Dissimilar electro-osmotic flow and ionic current recirculation patterns in porous media detected by NMR mapping experiments

Random-site percolation clusters were milled into ceramic (polar) and polystyrene (nonpolar) plates as a paradigm for porous media or complex microsystem channel networks. The pore space was filled with electrolyte solutions. Using NMR microscopy techniques, maps of the following quantities were recorded: (i) flow velocity driven by external pressure gradient, (ii) electro-osmotic flow (EOF) velocity, (iii) ionic current density in the presence of EOF, (iv) ionic current density in the absence of EOF. As far as possible, the experiments were supplemented by computational fluid dynamics simulations. It is shown that electro-osmotic flow as well as the electric current density include vortices and recirculation patterns. Remarkably, all transport patterns turned out to be dissimilar, and the occurrence and positions of vortices do not coincide in the different maps.     

Hadron masses and matrix elements from the QCD Schrödinger functional

We explain how masses and matrix elements can be computed in lattice QCD using Schrödinger functional boundary conditions. Numerical results in the quenched approximation demonstrate that good precision can be achieved. For a statistical sample of the same size, our hadron masses have a precision similar to what is achieved with standard methods, but for the computation of matrix elements such as the pseudoscalar decay constant the Schrödinger functional technique turns out to be much more efficient than the known alternatives.     

A multistep flux-corrected transport scheme

A multistep flux-corrected transport (MFCT) scheme is developed to achieve conservative and monotonic tracer transports for multistep dynamical cores. MFCT extends Zalesak two-time level scheme to any multistep time-differencing schemes by including multiple high-order fluxes in the antidiffusive flux, while computing the two-time level low-order monotone solution. The multistep time-differencing scheme used in this study is the third-order Adams–Bashforth (AB3) scheme implemented in a finite-volume icosahedral shallow-water model. The accuracy of AB3 MFCT is quantified by the shape-preserving advection experiments in non-divergent flow, as well as a cosine bell whose shape changes during advection in shear flow. AB3 MFCT has been shown to be insensitive to time step size. This make AB3 MFCT an attractive transport scheme for explicit high resolution model applications with small time step. MFCT is tested in shallow-water model simulations to demonstrate that the use of MFCT maintains positive-definite tracer transport, while at the same time conserving both fluid mass and tracer mass within round-off errors in the AB3 dynamic core.     

Second harmonic imaging of chloroplasts using the two-photon laser scanning microscope

BackgroundSecond harmonic information reveals information about the structure of spatially oriented structures with an asymmetry. We study the second harmonic images of the grana and intergranal parts of chloroplasts in the leaves of the shade moss Plagiomnium affine.ResultsA two-photon microscope with blocking filters to suppress fluorescence generated both forward and backward second harmonic illumination to be captured. In the starch free chloroplasts of the single cell layered laminae strong second harmonic generation (SHG) from the granal regions was emitted. Upon illumination the chloroplasts changed their orientation affecting the SHG signal. Chloroplast is reoriented upon illumination.ConclusionsSHG signals were successfully obtained from the grana without any possible confusion from SHG starch grains due to their absence.     

F-18-FDG uptake is a reliable predictory of functional recovery of akinetic but viable infarct regions as defined by magnetic resonance imaging before and after revascularization

Identification of akinetic but viable myocardium is important for the selection of patients for coronary revascularization. In order to assess predictive values of end-diastolic wall thickness and dobutamine induced wall thickening obtained by magnetic resonance imaging (MRI) and [18F]Fluorodeoxyglucose uptake assessed by positron emission tomography (F-18-FDG-PET), these parameters were compared to recovery of left ventricular function after successful revascularization. Forty patients with chronic myocardial infarction and regional a- or dyskinesia by ventriculography underwent rest- and dobutamine-MRI studies (10 microg dobutamine/kg body weight/min) and F-18-FDG-PET. Viability of the infarct region was considered to be present if; 1) end-diastolic wall thickness was > or =5.5 mm; 2) dobutamine induced wall thickening > or =2 mm could be measured; and 3) normalized F-18-FDG-uptake was > or =50% in > or =50% of akinetic segments. Preserved end-diastolic wall thickness was found in 32/40 patients, functional improvement during dobutamine infusion in 26/40 patients and preserved F-18-FDG-uptake in 29/40 patients. After revascularization regional left ventricular function improved in 25/40 patients. Positive and negative predictive values and diagnostic accuracy were 78%, 100%, and 83% for preserved end-diastolic wall thickness, 92%, 93%, and 93% for dobutamine inducible contraction reserve and 86%, 100%, and 90% for preserved F-18-FDG-uptake. Quantitative assessment of dobutamine induced systolic wall thickening by MRI and F-18-FDG-uptake by PET are highly accurate techniques for the identification of viable myocardium and prediction of functional recovery after successful revascularization. Preserved end-diastolic wall thickness results in an overestimation of viable myocardium compared to functional improvement, but wall thickness <5.5 mm excludes recovery of regional function.     

Forces between a single atom and its distant mirror image

An excited-state atom whose emitted light is backreflected by a distant mirror can experience trapping forces, because the presence of the mirror modifies both the electromagnetic vacuum field and the atom's own radiation reaction field. We demonstrate this mechanical action using a single trapped barium ion. We observe the trapping conditions to be notably altered when the distant mirror is translated across an optical wavelength. The well-localized barium ion enables the spatial dependence of the forces to be measured explicitly. The experiment has implications for quantum information processing and may be regarded as the most elementary optical tweezers.     

Flow measurements below 50 mum: NMR microscopy experiments in lithographic model pore spaces

Quasi two-dimensional random site percolation model objects have been prepared using a synchrotron radiation lithography technique with a spatial resolution better than 50 microm and an aspect ratio of up to 17. Flow of water through the pore space was studied with the aid of an NMR velocity mapping method and compared with a computational fluid dynamics simulation. In order to be able to measure and map widely distributed flow velocities with microscopic resolution (typically 40 x 40 microm), an experimental protocol that permits one to cover an effectively very wide velocity field of view (0.6-10 mm/s) had to be developed.     

Parametric processes in microstructured and highly nonlinear optical fibres

Optical parametric amplification is an important nonlinear process in photonic crystal fibres driven by the small effective area and the special dispersion characteristics of these fibres. Aside from its role in supercontinuum generation, parametric amplification can lead to efficient wavelength conversion, limited primarily by the uniformity of the diameter of currently available fibres. The related Bragg scattering process can be used for both wavelength conversion and optical switching, again limited by the physical characteristics of the fibres used.