esa-sceva/satcom-chunk-collection huggingface dataset:
## 3 Results and Discussion
### Generation of Multi-Order Orbital Angular Momentum Vortex Beams  
The OAM vortex beam has a helical wavefront and carries an orbital angular momentum of \(l\), which is related to many intriguing applications such as communication and imaging. Here, the topological charge \(l\) is the number of twists of the wavefront from 0 to \(2\pi\). the OAM vortex beam with a topological charge of \(l=1\) can be generated by a spiral phase profile ranging from 0 to \(2\pi\) with a gradient phase increment along the azimuthal direction [40]. A circular array with continuous gradient phase increment and uniform amplitude is an ideal scheme to generate an OAM wave. However, the continuous phase profile is not easy to achieve in both simulation and experiment. Therefore, it is common to divide the circle into several uniform sectors. In our design, only the circular region of the \(7\times 7\) array was excited to generate an OAM vortex beam. In exact words, three cells at each corner of the \(7\times 7\) array were not excited, and the other 37 cells were excited. For our designed radiation elements, the phase coverage from 0 to \(2\)N\(\pi\) could be achieved and the phase increment was \(2\)N\(\pi\)/7, where N = 1, 2, 3. In other words, we may actively achieve an OAM vortex beam with a topological charge of \(l=1\), 2, 3 by using the proposed structures.  
For demonstration, we manipulated the unit elements to uniformly change the phase along the azimuthal direction over 0-2\(\pi\). The simulated electric field intensity is shown in Figure 7a and the amplitude null in OAM mode can be clearly observed at the center, illustrating the good performance of the design. The corresponding spatial phase pattern with an evident abrupt phase jump from \(-\pi\) to \(\pi\) within a \(2\pi\) azimuthal range is shown in Figure 7d, which indicates that the topological charge of the patch array was 1. In addition, the generated OAM vortex waves can be actively tuned to the cases with larger topological charges by using higher-order phase gradients. When the second-order phase gradient of \(2\)N\(\pi\)/7 was adopted, the phase of the radiation field varied from 0 to \(4\pi\) along the azimuthal direction, therefore generating the OAM vortex beam with a topological charge of 2. Figure 7b shows the electric field intensity with the characteristic intensity minimum at the center, and the corresponding phase distribution in Figure 7e possesses two evident abrupt phase jumps from \(-\pi\) to \(\pi\). In addition, we can also generate an OAM vortex beam with a topological charge of 3 with the same approach. Figure 7c,f illustrates the simulated electric field intensity and phase distribution, further verifying the tunable performance of the proposed method.  
Figure 7: **(a–c)** The electric field intensity distributions and **(d–f)** the phase wavefronts of the generated OAM vortex beams with a topological charge of \(l=1\), 2, 3 based on the patch array with different order phase gradient.
## 4 Discussion  
Our analysis focused on deriving information relevant to updating city exposure datasets, particularly where both horizontal and vertical urban growth creates dynamic disaster risk. Historically, earth observation based urban growth assessments produce observations of 2D urban sprawl from image classifications applied to optical satellite imagery archives, such as those from the Landsat series [7]. Notably, these datasets do not show urban areas that undergo redevelopment through time, where low-rise buildings are replaced with taller vertical structures to accommodate urbanizing populations and economic activity (e.g., Figure 4). Therefore, these datasets cannot be used to assign building ages without first considering areas of redevelopment.
