Taylor dispersion and the position-to-time conversion in microfluidic mixing devices.

Microfluidic mixing devices are increasingly popular tools for probing the non-equilibrium dynamics of biomolecular systems. Commonly, hydrodynamic focusing is used to reduce the length scales that limit the time of diffusive mixing in the laminar flow regime, such that even sub-millisecond dead times for triggering a reaction have been achieved. Detection of a suitable signal at different points along the channel downstream of the mixing region, corresponding to different times after mixing, then allows the kinetics of the reaction to be obtained. However, the requisite accurate conversion of the positions in the channel to times after mixing is complicated by Taylor dispersion, the combined effect of diffusion and shear flow on the dispersion of the molecules in the microfluidic device. As a result, an accurate position-to-time conversion has only been possible in the limiting regimes, i.e. for very early times, where sample diffusion can be neglected, and for very long times, where the molecules have uniformly sampled the entire channel cross-section. Here, we use detailed three-dimensional, time-dependent finite-element calculations to obtain an accurate position-to-time conversion that bridges these two limits and allows us to quantify the effects of Taylor dispersion on the time resolution of a representative mixing device optimized for single-molecule fluorescence detection. The accuracy of the calculations is confirmed by direct comparison of the calculated velocity field with dual-focus fluorescence correlation spectroscopy measurements.

[General conditions concerning the implementation of an outpatient education programme--characteristics and distinctions from an inpatient training programme]. / Rahmenbedingungen für die Umsetzung eines ambulanten Schulungsprogramms--Besonderheiten und Abgrenzung zu einer stationären Schulung.

INTRODUCTION: The aim of the EVA study was to develop an outpatient education programme for women with endometriosis with a view to permanent transfer into routine care. Implementation of the programme generated several problems and obstacles that are not, or not to this extent, present in the inpatient setting of a rehabilitation clinic. METHODS: The patient education programme was developed in line with an existing inpatient programme, taking into account the criteria for evaluating such training programmes. Several adjustments to process, structure and content level had to be made to achieve the conditions of the outpatient setting. RESULTS: Since May 2008, 17 training courses took place in various outpatient and acute inpatient settings, and a total of 156 women with diagnosed endometriosis participated. The problems and obstacles that emerged affected similarly the process, structure and content of the training programme. DISCUSSION: On the structural level, especially problems with availability of rooms, technical equipment and trainers occurred, leading to significant time pressures. The main problem on the procedural level was the recruitment of participants, since--in contrast to the inpatient setting and to disease management programmes--no assignment by physicians or insurers takes place. Furthermore, gainful activity of the participants and the resulting shift of the training beyond the usual working and opening hours are important barriers for implementation. The unavailability of trainers in these settings requires creative solutions. Regarding the contents of the training it has to be taken into consideration that--unlike the inpatient setting--no aftercare intervention and no individual psychological consultation are possible. The training programme has to be designed in such a way that all problems that have occurred could be dealt with appropriately. CONCLUSION: In summary, the permanent implementation of an outpatient training programme is possible but is more time-consuming than inpatient trainings due to unfavourable conditions concerning recruitment, organization and procedure. It seems that "soft" factors such as motivation, integration into the clinic concept, well-defined acceptance of responsibility and experience in dealing with the disease and with patient groups are the critical success factors. Until now cost carriage by the health insurance funds has not been realized--except for disease management programmes; so there is still a need for action here.

Phase-state dependent current fluctuations in pure lipid membranes.

Current fluctuations in pure lipid membranes have been shown to occur under the influence of transmembrane electric fields (electroporation) as well as a result from structural rearrangements of the lipid bilayer during phase transition (soft perforation). We demonstrate that the ion permeability during lipid phase transition exhibits the same qualitative temperature dependence as the macroscopic heat capacity of a D15PC/DOPC vesicle suspension. Microscopic current fluctuations show distinct characteristics for each individual phase state. Although current fluctuations in the fluid phase show spikelike behavior of short timescales (approximately 2 ms) with a narrow amplitude distribution, the current fluctuations during lipid phase transition appear in distinct steps with timescales of approximately 20 ms. We propose a theoretical explanation for the origin of timescales and permeability based on a linear relationship between lipid membrane susceptibilities and relaxation times near the phase transition.

Phase transition induced fission in lipid vesicles.

