Characterization of ultrashort electron pulses by electron-laser pulse cross correlation

An all-optical method to determine the duration of ultrashort electron pulses is presented. This technique makes use of the laser pulse ponderomotive potential to effectively sample the temporal envelope of the electron pulse by sequentially scattering different sections of the pulse out of the main beam. Using laser pulse parameters that are easily accessible with modern tabletop chirped-pulse amplification laser sources, it is possible to measure the instantaneous duration of electron pulses shorter than 100 fs in the energy range that is most useful for electron diffraction studies, 10-300 keV.     

Diffractive optics implementation of six-wave mixing

Diffractive optics are applied to six-wave mixing processes to provide a single optic approach to attaining the required, relatively complex, phase-matching geometry to discriminate against lower-order nonlinear responses. The diffractive optics were designed specifically for broad-bandwidth operation and passive phase locking of the appropriate pulse pairs for use in femtosecond two-dimensional Raman studies of the dynamic structure of liquids. The fifth-order signal was studied in liquid CS>(2); two different colors were used for the excitation and the probe to reduce background scatter, as were two different phase-matching geometries with different degrees of suppression of cascaded third-order processes.     

Enhanced bandwidth noncollinear optical parametric amplification with a narrowband anamorphic pump

Through the use of anamorphic focusing, we present a method for generating broadband noncollinear optical parametric amplification in signal regions lacking a broadband phase-matching condition that is ideally suited for narrowband pump sources, herein based on an erbium-doped fiber oscillator. With a short focal length cylindrical lens to enhance the phase-matching condition and a long focal length cylindrical lens in the orthogonal plane to limit the pump power in the amplifying beta barium borate crystal, we amplify pulses in the blue-green spectral region with over 100 THz (～3500 cm(-1)) bandwidth. The amplified signal is subsequently compressed to 9.5 fs, near the transform limit.     

Control of NO Concentration in Solutions of Nitrosothiol Compounds by Light

We studied the thermal and photolytic decomposition of two S -nitrosothiols, S -nitrosoglutathione (GSNO) and S -nitroso- N -acetylpenicillamine (SNAP), in water or propanol solutions. A "concentration clamp" (relatively constant concentration of NO as a function of time) could be implemented in a closed volume by varying the pH, concentration of nitrovasodilator and intensity of the light source. Depending on the conditions, the light either stimulated NO release or sharply decreased NO concentration in the test solutions. Changes in the absorption spectra of GSNO solutions were monitored as a function of light exposure. Generation of superoxide as a product of a photolytic decomposition reaction of S -nitrosothiols and further oxidation of NO is the most likely mechanism for light suppression of NO concentration.     

A Gaussian-3X prediction on the enthalpies of formation of chlorinated phenols and dibenzo-p-dioxins

The standard gas-phase enthalpies of formation of chlorinated benzenes, phenols and dibenzo-p-dioxins have been predicted using G3X and/or G3XMP2 model chemistries coupled with isodesmic reactions and compared to the previous theoretical and experimental values. A set of values for chlorinated benzenes are first suggested based on experimental measurements and the closed agreed G3X calculations with different isodesmic reactions. The results on polychlorinated dibenzo-p-dioxins (PCDDs) show a large difference between G3XMP2 and previous experimental measurements and predictions using group additivity methods, semiempirical quantum chemistry, and DFT calculations, especially for highly chlorinated species. Using the well-balanced isodesmic reactions (IR3 and IR5), the discrepancies between G3XMP2 and DFT predictions on PCDDs can be reduced to within 16 kJ/mol. The relative stability of PCDD isomers can be rationalized by the positional interactions, and the overestimation by DFT with less balanced isodesmic reactions is due to the overestimation of the ortho-Cl-Cl repulsive interactions when comparing with G3XMP2. Our calculations suggest further experimental measurements, especially on highly chlorinated phenols and PCDDs.     

Rab5 in the regulation of cell motility and invasion

Cellular invasion requires careful regulation of the cell migration and apoptotic signaling cascades, allowing cell movement and survival of the emigrating populations. Components of the endosomal machinery are involved in these processes, and in particular the role of small GTPases of the Rab family has become appreciated. Rab5 is best known for its role in regulating the trafficking of early endosomes, however, it has recently been appreciated to associate with and regulate the routing of complexes containing integrins, the primary cellular receptors for the extracellular matrix. The association regulates the spatio temporal activation of signals of downstream growth factors and integrins. Rab proteins have also been linked to apoptosis mediated by cell surface death receptors, which elicit the activation of the death cascade via activation of caspase 8. Recently, the link between trafficking, apoptosis and cell migration was strengthened, as Rab5 was determined to work in conjunction with caspase 8 in promoting tumor cell motility and metastasis by regulating β1 integrin traffic. The capacity to connect and regulate these pathways identifies Rab5 as a key player in future studies of cell migration and tumor dissemination.     

Separation of two phenotypically similar cell types via a single common marker in microfluidic channels

To isolate clinically and biologically relevant cell types from a heterogeneous population, fluorescent or magnetic tagging together with knowledge of surface biomarker profiles represents the state of the art. To date, it remains exceedingly difficult to separate phenotypically and physically similar cell types from a mixed population. We report a microfluidic platform engineered to separate two highly similar cell types using a single antibody by taking advantage of subtle variations in surface receptor density and cell size. This platform utilizes antibody-conjugated surfaces in microfluidic channels together with precise modulation of fluid shear stresses to accomplish selective fractionation in a continuous flow process. Antibody conjugation density variation on the adhesive surfaces is achieved by covalently immobilizing an antibody in the presence of poly(ethylene glycol). This platform is used to demonstrate separation of two CD31 positive cell types, human umbilical vein endothelial cells and human micro vascular endothelial cells.     

What is the Unit?

Mathematicians are sometimes careless about the use of units of linear measure. Specifically, in geometry, it is common to list measurements without a unit. The specific unit selected usually has no effect on the generalizations made. For example, in a right triangle, the Pythagorean Theorem relationship is independent of the selected linear unit. However, the unit of measurement is often of particular importance when a comparison is made between two quantities.