esa-sceva/satcom-chunk-collection huggingface dataset:
## 3 Multicarrier CDMA Based Modulation Schemes
### McC-DS-CDMA
\begin{table}
\begin{tabular}{c l l} \hline
**Technique** & **Advantages** & **Limitations** \\ \hline \hline \multirow{6}{*}{OFDM and its variants} & 1. Easy implementation using FFT \& IFFT. & 1. Spectral leakage due to large side lobes. \\  & 2. Reconfigurability of parameters. & 2. Large PAPR except in Spread OFDM systems where PAPR is \\  & 3. Cyclic prefix allows simple one-tap channel equalization. & reduced at the cost of increased computational complexity. \\  & 4. Can be extended to a multiple access scheme & 3. Sensitive to frequency offsets. \\ \cline{1-1}  & called OFDMA. & 4. Loss in spectral efficiency due to cyclic prefix and guard bands. \\ \cline{1-1}  & 5. Non contiguous blocks of subcarriers can be used for & 5. FFT does not provide sufficient spectral dynamic range for \\ \cline{1-1}  & transmission in NC-OFDM. & spectrum sensing and hence may not be used for detecting low \\  & 6. NC-OFDM supports subcarrier deactivation without any & power users. \\  & degradation in its error robustness. & 6. Hard to synchronize when the subcarriers are shared among \\  & 7. Interoperability with current wireless standards. & primary and secondary users. \\ \hline \multirow{6}{*}{FBMC and its variants} & 1. No spectral leakage problem and hence there is no & \\  & adjacent carrier interference. & 1. Need for improved filter design. \\ \cline{1-1}  & 2. Better spectral efficiency because of the elimination of & 2. Increased latency. \\ \cline{1-1}  & guard bands and cyclic prefix. & 3. Increased computational complexity (equalizer and filters). \\ \cline{1-1}  & 3. More immune to narrowband interference. & 4. MIMO-FBMC implementation is non-trivial compared to \\ \cline{1-1}  & 4. Filter bank-based spectral analyzer can provide high & MIMO-OFDM implementation. \\ \cline{1-1}  & spectral dynamic range for spectrum sensing. & \\ \hline \multirow{6}{*}{MC-CDMA and its variants} & 1. Reduced PAPR compared to OFDM. & 1. Subcarrier deactivation causes loss of orthogonality among \\ \cline{1-1}  & 2. Increased number of users supported through pseudo- & Walsh-Hadamard spreading codes and hence it causes degradation \\ \cline{1-1}  & orthogonal codes. & 2. Requires synchronization in both time and frequency domains. \\ \cline{1-1}  & 3. Improved BER performance using diversity gain in a & 3. Overcrowding of the spectrum due to spreading of each bit \\ \cline{1-1}  & wireless channel. & 4. Switable for underlay cognitive radio systems where \\ \cline{1-1}  & distributed spectrum sensing is not required. & 4. Increased complexity compared to OFDM. \\ \cline{1-1}  & 5. It can support variable data rate cognitive radio users & 5. Requires multi user detection techniques in the uplink \\ \cline{1-1}  & through variable spreading factor. & transmission, because the code orthogonality among users will be \\ \cline{1-1}  & & distorted in a frequency selective fading channel. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the MCM Schemes for CR Systems: Their Advantages and Limitations. Figure 8: Bit error rate (BER) performance of the MC-DS-CDMA system.