In this work we demonstrate how the first order phase transition in giant unilamellar vesicles (GUVs) can function as a trigger for membrane fission. When driven through their gel-fluid phase transition GUVs exhibit budding or pearl formation. These buds remain connected to the mother vesicle presumably by a small neck. Cooling these vesicles from the fluid phase (T>T(m)) through the phase transition into the gel state (T

Thermodynamic relaxation drives expulsion in giant unilamellar vesicles.

We investigated the thermodynamic relaxation of giant unilamellar vesicles (GUVs) which contained small vesicles within their interior. Quenching these vesicles from their fluid phase (T > T(m)) through the phase transition in the gel state (T < T(m)) drives the inner vesicles to be expelled from the larger mother vesicle via the accompanying decrease in the vesicle area by approximately 25% which forces a pore to open in the mother vesicle. We demonstrate that the proceeding time evolution of the resulting efflux follows the relaxation of the membrane area and describes the entire relaxation process using an Onsager-like non-equilibrium thermodynamics ansatz. As a consequence of the volume efflux, internal vesicles are expelled from the mother vesicle. Although complete sealing of the pore may occur during the expulsion, the global relaxation dynamics is conserved. Finally, comparison of these results to morphological relaxation phenomena found in earlier studies reveals a universal relaxation behaviour in GUVs. When quenched from the fluid to gel phase the typical time scale of relaxation shows little variation and ranges between 4 and 5 s.

Interstitial and terminal deletion of chromosome Y in a male individual with cryptozoospermia.

A constitutional de-novo deletion of the long arm of the Y chromosome was detected by standard cytogenetic analysis in a 38-year old male who, except for small testes and cryptozoospermia, was phenotypically normal. The deletion was further characterized by fluorescent in-situ hybridization (FISH) and digital image analysis using contigs of overlapping yeast artificial chromosome (YAC) clones, spanning almost the entire Y chromosome. These results showed that the deletion involved a large interstitial segment on the proximal long arm of the Y chromosome (Yq11.1-->Yq11.22) as well as a more distal portion of the Y chromosome, including the entire heterochromatic region (Yq11.23-->qter). The breakpoints as determined by the YAC probes were defined within the published Vergnaud intervals so that region 6B and 6C was mostly retained. However, the AZFc region harbouring the DAZ locus on distal subinterval 6F was lost in the deletion, making the absence of this region the most probable location for the patient's infertility. The data underline the usefulness of FISH as an alternative technique to conventional banding for the refined detection of chromosome Y deletions/rearrangements.

Effects of molecular entanglements during electrospray of high molecular weight polymers.

Concentration-dependent bimodal size distributions (comprised of single-molecule particles and multimolecule clusters) observed by microscopic examination of particles collected during electrospray (ES) of dilute solutions of high molecular weight polymers suggest that chain entanglement can interfere with the droplet subdivisions believed to be intrinsic to the electrospray process. The feasibility of such interference is discussed in the context of the spray model of Kebarle, along with its potential impact on the ES mass spectrometry of macromolecules.

[Clinical, electroneurographic and neuroautonomic findings in patients with chronic renal insufficiency and following kidney transplantation]. / Klinische, elektroneurographische und neurovegetative Befunde bei Patienten mit chronischer Niereninsuffizienz und nach Nierentransplantation.

Orientation onsigns of sensomotor polyneuritis seems appropriate for monitoring the status of patients with chronic uremia. The maximum speed of motor and F-wave transmission by the N. fibularis and the mean instantaneous arrhythmia are parameters which, before clinical symptoms appear, permit the accurate assessment of motor and vegetative lesions and may be useful as a basis on which treatment can be corrected.

Air embolism as a complication of hip arthrography.

As an aid to correctly placing the needle tip within the hip joint during arthrography, injection of small amounts of air has been used to outline the joint space. Over a period of seven years, air embolus has been noted in three pediatric patients, twice with minor symptoms, and once with cardiac arrest. Even small amounts of air (less than 5 cc) injected accidentally intravenously may cause dangerous complications in small infants. If this technique is to be used, it is recommended that small amounts of carbon dioxide or oxygen be used instead of air.

Surface recrystallization of polyethylene extended-chain crystals.

Rough fracture surfaces of extended-chain polyethylene crystals become unstable at temperatures below the bulk melting point. There is no way for the extended chains, which are up to 20,000 methylene units long, to change position without collapse. As a result, the rough surfaces smooth out on heating by covering themselves with oriented folded-chain lamellae.