On stochastic processes in a multilevel control bulk queueing system

This article analyzes some stochastic processes that arise in a bulk single server queue with continuously operating server, state dependent compound Poisson input flow and general state dependent service process. The authors treat the queueing process as a semi–regenerative process and obtain the invariant probability measure and the transient distribution for the embedded Markov chain. The stationary probability measure for the queueing process with continuous time parameter is found by using semi-regenerative techniques. The authors also study the input and output processes and establish ergodic theorems for some functionals of these processes. The results are obtained in terms of the invariant probability measure for the embedded process and the stationary measure for the queueing process with continuous time parameter     

On the Soluble Graph of a Finite Simple Group

The maximal independent sets of the soluble graph of a finite simple group G are studied and their independence number is determined. In particular, it is shown that this graph in many cases has an independent set with three vertices.     

Periodic solutions in general scalar non-autonomous models with delays

Theorems for the existence of periodic solutions for diverse models of population dynamics are obtained as corollaries of a few basic theorems, thus unifying the analysis of a broad class of scalar models in a single setting. The latter mechanism allows to obtain existence conditions for a broad class of nonlinear, non-autonomous models and models with state-dependent delays. The technique fulfills multiple roles: it can be used to expand on well-known results as well as to shorten existing proofs. We provide some examples which illustrate the applicability of our results.     

Training-induced criticality in martensites

We propose an explanation for the self-organization towards criticality observed in martensites during the cyclic process known as "training." The scale-free behavior originates from the interplay between the reversible phase transformation and the concurrent activity of lattice defects. The basis of the model is a continuous dynamical system on a rugged energy landscape, which in the quasistatic limit reduces to a sandpile automaton. We reproduce all the principal observations in thermally driven martensites, including power-law statistics, hysteresis shakedown, asymmetric signal shapes, and correlated disorder.     

"Competitive quenching": a mechanism by which perihydroxylated perylenequinone photosensitizers can prevent adverse phototoxic damage caused by verteporfin during photodynamic therapy

Incorporation of photodynamic therapy into clinical practice for induction of vascular photo-occlusion highlights the need to prevent adverse phototoxicity to sensitive juxtaposed tissues, particularly in the retina. We developed a system termed "competitive quenching" to prevent adverse phototoxic damage. It involves differential compartmentalization of a photoactivator to the intravascular compartment for photoexcitation and delivery of phototoxicity to targeted vessels. A different photodynamic agent is partitioned to the extravascular retinal space to quench reactive oxygen species generated by photosensitization, thereby protecting the adjacent retinal tissues from adverse phototoxicity. The absorption spectra of quenchers must span wavelengths that are shorter and excluded from the spectral range of photoexcitation light to prevent photoactivation of the quencher. Perihydroxylated perylenequinones were found to be suitable to function as "competitive quenchers" with the prototype hypericin identified as a potent quencher. Here we examined the mechanisms operative in competitive quenching and suggest that hypericin forms a complex with verteporfin, thereby quenching singlet oxygen formation. Furthermore, we show that hypericin, with six phenolic hydroxyls, protects retinal and endothelial hybridoma cells from phototoxicity more effectively than the dimethyl tetrahydroxy helianthrone structural analog with only four such phenolic hydroxyls. The findings suggest that hydroxyl numbers contribute to the efficacy of competitive quenching.     

Synthesis and characterization of an iron(II) eta(2)-hydrazine complex

The iron phosphine complex cis-[Fe(DMeOPrPE)2(eta2-N2H4)][BPh4]2 {DMeOPrPE = 1,2-bis[bis(methoxypropyl)phosphino]ethane} was synthesized and structurally characterized. The structure exhibits the first eta2 coordination of hydrazine to iron, which may be relevant to intermediates trapped during nitrogenase turnover. The reaction of I with acid results in the formation of ammonia via a disproportionation reaction.     

Synthesis and aggregation behavior of pluronic F87/poly(acrylic acid) block copolymer in the presence of doxorubicin

Poly(acrylic acid) (PAA) was polymerized on both termini of Pluronic F87 copolymer using the atom transfer radical polymerization technique to produce a novel block copolymer, PAA-b-F87-b-PAA (F87PAA). The loading of a cationic anticancer drug, doxorubicin (DOX), to F87PAA at different pH values was investigated using isothermal titration calorimetry (ITC), laser light scattering techniques, and UV-vis spectroscopy. At pH of 4.3-7.1, the ITC profile exhibited a significant exothermic peak, which indicated that the drug loading is an enthalpically driven process. At a pH of 4.3, the enthalpy maximum was significantly reduced in the presence of 2 M urea, indicating the existence of hydrogen bonds between the DOX and F87PAA copolymer. At a pH of 7.1, the fraction of bound DOX was close to the stoichiometric proportion of 1:1 to the molar concentration of carboxyl groups in the copolymer, where the drug loading is governed by electrostatic and stacking interactions. The TEM image of the complex indicated the formation of large compound micelles induced by the binding of DOX to the PAA segments.     

1,2-BN cyclohexane: synthesis, structure, dynamics, and reactivity

BN/CC isosterism has emerged as a viable strategy to increase the structural diversity of carbon-based compounds. We present the first synthesis and characterization of the parent 1,2-BN cyclohexane, the BN-isostere of cyclohexane. 1,2-BN cyclohexane is an air- and water-stable compound that cleanly forms a trimer with release of dihydrogen when thermally activated. We also demonstrate that 1,2-BN cyclohexane has a lower activation barrier for ring inversion than cyclohexane due to BN/CC isosterism.