Importantly, modularity is mostly affected by the extinction rather than by rewiring mechanisms. These changes in community structure are reflected in the robustness and stability due to their positive correlation with modularity. Resource affinity-driven rewiring offers an increase of modularity, robustness, and stability which could be an evolutionary favored mechanism to prevent a cascade of co-extinctions.Understanding the response of ecological networks to perturbations and disruptive events is needed to anticipate the biodiversity loss and extinction cascades. Here, we study how network plasticity reshapes the topology of mutualistic networks in response to species loss. We analyze more than one hundred empirical mutualistic networks and considered random and targeted removal as mechanisms of species extinction. Network plasticity is modeled as either random rewiring, as the most parsimonious approach, or resource affinity-driven rewiring, as a proxy for encoding the phylogenetic similarity and functional redundancy among species. This redundancy should be positively correlated with the robustness of an ecosystem, as functions can be taken by other species once one of them is extinct. We show that effective modularity,  An important class of adaptation dynamics occurs as a consequence of extinction events altering network structure. Examples include the disappearance of companies and technologies due to innovations and market competition15, neurons extinction16, gene extinction17, extinction of the least populated molecular species18 local extinction of species in biological networks due to perturbation such as pollution or human disturbance20, habitat loss21, climate change23 or extinction of interaction partners25.Network adaptation reflects the ability of a system to respond to external  perturbations in terms of establishing dynamic interactions between the remaining elements. This sort of adaptation based on the coevolution of topologies and states appears in many network systems28. Understanding how ecosystems respond to species loss has hence been the subject of numerous theoretical and experimental studies30. While some communities exhibit density compensation32, a common form of adaptation in food webs is represented by the rewiring of feeding links among members of species in response to variation in resources37. Functional redundancy can help in the process of rewiring, as species have the ability to replace each other. So, for example, pollination networks have been shown to be fairly robust against species extinctions as a result of bipartite network asymmetry . However, trophic rewiring can lead to overexploitation of resources and aggravate the effects of species loss on food webs38.In ecosystems, loss or declining abundance of one species can cause the extinction of other dependent species39: robustness, defined in terms of the largest connected component40; nestedness, where specialists interact with a subset of the whole set of species that generalists interact with41; modularity, which refers to densely connected non-overlapping subsets of species (modules) with weak interactions between them43; and stability, which can be measured as the largest eigenvalue of the appropriate matrix44.From the perspective of the topological structure of the interactions of the species that compose ecosystems, recent studies have revealed key structural features which are believed to influence ecological dynamics46. Based on previous results, modular structure in species interactions of mutualistic networks hinders the loss of species and promotes the long term persistence of ecological communities, as the compartments buffer the propagation of extinctions across the network51. More recent research provided empirical evidence to test this hypothesis experimentally and confirmed that a modular network structure enhances species persistence52. Here we used a dynamical modeling approach to investigate how different extinction-induced rewiring scenarios modify the structure of ecological bipartite networks. In particular, we investigated the effects on topological robustness, measured as the degree of connectivity within the network; network modularity, seen as the compartmentalized nature of the networks, and finally, dynamical stability, measured through the change in the largest eigenvalue of the adjacency matrix.Some studies have analyzed these characteristics as the product of a temporal evolutionary process53 and55). We considered here only the presence or absence of the interaction, i.e. unweighted undirected bipartite networks.We analyzed 130 empirical mutualistic bipartite networks consisting of 101 plant-pollinator, 25 seed-dispersal, 3 plant-ant, and 1 host-symbiont association  captures the pairwise interactions between resources and consumers: Aij = 1 if there is a pairwise interaction between resource i and consumer j, and Aij = 0 otherwise. Thus, the adjacency matrix can be written asÃ is the incidence matrix, T indicates the matrix transpose and 0m×m is the all-zero matrix and the subindices indicate the number of rows and columns.Bipartite networks contain two types of nodes: resources and consumers. Resources represent plants  while consumers represent pollinators . They contain, thus, Extinction: a resource node is removed.Adaptation: each link that was attached to the extinct resource node is rewired to a different resource node with probability r.At each time step, the dynamics proceeds as follows:r varies between 0 and 1, where r = 0 represents the no-rewiring case and r = 1 the case where each link is attempted to be rewired.The rewiring probability i.e. the number of consumers interacting with it. We considered again two adaptation scenarios, in both cases the consumer is maintained while the resource is rewired: (i) random rewiring, where the extinct resource is replaced by an existing resource at random; and (ii) resource affinity-driven rewiring, where the extinct resource is replaced by another resource selected proportionally to the number of common consumers shared with it. Thus, for instance, in the case of a plant-pollination network, an extinct plant species would be replaced with the largest probability by another species sharing the highest number of pollinators with the extinct one, which is likely to be the phylogenetically most closely related or ecologically redundant species. Hence, if the resource j is selected for extinction, the number of shared consumers with resource k is given by:Ej and Ek are the set of consumers connected with resource j and k. Thus, the probability that resource k is selected as replacement of resource j by resource affinity-driven rewiring is given byWe explored two scenarios for extinction: (i) random extinction, selecting the resource for extinction at random from the available ones; and (ii) directed extinction, selecting the resource proportionally to its degree, If the new link already existed, no new link is added. In total, we explored four extinction-adaptation scenarios: RR, random extinction and random adaptation, RF, random extinction and resource affinity-driven adaptation, DR, directed extinction and random adaptation, and DF, directed extinction and resource affinity-driven adaptation Fig. .Figure 1S(f), reflects the ability of the network to maintain itself connected56. The behavior of the relative size of the largest component can be summarized in the robustness ρ, measured as the area under the S(f) curve:Due to the extinctions, the bipartite networks eventually break up in several components. The relative size of the largest connected component in the network after a fraction f of resource nodes are extinct, R close to one means that as nodes are being removed the network does not fragment, consisting of a single component all the way; while a value of ρ close to zero signals that the network fragments very easily into small disconnected components.A value of 57 asgi and hj are the community indices that resources i and consumers j are assigned to, and L is the number of links in the network. The expected probability of interactions between two types of nodes is given by matrix B. Based on the null model, that considers random pairings between two classes of nodes with given degree sequences, the Bij elements are proportional to the degree of resource ki and the degree of consumer dj in the original network 58 to find the community structure that maximizes Eq. : Qe = SQ.The sequence of extinction-rewiring events eventually breaks the bipartite networks in several components. To correct for the network breakout of the bipartite network, we introduced the effective modularity ij defined as the probability that two nodes remain in the same community if they were initially in the same community, Πij, where gi (hj) is the community to which node i (j) belongs.The changes in the community structure of bipartite networks can be quantified with the module persistence Π44. The assumption is that the adjacency matrix captures the linear stability of the dynamics of the ecosystem. In our case, the interaction is given by a matrix that reflects the bipartite structure and the mutualistic interactions, that is, all the entries are non-negative. In general, if the dynamics is given by a local dynamics and an interaction term:xi is the abundance of species i, f(xi) are the local dynamics, k is a coupling strength and Aij the adjacency matrix and therefore we only take into account positive interactions . The stability of this system around a fixed point kAij. If the local dynamics are the same for all the elements, the diagonal elements are all the same and thus only contribute to the largest eigenvalue as an offset. If all the eigenvalues have a negative real part, then the equilibrium is stable and the perturbed system will go back to the equilibrium, but if any of the eigenvalues have a positive real part, the perturbed system will move away from the equilibrium. Therefore the eigenvalues of the Jacobian can be analyzed in terms of the eigenvalues of the adjacency matrix59.To study the relationship between the structure and the stability of an ecosystem, May considered positive and negative interactions to represent the relations among species in an ecological community and analyzed the eigenvalues of the adjacency matrix as a measure of the stabilityλ, of the (n + m) × (n + m) adjacency matrix as extinction-adaptation events occur, with respect to the leading eigenvalue of the original matrix, λ0:We measured the change in stability of a mutualistic bipartite network as the relative change of the leading eigenvalue, i.e., a lower (higher) eigenvalue. In general, we are interested in expected valuesNote that the sign reflects an increase (positive) or a decrease (negative) of the stability, For each bipartite network analyzed, we reported the results of 100 realizations of the dynamics (unless otherwise indicated) for each scenario. For the sake of clarity, we show results for the five largest networks of different mutualistic interaction types: plant-pollinator (two of them), seed-dispersal, host-symbiont, and plant-ant Table .Table 1SFor our model, the breakup of the networks depended mostly on the extinction scenario, with a sharp decrease in size of the largest component with a few extinct resources in the directed scenario contrasting with a smoother decay in the random scenario Fig. . FurtherThe transformation