direct laser interference patterning of stainless steel by ultrashort pulses for antibacterial surfaces

Abstract Direct Laser Interference Patterning (DLIP) with ultrashort pulses was exploited to produce tailored periodic sub-micrometer structures on stainless steel surfaces to reduce bacterial attachment and retention. Laser pulses with wavelength 1030 nm and duration 8 ps were employed to form a two-beam line interference pattern that was applied in a two-pass strategy to produce fine cross-wise surface structures with a period of ~ 850 nm and a depth of ~ 500 nm. The laser setup and process parameters were selected based on a simple theoretical model of the resulting interference pattern and ablation depth to limit the number of contact points available for bacterial cells with dimensions 500–2000 nm. Periodic 'cones' and 'holes' were produced covering areas of 250 mm2 with the same interference pattern by exploiting the dependence of laser-induced periodic surface structures on polarization. Cones and holes yielded reductions in E. coli retention of 99.8% and 99.4%, respectively, and S. aureus retention of 70.6% and 79.1%, respectively, after two hours immersion in bacterial solution compared to reference samples. Such reductions achieved over large surface areas suggests that this approach is appropriate for upscaling and high throughput production of antibacterial metallic surfaces in the food and healthcare industries

Hyperactivation of the G12-Mediated Signaling Pathway in Caenorhabditis elegans Induces a Developmental Growth Arrest via Protein Kinase C

AbstractThe G12 type of heterotrimeric G-proteins play an important role in development and behave as potent oncogenes in cultured cells [1–5]. However, little is known about the molecular nature of the components that act in the G12-signaling pathway in an organism. We characterized a C. elegans Gα subunit gene, gpa-12, which is a homolog of mammalian G12/G13α, and found that animals defective in gpa-12 are viable. Expression of activated GPA-12 (G12QL) results in a developmental growth arrest caused by a feeding behavior defect that is due to a dramatic reduction in pharyngeal pumping. To elucidate the molecular nature of the signaling pathways in which G12 participates, we screened for suppressors of the G12QL phenotype. We isolated 50 suppressors that contain mutations in tpa-1, which encodes two protein kinase C isoforms, TPA-1A and TPA-1B, most similar to PKCθ/δ. TPA-1 mediates the action of the tumor promoter PMA [6]. Expression of G12QL and treatment of wild-type animals with PMA induce an identical growth arrest caused by inhibition of larval feeding, which is dependent on TPA-1A and TPA-1B function. These results suggest that TPA-1 is a downstream target of both G12 signaling and PMA in modulating feeding and growth in C. elegans. Taken together, our findings provide a potential molecular mechanism for the transforming capability of G12 proteins

Pulsed-laser deposition of MgB2 and B thin films

Thin films of the novel superconductor MgB2 were deposited from an Mg-enriched MgB2 target or by alternating ablation from Mg and B targets, depositing multilayers. The superconducting films were achieved in situ by a two-step process: deposition at low temperatures ranging from room temperature to 200 °C and subsequently heating to 600 °C. The color of the plasma originating from Mg or Mg-enriched MgB2 targets during the deposition is an indicator of the constituents of the plasma and can be used to adjust the plasma parameters like pressure and energy density. The films showed a reduced critical temperature (Tc) compared to the bulk value (39 K), which is attributed to the small grain sizes and the relatively high base pressure of the system (10-7 mbar) causing impurities (oxygen, carbon...). To investigate B oxidation and to determine the suitable deposition conditions for B, films made by pulsed-laser deposition (PLD) from B target were analyzed by XPS. The films are very sensitive to the ambient gas purity and the base pressure. We anticipate an improvement of Tc and the crystallinity of MgB2 thin films by using PLD in high vacuum and with a high purity Ar and H2 gas mixture

Density and molecular epidemiology of Aspergillus in air and relationship to outbreaks of Aspergillus infection

After five patients were diagnosed with nosocomial invasive aspergillosis caused by Aspergillus fumigatus and A. flavus, a 14-month surveillance program for pathogenic and nonpathogenic fungal conidia in the air within and outside the University Hospital in Rotterdam (The Netherlands) was begun. A. fumigatus isolates obtained from the Department of Hematology were studied for genetic relatedness by randomly amplified polymorphic DNA (RAPD) analysis. This was repeated with A. fumigatus isolates contaminating culture media in the microbiology laboratory. The density of the conidia of nonpathogenic fungi in the outside air showed a seasonal variation: higher densities were measured during the summer, while lower densities were determined during the fall and winter. Hardly any variation was found in the numbers of Aspergillus conidia. We found decreasing numbers of conidia when comparing air from outside the hospital to that inside the hospital and when comparing open areas within the hospital to the closed department of hematology. The increase in the number of patients with invasive aspergillosis could not be explained by an increase in the number of Aspergillus conidia in the outside air. The short-term presence of A. flavus can only be explained by the presence of a point source, which was probably patient related. Genotyping A. fumigatus isolates from the department of hematology showed that clonally related isolates were persistently present for more than 1 year. Clinical isolates of A. fumigatus obtained during the outbreak period were different from these persistent clones. A. fumigatus isolates contaminating culture media were all genotypically identical, indicating a causative point source. Kn

