The Maximum Number of Dominating Induced Matchings

A matching M of a graph G is a dominating induced matching (DIM) of G if every edge of G is either in M or adjacent with exactly one edge in M. We prove sharp upper bounds on the number of DIMs of a graph G and characterize all extremal graphs. Our results imply that if G is a graph of order n, then ; provided G is triangle‐free; and provided and G is connected.     

Catalytic asymmetric one-pot synthesis of α-methylene-γ-lactams

An organocatalytic enantioselective synthesis of α-methylene-γ-lactams has been developed. The reaction between protected 2-aminomalonates and Morita–Baylis–Hillman carbonates is catalyzed by chiral Lewis bases to afford the corresponding lactams in excellent yields and moderate to good enantioselectivities, after work-up.     

Field amplified sample injection‐capillary zone electrophoresis for the analysis of amprolium in eggs

Veterinary medicines are widely administered to farm animals since they keep animals healthy at overcrowded conditions. Nevertheless the continuous administration of medicines to farm animals can frequently lead to the presence of residues of veterinary drugs in consumption products. Amprolium is a quaternary ammonium compound used in the treatment of coccidiosis. In this paper, a method based on CZE to analyze residues of amprolium in eggs was developed and validated for the first time. Parameters such as electrolyte type, concentration, and pH were optimized. In order to improve sensitivity, field‐amplified sample injection (FASI) was used for in‐line preconcentration after a quick and simple sample treatment based on SPE (Envi‐Carb). During method‐validation studies using egg samples, a matrix interference was found at the migration time of amprolium. This compound was identified as thiamine and confirmed by MSⁿ experiments using CEcoupled to MS (CE‐MS) with an ion‐trap mass analyzer. CZE conditions were reoptimized to separate thiamine from amprolium allowing the quantification of amprolium in eggs at concentrations down to 75 μg/kg, which are far below the MRL‐legislated values.     

Determination of microcystins in biological samples from freshwater fish

A new HPLC–DAD method has been developed to identify and quantify free microcystins (MC) in biological samples from fish (intestine and liver). The toxins were extracted from 500 mg sample with a mixture of methanol–water (85 : 15, v/v) and the extracts obtained were purified employing immunoaffinity columns (IAC). The purification step was optimised by a full factorial 3² design. MC were separated using conventional C18 column and an acetonitrile-acidified water (pH 3) gradient. Detection and quantification limits resulted equal for the two toxins assayed (MC-RR and MC-LR) and were 0.15 and 0.5 µg g^?1, respectively. The accuracy for each MC in liver samples were 96% (range 80–113%) for MC-RR and 101% (range 93–118%) for MC-LR. The results were slightly lower for intestine samples, with recoveries ranging between 85% (75–93%) for MC-RR and 88% (80–97%) for MC-LR. The proposed method was applied for the determination of free MC in fish intoxicated with these toxins, in order to determine its utility to evaluate the potential risks for human health if MC-contaminated fish are consumed. The results showed the transference of MC-LR from cyanobacterial cells to fish tissues.     

Weak chaos and metastability in a symplectic system of many long-range-coupled standard maps

We introduce, and numerically study, a system of N symplectically and globally coupled standard maps localized in a d=1 lattice array. The global coupling is modulated through a factor r^-α, being r the distance between maps. Thus, interactions are long-range (nonintegrable) when 0≤α≤1, and short-range (integrable) when α>1. We verify that the largest Lyapunov exponent λ_M scales as λ_M ∝ N^-κ(α), where κ(α) is positive when interactions are long-range, yielding weak chaos in the thermodynamic limit N↦∞ (hence λ_M→0). In the short-range case, κ(α) appears to vanish, and the behaviour corresponds to strong chaos. We show that, for certain values of the control parameters of the system, long-lasting metastable states can be present. Their duration t_c scales as t_c ∝N^β(α), where β(α) appears to be numerically in agreement with the following behavior: β>0 for 0 ≤α< 1, and zero for α≥1. These results are consistent with features typically found in nonextensive statistical mechanics. Moreover, they exhibit strong similarity between the present discrete-time system, and the α-XY Hamiltonian ferromagnetic model.     

