Library

Notes: InxGa1−xAs layers (0≤x≤0.37) doped with carbon (〉1020 cm−3) were grown on semi-insulating GaAs substrates by chemical beam epitaxy using carbon tetrabromide (CBr4) as the dopant source. Hall measurements imply that all of the carbon was present as CAs for values of x up to 0.15. The C acceptors were passivated by exposing samples to a radio frequency hydrogen plasma for periods of up to 6 h. The nearest-neighbor bonding configurations of CAs were investigated by studying the nondegenerate antisymmetric hydrogen stretch mode (A−1 symmetry) and the symmetric XH mode (A+1 symmetry) of the H–CAs pairs using IR absorption and Raman scattering, respectively. Observed modes at 2635 and 450 cm−1 had been assigned to passivated Ga4CAs clusters. New modes at 2550 and 430 cm−1 increased in strength with increasing values of x and are assigned to passivated InGa3CAs clusters. These results were compared with ab initio local density functional theory. Modes due to AlInGaCAs clusters were detected in samples containing grown in Al and In. These results demonstrate that for InGaAs, CBr4 is an efficient C doping source since both In–CAs bonds as well as Ga–CAs bonds are formed, whereas there is no evidence for the formation of In–CAs bonds in samples doped with C derived from trimethylgallium or solid sources. © 1996 American Institute of Physics.

Notes: A linearly scalable plasma source based on the radio frequency generated hot hollow cathode discharge between two parallel plates with a magnetic field perpendicular to the plates near the outlet of the cathode is introduced. The magnetic field facilitates and confines the hollow cathode discharge which leads to a high power density and a high cathode wall temperature. The geometry and location of hot zones is directly controlled by magnetic field. The linear arc discharge (LAD) source exhibits similar features as the cylindrical radio frequency hollow cathode plasma jet. Experiments indicate a metastable assisted growth of TiN films. LAD source extends abilities of the radio frequency hollow cathode plasma jet to the large area processing. © 1997 American Institute of Physics.

Notes: An excess heat from an exothermic reaction of metastable Ar (43P0) and Ar (43P2) atoms with N2 molecules at low contents of N2 in Ar was found to be responsible for an enhanced thermionic emission, an enhanced production of Ti target vapor, an increased ionization, and consequently for an enhanced deposition rate of TiN films in the radio frequency hollow cathode plasma jet (RHCPJ). This finding emphasizes favorable geometry of hollow cathodes, as well as an important role of metastables in plasma-assisted processes. © 1995 American Institute of Physics.

Notes: The importance of submerged macrophytes and predation risk for habitat use by 0+ perch (Perca fluviatilis) and 0+ roach (Rutilus rutilus) was investigated in triplicate 78-m2 field enclosures with and without macrophytes in the middle. During three experimental runs, habitat use by fish were monitored every 6 h with Breder traps. Each period included 2 days of fish monitoring before stocking with piscivorous perch, and 2 days after. Predation risk significantly changed habitat use by 0+ perch in the morning, midday and evening, but not at night. By comparing with the unvegetated controls, we found a refuging effect of macrophytes in the morning. Under predation risk there was significant diel variation in habitat use by 0+ perch, suggesting a migration from the open water habitat at night into the macrophytes in the morning. Roach continued to use open water even after predators were stocked, but responded like perch by reducing overall activity.

