Mechanical properties in tension of mechanically attrited nanocrystalline iron by the use of the miniaturized disk bend test

The mechanical properties of warm compacted nanocrystalline (nc) iron powder compacts of near theoretical density in the grain size range between 8 and 33 nm were investigated. The elastic and plastic behavior were characterized by miniaturized disk bend tests and hardness measurements. Light and scanning electron microscopy (SEM) were used to document the deformation and fracture morphologies. The Young's modulus of the nc Fe was essentially the same as that of coarse grained Fe. All samples failed in a macroscopically brittle manner. Local plasticity in shear bands was observed in the samples with the larger grain sizes (>20 nm). An increasing failure stress with increasing grain size is probably due to a processing effect on the flaw controlled failure of the samples. The results are discussed in the context of the deformation and fracture behavior of micrometer grain size metals and alloys.     

Conjointanalyse-basierte Produkt(linien)gestaltung unter Berücksichtigung von Konkurrenzreaktionen Conjoint-based product (line) design considering competitive reactions

Ausgangspunkt unserer Untersuchungen zur Conjointanalyse-basierten wettbewerbsorientierten Produktgestaltung bilden segmentspezifische konditionale MNL-Modelle. Bisher auf diesem Gebiet entwickelte Ans?tze, die sich mit der Bestimmung von Marktgleichgewichten befassen, beschr?nken sich ausschlie?lich auf den Single-Produkt-Fall (z.B. Choi u. DeSarbo, 1993; Green u. Krieger, 1997). Unser Beitrag setzt sich ebenfalls mit dem Single-Produkt-Fall (d.h. ein Produkt je Anbieter) auseinander, behandelt darüber hinaus erstmals aber auch den Wettbewerb mit Produktlinien. Gegenstand der Untersuchungen sind insbesondere die Existenz und Eindeutigkeit simultaner Positions-Preis- Gleichgewichte, die Existenz ineffizienter Marktgleichgewichte sowie der Differenzierungsgrad zwischen Konkurrenzprodukten.     

Effect of bainite on the mechanical properties of dual-phase steels

The bainite-martensite-ferrite steels (tri-phase steels) were made in the laboratory by intercritical annealing, bainite transformation and oil quenching in sequence. With bainite inclusions, ductility was improved substantially without significant reduction of tensile strength. The ductility increase was found to be due to large deformation after necking and increased work-hardening.     

Femtosecond optical nonlinearities of CdSe quantum dots

Femtosecond differential absorption measurements of the quantum-confined transitions in CdSe microcrystallites are reported. Spectral hole burning is observed, which is accompanied by an induced absorption feature on the high-energy side. The spectral position of the burned hole depends on the excitation wavelength. For excitation on the low-energy side of the lowest quantum-confined transition, a slight shift of the hole towards the line center is observed. The hole width increases with pump intensity and the magnitude of the induced transparency saturates at the highest excitation level. The results are consistently explained by bleaching of one-pair states and induced absorption caused by the photoexcited two electron-hole pair states. It is concluded that the presence of one electron in the excited state prevents further absorption of photons at the pair-transition energy and accounts for the major portion of the bleaching of the transition     

Interference-aware scheduling in the multiuser MIMO-OFDM downlink - [topics in radio communications]

With the introduction of orthogonal frequency- division multiplexing and multiple antennas in cellular networks, there are new opportunities to adapt the transmission to propagation and interference conditions. In this article we describe a practical approach using space-frequency-selective multiuser MIMO scheduling. Frequency-selective feedback is provided on achievable data rates for preferred single- and multistream transmission modes. The base station selects the best mode while providing instantaneous fairness. We observe that multiuser transmission increases the probability of using multistream transmission. Besides the benefits from optimal combining at the physical layer, there is an additional gain at the MAC layer since the estimation of achievable rates becomes more precise. Altogether, 93 percent of the theoretical throughput can be realized by synchronizing the base stations and providing cell-specific reference signals. We have implemented essential functions of the approach in real time on an experimental 3GPP LTE prototype in 20 MHz bandwidth. Feasibility of the key features is proven in laboratory and field trials.     

Off-axis and inline electron holography: Experimental comparison

Electron holography is a very powerful technique for mapping static electric and magnetic potentials down to atomic resolution. While electron holography is commonly considered synonymous with its off-axis variant in the high energy electron microscopy community, inline electron holography is widely applied in low-energy electron microscopy, where the realization of the off-axis setup is still an experimental challenge. This paper demonstrates that both inline and off-axis holography may be used to recover amplitude and phase shift of the very same object, in our example latex spheres of 90 and 200 nm in diameter, producing very similar results, provided the object does not charge under the electron beam.     

Veränderung der Resonanzkurve eines Saitengalvanometers durch Parallelkondensator

Ohne ZusammenfassungHerr Professor Dr. Schering, der Leiter des Elektrotechnischen Institutes, ermöglichte es uns, die erforderlichen Versuche in seinem Institut auszuführen. Dafür sprechen wir ihm unseren Dank aus und danken außerdem ihm sowie Herrn Dr.-Ing. Potthof für verschiedene Anregungen.