Analysis of Radicals in Combustion Processes

This work reports on a variety of radical analysis applications in combustion that are performed in the laboratories of the Paul Scherrer Institute. Planar Laser-Induced Fluorescence and Resonant Holographic Interferometry is applied to the two-dimensional imaging of radicals in flames. The potential of Four-Wave Mixing Spectroscopy for non-perturbing combustion diagnostics is investigated and the method is applied to radicals in flames. Phase-Conjugation and the use of two different input frequencies are utilized to address typical problems in a combustion environment, i.e., lensing effects due to temperature and density gradients and congested spectra of the analyte due to significant thermal population of the ground state.More fundamentally, experiments are aimed to obtain detailed knowledge on the spectroscopy of many important radicals that are not yet characterized sufficiently for diagnostic purposes. A molecular beam apparatus has been set up where the collisionless and cold environment provides well defined experimental conditions to produce and investigate the relevant radicals. Finally, temporally and spectrally resolved fluorescence decays in the picosecond time domain are measured in an atmospheric pressure flame. These experiments yield results on vibrational and rotational energy transfer that are required for quantitative laser-induced fluorescence measurements

Scale-free static and dynamical correlations in melts of monodisperse and Flory-distributed homopolymers: A review of recent bond-fluctuation model studies

It has been assumed until very recently that all long-range correlations are screened in three-dimensional melts of linear homopolymers on distances beyond the correlation length $\xi$ characterizing the decay of the density fluctuations. Summarizing simulation results obtained by means of a variant of the bond-fluctuation model with finite monomer excluded volume interactions and topology violating local and global Monte Carlo moves, we show that due to an interplay of the chain connectivity and the incompressibility constraint, both static and dynamical correlations arise on distances $r \gg \xi$. These correlations are scale-free and, surprisingly, do not depend explicitly on the compressibility of the solution. Both monodisperse and (essentially) Flory-distributed equilibrium polymers are considered.Comment: 60 pages, 49 figure

Tribocorrosion behavior of beta titanium alloys in physiological solutions containing synovial components

In this work, the tribocorrosion behavior of Ti-12.5Mo, Ti-13Nb-13Zr and Ti-29Nb-13Ta-4.6Zr beta titanium alloys which are candidate biomaterials for joint prostheses is studied against ultra high molecular weight polyethylene in Hank's balanced salt solution. Ti-6Al-4Fe alpha+beta titanium alloy is also tested for comparison. Experiments were carried out at open circuit potential and at a passive applied potential using a pin-on-flat reciprocating sliding tribo-electrochemical apparatus. The potential, anodic current and friction coefficient were measured in situ as a function of time. The beta alloys exhibited a tendency to repassivate during sliding at passive and open circuit potential. The predominant wear mechanism of the metal-polyethylene pairs was 3 body wear, exhibited by the transfer of polyethylene to all titanium alloys. Polyethylene showed a comparatively low wear against beta titanium alloys. The effect of the addition of synovial fluid constituents, namely bovine serum albumin, hyaluronic acid and dipalmitoyphosphatidylcholine on the tribocorrosion of Ti-29Nb-13Ta-4.6Zr alloy was also studied. The presence of additives affected the friction coefficient, induced an increase of the wear volume, and a modification of the dominant wear mechanism which was identified as abrasion without transfer of polyethylene. (C) 2010 Elsevier B.V. All rights reserved

Effect of HLA matching in simultaneous pancreas-kidney transplantation.

Simultaneous pancreas-kidney (SPK) transplantation has become the therapy of choice for type 1 diabetic patients with end-stage renal disease. The current analysis examined the impact of HLA matching on graft outcome following SPK transplantation. The study population was obtained from patients enrolled in the Euro-SPK 001 study. PATIENTS AND METHODS: The effect of HLA matching on graft function and survival was assessed in 180 SPK recipients in whom complete donor-recipient HLA data were available. A group of 45 patients with 0 to 3 HLA mismatches (MM) was compared to 135 patients with 4 to 6 MM. RESULTS: There were no differences in 3-year kidney, pancreas, or patient survival rates between the 0 to 3 and 4 to 6 MM groups. Biological parameters of kidney and pancreas graft function were similar in both groups. Significantly more patients with 0 to 3 MM (66%) were rejection free at 3 years than those with 4 to 6 MM (41%; P = .003). The relative risk of acute rejection was 2.6 times higher among patients with 4 to 6 MM than among those with 0 to 3 MM. In conclusion, there was no evidence that HLA matching was associated with improved kidney or pancreas survival. However, a higher rate of acute rejection was observed with poor HLA matches, which may impact long-term survival

