Interaction dynamics of two diffusing particles: contact times and influence of nearby surfaces.

Interactions of diffusing particles are governed by hydrodynamics on different length and timescales. The local hydrodynamics can be influenced substantially by simple interfaces. Here, we investigate the interaction dynamics of two micron-sized spheres close to plane interfaces to mimic more complex biological systems or microfluidic environments. Using scanned line optical tweezers and fast 3D interferometric particle tracking, we are able to track the motion of each bead with precisions of a few nanometers and at a rate of 10 kilohertz. From the recorded trajectories, all spatial and temporal information is accessible. This way, we measure diffusion coefficients for two coupling particles at varying distances h to one or two glass interfaces. We analyze their coupling strength and length by cross-correlation analysis relative to h and find a significant decrease in the coupling length when a second particle diffuses nearby. By analysing the times the particles are in close contact, we find that the influence of nearby surfaces and interaction potentials reduce the diffusivity strongly, although we found that the diffusivity hardly affects the contact times and the binding probability between the particles. All experimental results are compared to a theoretical model, which is based on the number of possible diffusion paths following the Catalan numbers and a diffusion probability, which is biased by the spheres' surface potential. The theoretical and experimental results agree very well and therefore enable a better understanding of hydrodynamically coupled interaction processes.

A hydrothermal apparatus for x-ray absorption spectroscopy of hydrothermal fluids at DESY.

We present a new autoclave that enables in situ characterization of hydrothermal fluids at high pressures and high temperatures at synchrotron x-ray radiation sources. The autoclave has been specifically designed to enable x-ray absorption spectroscopy in fluids with applications to mineral solubility and element speciation analysis in hydrothermal fluids in complex compositions. However, other applications, such as Raman spectroscopy, in high-pressure fluids are also possible with the autoclave. First experiments were run at pressures between 100 and 600 bars and at temperatures between 25 °C and 550 °C, and preliminary results on scheelite dissolution in fluids of different compositions show that the autoclave is well suited to study the behavior of ore-forming metals at P-T conditions relevant to the Earth's crust.

Experimentally determined trace element partition coefficients between hibonite, melilite, spinel, and silicate melts.

This article provides new data on mineral/melt partitioning in systems relevant to the evolution of chondrites, Calcium Aluminum-Rich Inclusions (CAI) in chondrites and related meteorites. The data set includes experimentally determined mineral/melt partition coefficients between hibonite (CaAl12O19), melilite (Ca2(Al,Mg)2SiO7), spinel (MgAl2O4) and silicate melts for a wide range of trace elements: Sc, Ti, V, Cr, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Rh, Cs, Ba, La, Ce, r, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Pb, Th and U. The experiments were performed at high temperatures (1350 °C < T < 1550 °C) and ambient pressure. The experimental run products were analyzed using electron microprobe (EMPA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The partition coefficients for 38 trace elements were calculated from the LA-ICP-MS data.

Do twisted laser beams evoke nuclear hyperpolarization?

The hyperpolarization of nuclear spins promises great advances in chemical analysis and medical diagnosis by substantially increasing the sensitivity of nuclear magnetic resonance (NMR). Current methods to produce a hyperpolarized sample, however, are arduous, time-consuming or costly and require elaborate equipment. Recently, a much simpler approach was introduced that holds the potential, if harnessed appropriately, to revolutionize the production of hyperpolarized spins. It was reported that high levels of hyperpolarization in nuclear spins can be created by irradiation with a laser beam carrying orbital angular momentum (twisted light). Aside from these initial reports however, no further experimental verification has been presented. In addition, this effect has so far evaded a critical theoretical examination. In this contribution, we present the first independent attempt to reproduce the effect. We exposed a sample of immersion oil or a fluorocarbon liquid that was placed within a low-field NMR spectrometer to Laguerre-Gaussian and Bessel laser beams at a wavelength of 514.5nm and various topological charges. We acquired (1)H and (19)F NMR free induction decay data, either during or alternating with the irradiation that was parallel to B0. We observed an irregular increase in NMR signal in experiments where the sample was exposed to beams with higher values of the topological charge. However, at no time did the effect reach statistical significance of 95%. Given the measured sensitivity of our setup, we estimate that a possible effect did not exceed a hyperpolarization (at 5mT) of 0.14-6%, depending on the assumed hyperpolarized volume. It should be noted though, that there were some differences between our setup and the previous implementation of the experiment, which may have inhibited the full incidence of this effect. To approach a theoretical description of this effect, we considered the interaction of an electron with a plane wave, which is known to be able to induce electronic (e.g. in rubidium) and subsequent nuclear hyperpolarization. Compared to the plane wave, the additional transitions caused by a twisted wave are of the order of 10(-3) less. This suggests that the twist of the laser is unlikely to be responsible for the hyperpolarization of nuclear spins, unless a new mechanism of momentum transfer is identified.

