In situ molecular association of dystrophin with actin revealed by sensitized emission immuno-resonance energy transfer

A novel method was developed to detect molecular associations of dystrophin with actin in cryostat muscle tissue sections by combining resonance energy transfer technology with immunohistochemical techniques. This method takes advantage of the long phosphorescent lifetime of terbium chelates, a property that enables the accurate determination of energy transfer in biological tissues by lifetime measurements of sensitized emission. After a brief excitation pulse, terbium chelates emit for milliseconds after the intrinsically high autofluorescence of biological specimens has decayed to negligible levels. Rat skeletal muscle tissue sections were labeled with both anti-dystrophin monoclonal antibody conjugated to a terbium-based resonance energy transfer donor and anti-actin tetramethylrhodamine phalloidin as an acceptor. Resonance energy transfer between the two probes indicated that the distance separating the probes is within 10 nm (about the size of an IgG2b antibody molecule). The fraction of antibodies that participated in resonance energy transfer was estimated to be 80-90% because of the close agreement between the quenching of donor phosphorescence and the efficiency of resonance energy transfer revealed by lifetime measurements of sensitized emission by tetramethyl-rhodamine phalloidin. Sensitized emission was detectable only when both anti-dystrophin antibody and tetramethyl-rhodamine phalloidin were present. These results indicate that actin and dystrophin are closely associated within the cell. This method is potentially applicable to the investigation of many types of intracellular associations.     

Residual Stress in Alumina–Mullite Composites

Lattice strains have been measured by neutron diffraction from the alumina matrix in alumina–mullite composite cylinders. Infiltration processing results in a macroscopic variation of mullite concentration and residual stress throughout the samples. At the midheight of the cylinder, the stress component parallel to the cylinder axis is in a compression of −130 ± 30 MPa with respect to the value near the top surface. At the surfaces, the stress component parallel to the surface is in a compression of −130 ± 30 MPa with respect to values near the midheight of the cylinder. An overall tensile shift of the macroscopic stress profile in a fully infiltrated specimen is interpreted as a grain interaction effect between the alumina and mullite constituents. The positional dependence of the mullite phase concentration is also determined by neutron diffraction.     

On the Synthesis Mechanism of TiN,ZrN, and HfN During Combustion of Mixtures of Aluminum Nanopowder with TiO2, ZrO2, and HfO2

Refractories and Industrial Ceramics - The technology for synthesizing TiN, ZrN, and HfN involves combustion in air of mixtures of aluminum nanopowder (NPAl) and the corresponding dioxides and...     

A gel probe equilibrium sampler for measuring arsenic porewater profiles and sorption gradients in sediments: I. Laboratory development

A gel probe equilibrium sampler has been developed to study arsenic (As) geochemistry and sorption behavior in sediment porewater. The gels consist of a hydrated polyacrylamide polymer, which has a 92% water content. Two types of gels were used in this study. Undoped (clear) gels were used to measure concentrations of As and other elements in sediment porewater. The polyacrylamide gel was also doped with hydrous ferric oxide (HFO), an amorphous iron (Fe) oxyhydroxide. When deployed in the field, HFO-doped gels introduce a fresh sorbent into the subsurface thus allowing assessment of in situ sorption. In this study, clear and HFO-doped gels were tested under laboratory conditions to constrain the gel behavior prior to field deployment. Both types of gels were allowed to equilibrate with solutions of varying composition and re-equilibrated in acid for analysis. Clear gels accurately measured solution concentrations (+/-1%), and As was completely recovered from HFO-doped gels (+/-4%). Arsenic speciation was determined in clear gels through chromatographic separation of the re-equilibrated solution. For comparison to speciation in solution, mixtures of As(III) and As(V) adsorbed on HFO embedded in gel were measured in situ using X-ray absorption spectroscopy (XAS). Sorption densities for As(III) and As(V) on HFO embedded in gel were obtained from sorption isotherms at pH 7.1. When As and phosphate were simultaneously equilibrated (in up to 50-fold excess of As) with HFO-doped gels, phosphate inhibited As sorption by up to 85% and had a stronger inhibitory effect on As(V) than As(III). Natural organic matter (>200 ppm) decreased As adsorption by up to 50%, and had similar effects on As(V) and As(III). The laboratory results provide a basis for interpreting results obtained by deploying the gel probe in the field and elucidating the mechanisms controlling As partitioning between solid and dissolved phases in the environment.     

Real-time observations of the oxidation of mild steel at high temperature by neutron diffraction

The in situ characterization of the phase composition of iron oxides, “scale,” that form on low carbon steel during oxidation at elevated temperatures was carried out using the neutron diffraction technique. Growths in the intensities of diffraction peaks from the crystal planes of the various oxides (Fe _x O, Fe₃O₄, and Fe₂O₃) were monitored on-line. The volume fractions of the oxides in the scale were calculated on the basis of ideal structure factors and measured relative intensities of diffraction peaks. These were selected from a small region of the diffraction pattern. Calculated volume fractions of these oxides in the scale layer were in agreement with the area fractions obtained from scanning electron microscopy (SEM) analysis of the scale.     

Stability in linear estimation

The stability with respect to model uncertainty of linear estimators of the coefficients of a linear combination of deterministic signals in noise is investigated. A class of estimators having nominal performances constrained to be close to that of the nominal linear, unbiased, minimum-variance (LUMV) estimator is specified. Two estimator stability indexes are defined, one based on a worst-case estimate mean-square error and the other on a type of signal-to-noise ratio. The estimator minimizing each index, subject to the optimality constraints, is found by reference to related LUMV estimation results. In most cases, the minimizing (or most stable) estimator is the same under the two indexes     

An accurate scalar potential finite element method for linear,two-dimensional magnetostatics problems

We have assessed the accuracy of a commercially available computer software package for finite element method calculations of magnetostatic fields. The computer program, MSC/NASTRAN,

1 Available from the MacNeal-Schwendler Corporation, Los Angeles, CA 90041, U.S.A.

is well known for its wide applicability in structural analysis and heat transfer problems. We exploit the fact that the differential equations of magnetostatics are identical to those for heat transfer if the magnetic field problem is formulated with the reduced scalar potential.¹ Consequently, the powerful, optimized numerical routines of NASTRAN can immediately be applied to two- and three-dimensional linear magneto-statics problems. Application of the NASTRAN reduced scalar potential approach to a ‘worst case’ two-dimensional problem for which an analytic solution is available has yielded much better accuracy than was recently reported² for a reduced scalar potential calculation using a different finite element program. Furthermore, our method exhibits completely satisfactory performance with regard to computational expense and accuracy for a linear electromagnet with an air gap. Our analysis opens the way for large three-dimensional magnetostatics calculations at far greater economy than is possible with the more commonly used vector potential and boundary integral methods.