Critical evaluation of laboratory performance from IAEA-452 (fish scallop) inter-comparison exercise results

The International Atomic Energy Agency Marine Environmental Laboratory (IAEA-MEL) conducted an intercomparison exercise for the “Trace elements and methyl mercury in fish scallop: IAEA-452” in 2009. The Neutron Activation Analysis (NAA) laboratory at PINSTECH, Pakistan took part in this exercise. Comparison with the IAEA results showed that of the 18 elements reported to the IAEA 7 had unacceptable z-scores while the data for two elements was questionable (2< |z-score| <3). Upon investigation it was discovered that the large number of elements having unacceptable z-scores was due to human error and the greater difficulty in analyzing biological samples which have low amounts of trace elements. Therefore selection of values corresponding to matrix matched reference materials (RMs), such as IAEA-436 and IAEA-407, and to non-interfering peaks the results obtained became comparable to the IAEA results with only the result for As having |z-score|> 3.     

Smoothing with positivity‐preserving Padé schemes for parabolic problems with nonsmooth data

We introduce a new class of higher order numerical schemes for parabolic partial differential equations that are more robust than the well‐known Rannacher schemes. The new family of algorithms utilizes diagonal Padé schemes combined with positivity‐preserving Padé schemes instead of first subdiagonal Padé schemes. We utilize a partial fraction decomposition to address problems with accuracy and computational efficiency in solving the higher order methods and to implement the algorithms in parallel. Optimal order convergence for nonsmooth data is proved for the case of a self‐adjoint operator in Hilbert space as well as in Banach space for the general case. Numerical experiments support the theorems, including examples in pricing options with nonsmooth payoff in financial mathematics. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2005     

Computer simulations of nucleation of nanoparticle superclusters from solution

This paper presents simulation studies of nanoparticle supercluster (NPSC) nucleation from a temperature quenched system. The nanoparticles are represented as 5 nm, spherical gold nanoparticles ligated with alkane thiols. The pair potential accounts for the van der Waals interaction between the metallic cores and ligand-ligand and ligand-solvent interactions. Phenomena well-known for molecular systems are observed including a prenucleation induction period, fluctuating prenucleation clusters that predominately add monomers one at a time, a critical nucleus size, and growth of NPSCs from solution in the presence of an equilibrium supernatant, all consistent with classical nucleation theory. However, only the largest prenucleating clusters are dense, and the cluster size can occasionally range greater than the critical size in the prenucleation regime until a cluster with low enough energy occurs, then nucleation ensues. Late in the nucleation process, the clusters display a crystalline structure that is a random mix of face-centered cubic (fcc) and hexagonal close-packed (hcp) lattices and indistinguishable from a randomized icosahedra structure.     

Multiple free energies of activation of the chain oxygen atoms in the YBa2Cu3O7−δ

The desorption kinetics of the chain oxygen atoms in the YBa₂Cu₃O_7– (YBCO) superconductor were studied using isothermal vacuum annealing (VA). The number of the O(1) atoms per unit cell in the crystal was measured at three temperatures of 390, 415, and 450°C for various annealing times. From these measurements it was found that at high temperatures the loss of the O(1) atoms from the YBCO is very rapid, and so, low annealing temperatures must be used in order to see the fine details of the desorption phenomena. When the log of the instantaneous O(1) occupancy vs. time was plotted, three distinct linear segments were obtained for each temperature. This, I think is an indication of the existence of multiple desorption processes. From the slopes of these lines, I have evaluated three free energies of activation to be 1.14(6), 1.45(3), and 1.91(13) eV. These results are explained in terms of oxygen ordering in the chains.     

Delay-range-dependent local adaptive and robust adaptive synchronization approaches for time-delay chaotic systems

Nonlinear Dynamics - This paper studies the local adaptive and robust adaptive control methodologies for the synchronization of the chaotic drive and the response systems with finite time lags,...     

National intercomparison exercise, ZH-A for the measurement of hafnium and zirconium in zirconium ores

Summary A national intercomparison exercise was conducted to remove inconsistencies and improve analytical procedures in the measurement of hafnium and zirconium in zirconium ores. The ZH-A series of reference samples, prepared at the Pakistan Institute of Nuclear Science and Technology (PINSTECH), were used for this purpose. It was observed that measurement errors decreased with increasing Hf concentration (~298-17500 ppm) for most techniques, especially for AAS due to the sample preparation procedure required for this technique. Of all the tested techniques most reliable results were obtained with neutron activation analysis (NAA) for the measurement of Hf and Zr in such matrices.     

Study of oxidation of alloy 1.4306S (SS-304L) in air and steam at 1200°C using the Mössbauer technique

The Mössbauer technique has been used to study the oxidation of alloy 1.4306S (SS-304L) at 1200°C exposed in atmospheres of air and steam, for, 1, 6, 24, 100 and 400 hours. By oxidation in air the major products are -FE₂O₃, -FE₂O₃, and Fe₃O₄ while, during oxidation in steam they are -FeOOH, -Fe₂O₃ and Fe₃O₄. A minor phase detected following both kinds of oxidation may be ascribed to MnCrFeO₄, Cr₂FeO₄, -FeOOH and -FeOOH produced in steam only while the base material is found following air oxidation. The proportion of Fe₃O₄ on the scale remains constant for all exposure durations in air oxidation, while it becomes constant in steam oxidation only in cases where the entire sample has been oxidized.     

In Vitro Adventitious Shoot Regeneration via Indirect Organogenesis from Petiole Explants of Cassia angustifolia Vahl.—a Potential Medicinal Plant

An effective protocol was developed for in vitro regeneration of the Cassia angustifolia via indirect organogenesis from petiole explants excised from 21-day-old axenic seedlings. Organogenic callus were induced on Murashige and Skoog (MS) medium supplemented with 5.0 μM 2,4-dichlorophenoxy acetic acid and 2.5 μM thidiazuron (TDZ). Adventitious shoot regeneration was achieved on MS medium supplemented with 5.0 μM TDZ as it induced 8.5 ± 0.98 shoots in 85% cultures. The number of shoots and shoot length was significantly enhanced when cultures were subcultured on auxin–cytokinin-containing medium. The highest number of shoots (12.5 ± 1.10) and shoot length (4.3 ± 0.20 cm) was recorded on MS medium supplemented with 5.0 μM TDZ and 1.5 μM indole-3-acetic acid. Regenerated shoots were rooted best on MS medium supplemented with 10.0 μM indole-3-butyric acid followed by their transfer to liquid MS filter paper bridge medium. The plants were successfully hardened off in sterile soilrite followed by their establishment in garden soil with 70% survival rate. The plants showed normal morphological characteristics similar to the field grown plants.