# Organic Crystals for THz Photonics
## 5 Applications of Organic THz Sources
### Future Challenges and Opportunities for Practical Applications  
In the last decade, the rapid development of novel THz sources and detectors has opened additional possibilities of creating innovative imaging and sensing systems, allowing in situ measurements and real-time analysis of different materials. Among these, THz systems based on organic NLO crystals are very interesting due to their high THz-generation efficiencies, the possibility for high THz electric fields and a uniquely ultra-broadband nature. We can expect that the recent advances in the field will encourage new research in various disciplines with these systems. Taking into account also other studies performed by inorganic-based THz systems, we can soon expect some important studies in the field of biological and medical applications [219] because healthy and diseased tissue can be distinguished by THz waves due to the changes in water content, bacteria presence, structural and molecular changes. Therefore, THz spectroscopic and imaging analysis of small and macro biomolecules as well as cells and tissues is definitely one of the upcoming research opportunities for organic-crystals based systems. In addition, environmental applications are also an opportunity for laboratories operating with broadband THz systems such as based on organic NLO crystals. THz waves can penetrate even through rough environmental conditions like aerosol and heavily soot flames [220]. Since THz radiation has the ability to gain vibrational information due to inter- and intra-molecular modes and rotational modes, the obtained information can be valuable for gaseous molecules quantification and identification especially in cases of air pollutants detection and atmospheric monitoring. One should also not forget other fields such as art conservation and archeology [221], where THz technology can play a key role in diagnostics before restoration of  
Figure 17: (**a**) signal processing for particle analysis of THz image determining the voids within a polymer foam [176]. Detection of imperfections (**b**) and internal structures (**c**) by THz imaging [175]. Reprinted from Ref. [176] and Ref. [175] with permission from Elsevier.  
historical paintings and archaeological objects, and wood products industry [222]. Besides solids, which are already well explored in the THz region, more attention could also be given to liquids and aqueous solutions as well as gas spectroscopy.
###### Abstract  
Subsurface fires and smoldering events at landfills can present serious health hazards and threats to the environment. These fires are much more costly and difficult to extinguish than open fires at the landfill surface. The initiation of a subsurface fire may go unnoticed for a long period of time and undetected fires may spread over a large area. Unfortunately, not all landfill operators keep or publish heat elevation data and many landfills are not equipped with a landfill gas extraction system to control subsurface temperatures generated from the chemical reactions within. The timely and cost-effective identification of subsurface fires is an important and pressing issue. In this work, we describe a method for using satellite thermal infrared imagery at a moderate spatial resolution to identify the locations of subsurface fires and monitor their migration within landfills. The focus of this study was the Bridgeton Sanitary Landfill in Bridgeton, MO, USA where a subsurface fire was first identified in 2010 and continues to burn today. Observations from Landsat satellites over the last seventeen years were examined for surface temperature anomalies (or hot spots) that may be associated with subsurface fires. The results showed that the locations of hot spots identified in satellite imagery match the known locations of the subsurface fires. Changes in the hot-spot locations with time, as determined by in situ measurements, correspond to the spreading routes of the subsurface fires. These results indicate that the proposed approach based on satellite observations can be used as a tool for the identification of landfill subsurface fires by landfill owners/operators to monitor landfills and minimize the expenses associated with extinguishing landfill fires.  