of the modular structure over time with extinction-adaptation events shows that the removal of nodes and rewiring of links produce changes that affect the global organization of the mutualistic networks, as it can be qualitatively observed in the alluvial maps shown in Fig. Qe with rewiring. This is the case for the Coral Reef and Montane Forest networks . We clustered the empirical mutualistic networks and constructed a dendrogram of the empirical mutualistic networks based on the similarities of the response of the effective modularity to extinctions and rewiring  increases Qe more than any of the other scenarios. In the bottom panel of Fig. The effective modularity shows an idiosyncratic effect of the extinction-adaptation, in the sense that it depends mostly on the network analyzed and not on the specific extinction/rewiring scenario. In one extreme, bipartite networks show an increase in PM = 〈Πij〉. The extinction mechanism at play affects the results the most, as was the case for the robustness. The persistence of communities for random extinctions decays almost in a linear fashion as a function of the fraction of extinct resources, with a 50% probability to remain in the same community after 40% of the resources are removed. In contrast, for the directed extinction scenario, persistence decays to a baseline value of less than 30% when less than 20% of resources are removed  are in the same module for each extinction scenario but different adaptation, that is, we compared, on the one hand, RR with RF scenarios, and on the other, DR with DF. In both cases, resource affinity-driven rewiring leads to higher mean persistence values,   no new species enter the network and ii) only the binary presence/absence of interactions is considered (not interaction strength). For heterogeneous weight distributions, the results might differ and the dynamical rules have to be formulated to account for the weights. A parsimonious plasticity rule will introduce the rewiring probability as proportional to the weights, thus favoring species with interactions with the largest weights. This will likely introduce rich dynamics and can affect network plasticity depending on whether specialists or generalists have the strongest interactions.Mutualistic consumer-resource species interactions in ecosystems are well described by bipartite networks, where links inside the two groups of species are not allowed (between consumers and between resources)44: more complex and highly interconnected ecosystems are less likely to be stable. The trend we observe is that resource affinity rewiring leads to an increase of modularity, stability, and robustness in comparison to a random rewiring, which is used as a parsimonious rewiring. All these three properties are desirable for a mutualistic network as it provides resilience to disturbances. Thus resource affinity could be selected as an evolutionary mechanism to increase the survival of ecosystems. Earlier studies suggest that the adaptation mechanism in the topological approach increases the robustness of mutualistic networks to species removal67. Our results show that topological plasticity increases robustness, in agreement with those studies. Our simulations also suggest that resource affinity consumer rewiring induced by preferred species extinction is more detrimental to the robustness of the network than random rewiring.Altogether, we explored four extinction-adaptation scenarios to conclude that the extinction mechanism is crucial to determine the fate of the system concerning its robustness and stability. Directed extinctions lead to new networks that are less robust and more stable, an effect that decreases with growing rewiring probability. This result goes in the same direction as the seminal work by May68, at least for large connectance43 and especially for pollination networks69. Nevertheless, note that this relation is not mathematically proven except for the case of some models as in68. Stability is negatively correlated with nestedness as reported in some studies71, but positively correlated with modularity, in agreement with previous studies73. Positive correlations between robustness and modularity have been reported recently in plant-frugivore networks74. However, our results show a non-significant positive correlation between robustness and modularity.The increase in robustness is connected to changes in other structural metrics: modularity, stability, and robustness are positively correlated among them, but all negatively correlated with nestedness. Our results are consistent with the trends reported in these metrics although the literature shows some conflicting outcomes. Modularity and nestedness are observed to be negatively correlated, as found in several bipartite networks75. There is evidence for rewiring based on abundance78, temporal overlap79, trait matching83, and trait resemblance85. Temporal overlap, based on the phenology of the species, is a necessary condition for a rewiring among species to take place. So is it, to a certain degree, the abundance of species. Given that, species interactions might be constrained by the physiological capacity of one to interact with another, which is described by trait matching. This is the case for example in birds that can only pollinate certain species of flowers if the length of their bills coincides with the corolla length of the flowers. Another different but related case happens when a consumer decides to feed on a resource because another consumer species has a similar trait as his own. This is described by trait resemblance. Resource-affinity rewiring is a proxy for both trait matching and trait resemblance. On the one hand, in the absence of information about traits we expect that trait matching increases with resource overlap, that is, the more common resources are shared between pair of species more likely is that their traits match, On the other hand, we are using a stochastic approach, thus species can rewire to a resource that does not necessarily have the largest overlap, we are taking into account also trait resemblance. Trait matching is stricter than trait resemblance, and thus future innovations will require to consider nonlinear functions of the overlap to capture trait matching more precisely . The rewiring based on consumer overlap has been used in some literature, measures as Sorensen similarity index between a pair of plants proportional to the number of sharing pollinators over the sum of the pollinator species of both plants. This approach assumes that topological similarity is associated with phenotypic similarity (trait resemblance)86.The assumption that resource affinity may affect rewiring is based on the hypothesis that co-occurring species are functionally linked or equivalent. However, resource affinity rewiring patterns are rarely studied in ecosystems. In biological terms, such rewiring might imply that the likelihood that a consumer would use a particular resource used by a different species increases with the number of resources it shares with that species. In real ecosystems, there are several rewiring strategies taking place at the same time87. Whether this is the case in nature is not resolved, as dynamic rewiring of bipartite mutualistic networks following local extinctions are still poorly documented.Through analyzing a broad spectrum of bipartite mutualistic networks, we make the argument that evolutionary responses to the loss of species lead networks to become more modular, and the effect is largest when well-connected species were removed from the networks (directed extinctions). These responses could act in the same generation, as a behavioral response, or between generations as an evolutionary mechanism. Our results further demonstrate that adaptation in the form of resource affinity-driven consumer rewiring has the most significant impact on the degree of compartmentalization of the networks. This modular configuration of the network increases the capacity of absorbing disturbance (for example species loss) and hence has a positive effect on the dynamical stability of mutualistic networks. The effective network modularity shows a similar pattern for any of the extinction scenarios but depends on details of the original bipartite network, that is, the effective modularity is idiosyncratic. We also observed a marginal increase in effective modularity with resource affinity driven rewiring. Experiments show that, in agreement with theory, networks with a modular structure of species interactions benefit from localized dispersion of extinction88. Although there are many available resource species in the network, the set of plausible resources to rewire to is empty, as no other consumer that also used the extinct resource uses any of the available resources.Different scenarios lead a different number of unsuccessful rewiring attempts, thus some scenarios lose more links per extinction event than others. This can happen in two ways, either because the proposed rewired link already exists or because there are no plausible partners for the rewiring. The former happens for both rewirings, while the latter only in the resource-affinity rewiring. Nevertheless, we speculate that this consequence of resource-affinity rewiring can be interpreted as the existence of forbidden links90. The role of functional diversity in ecosystem stability has been previously explored based on simulated random extinctions84, but directed extinctions, as simulated here, were not assessed, nor was resource affinity used as a proxy of functional redundancy in previous simulation studies. Our analysis of the resilience of bipartite mutualistic networks predicts that functional redundancy should help stabilize biological networks against local extinctions. We put forward the hypothesis that resource affinity, as a proxy for functional redundancy, is a likely rewiring mechanism of mutualistic networks in the presence of local extinctions. That is to say, ecosystems have a higher chance of reconfiguration under species extinction. Testing these predictions through longitudinal observations of bipartite mutualistic networks or direct experimental manipulation is required to assess the value of resource affinity for ecosystems resilience, and implementing data-based plasticity mechanisms.We have shown that for the empirical bipartite networks, the normalized largest degree is correlated with the modularity of the original network. Thus, the success of niche compartmentalization with rewiring probability can be anticipated with the  largest degree. At the same time, nestedness showed to decrease as modularity increases, nestedness decreases. Finally, stability decreases as the largest degree correlate with stability. How ecosystems face disruptive, extreme events or continuous environmental changes cannot be predicted generically and requires specific knowledge on the species that will be most likely affected and the plasticity of the remaining species to reorganize the whole network. Our experiments with bipartite mutualistic networks consistently show that functional replacement, here modeled as resource affinity, can enhance the resilience of mutualistic networks by increasing the effective modularity as the bipartite networks lose species. Resource affinity is just a proxy for functional redundancy, which has been argued to add resilience to ecosystems under disturbanceSupplementary Information.


