Cementitious composites often crack because of their low tensile strength. The ability of self-healing cementitious composite to automatically repair cracks has attracted widespread attention. Lightweight aggregate (LWA) has a low density and a high porosity which can provide storage space for a healing agent. The healing mechanisms and healing compositions of lightweight self-healing concrete (LWSHC) have been summarized in this research. The workability, compressive strength, crack repairing, and durability of LWSHC performance is also illustrated. A LWA with interconnected pores and a high strength should be integrated into LWSHC to increase the crack closure rate and mechanical properties. Expanded perlite is the most suitable LWA carrier for bioremediation. The chemical healing agents are better than the biological healing agents at present since the biological healing agents have more negative effects. A sodium silicate solution is a good choice as a chemical healing agent. Vacuum conditions, high-temperature processing, and the use of coating technologies on LWAs can improve the healing effect of LWSHC. The addition of fibers also enhance the self-healing ability of LWSHC. Further, the use of numerical simulation supports the healing performance of LWSHC. The goal of this research is to investigate the most appropriate component of LWSHC to ensure a high crack closure rate, strength healing ratio, and great durability while being lightweight. It can then be adopted in high-rise and large-span concrete structures to extend the service life. Cementitious composites are currently widely used. However, due to the low tensile strength of concrete, cracks are inevitable. These cracks come from plastic shrinkage, drying shrinkage, chemical shrinkage, thermal stress, external load, the expansion of ettringite, and the coupling effect of multiple factors, causing significant durability and structural problems. It is difficult to heal the microcracks within concrete using traditional repairing methods. In addition, implementing the real-time monitoring of cracks also imposes a huge burden on construction costs. Self-healing technology has been introduced as a sustainable method for repairing cracks, extending the service life of structural concrete, and reducing maintenance costs. It does not require the real-time manual maintenance of concrete and can repair cracks autonomously . TherefoSelf-healing technology in a cementitious composite is generally divided into the following three categories: (1) The use of auxiliary cementitious materials for repairing by directly adding mineral admixtures, crystalline admixtures, and polymer materials into concrete. (2) The use of carriers with healing agents for self-healing  where thSelf-healing concrete needs pores to carry these healing agents. Lightweight aggregate concrete (LWC) has a high porosity, which can provide storage space for healing agents. A LWA releases the healing agent when the crack propagates to the pores and has the advantage of being lightweight. With a parametric design, it can be used in high-rise modern structures and large-span bridges as a building material . The appThis review summarizes the application of LWAs in the field of self-healing concrete, aiming to elevate the self-healing performance of LWSHC. The self-healing mechanisms and the healing components of LWSHC are analyzed in Previously, the main purpose of using LWC was to reduce the load of the concrete structure and the size of the load-bearing members . Figure Meanwhile, a lot of studies focused on the development of LWSHC using LWAs. It has been proven that using LWAs as carriers for healing agents in self-healing concrete is valid; damaged concrete was repaired with LWAs ,14,15,163 formed by this process is unstable [3 will be better. CaCO3 can fill 0.1 mm-wide cracks, which also indicates that the self-healing system of cement-based materials may be influenced by environmental factors.The self-healing of cementitious materials can be divided into autogenous healing and autonomous healing . Autogenunstable . In the 4·2H2O, calcium sulfoaluminate-based expansion agents, crystalline additives, and auxiliary cementing materials, have significantly improved performance as admixtures when they partially replace cement components [The self-healing properties of cement-based materials are greatly affected by their healing agents. Chemical repairing agents such as calcium carbonate, sodium silicate, CaHPOmponents ,50. TheyWater is one of the indispensable factors affecting self-healing effects . During 2SiO3) can effectively increase the elastic modulus of concrete when encapsulated with different microcapsules [The technology of impregnating LWC has been widely used ,56. Sodicapsules ,31,57. TIt is well known that C-S-H gel, as the main reaction product of Portland cement hydration, determines most of the properties of cement. Once sodium silicate is released from the impregnated LWA, it will react with calcium hydroxide (a product of cement hydration) to form a C-S-H gel, thereby restoring strength. The relevant chemical reaction is as follows :(1)Na2SiSodium silicate as a self-healing agent has a significant effect on restoring strength and improving durability. By using a sodium silicate solution, the impregnation of LWAs can create a self-healing effect in LWSHC. The impregnation of LWA particles with sodium silicate raised the strength recovery by more than five times and reduced capillary water absorption by nearly half .There are many new methods for improving the impregnation effect. The absorption rate was significantly improved under vacuum conditions compared with immersion under atmospheric conditions . Coarse The addition of carbonates to clay-like LWAs increased the content of calcium ions, and the strong chemical gradient between cement and clay promoted the formation of C-S-H gels and other white precipitation products ,60. In tWang et al.  used liqWhen sodium carbonate is retained as a healing material in the interior of the LWA, it is necessary to avoid excessive consumption of sodium carbonate by early hydration. During the stirring and curing process, there will be a certain amount of exudation, which contained about 50% sodium carbonate after 7 days . Yang etWang et al.  comparedThe research on self-healing concrete is often carried out by encapsulating bacteria in carriers. The most commonly used carriers are a polymer material, LWA, cementitious material, special minerals, nanomaterial, and waste-derived biomass . The carDifferent kinds of biological healing agents have different detailed healing mechanisms. A large number of recent studies have focused on the self-healing of microorganisms by using microorganisms to induce biomineralization and protection of microorganisms with LWAs. Biomineralization involves a series of biochemical reactions in which microorganisms initiate mineral precipitation. Microorganism-induced calcium carbonate precipitation (MICP) is an example of the biomineralization process, which is widely used in self-healing concrete ,69,70,71The advantages and limitations of various carriers were discussed in previous research . The bac3, and a porosity of 24.97%. The use of a LWA as a carrier can effectively protect Pasteurella to induce calcium carbonate precipitation. In addition, diatomaceous earth is resistant to high pH environments and can protect bacteria [LWAs prepared from clay and other raw materials were widely adopted as bacterial carriers ,77,78,79bacteria . Bundur bacteria  studied bacteria , porous bacteria , while abacteria . Further7 cells per milliliter on calcium carbonate precipitation. Three different fiber percentages  were adopted. Experimental results showed that adding bacteria and fibers simultaneously was effective and improved the compressive strength, tensile strength, and flexural strength. It also reduced the water absorption and permeability of the concrete in the sample. A comparison of bacterial samples showed that Bacillus Licheniformis and Bacillus Megateterium were superior to Sporosarcina Pasteurii and Sporosarcina Ureae in inducing calcium carbonate precipitation in LWSHC. In addition, microscopic analysis was carried out on the formed products. Calcium carbonate was formed in the cracks. The crystalline phase of calcite was characterized, indicating that calcium carbonate often existed in the form of calcite and vaterite. The results agreed with the study of different microbial self-healing technologies by Wasim et al. [m et al. . The nutm et al.  studied m et al. .In the preparation of LWSHC, the addition of minerals and treated LWAs influences the performance of the concrete. The workability of fresh concrete decreased due to the aggregate absorbing a large amount of mixing water . The mea2CO3 solution, which was consistent with the previous study [32−, Na+, and OH−. OH− first destroys the surface of some particles of the cementitious material and generates a large amount of Ca2+. CO32− and Ca2+ then generate calcium carbonate. It coats the surface of the unhydrated cementitious material, which raises the fluidity of the slurry. Therefore, in the case of LWAs and other substances loaded or wetted, the fluidity of concrete will not be reduced due to its higher porosity and more mixing water absorption. Increased fluidity may be caused by the outflow of solutions such as sodium carbonate that increase particle surface activity or inhibit hydration. Hence, the coating is needed when using LWAs and impregnation to avoid the influence on the workability of LWSHC. Upon crack formation, the coating is broken. The inner healing agents are released from the LWA particles and produce healing products, which then plug the cracks [When an external healing agent is applied, it may lead to changes in the properties of concrete, such as a change in workability. This change affects cement hydration, pore size, and porosity . Kim et us study . As a sue cracks . In ordee cracks .Different types of LWAs have different water absorption, which influences workability too. The water absorption of a LWA is affected not only by the physical and chemical properties of the material but also by the internal pore characteristics of the material to a certain extent. The expanded perlite and gravelly ceramsites have rough surfaces and micropores. Through the microscopic morphology analysis previously studied , it was 2 consumption came from the bacteria. Hence, the two-component healing agents can repair cracks effectively. Zhan et al. [With the development of self-healing technology, the width of healed cracks has risen. Different healing compositions of LWSHC have different crack closure rates. The crack closure rate is calculated by the reduced crack size after healing compared with the crack size before healing ,17,20. Tn et al. . After 2n et al. . If the n et al. . This con et al. ,89, excen et al. . The hean et al. . This isn et al. ,92. Howen et al. ,94 can in et al. . This isn et al. . In the Different types of LWAs have different inner structures which influence the crack closure rate of LWSHC. The interior of the expanded perlite is loose and porous and pores are interconnected . The ins3S or the production of hydration products. Organic substances could inhibit hydration, as they interfered with the contact of water and cement by combining with mineral particles. Further, the incorporation of ureolytic bacteria and nutrients in the mixing process could influence the change of phases and the ratio of hydration products, due to the metabolic activities of the ureolytic bacteria and the chemical degradation of nutrients during the hydration and hardening period. This will significantly lower the strength on all tested days, due to the low hydration rate from incorporating a large dosage of nutrients [3 content and compressive strength occurred within the cement-paste samples when vegetative S. pasteurii cells were inoculated into cement paste with their nutrient medium. Thus, the strength increase in the bacterial mortars is attributed to the biomineralization phenomena overcoming the inherent