Keywords:landfill internal elevated temperature; Landsat image processing; land surface thermal mapping; Bridgeton landfill +
Footnote †: journal: Applied Physics Letters
###### Abstract  
Background:Previous studies suggest that brain atrophy can not only be defined by its morphological extent, but also by the cerebral blood flow (CBF) within a certain area of the brain, including white and gray matter. The aim of this study is to investigate known atrophy patterns in different forms of dementia and to compare segmented brain volumetrics and pulsed arterial spin labeling (pASL) data to explore the correlation between brain maps with atrophy and this non-contrast-enhanced brain-perfusion method. Methods:Our study comprised 17 patients with diagnosed cognitive impairment (five Alzheimer's disease = AD, five frontotemporal dementia = FTD, seven mild cognitive impairment = MCI) and 19 healthy control subjects (CO). All patients and controls underwent 4D-pASL brain-perfusion MR imaging and T1w MPRAGE. The data were assessed regarding relative brain volume on the basis of 286 brain regions, and absolute and relative cerebral blood flow (CBF/rCBF) were derived from pASL data in the corresponding brain regions. Mini-Mental State Examination (MMSE) was performed to assess cognitive functions. Results:FTD patients demonstrated significant brain atrophy in 43 brain regions compared to CO. Patients with MCI showed significant brain atrophy in 18 brain regions compared to CO, whereas AD patients only showed six brain regions with significant brain atrophy compared to CO. There was good correlation of brain atrophy and pASL perfusion data in five brain regions of patients with diagnosed FTD, especially in the superior temporal gyrus (r = 0.900, \(p\) = 0.037), the inferior frontal white matter (pars orbitals; r = 0.968, \(p\) = 0.007) and the thalami (r = 0.810, \(p\) = 0.015). Patients with MCI demonstrated a correlation in one brain region (left inferior fronto-occipital fasciculus; r = 0.786, \(p\) = 0.036), whereas patients with diagnosed AD revealed no correlation. Conclusions:pASL can detect affected brain regions in cognitive impairment and corresponds with brain atrophy, especially for patients suffering from FTD and MCI. However, there was no correlation of perfusion alterations and brain atrophy in AD. pASL perfusion might thus represent a promising tool for noninvasive brain-perfusion evaluation in specific dementia subtypes as a complimentary imaging-based bio marker in addition to brain volumetry.  
dementia; Alzheimer's disease; frontotemporal dementia; mild cognitive impairment; brain volumetry; pulsed arterial spin labeling
###### Abstract  
Artificial intelligence (AI) agents are increasingly shaping vital sectors of society, including healthcare, education, supply chains, and finance. As their influence grows, AI alignment research plays a pivotal role in ensuring these systems are trustworthy, transparent, and aligned with human values. Leveraging blockchain technology, proven over the past decade in enabling transparent, tamper-resistant distributed systems, offers significant potential to strengthen AI alignment. However, despite its potential, the current AI alignment literature has yet to systematically explore the effectiveness of blockchain in facilitating secure and ethical behavior in AI agents. While existing systematic literature reviews (SLRs) in AI alignment address various aspects of AI safety and AI alignment, this SLR specifically examines the gap at the intersection of AI alignment, blockchain, and ethics. To address this gap, this SLR explores how blockchain technology can overcome the limitations of existing AI alignment approaches. We searched for studies containing keywords from AI, blockchain, and ethics domains in the Scopus database, identifying 7110 initial records on 28 May 2024. We excluded studies which did not answer our research questions and did not discuss the thematic intersection between AI, blockchain, and ethics to a sufficient extent. The quality of the selected studies was assessed on the basis of their methodology, clarity, completeness, and transparency, resulting in a final number of 46 included studies, the majority of which were journal articles. Results were synthesized through quantitative topic analysis and qualitative analysis to identify key themes and patterns. The contributions of this paper include the following: (i) presentation of the results of an SLR conducted to identify, extract, evaluate, and synthesize studies on the symbiosis of AI alignment, blockchain, and ethics; (ii) summary and categorization of the existing benefits and challenges in incorporating blockchain for AI alignment within the context of ethics; (iii) development of a framework that will facilitate new research activities; and (iv) establishment of the state of evidence with in-depth assessment. The proposed blockchain-based AI alignment framework in this study demonstrates that integrating blockchain with AI alignment can substantially enhance robustness, promote public trust, and facilitate ethical compliance in AI systems.  
**Keywords:** AI alignment; artificial intelligence; blockchain; ethical technology; systematic literature review
# An Established Theory of Digital Twin Model for Tunnel Construction Safety Assessment
## 3 Construction Safety Assessment Framework Based on DT  
Combined with the application of DT framework in other fields, a construction safety assessment framework is proposed [21]. This framework based on DT comprises three parts: an entity layer, digital layer, and function layer. The entity layer includes physical construction entities and sensor devices. The information, including man-machine, material, method, and environment are obtained by three-dimensional scanners and various sensor acquisition equipment. All the collected information is stored in the physical construction entities and can be synchronously mapped in the virtual construction model of the digital floor in real time. The digital layer is the core of the framework. The digital layer includes not only the virtual construction model that integrates all kinds of information data in the construction process but also the machine learning algorithm model. The machine learning algorithm model can be used to analyze the collected data and the simulation data obtained from the simulation of the virtual building model. The digital layer is a multi-dimensional model including a geometry model, physics model, and knowledge model. The functional layer can realize safety assessment and prediction based on the digital layer and the entity layer. To sum up, the entity layer is the foundation and data source for the establishment of the digital layer, the digital layer is the core for the realization of the functional layer, and the functional layer is the means for safety management. The DT construction safety assessment framework is shown in Figure 1.  
