Effective measurement of network vulnerability under random and intentional attacks

The study of the security and stability of complex networks plays a central role in reducing the risk and consequences of attacks or disfunctions of any type. The concept of vulnerability helps to measure the response of complex networks subjected to attacks on vertices and edges and it allows to spot the critical component of a network in order to improve its security. We introduce an accurate and computable definition of network vulnerability which is directly connected with its topology and we analyze its basic properties. We discuss the relationship of the vulnerability with other parameters of the network and we illustrate this with some examples.     

Structural and Magnetic Properties of Pr2BaCuO5 Oxide

The Pr₂BaCuO₅ oxide has been prepared by using a precursor method. X‐ray and neutron diffraction data reveal that this mixed oxide crystallizes with the so‐called Nd₂BaPtO₅‐type structure, showing tetragonal symmetry and space group P4/mbm. Magnetic susceptibility, magnetization and specific heat measurements reveal that Pr₂BaCuO₅ oxide behaves as antiferromagnet, where the Pr³⁺ and Cu²⁺ sublattices become simultaneously ordered at 15 K. Preliminary neutron diffraction studies confirm this proposed antiferromagnetic ordering and it can be described by the wave vector k = [0,0,0].     

On the determination of the activation energy of solid-state reactions from the maximum reaction rate of isothermal runs

The method of kinetic analysis of isothermal traces recently proposed by Dharwadkar et al. is criticized. It is concluded that this method would be a proper one in the case of reactions following the mechanism of Prout and Tompkins or Avrami-Erofeev, but it would lead to misinterpretation when diffusion or phase-boundarycontrolled reactions are involved.     

A new approximation of the p(x) function

A new approximation of the p(x) function has been developed giving an easy determination of the activation energy of solid-state reactions from a plot of ln g(α) vs. the reciprocal temperature, with an error lower than 6% when E/RT = 2.     

Reaction pathway and kinetics of the thermal decomposition of synthetic brochantite

The reaction pathway of the thermal decomposition of synthetic brochantite, Cu₄(OH)₆SO₄, to copper(II) oxide was investigated through the detailed kinetic characterization of the thermal dehydration and desulferation processes. The dehydration process was characterized by dividing into two overlapped kinetic processes with a possible formation of an intermediate compound, Cu₄O(OH)₄SO₄. The dehydrated sample, Cu₄O₃SO₄, was found first to be amorphous by means of XRD, followed by the crystallization to a mixture of CuO and CuO-CuSO₄ at around 776 K. The specific surface area and the crystallization behaviour of the amorphous dehydrated compound depend largely on the dehydration conditions. The thermal desulferation process is influenced by the gross diffusion of the gaseous product SO₃, which is governed by the advancement of the overall reaction interface from the top surface of the sample particle assemblage to the bottom.     

Direct automatic screening of soils for polycyclic aromatic hydrocarbons based on microwave-assisted extraction/fluorescence detection and on-line liquid chromatographic confirmation

An integrated screening-confirmation system for PAHs in soils is presented. The sample screening configuration comprises on-line microwave-assisted extraction of the selected pollutants, followed by continuous preconcentration and sample clean-up on RP-C18. Those samples for which the total concentration is close to or above the threshold limit established (10 microg/g) are subjected to liquid chromatographic separation for confirmation. An evaluation of the qualitative data obtained was also carried out, by calculating the unreliability zone as well as the false positive and false negative rates. The whole method (extraction/determination/confirmation) was validated using industrial soil and harbour sediment certified reference materials (IRMM, European Commission CRM 524 and CRM 535). Application to the screening of solid environmental samples with subsequent confirmation of the results is also presented.     

Influence of mass-transfer phenomena on the shape of EGA traces of solid-state reactions

A theoretical analysis of the influence of mass-transfer phenomena on the shape of EGA traces of the thermal decompositions of solids has been carried out by assuming that the partial pressures of the gases generated in the reactions are proportional to the reaction rate. It has been shown that the EGA curves move to higher temperatures and the apparent reaction ordern approaches zero as the efficiency of the system for removing the gas product decreases, while the activation energy remains nearly constant. These statements have been checked experimentally.

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Zusammenfassung Unter der Annahme der Proportionalität der partiellen Drücke der während der Reaktion entstehenden Gase zur Reaktionsgeschwindigkeit wurde eine theoretische Analyse des Einflusses von Stoffübergangserscheinungen auf die Gestalt von EGA-Kurven bei der thermischen Zersetzung von Feststoffen durchgeführt. Werden gasförmige Produkte vom System weniger wirksam abgegeben, verschieben sich die EGA-Kurven zu höheren Temperaturen und die scheinbare Reaktionsordnungn nähert sich Null, während die Aktivierungsenergie annähernd konstant bleibt. Die Feststellungen wurden experimentell überprüft.

     

Kinetic study of the riboflavin-sensitised photooxygenation of two hydroxyquinolines of biological interest

4-Hydroxyquinoline (4-OHQ) and 8-hydroxyquinoline (8-OHQ), two compounds of interest because of their bioactivity and their structural relation with bioactive products, are effectively photooxygenated when irradiated with visible light in the presence of riboflavin (Rf) (vitamin B2) in solution in air-saturated water-methanol (9:1). Rf behaves as a dye-sensitiser, since both quinolines are transparent to visible light. 8-OHQ degrades about five times faster than 4-OHQ. Kinetic data obtained through time-resolved and stationary detection of Rf-electronically excited states indicate that a superoxide radical anion-mediated mechanism exclusively operates for 4-OHQ, whereas singlet molecular oxygen--mainly--plus superoxide radical anion is the species that reacts with 8-OHQ. The sensitiser Rf, which is known to photodegrade under visible-light aerobic irradiation, is regenerated in the presence of any of the quinolines through an electron transfer process that produces superoxide radical anion. The overall picture indicates that both quinolines act as sacrificial scavengers of the photogenerated oxygen species, thus preventing the photodegradation of Rf.