An octahedral random network

Construction, topology and radial distribution functions of a 2064-atom continuous random network of AB₃ stoichiometry are described. It is composed of corner-sharing AB₆ octahedra, with no broken bonds. Odd-membered A rings predominate. Density is 11% greater than for the ideal AIF₃ structure.     

Quantitative Mössbauer analysis of maghemite-hematite mixtures in external applied field

Mixtures of synthetic maghemite and hematite have been studied by Mössbauer spectroscopy at room temperature with an applied magnetic field of 0.2 T. The results show that the relative area of each subspectrum reproduces very satisfactorily the weighted quantities, whereas the agreement is poor in absence of the external field, particularly for higher fractions of hematite.     

Magnetic heat capacity of an amorphous Gd-Al alloy

The magnetic specific heat of amorphous GdAl₂ shows a broad maximum near 17.5 K, the temperature of the spin-glass-like cusp in the magnetic susceptibility. At low temperatures it varies as $\text{T}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$, with a small negative intercept. This is interpreted in terms of ferromagnetic spin waves excited in regions some 35 Å in size.     

Simultaneous sensing of L-tyrosine and epinephrine using a glassy carbon electrode modified with nafion and CeO2 nanoparticles

An electrochemical sensor was developed and tested for detection of L-tyrosine in the presence of epinephrine by surface modification of a glassy carbon electrode (GCE) with Nafion and cerium dioxide nanoparticles. Fabrication parameters of a surfactant-assisted precipitation method were optimized to produce 2–3 nm CeO₂ nanoparticles with very high surface-to-volume ratio. The resulting nanocrystals were characterized structurally and morphologically by X-ray diffractometery (XRD), scanning and high resolution transmission electron microscopy (SEM and HR-TEM). The nanopowder is sonochemically dispersed in a Nafion solution which is then used to modify the surface of a GCE electrode. The electrochemical activity of L-tyrosine and epinephrine was investigated using both a Nafion-CeO₂ coated and a bare GCE. The modified electrode exhibits a significant electrochemical oxidation effect of L-tyrosine in a 0.2 M Britton-Robinson (B-R) buffer solution of pH 2. The electro-oxidation peak current increases linearly with the L-tyrosine concentration in the molar concentration range of 2 to 160 μM. By employing differential pulse voltammetry (DPV) for simultaneous measurements, we detected two reproducible peaks for L-tyrosine and epinephrine in the same solution with a peak separation of about 443 mV. The detection limit of the sensor (signal to noise ratio of 3) for L-tyrosine is ~90 nM and the sensitivity is 0.20 μA μM⁻¹, while for epinephrine these values are ~60 nM and 0.19 μA μM⁻¹. The sensor exhibited excellent selectivity, sensitivity, reproducibility and stability as well as a very good recovery time in real human blood serum samples.

Simultaneous electrochemical determination of L-tyrosine and epinephrine in blood plasma with Nafion-CeO₂/GCE modified electrode showing a 443 mV peak-to-peak potential difference between species oxidation peak currents.

     

Hyperfine interactions and crystal field effects in intermetallic compounds between Dy and 3d transition metals

A model based on the relative strengths of the magnetic exchange and electric field interactions is proposed for explaining the differences observed between the ¹⁶¹Dy Mössbauer spectrum of Dy₂Ni₁₇ where two dysprosium sites are observed and spectra of Dy₂Fe₁₇ and Dy₂Co₁₇ which show only one hyperfine pattern.