To develop recommendations for the management of rheumatic and musculoskeletal diseases (RMDs) during the COVID-19 pandemic.A task force comprising of 25 rheumatologists from the 5 regions of the continent was formed and operated through a hub-and-spoke model with a central working committee (CWC) and 4 subgroups. The subgroups championed separate scopes of the clinical questions and formulated preliminary statements of recommendations which were processed centrally in the CWC. The CWC and each subgroup met by several virtual meetings, and two rounds of voting were conducted on the drafted statements of recommendations. Votes were online-delivered and recommendations were pruned down according to predefined criteria. Each statement was rated between 1 and 9 with 1–3, 4–6 and 7–9 representing disagreement, uncertainty and agreement, respectively. The levels of agreement on the statements were stratified as low, moderate or high according to the spread of votes. A statement was retired if it had a mean vote below 7 or a ‘low’ level of agreement.A total of 126 initial statements of recommendations were drafted, and these were reduced to 22 after the two rounds of voting.The preliminary statements of recommendations will serve to guide the clinical practice of rheumatology across Africa amidst the changing practices and uncertainties in the current era of COVID-19. It is recognized that further updates to the recommendations will be needed as more evidence emerges. Since the advent of the COVID-19 pandemic and the rapid spread of the disease across the globe, the practice of rheumatology has found itself in the middle of crucial decision making and widespread service disruption. Across Africa, the impact of the pandemic is even more noticeable as there is a wide disparity in the availability and quality of healthcare services in the different countries and regions of the continent [The leadership of the African League Against Rheumatism (AFLAR) commissioned a task force to develop recommendations for the management of rheumatic and musculoskeletal diseases (RMDs) in the unprecedented situation of a continent faced with COVID-19. The task force had a very short time to deliver the project. However, the relatively delayed spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) across the continent a while after other continents such as Asia, North America and Europe allowed for some body of evidence to have been developed and recommendations made by other international rheumatology bodies which became available for the appraisal of the African team.The scope of the proposed recommendations was to address clinical questions encountered on a daily basis by the practicing rheumatologists in Africa in the complex situation where COVID-19 redefines clinical needs and standards. Recommendations were proposed to cover the management of RMDs among adult and paediatric patients in the context of COVID-19. The task excludes recommendations for the management of individual RMDs or the treatment of COVID-19. The lead and membership of the central working committee (CWC) and subsequently the full membership list of the larger task force were commissioned by the president of AFLAR to produce the recommendations within predefined deadlines.A hub-and-spoke model was adopted with the task force spreading out from the CWC formed by the leads of the four subgroups as well as the AFLAR president, an executive of the Pediatric African League Against Rheumatism (PAFLAR) and 2 members of the COVID-19 African Rheumatology Research Group. The leads of the subgroups were assigned and delegated with the tasks and the broad themes of each subgroup were as follows: subgroup 1, risk assessment and prevention of SARS-CoV-2 infection among patients with RMDs; subgroup 2, use of usual rheumatological treatments in patients at risk of SARS-CoV-2 infection; subgroup 3, treatment of patients with RMDs after exposure to known case of COVID-19; and subgroup 4, management of RMDs in patients infected with SARS-CoV-2. The subgroup leads were given the mandate to nominate the membership of their subgroups which were to be drawn from all five regions of the continent. The complete task force was made up of 25 practicing rheumatologists of which the scope of practice was adult only in 10, adult and paediatrics in 11 and paediatrics only in 4. In conjunction with other paediatric rheumatologists on the task force, the PAFLAR executive on the CWC led an independent review and representation of the paediatric-specific recommendations to the CWC.The CWC was set up on June 8, and the first virtual meeting was held on June 10 by video conferencing. The subsequent processes and timelines were agreed upon. The return of full preliminary list of task force membership was attained on June 12, and the submission of the first set of statements was completed by June 17. The first round of voting was held on June 20, while the second round commenced on June 21. Harmonization of statements and approval of final statements were completed on June 29.Published guidelines and recommendations of international rheumatology bodies outside Africa on management of RMDs in the context of COVID-19 were reviewed. This includes the recently published guidelines of the European League Against Rheumatism (EULAR), American College of Rheumatology (ACR), the Australian Rheumatology Association (ARA), the Asia Pacific League of Associations for Rheumatology (APLAR) and the National institute for Health and Care Excellence (NICE) of the UK –6. RelevThe primary target audience are practicing rheumatologists in Africa. This includes rheumatologists managing adult, paediatric or both categories of patients. The focus excludes patients, other physicians or policy-makers. However, recommendations covering advice to patients which are to be delivered by the rheumatologist are included.It was agreed that there is currently an insufficient body of evidence to conduct a meaningful systematic literature review. In addition, the short working timeline available to the task force precluded further delays. However, a limited non-systematic literature review was undertaken to support the largely expert opinion-based process. This was conducted between the 4 subgroup leads and harmonized in the CWC.Each subgroup was tasked to develop the clinical questions according to the theme of their subgroup and make preliminary recommendations to be submitted to the central working committee towards the first round of votes. The four subgroups turned in a total of one hundred and twenty-six preliminary statements of recommendation which were processed centrally. Overlaps, duplication and out-of-scope recommendations were removed or amended, and the first list for the first round of voting was agreed upon by the CWC. At the end of the first round of voting, there were twenty-four statements of recommendation. These were processed further into the second round of voting which led to the final agreement on twenty-two statements.Live online-delivered voting was done in two stages that were strictly time limited. All members of the task force were invited to participate and were pre-informed of the time of opening and closure of each round of votes. Unique access links were sent out, and anonymous votes were gathered and processed. Comments on re-phrasing, potential ambiguity, unidentified overlaps and so on were gathered regarding each statement at the same time in the voting process. Only the members of the task force who treat either both adults and children or children only voted on the statements that are specific to paediatric rheumatology.Each statement was rated between 1 and 9 with 1 being ‘complete disagreement’ and 9 being ‘complete agreement’. Generally, 1–3, 4–6 and 7–9 represented disagreement, uncertainty and agreement, respectively. There was no requirement to vote on all statements, and the members were encouraged to abstain if they felt that a statement fell outside their area of expertise. Therefore, an ‘uncertainty’ vote represented ‘unconvinced about the veracity of the recommendation’ and excludes ‘unsure of the current best practice in this context’. All statements were allowed for the entry of comments which were reviewed by the CWC after each round of voting. In the second round of votes, the members were further urged to leave comments wherever they voted a disagreement. This enabled the panel to identify an instance of misinterpretation of statement and invalidate the vote on that statement.The levels of agreement on each statement of recommendation were defined as ‘high’ if after the second round of votes, all votes on a statement fell into the agreement bracket; ‘low’ if at least one vote fell into each of the disagreement and uncertainty bracket or two or more fell into disagreement bracket; and ‘moderate’ for all other combinations. A statement was retired if it had a mean vote below 7 or a ‘low’ level of agreement.A total of twenty-two recommendations were generated, and a breakdown is presented in Table There is currently no evidence to say that patients with RMDs or on DMARDs are more prone to contracting SARS-CoV-2; therefore, the normal medications for various rheumatic diseases should be continued as indicated.The risk factors for getting infected with the novel coronavirus are similar for patients with RMDs as for the general populace, and these include older age and co-morbidities such as hypertension and diabetes , 7. PatiPatients should be routinely advised to observe regular infection-prevention practices against SARS-CoV-2 such as social distancing, frequent hand washing and wearing of face covering in public places.Standard infection-prevention practices should be frequently communicated and reinforced at every opportunity to the patients according to the recommendations in each member country of AFLAR , 3. ThisPatients should be advised to avoid using medicinal products with unproven efficacy against COVID-19. Such products could include herbal preparations, orthodox medicines, various supplements and complementary medications.It was recognized that a long list can be made of various unproven remedies which have attained different levels of fame in the media since the onset of COVID-19 pandemic. While this is not limited to Africa, the continent certainly has its fair share of promoted orthodox, herbal and complementary medicines of unproven efficacy against COVID-19. Some of these have been shown to be associated with some risks in earlier reports , 15.In a patient without COVID-19, it is safe to initiate or maintain the use of NSAIDs for RMDs where indicated.For many patients who depend on regular NSAID use for managing their RMDs, routine withdrawal of such treatment may be counterproductive to the goal of care. This is particularly noteworthy as exposure to NSAIDs has not been shown to increase the risk of infection with SARS-CoV-2. Whereas NSAIDs should generally be used in the lowest effective dose, the use in patients who go on to develop COVID-19 should be based on a favourable risk-benefit ratio , 16. CerIn a patient without COVID-19, oral or parenteral glucocorticoids may be used as indicated at the appropriate dose including pulse doses where necessary.It is recognized that the fear of glucocorticoid use in the era of COVID-19 may expose patients with organ-threatening diseases such as the vasculitides and aggressive connective tissue diseases to greater risks if appropriate interventions using the required immunosuppressive agents are not promptly adopted. Undoubtedly, patients with these conditions may face short-term risks of major organ damage or mortality without appropriate treatment . TherefoAnti-malarials such as HCQ and CQ do not protect against SARSCoV-2, and as such, patients on HCQ or CQ for RMDs should be advised to observe necessary precautions to prevent