strength reduction caused by replacing river sand with weaker LWAs [Many researchers rely on mechanical properties to verify the efficiency of self-healing see . Table 4utrients . The bioutrients ,18,19. Mutrients . Similarker LWAs . Such op2/σ1, where σ1 is the maximum stress for the virgin specimen and σ2 is the maximum stress for the healed specimen [The strength healing rate is calculated according to η = σspecimen . Considespecimen . The coaspecimen .The failure of concrete is due to the propagation of cracks. In ordinary concrete with high-strength stone as the aggregate, the bearing capacity of the stone itself is high; the concentrated stress generated by crack propagation is not enough to damage the aggregate and the cracks often develop along the direction of the interface area. The strength of concrete mainly depends on the interface strength between the cement paste and aggregate. However, the strength of LWAs is lower than the strength of cement paste, which is the weak part. In this case, cracks will continue to develop through the LWA, and the LWA will be damaged. Therefore, the strength of LWSHC mainly depends on the strength of the LWA itself. The strength of LWSHC is affected by the aggregate strength; generally, the higher the aggregate strength is, the higher the corresponding concrete strength is. Clinoptilolite zeolite particles and expanded vermiculite have a high strength, which can increase the mechanical properties of LWSHC from 2CO3 solution and lightweight clay aggregate, the self-healing admixtures system had a 16–20% reduction compared with that of the control group, considering the chloride diffusion coefficient [2CO3 solution and porous ceramsite [2 solution. With increasing chloride ions, the depth of water penetration using bacteria in the mixed water of ordinary concrete and LWC was reduced by approximately 35.6% compared to the control sample without bacteria immersed in the water. Therefore, it is also necessary to consider the environmental factor when using microbial self-healing in a degraded environment where urea exists to avoid deterioration. This was also verified by Nodehi et al. [LWSHC can have great durability due to its self-healing effect. With the hydration of cement particles and the evaporation of surface water, the humidity inside the concrete decreases continuously. When the relative humidity inside the cement paste is lower than that of the LWA, the water in the LWA migrates outward, which maintains a high relative humidity inside the cement paste for a certain time. The cement material inside the LWC is fully hydrated, and the aggregate plays an internal curing role, providing hydration water for cement particles during the curing period. Meanwhile, the microcracks are self-healed by healing agents, and a compact matrix enhances the durability of LWSHC. Compared with continuous water immersion, the LWSHC containing microorganisms has a better crack-sealing performance. When using bacillus subtilis and diatomite pellets , the watfficient . The calfficient ; hence, eramsite . The chleramsite . Howeveri et al.  who analThere are many methods for durability testing, including the water permeability test, chloride penetration test, carbonization test, steel corrosion test, etc. However, some tests of durability are not available, such as the durability test of self-healing concrete under freeze-thaw cycles. There are some limitations under these conditions . AlthougThe theoretical methods such as the finite element method and machine learning method have good ability in prediction and analysis, while the theoretical simulation of LWSHC is still lacking. Zemskov et al.  establisThe research on LWSHC has attracted much attention in recent years. This review has systematically revealed the healing mechanisms, compositions, and performances of LWSHC. The following conclusions are drawn.Some remarkable achievements have been made in the strength recovery and crack repair of LWSHC. The absorption rate is significantly improved under vacuum conditions. Using a coating technology on LWAs can retain more healing agents in the LWA, which increases the healing effect of LWSHC. Additionally, a low pH matrix can promote the healing effect. Some special treatments, such as high temperatures, on the LWAs are good for improving their properties. Adding healing agents and fibers simultaneously elevates mechanical properties. Using a nutrient solution instead of concrete mixing water is a method of introducing required nutrients when biological healing agents are adopted. Compared to previous research for perlite, vermiculite, zeolite, and silica supports, expanded perlite is the most suitable carrier for bioremediation. Bacillus Licheniformis, Bacillus Megateterium, and Bacillus alcalophilus are superior in inducing calcium carbonate precipitation in LWSHC. The raw materials of the healing agent and the outflow of nutrients lead to an increase in the fluidity of the concrete. The healing agent should therefore be chosen considering the configuration of cracks since the crack-closing ability of different healing agents is different, i.e, as a chemical healing agent, sodium silicate has a higher healing rate than sodium carbonate. Among healing methods, the microbial self-healing method can fill larger cracks, however, the healing is unstable. The biological self-healing system may have more negative aspects than the chemical self-healing system; hence, the chemical healing agents may be better than the biological healing agents in LWSHC at present. Additionally, the non-destructive detection of crack healing is more efficient and convenient for testing LWSHC. The reduction in durability has been partially solved in LWSHC, while the influence of the environment is inescapable. Therefore, theoretical prediction in the field of LWSHC is an emerging research hotspot. The use of LWSHC in construction is a fast and effective method to save materials and reduce costs in material design, thus the future research direction is to promote the application of LWAs in self-healing concrete.


Indoor signals are susceptible to NLOS propagation effects, multipath effects, and a dynamic environment, posing more challenges than outdoor signals despite decades of advancements in location services. In modern Wi-Fi networks that support both MIMO and OFDM techniques, Channel State Information (CSI) is now used as an enhanced wireless channel metric replacing the Wi-Fi received signal strength (RSS) fingerprinting method. The indoor multipath effects, however, make it less robust and stable. This study proposes a positive knowledge transfer-based heterogeneous data fusion method for representing the different scenarios of temporal variations in CSI-based fingerprint measurements generated in a complex indoor environment targeting indoor parking lots, while reducing the training calibration overhead. Extensive experiments were performed with real-world scenarios of the indoor parking phenomenon. Results revealed that the proposed algorithm proved to be an efficient algorithm with consistent positioning accuracy across all potential variations. In addition to improving indoor parking location accuracy, the proposed algorithm provides computationally robust and efficient location estimates in dynamic environments. A Cramer-Rao lower bound (CRLB) analysis was also used to estimate the lower bound of the parking lot location error variance under various temporal variation scenarios. Based on analytical derivations, we prove that the lower bound of the variance of the location estimator depends on the (i) angle of the base stations, (ii) number of base stations, (iii) distance between the target and the base station,  The rapid development of indoor positioning systems (IPS) has been fueled by the emergence of both fifth- and sixth-generation communication systems 5G and 6G) and the internet of things (IoT), as well as the growing commercial interest in location-based services (LBSs). Due to the incredible development of mobile applications, LBSs have gained significant importance in both industrial and commercial applications such as vehicle indoor parking lots , indoor G and 6G To achieve the desired goal of an IPS, two major predictors must be considered: (i) the type of signal features used to establish the fingerprint, such as received signal strength (RSS) , CSI 1313, time However, due to the additional infrastructure required for their implementation, most indoor positioning applications , radio frequency identification (RFID), and others) have extra construction costs. Unlike other wireless IPS, which have been criticized for their limited scalability due to the demand for additional hardware devices, RSS-based Wi-Fi fingerprinting is gaining popularity due to its low computational complexity, cost-effectiveness, and ease of implementation and compatibility with existing network infrastructure ,34,35. AHowever, as Wi-Fi network technology has advanced, the Channel State Information (CSI) signal feature can now be extracted from commercial Wi-Fi devices using network interface cards (NICs) that can provide multi-channel subcarrier phase and amplitude information, allowing to better characterize the signal propagation model with the help of multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) technologies. In comparison to RSS signal features, the CSI-signal feature is distinguished by its ability to depict: (a) fine-grained channel features, (b) higher dimension features, (c) the diversified physical layer of both phase and amplitude information, and (d) more robust and temporal stable features. In line with this, a comparative analysis of CSI and RSSI was performed , and theNonetheless, due to the complex indoor environment of multipath effects, the CSI-based IPS performance still faces challenges in severe dynamic range and fluctuations among high-dimensional channels . Various(1)We proposed a data fusion method to represent temporal signal variations by constructing new feature vector spaces based on the most significant predictors and enabling heterogeneous knowledge transfer with the goal of reducing calibration overhead in an indoor parking system.(2)To efficiently detect parking lots, we used the principal component analysis technique to reduce data noise caused by multipath effects, as the channel state information amplitude or fingerprints received from multiple base stations could be mis-matched with the actual target’s fingerprint patterns. In other words, multiple signals arriving at the receiver end from different paths may cause fingerprint duplication and degrades the overall performance of the system. This refers to the possibility of a high-dimensional curse for CSI-based fingerprinting in indoor parking scenarios.(3)The Cramer Rao lower bound (CRLB) analysis was used to estimate the lower bound variance for the estimator of data fusion methods of a vehicle’s indoor parking lot or to measure the unbiasedness of the location estimator for an indoor parking system-based channel state information fingerprinting.