Finite-time average consensus in a Byzantine environment using Set-Valued Observers

This paper addresses the problem of consensus in the presence of Byzantine faults, modeled by an attacker injecting a perturbation in the state of the nodes of a network. It is firstly shown that Set-Valued Observers (SVOs) attain finite-time consensus, even in the case where the state estimates are not shared between nodes, at the expenses of requiring large horizons, thus rendering the computation problem intractable in the general case. A novel algorithm is therefore proposed that achieves finite-time consensus, even if the aforementioned requirement is dropped, by intersecting the set-valued state estimates of neighboring nodes, making it suitable for practical applications and enabling nodes to determine a stopping time. This is in contrast with the standard iterative solutions found in the literature, for which the algorithms typically converge asymptotically and without any guarantees regarding the maximum error of the final consensus value, under faulty environments. The algorithm suggested is evaluated in simulation, illustrating, in particular, the finite-time consensus property

Distributed Fault Detection Using Relative Information in Linear Multi-Agent Networks

This paper addresses the problem of fault detection in the context of a collection of agents performing a shared task and exchanging relative information over a communication network. We resort to techniques in the literature to construct a meaningful observable system and overcome the issue that the system of systems is not observable. A solution involving Set-Valued Observers (SVOs) is proposed to estimate the state in a distributed fashion and a proof of convergence of the estimates is given under mild assumptions. The performance of the proposed algorithm is assessed through simulations

Fault detection for LPV systems using Set-Valued Observers: A coprime factorization approach

This paper addresses the problem of fault detection for linear parameter-varying systems in the presence of measurement noise and exogenous disturbances. The applicability of current methods is limited in the sense that, to increase accuracy, the detection requires a large number of past measurements and the boundedness of the set-valued estimates is only guaranteed for stable systems. In order to widen the class of systems to be modeled and also to reduce the associated computational cost, the aforementioned issues must be addressed. A solution involving left-coprime factorization and deadbeat observers is proposed in order to reduce the required number of past measurements without compromising accuracy and allowing the design of Set-Valued Observers (SVOs) for fault detection of unstable systems by using the resulting stable subsystems of the coprime factorization. The algorithm is shown to produce bounded set-valued estimates and an example is provided. Performance is assessed through simulations, illustrating, in particular that small-magnitude faults (compared to exogenous disturbances) can be detected under mild assumptions

Self-Triggered and Event-Triggered Set-Valued Observers

This paper addresses the problem of reducing the required network load and computational power for the implementation of Set-Valued Observers (SVOs) in Networked Control System (NCS). Event- and self-triggered strategies for NCS, modeled as discrete-time Linear Parameter-Varying (LPV) systems, are studied by showing how the triggering condition can be selected. The methodology provided can be applied to determine when it is required to perform a full (``classical'') computation of the SVOs, while providing low-complexity state overbounds for the remaining time, at the expenses of temporarily reducing the estimation accuracy. As part of the procedure, an algorithm is provided to compute a suitable centrally symmetric polytope that allows to find hyper-parallelepiped and ellipsoidal overbounds to the exact set-valued state estimates calculated by the SVOs. By construction, the proposed triggering techniques do not influence the convergence of the SVOs, as at some subsequent time instants, set-valued estimates are computed using the \emph{conventional} SVOs. Results are provided for the triggering frequency of the self-triggered strategy and two interesting cases: distributed systems when the dynamics of all nodes are equal up to a reordering of the matrix; and when the probability distribution of the parameters influencing the dynamics is known. The performance of the proposed algorithm is demonstrated in simulation by using a time-sensitive example

Analysis of the magnetic coupling in binuclear complexes. II. Derivation of valence effective Hamiltonians from ab initio Cl and DFT calculations

Most interpretations of the magnetic coupling J between two unpaired electrons rest upon simple valence models that involve essentially the ferromagnetic direct exchange contribution, Kab , and the antiferromagnetic effect of the delocalization resulting from the interaction between neutral and ionic determinants, tab , whose energy difference is U. Ab initio valence-only calculations give very poor estimates of J, whatever the definition of the magnetic orbitals, and large CI expansions are required to evaluate it properly. It is, however, possible to define valence effective Hamiltonians from the knowledge of the eigenenergies and the eigenvectors of these accurate CI calculations. When applied to four different complexes, this strategy shows that spin polarization may change the sign of the direct exchange interaction, Kab , and that dynamical correlation results in a dramatic reduction of the effective repulsion U. The present article also shows how Kab , tab , and U effective parameters can be extracted from density functional theory ~DFT! calculations and that the typical overestimation of J in DFT can be attributed to an excessive lowering of the effective on-site repulsio

Analysis of the magnetic coupling in binuclear systems. III. The role of the ligand to metal charge transfer excitations revisited