infection.Despite the in vitro anti-viral activities of HCQ and CQ which have been reported in various studies, these anti-malaria drugs have not been shown to prevent SAS-CoV-2 infection and patients with SLE on long-term treatment with anti-malarial drugs have not been shown to be spared from the infection or developing severe diseases . The tasWhere HCQ scarcity is being experienced, rheumatologists may consider using alternative csDMARDs for patients with rheumatoid arthritis.The recent pan-African survey through the network of the COVID-19 African Rheumatology Study Group has shown that shortage of HCQ was being experienced in more than 60% of rheumatologists’ services across the continent [Where possible, the use of subcutaneous formulations of bDMARDs and bsDMARDs should be considered instead of IV infusions to limit patients’ attendance to the hospital.The availability of biologic and biosimilar agents is highly varied across the continent of Africa. Many countries do not have access to any biosimilar drugs, and in others, the subcutaneous formulations of existing specific intravenously administered biologics are not available. It was agreed that rheumatologists will have to consider the options within the limit of the available agents in their country. However, the driving goal of limiting in-patient hospital visits for infusion administration should be pursued wherever possible.ACEIs and ARBs should not be routinely discontinued in patients with RMDs at risk of COVID-19.Whereas there is no evidence to suggest that ACEIs or ARBs increase the risk of SARS-CoV-2 infection, a large population-based study has revealed that the prevalence of use of these agents among patients with COVID19 is higher than in the general populace . This isPatients with stable RMDs should have their vaccination against influenza and pneumococci updated.The administration of influenza and pneumococcal vaccines to stable patients without COVID-19 was generally agreed upon. While it is not known if being vaccinated against influenza could reduce the severity of COVID-19, certainly, reducing this risk may cut down the potential confusion with COVID-19 among some patients , 24. TheRheumatologists should reduce patients’ hospital attendances by considering less frequent blood monitoring for DMARDs among stable patients, longer prescription periods and virtual clinics.Wherever routine blood monitoring for DMARDs requires the attendance of patients to the hospital, reducing the frequency of laboratory investigations among stable patients will likely be of benefit . This maRMD patients on glucocorticoids who have been exposed to SARS-CoV-2 should continue their glucocorticoids at the lowest effective dose for maintaining disease control.Recognizing the risk of adrenal suppression and the uncertain benefit of aggressive steroid tapering or withdrawal led to the task force agreeing on sustaining glucocorticoid treatments albeit at doses not more than required to keep treated conditions controlled. This seems to align with the recommendations of other international associations of rheumatology –4, 17.In patients who have been exposed to SARS-CoV-2 but are asymptomatic, continue anti-osteoporosis treatments including vitamin D and calcium supplementation.The task force noted that the widespread disruption of service may put osteoporosis service on a lower rung of priority than usual. In situations like this, efforts should be made, and patients are advised to sustain the ongoing use of osteoporosis prophylaxis or treatment in order to prevent the potentially devastating impacts of fragility fractures . While CFollowing exposure to SARS-CoV-2 infection, continue Pneumocystis jirovecii pneumonia (PJP) prophylaxis in a patient who is already on it.The appropriate use of PJP prophylaxis before the advent of the novel SARS-CoV-2 should not stop in the current pandemic. It is agreed that the potential confusion that may result from the presentations of both diseases can lead to avoidable clinical dilemmas especially as the impact of superimposed PJP on COVID-19 has not been determined. Anecdotal reports have now shown PJP pneumonia mimicking COVID-19, and recent guidelines have advocated the sustenance of PJP prophylaxis .Regardless of recent exposure to SARS-CoV-2, ACEIs and ARBs may be initiated or increased in a patient with RMD if indicated.Despite the fear that has been associated with the use of ACEIs and ARBs regarding SARS-CoV-2 infection, there has not been any evidence that the use of these drugs makes proven infection worse. The task force agrees that it is logical to sustain treatment with these drugs among patients who have ongoing indications for their use except if there are other clinical reasons for discontinuation. This is similar to the position of other professional rheumatology bodies in Europe and America , 17.Regardless of recent exposure to SARS-CoV-2, intra-articular steroid administration may be undertaken if indicated with the use of appropriate personal protective equipment (PPE).Where indicated, there is no evidence to avoid administering intra-articular steroids for patients where this is the best option of care after weighing the risk of hospital attendance. However, standard procedures regarding the use of personal protective equipment should be observed to limit the risk of transmission of SARS-CoV-2 infection between healthcare professionals and patients where such procedures are deemed justified .In an RMD patient with confirmed or presumed COVID-19, ongoing glucocorticoid treatment should not be stopped but should be maintained at the lowest effective dose.It is agreed that the abrupt cessation of ongoing long-term glucocorticoid treatment in patients who have been on it in the long term before developing COVID-19 serves to cause more problems than prevent unproven worse outcome. This is similar to the recommendation of the ACR and EULAR, and it was agreed that advising the patient in advance regarding the use of glucocorticoids in the event of developing COVID-19 will help to prepare them properly –4. In adIn an RMD patient with confirmed or presumed COVID-19, unless specifically indicated, routine stoppage of NSAIDs, analgesics, ACEIs or ARB is not required.Strictly speaking, the new diagnosis of COVID-19 should not be taken as an indication for discontinuation of analgesics, NSAIDs, ACEIs or ARBs. This recommendation is based on the lack of evidence of a worse outcome among patients on these treatments, where they are sustained throughout the management of their COVID-19 symptoms.Each rheumatology service should consider providing a helpline number to patients to use or for their doctors to use to seek rheumatological advice should they develop COVID-19.Various patterns of anxieties have been shown in the recent African survey of rheumatologists and their perception of their patients . Some ofThere is currently no proof that SARS-CoV-2 infection is transmitted through breastfeeding; thus, breastfeeding may be continued while observing personal hygiene precautions if a lactating woman has tested positive for SARS-CoV-2 infection.The nucleic acid of the SARS-CoV-2 virus has not been detected in breast milk, and it stands reasonable that the unlikely risk of transmission is much lower than the known benefits of continued breastfeeding. However, observation of standard infection-prevention practices should be advised . RoomingIn the event that a lactating mother with COVID-19 is too unwell to breastfeed the child, expressed breast milk or formula feeds should be considered, and these should be prepared using hygienic practices as recommended by government and regulatory bodies of the given region.Where the clinical status of the mother will make direct breastfeeding impractical, expressed breast milk is agreed on as an ideal feeding option, and this will not require pasteurization . FormulaAmong paediatric patients with suspected SARS-CoV-2 infection who have negative nasopharyngeal PCR test, PCR test on stool samples should be considered to help confirm the diagnosis.It may well be that relying only on the nasopharyngeal swab test for the diagnosis of COVID-19 in children will potentially lead to significant under-diagnosis, and, as such, it is agreed that faecal PCR test may be an additional screening method. Indeed, emerging data seem to suggest the possibility of faecal transmission as an additional route . This maIn the unprecedented experience of a world grappling with COVID-19, the task force was faced with a need to deliver a project backed by a limited amount of high-quality evidence. Certainly, this is a circumstance which rheumatology in Africa and beyond is not familiar with and which the rest of the world is currently struggling with as well. Preliminary preparation in the run up to setting out with this project included the consideration for commissioning a research and development company to conduct a systematic literature review of evidence in the shortest time possible. It soon became clear that the scanty amount and low quality of existing evidence on various relevant clinical questions as well as the lengthy duration needed for its execution made it an unworthy venture to proceed with. While a number of useful insights were drawn from the recommendations of national and international rheumatology societies outside Africa, aspects that are specific to paediatric rheumatology were excluded in most of these –4, 17. HA recognition of these variations meant that some flexibility is required with interpretation of some of these recommendations in the context of the prevailing local policies. Similarly, the relevance of some of the recommendations may succumb to the limit of available options of DMARDs and their formulations in some countries. Furthermore, the standard vaccination practices in some countries may dictate a contextual interpretation of the recommendation on influenza and pneumococcal vaccinations as provided in this document. It is recognized that with the emergence of more high-quality data over time, the need for current recommendations to evolve is acknowledged, and subsequent updated versions of these preliminary recommendations will be produced.In its history, this is the first time that the AFLAR convened an emergency task force to deliver a formal draft of recommendations within a very short time in circumstances that have not been experienced by any member of the task force before. The virtual convening, execution and delivery of the project with seamless efficacy within the limit of resources and published evidence, however, signal a future of more possibilities in executing daunting tasks under difficult circumstances and tight schedules. Whereas there are still unanswered questions about the management of RMDs in the world of COVID-19, we identify that there are endless needs for research and service improvement to deliver the best care to the African patients. The task force agreed to target rheumatologists and not policy-makers, other physicians or patients directly. However, relevant aspects of advice suitable for patients are directed towards the rheumatologist for delivery to the African patients.Certainly, patient education is crucial in the proper delivery of the safety practices and best approaches to dealing with RMDs in this precarious time of the pandemic. The coalition of national rheumatology societies within AFLAR will be a cornerstone in cascading the preliminary recommendations through their networks and working together to deliver subsequent updates with even more answers to clinical questions of wider pan-African spread. The immediate future calls for a continuation of seeking answers to various questions around the care for RMDs in the world of COVID-19, and it has become imperative that the lessons learnt so far be thoughtfully processed going forward.


