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| 2. |
- Ohrwall, G, et al.
(författare)
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Femtosecond interatomic Coulombic decay in free neon clusters: Large lifetime differences between surface and bulk
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 93:17
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Tidskriftsartikel (refereegranskat)abstract
- A quantitative determination of 2s vacancy lifetimes in surface and bulk atoms of free Ne clusters has been made. While for free atoms the 2s inner-valence hole has a ps lifetime, it reduces to 6+/-1 fs for cluster bulk atoms. For surface atoms, the lifetime is on average longer than 30 fs. The lifetime estimate was obtained from fits of high-resolution photoelectron spectra of Ne clusters. The shortening of the lifetime is attributed to the coordination dependent interatomic Coulombic decay, which is extremely sensitive to internuclear distances.
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| 3. |
- Ohrwall, G, et al.
(författare)
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Observation of elastic scattering effects on photoelectron angular distributions in free Xe clusters
- 2003
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 36:19, s. 3937-3949
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Tidskriftsartikel (refereegranskat)abstract
- We report an observation of substantial deviations in the photoelectron angular distribution for photoionization of atoms in free Xe clusters compared to the case of photoionization of free atoms. The cross section, however, seems not to vary between the cluster and free atoms. This observation was made in the vicinity of the Xe 4d Cooper minimum, where the atomic angular distribution is known to vary dramatically. The angular distribution of electrons emitted from atoms in the clusters is more isotropic than that of free atoms over the entire kinetic energy range studied. Furthermore, the angular distribution is more isotropic for atoms in the interior of the clusters than for atoms at the surface. We attribute this deviation to elastic scattering of the outgoing photoelectrons. We have investigated two average cluster sizes, (N) approximate to 4000 and 1000 and found no significant differences between these two cases.
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| 4. |
- Ristow, Michael, et al.
(författare)
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Frataxin deficiency in pancreatic islets causes diabetes due to loss of β cell mass
- 2003
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Ingår i: Journal of Clinical Investigation. - 0021-9738. ; 112:4, s. 527-534
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Tidskriftsartikel (refereegranskat)abstract
- Diabetes is caused by an absolute (type 1) or relative (type 2) deficiency of insulin-producing β cells. We have disrupted expression of the mitochondrial protein frataxin selectively in pancreatic β cells. Mice were born healthy but subsequently developed impaired glucose tolerance progressing to overt diabetes mellitus. These observations were explained by impairment of insulin secretion due to a loss of β cell mass in knockout animals. This phenotype was preceded by elevated levels of reactive oxygen species in knockout islets, an increased frequency of apoptosis, and a decreased number of proliferating β cells. Hence, disruption of the frataxin gene in pancreatic β cells causes diabetes following cellular growth arrest and apoptosis, paralleled by an increase in reactive oxygen species in islets. These observations might provide insight into the deterioration of β cell function observed in different subtypes of diabetes in humans.
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| 5. |
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| 6. |
- Schulz, Joachim, et al.
(författare)
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Energy absorption of free rare gas clusters irradiated by intense VUV pulses of a free electron laser
- 2003
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002. ; 507:1-2, s. 572-576
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Konferensbidrag (refereegranskat)abstract
- As one of the first experiments at the free electron laser of the TESLA Test Facility (TTF) the Coulomb explosion of Xenon clusters irradiated with high intensity pulses at a wavelength of 98 nm has been observed. Classical trajectory calculations have been performed in order to illuminate the energy absorption process. Comparison with typical parameters in the infrared regime shows that above barrier ionization is suppressed due to the fast oscillating field and thermionic ionization prevails.
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| 7. |
- Tchaplyguine, Maxim, et al.
(författare)
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The size of neutral free clusters as manifested in the relative bulk-to-surface intensity in core level photoelectron spectroscopy
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:1, s. 345-356
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Tidskriftsartikel (refereegranskat)abstract
- A new approach for obtaining an estimate of the effective size of the free neutral clusters is proposed. The approach relies on an experimental measure of the surface and interior or "bulk" cluster atoms provided by the x-ray photoelectron spectroscopy and on a model for the attenuation of photoelectrons ejected from the bulk of the cluster as the result of the ionizing irradiation. The experimental part gives the ratio of the electron signal from the bulk cluster atoms to that from the cluster surface atoms for a wide range of cluster sizes and electron kinetic energies. The attenuated response of the bulk atoms is modeled using an exponential law with the cluster size and kinetic-energy-dependent electron escape depth as parameters. For the experimental size range, model-based calculations for Ar, Kr, and Xe clusters are presented. The cluster size estimates obtained from comparison of the model calculations and experimental results agree well with those determined from the parameters of the cluster creation process. The combination of experiment and modeling also makes it possible to estimate the effective escape depth for electron propagation in free clusters. For Ar, Kr, and Xe clusters of varying mean size, absolute determination of the surface and bulk electron binding energies of the core levels used in the experiments has also been made. (C) 2004 American Institute of Physics.
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