\), with a fixed \(M=8\) and \(M=25\) compared with \(M_{opt}\) adopted to \(P_{Rx}\), without and with \(P_{BGL}=50\) nW and \(I_{dm}=2.5\) nA.
# Evaluation of Waste Express Bag as a Novel Bitumen Modifier
## Discussion
### High Temperature Performance
This explains why the phase angle of the high-dosage WEB-modified bitumen decreased with increasing temperature at temperatures above 88 \({}^{\circ}\)C.  
Similar to softening point the effect of CaCO\({}_{3}\) may also caused the improvement of high temperature performance. When the dosage of WEB reached a certain level, some virgin bitumen would combine with CaCO\({}_{3}\) and became modified asphalt mastic which may enhance the high temperature performance. In addition to the Superpave rutting factor (G*/sin\(\delta\)), the MSCR test was conducted for the rutting resistance ability of the WEB-modified bitumen. The test results are listed in Table 3. Three parameters were used for analysis including the average percent recovery (R), non-recoverable creep compliance (J\({}_{\text{nr}}\)), and the stress sensitivity parameter (J\({}_{\text{nr-diff}}\)). The percent recovery is an indicator of elastic behavior. Higher percent recovery indicates better elasticity. J\({}_{\text{nr}}\) presents the unrecoverable creep compliance of the bitumen binder at high temperature. A lower J\({}_{\text{nr}}\) indicates a superior capability to resist permanent deformation. The J\({}_{\text{nr-diff}}\) was used to assess the stress sensitivity of the bitumen binder. The MSCR results were in accordance with the G*/sin\(\delta\) test result. According to Table 3, the WEB-modified bitumen showed a higher elastic behavior and lower unrecoverable creep compliance, which means it had better rutting resistance. According to the ASSHTO specification, bitumen with more than 6% of modifiers meets the AASHTO requirement for the highest traffic level \"E\", while bitumen with a 4% WEB meets the requirements of level \"H\". The virgin bitumen and modified bitumen with a 2% WEB only meets the qualifications of level \"S\".
## 3 Proposed Methodology (SLF-RPL)
### Trust Model Evaluation  
Trust evaluation is a crucial step in the proposed model, as it helps to establish the initial trust between nodes and dynamically updates it with measured parameters as needed. The evaluation process compares the calculated trust values with a threshold value for each node in order to establish trust relations between nodes and their parent nodes for secure communication within the network topology. The evaluation process in the Subjective Logic Framework considers belief, disbelief, and uncertainty, with a threshold value of 0.5 for all parameters as presented in Table 2 below. The controller stores the trust-related measurements with a unique identifier (UID) for each device generated through a random function and evaluates trust values separately against the UIDs of each device.
## 4 Results and Discussion
### Synthetic imbalanced data set  
The bivariate plot of the synthetic imbalanced data set is given in Figure 11. It can be observed that objects in two majority classes have larger spans than the minority classes in the input space. The predictions of small classes by different ANNs are given in Table 5. The prediction results of the SCRBFN and RBFCCN models are better than the prediction results of the BNN and PLS-DA models. The RBFCCN, SVM, and RF methods have better predictions among all seven methods. The RBFN models have slightly worse prediction result than the three methods above. The trained models of the ANNs will have a relatively loose fit to the training set by setting the training error threshold to 0.2. The BNN and PLS-DA models trend to first model the majority classes in the prediction class. As a result, predictions of minority classes are poor.
# The Recent Advancement in Unmanned Aerial Vehicle Tracking Antenna: A Review
## 4 Recent Advancement on UAV Tracking Antenna
### Tracking Orientation  
Tracking orientation is responsible for obtaining the angular displacement of a body as well the coordinates. For the angular displacement of a moving UAV which comprises of yaw \(\psi\), pitch \(\theta\), and roll \(\phi\) to be properly tracked, two popular strategies are often deployed which are (i) keeping the coordinates constant; and (ii) allowing the object in this case the airborne platform to rotate. The other approaches are discussed below.
