Curves with nodes,cusps and ordinary triple points

Summary We prove a ?virtual connectedness? theorem for plane curves with nodes, cusps and ordinary triple points. Irreducible curves are so obtained from virtually connected arrangements of lines.

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Riassunto Viene dimostrato un teorema di ?virtuale connessione? per curve piane con nodi, cuspidi e punti tripli ordinari. Tale teorema viene poi applicato alla costruzione di curve irriducibili a partire da configurazioni di rette virtualmente connesse.

     

High count rate gamma spectrometry. A summary of recent experiments in high accuracy NAA applications

A source of error in the gamma-spectrometric registration of the analytical signal in neutron activation analysis is its dependency on the overall count rate. Losses in the accuracy of quantitation occur due to hardware and software. This paper presents examples for solutions to these problems and demonstrates that accurate NAA can be accomplished under high-rate counting conditions with commercially available technology.     

Synthesis and Spectroscopic Characterization of Dinuclear Calcium Complexes with Oxa‐Aza Macrocyclic Ligands

The syntheses of dinuclear calcium perchlorate and/or nitrate complexes by template and direct methods, employing macrocyclic ligands with 18, 20, 22, and 26 membered rings are reported. The presence of pendant arms provide with coordinative NxOy donor atoms in the smaller macrocycles, the high number of donor atoms between 7 and 10, and the dinuclear composition obtained in all the systems examined, point out that in the formed solid complexes both Ca²⁺ ions could be located inside of the macrocycle cavities. Transmetallation reaction of a lanthanide(III) complex, [L⁵Sm](ClO₄)₃·9H₂O, with Ca(ClO₄)₂·xH₂O leads the formation of the new dinuclear orange [L⁵Ca₂](ClO₄)₄·3H₂O complex, manifesting the versatility of this macrocyclic cavity. All complexes have been characterized by microanalysis, IR, UV‐vis, ¹H NMR spectroscopy, FAB mass spectrometry, FAAS spectroscopy, and conductivity measurements.     

Immobilization of Recombinant Human Catalase on Gold and Silver Nanoparticles

Human catalase cDNA was cloned into a pEX-C-His vector. Purified recombinant catalase was immobilized on nanoparticles. Gold and silver nanoparticles were synthesized in a variety of sizes by chemical reduction; no agglomerates or aggregates were observed in any of the colloids during dynamic light scattering or scanning transmission electron microscopy analysis. After immobilization on gold nanoparticles, recombinant catalase activity was found to be lower than that of the same amount of enzyme in aqueous solution. However, after 10 days of storage at room temperature, the activity of catalase immobilized on gold nanoparticles (AuNPs) of 13 and 20 nm and coverage of 133% was 68 and 83% greater than catalase in aqueous solution, respectively. During 10 days of experiment, percentage activity of catalase immobilized on those gold nanoparticles was higher in comparison to CAT in aqueous solution. Catalase immobilized on silver nanoparticles did not lose activity as significantly as catalase immobilized on AuNPs. Those results confirm the ability to produce recombinant human enzymes in a bacterial expression system and its potential use while immobilized on silver or gold nanoparticles.     

Copolymers dispersions designed to shaping of ceramic materials

Journal of Thermal Analysis and Calorimetry - To study the effect of ionic liquids (ILs) of the microstructure on the surface of the coal, four ILs ([Emim][BF4], [Bmim][BF4], [Bmim][NO3], and...     

Smooth non-special surfaces of ℙ4

We consider smooth non-degenerate surfaces in ℙ⁴, and prove that there is a finite number of such surfaces which are:

Reverse pulse voltammetry in ec2 reactions: Electrochemistry of 1-alkyl-4-t-butylpyridinium ions

The applications of the reverse pulse method are extended in order to distinguish between different paths of electrodimerization. The method for determination of rate constants of the chemical reaction coupled with charge transfer (ec₂) is further developed. Measurements of K′_d vs. t_p provide valuable information for the determination of rate constants.The reverse pulse method is applied in the study of the electrodimerization of 1-alkyl-4-t-butylpyridinium ions (1-alkyl=?CH₃; ?CH₂CH₃; ?CH(CH ₃)₂) in acetonitrile. It is found that the electrodimerization mechanism is consistent with the sequence: Py⁺ + e = Py ? $\text{1}\text{2}$ Py₂. The formal potential E^o′ is measured directly for 1-CH(CH₃)₂, and indirectly for the other pyridium ions. All values are identical within experimental error (E^o′ = ?1.835 V vs. Ag/Ag⁺).The values of k_d and k_m are measured. With an increase in the size of the l-alkyl group, k_d decreases and k_m increases. This is consistent with the expected “stabilization” of the radicals due to the increase of the l-alkyl group size which hinders the dimerization site (2- and 6-positions).     

Acetylene cyclotrimerization by early second-row transition metals in the gas phase. A theoretical study

The acetylene cyclotrimerization reaction mediated by the left-hand-side bare transition metal atoms Y, Zr, Nb, and Mo has been studied theoretically, employing DFT in its B3LYP formulation. The complete reaction mechanism has been analyzed, identifying intermediates and transition states. Both the ground spin state and at least one low-lying excited state have been considered to establish whether possible spin crossings between surfaces of different multiplicity can occur. Our results show that the overall reaction is highly favorable from a thermodynamic point of view and ground state transition states lie always below the energy limit represented by ground state reactants. After the activation of two acetylene molecules and formation of a bis-ligated complex, the reaction proceeds to give a metallacycle intermediate, as the alternative formation of a cyclobutadiene complex is energetically disfavored. All the examined reaction paths involve formation of a metallacycloheptatriene intermediate that in turn generates a metal-benzene adduct from which finally benzene is released. Similarities and differences in the behaviors of the considered four metal atoms have been examined.     

Gemini pyridinium surfactants: synthesis and conductometric study of a novel class of amphiphiles1

A new series of pyridinium cationic gemini surfactants was prepared by quaternization of the 2,2'-(alpha,omega-alkanediyl)bispyridines with N-alkylating agents, whose reactivity is briefly discussed. Particularly useful was the use of long-chain alkyl triflates (trifluoromethanesulfonates) for both overcoming the sterical hindrance in the pyridines and obtaining higher synthetic yields. Well-known 4,4'-(alpha,omega-alkanediyl)bis(1-alkylpyridinium) structures showed narrow temperature ranges for practical applications, due to their high Krafft points, while the new 2,2'-(alpha,omega-alkanediyl)bis(1-alkylpyridinium) series, accounted for good surface active properties. Due to the Krafft points below 0 degrees C, they could be exploited as solutions in water at any temperature. The characterization of the behavior of the series was performed by conductivity measurements. Some of the proposed structures exhibited unusual surface active behavior, which was interpreted in terms of particular conformational arrangements.