Spectroscopic spectral-domain optical coherence microscopy

The spectroscopic content within optical coherence tomography (OCT) data can provide a wealth of information. Spectroscopic OCT methods are frequently limited by time-frequency trade-offs that limit high spectral and spatial resolution simultaneously. We present spectroscopic spectral-domain optical coherence microscopy performed with a multimodality microscope. Restricting the spatial extent of the signal by using high-numerical-aperture optics makes high-resolution spectroscopic information accessible, facilitated with spectral-domain detection. Simultaneous acquisition of multiphoton microscopy images is used to validate tissue structure and localization of nuclei within individual cells.     

Gaussian Beam Construction for Adiabatic Perturbations

We construct wave packets concentrated near a single space-time trajectory of the semi-classical Hamiltonian for a Bloch electron in a crystal lattice subject to slowly varying external electric and magnetic fields. The use of an analog of the Gaussian beam Ansatz make it possible to construct packets for arbitrarily long finite times.      

Predicting performance in a first engineering calculus course: implications for interventions

At the University of Louisville, a large, urban institution in the south-east United States, undergraduate engineering students take their mathematics courses from the school of engineering. In the fall of their freshman year, engineering students take Engineering Analysis I, a calculus-based engineering analysis course. After the first two weeks of the semester, many students end up leaving Engineering Analysis I and moving to a mathematics intervention course. In an effort to retain more students in Engineering Analysis I, the department collaborated with university academic support services to create a summer intervention programme. Students were targeted for the summer programme based on their score on an algebra readiness exam (ARE). In a previous study, the ARE scores were found to be a significant predictor of retention and performance in Engineering Analysis I. This study continues that work, analysing data from students who entered the engineering school in the fall of 2012. The predictive validity of the ARE was verified, and a hierarchical linear regression model was created using math American College Testing (ACT) scores, ARE scores, summer intervention participation, and several metacognitive and motivational factors as measured by subscales of the Motivated Strategies for Learning Questionnaire. In the regression model, ARE score explained an additional 5.1% of the variation in exam performance in Engineering Analysis I beyond math ACT score. Students took the ARE before and after the summer interventions and scores were significantly higher following the intervention. However, intervention participants nonetheless had lower exam scores in Engineering Analysis I. The following factors related to motivation and learning strategies were found to significantly predict exam scores in Engineering Analysis I: time and study environment management, internal goal orientation, and test anxiety. The adjusted R² for the full model was 0.42, meaning that the model could explain 42% of the variation in Engineering Analysis I exam scores.     

Influence of very small bubbles on particle/bubble heterocoagulation

Very small bubbles which partially coat the surface of particles influence whether or not heterocoagulation between a particle and a bubble occurs. The electrostatic and van der Waals forces of interaction between particles and bubbles were calculated as a function of electrolyte concentration, particle size, and the size and distributions of these very small bubbles present on the particle surface. The height of the surface force barrier was compared with the hydrodynamic pressing force under conditions of flotation. The presence of these very small bubbles has a profound effect on the interaction between particles and bubbles and, in particular, strongly decreases the critical particle radius for heterocoagulation.     

Advancements and Application of Microsecond Synchrotron X-ray Footprinting at the Advanced Light Source

The method of synchrotron X-ray protein footprinting (XF-MS) is used to determine protein conformational changes, folding, protein-protein and protein-ligand interactions, providing information which is often difficult to obtain using X-ray crystallography and other common structural biology methods [1 G. Xu and M.R. Chance, Chemical Reviews 107, 3514–3543 (2007).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–3 V.N. Bavro, Biochem Soc Trans 43, 983–994 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. The technique uses comparative in situ labeling of solvent-accessible side chains by highly reactive hydroxyl radicals (?OH) in buffered aqueous solution under different assay conditions. In regions where a protein is folded or binds a partner, these ?OH susceptible sites are inaccessible to solvent, and therefore protected from labeling. The ?OH are generated by the ionization of water using high-flux-density X-rays. High-flux density is a key factor for XF-MS labeling because obtaining an adequate steady-state concentration of hydroxyl radical within a short irradiation time is necessary to minimize radiation-induced secondary damage and also to overcome various scavenging reactions that reduce the yield of labeled side chains.     

HYDRATED ELECTRON FORMATION IN NANOSECOND and PICOSECOND LASER FLASH PHOTOLYSIS OF HEMATOPORPHYRIN IN AQUEOUS SOLUTION

Nanosecond (lambda exc = 266, 355 and 532 nm) and picosecond (lambda exc = 355 nm) laser flash photolysis of hematoporphyrin (Hp) was performed in neutral (pH 7.4) and alkaline (pH 12) aqueous solution, as well as in the presence of 0.1% Triton X-100. The dependence of the yield of photoproduced hydrated electrons (e-aq) on laser pulse energy was studied over a wide range of energies (0.2 to greater than 1000 mJ cm-2). The results show that e-aq are predominantly formed in a two-photon process at lambda exc = 266 and 355 nm. One-photon quantum yields are higher at lambda exc = 266 nm than at lambda exc = 355 nm. Both one-photon and two-photon pathways are less efficient at higher Hp concentration, reflecting the influence of Hp self-aggregation. Two-photon e-aq formation is more efficient when 30 ps pulses are used for excitation, as compared to 10 ns pulses. No e-aq could be detected at lambda exc = 532 nm. Nanosecond pulse-induced transient spectra obtained at pH 7.4 are also discussed.     

Discrete shock profiles for systems of conservation laws

The existence of discrete shock profiles for difference schemes approximating a system of conservation laws is the major topic studied in this paper. The basic theorem established here applies to first-order accurate difference schemes; for weak shocks, this theorem provides necessary and sufficient conditions involving the truncation error of the linearized scheme which guarantee entropy satisfying or entropy violating discrete shock profiles. Several explicit difference schemes are used as examples illustrating the interplay between the entropy condition, monotonicity, and linearized stability. Entropy violating stationary shocks for second-order accurate Lax-Wendroff schemes approximating systems are also constructed. The only tools used in the proofs are local analysis and the center manifold theorem.