Multicenter Assessment of Animal-free Collagenase AF-1 for Human Islet Isolation

Animal-free (AF) SERVA Collagenase AF-1 and Neutral Protease (NP) AF GMP Grade have recently become available for human islet isolation. This report describes the initial experiences of 3 different islet transplant centers. Thirty-four human pancreases were digested using 1 vial of the 6 different lots of Collagenase AF-1 (2,000-2,583 PZ-U/vial) supplemented with 4 different lots of NP AF in a range of 50 to 160 DMC-U per pancreas. Isolation, culture, and quality assessment were performed using standard techniques as previously described. All data are presented as mean +/- standard error of the mean (SEM). Variability of pancreas weight was associated with a wide range of collagenase and NP activities, ranging from 12.7 to 46.6 PZ-U/g (26.0 +/- 1.5 PZ-U/g) and 0.4 to 3.0 DMC-U/g (1.5 +/- 0.1 DMC-U/g), respectively. Postpurification islet yield was 296,494 +/- 33,620 islet equivalents (IEQ) equivalent to 3,274 +/- 450 IEQ/g with a purity of 55.9% +/- 3.2%. Quality assessment performed after 2 to 4 d of culture demonstrated a viability of 88.1% +/- 1.5% and a stimulation index of 3.7 +/- 0.7. Eighteen of the 34 preparations were transplanted into type 1 diabetic patients equivalent to a transplantation rate of 52.9%. Six preparations, which were infused into patients as first transplant, could be analyzed and increased the fasting C-peptide level from 0.11 +/- 0.08 pretransplant to 1.23 +/- 0.24 and 2.27 +/- 0.31 ng/mL 3 and 6 mo posttransplant (P < 0.05), respectively. Insulin requirements were simultaneously reduced at the same time from 39.2 +/- 3.8 IU/d before transplantation to 10.8 +/- 4.1 and 4.0 +/- 2.3 IU/d, after 3 and 6 mo posttransplant (P < 0.05), respectively. This study demonstrates the efficiency of AF SERVA Collagenase AF-1 and NP AF for clinical islet isolation and transplantation. The new plant-based production process makes these products a safe new option for the islet field

Clinical magnetic resonance imaging of pancreatic islet grafts after iron nanoparticle labeling

There is a crucial need for noninvasive assessment tools after cell transplantation. This study investigates whether a magnetic resonance imaging (MRI) strategy could be clinically applied to islet transplantation. The purest fractions of seven human islet preparations were labeled with superparamagnetic iron oxide particles (SPIO, 280 microg/mL) and transplanted into four patients with type 1 diabetes. MRI studies (T2*) were performed prior to and at various time points after transplantation. Viability and in vitro and in vivo functions of labeled islets were similar to those of control islets. All patients could stop insulin after transplantation. The first patient had diffuse hypointense images on her baseline liver MRI, typical for spontaneous high iron content, and transplant-related modifications could not be observed. The other three patients had normal intensity on pretransplant images, and iron-loaded islets could be identified after transplantation as hypointense spots within the liver. In one of them, i.v. iron therapy prevented subsequent visualization of the spots because of diffuse hypointense liver background. Altogether, this study demonstrates the feasibility and safety of MRI-based islet graft monitoring in clinical practice. Iron overload (spontaneous or induced) represents the major obstacle to the technique

Fretting corrosion processes and wear mechanisms in medical implants

International audienceTwo materials (one is metal) under slight relative motion in a liquid medium are submitted to fretting corrosion. This chapter is dedicated on studying fretting corrosion of implants. After describing the most significant implants submitted to fretting, fretting corrosion is defined. Fretting corrosion is a particular mechanism of degradations; it highlights the key role of passive film, crevice corrosion, etc. For understanding the electrochemical effect of the fretting corrosion of metal, some investigations are presented at free corrosion potential and at applied potential in order to measure the specific current density. Moreover the role of proteins is investigated because they constitute the biological environment. Thus they play a significant role in the fretting corrosion processes. Finally results from Atomic Force Microscopy (AFM) show the particular debris, size about 100 nm. Problem about debris influence is discusse