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Synthetic bulk and natural pyrite from the hydrothermal mine in Schönbrunn (Saxony, Germany) are confirmed to be stoichiometric FeS2 compounds and stable (for thermoelectric applications) up to ∼600 K by combined thermal, chemical, spectroscopic and X-ray diffraction analyses. Natural pyrite with a small amount (＜0.6 wt%) of well-defined transition metal carbonates revealed characteristics of a nondegenerate semiconductor and is suitable as a model system for the investigation of thermoelectric performance. In the temperature range 50–600 K both natural and synthetic high quality bulk FeS2 samples show electrical resistivity and Seebeck coefficients varying within 220–5 × 10−3Ω m and 4 – (−450) μV K−1, respectively. The large thermal conductivity (∼40 W m−1 K−1 at 300 K) is exclusively due to phononic contribution, showing a well pronounced maximum centered at ∼75 K for natural pyrite (grain size ≤5 mm). It becomes almost completely suppressed in the sintered bulk samples due to the increase of point defect concentration and additional scattering on the grain boundaries (grain size ≤100 μm). The thermoelectric performance of pure pyrite with ZT∼ 10−6 at 600 K is indeed by a factor of ∼1000 worse than those reported earlier for some minerals and synthetic samples. [ABSTRACT FROM AUTHOR]

The mechanical response of shock wave-prestrained high-alloy Cr16-Mn7-Ni6 TRIP steel was investigated under compressive and tensile loading at room temperature. Previous shock wave loading was carried out using a flyer-plate assembly with different amounts of explosives in order to achieve shock pressures of 0.3, 0.6, 0.9, and 1.2 Mbar. A significant increase in hardness and strength was observed as compared with the initial as-cast condition. In contrast, a slight decrease in strain hardening rates was measured together with a decrease in fracture elongation in the tensile test. Microstructural analyses of the shock-loaded samples were performed by light optical and scanning electron microscopy. The microstructure revealed a high density of deformation bands consisting of separated stacking faults, ε-martensite, or twins. Significant amounts of deformation-induced α′-martensite were only present at the highest shock pressure of 1.2 Mbar. The thickness of the deformation bands and the number of martensite nuclei at their intersections increased with increasing shock pressure. In all shock-loaded specimens, pronounced phase transformation occurred during subsequent mechanical testing. Consequently, the amount of the deformation-induced α′-martensite in the shock-loaded specimens was higher than in the unshocked as-cast samples. [ABSTRACT FROM AUTHOR]

Pressure-dependent thermodynamic properties of the ambient and high pressure phases of aluminum nitride (w-AlN andrs-AlN) were calculated from first principles in order to determine their phase boundary in thep−Tphase diagram. These predictions were checked by static HP/HT experiments, using a multianvil press and an Al/N/H precursor with low decomposition temperature as educt. The experimental data show that at temperatures between 1000 and 2000 K, the boundary line between the two phases is situated between 11 and 12 GPa, which is ∼1.3 GPa lower than the theoretical result and generally lower than previously assumed. The hardness ofrs-AlN – measured for the first time – is ∼30 GPa (Knoop indenter at loads of 25–50 g), twice as hard asw-AlN. Shock wave recovery experiments on nanow-AlN allowed testing of the chemical and thermal stability ofrs-AlN, and determination of its infrared absorption and27Al NMR data. The shock wave technique will eventually enable the synthesis of larger amounts ofrs-AlN, making it available for technological use. Finally, implications on the high pressure stability of phases in the Si–Al–O–N system are discussed in the light of thermoelastic properties of AlN. [ABSTRACT FROM AUTHOR]

The high pressure phase of aluminium nitride with rocksalt structure (rs) is a ceramic with high potential and a challenging material to investigate. The rs-AlN was synthesised and recovered by shock wave experiments using the flyer-plate method with multiple reflections at peak pressures between 15 and 43 GPa. Successful syntheses were carried out using AlN nanopowder with ambient pressure wurtzite structure (w-AlN) as starting material. The high pressure modification could, however, not be obtained when starting from submicron w-AlN. The recovery of rs-AlN is sensitive to the synthesis conditions as these influence the reconversion of rs-AlN to w-AlN. [ABSTRACT FROM PUBLISHER]

The article highlights the results of an intensive monitoring program on the acceptance of building occupants about the use of different shading and light directing equipment. Topics mentioned include the evaluation of lighting quality, the rating of the indoor lighting environment, and the space perception in correlation to lighting levels and light distribution.