# A Study on the Feasibility of Natural Frequency-Based Crack Detection
## 5 Numerical Examples and Discussion
### Cracked Plates Made of Brittle Metals
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Safety Factor \(\chi\)**} & \multicolumn{5}{c}{**Natural Frequency Drop \(\Delta\omega\) (Hz)**} \\ \cline{2-9}  & **Mode 1** & **Mode 2** & **Mode 3** & **Mode 4** & **Mode 5** & **Mode 6** \\ \hline
3.5 & 1.201\% & \(-\)0.01 & 0 & \(-\)0.04 & \(-\)0.07 & \(-\)0.09 & 0.03 \\
4 & 1.561\% & \(-\)0.01 & 0.01 & \(-\)0.04 & \(-\)0.07 & 0 & 0.08 \\
4.5 & 1.975\% & 0 & 0.01 & \(-\)0.04 & \(-\)0.06 & 0.04 & **0.15** \\
5 & 2.428\% & \(-\)0.01 & 0.02 & \(-\)0.06 & \(-\)0.05 & **0.10** & **0.25** \\
5.5 & 2.925\% & \(-\)0.01 & 0.03 & \(-\)0.08 & \(-\)0.04 & **0.17** & **0.35** \\
6 & 3.462\% & 0 & 0.03 & \(-\)0.09 & \(-\)0.04 & **0.24** & **0.46** \\
6.5 & 4.038\% & 0 & 0.05 & \(\mathbf{-0.12}\) & \(-\)0.03 & **0.32** & **0.59** \\
7 & 4.650\% & 0.01 & 0.07 & \(\mathbf{-0.16}\) & \(-\)0.03 & **0.42** & **0.75** \\
7.5 & 5.294\% & 0.02 & 0.08 & \(\mathbf{-0.25}\) & \(-\)0.03 & **0.57** & **0.97** \\
8 & 5.967\% & 0.02 & **0.10** & \(\mathbf{-0.25}\) & \(-\)0.06 & **0.69** & **1.14** \\
8.5 & 6.667\% & 0.03 & **0.12** & \(\mathbf{-0.29}\) & **0.20** & **0.83** & **1.36** \\
9 & 7.390\% & 0.05 & **0.15** & \(\mathbf{-0.32}\) & **0.11** & **1.00** & **1.61** \\
9.5 & 8.131\% & 0.06 & **0.17** & \(\mathbf{-0.37}\) & **0.13** & **1.19** & **1.88** \\
10 & 8.887\% & 0.07 & **0.20** & **0.13** & \(\mathbf{-0.41}\) & **1.34** & **2.15** \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Results of the loaded CFCF single-edge cracked plate made of 2014-T651 aluminium alloy. introducing a crack. This is not unusual and could also happen in experiments investigating cracked beams and plates [15; 16; 47; 48], especially at low modes and when the crack is small. This could be the synergistic effect between crack location, crack severity, and mode shape. However, those negative results of \(\Delta\omega\) in Table 7 have been verified using finite element models in ANSYS and the accuracy of the results is assured. According to the above discussion, one may speculate that when the brittleness of material is reduced, namely, when a common ductile metal is used, the natural frequency drop may be measurable even when the safety factor is low, and early crack detection based on natural frequency measurement may be feasible. Cracked plates made of 6061-T6 aluminium alloy are studied in the next subsection and it will be shown that the above speculation stands.
## 3 Proposed Method  
In this study, we propose a security requirement recommendation method using the CBR method by combining the concept of cases with PDO based on extensions of the methods in [11; 12]. We describe the construction of the CB-PDO, in which case elements are added to the ontological structure and validated through existing case studies. We then employ the CB-PDO to analyze the attack elements in input scenarios and describe procedures and methods according to the CBR process. Furthermore, we propose a similarity metric that is suitable for our domain. It consists of a basic similarity algorithm (baseline) and an APT property called a weight. This section then describes the process of recommending security requirements to provide detailed information to users and help them make decisions according to the subsequent processes. We also define a study question to validate the method and evaluate whether the answer is explainable and justifiable.  
Figure 2 provides an overview of the security requirement recommendation method proposed in this study. This method consists of four steps of CBR and one step of preprocessing, and the process performed in each step is shown in the figure. The results generated at each step are used as the input for the next step and can be reviewed and analyzed by security experts to specify security requirements. In addition, our proposed CB-PDO was utilized to provide the knowledge and information necessary to derive the required results. The scenario preprocessing step before the conventional CBR step is converted into an attack template to make it easier to analyze the given attack scenario and provide expert-analyzed attack information. In the case retrieval step, the previous cases that are most similar to the attack components are determined using the similarity metrics. The previous cases included information about attacks performed by threat groups in the past and the security requirements used to prevent them. Therefore, in the case reuse step, we perform an adaptation process to reuse requirements specified in the past to solve the current problem. This step is not necessary if the solution can be used as is; however, if there is a difference in the cases, the solution needs to be optimized so that it is suitable for the current problem. Accordingly, information for optimization is provided to the security experts in the case revision stage. Finally, if an expert determines that the problem was correctly solved, it is then stored in the CB-PDO as a case. The processes and components of each step are described in detail in this subsection.  
Figure 2: Overview of our proposed method.
