Preliminary Results of Microwave Induced Thermoacoustics Imaging in Geological Media

Seismic and electromagnetic imaging modalities are conventionally used in subsurface situational awareness applications. These modalities have been very effective at characterizing the geological media in terms of its constitutive mechanical properties such as density and compressibility, as well as electromagnetic properties such as electric conductivity, permeability, and permittivity. In order to enhance these imaging capabilities, a Thermoacoustic (TA) imaging system is used in this work. TA imaging relies on the coupling of mechanical and electromagnetic waves through a thermodynamic process, and it has the potential to reconstruct thermodynamic constitutive properties such as volumetric expansion coefficient and heat capacity. TA imaging has been mostly used in biological applications; this is due to the low signal-to-noise ratio that can be created with this physical mechanism. This work is aimed at addressing such limitation and exploring the use of TA imaging in geophysical applications. Conventionally, a short microwave pulse excitation is used to create the TA wave; so that the stress confinement condition is met while providing high resolution images. This approach requires the use of expensive high power amplifiers to create a detectable TA signal. This limitation can be addressed by using a frequency-modulated continuous wave (FMCW) excitation, which has been recently proposed as a suitable mechanism to enhance the signal-to-noise ratio of the TA signal generated for a given peak power constrain. This paper discusses and compares both pulsed and FMCW TA imaging in geological media. Preliminary experimental results show the efficacy of this approach to image a rock immersed in an oil bath; thus paving the way towards its future use for subsurface sensing and imaging of fluid flow and transport in porous media.

Thermal Transitions of Cocoa Butter: A Novel Characterization Method by Temperature Modulation

For the first time, the novel experimental technique Temperature Modulated Optical Refractometry (TMOR) was employed for cocoa butter thermal transitions characterization. The average refractive index (NMEAN), the volume (v) change, and the volumetric expansion coefficient ( β q ) as well as the dynamic quantities β ′ and β ″ (real and imaginary volumetric expansion coefficient, respectively) were monitored during cooling and heating and compared to the heat flow curves obtained via the standard technique dynamic scanning calorimetry (DSC). The investigation of these quantities showed that TMOR analysis can yield not only thermal transitions temperatures that are comparable to DSC results, but also some new thermal events that are not detected by DSC. This outcome suggests that TMOR might provide some additional insights on cocoa butter melting and crystallization by means of frequency-dependent measurements due to temperature modulation. This new information that can be accessed during temperature ramps might provide a deeper insight into thermal behavior of fat-based foods, evidencing TMOR value as a tool for thermal transitions investigation.

Production and Characterization of Sugary Cassava Syrup

A group of cassava landraces that occur naturally in Amazonia (Manihot esculenta Crantz) are known as mandiocaba or sugary cassava because they have high free sugar content, making them a possible feedstock for the production of syrup. The objective of the study was to evaluate the technological viability of obtaining sugary cassava syrup and to characterize the physical and physicochemical properties of the product. The yield of the syrup (80 °Brix) obtained from the manipueira (liquid obtained by crushing and filtering the cassava) concentration was 262.72 g per plant. The reducing sugars represented 77.26% of total sugars, the density was 1.4210 g cm–3 at 20°C, and the volumetric expansion coefficient was 38.6 m K–1. The Newtonian behavior and activation energy (≥69.65 kJ gmol–1) were similar to that of honey found in the literature.

The incompressibility and thermal expansivity of D2O ice II determined by powder neutron diffraction

Using high-resolution neutron powder diffraction, the molar volume of a pure sample of D2O ice II has been measured, within its stability field, at 225 K, over the pressure range 0.25 <P< 0.45 GPa. Ar gas was used as the pressure medium, to avoid the formation of `stuffed ice' gas hydrates encountered when using He. The third-order Birch–Murnaghan equation of state parameters of helium-free D2O ice II, referenced to 225 K, are:V0,225= 306.95 ± 0.04 Å3(1299.7 ± 0.2 kg m−3),K0,225= 12.13 ± 0.07 GPa, with K'_{0,225} fixed at 6.0. The thermal expansivity of metastable D2O ice II samples recovered to ambient pressure has also been measured, over the range 4.2 <T< 160 K; above 160 K an irreversible transition to ice Icwas observed. The volumetric expansion coefficient, αV, atP= 0 andT= 225 K, is predicted to be 2.48 × 10−4 K−1.

Isothermal Dendritic Growth - A Low Gravity Experiment

The growth of dendrites in pure melts and alloys is controlled by diffusion-limited transport of heat and/or solute. The presence of temperature or concentration gradients within a molten phase subject to gravitational forces generally promotes convection, which in turn, modifies the diffusion processes. The vigor of melt convection is controlled by several parameters often expressed as a lumped dimensionless group, the Grashof number Gr = gβΔTℓ3/ν2, where g is the acceleration due to gravity; is the volumetric expansion coefficient; ΔT is the undercooling; ν is the kinematic viscosity; and ℓ is the relevant length scale, e.g., the characteristic diffusion distance. Dendritic growth, by its nature, does not permit independent manipulation of the controlling length scale, ℓ, which is determined by materials properties (e.g. diffusion coefficient or thermal diffusivity) and the undercooling or supersaturation. The reduction of g through orbital free fall is often the only practical way to lower Gr sufficiently to permit careful observation of the morphological and kinetic characteristics of isothermal dendritic growth. Previously conducted ground-based studies and the current approach to performing these studies in low earth orbit will be described.