On search by address computation

We study the effect of data distribution on address computation data structures for searching, as typified by the priority queue problem. We compare several techniques showing that, in contrast to sorting, neither one nor multilevel bucket methods are uniformly efficient for this task. However, an enhancement of order preserving extendible hashing is shown to behave asymptotically independently of the amount of data and its distribution. Also conclusions regarding multiattribute file structures are presented.     

Study on the Chemistry and Structure of (Na(1−x)Bix)(Nb(1−y)Mny)O3 Ceramics by XPS, AES and EPMA

The (Na_1–xBi_x)(Mn_yNb_1–y)O₃ ceramics are new compounds, obtained for the first time, on the base of sodium niobate with substitution of bismuth manganite. It was shown that the solubility limit for Mn ions in sodium niobate lattice does not exceed 1% at. Therefore, the co-doping with Bi ions was proposed to increase this limit. Bismuth ions are expected to replace Na ions and to ensure charge compensation in the formed compound, thus enhancing possibility of accumulation of the Mn ions in solution without losing the appropriate electrical and optical properties. To study the morphology of produced ceramic four methods of sample characterization were used: X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), electron microprobe analysis (EPMA) and Scanning Electron Microscopy (SEM).     

Synthesis and characterisation of cyclopentadienyl complexes of barium: precursors for atomic layer deposition of BaTiO3

Cyclopentadienyl complexes Ba(C5Me5)2(THF)2 (1), Ba(C5Me5)2(A) (A = THF, dien, trien, diglyme, triglyme) (2-5), Ba(Pr(i)3C5H2)2(THF)2 (6), Ba(Bu(t)3C5H2)2(THF) (7), Ba(Me2NC2H4C5Me4)2 (8) and Ba(EtOC2H4C5Me4)2 (9) were prepared and characterised with TGA/SDTA, NMR and MS. Crystal structures of 2, 4, 5, 7, 8 and 9 are presented. All complexes prepared sublime under reduced pressure and complexes 1, 6 and 7 showed volatility also under atmospheric pressure. Complexes 1, 6 and 7 lose the coordinated THF when evaporated while complexes 2-5 are sublimable as complete molecules under reduced pressure. Complexes with bulky cyclopentadienyl ligands (6 and 7) are the most thermally stable and volatile among the prepared barocenes. X-ray structure determinations reveal that all the complexes studied are monomeric. Complexes 1, 7 and 8 were successfully tested in BaTiO3 thin film depositions by atomic layer deposition (ALD).     

Homogeneous nucleation rates of higher n-alcohols measured in a laminar flow diffusion chamber

Nucleation rate isotherms of n-butanol, n-pentanol, n-hexanol, n-heptanol, and n-octanol were measured in a laminar flow diffusion chamber using helium as carrier gas. The measurements were made at 250-310 K, corresponding to reduced temperatures of 0.43-0.50, and at atmospheric pressure. Experimental nucleation rate range was from 10(3) to 10(7) cm(-3) s(-1). The expression and accuracy of thermodynamic parameters, in particular equilibrium vapor pressure, were found to have a significant effect on calculated nucleation rates. The results were compared to the classical nucleation theory (CNT), the self-consistency corrected classical theory (SCC) and the Hale's scaled model of the CNT. The average ratio between the experimental and theoretical nucleation rates for all alcohols used was 1.5x10(3) when the CNT was used, and 0.2x10(-1) when the SCC was used and 0.7x10(-1) when the Hale's scaled theory was used. The average values represent all the alcohols used at the same reduced temperatures. The average ratio was about the same throughout the temperature range, although J(exp)/J(the) calculated with the Hale's scaled theory increased slightly with increasing temperature. The saturation ratio dependency was predicted closest to experiment with the classical nucleation theory. The nucleation rates were compared to those found in the literature. The measurements were in reasonable agreement with each other. The molecular content of critical alcohol clusters was between 35 and 80 molecules. At a fixed reduced temperature, the number of molecules in a critical cluster decreased as a function of alcohol carbon chain length. The number of molecules in critical clusters was compared to those predicted by the Kelvin equation. The theory predicted the critical cluster sizes well.     

