Experimental investigation of long-wavelength optical lattice vibrations in quaternary AlxInyGa1−x−yN alloys and comparison with results from the pseudo-unit cell model

Raman and Fourier transform infrared (FTIR) spectroscopies have been utilized to measure long-wavelength optical lattice vibrations of high-quality quaternary Al_xIn_yGa_1−x−yN thin films at room temperature. The Al_xIn_yGa_1−x−yN films were grown on c-plane (0 0 0 1) sapphire substrates with AlN as buffer layers using plasma assisted molecular beam epitaxy (PA-MBE) technique with aluminum (Al) mole fraction x ranging from 0.0 to 0.2 and constant indium (In) mole fraction y=0.1. Pseudo unit cell (PUC) model was applied to investigate the phonons frequency, mode number, static dielectric constant, and high frequency dielectric constant of the Al_xIn_yGa_1−x−yN mixed crystals. The theoretical results were compared with the experimental results obtained from the quaternary samples by using Raman and FTIR spectroscopies. The experimental results indicated that the Al_xIn_yGa_1−x−yN alloy had two-mode behavior, which includes A₁(LO), E₁(TO), and E₂(H). Thus, these results are in agreement with the theoretical results of PUC model, which also revealed a two-mode behavior for the quaternary nitride. We also obtained new values of E₁(TO) and E₂(H) for the quaternary nitride samples that have not yet been reported in the literature.     

LINEAR SEARCH FOR A BROWNIAN TARGET MOTION

A target is assumed to move according to a Brownian motion on the real line. The searcher starts from the origin and moves in the two directions from the starting point.The object is to detect the target. The purpose of this paper is to find the conditions under which the expected value of the first meeting time of the searcher and the target is finite,and to show the existence of a search plan which made this expected value minimum.     

Design of polyethers,thioethers, and amines with pendent iron moieties

Soluble organoiron polyethers, thioethers, and amines were synthesized via nucleophilic aromatic substitution reactions. The synthesis of these classes of organometallic polymers involved either the reaction of cyclopentadienyliron complexes of dichloroarenes with various oxygen and sulfur dinucleophiles or the reaction of ether‐ or amine‐containing diiron complexes with dithiols. Polymerization reactions with the diiron complexes gave rise to organoiron polymers with alternating ether/thioether or amine/thioether bridges. Removal of the iron moieties from the backbone of these polymers allowed for the production of the corresponding organic materials. Furthermore, the organometallic polymers had much higher solubilities than their organic analogues. Thermogravimetric analysis of the organoiron polymers indicated that the polymers lost their metallic moieties at approximately 200 °C, whereas degradation of the polymer backbones occurred around 500 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1216–1231, 2001     

Verticillane‐Type Diterpenoids and an Eudesmanolide‐Type Sesquiterpene from the Formosan Soft Coral Cespitularia hypotentaculata

Four new diterpenes, cespihypotins W–Z ( 1 – 4 ), having the verticillane skeleton and characterized by an α,β‐unsaturated γ‐hydroxycyclopentanone moiety, and a new eudesmanolide‐type sesquiterpene, cespilactam A ( 5 ), containing an α,β‐unsaturated γ‐lactam residue, were isolated from the AcOEt‐soluble fraction of the Taiwanese soft coral Cespitularia hypotentaculata. The structure and relative configuration of these metabolites was elucidated through extensive interpretation of MS, COSY, HSQC, HMBC, and NOESY experiments and by comparison of their NMR data with those of related compounds.     

Investigation of the effect of drying and refining on the fiber–fiber shear bond strength measured using tensile fracture line analysis of sheets weakened by acid gas exposure

No reliable method exists for measuring the cellulose fiber–fiber shear bond strength in paper. This paper reports a simple method for measuring the fiber–fiber shear bond strength by weakening the fibers independently of the bonds in a sheet of paper, using acid vapor, until all the fibers break across the fracture line. The bond strength is then calculated from the fiber strength, as measured by the zero span test, at the point where the fibers first are weakened such that they all break. The method was used to calculate the average bond strength of handsheets made out of two different pulps. The first pulp was a never dried, 60% yield, unbleached radiata pine. The bond strength was 25.0 ± 3.3 MPa. Drying the fibers before reslushing and making sheets reduced the bond strength by up to 33%, with the reduction depending on the severity of the drying treatment. The second pulp was a bleached dried softwood kraft and was used to investigate the effect of low consistency refining on bond strength. The bond strength increased from 13.7 ± 1.0 MPa for the sheets made from the unrefined pulp to 37.0 ± 1.0 MPa, for the sheets made from the most heavily refined pulp. The bond strength measurements are considerably higher than previous literature estimates for the shear bond strength. The causes for the discrepancy include stress concentrations in tests of single fiber–fiber bonds.     

On the Synthesis and Reactions of Indole-2-carboxylic Acid Hydrazide

Summary.  Indole-2-carboxylic acid hydrazide was prepared and allowed to react with aromatic aldehydes in acidic medium to give the corresponding hydrazone derivatives in good yields. The hydrazones were cyclized to indolo[2,3-d]pyridazine derivatives by refluxing with acetyl chloride. The indole carbohydrazide was converted to 2-triazolylindoles which acted as starting materials for several indole derivatives. A number of new indole derivatives were also prepared and structurally confirmed. Received October 17, 2000. Accepted (revised) December 12, 2000     

名义组份Bi6Se9Ge4CuOx块材和粉末压实样品的热电势和电导率

采用熔化淬火工艺制备Bi6Se9Ge4CuOx。块材和粉末压实样品均在300℃进行了热处理，该温度远低于玻璃转变温度419℃（由DTA热重分析得知）。无论是末经处理还是热处理后的样品，都具有多相结构。热电势测量结果表明，可能有电子和空穴的导电。载流子的导电类型主要取决于热处理条件。热电势以扩散分量为主，声子曳引可以忽略。跳跃导电是常见的，而半金属行为只在特殊的热处理条件下出现。     

Coulomb dissociation of incident 16O at 4.5 GeV/c

Projectile multifragment breakup of ¹⁶O, ²C and ⁷Li at energies 3.0–4.5 A-GeV is studied by means of the Weizsäcker-Williams method. The fragmentation channels of the ¹⁶O projectile at 4.5 A-GeV are investigated and compared with that of ¹⁶O at 200 A-GeV. The events characterized by N _h=0 and the events due to both Coulomb and diffraction dissociation have been selected and analyzed as a function of impact parameter. Also, the dependence of the electromagnetic dissociation cross-section on incident energy and the charge of projectile and target is found.     

Fuzzy weakly preopen (preclosed) function in Kubiak–Šostak fuzzy topological spaces

In this paper, we introduce and characterize fuzzy weakly preopen and fuzzy weakly preclosed functions between L-fuzzy topological spaces in Kubiak–?ostak sense and also study these functions in relation to some other types of already known functions.