Sulphur diffusion as a function of temperature and oxygen partial pressure was measured in a technical alkali-poor barium alumoborosilicate glass melt (AF45, Schott AG) using the radioactive tracer diffusion method. Under oxidising conditions sulphur diffusion could be described for temperatures between 900-1400°C using a frequency factor D0=(1·7±O·2 )x10-4 m²/s and an activation energy Q=258±10 kJ/mol, whereas under reducing conditions the values were found to be D0=(3.6±O.6)x10-4 m²/s and Q=257±16 kJ/mol. The weak Po2 dependence together with the identical activation energies indicates that the transport mechanisms are similar. Furthermore, although a correlation between sulphur diffusion and viscous flow was found there was no link to the diffusion controlling species. Thus, it is suggested that network coupled transport mechanisms apply to these different redox conditions, similar to the mechanism of network oxygen transport. [ABSTRACT FROM AUTHOR]

Many studies show consistently that repetitive transcranial magnetic stimulation (rTMS) with a frequency of 1 Hz and an intensity above the resting motor threshold (RMT) performed for several minutes over the primary motor cortex (M1) leads to a depression of cortical excitability. Furthermore, most studies concur on a facilitation of the non-stimulated contralateral M1. Little is known, however, about the physiological mechanisms underlying these effects. In 11 healthy volunteers, we stimulated the left M1 for 15 min with 1 Hz-rTMS of 115% RMT. Before, immediately after, and 30 min after the rTMS train, we examined short-interval intracortical inhibition (SICI; interstimulus interval (ISI) of 2 and 4 ms), intracortical facilitation (ICF; ISI 10 ms), and short-interval intracortical facilitation (SICF; ISI 1.5 ms) with established paired-pulse protocols. Mean unconditioned motor evoked potential (MEP) amplitudes and RMT were also measured. Two sessions were run at least 1 week apart, in one excitability of the stimulated M1 was tested, in the other one excitability of the non-stimulated M1. rTMS led to the expected reduction of MEP amplitude of the stimulated M1, which was significant only immediately after the rTMS train. rTMS increased MEP amplitude of the non-stimulated M1, which lasted for at least 30 min. RMT, SICI, ICF and SICF did not show any significant change in either M1, except for a long lasting increase of SICF in the non-stimulated M1. In conclusion, the MEP increase in the non-stimulated M1 lasted longer than the MEP decrease in the stimulated M1. Only the long-lasting MEP increase was associated with a specific change in intracortical excitability (increase in SICF). Modulation of motor cortical inhibition did not play a role in explaining the rTMS induced changes in MEP amplitude. [ABSTRACT FROM AUTHOR]

This paper describes a computer modelling study of the F- and OH- forms of topaz, Al 2 SiO 4 (OH,F) 2 . A potential model is developed, and used to calculate the perfect lattice and defect properties of both forms of the mineral. This information is useful in optimising the properties of topaz for applications in dosimeter devices. [ABSTRACT FROM AUTHOR]

Defect structure and the defect formation in mullites and sillimanites have been investigated using computer simulation techniques. From point defect chemistry and computer simulations, oxygen vacancies are identified as the majority defect responsible for oxygen transport in mullite. The defect formation energies are between 3 and 4 eV. Using supercell calculation methods, the random structure is identified to be stable in mullites, whereas the ordered structure can be confirmed to be more stable in sillimanite. An energy of 0.7–1.0 eV for the association of oxygen vacancies with cations is estimated. [ABSTRACT FROM AUTHOR]

Objective: In response to loud clicks, a vestibular evoked potential can be recorded from sternocleidomastoid muscles, called "click evoked myogenic potential" (CEMP). This paper reports on the usefulness of CEMP in the differential diagnosis of acute vertigo of presumed vestibular origin.Methods: CEMP was examined in 40 patients with acute vertigo of vestibular origin (26 with acute peripheral vestibulopathy, five with Ménière's disease, three with benign paroxysmal positioning vertigo (BPPV), six with psychogenic vertigo) and the results compared with standard caloric reaction (CR). For CEMPs, clicks were delivered unilaterally via a pair of headphones. EMG activity was collected by surface electrodes placed on the sternocleidomastoid belly and averaged.Results: In 29 patients, CR was unilaterally abnormal, pointing to a peripheral vestibular lesion. Seventeen of them had a corresponding loss of CEMPs; the other 12 patients had a normal CEMP. The remaining 11 patients had normal results in both tests. In comparison with CR, CEMP showed a sensitivity of 59% and a specificity of 100% for peripheral vestibular disorders.Conclusion: CR is a test of the horizontal canal whereas CEMP is thought to be a sacculus test. Different results of CR and CEMP may be due to this difference between target organs stimulated and may be of prognostic value. [ABSTRACT FROM AUTHOR]

