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101.
In psychological measurement it is important to determine when a particular examinee's test or scale score provides an invalid measure of the trait or attitude being assessed. In this article we present several quantitative indices that have been found to effectively identify some types of inappropriate scores. These measures, termed appropriateness indices, are all derived from item response theory. They are computed directly from the item responses that are combined to form the test or scale of interest; information from other scales or tests is not needed. A decision-theoretic approach to the use of appropriateness indices in selection decisions and theoretical research is introduced. An example is then presented to illustrate how researchers can use appropriateness indices. Finally, we discuss policy options that are available for dealing with individuals who are identified as having inappropriate scores. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
102.
Ute Förster Katharina Lommel Daniel Sauter Christian Grünewald Joachim W. Engels Prof. Dr. Josef Wachtveitl Prof. Dr. 《Chembiochem : a European journal of chemical biology》2010,11(5):664-672
A series of short RNA duplexes containing one or two 1‐ethynylpyrene‐modified adenine bases was synthesised. The melting behaviour of these duplexes was examined by monitoring temperature‐dependent pyrene fluorescence. In the singly modified RNA duplexes, the bases flanking the ethynylpyrene‐rA were varied to examine the sequence specificity of the fluorescence change of pyrene upon RNA hybridisation. Because an increase in pyrene fluorescence upon melting of the duplex can be correlated with intercalation of pyrene, and a decrease is usually associated with the position of pyrene outside the strand, a relationship between the flanking bases and the tendency of the dye to intercalate has been established. It was found that pyrene intercalation is less likely to take place if the modified base is flanked only by A–U base pairs. Flanking G–C base pairs, even only in the 5′‐direction of the modified base, will favour intercalation. In addition, we examined a doubly modified compound that had a pyrene located on each strand. The spectra indicated that the two pyrenes were close enough for interaction. Upon melting of the strand, a fluorescence blue shift corresponding to the dissociation of the pyrene–pyrene complex could be observed in addition to the intensity effect already known from the singly modified compounds. Two melting curves based on the different properties of the fluorophore could be extracted, leading to different melting points corresponding to the global duplex melting and to the change of local pyrene environment, respectively. 相似文献
103.
S. Jacobsen H. G. Fritz Ph. Dege Ph. Dubois R. Jrme 《Polymer Engineering and Science》1999,39(7):1311-1319
Poly(lactide) (PLA), a biodegradable aliphatic polyester with excellent properties for different polymer applications, has been used mostly in the biomedical field, mainly because of its high price, resulting from expensive polymerization and purification techniques. Although this polymer can play a major role in future markets for biodegradable polymers, the current high price has to be reduced significantly to at least $4 US/kg. Therefore, this paper aims to partially review the polymerization techniques traditionally used in PLA synthesis and to propose new developments that enable us to produce these polymers by an innovative process for just a portion of the costs traditionally charged, using reactive extrusion techniques in a closely intermeshing co-rotating twin screw extruder. This paper gives an overview of attainable mechanical properties and future markets. 相似文献
104.
Crystallization of Polymer-Derived Silicon Carbonitride at 1873 K under Nitrogen Overpressure 总被引:1,自引:0,他引:1
Martin Friess Joachim Bill Jerzy Golczewski re Zimmermann Fritz Aldinger Ralf Riedel Rishi Raj 《Journal of the American Ceramic Society》2002,85(10):2587-2589
The chemical stability of an amorphous silicon carbonitride ceramic, having the composition 0.57SiC·0.43Si3 N4 ·0.49C is studied as a function of nitrogen overpressure at 1873 K. The ceramic suffers a weight loss at p N2 < 3.5 bar (1 bar = 100 kPa), does not show a weight change from 3.5 to 11 bar, and gains weight above 11 bar. The structure of the ceramic changes with pressure: it is crystalline from 1 to 6 bar, amorphous at ∼10 bar, and is crystalline above ∼10 bar. The weight-loss transition, at 3.5 bar, is in excellent agreement with the prediction from thermodynamic analysis when the activities of carbon, SiC, and Si3 N4 are set equal to those of the crystalline forms; this implies that the material crystallizes before decomposition. The amorphous to crystalline transition that occurs at ∼10 bar, and which is accompanied by weight gain, is likely to have taken place by a different mechanism. A nucleation and growth reaction with the atmospheric nitrogen is proposed as the likely mechanism. The supersaturation required to nucleate α-Si3 N4 crystals is calculated to be 30 kJ/mol. 相似文献
105.
The preparation of thioethers by S-alkylation of various thiols with alkyl halides under solvent-free reaction conditions using potassium fluoride on alumina (KF/Al2O3) as a solid catalyst has been investigated in detail with respect to three different modes of reaction activation (ultrasound irradiation, microwave irradiation, and conventional heating) for obtaining maximum yield of the thioether. The importance of KF/Al2O3 as a particularly efficient catalyst was corroborated for all three modes of reaction activation, although the reaction time was found to be strongly dependent on the mode of activation. The yield of the thioethers was also found to depend on the amount of the solid catalyst relative to the equimolar amounts of the two reactants. 相似文献
106.
