A Lower Bound for the Spectral Radius of Graphs with Fixed Diameter

AMS classifications: 05C50, 05E99;graphs;spectral radius;diameter;bound;degree/diameter

Asymptotic Results on the Spectral Radius and the Diameter of Graphs

2000 Mathematics Subject Classification: 05C50, 05E99;graphs;spectral radius;diameter;limit points;quipus

A simulation study on the interactive effects of radiation and plant density on growth of cut chrysanthemum

In the present study, we used a photosynthesis-driven crop growth model to determine acceptable plant densities for cut chrysanthemum throughout the year at different intensities of supplementary light. Dry matter partitioning between leaves, stems, and flowers was simulated as a function of crop developmental stage. Leaf area index was simulated as leaf dry mass multiplied by specific leaf area, the latter being a function of season. Climatic data (hourly global radiation, greenhouse temperature, and CO2 concentration) and initial organ dry mass were model inputs. Assimilation lights were switched on and off based on time and ambient global radiation intensity. Simulated plant fresh mass with supplementary light (49 µmol m-2 s-1) for 52 cultivations (weekly plantings, reference plant densities, and length of the long and short day period) was used as reference plant fresh mass. For four other supplementary light intensities (31, 67, 85, and 104 µmol m-2 s-1), dry matter production was simulated with the reference plant density and length of the long and short day period for each planting week and plant fresh mass was calculated. The acceptable plant density was then calculated as the ratio between plant fresh mass and reference plant fresh mass multiplied by the reference density. Under low natural light intensities, plant density could be increased substantially (>30%) at increased supplementary light intensities, while maintaining the desired plant mass. Simulated light use efficiency (g additional dry mass ¿ MJ-1 additional supplementary light) was higher in winter (4.7) than in summer (3.5), whereas it hardly differed between the supplementary light intensities. This type of simulations can be used to support decisions on the acceptable level of plant density at different intensities of supplementary lighting or lighting strategies and on optimum supplementary light intensities

QCD Corrections to Electroweak Annihilation Decays of Superheavy Quarkonia

QCD corrections to all the allowed decays of superheavy groundstate quarkonia into electroweak gauge and Higgs bosons are presented. For quick estimates, approximations that reproduce the exact results within less than at worst two percent are also given.Comment: 20 pages RevTeX, 9 figures. The complete paper, including figures, is also available via anonymous ftp at (129.13.102.139) as ftp://ttpux2.physik.uni-karlsruhe.de/ttp95-05/ttp95-05.ps, or via www at http://ttpux2.physik.uni-karlsruhe.de/cgi-bin/preprints

High-energy expansion of Coulomb corrections to the e+e- photoproduction cross section

First correction to the high-energy asymptotics of the total $e^+e^-$ photoproduction cross section in the electric field of a heavy atom is derived with the exact account of this field. The consideration is based on the use of the quasiclassical electron Green function in an external electric field. The next-to-leading correction to the cross section is discussed. The influence of screening on the Coulomb corrections is examined in the leading approximation. It turns out that the high-energy asymptotics of the corresponding correction is independent of the photon energy. In the region where both produced particles are relativistic, the corrections to the high-energy asymptotics of the electron (positron) spectrum are derived. Our results for the total cross section are in good agreement with experimental data for photon energies down to a few $MeV$. In addition, the corrections to the bremsstrahlung spectrum are obtained from the corresponding results for pair production.Comment: 22 pages, 7 figures, RevTeX.Typos are corrected. The numerical results, figures and conclusions remain unchanged as they were obtained using correct formula

Efficient low-threshold lasers based on an erbium-doped holey fiber

We report experimental results on the continuous-wave lasers based on a small core erbium-doped holey fiber. In a simple Fabry-Perot-type cavity with high output coupling, we demonstrate low-threshold (0.55 mW) high slope-efficiency (57.3%) operation confirming both the quality and exceptionally high gain efficiency of the fiber. In an all-fiber ring cavity where the cavity loss is reduced, we show that it is possible to achieve a low-threshold laser with extremely wide tunability (>100 nm around 1550 nm). Our results illustrate some of the unique opportunities provided by active small core holey fibers

A holey fiber based Brillouin laser

We demonstrate for the first time a Brillouin laser based on a Holey Fiber (HF). Using a simple Fabry-Perot resonator scheme containing a 75m long highly nonlinear HF with an effective area of 2.85µm2 we obtain a threshold of 125mW and a slope efficiency of ~70%