Influence of N-donor bases and the solvent in oxodiperoxomolybdenum catalysed olefin epoxidation with hydrogen peroxide in ionic liquids

Biphasic catalytic olefin epoxidation systems consisting of oxodiperoxomolybdenum catalysts in 1-n-alkyl-3-methylimidazolium hexafluorophosphate ionic liquid (IL) media with aqueous hydrogen peroxide oxidant were optimised by tuning the molecular structure of the IL and employing N-heterocyclic donor base additives to inhibit hydrolysis and enhance the activity of the catalyst. The latter study was only made possible by the solubilising properties of the IL media. Of the bases investigated, pyrazoles were identified as the most efficient additive species and the best results were obtained using 3,5-dimethylpyrazole. Immobilisation of the catalyst in the IL allowed for very efficient catalyst recycling. Finally, the compound [MoO(O(2))(2)(3-Mepz)(2)] (3-Mepz = 3-methylpyrazole) was characterised and its structure determined by X-ray crystallography.     

Analysis of bisphenols in soft drinks by on-line solid phase extraction fast liquid chromatography-tandem mass spectrometry

In this study, an automated on-line solid-phase extraction coupled to fast liquid chromatography–tandem mass spectrometry (on-line SPE fast LC–MS/MS) method was developed for the simultaneous analysis of bisphenol A (BPA), bisphenol F (BPF), bisphenol E (BPE), bisphenol B (BPB) and bisphenol S (BPS) in canned soft drinks without any previous sample treatment. A C18 (12 μm particle size) loading column was used for the SPE on-line preconcentration before the liquid chromatography baseline separation of bisphenol compounds using a C18 Fused-Core™ (50 mm × 2.1 mm i.d.) column, which took less than 3 min. Gradient elution and heated electrospray were used to reduce matrix effect and improve ionization efficiency. To select the most intense and selective transitions, fragmentation studies were performed by multiple-stage mass spectrometry in an ion trap mass analyzer and tandem mass spectrometry in a triple quadrupole instrument, this latter instrument being used for quantitation in SRM mode. Quality parameters of the method were established and we obtained a simple, fast, reproducible (RSD values lower than 10%) and accurate (precision higher than 93%) method for the analysis of bisphenols in canned soft drinks at the ng L⁻¹ level using matrix-matched calibration.     

Highly enantioselective organocatalytic cascade reaction for the synthesis of piperidines and oxazolidines

The synthesis of piperidines and piperidines derivatives in enantiopure fashion has been a challenging goal for organic chemists. In this report we developed a nice cascade reaction for piperidine derivatives based in an amidomalonate Michael addition to enals followed by an intramolecular hemiaminal formation with good yields and enantioselectivities. Moreover we studied the ‘in situ’ intramolecular cyclization of this hemiaminals with alcohols forming fused piperidine-oxazolidines.     

Communities and dynamical processes in a complex software network

Complex technological networks represent a growing challenge to support and maintain as their number of elements become higher and their interdependencies more involved. On the other hand, for networks that grow in a decentralized manner, it is possible to observe certain patterns in their overall structure that may be taken into account for a more tractable analysis. An example of such a pattern is the spontaneous formation of communities or modules. An important question regarding the detection of communities is if these are really representative of any internal network feature. In this work, we explore the community structure of a real complex software network, and correlate this modularity information with the internal dynamical processes that the network is designed to support. Our results show that the dependence between community structure and internal dynamical processes is remarkable, supporting the fact that a community division of this complex network is helpful in the assessment of the underlying dynamical structure, and thus is a useful tool to achieve a simpler representation of the complexity of the network.     

Information transfer dynamics in fixed-pathways networks

Most complex technological networks are defined in such a way that their global properties are manifested at a dynamical level. An example of this is when internal dynamical processes are constrained to predefined pathways, without the possibility of alternate routes. For instance, large corporation software networks, where several flow processes take place, are typically routed along specific paths. In this work, we propose a model to describe the global characteristics of this kind of processes, where the dynamics depends on the state of the nodes, represented by two possibilities: responsive or blocked. We present numerical simulations that show rich global behavior with unexpected emerging properties. In particular, we show that two different regimes appear as a function of the total network load. Each regime is characterized by developing either a unimodal or a bimodal distribution for the density of responsive nodes, directly related to global efficiency. We provide a detailed explanation for the main characteristics of our results as well as an analysis of the implications for real technological systems.