The objective of this study is to develop a new vibration-free excavation method based on vermiculite expansion for rock cracking and to evaluate the performance of the heating system via elastic wave monitoring. Natural vermiculites expand rapidly in volume when heated above 800 °C. MgO powder is used to evenly transmit the surface temperature of a heater rod, which can attain high temperatures rapidly, to the vermiculites. The insertion direction of the heater rod greatly affects the expansion pressure. Three cuboid rock specimens are prepared and equipped with the heating system at different hole-to-face distances. Crack propagation is monitored by a pair of disk-shaped piezoelectric transducers. For short hole-to-face distances, the wave velocity and maximum amplitude rapidly decrease after certain time. For the greatest hole-to-face distance, the shear wave velocity remains constant during the test, while the maximum amplitude decreases after a certain time. The time taken for the velocity and amplitude of the shear waves to decrease reasonably corresponded to that taken for detectable crack propagation to occur on the surface of the rock specimen. The proposed method and materials may be useful from the viewpoints of rapid expansion, economy, and crack control. Various excavation methods are employed for constructing tunnels and underground spaces; drilling and blasting is one of the common excavation methods. However, the propagation of the stress waves, which are induced during the blasting process, to the ground surface may cause vibration and noise. To minimize such vibration, controlled blasting methods such as line-drilling and pre-splitting are used at the tunnel perimeter . NeverthVarious excavation methods were developed to reduce the blast-induced vibration. Jeng et al.  suggesteVibration-free excavation methods using non-explosive expansion materials have been widely used in rock quarry mining ,10,11. WMacroscopic brittle failure of rock induced by stress and thermal conditions can be observed easily by the naked eye. However, before brittle failure, microcracking can be detected by several methods such as a reflection technique based on acoustic emission, volumetric strain measurements, and elastic wave velocity monitoring . ElasticThis paper describes the development of a modified heating system based on vermiculite expansion for rock fracture and the monitoring of the performance of the heating system by using elastic waves. First, the material properties of vermiculite and its expansion characteristics are introduced. This is followed by a description of the modified heating system developed in this study. The process of the vibration-free excavation method based on the expansion of vermiculite is then explained. The piezoelectric transducers and experimental setup for elastic wave measurement are described. Furthermore, the analysis of the elastic waves propagated through three different large rock specimens using piezoelectric transducers is described. The elastic wave characteristics and elapsed time to crack propagation are discussed according to the distance from the borehole to the free face.17 Ω·cm) and high thermal conductivity (≥ 40 W/mK). The ratio of the amount of the vermiculite and MgO was experimentally determined [Vermiculite, a multilayer silicate mineral, consists of hydrated silicates of aluminum, magnesium, iron, calcium and potassium. When the vermiculite is heated rapidly over 800 °C, its volume increases up to 20–30 times. Note that the expansion depends on vermiculite composition . Expandetermined ,15.In this study, a modified heating system was developed to overcome the limitation of the inability of increasing the temperature rapidly in early research . Figure The structure of the heater rod was designed as shown in Three cuboid specimens of dimensions 500 (length) × 500 (width) × 400 (height) mm were prepared for the application of the heat-based expansion technique. Holes of depth 350 mm and diameter 50 mm were drilled in each rock specimen. A pair of disk-shaped piezoelectric transducers was used to monitor the crack propagation in a rock specimen. A pulse-transmission method using the two piezoelectric transducers was employed to directly estimate the dynamic properties of a material placed between the two transducers. An impulse signal was generated by a pulser  to excite the source transducer, as shown in The elapsed time after heating the system was recorded from 0 to 30 min, and the output signals were obtained from the elastic wave measurement system every 10 s. The typical waveforms obtained for a rock specimen with the elapsed time are plotted in The evolution of the shear wave velocity evaluated from the travel distance of the elastic wave and the first arrival time along the elapsed time is plotted in The maximum amplitude measured for each output signal was normalized with that measured for the output signal before heating. rT) along the hole-to-face distance is plotted in The surface of the rock specimen was observed by the naked eye during the expansion test to investigate crack propagation. For the three rock specimens, the crack propagation on the surface was located at the midpoint of the width of each specimen, as shown in vT and aT) are also plotted in The elapsed times until the fall in the velocity and amplitude of the shear waves (A new vibration-free excavation method based on vermiculite expansion for rock fracture was proposed in this study. The vermiculite-based filling material and rectangular heater rod were developed to improve the transfer of mechanical expansion from the borehole to the rock specimen. A modified heating system using a transformer resulted in both lower voltage for safety and higher current for rapid heating of the heater rod. The rectangular heater rod is durable at high temperatures owing to its large surface area and can be used to control the direction of rock cracking due to the difference in expansion pressure depending on the direction. Expansion tests were performed using the heating system and filling material for three large rock specimens with different hole-to-face distances. During the expansion tests, crack propagation was monitored by an elastic wave measurement system. For the two small hole-to-face distances, the wave velocity and maximum amplitude at the initial stage remained almost constant and then decreased after a certain elapsed time. For the greatest hole-to-face distance, shear wave velocity did not decrease, whereas the maximum amplitudes decreased after a certain time. The constant shear wave velocity maintained during the expansion test demonstrated that the rock crack in the specimen was influenced mainly by the mechanical expansion of vermiculite with minimal heat transfer from the heater at a high temperature. The elapsed times until the decrease in velocity and amplitude of shear waves reasonably corresponded to those until the crack propagation was detected on the surface of the rock specimens. In conclusion, the new excavation method with the expansion-induced materials has many advantages over other vibration-free methods in terms of rapid expansion, affordability, and crack control. The elastic wave monitoring system with the piezoelectric transducers may be effectively used to detect crack propagation when applying the heater system to a rock mass.


This work has the goal of detailing a best practice method and evaluate the reliability of this general-purpose algorithm for all the classes. Preliminary results show that most of the combinations of feature extraction and machine learning present acceptable results in most of the described corpora. Nevertheless, there is a combination that outperforms the others: the use of GTCC together with kNN, and its results are further analyzed for all the corpora.Acoustic event detection and analysis has been widely developed in the last few years for its valuable application in monitoring elderly or dependant people, for surveillance issues, for multimedia retrieval, or even for biodiversity metrics in natural environments. For this purpose, sound source identification is a key issue to give a smart technological answer to all the aforementioned applications. Diverse types of sounds and variate environments, together with a number of challenges in terms of application, widen the choice of artificial intelligence algorithm proposal. This paper presents a comparative study on combining several feature extraction algorithms (Mel Frequency Cepstrum Coefficients (MFCC), Gammatone Cepstrum Coefficients (GTCC), and Narrow Band (NB)) with a group of machine learning algorithms ( Years after the first surveillance systems, mainly based on camera networks , privacyAny acoustic event detection algorithm previously analyzed and evolved in the laboratory can today be easily deployed in a real-time signal processing Wireless Acoustic Sensor Network (WASN) , due to Detecting sounds in outdoor environments has also several applications ranging from traffic noise mapping in a city  to soundk-Nearest Neighbor (kNN), Support Vector Machines (SVM), and Gaussian Mixture Model (GMM), offer viable solutions [The AED process requires extracting acoustic features out of the data available and feeding them into a machine learning (ML) algorithm responsible for the classification. Multiple combinations of feature extraction (FE) methods and ML algorithms have been used in recent years on a wide range of scenarios. Mel Frequency Cepstrum Coefficients (MFCC)  are ofteolutions , the useolutions .This paper aimed to study multiple combinations of classical ML algorithms with FE methods. The goal was to use some of the most relevant FE methods, which include MFCC, GTCC, and Narrow Band Auto-Correlation Features (NB-ACF), in addition to several ML algorithms , to apply to different environments and corpora with the final goal of obtaining the most flexible classical acoustic event detection algorithm to be deployed in any low-cost acoustic sensor platform. Among the audio data chosen, there are indoor, outdoor, soundscapes, surveillance-related, and birds sounds distributed in five multi-class datasets. One of the main objectives was to spot the strengths and weaknesses of each FE/ML pairing while assessing their performance according to different kinds of sounds and corpora. Related literature often opts for a vertical approach centering on a particular set of data. Results vary according to the kind of sounds and the time window chosen when performing its detection and classification, making an across-the-board comparison difficult. The goal of this paper was to offer a more general approach to evaluate the performance comparison of all the implemented algorithms over the proposed scenarios. It is known from previous works that the training and test of machine learning algorithms varies substantially  when goiThis paper is structured as follows. In this section, we summarize some of the most relevant recent research on audio recognition and events detection in different environments, paying special attention to the ones that share the same FE methods and ML techniques chosen in this paper. As the number of studies on audio recognition is very extensive, only those that work with datasets similar to the ones in this project have been taken into account.AED is typically achieved by two sequentially performed stages consisting in a process of FE followed by a ML algorithm. Firstly, the FE method provides a feature vector for each portion of the chosen audio. This vector is a highly compacted representation of the given signal, which is imperative to reduce the computational cost of the following step. Secondly, the ML algorithm is trained with this representative data in order to create a model of the sounds of interest which, in turn, will be used to predict future apparitions of those.MFCC is probably one of the most broadly used methods in audio recognition, not only for speech  but alsoMFCC has been repeatedly used in studies about urban and road traffic environments. In Reference , authorsThis general use as a baseline method for features extraction is not restricted to outdoor and soundscape datasets. MFCC is chosen to perform a comparative between several classifying algorithms in Reference , using dFinally, MFCC has appeared multiple times in recent studies on bird songs recognition ,36, wherEven if MFCC is probably the most widely spread, there are other feature extraction techniques that are being used in AED and