Vitamin D rescues dysfunction of fetal endothelial colony forming cells from individuals with gestational diabetes.

INTRODUCTION: Gestational diabetes (GDM) is associated with long-term cardiovascular and metabolic diseases in offspring. However, the mechanisms are not well understood. We explored whether fetal exposure to a diabetic environment is associated with fetal endothelial progenitor cell dysfunction, and whether vitamin D can reverse the impairment. METHODS: Nineteen women with uncomplicated pregnancies and 18 women with GDM were recruited before delivery. Time to first appearance of endothelial colony forming cell (ECFC) colonies and number of ECFC colonies formed from culture of cord peripheral blood mononuclear cells were determined. Angiogenesis-related functions of ECFCs in vitro were tested in the presence or absence of vitamin D. RESULTS: Fetal ECFCs from GDM pregnancies formed fewer colonies in culture (P = 0.04) and displayed reduced proliferation (P = 0.02), migration (P = 0.04) and tubule formation (P = 0.03) compared to uncomplicated pregnancies. Fetal ECFCs exposed to hyperglycemia in vitro exhibited less migration (P < 0.05) and less tubule formation (P < 0.05) than normoglycemic control. Vitamin D significantly improved the dysfunction of fetal ECFCs from pregnancies complicated by GDM or after exposure of healthy ECFCs to hyperglycemia. DISCUSSION: Fetal ECFCs from GDM pregnancies or ECFCs exposed to hyperglycemia in vitro exhibit reduced quantity and impaired angiogenesis-related functions. Vitamin D significantly rescues these functions. These findings may have implications for vascular function of infants exposed to a diabetic intrauterine environment.

[Halogenated anesthetic vaporizers: importance of maintenance regulations]. / Evaporateurs d'anesthésiques halogénés: importance des prescriptions d'entretien.

We report a serious dysfunction of 19 halothane vaporisers Vapor 19.3 (Dräger) which delivered a much higher concentration of agent than indicated on the dial. This inaccuracy was linked to a major corrosion of the inner layers of the vaporiser, with a deposit of zinc bromide and chloride in the bypass channel. The main cause for this dysfunction was the absence of an adequate maintenance of the vaporisers since their purchase 3 years before.

Observing secretory granules with a multiangle evanescent wave microscope.

In total internal reflection fluorescence microscopy (TIRFM), fluorophores near a surface can be excited with evanescent waves, which decay exponentially with distance from the interface. Penetration depths of evanescent waves from 60 nm to 300 nm were generated by varying the angle of incidence of a laser beam. With a novel telecentric multiangle evanescent wave microscope, we monitored and investigated both single secretory granules and pools of granules in bovine chromaffin cells. By measuring the fluorescence intensity as a function of penetration depth, it is possible through a Laplace transform to obtain the fluorophore distribution as a function of axial position. We discuss the extent to which it is possible to determine distances and diameters of granules with this microscopy technique by modeling the fluorescent volumes of spheres in evanescent fields. The anisotropic near-field detection of fluorophores and the influence of the detection point-spread function are considered. The diameters of isolated granules between 70 nm and 300 nm have been reconstructed, which is clearly beyond the resolution limit of a confocal microscope. Furthermore, the paper demonstrates how evanescent waves propagate along surfaces and scatter at objects with a higher refractive index. TIRFM will have a limited applicability for quantitative measurements when the parameters used to define evanescent waves are not optimally selected.

[Sevoflurane in obstetric anesthesia]. / Sevofluran in der geburtshilflichen Anästhesie.