Figure 1: Construction safety risk assessment framework.  
In Figure 1, A represents Men, B represents Machines, C represents Materials, D represents Method, E represents Environment, P represents the Physical model, G represents the Geometric models, and K represents the Knowledge model.  
The expression of the digital twin model is as follows:  
\[M_{CDT}=(M_{CP},M_{CV},M_{CN}) \tag{1}\]  
\[M_{CV}=(M_{G},M_{P},M_{K}) \tag{2}\]  
In formula, \(M_{CDT}\) is a digital twin model for construction safety assessment, \(M_{CP}\) is a physical construction site, \(M_{CN}\) is the connection between two parts, \(M_{CV}\) is a virtual construction model, \(M_{G}\) is a geometric model, and \(M_{P}\) is a physical model.
# Label-Guided Data Augmentation for Chinese Named Entity Recognition
###### Abstract  
Chinese named entity recognition (NER) is a fundamental natural language processing (NLP) task that involves identifying and categorizing entities in text. It plays a crucial role in applications such as information extraction, machine translation, and question-answering systems, enhancing the efficiency and accuracy of text processing and language understanding. However, existing methods for Chinese NER face challenges due to the disruption of character-level semantics in traditional data augmentation, leading to misaligned entity labels and reduced prediction accuracy. Moreover, the reliance on English-centric fine-grained annotated datasets and the simplistic concatenation of label semantic embeddings with original samples limits their effectiveness, particularly in addressing class imbalances in low-resource scenarios. To address these issues, we propose a novel Chinese NER model, LGDA, which leverages Label-Guided Data Augmentation to mitigate entity label misalignment and sample distribution imbalances. The LGDA model consists of three key components: a data augmentation module, a label semantic fusion module, and an optimized loss function. It operates in two stages: (1) the enhancement of data with a masked entity generation model and (2) the integration of label annotations to refine entity recognition. By employing twin encoders and a cross-attention mechanism, the model fuses sample and label semantics, while the optimized loss function adapts to class imbalances. Extensive experiments on two public datasets, OntoNotes 4.0 (Chinese) and MSRA, demonstrate the effectiveness of LGDA, achieving significant performance improvements over baseline models. Notably, the data augmentation module proves particularly effective in few-shot settings.  
Aticle  
1  
Chinese named entity recognition; low resource; data augmentation; label semantic fusion
## 2 Materials and Methods
### Parameter Selection
#### 2.2.4 Mission Categorization  
As the UAV industry continues to expand, the authors considered the option to classify UAVs based on their specific applications and functionalities (from now on to be referred to as \"missions\") [18; 27]. The suggested mission categories are comprehensive, ensuring that no UAV is left out of the categorization process, and are listed as follows:  
1. ISTAR (Intelligence, Surveillance, Target Acquisition and Reconnaissance) tactical, for UAVs intended to act as \"eyes in the sky\" for military and civilian use and operational range in line of sight from its command center (LOS);
2. ISTAR strategic, for UAVs that have a similar role to the previous category, but their range is limited only by their performance parameters (not by their telecommunication systems);
3. Attack, for UAVs that carry armament and have ground attack capabilities (UCAV);
4. Target, for UAVs used as practice targets for manned aircraft;
5. Loitering Munitions (LM), for single-use UAVs used as ordnance delivery systems;
6. Utility, for UAVs with missions that cannot be classified into the above.
# A Data Sharing Scheme for GDPR-Compliance Based on Consortium Blockchain
## 5 Analysis and Discussion
### Limitation  
The proposed scheme is only designed and tested for general personal data sharing scenarios, while different data also have different transmission requirements [25]. For example, there are special standards for health care and crime data in GDPR, which is not within the scope of our research.  
