Effects of the Adulteration Technique on the Near-Infrared Detection of Melamine in Milk Powder.

The United States Pharmacopeial Convention has led an international collaborative project to develop a toolbox of screening methods and reference standards for the detection of milk powder adulteration. During the development of adulterated milk powder reference standards, blending methods used to combine melamine and milk had unanticipated strong effects on the near-infrared (NIR) spectrum of melamine. The prominent absorbance band at 1468 nm of melamine was retained when it was dry-blended with skim milk powder but disappeared in wet-blended mixtures, where spray-dried milk powder samples were prepared from solution. Analyses using polarized light microscopy, Raman spectroscopy, dielectric relaxation spectroscopy, X-ray diffraction, and mass spectrometry indicated that wet blending promoted reversible and early Maillard reactions with lactose that are responsible for differences in melamine NIR spectra between wet- and dry-blended samples. Targeted detection estimates based solely on dry-blended reference standards are likely to overestimate NIR detection capabilities in wet-blended samples as a result of previously overlooked matrix effects arising from changes in melamine hydrogen-bonding status, covalent complexation with lactose, and the lower but more homogeneous melamine local concentration distribution produced in wet-blended samples. Techniques used to incorporate potential adulterants can determine the suitability of milk reference standards for use with rapid detection methods.

Using Dielectric Relaxation Spectroscopy to Characterize the Glass Transition Time of Polydextrose.

Dielectric relaxation spectroscopy was used to characterize the glass transition time, tg , of polydextrose, where the glass transition temperature, Tg , and water activity, aw (relative humidity), were held constant during polydextrose relaxation. The tg was determined from a shift in the peak frequency of the imaginary capacitance spectrum with time. It was found that when the peak frequency reaches 30 mHz, polydextrose undergoes glass transition. Glass transition time, tg , is the time for polydextrose to undergo glass transition at a specific Tg and aw . Results lead to a modified state diagram, where Tg is depressed with increasing aw . This curve forms a boundary: (a) below the boundary, polydextrose does not undergo glass transition and (b) above the boundary, polydextrose rapidly undergoes glass transition. As the boundary curve is specified by a tg value, it can assist in the selection of storage conditions. An important point on the boundary curve is at aw = 0, where Tg0 = 115 °C. The methodology can also be used to calculate the stress-relaxation viscosity of polydextrose as a function of Tg and aw , which is important when characterizing the flow properties of polydextrose initially in powder form.

Using electrical impedance spectroscopy to detect water in planetary regoliths.

We present data in examination of the utility of electrical impedance spectroscopy measurements for in situ surveys to determine the water content, distribution, and phase in unconsolidated planetary regolith. We conducted calibration experiments under conditions relevant to Mars: the concentration of electrolytes in solution was varied up to 1 M to simulate the effects of unsaturated dissolved minerals and brines. We also varied the water content of heterogeneous water/sand mixtures, made with these electrolytic solutions from 0.01 wt% to 10 wt%. Tests were performed at temperatures from +25 degrees C to -65 degrees C. Conductivity and dielectric permittivity calculated from the impedance measurements indicate an expected dependence on electrolyte concentration and relative independence from electrolyte type for both liquid water and water ice. Conductivity and calculated dielectric relaxation times for these aqueous solutions agree with existing data in the literature. The relative permittivity for heterogeneous water/sand mixtures is dominated by polarization effects for the electrode configuration used. However, the characteristic orientational relaxation of ice is still visible. The conductivity retains the strong dependence on electrolyte concentration, and the permittivity is still not affected by electrolyte type. A "universal" curve between conductivity and water content establishes detectability limits of <0.01 wt% and approximately 0.3 wt% for water/sand mixtures containing liquid water and ice, respectively.

Mechanical aspects of legged locomotion control.

We review the mechanical components of an approach to motion science that enlists recent progress in neurophysiology, biomechanics, control systems engineering, and non-linear dynamical systems to explore the integration of muscular, skeletal, and neural mechanics that creates effective locomotor behavior. We use rapid arthropod terrestrial locomotion as the model system because of the wealth of experimental data available. With this foundation, we list a set of hypotheses for the control of movement, outline their mathematical underpinning and show how they have inspired the design of the hexapedal robot, RHex.

Monitoring space shuttle air quality using the Jet Propulsion Laboratory electronic nose.

A miniature electronic nose (ENose) has been designed and built at the Jet Propulsion Laboratory (JPL), Pasadena, CA, and was designed to detect, identify, and quantify ten common contaminants and relative humidity changes. The sensing array includes 32 sensing films made from polymer carbon-black composites. Event identification and quantification were done using the Levenberg-Marquart nonlinear least squares method. After successful ground training, this ENose was used in a demonstration experiment aboard STS-95 (October-November, 1998), in which the ENose was operated continuously for six days and recorded the sensors' response to the air in the mid-deck. Air samples were collected daily and analyzed independently after the flight. Changes in shuttle-cabin humidity were detected and quantified by the JPL ENose; neither the ENose nor the air samples detected any of the contaminants on the target list. The device is microgravity insensitive.