M. Pfeiffer A. Beyer B. Plnnigs A. Nollau T. Fritz K. Leo D. Schlettwein S. Hiller D. Whrle 《Solar Energy Materials & Solar Cells》2000,63(1):83
We present a systematic study on doping of vanadyl- and zinc-pathalocyanine by a fully fluorinated form of tetracyano-quinodimethane as an example of controlled doping of thin organic films by cosublimation of matrix and dopant. The films are characterized in situ by temperature dependent Seebeck and conductivity measurements. We observe a drastic increase of conductivity and a corresponding shift of the Fermi level towards the valence states with increasing dopant concentration. We thus conclude that doping has the potential of both reducing the series resistance and increasing the photovoltage of organic solar cells. As a first step to exploit this potential, we present two different ways of preparing diodes with rectification ratios in excess of 104 using doped phthalocyanines. By adding an undoped interlayer between the contact and the doped layer, we have produced diodes which work already in the strict absence of oxygen and are stable in air. To increase the efficiency of charge carrier generation in photovoltaic cells, we need to use photoactive donor–acceptor-heterojunctions. We present here first examples of pn- and pin-type heterojunctions combining p-doped and nominally undoped layers. 相似文献
107.
Daniel Röhnert Fritz Phillipp Helfried Reuther Till Weber Egbert Wessel Michael Schütze 《Oxidation of Metals》2007,68(5-6):271-293
The initial stages of the metal-dusting process on Alloy 800 at 620 °C were investigated by light optical microscopy, RAMAN
spectroscopy, atomic-force microscopy, Auger electron spectroscopy, transmission-electron microscopy and electron back-scatter
diffraction. As it turned out the incubation period for metal-dusting is characterized by simultaneous formation of a heterogeneously
growing oxide scale and deposition of carbon. The material surface shows different tarnish colors depending on the substrate-grain
orientation with different susceptibility to the beginning of metal-dusting attack. “Low-index” grains were not attacked within
the times investigated while the other grain orientations showed pitting. Carbon is evidently incorporated into the oxide
scale from the very beginning of exposure with different intensities depending on the underlying substrate-grain orientation
leading to differences in the tarnish colors. As a consequence carbides are formed even underneath “dense” oxide layers. Evidently
metal-dusting attack starts at positions of the oxide scale where “higher carbon concentrations” are present. 相似文献
108.
Surgical instruments have to meet strict requirements on functionality and stable performance. The functional properties of
scalpels, for example, are mainly dependent on a precise cutting edge geometry and high blade sharpness. To achieve a reliable
production of scalpels, it is necessary to establish a holistic understanding of the process chain as well as the interactions
of all machining processes. An innovative zirconium oxide offers high toughness and high wear resistance, leading to its use
in ophthalmic scalpels. A cooperative project has been conducted by two universities and two industrial partners, funded by
the German Federal Ministry of Economics and Technology (BMWi).The project focuses particularly on the grinding process as
a controlling factor for the scalpel’s functionality and sharpness. The complex process chain with various interactions of
kinematics, vibrations and tool micro-topography was developed for high reliability and efficiency. The performance of in-machine
dressing of diamond wheels with diamond form rollers was decisive for scalpel quality. 相似文献
109.
The development of methods facilitating the detection of cyanobacterial blooms in drinking water reservoirs at an early stage is of great importance. Fluorescence spectroscopy could meet these requirements. The study contains the examination of possible correlations between the different maxima of a fluorescence excitation-emission matrix and the amount of produced and excreted toxins of a lab culture of Microcystis aeruginosa at different stages of growth. Various fluorescence signals (protein-like and humic-like substances, pigments) are suited for an estimation of cell density and actual intra- and extracellular toxin concentration. One signal at 315 nm/396 nm presumably originating from protein-like substances might be useful as a tool for the prediction of increasing cyanobacterial toxin concentrations. As the measurement of fluorescence matrices is still time consuming, synchronous scans with Δλ = 80 nm were tested as a potential alternative. They accurately depict the course of protein-like and humic-like fluorescence during the different stages of growth although especially the latter one is not captured at its maximum. However, due to insufficient separation of chlorophyll a and phycocyanin, the image of the matrix maxima by synchronous scans with Δλ = 80 nm can only be used with minor restrictions. Nevertheless, fluorescence spectroscopy seems to be a powerful tool for the evaluation of cyanobacterial blooms. 相似文献
110.
Helfried Näfe Ruhul Amin Fritz Aldinger 《Journal of the American Ceramic Society》2007,90(10):3224-3226
The literature about the thermodynamic properties of NaNbO3 and Na3 NbO4 has mainly been governed by estimations. The only exceptions are two current calorimetric investigations on the standard enthalpy of formation of NaNbO3 and, in addition, an old and inappropriately evaluated study on the carbon dioxide equilibrium gas pressure over the phase mixture NaNbO3 /Na3 NbO4 /Na2 CO3 . Upon reevaluating the latter results, first experimentally proven data on the difference of the Gibbs-free energies have been obtained (715°–822°C): 相似文献