(4)We conducted a comparative analysis of the proposed algorithms in terms of the performance of indoor positioning estimation-based channel state information fingerprinting in comparison with the most popular algorithms in the field of machine learning using predictive modeling as a baseline.The primary goal of this article is to improve CSI-based fingerprint indoor positioning by using data fusion methods to represent temporal signal variations of a location estimator in indoor parking lots. Furthermore, the heterogeneous transfer learning method (HetTL) was used in conjunction with principal component analysis (PCA) to reduce time complexity and ensure cost effectiveness by avoiding unnecessarily high costs associated with extra Wi-Fi access points (Wi-Fi APs) deployment  from the model. This study, on the other hand, uses Cramer-Rao lower bound analysis to estimate the lower bound variance for the estimator data fusion method of CSI-based fingerprint indoor positioning. In this study, the contributions are fourfold:The rest of this study is organized as follows: related works are presented in This section provides a brief overview of fingerprint-based methods and data fusion techniques used to address the indoor positioning problem (IPP), system modeling of IP-based CSI fingerprinting, performance evaluation metrics for positioning estimation, and challenges that limit the applications of various signal features used in IPP. Since vehicle positioning is essential in applications such as indoor parking lots, indoor navigation, driver assistance and autonomous driving, accurate information about mobility patterns and vehicle trajectories are essential to improve positioning performance. Generally, three positioning algorithms  are applVarious signal features were proposed and investigated to address IPP, mainly: time of arrival (TOA/TDOA) , angle oIn contrast, the wireless fidelity signal (Wi-Fi: 802.11) has received significant acceptance for IPS both in academia and industry communities  mainly fThe signal feature of the channel state information, however, has emerged as an enhanced wireless channel metric with significant data throughput ,43 to reTowards this end, several CSI-based object detection schemes in WLAN systems have been studied ,71,72 and is the estimated distance (in meters (m)) between the transmitter and receiver in an indoor environment setting, Channel state information (CSI) has emerged as an enhanced wireless channel metric (significantly enhanced data throughput) ,75 in pl In MIMO  systems ream. In  proposedSimilarly, the individual path characteristics in a wireless propagation channel are modeled as a temporal linear filter, known as the channel impulse response (CIR) . Given treported  in the cThus, the CSI amplitude is a measure of the power of the Wi-Fi link between the transceiver. Using Equation (10), from Euler’s property, And the channel state information amplitude for each subcarrier isIn the above Equation (9), the total number of paths are hadowing , a0 can nsmitted , which cThis section presents an overview of the framework and problem formulation of CSI-based fingerprint IPS with emphasis on: (a) data fusion techniques, (b) process of database construction-based CSI-fingerprinting for both instances of training and testing datasets, (c) the system architecture of CSI-based fingerprinting for IPS, (d) approaches of knowledge transfer learning and the CRLB analysis applied to IPS.It has been noted in various types of research that RSS fingerprinting based on positioning functionality has a fundamental problem in terms of accuracy and robustness in IPS and that both temporal and spatial signal fluctuations cause spontaneous or inestimable localization errors, regardless of the affordability and ease of implementation. A survey conducted in  stated tWe have noted that positioning characteristics-based RSS fingerprinting still has a fundamental problem in accuracy and robustness in IPS, and both temporal and spatial signal fluctuations cause spontaneous or inestimable localization errors. It has been shown that the CSI at each subcarrier in OFDM can be used to characterize the target’s behaviors through the two important features of amplitude and phase fluctuations of the targets in a frequency-selective fading channel. Additionally, due to the MIMO technology integrated into CSI, high-dimensional features are possibly produced in WLAN systems and can be considered as opportunity to improve the positioning performance, although computational complexity is the main trade-off needed to be addressed. Of course, the high dimensions of features by its own may not be a positive predictor for the localization process; thus, identifying the most significant predictors is a must otherwise some redundant features may degrade or inflate  the system modeling. In line with this, a comparative analysis between CSI and RSSI was conducted and the study revealed that the physical characteristics of CSI can significantly reduce the problem of RSSI, such that (a) multipath effect propagation can be better handled (b) strong stability is provided, especially in a static environment, and relatively stable to the dynamics of the indoor environment (c) reduce radio interference of carrier frequency signals. In this study, as depicted in The fingerprint database is described explicitly as: With the advancement of Wi-Fi network technology, the CSI signal feature can now be extracted from commercial Wi-Fi devices using network interface cards (NICs) that can provide multi-channel subcarrier phase and amplitude information, allowing to better characterize the signal propagation model with the help of MIMO-OFDM technologies. Thus, CSI can present different subcarrier amplitude and phase characteristics for different propagation environments and the overall structure characteristics of CSI remain relatively stable compared with the RSS signal feature, though appropriate signal processing technology (SPT) is required. Nevertheless, the CSI-based IPS still has a challenging problem in severe dynamic range and fluctuations among high-dimensional channels mainly due to indoor multipath effects and temporal variations. This could be justified because the spread of the CSI in both the amplitude and phase values measured at a particular reference point is so dynamic in nature. Additionally, the inherent heterogeneity of the environment resulting from multipath effects and time differences of when measurements were taken have a significant effect on the distribution of the CSI values received at each reference point. Thus, there is no guarantee that the signal variations be represented by a single value for a target’s position even with the same device. To address these issues, we proposed a data fusion technique for reducing channel fluctuations and improving target positioning-based heterogeneous knowledge transfer by creating a new feature vector based on the most significant predictors. Furthermore, we used the principal component analysis (PCA) technique to reduce noise and irrelevant or insignificant features, because the CSI amplitude or fingerprints received from multiple base station antennas could be mismatched with the actual target’s fingerprint patterns due to fingerprint duplication. Moreover, with the use of the PCA, we addressed the high-dimensional curse for the CSI-based fingerprint method. The data preprocessing of PCA was used to reduce computational complexity and ensure cost effectiveness by avoiding unnecessarily high costs associated with extra Wi-Fi access points (Wi-Fi APs) deployment  from the model.Recall that the The variances of the measurements Equivalently, we can write the above equation in (19) as: (a)Standardize each CSI measurement as: (b)Calculate the covariance matrix of the CSI sample measurements: (c)Obtain Eigen value decomposition of covariance matrix(d)Obtain projection matrixTo this end, the PCA algorithm comprises four major steps:Algorithm 1 is a pseudo code used to derive the new fingerprints of features-based CSI using both data fusion techniques and principal component analysis.Algorithm 1 Construction of the new dimension of CSI fingerprint feature vectors-based data fusion and PCAInput: Multiple Sources Fingerprints 1. Input: CSI testing dataset2. Output: Refined CSI Fingerprint 3. for4. for5.    for6.     7.      for8.     fuse the data as 9.             Standardize each CSI measurement using (21)10.           Calculate the covariance matrix of the CSI measurements as in (19) or (22) 11.           Compute the eigenvectors and eigenvalues of the new vector feature 12.          Create feature vectors 13.          Obtain projection matrix: end for14.     end for15.    end for16.   end for17. 18. return In this study, the CSI fingerprints were first collected from each antenna of a base station (BS) located at four different locations  within the defined reference points (RPs) and partitioned into two parts as t training set and testing set for different purposes. Along with this, we have noted that there are two major challenges that need to be considered in heterogenous transfer learning: (i) the CSI amplitude and phase received at a reference point from multiple antennas of a base station assumed to be independent such that the RF signals transmitted from different BSs are transmitted independently and do not interfere with each other. In practice, however, the CSI amplitude of a grid point can be duplicated, possibly by multiple BSs, and this causes the matching patterns to interfere with the actual target’s fingerprint due to random noise or indoor multipath effect scenarios and ultimately have a negative effect on positioning performance. (ii) Although channel state information could help us provide more feature spaces, the higher dimensional curse must be handled. Thus, we proposed the data fusion technique to minimize the temporal CSI amplitude fluctuations by considering different measurements over several days that could have different patterns due to the inherent environmental heterogeneity and multipath effects. Additionally, potentially duplicated CSI fingerprints and the dependence of CSI measurements on different BS antennas were managed through principal component analysis.Thus, the objective function was minimized over the new feature spaces such that the most significant features, independent features, and related source knowledge could be leveraged to the target domain. The Minkowski is a generalized distance metric between two vectors and given as:We have used the Lagrangian multiplier method to solve the constrained optimization problem of Equation (24), and we assumed the location estimate at the By adding up the first And substituting Equation (27) into Equation (26) gives the estimated transfer coefficients as:The pseudo code for positioning using the heterogenous knowledge transfer-based data fusion technique is provided in Algorithm 2.Algorithm 2 The proposed heterogenous knowledge transfer-based CSI-fingerprint indoor positioning systemInput: Refined Sources Fingerprint 1. Input: Refined CSI testing dataset2. Output: Fused refined CSI fingerprints 3. for4. for5.  for6.   for8. repeat9.   Step 1:7.  11.   Step 2:10.     Fuse the CSI amplitude fingerprints from all the sources with temporal variations as in Algorithm 113.   Step 3:12.      Obtain projection matrix: 14.      Compute end for15.      end for16.     end for17.    end for18. 