Zur Elektrodenkinetik von Reinst – Eisen im Phosphatelektrolyten bei Feststoffeinschlag (Simulation von Erosionskorrosion)

Electrode kinetics of high purity iron in phosphate electrolytes under solid particle impact (Simulation of erosion corrosion) Erosion-corrosion of high purity iron was simulated by means of a vibration cell in a neutral phosphate electrolyte. The investigations were carried out to explain the initiation processes of this type of corrosion. The results confirm the general conception of the central role of reaction layer destruction in erosion-corrosion processes. Under these conditions a qualitative change in reaction layer formation occur. By solid impact the layers are destroyed locally and so conditions of pit nucleation exist. The destruction of the layers depends on the action of shear forces resulting from tensile or compressive strains.     

Modernisierung des Datenschutzes: Herausforderungen durch die Technik

Auf Einladung des Innenausschusses des Deutschen Bundestages fand am 5. M?rz 2007 eine ?ffentliche Anh?rung zum Thema der Modernisierung des Datenschutzes statt. Gegenstand waren Entschlie?ungsantr?ge der Fraktionen der FDP sowie von Bündnis90/Die Grünen zum Datenschutzaudit¹ sowie zum Scoring und zu Auskunftspflichten bei Datenschutzpannen.² Eingeladen war auch der Landesbeauftragte für den Datenschutz Mecklenburg Vorpommern, dessen schriftliche Analyse wir mit den Schwerpunkten der Herausforderungen durch die Technik und des Datenschutzaudits abdrucken.     

Using dynamic explanations to enhance novice programmer instruction via the WWW

This paper describes how the World Wide Web (WWW)-delivered visual explanations of programming constructs have been developed and used to supplement the conventional instructional methods and materials traditionally employed in introductory programming courses. The explanations are constructed using inexpensive commercial software that supports the use of animation, graphics, color, and narrative to help students visualize a wide range of concepts and relationships. Initial student feedback suggests WWW-delivered visual explanations appear to be an effective means of addressing the individual learning needs of novice programmers.     

Preoperative biliary drainage, colonisation of bile and postoperative complications in patients with tumours of the pancreatic head: a retrospective analysis of 241 consecutive patients

OBJECTIVE: To analyse the outcome of preoperative biliary drainage in patients being operated on for a tumour in the pancreatic head. DESIGN: Retrospective study. SETTING: University hospital, The Netherlands. SUBJECTS: Consecutive series of 241 patients. MAIN OUTCOME MEASURES: Decline in bilirubin concentrations and bacterial contamination of bile as a result of preoperative drainage. Incidence of postoperative complications in patients who underwent preoperative drainage and those who did not. RESULTS: 184/241 patients underwent preoperative biliary drainage. Endoscopic drainage was the most effective, shown by a median reduction in bilirubin concentrations of 82%, 74%, and 50% after endoscopic drainage (n = 149), papillotomy (n = 25) and external drainage (n = 10), respectively. Bacterial contamination of bile was significantly more common when an endoprosthesis was used, but did not result in a higher rate of infective complications. 163 Whipple's resections, 33 total pancreatectomies, and 45 biliary-enteric bypasses were performed. 137/241 (57%) patients had postoperative complications. There was no significant difference in the incidence of postoperative complications between patients who had preoperative biliary drainage and those who did not (p = 0.4).     

Mode-locking external-cavity laser-diode sensor for displacement measurements of technical surfaces

A novel laser sensor for position measurements of technical solid-state surfaces is proposed. An external Fabry-Perot laser cavity is assembled by use of an antireflection-coated laser diode together with the technical surface. Mode locking results from pumping the laser diode synchronously to the mode spacing of the cavity. The laser cavity length, i.e., the distance to the measurement object, is determined by evaluation of the modulation transfer function of the cavity by means of a phase-locked loop. The mode-locking external-cavity laser sensor incorporates a resonance effect that results in highly resolving position and displacement measurements. More than a factor-of-10 higher resolution than with conventional nonresonant sensing principles is achieved. Results of the displacement measurements of various technical surfaces are reported. Experimental and theoretical investigations are in good agreement.     

Holography in commercially available photoetchable glasses

Volume holographic gratings are recorded and retrieved in two commercially available glasses: Schott Foturan and Hoya PEG3. These materials are photoetchable, which describes their major application, but they also allow storage of volume holograms without any chemical etching. The samples are illuminated with ultraviolet light at a wavelength of 325 nm and thermally processed to achieve a maximum diffraction efficiency of approximately 9% for a 1-mm-thick sample. The two glasses show similar behavior; the diffraction efficiencies in Foturan tend to be slightly larger, whereas PEG3 tends to have weaker light scattering.     

Large-area Fabry-Perot modulator based on electro-optic polymers

We present a large-area electro-optic Fabry-Perot modulator utilizing a photoaddressable bis-azo polymer placed between two dielectric mirrors with an open aperture of 2 cm. A modulation efficiency of 1% at an effective modulation voltage of 20 V for a wavelength of 1.55 microm is demonstrated. By comparing distance tuning of the cavity with wavelength tuning, an effective electro-optic coefficient of -7 pm/V is measured.     

Quasi-spherical focal spot in two-photon scanning microscopy by three-ring apodization

We present a beam-shaping technique for two-photon excitation (TPE) fluorescence microscopy. We show that by inserting a properly designed three-ring pupil filter in the illumination beam of the microscope, the effective optical sectioning capacity of such a system improves so that the point spread function gets a quasi-spherical shape. Such an improvement, which allows the acquisition of 3D images with isotropic quality, is obtained at the expense of only a small increase of the overall energy in the axial sidelobes. The performance of this technique is illustrated with a scanning TPE microscopy experiment in which the image of small beads is obtained. We demonstrate an effective narrowing of 12.5% in the axial extent of the point spread function, while keeping the 82% of the spot-fluorescence efficiency.