# Postural Control Disturbances Induced by Virtual Reality in Stroke Patients
## 1 Introduction  
A stroke is a serious life-threatening medical condition characterized by the interruption of blood flow to a part of the central nervous system due to an ischemic or hemorrhagic vascular injury [1]. Patients who survive a stroke (SP) suffer from various somatosensory impairments, motor dysfunction, perceptual, visual disturbances, and altered spatial cognition with reference to the upright body position [2; 3; 4], resulting in balance disorders [2; 3]. PS show changes in motor strategies for postural control with delayed and reduced anticipatory postural adjustments [4] and a shift in sensory weighting, with an increased reliance on visual information [5]. Balance disorders are responsible for medical complications due to falls and are associated with the inability to perform activities of daily life [4].  
Among the wide variety of motor rehabilitation programs, virtual reality (VR) has shown promising results as a means of improving postural control abilities [6; 7]. VR is defined as \"the use of interactive simulations created with computer hardware and software to present users with opportunities to engage in environments that appear and feel similar to real-world objects and events\" [8] and features immersive systems such as head-mounteddisplay [9]. Immersive VR using a head-mounted display seems to be safe and feasible in stroke patient rehabilitation [10]. VR technology offers the possibility to immerse people in a 3D environment that can mimic a real-life scenario, allowing assessment of postural control in more realistic situations with the possibility to manipulate, in a reproducible way, the task complexity [11].  
Previous work indicates that static virtual environments (VE) do not appear to challenge postural control [12, 13] whereas dynamic scenes induce postural perturbations in healthy young adults (HA) [12] and older adults [14]. However, [PERSON] et al. [15] reported lesser postural perturbations in SP and older HA compared with young HA in semi-immersive environment. To date, there exists no clear evidence on the effects of static and dynamic immersive VE on postural control in SP, specifically in ecological environments with irregular visual flows. Immersive VR, compared to semi-immersive or screen projection, improves the immersion and the presence (being in the virtual world) of the patients [16] and should be preferred in investigating the VR effect on postural control and in rehabilitation programs.  
The current study aimed to investigate the effects of dynamic VE on the postural control in SP and HA. Dynamic VE consisted of visual flow modulation including a crowd of walking avatars. We hypothesized that stroke patients would show greater postural perturbations in dynamic VE than HA, given that they are strongly reliant to visual information to maintain postural control, with increased responses in more challenging VE.
# IoT-Enabled Smart Cities: Evolution and Outlook
## 2 IoT-Enabled Smart Cities Landscape
### Amsterdam  
Amsterdam is taking a bottom-up approach to developing a smart city. A public-private partnership with more than 600 partner organizations has been set up. The idea is that rather than being technology-centred or city government-driven, the citizens and the value that smart city solutions bring to them should be the focus [26]. Some high-level goals have been defined, like _sustainable economic growth_, _efficient use of natural resources_ and _high quality of life_. In general, the smart city approach has a \"think globally, act locally\" angle [27].  
The following describes a selection of projects that are or have been conducted as part of \"Amsterdam Smart City\", with a focus on those that have a relation to IoT technologies [28; 29]  
* **Open Data:** Availability of open data from about 30 city departments, including topographical and address data, land value and ownership information, healthcare data, traffic data and more. In most cases the open data is provided as Excel sheets accessible from a web site, i.e., easily accessible to humans, but not directly linkable and automatically accessible to machines.
* **MyNeighbour App (MijnBuur):** provides a direct connection between neighbours, e.g., for the purpose of alerting about dangers and identifying something that needs to be done. The idea is to strengthen social responsibility and direct interactions between citizens without having to involve the municipality.
* **Wyzer App:** implements the idea of keeping people off the main track, thus reducing congestion and improving their city experience at the same time. With fuzzy navigation, they are directed in the right direction, but not on the main route. The application highlights \"hidden gems\" on the way.
* **Plastic free rivers:** is a pilot for stopping plastic floating on rivers. A tube with holes is placed at the bottom of a river and air is pumped through it. This creates a \"bubble barrier\" that stops floating plastic and guides it to the river banks for collection.
* **Social Glass:** does big data analysis on social media and, on this basis, determines the emotions of the public. This information is cross-referenced with geolocation and other data, which enables establishing patterns and mapping the mood of the city.
* **IoT Living Lab:** An IoT Living Lab has been set up, covering a stretch of more than 3 km with iBeacons using LoRaWan technology. Users can use it to send small data packets to the cloud, which can then be accessed and used for smart city apps.