19. Train a classifier from 20. Estimate target’s location return 21. This section presents the metrics applied to evaluate the positioning performance, and we compared the performance of the proposed algorithms against different machine learning algorithms taken as baselines and validated through extensive real-life experimentations. The dataset were collected over several days with potential temporal signal fluctuations based on CSI-fingerprinting of the real measurements. In this study, the root mean square error was used to evaluate the positioning performance of the proposed algorithm, and it is defined as:This section presents the analysis of CRLB for location estimation-based channel state information-measurements used to evaluate the performance of indoor positioning system and estimates a lower limit for the variance of any unbiased estimator of an unknown parameter. Additionally, the CRLB is suitable for stationary gaussian parameter estimation ,87,88,89In line with this, the distributions of the CSI values measured at a particular reference point are so dynamic in nature due to the inherent heterogeneity of the environment, and time differences in measurements being taken have a significant effect on the distribution of the CSI values received at each RP. As a result, there is no guarantee that the signal fluctuations will be represented by a single value for a specific position even with the same device. The CRLB used the CSI real measurements to analyze the lower bound of the location estimation error, and it is significantly important to characterize the properties of this lower bound to evaluate the impact of different parameters on the accuracy of a target’s localization. Moreover, the CRLB analysis can also provide important system design suggestions by revealing error trends with the indoor localization system deployment. To estimate the lower bound of the position error variance, first assume that the position of the The diagonal elements of (32) denote the mean squared errors, and the off-diagonal elements are the covariances between different parameters. Additionally, consider that And, the By definition, the CRLB of the unbiased estimator One can describe the CRLB as just the inverse of FIM and rewrite Equation (19) as:Thus, the variance of the unbiased estimator for Now, from the above Equations (33) and (37), one can observe the relationship between the variance of the unbiased estimator One can observe from Equation (38), the MSE of s is the number of CSI source feature vectors, In this study, the multiple measurements of CSI-based fingerprints collected on different days were used as different sources to estimate the lower bound of the error variance of the target’s location using the application of CRLB. We considered that the CSI amplitudes collected on various days follow a multivariate normal distribution. This is consistent with the assumption that different signal features including the well-known features such as RSS, CSI, TOA, and AOA follow a normal distribution ,90. RecaThus, one can denote ed as in :(45)CRLBScenario 1: Consider eight temporal variations of measurements of month 1 as different sources due to their distribution follow different patterns: Thus, we consider eight different sources for evaluating the positioning performanceAnd,Scenario 2: Consider five temporal variations of measurements of month 2 as different sources due to their distribution follow different patterns: Thus, we consider five different sources for evaluating the positioning performanceAnd,Scenario 3: Consider the aggregate temporal variations of measurements of various sources of both months into two different sources and calculate the CRLB of those fused different sources for evaluating the positioning performance purpose:AndNow, to estimate the lower bound of the position error variance, first consider that the position of the tion. In  have proSimilarly, Thus, the probability density function of the Thus, one can rewrite Equation (57) for the CRLB based CSI-fingerprint measurements in relation to the angle as follows:The CRLB of the fused data from different sources can be calculated based on the concept given in the above Equation (52), and the CRLB or lower bound error of the location for the two fused sources of CSI-based fingerprint measurements collected in two separate months of several days can be given as:In conclusion, the above derivation revealed that the lower bound of the variance of the location estimator depends on (a) the angle of the base stations, (b) number of base stations, (c) distance between the target and base station, This section presents a number of real-world experiments that were carried out on various occasions, or on a daily basis to measure the temporal signal fluctuations using the fingerprints of the channel state information (interested in variations among the measurement days), and we assess our proposed algorithms as they were applied to these CSI real measurements of various distributions. First, experimental conditions, datasets, and an analysis of the algorithms’ overall performance were presented.(1)Datasets2, which contained 225 and 110 reference points (RPs), respectively, all of which were evenly dispersed (≥0.5 m) from each other as shown in The experiments were carried out at Huawei on an area of 75 mThe distribution of the principal components and their corresponding reference points of both training and testing instances of the fused CSI-based fingerprint of real measurements collected over several days in October 2020 is depicted in This section presents extensive real-life experiments conducted on various occasions or daily to measure the temporal signal fluctuations observed for indoor parking lots-based CSI fingerprint measurements. We compared our proposed algorithms applied to these CSI-based real measurements of different distributions to popular machine learning algorithms used in prediction tasks. In contrast, results show that both decision tree (DT) and random forest (RF) classifiers performed better in separate datasets of both months . HoweverOn the other side, Moreover, the following This section compares the computational complexity of our proposed algorithm, which was applied to the fused CSI-based real measurements of different distributions collected in separate days of two months, to popular machine learning algorithms used in prediction tasks to represent the temporal signal variations observed for indoor parking lots. The algorithms in this study were executing on a laptop computer equipped with an AMD Ryzen 3 3200U CPU (2.60 GHz) and 16 GB of RAM. The complexity of an algorithm is primarily determined by two scenarios of complexity: time and space. We used both the functional analysis of Big O and average elapsed execution testing time to compare the time complexity of the algorithms. The Big O functional analysis of time complexity provided us with the overall worst-case computational cost analysis, and all of the algorithms we used have an average of worst-case time complexity of 2 constituting 225 and 110 reference points (RPs) in total. The data were collected over separate dates on September and October 2020, respectively. Each RP was equidistant (>=0.5 m) from the next reference point. The number of measurements considered from each antenna of a base station was unequal in size. Similarly, the number of labels was not totally balanced. Thus, our analysis used the feature scaling technique to avoid possible discrepancies created due to the imbalance of data. To this end, we proposed a heterogeneous data fusion method based on positive knowledge transfer to represent the different temporal variation scenarios of CSI-based fingerprint measurements generated in a complex indoor environment targeting indoor parking lots, while reducing training calibration overheads. Extensive experiments were carried out with real-world scenarios of the indoor parking phenomenon. Experimental results revealed that the proposed algorithm proved to be an efficient algorithm with consistent positioning accuracy across all potential variations. The proposed algorithm not only improves indoor parking location accuracy, but it is also a computationally robust and efficient estimator for a dynamic indoor environment unlike the decision tree and random forest algorithms, which are significantly affected by the temporal signal fluctuations.In this study, we considered various scenarios of temporal variations that generated the CSI-based fingerprinting measurements applied to indoor environment settings aimed at vehicles’ indoor parking lots. Along with this, extensive real-life experiments were conducted at Huawei company in a different time with an area of 75 mThe results also show that the training computational complexity for all algorithms was much higher than the overall testing time, and that the proposed algorithm required higher computational complexity for the training and testing phases, followed by support vector machine and neural network algorithms. However, an interesting finding was observed for the vehicle’s indoor parking lots of CSI-based fingerprints of the fused data-based PCA method. The indoor parking positioning performance significantly improved after the transfer learning method was applied to both the fused data and separate datasets. Nevertheless, the positioning performance for the separate datasets of both months was significantly reduced after the principal component method was used to minimize computational cost. This revealed that the use of the PCA method, or considering 95% of the total variations of the model, could not represent the entire dynamics of the environment, but knowledge transfer could be leveraged from the training instances to enhance target positioning. In contrast, the positioning performance for the fused data of month 2, October 2020 maintained equal performance as that achieved in separate dataset, while significant improvement was also observed in computational cost. Moreover, heterogeneous knowledge transfer of the fused data-based PCA not only improved indoor parking positioning performance, but was also very efficient in terms of computational cost as depicted in The CRLB analysis technique was also applied to estimate the lower bound of the position error variance aimed at indoor parking lots. Similarly, different scenarios of temporal variations were also considered for CRLB analysis of CSI-based fingerprint measurements applied to indoor environment settings, such as vehicles’ indoor parking lots. Thus, the analytical derivation of the CRLB analysis revealed that the lower bound of the variance of the location estimator depends on (a) the angle of the base stations, (b) the number of base stations, (c) the distance between the target and base station, (1)Even though we limited our scope to CSI-amplitude information based on our objective, the phase information of CSI can also be used as fingerprints to location.(2)Fusion of various signal measurements also could result in a robust and efficient estimator for parking lots, although advanced signal processing technology is required in real life to minimize computational cost.(3)Correlation feature extraction of the various signal metrics can also be considered in addressing signal fluctuations resulted due to the dynamic environment.(4)Effective data preprocessing approaches are highly recommended in improving the positioning performance.(5)Handling the data dimensionality curse could also improve the computational complexity. Thus, various approaches of data reduction techniques are highly important and worth further investigations.The database consists of values of different signal features as clearly mentioned on


The Black Lives Matter (BLM) protests against racialized police violence represents the most prolific mass social movement in modern times. It has been met by sustained and repressive violence by state authorities and right-wing groups. This review seeks to synthesize existing scholarly, journalistic, case report, and crowd sourced data on violence directed against BLM protestors.Data from various sources suggests that police disproportionately target BLM protests for violent intervention. There is also mounting evidence of organized and vigilante right-wing violence targeting BLM protestors. While police frequently use chemical irritants and projectiles, right-wing protestors often use car ramming to bluntly injure protestors. The true scale and nature of injuries affecting BLM protestors remains unknown though injuries resulting in the need for intensive care, operative intervention, permanent morbidity, and mortality have been reported.State and conservative civilian violence against BLM protestors represents an ongoing threat to the right to organize and publicly dissent. The use of force manifested by police and right-wing groups against BLM protestors resulted in significant injury and mortality. During the summer of 2020, following police killings of Black Americans, the USA saw perhaps the most widespread protest movement in its history . This waIn addition to state violence against BLM protestors, the summer of 2020 and beyond also saw a precipitous rise in violence by right-wing militias and counter-protestors. Similar to police violence reporting, there is no legal obligation for law enforcement to report hate crimes or politically directed violence . The FBIThe purpose of this review is to (a) provide a historical context to state repression of political actors in the USA, (b) review the existing scholarly, journalistic, and civilian-collected data describing state and far-right militia and vigilante violence against BLM organizers and protestors starting in the summer of 2020, and (c) provide a framework for collecting data on state violence against protestors. Importantly, given