esa-sceva/satcom-chunk-collection huggingface dataset:
# Terahertz Photoconductive Antenna Based on a Topological Insulator Nanofilm
## 4 Discussion
As it was shown in previous experimental works [40; 41], in case of the normal incidence of the pump beam on BSTS, PD effect is negligible in comparison with PG generation. In our case, at zero bias voltage we detected the same bipolar shapes of the temporal waveforms (Figure 6b) as in [15]. Thus, we can relate the THz fields observed in the unbiased TI to the PG effect. By comparing expression (4) for PG current with the general presentation of the induced currents in form (3), one can see that (4) seemingly depicts an effect of resonant nonlinear generation of an effective field \(\widetilde{\mathbf{E}}\), which is responsible for the directional motion of free carriers. More accurate calculations, performed by considering the kinetic Boltzmann distribution equation for the electron distribution function within the semi-classical approach [40], can be treated so that an effective field \(\widetilde{\mathbf{E}}\) appears here as a result of two processes: an alignment of carrier moments along the pump electric field, and an asymmetric scattering of carriers at the surface of TI [41]. However, this theory describes quadratic dependence on the pump field for THz field generated under below-bandgap excitation, but needs further assumptions to explain generation under above-bandgap pumping. Indeed, the below-bandgap excitation did not change the carrier's concentration, \(N(t)\) was almost constant in (3), and only the temporal change of effective \(\widetilde{\mathbf{E}}\) determined a short PG current pulse, which scaled up quadratically with the pump electric field. At the same time, when the pump photon energy exceeded the bandgap, the concentration of charge carriers also grew quadratically with the pump field. This was the case for bulk electrons, while a saturation of the concentration of the surface electrons may occur. However, no fourth-order dependence on the pump field was observed under above-bandgap excitation. So, taking all the above considerations into account, we can conclude that: (1) the impact of the PG effect, and accompanying effective PG field \(\widetilde{\mathbf{E}}\), into THz generation in the biased THz antenna was negligible. Generation occurred due to photo-excited _bulk_ carriers and its relaxation through the surface states in the presence of the constant field \(\mathbf{E}_{dc}\). The temporal shape of \(N(t)\) determined THz generation waveform and the width of the antenna spectral response; and (2) in the absence of an external biased field, THz generation took place due to the PG effect by _surface_ electrons, which had almost the same concentration during the whole generation pulse. The temporal shape of effective \(\widetilde{\mathbf{E}}(t)\) determined the THz generation specific waveform and the width of the BSTS spectral response. Figure 7: Relaxation of carriers in BSTS film.
# Fast Ferroelectric Liquid Crystal Based Optical Switch: Simulation and Experiments
## 3 Optical Switching in FLC Modulator
### Principle of Operation  
The principle of operation is that the birefringent plate at the input port manipulates the polarization states to the desired ones. The most important element in the binary switch is FLC, in conjunction with the lateral beam splitters (LBS). In the absence of the electric field, the input signal passes through the FLC cell and polarization beam splitter with the same polarization. The schematics of optical switching through the FLC cell and the LBS are shown in Figure 4.  
Through the application of an electric field, FLC molecules rotate the polarizations of the signal passing through it. With the sufficient electric field, optical signal polarizations rotate to the orthogonal ones and the LBS passes the signal to the other output port. The principle of basic switch matrix mechanism is reported by [PERSON] et al. in 2007 [PERSON] et al. (2007). In this study, we are introducing a faster FLC instead of a twist nematic (TN) LC. In general, the optical parameters of FL  
Figure 4: Schematics of possible switching through the ferroelectric liquid crystal (FLC) binary switch which consist of lateral beam splitters (LBS) and FLC material.  
Figure 3: (**a**) Representation of two possible states of molecules in SmC* mesophase under crossed polarizers and (**b**) its polarization-dependent orientations. Note: A = analyzer; P = polarizer  
but the main source for cross-talk is non-ideal beam splitters, and this problem can be fixed by the insertion of final cross-talk removal stages. In this case, the optical parameters of LC-SLM (liquid crystal special light modulator) are not important and FLCs may be used for fast matrix switch.
