Showing papers by "Leibniz University of Hanover published in 1996"

Hierarchical partitioning

Abstract: Partitioning of digital circuits has become a key problem area during the last five years. Benefits from new technologies like Multi-Chip-Modules or logic emulation strongly depend on partitioning results. Most published approaches are based on abstract graph models constructed from flat netlists, which consider only connectivity information. The approach presented in this paper uses information on design hierarchy in order to improve partitioning results and reduce problem complexity. Designs up to 150 k gates have been successfully partitioned by descending and ascending the hierarchy. Compared to. Standard k-way iterative improvement partitioning approach results are improved by up to 65% and runtimes are decreased by up to 99%.

Steep dispersion and group velocity below c/3000 in coherent population trapping.

Abstract: We have measured the index of refraction in the region of a coherent population trapping resonance in a cesium vapor cell with an interferometric technique. We find very high normal dispersion (up to $\frac{\mathrm{dn}}{\mathrm{df}}=9.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ ${\mathrm{Hz}}^{\ensuremath{-}1}$) at low absorption. From our spectra we obtain very small group velocities below $\frac{c}{3000}$. This corresponds to a delay time of more than 200 ns for a cesium cell 20 mm in length, equivalent to more than 60 m of propagation in vacuum.

Bifurcation and stability analysis for a non-smooth friction oscillator

Abstract: Friction-induced self-sustained oscillations, also known as stick-slip vibrations, occur in mechanical systems as well as in everyday life. On the basis of a one-dimensional map, the bifurcation behaviour including unstable branches is investigated for a friction oscillator with simultaneous self-and external excitation. The chosen way of mapping also allows a simple determination of Lyapunov exponents.

Postoperative function after implant insertion in vascularized bone grafts in maxilla and mandible.

Abstract: Between 1988 and 1992, 80 Branemark-type implants were inserted in 18 patients during reconstruction of the mandible or maxilla with vascularized iliac crest or scapula grafts with or without additional soft tissue pedicles. In these procedures, nine vascularized bone grafts were combined with a primary insertion of 32 implants and a secondary insertion of 48 implants. Twelve patients are currently wearing the implant-borne dentures. From 32 implants inserted primarily, eight could not be used for prosthodontic rehabilitation because three were lost with a graft, three were left as sleepers, and two demonstrated a lack of osseointegration. None of the implants inserted secondarily in grafts were lost. Primary implant insertion should be performed only in close cooperation with the prosthodontist and in selected cases, for example, in free-end reconstruction of the mandible with a straight graft and where a limited number of implants is needed. Although restoration of masticatory function in patients with head and neck cancer can be achieved, compared with a healthy control group, functional impairments remain. Patients subjectively favor the nonreconstructed side of the mandible or maxilla for chewing. These findings can be correlated with a postoperative follow-up investigation using a miniature force transducer and the T-scan system.

Production of cosmogenic nuclides in meteoroids: accelerator experiments and model calculations to decipher the cosmic ray record in extraterrestrial matter

Abstract: Accelerator experiments at low and medium energies provide a basis for the development of models describing the production of cosmogenic nuclides by solar and galactic cosmic ray particles. Here, recent efforts to understand cosmogenic nuclide production are outlined taking their production in meteoroids as an example. Thin-target and thick-target experiments are described, by which the relevant cross sections are measured and in which the isotropic irradiation of meteoroids in space is simulated under completely controlled conditions. Thin-target and thick-target data are combined to develop and to validate model calculations of cosmogenic nuclide production rates by solar and galactic cosmic ray particles. The model calculations provide the basis to interpret the observed abundances of cosmogenic nuclides with respect to the exposure history of the irradiated matter and to the history of the cosmic radiation itself.

Observation of individual neutral atoms in magnetic and magneto-optical traps

Abstract: We have identified and photographed individual cesium atoms in a magneto-optical trap with steep magnetic gradients. By switching off the trapping light fields, single atoms were released to a bound state of the magnetic potential. A storage time of 38 s was measured for purely magnetic trapping, whereas a storage time of 147 s was observed in the corresponding magneto-optical trap.

Regulation of nitrogen uptake on the whole plant level

Abstract: The largest part of nitrogen requirements of crops is mostly covered by nitrate. The uptake of this ion is thermody- namically uphill and thus dependent on metabolism. This article considers regulation of N uptake in higher plants putting emphasis on NO3¯ and the whole plant level.

Continuous resonant four-wave mixing in double-lambda level configurations of na2

Abstract: Efficient continuous resonant frequency mixing ω4 = ω1 − ω2 + ω3 in Na2 has been realized. A bichromatic field (λ1 = 488 nm, λ2 = 525 nm), generated by an Ar+-laser-pumped Na2 Raman laser, and radiation at λ3 = 655 nm from a dye laser interact resonantly with corresponding transitions X1∑g+(υ=3,J=43) → B1Πu(6, 43) → X1∑g+(13,43)→A1∑g+(24,44) in a test Na2 heat pipe. For input powers of 200, 25, and 400 mW an output beam of as much as 0.2 mW at λ4 = 599 nm has been observed. Measured parameter dependences indicate an influence of interference effects. This is directly related to the discussion of lasing without inversion.

Molecular genetic analysis and human chorionic gonadotropin stimulation tests in the diagnosis of prepubertal patients with partial 5α-reductase deficiency

Abstract: Reduced conversion of testosterone (T) to dihydrotestosterone (DHT) results in defective virilization in karyotypic males. Different mutations in the 5α-reductase type 2 gene cause the phenotypic variability of the disease. In this report we describe four prepubertal patients with a predominantly male phenotype who carry homozygous point mutations in the 5α-reductase type 2 gene and address the specific T and DHT response to different human chorionic gonadotropin (hCG) stimulation tests. For molecular genetic analysis, DNA from peripheral blood leucocytes was studied. The coding region of the 5α-reductase type 2 gene was characterized by exon-specific polymerase chain reaction amplification, non-radioactive single strand polymorphism analysis, and direct sequencing. Three different homozygous point mutations (Gly196−Ser, Arg227−Gln and Ala228−Thr) were identified in the patients. In contrast, in the DNA from 100 phenotypically normal males only two heterozygous abnormalities (Ile196−Ile, ΔMet157) were characterized. For hormonal studies, T and DHT were measured in serum before and after hCG stimulation employing different protocols. HCG stimulation with 5000 IU/m2 once and prolonged stimulation with seven injections of 1500 IU hCG per single dose every other day were used. While abnormal T/DHT ratios were identified with both hCG protocols in the patients, prolonged stimulation lead to higher T values and to higher T/DHT ratios, and hence to a better discrimination of pathologic results.

Distraction osteogenesis in the mandible with a motor-driven plate : a preliminary animal study

Abstract: Distraction osteogenesis is an established method for lengthening of the mandible and for reconstruction of bony defects. We report on our first experience with a motor-driven 2.7 mm plate which was fixed at the lingual surface of the body of the mandible in Gottingen minipigs following osteotomy of the mandible. The power supply and the timer module were inserted subcutaneously in a neck pocket. A maximum distraction of 13 mm was observed. Further research is necessary before clinical application of a comparable system.