Wavelength and temperature dependences of the absorption and scattering cross sections of soot

We have inferred the wavelength and temperature dependence of the absorption and scattering cross sections of mature soot in an ethylene flame from laser-induced incandescence (LII) and transmittance measurements at 532 and 1064 nm. The LII measurements indicate that the emissivity of soot in a flame deviates from the expected 1/λ dependence. Combining the LII results with transmittance measurements yields single-scattering albedos of 0.058-0.077 at 1064 nm and 0.22-0.29 at 532 nm and values of F(m)/E(m) of 2.2-2.9 at 532 nm and 2.4-3.3 at 1064 nm. These values confirm that scattering must be taken into account when interpreting extinction data at these wavelengths. Our results also indicate increases in the absorption cross section and decreases in the scattering cross section with increasing fluence at low fluences. The increase in absorption cross section is consistent with increases in primary particle size with increasing particle temperature during laser heating. The decrease in scattering cross section could be attributable to an increase in the radius of gyration or a decrease in the fractal dimension of the aggregate with increasing temperature. Alternatively these trends might be the result of changes to the optical properties of the particles with increasing temperature.     

Ultrathin fluorescent layers for monitoring the axial resolution in confocal and two-photon fluorescence microscopy

Monomolecular films of polymerized dimethyl-bis[pentacosadiinoic-oxyethyl] ammonium bromide (EDIPAB) provide one- and two-photon excited fluorescence that is sufficiently high to quantify the axial resolution of 3-D fluorescence microscopes. When scanned along the optical axis, the fluorescence of these layers is bright enough to allow online observation of the axial response of these microscopes, thus facilitating alignment and fluorescence throughput control. The layers can be used for directly measuring and monitoring the axial response of 4Pi-confocal microscopes, as well as for their initial alignment and phase adjustment. The proposed technique has the potential to supersede the conventional technique of calculating the derivative of the axial edges of a thick fluorescent layer. Coverslips with EDIPAB-layers can be used as substrates for the cultivation of cells.     

Bang-bang impact control using hybrid impedance/time-delay control

For stabilization of a robot manipulator upon collision with a stiff environment, a nonlinear bang-bang impact controller is developed. Under this control, a robot can successfully achieve contact tasks without changing the control algorithm or controller gains throughout all three modes: free space, transition and constrained motion. It uses a robust hybrid impedance/time-delay control algorithm to first absorb impact forces and stabilize the system. This control input alternates with zero when no environment force is sensed due to loss of contact. This alternation of control action repeats until the impact transient subsides and steady state is attained. After impact transient, the hybrid impedance/time-delay control algorithm is again utilized. This bang-bang control method provides stable interaction between a robot with severe nonlinear joint friction and a stiff environment, and achieves rapid response while minimizing force overshoots. During contact transition, we employ one simple control algorithm that switches only to zero and maintains the same gains, while other controllers use more than one control algorithm or different control gains. It is shown via experiments that overall performance is superior or comparable to more complicated existing impact force control techniques.     

Characterization of the growth of sol-gel derived Ba---Ti---O thin films by laser Raman spectroscopy

The isothermal growth kinetics of sol-gel derived BaTi₅O₁₁ thin films has been studied by laser Raman spectroscopy. Thin films of the precursors were spin coated on silicon wafers with platinum or gold overlayers. The films were then annealed isothermally, and Raman spectra were recorded in situ. The time-dependent intensity changes of the Raman bands could be analyzed in terms of Avrami models. The interaction of the BaTi₅O₁₁ film with the platinum or gold overlayers during heat treatment apparently increased the Raman intensity by a factor of about 100.     

Family problem solving versus home notes as early intervention with high-risk children.