## 6 Engineering Application
### Chamber Deformation Measurement  
In order to monitor the surrounding rock deformation at different depths, the measuring points of the multi-point displacement meter are arranged at 2 m, 4 m, 6 m, 8 m and 10 m depth of the chamber dome surrounding rock, as shown in Figure 19.  
It can be seen from Figure 19 that the roof separation of the chamber dome in the range of 0 m to 4 m is relatively large. The maximum roof separation is 0.012 m, corresponding to the crack initiation and expansion area. The amount of separation is basically maintained at 0.009 m within 4 m to 10 m, corresponding to the intact area. Based on the above rules, it can be concluded that the deformation of the surrounding rock of the chamber dome is well controlled and roof fall hazard would not occur.
# Computed Tomography-Driven Design and Fused Filament Fabrication of Graded Density Bone Scaffolds
## 1 Introduction
### Design Methods of Scaffolds for AM  
The design and manufacturing of scaffolds are guided by specific mechanical, biological, and physicochemical requirements [2]. Scaffolds are engineered to promote desirable cellular interactions, thereby supporting the formation of new functional tissues. Additionally, factors such as the interconnectivity, pore shape, pore size, surface area, mechanical strength, and degradation rate must be carefully considered to ensure compatibility with the surrounding tissue [16; 17]. In this sense, the porosity and its complementary quantity, the relative density (or volumetric fraction), play a fundamental role in determining the mechanical (as described in the well-established Gibson and Ashby models [18]) and biological performance of scaffolds [19].  
Lattice structures are a viable solution for the realization of customized scaffolds (or even porous prostheses) with tailored properties based on porosity [19; 20]. The macroporosity is geometrically modeled in CAD software but the meso- to micro-porosity can be obtained during the AM process or even in post-processing operations [21].  
Lattice structures combined with AM allow for the multi-level customization of the geometry, material properties, and manufacturing parameters. Geometric customization involves tuning the unit cell shape, size, and relative density [20; 22]; material customization can be achieved by modifying the micro-structure or using multi-material strategies to create functionally graded scaffolds; process parameters are customized to tune the final structure's properties. For example, in fused filament fabrication (FFF), factors such as the temperature and printing speed impact the flow rate, dimensional accuracy, interlayer adhesion, and anisotropy.  
One of the main classification criteria is based on the type of lattice structure, being either beam-based (or strut-based) or surface-based (or sheet-based). The former includes structures such as cubic, octet, and similar lattices, while the latter comprises TPMS structures, including gyroid, p-surface, and other lattices [23]. For bone-substitute applications, TPMS structures are known to present some advantages over strut-based lattices [24].  
Several geometric modeling approaches for lattice structures exist, some of which have been widely adopted and are now integrated into commercial software solutions such as nTopology, Materialise 3-matic, Autodesk Fusion 360, ANSYS Additive Suite, Siemens NX, and various addons for Grasshopper/Rhinoceros [2; 19].
# Experimental Study on the Straw Flexible Space Assembly Flood Control System
## 4 Testing of Flood Control System
### Hydrostatic Test Results  
The strain gauge data were exported and the data were processed to obtain the strain-strain gauge height dotted line graph. As can be seen from Figure 7a, as the water level became deeper, the effect of hydrostatic pressure on the flood control system became more significant. At the strain gauge height of 75 mm, the strain values of R1 and L1 were greater than M1, and at the strain gauge heights of 375 and 675 mm, the strain values of M2 and M3 were greater than R2 and L2, and the strain data measured on the left and right baffles were the same. As the structure of the baffle tester and the reduced scale model were symmetrical, the strain gauges were also arranged in symmetrical positions and the strain values measured on the left and right baffles were the same. As can be seen from Figure 7b, the value with straw was greater than that without straw, indicating that the straw absorbed water and expanded to support the water baffles, causing the strain value to increase. Thus, the straw as a filler can enhance the stability of the flood control system.  
Figure 8 shows the results of the ABAQUS numerical analysis of the hydrostatic test of the flood control system. The pressure equation (\(P=\rho gh\)) was used to calculate the pressure at different water level heights. The numerical model was established under hydrostatic conditions, the parameters were input into the numerical model, and the strain values of the water baffles were analyzed. As can be seen from the figure, the strain values of  
Figure 5: Strain gauge layout.  