In magnetic coordination compounds and solids the magnetic orbitals are essentially located on metallic centers but present some delocalization tails on adjacent ligands. Mean field variational calculations optimize this mixing and validate a single band modelization of the intersite magnetic exchange. In this approach, due to the Brillouin’s theorem, the ligand to metal charge transfer LMCT excitations play a minor role. On the other hand the extensive configuration interaction calculations show that the determinants obtained by a single excitation on the top of the LMCT configurations bring an important antiferromagnetic contribution to the magnetic coupling. Perturbative and truncated variational calculations show that contrary to the interpretation given in a previous article C. J. Calzado et al., J. Chem. Phys. 116, 2728 2002 the contribution of these determinants to the magnetic coupling constant is not a second-order one. An analytic development enables one to establish that they contribute at higher order as a correlation induced increase in the LMCT components of the wave function, i.e., of the mixing between the ligand and the magnetic orbitals. This larger delocalization of the magnetic orbitals results in an increase in both the ferroand antiferromagnetic contributions to the coupling constan

Parasitismo em canídeos do Concelho de Óbidos

Apresentação em painelO grande interesse manifestado pelos Serviços Veterinários Municipais do Concelho de Óbidos na implementação de medidas preventivas para minimizar os riscos de contaminação ambiental e de Saúde Pública, levou à realização dum estudo, durante o ano de 2009, nos canídeos deste concelho com vista à identificação do parasitismo e determinação dos períodos e áreas de maior risco de contaminação. Nas nove freguesias, recolheu-se um total de 548 amostras de fezes de canídeos (5,00 % do efectivo canino). Realizaram-se análises coprológicas qualitativas (métodos de Willis e sedimentação espontânea) e quantitativas (método de McMaster). Efectuaram-se ainda colheitas de ixodídeos em cerca de 10% da população de cães, durante o período de Vacinação anti-rábica e o seu estudo taxonómico baseou-se em Travassos Dias (1994) e Walker et al. (2000). Das amostras de fezes observadas, 274 (50%00 %) apresentaram formas de eliminação parasitária. Nas amostras positivas identificaram-se ovos de Ancylostomatidae (79,92%), (Ascarididae - Toxocara canis e Toxascaris leonina) (12,04%), Trichuris sp. (40,15%), Strongyloides sp. (18,98%), oocistos de Isospora sp. (2,55%) e Sarcocystis sp. (0,37%) e proglótides grávidos de Dipylidium caninum (0,74%). A prevalência variou consoante a freguesia em estudo (mínimo - 15,63%, em Sobral da Lagoa; máximo – 73,86%, no Vau). Predominarem as infecções simples na maioria das freguesias (55,56%), no entanto, quatro delas (44,44%), apresentaram superioridade de associações mistas (A-dos-Negros, Olho Marinho, Usseira e Vau). O estudo estacional permitiu evidenciar um aumento do número de amostras positivas, ao longo do ano: Inverno - 9,67%; Primavera - 11,86%; Verão - 13,50%; Outono - 14,96%. Com excepção do Inverno, onde se registou maior gravidade das infecções com superioridade de associações (50,94%), nas restantes estações, predominaram as infecções simples. No estudo dos ixodídeos, a carga parasitária média por animal foi de 5 exemplares. Predominaram os exemplares adultos (98,80%) relativamente às formas imaturas (1,21%). Verificou-se uma maior preponderância de machos (90 exemplares, 54,22%), relativamente às fêmeas (74 espécimes, 27,82%). Nos 166 exemplares colhidos identificaram-se duas espécies: Rhipicephalus sanguineus, com 150 exemplares, o que corresponde a 90,36%, e Rhipicephalus pusillus, com um total de 16 espécimes (10 machos e 6 fêmeas), equivalente a 9,64%. The great interest showed by the Veterinary County Offices on the implementation of prophylactic measures to minimize the risks of parasitic environmental contamination by dog faeces and its impact on Public Health, led to a study, to understand the existing parasitism and to assess the period and area of major risk of transmission. A total of 548 dog faeces samples (5% of the local canine population) was collected from public spaces, pavements, gardens and abandoned fields in nine sites. Coprological exams were performed by qualitative (Willis and spontaneous sedimentation methods) and quantitative techniques (McMaster method). Ixodid specimens were also collected from 10% of the local canine population, during the anti-rabic vaccination, and identified based on Travassos Dias (1994) and Walker et al. (2000) criteria. Egg output was registered in a total of 274 (50%) samples. Ancylostomatidae (79,92%), (Ascarididae - Toxocara canis and Toxascaris leonina) (12,04%), Trichuris sp. (40,15%) and Strongyloides sp. (18,98%) eggs, and Isospora sp. (2,55%) and Sarcocystis sp. (0,37%) oocysts were observed. Gravid proglotids of Dipylidium caninum (0,74%) was also evidenced. In the study area the overall prevalence varied from 15,63%, in Sobral da Lagoa to 73,86%, in Vau. Simple infection was predominant in the great majority of the studied areas, although four of them showed higher co-infections (A-dos-Negros, Olho Marinho, Usseira and Vau). Seasonal study enhanced an increase in the number of positive samples along the year (Winter - 9,67%; Spring - 11,86%; Summer - 13,50%; Autumn - 14,96%), excluding the Winter period, when more severe infections related to co-infections were noticed (50,94%), simple infections prevailed. In ixodid studies, the average of parasitic load was 5 specimens for dog. Adults were predominant (98,80%) in relation to immature (1,21%) and the number of males (90 specimens, 54,22%) was higher than females (74, 27,82). In a sample of 166 ixodids two species were identified: Rhipicephalus sanguineus, (150 individuals, 90,36%), and Rhipicephalus pusillus, (16 specimens, 9,64%)