Liposomal amphotericin B (AmBisome) reduces dissemination of infection as compared with amphotericin B deoxycholate (Fungizone) in a rate model of pulmonary aspergillosis

The efficacy of AmBisome, a liposomal formulation of amphotericin B, was compared with that of Fungizone (amphotericin B desoxycholate), in a rat model of unilateral, pulmonary aspergillosis. Repeated administration of cyclophosphamide resulted in persistent, severe granulocytopenia. The left lung was inoculated with a conidial suspension of Aspergillus fumigatus, thus establishing an unilateral infection. Antifungal treatment was started 40 h after fungal inoculation, at which time mycelial disease was confirmed by histological examination. Both Fungizone 1 mg/kg and AmBisome 10 mg/kg resulted in increased survival in terms of delayed as well as reduced mortality. Quantitative cultures of lung tissue showed that only AmBisome 10 mg/kg resulted in reduction of the number of fungal cfus in the inoculated left lung. Compared with Fungizone, both AmBisome 1 mg/kg/day and AmBisome 10 mg/kg/day significantly prevented dissemination from the infected left lung to the right lung. In addition, both AmBisome regimens reduced hepatosplenic dissemination, and the 10 m/kg dosage fully prevented this complication. In conclusion, when compared with Fungizone, in this model AmBisome is more effective in reducing dissemination of unilateral, pulmonary aspergillosis, even when given in relatively low dosage. Such low dosages may have a place in prophylactic settings

Geometry of Frictionless and Frictional Sphere Packings

We study static packings of frictionless and frictional spheres in three dimensions, obtained via molecular dynamics simulations, in which we vary particle hardness, friction coefficient, and coefficient of restitution. Although frictionless packings of hard-spheres are always isostatic (with six contacts) regardless of construction history and restitution coefficient, frictional packings achieve a multitude of hyperstatic packings that depend on system parameters and construction history. Instead of immediately dropping to four, the coordination number reduces smoothly from $z=6$ as the friction coefficient $\mu$ between two particles is increased.Comment: 6 pages, 9 figures, submitted to Phys. Rev.

Confined granular packings: structure, stress, and forces

The structure and stresses of static granular packs in cylindrical containers are studied using large-scale discrete element molecular dynamics simulations in three dimensions. We generate packings by both pouring and sedimentation and examine how the final state depends on the method of construction. The vertical stress becomes depth-independent for deep piles and we compare these stress depth-profiles to the classical Janssen theory. The majority of the tangential forces for particle-wall contacts are found to be close to the Coulomb failure criterion, in agreement with the theory of Janssen, while particle-particle contacts in the bulk are far from the Coulomb criterion. In addition, we show that a linear hydrostatic-like region at the top of the packings unexplained by the Janssen theory arises because most of the particle-wall tangential forces in this region are far from the Coulomb yield criterion. The distributions of particle-particle and particle-wall contact forces $P(f)$ exhibit exponential-like decay at large forces in agreement with previous studies.Comment: 11 pages, 11 figures, submitted to PRE (v2) added new references, fixed typo

The road to magnesium-diboride thin films, Josephson junctions and SQUIDs

The remarkably high critical temperature at which magnesium diboride (MgB2) undergoes transition to the superconducting state, Tc approx 40 K, has aroused great interest and has encouraged many groups to explore the properties and application potential of this novel superconductor. For many electronic applications and further basic studies, the availability of superconducting thin films is of great importance. Several groups have succeeded in fabricating superconducting MgB2 films. An overview of the deposition techniques for MgB2 thin film growth will be given, with a special focus on the in situ two-step process

Can we avoid high coupling?

It is considered good software design practice to organize source code into modules and to favour within-module connections (cohesion) over between-module connections (coupling), leading to the oft-repeated maxim "low coupling/high cohesion". Prior research into network theory and its application to software systems has found evidence that many important properties in real software systems exhibit approximately scale-free structure, including coupling; researchers have claimed that such scale-free structures are ubiquitous. This implies that high coupling must be unavoidable, statistically speaking, apparently contradicting standard ideas about software structure. We present a model that leads to the simple predictions that approximately scale-free structures ought to arise both for between-module connectivity and overall connectivity, and not as the result of poor design or optimization shortcuts. These predictions are borne out by our large-scale empirical study. Hence we conclude that high coupling is not avoidable--and that this is in fact quite reasonable