Figure 6: Hydrostatic tests.  
the flood control system under the hydrostatic test were symmetrically distributed to the left and right. The maximum strain values of the whole flood control system appeared symmetrically in the lower left and right corners, which are the position of the column foot, indicating that the hydrostatic pressure causes the column to deform and the column is the main force-bearing structure of the flood control system. Figure 9 shows the water level-strain diagram obtained from the comparison between the hydrostatic test results and the numerical analysis results. The data obtained from the hydrostatic test and the numerical simulation were the same in terms of law and magnitude. The results of the hydrostatic tests showed that the flood control system can maintain stability under normal conditions, and a good fit was observed between the test results and the numerical analysis results, with an error within 5%.
# Analytical TCP Model for Millimeter-Wave 5G NR Systems in Dynamic Human Body Blockage Environment
## 4 Numerical Results
### TCP Throughput  
A comparison of the TCP throughput conditioned on the blocked and non-blocked states as well as the unconditional TCP throughput for \(\lambda_{B}=0.1\), \(v_{B}=1\) m/s, is shown in Figure 7. First, we note that the rates in the blocked and non-blocked states differ considerably across the entire range of the considered distances. For smaller distances, when non-blocked intervals dominate, the TCP throughput is close to the one in the non-blocked state. Further, as blocked durations increase, the throughput becomes closer to the one experienced in the blocked state. Such a trend is smooth and has no abrupt changes.  
The effect of blocker speed, \(v_{B}\), is assessed in Figure fig:rateTCPb. Since an increase in \(v_{B}\) leads to longer blocked periods, higher values of \(v_{B}\) result in worse TCP throughput, as it is shown in Figure 5. Note that the difference is not severe for \(v_{B}=0.1\) m/s and \(v_{B}=1\) m/s but it increases rapidly for higher blocker speeds. Recalling that the LoS blockage zone grows with the distance between the BS and the UE, the difference between the curves becomes larger for the higher values of \(d\). Analyzing Figure 8, one may notice that there is no drastic difference in TCP throughput for the practical values of RTT. The reason is that the RTT in the modern Internet is several times smaller than the mean duration of the blocked and non-blocked intervals, as evident from Figures 5 and 6.  
Figure 5: Blocked and non-blocked durations as functions of user equipment (UE)-Base Station (BS) distance and blockers’ density.  
Figure 6: Blocked and non-blocked durations as a function of blockers’ speed.
## 4 Conclusions  
In this paper, an efficient cross-layer SDVN routing scheme for P2P communication was presented. The novelty of this work lies in its unique design based on Software-Defined vehicular networks. Taking into account the existing SDVN framework, the proposed algorithm calculates globally optimized routes for V2V communication by SDN/OpenFlow controllers, while generating much lower end-to-end delay. Specially, the path selection from source to destination is determined based on the cross-layer metrics including forwarding probability, available bandwidth, and link duration. Consequently, its link stability-based routing decision also reduces the probability of link failure resulting in a lower rate of path disconnection. The overall performance of our proposed scheme was evaluated with varying vehicle speed and density, and compared with efficient AODV without SDN, SVAO with SDN, and SDGR with SDN in simulation scenarios. The result has proven that it is superior to the other three protocols in terms of routing overhead, average end-to-end delay, packet drop ratio, and average throughput.  
Fifth generation (5G) VANET is considered as a promising technology due to the merits of 5G architecture such as high mobility and scalability support, massive connectivity, and reduced latency, which overcome the limitations of the 4G technology. The proposed scheme is reliable and efficient, which is suitable for 5G applications. In addition, the SDN-based global routing greatly increases the computing load of remote controllers, which can be further solved by cloud computing and big data technologies.  
Methodology, Z.Y. and G.C.; software, P.C.; validation, Z.Y. and P.C.; investigation, Y.W.; writing--original draft preparation, Z.Y.; writing--review and editing, S.C. and G.C.  
