Paul Scherrer Institute

About: Paul Scherrer Institute is a facility organization based out in Villigen, Switzerland. It is known for research contribution in the topics: Neutron & Large Hadron Collider. The organization has 9248 authors who have published 23984 publications receiving 890129 citations. The organization is also known as: PSI.

Ptychographic coherent diffractive imaging of weakly scattering specimens

Abstract: Applying iterative phase retrieval schemes to ptychographic data, i.e. diffraction patterns collected with a localized illumination probe from overlapping regions of a specimen, has enabled the investigation of extended specimens previously inaccessible by other coherent x-ray diffractive imaging methods. While the technique had initially been limited by the requirement of precise knowledge of the illumination function, recent algorithmic developments allow now the simultaneous reconstruction of both the probe and the object. However, these new approaches suffer from an inherent ambiguity, which affects especially the case of weakly scattering specimens. We present new schemes to circumvent this problem and introduce new tools for obtaining information about the scattering behaviour of weak phase objects already during data collection. The new techniques are experimentally demonstrated for a data set taken on Magnetospirillum gryphiswaldense.

Experimental studies on particle emissions from cruising ship, their characteristic properties, transformation and atmospheric lifetime in the marine boundary layer

Abstract: Particle emissions from ship engines and their atmospheric transformation in the marine boundary layer (MBL) were investigated in engine test bed studies and in airborne measurements of expanding ship plumes. During the test rig studies, detailed aerosol microphysical and chemical properties were measured in the exhaust gas of a serial MAN B&W seven-cylinder four-stroke marine diesel engine under various load conditions. The emission studies were complemented by airborne aerosol transformation studies in the plume of a large container ship in the English Channel using the DLR aircraft Falcon 20 E-5. Observations from emission studies and plume studies combined with a Gaussian plume dispersion model yield a consistent picture of particle transformation processes from emission to atmospheric processing during plume expansion. Particulate matter emission indices obtained from plume measurements are 8.8±1.0×10 15 (kg fuel) −1 by number for non-volatile particles and 174±43 mg (kg fuel) −1 by mass for Black Carbon (BC). Values determined for test rig conditions between 85 and 110% engine load are of similar magnitude. For the total particle number including volatile compounds no emission index can be derived since the volatile aerosol fraction is subject to rapid transformation processes in the plume. Ship exhaust particles occur in the size range D p D p ≤0.02 μm. From the decay of ship exhaust particle number concentrations in an expanding plume, a maximum plume life time of approx. 24 h is estimated for a well-mixed marine boundary layer.

Investigation of the selective catalytic reduction of NO by NH3 on Fe-ZSM5 monolith catalysts

Abstract: Fe-ZSM5 coated on cordierite monolith was investigated in the selective catalytic reduction (SCR) of NO with ammonia over a broad temperature range, applying simulated diesel exhaust gas conditions. The catalyst exhibited over 80% NOx reduction (DeNOx) from 400 to 650 °C at very good selectivity. The dosage of variable amounts of ammonia in the catalytic tests revealed that the SCR reaction is inhibited by ammonia. At very high temperatures DeNOx is reduced due to the selective catalytic oxidation (SCO) of ammonia to nitrogen and the oxidation to NO. Water-free experiments resulted in generally higher DeNOx values, which are explained by the inhibiting effect of water on the NO oxidation capability of Fe-ZSM5. The catalyst was stable upon thermal ageing and only 5–15% loss in DeNOx activity was observed after hydrothermal treatment. This loss in DeNOx is in parallel with a loss of ammonia storage capacity of the aged catalyst. Characterization by NH3 TPD and MAS 27Al NMR spectroscopy revealed dealumination of the zeolite by hydrothermal ageing, which reduces the Bronsted acidity of the catalyst.

Design and performance of a DNP prepolarizer coupled to a rodent MRI scanner

Abstract: For most of the last forty years, the techniques of Dynamic Nuclear Polarization (DNP) have been confined to particle-physics laboratories building polarized targets, but recently it has been shown that samples similar to a solid target can be transformed into room temperature liquid solutions while retaining a high nuclear polarization. This method of "hyperpolarization" is of interest in NMR/MRI/MRS. We describe a 3.35 T DNP/9.4 T MRI installation based on a continuous-flow cryostat, using a standard wide-bore low-field NMR magnet as prepolarizer magnet and a widely available radical as polarizing agent. The interfacing to a rodent scanner requires that the infusion of the polarized solution in the animal be remotely controlled, because of limited access inside the magnet bore. Physiological constraints on the infusion rate can be a serious source of polarization loss, and the discussion of efficiency is therefore limited to that of the prepolarizer itself, i.e., the spin temperatures obtained in the solid state. To put our results in context, we summarize data obtained in targets with different types of radicals, and provide a short review of the DNP mechanisms needed in their discussion. (C) 2007 Wiley Periodicals, Inc.