Recollements of Module Categories

We establish a correspondence between recollements of abelian categories up to equivalence and certain TTF-triples. For a module category we show, moreover, a correspondence with idempotent ideals, recovering a theorem of Jans. Furthermore, we show that a recollement whose terms are module categories is equivalent to one induced by an idempotent element, thus answering a question by Kuhn.Comment: Comments are welcom

Stabilization of the ζ-Cu10Sn3 Phase by Ni at Soldering-Relevant Temperatures

A current issue in electrical engineering is the enhancement of the quality of solder joints. This is mainly associated with the ongoing electrification of transportation as well as the miniaturization of (power) electronics. For the reliability of solder joints, intermetallic phases in the microstructure of the solder are of great importance. The formation of the intermetallic phases in the Cu-Sn solder system was investigated for different annealing temperatures between 472 K and 623 K using pure Cu as well as Cu-1at.%Ni and Cu-3at.%Ni substrate materials. These are relevant for lead frame materials in electronic components. The Cu and Cu-Ni alloys were in contact to galvanic plated Sn. This work is focused on the unexpected formation of the hexagonal ζ-(Cu,Ni)10Sn3 phase at annealing temperatures of 523–623 K, which is far below the eutectoid decomposition temperature of binary ζ-Cu10Sn3 of about 855 K. By using scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction and X-ray diffraction the presence of the ζ phase was confirmed and its structural properties were analyzed

EXPERIMENTAL INVESTIGATIONS OF GASDYNAMIC N2/CO2 MIXING LASERS

N2/CO2 mixing lasers with thermal excitation of the N2 in arc-heaters and with screen nozzles for the expansion and mixing process are investigated. Results obtained with two devices having different cross-sections of the laser channel are compared. For equal operating conditions the small signal gain is well correlated by a normalized distance downstream of the nozzle exit plane. The distribution of gain along the flow direction is mainly determined by the stagnation temperature, the ratio of N2/CO2 and the presence of He. Values of small signal gain up to 3 % cm-1 are achieved. The effect of replacing N2 by CO is studied in detail. The observed reduction of laser performance depends on the ratio of N2/CO/CO2 but is almost independent of stagnation temperature. In addition, preliminary experiments aiming at the substitution of N2 by air yield a specific laser energy of 5 J/g

MICROWAVE DISCHARGE IN A SUPERSONIC FLOW

The possibility of effectively ionizing a supersonic flow by a strong microwave field within a waveguide has been demonstrated. Electron densities beyond the cut off have been achieved at gas temperatures far below room temperature. Hence this method promises to be a good candidate to preionize and stabilize supersonic, non-selfsustained laser discharges

CW CARBON MONOXIDE LASER WITH MICROWAVE EXCITATION IN THE SUPERSONIC FLOW

A new technique of efficiently coupling microwave energy into a supersonic gas flow is described. The stable self-sustained microwave discharge is applied to excite a cw CO gasdynamic laser. Electron densities well above the cut-off value have been achieved together with a reduced field strength within the discharge that is appropriate for efficient vibrational excitation. With an energy loading of 0.15 eV/CO a laser power of 340 Watts is obtained at an overall efficiency of 7 %. The effect of some additives on stability and laser performance is studied