The study reported here was performed to find out whether changes in the number of mycobacteria in various organs of BCG-infected mice can be related to changes in the phenotype of monocytes, macrophages and lymphocytes in the blood, various tissues and peritoneal cavity and to the formation of granulomas in the spleen, liver and lungs. The relative amounts of various antigens on the leukocytes were assessed semi-quantitatively after immunocytochemical detection of the binding of monoclonal antibodies. Granuloma formation was determined after immunocytochemical staining of cells in sections of liver and lung tissue with a monoclonal antibody against the common leukocyte antigen and in sections of the spleen with a monoclonal antibody against the Mac-2 antigen. The results showed that during the first week of infection the number of BCG in spleen, liver and lungs declined considerably. Multiplication of mycobacteria during the second week of infection was associated with decreased expression of antigen F4/80 and increased expression of Ia antigen and Mac-2 antigen by blood monocytes and macrophages. Reduction of the numbers of BCG in the spleen and liver during the third week after i.v. injection of BCG and in lungs during the fourth week of the infection was found to be correlated with the degree of granuloma formation in these organs. After in traveneous injection of killed BCG no changes were observed in the phenotype of monocytes and the macrophages in spleen, liver, lungs and peritoneal cavity. These mice showed considerably less granuloma formation than BCG-infected mice. The present results indicate that live but not killed mycobacteria induce macrophage activation. [ABSTRACT FROM AUTHOR]

Based on the constructivist principle of active learning, we focus on children's transformation of their cognitive play activity into what we regard as independent mathematical activity. We analyze how, in the process of this transformation, children modify their cognitive play activities. For such a modification to occur, we argue that the cognitive play activity has to involve operations of intelligence which yield situations of mathematical schemes. We present two distinctly different cases. In the first case, the medium of the cognitive play activity was a discrete computer microworld. In the second case, the medium was a continuous microworld. We specify several types of accommodations induced by social interaction, accommodations we see as critical for understanding active mathematics learning. Finally, we illustrate how a playful orientation of independent mathematical activity can be inherited from cognitive play. [ABSTRACT FROM PUBLISHER]

Focuses on children's transformation of their cognitive play activity into an independent mathematical activity. Constructivist principle of active learning as basis; Modification of cognitive play activities; Involvement of operations of intelligence to yield situation of mathematical schemes; Continuous and discrete computer microworld as media.

Starch-gel electrophoresis for adenylate kinase (AK) was performed on 2519 haemolysates from 6 population samples of unrelated males in Finland, 4 Finnish Lapp populations, the Maris (Cheremisses) in the USSR, and an Eskimo population in NW Greenland. Between the Finland Swedes and Finns no significant difference in AK polymorphism was observed and the allele frequency estimates of AK were comparable with those found in other Europeans. The indigenous 'pure' Skolt Lapps showed absence of the AK gene, which was also extremely low in the Fisher and Mountain Lapps. All the Lapp populations so far studied show an extremely low frequency of the AK gene. The rarity of AK in Lapps may offer a better approach to the estimation of intermixture than certain other genes which vary in frequency in different Lapp populations. Among the Maris AK frequencies are lower (0.017) than among other Europeans. The AK was also very low (0.016) in the Greenland Eskimo population on Augpilagtok Island. The results obtained for the AK phenotypes in 149 Lapp families and in 84 mothers and their children are in agreement with the hypothesis that AK and AK are alleles at one and the same autosomal locus. The present family and mother-child studies add further evidence for the acceptance of the AK system as a valuable tool in cases of disputed paternity. [ABSTRACT FROM AUTHOR]

The polymorphism of the major component of human complement (C′3 or $$\beta _{1^C }$$ -globulin) at that time is interpreted formally by the genetic model '5 codominant alleles at one autosomal locus'. Examination of this hypothesis has been performed examinating a sample of 482 unrelated persons in the two populations, 71 families with 127 children and 115 mother/child combinations in a German population. It could be stated that 4 alleles or more are involved in this polymorphism. [ABSTRACT FROM AUTHOR]

Frequencies and phenotype distribution of red cell adenosine deaminase (ADA), adenylate kinase (AK), phosphoglucomutase (PGM), acid phosphatase (AP) and serum α-antitrypsin (α-at or Pi) were examined in a German group of the area of Hamburg. The observed distribution of phenotypes in all five systems is consistent with that expected by the Hardy-Weinberg equilibrium. Within the mother/child combinations we found no incompatible combination. The results of additional family investigations for α-antitrypsin are consistent with Mendelian expectation. [ABSTRACT FROM AUTHOR]

Presents an introduction to the September 2001 issue of "Journal of Mathematics Teacher Education."

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