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A radiative transport method based on efficient coupled forward-adjoint Monte Carlo simulations is used for the analysis of diagnostic fiber optic probes. Results are shown for various probe geometries within a layered tissue model. © 2011 Optical Society of America.

We have developed a computational platform that simulates light transport in tissue in support of biomedical optics research. Although in its initial stage of development, this platform is being used to answer important questions regarding the detection of tissue changes, and the optimal design and positioning of optical probes to 'interrogate' the tissue best. We provide answers to such questions by applying perturbation and midway surface Monte Carlo techniques. Derivation of these methods makes rigorous use of the radiative transport equation which is essential if the methods are to provide accurate solutions for highly complex media such as biological tissue. © 2008 Springer-Verlag Berlin Heidelberg.

We introduce a novel and efficient method to provide solutions to inverse photon migration problems in heterogeneous turbid media. The method extracts derivative information from a single Monte Carlo simulation to permit the rapid determination of rates of change in the detected photon signal with respect to perturbations in background tissue optical properties. We then feed this derivative information to a nonlinear optimization algorithm to determine the optical properties of the tissue heterogeneity under examination. We demonstrate the use of this approach to solve rapidly a two-region inverse problem of photon migration in the transport regime, for which diffusion-approximation-based approaches are not applicable.

Herein we report on a systematic investigation of the thermal expansion of select Mn+1AXn phases. The bulk dilatometric thermal expansion coefficient αdil was measured in the 25–1200 °C temperature range and the thermal expansion of more than 15 of these phases was studied by x-ray diffraction in the 25–800 °C temperature range. The coefficient of thermal expansion for the a axis αa ranged between (2.9±0.1)×10-6 °C-1 (Nb2AsC) and (12.9±0.1)×10-6 °C-1 (Cr2GeC) while the coefficient for the c axis (αc) ranged between (6.4±0.2)×10-6 °C-1 (Ta2AlC) and (17.6±0.2)×10-6 °C-1 (Cr2GeC). Weak anisotropy in the thermal expansion was seen in most phases, with the largest value of αc/αa belonging to Nb2AsC. The Grüneisen parameters along the a and c directions were calculated from ab initio values for the elastic compliances and were relatively isotropic. A good correlation was found between the thermal expansion anisotropy and the elastic constant c13 and we conclude that the anisotropy in thermal expansion is related to the bonding between the M-A elements. [ABSTRACT FROM AUTHOR]

We report on the electronic, thermal, and elastic properties of the layered ternary, Ti2SC. Resistivity, Hall effect, and magnetoresistance were measured as a function of temperature between 2 and 300 K and at fields up to 9 T. The Hall coefficient is negative and roughly temperature independent. The transport results were analyzed within a two-band framework, with electrons as the dominant charge carrier. The room-temperature thermal conductivity (≈60 W/m K) is the highest of any MAX phase measured to date, with a substantial phonon contribution. The specific heat was measured from 2 to 300 K, yielding a Debye temperature of 765 K and in agreement with the Debye temperature of 745 K found from ultrasonic time-of-flight measurements. Young’s, shear, and bulk moduli from the latter measurements were 290, 125, and 145 GPa, respectively. The calculated values of the lattice parameters (a=3.2051 Å and c=11.2636 Å), and Young’s, shear, and bulk moduli (329, 138, and 179 GPa, respectively), based on the results of density functional theoretical simulations, compare favorably with measurements. [ABSTRACT FROM AUTHOR]

Herein we report on the heat capacities cp of bulk predominantly single-phase polycrystalline samples of Ti2SC and Cr2GeC in the 3–1500 K temperature range and Ta2AlC in the 3–260 K range. At temperatures up to 10 K the main contributors to cp for Ta2AlC and Cr2GeC are electronic, with electronic coefficients γ of 7.13 and 26.12 mJ/mol K2, respectively. The latter is exceptionally high and is a record for this family of layered ternary carbides and nitrides also known as the MAX phases. In Ti2SC another low-temperature contribution—in addition to a γ of 3.8 mJ/mol K2—is manifested by an upturn in cp/T observed at the lowest temperatures. This feature, appearing as a Schottky-like anomaly, has a local maximum near 4.5 K and an intensity of ∼1.9×10-2 J/mol K. A defect concentration of ∼3×1021 /mol presumably on the S-sublattice, is proposed as the origin of a two-level energy system responsible for this anomaly. As in previous work on these compounds, the lattice contributions to cp in all compounds are analyzed using the Debye and Einstein model approximations. The main effect of increasing the atomic number of the transition metal is a reduction in Debye temperature. [ABSTRACT FROM AUTHOR]

The heat capacities of [c.sub.p] of bulk predominantly single-phase polycrystalline samples of [Ti.sub.2]SC and [Cr.sub.2]GeC and [Ta.sub.2]AlC are analyzed. The lattice contributions to [c.sub.p] in all compounds are analyzed and the main effect of increasing the atomic number of the transition metal is a reduction in Debye temperature.

Discusses a study which presented room-temperature reflectance measurements of thick, monocrystalline, p-type porous 6H silicon carbide layers. Theoretical background; Methods used; Results.