Although there are regulatory agencies, the consortium blockchain cannot guarantee complete decentralization, posing a certain threat to user data and records. Additionally, the concept of our scheme is not the definitive solution for GDPR personal data sharing. For example, an attacker can find the decryption key through nefarious means or by discovering the limitations of the encryption technology itself, which is the future research direction of blockchain-based solutions. Moreover, for the other data protection regulation such as Data Security Law of the People's Republic of China (DSL), our scheme is not completely applicable.
# Use of Surface Acoustic Waves for Crack Detection on Railway Track Components--Laboratory Tests
## 4 Discussion  
To analyze the evolution of the wave attenuation due to RCF damage, the observed peak amplitudes (as illustrated in Figure 15 for the pristine state and in Figure 16 for the state after 310,000 wheel passes) were extracted and normalized to the undamaged peak at the sensing location, see Figure 17. It can be seen that the sensors at positions HR (head right) and HBR (head bottom right) showed increasing attenuation, i.e., decreasing signal peak values, with increasing number of load cycles (wheel passes). Position WR (web right) has not been evaluated due to the difficulties in detecting the peak of the extremely distorted wave packet, cf. Figure 16. A linear regression analysis gave slopes of (\(-2.12\)\(\pm\)\(0.17\)) \(\times\)\(10^{-5}\) and (\(-1.87\)\(\pm\)\(0.32\)) \(\times\)\(10^{-5}\) dB/cycle for positions HR and HBR, respectively (estimate \(\pm\) standard deviation for the slope). The associated significance values \(p\) of \(5.92\)\(\times\)\(10^{-6}\) and \(6.38\)\(\times\)\(10^{-4}\) from the \(t\)-statistic corroborate from a statistical point of view the hypothesis of a clear negative correlation between the number of wheel passes and the attenuation of the surface acoustic waves (\(p<<0.05\)).  
Figure 17: Evolution of measured signal amplitudes over cycle number for sender at position HBL and receiver in transmission mode at the positions HR and HBR, with linear regression curves for each position (mean curves solid, \(\pm 2\) standard deviation curves dashed).  
From a physical point of view, this behavior is related to the development of the head checks.  
Figure 18 shows a thin section of the rail gauge corner taken at the end of the RCF experiment after 310,000 load cycles (wheel passes) at the measurement cross-section, displaying a pronounced head check pattern. The average depth of these cracks amounted to 0.62 mm, giving a ratio of \(\mathrm{d}/\lambda_{\mathrm{R}}\approx 0.62\) mm/2.9 mm \(\approx 0.21\). At that time, an attenuation of \(-6.5\) dB can be read from Figure 17, which corresponds to a transmission coefficient of \(\approx\)0.47. This agrees reasonably well with our 2D EFIT simulation results for two cracks, Figure 14b, and with the theoretical results from [PERSON] and [PERSON] [11], cf. the plot of attenuation vs. \(\mathrm{d}/\lambda_{\mathrm{R}}\) in Figure 4e.  
As it is clearly impossible to mount a permanent sensor on the side of the rail head, the technologically relevant sensor position for future condition monitoring applications is the head bottom (position HBR). Compared to position HR, the absolute value of the slope of the trend line is slightly smaller, and the residual standard deviation \(SD\) of the regression analysis is somewhat higher (0.872 vs. 0.506 dB). Still, the \(\pm 2\times SD\) scatter bands corresponding to a statistical coverage of about 95% overlap almost entirely, making position HBR an adequate choice for future applications.