the existing limitations in data collection described above and the relative opacity of modern municipal police departments, this review combines descriptive analysis with a review of existing, though incomplete, data sources on violence targeting BLM protestors. A primary goal of this review is to capture the scale and nature of state violence and mistreatment of political actors in the USA with a special focus on the events of the summer of 2020.Violence has been central to US state building since its inception and long before the BLM movement. Much historical research has described how the incipient US state explicitly sponsored White vigilante violence to occupy indigenous lands. For example, as White settlers sought to occupy indigenous lands, the US government offered material rewards for the scalps of those it sought to displace . Anti-BlViolence against BLM protestors exists in a long historical arc of state repression of internal political challengers to the US state and capitalism . For exaOn June 4, 2020, Martin Gugino, a 75 year-old peace activist with the Catholic Worker Movement, was in attendance at a nonviolent Black Lives Matter demonstration in Niagara Square Buffalo, New York. During the demonstration he was walking towards approaching police and was first met with a forceful baton to his chest from one officer followed immediately by a push from another officer. Mr. Gugino stumbled backwards, fell and struck his head on the pavement. He lay motionless, bleeding from his ear as several officers walked past. Mr. Gugino suffered a skull fracture and subdural hemorrhage requiring a two-week intensive care unit admission . Gugino is one of the many BLM protestors and organizers who have faced direct physical harm secondary to police action during the summer of 2020. Given the lack of aggregated data collection, the full scale of police-related physical injury of BLM protestors is difficult to capture in its entirety. However, this part of the review will delve into what is known — the nature and recorded scale of police mistreatment of protestors — and its implications for the future of civic action in the USA.In the absence of official state or legal data, the Armed Conflict Location and Event Data project (ACLED) exists as one of the most reliable source of data to track protest-related political violence in the USA during the summer of 2020 [The ACLED collects data by coding over 2800 sources of data including local, state, and national media to identify political violence. In addition to media reports, the ACLED also collects information from data aggregators such as the Crowd Counting Consortium to tabulate political violence . An inheThe ACLED dataset describing political violence during the summer of 2020 — the “US Crisis Monitor” — found that 9% of BLM demonstrations were met by some form of state intervention  compared to 4% of right-wing demonstrations and 3% of all other demonstrations in the same year. This targeting of BLM protestors is despite the fact that 94% of BLM demonstrations were non-violent and non-destructive compared to 86% of right-wing protests. Importantly state intervention at BLM protests was typically more violent than those at right-wing demonstrations. Indeed 51% of BLM protests were met with physical force  compared to 33% of right-wing demonstrations and 26% of other demonstrations . The ACLACLED data also re-affirms the historically consistent reciprocity between the US state and right-wing militia actors. Similar to the collusive episode during the CIvil Rights era, described earlier, between Alabama state authorities and the Ku Klux Klan, there have been important interplays between the US state authorities and White right-wing militia groups like the Proud Boys. Indeed in response to Trump’s command to such extra-legal entities to “stand back, stand by” there were multiple subsequent episodes of Proud Boys initiated street-fighting during demonstrations in North Carolina, New York, California and Washington DC . There aMany of the technologies and vehicles deployed during the mass protests in the summer of 2020 and beyond reflect the growing militarization of United States municipal police . AdditioSome specific examples of police militarization during BLM protests include the use of Mine-Resistant Ambush Protected or MRAP armored vehicles typically designed for military conflict zones. Such vehicles have been deployed around the country both as an intimidation and crowd control technique .Additionally, human rights organizations document that police utilized a basic, recurring set of techniques to escalate protests and make violent confrontation more likely such as “trap and detain” or “kettling” whereby militarized vehicles are employed to encircle protestors. These situations often lead to use of physical force and create pretexts for mass arrests .Importantly, as indicated earlier, in addition to state authorities, far-right civilian militias have engaged in violence directly against BLM protestors and often complement or synergize with police-based tactics to stifle dissent. Indeed the scale of counter-demonstrations to BLM protests has been substantial with the ACLED recording over 750 distinct counter-demonstrations directly in response to BLM demonstrations between January 2020 and April 2021 . Within Individuals ideologically connected to far-right movements in virtual spaces often acted independently to contest various BLM protests. One such example, mentioned earlier was Kyle Rittenhouse’s response to the Kenosha Guard muster call and his subsequent killing of two BLM protestors. In fact armed individuals associated with right-wing movements may see themselves as auxiliary to police or military and respond to their perceived calls. Similar to Rittenhouse, Steven Ray Baca responded to a muster call by the New Mexico Civil Guard. During a symbolic struggle over the statue of Spanish conquistador Juan de Oñate, Baca shot and wounded a BLM protestor. Both Baca and Rittenhouse demonstrated ties to the conservative political establishment. Baca ran for city council as a board member of the Albuquerque Tea Party . In the Far-right militias constitute organized and armed citizens that essentially operate as a paramilitary force . In the Such far-right militias and militant groups have displayed an increasing presence at BLM protests over time. Indeed there have been at least 38 distinctly named far right militia or militant social groups that have directly confronted BLM protests. According to ACLED data the most common organization involved has been the Proud Boys. This group has countered almost 50 demonstrations and in over 36% of these engaged in violence or destructive acts .Importantly, the different far right militias or militant groups are aligned ideologically in their opposition to BLM though they often have different strategies of inciting violence against protestors. For example, the Boogaloo Boys — an extremist far-right group aiming to trigger widespread violence and societal collapse — has located itself in BLM protests as provocateurs, hoping to catalyze large-scale violence. Interestingly, the Boogaloo Boys, distinct from other groups, is not monolithically a White supremacist organization and is knit together by their shared anti-governmental ideology and a desire for the collapse of society . The comA key and common strategic response of these groups has been to establish an armed presence at BLM protests. At least 25 distinctly named groups have brought visibly armed members to BLM protests often in the self-proclaimed role of containing the violent or destructive behaviors of protestors, again indicating their self-perception as an auxiliary to state violence .In addition to the scale of violence against BLM protestors during the summer of 2020, it is important to note the type of injuries sustained. This next section delves deeper into the discrete public health and clinical impact of the violence inflicted by state authorities and right-wing counter-protestors against BLM activists.The racial justice protests of 2020 revealed law enforcement reliance on a particular set of technologies to quell protest. One particularly widespread technology used were chemical irritants, such as tear gas, to disperse gathered crowds. A systematic review of studies on the health impacts of tear gas spanning 29 studies (including 7 from the United States) across 11 countries and 5131 individuals found a total of 9261 injuries and that two people died related to chemical irritant complications and 58 suffered permanent disability . Out of n = 1931), 300 people suffered permanent disability, most commonly vision loss and abdominal injuries requiring splenectomy or colostomies. Two people suffered limb amputation. This study also found that the muzzle velocity of the “less than lethal” projectiles matched that of lethal ammunition [Significantly, the most serious tear gas related injuries stem from the projectile canister rather than the chemical irritant. Indeed state authorities made widespread use of so-called “less than lethal” or “non-lethal” projectiles against BLM protestors that included rubber bullets, pepper balls, beanbag rounds and propelled tear gas canisters. A systematic review spanning 26 articles (including three from the United States) from 1990 to 2017 compiled injury data on 1984 individuals of which 53 died from such projectiles . Half ofmunition .The exact scale of penetrating and chemical irritant related morbidity and mortality secondary to state action during the protests of the summer of 2020 remains unknown. However, case series during the BLM protests give a sense of the type of injuries these police technologies can inflict. One particular report from Austin, Texas following two days of BLM protests describes the impact of beanbag and rubber bullet munitions on 19 patients treated at the local level 1 trauma center.  Eight ofAnother larger sample study of “less than lethal” munitions injuries during the summer of 2020 from Minnesota performed a retrospective review between May 26 and June 15, 2020 of all patients possibly injured during protests . During A final case series of penetrating injury secondary to police projectiles reviewed 14 patients presenting to a level 1 trauma center in Los Angeles over a 48-h period during BLM protests . This seBeyond the documented clinical case series of projectile injuries, blunt injury by car rammings has also been an increasingly prevalent form of violence directed against BLM protestors. Car rammings occurred eight times more frequently at BLM protests compared to other demonstrations and were exclusively initiated by right-wing individuals or groups . There hmore peaceful over time. Between May 25 and June 4, 2020, 89% of protest demonstrations were non-violent while later between June and September 2020 more than 96% of BLM associated protests were non-violent [It is important to note that while the BLM protests generally become more peaceful over time the public perception was that they were becoming more violent. As described earlier, this is in marked contrast to how the public perceived the civil rights movement which gained more public and more White support as televisions streamed the undeniable state violence against peaceful protestors. Such a difference points to the relative importance of curated social media in shaping today’s public views. Indeed according to Pew surveys the BLM protests became -violent . Nonethe-violent .As evidenced by this review the ability to understand the scale and nature of state violence against political actors is limited by the sources of data available. The particular challenge of collecting data on state violence is that the government, which usually has the resources and institutional reach to collect the necessary information for a data set, is also the very entity being interrogated. To come around this problem, researchers and advocates have long proposed alternate methods to improve data collection on officer-involved violence such as equipping trauma centers to gather this information