Towards Laser-Textured Antibacterial Surfaces.

Escherichia coli and Staphylococcus aureus bacterial retention on mirror-polished and ultrashort pulse laser-textured surfaces is quantified with a new approach based on ISO standards for measurement of antibacterial performance. It is shown that both wettability and surface morphology influence antibacterial behavior, with neither superhydrophobicity nor low surface roughness alone sufficient for reducing initial retention of either tested cell type. Surface structures comprising spikes, laser-induced periodic surface structures (LIPSS) and nano-pillars are produced with 1030 nm wavelength 350 fs laser pulses of energy 19.1 µJ, 1.01 µJ and 1.46 µJ, respectively. SEM analysis, optical profilometry, shear force microscopy and wettability analysis reveal surface structures with peak separations of 20-40 µm, 0.5-0.9 µm and 0.8-1.3 µm, average areal surface roughness of 8.6 µm, 90 nm and 60 nm and static water contact angles of 160°, 119° and 140°, respectively. E. coli retention is highest for mirror-polished specimens and spikes whose characteristic dimensions are much larger than the cell size. S. aureus retention is instead found to be inhibited under the same conditions due to low surface roughness for mirror-polished samples (Sa: 30 nm) and low wettability for spikes. LIPSS and nano-pillars are found to reduce E. coli retention by 99.8% and 99.2%, respectively, and S. aureus retention by 84.7% and 79.9% in terms of viable colony forming units after two hours of immersion in bacterial broth due to both low wettability and fine surface features that limit the number of available attachment points. The ability to tailor both wettability and surface morphology via ultrashort pulsed laser processing confirms this approach as an important tool for producing the next generation of antibacterial surfaces.

Effect of heating mode on sinterability of Fe-Ni steels.

The present study examines the effect of heating mode on the densification, microstructure, and mechanical properties of iron-nickel steel with graphite and phosphorus addition. The compacts were sintered in conventional (radiatively-heated) and microwave (2.45 GHz, multimode) furnaces at 1120 degrees C for 1 hour in forming gas (dissociated ammonia atmosphere, 95% N2-5% H2). The experimental results show that microwave sintered alloy has better properties compared with the conventionally sintered counterparts. Detailed analyses by using optical microscopy and scanning electron microscopy (SEM) reveal that microwave sintered sample has finer microstructure. SEM examination of the fractured surfaces indicate that a mixed mode fracture containing both, ductile and brittle types, is present in microwave sintered alloy, in contrast with the brittle fracture only in conventional sintered counterpart.

Temporal and spatial evolution of a laser-induced plasma from a steel target.

The space and time evolution of a laser-induced plasma from a steel target has been studied using optical time-of-flight and shadowgraphic techniques. The results, obtained for two distinct laser energy regimes, allow us to individuate two different regions in the plume, one characterized by air and continuum emissions produced by the shock wave ionization and the other characterized by emissions from ablated material. Moreover, it was shown that a sufficiently high laser fluence and short delay time of acquisition are needed to avoid inhomogeneous effects in the plasma, as required in analytical applications such as laser-induced breakdown spectroscopy.

Dose perturbation in the presence of metallic implants: treatment planning system versus Monte Carlo simulations.

An increasing number of patients receiving radiation therapy have metallic implants such as hip prostheses. Therefore, beams are normally set up to avoid irradiation through the implant; however, this cannot always be accomplished. In such situations, knowledge of the accuracy of the used treatment planning system (TPS) is required. Two algorithms, the pencil beam (PB) and the collapsed cone (CC), are implemented in the studied TPS. Comparisons are made with Monte Carlo simulations for 6 and 18 MV. The studied materials are steel, CoCrMo, Orthinox, TiAlV and Ti. Monte Carlo simulated depth dose curves and dose profiles are compared to CC and PB calculated data. The CC algorithm shows overall a better agreement with Monte Carlo than the PB algorithm. Thus, it is recommended to use the CC algorithm to get the most accurate dose calculation both for the planning target volume and for tissues adjacent to the implants when beams are set up to pass through implants.

Residual 60Co activity in steel samples exposed to the Hiroshima atomic-bomb neutrons.

Residual 60Co radioactivity produced by the neutrons from the Hiroshima atomic bomb has been measured by means of gamma-ray spectrometry for seven steel samples located up to 1,800 m slant range and one control sample obtained at 4.5 km from the hypocenter. After removing the main constituent of iron ions from the steel sample by the solvent extraction method, nickel and cobalt were chemically separated by the ion exchange process. Gamma-ray measurements were performed with a low background well-type germanium detector. Derived specific activities 60Co:Co were compared with previous measurements and with the calculation based on the neutron fluence of current dosimetry system DS86. It has been shown that a systematic discrepancy exists between the measured and calculated activity. The calculated-to-measured ratios for 60Co are consistent with those of 152Eu and 36Cl activity.

Photoneutron fields in medical accelerator rooms with primary barriers constructed of concrete and metals.

This study investigates the photoneutron field found in medical accelerator rooms with primary barriers constructed of metal slabs plus concrete. An increased neutron dose equivalent was observed for barriers containing lead or steel as compared to barriers fabricated entirely of concrete. The effect of the beam's size and distance from the primary barriers on the neutron dose was evaluated and the portion of the neutron dose due to the metal slabs was determined.

Determination of 60Co activity in steel samples in Hiroshima.

Specific activity of 60C in two steel samples taken at 687m S and 1295m NNW from the hypocenter was measured by gamma-ray spectrometry and neutron activation analysis. The results are consistent with previous data by Hashizume et al. for steel rings on the surface of roofs of buildings. content of nickel and copper in the samples was found to be too small to account for any significant 60Co production by fast neutron reactions.

Determination of specific activity of cobalt (60Co/Co) in steel samples exposed to the atomic bomb in Hiroshima.

Specific activity 60Co/Co in two steel samples taken at 687m S and 1295m NNW from the hypocenter was measured by gamma-ray spectrometry and neutron activation analysis. The results were, respectively, (2.64 +/- 0.38) x 10(1) and (3.09 +/- 0.48) x 10(-1) dpm/mg Co at the time of bombing, which are consistent with previous data by Hashizume et al. for steel rings on the surface of roofs of buildings. The present data are expected to serve as verification of the bomb neutron transport calculations. Content of nickel and copper in the samples, determined by colorimetric and neutron activation methods, respectively, was too small to account for any significant 60Co production by the (n,p) and (n, alpha) reactions.

Element-sensitive computed tomography with fast neutrons.

Neutrons and X-rays are mathematically equivalent as probes in computed tomography. However, structure in the energy dependence of neutron total cross sections and the feasibility of using time-of-flight techniques for energy sensitivity in neutron detection suggest that spatial distributions of specific substances can be determined from neutron transmission data. We demonstrate that this is possible by tomographically reconstructing from such data a phantom containing several different structural materials.