This research was supported by the National Natural Science Fund under grand 61462015, was also partially funded by the University-Industry-Research Innovation Foundation of Ministry of Education No. 2018A05021 and the Science and Technology Foundation of Guizhou Province No. LH [2014] 7045 and the Science and Technology Foundation of Guizhou Province No. LH [2014] 7049.  
The authors declare no conflict of interest.
## 3 Results and Discussion
### Effect of Contaminated Soil on PSC Characteristics
It is therefore suspect that the radio-components of the contaminated soil affected the original PSC in a way that more IR bands in the region below 2000 cm\({}^{-1}\) could appear clearly and, as a consequence, identify the barium already existing in the original PSC. However, more investigation is needed to demonstrate how barium carbonate was formed by radio-substances in the contaminated soil. \begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Constituents**} & **Before** & **After** & **Difference between before and** \\  & **Contamination** & **Contamination** & **after Contamination (\%)** \\ \hline Si (as SiO\({}_{2}\)) & 9625 & 10,667 & & \\ Ca (as CaO) & 137,115 & 124,020 & & 9.6 \\ Al (as Al\({}_{2}\)O\({}_{3}\)) & 2261 & 2499 & & \\ Fe (as Fe\({}_{2}\)O\({}_{3}\)) & 31,536 & 30,885 & 2.1 & \\ Mg (as MgO) & 11,655 & 10,453 & 10.3 & \\ Ti (as TiO\({}_{2}\)) & 375 & 387 & & \\ Zn (as ZnO) & 404 & 448 & & \\ Cu (as CuO) & \(1.30\times 10^{2}\) & \(1.17\times 10^{2}\) & 10.0 & \\ Mn (as MnO\({}_{2}\)) & 40.3 & 41.2 & & \\ K (as K\({}_{2}\)O) & 178 & 153 & 14.0 & \\ Cl (as ClO\({}_{2}\)) & 98.1 & 21.0 & 78.6 & \\ S (as SO\({}_{2}\)) & \(1.44\times 10^{2}\) & \(1.11\times 10^{2}\) & 22.9 & \\ Ba (as BaO) & 89.2 & 79.9 & 10.4 & \\ C & 384,720 & 403,320 & & \\ \hline \end{tabular}  
Unit of components: ppm.  
\end{table} 
Table 5: Changes in the components of the PSC after contact with a contaminated soil for 10 days.
# An Applicable Predictive Maintenance Framework for the Absence of Run-to-Failure Data
## 3 Proposed Framework
### Predict the Remaining Useful Life (RUL)  
As mentioned in Section 2, when aging or abnormality occurs in the equipment, the trend of the HI may arise. Then, it is possible to predict the future value of the HI using time series prediction algorithms. When an incident ends, the configuration can be updated based on the failure data. In this way, the more the proposed framework is applied, as knowledge of failure data is accumulated, the performance can be improved [28]. In this paper, simple linear regression is used. Similarly, RUL can be calculated using regression. The RUL is the difference between the current time (index) and the predicted failure time where the regression prediction line meets the threshold. In addition, regression has the advantage of providing more accurate predictions because it can give confidence intervals for future time points. This is illustrated in Figure 3.  
In this case, the number of samples for fitting the regression line is important. This is because in general, the closer the failure point, the more spurred abruptly the HI changes. Figure 4 compares the results of the last 50 samples with the total sample. Fitting to the full sample makes it difficult to predict the exact RUL even if the failure is imminent while fitting to the latest sample can predict a more accurate RUL.  
To demonstrate the performance of the proposed methodology, In Sections 4 and 5, we conducted a case study on real data cases: a pump and a robot arm case.  
Figure 3: The example of the Health Index and the RUL prediction.
