Discussion No. 2

The original version of the half-normal plot [C. Daniel, Technometrics, t, (1959), 311–34] is reviewed and two modified versions are introduced. The modified versions incorporate corrections of a major flaw in the original version relating to critical values and a minor flaw relating to plotting positions. The critical values given in this article control the probability error rate, the probability of at least one false positive in the analysis of an experiment, and are considerably different from those given by Daniel. One of the modified versions is more powerful than Daniel's original procedure. Anothe improvement made in the modified versions is that only the smallest 70%, of the contrasts not declared significant, are used to constuct the final estimate of the error variance. This results in an appreciable redaction in the mean square error of this estimate. Examples are plesented to illustrate the use of the various half-normal plot versions.     

High-temperature stabilities of YCuO2, BaCu2O2 and Ba2CuO3 from oxide electrolyte e.m.f. measurements

The oxygen potentials in the system YCuO₂/Y₂O₃/Cu and Y₂O₃/YCuO₂/CuO were measured over the ranges 1113–1255 K and 782–1122 K by employing oxide electrolyte galvanic cells with air/platinum as the reference electrode, and the expression $$\Delta G_{f, ox}^o (YCuO_2 )( \pm 0.19)(kJ mol^{ - 1} ) = - 5.346 + 0.00384{\text{ }}T (K)$$ was determined. Similar e.m.f. measurements were carried out on the electrodes BaCuO₂/BaCu₂O₂/Cu₂O and Ba₂CuO₃/BaCuO₂/BaCu₂O₂ were measured over the ranges 1003–1132 K and 1175–1235 K and from the results, the ΔG _f,ox ^o of BaCu₂O₂ and Ba₂CuO₃ were determined to be $$\begin{gathered} \Delta G_{f, ox}^o (BaCu_2 O_2 )(kJ mol^{ - 1} ) = - 25.09 + 0.01548{\text{ }}T (K) \hfill \\ \Delta G_{f, ox}^o (BaCu_2 O_3 )(kJ mol^{ - 1} ) = - 5.79 - 0.07492{\text{ }}T (K) \hfill \\ \end{gathered} $$      

TANGO Array.: 2. Simulations

The angular and energy resolutions of the TANGO Array were obtained using extensive Monte Carlo simulations performed with a double purpose: (1) to determine the appropriate parameters for the array fitting to the desired range of sensitivity (the knee energy region), and (2) to construct a reliable shower database required for reference in the analysis of experimental data. The AIRES code, with the SIBYLL hadronic collision package, was used to simulate Extended Air Showers produced by primary cosmic rays (assuming protons and iron nuclei), with energies ranging from 10¹⁴ to 10¹⁸ eV. These data were fed into a realistic code which simulates the response of the detectors (water Cherenkov detectors), including the electronics, pickup noise, and the signal attenuation in the connecting cables. The trigger stage was considered in the simulations in order to estimate the trigger efficiency of the array and to verify the accuracy of the reconstruction codes. This paper delineates the simulations performed to obtain the expected behavior of the array, and describes the simulated data. The results of these simulations suggest that we can expect an error in the energy of the primary cosmic-ray of ∼60% of the estimated value and that the error in the measurement of the direction of arrival can be estimated as ∼4°. The present simulations also indicate that unambiguous assignments of the primary energy cannot be obtained because of the uncertainty in the nature of the primary cosmic ray.     

Mictomagnetism in a new BaO.Fe2O3.B2O3 glass.

An homogeneous BaO ·Fe₂O₃ ·B₂O₃ glass containing 30% Fe₂O₃ is prepared by a splat-cooling technique. X-ray and electron diffraction reveal the product to be amorphous at room temperature. The crystallization, as shown by DTA studies, begins at 750 K, and up to 950 K, a temperature at which BaFe₁₂O₁₉ is shown to be present, the crystallizing products are mainly evolutive.The magnetic measurements show a probably mictomagnetic behaviour at low temperature with a maximum of magnetic susceptibility at 12 (±1) K. At higher temperature the susceptibility obeys a Curie-Weiss law with large negative Weiss constant and low Curie constant per Fe³⁺ ions. After crystallization the product is ferrimagnetic and could be used as a permanent magnet.Mössbauer study reveals that the glass mainly consists of Fe³⁺ ions in distorted sites and a hyperfine structure at low temperature; the magnetic ordering temperature is estimated to be about 44 (±1) K.     

Electrokinetic transport in nanochannels. 2. Experiments

We present an experimental study of nanoscale electrokinetic transport in custom-fabricated quartz nanochannels using quantitative epifluorescence imaging and current monitoring techniques. One aim is to yield insight into electrical double layer physics and study the applicability of continuum theory to nanoscale electrokinetic systems. A second aim is to explore a new separation modality offered by nanoscale electrophoretic separations. We perform parametric variations of applied electric field, channel depth, background buffer concentration, and species valence to impose variations on zeta potential, effective mobility, and Debye length among other parameters. These measurements were used to validate a continuum theory-based analytical model presented in the first of this two-paper series. Our results confirm the usefulness of continuum theory in predicting electrokinetic transport and electrophoretic separations in nanochannels. Our model leverages independent measurements of zeta potential performed in a microchannel system at electrolyte concentrations of interest. These data yield a zeta potential versus concentration relation that is used as a boundary condition for the nanochannel electrokinetic transport model. The data and model comparisons together show that the effective mobility governing electrophoretic transport of charged species in nanochannels depends not only on ion mobility values but also on the shape of the electric double layer and analyte ion valence. We demonstrate a method we term electrokinetic separation by ion valence, whereby both ion valence and mobility may be determined independently from a comparison of micro- and nanoscale transport measurements.     

Chemical plume tracking. 2. Multiple-frequency modulation

The purpose of this research is to estimate the effect of turbulent mixing on the information content in a chemically encoded signal, to investigate the effect of the presence of multiple encoded frequencies, and to evaluate the information contained in the higher harmonics of the coherence spectra. The virtual plume instrument is used to mimic the flow conditions and signal patterns in a real chemical plume. Two-frequency modulation experiments are performed using solenoid valves to introduce concentration plugs of a marker into the carrier flows at certain constant frequencies. In our experiments, the length of the delay elements and the dispersion were varied to mimic different characteristics of the turbulent plume. In addition, an artificial but uncorrelated white noise was added to the raw amperometric signals in order to simulate the "noisy" conditions existing in a real plume. Our experiments reveal that the introduced turbulence has only a marginal effect on the coherence spectra. Moreover, it is shown that when the second frequency is present in the plume, both fundamental frequencies can be unambiguously assigned. Higher harmonics in the coherence spectra have been found to depend on the distance from the source. These findings are important for understanding of the mechanism of chemotaxis and may also lead to the design of optimized search algorithms for chemical plume tracking robots.     

A.c. conductivity for amorphous TeO2-P2O5 glass system

The a.c. conductivity for the TeO₂-P₂O₅ glassy system was measured in the temperature range 300–573 K and in the frequency range 100 Hz to 10 kHz. The a.c. conductivity () increased with frequency according to the relation ()^s. The frequency exponent s was found to decrease with increasing temperature. The composition dependence of the conductivity was also investigated. The density of states was also calculated using the Elliott model. The a.c. conductivity increased over the studied temperature range. The obtained experimental data have been analysed with reference to various theoretical models. The analysis shows that the correlated barrier hopping (CBH) model is the most appropriate mechanism for conduction in the TeO₂-P₂O₅ glass system.