Magnetic properties of amorphous ferromagnet Fe78Mo2B20

Low-field magnetic susceptibility and the magnetic field dependence of magnetization of Metglas 2605 A (Fe₇₈Mo₂B₂₀) were studied between 300 and 600 K and in fields up to 10kG. It is shown here that for an amorphous ferromagnetic alloy, the various methods of determination of Curie temperature T_c give the same value, which in this case is (564 ± 1) K. The critical exponent γ is 1.7 ± 0.1. Our low-field susceptibility measurements on Metglas 2605 (Fe₈₀B₂₀) gives a T_c of (634 ± 3) K while the reported high-field method value is 647 K. These results are discussed in terms of crystallization temperatures.     

Characterization of grafting density and binding efficiency of DNA and proteins on gold surfaces

The surface grafting density of biomolecules is an important factor for quantitative assays using a wide range of biological sensors. We use a fluorescent measurement technique to characterize the immobilization density of thiolated probe DNA on gold and hybridization efficiency of target DNA as a function of oligonucleotide length and salt concentration. The results indicate the dominance of osmotic and hydration forces in different regimes of salt concentration, which was used to validate previous simulations and to optimize the performance of surface-stress based microcantilever biosensors. The difference in hybridization density between complementary and mismatched target sequences was also measured to understand the response of these sensors in base-pair mismatch detection experiments. Finally, two different techniques for immobilizing proteins on gold were considered and the surface densities obtained in both cases were compared.     

Sub- and above-barrier fusion of loosely bound 6Li with 28Si

Fusion excitation functions are measured for the system ⁶Li + ²⁸Si using the characteristic $ \gamma$ -ray method, encompassing both the sub-barrier and above-barrier regions, viz, E _lab = 7-24 MeV. Two separate experiments were performed, one for the above-barrier region ( E _lab = 11-24 MeV) and another for the below-barrier region ( E _lab = 7-10 MeV). The results were compared with our previously measured fusion cross-section for the ⁷Li + ²⁸Si system. We observed the enhancement of the fusion cross-section at sub-barrier regions for both ⁶Li and ⁷Li , but the yield was substantially larger for ⁶Li . However, for well-above-barrier regions, a similar type of suppression was identified for both the systems.     

Domain formation and orbital ordering transition in a doped Jahn-Teller insulator

The ground state of a double-exchange model for orbitally degenerate e(g) electrons with Jahn-Teller lattice coupling and weak disorder is found to be spatially inhomogeneous near half filling. Using a real-space Monte Carlo method we show that doping the half-filled orbitally ordered insulator leads to the appearance of hole-rich disordered regions in an orbitally ordered environment. The doping driven orbital order to disorder transition is accompanied by the emergence of metallic behavior. We present results on transport and optical properties along with spatial patterns for lattice distortions and charge densities, providing a basis for an overall understanding of the low-doping phase diagram of La1 - xCaxMnO3.     

Isotope effect on the thermal conductivity of boron nitride nanotubes

We have measured the temperature-dependent thermal conductivity kappa(T) of individual multiwall boron nitride nanotubes using a microfabricated test fixture that allows direct transmission electron microscopy characterization of the tube being measured. kappa(T) is exceptionally sensitive to isotopic substitution, with a 50% enhancement in kappa(T) resulting for boron nitride nanotubes with 99.5% 11B. For isotopically pure boron nitride nanotubes, kappa rivals that of carbon nanotubes of similar diameter.     

Zero Temperature Phases of the Frustrated <Emphasis Type="Italic">J</Emphasis><Subscript>1</Subscript>–<Emphasis Type="Italic">J</Emphasis><Subscript>2</Subscript> Antiferromagnetic Spin-1/2 Heisenberg Model on a Simple Cubic Lattice

At zero temperature magnetic phases of the quantum spin-1/2 Heisenberg antiferromagnet on a simple cubic lattice with competing first and second neighbor exchanges (J ₁ and J ₂) is investigated using the non-linear spin wave theory. We find existence of two phases: a two sublattice Néel phase for small J ₂ (AF), and a collinear antiferromagnetic phase at large J ₂ (CAF). We obtain the sublattice magnetizations and ground state energies for the two phases and find that there exists a first order phase transition from the AF-phase to the CAF-phase at the critical transition point, p _c =0.56 or J ₂/J ₁=0.28. We also show that the quartic 1/S corrections due spin-wave interactions enhance the sublattice magnetization in both the phases which causes the intermediate paramagnetic phase predicted from linear spin wave theory to disappear.     

Deposition of aluminide and silicide based protective coatings on niobium

We compare aluminide and alumino-silicide composite coatings on niobium using halide activated pack cementation (HAPC) technique for improving its oxidation resistance. The coated samples are characterized by SEM, EDS, EPMA and hardness measurements. We observe formation of NbAl₃ in aluminide coating of Nb, though the alumino-silicide coating leads to formation primarily of NbSi₂ in the inner layer and a ternary compound of Nb-Si-Al in the outer layer, as reported earlier (Majumdar et al. [11]). Formation of niobium silicide is preferred over niobium aluminide during alumino-silicide coating experiments, indicating Si is more strongly bonded to Nb than Al, although equivalent quantities of aluminium and silicon powders were used in the pack chemistry. We also employ first-principles density functional pseudopotential-based calculations to calculate the relative stability of these intermediate phases and the adhesion strength of the Al/Nb and Si/Nb interfaces. NbSi₂ exhibits much stronger covalent character as compared to NbAl₃. The ideal work of adhesion for the relaxed Al/Nb and Si/Nb interfaces are calculated to be 3226 mJ/m² and 3545 mJ/m², respectively, indicating stronger Nb-Si bonding across the interface.     

Interaction-driven real-space condensation

We study real-space condensation in a broad class of stochastic mass transport models. We show that the steady state of such models has a pair-factorized form which generalizes the standard factorized steady states. The condensation in this class of models is driven by interactions which give rise to a spatially extended condensate that differs fundamentally from the previously studied examples. We present numerical results as well as a theoretical analysis of the condensation transition and show that the criterion for condensation is related to the binding-unbinding transition of solid-on-solid interfaces.     

Mechanism of disease in early osteoarthritis: application of modern MR imaging techniques — a technical report

The application of biomolecular magnetic resonance imaging becomes increasingly important in the context of early cartilage changes in degenerative and inflammatory joint disease before gross morphological changes become apparent. In this limited technical report, we investigate the correlation of MRI T1, T2 and T1ρ relaxation times with quantitative biochemical measurements of proteoglycan and collagen contents of cartilage in close synopsis with histologic morphology. A recently developed MRI sequence, T1ρ, was able to detect early intracartilaginous degeneration quantitatively and also qualitatively by color mapping demonstrating a higher sensitivity than standard T2-weighted sequences. The results correlated highly with reduced proteoglycan content and disrupted collagen architecture as measured by biochemistry and histology. The findings lend support to a clinical implementation that allows rapid visual capturing of pathology on a local, millimeter level. Further information about articular cartilage quality otherwise not detectable in vivo, via normal inspection, is needed for orthopedic treatment decisions in the present and future.