sounds recognition. GTCC, for instance, has been chosen lately in several AED studies showing improvements in the accuracy of the detection when combined with different machine learning algorithms. In Reference , GTCC waFor the specific case of soundscape classification, ACF and, specifically, Narrow-Band ACF (NB-ACF), have been used in the past years. For example, in Reference , Valero There are many classifying algorithms that appear consistently in many works related to multi-class AED. One of the most spread choices is the Gaussian Mixture Model (GMM), which appears in conjunction with all kinds of corpora in the literature.In the aforementioned reference , the feaBotaurus stellaris (an endangered bird species).In Reference , the indIn addition to Reference , kNN hasDifferent approaches to Neural Networks are being used as classifying methods: standard Neural Networks (NN), Deep Neural Networks (DNN), and Convolutional Neural Networks (CNN). It was already mentioned that DNN were used in Reference , but anoA total of five sound corpora were employed in this work, in order to widen the type of sounds and environments. In this section, the composition and origin of each corpus is described.The first corpus is a collection of indoor sounds originally compiled in Reference  from colThe second corpus is composed by 15 different outdoor general sounds collected from at least four different origins for guaranteeing data variability. It is composed by audio samples collected from common sound libraries , collabohttps://bksv.com/downloads/2250/be1713.pdf). They are high quality loss-less (WAV) recordings obtained at a sampling rate of 48 kHz. For diversity purposes, part of the corpus was complemented with samples extracted from Reference [The third corpus is composed by fifteen different soundscapes, including indoor and outdoor settings. A detailed description can be found in eference . Each soThe fourth corpus includes six classes of environmental surveillance-related sounds. This corpus was first used in Reference  and is cPicidae species obtained from the Xeno-Canto repository [The fifth and last corpus is thoroughly described in Reference . It is apository . The WAVA selection of spectrograms for some different classes of sounds contained in each corpus is shown in The third row shows three examples of sound scenes . The soundscapes, being formed by a combination of several sound sources, are quite unchanging in time  as can be seen in g and Fih even ifPicidae species contained in the fifth and last corpus can be found. While some birds have a repetitive call pattern, like the Dendrocopos medius . Most of these sounds are impulsive , which is a measure used in psychoacoustics to approximate the bandwidth of the human auditory filters in each point of the cochlea. For a given order n is the order of the approximation.The ERB is calculated as:i is the GT filter index, and N being the number of filters, and The central frequency of each filter Equation , i is thThe process of feature extraction using the aforementioned GT filter is analogous to the one described in N narrow band signals with the help of a Gammatone filter bank, and the autocorrelation function (ACF) is calculated on each of them. Finally, the ACF is analyzed by extracting the following adapted five parameters that are merged into a single feature vector [i-th narrow band signal τ1,ii-th band ACF signal (i-th band. Both i-th band crosses the zero amplitude level (de level .(8)AZCRTo implement this technique, the chosen signal is framed and an A-weighing filter is applied in order to model the spectral response of the human auditory system. Subsequently, the windowed signal is split into e vector :ϕi(0): eK instances that are deemed to be more similar following some appropriate measurement , as we can see in kNN  is a widNN are designed to model the human brain behavior when performing a particular task. As such, it is a parallel distributed machine that is constituted by simple processing units (neurons) with the capability of storing knowledge. This knowledge is acquired from the system inputs through a learning process and uses synaptic weights to store it .Several logistic units are structured in layers to form a neural network. There is always a first layer of input units followed by one or multiple hidden layers of neurons and by a final output layer. The activation functions are calculated using the different weights or parameters of the network.A neural network can be effectively used as a machine learning method by using a training dataset to compute the fitting weights of each internode relationship through a backpropagation algorithm. For further understanding of the way the backpropagation algorithm works, please read Reference , ChapterK component distributions that collectively make a mixture distribution i-th component.A mixture model is a combination of ion f(x) . In a GaThe GMM is a multimodal distribution that allows a clustering of the data similar to that achieved with the k-means algorithm . The goalgorithm .The goal of the following evaluations is to determine which of the pool of FE methods and ML algorithms chosen achieves better classification rates in the different evaluated datasets. To that extent, accuracy, in addition to recall, will be the main metrics used to sort out the different settings. Afterwards, the most accurate FE/ML pairing will be scrutinized via its confusion matrices in the search for the most often correctly and erroneously classified sounds.During the process of feature extraction, a sampling rate of 48 kHz was used. The framing of the input signal depends on the feature extraction method selected. A 30-ms frame length is chosen when working with MFCC and GTCC with a 50% overlapping of the time frame applied (15-ms step) . On the To generate the features vector through the baseline MFCC algorithm, the setup in An optimized GTCC implementation is used, adapted from the algorithm in Reference  with a GEquation .In the NB-ACF scenario, the framed signal is passed through a filter bank that splits the signal into eference . The fivA heuristic approach was used during the set-up of the ML algorithms. Sweeps involving several parameters were used to determine and choose the following higher-performers on a classification accuracy level. The number of neighbors from the kNN  and three machine learning algorithms  giving a total of 45 sets of results. It is unfeasible to explicitly include all the detailed results, including confusion matrices, in this present paper due to their extension. Nevertheless, all 45 sets were evaluated to draw the final conclusions.In this current work on audio classification, accuracy is defined as the ratio of correctly classified data frames to the total frames attempted .(10)AccWhen it comes to the machine learning algorithms, kNN outperforms both GMM and NN in most of the cases. Only the surveillance-related dataset gives GMM comparable or even slightly better results when combined with GTCC. GMM is second in the accuracy ranking, while NN lags behind. It is to be noted that the set GMM + NB-ACF struggles to converge when there is not enough data available in the dataset.As we can see in Some datasets’ results are more dependant on the combination of FE method and ML algorithm than others. In Some other metrics, such as Recall and F1-score, can give us some more insight and validate the results presented through the previous accuracy’s analysis. Recall or sensitivity is defined as the ratio of correctly predicted positive observations (true positives) to all the observations of the current class .(11)RecIndeed, in Firstly, in some of the datasets where kNN outperformed GMM at an accuracy level, they swap positions when Recall is taken into account. It is the case of the indoor and surveillance-related sounds. In both cases, the pairings of GMM with GTCC or MFCC offer better Recalls than the pairings of kNN with the same FE methods.Secondly, in the surveillance-related database, all NB-ACF solutions widely underperform GTCC and MFCC on a Recall basis. Not only do they offer a below par mean figure but also a larger variance, even with the normally robust kNN. This last observation is also confirmed with another metric, F1-score, which otherwise parallels accuracy top to bottom.As seen in Confusion matrices are shown in Most of the classes attain very high accuracy rates, no matter the database considered, except for one or two classes which are clearly below par. The classes that present higher confusion are shown in As for the second database, only applause has less than 95% of true positives, while up to 13 classes have over 98% accuracy. Nevertheless, this corpus present very stable results; with high accuracy values of classification and no clear deviation in the misclassification scenario, all the confusions present very low values of appearance.In the soundscapes dataset, the situation is similar to the indoor one with 11 classes over 95% and only libraries and offices below 93%. Despite the fact that the global performance of the FE and ML in this corpus is brilliant with accuracy values mainly over 90%, there are two clear confusions, between libraries and offices, which, by the way, present the lower accuracy values. In Dog barking obtains the worst result in the surveillance-related dataset, with just over 93%, and only two classes fail to reach 98% between the birds, i.e., major-drum and medius-song.Finally, some of the classes produce almost perfect classification records, with close to 100% accuracy rates, as seen in This paper presents a detailed evaluation of three FE methods , together with three ML methods , tested over five acoustic corpora corresponding to diverse environments , to be deployed to perform real-time in a WASN framework. Despite the fact that the used algorithms have been widely studied in the literature, a wide survey, including the combination of the three FE algorithms with the three ML procedures, against the five corpora, shows an extensive picture of the strengths and weaknesses of the different approximations. The results show a moderate to high accuracy and recall results for most of the combinations of the FE and ML methods, using a 4-fold cross-validation technique to obtain the results.The lower accuracy results are obtained by NB-ACF in situations where they have to support impulsive acoustic sounds, despite the fact that pairing with kNN presents the best possible results in soundscape detection. GTCC produces the best results in most of the corpora, outperforming MFCC, which is traditionally considered the baseline. In terms of ML algorithms, the best results are shown by kNN, apart from the surveillance-related corpus, where GMM shows similar results.These results lead us to present a general-purpose proposal using GTCC and kNN for all the corpora class identification. A deeper analysis of this combination manifests that the results show both high accuracy and recall, as well as that there are few classes in the indoor corpus and the soundscape corpus that present relevant confusion values. Nevertheless, we have to state that there is no mean accuracy value lower than 79% in any of the tests conducted by means of the 4-fold cross-validation.Future work is centered in testing all this test-bed over larger corpora to evaluate their generalization capability; in terms of the outdoor corpus, it will be tested over a wide suburban  and urba


