Static Properties of a Simulated Supercooled Polymer Melt: Structure Factors, Monomer Distributions Relative to the Center of Mass, and Triple Correlation Functions

We analyze structural and conformational properties in a simulated bead-spring model of a non-entangled, supercooled polymer melt. We explore the statics of the model via various structure factors, involving not only the monomers, but also the center of mass (CM). We find that the conformation of the chains and the CM-CM structure factor, which is well described by a recently proposed approximation [Krakoviack et al., Europhys. Lett. 58, 53 (2002)], remain essentially unchanged on cooling toward the critical glass transition temperature of mode-coupling theory. Spatial correlations between monomers on different chains, however, depend on temperature, albeit smoothly. This implies that the glassy behavior of our model cannot result from static intra-chain or CM-CM correlations. It must be related to inter-chain correlations at the monomer level. Additionally, we study the dependence of inter-chain correlation functions on the position of the monomer along the chain backbone. We find that this site-dependence can be well accounted for by a theory based on the polymer reference interaction site model (PRISM). We also analyze triple correlations by means of the three-monomer structure factors for the melt and for the chains. These structure factors are compared with the convolution approximation that factorizes them into a product of two-monomer structure factors. For the chains this factorization works very well, indicating that chain connectivity does not introduce special triple correlations in our model. For the melt deviations are more pronounced, particularly at wave vectors close to the maximum of the static structure factor.Comment: REVTeX4, 16 pages, 16 figures, accepted for publication in Physical Review

Yb-doped large mode area fiber for beam quality improvement using local adiabatic tapers with reduced dopant diffusion

A newly designed all-solid step-index Yb-doped aluminosilicate large mode area fiber for achieving high peak power at near diffraction limited beam quality with local adiabatic tapering is presented. The 45µm diameter fiber core and pump cladding consist of active/passively doped aluminosilicate glass produced by powder sinter technology (REPUSIL). A deliberate combination of innovative cladding and core materials was aspired to achieve low processing temperature reducing dopant diffusion during fiber fabrication, tapering and splicing. By developing a short adiabatic taper, robust seed coupling is achieved by using this Yb-doped LMA fiber as final stage of a nanosecond fiber Master Oscillator Power Amplifier (MOPA) system while maintaining near diffraction limited beam quality by preferential excitation of the fundamental mode. After application of a fiber-based endcap, the peak power could be scaled up to 375 kW with high beam quality and a measured M2 value of 1.3~1.7.A newly designed all-solid step-index Yb-doped aluminosilicate large mode area fiber for achieving high peak power at near diffraction limited beam quality with local adiabatic tapering is presented. The 45µm diameter fiber core and pump cladding consist of active/passively doped aluminosilicate glass produced by powder sinter technology (REPUSIL). A deliberate combination of innovative cladding and core materials was aspired to achieve low processing temperature reducing dopant diffusion during fiber fabrication, tapering and splicing. By developing a short adiabatic taper, robust seed coupling is achieved by using this Yb-doped LMA fiber as final stage of a nanosecond fiber Master Oscillator Power Amplifier (MOPA) system while maintaining near diffraction limited beam quality by preferential excitation of the fundamental mode. After application of a fiber-based endcap, the peak power could be scaled up to 375 kW with high beam quality and a measured M2 value of 1.3~1.7

Two-Step-Model of Photosensitivity in Cerium-doped Fibers

The photosensitivity of various cerium-doped fibers has been experimentally investigated for both excimer- and femtosecond-laser illumination. The results of single-pulse, few-pulse and multi-pulse inscription of fiber-Bragg-gratings with both laser systems and the thermal aging of those gratings demonstrated the restrictions of the conventional color center model for cerium-doped fibers. To explain the short-term stability of single-pulse gratings against long-term stability of multi-pulse gratings, an extension into a two-step-model was deduced

Structural and conformational dynamics of supercooled polymer melts: Insights from first-principles theory and simulations

We report on quantitative comparisons between simulation results of a bead-spring model and mode-coupling theory calculations for the structural and conformational dynamics of a supercooled, unentangled polymer melt. We find semiquantitative agreement between simulation and theory, except for processes that occur on intermediate length scales between the compressibility plateau and the amorphous halo of the static structure factor. Our results suggest that the onset of slow relaxation in a glass-forming melt can be described in terms of monomer-caging supplemented by chain connectivity. Furthermore, a unified atomistic description of glassy arrest and of conformational fluctuations that (asymptotically) follow the Rouse model, emerges from our theory.Comment: 54 pages, 10 figure

Protozoan Parasites and Type I IFNs

International audienceFor many years, the role of interferon (IFN)-I has been characterized primarily in the context of viral infections. However, regulatory functions mediated by IFN-I have also been described against bacterial infections and in tumor immunology. Only recently, the interest in understanding the immune functions mediated by IFN-I has dramatically increased in the field of protozoan infections. In this review, we discuss the discrete role of IFN-I in the immune response against major protozoan infections: Plasmodium, Leishmania, Trypanosoma, and Toxoplasma

Expression and Antimicrobial Function of Bactericidal Permeability-Increasing Protein in Cystic Fibrosis Patients

In cystic fibrosis (CF), the condition limiting the prognosis of affected children is the chronic obstructive lung disease accompanied by chronic and persistent infection with mostly mucoid strains of Pseudomonas aeruginosa. The majority of CF patients have antineutrophil cytoplasmic antibodies (ANCA) primarily directed against the bactericidal permeability-increasing protein (BPI) potentially interfering with antimicrobial effects of BPI. We analyzed the expression of BPI in the airways of patients with CF. In their sputum samples or bronchoalveolar lavage specimens, nearly all patients expressed BPI mRNA and protein, which were mainly products of neutrophil granulocytes as revealed by intracellular staining and subsequent flow cytometry. Repeated measurements revealed consistent individual BPI expression levels during several months quantitatively correlating with interleukin-8. In vitro, P. aeruginosa isolates from CF patients initiated the rapid release of BPI occurring independently of protein de novo syntheses. Furthermore, purified natural BPI as well as a 27-mer BPI-derived peptide displayed antimicrobial activity against even patient-derived mucoid P. aeruginosa strains and bacteria resistant against all antibiotics tested. Thus, BPI that is functionally active against mucoid P. aeruginosa strains is expressed in the airways of CF patients but may be hampered by autoantibodies, resulting in chronic infection

Terminal Model Application for Characterizing Conducted EMI in Boost Converter System

A terminal model is a common method to create equivalent models of boost converters in order to predict conducted emissions. In this paper, a characterization board was designed to measure the voltages across and currents flowing into the input side of a DC-DC boost converter automatically by changing the load conditions using the relays as switches. After the equivalent source was determined, the induced noise voltage at the test load was compared to that predicted by the model. The results indicate that the agreement with the direct measurement is quite good up to 100 MHz when the load is within the characterization range. The model is able to correctly predict the conducted emission of the converter in situations quite different from the characterization conditions, for example when an EMI filter is added

Source Isolation Measurements in a Multi-Source Coupled System

An electronic system will commonly have multiple emission (or noise) sources, some of which are correlated while others are un-correlated. Measuring the contribution to a node voltage or branch current by an individual source with high accuracy in such a multi source inter-coupled system is a fundamental problem. The problem is further amplified when the signal processing following the measurements is highly sensitive to the error in the measured parameters. This article describes a filtering method which can isolate the measured parameter (voltage or current) of the contribution of other such sources while preserving the phase and magnitude associated with the source under consideration