Job-shop scheduling with multi-purpose machines

Consider the following generalization of the classical job-shop scheduling problem in which a set of machines is associated with each operation of a job. The operation can be processed on any of the machines in this set. For each assignment μ of operations to machines letP(μ) be the corresponding job-shop problem andf(μ) be the minimum makespan ofP(μ). How to find an assignment which minimizesf(μ)? For problems with two jobs a polynomial algorithm is derived.     

Laser-engineered topography: correlation between structure dimensions and cell control

Topographical cues have a significant impact on cell responses and by this means, on the fabrication of innovative implant materials. However, analysis of cell-topography interactions in dependence of the surface feature dimensions is still challenging due to limitations in the fabrication technology. Here, we introduce surface structuring via picosecond laser systems, which enable a fast production of micro-sized topologies. Changes in the processing parameters further control the feature sizes of so-called spikes. Using surfaces with big and small spike-to-spike-distances for comparisons, we focussed on cell adhesion via extracellular matrix adsorption and focal adhesion complexes, morphology, localisation and proliferation of fibroblasts. The observed cell control was dependent on a turnover point related to the structure dimensions: only big spike-to-spike-distances reduced cell behaviour. Therefore, this technology offers a platform to study cell and tissue interactions with a defined microenvironment.     

Repetitively pulsed, 70-J photolytic iodine laser with excellentoptical and long/reliable operation

The performance of a repetitively pulsed, 70 joule, closed cycle 1.3 μM photolytic atomic iodine laser with excellent beam quality (BQ=1.15) is presented. This BQ was exhibited in the fundamental mode from a M=3.1 confocal unstable resonator at a 0.5 Hz repetition rate. A closed cycle scrubber/laser fuel system consisting of a condensative-evaporative section, two Cu wool I₂ reactor regions, and an internal turbo-blower enabled the laser to operate very reliably with low maintenance. The fuel system provided C₃F ₇I gas at 10-60 torr absent of the photolytic quenching by-product I₂. Using a turbo-molecular blower longitudinal flow velocities greater than 10 m/s were achieved through the 150 cm long by 7.5×7.5 cm² cross sectional photolytic iodine gain region. In addition to the high laser output and excellent BQ, the resulting 8-12 μs laser pulse had a coherence length greater than 45 meters and polarization extinction ratio better than 100:1. Projections from this pulsed photolytic atomic iodine laser technology to larger energies, higher repetition rates, and variable pulse widths are discussed     

Increased Enantioselectivity by Engineering Bottleneck Mutants in an Esterase from Pseudomonas fluorescens

Four hydrophobic and bulky amino acid residues (F126, F144, F159, and I225) were identified to form a bottleneck guarding the entrance to the active site of an esterase from Pseudomonas fluorescens (PFE I). Hence, a range of nonpolar amino acids were introduced into PFE I to broaden the substrate range and to increase enantioselectivity while preserving the hydrophobicity of the tunnel. First, single variants were created and then the most enantioselective ones were combined to find cooperative effects. This resulted in several mutants, which showed substantially enhanced enantioselectivity; for instance, in the kinetic resolution of 1‐phenyl‐1‐propyl acetate, with which the wild type only showed E=1.2, two mutants gave E>46. For 1‐phenyl‐1‐ethyl acetate enantioselectivity increased from ～50 to >100 for all mutants studied. Furthermore, higher conversions could be found at shorter reaction times; this indicates that the mutations not only enhanced selectivity, but that also the entrance into the active site was indeed facilitated by these mutations. The experimental results could be explained by computer modeling.     

Long operating time CW atomic iodine probe laser at 1.315 µm

A photolytically pumped longitudinal flow CW atomic iodine laser at1.315 mum with virtually an unlimited operating time and easy operation is reported. Several weeks of continual operation is easily attainable. The prolonged lasing is achieved by employing a passive closed cycle flow system of the C3F7I laser fuel. A high pressure dc Hg arc lamp is used for the photolytic pumping. Peak CW powers of 38 mW have been obtained along with good stability (∼1 percent amplitude fluctuations) in the fundamental TEM00mode via the use of an internal lens.     

Extraction of radiative and nonradiative rates in Sb based midwave infrared lasers using a novel approach

We developed a technique using nonlinear correlation of photoluminescence (PL) to characterize midwave infrared lasers by extracting the density and temperature dependence of the carrier lifetime and its exact branching into radiative and nonradiative processes. This was accomplished, without time resolving the PL recovery, through mathematical optimization. We extracted this information by using a laser source that can be operated in both continuous-wave and short pulse modes. Through fitting of the PL signal and its nonlinear correlation for both laser modes of operation, the carrier lifetime as a function of density is extracted. As a proof of principle, we investigated a midinfrared Sb based laser and showed that the radiative branching ratio drops from approximately 54% at 80 K to about 3% at room temperature, resulting from an order of magnitude increase in the nonradiative rate coupled with a factor of 2 reduction in the radiative rate. We believe that this is a very generic approach and can be extended to various luminescing material systems.     

Radial profile of neon 1s5atoms in a He-Ne active discharge and their lens effect on lasing at 6401 Å

A laser interferometer was used to determine the spatial distribution of the neon1s_{5}metastable states in an auxiliary active discharge, identical to the one used for a He-Ne laser at 6401 Å. The resulting distribution was a parabola, which crossed zero at the discharge tube walls. Measurements of the 6401-Å spot size were used to determine the axial metastable density from the calculation of the gas lens effect associated with this radial distribution. Excellent agreement was obtained between the two methods. The results show that the lens effect of these metastables is responsible for the anomalous appearance of lasering at 6401 Å in near-hemispherical cavities. For such resonators, the effective radius of curvature of the spherical mirror is increased while the equivalent mirror spacing is decreased; thus, the diffraction losses at 6401 Å are significantly reduced. Preliminary results are also given to show that the lens effect is more pronounced for the higher order modes.