Active nanoplasmonics have recently led to the emergence of many promising applications. One of them is the spaser (surface plasmons amplification by stimulated emission of radiation) that has been shown to generate coherent and intense fields of selected surface plasmon modes that are strongly localized in the nanoscale. We propose a novel nanospaser composed of a metal nanoparticles-graphene nanodisks hybrid plasmonic system as its resonator and a quantum dots cascade stack as its gain medium. We derive the plasmonic fields induced by pulsed excitation through the use of the effective medium theory. Based on the density matrix approach and by solving the Lindblad quantum master equation, we analyze the ultrafast dynamics of the spaser associated with coherent amplified plasmonic fields. The intensity of the plasmonic field is significantly affected by the width of the metallic contact and the time duration of the laser pulse used to launch the surface plasmons. The proposed nanospaser shows an extremely low spasing threshold and operates in the mid-infrared region that has received much attention due to its wide biomedical, chemical and telecommunication applications. Over the last decade, plasmonic nanosources have attracted significant attention as coherent and intense near-field generators of nanolocalized optical fields, eliminating the need for a coupling mechanism between photons and surface plasmons (SPs), and paving the way to many promising applications ,2. The sBecause the losses are often a serious limitation for practical applications of nanoplasmonics, many efforts have been devoted to proposing loss compensation and amplification approaches by introducing a gain medium in the dielectric surrounding the metal. Specifically, Seidel et al. reported the first experiment demonstrating amplification of surface plasmons on a flat silver film surrounded by dye molecules . This woDue to their ability to confine the optical energy near the surface, the spaser can utilize plasmonic components as its resonators to support the plasmonic modes and externally excited population-inverted gain media in order to provide the energy for spasing modes. The demonstration of spasing involves a resonant energy transfer from optical transitions in the gain medium to plasmon excitations in the metal, as well as a stimulated emission of surface plasmons due to the high local fields created by plasmons that excite the gain medium and stimulate more emission of selected plasmonic modes, leading to the required amplification .The performance of a spaser is limited by the relaxation rates of the surface plasmons and the gain medium. To overcome the former limitation, plasmons in graphene provide a suitable alternative to those of metals due to the high mobility of its charge carriers, leading to tight confinement and a relatively long propagation distance, as well as the tunability of graphene’s plasmons via electrostatic gating ,25,26,27However, the quantum well cascade suffers from nonradiative relaxation of electrons in the upper radiative state, due to thermally activated electron-longitudinal optical phonon scattering . InteresRecently, it has been shown that a metal nanoparticles-graphene nanodisks-quantum dots hybrid system can support the ultrafast energy transfer between excitons and plasmons . SpecifiClearly, there is continuous interest in developing novel spaser devices with lower spasing thresholds, a simplified but robust structure, high amplification and stable performance. In the present work, we propose a novel nanospaser composed of an MNP-GND hybrid plasmonic system as its resonator and a quantum dots cascade as its gain medium to take advantage of the tunability of long-lived plasmons in graphene  and the W, on top of a periodic lattice of GNDs, located at We aim to study the properties of the proposed spaser depicted in ing mode . Let us x-axis). The launching pulse induces the fields y-direction, the fields have transverse magnetic polarization (TM) with x-direction as:q is the wavenumber of the SPs waves propagating along the interface. In the following, the dependence on time will be dropped in order to simplify the notation and focus on the spatial dependence. Using Maxwell’s equations in the spectral representation, one can find:Consider a transform limited pulse propagating along the z-direction, with its linear polarization along the interface between the GNDs layer and the dielectric ExindW, which can be written as a Fourier expansion:Combining Equations  and 3)  3) leadsll space :6)ExEx,uBy,uThe propagation of surface plasmons is governed by the dispersion relation derived by using the condition of the discontinuity of To study the properties of the proposed MNPs-GNDs-QDs hybrid-system-based spaser, we focus on the z-component of the electric field, which describes the confined plasmonic field in the direction perpendicular to the interface, since the dipole transitions of the gain medium are only allowed along this direction . Let thee medium :(15)14∫dt and Fermi energy Solving Equation  yields ts placed:E^z,u=4ħωEquation :(18)dudωThe model of the proposed mid-infrared MNPs-GNDs-QDs hybrid-system-based spaser is shown in ate γout .e is the charge of an electron, affects the coherence and population terms that are related to the upper level [In the presence of a SPs mode resonant with the dipole transition energy given by :(26)Lρ=γ(mQD) as :(27)γoutgiven as :(28a)ρ˙z-direction, we focus on the z-component of the electric field given by Equation Eτ≥τmv et al. , implyinClearly, the transient regime represents the region where the spaser can act as a plasmonic amplifier with a gain exceeding the losses, achieving an amplification of a selected mode of SPs that can be controlled by the width of metallic contact and the time duration of the launching pulse, leading to an enhancement of plasmonics.In this paper, we have studied the properties of the proposed MNPs-GNDs-QDs hybrid-system-based spaser. Firstly, we investigated the confined plasmonic fields near the interface of the GNDs lattice with a metallic contact, represented by an Ag NPs lattice, induced by the launching pulse that has its linear polarization along the interface between the GNDs layer and the dielectric environment. We have found that the plasmonic field can be enhanced for a small width of the metallic contact and a small dielectric constant of the surrounding medium, because then the retardation effects are limited. Moreover, the confined plasmonic field is enhanced for a small thickness of the GNDs and large doping levels that lead to a relatively large density of charge carriers. A large packing density in the MNPs lattice compared to that of the GNDs can also significantly enhance the confined plasmonic fields.Subsequently, we have studied the dynamics of the proposed spaser with a GaN QDs cascade emitter chosen to be the gain medium. A novel MNPs-GNDs-QDs hybrid-system-based spaser is obtained with a transient amplification of the SPs mode, providing a plasmonic amplifier. The number of SPs that determines the intensity of the obtained plasmonic field is significantly affected by the width of the metallic contact, emphasizing the important role of the MNPs lattice in the spasing process. In particular, the presence of an MNPs lattice provides more options for controlling and enhancing the amplification of the plasmonic fields.Interestingly, the various factors in our scheme, which was identified to affect the amplification of the plasmonic fields, act cooperatively and cumulatively. They are within reach of present-day materials technology, and various combinations of them, within the theoretically identified limits, could result in plasmonic amplifiers with a low spasing threshold and significant amplification. This feature adds a degree of flexibility in the realization of the herein proposed plasmonic amplifier. Therefore, the proposed controllable SPs amplification scheme could prove useful for various interesting applications, such as stand-alone components or gain sections integrated with other plasmonic elements to compensate for losses and improve the performance of plasmonic devices.


In wireless sensor networks (WSNs), detection and report of continuous object, such as forest fire and toxic gas leakage, is one of the major applications. In large-scale continuous object tracking in WSNs, there might be many source nodes simultaneously, detecting the continuous object. Each nodes reports its data to both a base station and mobile workers in the industry field. For communication between the source nodes and a mobile worker, sink location service is needed to continuously notify the location of the mobile worker. But, as the application has a large number of sources, it causes a waste of energy consumption. To address this issue, in this paper, we propose a two-phase sink location service scheme. In the first phase, the proposed scheme constructs a virtual grid structure for merging the source nodes. Then, the proposed scheme aggregates the merging points from an originated merging point as the second phase. Simulation results show that the proposed scheme is superior to other schemes in terms of energy consumption. The amount of damages from either disasters or accidents is influenced by the level of the prevention and countermeasures system. Especially, in case of the distant areas from the social infrastructures, such as a mountainous region and a forest area, a prevention system exerts a stronger influence then the case of a downtown area because of their low accessibility. As a promising solution for a prevention system in inhospitable areas, Wireless Sensor Networks (WSNs) have been receiving significant attention. A WSN consists of low-cost and small sensor nodes and is able to provide sensing information to remote users by self-organizing manner. These advantages enable construction of high-level prevention systems using WSNs with low-price. This paper is the part of an effort to facilitate advanced disaster prevention and environment monitoring system using WSNs. Concretely, we focus on increasing the usefulness by reducing energy consumption in communication parts. After sensor nodes are deployed in interested field, they organize a network by self-organizing manner. The information about the base station, called a sink, is embedded into sensor nodes before deployment or advertised on the network after deployment. Once an event is occurred, the sensor nodes exchange messages with each other to elect a reporting node, called a source. The source generates a data packet and sends it to the sink by multi-hop transmission. These features leverage the applications of sensor networks ranging from military surveillance to habitat monitoring ,2.Object tracking is one of the important applications in WSNs where sensor nodes detect where and when the object exists. There have been many researches on object tracking with sensor networks. Target objects are divided into two categories: individual objects and continuous objects. The individual objects usually have very small size comparing with the large area with sensor network deployed. An individual object is sensed by one or few sensor nodes. For example, an individual object might be an animal in habitat monitoring or an intruder in military surveillance.In contrast with the individual object, a continuous object is a large-scale phenomenon which is originated from a specific point  and spreads continuously. Then, the continuous object occupies large area and it is detected by many sensors simultaneously. The continuous object might be fire in forest fire monitoring system and harmful gas in leakage alarm system. Therefore, continuous object tracking is suitable for prevention of disasters and environment monitoring. Sink mobility support: In case of a static sink, it is possible that providing sensor nodes with its location information as a priori knowledge because its location is fixed. On the other hand, a mobile sink has to notify its location to the network periodically because it moves continuously.Reducing data report cost: Because a continuous object is a very large phenomenon and continuously diffuses, the detecting information generated by a number of sources brings considerable communication overhead for reporting data. The overhead might shorten network life time. To prolong network lifetime, the data report cost have to be reduced.In the scenario described above, the applications should satisfy the following requirements:The existing continuous object tracking studies ,9,10,11 Intuitively, the most simple approach is the flooding. A mobile sink could notify its current location by flooding the location to whole network like To avoid the problems in flooding-based or intermediary-based approach, the adoption of existing studies for supporting sink mobility is a reasonable alternative. One of the most important issues in sink mobility support studies is how to notify the current location of a mobile sink. However, the studies are not suitable in continuous object tracking because they have dealt with not continuous objects but individual objects. In case of tracking individual objects like We intensively investigated the energy efficiency in continuous object tracking with mobile sink by analyzing the location update and data report to prevent hot spot problem and to prolonging network lifetime.The proposed scheme provides the integrated location update by mobile sink and distributed data report for reducing overall energy consumption and mitigating