Collaborative writing in multiple discourse contexts

Research in computer-supported writing has traditionally compared electronic communication with oral, face-to-face communication to identify the benefits and weaknesses of each, as if they entailed dichotomous choices. In this article, we challenge that view and argue instead that any form of communication and its educational usefulness is shaped by the situation in which it is used, the backgrounds and goals of the participants, the institutional and technological setup, and the intended purpose of the medium. Three modes of communication in one graduate course are examined — oral discussion, synchronous written discussion on a local area network, and asynchronous written postings on an email list set up for the class. It was found that patterns of participation, topic introduction, and topic development differed across the three communication modes, but that the three were interwoven with each other and embedded within the larger classroom context and forms of knowledge creation in the class. Thus, rather than examining different communication media separately, researchers interested in understanding computer-supported collaborative writing need to look at how different media are used to create a meta-medium, which is established by the discourse community involved.     

Identification and Avoidance of Systematic Measurement Errors in Lamb Wave Observation With One‐Dimensional Scanning Laser Vibrometry

Abstract: Scanning laser vibrometry is a widely used tool to observe Lamb wave fields for structural health monitoring (SHM) purposes. Lamb waves propagate over long distances in thin‐walled structures and interact with structural inhomogeneities, for example, damages, in spite of wavelengths several times of the damage size. In SHM of sheets and glass‐ or carbon‐fibre‐reinforced plastic plates, this effect is used for determining the position as well as the size of structural faults. With the often employed one‐dimensional vibrometry, a geometrically induced, systematic error occurs when measuring oblique‐angled motion. This error can be, in the specific case of Lamb waves, of a non‐negligible quantity. The nature of this geometrical measurement error in general and concerning Lamb waves in special is discussed analytically for both amplitude and phase data. It is shown that this matter should be taken into account in some applications.     

Defect Chemistry and Microstructure of Hydrothermal Barium Titanate

Hydrothermal powders of BaTiO₃ and (Ba,Ca)(Ti,Zr)O₃ contain large amounts of protons in the oxygen sublattice. The proton defects are compensated by vacancies on metal sites. When the powder is annealed, water is released and the point defects disappear in the temperature range of 100°–600°C. Metal and oxygen vacancies combine to small nanometer-sized intragranular pores. At temperatures of >800°C, the intragranular pores migrate to the grain boundaries and disappear. In multilayer ceramic capacitors that have been prepared from hydrothermal powders, the intragranular pores are preferentially collected at the inner electrodes, which results in "bloating," cracks, and delamination.     

Enhancing Post-Stroke Rehabilitation and Preventing Exo-Focal Dopaminergic Degeneration in Rats—A Role for Substance P

Dopaminergic signaling is a prerequisite for motor learning. Delayed degeneration of dopaminergic neurons after stroke is linked to motor learning deficits impairing motor rehabilitation. This study investigates safety and efficacy of substance P (SP) treatment on post-stroke rehabilitation, as this neuropeptide combines neuroprotective and plasticity-promoting properties. Male Sprague Dawley rats received a photothrombotic stroke within the primary motor cortex (M1) after which a previously acquired skilled reaching task was rehabilitated. Rats were treated with intraperitoneal saline (control group, n = 7) or SP-injections (250 µg/kg) 30 min before (SP-pre; n = 7) or 16 h (SP-post; n = 6) after rehabilitation training. Dopaminergic neurodegeneration, microglial activation and substance P-immunoreactivity (IR) were analyzed immunohistochemically. Systemic SP significantly facilitated motor rehabilitation. This effect was more pronounced in SP-pre compared to SP-post animals. SP prevented dopaminergic cell loss after stroke, particularly in the SP-pre condition. Despite its proinflammatory propensity, SP administration did not increase stroke volumes, post-stroke deficits or activation of microglia in the midbrain. Finally, SP administration prevented ipsilesional hypertrophy of striatal SPergic innervation, particularly in the SP-post condition. Mechanistically, SP-pre likely involved plasticity-promoting effects in the early phase of rehabilitation, whereas preservation of dopaminergic signaling may have ameliorated rehabilitative success in both SP groups during later stages of training. Our results demonstrate the facilitating effect of SP treatment on motor rehabilitation after stroke, especially if administered prior to training. SP furthermore prevented delayed dopaminergic degeneration and preserved physiological endogenous SPergic innervation.     

Progress in the Synthesis of Nanocrystalline BaTiO3 Powders for MLCC

Future improvements in the development of highly volume-efficient multilayer ceramic capacitors (MLCC) require manufacturing processes that allow for a reduced dielectric thickness well below 1 μm. Obviously, such thin dielectric layers can only be produced if nanosized dielectric powders are applied and deposited by techniques more advanced than tape casting and screen printing. These processes require high-purity, homogeneous, weakly agglomerated ultrafine powders. Over the past few years, significant progress has been made in the synthesis of nanocrystalline BaTiO₃-based powders for use in MLCC. The present review article aims to summarize the present state of the art with respect to some of the technically and industrially most relevant preparation routes, including methods based on solid-state reactions and, more importantly, solution-based approaches.     

Grain growth and crystallinity of ultrafine barium titanate particles prepared by various routes

Variations in tetragonal distortion and the degree of crystallinity of ultrafine BaTiO₃ particles—both industrially applied criteria qualifying their polar characteristics—upon growth during annealing were studied on powders, prepared by the hydrothermal synthesis and by the oxalate route respectively. Regardless of the synthetic route both these properties were found to develop approximately to the same extent with increasing primary particle size. The degree of crystallinity was detectable only above a critical value of c/a=1.007 at an average particle size of around 120 nm. Intragranular porosity in hydrothermal powders and the stoichiometric Ba/Ti-ratio are of minor influence. However, distinct differences in particle growth behavior for both powders were observed. This discrepancy is ascribed to a special morphology of the hydrothermal product, where enhanced particle growth was found to be governed by oriented attachment of individual crystallites and by the motion of solid–solid interfaces.     

Zur bors?urefreien Haltbarmachung von frischen Speisegarnelen und Garnelenfleisch II. Mitteilung

Zusammenfassung Im Hinblick auf das zu erwartende Verbot der bisher zur Konservierung von Speisegarnelen benutzten Borsäure wurden Koch- und Konservierungsversuche mit unbedenklichen Konservierungsmitteln durchgeführt, deren Ergebnisse erkennen lassen, daß im Gegensatz zur Wirkungsweise der Borsäure die untersuchten unbedenklichen Konservierungsmittel nur dann eine ausreichende Wirkung entfalten, wenn sie den Garnelen unmittelbar nach der Kochung zugesetzt werden, wie es nach den z.Z. gültigen Bestimmungen nur bei einer Landkochung geschehen kann.Es wurden deshalb Transportversuche mit lebenden Garnelen angeschlossen, die zeigten, daß die in den kühleren Frühjahrs- und Herbstmonaten gefangenen Garnelen einen 8stündigen Transport ohne besondere Vorkehrungen an Bord der Fangfahrzeuge praktisch verlustfrei lebend überstehen, daß dagegen die in den Sommermonaten aus wärmerem Wasser gefangenen Garnelen schon so ermattet an Bord kommen, daß sie auch beim Transport in einem Kühlbehälter bei 5° C nicht mit Sicherheit zu 100% bis zur Anlandung am Leben gehalten werden können.Weitere Maßnahmen zur borsäurefreien Konservierung und zur Lebenderhaltung der Garnelen während des Transports, die in Versuchen geprüft werden sollen, werden erörtert.