Reconsideration of solvent effects calculated by semiempirical quantum chemical methods

AM1 and PM3 semiempirical calculations are reported for the solvent effects on the tautomeric equilibria of 2-pyridone/2-hydroxypyridine and 4-pyridone/4-hydroxypyridine in the gas phase and solution. The solvent effects on the tautomeric equilibria were investigated by self-consistent reaction field (SCRF) theory implemented in the AMPAC and MOPAC program in two different ways: one in which all the solvent relaxation is included in the quantum mechanics and the total energy must be corrected for the solvent change in energy, method A; and a second in which the quantum mechanics directly includes this term, method B. The calculated (AM1, method A) tautomeric equilibrium constants (log K₁) for 2-pyridone in the gas phase, cyclohexane, chloroform, and acetonitrile are ?0.3, 0.3, 0.8, and 1.3, respectively, in good agreement with the experimental data (?0.4, 0.24, 0.78, and 2.17, respectively). For 4-pyridone/4-hydroxypyridine differences between calculated log K₁ for the gas phase, chloroform and acetonitrile (?6.0, ?2.6, and ?1.2, respectively) and experimental data (< ?1, 0.11, and 0.66, respectively) are larger but the experimental values are also less certain. The experimental acetonitrile data are disturbed by specific interactions. An extension of the SCRF for aqueous solutions is reviewed. © 1993 John Wiley & Sons, Inc.     

Linear upper bounds for local Ramsey numbers

A coloring of the edges of a graph is called alocal k-coloring if every vertex is incident to edges of at mostk distinct colors. For a given graphG, thelocal Ramsey number, r _loc ^k (G), is the smallest integern such that any localk-coloring ofK _n , (the complete graph onn vertices), contains a monochromatic copy ofG. The following conjecture of Gyárfás et al. is proved here: for each positive integerk there exists a constantc = c(k) such thatr _loc ^k (G) cr ^k (G), for every connected grraphG (wherer ^k (G) is theusual Ramsey number fork colors). Possible generalizations for hypergraphs are considered.On leave from the Institute of Mathematics, Technical University of Warsaw, Poland.While on leave at University of Louisville, Fall 1985.     

Spectroscopic temperature determination of aluminum monoxide in laser ablation with 266-nm radiation

We report time-resolved measurements of diatomic aluminum monoxide spectra in the study of laser ablation by the use of frequency-quadrupled 266 nm Nd:YAG laser radiation. Spectroscopic temperatures of 3432(35) K and 3329(13) K are obtained at a delay time of 20mu, respectively, by the use of the modified diatomic Boltzmann plot and by the use of the Nelder-Mead algorithm in the fitting of the recorded spectrum.     

X-ray structures of 1,3-dithiolo[4,5-c]quinoline and 2,3-dihydro-1,4-dithiino[5,6-c]quinoline

The title compound I (C₁₀H₇NS₂) is orthorhombic: Pbca,a=16.223(6),b=15.065(5),c=7.356(4) Å. The conformation of 1,3-dithiol ring is of an envelope-type. A very short intramolecular sulfur-sulfur distance of 2.94 Å was observed. The compoundII (C₁₁H₉NS₂) is monoclinic: P2₁/c,a=5.113(2),b=11.978(4),c=16.444(5) Å, =98.00(5) deg. The conformation of the 1,4-dithiin rings is a half-chair. As compared to other 3,4-quinolinediyl bis-sulfides an elongated intramolecular sulfur-sulfur distance of 3.437(4) Å in dihydrodithiinoquinolineII was observed.Part XXXI in the series of Azinyl Sulfides.     

Fourier and Hermite series estimates of regression functions

Summary In the paper we estimate a regressionm(x)=E {Y|X=x} from a sequence of independent observations (X ₁,Y ₁),…, (X _n, Y_n) of a pair (X, Y) of random variables. We examine an estimate of a type , whereN depends onn andϕ _N is Dirichlet kernel and the kernel associated with the hermite series. Assuming, that E|Y|<∞ and |Y|≦γ≦∞, we give condition for to converge tom(x) at almost allx, provided thatX has a density. if the regression hass derivatives, then converges tom(x) as rapidly asO(nC^{−(2s−1)/4s}) in probability andO(n ^{−(2s−1)/4s} logn) almost completely.     

