Pressure-induced phase transition in tysonite LaF3

We have studied the high-pressure phase stability of LaF₃ using full-potential linear augmented plane wave method. We have shown that experimentally observed orthorhombic phase is less stable compared to the theoretically predicted tetragonal structure above 25 GPa pressure. The structural transition is mainly due to the steric repulsion of ions and electrons to higher pressures.     

The enhancement effect in K-shell radiative recombination of \mbox{\sffamily\bfseries U}^{\hbox{\sffamily\bfseries\fontsize{10}{12}\selectfont 92+}} ions with cooling electrons

We report the results of the x-ray radiative recombination (RR) experiment at the electron cooler of the ESR storage ring performed, for the first time, for detuned (off-cooling) electron energies. In this experiment the recombination of stored, decelerated bare uranium ions with electrons in the energy range 0–1000 meV was studied by observing K-RR x-ray photons emitted from direct radiative recombination to the lowest n=1 state. In this way the RR process was studied in a state selective manner for several off-cooling electron energies. The measured dependency of the recombination rate on the relative electron energies for K-shell RR x-ray photons are compared with the predictions of both nonrelativistic and fully relativistic calculations for the radiative recombination. A role of the relativistic effects, which contribute substantially for higher relative electron energies, are discussed. Strong enhancement of the recombination rate is observed for the the zero relative electron energy (cooling condition) for the K-shell.     

Aggregation and adhesion of gold nanoparticles in phosphate buffered saline

In applications in medicine and more specifically drug delivery, the dispersion stability of nanoparticles plays a significant role on their final performances. In this study, with the use of two laser technologies, dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA), we report a simple method to estimate the stability of nanoparticles dispersed in phosphate buffered saline (PBS). Stability has two features: (1) self-aggregation as the particles tend to stick to each other; (2) disappearance of particles as they adhere to surrounding substrate surfaces such as glass, metal, or polymer. By investigating the effects of sonication treatment and surface modification by five types of surfactants, including nonylphenol ethoxylate (NP9), polyvinyl pyrrolidone (PVP), human serum albumin (HSA), sodium dodecyl sulfate (SDS) and citrate ions on the dispersion stability, the varying self-aggregation and adhesion of gold nanoparticles dispersed in PBS are demonstrated. The results showed that PVP effectively prevented aggregation, while HSA exhibited the best performance in avoiding the adhesion of gold nanoparticle in PBS onto glass and metal. The simple principle of this method makes it a high potential to be applied to other nanoparticles, including virus particles, used in dispersing and processing.     

Effect of holmium substitution for the improvement of multiferroic properties of BiFeO3

This paper reports on multiferroic properties of Ho substituted BiFeO₃ (Bi_1−xHo_xFeO₃) ceramics. It is observed that for x=0.15, a prominent ferroelectric loop is seen at 300 K even if the system remains in rhombohedral (R3c) phase without appearance of any observable impurity phases. A well shaped M-H loop is observed at 10 K for x=0.15. However it showed ferromagnetism, confirming the contribution of Ho³⁺ towards enhancement of ferromagnetic properties of BiFeO₃ at 300 K. Suppression of impurity phases of pure BiFeO₃ bulk ceramic favors the reduction of mobile oxygen vacancies and reduces leakage current, due to which ferroelectric properties of BiFeO₃ is enhanced. We argue that Ho substitution at Bi site is likely to suppress the spiral spin modulation and at the same time increase the canting angle, which favors enhanced multiferroic properties. XRD, SEM, magnetization, polarization and chemical bonding analysis measurements were carried out to explain the multiferroic behavior.     

New approach to the η-proximal point algorithm and nonlinear variational inclusion problems

A new approach using the over-relaxed proximal point algorithm in the context of solving a class of inclusion problems based on the notion of maximal (η)-monotonicity is developed and examined. Convergence analysis seems to be reasonable, and finally, some specializations are included. Furthermore, the model developed in this communication seems to be appropriate to the Yosida approximation in the sense that it can be applied to first-order evolution equations/inclusions as well.     