directly from patients. Nonetheless systematic approaches or legal mandates to acquire this information remain notably absent.The current era of public organizing has been accompanied by dramatic episodes of violent repression that highlights the importance of data collection and dissemination. In response, activist individuals and organizations have deployed numerous extra-institutional approaches to data gathering. Considerations for collecting data on political violence against protestors, a review of current data collection efforts and ways to politicize such data are described further.Protestors may be less likely, especially in the era of COVID-19, to present to the formal healthcare system following state-sanctioned injuriesWhile medical professionals and healthcare systems should continue collecting data on state violence as it impacts their patients, episodic violence impacting protestors requires specialized considerations:2.Protestors may be less likely to report state violence to institutional authoritiesData demonstrates a global decrease in utilization of emergency room services since the beginning of the COVID-19 pandemic . This de3.Creating open source data portals allows multiple types of mistreatment to be capturedFor the same reasons listed above, namely general distrust of institutional authority, even those protestors who present to a hospital-based setting may be less likely to report state-sanctioned violence. This distrust is further heightened amongst Black Americans given historical abuse by medical institutions . Indeed Publicly available social media data archiving over a thousand separate instances of state violence and mistreatment against protestors reveals an incredible range of events that may only be partially captured by current dataset, such as ACLED, reliance on media based reports. This includes physical violence as well as verbal abuse and arbitrary arrest. Extra-institutional data collection methodologies should be flexible to capture the entire range of state-based mistreatment of protestors.Linked to the first two reasons described above formal trauma databases, such as the National Trauma Data Bank (NTDB), which collect comprehensive injury related data as reported directly from hospital trauma centers, may only capture a portion of protest injury data . Thus moTwitter archives: Twitter has been a central source of reporting and collecting data on state repression of protests as evidenced by the archive of instances amassed by T. Greg Doucette . VariousThe Witness Archives: An independent initiative to collect and publish incidents of police violence and mistreatment against protestors captured on video by protestors .Geographic Information Systems (GIS) spatial mapping of police brutality: Several independent efforts have sought to synthesize social media derived data into GIS based maps highlighting the regional scale of state violence against protestors .Raheem: Another independent portal to collect data on police brutality. This service mobilizes the narratives of those impacted by the police and translates them into various forms of political engagement including formal complaints and pursuits of justice .Ongoing movements for racial justice as well as the movement to collect data on racialized police brutality are increasingly decentralized. Data for Black Lives is an example of efforts to collect data to bolster the movement with the mission of “using data science to create concrete and measurable change in the lives of Black people” . AnotherIn addition to the efforts listed above, there remains an enormous potential to widen data collection by empowering protestors to directly report state violence and mistreatment in real time. An ultimate, longer-term data goal would be to synthesize the various reporting mechanisms into a central database for research and policymaking purposes. Information about the scale and nature of political violence and mistreatment against protestors can inform policy at local, state and national levels. Specifically this data can be brought to bear on hearings or directly provided to legislators considering the impact of state and right-wing violence on communities.Finally, synthesizing and analyzing such data is particularly important to health professionals caring for trauma patients regardless of one’s political values. As noted above the nature of injuries sustained by BLM protestors, whether due to state or right-wing actors, resulted in significant morbidity and mortality during the 2020 BLM demonstrations. Protestors often required operative intervention and critical care for the treatment of their injuries. Trauma surgeons are often the primary treating clinicians for such injuries and, as such, may be trusted with important information regarding protest related injury. Indeed recent literature has demonstrated the unique trust patients place in their surgeons . This maThis review has sought to provide a quantitative and descriptive sense of violence against BLM protestors in 2020. Importantly this violence exists in historical continuity with other challenges to US state legitimacy including explicit attempts to undermine larger scale political projects for racial justice by groups like the Black Panther Party and myriad others during the civil rights era.The data that currently exists on violence against BLM protestors is incomplete and biased towards media reports on larger scale urban protests. It is apparent, however, that BLM protestors, relative to other demonstrators, have been disproportionately affected by state and right-wing violence. Predominant mechanisms of injury include chemical irritants, projectiles and intentional blunt automobile impact. In reviewing the damage incurred by chemical irritants and “less than lethal” projectiles it is clear these technologies can cause major injuries and even mortality. Additionally, blunt trauma in the form of car rammings, and the legal protections for those who engage in them, represent a highly morbid and often lethal technique used by right-wing actors against BLM protestors. Overall the data reviewed is limited by the inherent biases of media based reports that may be even more pronounced in the case of BLM , 47. HowThere exists growing evidence that the political action of BLM protests has impacted police lethal use of force with a May 2021 study demonstrating a 15–20% decrease in police homicides in census tracts with protests between 2014 and 2019 . This re


Reducing the negative environmental impact of a widely spread building material such as concrete is possible by decreasing the amount of cement in this composite material, especially when specific waste is included as a substitution for the binder. Another important environmental issue is accumulated aquaculture waste. This work justifies the possibility of achieving modified concrete with improved properties based on sea mussel shell powder (MSP). An improved environmentally friendly concrete was obtained and modified with MSP as a result of experimental studies. The dosage of MSP in the amount of 6% instead of part of the cement turned out to be optimal and most effective. Because of the modification, it was possible to increase the strength properties: the increments were up to 12% for the compressive strength (CS), up to 13% for the axial CS, up to 14% for the tensile strength (TS) in bending, and up to 12% for the axial TS. The ultimate strains under axial compression and tension decreased to 9% and 12%, respectively, and the elastic modulus increased to 15%. SEM analysis showed a more integral microstructure without voids and cracks in this composite with a modifier content of 6% compared with the sample of the ordinary composition. Economic efficiency is expressed in reducing the total cost of new concrete compared to traditional ones by about 17% and the cost of building construction by up to 15% due to a decrease in the percentage of defects. Currently, there are several significant problems in the fields of ecology and engineering. A number of these problems are directly interconnected and justified by the fact that engineers, in turn, experience a lack and shortage of environmentally friendly production methods while, at the same time, ecology and the environment suffer quite seriously ,2,3,4,5.Thus, there is a considerable environmental problem that needs to be addressed in the most efficient way. At the same time, taking into account deficiencies in the field of engineering knowledge on building material manufacture, there is a need to develop new production technologies, create new recipes, as well as conduct fundamental research on the issues of structure formation and establish dependencies of “composition-structure-property”, that are related to the study of various components for concrete and the properties of concretes themselves in general ,14,15.3), “which is comparable to the CaCO3 content in limestone powders used in the manufacture of Portland cement” 39], the The main steps in the manufacture of finely ground powder from mussel shells are presented in a flowchart  as folloThe thermal treatment of mussel shells at a temperature of 300 °C was carried out in order to completely remove the organic residues that remained after washing.The design of the concrete mixture composition was carried out according to the GOST 27,006 “Concretes. Rules for mix proposing”  based onIn laboratory conditions, samples were made of concrete with approximately 40–45 MPa of strength, with the composition presented in –Dosing the CM components;–Mixing Portland cement and quartz sand in a concrete mixer for 2 min;–Adding the required dosage of MSP and mixing until a homogeneous consistency was obtained;–Introduction of mixing water and coarse aggregate;–Mixing of the concrete mix to a homogeneous condition;–Unloading the resulting mixture from the concrete mixer and molding the samples;–Smoothing the surface of the samples compacted for 1 min by vibrating and marking them ,43,44,45The production of CMs, samples-cubes, and prisms with different dosages of powder from mussel shells was introduced instead of part of the cement and proceeded as follows:The hardening of the samples took place in the normal hardening chamber for 1 day; then, the specimens were stripped and kept in a chamber under normal curing conditions for 27 days. After 28 days of curing, the specimens were tested on a hydraulic press and a tensile testing machine.Determination of compressive strength (CS), tensile strength (TS) in bending, and axial TS proceeded following the GOST 10,180 “Concretes. Methods for strength determination using reference specimens” . The detThe main technological, testing laboratory equipment, and measuring instruments for the manufacture of finely ground powder from mussel shells, concrete mixes and laboratory samples with different percentages of cement replacement by powder from mussel shells were used the same as in ,43,44,45The microstructure of the hardened cement paste with the addition of mussel shell powder was studied using an electron microscope, which was also equipped with a special device for chemical analysis . The parThe X-ray diffraction of samples of the obtained powder was carried out on a Difrey X-ray diffractometer  with Cu K radiation operating at 40 kV and 40 mA. The diffraction angle was continuously scanned from 10° to 60° in 2θ at a scanning rate of 2°/min.Based on The results of the SSC of the studied concrete samples with a different proportion of MSP instead of a part of cement are presented in the form of graphs in b.cubR as determined by the cubed samples and MSP dosage.According to the results of the study on concrete for compression, The dependence of the axial CS  on MSP lFollowing the data presented in Y(x) with the addition of MSP  were approximated by the “saturation” function [The characteristics of the concrete strength function  in the fC0 is characteristic of concrete without the addition of MSP; A, b, ω, φ are constants to be determined. Here, x)Equations (2)–(5) show a high degree of closeness to the connection (determination coefficient