# Emergence of White Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence
## 2 Fundamental Concepts of TADF
### Types of TADF Emitters  
In 1961, [PERSON] et al. first discovered purely organic TADF in the eosin dye, which is named as E-type delayed fluorescence previously [85]. Then, TADF phenomena in metal-containing material Cu(I)-complex [86] or fullerenes [87] were observed. In 2009, [PERSON] et al. applied TADF materials in OLEDs but the performance is very poor [88]. Only after the breakthrough made by [PERSON] et al. in 2012 [43], TADF-based OLEDs rapidly grow. So far, the highest EQE of green TADF OLEDs can be \(>\)30%, clearly breaking the efficiency limitation of conventional fluorescence OLEDs and is comparable to the rare metal-complex phosphorescence OLEDs [89, 90]. In general, there are two distinct unimolecular mechanisms for TADF: promote and delayed fluorescence. For the promote fluorescence, the emission occurs almost immediately after the excitation with a fast decay from the S\({}_{1}\) to S\({}_{0}\) state (within several nanoseconds). In the case of delayed fluorescence, triplets have to be converted into luminescent singlets for the promote fluorescence process via RISC, resulting in an increased fluorescent lifetime up to several microseconds.  
For TADF emitters, TADF emissions can be observed from fullerenes or metal-organic complexes, such as Cu(I), Ag(I), Au(I) and Sn(IV) Complexes [91, 92, 93]. However, they are usually not efficient for OLEDs. Hence, recent attentions are mostly paid on D-A molecular systems in OLEDs, since D-A molecular systems with pronounced intra/inter-molecular charge transfer character are very suitable to realize small \(\Delta\)E\({}_{\text{ST}}\) through separated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for TADF emission [89]. On one hand, in the intramolecular D-A structure (known as TADF material), a donor and an acceptor are connected by a suitable bridge to form a D-A molecule. On the other hand, the intermolecular D-A structure is formed between electron-donating and electron-accepting molecules via charge transfer under electrical excitation (known as TADF exciplex) [94, 95, 96]. By codoping in one layer or depositing the two kinds of materials sequentially, the exciplex emission can be formed [97, 98, 99]. To achieve efficient TADF exciplex, some requirements are needed: (i) Electron-donating and -accepting molecules should have high T\({}_{1}\), confining the triplet exciplex state to prevent the quenching of the triplet state via the triplet energy back transfer to the donor or acceptor; (ii) shallow HOMO in donor molecules, deep LUMO in acceptor molecules and high photoluminescence efficiency are significant [94]. Generally, both TADF materials and TADF exciplexes can be applied to WOLEDs.
# A Formal Analysis of the Mimblewimble Cryptocurrency Protocol +
## 2 The Mimblewimble Protocol  
Confidential transactions ([PERSON], 1998; [PERSON], 2000) are at the core of the MW protocol. A transaction allows a sender to encrypt the amount of bitcoins by using blinding factors. In a confidential transaction only the two parties involved know the amount of bitcoins being exchanged. However, for anyone observing that transaction it is possible to verify its validity by comparing the number of inputs and outputs; if both are the same, then the transaction will be considered valid. Such procedure ensures that no bitcoins have been created from nothing and is key in preserving the integrity of the system. In MW transactions, the recipient randomly selects a range of blinding factors provided by the sender, which are then used as proof of ownership by the receiver.  
The MW protocol aims at providing the following properties ([PERSON], 2018; [PERSON], 2018):  
* Verification of zero sums without revealing the actual amounts involved in a transaction, which implies confidentiality.
* Authentication of transaction outputs without signing the transaction.
* Good scalability, while preserving security, by generating smaller blocks--or better, reducing the size of old blocks, producing a blockchain whose size does not grow in time as much as, for instance, Bitcoin's.  
The first two properties are achieved by relying on Elliptic Curves Cryptography (ECC) operations and properties. The third one is a consequence of the first two.
# Sleep Apnea Classification Using the Mean Euler-Poincare Characteristic and AI Techniques
## 4 Methodology  
Figure 1 represents the proposed methodology used for classifying sleep apnea. The methodology consists of the following five steps:  
1. Pre-processing: As part of this step, the ECG signals were filtered using random polynomials. This process is referred to as _polynomialization_.
2. Random field transformation: The filtered signal was used to build the NGPRF, collapsing \(c\) number of cycles into a geometric structure.
3. Geometrical property: Each NGPRF was sectioned at several levels, denoted by \(\lambda\), known as excursion sets.
4. Feature extraction: For each excursion set, a value was calculated that represented the difference between the number of connected components and the number of holes, capturing key aspects of the set's geometric structure. This feature is referred to as the _Euler-Poincare characteristic_.