Chemical structures from the analysis of domain-averaged fermi holes. Nature of the Mn-Mn bond in bis(pentacarbonylmanganese)

Because of conflicting and contradictory classification based on traditional AIM characteristics, the nature of the Mn-Mn bond has been and still is the subject of continuing discussions. To overcome the existing inconsistencies in the interpretation of the nature of this bond, the bonding in Mn2(CO)10 has been analyzed and discussed in terms of new recently proposed methodology known as the analysis of domain-averaged Fermi holes. It has been shown that this analysis is able to reconcile the conflicting conclusions of earlier AIM-based studies with traditional anticipations based on simple electron counting rules. According to Fermi hole analysis, the Mn-Mn bond has the character of the more or less ordinary covalent single sigma bond, but the analysis also brings clear evidence in favor of Mn . . . (CO) intramolecular interactions between the metal atom and the ligands bonded to the other metal atom. These interactions could be responsible for the observed decrease of electron density at the bond critical point detected in AIM studies.     

Microwave-assisted decarboxylation of bicyclic 2-pyridone scaffolds and identification of Abeta-peptide aggregation inhibitors

A reagent-free microwave-assisted decarboxylation procedure for carboxylic acid functionalized bicyclic 2-pyridones has been developed. This new method, based on microwave heating at 220 degrees C for 600 seconds in N-methyl pyrrolidone (NMP), proved to be practical and very efficient, resulting in decarboxylated 2-pyridones in near-quantitative yields. The decarboxylated products and the intermediate 2-pyridones in the form of carboxylic acid methyl esters and carboxylic acids were screened for their effect on Abeta-peptide aggregation. Two out of the 21 2-pyridones described in this study inhibited amyloid formation of the Alzheimer Abeta(1-40) peptide. The effect was seen even at a 4 : 1 ratio of 2-pyridone and monomeric Abeta-peptide.     

Microwave-assisted synthesis of highly substituted aminomethylated 2-pyridones

By employing microwave-assisted organic synthesis (MAOS) efficient conditions to introduce aminomethylene substituents in highly substituted bicyclic 2-pyridones have been established. Primary amino methylene substituents were introduced via a cyanodehalogenation followed by a borane dimethyl sulfide reduction of the afforded nitrile. In both of these transformations, microwave irradiation proved to be superior to traditional conditions and the primary amines were obtained in good overall yields (55-58% over three steps). To incorporate tertiary aminomethylene substituents in the 2-pyridone framework, a microwave-assisted Mannich reaction using preformed iminium salts proved to be effective. Thus highly substituted 2-pyridones were obtained in 48-93% yields.     

Polarized infrared spectra: Part 1. Stretched polymer method. Fundamental vibrations of some mono- and di-substituted benzenes

Polarized IR spectra of five benzene derivatives (four of C_2v symmetry and one of D_2h symmetry) have been recorded using the stretched polymer method. It has been found that the values of the dichroic ratios depend systematically on the symmetry class of the vibration in question. The IR-active vibrations can thus be unambiguously divided into the correct symmetry classes. The general validity of the method, as well as its value for vibrational analysis, is discussed.     

A gate to organokrypton chemistry: HKrCCH

An organic molecule containing krypton, HKrCCH, is reported. The preparation of HKrCCH includes 193-nm photolysis of H2C2/Kr solid mixtures at 8 K and subsequent thermal mobilization of hydrogen atoms at >/=30 K. The identification is based on infrared absorption spectroscopy and supported by ab initio calculations which show ionic and covalent contributions to the bonding. We believe that a series of similar organokrypton molecules can be prepared as computationally demonstrated for HKrC4H and HKrC3H3. These results feature a generally novel way for activating chemically the H-CC- group, which can find practical applications of the krypton catalysis.     

Speciation of activators in electroluminescent thin films: an EXAFS study of cerium and terbium doped strontium sulfide

Extended X-ray absorption fine structure (EXAFS) was used to determine the local structure of the luminescent centers in Tb³⁺ and Ce³⁺ -doped strontium sulfide thin films deposited by Atomic Layer Epitaxy (ALE). The rare earths were observed to enter mainly the substitutional sites but at the same time a part of the atoms form RES clusters (RE = rare earth). The presence of both substitutional sites and RES clusters has been observed for the first time in this study for rare earths in II–VI compounds. Received: 9 February 1998 / Revised: 22 May 1998 / Accepted: 29 May 1998