Four-spin cyclic exchange in spin ladder cuprates

The four-spin cyclic exchange term Jring of three spin-ladder cuprates (SrCu2O3, Sr2Cu3O5, and CaCu2O3) has been calculated from ab initio quantum chemistry calculations. For the first two compounds, a non-negligible cyclic exchange is found, aproximately 20% of the magnetic coupling across the rungs, J⊥, and always larger than the value obtained for two-dimensional La2CuO4 system. In the case of CaCu2O3, the Jring value is quite small, due to the folding of the Cu-O-Cu rung angle, but the Jring/J⊥ ratio is also 0.2 as in the two other system

Ixodídeos em cães do concelho de Óbidos

Apresentação em PainelNo sentido de se conhecer o papel do cão na manutenção do ciclo de vida de ixodídeos no concelho da Vila de Óbidos, efectuaram-se observações e sua colheita em cerca de 10% da população de cães das freguesias daquele concelho, entre Maio e Junho de 2009, durante período de Vacinação anti-rábica efectuada pelos serviços oficiais. A pesquisa de ixodídeos e a sua colheita realizou-se manualmente, tendo sido acondicionados em tubos de PVC e conservados em álcool a 70º, devidamente identificados. O estudo das características morfológicas baseou-se em Travassos Dias (1994) e Walker et al. (2000). Dos animais observados, 34 estavam parasitados por ixodídeos, com um número médio por hospedeiro de 5. A identificação revelou que, à excepção de um único exemplar (R. bursa), todos os outros se incluem no grupo Rhipicephalus sanguineus, com a seguinte distribuição: 149 exemplares (89,76%) apresentam semelhanças morfológicas compatíveis com R. sanguineus e 16 (9,46%) identificaram-se como R. pusillus. Os autores referem-se a diversos tipos morfológicas nos machos e na genitália das fêmeas observada nos exemplares de R. sanguineus, o que poderá ser compatível com a existência de outras espécies ou com uma grande variabilidade intraespecífica

Eliminação parasitária em fezes de canídeos no Concelho de Óbidos - estudo geral

Apresentação em PainelNa sequência de estudos anteriormente realizados sobre “Contaminação ambiental por endo e ectoparasitas de canídeos da Região do Ribatejo e Oeste e do Vale do Tejo”, e no interesse manifestado pelos Serviços Veterinários Municipais na implementação de medidas preventivas para minimizar os riscos de contaminação ambiental e de Saúde Pública no Concelho de Óbidos, realizou-se durante o ano de 2009 um estudo sobre o tipo e o grau de parasitismo em canídeos deste concelho e períodos de maior risco de contaminação ambiental. Colheram-se de 548 amostras de fezes de canídeos, com uma recolha por estação do ano de 137 amostras, correspondentes a 5,00 % do efectivo canino. As amostras foram sujeitas a análises coprológicas qualitativas e quantitivas, respectivamente pelos métodos de Willis e de McMaster. Das amostras de fezes observadas, 274 (50%00 %) apresentaram formas de eliminação parasitária. Nas amostras positivas identificaram-se ovos de Ancylostomatidae (79,92%) (Ascarididae - Toxocara canis e Toxascaris leonina) (12,04%), Trichuris sp. (Trichuridae) (40,15%), Strongyloides sp. (Strongyloididae) (18,98%), oocistos de Isospora sp. (Eimeriidae) (2,55%) e Sarcocystis sp. (Sarcocystidae) (0,37%) e proglótides grávidos de Dipylidium caninum (0,74%), apresentando a maioria infecção simples, com 52,92%, e as restantes, infecções mistas (39,42% - infecções duplas; - 7,66% infecções triplas). O estudo estacional permitiu evidenciar um aumento do número de amostras positivas, ao longo do ano, com a seguinte distribuição: Inverno - 9,67%; Primavera - 11,86%; Verão - 13,50%; Outono - 14,96%. Independentemente da estação do ano, identificaram-se ovos de Ancylostomatidae, Ascarididae, Trichuris sp., Strongyloides sp. e oocistos de Isospora sp., e as maiores prevalências foram sempre registadas no Outono (90, 24%) para Ancylostomatidae. Com excepção do Inverno, onde se registou maior gravidade das infecções com superioridade de associações (50,94%), nas restantes estações, predominaram as infecções simples, embora, a prevalência das infecções de maior gravidade (triplas), tenham ocorrido na Primavera, com 15,38%. Apesar de ter sido no Inverno que se registaram as infecções mais graves, o maior risco de contaminação é no Outono, estação onde se observou maior diversidade parasitária e maior número de amostras com infecção. Relativamente a estudos anteriores, este concelho apesar de ter registados menor diversidade parasitária, apresentou maior número de animais infectados e infecções mais graves