The mechanism and kinetics of interactions between dimethyl methylphosphonate (DMMP), a key chemical warfare agent (CWA) simulant, and Zr6-based metal organic frameworks (MOFs) have been investigated with in situ infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), and DFT calculations. DMMP was found to adsorb molecularly to UiO-66 through the formation of hydrogen bonds between the phosphoryl oxygen and the free hydroxyl groups associated with Zr6 nodes on the surface of crystallites and not within the bulk MOF structure. Unlike UiO-66, the infrared spectra for UiO-67 and MOF-808, recorded during DMMP exposure, suggest that uptake occurs through both physisorption and chemisorption. The XPS spectra of MOF-808 zirconium 3d electrons reveal a charge redistribution following exposure to DMMP. In addition, analysis of the phosphorus 2p electrons following exposure and thermal annealing to 600 K indicates that two types of stable phosphorus-containing species exist within the MOF. DFT calculations, used to guide the IR band assignments and to help interpret the XPS features, suggest that uptake is driven by nucleophilic addition of an OH group to DMMP with subsequent elimination of a methoxy substituent to form strongly bound methyl methylphosphonic acid (MMPA). The rates of product formation indicate that there are likely two distinct uptake processes, requiring rate constants that differ by approximately an order of magnitude. However, the rates of molecular uptake were found to be nearly identical to the rates of reaction, which strongly suggests that the reaction rates are diffusion-limited. The final products were found to inhibit further reactions within the MOFs, and these products could not be thermally driven from the MOFs prior to decomposition of the MOFs themselves.

Elastography is developed as a quantitative approach to imaging linear elastic properties of tissues to detect suspicious tumors. In this paper a nonlinear elastography method is introduced for reconstruction of complex breast tissue properties. The elastic parameters are estimated by optimally minimizing the difference between the computed forces and experimental measures. A nonlinear adjoint method is derived to calculate the gradient of the objective function, which significantly enhances the numerical efficiency and stability. Simulations are conducted on a three-dimensional heterogeneous breast phantom extracting from real imaging including fatty tissue, glandular tissue, and tumors. An exponential-form of nonlinear material model is applied. The effect of noise is taken into account. Results demonstrate that the proposed nonlinear method opens the door toward nonlinear elastography and provides guidelines for future development and clinical application in breast cancer study.

The conventional attenuation contrast imaging does not yield satisfactory sensitivity and specificity for weakly absorbing media, such as biological soft tissues. The x-ray scattering offer an important contrast mechanism to reveal structural features and density fluctuation within an object. This scattering signal carries information at the molecular and supra-molecular level, and has a tremendous implication for biomedical and other applications. In this paper, we develop a scattering imaging approach to reconstruct the electron density distribution of an object and demonstrate its feasibility in the numerical simulation.

Abstract

A reconstruction method of bioluminescence sources is proposed based on a phase approximation model. Compared with the diffuse approximation, this phase approximation model more correctly predicts bioluminescence photon propagation in biological tissues, so that bioluminescence tomography can accurately locate and quantify the distribution of bioluminescence sources. The compressive sensing (CS) technique is applied to regularize the inverse source reconstruction to enhance numerical stability and efficiency. The numerical simulation and phantom experiments demonstrate the feasibility of the proposed approach.