# High-Durability Concrete Using Eco-Friendly Slag-Pozzolanic Cements and Recycled Aggregate
## 1 Introduction
### Aims, Materials, and Methods  
The overall aims of the presented research can be summarized and listed as follows:  
* creating various slag-pozzolanic cement admixtures reducing the clinker component while still exhibiting suitable binder properties
* characterization of the different cementitious constituents used to produce the slag-pozzolanic CEM V cement types
* identifying the cement characteristics of the designed CEM V cement types
* developing concrete formulas and gathering the concrete properties using the manufactured CEM V cements
* further ecological improvement by replacement of the standard aggregate by recycled aggregate for concrete
* acquiring the basic characteristics of the developed concrete mixtures with a focus on concrete durability  
To reach the desired objectives, binder and concrete manufacture, as well as intensive material testing, was performed including the following: (1) Various testing methods were applied to characterize at first the cement admixtures and cement properties of the produced CEM V cement types:  
* X-ray diffraction analysis XRD (Philips X-ray diffractometer PW1730, Malvern Panalytical GmbH, Kassel, Germany) to examine the mineralogical composition,
* X-ray fluorescence XRF (PANalytical X'Pert Pro, Malvern Panalytical GmbH, Kassel, Germany) to record the chemical composition,
* Frattini-testing to demonstrate the pozzolanic activity of the cementitious constituents,
* fresh cement mortars testing (slump, density, air content, setting time, soundness),
* hardened cement mortars testing (recording compressive strength and bending tensile strength at 2, 7, 28, 56, and 84 days of curing time to gather strength development data as well) with an additional focus on the durability-relevant parameters, porosity and passivation ability.  
Subsequently, (2) standard concrete compositions using the generated cements were tested to identify the concrete characteristics:  
* fresh concrete testing (flow, density, air content)
* hardened concrete testing (compressive strength, bending tensile strength, modulus of elasticity) with a focus on the durability-relevant parameters, frost-resistance and permeability  
In a third step, (3) standard aggregate for concrete was replaced by recycled aggregate from nonstandard crushed metamorphic rock arising during tunnel excavation. These concrete mixtures--now consisting of a newly developed CEM V cement admixture and processed and recycled aggregate from schist rocks--were also examined with regard to workability (fresh concrete density, flow spread, air content), strength (compressive and bending tensile strength, as well as the fracture energy), and particularly with regard to durability, as the designed concrete composition may be used in tunnel constructions, where the recycled aggregate is generated, exhibiting long service lifetimes of up to 200 years.  
At all investigation levels, an additional comparison to standard cement was made.
# Rapid and Cost-Effective Fabrication and Performance Evaluation of Force-Sensing Resistor Sensors
###### Abstract  
In this study, we developed a cost-effective and rapid method for fabricating force-sensing resistor (FSR) sensors as an alternative to commercial force sensors. Our aim was to achieve performance characteristics comparable to existing commercial products while significantly reducing costs and fabrication time. We analyzed the material composition of two widely used commercial force sensors: Interlink FSR-402 and Flexiforce A201-1. Based on this analysis, we selected 4B and 9B pencils, which contain high concentrations of graphite, and silicone sealant to replicate these material properties. The fabrication process involved creating piezoresistive sheets by shading A4 copy paper with 4B and 9B pencils to form a uniform layer of graphite. Additionally, we prepared a mixture of 9B pencil lead powder and silicone sealant, ensuring a consistent application on the paper substrate. Measurement results indicated that the force sensor fabricated using a mixture of 9B pencil powder and silicone sealant exhibited electrical and mechanical characteristics closely resembling those of commercial sensors. Load tests revealed that the hand-made sensors provided a proportional voltage output in response to increasing and decreasing loads, similar to commercial FSR sensors. These results suggest that our fabrication method can produce reliable and accurate FSR sensors suitable for various applications, including wearable technology, robotics, and force-sensing interfaces. Overall, this study demonstrates the potential for creating cost-effective and high-performance FSR sensors using readily available materials and simple fabrication techniques.  
force-sensing resistor; flexiforce; interlink; rapid and cost-effective; pencil graphite +
Footnote †: journal: Applied Sciences