Notes: Zusammenfassung Da das Ausmaß der Veränderungen in und an Knochen sicher mit den äußeren Bedingungen variiert, denen die Knochen nach dem Tode ausgesetzt waren, kann man den Grad von Umbildungsvorgängen nicht schematisch als ein Maß der Zeit betrachten, die seit dem Ableben des Individuums verstrichen ist. Wenn auch naturgemäß die Wahrscheinlichkeit umfangreicherer postmortaler Umsetzungen mit der Länge der Liegezeit steigt, so wird sich doch voraussichtlich aus Einzelkriterien des Dekompositionsgrades keine allgemein gültige Beziehung zwischen der Zerstörung der organischen Substanz und dem Alter von Knochen finden lassen, sieht man von der Radiocarbonmethode, der einzigen Möglichkeit ab, die an sich geeignet ist, aus der Bestimmung des C14: C12-Verhältnisses in der organischen Substanz die absolute Länge der Zeit zu erfassen, die seit dem Tode des Individuums vergangen ist. Der Anwendung dieser Methode auf Objekte mit geringer Alterung scheint indessen vorerst noch die zu hohe Fehlergrenze entgegen zu stehen. Erwartungsgemäß ergibt sich aus den bisherigen Untersuchungsbefunden, daß die Beurteilungsgrundlage einer Knochenaltersbestimmung letztlich nur aus der Summe aller aus den bisher bekannten und den mitgeteilten neuen Verfahren erzielbaren Detailergebnisse zu schaffen ist. So gelangt man zu Aussagen, die zumindest der Durchschnittswahrheit entsprechen. Unverkennbare diagnostische Vorteile, die die erstmals zur Diskussion gestellte Ultraschall-Meßmethode im Rahmen der Problemstellung bietet, leiten sich aus der, der fortschreitenden Liegedauer entsprechend kontinuierlich sinkenden Longitudinalgeschwindigkeit (V L) des Knochenmaterials ab. Vor allem für das zweite bis fünfte Jahrzehnt der Lagerung im Erdgrab ergaben sich bei allen Methoden keine so markannten Veränderungen des Dekompositionsgrades, daß eine Unterscheidung der Liegezeiten innerhalb dieser Phase mit der wünschenswerten Regelmäßigkeit gewährleistet erschiene. Auch die Ultraschall-Methode verlangt selbstverständlich die Berücksichtigung all jener milieubedingter Faktoren, die für die Entstehung von Merkmalen einer bevorzugten oder verzögerten Knochenalterung verantwortlich sind. Die kombinatorische Prüfung des Materials im UV-Licht, hinsichtlich der Anfärbbarkeit mit Indophenol/ Nilblau sowie des mikroanatomischen Strukturzersatzes und der Ultraschallgeschwindigkeit läßt aber eine zweifelsfreie Abgrenzung von Skeletteilen des ersten postmortalen Jahrzehnts gegenüber solchen der vier Folgejahrzehnte und vor allem der zweiten Hälfte des ersten Jahrhunderts zu. Deutliche, die Altersansprache ermöglichende Wertabstufungen erhält man mit diesen Methoden, besonders drastisch mit dem Ultraschallverfahren, bei der Prüfung historischer Knochenfunde, und zwar im Gegensatz zu manchen chemischen Prüfmethoden, die über Jahrhunderte hinweg weitgehend gleichbleibende, diagnostisch somit kaum voll verwertbare Ergebnisse liefern können. Die objektive Abgrenzung solcher älteren Knochenfunde entspricht einer Notwendigkeit; denn die subjektive, grobsinnliche Schätzung der Liegedauer kann — wie die Praxis zeigt — zu erheblichen Irrtümern führen, und zwar auf Grund speziell konservierender Einflüsse des Einbettungsmaterials gelegentlich sogar noch bei subfossilen Skeleten.

Notes: Abstract Objective: Evaluate A-mode ultrasonographic examination of maxillary sinus disease in mechanically ventilated, critically ill patients using sinoscopy as criterion standard. Design: Prospective case series. Setting: The intensive care units of a tertiary care hospital. Patients: 25 mechanically ventilated, critically ill patients with nasotracheal intubation or a tracheotomy were followed up by ultrasonographic examination of the maxillary sinuses in supine and semirecumbent positions. Infectious sinusitis was suspected in 15 patients, who were bilaterally sinoscoped combined with sampling for bacterial culture. Results: The frequency of oedema and/or secretions was high: 29 antra of 30 examined. Only 2 of 30 antra showed bacterial infection. Ultrasonographic examinations were sensitive to general pathological changes but less accurate in specific diagnostics such as the presence of secretions (sensitivity for fluid 75 %, oedema 81 %). The sensitivity of ultrasonographic diagnosis improved when the examination was made in the semirecumbent position (sensitivity for fluid 91 %, oedema 81 %). Conclusions: A-mode ultrasonography is a useful method for daily use, being easy to perform and without discomfort to the patient. It is fast and gives an immediate diagnosis. In intensive care unit patients, it should be the method of choice for day-to-day studies of effects and changes in the upper airways. For the differential diagnosis of oedema and/or secretions, it is not reliable enough to be used as the sole diagnostic method. A complementary investigation, such as computed tomography or sinoscopy, which also provides the opportunity to take samples, is needed for diagnostic confidence.

Notes: Abstract Invasive group B streptococcal (GBS) infections are common in neonates but are rare after the 1st month of life. It is not known why GBS infections have this age distribution which differs from that of invasive infections caused by other encapsulated bacteria. The aim of this study was to test the possibility that serum antibodies against the GBS capsular polysaccharides (CPS) are acquired during the first months of life thereby preventing infections after the neonatal period. Cord sera were collected from 321 healthy term newborns. A second blood sample was collected at 2, 4, 8, 13 or 26 weeks of age. IgG CPS antibodies (measured by ELISA) against serotypes Ia, II and III were present in 98%–100% of all cord sera and decreased continuously during the first 6 months of life. No IgM antibodies against serotype III CPS were present in cord sera. Only 16%–17% of the children acquired IgM antibodies against serotype III CPS at 3 and 6 months of age. Conclusion Early acquisition of IgG or IgM antibodies against CPS of the most common GBS serotypes was not demonstrated and cannot explain the rare occurrence of invasive GBS infections in children after the 1st month of life.