Magnetic ordering of interstitial iron in Fe1+xSb alloys

Mössbauer and magnetization measurements have been used to observe the magnetic ordering of interstitial iron atoms in the Fe_1+xSb phase in seven Fe:FeSb alloys. Short range magnetic ordering of the interstitials occurs only at temperatures well below the FeSb lattice Néel temperature. Magnetization measurements show that the interstitials form magnetic clusters which freeze in typical mictomagnetic fashion around 30 K. Field cooled alloys show an irreversible magnetization better described as classical superparamagnetism. Variations in the cluster freezing temperature with applied field are observed.     

The trifluoromethylation of chloroaromatics using the copper-CF2Br2 - dialkylamide reaction system

The in situ generation of CuCF₃ from the reaction of copper, dibromodifluoromethane at either N,N-dimethylformamide or N,N-dimethylacetamide (Burton's reagent) has been used for the direct substitution of chlorine by CF₃ in a number of aromatic substrates. Particular attention has been paid to the effects of ring substituents on the efficiency of reaction.     

Continuity of flow alignment parameters across the nematic-isotropic phase transition

We use existing data to show that the parameter which characterizes the reactive coupling of molecular orientation to shear strain in the nematic liquid crystal N-(p'-methoxybenzylidene)-p-n-butylaniline (MBBA) is continuous across the nematic-isotropic phase transition.     

Surface modification by plasma techniques. I. The interactions of a hydrogen plasma with fluoropolymer surfaces

The rapid defluorination of fluoropolymer surfaces by their exposure to a hydrogen plasma excited by an inductively coupled RF field has been studied using ESCA. The results are interpreted in terms of a reaction/depth profile; the reaction is not uniform with depth leading to the formation of an approximately 20 Å thick boundary layer of defluorinated material.     

Optimal Risk-Sharing When Risk Preferences are Uncertain

In many cases, a firm or agency needs a product that only one vendor can supply and for which the final cost is uncertain. An optimal risk-sharing arrangement is sought when the buyer and contractor agree on the probability distribution of cost but the buyer is uncertain of the contractor's risk-preferences. We find that when the buyer and contractor have exponential utilities, the optimal profit arrangement for the higher risk-averse contractor is no longer linear but concave in the costs. The degree of concavity is affected by the probabilistic beliefs on the contractor's risk-preferences. As the more risk-averse contractor becomes more likely, her chosen profit arrangement becomes less concave approaching the ideal, linear arrangement. The less risk-averse contractor is provided a profit arrangement with a certainty equivalent above her reservation price. This is the price the buyer must pay in order to entice a less risk-averse contractor into agreeing to accept a more risky profit arrangement.Another formulation is considered that assumes the buyer and contractor maximize approximations to their certainty equivalents in order to provide a more practical and possibly viable approach to sole-source contracting.     

MRI appearance of disseminated osseous tuberculosis

Disseminated osseous tuberculosis is a rare disease. This is a report of two cases of disseminated osseous tuberculosis imaged with MRI at 1.5-T, CT, plain radiography and bone scintigraphy. CT and plain radiography demonstrated either highly destructive or cystic lesions with sclerotic margins. Bone scintigraphy and plain radiography were quite insensitive in detecting areas of involvement compared to MRI. On MRI the abnormal areas had short T-1 relaxation values, which is an atypical appearance for bony infections, and prolonged T-2 relaxation values. The reason for the T-1 relaxation behavior is uncertain. MRI also provided delineation of epidural extent.     

Psychophysical studies relevant to the design of a digital electrotactile speech processor

Psychophysical tests were carried out to investigate the perception of electrocutaneous stimuli delivered to the digital nerve bundles. The tests provided data for defining the operating range of a tactile aid for patients with profound-to-total hearing loss, as well as the individual differences between subjects and the information that could be transmitted. Monopolar biphasic constant current pulses with variable pulse widths were used. Threshold pulse widths varied widely between subjects and between fingers for the same subject. Thresholds were reasonably stable, but maximum comfortable levels increased with time. Perceived intensity was weakly dependent on pulse rate. Absolute identification of stimuli differing in pulse width gave information transmissions from 1.3-2.1 bits, limited by the dynamic ranges of the stimuli (3-17 dB). Stimuli from electrodes placed on either side of each finger were identified easily by all subjects. Absolute identification of stimuli differing in pulse rate gave information transmissions from 0.5-2.0 bits. Difference limens for pulse rate varied between subjects and were generally poor above 100 pps. On the basis of the results, an electrotactile speech processor is proposed, which codes the speech amplitude as pulse width, the fundamental frequency as pulse rate, and the second formant frequency as electrode position. Variable performances on tasks relying on amplitude and fundamental frequency cues are expected to arise from the intersubject differences in dynamic range and pulse rate discrimination. The psychophysical results for electrotactile stimulation are compared with previously published results for electroauditory stimulation with a multiple-channel cochlear implant.     

Heterocyclic studies—XXV: Mass spectra of some 4-trifluoromethylpteridine derivatives

Mass spectra of 4-trifluoromethylpteridine and nine of its derivatives are recorded. Electron impact induced fragmentations of 4-trifluoromethylpteridine and its 2-chloro-, 7-methyl- and 6, 7-dimethyl-derivatives resemble those of pteridine and simple methylpteridines except that loss of a trifluoromethyl radical usually intervenes at some stage. Fragmentation of 4-trifluoromethyl-pteridine derivatives with an amino, substituted-amino, alkoxy or alkylthio group in the 2-position fragment by a variety of mechanisms. Accurate mass measurements and deuterium labelling were used to help elucidate some fragmentation pathways.     

Mössbauer measurements on lattice and interstitial iron atoms in Fe1+xSb alloys

Mössbauer measurements on the Fe_1+xSb phase in seven samples of Fe : FeSb have been used to observe the independent magnetic ordering of lattice and interstitial iron atoms. An ordering temperature of (55 ± 5) K is deduced for the interstitial iron atoms. The anomalous behaviour of the lattice iron hyperfine fields at about the interstitial ordering temperature is attributed to the perturbation of the superexchange interaction between lattice atoms by the magnetic ordering of the interstitials.