Assigned 69 2nd–6th graders, identified as inconsistent because of extreme variability over baseline in math class work, to a home-note, family problem-solving, or control condition. Teachers scored Ss' math daily and sent home a Good-News Note with Ss in both intervention conditions when their daily means equaled or exceeded their baseline means. Ss in the family problem-solving condition wrote contingency contracts with their families, guided by a problem-solving board game, specifying consequences for receipt of Good-News Notes. Families in the home-note condition were instructed by letter to deliver favorable consequences on receipt of Good-News Notes. Compared to no treatment both forms of intervention significantly reduced class work scatter. Whereas Ss in the control and home-note conditions became less accurate during intervention, Ss in the family problem-solving condition maintained their accuracy. Only Ss in the family problem-solving condition demonstrated generalization to nonreinforced intervention probes. Involvement of the family meant that children produced high quality work even when their classmates' work dropped in quality and that they worked hard even when they expected no reward. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of Gas Temperatures Measured by Coherent Anti-Stokes Raman Spectroscopy (CARS) of O(2) and N(2)

We investigate the accuracy of temperature measurements by coherent anti-Stokes Raman spectroscopy (CARS) of O(2) and use measurements taken with N(2) CARS and a thermocouple for comparison. Scanning vibrational CARS spectra of O(2) and N(2) were recorded over a broad range of temperatures: between 294 K and 1900 K in air that was heated in a tube furnace and at approximately 2450 K in a fuel-lean CH(4)-O(2)-N(2) flame. Temperatures were derived from least-squares fits of simulated and experimental spectra. Both the fundamental vibrational band and the first hot vibrational band were included in fitting. In the case of the tube furnace, the N(2) and the O(2) CARS temperature measurements agreed to within 3%, and results were similar with the thermocouple; in the flame the agreement was to within 1%. We conclude that, for cases in which O(2) is present in sufficient concentrations ( approximately 10% or greater), the accuracy of O(2) thermometry is comparable with that of N(2).     

Rheological properties and microstructure of model processed cheese containing low molecular weight emulsifiers

The influence of low molecular weight emulsifiers (SDS, CTAB, lecithin, mono-diglycerides) on rheological properties and the microstructure of model processed cheese, made using rennet casein, at three different pH values was investigated. Interactions between the low molecular weight emulsifiers and rennet caseins in model processed cheese are consistent with those found in model food emulsions of liquid continuous phase. Compared with the control, the addition of CTAB (cationic) resulted in the hardest and most elastic processed cheese, while the incorporation of SDS (anionic) produced the softest and least elastic cheese. Processed cheese with added lecithin or mono-diglycerides behaved much like the controls, but with an increase in syneresis level. No syneresis was observed with the SDS cheeses. In general, low pH cheeses (pH 5.45) were harder than high pH cheeses (pH 6.05). Rheologically, all the processed cheese samples can be described as [weak gels]. The protein matrix of the high pH processed cheese containing CTAB consisted mainly of protein particles linked into a chain-like form, while those containing lecithin and SDS showed a mixture of individual as well as short chained protein aggregates, and the control had protein aggregates of intermediate size. The added low molecular weight emulsifiers resulted in a finer dispersion of the fat in the protein matrix. Protein-emulsifier charge interactions seem to be the prime determinant of the rheological properties of these model processed cheeses.     

Native casein micelles as nanocarriers for β‐carotene: pH‐and temperature‐induced opening of the micellar structure

To apply native casein micelles (CM) as nanocarriers for lipophilic substances in non‐ or low‐fat food products, they have to be conditioned before loading. In this study, an experimental set‐up for the production and loading of CM was developed. Microfiltration was used to separate CM from skimmed milk. To identify optimal loading conditions temperatures (2, 20, 40 °C), pH values (6.8 and 5.5) and holding times (5, 15, 30, 60 min) were varied. The release of calcium, phosphate and protein from the micellar phase as well as static light scattering and transmission electron microscopy showed that CM were optimally primed at 2 °C and a pH of 5.5 for 5 min. Therefore, loading with β‐carotene was performed under those conditions. After the back‐extraction of β‐carotene, the photometrical analyses revealed total recovery rates of >79% whereby 94% of it was associated with the native CM.