Identification of antischistosomal leads by evaluating peroxides of beta-dicarbonyl compounds and their heteroanalogs : bridged 1,2,4,5-tetraoxanes and alphaperoxides, and beta,delta-triketones: tricyclic monoperoxides

Although antischistosomal properties of peroxides were studied in recent years, systematic structure-activity relationships have not been conducted. We evaluated the antischistosomal potential of 64 peroxides belonging to bridged 1,2,4,5-tetraoxanes, alphaperoxides and beta,delta-triketones. Thirty-nine compounds presented IC50 values > 15 microM on newly transformed schistosomula. Active drugs featured phenyl-, adamantane- or alkyl residues at the methylene bridge. Lower susceptibility was documented on adult schistosomes, with most hit compounds being tricyclic monoperoxides (IC50: 7.7-13.4 microM). A bridged 1,2,4,5-tetraoxane characterized by an adamantane residue showed the highest activity (IC50: 0.3 microM) on adult Schistosoma mansoni. Studies with hemin and heme supplemented medium indicated that antischistosomal activation of peroxides is not necessarily triggered by iron porphyrins. Two compounds (tricyclic monoperoxide; bridged 1,2,4,5-tetraoxane) revealed high worm burden reductions in the chronic (WBR: 75.4-82.8 %) but only moderate activity in the juvenile (WBR:18.9-43.1%) S. mansoni mouse model. Our results might serve as starting point for the preparation and evaluation of related derivative

Heavy-to-Light Form Factors in the Final Hadron Large Energy Limit: Covariant Quark Model Approach

We prove the full covariance of the heavy-to-light weak current matrix elements based on the Bakamjian-Thomas construction of relativistic quark models, in the heavy mass limit for the parent hadron and the large energy limit for the daughter one. Moreover, this quark model representation of the heavy-to-light form factors fulfills the general relations that were recently argued to hold in the corresponding limit of QCD, namely that there are only three independent form factors describing the B -> pi (rho) matrix elements, as well as the factorized scaling law sqrt(M)z(E) of the form factors with respect to the heavy mass M and large energy E. These results constitute another good property of the quark models \`a la Bakamjian-Thomas, which were previously shown to exhibit covariance and Isgur-Wise scaling in the heavy-to-heavy case.Comment: 11 pages, LaTex2e, no figur

Cyclic peroxides and related initiating systems for radical polymerization of methyl methacrylate

Cyclic peroxides as initiators for the radical polymerization of methyl methacrylate were proposed. The initial rates, initiation rates, and effective activation energies of polymerization initiated by cyclic peroxides and cyclic peroxide-1-pyridyl-2-ferrocene systems were determined. The radical yields to the volume upon the thermal decomposition of cyclic peroxides and their catalytic decomposition in the presence of 1-pyridyl-2-ferrocene were determined. In combination with 1-pyridyl-2-ferrocene cyclic peroxides form efficient initiating systems favoring an increase in the polymerization rate, a decrease in the molecular weights, and an increase in syndiotacticity of the synthesized poly(methyl methacrylate). © 2013 Springer Science+Business Media New York

Effect of additions of zinc stearate on the properties of sintered Nd-Fe-B magnets

Zinc stearate additions have been used to increase the remanence of sintered Nd-Fe-B magnets produced by the powder metallurgy without powder pressing. Zinc stearate acts as an internal lubricant, i.e., it decreases the friction forces between the particles and favors an increase in the degree of texture of the powders, which is induced by the magnetic field. It is shown that the density and the magnetic hysteresis characteristics of sintered magnets produced using additions of 0.15 wt % zinc stearate exceeds the corresponding values obtained for magnets produced without this addition at a filling density of powders in containers of more than 2.9 and 3.0 g/cm3 in dry and wet states, respectively. Using additions of zinc stearate in the amount of 0.15% with respect to the weight of the powder, magnets with a density of 7.55 g/cm3, B r = 14.02 kG, H c = 7.91 kOe, and (BH)max = 46.1 MG Oe have been produced. © 2013 Pleiades Publishing, Ltd

Rotational covariance and light-front current matrix elements

Light-front current matrix elements for elastic scattering from hadrons with spin~1 or greater must satisfy a nontrivial constraint associated with the requirement of rotational covariance for the current operator. Using a model $\rho$ meson as a prototype for hadronic quark models, this constraint and its implications are studied at both low and high momentum transfers. In the kinematic region appropriate for asymptotic QCD, helicity rules, together with the rotational covariance condition, yield an additional relation between the light-front current matrix elements.Comment: 16 pages, [no number

Deuteron Magnetic and Quadrupole Moments with a Poincar\'e Covariant Current Operator in the Front-Form Dynamics

The deuteron magnetic and quadrupole moments are unambiguosly determined within the front-form Hamiltonian dynamics, by using a new current operator which fulfills Poincar\'e, parity and time reversal covariance, together with hermiticity and the continuity equation. For both quantities the usual disagreement between theoretical and experimental results is largely removed.Comment: To appear in Phys. Rev. Let

Deep inelastic scattering and final state interaction in an exactly solvable relativistic model

In the theory of deep inelastic scattering (DIS) the final state interaction (FSI) between the struck quark and the remnants of the target is usually assumed to be negligible in the Bjorken limit. This assumption, still awaiting a full validation within nonperturbative QCD, is investigated in a model composed by two relativistic particles, interacting via a relativistic harmonic oscillator potential, within light-cone hamiltonian dynamics. An electromagnetic current operator whose matrix elements behave properly under Poincar\'e transformations is adopted. It is shown that: i) the parton model is recovered, once the standard parton model assumptions are adopted; and ii) when relativistic, interacting eigenfunctions are exactly taken into account for both the initial and final states, the values of the structure functions, averaged over small, but finite intervals of the Bjorken variable $x$, coincide with the results of the parton model in the Bjorken limit.Comment: 26 pages, to appear in Phys. Rev. C (May 1998