5. Classifier selection: An EKNN model is proposed to classify OSA from the EPC models. The training dataset was used for learning, and the test dataset was used to validate the model. Also, a feedforward multi-layer neural network is proposed for the binary classification.  
Figure 1: Methodology to classify sleep apnea. The first stage involves the data or ECG. The second stage involves pre-processing, where the ECG is cleaned. The third stage involves random field conversion. The fourth stage focuses on geometrical properties, where the excursion set is obtained. The fifth stage is feature extraction. Finally, the last stage involves selecting a classifier model (EKNN, SVM, FNN) to differentiate between an apnea patient and a non-apnea patient.
## 3 Experiments
### Experimental Setup  
According to the theoretical analysis, we need to measure the Revolutions Per Minute (RPM), thrust, torque, and power consumption (current and voltage) to obtain the \(PL\) during the experiments. In addition, a low-speed wind tunnel was applied to simulate the horizontal airflow, and the wind speed was set as 0 m/s, 2.5 m/s, and 4 m/s. The experimental setup is shown in Figure 2.  
As shown in Figure 2, the main measurement components include: (1) Optical tachometer (model: DT-2234C, accuracy: 6 \(\pm\) (0.05% + 1d)) was applied to record the rotation speed; (2) thrust sensor (model: CZL605, accuracy: 0.02% FS) converted the thrust signal into an electrical signal output; (3) torque sensor (model: HLT-131, Accuracy: 0.5% F.S) was fixed on the motor to obtain rotor torque as measured by resistance strain gauge technology. The signal process is shown in Figure 3.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Radius (m)** & **Pitch (m)** & **Twist Angle** & **RPM** & **Mach** & **Reynolds** & **Max** \\
**Number** & **Number** & **Number (10\({}^{5}\))** & **Number** \\ \hline
0.2 & 0.157 & 0 & 1500–2400 & 0.1–0.14 & 0.8–1.2 & 5.5\% \\ \hline \hline \end{tabular}
\end{table}
Table 1: The characteristics of the propeller. RPM: Revolutions Per Minute  
Figure 1: Propeller profile.
# A Review on Nanocomposite Materials for
## 4 Cathode
### Spinel, LiM\({}_{2}\)O\({}_{4}\) (M = Mn, and Mixtures of Co and Ni)
Synthesis of nano or submicron size LiMn\({}_{2}\)O\({}_{4}\) particles and doping (i.e., partially substituting Mn site in LiMn\({}_{2}\)O\({}_{4}\)) LiMn\({}_{2}\)O\({}_{4}\) with transition and nontransition metals were shown to reduce the Mn dissolution upon cycling hence improved the cycle life of LiMn\({}_{2}\)O\({}_{4}\)[89, 90, 91, 92, 93, 94]. LiMn\({}_{2}\)O\({}_{4}\) prepared by the one-pot molten salt method resulted in nano sized (\(\sim\)50 nm) hollow spherical particles which showed improved capacity retention even at high C-rates (i.e., 96% retention at 5C rate) [89]. These nano sized spherical LiMn\({}_{2}\)O\({}_{4}\) particles were also performed well at 50 \({}^{\circ}\)C which was associated with their high crystallinity and the presence of spherical particles [89]. In another study, Ru doped LiMn\({}_{2-x}\)Ru\({}_{x}\)O\({}_{4}\) (x = 0.1 and 0.25) was shown to reduce the capacity fading as compared to undoped sample by mitigating the spinel-to-double-hexagonal transition at 4.5 V, and due to the presence of Ru\({}^{4+}\leftrightarrow\) Ru\({}^{5+}\) redox couple and better electronic conductivity of the Ru doped samples [92]. The other dopants studied for LiMn\({}_{2}\)O\({}_{4}\) were Co, Cr, Al, Ni and Fe [90, 91, 95, 96]. [PERSON] et al. obtained a notable 94% capacity retention at the end of 1000 cycles at 5C rate by the Co doped LiMn\({}_{2}\)O\({}_{4}\) (i.e., Li(Co\({}_{1/6}\)Mn\({}_{11/6}\))O\({}_{4}\)). Most of the aforementioned coatings and dopants are inactive materials, and in practice, these materials lower the overall capacity of the spinel LiMn\({}_{2}\)O\({}_{4}\) and increase the cost of material preparation. An alternative strategy is to mix the LiMn\({}_{2}\)O\({}_{4}\) with a more stable cathode material such as NMC [86].