Growth and optical homogeneity investigations of Fe and Fe:Mn codoped LiNbO3 crystals

Lithium niobate (LiNbO₃) crystals doped with Fe and Fe:Mn were grown by Czochralski technique. The doping concentrations of Fe and Mn were optimized. Transmission studies reveal broad absorption band centered at 488 nm. The UV cutoff observed for Fe doped LiNbO₃ is 358 nm whereas for Fe:Mn codoped LiNbO₃ is 352 nm. This decrease in UV cutoff for Fe and Mn codoped LiNbO₃ compared to only Fe doped LiNbO₃ is due to the increase in Li/Nb ratio. Optical homogeneity was assessed using conoscopy and birefringence interferometry. Dark and photo conductivity measurements prove that LiNbO₃ is a negative photo conducting material. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of k 0-factors and validation of k 0-INAA for short-lived nuclides

For standardization of k ₀-based instrumental neutron activation analysis, k ₀-factors for short-lived nuclides (half-lives—11 s to 37 min) of elements F, Se, Sc, Al, V, Ti, Cu, Ca, Mg, I, and Cl with respect to gold (¹⁹⁷Au) were determined using pneumatic carrier facility (PCF) at CIRUS reactor of BARC, Mumbai. Characterization of PCF was carried out by cadmium-ratio method using Au and Zr. The experimental k ₀-factors of the isotopes were found to be in good agreement with the recommended k ₀-factors in most of the cases, as evident from the values of % error and U-score at 95% confidence level. The method was validated by determining concentrations of elements through their short-lived nuclides in one type of the synthetic multielement standards (SMELS-I) obtained from SCK-CEN, Belgium. The method was also applied for determination of concentrations of some of the elements in two reference materials of IAEA, SL-3, and SL-1.     

Effect of zinc concentration on the structural,electrical and magnetic properties of mixed Mn–Zn and Ni–Zn ferrites synthesized by the citrate precursor technique

Mixed manganese-zinc and nickel-zinc ferrites of composition Mn_0.2Ni_0.8−xZn_xFe₂O₄ where x=0.4$x=0.4$, 0.5 and 0.6 have been synthesized by the citrate precursor technique. Decomposition of the precursor at temperatures as low as 500 °C gives the ferrite powder. The ferrites have been investigated for their electrical and magnetic properties such as saturation magnetization, initial permeability, Curie temperature, AC-resistivity and dielectric constant as a function of sintering temperature and zinc content. Structural properties such as lattice parameter, grain size and density are also studied. The mixed compositions exhibited higher saturation magnetizations at sintering temperatures as low as 1200 °C. While the Curie temperature decreased with zinc content, the permeability was found to increase. The AC-resistivity ranged from 10⁵–10⁷ Ω cm and decreased with zinc content and sintering temperature. The dielectric constants were lower than those normally reported for the Mn–Zn ferrites. Samples sintered at 1400 °C densified to about 94% of the theoretical density and the grain size was of the order of about 1.5 μm for the samples sintered at 1200 °C and increased subsequently with sintering temperature.     

Embedded template-assisted fabrication of complex microchannels in PDMS and design of a microfluidic adhesive

In this paper, we describe a novel method for fabricating 2-D and 3-D microchannel patterns in a flexible platform of cross-linked poly(dimethylsiloxane) (PDMS). Here, a slender nylon thread formed into different 2-D and 3-D shapes is used as a template that is embedded inside a block of cross-linked PDMS. The cross-linked network is then allowed to swell in a suitable solvent that swells the network selectively but leaves the nylon thread unaltered. The thread is then gently removed from the swollen network leaving behind a microchannel. Channels of a variety of topologically complex orientations like knots, helices, super-helices, and channels of a variety of cross-sections can be generated using this simple method. Finally, we have presented an application by generating inside layers of adhesive in these microchannels, which are observed to enhance the adhesion strength significantly.     

Photoacoustic FTIR spectroscopic study of undisturbed nacre from red abalone

In this work, photoacoustic Fourier transform infrared (PA-FTIR) spectroscopy has been utilized to study interfacial interactions of undisturbed nacre and nacre powder from red abalone shell. The spectra of both undisturbed nacre and nacre powder showed characteristic bands of aragonite and proteins. Although nacre powder and undisturbed nacre are chemically identical, PA-FTIR spectrum of undisturbed nacre is found to be significantly different from that of nacre powder. A broad and strong band is observed at around 1485 cm(-1) in nacre powder. The intensity of this band is notably reduced in undisturbed nacre. This result is explained on the basis of interfacial interactions between aragonite platelets and acidic proteins. It is also observed that band at around 1788 cm(-1) originates from three overlapping bands 1797, 1787 and 1778 cm(-1). The band at around 1787 cm(-1) is assigned to CO stretching of carboxylate groups of acidic proteins. The other two bands at 1797 and 1778 cm(-1), originate from aragonite and have been assigned to combination bands, nu(3)+nu(4a) and nu(3)+nu(4b), respectively. For the study of stratification in undisturbed nacre, PA-FTIR spectra have been collected in step scan mode. The variation in spectra with depth can be attributed to changes in conformation of proteins as well as interfacial interactions.