Helsinki University of Technology

About: Helsinki University of Technology is a based out in . It is known for research contribution in the topics: Thin film & Vortex. The organization has 8962 authors who have published 20136 publications receiving 723787 citations. The organization is also known as: TKK & Teknillinen korkeakoulu.

Theoretical and experimental study of positron annihilation with core electrons in solids

Abstract: A theory for calculating the momentum distribution of annihilating positron-electron pairs in solids is presented. To test the theory, momentum distributions are measured by the Doppler broadening of the annihilation radiation for several bulk metals and semiconductors, as well as for semiconductor alloys and for positrons trapped at vacancies in semiconductors. The theory is based on a two-particle description of the annihilating electron-positron pair. Then, the electron-positron correlation effects, i.e., the enhancement of the electron density at the positron, depend on the electronic state in question. The theory is suited for calculating the high-momentum part of the annihilation spectrum that arises from the core electrons and which can be measured by the Doppler broadening using coincidence techniques. The ideas of the theory are justified by a good agreement between theory and experiment in the case of positron annihilation in undefected bulk lattices. Moreover, the comparison of the theoretical and experimental spectra for alloys and vacancy defects tests the theoretical description for the positron distribution in delocalized and localized states, respectively. @S01631829~96!04327-5#

Three-dimensional structures of thermophilic beta-1,4-xylanases from Chaetomium thermophilum and Nonomuraea flexuosa. Comparison of twelve xylanases in relation to their thermal stability.

Abstract: The crystal structures of thermophilic xylanases from Chaetomium thermophilum and Nonomuraea flexuosa were determined at 1.75 and 2.1 A resolution, respectively. Both enzymes have the overall fold typical to family 11 xylanases with two highly twisted β-sheets forming a large cleft. The comparison of 12 crystal structures of family 11 xylanases from both mesophilic and thermophilic organisms showed that the structures of different xylanases are very similar. The sequence identity differences correlated well with the structural differences. Several minor modifications appeared to be responsible for the increased thermal stability of family 11 xylanases: (a) higher Thr : Ser ratio (b) increased number of charged residues, especially Arg, resulting in enhanced polar interactions, and (c) improved stabilization of secondary structures involved the higher number of residues in the β-strands and stabilization of the α-helix region. Some members of family 11 xylanases have a unique strategy to improve their stability, such as a higher number of ion pairs or aromatic residues on protein surface, a more compact structure, a tighter packing, and insertions at some regions resulting in enhanced interactions.

Some Quantitative Relations between Indoor Environmental Qualityand Work Performance or Health

Abstract: Poor indoor environmental quality (IEQ) has been related to increases in sick building syndrome (SBS) symptoms, respiratory illnesses, sick leave, and loss in productivity. Calculations indicate that the cost of poor IEQ can be higher than energy costs FOR space conditioning and ventilation and that many measures taken to improve indoor IEQ will be highly cost-effective when accounting for the monetary savings resulting from improved health or productivity. To enable building professionals to select of building designs and operating practices that account for effects on health and productivity, we need models for quantifying the health and productivity benefits of better indoor environments. Therefore, we have reviewed the literature on the effects of indoor environment on health and performance and used existing data, when possible, to develop some initial models. Based on the best available evidence, we present quantitative relationships between ventilation rates and short-term sick leave, ventilation r...

Design, construction, and performance of a large-volume magnetic shield

Abstract: A cubic magnetically shielded room has been constructed. The room consists of three concentric cubic shields, and the side length of the smallest shell is 2A5 m. It utilizes ferromagnetic and eddy current shielding, active noise compensation, and shaking to achieve a shielding factor of about 400 000 between 1 Hz and 100 Hz. At lower frequencies, the shielding drops gradually and is about 16 000 for a 0.1-Hz disturbance. The residual magnetic induction in the room is less than 5 nT, and the magnetic noise above 0.5 Hz is lower than that of the superconducting quantum interference device (SQUID) magnetometer used in the measurements. When the room was completed, its performance in shielding was better than that of any other room made before.