Characterization of a discontinuous epitope of the HIV envelope protein gp120 recognized by a human monoclonal antibody using chemical modification and mass spectrometric analysis

A subset of the neutralizing anti-HIV antibodies recognize epitopes on the envelope protein gp120 of the human immunodeficiency virus. These epitopes are exposed during conformational changes when gp120 binds to its primary receptor CD4. Based on chemical modification of lysine and arginine residues followed by mass spectrometric analysis, we determined the epitope on gp120 recognized by the human monoclonal antibody 559/64-D, which was previously found to be specific for the CD4 binding domain. Twenty-four lysine and arginine residues in recombinant full-length glycosylated gp120 were characterized; the relative reactivities of two lysine residues and five arginine residues were affected by the binding of 559/64-D. The data show that the epitope is discontinuous and is located in the proximity of the CD4-binding site. Additionally, the reactivities of a residue that is located in the secondary receptor binding region and several residues distant from the CD4 binding site were also altered by Ab binding. These data suggest that binding of 559/64-D induced conformational changes which result in altered surface exposure of specific amino acids distant from the CD4-binding site. Consequently, binding of 559/64-D to gp120 affects not only the CD4-binding site, which is recognized as the epitope, but appears to have a global effect on surface exposed residues of the full-length glycosylated gp120.     

Beam propagation method in rectangular structures with a high step index

In this paper a simple and effective method to analyze rectangular media with a high step of the refractive index is shown. Comparison of the method with a classical Beam Propagation Method and with analytical solutions for the planar waveguides in the (1+1)dimensional case are presented. There is also shown an influence of a high step of refractive index in (2+1)dimensional structures on the field distribution of guided beams as well as on the far field diffraction. The presented results show that the proposed method is very exact and relatively fast in comparison with other methods.     

Mn–Co spinel protective–conductive coating on AL453 ferritic stainless steel for IT-SOFC interconnect applications

This paper presents research on the synthesis and properties of the Mn_1.5Co_1.5O₄ (MC) spinel powder, as well as its application for the preparation of a MC thick film on the AL453 steel to be used for metallic interconnect material in IT-SOFCs. In order to prepare the MC micropowder with excellent homogeneity of the chemical and phase compositions, EDTA gel processes were utilized. In order to improve the contact electrical resistance between an AL453 steel interconnect and the La_0.8Sr_0.2FeO₃ (LSF) cathode and protect the cathode from Cr poisoning, the surface of the AL453 steel was coated with a protective manganese cobaltite spinel matrix using screen printing in combination with an appropriate heat treatment. The oxidation of the AL453/MC composite layer carried out in the air–H₂O gas mixture at 1,073 K for 55 h showed that the spinel coating may serve as an effective barrier against outward Cr diffusion from the AL453 steel and, therefore, significantly inhibit the formation of volatile Cr vapors from the chromia scale. The contact ASR study of the interconnect–cathode interface in the AL453/MC/LSCM/LSF/LSCM/MC/AL453 system carried out in the range of 723?1,073 K in air showed a very large drop in ASR compared to the resistance of the AL453/LSCM/LSF/LSCM/AL453 system without the spinel coating.     

Luminescent silicate core-shell nanoparticles: synthesis, functionalization, optical, and structural properties

SiO(2)/Zn(2)SiO(4):Mn(2+) core-shell nanoparticles with mean diameters in the range of 55-220 nm were prepared by a modified Pechini sol-gel method followed by lyophilization and annealing at temperatures of 800-1100°C. The as-synthesized nanoparticles were characterized by transmission electron microscopy, X-ray diffraction analysis, and photoluminescence spectroscopy. The results demonstrate that the crystal structure of the shell and the optical properties can be tuned by the annealing temperature and a variation of the concentration of doping ions. Under UV excitation, the samples emit green luminescence with its maximum at 525 nm, typical for the Mn(2+) ions in α-Zn(2)SiO(4). The resulting nanoparticles were successfully modified with amine and carboxyl functions with respect to a later attachment of biological moieties.     

Metaheuristic hybridizations for the regenerator placement and dimensioning problem in sub-wavelength switching optical networks

Physical layer impairments severely limit the reach and capacity of optical systems, thereby hampering the deployment of transparent optical networks (i.e., no electrical signal regenerators are required). Besides, the high cost and power-consumption of regeneration devices makes it unaffordable for network operators to consider the opaque architecture (i.e., regeneration is available at every network node). In this context, translucent architectures (i.e., regeneration is only available at selected nodes) have emerged as the most promising short term solution to decrease costs and energy consumption in optical backbone networks. Concurrently, the coarse granularity and inflexibility of legacy optical technologies have re-fostered great interest in sub-wavelength switching optical networks, which introduce optical switching in the time domain so as to further improve resources utilization. In these networks, the complex regenerator placement and dimensioning problem emerges. In short, this problem aims at minimizing the number of electrical regenerators deployed in the network. To tackle it, in this paper both a greedy randomized adaptive search procedure and a biased random-key genetic algorithm are developed. Further, we enhance their performance by introducing both path-relinking and variable neighborhood descent as effective intensification procedures. The resulting hybridizations are compared among each other as well as against results from optimal and heuristic mixed integer linear programming formulations. Illustrative results over a broad range of network scenarios show that the biased random-key genetic algorithm working in conjunction with these two intensification mechanisms represents a compelling network planning algorithm for the design of future sub-wavelength optical networks.