hot spot problem.Our simulation results in various environment provides the analytical insights for revealing the radical limitation of the existing schemes and the key principles of the proposed scheme thereby promoting the future developments.Our aim is to design an energy efficient sink mobility support scheme for continuous object tracking. The previous continuous object tracking researches focus on reducing communication cost of reporting data from a number of sources without considering of sink mobility. Unfortunately, the existing studies for supporting sink mobility are inappropriate in continuous object tracking because they have dealt with individual objects. To facilitate advanced continuous object tracking, the sink mobility support scheme being suitable for continuous object tracking is required. The main problem in existing sink mobility support studies is the individual location updates to the sources detecting a continuous object. The location updates are essential for supporting sink mobility, but lead to wasting energy. Our previous work focuses on the connection the origin point to each sinks . We exteThe rest of the paper is organized as follows. We present the related work in WSN is used for various applications such as forest fire monitoring, gas leakage monitoring, and radiation monitoring because it is easy to use and provides cost-efficiency and flexibility compared to wired networks . For exaIn wireless sensor networks, several protocols to detect and track continuous object have been developed. They focus on how to efficiently detect the continuous object and reduce the amount of reports about continuous object toward a static sink. On the other hands, many protocols to support sink mobility have been proposed with the aim of disseminating data to mobile sinks. In this chapter, we briefly introduce continuous object tracking schemes and evaluate the protocols for sink mobility support with features of continuous object tracking.According to ,18, sinkA number of WSN researchers have interested in supporting sink mobility . They assource-based structure and independent structure.In such a context, the difficulty for sensor nodes is to efficiently update the mobile sink location to report sensor data. In many researches, overlaying a virtual infrastructure over the physical network has been investigated as an efficient strategy for an effective data dissemination to mobile sinks ,22. TheySome researches on the sink mobility exploit source-based structure. In the approach, a source detecting an event initiates construction of a structure. The structure provides the route tending to the source on whole network. A mobile sink might loads location update message thereby delivering the message to the source. The source reports detecting data to the sink through the reverse route. The most representative is Two-Tier Data Dissemination (TTDD) model for large-scale WSNs .In TTDD, once an event is detected, the source pro-actively builds a virtual grid structure, as shown in On the other hands, in continuous object tracking, TTDD might causes a serious dissipation of energy. As mentioned above, in TTDD, the grid structure is constructed by a source as the initiator. In continuous object tracking, a number of sources are generated because a continuous object is large and diffusing continuously. Therefore, the sources initiate the construction of grid structures respectively like in Meanwhile, several researches exploit independent structure for supporting sink mobility ,24,25,26w wide and consists of h sized groups. The line is placed in the center of the sensor field so that sensor nodes and a mobile sink might easily access it. The nodes within the line are In LBDD, the independent structure is vertical virtual node① in  left. Thnode① in  left. Thnode① in  left. EvHowever, in continuous object tracking, LBDD might lead to a serious concentration of messages. Inherently, all messages generated in the sensor field, including data from sources and queries from sinks, pass through the line area like in Existing continuous object tracking studies focus on reducing reporting cost considering a static sink. To support sink mobility, the adoption of existing sink mobility support researches is a reasonable solution. The researches provide sink mobility efficiently in individual object tracking by overlaying virtual structures. However, in continuous object tracking, they cause critical problems shown as following A mobile sink should notify its current location to sources to collect data from the interested data. Generally, the location update message is directly delivered by unicasting. Namely, the location update cost increases proportional to the number of sources. So, in continuous object tracking, the location update consumes an amount of energy because a continuous object is detected by a number of sources. In energy constrained WSNs, reducing the cost of sink location update should be considered.R for presenting the efficiency of the integrated location updated compared to the individual location update asx is the x-coordinate of the location agent, n is the number of boundary points  when the location agent is within the continuous object. The cost of the integrated location update tends to decrease as the agent is closer to the center of the continuous object whereas the value increases sharply as the agent far from the continuous object. Second, the location of the agent should be fixed and unique. In R is approximately 0.1 . It means the most efficient location of the agent is not deterministic but vary according to the shape of the continuous object and the location of the sink. However, calculating the most efficient location is extremely difficult because it has to consider both the location of a mobile sink and the locations of all sources in real time. Moreover, the location update process for the agent is needed if the agent’s location can be changed. To summarize, we derive the following requirements about an agent from above observation.An agent should be within targeted continuous object.An agent should be at fixed and unique location.We select the origin point of a continuous object as an agent. Generally, a continuous object tends to be originated at specific point and to diffuse slowly. With the features, designating the origin point as the location of an agent completely satisfies above requirements. First, the origin point is located within a continuous object because the continuous object diffuses toward its surroundings. Second, the origin point is fixed although the continuous object changes its shape and size. Additionally, there is no need to calculate the location of the origin point because it is surely detected by a specific source. With the origin point, we exploit overlaying virtual structure for supporting sink mobility. The structure should satisfy the following design principles: construction of structure regardless of the number of sources and decentralization of messages for avoiding hot-spot problem.We exploit the origin-based structure for supporting sink mobility. The brief introduction of our design is as followings. The origin-based structure delivery location update messages from mobile sinks to the origin point. The node on the origin point is responsible for forwarding the messages to sources. The sources receiving the location update message report data to the sink’s location in the messages directly. The origin-based structure is constructed regardless of the number of sources. Moreover, the direct data reporting prevents concentration of messages of the structure. With this, our design satisfies above principles. Additionally, we exploit clustering to reduce data report overhead.A two-dimensional sensor field is covered by a large number of homogeneous sensor nodes which communicate with each other through short-range radios. So, long distance message delivery is achieved by multi-hop transmission. All sensor nodes in the sensor field are aware of their own locations through either the GPS  or otherThe sensor nodes are periodically awoken and observe the targeted object. Once a stimulus appears or the message is forwarded at specific geographical location, the sensors surrounding it collectively process the signal and one of them becomes the source of the stimulus or the destination of the location.The scheme uses simple greedy forwarding  as underWe assume for the design of OCOT as followings:grid construction messages to the four neighboring grid points. When the location of the origin node is When a continuous object occurs at the origin point, the first source node becomes the origin node that starts the construction of grid structure. The messages spread the whole network and the node closest to each grid point becomes the grid node. A grid node keeps the information about the grid point O indicated with a black square, and its virtual grid structure. The black dots indicate grid points and the white triangles around each grid point are the grid nodes. The gray area indicates a cluster. After the grid structure and clusters are completely built in the sensor field, all sensor nodes become to know their cluster heads, to whom they should deliver their detection information. The cluster head receiving data from ordinary nodes becomes boundary cluster head and has responsibility for data reporting to sinks.A in A is activate node because its all neighbors detect the continuous object, so it does not report data to the cluster head. The number of boundary nodes K can be estimated by calculating boundary area. For example, the continuous object has circular shape,R is the radius of the continuous object, and r is the communication range of sensors. If R is 100 m and r is 15 m, the A continuous object gets a great number of sensor nodes activated so it is more efficient to gather detection information only from boundary nodes rather than all activated sensor nodes. As an integrated location update scheme, in OCOT, the location update message from the mobile sink is delivered to the origin node through the grid structure as shown in We evaluate our Origin-based Continuous Object Tracking (OCOT) through computational simulation with existing studies: TTDD  and LBDDWe choose two metrics to analyze the performance of OCOT. The total energy consumption is defined as the communication  energy the network consumes during a simulation round. The total energy consumption means efficiency of message delivery. The idle energy is not counted since it depends largely on the message generation interval and does not indicate the efficiency of massage delivery. Thedistribution of energy consumption is the map including the location of each node and used energy of the node. We might deduce the possibility of the hot-spot problem in each scheme from the distribution of energy consumption. We divide the network into 20 × 20 cells and observe the average used energy of the nodes in each cell. We implement OCOT in MATLAB . The defUnfortunately, comparison with existing studies is not reasonable because they focus on sink mobility support in individual object tracking. So, we assume that TTDD and LBDD have exploited DCS  for tracThe distribution of energy consumption indicates the operational efficiency and existence of hot spot problem. Therefore, we can tangibly estimate overall energy efficiency and network lifetime. We divide the 1000 m × 1000 m network into 20 × 20 cells and observe the average used energy of the nodes in each cell. In this paper, we propose a novel continuous object tracking scheme, Origin-based Continuous Object Tracking (OCOT), which provides energy-efficient sink mobility support in wireless sensor network. OCOT integrates location updates from a mobile sink using regional locality of sources detecting a continuous object. Also, OCOT exploits distributed data report to avoid the hot-spot problem. Additionally, the reactive and static clustering in OCOT increases the efficiency of location update and data report. Simulation result proves that OCOT is greatly efficient in terms of the total energy consumption and distributional energy consumption. Especially, OCOT reduces at least 49% of energy compared to the existing scheme during 100 s of continuous object tracking process. Under the same simulation setting, in addition, the over 7.25% and 1.25% of sensors consumed over 25% of the energy budget in the existing schemes and OCOT respectively, which suggests that the enhanced network lifetime of OCOT.