In obstetrics, general anaesthesia is increasingly being replaced by peridural anaesthesia. The cases where general anaesthesia is still used are those involving increased risk. It is therefore not surprising that, for example, maternal mortality in cases of caesarian section under general anaesthesia has not decreased. Indeed, large-scale statistical analyses in the USA and the UK show an increase in relative risk. For this reason, continuing efforts have to be made to improve obstetric general anaesthesia. Inhalational anaesthetics have an important role to play, as they represent the only acceptable compromise between the dangers of maternal awareness and neonatal depression. We used literature data and our own experience of urgent caesarian sections to investigate whether the new inhalational anaesthetic sevoflurane is suitable for this purpose. In a comparison of sevoflurane and peridural anaesthesia, there was no difference in outcome for the child and the maternal results showed only the expected procedure-specific differences in circulatory parameters and early postoperative analgesia requirement. A second study involving continuous pEEG monitoring (SEF90) showed advantages of sevoflurane over isoflurane in the initial phase of surgery and in the recovery phase. However, the value of sevoflurane in obstetric anaesthesia will have to be confirmed in more extensive studies.

Surface-relief phase structures generated by light-initiated polymerization.

A method for fabricating refractive micro-optical elements by structuring poly(methyl methacrylate) layers is presented. With this flexible and simple method a surface growth of several micrometers can be achieved. For smooth surface reliefs a nearly linear response of the phase growth to the UV intensity can be achieved over a range of 8π. The edge steepness depends on the maximum height and can reach values as high as 2π above 4 µm. We describe the fabrication process, establish a mathematical model of the surface growth, and also present as experimental results some components fabricated by this method.

Optical trapping of dielectric particles in arbitrary fields.

We present a new method to calculate trapping forces of dielectric particles with diameters D < or = lambda in arbitrary electromagnetic, time-invariant fields. The two components of the optical force, the gradient force and the scattering force, are determined separately. Both the arbitrary incident field and the scatterer are represented by plane-wave spectra. The scattering force is determined by means of the momentum transfer in either single- or double-scattering processes. Therefore the second-order Born series is evaluated and solved in the frequency domain by Ewald constructions. Numerical results of our two-force-component approach and an established calculation method are compared and show satisfying agreement. Our procedure is applied to investigate axial trapping by focused waves experiencing effects of aperture illumination and refractive-index mismatch.

Role of actin cortex in the subplasmalemmal transport of secretory granules in PC-12 cells.

In neuroendocrine PC-12 cells, evanescent-field fluorescence microscopy was used to track motions of green fluorescent protein (GFP)-labeled actin or GFP-labeled secretory granules in a thin layer of cytoplasm where cells adhered to glass. The layer contained abundant filamentous actin (F-actin) locally condensed into stress fibers. More than 90% of the granules imaged lay within the F-actin layer. One-third of the granules did not move detectably, while two-thirds moved randomly; the average diffusion coefficient was 23 x 10(-4) microm(2)/s. A small minority (<3%) moved rapidly and in a directed fashion over distances more than a micron. Staining of F-actin suggests that such movement occurred along actin bundles. The seemingly random movement of most other granules was not due to diffusion since it was diminished by the myosin inhibitor butanedione monoxime, and blocked by chelating intracellular Mg(2+) and replacing ATP with AMP-PNP. Mobility was blocked also when F-actin was stabilized with phalloidin, and was diminished when the actin cortex was degraded with latrunculin B. We conclude that the movement of granules requires metabolic energy, and that it is mediated as well as limited by the actin cortex. Opposing actions of the actin cortex on mobility may explain why its degradation has variable effects on secretion.

[Effect of peridural analgesia on labor progress]. / Der Einfluss der Periduralanalgesie auf den Geburtsverlauf.

Epidural analgesia (EDA) is the most effective method of intrapartum pain relief. Its influence on the course of labor continues to be controversial. Although a cause-and-effect relationship has not been proven, this form of analgesia has been blamed for a host of adverse maternal/fetal events during labor, including prolonged first and second stage of labor, dystocia, malrotation of the fetal head and an increased risk of operative delivery (instrumental delivery, Caesarean section). Our own data from the Department of Obstetrics and Gynaecology at the University of Leipzig demonstrate that women with epidural analgesia had a longer duration of labor (the greater proportion taking more than 13 hours), although labor was often already protracted before the start of epidural analgesia. Early epidural analgesia with a cervical dilatation of less than 4 cm does not have any negative impact on the progress of labor. The duration of second-stage pushing and the rate of instrumental deliveries were not increased in our patients. Although the Caesarean section rate for women with an EDA was elevated, the total proportion of secondary Caesarean section remained unchanged despite increased use of EDA. Our findings suggest that women selected for intrapartal EDA already represent a population with an increased risk of an unfavourable course of labor, priming of the cervix, increased need of oxytocin and nulliparity. Pain relief in itself is sufficient indication for the use of intrapartal epidural analgesia.