The dependences of the ultimate strains in compression (USAC) and in tension (USAT) are shown in x (6), (7)The deformation characteristics were also approximated by the “saturation” function , which rChanges in the values of USAC The ME, depending on the content of the MSP, is well approximated by the saturation function (8):Analyzing The graphs presented in The microstructure photos of the hardened cement samples with 6% MSP and the control composition are presented in The SEM analysis data show that a concrete sample with MSP in an amount of 6% has the most complete microstructure, without voids and cracks  compared++ ions is created. After the formation of gel shells, the diffusion of calcium ions in the direction from the cement particle to the liquid phase continues at a relatively high rate, and after the saturation of the solution, the reverse diffusion process occurs, caused by a decrease in the concentration of Ca++ ions due to the formation of crystalline hydrates  in the thickness cement particles under the shell [The mechanism of the formation of additional CSH-gel zones during the hydration of Portland cement can be explained as follows. The formation of semi-permeable shells on the surface of the initial cement particles is preceded by a long induction period, during which a solution supersaturated with Cahe shell . Due to Thus, SEM analysis confirms the effectiveness of the adopted composition, technological solution, and the established rational dosage of MSP, which became possible due to a comparative analysis according to the criterion of structural integrity and the nature of microcracking, which cannot be established with the naked eye. The creation of a denser structure, the better packing of particles at the micro level due to modification, and the creation of additional crystallization centers make it possible to obtain a better, denser, and more durable structure of a new environmentally friendly concrete based on the finely ground powder of mussel shells.To achieve a more precise trend of the transformation of the characteristics of concrete related to the amount of MSP additive applied instead of cement, the nature of their change is presented in graphical form .The improvement in the characteristics of concrete modified with MSP is explained by the fact that the good compatibility of the MSP shell powder instead of part of the cement in an amount of up to 10% contributes to the development and a more complete process of hydration reactions with the additional formation of CSH gel zones. This also agrees well with the chemistry of MSP. In addition, at the micro- and macro-levels, denser packing of particles is observed at an MSP dosage of 6%. It has been experimentally established and confirmed using SEM analysis that MSP in the proportion of 6% leads to the best organization of the concrete structure, which is confirmed by the best SSC of the studied concrete ,50.The results of the experimental studies are in good agreement with the results of similar experimental data by a number of other scientists ,52,53,54The authors of ,28,29,30In most works ,36,38,54Discussing the nature of change in the deformation characteristics of the resulting concrete, it should be noted that the modification of concrete is a prescription technique that differs significantly in its result from other previously known methods for controlling the properties of concrete-dispersed fiber reinforcement . This diThus, the operational efficiency of the proposed method for use in buildings and structures with increased requirements for the strength of concrete is confirmed.The effectiveness of the use of powders from various types of aquaculture waste, including mussel shells, is explained by the higher content of calcium in it and the high dispersion of particles, which contribute to the hydration of cement due to its high activity and the dissolution of calcium, which is present in large quantities in the shells of seashells. (1)The modification of concrete with the finely ground powder of mussel shells makes it possible to enhance the structure formation and SSC, provided that the optimal dosage of such a modifier is observed.(2)Replacing part of the cement in the concrete with mussel shell powder at an amount of 6% leads to better concrete performance values.(3)Replacing cement with MSP by up to 10% does not adversely affect strength characteristics, while adding more than 10% MSP leads to a drop in strength characteristics.(4)The modification of concrete with MSP at an amount of 6% provides an increase in CS by up to 12%, axial CS-up to 13%, TS in bending-up to 14%, axial TS-up to 12%, and ME-up to 15%. The addition of MSP in an amount from 0 to 6% gives a smooth increase in concrete strength and ME, while the addition of MSP from 6 to 12% leads to a sharp drop in concrete strength and ME.(5)The modification of concrete with MSP at an amount of 6% provides a reduction in the ultimate deformations of compression and tension by up to 12%, and an increase in the dosage by 12% leads to an increase in deformations up to 14%.(6)SEM analysis showed that concrete with 6% MSP has a more integral microstructure, without voids and cracks in comparison with the control sample, and also contributes to the additional formation of CSH gel zones, which ensures an increase in the strength characteristics of the composite.In general, the obtained results of SSC for concrete allow us to draw the following main conclusions regarding this study:The significance of the study is not only scientific but also applied. The environmental friendliness of the new concrete is to clean up the environment from polluting aquaculture waste and reduce the number of consumed resources and emissions by replacing some of the produced concrete components with a powder of natural origin. Economic efficiency is expressed in the reduction of the cost of new concrete compared to traditional ones by about 17% and the cost of building construction by up to 15% due to a decrease in the percentage of defects.


Escherichia coli genome-scale model, iAF1260.The multidrug resistance of numerous pathogenic microorganisms is a serious challenge that raises global healthcare concerns. Multi-target medications and combinatorial therapeutics are much more effective than single-target drugs due to their synergistic impact on the systematic activities of microorganisms. Designing efficient combinatorial therapeutics can benefit from identification of synthetic lethals (SLs). An SL is a set of non-essential targets  that prevent the proliferation of a microorganism when they are “knocked out” simultaneously. To facilitate the identification of SLs, we introduce Rapid-SL, a new multimodal implementation of the Fast-SL method, using the depth-first search algorithm. The advantages of Rapid-SL over Fast-SL include: (a) the enumeration of all SLs that have an arbitrary cardinality, (b) a shorter runtime due to search space reduction, (c) embarrassingly parallel computations, and (d) the targeted identification of SLs. Targeted identification is important because the enumeration of higher order SLs demands the examination of too many reaction sets. Accordingly, we present specific applications of Rapid-SL for the efficient targeted identification of SLs. In particular, we found up to 67% of all quadruple SLs by investigating about 1% of the search space. Furthermore, 307 sextuples, 476 septuples, and over 9000 octuples are found for  Most of these species benefit from several pathogenicity factors  and broad drug-resistance mechanisms . Hence, disrupting the activity of only a single gene in these microorganisms does not guarantee to prevent their growth or the biosynthesis of virulence factors. Furthermore, targeting the essential reactions or genes in some pathogens may cause a significant increase in biofilm-associated reactions. This implies that single essential genes may not be proper targets for these types of microorganisms3. In contrast, multi-target medications and combinatorial therapeutics synergistically impress the microorganisms’ systematic activities; thus, they have been recommended to be much more operative and they show less drug resistance than single targets4.A number of human pathogenic microorganisms show multidrug resistance, which is a serious challenge in the era of global healthcare5. Constraint-based models (CBMs) are very influential in this regard. These models are successfully employed as operative mathematical representations of genome-scale metabolic models (GEMMs) by imposing the governing context- and condition-specific constraints on genome-scale metabolic network reconstructions (GENREs). CBMs can comprehensively analyze metabolic activities and examine the physiological properties of biological systems. Deploying CBMs, systematic analyses can be performed by applying the potent class of computational techniques that are available in constraint-based reconstruction and analysis (COBRA) toolbox8.Computational systems biology proposes powerful methodologies to address biomedical queries  via a multidisciplinary systems-level study that considers multifaceted interactions between many elements in biological networks9: (a) targeting virulence factors3, (b) metabolite-centric targeting12, and (c) targeting essential reactions and genes17. The last perspective is known as the most common method for identifying potential drug targets, and it is not limited to the deletion of only one reaction or gene. Synthetic lethals (SLs) are pairs of non-essential reactions or genes that are deleterious to an organism when they are disrupted simultaneously18. Similarly, when the number of targets increases, higher order synthetic lethal sets (n > 2) can be obtained18.Because in silico studies save significant time and expense, these methods are widely employed to identify the various effects of reaction and gene knockouts on the flux distribution of the metabolic networks of interest. These knockout studies can be implemented to identify new drug targets from three perspectives19. However, this concept, not certainly by design, might have been deployed already for many drug combination strategies. One example of this strategy is the combination of daptomycin, cefoperazone, and doxycycline for eradication of Borrelia burgdorferi, through loss of membrane potential as well as inhibition of energy metabolism, cell wall peptidoglycan synthesis, and protein synthesis20. There are other examples in cancer therapeutics such as the combination of BRAF and EGFR inhibitors which effectually influence AKT, MEK and ERK signaling, suggested for colon cancer patients with BRAF mutations19. In the mentioned cases, combinatorial therapeutics resulted in more effective impacts compared to monotherapies due to the synergistic effects on different functionalities of the cells.We should note that although the identification of higher order synthetic lethal sets can bring in new targets for utilizing different drugs in the design of combinatorial therapeutics, this approach is not common in practice21, but applying this approach to identify higher order SLs, especially when the cardinality of SLs is greater than three, is not feasible due to computational time problems. Based on the available computational resources, we estimated that the required computational time for the exhaustive search would be over 180 days to obtain all quadruple SLs for Escherichia coli using iAF126022 GEMM. Therefore, other methods are required to handle such problems by reducing the search space. Depending on the suggested criteria used to reduce the search space, some of these methods can find only a fraction of the higher order SLs18, while some other methods aim to find all the SLs28.Two approaches are used to computationally identify SLs: exhaustive search and search space reduction. Exhaustive search is straightforward and has been used in some studies18. In order to reduce the search space, this method employs the flux-coupling analysis29 to add only one of the fully coupled reactions in the knockout list. This approach was used to discover all double and