# Switchable Chiral Metasurface for Terahertz Anomalous Reflection Based on Phase Change Material
###### Abstract  
A switchable chiral metasurface based on a phase change material Ge\({}_{2}\)Sb\({}_{2}\)Te\({}_{5}\), which can switch between a right-handed circularly polarized mirror and a left-handed circularly polarized mirror, is theoretically discussed. When the conductivity of Ge\({}_{2}\)Sb\({}_{2}\)Te\({}_{5}\)\(\sigma\) is 0 S/m, the metasurface will reflect incident right-handed circularly polarized light and absorb incident left-handed circularly polarized light at 0.76 THz. As \(\sigma\) is set to 3 \(\times\) 10\({}^{5}\) S/m, the response of the metasurface to circularly polarized light will be reversed. That is, it reflects the incident left-handed circularly polarized light and absorbs the incident right-handed circularly polarized light at 0.66 THz. The circular dichroism is from 76% to \(-\)64%. Then, we also study the performance of the mirror structure of the initial metasurface. By simulating the reflected spectra with different conductivities and the surface current distribution, the reason for the switchable function is clear. Moreover, the switchable chiral metasurface can be applied in spin-selective beam deflectors, which is proven by simulation. This work provides a new strategy for the development of tunable chiral devices.  
switchable; circular dichroism; anomalous reflection; terahertz wave +
Footnote †: journal: Applied Sciences
## 3 Results and Discussion  
### The Urea SERS  
In this experiment, the water-soluble nitrogen in soil mainly came from urea. Therefore, analyzing the urea molecule and finding the assignment of Raman peaks of the urea molecule were conducive to current knowledge on the vibration forms of soil water-soluble nitrogen. Urea (molecular formula: CO(NH\({}_{2}\))\({}_{2}\)), is mainly composed of C-N, C-H and NH\({}_{2}\) groups with a relative molecular mass of 60.06. The urea molecular space structure and planar structure are shown in Figure 1. In order to further understand the speciation of water-soluble nitrogen, the 100 mg/L standard urea solution RS (solution-RS), 100 mg/L standard urea solution SERS, and solid RS (solid-RS) were collected. Figure 2 displays the spectral curves of solution-RS, SERS, and solid-RS.  
The assignment of SERS peaks can be concluded with Figure 2 and Table 1. According to Figure 2, there were no characteristic peaks in the solution-RS curve. However, there were some significant characteristic peaks when nanoenhancers (OTR 202) were added, which suggested that nano-enhancers could improve the signal of nitrogen detection. Among them, 544 cm\({}^{-1}\) belonged to the C-N in-plane bending, 995 cm\({}^{-1}\) belonged to the N-H stretching vibration, 1008 and 1027 cm\({}^{-1}\) were the C-N stretching vibration, 1182 cm\({}^{-1}\) was the N-H in-plane bending, 1370 cm\({}^{-1}\) was the N-H stretching vibration, 1540 and 1555 cm\({}^{-1}\) were the C=O stretching vibration, 1630 cm\({}^{-1}\) belonged to the N-H stretching vibration, and 1650 cm\({}^{-1}\) was the NH\({}_{2}\) in-plane swaying vibration. Similar results can be found in studies by [PERSON] [29], [PERSON] [30] and [PERSON] [31].  
Figure 1: Schematic diagram of urea molecular structure: (**a**) space structure; (**b**) planar structure.  
Figure 2: Spectral curves of solution-RS (Raman spectroscopy), SERS (Surface-enhanced Raman spectroscopy), and solid-RS: (**a**) solution-RS; (**b**) SERS; (**c**) solid-RS. RS: Raman spectroscopy; SERS: surface-enhanced Raman spectroscopy.  
It can be seen that the solid-RS had obvious characteristic peaks at 544, 1008, 1176, 1540, and 1650 cm\({}^{-1}\). The characteristic peaks at 544, 1008, and 1650 cm\({}^{-1}\) were the special molecular vibrations in the solid. As for the SERS, the characteristic peaks at 1370 cm\({}^{-1}\) occurred but they did not appear in solid-RS. The reason might be that the NH\({}_{2}\) group transformed to N-H when the solid urea dissolved in water. With the exception of 1555 cm\({}^{-1}\) (the stretching vibration of the C=O), the vibrations of the other bonds were all related to N, and their characteristic peaks in order of intensity strength were 1370, 1027, 1630, and 995 cm\({}^{-1}\). Furthermore, the intensity strength was the highest at 1008 cm\({}^{-1}\) in solid-RS. The reason was that the quantity of C-N in the urea molecule was the largest, and the vibration of the molecule was the greatest. In addition, the absorption intensity which was caused by the vibration of N-H at 1370 cm\({}^{-1}\) was the strongest in SERS.