triple SLs and conduct a targeted identification of a few quadruple and quintuple SLs for iAF1260 GENRE of E. coli.One of these methods, called “SL Finder,” performs an optimization-based search for the exhaustive and targeted identification of SLs30 of the corresponding metabolic network23. It is a powerful approach especially for metabolic engineering applications. Further improvements were made on this approach to obtain the generalized framework of MCSEnumerator and accelerate the dual calculations26. MCSEnumerator was applied to find all double to quintuple SLs in iAF126023. However, the computational time increases exponentially for SLs that have higher cardinalities, and therefore, the search procedure needs to be stopped after finding a predefined number of SLs or a time limit is reached. Alternatively, in this paper, we propose a targeted enumeration algorithm aiming to increase search efficiency.MCSEnumerator finds instead intervention strategies by enumerating the elementary modes of the dual network27. Fast-SL computes a flux distribution that maximizes the growth rate using a minimum value for the sum of fluxes  must be solved to find SLs. Hence, this method becomes extremely time consuming to perform knockouts regarding higher order SLs.Logic transformation of model (LTM) is another method used in this field. This method changes the stoichiometry matrix  by adding pseudo-metabolites and reactions to consider the gene-protein-reaction associations (GPRs)As mentioned earlier, drug resistance is an important concern and identification of new drug targets based on the concept of synthetic lethality can be a suitable solution for this issue. However, comparing the effects of the different synthetic lethal sets on the metabolic network and its functionalities reveals that some of the sets with higher cardinalities can make stronger and deeper impacts on the network. For instance, we can categorize the synthetic lethal sets into two types: (a) SLs that yield auxotroph strains and (b) SLs that yield strains lacking essential functionalities. The first type of SLs yields strains that are able to restore their growth if the missing nutrients are supplied. In contrast, the strains yielded in the second group cannot restore their growth even if extra components are provided in the growth medium. We expect that the SLs of the second group function more effectively and enable us to aim targets that are harder to resist by pathogens. Based on our in silico observations, higher order SLs provide us with more of these more effective SLs.Rapid-SL, which has two major steps that are iteratively performed based on the depth-first search (DFS) algorithm31: (1) identification of the seed space  and (2) searching within the seed space to find the solutions. The main difference between this new implementation and the original Fast-SL is the compartmentalization of the searching process into several branches. This branching allows embarrassing parallelization32 and prevents the examination of duplicate cases. This reduces the search space by about 35–60% compared to Fast-SL. However, in the modern drug discovery process, the target identification is typically the beginning step. Therefore, as in the case of Fast-SL, further analysis on the Rapid-SL results, as a biological hypothesis, is required to reach an approved drug.The purpose of the current work is to develop a comprehensive and straightforward reimplementation of the Fast-SL algorithm to facilitate the identification of higher order SLs. We call our implementation n = 8) SL reactions were reported for E. coli using iAF1260 GEMM. We hope that the identification of higher order synthetic lethal sets using efficient tools such as Rapid-SL paves the way for systematic designing of effective combinatorial therapeutics in future studies.In order to examine the performance of the developed method, we compared the results of Rapid-SL and Fast-SL for three microorganisms. Afterwards, we introduced three applications for Rapid-SL that could be effective for the targeted identification of higher order SLs, particularly when the cardinality of SLs is greater than four targets. Accordingly, we can: (1) search among a specific list of reactions chosen consistent with a biological context, (2) apply graph-based search methods, and (3) selectively enumerate the SLs among the DFS branches. Based on our in silico experiments in the current work, over 9000 octuple  in this work. In the second step, we search for the SLs within the seed space. Moreover, each non-lethal subset of the seed space defines a new proliferating mutant strain. Using a DFS approach, we repeat the first and second steps for each of the new mutant strains -related LPs33 are considered and solved. These LPs lead to the identification of a flux distribution that maximizes the flux of the biomass objective function (νbio), while the bio,WT is the growth of the wild-type strain calculated by solving the following LP problem:We denote the flux of reactions by νseed space.The goal of computing this flux distribution is to characterize the flux-carrying reactions, or the 34 instead of computing Applying flux-variability analysis (FVA)All combinations of the reactions in the seed space have the potential to form SLs; therefore, the exhaustive search is performed in the second step. However, when an SL is found in this step, the corresponding supersets are excluded to prevent the investigation of duplicated cases or the production of trivial answers. Furthermore, each non-lethal set identified in this step defines a proliferating mutant . This second step also includes the listing of all non-lethal sets to investigate their related proliferating mutants by removing more potential reactions in the next level of the search. Figure 27, removing a set of reactions that includes only non-flux-carrying reactions would have no effect on the flux of biomass formation reaction; therefore, at least one reaction in the seed space of the wild-type strain (Jnz) should participate in each SL. Here, we generalized this statement from the wild-type strain to any virtual strain obtained during our search procedure. In other words, each reaction designated for removal in subsequent steps of the DFS algorithm should originate from the seed space of the parent virtual strain. Therefore, after we evaluate the first and the second steps for the wild-type strain, we iteratively repeat these two steps for all the resulting virtual strains identified in the second step of the previous level. Each of these mutants is treated the same as the wild-type strain; therefore, we face an iterative problem, which is handled using the DFS algorithm .Figure 37 effectively use this feature for identification of synthetic lethal genes.To enumerate the synthetic lethal gene sets, the same procedure is employed, except that those non-zero-flux reactions obtained in each part are converted to the functioning genes using GPR rules  using the algorithms that are currently available40. The results obtained in this application are presented in Supplementary File The simplest method to find a fraction of solutions is to specify only a limited group of reactions. However, it is not clear what reactions should be selected. These reactions may be selected from a specific subsystem or pathway that has been diagnosed as important for the growth of the microorganism. For example, we performed a search to find octuple SLs  among 65 core reactions introduced by Hädicke and Klamt for generating a core model from iJO1366Our new implementation makes this analysis feasible, but at the first sight, it may seem that using Rapid-SL is not necessary, and it may seem sufficient to find these results using an exhaustive search because of the small number of reactions involved in the analysis. However, Rapid-SL uses a search space that is about 50 times smaller than the exhaustive search, which consequently requires an extremely time-consuming process even for small numbers of reactions. Also, it is not feasible to perform this analysis using the original Fast-SL, because separated algorithms should be devised for the cardinality of each SL.n = 8) for iAF1260 are presented in the Supplementary File Since Rapid-SL applies the DFS algorithm to investigate the search space, it is possible to define thresholds or conditions to limit the branching and search only the more probable parts of the corresponding tree. For example, we established a criterion in which sets are allowed to branch only if their deletion reduces the growth rate of the corresponding strain by at least 1%. The results obtained by applying this criterion to the process of identifying octuple SLs  with a different genome-scale model (i.e. iJO1366) and also for a different type of microorganism  to check the generalizability of this observation  decreased the number of evaluated LP problems by about 35–60%. The original implementation of Fast-SL is not embarrassingly parallel and suffers from time consuming sequential computations in some of its steps. Accordingly, for larger models and higher order SLs, the difference between the computational time of Fast-SL and Rapid-SL increases and Rapid-SL becomes more and more efficient. Although Rapid-SL is not limited in terms of the cardinality of SLs, it is not feasible to seek for all SLs with higher cardinalities, especially when n > 4, without using computer clusters. When using a single conventional computer, the runtime of this examination may extend to several months because of the tremendous number of potential cases. Owing to our proper implementation, Rapid-SL can effectively find a considerable portion of higher order SLs by searching only a relatively small fraction of potential cases. Accordingly, three Rapid-SL applications were introduced: (a) searching among a selected list of potential reactions, (b) applying constraints on the branching of the DFS, and (c) selective enumeration among the DFS branches. These applications identified up to 67% of quadruple SLs by searching about 1% of the potential cases. Particularly, over 9,000 octuple synthetic reactions were found for iAF1260 in the third application. Accordingly, Rapid-SL can be effective for investigating large models such as genome-scale metabolic models of human cells to find drug targets with high cardinalities.In this paper, we introduce Rapid-SL as a new implementation of Fast-SL that enables the algorithm to find higher order SLs with arbitrary cardinalities. Unlike Fast-SL, this new implementation fully supports Although the first two applications find fewer SLs than the other application, they may still be useful for seeking SLs with specific biological considerations. The importance of this feature becomes clearer noting that a single organism may have more than several thousands SLs with high cardinalities, and experimental validation of all of these SLs is not feasible due to the immense number of required experiments. Therefore, the both scenarios require the consideration of biological criteria when searching for useful SL sets. In future work, we will focus on defining new criteria to reduce the number of potential drug-targetable SLs.Although the combinatorial therapeutics are expected to be effective against drug resistance pathogens and higher order SLs can potentially nominate candidates for simultaneously attacking multiple targets, it is still challenging to determine which combination would be practical and most useful. For example, possible negative synergistic effects narrow down the practical drug combinations. Furthermore, when the number of targets in an SL increases, the chance of finding a set with all druggable targets decreases. Therefore, it would be desirable to devise a systematic pipeline to investigate the identified higher order SLs as the starting point and derive a combinatorial therapeutic design as the outcome.Supplementary Information 1.Supplementary Information 2.Supplementary Information 3.Supplementary Information 4.Supplementary Information 5.Supplementary Information 6.Supplementary Information 7.Supplementary Information 8.